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Sample records for dot interfacial layer

  1. A layer-by-layer ZnO nanoparticle-PbS quantum dot self-assembly platform for ultrafast interfacial electron injection.

    PubMed

    Eita, Mohamed; Usman, Anwar; El-Ballouli, Ala'a O; Alarousu, Erkki; Bakr, Osman M; Mohammed, Omar F

    2015-01-01

    Absorbent layers of semiconductor quantum dots (QDs) are now used as material platforms for low-cost, high-performance solar cells. The semiconductor metal oxide nanoparticles as an acceptor layer have become an integral part of the next generation solar cell. To achieve sufficient electron transfer and subsequently high conversion efficiency in these solar cells, however, energy-level alignment and interfacial contact between the donor and the acceptor units are needed. Here, the layer-by-layer (LbL) technique is used to assemble ZnO nanoparticles (NPs), providing adequate PbS QD uptake to achieve greater interfacial contact compared with traditional sputtering methods. Electron injection at the PbS QD and ZnO NP interface is investigated using broadband transient absorption spectroscopy with 120 femtosecond temporal resolution. The results indicate that electron injection from photoexcited PbS QDs to ZnO NPs occurs on a time scale of a few hundred femtoseconds. This observation is supported by the interfacial electronic-energy alignment between the donor and acceptor moieties. Finally, due to the combination of large interfacial contact and ultrafast electron injection, this proposed platform of assembled thin films holds promise for a variety of solar cell architectures and other settings that principally rely on interfacial contact, such as photocatalysis. PMID:25163799

  2. Influence of interfacial oxide on the optical properties of single layer CdTe/CdS quantum dots in porous silicon scaffolds

    NASA Astrophysics Data System (ADS)

    Gaur, Girija; Koktysh, Dmitry S.; Fleetwood, Daniel M.; Weller, Robert A.; Reed, Robert A.; Weiss, Sharon M.

    2015-08-01

    Using a combination of continuous wave and time-resolved spectroscopy, we study the effects of interfacial conditions on the radiative lifetimes and photoluminescence intensities of sub-monolayer colloidal CdTe/CdS quantum dots (QDs) embedded in a three-dimensional porous silicon (PSi) scaffold. The PSi matrix was thermally oxidized under different conditions to change the interfacial oxide thickness. QDs embedded in a PSi matrix with ˜0.4 nm of interfacial oxide exhibited reduced photoluminescence intensity and nearly five times shorter radiative lifetimes (˜16 ns) compared to QDs immobilized within completely oxidized, porous silica (PSiO2) frameworks (˜78 ns). The exponential dependence of QD lifetime on interfacial oxide thickness in the PSi scaffolds suggests charge transfer plays an important role in the exciton dynamics.

  3. Influence of interfacial oxide on the optical properties of single layer CdTe/CdS quantum dots in porous silicon scaffolds

    SciTech Connect

    Gaur, Girija; Fleetwood, Daniel M.; Weller, Robert A.; Reed, Robert A.; Weiss, Sharon M.; Koktysh, Dmitry S.

    2015-08-10

    Using a combination of continuous wave and time-resolved spectroscopy, we study the effects of interfacial conditions on the radiative lifetimes and photoluminescence intensities of sub-monolayer colloidal CdTe/CdS quantum dots (QDs) embedded in a three-dimensional porous silicon (PSi) scaffold. The PSi matrix was thermally oxidized under different conditions to change the interfacial oxide thickness. QDs embedded in a PSi matrix with ∼0.4 nm of interfacial oxide exhibited reduced photoluminescence intensity and nearly five times shorter radiative lifetimes (∼16 ns) compared to QDs immobilized within completely oxidized, porous silica (PSiO{sub 2}) frameworks (∼78 ns). The exponential dependence of QD lifetime on interfacial oxide thickness in the PSi scaffolds suggests charge transfer plays an important role in the exciton dynamics.

  4. Interfacial Engineering for Quantum-Dot-Sensitized Solar Cells.

    PubMed

    Shen, Chao; Fichou, Denis; Wang, Qing

    2016-04-20

    Quantum-dot-sensitized solar cells (QDSCs) are promising solar-energy-conversion devices, as low-cost alternatives to the prevailing photovoltaic technologies. Compared with molecular dyes, nanocrystalline quantum dot (QD) light absorbers exhibit higher molar extinction coefficients and a tunable photoresponse. However, the power-conversion efficiencies (PCEs) of QDSCs are generally below 9.5 %, far behind their molecular sensitizer counterparts (up to 13 %). These low PCEs have been attributed to a large free-energy loss during sensitizer regeneration, energy loss during the charge-carrier transport and transfer processes, and inefficient charge separation at the QD/electrolyte interfaces, and various interfacial engineering strategies for enhancing the PCE and cell stability have been reported. Herein, we review recent progress in the interfacial engineering of QDSCs and discuss future prospects for the development of highly efficient and stable QDSCs. PMID:26879244

  5. Tailored interfacial rheology for gastric stable adsorption layers.

    PubMed

    Scheuble, N; Geue, T; Windhab, E J; Fischer, P

    2014-08-11

    Human lipid digestion begins at the interface of oil and water by interfacial adsorption of lipases. Tailoring the available surface area for lipase activity can lead to specific lipid sensing in the body, thus, tailored satiety hormone release. In this study we present biopolymer layers at the MCT-oil/water interface with different stabilities under human gastric environment (37 °C, pH 2, pepsin). Physicochemical changes and enzymatic degradation of interfacial layers were monitored online by interfacial shear rheology. We show the weakening of β-lactoglobulin (β-lg) layers at body temperature and acidification and their hydrolysis by pepsin. If sufficient concentrations of nanocrystalline cellulose (NCC) are given to an existing β-lg layer, this weakening is buffered and the proteolysis delayed. A synergistic, composite layer is formed by adding methylated NCC to the β-lg layer. This layer thermogels at body temperature and resists hydrolysis by pepsin. Coexistence of these two emulsifiers at the air/water interface is evidenced by neutron reflectometry measurements, where morphological information are extracted. The utilized layers and their analysis provide knowledge of physicochemical changes during in vitro digestion of interfaces, which promote functional food formulations. PMID:25029559

  6. Graphene as an efficient interfacial layer for electrochromic devices.

    PubMed

    Lin, Feng; Bult, Justin B; Nanayakkara, Sanjini; Dillon, Anne C; Richards, Ryan M; Blackburn, Jeffrey L; Engtrakul, Chaiwat

    2015-06-01

    This study presents an interfacial modification strategy to improve the performance of electrochromic films that were fabricated by a magnetron sputtering technique. High-quality graphene sheets, synthesized by chemical vapor deposition, were used to modify fluorine-doped tin oxide substrates, followed by the deposition of high-performance nanocomposite nickel oxide electrochromic films. Electrochromic cycling results revealed that a near-complete monolayer graphene interfacial layer improves the electrochromic performance in terms of switching kinetics, activation period, coloration efficiency, and bleached-state transparency, while maintaining ∼100% charge reversibility. The present study offers an alternative route for improving the interfacial properties between electrochromic and transparent conducting oxide films without relying on conventional methods such as nanostructuring or thin film composition control. PMID:25950270

  7. Interfacial layers of complex-forming ionic surfactants with gelatin.

    PubMed

    Derkach, Svetlana R

    2015-08-01

    This review is devoted to discussing the results of studies of the influence of low-molecular weight surfactant additions on the composition and properties of gelatin adsorbed layers which are spontaneously created at water/air and water/non-polar-liquid interfaces. The interaction of surfactant with gelatin leads to the formation of complexes of variable content in the bulk of the aqueous phase. The composition content is determined by the component ratio and concentration of the added surfactant. The role of surfactants (anionic, cationic, non-ionic) capable of forming complexes with gelatin due to electrostatic and hydrophobic interactions is considered. Analysis of the interfacial layer properties is based on literature information, as well as the own author's data. These data include the results of measuring thermodynamic properties (interface tension), laws of formation (adsorption kinetics and thickness), and rheological properties of the layers, which are considered to be dependent on gelatin and surfactant concentration, pH, and temperature. The evolution of the interfacial layers' properties (with increasing surfactant concentration) is discussed in connection with the properties and content of gelatin-surfactant complexes appearing in the aqueous phase. Such an approach allows us to explain the main peculiarities of the layers' behavior including their stabilizing activity in relation to bilateral foam and emulsion films. PMID:24970019

  8. Organic photovoltaic device with interfacial layer and method of fabricating same

    SciTech Connect

    Marks, Tobin J.; Hains, Alexander W.

    2013-03-19

    An organic photovoltaic device and method of forming same. In one embodiment, the organic photovoltaic device has an anode, a cathode, an active layer disposed between the anode and the cathode; and an interfacial layer disposed between the anode and the active layer, the interfacial layer comprising 5,5'-bis[(p-trichlorosilylpropylphenyl)phenylamino]-2,2'-bithiophene (PABTSi.sub.2).

  9. Increased Quantum Dot Loading by pH Control Reduces Interfacial Recombination in Quantum-Dot-Sensitized Solar Cells.

    PubMed

    Roelofs, Katherine E; Herron, Steven M; Bent, Stacey F

    2015-08-25

    The power conversion efficiency of quantum-dot-sensitized solar cells (QDSSCs) hinges on interfacial charge transfer. Increasing quantum dot (QD) loading on the TiO2 anode has been proposed as a means to block recombination of electrons in the TiO2 to the hole transport material; however, it is not known whether a corresponding increase in QD-mediated recombination processes might lead to an overall higher rate of recombination. In this work, a 3-fold increase in PbS QD loading was achieved by the addition of an aqueous base to negatively charge the TiO2 surface during Pb cation deposition. Increased QD loading improved QDSSC device efficiencies through both increased light absorption and an overall reduction in recombination. Unexpectedly, we also found increased QD size had the detrimental effect of increasing recombination. Kinetic modeling of the effect of QD size on interfacial charge transfer processes provided qualitative agreement with the observed variation in recombination lifetimes. These results demonstrate a robust method of improving QD loading, identify the specific mechanisms by which increased QD deposition impacts device performance, and provide a framework for future efforts optimizing the device architecture of QDSSCs. PMID:26244426

  10. The effect of chain rigidity on the interfacial layer thickness and dynamics of polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Cheng, Shiwang; Carrillo, Jan-Michael Y.; Carroll, Bobby; Sumpter, Bobby G.; Sokolov, Alexei P.

    There are growing experimental evidences showing the existence of an interfacial layer that has a finite thickness with slowing down dynamics in polymer nanocomposites (PNCs). Moreover, it is believed that the interfacial layer plays a significant role on various macroscopic properties of PNCs. A thicker interfacial layer is found to have more pronounced effect on the macroscopic properties such as the mechanical enhancement. However, it is not clear what molecular parameter controls the interfacial layer thickness. Inspired by our recent computer simulations that showed the chain rigidity correlated well with the interfacial layer thickness, we performed systematic experimental studies on different polymer nanocomposites by varying the chain stiffness. Combining small-angle X-ray scattering, broadband dielectric spectroscopy and temperature modulated differential scanning calorimetry, we find a good correlation between the polymer Kuhn length and the thickness of the interfacial layer, confirming the earlier computer simulations results. Our findings provide a direct guidance for the design of new PNCs with desired properties.

  11. On the influence of interfacial properties to the bending rigidity of layered structures

    NASA Astrophysics Data System (ADS)

    Peng, Shenyou; Wei, Yujie

    2016-07-01

    Layered structures are ubiquitous, from one-atom thick layers in two-dimensional materials, to nanoscale lipid bi-layers, and to micro and millimeter thick layers in composites. The mechanical behavior of layered structures heavily depends on the interfacial properties and is of great interest in engineering practice. In this work, we give an analytical solution of the bending rigidity of bilayered structures as a function of the interfacial shear strength. Our results show that while the critical bending stiffness when the interface starts to slide plastically is proportional to the interfacial shear strength, there is a strong nonlinearity between the rigidity and the applied bending after interfacial plastic shearing. We further give semi-analytical solutions to the bending of bilayers when both interfacial shearing and pre-existing crack are present in the interface of rectangular and circular bilayers. The analytical solutions are validated by using finite element simulations. Our analysis suggests that interfacial shearing resistance, interfacial stiffness and preexisting cracks dramatically influence the bending rigidity of bilayers. The results can be utilized to understand the significant stiffness difference in typical biostructures and novel materials, and may also be used for non-destructive detection of interfacial crack in composites when stiffness can be probed through vibration techniques.

  12. Two-Dimensional Layered Oxide Structures Tailored by Self-Assembled Layer Stacking via Interfacial Strain.

    PubMed

    Zhang, Wenrui; Li, Mingtao; Chen, Aiping; Li, Leigang; Zhu, Yuanyuan; Xia, Zhenhai; Lu, Ping; Boullay, Philippe; Wu, Lijun; Zhu, Yimei; MacManus-Driscoll, Judith L; Jia, Quanxi; Zhou, Honghui; Narayan, Jagdish; Zhang, Xinghang; Wang, Haiyan

    2016-07-01

    Study of layered complex oxides emerge as one of leading topics in fundamental materials science because of the strong interplay among intrinsic charge, spin, orbital, and lattice. As a fundamental basis of heteroepitaxial thin film growth, interfacial strain can be used to design materials that exhibit new phenomena beyond their conventional forms. Here, we report a strain-driven self-assembly of bismuth-based supercell (SC) with a two-dimensional (2D) layered structure. With combined experimental analysis and first-principles calculations, we investigated the full SC structure and elucidated the fundamental growth mechanism achieved by the strain-enabled self-assembled atomic layer stacking. The unique SC structure exhibits room-temperature ferroelectricity, enhanced magnetic responses, and a distinct optical bandgap from the conventional double perovskite structure. This study reveals the important role of interfacial strain modulation and atomic rearrangement in self-assembling a layered singe-phase multiferroic thin film, which opens up a promising avenue in the search for and design of novel 2D layered complex oxides with enormous promise. PMID:27295399

  13. High reduction of interfacial charge recombination in colloidal quantum dot solar cells by metal oxide surface passivation

    NASA Astrophysics Data System (ADS)

    Chang, Jin; Kuga, Yuki; Mora-Seró, Iván; Toyoda, Taro; Ogomi, Yuhei; Hayase, Shuzi; Bisquert, Juan; Shen, Qing

    2015-03-01

    Bulk heterojunction (BHJ) solar cells based on colloidal QDs and metal oxide nanowires (NWs) possess unique and outstanding advantages in enhancing light harvesting and charge collection in comparison to planar architectures. However, the high surface area of the NW structure often brings about a large amount of recombination (especially interfacial recombination) and limits the open-circuit voltage in BHJ solar cells. This problem is solved here by passivating the surface of the metal oxide component in PbS colloidal quantum dot solar cells (CQDSCs). By coating thin TiO2 layers onto ZnO-NW surfaces, the open-circuit voltage and power conversion efficiency have been improved by over 40% in PbS CQDSCs. Characterization by transient photovoltage decay and impedance spectroscopy indicated that the interfacial recombination was significantly reduced by the surface passivation strategy. An efficiency as high as 6.13% was achieved through the passivation approach and optimization for the length of the ZnO-NW arrays (device active area: 16 mm2). All solar cells were tested in air, and exhibited excellent air storage stability (without any performance decline over more than 130 days). This work highlights the significance of metal oxide passivation in achieving high performance BHJ solar cells. The charge recombination mechanism uncovered in this work could shed light on the further improvement of PbS CQDSCs and/or other types of solar cells.Bulk heterojunction (BHJ) solar cells based on colloidal QDs and metal oxide nanowires (NWs) possess unique and outstanding advantages in enhancing light harvesting and charge collection in comparison to planar architectures. However, the high surface area of the NW structure often brings about a large amount of recombination (especially interfacial recombination) and limits the open-circuit voltage in BHJ solar cells. This problem is solved here by passivating the surface of the metal oxide component in PbS colloidal quantum dot solar

  14. Interfacial layer effects on surface capacitances and electro-osmosis in electrolytes.

    PubMed

    Bonthuis, Douwe Jan; Uematsu, Yuki; Netz, Roland R

    2016-02-13

    Many properties of the interfacial layer of water at surfaces differ significantly from those of bulk water. The consequences are most significant for the double-layer capacitance and the electrokinetic properties. We model the interfacial hydration layer by a modified dielectric constant and a modified local viscosity over a single interfacial width. Analytic expressions in the low-charge Debye-Hückel approximation are derived and shown to describe experimental surface capacitance and electro-osmotic data in a unified framework. PMID:26712645

  15. Effect of interfacial oxide layers on the current-voltage characteristics of Al-Si contacts

    NASA Technical Reports Server (NTRS)

    Porter, W. A.; Parker, D. L.

    1976-01-01

    Aluminum-silicon contacts with very thin interfacial oxide layers and various surface impurity concentrations are studied for both n and p-type silicon. To determine the surface impurity concentrations on p(+)-p and n(+)-n structures, a modified C-V technique was utilized. Effects of interfacial oxide layers and surface impurity concentrations on current-voltage characteristics are discussed based on the energy band diagrams from the conductance-voltage plots. The interfacial oxide and aluminum layer causes image contrasts on X-ray topographs.

  16. Effect of interfacial layer on water flow in nanochannels: Lattice Boltzmann simulations

    NASA Astrophysics Data System (ADS)

    Jin, Yakang; Liu, Xuefeng; Liu, Zilong; Lu, Shuangfang; Xue, Qingzhong

    2016-04-01

    A novel interfacial model was proposed to understand water flow mechanism in nanochannels. Based on our pore-throat nanochannel model, the effect of interfacial layer on water flow in nanochannels was quantitatively studied using Lattice Boltzmann method (LBM). It is found that both the permeability of nanochannel and water velocity in the nanochannel dramatically decrease with increasing the thickness of interfacial layer. The permeability of nanochannel with pore radius of 10 nm decreases by about three orders of magnitude when the thickness of interfacial layer is changed from 0 nm to 3 nm gradually. Furthermore, it has been demonstrated that the cross-section shape has a great effect on the water flow inside nanochannel and the effect of interfacial layer on the permeability of nanochannel has a close relationship with cross-section shape when the pore size is smaller than 12 nm. Besides, both pore-throat ratio and throat length can greatly affect water flow in nanochannels, and the influence of interfacial layer on water flow in nanochannels becomes more evident with increasing pore-throat ratio and throat length. Our theoretical results provide a simple and effective method to study the flow phenomena in nano-porous media, particularly to quantitatively study the interfacial layer effect in nano-porous media.

  17. Ultrafast interfacial charge transfer dynamics in dye-sensitized and quantum dot solar cell

    NASA Astrophysics Data System (ADS)

    Ghosh, Hirendra N.

    2013-02-01

    Dye sensitized solar cell (DSSC) appeared to be one of the good discovery for the solution of energy problem. We have been involved in studying ultrafast interfacial electron transfer dynamics in DSSC using femtosecond laser spectroscopy. However it has been realized that it is very difficult to design and develop higher efficient one, due to thermodynamic limitation. Again in DSSC most of the absorbed photon energy is lost as heat within the cell, which apart from decreasing the efficiency also destabilizes the device. It has been realized that quantum dot solar cell (QDSC) are the best bet where the sensitizer dye molecules can be replaced by suitable quantum dot (QD) materials in solar cell. The quantum-confinement effect in semiconductors modifies their electronic structure, which is a very important aspect of these materials. For photovoltaic applications, a long-lived charge separation remains one of the most essential criteria. One of the problems in using QDs for photovoltaic applications is their fast charge recombination caused by nonradiative Auger processes, which occur predominantly at lower particle sizes due to an increase in the Coulomb interaction between electrons and holes. Various approaches, such as the use of metal-semiconductor composites, semiconductor-polymer composite, and semiconductor core-shell heterostructures, have been attempted to minimize the fast recombination between electrons and holes. To make higher efficient solar devices it has been realised that it is very important to understand charge carrier and electron transfer dynamics in QD and QD sensitized semiconductor nanostructured materials. In the present talk, we are going to discuss on recent works on ultrafast electron transfer dynamics in dye-sensitized TiO2 nanoparticles/film [1-12] and charge (electron/hole) transfer dynamics in quantum dot core-shell nano-structured materials [13-17].

  18. TFB:TPDSi2 interfacial layer usable in organic photovoltaic cells

    DOEpatents

    Marks, Iobin J.; Hains, Alexander W.

    2011-02-15

    The present invention, in one aspect, relates to a solar cell. In one embodiment, the solar cell includes an anode; an active organic layer comprising an electron-donating organic material and an electron-accepting organic material; and an interfacial layer formed between the anode and active organic layer, where the interfacial layer comprises a hole-transporting polymer characterized with a hole-mobility higher than that of the electron-donating organic material in the active organic layer, and a small molecule that has a high hole-mobility and is capable of crosslinking on contact with air.

  19. Molecular dynamics simulations of the microstructure of the aluminum/alumina interfacial layer

    NASA Astrophysics Data System (ADS)

    Mei, Hai; Liu, Qiwen; Liu, Lisheng; Lai, Xin; She, Wuchang; Zhai, Pengcheng

    2015-01-01

    The atomic structure and charge distribution pattern of the Al/α-Al2O3 interface were studied utilizing molecular dynamics simulations. In order to accurately describe the interactions between the atoms around the interface, the charge transfer ionic and embedded atom method potential was used. Energetically preferable Al/α-Al2O3 interface systems were first determined to study the layer structures of the interface systems. Two energetically preferable Al/α-Al2O3 interface systems with a [ 1 bar 1 0 ](1 1 1) Al ∥ [ 1 0 1 bar 0 ](0 0 0 1) Al2O3 orientation relationship were obtained, corresponding to the atop-O Al-terminated and atop-O O-terminated relaxed models, respectively. Further studies revealed the presence of an interfacial layer, which is consistent with experimental results. The models predict a thickness of the interfacial layer between 12.14 Å and 16.82 Å. It is composed of aluminum suboxide (with an Al to O atomic ratio between 1:1.07 and 1:1.17). In addition, both the combination between the interfacial layer and the metallic Al layer and the interfacial layer and the ceramic α-Al2O3 were perfect. In order to further study the atomic structure of the Al/α-Al2O3 interfacial layer, it was isolated from the system and modeled separately. An analysis of the radial distribution function revealed that the interfacial layer inherits its structure from the α-Al2O3 moiety. The study of the charge distributions in the interface systems indicates that the charge of the Al atoms in the interfacial layer is mainly in the range from +2.1 e to +2.6 e while the charge of the O atoms is at the saturated state of -2e.

  20. Efficient zinc phthalocyanine/C60 heterojunction photovoltaic devices employing tetracene anode interfacial layers.

    PubMed

    Fleetham, Tyler B; Mudrick, John P; Cao, Weiran; Klimes, Kody; Xue, Jiangeng; Li, Jian

    2014-05-28

    We report the development of efficient small molecular organic photovoltaic devices incorporating tetracene anode interfacial layers. Planar heterojunction devices employing the tetracene anode interfacial layer achieved an EQE enhancement of 150% in the spectral region corresponding to ZnPc absorption. We demonstrate that this enhancement is due to the combined effect of the tetracene layer providing exciton-blocking at the anode/donor interface and potentially an increase in the exciton diffusion length in the ZnPc layer due to increased crystallinity and more preferred molecular stacking orientation. A power conversion efficiency of 4.7% was achieved for a planar heterojunction of a modified zinc phthalocyanine based material and C60 when employing the tetracene anode interfacial layer. By utilizing a planar-mixed heterojunction structure a peak EQE of nearly 70% and a power conversion efficiency of 5.8% was achieved. PMID:24708488

  1. Optimization of Residual Stresses in MMC's Using Compensating/Compliant Interfacial Layers. Part 2: OPTCOMP User's Guide

    NASA Technical Reports Server (NTRS)

    Pindera, Marek-Jerzy; Salzar, Robert S.; Williams, Todd O.

    1994-01-01

    A user's guide for the computer program OPTCOMP is presented in this report. This program provides a capability to optimize the fabrication or service-induced residual stresses in uni-directional metal matrix composites subjected to combined thermo-mechanical axisymmetric loading using compensating or compliant layers at the fiber/matrix interface. The user specifies the architecture and the initial material parameters of the interfacial region, which can be either elastic or elastoplastic, and defines the design variables, together with the objective function, the associated constraints and the loading history through a user-friendly data input interface. The optimization procedure is based on an efficient solution methodology for the elastoplastic response of an arbitrarily layered multiple concentric cylinder model that is coupled to the commercial optimization package DOT. The solution methodology for the arbitrarily layered cylinder is based on the local-global stiffness matrix formulation and Mendelson's iterative technique of successive elastic solutions developed for elastoplastic boundary-value problems. The optimization algorithm employed in DOT is based on the method of feasible directions.

  2. Probing nonlinear rheology layer-by-layer in interfacial hydration water

    PubMed Central

    Kim, Bongsu; Kwon, Soyoung; Lee, Manhee; Kim, QHwan; An, Sangmin; Jhe, Wonho

    2015-01-01

    Viscoelastic fluids exhibit rheological nonlinearity at a high shear rate. Although typical nonlinear effects, shear thinning and shear thickening, have been usually understood by variation of intrinsic quantities such as viscosity, one still requires a better understanding of the microscopic origins, currently under debate, especially on the shear-thickening mechanism. We present accurate measurements of shear stress in the bound hydration water layer using noncontact dynamic force microscopy. We find shear thickening occurs above ∼ 106 s−1 shear rate beyond 0.3-nm layer thickness, which is attributed to the nonviscous, elasticity-associated fluidic instability via fluctuation correlation. Such a nonlinear fluidic transition is observed due to the long relaxation time (∼ 10−6 s) of water available in the nanoconfined hydration layer, which indicates the onset of elastic turbulence at nanoscale, elucidating the interplay between relaxation and shear motion, which also indicates the onset of elastic turbulence at nanoscale above a universal shear velocity of ∼ 1 mm/s. This extensive layer-by-layer control paves the way for fundamental studies of nonlinear nanorheology and nanoscale hydrodynamics, as well as provides novel insights on viscoelastic dynamics of interfacial water. PMID:26644571

  3. Understanding the interfacial layer dynamics of polymer nanocomposites from broadband dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Carroll, Robert; Cheng, Shiwang; Sokolov, Alexei

    Polymer nanocomposites show many advanced mechanical, thermal, optical, and transport properties mainly due to the vast interfacial area between the polymer matrix and nanoparticles. Recent studies show that there is an interfacial polymer layer with structure and dynamics that are different from the bulk polymer, and that contributes to the advanced macroscopic properties. It has been shown that broadband dielectric spectroscopy provides good method to study the interfacial dynamics in nanocomposites. However, current dielectric spectroscopy studies ignore the heterogeneous nature of polymer nanocomposites. Models based on a simple superposition of bulk polymer and interfacial layer spectra, or those that assume the interfacial layer is dynamically ``dead'' are inaccurate. In this talk, the prevailing methods in the literature will be compared with an accurate method accounting for the heterogeneity of the nanocomposites. Different nanocomposites with well-dispersed nanoparticles will be used as examples. The analysis clearly shows that the width and the amplitude of the relaxation peaks are affected by the data analysis. Thus accurate quantitative conclusions on properties and thickness of the interfacial layer can be achieved only using heterogeneous models.

  4. Polyfluorene Electrolytes Interfacial Layer for Efficient Polymer Solar Cells: Controllably Interfacial Dipoles by Regulation of Polar Groups.

    PubMed

    Liu, Huimin; Hu, Lin; Wu, Feiyan; Chen, Lie; Chen, Yiwang

    2016-04-20

    The polar groups in the conjugated polyelectrolytes (CPEs) can create the favorable dipoles at the electrode/active layer interface, which is critical for the CPEs to minimize the interfacial energy barrier in polymer solar cells (PSCs). Herein, a series of CPEs based on poly [(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-co-2,7-(9,9-dioctylfluorene)] derivates (PFNs) (PFN30, PFN50, PFN70, and PFN100) with different mole ratio of polar groups (-N(C2H5)2) were designed and synthesized to investigate the effect of the numbers of polar groups on the interfacial dipoles. Controllably interfacial dipoles could be readily achieved by only tuning the numbers of -N(C2H5)2 in PFNs, as revealed by the work function of the PFNs modified ITO gradually reduced as the loadings of the -N(C2H5)2 increased. In addition, increasing the numbers of -N(C2H5)2 in PFNs were also favorable for developing the smooth and homogeneous morphology of the active layer. As a result, the content of the polar amine in the PFNs exerted great influence on the performance of polymer solar cells. Increasing the numbers of the pendent -N(C2H5)2 could effectively improve the power conversion efficiency (PCE) of the devices. Among these PFNs, PFN100 with the highest content of -N(C2H5)2 polar groups delivered the device with the best PCE of 3.27%. It indicates tailoring the content of the polar groups in the CPEs interlayer is a facial and promising approach for interfacial engineering to developing high performance PSCs. PMID:27028166

  5. Formation of Interfacial Carbide Layers in Multilayer Ti/DLC Thin Films

    NASA Astrophysics Data System (ADS)

    Scaramazza, Jasen; Buck, Zachary; Donato, Tyler; Curran, Brittany; Lunk, C. A.; Lofland, S. E.; Hettinger, J. D.

    2012-02-01

    Titanium (Ti)/Diamond-like-carbon (DLC) and Chromium (Cr)/Carbon (C) multilayer films were prepared on c-axis oriented single crystal sapphire (Al2O3) substrates using magnetron sputtering. Interfacial properties of the films were analyzed using x-ray reflectivity and scanning electron microscopy. When DLC is sputtered on a layer of Ti, an interfacial layer of titanium carbide (TiC) forms which is reported for the first time. Energy provided by the substrate bias necessary to facilitate DLC sp3 bond formation is suspected of allowing TiC to synthesize in a thin layer before DLC forms. It was also found that DLC has difficulty forming on Cr. These results are relevant to biomedical applications where DLC is applied as a low friction/wear film that can be formed on the surface of implants composed mainly of titanium. Further investigation into the medical and tribological effects of TiC interfacial layers is suggested.

  6. The effect of interfacial layers on charge transport in organic solar cell

    NASA Astrophysics Data System (ADS)

    Mbuyise, Xolani G.; Tonui, Patrick; Mola, Genene Tessema

    2016-09-01

    The effect of interfacial buffer layers in organic photovoltaic cell (OPV) whose active layer is composed of poly(3 hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend was studied. The electrical properties of OPV devices produced with and without interfacial layers are compared and discussed in terms of measured parameters of the cells. The charge transport properties showed significant difference on the mobility and activation factor between the two types of device structures. The life time measurements in the unprotected conditions are also presented and discussed.

  7. An identification algorithm of model kinetic parameters of the interfacial layer growth in fiber composites

    NASA Astrophysics Data System (ADS)

    Zubov, V.; Lurie, S.; Solyaev, Y.

    2016-04-01

    This paper considers the identification algorithm of parameters included in a parabolic law that is often used to predict the time dependence of the thickness of the interfacial layers in the structure of composite materials based on a metal matrix. The incubation period of the process and the speed of reaction and pressure are taken into account. The proposed algorithm of identification is based on the introduction of a minimized objective function of a special kind. The problem of identification of unknown parameters in the parabolic law is formulated in a variational form. The authors of the paper have determined the desired parameters, under which the objective function has a minimum value. It is shown that on the basis of four known experimental values of the interfacial layer thickness, corresponding to different values of temperature, pressure and the time of the interfacial layer growth, it is possible to identified four model parameters. They are the activation energy, a pre-exponential parameter, the delay time of the start of the interfacial layer formation, and the parameter determining the pressure effect on the rate of interfacial layer growth. The stability of the proposed identification algorithm is also studied.

  8. Surface-interface exploration of Mg deposited on Si(100) and oxidation effect on interfacial layer

    SciTech Connect

    Sarpi, B.; Daineche, R.; Girardeaux, C.; Bertoglio, M.; Derivaux, F.; Vizzini, S.; Biberian, J. P.; Hemeryck, A.

    2015-01-12

    Using scanning tunneling microscopy and spectroscopy, Auger electron spectroscopy, and low energy electron diffraction, we have studied the growth of Mg deposited on Si(100)-(2 × 1). Coverage from 0.05 monolayer (ML) to 3 ML was investigated at room temperature. The growth mode of the magnesium is a two steps process. At very low coverage, there is formation of an amorphous ultrathin silicide layer with a band gap of 0.74 eV, followed by a layer-by-layer growth of Mg on top of this silicide layer. Topographic images reveal that each metallic Mg layer is formed by 2D islands coalescence process on top of the silicide interfacial layer. During oxidation of the Mg monolayer, the interfacial silicide layer acts as diffusion barrier for the oxygen atoms with a decomposition of the silicide film to a magnesium oxide as function of O{sub 2} exposure.

  9. Correlation of photoluminescent quantum efficiency and device characteristics for the soluble electrophosphorescent light emitter with interfacial layers

    NASA Astrophysics Data System (ADS)

    Kang, Nam Su; Ju, Byeong-Kwon; Kim, Ji Whan; Kim, Jang-Joo; Yu, Jae-Woong; Chin, Byung Doo

    2008-07-01

    We have investigated the effects of interfacial layers on the properties of soluble phosphorescent organic light emitting devices. Two kinds of polyfluorene-based interfacial layer materials have been studied; both were spin coated on top of PEDOT:PSS to form the insoluble layers by thermal annealing. The molecular-doped, phosphorescent light emitting layer comprising a polymeric host, small molecular host, and guest molecule was fabricated onto the thin interfacial layer. The photoluminescence quantum yield (PLQY) of these layers was measured with an integrating sphere. We have calculated the PLQY values of the single phosphorescent light emitting layer and various organic multilayers incorporating the interfacial layers, showing that a reduction in PLQY due to the interfacial quenching is more significant in the thicker interfacial layer structures. In spite of the decrease in PLQY induced by the triplet energy mismatch, polyfluorene-based interfacial layers improved the charge injection from PEDOT:PSS to the emitting layer, which results in the enhanced brightness and current. The triplet quenching by the interfacial layer could explain the reduction in luminous efficiency of the devices compared to the reference. This was also investigated by studying the charge carrier trapping, change in the spectral characteristics induced by the shift in the emission zone, and the analysis on the carrier balance of devices.

  10. Studies of Interfacial Layer and Its Effect on Magnetic Properties of Glass-Coated Microwires

    NASA Astrophysics Data System (ADS)

    Zhukov, Arcady; Shuvaeva, Evgenia; Kaloshkin, Sergei; Churyukanova, Margarita; Kostitsyna, Elena; Zhdanova, Margarita; Talaat, Ahmed; Ipatov, Mihail; Zhukova, Valentina

    2016-05-01

    We present studies of the interfacial layer between the metallic nucleus and glass coating in ferromagnetic Fe- and Co-rich microwires. Using a scanning electron microscope, we obtained the image of the interfacial layer and the elements distribution within the glass coating and metallic nucleus. This allowed us to estimate the thickness of the interfacial layer ( t il). For both Fe- and Co-rich microwires, t il ≈ 0.5 μm. We measured the frequency dependence of the giant magnetoimpedance ratio in Fe and Co-rich microwires, estimated the minimum penetration depth, and discussed the optimum frequency for different microwires considering the difference of the magnetic structure and the magnetic anisotropy inside the microwire and near the surface.

  11. Effect of interfacial interactions on the thermal conductivity and interfacial thermal conductance in tungsten–graphene layered structure

    SciTech Connect

    Jagannadham, K.

    2014-09-01

    Graphene film was deposited by microwave plasma assisted deposition on polished oxygen free high conductivity copper foils. Tungsten–graphene layered film was formed by deposition of tungsten film by magnetron sputtering on the graphene covered copper foils. Tungsten film was also deposited directly on copper foil without graphene as the intermediate film. The tungsten–graphene–copper samples were heated at different temperatures up to 900 °C in argon atmosphere to form an interfacial tungsten carbide film. Tungsten film deposited on thicker graphene platelets dispersed on silicon wafer was also heated at 900 °C to identify the formation of tungsten carbide film by reaction of tungsten with graphene platelets. The films were characterized by scanning electron microscopy, Raman spectroscopy, and x-ray diffraction. It was found that tungsten carbide film formed at the interface upon heating only above 650 °C. Transient thermoreflectance signal from the tungsten film surface on the samples was collected and modeled using one-dimensional heat equation. The experimental and modeled results showed that the presence of graphene at the interface reduced the cross-plane effective thermal conductivity and the interfacial thermal conductance of the layer structure. Heating at 650 and 900 °C in argon further reduced the cross-plane thermal conductivity and interface thermal conductance as a result of formation nanocrystalline tungsten carbide at the interface leading to separation and formation of voids. The present results emphasize that interfacial interactions between graphene and carbide forming bcc and hcp elements will reduce the cross-plane effective thermal conductivity in composites.

  12. Visualization and characterization of interfacial polymerization layer formation.

    PubMed

    Zhang, Yali; Benes, Nieck E; Lammertink, Rob G H

    2015-01-21

    We present a microfluidic platform to visualize the formation of free-standing films by interfacial polymerization. A microfluidic device is fabricated, with an array of micropillars to stabilize an aqueous-organic interface that allows a direct observation of the films formation process via optical microscopy. Three different amines are selected to react with trimesoyl chloride: piperazine, JEFFAMINE(®)D-230, and an ammonium functionalized polyhedral oligomeric silsesquioxane. Tracking the formation of the free-standing films in time reveals strong effects of the characteristics of the amine precursor on the morphological evolution of the films. Piperazine exhibits a rapid reaction with trimesoyl chloride, forming a film up to 20 μm thick within half a minute. JEFFAMINE(®)D-230 displays much slower film formation kinetics. The location of the polymerization reaction was initially in the aqueous phase and then shifted into the organic phase. Our in situ real-time observations provide information on the kinetics and the changing location of the polymerization. This provides insights with important implications for fine-tuning of interfacial polymerizations for various applications. PMID:25421971

  13. Electrode dependent interfacial layer variation in metal-oxide-semiconductor capacitor

    NASA Astrophysics Data System (ADS)

    Park, I.-S.; Jung, Y. C.; Lee, M.; Seong, S.; Ahn, J.

    2014-03-01

    The interfacial layer between oxide and semiconductor in metal-oxide-semiconductor (MOS) capacitors depends on the metal electrode material. The metal/HfO2/Si and metal/HfO2/Ge capacitor were made using an atomic layer deposited HfO2 dielectric films and Mo, Ru, and Pt electrodes above Si substrate and Ti, Ru, and Pt electrodes above Ge substrate. The measured saturation capacitance was varied with electrode and evaluated to capacitance equivalent thickness (CET). In Si-based MOS capacitor, the CET value of the capacitor with Pt electrode is larger than those with Mo and Ru electrode. In addition, the CET is 27.4 A, 38.2 A, and 30.8 A for Ti, Ru, and Pt electrode, respectively, for Ge-based MOS capacitors. The CET variation with electrode is attributed the variation of dielectric constant of HfO2 dielectric and the difference of interfacial layer. The CET variation is well in agreement with the interfacial layer thickness taken by a transmission electron microscopy. The thickness variation of interfacial layer results from the oxygen gettering ability of the electrode even though they are apart.

  14. Solid-liquid interfaces of ionic liquid solutions—Interfacial layering and bulk correlations

    NASA Astrophysics Data System (ADS)

    Mezger, Markus; Roth, Roland; Schröder, Heiko; Reichert, Peter; Pontoni, Diego; Reichert, Harald

    2015-04-01

    The influence of the polar, aprotic solvent propylene carbonate on the interfacial structure of the ionic liquid (IL) 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate on sapphire was investigated by high-energy x-ray reflectivity. Experiments at solvent concentrations between 17 mol. % and 83 mol. % bridge the gap between diluted electrolytes described by the classical Gouy-Chapman theory and pure ionic liquids. Analysis of our experimental data revealed interfacial profiles comprised of alternating anion and cation enriched regions decaying gradually into the bulk liquid. With increasing solvent concentration, we observed a decrease in correlation length of the interfacial layering structure. At high ion concentrations, solvent molecules were found to accumulate laterally within the layers. By separating like-charged ions, they reduce their Coulomb repulsion. The results are compared with the bulk structure of IL/solvent blends probed by x-ray scattering and predictions from fundamental fluid theory.

  15. Interfacial and gravitational convection in immiscible liquid layers

    NASA Technical Reports Server (NTRS)

    Prakash, A.; Koster, J. N.

    1992-01-01

    Liquid encapsulation of electronic melts is currently being investigated by several materials science research groups. Pertinent fluid dynamics of immiscible liquid layers is the objective of this investigation. First results on convective flow in double liquid layers, in preparation for a spaceflight experiment aboard the International Microgravity Laboratory, IML-2, are discussed.

