Molecular implementation of molecular shift register memories

NASA Technical Reports Server (NTRS)

Beratan, David N. (Inventor); Onuchic, Jose N. (Inventor)

1991-01-01

An electronic shift register memory (20) at the molecular level is described. The memory elements are based on a chain of electron transfer molecules (22) and the information is shifted by photoinduced (26) electron transfer reactions. Thus, multi-step sequences of charge transfer reactions are used to move charge with high efficiency down a molecular chain. The device integrates compositions of the invention onto a VLSI substrate (36), providing an example of a molecular electronic device which may be fabricated. Three energy level schemes, molecular implementation of these schemes, optical excitation strategies, charge amplification strategies, and error correction strategies are described.

Pattern classification using charge transfer devices

NASA Technical Reports Server (NTRS)

1980-01-01

The feasibility of using charge transfer devices in the classification of multispectral imagery was investigated by evaluating particular devices to determine their suitability in matrix multiplication subsystem of a pattern classifier and by designing a protype of such a system. Particular attention was given to analog-analog correlator devices which consist of two tapped delay lines, chip multipliers, and a summed output. The design for the classifier and a printed circuit layout for the analog boards were completed and the boards were fabricated. A test j:g for the board was built and checkout was begun.

The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

DOE PAGES

Wang, Han; Bang, Junhyeok; Sun, Yiyang; ...

2016-05-10

Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherentmore » charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.« less

The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Han; Bang, Junhyeok; Sun, Yiyang

Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherentmore » charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.« less

Development of InSb charge-coupled infrared imaging devices: Linear imager

NASA Technical Reports Server (NTRS)

Phillips, J. D.

1976-01-01

The following results were accomplished in the development of charge coupled infrared imaging devices: (1) a four-phase overlapping gate with 9 transfers (2-bits) and 1.0-mil gate lengths was successfully operated, (2) the measured transfer efficiency of 0.975 for this device is in excellent agreement with predictions for the reduced gate length device, (3) mask revisions of the channel stop metal on the 8582 mask have been carried out with the result being a large increase in the dc yield of the tested devices, (4) partial optical sensitivity to chopped blackbody radiation was observed for an 8582 9-bit imager, (5) analytical consideration of the modulation transfer function degradation caused by transfer inefficiency in the CCD registers was presented, and (6) for larger array lengths or for the insertion of isolated bits between sensors, improvements in InSb fabrication technology with corresponding decrease in the interface state density are required.

Conjugated block copolymers as model materials to examine charge transfer in donor-acceptor systems

NASA Astrophysics Data System (ADS)

Gomez, Enrique; Aplan, Melissa; Lee, Youngmin

Weak intermolecular interactions and disorder at junctions of different organic materials limit the performance and stability of organic interfaces and hence the applicability of organic semiconductors to electronic devices. The lack of control of interfacial structure has also prevented studies of how driving forces promote charge photogeneration, leading to conflicting hypotheses in the organic photovoltaic literature. Our approach has focused on utilizing block copolymer architectures -where critical interfaces are controlled and stabilized by covalent bonds- to provide the hierarchical structure needed for high-performance organic electronics from self-assembled soft materials. For example, we have demonstrated control of donor-acceptor heterojunctions through microphase-separated conjugated block copolymers to achieve 3% power conversion efficiencies in non-fullerene photovoltaics. Furthermore, incorporating the donor-acceptor interface within the molecular structure facilitates studies of charge transfer processes. Conjugated block copolymers enable studies of the driving force needed for exciton dissociation to charge transfer states, which must be large to maximize charge photogeneration but must be minimized to prevent losses in photovoltage in solar cell devices. Our work has systematically varied the chemical structure, energetics, and dielectric constant to perturb charge transfer. As a consequence, we predict a minimum dielectric constant needed to minimize the driving force and therefore simultaneously maximize photocurrent and photovoltage in organic photovoltaic devices.

Symmetry-breaking charge transfer in a zinc chlorodipyrrin acceptor for high open circuit voltage organic photovoltaics.

PubMed

Bartynski, Andrew N; Gruber, Mark; Das, Saptaparna; Rangan, Sylvie; Mollinger, Sonya; Trinh, Cong; Bradforth, Stephen E; Vandewal, Koen; Salleo, Alberto; Bartynski, Robert A; Bruetting, Wolfgang; Thompson, Mark E

2015-04-29

Low open-circuit voltages significantly limit the power conversion efficiency of organic photovoltaic devices. Typical strategies to enhance the open-circuit voltage involve tuning the HOMO and LUMO positions of the donor (D) and acceptor (A), respectively, to increase the interfacial energy gap or to tailor the donor or acceptor structure at the D/A interface. Here, we present an alternative approach to improve the open-circuit voltage through the use of a zinc chlorodipyrrin, ZCl [bis(dodecachloro-5-mesityldipyrrinato)zinc], as an acceptor, which undergoes symmetry-breaking charge transfer (CT) at the donor/acceptor interface. DBP/ZCl cells exhibit open-circuit voltages of 1.33 V compared to 0.88 V for analogous tetraphenyldibenzoperyflanthrene (DBP)/C60-based devices. Charge transfer state energies measured by Fourier-transform photocurrent spectroscopy and electroluminescence show that C60 forms a CT state of 1.45 ± 0.05 eV in a DBP/C60-based organic photovoltaic device, while ZCl as acceptor gives a CT state energy of 1.70 ± 0.05 eV in the corresponding device structure. In the ZCl device this results in an energetic loss between E(CT) and qV(OC) of 0.37 eV, substantially less than the 0.6 eV typically observed for organic systems and equal to the recombination losses seen in high-efficiency Si and GaAs devices. The substantial increase in open-circuit voltage and reduction in recombination losses for devices utilizing ZCl demonstrate the great promise of symmetry-breaking charge transfer in organic photovoltaic devices.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kar, Durga P.; Nayak, Praveen P.; Bhuyan, Satyanarayan

In order to power or charge electronic devices wirelessly, a bi-directional wireless power transfer method has been proposed and experimentally investigated. In the proposed design, two receiving coils are used on both sides of a transmitting coil along its central axis to receive the power wirelessly from the generated magnetic fields through strongly coupled magnetic resonance. It has been observed experimentally that the maximum power transfer occurs at the operating resonant frequency for optimum electric load connected across the receiving coils on both side. The optimum wireless power transfer efficiency is 88% for the bi-directional power transfer technique compared 84%more » in the one side receiver system. By adopting the developed bi-directional power transfer method, two electronic devices can be powered up or charged simultaneously instead of a single device through usual one side receiver system without affecting the optimum power transfer efficiency.« less

Active pixel sensor having intra-pixel charge transfer with analog-to-digital converter

NASA Technical Reports Server (NTRS)

Fossum, Eric R. (Inventor); Mendis, Sunetra K. (Inventor); Pain, Bedabrata (Inventor); Nixon, Robert H. (Inventor); Zhou, Zhimin (Inventor)

2003-01-01

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node and an analog-to-digital converter formed in the substrate connected to the output of the readout circuit.

Active pixel sensor having intra-pixel charge transfer with analog-to-digital converter

NASA Technical Reports Server (NTRS)

Fossum, Eric R. (Inventor); Mendis, Sunetra K. (Inventor); Pain, Bedabrata (Inventor); Nixon, Robert H. (Inventor); Zhou, Zhimin (Inventor)

2000-01-01

An imaging device formed as a monolithic complementary metal oxide semiconductor Integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node and an analog-to-digital converter formed in the substrate connected to the output of the readout circuit.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ran, Niva A.; Roland, Steffen; Love, John A.

Here, a long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics—however, the results have important implications on the operation of all optoelectronic devices with donor/acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting inmore » larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation.« less

Are hot charge transfer states the primary cause of efficient free-charge generation in polymer:fullerene organic photovoltaic devices? A kinetic Monte Carlo study.

PubMed

Jones, Matthew L; Dyer, Reesha; Clarke, Nigel; Groves, Chris

2014-10-14

Kinetic Monte Carlo simulations are used to examine the effect of high-energy, 'hot' delocalised charge transfer (HCT) states for donor:acceptor and mixed:aggregate blends, the latter relating to polymer:fullerene photovoltaic devices. Increased fullerene aggregation is shown to enhance charge generation and short-circuit device current - largely due to the increased production of HCT states at the aggregate interface. However, the instances where HCT states are predicted to give internal quantum efficiencies in the region of 50% do not correspond to HCT delocalisation or electron mobility measured in experiments. These data therefore suggest that HCT states are not the primary cause of high quantum efficiencies in some polymer:fullerene OPVs. Instead it is argued that HCT states are responsible for the fast charge generation seen in spectroscopy, but that regional variation in energy levels are the cause of long-term, efficient free-charge generation.

Impact of interfacial molecular orientation on radiative recombination and charge generation efficiency

DOE PAGES

Ran, Niva A.; Roland, Steffen; Love, John A.; ...

2017-07-19

Here, a long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics—however, the results have important implications on the operation of all optoelectronic devices with donor/acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting inmore » larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation.« less

Through-Space Intervalence Charge Transfer as a Mechanism for Charge Delocalisation in Metal-Organic Frameworks.

PubMed

Hua, Carol; Doheny, Patrick William; Ding, Bowen; Chan, Bun; Yu, Michelle; Kepert, Cameron J; D'Alessandro, Deanna M

2018-05-04

Understanding the nature of charge transfer mechanisms in 3-dimensional Metal-Organic Frameworks (MOFs) is an important goal owing to the possibility of harnessing this knowledge to design conductive frameworks. These materials have been implicated as the basis for the next generation of technological devices for applications in energy storage and conversion, including electrochromic devices, electrocatalysts, and battery materials. After nearly two decades of intense research into MOFs, the mechanisms of charge transfer remain relatively poorly understood, and new strategies to achieve charge mobility remain elusive and challenging to experimentally explore, validate and model. We now demonstrate that aromatic stacking interactions in Zn(II) frameworks containing cofacial thiazolo[5,4-d]thiazole units lead to a mixed-valence state upon electrochemical or chemical reduction. This through-space Intervalence Charge Transfer (IVCT) phenomenon represents a new mechanism for charge delocalisation in MOFs. Computational modelling of the optical data combined with application of Marcus-Hush theory to the IVCT bands for the mixed-valence framework has enabled quantification of the degree of delocalisation using both in situ and ex situ electro- and spectro-electrochemical methods. A distance dependence for the through-space electron transfer has also been identified on the basis of experimental studies and computational calculations. This work provides a new window into electron transfer phenomena in 3-dimensional coordination space, of relevance to electroactive MOFs where new mechanisms for charge transfer are highly sought after, and to understanding biological light harvesting systems where through-space mixed-valence interactions are operative.

Electroluminescence Properties of IrQ(ppy)2 Dual-Emitter Organometallic Compound in Organic Light-Emitting Devices

NASA Astrophysics Data System (ADS)

Ciobotaru, Constantin Claudiu; Polosan, Silviu; Ciobotaru, Iulia Corina

2018-02-01

This paper reports the influence of the charge carrier mobility on the electroluminescent properties of a dual-emitter organometallic compound dispersed in two conjugated organic small-molecule host materials and embedded in organic light-emitting devices (OLEDs). The electroluminescent processes in OLEDs are strongly influenced by the host-guest interaction. The charge carrier mobility in the host material plays an important role in the electroluminescent processes but also depends on the triplet-triplet interaction with the organometallic compound. The low charge carrier mobility in 4,4'-bis( N-carbazolyl)-1,1'-biphenyl (CBP) host material reduces the electroluminescent processes, but they are slightly enhanced by the triplet-triplet exothermic charge transfer. The higher charge carrier mobility in the case of N, N'-bis(3-methylphenyl)- N, N'-diphenylbenzidine (TPD) host material influences the electroluminescent processes by the endothermic energy transfer at room temperature, which facilitates the triplet-triplet harvesting in the host-guest system. The excitation is transferred to the guest molecules by triplet-triplet interaction as a Dexter transfer, which occurs by endothermic transfer from the triplet exciton in the host to the triplet exciton in the guest.

Charge-transfer complexes and their role in exciplex emission and near-infrared photovoltaics.

PubMed

Ng, Tsz-Wai; Lo, Ming-Fai; Fung, Man-Keung; Zhang, Wen-Jun; Lee, Chun-Sing

2014-08-20

Charge transfer and interactions at organic heterojunctions (OHJs) are known to have critical influences on various properties of organic electronic devices. In this Research News article, a short review is given from the electronic viewpoint on how the local molecular interactions and interfacial energetics at P/N OHJs contribute to the recombination/dissociation of electron-hole pairs. Very often, the P-type materials donate electrons to the N-type materials, giving rise to charge-transfer complexes (CTCs) with a P(δ+) -N(δ-) configuration. A recently observed opposite charge-transfer direction in OHJs is also discussed (i.e., N-type material donates electrons to P-type material to form P(δ-) -N(δ+) ). Recent studies on the electronic structures of CTC-forming material pairs are also summarized. The formation of P(δ-) -N(δ+) -type CTCs and their correlations with exciplex emission are examined. Furthermore, the potential applications of CTCs in NIR photovoltaic devices are reviewed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Transistor and memory devices based on novel organic and biomaterials

NASA Astrophysics Data System (ADS)

Tseng, Jia-Hung

Organic semiconductor devices have aroused considerable interest because of the enormous potential in many technological applications. Organic electroluminescent devices have been extensively applied in display technology. Rapid progress has also been made in transistor and memory devices. This thesis considers aspects of the transistor based on novel organic single crystals and memory devices using hybrid nanocomposites comprising polymeric/inorganic nanoparticles, and biomolecule/quantum dots. Organic single crystals represent highly ordered structures with much less imperfections compared to amorphous thin films for probing the intrinsic charge transport in transistor devices. We demonstrate that free-standing, thin organic single crystals with natural flexing ability can be fabricated as flexible transistors. We study the surface properties of the organic crystals to determine a nearly perfect surface leading to high performance transistors. The flexible transistors can maintain high performance under reversible bending conditions. Because of the high quality crystal technique, we further develop applications on organic complementary circuits and organic single crystal photovoltaics. In the second part, two aspects of memory devices are studied. We examine the charge transfer process between conjugated polymers and metal nanoparticles. This charge transfer process is essential for the conductance switching in nanoseconds to induce the memory effect. Under the reduction condition, the charge transfer process is eliminated as well as the memory effect, raising the importance of coupling between conjugated systems and nanoparticle accepters. The other aspect of memory devices focuses on the interaction of virus biomolecules with quantum dots or metal nanoparticles in the devices. We investigate the impact of memory function on the hybrid bio-inorganic system. We perform an experimental analysis of the charge storage activation energy in tobacco mosaic virus with platinum nanoparticles. It is established that the effective barrier height in the materials systems needs to be further engineered in order to have sufficiently long retention times. Finally other novel architectures such as negative differential resistance devices and high density memory arrays are investigated for their influence on memory technology.

Organic nanoparticles for photovoltaic and sensing applications

NASA Astrophysics Data System (ADS)

Venkatraman, B. Harihara

2011-12-01

Can organic semiconducting nanoparticles be used as building blocks for fabricating electronic devices? The first half of this dissertation focuses on addressing this question and the associated research challenges for attaining morphological control pertaining to organic photovoltaic devices by nanoparticle assembly. Conjugated polymer nanoparticles were synthesized using miniemulsion technique and their optical, charge transfer and charge transport properties were studied. Some degree of control in polymer chain packing within the nanoparticle was also demonstrated. The optical, charge transfer and charge transport properties of these nanoparticles were found to be similar to that of parent conjugated polymer irrespective of the surface charge. From the initial photovoltaic measurements, it is shown that these nanoparticles are potential candidates for fabricating future photovoltaic devices. The second half of this dissertation is focused on developing a novel and viable strategy for sensing aqueous based nitroaromatic compounds. Nitroaromatic compounds are commonly used as explosives and possess serious health hazards. Thiophene-based conjugated polymer nanoparticles were synthesized and were shown to effectively detect aqueous based nitroaromatic explosives.

Spin Transfer Torque in Graphene

NASA Astrophysics Data System (ADS)

Lin, Chia-Ching; Chen, Zhihong

2014-03-01

Graphene is an idea channel material for spin transport due to its long spin diffusion length. To develop graphene based spin logic, it is important to demonstrate spin transfer torque in graphene. Here, we report the experimental measurement of spin transfer torque in graphene nonlocal spin valve devices. Assisted by a small external in-plane magnetic field, the magnetization reversal of the receiving magnet is induced by pure spin diffusion currents from the injector magnet. The magnetization switching is reversible between parallel and antiparallel configurations by controlling the polarity of the applied charged currents. Current induced heating and Oersted field from the nonlocal charge flow have also been excluded in this study. Next, we further enhance the spin angular momentum absorption at the interface of the receiving magnet and graphene channel by removing the tunneling barrier in the receiving magnet. The device with a tunneling barrier only at the injector magnet shows a comparable nonlocal spin valve signal but lower electrical noise. Moreover, in the same preset condition, the critical charge current density for spin torque in the single tunneling barrier device shows a substantial reduction if compared to the double tunneling barrier device.

Charge Transfer and Catalysis at the Metal Support Interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, Lawrence Robert

Kinetic, electronic, and spectroscopic characterization of model Pt–support systems are used to demonstrate the relationship between charge transfer and catalytic activity and selectivity. The results show that charge flow controls the activity and selectivity of supported metal catalysts. This dissertation builds on extensive existing knowledge of metal–support interactions in heterogeneous catalysis. The results show the prominent role of charge transfer at catalytic interfaces to determine catalytic activity and selectivity. Further, this research demonstrates the possibility of selectively driving catalytic chemistry by controlling charge flow and presents solid-state devices and doped supports as novel methods for obtaining electronic control over catalyticmore » reaction kinetics.« less

Wireless power transfer electric vehicle supply equipment installation and validation tool

DOEpatents

Jones, Perry T.; Miller, John M.

2015-05-19

A transmit pad inspection device includes a magnetic coupling device, which includes an inductive circuit that is configured to magnetically couple to a primary circuit of a charging device in a transmit pad through an alternating current (AC) magnetic field. The inductive circuit functions as a secondary circuit for a set of magnetically coupled coils. The magnetic coupling device further includes a rectification circuit, and includes a controllable load bank or is configured to be connected to an external controllable load back. The transmit pad inspection device is configured to determine the efficiency of power transfer under various coupling conditions. In addition, the transmit pad inspection device can be configured to measure residual magnetic field and the frequency of the input current, and to determine whether the charging device has been installed properly.

Design principle for efficient charge separation at the donor-acceptor interface for high performance organic solar cell device

NASA Astrophysics Data System (ADS)

Nie, Wanyi; Gupta, Gautam; Crone, Brian; Wang, Hsing-Lin; Mohite, Aditya; MPA-11 Material synthesis and integrated device Team; MPA-chemistry Team

2014-03-01

The performance of donor (D) /acceptor (A) structure based organic electronic devices, such as solar cell, light emitting devices etc., relays on the charge transfer process at the interface dramatically. In organic solar cell, the photo-induced electron-hole pair is tightly bonded and will form a charge transfer (CT) state at the D/A interface after dissociation. There is a large chance for them to recombine through CT state and thus is a major loss that limit the overall performance. Here, we report three different strategies that allow us to completely suppress the exciplex (or charge transfer state) recombination between any D/A system. We observe that the photocurrent increases by 300% and the power conversion efficiency increases by 4-5 times simply by inserting a spacer layer in the form of an a) insulator b) Oliogomer or using a c) heavy atom at the donor-acceptor interface in a P3HT/C60 bilayer device. By using those different functional mono layers, we successfully suppressed the exciplex recombination in evidence of increased photocurrent and open circuit voltage. Moreover, these strategies are applicable universally to any donor-acceptor interface. And we demonstrated such strategies in a bulk-heterojunction device which improved the power conversion efficiency from 3.5% up to 4.6%.

Chemical and charge transfer studies on interfaces of a conjugated polymer and ITO

NASA Astrophysics Data System (ADS)

David, Tanya M. S.; Arasho, Wondwosson; Smith, O'Neil; Hong, Kunlun; Bonner, Carl; Sun, Sam-Shajing

2017-08-01

Conjugated oligomers and polymers are very attractive for potential future plastic electronic and opto-electronic device applications such as plastic photo detectors and solar cells, thermoelectric devices, field effect transistors, and light emitting diodes. Understanding and optimizing charge transport between an active polymer layer and conductive substrate is critical to the optimization of polymer based electronic and opto-electronic devices. This study focused on the design, synthesis, self-assembly, and electron transfers and transports of a phosphonic acid end-functionalized polyphenylenevinylene (PPV) that was covalently attached and self-assembled onto an Indium Tin Oxide (ITO) substrate. This study demonstrated how atomic force microscopy (AFM) can be an effective characterization technique in conjunction with conventional electron transfer methods, including cyclic voltammetry (CV), towards determining electron transfer rates in polymer and polymer/conductor interface systems. This study found that the electron transfer rates of covalently attached and self-assembled films were much faster than the spin coated films. The knowledge from this study can be very useful for designing potential polymer based electronic and opto-electronic thin film devices.

InSb charge coupled infrared imaging device: The 20 element linear imager

NASA Technical Reports Server (NTRS)

Thom, R. D.; Koch, T. L.; Parrish, W. J.; Langan, J. D.; Chase, S. C.

1980-01-01

The design and fabrication of the 8585 InSb charge coupled infrared imaging device (CCIRID) chip are reported. The InSb material characteristics are described along with mask and process modifications. Test results for the 2- and 20-element CCIRID's are discussed, including gate oxide characteristics, charge transfer efficiency, optical mode of operation, and development of the surface potential diagram.

Spectral resolution of states relevant to photoinduced charge transfer in modified pentacene/ZnO field-effect transistors

NASA Astrophysics Data System (ADS)

Spalenka, Josef W.; Mannebach, Ehren M.; Bindl, Dominick J.; Arnold, Michael S.; Evans, Paul G.

2011-11-01

Pentacene field-effect transistors incorporating ZnO quantum dots can be used as a sensitive probe of the optical properties of a buried donor-acceptor interface. Photoinduced charge transfer between pentacene and ZnO in these devices varies with incident photon energy and reveals which energies will contribute most to charge transfer in other structures. A subsequent slow return to the dark state following the end of illumination arises from near-interface traps. Charge transfer has a sharp onset at 1.7 eV and peaks at 1.82 and 2.1 eV due to transitions associated with excitons, features absent in pentacene FETs without ZnO.

Investigation of charge coupled device correlation techniques

NASA Technical Reports Server (NTRS)

Lampe, D. R.; Lin, H. C.; Shutt, T. J.

1978-01-01

Analog Charge Transfer Devices (CTD's) offer unique advantages to signal processing systems, which often have large development costs, making it desirable to define those devices which can be developed for general system's use. Such devices are best identified and developed early to give system's designers some interchangeable subsystem blocks, not requiring additional individual development for each new signal processing system. The objective of this work is to describe a discrete analog signal processing device with a reasonably broad system use and to implement its design, fabrication, and testing.

Investigating Wireless Power Transfer

ERIC Educational Resources Information Center

St. John, Stuart A.

2017-01-01

Understanding Physics is a great end in itself, but is also crucial to keep pace with developments in modern technology. Wireless power transfer, known to many only as a means to charge electric toothbrushes, will soon be commonplace in charging phones, electric cars and implanted medical devices. This article outlines how to produce and use a…

High Performance Polymer Memory and Its Formation

DTIC Science & Technology

2007-04-26

the retention time of the device was performed to estimate the barrier height of the charge trap . The activation energy was approximated to be about...characteristics and presented a model to explain the mechanism of electrical switching in the device. By exploiting an electric-field induced charge transfer...electrical current in the high conductivity state would be due to some temperature-independent charge tunneling processes. The IV curves could be

Phonon-Assisted Ultrafast Charge Transfer at van der Waals Heterostructure Interface.

PubMed

Zheng, Qijing; Saidi, Wissam A; Xie, Yu; Lan, Zhenggang; Prezhdo, Oleg V; Petek, Hrvoje; Zhao, Jin

2017-10-11

The van der Waals (vdW) interfaces of two-dimensional (2D) semiconductor are central to new device concepts and emerging technologies in light-electricity transduction where the efficient charge separation is a key factor. Contrary to general expectation, efficient electron-hole separation can occur in vertically stacked transition-metal dichalcogenide heterostructure bilayers through ultrafast charge transfer between the neighboring layers despite their weak vdW bonding. In this report, we show by ab initio nonadiabatic molecular dynamics calculations, that instead of direct tunneling, the ultrafast interlayer hole transfer is strongly promoted by an adiabatic mechanism through phonon excitation occurring on 20 fs, which is in good agreement with the experiment. The atomic level picture of the phonon-assisted ultrafast mechanism revealed in our study is valuable both for the fundamental understanding of ultrafast charge carrier dynamics at vdW heterointerfaces as well as for the design of novel quasi-2D devices for optoelectronic and photovoltaic applications.

Applications of charge-coupled device transversal filters to communication

NASA Technical Reports Server (NTRS)

Buss, D. D.; Bailey, W. H.; Brodersen, R. W.; Hewes, C. R.; Tasch, A. F., Jr.

1975-01-01

The paper discusses the computational power of state-of-the-art charged-coupled device (CCD) transversal filters in communications applications. Some of the performance limitations of CCD transversal filters are discussed, with attention given to time delay and bandwidth, imperfect charge transfer efficiency, weighting coefficient error, noise, and linearity. The application of CCD transversal filters to matched filtering, spectral filtering, and Fourier analysis is examined. Techniques for making programmable transversal filters are briefly outlined.

Hole transfer from CdSe nanoparticles to TQ1 polymer in hybrid solar cell device

NASA Astrophysics Data System (ADS)

Sohail, Muhammad; Shah, Zawar Hussain; Saeed, Shomaila; Bibi, Nasreen; Shahbaz, Sadia; Ahmed, Safeer; Shabbir, Saima; Siddiq, Muhammad; Iqbal, Azhar

2018-05-01

In view of realizing the economic viability, we fabricate a solar cell device containing low band gap and easily processable polymer 5-yl-8-(thiophene-2,5-diyl)-2,3-bis(3-(octyloxy)phenyl) quinoxaline (TQ1) and CdSe nanoparticles (NPs) and investigate its charge transport properties. When the TQ1 is combined with the CdSe NPs a strong photoluminescence quenching and shortening of photoluminescence lifetime of the TQ1 is observed indicating exciton transfer from TQ1 to the CdSe NPs. The time-resolved photoluminescence further reveals that the exciton transfer from the polymer to CdSe NPs is very efficient (68%) and it occurs in <1 ns. The exciton transfer from TQ1 to the NPs and electron-hole pair separation followed by hole transfer from the NPs to the TQ1 at the interface indeed increases the lifetime of the charge carriers. This in turn increases the efficiency of the solar cell as compared to polymer only device. These observations suggest the importance of other II-VI semiconductor NPs to achieve higher efficiency for photovoltaic devices containing TQ1 polymer.

Molecular controlled of quantum nano systems

NASA Astrophysics Data System (ADS)

Paltiel, Yossi

2014-03-01

A century ago quantum mechanics created a conceptual revolution whose fruits are now seen in almost any aspect of our day-to-day life. Lasers, transistors and other solid state and optical devices represent the core technology of current computers, memory devices and communication systems. However, all these examples do not exploit fully the quantum revolution as they do not take advantage of the coherent wave-like properties of the quantum wave function. Controlled coherent system and devices at ambient temperatures are challenging to realize. We are developing a novel nano tool box with control coupling between the quantum states and the environment. This tool box that combines nano particles with organic molecules enables the integration of quantum properties with classical existing devices at ambient temperatures. The nano particles generate the quantum states while the organic molecules control the coupling and therefore the energy, charge, spin, or quasi particle transfer between the layers. Coherent effects at ambient temperatures can be measured in the strong coupling regime. In the talk I will present our nano tool box and show studies of charge transfer, spin transfer and energy transfer in the hybrid layers as well as collective transfer phenomena. These enable the realization of room temperature operating quantum electro optical devices. For example I will present in details, our recent development of a new type of chiral molecules based magnetless universal memory exploiting selective spin transfer.

High performance organic integrated device with ultraviolet photodetective and electroluminescent properties consisting of a charge-transfer-featured naphthalimide derivative

NASA Astrophysics Data System (ADS)

Wang, Hanyu; Zhou, Jie; Wang, Xu; Lu, Zhiyun; Yu, Junsheng

2014-08-01

A high performance organic integrated device (OID) with ultraviolet photodetective and electroluminescent (EL) properties was fabricated by using a charge-transfer-featured naphthalimide derivative of 6-{3,5-bis-[9-(4-t-butylphenyl)-9H-carbazol-3-yl]-phenoxy}-2-(4-t-butylphenyl)-benzo[de]isoquinoline-1,3-dione (CzPhONI) as the active layer. The results showed that the OID had a high detectivity of 1.5 × 1011 Jones at -3 V under the UV-350 nm illumination with an intensity of 0.6 mW/cm2, and yielded an exciplex EL light emission with a maximum brightness of 1437 cd/m2. Based on the energy band diagram, both the charge transfer feature of CzPhONI and matched energy level alignment were responsible for the dual ultraviolet photodetective and EL functions of OID.

Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

NASA Astrophysics Data System (ADS)

Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

2015-10-01

Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

Efficient charge transfer and field-induced tunneling transport in hybrid composite device of organic semiconductor and cadmium telluride quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varade, Vaibhav, E-mail: vaibhav.tvarade@gmail.com; Jagtap, Amardeep M.; Koteswara Rao, K. S. R.

2015-06-07

Temperature and photo-dependent current–voltage characteristics are investigated in thin film devices of a hybrid-composite comprising of organic semiconductor poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and cadmium telluride quantum dots (CdTe QDs). A detailed study of the charge injection mechanism in ITO/PEDOT:PSS-CdTe QDs/Al device exhibits a transition from direct tunneling to Fowler–Nordheim tunneling with increasing electric field due to formation of high barrier at the QD interface. In addition, the hybrid-composite exhibits a huge photoluminescence quenching compared to aboriginal CdTe QDs and high increment in photoconductivity (∼ 400%), which is attributed to the charge transfer phenomena. The effective barrier height (Φ{sub B} ≈ 0.68 eV) ismore » estimated from the transition voltage and the possible origin of its variation with temperature and photo-illumination is discussed.« less

Mechanistic insights into the photoinduced charge carrier dynamics of BiOBr/CdS nanosheet heterojunctions for photovoltaic application.

PubMed

Jia, Huimin; Zhang, Beibei; He, Weiwei; Xiang, Yong; Zheng, Zhi

2017-03-02

The rational design of high performance hetero-structure photovoltaic devices requires a full understanding of the photoinduced charge transfer mechanism and kinetics at the interface of heterojunctions. In this paper, we intelligently fabricated p-BiOBr/n-CdS heterojunctions with perfect nanosheet arrays by using a facile successive ionic layer adsorption and reaction and chemical bath deposition methods at low temperature. A BiOBr/CdS heterojunction based solar cell has been fabricated which exhibited enhanced photovoltaic responses. Assisted by the surface photovoltage (SPV), transient photovoltage (TPV) and Kelvin probe technique, the photoinduced charge transfer dynamics on the BiOBr nanosheet and p-BiOBr/n-CdS interface were systematically investigated. It was found that the BiOBr/CdS nanosheet array heterojunctions were more efficient in facilitating charge carrier separation than both bare BiOBr and CdS films. The mechanism underlying the photoinduced charge carrier transfer behaviour was unravelled by allying the energy band of BiOBr/CdS p-n junctions from both the interfacial electric field and surface electric field. In addition, the CdS loading thickness in the p-BiOBr/n-CdS heterojunction and the incident wavelength affected greatly the transfer behavior of photoinduced charges, which was of great value for design of photovoltaic devices.

Phonon-coupled ultrafast interlayer charge oscillation at van der Waals heterostructure interfaces

NASA Astrophysics Data System (ADS)

Zheng, Qijing; Xie, Yu; Lan, Zhenggang; Prezhdo, Oleg V.; Saidi, Wissam A.; Zhao, Jin

2018-05-01

Van der Waals (vdW) heterostructures of transition-metal dichalcogenide (TMD) semiconductors are central not only for fundamental science, but also for electro- and optical-device technologies where the interfacial charge transfer is a key factor. Ultrafast interfacial charge dynamics has been intensively studied, however, the atomic scale insights into the effects of the electron-phonon (e-p) coupling are still lacking. In this paper, using time dependent ab initio nonadiabatic molecular dynamics, we study the ultrafast interfacial charge transfer dynamics of two different TMD heterostructures MoS2/WS2 and MoSe2/WSe2 , which have similar band structures but different phonon frequencies. We found that MoSe2/WSe2 has softer phonon modes compared to MoS2/WS2 , and thus phonon-coupled charge oscillation can be excited with sufficient phonon excitations at room temperature. In contrast, for MoS2/WS2 , phonon-coupled interlayer charge oscillations are not easily excitable. Our study provides an atomic level understanding on how the phonon excitation and e-p coupling affect the interlayer charge transfer dynamics, which is valuable for both the fundamental understanding of ultrafast dynamics at vdW hetero-interfaces and the design of novel quasi-two-dimensional devices for optoelectronic and photovoltaic applications.

Tuning charge transfer in the LaTiO3/RO/LaNiO3 (R = rare-earth) superlattices by the rare-earth oxides interfaces from a first-principles calculation

NASA Astrophysics Data System (ADS)

Yao, Fen; Zhang, Lifang; Meng, Junling; Liu, Xiaojuan; Zhang, Xiong; Zhang, Wenwen; Meng, Jian; Zhang, Hongjie

2018-03-01

We investigate the internal charge transfer at the isopolar interfaces in LaTiO3/RO/LaNiO3 (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) superlattices by means of density functional theory calculations. The charge transfer from Ti sites to Ni sites in all superlattices is induced by the electronegativity difference between the elements Ti and Ni, and the lanthanide oxides interfaces can modulate the amount of charge transfer. Comparison of the perovskite heterostructures with the different rare-earth interfaces shows that increasing the deviations of bond angles from 180.0° and the oxygen motions near the interfaces enhance charge transfer. The 4f electrons themselves of rare-earth elements have faint influences on charge transfer. In addition, the reasons why our calculated 4f states of Sm and Tm elements disagree with the experimental systems have been provided. It is hoped that all the calculated results could be used to design new functional nanoelectronic devices in perovskite oxides.

Charge-pump voltage converter

DOEpatents

Brainard, John P [Albuquerque, NM; Christenson, Todd R [Albuquerque, NM

2009-11-03

A charge-pump voltage converter for converting a low voltage provided by a low-voltage source to a higher voltage. Charge is inductively generated on a transfer rotor electrode during its transit past an inductor stator electrode and subsequently transferred by the rotating rotor to a collector stator electrode for storage or use. Repetition of the charge transfer process leads to a build-up of voltage on a charge-receiving device. Connection of multiple charge-pump voltage converters in series can generate higher voltages, and connection of multiple charge-pump voltage converters in parallel can generate higher currents. Microelectromechanical (MEMS) embodiments of this invention provide a small and compact high-voltage (several hundred V) voltage source starting with a few-V initial voltage source. The microscale size of many embodiments of this invention make it ideally suited for MEMS- and other micro-applications where integration of the voltage or charge source in a small package is highly desirable.

Design considerations for imaging charge-coupled device

NASA Astrophysics Data System (ADS)

1981-04-01

The image dissector tube, which was formerly used as detector in star trackers, will be replaced by solid state imaging devices. The technology advances of charge transfer devices, like the charge-coupled device (CCD) and the charge-injection device (CID) have made their application to star trackers an immediate reality. The Air Force in 1979 funded an American Aerospace company to develop an imaging CCD (ICCD) star sensor for the Multimission Attitude Determination and Autonomous Navigation (MADAN) system. The MADAN system is a technology development for a strapdown attitude and navigation system which can be used on all Air Force 3-axis stabilized satellites. The system will be autonomous and will provide real-time satellite attitude and position information. The star sensor accuracy provides an overall MADAN attitude accuracy of 2 arcsec for star rates up to 300 arcsec/sec. The ICCD is basically an integrating device. Its pixel resolution in not yet satisfactory for precision applications.

Charge transfer properties of pentacene adsorbed on silver: DFT study

NASA Astrophysics Data System (ADS)

N, Rekha T.; Rajkumar, Beulah J. M.

2015-06-01

Charge transfer properties of pentacene adsorbed on silver is investigated using DFT methods. Optimized geometry of pentacene after adsorption on silver indicates distortion in hexagonal structure of the ring close to the silver cluster and deviations in co-planarity of carbon atoms due to the variations in bond angles and dihedral angles. Theoretically simulated absorption spectrum has a symmetric surface plasmon resonance peak around 486nm corresponding to the transfer of charge from HOMO-2 to LUMO. Theoretical SERS confirms the process of adsorption, tilted orientation of pentacene on silver surface and the charge transfers reported. Localization of electron density arising from redistribution of electrostatic potential together with a reduced bandgap of pentacene after adsorption on silver suggests its utility in the design of electro active organic semiconducting devices.

Study of digital charge coupled devices

NASA Technical Reports Server (NTRS)

Wilson, D. D.; Young, V. F.

1980-01-01

Charge coupled devices represent unique usage of the metal oxide semiconductor concept. These devices can sample an AC signal at the input, transfer charge proportional to this signal through the CCD shift register and then provide an output of the same frequency and shape as the input. The delay time between input and output is controlled by the CCD operating frequency and the number of stages in the shift resistor. This work is a reliability evaluation of the buried channel and surface channel CCD technologies. The constructions are analyzed, failure modes are described, and test results are reported.

Photochromic, electrochromic, photoelectrochromic and photovoltaic devices

DOEpatents

Kostecki, Robert; McLarnon, Frank R.

2000-01-01

A light activated photoelectrochromic device is formed of a two-component system formed of a photoactive charge carrier generating material and electrochromic material (plus an elecrolyte). Light interacts with a semiconductive material to generate hole-electron charge carriers which cause a redox reaction in the electrochromic material. One device is formed of hydrated nickel oxide as the electrochromic layer and polycrystalline titanium dioxide as the charge generating material. The materials may be formed as discrete layers or mixed together. Because of the direct charge transfer between the layers, a circuit to apply a voltage to drive the electrochromic reaction is not required, although one can be used to enhance the reaction. The hydrated nickel oxide-titanium dioxide materials can also be used to form a photovoltaic device for generating electricity.

Transfer Printing Method to Obtain Polarized Light Emission in Organic Light-Emitting Device

NASA Astrophysics Data System (ADS)

Noh, Hee Yeon; Park, Chang-sub; Park, Ji-Sub; Kang, Shin-Won; Kim, Hak-Rin

2012-06-01

We demonstrate a transfer printing method to obtain polarized light emission in organic light-emitting devices (OLEDs). On a rubbed self-assembled monolayer (SAM), a spin-coated liquid crystalline light-emissive polymer is aligned along the rubbing direction because of the anisotropic interfacial intermolecular interaction. Owing to the low surface energy of the SAM surface, the light-emissive layer was easily transferred to a patterned poly(dimethylsiloxane) (PDMS) stamp surface without degrading the ordering. Finally, a polarized light-emissive OLED device was prepared by transferring the patterned light-emissive layer to the charge transport layer of the OLED structure.

Two-phase charge-coupled device

NASA Technical Reports Server (NTRS)

Kosonocky, W. F.; Carnes, J. E.

1973-01-01

A charge-transfer efficiency of 99.99% per stage was achieved in the fat-zero mode of operation of 64- and 128-stage two-phase charge-coupled shift registers at 1.0-MHz clock frequency. The experimental two-phase charge-coupled shift registers were constructed in the form of polysilicon gates overlapped by aluminum gates. The unidirectional signal flow was accomplished by using n-type substrates with 0.5 to 1.0 ohm-cm resistivity in conjunction with a channel oxide thickness of 1000 A for the polysilicon gates and 3000 A for the aluminum gates. The operation of the tested shift registers with fat zero is in good agreement with the free-charge transfer characteristics expected for the tested structures. The charge-transfer losses observed when operating the experimental shift registers without the fat zero are attributed to fast interface state trapping. The analytical part of the report contains a review backed up by an extensive appendix of the free-charge transfer characteristics of CCD's in terms of thermal diffusion, self-induced drift, and fringing field drift. Also, a model was developed for the charge-transfer losses resulting from charge trapping by fast interface states. The proposed model was verified by the operation of the experimental two-phase charge-coupled shift registers.

Subterahertz acoustical pumping of electronic charge in a resonant tunneling device.

PubMed

Young, E S K; Akimov, A V; Henini, M; Eaves, L; Kent, A J

2012-06-01

We demonstrate that controlled subnanosecond bursts of electronic charge can be transferred through a resonant tunneling diode by successive picosecond acoustic pulses. The effect exploits the nonlinear current-voltage characteristics of the device and its asymmetric response to the compressive and tensile components of the strain pulse. This acoustoelectronic pump opens new possibilities for the control of quantum phenomena in nanostructures.

Solvent Dependence of Lateral Charge Transfer in a Porphyrin Monolayer

DOE PAGES

Brennan, Bradley J.; Regan, Kevin P.; Durrell, Alec C.; ...

2016-12-19

Lateral charge transport in a redox)active monolayer can be utilized for solar energy harvesting. We chose the porphyrin system to study the influence of the solvent on lateral hole hopping, which plays a crucial role in the charge)transfer kinetics. We also examined the influence of water, acetonitrile, and propylene carbonate as solvents. Hole)hopping lifetimes varied by nearly three orders of magnitude among solvents, ranging from 3 ns in water to 2800 ns in propylene carbonate, and increased nonlinearly as a function of added acetonitrile in aqueous solvent mixtures. Our results elucidate the important roles of solvation, molecular packing dynamics, andmore » lateral charge)transfer mechanisms that have implications for all dye)sensitized photoelectrochemical device designs.« less

Utilizing Electrical Characteristics of Individual Nanotube Devices to Study the Charge Transfer between CdSe Quantum Dots and Double-Walled Nanotubes

DOE PAGES

Zhu, Yuqi; Zhou, Ruiping; Wang, Lei; ...

2017-03-02

To study the charge transfer between cadmium selenide (CdSe) quantum dots (QDs) and double-walled nanotubes (DWNTs), various sizes of CdSe-ligand-DWNT structures are synthesized, and field-effect transistors (FETs) from individual functionalized DWNTs rather than networks of the same are fabricated. From the electrical measurements, two distinct electron transfer mechanisms from the QD system to the nanotube are identified. By the formation of the CdSe-ligand-DWNT heterostructure, an effectively n-doped nanotube is created due to the smaller work function of CdSe as compared with the nanotube. In addition, once the QD-DWNT system is exposed to laser light, further electron transfer from the QDmore » through the ligand, i.e. 4-mercaptophenol (MTH), to the nanotube occurs and a clear QD-size dependent tunneling process is observed. Furthermore, the detailed analysis of a large set of devices and the particular methodology employed here for the first time allowed for extracting a wavelength and quantum dot size dependent charge transfer efficiency – a quantity that is evaluated for the first time through electrical measurement.« less

Utilizing Electrical Characteristics of Individual Nanotube Devices to Study the Charge Transfer between CdSe Quantum Dots and Double-Walled Nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Yuqi; Zhou, Ruiping; Wang, Lei

To study the charge transfer between cadmium selenide (CdSe) quantum dots (QDs) and double-walled nanotubes (DWNTs), various sizes of CdSe-ligand-DWNT structures are synthesized, and field-effect transistors (FETs) from individual functionalized DWNTs rather than networks of the same are fabricated. From the electrical measurements, two distinct electron transfer mechanisms from the QD system to the nanotube are identified. By the formation of the CdSe-ligand-DWNT heterostructure, an effectively n-doped nanotube is created due to the smaller work function of CdSe as compared with the nanotube. In addition, once the QD-DWNT system is exposed to laser light, further electron transfer from the QDmore » through the ligand, i.e. 4-mercaptophenol (MTH), to the nanotube occurs and a clear QD-size dependent tunneling process is observed. Furthermore, the detailed analysis of a large set of devices and the particular methodology employed here for the first time allowed for extracting a wavelength and quantum dot size dependent charge transfer efficiency – a quantity that is evaluated for the first time through electrical measurement.« less

Synthesis of Stable Interfaces on SnO2 Surfaces for Charge-Transfer Applications

NASA Astrophysics Data System (ADS)

Benson, Michelle C.

The commercial market for solar harvesting devices as an alternative energy source requires them to be both low-cost and efficient to replace or reduce the dependence on fossil fuel burning. Over the last few decades there has been promising efforts towards improving solar devices by using abundant and non-toxic metal oxide nanomaterials. One particular metal oxide of interest has been SnO2 due to its high electron mobility, wide-band gap, and aqueous stability. However SnO2 based solar cells have yet to reach efficiency values of other metal oxides, like TiO2. The advancement of SnO2 based devices is dependent on many factors, including improved methods of surface functionalization that can yield stable interfaces. This work explores the use of a versatile functionalization method through the use of the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The CuAAC reaction is capable of producing electrochemically, photochemically, and electrocatalytically active surfaces on a variety of SnO2 materials. The resulting charge-transfer characteristics were investigated as well as an emphasis on understanding the stability of the resulting molecular linkage. We determined the CuAAC reaction is able to proceed through both azide-modified and alkyne-modified surfaces. The resulting charge-transfer properties showed that the molecular tether was capable of supporting charge separation at the interface. We also investigated the enhancement of electron injection upon the introduction of an ultra-thin ZrO2 coating on SnO2. Several complexes were used to fully understand the charge-transfer capabilities, including model systems of ferrocene and a ruthenium coordination complex, a ruthenium mononuclear water oxidation catalyst, and a commercial ruthenium based dye.

Room-temperature current blockade in atomically defined single-cluster junctions

NASA Astrophysics Data System (ADS)

Lovat, Giacomo; Choi, Bonnie; Paley, Daniel W.; Steigerwald, Michael L.; Venkataraman, Latha; Roy, Xavier

2017-11-01

Fabricating nanoscopic devices capable of manipulating and processing single units of charge is an essential step towards creating functional devices where quantum effects dominate transport characteristics. The archetypal single-electron transistor comprises a small conducting or semiconducting island separated from two metallic reservoirs by insulating barriers. By enabling the transfer of a well-defined number of charge carriers between the island and the reservoirs, such a device may enable discrete single-electron operations. Here, we describe a single-molecule junction comprising a redox-active, atomically precise cobalt chalcogenide cluster wired between two nanoscopic electrodes. We observe current blockade at room temperature in thousands of single-cluster junctions. Below a threshold voltage, charge transfer across the junction is suppressed. The device is turned on when the temporary occupation of the core states by a transiting carrier is energetically enabled, resulting in a sequential tunnelling process and an increase in current by a factor of ∼600. We perform in situ and ex situ cyclic voltammetry as well as density functional theory calculations to unveil a two-step process mediated by an orbital localized on the core of the cluster in which charge carriers reside before tunnelling to the collector reservoir. As the bias window of the junction is opened wide enough to include one of the cluster frontier orbitals, the current blockade is lifted and charge carriers can tunnel sequentially across the junction.

Method of acquiring an image from an optical structure having pixels with dedicated readout circuits

NASA Technical Reports Server (NTRS)

Fossum, Eric R. (Inventor); Mendis, Sunetra (Inventor); Kemeny, Sabrina E. (Inventor)

2006-01-01

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node.

Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

DOE PAGES

Ma, X.; Fang, F.; Li, Q.; ...

2015-10-28

In this study, optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recoverymore » time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.« less

The design of an energy harvesting device for prolonging the working time of DC equipment

NASA Astrophysics Data System (ADS)

Wen, Yayuan; Deng, Huaxia; Zhang, Jin; Yu, Liandong

2016-01-01

Energy harvesting (EH) derives from the idea of converting the ambient energy into electric energy, which can solve the problem of DC supply for some electronic equipment. PZT is a typical piezoelectric material of inorganic, which has been developed as EH devices to transfer ambient vibration energy into electric energy. However, these PZT devices require relatively violent excitation, and easy to be fatigue fracture under the resonance condition. In this paper, PVDF, which is a kind of soft piezoelectric polymer, is adopted for developing transducer. The PVDF devices are flexible and have longer life time than PZT devices under the harmonic environment. The EH researches are mainly focused on the development of energy transfer efficiency either by the mechanical structure of transducer or the improvement of circuit. However, the practicality and stability of the EH devices are important in the practical engineering applications. In this paper, a charge amplifier is introduced in the circuit in order to guarantee the stability of the battery charging under small ambient vibration conditions. The model of the mechanical structure of PVDF and the electric performance of circuit are developed. The experimental results and simulation show that the stability of battery charging is improved and the working time of DC equipment is prolonged.

Balancing the Electron and Hole Transfer for Efficient Quantum Dot Light-Emitting Diodes by Employing a Versatile Organic Electron-Blocking Layer.

PubMed

Jin, Xiao; Chang, Chun; Zhao, Weifeng; Huang, Shujuan; Gu, Xiaobing; Zhang, Qin; Li, Feng; Zhang, Yubao; Li, Qinghua

2018-05-09

The electron-blocking layer (EBL) is important to balance the charge carrier transfer and achieve highly efficient quantum dot light-emitting diodes (QLEDs). Here, we report the utilization of a soluble tert-butyldimethylsilyl chloride-modified poly( p-phenylene benzobisoxazole) (TBS-PBO) as an EBL for simultaneous good charge carrier transfer balance while maintaining a high current density. We show that the versatile TBS-PBO blocks excess electron injection into the quantum dots (QDs), thus leading to better charge carrier transfer balance. It also restricts the undesired QD-to-EBL electron-transfer process, which preserves the superior emission capabilities of the emitter. As a consequence, the TBS-PBO device delivers an external quantum efficiency (EQE) maximum of 16.7% along with a remarkable current density as high as 139 mA/cm 2 with a brightness of 5484 cd/m 2 . The current density of our device is higher than those of insulator EBL-based devices because of the higher conductivity of the TBS-PBO versus insulator EBL, thus helping achieve high luminance values ranging from 1414 to 20 000 cd/cm 2 with current densities ranging from 44 to 648 mA/cm 2 and EQE > 14%. We believe that these unconventional features of the present TBS-PBO-based QLEDs will expand the wide use of TBS-PBO as buffer layers in other advanced QLED applications.

Tunable charge transfer properties in metal-phthalocyanine heterojunctions.

PubMed

Siles, P F; Hahn, T; Salvan, G; Knupfer, M; Zhu, F; Zahn, D R T; Schmidt, O G

2016-04-28

Organic materials such as phthalocyanine-based systems present a great potential for organic device applications due to the possibility of integrating films of different organic materials to create organic heterostructures which combine the electrical capabilities of each material. This opens the possibility to precisely engineer and tune new electrical properties. In particular, similar transition metal phthalocyanines demonstrate hybridization and charge transfer properties which could lead to interesting physical phenomena. Although, when considering device dimensions, a better understanding and control of the tuning of the transport properties still remain in the focus of research. Here, by employing conductive atomic force microscopy techniques, we provide an insight about the nanoscale electrical properties and transport mechanisms of MnPc and fluorinated phthalocyanines such as F16CuPc and F16CoPc. We report a transition from typical diode-like transport mechanisms for pure MnPc thin films to space-charge-limited current transport regime (SCLC) for Pc-based heterostructures. The controlled addition of fluorinated phthalocyanine also provides highly uniform and symmetric-polarized transport characteristics with conductance enhancements up to two orders of magnitude depending on the polarization. We present a method to spatially map the mobility of the MnPc/F16CuPc structures with a nanoscale resolution and provide theoretical calculations to support our experimental findings. This well-controlled nanoscale tuning of the electrical properties for metal transition phthalocyanine junctions stands as key step for future phthalocyanine-based electronic devices, where the low dimension charge transfer, mediated by transition metal atoms could be intrinsically linked to a transfer of magnetic moment or spin.

Surface Charge Transfer Doping via Transition Metal Oxides for Efficient p-Type Doping of II-VI Nanostructures.

PubMed

Xia, Feifei; Shao, Zhibin; He, Yuanyuan; Wang, Rongbin; Wu, Xiaofeng; Jiang, Tianhao; Duhm, Steffen; Zhao, Jianwei; Lee, Shuit-Tong; Jie, Jiansheng

2016-11-22

Wide band gap II-VI nanostructures are important building blocks for new-generation electronic and optoelectronic devices. However, the difficulty of realizing p-type conductivity in these materials via conventional doping methods has severely handicapped the fabrication of p-n homojunctions and complementary circuits, which are the fundamental components for high-performance devices. Herein, by using first-principles density functional theory calculations, we demonstrated a simple yet efficient way to achieve controlled p-type doping on II-VI nanostructures via surface charge transfer doping (SCTD) using high work function transition metal oxides such as MoO 3 , WO 3 , CrO 3 , and V 2 O 5 as dopants. Our calculations revealed that these oxides were capable of drawing electrons from II-VI nanostructures, leading to accumulation of positive charges (holes injection) in the II-VI nanostructures. As a result, Fermi levels of the II-VI nanostructures were shifted toward the valence band regions after surface modifications, along with the large enhancement of work functions. In situ ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy characterizations verified the significant interfacial charge transfer between II-VI nanostructures and surface dopants. Both theoretical calculations and electrical transfer measurements on the II-VI nanostructure-based field-effect transistors clearly showed the p-type conductivity of the nanostructures after surface modifications. Strikingly, II-VI nanowires could undergo semiconductor-to-metal transition by further increasing the SCTD level. SCTD offers the possibility to create a variety of electronic and optoelectronic devices from the II-VI nanostructures via realization of complementary doping.

A chiral-based magnetic memory device without a permanent magnet

PubMed Central

Dor, Oren Ben; Yochelis, Shira; Mathew, Shinto P.; Naaman, Ron; Paltiel, Yossi

2013-01-01

Several technologies are currently in use for computer memory devices. However, there is a need for a universal memory device that has high density, high speed and low power requirements. To this end, various types of magnetic-based technologies with a permanent magnet have been proposed. Recent charge-transfer studies indicate that chiral molecules act as an efficient spin filter. Here we utilize this effect to achieve a proof of concept for a new type of chiral-based magnetic-based Si-compatible universal memory device without a permanent magnet. More specifically, we use spin-selective charge transfer through a self-assembled monolayer of polyalanine to magnetize a Ni layer. This magnitude of magnetization corresponds to applying an external magnetic field of 0.4 T to the Ni layer. The readout is achieved using low currents. The presented technology has the potential to overcome the limitations of other magnetic-based memory technologies to allow fabricating inexpensive, high-density universal memory-on-chip devices. PMID:23922081

A chiral-based magnetic memory device without a permanent magnet.

PubMed

Ben Dor, Oren; Yochelis, Shira; Mathew, Shinto P; Naaman, Ron; Paltiel, Yossi

2013-01-01

Several technologies are currently in use for computer memory devices. However, there is a need for a universal memory device that has high density, high speed and low power requirements. To this end, various types of magnetic-based technologies with a permanent magnet have been proposed. Recent charge-transfer studies indicate that chiral molecules act as an efficient spin filter. Here we utilize this effect to achieve a proof of concept for a new type of chiral-based magnetic-based Si-compatible universal memory device without a permanent magnet. More specifically, we use spin-selective charge transfer through a self-assembled monolayer of polyalanine to magnetize a Ni layer. This magnitude of magnetization corresponds to applying an external magnetic field of 0.4 T to the Ni layer. The readout is achieved using low currents. The presented technology has the potential to overcome the limitations of other magnetic-based memory technologies to allow fabricating inexpensive, high-density universal memory-on-chip devices.

CCD radiation damage in ESA Cosmic Visions missions: assessment and mitigation

NASA Astrophysics Data System (ADS)

Lumb, David H.

2009-08-01

Charge Coupled Device (CCD) imagers have been widely used in space-borne astronomical instruments. A frequent concern has been the radiation damage effects on the CCD charge transfer properties. We review some methods for assessing the Charge Transfer Inefficiency (CTI) in CCDs. Techniques to minimise degradation using background charge injection and p-channel CCD architectures are discussed. A critical review of the claims for p-channel architectures is presented. The performance advantage for p-channel CCD performance is shown to be lower than claimed previously. Finally we present some projections for the performance in the context of some future ESA missions.

What Controls the Rate of Ultrafast Charge Transfer and Charge Separation Efficiency in Organic Photovoltaic Blends.

PubMed

Jakowetz, Andreas C; Böhm, Marcus L; Zhang, Jiangbin; Sadhanala, Aditya; Huettner, Sven; Bakulin, Artem A; Rao, Akshay; Friend, Richard H

2016-09-14

In solar energy harvesting devices based on molecular semiconductors, such as organic photovoltaics (OPVs) and artificial photosynthetic systems, Frenkel excitons must be dissociated via charge transfer at heterojunctions to yield free charges. What controls the rate and efficiency of charge transfer and charge separation is an important question, as it determines the overall power conversion efficiency (PCE) of these systems. In bulk heterojunctions between polymer donor and fullerene acceptors, which provide a model system to understand the fundamental dynamics of electron transfer in molecular systems, it has been established that the first step of photoinduced electron transfer can be fast, of order 100 fs. But here we report the first study which correlates differences in the electron transfer rate with electronic structure and morphology, achieved with sub-20 fs time resolution pump-probe spectroscopy. We vary both the fullerene substitution and donor/fullerene ratio which allow us to control both aggregate size and the energetic driving force for charge transfer. We observe a range of electron transfer times from polymer to fullerene, from 240 fs to as short as 37 fs. Using ultrafast electro-optical pump-push-photocurrent spectroscopy, we find the yield of free versus bound charges to be weakly dependent on the energetic driving force, but to be very strongly dependent on fullerene aggregate size and packing. Our results point toward the importance of state accessibility and charge delocalization and suggest that energetic offsets between donor and acceptor levels are not an important criterion for efficient charge generation. This provides design rules for next-generation materials to minimize losses related to driving energy and boost PCE.

The Role of FRET in Non-Fullerene Organic Solar Cells: Implications for Molecular Design.

PubMed

Gautam, Bhoj R; Younts, Robert; Carpenter, Joshua; Ade, Harald; Gundogdu, Kenan

2018-04-19

Non-fullerene acceptors (NFAs) have been demonstrated to be promising candidates for highly efficient organic photovoltaic (OPV) devices. The tunability of absorption characteristics of NFAs can be used to make OPVs with complementary donor-acceptor absorption to cover a broad range of the solar spectrum. However, both charge transfer from donor to acceptor moieties and energy (energy) transfer from high-bandgap to low-bandgap materials are possible in such structures. Here, we show that when charge transfer and exciton transfer processes are both present, the coexistence of excitons in both domains can cause a loss mechanism. Charge separation of excitons in a low-bandgap material is hindered due to exciton population in the larger bandgap acceptor domains. Our results further show that excitons in low-bandgap material should have a relatively long lifetime compared to the transfer time of excitons from higher bandgap material in order to contribute to the charge separation. These observations provide significant guidance for design and development of new materials in OPV applications.

Electronic structure and charge transfer excited states of endohedral fullerene containing electron donoracceptor complexes utilized in organic photovoltaics

NASA Astrophysics Data System (ADS)

Amerikheirabadi, Fatemeh

Organic Donor-Acceptor complexes form the main component of the organic photovoltaic devices (OPVs). The open circuit voltage of OPVs is directly related to the charge transfer excited state energies of these complexes. Currently a large number of different molecular complexes are being tested for their efficiency in photovoltaic devices. In this work, density functional theory as implemented in the NRLMOL code is used to investigate the electronic structure and related properties of these donor-acceptor complexes. The charge transfer excitation energies are calculated using the perturbative delta self-consistent field method recently developed in our group as the standard time dependent density functional approaches fail to accurately provide them. The model photovoltaics systems analyzed are as follows: Sc3N C 80--ZnTPP, Y3 N C80-- ZnTPP and Sc3 N C80-- ZnPc. In addition, a thorough analysis of the isolated donor and acceptor molecules is also provided. The studied acceptors are chosen from a class of fullerenes named trimetallic nitride endohedral fullerenes. These molecules have shown to possess advantages as acceptors such as long lifetimes of the charge-separated states.

Carbon Nanotube Embedded Nanostructure for Biometrics.

PubMed

Park, Juhyuk; Youn, Jae Ryoun; Song, Young Seok

2017-12-27

Low electric energy loss is a very important problem to minimize the decay of transferred energy intensity due to impedance mismatch. This issue has been dealt with by adding an impedance matching layer at the interface between two media. A strategy was proposed to improve the charge transfer from the human body to a biometric device by using an impedance matching nanostructure. Nanocomposite pattern arrays were fabricated with shape memory polymer and carbon nanotubes. The shape recovery ability of the nanopatterns enhanced durability and sustainability of the structure. It was found that the composite nanopatterns improved the current transfer by two times compared with the nonpatterned composite sample. The underlying mechanism of the enhanced charge transport was understood by carrying out a numerical simulation. We anticipate that this study can provide a new pathway for developing advanced biometric devices with high sensitivity to biological information.

Size and Temperature Dependence of Electron Transfer between CdSe Quantum Dots and a TiO 2 Nanobelt

DOE PAGES

Tafen, De Nyago; Prezhdo, Oleg V.

2015-02-24

Understanding charge transfer reactions between quantum dots (QD) and metal oxides is fundamental for improving photocatalytic, photovoltaic and electronic devices. The complexity of these processes makes it difficult to find an optimum QD size with rapid charge injection and low recombination. We combine time-domain density functional theory with nonadiabatic molecular dynamics to investigate the size and temperature dependence of the experimentally studied electron transfer and charge recombination at CdSe QD-TiO 2 nanobelt (NB) interfaces. The electron injection rate shows strong dependence on the QD size, increasing for small QDs. The rate exhibits Arrhenius temperature dependence, with the activation energy ofmore » the order of millielectronvolts. The charge recombination process occurs due to coupling of the electronic subsystem to vibrational modes of the TiO 2 NB. Inelastic electron-phonon scattering happens on a picosecond time scale, with strong dependence on the QD size. Our simulations demonstrate that the electron-hole recombination rate decreases significantly as the QD size increases, in excellent agreement with experiments. The temperature dependence of the charge recombination rates can be successfully modeled within the framework of the Marcus theory through optimization of the electronic coupling and the reorganization energy. Our simulations indicate that by varying the QD size, one can modulate the photoinduced charge separation and charge recombination, fundamental aspects of the design principles for high efficiency devices.« less

Electron transport limitation in P3HT:CdSe nanorods hybrid solar cells.

PubMed

Lek, Jun Yan; Xing, Guichuan; Sum, Tze Chien; Lam, Yeng Ming

2014-01-22

Hybrid solar cells have the potential to be efficient solar-energy-harvesting devices that can combine the benefits of solution-processable organic materials and the extended absorption offered by inorganic materials. In this work, an understanding of the factors limiting the performance of hybrid solar cells is explored. Through photovoltaic-device characterization correlated with transient absorption spectroscopy measurements, it was found that the interfacial charge transfer between the organic (P3HT) and inorganic (CdSe nanorods) components is not the factor limiting the performance of these solar cells. The insulating original ligands retard the charge recombination between the charge-transfer states across the CdSe-P3HT interface, and this is actually beneficial for charge collection. These cells are, in fact, limited by the subsequent electron collection via CdSe nanoparticles to the electrodes. Hence, the design of a more continuous electron-transport pathway should greatly improve the performance of hybrid solar cells in the future.

Quantum Mechanical Calculations of Free Energy and Open-Circuit Voltage in Lattice Modeled Organic Photovoltaic Devices

NASA Astrophysics Data System (ADS)

Lankevich, Vladimir; Bittner, Eric

In organic photovoltaic devices (OPVs), initially bound electron and hole can take many different paths to dissociate and become free charge carriers. This leads to the increase in their density of states and therefore increase in the entropy of the system. Accurate description of the energy barriers that charges have to overcome, therefore requires calculation of the free energy. Free energy of an OPV is directly related to its open-circuit voltage and depends only on few important parameters such as average life-time of a charge-transfer state, average energy of the charge-transfer state and energetic disorder in the system. We extend these ideas to the quantum mechanical simulations of the dissociation in the lattice modeled bulk-heterojunction system. We observe average excitonic and free energies that agree with theoretical predictions and the number of experimental results from previous studies. We study effects of the energy disorder and importance of the dimensionality and morphology in materials such as polymer-fullerene blends.

Molecular Photovoltaics in Nanoscale Dimension

PubMed Central

Burtman, Vladimir; Zelichonok, Alexander; Pakoulev, Andrei V.

2011-01-01

This review focuses on the intrinsic charge transport in organic photovoltaic (PVC) devices and field-effect transistors (SAM-OFETs) fabricated by vapor phase molecular self-assembly (VP-SAM) method. The dynamics of charge transport are determined and used to clarify a transport mechanism. The 1,4,5,8-naphthalene-tetracarboxylic diphenylimide (NTCDI) SAM devices provide a useful tool to study the fundamentals of polaronic transport at organic surfaces and to discuss the performance of organic photovoltaic devices in nanoscale. Time-resolved photovoltaic studies allow us to separate the charge annihilation kinetics in the conductive NTCDI channel from the overall charge kinetic in a SAM-OFET device. It has been demonstrated that tuning of the type of conductivity in NTCDI SAM-OFET devices is possible by changing Si substrate doping. Our study of the polaron charge transfer in organic materials proposes that a cation-radical exchange (redox) mechanism is the major transport mechanism in the studied SAM-PVC devices. The role and contribution of the transport through delocalized states of redox active surface molecular aggregates of NTCDI are exposed and investigated. This example of technological development is used to highlight the significance of future technological development of nanotechnologies and to appreciate a structure-property paradigm in organic nanostructures. PMID:21339983

Atomic layer deposited oxide films as protective interface layers for integrated graphene transfer

NASA Astrophysics Data System (ADS)

Cabrero-Vilatela, A.; Alexander-Webber, J. A.; Sagade, A. A.; Aria, A. I.; Braeuninger-Weimer, P.; Martin, M.-B.; Weatherup, R. S.; Hofmann, S.

2017-12-01

The transfer of chemical vapour deposited graphene from its parent growth catalyst has become a bottleneck for many of its emerging applications. The sacrificial polymer layers that are typically deposited onto graphene for mechanical support during transfer are challenging to remove completely and hence leave graphene and subsequent device interfaces contaminated. Here, we report on the use of atomic layer deposited (ALD) oxide films as protective interface and support layers during graphene transfer. The method avoids any direct contact of the graphene with polymers and through the use of thicker ALD layers (≥100 nm), polymers can be eliminated from the transfer-process altogether. The ALD film can be kept as a functional device layer, facilitating integrated device manufacturing. We demonstrate back-gated field effect devices based on single-layer graphene transferred with a protective Al2O3 film onto SiO2 that show significantly reduced charge trap and residual carrier densities. We critically discuss the advantages and challenges of processing graphene/ALD bilayer structures.

Long-range energy transfer in self-assembled quantum dot-DNA cascades

NASA Astrophysics Data System (ADS)

Goodman, Samuel M.; Siu, Albert; Singh, Vivek; Nagpal, Prashant

2015-11-01

The size-dependent energy bandgaps of semiconductor nanocrystals or quantum dots (QDs) can be utilized in converting broadband incident radiation efficiently into electric current by cascade energy transfer (ET) between layers of different sized quantum dots, followed by charge dissociation and transport in the bottom layer. Self-assembling such cascade structures with angstrom-scale spatial precision is important for building realistic devices, and DNA-based QD self-assembly can provide an important alternative. Here we show long-range Dexter energy transfer in QD-DNA self-assembled single constructs and ensemble devices. Using photoluminescence, scanning tunneling spectroscopy, current-sensing AFM measurements in single QD-DNA cascade constructs, and temperature-dependent ensemble devices using TiO2 nanotubes, we show that Dexter energy transfer, likely mediated by the exciton-shelves formed in these QD-DNA self-assembled structures, can be used for efficient transport of energy across QD-DNA thin films.The size-dependent energy bandgaps of semiconductor nanocrystals or quantum dots (QDs) can be utilized in converting broadband incident radiation efficiently into electric current by cascade energy transfer (ET) between layers of different sized quantum dots, followed by charge dissociation and transport in the bottom layer. Self-assembling such cascade structures with angstrom-scale spatial precision is important for building realistic devices, and DNA-based QD self-assembly can provide an important alternative. Here we show long-range Dexter energy transfer in QD-DNA self-assembled single constructs and ensemble devices. Using photoluminescence, scanning tunneling spectroscopy, current-sensing AFM measurements in single QD-DNA cascade constructs, and temperature-dependent ensemble devices using TiO2 nanotubes, we show that Dexter energy transfer, likely mediated by the exciton-shelves formed in these QD-DNA self-assembled structures, can be used for efficient transport of energy across QD-DNA thin films. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04778a

Gate bias stress in pentacene field-effect-transistors: Charge trapping in the dielectric or semiconductor

NASA Astrophysics Data System (ADS)

Häusermann, R.; Batlogg, B.

2011-08-01

Gate bias stress instability in organic field-effect transistors (OFETs) is a major conceptual and device issue. This effect manifests itself by an undesirable shift of the transfer characteristics and is associated with long term charge trapping. We study the role of the dielectric and the semiconductor separately by producing OFETs with the same semiconductor (pentacene) combined with different dielectrics (SiO2 and Cytop). We show that it is possible to fabricate devices which are immune to gate bias stress. For other material combinations, charge trapping occurs in the semiconductor alone or in the dielectric.

DOE Office of Scientific and Technical Information (OSTI.GOV)

N, Rekha T.; Rajkumar, Beulah J. M., E-mail: beulah-rajkumar@yahoo.co.in

Charge transfer properties of pentacene adsorbed on silver is investigated using DFT methods. Optimized geometry of pentacene after adsorption on silver indicates distortion in hexagonal structure of the ring close to the silver cluster and deviations in co-planarity of carbon atoms due to the variations in bond angles and dihedral angles. Theoretically simulated absorption spectrum has a symmetric surface plasmon resonance peak around 486nm corresponding to the transfer of charge from HOMO-2 to LUMO. Theoretical SERS confirms the process of adsorption, tilted orientation of pentacene on silver surface and the charge transfers reported. Localization of electron density arising from redistributionmore » of electrostatic potential together with a reduced bandgap of pentacene after adsorption on silver suggests its utility in the design of electro active organic semiconducting devices.« less

A comparison of various surface charge transfer hole doping of graphene grown by chemical vapour deposition

NASA Astrophysics Data System (ADS)

Chandramohan, S.; Seo, Tae Hoon; Janardhanam, V.; Hong, Chang-Hee; Suh, Eun-Kyung

2017-10-01

Charge transfer doping is a renowned route to modify the electrical and electronic properties of graphene. Understanding the stability of potentially important charge-transfer materials for graphene doping is a crucial first step. Here we present a systematic comparison on the doping efficiency and stability of single layer graphene using molybdenum trioxide (MoO3), gold chloride (AuCl3), and bis(trifluoromethanesulfonyl)amide (TFSA). Chemical dopants proved to be very effective, but MoO3 offers better thermal stability and device fabrication compatibility. Single layer graphene films with sheet resistance values between 100 and 200 ohm/square were consistently produced by implementing a two-step growth followed by doping without compromising the optical transmittance.

Interfacial Charge Transfer States in Condensed Phase Systems

NASA Astrophysics Data System (ADS)

Vandewal, Koen

2016-05-01

Intermolecular charge transfer (CT) states at the interface between electron-donating (D) and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. CT states efficiently generate charge carriers for some D-A combinations, and others show high fluorescence quantum efficiencies. These properties are exploited in organic solar cells, photodetectors, and light-emitting diodes. This review summarizes experimental and theoretical work on the electronic structure and interfacial energy landscape at condensed matter D-A interfaces. Recent findings on photogeneration and recombination of free charge carriers via CT states are discussed, and relations between CT state properties and optoelectronic device parameters are clarified.

Specialized CCDs for high-frame-rate visible imaging and UV imaging applications

NASA Astrophysics Data System (ADS)

Levine, Peter A.; Taylor, Gordon C.; Shallcross, Frank V.; Tower, John R.; Lawler, William B.; Harrison, Lorna J.; Socker, Dennis G.; Marchywka, Mike

1993-11-01

This paper reports recent progress by the authors in two distinct charge coupled device (CCD) technology areas. The first technology area is high frame rate, multi-port, frame transfer imagers. A 16-port, 512 X 512, split frame transfer imager and a 32-port, 1024 X 1024, split frame transfer imager are described. The thinned, backside illuminated devices feature on-chip correlated double sampling, buried blooming drains, and a room temperature dark current of less than 50 pA/cm2, without surface accumulation. The second technology area is vacuum ultraviolet (UV) frame transfer imagers. A developmental 1024 X 640 frame transfer imager with 20% quantum efficiency at 140 nm is described. The device is fabricated in a p-channel CCD process, thinned for backside illumination, and utilizes special packaging to achieve stable UV response.

Measurement of charge transfer potential barrier in pinned photodiode CMOS image sensors

NASA Astrophysics Data System (ADS)

Chen, Cao; Bing, Zhang; Junfeng, Wang; Longsheng, Wu

2016-05-01

The charge transfer potential barrier (CTPB) formed beneath the transfer gate causes a noticeable image lag issue in pinned photodiode (PPD) CMOS image sensors (CIS), and is difficult to measure straightforwardly since it is embedded inside the device. From an understanding of the CTPB formation mechanism, we report on an alternative method to feasibly measure the CTPB height by performing a linear extrapolation coupled with a horizontal left-shift on the sensor photoresponse curve under the steady-state illumination. The theoretical study was performed in detail on the principle of the proposed method. Application of the measurements on a prototype PPD-CIS chip with an array of 160 × 160 pixels is demonstrated. Such a method intends to shine new light on the guidance for the lag-free and high-speed sensors optimization based on PPD devices. Project supported by the National Defense Pre-Research Foundation of China (No. 51311050301095).

A numerical investigation of a thermodielectric power generation system

NASA Astrophysics Data System (ADS)

Sklar, Akiva A.

The performance of a novel micro-thermodielectric power generation system was investigated in order to determine if thermodielectric power generation can be practically employed and if its performance can compete with current portable power generation technologies. Thermodielectric power generation is a direct energy conversion technology that converts heat directly into high voltage direct current. It requires dielectric (i.e., capacitive) materials whose charge storing capabilities are a function of temperature. This property can be exploited by heating these materials after they are charged; as their temperature increases, their charge storage capability decreases, forcing them to eject a portion of their surface charge. This ejected charge can then be supplied to an appropriate electronic storage device. There are several advantages associated with thermodielectric energy conversion; first, it requires heat addition at relatively low conventional power generation temperatures, i.e., less than 600 °K, and second, devices that utilize it have the potential for excellent power density and device reliability. The predominant disadvantage of using this power generation technique is that the device must operate in an unsteady manner; this can lead to substantial heat transfer losses that limit the device's thermal efficiency. The studied power generation system was designed so that the power generating components of the system (i.e., the thermodielectric materials) are integrated within a micro-scale heat exchange apparatus designed specifically to provide the thermodielectric materials with the unsteady heating and cooling necessary for efficient power generation. This apparatus is designed to utilize a liquid as a working fluid in order to maximize its heat transfer capabilities, minimize the size of the heat exchanger, and maximize the power density of the power generation system. The thermodielectric materials are operated through a power generation cycle that consists of four processes; the first process is a charging process, during which an electric field is applied to a thermodielectric material, causing it to acquire electrical charge on its surface (this process is analogous to the isentropic compression process of a Brayton cycle). The second process is a heating process in which the temperature of the dielectric material is increased via heat transfer from an external source. During this process, the thermodielectric material is forced to eject a portion of its surface charge because its charge storing capability decreases as the temperature increases; the ejected charge is intended for capture by external circuitry connected to the thermodielectric material, where it can be routed to an electrochemical storage device or an electromechanical device requiring high voltage direct current. The third process is a discharging process, during which the applied electric field is reduced to its initial strength (analogous to the isentropic expansion process of a Brayton cycle). The final process is a cooling process in which the temperature of the dielectric material is decreased via heat transfer from an external source, returning it to its initial temperature. Previously, predicting the performance of a thermodielectric power generator was hindered by a poor understanding of the material's thermodynamic properties and the effect unsteady heat transfer losses have on system performance. In order to improve predictive capabilities in this study, a thermodielectric equation of state was developed that relates the strength of the applied electric field, the amount of surface charge stored by the thermodielectric material, and its temperature. This state equation was then used to derive expressions for the material's thermodynamic states (internal energy, entropy), which were subsequently used to determine the optimum material properties for power generation. Next, a numerical simulation code was developed to determine the heat transfer capabilities of a micro-scale parallel plate heat recuperator (MPPHR), a device designed specifically to (a) provide the unsteady heating and cooling necessary for thermodielectric power generation and (b) minimize the unsteady heat transfer losses of the system. The simulation code was used to find the optimum heat transfer and heat recuperation regimes of the MPPHR. The previously derived thermodynamic equations that describe the behavior of the thermodielectric materials were then incorporated into the model for the walls of the parallel plate channel in the numerical simulation code, creating a tool capable of determining the thermodynamic performance of an MTDPG, in terms of the thermal efficiency, percent Carnot efficiency, and energy/power density. A detailed parameterization of the MTDPG with the simulation code yielded the critical non-dimensional numbers that determine the relationship between the heat exchange/recuperation abilities of the flow and the power generation capabilities of the thermodielectric materials. These relationships were subsequently used to optimize the performance of an MTDPG with an operating temperature range of 300--500 °K. The optimization predicted that the MTDPG could provide a thermal efficiency of 29.7 percent with the potential to reach 34 percent. These thermal efficiencies correspond to 74.2 and 85 percent of the Carnot efficiency, respectively. The power density of this MTDPG depends on the operating frequency and can exceed 1,000,000 W/m3.

Charge transfer in photorechargeable composite films of TiO2 and polyaniline

NASA Astrophysics Data System (ADS)

Nomiyama, Teruaki; Sasabe, Kenichi; Sakamoto, Kenta; Horie, Yuji

2015-07-01

A photorechargeable battery (PRB) is a photovoltaic device having an energy storage function in a single cell. The photoactive electrode of PRB is a bilayer film consisting of bare porous TiO2 and a TiO2-polyaniline (PANi) mixture that work as a photovoltaic current generator and an electrochemical energy storage by ion dedoping, respectively. To study the charge transfer between TiO2 and PANi, the photorechargeable quantum efficiency QE ([electron count on discharge]/[incident photon count on photocharge]) was measured by varying the thickness LS of the TiO2-PANi mixture. The quantum efficiency QEuv for UV photons had a maximum of ˜7% at LS ˜ 7 µm. The time constant τTP for the charge transfer was about 10-1 s, which was longer ten times or more than the lifetime of excited electrons within TiO2. These facts reveal that the main rate-limiting factor in the photocharging process is the charge transfer between TiO2 and PANi.

Evidences For Charge Transfer-Induced Conformational Changes In Carbon Nanostructure-Protein Corona

PubMed Central

Podila, R.; Vedantam, P.; Ke, P. C.; Brown, J. M.; Rao, A. M.

2012-01-01

The binding of proteins to a nanostructure often alters protein secondary and tertiary structures. However, the main physical mechanisms that elicit protein conformational changes in the presence of the nanostructure have not yet been fully established. Here we performed a comprehensive spectroscopic study to probe the interactions between bovine serum albumin (BSA) and carbon-based nanostructures of graphene and single-walled carbon nanotubes (SWNTs). Our results showed that the BSA “corona” acted as a weak acceptor to facilitate charge transfer from the carbon nanostructures. Notably, we observed that charge transfer occurred only in the case of SWNTs but not in graphene, resulting from the sharp and discrete electronic density of states of the former. Furthermore, the relaxation of external α–helices in BSA secondary structure increased concomitantly with the charge transfer. These results may help guide controlled nanostructure-biomolecular interactions and prove beneficial for developing novel drug delivery systems, biomedical devices and engineering of safe nanomaterials. PMID:23243478

Hysteresis in the transfer characteristics of MoS2 transistors

NASA Astrophysics Data System (ADS)

Di Bartolomeo, Antonio; Genovese, Luca; Giubileo, Filippo; Iemmo, Laura; Luongo, Giuseppe; Foller, Tobias; Schleberger, Marika

2018-01-01

We investigate the origin of the hysteresis observed in the transfer characteristics of back-gated field-effect transistors with an exfoliated MoS2 channel. We find that the hysteresis is strongly enhanced by increasing either gate voltage, pressure, temperature or light intensity. Our measurements reveal a step-like behavior of the hysteresis around room temperature, which we explain as water-facilitated charge trapping at the MoS2/SiO2 interface. We conclude that intrinsic defects in MoS2, such as S vacancies, which result in effective positive charge trapping, play an important role, besides H2O and O2 adsorbates on the unpassivated device surface. We show that the bistability associated to the hysteresis can be exploited in memory devices.

Investigating wireless power transfer

NASA Astrophysics Data System (ADS)

St John, Stuart A.

2017-09-01

Understanding Physics is a great end in itself, but is also crucial to keep pace with developments in modern technology. Wireless power transfer, known to many only as a means to charge electric toothbrushes, will soon be commonplace in charging phones, electric cars and implanted medical devices. This article outlines how to produce and use a simple set of equipment to both demonstrate and investigate this phenomenon. It presents some initial findings and aims to encourage Physics educators and their students to conduct further research, pushing the bounds of their understanding.

Technological inductive power transfer systems

NASA Astrophysics Data System (ADS)

Madzharov, Nikolay D.; Nemkov, Valentin S.

2017-05-01

Inductive power transfer is a very fast expanding technology with multiple design principles and practical implementations ranging from charging phones and computers to bionic systems, car chargers and continuous power transfer in technological lines. Only a group of devices working in near magnetic field is considered. This article is devoted to overview of different inductive power transfer (IPT) devices. The review of literature in this area showed that industrial IPT are not much discussed and examined. The authors have experience in design and implementation of several types of IPTs belonging to wireless automotive chargers and to industrial application group. Main attention in the article is paid to principles and design of technological IPTs

High-surface-area architectures for improved charge transfer kinetics at the dark electrode in dye-sensitized solar cells.

PubMed

Hoffeditz, William L; Katz, Michael J; Deria, Pravas; Martinson, Alex B F; Pellin, Michael J; Farha, Omar K; Hupp, Joseph T

2014-06-11

Dye-sensitized solar cell (DSC) redox shuttles other than triiodide/iodide have exhibited significantly higher charge transfer resistances at the dark electrode. This often results in poor fill factor, a severe detriment to device performance. Rather than moving to dark electrodes of untested materials that may have higher catalytic activity for specific shuttles, the surface area of platinum dark electrodes could be increased, improving the catalytic activity by simply presenting more catalyst to the shuttle solution. A new copper-based redox shuttle that experiences extremely high charge-transfer resistance at conventional Pt dark electrodes yields cells having fill-factors of less than 0.3. By replacing the standard Pt dark electrode with an inverse opal Pt electrode fabricated via atomic layer deposition, the dark electrode surface area is boosted by ca. 50-fold. The resulting increase in interfacial electron transfer rate (decrease in charge-transfer resistance) nearly doubles the fill factor and therefore the overall energy conversion efficiency, illustrating the utility of this high-area electrode for DSCs.

Delayed Triplet-State Formation through Hybrid Charge Transfer Exciton at Copper Phthalocyanine/GaAs Heterojunction.

PubMed

Lim, Heeseon; Kwon, Hyuksang; Kim, Sang Kyu; Kim, Jeong Won

2017-10-05

Light absorption in organic molecules on an inorganic substrate and subsequent electron transfer to the substrate create so-called hybrid charge transfer exciton (HCTE). The relaxation process of the HCTE states largely determines charge separation efficiency or optoelectronic device performance. Here, the study on energy and time-dispersive behavior of photoelectrons at the hybrid interface of copper phthalocyanine (CuPc)/p-GaAs(001) upon light excitation of GaAs reveals a clear pathway for HCTE relaxation and delayed triplet-state formation. According to the ground-state energy level alignment at the interface, CuPc/p-GaAs(001) shows initially fast hole injection from GaAs to CuPc. Thus, the electrons in GaAs and holes in CuPc form an unusual HCTE state manifold. Subsequent electron transfer from GaAs to CuPc generates the formation of the triplet state in CuPc with a few picoseconds delay. Such two-step charge transfer causes delayed triplet-state formation without singlet excitation and subsequent intersystem crossing within the CuPc molecules.

Charge transfer in the weak driving force limit in blends of MDMO-PPV and dithienylthiazolo[5,4-d]thiazoles towards organic photovoltaics with high V(OC).

PubMed

Nevil, Nissy; Ling, Yun; Van Mierloo, Sarah; Kesters, Jurgen; Piersimoni, Fortunato; Adriaensens, Peter; Lutsen, Laurence; Vanderzande, Dirk; Manca, Jean; Maes, Wouter; Van Doorslaer, Sabine; Goovaerts, Etienne

2012-12-05

A series of three 5'-aryl-2,5-dithienylthiazolo[5,4-d]thiazole (DTTzTz) semiconducting molecules with different aryl substituents has been investigated as alternative acceptor materials in combination with the donor polymer poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) in order to evaluate the photoinduced charge transfer (CT) efficiency in the resulting blends, designed towards possible application in organic photovoltaics. Photoluminescence quenching together with polaron detection by electron paramagnetic resonance and photoinduced absorption (PIA) demonstrate an increasing charge transfer efficiency when the DTTzTz substituents are varied from thien-2-yl to 4-trifluoromethylphenyl and 4-cyanophenyl groups, correlating well with the increasing acceptor strength in this series of molecules. In line with this observation, there is a decrease in the effective optical bandgap relative to pure MDMO-PPV that becomes more pronounced along this series of acceptor compounds, reaching 0.12 eV in the blend with 4-CN-Ph-DTTzTz. Intermolecular interactions between the blend components lead to lower energy transitions which are found to contribute significantly to the device external quantum efficiency. The high V(OC) reached in devices based on MDMO-PPV:4-CN-Ph-DTTzTz blends meets the expectations for such a donor:acceptor combination. However, thermal activation of charge carrier recombination occurs because of the weak driving force for charge transfer, as shown by time-dependent PIA measurements, and this is suggested as a cause for the observed low photovoltaic performance.

Single-crystal charge transfer interfaces for efficient photonic devices (Conference Presentation)

NASA Astrophysics Data System (ADS)

Alves, Helena; Pinto, Rui M.; Maçôas, Ermelinda M. S.; Baleizão, Carlos; Santos, Isabel C.

2016-09-01

Organic semiconductors have unique optical, mechanical and electronic properties that can be combined with customized chemical functionality. In the crystalline form, determinant features for electronic applications such as molecular purity, the charge mobility or the exciton diffusion length, reveal a superior performance when compared with materials in a more disordered form. Combining crystals of two different conjugated materials as even enable a new 2D electronic system. However, the use of organic single crystals in devices is still limited to a few applications, such as field-effect transistors. In 2013, we presented the first system composed of single-crystal charge transfer interfaces presenting photoconductivity behaviour. The system composed of rubrene and TCNQ has a responsivity reaching 1 A/W, corresponding to an external quantum efficiency of nearly 100%. A similar approach, with a hybrid structure of a PCBM film and rubrene single crystal also presents high responsivity and the possibility to extract excitons generated in acceptor materials. This strategy led to an extended action towards the near IR. By adequate material design and structural organisation of perylediimides, we demonstrate that is possible to improve exciton diffusion efficiency. More recently, we have successfully used the concept of charge transfer interfaces in phototransistors. These results open the possibility of using organic single-crystal interfaces in photonic applications.

GMAG Dissertation Award Talk: All Spin Logic -- Multimagnet Networks interacting via Spin currents

NASA Astrophysics Data System (ADS)

Srinivasan, Srikant

2012-02-01

Digital logic circuits have traditionally been based on storing information as charge on capacitors, and the stored information is transferred by controlling the flow of charge. However, electrons carry both charge and spin, the latter being responsible for magnetic phenomena. In the last few decades, there has been a significant improvement in our ability to control spins and their interaction with magnets. All Spin Logic (ASL) represents a new approach to information processing where spins and magnets now mirror the roles of charges and capacitors in conventional logic circuits. In this talk I first present a model [1] that couples non-collinear spin transport with magnet-dynamics to predict the switching behavior of the basic ASL device. This model is based on established physics and is benchmarked against available experimental data that demonstrate spin-torque switching in lateral structures. Next, the model is extended to simulate multi-magnet networks coupled with spin transport channels. The simulations suggest ASL devices have the essential characteristics for building logic circuits. In particular, (1) the example of an ASL ring oscillator [2, 3] is used to provide a clear signature of directed information transfer in cascaded ASL devices without the need for external control circuitry and (2) a simulated NAND [4] gate with fan-out of 2 suggests that ASL can implement universal logic and drive subsequent stages. Finally I will discuss how ASL based circuits could also have potential use in the design of neuromorphic circuits suitable for hybrid analog/digital information processing because of the natural mapping of ASL devices to neurons [4]. [4pt] [1] B. Behin-Aein, A. Sarkar, S. Srinivasan, and S. Datta, ``Switching Energy-Delay of All-Spin Logic devices,'' Appl. Phys. Lett., 98, 123510 (2011).[0pt] [2] S. Srinivasan, A. Sarkar, B. Behin-Aein, and S. Datta, ``All Spin Logic Device with Inbuilt Non-reciprocity,'' IEEE Trans. Magn., 47, 10 (2011).[0pt] [3] S. Srinivasan, A. Sarkar, B. Behin-Aein and S. Datta, ``Unidirectional Information transfer with cascaded All Spin Logic devices: A Ring Oscillator,'' IEEE Device Research Conference (2011).[0pt] [4] A. Sarkar, S. Srinivasan, B. Behin-Aein and S. Datta, ``Multimagnet networks interacting via spin currents'' IEEE International Electron Devices Meeting 2011. (to appear).

Charge-transfer channel in quantum dot-graphene hybrid materials

NASA Astrophysics Data System (ADS)

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-01

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd13Se13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Charge-transfer channel in quantum dot-graphene hybrid materials.

PubMed

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-06

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd 13 Se 13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Spin and charge transport across cobalt/graphene interfaces

NASA Astrophysics Data System (ADS)

Chshiev, Mairbek; Kalitsov, Alan; Mryasov, Oleg

We report ballistic calculations of in-plane and out-of-plane spin and charge transport through graphene attached to the hcp-Co electrodes. Our calculations are based on the Keldysh non-equilibrium Green Function formalism and the tight binding Hamiltonian model tailored to treat both lateral and vertical device configurations. We present results for (i) vertical device that consists of a one-side fluorinated C4F graphene sandwiched between two hcp Co electrodes and (ii) lateral device consisting of pristine graphene/C4F graphene bilayer with two top hcp-Co electrodes Our calculations predict large magnetoresistance with small resistance-area product and significant deviation from sinusoidal behavior of spin transfer torque for the vertical device configuration.

Active pixel sensor pixel having a photodetector whose output is coupled to an output transistor gate

NASA Technical Reports Server (NTRS)

Fossum, Eric R. (Inventor); Nakamura, Junichi (Inventor); Kemeny, Sabrina E. (Inventor)

2005-01-01

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node. There is also a readout circuit, part of which can be disposed at the bottom of each column of cells and be common to all the cells in the column. A Simple Floating Gate (SFG) pixel structure could also be employed in the imager to provide a non-destructive readout and smaller pixel sizes.

Ultrafast Photoinduced Electron Transfer in a π-Conjugated Oligomer/Porphyrin Complex.

PubMed

Aly, Shawkat M; Goswami, Subhadip; Alsulami, Qana A; Schanze, Kirk S; Mohammed, Omar F

2014-10-02

Controlling charge transfer (CT), charge separation (CS), and charge recombination (CR) at the donor-acceptor interface is extremely important to optimize the conversion efficiency in solar cell devices. In general, ultrafast CT and slow CR are desirable for optimal device performance. In this Letter, the ultrafast excited-state CT between platinum oligomer (DPP-Pt(acac)) as a new electron donor and porphyrin as an electron acceptor is monitored for the first time using femtosecond (fs) transient absorption (TA) spectroscopy with broad-band capability and 120 fs temporal resolution. Turning the CT on/off has been shown to be possible either by switching from an organometallic oligomer to a metal-free oligomer or by controlling the charge density on the nitrogen atom of the porphyrin meso unit. Our time-resolved data show that the CT and CS between DPP-Pt(acac) and cationic porphyrin are ultrafast (approximately 1.5 ps), and the CR is slow (ns time scale), as inferred from the formation and the decay of the cationic and anionic species. We also found that the metallic center in the DPP-Pt(acac) oligomer and the positive charge on the porphyrin are the keys to switching on/off the ultrafast CT process.

Analysis of charge injection and contact resistance as a function of electrode surface treatment in ambipolar polymer transistors

NASA Astrophysics Data System (ADS)

Lee, Seon Jeng; Kim, Chaewon; Jung, Seok-Heon; Di Pietro, Riccardo; Lee, Jin-Kyun; Kim, Jiyoung; Kim, Miso; Lee, Mi Jung

2018-01-01

Ambipolar organic field-effect transistors (OFETs) have both of hole and electron enhancements in charge transport. The characteristics of conjugated diketopyrrolopyrrole ambipolar OFETs depend on the metal-contact surface treatment for charge injection. To investigate the charge-injection characteristics of ambipolar transistors, these devices are processed via various types of self-assembled monolayer treatments and annealing. We conclude that treatment by the self-assembled monolayer 1-decanethiol gives the best enhancement of electron charge injection at both 100 and 300 °C annealing temperature. In addition, the contact resistance is calculated by using two methods: One is the gated four-point probe (gFPP) method that gives the voltage drop between channels, and the other is the simultaneous contact resistance extraction method, which extracts the contact resistance from the general transfer curve. We confirm that the gFPP method and the simultaneous extraction method give similar contact resistance, which means that we can extract contact resistance from the general transfer curve without any special contact pattern. Based on these characteristics of ambipolar p- and n-type transistors, we fabricate inverter devices with only one active layer. [Figure not available: see fulltext.

Enhanced Internal Quantum Efficiency in Dye-Sensitized Solar Cells: Effect of Long-Lived Charge-Separated State of Sensitizers.

PubMed

Sun, Haiya; Liu, Dongzhi; Wang, Tianyang; Lu, Ting; Li, Wei; Ren, Siyao; Hu, Wenping; Wang, Lichang; Zhou, Xueqin

2017-03-22

Effective charge separation is one of the key determinants for the photovoltaic performance of the dye-sensitized solar cells (DSSCs). Herein, two charge-separated (CS) sensitizers, MTPA-Pyc and YD-Pyc, have been synthesized and applied in DSSCs to investigate the effect of the CS states of the sensitizers on the device's efficiency. The CS states with lifetimes of 64 and 177 ns for MTPA-Pyc and YD-Pyc, respectively, are formed via the photoinduced electron transfer (PET) from the 4-styryltriphenylamine (MTPA) or 4-styrylindoline (YD) donor to the pyrimidine cyanoacrylic acid (Pyc) acceptor. DSSCs based on MTPA-Pyc and YD-Pyc exhibit high internal quantum efficiency (IQE) values of over 80% from 400 to 600 nm. In comparison, the IQEs of the charge transfer (CT) sensitizer cells are 10-30% lower in the same wavelength range. The enhanced IQE values in the devices based on the CS sensitizers are ascribed to the higher electron injection efficiencies and slower charge recombination. The results demonstrate that taking advantage of the CS states in the sensitizers can be a promising strategy to improve the IQEs and further enhance the overall efficiencies of the DSSCs.

Influence of dehydrated nanotubed titanic acid on charge transport and luminescent properties of polymer light-emitting diodes with fluorescent dye

NASA Astrophysics Data System (ADS)

Qian, Lei; Bera, Debasis; Jin, Zhen-Sheng; Du, Zu-Liang; Xu, Zheng; Teng, Feng; Liu, Wei

2007-09-01

In this paper, we discuss the influence of dehydrated nanotubed titanic acid (DNTA) on charge transport and luminescent properties of polymer light-emitting diodes (PLEDs) doped with fluorescent dye. Photoluminescence results confirm the efficient energy transfer from PVK to 4-(dicyanom-ethylene)-2- t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) and tris-(8-hydroxtquinoline) aluminum (Alq 3) in a DNTA-doped device. The device showed lower turn-on voltages and higher charge current by doping with DNTA, which also caused a shift in the exciton's recombination region.

Solution processed transition metal oxide anode buffer layers for efficiency and stability enhancement of polymer solar cells

NASA Astrophysics Data System (ADS)

Ameen, M. Yoosuf; Shamjid, P.; Abhijith, T.; Reddy, V. S.

2018-01-01

Polymer solar cells were fabricated with solution-processed transition metal oxides, MoO3 and V2O5 as anode buffer layers (ABLs). The optimized device with V2O5 ABL exhibited considerably higher power conversion efficiency (PCE) compared to the devices based on MoO3 and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) ABLs. The space charge limited current measurements and impedance spectroscopy results of hole-only devices revealed that V2O5 provided a very low charge transfer resistance and high hole mobility, facilitating efficient hole transfer from the active layer to the ITO anode. More importantly, incorporation of V2O5 as ABL resulted in substantial improvement in device stability compared to MoO3 and PEDOT:PSS based devices. Unencapsulated PEDOT:PSS-based devices stored at a relative humidity of 45% have shown complete failure within 96 h. Whereas, MoO3 and V2O5 based devices stored in similar conditions retained 22% and 80% of their initial PCEs after 96 h. Significantly higher stability of the V2O5-based device is ascribed to the reduction in degradation of the anode/active layer interface, as evident from the electrical measurements.

Charge Versus Energy Transfer in Atomically Thin Graphene-Transition Metal Dichalcogenide van der Waals Heterostructures

NASA Astrophysics Data System (ADS)

Froehlicher, Guillaume; Lorchat, Etienne; Berciaud, Stéphane

2018-01-01

Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, MoSe2 )] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in graphene /MoSe2 is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps) room-temperature MoSe2 exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and MoSe2 Raman modes, which reveals net photoinduced electron transfer from MoSe2 to graphene and hole accumulation in MoSe2 . Remarkably, the steady-state Fermi energy of graphene saturates at 290 ±15 meV above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets) and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in graphene /MoSe2 . This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron exchange or dipole-dipole interaction) is the dominant interlayer coupling mechanism between atomically thin TMDs and graphene.

Non-destructive single-pass low-noise detection of ions in a beamline

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, Stefan; Institut für Kernchemie, Johannes Gutenberg–Universität Mainz, 55099 Mainz; Murböck, Tobias

2015-11-15

We have conceived, built, and operated a device for the non-destructive single-pass detection of charged particles in a beamline. The detector is based on the non-resonant pick-up and subsequent low-noise amplification of the image charges induced in a cylindrical electrode surrounding the particles’ beam path. The first stage of the amplification electronics is designed to be operated from room temperature down to liquid helium temperature. The device represents a non-destructive charge counter as well as a sensitive timing circuit. We present the concept and design details of the device. We have characterized its performance and show measurements with low-energy highlymore » charged ions (such as Ar{sup 13+}) passing through one of the electrodes of a cylindrical Penning trap. This work demonstrates a novel approach of non-destructive, low noise detection of charged particles which is, depending on the bunch structure, suitable, e.g., for ion traps, low-energy beamlines or accelerator transfer sections.« less

Real-space observation of unbalanced charge distribution inside a perovskite-sensitized solar cell.

PubMed

Bergmann, Victor W; Weber, Stefan A L; Javier Ramos, F; Nazeeruddin, Mohammad Khaja; Grätzel, Michael; Li, Dan; Domanski, Anna L; Lieberwirth, Ingo; Ahmad, Shahzada; Berger, Rüdiger

2014-09-22

Perovskite-sensitized solar cells have reached power conversion efficiencies comparable to commercially available solar cells used for example in solar farms. In contrast to silicon solar cells, perovskite-sensitized solar cells can be made by solution processes from inexpensive materials. The power conversion efficiency of these cells depends substantially on the charge transfer at interfaces. Here we use Kelvin probe force microscopy to study the real-space cross-sectional distribution of the internal potential within high efficiency mesoscopic methylammonium lead tri-iodide solar cells. We show that the electric field is homogeneous through these devices, similar to that of a p-i-n type junction. On illumination under short-circuit conditions, holes accumulate in front of the hole-transport layer as a consequence of unbalanced charge transport in the device. After light illumination, we find that trapped charges remain inside the active device layers. Removing these traps and the unbalanced charge injection could enable further improvements in performance of perovskite-sensitized solar cells.

Titanium dioxide nanotube membranes for solar energy conversion: effect of deep and shallow dopants.

PubMed

Ding, Yuchen; Nagpal, Prashant

2017-04-12

Nanostructured titanium dioxide (TiO 2 ) has been intensively investigated as a material of choice for solar energy conversion in photocatalytic, photoelectrochemical, photovoltaic, and other photosensitized devices for converting light into chemical feedstocks or electricity. Towards management of light absorption in TiO 2 , while the nanotubular structure improves light absorption and simultaneous charge transfer to mitigate problems due to the indirect bandgap of the semiconductor, typically dopants are used to improve light absorption of incident solar irradiation in the wide bandgap of TiO 2 . While these dopants can be critical to the success of these solar energy conversion devices, their effect on photophysical and photoelectrochemical properties and detailed photokinetics are relatively under-studied. Here, we show the effect of deep and shallow metal dopants on the kinetics of photogenerated charged carriers in TiO 2 and the resulting effect on photocatalytic and photoelectrochemical processes using these nanotube membranes. We performed a detailed optical, electronic, voltammetry and electrochemical impedance study to understand the effect of shallow and deep metal dopants (using undoped and niobium- and copper-doped TiO 2 nanotubes) on light absorption, charge transport and charge transfer processes. Using wireless photocatalytic methylene blue degradation and carbon dioxide reduction, and wired photoelectrochemical device measurements, we elucidate the effect of different dopants on solar-to-fuel conversion efficiency and simultaneously describe the photokinetics using a model, to help design better energy conversion devices.

MIMIC-compatible GaAs and InP field effect controlled transferred electron (FECTED) oscillators

NASA Astrophysics Data System (ADS)

Scheiber, Helmut; Luebke, Kurt; Diskus, Christian G.; Thim, Hartwig W.; Gruetzmacher, D.

1989-12-01

A MIMIC-(millimeter and microwave integrated circuit) compatible transferred electron oscillator is investigated which utilizes the frequency-independent negative resistance of the stationary charge dipole domain that forms in the channel of a MESFET. The device structure, analysis, and simulation are described. Devices fabricated from GaAs and InP exhibit very high power levels of 56 mW at 29 GHz and 55 mW at 34 GHz, respectively. Continuous wave power levels are somewhat lower (30 mW).

The Optimization Based Dynamic and Cyclic Working Strategies for Rechargeable Wireless Sensor Networks with Multiple Base Stations and Wireless Energy Transfer Devices

PubMed Central

Ding, Xu; Han, Jianghong; Shi, Lei

2015-01-01

In this paper, the optimal working schemes for wireless sensor networks with multiple base stations and wireless energy transfer devices are proposed. The wireless energy transfer devices also work as data gatherers while charging sensor nodes. The wireless sensor network is firstly divided into sub networks according to the concept of Voronoi diagram. Then, the entire energy replenishing procedure is split into the pre-normal and normal energy replenishing stages. With the objective of maximizing the sojourn time ratio of the wireless energy transfer device, a continuous time optimization problem for the normal energy replenishing cycle is formed according to constraints with which sensor nodes and wireless energy transfer devices should comply. Later on, the continuous time optimization problem is reshaped into a discrete multi-phased optimization problem, which yields the identical optimality. After linearizing it, we obtain a linear programming problem that can be solved efficiently. The working strategies of both sensor nodes and wireless energy transfer devices in the pre-normal replenishing stage are also discussed in this paper. The intensive simulations exhibit the dynamic and cyclic working schemes for the entire energy replenishing procedure. Additionally, a way of eliminating “bottleneck” sensor nodes is also developed in this paper. PMID:25785305

The optimization based dynamic and cyclic working strategies for rechargeable wireless sensor networks with multiple base stations and wireless energy transfer devices.

PubMed

Ding, Xu; Han, Jianghong; Shi, Lei

2015-03-16

In this paper, the optimal working schemes for wireless sensor networks with multiple base stations and wireless energy transfer devices are proposed. The wireless energy transfer devices also work as data gatherers while charging sensor nodes. The wireless sensor network is firstly divided into sub networks according to the concept of Voronoi diagram. Then, the entire energy replenishing procedure is split into the pre-normal and normal energy replenishing stages. With the objective of maximizing the sojourn time ratio of the wireless energy transfer device, a continuous time optimization problem for the normal energy replenishing cycle is formed according to constraints with which sensor nodes and wireless energy transfer devices should comply. Later on, the continuous time optimization problem is reshaped into a discrete multi-phased optimization problem, which yields the identical optimality. After linearizing it, we obtain a linear programming problem that can be solved efficiently. The working strategies of both sensor nodes and wireless energy transfer devices in the pre-normal replenishing stage are also discussed in this paper. The intensive simulations exhibit the dynamic and cyclic working schemes for the entire energy replenishing procedure. Additionally, a way of eliminating "bottleneck" sensor nodes is also developed in this paper.

Metal oxide induced charge transfer doping and band alignment of graphene electrodes for efficient organic light emitting diodes.

PubMed

Meyer, Jens; Kidambi, Piran R; Bayer, Bernhard C; Weijtens, Christ; Kuhn, Anton; Centeno, Alba; Pesquera, Amaia; Zurutuza, Amaia; Robertson, John; Hofmann, Stephan

2014-06-20

The interface structure of graphene with thermally evaporated metal oxide layers, in particular molybdenum trioxide (MoO3), is studied combining photoemission spectroscopy, sheet resistance measurements and organic light emitting diode (OLED) characterization. Thin (<5 nm) MoO3 layers give rise to an 1.9 eV large interface dipole and a downwards bending of the MoO3 conduction band towards the Fermi level of graphene, leading to a near ideal alignment of the transport levels. The surface charge transfer manifests itself also as strong and stable p-type doping of the graphene layers, with the Fermi level downshifted by 0.25 eV and sheet resistance values consistently below 50 Ω/sq for few-layer graphene films. The combination of stable doping and highly efficient charge extraction/injection allows the demonstration of simplified graphene-based OLED device stacks with efficiencies exceeding those of standard ITO reference devices.

Tunable electrical conductivity in metal-organic framework thin film devices

DOEpatents

Talin, Albert Alec; Allendorf, Mark D.; Stavila, Vitalie; Leonard, Francois

2016-08-30

A composition including a porous metal organic framework (MOF) including an open metal site and a guest species capable of charge transfer that can coordinate with the open metal site, wherein the composition is electrically conductive. A method including infiltrating a porous metal organic framework (MOF) including an open metal site with a guest species that is capable of charge transfer; and coordinating the guest species to the open metal site to form a composition including an electrical conductivity greater than an electrical conductivity of the MOF.

Tunable electrical conductivity in metal-organic framework thin film devices

DOEpatents

Talin, Albert Alec; Allendorf, Mark D.; Stavila, Vitalie; Leonard, Francois

2016-05-24

A composition including a porous metal organic framework (MOF) including an open metal site and a guest species capable of charge transfer that can coordinate with the open metal site, wherein the composition is electrically conductive. A method including infiltrating a porous metal organic framework (MOF) including an open metal site with a guest species that is capable of charge transfer; and coordinating the guest species to the open metal site to form a composition including an electrical conductivity greater than an electrical conductivity of the MOF.

Performance of an extended dynamic range time delay integration charge coupled device (XDR TDI CCD) for high-intrascene dynamic range scanning

NASA Astrophysics Data System (ADS)

Levine, Peter A.; Dawson, Robin M.; Andrews, James T.; Bhaskaran, Mahalingham; Furst, David; Hsueh, Fu-Lung; Meray, Grazyna M.; Sudol, Thomas M.; Swain, Pradyumna K.; Tower, John R.

2003-05-01

Many applications, such as industrial inspection and overhead reconnaissance benefit from line scanning architectures where time delay integration (TDI) significantly improves sensitivity. CCDs are particularly well suited to the TDI architecture since charge is transferred virtually noiselessly down the column. Sarnoff's TDI CCDs have demonstrated extremely high speeds where a 7200 x 64, 8 um pixel device with 120 output ports demonstrated a vertical line transfer rate greater than 800 kHz. The most recent addition to Sarnoff's TDI technology is the implementation of extended dynamic range (XDR) in high speed, back illuminated TDI CCDs. The optical, intrascene dynamic range can be adjusted in the design of the imager with measured dynamic ranges exceeding 2,000,000:1 with no degradation in low light performance. The device provides a piecewise linear response to light where multiple slopes and break points can be set during the CCD design. A description of the device architecture and measured results from fabricated XDR TDI CCDs are presented.

Effects of the charge-transfer reorganization energy on the open-circuit voltage in small-molecular bilayer organic photovoltaic devices: comparison of the influence of deposition rates of the donor.

PubMed

Lee, Chih-Chien; Su, Wei-Cheng; Chang, Wen-Chang

2016-05-14

The theoretical maximum of open-circuit voltage (VOC) of organic photovoltaic (OPV) devices has yet to be determined, and its origin remains debated. Here, we demonstrate that VOC of small-molecule OPV devices can be improved by controlling the deposition rate of a donor without changing the interfacial energy gap at the donor/acceptor interface. The measurement of external quantum efficiency and electroluminescence spectra facilitates the observation of the existence of charge transfer (CT) states. A simplified approach by reusing the reciprocity relationship for obtaining the properties of the CT states is proposed without introducing complex techniques. We compare experimental and fitting results and propose that reorganization energy is the primary factor in determining VOC instead of either the CT energy or electronic coupling term in bilayer OPV devices. Atomic force microscopy images indicate a weak molecular aggregation when a higher deposition rate is used. The results of temperature-dependent measurements suggest the importance of molecular stacking for the CT properties.

Energy and charge transfer in nanoscale hybrid materials.

PubMed

Basché, Thomas; Bottin, Anne; Li, Chen; Müllen, Klaus; Kim, Jeong-Hee; Sohn, Byeong-Hyeok; Prabhakaran, Prem; Lee, Kwang-Sup

2015-06-01

Hybrid materials composed of colloidal semiconductor quantum dots and π-conjugated organic molecules and polymers have attracted continuous interest in recent years, because they may find applications in bio-sensing, photodetection, and photovoltaics. Fundamental processes occurring in these nanohybrids are light absorption and emission as well as energy and/or charge transfer between the components. For future applications it is mandatory to understand, control, and optimize the wide parameter space with respect to chemical assembly and the desired photophysical properties. Accordingly, different approaches to tackle this issue are described here. Simple organic dye molecules (Dye)/quantum dot (QD) conjugates are studied with stationary and time-resolved spectroscopy to address the dynamics of energy and ultra-fast charge transfer. Micellar as well as lamellar nanostructures derived from diblock copolymers are employed to fine-tune the energy transfer efficiency of QD donor/dye acceptor couples. Finally, the transport of charges through organic components coupled to the quantum dot surface is discussed with an emphasis on functional devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuning electronic properties of graphene nanoflake polyaromatic hydrocarbon through molecular charge-transfer interactions

NASA Astrophysics Data System (ADS)

Sharma, Vaishali; Dabhi, Shweta D.; Shinde, Satyam; Jha, Prafulla K.

2018-05-01

By means of first principles calculation we have tuned the electronic properties of graphene nanoflake polyaromatic hydrocarbon via molecular charge transfer. Acceptor/donor Tetracyanoquinodimethane (TCNQ) and Tetrathiafulvalene (TTF) organic molecules are adsorbed on polyaromatic hydrocarbons (PAH) in order to introduce the charge transfer. The substrate's n- or p- type nature depends on the accepting/donating behavior of dopant molecules. Two different classes of PAH (extended form of triangulene) namely Bow-tie graphene nanoflake (BTGNF) and triangular zigzag graphene nanoflake (TZGNF). It is revealed that all the TCNQ and TTF modified graphene nanoflakes exhibit significant changes in HOMO-LUMO gap in range from 0.58 eV to 0.64 eV and 0.01 eV to 0.05 eV respectively. The adsorption energies are in the range of -0.05 kcal/mol to -2.6 kcal/mol. The change in work function is also calculated and discussed, the maximum charge transfer is for TCNQ adsorbed BTGNF. These alluring findings in the tuning of electronic properties will be advantageous for promoting graphene nanoflake polyaromatic hydrocarbon for their applications in electronic devices.

Chemiresistive and Gravimetric Dual-Mode Gas Sensor toward Target Recognition and Differentiation.

PubMed

Chen, Yan; Zhang, Hao; Feng, Zhihong; Zhang, Hongxiang; Zhang, Rui; Yu, Yuanyuan; Tao, Jin; Zhao, Hongyuan; Guo, Wenlan; Pang, Wei; Duan, Xuexin; Liu, Jing; Zhang, Daihua

2016-08-24

We demonstrate a dual-mode gas sensor for simultaneous and independent acquisition of electrical and mechanical signals from the same gas adsorption event. The device integrates a graphene field-effect transistor (FET) with a piezoelectric resonator in a seamless manner by leveraging multiple structural and functional synergies. Dual signals resulting from independent physical processes, i.e., mass attachment and charge transfer can reflect intrinsic properties of gas molecules and potentially enable target recognition and quantification at the same time. Fabrication of the device is based on standard Integrated Circuit (IC) foundry processes and fully compatible with system-on-a-chip (SoC) integration to achieve extremely small form factors. In addition, the ability of simultaneous measurements of mass adsorption and charge transfer guides us to a more precise understanding of the interactions between graphene and various gas molecules. Besides its practical functions, the device serves as an effective tool to quantitatively investigate the physical processes and sensing mechanisms for a large library of sensing materials and target analytes.

The future scientific CCD

NASA Technical Reports Server (NTRS)

Janesick, J. R.; Elliott, T.; Collins, S.; Marsh, H.; Blouke, M. M.

1984-01-01

Since the first introduction of charge-coupled devices (CCDs) in 1970, CCDs have been considered for applications related to memories, logic circuits, and the detection of visible radiation. It is pointed out, however, that the mass market orientation of CCD development has left largely untapped the enormous potential of these devices for advanced scientific instrumentation. The present paper has, therefore, the objective to introduce the CCD characteristics to the scientific community, taking into account prospects for further improvement. Attention is given to evaluation criteria, a summary of current CCDs, CCD performance characteristics, absolute calibration tools, quantum efficiency, aspects of charge collection, charge transfer efficiency, read noise, and predictions regarding the characteristics of the next generation of silicon scientific CCD imagers.

Direct detection of a transport-blocking trap in a nanoscaled silicon single-electron transistor by radio-frequency reflectometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Villis, B. J.; Sanquer, M.; Jehl, X.

2014-06-09

The continuous downscaling of transistors results in nanoscale devices which require fewer and fewer charged carriers for their operation. The ultimate charge controlled device, the single-electron transistor (SET), controls the transfer of individual electrons. It is also the most sensitive electrometer, and as a result the electron transport through it can be dramatically affected by nearby charges. Standard direct-current characterization techniques, however, are often unable to unambiguously detect and resolve the origin of the observed changes in SET behavior arising from changes in the charge state of a capacitively coupled trap. Using a radio-frequency (RF) reflectometry technique, we are ablemore » to unequivocally detect this process, in very close agreement with modeling of the trap's occupation probability.« less

Active pixel sensor array with multiresolution readout

NASA Technical Reports Server (NTRS)

Fossum, Eric R. (Inventor); Kemeny, Sabrina E. (Inventor); Pain, Bedabrata (Inventor)

1999-01-01

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node. There is also a readout circuit, part of which can be disposed at the bottom of each column of cells and be common to all the cells in the column. The imaging device can also include an electronic shutter formed on the substrate adjacent the photogate, and/or a storage section to allow for simultaneous integration. In addition, the imaging device can include a multiresolution imaging circuit to provide images of varying resolution. The multiresolution circuit could also be employed in an array where the photosensitive portion of each pixel cell is a photodiode. This latter embodiment could further be modified to facilitate low light imaging.

Electronic and magnetic properties of transition metal doped graphyne

NASA Astrophysics Data System (ADS)

Gangan, Abhijeet Sadashiv; Yadav, Asha S.; Chakraborty, Brahmananda; Ramaniah, Lavanya M.

2017-05-01

We have theoretically investigated the interaction of few 3d (V,Mn) and 4d (Y,Zr) transition metals with the γ-graphyne structure using the spin-polarized density functional theory for its potentials application in Hydrogen storage, spintronics and nano-electronics. By doping different TMs we have observed that the system can be either metallic(Y), semi-conducting or half metallic. The system for Y and Zr doped graphyne becomes non-magnetic while V and Mn doped graphyne have a magnetic moments of l μB and 3 μB respectively From bader charge analysis it is seen that there is a charge transfer from the TM atom to the graphyne. Zr and Y have a net charge transfer of 2.15e and 1.73e respectively. Charge density analysis also shows the polarization on the carbon skeleton which becomes larger as the charge transfer for the TM atom increases. Thus we see Y and Zr are better candidates for hydrogen storage devices since they are non-magnetic and have less d electrons which is ideal for kubas-type interactions between hydrogen molecule and TM.

Breadboard stellar tracker system test report

NASA Technical Reports Server (NTRS)

Kollodge, J. C.; Parrish, K. A.

1984-01-01

BASD has, in the past, developed several unique position tracking algorithms for charge transfer device (CTD) sensors. These algorithms provide an interpixel transfer function with the following characteristics: (1) high linearity; (2) simplified track logic; (3) high gain; and (4) high noise rejection. A previous test program using the GE charge injection device (CID) showed that accuracy for BASD's breadboard was limited to approximately 2% of a pixel (1 sigma) whereas analysis and simulation indicated the limit should be less than 0.5% of a pixel, assuming the limit to be detector response and dark current noise. The test program was conducted under NASA contract No. NAS8-34263. The test approach for that program did not provide sufficient data to identify the sources of error and left open the amount of contribution from parameters such as image distribution, geometric distortion and system alignment errors.

Overvoltage protection system for wireless power transfer systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chambon, Paul H.; Jones, Perry T.; Miller, John M.

A wireless power transfer overvoltage protection system is provided. The system includes a resonant receiving circuit. The resonant receiving circuit includes an inductor, a resonant capacitor and a first switching device. The first switching device is connected the ends of the inductor. The first switching device has a first state in which the ends of the inductor are electrically coupled to each other through the first switching device, and a second state in which the inductor and resonant capacitor are capable of resonating. The system further includes a control module configured to control the first switching device to switching betweenmore » the first state and the second state when the resonant receiving circuit is charging a load and a preset condition is satisfied and otherwise, the first switching device is maintained in the first state.« less

An acoustic charge transport imager for high definition television applications

NASA Technical Reports Server (NTRS)

Hunt, W. D.; Brennan, K. F.; Summers, C. J.

1994-01-01

The primary goal of this research is to develop a solid-state television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels/frame. This imager will offer an order of magnitude improvements in speed over CCD designs and will allow for monolithic imagers operating from the IR to UV. The technical approach of the project focuses on the development of the three basic components of the imager and their subsequent integration. The camera chip can be divided into three distinct functions: (1) image capture via an array of avalanche photodiodes (APD's); (2) charge collection, storage, and overflow control via a charge transfer transistor device (CTD); and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the optimization of each of these component devices. In addition to the development of each of the three distinct components, work towards their integration and manufacturability is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail.

Measurement and investigation of proton irradiation-induced charge transfer inefficiency in PPD CIS at different integration times

NASA Astrophysics Data System (ADS)

Xue, Yuanyuan; Wang, Zujun; Zhang, Fengqi; Bian, Jingying; Yao, Zhibin; He, Baoping; Liu, Minbo; Sheng, Jiangkun; Ma, Wuying; Dong, Guantao; Jin, Junshan

2018-04-01

Charge transfer inefficiency (CTI) is an important parameter for photodiode (PPD) CMOS image sensors (CISs). A test system was built and used to measure the CTI of PPD CIS devices at different integration times. The radiation effects of 3 MeV and 10 MeV protons on the CTI were investigated. The experiments were carried out at the EN Tandem Van de Graaff accelerator at proton fluences in the range 1010 to 1011 p/cm2. The CTI was measured within the 2 h following proton radiations. The dependence of CTI on integration time, proton energy and fluence were investigated. The CTI was observed to increase after proton irradiation: with the effect of irradiation with 3 MeV proton being more severe than that with 10 MeV protons. The CTI was also observed to decrease with increasing integration time, which is thought to be related to the charge density in the space charge region (SCR) of the CIS devices. This work has provided a simple method to measure the CTI and helped us to understand proton radiation effects on the CTI of PPD CISs.

Three-dimensional charge coupled device

DOEpatents

Conder, Alan D.; Young, Bruce K. F.

1999-01-01

A monolithic three dimensional charged coupled device (3D-CCD) which utilizes the entire bulk of the semiconductor for charge generation, storage, and transfer. The 3D-CCD provides a vast improvement of current CCD architectures that use only the surface of the semiconductor substrate. The 3D-CCD is capable of developing a strong E-field throughout the depth of the semiconductor by using deep (buried) parallel (bulk) electrodes in the substrate material. Using backside illumination, the 3D-CCD architecture enables a single device to image photon energies from the visible, to the ultra-violet and soft x-ray, and out to higher energy x-rays of 30 keV and beyond. The buried or bulk electrodes are electrically connected to the surface electrodes, and an E-field parallel to the surface is established with the pixel in which the bulk electrodes are located. This E-field attracts charge to the bulk electrodes independent of depth and confines it within the pixel in which it is generated. Charge diffusion is greatly reduced because the E-field is strong due to the proximity of the bulk electrodes.

Process for fabricating a charge coupled device

DOEpatents

Conder, Alan D.; Young, Bruce K. F.

2002-01-01

A monolithic three dimensional charged coupled device (3D-CCD) which utilizes the entire bulk of the semiconductor for charge generation, storage, and transfer. The 3D-CCD provides a vast improvement of current CCD architectures that use only the surface of the semiconductor substrate. The 3D-CCD is capable of developing a strong E-field throughout the depth of the semiconductor by using deep (buried) parallel (bulk) electrodes in the substrate material. Using backside illumination, the 3D-CCD architecture enables a single device to image photon energies from the visible, to the ultra-violet and soft x-ray, and out to higher energy x-rays of 30 keV and beyond. The buried or bulk electrodes are electrically connected to the surface electrodes, and an E-field parallel to the surface is established with the pixel in which the bulk electrodes are located. This E-field attracts charge to the bulk electrodes independent of depth and confines it within the pixel in which it is generated. Charge diffusion is greatly reduced because the E-field is strong due to the proximity of the bulk electrodes.

Charge transfer through amino groups-small molecules interface improving the performance of electroluminescent devices

NASA Astrophysics Data System (ADS)

Havare, Ali Kemal; Can, Mustafa; Tozlu, Cem; Kus, Mahmut; Okur, Salih; Demic, Şerafettin; Demirak, Kadir; Kurt, Mustafa; Icli, Sıddık

2016-05-01

A carboxylic group functioned charge transporting was synthesized and self-assembled on an indium tin oxide (ITO) anode. A typical electroluminescent device [modified ITO/TPD (50 nm)/Alq3 (60 nm)/LiF (2 nm)/(120 nm)] was fabricated to investigate the effect of the amino groups-small molecules interface on the characteristics of the device. The increase in the surface work function of ITO is expected to facilitate the hole injection from the ITO anode to the Hole Transport Layer (HTL) in electroluminescence. The modified electroluminescent device could endure a higher current and showed a much higher luminance than the nonmodified one. For the produced electroluminescent devices, the I-V characteristics, optical characterization and quantum yields were performed. The external quantum efficiency of the modified electroluminescent device is improved as the result of the presence of the amino groups-small molecules interface.

Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer

DOE PAGES

Pelzer, Kenley M.; Vázquez-Mayagoitia, Álvaro; Ratcliff, Laura E.; ...

2017-01-01

Organic photovoltaics (OPVs) are a promising carbon-neutral energy conversion technology, with recent improvements pushing power conversion efficiencies over 10%. A major factor limiting OPV performance is inefficiency of charge transport in organic semiconducting materials (OSCs). Due to strong coupling with lattice degrees of freedom, the charges form polarons, localized quasi-particles comprised of charges dressed with phonons. These polarons can be conceptualized as pseudo-atoms with a greater effective mass than a bare charge. Here we propose that due to this increased mass, polarons can be modeled with Langevin molecular dynamics (LMD), a classical approach with a computational cost much lower thanmore » most quantum mechanical methods. Here we present LMD simulations of charge transfer between a pair of fullerene molecules, which commonly serve as electron acceptors in OSCs. We find transfer rates consistent with experimental measurements of charge mobility, suggesting that this method may provide quantitative predictions of efficiency when used to simulate materials on the device scale. Our approach also offers information that is not captured in the overall transfer rate or mobility: in the simulation data, we observe exactly when and why intermolecular transfer events occur. In addition, we demonstrate that these simulations can shed light on the properties of polarons in OSCs. In conclusion, much remains to be learned about these quasi-particles, and there are no widely accepted methods for calculating properties such as effective mass and friction. Lastly, our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs.« less

Crystallochromy of perylene pigments: Interference between Frenkel excitons and charge-transfer states

NASA Astrophysics Data System (ADS)

Gisslén, Linus; Scholz, Reinhard

2009-09-01

The optical properties of perylene-based pigments are arising from the interplay between neutral molecular excitations and charge transfer between adjacent molecules. In the crystalline phase, these excitations are coupled via electron and hole transfer, two quantities relating directly to the width of the conduction and valence band in the crystalline phase. Based on the crystal structure determined by x-ray diffraction, density-functional theory (DFT) and Hartree-Fock are used for the calculation of the electronic states of a dimer of stacked molecules. The resulting transfer parameters for electron and hole are used in an exciton model for the coupling between Frenkel excitons and charge-transfer states. The deformation of the positively or negatively charged molecular ions with respect to the neutral ground state is calculated with DFT and the geometry in the optically excited state is deduced from time-dependent DFT and constrained DFT. All of these deformations are interpreted in terms of the elongation of an effective internal vibration which is used subsequently in the exciton model for the crystalline phase. A comparison between the calculated dielectric function and the observed optical spectra allows to deduce the relative energetic position of Frenkel excitons and the charge-transfer state involving stack neighbors, a key parameter for various electronic and optoelectronic device applications. For five out of six perylene pigments studied in the present work, this exciton model results in excellent agreement between calculated and observed optical properties.

Charge transfer at the interface between ferromagnetic La0.7Sr0.3MnO3 and superconducting EuBa2Cu3O7 probed by STM/STS

NASA Astrophysics Data System (ADS)

Liu, Yinghao; Xiong, Jie

2012-02-01

La0.7Sr0.3MnO3 (LSMO) is a ferromagnetic half-metallic compound with nearly 100% spin polarization at room temperature, making it an ideal candidate for applications in spintronic devices. However, this useful functionality disappears when the thickness of LSMO film grown on SrTiO3 substrate is reduced to below 4 nm, limiting its application in nanoscale devices. Here, we show that metallic and ferromagnetic properties of ultrathin (< 4nm) LSMO film can be restored by interfacing it with a superconductor EuBa2Cu3O7- δ (EBCO). We use scanning tunneling microscopy and spectroscopy to probe the evolution of the electronic structure of LSMO film grown on EBCO as functions of LSMO layer thickness and aging of bilayer LSMO/EBCO. Our results reveal that the charge (hole) transfer at LSMO/EBCO interface is responsible for driving LSMO film (of only five-unit-cell thickness) to metallic state. The conductive behavior of aged LSMO/EBCO bilayers varies systematically with the thickness of LSMO layer, allowing us to estimate the charge-transfer depth to be 4˜5 nm on the LSMO side.

Combining Charge Couple Devices and Rate Sensors for the Feedforward Control System of a Charge Coupled Device Tracking Loop.

PubMed

Tang, Tao; Tian, Jing; Zhong, Daijun; Fu, Chengyu

2016-06-25

A rate feed forward control-based sensor fusion is proposed to improve the closed-loop performance for a charge couple device (CCD) tracking loop. The target trajectory is recovered by combining line of sight (LOS) errors from the CCD and the angular rate from a fiber-optic gyroscope (FOG). A Kalman filter based on the Singer acceleration model utilizes the reconstructive target trajectory to estimate the target velocity. Different from classical feed forward control, additive feedback loops are inevitably added to the original control loops due to the fact some closed-loop information is used. The transfer function of the Kalman filter in the frequency domain is built for analyzing the closed loop stability. The bandwidth of the Kalman filter is the major factor affecting the control stability and close-loop performance. Both simulations and experiments are provided to demonstrate the benefits of the proposed algorithm.

Mesoporous nanocrystalline film architecture for capacitive storage devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dunn, Bruce S.; Tolbert, Sarah H.; Wang, John

A mesoporous, nanocrystalline, metal oxide construct particularly suited for capacitive energy storage that has an architecture with short diffusion path lengths and large surface areas and a method for production are provided. Energy density is substantially increased without compromising the capacitive charge storage kinetics and electrode demonstrates long term cycling stability. Charge storage devices with electrodes using the construct can use three different charge storage mechanisms immersed in an electrolyte: (1) cations can be stored in a thin double layer at the electrode/electrolyte interface (non-faradaic mechanism); (2) cations can interact with the bulk of an electroactive material which then undergoesmore » a redox reaction or phase change, as in conventional batteries (faradaic mechanism); or (3) cations can electrochemically adsorb onto the surface of a material through charge transfer processes (faradaic mechanism).« less

An autonomous photosynthetic device in which all charge carriers derive from surface plasmons.

PubMed

Mubeen, Syed; Lee, Joun; Singh, Nirala; Krämer, Stephan; Stucky, Galen D; Moskovits, Martin

2013-04-01

Solar conversion to electricity or to fuels based on electron-hole pair production in semiconductors is a highly evolved scientific and commercial enterprise. Recently, it has been posited that charge carriers either directly transferred from the plasmonic structure to a neighbouring semiconductor (such as TiO₂) or to a photocatalyst, or induced by energy transfer in a neighbouring medium, could augment photoconversion processes, potentially leading to an entire new paradigm in harvesting photons for practical use. The strong dependence of the wavelength at which the local surface plasmon can be excited on the nanostructure makes it possible, in principle, to design plasmonic devices that can harvest photons over the entire solar spectrum and beyond. So far, however, most such systems show rather small photocatalytic activity in the visible as compared with the ultraviolet. Here, we report an efficient, autonomous solar water-splitting device based on a gold nanorod array in which essentially all charge carriers involved in the oxidation and reduction steps arise from the hot electrons resulting from the excitation of surface plasmons in the nanostructured gold. Each nanorod functions without external wiring, producing 5 × 10(13) H₂ molecules per cm(2) per s under 1 sun illumination (AM 1.5 and 100 mW cm(-2)), with unprecedented long-term operational stability.

Postirradiation behavior of p-channel charge-coupled devices irradiated at 153 K

NASA Astrophysics Data System (ADS)

Gow, Jason P. D.; Wood, Daniel; Murray, Neil J.; Burt, David; Hall, David J.; Dryer, Ben; Holland, Andrew D.

2016-04-01

The displacement damage hardness that can be achieved using p-channel charge-coupled devices (CCD) was originally demonstrated in 1997, and since then a number of other studies have demonstrated an improved tolerance to radiation-induced charge transfer inefficiency when compared to n-channel CCDs. A number of recent studies have also shown that the temperature history of the device after the irradiation impacts the performance of the detector, linked to the mobility of defects at different temperatures. The initial results from an e2v technologies p-channel CCD204 irradiated at 153 K with 10-MeV equivalent proton fluences of 1.24×109 and 1.24×1011 protons cm-2 is described. The dark current, cosmetic quality, and the number of defects identified using trap pumping immediately were monitored after the irradiation for a period of 150 h with the device held at 153 K and then after different periods of time at room temperature. The device also exhibited a flatband voltage shift of around 30 mV/krad, determined by the reduction in full well capacity.

Electron spin resonance observation of charge carrier concentration in organic field-effect transistors during device operation

NASA Astrophysics Data System (ADS)

Tanaka, Hisaaki; Hirate, Masataka; Watanabe, Shun-ichiro; Kaneko, Kazuaki; Marumoto, Kazuhiro; Takenobu, Taishi; Iwasa, Yoshihiro; Kuroda, Shin-ichi

2013-01-01

Charge carrier concentration in operating organic field-effect transistors (OFETs) reflects the electric potential within the channel, acting as a key quantity to clarify the operation mechanism of the device. Here, we demonstrate a direct determination of charge carrier concentration in the operating devices of pentacene and poly(3-hexylthiophene) (P3HT) by field-induced electron spin resonance (FI-ESR) spectroscopy. This method sensitively detects polarons induced by applying gate voltage, giving a clear FI-ESR signal around g=2.003 in both devices. Upon applying drain-source voltage, carrier concentration decreases monotonically in the FET linear region, reaching about 70% of the initial value at the pinch-off point, and stayed constant in the saturation region. The observed results are reproduced well from the theoretical potential profile based on the gradual channel model. In particular, the carrier concentration at the pinch-off point is calculated to be β/(β+1) of the initial value, where β is the power exponent in the gate voltage (Vgs) dependence of the mobility (μ), expressed as μ∝Vgsβ-2, providing detailed information of charge transport. The present devices show β=2.6 for the pentacene and β=2.3 for the P3HT cases, consistent with those determined by transfer characteristics. The gate voltage dependence of the mobility, originating from the charge trapping at the device interface, is confirmed microscopically by the motional narrowing of the FI-ESR spectra.

Excitation of Terahertz Charge Transfer Plasmons in Metallic Fractal Structures

NASA Astrophysics Data System (ADS)

Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Vabbina, Phani Kiran; Karabiyik, Mustafa; Pala, Nezih

2017-08-01

There have been extensive researches on terahertz (THz) plasmonic structures supporting resonant modes to demonstrate nano and microscale devices with high efficiency and responsivity as well as frequency selectivity. Here, using antisymmetric plasmonic fractal Y-shaped (FYS) structures as building blocks, we introduce a highly tunable four-member fractal assembly to support charge transfer plasmons (CTPs) and classical dipolar resonant modes with significant absorption cross section in the THz domain. We first present that the unique geometrical nature of the FYS system and corresponding spectral response allow for supporting intensified dipolar plasmonic modes under polarised light exposure in a standalone structure. In addition to classical dipolar mode, for the very first time, we demonstrated CTPs in the THz domain due to the direct shuttling of the charges across the metallic fractal microantenna which led to sharp resonant absorption peaks. Using both numerical and experimental studies, we have investigated and confirmed the excitation of the CTP modes and highly tunable spectral response of the proposed plasmonic fractal structure. This understanding opens new and promising horizons for tightly integrated THz devices with high efficiency and functionality.

Molecular Structure Controlled Transitions between Free-Charge Generation and Trap Formation in a Conjugated Copolymer Series

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandit, Bill; Jackson, Nicholas E.; Zheng, Tianyue

2016-03-03

Charge transfer copolymers, where each repeating unit has at least one “donor” and one “acceptor” block, have played important roles in recent advances in organic photovoltaic (OPV) devices, however design criteria for these materials are still not completely clear. Here we show that the well-recognized LUMO-LUMO energy off-set design criterion for OPV materials using a fullerene acceptor is challenged in a series of copolymers, PTRn (n = 3, 5, 7 and 9), where n is the number of fused aromatic rings in the “donor” block and thienothiophene is the “acceptor” block in each repeating unit. Photoexcitation dynamics of PTRn copolymersmore » in solution and BHJ (bulk heterojunction) films demonstrated that local push-pull interactions between the “donor” block and the “acceptor” block weakens with increasing n, whereas the LUMO-LUMO off-set between the polymer and PC71BM (Phenyl-C71-butyric acid methyl ester) increases. Such a counter intuitive trend can be explained by local energetics of each repeating unit as a function of n. The energetic changes transform the copolymer with strong local charge transfer character for efficient hole-electron separation to localized hole-electron pairs with low mobility, despite the apparent increase of the polymer/PC71BM LUMO-LUMO off-set. This suggests the importance of local charge transfer character in these copolymers in the initial exciton splitting dynamics, which could ultimately be reflected in the device performance.« less

Electronic structures of 1-ML C84/Ag(111): Energy level alignment and work function variation

NASA Astrophysics Data System (ADS)

Wang, Peng; Zhao, Li-Li; Zhang, Jin-Juan; Li, Wen-Jie; Liu, Wei-Hui; Chen, Da; Sheng, Chun-Qi; Wang, Jia-Ou; Qian, Hai-Jie; Ibrahim, Kurash; Li, Hong-Nian

2017-12-01

The electronic structures of fullerene/metal interface are critical to the performance of devices based on fullerene in molecular electronics and organic electronics. Herein, we investigate the electronic structures at the interface between C84 and Ag(111) by photoelectron spectroscopy and soft X-ray absorption spectroscopy techniques. It is observed that C84 monolayer on Ag(111) surface (1-ML C84/Ag(111)) has metallic nature. A charge transfer from substrate to the unoccupied states of C84 is determined to be 1.3 electrons per molecule. However, the work function of 1-ML C84 (4.72 eV) is observed slightly larger than that of the clean Ag(111) substrate (4.50 eV). A bidirectional charge transfer model is introduced to understand the work function variation of the fullerene/metal system. In addition to the charge transfer from substrate to the adsorbate's unoccupied states, there exists non-negligible back charge transfer from fullerene occupied molecular orbital to the metal substrate through interfacial hybridization. The Fermi level will be pinned at ∼4.72 eV for C84 monolayer on coinage metal substrate.

Investigating the Consistency of Models for Water Splitting Systems by Light and Voltage Modulated Techniques.

PubMed

Bertoluzzi, Luca; Bisquert, Juan

2017-01-05

The optimization of solar energy conversion devices relies on their accurate and nondestructive characterization. The small voltage perturbation techniques of impedance spectroscopy (IS) have proven to be very powerful to identify the main charge storage modes and charge transfer processes that control device operation. Here we establish the general connection between IS and light modulated techniques such as intensity modulated photocurrent (IMPS) and photovoltage spectroscopies (IMVS) for a general system that converts light to energy. We subsequently show how these techniques are related to the steady-state photocurrent and photovoltage and the external quantum efficiency. Finally, we express the IMPS and IMVS transfer functions in terms of the capacitive and resistive features of a general equivalent circuit of IS for the case of a photoanode used for solar fuel production. We critically discuss how much knowledge can be extracted from the combined use of those three techniques.

Characterization of Custom-Designed Charge-Coupled Devices for Applications to Gas and Aerosol Monitoring Sensorcraft Instrument

NASA Technical Reports Server (NTRS)

Refaat, Tamer F.; Abedin, M. Nurul; Farnsworth, Glenn R.; Garcia, Christopher S.; Zawodny, Joseph M.