  16. Mechanisms governing the interfacial delamination of thermal barrier coating system with double ceramic layers

    NASA Astrophysics Data System (ADS)

    Xu, Rong; Fan, Xueling; Wang, T. J.

    2016-05-01

    A systematic study of factors affecting the interfacial delamination of thermal barrier coating system (TBCs) with double ceramic layers (DCL) is presented. Crack driving forces for delaminations at two weak interfaces are examined. The results show that a thicker outermost ceramic layer can induce dramatic increase in crack driving force and make the interface between two ceramic coatings become more prone to delamination. The behavior is shown to be more prominent in TBCs with stiffer outmost coating. The thickness ratio of two ceramic layers is an important parameter for controlling the failure mechanisms and determining the lifetime of DCL TBCs under inservice condition. By accounting for the influences of thickness ratio of two ceramic layers and interfacial fracture toughnesses of two involved interfaces, the fracture mechanism map of DCL TBCs has been constructed, in which different failure mechanisms are identified. The results quanlitatively agree with the aviliable experimental data.

  17. Optimization of residual stresses in MMC's through the variation of interfacial layer architectures and processing parameters

    NASA Technical Reports Server (NTRS)

    Pindera, Marek-Jerzy; Salzar, Robert S.

    1996-01-01

    The objective of this work was the development of efficient, user-friendly computer codes for optimizing fabrication-induced residual stresses in metal matrix composites through the use of homogeneous and heterogeneous interfacial layer architectures and processing parameter variation. To satisfy this objective, three major computer codes have been developed and delivered to the NASA-Lewis Research Center, namely MCCM, OPTCOMP, and OPTCOMP2. MCCM is a general research-oriented code for investigating the effects of microstructural details, such as layered morphology of SCS-6 SiC fibers and multiple homogeneous interfacial layers, on the inelastic response of unidirectional metal matrix composites under axisymmetric thermomechanical loading. OPTCOMP and OPTCOMP2 combine the major analysis module resident in MCCM with a commercially-available optimization algorithm and are driven by user-friendly interfaces which facilitate input data construction and program execution. OPTCOMP enables the user to identify those dimensions, geometric arrangements and thermoelastoplastic properties of homogeneous interfacial layers that minimize thermal residual stresses for the specified set of constraints. OPTCOMP2 provides additional flexibility in the residual stress optimization through variation of the processing parameters (time, temperature, external pressure and axial load) as well as the microstructure of the interfacial region which is treated as a heterogeneous two-phase composite. Overviews of the capabilities of these codes are provided together with a summary of results that addresses the effects of various microstructural details of the fiber, interfacial layers and matrix region on the optimization of fabrication-induced residual stresses in metal matrix composites.

  18. GaAs interfacial self-cleaning by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Hinkle, C. L.; Sonnet, A. M.; Vogel, E. M.; McDonnell, S.; Hughes, G. J.; Milojevic, M.; Lee, B.; Aguirre-Tostado, F. S.; Choi, K. J.; Kim, H. C.; Kim, J.; Wallace, R. M.

    2008-02-01

    The reduction and removal of surface oxides from GaAs substrates by atomic layer deposition (ALD) of Al2O3 and HfO2 are studied using in situ monochromatic x-ray photoelectron spectroscopy. Using the combination of in situ deposition and analysis techniques, the interfacial "self-cleaning" is shown to be oxidation state dependent as well as metal organic precursor dependent. Thermodynamics, charge balance, and oxygen coordination drive the removal of certain species of surface oxides while allowing others to remain. These factors suggest proper selection of surface treatments and ALD precursors can result in selective interfacial bonding arrangements.

  19. Nanoscopic characterization of the water vapor-salt interfacial layer reveals a unique biphasic adsorption process

    PubMed Central

    Yang, Liu; He, Jianfeng; Shen, Yi; Li, Xiaowei; Sun, Jielin; Czajkowsky, Daniel M.; Shao, Zhifeng

    2016-01-01

    Our quantitative understanding of water adsorption onto salt surfaces under ambient conditions is presently quite poor owing to the difficulties in directly characterizing this interfacial layer under these conditions. Here we determine the thickness of the interfacial layer on NaCl at different relative humidities (RH) based on a novel application of atomic force spectroscopy and capillary condensation theory. In particular, we take advantage of the microsecond-timescale of the capillary condensation process to directly resolve the magnitude of its contribution in the tip-sample interaction, from which the interfacial water thickness is determined. Further, to correlate this thickness with salt dissolution, we also measure surface conductance under similar conditions. We find that below 30% RH, there is essentially only the deposition of water molecules onto this surface, typical of conventional adsorption onto solid surfaces. However, above 30% RH, adsorption is simultaneous with the dissolution of ions, unlike conventional adsorption, leading to a rapid increase of surface conductance. Thus, water adsorption on NaCl is an unconventional biphasic process in which the interfacial layer not only exhibits quantitative differences in thickness but also qualitative differences in composition. PMID:27527905

  20. Nanoscopic characterization of the water vapor-salt interfacial layer reveals a unique biphasic adsorption process.

    PubMed

    Yang, Liu; He, Jianfeng; Shen, Yi; Li, Xiaowei; Sun, Jielin; Czajkowsky, Daniel M; Shao, Zhifeng

    2016-01-01

    Our quantitative understanding of water adsorption onto salt surfaces under ambient conditions is presently quite poor owing to the difficulties in directly characterizing this interfacial layer under these conditions. Here we determine the thickness of the interfacial layer on NaCl at different relative humidities (RH) based on a novel application of atomic force spectroscopy and capillary condensation theory. In particular, we take advantage of the microsecond-timescale of the capillary condensation process to directly resolve the magnitude of its contribution in the tip-sample interaction, from which the interfacial water thickness is determined. Further, to correlate this thickness with salt dissolution, we also measure surface conductance under similar conditions. We find that below 30% RH, there is essentially only the deposition of water molecules onto this surface, typical of conventional adsorption onto solid surfaces. However, above 30% RH, adsorption is simultaneous with the dissolution of ions, unlike conventional adsorption, leading to a rapid increase of surface conductance. Thus, water adsorption on NaCl is an unconventional biphasic process in which the interfacial layer not only exhibits quantitative differences in thickness but also qualitative differences in composition. PMID:27527905

  1. Optimum Interfacial Layers For Fiber/Metal Composites

    NASA Technical Reports Server (NTRS)

    Lerch, Bradley A.; Ghosn, Louis J.

    1993-01-01

    Report presents theoretical stress-analysis study of some of factors affecting choice of thin layer of material placed at interface between each fiber and matrix of ceramic-fiber/metal-matrix composite. Effects of thickness, modulus of elasticity, and coefficient of thermal expansion considered.

  2. Interfacial Atomic Structure of Twisted Few-Layer Graphene

    PubMed Central

    Ishikawa, Ryo; Lugg, Nathan R.; Inoue, Kazutoshi; Sawada, Hidetaka; Taniguchi, Takashi; Shibata, Naoya; Ikuhara, Yuichi

    2016-01-01

    A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene. PMID:26888259

  3. Interfacial Atomic Structure of Twisted Few-Layer Graphene.

    PubMed

    Ishikawa, Ryo; Lugg, Nathan R; Inoue, Kazutoshi; Sawada, Hidetaka; Taniguchi, Takashi; Shibata, Naoya; Ikuhara, Yuichi

    2016-01-01

    A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene. PMID:26888259

  4. Double-layer-gate architecture for few-hole GaAs quantum dots.

    PubMed

    Wang, D Q; Hamilton, A R; Farrer, I; Ritchie, D A; Klochan, O

    2016-08-19

    We report the fabrication of single and double hole quantum dots using a double-layer-gate design on an undoped accumulation mode [Formula: see text]/GaAs heterostructure. Electrical transport measurements of a single quantum dot show varying addition energies and clear excited states. In addition, the two-level-gate architecture can also be configured into a double quantum dot with tunable inter-dot coupling. PMID:27389108

  5. Double-layer-gate architecture for few-hole GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Wang, D. Q.; Hamilton, A. R.; Farrer, I.; Ritchie, D. A.; Klochan, O.

    2016-08-01

    We report the fabrication of single and double hole quantum dots using a double-layer-gate design on an undoped accumulation mode {{Al}}x{{Ga}}1-x{As}/GaAs heterostructure. Electrical transport measurements of a single quantum dot show varying addition energies and clear excited states. In addition, the two-level-gate architecture can also be configured into a double quantum dot with tunable inter-dot coupling.

  6. Nanoengineering and interfacial engineering of photovoltaics by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Bakke, Jonathan R.; Pickrahn, Katie L.; Brennan, Thomas P.; Bent, Stacey F.

    2011-09-01

    Investment into photovoltaic (PV) research has accelerated over the past decade as concerns over energy security and carbon emissions have increased. The types of PV technology in which the research community is actively engaged are expanding as well. This review focuses on the burgeoning field of atomic layer deposition (ALD) for photovoltaics. ALD is a self-limiting thin film deposition technique that has demonstrated usefulness in virtually every sector of PV technology including silicon, thin film, tandem, organic, dye-sensitized, and next generation solar cells. Further, the specific applications are not limited. ALD films have been deposited on planar and nanostructured substrates and on inorganic and organic devices, and vary in thickness from a couple of angstroms to over 100 nm. The uses encompass absorber materials, buffer layers, passivating films, anti-recombination shells, and electrode modifiers. Within the last few years, the interest in ALD as a PV manufacturing technique has increased and the functions of ALD have expanded. ALD applications have yielded fundamental understanding of how devices operate and have led to increased efficiencies or to unique architectures for some technologies. This review also highlights new developments in high throughput ALD, which is necessary for commercialization. As the demands placed on materials for the next generation of PV become increasingly stringent, ALD will evolve into an even more important method for research and fabrication of solar cell devices.

  7. Thermodynamics, interfacial pressure isotherms and dilational rheology of mixed protein-surfactant adsorption layers.

    PubMed

    Fainerman, V B; Aksenenko, E V; Krägel, J; Miller, R

    2016-07-01

    Proteins and their mixtures with surfactants are widely used in many applications. The knowledge of their solution bulk behavior and its impact on the properties of interfacial layers made great progress in the recent years. Different mechanisms apply to the formation process of protein/surfactant complexes for ionic and non-ionic surfactants, which are governed mainly by electrostatic and hydrophobic interactions. The surface activity of these complexes is often remarkably different from that of the individual protein and has to be considered in respective theoretical models. At very low protein concentration, small amounts of added surfactants can change the surface activity of proteins remarkably, even though no strongly interfacial active complexes are observed. Also small added amounts of non-ionic surfactants change the surface activity of proteins in the range of small bulk concentrations or surface coverages. The modeling of the equilibrium adsorption behavior of proteins and their mixtures with surfactants has reached a rather high level. These models are suitable also to describe the high frequency limits of the dilational viscoelasticity of the interfacial layers. Depending on the nature of the protein/surfactant interactions and the changes in the interfacial layer composition rather complex dilational viscoelasticities can be observed and described by the available models. The differences in the interfacial behavior, often observed in literature for studies using different experimental methods, are at least partially explained by a depletion of proteins, surfactants and their complexes in the range of low concentrations. A correction of these depletion effects typically provides good agreement between the data obtained with different methods, such as drop and bubble profile tensiometry. PMID:26198014

  8. Efficiency enhancement in small molecular organic photovoltaic devices employing dual anode interfacial layers

    NASA Astrophysics Data System (ADS)

    Fleetham, Tyler; O'Brien, Barry; Mudrick, John P.; Xue, Jiangeng; Li, Jian

    2013-10-01

    We demonstrated enhanced efficiency in small molecule organic photovoltaic devices using dual organic interfacial layers of PEDOT:PSS followed by tetracene between the ITO anode and the organic donor material. The use of a small molecular templating layer, such as tetracene, proved to increase the molecular stacking of the subsequent phthalocyanine (Pc) based donor materials. Upon application in planar heterojunction devices of ZnPc and C60, an enhancement of over 80 percent in the donor contribution to the external quantum efficiency was observed attributed to the combination of exciton blocking by the higher band gap tetracene layer and enhanced exciton diffusion and charge transport resulting from the increased crystallinity.

  9. Interfacial properties of germanium nitride dielectric layers in germanium

    NASA Astrophysics Data System (ADS)

    Meiners, L. G.

    The first year's effort on this project has been primarily devoted to the design and construction of a low-pressure chemical vapor deposition system for growth of the germanium nitride layers. The gas manifold layout is shown schematically, as is the reactor assembly, and the vacuum pumping assembly. The generator-cavity system is capable of delivering 0-600 W of microwave power at 2.45 GHz. The power generating section has been constructed from components contained in a portable home microwave oven and the cavity was assembled from easily machinable pieces. The cw magnetron source was mounted directly on a cylindrical microwave cavity. The plasma was contained in an on-axis 20-mm o.d. quartz tube. Design tradeoffs and operating information are discussed.

  10. Layered insulator hexagonal boron nitride for surface passivation in quantum dot solar cell

    SciTech Connect

    Shanmugam, Mariyappan; Jain, Nikhil; Jacobs-Gedrim, Robin; Yu, Bin; Xu, Yang

    2013-12-09

    Single crystalline, two dimensional (2D) layered insulator hexagonal boron nitride (h-BN), is demonstrated as an emerging material candidate for surface passivation on mesoporous TiO{sub 2}. Cadmium selenide (CdSe) quantum dot based bulk heterojunction (BHJ) solar cell employed h-BN passivated TiO{sub 2} as an electron acceptor exhibits photoconversion efficiency ∼46% more than BHJ employed unpassivated TiO{sub 2}. Dominant interfacial recombination pathways such as electron capture by TiO{sub 2} surface states and recombination with hole at valence band of CdSe are efficiently controlled by h-BN enabled surface passivation, leading to improved photovoltaic performance. Highly crystalline, confirmed by transmission electron microscopy, dangling bond-free 2D layered h-BN with self-terminated atomic planes, achieved by chemical exfoliation, enables efficient passivation on TiO{sub 2}, allowing electronic transport at TiO{sub 2}/h-BN/CdSe interface with much lower recombination rate compared to an unpassivated TiO{sub 2}/CdSe interface.

  11. Interfacial microrheology study of layer formation by staphylococcal nuclease protein and its disordered variant

    NASA Astrophysics Data System (ADS)

    Tzolova, Bilyana; Allan, Daniel; Firester, Daniel; Garcia-Moreno, Bertrand; Reich, Daniel; Leheny, Robert

    We study the formation of layers of staphylococcal nuclease protein adsorbing at the air-water interface. In a series of experiments, we follow the evolution of the rheological response of the layer using an active microrheology technique that involves tracking the rotational motion of magnetic nanowires at the interface in response to time-dependent external magnetic fields. At early stages of layer formation, the wire mobility can be interpreted using a model for viscous drag with an interfacial viscosity that increases rapidly with layer age; however, at later ages deviations from a simple viscous response indicating non-Newtonian behavior are observed. We compare the evolution in microrheology of layers forming from wild-type protein that assumes a folded conformation in solution with a variant that is disordered due to substitution of a single amino acid, thereby gaining a perspective on the impact of initial protein state on the layer formation and rheology.

  12. Electrostatic modulation and enzymatic cross-linking of interfacial layers impacts gastrointestinal fate of multilayer emulsions.

    PubMed

    Zeeb, Benjamin; Weiss, Jochen; McClements, David Julian

    2015-08-01

    In this study, membrane properties were modulated using layer-by-layer electrostatic depositioning in combination with salt and/or enzyme treatment to control the gastrointestinal fate of emulsified oils. Lipid droplets coated by a single-layer of biopolymers (gelatin) were prepared by high pressure homogenization. Lipid droplets coated by a double-layer of biopolymers (gelatin-pectin) were prepared by electrostatically depositing sugar beet pectin on the gelatin-coated droplets. Laccase was added to the double-layer emulsions to covalently crosslink the adsorbed pectin molecules, whereas sodium chloride was added to modulate interfacial properties through electrostatic screening effects. Non-cross-linked and cross-linked double-layer emulsions (with and without salt) were then passed through a simulated gastrointestinal tract (GIT) that included mouth, gastric and intestinal phases. Free fatty acid release profiles suggested that the stability of the emulsified droplets within the GIT played a more important role in determining the rate and extent of lipid digestion than the initial interfacial layer properties. PMID:25766826

  13. Effects of fiber and interfacial layer architectures on the thermoplastic response of metal matrix composites

    NASA Technical Reports Server (NTRS)

    Pindera, Marek-Jerzy; Freed, Alan D.; Arnold, Steven M.

    1992-01-01

    Examined here is the effect of fiber and interfacial layer morphologies on thermal fields in metal matrix composites (MMCs). A micromechanics model based on an arbitrarily layered concentric cylinder configuration is used to calculate thermal stress fields in MMCs subjected to spatially uniform temperature changes. The fiber is modelled as a layered material with isotropic or orthotropic elastic layers, whereas the surrounding matrix, including interfacial layers, is treated as a strain-hardening, elastoplastic, von Mises solid with temperature-dependent parameters. The solution to the boundary-value problem of an arbitrarily layered concentric cylinder under the prescribed thermal loading is obtained using the local/global stiffness matrix formulation originally developed for stress analysis of multilayered elastic media. Examples are provided that illustrate how the morphology of the SCS6 silicon carbide fiber and the use of multiple compliant layers at the fiber/matrix interface affect the evolution of residual stresses in SiC/Ti composites during fabrication cool-down.

  14. Fatigue crack growth simulations of interfacial cracks in bi-layered FGMs using XFEM

    NASA Astrophysics Data System (ADS)

    Bhattacharya, S.; Singh, I. V.; Mishra, B. K.; Bui, T. Q.

    2013-10-01

    An investigation of fatigue crack growth of interfacial cracks in bi-layered materials using the extended finite element method is presented. The bi-material consists of two layers of dissimilar materials. The bottom layer is made of aluminium alloy while the upper one is made of functionally graded material (FGM). The FGM layer consists of 100 % aluminium alloy on the left side and 100 % ceramic (alumina) on the right side. The gradation in material property of the FGM layer is assumed to be exponential from the alloy side to the ceramic side. The domain based interaction integral approach is extended to obtain the stress intensity factors for an interfacial crack under thermo-mechanical load. The edge and centre cracks are taken at the interface of bi-layered material. The fatigue life of the interface crack plate is obtained using the Paris law of fatigue crack growth under cyclic mode-I, mixed-mode and thermal loads. This study reveals that the crack propagates into the FGM layer under all types of loads.

  15. Role of interfacial transition layers in VO2/Al2O3 heterostructures

    SciTech Connect

    Zhou, Honghui; Chisholm, Matthew F; Yang, Tsung-Han; Pennycook, Stephen J; Narayan, Jagdish

    2011-01-01

    Epitaxial VO2 films grown by pulsed laser deposition (PLD) on c-cut sapphire substrates ((0001) Al2O3) were studied by aberration-corrected scanning transmission electron microscopy (STEM). A number of film/substrate orientation relationships were found and are discussed in the context of the semiconductor-metal transition (SMT) characteristics. A structurally and electronically modified buffer layer was revealed on the interface and was attributed to the interface free-energy minimization process of accommodating the symmetry mismatch between the substrate and the film. This interfacial transition layer is expected to affect the SMT behavior when the interfacial region is a significant fraction of the VO2 film thickness.

  16. Interfacial sliding near a free surface in a fibrous or layered composite during thermal cycling

    NASA Technical Reports Server (NTRS)

    Cox, B. N.

    1990-01-01

    This paper presents a simple shear lag model of interfacial sliding at a free surface in a layered or continuous fiber composite. The interface is characterized by a critical interfacial shear stress, tau0, which might represent the critical stress for frictional sliding at a weakly bonded interface, or the shear flow stress of a thin ductile interface layer at a well bonded interface. The history, during heating and cooling, of the relative normal displacement of the reinforcing inclusions and the matrix on a free surface cut normal to the inclusions is calculated and shown to depend on both the absolute value and the temperature dependence of tau0, as well as on the magnitudes of the bulk residual stresses. The variety of possible displacement histories suggests that they are a rich source of information about tau0 and the residual stresses.

  17. Numerical simulations of the role of a ferroelectric polymer interfacial layer in organic solar cells.

    PubMed

    Liu, Bo; Xu, Feng; Zhang, Xinghua; Yan, Dadong; Lu, Dan

    2016-02-21

    A Pauli master equation method is adopted for the simulation of polymer bulk heterojunction (BHJ) solar cells with vinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)) films as interfacial layers. According to previous reports, using highly crystalline P(VDF-TrFE) films as interfacial layers can highly enhance the efficiency of polymer BHJ solar cells, and possible mechanisms for the enhancement by two different groups were given as the dipole induced permanent internal electric field or simply the electrode improvement which implied that the origin is the barrier lowering effect. The correlation between the appearance of S-shaped current density-voltage (J-V) characteristics and the energy barrier is studied first, and then further results indicate that the previous electrode improvement model provides a consistent explanation for the origin of performance enhancement due to the insertion of polarized P(VDF-TrFE) interfacial layers. Moreover, the phenomenon of an increase of the internal electric field observed before can be attributed to better contact conditions which help reduce the bimolecular recombination rate. Comparatively speaking, the electrode improvement model can give a more rational explanation for the origin of performance enhancement experimentally found. In contrast, the dipole induced permanent internal electric field model was not complete enough. PMID:26822850

  18. Formation of interfacial layer and long-term cyclability of Li-O₂ batteries.

    PubMed

    Nasybulin, Eduard N; Xu, Wu; Mehdi, B Layla; Thomsen, Edwin; Engelhard, Mark H; Massé, Robert C; Bhattacharya, Priyanka; Gu, Meng; Bennett, Wendy; Nie, Zimin; Wang, Chongmin; Browning, Nigel D; Zhang, Ji-Guang

    2014-08-27

    The long-term operation of Li-O2 batteries under full discharge/charge conditions is investigated in a glyme-based electrolyte. The formation of stable interfacial layer on the electrode surface during the initial cycling stabilizes reaction products at subsequent cycling stages as demonstrated by quantitative analyses of the discharge products and the gases released during charging. There is a quick switch from the predominant formation of Li2O2 to the predominant formation of side products during the first few cycles. However, after the formation of the stable interfacial layer, the yield of Li2O2 in the reaction products is stabilized at about 33-40%. Extended cycling under full discharge/charge conditions is achievable upon selection of appropriate electrode materials (carbon source and catalyst) and cycling protocol. Further investigation on the interfacial layer, which in situ forms on air electrode, may increase the long-term yield of Li2O2 during the cycling and enable highly reversible Li-O2 batteries required for practical applications. PMID:25068384

  19. Improvement of the interfacial Dzyaloshinskii-Moriya interaction by introducing a Ta buffer layer

    SciTech Connect

    Kim, Nam-Hui; Jung, Jinyong; Cho, Jaehun; You, Chun-Yeol; Han, Dong-Soo; Kim, June-Seo Swagten, Henk J. M.

    2015-10-05

    We report systematic measurements of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) by employing Brillouin light scattering in Pt/Co/AlO{sub x} and Ta/Pt/Co/AlO{sub x} structures. By introducing a tantalum buffer layer, the saturation magnetization and the interfacial perpendicular magnetic anisotropy are significantly improved due to the better interface between heavy metal and ferromagnetic layer. From the frequency shift between Stokes- and anti-Stokes spin-waves, we successively obtain considerably larger iDM energy densities (D{sub max} = 1.65 ± 0.13 mJ/m{sup 2} at t{sub Co} = 1.35 nm) upon adding the Ta buffer layer, despite the nominally identical interface materials. Moreover, the energy density shows an inverse proportionality with the Co layer thickness, which is the critical clue that the observed iDMI is indeed originating from the interface between the Pt and Co layers.

  20. Investigation on the Microstructure, Interfacial IMC Layer, and Mechanical Properties of Cu/Sn-0.7Cu-xNi/Cu Solder Joints

    NASA Astrophysics Data System (ADS)

    Yang, Li; Ge, Jinguo; Zhang, Yaocheng; Dai, Jun; Liu, Haixiang; Xiang, Jicen

    2016-04-01

    Sn-0.7Cu-xNi composite solder has been fabricated via mechanical mixing of different weight percentages of Ni particles with Sn-0.7Cu solder paste, and the effect of the Ni concentration on the microstructure, wettability, and tensile properties of Cu/Sn-0.7Cu-xNi/Cu solder joints investigated. The results show that refined dot-shaped particles of intermetallic compounds (IMCs) are uniformly dispersed in a primary β-Sn matrix in the Cu/Sn-0.7Cu-(0.05-0.1)Ni/Cu solder joints. The interfacial IMC layer thickness increased slightly when adding Ni content to 0.05 wt.%, then rapidly when further increasing the Ni concentration to 0.4 wt.%. Excellent wettability with bright appearance was obtained for the Sn-0.7Cu-0.05Ni solder due to diminished interfacial tension. The tensile properties improved after adding Ni content to 0.05 wt.% due to the presence of the refined dot-like IMC particles, in agreement with theoretical predictions based on the combination of dispersion and grain-refinement strengthening mechanisms. Refined microstructure and enhanced mechanical properties were obtained for the Cu/Sn-0.7Cu-0.05Ni/Cu solder joint.

  1. Investigation on the Microstructure, Interfacial IMC Layer, and Mechanical Properties of Cu/Sn-0.7Cu- xNi/Cu Solder Joints

    NASA Astrophysics Data System (ADS)

    Yang, Li; Ge, Jinguo; Zhang, Yaocheng; Dai, Jun; Liu, Haixiang; Xiang, Jicen

    2016-07-01

    Sn-0.7Cu- xNi composite solder has been fabricated via mechanical mixing of different weight percentages of Ni particles with Sn-0.7Cu solder paste, and the effect of the Ni concentration on the microstructure, wettability, and tensile properties of Cu/Sn-0.7Cu- xNi/Cu solder joints investigated. The results show that refined dot-shaped particles of intermetallic compounds (IMCs) are uniformly dispersed in a primary β-Sn matrix in the Cu/Sn-0.7Cu-(0.05-0.1)Ni/Cu solder joints. The interfacial IMC layer thickness increased slightly when adding Ni content to 0.05 wt.%, then rapidly when further increasing the Ni concentration to 0.4 wt.%. Excellent wettability with bright appearance was obtained for the Sn-0.7Cu-0.05Ni solder due to diminished interfacial tension. The tensile properties improved after adding Ni content to 0.05 wt.% due to the presence of the refined dot-like IMC particles, in agreement with theoretical predictions based on the combination of dispersion and grain-refinement strengthening mechanisms. Refined microstructure and enhanced mechanical properties were obtained for the Cu/Sn-0.7Cu-0.05Ni/Cu solder joint.

  2. Optimization of Residual Stresses in MMC's through Process Parameter Control and the use of Heterogeneous Compensating/Compliant Interfacial Layers. OPTCOMP2 User's Guide

    NASA Technical Reports Server (NTRS)

    Pindera, Marek-Jerzy; Salzar, Robert S.

    1996-01-01

    A user's guide for the computer program OPTCOMP2 is presented in this report. This program provides a capability to optimize the fabrication or service-induced residual stresses in unidirectional metal matrix composites subjected to combined thermomechanical axisymmetric loading by altering the processing history, as well as through the microstructural design of interfacial fiber coatings. The user specifies the initial architecture of the composite and the load history, with the constituent materials being elastic, plastic, viscoplastic, or as defined by the 'user-defined' constitutive model, in addition to the objective function and constraints, through a user-friendly data input interface. The optimization procedure is based on an efficient solution methodology for the inelastic response of a fiber/interface layer(s)/matrix concentric cylinder model where the interface layers can be either homogeneous or heterogeneous. The response of heterogeneous layers is modeled using Aboudi's three-dimensional method of cells micromechanics model. The commercial optimization package DOT is used for the nonlinear optimization problem. The solution methodology for the arbitrarily layered cylinder is based on the local-global stiffness matrix formulation and Mendelson's iterative technique of successive elastic solutions developed for elastoplastic boundary-value problems. The optimization algorithm employed in DOT is based on the method of feasible directions.

  3. Interfacial magnetic anisotropy of Co90Zr10 on Pt layer.

    PubMed

    Kil, Joon Pyo; Bae, Gi Yeol; Suh, Dong Ik; Choi, Won Joon; Noh, Jae Sung; Park, Wanjun

    2014-11-01

    Spin Transfer Torque (STT) is of great interest in data writing scheme for the Magneto-resistive Random Access Memory (MRAM) using Magnetic Tunnel Junction (MTJ). Scalability for high density memory requires ferromagnetic electrodes having the perpendicular magnetic easy axis. We investigated CoZr as the ferromagnetic electrode. It is observed that interfacial magnetic anisotropy is preferred perpendicular to the plane with thickness dependence on the interfaces with Pt layer. The anisotropy energy (K(u)) with thickness dependence shows a change of magnetic-easy-axis direction from perpendicular to in-plane around 1.2 nm of CoZr. The interfacial anisotropy (K(i)) as the directly related parameters to switching and thermal stability, are estimated as 1.64 erg/cm2 from CoZr/Pt multilayered system. PMID:25958513

  4. Layered double hydroxides as carriers for quantum dots@silica nanospheres

    NASA Astrophysics Data System (ADS)

    Stoica, Georgiana; Castelló Serrano, Iván.; Palomares, Emilio

    2013-02-01

    Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot synthesis. The process is very fast and a priori delamination of hydrotalcite is not a prerequisite for the intercalation of quantum dots. The novel materials were extensively characterized by X-ray diffraction, thermogravimetry, infrared spectroscopy, transmission electron microscopy, true color fluorescence microscopy, photoluminescence, and nitrogen adsorption. The quantum dot-hydrotalcite nanomaterials display extremely high stability in mimicking physiological media such as saline serum (pH 5.5) and PBS (pH 7.2). Yet, quantum dot release from the solid structure is noted. In order to prevent the leaking of quantum dots we have developed a novel strategy which consists on using tailor made double layered hydrotalcites as protecting shells for quantum dots embedded into silica nanospheres without changing either the materials or the optical properties.

  5. Layered double hydroxides as carriers for quantum dots@silica nanospheres

    NASA Astrophysics Data System (ADS)

    Stoica, Georgiana; Castelló Serrano, Iván; Figuerola, Albert; Ugarte, Irati; Pacios, Roberto; Palomares, Emilio

    2012-08-01

    Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot synthesis. The process is very fast and a priori delamination of hydrotalcite is not a prerequisite for the intercalation of quantum dots. The novel materials were extensively characterized by X-ray diffraction, thermogravimetry, infrared spectroscopy, transmission electron microscopy, true color fluorescence microscopy, photoluminescence, and nitrogen adsorption. The quantum dot-hydrotalcite nanomaterials display extremely high stability in mimicking physiological media such as saline serum (pH 5.5) and PBS (pH 7.2). Yet, quantum dot release from the solid structure is noted. In order to prevent the leaking of quantum dots we have developed a novel strategy which consists of using tailor made double layered hydrotalcites as protecting shells for quantum dots embedded into silica nanospheres without changing either the materials or the optical properties.

  6. Enhanced photoelectrochemical performance of quantum dot-sensitized TiO2 nanotube arrays with Al2O3 overcoating by atomic layer deposition.

    PubMed

    Zeng, Min; Peng, Xiange; Liao, Jianjun; Wang, Guizhen; Li, Yanfang; Li, Jianbao; Qin, Yong; Wilson, Joshua; Song, Aimin; Lin, Shiwei

    2016-06-29

    While TiO2 nanotube arrays cosensitized with CdS and PbS quantum dots can achieve water splitting under visible light excitation, the use of quantum dots is limited by the relatively slow interfacial hole transfer rate and low internal quantum efficiencies in the visible region. Al2O3 overcoating by atomic layer deposition (ALD) can drastically enhance the photoelectrochemical performance of the quantum dot-sensitized TiO2 nanotube arrays. 30 ALD cycles of the Al2O3 overlayer can achieve a good balance between surface coverage and charge transfer resistance. The resulting maximum photocurrent density of 5.19 mA cm(-2) under simulated solar illumination shows a 52 times improvement over the pure TiO2 nanotube arrays, and more significantly, a 60% enhancement over bare quantum dot-sensitized TiO2 nanotube arrays. The incident photon-to-current conversion efficiency can reach the record value of 83% at 350 nm and remain above 30% up to 450 nm. A systematic examination of the role of the ALD Al2O3 overlayer indicates that surface recombination passivation, catalytic improvement in interfacial charge transfer kinetics, and chemical stabilization might synergistically enhance the photoelectrochemical performance in the visible region. These results provide a physical insight into the facile surface treatment, which could be applied to develop and optimize high-performance photoelectrodes for artificial photosynthesis. PMID:27138558

  7. The effect of skin-depth interfacial defect layer in perovskite solar cell

    NASA Astrophysics Data System (ADS)

    Gebremichael, Bizuneh; Mola, Genene Tessema

    2016-08-01

    The hole transport buffer layer (HTL) known as PEDOT:PSS is found to be sensitive to polar solvents often used in the preparation of solution-processed perovskite-based solar cell. We employed {CH}3 {NH}3 {PbI}3 perovskite absorber sandwiched between two charge transport layers to analyze the effect of precursor solvent. By introducing skin-depth interfacial defect layer (IDL) on PEDOT:PSS film we studied the overall performance of the devices using one-dimensional device simulator. Both enhanced conductivity and variations in valence band offset (VBO) of IDL were considered to analyze device performance. A power conversion efficiency (PCE) of the devices was found to grow by 35 % due to increased conductivity of IDL by a factor of 1000. Furthermore, we noted a drastic reduction in PCE of the device by reducing the work function of IDL by more than 0.3eV . The thickness of interfacial defect layer was also analyzed and found to decrease the PCE of the devices by 18 % for fourfold increase in IDL thickness. The analysis was remarkably reproduced the experimentally generated device parameters and will help to understand the underlying physical process in perovskite-based solar cell.

  8. Effects of Interfacial Layers Fracture on the Dissolution Mechanism of Solid Fe in Liquid Al

    NASA Astrophysics Data System (ADS)

    Rezaei, H.; Akbarpour, M. R.; Shahverdi, H. R.

    2015-07-01

    Solid Fe and liquid Al interaction was studied in the temperature range of 750-900°C by immersion tests in the absence of convection to better understand interfacial reactions during the first instances of immersion (10-80 s). Solidified interface profiles were characterized using a scanning electron microscope and an electron probe micro-analyzer. The results showed the formation of a transition layer with a composition close to pure Fe on the Fe side as a result of Al diffusion from the melt into the solid at initial times of the immersion test, before the formation of an intermetallic compound. At longer immersion times, two intermetallic layers were observed, Fe2Al5 and FeAl3. With increasing immersion time, the intermetallic compounds were thickened, and cracks formed at the interface layers. The formation of cracks accelerated the fracture of the interfacial layers and enhanced the Al diffusion toward solid Fe. As a result of the detachment and dissolution of the intermetallic phases in liquid Al, precipitates of FeAl3 with needle-like morphology were found in the Al phase. A model is proposed for the interface reaction of solid Fe with liquid Al at the first instance of immersion.

  9. Interface feature characterization and Schottky interfacial layer confirmation of TiO2 nanotube array film

    NASA Astrophysics Data System (ADS)

    Li, Hongchao; Tang, Ningxin; Yang, Hongzhi; Leng, Xian; Zou, Jianpeng

    2015-11-01

    We report here characterization of the interfacial microstructure and properties of titanium dioxide (TiO2) nanotube array films fabricated by anodization. Field effect scanning electron microscopy (FESEM), X-ray diffraction (XRD), nanoindentation, atomic force microscopy (AFM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the interface of the film. With increasing annealing temperature from 200 °C to 800 °C, the interfacial fusion between the film and the Ti substrate increased. The phase transformation of the TiO2 nanotube film from amorphous to anatase to rutile took place gradually; as the phase transformation progressed, the force needed to break the film increased. The growth of TiO2 nanotube arrays occurs in four stages: barrier layer formation, penetrating micropore formation, regular nanotube formation, and nanofiber formation. The TiO2 nanotubes grow from the Schottky interface layer rather than from the Ti substrate. The Schottky interface layer's thickness of 35-45 nm was identified as half the diameter of the corresponding nanotube, which shows good agreement to the Schottky interface layer growth model. The TiO2 nanotube film was amorphous and the Ti substrate was highly crystallized with many dislocation walls.

  10. Interfacially polymerized layers for oxygen enrichment: a method to overcome Robeson's upper-bound limit.

    PubMed

    Tsai, Ching-Wei; Tsai, Chieh; Ruaan, Ruoh-Chyu; Hu, Chien-Chieh; Lee, Kueir-Rarn

    2013-06-26

    Interfacial polymerization of four aqueous phase monomers, diethylenetriamine (DETA), m-phenylenediamine (mPD), melamine (Mela), and piperazine (PIP), and two organic phase monomers, trimethyl chloride (TMC) and cyanuric chloride (CC), produce a thin-film composite membrane of polymerized polyamide layer capable of O2/N2 separation. To achieve maximum efficiency in gas permeance and O2/N2 permselectivity, the concentrations of monomers, time of interfacial polymerization, number of reactive groups in monomers, and the structure of monomers need to be optimized. By controlling the aqueous/organic monomer ratio between 1.9 and 2.7, we were able to obtain a uniformly interfacial polymerized layer. To achieve a highly cross-linked layer, three reactive groups in both the aqueous and organic phase monomers are required; however, if the monomers were arranged in a planar structure, the likelihood of structural defects also increased. On the contrary, linear polymers are less likely to result in structural defects, and can also produce polymer layers with moderate O2/N2 selectivity. To minimize structural defects while maximizing O2/N2 selectivity, the planar monomer, TMC, containing 3 reactive groups, was reacted with the semirigid monomer, PIP, containing 2 reactive groups to produce a membrane with an adequate gas permeance of 7.72 × 10(-6) cm(3) (STP) s(-1) cm(-2) cm Hg(-1) and a high O2/N2 selectivity of 10.43, allowing us to exceed the upper-bound limit of conventional thin-film composite membranes. PMID:23731366

  11. Layer-by-layer nucleation mechanism for quantum dot formation in strained heteroepitaxy.

    PubMed

    Xiang, Ruoxi; Lung, M T; Lam, Chi-Hang

    2010-08-01

    We study the spontaneous formation of quantum dots in the form of three-dimensional (3D) islands on facetted surfaces in heteroepitaxy. Island development from fast kinetic Monte Carlo (KMC) simulations at low deposition rates is found to follow a layer-by-layer nucleation pathway characterized by energetics driven continuous lateral expansion interrupted by a sequence of independent two-dimensional (2D) upper-layer nucleation events. The process involves only unstable 2D upper-layer nuclei but no unstable 3D nucleus. We have calculated analytically the elastic strain energy of an island in the form of an axisymmetric stepped mound using a small-slope approximation. The total free energy of a system with a 3D island and an adatom bath is obtained. Our theory explains island formation via a free energy driven layer-by-layer nucleation mechanism. Upper-layer nucleation energy barrier, nucleation time, critical radius, and island step spacings are estimated. The relevance of entropic step-step repulsion is discussed. Our theory satisfactorily explains the 3D KMC simulations and may describe the initial evolution of islands in the form of stepped mounds observed in experiments. PMID:20866820

  12. Effects of the interfacial polarization on tunneling in surface coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Virk, Kuljit S.; Reichman, David R.; Hybertsen, Mark S.

    2012-10-01

    Polarization effects are included exactly in a model for a quantum dot in close proximity to a planar interface. Efficient incorporation of this potential into the Schrödinger equation is utilized to map out the influence of the image potential effects on carrier tunneling in such heterostructures. In particular, the interplay between carrier mass and the dielectric constants of a quantum dot, its surrounding matrix, and the electrode is studied. We find that the polarizability of the planar electrode structure can significantly increase the tunneling rates for heavier carriers, potentially resulting in a qualitative change in the dependence of tunneling rate on mass. Our method for treating polarization can be generalized to the screening of two-particle interactions and can thus be applied to calculations such as exciton dissociation and the Coulomb blockade. In contrast to tunneling via intermediate surface localized states of the quantum dot, our work identifies the parameter space over which volume states undergo significant modification in their tunneling characteristics.

  13. Effects of disorder state and interfacial layer on thermal transport in copper/diamond system

    SciTech Connect

    Sinha, V.; Gengler, J. J.; Muratore, C.; Spowart, J. E.

    2015-02-21

    The characterization of Cu/diamond interface thermal conductance (h{sub c}) along with an improved understanding of factors affecting it are becoming increasingly important, as Cu-diamond composites are being considered for electronic packaging applications. In this study, ∼90 nm thick Cu layers were deposited on synthetic and natural single crystal diamond substrates. In several specimens, a Ti-interface layer of thickness ≤3.5 nm was sputtered between the diamond substrate and the Cu top layer. The h{sub c} across Cu/diamond interfaces for specimens with and without a Ti-interface layer was determined using time-domain thermoreflectance. The h{sub c} is ∼2× higher for similar interfacial layers on synthetic versus natural diamond substrate. The nitrogen concentration of synthetic diamond substrate is four orders of magnitude lower than natural diamond. The difference in nitrogen concentration can lead to variations in disorder state, with a higher nitrogen content resulting in a higher level of disorder. This difference in disorder state potentially can explain the variations in h{sub c}. Furthermore, h{sub c} was observed to increase with an increase of Ti-interface layer thickness. This was attributed to an increased adhesion of Cu top layer with increasing Ti-interface layer thickness, as observed qualitatively in the current study.

  14. Enhanced electron extraction capability of polymer solar cells via modifying the cathode buffer layer with inorganic quantum dots.

    PubMed

    Li, Zhiqi; Li, Shujun; Zhang, Zhihui; Zhang, Xinyuan; Li, Jingfeng; Liu, Chunyu; Shen, Liang; Guo, Wenbin; Ruan, Shengping

    2016-04-20

    Enhanced performance of polymer solar cells (PSCs) based on the blend of poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT):[6,6]-phenyl-C70-butyric acid methyl ester (PC71BM) is demonstrated by titanium dioxide (TiO2) interface modification via CuInS2/ZnS quantum dots (CZdots). Devices with a TiO2/CZdots composite buffer layer exhibit both a high short-circuit current density (Jsc) and fill factor (FF), leading to a power conversion efficiency (PCE) up to 7.01%. The charge transport recombination mechanisms are investigated by an impedance behavior model, which indicates that TiO2 interfacial modification results in not only increasing the electron extraction but also reducing impedance. This study provides an important and beneficial approach to develop high efficiency PSCs. PMID:27055908

  15. Hydrophobic and high adhesive polyaniline layer of rectangular microtubes fabricated by a modified interfacial polymerization

    NASA Astrophysics Data System (ADS)

    Zhou, Chuanqiang; Gong, Xiangxiang; Qu, Yun; Han, Jie

    2016-08-01

    A modified interfacial polymerization of aniline is developed to fabricate hydrophobic and adhesive polyaniline (PANI) layer of rectangular microtubes on the glass substrate. The modified method uses pentanol as an organic medium to dissolve aniline monomer, with the water film of oxidant and surfactant on the glass substrate as water phase. The effects of some synthetic parameters (such as monomer concentration, alcohol molecular structure and surfactant type) on the morphology of PANI layer are studied for better understanding the fabrication of PANI nanostructures on the film. The alcohol molecular structure plays key role for the supermolecular assembly of PANI chains into nanostructures, while the surfactant may direct the array and deposition of these nanostructures on the glass substrate. The formation reason of PANI rectangular sub-microtubes is roughly interpreted according to our previous works. Wettability experiment indicates that the as-prepared PANI layer exhibits excellent hydrophobicity and high adhesive properties to water drop.

  16. Thermal conduction in polymeric nanofluids under mean field approximation: role of interfacial adsorption layers

    NASA Astrophysics Data System (ADS)

    Nisha, M. R.; Philip, J.

    2013-07-01

    Polymeric nanofluids of TiO2/PVA (polyvinyl alcohol) and Cu/PVA have been prepared by dispersing nanoparticles of TiO2 or metallic copper in PVA. The thermal diffusivities and thermal conductivities of these nanofluids have been measured as a function of particle loading following a thermal wave interference technique in a thermal wave resonant cavity. It is found that in both cases thermal conductivity increases with particle concentration, with Cu/PVA nanofluids showing a much larger increase. The results have been compared with the corresponding values calculated following different theoretical models. Comparison of the results with model-based calculations shows that the thermal conductivity variations in these nanofluids are within the framework of the classical mean field theory including the formation of thin interfacial adsorption layers around nanoparticles. Although the molecular weight of PVA is very high, it is found that the adsorption layer thickness is limited by the hydrodynamic radius of the nanoparticles. It is found that particle clustering followed by interfacial layering accounts for the larger increase in thermal conductivity found for Cu/PVA compared to TiO2/PVA.

  17. Performance enhancement in inverted solar cells by interfacial modification of ZnO nanoparticle buffer layer.

    PubMed

    Ambade, Swapnil B; Ambade, Rohan B; Kim, Seojin; Park, Hanok; Yoo, Dong Jin; Leel, Soo-Hyoung

    2014-11-01

    Polymer solar cells (PSCs) have attracted increasing attention in recent years. The rapid progress and mounting interest suggest the feasibility of PSC commercialization. However, critical issues such as stability and the weak nature of their interfaces posses quite a challenge. In the context of improving stability, PSCs with inverted geometry consising of inorganic oxide layer acting as an n-buffer offer quite the panacea. Zinc oxide (ZnO) is one of the most preferred semiconducting wide band gap oxides as an efficient cathode layer that effectively extracts and transports photoelectrons from the acceptor to the conducting indium-doped tin oxide (ITO) due to its high conductivity and transparency. However, the existence of a back charge transfer from metal oxides to electron-donating conjugated polymer and poor contact with the bulk heterojunction (BHJ) active layer results in serious interfacial recombination and leads to relatively low photovoltaic performance. One approach to improving the performance and charge selectivity of these types of inverted devices consists of modifying the interface between the inorganic metal oxide (e.g., ZnO) and organic active layer using a sub-monolayer of interfacial materials (e.g., functional dyes). In this work, we demonstrate that the photovoltaic parameters of inverted solar cells comprising a thin overlayer of functional dyes over ZnO nanoparticle as an n-buffer layer are highly influenced by the anchoring groups they possess. While an inverted PSC containing an n-buffer of only ZnO exhibited an overall power conversion efficiency (PCE) of 2.87%, the devices with an interlayer of dyes containing functional cyano-carboxylic, cyano-cyano, and carboxylic groups exhibited PCE of 3.52%, 3.39%, and 3.21%, respectively, due to increased forward charge collection resulting from enhanced electronic coupling between the ZnO and BHJ active layers. PMID:25958563

  18. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

    PubMed Central

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L.; Zhang, Qianfan; Zhao, Weisheng

    2015-01-01

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM. PMID:26656721

  19. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures.

    PubMed

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L; Zhang, Qianfan; Zhao, Weisheng

    2015-01-01

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM. PMID:26656721

  20. A brilliant sandwich type fluorescent nanostructure incorporating a compact quantum dot layer and versatile silica substrates.

    PubMed

    Huang, Liang; Wu, Qiong; Wang, Jing; Foda, Mohamed; Liu, Jiawei; Cai, Kai; Han, Heyou

    2014-03-18

    A "hydrophobic layer in silica" structure was designed to integrate a compact quantum dot (QD) layer with high quantum yield into scalable silica hosts containing desired functionality. This was based on metal affinity driven assembly of hydrophobic QDs with versatile silica substrates and homogeneous encapsulation of organosilica/silica layers. PMID:24492702

  1. Formation of alternating interfacial layers in Au-12Ge/Ni joints

    PubMed Central

    Lin, Shih-kang; Tsai, Ming-yueh; Tsai, Ping-chun; Hsu, Bo-hsun

    2014-01-01

    Au-Ge alloys are promising materials for high-power and high-frequency packaging, and Ni is frequently used as diffusion barriers. This study investigates interfacial reactions in Au-12Ge/Ni joints at 300°C and 400°C. For the reactions at 300°C, typical interfacial morphology was observed and the diffusion path was (Au) + (Ge)/NiGe/Ni5Ge3/Ni. However, an interesting phenomenon – the formation of (Au,Ni,Ge)/NiGe alternating layers – was observed for the reactions at 400°C. The diffusion path across the interface was liquid/(Au,Ni,Ge)/NiGe/···/(Au,Ni,Ge)/NiGe/Ni2Ge/Ni. The periodic thermodynamic instability at the NiGe/Ni2Ge interface caused the subsequent nucleation of new (Au,Ni,Ge)/NiGe pairs. The thermodynamic foundation and mechanism of formation of the alternating layers are elaborated in this paper. PMID:24690992

  2. Interfacial Layer Control by Dry Cleaning Technology for Polycrystalline and Single Crystalline Silicon Growth.

    PubMed

    Im, Dong-Hyun; Kong-Soo Lee; Kang, Yoongoo; Jeong, Myoungho; Park, Kwang Wuk; Lee, Soon-Gun; Ma, Jin-Won; Kim, Youngseok; Kim, Bonghyun; Im, Ki-Vin; Lim, Hanjin; Lee, Jeong Yong

    2016-05-01

    Native oxide removal prior to poly-Si contact and epitaxial growth of Si is the most critical technology to ensure process and device performances of poly-Si plugs and selective epitaxial growth (SEG) layers for DRAM, flash memory, and logic device. Recently, dry cleaning process for interfacial oxide removal has attracted a world-wide attention due to its superior passivation properties to conventional wet cleaning processes. In this study, we investigated the surface states of Si substrate during and after dry cleaning process, and the role of atomic elements including fluorine and hydrogen on the properties of subsequent deposited silicon layer using SIMS, XPS, and TEM analysis. The controlling of residual fluorine on the Si surface after dry cleaning is a key factor for clean interface. The mechanism of native oxide re-growth caused by residual fluorine after dry cleaning is proposed based on analytical results. PMID:27483844

  3. Non-blinking (Zn)CuInS/ZnS Quantum Dots Prepared by In Situ Interfacial Alloying Approach

    PubMed Central

    Zhang, Aidi; Dong, Chaoqing; Li, Liang; Yin, Jinjin; Liu, Heng; Huang, Xiangyi; Ren, Jicun

    2015-01-01

    Semiconductor quantum dots (QDs) are very important optical nanomaterials with a wide range of potential applications. However, blinking behavior of single QD is an intrinsic drawback for some biological and photoelectric applications based on single-particle emission. Herein we present a rational strategy for fabrication of non-blinking (Zn)CuInS/ZnS QDs in organic phase through in situ interfacial alloying approach. This new strategy includes three steps: synthesis of CuInS QDs, eliminating the interior traps of QDs by forming graded (Zn)CuInS alloyed QDs, modifying the surface traps of QDs by introducing ZnS shells onto (Zn)CuInS QDs using alkylthiols as sulfur source and surface ligands. The suppressed blinking mechanism was mainly attributed to modifying QDs traps from interior to exterior via a step-by-step modification. Non-blinking QDs show high quantum yield, symmetric emission spectra and excellent crystallinity, and will enable applications from biology to optoelectronics that were previously hindered by blinking behavior of traditional QDs. PMID:26458511

  4. Non-blinking (Zn)CuInS/ZnS Quantum Dots Prepared by In Situ Interfacial Alloying Approach

    NASA Astrophysics Data System (ADS)

    Zhang, Aidi; Dong, Chaoqing; Li, Liang; Yin, Jinjin; Liu, Heng; Huang, Xiangyi; Ren, Jicun

    2015-10-01

    Semiconductor quantum dots (QDs) are very important optical nanomaterials with a wide range of potential applications. However, blinking behavior of single QD is an intrinsic drawback for some biological and photoelectric applications based on single-particle emission. Herein we present a rational strategy for fabrication of non-blinking (Zn)CuInS/ZnS QDs in organic phase through in situ interfacial alloying approach. This new strategy includes three steps: synthesis of CuInS QDs, eliminating the interior traps of QDs by forming graded (Zn)CuInS alloyed QDs, modifying the surface traps of QDs by introducing ZnS shells onto (Zn)CuInS QDs using alkylthiols as sulfur source and surface ligands. The suppressed blinking mechanism was mainly attributed to modifying QDs traps from interior to exterior via a step-by-step modification. Non-blinking QDs show high quantum yield, symmetric emission spectra and excellent crystallinity, and will enable applications from biology to optoelectronics that were previously hindered by blinking behavior of traditional QDs.

  5. Selective Probing of Gaseous Ammonia Using Red-Emitting Carbon Dots Based on an Interfacial Response Mechanism.

    PubMed

    Jiang, Bang-Ping; Zhou, Bo; Shen, Xing-Can; Yu, Yun-Xiang; Ji, Shi-Chen; Wen, Chang-Chun; Liang, Hong

    2015-12-21

    Solid-state fluorescence sensing is one of the most appealing detection techniques because of its simplicity and convenience in practical operation. Herein, we report the development of a red-emitting carbon dots (RCDs)-based material as a solid-state fluorescence sensor for the selective probing of gaseous ammonia. The RCDs were prepared by a low-cost, one-step carbonization method using sugar cane bagasse as the carbon precursor. The pristine RCDs were then directly coated on polyvinylidene fluoride membrane to produce a new fluorescence sensor capable of selectively distinguishing toxic gaseous ammonia from other analyte vapors through sensitive fluorescence quenching with a low detection limit. More importantly, the interfacial response mechanism occurring on the surface of the RCDs has been studied by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Raman measurements. The results indicate that fluorescence quenching in the RCDs might result from ammonia-induced Michael addition through insertion of N into the C=C group and deprotonation of the carboxyl group. To the best of our knowledge, this is the first report that provides clear insight into the mechanism of surface chemistry on CDs in the solid state. PMID:26514914

  6. Change of interface dipole energy with interfacial layer thickness and O2 plasma treatment in metal/organic interface

    NASA Astrophysics Data System (ADS)

    Kim, Soo Young; Hong, Kihyon; Lee, Jong-Lam

    2007-04-01

    The authors determined the interface dipole energies between interfacial layers with different thicknesses coated on indium tin oxides (ITOs) and 4,4'-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl using ultraviolet and synchrotron radiation photoemission spectroscopy. The interface dipole energy increased as a function of interfacial layer thickness up to 4nm. After O2 plasma treatment on thick-metal (>4nm) coated ITO, the work function and interface dipole energy increased. In thin-metal (<2nm) coated ITO, no change in the interface dipole energy was found though the work function increased. Thus, the O2 plasma treated thin (<2nm) interfacial layer reduced the hole injection barrier.

  7. Effects of cathode electrolyte interfacial (CEI) layer on long term cycling of all-solid-state thin-film batteries

    NASA Astrophysics Data System (ADS)

    Wang, Ziying; Lee, Jungwoo Z.; Xin, Huolin L.; Han, Lili; Grillon, Nathanael; Guy-Bouyssou, Delphine; Bouyssou, Emilien; Proust, Marina; Meng, Ying Shirley

    2016-08-01

    All-solid-state lithium-ion batteries have the potential to not only push the current limits of energy density by utilizing Li metal, but also improve safety by avoiding flammable organic electrolyte. However, understanding the role of solid electrolyte - electrode interfaces will be critical to improve performance. In this study, we conducted long term cycling on commercially available lithium cobalt oxide (LCO)/lithium phosphorus oxynitride (LiPON)/lithium (Li) cells at elevated temperature to investigate the interfacial phenomena that lead to capacity decay. STEM-EELS analysis of samples revealed a previously unreported disordered layer between the LCO cathode and LiPON electrolyte. This electrochemically inactive layer grew in thickness leading to loss of capacity and increase of interfacial resistance when cycled at 80 °C. The stabilization of this layer through interfacial engineering is crucial to improve the long term performance of thin-film batteries especially under thermal stress.

  8. Effects of cathode electrolyte interfacial (CEI) layer on long term cycling of all-solid-state thin-film batteries

    NASA Astrophysics Data System (ADS)

    Wang, Ziying; Lee, Jungwoo Z.; Xin, Huolin L.; Han, Lili; Grillon, Nathanael; Guy-Bouyssou, Delphine; Bouyssou, Emilien; Proust, Marina; Meng, Ying Shirley

    2016-08-01

    All-solid-state lithium-ion batteries have the potential to not only push the current limits of energy density by utilizing Li metal, but also improve safety by avoiding flammable organic electrolyte. However, understanding the role of solid electrolyte - electrode interfaces will be critical to improve performance. In this study, we conducted long term cycling on commercially available lithium cobalt oxide (LCO)/lithium phosphorus oxynitride (LiPON)/lithium (Li) cells at elevated temperature to investigate the interfacial phenomena that lead to capacity decay. STEM-EELS analysis of samples revealed a previously unreported disordered layer between the LCO cathode and LiPON electrolyte. This electrochemically inactive layer grew in thickness leading to loss of capacity and increase of interfacial resistance when cycled at 80 °C. The stabilization of this layer through interfacial engineering is crucial to improve the long term performance of thin-film batteries especially under thermal stress.

  9. Influence of a thin interfacial oxide layer on the ion beam assisted epitaxial crystallization of deposited Si

    NASA Astrophysics Data System (ADS)

    Priolo, F.; La Ferla, A.; Spinella, C.; Rimini, E.; Ferla, G.; Baroetto, F.; Licciardello, A.

    1988-12-01

    The epitaxial crystallization of chemical vapor deposited Si layers on <100> Si substrates with a thin interfacial oxide layer was induced by a 600 keV Kr beam in the temperature range 350-500 °C. During irradiation the single crystal-amorphous interface velocity was measured in situ by monitoring the reflectivity of He-Ne laser light. We show that a critical irradiation dose is needed before the interfacial oxide breaks down and epitaxial regrowth can take place. This critical dose depends exponentially on the reciprocal temperature with an activation energy of 0.44 eV.

  10. Novel layer-by-layer interfacial [Ni(salen)]-polyelectrolyte hybrid films.

    PubMed

    Patrício, Sónia; Cruz, Ana I; Biernacki, Krzysztof; Ventura, João; Eaton, Peter; Magalhães, Alexandre L; Moura, Cosme; Hillman, A Robert; Freire, Cristina

    2010-07-01

    A novel multilayer film containing a cationic phosphonium-derivatized Ni(salen)-type complex and poly(sodium-4-styrenesulfonate (NaPSS) was assembled onto quartz, mica, and metal surfaces using the layer-by-layer (LbL) technique. Spectroscopic (UV-vis) and gravimetric (QCM) responses for the multilayer films show regular stepwise growth and the signature of strong electrostatic interactions between the component layers. The gravimetric responses indicate the presence of substantial additional (net neutral) material in the PSS layers, which XPS shows is not polyelectrolyte or salt, so charge compensation is intrinsic; we deduce the presence of space-filling solvent. Direct electrostatic interaction of the two-component layers is enhanced by a secondary noncovalent interaction between the delocalized pi-systems of the two components. Permeability of the film to the redox probe [Fe(CN)(6)](3-/4-) was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Qualitatively similar results were obtained in the absence and presence of a precursor PSS/PAH multilayer, but with a general shift in kinetic and diffusional processes to longer time scales (lower frequencies) in the presence of the precursor layer and with increasing numbers of PSS/[Ni(salen)] bilayers. Quantitatively, the EIS data were interpreted using a capillary membrane model (CMM) to yield values of coverage, apparent charge transfer resistance, double-layer capacitance, pore size, and diffusion coefficient. The coverage values were consistent with a model in which there are no preferential growth sites and the surface charge density is independent of the number of bilayers. PMID:20476725

  11. Probing Interfacial Electronic States in CdSe Quantum Dots using Second Harmonic Generation Spectroscopy

    SciTech Connect

    Doughty, Benjamin L.; Ma, Yingzhong; Shaw, Robert W

    2015-01-07

    Understanding and rationally controlling the properties of nanomaterial surfaces is a rapidly expanding field of research due to the dramatic role they play on the optical and electronic properties vital to light harvesting, emitting and detection technologies. This information is essential to the continued development of synthetic approaches designed to tailor interfaces for optimal nanomaterial based device performance. In this work, closely spaced electronic excited states in model CdSe quantum dots (QDs) are resolved using second harmonic generation (SHG) spectroscopy, and the corresponding contributions from surface species to these states are assessed. Two distinct spectral features are observed in the SHG spectra, which are not readily identified in linear absorption and photoluminescence excitation spectra. These features include a weak band at 395 6 nm, which coincides with transitions to the 2S1/2 1Se state, and a much more pronounced band at 423 4 nm arising from electronic transitions to the 1P3/2 1Pe state. Chemical modification of the QD surfaces through oxidation resulted in disappearance of the SHG band corresponding to the 1P3/2 1Pe state, indicating prominent surface contributions. Signatures of deep trap states localized on the surfaces of the QDs are also observed. We further find that the SHG signal intensities depend strongly on the electronic states being probed and their relative surface contributions, thereby offering additional insight into the surface specificity of SHG signals from QDs.

  12. Probing Interfacial Electronic States in CdSe Quantum Dots using Second Harmonic Generation Spectroscopy

    DOE PAGESBeta

    Doughty, Benjamin L.; Ma, Yingzhong; Shaw, Robert W

    2015-01-07

    Understanding and rationally controlling the properties of nanomaterial surfaces is a rapidly expanding field of research due to the dramatic role they play on the optical and electronic properties vital to light harvesting, emitting and detection technologies. This information is essential to the continued development of synthetic approaches designed to tailor interfaces for optimal nanomaterial based device performance. In this work, closely spaced electronic excited states in model CdSe quantum dots (QDs) are resolved using second harmonic generation (SHG) spectroscopy, and the corresponding contributions from surface species to these states are assessed. Two distinct spectral features are observed in themore » SHG spectra, which are not readily identified in linear absorption and photoluminescence excitation spectra. These features include a weak band at 395 6 nm, which coincides with transitions to the 2S1/2 1Se state, and a much more pronounced band at 423 4 nm arising from electronic transitions to the 1P3/2 1Pe state. Chemical modification of the QD surfaces through oxidation resulted in disappearance of the SHG band corresponding to the 1P3/2 1Pe state, indicating prominent surface contributions. Signatures of deep trap states localized on the surfaces of the QDs are also observed. We further find that the SHG signal intensities depend strongly on the electronic states being probed and their relative surface contributions, thereby offering additional insight into the surface specificity of SHG signals from QDs.« less

  13. Interfacial charge transfer between CdTe quantum dots and Gram negative vs. Gram positive bacteria.

    SciTech Connect

    Dumas, E.; Gao, C.; Suffern, D.; Bradforth, S. E.; Dimitrejevic, N. M.; Nadeau, J. L.; McGill Univ.; Univ. of Southern California

    2010-01-01

    Oxidative toxicity of semiconductor and metal nanomaterials to cells has been well established. However, it may result from many different mechanisms, some requiring direct cell contact and others resulting from the diffusion of reactive species in solution. Published results are contradictory due to differences in particle preparation, bacterial strain, and experimental conditions. It has been recently found that C{sub 60} nanoparticles can cause direct oxidative damage to bacterial proteins and membranes, including causing a loss of cell membrane potential (depolarization). However, this did not correlate with toxicity. In this study we perform a similar analysis using fluorescent CdTe quantum dots, adapting our tools to make use of the particles fluorescence. We find that two Gram positive strains show direct electron transfer to CdTe, resulting in changes in CdTe fluorescence lifetimes. These two strains also show changes in membrane potential upon nanoparticle binding. Two Gram negative strains do not show these effects - nevertheless, they are over 10-fold more sensitive to CdTe than the Gram positives. We find subtoxic levels of Cd{sup 2+} release from the particles upon irradiation of the particles, but significant production of hydroxyl radicals, suggesting that the latter is a major source of toxicity. These results help establish mechanisms of toxicity and also provide caveats for use of certain reporter dyes with fluorescent nanoparticles which will be of use to anyone performing these assays. The findings also suggest future avenues of inquiry into electron transfer processes between nanomaterials and bacteria.

  14. Ultrathin two-dimensional atomic crystals as stable interfacial layer for improvement of lithium metal anode.

    PubMed

    Yan, Kai; Lee, Hyun-Wook; Gao, Teng; Zheng, Guangyuan; Yao, Hongbin; Wang, Haotian; Lu, Zhenda; Zhou, Yu; Liang, Zheng; Liu, Zhongfan; Chu, Steven; Cui, Yi

    2014-10-01

    Stable cycling of lithium metal anode is challenging due to the dendritic lithium formation and high chemical reactivity of lithium with electrolyte and nearly all the materials. Here, we demonstrate a promising novel electrode design by growing two-dimensional (2D) atomic crystal layers including hexagonal boron nitride (h-BN) and graphene directly on Cu metal current collectors. Lithium ions were able to penetrate through the point and line defects of the 2D layers during the electrochemical deposition, leading to sandwiched lithium metal between ultrathin 2D layers and Cu. The 2D layers afford an excellent interfacial protection of Li metal due to their remarkable chemical stability as well as mechanical strength and flexibility, resulting from the strong intralayer bonds and ultrathin thickness. Smooth Li metal deposition without dendritic and mossy Li formation was realized. We showed stable cycling over 50 cycles with Coulombic efficiency ∼97% in organic carbonate electrolyte with current density and areal capacity up to the practical value of 2.0 mA/cm(2)and 5.0 mAh/cm(2), respectively, which is a significant improvement over the unprotected electrodes in the same electrolyte. PMID:25166749

  15. Electron Transfer as a Probe of the Interfacial Quantum Dot-Organic Molecule Interaction

    NASA Astrophysics Data System (ADS)

    Peterson, Mark D.

    This dissertation describes a set of experimental and theoretical studies of the interaction between small organic molecules and the surfaces of semiconductor nanoparticles, also called quantum dots (QDs). Chapter 1 reviews the literature on the influence of ligands on exciton relaxation dynamics following photoexcitation of semiconductor QDs, and describes how ligands promote or inhibit processes such as emission, nonradiative relaxation, and charge transfer to redox active adsorbates. Chapter 2 investigates the specific interaction of alkylcarboxylated viologen derivatives with CdS QDs, and shows how a combination of steady-state photoluminescence (PL) and transient absorption (TA) experiments can be used to reveal the specific binding geometry of redox active organic molecules on QD surfaces. Chapter 3 expands on Chapter 2 by using PL and TA to provide information about the mechanisms through which methyl viologen (MV 2+) associates with CdS QDs to form a stable QD/MV2+ complex, suggesting two chemically distinct reactions. We use our understanding of the QD/molecule interaction to design a drug delivery system in Chapter 4, which employs PL and TA experiments to show that conformational changes in a redox active adsorbate may follow electron transfer, "activating" a biologically inert Schiff base to a protein inhibitor form. The protein inhibitor limits cell motility and may be used to prevent tumor metastasis in cancer patients. Chapter 5 discusses future applications of QD/molecule redox couples with an emphasis on efficient multiple charge-transfer reactions -- a process facilitated by the high degeneracy of band-edge states in QDs. These multiple charge-transfer reactions may potentially increase the thermodynamic efficiency of solar cells, and may also facilitate the splitting of water into fuel. Multiple exciton generation procedures, multi-electron transfer experiments, and future directions are discussed.

  16. Mechanism of lateral ordering of InP dots grown on InGaP layers

    SciTech Connect

    Bortoleto, J.R.R.; Gutierrez, H.R.; Cotta, M.A.; Bettini, J.

    2005-07-04

    The mechanisms leading to the spontaneous formation of a two-dimensional array of InP/InGaP dots grown by chemical-beam epitaxy are discussed. Samples where the InGaP buffer layer was grown at different conditions were characterized by transmission electron microscopy. Our results indicate that a periodic strain field related to lateral two-dimensional compositional modulation in the InGaP buffer layer determines the dot nucleation positions during InP growth. Although the periodic strain field in the InGaP is large enough to align the InP dots, both their shape and optical properties are effectively unaltered. This result shows that compositional modulation can be used as a tool for in situ dot positioning.

  17. Thermoelectric energy conversion in layered structures with strained Ge quantum dots grown on Si surfaces

    NASA Astrophysics Data System (ADS)

    Korotchenkov, Oleg; Nadtochiy, Andriy; Kuryliuk, Vasyl; Wang, Chin-Chi; Li, Pei-Wen; Cantarero, Andres

    2014-03-01

    The efficiency of the energy conversion devices depends in many ways on the materials used and various emerging cost-effective nanomaterials have promised huge potentials in highly efficient energy conversion. Here we show that thermoelectric voltage can be enhanced by a factor of 3 using layer-cake growth of Ge quantum dots through thermal oxidation of SiGe layers stacked in SiO2/Si3N4 multilayer structure. The key to achieving this behavior has been to strain the Ge/Si interface by Ge dots migrating to Si substrate. Calculations taking into account the carrier trapping in the dot with a quantum transmission into the neighboring dot show satisfactory agreement with experiments above ≈200 K. The results may be of interest for improving the functionality of thermoelectric devices based on Ge/Si.

  18. Probing confined interfacial excitations in buried layers by Brillouin light scattering

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Sooryakumar, R.

    2002-06-01

    Brillouin light scattering from silicon oxynitride films grown on GaAs reveals an excitation at frequencies lying below that of the Rayleigh surface wave. The mode, identified as a localized interfacial excitation, arises from the presence of a soft, thin transition layer between the film and substrate. The results are discussed in the framework of a Green's function formalism that reproduces the experimental features and illustrates the nature of the mode and its difference from Stoneley excitations that exist in special cases for an abrupt interface separating two semi-infinite solid media. Observations of this low-frequency excitation offer a previously unexplored approach to characterize, nondestructively, the elastic properties of buried interfaces.

  19. Electric-field-induced interfacial instabilities of a soft elastic membrane confined between viscous layers

    NASA Astrophysics Data System (ADS)

    Dey, Mohar; Bandyopadhyay, Dipankar; Sharma, Ashutosh; Qian, Shizhi; Joo, Sang Woo

    2012-10-01

    We explore the electric-field-induced interfacial instabilities of a trilayer composed of a thin elastic film confined between two viscous layers. A linear stability analysis (LSA) is performed to uncover the growth rate and length scale of the different unstable modes. Application of a normal external electric field on such a configuration can deform the two coupled elastic-viscous interfaces either by an in-phase bending or an antiphase squeezing mode. The bending mode has a long-wave nature, and is present even at a vanishingly small destabilizing field. In contrast, the squeezing mode has finite wave-number characteristics and originates only beyond a threshold strength of the electric field. This is in contrast to the instabilities of the viscous films with multiple interfaces where both modes are found to possess long-wave characteristics. The elastic film is unstable by bending mode when the stabilizing forces due to the in-plane curvature and the elastic stiffness are strong and the destabilizing electric field is relatively weak. In comparison, as the electric field increases, a subdominant squeezing mode can also appear beyond a threshold destabilizing field. A dominant squeezing mode is observed when the destabilizing field is significantly strong and the elastic films are relatively softer with lower elastic modulus. In the absence of liquid layers, a free elastic film is also found to be unstable by long-wave bending and finite wave-number squeezing modes. The LSA asymptotically recovers the results obtained by the previous formulations where the membrane bending elasticity is approximately incorporated as a correction term in the normal stress boundary condition. Interestingly, the presence of a very weak stabilizing influence due to a smaller interfacial tension at the elastic-viscous interfaces opens up the possibility of fabricating submicron patterns exploiting the instabilities of a trilayer.

  20. Magneto-optical response of layers of semiconductor quantum dots and nanorings

    NASA Astrophysics Data System (ADS)

    Voskoboynikov, O.; Wijers, C. M. J.; Liu, J. L.; Lee, C. P.

    2005-06-01

    In this paper a comparative theoretical study was made of the magneto-optical response of square lattices of nanoobjects (dots and rings). Expressions for both the polarizability of the individual objects as their mutual electromagnetic interactions (for a lattice in vacuum) was derived. The quantum-mechanical part of the derivation is based upon the commonly used envelope function approximation. The description is suited to investigate the optical response of these layers in a narrow region near the interband transitions onset, particularly when the contribution of individual level pairs can be separately observed. A remarkable distinction between clearly quantum-mechanical and classical electromagnetic behavior was found in the shape and volume dependence of the polarizability of the dots and rings. This optical response of a single plane of quantum dots and nanorings was explored as a function of frequency, magnetic field, and angle of incidence. Although the reflectance of these layer systems is not very strong, the ellipsometric angles are large. For these isolated dot-ring systems they are of the order of magnitude of degrees. For the ring systems a full oscillation of the optical Bohm-Ahronov effect could be isolated. Layers of dots do not display any remarkable magnetic field dependence. Both type of systems, dots and rings, exhibit an outspoken angular-dependent dichroism of quantum-mechanical origin.

  1. Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells.

    PubMed

    Zhou, Nanjia; Kim, Myung-Gil; Loser, Stephen; Smith, Jeremy; Yoshida, Hiroyuki; Guo, Xugang; Song, Charles; Jin, Hosub; Chen, Zhihua; Yoon, Seok Min; Freeman, Arthur J; Chang, Robert P H; Facchetti, Antonio; Marks, Tobin J

    2015-06-30

    In diverse classes of organic optoelectronic devices, controlling charge injection, extraction, and blocking across organic semiconductor-inorganic electrode interfaces is crucial for enhancing quantum efficiency and output voltage. To this end, the strategy of inserting engineered interfacial layers (IFLs) between electrical contacts and organic semiconductors has significantly advanced organic light-emitting diode and organic thin film transistor performance. For organic photovoltaic (OPV) devices, an electronically flexible IFL design strategy to incrementally tune energy level matching between the inorganic electrode system and the organic photoactive components without varying the surface chemistry would permit OPV cells to adapt to ever-changing generations of photoactive materials. Here we report the implementation of chemically/environmentally robust, low-temperature solution-processed amorphous transparent semiconducting oxide alloys, In-Ga-O and Ga-Zn-Sn-O, as IFLs for inverted OPVs. Continuous variation of the IFL compositions tunes the conduction band minima over a broad range, affording optimized OPV power conversion efficiencies for multiple classes of organic active layer materials and establishing clear correlations between IFL/photoactive layer energetics and device performance. PMID:26080437

  2. Power Enhancement of Lithium-Ion Batteries by a Graphene Interfacial Layer.

    PubMed

    Song, Young Il; An, Ja Hwa; Kim, Tae Yoo; Lee, Jung Woo; Yoo, Young Zo; Suh, Su Jeong; Kim, Sung-Soo

    2015-11-01

    We achieved a method for power enhancement of heavy-duty lithium-ion batteries (LIBs) by synthesizing a graphene interfacial layer onto the anode copper current collector (ACCC). We tested fabricated coin cells, which used either 35-μm-thick rolled pristine copper foil or graphene synthesized onto the pristine copper foil for power output estimation of the LIBs. We observed the copper surface morphology with a scanning electron microscope (SEM). Raman spectroscopy was used to measure the bonding characteristics and estimate the layers of graphene films. In addition, transmittance and electrical resistance were measured by ultra-violet visible near-infrared spectroscopy (UV-Vis IR) and 4 point probe surface resistance measurement. The graphene films on polyethylene terephthalate (PET) substrate obtained a transmittance of 97.5% and sheet resistance of 429 Ω/square. Power enhancement performances was evaluated using LIB coin cells. After 5C current discharge rate of -1.7 A/g reversible capacity of 293 mAh/g and 326 mAh/g were obtained for pristine and synthesized graphene anode current collectors, respectively. The graphene synthesized onto the ACCC showed superior power performance. The results presented herein demonstrate a power enhancement of LIBs by a decrease in electron flow resistivity between active materials and the ACCC and removal of the native oxide layer on the anode copper surface using high quality graphene synthesized onto the ACCC. PMID:26726638

  3. Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells

    PubMed Central

    Zhou, Nanjia; Kim, Myung-Gil; Loser, Stephen; Smith, Jeremy; Yoshida, Hiroyuki; Guo, Xugang; Song, Charles; Jin, Hosub; Chen, Zhihua; Yoon, Seok Min; Freeman, Arthur J.; Chang, Robert P. H.; Facchetti, Antonio; Marks, Tobin J.

    2015-01-01

    In diverse classes of organic optoelectronic devices, controlling charge injection, extraction, and blocking across organic semiconductor–inorganic electrode interfaces is crucial for enhancing quantum efficiency and output voltage. To this end, the strategy of inserting engineered interfacial layers (IFLs) between electrical contacts and organic semiconductors has significantly advanced organic light-emitting diode and organic thin film transistor performance. For organic photovoltaic (OPV) devices, an electronically flexible IFL design strategy to incrementally tune energy level matching between the inorganic electrode system and the organic photoactive components without varying the surface chemistry would permit OPV cells to adapt to ever-changing generations of photoactive materials. Here we report the implementation of chemically/environmentally robust, low-temperature solution-processed amorphous transparent semiconducting oxide alloys, In-Ga-O and Ga-Zn-Sn-O, as IFLs for inverted OPVs. Continuous variation of the IFL compositions tunes the conduction band minima over a broad range, affording optimized OPV power conversion efficiencies for multiple classes of organic active layer materials and establishing clear correlations between IFL/photoactive layer energetics and device performance. PMID:26080437

  4. The growth of interfacial passive layers under thermal passivation of integrated Pb(Zr ,Ti)O3 thin films

    NASA Astrophysics Data System (ADS)

    Jiang, A. Q.; Lin, Y. Y.; Tang, T. A.

    2007-10-01

    Pb(Zr ,Ti)O3 thin films suffer from progressive degradation of remanent polarization after thermal shocks of step-by-step integration of ferroelectric random access memories. The polarization degradation accelerates with the enhancement of the shocked number per time interval as well as thermal duration at 350°C in the flowing air. However, the degradation progresses in a slow rate for the sample heated in a sealed furnace with a homogeneous distribution of a thermal field. The previous steplike current transient of domain switching with time in the film becomes tilted in conjunction with polarization degradation, which is recognized as the growth of interfacial passive layers during thermal treatment. The interfacial passive layers can grow throughout the film thickness under the thermal stressing for 279h with a dielectric constant of ɛi=48, as estimated from capacitance-voltage (C-V) measurements, and time evolution of interfacial-layer thickness at 350°C is thus derived from domain switching performance. The thickened interfacial passive layers essential for polarization degradation can build in an enhanced internal field in backswitching of partial domains to block the total polarization reversal.

  5. Specific effects of Ca(2+) ions and molecular structure of β-lactoglobulin interfacial layers that drive macroscopic foam stability.

    PubMed

    Braunschweig, Björn; Schulze-Zachau, Felix; Nagel, Eva; Engelhardt, Kathrin; Stoyanov, Stefan; Gochev, Georgi; Khristov, Khr; Mileva, Elena; Exerowa, Dotchi; Miller, Reinhard; Peukert, Wolfgang

    2016-07-01

    β-Lactoglobulin (BLG) adsorption layers at air-water interfaces were studied in situ with vibrational sum-frequency generation (SFG), tensiometry, surface dilatational rheology and ellipsometry as a function of bulk Ca(2+) concentration. The relation between the interfacial molecular structure of adsorbed BLG and the interactions with the supporting electrolyte is additionally addressed on higher length scales along the foam hierarchy - from the ubiquitous air-water interface through thin foam films to macroscopic foam. For concentrations <1 mM, a strong decrease in SFG intensity from O-H stretching bands and a slight increase in layer thickness and surface pressure are observed. A further increase in Ca(2+) concentrations above 1 mM causes an apparent change in the polarity of aromatic C-H stretching vibrations from interfacial BLG which we associate to a charge reversal at the interface. Foam film measurements show formation of common black films at Ca(2+) concentrations above 1 mM due to considerable decrease of the stabilizing electrostatic disjoining pressure. These observations also correlate with a minimum in macroscopic foam stability. For concentrations >30 mM Ca(2+), micrographs of foam films show clear signatures of aggregates which tend to increase the stability of foam films. Here, the interfacial layers have a higher surface dilatational elasticity. In fact, macroscopic foams formed from BLG dilutions with high Ca(2+) concentrations where aggregates and interfacial layers with higher elasticity are found, showed the highest stability with much smaller bubble sizes. PMID:27337699

  6. Layer-by-Layer Assembly of Stable Aqueous Quantum Dots for Luminescent Planar Plate.

    PubMed

    Zhang, Xuejing; Zhou, Changhua; Zang, Shuaipu; Shen, Huaibin; Dai, Pengpeng; Zhang, Xintong; Li, Lin Song

    2015-07-15

    This work reports the fabrication of a luminescent planar plate based on stable aqueous quantum dots (QDs) and poly(diallyldimethylammonium chloride) (PDDA) via a layer-by-layer (LBL) assembly technique. Preparation of aqueous QDs with facile monoalkyl maleate amphiphilic surfactants as the coating agent is conducted by a robust and efficient phase-transfer method. The as-prepared aqueous QDs exhibit bright emission, and their surface has very large negative zeta potential values, which are useful for electrostatic LBL assembly. Red, green, and blue luminescent planar plates are successfully fabricated via LBL assembly of the monocolor QDs, respectively. Through accurately adjusting the relative proportion of each monocolor luminescent component, we obtain an inspiring luminescent planar plate, which emits bright white light with a color coordinate of (0.3509, 0.3483), a correlated color temperature (CCT) of 4766 K, and a high color rendering index (CRI, Ra) of 89.5 under the irradiation of UV light. Therefore, this paper reports a facile process for the design and preparation of luminescent planar plates, which have potential applications in display and solid-state lighting devices. PMID:26091336

  7. Numerical simulation on white OLEDs with dotted-line doped emitting layers

    NASA Astrophysics Data System (ADS)

    Chang, Shu-Hsuan; Wen, Chien-Yang; Huang, Yi-Hsiang; Kuo, Yen-Kuang

    2009-02-01

    White organic light-emitting diodes (OLEDs) have attracted great attention recently. In this study, high-efficiency white organic light-emitting diodes with dotted-line doped layers are numerically investigated with the APSYS (abbreviation of Advanced Physical Model of Simulation Devices) simulation program. The APSYS simulation program, developed by Crosslight Inc., is capable of dealing with the optical, electrical, and thermal characteristics of OLED devices. To approach the real situation, the OLED device fabricated by Park et al. (Current Applied Physics 1, 116, 2001) was first modeled by adjusting the appropriate physical parameters. Based on this OLED structure, a new structure of ITO/α-NPD (40 nm)/Alq3:DCJTB (30 nm)/Alq3 (30 nm)/Mg:Ag emitting quasi-white light was then proposed. Then, the single layer of Alq3:DCJTB was replaced by multi-(Alq3:DCJTB/Alq3)n layers, which are the so-called dotted-line doped layers (see, e.g., paper by Han et al., Solid State Communications 141, 332, 2007), to further improve the optical performance. The optical properties of the white OLEDs with different pairs of (Alq3:DCJTB/Alq3)n dotted-line doped layers are investigated and discussed in detail. Optimization of the proposed quasi-white OLED structures is attempted. The simulation results indicate that the OLED with dotted-line doped layers has higher radiative recombination rate and better emission efficiency than that with a single Alq3:DCJTB layer. The physical origin of the improved optical performance for the OLED with dotted-line doped layers could be due to the increased electrons and holes at the interfaces between the Alq3:DCJTB and Alq3 layers, which thus results in higher radiative recombination rate and better emission efficiency.