2005-01-01

Custom-designed charge-coupled devices (CCD) for Gas and Aerosols Monitoring Sensorcraft instrument were developed. These custom-designed CCD devices are linear arrays with pixel format of 512x1 elements and pixel size of 10x200 sq m. These devices were characterized at NASA Langley Research Center to achieve a full well capacity as high as 6,000,000 e-. This met the aircraft flight mission requirements in terms of signal-to-noise performance and maximum dynamic range. Characterization and analysis of the electrical and optical properties of the CCDs were carried out at room temperature. This includes measurements of photon transfer curves, gain coefficient histograms, read noise, and spectral response. Test results obtained on these devices successfully demonstrated the objectives of the aircraft flight mission. In this paper, we describe the characterization results and also discuss their applications to future mission.

Working Mechanism for Flexible Perovskite Solar Cells with Simplified Architecture.

PubMed

Xu, Xiaobao; Chen, Qi; Hong, Ziruo; Zhou, Huanping; Liu, Zonghao; Chang, Wei-Hsuan; Sun, Pengyu; Chen, Huajun; De Marco, Nicholas; Wang, Mingkui; Yang, Yang

2015-10-14

In this communication, we report an efficient and flexible perovskite solar cell based on formamidinium lead trihalide (FAPbI3) with simplified configuration. The device achieved a champion efficiency of 12.70%, utilizing direct contact between metallic indium tin oxide (ITO) electrode and perovskite absorber. The underlying working mechanism is proposed subsequently, via a systematic investigation focusing on the heterojunction within this device. A significant charge storage has been observed in the perovskite, which is believed to generate photovoltage and serves as the driving force for charge transferring from the absorber to ITO electrode as well. More importantly, this simplified device structure on flexible substrates suggests its compatibility for scale-up fabrication, which paves the way for commercialization of perovskite photovoltaic technology.

On electrode pinning and charge blocking layers in organic solar cells

NASA Astrophysics Data System (ADS)

Magen, Osnat; Tessler, Nir

2017-05-01

We use device modelling for studying the losses introduced by metallic electrodes in organic solar cells' device structure. We first discuss the inclusion of pinning at the integer charge transfer state in device models, with and without using the image charge potential. In the presence of disorder, the space charge introduced due to the image potential enhances the pinning by more than 0.2 eV. The explicit introduction of the image potential creates band-gap narrowing at the contact, thus affecting both dark leakage current and photo conversion efficiency. We find that there are two regimes in which the contacts may limit the performance. For low (moderate) barriers, the contacts introduce minority carrier recombination at the contacts that adds to the bulk recombination channels. Only for high barriers, the contacts directly limit the open circuit voltage and impose a value that is equal to the contact's energy difference. Examining the device structures with blocking layers, we find that these are mainly useful for the low to moderate contacts' barriers and that for the high barrier case, the enhancement of open circuit voltage may be accompanied by the introduction of serial resistance or S shape.

Improved utilization of photogenerated charge using fluorine-doped TiO(2) hollow spheres scattering layer in dye-sensitized solar cells.

PubMed

Song, Junling; Yang, Hong Bin; Wang, Xiu; Khoo, Si Yun; Wong, C C; Liu, Xue-Wei; Li, Chang Ming

2012-07-25

We demonstrate a strategy to improve utilization of photogenerated charge in dye-sensitized solar cells (DSSCs) with fluorine-doped TiO2 hollow spheres as the scattering layer, which improves the fill factor from 69.4% to 74.1% and in turn results in an overall efficiency of photoanode increased by 13% (from 5.62% to 6.31%) in comparison with the control device using undoped TiO2 hollow spheres. It is proposed that the fluorine-doping improves the charge transfer and inhibition of charge recombination to enhance the utilization of the photogenerated charge in the photoanode.

Transfer characteristics and low-frequency noise in single- and multi-layer MoS{sub 2} field-effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Deepak; Theiss Research, Inc., La Jolla, California 92037; Department of Electrical and Computer Engineering, George Mason University, Fairfax, Virginia 22030

Leveraging nanoscale field-effect transistors (FETs) in integrated circuits depends heavily on its transfer characteristics and low-frequency noise (LFN) properties. Here, we report the transfer characteristics and LFN in FETs fabricated with molybdenum disulfide (MoS{sub 2}) with different layer (L) counts. 4L to 6L devices showed highest I{sub ON}-I{sub OFF} ratio (≈10{sup 8}) whereas LFN was maximum for 1L device with normalized power spectral density (PSD) ≈1.5 × 10{sup −5 }Hz{sup −1}. For devices with L ≈ 6, PSD was minimum (≈2 × 10{sup −8 }Hz{sup −1}). Further, LFN for single and few layer devices satisfied carrier number fluctuation (CNF) model in both weak andmore » strong accumulation regimes while thicker devices followed Hooge's mobility fluctuation model in the weak accumulation regime and CNF model in strong accumulation regime, respectively. Transfer-characteristics and LFN experimental data are explained with the help of model incorporating Thomas-Fermi charge screening and inter-layer resistance coupling.« less

Charge Transfer and Collection in Dilute Organic Donor-Acceptor Heterojunction Blends.

PubMed

Ding, Kan; Liu, Xiao; Forrest, Stephen R

2018-05-09

Experimental and theoretical approaches are used to understand the role of nanomorphology on exciton dissociation and charge collection at dilute donor-acceptor (D-A) organic heterojunctions (HJs). Specifically, two charge transfer (CT) states in D-A mixed HJs comprising nanocrystalline domains of tetraphenyldibenzoperiflanthene (DBP) as the donor and C 70 as the acceptor are unambiguously related to the nanomorphology of the mixed layer. Alternating DBP:C 70 multilayer stacks are used to identify and control the optical properties of the CT states, as well as to simulate the dilute mixed heterojunctions. A kinetic Monte Carlo model along with photoluminescence spectroscopy and scanning transmission electron microscopy are used to quantitatively evaluate the layer morphology under various growth conditions. As a result, we are able to understand the counterintuitive observation of high charge extraction efficiency and device performance of DBP:C 70 mixed layer photovoltaics at surprisingly low (∼10%) donor concentrations.

Can direct electron detectors outperform phosphor-CCD systems for TEM?

NASA Astrophysics Data System (ADS)

Moldovan, G.; Li, X.; Kirkland, A.

2008-08-01

A new generation of imaging detectors is being considered for application in TEM, but which device architectures can provide the best images? Monte Carlo simulations of the electron-sensor interaction are used here to calculate the expected modulation transfer of monolithic active pixel sensors (MAPS), hybrid active pixel sensors (HAPS) and double sided Silicon strip detectors (DSSD), showing that ideal and nearly ideal transfer can be obtained using DSSD and MAPS sensors. These results highly recommend the replacement of current phosphor screen and charge coupled device imaging systems with such new directly exposed position sensitive electron detectors.

An acoustic charge transport imager for high definition television applications

NASA Technical Reports Server (NTRS)

Hunt, W. D.; Brennan, Kevin F.

1994-01-01

The primary goal of this research is to develop a solid-state high definition television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels per frame. This imager offers an order of magnitude improvement in speed over CCD designs and will allow for monolithic imagers operating from the IR to the UV. The technical approach of the project focuses on the development of the three basic components of the imager and their integration. The imager chip can be divided into three distinct components: (1) image capture via an array of avalanche photodiodes (APD's), (2) charge collection, storage and overflow control via a charge transfer transistor device (CTD), and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the development of manufacturable designs for each of these component devices. In addition to the development of each of the three distinct components, work towards their integration is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail in Sections 2-4.

The dynamics of energy and charge transfer in low and hyperthermal energy ion-solid interactions

NASA Astrophysics Data System (ADS)

Ray, Matthew Preston

The energy and charge transfer dynamics for low and hyperthermal energy (10 eV to 2 keV) alkali and noble gas ions impacting noble metals as a function of incident energy, species and scattering geometry has been studied. The experiments were performed in an ultra-high vacuum scattering chamber attached to a low and hyperthermal energy beamline. The energy transfer was measured for K+ scattered from a Ag(001) surface along the [110] crystalline direction at a fixed laboratory angle of 90°. It was found that as the incident energy is reduced from 100 to 10 eV, the normalized scattered energy increased. Previous measurements have shown a decrease in the normalized energy as the incident ion energy is reduced due to an attractive image force. Trajectory analysis of the data using a classical scattering simulation revealed that instead of undergoing sequential binary collisions as in previous studies, the ion scatters from two surface atoms simultaneously leading to an increased normalized energy. Additionally, charge transfer measurements have been performed for Na + scattering from Ag(001) along the [110] crystalline direction at a fixed laboratory angle of 70°. It was found that over the range of energies used (10 eV to 2 keV), the neutralization probability of the scattered ions varied from ˜30% to ˜70% depending on the incident velocity, consistent with resonant charge transfer. A fully quantum mechanical model that treats electrons independently accurately reproduces the observed data. Measurements of electron-hole pair excitations were used to explore the pathways which a solid uses to dissipate the energy imparted by the incident ion beam. Ultrathin film (10 nm) metal-oxide-semiconductor (Au/SiO2/n-Si) devices were used to detect the electron-hole pairs for cases when the ion deposited all of its translational energy into the solid. The incident ions were incident at an angle normal to the surface of the device to maximize energy deposition and consequently electron-hole pair production. The rectifying metal-oxide-semiconductor device separates the electrons from the holes, allowing a current associated with electron-hole pair production to be measured. In these experiments a number of ion species (He+, Li+ , Ar+, K+) were made incident on multiple devices and the incident energy ranged from 100 eV to 2 keV. It was found that electron-hole pair production increased with incident ion velocity consistent with a kinetic electron excitation model where the electrons in the metal are partially confined to the surface.

Thickness dependent charge transfer states and dark carriers density in vacuum deposited small molecule organic photocell

NASA Astrophysics Data System (ADS)

Shekhar, Himanshu; Tzabari, Lior; Solomeshch, Olga; Tessler, Nir

2016-10-01

We have investigated the influence of the active layer thickness on the balance of the internal mechanisms affecting the efficiency of copper phthalocyanine - fullerene (C60) based vacuum deposited bulk heterojunction organic photocell. We fabricated a range of devices for which we varied the thickness of the active layer from 40 to 120 nm and assessed their performance using optical and electrical characterization techniques. As reported previously for phthalocyanine:C60, the performance of the device is highly dependent on the active layer thickness and of all the thicknesses we tried, the 40 nm thin active layer device showed the best solar cell characteristic parameters. Using the transfer matrix based optical model, which includes interference effects, we calculated the optical power absorbed in the active layers for the entire absorption band, and we found that this cannot explain the trend with thickness. Measurement of the cell quantum efficiency as a function of light intensity showed that the relative weight of the device internal processes changes when going from 40 nm to 120 nm thick active layer. Electrical modeling of the device, which takes different internal processes into account, allowed to quantify the changes in the processes affecting the generation - recombination balance. Sub gap external quantum efficiency and morphological analysis of the surface of the films agree with the model's result. We found that as the thickness grows the density of charge transfer states and of dark carriers goes up and the uniformity in the vertical direction is reduced.

A theoretical study on hot charge-transfer states and dimensional effects of organic photocells based on an ideal diode model.

PubMed

Shimazaki, Tomomi; Nakajima, Takahito

2017-05-21

This paper discusses an ideal diode model with hot charge-transfer (CT) states to analyze the power conversion efficiency of an organic photocell. A free carrier generation mechanism via sunlight in an organic photocell consists of four microscopic processes: photon absorption, exciton dissociation, CT, and charge separation. The hot CT state effect has been actively investigated to understand the charge separation process. We previously reported a theoretical method to calculate the efficiency of the charge separation process via a hot CT state (T. Shimazaki et al., Phys. Chem. Chem. Phys., 2015, 17, 12538 and J. Chem. Phys., 2016, 144, 234906). In this paper, we integrate the simulation method into the ideal photocell diode model and calculate several properties such as short circuit current, open circuit voltage, and power conversion efficiency. Our results highlight that utilizing the dimensional (entropy) effect together with the hot CT state can play an essential role in developing more efficient organic photocell devices.

N-type molecular electrical doping in organic semiconductors: formation and dissociation efficiencies of charge transfer complex

NASA Astrophysics Data System (ADS)

Kim, Jae-Min; Yoo, Seung-Jun; Moon, Chang-Ki; Sim, Bomi; Lee, Jae-Hyun; Lim, Heeseon; Kim, Jeong Won; Kim, Jang-Joo

2016-09-01

Electrical doping is an important method in organic electronics to enhance device efficiency by controlling Fermi level, increasing conductivity, and reducing injection barrier from electrode. To understand the charge generation process of dopant in doped organic semiconductors, it is important to analyze the charge transfer complex (CTC) formation and dissociation into free charge carrier. In this paper, we correlate charge generation efficiency with the CTC formation and dissociation efficiency of n-dopant in organic semiconductors (OSs). The CTC formation efficiency of Rb2CO3 linearly decreases from 82.8% to 47.0% as the doping concentration increases from 2.5 mol% to 20 mol%. The CTC formation efficiency and its linear decrease with doping concentration are analytically correlated with the concentration-dependent size and number of dopant agglomerates by introducing the degree of reduced CTC formation. Lastly, the behavior of dissociation efficiency is discussed based on the picture of the statistical semiconductor theory and the frontier orbital hybridization model.

Observation of Frenkel and charge transfer excitons in pentacene single crystals using spectroscopic generalized ellipsometry

NASA Astrophysics Data System (ADS)

Qi, Dongchen; Su, Haibin; Bastjan, M.; Jurchescu, O. D.; Palstra, T. M.; Wee, Andrew T. S.; Rübhausen, M.; Rusydi, A.

2013-09-01

We report on the emerging and admixture of Frenkel and charge transfer (CT) excitons near the absorption onset in pentacene single crystals. Using high energy-resolution spectroscopic generalized ellipsometry with in-plane polarization dependence, the excitonic nature of three lowest lying excitations is discussed. Their distinct polarization dependence strongly indicates the presence of both Frenkel and CT types of excitons near the excitation onset. In particular, the peculiar polarization behavior of the second excitation can only be rationalized by taking into account the inherent CT transition dipole moment. This observation has important implications for the pentacene-based optoelectronic devices.

Low-background performance of a monolithic InSb CCD array

NASA Technical Reports Server (NTRS)

Bregman, J. D.; Goebel, J. H.; Mccreight, C. R.; Matsumoto, T.

1982-01-01

A 20 element monolithic InSb charge coupled device (CCD) detector array was measured under low background conditions to assess its potential for orbital astronomical applications. At a temperature of 64 K, previous results for charge transfer efficiency (CTE) were reproduced, and a sensitivity of about 2 x 10 to the minus 15th power joules was measured. At 27 and 6 K, extended integration times were achieved, but CTE was substantially degraded. The noise was approximately 6000 charges, which was in excess of the level where statistical fluctuations from the illumination could be detected. A telescope demonstration was performed showing that the array sensitivity and difficulty of operation were not substantially different from laboratory levels. Ways in which the device could be improved for astronomical applications were discussed.

Two dimensional simulation of patternable conducting polymer electrode based organic thin film transistor

NASA Astrophysics Data System (ADS)

Nair, Shiny; Kathiresan, M.; Mukundan, T.

2018-02-01

Device characteristics of organic thin film transistor (OTFT) fabricated with conducting polyaniline:polystyrene sulphonic acid (PANi-PSS) electrodes, patterned by the Parylene lift-off method are systematically analyzed by way of two dimensional numerical simulation. The device simulation was performed taking into account field-dependent mobility, low mobility layer at the electrode-semiconductor interface, trap distribution in pentacene film and trapped charge at the organic/insulator interface. The electrical characteristics of bottom contact thin film transistor with PANi-PSS electrodes and pentacene active material is superior to those with palladium electrodes due to a lower charge injection barrier. Contact resistance was extracted in both cases by the transfer line method (TLM). The extracted charge concentration and potential profile from the two dimensional numerical simulation was used to explain the observed electrical characteristics. The simulated device characteristics not only matched the experimental electrical characteristics, but also gave an insight on the charge injection, transport and trap properties of the OTFTs as a function of different electrode materials from the perspectives of transistor operation.

Electronic, structural and chemical effects of charge-transfer at organic/inorganic interfaces

NASA Astrophysics Data System (ADS)

Otero, R.; Vázquez de Parga, A. L.; Gallego, J. M.

2017-07-01

During the last decade, interest on the growth and self-assembly of organic molecular species on solid surfaces spread over the scientific community, largely motivated by the promise of cheap, flexible and tunable organic electronic and optoelectronic devices. These efforts lead to important advances in our understanding of the nature and strength of the non-bonding intermolecular interactions that control the assembly of the organic building blocks on solid surfaces, which have been recently reviewed in a number of excellent papers. To a large extent, such studies were possible because of a smart choice of model substrate-adsorbate systems where the molecule-substrate interactions were purposefully kept low, so that most of the observed supramolecular structures could be understood simply by considering intermolecular interactions, keeping the role of the surface always relatively small (although not completely negligible). On the other hand, the systems which are more relevant for the development of organic electronic devices include molecular species which are electron donors, acceptors or blends of donors and acceptors. Adsorption of such organic species on solid surfaces is bound to be accompanied by charge-transfer processes between the substrate and the adsorbates, and the physical and chemical properties of the molecules cannot be expected any longer to be the same as in solution phase. In recent years, a number of groups around the world have started tackling the problem of the adsorption, self- assembly and electronic and chemical properties of organic species which interact rather strongly with the surface, and for which charge-transfer must be considered. The picture that is emerging shows that charge transfer can lead to a plethora of new phenomena, from the development of delocalized band-like electron states at molecular overlayers, to the existence of new substrate-mediated intermolecular interactions or the strong modification of the chemical reactivity of the adsorbates. The aim of this review is to start drawing general conclusions and developing new concepts which will help the scientific community to proceed more efficiently towards the understanding of organic/inorganic interfaces in the strong interaction limit, where charge-transfer effects must be taken into consideration.

Defect states and charge transport in quantum dot solids

DOE PAGES

Brawand, Nicholas P.; Goldey, Matthew B.; Vörös, Márton; ...

2017-01-16

Defects at the surface of semiconductor quantum dots (QDs) give rise to electronic states within the gap, which are detrimental to charge transport properties of QD devices. We investigated charge transport in silicon quantum dots with deep and shallow defect levels, using ab initio calculations and constrained density functional theory. We found that shallow defects may be more detrimental to charge transport than deep ones, with associated transfer rates differing by up to 5 orders of magnitude for the small dots (1-2 nm) considered here. Hence, our results indicate that the common assumption, that the ability of defects to trapmore » charges is determined by their position in the energy gap of the QD, is too simplistic, and our findings call for a reassessment of the role played by shallow defects in QD devices. Altogether, our results highlight the key importance of taking into account the atomistic structural properties of QD surfaces when investigating transport properties.« less

Solid state television camera

NASA Technical Reports Server (NTRS)

1976-01-01

The design, fabrication, and tests of a solid state television camera using a new charge-coupled imaging device are reported. An RCA charge-coupled device arranged in a 512 by 320 format and directly compatible with EIA format standards was the sensor selected. This is a three-phase, sealed surface-channel array that has 163,840 sensor elements, which employs a vertical frame transfer system for image readout. Included are test results of the complete camera system, circuit description and changes to such circuits as a result of integration and test, maintenance and operation section, recommendations to improve the camera system, and a complete set of electrical and mechanical drawing sketches.

Theory of Excitation Transfer between Two-Dimensional Semiconductor and Molecular Layers

NASA Astrophysics Data System (ADS)

Specht, Judith F.; Verdenhalven, Eike; Bieniek, Björn; Rinke, Patrick; Knorr, Andreas; Richter, Marten

2018-04-01

The geometry-dependent energy transfer rate from an electrically pumped inorganic semiconductor quantum well into an organic molecular layer is studied theoretically. We focus on Förster-type nonradiative excitation transfer between the organic and inorganic layers and include quasimomentum conservation and intermolecular coupling between the molecules in the organic film. (Transition) partial charges calculated from density-functional theory are used to calculate the coupling elements. The partial charges describe the spatial charge distribution and go beyond the common dipole-dipole interaction. We find that the transfer rates are highly sensitive to variations in the geometry of the hybrid inorganic-organic system. For instance, the transfer efficiency is improved by up to 2 orders of magnitude by tuning the spatial arrangement of the molecules on the surface: Parameters of importance are the molecular packing density along the effective molecular dipole axis and the distance between the molecules and the surface. We also observe that the device performance strongly depends on the orientation of the molecular dipole moments relative to the substrate dipole moments determined by the inorganic crystal structure. Moreover, the operating regime is identified where inscattering dominates over unwanted backscattering from the molecular layer into the substrate.

Charge transfer at organic-organic heterojunctions, and remote doping of a pentacene transistor

NASA Astrophysics Data System (ADS)

Zhao, Wei

Organic-organic heterojunctions (OOHs) are the fundamental building blocks of organic devices, such as organic light-emitting diodes, organic photovoltaic cells, and photo detectors. Transport of free electrons and holes, exciton formation, recombination or dissociation, and various other physical processes all take place in OOHs. Understanding the electronic structures of OOH is critical for studying device physics and further improving the performance of organic devices. This work focuses on the electronic structure, i.e., the energy level alignment, at OOHs, investigated by ultraviolet and inverse photoemission spectroscopy (UPS and IPES). The weak interaction that generally prevails at OOH interfaces leads to small interface dipoles of 0˜0.5eV. The experimental observations on the majority of OOHs studied can be semi-quantitatively predicted by the model derived from the induced density of interface states and charge neutrality level (IDIS/CNL). However, we also find that the electronic structure of interfaces between two small-band-gap semiconductors, e.g., using copper phthalocyanine (CuPc) as the donor and a tris(thieno)-hexaazatriphenylene derivative (THAP) as the acceptor, is strongly influenced by changes in the substrate work function. In these cases, the charge transfer that takes place at the interface is governed by thermodynamic equilibrium, dominating any subtle interaction due to IDIS/CNL. The impact of doping on the energy level alignment of OOHs is also studied. The charges donated by the dopant molecules transfer from the parent doped layer to the adjacent undoped layer, taking advantage of the molecular level offset, and are then spatially separated from the dopant molecules. Remote doping, based on this charge transfer mechanism, is demonstrated with the heterojunction formed between pentacene and N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'bisphenyl-4,4'diazine (alpha-NPD) p-doped with tris[1,2-bis(trifluoromethyl) ethane-1,2-dithiolene] (Mo(tfd)3). A remotely doped pentacene transistor, based on this type of hetero-structure, exhibits increased conductivity, decreased activation energy for carrier hopping, and enhanced mobility, compared to an undoped transistor. Another featured improvement of the remotely doped transistor is that it can be reasonably switched off by placing an undoped interlayer in the structure. Our preliminary results show chemical doping technology can potentially benefit the organic thin film transistors.

Effects of Charge-Transfer Excitons on the Photophysics of Organic Semiconductors

NASA Astrophysics Data System (ADS)

Hestand, Nicholas J.

The field of organic electronics has received considerable attention over the past several years due to the promise of novel electronic materials that are cheap, flexible and light weight. While some devices based on organic materials have already emerged on the market (e.g. organic light emitting diodes), a deeper understanding of the excited states within the condensed phase is necessary both to improve current commercial products and to develop new materials for applications that are currently in the commercial pipeline (e.g. organic photovoltaics, wearable displays, and field effect transistors). To this end, a model for pi-conjugated molecular aggregates and crystals is developed and analyzed. The model considers two types of electronic excitations, namely Frenkel and charge-transfer excitons, both of which play a prominent role in determining the nature of the excited states within tightly-packed organic systems. The former consist of an electron-hole pair bound to the same molecule while in the later the electron and hole are located on different molecules. The model also considers the important nuclear reorganization that occurs when the system switches between electronic states. This is achieved using a Holstein-style Hamiltonian that includes linear vibronic coupling of the electronic states to the nuclear motion associated with the high frequency vinyl-stretching and ring-breathing modes. Analysis of the model reveals spectroscopic signatures of charge-transfer mediated J- and H-aggregation in systems where the photophysical properties are determined primarily by charge-transfer interactions. Importantly, such signatures are found to be sensitive to the relative phase of the intermolecular electron and hole transfer integrals, and the relative energy of the Frenkel and charge-transfer states. When the charge-transfer integrals are in phase and the energy of the charge-transfer state is higher than the Frenkel state, the system exhibits J-aggregate characteristics including a positive band curvature, a red shifted main absorption peak, and an increase in the ratio of the first two vibronic peaks relative to the monomer. On the other hand, when the charge-transfer integrals are out of phase and the energy of the charge-transfer state is higher than the Frenkel state, the system exhibits H-aggregate characteristics including a negative band curvature, a blue shifted main absorption peak, and a decrease in the ratio of the first two vibronic peaks relative to the monomer. Notably, these signatures are consistent with those exhibited by Coulombically coupled J- and H-aggregates. Additional signatures of charge-transfer J- and H-aggregation are also discovered, the most notable of which is the appearance of a second absorption band when the charge-transfer integrals are in phase and the charge-transfer and Frenkel excitons are near resonance. In such instances, the peak-to-peak spacing is found to be proportional to the sum of the electron and hole transfer integrals. Further analysis of the charge-transfer interactions within the context of an effective Frenkel exciton coupling reveals that the charge-transfer interactions interfere directly with the intermolecular Coulombic coupling. The interference can be either constructive or destructive resulting in either enhanced or suppressed J- or H- aggregate behavior relative to what is expected based on Coulombic coupling alone. Such interferences result in four new aggregate types, namely HH-, HJ-, JH-, and JJ-aggregates, where the first letter indicates the nature of the Coulombic coupling and the second indicates the nature of the charge-transfer coupling. Vibronic signatures of such aggregates are developed and provide a means by which to rapidly screen materials for certain electronic characteristics. Notably, a large total (Coulombic plus charge-transfer) exciton coupling is associated with an absorption spectrum in which the ratio of the first two vibronic peaks deviates significantly from that of the unaggregated monomer. Hence, strongly coupled, high exciton mobility aggregates can be readily distinguished from low mobility aggregates by the ratio of their first two vibronic peaks. (Abstract shortened by ProQuest.).

Ultrafast Exciton Dissociation and Long-Lived Charge Separation in a Photovoltaic Pentacene-MoS2 van der Waals Heterojunction.

PubMed

Bettis Homan, Stephanie; Sangwan, Vinod K; Balla, Itamar; Bergeron, Hadallia; Weiss, Emily A; Hersam, Mark C

2017-01-11

van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unique opportunities for gate-tunable optoelectronic devices. Mixed-dimensional p-n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS 2 (2D), are especially interesting for photovoltaic applications where the absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library of organic molecules and 2D materials. Here, we study the kinetics of excited carriers in pentacene-MoS 2 p-n type-II heterojunctions by transient absorption spectroscopy. These measurements show that the dissociation of MoS 2 excitons occurs by hole transfer to pentacene on the time scale of 6.7 ps. In addition, the charge-separated state lives for 5.1 ns, up to an order of magnitude longer than the recombination lifetimes from previously reported 2D material heterojunctions. By studying the fractional amplitudes of the MoS 2 decay processes, the hole transfer yield from MoS 2 to pentacene is found to be ∼50%, with the remaining holes undergoing trapping due to surface defects. Overall, the ultrafast charge transfer and long-lived charge-separated state in pentacene-MoS 2 p-n heterojunctions suggest significant promise for mixed-dimensional van der Waals heterostructures in photovoltaics, photodetectors, and related optoelectronic technologies.

Optical and dark characterization of the PLATO CCD at ESA

NASA Astrophysics Data System (ADS)

Verhoeve, Peter; Prod'homme, Thibaut; Oosterbroek, Tim; Duvet, Ludovic; Beaufort, Thierry; Blommaert, Sander; Butler, Bart; Heijnen, Jerko; Lemmel, Frederic; van der Luijt, Cornelis; Smit, Hans; Visser, Ivo

2016-07-01

PLATO - PLAnetary Transits and Oscillations of stars - is the third medium-class mission (M3) to be selected in the European Space Agency (ESA) Science and Robotic Exploration Cosmic Vision programme. It is due for launch in 2025 with the main objective to find and study terrestrial planets in the habitable zone around solar-like stars. The payload consists of >20 cameras; with each camera comprising 4 Charge-Coupled Devices (CCDs), a large number of flight model devices procured by ESA shall ultimately be integrated on the spacecraft. The CCD270 - specially designed and manufactured by e2v for the PLATO mission - is a large format (8 cm x 8 cm) back-illuminated device operating at 4 MHz pixel rate and coming in two variants: full frame and frame transfer. In order to de-risk the PLATO CCD procurement and aid the mission definition process, ESA's Payload Technology Validation section is currently validating the PLATO CCD270. This validation consists in demonstrating that the device achieves its specified electrooptical performance in the relevant environment: operated at 4 MHz, at cold and before and after proton irradiation. As part of this validation, CCD270 devices have been characterized in the dark as well as optically with respect to performance parameters directly relevant for the photometric application of the CCDs. Dark tests comprise the measurement of gain sensitivity to bias voltages, charge injection tests, and measurement of hot and variable pixels after irradiation. In addition, the results of measurements of Quantum Efficiency for a range of angles of incidence, intra- pixel response (non-)uniformity, and response to spot illumination, before and after proton irradiation. In particular, the effect of radiation induced degradation of the charge transfer efficiency on the measured charge in a star-like spot has been studied as a function of signal level and of position on the pixel grid, Also, the effect of various levels of background light on the amount of charge lost from a star image are described. These results can serve as a direct input to the PLATO consortium to study the mission performance and as a basis for further optimization of the CCD operation.

Scientific, Back-Illuminated CCD Development for the Transiting Exoplanet Survey Satellite

NASA Technical Reports Server (NTRS)

Suntharalingam, V.; Ciampi, J.; Cooper, M. J.; Lambert, R. D.; O'Mara, D. M.; Prigozhin, I.; Young, D. J.; Warner, K.; Burke, B. E.

2015-01-01

We describe the development of the fully depleted, back illuminated charge coupled devices for the Transiting Exoplanet Survey Satellite, which includes a set of four wide angle telescopes, each having a 2x2 array of CCDs. The devices are fabricated on the newly upgraded 200-mm wafer line at Lincoln Laboratory. We discuss methods used to produce the devices and present early performance results from the 100- micron thick, 15x15-microns, 2k x 4k pixel frame transfer CCDs.

Ab initio modeling of steady-state and time-dependent charge transport in hole-only α-NPD devices

NASA Astrophysics Data System (ADS)

Liu, Feilong; Massé, Andrea; Friederich, Pascal; Symalla, Franz; Nitsche, Robert; Wenzel, Wolfgang; Coehoorn, Reinder; Bobbert, Peter A.

2016-12-01

We present an ab initio modeling study of steady-state and time-dependent charge transport in hole-only devices of the amorphous molecular semiconductor α-NPD [N ,N'-Di(1 -naphthyl)-N ,N'-diphenyl-(1 ,1'-biphenyl)-4 ,4'-diamine] . The study is based on the microscopic information obtained from atomistic simulations of the morphology and density functional theory calculations of the molecular hole energies, reorganization energies, and transfer integrals. Using stochastic approaches, the microscopic information obtained in simulation boxes at a length scale of ˜10 nm is expanded and employed in one-dimensional (1D) and three-dimensional (3D) master-equation modeling of the charge transport at the device scale of ˜100 nm. Without any fit parameter, predicted current density-voltage and impedance spectroscopy data obtained with the 3D modeling are in very good agreement with measured data on devices with different α-NPD layer thicknesses in a wide range of temperatures, bias voltages, and frequencies. Similarly good results are obtained with the computationally much more efficient 1D modeling after optimizing a hopping prefactor.

Mesoscopic features of charge generation in organic semiconductors.

PubMed

Savoie, Brett M; Jackson, Nicholas E; Chen, Lin X; Marks, Tobin J; Ratner, Mark A

2014-11-18

CONSPECTUS: In the past two decades, organic materials have been extensively investigated by numerous research groups worldwide for implementation in organic photovoltaic (OPV) devices. The interest in organic semiconductors is spurred by their potential low cost and facile tunability, making OPV devices a potentially disruptive technology. To study OPV operating mechanisms is also to explore a knowledge gap in our general understanding of materials, because both the time scales (femtosecond to microsecond) and length scales (nanometer to micrometer) relevant to OPV functionality occupy a challenging and fascinating space between the traditional regimes of quantum chemistry and solid-state physics. New theoretical frameworks and computational tools are needed to bridge the aforementioned length and time scales, and they must satisfy the criteria of computational tractability for systems involving 10(4)-10(6) atoms, while also maintaining predictive utility. While this challenge is far from solved, advances in density functional theory (DFT) have allowed researchers to investigate the ground- and excited-state properties of many intermediate sized systems (10(2)-10(3) atoms) that provide the outlines of the larger problem. Results on these smaller systems are already sufficient to predict optical gaps and trends in valence band energies, correct erroneous interpretations of experimental data, and develop models for charge generation and transport in OPV devices. The active films of high-efficiency OPV devices are comprised of mesoscopic mixtures of electron donor (D) and electron acceptor (A) species, a "bulk-heterojunction" (BHJ) device, subject to variable degrees of structural disorder. Depending on the degree of intermolecular electronic coupling and energy level alignment, the spatial delocalization of photoexcitations and charge carriers can affect the dynamics of the solar cell. In this Account, we provide an overview of three pivotal characteristics of solar cells that possess strong delocalization dependence: (1) the exciton binding energy, (2) charge transfer at the D-A heterojunction, and (3) the energy landscape in the vicinity of the D-A heterojunction. In each case, the length scale dependence can be assessed through DFT calculations on reference systems, with a view to establishing general trends. Throughout the discussion, we draw from the experimental and theoretical literature to provide a consistent view of what is known about these properties in actual BHJ blends. A consistent interpretation of the results to date affords the following view: transient delocalization effects and resonant charge transfer at the heterojunction are capable of funneling excitations away from trap states and mediating exciton dissociation; these factors alone are capable of explaining the remarkably good charge generation currently achieved in OPV devices. The exciton binding energy likely plays a minimal role in modern OPV devices, since the presence of the heterojunction serves to bypass the costly exciton-to-free-charge transition state.

Triboelectric effect: A new perspective on electron transfer process

NASA Astrophysics Data System (ADS)

Pan, Shuaihang; Zhang, Zhinan

2017-10-01

As interest in the triboelectric effect increases in line with the development of tribo-electrification related devices, the mechanisms involved in this phenomenon require more systematic review from the dual perspectives of developed classical insights and emerging quantum understanding. In this paper, the clear energy changing and transferring process of electrons have been proposed from the quantum point of view as the trigger for the charging initiation process in the triboelectric effect, and the phonon modes on the friction surfaces are believed to hold great importance as one of the main driving forces. Compatible with Maxwell Displacement Current theory, the complete consideration for charging steady state, i.e., the competition mechanisms between the breakdown process and the continuously charging process, and the balance mechanisms of phonon-electron interaction, built voltage, and induced polarization, are illustrated. In brief, the proposed theory emphasizes the fundamental role of electron transferring in tribo-electrical fields. By comparing certain experimental results from the previous studies, the theory is justified.

Synthesis, structural, spectroscopic and optical studies of charge transfer complex salts.

PubMed

Manikandan, Maruthappan; Mahalingam, Thaiyan; Hayakawa, Yasuhiro; Ravi, Ganesan

2013-01-15

New charge transfer molecular complex adducts of picric acid (C6H3N3O7) with triethylamine (C6H15N) and dimethylformamide (HCON(CH3)2) were synthesized successfully for the first time. Chemical composition and stoichiometry of the synthesized complex salts were verified by CHN elemental analysis. Solubility of the complex salts have been determined by gravimetric method and single crystals of two new salts were grown by low temperature solution growth technique. Crystal system, crystalline nature and cell parameters of the grown crystals were determined by single crystal X-ray diffraction (SXRD) and powder X-ray diffraction (PXRD) analyses. The formations of the charge-transfer complex, functional groups and the modes of vibrations have been confirmed by Fourier transform infrared (FTIR) spectroscopy. In order to know the linear and nonlinear optical suitability for device fabrication, UV-Vis (UV) spectral analysis and relative second harmonic generation (SHG) efficiency test were performed for the grown crystals. Copyright © 2012 Elsevier B.V. All rights reserved.

Synthesis, structural, spectroscopic and optical studies of charge transfer complex salts

NASA Astrophysics Data System (ADS)

Manikandan, Maruthappan; Mahalingam, Thaiyan; Hayakawa, Yasuhiro; Ravi, Ganesan

2013-01-01

New charge transfer molecular complex adducts of picric acid (C6H3N3O7) with triethylamine (C6H15N) and dimethylformamide (HCON(CH3)2) were synthesized successfully for the first time. Chemical composition and stoichiometry of the synthesized complex salts were verified by CHN elemental analysis. Solubility of the complex salts have been determined by gravimetric method and single crystals of two new salts were grown by low temperature solution growth technique. Crystal system, crystalline nature and cell parameters of the grown crystals were determined by single crystal X-ray diffraction (SXRD) and powder X-ray diffraction (PXRD) analyses. The formations of the charge-transfer complex, functional groups and the modes of vibrations have been confirmed by Fourier transform infrared (FTIR) spectroscopy. In order to know the linear and nonlinear optical suitability for device fabrication, UV-Vis (UV) spectral analysis and relative second harmonic generation (SHG) efficiency test were performed for the grown crystals.

Large Modulation of Charge Carrier Mobility in Doped Nanoporous Organic Transistors.

PubMed

Zhang, Fengjiao; Dai, Xiaojuan; Zhu, Weikun; Chung, Hyunjoong; Diao, Ying

2017-07-01

Molecular doping of organic electronics has shown promise to sensitively modulate important device metrics. One critical challenge is the disruption of structure order upon doping of highly crystalline organic semiconductors, which significantly reduces the charge carrier mobility. This paper demonstrates a new method to achieve large modulation of charge carrier mobility via channel doping without disrupting the molecular ordering. Central to the method is the introduction of nanopores into the organic semiconductor thin films via a simple and robust templated meniscus-guided coating method. Using this method, the charge carrier mobility of C 8 -benzothieno[3,2-b]benzothiophene transistors is boosted by almost sevenfold. This paper further demonstrates enhanced electron transport by close to an order of magnitude in a diketopyrrolopyrrole-based donor-acceptor polymer. Combining spectroscopic measurements, density functional theory calculations, and electrical characterizations, the doping mechanism is identified as partial-charge-transfer induced trap filling. The nanopores serve to enhance the dopant/organic semiconductor charge transfer reaction by exposing the π-electrons to the pore wall. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Large Modulation of Charge Carrier Mobility in Doped Nanoporous Organic Transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Fengjiao; Dai, Xiaojuan; Zhu, Weikun

Molecular doping of organic electronics has shown promise to sensitively modulate important device metrics. One critical challenge is the disruption of structure order upon doping of highly crystalline organic semiconductors, which significantly reduces the charge carrier mobility. This paper demonstrates a new method to achieve large modulation of charge carrier mobility via channel doping without disrupting the molecular ordering. Central to the method is the introduction of nanopores into the organic semiconductor thin films via a simple and robust templated meniscus-guided coating method. Using this method, the charge carrier mobility of C8-benzothieno[3,2-b]benzothiophene transistors is boosted by almost sevenfold. This papermore » further demonstrates enhanced electron transport by close to an order of magnitude in a diketopyrrolopyrrole-based donor–acceptor polymer. Combining spectroscopic measurements, density functional theory calculations, and electrical characterizations, the doping mechanism is identified as partial-charge-transfer induced trap filling. The nanopores serve to enhance the dopant/organic semiconductor charge transfer reaction by exposing the π-electrons to the pore wall.« less

Method for eliminating artifacts in CCD imagers

DOEpatents

Turko, B.T.; Yates, G.J.

1992-06-09

An electronic method for eliminating artifacts in a video camera employing a charge coupled device (CCD) as an image sensor is disclosed. The method comprises the step of initializing the camera prior to normal read out and includes a first dump cycle period for transferring radiation generated charge into the horizontal register while the decaying image on the phosphor being imaged is being integrated in the photosites, and a second dump cycle period, occurring after the phosphor image has decayed, for rapidly dumping unwanted smear charge which has been generated in the vertical registers. Image charge is then transferred from the photosites and to the vertical registers and read out in conventional fashion. The inventive method allows the video camera to be used in environments having high ionizing radiation content, and to capture images of events of very short duration and occurring either within or outside the normal visual wavelength spectrum. Resultant images are free from ghost, smear and smear phenomena caused by insufficient opacity of the registers and, and are also free from random damage caused by ionization charges which exceed the charge limit capacity of the photosites. 3 figs.

Origin of Reduced Open-Circuit Voltage in Highly Efficient Small-Molecule-Based Solar Cells upon Solvent Vapor Annealing.

PubMed

Deng, Wanyuan; Gao, Ke; Yan, Jun; Liang, Quanbin; Xie, Yuan; He, Zhicai; Wu, Hongbin; Peng, Xiaobin; Cao, Yong

2018-03-07

In this study, we demonstrate that remarkably reduced open-circuit voltage in highly efficient organic solar cells (OSCs) from a blend of phenyl-C 61 -butyric acid methyl ester and a recently developed conjugated small molecule (DPPEZnP-THD) upon solvent vapor annealing (SVA) is due to two independent sources: increased radiative recombination and increased nonradiative recombination. Through the measurements of electroluminescence due to the emission of the charge-transfer state and photovoltaic external quantum efficiency measurement, we can quantify that the open-circuit voltage losses in a device with SVA due to the radiative recombination and nonradiative recombination are 0.23 and 0.31 V, respectively, which are 0.04 and 0.07 V higher than those of the as-cast device. Despite of the reduced open-circuit voltage, the device with SVA exhibited enhanced dissociation of charge-transfer excitons, leading to an improved short-circuit current density and a remarkable power conversion efficiency (PCE) of 9.41%, one of the best for solution-processed OSCs based on small-molecule donor materials. Our study also clearly shows that removing the nonradiative recombination pathways and/or suppressing energetic disorder in the active layer would result in more long-lived charge carriers and enhanced open-circuit voltage, which are prerequisites for further improving the PCE.

Charge carrier dynamics and surface plasmon interaction in gold nanorod-blended organic solar cell

NASA Astrophysics Data System (ADS)

Rana, Aniket; Gupta, Neeraj; Lochan, Abhiram; Sharma, G. D.; Chand, Suresh; Kumar, Mahesh; Singh, Rajiv K.

2016-08-01

The inclusion of plasmonic nanoparticles into organic solar cell enhances the light harvesting properties that lead to higher power conversion efficiency without altering the device configuration. This work defines the consequences of the nanoparticle overloading amount and energy transfer process between gold nanorod and polymer (active matrix) in organic solar cells. We have studied the hole population decay dynamics coupled with gold nanorods loading amount which provides better understanding about device performance limiting factors. The exciton and plasmon together act as an interacting dipole; however, the energy exchange between these two has been elucidated via plasmon resonance energy transfer (PRET) mechanism. Further, the charge species have been identified specifically with respect to their energy levels appearing in ultrafast time domain. The specific interaction of these charge species with respective surface plasmon resonance mode, i.e., exciton to transverse mode of oscillation and polaron pair to longitudinal mode of oscillations, has been explained. Thus, our analysis reveals that PRET enhances the carrier population density in polymer via non-radiative process beyond the concurrence of a particular plasmon resonance oscillation mode and polymer absorption range. These findings give new insight and reveal specifically the factors that enhance and control the performance of gold nanorods blended organic solar cells. This work would lead in the emergence of future plasmon based efficient organic electronic devices.

Charge carrier dynamics and surface plasmon interaction in gold nanorod-blended organic solar cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rana, Aniket; Lochan, Abhiram; Chand, Suresh

The inclusion of plasmonic nanoparticles into organic solar cell enhances the light harvesting properties that lead to higher power conversion efficiency without altering the device configuration. This work defines the consequences of the nanoparticle overloading amount and energy transfer process between gold nanorod and polymer (active matrix) in organic solar cells. We have studied the hole population decay dynamics coupled with gold nanorods loading amount which provides better understanding about device performance limiting factors. The exciton and plasmon together act as an interacting dipole; however, the energy exchange between these two has been elucidated via plasmon resonance energy transfer (PRET)more » mechanism. Further, the charge species have been identified specifically with respect to their energy levels appearing in ultrafast time domain. The specific interaction of these charge species with respective surface plasmon resonance mode, i.e., exciton to transverse mode of oscillation and polaron pair to longitudinal mode of oscillations, has been explained. Thus, our analysis reveals that PRET enhances the carrier population density in polymer via non-radiative process beyond the concurrence of a particular plasmon resonance oscillation mode and polymer absorption range. These findings give new insight and reveal specifically the factors that enhance and control the performance of gold nanorods blended organic solar cells. This work would lead in the emergence of future plasmon based efficient organic electronic devices.« less

Engineering of an ultra-thin molecular superconductor by charge transfer

DOEpatents

Hla, Saw Wai; Hassanien, Abdelrahim; Kendal, Clark

2016-06-07

A method of forming a superconductive device of a single layer of (BETS).sub.2GaCl.sub.4 molecules on a substrate surface which displays a superconducting gap that increases exponentially with the length of the molecular chain is provided.

Efficient Carbon-Based CsPbBr3 Inorganic Perovskite Solar Cells by Using Cu-Phthalocyanine as Hole Transport Material

NASA Astrophysics Data System (ADS)

Liu, Zhiyong; Sun, Bo; Liu, Xingyue; Han, Jinghui; Ye, Haibo; Shi, Tielin; Tang, Zirong; Liao, Guanglan

2018-06-01

Metal halide perovskite solar cells (PSCs) have attracted extensive research interest for next-generation solution-processed photovoltaic devices because of their high solar-to-electric power conversion efficiency (PCE) and low fabrication cost. Although the world's best PSC successfully achieves a considerable PCE of over 20% within a very limited timeframe after intensive efforts, the stability, high cost, and up-scaling of PSCs still remain issues. Recently, inorganic perovskite material, CsPbBr3, is emerging as a promising photo-sensitizer with excellent durability and thermal stability, but the efficiency is still embarrassing. In this work, we intend to address these issues by exploiting CsPbBr3 as light absorber, accompanied by using Cu-phthalocyanine (CuPc) as hole transport material (HTM) and carbon as counter electrode. The optimal device acquires a decent PCE of 6.21%, over 60% higher than those of the HTM-free devices. The systematic characterization and analysis reveal a more effective charge transfer process and a suppressed charge recombination in PSCs after introducing CuPc as hole transfer layer. More importantly, our devices exhibit an outstanding durability and a promising thermal stability, making it rather meaningful in future fabrication and application of PSCs.[Figure not available: see fulltext.

Control of Geminate Recombination by the Material Composition and Processing Conditions in Novel Polymer: Nonfullerene Acceptor Photovoltaic Devices.

PubMed

Zhang, Jiangbin; Gu, Qinying; Do, Thu Trang; Rundel, Kira; Sonar, Prashant; Friend, Richard H; McNeill, Christopher R; Bakulin, Artem A

2018-02-08

Herein, we report on the charge dynamics of photovoltaic devices based on two novel small-molecule nonfullerene acceptors featuring a central ketone unit. Using ultrafast near-infrared spectroscopy with optical and photocurrent detection methods, we identify one of the key loss channels in the devices as geminate recombination (GR) of interfacial charge transfer states (CTSs). We find that the magnitude of GR is highly sensitive to the choice of solvent and annealing conditions. Interestingly, regardless of these processing conditions, the same lifetime for GR (∼130 ps) is obtained by both detection methods upon decomposing the complex broadband transient optical spectra, suggesting this time scale is inherent and independent of morphology. These observations suggest that the CTSs in the studied material blends are mostly strongly bound, and that charge generation from these states is highly inefficient. We further rationalize our results by considering the impact of the processing on the morphology of the mixed donor and acceptor domains and discuss the potential consequences of the early charge dynamics on the performance of emerging nonfullerene photovoltaic devices. Our results demonstrate that careful choice of processing conditions enables enhanced exciton harvesting and suppression of GR by more than 3 orders of magnitude.

Charge-Transfer-Induced p-Type Channel in MoS2 Flake Field Effect Transistors.

PubMed

Min, Sung-Wook; Yoon, Minho; Yang, Sung Jin; Ko, Kyeong Rok; Im, Seongil

2018-01-31

The two-dimensional transition-metal dichalcogenide semiconductor MoS 2 has received extensive attention for decades because of its outstanding electrical and mechanical properties for next-generation devices. One weakness of MoS 2 , however, is that it shows only n-type conduction, revealing its limitations for homogeneous PN diodes and complementary inverters. Here, we introduce a charge-transfer method to modify the conduction property of MoS 2 from n- to p-type. We initially deposited an n-type InGaZnO (IGZO) film on top of the MoS 2 flake so that electron charges might be transferred from MoS 2 to IGZO during air ambient annealing. As a result, electron charges were depleted in MoS 2 . Such charge depletion lowered the MoS 2 Fermi level, which makes hole conduction favorable in MoS 2 when optimum source/drain electrodes with a high work function are selected. Our IGZO-supported MoS 2 flake field effect transistors (FETs) clearly display channel-type conversion from n- to p-channel in this way. Under short- and long-annealing conditions, n- and p-channel MoS 2 FETs are achieved, respectively, and a low-voltage complementary inverter is demonstrated using both channels in a single MoS 2 flake.

Layer and doping tunable ferromagnetic order in two-dimensional Cr S2 layers

NASA Astrophysics Data System (ADS)

Wang, Cong; Zhou, Xieyu; Pan, Yuhao; Qiao, Jingsi; Kong, Xianghua; Kaun, Chao-Cheng; Ji, Wei

2018-06-01

Interlayer coupling is of vital importance for manipulating physical properties, e.g., electronic band gap, in two-dimensional materials. However, tuning magnetic properties in these materials is yet to be addressed. Here, we found the in-plane magnetic orders of Cr S2 mono and few layers are tunable between striped antiferromagnetic (sAFM) and ferromagnetic (FM) orders by manipulating charge transfer between Cr t2 g and eg orbitals. Such charge transfer is realizable through interlayer coupling, direct charge doping, or substituting S with Cl atoms. In particular, the transferred charge effectively reduces a portion of Cr4 + to Cr3 +, which, together with delocalized S p orbitals and their resulting direct S-S interlayer hopping, enhances the double-exchange mechanism favoring the FM rather than sAFM order. An exceptional interlayer spin-exchange parameter was revealed over -10 meV , an order of magnitude stronger than available results of interlayer magnetic coupling. It addition, the charge doping could tune Cr S2 between p - and n -doped magnetic semiconductors. Given these results, several prototype devices were proposed for manipulating magnetic orders using external electric fields or mechanical motion. These results manifest the role of interlayer coupling in modifying magnetic properties of layered materials and shed considerable light on manipulating magnetism in these materials.

46 CFR 199.30 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-10-01

... surveys, atmospheric research, and biological research. Officer in Charge, Marine Inspection (OCMI), means... other similar places open to persons on board. Anti-exposure suit means a protective suit designed for... means the method or devices designed to transfer a survival craft or rescue boat from its stowed...

46 CFR 199.30 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-10-01

... surveys, atmospheric research, and biological research. Officer in Charge, Marine Inspection (OCMI), means... other similar places open to persons on board. Anti-exposure suit means a protective suit designed for... means the method or devices designed to transfer a survival craft or rescue boat from its stowed...

46 CFR 199.30 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-10-01

... surveys, atmospheric research, and biological research. Officer in Charge, Marine Inspection (OCMI), means... other similar places open to persons on board. Anti-exposure suit means a protective suit designed for... means the method or devices designed to transfer a survival craft or rescue boat from its stowed...

Heavily doped n-type PbSe and PbS nanocrystals using ground-state charge transfer from cobaltocene

DOE PAGES

Koh, Weon-kyu; Koposov, Alexey Y.; Stewart, John T.; ...

2013-06-18

Colloidal nanocrystals (NCs) of lead chalcogenides are a promising class of tunable infrared materials for applications in devices such as photodetectors and solar cells. Such devices typically employ electronic materials in which charge carrier concentrations are manipulated through “doping;” however, persistent electronic doping of these NCs remains a challenge. In this paper, we demonstrate that heavily doped n-type PbSe and PbS NCs can be realized utilizing ground-state electron transfer from cobaltocene. This allows injecting up to eight electrons per NC into the band-edge state and maintaining the doping level for at least a month at room temperature. Doping is confirmedmore » by inter- and intra-band optical absorption, as well as by carrier dynamics. In conclusion, FET measurements of doped NC films and the demonstration of a p-n diode provide additional evidence that the developed doping procedure allows for persistent incorporation of electrons into the quantum-confined NC states.« less

Synthesis and Exciton Dynamics of Donor-Orthogonal Acceptor Conjugated Polymers: Reducing the Singlet-Triplet Energy Gap.

PubMed

Freeman, David M E; Musser, Andrew J; Frost, Jarvist M; Stern, Hannah L; Forster, Alexander K; Fallon, Kealan J; Rapidis, Alexandros G; Cacialli, Franco; McCulloch, Iain; Clarke, Tracey M; Friend, Richard H; Bronstein, Hugo

2017-08-16

The presence of energetically low-lying triplet states is a hallmark of organic semiconductors. Even though they present a wealth of interesting photophysical properties, these optically dark states significantly limit optoelectronic device performance. Recent advances in emissive charge-transfer molecules have pioneered routes to reduce the energy gap between triplets and "bright" singlets, allowing thermal population exchange between them and eliminating a significant loss channel in devices. In conjugated polymers, this gap has proved resistant to modification. Here, we introduce a general approach to reduce the singlet-triplet energy gap in fully conjugated polymers, using a donor-orthogonal acceptor motif to spatially separate electron and hole wave functions. This new generation of conjugated polymers allows for a greatly reduced exchange energy, enhancing triplet formation and enabling thermally activated delayed fluorescence. We find that the mechanisms of both processes are driven by excited-state mixing between π-π*and charge-transfer states, affording new insight into reverse intersystem crossing.

Graphene/h-BN/GaAs sandwich diode as solar cell and photodetector.

PubMed

Li, Xiaoqiang; Lin, Shisheng; Lin, Xing; Xu, Zhijuan; Wang, Peng; Zhang, Shengjiao; Zhong, Huikai; Xu, Wenli; Wu, Zhiqian; Fang, Wei

2016-01-11

In graphene/semiconductor heterojunction, the statistic charge transfer between graphene and semiconductor leads to decreased junction barrier height and limits the Fermi level tuning effect in graphene, which greatly affects the final performance of the device. In this work, we have designed a sandwich diode for solar cells and photodetectors through inserting 2D hexagonal boron nitride (h-BN) into graphene/GaAs heterostructure to suppress the static charge transfer. The barrier height of graphene/GaAs heterojunction can be increased from 0.88 eV to 1.02 eV by inserting h-BN. Based on the enhanced Fermi level tuning effect with interface h-BN, through adopting photo-induced doping into the device, power conversion efficiency (PCE) of 10.18% has been achieved for graphene/h-BN/GaAs compared with 8.63% of graphene/GaAs structure. The performance of graphene/h-BN/GaAs based photodetector is also improved with on/off ratio increased by one magnitude compared with graphene/GaAs structure.

Sensing of molecules using quantum dynamics

PubMed Central

Migliore, Agostino; Naaman, Ron; Beratan, David N.

2015-01-01

We design sensors where information is transferred between the sensing event and the actuator via quantum relaxation processes, through distances of a few nanometers. We thus explore the possibility of sensing using intrinsically quantum mechanical phenomena that are also at play in photobiology, bioenergetics, and information processing. Specifically, we analyze schemes for sensing based on charge transfer and polarization (electronic relaxation) processes. These devices can have surprising properties. Their sensitivity can increase with increasing separation between the sites of sensing (the receptor) and the actuator (often a solid-state substrate). This counterintuitive response and other quantum features give these devices favorable characteristics, such as enhanced sensitivity and selectivity. Using coherent phenomena at the core of molecular sensing presents technical challenges but also suggests appealing schemes for molecular sensing and information transfer in supramolecular structures. PMID:25911636

STM/STS study of graphene directly grown on h-BN films on Cu foils

NASA Astrophysics Data System (ADS)

Jang, Won-Jun; Wang, Min; Jang, Seong-Gyu; Kim, Minwoo; Park, Seong-Yong; Kim, Sang-Woo; Kahng, Se-Jong; Choi, Jae-Young; Song, Young; Lee, Sungjoo; Sanit Collaboration; Department Of Physics, Korea University Collaboration; Graphene Research Center, Samsung Advanced Institute Of Technology Collaboration

2013-03-01

Graphene-based devices on standard SiO2 substrate commonly exhibit inferior characteristics relative to the expected intrinsic properties of graphene, due to the disorder existing at graphene-SiO2 interface. Recently, it has been shown that exfoliated and chemical vapor deposition (CVD) graphene transferred onto hexagonal boron nitride (h-BN) possesses significantly reduced charge inhomogeneity, and yields improved device performance. Here we report the scanning tunneling microscopy (STM) and spectroscopy (STS) results obtained from a graphene layer directly grown on h-BN insulating films on Cu foils. STS measurements illustrate that graphene/h-BN film is charge neutral without electronic perturbation from h-BN/Cu substrate. Corresponding Author

Redox probing study of the potential dependence of charge transport through Li 2O 2

DOE PAGES

Knudsen, Kristian B.; Luntz, Alan C.; Jensen, Søren H.; ...

2015-11-20

In the field of energy storage devices the pursuit for cheap, high energy density, reliable secondary batteries is at the top of the agenda. The Li–O 2 battery is one of the possible technologies that, in theory, should be able to close the gap, which exists between the present state-of-the-art Li-ion technologies and the demand placed on batteries by technologies such as electrical vehicles. Here we present a redox probing study of the charge transfer across the main deposition product lithium peroxide, Li 2O 2, in the Li–O 2 battery using outer-sphere redox shuttles. The change in heterogeneous electron transfermore » exchange rate as a function of the potential and the Li 2O 2 layer thickness (~depth-of-discharge) was determined using electrochemical impedance spectroscopy. In addition, the attenuation of the electron transfer exchange rate with film thickness is dependent on the probing potential, providing evidence that hole transport is the dominant process for charge transfer through Li 2O 2 and showing that the origin of the sudden death observed upon discharge is due to charge transport limitations.« less

Solution Phase Exciton Diffusion Dynamics of a Charge-Transfer Copolymer PTB7 and a Homopolymer P3HT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, Sung; Rolczynski, Brian S.; Xu, Tao

2015-06-18

Using ultrafast polarization-controlled transient absorption (TA) measurements, dynamics of the initial exciton states were investigated on the time scale of tens of femtoseconds to about 80 ps in two different types of conjugated polymers extensively used in active layers of organic photovoltaic devices. These polymers are poly(3-fluorothienothiophenebenzodithiophene) (PTB7) and poly-3-hexylthiophene (P3HT), which are charge-transfer polymers and homopolymers, respectively. In PTB7, the initial excitons with excess vibrational energy display two observable ultrafast time constants, corresponding to coherent exciton diffusion before the vibrational relaxation, and followed by incoherent exciton diffusion processes to a neighboring local state after the vibrational relaxation. In contrast,more » P3HT shows only one exciton diffusion or conformational motion time constant of 34 ps, even though its exciton decay kinetics are multiexponential. Based on the experimental results, an exciton dynamics mechanism is conceived taking into account the excitation energy and structural dependence in coherent and incoherent exciton diffusion processes, as well as other possible deactivation processes including the formation of the pseudo-charge-transfer and charge separate states, as well as interchain exciton hopping or coherent diffusion.« less

Solution Phase Exciton Diffusion Dynamics of a Charge-Transfer Copolymer PTB7 and a Homopolymer P3HT.

PubMed

Cho, Sung; Rolczynski, Brian S; Xu, Tao; Yu, Luping; Chen, Lin X

2015-06-18

Using ultrafast polarization-controlled transient absorption (TA) measurements, dynamics of the initial exciton states were investigated on the time scale of tens of femtoseconds to about 80 ps in two different types of conjugated polymers extensively used in active layers of organic photovoltaic devices. These polymers are poly(3-fluorothienothiophenebenzodithiophene) (PTB7) and poly-3-hexylthiophene (P3HT), which are charge-transfer polymers and homopolymers, respectively. In PTB7, the initial excitons with excess vibrational energy display two observable ultrafast time constants, corresponding to coherent exciton diffusion before the vibrational relaxation, and followed by incoherent exciton diffusion processes to a neighboring local state after the vibrational relaxation. In contrast, P3HT shows only one exciton diffusion or conformational motion time constant of 34 ps, even though its exciton decay kinetics are multiexponential. Based on the experimental results, an exciton dynamics mechanism is conceived taking into account the excitation energy and structural dependence in coherent and incoherent exciton diffusion processes, as well as other possible deactivation processes including the formation of the pseudo-charge-transfer and charge separate states, as well as interchain exciton hopping or coherent diffusion.

Energy level engineering in ternary organic solar cells: Evaluating exciton dissociation at organic semiconductor interfaces

NASA Astrophysics Data System (ADS)

Feron, Krishna; Thameel, Mahir N.; Al-Mudhaffer, Mohammed F.; Zhou, Xiaojing; Belcher, Warwick J.; Fell, Christopher J.; Dastoor, Paul C.

2017-03-01

Electronic energy level engineering, with the aim to improve the power conversion efficiency in ternary organic solar cells, is a complex problem since multiple charge transfer steps and exciton dissociation driving forces must be considered. Here, we examine exciton dissociation in the ternary system poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester:2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (P3HT:PCBM:DIBSq). Even though the energy level diagram suggests that exciton dissociation at the P3HT:DIBSq interface should be efficient, electron paramagnetic resonance and external quantum efficiency measurements of planar devices show that this interface is not capable of generating separated charge carriers. Efficient exciton dissociation is still realised via energy transfer, which transports excitons from the P3HT:DIBSq interface to the DIBSq:PCBM interface, where separated charge carriers can be generated efficiently. This work demonstrates that energy level diagrams alone cannot be relied upon to predict the exciton dissociation and charge separation capability of an organic semiconductor interface and that energy transfer relaxes the energy level constraints for optimised multi-component organic solar cells.

High-Efficiency Photovoltaic Devices using Trap-Controlled Quantum-Dot Ink prepared via Phase-Transfer Exchange.

PubMed

Aqoma, Havid; Al Mubarok, Muhibullah; Hadmojo, Wisnu Tantyo; Lee, Eun-Hye; Kim, Tae-Wook; Ahn, Tae Kyu; Oh, Seung-Hwan; Jang, Sung-Yeon

2017-05-01

Colloidal-quantum-dot (CQD) photovoltaic devices are promising candidates for low-cost power sources owing to their low-temperature solution processability and bandgap tunability. A power conversion efficiency (PCE) of >10% is achieved for these devices; however, there are several remaining obstacles to their commercialization, including their high energy loss due to surface trap states and the complexity of the multiple-step CQD-layer-deposition process. Herein, high-efficiency photovoltaic devices prepared with CQD-ink using a phase-transfer-exchange (PTE) method are reported. Using CQD-ink, the fabrication of active layers by single-step coating and the suppression of surface trap states are achieved simultaneously. The CQD-ink photovoltaic devices achieve much higher PCEs (10.15% with a certified PCE of 9.61%) than the control devices (7.85%) owing to improved charge drift and diffusion. Notably, the CQD-ink devices show much lower energy loss than other reported high-efficiency CQD devices. This result reveals that the PTE method is an effective strategy for controlling trap states in CQDs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc04547b Click here for additional data file.

PubMed Central

Vázquez-Mayagoitia, Álvaro; Ratcliff, Laura E.; Tretiak, Sergei; Bair, Raymond A.; Gray, Stephen K.; Van Voorhis, Troy; Larsen, Ross E.; Darling, Seth B.

2017-01-01

Organic photovoltaics (OPVs) are a promising carbon-neutral energy conversion technology, with recent improvements pushing power conversion efficiencies over 10%. A major factor limiting OPV performance is inefficiency of charge transport in organic semiconducting materials (OSCs). Due to strong coupling with lattice degrees of freedom, the charges form polarons, localized quasi-particles comprised of charges dressed with phonons. These polarons can be conceptualized as pseudo-atoms with a greater effective mass than a bare charge. We propose that due to this increased mass, polarons can be modeled with Langevin molecular dynamics (LMD), a classical approach with a computational cost much lower than most quantum mechanical methods. Here we present LMD simulations of charge transfer between a pair of fullerene molecules, which commonly serve as electron acceptors in OSCs. We find transfer rates consistent with experimental measurements of charge mobility, suggesting that this method may provide quantitative predictions of efficiency when used to simulate materials on the device scale. Our approach also offers information that is not captured in the overall transfer rate or mobility: in the simulation data, we observe exactly when and why intermolecular transfer events occur. In addition, we demonstrate that these simulations can shed light on the properties of polarons in OSCs. Much remains to be learned about these quasi-particles, and there are no widely accepted methods for calculating properties such as effective mass and friction. Our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs. PMID:28553494

Architectures for Improved Organic Semiconductor Devices

NASA Astrophysics Data System (ADS)

Beck, Jonathan H.

Advancements in the microelectronics industry have brought increasing performance and decreasing prices to a wide range of users. Conventional silicon-based electronics have followed Moore's law to provide an ever-increasing integrated circuit transistor density, which drives processing power, solid-state memory density, and sensor technologies. As shrinking conventional integrated circuits became more challenging, researchers began exploring electronics with the potential to penetrate new applications with a low price of entry: "Electronics everywhere." The new generation of electronics is thin, light, flexible, and inexpensive. Organic electronics are part of the new generation of thin-film electronics, relying on the synthetic flexibility of carbon molecules to create organic semiconductors, absorbers, and emitters which perform useful tasks. Organic electronics can be fabricated with low energy input on a variety of novel substrates, including inexpensive plastic sheets. The potential ease of synthesis and fabrication of organic-based devices means that organic electronics can be made at very low cost. Successfully demonstrated organic semiconductor devices include photovoltaics, photodetectors, transistors, and light emitting diodes. Several challenges that face organic semiconductor devices are low performance relative to conventional devices, long-term device stability, and development of new organic-compatible processes and materials. While the absorption and emission performance of organic materials in photovoltaics and light emitting diodes is extraordinarily high for thin films, the charge conduction mobilities are generally low. Building highly efficient devices with low-mobility materials is one challenge. Many organic semiconductor films are unstable during fabrication, storage, and operation due to reactions with water, oxygen and hydroxide. A final challenge facing organic electronics is the need for new processes and materials for electrodes, semiconductors and substrates compatible with low-temperature, flexible, and oxygenated and aromatic solvent-free fabrication. Materials and processes must be capable of future high volume production in order to enable low costs. In this thesis we explore several techniques to improve organic semiconductor device performance and enable new fabrication processes. In Chapter 2, I describe the integration of sub-optical-wavelength nanostructured electrodes that improve fill factor and power conversion efficiency in organic photovoltaic devices. Photovoltaic fill factor performance is one of the primary challenges facing organic photovoltaics because most organic semiconductors have poor charge mobility. Our electrical and optical measurements and simulations indicate that nanostructured electrodes improve charge extraction in organic photovoltaics. In Chapter 3, I describe a general method for maximizing the efficiency of organic photovoltaic devices by simultaneously optimizing light absorption and charge carrier collection. We analyze the potential benefits of light trapping strategies for maximizing the overall power conversion efficiency of organic photovoltaic devices. This technique may be used to improve organic photovoltaic materials with low absorption, or short exciton diffusion and carrier-recombination lengths, opening up the device design space. In Chapter 4, I describe a process for high-quality graphene transfer onto chemically sensitive, weakly interacting organic semiconductor thin-films. Graphene is a promising flexible and highly transparent electrode for organic electronics; however, transferring graphene films onto organic semiconductor devices was previously impossible. We demonstrate a new transfer technique based on an elastomeric stamp coated with an fluorinated polymer release layer. We fabricate three classes of organic semiconductor devices: field effect transistors without high temperature annealing, transparent organic light-emitting diodes, and transparent small-molecule organic photovoltaic devices.

Charge transfer from an adsorbed ruthenium-based photosensitizer through an ultra-thin aluminium oxide layer and into a metallic substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gibson, Andrew J.; Temperton, Robert H.; Handrup, Karsten

2014-06-21

The interaction of the dye molecule N3 (cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4′-dicarbo-xylato) -ruthenium(II)) with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied using synchrotron radiation based photoelectron spectroscopy, resonant photoemission spectroscopy, and near edge X-ray absorption fine structure spectroscopy. Calibrated X-ray absorption and valence band spectra of the monolayer and multilayer coverages reveal that charge transfer is possible from the molecule to the AlNi(110) substrate via tunnelling through the ultra-thin oxide layer and into the conduction band edge of the substrate. This charge transfer mechanism is possible from the LUMO+2 and 3 in the excited state but not from the LUMO,more » therefore enabling core-hole clock analysis, which gives an upper limit of 6.0 ± 2.5 fs for the transfer time. This indicates that ultra-thin oxide layers are a viable material for use in dye-sensitized solar cells, which may lead to reduced recombination effects and improved efficiencies of future devices.« less

Phosphorene quantum dot-fullerene nanocomposites for solar energy conversion: An unexplored inorganic-organic nanohybrid with novel photovoltaic properties

NASA Astrophysics Data System (ADS)

Rajbanshi, Biplab; Kar, Moumita; Sarkar, Pallavi; Sarkar, Pranab

2017-10-01

Using the self-consistent charge density-functional based tight-binding (SCC-DFTB) method, coupled with time-dependent density functional theory (TDDFT) calculations, for the first time we explore the possibility of use of phosphorene quantum dots in solar energy harvesting devices. The phosphorene quantum dots-fullerene (PQDs-PCBA) nanocomposites show type-II band alignment indicating spatial separation of charge carriers. The TDDFT calculations also show that the PQD-fullerene nanocomposites seem to be exciting material for future generation solar energy harvester, with extremely fast charge transfer and very poor recombination rate.

Active Pixel Sensors: Are CCD's Dinosaurs?