  8. Interfacial diffusion behavior in Ni-BaTiO 3 MLCCs with ultra-thin active layers

    NASA Astrophysics Data System (ADS)

    Gong, Huiling; Wang, Xiaohui; Tian, Zhibin; Zhang, Hui; Li, Longtu

    2014-03-01

    The interfacial structure and diffusion behavior between the dielectric layers (BaTiO3) and internal electrode layers (Ni) in X5R-type multilayer ceramic capacitors (MLCCs, from -55°C to 85°C, at a temperature capacitance coefficient within ±15%) with ultra-thin active layers ( T = 1-3 µm) have been investigated by several microstructural techniques (SEM/TEM/HRTEM) with energy-dispersive x-ray spectroscopy (EDS). In the MLCC samples with different active layer thicknesses (1-3 µm), weak interfacial diffusion was observed between BaTiO3 and Ni. It was also found that the diffusion capability of Ni into the BaTiO3 layer was stronger than that of BaTiO3 to the Ni electrode, which indicated that the diffusion of Ni was the dominant factor for the interfacial diffusion behavior in the ultra-thin layered MLCCs. The mechanism of Ni diffusion is discussed in this study as well.

  9. A comparison between semi-spheroid- and dome-shaped quantum dots coupled to wetting layer

    SciTech Connect

    Shahzadeh, Mohammadreza; Sabaeian, Mohammad

    2014-06-15

    During the epitaxial growth method, self-assembled semi-spheroid-shaped quantum dots (QDs) are formed on the wetting layer (WL). However for sake of simplicity, researchers sometimes assume semi-spheroid-shaped QDs to be dome-shaped (hemisphere). In this work, a detailed and comprehensive study on the difference between electronic and transition properties of dome- and semi-spheroid-shaped quantum dots is presented. We will explain why the P-to-S intersubband transition behaves the way it does. The calculated results for intersubband P-to-S transition properties of quantum dots show two different trends for dome-shaped and semi-spheroid-shaped quantum dots. The results are interpreted using the probability of finding electron inside the dome/spheroid region, with emphasis on the effects of wetting layer. It is shown that dome-shaped and semi-spheroid-shaped quantum dots feature different electronic and transition properties, arising from the difference in lateral dimensions between dome- and semi-spheroid-shaped QDs. Moreover, an analogy is presented between the bound S-states in the quantum dots and a simple 3D quantum mechanical particle in a box, and effective sizes are calculated. The results of this work will benefit researchers to present more realistic models of coupled QD/WL systems and explain their properties more precisely.

  10. Electrotransport of Molybdenum Through an Electrodialysis Membrane. Concentration and Potentiel Profiles in Aqueous Interfacial Layers

    NASA Astrophysics Data System (ADS)

    Lounis, Azzedine; Benmhidi, Kamel

    In the first part we have observed the electrotransport of molybdenum in carbonate media (OH-,CO=3) through a commercial electrodialysis anion exchange membrane. The values of the molybdenum, hydrogen oxide and carbonate fluxes obtained in this study show that molybdenum is present as molybdate ion MoO=4 in carbonate solution and that the molybdyl tricarbonate ion existence hypothesis MoO2(CO3)4-3 an't no longer be maintained. In order to confirm this result we have studied the electrotransport of molybdenum and carbonate ions with different CO=3/MoO=4 ratio. The used theory is based on the fact that, the concentration ratio in the membrane equals the one of the same species within the solution. These hypothesis have to be justified given that this equality is actually usual for unstirred layers extremity. Therefore, in the second part the concentration and the potential profiles in aqueous interfacial layers were determined by a numerical resolution of the Nernst-Planck electrodiffusion equation coupled with the Poisson equation. The obtained concentration profiles from numerical resolution differ from 3 to 6% from the ones acquired by analytical resolution method assuming the constant electrical field hypothesis for OH-, CO=3 ions, respectively. However the potential profiles display that constant electrical field hypothesis is strictly valid.

  11. Interface investigation of the alcohol-/water-soluble conjugated polymer PFN as cathode interfacial layer in organic solar cells

    NASA Astrophysics Data System (ADS)

    Zhong, Shu; Wang, Rui; Ying Mao, Hong; He, Zhicai; Wu, Hongbin; Chen, Wei; Cao, Yong

    2013-09-01

    In this work, in situ ultraviolet photoelectron spectroscopy measurements were used to investigate the working mechanism of an alcohol-/water-soluble conjugated polymer poly [(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) as the cathode interfacial layer in organic solar cells from the view of interfacial energy level alignment. Fullerene (C60) was chosen as the model acceptor material in contact with PFN as well as two other cathode interfacial layers ZnO and TiO2 in the configuration of an inverted solar cell structure. Significant charge transfer between PFN modified ITO (indium tin oxide) electrode and C60 is observed due to the low work function of PFN. This results in the Fermi level of the substrate pinned very close to the lowest unoccupied molecular orbital of C60 as well as an additional electric field at the cathode/acceptor interface. Both of them facilitate the electron extraction from the acceptor C60 to the ITO cathode, as confirmed by the electrical measurements of the electron-only devices with PFN modification. The better electron extraction originated from the Fermi level pinning and the additional interface electric field are believed to contribute to the efficiency enhancement of the inverted organic solar cells employing PFN as cathode interfacial layer.

  12. Probing the Interfacial Interaction in Layered-Carbon-Stabilized Iron Oxide Nanostructures: A Soft X-ray Spectroscopic Study.

    PubMed

    Zhang, Hui; Liu, Jinyin; Zhao, Guanqi; Gao, Yongjun; Tyliszczak, Tolek; Glans, Per-Anders; Guo, Jinghua; Ma, Ding; Sun, Xu-Hui; Zhong, Jun

    2015-04-22

    We have stabilized the iron oxide nanoparticles (NPs) of various sizes on layered carbon materials (Fe-oxide/C) that show excellent catalytic performance. From the characterization of X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES), scanning transmission X-ray microscopy (STXM) and X-ray magnetic circular dichroism spectroscopy (XMCD), a strong interfacial interaction in the Fe-oxide/C hybrids has been observed between the small iron oxide NPs and layered carbon in contrast to the weak interaction in the large iron oxide NPs. The interfacial interaction between the NPs and layered carbon is found to link with the improved catalytic performance. In addition, the Fe L-edge XMCD spectra show that the large iron oxide NPs are mainly γ-Fe2O3 with a strong ferromagnetic property, whereas the small iron oxide NPs with strong interfacial interaction are mainly α-Fe2O3 or amorphous Fe2O3 with a nonmagnetic property. The results strongly suggest that the interfacial interaction plays a key role for the catalytic performance, and the experimental findings may provide guidance toward rational design of high-performance catalysts. PMID:25839786

  13. Investigations of segregation phenomena in highly strained Mn-doped Ge wetting layers and Ge quantum dots embedded in silicon

    SciTech Connect

    Prestat, E. Porret, C.; Favre-Nicolin, V.; Tainoff, D.; Boukhari, M.; Bayle-Guillemaud, P.; Jamet, M.; Barski, A.

    2014-03-10

    In this Letter, we investigate manganese diffusion and the formation of Mn precipitates in highly strained, few monolayer thick, Mn-doped Ge wetting layers and nanometric size Ge quantum dot heterostructures embedded in silicon. We show that in this Ge(Mn)/Si system manganese always precipitates and that the size and the position of Mn clusters (precipitates) depend on the growth temperature. At high growth temperature, manganese strongly diffuses from germanium to silicon, whereas decreasing the growth temperature reduces the manganese diffusion. In the germanium quantum dots layers, Mn precipitates are detected, not only in partially relaxed quantum dots but also in fully strained germanium wetting layers between the dots.

  14. Study of heterostructures with a combined In(Ga)As/GaAs quantum dot/quantum well layer and a Mn δ layer

    SciTech Connect

    Pavlova, E. D. Gorshkov, A. P.; Bobrov, A. I.; Malekhonova, N. V.; Zvonkov, B. N.

    2013-12-15

    Using high-resolution transmission electron microscopy and photoelectric spectroscopy methods, the effect of Mn δ layer embedding and GaAs coating layer growth techniques in structures with In(Ga)As/GaAs quantum dots and wells on their structural and optoelectronic characteristics is studied. It is shown that the low-temperature GaAs coating layer in a structure with a Mn δ layer is structurally inhomogeneous and can cause a decrease in the quantum-dot photosensitivity.

  15. Electrostatically transparent graphene quantum-dot trap layers for efficient nonvolatile memory

    NASA Astrophysics Data System (ADS)

    Kim, Young Rae; Jo, Yong Eun; Shin, Yong Seon; Kang, Won Tae; Sung, Yeo Hyun; Won, Ui Yeon; Lee, Young Hee; Yu, Woo Jong

    2015-03-01

    In this study, we have demonstrated nonvolatile memory devices using graphene quantum-dots (GQDs) trap layers with indium zinc oxide (IZO) semiconductor channel. The Fermi-level of GQD was effectively modulated by tunneling electrons near the Dirac point because of limited density of states and weak electrostatic screening in monolayer graphene. As a result, large gate modulation was driven in IZO channel to achieve a subthreshold swing of 5.21 V/dec (300 nm SiO2 gate insulator), while Au quantum-dots memory shows 15.52 V/dec because of strong electrostatic screening in metal quantum-dots. Together, discrete charge traps of GQDs enable stable performance in the endurance test beyond 800 cycles of programming and erasing. Our study suggests the exciting potential of GQD trap layers to be used for a highly promising material in non-volatile memory devices.

  16. Electrostatically transparent graphene quantum-dot trap layers for efficient nonvolatile memory

    SciTech Connect

    Kim, Young Rae; Jo, Yong Eun; Sung, Yeo Hyun; Won, Ui Yeon; Shin, Yong Seon; Kang, Won Tae; Yu, Woo Jong E-mail: micco21@skku.edu; Lee, Young Hee E-mail: micco21@skku.edu

    2015-03-09

    In this study, we have demonstrated nonvolatile memory devices using graphene quantum-dots (GQDs) trap layers with indium zinc oxide (IZO) semiconductor channel. The Fermi-level of GQD was effectively modulated by tunneling electrons near the Dirac point because of limited density of states and weak electrostatic screening in monolayer graphene. As a result, large gate modulation was driven in IZO channel to achieve a subthreshold swing of 5.21 V/dec (300 nm SiO{sub 2} gate insulator), while Au quantum-dots memory shows 15.52 V/dec because of strong electrostatic screening in metal quantum-dots. Together, discrete charge traps of GQDs enable stable performance in the endurance test beyond 800 cycles of programming and erasing. Our study suggests the exciting potential of GQD trap layers to be used for a highly promising material in non-volatile memory devices.

  17. Highly efficient multiple-layer CdS quantum dot sensitized III-V solar cells.

    PubMed

    Lin, Chien-Chung; Han, Hau-Vei; Chen, Hsin-Chu; Chen, Kuo-Ju; Tsai, Yu-Lin; Lin, Wein-Yi; Kuo, Hao-Chung; Yu, Peichen

    2014-02-01

    In this review, the concept of utilization of solar spectrum in order to increase the solar cell efficiency is discussed. Among the three mechanisms, down-shifting effect is investigated in detail. Organic dye, rare-earth minerals and quantum dots are three most popular down-shift materials. While the enhancement of solar cell efficiency was not clearly observed in the past, the advances in quantum dot fabrication have brought strong response out of the hybrid platform of a quantum dot solar cell. A multiple layer structure, including PDMS as the isolation layer, is proposed and demonstrated. With the help of pulse spray system, precise control can be achieved and the optimized concentration can be found. PMID:24749412

  18. Improvement in Mobility and Stability of n-Type Organic Field-Effect Transistors with a Hole Transporting Interfacial Layer

    NASA Astrophysics Data System (ADS)

    Nakayama, Ken-ichi; Ishikawa, Motomi; Yokoyama, Masaaki

    2009-02-01

    Field-effect electron mobility and stability of N,N'-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8H) improved when a hole-transporting layer, used in organic light-emitting diodes, was inserted between the gate insulator and the channel layer. This result suggests that insertion of an electronically active interfacial layer of an organic semiconductor is more effective in eliminating electron traps of the insulator surface compared to conventional surface treatment to obtain an inert surface.

  19. Effects of interfacial layer structures on crystal structural properties of ZnO films

    SciTech Connect

    Park, J. S.; Minegishi, T.; Lee, S. H.; Im, I. H.; Park, S. H.; Hanada, T.; Goto, T.; Cho, M. W.; Yao, T.; Hong, S. K.; Chang, J. H.

    2008-01-15

    Single crystalline ZnO films were grown on Cr compound buffer layers on (0001) Al{sub 2}O{sub 3} substrates by plasma assisted molecular beam epitaxy. In terms of lattice misfit reduction between ZnO and substrate, the CrN and Cr{sub 2}O{sub 3}/CrN buffers are investigated. The structural and optical qualities of ZnO films suggest the feasibility of Cr compound buffers for high-quality ZnO films growth on (0001) Al{sub 2}O{sub 3} substrates. Moreover, the effects of interfacial structures on selective growth of different polar ZnO films are investigated. Zn-polar ZnO films are grown on the rocksalt CrN buffer and the formation of rhombohedral Cr{sub 2}O{sub 3} results in the growth of O-polar films. The possible mechanism of polarity conversion is proposed. By employing the simple patterning and regrowth procedures, a periodical polarity converted structure in lateral is fabricated. The periodical change of the polarity is clearly confirmed by the polarity sensitive piezo response microscope images and the opposite hysteretic characteristic of the piezo response curves, which are strict evidences for the validity of the polarity controlling method as well as the successful fabrication of the periodical polarity controlled ZnO structure.

  20. Self-Doping, O2-Stable, n-Type Interfacial Layer for Organic Electronics

    SciTech Connect

    Reilly, T. H. III; Hains, A. W.; Chen, H. Y.; Gregg, B. A.

    2012-04-01

    Solid films of a water-soluble dicationic perylene diimide salt, perylene bis(2-ethyltrimethylammonium hydroxide imide), Petma{sup +}OH{sup -}, are strongly doped n-type by dehydration and reversibly de-doped by hydration. The hydrated films consist almost entirely of the neutral perylene diimide, PDI, while the dehydrated films contain {approx}50% PDI anions. The conductivity increases by five orders of magnitude upon dehydration, probably limited by film roughness, while the work function decreases by 0.74 V, consistent with an n-type doping density increase of {approx}12 orders of magnitude. Remarkably, the PDI anions are stable in dry air up to 120 C. The work function of the doped film, {phi} (3.96 V vs. vacuum), is unusually negative for an O{sub 2}-stable contact. Petma{sup +} OH{sup -} is also characterized as an interfacial layer, IFL, in two different types of organic photovoltaic cells. Results are comparable to state of the art cesium carbonate IFLs, but may improve if film morphology can be better controlled. The films are stable and reversible over many months in air and light. The mechanism of this unusual self-doping process may involve the change in relative potentials of the ions in the film caused by their deshielding and compaction as water is removed, leading to charge transfer when dry.

  1. "Supersaturated" self-assembled charge-selective interfacial layers for organic solar cells.

    PubMed

    Song, Charles Kiseok; Luck, Kyle A; Zhou, Nanjia; Zeng, Li; Heitzer, Henry M; Manley, Eric F; Goldman, Samuel; Chen, Lin X; Ratner, Mark A; Bedzyk, Michael J; Chang, Robert P H; Hersam, Mark C; Marks, Tobin J

    2014-12-24

    To achieve densely packed charge-selective organosilane-based interfacial layers (IFLs) on the tin-doped indium oxide (ITO) anodes of organic photovoltaic (OPV) cells, a series of Ar2N-(CH2)n-SiCl3 precursors with Ar = 3,4-difluorophenyl, n = 3, 6, 10, and 18, was synthesized, characterized, and chemisorbed on OPV anodes to serve as IFLs. To minimize lateral nonbonded -NAr2···Ar2N- repulsions which likely limit IFL packing densities in the resulting self-assembled monolayers (SAMs), precursor mixtures having both small and large n values are simultaneously deposited. These "heterogeneous" SAMs are characterized by a battery of techniques: contact angle measurements, X-ray reflectivity, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), cyclic voltammetry, and DFT computation. It is found that the headgroup densities of these "supersaturated" heterogeneous SAMs (SHSAMs) are enhanced by as much as 17% versus their homogeneous counterparts. Supersaturation significantly modifies the IFL properties including the work function (as much as 16%) and areal dipole moment (as much as 49%). Bulk-heterojunction OPV devices are fabricated with these SHSAMs: ITO/IFL/poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][2-[[(2-ethylhexyl)oxy]carbonyl]-3-fluorothieno[3,4-b]thiophenediyl

  2. High performance red-emitting multiple layer InGaN/GaN quantum dot lasers

    NASA Astrophysics Data System (ADS)

    Frost, Thomas; Hazari, Arnab; Aiello, Anthony; Zunaid Baten, Md; Yan, Lifan; Mirecki-Millunchick, Joanna; Bhattacharya, Pallab

    2016-03-01

    InGaN/GaN self-organized quantum dots can provide useful advantages over quantum wells for the realization of long-wavelength visible light sources because the dots are formed by strain relaxation. A III-nitride based laser emitting in the red (λ ˜ 630 nm), which has not been demonstrated with quantum wells, would be useful for a host of applications. We have investigated the epitaxy and characteristics of self-organized InGaN/GaN multiple layer quantum dots grown by plasma-assisted molecular beam epitaxy and have optimized their properties by tuning the growth parameters. Red-emitting (λ ˜ 630 nm) quantum dots have radiative lifetime ˜2.5 ns and internal quantum efficiency greater than 50%. Edge-emitting red-lasers with multi-dot layers in the active region exhibit an extremely low threshold current density of 1.6 kA/cm2, a high temperature coefficient T0 = 240 K, and a large differential gain dg/dn = 9 × 10-17 cm2.

  3. Dithiapyrannylidenes as efficient hole collection interfacial layers in organic solar cells.

    PubMed

    Berny, Stéphane; Tortech, Ludovic; Véber, Michelle; Fichou, Denis

    2010-11-01

    One inherent limitation to the efficiency of photovoltaic solar cells based on polymer/fullerene bulk heterojunctions (BHJs) is the accumulation of positive charges at the anodic interface. The unsymmetrical charge collection of holes and electrons dramatically decreases the short-circuit current. Interfacial layers (IFLs) such as poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) have no effect on the unbalanced electron/hole transport across the BHJ. We report here on the use of dithiapyrannylidenes (DITPY), a new class of planar quinoid compounds, as efficient hole-transporting/electron-blocking layers in organic solar cells based on poly(3-hexylthiophene)/[6,6]-phenyl-C(61)-butyric acid methyl ester (P3HT:PCBM) BHJs. Inserting a 15-nm-thick IFL of 4,4'-bis(diphenyl-2,6-thiapyrannylidene) (DITPY-Ph(4)) between the indium-tin oxide electrode and the P3HT:PCBM BHJ prevents detrimental space-charge effects and favors recombination-limited currents. Current-sensing atomic force microscopy reveals a drastic increase of the hole-carrying pathways in DITPY-Ph(4) compared to PEDOT:PSS. In ambient conditions, photovoltaic cells using DITPY-Ph(4) exhibit an 8% increase in the current density, although the conversion efficiency remains slightly lower compared to PEDOT:PSS-based devices. Finally, we present a detailed analysis of the photocurrent generation, showing that DITPY-Ph(4) IFLs induce a transition from unproductive space-charge-limited currents to recombination-limited currents. PMID:21028838

  4. Improvement in the breakdown endurance of high-κ dielectric by utilizing stacking technology and adding sufficient interfacial layer

    PubMed Central

    2014-01-01

    Improvement in the time-zero dielectric breakdown (TZDB) endurance of metal-oxide-semiconductor (MOS) capacitor with stacking structure of Al/HfO2/SiO2/Si is demonstrated in this work. The misalignment of the conduction paths between two stacking layers is believed to be effective to increase the breakdown field of the devices. Meanwhile, the resistance of the dielectric after breakdown for device with stacking structure would be less than that of without stacking structure due to a higher breakdown field and larger breakdown power. In addition, the role of interfacial layer (IL) in the control of the interface trap density (Dit) and device reliability is also analyzed. Device with a thicker IL introduces a higher breakdown field and also a lower Dit. High-resolution transmission electron microscopy (HRTEM) of the samples with different IL thicknesses is provided to confirm that IL is needed for good interfacial property. PMID:25246869

  5. Selective modulation of charge-carrier transport of a photoanode in a photoelectrochemical cell by a graphitized fullerene interfacial layer.

    PubMed

    Park, Sun-Young; Lim, Dong Chan; Hong, Eun Mi; Lee, Joo-Yeoul; Heo, Jinhee; Lim, Jae Hong; Lee, Chang-Lyoul; Kim, Young Dok; Mul, Guido

    2015-01-01

    We show that a graphitic carbon interfacial layer, derived from C70 by annealing at 500 °C, results in a significant increase in the attainable photocurrent of a photoelectrochemical cell that contains a WO3 -functionalized fluorine-doped tin oxide (FTO) photoanode. Time-resolved photoluminescence spectroscopy, photoconductive atomic force microscopy, Hall measurements, and electrochemical impedance spectroscopy show that the increase in photocurrent is the result of fast and selective electron transport from optically excited WO3 through the graphitic carbon interfacial layer to the FTO-coated glass electrode. Thus the energy efficiency of perspective solar-to-fuel devices can be improved by modification of the interface of semiconductors and conducting substrate electrodes by using graphitized fullerene derivatives. PMID:25410298

  6. Quantum dots protected from oxidative attack using alumina shells synthesized by atomic layer deposition.

    PubMed

    Yin, B; Sadtler, B; Berezin, M Y; Thimsen, E

    2016-09-25

    Applications of luminescent quantum dots require the materials to be stable under a wide range of temperatures, photon fluxes and chemical environments. In this work, we demonstrate that Al2O3 shells synthesized by atomic layer deposition on films of CdTe quantum dots are effective to prevent chemical degradation for up to 17 hours under continuous illumination at 90 °C in ambient air. Control samples with no Al2O3 coating experienced extensive oxidation and severe quenching of the photoluminescence intensity under these conditions. PMID:27550790

  7. Interfacial Layer Growth Condition Dependent Electrical Conduction in HfO2/SiO2 Heterostructured Thin Films

    SciTech Connect

    Sahoo, S. K.; Misra, D.

    2012-01-01

    The electrical conduction mechanism contributing to the leakage current at different field regions has been studied in this work. The current-voltage (I-V) measurement of TiN/HfO{sub 2}/SiO{sub 2}/P-Si nMOS capacitor has been taken for two different interfacial layer (SiO{sub 2}) growth conditions such as in situ steam grown (ISSG) and chemical processes. It is observed that Poole-Frenkel mechanism is the dominant conduction mechanism in high field region whereas Ohmic conduction is dominant in the low field region. Also it is seen that the gate leakage current is reduced for the devices having chemically grown interfacial layer compared to that of ISSG devices. Both trap energy level ({phi}{sub t}) and activation energy (E{sub a}) increase in the chemically grown interfacial layer devices for the Poole-Frenkel and Ohmic conduction mechanisms respectively in comparison to ISSG devices. Trap energy level ({phi}{sub t}) of {approx} 0.2 eV, obtained from Poole-Frenkel mechanism indicates that the doubly ionized oxygen vacancies (V{sup 2-}) are the active defects and are contributing to the leakage current in these devices.

  8. Distinction between interfacial layer effect and trap passivation effect of N2 plasma treatment on LTPS-TFTs

    NASA Astrophysics Data System (ADS)

    Ma, William Cheng-Yu

    2014-10-01

    In this paper, N2 plasma surface treatment on high performance low-temperature poly-Si thin-film transistors (LTPS-TFTs) with HfO2 gate dielectric is demonstrated. A significant performance improvement by N2 plasma surface treatment is observed, including the threshold voltage VTH reduction ∼ -0.94 V, subthreshold swing S.S. improvement from 0.227 V/dec. to 0.188 V/dec., field effect mobility μFE enhancement ∼ +61% and driving current Idrv enhancement ∼ +95%. The individual impacts of interfacial layer growth effect and trap passivation effect of poly-Si channel film are investigated by the plasma induced interfacial layer (PIL) removal process. The results show that the PIL growth effect has more contribution to the improvement of VTH reduction and Idrv enhancement than the trap passivation effect of poly-Si channel film. Consequently, the interfacial layer engineering would be very important for the development of high performance LTPS-TFTs.

  9. Enhanced Electron Extraction Capability of Polymer Solar Cells via Employing Electrostatically Self-Assembled Molecule on Cathode Interfacial Layer.

    PubMed

    Li, Zhiqi; Zhang, Xinyuan; Liu, Chunyu; Zhang, Zhihui; Li, Jinfeng; Shen, Liang; Guo, Wenbin; Ruan, Shengping

    2016-03-01

    In this paper, high-performance inverted polymer solar cells (PSCs) with a modified cathode buffer layer, titanium dioxide:polyethylenimine (TiO2:PEI), are demonstrated. The TiO2-O-PEI transport layer was fabricated by electrostatically self-assembled monolayers (ESAM) of PEI molecules. Protonated amine functional groups of PEI can combine protons (H(+)) hydrolyzing from its aqueous solution. Also, PEI could produce ESAM on the surface of hydroxylated TiO2 because of its cationic characteristics. The incorporation of the TiO2-O-PEI layer enhances the photocurrent and power conversion efficiency (PCE) due to the improved interfacial electron transport and extraction of the TiO2-O-PEI surface and the increased light absorption of the active layer. The enhanced PCE, low-cost materials, and solution process of TiO2-O-PEI buffer layers provide a promising method for highly efficient PSCs. PMID:26955888

  10. Ab Initio study of multiple exciton generation in layered structure quantum dots

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiyong; Zimmerman, Paul; Cui, Yi; Musgrave, Charles

    2011-03-01

    Multiple Exciton Generation (MEG) can potentially increase the photovoltaic conversion efficiency significantly and has been reported in a large number of systems and has been extensively studies theoretically and experimentally. Here we report our study of the MEG process in inorganic layered structure quantum dots using high level Ab Initio methods that are capable of electronic states of multi-exciton in character. Our results show that multiple states that are of multi-exciton character exist in quantum dots and different mechanisms govern the MEG process in quantum dots: (1) MEG through an internal crossing mechanism from a optically active state to an optically dark multi-exciton state, as in the singlet fission process of pentacene; and (2) direct multi-exciton generation through an optically active excited state. We also discuss detailed structure evolution of quantum dots, from stable molecular like structures of various shapes and sizes, to larger quantum dots of bulk like bonding motifs with distinctive surface structures and illustrate the correlation between structure and the multi-exciton states.

  11. The doping of the polyimide alignment layer by semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Konshina, E. A.; Galin, I. F.; Gavrish, E. O.; Vakulin, D. A.

    2013-08-01

    We investigated the electro-optic properties of nematic liquid crystal cells oriented by polyimide (PI) layer doped with 3.5 nm semiconductor quantum dots (QDs) CdSe/ZnS at concentrations of 0.05 and 0.1 wt. %. It is shown that doping PI orienting layer by QDs reduces the permittivity and the phase delay, as well as increases the electrical resistance of the cells. Also we observed deceleration of liquid crystal (LC) optical response caused by the screening effect of the orienting layer.

  12. Bound to continuum intersubband transition optical properties in the strain reducing layer-assisted InAs quantum dot structure

    NASA Astrophysics Data System (ADS)

    Parvizi, R.; Rezaei, G.

    2016-01-01

    In this paper, the impact of wetting layer, strain reducing layer and dot height on the electronic, linear and nonlinear optical properties of bound to continuum states transitions are investigated in a system of InAs truncated conical shaped quantum dot covered with the InxGa1-x As strain reducing layer. The electronic structure, containing two main states of S and wetting layer states (WL), was calculated by solving one electronic band Hamiltonian with effective-mass approximation. The results reveal that the presence of the strain reducing layer in the structure extends the quantum dot emission to longer wavelength which is reported as a red-shift of the photoluminescence (PL) peak in the experimental measurement. This study also highlights the possibility of improving the intersubband optical properties based on the significant size-dependence of the three layer dot matrix by employing the strain reducing and wetting layers. According to this simulation, relatively tall dots on the thick wetting layer introduce the optimized structure size for practical applications to meet the SRL assisted enhanced dot structure.

  13. Optical and electronic properties of layer-by-layer and composite polyaniline-cadmium selenide quantum dot films

    NASA Astrophysics Data System (ADS)

    Ayub, Ambreen; Shakoor, Abdul; Elahi, Asmat; Rizvi, Tasneem Zahra

    2015-08-01

    Two organic-inorganic hybrid films of intrinsically conducting polymer; polyaniline and cadmium selenide quantum dots were prepared. One by layer-by-layer deposition of polyaniline and cadmium selenide films on PEDOT-PSS/ITO coated glass substrate (ITO/PEDOT-PSS/PANI/CdSe) and other by depositing polyaniline-cadmium selenide quantum dots composite film on the same substrate (ITO/PEDOT-PSS/PANI-CdSe) using spin coating technique. Pure polyaniline, cadmium selenide quantum dots and their composites thus obtained were characterized using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and UV/VIS/NIR absorption spectroscopy. The surface morphologies were studied by Scanning Electron Microscopy (SEM). The diode performance parameters were compared and contrasted for the two devices obtained by different deposition routes. J-V characteristics of these devices showed a rectifying contact with Al metal, however with variation in performance parameters like barrier height, ideality factor and reverse saturation current the ITO/PEDOT-PSS/PANI-CdSe/Al device exhibited better diode performance as compared to ITO/PEDOT-PSS/PANI/CdSe/Al device.

  14. The interfacial amorphous double layer and the homogeneous nucleation in reflow of a Sn-Zn solder on Cu substrate

    SciTech Connect

    Pan, Chien-Cheng; Lin, Kwang-Lung

    2011-05-15

    To illustrate the interfacial reaction mechanism, the Sn-Zn[Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga (wt%)] solder was reflowed on Cu substrate at 250 deg. C for 15 s followed by immediate quench in liquid nitrogen. The frozen interfacial microstructure was investigated with high resolution transmission electron microscope. An amorphous double layer was formed at the interface which consists of a 5 nm pure Cu region and a Cu-Zn diffusion region. Nanocrystalline intermetallic compound (IMC) Cu{sub 5}Zn{sub 8} were observed in the Cu-Zn diffusion region. These nanocrystalline IMCs are suggested to form via a homogeneous nucleation process.

  15. The interfacial amorphous double layer and the homogeneous nucleation in reflow of a Sn-Zn solder on Cu substrate

    NASA Astrophysics Data System (ADS)

    Pan, Chien-Cheng; Lin, Kwang-Lung

    2011-05-01

    To illustrate the interfacial reaction mechanism, the Sn-Zn[Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga (wt%)] solder was reflowed on Cu substrate at 250 °C for 15 s followed by immediate quench in liquid nitrogen. The frozen interfacial microstructure was investigated with high resolution transmission electron microscope. An amorphous double layer was formed at the interface which consists of a 5 nm pure Cu region and a Cu-Zn diffusion region. Nanocrystalline intermetallic compound (IMC) Cu5Zn8 were observed in the Cu-Zn diffusion region. These nanocrystalline IMCs are suggested to form via a homogeneous nucleation process.

  16. GaN as an interfacial passivation layer: tuning band offset and removing fermi level pinning for III-V MOS devices.

    PubMed

    Zhang, Zhaofu; Cao, Ruyue; Wang, Changhong; Li, Hao-Bo; Dong, Hong; Wang, Wei-Hua; Lu, Feng; Cheng, Yahui; Xie, Xinjian; Liu, Hui; Cho, Kyeongjae; Wallace, Robert; Wang, Weichao

    2015-03-11

    The use of an interfacial passivation layer is one important strategy for achieving a high quality interface between high-k and III-V materials integrated into high-mobility metal-oxide-semiconductor field-effect transistor (MOSFET) devices. Here, we propose gallium nitride (GaN) as the interfacial layer between III-V materials and hafnium oxide (HfO2). Utilizing first-principles calculations, we explore the structural and electronic properties of the GaN/HfO2 interface with respect to the interfacial oxygen contents. In the O-rich condition, an O8 interface (eight oxygen atoms at the interface, corresponding to 100% oxygen concentration) displays the most stability. By reducing the interfacial O concentration from 100 to 25%, we find that the interface formation energy increases; when sublayer oxygen vacancies exist, the interface becomes even less stable compared with O8. The band offset is also observed to be highly dependent on the interfacial oxygen concentration. Further analysis of the electronic structure shows that no interface states are present at the O8 interface. These findings indicate that the O8 interface serves as a promising candidate for high quality III-V MOS devices. Moreover, interfacial states are present when such interfacial oxygen is partially removed. The interface states, leading to Fermi level pinning, originate from unsaturated interfacial Ga atoms. PMID:25639492

  17. Controlling Interfacial Reactions and Intermetallic Compound Growth at the Interface of a Lead-free Solder Joint with Layer-by-Layer Transferred Graphene.

    PubMed

    Ko, Yong-Ho; Lee, Jong-Dae; Yoon, Taeshik; Lee, Chang-Woo; Kim, Taek-Soo

    2016-03-01

    The immoderate growth of intermetallic compounds (IMCs) formed at the interface of a solder metal and the substrate during soldering can degrade the mechanical properties and reliability of a solder joint in electronic packaging. Therefore, it is critical to control IMC growth at the solder joints between the solder and the substrate. In this study, we investigated the control of interfacial reactions and IMC growth by the layer-by-layer transfer of graphene during the reflow process at the interface between Sn-3.0Ag-0.5Cu (in wt %) lead-free solder and Cu. As the number of graphene layers transferred onto the surface of the Cu substrate increased, the thickness of the total IMC (Cu6Sn5 and Cu3Sn) layer decreased. After 10 repetitions of the reflow process for 50 s above 217 °C, the melting temperature of Sn-3.0Ag-0.5Cu, with a peak temperature of 250 °C, the increase in thickness of the total IMC layer at the interface with multiple layers of graphene was decreased by more than 20% compared to that at the interface of bare Cu without graphene. Furthermore, the average diameter of the Cu6Sn5 scallops at the interface with multiple layers of graphene was smaller than that at the interface without graphene. Despite 10 repetitions of the reflow process, the growth of Cu3Sn at the interface with multiple layers of graphene was suppressed by more than 20% compared with that at the interface without graphene. The multiple layers of graphene at the interface between the solder metal and the Cu substrate hindered the diffusion of Cu atoms from the Cu substrate and suppressed the reactions between Cu and Sn in the solder. Thus, the multiple layers of graphene transferred at the interface between dissimilar metals can control the interfacial reaction and IMC growth occurring at the joining interface. PMID:26856638

  18. The coupling of interfacial instabilities and the stabilization of two-layer annular flows

    NASA Technical Reports Server (NTRS)

    Dijkstra, Henk A.

    1992-01-01

    In this paper the stability of annular pressure-driven parallel flows of two liquids sandwiching a free cylindrical interface is considered. For small to moderate Reynolds numbers, the interface is susceptible to capillary and interfacial wave instabilities, the latter instability caused by a jump in viscosity at the interface. It is shown that favorable velocity profiles in both liquids may stabilize capillary breakup of the interface and suppress the axisymmetric interfacial wave instability. A long-wave analysis leads to the physical mechanism responsible for stabilization of capillary breakup. This physical mechanism is a generalization of that by which capillary breakup is stabilized by interfacial shear in an annular film of a single liquid. Stabilization of intermediate wavelengths is studied with a mechanical energy analysis, which leads to a description of the energetic processes at work.

  19. Improved Gate Dielectric Deposition and Enhanced Electrical Stability for Single-Layer MoS2 MOSFET with an AlN Interfacial Layer

    PubMed Central

    Qian, Qingkai; Li, Baikui; Hua, Mengyuan; Zhang, Zhaofu; Lan, Feifei; Xu, Yongkuan; Yan, Ruyue; Chen, Kevin J.

    2016-01-01

    Transistors based on MoS2 and other TMDs have been widely studied. The dangling-bond free surface of MoS2 has made the deposition of high-quality high-k dielectrics on MoS2 a challenge. The resulted transistors often suffer from the threshold voltage instability induced by the high density traps near MoS2/dielectric interface or inside the gate dielectric, which is detrimental for the practical applications of MoS2 metal-oxide-semiconductor field-effect transistor (MOSFET). In this work, by using AlN deposited by plasma enhanced atomic layer deposition (PEALD) as an interfacial layer, top-gate dielectrics as thin as 6 nm for single-layer MoS2 transistors are demonstrated. The AlN interfacial layer not only promotes the conformal deposition of high-quality Al2O3 on the dangling-bond free MoS2, but also greatly enhances the electrical stability of the MoS2 transistors. Very small hysteresis (ΔVth) is observed even at large gate biases and high temperatures. The transistor also exhibits a low level of flicker noise, which clearly originates from the Hooge mobility fluctuation instead of the carrier number fluctuation. The observed superior electrical stability of MoS2 transistor is attributed to the low border trap density of the AlN interfacial layer, as well as the small gate leakage and high dielectric strength of AlN/Al2O3 dielectric stack. PMID:27279454

  20. Improved Gate Dielectric Deposition and Enhanced Electrical Stability for Single-Layer MoS2 MOSFET with an AlN Interfacial Layer.

    PubMed

    Qian, Qingkai; Li, Baikui; Hua, Mengyuan; Zhang, Zhaofu; Lan, Feifei; Xu, Yongkuan; Yan, Ruyue; Chen, Kevin J

    2016-01-01

    Transistors based on MoS2 and other TMDs have been widely studied. The dangling-bond free surface of MoS2 has made the deposition of high-quality high-k dielectrics on MoS2 a challenge. The resulted transistors often suffer from the threshold voltage instability induced by the high density traps near MoS2/dielectric interface or inside the gate dielectric, which is detrimental for the practical applications of MoS2 metal-oxide-semiconductor field-effect transistor (MOSFET). In this work, by using AlN deposited by plasma enhanced atomic layer deposition (PEALD) as an interfacial layer, top-gate dielectrics as thin as 6 nm for single-layer MoS2 transistors are demonstrated. The AlN interfacial layer not only promotes the conformal deposition of high-quality Al2O3 on the dangling-bond free MoS2, but also greatly enhances the electrical stability of the MoS2 transistors. Very small hysteresis (ΔVth) is observed even at large gate biases and high temperatures. The transistor also exhibits a low level of flicker noise, which clearly originates from the Hooge mobility fluctuation instead of the carrier number fluctuation. The observed superior electrical stability of MoS2 transistor is attributed to the low border trap density of the AlN interfacial layer, as well as the small gate leakage and high dielectric strength of AlN/Al2O3 dielectric stack. PMID:27279454

  1. Improved Gate Dielectric Deposition and Enhanced Electrical Stability for Single-Layer MoS2 MOSFET with an AlN Interfacial Layer

    NASA Astrophysics Data System (ADS)

    Qian, Qingkai; Li, Baikui; Hua, Mengyuan; Zhang, Zhaofu; Lan, Feifei; Xu, Yongkuan; Yan, Ruyue; Chen, Kevin J.

    2016-06-01

    Transistors based on MoS2 and other TMDs have been widely studied. The dangling-bond free surface of MoS2 has made the deposition of high-quality high-k dielectrics on MoS2 a challenge. The resulted transistors often suffer from the threshold voltage instability induced by the high density traps near MoS2/dielectric interface or inside the gate dielectric, which is detrimental for the practical applications of MoS2 metal-oxide-semiconductor field-effect transistor (MOSFET). In this work, by using AlN deposited by plasma enhanced atomic layer deposition (PEALD) as an interfacial layer, top-gate dielectrics as thin as 6 nm for single-layer MoS2 transistors are demonstrated. The AlN interfacial layer not only promotes the conformal deposition of high-quality Al2O3 on the dangling-bond free MoS2, but also greatly enhances the electrical stability of the MoS2 transistors. Very small hysteresis (ΔVth) is observed even at large gate biases and high temperatures. The transistor also exhibits a low level of flicker noise, which clearly originates from the Hooge mobility fluctuation instead of the carrier number fluctuation. The observed superior electrical stability of MoS2 transistor is attributed to the low border trap density of the AlN interfacial layer, as well as the small gate leakage and high dielectric strength of AlN/Al2O3 dielectric stack.

  2. Production of three-dimensional quantum dot lattice of Ge/Si core-shell quantum dots and Si/Ge layers in an alumina glass matrix.

    PubMed

    Buljan, M; Radić, N; Sancho-Paramon, J; Janicki, V; Grenzer, J; Bogdanović-Radović, I; Siketić, Z; Ivanda, M; Utrobičić, A; Hübner, R; Weidauer, R; Valeš, V; Endres, J; Car, T; Jerčinović, M; Roško, J; Bernstorff, S; Holy, V

    2015-02-13

    We report on the formation of Ge/Si quantum dots with core/shell structure that are arranged in a three-dimensional body centered tetragonal quantum dot lattice in an amorphous alumina matrix. The material is prepared by magnetron sputtering deposition of Al2O3/Ge/Si multilayer. The inversion of Ge and Si in the deposition sequence results in the formation of thin Si/Ge layers instead of the dots. Both materials show an atomically sharp interface between the Ge and Si parts of the dots and layers. They have an amorphous internal structure that can be crystallized by an annealing treatment. The light absorption properties of these complex materials are significantly different compared to films that form quantum dot lattices of the pure Ge, Si or a solid solution of GeSi. They show a strong narrow absorption peak that characterizes a type II confinement in accordance with theoretical predictions. The prepared materials are promising for application in quantum dot solar cells. PMID:25605224

  3. Effects of the interfacial layer on electrical characteristics of Al 2O 3/TiO 2/Al 2O 3 thin films for gate dielectrics

    NASA Astrophysics Data System (ADS)

    Kim, Chang Eun; Yun, Ilgu

    2012-01-01

    Effects of thermal annealing on the electrical properties of Al2O3/TiO2/Al2O3 (ATA) dielectric thin films prepared by atomic layer deposition are investigated. The structural properties and chemical states in the interfacial layer are analyzed with varying the annealing temperature. The dielectric constant and leakage current are affected by the formation of Al2O3-TiO2 composite and interfacial layer including SiOx in the interface by the annealing. The transformation of interfacial layer at the interface of the ATA/Si substrate due to the annealing is a critical point to apply ATA thin films as gate dielectric layers.

  4. Quality improvements of ZnxCdyMg1-x-ySe layers grown on InP substrates by a thin ZnCdSe interfacial layer

    NASA Astrophysics Data System (ADS)

    Zeng, L.; Yang, B. X.; Tamargo, M. C.; Snoeks, E.; Zhao, L.

    1998-03-01

    The quality of lattice-matched ZnxCdyMg1-x-ySe epitaxial layers grown on (001) InP substrates with a III-V buffer layer has been improved by initially growing a ZnCdSe interfacial layer (50 Å) at low temperature. The widths of double crystal x-ray rocking curves for ZnxCdyMg1-x-ySe epilayers with band gaps as high as 3.05 eV were reduced to about 70 arcsec. The defect density evaluated from etch pit density and plan-view transmission electron microscopy measurements was reduced by two orders of magnitude, to 106-107cm-2. The photoluminescence band edge emission became more symmetric and slightly narrower. It is proposed that an initial two-dimensional growth mode has been achieved by incorporating such a lattice-matched ZnCdSe layer.

  5. High efficiency and high photo-stability zinc-phthalocyanine based planar heterojunction solar cells with a double interfacial layer

    NASA Astrophysics Data System (ADS)

    Kim, Tae-Min; Whan Kim, Ji; Shim, Hyun-Sub; Kim, Jang-Joo

    2012-09-01

    The use of CuI and MoO3 as a double interfacial layer between indium tin oxide (ITO) and a zinc phthalocyanine (ZnPc) layer improves the power conversion efficiency (ηp) and the photo-stability at the same time in ZnPc based solar cells. Insertion of CuI without MoO3 increased ηp more than 2 times to 3.3%. However, the photo-stability is lowered even further due to diffusion of Cu. Insertion of the MoO3 layer between the ITO and CuI prevents the diffusion of Cu under UV illumination to achieve the improved photo-stability and ηp.

  6. Graded composite diamond coatings with top-layer nanocrystallinity and interfacial integrity: Cross-sectional Raman mapping

    NASA Astrophysics Data System (ADS)

    Dumpala, Ravikumar; Ramamoorthy, B.; Rao, M. S. Ramachandra

    2014-01-01

    Cross-sectional structural characteristics of the CVD diamond coatings deposited on the tungsten carbide (WC-Co) substrates were analysed using Raman imaging technique. The grain size of the nanocrystalline diamond (NCD) coatings was observed to deviate from the nanocrystallinity with increasing thickness and exhibited the surface characteristics of microcrystalline diamond (MCD). However, thick diamond coatings with surface nanocrystallinity is the key requirement for load-bearing tribological applications. Tribological tests have clearly indicated the significance and need for the top-layer nanocrystallinity. Graded composite diamond coatings with an architecture of NCD/transition-layer/MCD/WC-Co are potentail candiadates to realize thick diamond coatings with top-layer nanocrystallinity. Residual stresses along the cross-section of the graded composite diamond coatings were analysed using Raman imaging technique, which confirmed the improved interfacial integrity of the graded composite diamond coatings

  7. Interfacial quality improvement of Cu(In,Ga)Se2 thin film solar cells by Cu-depletion layer formation

    NASA Astrophysics Data System (ADS)

    Nishimura, Takahito; Toki, Soma; Sugiura, Hiroki; Nakada, Kazuyoshi; Yamada, Akira

    2016-09-01

    Se irradiation with time, t Se, was introduced after the second stage of a three-stage process to control the Cu2Se layer during Cu(In,Ga)Se2 (CIGS) deposition. Open circuit voltage and fill factor of CIGS solar cells could be improved by introducing Se irradiation. We concluded that the control of the Cu2Se layer led to the formation of a Cu-depletion CIGS layer (CDL), which improved conversion efficiency owing to suppression of interfacial recombination by a valence band offset formed between CIGS and the CDL. Finally, highest efficiency of 19.8% was achieved with t Se of 5 min. This very simple and new technique is promising for the improvement of photovoltaic performance.

  8. Nonlinear switching in Al/Li:NiO/ITO forming-free resistive memories caused by interfacial layer

    NASA Astrophysics Data System (ADS)

    Yuan, Xin-Cai; Wei, Xian-Hua; Dai, Bo; Zeng, Hui-Zhong

    2016-01-01

    Nonlinear bipolar resistive switching (BRS) of Al/NiO/ITO without forming is demonstrated in this paper. Compared with the linear BRS needing forming, the forming-free nonlinear BRS can be operated using a smaller current about two orders at a smaller switching voltage in the same device. Different from the Joule heating mechanism of the linear BRS behavior after forming, the conduction of the nonlinear BRS is dominated by oxygen vacancy drift induced by electric field across the interface between metal Al, NiO film, and conducting ITO, in which Al/NiO interfacial layer and ITO act as a dual-oxygen reservoir. Furthermore, the doping of Li into NiO layer improves switching properties such as the ON/OFF ratio and reproducibility due to the increase of oxygen vacancy. The results imply that forming-free nonlinear BRS of binary oxides caused by interface layer is feasible in similar dual-oxygen reservoir structure.

  9. Effects of Strain and Buffer Layer on Interfacial Magnetization in Sr2CrReO6 Films

    NASA Astrophysics Data System (ADS)

    Liu, Yaohua; Te Velthuis, S. G. E.; Glavic, A.; Ambaye, H.; Lauter, V.; Lucy, J. M.; Yang, F. Y.

    2015-03-01

    Magnetic double-perovskite Sr2CrReO6 (SCRO) has several functional properties including a TC > 500 K, high spin polarization, large spin-orbit interaction, and semiconducting behavior in highly ordered films. However, fabrication of highly ordered films is still challenging, and progress toward device applications requires an in-depth understanding of the electronic and magnetic properties, especially at interfaces. We have investigated how the Cr/Re antisite disorder and strain affect the interfacial magnetization in SCRO films via x-ray and polarized neutron reflectometry. We find that the magnetization of SCRO films is reduced near the interface with the substrate. The width of this interfacial layer weakly depends on the strain and decreases when a SrCr0.5Nb0.5O3 (SCNO) buffer layer is used to reduce the antisite disorder. Interestingly, for the SCRO film deposited on a SCNO buffer layer, the region with reduced magnetization is wider than the antisite disorder region at the SCRO/SCNO interface, suggesting that antisite disorder is not the only mechanism reducing the magnetization. Work at ANL was supported by the DOE-BES, MSE, at OSU by the Center for Emergent Materials, a NSF MRSEC (DMR-1420451), at ORNL by DOE-BES, Scientific User Facilities Division.

  10. UV-treated graphene oxide as anode interfacial layers for P3HT : PCBM solar cells

    NASA Astrophysics Data System (ADS)

    Cheng, Cheng-En; Tsai, Cheng-Wei; Pei, Zingway; Lin, Tsung-Wu; Chang, Chen-Shiung; Shih-Sen Chien, Forest

    2015-06-01

    Solution-processable graphene oxide (GO) ultrathin films were introduced as anode interfacial layers (AILs) for polymer solar cells (PSCs). The photovoltaic performance of PSCs containing thermal- and UV-treated GO was comparable to that of PSCs with conventional poly(3,4-ethyledioxythiphene):poly(styrenesulfonate) AILs. UV treatment induced the surface activation of GO; an increase in the work function of UV-treated GO improved the energy band alignment at the GO/poly(3-hexylthiophene) interface, which accounted for the efficient hole collection and photovoltaic performance of PSCs with treated GO.

  11. Impact of Gd2O3 passivation layer on interfacial and electrical properties of atomic-layer-deposited ZrO2 gate dielectric on GaAs

    NASA Astrophysics Data System (ADS)

    Gong, Youpin; Zhai, Haifa; Liu, Xiaojie; Kong, Jizhou; Wu, Di; Li, Aidong

    2014-02-01

    ZrO2 gate dielectric films were fabricated on n-GaAs substrates by atomic layer deposition (ALD), using metal organic chemical vapor deposition (MOCVD)-derived ultrathin Gd2O3 film as interfacial control layer between ZrO2 and n-GaAs. The interfacial structure, capacitance-voltage and current-voltage properties of ZrO2/n-GaAs and ZrO2/Gd2O3/n-GaAs metal-oxide-semiconductor (MOS) capacitors have been investigated. The introduction of an ultrathin Gd2O3 control layer can effectively suppress the formation of As oxides and high valence Ga oxide at the high k/GaAs interface which evidently improved the electrical properties of GaAs-based MOS capacitors, such as higher accumulation capacitance and lower leakage current density. It was found that the current conduction mechanism of MOS capacitors varied from Poole-Frenkel emission to Schottky-Richardson emission after introducing the thin Gd2O3 layer. The band alignments of interfaces for ZrO2/GaAs and ZrO2/Gd2O3/GaAs were established, which indicates that the conduction band offset (CBO) for ZrO2/GaAs and ZrO2/Gd2O3/GaAs stacks are ˜1.45 and ˜1.62 eV, correspondingly.

  12. Surface-Engineered Graphene Quantum Dots Incorporated into Polymer Layers for High Performance Organic Photovoltaics

    PubMed Central

    Kim, Jung Kyu; Kim, Sang Jin; Park, Myung Jin; Bae, Sukang; Cho, Sung-Pyo; Du, Qing Guo; Wang, Dong Hwan; Park, Jong Hyeok; Hong, Byung Hee

    2015-01-01

    Graphene quantum dots (GQDs), a newly emerging 0-dimensional graphene based material, have been widely exploited in optoelectronic devices due to their tunable optical and electronic properties depending on their functional groups. Moreover, the dispersibility of GQDs in common solvents depending on hydrophobicity or hydrophilicity can be controlled by chemical functionalization, which is particularly important for homogeneous incorporation into various polymer layers. Here we report that a surface-engineered GQD-incorporated polymer photovoltaic device shows enhanced power conversion efficiency (PCE), where the oxygen-related functionalization of GQDs enabled good dispersity in a PEDOT:PSS hole extraction layer, leading to significantly improved short circuit current density (Jsc) value. To maximize the PCE of the device, hydrophobic GQDs that are hydrothermally reduced (rGQD) were additionally incorporated in a bulk-heterojunction layer, which is found to promote a synergistic effect with the GQD-incorporated hole extraction layer. PMID:26392211

  13. Improvement of Electrical Properties of Silicon Quantum Dot Superlattice Solar Cells with Diffusion Barrier Layers

    NASA Astrophysics Data System (ADS)

    Yamada, Shigeru; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Konagai, Makoto

    2013-04-01

    We investigate the effects of a niobium-doped titanium dioxide (TiO2:Nb) diffusion barrier layer on the performance of silicon quantum dot superlattice (Si-QDSL) solar cells. The insertion of a 2-nm-thick TiO2:Nb layer significantly reduces phosphorus diffusion from a highly doped n-type layer into a Si-QDSL layer during thermal annealing at 900 °C. The phosphorous concentration in the Si-QDSL layer of the solar cell with the TiO2:Nb diffusion barrier layer was found to be less than 1018 cm-3, which is approximately two orders of magnitude lower than that of the solar cell without the diffusion barrier layer. The reduction in phosphorous concentration leads to the improvement of photo-generated carrier collection in the Si-QDSL layer. The short circuit current density of the solar cell with the diffusion barrier layer was dramatically improved to 1.6 mA/cm2 without the degradation of open circuit voltage and fill factor.

  14. Multi-color colloidal quantum dot based light emitting diodes micropatterned on silicon hole transporting layers

    NASA Astrophysics Data System (ADS)

    Gopal, Ashwini; Hoshino, Kazunori; Kim, Sunmin; Zhang, Xiaojing

    2009-06-01

    We present a colloidal quantum dot based light emitting diode (QD-LED) which utilizes the p-type silicon substrate as the hole transporting layer. A microcontact printing technique was introduced to pattern self-assembled CdSe/ZnS QD films, which allowed creation of an LED with well-defined geometry suitable for monolithic integration on silicon substrates. Our QD-LED consists of multi-layers of inorganic materials: a combination of Au (thickness: 5 nm) and Ag (12 nm) as the cathode, a ZnO:SnO2 mixture (ratio 3:1, 40 nm) as the electron transporting layer, CdSe/ZnS QDs as the light emission layer, 1 nm SiO2 as an energy barrier layer, and p-type silicon as the hole transporting layer. These printed QD-LEDs are capable of multi-color emission peaked at wavelengths of 576 nm, 598 nm, and 622 nm, corresponding to sizes of the embedded QDs with the diameters of 8.4 nm, 9.0 nm, and 9.8 nm respectively. The optimal thickness of the quantum dot layers needed for light emission is characterized using atomic force microscopy: for 8.4 nm QDs, the value is 33 nm (± 5 nm) or ~4 ML (monolayers). Larger turn on voltages were measured (2, 4 and 5 V) for the smaller average particle diameters (9.8 nm, 9.0 nm and 8.4 nm, respectively). The mixture ratio of Zn and Sn was optimized (40% Zn and 25% Sn) to maintain proper hole-electron recombination at the QD layer and avoid the yellowish-white emission from ZnO/SnO2.

  15. The micropatterning of layers of colloidal quantum dots with inorganic ligands using selective wet etching.

    PubMed

    Hu, Chen; Aubert, Tangi; Justo, Yolanda; Flamee, Stijn; Cirillo, Marco; Gassenq, Alban; Drobchak, Oksana; Beunis, Filip; Roelkens, Günther; Hens, Zeger

    2014-05-01

    The micropatterning of layers of colloidal quantum dots (QDs) stabilized by inorganic ligands is demonstrated using PbS core and CdSe/CdS core/shell QDs. A layer-by-layer approach is used to assemble the QD films, where each cycle involves the deposition of a QD layer by dip-coating, and the replacement of the native organic ligands by inorganic moieties, such as OH(-) and S(2-), followed by a thorough cleaning of the resulting film. This results in a smooth and crack-free QD film on which a photoresist can be spun. The micropatterns are defined by a positive photoresist, followed by the removal of uncovered QDs by selective wet etching with an HCl/H3PO4 mixture. The resulting patterns can have submicron feature dimensions, limited by the resolution of the lithographic process, and can be formed on planar and 3D substrates. It is shown that the photolithography and wet etching steps have little effect on the photoluminescence quantum yield of CdSe/CdS QDs. Compared with the unpatterned CdSe/CdS QD film, only a 10% degradation in the quantum yield is observed. These results demonstrate the feasibility of the proposed micropatterning method to implement the large-scale device integration of colloidal quantum dots. PMID:24722007

  16. Linearity optimization of atomic layer deposited ZrO2 metal-insulator-metal capacitors by inserting interfacial Zr-doped chromia layers

    NASA Astrophysics Data System (ADS)

    Lutzer, B.; Simsek, S.; Zimmermann, C.; Stoeger-Pollach, M.; Bethge, O.; Bertagnolli, E.

    2016-03-01

    In order to improve the electrical behaviour of metal-insulator-metal capacitors with ZrO2 insulator grown by Atomic Layer Deposition, the influence of the insertion of interfacial Cr layers between Pt electrodes and the zirconia is investigated. An improvement of the α-voltage coefficient of capacitance as low as 567 ppm/V2 is achieved for a single layer of Cr while maintaining a high capacitance density of 10.7 fF/μm2 and a leakage current of less than 1.2 × 10-8 A/cm2 at +1 V. The role of the interface is discussed by means of X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy showing the formation of Zr stabilized chromia oxide phase with a dielectric constant of 16.

  17. Ultrathin ZnS and ZnO Interfacial Passivation Layers for Atomic-Layer-Deposited HfO2 Films on InP Substrates.

    PubMed

    Kim, Seung Hyun; Joo, So Yeong; Jin, Hyun Soo; Kim, Woo-Byoung; Park, Tae Joo

    2016-08-17

    Ultrathin ZnS and ZnO films grown by atomic layer deposition (ALD) were employed as interfacial passivation layers (IPLs) for HfO2 films on InP substrates. The interfacial layer growth during the ALD of the HfO2 film was effectively suppressed by the IPLs, resulting in the decrease of electrical thickness, hysteresis, and interface state density. Compared with the ZnO IPL, the ZnS IPL was more effective in reducing the interface state density near the valence band edge. The leakage current density through the film was considerably lowered by the IPLs because the film crystallization was suppressed. Especially for the film with the ZnS IPL, the leakage current density in the low-voltage region was significantly lower than that observed for the film with the ZnO IPL, because the direct tunneling current was suppressed by the higher conduction band offset of ZnS with the InP substrate. PMID:27467383

  18. The role of MoS2 as an interfacial layer in graphene/silicon solar cells.

    PubMed

    Jiao, Kejia; Duan, Chunyang; Wu, Xiaofeng; Chen, Jiayuan; Wang, Yu; Chen, Yunfa

    2015-03-28

    The role of MoS2 as an effective interfacial layer in graphene/silicon solar cells is systematically investigated by varying MoS2 film annealing temperature and thickness. It is found that the power conversion efficiency (PCE) is increased by ∼100% from ∼2.3% to ∼4.4% with 80 °C annealed MoS2 film whereas it drops significantly to ∼0.6% with 200 °C annealed MoS2 film. The results are well explained based on the device energy band diagram. That is, the incorporation of MoS2(80) films leads to the formation of type II structure, facilitating hole transport; while valence band mismatch is formed with MoS2(200) films due to the increase in the work function of MoS2. Besides, the PCE increases gradually with decreasing MoS2 film thickness, and "saturates" at about 2 nm. The PCE can be further enhanced to ∼6.6% with the aid of silicon surface passivation. Our work demonstrates that MoS2 is an excellent interfacial layer to improve the PCE with low-temperature annealing (80 °C in air), which may be helpful in developing efficient and low-cost G/Si solar cells. PMID:25728709

  19. Modulation in current density of metal/n-SiC contact by inserting Al2O3 interfacial layer

    PubMed Central

    2013-01-01

    Metal contact to SiC is not easy to modulate since the contact can be influenced by the metal, the termination of the SiC, the doping, and the fabrication process. In this work, we introduce a method by inserting a thin Al2O3 layer between metal and SiC to solve this problem simply but effectively. The Al2O3/n-SiC interface composition was obtained with X-ray photoemission spectroscopy, and the electrical properties of subsequently deposited metal contacts were characterized by current–voltage method. We can clearly demonstrate that the insertion of Al2O3 interfacial layer can modulate the current density effectively and realize the transfer between the Schottky contact and ohmic contact. PMID:23452618

  20. Infrared focal plane arrays based on dots in a well and strained layer superlattices

    NASA Astrophysics Data System (ADS)

    Krishna, Sanjay

    2009-01-01

    In this paper, we will review some of the recent progress that we have made on developing single pixel detectors and focal plane arrays based on dots-in-a-well (DWELL) heterostructure and Type II strained layer superlattice (SLS). The DWELL detector consists of an active region composed of InAs quantum dots embedded in InGaAs/GaAs quantum wells. By varying the thickness of the InGaAs well, the DWELL heterostructure allows for the manipulation of the operating wavelength and the nature of the transitions (bound-to-bound, bound-to-quasibound and bound-to-continuum) of the detector. Based on these principles, DWELL samples were grown using molecular beam epitaxy and fabricated into 320 x 256 focal plane arrays (FPAs) with Indium bumps using standard lithography at the University of New Mexico. The FPA evaluated was hybridized to an Indigo 9705 readout integrated circuit (ROIC). From this evaluation, we have reported the first two-color, co-located quantum dot based imaging system that can be used to take multicolor images using a single FPA. We have also been investigating the use of miniband transitions in Type II SLS to develop infrared detectors using PIN and nBn based designs.

  1. Inkjet printed fluorescent nanorod layers exhibit superior optical performance over quantum dots

    NASA Astrophysics Data System (ADS)

    Halivni, Shira; Shemesh, Shay; Waiskopf, Nir; Vinetsky, Yelena; Magdassi, Shlomo; Banin, Uri

    2015-11-01

    Semiconductor nanocrystals exhibit unique fluorescence properties which are tunable in size, shape and composition. The high quantum yield and enhanced stability have led to their use in biomedical imaging and flat panel displays. Here, semiconductor nanorod based inkjet inks are presented, overcoming limitations of the commonly reported quantum dots in printing applications. Fluorescent seeded nanorods were found to be outstanding candidates for fluorescent inks, due to their low particle-particle interactions and negligible self-absorption. This is manifested by insignificant emission shifts upon printing, even in highly concentrated printed layers and by maintenance of a high fluorescence quantum yield, unlike quantum dots which exhibit fluorescence wavelength shifts and quenching effects. This behavior results from the reduced absorption/emission overlap, accompanied by low energy transfer efficiencies between the nanorods as supported by steady state and time resolved fluorescence measurements. The new seeded nanorod inks enable patterning of thin fluorescent layers, for demanding light emission applications such as signage and displays.Semiconductor nanocrystals exhibit unique fluorescence properties which are tunable in size, shape and composition. The high quantum yield and enhanced stability have led to their use in biomedical imaging and flat panel displays. Here, semiconductor nanorod based inkjet inks are presented, overcoming limitations of the commonly reported quantum dots in printing applications. Fluorescent seeded nanorods were found to be outstanding candidates for fluorescent inks, due to their low particle-particle interactions and negligible self-absorption. This is manifested by insignificant emission shifts upon printing, even in highly concentrated printed layers and by maintenance of a high fluorescence quantum yield, unlike quantum dots which exhibit fluorescence wavelength shifts and quenching effects. This behavior results from the

  2. InGaAs/GaAs quantum dot interdiffiusion induced by cap layer overgrowth

    SciTech Connect

    Jasinski, J.; Babinski, A.; Czeczott, M.; Bozek, R.

    2000-06-28

    The effect of thermal treatment during and after growth of InGaAs/GaAs quantum dot (QD) structures was studied. Transmission electron microscopy and atomic force microscopy confirmed the presence of interacting QDs, as was expected from analysis of temperature dependence of QD photoluminescence (PL) peak. The results indicate that the effect of post-growth annealing can be similar to the effect of elevated temperature of capping layer growth. Both, these thermal treatments can lead to a similar In and Ga interdiffiusion resulting in a similar blue-shift of QD PL peak.

  3. Silicon dioxide with a silicon interfacial layer as an insulating gate for highly stable indium phosphide metal-insulator-semiconductor field effect transistors

    NASA Technical Reports Server (NTRS)

    Kapoor, V. J.; Shokrani, M.

    1991-01-01

    A novel gate insulator consisting of silicon dioxide (SiO2) with a thin silicon (Si) interfacial layer has been investigated for high-power microwave indium phosphide (InP) metal-insulator-semiconductor field effect transistors (MISFETs). The role of the silicon interfacial layer on the chemical nature of the SiO2/Si/InP interface was studied by high-resolution X-ray photoelectron spectroscopy. The results indicated that the silicon interfacial layer reacted with the native oxide at the InP surface, thus producing silicon dioxide, while reducing the native oxide which has been shown to be responsible for the instabilities in InP MISFETs. While a 1.2-V hysteresis was present in the capacitance-voltage (C-V) curve of the MIS capacitors with silicon dioxide, less than 0.1 V hysteresis was observed in the C-V curve of the capacitors with the silicon interfacial layer incorporated in the insulator. InP MISFETs fabricated with the silicon dioxide in combination with the silicon interfacial layer exhibited excellent stability with drain current drift of less than 3 percent in 10,000 sec, as compared to 15-18 percent drift in 10,000 sec for devices without the silicon interfacial layer. High-power microwave InP MISFETs with Si/SiO2 gate insulators resulted in an output power density of 1.75 W/mm gate width at 9.7 GHz, with an associated power gain of 2.5 dB and 24 percent power added efficiency.

  4. Electrical and physicochemical properties of atomic-layer-deposited HfO2 film on Si substrate with interfacial layer grown by nitric acid oxidation

    NASA Astrophysics Data System (ADS)

    Kim, Seung Hyun; Seok, Tae Jun; Jin, Hyun Soo; Kim, Woo-Byoung; Park, Tae Joo

    2016-03-01

    The ultrathin SiO2 interfacial layer (IL) was adopted at the interface between atomic-layer-deposited HfO2 gate dielectric film and a Si substrate, which was grown using nitric acid oxidation (NAO) and O3 oxidation (OZO) prior to HfO2 film deposition. X-ray photoelectron spectroscopy result revealed that Si diffusion from the substrate into the film was suppressed for the film with NAO compared to that with OZO, which was attributed to the higher physical density of IL. The electrical measurement using metal-insulator-semiconductor devices showed that the film with NAO exhibited higher effective permittivity and lower densities of fixed charge and slow state at the interface. Furthermore, the leakage current density at an equivalent electrical thickness was lower for the film with NAO than OZO.

  5. Role of interfacial oxygen on the quality and strain stability of pseudomorphic silicon-germanium layers grown on Si substrates

    NASA Astrophysics Data System (ADS)

    Bedell, S. W.; Adam, T. N.; Turansky, A.; Sadana, D. K.

    2011-02-01

    A commercially available 300 mm single-wafer UHV-CVD reactor was used to grow strained pseudomorphic Si 0.79Ge 0.21 layers beyond the critical thickness on Si substrates. A unique in situ method of introducing controlled amounts of oxygen at the growth interface, combined with a very sensitive defect etching technique, was used to study the crystal defects present in the strained SiGe layers immediately after growth and after thermal annealing over large areas (many square centimeters). The etching results showed that the density of growth-related defects (stacking faults) originating from residual O at the epitaxy/substrate interface increases exponentially when the interfacial O concentration exceeds a level of about 10 13 O/cm 2 as measured by secondary ion mass spectroscopy. By defect etching the annealed samples we demonstrate that all the strain-relieving defects (dislocations) we observed originate from these growth defects. Therefore, we confirm previous claims that the strain metastability of low-misfit SiGe layers is controlled mainly by the initial concentration of growth defects. These findings have important implications regarding historical studies of metastability in the strained SiGe/Si system as well as contemporary efforts to grow highly metastable strained layers for IC applications.

  6. Role of the wetting layer in the enhanced responsivity of InAs/GaAsSb quantum dot infrared photodetectors

    SciTech Connect

    Guzmán, Álvaro Yamamoto, Kenji; Ulloa, J. M.; Hierro, Adrian; Llorens, J. M.

    2015-07-06

    InAs/GaAs{sub 1−x}Sb{sub x} Quantum Dot (QD) infrared photodetectors are analyzed by photocurrent spectroscopy. We observe that the integrated responsivity of the devices is improved with the increasing Sb mole fraction in the capping layer, up to 4.2 times for x = 17%. Since the QD layers are not vertically aligned, the vertical transport of the carriers photogenerated within the QDs takes place mainly through the bulk material and the wetting layer of the additional QD regions. The lower thickness of the wetting layer for high Sb contents results in a reduced capture probability of the photocarriers, thus increasing the photoconductive gain and hence, the responsivity of the device. The growth of not vertically aligned consecutive QD layers with a thinner wetting layer opens a possibility to improve the performance of quantum dot infrared photodetectors.

  7. Interfacial electronic structure and charge transfer of hybrid graphene quantum dot and graphitic carbon nitride nanocomposites: insights into high efficiency for photocatalytic solar water splitting.

    PubMed

    Ma, Zuju; Sa, Rongjian; Li, Qiaohong; Wu, Kechen

    2016-01-14

    New metal-free carbon nanodot/carbon nitride (C3N4) nanocomposites have shown to exhibit high efficiency for photocatalytic solar water splitting. (J. Liu, et al., Science, 2015, 347, 970) However, the mechanism underlying the ultrahigh performance of these nanocomposites and consequently the possibilities for further improvements are not at present clear. In this work, we performed hybrid functional calculations and included long-range dispersion corrections to accurately characterize the interfacial electron coupling of the graphene quantum dot-graphitic carbon nitride composites (Gdot/g-C3N4). The results revealed that the band gap of Gdot/g-C3N4 could be engineered by changing the lateral size of Gdots. In particular, the C24H12/g-C3N4 composites present an ideal band gap of 1.92 eV to harvest a large part of solar light. More interestingly, a type-II heterojunction is formed at the interface of the Gdot/g-C3N4 composites, a desirable feature for enhanced photocatalytic activity. The charge redistribution at the interface leads to strong electron depletion above the Gdot sheet and electron accumulation below the g-C3N4 monolayer, potentially facilitating the separation of H2O oxidation and reduction reactions. Furthermore, we suggested that the photocatalytic performance of the Gdot/g-C3N4 nanocomposites can be further improved by decreasing the thickness of Gdots and tuning the size of Gdots. PMID:26659558

  8. Graphene Quantum Dot Layers with Energy-Down-Shift Effect on Crystalline-Silicon Solar Cells.

    PubMed

    Lee, Kyung D; Park, Myung J; Kim, Do-Yeon; Kim, Soo M; Kang, Byungjun; Kim, Seongtak; Kim, Hyunho; Lee, Hae-Seok; Kang, Yoonmook; Yoon, Sam S; Hong, Byung H; Kim, Donghwan

    2015-09-01

    Graphene quantum dot (GQD) layers were deposited as an energy-down-shift layer on crystalline-silicon solar cell surfaces by kinetic spraying of GQD suspensions. A supersonic air jet was used to accelerate the GQDs onto the surfaces. Here, we report the coating results on a silicon substrate and the GQDs' application as an energy-down-shift layer in crystalline-silicon solar cells, which enhanced the power conversion efficiency (PCE). GQD layers deposited at nozzle scan speeds of 40, 30, 20, and 10 mm/s were evaluated after they were used to fabricate crystalline-silicon solar cells; the results indicate that GQDs play an important role in increasing the optical absorptivity of the cells. The short-circuit current density was enhanced by about 2.94% (0.9 mA/cm(2)) at 30 mm/s. Compared to a reference device without a GQD energy-down-shift layer, the PCE of p-type silicon solar cells was improved by 2.7% (0.4 percentage points). PMID:26264738

  9. Improve molecular beam epitaxy growth of HgCdTe on CdZnTe (211)B substrates using interfacial layers of HgTe/CdTe superlattices

    SciTech Connect

    Chang Yong; Grein, C. H.; Zhao, J.; Sivanathan, S.; Wang, C. Z.; Aoki, T.; Smith, David J.; Wijewarnasuriya, P. S.; Nathan, V.

    2006-12-01

    HgTe/CdTe superlattices (SLs) have been grown on CdZnTe (211)B substrates as interfacial layers to improve the reproducibility and material properties of epitaxial HgCdTe. The interfacial SL layer is found by transmission electron microscopy to be capable of smoothing out the substrate's surface roughness and to bend or block threading dislocations from propagating from the substrate into the functional HgCdTe epilayers. The best etch pit density values of 4x10{sup 4} cm{sup -2} were achieved in long-wavelength infrared HgCdTe epilayers with such interfacial layers, while typical values were in the low 10{sup 5} cm{sup -2} range. The recombination mechanisms in such layers were dominated by radiative and Auger intrinsic recombination mechanisms, whereas the contributions from the Shockley-Read-Hall mechanism become negligible, which demonstrated that the use of the SL interfacial layers was beneficial for HgCdTe growth using molecular beam epitaxy or MBE.

  10. The role of interfacial layers in the enhanced thermal conductivity of nanofluids : a renovated Hamilton-Crosser model.

    SciTech Connect

    Yu, W.; Choi, S. U.-S.; Energy Technology

    2004-08-01

    We previously developed a renovated Maxwell model for the effective thermal conductivity of nanofluids and determined that the solid/liquid interfacial layers play an important role in the enhanced thermal conductivity of nanofluids. However, this renovated Maxwell model is limited to suspensions with spherical particles. Here, we extend the Hamilton--Crosser model for suspensions of nonspherical particles to include the effect of a solid/liquid interface. The solid/liquid interface is described as a confocal ellipsoid with a solid particle. The new model for the three-phase suspensions is mathematically expressed in terms of the equivalent thermal conductivity and equivalent volume fraction of anisotropic complex ellipsoids, as well as an empirical shape factor. With a generalized empirical shape factor, the renovated Hamilton-Crosser model correctly predicts the magnitude of the thermal conductivity of nanotube-in-oil nanofluids. At present, this new model is not able to predict the nonlinear behavior of the nanofluid thermal conductivity.

  11. Improved interfacial and electrical properties of Ge MOS devices with ZrON/GeON dual passivation layer

    NASA Astrophysics Data System (ADS)

    Wenyu, Yuan; Jingping, Xu; Lu, Liu; Yong, Huang; Zhixiang, Cheng

    2016-05-01

    The interfacial and electrical characteristics of Ge metal–oxide–semiconductor (MOS) devices with a dual passivation layer of ZrON/GeON formed by NH3- or N2-plasma treatment are investigated. The experimental results show that the NH3-plasma treated sample exhibits significantly improved interfacial and electrical properties as compared to the samples with N2-plasma treatment and no treatment: a lower interface-state density at the midgap (1.64 × 1011 cm‑2 · eV‑1) and gate leakage current (9.32 × 10‑5 A/cm2 at Vfb + 1 V), a small capacitance equivalent thickness (1.11 nm) and a high k value (32). X-ray photoelectron spectroscopy is used to analyze the involved mechanisms. It is indicated that more GeON and less GeOx (x < 2) are formed on the Ge surface during NH3-plasma treatment than the N2-plasma treatment, resulting in a high-quality high-k/Ge interface, because H atoms and NH radicals in NH3-plasma can enhance volatilization of the unstable low-k GeOx, creating high-quality GeON passivation layer. Moreover, more nitrogen incorporation in ZrON/GeON induced by NH3-plasma treatment can build a stronger N barrier and thus more effectively inhibit in-diffusion of O and Ti from high-k gate dielectric and out-diffusion of Ge. Project supported by the National Natural Science Foundation of China (Nos. 6127411261176100, 61404055).

  12. On PbTiO{sub 3}-(111)-Pt interfacial layers and their x-ray photoelectron spectroscopy signature

    SciTech Connect

    Habouti, S.; Solterbeck, C-H.; Es-Souni, M.; Zaporojtchenko, V.

    2008-11-15

    In this work emphasis is placed on the investigation of interfacial layers between sol-gel processed PbTiO{sub 3} (PTO) thin films and (111)Pt terminated silicon substrates. The methods used are x-ray diffraction, x-ray photoelectron spectroscopy (XPS) combined with depth profiling, and atomic force microscopy (AFM). In order to avoid artifacts related to ion bombardment, e.g., reduction of Pb ions and preferential sputtering, gentle argon ion bombardment conditions were first derived. AFM investigations of native and ion bombarded films at different stages of depth profiling show that the films are homogenously sputtered, whereby the film roughness remains practically unchanged in the course of sputtering. An annealing treatment at 550 deg. C under reducing atmosphere was used to provoke the formation of an interfacial intermetallic (111)Pt{sub x}Pb phase, which is shown to coexist with an amorphous oxide film. This could allow us to establish the XPS signature of the intermetallic phase. A negative shift of the Pt (4f) binding energy and a large full width at half maximum of the Pb (4f) peak are the attributes of this signature. PTO-film annealing in air at temperatures between 350 and 600 deg. C leads to the formation of the perovskite phase, starting at 500 deg. C, directly from the amorphous phase. Based on its derived XPS signature it is shown that the intermetallic phase still exists at the interface with variable thickness depending on the annealing temperature. The pronounced (111) texture of the PTO-crystallized films is thought to be the direct consequence of this intermetallic template layer. It is also shown that the outermost surface of the PTO film is enriched with PbO as a result of segregation phenomena.

  13. Comparison of hydrolytic and non-hydrolytic atomic layer deposition chemistries: Interfacial electronic properties at alumina-silicon interfaces

    NASA Astrophysics Data System (ADS)

    Marstell, Roderick J.; Strandwitz, Nicholas C.

    2015-11-01

    We report the differences in the passivation and electronic properties of aluminum oxide (Al2O3) deposited on silicon via traditional hydrolytic atomic layer deposition (ALD) and non-hydrolytic (NH) ALD chemistries. Traditional films were grown using trimethylaluminum (TMA) and water and NHALD films grown using TMA and isopropanol at 300 °C. Hydrolytically grown ALD films contain a smaller amount of fixed charge than NHALD films (oxide fixed charge Qf Traditional = -8.1 × 1011 cm-2 and Qf NHALD = -3.6 × 1012 cm-2), and a larger degree of chemical passivation than NHALD films (density of interface trap states, Dit Traditional = 5.4 × 1011 eV-1 cm-2 and Dit NHALD = 2.9 × 1012 eV-1 cm-2). Oxides grown with both chemistries were found to have a band gap of 7.1 eV. The conduction band offset was 3.21 eV for traditionally grown films and 3.38 eV for NHALD. The increased Dit for NHALD films may stem from carbon impurities in the oxide layer that are at and near the silicon surface, as evidenced by both the larger trap state time constant (τTraditional = 2.2 × 10-9 s and τNHALD = 1.7 × 10-7 s) and the larger carbon concentration. We have shown that the use of alcohol-based oxygen sources in NHALD chemistry can significantly affect the resulting interfacial electronic behavior presenting an additional parameter for understanding and controlling interfacial electronic properties at semiconductor-dielectric interfaces.