NASA Technical Reports Server (NTRS)

Fossum, Eric R.

1993-01-01

Charge-coupled devices (CCD's) are presently the technology of choice for most imaging applications. In the 23 years since their invention in 1970, they have evolved to a sophisticated level of performance. However, as with all technologies, we can be certain that they will be supplanted someday. In this paper, the Active Pixel Sensor (APS) technology is explored as a possible successor to the CCD. An active pixel is defined as a detector array technology that has at least one active transistor within the pixel unit cell. The APS eliminates the need for nearly perfect charge transfer -- the Achilles' heel of CCDs. This perfect charge transfer makes CCD's radiation 'soft,' difficult to use under low light conditions, difficult to manufacture in large array sizes, difficult to integrate with on-chip electronics, difficult to use at low temperatures, difficult to use at high frame rates, and difficult to manufacture in non-silicon materials that extend wavelength response.

Optical, electrical, and magnetic field studies of organic materials for light emitting diodes and photovoltaic applications

NASA Astrophysics Data System (ADS)

Basel, Tek Prasad

We studied optical, electrical, and magnetic field responses of films and devices based on organic semiconductors that are used for organic light emitting diodes (OLEDs) and photovoltaic (OPV) solar cell applications. Our studies show that the hyperfine interaction (HFI)-mediated spin mixing is the key process underlying various magnetic field effects (MFE) and spin transport in aluminum tris(8-hydroxyquinoline)[Alq3]-based OLEDs and organic spin-valve (OSV). Conductivity-detected magnetic resonance in OLEDs and magneto-resistance (MR) in OSVs show substantial isotope dependence. In contrast, isotope-insensitive behavior in the magneto-conductance (MC) of same devices is explained by the collision of spin ½ carriers with triplet polaron pairs. We used steady state optical spectroscopy for studying the energy transfer dynamics in films and OLEDs based on host-guest blends of the fluorescent polymer and phosphorescent molecule. We have also studied the magnetic-field controlled color manipulation in these devices, which provide a strong proof for the `polaron-pair' mechanism underlying the MFE in organic devices. The critical issue that hampers organic spintronics device applications is significant magneto-electroluminescence (MEL) at room temperature (RT). Whereas inorganic spin valves (ISVs) show RT magneto-resistance, MR>80%, however, the devices do not exhibit electroluminescence (EL). In contrast, OLEDs show substantive EL emission, and are particularly attractive because of their flexibility, low cost, and potential for multicolor display. We report a conceptual novel hybrid organic/inorganic spintronics device (h-OLED), where we employ both ISV with large MR at RT, and OLED that has efficient EL emission. We investigated the charge transfer process in an OPV solar cell through optical, electrical, and magnetic field measurements of thin films and devices based on a low bandgap polymer, PTB7 (fluorinated poly-thienothiophene-benzodithiophene). We found that one of the major losses that limit the power conversion efficiency of OPV devices is the formation of triplet excitons in the polymer through recombination of charge-transfer (CT) excitons at the interface, and presented a method to suppress the dissociation of CT states by incorporating the spin ½ additive, galvinoxyl in the bulk heterojunction architecture of the active organic blend layer.

A smart mobile pouch as a biomechanical energy harvester towards self-powered smart wireless power transfer applications.

PubMed

Chandrasekhar, Arunkumar; Alluri, Nagamalleswara Rao; Sudhakaran, M S P; Mok, Young Sun; Kim, Sang-Jae

2017-07-20

A Smart Mobile Pouch Triboelectric Nanogenerator (SMP-TENG) is introduced as a promising eco-friendly approach for scavenging biomechanical energy for powering next generation intelligent devices and smart phones. This is a cost-effective and robust method for harvesting energy from human motion, by utilizing worn fabrics as a contact material. The SMP-TENG is capable of harvesting energy in two operational modes: lateral sliding and vertical contact and separation. Moreover, the SMP-TENG can also act as a self-powered emergency flashlight and self-powered pedometer during normal human motion. A wireless power transmission setup integrated with SMP-TENG is demonstrated. This upgrades the traditional energy harvesting device into a self-powered wireless power transfer SMP-TENG. The wirelessly transferred power can be used to charge a Li-ion battery and light LEDs. The SMP-TENG opens a wide range of opportunities in the field of self-powered devices and low maintenance energy harvesting systems for portable and wearable electronic gadgets.

Designing Hybrids of Graphene Oxide and Gold Nanoparticles for Nonlinear Optical Response

NASA Astrophysics Data System (ADS)

Yadav, Rajesh Kumar; Aneesh, J.; Sharma, Rituraj; Abhiramnath, P.; Maji, Tuhin Kumar; Omar, Ganesh Ji; Mishra, A. K.; Karmakar, Debjani; Adarsh, K. V.

2018-04-01

Nonlinear optical absorption of light by materials is weak due to its perturbative nature, although a strong nonlinear response is of crucial importance to applications in optical limiting and switching. Here we demonstrate experimentally and theoretically an extremely efficient scheme of excited-state absorption by charge transfer between donor and acceptor materials as a method to enhance the nonlinear absorption by orders of magnitude. With this idea, we demonstrate a strong excited-state absorption (ESA) in reduced graphene oxide that otherwise shows an increased transparency at high fluence and enhancement of ESA by one order of magnitude in graphene oxide by attaching gold nanoparticles (Au NP) in the tandem configuration that acts as an efficient charge-transfer pair when excited at the plasmonic wavelength. To explain the unprecedented enhancement, we develop a five-level rate-equation model based on the charge transfer between the two materials and numerically simulate the results. To understand the correlation of interfacial charge transfer with the concentration and type of the functional ligands attached to the graphene oxide sheet, we investigate the Au-NP—graphene oxide interface with various possible ligand configurations from first-principles calculations. By using the strong ESA of our hybrid materials, we fabricate liquid cell-based high-performance optical limiters with important device parameters better than that of the benchmark optical limiters.

Ligand-dependent exciton dynamics and photovoltaic properties of PbS quantum dot heterojunction solar cells.

PubMed

Chang, Jin; Ogomi, Yuhei; Ding, Chao; Zhang, Yao Hong; Toyoda, Taro; Hayase, Shuzi; Katayama, Kenji; Shen, Qing

2017-03-01

The surface chemistry of colloidal quantum dots (QDs) plays an important role in determining the photoelectric properties of QD films and the corresponding quantum dot heterojunction solar cells (QDHSCs). To investigate the effects of the ligand structure on the photovoltaic performance and exciton dynamics of QDHSCs, PbS QDHSCs were fabricated by the solid state ligand exchange method with mercaptoalkanoic acid as the cross-linking ligand. Temperature-dependent photoluminescence and ultrafast transient absorption spectra show that the electronic coupling and charge transfer rate within QD ensembles were monotonically enhanced as the ligand length decreased. However, in practical QDHSCs, the second shortest ligand 3-mercaptopropionic acid (MPA) showed higher power conversion efficiency than the shortest ligand thioglycolic acid (TGA). This could be attributed to the difference in their surface trap states, supported by thermally stimulated current measurements. Moreover, compared with the non-conjugated ligand MPA, the conjugated ligand 4-mercaptobenzoic acid (MBA) introduces less trap states and has a similar charge transfer rate in QD ensembles, but has poor photovoltaic properties. This unexpected result could be contributed by the QD-ligand orbital mixing, leading to the charge transfer from QDs to ligands instead of charge transfer between adjacent QDs. This work highlights the significant effects of ligand structures on the photovoltaic properties and exciton dynamics of QDHSCs, which would shed light on the further development of QD-based photoelectric devices.

Method for eliminating artifacts in CCD imagers

DOEpatents

Turko, Bojan T.; Yates, George J.

1992-01-01

An electronic method for eliminating artifacts in a video camera (10) employing a charge coupled device (CCD) (12) as an image sensor. The method comprises the step of initializing the camera (10) prior to normal read out and includes a first dump cycle period (76) for transferring radiation generated charge into the horizontal register (28) while the decaying image on the phosphor (39) being imaged is being integrated in the photosites, and a second dump cycle period (78), occurring after the phosphor (39) image has decayed, for rapidly dumping unwanted smear charge which has been generated in the vertical registers (32). Image charge is then transferred from the photosites (36) and (38) to the vertical registers (32) and read out in conventional fashion. The inventive method allows the video camera (10) to be used in environments having high ionizing radiation content, and to capture images of events of very short duration and occurring either within or outside the normal visual wavelength spectrum. Resultant images are free from ghost, smear and smear phenomena caused by insufficient opacity of the registers (28) and (32), and are also free from random damage caused by ionization charges which exceed the charge limit capacity of the photosites (36) and (37).

Quantum State Transmission in a Superconducting Charge Qubit-Atom Hybrid

PubMed Central

Yu, Deshui; Valado, María Martínez; Hufnagel, Christoph; Kwek, Leong Chuan; Amico, Luigi; Dumke, Rainer

2016-01-01

Hybrids consisting of macroscopic superconducting circuits and microscopic components, such as atoms and spins, have the potential of transmitting an arbitrary state between different quantum species, leading to the prospective of high-speed operation and long-time storage of quantum information. Here we propose a novel hybrid structure, where a neutral-atom qubit directly interfaces with a superconducting charge qubit, to implement the qubit-state transmission. The highly-excited Rydberg atom located inside the gate capacitor strongly affects the behavior of Cooper pairs in the box while the atom in the ground state hardly interferes with the superconducting device. In addition, the DC Stark shift of the atomic states significantly depends on the charge-qubit states. By means of the standard spectroscopic techniques and sweeping the gate voltage bias, we show how to transfer an arbitrary quantum state from the superconducting device to the atom and vice versa. PMID:27922087

Highly Efficient Simplified Single-Emitting-Layer Hybrid WOLEDs with Low Roll-off and Good Color Stability through Enhanced Förster Energy Transfer.

PubMed

Zhang, Dongdong; Cai, Minghan; Zhang, Yunge; Zhang, Deqiang; Duan, Lian

2015-12-30

Single-emitting layer hybrid white organic light-emitting diodes (SEL-hybrid-WOLEDs) usually suffer from low efficiency, significant roll-off, and poor color stability, attributed to the incomplete energy transfer from the triplet states of the blue fluorophores to the phosphors. Here, we demonstrate highly efficient SEL-hybrid-WOLEDs with low roll-off and good color-stability utilizing blue thermally activated delayed fluorescence (TADF) materials as the host emitters. The triplet states of the blue TADF host emitter can be up-converted into its singlet states, and then the energy is transferred to the complementary phosphors through the long-range Förster energy transfer, enhancing the energy transfer from the host to the dopant. Simplified SEL-hybrid-WOLEDs achieve the highest forward-viewing external quantum efficiency (EQE) of 20.8% and power efficiency of 51.2 lm/W with CIE coordinates of (0.398, 0.456) at a luminance of 500 cd/m(2). The device EQE only slightly drops to 19.6% at a practical luminance of 1000 cd/m(2) with a power efficiency of 38.7 lm/W. Furthermore, the spectra of the device are rather stable with the raising voltage. The reason can be assigned to the enhanced Förster energy transfer, wide charge recombination zone, as well as the bipolar charge transporting ability of the host emitter. We believe that our work may shed light on the future development of highly efficient SEL-hybrid-WOLEDs with simultaneous low roll-off and good color stability.

Design of a CCD Camera for Space Surveillance

DTIC Science & Technology

2016-03-05

Laboratory fabricated CCID-51M, a 2048x1024 pixel Charge Couple Device (CCD) imager. [1] The mission objective is to observe and detect satellites in...phased to transfer the charge to the outputs. An electronic shutter is created by having an equal area of pixels covered by an opaque metal mask. The...Figure 4 CDS Timing Diagram By design the CCD readout rate is 400 KHz. This rate was chosen so reading the 2E6 pixels from one output is less than

Probing charge transfer during metal-insulator transitions in graphene-LaAlO3/SrTiO3 systems

NASA Astrophysics Data System (ADS)

Aliaj, I.; Sambri, A.; Miseikis, V.; Stornaiuolo, D.; di Gennaro, E.; Coletti, C.; Pellegrini, V.; Miletto Granozio, F.; Roddaro, S.

2018-06-01

Two-dimensional electron systems (2DESs) at the interface between LaAlO3 (LAO) and SrTiO3 (STO) perovskite oxides display a wide class of tunable phenomena ranging from superconductivity to metal-insulator transitions. Most of these effects are strongly sensitive to surface physics and often involve charge transfer mechanisms, which are, however, hard to detect. In this work, we realize hybrid field-effect devices where graphene is used to modulate the transport properties of the LAO/STO 2DES. Different from a conventional gate, graphene is semimetallic and allows us to probe charge transfer with the oxide structure underneath the field-effect electrode. In LAO/STO samples with a low initial carrier density, graphene-covered regions turn insulating when the temperature is lowered to 3 K, but conduction can be restored in the oxide structure by increasing the temperature or by field effect. The evolution of graphene's electron density is found to be inconsistent with a depletion of LAO/STO, but it rather points to a localization of interfacial carriers in the oxide structure.

Energy Transfer Kinetics in Photosynthesis as an Inspiration for Improving Organic Solar Cells.

PubMed

Nganou, Collins; Lackner, Gerhard; Teschome, Bezu; Deen, M Jamal; Adir, Noam; Pouhe, David; Lupascu, Doru C; Mkandawire, Martin

2017-06-07

Clues to designing highly efficient organic solar cells may lie in understanding the architecture of light-harvesting systems and exciton energy transfer (EET) processes in very efficient photosynthetic organisms. Here, we compare the kinetics of excitation energy tunnelling from the intact phycobilisome (PBS) light-harvesting antenna system to the reaction center in photosystem II in intact cells of the cyanobacterium Acaryochloris marina with the charge transfer after conversion of photons into photocurrent in vertically aligned carbon nanotube (va-CNT) organic solar cells with poly(3-hexyl)thiophene (P3HT) as the pigment. We find that the kinetics in electron hole creation following excitation at 600 nm in both PBS and va-CNT solar cells to be 450 and 500 fs, respectively. The EET process has a 3 and 14 ps pathway in the PBS, while in va-CNT solar cell devices, the charge trapping in the CNT takes 11 and 258 ps. We show that the main hindrance to efficiency of va-CNT organic solar cells is the slow migration of the charges after exciton formation.

Electrostatic Assist of Liquid Transfer in Printing Processes

NASA Astrophysics Data System (ADS)

Huang, Chung-Hsuan; Kumar, Satish

2016-11-01

Transfer of liquid from one surface to another plays an important role in many printing processes. Incomplete liquid transfer can produce defects that are detrimental to the operation of printed electronic devices, and one strategy for minimizing these defects is to apply an electric field, a technique known as electrostatic assist (ESA). However, the underlying physical mechanisms of ESA remain a mystery. To better understand these mechanisms, slender-jet models for both perfect dielectric and leaky dielectric Newtonian liquid bridges with moving contact lines are developed. Nonlinear partial differential equations describing the time- and axial-evolution of the bridge radius and interfacial charge are derived, and then solved using finite-element methods. For perfect dielectrics, it is found that application of an electric field enhances transfer of liquid to the more wettable surface. For leaky dielectrics, application of an electric field can augment or oppose the influence of wettability differences, depending on the direction of the electric field and the sign of the interfacial charge. The physical mechanisms underlying these observations will be discussed.

Magnetoresistance of vertical Co-graphene-NiFe junctions controlled by charge transfer and proximity-induced spin splitting in graphene

NASA Astrophysics Data System (ADS)

Asshoff, P. U.; Sambricio, J. L.; Rooney, A. P.; Slizovskiy, S.; Mishchenko, A.; Rakowski, A. M.; Hill, E. W.; Geim, A. K.; Haigh, S. J.; Fal'ko, V. I.; Vera-Marun, I. J.; Grigorieva, I. V.

2017-09-01

Graphene is hailed as an ideal material for spintronics due to weak intrinsic spin-orbit interaction that facilitates lateral spin transport and tunability of its electronic properties, including a possibility to induce magnetism in graphene. Another promising application of graphene is related to its use as a spacer separating ferromagnetic metals (FMs) in vertical magnetoresistive devices, the most prominent class of spintronic devices widely used as magnetic sensors. In particular, few-layer graphene was predicted to act as a perfect spin filter. Here we show that the role of graphene in such devices (at least in the absence of epitaxial alignment between graphene and the FMs) is different and determined by proximity-induced spin splitting and charge transfer with adjacent ferromagnetic metals, making graphene a weak FM electrode rather than a spin filter. To this end, we report observations of magnetoresistance (MR) in vertical Co-graphene-NiFe junctions with 1-4 graphene layers separating the ferromagnets, and demonstrate that the dependence of the MR sign on the number of layers and its inversion at relatively small bias voltages is consistent with spin transport between weakly doped and differently spin-polarized layers of graphene. The proposed interpretation is supported by the observation of an MR sign reversal in biased Co-graphene-hBN-NiFe devices and by comprehensive structural characterization. Our results suggest a new architecture for vertical devices with electrically controlled MR.

Sensing of molecules using quantum dynamics

DOE PAGES

Migliore, Agostino; Naaman, Ron; Beratan, David N.

2015-04-24

In this study, we design sensors where information is transferred between the sensing event and the actuator via quantum relaxation processes, through distances of a few nanometers. We thus explore the possibility of sensing using intrinsically quantum mechanical phenomena that are also at play in photobiology, bioenergetics, and information processing. Specifically, we analyze schemes for sensing based on charge transfer and polarization (electronic relaxation) processes. These devices can have surprising properties. Their sensitivity can increase with increasing separation between the sites of sensing (the receptor) and the actuator (often a solid-state substrate). This counterintuitive response and other quantum features givemore » these devices favorable characteristics, such as enhanced sensitivity and selectivity. Finally, using coherent phenomena at the core of molecular sensing presents technical challenges but also suggests appealing schemes for molecular sensing and information transfer in supramolecular structures.« less

Polarization Enhanced Charge Transfer: Dual-Band GaN-Based Plasmonic Photodetector.

PubMed

Jia, Ran; Zhao, Dongfang; Gao, Naikun; Liu, Duo

2017-01-13

Here, we report a dual-band plasmonic photodetector based on Ga-polar gallium nitride (GaN) for highly sensitive detection of UV and green light. We discover that decoration of Au nanoparticles (NPs) drastically increases the photoelectric responsivities by more than 50 times in comparition to the blank GaN photodetector. The observed behaviors are attributed to polarization enhanced charge transfer of optically excited hot electrons from Au NPs to GaN driven by the strong spontaneous polarization field of Ga-polar GaN. Moreover, defect ionization promoted by localized surface plasmon resonances (LSPRs) is also discussed. This novel type of photodetector may shed light on the design and fabrication of photoelectric devices based on polar semiconductors and microstructural defects.

ALD-Developed Plasmonic Two-Dimensional Au-WO3-TiO2 Heterojunction Architectonics for Design of Photovoltaic Devices.

PubMed

Karbalaei Akbari, Mohammad; Hai, Zhenyin; Wei, Zihan; Detavernier, Christophe; Solano, Eduardo; Verpoort, Francis; Zhuiykov, Serge

2018-03-28

Electrically responsive plasmonic devices, which benefit from the privilege of surface plasmon excited hot carries, have supported fascinating applications in the visible-light-assisted technologies. The properties of plasmonic devices can be tuned by controlling charge transfer. It can be attained by intentional architecturing of the metal-semiconductor (MS) interfaces. In this study, the wafer-scaled fabrication of two-dimensional (2D) TiO 2 semiconductors on the granular Au metal substrate is achieved using the atomic layer deposition (ALD) technique. The ALD-developed 2D MS heterojunctions exhibited substantial enhancement of the photoresponsivity and demonstrated the improvement of response time for 2D Au-TiO 2 -based plasmonic devices under visible light illumination. To circumvent the undesired dark current in the plasmonic devices, a 2D WO 3 nanofilm (∼0.7 nm) was employed as the intermediate layer on the MS interface to develop the metal-insulator-semiconductor (MIS) 2D heterostructure. As a result, 13.4% improvement of the external quantum efficiency was obtained for fabricated 2D Au-WO 3 -TiO 2 heterojunctions. The impedancometry measurements confirmed the modulation of charge transfer at the 2D MS interface using MIS architectonics. Broadband photoresponsivity from the UV to the visible light region was observed for Au-TiO 2 and Au-WO 3 -TiO 2 heterostructures, whereas near-infrared responsivity was not observed. Consequently, considering the versatile nature of the ALD technique, this approach can facilitate the architecturing and design of novel 2D MS and MIS heterojunctions for efficient plasmonic devices.

Tuning the Direction of Intramolecular Charge Transfer and the Nature of the Fluorescent State in a T-Shaped Molecular Dyad.

PubMed

Felouat, Abdellah; D'Aléo, Anthony; Charaf-Eddin, Azzam; Jacquemin, Denis; Le Guennic, Boris; Kim, Eunsun; Lee, Kwang Jin; Woo, Jae Heun; Ribierre, Jean-Charles; Wu, Jeong Weon; Fages, Frédéric

2015-06-18

Controlling photoinduced intramolecular charge transfer at the molecular scale is key to the development of molecular devices for nanooptoelectronics. Here, we describe the design, synthesis, electronic characterization, and photophysical properties of two electron donor-acceptor molecular systems that consist of tolane and BF2-containing curcuminoid chromophoric subunits connected in a T-shaped arrangement. The two π-conjugated segments intersect at the electron acceptor dioxaborine core. From steady-state electronic absorption and fluorescence emission, we find that the photophysics of the dialkylamino-substituted analogue is governed by the occurrence of two closely lying excited states. From DFT calculations, we show that excitation in either of these two states results in a distinct shift of the electron density, whether it occurs along the curcuminoid or tolane moiety. Femtosecond transient absorption spectroscopy confirmed these findings. As a consequence, the nature of the emitting state and the photophysical properties are strongly dependent on solvent polarity. Moreover, these characteristics can also be switched by protonation or complexation at the nitrogen atom of the amino group. These features set new approaches toward the construction of a three-terminal molecular system in which the lateral branch would transduce a change of electronic state and ultimately control charge transport in a molecular-scale device.

Micro-cooler enhancements by barrier interface analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stephen, A.; Dunn, G. M.; Glover, J.

A novel gallium arsenide (GaAs) based micro-cooler design, previously analysed both experimentally and by an analytical Heat Transfer (HT) model, has been simulated using a self-consistent Ensemble Monte Carlo (EMC) model for a more in depth analysis of the thermionic cooling in the device. The best fit to the experimental data was found and was used in conjunction with the HT model to estimate the cooler-contact resistance. The cooling results from EMC indicated that the cooling power of the device is highly dependent on the charge distribution across the leading interface. Alteration of this charge distribution via interface extensions onmore » the nanometre scale has shown to produce significant changes in cooler performance.« less

Functionalized graphene and other two-dimensional materials for photovoltaic devices: device design and processing.

PubMed

Liu, Zhike; Lau, Shu Ping; Yan, Feng

2015-08-07

Graphene is the thinnest two-dimensional (2D) carbon material and has many advantages including high carrier mobilities and conductivity, high optical transparency, excellent mechanical flexibility and chemical stability, which make graphene an ideal material for various optoelectronic devices. The major applications of graphene in photovoltaic devices are for transparent electrodes and charge transport layers. Several other 2D materials have also shown advantages in charge transport and light absorption over traditional semiconductor materials used in photovoltaic devices. Great achievements in the applications of 2D materials in photovoltaic devices have been reported, yet numerous challenges still remain. For practical applications, the device performance should be further improved by optimizing the 2D material synthesis, film transfer, surface functionalization and chemical/physical doping processes. In this review, we will focus on the recent advances in the applications of graphene and other 2D materials in various photovoltaic devices, including organic solar cells, Schottky junction solar cells, dye-sensitized solar cells, quantum dot-sensitized solar cells, other inorganic solar cells, and perovskite solar cells, in terms of the functionalization techniques of the materials, the device design and the device performance. Finally, conclusions and an outlook for the future development of this field will be addressed.

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

PubMed Central

Deng, Dan; Zhang, Yajie; Zhang, Jianqi; Wang, Zaiyu; Zhu, Lingyun; Fang, Jin; Xia, Benzheng; Wang, Zhen; Lu, Kun; Ma, Wei; Wei, Zhixiang

2016-01-01

Solution-processable small molecules for organic solar cells have attracted intense attention for their advantages of definite molecular structures compared with their polymer counterparts. However, the device efficiencies based on small molecules are still lower than those of polymers, especially for inverted devices, the highest efficiency of which is <9%. Here we report three novel solution-processable small molecules, which contain π-bridges with gradient-decreased electron density and end acceptors substituted with various fluorine atoms (0F, 1F and 2F, respectively). Fluorination leads to an optimal active layer morphology, including an enhanced domain purity, the formation of hierarchical domain size and a directional vertical phase gradation. The optimal morphology balances charge separation and transfer, and facilitates charge collection. As a consequence, fluorinated molecules exhibit excellent inverted device performance, and an average power conversion efficiency of 11.08% is achieved for a two-fluorine atom substituted molecule. PMID:27991486

Performance of Liquid Phase Exfoliated Graphene As Electrochemical Double Layer Capacitors Electrodes

NASA Astrophysics Data System (ADS)

Huffstutler, Jacob; Wasala, Milinda; Richie, Julianna; Winchester, Andrew; Ghosh, Sujoy; Kar, Swastik; Talapatra, Saikat

2014-03-01

We will present the results of our investigations of electrochemical double layer capacitors (EDLCs) or supercapacitors (SC) fabricated using liquid-phase exfoliated graphene. Several electrolytes, such as aqueous potassium hydroxide KOH (6M), ionic 1-Butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], and ionic 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate[BMP][FAP] were used. These EDLC's show good performance compared to other carbon nanomaterials based EDLC's devices. We found that the liquid phase exfoliated graphene based devices possess specific capacitance values as high as 262 F/g, when used with ionic liquid electrolyte[BMP][FAP], with power densities (~ 454 W/kg) and energy densities (~ 0.38Wh/kg). Further, these devices indicated rapid charge transfer response even without the use of any binders or specially prepared current collectors. A detailed electrochemical impedance spectroscopy analysis in order to understand the phenomenon of charge storage in these materials will be presented.

Charge Generation and Recombination in Organic Materials for Photovoltaics

NASA Astrophysics Data System (ADS)

Ramirez, Jessica Jacklyn

Understanding the nature of molecular exciton states is critical for the design of organic photovoltaic materials that push current device efficiencies into the next realm. This thesis describes several research projects that have sought to further our understanding of the generation and recombination of charge carriers, facilitated by such excitonic states, in organic systems. We begin with fundamental studies on the excited-state dynamics of several fullerene derivatives. We also venture away from the traditional fullerene-based electron acceptors and consider several derivatized perylene diimides as alternate electron acceptors. We then report on the observation of a broad, structureless, emission emanating from charge-generating films comprised of perfluoroalkyl fullerene derivatives dilutely dispersed in polyfluorene hosts. We have determined that this red-shifted PL signature is the result of radiative recombination from a charge-transfer state that is populated initially as a precursor to charge generation, and may be repopulated upon charge recombination. Our data offers an observable link between charge-generation and charge-transfer emission that is kinetically associated with carrier recombination, and we utilize this link to probe the influence of driving force and polymer microstructure in the fundamental processes of charge generation and decay in small molecule/polymer heterojunctions. Thereafter, we sought to develop our understanding of a novel photophysical mechanism (known as energy pooling) which would allow for the energy of multiple excitons to be 'pooled' towards a central molecular moiety, where the individual exciton energies may add together to create a single highly excited excitonic state. This upconversion-like process would facilitate more efficient photocurrent generation in devices utilizing this mode of charge separation. The primary modes of inquiry utilized in this work come from the spectroscopic techniques of absorbance, steady-state and time-resolved photoluminescence, transient absorption and time-resolved microwave conductivity. Some secondary methods employed include cyclic voltammetry, X-ray diffraction and computational tools from density functional theory. This utilization of both experimental and theoretical methodologies provides a powerful approach to furthering our understanding of both the fundamental photophysics of the systems studied, as well as the charge generation and recombination pathways occurring at organic donor-acceptor interfaces, helping to guide the design of more efficient organic photovoltaics.

Charge carrier dynamics investigation of CuInS2 quantum dots films using injected charge extraction by linearly increasing voltage (i-CELIV): the role of ZnS Shell

NASA Astrophysics Data System (ADS)

Bi, Ke; Sui, Ning; Zhang, Liquan; Wang, Yinghui; Liu, Qinghui; Tan, Mingrui; Zhou, Qiang; Zhang, Hanzhuang

2016-12-01

The role of ZnS shell on the photo-physical properties within CuInS2/ZnS quantum dots (QDs) is carefully studied in optoelectronic devices. Linearly increasing voltage technique has been employed to investigate the charge carrier dynamics of both CuInS2 and CuInS2/ZnS QDs films. This study shows that charge carriers follow a similar behavior of monomolecular recombination in this film, with their charge transfer rate correlates to the increase of applied voltage. It turns out that the ZnS shell could affect the carrier diffusion process through depressing the trapping states and would build up a potential barrier.

Single-step electron transfer on the nanometer scale: ultra-fast charge shift in strongly coupled zinc porphyrin-gold porphyrin dyads.

PubMed

Fortage, Jérôme; Boixel, Julien; Blart, Errol; Hammarström, Leif; Becker, Hans Christian; Odobel, Fabrice

2008-01-01

The synthesis, electrochemical properties, and photoinduced electron transfer processes of a series of three novel zinc(II)-gold(III) bisporphyrin dyads (ZnP--S--AuP(+)) are described. The systems studied consist of two trisaryl porphyrins connected directly in the meso position via an alkyne unit to tert-(phenylenethynylene) or penta(phenylenethynylene) spacers. In these dyads, the estimated center to center interporphyrin separation distance varies from 32 to 45 A. The absorption, emission, and electrochemical data indicate that there are strong electronic interactions between the linked elements, thanks to the direct attachment of the spacer on the porphyrin ring through the alkyne unit. At room temperature in toluene, light excitation of the zinc porphyrin results in almost quantitative formation of the charge shifted state (.+)ZnP--S--AuP(.), whose lifetime is in the order of hundreds of picoseconds. In this solvent, the charge-separated state decays to the ground state through the intermediate population of the zinc porphyrin triplet excited state. Excitation of the gold porphyrin leads instead to rapid energy transfer to the triplet ZnP. In dichloromethane the charge shift reactions are even faster, with time constants down to 2 ps, and may be induced also by excitation of the gold porphyrin. In this latter solvent, the longest charge-shifted lifetime (tau=2.3 ns) was obtained with the penta-(phenylenethynylene) spacer. The charge shift reactions are discussed in terms of bridge-mediated super-exchange mechanisms as electron or hole transfer. These new bis-porphyrin arrays, with strong electronic coupling, represent interesting molecular systems in which extremely fast and efficient long-range photoinduced charge shift occurs over a long distance. The rate constants are two to three orders of magnitude larger than for corresponding ZnP--AuP(+) dyads linked via meso-phenyl groups to oligo-phenyleneethynylene spacers. This study demonstrates the critical impact of the attachment position of the spacer on the porphyrin on the electron transfer rate, and this strategy can represent a useful approach to develop molecular photonic devices for long-range charge separations.

Heterojunction PbS nanocrystal solar cells with oxide charge-transport layers.

PubMed

Hyun, Byung-Ryool; Choi, Joshua J; Seyler, Kyle L; Hanrath, Tobias; Wise, Frank W

2013-12-23

Oxides are commonly employed as electron-transport layers in optoelectronic devices based on semiconductor nanocrystals, but are relatively rare as hole-transport layers. We report studies of NiO hole-transport layers in PbS nanocrystal photovoltaic structures. Transient fluorescence experiments are used to verify the relevant energy levels for hole transfer. On the basis of these results, planar heterojunction devices with ZnO as the photoanode and NiO as the photocathode were fabricated and characterized. Solution-processed devices were used to systematically study the dependence on nanocrystal size and achieve conversion efficiency as high as 2.5%. Optical modeling indicates that optimum performance should be obtained with thinner oxide layers than can be produced reliably by solution casting. Room-temperature sputtering allows deposition of oxide layers as thin as 10 nm, which enables optimization of device performance with respect to the thickness of the charge-transport layers. The best devices achieve an open-circuit voltage of 0.72 V and efficiency of 5.3% while eliminating most organic material from the structure and being compatible with tandem structures.

Electric power processing, distribution, management and energy storage

NASA Astrophysics Data System (ADS)

Giudici, R. J.

1980-07-01

Power distribution subsystems are required for three elements of the SPS program: (1) orbiting satellite, (2) ground rectenna, and (3) Electric Orbiting Transfer Vehicle (EOTV). Power distribution subsystems receive electrical power from the energy conversion subsystem and provide the power busses rotary power transfer devices, switchgear, power processing, energy storage, and power management required to deliver control, high voltage plasma interactions, electric thruster interactions, and spacecraft charging of the SPS and the EOTV are also included as part of the power distribution subsystem design.

Electric power processing, distribution, management and energy storage

NASA Technical Reports Server (NTRS)

Giudici, R. J.

1980-01-01

Power distribution subsystems are required for three elements of the SPS program: (1) orbiting satellite, (2) ground rectenna, and (3) Electric Orbiting Transfer Vehicle (EOTV). Power distribution subsystems receive electrical power from the energy conversion subsystem and provide the power busses rotary power transfer devices, switchgear, power processing, energy storage, and power management required to deliver control, high voltage plasma interactions, electric thruster interactions, and spacecraft charging of the SPS and the EOTV are also included as part of the power distribution subsystem design.

Environmental Effects on Hysteresis of Transfer Characteristics in Molybdenum Disulfide Field-Effect Transistors

NASA Astrophysics Data System (ADS)

Shimazu, Yoshihiro; Tashiro, Mitsuki; Sonobe, Satoshi; Takahashi, Masaki

2016-07-01

Molybdenum disulfide (MoS2) has recently received much attention for nanoscale electronic and photonic applications. To explore the intrinsic properties and enhance the performance of MoS2-based field-effect transistors, thorough understanding of extrinsic effects such as environmental gas and contact resistance of the electrodes is required. Here, we report the effects of environmental gases on the transport properties of back-gated multilayered MoS2 field-effect transistors. Comparisons between different gases (oxygen, nitrogen, and air and nitrogen with varying relative humidities) revealed that water molecules acting as charge-trapping centers are the main cause of hysteresis in the transfer characteristics. While the hysteresis persisted even after pumping out the environmental gas for longer than 10 h at room temperature, it disappeared when the device was cooled to 240 K, suggesting a considerable increase in the time constant of the charge trapping/detrapping at these modestly low temperatures. The suppression of the hysteresis or instability in the easily attainable temperature range without surface passivation is highly advantageous for the device application of this system. The humidity dependence of the threshold voltages in the transfer curves indicates that the water molecules dominantly act as hole-trapping centers. A strong dependence of the on-state current on oxygen pressure was also observed.

Experimental verification of orbital engineering at the atomic scale: Charge transfer and symmetry breaking in nickelate heterostructures

NASA Astrophysics Data System (ADS)

Phillips, Patrick J.; Rui, Xue; Georgescu, Alexandru B.; Disa, Ankit S.; Longo, Paolo; Okunishi, Eiji; Walker, Fred; Ahn, Charles H.; Ismail-Beigi, Sohrab; Klie, Robert F.

2017-05-01

Epitaxial strain, layer confinement, and inversion symmetry breaking have emerged as powerful new approaches to control the electronic and atomic-scale structural properties of complex metal oxides. Trivalent rare-earth (RE) nickelate R E NiO3 heterostructures have been shown to be exemplars since the orbital occupancy, degeneracy, and, consequently, electronic/magnetic properties can be altered as a function of epitaxial strain, layer thickness, and superlattice structure. One recent example is the tricomponent LaTiO3-LaNiO3-LaAlO3 superlattice which exhibits charge transfer and orbital polarization as the result of its interfacial dipole electric field. A crucial step towards control of these parameters for future electronic and magnetic device applications is to develop an understanding of both the magnitude and range of the octahedral network's response towards interfacial strain and electric fields. An approach that provides atomic-scale resolution and sensitivity towards the local octahedral distortions and orbital occupancy is therefore required. Here, we employ atomic-resolution imaging coupled with electron spectroscopies and first-principles theory to examine the role of interfacial charge transfer and symmetry breaking in a tricomponent nickelate superlattice system. We find that nearly complete charge transfer occurs between the LaTiO3 and LaNiO3 layers, resulting in a mixed Ni2 +/Ni3 + valence state. We further demonstrate that this charge transfer is highly localized with a range of about 1 unit cell within the LaNiO3 layers. We also show how Wannier-function-based electron counting provides a simple physical picture of the electron distribution that connects directly with formal valence charges. The results presented here provide important feedback to synthesis efforts aimed at stabilizing new electronic phases that are not accessible by conventional bulk or epitaxial film approaches.

Graphene-on-semiconductor substrates for analog electronics

DOEpatents

Lagally, Max G.; Cavallo, Francesca; Rojas-Delgado, Richard

2016-04-26

Electrically conductive material structures, analog electronic devices incorporating the structures and methods for making the structures are provided. The structures include a layer of graphene on a semiconductor substrate. The graphene layer and the substrate are separated by an interfacial region that promotes transfer of charge carriers from the surface of the substrate to the graphene.

Conductive polymer/fullerene blend thin films with honeycomb framework for transparent photovoltaic application

DOEpatents

Cotlet, Mircea; Wang, Hsing-Lin; Tsai, Hsinhan; Xu, Zhihua

2015-04-21

Optoelectronic devices and thin-film semiconductor compositions and methods for making same are disclosed. The methods provide for the synthesis of the disclosed composition. The thin-film semiconductor compositions disclosed herein have a unique configuration that exhibits efficient photo-induced charge transfer and high transparency to visible light.

Hybrid electric vehicle power management system

DOEpatents

Bissontz, Jay E.

2015-08-25

Level voltage levels/states of charge are maintained among a plurality of high voltage DC electrical storage devices/traction battery packs that are arrayed in series to support operation of a hybrid electric vehicle drive train. Each high voltage DC electrical storage device supports a high voltage power bus, to which at least one controllable load is connected, and at least a first lower voltage level electrical distribution system. The rate of power transfer from the high voltage DC electrical storage devices to the at least first lower voltage electrical distribution system is controlled by DC-DC converters.

Interface designed MoS2/GaAs heterostructure solar cell with sandwich stacked hexagonal boron nitride

PubMed Central

Lin, Shisheng; Li, Xiaoqiang; Wang, Peng; Xu, Zhijuan; Zhang, Shengjiao; Zhong, Huikai; Wu, Zhiqian; Xu, Wenli; Chen, Hongsheng

2015-01-01

MoS2 is a layered two-dimensional semiconductor with a direct band gap of 1.8 eV. The MoS2/bulk semiconductor system offers a new platform for solar cell device design. Different from the conventional bulk p-n junctions, in the MoS2/bulk semiconductor heterostructure, static charge transfer shifts the Fermi level of MoS2 toward that of bulk semiconductor, lowering the barrier height of the formed junction. Herein, we introduce hexagonal boron nitride (h-BN) into MoS2/GaAs heterostructure to suppress the static charge transfer, and the obtained MoS2/h-BN/GaAs solar cell exhibits an improved power conversion efficiency of 5.42%. More importantly, the sandwiched h-BN makes the Fermi level tuning of MoS2 more effective. By employing chemical doping and electrical gating into the solar cell device, PCE of 9.03% is achieved, which is the highest among all the reported monolayer transition metal dichalcogenide based solar cells. PMID:26458358

Energy Level Alignment of N-Doping Fullerenes and Fullerene Derivatives Using Air-Stable Dopant.

PubMed

Bao, Qinye; Liu, Xianjie; Braun, Slawomir; Li, Yanqing; Tang, Jianxin; Duan, Chungang; Fahlman, Mats

2017-10-11

Doping has been proved to be one of the powerful technologies to achieve significant improvement in the performance of organic electronic devices. Herein, we systematically map out the interface properties of solution-processed air-stable n-type (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl) doping fullerenes and fullerene derivatives and establish a universal energy level alignment scheme for this class of n-doped system. At low doping levels at which the charge-transfer doping induces mainly bound charges, the energy level alignment of the n-doping organic semiconductor can be described by combining integer charger transfer-induced shifts with a so-called double-dipole step. At high doping levels, significant densities of free charges are generated and the charge flows between the organic film and the conducting electrodes equilibrating the Fermi level in a classic "depletion layer" scheme. Moreover, we demonstrate that the model holds for both n- and p-doping of π-backbone molecules and polymers. With the results, we provide wide guidance for identifying the application of the current organic n-type doping technology in organic electronics.

Improper ferroelectric polarization in a perovskite driven by intersite charge transfer and ordering

NASA Astrophysics Data System (ADS)

Chen, Wei-Tin; Wang, Chin-Wei; Wu, Hung-Cheng; Chou, Fang-Cheng; Yang, Hung-Duen; Simonov, Arkadiy; Senn, M. S.

2018-04-01

It is of great interest to design and make materials in which ferroelectric polarization is coupled to other order parameters such as lattice, magnetic, and electronic instabilities. Such materials will be invaluable in next-generation data storage devices. Recently, remarkable progress has been made in understanding improper ferroelectric coupling mechanisms that arise from lattice and magnetic instabilities. However, although theoretically predicted, a compact lattice coupling between electronic and ferroelectric (polar) instabilities has yet to be realized. Here we report detailed crystallographic studies of a perovskite HgAMn3A'Mn4BO12 that is found to exhibit a polar ground state on account of such couplings that arise from charge and orbital ordering on both the A'- and B-sites, which are themselves driven by a highly unusual MnA '-MnB intersite charge transfer. The inherent coupling of polar, charge, orbital, and hence magnetic degrees of freedom make this a system of great fundamental interest, and demonstrating ferroelectric switching in this and a host of recently reported hybrid improper ferroelectrics remains a substantial challenge.

Light emission mechanism of mixed host organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Song, Wook; Lee, Jun Yeob

2015-03-01

Light emission mechanism of organic light-emitting diodes with a mixed host emitting layer was studied using an exciplex type mixed host and an exciplex free mixed host. Monitoring of the current density and luminance of the two type mixed host devices revealed that the light emission process of the exciplex type mixed host was dominated by energy transfer, while the light emission of the exciplex free mixed host was controlled by charge trapping. Mixed host composition was also critical to the light emission mechanism, and the contribution of the energy transfer process was maximized at 50:50 mixed host composition. Therefore, it was possible to manage the light emission process of the mixed host devices by managing the mixed host composition.

Distinct Optoelectronic Signatures for Charge Transfer and Energy Transfer in Quantum Dot-MoS 2 Hybrid Photodetectors Revealed by Photocurrent Imaging Microscopy

DOE PAGES

Li, Mingxing; Chen, Jia-Shiang; Routh, Prahlad K.; ...

2018-05-17

Atomically thin transition metal dichalcogenides (TMDCs) have intriguing nanoscale properties like high charge mobility, photosensitivity, layer-thickness-dependent bandgap, and mechanical flexibility, which are all appealing for the development of next generation optoelectronic, catalytic, and sensory devices. Their atomically thin thickness, however, renders TMDCs poor absorptivity. For this study, bilayer MoS 2 is combined with core-only CdSe QDs and core/shell CdSe/ZnS QDs to obtain hybrids with increased light harvesting and exhibiting interfacial charge transfer (CT) and nonradiative energy transfer (NET), respectively. Field-effect transistors based on these hybrids and their responses to varying laser power and applied gate voltage are investigated with scanningmore » photocurrent microscopy (SPCM) in view of their potential utilization in light harvesting and photodetector applications. CdSe–MoS 2 hybrids are found to exhibit encouraging properties for photodetectors, like high responsivity and fast on/off response under low light exposure while CdSe/ZnS–MoS 2 hybrids show enhanced charge carrier generation with increased light exposure, thus suitable for photovoltaics. While distinguishing optically between CT and NET in QD–TMDCs is nontrivial, it is found that they can be differentiated by SPCM as these two processes exhibit distinctive light-intensity dependencies: CT causes a photogating effect, decreasing the photocurrent response with increasing light power while NET increases the photocurrent response with increasing light power, opposite to CT case.« less

Determining Li+-Coupled Redox Targeting Reaction Kinetics of Battery Materials with Scanning Electrochemical Microscopy.

PubMed

Yan, Ruiting; Ghilane, Jalal; Phuah, Kia Chai; Pham Truong, Thuan Nguyen; Adams, Stefan; Randriamahazaka, Hyacinthe; Wang, Qing

2018-02-01

The redox targeting reaction of Li + -storage materials with redox mediators is the key process in redox flow lithium batteries, a promising technology for next-generation large-scale energy storage. The kinetics of the Li + -coupled heterogeneous charge transfer between the energy storage material and redox mediator dictates the performance of the device, while as a new type of charge transfer process it has been rarely studied. Here, scanning electrochemical microscopy (SECM) was employed for the first time to determine the interfacial charge transfer kinetics of LiFePO 4 /FePO 4 upon delithiation and lithiation by a pair of redox shuttle molecules FcBr 2 + and Fc. The effective rate constant k eff was determined to be around 3.70-6.57 × 10 -3 cm/s for the two-way pseudo-first-order reactions, which feature a linear dependence on the composition of LiFePO 4 , validating the kinetic process of interfacial charge transfer rather than bulk solid diffusion. In addition, in conjunction with chronoamperometry measurement, the SECM study disproves the conventional "shrinking-core" model for the delithiation of LiFePO 4 and presents an intriguing way of probing the phase boundary propagations induced by interfacial redox reactions. This study demonstrates a reliable method for the kinetics of redox targeting reactions, and the results provide useful guidance for the optimization of redox targeting systems for large-scale energy storage.

Distinct Optoelectronic Signatures for Charge Transfer and Energy Transfer in Quantum Dot-MoS 2 Hybrid Photodetectors Revealed by Photocurrent Imaging Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Mingxing; Chen, Jia-Shiang; Routh, Prahlad K.

Atomically thin transition metal dichalcogenides (TMDCs) have intriguing nanoscale properties like high charge mobility, photosensitivity, layer-thickness-dependent bandgap, and mechanical flexibility, which are all appealing for the development of next generation optoelectronic, catalytic, and sensory devices. Their atomically thin thickness, however, renders TMDCs poor absorptivity. For this study, bilayer MoS 2 is combined with core-only CdSe QDs and core/shell CdSe/ZnS QDs to obtain hybrids with increased light harvesting and exhibiting interfacial charge transfer (CT) and nonradiative energy transfer (NET), respectively. Field-effect transistors based on these hybrids and their responses to varying laser power and applied gate voltage are investigated with scanningmore » photocurrent microscopy (SPCM) in view of their potential utilization in light harvesting and photodetector applications. CdSe–MoS 2 hybrids are found to exhibit encouraging properties for photodetectors, like high responsivity and fast on/off response under low light exposure while CdSe/ZnS–MoS 2 hybrids show enhanced charge carrier generation with increased light exposure, thus suitable for photovoltaics. While distinguishing optically between CT and NET in QD–TMDCs is nontrivial, it is found that they can be differentiated by SPCM as these two processes exhibit distinctive light-intensity dependencies: CT causes a photogating effect, decreasing the photocurrent response with increasing light power while NET increases the photocurrent response with increasing light power, opposite to CT case.« less

Generation and characterization of a perfect vortex beam with a large topological charge through a digital micromirror device.

PubMed

Chen, Yue; Fang, Zhao-Xiang; Ren, Yu-Xuan; Gong, Lei; Lu, Rong-De

2015-09-20

Optical vortices are associated with a spatial phase singularity. Such a beam with a vortex is valuable in optical microscopy, hyper-entanglement, and optical levitation. In these applications, vortex beams with a perfect circle shape and a large topological charge are highly desirable. But the generation of perfect vortices with high topological charges is challenging. We present a novel method to create perfect vortex beams with large topological charges using a digital micromirror device (DMD) through binary amplitude modulation and a narrow Gaussian approximation. The DMD with binary holograms encoding both the spatial amplitude and the phase could generate fast switchable, reconfigurable optical vortex beams with significantly high quality and fidelity. With either the binary Lee hologram or the superpixel binary encoding technique, we were able to generate the corresponding hologram with high fidelity and create a perfect vortex with topological charge as large as 90. The physical properties of the perfect vortex beam produced were characterized through measurements of propagation dynamics and the focusing fields. The measurements show good consistency with the theoretical simulation. The perfect vortex beam produced satisfies high-demand utilization in optical manipulation and control, momentum transfer, quantum computing, and biophotonics.

Charge carrier transfer in tungsten disulfide—black phosphorus heterostructures

NASA Astrophysics Data System (ADS)

Zhao, Siqi; He, Dawei; Wang, Yongsheng; Zhang, Xinwu; He, Jiaqi

2017-11-01

Photocarrier dynamics in tungsten disulfide—black phosphorus (BP) heterostructures were studied by time-resolved differential reflection measurements. The heterostructures were fabricated by stacking together monolayer WS2 and BP flakes that are both fabricated by mechanical exfoliation. Efficient and ultrafast transfer of photocarriers from WS2 to BP flakes was observed. This confirms the type-I band alignment of WS2/BP heterostructures that was predicted by theory. Accompanied with the photocarrier interlayer transfer process from WS2 to BP flakes, the change of the absorption of WS2 persists for several nanoseconds. These results promote the consciousness about the carrier dynamics of interlayer transfer process in van der Waals heterostructures and its application in optoelectronic devices.

Effect of CdS nanocrystals on charge transport mechanism in poly(3-hexylthiophene)

NASA Astrophysics Data System (ADS)

Khan, Mohd Taukeer; Almohammedi, Abdullah

2017-08-01

The present manuscript demonstrates the optical and electrical characteristics of poly(3-hexylthiophene) (P3HT) and cadmium sulphide (CdS) hybrid nanocomposites. Optical results suggest that there is a formation of charge transfer complex (CTC) between host P3HT and guest CdS nanocrystals (NCs). Electrical properties of P3HT and P3HT-CdS thin films have been studied in hole only device configurations at different temperatures (290 K-150 K), and results were analysed by the space charge limited conduction mechanism. Density of traps and characteristic trap energy increase on incorporation of inorganic NCs in the polymer matrix, which might be due to the additional favourable energy states created by CdS NCs in the band gap of P3HT. These additional trap states assist charge carriers to move quicker which results in enhancement of hole mobility from 7 × 10-6 to 5.5 × 10-5 cm2/V s in nanocomposites. These results suggest that the P3HT-CdS hybrid system has desirable optical and electrical properties for its applications to photovoltaics devices.

Interface for Light-Driven Electron Transfer by Photosynthetic Complexes Across Block Copolymer Membranes.

PubMed

Kuang, Liangju; Olson, Tien L; Lin, Su; Flores, Marco; Jiang, Yunjiang; Zheng, Wan; Williams, JoAnn C; Allen, James P; Liang, Hongjun

2014-03-06

Incorporation of membrane proteins into nanodevices to mediate recognition and transport in a collective and scalable fashion remains a challenging problem. We demonstrate how nanoscale photovoltaics could be designed using robust synthetic nanomembranes with incorporated photosynthetic reaction centers (RCs). Specifically, RCs from Rhodobacter sphaeroides are reconstituted spontaneously into rationally designed polybutadiene membranes to form hierarchically organized proteopolymer membrane arrays via a charge-interaction-directed reconstitution mechanism. Once incorporated, the RCs are fully active for prolonged periods based upon a variety of spectroscopic measurements, underscoring preservation of their 3D pigment configuration critical for light-driven charge transfer. This result provides a strategy to construct solar conversion devices using structurally versatile proteopolymer membranes with integrated RC functions to harvest broad regions of the solar spectrum.

Engineering high charge transfer n-doping of graphene electrodes and its application to organic electronics.

PubMed

Sanders, Simon; Cabrero-Vilatela, Andrea; Kidambi, Piran R; Alexander-Webber, Jack A; Weijtens, Christ; Braeuninger-Weimer, Philipp; Aria, Adrianus I; Qasim, Malik M; Wilkinson, Timothy D; Robertson, John; Hofmann, Stephan; Meyer, Jens

2015-08-14

Using thermally evaporated cesium carbonate (Cs2CO3) in an organic matrix, we present a novel strategy for efficient n-doping of monolayer graphene and a ∼90% reduction in its sheet resistance to ∼250 Ohm sq(-1). Photoemission spectroscopy confirms the presence of a large interface dipole of ∼0.9 eV between graphene and the Cs2CO3/organic matrix. This leads to a strong charge transfer based doping of graphene with a Fermi level shift of ∼1.0 eV. Using this approach we demonstrate efficient, standard industrial manufacturing process compatible graphene-based inverted organic light emitting diodes on glass and flexible substrates with efficiencies comparable to those of state-of-the-art ITO based devices.

Optically-energized, emp-resistant, fast-acting, explosion initiating device

DOEpatents

Benson, David A.; Kuswa, Glenn W.

1987-01-01

Optical energy, provided from a remote user-operated source, is utilized to initially electrically charge a capacitor in a circuit that also contains an explosion initiating transducer in contact with a small explosive train contained in an attachable housing. Additional optical energy is subsequently supplied in a preferred embodiment to an optically responsive phototransistor acting in conjunction with a silicon controlled rectifer to release the stored electrical energy through the explosion initiating transducer to set off the explosive train. All energy transfers between the user and the explosive apparatus, either for charging it up or for setting it off, are conveyed optically and may be accomplished in a single optical fiber with coding to distinguish between specific optical energy transfers and between these and any extraneous signals.

Nanocrystal-mediated charge screening effects in nanowire field-effect transistors

NASA Astrophysics Data System (ADS)

Yoon, C. J.; Yeom, D. H.; Jeong, D. Y.; Lee, M. G.; Moon, B. M.; Kim, S. S.; Choi, C. Y.; Koo, S. M.

2009-03-01

ZnO nanowire field-effect transistors having an omega-shaped floating gate (OSFG) have been successfully fabricated by directly coating CdTe nanocrystals (˜6±2.5 nm) at room temperature, and compared to simultaneously prepared control devices without nanocrystals. Herein, we demonstrate that channel punchthrough may occur when the depletion from the OSFG takes place due to the trapped charges in the nanocrystals. Electrical measurements on the OSFG nanowire devices showed static-induction transistorlike behavior in the drain output IDS-VDS characteristics and a hysteresis window as large as ˜3.1 V in the gate transfer IDS-VGS characteristics. This behavior is ascribed to the presence of the CdTe nanocrystals, and is indicative of the trapping and emission of electrons in the nanocrystals. The numerical simulations clearly show qualitatively the same characteristics as the experimental data and confirm the effect, showing that the change in the potential distribution across the channel, induced by both the wrapping-around gate and the drain, affects the transport characteristics of the device. The cross-sectional energy band and potential profile of the OSFG channel corresponding to the "programed (noncharged)" and "erased (charged)" operations for the device are also discussed on the basis of the numerical capacitance-voltage simulations.

Theoretical investigation of carrier transfer by an optical contacting scheme for optoelectronic application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Jianfeng, E-mail: jianfeng.yang@student.unsw.edu.au; Zhang, Zhilong; Chen, Weijian

2016-04-21

As a promising charge carrier transfer scheme, optical coupling could potentially improve the performance of an optoelectronic device for energy harvesting based on well developed nanotechnology. By extracting carriers optically, the functional features of the nano-structured material could be better used by minimizing the concerns about its electrical properties. In this paper, we present a rigorous electromagnetic model to analyze the optical carrier transfer problem. The flow of the energy is analyzed carefully by the photon transfer spectrum, and the photon emitters (electron-hole pairs) are assumed in a thermal equilibrium described by Bose-Einstein distribution. The result shows that an energymore » selective carrier transfer can be optically achieved at the device level by integrating the emitter and receiver into a nano-optical resonator, where both the photon emission and absorption are significantly amplified by a near-field coupling around the resonant frequency. General design and optimization schemes in practice are addressed by examining the influence of the photonic design and an energy dependent emissivity of the emitter, which can be used to develop the optical contacting concept further.« less

Upsets in Erased Floating Gate Cells With High-Energy Protons

DOE PAGES

Gerardin, S.; Bagatin, M.; Paccagnella, A.; ...

2017-01-01

We discuss upsets in erased floating gate cells, due to large threshold voltage shifts, using statistical distributions collected on a large number of memory cells. The spread in the neutral threshold voltage appears to be too low to quantitatively explain the experimental observations in terms of simple charge loss, at least in SLC devices. The possibility that memories exposed to high energy protons and heavy ions exhibit negative charge transfer between programmed and erased cells is investigated, although the analysis does not provide conclusive support to this hypothesis.

Vehicle to wireless power transfer coupling coil alignment sensor

DOEpatents

Miller, John M.; Chambon, Paul H.; Jones, Perry T.; White, Clifford P.

2016-02-16

A non-contacting position sensing apparatus includes at least one vehicle-mounted receiver coil that is configured to detect a net flux null when the vehicle is optimally aligned relative to the primary coil in the charging device. Each of the at least one vehicle-mounted receiver coil includes a clockwise winding loop and a counterclockwise winding loop that are substantially symmetrically configured and serially connected to each other. When the non-contacting position sensing apparatus is located directly above the primary coil of the charging device, the electromotive forces from the clockwise winding loop and the counterclockwise region cancel out to provide a zero electromotive force, i.e., a zero voltage reading across the coil that includes the clockwise winding loop and the counterclockwise winding loop.

Ageing and proton irradiation damage of a low voltage EMCCD in a CMOS process

NASA Astrophysics Data System (ADS)

Dunford, A.; Stefanov, K.; Holland, A.

2018-02-01

Electron Multiplying Charge Coupled Devices (EMCCDs) have revolutionised low light level imaging, providing highly sensitive detection capabilities. Implementing Electron Multiplication (EM) in Charge Coupled Devices (CCDs) can increase the Signal to Noise Ratio (SNR) and lead to further developments in low light level applications such as improvements in image contrast and single photon imaging. Demand has grown for EMCCD devices with properties traditionally restricted to Complementary Metal-Oxide-Semiconductor (CMOS) image sensors, such as lower power consumption and higher radiation tolerance. However, EMCCDs are known to experience an ageing effect, such that the gain gradually decreases with time. This paper presents results detailing EM ageing in an Electron Multiplying Complementary Metal-Oxide-Semiconductor (EMCMOS) device and its effect on several device characteristics such as Charge Transfer Inefficiency (CTI) and thermal dark signal. When operated at room temperature an average decrease in gain of over 20% after an operational period of 175 hours was detected. With many image sensors deployed in harsh radiation environments, the radiation hardness of the device following proton irradiation was also tested. This paper presents the results of a proton irradiation completed at the Paul Scherrer Institut (PSI) at a 10 MeV equivalent fluence of 4.15× 1010 protons/cm2. The pre-irradiation characterisation, irradiation methodology and post-irradiation results are detailed, demonstrating an increase in dark current and a decrease in its activation energy. Finally, this paper presents a comparison of the damage caused by EM gain ageing and proton irradiation.

Electrochemistry of poly(3,4-ethylenedioxythiophene)-polyaniline/ Prussian blue electrochromic devices containing an ionic liquid based gel electrolyte film.

PubMed

Deepa, Melepurath; Awadhia, Arvind; Bhandari, Shweta

2009-07-21

Electrochromic devices based on poly(3,4-ethylenedioxythiophene) (PEDOT) as the cathodic coloring electrode and polyaniline (PANI) or Prussian blue (PB) as the counter electrode containing a highly conductive, self-supporting, distensible and transparent polymer-gel electrolyte film encapsulating an ionic liquid, 1-butyl-1-methylpyrrolidiniumbis-(trifluoromethylsulfonyl)imide, have been fabricated. Polarization, charge transfer and diffusion processes control the electrochemistry of the functional electrodes during coloration and bleaching and these phenomena differ when PEDOT and PANI/PB were employed alternately as working electrodes. While the electrochemical impedance response shows good similitude for PEDOT and PANI electrodes, the responses of PEDOT and PB were significantly different in the PEDOT-PB device, especially during reduction of PB, wherein the overall amplitude of the impedance response is enormous. Large values of the coloration efficiency maxima of 281 cm2 C(-1) (lambda = 583 nm) and 274 cm2 C(-1) (lambda = 602 nm), achieved at -1.0 and -1.5 V for the PEDOT PANI and PEDOT-PB devices have been correlated to the particularly low magnitude of charge transfer resistance and high polarization capacitance operative at the PEDOT ionic liquid based electrolyte interface at these dc potentials, thus allowing facile ion-transport and consequently resulting in enhanced absorption modulation. Moderately fast switching kinetics and the ability of these devices to sustain about 2500 cycles of clear-to-dark and dark-to-clear without incurring major losses in the optical contrast, along with the ease of construction of these cells in terms of high scalability and reproducibility of the synthetic procedure for fabrication of the electrochromic films and the ionic liquid based gel electrolyte film, are indicators of the promise these devices hold for practical applications like electrochromic windows and displays.

Robust wireless power transfer using a nonlinear parity-time-symmetric circuit.

PubMed

Assawaworrarit, Sid; Yu, Xiaofang; Fan, Shanhui

2017-06-14

Considerable progress in wireless power transfer has been made in the realm of non-radiative transfer, which employs magnetic-field coupling in the near field. A combination of circuit resonance and impedance transformation is often used to help to achieve efficient transfer of power over a predetermined distance of about the size of the resonators. The development of non-radiative wireless power transfer has paved the way towards real-world applications such as wireless powering of implantable medical devices and wireless charging of stationary electric vehicles. However, it remains a fundamental challenge to create a wireless power transfer system in which the transfer efficiency is robust against the variation of operating conditions. Here we propose theoretically and demonstrate experimentally that a parity-time-symmetric circuit incorporating a nonlinear gain saturation element provides robust wireless power transfer. Our results show that the transfer efficiency remains near unity over a distance variation of approximately one metre, without the need for any tuning. This is in contrast with conventional methods where high transfer efficiency can only be maintained by constantly tuning the frequency or the internal coupling parameters as the transfer distance or the relative orientation of the source and receiver units is varied. The use of a nonlinear parity-time-symmetric circuit should enable robust wireless power transfer to moving devices or vehicles.

Robust wireless power transfer using a nonlinear parity-time-symmetric circuit

NASA Astrophysics Data System (ADS)

Assawaworrarit, Sid; Yu, Xiaofang; Fan, Shanhui

2017-06-01

Considerable progress in wireless power transfer has been made in the realm of non-radiative transfer, which employs magnetic-field coupling in the near field. A combination of circuit resonance and impedance transformation is often used to help to achieve efficient transfer of power over a predetermined distance of about the size of the resonators. The development of non-radiative wireless power transfer has paved the way towards real-world applications such as wireless powering of implantable medical devices and wireless charging of stationary electric vehicles. However, it remains a fundamental challenge to create a wireless power transfer system in which the transfer efficiency is robust against the variation of operating conditions. Here we propose theoretically and demonstrate experimentally that a parity-time-symmetric circuit incorporating a nonlinear gain saturation element provides robust wireless power transfer. Our results show that the transfer efficiency remains near unity over a distance variation of approximately one metre, without the need for any tuning. This is in contrast with conventional methods where high transfer efficiency can only be maintained by constantly tuning the frequency or the internal coupling parameters as the transfer distance or the relative orientation of the source and receiver units is varied. The use of a nonlinear parity-time-symmetric circuit should enable robust wireless power transfer to moving devices or vehicles.

Imaging the motion of electrons in 2D semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Dani, Keshav

Technological progress since the late 20th century has centered on semiconductor devices, such as transistors, diodes, and solar cells. At the heart of these devices, is the internal motion of electrons through semiconductor materials due to applied electric fields or by the excitation of photocarriers. Imaging the motion of these electrons would provide unprecedented insight into this important phenomenon, but requires high spatial and temporal resolution. Current studies of electron dynamics in semiconductors are generally limited by the spatial resolution of optical probes, or by the temporal resolution of electronic probes. In this talk, we combine femtosecond pump-probe techniques with spectroscopic photoemission electron microscopy to image the motion of photoexcited electrons from high-energy to low-energy states in a 2D InSe/GaAs heterostructure exhibiting a type-II band alignment. At the instant of photoexcitation, energy-resolved photoelectron images reveal a highly non-equilibrium distribution of photocarriers in space and energy. Thereafter, in response to the out-of-equilibrium photocarriers, we observe the spatial redistribution of charges, thus forming internal electric fields, bending the semiconductor bands, and finally impeding further charge transfer. By assembling images taken at different time-delays, we make a movie lasting a few tens of picoseconds of the electron transfer process in the photoexcited type-II heterostructure - a fundamental phenomenon in semiconductor devices like solar cells. Quantitative analysis and theoretical modeling of spatial variations in the video provide insight into future solar cells, electron dynamics in 2D materials, and other semiconductor devices.

Imaging the motion of electrons across semiconductor heterojunctions.

PubMed

Man, Michael K L; Margiolakis, Athanasios; Deckoff-Jones, Skylar; Harada, Takaaki; Wong, E Laine; Krishna, M Bala Murali; Madéo, Julien; Winchester, Andrew; Lei, Sidong; Vajtai, Robert; Ajayan, Pulickel M; Dani, Keshav M

2017-01-01

Technological progress since the late twentieth century has centred on semiconductor devices, such as transistors, diodes and solar cells. At the heart of these devices is the internal motion of electrons through semiconductor materials due to applied electric fields or by the excitation of photocarriers. Imaging the motion of these electrons would provide unprecedented insight into this important phenomenon, but requires high spatial and temporal resolution. Current studies of electron dynamics in semiconductors are generally limited by the spatial resolution of optical probes, or by the temporal resolution of electronic probes. Here, by combining femtosecond pump-probe techniques with spectroscopic photoemission electron microscopy, we imaged the motion of photoexcited electrons from high-energy to low-energy states in a type-II 2D InSe/GaAs heterostructure. At the instant of photoexcitation, energy-resolved photoelectron images revealed a highly non-equilibrium distribution of photocarriers in space and energy. Thereafter, in response to the out-of-equilibrium photocarriers, we observed the spatial redistribution of charges, thus forming internal electric fields, bending the semiconductor bands, and finally impeding further charge transfer. By assembling images taken at different time-delays, we produced a movie lasting a few trillionths of a second of the electron-transfer process in the photoexcited type-II heterostructure-a fundamental phenomenon in semiconductor devices such as solar cells. Quantitative analysis and theoretical modelling of spatial variations in the movie provide insight into future solar cells, 2D materials and other semiconductor devices.

Imaging the motion of electrons across semiconductor heterojunctions

NASA Astrophysics Data System (ADS)

Man, Michael K. L.; Margiolakis, Athanasios; Deckoff-Jones, Skylar; Harada, Takaaki; Wong, E. Laine; Krishna, M. Bala Murali; Madéo, Julien; Winchester, Andrew; Lei, Sidong; Vajtai, Robert; Ajayan, Pulickel M.; Dani, Keshav M.

2017-01-01

Technological progress since the late twentieth century has centred on semiconductor devices, such as transistors, diodes and solar cells. At the heart of these devices is the internal motion of electrons through semiconductor materials due to applied electric fields or by the excitation of photocarriers. Imaging the motion of these electrons would provide unprecedented insight into this important phenomenon, but requires high spatial and temporal resolution. Current studies of electron dynamics in semiconductors are generally limited by the spatial resolution of optical probes, or by the temporal resolution of electronic probes. Here, by combining femtosecond pump-probe techniques with spectroscopic photoemission electron microscopy, we imaged the motion of photoexcited electrons from high-energy to low-energy states in a type-II 2D InSe/GaAs heterostructure. At the instant of photoexcitation, energy-resolved photoelectron images revealed a highly non-equilibrium distribution of photocarriers in space and energy. Thereafter, in response to the out-of-equilibrium photocarriers, we observed the spatial redistribution of charges, thus forming internal electric fields, bending the semiconductor bands, and finally impeding further charge transfer. By assembling images taken at different time-delays, we produced a movie lasting a few trillionths of a second of the electron-transfer process in the photoexcited type-II heterostructure—a fundamental phenomenon in semiconductor devices such as solar cells. Quantitative analysis and theoretical modelling of spatial variations in the movie provide insight into future solar cells, 2D materials and other semiconductor devices.

Observation of Internal Photoinduced Electron and Hole Separation in Hybrid Two-Dimentional Perovskite Films.

PubMed

Liu, Junxue; Leng, Jing; Wu, Kaifeng; Zhang, Jun; Jin, Shengye

2017-02-01

Two-dimensional (2D) organolead halide perovskites are promising for various optoelectronic applications. Here we report a unique spontaneous charge (electron/hole) separation property in multilayered (BA) 2 (MA) n-1 Pb n I 3n+1 (BA = CH 3 (CH 2 ) 3 NH 3 + , MA = CH 3 NH 3 + ) 2D perovskite films by studying the charge carrier dynamics using ultrafast transient absorption and photoluminescence spectroscopy. Surprisingly, the 2D perovskite films, although nominally prepared as "n = 4", are found to be mixture of multiple perovskite phases, with n = 2, 3, 4 and ≈ ∞, that naturally align in the order of n along the direction perpendicular to the substrate. Driven by the band alignment between 2D perovskites phases, we observe consecutive photoinduced electron transfer from small-n to large-n phases and hole transfer in the opposite direction on hundreds of picoseconds inside the 2D film of ∼358 nm thickness. This internal charge transfer efficiently separates electrons and holes to the upper and bottom surfaces of the films, which is a unique property beneficial for applications in photovoltaics and other optoelectronics devices.