  14. Effects of reaction layer on interfacial shear properties and strength of fiber in silicon-carbide (SiC) fiber-reinforced titanium alloy composite

    SciTech Connect

    Kagawa, Yutaka; Masuda, Chitoshi; Fujiwara, Chikara; Fukushima, Akira

    1996-12-31

    The effect of the interfacial thickness of the reaction layer on the interfacial shear properties and the tensile strength of double carbon-coated SCS-6 SiC fiber in Ti-15Mo-5Zr-3Al alloy matrix composite was examined. The major reaction layer thickness, that is, titanium-carbide (TiC) layer thickness, varied with heat-exposure temperature and time, respectively, and the resultant mean thickness of the reaction layer of the composite ranged from 0.4 to 1.7 {micro}m. The critical interfacial toughness, G{sub i}{sup c}, and the mean shear sliding resistance, {tau}{sub s}, were evaluated by the thin specimen pushout technique. Tensile strength of the silicon-carbide (SiC) fiber extracted from the titanium alloy matrix before and after the heat exposure was determined in relationship to the thickness of the reaction layer. The critical interface toughness, G{sub i}{sup c}, for the failure of the root of the reaction layer was {approx}4 J/m{sup 2}, and the average shear sliding resistance of the interface, {tau}{sub s}, was 102 to 118 MPa. The interfacial shear mechanical properties were adequate to prevent failure of the fiber due to the stress concentration caused by cracks that formed first in the reaction layer. The results showed that when the growth of reaction layer was within 1.7 {micro}m, the mean strength of the extracted fiber was unaffected by the existence of the reaction layer because of weak bonding between it and the fiber. However, with the increase of the reaction layer thickness, the strength distribution of the extracted fiber tended to Weibull bimodal distribution.

  15. Voltage-Controlled Interfacial Layering in an Ionic Liquid on SrTiO3.

    PubMed

    Petach, Trevor A; Mehta, Apurva; Marks, Ronald; Johnson, Bart; Toney, Michael F; Goldhaber-Gordon, David

    2016-04-26

    One prominent structural feature of ionic liquids near surfaces is formation of alternating layers of anions and cations. However, how this layering responds to an applied potential is poorly understood. We focus on the structure of 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate (BMPY-FAP) near the surface of a strontium titanate (SrTiO3) electric double-layer transistor. Using X-ray reflectivity, we show that at positive bias the individual layers in the ionic liquid double layer thicken and the layering persists further away from the interface. We model the reflectivity using a modified distorted crystal model with alternating cation and anion layers, which allows us to extract the charge density and the potential near the surface. We find that the charge density is strongly oscillatory with and without applied potential and that with an applied gate bias of 4.5 V the first two layers become significantly more cation rich than at zero bias, accumulating about 2.5 × 10(13) cm(-2) excess charge density. PMID:26959226

  16. Versatile electron-collecting interfacial layer by in situ growth of silver nanoparticles in nonconjugated polyelectrolyte aqueous solution for polymer solar cells.

    PubMed

    Yuan, Kai; Chen, Lie; Chen, Yiwang

    2014-10-01

    Novel PEIE-Ag composites by in situ growth of silver nanoparticles in poly(ethylenimine)-ethoxylated (PEIE) aqueous solution are explored as an efficient interfacial layer for improving inverted polymer solar cells (PSCs) performance. The hybrid PEIE-Ag interfacial material is simple to fabricate only via ultraviolet irradiation with good water-solubility and unique film formation. The generated Ag nanoparticles can anchor in the PEIE polymer chains to form a conductive continuous interpenetrating network structure. Combining of the advantages of PEIE and Ag nanoparticles, the PEIE-Ag shows enhanced charge transport, electron selective and collection, and improved light-harvesting, mainly due to the surface plasmon resonance effect, better energy alignment induced by the formation of ideal dipole layer, as well as the improved conductivity. These distinguished interfacial properties result in the power conversion efficiency of inverted PSCs based on poly[4,8-bis(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b]dithiophene-2,6-diyl]-alt-[2-(2-ethyl-hexanoyl)-thieno[3,4-b]thiophen-4,6-diyl] (PBDTTT-C-T) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) photoactive layer substantially improved up to 7.66% from 6.11%. Moreover, the device performance is insensitively dependent on the thickness of the PEIE-Ag interfacial layer, broadening the thicknesses selection window for interfacial materials. These results demonstrate that PEIE-Ag is a potential interfacial material compatible with roll-to-roll techniques and suitable for printed electronic devices. PMID:25207753

  17. Simply synthesized TiO2 nanorods as an effective scattering layer for quantum dot sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Mahmoud, Samadpour; Azam Iraji, zad; Mehdi, Molaei

    2014-04-01

    TiO2 nanorod layers are synthesized by simple chemical oxidation of Ti substrates. Diffuse reflectance spectroscopy measurements show effective light scattering properties originating from nanorods with length scales on the order of one micron. The films are sensitized with CdSe quantum dots (QDs) by successive ionic layer adsorption and reaction (SILAR) and integrated as a photoanode in quantum dot sensitized solar cells (QDSCs). Incorporating nanorods in photoanode structures provided 4- to 8-fold enhancement in light scattering, which leads to a high power conversion efficiency, 3.03% (Voc = 497 mV, Jsc = 11.32 mA/cm2, FF = 0.54), in optimized structures. High efficiency can be obtained just by tuning the photoanode structure without further treatments, which will make this system a promising nanostructure for efficient quantum dot sensitized solar cells.

  18. Interfacial Adhesion Study for Multi-Layer Structures with m-ELT Method and FEM Simulation

    NASA Astrophysics Data System (ADS)

    Hasunuma, Masahiko; Ito, Sachiyo; Kittaka, Hideyoshi

    2004-12-01

    The m-ELT method is widely used because of the simplicity. And the fracture mode of this method is similar to that of the actual TCT (Temperature Cycling Test) that is used for the reliability test of an LSI package. In this method, only the thermal stress that is stored in epoxy has been taken into consideration and the effects of very thin ILD layers have been ignored. In this study, we have considered a crack initiation state, so we have paid our attention to the thermal stress singularity field generated in the free edge of ILD in m-ELT measurement. We have evaluated the fracture toughness with two stress singularity parameters, lambda and Kf, in the tensile singular stress produced in ILDs' interface near the slit tip. And we have elucidated the effect of low-k film thickness and the effect of multiple-layer stacking modules that have plural identical interfaces by the m-ELT and FEM (finite element method) for the stress simulation. Especially the free-edge interface between SiOC and SiCN has been discussed, because this interface has lowest adhesion strength in this study. As a result, it has been derived that the low-k layer thickness has not affect stress singularity field. Moreover the Kapp estimated by the m-ELT has been affected by global layer (upper thick SiO2 layer) thickness. The stress relaxation caused by upper rigid layers makes the apparent value of Kapp increase. The stress concentration at the tip of a slit will change with ILD properties and detailed multi-layer structure. Therefore, in order to derive fracture toughness from the peeling temperature of the m-ELT method, it is the necessity of taking this change into consideration. Singularity parameters derived by a FEM simulation has been confirmed to be effective for deducing a fracture toughness criterion of an interface that has a stress singularity field.

  19. Interfacial and structural properties of sputtered HfO{sub 2} layers

    SciTech Connect

    Aygun, G.; Yildiz, I.

    2009-07-01

    Magnetron sputtered HfO{sub 2} layers formed on a heated Si substrate were studied by spectroscopic ellipsometer (SE), x-ray diffraction (XRD), Fourier transform infrared (FTIR), and x-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiO{sub x} suboxide layer at the HfO{sub 2}/Si interface is unavoidable. The HfO{sub 2} thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O{sub 2}/Ar gas ratio during sputtering, sputtering time, and substrate temperature. XRD spectra show that the deposited film has (111) monoclinic phase of HfO{sub 2}, which is also supported by FTIR spectra. The atomic concentration and chemical environment of Si, Hf, and O have been measured as a function of depth starting from the surface of the sample by XPS technique. It shows that HfO{sub 2} layers of a few nanometers are formed at the top surface. Below this thin layer, Si-Si bonds are detected just before the Si suboxide layer, and then the Si substrate is reached during the depth profiling by XPS. It is clearly understood that the highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO{sub 2} to form HfO{sub 2}, leaving Si-Si bonds behind.

  20. Passivation effects on quantum dots prepared by successive ionic layer adsorption and reaction

    NASA Astrophysics Data System (ADS)

    Dai, Qilin; Maloney, Scott; Chen, Weimin; Poudyal, Uma; Wang, Wenyong

    2016-06-01

    ZnS is typically used to passivate semiconductor quantum dots (QDs) prepared by the successive ionic layer adsorption and reaction (SILAR) method for solar cell applications, while for colloidal QDs, organic ligands are usually used for this passivation purpose. In this study we utilized oleylamine and oleic acid ligands, besides ZnS, to passivate QDs prepared by the SILAR approach, and investigated their effects on the incident photon-to-current efficiency (IPCE) performance of the solar cells. It was observed that oleylamine passivation decreased device performance, while oleic acid passivation improved the IPCE of the cells. Redshift of the IPCE onset wavelength was also observed after oleic acid coating, which was attributed to the delocalization of excitons in the CdS QDs.

  1. Narrow Band Gap Lead Sulfide Hole Transport Layers for Quantum Dot Photovoltaics.

    PubMed

    Zhang, Nanlin; Neo, Darren C J; Tazawa, Yujiro; Li, Xiuting; Assender, Hazel E; Compton, Richard G; Watt, Andrew A R

    2016-08-24

    The band structure of colloidal quantum dot (CQD) bilayer heterojunction solar cells is optimized using a combination of ligand modification and QD band gap control. Solar cells with power conversion efficiencies of up to 9.33 ± 0.50% are demonstrated by aligning the absorber and hole transport layers (HTL). Key to achieving high efficiencies is optimizing the relative position of both the valence band and Fermi energy at the CQD bilayer interface. By comparing different band gap CQDs with different ligands, we find that a smaller band gap CQD HTL in combination with a more p-type-inducing CQD ligand is found to enhance hole extraction and hence device performance. We postulate that the efficiency improvements observed are largely due to the synergistic effects of narrower band gap QDs, causing an upshift of valence band position due to 1,2-ethanedithiol (EDT) ligands and a lowering of the Fermi level due to oxidation. PMID:27421066

  2. Passivation effects on quantum dots prepared by successive ionic layer adsorption and reaction.

    PubMed

    Dai, Qilin; Maloney, Scott; Chen, Weimin; Poudyal, Uma; Wang, Wenyong

    2016-06-01

    ZnS is typically used to passivate semiconductor quantum dots (QDs) prepared by the successive ionic layer adsorption and reaction (SILAR) method for solar cell applications, while for colloidal QDs, organic ligands are usually used for this passivation purpose. In this study we utilized oleylamine and oleic acid ligands, besides ZnS, to passivate QDs prepared by the SILAR approach, and investigated their effects on the incident photon-to-current efficiency (IPCE) performance of the solar cells. It was observed that oleylamine passivation decreased device performance, while oleic acid passivation improved the IPCE of the cells. Redshift of the IPCE onset wavelength was also observed after oleic acid coating, which was attributed to the delocalization of excitons in the CdS QDs. PMID:27103144

  3. Effects of interfacial layer wettability and thickness on the coating morphology and sirolimus release for drug-eluting stent.

    PubMed

    Bedair, Tarek M; Yu, Seung Jung; Im, Sung Gap; Park, Bang Ju; Joung, Yoon Ki; Han, Dong Keun

    2015-12-15

    Drug-eluting stents (DESs) have been used to treat coronary artery diseases by placing in the arteries. However, current DESs still suffer from polymer coating defects such as delamination and peeling-off that follows stent deployment. Such coating defects could increase the roughness of DES and might act as a source of late or very late thrombosis and might increase the incident of restenosis. In this regard, we modified the cobalt-chromium (Co-Cr) alloy surface with hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) or hydrophobic poly(2-hydroxyethyl methacrylate)-grafted-poly(caprolactone) (PHEMA-g-PCL) brushes. The resulting surfaces were biocompatible and biodegradable, which could act as anchoring layer for the drug-in-polymer matrix coating. The two modifications were characterized by ATR-FTIR, XPS, water contact angle measurements, SEM and AFM. On the control and modified Co-Cr samples, a sirolimus (SRL)-containing poly(D,L-lactide) (PDLLA) were ultrasonically spray-coated, and the drug release was examined for 8weeks under physiological conditions. The results demonstrated that PHEMA as a primer coating improved the coating stability and degradation morphology, and drug release profile for short-term as compared to control Co-Cr, but fails after 7weeks in physiological buffer. On the other hand, the hydrophobic PHEMA-g-PCL brushes not only enhanced the stability and degradation morphology of the PDLLA coating layer, but also sustained SRL release for long-term. At 8-week of release test, the surface morphologies and release profiles of coated PDLLA layers verified the beneficial effect of hydrophobic PCL brushes as well as their thickness on coating stability. Our study concludes that 200nm thickness of PHEMA-g-PCL as interfacial layer affects the stability and degradation morphology of the biodegradable coating intensively to be applied for various biodegradable-based DESs. PMID:26319336

  4. Instability of Two-Layer Rayleigh Bénard Convection with Interfacial Thermocapillary Effect

    NASA Astrophysics Data System (ADS)

    Liu, Qiu-Sheng; Zhou, Bing-Hong; Nguyen Thi, Henri; Hu, Wen-Rui

    2004-04-01

    The linear instability analysis of the Rayleigh-Marangoni-Bénard convection in a two-layer system of silicon oil 10 cS and fluorinert FC70 liquids are performed in a larger range of two-layer depth ratios Hr from 0.2 to 5.0 for different total depth Hleq12 mm. Our results are different from the previous study on the Rayleigh-Bénard instability and show strong effects of thermocapillary force at the interface on the time-dependent oscillations arising from the onset of instability convection.

  5. Strong interfacial attrition developed by oleate/layered double hydroxide nanoplatelets dispersed into poly(butylene succinate).

    PubMed

    Zhou, Qian; Verney, Vincent; Commereuc, Sophie; Chin, In-Joo; Leroux, Fabrice

    2010-09-01

    Poly(butylene succinate) (PBS) nanocomposite structure was studied as a function of the filler percentage loading. The resulting state of dispersion was evaluated by XRD and TEM, and the interfacial attrition between PBS chain and lamellar platelets by the melt rheological properties. Hybrid organic inorganic (O/I) layered double hydroxide (LDH) organo-modified by oleate anions was used as filler. It was found that the confinement supplied by the LDH framework forces the interleaved organic molecule to be more distant from each other than in the case of oleate salt, this having as an effect to decrease strongly the homonuclear intermolecular (1)H(1)H dipolar interaction. An additional consequence of this relatively free molecular rotation, affecting the (13)C CPMAS response as well, is to facilitate the delamination of the 2D-stacked layers during extrusion since an quasi-exfoliated PBS:Mg(2)Al/oleate structure is observed for filler loading lower than 5% w/w. This is in association to a non-linear viscoelasticity in the low-omega region and the observed shear-thinning tendency compares better than other PBS:silicate nanocomposite derivatives and is here explained by the presence of a percolated LDH nanoparticle network. Indeed the plastic deformation in the low-omega region is found to be restricted by well-dispersed LDH tactoids in association with a rather strong attrition phenomenon between tethered oleate anions and PBS chains. PMID:20605578

  6. Formation of carbonaceous nano-layers under high interfacial pressures during lubrication with mineral and bio-based oils

    SciTech Connect

    Baltrus, John P.

    2014-01-01

    In order to better protect steel surfaces against wear under high loads, understanding of chemical reactions between lubricants and metal at high interfacial pressures and elevated temperatures needs to be improved. Solutions at 5 to 20 wt. % of zinc di-2-ethylhexyl dithio phosphate (ZDDP) and chlorinated paraffins (CP) in inhibited paraffinic mineral oil (IPMO) and inhibited soy bean oil (ISBO) were compared on a Twist Compression Tribotester (TCT) at 200 MPa. Microscopy of wear tracks after 10 seconds tribotesting showed much smoother surface profiles than those of unworn areas. X-ray photoelectron spectroscopy (XPS) coupled with Ar-ion sputtering demonstrated that additive solutions in ISBO formed 2–3 times thicker carbon-containing nano-layers compared to IPMO. The amounts of Cl, S or P were unexpectedly low and detectable only on the top surface with less than 5 nm penetration. CP blends in IPMO formed more inorganic chlorides than those in ISBO. It can be concluded that base oils are primarily responsible for the thickness of carbonaceous nano-layers during early stages of severe boundary lubrication, while CP or ZDDP additive contributions are important, but less significant.

  7. Tensile properties and interfacial bonding of multi-layered, high-purity titanium strips fabricated by ARB process.

    PubMed

    Ghafari-Gousheh, Soroush; Nedjad, Syamak Hossein; Khalil-Allafi, Jafar

    2015-11-01

    Severe plastic deformation (SPD) processing has shown very effective in promotion of mechanical properties of metals and alloys. In this study, the results of investigating mechanical properties and also inter-layer bond performance of accumulative roll bonded high purity titanium (HP-Ti) strips are presented. High purity titanium plates were severely deformed by use of a combination of cold rolling (CR) to a thickness reduction of approximately 87% and then accumulative roll bonding (ARB) for three cycles (N=3) at ambient temperature. Optical and scanning electron microscopy, tensile testing, and hardness measurements were conducted. The ARB strips exhibited lower tensile strength and ductility in comparison to cold rolled one which can basically be attributed to the poor function of the latest bonds established in the centerlines of the strips. Fractographic examinations revealed the interfacial de-bonding along the centerline between the layers having undergone roll bonding for just one cycle. It was while the interfaces having experienced roll bonding for more cycles showed much higher resistance against delaminating. PMID:26253205

  8. Theory of multiple quantum dot formation in strained-layer heteroepitaxy

    NASA Astrophysics Data System (ADS)

    Du, Lin; Maroudas, Dimitrios

    2016-07-01

    We develop a theory for the experimentally observed formation of multiple quantum dots (QDs) in strained-layer heteroepitaxy based on surface morphological stability analysis of a coherently strained epitaxial thin film on a crystalline substrate. Using a fully nonlinear model of surface morphological evolution that accounts for a wetting potential contribution to the epitaxial film's free energy as well as surface diffusional anisotropy, we demonstrate the formation of multiple QD patterns in self-consistent dynamical simulations of the evolution of the epitaxial film surface perturbed from its planar state. The simulation predictions are supported by weakly nonlinear analysis of the epitaxial film surface morphological stability. We find that, in addition to the Stranski-Krastanow instability, long-wavelength perturbations from the planar film surface morphology can trigger a nonlinear instability, resulting in the splitting of a single QD into multiple QDs of smaller sizes, and predict the critical wavelength of the film surface perturbation for the onset of the nonlinear tip-splitting instability. The theory provides a fundamental interpretation for the observations of "QD pairs" or "double QDs" and other multiple QDs reported in experimental studies of epitaxial growth of semiconductor strained layers and sets the stage for precise engineering of tunable-size nanoscale surface features in strained-layer heteroepitaxy by exploiting film surface nonlinear, pattern forming phenomena.

  9. Ligand Layer Engineering To Control Stability and Interfacial Properties of Nanoparticles.

    PubMed

    Schulz, Florian; Dahl, Gregor T; Besztejan, Stephanie; Schroer, Martin A; Lehmkühler, Felix; Grübel, Gerhard; Vossmeyer, Tobias; Lange, Holger

    2016-08-01

    The use of mixed ligand layers including poly(ethylene glycol)-based ligands for the functionalization of nanoparticles is a very popular strategy in the context of nanomedicine. However, it is challenging to control the composition of the ligand layer and maintain high colloidal and chemical stability of the conjugates. A high level of control and stability are crucial for reproducibility, upscaling, and safe application. In this study, gold nanoparticles with well-defined mixed ligand layers of α-methoxypoly(ethylene glycol)-ω-(11-mercaptoundecanoate) (PEGMUA) and 11-mercaptoundecanoic acid (MUA) were synthesized and characterized by ATR-FTIR spectroscopy and gel electrophoresis. The colloidal and chemical stability of the conjugates was tested by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and UV/vis spectroscopy based experiments, and their interactions with cells were analyzed by elemental analysis. We demonstrate that the alkylene spacer in PEGMUA is the key feature for the controlled synthesis of mixed layer conjugates with very high colloidal and chemical stability and that a controlled synthesis is not possible using regular PEG ligands without the alkylene spacer. With the results of our stability tests, the molecular structure of the ligands can be clearly linked to the colloidal and chemical stabilization. We expect that the underlying design principle can be generalized to improve the level of control in nanoparticle surface chemistry. PMID:27458652

  10. Multifunctional Role of Nanostructured CdS Interfacial Layers in Hybrid Solar Cells.

    PubMed

    Grynko, D O; Fedoryak, O M; Smertenko, P S; Ogurtsov, N A; Pud, A A; Noskov, Yu V; Dimitriev, O P

    2015-01-01

    We demonstrate here a multifunctional application of CdS layers with nanotextured and nanowire morphology in four types of hybrid solar cells, i.e., (i) nanocrystal-polymer cell, (ii) nanocrystal-organic donor-acceptor bulk heterojunction (BHJ) inverted cell, (iii) nanocrystal-dye sensitized solid state cell and (iv) nanocrystal-dye sensitized electrochemical cell. The role of CdS layer in each type of the above cells has been elucidated and the photovoltaic (PV) performance of the PV cells has been compared. It is shown that CdS acts as acceptor in the cells of types (i) and (iii), while it plays the role of an electron-selective (hole-blocking) layer to direct electrons from the organic counterpart to anode in the cases (ii) and (iv). Morphology of the CdS layer makes a noticeable effect on the PV performance. In particular, the nanowire array demonstrated an improved efficiency of collection of charge carriers as compared with the continuous textured surface due to the increased organic-CdS interface area in PV cells of practically all types. It is demonstrated that the same nanocrystal-dye structure can operate either as PV cell of type (iii) or PV cell of type (iv). PMID:26328438

  11. Improvement of InAs quantum-dot optical properties by strain compensation with GaNAs capping layers

    NASA Astrophysics Data System (ADS)

    Zhang, X. Q.; Ganapathy, S.; Suemune, I.; Kumano, H.; Uesugi, K.; Nabetani, Yoichi; Matsumoto, Takashi

    2003-12-01

    Two kinds of self-assembled InAs quantum dots (QDs) grown on GaAs (001) substrates were studied. One is capped with GaAs layers and the other with GaNAs strain-compensating layers. Photoluminescence (PL) measurements on the two kinds of InAs QDs showed distinct dependence on the selection of the capping layers. The homogeneity and luminescence efficiency of the InAs QDs were much improved when the net strain was reduced with GaNAs layers. These results demonstrate the importance of net strain compensation for the improved optical quality of InAs QDs.

  12. Graphene oxide as a water dissociation catalyst in the bipolar membrane interfacial layer.

    PubMed

    McDonald, Michael B; Freund, Michael S

    2014-08-27

    Bipolar membranes are formed by the lamination of an anion- and cation-exchange layer. Upon a sufficient applied reverse bias, water molecules at the layer junction dissociate, generating OH(-) and H(+), which can be useful in electrodialysis and electrosynthesis applications. Graphene oxide has been introduced into bipolar membrane junctions (illustrated in the adjacent graphic) and is shown to be an efficient new water dissociation catalyst, lowering the overpotential by 75% compared to a control membrane. It was found that adjusting deposition conditions changes the nature of the graphene oxide films, leading to tunable membrane performance. Additionally, it is shown that their low overpotentials are stable, making for industrially viable, high-performance bipolar membranes. PMID:25046580

  13. A moving contact line as a rheometer for nanometric interfacial layers.

    PubMed

    Lhermerout, Romain; Perrin, Hugo; Rolley, Etienne; Andreotti, Bruno; Davitt, Kristina

    2016-01-01

    How a liquid drop sits or moves depends on the physical and mechanical properties of the underlying substrate. This can be seen in the hysteresis of the contact angle made by a drop on a solid, which is known to originate from surface heterogeneities, and in the slowing of droplet motion on deformable solids. Here, we show how a moving contact line can be used to characterize a molecularly thin polymer layer on a solid. We find that the hysteresis depends on the polymerization index and can be optimized to be vanishingly small (<0.07°). The mechanical properties are quantitatively deduced from the microscopic contact angle, which is proportional to the speed of the contact line and the Rouse relaxation time divided by the layer thickness, in agreement with theory. Our work opens the prospect of measuring the properties of functionalized interfaces in microfluidic and biomedical applications that are otherwise inaccessible. PMID:27562022

  14. A moving contact line as a rheometer for nanometric interfacial layers

    PubMed Central

    Lhermerout, Romain; Perrin, Hugo; Rolley, Etienne; Andreotti, Bruno; Davitt, Kristina

    2016-01-01

    How a liquid drop sits or moves depends on the physical and mechanical properties of the underlying substrate. This can be seen in the hysteresis of the contact angle made by a drop on a solid, which is known to originate from surface heterogeneities, and in the slowing of droplet motion on deformable solids. Here, we show how a moving contact line can be used to characterize a molecularly thin polymer layer on a solid. We find that the hysteresis depends on the polymerization index and can be optimized to be vanishingly small (<0.07°). The mechanical properties are quantitatively deduced from the microscopic contact angle, which is proportional to the speed of the contact line and the Rouse relaxation time divided by the layer thickness, in agreement with theory. Our work opens the prospect of measuring the properties of functionalized interfaces in microfluidic and biomedical applications that are otherwise inaccessible. PMID:27562022

  15. Inverted polymer solar cells with enhanced fill factor by inserting the potassium stearate interfacial modification layer

    NASA Astrophysics Data System (ADS)

    Li, Jiangsheng; Jiu, Tonggang; Li, Bairu; Kuang, Chaoyang; Chen, Qiushan; Ma, Sushuang; Shu, Jie; Fang, Junfeng

    2016-05-01

    A thin potassium stearate (KSt) film combined with an optimized ZnO film was introduced to improve the fill factor (FF) of highly efficient inverted polymer solar cells (PSCs). Atomic force microscopy and contact angle measurements were used to show that the introduction of KSt did not change the morphology of interlayer. On the contrary, it is beneficial for the spread of the active layer on the interlayer. The origin of enhanced FF was systematically studied by the ideal current-voltage model for a single heterojunction solar cell and electrochemical impedance spectroscopy. On the basis of the data analysis, the reduced charge recombination loss was responsible for this improved FF. At last, when KSt was replaced by sodium stearate (NaSt), the similar experiment phenomenon was observed. This indicates that inserting a metallic stearate modified layer is a promising strategy to enhance inverted PSCs performance.

  16. New concepts on the interfacial friction behavior between flat steel ribbon layers

    SciTech Connect

    Zheng, J.; Zhu, G.

    1995-11-01

    Flat steel ribbon wound pressure vessels are widely used in chemical, petrochemical, and other industries. However, no satisfactory theoretical formulae are available to estimate the additional strengthening induced by the friction between the layers. Effective normal stress in the ribbon wide direction and shear stress are new concepts for describing such strengthening effect. These concepts are analyzed further to obtain expressions for both axial and circumferential bursting pressure, and stresses of the vessel. Comparison with one set of experimental results shows excellent agreement.

  17. Running interfacial waves in a two-layer fluid system subject to longitudinal vibrations.

    PubMed

    Goldobin, D S; Pimenova, A V; Kovalevskaya, K V; Lyubimov, D V; Lyubimova, T P

    2015-05-01

    We study the waves at the interface between two thin horizontal layers of immiscible fluids subject to high-frequency horizontal vibrations. Previously, the variational principle for energy functional, which can be adopted for treatment of quasistationary states of free interface in fluid dynamical systems subject to vibrations, revealed the existence of standing periodic waves and solitons in this system. However, this approach does not provide regular means for dealing with evolutionary problems: neither stability problems nor ones associated with propagating waves. In this work, we rigorously derive the evolution equations for long waves in the system, which turn out to be identical to the plus (or good) Boussinesq equation. With these equations one can find all the time-independent-profile solitary waves (standing solitons are a specific case of these propagating waves), which exist below the linear instability threshold; the standing and slow solitons are always unstable while fast solitons are stable. Depending on initial perturbations, unstable solitons either grow in an explosive manner, which means layer rupture in a finite time, or falls apart into stable solitons. The results are derived within the long-wave approximation as the linear stability analysis for the flat-interface state [D.V. Lyubimov and A.A. Cherepanov, Fluid Dynamics 21, 849 (1986)] reveals the instabilities of thin layers to be long wavelength. PMID:26066252

  18. Comparison of hydrolytic and non-hydrolytic atomic layer deposition chemistries: Interfacial electronic properties at alumina-silicon interfaces

    SciTech Connect

    Marstell, Roderick J.; Strandwitz, Nicholas C.

    2015-11-14

    We report the differences in the passivation and electronic properties of aluminum oxide (Al{sub 2}O{sub 3}) deposited on silicon via traditional hydrolytic atomic layer deposition (ALD) and non-hydrolytic (NH) ALD chemistries. Traditional films were grown using trimethylaluminum (TMA) and water and NHALD films grown using TMA and isopropanol at 300 °C. Hydrolytically grown ALD films contain a smaller amount of fixed charge than NHALD films (oxide fixed charge Q{sub f} {sub Traditional} = −8.1 × 10{sup 11 }cm{sup −2} and Q{sub f} {sub NHALD} = −3.6 × 10{sup 12 }cm{sup −2}), and a larger degree of chemical passivation than NHALD films (density of interface trap states, D{sub it} {sub Traditional} = 5.4 × 10{sup 11 }eV{sup −1 }cm{sup −2} and D{sub it} {sub NHALD} = 2.9 × 10{sup 12 }eV{sup −1 }cm{sup −2}). Oxides grown with both chemistries were found to have a band gap of 7.1 eV. The conduction band offset was 3.21 eV for traditionally grown films and 3.38 eV for NHALD. The increased D{sub it} for NHALD films may stem from carbon impurities in the oxide layer that are at and near the silicon surface, as evidenced by both the larger trap state time constant (τ{sub Traditional} = 2.2 × 10{sup −9} s and τ{sub NHALD} = 1.7 × 10{sup −7} s) and the larger carbon concentration. We have shown that the use of alcohol-based oxygen sources in NHALD chemistry can significantly affect the resulting interfacial electronic behavior presenting an additional parameter for understanding and controlling interfacial electronic properties at semiconductor-dielectric interfaces.

  19. Current-voltage characteristics of organic semiconductors: Interfacial control between organic layers and electrodes

    NASA Astrophysics Data System (ADS)

    Kondo, Takeshi

    2007-12-01

    Current-voltage (I-V) characteristics of organic molecular glasses and solution processable materials embedded between two electrodes were studied to find materials possessing high charge-carrier mobilities and to design organic memory devices. The comparison studies between TOF, FET and SCLC measurements confirm the validity of using analyses of I-V characteristics to determine the mobility of organic semiconductors. Hexaazatrinaphthylene derivatives tri-substituted by electron withdrawing groups were characterized as potential electron transporting molecular glasses. The presence of two isomers has important implications for film morphology and effective mobility. The statistical isomer mixture of hexaazatrinaphthylene derivatized with pentafluoro-phenylmethyl ester is able to form amorphous films, and electron mobilities with the range of 10--2 cm2/Vs are observed in their I-V characteristics. Single-layer organic memory devices consisting of a polymer layer embedded between an Al electrode and ITO modified with Ag nanodots (Ag-NDs) prepared by a solution-based surface assembly demonstrated a potential capability as nonvolatile organic memory device with high ON/OFF switching ratios of 10 4. This level of performance could be achieved by modifying the ITO electrodes with some Ag-NDs that act as trapping sites, reducing the current in the OFF state. Based upon the observed electrical characteristics, the currents of the low-resistance state can be attributed to a tunneling through low-resistance pathways of metal particles originating from the metal top electrode in the organic layer and that the high-resistance state is controlled by charge trapping by the metal particles including Ag-NDs. In an alternative approach, complex films of AgNO3: hexaazatrinaphthylene derivatives were studied as the active layers for all-solution processed and air-stable organic memory devices. Rewritable memory effects were observed in the devices comprised of a thin polymer

  20. Multiple moving interfacial cracks between two dissimilar piezoelectric layers under electromechanical loading

    NASA Astrophysics Data System (ADS)

    Nourazar, Mahsa; Ayatollahi, Mojtaba

    2016-07-01

    The dynamic problem of several moving cracks at the interface between two dissimilar piezoelectric materials is analyzed. The combined out-of-plane mechanical and in-plane electrical loads are applied to the layers. Fourier transforms are used to reduce the problem to a system of singular integral equations with simple Cauchy kernel. The integral equations are solved numerically by converting to a system of linear algebraic equations and by using a collocation technique. The results presented consist of the stress intensity factors and the electric displacement intensity factors. It is found that generally the field intensity factors increase with increasing crack propagation speed.

  1. Assembling carbon quantum dots to a layered carbon for high-density supercapacitor electrodes.

    PubMed

    Chen, Guanxiong; Wu, Shuilin; Hui, Liwei; Zhao, Yuan; Ye, Jianglin; Tan, Ziqi; Zeng, Wencong; Tao, Zhuchen; Yang, Lihua; Zhu, Yanwu

    2016-01-01

    It is found that carbon quantum dots (CQDs) self-assemble to a layer structure at ice crystals-water interface with freeze- drying. Such layers interconnect with each other, forming a free-standing CQD assembly, which has an interlayer distance of about 0.366 nm, due to the existence of curved carbon rings other than hexagons in the assembly. CQDs are fabricated by rupturing C60 by KOH activation with a production yield of ~15 wt.%. The CQDs obtained have an average height of 1.14 nm and an average lateral size of 7.48 nm, and are highly soluble in water. By packaging annealed CQD assembly to high density (1.23 g cm(-3)) electrodes in supercapacitors, a high volumetric capacitance of 157.4 F cm(-3) and a high areal capacitance of 0.66 F cm(-2) (normalized to the loading area of electrodes) are demonstrated in 6 M KOH aqueous electrolyte with a good rate capability. PMID:26754463

  2. Assembling carbon quantum dots to a layered carbon for high-density supercapacitor electrodes

    PubMed Central

    Chen, Guanxiong; Wu, Shuilin; Hui, Liwei; Zhao, Yuan; Ye, Jianglin; Tan, Ziqi; Zeng, Wencong; Tao, Zhuchen; Yang, Lihua; Zhu, Yanwu

    2016-01-01

    It is found that carbon quantum dots (CQDs) self-assemble to a layer structure at ice crystals-water interface with freeze- drying. Such layers interconnect with each other, forming a free-standing CQD assembly, which has an interlayer distance of about 0.366 nm, due to the existence of curved carbon rings other than hexagons in the assembly. CQDs are fabricated by rupturing C60 by KOH activation with a production yield of ~15 wt.%. The CQDs obtained have an average height of 1.14 nm and an average lateral size of 7.48 nm, and are highly soluble in water. By packaging annealed CQD assembly to high density (1.23 g cm−3) electrodes in supercapacitors, a high volumetric capacitance of 157.4 F cm−3 and a high areal capacitance of 0.66 F cm−2 (normalized to the loading area of electrodes) are demonstrated in 6 M KOH aqueous electrolyte with a good rate capability. PMID:26754463

  3. Forming double layer-encapsulated quantum dots for bio-imaging and cell targeting

    NASA Astrophysics Data System (ADS)

    Fahmi, Mochamad Zakki; Chang, Jia-Yaw

    2013-01-01

    We report a simple and effective approach for the preparation of double layer-encapsulated quantum dots (DL-Qdots) composed of alkyl-capping ligands to interdigitate with hydrophobic, protective agents on the surface of AgInS2/ZnS quantum dots (Qdots), which allow phase transfer of hydrophobic Qdots from the organic phase into the aqueous phase. The alkyl-capping ligands consist of a hydrophobic, aliphatic chain and different functional terminal groups (e.g., carboxyl, amine, hydroxyl, and thiol groups) that can serve as reactive sites to chemically couple with other materials. The resulting DL-Qdots bearing various functional groups retain good fluorescence properties and show excellent solubility as well as stability over a range of pH in the aqueous phase. Cytotoxicity studies of DL-Qdots bearing carboxyl groups (DL-Qdots-COOH) were carried out against human cervical (HeLa) cancer cells to elicit no apparent toxicity even at high concentrations of 300 μg mL-1 and 24 h of incubation. To demonstrate their potential biomedical application, DL-Qdots-COOH were further conjugated with folate for staining in HeLa, human liver carcinoma (HepG2), and human breast (MCF-7) cancer cells. Confocal imaging characterization revealed that folate-conjugated DL-Qdots could target most specifically and effectively HeLa cells via folate receptor-mediated targeted delivery compared to HepG2 and MCF-7 cells. The generality and simplicity of this newly developed strategy can possibly be extended to a large variety of hydrophobic Qdots and nanocrystals whose surface protective agents have a long aliphatic chain.

  4. Organic/inorganic hybrid pn-junction between copper phthalocyanine and CdSe quantum dot layers as solar cells

    NASA Astrophysics Data System (ADS)

    Saha, Sudip K.; Guchhait, Asim; Pal, Amlan J.

    2012-08-01

    We have introduced an organic/inorganic hybrid pn-junction for solar cell applications. Layers of II-VI quantum dots and a metal-phthalocyanine in sequence have been used as n- and p-type materials, respectively, to form a junction. The film of quantum dots has been formed through a layer-by-layer process by replacing the long-chain ligands of the nanoparticles in each ultrathin layer or a monolayer with short-chain ones so that interparticle distance becomes small leading to a decrease in resistance of the quantum dot layer. With indium tin oxide and Au as electrodes, we have formed an inverted sandwiched structure. These electrodes formed ohmic contacts with the neighboring materials. From the current-voltage characteristics of the hybrid heterostructure, we have inferred formation of a depletion region at the pn-junction that played a key role in charge separation and correspondingly a photocurrent in the external circuit. For comparison, we have also formed and characterized Schottky devices based on components of the pn-junction keeping the electrode combination same. From capacitance-voltage characteristics, we have observed that the depletion region of the hybrid pn-junction was much wider as compared to that in Schottky devices based on components of the junction.

  5. Three-dimensional nanostructures on Ge/Si(100) wetting layers: Hillocks and pre-quantum dots

    NASA Astrophysics Data System (ADS)

    Ramalingam, Gopalakrishnan; Floro, Jerrold A.; Reinke, Petra

    2016-05-01

    The annealing of sub-critical Ge wetting layers (WL < 3.5 ML) initiates the formation of 3D nanostructures, whose shape and orientation is determined by the WL thickness and thus directly related to the strain energy. The emergence of these nanostructures, hillocks and pre-quantum dots, is studied by scanning tunneling microscopy. A wetting layer deposited at 350 °C is initially rough on the nanometer length-scale and undergoes a progressive transformation and smoothening during annealing at T < 460 °C when vacancy lines and the 2xn reconstruction are observed. The metastable Ge WL then collapses to form 3D nanostructures whose morphology is controlled by the WL thickness: first, the hillocks, with a wedding cake-type structure where the step edges run parallel to the ⟨110⟩ direction, are formed from thin wetting layers, while {105}-faceted structures, called pre-quantum dots (p-QDs), are formed from thicker layers. The wetting layer thickness and thus the misfit strain energy controls the type of structure. The crossover thickness between the hillock and p-QDs regime is between 1.6 and 2.1 ML. The hillocks have larger lateral dimensions and volumes than p-QDs, and the p-QDs are exceptionally small quantum dots with a lower limit of 10 nm in width. Our work opens a new pathway to the control of nanostructure morphology and size in the elastically strained Ge/Si system.