Photoelectron spectroscopy study of the electronic structures at CoPc/Bi(111) interface

NASA Astrophysics Data System (ADS)

Sun, Haoliang; Liang, Zhaofeng; Shen, Kongchao; Hu, Jinbang; Ji, Gengwu; Li, Zheshen; Li, Haiyang; Zhu, Zhiyuan; Li, Jiong; Gao, Xingyu; Han, Huang; Jiang, Zheng; Song, Fei

2017-07-01

Self-assembly of functional molecules on solid substrate has been recognized as an appealing approach for the fabrication of diverse nanostructures for nanoelectronics. Herein, we investigate the growth of cobalt phthalocyanine (CoPc) on a Bi(111) surface with focus on the interface electronic structures utilizing photoelectron spectroscopy. While charge transfer from bismuth substrate to the molecule results in the emergence of an interface component in the Co 3p core level at lower binding energy, core-levels associated to the molecular ligand (C 1s and N 1s) are less influenced by the adsorption. In addition, density functional theory (DFT) calculations also support the empirical inference that the molecule-substrate interaction mainly involves the out-of-plane empty Co 3d orbital and bismuth states. Finally, valence band spectra demonstrate the molecule-substrate interaction is induced by interface charge transfer, agreeing well with core level measurements. Charge transfer is shown to be mainly from the underlying bismuth substrate to the empty states located at the central Co atom in the CoPc molecules. This report may provide a fundamental basis to the on-surface engineering of interfaces for molecular devices and spintronics.

Field-induced exciton dissociation in PTB7-based organic solar cells

NASA Astrophysics Data System (ADS)

Gerhard, Marina; Arndt, Andreas P.; Bilal, Mühenad; Lemmer, Uli; Koch, Martin; Howard, Ian A.

2017-05-01

The physics of charge separation in organic semiconductors is a topic of ongoing research of relevance to material and device engineering. Herein, we present experimental observations of the field and temperature dependence of charge separation from singlet excitons in PTB7 and PC71BM , and from charge-transfer states created across interfaces in PTB 7 /PC71BM bulk heterojunction solar cells. We obtain this experimental data by time-resolving the near infrared emission of the states from 10 K to room temperature and electric fields from 0 to 2.5 MVcm -1 . Examining how the luminescence is quenched by field and temperature gives direct insight into the underlying physics. We observe that singlet excitons can be split by high fields, and that disorder broadens the high threshold fields needed to split the excitons. Charge-transfer (CT) states, on the other hand, can be separated by both field and temperature. Also, the data imply a strong reduction of the activation barrier for charge splitting from the CT state relative to the exciton state. The observations provided herein of the field-dependent separation of CT states as a function of temperature offer a rich data set against which theoretical models of charge separation can be rigorously tested; it should be useful for developing the more advanced theoretical models of charge separation.

Ultrafast magnetization reversal by picosecond electrical pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Yang; Wilson, Richard B.; Gorchon, Jon

The field of spintronics involves the study of both spin and charge transport in solid-state devices. Ultrafast magnetism involves the use of femtosecond laser pulses to manipulate magnetic order on subpicosecond time scales. Here, we unite these phenomena by using picosecond charge current pulses to rapidly excite conduction electrons in magnetic metals. We observe deterministic, repeatable ultrafast reversal of the magnetization of a GdFeCo thin film with a single sub–10-ps electrical pulse. The magnetization reverses in ~10 ps, which is more than one order of magnitude faster than any other electrically controlled magnetic switching, and demonstrates a fundamentally new electricalmore » switching mechanism that does not require spin-polarized currents or spin-transfer/orbit torques. The energy density required for switching is low, projecting to only 4 fJ needed to switch a (20 nm) 3 cell. This discovery introduces a new field of research into ultrafast charge current–driven spintronic phenomena and devices.« less

Tracing Single Electrons in a Disordered Polymer Film at Room Temperature.

PubMed

Wilma, Kevin; Issac, Abey; Chen, Zhijian; Würthner, Frank; Hildner, Richard; Köhler, Jürgen

2016-04-21

The transport of charges lies at the heart of essentially all modern (opto-) electronic devices. Although inorganic semiconductors built the basis for current technologies, organic materials have become increasingly important in recent years. However, organic matter is often highly disordered, which directly impacts the charge carrier dynamics. To understand and optimize device performance, detailed knowledge of the transport mechanisms of charge carriers in disordered matter is therefore of crucial importance. Here we report on the observation of the motion of single electrons within a disordered polymer film at room temperature, using single organic chromophores as probe molecules. The migration of a single electron gives rise to a varying electric field in its vicinity, which is registered via a shift of the emission spectra (Stark shift) of a chromophore. The spectral shifts allow us to determine the electron mobility and reveal for each nanoenvironment a distinct number of different possible electron-transfer pathways within the rugged energy landscape of the disordered polymer matrix.

Upconversion-Triggered Charge Separation in Polymer Semiconductors.

PubMed

Jang, Yu Jin; Kim, Eunah; Ahn, Seonghyeon; Chung, Kyungwha; Kim, Jihyeon; Kim, Heejun; Wang, Huan; Lee, Jiseok; Kim, Dong-Wook; Kim, Dong Ha

2017-01-19

Upconversion is a unique optical property that is driven by a sequential photon pumping and generation of higher energy photons in a consecutive manner. The efficiency improvement in photovoltaic devices can be achieved when upconverters are integrated since upconverters contribute to the generation of extra photons. Despite numerous experimental studies confirming the relationship, fundamental explanations for a real contribution of upconversion to photovoltaic efficiency are still in demand. In this respect, we suggest a new approach to visualize the upconversion event in terms of surface photovoltage (SPV) by virtue of Kelvin probe force microscopy (KPFM). One of the most conventional polymer semiconductors, poly(3-hexyl thiophene) (P3HT), is employed as a sensitizer to generate charge carriers by upconverted light. KPFM measurements reveal that the light upconversion enabled the formation of charge carriers in P3HT, resulting in large SPV of -54.9 mV. It confirms that the energy transfer from upconverters to P3HT can positively impact the device performance in organic solar cells (OSCs).

Ultrafast magnetization reversal by picosecond electrical pulses

DOE PAGES

Yang, Yang; Wilson, Richard B.; Gorchon, Jon; ...

2017-11-03

The field of spintronics involves the study of both spin and charge transport in solid-state devices. Ultrafast magnetism involves the use of femtosecond laser pulses to manipulate magnetic order on subpicosecond time scales. Here, we unite these phenomena by using picosecond charge current pulses to rapidly excite conduction electrons in magnetic metals. We observe deterministic, repeatable ultrafast reversal of the magnetization of a GdFeCo thin film with a single sub–10-ps electrical pulse. The magnetization reverses in ~10 ps, which is more than one order of magnitude faster than any other electrically controlled magnetic switching, and demonstrates a fundamentally new electricalmore » switching mechanism that does not require spin-polarized currents or spin-transfer/orbit torques. The energy density required for switching is low, projecting to only 4 fJ needed to switch a (20 nm) 3 cell. This discovery introduces a new field of research into ultrafast charge current–driven spintronic phenomena and devices.« less

An efficient wireless power transfer system with security considerations for electric vehicle applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zhen; Chau, K. T., E-mail: ktchau@eee.hku.hk; Liu, Chunhua

2014-05-07

This paper presents a secure inductive wireless power transfer (WPT) system for electric vehicle (EV) applications, such as charging the electric devices inside EVs and performing energy exchange between EVs. The key is to employ chaos theory to encrypt the wirelessly transferred energy which can then be decrypted by specific receptors in the multi-objective system. In this paper, the principle of encrypted WPT is first revealed. Then, computer simulation is conducted to validate the feasibility of the proposed system. Moreover, by comparing the WPT systems with and without encryption, the proposed energy encryption scheme does not involve noticeable power consumption.

Assessment of Electromagnetic Interference with Active Cardiovascular Implantable Electronic Devices (CIEDs) Caused by the Qi A13 Design Wireless Charging Board.

PubMed

Seckler, Tobias; Jagielski, Kai; Stunder, Dominik

2015-05-27

Electromagnetic interference is a concern for people wearing cardiovascular implantable electronic devices (CIEDs). The aim of this study was to assess the electromagnetic compatibility between CIEDs and the magnetic field of a common wireless charging technology. To do so the voltage induced in CIEDs by Qi A13 design magnetic fields were measured and compared with the performance limits set by ISO 14117. In order to carry this out a measuring circuit was developed which can be connected with unipolar or bipolar pacemaker leads. The measuring system was positioned at the four most common implantation sites in a torso phantom filled with physiological saline solution. The phantom was exposed by using Helmholtz coils from 5 µT to 27 µT with 111 kHz sine‑bursts or by using a Qi A13 design wireless charging board (Qi‑A13‑Board) in two operating modes "power transfer" and "pinging". With the Helmholtz coils the lowest magnetic flux density at which the performance limit was exceeded is 11 µT. With the Qi‑A13‑Board in power transfer mode 10.8% and in pinging mode 45.7% (2.2% at 10 cm distance) of the performance limit were reached at maximum. In neither of the scrutinized cases, did the voltage induced by the Qi‑A13‑Board exceed the performance limits.

Computational insights into charge transfer across functionalized semiconductor surfaces

NASA Astrophysics Data System (ADS)

Kearney, Kara; Rockett, Angus; Ertekin, Elif

2017-12-01

Photoelectrochemical water-splitting is a promising carbon-free fuel production method for producing H2 and O2 gas from liquid water. These cells are typically composed of at least one semiconductor photoelectrode which is prone to degradation and/or oxidation. Various surface modifications are known for stabilizing semiconductor photoelectrodes, yet stabilization techniques are often accompanied by a decrease in photoelectrode performance. However, the impact of surface modification on charge transport and its consequence on performance is still lacking, creating a roadblock for further improvements. In this review, we discuss how density functional theory and finite-element device simulations are reliable tools for providing insight into charge transport across modified photoelectrodes.

Proton radiation damage experiment on P-Channel CCD for an X-ray CCD camera onboard the ASTRO-H satellite

NASA Astrophysics Data System (ADS)

Mori, Koji; Nishioka, Yusuke; Ohura, Satoshi; Koura, Yoshiaki; Yamauchi, Makoto; Nakajima, Hiroshi; Ueda, Shutaro; Kan, Hiroaki; Anabuki, Naohisa; Nagino, Ryo; Hayashida, Kiyoshi; Tsunemi, Hiroshi; Kohmura, Takayoshi; Ikeda, Shoma; Murakami, Hiroshi; Ozaki, Masanobu; Dotani, Tadayasu; Maeda, Yukie; Sagara, Kenshi

2013-12-01

We report on a proton radiation damage experiment on P-channel CCD newly developed for an X-ray CCD camera onboard the ASTRO-H satellite. The device was exposed up to 109 protons cm-2 at 6.7 MeV. The charge transfer inefficiency (CTI) was measured as a function of radiation dose. In comparison with the CTI currently measured in the CCD camera onboard the Suzaku satellite for 6 years, we confirmed that the new type of P-channel CCD is radiation tolerant enough for space use. We also confirmed that a charge-injection technique and lowering the operating temperature efficiently work to reduce the CTI for our device. A comparison with other P-channel CCD experiments is also discussed. We performed a proton radiation damage experiment on a new P-channel CCD. The device was exposed up to 109 protons cm-2 at 6.7 MeV. We confirmed that it is radiation tolerant enough for space use. We confirmed that a charge-injection technique reduces the CTI. We confirmed that lowering the operating temperature also reduces the CTI.

On Practical Charge Injection at the Metal/Organic Semiconductor Interface

PubMed Central

Kumatani, Akichika; Li, Yun; Darmawan, Peter; Minari, Takeo; Tsukagoshi, Kazuhito

2013-01-01

We have revealed practical charge injection at metal and organic semiconductor interface in organic field effect transistor configurations. We have developed a facile interface structure that consisted of double-layer electrodes in order to investigate the efficiency through contact metal dependence. The metal interlayer with few nanometers thickness between electrode and organic semiconductor drastically reduces the contact resistance at the interface. The improvement has clearly obtained when the interlayer is a metal with lower standard electrode potential of contact metals than large work function of the contact metals. The electrode potential also implies that the most dominant effect on the mechanism at the contact interface is induced by charge transfer. This mechanism represents a step forward towards understanding the fundamental physics of intrinsic charge injection in all organic devices. PMID:23293741

Photophysics and morphology of poly (3-dodecylthienylenevinylene)-[6,6]-phenyl-C{sub 61}-butyric acid methyl ester composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lafalce, E.; Toglia, P.; Jiang, X.

2012-05-21

A series of low band gap poly(3-dodecylthienylenevinylene) (PTV) with controlled morphological order have been synthesized and blended with the electron acceptor [6,6]-phenyl-C{sub 61}-butyric acid methyl ester (PCBM) for organic photovoltaic devices. Two polymers with the most and least side chain regioregularity were chosen in this work, namely the PTV010 and PTV55, respectively. Using photoluminescence, photo-induced absorption spectroscopy, and atomic force microscopy, we find no direct evidence of photoinduced charge transfer between the two constituents, independent of the bulk-heterojunction morphology of the film, although the possibility of formation of P{sup +}/C{sub 60}{sup -} charge transfer complex was not completely ruled out.more » The large exciton binding energy (E{sub b} = 0.6 eV) in PTV inhibits the photoinduced electron transfer from PTV to PCBM. In addition, excitons formed on polymer chains suffer ultrafast (« less

Bi-anchoring organic sensitizers of type D-(π-A)2 comprising thiophene-2-acetonitrile as π-spacer and malonic acid as electron acceptor for dye sensitized solar cell applications

NASA Astrophysics Data System (ADS)

Reddy, Gachumale Saritha; Ramkumar, Sekar; Asiri, Abdullah M.; Anandan, Sambandam

2015-06-01

Two new bi-anchoring organic sensitizers of type D-(π-A)2 comprising the identical π-spacer (thiophene-2-acetonitrile) and electron acceptor (malonic acid) but different aryl amine as electron donors (diphenylamine and carbazole) were synthesized, characterized and fabricated metal free dye-sensitized solar cell devices. The intra molecular charge transfer property and electrochemical property of these dyes were investigated by molecular absorption, emission, cyclic voltammetric experiments and in addition, quantum chemical calculation studies were performed to provide sufficient driving force for the electron injection into the conduction band of TiO2 which leads to efficient charge collection. Among the fabricated devices, carbazole based device exhibits high current conversion efficiency (η = 4.7%) with a short circuit current density (JSC) 15.3 mA/cm2, an open circuit photo voltage (VOC) of 0.59 V and a fill factor of 0.44 under AM 1.5 illumination (85 mW/cm2) compared to diphenylamine based device.

Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rury, Aaron S., E-mail: arury@usc.edu; Sorenson, Shayne; Dawlaty, Jahan M.

2016-03-14

Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone,more » we find sub-cm{sup −1} oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology.« less

Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid

NASA Astrophysics Data System (ADS)

Rury, Aaron S.; Sorenson, Shayne; Dawlaty, Jahan M.

2016-03-01

Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm-1 oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology.

Excitonic processes at organic heterojunctions

NASA Astrophysics Data System (ADS)

He, ShouJie; Lu, ZhengHong

2018-02-01

Understanding excitonic processes at organic heterojunctions is crucial for development of organic semiconductor devices. This article reviews recent research on excitonic physics that involve intermolecular charge transfer (CT) excitons, and progress on understanding relationships between various interface energy levels and key parameters governing various competing interface excitonic processes. These interface excitonic processes include radiative exciplex emission, nonradiative recombination, Auger electron emission, and CT exciton dissociation. This article also reviews various device applications involving interface CT excitons, such as organic light-emitting diodes (OLEDs), organic photovoltaic cells, organic rectifying diodes, and ultralow-voltage Auger OLEDs.

Capacitance of graphenes

NASA Astrophysics Data System (ADS)

Young, Andrea; Dean, Cory; Meric, Inanc; Hone, Jim; Shepard, Ken; Kim, Philip

2010-03-01

Using a transfer procedure and single crystal hexagonal Boron Nitride gate dielectric, we are able to fabricate high mobility graphene devices with local top and back gates. The novel geometry of these devices allows us to measure the spatially averaged compressibility of mono- and bilayer graphene using the ``penetration field'' technique [Eisenstein, J.P. et al. Phys. Rev. Lett. 68, 674 (1992)]. In particular, we analyze the the effects of strong transverse electric fields on the compressibility of graphenes, especially as pertains to charged impurity scattering in single layer graphene and the opening of an energy gap in bilayer.

A tunable few electron triple quantum dot

NASA Astrophysics Data System (ADS)

Gaudreau, L.; Kam, A.; Granger, G.; Studenikin, S. A.; Zawadzki, P.; Sachrajda, A. S.

2009-11-01

In this paper, we report on a tunable few electron lateral triple quantum dot design. The quantum dot potentials are arranged in series. The device is aimed at studies of triple quantum dot properties where knowing the exact number of electrons is important as well as quantum information applications involving electron spin qubits. We demonstrate tuning strategies for achieving required resonant conditions such as quadruple points where all three quantum dots are on resonance. We find that in such a device resonant conditions at specific configurations are accompanied by complex charge transfer behavior.

Theoretical insights into multiscale electronic processes in organic photovoltaics

NASA Astrophysics Data System (ADS)

Tretiak, Sergei

Present day electronic devices are enabled by design and implementation of precise interfaces that control the flow of charge carriers. This requires robust and predictive multiscale approaches for theoretical description of underlining complex phenomena. Combined with thorough experimental studies such approaches provide a reliable estimate of physical properties of nanostructured materials and enable a rational design of devices. From this perspective I will discuss first principle modeling of small-molecule bulk-heterojunction organic solar cells and push-pull chromophores for tunable-color organic light emitters. The emphasis is on electronic processes involving intra- and intermolecular energy or charge transfer driven by strong electron-phonon coupling inherent to pi-conjugated systems. Finally I will describe how precise manipulation and control of organic-organic interfaces in a photovoltaic device can increase its power conversion efficiency by 2-5 times in a model bilayer system. Applications of these design principles to practical architectures like bulk heterojunction devices lead to an enhancement in power conversion efficiency from 4.0% to 7.0%. These interface manipulation strategies are universally applicable to any donor-acceptor interface, making them both fundamentally interesting and technologically important for achieving high efficiency organic electronic devices.

Analytical Performance of a Venturi-assisted Array of Micromachined UltraSonic Electrosprays (AMUSE) Coupled to Ion Trap Mass Spectrometry for the Analysis of Peptides and Proteins

PubMed Central

Hampton, Christina Y.; Forbes, Thomas P.; Varady, Mark J.; Meacham, J. Mark; Fedorov, Andrei G.; Degertekin, F. Levent; Fernández, Facundo M.

2008-01-01

The analytical characterization of a novel ion source for mass spectrometry named Array of Micromachined UltraSonic Electrosprays (AMUSE) is presented here. This is a fundamentally different type of ion generation device, consisting of three major components: 1) a piezoelectric transducer that creates ultrasonic waves at one of the resonant frequencies of the sample-filled device, 2) an array of pyramidally-shaped nozzles micromachined on a silicon wafer, and 3) a spacer which prevents contact between the array and transducer ensuring the transfer of acoustic energy to the sample. A high pressure gradient generated at the apices of the nozzle pyramids forces the periodic ejection of multiple droplet streams from the device. With this device, the processes of droplet formation and droplet charging are separated, hence, the limitations of conventional electrospray-type ion sources, including the need for high charging potentials and the addition of organic solvent to decrease surface tension can be avoided. In this work, a Venturi device is coupled with AMUSE in order to increase desolvation, droplet focusing, and signal stability. Results show that ionization of model peptides and small tuning molecules is possible with DC charging potentials of 100 VDC or less. Ionization in RF-only mode (without DC biasing) was also possible. It was observed that, when combined with AMUSE, the Venturi device provides a 10-fold gain in signal-to-noise ratio for 90% aqueous sample solutions. Further reduction in the diameter of the orifices of the micromachined arrays, led to an additional signal gain of at least 3 orders of magnitude, a 2- to 10-fold gain in the signal-to-noise ratio, and an improvement in signal stability from 47% to 8.5% RSD. The effectiveness of this device for the soft ionization of model proteins in aqueous media, such as cytochrome C was also examined, yielding spectra with an average charge state of 8.8 when analyzed with a 100 VDC charging potential. Ionization of model proteins was also possible in RF-only mode. PMID:17914864

The strain and thermal induced tunable charging phenomenon in low power flexible memory arrays with a gold nanoparticle monolayer

NASA Astrophysics Data System (ADS)

Zhou, Ye; Han, Su-Ting; Xu, Zong-Xiang; Roy, V. A. L.

2013-02-01

The strain and temperature dependent memory effect of organic memory transistors on plastic substrates has been investigated under ambient conditions. The gold (Au) nanoparticle monolayer was prepared and embedded in an atomic layer deposited aluminum oxide (Al2O3) as the charge trapping layer. The devices exhibited low operation voltage, reliable memory characteristics and long data retention time. Experimental analysis of the programming and erasing behavior at various bending states showed the relationship between strain and charging capacity. Thermal-induced effects on these memory devices have also been analyzed. The mobility shows ~200% rise and the memory window increases from 1.48 V to 1.8 V when the temperature rises from 20 °C to 80 °C due to thermally activated transport. The retention capability of the devices decreases with the increased working temperature. Our findings provide a better understanding of flexible organic memory transistors under various operating temperatures and validate their applications in various areas such as temperature sensors, temperature memory or advanced electronic circuits. Furthermore, the low temperature processing procedures of the key elements (Au nanoparticle monolayer and Al2O3 dielectric layer) could be potentially integrated with large area flexible electronics.The strain and temperature dependent memory effect of organic memory transistors on plastic substrates has been investigated under ambient conditions. The gold (Au) nanoparticle monolayer was prepared and embedded in an atomic layer deposited aluminum oxide (Al2O3) as the charge trapping layer. The devices exhibited low operation voltage, reliable memory characteristics and long data retention time. Experimental analysis of the programming and erasing behavior at various bending states showed the relationship between strain and charging capacity. Thermal-induced effects on these memory devices have also been analyzed. The mobility shows ~200% rise and the memory window increases from 1.48 V to 1.8 V when the temperature rises from 20 °C to 80 °C due to thermally activated transport. The retention capability of the devices decreases with the increased working temperature. Our findings provide a better understanding of flexible organic memory transistors under various operating temperatures and validate their applications in various areas such as temperature sensors, temperature memory or advanced electronic circuits. Furthermore, the low temperature processing procedures of the key elements (Au nanoparticle monolayer and Al2O3 dielectric layer) could be potentially integrated with large area flexible electronics. Electronic supplementary information (ESI) available: UV-vis spectrum of Au nanoparticle aqueous solution, transfer characteristics of the transistors without inserting an Au nanoparticle monolayer, AFM image of the pentacene layer, transfer characteristics at different program voltages and memory windows with respect to the P/E voltage. See DOI: 10.1039/c2nr32579a

Designing high efficiency organic photovoltaics by controlling the ordering at the donor-acceptor interface

NASA Astrophysics Data System (ADS)

Mohite, Aditya; Nie, Wanyi; Gupta, Gautam; Crone, Brian; Kuo, Chenyu; Tsai, Hsinhan; Smith, Darryl; Ruden, Paul; Liu, Feilong; Wang, Hsing-Lin; Tretiak, Sergei

2014-03-01

The overall power conversion efficiency in an organic solar cell depends on the balance between the rates of exciton dissociation, recombination and separation at the donor acceptor interface. Inability to design, control and engineer these interfaces remains a key bottleneck in their widespread use for the next generation organic electronic devices. Here, we show that we can control the ordering at the P3HT/C60 interface in bilayer device geometry by inserting a monolayer of oligothiophenes, which leads to a complete suppression in the exciplex (or charge transfer state) recombination. We observe that the photocurrent increases by 500%, which in turn results in an increase in the overall power conversion efficiency by an order of magnitude. Moreover, we find that the oligothiophene with an odd number of rings (ter and penta oligothiophene) exhibit a much higher increase in the photocurrent in comparison to the oligothiophene with an even number of rings (tetra oligothiphene). STM measurements reveal that the oligothiophene with odd and even number of rings differ in their ordering respectively, that has a big effect on the overall device performance. We also find that this ordering is highly dependent on the side functional groups in the oligothiophenes. The mechanism of photocurrent generation will be discussed and a simple transport model will be used to explain the change in the charge transfer and recombination rates and predict current-voltage curves.

Challenges in photon-starved space astronomy in a harsh radiation environment using CCDs

NASA Astrophysics Data System (ADS)

Hall, David J.; Bush, Nathan; Murray, Neil; Gow, Jason; Clarke, Andrew; Burgon, Ross; Holland, Andrew

2015-09-01

The Charge Coupled Device (CCD) has a long heritage for imaging and spectroscopy in many space astronomy missions. However, the harsh radiation environment experienced in orbit creates defects in the silicon that capture the signal being transferred through the CCD. This radiation damage has a detrimental impact on the detector performance and requires carefully planned mitigation strategies. The ESA Gaia mission uses 106 CCDs, now orbiting around the second Lagrange point as part of the largest focal-plane ever launched. Following readout, signal electrons will be affected by the traps generated in the devices from the radiation environment and this degradation will be corrected for using a charge distortion model. ESA's Euclid mission will contain a focal plane of 36 CCDs in the VIS instrument. Moving further forwards, the World Space Observatory (WSO) UV spectrographs and the WFIRST-AFTA coronagraph intend to look at very faint sources in which mitigating the impact of traps on the transfer of single electron signals will be of great interest. Following the development of novel experimental and analysis techniques, one is now able to study the impact of radiation on the detector to new levels of detail. Through a combination of TCAD simulations, defect studies and device testing, we are now probing the interaction of single electrons with individual radiation-induced traps to analyse the impact of radiation in photon-starved applications.

Molecular design and nanoscale engineering of organic nanofibril donor-acceptor heterojunctions

NASA Astrophysics Data System (ADS)

Huang, Helin

Organic nanofibril heterojunction materials have gained increasing research interest due to their broad applications in organic semiconductor devices. In order to enhance the device performance, we have investigated the structure-property relationship of these nanostructures by designing and synthesizing functional building block molecules, selfassembling the molecules into well-defined nanofibers, fabricating the nanofibers into optical and electrical devices, and testing their photoconductivity and sensor properties. In Chapter 2, we present a simple approach to fabricate efficient nanofibril heterojunctions by interfacial engineering of electron donor (D) coating onto acceptor (A) nanofibers. The nanofibers both create a large D/A interface for increased charge separation and act as long-range transport pathways for photogenerated charge carriers towards the electrodes, and the alkyl groups modified at the A molecules not only enable effective surface adsorption of D molecules on the nanofibers for effective electron-transfer communication, but also spatially separate the photogenerated charge carriers to prevent their recombination. In Chapter 3, we further investigated the effect of D molecular structure and coating morphology on photoconductivity of organic nanofiber materials. A series of D molecules with varying side-chain modifications were synthesized and investigated for the different intermolecular arrangements caused by pi-pi stacking in balance with steric hindrance of side-chains. Different molecular assemblies of D resulted in distinctive phase segregation between D and A nanofiber, which significantly affects the interfacial charge separation. In Chapter 4, we developed an alternative nanofibril heterojunction structure that is composed of D as the nanofiber, onto which a monolayer of A molecule was coated. Due to the strong redox (charge transfer) interaction between D and A, the nanofibril junction demonstrated high conductivity even without light illumination, which makes this material suitable for applications in chemiresistor sensors for detection of amines. In Chapter 5, a series of perylene tetracarboxylic monoimides were synthesized through a one-step reaction between cycloalkyl amines and the parent perylene dianhydride. The selection of appropriate reaction medium is the most critical for achieving the high purity of product. This approach opens up a new way for large scale production of the monoimides, which are the precursor for making a variety of perylene based building block molecules.

A Charge Coupled Device Imaging System For Ophthalmology

NASA Astrophysics Data System (ADS)

Rowe, R. Wanda; Packer, Samuel; Rosen, James; Bizais, Yves

1984-06-01

A digital camera system has been constructed for obtaining reflectance images of the fundus of the eye with monochromatic light. Images at wavelengths in the visible and near infrared regions of the spectrum are recorded by a charge-coupled device array and transferred to a computer. A variety of image processing operations are performed to restore the pictures, correct for distortions in the image formation process, and extract new and diagnostically useful information. The steps involved in calibrating the system to permit quantitative measurement of fundus reflectance are discussed. Three clinically important applications of such a quantitative system are addressed: the characterization of changes in the optic nerve arising from glaucoma, the diagnosis of choroidal melanoma through spectral signatures, and the early detection and improved management of diabetic retinopathy by measurement of retinal tissue oxygen saturation.

An abuttable CCD imager for visible and X-ray focal plane arrays

NASA Technical Reports Server (NTRS)

Burke, Barry E.; Mountain, Robert W.; Harrison, David C.; Bautz, Marshall W.; Doty, John P.

1991-01-01

A frame-transfer silicon charge-coupled-device (CCD) imager has been developed that can be closely abutted to other imagers on three sides of the imaging array. It is intended for use in multichip arrays. The device has 420 x 420 pixels in the imaging and frame-store regions and is constructed using a three-phase triple-polysilicon process. Particular emphasis has been placed on achieving low-noise charge detection for low-light-level imaging in the visible and maximum energy resolution for X-ray spectroscopic applications. Noise levels of 6 electrons at 1-MHz and less than 3 electrons at 100-kHz data rates have been achieved. Imagers have been fabricated on 1000-Ohm-cm material to maximize quantum efficiency and minimize split events in the soft X-ray regime.

Extreme electron polaron spatial delocalization in π-conjugated materials

DOE PAGES

Rawson, Jeff; Angiolillo, Paul J.; Therien, Michael J.

2015-10-28

The electron polaron, a spin-1/2 excitation, is the fundamental negative charge carrier in π-conjugated organic materials. Large polaron spatial dimensions result from weak electron-lattice coupling and thus identify materials with unusually low barriers for the charge transfer reactions that are central to electronic device applications. In this paper, we demonstrate electron polarons in π-conjugated multiporphyrin arrays that feature vast areal delocalization. This finding is evidenced by concurrent optical and electron spin resonance measurements, coupled with electronic structure calculations that suggest atypically small reorganization energies for one-electron reduction of these materials. Finally, because the electron polaron dimension can be linked tomore » key performance metrics in organic photovoltaics, light-emitting diodes, and a host of other devices, these findings identify conjugated materials with exceptional optical, electronic, and spintronic properties.« less

Field-modulation spectroscopy of pentacene thin films using field-effect devices: Reconsideration of the excitonic structure

NASA Astrophysics Data System (ADS)

Haas, Simon; Matsui, Hiroyuki; Hasegawa, Tatsuo

2010-10-01

We report pure electric-field effects on the excitonic absorbance of pentacene thin films as measured by unipolar field-effect devices that allowed us to separate the charge accumulation effects. The field-modulated spectra between 1.8 and 2.6 eV can be well fitted with the first derivative curve of Frenkel exciton absorption and its vibronic progression, and at higher energy a field-induced feature appears at around 2.95 eV. The results are in sharp contrast to the electroabsorption spectra reported by Sebastian in previous studies [Chem. Phys. 61, 125 (1981)10.1016/0301-0104(81)85055-0], and leads us to reconsider the excitonic structure including the location of charge-transfer excitons. Nonlinear π -electronic response is discussed based on second-order electro-optic (Kerr) spectra.

Directional charge separation in isolated organic semiconductor crystalline nanowires

DOE PAGES

Labastide, J. A.; Thompson, H. B.; Marques, S. R.; ...

2016-02-25

One of the fundamental design paradigms in organic photovoltaic device engineering is based on the idea that charge separation is an extrinsically driven process requiring an interface for exciton fission. This idea has driven an enormous materials science engineering effort focused on construction of domain sizes commensurate with a nominal exciton diffusion length of order 10 nm. Here, we show that polarized optical excitation of isolated pristine crystalline nanowires of a small molecule n-type organic semiconductor, 7,8,15,16-tetraazaterrylene, generates a significant population of charge-separated polaron pairs along the π-stacking direction. Charge separation was signalled by pronounced power-law photoluminescence decay polarized alongmore » the same axis. In the transverse direction, we observed exponential decay associated with excitons localized on individual monomers. We propose that this effect derives from an intrinsic directional charge-transfer interaction that can ultimately be programmed by molecular packing geometry.« less

Face-on stacking and enhanced out-of-plane hole mobility in graphene-templated copper phthalocyanine.

PubMed

Mativetsky, Jeffrey M; Wang, He; Lee, Stephanie S; Whittaker-Brooks, Luisa; Loo, Yueh-Lin

2014-05-25

Efficient out-of-plane charge transport is required in vertical device architectures, such as organic solar cells and organic light emitting diodes. Here, we show that graphene, transferred onto different technologically-relevant substrates, can be used to induce face-on molecular stacking and improve out-of-plane hole transport in copper phthalocyanine thin films.

Apparatus and methods for storing and releasing hydrogen

DOEpatents

Heung, Leung K.

2001-01-01

A rechargeable device that stores and discharges hydrogen is described. The device stores hydrogen in a solid form and supplies hydrogen as a gas when needed. The solid storage medium may be metal hydride in a ground particle form that avoids the need for compaction or other treatment. Dividers partition a container into separate chambers, each provided with a matrix, formed from an appropriate material like a thermally-conductive aluminum foam, which forms a number of cells. For proper chamber size, the ratio of chamber length to container diameter should be between about 0.5 and 2. Metal hydride particles (or other hydrogen storage medium) may be placed within the cells, which help prevent excessive particle settling. The container is provided with a hydrogen transfer port through which hydrogen gas passes upon either discharging from or charging of the metal hydride particles. A filter may be placed within the port to allow hydrogen to flow but prevent particles from escaping. A heat transferring surface is formed by, for instance, a channel that is thermally coupled with the aluminum foam. Fluid flows through the channel to deliver or remove heat during the respective hydrogen discharging or charging processes.

Apparatus and methods for storing and releasing hydrogen

DOEpatents

Heung, Leung K.

2000-01-01

A rechargeable device that stores and discharges hydrogen is described. The device stores hydrogen in a solid form and supplies hydrogen as a gas when needed. The solid storage medium may be metal hydride in a ground particle form that avoids the need for compaction or other treatment. Dividers partition a container into separate chambers, each provided with a matrix, formed from an appropriate material like a thermally-conductive aluminum foam, which forms a number of cells. For proper chamber size, the ratio of chamber length to container diameter should be between about 0.5 and 2. Metal hydride particles (or other hydrogen storage medium) may be placed within the cells, which help prevent excessive particle settling. The container is provided with a hydrogen transfer port through which hydrogen gas passes upon either discharging from or charging of the metal hydride particles. A filter may be placed within the port to allow hydrogen to flow but prevent particles from escaping. A heat transferring surface is formed by, for instance, a channel that is thermally coupled with the aluminum foam. Fluid flows through the channel to deliver or remove heat during the respective hydrogen discharging or charging processes.

Enhanced Charge Separation in Ternary P3HT/PCBM/CuInS2 Nanocrystals Hybrid Solar Cells

PubMed Central

Lefrançois, Aurélie; Luszczynska, Beata; Pepin-Donat, Brigitte; Lombard, Christian; Bouthinon, Benjamin; Verilhac, Jean-Marie; Gromova, Marina; Faure-Vincent, Jérôme; Pouget, Stéphanie; Chandezon, Frédéric; Sadki, Saïd; Reiss, Peter

2015-01-01

Geminate recombination of bound polaron pairs at the donor/acceptor interface is one of the major loss mechanisms in organic bulk heterojunction solar cells. One way to overcome Coulomb attraction between opposite charge carriers and to achieve their full dissociation is the introduction of high dielectric permittivity materials such as nanoparticles of narrow band gap semiconductors. We selected CuInS2 nanocrystals of 7.4 nm size, which present intermediate energy levels with respect to poly(3-hexylthiophene) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM). Efficient charge transfer from P3HT to nanocrystals takes place as evidenced by light-induced electron spin resonance. Charge transfer between nanocrystals and PCBM only occurs after replacing bulky dodecanethiol (DDT) surface ligands with shorter 1,2-ethylhexanethiol (EHT) ligands. Solar cells containing in the active layer a ternary blend of P3HT:PCBM:CuInS2-EHT nanocrystals in 1:1:0.5 mass ratio show strongly improved short circuit current density and a higher fill factor with respect to the P3HT:PCBM reference device. Complementary measurements of the absorption properties, external quantum efficiency and charge carrier mobility indicate that enhanced charge separation in the ternary blend is at the origin of the observed behavior. The same trend is observed for blends using the glassy polymer poly(triarylamine) (PTAA). PMID:25588811

Directional interlayer spin-valley transfer in two-dimensional heterostructures

DOE PAGES

Schaibley, John R.; Rivera, Pasqual; Yu, Hongyi; ...

2016-12-14

Van der Waals heterostructures formed by two different monolayer semiconductors have emerged as a promising platform for new optoelectronic and spin/valleytronic applications. In addition to its atomically thin nature, a two-dimensional semiconductor heterostructure is distinct from its three-dimensional counterparts due to the unique coupled spin-valley physics of its constituent monolayers. In this paper, we report the direct observation that an optically generated spin-valley polarization in one monolayer can be transferred between layers of a two-dimensional MoSe 2–WSe 2 heterostructure. Using non-degenerate optical circular dichroism spectroscopy, we show that charge transfer between two monolayers conserves spin-valley polarization and is only weaklymore » dependent on the twist angle between layers. Finally, our work points to a new spin-valley pumping scheme in nanoscale devices, provides a fundamental understanding of spin-valley transfer across the two-dimensional interface, and shows the potential use of two-dimensional semiconductors as a spin-valley generator in two-dimensional spin/valleytronic devices for storing and processing information.« less

Diffusive charge transport in graphene

NASA Astrophysics Data System (ADS)

Chen, Jianhao

The physical mechanisms limiting the mobility of graphene on SiO 2 are studied and printed graphene devices on a flexible substrate are realized. Intentional addition of charged scattering impurities is used to study the effects of charged impurities. Atomic-scale defects are created by noble-gas ions irradiation to study the effect of unitary scatterers. The results show that charged impurities and atomic-scale defects both lead to conductivity linear in density in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates. While charged impurities cause intravalley scattering and induce a small change in the minimum conductivity, defects in graphene scatter electrons between the valleys and suppress the minimum conductivity below the metallic limit. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a small resistivity which is linear in temperature and independent of carrier density; at higher temperatures, polar optical phonons of the SiO2 substrate give rise to an activated, carrier density-dependent resistivity. Graphene is also made into high mobility transparent and flexible field effect device via the transfer-printing method. Together the results paint a complete picture of charge carrier transport in graphene on SiO2 in the diffusive regime, and show the promise of graphene as a novel electronic material that have potential applications not only on conventional inorganic substrates, but also on flexible substrates.

Highly Efficient Full-Color Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes: Extremely Low Efficiency Roll-Off Utilizing a Host with Small Singlet-Triplet Splitting.

PubMed

Zhang, Dongdong; Zhao, Chongguang; Zhang, Yunge; Song, Xiaozeng; Wei, Pengcheng; Cai, Minghan; Duan, Lian

2017-02-08

Numerous efforts have been devoted to boost the efficiency of thermally activated delayed fluorescence (TADF) devices; however, strategies to suppress the device efficiency roll-off are still in urgent need. Here, a general and effective approach to suppress the efficiency roll-off of TADF devices is proposed, that is, utilizing TADF materials as the hosts for TADF emitters. Bearing small singlet-triplet splitting (ΔE ST ) with donor and acceptor units, TADF materials as the hosts possess the potential to achieve matched frontier energy levels with the adjacent transporting layers, facilitating balanced charge injection as well as bipolar charge transport mobilities beneficial to the balanced charges transportation. Furthermore, an enhanced Förster energy transfer from the host to the dopant can be anticipated, helpful to reduce the exciton concentration. Based on the principles, a new TADF material based on indeno[2,1-b]carbazole/1,3,5-triazin derivation is synthesized and used as the universal host for the full-color TADF devices. Remarkable low efficiency roll-off was achieved with above 90% of the maximum external quantum efficiencies (EQE max 's) maintained even at a brightness of 2000 cd/m 2 , along with EQE max 's of 23.2, 21.0, and 19.2% for orange, green, and sky-blue TADF devices, respectively. Through computational simulation, we identified the suppressed exciton annihilation rates compared with devices adopting conventional hosts. The state-of-the-art low efficiency roll-off of those TADF devices manifests the great potential of such host design strategy, paving an efficient strategy toward their practical application.

High-efficiency piezoelectric micro harvester for collecting low-frequency mechanical energy.

PubMed

Li, Xin; Song, Jinhui; Feng, Shuanglong; Xie, Xiong; Li, Zhenhu; Wang, Liang; Pu, Yayun; Soh, Ai Kah; Shen, Jun; Lu, Wenqiang; Liu, Shuangyi

2016-12-02

A single-layer zinc oxide (ZnO) nanorod array-based micro energy harvester was designed and integrated with a piezoelectric metacapacitor. The device presents outstanding low-frequency (1-10 Hz) mechanical energy harvesting capabilities. When compared with conventional pristine ZnO nanostructured piezoelectric harvesters or generators, both open-circuit potential and short-circuit current are significantly enhanced (up to 3.1 V and 124 nA cm -2 ) for a single mechanical knock (∼34 kPa). Higher electromechanical conversion efficiency (1.3 pC/Pa) is also observed. The results indicate that the integration of the piezoelectric metacapacitor is a crucial factor for improving the low-frequency energy harvesting performance. A double piezoelectric-driven mechanism is proposed to explain current higher output power, in which the metacapacitor plays the multiple roles of charge pumping, storing and transferring. An as-fabricated prototype device for lighting an LED demonstrates high power transference capability, with over 95% transference efficiency to the external load.

Local light-induced magnetization using nanodots and chiral molecules.

PubMed

Dor, Oren Ben; Morali, Noam; Yochelis, Shira; Baczewski, Lech Tomasz; Paltiel, Yossi

2014-11-12

With the increasing demand for miniaturization, nanostructures are likely to become the primary components of future integrated circuits. Different approaches are being pursued toward achieving efficient electronics, among which are spin electronics devices (spintronics). In principle, the application of spintronics should result in reducing the power consumption of electronic devices. Recently a new, promising, effective approach for spintronics has emerged, using spin selectivity in electron transport through chiral molecules. In this work, using chiral molecules and nanocrystals, we achieve local spin-based magnetization generated optically at ambient temperatures. Through the chiral layer, a spin torque can be transferred without permanent charge transfer from the nanocrystals to a thin ferromagnetic layer, creating local perpendicular magnetization. We used Hall sensor configuration and atomic force microscopy (AFM) to measure the induced local magnetization. At low temperatures, anomalous spin Hall effects were measured using a thin Ni layer. The results may lead to optically controlled spintronics logic devices that will enable low power consumption, high density, and cheap fabrication.

Engineering Topological Surface State of Cr-doped Bi2Se3 under external electric field

NASA Astrophysics Data System (ADS)

Zhang, Jian-Min; Lian, Ruqian; Yang, Yanmin; Xu, Guigui; Zhong, Kehua; Huang, Zhigao

2017-03-01

External electric field control of topological surface states (SSs) is significant for the next generation of condensed matter research and topological quantum devices. Here, we present a first-principles study of the SSs in the magnetic topological insulator (MTI) Cr-doped Bi2Se3 under external electric field. The charge transfer, electric potential, band structure and magnetism of the pure and Cr doped Bi2Se3 film have been investigated. It is found that the competition between charge transfer and spin-orbit coupling (SOC) will lead to an electrically tunable band gap in Bi2Se3 film under external electric field. As Cr atom doped, the charge transfer of Bi2Se3 film under external electric field obviously decreases. Remarkably, the band gap of Cr doped Bi2Se3 film can be greatly engineered by the external electric field due to its special band structure. Furthermore, magnetic coupling of Cr-doped Bi2Se3 could be even mediated via the control of electric field. It is demonstrated that external electric field plays an important role on the electronic and magnetic properties of Cr-doped Bi2Se3 film. Our results may promote the development of electronic and spintronic applications of magnetic topological insulator.

Effects of Magnetic Nanoparticles and External Magnetostatic Field on the Bulk Heterojunction Polymer Solar Cells

DOE PAGES

Wang, Kai; Yi, Chao; Liu, Chang; ...

2015-03-18

The price of energy to separate tightly bound electron-hole pair (or charge-transfer state) and extract freely movable charges from low-mobility materials represents fundamental losses for many low-cost photovoltaic devices. In bulk heterojunction (BHJ) polymer solar cells (PSCs), approximately 50% of the total efficiency lost among all energy loss pathways is due to the photogenerated charge carrier recombination within PSCs and low charge carrier mobility of disordered organic materials. To address these issues, we introduce magnetic nanoparticles (MNPs) and orientate these MNPS within BHJ composite by an external magnetostatic field. Over 50% enhanced efficiency was observed from BHJ PSCs incorporated withmore » MNPs and an external magnetostatic field alignment when compared to the control BHJ PSCs. The optimization of BHJ thin film morphology, suppression of charge carrier recombination, and enhancement in charge carrier collection result in a greatly increased short-circuit current density and fill factor, as a result, enhanced power conversion efficiency.« less

Laser pulse detection method and apparatus

NASA Technical Reports Server (NTRS)

Goss, W.; Janesick, J. R. (Inventor)

1984-01-01

A sensor is described for detecting the difference in phase of a pair of returned light pulse components, such as two components of a light pulse of an optical gyro. In an optic gyro, the two light components have passed in opposite directions through a coil of optical fiber, with the difference in phase of the returned light components determining the intensity of light shining on the sensor. The sensor includes a CCD (charge coupled device) that receives the pair of returned light components to generate a charge proportional to the number of photons in the received light. The amount of the charge represents the phase difference between the two light components. At a time after the transmission of the light pulse and before the expected time of arrival of the interfering light components, charge accumulating in the CCD as a result of reflections from components in the system, are repeatedly removed from the CCD, by transferring out charges in the CCD and dumping these charges.

Effect of Fullerene Passivation on the Charging and Discharging Behavior of Perovskite Solar Cells: Reduction of Bound Charges and Ion Accumulation.

PubMed

Shih, Yen-Chen; Wang, Leeyih; Hsieh, Hsiao-Chi; Lin, King-Fu

2018-04-11

Ion accumulation of organometal halide perovskites (OHPs) induced by electrode polarization of perovskite solar cells (PSCs) under illumination has been intensely studied and associated with a widely observed current-voltage hysteresis behavior. This work is dedicated to the investigation of the behavior of charged species at the compact TiO 2 /OHP interface with respect to electrode polarization in PSC devices. By providing a comprehensive discussion of open-circuit voltage ( V OC ) buildup and V OC decay under illumination and in the dark for the PSCs modified with [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) at the TiO 2 /OHP interface and their corresponding electrochemical impedance spectroscopies (EISs), a justified mechanism is proposed attempting to elucidate the dynamics of interfacial species with respect to the time and frequency domains. Our results demonstrate that the retarded V OC buildup and decay observed in PSC devices are related to the formation of bound charges in TiO 2 , which is essential to neutralize the oppositely charged ions accumulating at the OHP side. Besides, inserting a thicker PCBM at the TiO 2 /OHP interface as a passivation layer can alleviate the electrode polarization more efficiently as verified by the low dielectric constant measured from EIS. Moreover, photoluminescence measurements indicate that PCBM at the TiO 2 /OHP interface is capable of passivating a trap state and improving charge transfer. However, with respect to the time scale investigated in this work, the reduction of the hysteresis behavior on a millisecond scale is more likely due to less bound charge formation at the interface rather than shallow trap-state passivation by PCBM. After all, this work comprehensively demonstrates the interfacial properties of PSCs associated with PCBM passivation and helps to further understand its impact on charging/discharging as well as device performance.

Ultrathin Graphene Membranes as Flexible Electrodes for Electrochemical Double Layer Capacitors

NASA Astrophysics Data System (ADS)

Talapatra, Saikat; Kar, Swastik; Shah, Rakesh; Ghosh, Sujoy; An, Xiaohong; Simmons, Trevor; Washington, Morris; Nayak, Saroj

2010-03-01

We will present the results of our investigations of electrochemical double layer capacitors (EDLCs) or supercapacitors (SC) fabricated using graphene based ultra thin membranes. These EDLC's show far superior performance compared to other carbon nanomaterials based EDLC's devices. We found that the graphene based devices possess specific capacitance values as high as 120 F/g, with impressive power densities (˜105 kW/kg) and energy densities (˜9.2 Wh/kg). Further, these devices indicated rapid charge transfer response even without the use of any binders or specially prepared current collectors. Our ultracapacitors reflect a significant improvement over previously reported graphene-based ultracapacitors and are substantially better than those obtained with carbon nanotubes.

Adsorption of NO2 molecules on armchair phosphorene nanosheet for nano sensor applications - A first-principles study.

PubMed

Nagarajan, V; Chandiramouli, R

2017-08-01

The electronic and NO 2 adsorption properties of hydrogenated armchair phosphorene nanosheet device is investigated through density functional theory (DFT) and non-equilibrium Green's function method (NEGF). The armchair phosphorene nanosheet is used for the detection of NO 2 gas in phosphorene molecular device. The DOS spectrum demonstrates the change in peak maxima due to transfer of electrons between NO 2 gas and phosphorene base material. The change in the peak amplitude is observed along the valance band as well as in the conduction band in the transmission spectrum of phosphorene device. I-V characteristics support the change in the current upon adsorption of NO 2 gas molecule on phosphorene molecular device. Using formation energy, structural stability of phosphorene nanosheet has been studied. The adsorption properties of NO 2 on phosphorene nanosheet have also been investigated with the help of adsorption energy, Mulliken charge and Bader charge analysis. In order to ascertain the selectivity of NO 2 gas along phosphorene molecular device in the ambient condition, the adsorption behavior of O 2 and CO 2 is also studied. The findings of the present work confirm that phosphorene molecular device can be used as a NO 2 gas sensor and also the influence of Al substitution in phosphorene nanosheet device is explored and reported. Copyright © 2017 Elsevier Inc. All rights reserved.

Robust singlet fission in pentacene thin films with tuned charge transfer interactions.

PubMed

Broch, K; Dieterle, J; Branchi, F; Hestand, N J; Olivier, Y; Tamura, H; Cruz, C; Nichols, V M; Hinderhofer, A; Beljonne, D; Spano, F C; Cerullo, G; Bardeen, C J; Schreiber, F

2018-03-05

Singlet fission, the spin-allowed photophysical process converting an excited singlet state into two triplet states, has attracted significant attention for device applications. Research so far has focused mainly on the understanding of singlet fission in pure materials, yet blends offer the promise of a controlled tuning of intermolecular interactions, impacting singlet fission efficiencies. Here we report a study of singlet fission in mixtures of pentacene with weakly interacting spacer molecules. Comparison of experimentally determined stationary optical properties and theoretical calculations indicates a reduction of charge-transfer interactions between pentacene molecules with increasing spacer molecule fraction. Theory predicts that the reduced interactions slow down singlet fission in these blends, but surprisingly we find that singlet fission occurs on a timescale comparable to that in pure crystalline pentacene. We explain the observed robustness of singlet fission in such mixed films by a mechanism of exciton diffusion to hot spots with closer intermolecular spacings.

Phenomenal enhancement of optical nonlinearity in PTZ-I based ZnS/ZnSe nanocomposites

NASA Astrophysics Data System (ADS)

Divyasree, M. C.; Shiju, E.; Vijisha, M. V.; Ramesan, M. T.; Chandrasekharan, K.

2018-05-01

The enhanced nonlinear optical properties of phenothiazine-iodine (PTZ-I) charge transfer complex (CTC) on composite formation with ZnS/ZnSe nanostructures are reported. The interaction between the components was confirmed by the FTIR spectra. Structural and morphological changes on nanocomposite formation were analyzed by scanning electron microscopy and X-ray diffraction spectra. The absorption and emission features of both the nanocomposites and their constituent components were studied. Nonlinear optical properties of all the samples in nanosecond regime were investigated by the Z-scan technique using Nd: YAG laser with 532 nm wavelength and 7 ns pulse width. The optical nonlinearity of PTZ-I CTC was found to be improved considerably on composite formation and the new systems can be proposed as excellent candidates for photonic devices. Enhanced optical nonlinearity of the composites could be attributed to charge/energy transfer mechanism between PTZ-I CTC and the nanostructures.

Peripheral Hole Acceptor Moieties on an Organic Dye Improve Dye‐Sensitized Solar Cell Performance

PubMed Central

Hao, Yan; Gabrielsson, Erik; Lohse, Peter William; Yang, Wenxing; Johansson, Erik M. J.; Hagfeldt, Anders

2015-01-01

Investigation of charge transfer dynamics in dye‐sensitized solar cells is of fundamental interest and the control of these dynamics is a key factor for developing more efficient solar cell devices. One possibility for attenuating losses through recombination between injected electrons and oxidized dye molecules is to move the positive charge further away from the metal oxide surface. For this purpose, a metal‐free dye named E6 is developed, in which the chromophore core is tethered to two external triphenylamine (TPA) units. After photoinduced electron injection into TiO2, the remaining hole is rapidly transferred to a peripheral TPA unit. Electron–hole recombination is slowed down by 30% compared to a reference dye without peripheral TPA units. Furthermore, it is found that the added TPA moieties improve the electron blocking effect of the dye, retarding recombination of electrons from TiO2 to the cobalt‐based electrolyte. PMID:27722076

Investigation of Charge Transfer Kinetics at Carbon/Hydroquinone Interfaces for Redox-Active-Electrolyte Supercapacitors.

PubMed

Park, Jinwoo; Kumar, Vipin; Wang, Xu; Lee, Pooi See; Kim, Woong

2017-10-04

The redox-active electrolyte supercapacitor (RAES) is a relatively new type of energy storage device. Simple addition of selected redox species in the electrolyte can greatly enhance the energy density of supercapacitors relative to traditional electric double layer capacitors (EDLCs) owing to redox reactions. Studies on the kinetics at the interface of the electrode and redox mediator are important when developing RAESs. In this work, we employ highly accurate scanning electrochemical microscopy (SECM) to extract the kinetic constants at carbon/hydroquinone interfaces. The charge transfer rate constants are 1.2 × 10 -2 and 1.3 × 10 -2 cm s -1 for the carbon nanotube/hydroquinone and reduced graphene oxide/hydroquinone interfaces, respectively. These values are higher than those obtained by the conventional cyclic voltammetry method, approximately by an order of magnitude. The evaluation of heterogeneous rate constants with SECM would be the cornerstone for understanding and developing high performance RAESs.

Energy level alignment at planar organic heterojunctions: influence of contact doping and molecular orientation.

PubMed

Opitz, Andreas

2017-04-05

Planar organic heterojunctions are widely used in photovoltaic cells, light-emitting diodes, and bilayer field-effect transistors. The energy level alignment in the devices plays an important role in obtaining the aspired gap arrangement. Additionally, the π-orbital overlap between the involved molecules defines e.g. the charge-separation efficiency in solar cells due to charge-transfer effects. To account for both aspects, direct/inverse photoemission spectroscopy and near edge x-ray absorption fine structure spectroscopy were used to determine the energy level landscape and the molecular orientation at prototypical planar organic heterojunctions. The combined experimental approach results in a comprehensive model for the electronic and morphological characteristics of the interface between the two investigated molecular semiconductors. Following an introduction on heterojunctions used in devices and on energy levels of organic materials, the energy level alignment of planar organic heterojunctions will be discussed. The observed energy landscape is always determined by the individual arrangement between the energy levels of the molecules and the work function of the electrode. This might result in contact doping due to Fermi level pinning at the electrode for donor/acceptor heterojunctions, which also improves the solar cell efficiency. This pinning behaviour can be observed across an unpinned interlayer and results in charge accumulation at the donor/acceptor interface, depending on the transport levels of the respective organic semiconductors. Moreover, molecular orientation will affect the energy levels because of the anisotropy in ionisation energy and electron affinity and is influenced by the structural compatibility of the involved molecules at the heterojunction. High structural compatibility leads to π-orbital stacking between different molecules at a heterojunction, which is of additional interest for photovoltaic active interfaces and for ground-state charge-transfer.

Supplying the power requirements to a sensor network using radio frequency power transfer.

PubMed

Percy, Steven; Knight, Chris; Cooray, Francis; Smart, Ken

2012-01-01

Wireless power transmission is a method of supplying power to small electronic devices when there is no wired connection. One way to increase the range of these systems is to use a directional transmitting antenna, the problem with this approach is that power can only be transmitted through a narrow beam and directly forward, requiring the transmitter to always be aligned with the sensor node position. The work outlined in this article describes the design and testing of an autonomous radio frequency power transfer system that is capable of rotating the base transmitter to track the position of sensor nodes and transferring power to that sensor node. The system's base station monitors the node's energy levels and forms a charge queue to plan charging order and maintain energy levels of the nodes. Results show a radio frequency harvesting circuit with a measured S11 value of -31.5 dB and a conversion efficiency of 39.1%. Simulation and experimentation verified the level of power transfer and efficiency. The results of this work show a small network of three nodes with different storage types powered by a central base node.

Exciton size and binding energy limitations in one-dimensional organic materials.

PubMed

Kraner, S; Scholz, R; Plasser, F; Koerner, C; Leo, K

2015-12-28

In current organic photovoltaic devices, the loss in energy caused by the charge transfer step necessary for exciton dissociation leads to a low open circuit voltage, being one of the main reasons for rather low power conversion efficiencies. A possible approach to avoid these losses is to tune the exciton binding energy to a value of the order of thermal energy, which would lead to free charges upon absorption of a photon, and therefore increase the power conversion efficiency towards the Shockley-Queisser limit. We determine the size of the excitons for different organic molecules and polymers by time dependent density functional theory calculations. For optically relevant transitions, the exciton size saturates around 0.7 nm for one-dimensional molecules with a size longer than about 4 nm. For the ladder-type polymer poly(benzimidazobenzophenanthroline), we obtain an exciton binding energy of about 0.3 eV, serving as a lower limit of the exciton binding energy for the organic materials investigated. Furthermore, we show that charge transfer transitions increase the exciton size and thus identify possible routes towards a further decrease of the exciton binding energy.

Boosting surface charge-transfer doping efficiency and robustness of diamond with WO3 and ReO3

NASA Astrophysics Data System (ADS)

Tordjman, Moshe; Weinfeld, Kamira; Kalish, Rafi

2017-09-01

An advanced charge-transfer yield is demonstrated by employing single monolayers of transition-metal oxides—tungsten trioxide (WO3) and rhenium trioxide (ReO3)—deposited on the hydrogenated diamond surface, resulting in improved p-type sheet conductivity and thermal stability. Surface conductivities, as determined by Hall effect measurements as a function of temperature for WO3, yield a record sheet hole carrier concentration value of up to 2.52 × 1014 cm-2 at room temperature for only a few monolayers of coverage. Transfer doping with ReO3 exhibits a consistent narrow sheet carrier concentration value of around 3 × 1013 cm-2, exhibiting a thermal stability of up to 450 °C. This enhanced conductivity and temperature robustness exceed those reported for previously exposed surface electron acceptor materials used so far on a diamond surface. X-ray photoelectron spectroscopy measurements of the C1s core level shift as a function of WO3 and ReO3 layer thicknesses are used to determine the respective increase in surface band bending of the accumulation layers, leading to a different sub-surface two-dimensional hole gas formation efficiency in both cases. This substantial difference in charge-exchange efficiency is unexpected since both surface acceptors have very close work functions. Consequently, these results lead us to consider additional factors influencing the transfer doping mechanism. Transfer doping with WO3 reveals the highest yet reported transfer doping efficiency per minimal surface acceptor coverage. This improved surface conductivity performance and thermal stability will promote the realization of 2D diamond-based electronic devices facing process fabrication challenges.

RF Power Transfer, Energy Harvesting, and Power Management Strategies

NASA Astrophysics Data System (ADS)

Abouzied, Mohamed Ali Mohamed

Energy harvesting is the way to capture green energy. This can be thought of as a recycling process where energy is converted from one form (here, non-electrical) to another (here, electrical). This is done on the large energy scale as well as low energy scale. The former can enable sustainable operation of facilities, while the latter can have a significant impact on the problems of energy constrained portable applications. Different energy sources can be complementary to one another and combining multiple-source is of great importance. In particular, RF energy harvesting is a natural choice for the portable applications. There are many advantages, such as cordless operation and light-weight. Moreover, the needed infra-structure can possibly be incorporated with wearable and portable devices. RF energy harvesting is an enabling key player for Internet of Things technology. The RF energy harvesting systems consist of external antennas, LC matching networks, RF rectifiers for ac to dc conversion, and sometimes power management. Moreover, combining different energy harvesting sources is essential for robustness and sustainability. Wireless power transfer has recently been applied for battery charging of portable devices. This charging process impacts the daily experience of every human who uses electronic applications. Instead of having many types of cumbersome cords and many different standards while the users are responsible to connect periodically to ac outlets, the new approach is to have the transmitters ready in the near region and can transfer power wirelessly to the devices whenever needed. Wireless power transfer consists of a dc to ac conversion transmitter, coupled inductors between transmitter and receiver, and an ac to dc conversion receiver. Alternative far field operation is still tested for health issues. So, the focus in this study is on near field. The goals of this study are to investigate the possibilities of RF energy harvesting from various sources in the far field, dc energy combining, wireless power transfer in the near field, the underlying power management strategies, and the integration on silicon. This integration is the ultimate goal for cheap solutions to enable the technology for broader use. All systems were designed, implemented and tested to demonstrate proof-of concept prototypes.

Applications of Charge Transfer Devices in Spectroscopy.

DTIC Science & Technology

1988-02-04

Langmuir - Blodgett films deposited on glass and silicon substrates. A direct comparison by Pemberton and Sobocinski (18) of the Raman spectra obtained...wavelength. The measurements are then repeated with an uncoated sheet of poly - ester serving as the reference blank. The double monochromator...give the best sensitivity at trace concentration levels. The less intense lines resulting from non-reson- -’ ance and ionic transitions are used for

Wireless power transfer for a pacemaker application.

PubMed

Vulfin, Vladimir; Sayfan-Altman, Shai; Ianconescu, Reuven

2017-05-01

An artificial pacemaker is a small medical device that uses electrical impulses, delivered by electrodes contracting the heart muscles, to regulate the beating of the heart. The pacemaker is implanted under the skin, and uses for many years regular non-rechargeable batteries. However, the demand for rechargeable batteries in pacemakers increased, and the aim of this work is to design an efficient charging system for pacemakers.

Comparing simulations and test data of a radiation damaged charge-coupled device for the Euclid mission

NASA Astrophysics Data System (ADS)

Skottfelt, Jesper; Hall, David J.; Gow, Jason P. D.; Murray, Neil J.; Holland, Andrew D.; Prod'homme, Thibaut

2017-04-01

The visible imager instrument on board the Euclid mission is a weak-lensing experiment that depends on very precise shape measurements of distant galaxies obtained by a large charge-coupled device (CCD) array. Due to the harsh radiative environment outside the Earth's atmosphere, it is anticipated that the CCDs over the mission lifetime will be degraded to an extent that these measurements will be possible only through the correction of radiation damage effects. We have therefore created a Monte Carlo model that simulates the physical processes taking place when transferring signals through a radiation-damaged CCD. The software is based on Shockley-Read-Hall theory and is made to mimic the physical properties in the CCD as closely as possible. The code runs on a single electrode level and takes the three-dimensional trap position, potential structure of the pixel, and multilevel clocking into account. A key element of the model is that it also takes device specific simulations of electron density as a direct input, thereby avoiding making any analytical assumptions about the size and density of the charge cloud. This paper illustrates how test data and simulated data can be compared in order to further our understanding of the positions and properties of the individual radiation-induced traps.

Optimizing low-light microscopy with back-illuminated electron multiplying charge-coupled device: enhanced sensitivity, speed, and resolution.

PubMed

Coates, Colin G; Denvir, Donal J; McHale, Noel G; Thornbury, Keith D; Hollywood, Mark A

2004-01-01

The back-illuminated electron multiplying charge-coupled device (EMCCD) camera is having a profound influence on the field of low-light dynamic cellular microscopy, combining highest possible photon collection efficiency with the ability to virtually eliminate the readout noise detection limit. We report here the use of this camera, in 512 x 512 frame-transfer chip format at 10-MHz pixel readout speed, in optimizing a demanding ultra-low-light intracellular calcium flux microscopy setup. The arrangement employed includes a spinning confocal Nipkow disk, which, while facilitating the need to both generate images at very rapid frame rates and minimize background photons, yields very weak signals. The challenge for the camera lies not just in detecting as many of these scarce photons as possible, but also in operating at a frame rate that meets the temporal resolution requirements of many low-light microscopy approaches, a particular demand of smooth muscle calcium flux microscopy. Results presented illustrate both the significant sensitivity improvement offered by this technology over the previous standard in ultra-low-light CCD detection, the GenIII+intensified charge-coupled device (ICCD), and also portray the advanced temporal and spatial resolution capabilities of the EMCCD. Copyright 2004 Society of Photo-Optical Instrumentation Engineers.

Charge versus Energy Transfer Effects in High-Performance Perylene Diimide Photovoltaic Blend Films.

PubMed

Singh, Ranbir; Shivanna, Ravichandran; Iosifidis, Agathaggelos; Butt, Hans-Jürgen; Floudas, George; Narayan, K S; Keivanidis, Panagiotis E

2015-11-11

Perylene diimide (PDI)-based organic photovoltaic devices can potentially deliver high power conversion efficiency values provided the photon energy absorbed is utilized efficiently in charge transfer (CT) reactions instead of being consumed in nonradiative energy transfer (ET) steps. Hitherto, it remains unclear whether ET or CT primarily drives the photoluminescence (PL) quenching of the PDI excimer state in PDI-based blend films. Here, we affirm the key role of the thermally assisted PDI excimer diffusion and subsequent CT reaction in the process of PDI excimer PL deactivation. For our study we perform PL quenching experiments in the model PDI-based composite made of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2-6-diyl] (PBDTTT-CT) polymeric donor mixed with the N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (PDI) acceptor. Despite the strong spectral overlap between the PDI excimer PL emission and UV-vis absorption of PBDTTT-CT, two main observations indicate that no significant ET component operates in the overall PL quenching: the PL intensity of the PDI excimer (i) increases with decreasing temperature and (ii) remains unaffected even in the presence of 10 wt % content of the PBDTTT-CT quencher. Temperature-dependent wide-angle X-ray scattering experiments further indicate that nonradiative resonance ET is highly improbable due to the large size of PDI domains. The dominance of the CT over the ET process is verified by the high performance of devices with an optimum composition of 30:70 PBDTTT-CT:PDI. By adding 0.4 vol % of 1,8-diiodooctane we verify the plasticization of the polymer side chains that balances the charge transport properties of the PBDTTT-CT:PDI composite and results in additional improvement in the device efficiency. The temperature-dependent spectral width of the PDI excimer PL band suggests the presence of energetic disorder in the PDI excimer excited state manifold.

Experimental Study of RF Energy Transfer System in Indoor Environment

NASA Astrophysics Data System (ADS)

Adami, S.-E.; Proynov, P. P.; Stark, B. H.; Hilton, G. S.; Craddock, I. J.

2014-11-01

This paper presents a multi-transmitter, 2.43 GHz Radio-Frequency (RF) wireless power transfer (WPT) system for powering on-body devices. It is shown that under typical indoor conditions, the received power range spans several orders of magnitude from microwatts to milliwatts. A body-worn dual-polarised rectenna (rectifying antenna) is presented, designed for situations where the dominant polarization is unpredictable, as is the case for the on-body sensors. Power management circuitry is demonstrated that optimally loads the rectenna even under highly intermittent conditions, and boosts the voltage to charge an on-board storage capacitor.

Molecular Strategies for Morphology Control in Semiconducting Polymers for Optoelectronics.

PubMed

Rahmanudin, Aiman; Sivula, Kevin

2017-06-28

Solution-processable semiconducting polymers have been explored over the last decades for their potential applications in inexpensively fabricated transistors, diodes and photovoltaic cells. However, a remaining challenge in the field is to control the solid-state self-assembly of polymer chains in thin films devices, as the aspects of (semi)crystallinity, grain boundaries, and chain entanglement can drastically affect intra-and inter-molecular charge transport/transfer and thus device performance. In this short review we examine how the aspects of molecular weight and chain rigidity affect solid-state self-assembly and highlight molecular engineering strategies to tune thin film morphology. Side chain engineering, flexibly linking conjugation segments, and block co-polymer strategies are specifically discussed with respect to their effect on field effect charge carrier mobility in transistors and power conversion efficiency in solar cells. Example systems are taken from recent literature including work from our laboratories to illustrate the potential of molecular engineering semiconducting polymers.

Charge transfer in TATB and HMX under extreme conditions.

PubMed

Zhang, Chaoyang; Ma, Yu; Jiang, Daojian

2012-11-01

Charge transfer is usually accompanied by structural changes in materials under different conditions. However, the charge transfer in energetic materials that are subjected to extreme conditions has seldom been explored by researchers. In the work described here, the charge transfer in single molecules and unit cells of the explosives TATB and HMX under high temperatures and high pressures was investigated by performing static and dynamic calculations using three DFT methods, including the PWC functional of LDA, and the BLYP and PBE functionals of GGA. The results showed that negative charge is transferred from the nitro groups of molecular or crystalline TATB and HMX when they are heated. All DFT calculations for the compressed TATB unit cell indicate that, generally, negative charge transfer occurs to its nitro groups as the compression increases. PWC and PBE calculations for crystalline HMX show that negative charge is first transferred to the nitro groups but, as the compression increases, the negative charge is transferred from the nitro groups. However, the BLYP calculations indicated that there was gradual negative charge transfer to the nitro groups of HMX, similar to the case for TATB. The unrelaxed state of the uniformly compressed TATB causes negative charge to be transferred from its nitro groups, in contrast to what is seen in the relaxed state. Charge transfer in TATB is predicted to occur much more easily than in HMX.

The effect of structural changes on charge transfer states in a light-harvesting carotenoid-diaryl-porphyrin-C{sub 60} molecular triad

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olguin, Marco; Basurto, Luis; Zope, Rajendra R.

We present a detailed study of charge transfer (CT) excited states for a large number of configurations in a light-harvesting Carotenoid-diaryl-Porphyrin-C{sub 60} (CPC{sub 60}) molecular triad. The chain-like molecular triad undergoes photoinduced charge transfer process exhibiting a large excited state dipole moment, making it suitable for application to molecular-scale opto-electronic devices. An important consideration is that the structural flexibility of the CPC{sub 60} triad impacts its dynamics in solvents. Since experimentally measured dipole moments for the triad of ∼110 D and ∼160 D strongly indicate a range in structural variability in the excited state, studying the effect of structural changesmore » on the CT excited state energetics furthers the understanding of its charge transfer states. We have calculated the variation in the lowest CT excited state energies by performing a scan of possible variation in the structure of the triad. Some of these configurations were generated by incrementally scanning a 360° torsional (dihedral) twist at the C{sub 60}-porhyrin linkage and the porphyrin-carotenoid linkage. Additionally, five different CPC{sub 60} conformations were studied to determine the effect of pi-conjugation and particle-hole Coulombic attraction on the CT excitation energies. Our calculations show that configurational changes in the triad induces a variation of ∼0.6 eV in CT excited state energies in the gas-phase. The corresponding calculated excited state dipoles show a range of 47 D–188 D. The absorption spectra and density of states of these structures show little variation except for the structures where the porphyrin and aryl conjugation is changed.« less

First-principles calculation of photo-induced electron transfer rate constants in phthalocyanine-C60 organic photovoltaic materials: Beyond Marcus theory

NASA Astrophysics Data System (ADS)

Lee, Myeong H.; Dunietz, Barry D.; Geva, Eitan

2014-03-01

Classical Marcus theory is commonly adopted in solvent-mediated charge transfer (CT) process to obtain the CT rate constant, but it can become questionable when the intramolecular vibrational modes dominate the CT process as in OPV devices because Marcus theory treats these modes classically and therefore nuclear tunneling is not accounted for. We present a computational scheme to obtain the electron transfer rate constant beyond classical Marcus theory. Within this approach, the nuclear vibrational modes are treated quantum-mechanically and a short-time approximation is avoided. Ab initio calculations are used to obtain the basic parameters needed for calculating the electron transfer rate constant. We apply our methodology to phthalocyanine(H2PC)-C60 organic photovoltaic system where one C60 acceptor and one or two H2PC donors are included to model the donor-acceptor interface configuration. We obtain the electron transfer and recombination rate constants for all accessible charge transfer (CT) states, from which the CT exciton dynamics is determined by employing a master equation. The role of higher lying excited states in CT exciton dynamics is discussed. This work is pursued as part of the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the US Department of Energy Office of Science, Office of Basic Energy Sciences under 390 Award No. DE-SC0000957.

Modeling the impact of preflushing on CTE in proton irradiated CCD-based detectors

NASA Astrophysics Data System (ADS)

Philbrick, R. H.

2002-04-01

A software model is described that performs a "real world" simulation of the operation of several types of charge-coupled device (CCD)-based detectors in order to accurately predict the impact that high-energy proton radiation has on image distortion and modulation transfer function (MTF). The model was written primarily to predict the effectiveness of vertical preflushing on the custom full frame CCD-based detectors intended for use on the proposed Kepler Discovery mission, but it is capable of simulating many other types of CCD detectors and operating modes as well. The model keeps track of the occupancy of all phosphorous-silicon (P-V), divacancy (V-V) and oxygen-silicon (O-V) defect centers under every CCD electrode over the entire detector area. The integrated image is read out by simulating every electrode-to-electrode charge transfer in both the vertical and horizontal CCD registers. A signal level dependency on the capture and emission of signal is included and the current state of each electrode (e.g., barrier or storage) is considered when distributing integrated and emitted signal. Options for performing preflushing, preflashing, and including mini-channels are available on both the vertical and horizontal CCD registers. In addition, dark signal generation and image transfer smear can be selectively enabled or disabled. A comparison of the charge transfer efficiency (CTE) data measured on the Hubble space telescope imaging spectrometer (STIS) CCD with the CTE extracted from model simulations of the STIS CCD show good agreement.

The Physical Electronics of Graphene on Germanium

NASA Astrophysics Data System (ADS)

Rojas Delgado, Richard

The properties of graphene make it an outstanding candidate for electronic-device applications, especially those that require no band gap but a high conductance. The conductance, involving both carrier mobility and carrier concentration, will depend critically on the substrate to which graphene is transferred. I demonstrate an exceptionally high conductance in graphene transferred to Ge(001) and provide an understanding of the mechanism. Essential in this understanding is an interfacial chemistry consisting of Ge oxide and suboxide layers that provide the necessary charges to dope the graphene sheet, and whose chemical behavior is such that one can obtain long-term stability in the conductance. In contrast, when high-quality graphene is grown directly on Ge (100), (111), or (110), the conductance is unexceptional, but oxidation of the surface is significantly delayed and slowed, relative to both clean Ge and Ge with graphene transferred to its surface. [2,3] I fabricate Hall bars in graphene transferred to Ge(001) and graphene grown on Ge(001) using atmospheric-pressure chemical vapor deposition (CVD) with methane precursors, and measure the sheet resistance and Hall effect from 300K to 10K. Values of mobility and carrier concentration are extracted. I obtain the highest combination of mobility and carrier concentration yet reported in graphene (suspended or supported) for temperatures from 10 to 300K. The implication is that the primary mechanisms for scattering charge in the graphene, roughness and a non-uniform electrostatic potential due to fixed charges, have limited effect when the substrate is oxidized Ge.

Universal Strategy To Reduce Noise Current for Sensitive Organic Photodetectors.

PubMed

Xiong, Sixing; Li, Lingliang; Qin, Fei; Mao, Lin; Luo, Bangwu; Jiang, Youyu; Li, Zaifang; Huang, Jinsong; Zhou, Yinhua

2017-03-15

Low noise current is critical for achieving high-detectivity organic photodetectors. Inserting charge-blocking layers is an effective approach to suppress the reverse-biased dark current. However, in solution-processed organic photodetectors, the charge-transport material needs to be dissolved in solvents that do not dissolve the underneath light-absorbing layer, which is not always possible for all kinds of light-absorbing materials developed. Here, we introduce a universal strategy of transfer-printing a conjugated polymer, poly(3-hexylthiophene) (P3HT), as the electron-blocking layer to realize highly sensitive photodetectors. The transfer-printed P3HT layers substantially and universally reduced the reverse-biased dark current by about 3 orders of magnitude for various photodetectors with different active layers. These photodetectors can detect the light signal as weak as several picowatts per square centimeter, and the device detectivity is over 10 12 Jones. The results suggest that the strategy of transfer-printing P3HT films as the electron-blocking layer is universal and effective for the fabrication of sensitive organic photodetectors.

Electroactive SWNT/PEGDA hybrid hydrogel coating for bio-electrode interface.

PubMed

He, Lei; Lin, Demeng; Wang, Yanping; Xiao, Yinghong; Che, Jianfei

2011-10-15

Electric interface between neural tissue and electrode plays a significant role in the development of implanted devices for continuous monitoring and functional stimulation of central nervous system in terms of electroactivity, biocompatibility and long-term stability. To engineer an interface that possesses these merits, a polymeric hydrogel based on poly(ethylene glycol) diacrylate (PEGDA) and single-walled carbon nanotubes (SWNTs) were employed to fabricate a hybrid hydrogel via covalent anchoring strategy, i.e., self-assembly of cysteamine (Cys) followed by Michael addition between Cys and PEGDA. XPS characterization proves that the Cys molecules are linked to gold surface via the strong S-Au bond and that the PEGDA macromers are covalently bonded to Cys. FTIR spectra indicate the formation of hybrid hydrogel coating during photopolymerization. Electrochemical measurements using cyclic voltammetry (CV) and impedance spectrum clearly show the enhancement of electric properties to the hydrogel by the SWNTs. The charge transfer of the hybrid hydrogel-based electrode is quasi-reversible and charge transfer resistance decreases to the tenth of that of the pure hydrogel due to electron hopping along the SWNTs. Additionally, this hybrid hydrogel provides a favorable biomimetic microenvironment for cell attachment and growth due to its inherent biocompatibility. Combination of these merits yields hybrid hydrogels that can be good candidates for application to biosensors and biomedical devices. More importantly, the hybrid hydrogel coatings fabricated via the current strategy have good adhesion to the electrode substrate which is highly desired for chronically implantable devices. Copyright © 2011 Elsevier B.V. All rights reserved.

Comparison of trapped charges and hysteresis behavior in hBN encapsulated single MoS2 flake based field effect transistors on SiO2 and hBN substrates.

PubMed

Lee, Changhee; Rathi, Servin; Khan, Muhammad Atif; Lim, Dongsuk; Kim, Yunseob; Yun, Sun Jin; Youn, Doo-Hyeb; Watanabe, Kenji; Taniguchi, Takashi; Kim, Gil-Ho

2018-08-17

Molybdenum disulfide (MoS 2 ) based field effect transistors (FETs) are of considerable interest in electronic and opto-electronic applications but often have large hysteresis and threshold voltage instabilities. In this study, by using advanced transfer techniques, hexagonal boron nitride (hBN) encapsulated FETs based on a single, homogeneous and atomic-thin MoS 2 flake are fabricated on hBN and SiO 2 substrates. This allows for a better and a precise comparison between the charge traps at the semiconductor-dielectric interfaces at MoS 2 -SiO 2 and hBN interfaces. The impact of ambient environment and entities on hysteresis is minimized by encapsulating the active MoS 2 layer with a single hBN on both the devices. The device to device variations induced by different MoS 2 layer is also eliminated by employing a single MoS 2 layer for fabricating both devices. After eliminating these additional factors which induce variation in the device characteristics, it is found from the measurements that the trapped charge density is reduced to 1.9 × 10 11 cm -2 on hBN substrate as compared to 1.1 × 10 12 cm -2 on SiO 2 substrate. Further, reduced hysteresis and stable threshold voltage are observed on hBN substrate and their dependence on gate sweep rate, sweep range, and gate stress is also studied. This precise comparison between encapsulated devices on SiO 2 and hBN substrates further demonstrate the requirement of hBN substrate and encapsulation for improved and stable performance of MoS 2 FETs.

High-potential perfluorinated phthalocyanine-fullerene dyads for generation of high-energy charge-separated states: formation and photoinduced electron-transfer studies.

PubMed

Das, Sushanta K; Mahler, Andrew; Wilson, Angela K; D'Souza, Francis

2014-08-25

High oxidation potential perfluorinated zinc phthalocyanines (ZnF(n)Pcs) are synthesised and their spectroscopic, redox, and light-induced electron-transfer properties investigated systematically by forming donor-acceptor dyads through metal-ligand axial coordination of fullerene (C60) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine- (Py) and phenylimidazole-functionalised fullerene (C60Im) derivatives to the zinc centre of the F(n)Pcs. The determined binding constants, K, in o-dichlorobenzene for the 1:1 complexes are in the order of 10(4) to 10(5) M(-1); nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6-31G* method. The HOMO and LUMO levels are located on the Pc and C60 entities, respectively; this suggests the formation of ZnF(n)Pc(.+)-C60Im(.-) and ZnF(n)Pc(.+)-C60Py(.-) (n=0, 8 or 16) intra-supramolecular charge-separated states during electron transfer. Electrochemical studies on the ZnPc-C60 dyads enable accurate determination of their oxidation and reduction potentials and the energy of the charge-separated states. The energy of the charge-separated state for dyads composed of ZnF(n)Pc is higher than that of normal ZnPc-C60 dyads and reveals their significance in harvesting higher amounts of light energy. Evidence for charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast charge separation and charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar-energy harvesting and optoelectronic device building applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermal emission from large area chemical vapor deposited graphene devices

NASA Astrophysics Data System (ADS)

Luxmoore, I. J.; Adlem, C.; Poole, T.; Lawton, L. M.; Mahlmeister, N. H.; Nash, G. R.

2013-09-01

The spatial variation of thermal emission from large area graphene grown by chemical vapor deposition, transferred onto SiO2/Si substrates and fabricated into field effect transistor structures, has been investigated using infra-red microscopy. A peak in thermal emission occurs, the position of which can be altered by reversal of the current direction. The experimental results are compared with a one dimensional finite element model, which accounts for Joule heating and electrostatic effects, and it is found that the thermal emission is governed by the charge distribution in the graphene and maximum Joule heating occurs at the point of minimum charge density.

Activation of molecular catalysts using semiconductor quantum dots

DOEpatents

Meyer, Thomas J [Chapel Hill, NC; Sykora, Milan [Los Alamos, NM; Klimov, Victor I [Los Alamos, NM

2011-10-04

Photocatalytic materials based on coupling of semiconductor nanocrystalline quantum dots (NQD) and molecular catalysts. These materials have capability to drive or catalyze non-spontaneous chemical reactions in the presence of visible radiation, ultraviolet radiation, or both. The NQD functions in these materials as a light absorber and charge generator. Following light absorption, the NQD activates a molecular catalyst adsorbed on the surface of the NQD via transfer of one or more charges (either electrons or electron-holes) from the NQD to the molecular catalyst. The activated molecular catalyst can then drive a chemical reaction. A photoelectrolytic device that includes such photocatalytic materials is also described.

Binder free MnO2/PIn electrode material for supercapacitor application

NASA Astrophysics Data System (ADS)

Purty, B.; Choudhary, R. B.; Kandulna, R.; Singh, R.

2018-05-01

Electrochemically stable MnO2/PIn nanocomposite was synthesized via in-situ chemical oxidative polymerization process. The structural and morphological properties were studied through FTIR and FESEM characterizing techniques. Sphere like PIn and MnO2 nanorods offers interacting surface for charge transfer action. The electrochemical properties were investigated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopic (EIS) techniques. The significant enhancement in capacitance value with 95% coulombic efficiency and relatively low equivalent series resistance (ESR)˜0.4 Ω proved that MnO2/PIn nanocomposite is an excellent performer as an electrode material in the spectrum of supercapcitors and optoelectronic devices.

Hybrid quantum dot-tin disulfide field-effect transistors with improved photocurrent and spectral responsivity

DOE PAGES

Cotlet, Mircea; Huang, Yuan Zang; Chen, Jia -Shiang; ...

2016-03-24

We report an improved photosensitivity in few-layer tin disulfide (SnS 2) field-effect transistors(FETs) following doping with CdSe/ZnS core/shell quantum dots(QDs). The hybrid QD-SnS 2 FET devices achieve more than 500% increase in the photocurrent response compared with the starting SnS 2-only FET device and a spectral responsivity reaching over 650 A/W at 400 nm wavelength. The negligible electrical conductance in a control QD-only FET device suggests that the energy transfer between QDs and SnS 2 is the main mechanism responsible for the sensitization effect, which is consistent with the strong spectral overlap between QDphotoluminescence and SnS 2 optical absorption asmore » well as the large nominal donor-acceptor interspacing between QD core and SnS 2. Furthermore, we also find enhanced charge carrier mobility in hybrid QD-SnS 2 FETs which we attribute to a reduced contact Schottky barrier width due to an elevated background charge carrier density.« less

Effects of Gold Nanoparticles on Pentacene Organic Field-Effect Transistors

NASA Astrophysics Data System (ADS)

Lee, Keanchuan; Weis, Martin; Ou-Yang, Wei; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

2011-04-01

The effect of gold nanoparticles (NPs) on pentacene organic field-effect transistors (OFETs) was being investigated by both DC and AC methods, which are current-voltage (I-V) measurements in steady-state and impedance spectroscopy (IS) respectively. Here poly(vinyl alcohol) (PVA) and PVA blended with Au NPs as composite are spin-coated on SiO2 as gate-insulator for top-contact pentacene OFET. The characteristics of the device were being investigated based on the contact resistance, trapped charges, effective mobility and threshold voltage based on transfer characteristics of OFET. Results revealed that OFET with NPs exhibited larger hysteresis and higher contact resistance at high voltage region. IS measurements were performed and the fitting of results by the Maxwell-Wagner equivalent circuit showed that for device with NPs a series of capacitance and resistance which represents trapping must be introduced in order to have agreeable fitting. The fitting had helped to clarify the reason behind the higher contact resistance and bigger hysteresis which was mainly caused by the space charge field formed by the traps when Au NPs were introduced into the device.

Proton radiation damage assessment of a CCD for use in a Ultraviolet and Visible Spectrometer

NASA Astrophysics Data System (ADS)

Gow, J. P. D.; Mason, J.; Leese, M.; Hathi, B.; Patel, M.

2017-01-01

This paper describes the radiation environment and radiation damage analysis performed for the Nadir and Occultation for MArs Discovery (NOMAD) Ultraviolet and Visible Spectrometer (UVIS) channel launched onboard the ExoMars Trace Gas Orbiter (TGO) in 2016. The aim of the instrument is to map the temporal and spatial variation of trace gases such as ozone and dust/cloud aerosols in the atmosphere of Mars. The instrument consists of a set of two miniature telescope viewing optics which allow for selective input onto the optical bench, where an e2v technologies CCD30-11 will be used as the detector. A Geometry Description Markup Language model of the spacecraft and instrument box was created and through the use of ESA's SPace ENVironment Information System (SPENVIS) an estimate of the 10 MeV equivalent proton fluence was made at a number of radiation sensitive regions within NOMAD, including that of the CCD30-11 which is the focus of this paper. The end of life 10 MeV equivalent proton fluence at the charge coupled device was estimated to be 4.7 × 109 protons.cm-2 three devices were irradiated at different levels up a 10 MeV equivalent fluence of 9.4 × 109 protons.cm-2. The dark current, charge transfer inefficiency, charge storage, and cosmetic quality of the devices was investigated pre- and post-irradiation, determining that the devices will continue to provide excellent science throughout the mission.

Dynamics of charge-transfer excitons in type-II semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Stein, M.; Lammers, C.; Richter, P.-H.; Fuchs, C.; Stolz, W.; Koch, M.; Vänskä, O.; Weseloh, M. J.; Kira, M.; Koch, S. W.

2018-03-01

The formation, decay, and coherence properties of charge-transfer excitons in semiconductor heterostructures are investigated by applying four-wave-mixing and terahertz spectroscopy in combination with a predictive microscopic theory. A charge-transfer process is identified where the optically induced coherences decay directly into a charge-transfer electron-hole plasma and exciton states. It is shown that charge-transfer excitons are more sensitive to the fermionic electron-hole substructure than regular excitons.

Carbon materials for enhancing charge transport in the advancements of perovskite solar cells

NASA Astrophysics Data System (ADS)

Hu, Ruiyuan; Chu, Liang; Zhang, Jian; Li, Xing'ao; Huang, Wei

2017-09-01

Organic-inorganic halide perovskite solar cells (PSCs) have become a new favorite in the photovoltaic field, due to the boosted efficiency up to 22.1%. Despite a flow of achievements, there are certain challenges to simultaneously meet high efficiency, large scale, low cost and high stability. Due to the low cost, extensive sources, high electrical conductivity and chemical stability, carbon materials have made undeniable contributions to play positive roles in developing PSCs. Carbon materials not only have the favorable conductivity but also bipolar advantage, which can transfer both electrons and holes. In this review, we will discuss how the carbon materials transfer charge or accelerate charge transport by incorporation in PSCs. Carbon materials can replace transparent conductive oxide layers, and enhance electron transport in electron transport layers. Moreover, carbon materials with continuous structure, especially carbon nanotubes and graphene, can provide direct charge transport channel that make them suitable additives or even substitutes in hole transport layers. Especially, the successful application of carbon materials as counter electrodes makes the devices full-printable, low temperature and high stability. Finally, a brief outlook is provided on the future development of carbon materials for PSCs, which are expected to devote more contributions in the future photovoltaic market.

Solid State Research.

DTIC Science & Technology

1982-11-22

48 Fabricated in Zone-Melting-Recrystallized Si Films on Si0 2-Coated Si Substrates V 4. MICROELECTRONICS 55 4.1 Charge-Coupled Devices: Time...OMCVD to the CLEFT (cleavage of lateral epitaxial films for transfer) process, a continuous epitaxial GaAs layer 3 Ym thick has been grown over a...complete-island-etch or local-oxidation-of-Si isolation, that were fabricated in zone-melting-recrystallized Si films on Si02-coated Si substrates. As

A Study of Energy Conversion Devices Using Photoactive Organometallic Electrocatalysts.

DTIC Science & Technology

1986-05-23

arylisocyanide complexes confined to polymeric thin films in solar energy conversion systems . The chemical systems of interest were chromium...The goals of the project then became threefold: 1) examine the thermo- dynamics an- ’ kinetics of charge transfer in the systems in which we had shown...complexes confined to polymeric thin films in solar energy conversion systems . The chemical systems of interest were chromium, molybdenum and

Optical emission of GaN/AlN quantum-wires - the role of charge transfer from a nanowire template.

PubMed

Müßener, Jan; Greif, Ludwig A Th; Kalinowski, Stefan; Callsen, Gordon; Hille, Pascal; Schörmann, Jörg; Wagner, Markus R; Schliwa, Andrei; Martí-Sánchez, Sara; Arbiol, Jordi; Hoffmann, Axel; Eickhoff, Martin

2018-03-28

We show that one-dimensional (1d) GaN quantum-wires (QWRs) exhibit intense and spectrally sharp emission lines. These QWRs are realized in an entirely self-assembled growth process by molecular beam epitaxy (MBE) on the side facets of GaN/AlN nanowire (NW) heterostructures. Time-integrated and time-resolved photoluminescence (PL) data in combination with numerical calculations allow the identification and assignment of the manifold emission features to three different spatial recombination centers within the NWs. The recombination processes in the QWRs are driven by efficient charge carrier transfer effects between the different optically active regions, providing high intense QWR luminescence despite their small volume. This is deduced by a fast rise time of the QWR PL, which is similar to the fast decay-time of adjacent carrier reservoirs. Such processes, feeding the ultra-narrow QWRs with carriers from the relatively large NWs, can be the key feature towards the realization of future QWR-based devices. While processing of single quantum structures with diameters in the nm range presents a serious obstacle with respect to their integration into electronic or photonic devices, the QWRs presented here can be analyzed and processed using existing techniques developed for single NWs.

The impact of long-range electron-hole interaction on the charge separation yield of molecular photocells

NASA Astrophysics Data System (ADS)

Nemati Aram, Tahereh; Ernzerhof, Matthias; Asgari, Asghar; Mayou, Didier

2017-01-01

We discuss the effects of charge carrier interaction and recombination on the operation of molecular photocells. Molecular photocells are devices where the energy conversion process takes place in a single molecular donor-acceptor complex attached to electrodes. Our investigation is based on the quantum scattering theory, in particular on the Lippmann-Schwinger equation; this minimizes the complexity of the problem while providing useful and non-trivial insight into the mechanism governing photocell operation. In this study, both exciton pair creation and dissociation are treated in the energy domain, and therefore there is access to detailed spectral information, which can be used as a framework to interpret the charge separation yield. We demonstrate that the charge carrier separation is a complex process that is affected by different parameters, such as the strength of the electron-hole interaction and the non-radiative recombination rate. Our analysis helps to optimize the charge separation process and the energy transfer in organic solar cells and in molecular photocells.

Working cycles of devices based on bistable carbon nanotubes

NASA Astrophysics Data System (ADS)

Shklyaev, Oleg; Mockensturm, Eric; Crespi, Vincent; Carbon Nanotubes Collaboration

2013-03-01

Shape-changing nanotubes are an example of variable-shape sp2 carbon-based systems where the competition between strain and surface energies can be moderated by an externally controllable stimuli such as applied voltage, temperature, or pressure of gas encapsulated inside the tube. Using any of these stimuli one can transition a bistable carbon nanotube between the collapsed and inflated states and thus perform mechanical work. During the working cycle of such a device, energy from an electric or heat source is transferred to mechanical energy. Combinations of these stimuli allow the system to convert energy between different sources using the bistable shape-changing tube as a mediator. For example, coupling a bistable carbon nanotube to the heat and charge reservoirs can enable energy transfer between heat and electric forms. The developed theory can be extended to other nano-systems which change configurations in response to external stimuli.

Megawatt level electric propulsion perspectives

NASA Technical Reports Server (NTRS)

Jahn, Robert G.; Kelly, Arnold J.

1987-01-01

For long range space missions, deliverable payload fraction is an inverse exponential function of the propellant exhaust velocity or specific impulse of the propulsion system. The exhaust velocity of chemical systems are limited by their combustion chemistry and heat transfer to a few km/s. Nuclear rockets may achieve double this range, but are still heat transfer limited and ponderous to develop. Various electric propulsion systems can achieve exhaust velocities in the 10 km/s range, at considerably lower thrust densities, but require an external electrical power source. A general overview is provided of the currently available electric propulsion systems from the perspective of their characteristics as a terminal load for space nuclear systems. A summary of the available electric propulsion options is shown and generally characterized in the power vs. exhaust velocity plot. There are 3 general classes of electric thruster devices: neutral gas heaters, plasma devices, and space charge limited electrostatic or ion thrusters.

Operation of a quantum dot in the finite-state machine mode: Single-electron dynamic memory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klymenko, M. V.; Klein, M.; Levine, R. D.

2016-07-14

A single electron dynamic memory is designed based on the non-equilibrium dynamics of charge states in electrostatically defined metallic quantum dots. Using the orthodox theory for computing the transfer rates and a master equation, we model the dynamical response of devices consisting of a charge sensor coupled to either a single and or a double quantum dot subjected to a pulsed gate voltage. We show that transition rates between charge states in metallic quantum dots are characterized by an asymmetry that can be controlled by the gate voltage. This effect is more pronounced when the switching between charge states correspondsmore » to a Markovian process involving electron transport through a chain of several quantum dots. By simulating the dynamics of electron transport we demonstrate that the quantum box operates as a finite-state machine that can be addressed by choosing suitable shapes and switching rates of the gate pulses. We further show that writing times in the ns range and retention memory times six orders of magnitude longer, in the ms range, can be achieved on the double quantum dot system using experimentally feasible parameters, thereby demonstrating that the device can operate as a dynamic single electron memory.« less

Suppression of surface charge accumulation on Al{sub 2}O{sub 3}-filled epoxy resin insulator under dc voltage by direct fluorination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Boya; Zhang, Guixin, E-mail: guixin@mail.tsinghua.edu.cn; Li, Chuanyang

2015-12-15

Surface charge accumulation on insulators under high dc voltage is a major factor that may lead to the reduction of insulation levels in gas insulated devices. In this paper, disc insulators made of Al{sub 2}O{sub 3}-filled epoxy resin were surface fluorinated using a F{sub 2}/N{sub 2} mixture (12.5% F{sub 2}) at 50 °C and 0.1 MPa for different durations of 15 min, 30 min and 60 min. A dc voltage was applied to the insulator for 30 min and the charge density on its surface was measured by an electrostatic probe. The results revealed significant lower surface charge densities on themore » fluorinated insulators in comparison with the original one. Surface conductivity measurements indicated a higher surface conductivity by over three orders of magnitude after fluorination, which would allow the charges to transfer along the surface and thus may suppress their accumulation. Further, attenuated total reflection infrared analysis and surface morphology observations of the samples revealed that the introduction of fluoride groups altered the surface physicochemical properties. These structure changes, especially the physical defects reduced the depth of charge traps in the surface layer, which was verified by the measurement of energy distributions of the electron and hole traps based on the isothermal current theory. The results in this paper demonstrate that fluorination can be a promising and effective method to suppress surface charge accumulation on epoxy insulators in gas insulated devices.« less

Charge-transfer cross sections in collisions of ground-state Ca and H+

NASA Astrophysics Data System (ADS)

Dutta, C. M.; Oubre, C.; Nordlander, P.; Kimura, M.; Dalgarno, A.

2006-03-01

We have investigated collisions of Ca(4s2) with H+ in the energy range of 200eV/u-10keV/u using the semiclassical molecular-orbital close-coupling (MOCC) method with 18 coupled molecular states ( 11Σ+1 and seven Π+1 states) to determine charge-transfer cross sections. Except for the incoming channel 6Σ+1 , the molecular states all correspond to charge-transfer channels. Inclusion of Ca2+-H- is crucial in the configuration-interaction calculation for generating the molecular wave functions and potentials. Because of the Coulomb attraction, the state separating to Ca2+-H- creates many avoided crossings, even though at infinite separation it lies energetically above all other states that we included. Because of the avoided crossings between the incoming channel 6Σ+1 and the energetically close charge-transfer channel 7Σ+1 the charge-transfer interaction occurs at long range. This makes calculations of charge-transfer cross sections by the MOCC method very challenging. The total charge-transfer cross sections increase monotonically from 3.4×10-15cm2 at 200eV/u to 4.5×10-15cm2 at 10keV/u . Charge transfer occurs mostly to the excited Ca+(5p) state in the entire energy range, which is the sum of the charge transfer to 7Σ+1 and 4Π+1 . It accounts for ˜47% of the total charge transfer cross sections at 200eV/u . However, as the energy increases, transfer to Ca+(4d) increases, and at 10keV/u the charge-transfer cross sections for Ca+(5p) and Ca+(4d) become comparable, each giving ˜38% of the total cross section.

An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

NASA Astrophysics Data System (ADS)

Hendrickson, Heidi Phillips

A fundamental understanding of charge separation in organic materials is necessary for the rational design of optoelectronic devices suited for renewable energy applications and requires a combination of theoretical, computational, and experimental methods. Density functional theory (DFT) and time-dependent (TD)DFT are cost effective ab-initio approaches for calculating fundamental properties of large molecular systems, however conventional DFT methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems. In this dissertation, these shortcomings are addressed by implementing an optimally-tuned range-separated hybrid (OT-RSH) functional approach within DFT and TDDFT. The first part of this thesis presents the way in which RSH-DFT addresses the shortcomings in conventional DFT. Environmentally-corrected RSH-DFT frontier orbital energies are shown to correspond to thin film measurements for a set of organic semiconducting molecules. Likewise, the improved RSH-TDDFT description of charge transfer excitations is benchmarked using a model ethene dimer and silsesquioxane molecules. In the second part of this thesis, RSH-DFT is applied to chromophore-functionalized silsesquioxanes, which are currently investigated as candidates for building blocks in optoelectronic applications. RSH-DFT provides insight into the nature of absorptive and emissive states in silsesquioxanes. While absorption primarily involves transitions localized on one chromophore, charge transfer between chromophores and between chromophore and silsesquioxane cage have been identified. The RSH-DFT approach, including a protocol accounting for complex environmental effects on charge transfer energies, was tested and validated against experimental measurements. The third part of this thesis addresses quantum transport through nano-scale junctions. The ability to quantify a molecular junction via spectroscopic methods is crucial to their technological design and development. Time dependent perturbation theory, employed by non-equilibrium Green's function formalism, is utilized to study the effect of quantum coherences on electron transport and the effect of symmetry breaking on the electronic spectra of model molecular junctions. The fourth part of this thesis presents the design of a physical chemistry course based on a pedagogical approach called Writing-to-Teach. The nature of inaccuracies expressed in student-generated explanations of quantum chemistry topics, and the ability of a peer review process to engage these inaccuracies, is explored within this context.

Charge transport in vertically aligned, self-assembled peptide nanotube junctions.

PubMed

Mizrahi, Mordechay; Zakrassov, Alexander; Lerner-Yardeni, Jenny; Ashkenasy, Nurit

2012-01-21

The self-assembly propensity of peptides has been extensively utilized in recent years for the formation of supramolecular nanostructures. In particular, the self-assembly of peptides into fibrils and nanotubes makes them promising building blocks for electronic and electro-optic applications. However, the mechanisms of charge transfer in these wire-like structures, especially in ambient conditions, are not yet fully understood. We describe here a layer-by-layer deposition methodology of short self-assembled cyclic peptide nanotubes, which results in vertically oriented nanotubes on gold substrates. Using this novel deposition methodology, we have fabricated molecular junctions with a conductive atomic force microscopy tip as a second electrode. Studies of the junctions' current-voltage characteristics as a function of the nanotube length revealed an efficient charge transfer in these supramolecular structures, with a low current attenuation constant of 0.1 Å(-1), which indicate that electron transfer is dominated by hopping. Moreover, the threshold voltage to field-emission dominated transport was found to increase with peptide length in a manner that depends on the nature of the contact with the electrodes. The flexibility in the design of the peptide monomers and the ability to control their sequential order over the nanotube by means of the layer-by-layer assembly process, which is demonstrated in this work, can be used to engineer the electronic properties of self-assembled peptide nanotubes toward device applications.

Photoelectrochemical devices for solar water splitting - materials and challenges.

PubMed

Jiang, Chaoran; Moniz, Savio J A; Wang, Aiqin; Zhang, Tao; Tang, Junwang

2017-07-31

It is widely accepted within the community that to achieve a sustainable society with an energy mix primarily based on solar energy we need an efficient strategy to convert and store sunlight into chemical fuels. A photoelectrochemical (PEC) device would therefore play a key role in offering the possibility of carbon-neutral solar fuel production through artificial photosynthesis. The past five years have seen a surge in the development of promising semiconductor materials. In addition, low-cost earth-abundant co-catalysts are ubiquitous in their employment in water splitting cells due to the sluggish kinetics of the oxygen evolution reaction (OER). This review commences with a fundamental understanding of semiconductor properties and charge transfer processes in a PEC device. We then describe various configurations of PEC devices, including single light-absorber cells and multi light-absorber devices (PEC, PV-PEC and PV/electrolyser tandem cell). Recent progress on both photoelectrode materials (light absorbers) and electrocatalysts is summarized, and important factors which dominate photoelectrode performance, including light absorption, charge separation and transport, surface chemical reaction rate and the stability of the photoanode, are discussed. Controlling semiconductor properties is the primary concern in developing materials for solar water splitting. Accordingly, strategies to address the challenges for materials development in this area, such as the adoption of smart architectures, innovative device configuration design, co-catalyst loading, and surface protection layer deposition, are outlined throughout the text, to deliver a highly efficient and stable PEC device for water splitting.

Consideration of Cost of Care in Pediatric Emergency Transfer-An Opportunity for Improvement.

PubMed

Gattu, Rajender K; De Fee, Ann-Sophie; Lichenstein, Richard; Teshome, Getachew

2017-05-01

Pediatric interhospital transfers are an economic burden to the health care, especially when deemed unnecessary. Physicians may be unaware of the cost implications of pediatric emergency transfers. A cost analysis may be relevant to reduce cost. To characterize children transferred from outlying emergency departments (EDs) to pediatric ED (PED) with a specific focus on transfers who were discharged home in 12 hours or less after transfer without intervention in PED and analyze charges associated with them. Charts of 352 patients (age, 0-18 years) transferred from 31 outlying EDs to PED during July 2009 to June 2010 were reviewed. Data were collected on the range, unit charge and volume of services provided in PED, length of stay, and final disposition. The average charge per patient transfer is calculated based on unit charge times total service units per 1000 patients per year and divided by 1000. Hospital charges were divided into fixed and variable. Of 352 patients transferred, 108 (30.7%) were admitted to pediatric inpatient service, 42 (11.9%) to intensive care; 36 (10.2%) went to the operating room, and 166 (47.2%) were discharged home. The average hospital charge per transfer was US $4843. Most (89%) of the charges were fixed, and 11% were variable. One hundred one (28.7%) patients were discharged home from PED in 12 hours or less without intervention. The hospital charges for these transfers were US $489,143. Significant number of transfers was discharged 12 hours or less without any additional intervention in PED. Fixed charges contribute to majority of total charges. Cost saving can be achieved by preventing unnecessary transfer.

Electronic excited states and relaxation dynamics in polymer heterojunction systems

NASA Astrophysics Data System (ADS)

Ramon, John Glenn Santos

The potential for using conducting polymers as the active material in optoelectronic devices has come to fruition in the past few years. Understanding the fundamental photophysics behind their operations points to the significant role played by the polymer interface in their performance. Current device architectures involve the use of bulk heterojunctions which intimately blend the donor and acceptor polymers to significantly increase not only their interfacial surface area but also the probability of exciton formation within the vicinity of the interface. In this dissertation, we detail the role played by the interface on the behavior and performance of bulk heterojunction systems. First, we explore the relation between the exciton binding energy to the band offset in determining device characteristics. As a general rule, when the exciton binding energy is greater than the band offset, the exciton remains the lowest energy excited state leading to efficient light-emitting properties. On the other hand, if the offset is greater than the binding energy, charge separation becomes favorable leading to better photovoltaic behavior. Here, we use a Wannier function, configuration interaction based approach to examine the essential excited states and predict the vibronic absorption and emission spectra of the PPV/BBL, TFB/F8BT and PFB/F8BT heterojunctions. Our results underscore the role of vibrational relaxation in the formation of charge-transfer states following photoexcitation. In addition, we look at the relaxation dynamics that occur upon photoexcitation. For this, we adopt the Marcus-Hush semiclassical method to account for lattice reorganization in the calculation of the interconversion rates in TFB/F8BT and PFB/F8BT. We find that, while a tightly bound charge-transfer state (exciplex) remains the lowest excited state, a regeneration pathway to the optically active lowest excitonic state in TFB/F8BT is possible via thermal repopulation from the exciplex. Finally, we examine the effect of the nanoscale interfacial morphology and solvation on the electronic excited states of TFB/F8BT. Here, we employ time-dependent density functional theory (TD-DFT) to investigate the relevant excited states of two stacking configurations. We show that the calculated states agree with the excited states responsible for the experimentally observed emission peaks and that these states are blue shifted relative to those of the isolated chain. Furthermore, slight lateral shifts in the stacking orientation not only shift the excited state energies; more importantly, they alter the nature of these states altogether. Lastly, we see that solvation greatly stabilizes the charge-transfer states.

Mechanisms of transport and electron transfer at conductive polymer/liquid interfaces

NASA Astrophysics Data System (ADS)

Ratcliff, Erin

Organic semiconductors (OSCs) have incredible prospects for next-generation, flexible electronic devices including bioelectronics, thermoelectrics, opto-electronics, and energy storage and conversion devices. Yet many fundamental challenges still exist. First, solution processing prohibits definitive control over microstructure, which is fundamental for controlling electrical, ionic, and thermal transport properties. Second, OSCs generally suffer from poor electrical conductivities due to a combination of low carriers and low mobility. Third, polymeric semiconductors have potential-dependent, dynamically evolving electronic and chemical states, leading to complex interfacial charge transfer properties in contact with liquids. This talk will focus on the use of alternative synthetic strategies of oxidative chemical vapor deposition and electrochemical deposition to control physical, electronic, and chemical structure. We couple our synthetic efforts with energy-, time-, and spatially resolved spectroelectrochemical and microscopy techniques to understand the critical interfacial chemistry-microstructure-property relationships: first at the macroscale, and then moving towards the nanoscale. In particular, approaches to better understand electron transfer events at polymer/liquid interfaces as a function of: 1.) chemical composition; 2.) electronic density of states (DOS); and 3.) crystallinity and microstructure will be discussed.

Understanding the free energy barrier and multiple timescale dynamics of charge separation in organic photovoltaic cells.

PubMed

Yan, Yaming; Song, Linze; Shi, Qiang

2018-02-28

By employing several lattice model systems, we investigate the free energy barrier and real-time dynamics of charge separation in organic photovoltaic (OPV) cells. It is found that the combined effects of the external electric field, entropy, and charge delocalization reduce the free energy barrier significantly. The dynamic disorder reduces charge carrier delocalization and results in the increased charge separation barrier, while the effect of static disorder is more complicated. Simulation of the real-time dynamics indicates that the free charge generation process involves multiple time scales, including an ultrafast component within hundreds of femtoseconds, an intermediate component related to the relaxation of the hot charge transfer (CT) state, and a slow component on the time scale of tens of picoseconds from the thermally equilibrated CT state. Effects of hot exciton dissociation as well as its dependence on the energy offset between the Frenkel exciton and the CT state are also analyzed. The current results indicate that only a small energy offset between the band gap and the lowest energy CT state is needed to achieve efficient free charge generation in OPV devices, which agrees with recent experimental findings.

Understanding the free energy barrier and multiple timescale dynamics of charge separation in organic photovoltaic cells

NASA Astrophysics Data System (ADS)

Yan, Yaming; Song, Linze; Shi, Qiang

2018-02-01

By employing several lattice model systems, we investigate the free energy barrier and real-time dynamics of charge separation in organic photovoltaic (OPV) cells. It is found that the combined effects of the external electric field, entropy, and charge delocalization reduce the free energy barrier significantly. The dynamic disorder reduces charge carrier delocalization and results in the increased charge separation barrier, while the effect of static disorder is more complicated. Simulation of the real-time dynamics indicates that the free charge generation process involves multiple time scales, including an ultrafast component within hundreds of femtoseconds, an intermediate component related to the relaxation of the hot charge transfer (CT) state, and a slow component on the time scale of tens of picoseconds from the thermally equilibrated CT state. Effects of hot exciton dissociation as well as its dependence on the energy offset between the Frenkel exciton and the CT state are also analyzed. The current results indicate that only a small energy offset between the band gap and the lowest energy CT state is needed to achieve efficient free charge generation in OPV devices, which agrees with recent experimental findings.

Exciton-dissociation and charge-recombination processes in pentacene/C60 solar cells: theoretical insight into the impact of interface geometry.

PubMed

Yi, Yuanping; Coropceanu, Veaceslav; Brédas, Jean-Luc

2009-11-04

The exciton-dissociation and charge-recombination processes in organic solar cells based on pentacene/C(60) heterojunctions are investigated by means of quantum-mechanical calculations. The electronic couplings and the rates of exciton dissociation and charge recombination have been evaluated for several geometrical configurations of the pentacene/C(60) complex, which are relevant to bilayer and bulk heterojunctions. The results suggest that, irrespective of the actual pentacene-fullerene orientation, both pentacene-based and C(60)-based excitons are able to dissociate efficiently. Also, in the case of parallel configurations of the molecules at the pentacene/C(60) interface, the decay of the lowest charge-transfer state to the ground state is calculated to be very fast; as a result, it can compete with the dissociation process into mobile charge carriers. Since parallel configurations are expected to be found more frequently in bulk heterojunctions than in bilayer heterojunctions, the performance of pentacene/C(60) bulk-heterojunction solar cells is likely to be more affected by charge recombination than that of bilayer devices.

Quantum Theory of Atoms in Molecules Charge-Charge Transfer-Dipolar Polarization Classification of Infrared Intensities.

PubMed

Duarte, Leonardo J; Richter, Wagner E; Silva, Arnaldo F; Bruns, Roy E

2017-10-26

Fundamental infrared vibrational transition intensities of gas-phase molecules are sensitive probes of changes in electronic structure accompanying small molecular distortions. Models containing charge, charge transfer, and dipolar polarization effects are necessary for a successful classification of the C-H, C-F, and C-Cl stretching and bending intensities. C-H stretching and in-plane bending vibrations involving sp 3 carbon atoms have small equilibrium charge contributions and are accurately modeled by the charge transfer-counterpolarization contribution and its interaction with equilibrium charge movement. Large C-F and C═O stretching intensities have dominant equilibrium charge movement contributions compared to their charge transfer-dipolar polarization ones and are accurately estimated by equilibrium charge and the interaction contribution. The C-F and C-Cl bending modes have charge and charge transfer-dipolar polarization contribution sums that are of similar size but opposite sign to their interaction values resulting in small intensities. Experimental in-plane C-H bends have small average intensities of 12.6 ± 10.4 km mol -1 owing to negligible charge contributions and charge transfer-counterpolarization cancellations, whereas their average out-of-plane experimental intensities are much larger, 65.7 ± 20.0 km mol -1 , as charge transfer is zero and only dipolar polarization takes place. The C-F bending intensities have large charge contributions but very small intensities. Their average experimental out-of-plane intensity of 9.9 ± 12.6 km mol -1 arises from the cancellation of large charge contributions by dipolar polarization contributions. The experimental average in-plane C-F bending intensity, 5.8 ± 7.3 km mol -1 , is also small owing to charge and charge transfer-counterpolarization sums being canceled by their interaction contributions. Models containing only atomic charges and their fluxes are incapable of describing electronic structure changes for simple molecular distortions that are of interest in classifying infrared intensities. One can expect dipolar polarization effects to also be important for larger distortions of chemical interest.

Active implantable medical device EMI assessment for wireless power transfer operating in LF and HF bands.

PubMed

Hikage, Takashi; Nojima, Toshio; Fujimoto, Hiroshi

2016-06-21

The electromagnetic interference (EMI) imposed on active implantable medical devices by wireless power transfer systems (WPTSs) is discussed based upon results of in vitro experiments. The purpose of this study is to present comprehensive EMI test results gathered from implantable-cardiac pacemakers and implantable cardioverter defibrillators exposed to the electromagnetic field generated by several WPTSs operating in low-frequency (70 kHz-460 kHz) and high-frequency (6.78 MHz) bands. The constructed in vitro experimental test system based upon an Irnich's flat torso phantom was applied. EMI test experiments are conducted on 14 types of WPTSs including Qi-compliant system and EV-charging WPT system mounted on current production EVs. In addition, a numerical simulation model for active implantable medical device (AIMD) EMI estimation based on the experimental test system is newly proposed. The experimental results demonstrate the risk of WPTSs emitting intermittent signal to affect the correct behavior of AIMDs when operating at very short distances. The proposed numerical simulation model is applicable to obtain basically the EMI characteristics of various types of WPTSs.

Active implantable medical device EMI assessment for wireless power transfer operating in LF and HF bands

NASA Astrophysics Data System (ADS)

Hikage, Takashi; Nojima, Toshio; Fujimoto, Hiroshi

2016-06-01

The electromagnetic interference (EMI) imposed on active implantable medical devices by wireless power transfer systems (WPTSs) is discussed based upon results of in vitro experiments. The purpose of this study is to present comprehensive EMI test results gathered from implantable-cardiac pacemakers and implantable cardioverter defibrillators exposed to the electromagnetic field generated by several WPTSs operating in low-frequency (70 kHz-460 kHz) and high-frequency (6.78 MHz) bands. The constructed in vitro experimental test system based upon an Irnich’s flat torso phantom was applied. EMI test experiments are conducted on 14 types of WPTSs including Qi-compliant system and EV-charging WPT system mounted on current production EVs. In addition, a numerical simulation model for active implantable medical device (AIMD) EMI estimation based on the experimental test system is newly proposed. The experimental results demonstrate the risk of WPTSs emitting intermittent signal to affect the correct behavior of AIMDs when operating at very short distances. The proposed numerical simulation model is applicable to obtain basically the EMI characteristics of various types of WPTSs.

Reconfigurable electronics using conducting metal-organic frameworks

DOEpatents

Allendorf, Mark D.; Talin, Albert Alec; Leonard, Francois; Stavila, Vitalie

2017-07-18

A device including a porous metal organic framework (MOF) disposed between two terminals, the device including a first state wherein the MOF is infiltrated by a guest species to form an electrical path between the terminals and a second state wherein the electrical conductivity of the MOF is less than the electrical conductivity in the first state. A method including switching a porous metal organic framework (MOF) between two terminals from a first state wherein a metal site in the MOF is infiltrated by a guest species that is capable of charge transfer to a second state wherein the MOF is less electrically conductive than in the first state.

New low noise CCD cameras for Pi-of-the-Sky project

NASA Astrophysics Data System (ADS)

Kasprowicz, G.; Czyrkowski, H.; Dabrowski, R.; Dominik, W.; Mankiewicz, L.; Pozniak, K.; Romaniuk, R.; Sitek, P.; Sokolowski, M.; Sulej, R.; Uzycki, J.; Wrochna, G.

2006-10-01

Modern research trends require observation of fainter and fainter astronomical objects on large areas of the sky. This implies usage of systems with high temporal and optical resolution with computer based data acquisition and processing. Therefore Charge Coupled Devices (CCD) became so popular. They offer quick picture conversion with much better quality than film based technologies. This work is theoretical and practical study of the CCD based picture acquisition system. The system was optimized for "Pi of The Sky" project. But it can be adapted to another professional astronomical researches. The work includes issue of picture conversion, signal acquisition, data transfer and mechanical construction of the device.

Introduction of Interfacial Charges to Black Phosphorus for a Family of Planar Devices

NASA Astrophysics Data System (ADS)

Bao, Lihong; Wang, Guocai; Du, Shixuan; Pantelides, Sokrates; Gao, Hong-Jun

As a young member in the family of two dimensional materials, black phosphorus (BP) has attracted great attention since its discovery due to its high hole mobility and a sizable and tunable bandgap, which meets the basic requirements for logic circuits applications. Naturally, for realization of complementary logic operation, the challenge lies in how to control the conduction type in BP FETs, i.e., the dominant carrier types, holes (p-type) or electrons (n-type). However, the absence of reliable substitutional doping techniques makes this task a great challenge. Introducing interfacial charges into 2D materials has been proven to be a successfulway to control conduction. In this work, we, for the first time, demonstrate that capping a thin BP layer with a layer of cross-linked PMMA can modify the conductivity type of the BP by a surface charge transfer process, converting a BP layer dominated by hole conduction in the absence of an external electric field (p-type) to one dominated by electron conduction (n-type). Combining BP films capped by cross-linked PMMA with standard BP, a familyof planar devices can be created, including BP gated diodes and bidirectional recitifiers (rectification ratio >102) and BP logic inverter (gain¡«0.75) which are capable of performing current rectification, switching, and signal inversion operations. The device performance demonstrated here suggests a promising route for developing 2D-based electronics.

CHARGING OF DEVICES BY MICROWAVE POWER BEAMING

NASA Technical Reports Server (NTRS)

Landis, Geoffrey A. (Inventor)

2005-01-01

A system for providing wireless, charging power and/or primary power to electronic/electrical devices is described whereby microwave energy is employed. Microwave energy is focused by a power transmitter comprising one or more adaptively-phased microwave array emitters onto a device to be charged. Rectennas within the device to be charged receive and rectify the microwave energy and use it for battery charging and/or for primary power. A locator signal generated by the device to be charged is analyzed by the system to determine the location of the device to be charged relative to the microwave array emitters, permitting thc microwave energy to be directly specifically towards the device to be charged. Backscatter detectors respond to backscatter energy reflected off of any obstacle between the device to be charged and the microwave array emitters. Power to any obstructed microwave array emitter is reduced until the obstruction is removed. Optionally, data can be modulated onto microwave energy beams produced by the array emitter and demodulated by the device, thereby providing means of data communication from the power transmitter to the device. Similarly, data can be modulated onto the locator signal and demodulated in the power transmitter, thereby providing means of data communication from the device to the power transmitter.

Gradual plasmon evolution and huge infrared near-field enhancement of metallic bridged nanoparticle dimers.

PubMed

Huang, Yu; Ma, Lingwei; Hou, Mengjing; Xie, Zheng; Zhang, Zhengjun

2016-01-28

By three-dimensional (3D) finite element method (FEM) plasmon mapping, gradual plasmon evolutions of both bonding dipole plasmon (BDP) and charge transfer plasmon (CTP) modes are visualized. In particular, the evolved BDP mode provides a physical insight into the rapid degeneration of electromagnetic hot spots in practical applications, while the rising CTP mode enables a huge near-field enhancement for potential plasmonic devices at infrared wavelengths.

Trap and transfer. two-step hole injection across the Sb2S3/CuSCN interface in solid-state solar cells.

PubMed

Christians, Jeffrey A; Kamat, Prashant V

2013-09-24

In solid-state semiconductor-sensitized solar cells, commonly known as extremely thin absorber (ETA) or solid-state quantum-dot-sensitized solar cells (QDSCs), transfer of photogenerated holes from the absorber species to the p-type hole conductor plays a critical role in the charge separation process. Using Sb2S3 (absorber) and CuSCN (hole conductor), we have constructed ETA solar cells exhibiting a power conversion efficiency of 3.3%. The hole transfer from excited Sb2S3 into CuSCN, which limits the overall power conversion efficiency of these solar cells, is now independently studied using transient absorption spectroscopy. In the Sb2S3 absorber layer, photogenerated holes are rapidly localized on the sulfur atoms of the crystal lattice, forming a sulfide radical (S(-•)) species. This trapped hole is transferred from the Sb2S3 absorber to the CuSCN hole conductor with an exponential time constant of 1680 ps. This process was monitored through the spectroscopic signal seen for the S(-•) species in Sb2S3, providing direct evidence for the hole transfer dynamics in ETA solar cells. Elucidation of the hole transfer mechanism from Sb2S3 to CuSCN represents a significant step toward understanding charge separation in Sb2S3 solar cells and provides insight into the design of new architectures for higher efficiency devices.

Charge carrier mobility in conjugated organic polymers: simulation of an electron mobility in a carbazole-benzothiadiazole-based polymer

NASA Astrophysics Data System (ADS)

Li, Yaping; Lagowski, Jolanta B.

2011-08-01

Inorganic (mostly silicon based) solar cells are important devices that are used to solve the world energy and environmental needs. Now days, organic solar cells are attracting considerable attention in the field of photovoltaic cells because of their low cost and processing flexibility. Often conjugated polymers are used in the construction of the organic solar cells. We study the conjugated polymers' charge transport using computational approach that involves the use of the density functional theory (DFT), semiempirical (ZINDO), and Monte Carlo (MC) theoretical methods in order to determine their transfer integrals, reorganization energies, transfer rates (with the use of Marcus-Hush equation) and mobilities. We employ the experimentally determined three dimensional (3D) structure of poly(9,9'-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) to estimate the electron mobility in a similar co-alternating polymer consisting of carbazole and benzothiadiazole units (C8BT). In agreement with our previous work, we found that including an orientational disorder in the crystal reduces the electron mobility in C8BT. We hope that the proposed computational approach can be used to predict charge mobility in organic materials that are used in solar cells.

Exciton size and binding energy limitations in one-dimensional organic materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraner, S., E-mail: stefan.kraner@iapp.de; Koerner, C.; Leo, K.

2015-12-28

In current organic photovoltaic devices, the loss in energy caused by the charge transfer step necessary for exciton dissociation leads to a low open circuit voltage, being one of the main reasons for rather low power conversion efficiencies. A possible approach to avoid these losses is to tune the exciton binding energy to a value of the order of thermal energy, which would lead to free charges upon absorption of a photon, and therefore increase the power conversion efficiency towards the Shockley-Queisser limit. We determine the size of the excitons for different organic molecules and polymers by time dependent densitymore » functional theory calculations. For optically relevant transitions, the exciton size saturates around 0.7 nm for one-dimensional molecules with a size longer than about 4 nm. For the ladder-type polymer poly(benzimidazobenzophenanthroline), we obtain an exciton binding energy of about 0.3 eV, serving as a lower limit of the exciton binding energy for the organic materials investigated. Furthermore, we show that charge transfer transitions increase the exciton size and thus identify possible routes towards a further decrease of the exciton binding energy.« less

Interfacial Chemical Composition and Molecular Order in Organic Photovoltaic Blend Thin Films Probed by Surface-Enhanced Raman Spectroscopy.

PubMed

Razzell-Hollis, Joseph; Thiburce, Quentin; Tsoi, Wing C; Kim, Ji-Seon

2016-11-16

Organic electronic devices invariably involve transfer of charge carriers between the organic layer and at least one metal electrode, and they are sensitive to the local properties of the organic film at those interfaces. Here, we demonstrate a new approach for using an advanced technique called surface-enhanced raman spectroscopy (SERS) to quantitatively probe interfacial properties relevant to charge injection/extraction. Exploiting the evanescent electric field generated by a ∼7 nm thick layer of evaporated silver, Raman scattering from nearby molecules is enhanced by factors of 10-1000× and limited by a distance dependence with a measured decay length of only 7.6 nm. When applied to the study of an all-polymer 1:1 blend of P3HT and F8TBT used in organic solar cells, we find that the as-cast film is morphologically suited to charge extraction in inverted devices, with a top (anode) interface very rich in hole-transporting P3HT (74.5%) and a bottom (cathode) interface slightly rich in electron-transporting F8TBT (55%). While conventional, uninverted P3HT:F8TBT devices are reported to perform poorly compared to inverted devices, their efficiency can be improved by thermal annealing but only after evaporation of a metallic top electrode. This is explained by changes in composition at the top interface: annealing prior to silver evaporation leads to a greater P3HT concentration at the top interface to 83.3%, exaggerating the original distribution that favored inverted devices, while postevaporation annealing increases the concentration of F8TBT at the top interface to 34.8%, aiding the extraction of electrons in a conventional device. By nondestructively probing buried interfaces, SERS is a powerful tool for understanding the performance of organic electronic devices.

Graphene Charge Transfer, Spectroscopy, and Photochemical Reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brus, Louis

This project focused on the special electronic and optical properties of graphene and adsorbed molecular species. Graphene makes an excellent substrate for current collection in nanostructured photovoltaic designs. Graphene is almost transparent, and can be used as a solar cell window. It also has no surface states, and thus current is efficiently transported over long distances. Progress in graphene synthesis indicates that there will soon be practical methods for making large pieces of graphene for devices. We now need to understand exactly what happens to both ground state and electronically excited molecules and Qdots near graphene, if we are goingmore » to use them to absorb light in a nano-structured photovoltaic device using graphene to collect photocurrent. We also need to understand how to shift the graphene Fermi level, to optimize the kinetics of electron transfer to graphene. And we need to learn how to convert local graphene areas to semiconductor structure, to make useful spatially patterned graphenes. In this final report, we describe how we addressed these goals. We explored the question of possible Surface Enhanced Raman spectroscopy from molecular Charge Transfer onto Graphene substrates. We observed strong hole doping of graphene by adsorbed halogens as indicated by the shift of the graphene G Raman band. In the case of iodine adsorption, we also observed the anionic species made by hole doping. At low frequency in the Raman spectrum, we saw quite intense lines from I 3 - and I 5 - , suggesting possible SERS. We reported on Fresnel calculations on this thin film system, which did not show any net electromagnetic field enhancement.« less

Charge Transfer Inefficiency in Pinned Photodiode CMOS image sensors: Simple Montecarlo modeling and experimental measurement based on a pulsed storage-gate method

NASA Astrophysics Data System (ADS)

Pelamatti, Alice; Goiffon, Vincent; Chabane, Aziouz; Magnan, Pierre; Virmontois, Cédric; Saint-Pé, Olivier; de Boisanger, Michel Breart

2016-11-01

The charge transfer time represents the bottleneck in terms of temporal resolution in Pinned Photodiode (PPD) CMOS image sensors. This work focuses on the modeling and estimation of this key parameter. A simple numerical model of charge transfer in PPDs is presented. The model is based on a Montecarlo simulation and takes into account both charge diffusion in the PPD and the effect of potential obstacles along the charge transfer path. This work also presents a new experimental approach for the estimation of the charge transfer time, called pulsed Storage Gate (SG) method. This method, which allows reproduction of a ;worst-case; transfer condition, is based on dedicated SG pixel structures and is particularly suitable to compare transfer efficiency performances for different pixel geometries.

Critical Role of the Sorting Polymer in Carbon Nanotube-Based Minority Carrier Devices.

PubMed

Mallajosyula, Arun T; Nie, Wanyi; Gupta, Gautam; Blackburn, Jeffrey L; Doorn, Stephen K; Mohite, Aditya D

2016-12-27

A prerequisite for carbon nanotube-based optoelectronic devices is the ability to sort them into a pure semiconductor phase. One of the most common sorting routes is enabled through using specific wrapping polymers. Here we show that subtle changes in the polymer structure can have a dramatic influence on the figures of merit of a carbon nanotube-based photovoltaic device. By comparing two commonly used polyfluorenes (PFO and PFO-BPy) for wrapping (7,5) and (6,5) chirality SWCNTs, we demonstrate that they have contrasting effects on the device efficiency. We attribute this to the differences in their ability to efficiently transfer charge. Although PFO may act as an efficient interfacial layer at the anode, PFO-BPy, having the additional pyridine side groups, forms a high resistance layer degrading the device efficiency. By comparing PFO|C 60 and C 60 -only devices, we found that presence of a PFO layer at low optical densities resulted in the increase of all three solar cell parameters, giving nearly an order of magnitude higher efficiency over that of C 60 -only devices. In addition, with a relatively higher contribution to photocurrent from the PFO-C 60 interface, an open circuit voltage of 0.55 V was obtained for PFO-(7,5)-C 60 devices. On the other hand, PFO-BPy does not affect the open circuit voltage but drastically reduces the short circuit current density. These results indicate that the charge transport properties and energy levels of the sorting polymers have to be taken into account to fully understand their effect on carbon nanotube-based solar cells.

Design of an electrostatic phase shifting device for biological transmission electron microscopy.

PubMed

Koeck, Philip J B

2018-04-01

I suggest an electrostatic phase plate designed to broaden the contrast transfer function of a transmission electron microscope operated close to Scherzer defocus primarily in the low resolution direction. At higher defocus the low frequency behavior is equal to that close to Scherzer defocus, but CTF-correction becomes necessary to extend image interpretation to higher resolution. One simple realization of the phase plate consists of two ring shaped electrodes symmetrically surrounding the central beam. Since no physical components come into contact with the central beam and charge on the electrodes is controlled by an external voltage supply, problems with uncontrolled charging are expected to be reduced. Copyright © 2018 Elsevier B.V. All rights reserved.

Charge transfer efficiency improvement of 4T pixel for high speed CMOS image sensor

NASA Astrophysics Data System (ADS)

Jin, Xiangliang; Liu, Weihui; Yang, Hongjiao; Tang, Lizhen; Yang, Jia

2015-03-01

The charge transfer efficiency improvement method is proposed by optimizing the electrical potential distribution along the transfer path from the PPD to the FD. In this work, we present a non-uniform doped transfer transistor channel, with the adjustments to the overlap length between the CPIA layer and the transfer gate, and the overlap length between the SEN layer and transfer gate. Theory analysis and TCAD simulation results show that the density of the residual charge reduces from 1e11 /cm3 to 1e9 /cm3, and the transfer time reduces from 500 ns to 143 ns, and the charge transfer efficiency is about 77 e-/ns. This optimizing design effectively improves the charge transfer efficiency of 4T pixel and the performance of 4T high speed CMOS image sensor.

Low-Temperature Solution-Processed ZnSe Electron Transport Layer for Efficient Planar Perovskite Solar Cells with Negligible Hysteresis and Improved Photostability.

PubMed

Li, Xin; Yang, Junyou; Jiang, Qinghui; Lai, Hui; Li, Shuiping; Xin, Jiwu; Chu, Weijing; Hou, Jingdi

2018-05-15

For a typical perovskite solar cell (PKSC), the electron transport layer (ETL) has a great effect on device performance and stability. Herein, we manifest that low-temperature solution-processed ZnSe can be used as a potential ETL for PKSCs. Our optimized device with ZnSe ETL has achieved a high power conversion efficiency (PCE) of 17.78% with negligible hysteresis, compared with the TiO 2 based cell (13.76%). This enhanced photovoltaic performance is attributed to the suitable band alignment, high electron mobility, and reduced charge accumulation at the interface of ETL/perovskite. Encouraging results were obtained when the thin layer of ZnSe cooperated with TiO 2 . It shows that the device based on the TiO 2 /ZnSe ETL with cascade conduction band level can effectively reduce the interfacial charge recombination and promote carrier transfer with the champion PCE of 18.57%. In addition, the ZnSe-based device exhibits a better photostability than the control device due to the greater ultraviolet (UV) light harvesting of the ZnSe layer, which can efficiently prevent the perovskite film from intense UV-light exposure to avoid associated degradation. Consequently, our results present that a promising ETL can be a potential candidate of the n-type ETL for commercialization of efficient and photostable PKSCs.

A photovoltaic device structure based on internal electron emission.

PubMed

McFarland, Eric W; Tang, Jing

2003-02-06

There has been an active search for cost-effective photovoltaic devices since the development of the first solar cells in the 1950s (refs 1-3). In conventional solid-state solar cells, electron-hole pairs are created by light absorption in a semiconductor, with charge separation and collection accomplished under the influence of electric fields within the semiconductor. Here we report a multilayer photovoltaic device structure in which photon absorption instead occurs in photoreceptors deposited on the surface of an ultrathin metal-semiconductor junction Schottky diode. Photoexcited electrons are transferred to the metal and travel ballistically to--and over--the Schottky barrier, so providing the photocurrent output. Low-energy (approximately 1 eV) electrons have surprisingly long ballistic path lengths in noble metals, allowing a large fraction of the electrons to be collected. Unlike conventional cells, the semiconductor in this device serves only for majority charge transport and separation. Devices fabricated using a fluorescein photoreceptor on an Au/TiO2/Ti multilayer structure had typical open-circuit photovoltages of 600-800 mV and short-circuit photocurrents of 10-18 micro A cm(-2) under 100 mW cm(-2) visible band illumination: the internal quantum efficiency (electrons measured per photon absorbed) was 10 per cent. This alternative approach to photovoltaic energy conversion might provide the basis for durable low-cost solar cells using a variety of materials.

How well can charge transfer inefficiency be corrected? A parameter sensitivity study for iterative correction

NASA Astrophysics Data System (ADS)

Israel, Holger; Massey, Richard; Prod'homme, Thibaut; Cropper, Mark; Cordes, Oliver; Gow, Jason; Kohley, Ralf; Marggraf, Ole; Niemi, Sami; Rhodes, Jason; Short, Alex; Verhoeve, Peter

2015-10-01

Radiation damage to space-based charge-coupled device detectors creates defects which result in an increasing charge transfer inefficiency (CTI) that causes spurious image trailing. Most of the trailing can be corrected during post-processing, by modelling the charge trapping and moving electrons back to where they belong. However, such correction is not perfect - and damage is continuing to accumulate in orbit. To aid future development, we quantify the limitations of current approaches, and determine where imperfect knowledge of model parameters most degrades measurements of photometry and morphology. As a concrete application, we simulate 1.5 × 109 `worst-case' galaxy and 1.5 × 108 star images to test the performance of the Euclid visual instrument detectors. There are two separable challenges. If the model used to correct CTI is perfectly the same as that used to add CTI, 99.68 per cent of spurious ellipticity is corrected in our setup. This is because readout noise is not subject to CTI, but gets overcorrected during correction. Secondly, if we assume the first issue to be solved, knowledge of the charge trap density within Δρ/ρ = (0.0272 ± 0.0005) per cent and the characteristic release time of the dominant species to be known within Δτ/τ = (0.0400 ± 0.0004) per cent will be required. This work presents the next level of definition of in-orbit CTI calibration procedures for Euclid.

Variable charge transfer state energies at nanostructured pentacene/C60 interfaces

NASA Astrophysics Data System (ADS)

Lin, YunHui L.; Zhang, Fengyu; Kerner, Ross A.; Yang, Terry Chien-Jen; Kahn, Antoine; Rand, Barry P.

2018-05-01

While it has recently been recognized that organic donor-acceptor charge transfer (CT) state energies can vary substantially under different interfacial morphologies, this behavior is under-appreciated in the context of organic singlet fission solar cells where a specific alignment between the triplet state of the fission material and the CT state of the donor-acceptor interface is necessary to the function of the device. In this work, we demonstrate that the CT state energy of a prototypical pentacene-C60 singlet fission system is around 1 eV in most systems, but can vary over 300 meV depending on the composition and morphology of the interface. Moreover, we show that the inclusion of a poly(3-hexylthiophene-2,5-diyl) underlayer, which commonly serves as a triplet blocker and hole collector in pentacene/C60 solar cells, helps promote active layer morphologies with stabilized, low energy CT states. These trends in the interfacial energetics are correlated with structural characterization of the films by atomic force microscopy and x-ray diffraction.

Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics.

PubMed

Mora-Sero, Ivan; Bertoluzzi, Luca; Gonzalez-Pedro, Victoria; Gimenez, Sixto; Fabregat-Santiago, Francisco; Kemp, Kyle W; Sargent, Edward H; Bisquert, Juan

2013-01-01

Colloidal quantum dot solar cells achieve spectrally selective optical absorption in a thin layer of solution-processed, size-effect tuned, nanoparticles. The best devices built to date have relied heavily on drift-based transport due to the action of an electric field in a depletion region that extends throughout the thickness of the quantum dot layer. Here we study for the first time the behaviour of the best-performing class of colloidal quantum dot films in the absence of an electric field, by screening using an electrolyte. We find that the action of selective contacts on photovoltage sign and amplitude can be retained, implying that the contacts operate by kinetic preferences of charge transfer for either electrons or holes. We develop a theoretical model to explain these experimental findings. The work is the first to present a switch in the photovoltage in colloidal quantum dot solar cells by purposefully formed selective contacts, opening the way to new strategies in the engineering of colloidal quantum dot solar cells.

The optimum titanium precursor of fabricating TiO2 compact layer for perovskite solar cells.

PubMed

Qin, Jianqiang; Zhang, Zhenlong; Shi, Wenjia; Liu, Yuefeng; Gao, Huiping; Mao, Yanli

2017-12-29

Perovskite solar cells (PSCs) have attracted tremendous attentions due to its high performance and rapid efficiency promotion. Compact layer plays a crucial role in transferring electrons and blocking charge recombination between the perovskite layer and fluorine-doped tin oxide (FTO) in PSCs. In this study, compact TiO 2 layers were synthesized by spin-coating method with three different titanium precursors, titanium diisopropoxide bis (acetylacetonate) (c-TTDB), titanium isopropoxide (c-TTIP), and tetrabutyl titanate (c-TBOT), respectively. Compared with the PSCs based on the widely used c-TTDB and c-TTIP, the device based on c-TBOT has significantly enhanced performance, including open-circuit voltage, short-circuit current density, fill factor, and hysteresis. The significant enhancement is ascribed to its excellent morphology, high conductivity and optical properties, fast charge transfer, and large recombination resistance. Thus, a power conversion efficiency (PCE) of 17.03% has been achieved for the solar cells based on c-TBOT.