  6. Interfacial n-Doping Using an Ultrathin TiO2 Layer for Contact Resistance Reduction in MoS2.

    PubMed

    Kaushik, Naveen; Karmakar, Debjani; Nipane, Ankur; Karande, Shruti; Lodha, Saurabh

    2016-01-13

    We demonstrate a low and constant effective Schottky barrier height (ΦB ∼ 40 meV) irrespective of the metal work function by introducing an ultrathin TiO2 ALD interfacial layer between various metals (Ti, Ni, Au, and Pd) and MoS2. Transmission line method devices with and without the contact TiO2 interfacial layer on the same MoS2 flake demonstrate reduced (24×) contact resistance (RC) in the presence of TiO2. The insertion of TiO2 at the source-drain contact interface results in significant improvement in the on-current and field effect mobility (up to 10×). The reduction in RC and ΦB has been explained through interfacial doping of MoS2 and validated by first-principles calculations, which indicate metallic behavior of the TiO2-MoS2 interface. Consistent with DFT results of interfacial doping, X-ray photoelectron spectroscopy (XPS) data also exhibit a 0.5 eV shift toward higher binding energies for Mo 3d and S 2p peaks in the presence of TiO2, indicating Fermi level movement toward the conduction band (n-type doping). Ultraviolet photoelectron spectroscopy (UPS) further corroborates the interfacial doping model, as MoS2 flakes capped with ultrathin TiO2 exhibit a reduction of 0.3 eV in the effective work function. Finally, a systematic comparison of the impact of selective doping with the TiO2 layer under the source-drain metal relative to that on top of the MoS2 channel shows a larger benefit for transistor performance from the reduction in source-drain contact resistance. PMID:26649572

  7. Interfacial Energy Alignment at the ITO/Ultra-Thin Electron Selective Dielectric Layer Interface and Its Effect on the Efficiency of Bulk-Heterojunction Organic Solar Cells.

    PubMed

    Itoh, Eiji; Goto, Yoshinori; Saka, Yusuke; Fukuda, Katsutoshi

    2016-04-01

    We have investigated the photovoltaic properties of an inverted bulk heterojunction (BHJ) cell in a device with an indium-tin-oxide (ITO)/electron selective layer (ESL)/P3HT:PCBM active layer/MoOx/Ag multilayered structure. The insertion of only single layer of poly(diallyl-dimethyl-ammonium chloride) (PDDA) cationic polymer film (or poly(ethyleneimine) (PEI) polymeric interfacial dipole layer) and titanium oxide nanosheet (TN) films as an ESL effectively improved cell performance. Abnormal S-shaped curves were observed in the inverted BHJ cells owing to the contact resistance across the ITO/active layer interface and the ITO/PDDA/TN/active layer interface. The series resistance across the ITO/ESL interface in the inverted BHJ cell was successfully reduced using an interfacial layer with a positively charged surface potential with respect to ITO base electrode. The positive dipole in PEI and the electronic charge phenomena at the electrophoretic deposited TN (ED-TN) films on ITO contributed to the reduction of the contact resistance at the electrode interface. The surface potential measurement revealed that the energy alignment by the transfer of electronic charges from the ED-TN to the base electrodes. The insertion of the ESL with a large positive surface potential reduced the potential barrier for the electron injection at ITO/TN interface and it improved the photovoltaic properties of the inverted cell with an ITO/TN/active layer/MoOx/Ag structure. PMID:27451612

  8. A study of the interfacial resistive switching mechanism by proton exchange reactions on the SiO(x) layer.

    PubMed

    Zhou, Fei; Chang, Yao-Feng; Chen, Ying-Chen; Wu, Xiaohan; Zhang, Ye; Fowler, Burt; Lee, Jack C

    2016-01-14

    In this work, we investigated SiO(x)-based interfacial resistive switching in planar metal-insulator-metal structures using physical/chemical/electrical analyses. This work helps clarify the interfacial reaction process and mechanism in SiO(x), and also shows the potential for high temperature operation in future nonvolatile memory applications. PMID:26659556

  9. Contrasting suspended covers reveal the impact of an artificial monolayer on heat transfer processes at the interfacial boundary layer.

    PubMed

    Pittaway, P; Martínez-Alvarez, V; Hancock, N

    2015-01-01

    The highly variable performance of artificial monolayers in reducing evaporation from water storages has been attributed to wind speed and wave turbulence. Other factors operating at the interfacial boundary layer have seldom been considered. In this paper, two physical shade covers differing in porosity and reflectivity were suspended over 10 m diameter water tanks to attenuate wind and wave turbulence. The monolayer octadecanol was applied to one of the covered tanks, and micrometeorological conditions above and below the covers were monitored to characterise diurnal variation in the energy balance. A high downward (air-to-water) convective heat flux developed under the black cover during the day, whereas diurnal variation in the heat flux under the more reflective, wind-permeable white cover was much less. Hourly air and water temperature profiles under the covers over 3 days when forced convection was minimal (low wind speed) were selected for analysis. Monolayer application reduced temperature gain in surface water under a downward convective heat flux, and conversely reduced temperature loss under an upward convective heat flux. This 'dual property' may explain why repeat application of an artificial monolayer to retard evaporative loss (reducing latent heat loss) does not inevitably increase water temperature. PMID:26524454

  10. Role of interfacial friction for flow instabilities in a thin polar-ordered active fluid layer.

    PubMed

    Sarkar, Niladri; Basu, Abhik

    2015-11-01

    We construct a generic coarse-grained dynamics of a thin inflexible planar layer of polar-ordered suspension of active particles that is frictionally coupled to an embedding isotropic passive fluid medium with a friction coefficient Γ. Being controlled by Γ, our model provides a unified framework to describe the long-wavelength behavior of a variety of thin polar-ordered systems, ranging from wet to dry active matter and free-standing active films. Investigations of the linear instabilities around a chosen orientationally ordered uniform reference state reveal generic moving and static instabilities in the system that can depend sensitively on Γ. Based on our results, we discuss estimation of bounds on Γ in experimentally accessible systems. PMID:26651694

  11. Probing confined interfacial excitations in buried layers by Brillouin light scattering

    NASA Astrophysics Data System (ADS)

    Zhang, Xinya; Sooryakumar, R.

    2002-03-01

    Brillouin light scattering from silicon oxynitride films grown on GaAs reveals a low frequency elastic wave excitation at frequencies lying below that of the Rayleigh surface wave. This mode, identified as an excitation localized by the interface, arises from the presence of a soft, thin transition layer between the film and substrate. The results are discussed in the framework of a Green's function formalism that reproduces the experimental features and illustrates the nature of the mode and its difference from Stoneley excitations that are predicted in special cases for an abrupt interface separating two semi-infinite solid media. Observations of this low frequency excitation offer a previously unexplored approach to characterize, non-destructively, the elastic properties of buried interfaces.

  12. Role of interfacial friction for flow instabilities in a thin polar-ordered active fluid layer

    NASA Astrophysics Data System (ADS)

    Sarkar, Niladri; Basu, Abhik

    2015-11-01

    We construct a generic coarse-grained dynamics of a thin inflexible planar layer of polar-ordered suspension of active particles that is frictionally coupled to an embedding isotropic passive fluid medium with a friction coefficient Γ . Being controlled by Γ , our model provides a unified framework to describe the long-wavelength behavior of a variety of thin polar-ordered systems, ranging from wet to dry active matter and free-standing active films. Investigations of the linear instabilities around a chosen orientationally ordered uniform reference state reveal generic moving and static instabilities in the system that can depend sensitively on Γ . Based on our results, we discuss estimation of bounds on Γ in experimentally accessible systems.

  13. [Research on the Highly Stable White LED with CdSe/ZnS Quantum Dot as Light Conversion Layer].

    PubMed

    Cao, Jin; Zhou, Jie; Xie, Jing-weil; Chen, An-ping; Zhang, Xuel; Yin, Lu-qiao; Zhang, Jian-hua

    2016-02-01

    In accordance with the one-step synthesis, in this paper, we synthesized 510, 550 and 630 nm three emission peaks CdSe/ZnS core-shell quantum dots with high stability and high quantum yield whose quantum yield were 82%, 98% and 97%. We used the quantum dot material to replace the phosphor material, and mixed QDs with the silicone uniformly, then dispersed the QDs/silicone composites onto the blue InGaN LEDs to fabricate the QDs-WLEDs. By successively adding different colors of quantum dots for the preparation of quantum dot light converting layer, We investigated that how does the ratio of the three kind of quantum dots whose peaks were 510, 550 and 630 nm effect on the properties of the white LED devices. This paper also studied the mechanism of energy conversion between different colors of quantum dots. We also utilized the mechanism that the quantum dots effect on the white spectrum and color coordinates; we got the results of the optimization of the white device and the ratio of three-color quantum dots. The results show that when the quantum dot ratio is 24:7:10, white LED devices with high stability and high efficiency can be obtained, in the current range of 20-200 mA, the range of color temperature is from 4 607 to 5 920 K, the CIE-1931 coordinates is from (0.355 1,0.348 3) to (0.323 4, 0.336 1), the color rendering index is from 77. 6 to 84. 2, and the highest power efficiency of the devices achieves to 31.69 lm · W⁻¹ @ 20 mA. In addition, in order to further investigate the reason of stable device performance, We studied the effects of time, temperature, UV treatment on the stability of CdSe/ZnS QDs/silicone light conversion material, the results show that the excellent stability of the devices attributes to the stability of the one-step synthesis of core-shell structure of the quantum dot material, the final optimized device is a low-power high-quality white light source and the device has good application prospects in the field of standard white

  14. Interfacial hydrodynamic drag on nanowires embedded in thin oil films and protein layers.

    PubMed

    Lee, Myung Han; Lapointe, Clayton P; Reich, Daniel H; Stebe, Kathleen J; Leheny, Robert L

    2009-07-21

    We investigate the motion of ferromagnetic nanowires confined to nanometer-scale oil films at an air/aqueous interface in response to the application of external magnetic fields and field gradients. By varying the oil viscosity, film thickness, and wire length, we cover two regimes of response suggested by theory: one where the surface viscosity is expected to dominate the wire's motion and one where the subphase viscosity is expected to dominate [Levine, A. J.; Liverpool, T. B.; MacKintosh, F. C. Phys. Rev. E 2004, 69, 021503]. For wire motion parallel to the long axis of the wire, the observed drag agrees reasonably with theoretical predictions. However, the drag on wires moving perpendicular to their long axis or rotating about a short axis is unexpectedly insensitive to the film properties over the full range of measurements. This behavior is in contrast to the rotational and translational drag on nanowires in molecularly thin protein layers, which follow theoretical expectations. The observations in the oil films, which are explained in terms of the manner in which the wire immerses dynamically in the film and subphase, demonstrate how the effective drag viscosity of an aspherical particle confined to a fluid interface can depend on its direction of motion. PMID:19594180

  15. Researching the silicon direct wafer bonding with interfacial SiO2 layer

    NASA Astrophysics Data System (ADS)

    Xiaoqing, Wang; Yude, Yu; Jin, Ning

    2016-05-01

    A silicon wafer direct bonding with a thin SiO2 layer at the interface was investigated. An atomic force microscope (AFM) was employed to characterize the surface roughness and a shearing test was carried out to evaluate the bonding strength. Experiments were performed to analyze the relations of surface roughness and bonding strength with the thickness of SiO2 which was grown by thermal oxidation and plasma enhanced chemical vapor deposition (PECVD) respectively. The bonding strength can reach up to 18 MPa for thermal oxidation and 8 MPa for PECVD after a 2-h 400 °C annealing. Results indicate that the bonding strength is negatively correlated to the thickness of SiO2 at the interface, which is important in designing the MEMS-based devices and other devices built with wafer direct bonding. Project supported by the Key Program of the National Natural Science Foundation of China (No. 61334008) and the National Natural Science Foundation of China (No. 61376072).

  16. Performance and reproducibility enhancement of HgCdTe molecular beam epitaxy growth on CdZnTe substrates using interfacial HgTe/CdTe superlattice layers

    SciTech Connect

    Chang Yong; Zhao Jun; Abad, Hisham; Grein, Christoph H.; Sivananthan, Sivalingam; Aoki, Toshihiro; Smith, David J.

    2005-03-28

    Interfacial layers including HgTe/CdTe superlattices (SLs) were introduced during the molecular-beam epitaxy growth of HgCdTe on CdZnTe (211)B substrates. Transmission-electron-microscopic observations show that the SLs smooth out the substrates' surface roughness during growth, and can also bend or block threading dislocations in a way that prevents their propagation from the substrate into the functional HgCdTe epilayers. An average etch pit density value in the low-10{sup 5} cm{sup -2} range was reproducibly achieved in long wavelength HgCdTe samples, with the best value being 4x10{sup 4} cm{sup -2}. Photoconductive decay lifetime measurements give values approaching theoretical limits, as determined by the intrinsic radiative and Auger recombination mechanisms. The use of such interfacial layers thus leads to enhanced growth yields and material properties.

  17. Poly(3-hexylthiophene-2,5-diyl) as a Hole Transport Layer for Colloidal Quantum Dot Solar Cells.

    PubMed

    Neo, Darren C J; Zhang, Nanlin; Tazawa, Yujiro; Jiang, Haibo; Hughes, Gareth M; Grovenor, Chris R M; Assender, Hazel E; Watt, Andrew A R

    2016-05-18

    Lead sulfide colloidal quantum dot (CQD) solar cells demonstrate extremely high short-circuit currents (Jsc) and are making decent progress in power conversion efficiencies. However, the low fill factors (FF) and open-circuit voltages have to be addressed with urgency to prevent the stalling of efficiency improvements. This paper highlights the importance of improving hole extraction, which received much less attention as compared to the electron-accepting component of the device architecture (e.g., TiO2 or ZnO). Here, we show the use of semiconducting polymer poly(3-hexylthiophene-2,5-diyl) to create efficient CQD devices by improving hole transport, removing interfacial barriers, and minimizing shunt pathways, thus resulting in an overall improvement in device performance stemming from better Jsc and FF. PMID:27090378

  18. Effect with high density nano dot type storage layer structure on 20 nm planar NAND flash memory characteristics

    NASA Astrophysics Data System (ADS)

    Sasaki, Takeshi; Muraguchi, Masakazu; Seo, Moon-Sik; Park, Sung-kye; Endoh, Tetsuo

    2014-01-01

    The merits, concerns and design principle for the future nano dot (ND) type NAND flash memory cell are clarified, by considering the effect of storage layer structure on NAND flash memory characteristics. The characteristics of the ND cell for a NAND flash memory in comparison with the floating gate type (FG) is comprehensively studied through the read, erase, program operation, and the cell to cell interference with device simulation. Although the degradation of the read throughput (0.7% reduction of the cell current) and slower program time (26% smaller programmed threshold voltage shift) with high density (10 × 1012 cm-2) ND NAND are still concerned, the suppress of the cell to cell interference with high density (10 × 1012 cm-2) plays the most important part for scaling and multi-level cell (MLC) operation in comparison with the FG NAND. From these results, the design knowledge is shown to require the control of the number of nano dots rather than the higher nano dot density, from the viewpoint of increasing its memory capacity by MLC operation and suppressing threshold voltage variability caused by the number of dots in the storage layer. Moreover, in order to increase its memory capacity, it is shown the tunnel oxide thickness with ND should be designed thicker (>3 nm) than conventional designed ND cell for programming/erasing with direct tunneling mechanism.

  19. Nonradiative Energy Transfer from Individual CdSe/ZnS Quantum Dots to Single-Layer and Few-Layer Tin Disulfide.

    PubMed

    Zang, Huidong; Routh, Prahlad K; Huang, Yuan; Chen, Jia-Shiang; Sutter, Eli; Sutter, Peter; Cotlet, Mircea

    2016-04-26

    The combination of zero-dimensional (0D) colloidal CdSe/ZnS quantum dots with tin disulfide (SnS2), a two-dimensional (2D)-layered metal dichalcogenide, results in 0D-2D hybrids with enhanced light absorption properties. These 0D-2D hybrids, when exposed to light, exhibit intrahybrid nonradiative energy transfer from photoexcited CdSe/ZnS quantum dots to SnS2. Using single nanocrystal spectroscopy, we find that the rate for energy transfer in 0D-2D hybrids increases with added number of SnS2 layers, a positive manifestation toward the potential functionality of such 2D-based hybrids in applications such as photovoltaics and photon sensing. PMID:27031885

  20. Annealing induced interfacial layers in niobium-clad stainless steel developed as a bipolar plate material for polymer electrolyte membrane fuel cell stacks

    SciTech Connect

    Hong, Sung Tae; Weil, K. Scott; Choi, Jung-Pyung; Bae, In-Tae; Pan, Jwo

    2010-05-01

    Niobium (Nb)-clad 304L stainless steel (SS) manufactured by cold rolling is currently under consideration for use as a bipolar plate material in polymer electrolyte membrane fuel cell (PEMFC) stacks. To make the fabrication of bipolar plates using the Nb-clad SS feasible, annealing may be necessary for the Nb-clad SS to reduce the springback induced by cold rolling. However, the annealing can develop an interfacial layer between the Nb cladding and the SS core and the interfacial layer plays a key role in the failure of the Nb-clad SS as reported earlier [JPS our work]. In this investigation, the Nb-clad SS specimens in as-rolled condition were annealed at different combinations of temperature and time. Based on the results of scanning electron microscope (SEM) analysis, an annealing process map for the Nb-clad SS was obtained. The results of SEM analysis and Transmission Electron Microscope (TEM) analysis also suggest that different interfacial layers occurred based on the given annealing conditions.

  1. Microscale X-ray tomographic investigation of the interfacial morphology between the catalyst and micro porous layers in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Prass, Sebastian; Hasanpour, Sadegh; Sow, Pradeep Kumar; Phillion, André B.; Mérida, Walter

    2016-07-01

    The interfacial morphology between the catalyst layer (CL) and micro porous layer (MPL) influences the performance of proton exchange membrane fuel cells (PEMFCs). Here we report a direct method to investigate the CL-MPL interfacial morphology of stacked and compressed gas diffusion layer (GDL with MPL)-catalyst coated membrane (CCM) assemblies. The area, origin and dimensions of interfacial gaps are studied with high-resolution X-ray micro computed tomography (X-μCT). The projected gap area (fraction of the CL-MPL interface separated by gaps) is higher for GDL-CCM assemblies with large differences in the surface roughness between CL and MPL but reduces with increasing compression and similarity in roughness. Relatively large continuous gaps are found in proximity to cracks in the MPL. These are hypothesized to form due to the presence of large pores on the surface of the GDL. Smaller gaps are induced by the surface roughness features throughout the CL-MPL interface. By modification of the pore sizes on the GDL surface serving as substrate for the MPL, the number and dimension of MPL crack induced gaps can be manipulated. Moreover, adjusting the CL and MPL surface roughness parameters to achieve similar orders of roughness can improve the surface mating characteristics of these two components.

  2. Detection of single photons by a resonant tunneling heterostructure with a quantum dot layer

    SciTech Connect

    Khanin, Yu. N. Vdovin, E. E.

    2010-08-15

    Light absorption by GaAs/AlAs heterostructures with a layer of self-assembled InAs quantum dots (QDs) at resonant tunneling through an energy-selected QD has been investigated. A high sensitivity of the current through this selected tunneling channel to the absorption of single photons with a wavelength {lambda} {<=} 860 nm up to a temperature of 50 K is demonstrated; this sensitivity is caused by the Coulomb effect of the photoexcited holes captured by surrounding QDs on the resonance conditions. It is shown that single-photon absorption can discretely change the current through the system under study by a factor of more than 50. The captured-hole lifetimes have been measured, and a model has been developed to qualitatively describe the experimental data. It is also demonstrated that the InAs monolayer can effectively absorb photons. The properties of the heterostructure studied can be used not only to detect photons but also to design logical valves and optical memory devices.

  3. Anisotropic Lattice Deformation of InAs Self-Assembled Quantum Dots Embedded in GaNAs Strain Compensating Layers

    NASA Astrophysics Data System (ADS)

    Matsumura, N.; Muto, S.; Ganapathy, S.; Suemune, I.; Numata, K.; Yabuta, K.

    2006-01-01

    Lattice deformations of InAs self-assembled quantum dots, which were grown on (001)GaAs substrates and embedded in GaNAs strain compensating layers (SCLs), were examined with an ion-channeling method in Rutherford backscattering spectrometry. The channeling experiments demonstrated that the increase of the nitrogen concentrations in the GaNAs SCLs caused the indium lattice displacements along the [001] growth direction while those parallel to the (001) crystal plane were kept unchanged.

  4. Effect of self-assembled InAs islands on the interfacial roughness of optical-switched resonant tunneling diode.

    PubMed

    Tian, Haitao; Wang, Lu; Shi, Zhenwu; Gao, Huaiju; Zhang, Shuhui; Wang, Wenxin; Chen, Hong

    2012-01-01

    Embedding a quantum dot [QD] layer between the double barriers of resonant tunneling diode [RTD] is proved to be an effective method to increase the sensitivity of QD-RTD single-photon detector. However, the interfacial flatness of this device would be worsened due to the introduction of quantum dots. In this paper, we demonstrate that the interfacial quality of this device can be optimized through increasing the growth temperature of AlAs up barrier. The glancing incidence X-ray reflectivity and the high-resolution transmission electron microscopy measurements show that the interfacial smoothness has been greatly improved, and the photo-luminescence test indicated that the InAs QDs were maintained at the same time. The smoother interface was attributed to the evaporation of segregated indium atoms at InGaAs surface layer. PACS: 73.40.GK, 73.23._b, 73.21.La, 74.62.Dh. PMID:22333518

  5. Effect of self-assembled InAs islands on the interfacial roughness of optical-switched resonant tunneling diode

    PubMed Central

    2012-01-01

    Embedding a quantum dot [QD] layer between the double barriers of resonant tunneling diode [RTD] is proved to be an effective method to increase the sensitivity of QD-RTD single-photon detector. However, the interfacial flatness of this device would be worsened due to the introduction of quantum dots. In this paper, we demonstrate that the interfacial quality of this device can be optimized through increasing the growth temperature of AlAs up barrier. The glancing incidence X-ray reflectivity and the high-resolution transmission electron microscopy measurements show that the interfacial smoothness has been greatly improved, and the photo-luminescence test indicated that the InAs QDs were maintained at the same time. The smoother interface was attributed to the evaporation of segregated indium atoms at InGaAs surface layer. PACS 73.40.GK, 73.23._b, 73.21.La, 74.62.Dh PMID:22333518

  6. Ultrafine nickel oxide quantum dots enbedded with few-layer exfoliative graphene for an asymmetric supercapacitor: Enhanced capacitances by alternating voltage

    NASA Astrophysics Data System (ADS)

    Jing, Mingjun; Wang, Chiwei; Hou, Hongshuai; Wu, Zhibin; Zhu, Yirong; Yang, Yingchang; Jia, Xinnan; Zhang, Yan; Ji, Xiaobo

    2015-12-01

    A green and one-step method of electrochemical alternating voltage has been utilized to form NiO quantum dots/graphene flakes (NiO-dots/Gh) for supercapacitor applications. NiO quantum dots (∼3 nm) are uniformly deposited on few-layer graphene surfaces by oxygen functional groups on graphene surface that is naturally utilized to bridge NiO and graphene through Ni-O-C bands, which exhibits outstanding specific capacitance 1181.1 F g-1 at a current density of 2.1 A g-1 and rate behavior 66.2% at 42 A g-1 as NiO dots can be fleetly wired up to current collector through the underlying graphene two-dimensional layers. The NiO-dots/Gh composite is further undertaken in asymmetric supercapacitors with high energy density (27.3 Wh kg-1 at 1562.6 W kg-1).

  7. Initial stages of chain formation in a single layer of (In,Ga)As quantum dots grown on GaAs (100)

    SciTech Connect

    Schmidbauer, M.; Wang, Zh. M.; Mazur, Yu. I.; Lytvyn, P. M.; Salamo, G. J.; Grigoriev, D.; Schaefer, P.; Koehler, R.; Hanke, M.

    2007-08-27

    The self-organized formation of In{sub 0.40}Ga{sub 0.60}As quantum dot chains was investigated using x-ray scattering. Two samples were compared grown on GaAs(100) by molecular beam epitaxy. The first sample with a single layer of In{sub 0.40}Ga{sub 0.60}As dots shows weak quantum dot alignment and a corresponding elongated shape along [011], while the top layer of a multilayered In{sub 0.40}Ga{sub 0.60}As/GaAs sample exhibits extended and highly regular quantum dot chains oriented along [011]. Numerical calculations of the three-dimensional strain fields are used to explain the initial stages of chain formation by anisotropic strain relaxation induced by the elongated dot shape.

  8. Efficient, air-stable colloidal quantum dot solar cells encapsulated using atomic layer deposition of a nanolaminate barrier

    SciTech Connect

    Ip, Alexander H.; Labelle, André J.; Sargent, Edward H.

    2013-12-23

    Atomic layer deposition was used to encapsulate colloidal quantum dot solar cells. A nanolaminate layer consisting of alternating alumina and zirconia films provided a robust gas permeation barrier which prevented device performance degradation over a period of multiple weeks. Unencapsulated cells stored in ambient and nitrogen environments demonstrated significant performance losses over the same period. The encapsulated cell also exhibited stable performance under constant simulated solar illumination without filtration of harsh ultraviolet photons. This monolithically integrated thin film encapsulation method is promising for roll-to-roll processed high efficiency nanocrystal solar cells.

  9. Improved Optical Performance of InAs Quantum Dot Structure via Suitable Manipulation of GaAs Cap Layer Growth

    NASA Astrophysics Data System (ADS)

    Qi, Zhiqiang; Li, Senlin; Sun, Shichuang; Zhang, Wei; Ye, Wei; Fang, Yanyan; Dai, Jiangnan; Chen, Changqing

    2016-01-01

    The influences of the different growth methods of GaAs cap layer on the self-assembled InAs quantum dots were investigated via photoluminescence and transmission electron microscopy. A two-step growth technique, consisting of a low temperature pulsed atomic layer epitaxy and a high temperature conventional continuous growth method, could improve the surface morphology and photoluminescence intensity due to the enhancement of Ga atomic mobility and the reduction in dislocation density. Furthermore, the photoluminescence peak shows a red shift instead of a blue shift due to the strain relaxation.

  10. Enhancing the performances of P3HT:PCBM – MoS3 based H2-evolving photocathodes with interfacial layers

    PubMed Central

    Bourgeteau, Tiphaine; Tondelier, Denis; Geffroy, Bernard; Brisse, Romain; Cornut, Renaud; Artero, Vincent; Jousselme, Bruno

    2015-01-01

    Organic semiconductors have great potential for producing hydrogen in a durable and economically viable manner, as they rely on readily available materials and can be solution-processed over large areas. With the objective of building efficient hybrid organic-inorganic photo-electrochemical cells, we combined a noble metal-free and solution-processable catalyst for proton reduction, MoS3, and a poly-(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction (BHJ). Different interfacial layers were investigated to improve the charge transfer between P3HT:PCBM and MoS3. Metallic Al\\Ti interfacial layers led to an increase of the photocurrent up to 8 mA cm−2 at reversible hydrogen electrode (RHE) potential with a 0.6 V anodic shift of the HER onset potential, a value close to the open circuit potential of the P3HT:PCBM solar cell. A 50 nm thick C60 layer also works as interfacial layer, with current density reaching 1 mA cm−2 at RHE potential. Moreover, two recently highlighted1 figures-of-merit, measuring the ratio of power saved, Φsaved,ideal and Φsaved,NPAC, were evaluated and discussed to compare the performances of various photocathodes assessed in a three-electrode configuration. Φsaved,ideal and Φsaved,NPAC use the RHE and a non-photoactive electrode with identical catalyst as dark electrode, respectively. They provide different information especially for the differentiation of the role of the photogenerating layer and the role of the catalyst. Best results were obtained with the Al\\Ti metallic interlayer, with Φsaved,ideal and Φsaved,NPAC reaching 0.64 % and 2.05 % respectively. PMID:26151685

  11. n-Type Transition Metal Oxide as a Hole Extraction Layer in PbS Quantum Dot Solar Cells

    SciTech Connect

    Gao, Jianbo; Perkins, Craig L.; Luther, Joseph M.; Hanna, Mark C.; Chen, Hsiang-Yu; Semonin, Octavi E.; Nozik, Arthur J.; Ellingson, Randy J.; Beard, Matthew C.

    2011-08-10

    The n-type transition metal oxides (TMO) consisting of molybdenum oxide (MoO{sub x}) and vanadium oxide (V₂O{sub x}) are used as an efficient hole extraction layer (HEL) in heterojunction ZnO/PbS quantum dot solar cells (QDSC). A 4.4% NREL-certified device based on the MoO{sub x} HEL is reported with Al as the back contact material, representing a more than 65% efficiency improvement compared with the case of Au contacting the PbS quantum dot (QD) layer directly. We find the acting mechanism of the hole extraction layer to be a dipole formed at the MoO{sub x} and PbS interface enhancing band bending to allow efficient hole extraction from the valence band of the PbS layer by MoO{sub x}. The carrier transport to the metal anode is likely enhanced through shallow gap states in the MoO{sub x} layer.

  12. Core-level spectroscopy of the Ni/W(110) interface: Correlation of W interfacial core-level shifts with first-layer Ni phases

    SciTech Connect

    Riffe,D.; Franckowiak, R.; Shinn, N.; Kim, B.; Kim, K.; Kang, T.

    2008-01-01

    We have measured W 4f7/2 core-level photoemission spectra from W(1 1 0) in the presence of Ni overlayers, from {approx}0.2 to {approx}3 monolayers. Interfacial core-level shifts associated with first-layer Ni phases have been identified: -230 {+-} 15 meV for the 1 x 1 pseudomorphic phase and -70 {+-} 7 meV for the 7 x 1 close-packed commensurate phase. At higher Ni coverages the interfacial core-level shift is -100 {+-} 10 meV. These shifts are analyzed using the partial-shift model of Nilsson et al.; the analysis indicates that the difference in binding energies between the 1 x 1 and 7 x 1 phases has a large contribution from structural differences between the two phases.

  13. Effect of atomic layer deposition growth temperature on the interfacial characteristics of HfO{sub 2}/p-GaAs metal-oxide-semiconductor capacitors

    SciTech Connect

    Liu, C.; Zhang, Y. M.; Zhang, Y. M.; Lv, H. L.

    2014-12-14

    The effect of atomic layer deposition (ALD) growth temperature on the interfacial characteristics of p-GaAs MOS capacitors with ALD HfO{sub 2} high-k dielectric using tetrakis(ethylmethyl)amino halfnium precursor is investigated in this study. Using the combination of capacitance-voltage (C-V) and X-ray photoelectron spectroscopy (XPS) measurements, ALD growth temperature is found to play a large role in controlling the reaction between interfacial oxides and precursor and ultimately determining the interface properties. The reduction of surface oxides is observed to be insignificant for ALD at 200 °C, while markedly pronounced for growth at 300 °C. The corresponding C-V characteristics are also shown to be ALD temperature dependent and match well with the XPS results. Thus, proper ALD process is crucial in optimizing the interface quality.

  14. Role of interfacial layer on complementary resistive switching in the TiN/HfO{sub x}/TiN resistive memory device

    SciTech Connect

    Zhang, H. Z.; Ang, D. S. Gu, C. J.; Yew, K. S.; Wang, X. P.; Lo, G. Q.

    2014-12-01

    The role of the bottom interfacial layer (IL) in enabling stable complementary resistive switching (CRS) in the TiN/HfO{sub x}/IL/TiN resistive memory device is revealed. Stable CRS is obtained for the TiN/HfO{sub x}/IL/TiN device, where a bottom IL comprising Hf and Ti sub-oxides resulted from the oxidation of TiN during the initial stages of atomic-layer deposition of HfO{sub x} layer. In the TiN/HfO{sub x}/Pt device, where formation of the bottom IL is suppressed by the inert Pt metal, no CRS is observed. Oxygen-ion exchange between IL and the conductive path in HfO{sub x} layer is proposed to have caused the complementary bipolar switching behavior observed in the TiN/HfO{sub x}/IL/TiN device.

  15. Inkjet-assisted layer-by-layer printing of quantum dot/enzyme microarrays for highly sensitive detection of organophosphorous pesticides.

    PubMed

    Luan, Enxiao; Zheng, Zhaozhu; Li, Xinyu; Gu, Hongxi; Liu, Shaoqin

    2016-04-15

    We present a facile fabrication of layer-by-layer (LbL) microarrays of quantum dots (QDs) and acetylcholinesterase enzyme (AChE). The resulting arrays had several unique properties, such as low cost, high integration and excellent flexibility and time-saving. The presence of organophosphorous pesticides (OPs) can inhibit the AChE activity and thus changes the fluorescent intensity of QDs/AChE microscopic dot arrays. Therefore, the QDs/AChE microscopic dot arrays were used for the sensitive visual detection of OPs. Linear calibration for parathion and paraoxon was obtained in the range of 5-100 μg L(-1) under the optimized conditions with the limit of detection (LOD) of 10 μg L(-1). The arrays have been successfully used for detection of OPs in fruits and water real samples. The new array was validated by comparison with conventional high performance liquid chromatography-mass spectrometry (HPLC-MS). PMID:27016441

  16. Effect of anode buffer layer on the efficiency of inverted quantum-dot light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Ram Cho, Ye; Kang, Pil-Gu; Shin, Dong Heon; Kim, Ji-Hoon; Maeng, Min-Jae; Sakong, Jeonghun; Hong, Jong-Am; Park, Yongsup; Suh, Min Chul

    2016-01-01

    The impact of anode buffer layers (ABLs) on the performance of CdSe quantum-dot light-emitting diodes (QLED) with a ZnO nanoparticle (NP) electron-transport layer and 4,4‧-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) hole-transport layer was studied. Either MoO3 or 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) was used as the ABL. The QLED with a HAT-CN ABL exhibited better luminance performance, while the ultraviolet photoelectron spectroscopy and hole-only devices indicated that MoO3 was a superior hole injector. These results suggest that the QLED with a MoO3 ABL suffered from a severe charge carrier imbalance. Therefore, electron injection through the ZnO NP layer must be improved to further enhance the QLED performance.

  17. Optical properties of multi-layer type II InP/GaAs quantum dots studied by surface photovoltage spectroscopy

    NASA Astrophysics Data System (ADS)

    Ivanov, Ts.; Donchev, V.; Germanova, K.; Gomes, P. F.; Iikawa, F.; Brasil, M. J. S. P.; Cotta, M. A.

    2011-09-01

    We present a low-temperature (73 K) study of the optical properties of multi-layer type II InP/GaAs self-assembled quantum dots by means of surface photovoltage (SPV) spectroscopy, taking advantage of its high sensitivity and contactless nature. The samples contain 10 periods of InP quantum dot planes separated by 5 nm GaAs spacers. The SPV amplitude spectra reveal two major broad peaks, situated at low and high energies, respectively. These features are analyzed taking into account the type II character of the structure, the quantum coupling effects, the spectral behavior of the SPV phase, and the photoluminescence spectra. As a result they have been attributed to optical transitions in the quantum dots and the wetting layers, respectively. The main mechanism for carrier separation in the SPV generation process is clarified via the analysis of the SPV phase spectra. The influence of the substrate absorption on the SPV spectra is discussed in details.

  18. PbS Quantum Dots Sensitized TiO2 Solar Cells Prepared by Successive Ionic Layer Absorption and Reaction with Different Adsorption Layers.

    PubMed

    Yi, Jie; Duan, Yanfang; Liu, Chunxia; Gao, Shaohong; Han, Xueting; An, Limin

    2016-04-01

    Lead sulfide (PbS) quantum dots (QDs) have been synthesized via successive ionic layer adsorption and reaction (SILAR) on a titanium dioxide (TiO2) nanoporous film for the fabrication of quantum dot-sensitized solar cells (QDSCs). The reaction is environmental friendly and energy saving. The green synthesized PbS QDs match the maximum remittance region of the solar spectrum and are suitable as sensitizers for TiO2 electrodes for cell devices application. PbS QDs were adsorbed in different adsorption layers in order to improve the solar cell performance. The optical properties of PbS sensitized TiO2 films were studied by scanning electron microscopy and UV-Vis absorbance spectroscopy. The photovoltaic characteristics of the PbS QDSCs were analyzed by I-V characteristics and electrochemical impedance spectroscopy. As a result, the light harvesting was enhanced with increasing SILAR adsorption layers. The maximum photovoltaic conversion efficiency of the PbS QDSCs (3.14%) was obtained at the 12 adsorption layers with the highest short circuit current density and lowest charge transfer resistance. PMID:27451735

  19. Electric Interfacial Layer of Modified Cellulose Nanocrystals in Aqueous Electrolyte Solution: Predictions by the Molecular Theory of Solvation.

    PubMed

    Lyubimova, Olga; Stoyanov, Stanislav R; Gusarov, Sergey; Kovalenko, Andriy

    2015-06-30

    The X-ray crystal structure-based models of Iα cellulose nanocrystals (CNC), both pristine and containing surface sulfate groups with negative charge 0-0.34 e/nm(2) produced by sulfuric acid hydrolysis of softwood pulp, feature a highly polarized "crystal-like" charge distribution. We perform sampling using molecular dynamics (MD) of the structural relaxation of neutral pristine and negatively charged sulfated CNC of various lengths in explicit water solvent and then employ the statistical mechanical 3D-RISM-KH molecular theory of solvation to evaluate the solvation structure and thermodynamics of the relaxed CNC in ambient aqueous NaCl solution at a concentration of 0.0-0.25 mol/kg. The MD sampling induces a right-hand twist in CNC and rearranges its initially ordered structure with a macrodipole of high-density charges at the opposite faces into small local spots of alternating charge at each face. This surface charge rearrangement observed for both neutral and charged CNC significantly affects the distribution of ions around CNC in aqueous electrolyte solution. The solvation free energy (SFE) of charged sulfated CNC has a minimum at a particular electrolyte concentration depending on the surface charge density, whereas the SFE of neutral CNC increases linearly with NaCl concentration. The SFE contribution from Na(+) counterions exhibits behavior similar to the NaCl concentration dependence of the whole SFE. An analysis of the 3D maps of Na(+) density distributions shows that these model CNC particles exhibit the behavior of charged nanocolloids in aqueous electrolyte solution: an increase in electrolyte concentration shrinks the electric interfacial layer and weakens the effective repulsion between charged CNC particles. The 3D-RISM-KH method readily treats solvent and electrolyte of a given nature and concentration to predict effective interactions between CNC particles in electrolyte solution. We provide CNC structural models and a modeling procedure for

  20. Fabrication of quantum dots in undoped Si/Si0.8Ge0.2 heterostructures using a single metal-gate layer

    DOE PAGESBeta

    Lu, T. M.; Gamble, J. K.; Muller, R. P.; Nielsen, E.; Bethke, D.; Ten Eyck, G. A.; Pluym, T.; Wendt, J. R.; Dominguez, J.; Lilly, M. P.; et al

    2016-08-29

    Enhancement-mode Si/SiGe electron quantum dots have been pursued extensively by many groups for their potential in quantum computing. Most of the reported dot designs utilize multiple metal-gate layers and use Si/SiGe heterostructures with Ge concentration close to 30%. Here, we report the fabrication and low-temperature characterization of quantum dots in the Si/Si0.8Ge0.2 heterostructures using only one metal-gate layer. We find that the threshold voltage of a channel narrower than 1 μm increases as the width decreases. The higher threshold can be attributed to the combination of quantum confinement and disorder. We also find that the lower Ge ratio used heremore » leads to a narrower operational gate bias range. The higher threshold combined with the limited gate bias range constrains the device design of lithographic quantum dots. We incorporate such considerations in our device design and demonstrate a quantum dot that can be tuned from a single dot to a double dot. Furthermore, the device uses only a single metal-gate layer, greatly simplifying device design and fabrication.« less

  1. Iridium Interfacial Stack (IRIS)

    NASA Technical Reports Server (NTRS)

    Spry, David James (Inventor)

    2015-01-01

    An iridium interfacial stack ("IrIS") and a method for producing the same are provided. The IrIS may include ordered layers of TaSi.sub.2, platinum, iridium, and platinum, and may be placed on top of a titanium layer and a silicon carbide layer. The IrIS may prevent, reduce, or mitigate against diffusion of elements such as oxygen, platinum, and gold through at least some of its layers.

  2. Wavefunction engineering: From quantum wells to near-infrared type-II colloidal quantum dots synthesized by layer-by-layer colloidal epitaxy.