The optimum titanium precursor of fabricating TiO2 compact layer for perovskite solar cells

NASA Astrophysics Data System (ADS)

Qin, Jianqiang; Zhang, Zhenlong; Shi, Wenjia; Liu, Yuefeng; Gao, Huiping; Mao, Yanli

2017-12-01

Perovskite solar cells (PSCs) have attracted tremendous attentions due to its high performance and rapid efficiency promotion. Compact layer plays a crucial role in transferring electrons and blocking charge recombination between the perovskite layer and fluorine-doped tin oxide (FTO) in PSCs. In this study, compact TiO2 layers were synthesized by spin-coating method with three different titanium precursors, titanium diisopropoxide bis (acetylacetonate) (c-TTDB), titanium isopropoxide (c-TTIP), and tetrabutyl titanate (c-TBOT), respectively. Compared with the PSCs based on the widely used c-TTDB and c-TTIP, the device based on c-TBOT has significantly enhanced performance, including open-circuit voltage, short-circuit current density, fill factor, and hysteresis. The significant enhancement is ascribed to its excellent morphology, high conductivity and optical properties, fast charge transfer, and large recombination resistance. Thus, a power conversion efficiency (PCE) of 17.03% has been achieved for the solar cells based on c-TBOT.

Self-aligned nanoforest in silicon nanowire for sensitive conductance modulation.

PubMed

Seol, Myeong-Lok; Ahn, Jae-Hyuk; Choi, Ji-Min; Choi, Sung-Jin; Choi, Yang-Kyu

2012-11-14

A self-aligned and localized nanoforest structure is constructed in a top-down fabricated silicon nanowire (SiNW). The surface-to-volume ratio (SVR) of the SiNW is enhanced due to the local nanoforest formation. The conductance modulation property of the SiNWs, which is an important characteristic in sensor and charge transfer based applications, can be largely enhanced. For the selective modification of the channel region, localized Joule-heating and subsequent metal-assisted chemical etching (mac-etch) are employed. The nanoforest is formed only in the channel region without misalignment due to the self-aligned process of Joule-heating. The modified SiNW is applied to a porphyrin-silicon hybrid device to verify the enhanced conductance modulation. The charge transfer efficiency between the porphyrin and the SiNW, which is caused by external optical excitation, is clearly increased compared to the initial SiNW. The effect of the local nanoforest formation is enhanced when longer etching times and larger widths are used.

Photocatalysis versus photosynthesis: A sensitivity analysis of devices for solar energy conversion and chemical transformations

DOE PAGES

Osterloh, Frank E.

2017-01-18

Here, the chemical literature often does not differentiate between photocatalytic (PC) and photosynthetic (PS) processes (including artificial photosynthesis) even though these reactions differ in their thermodynamics. Photocatalytic processes are thermodynamically downhill (ΔG < 0) and are merely accelerated by the catalyst, whereas photosynthetic processes are thermodynamically unfavorable (ΔG > 0) and require photochemical energy input to occur. Here we apply this differentiation to analyze the basic functions of PC and PS devices and to formulate design criteria for improved performance. As will be shown, the corresponding devices exhibit distinctly different sensitivities to their functional parameters. For example, under conditions ofmore » optimal light absorption, carrier lifetimes, and electrochemical rates, the performance of PCs is limited only by their surface area, while type 1 PS devices are limited by their carrier mobility and mass transport, and type 2 PS devices are limited by electrochemical charge-transfer selectivity. Strategies for the optimization of type 1 and 2 photosynthetic devices and photocatalysts are also discussed.« less

Photocatalysis versus photosynthesis: A sensitivity analysis of devices for solar energy conversion and chemical transformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osterloh, Frank E.

Here, the chemical literature often does not differentiate between photocatalytic (PC) and photosynthetic (PS) processes (including artificial photosynthesis) even though these reactions differ in their thermodynamics. Photocatalytic processes are thermodynamically downhill (ΔG < 0) and are merely accelerated by the catalyst, whereas photosynthetic processes are thermodynamically unfavorable (ΔG > 0) and require photochemical energy input to occur. Here we apply this differentiation to analyze the basic functions of PC and PS devices and to formulate design criteria for improved performance. As will be shown, the corresponding devices exhibit distinctly different sensitivities to their functional parameters. For example, under conditions ofmore » optimal light absorption, carrier lifetimes, and electrochemical rates, the performance of PCs is limited only by their surface area, while type 1 PS devices are limited by their carrier mobility and mass transport, and type 2 PS devices are limited by electrochemical charge-transfer selectivity. Strategies for the optimization of type 1 and 2 photosynthetic devices and photocatalysts are also discussed.« less

Charge compensation mechanisms in favor of the incorporation of the Eu3+ ion into the ZnO host lattice

NASA Astrophysics Data System (ADS)

Baira, M.; Bekhti-Siad, A.; Hebali, K.; Bouhani-Benziane, H.; Sahnoun, M.

2018-05-01

Eu3+ doped phosphors with charge compensation are potential candidates of red emitting phosphors for lamp applications. Charge compensation improves the luminescence performance of the material. The charge compensation can most probably be achieved by three possible mechanisms: (a) two Zn2+ ions are replaced by one Eu3+ ions and one monovalent cation, 2Zn2+ →Eu3++ Li+, where Li+ is acting as a charge compensator; (b) the charge compensation is provided by a zinc vacancy (VZn) defects, 3Zn2+ → 2Eu3++ VZn, the subscript Zn denotes an ion in a normal zinc site in the lattice; (c) two Zn2+ ions are replaced by one Eu3+ ions with the presence of interstitial oxygen (Oi), 2Zn2+ → 2Eu3++ Oi. Electronic structures of the crystals corresponding to the three models are evaluated by the first-principles quantum mechanical calculations based on the density functional theory. It is found that the charge compensator defects make Eu3+ doping in ZnO energetically more favorable. They break the local symmetry around the Eu3+ ion and lead to deep states below the empty upper band, the conduction band that could facilitate intra-4f shell transitions, which can obviously improve the emission intensity of Eu3+-doped ZnO. Therefore, the effect of these defects on the host crystals electronic band states relative to the Eu3+ states is reported, since both electron transfer and electronically energy transfer processes enhance the performance of optoelectronic devices based on this material. These theoretical insights are helpful for designing rare-earth doped oxide materials with high photoluminescence (PL) performance.

Terahertz magnonics: Feasibility of using terahertz magnons for information processing

NASA Astrophysics Data System (ADS)

Zakeri, Khalil

2018-06-01

An immediate need of information technology is designing fast, small and low-loss devices. One of the ways to design such devices is using the bosonic quasiparticles, such as magnons, for information transfer/processing. This is the main idea behind the field of magnonics. When a magnon propagates through a magnetic medium, no electrical charge transport is involved and therefore no energy losses, creating Joule heating, occur. This is the most important advantage of using magnons for information transfer. Moreover the mutual conversion between magnons and the other carriers e.g. electrons, photons and plasmons shall open new opportunities to realize tunable multifunctional devices. Magnons cover a very wide range of frequency, from sub-gigahertz up to a few hundreds of terahertz. The magnon frequency has an important impact on the performance of magnon-based devices (the larger the excitation frequency, the faster the magnons). This means that the use of high-frequency (terahertz) magnons would provide a great opportunity for the design of ultrafast devices. However, up to now the focus in magnonics has been on the low-frequency gigahertz magnons. Here we discuss the feasibility of using terahertz magnons for application in magnonic devices. We shall bring the concept of terahertz magnonics into discussion. We discuss how the recently discovered phenomena in the field of terahertz magnons may inspire ideas for designing new magnonic devices. We further introduce methods to tune the fundamental properties of terahertz magnons, e.g. their eigenfrequency and lifetime.

Pulse switching for high energy lasers

NASA Technical Reports Server (NTRS)

Laudenslager, J. B.; Pacala, T. J. (Inventor)

1981-01-01

A saturable inductor switch for compressing the width and sharpening the rise time of high voltage pulses from a relatively slow rise time, high voltage generator to an electric discharge gas laser (EDGL) also provides a capability for efficient energy transfer from a high impedance primary source to an intermediate low impedance laser discharge network. The switch is positioned with respect to a capacitive storage device, such as a coaxial cable, so that when a charge build-up in the storage device reaches a predetermined level, saturation of the switch inductor releases or switches energy stored in the capactive storage device to the EDGL. Cascaded saturable inductor switches for providing output pulses having rise times of less than ten nanoseconds and a technique for magnetically biasing the saturable inductor switch are disclosed.

Carrier and photon dynamics in a topological insulator Bi{sub 2}Te{sub 3}/GaN type II staggered heterostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chaturvedi, P.; Chouksey, S.; Banerjee, D.

2015-11-09

We have demonstrated a type-II band-aligned heterostructure between pulsed laser deposited topological insulator bismuth telluride and metal organic-chemical-vapour deposited GaN on a sapphire substrate. The heterostructure shows a large valence band-offset of 3.27 eV as determined from x-ray photoelectron spectroscopy, which is close to the bandgap of GaN (3.4 eV). Further investigation using x-ray diffraction, Raman spectroscopy, and energy-dispersive x-ray spectrum reveals the stoichiometric and material properties of bismuth telluride on GaN. Steady state photon emission from GaN is found to be modulated by the charge transfer process due to diffusion across the junction. The time constant involved with the charge transfermore » process is found to be 0.6 ns by transient absorption spectroscopy. The heterostructure can be used for designing devices with different functionalities and improving the performance of the existing devices on GaN.« less

Conjugated ionic state and its distribution in perylene bisimide doped film: A characterization of Z-scanning in confocal Raman spectroscopy.

PubMed

Zhou, Xuehong; Zhang, Wenqiang; Wang, Cong; Zhou, Jiadong; Liu, Linlin; Xie, Zengqi; Ma, Yuguang

2018-04-27

Ion-doped states are significant for improving the performance in organic semiconductor-based devices, which require clear characterization to understand their relationship with conductivity and charge transporting mechanisms. In this paper, Raman spectroscopy is used to track the evolution of a dianion-anion-neutral mixture in a perylene bisimide (PBI)-doped film under air, with z-scanning carried out in the confocal mode. The precise distribution for the different states along the film depth is realized within 3.5 μm. The whole film is clearly divided into three regions: the ion-poor state, transition region and ion-rich state. The ion ratio and distribution are strongly related to the film conductivity and the onset voltage shift. Changes in the distribution of the ionic species during oxidation and electrode catalysis are clearly recorded by z-scanning, which is beneficial for understanding the charge transfer properties as well as the mechanism underlying working devices. Copyright © 2018 Elsevier B.V. All rights reserved.

High performance symmetric supercapacitor based on zinc hydroxychloride nanosheets and 3D graphene-nickel foam composite

NASA Astrophysics Data System (ADS)

Khamlich, S.; Abdullaeva, Z.; Kennedy, J. V.; Maaza, M.

2017-05-01

In this work, zinc hydroxychloride nanosheets (ZHCNs) were deposited on 3d graphene-nickel foam (NiF-G) by employing a simple hydrothermal synthesis method to form NiF-G/ZHCNs composite electrode materials. The fabricated NiF-G/ZHCNs electrode revealed a well-developed pore structures with high specific surface area of 119 m2 g-1, and used as electrode materials for symmetric supercapacitor with aqueous alkaline electrolyte. The specific areal capacitance and electron charge transfer resistance (Rct) were 222 mF cm-2 (at current density of 1.0 mA cm-2) and 1.63 Ω, respectively, in a symmetric two-electrode system. After 5000 cycles with galvanostatic charge/discharge, the device can maintain 96% of its initial capacitance under 1.0 mA cm-2 and showed low Rct of about 9.84 Ω. These results indicate that NiF-G/ZHCNs composite is an excellent electrode material for electrochemical energy storage devices.

Gate-Driven Pure Spin Current in Graphene

NASA Astrophysics Data System (ADS)

Lin, Xiaoyang; Su, Li; Si, Zhizhong; Zhang, Youguang; Bournel, Arnaud; Zhang, Yue; Klein, Jacques-Olivier; Fert, Albert; Zhao, Weisheng

2017-09-01

The manipulation of spin current is a promising solution for low-power devices beyond CMOS. However, conventional methods, such as spin-transfer torque or spin-orbit torque for magnetic tunnel junctions, suffer from large power consumption due to frequent spin-charge conversions. An important challenge is, thus, to realize long-distance transport of pure spin current, together with efficient manipulation. Here, the mechanism of gate-driven pure spin current in graphene is presented. Such a mechanism relies on the electrical gating of carrier-density-dependent conductivity and spin-diffusion length in graphene. The gate-driven feature is adopted to realize the pure spin-current demultiplexing operation, which enables gate-controllable distribution of the pure spin current into graphene branches. Compared with the Elliott-Yafet spin-relaxation mechanism, the D'yakonov-Perel spin-relaxation mechanism results in more appreciable demultiplexing performance. The feature of the pure spin-current demultiplexing operation will allow a number of logic functions to be cascaded without spin-charge conversions and open a route for future ultra-low-power devices.

Hot Charge Carrier Transmission from Plasmonic Nanostructures

NASA Astrophysics Data System (ADS)

Christopher, Phillip; Moskovits, Martin

2017-05-01

Surface plasmons have recently been harnessed to carry out processes such as photovoltaic current generation, redox photochemistry, photocatalysis, and photodetection, all of which are enabled by separating energetic (hot) electrons and holes—processes that, previously, were the domain of semiconductor junctions. Currently, the power conversion efficiencies of systems using plasmon excitation are low. However, the very large electron/hole per photon quantum efficiencies observed for plasmonic devices fan the hope of future improvements through a deeper understanding of the processes involved and through better device engineering, especially of critical interfaces such as those between metallic and semiconducting nanophases (or adsorbed molecules). In this review, we focus on the physics and dynamics governing plasmon-derived hot charge carrier transfer across, and the electronic structure at, metal-semiconductor (molecule) interfaces, where we feel the barriers contributing to low efficiencies reside. We suggest some areas of opportunity that deserve early attention in the still-evolving field of hot carrier transmission from plasmonic nanostructures to neighboring phases.

Charge migration and charge transfer in molecular systems

PubMed Central

Wörner, Hans Jakob; Arrell, Christopher A.; Banerji, Natalie; Cannizzo, Andrea; Chergui, Majed; Das, Akshaya K.; Hamm, Peter; Keller, Ursula; Kraus, Peter M.; Liberatore, Elisa; Lopez-Tarifa, Pablo; Lucchini, Matteo; Meuwly, Markus; Milne, Chris; Moser, Jacques-E.; Rothlisberger, Ursula; Smolentsev, Grigory; Teuscher, Joël; van Bokhoven, Jeroen A.; Wenger, Oliver

2017-01-01

The transfer of charge at the molecular level plays a fundamental role in many areas of chemistry, physics, biology and materials science. Today, more than 60 years after the seminal work of R. A. Marcus, charge transfer is still a very active field of research. An important recent impetus comes from the ability to resolve ever faster temporal events, down to the attosecond time scale. Such a high temporal resolution now offers the possibility to unravel the most elementary quantum dynamics of both electrons and nuclei that participate in the complex process of charge transfer. This review covers recent research that addresses the following questions. Can we reconstruct the migration of charge across a molecule on the atomic length and electronic time scales? Can we use strong laser fields to control charge migration? Can we temporally resolve and understand intramolecular charge transfer in dissociative ionization of small molecules, in transition-metal complexes and in conjugated polymers? Can we tailor molecular systems towards specific charge-transfer processes? What are the time scales of the elementary steps of charge transfer in liquids and nanoparticles? Important new insights into each of these topics, obtained from state-of-the-art ultrafast spectroscopy and/or theoretical methods, are summarized in this review. PMID:29333473

Event-driven charge-coupled device design and applications therefor

NASA Technical Reports Server (NTRS)

Doty, John P. (Inventor); Ricker, Jr., George R. (Inventor); Burke, Barry E. (Inventor); Prigozhin, Gregory Y. (Inventor)

2005-01-01

An event-driven X-ray CCD imager device uses a floating-gate amplifier or other non-destructive readout device to non-destructively sense a charge level in a charge packet associated with a pixel. The output of the floating-gate amplifier is used to identify each pixel that has a charge level above a predetermined threshold. If the charge level is above a predetermined threshold the charge in the triggering charge packet and in the charge packets from neighboring pixels need to be measured accurately. A charge delay register is included in the event-driven X-ray CCD imager device to enable recovery of the charge packets from neighboring pixels for accurate measurement. When a charge packet reaches the end of the charge delay register, control logic either dumps the charge packet, or steers the charge packet to a charge FIFO to preserve it if the charge packet is determined to be a packet that needs accurate measurement. A floating-diffusion amplifier or other low-noise output stage device, which converts charge level to a voltage level with high precision, provides final measurement of the charge packets. The voltage level is eventually digitized by a high linearity ADC.

The damage equivalence of electrons, protons, and gamma rays in MOS devices

NASA Technical Reports Server (NTRS)

Brucker, G. J.; Stassinopoulos, E. G.; Van Gunten, O.; August, L. S.; Jordan, T. M.

1982-01-01

The results of laboratory tests to determine the radiation damage effects induced on MOS devices from Co-60, electron, and proton radiation are reported. The tests are performed to establish the relationship between the Co-60 gamma rays and the level of damage to the MOS devices in regards to different damages which can be expected with the electron and particle bombardments experienced in space applications. CMOS devices were exposed to the Co-60 gamma rays, 1 MeV electrons, and 1 MeV protons while operating at 3, 10, and 15 V. The test data indicated that the Co-60 source was reliable for an initial evaluation of the electron damages up to 2 MeV charge. A correction factor was devised for transferring the Co-60 measurements to proton damages, independent of bias and transistor types, for any orbit or environment.

Quantum Dot Light-Emitting Devices: Beyond Alignment of Energy Levels

DOE PAGES

Zaiats, Gary; Ikeda, Shingo; Kinge, Sachin; ...

2017-08-25

Multinary semiconductor nanoparticles such as CuInS 2, AgInS 2, and the corresponding alloys with ZnS hold promise for designing future quantum dot light-emitting devices (QLED). The QLED architectures require matching of energy levels between the different electron and hole transport layers. In addition to energy level alignment, conductivity and charge transfer interactions within these layers determine the overall efficiency of QLED. By employing CuInS 2-ZnS QDs we succeeded in fabricating red-emitting QLED using two different hole-transporting materials, polyvinylcarbazole and poly(4- butylphenyldiphenylamine). Despite the similarity of the HOMO-LUMO energy levels of these two hole transport materials, the QLED devices exhibit distinctlymore » different voltage dependence. The difference in onset voltage and excited state interactions shows the complexity involved in selecting the hole transport materials for display devices.« less

CTAB-Aided Synthesis of Stacked V2O5 Nanosheets: Morphology, Electrochemical Features and Asymmetric Device Performance

NASA Astrophysics Data System (ADS)

Saravanakumar, B.; Maruthamuthu, S.; Umadevi, V.; Saravanan, V.

To accomplish superior performance in supercapacitors, a fresh class of electrode materials with advantageous structures is essential. Owing to its rich electrochemical activity, vanadium oxides are considered to be an attractive electrode material for energy storing devices. In this work, vanadium pentoxide (V2O5) nanostructures were prepared using surfactant (CTAB)-assisted hydrothermal route. Stacked V2O5 sheets enable additional channels for electrolyte ion intercalation. These stacked V2O5 nanosheets show highest specific capacitance of 466Fg-1 at 0.5Ag-1. In addition, it exhibits good rate capacity, lower value of charge transfer resistance and good stability when used as an electrode material for supercapacitors. Further, an asymmetric supercapacitor device was assembled utilizing the stacked V2O5 sheets and activated carbon as electrodes. The electrochemical features of the device are also discussed.

Negative differential resistance observation in complex convoluted fullerene junctions

NASA Astrophysics Data System (ADS)

Kaur, Milanpreet; Sawhney, Ravinder Singh; Engles, Derick

2018-04-01

In this work, we simulated the smallest fullerene molecule, C20 in a two-probe device model with gold electrodes. The gold electrodes comprised of (011) miller planes were carved to construct the novel geometry based four unique shapes, which were strung to fullerene molecules through mechanically controlled break junction techniques. The organized devices were later scrutinized using non-equilibrium Green's function based on the density functional theory to calculate their molecular orbitals, energy levels, charge transfers, and electrical parameters. After intense scrutiny, we concluded that five-edged and six-edged devices have the lowest and highest current-conductance values, which result from their electrode-dominating and electrode-subsidiary effects, respectively. However, an interesting observation was that the three-edged and four-edged electrodes functioned as semi-metallic in nature, allowing the C20 molecule to demonstrate its performance with the complementary effect of these electrodes in the electron conduction process of a two-probe device.

Quantum Dot Light-Emitting Devices: Beyond Alignment of Energy Levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaiats, Gary; Ikeda, Shingo; Kinge, Sachin

Multinary semiconductor nanoparticles such as CuInS 2, AgInS 2, and the corresponding alloys with ZnS hold promise for designing future quantum dot light-emitting devices (QLED). The QLED architectures require matching of energy levels between the different electron and hole transport layers. In addition to energy level alignment, conductivity and charge transfer interactions within these layers determine the overall efficiency of QLED. By employing CuInS 2-ZnS QDs we succeeded in fabricating red-emitting QLED using two different hole-transporting materials, polyvinylcarbazole and poly(4- butylphenyldiphenylamine). Despite the similarity of the HOMO-LUMO energy levels of these two hole transport materials, the QLED devices exhibit distinctlymore » different voltage dependence. The difference in onset voltage and excited state interactions shows the complexity involved in selecting the hole transport materials for display devices.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Pingrui; Liu, Ziyang; Liu, Dongyang

Pentacene organic thin-film transistors (OTFTs) were prepared by introducing 4, 4″-tris(3-methylphenylphenylamino) triphenylamine (m-MTDATA): MoO{sub 3}, Pentacene: MoO{sub 3}, and Pentacene: m-MTDATA: MoO{sub 3} as buffer layers. These OTFTs all showed significant performance improvement comparing to the reference device. Significantly, we observe that the device employing Pentacene: m-MTDATA: MoO{sub 3} buffer layer can both take advantage of charge transfer complexes formed in the m-MTDATA: MoO{sub 3} device and suitable energy level alignment existed in the Pentacene: MoO{sub 3} device. These two parallel paths led to a high mobility, low threshold voltage, and contact resistance of 0.72 cm{sup 2}/V s, −13.4 V,more » and 0.83 kΩ at V{sub ds} = − 100 V. This work enriches the understanding of MoO{sub 3} doped organic materials for applications in OTFTs.« less

Tuning charge balance in PHOLEDs with ambipolar host materials to achieve high efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Padmaperuma, Asanga B.; Koech, Phillip K.; Cosimbescu, Lelia

2009-08-27

The efficiency and stability of blue organic light emitting devices (OLEDs) continue to be a primary roadblock to developing organic solid state white lighting. For OLEDs to meet the high power conversion efficiency goal, they will require both close to 100% internal quantum efficiency and low operating voltage in a white light emitting device.1 It is generally accepted that such high quantum efficiency, can only be achieved with the use of organometallic phosphor doped OLEDs. Blue OLEDs are particularly important for solid state lighting. The simplest (and therefore likely the lowest cost) method of generating white light is to downmore » convert part of the emission from a blue light source with a system of external phosphors.2 A second method of generating white light requires the superposition of the light from red, green and blue OLEDs in the correct ratio. Either of these two methods (and indeed any method of generating white light with a high color rendering index) critically depends on a high efficiency blue light component.3 A simple OLED generally consists of a hole-injecting anode, a preferentially hole transporting organic layer (HTL), an emissive layer that contains the recombination zone and ideally transports both holes and electrons, a preferentially electron-transporting layer (ETL) and an electron-injecting cathode. Color in state-of-the-art OLEDs is generated by an organometallic phosphor incorporated by co-sublimation into the emissive layer (EML).4 New materials functioning as hosts, emitters, charge transporting, and charge blocking layers have been developed along with device architectures leading to electrophosphorescent based OLEDs with high quantum efficiencies near the theoretical limit. However, the layers added to the device architecture to enable high quantum efficiencies lead to higher operating voltages and correspondingly lower power efficiencies. Achievement of target luminance power efficiencies will require new strategies for lowering operating voltages, particularly if this is to be achieved in a device that can be manufactured at low cost. To avoid the efficiency losses associated with phosphorescence quenching by back-energy transfer from the dopant onto the host, the triplet excited states of the host material must be higher in energy than the triplet excited state of the dopant.5 This must be accomplished without sacrificing the charge transporting properties of the composite.6 Similar problems limit the efficiency of OLED-based displays, where blue light emitters are the least efficient and least stable. We previously demonstrated the utility of organic phosphine oxide (PO) materials as electron transporting HMs for FIrpic in blue OLEDs.7 However, the high reluctance of PO materials to oxidation and thus, hole injection limits the ability to balance charge injection and transport in the EML without relying on charge transport by the phosphorescent dopant. PO host materials were engineered to transport both electrons and holes in the EML and still maintain high triplet exciton energy to ensure efficient energy transfer to the dopant (Figure 1). There are examples of combining hole transporting moieties (mainly aromatic amines) with electron transport moieties (e.g., oxadiazoles, triazines, boranes)8 to develop new emitter and host materials for small molecule and polymer9 OLEDs. The challenge is to combine the two moieties without lowering the triplet energy of the target molecule. For example, coupling of a dimesitylphenylboryl moiety with a tertiary aromatic amine (FIAMBOT) results in intramolecular electron transfer from the amine to the boron atom through the bridging phenyl. The mesomeric effect of the dimesitylphenylboryl unit acts to extend conjugation and lowers triplet exciton energies (< 2.8 eV) rendering such systems inadequate as ambipolar hosts for blue phosphors.« less

Targeting ideal acceptor-donor materials based on hexabenzocoronene

NASA Astrophysics Data System (ADS)

Santos Silva, H.; Metz, Sebastian; Hiorns, Roger C.; Bégué, D.

2018-06-01

A series of new hybrid donor-acceptor materials based on hexabenzocoronenes (HBC) functionalized with electron donors is investigated by combining a variety of quantum mechanical and molecular dynamic methodologies for use in organic photovoltaic (OPV) devices. Segments of a low band gap alternating copolymer constructed of benzo[1,2-b;3,4-b]dithiophene and thieno[3,4-c]pyrrole-4,6-dione were attached to the conjugated HBC core. The copolymer was chosen for its known high performance in OPVs, and both moieties were singled out due to their exceptional resistance to photo-oxidation, an important requirement for such applications. The macromolecular topology of these systems are expected to induce supra-molecular columns, such as those common to discotic liquid crystals, conducive to the effective percolation of electrons in OPV devices. A challenge with these systems, that of the mixing of the electronic structures of the donor and acceptor moieties that result in excitonic losses and charge recombination, was diminished by trialling a range of linking units. It was found possible to propose ideal donor-acceptor structures with enhanced charge dissociations and transfers in the π-stacking direction for use in OPV and other organic electronic devices.

Lithographically patterned thin activated carbon films as a new technology platform for on-chip devices.

PubMed

Wei, Lu; Nitta, Naoki; Yushin, Gleb

2013-08-27

Continuous, smooth, visibly defect-free, lithographically patterned activated carbon films (ACFs) are prepared on the surface of silicon wafers. Depending on the synthesis conditions, porous ACFs can either remain attached to the initial substrate or be separated and transferred to another dense or porous substrate of interest. Tuning the activation conditions allows one to change the surface area and porosity of the produced carbon films. Here we utilize the developed thin ACF technology to produce prototypes of functional electrical double-layer capacitor devices. The synthesized thin carbon film electrodes demonstrated very high capacitance in excess of 510 F g(-1) (>390 F cm(-3)) at a slow cyclic voltammetry scan rate of 1 mV s(-1) and in excess of 325 F g(-1) (>250 F cm(-3)) in charge-discharge tests at an ultrahigh current density of 45,000 mA g(-1). Good stability was demonstrated after 10,000 galvanostatic charge-discharge cycles. The high values of the specific and volumetric capacitances of the selected ACF electrodes as well as the capacity retention at high current densities demonstrated great potential of the proposed technology for the fabrication of various on-chip devices, such as micro-electrochemical capacitors.

Impact of charge-transfer excitons in regioregular polythiophene on the charge separation at polythiophene-fullerene heterojunctions

NASA Astrophysics Data System (ADS)

Polkehn, M.; Tamura, H.; Burghardt, I.

2018-01-01

This study addresses the mechanism of ultrafast charge separation in regioregular oligothiophene-fullerene assemblies representative of poly-3-hexylthiophene (P3HT)-[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) heterojunctions, with special emphasis on the inclusion of charge transfer excitons in the oligothiophene phase. The formation of polaronic inter-chain charge separated species in highly ordered oligothiophene has been demonstrated in recent experiments and could have a significant impact on the net charge transfer to the fullerene acceptor. The present approach combines a first-principles parametrized multi-site Hamiltonian, based on time-dependent density functional theory calculations, with accurate quantum dynamics simulations using the multi-layer multi-configuration time-dependent Hartree method. Quantum dynamical studies are carried out for up to 182 electronic states and 112 phonon modes. The present analysis follows up on our previous study of (Huix-Rotllant et al 2015 J. Phys. Chem. Lett. 6 1702) and significantly expands the scope of this analysis by including the dynamical role of charge transfer excitons. Our investigation highlights the pronounced mixing of photogenerated Frenkel excitons with charge transfer excitons in the oligothiophene domain, and the opening of new transfer channels due the creation of such charge-separated species. As a result, it turns out that the interfacial donor/acceptor charge transfer state can be largely circumvented due to the presence of charge transfer excitons. However, the latter states in turn act as a trap, such that the free carrier yield observed on ultrafast time scales is tangibly reduced. The present analysis underscores the complexity of the transfer pathways at P3HT-PCBM type junctions.

Bio-Photoelectrochemical Solar Cells Incorporating Reaction Center and Reaction Center Plus Light Harvesting Complexes

NASA Astrophysics Data System (ADS)

Yaghoubi, Houman

Harvesting solar energy can potentially be a promising solution to the energy crisis now and in the future. However, material and processing costs continue to be the most important limitations for the commercial devices. A key solution to these problems might lie within the development of bio-hybrid solar cells that seeks to mimic photosynthesis to harvest solar energy and to take advantage of the low material costs, negative carbon footprint, and material abundance. The bio-photoelectrochemical cell technologies exploit biomimetic means of energy conversion by utilizing plant-derived photosystems which can be inexpensive and ultimately the most sustainable alternative. Plants and photosynthetic bacteria harvest light, through special proteins called reaction centers (RCs), with high efficiency and convert it into electrochemical energy. In theory, photosynthetic RCs can be used in a device to harvest solar energy and generate 1.1 V open circuit voltage and ~1 mA cm-2 short circuit photocurrent. Considering the nearly perfect quantum yield of photo-induced charge separation, efficiency of a protein-based solar cell might exceed 20%. In practice, the efficiency of fabricated devices has been limited mainly due to the challenges in the electron transfer between the protein complex and the device electrodes as well as limited light absorption. The overarching goal of this work is to increase the power conversion efficiency in protein-based solar cells by addressing those issues (i.e. electron transfer and light absorption). This work presents several approaches to increase the charge transfer rate between the photosynthetic RC and underlying electrode as well as increasing the light absorption to eventually enhance the external quantum efficiency (EQE) of bio-hybrid solar cells. The first approach is to decrease the electron transfer distance between one of the redox active sites in the RC and the underlying electrode by direct attachment of the of protein complex onto Au electrodes via surface exposed cysteine residues. This resulted in photocurrent densities as large as ~600 nA cm-2 while still the incident photon to generated electron quantum efficiency was as low as %3 x 10-4. 2- The second approach is to immobilize wild type RCs of Rhodobacter sphaeroides on the surface of a Au underlying electrode using self-assembled monolayers of carboxylic acid terminated oligomers and cytochrome c charge mediating layers, with a preferential orientation from the primary electron donor site. This approach resulted in EQE of up to 0.06%, which showed 200 times efficiency improvement comparing to the first approach. In the third approach, instead of isolated protein complexes, RCs plus light harvesting (LH) complexes were employed for a better photon absorption. Direct attachment of RC-LH1 complexes on Au working electrodes, resulted in 0.21% EQE which showed 3.5 times efficiency improvement over the second approach (700 times higher than the first approach). The main impact of this work is the harnessing of biological RCs for efficient energy harvesting in man-made structures. Specifically, the results in this work will advance the application of RCs in devices for energy harvesting and will enable a better understanding of bio and nanomaterial interfaces, thereby advancing the application of biological materials in electronic devices. At the end, this work offers general guidelines that can serve to improve the performance of bio-hybrid solar cells.

Stimulated emission within the exciplex band by plasmonic-nanostructured polymeric heterojunctions

NASA Astrophysics Data System (ADS)

Zhang, Xinping; Li, Hongwei; Wang, Yimeng; Liu, Feifei

2015-03-01

Organic heterojunctions have been extensively employed in the design of light-emitting diodes, photovoltaic devices, and thin-film field-effect transistors, which can be achieved by constructing a bilayer or a multi-layered thin-film deposition, or by blending two or more organic semiconductors with different charge-transport performances. Charge transfer excited states or exciplex may form on the heterointerfaces. Efficient light-emitting diodes have been demonstrated using exciplex emission. However, lasing or stimulated emission processes have not been observed with exciplex formation at organic heterojunctions. In this work, we demonstrate strong coherent interaction between photons and exciplex formation in the blends of poly-9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-l,4-phenylenediamine (PFB) and poly-9,9'-dioctylfluorene-co-benzothiadiazole (F8BT), leading to transient stimulated exciplex emission. The responsible mechanisms involve plasmonic local-field enhancement and plasmonic feedback in a three-dimensional gold-nanoparticle matrix.Organic heterojunctions have been extensively employed in the design of light-emitting diodes, photovoltaic devices, and thin-film field-effect transistors, which can be achieved by constructing a bilayer or a multi-layered thin-film deposition, or by blending two or more organic semiconductors with different charge-transport performances. Charge transfer excited states or exciplex may form on the heterointerfaces. Efficient light-emitting diodes have been demonstrated using exciplex emission. However, lasing or stimulated emission processes have not been observed with exciplex formation at organic heterojunctions. In this work, we demonstrate strong coherent interaction between photons and exciplex formation in the blends of poly-9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-l,4-phenylenediamine (PFB) and poly-9,9'-dioctylfluorene-co-benzothiadiazole (F8BT), leading to transient stimulated exciplex emission. The responsible mechanisms involve plasmonic local-field enhancement and plasmonic feedback in a three-dimensional gold-nanoparticle matrix. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00140d

Interface design principles for high-performance organic semiconductor devices

DOE PAGES

Nie, Wanyi; Gupta, Gautam; Crone, Brian K.; ...

2015-03-23

Organic solar cells (OSCs) are a promising cost-effective candidate in next generation photovoltaic technology. However, a critical bottleneck for OSCs is the electron/hole recombination loss through charge transfer state at the interface, which greatly limits the power conversion efficiency. W. Nie, A. Mohite, and co-workers demonstrate a simple strategy of suppressing the recombination rate by inserting a spacer layer at the donor-acceptor interface, resulting in a dramatic increase in power conversion efficiency.

Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes

NASA Technical Reports Server (NTRS)

Santos, Javier; Bu, Xiu R.; Mintz, Eric A.

2001-01-01

The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

Shuttle and Transfer Orbit Thermal Analysis and Testing of the Chandra X-Ray Observatory Charge-Couple Device Imaging Spectrometer Radiator Shades

NASA Technical Reports Server (NTRS)

Sharp, John R.

1999-01-01

Thermal analyses of the Shuttle and Transfer Orbit of the Advanced X-Ray Astrophysics Facility Charge-Coupled Device (CCD) Imaging Spectrometer (ACIS), one of two science instruments on the Chandra X-Ray Observatory, revealed a low-earth orbit (LEO) overheating problem on the goldized Kapton faces of two radiator shades. The shades were coated with the goldized Kapton to provide a low hemispherical emittance to minimize direct and backloaded heating from the sun and the observatory and high specularity to optimize the coupling to space on two passive radiators which cool the focal plane to -120 C +/- 1 C during on-orbit operations. Since the observatory has a highly elliptical final orbit of 10,000 kilometers by 140,000 kilometers and the ACIS radiators and shades are oriented anti-sun, the high solar absorptance to emittance ratio of the goldized Kapton was not an issue. However, during Shuttle bay-to-earth operations, the short duration solar heating occurring near the eclipse entry and exit resulted in shade temperatures in excess of the cure temperature of the adhesive used to bond the goldized Kapton and honeycomb face-sheets. The detailed thermal analysis demonstrating the LEO overheating as well as the redesign options and thermal testing of a redesigned development unit shade are presented.

The interface between ferroelectric and 2D material for a Ferroelectric Field-Effect Transistor

NASA Astrophysics Data System (ADS)

Park, Nahee; Kang, Haeyong; Lee, Sang-Goo; Lee, Young Hee; Suh, Dongseok

We have studied electrical property of ferroelectric field-effect transistor which consists of graphene on hexagonal Boron-Nitride (h-BN) gated by a ferroelectric, PMN-PT (i.e. (1-x)Pb(Mg1/3Nb2/3) O3-xPbTiO3) single-crystal substrate. The PMN-PT was expected to have an effect on polarization field into the graphene channel and to induce a giant amount of surface charge. The hexagonal Boron-Nitride (h-BN) flake was directly exfoliated on the PMN-PT substrate for preventing graphene from directly contacting on the PMN-PT substrate. It can make us to observe the effect of the interface between ferroelectric and 2D material on the device operation. Monolayer graphene as 2D channel material, which was confirmed by Raman spectroscopy, was transferred on top of the hexagonal Boron-Nitride (h-BN) by using the conventional dry-transfer method. Here, we can demonstrate that the structure of graphene/hexagonal-BN/ferroelectric field-effect transistor makes us to clearly understand the device operation as well as the interface between ferroelectric and 2D materials by inserting h-BN between them. The phenomena such as anti-hysteresis, current saturation behavior, and hump-like increase of channel current, will be discussed by in terms of ferroelectric switching, polarization-assisted charge trapping.

Interfacial Molecular Packing Determines Exciton Dynamics in Molecular Heterostructures: The Case of Pentacene-Perfluoropentacene.

PubMed

Rinn, Andre; Breuer, Tobias; Wiegand, Julia; Beck, Michael; Hübner, Jens; Döring, Robin C; Oestreich, Michael; Heimbrodt, Wolfram; Witte, Gregor; Chatterjee, Sangam

2017-12-06

The great majority of electronic and optoelectronic devices depend on interfaces between p-type and n-type semiconductors. Finding matching donor-acceptor systems in molecular semiconductors remains a challenging endeavor because structurally compatible molecules may not necessarily be suitable with respect to their optical and electronic properties, and the large exciton binding energy in these materials may favor bound electron-hole pairs rather than free carriers or charge transfer at an interface. Regardless, interfacial charge-transfer exciton states are commonly considered as an intermediate step to achieve exciton dissociation. The formation efficiency and decay dynamics of such states will strongly depend on the molecular makeup of the interface, especially the relative alignment of donor and acceptor molecules. Structurally well-defined pentacene-perfluoropentacene heterostructures of different molecular orientations are virtually ideal model systems to study the interrelation between molecular packing motifs at the interface and their electronic properties. Comparing the emission dynamics of the heterosystems and the corresponding unitary films enables accurate assignment of every observable emission signal in the heterosystems. These heterosystems feature two characteristic interface-specific luminescence channels at around 1.4 and 1.5 eV that are not observed in the unitary samples. Their emission strength strongly depends on the molecular alignment of the respective donor and acceptor molecules, emphasizing the importance of structural control for device construction.

Accumulative charge separation for solar fuels production: coupling light-induced single electron transfer to multielectron catalysis.

PubMed

Hammarström, Leif

2015-03-17

The conversion and storage of solar energy into a fuel holds promise to provide a significant part of the future renewable energy demand of our societies. Solar energy technologies today generate heat or electricity, while the large majority of our energy is used in the form of fuels. Direct conversion of solar energy to a fuel would satisfy our needs for storable energy on a large scale. Solar fuels can be generated by absorbing light and converting its energy to chemical energy by electron transfer leading to separation of electrons and holes. The electrons are used in the catalytic reduction of a cheap substrate with low energy content into a high-energy fuel. The holes are filled by oxidation of water, which is the only electron source available for large scale solar fuel production. Absorption of a single photon typically leads to separation of a single electron-hole pair. In contrast, fuel production and water oxidation are multielectron, multiproton reactions. Therefore, a system for direct solar fuel production must be able to accumulate the electrons and holes provided by the sequential absorption of several photons in order to complete the catalytic reactions. In this Account, the process is termed accumulative charge separation. This is considerably more complicated than charge separation on a single electron level and needs particular attention. Semiconductor materials and molecular dyes have for a long time been optimized for use in photovoltaic devices. Efforts are made to develop new systems for light harvesting and charge separation that are better optimized for solar fuel production than those used in the early devices presented so far. Significant progress has recently been made in the discovery and design of better homogeneous and heterogeneous catalysts for solar fuels and water oxidation. While the heterogeneous ones perform better today, molecular catalysts based on transition metal complexes offer much greater tunability of electronic and structural properties, they are typically more amenable to mechanistic analysis, and they are small and therefore require less material. Therefore, they have arguably greater potential as future efficient catalysts but must be efficiently coupled to accumulative charge separation. This Account discusses accumulative charge separation with focus on molecular and molecule-semiconductor hybrid systems. The coupling between charge separation and catalysis involves many challenges that are often overlooked, and they are not always apparent when studying water oxidation and fuel formation as separate half-reactions with sacrificial agents. Transition metal catalysts, as well as other multielectron donors and acceptors, cycle through many different states that may quench the excited sensitizer by nonproductive pathways. Examples where this has been shown, often with ultrafast rates, are reviewed. Strategies to avoid these competing energy-loss reactions and still obtain efficient coupling of charge separation to catalysis are discussed. This includes recent examples of dye-sensitized semiconductor devices with molecular catalysts and dyes that realize complete water splitting, albeit with limited efficiency.

Directing the path of light-induced electron transfer at a molecular fork using vibrational excitation

NASA Astrophysics Data System (ADS)

Delor, Milan; Archer, Stuart A.; Keane, Theo; Meijer, Anthony J. H. M.; Sazanovich, Igor V.; Greetham, Gregory M.; Towrie, Michael; Weinstein, Julia A.

2017-11-01

Ultrafast electron transfer in condensed-phase molecular systems is often strongly coupled to intramolecular vibrations that can promote, suppress and direct electronic processes. Recent experiments exploring this phenomenon proved that light-induced electron transfer can be strongly modulated by vibrational excitation, suggesting a new avenue for active control over molecular function. Here, we achieve the first example of such explicit vibrational control through judicious design of a Pt(II)-acetylide charge-transfer donor-bridge-acceptor-bridge-donor 'fork' system: asymmetric 13C isotopic labelling of one of the two -C≡C- bridges makes the two parallel and otherwise identical donor→acceptor electron-transfer pathways structurally distinct, enabling independent vibrational perturbation of either. Applying an ultrafast UVpump(excitation)-IRpump(perturbation)-IRprobe(monitoring) pulse sequence, we show that the pathway that is vibrationally perturbed during UV-induced electron transfer is dramatically slowed down compared to its unperturbed counterpart. One can thus choose the dominant electron transfer pathway. The findings deliver a new opportunity for precise perturbative control of electronic energy propagation in molecular devices.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mallajosyula, Arun T.; Nie, Wanyi; Gupta, Gautam

A prerequisite for carbon nanotube-based optoelectronic devices is the ability to sort them into a pure semiconductor phase. One of the most common sorting routes is enabled through using specific wrapping polymers. Here we show that subtle changes in the polymer structure can have a dramatic influence on the figures of merit of a carbon nanotube-based photovoltaic device. By comparing two commonly used polyfluorenes (PFO and PFO-BPy) for wrapping (7,5) and (6,5) chirality SWCNTs, we demonstrate that they have contrasting effects on the device efficiency. We attribute this to the differences in their ability to efficiently transfer charge. Although PFOmore » may act as an efficient interfacial layer at the anode, PFO-BPy, having the additional pyridine side groups, forms a high resistance layer degrading the device efficiency. By comparing PFO|C 60 and C 60-only devices, we found that presence of a PFO layer at low optical densities resulted in the increase of all three solar cell parameters, giving nearly an order of magnitude higher efficiency over that of C 60-only devices. In addition, with a relatively higher contribution to photocurrent from the PFO-C 60 interface, an open circuit voltage of 0.55 V was obtained for PFO-(7,5)-C 60 devices. On the other hand, PFO-BPy does not affect the open circuit voltage but drastically reduces the short circuit current density. Lastly, these results indicate that the charge transport properties and energy levels of the sorting polymers have to be taken into account to fully understand their effect on carbon nanotube-based solar cells.« less

Charge transfer and injection barrier at the metal-organic interfaces

NASA Astrophysics Data System (ADS)

Yan, Li

2002-09-01

The metal-organic interface plays a critical role in determining the functionality and performance of many innovative organic based devices. It has attracted extensive research interests in recent years. This thesis presents investigations of the electronic structures of organic materials, such as tris-(8-hydroxyquinoline) aluminum (Alq3) and copper phthalocyanine (CuPc), during their interface formation with metals. The characterization is accomplished by X-ray and ultraviolet photoelectron spectroscopes (XPS and UPS) and inverse photoelectron spectroscopy (IPES). As discussed herein, both occupied and unoccupied electronic states at the interfaces are carefully examined in different aspects. In Chapter 4, the charge transfer and chemical reaction at various metal/Alq3 interfaces are investigated using XPS and UPS to study the electron injection into the Alga film. Electron transfer from the low work function metal and Al/LiF(CsF) bilayer to the Alga has been observed. The role of the dielectric and possible chemistry at the interface are discussed in comparison of the low work function metals. Further in Chapter 5, the origin of the metal-interface dipole and the estimation of charge injection barrier is explored using several organic materials. A thermodynamic equilibrium model is extended to explain the relation between the charge transfer process ad the interface dipole. Further, in Chapter 6 the combination of XPS, UPS and IPES detailed the evolution of both occupied and unoccupied energy states during the alkali metal doping. The energy gap modification in organic due to metal doping is observed directly for the spectra. Chapter 7 provides stability study of the organic thin films under x-ray and UV light. The results verify the usability of UPS and XPS for the organic materials used in the thesis. Chapter 7 also shows the secondary ion mass spectroscopy results of metal diffusion in organic thin films.

An insight into the mechanism of charge transfer properties of hybrid organic (MEH-PPV): Inorganic (TiO{sub 2}) nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mittal, Tanu, E-mail: chemtanu9@gmail.com; Tiwari, Sangeeta, E-mail: stiwari2@amity.edu; Mehta, Aarti, E-mail: aks302117@gmail.com

2016-04-13

Now a days, inorganic nanoparticles are gaining importance and are potential candidate in different organic electronic device application like (LEDs, PVs) due to their novel properties and confinement in Nano-dimensions. {sup [1,} {sup 2]} In the present work, we have compared the properties of titanium di oxide (TiO{sub 2}) nanoparticles (NPs) synthesized by using two different chemical routes aqueous and ethanol respectively. These synthesized TiO{sub 2} nanoparticles have been characterized by X-ray diffraction spectroscopy (XRD) for phase confirmation. It was observed that synthesized nanoparticles are in anatase phase for both preparation routes. Morphological information was collected by scanning electron microscopymore » (SEM) which confirms that particles are almost spherical in shape and distributed uniformly which is further ensured by transmission electron microscopy (TEM). Dynamic light scattering (DLS) technique was also used for further confirmation of size distribution of as-synthesized nanoparticles. Optical properties were also investigated by photoluminescence and UV-Vis spectroscopy and calculated bandgap was found to be in the range of 3.3-3.5eV for TiO{sub 2} (aq/eth) nanoparticles. The increase in bandgap values with respect to bulk (3.2 eV) confirms that as- synthesized nanoparticles are confined in nanodimensions. As synthesized nanoparticles were interacted with MEHPPV polymer (donor) matrix to make their respective MEHPPV: TiO{sub 2} nanocomposites and to confirm the charge transfer mechanism from polymer to nanoparticles. It can be observed from photoluminescence (PL) quenching experiments that continuous quenching obtained for respective nanocomposites confirms better charge transfer from polymer to inorganic TiO{sub 2} nanoparticles respectively. Because of, better quenching and simultaneously enhanced charge transfer of respective nanocomposites, ensures that these nanocomposites are greatly applicable for photovoltaics (PVs) especially in Hybrid Solar cells (HSCs).« less

Spontaneous charged lipid transfer between lipid vesicles.

PubMed

Richens, Joanna L; Tyler, Arwen I I; Barriga, Hanna M G; Bramble, Jonathan P; Law, Robert V; Brooks, Nicholas J; Seddon, John M; Ces, Oscar; O'Shea, Paul

2017-10-03

An assay to study the spontaneous charged lipid transfer between lipid vesicles is described. A donor/acceptor vesicle system is employed, where neutrally charged acceptor vesicles are fluorescently labelled with the electrostatic membrane probe Fluoresceinphosphatidylethanolamine (FPE). Upon addition of charged donor vesicles, transfer of negatively charged lipid occurs, resulting in a fluorescently detectable change in the membrane potential of the acceptor vesicles. Using this approach we have studied the transfer properties of a range of lipids, varying both the headgroup and the chain length. At the low vesicle concentrations chosen, the transfer follows a first-order process where lipid monomers are transferred presumably through the aqueous solution phase from donor to acceptor vesicle. The rate of transfer decreases with increasing chain length which is consistent with energy models previously reported for lipid monomer vesicle interactions. Our assay improves on existing methods allowing the study of a range of unmodified lipids, continuous monitoring of transfer and simplified experimental procedures.

Single crystal absorption spectra of synthetic Ti, Fe-substituted pyropes

NASA Astrophysics Data System (ADS)

Khomenko, V. M.; Langer, K.; Andrut, M.; Koch-Müller, M.; Vishnevsky, A. A.

1994-11-01

Synthetic pyrope crystals up to 0.5 mm in diameter, substituted by titanium or by titanium plus iron, were grown under defined conditions of P, T, f_{O_2 } in the presence of water using a piston-cylinder device. The crystals were characterized by X-ray and microprobe techniques. Their single-crystal optical absorption spectra were measured by means of a microscope-spectrometer. Two absorption bands at 16100 and 22300 cm{cm-1} in the spectra of pale-blue Fe-free Ti-bearing pyropes, grown under reduced conditions, were identified as originating from spin-allowed transitions, derived from 2 T 2g → 2 E g of octahedral Ti3+ ions. The splitting value of the excited 2E g state, 6200 cm-1, and the crystal field parameter of Ti3+ in pyrope Δ 0 = 19 200 cm-1 are both in agreement with literature data. In spectra of brown Fe, Ti-bearing garnets, a broad band at 23000 cm-1 was interpreted as a Fe2+[8] → Ti4+[6] charge-transfer band. The spectral position and width of this band agree with those observed for a FeTi charge transfer band in natural garnets. Fe, Ti-containing garnets synthesized at relatively high oxygen fugacity (10-11,0 atm), which permits a fraction of Fe3+ to enter the garnet, show an additional Fe2+[8] → Fe3+[6] charge transfer band at 19800 cm-1.

Change control microcomputer device for vehicle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morishita, M.; Kouge, S.

1986-08-19

A charge control microcomputer device for a vehicle is described which consists of: a clutch device for transmitting the rotary output of an engine; a charging generator driven by the clutch device; a battery charged by an output of the charging generator; a voltage regulator for controlling an output voltage of the charging generator to a predetermined value; an engine controlling microcomputer for receiving engine data, to control the engine; and a charge control microcomputer for processing the engine data from the engine controlling microcomputer and charge system data including terminal voltage data from the battery and generated voltage datamore » from the charging generator, to determine a reference voltage for the voltage regulator in accordance with the engine data and the charge system data, and for processing an engine rotation signal to generate and apply an operating instruction to the clutch device in accordance with the engine data and the charge system data, such that the charging generator is driven within a predetermined range of revolutions per minute at all times.« less

Theoretical prediction of the impact of Auger recombination on charge collection from an ion track

NASA Technical Reports Server (NTRS)

Edmonds, Larry D.

1991-01-01

A recombination mechanism that significantly reduces charge collection from very dense ion tracks in silicon devices was postulated by Zoutendyk et al. The theoretical analysis presented here concludes that Auger recombination is such a mechanism and is of marginal importance for higher density tracks produced by 270-MeV krypton, but of major importance for higher density tracks. The analysis shows that recombination loss is profoundly affected by track diffusion. As the track diffuses, the density and recombination rate decrease so fast that the linear density (number of electron-hole pairs per unit length) approaches a non-zero limiting value as t yields infinity. Furthermore, the linear density is very nearly equal to this limiting value in a few picoseconds or less. When Auger recombination accompanies charge transport processes that have much longer time scales, it can be simulated by assigning a reduced linear energy transfer to the ion.

Laboratory Studies of Thermal Energy Charge Transfer of Silicon and Iron Ions in Astrophysical Plasmas

NASA Technical Reports Server (NTRS)

Kwong, Victor H. S.

1996-01-01

Charge transfer at electron-volt energies between multiply charged atomic ions and neutral atoms and molecules is of considerable importance in astrophysics, plasma physics, and in particular, fusion plasmas. In the year covered by this report, several major tasks were completed. These include: (1) the re-calibration of the ion gauge to measure the absolute particle densities of H2, He, N2, and CO for our current measurements; (2) the analysis of data for charge transfer reactions of N(exp 2 plus) ion and He, H2, N2, and CO; (3) measurement and data analysis of the charge transfer reaction of (Fe(exp 2 plus) ion and H2; (4) charge transfer measurement of Fe(exp 2 plus) ion and H2; and (5) redesign and modification of the ion detection and data acquisition system for the low energy beam facility (reflection time of flight mass spectrometer) dedicated to the study of state select charge transfer.

Anomalous temperature dependent magneto-conductance in organic light-emitting diodes with multiple emissive states

NASA Astrophysics Data System (ADS)

Zhao, Chen-xiao; Jia, Wei-yao; Huang, Ke-Xun; Zhang, Qiao-ming; Yang, Xiao-hui; Xiong, Zu-hong

2015-07-01

The temperature dependence of the magneto-conductance (MC) in organic electron donor-acceptor hybrid and layer heterojunction diodes was studied. The MC value increased with temperature in layer heterojunction and in 10 wt. % hybrid devices. An anomalous decrease of the MC with temperature was observed in 25 wt. %-50 wt. % hybrid devices. Further increasing donor concentration to 75 wt. %, the MC again increased with temperature. The endothermic exciplex-exciton energy transfer and the change in electroplex/exciton ratio caused by change in charge transport with temperature may account for these phenomena. Comparative studies of the temperature evolutions of the IV curves and the electroluminescence and photoluminescence spectra back our hypothesis.

Programmable Electrochemical Rectifier Based on a Thin-Layer Cell.

PubMed

Park, Seungjin; Park, Jun Hui; Hwang, Seongpil; Kwak, Juhyoun

2017-06-21

A programmable electrochemical rectifier based on thin-layer electrochemistry is described here. Both the rectification ratio and the response time of the device are programmable by controlling the gap distance of the thin-layer electrochemical cell, which is easily controlled using commercially available beads. One of the electrodes was modified using a ferrocene-terminated self-assembled monolayer to offer unidirectional charge transfers via soluble redox species. The thin-layer configuration provided enhanced mass transport, which was determined by the gap thickness. The device with the smallest gap thickness (∼4 μm) showed an unprecedented, high rectification ratio (up to 160) with a fast response time in a two-terminal configuration using conventional electronics.

Molecular orbital (SCF-Xα-SW) theory of metal-metal charge transfer processes in minerals - II. Application to Fe2+ --> Ti4+ charge transfer transitions in oxides and silicates

USGS Publications Warehouse

Sherman, David M.

1987-01-01

A molecular orbital description, based on Xα-Scattered wave calculations on a (FeTiO10)14− cluster, is given for Fe2+ → Ti4+ charge transfer transitions in minerals. The calculated energy for the lowest Fe2+ → Ti4+ metal-metal charge transfer transition is 18040 cm−1 in reasonable agreement with energies observed in the optical spectra of Fe-Ti oxides and silicates. As in the case of Fe2+ → Fe3+ charge transfer in mixed-valence iron oxides and silicates, Fe2+ → Ti4+ charge transfer is associated with Fe-Ti bonding across shared polyhedral edges. Such bonding results from the overlap of the Fe(t 2g ) and Ti(t 2g ) 3d orbitals.

Charge transfer transitions in optical spectra of NicMg1-cO oxides

NASA Astrophysics Data System (ADS)

Churmanov, V. N.; Sokolov, V. I.; Pustovarov, V. A.; Gruzdev, N. B.; Uimin, M. A.; Byzov, I. V.; Druzhinin, A. V.; Korolyov, A. V.; Kim, G. A.; Zatsepin, A. F.; Kuznetsova, J. A.

2017-04-01

Radiative recombination with charge transfer was observed in NicMg1-cO (c = 0.008) oxides over the 8-300 K temperature range. This recombination occurs as a result of strong hybridization of the Ni2+ ion 3d-states and the band states. The charge transfer radiation excitation spectrum shows vibrational LO repeats of two exciton lines having charge transfer energy intervals of about 35 meV. The NiO nanocrystal absorption spectrum shows two weak peaks with energies of 3.510 and 3.543 eV, which are highly dependent on temperature. They are interpreted as charge transfer excitons at the edge of NiO fundamental absorption. The distance between the charge transfer exciton lines in the NicMg1-cO oxide spectra are caused by spin-orbit splitting of the valence band peak that was formed by the p-states of the oxygen ion.

Integration of High-Charge-Injection-Capacity Electrodes onto Polymer Softening Neural Interfaces.

PubMed

Arreaga-Salas, David E; Avendaño-Bolívar, Adrian; Simon, Dustin; Reit, Radu; Garcia-Sandoval, Aldo; Rennaker, Robert L; Voit, Walter

2015-12-09

Softening neural interfaces are implanted stiff to enable precise insertion, and they soften in physiological conditions to minimize modulus mismatch with tissue. In this work, a high-charge-injection-capacity iridium electrode fabrication process is detailed. For the first time, this process enables integration of iridium electrodes onto softening substrates using photolithography to define all features in the device. Importantly, no electroplated layers are utilized, leading to a highly scalable method for consistent device fabrication. The iridium electrode is metallically bonded to the gold conductor layer, which is covalently bonded to the softening substrate via sulfur-based click chemistry. The resulting shape-memory polymer neural interfaces can deliver more than 2 billion symmetric biphasic pulses (100 μs/phase), with a charge of 200 μC/cm(2) and geometric surface area (GSA) of 300 μm(2). A transfer-by-polymerization method is used in combination with standard semiconductor processing techniques to fabricate functional neural probes onto a thiol-ene-based, thin film substrate. Electrical stability is tested under simulated physiological conditions in an accelerated electrical aging paradigm with periodic measurement of electrochemical impedance spectra (EIS) and charge storage capacity (CSC) at various intervals. Electrochemical characterization and both optical and scanning electron microscopy suggest significant breakdown of the 600 nm-thick parylene-C insulation, although no delamination of the conductors or of the final electrode interface was observed. Minor cracking at the edges of the thin film iridium electrodes was occasionally observed. The resulting devices will provide electrical recording and stimulation of the nervous system to better understand neural wiring and timing, to target treatments for debilitating diseases, and to give neuroscientists spatially selective and specific tools to interact with the body. This approach has uses for cochlear implants, nerve cuff electrodes, penetrating cortical probes, spinal stimulators, blanket electrodes for the gut, stomach, and visceral organs and a host of other custom nerve-interfacing devices.

Parametric study of thermal storage containing rocks or fluid filled cans for solar heating and cooling, phase 2

NASA Technical Reports Server (NTRS)

Saha, H.

1981-01-01

The test data and an analysis of the heat transfer characteristics of a solar thermal energy storage bed utilizing water filled cans and standard bricks as energy storage medium are presented. This experimental investigation was initiated to find a usable heat intensive solar thermal storage device other than rock storage and water tank. Four different sizes of soup cans were stacked in a chamber in three different arrangements-vertical, horizontal, and random. Air is used as transfer medium for charging and discharge modes at three different mass flow rates and inlet air temperature respectively. These results are analyzed and compared, which show that a vertical stacking and medium size cans with Length/Diameter (L/D) ratio close to one have better average characteristics of heat transfer and pressure drop.

Characterization of a 512x512-pixel 8-output full-frame CCD for high-speed imaging

NASA Astrophysics Data System (ADS)

Graeve, Thorsten; Dereniak, Eustace L.

1993-01-01

The characterization of a 512 by 512 pixel, eight-output full frame CCD manufactured by English Electric Valve under part number CCD13 is discussed. This device is a high- resolution Silicon-based array designed for visible imaging applications at readout periods as low as two milliseconds. The characterization of the device includes mean-variance analysis to determine read noise and dynamic range, as well as charge transfer efficiency, MTF, and quantum efficiency measurements. Dark current and non-uniformity issues on a pixel-to-pixel basis and between individual outputs are also examined. The characterization of the device is restricted by hardware limitations to a one MHz pixel rate, corresponding to a 40 ms readout time. However, subsections of the device have been operated at up to an equivalent 100 frames per second. To maximize the frame rate, the CCD is illuminated by a synchronized strobe flash in between frame readouts. The effects of the strobe illumination on the imagery obtained from the device is discussed.

Supramolecular core-shell nanoparticles for photoconductive device applications

NASA Astrophysics Data System (ADS)

Cheng, Chih-Chia; Chen, Jem-Kun; Shieh, Yeong-Tarng; Lee, Duu-Jong

2016-08-01

We report a breakthrough discovery involving supramolecular-based strategies to construct novel core-shell heterojunction nanoparticles with hydrophilic adenine-functionalized polythiophene (PAT) as the core and hydrophobic phenyl-C61-butyric acid methyl ester (PCBM) as the shell, which enables the conception of new functional supramolecular assemblies for constructing functional nanomaterials for applications in optoelectronic devices. The generated nanoparticles exhibit uniform spherical shape, well-controlled tuning of particle size with narrow size distributions, and excellent electrochemical stability in solution and the solid state owing to highly efficient energy transfer from PAT to PCBM. When the PAT/PCBM nanoparticles were fabricated into a photoconducting layer in an electronic device, the resulting device showed excellent electric conduction characteristics, including an electrically-tunable voltage-controlled switch, and high short-circuit current and open-circuit voltage. These observations demonstrate how the self-assembly of PAT/PCBM into specific nanostructures may help to promote efficient charge generation and transport processes, suggesting potential for a wide variety of applications as a promising candidate material for bulk heterojunction polymer devices.

Improving Light Harvesting in Dye-Sensitized Solar Cells Using Hybrid Bimetallic Nanostructures

DOE PAGES

Zarick, Holly F.; Erwin, William R.; Boulesbaa, Abdelaziz; ...

2016-01-25

In this paper, we demonstrate improved light trapping in dye-sensitized solar cells (DSSCs) with hybrid bimetallic gold core/silver shell nanostructures. Silica-coated bimetallic nanostructures (Au/Ag/SiO 2 NSs) integrated in the active layer of DSSCs resulted in 7.51% power conversion efficiency relative to 5.97% for reference DSSCs, giving rise to 26% enhancement in device performance. DSSC efficiencies were governed by the particle density of Au/Ag/SiO 2 NSs with best performing devices utilizing only 0.44 wt % of nanostructures. We performed transient absorption spectroscopy of DSSCs with variable concentrations of Au/Ag/SiO 2 NSs and observed an increase in amplitude and decrease in lifetimemore » with increasing particle density relative to reference. Finally, we attributed this trend to plasmon resonant energy transfer and population of the singlet excited states of the sensitizer molecules at the optimum concentration of NSs promoting enhanced exciton generation and rapid charge transfer into TiO 2.« less

Acentric 2-D ensembles of D-br-A electron-transfer chromophores via vectorial orientation within amphiphilic n-helix bundle peptides for photovoltaic device applications.

PubMed

Koo, Jaseung; Park, Jaehong; Tronin, Andrey; Zhang, Ruili; Krishnan, Venkata; Strzalka, Joseph; Kuzmenko, Ivan; Fry, H Christopher; Therien, Michael J; Blasie, J Kent

2012-02-14

We show that simply designed amphiphilic 4-helix bundle peptides can be utilized to vectorially orient a linearly extended donor-bridge-acceptor (D-br-A) electron transfer (ET) chromophore within its core. The bundle's interior is shown to provide a unique solvation environment for the D-br-A assembly not accessible in conventional solvents and thereby control the magnitudes of both light-induced ET and thermal charge recombination rate constants. The amphiphilicity of the bundle's exterior was employed to vectorially orient the peptide-chromophore complex at a liquid-gas interface, and its ends were tailored for subsequent covalent attachment to an inorganic surface, via a "directed assembly" approach. Structural data, combined with evaluation of the excited state dynamics exhibited by these peptide-chromophore complexes, demonstrate that densely packed, acentrically ordered 2-D monolayer ensembles of such complexes at high in-plane chromophore densities approaching 1/200 Å(2) offer unique potential as active layers in binary heterojunction photovoltaic devices.

Self-powered fluorescence display devices based on a fast self-charging/recharging battery (Mg/Prussian blue).

PubMed

Zhang, Hui; Yu, You; Zhang, Lingling; Zhai, Yiwen; Dong, Shaojun

2016-11-01

Stimuli-responsive (such as voltage and/or light) fluorescence display systems have attracted particular attention in their promising fields of application. However, there are few examples of self-powered fluorescence display devices. Here we designed and fabricated a self-powered fluorescence display device based on a fast-charging/recharging battery. The specially designed battery was composed of a Prussian blue (PB) cathode and a magnesium metal anode with a high theoretical redox potential difference (∼2.8 V). Moreover, smartly adding a trace amount of NaClO in the electrolyte could realize oxidizing PW to PB ∼480 times faster than when oxidizing without NaClO, leading to the fast self-charging and high power density (maximum power density of 13.34 mW cm -2 , about two to three orders of magnitude larger than previous bio-fuel cells) of the Mg/PB battery. Most importantly, PB was used as not only the cathodic catalyst but also as an electrochromic material, making it possible to construct a self-powered and rechargeable electrochromic fluorescence display with only two electrodes. Besides, fluorescent [Ru(bpy) 3 ] 2+ -doped silica nanoparticles (Ru@SiO 2 ), were selected as the fluorescence resonance energy transfer (FRET) donor to match PB (FRET acceptor). To the best of our knowledge, we demonstrated a self-powered and rechargeable electrochromic fluorescence display with only two electrodes for the first time.

Rapid synthesis and decoration of reduced graphene oxide with gold nanoparticles by thermostable peptides for memory device and photothermal applications.

PubMed

Otari, Sachin V; Kumar, Manoj; Anwar, Muhammad Zahid; Thorat, Nanasaheb D; Patel, Sanjay K S; Lee, Dongjin; Lee, Jai Hyo; Lee, Jung-Kul; Kang, Yun Chan; Zhang, Liaoyuan

2017-09-08

This article presents novel, rapid, and environmentally benign synthesis method for one-step reduction and decoration of graphene oxide with gold nanoparticles (NAuNPs) by using thermostable antimicrobial nisin peptides to form a gold-nanoparticles-reduced graphene oxide (NAu-rGO) nanocomposite. The formed composite material was characterized by UV/Vis spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM). HR-TEM analysis revealed the formation of spherical AuNPs of 5-30 nm in size on reduced graphene oxide (rGO) nanosheets. A non-volatile-memory device was prepared based on a solution-processed ZnO thin-film transistor fabricated by inserting the NAu-rGO nanocomposite in the gate dielectric stack as a charge trapping medium. The transfer characteristic of the ZnO thin-film transistor memory device showed large clockwise hysteresis behaviour because of charge carrier trapping in the NAu-rGO nanocomposite. Under positive and negative bias conditions, clear positive and negative threshold voltage shifts occurred, which were attributed to charge carrier trapping and de-trapping in the ZnO/NAu-rGO/SiO 2 structure. Also, the photothermal effect of the NAu-rGO nanocomposites on MCF7 breast cancer cells caused inhibition of ~80% cells after irradiation with infrared light (0.5 W cm -2 ) for 5 min.

Calculation of rates of exciton dissociation into hot charge-transfer states in model organic photovoltaic interfaces

NASA Astrophysics Data System (ADS)

Vázquez, Héctor; Troisi, Alessandro

2013-11-01

We investigate the process of exciton dissociation in ordered and disordered model donor/acceptor systems and describe a method to calculate exciton dissociation rates. We consider a one-dimensional system with Frenkel states in the donor material and states where charge transfer has taken place between donor and acceptor. We introduce a Green's function approach to calculate the generation rates of charge-transfer states. For disorder in the Frenkel states we find a clear exponential dependence of charge dissociation rates with exciton-interface distance, with a distance decay constant β that increases linearly with the amount of disorder. Disorder in the parameters that describe (final) charge-transfer states has little effect on the rates. Exciton dissociation invariably leads to partially separated charges. In all cases final states are “hot” charge-transfer states, with electron and hole located far from the interface.

Critical role of the sorting polymer in carbon nanotube-based minority carrier devices

DOE PAGES

Mallajosyula, Arun T.; Nie, Wanyi; Gupta, Gautam; ...

2016-11-27

A prerequisite for carbon nanotube-based optoelectronic devices is the ability to sort them into a pure semiconductor phase. One of the most common sorting routes is enabled through using specific wrapping polymers. Here we show that subtle changes in the polymer structure can have a dramatic influence on the figures of merit of a carbon nanotube-based photovoltaic device. By comparing two commonly used polyfluorenes (PFO and PFO-BPy) for wrapping (7,5) and (6,5) chirality SWCNTs, we demonstrate that they have contrasting effects on the device efficiency. We attribute this to the differences in their ability to efficiently transfer charge. Although PFOmore » may act as an efficient interfacial layer at the anode, PFO-BPy, having the additional pyridine side groups, forms a high resistance layer degrading the device efficiency. By comparing PFO|C 60 and C 60-only devices, we found that presence of a PFO layer at low optical densities resulted in the increase of all three solar cell parameters, giving nearly an order of magnitude higher efficiency over that of C 60-only devices. In addition, with a relatively higher contribution to photocurrent from the PFO-C 60 interface, an open circuit voltage of 0.55 V was obtained for PFO-(7,5)-C 60 devices. On the other hand, PFO-BPy does not affect the open circuit voltage but drastically reduces the short circuit current density. Lastly, these results indicate that the charge transport properties and energy levels of the sorting polymers have to be taken into account to fully understand their effect on carbon nanotube-based solar cells.« less

Photocurrent generation by direct electron transfer using photosynthetic reaction centres

NASA Astrophysics Data System (ADS)

Mahmoudzadeh, A.; Saer, R.; Jun, D.; Mirvakili, S. M.; Takshi, A.; Iranpour, B.; Ouellet, E.; Lagally, E. T.; Madden, J. D. W.; Beatty, J. T.

2011-09-01

Photosynthetic reaction centres (RCs) convert light into separated charges with nearly perfect quantum efficiency, and have been used to generate photocurrent. Previous work has shown that electron tunnelling rates between redox centres in proteins depend exponentially on the tunnelling distance. In this work the RC from Rhodobacter sphaeroides was genetically modified with the aim of achieving the shortest tunnelling distances yet demonstrated between the RC's electron-accepting P site and underlying graphite and gold electrodes, and between the electron donor Q site and graphite electrodes. Opposite charges are carried to counter electrodes using mobile mediators, as in dye-sensitised solar cells. Native RCs are bound to graphite surfaces through N-(1-pyrene)iodoacetamide. Although the linker's length is only 4 Å, the electron transfer pathway between the Q electron donor site on the RC and the electrode surface is still too large for current to be significant. A mutant version with the electron acceptor P side close to the graphite surface produced currents of 15 nA cm-2 upon illumination. Direct binding of RCs to a gold surface is shown, resulting in currents of 5 nA cm-2. In both cases the current was unaffected by mediator concentration but increased with illumination, suggesting that direct electron transfer was achieved. The engineering of an RC to achieve direct electron transfer will help with long term efforts to demonstrate RC-based photovoltaic devices.

The safety and reliability of the S and A mechanism designed for the NASA/LSPE program

NASA Technical Reports Server (NTRS)

Montesi, L. J.

1973-01-01

Under contract to the Manned Spacecraft Center, NASA/Houston, NOL developed a number of explosive charges for use in studying the surface of the moon during Apollo 17 activities. The charges were part of the Lunar Seismic Profiling Experiment (LSPE). When the Safety and Arming Device used in the previous ALSEP experiments was found unsuitable for use with the new explosive packages, NOL also designed the Safety and Arming Mechanism, and the safety and reliability tests conducted are described. The results of the test program indicate that the detonation transfer probability between the armed explosive components exceeds 0.9999, and is less than 0.0001 when the explosive components are in the safe position.

Role of charge separation mechanism and local disorder at hybrid solar cell interfaces

NASA Astrophysics Data System (ADS)

Ehrenreich, Philipp; Pfadler, Thomas; Paquin, Francis; Dion-Bertrand, Laura-Isabelle; Paré-Labrosse, Olivier; Silva, Carlos; Weickert, Jonas; Schmidt-Mende, Lukas

2015-01-01

Dye-sensitized metal oxide polymer hybrid solar cells deliver a promising basis in organic solar cell development due to many conceptual advantages. Since the power conversion efficiency is still in a noncompetitive state, it has to be understood how the photocurrent contribution can be maximized (i.e., which dye-polymer properties are most beneficial for efficient charge generation in hybrid solar cells). By the comparison of three model systems for hybrid solar cells with Ti O2 -dye-polymer interfaces, this paper was aimed at elucidating the role of the exact mechanism of charge generation. In the exciton dissociation (ED) case, an exciton that is generated in the polymer is split at the dye-polymer interface. Alternatively, this exciton can be transferred to the dye via an energy transfer (ET), upon which charge separation occurs between dye and Ti O2 . For comparison, the third case is included in which the high lowest unoccupied molecular orbital of the dye does not allow exciton separation or ET from the dye to the polymer, so that the dye only is responsible for charge generation. To separate effects owing to differences in energy levels of the involved materials from the impact of local order and disorder in the polymer close to the interface, this paper further comprises a detailed analysis of the polymer crystallinity based on the H-aggregate model. While the massive impact of the poly(3-hexylthiophene) crystallinity on device function has been outlined for bare metal oxide-polymer interfaces, it has not been considered for hybrid solar cells with dye-sensitized Ti O2 . The results presented here indicate that all dye molecules in general influence the polymer morphology, which has to be taken into account for future optimization of hybrid solar cells. Apart from that, it can be suggested that ED on the polymer needs an additional driving force to work efficiently; thus, energy transfer seems to be currently the most promising strategy to increase the polymer photocurrent contribution.

Capillary electrophoresis electrospray ionization mass spectrometry interface

DOEpatents

Smith, Richard D.; Severs, Joanne C.

1999-01-01

The present invention is an interface between a capillary electrophoresis separation capillary end and an electrospray ionization mass spectrometry emitter capillary end, for transporting an anolyte sample from a capillary electrophoresis separation capillary to a electrospray ionization mass spectrometry emitter capillary. The interface of the present invention has: (a) a charge transfer fitting enclosing both of the capillary electrophoresis capillary end and the electrospray ionization mass spectrometry emitter capillary end; (b) a reservoir containing an electrolyte surrounding the charge transfer fitting; and (c) an electrode immersed into the electrolyte, the electrode closing a capillary electrophoresis circuit and providing charge transfer across the charge transfer fitting while avoiding substantial bulk fluid transfer across the charge transfer fitting. Advantages of the present invention have been demonstrated as effective in providing high sensitivity and efficient analyses.

Fullerene-Assisted Photoinduced Charge Transfer of Single-Walled Carbon Nanotubes through a Flavin Helix.

PubMed

Mollahosseini, Mehdi; Karunaratne, Erandika; Gibson, George N; Gascón, Jose A; Papadimitrakopoulos, Fotios

2016-05-11

One of the greatest challenges with single-walled carbon nanotube (SWNT) photovoltaics and nanostructured devices is maintaining the nanotubes in their pristine state (i.e., devoid of aggregation and inhomogeneous doping) so that their unique spectroscopic and transport characteristics are preserved. To this effect, we report on the synthesis and self-assembly of a C60-functionalized flavin (FC60), composed of PCBM and isoalloxazine moieties attached on either ends of a linear, C-12 aliphatic spacer. Small amounts of FC60 (up to 3 molar %) were shown to coassembly with an organic soluble derivative of flavin (FC12) around SWNTs and impart effective dispersion and individualization. A key annealing step was necessary to perfect the isoalloxazine helix and expel the C60 moiety away from the nanotubes. Steady-state and transient absorption spectroscopy illustrate that 1% or higher incorporation of FC60 allows for an effective photoinduced charge transfer quenching of the encased SWNTs through the seamless helical encase. This is enabled via the direct π-π overlap between the graphene sidewalls, isoalloxazine helix, and the C60 cage that facilitates SWNT exciton dissociation and electron transfer to the PCBM moiety. Atomistic molecular simulations indicate that the stability of the complex originates from enhanced van der Waals interactions of the flexible spacer wrapped around the fullerene that brings the C60 in π-π overlap with the isoalloxazine helix. The remarkable spectral purity (in terms of narrow E(S)ii line widths) for the resulting ground-state complex signals a new class of highly organized supramolecular nanotube architecture with profound importance for advanced nanostructured devices.

Preface: Charge transport in nanoscale junctions

NASA Astrophysics Data System (ADS)

Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

2008-09-01

Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for single molecule rectification of the current, inelastic electron spectra and SERS spectroscopy. Three terminal architectures allowing (electrochemical) gating and transistor effects. Electrochemical nanojunctions and gating: intermolecular electron transfer in multi-redox metalloproteins, contact force modulation, characteristic current-noise patterns due to conformational fluctuations, resonance effects and electrocatalysis. Novel architectures: linear coupled quantum-dot-bridged junctions, electrochemical redox mediated transfer in two center systems leading to double maxima current-voltage plots and negative differential resistance, molecular-nanoparticle hybrid junctions and unexpected mesoscopic effects in polymeric wires. Device integration: techniques for creating stable metal/molecule/metal junctions using 'nano-alligator clips' and integration with 'traditional' silicon-based technology. The Guest Editors would like to thank all of the authors and referees of this special issue for their meticulous work in making each paper a valuable contribution to this research area, the early-bird authors for their patience, and Journal of Physics: Condensed Matter editorial staff in Bristol for their continuous support.

Charge transport in nanoscale junctions.

PubMed

Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

2008-09-03

Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for single molecule rectification of the current, inelastic electron spectra and SERS spectroscopy. Three terminal architectures allowing (electrochemical) gating and transistor effects. Electrochemical nanojunctions and gating: intermolecular electron transfer in multi-redox metalloproteins, contact force modulation, characteristic current-noise patterns due to conformational fluctuations, resonance effects and electrocatalysis. Novel architectures: linear coupled quantum-dot-bridged junctions, electrochemical redox mediated transfer in two center systems leading to double maxima current-voltage plots and negative differential resistance, molecular-nanoparticle hybrid junctions and unexpected mesoscopic effects in polymeric wires. Device integration: techniques for creating stable metal/molecule/metal junctions using 'nano-alligator clips' and integration with 'traditional' silicon-based technology. The Guest Editors would like to thank all of the authors and referees of this special issue for their meticulous work in making each paper a valuable contribution to this research area, the early-bird authors for their patience, and Journal of Physics: Condensed Matter editorial staff in Bristol for their continuous support.

A low cost X-ray imaging device based on BPW-34 Si-PIN photodiode

NASA Astrophysics Data System (ADS)

Emirhan, E.; Bayrak, A.; Yücel, E. Barlas; Yücel, M.; Ozben, C. S.

2016-05-01

A low cost X-ray imaging device based on BPW-34 silicon PIN photodiode was designed and produced. X-rays were produced from a CEI OX/70-P dental tube using a custom made ±30 kV power supply. A charge sensitive preamplifier and a shaping amplifier were built for the amplification of small signals produced by photons in the depletion layer of Si-PIN photodiode. A two dimensional position control unit was used for moving the detector in small steps to measure the intensity of X-rays absorbed in the object to be imaged. An Aessent AES220B FPGA module was used for transferring the image data to a computer via USB. Images of various samples were obtained with acceptable image quality despite of the low cost of the device.

Interference-free optical detection for Raman spectroscopy

NASA Technical Reports Server (NTRS)

Fischer, David G (Inventor); Kojima, Jun (Inventor); Nguyen, Quang-Viet (Inventor)

2012-01-01

An architecture for spontaneous Raman scattering (SRS) that utilizes a frame-transfer charge-coupled device (CCD) sensor operating in a subframe burst gating mode to realize time-resolved combustion diagnostics is disclosed. The technique permits all-electronic optical gating with microsecond shutter speeds (<5 .mu.s), without compromising optical throughput or image fidelity. When used in conjunction with a pair of orthogonally-polarized excitation lasers, the technique measures time-resolved vibrational Raman scattering that is minimally contaminated by problematic optical background noise.

Effects of Molecular Stresses on Energy Transfer Pathways in Opto- and Electro-Excited Conjugated Polymers for High-Efficiency Optoelectronic Devices

DTIC Science & Technology

2014-10-20

unless it hops, and lead to obstructed recombination for PL or charge separation for solar cells and the reduced quantum efficiencies of the...excitons (Fig. 1a and 1b). For the free-moving delocalized states of the Wannier-Mott excitons, the binding energy in silicon , for example, is around...typically encompass many unit cells and typically exist in materials of small bandgap and large dielectric constant. In converse, the the tightly

Optical implementation of systolic array processing

NASA Technical Reports Server (NTRS)

Caulfield, H. J.; Rhodes, W. T.; Foster, M. J.; Horvitz, S.

1981-01-01

Algorithms for matrix vector multiplication are implemented using acousto-optic cells for multiplication and input data transfer and using charge coupled devices detector arrays for accumulation and output of the results. No two dimensional matrix mask is required; matrix changes are implemented electronically. A system for multiplying a 50 component nonnegative real vector by a 50 by 50 nonnegative real matrix is described. Modifications for bipolar real and complex valued processing are possible, as are extensions to matrix-matrix multiplication and multiplication of a vector by multiple matrices.

The origin of excellent gate-bias stress stability in organic field-effect transistors employing fluorinated-polymer gate dielectrics.

PubMed

Kim, Jiye; Jang, Jaeyoung; Kim, Kyunghun; Kim, Haekyoung; Kim, Se Hyun; Park, Chan Eon

2014-11-12

Tuning of the energetic barriers to charge transfer at the semiconductor/dielectric interface in organic field-effect transistors (OFETs) is achieved by varying the dielectric functionality. Based on this, the correlation between the magnitude of the energy barrier and the gate-bias stress stability of the OFETs is demonstrated, and the origin of the excellent device stability of OFETs employing fluorinated dielectrics is revealed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Miniaturized ultrafine particle sizer and monitor

NASA Technical Reports Server (NTRS)

Qi, Chaolong (Inventor); Chen, Da-Ren (Inventor)

2011-01-01

An apparatus for measuring particle size distribution includes a charging device and a precipitator. The charging device includes a corona that generates charged ions in response to a first applied voltage, and a charger body that generates a low energy electrical field in response to a second applied voltage in order to channel the charged ions out of the charging device. The corona tip and the charger body are arranged relative to each other to direct a flow of particles through the low energy electrical field in a direction parallel to a direction in which the charged ions are channeled out of the charging device. The precipitator receives the plurality of particles from the charging device, and includes a disk having a top surface and an opposite bottom surface, wherein a predetermined voltage is applied to the top surface and the bottom surface to precipitate the plurality of particles.

Site energies and charge transfer rates near pentacene grain boundaries from first-principles calculations

NASA Astrophysics Data System (ADS)

Kobayashi, Hajime; Tokita, Yuichi

2015-03-01

Charge transfer rates near pentacene grain boundaries are derived by calculating the site energies and transfer integrals of 37 pentacene molecules using first-principles calculations. The site energies decrease considerably near the grain boundaries, and electron traps of up to 300 meV and hole barriers of up to 400 meV are generated. The charge transfer rates across the grain boundaries are found to be reduced by three to five orders of magnitude with a grain boundary gap of 4 Å because of the reduction in the transfer integrals. The electron traps and hole barriers also reduce the electron and hole transfer rates by factors of up to 10 and 50, respectively. It is essential to take the site energies into consideration to determine charge transport near the grain boundaries. We show that the complex site energy distributions near the grain boundaries can be represented by an equivalent site energy difference, which is a constant for any charge transfer pass. When equivalent site energy differences are obtained for various grain boundary structures by first-principles calculations, the effects of the grain boundaries on the charge transfer rates are introduced exactly into charge transport simulations, such as the kinetic Monte Carlo method.

Charge Transfer and Orbital Level Alignment at Inorganic/Organic Interfaces: The Role of Dielectric Interlayers.

PubMed

Hollerer, Michael; Lüftner, Daniel; Hurdax, Philipp; Ules, Thomas; Soubatch, Serguei; Tautz, Frank Stefan; Koller, Georg; Puschnig, Peter; Sterrer, Martin; Ramsey, Michael G

2017-06-27

It is becoming accepted that ultrathin dielectric layers on metals are not merely passive decoupling layers, but can actively influence orbital energy level alignment and charge transfer at interfaces. As such, they can be important in applications ranging from catalysis to organic electronics. However, the details at the molecular level are still under debate. In this study, we present a comprehensive analysis of the phenomenon of charge transfer promoted by a dielectric interlayer with a comparative study of pentacene adsorbed on Ag(001) with and without an ultrathin MgO interlayer. Using scanning tunneling microscopy and photoemission tomography supported by density functional theory, we are able to identify the orbitals involved and quantify the degree of charge transfer in both cases. Fractional charge transfer occurs for pentacene adsorbed on Ag(001), while the presence of the ultrathin MgO interlayer promotes integer charge transfer with the lowest unoccupied molecular orbital transforming into a singly occupied and singly unoccupied state separated by a large gap around the Fermi energy. Our experimental approach allows a direct access to the individual factors governing the energy level alignment and charge-transfer processes for molecular adsorbates on inorganic substrates.

Testing fully depleted CCD

NASA Astrophysics Data System (ADS)

Casas, Ricard; Cardiel-Sas, Laia; Castander, Francisco J.; Jiménez, Jorge; de Vicente, Juan

2014-08-01

The focal plane of the PAU camera is composed of eighteen 2K x 4K CCDs. These devices, plus four spares, were provided by the Japanese company Hamamatsu Photonics K.K. with type no. S10892-04(X). These detectors are 200 μm thick fully depleted and back illuminated with an n-type silicon base. They have been built with a specific coating to be sensitive in the range from 300 to 1,100 nm. Their square pixel size is 15 μm. The read-out system consists of a Monsoon controller (NOAO) and the panVIEW software package. The deafualt CCD read-out speed is 133 kpixel/s. This is the value used in the calibration process. Before installing these devices in the camera focal plane, they were characterized using the facilities of the ICE (CSIC- IEEC) and IFAE in the UAB Campus in Bellaterra (Barcelona, Catalonia, Spain). The basic tests performed for all CCDs were to obtain the photon transfer curve (PTC), the charge transfer efficiency (CTE) using X-rays and the EPER method, linearity, read-out noise, dark current, persistence, cosmetics and quantum efficiency. The X-rays images were also used for the analysis of the charge diffusion for different substrate voltages (VSUB). Regarding the cosmetics, and in addition to white and dark pixels, some patterns were also found. The first one, which appears in all devices, is the presence of half circles in the external edges. The origin of this pattern can be related to the assembly process. A second one appears in the dark images, and shows bright arcs connecting corners along the vertical axis of the CCD. This feature appears in all CCDs exactly in the same position so our guess is that the pattern is due to electrical fields. Finally, and just in two devices, there is a spot with wavelength dependence whose origin could be the result of a defectous coating process.

Stable Water Oxidation in Acid Using Manganese-Modified TiO2 Protective Coatings.

PubMed

Siddiqi, Georges; Luo, Zhenya; Xie, Yujun; Pan, Zhenhua; Zhu, Qianhong; Röhr, Jason A; Cha, Judy J; Hu, Shu

2018-06-06

Accomplishing acid-stable water oxidation is a critical matter for achieving both long-lasting water-splitting devices and other fuel-forming electro- and photocatalytic processes. Because water oxidation releases protons into the local electrolytic environment, it becomes increasingly acidic during device operation, which leads to corrosion of the photoactive component and hence loss in device performance and lifetime. In this work, we show that thin films of manganese-modified titania, (Ti,Mn)O x , topped with an iridium catalyst, can be used in a coating stabilization scheme for acid-stable water oxidation. We achieved a device lifetime of more than 100 h in pH = 0 acid. We successfully grew (Ti,Mn)O x coatings with uniform elemental distributions over a wide range of manganese compositions using atomic layer deposition (ALD), and using X-ray photoelectron spectroscopy, we show that (Ti,Mn)O x films grown in this manner give rise to closer-to-valence-band Fermi levels, which can be further tuned with annealing. In contrast to the normally n-type or intrinsic TiO 2 coatings, annealed (Ti,Mn)O x films can make direct charge transfer to a Fe(CN) 6 3-/4- redox couple dissolved in aqueous electrolytes. Using the Fe(CN) 6 3-/4- redox, we further demonstrated anodic charge transfer through the (Ti,Mn)O x films to high work function metals, such as iridium and gold, which is not previously possible with ALD-grown TiO 2 . We correlated changes in the crystallinity (amorphous to rutile TiO 2 ) and oxidation state (2+ to 3+) of the annealed (Ti,Mn)O x films to their hole conductivity and electrochemical stability in acid. Finally, by combining (Ti,Mn)O x coatings with iridium, an acid-stable water-oxidation anode, using acid-sensitive conductive fluorine-doped tin oxides, was achieved.

Morphological study of electrophoretically deposited TiO2 film for DSSC application

NASA Astrophysics Data System (ADS)

Patel, Alkesh B.; Patel, K. D.; Soni, S. S.; Sonigara, K. K.

2018-05-01

In the immerging field of eco-friendly and low cost photovoltaic devices, dye sensitized solar cell (DSSC) [1] has been investigated as promising alternative to the conventional silicon-based solar cells. In the DSSC device, photoanode is crucial component that take charge of holding sensitizer on it and inject the electrons from the sensitizer to current collector. Nanoporous TiO2 is the most relevant candidate for the preparation of photoanode in DSSCs. Surface properties, morphology, porosity and thickness of TiO2 film as well as preparation technique determine the performance of device. In the present work we have report the study of an effect of nanoporous anatase titanium dioxide (TiO2) film thickness on DSSC performance. Photoanode TiO2 (P25) film was deposited on conducting substrate by electrophoresis technique (EPD) and film thickness was controlled during deposition by applying different current density for a constant time interval. Thickness and surface morphology of prepared films was studied by SEM and transmittance analysis. The same set of photoanode was utilized in DSSC devices using metal free organic dye sensitizer to evaluate the photovoltaic performance. Devices were characterized through Current-Voltage (I-V) characteristic, electrochemical impedance spectroscopy (EIS) and open circuit voltage decay curves. Dependency of device performance corresponding to TiO2 film thickness is investigated through the lifetime kinetics of electron charge transfer mechanism trough impedance fitting. It is concluded that appropriate thickness along with uniformity and porosity are required to align the dye molecules to respond efficiently the incident light photons.

Electrochemical control over photoinduced electron transfer and trapping in CdSe-CdTe quantum-dot solids.

PubMed

Boehme, Simon C; Walvis, T Ardaan; Infante, Ivan; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Houtepen, Arjan J

2014-07-22

Understanding and controlling charge transfer between different kinds of colloidal quantum dots (QDs) is important for devices such as light-emitting diodes and solar cells and for thermoelectric applications. Here we study photoinduced electron transfer between CdTe and CdSe QDs in a QD film. We find that very efficient electron trapping in CdTe QDs obstructs electron transfer to CdSe QDs under most conditions. Only the use of thiol ligands results in somewhat slower electron trapping; in this case the competition between trapping and electron transfer results in a small fraction of electrons being transferred to CdSe. However, we demonstrate that electron trapping can be controlled and even avoided altogether by using the unique combination of electrochemistry and transient absorption spectroscopy. When the Fermi level is raised electrochemically, traps are filled with electrons and electron transfer from CdTe to CdSe QDs occurs with unity efficiency. These results show the great importance of knowing and controlling the Fermi level in QD films and open up the possibility of studying the density of trap states in QD films as well as the systematic investigation of the intrinsic electron transfer rates in donor-acceptor films.

Multiconfiguration Pair-Density Functional Theory Outperforms Kohn-Sham Density Functional Theory and Multireference Perturbation Theory for Ground-State and Excited-State Charge Transfer.

PubMed

Ghosh, Soumen; Sonnenberger, Andrew L; Hoyer, Chad E; Truhlar, Donald G; Gagliardi, Laura

2015-08-11

The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of density functional called an on-top density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.

Review on charge transfer and chemical activity of TiO2: Mechanism and applications

NASA Astrophysics Data System (ADS)

Cai, Yongqing; Feng, Yuan Ping

2016-12-01

Charge separation and transfer at the interface between two materials play a significant role in various atomic-scale processes and energy conversion systems. In this review, we present the mechanism and outcome of charge transfer in TiO2, which is extensively explored for photocatalytic applications in the field of environmental science. We list several experimental and computational methods to estimate the amount of charge transfer. The effects of the work function, defects and doping, and employment of external electric field on modulating the charge transfer are presented. The interplay between the band bending and carrier transport across the surface and interface consisting of TiO2 is discussed. We show that the charge transfer can also strongly affect the behavior of deposited nanoparticles on TiO2 through built-in electric field that it creates. This review encompasses several advances of composite materials where TiO2 is combined with two-dimensional materials like graphene, MoS2, phosphorene, etc. The charge transport in the TiO2-organohalide perovskite with respect to the electron-hole separation at the interface is also discussed.

Two-dimensional molybdenum disulphide nanosheet-covered metal nanoparticle array as a floating gate in multi-functional flash memories

NASA Astrophysics Data System (ADS)

Han, Su-Ting; Zhou, Ye; Chen, Bo; Zhou, Li; Yan, Yan; Zhang, Hua; Roy, V. A. L.

2015-10-01

Semiconducting two-dimensional materials appear to be excellent candidates for non-volatile memory applications. However, the limited controllability of charge trapping behaviors and the lack of multi-bit storage studies in two-dimensional based memory devices require further improvement for realistic applications. Here, we report a flash memory consisting of metal NPs-molybdenum disulphide (MoS2) as a floating gate by introducing a metal nanoparticle (NP) (Ag, Au, Pt) monolayer underneath the MoS2 nanosheets. Controlled charge trapping and long data retention have been achieved in a metal (Ag, Au, Pt) NPs-MoS2 floating gate flash memory. This controlled charge trapping is hypothesized to be attributed to band bending and a built-in electric field ξbi between the interface of the metal NPs and MoS2. The metal NPs-MoS2 floating gate flash memories were further proven to be multi-bit memory storage devices possessing a 3-bit storage capability and a good retention capability up to 104 s. We anticipate that these findings would provide scientific insight for the development of novel memory devices utilizing an atomically thin two-dimensional lattice structure.Semiconducting two-dimensional materials appear to be excellent candidates for non-volatile memory applications. However, the limited controllability of charge trapping behaviors and the lack of multi-bit storage studies in two-dimensional based memory devices require further improvement for realistic applications. Here, we report a flash memory consisting of metal NPs-molybdenum disulphide (MoS2) as a floating gate by introducing a metal nanoparticle (NP) (Ag, Au, Pt) monolayer underneath the MoS2 nanosheets. Controlled charge trapping and long data retention have been achieved in a metal (Ag, Au, Pt) NPs-MoS2 floating gate flash memory. This controlled charge trapping is hypothesized to be attributed to band bending and a built-in electric field ξbi between the interface of the metal NPs and MoS2. The metal NPs-MoS2 floating gate flash memories were further proven to be multi-bit memory storage devices possessing a 3-bit storage capability and a good retention capability up to 104 s. We anticipate that these findings would provide scientific insight for the development of novel memory devices utilizing an atomically thin two-dimensional lattice structure. Electronic supplementary information (ESI) available: Energy-dispersive X-ray spectroscopy (EDS) spectra of the metal NPs, SEM image of MoS2 on Au NPs, erasing operations of the metal NPs-MoS2 memory device, transfer characteristics of the standard FET devices and Ag NP devices under programming operation, tapping-mode AFM height image of the fabricated MoS2 film for pristine MoS2 flash memory, gate signals used for programming the Au NPs-MoS2 and Pt NPs-MoS2 flash memories, and data levels recorded for 100 sequential cycles. See DOI: 10.1039/c5nr05054e

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory.

PubMed

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G

2011-08-28

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi-Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi-Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. © 2011 American Institute of Physics

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory

PubMed Central

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G.

2011-01-01

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi–Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi–Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. PMID:21895159

Performing the Millikan experiment at the molecular scale: Determination of atomic Millikan-Thomson charges by computationally measuring atomic forces.

PubMed

Rogers, T Ryan; Wang, Feng

2017-10-28

An atomic version of the Millikan oil drop experiment is performed computationally. It is shown that for planar molecules, the atomic version of the Millikan experiment can be used to define an atomic partial charge that is free from charge flow contributions. We refer to this charge as the Millikan-Thomson (MT) charge. Since the MT charge is directly proportional to the atomic forces under a uniform electric field, it is the most relevant charge for force field developments. The MT charge shows good stability with respect to different choices of the basis set. In addition, the MT charge can be easily calculated even at post-Hartree-Fock levels of theory. With the MT charge, it is shown that for a planar water dimer, the charge transfer from the proton acceptor to the proton donor is about -0.052 e. While both planar hydrated cations and anions show signs of charge transfer, anions show a much more significant charge transfer to the hydration water than the corresponding cations. It might be important to explicitly model the ion charge transfer to water in a force field at least for the anions.

Enhanced Charge Separation and FRET at Heterojunctions between Semiconductor Nanoparticles and Conducting Polymer Nanofibers for Efficient Solar Light Harvesting

PubMed Central

Sardar, Samim; Kar, Prasenjit; Remita, Hynd; Liu, Bo; Lemmens, Peter; Kumar Pal, Samir; Ghosh, Srabanti

2015-01-01

Energy harvesting from solar light employing nanostructured materials offer an economic way to resolve energy and environmental issues. We have developed an efficient light harvesting heterostructure based on poly(diphenylbutadiyne) (PDPB) nanofibers and ZnO nanoparticles (NPs) via a solution phase synthetic route. ZnO NPs (~20 nm) were homogeneously loaded onto the PDPB nanofibers as evident from several analytical and spectroscopic techniques. The photoinduced electron transfer from PDPB nanofibers to ZnO NPs has been confirmed by steady state and picosecond-resolved photoluminescence studies. The co-sensitization for multiple photon harvesting (with different energies) at the heterojunction has been achieved via a systematic extension of conjugation from monomeric to polymeric diphenyl butadiyne moiety in the proximity of the ZnO NPs. On the other hand, energy transfer from the surface defects of ZnO NPs (~5 nm) to PDPB nanofibers through Förster Resonance Energy Transfer (FRET) confirms the close proximity with molecular resolution. The manifestation of efficient charge separation has been realized with ~5 fold increase in photocatalytic degradation of organic pollutants in comparison to polymer nanofibers counterpart under visible light irradiation. Our results provide a novel approach for the development of nanoheterojunctions for efficient light harvesting which will be helpful in designing future solar devices. PMID:26611253

Charging/discharging behavior and mechanism of silicon quantum dots embedded in amorphous silicon carbide films

NASA Astrophysics Data System (ADS)

Wen, Xixing; Zeng, Xiangbin; Zheng, Wenjun; Liao, Wugang; Feng, Feng

2015-01-01

The charging/discharging behavior of Si quantum dots (QDs) embedded in amorphous silicon carbide (a-SiCx) was investigated based on the Al/insulating layer/Si QDs embedded in a-SiCx/SiO2/p-Si (metal-insulator-quantum dots-oxide-silicon) multilayer structure by capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Transmission electron microscopy and Raman scattering spectroscopy measurements reveal the microstructure and distribution of Si QDs. The occurrence and shift of conductance peaks indicate the carrier transfer and the charging/discharging behavior of Si QDs. The multilayer structure shows a large memory window of 5.2 eV at ±8 V sweeping voltage. Analysis of the C-V and G-V results allows a quantification of the Coulomb charging energy and the trapped charge density associated with the charging/discharging behavior. It is found that the memory window is related to the size effect, and Si QDs with large size or low Coulomb charging energy can trap two or more electrons by changing the charging voltage. Meanwhile, the estimated lower potential barrier height between Si QD and a-SiCx, and the lower Coulomb charging energy of Si QDs could enhance the charging and discharging effect of Si QDs and lead to an enlarged memory window. Further studies of the charging/discharging mechanism of Si QDs embedded in a-SiCx can promote the application of Si QDs in low-power consumption semiconductor memory devices.

Nanoscale phase engineering of thermal transport with a Josephson heat modulator.

PubMed

Fornieri, Antonio; Blanc, Christophe; Bosisio, Riccardo; D'Ambrosio, Sophie; Giazotto, Francesco

2016-03-01

Macroscopic quantum phase coherence has one of its pivotal expressions in the Josephson effect, which manifests itself both in charge and energy transport. The ability to master the amount of heat transferred through two tunnel-coupled superconductors by tuning their phase difference is the core of coherent caloritronics, and is expected to be a key tool in a number of nanoscience fields, including solid-state cooling, thermal isolation, radiation detection, quantum information and thermal logic. Here, we show the realization of the first balanced Josephson heat modulator designed to offer full control at the nanoscale over the phase-coherent component of thermal currents. Our device provides magnetic-flux-dependent temperature modulations up to 40 mK in amplitude with a maximum of the flux-to-temperature transfer coefficient reaching 200 mK per flux quantum at a bath temperature of 25 mK. Foremost, it demonstrates the exact correspondence in the phase engineering of charge and heat currents, breaking ground for advanced caloritronic nanodevices such as thermal splitters, heat pumps and time-dependent electronic engines.

Optically active charge transfer in hybrids of Alq3 nanoparticles and MoS2 monolayer

NASA Astrophysics Data System (ADS)

Ghimire, Ganesh; Dhakal, Krishna P.; Neupane, Guru P.; Jo, Seong Gi; Kim, Hyun; Seo, Changwon; Lee, Young Hee; Joo, Jinsoo; Kim, Jeongyong

2017-05-01

Organic/inorganic hybrid structures have been widely studied because of their enhanced physical and chemical properties. Monolayers of transition metal dichalcogenides (1L-TMDs) and organic nanoparticles can provide a hybridization configuration between zero- and two-dimensional systems with the advantages of convenient preparation and strong interface interaction. Here, we present such a hybrid system made by dispersing π-conjugated organic (tris (8-hydroxyquinoline) aluminum(III)) (Alq3) nanoparticles (NPs) on 1L-MoS2. Hybrids of Alq3 NP/1L-MoS2 exhibited a two-fold increase in the photoluminescence of Alq3 NPs on 1L-MoS2 and the n-doping effect of 1L-MoS2, and these spectral and electronic modifications were attributed to the charge transfer between Alq3 NPs and 1L-MoS2. Our results suggested that a hybrid of organic NPs/1L-TMD can offer a convenient platform to study the interface interactions between organic and inorganic nano objects and to engineer optoelectronic devices with enhanced performance.

Organic nanowire hierarchy over fabric platform for flexible cold cathode

NASA Astrophysics Data System (ADS)

Maiti, Soumen; Narayan Maiti, Uday; Pal, Shreyasi; Chattopadhyay, Kalyan Kumar

2013-11-01

Organic charge transfer (CT) complexes initiated a growing interest in modern electronic devices owing to their easy processability and unique characteristics. In this work, three-dimensional field emitters comprising metal-organic charge transfer complex nanostructures of AgTCNQ and CuTCNQ (TCNQ, 7,7,8,8-tetracyanoquinodimethane) over flexible fabric substrate are realized. Deliberate control over the reaction parameter during organic solid phase reaction leads to modification in structural parameters of the nanowires (i.e. length, diameter) as well as their arrangement atop the carbon fibers. The optimized arrays of AgTCNQ and CuTCNQ nanowires exhibit excellent field electron emission performance with very low turn-on (1.72 and 2.56 V μm-1) and threshold fields (4.21 and 6.33 V μm-1) respectively, which are comparable to those of the best organic field emitters reported to date. The underlying conducting carbon cloth with special woven-like geometry not only offers a flexible platform for nanowire growth, but also provides an additional field enhancement to ease the electron emission.

Optically active charge transfer in hybrids of Alq3 nanoparticles and MoS2 monolayer.

PubMed

Ghimire, Ganesh; Dhakal, Krishna P; Neupane, Guru P; Gi Jo, Seong; Kim, Hyun; Seo, Changwon; Hee Lee, Young; Joo, Jinsoo; Kim, Jeongyong

2017-05-05

Organic/inorganic hybrid structures have been widely studied because of their enhanced physical and chemical properties. Monolayers of transition metal dichalcogenides (1L-TMDs) and organic nanoparticles can provide a hybridization configuration between zero- and two-dimensional systems with the advantages of convenient preparation and strong interface interaction. Here, we present such a hybrid system made by dispersing π-conjugated organic (tris (8-hydroxyquinoline) aluminum(III)) (Alq 3 ) nanoparticles (NPs) on 1L-MoS 2 . Hybrids of Alq 3 NP/1L-MoS 2 exhibited a two-fold increase in the photoluminescence of Alq 3 NPs on 1L-MoS 2 and the n-doping effect of 1L-MoS 2 , and these spectral and electronic modifications were attributed to the charge transfer between Alq 3 NPs and 1L-MoS 2 . Our results suggested that a hybrid of organic NPs/1L-TMD can offer a convenient platform to study the interface interactions between organic and inorganic nano objects and to engineer optoelectronic devices with enhanced performance.

Highly Luminescent 2D-Type Slab Crystals Based on a Molecular Charge-Transfer Complex as Promising Organic Light-Emitting Transistor Materials.

PubMed

Park, Sang Kyu; Kim, Jin Hong; Ohto, Tatsuhiko; Yamada, Ryo; Jones, Andrew O F; Whang, Dong Ryeol; Cho, Illhun; Oh, Sangyoon; Hong, Seung Hwa; Kwon, Ji Eon; Kim, Jong H; Olivier, Yoann; Fischer, Roland; Resel, Roland; Gierschner, Johannes; Tada, Hirokazu; Park, Soo Young

2017-09-01

A new 2:1 donor (D):acceptor (A) mixed-stacked charge-transfer (CT) cocrystal comprising isometrically structured dicyanodistyrylbenzene-based D and A molecules is designed and synthesized. Uniform 2D-type morphology is manifested by the exquisite interplay of intermolecular interactions. In addition to its appealing structural features, unique optoelectronic properties are unveiled. Exceptionally high photoluminescence quantum yield (Φ F ≈ 60%) is realized by non-negligible oscillator strength of the S 1 transition, and rigidified 2D-type structure. Moreover, this luminescent 2D-type CT crystal exhibits balanced ambipolar transport (µ h and µ e of ≈10 -4 cm 2 V -1 s -1 ). As a consequence of such unique optoelectronic characteristics, the first CT electroluminescence is demonstrated in a single active-layered organic light-emitting transistor (OLET) device. The external quantum efficiency of this OLET is as high as 1.5% to suggest a promising potential of luminescent mixed-stacked CT cocrystals in OLET applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A zinc phthalocyanine based periodic mesoporous organosilica exhibiting charge transfer to fullerenes.

PubMed

Auras, Florian; Li, Yan; Löbermann, Florian; Döblinger, Markus; Schuster, Jörg; Peter, Laurence M; Trauner, Dirk; Bein, Thomas

2014-11-10

Periodic mesoporous organosilica (PMO) materials offer a strategy to position molecular semiconductors within a highly defined, porous network. We developed thin films of a new semiconducting zinc phthalocyanine-bridged PMO exhibiting a face-centered orthorhombic pore structure with an average pore diameter of 11 nm. The exceptional degree of order achieved with this PMO enabled us to create thin films consisting of a single porous domain throughout their entire thickness, thus providing maximal accessibility for subsequent incorporation of a complementary phase. The phthalocyanine building blocks inside the pore walls were found to be well-aggregated, enabling electronic conductivity and extending the light-harvesting capabilities to the near IR region. Ordered 3D heterojunctions capable of promoting photo-induced charge transfer were constructed by impregnation of the PMO with a fullerene derivative. When integrated into a photovoltaic device, the infiltrated PMO is capable of producing a high open-circuit voltage and a considerable photocurrent, which represents a significant step towards potential applications of PMOs in optoelectronics. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanoscale phase engineering of thermal transport with a Josephson heat modulator

NASA Astrophysics Data System (ADS)

Fornieri, Antonio; Blanc, Christophe; Bosisio, Riccardo; D'Ambrosio, Sophie; Giazotto, Francesco

2016-03-01

Macroscopic quantum phase coherence has one of its pivotal expressions in the Josephson effect, which manifests itself both in charge and energy transport. The ability to master the amount of heat transferred through two tunnel-coupled superconductors by tuning their phase difference is the core of coherent caloritronics, and is expected to be a key tool in a number of nanoscience fields, including solid-state cooling, thermal isolation, radiation detection, quantum information and thermal logic. Here, we show the realization of the first balanced Josephson heat modulator designed to offer full control at the nanoscale over the phase-coherent component of thermal currents. Our device provides magnetic-flux-dependent temperature modulations up to 40 mK in amplitude with a maximum of the flux-to-temperature transfer coefficient reaching 200 mK per flux quantum at a bath temperature of 25 mK. Foremost, it demonstrates the exact correspondence in the phase engineering of charge and heat currents, breaking ground for advanced caloritronic nanodevices such as thermal splitters, heat pumps and time-dependent electronic engines.

Time-domain ab initio modeling of photoinduced dynamics at nanoscale interfaces.

PubMed

Wang, Linjun; Long, Run; Prezhdo, Oleg V

2015-04-01

Nonequilibrium processes involving electronic and vibrational degrees of freedom in nanoscale materials are under active experimental investigation. Corresponding theoretical studies are much scarcer. The review starts with the basics of time-dependent density functional theory, recent developments in nonadiabatic molecular dynamics, and the fusion of the two techniques. Ab initio simulations of this kind allow us to directly mimic a great variety of time-resolved experiments performed with pump-probe laser spectroscopies. The focus is on the ultrafast photoinduced charge and exciton dynamics at interfaces formed by two complementary materials. We consider purely inorganic materials, inorganic-organic hybrids, and all organic interfaces, involving bulk semiconductors, metallic and semiconducting nanoclusters, graphene, carbon nanotubes, fullerenes, polymers, molecular crystals, molecules, and solvent. The detailed atomistic insights available from time-domain ab initio studies provide a unique description and a comprehensive understanding of the competition between electron transfer, thermal relaxation, energy transfer, and charge recombination processes. These advances now make it possible to directly guide the development of organic and hybrid solar cells, as well as photocatalytic, electronic, spintronic, and other devices relying on complex interfacial dynamics.

Ultrasonic power transfer from a spherical acoustic wave source to a free-free piezoelectric receiver: Modeling and experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shahab, S.; Gray, M.; Erturk, A., E-mail: alper.erturk@me.gatech.edu

2015-03-14

Contactless powering of small electronic components has lately received growing attention for wireless applications in which battery replacement or tethered charging is undesired or simply impossible, and ambient energy harvesting is not a viable solution. As an alternative to well-studied methods of contactless energy transfer, such as the inductive coupling method, the use of ultrasonic waves transmitted and received by piezoelectric devices enables larger power transmission distances, which is critical especially for deep-implanted electronic devices. Moreover, energy transfer by means of acoustic waves is well suited in situations where no electromagnetic fields are allowed. The limited literature of ultrasonic acousticmore » energy transfer is mainly centered on proof-of-concept experiments demonstrating the feasibility of this method, lacking experimentally validated modeling efforts for the resulting multiphysics problem that couples the source and receiver dynamics with domain acoustics. In this work, we present fully coupled analytical, numerical, and experimental multiphysics investigations for ultrasonic acoustic energy transfer from a spherical wave source to a piezoelectric receiver bar that operates in the 33-mode of piezoelectricity. The fluid-loaded piezoelectric receiver under free-free mechanical boundary conditions is shunted to an electrical load for quantifying the electrical power output for a given acoustic source strength of the transmitter. The analytical acoustic-piezoelectric structure interaction modeling framework is validated experimentally, and the effects of system parameters are reported along with optimal electrical loading and frequency conditions of the receiver.« less

Continuous operation of an ultra-low-power microcontroller using glucose as the sole energy source.

PubMed

Lee, Inyoung; Sode, Takashi; Loew, Noya; Tsugawa, Wakako; Lowe, Christopher Robin; Sode, Koji

2017-07-15

An ultimate goal for those engaged in research to develop implantable medical devices is to develop mechatronic implantable artificial organs such as artificial pancreas. Such devices would comprise at least a sensor module, an actuator module, and a controller module. For the development of optimal mechatronic implantable artificial organs, these modules should be self-powered and autonomously operated. In this study, we aimed to develop a microcontroller using the BioCapacitor principle. A direct electron transfer type glucose dehydrogenase was immobilized onto mesoporous carbon, and then deposited on the surface of a miniaturized Au electrode (7mm 2 ) to prepare a miniaturized enzyme anode. The enzyme fuel cell was connected with a 100 μF capacitor and a power boost converter as a charge pump. The voltage of the enzyme fuel cell was increased in a stepwise manner by the charge pump from 330mV to 3.1V, and the generated electricity was charged into a 100μF capacitor. The charge pump circuit was connected to an ultra-low-power microcontroller. Thus prepared BioCapacitor based circuit was able to operate an ultra-low-power microcontroller continuously, by running a program for 17h that turned on an LED every 60s. Our success in operating a microcontroller using glucose as the sole energy source indicated the probability of realizing implantable self-powered autonomously operated artificial organs, such as artificial pancreas. Copyright © 2016 Elsevier B.V. All rights reserved.

Supramolecular networks with electron transfer in two dimensions

DOEpatents

Stupp, Samuel I.; Stoddart, J. Fraser; Shveyd, Alexander K.; Tayi, Alok S.; Sue, Chi-Hau; Narayanan, Ashwin

2016-09-13

Organic charge-transfer (CT) co-crystals in a crossed stack system are disclosed. The co-crystals exhibit bidirectional charge transfer interactions where one donor molecule shares electrons with two different acceptors, one acceptor face-to-face and the other edge-to-face. The assembly and charge transfer interaction results in a pleochroic material whereby the optical absorption continuously changes depending on the polarization angle of incident light.

Fabrication of ultra-fine nanostructures using edge transfer printing.

PubMed

Xue, Mianqi; Li, Fengwang; Cao, Tingbing

2012-03-21

The exploration of new methods and techniques for application in diverse fields, such as photonics, microfluidics, biotechnology and flexible electronics is of increasing scientific and technical interest for multiple uses over distance of 10-100 nm. This article discusses edge transfer printing--a series of unconventional methods derived from soft lithography for nanofabrication. It possesses the advantages of easy fabrication, low-cost and great serviceability. In this paper, we show how to produce exposed edges and use various materials for edge transfer printing, while nanoskiving, nanotransfer edge printing and tunable cracking for nanogaps are introduced. Besides this, different functional materials, such as metals, inorganic semiconductors and polymers, as well as localised heating and charge patterning, are described here as unconventional "inks" for printing. Edge transfer printing, which can effectively produce sub-100 nm scale ultra-fine structures, has broad applications, including metallic nanowires as nanoelectrodes, semiconductor nanowires for chemical sensors, heterostructures of organic semiconductors, plasmonic devices and so forth. This journal is © The Royal Society of Chemistry 2012

Out-of-plane heat transfer in van der Waals stacks through electron-hyperbolic phonon coupling

NASA Astrophysics Data System (ADS)

Tielrooij, Klaas-Jan; Hesp, Niels C. H.; Principi, Alessandro; Lundeberg, Mark B.; Pogna, Eva A. A.; Banszerus, Luca; Mics, Zoltán; Massicotte, Mathieu; Schmidt, Peter; Davydovskaya, Diana; Purdie, David G.; Goykhman, Ilya; Soavi, Giancarlo; Lombardo, Antonio; Watanabe, Kenji; Taniguchi, Takashi; Bonn, Mischa; Turchinovich, Dmitry; Stampfer, Christoph; Ferrari, Andrea C.; Cerullo, Giulio; Polini, Marco; Koppens, Frank H. L.

2018-01-01

Van der Waals heterostructures have emerged as promising building blocks that offer access to new physics, novel device functionalities and superior electrical and optoelectronic properties1-7. Applications such as thermal management, photodetection, light emission, data communication, high-speed electronics and light harvesting8-16 require a thorough understanding of (nanoscale) heat flow. Here, using time-resolved photocurrent measurements, we identify an efficient out-of-plane energy transfer channel, where charge carriers in graphene couple to hyperbolic phonon polaritons17-19 in the encapsulating layered material. This hyperbolic cooling is particularly efficient, giving picosecond cooling times for hexagonal BN, where the high-momentum hyperbolic phonon polaritons enable efficient near-field energy transfer. We study this heat transfer mechanism using distinct control knobs to vary carrier density and lattice temperature, and find excellent agreement with theory without any adjustable parameters. These insights may lead to the ability to control heat flow in van der Waals heterostructures.

Study of the effect of distance and misalignment between magnetically coupled coils for wireless power transfer in intraocular pressure measurement.

PubMed

Rendon-Nava, Adrian E; Díaz-Méndez, J Alejandro; Nino-de-Rivera, Luis; Calleja-Arriaga, Wilfrido; Gil-Carrasco, Felix; Díaz-Alonso, Daniela

2014-01-01

An analysis of the effect of distance and alignment between two magnetically coupled coils for wireless power transfer in intraocular pressure measurement is presented. For measurement purposes, a system was fabricated consisting of an external device, which is a Maxwell-Wien bridge circuit variation, in charge of transferring energy to a biomedical implant and reading data from it. The biomedical implant is an RLC tank circuit, encapsulated by a polyimide coating. Power transfer was done by magnetic induction coupling method, by placing one of the inductors of the Maxwell-Wien bridge circuit and the inductor of the implant in close proximity. The Maxwell-Wien bridge circuit was biased with a 10 MHz sinusoidal signal. The analysis presented in this paper proves that wireless transmission of power for intraocular pressure measurement is feasible with the measurement system proposed. In order to have a proper inductive coupling link, special care must be taken when placing the two coils in proximity to avoid misalignment between them.

Observation of energy transfer phenomenon via up and down conversion in Eu3+ ions for BaMoO4:Er3+-Eu3+ nanophosphor

NASA Astrophysics Data System (ADS)

Soni, Abhishek Kumar; Ningthoujam, Raghumani Singh

2018-04-01

The Er3+-Eu3+ codoped BaMoO4 nanophosphor has been synthesized by using urea hydrolysis in ethylene glycol medium. The tetragonal phase formation of the codoped nanophosphor has been confirmed by the X-ray diffraction analysis. The up and down conversion emission spectra have been recorded via 980 and 270 nm excitation, respectively. The Eu3+ emission arising in the prepared Er3+-Eu3+ codoped BaMoO4 nanophosphor is basically due to the efficient energy transfer process. The energy level diagram has been sketched to show the energy transfer phenomenon in the Eu3+ ion from charge transfer band (host lattice absorption) and excited level of the Er3+ ion (multiphoton absorption). The values of colour co-ordinates suggest that materials can produce the red to yellow. The developed nanophosphor could be useful as an effective up and down converting optical material and lighting device applications.

Charge transfer polarisation wave and carrier pairing in the high T(sub c) copper oxides

NASA Technical Reports Server (NTRS)

Chakraverty, B. K.

1990-01-01

The High T(sub c) oxides are highly polarizable materials and are charge transfer insulators. The charge transfer polarization wave formalism is developed in these oxides. The dispersion relationships due to long range dipole-dipole interaction of a charge transfer dipole lattice are obtained in 3-D and 2-D. These are high frequency bosons and their coupling with carriers is weak and antiadiabatic in nature. As a result, the mass renormalization of the carriers is negligible in complete contrast to conventional electron-phonon interaction, that give polarons and bipolarons. Both bound and superconducting pairing is discussed for a model Hamiltonian valid in the antiadiabatic regime, both in 3-D and 2-D. The stability of the charge transfer dipole lattice has interesting consequences that are discussed.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant.

PubMed

Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

2015-05-15

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant

NASA Astrophysics Data System (ADS)

Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

2015-05-01

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant

PubMed Central

Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

2015-01-01

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies. PMID:25975371

The Physics of Polarization

NASA Astrophysics Data System (ADS)

Landi Degl'Innocenti, Egidio

2015-10-01

The introductory lecture that has been delivered at this Symposium is a condensed version of an extended course held by the author at the XII Canary Island Winter School from November 13 to November 21, 2000. The full series of lectures can be found in Landi Degl'Innocenti (2002). The original reference is organized in 20 Sections that are here itemized: 1. Introduction, 2. Description of polarized radiation, 3. Polarization and optical devices: Jones calculus and Muller matrices, 4. The Fresnel equations, 5. Dichroism and anomalous dispersion, 6. Polarization in everyday life, 7. Polarization due to radiating charges, 8. The linear antenna, 9. Thomson scattering, 10. Rayleigh scattering, 11. A digression on Mie scattering, 12. Bremsstrahlung radiation, 13. Cyclotron radiation, 14. Synchrotron radiation, 15. Polarization in spectral lines, 16. Density matrix and atomic polarization, 17. Radiative transfer and statistical equilibrium equations, 18. The amplification condition in polarized radiative transfer, and 19. Coupling radiative transfer and statistical equilibrium equations.

Light and colour as analytical detection tools: a journey into the periodic table using polyamines to bio-inspired systems as chemosensors.

PubMed

Lodeiro, Carlos; Capelo, José Luis; Mejuto, Juan Carlos; Oliveira, Elisabete; Santos, Hugo M; Pedras, Bruno; Nuñez, Cristina

2010-08-01

This critical review describes some developments on the chemistry of fluorescent and colorimetric molecular probes or chemosensors, based on polyamines and associated compounds having oxygen and/or sulfur as donor atoms. The reported systems are essentially based on some selected published work in this field in the last five years, and in the work developed by the authors from 2000 onwards. Some interesting properties beyond sensing molecules, ions or/and cations by fluorescence, colorimetry as well as by MALDI-TOF MS spectrometry can arise from these systems. A short brief on different examples activated by PET (photoinduced electron transfer), ICT (internal charge transfer) and EET (electronic energy transfer) phenomena will be provided. Finally the introduction of bio-inspired compounds derived from emissive amino acid or short peptide systems and nanoparticle devices to detect metal ions will be reviewed (202 references).

Electron transport in doped fullerene molecular junctions

NASA Astrophysics Data System (ADS)

Kaur, Milanpreet; Sawhney, Ravinder Singh; Engles, Derick

The effect of doping on the electron transport of molecular junctions is analyzed in this paper. The doped fullerene molecules are stringed to two semi-infinite gold electrodes and analyzed at equilibrium and nonequilibrium conditions of these device configurations. The contemplation is done using nonequilibrium Green’s function (NEGF)-density functional theory (DFT) to evaluate its density of states (DOS), transmission coefficient, molecular orbitals, electron density, charge transfer, current, and conductance. We conclude from the elucidated results that Au-C16Li4-Au and Au-C16Ne4-Au devices behave as an ordinary p-n junction diode and a Zener diode, respectively. Moreover, these doped fullerene molecules do not lose their metallic nature when sandwiched between the pair of gold electrodes.

Sensing Responses Based on Transfer Characteristics of InAs Nanowire Field-Effect Transistors

PubMed Central

Savelyev, Igor; Blumin, Marina; Wang, Shiliang; Ruda, Harry E.

2017-01-01

Nanowire-based field-effect transistors (FETs) have demonstrated considerable promise for a new generation of chemical and biological sensors. Indium arsenide (InAs), by virtue of its high electron mobility and intrinsic surface accumulation layer of electrons, holds properties beneficial for creating high performance sensors that can be used in applications such as point-of-care testing for patients diagnosed with chronic diseases. Here, we propose devices based on a parallel configuration of InAs nanowires and investigate sensor responses from measurements of conductance over time and FET characteristics. The devices were tested in controlled concentrations of vapour containing acetic acid, 2-butanone and methanol. After adsorption of analyte molecules, trends in the transient current and transfer curves are correlated with the nature of the surface interaction. Specifically, we observed proportionality between acetic acid concentration and relative conductance change, off current and surface charge density extracted from subthreshold behaviour. We suggest the origin of the sensing response to acetic acid as a two-part, reversible acid-base and redox reaction between acetic acid, InAs and its native oxide that forms slow, donor-like states at the nanowire surface. We further describe a simple model that is able to distinguish the occurrence of physical versus chemical adsorption by comparing the values of the extracted surface charge density. These studies demonstrate that InAs nanowires can produce a multitude of sensor responses for the purpose of developing next generation, multi-dimensional sensor applications. PMID:28714903

Bio-inspired photo-electronic material based on photosynthetic proteins

NASA Astrophysics Data System (ADS)

Lebedev, Nikolai; Trammell, Scott A.; Tsoi, Stanislav; Spano, Anthony; Kim, Jin Ho; Xu, Jimmy; Twigg, Mark E.; Schnur, Joel M.

2009-08-01

The construction of efficient light energy converting (photovoltaic and photo-electronic) devices is a current and great challenge in science and technology and one that will have important economic consequences. Several innovative nanoelectronic materials were proposed to achieve this goal, semiconductor quantum dots, metallic nanowires and carbon nanotubes (CNT) are among them. As a charge separating unit for light energy conversion, we propose the utilization of the most advanced photoelectronic material developed by nature, photosynthetic reaction center proteins. As a first step in this direction, we constructed a novel bioinorganic nanophotoelectronic material with photoactive photosynthetic reaction center (RC) proteins encapsulated inside a multiwall CNT arrayed electrode. The material consists of photosynthetic RC-cytochrome complexes acting as charge separating units bound to the inner walls of a CNT electrode and ubiquinone-10 (Q2) serving as a soluble electron-transfer mediator to the counter electrode. The proteins were immobilized inside carbon nanotubes by a Ni(NTA)-alkane-pyrene linker, forming a self-assembled monolayer (SAM) on the surface of inner CNT walls and allowing for unidirectional protein orientation. The material demonstrates an enhanced photoinduced electron transfer rate and shows substantial improvement in photocurrent density compared to that obtained with the same proteins when immobilized on planar graphite (HOPG) electrode. The results suggest that protein encapsulation in precisely organized arrayed tubular electrode architecture can considerably improve the performance of photovoltaic, photoelectronic, or biofuel cell devices. They demonstrate the potential for substantial advantages of precisely organized nano electrode tubular arrayed architecture for variety biotechnological applications.

Emergent magnetism at transition-metal–nanocarbon interfaces

PubMed Central

Al Ma’Mari, Fatma; Rogers, Matthew; Alghamdi, Shoug; Moorsom, Timothy; Lee, Stephen; Prokscha, Thomas; Luetkens, Hubertus; Valvidares, Manuel; Flokstra, Machiel; Stewart, Rhea; Ali, Mannan; Burnell, Gavin; Hickey, B. J.

2017-01-01

Charge transfer at metallo–molecular interfaces may be used to design multifunctional hybrids with an emergent magnetization that may offer an eco-friendly and tunable alternative to conventional magnets and devices. Here, we investigate the origin of the magnetism arising at these interfaces by using different techniques to probe 3d and 5d metal films such as Sc, Mn, Cu, and Pt in contact with fullerenes and rf-sputtered carbon layers. These systems exhibit small anisotropy and coercivity together with a high Curie point. Low-energy muon spin spectroscopy in Cu and Sc–C60 multilayers show a quick spin depolarization and oscillations attributed to nonuniform local magnetic fields close to the metallo–carbon interface. The hybridization state of the carbon layers plays a crucial role, and we observe an increased magnetization as sp3 orbitals are annealed into sp2−π graphitic states in sputtered carbon/copper multilayers. X-ray magnetic circular dichroism (XMCD) measurements at the carbon K edge of C60 layers in contact with Sc films show spin polarization in the lowest unoccupied molecular orbital (LUMO) and higher π*-molecular levels, whereas the dichroism in the σ*-resonances is small or nonexistent. These results support the idea of an interaction mediated via charge transfer from the metal and dz–π hybridization. Thin-film carbon-based magnets may allow for the manipulation of spin ordering at metallic surfaces using electrooptical signals, with potential applications in computing, sensors, and other multifunctional magnetic devices. PMID:28507160

Importance of network density of nanotube: Effect on nitrogen dioxide gas sensing by solid state resistive sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mishra, Prabhash; Grachyova, D. V.; Moskalenko, A. S.

2016-04-13

Dispersion of single-walled carbon nanotubes (SWCNTs) is an established fact, however, its effect on toxic gas sensing for the development of solid state resistive sensor was not well reported. In this report, the dispersion quality of SWCNTs has been investigated and improved, and this well-dispersed SWCNTs network was used for sensor fabrication to monitor nitrogen dioxide gas. Ultraviolet (UV)-visible spectroscopic studies shows the strength of SWNTs dispersion and scanning electron microscopy (SEM) imaging provides the morphological properties of the sensor device. In this gas sensor device, two sets of resistive type sensors were fabricated that consisting of a pair ofmore » interdigitated electrodes (IDEs) using dielectrophoresis technique with different SWCNTs network density. With low-density SWCNTs networks, this fabricated sensor exhibits a high response for nitrogen dioxide sensing. The sensing of nitrogen dioxide is mainly due to charge transfer from absorbed molecules to sidewalls of nanotube and tube-tube screening acting a major role for the transport properties of charge carriers.« less

Photoelectrochemical Complexes of Fucoxanthin-Chlorophyll Protein for Bio-Photovoltaic Conversion with a High Open-Circuit Photovoltage.

PubMed

Zhang, Tianning; Liu, Cheng; Dong, Wenjing; Wang, Wenda; Sun, Yan; Chen, Xin; Yang, Chunhong; Dai, Ning

2017-12-05

Open-circuit photovoltage (V oc ) is among the critical parameters for achieving an efficient light-to-charge conversion in existing solar photovoltaic devices. Natural photosynthesis exploits light-harvesting chlorophyll (Chl) protein complexes to transfer sunlight energy efficiently. We describe the exploitation of photosynthetic fucoxanthin-chlorophyll protein (FCP) complexes for realizing photoelectrochemical cells with a high V oc . An antenna-dependent photocurrent response and a V oc up to 0.72 V are observed and demonstrated in the bio-photovoltaic devices fabricated with photosynthetic FCP complexes and TiO 2 nanostructures. Such high V oc is determined by fucoxanthin in FCP complexes, and is rarely found in photoelectrochemical cells with other natural light-harvesting antenna. We think that the FCP-based bio-photovoltaic conversion will provide an opportunity to fabricate environmental benign photoelectrochemical cells with high V oc , and also help improve the understanding of the essential physics behind the light-to-charge conversion in photosynthetic complexes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Intermolecular interaction approach for TADF (Conference Presentation)

NASA Astrophysics Data System (ADS)

Wong, Ken-Tsung

2016-09-01

Materials with thermally activated delayed fluorescence (TADF) have recently emerged as new fluorescent emitters for highly efficient organic light-emitting diodes (OLEDs). Molecule with TADF behavior needs to have a small singlet-triplet energy difference (ΔES-T) that allows the up-conversion from nonradiative triplet state (T1) to radiative singlet state (S1) via reverse intersystem crossing (RISC) process. Generally, molecules with small ΔES-T can be obtained via carefully manipulate the degree of "intramolecular" charge transfer (ICT) between electron-donating and -accepting components, such that the electron exchange energy that contributes to ΔES-T, can be minimized. Alternatively, excited state with small ΔES-T can be feasibly realized via "intermolecular" charge transfer occurring at the interface between spatially separating donor (D) and acceptor (A) molecules. Because the exchange energy decreases as the HOMO-LUMO separation distance increases, theoretically, the intermolecular D/A charge transfer state (or exciplex) should have rather small ΔES-T, leading to efficient TADF. However, it is still a challenge to access highly efficient exciplex systems. This is mainly because exciplex formation is commonly accompanied with a large red shift of emission spectra and long radiative lifetime, which tend to diminish photoluminescence quantum yield (PLQY) as well as electroluminescence (EL) performance. Until now, exciplex-based OLEDs with external quantum efficiency (EQE) above 10% are still limited. By judicious selection of donor and acceptor, the formation of efficient exciplex can be feasibly achieved. In this conference, our recent efforts on highly efficient exciplexes using C3-symmetry triazine acceptors and various donors, and their device characteristics will be presented.

A density functional theory study on the thermodynamic and dynamic properties of anthraquinone analogue cathode materials for rechargeable lithium ion batteries.

PubMed

Yang, Shu-Jing; Qin, Xiao-Ya; He, Rongxing; Shen, Wei; Li, Ming; Zhao, Liu-Bin

2017-05-21

Organic redox compounds have become the emerging electrode materials for rechargeable lithium ion batteries. The high electrochemical performance provides organic electrode materials with great opportunities to be applied in electric energy storage devices. Among the different types of organic materials, conjugated carbonyl compounds are the most promising type at present, because only they can simultaneously achieve, high energy density, high cycling stability, and high power density. In this research, a series of heteroatom substituted anthraquinone (AQ) derivatives were designed theoretically so that the high theoretical capacity of AQ remained. The discharge and charge mechanism as well as the thermodynamic and dynamic properties of AQ and its derivatives were investigated using first-principles density functional theory. Using heteroatom substitution, both the thermodynamic and dynamic properties of AQ as cathode materials could be largely improved. Among these conjugated carboxyl compounds, BDOZD and BDIOZD with a simultaneously high theoretical capacity and high working potential exhibit the largest energy density of about 780 W h kg -1 , which is 41% larger than that of AQ. The PQD with the smallest value of λ gives the largest charge transfer rate constant, which is about four times as large as the prototype molecule, AQ. The most interesting finding is that the lithium ion transfer plays a very important role in influencing both the discharge potential and electrochemical charge transfer rate. The present study illustrates that theoretical calculations provide a highly effective way to discover potential materials for use with rechargeable lithium ion batteries.

The influence of electrode and separator thickness on the cell resistance of symmetric cellulose-polypyrrole-based electric energy storage devices

NASA Astrophysics Data System (ADS)

Tammela, Petter; Olsson, Henrik; Strømme, Maria; Nyholm, Leif

2014-12-01

The influence of the cell design of symmetric polypyrrole and cellulose-based electric energy storage devices on the cell resistance was investigated using chronopotentiometric and ac impedance measurements with different separator and electrode thicknesses. The cell resistance was found to be dominated by the electrolyte and current collector resistances while the contribution from the composite electrode material was negligible. Due to the electrolyte within the porous electrodes thin separators could be used in combination with thick composite electrodes without loss of performance. The paper separator contributed with a resistance of ∼1.5 Ω mm-1 in a 1.0 M NaNO3 electrolyte and the tortuosity value for the separator was about 2.5. The contribution from the graphite foil current collectors was about ∼0.4-1.1 Ω and this contribution could not be reduced by using platinum foil current collectors due to larger contact resistances. The introduction of chopped carbon fibres into the electrode material or the application of pressure across the cells, however, decreased the charge transfer resistance significantly. As the present results demonstrate that cells with higher charge storage capacities but with the same cell resistance can be obtained by increasing the electrode thickness, the development of paper based energy storage devices is facilitated.

Controlled Defects of Fluorine-incorporated ZnO Nanorods for Photovoltaic Enhancement

PubMed Central

Lee, Hock Beng; Ginting, Riski Titian; Tan, Sin Tee; Tan, Chun Hui; Alshanableh, Abdelelah; Oleiwi, Hind Fadhil; Yap, Chi Chin; Jumali, Mohd Hafizuddin Hj.; Yahaya, Muhammad

2016-01-01

Anion passivation effect on metal-oxide nano-architecture offers a highly controllable platform for improving charge selectivity and extraction, with direct relevance to their implementation in hybrid solar cells. In current work, we demonstrated the incorporation of fluorine (F) as an anion dopant to address the defect-rich nature of ZnO nanorods (ZNR) and improve the feasibility of its role as electron acceptor. The detailed morphology evolution and defect engineering on ZNR were studied as a function of F-doping concentration (x). Specifically, the rod-shaped arrays of ZnO were transformed into taper-shaped arrays at high x. A hypsochromic shift was observed in optical energy band gap due to the Burstein-Moss effect. A substantial suppression on intrinsic defects in ZnO lattice directly epitomized the novel role of fluorine as an oxygen defect quencher. The results show that 10-FZNR/P3HT device exhibited two-fold higher power conversion efficiency than the pristine ZNR/P3HT device, primarily due to the reduced Schottky defects and charge transfer barrier. Essentially, the reported findings yielded insights on the functions of fluorine on (i) surface –OH passivation, (ii) oxygen vacancies (Vo) occupation and (iii) lattice oxygen substitution, thereby enhancing the photo-physical processes, carrier mobility and concentration of FZNR based device. PMID:27587295

Electrical conductivity measurements of bacterial nanowires from Pseudomonas aeruginosa

NASA Astrophysics Data System (ADS)

Maruthupandy, Muthusamy; Anand, Muthusamy; Maduraiveeran, Govindhan; Sait Hameedha Beevi, Akbar; Jeeva Priya, Radhakrishnan

2015-12-01

The extracellular appendages of bacteria (flagella) that transfer electrons to electrodes are called bacterial nanowires. This study focuses on the isolation and separation of nanowires that are attached via Pseudomonas aeruginosa bacterial culture. The size and roughness of separated nanowires were measured using transmission electron microscopy (TEM) and atomic force microscopy (AFM), respectively. The obtained bacterial nanowires indicated a clear image of bacterial nanowires measuring 16 nm in diameter. The formation of bacterial nanowires was confirmed by microscopic studies (AFM and TEM) and the conductivity nature of bacterial nanowire was investigated by electrochemical techniques. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which are nondestructive voltammetry techniques, suggest that bacterial nanowires could be the source of electrons—which may be used in various applications, for example, microbial fuel cells, biosensors, organic solar cells, and bioelectronic devices. Routine analysis of electron transfer between bacterial nanowires and the electrode was performed, providing insight into the extracellular electron transfer (EET) to the electrode. CV revealed the catalytic electron transferability of bacterial nanowires and electrodes and showed excellent redox activities. CV and EIS studies showed that bacterial nanowires can charge the surface by producing and storing sufficient electrons, behave as a capacitor, and have features consistent with EET. Finally, electrochemical studies confirmed the development of bacterial nanowires with EET. This study suggests that bacterial nanowires can be used to fabricate biomolecular sensors and nanoelectronic devices.