    PubMed

    Li, J Jack; Tsay, James M; Michalet, Xavier; Weiss, Shimon

    2005-11-15

    We review the concept and the evolution of bandgap and wavefunction engineering, the seminal contributions of Dr. Chemla to the understanding of the rich phenomena displayed in epitaxially grown quantum confined systems, and demonstrate the application of these concepts to the colloidal synthesis of high quality type-II CdTe/CdSe quantum dots using successive ion layer adsorption and reaction chemistry. Transmission electron microscopy reveals that CdTe/CdSe can be synthesized layer by layer, yielding particles of narrow size distribution. Photoluminescence emission and excitation spectra reveal discrete type-II transitions, which correspond to energy lower than the type-I bandgap. The increase in the spatial separation between photoexcited electrons and holes as a function of successive addition of CdSe monolayers was monitored by photoluminescence lifetime measurements. Systematic increase in lifetimes demonstrates the high level of wavefunction engineering and control in these systems. PMID:22865949

  3. Low-temperature studies of magnetic phases of the interfacial layers for Co/Ge(100) and Co/Ge(111) films

    NASA Astrophysics Data System (ADS)

    Tsay, J. S.; Su, C. W.; Hwang, C. H.; Yao, Y. D.

    2005-07-01

    Magnetic phases of the interfacial layers were comparatively investigated for Co/Ge(100) and Co/Ge(111) films thinner than 13 ML using surface magneto-optic Kerr effect technique. Co/Ge(100) films are nonferromagnetic up to 12 ML as deposited and measured at 300 K. A transition from nonferromagnetism to ferromagnetism occurs upon cryogenic treatments. Systematic investigations of the magnetic properties for Co/Ge(100) reveal a magnetic phase diagram. The boundary between nonferromagnetic and ferromagnetic phases was experimentally determined to be from below 150 K to above 300 K as the cobalt thickness increases from 9 to 13 ML. This behavior is consistent with the thickness-dependent scaling law of the Curie temperature for a thin film system. Because of the difference of the densities of surface atoms, the different thickness of the formed interfacial compounds could explain the shift of the phase boundary to higher Co thickness side as compared to the Co/Ge(111) system. In addition, the critical exponent β in the power law relationship of magnetization for Co/Ge(100) films lies close to the value expected by the three-dimensional Heisenberg model, while the critical exponent of Co/Ge(111) is close to the value of the two-dimensional XY model. The different behaviors of the magnetic transition are attributed to the different interfacial structures.

  4. Performance enhancement of GaN metal–semiconductor–metal ultraviolet photodetectors by insertion of ultrathin interfacial HfO{sub 2} layer

    SciTech Connect

    Kumar, Manoj E-mail: aokyay@ee.bilkent.edu.tr; Tekcan, Burak; Okyay, Ali Kemal E-mail: aokyay@ee.bilkent.edu.tr

    2015-03-15

    The authors demonstrate improved device performance of GaN metal–semiconductor–metal ultraviolet (UV) photodetectors (PDs) by ultrathin HfO{sub 2} (UT-HfO{sub 2}) layer on GaN. The UT-HfO{sub 2} interfacial layer is grown by atomic layer deposition. The dark current of the PDs with UT-HfO{sub 2} is significantly reduced by more than two orders of magnitude compared to those without HfO{sub 2} insertion. The photoresponsivity at 360 nm is as high as 1.42 A/W biased at 5 V. An excellent improvement in the performance of the devices is ascribed to allowed electron injection through UT-HfO{sub 2} on GaN interface under UV illumination, resulting in the photocurrent gain with fast response time.

  5. Temperature dependence of interlayer coupling between perpendicular magnetic [CoFeB/Pd] multilayers: Influence of interfacial CoFeB layer

    NASA Astrophysics Data System (ADS)

    Xiao, Yili; Zhang, Zongzhi; Ma, Bin; Jin, Q. Y.; Liu, Yaowen

    2014-02-01

    Temperature dependence of interlayer coupling field in the perpendicular antiferromagnetic structure of [Pd/CoFeB]2/Pd/CoFeB(tCFB)/Ru(tRu)/CoFeB(tCFB)/Pd/[CoFeB/Pd]2 is found to be sensitive to tCFB, showing various non-monotonic behaviors. The coupling strength increases with tCFB, reaching bulk-like value of up to 0.28 erg/cm2 at room temperature as tCFB is over 0.6 nm. We attribute the phenomena to interfacial effects, including lowered Curie temperature in ultrathin CoFeB layers and increased effective dead layer thickness. The coupling peak position of tRu also shifts with temperature and tCFB, corresponding to variations in dead layer thicknesses. These effects should be considered when designing practical devices employing perpendicular synthetic antiferromagnetic structures.

  6. Tuning the interfacial hole injection barrier between p-type organic materials and Co using a MoO{sub 3} buffer layer

    SciTech Connect

    Wang Yuzhan; Wee, Andrew T. S.; Cao Liang; Qi Dongchen; Chen Wei; Gao Xingyu

    2012-08-01

    We demonstrate that the interfacial hole injection barrier {Delta}{sub h} between p-type organic materials (i.e., CuPc and pentacene) and Co substrate can be tuned by the insertion of a MoO{sub 3} buffer layer. Using ultraviolet photoemission spectroscopy, it was found that the introduction of MoO{sub 3} buffer layer effectively reduces the hole injection barrier from 0.8 eV to 0.4 eV for the CuPc/Co interface, and from 1.0 eV to 0.4 eV for the pentacene/Co interface, respectively. In addition, by varying the thickness of the buffer, the tuning effect of {Delta}{sub h} is shown to be independent of the thickness of MoO{sub 3} interlayer at both CuPc/Co and pentacene/Co interfaces. This Fermi level pinning effect can be explained by the integer charge-transfer model. Therefore, the MoO{sub 3} buffer layer has the potential to be applied in p-type organic spin valve devices to improve the device performance via reducing the interfacial hole injection barrier.

  7. Influence of post-deposition annealing on interfacial properties between GaN and ZrO{sub 2} grown by atomic layer deposition

    SciTech Connect

    Ye, Gang; Wang, Hong Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Geok Ng, Serene Lay; Ji, Rong; Liu, Zhi Hong

    2014-10-13

    Influence of post-deposition annealing on interfacial properties related to the formation/annihilation of interfacial GaO{sub x} layer of ZrO{sub 2} grown by atomic layer deposition (ALD) on GaN is studied. ZrO{sub 2} films were annealed in N{sub 2} atmospheres in temperature range of 300 °C to 700 °C and analyzed by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It has been found that Ga-O bond to Ga-N bond area ratio decreases in the samples annealed at temperatures lower than 500 °C, which could be attributed to the thinning of GaO{sub x} layer associated with low surface defect states due to “clean up” effect of ALD-ZrO{sub 2} on GaN. However, further increase in annealing temperature results in deterioration of interface quality, which is evidenced by increase in Ga-O bond to Ga-N bond area ratio and the reduction of Ga-N binding energy.

  8. GeOx interfacial layer scavenging remotely induced by metal electrode in metal/HfO2/GeOx/Ge capacitors

    NASA Astrophysics Data System (ADS)

    Lee, Taehoon; Jung, Yong Chan; Seong, Sejong; Lee, Sung Bo; Park, In-Sung; Ahn, Jinho

    2016-07-01

    The metal gate electrodes of Ni, W, and Pt have been investigated for their scavenging effect: a reduction of the GeOx interfacial layer (IL) between HfO2 dielectric and Ge substrate in metal/HfO2/GeOx/Ge capacitors. All the capacitors were fabricated using the same process except for the material used in the metal electrodes. Capacitance-voltage measurements, scanning transmission electron microscopy, and electron energy loss spectroscopy were conducted to confirm the scavenging of GeOx IL. Interestingly, these metals are observed to remotely scavenge the interfacial layer, reducing its thickness in the order of Ni, W, and then Pt. The capacitance equivalent thickness of these capacitors with Ni, W, and Pt electrodes are evaluated to be 2.7 nm, 3.0 nm, and 3.5 nm, and each final remnant physical thickness of GeOx IL layer is 1.1 nm 1.4 nm, and 1.9 nm, respectively. It is suggested that the scavenging effect induced by the metal electrodes is related to the concentration of oxygen vacancies generated by oxidation reaction at the metal/HfO2 interface.

  9. A CdSe thin film: a versatile buffer layer for improving the performance of TiO2 nanorod array:PbS quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Tan, Furui; Wang, Zhijie; Qu, Shengchun; Cao, Dawei; Liu, Kong; Jiang, Qiwei; Yang, Ying; Pang, Shan; Zhang, Weifeng; Lei, Yong; Wang, Zhanguo

    2016-05-01

    To fully utilize the multiple exciton generation effects in quantum dots and improve the overall efficiency of the corresponding photovoltaic devices, nanostructuralizing the electron conducting layer turns out to be a feasible strategy. Herein, PbS quantum dot solar cells were fabricated on the basis of morphologically optimized TiO2 nanorod arrays. By inserting a thin layer of CdSe quantum dots into the interface of TiO2 and PbS, a dramatic enhancement in the power conversion efficiency from 4.2% to 5.2% was realized and the resulting efficiency is one of the highest values for quantum dot solar cells based on nanostructuralized buffer layers. The constructed double heterojunction with a cascade type-II energy level alignment is beneficial for promoting photogenerated charge separation and reducing charge recombination, thereby responsible for the performance improvement, as revealed by steady-state analyses as well as ultra-fast photoluminescence and photovoltage decays. Thus this paper provides a good buffer layer to the community of quantum dot solar cells.To fully utilize the multiple exciton generation effects in quantum dots and improve the overall efficiency of the corresponding photovoltaic devices, nanostructuralizing the electron conducting layer turns out to be a feasible strategy. Herein, PbS quantum dot solar cells were fabricated on the basis of morphologically optimized TiO2 nanorod arrays. By inserting a thin layer of CdSe quantum dots into the interface of TiO2 and PbS, a dramatic enhancement in the power conversion efficiency from 4.2% to 5.2% was realized and the resulting efficiency is one of the highest values for quantum dot solar cells based on nanostructuralized buffer layers. The constructed double heterojunction with a cascade type-II energy level alignment is beneficial for promoting photogenerated charge separation and reducing charge recombination, thereby responsible for the performance improvement, as revealed by steady

  10. Improvement of performance of InAs quantum dot solar cell by inserting thin AlAs layers

    PubMed Central

    2011-01-01

    A new measure to enhance the performance of InAs quantum dot solar cell is proposed and measured. One monolayer AlAs is deposited on top of InAs quantum dots (QDs) in multistack solar cells. The devices were fabricated by molecular beam epitaxy. In situ annealing was intended to tune the QD density. A set of four samples were compared: InAs QDs without in situ annealing with and without AlAs cap layer and InAs QDs in situ annealed with and without AlAs cap layer. Atomic force microscopy measurements show that when in situ annealing of QDs without AlAs capping layers is investigated, holes and dashes are present on the device surface, while capping with one monolayer AlAs improves the device surface. On unannealed samples, capping the QDs with one monolayer of AlAs improves the spectral response, the open-circuit voltage and the fill factor. On annealed samples, capping has little effect on the spectral response but reduces the short-circuit current, while increasing the open-circuit voltage, the fill factor and power conversion efficiency. PMID:21711628

  11. Interfacial Characterizations of a Nickel-Phosphorus Layer Electrolessly Deposited on a Silane Compound-Modified Silicon Wafer Under Thermal Annealing

    NASA Astrophysics Data System (ADS)

    Lai, Kuei-Chang; Wu, Pei-Yu; Chen, Chih-Ming; Wei, Tzu-Chien; Wu, Chung-Han; Feng, Shien-Ping

    2016-06-01

    Front-side metallization of a Si wafer was carried out using electroless deposition of nickel-phosphorus (Ni-P) catalyzed by polyvinylpyrrolidone-capped palladium nanoclusters (PVP-nPd). A 3-[2-(2-Aminoethylamino)ethylamino] propyl-trimethoxysilane (ETAS) layer was covalently bonded on the Si surface as bridge linker to the Pd cores of PVP-nPd clusters for improving adhesion between the Ni-P layer and the Si surface. To investigate the effects of an interfacial ETAS layer on the Ni silicide formation at the Ni-P/Si contact, the Ni-P-coated Si samples were thermally annealed via rapid thermal annealing (RTA) from 500°C to 900°C for 2 min. To compare with the ETAS sample, the sputtered Ni layer on Si and electroless Ni-P layer on ion-Pd-catalyzed Si (both are standard processes) were also investigated. The microstructural characterizations for the Ni-P or Ni layer deposited on the Si wafer were performed using x-ray diffractometer, scanning electron microscopy, and transmission electron microscopy. Our results showed that the ETAS layer acted as a barrier to slow the atomic diffusion of Ni toward the Si side. Although the formation of Ni silicides required a higher annealing temperature, the adhesion strength and contact resistivity measurements of annealed Ni-P/Si contacts showed satisfactory results, which were essential to the device performance and reliability during thermal annealing.

  12. Investigation and optimization of intraband electromagnetically induced transparency in strained InAs quantum dot/wetting layer structures

    NASA Astrophysics Data System (ADS)

    Parvizi, R.; Rezaei, G.

    2016-01-01

    In this work, effects of the shape and size on the optical properties and optimization of the intersubband electromagnetically induced transparency in the Infra-red region of three-dimensional strained truncated pyramid-shaped InAs/GaAs quantum dot (QD) were investigated in detail. More precisely, within the density matrix approach, the probe absorption and group velocity along with the refractive index of the medium were studied with respect to their dependence on the dephasing rates and the Rabi frequencies of the probe and coupling fields for different QD heights and wetting layer (WL) thicknesses. It is found that the slow-down factors, group index, and absorption coefficient are inversely proportional to the width of the transparency window and proportional to the depth of the transparency window. The optimized transparency window can be achieved by varying the dot height and the WL thickness such that the tall dots with thin WL thickness induce significant enhancements at a fixed resonant peak position of Rabi frequency of the coupling field. The physical reasons behind these interesting phenomena were also explained based on the polarized features of intersubband transitions.

  13. Wetting layer evolution and its temperature dependence during self-assembly of InAs/GaAs quantum dots

    PubMed Central

    2012-01-01

    For InAs/GaAs(001) quantum dot (QD) system, the wetting layer (WL) evolution and its temperature dependence were studied using reflectance difference spectroscopy and were analyzed with a rate equation model. WL thicknesses showed a monotonic increase at relatively low growth temperatures but showed an initial increase and then decrease at higher temperatures, which were unexpected from a thermodynamic understanding. By adopting a rate equation model, the temperature dependence of QD formation rate was assigned as the origin of different WL evolutions. A brief discussion on the indium desorption was given. Those results gave hints of the kinetic aspects of QD self-assembly. PMID:23110846

  14. Transport properties of interfacial Si-rich layers formed on silicate minerals during weathering: Implications for environmental concerns

    NASA Astrophysics Data System (ADS)

    Daval, Damien; Rémusat, Laurent; Bernard, Sylvain; Wild, Bastien; Micha, Jean-Sébastien; Rieutord, François; Fernandez-Martinez, Alejandro

    2015-04-01

    The dissolution of silicate minerals is of primary importance for various processes ranging from chemical weathering to CO2 sequestration. Whether it determines the rates of soil formation, CO2 uptake and its impact on climate change, channeling caused by hydrothermal circulation in reservoirs of geothermal power plants, durability of radioactive waste confinement glasses or geological sequestration of CO2, the same strategy is commonly applied for determining the long term evolution of fluid-rock interactions. This strategy relies on a bottom-up approach, where the kinetic rate laws governing silicate mineral dissolution are determined from laboratory experiments. However, a long-standing problem regarding this approach stems from the observation that laboratory-derived dissolution rates overestimate their field counterparts by orders of magnitude, casting doubt on the accuracy and relevance of predictions based on reactive-transport simulations. Recently [1], it has been suggested that taking into account the formation of amorphous Si-rich surface layers (ASSL) as a consequence of mineral dissolution may contribute to decrease the large gap existing between laboratory and natural rates. Our ongoing study is aimed at deciphering the extent to which ASSL may represent a protective entity which affects the dissolution rate of the underlying minerals, both physically (passivation) and chemically (by promoting the formation of a local chemical medium which significantly differs from that of the bulk solution). Our strategy relies on the nm-scale measurement of the physicochemical properties (diffusivity, thickness and density) of ASSL formed on cleavages of a model mineral (wollastonite) and their evolution as a function of reaction progress. Our preliminary results indicate that the diffusivity of nm-thick ASSL formed on wollastonite surface is ~1,000,000 times smaller than that reported for an aqueous medium, as estimated from the monitoring of the progression of a

  15. Voltage sharing effect and interface state calculation of a wafer-bonding Ge/Si avalanche photodiode with an interfacial GeO2 insulator layer.

    PubMed

    Ke, Shaoying; Lin, Shaoming; Li, Xin; Li, Jun; Xu, Jianfang; Li, Cheng; Chen, Songyan

    2016-02-01

    The tunneling effect and interface state in the p-Ge/GeO2p-Si structure of a wafer-bonding Ge/Si avalanche photodiode (APD) are investigated. It is found that the thin interfacial GeO2 layer (1-2 nm) formed by the hydrophilic reaction at the wafer-bonding interface significantly affects the performance of the Ge/Si APD. With the increase of the GeO2 thickness, the dark current of the Ge/Si APD decreases enormously due to the blocking effect of this GeO2 layer. Owing to the carrier accumulation in Ge layer under illumination condition, the voltage sharing effect of the GeO2 layer (thicker) becomes serious, leading to the absence of the electric field in Ge layer. The photon-generated electrons at Ge/GeO2 interface can be captured and released by the interface states at certain reverse bias. This can adjust the avalanche current of the Ge/Si APD. The stronger interface recombination induced by the larger interface state density (ISD) results in the decrease of the electric field in Ge layer. This increases the transit time of carriers, which in turn decreases the 3dB-bandwidth. Due to the drastic increase of the dark current (larger ISD), the gain of the Ge/Si APD decreases. PMID:26906771

  16. Low resistivity contact on n-type Ge using low work-function Yb with a thin TiO2 interfacial layer

    NASA Astrophysics Data System (ADS)

    Dev, Sachin; Remesh, Nayana; Rawal, Yaksh; Manik, Prashanth Paramahans; Wood, Bingxi; Lodha, Saurabh

    2016-03-01

    This work demonstrates the benefit of a lower contact barrier height, and hence reduced contact resistivity (ρc), using a low work-function metal (Yb) in unpinned metal-interfacial layer-semiconductor (MIS) contacts on n-type Ge. Fermi-level unpinning in MIS contacts on n-Ge is first established by introducing a 2 nm TiO2-x interfacial layer between various contact metals (Yb, Ti, Ni, Pt) and n-Ge. Further, Yb/TiO2-x/n-Ge MIS contact diodes exhibit higher current densities (up to 100×) and lower effective contact barrier height (up to 30%) versus Ti/TiO2-x control devices over a wide range of TiO2-x thickness (1-5 nm). Finally, low work-function Yb combined with doped TiO2-x having a low conduction band offset with Ge and high substrate doping (n+-Ge: 2.5 ×1019 cm-3) is shown to result in an ultra-low ρc value of 1.4 × 10-8 Ω cm2, 10 × lower than Ti/TiO2-x control devices.

  17. Forward-bias diode parameters, electronic noise, and photoresponse of graphene/silicon Schottky junctions with an interfacial native oxide layer

    NASA Astrophysics Data System (ADS)

    An, Yanbin; Behnam, Ashkan; Pop, Eric; Bosman, Gijs; Ural, Ant

    2015-09-01

    Metal-semiconductor Schottky junction devices composed of chemical vapor deposition grown monolayer graphene on p-type silicon substrates are fabricated and characterized. Important diode parameters, such as the Schottky barrier height, ideality factor, and series resistance, are extracted from forward bias current-voltage characteristics using a previously established method modified to take into account the interfacial native oxide layer present at the graphene/silicon junction. It is found that the ideality factor can be substantially increased by the presence of the interfacial oxide layer. Furthermore, low frequency noise of graphene/silicon Schottky junctions under both forward and reverse bias is characterized. The noise is found to be 1/f dominated and the shot noise contribution is found to be negligible. The dependence of the 1/f noise on the forward and reverse current is also investigated. Finally, the photoresponse of graphene/silicon Schottky junctions is studied. The devices exhibit a peak responsivity of around 0.13 A/W and an external quantum efficiency higher than 25%. From the photoresponse and noise measurements, the bandwidth is extracted to be ˜1 kHz and the normalized detectivity is calculated to be 1.2 ×109 cm Hz1/2 W-1. These results provide important insights for the future integration of graphene with silicon device technology.

  18. Organosilane-functionalized graphene quantum dots and their encapsulation into bi-layer hollow silica spheres for bioimaging applications.

    PubMed

    Wen, Ting; Yang, Baocheng; Guo, Yanzhen; Sun, Jing; Zhao, Chunmei; Zhang, Shouren; Zhang, Miao; Wang, Yonggang

    2014-11-14

    Graphene quantum dots (GQDs) represent an important class of luminescent quantum dots owing to their low toxicity and superior biocompatibility. Chemical functionalization of GQDs and subsequent combination with other materials further provide attractive techniques for advanced bioapplications. Herein, we report the facile fabrication of fluorescent organosilane-functionalized graphene quantum dots (Si-GQDs) and their embedding into mesoporous hollow silica spheres as a biolabel for the first time. Well-proportioned Si-GQDs with bright and excitation dependent tunable emissions in the visible region were obtained via a simple and economical solvothermal route adopting graphite oxide as a carbon source and 3-(2-aminoethylamino)-propyltrimethoxysilane as a surface modifier. The as-synthesized Si-GQDs can be well dispersed and stored in organic solvents, easily manufactured into transparent film and bulk form, and particularly provide great potential to be combined with other materials. As a proof-of-principle experiment, we demonstrate the successful incorporation of Si-GQDs into hollow mesoporous silica spheres and conduct preliminary cellular imaging experiments. Interestingly, the Si-GQDs not only serve as fluorescent chromophores in the composite material, but also play a crucial role in the formation of mesoporous hollow silica spheres with a distinctive bi-layer architecture. The layer thickness and optical properties can be precisely controlled by simply adjusting the silane coupling agent addition procedure in the preparation process. Our demonstration of low-cost Si-GQDs and their encapsulation into multifunctional composites may expand the applications of carbon-based nanomaterials for future biomedical imaging and other optoelectronic applications. PMID:25255171

  19. The effects of Bi4Ti3O12 interfacial ferroelectric layer on the dielectric properties of Au/n-Si structures

    NASA Astrophysics Data System (ADS)

    Gökçen, Muharrem; Yıldırım, Mert

    2015-06-01

    Au/n-Si metal-semiconductor (MS) and Au/Bi4Ti3O12/n-Si metal-ferroelectric-semiconductor (MFS) structures were fabricated and admittance measurements were held between 5 kHz and 1 MHz at room temperature so that dielectric properties of these structures could be investigated. The ferroelectric interfacial layer Bi4Ti3O12 decreased the polarization voltage by providing permanent dipoles at metal/semiconductor interface. Depending on different mechanisms, dispersion behavior was observed in dielectric constant, dielectric loss and loss tangent versus bias voltage plots of both MS and MFS structures. The real and imaginary parts of complex modulus of MFS structure take smaller values than those of MS structure, because permanent dipoles in ferroelectric layer cause a large spontaneous polarization mechanism. While the dispersion in AC conductivity versus frequency plots of MS structure was observed at high frequencies, for MFS structure it was observed at lower frequencies.

  20. p-Type semiconducting nickel oxide as an efficiency-enhancing anodal interfacial layer in bulk heterojunction solar cells

    SciTech Connect

    Irwin, Michael D; Buchholz, Donald B; Marks, Tobin J; Chang, Robert P. H.

    2014-11-25

    The present invention, in one aspect, relates to a solar cell. In one embodiment, the solar cell includes an anode, a p-type semiconductor layer formed on the anode, and an active organic layer formed on the p-type semiconductor layer, where the active organic layer has an electron-donating organic material and an electron-accepting organic material.

  1. Mapping bound plasmon propagation on a nanoscale stripe waveguide using quantum dots: influence of spacer layer thickness.

    PubMed

    Perera, Chamanei S; Funston, Alison M; Cheng, Han-Hao; Vernon, Kristy C

    2015-01-01

    In this paper we image the highly confined long range plasmons of a nanoscale metal stripe waveguide using quantum emitters. Plasmons were excited using a highly focused 633 nm laser beam and a specially designed grating structure to provide stronger incoupling to the desired mode. A homogeneous thin layer of quantum dots was used to image the near field intensity of the propagating plasmons on the waveguide. We observed that the photoluminescence is quenched when the QD to metal surface distance is less than 10 nm. The optimised spacer layer thickness for the stripe waveguides was found to be around 20 nm. Authors believe that the findings of this paper prove beneficial for the development of plasmonic devices utilising stripe waveguides. PMID:26665075

  2. A CdSe thin film: a versatile buffer layer for improving the performance of TiO2 nanorod array:PbS quantum dot solar cells.

    PubMed

    Tan, Furui; Wang, Zhijie; Qu, Shengchun; Cao, Dawei; Liu, Kong; Jiang, Qiwei; Yang, Ying; Pang, Shan; Zhang, Weifeng; Lei, Yong; Wang, Zhanguo

    2016-05-21

    To fully utilize the multiple exciton generation effects in quantum dots and improve the overall efficiency of the corresponding photovoltaic devices, nanostructuralizing the electron conducting layer turns out to be a feasible strategy. Herein, PbS quantum dot solar cells were fabricated on the basis of morphologically optimized TiO2 nanorod arrays. By inserting a thin layer of CdSe quantum dots into the interface of TiO2 and PbS, a dramatic enhancement in the power conversion efficiency from 4.2% to 5.2% was realized and the resulting efficiency is one of the highest values for quantum dot solar cells based on nanostructuralized buffer layers. The constructed double heterojunction with a cascade type-II energy level alignment is beneficial for promoting photogenerated charge separation and reducing charge recombination, thereby responsible for the performance improvement, as revealed by steady-state analyses as well as ultra-fast photoluminescence and photovoltage decays. Thus this paper provides a good buffer layer to the community of quantum dot solar cells. PMID:27124650

  3. Defect characterization of proton irradiated GaAs pn-junction diodes with layers of InAs quantum dots

    NASA Astrophysics Data System (ADS)

    Sato, Shin-ichiro; Schmieder, Kenneth J.; Hubbard, Seth M.; Forbes, David V.; Warner, Jeffrey H.; Ohshima, Takeshi; Walters, Robert J.

    2016-05-01

    In order to expand the technology of III-V semiconductor devices with quantum structures to both terrestrial and space use, radiation induced defects as well as native defects generated in the quantum structures should be clarified. Electrically active defects in GaAs p+n diodes with embedded ten layers of InAs quantum dots (QDs) are investigated using Deep Level Transient Fourier Spectroscopy. Both majority carrier (electron) and minority carrier (hole) traps are characterized. In the devices of this study, GaP layers are embedded in between the QD layers to offset the compressive stress introduced during growth of InAs QDs. Devices are irradiated with high energy protons for three different fluences at room temperature in order to characterize radiation induced defects. Seven majority electron traps and one minority hole trap are found after proton irradiation. It is shown that four electron traps induced by proton irradiation increase in proportion to the fluence, whereas the EL2 trap, which appears before irradiation, is not affected by irradiation. These defects correspond to electron traps previously identified in GaAs. In addition, a 0.53 eV electron trap and a 0.14 eV hole trap are found in the QD layers before proton irradiation. It is shown that these native traps are also unaffected by irradiation. The nature of the 0.14 eV hole trap is thought to be Ga-vacancies in the GaP strain balancing layers.

  4. Greatly improved interfacial passivation of in-situ high κ dielectric deposition on freshly grown molecule beam epitaxy Ge epitaxial layer on Ge(100)

    SciTech Connect

    Chu, R. L.; Liu, Y. C.; Lee, W. C.; Huang, M. L.; Kwo, J. E-mail: mhong@phys.ntu.edu.tw; Lin, T. D.; Hong, M. E-mail: mhong@phys.ntu.edu.tw; Pi, T. W.

    2014-05-19

    A high-quality high-κ/Ge interface has been achieved by combining molecule beam epitaxy grown Ge epitaxial layer and in-situ deposited high κ dielectric. The employment of Ge epitaxial layer has sucessfully buried and/or removed the residue of unfavorable carbon and native oxides on the chemically cleaned and ultra-high vacuum annealed Ge(100) wafer surface, as studied using angle-resolved x-ray photoelectron spectroscopy. Moreover, the scanning tunneling microscopy analyses showed the significant improvements in Ge surface roughness from 3.5 Å to 1 Å with the epi-layer growth. Thus, chemically cleaner, atomically more ordered, and morphologically smoother Ge surfaces were obtained for the subsquent deposition of high κ dielectrics, comparing with those substrates without Ge epi-layer. The capacitance-voltage (C-V) characteristics and low extracted interfacial trap density (D{sub it}) reveal the improved high-κ/Ge interface using the Ge epi-layer approach.

  5. Tuning the dead-layer behavior of La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/SrTiO{sub 3} via interfacial engineering

    SciTech Connect

    Peng, R.; Xu, H. C.; Xia, M.; Zhao, J. F.; Xie, X.; Xu, D. F.; Xie, B. P. Feng, D. L.

    2014-02-24

    The dead-layer behavior, deterioration of the bulk properties in near-interface layers, restricts the applications of many oxide heterostructures. We present the systematic study of the dead-layer in La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/SrTiO{sub 3} grown by ozone-assisted molecular beam epitaxy. Dead-layer behavior is systematically tuned by varying the interfacial doping, while unchanged with varied doping at any other atomic layers. In situ photoemission and low energy electron diffraction measurements suggest intrinsic oxygen vacancies at the surface of ultra-thin La{sub 0.67}Sr{sub 0.33}MnO{sub 3}, which are more concentrated in thinner films. Our results show correlation between interfacial doping, oxygen vacancies, and the dead-layer, which can be explained by a simplified electrostatic model.

  6. Structural and electrical characteristics of ALD-HfO2/n-Si gate stack with SiON interfacial layer for advanced CMOS technology

    NASA Astrophysics Data System (ADS)

    Gupta, Richa; Rajput, Renu; Prasher, Rakesh; Vaid, Rakesh

    2016-09-01

    We report the fabrication of an ultra-thin silicon oxynitride (SiON) as an interfacial layer (IL) for n-Si/ALD-HfO2 gate stack with reduced leakage current. The XRD, AFM, FTIR, FESEM and EDAX characterizations have been performed for structural and morphological studies. Electrical parameters such as dielectric constant (K), interface trap density (Dit), leakage current density (J), effective oxide charge (Qeff), barrier height (Φbo), ideality factor (ƞ), breakdown-voltage (Vbr) and series resistance (Rs) were extracted through C-V, G-V and I-V measurements. The determined values of K, Dit, J, Qeff, Φbo, ƞ, Vbr and Rs are 14.4, 0.5 × 10 11 eV-1 cm-2, 2.2 × 10-9 A/cm2, 0.3 × 1013 cm-2, 0.42, 2.1, -0.33 and 14.5 MΩ respectively. SiON growth prior to HfO2 deposition has curtailed the problem of high leakage current density and interfacial traps due to sufficient amount of N2 incorporated at the interface.

  7. HfO2 gate dielectric on Ge (1 1 1) with ultrathin nitride interfacial layer formed by rapid thermal NH3 treatment

    NASA Astrophysics Data System (ADS)

    Agrawal, Khushabu S.; Patil, Vilas S.; Khairnar, Anil G.; Mahajan, Ashok M.

    2016-02-01

    Interfacial properties of the ALD deposited HfO2 over the surface nitrided germanium substrate have been studied. The formation of GeON (∼1.7 nm) was confirmed by X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron spectroscopy (HRTEM) over the germanium surface. The effect of post deposition annealing temperature was investigated to study the interfacial and electrical properties of hafnium oxide/germanium oxynitride gate stacks. The high-k MOS devices with ultrathin GeON layer shows the good electrical characteristics including higher k value ∼18, smaller equivalent oxide thickness (EOT) around 1.5 nm and smaller hysteresis value less than 170 mV. The Qeff and Dit values are somewhat greater due to the (1 1 1) orientation of the germanium and may be due to the presence of nitrogen at the interface. The Fowler-Northeim (FN) tunneling of Ge MOS devices has been studied. The barrier height ΦB extracted from the plot is ∼1 eV.

  8. Temperature dependent interfacial and electrical characteristics during atomic layer deposition and annealing of HfO2 films in p-GaAs metal-oxide-semiconductor capacitors

    NASA Astrophysics Data System (ADS)

    Chen, Liu; Yuming, Zhang; Yimen, Zhang; Hongliang, Lü; Bin, Lu

    2015-12-01

    We have investigated the temperature dependent interfacial and electrical characteristics of p-GaAs metal-oxide-semiconductor capacitors during atomic layer deposition (ALD) and annealing of HfO2 using the tetrakis (ethylmethyl) amino hafnium precursor. The leakage current decreases with the increase of the ALD temperature and the lowest current is obtained at 300 °C as a result of the Frenkel-Poole conduction induced leakage current being greatly weakened by the reduction of interfacial oxides at the higher temperature. Post deposition annealing (PDA) at 500 °C after ALD at 300 °C leads to the lowest leakage current compared with other annealing temperatures. A pronounced reduction in As oxides during PDA at 500 °C has been observed using X-ray photoelectron spectroscopy at the interface resulting in a proportional increase in Ga2O3. The increment of Ga2O3 after PDA depends on the amount of residual As oxides after ALD. Thus, the ALD temperature plays an important role in determining the high-k/GaAs interface condition. Meanwhile, an optimum PDA temperature is essential for obtaining good dielectric properties. Project supported by the Advance Research Project of China (No. 5130803XXXX) and the National Natural Science Foundation of China (No. 61176070).

  9. Two-Step Physical Deposition of a Compact CuI Hole-Transport Layer and the Formation of an Interfacial Species in Perovskite Solar Cells.

    PubMed

    Gharibzadeh, Saba; Nejand, Bahram Abdollahi; Moshaii, Ahmad; Mohammadian, Nasim; Alizadeh, Amir Hossein; Mohammadpour, Rahele; Ahmadi, Vahid; Alizadeh, Abdolali

    2016-08-01

    A simple and practical approach is introduced for the deposition of CuI as an inexpensive inorganic hole-transport material (HTM) for the fabrication of low cost perovskite solar cells (PSCs) by gas-solid phase transformation of Cu to CuI. The method provides a uniform and well-controlled CuI layer with large grains and good compactness that prevents the direct connection between the contact electrodes. Solar cells prepared with CuI as the HTM with Au electrodes displays an exceptionally high short-circuit current density of 32 mA cm(-2) , owing to an interfacial species formed between the perovskite and the Cu resulting in a long wavelength contribution to the incident photon-to-electron conversion efficiency (IPCE), and an overall power conversion efficiency (PCE) of 7.4 %. The growth of crystalline and uniform CuI on a low roughness perovskite layer leads to remarkably high charge extraction in the cells, which originates from the high hole mobility of CuI in addition to a large number of contact points between CuI and the perovskite layer. In addition, the solvent-free method has no damaging side effect on the perovskite layer, which makes it an appropriate method for large scale applications of CuI in perovskite solar cells. PMID:27357330

  10. Effect of space layer doping on photoelectric conversion efficiency of InAs/GaAs quantum dot solar cells

    NASA Astrophysics Data System (ADS)

    Lee, Kyoung Su; Lee, Dong Uk; Kim, Eun Kyu; Choi, Won Jun

    2015-11-01

    We report an effect of photoelectric conversion efficiency (PCE) by space layer doping in InAs/GaAs quantum dot solar cells (QDSC) and δ-doped QDSC grown by molecular beam epitaxy. The PCEs of QDSC and δ-doped QDSC without anti-reflection coating were 10.8% and 4.3%, respectively. The QDSC had about four electrons per QD, and its ideality factor was temperature-independent, which implies that recombination of electron-hole pairs is suppressed by strong potential barriers around charged dots. From the deep level transient spectroscopy measurements, four defect levels, including QD with the activation energy ranges from 0.08 eV to 0.50 eV below GaAs conduction band edge, appeared. Especially, the M1 defect (Ec-0.14 eV) was newly formed in δ-doped QDSC and its density was higher than those of M3 (Ec-0.35 eV) and M4 (Ec-0.50 eV) levels in QDSC. These results suggest that the photo-carriers recombining at M1 defect might be responsible for the reduction of PCE in δ-doped QDSC.

  11. Effect of space layer doping on photoelectric conversion efficiency of InAs/GaAs quantum dot solar cells

    SciTech Connect

    Lee, Kyoung Su; Lee, Dong Uk; Kim, Eun Kyu; Choi, Won Jun

    2015-11-16

    We report an effect of photoelectric conversion efficiency (PCE) by space layer doping in InAs/GaAs quantum dot solar cells (QDSC) and δ-doped QDSC grown by molecular beam epitaxy. The PCEs of QDSC and δ-doped QDSC without anti-reflection coating were 10.8% and 4.3%, respectively. The QDSC had about four electrons per QD, and its ideality factor was temperature-independent, which implies that recombination of electron-hole pairs is suppressed by strong potential barriers around charged dots. From the deep level transient spectroscopy measurements, four defect levels, including QD with the activation energy ranges from 0.08 eV to 0.50 eV below GaAs conduction band edge, appeared. Especially, the M1 defect (E{sub c}-0.14 eV) was newly formed in δ-doped QDSC and its density was higher than those of M3 (E{sub c}-0.35 eV) and M4 (E{sub c}-0.50 eV) levels in QDSC. These results suggest that the photo-carriers recombining at M1 defect might be responsible for the reduction of PCE in δ-doped QDSC.

  12. Suppression of interdiffusion in InGaAs/GaAs quantum dots using dielectric layer of titanium dioxide

    NASA Astrophysics Data System (ADS)

    Fu, L.; Lever, P.; Tan, H. H.; Jagadish, C.; Reece, P.; Gal, M.

    2003-04-01

    In this work, titanium dioxide (TiO2) film was deposited onto the In0.5Ga0.5As/GaAs quantum-dot structure by electron-beam evaporation to investigate its effect on interdiffusion. A large redshifted and broadened spectrum from the dot emission was observed compared with that from the uncapped (but annealed) reference sample, indicating the suppression of thermal interdiffusion due to TiO2 deposition. The structure was also capped with a silicon dioxide (SiO2) single layer or SiO2/TiO2 bilayer with the thickness of SiO2 varied from ˜6 to ˜145 nm. In the former case, an increased amount of impurity-free vacancy disordering (IFVD) was introduced with the increase of SiO2 thickness due to the enhanced Ga outdiffusion into the film. With TiO2 deposited on top, IFVD and thermal interdiffusion were suppressed to different extents with the variation of SiO2 thickness. To explain the suppression of interdiffusion, thermal stress introduced by the large thermal expansion coefficient of TiO2 (when compared with GaAs) as well as the metallurgical reactions between the TiO2 and GaAs were proposed as possible mechanisms.

  13. Phase Recovery Acceleration of Quantum-Dot Semiconductor Optical Amplifiers by Optical Pumping to Quantum-Well Wetting Layer

    NASA Astrophysics Data System (ADS)

    Kim, Jungho

    2013-11-01

    We theoretically investigate the phase recovery acceleration of quantum-dot (QD) semiconductor optical amplifiers (SOAs) by means of the optical pump injection to the quantum-well (QW) wetting layer (WL). We compare the ultrafast gain and phase recovery responses of QD SOAs in either the electrical or the optical pumping scheme by numerically solving 1088 coupled rate equations. The ultrafast gain recovery responses on the order of sub-picosecond are nearly the same for the two pumping schemes. The ultrafast phase recovery is not significantly accelerated by increasing the electrical current density, but greatly improved by increasing the optical pumping power to the QW WL. Because the phase recovery time of QD SOAs with the optical pumping scheme can be reduced down to several picoseconds, the complete phase recovery can be achieved when consecutive pulse signals with a repetition rate of 100 GHz is injected.

  14. The effect of metal nano particle on optical absorption coefficient of multi-layer spherical quantum dot

    NASA Astrophysics Data System (ADS)

    Zamani, N.; Keshavarz, A.; Nadgaran, H.

    2016-06-01

    In this paper, we investigate the optical absorption coefficient of hybrid structure consisting of metal nano particle (MNP) coupled to multi-layer spherical quantum dot (MSQD). Energy eigenvalues and eigenfunctions of Schrödinger equation in this structure are obtained by using numerical solution (by the fourth-order Runge-Kutta method). The effect of MNP in the vicinity of MSQD is calculated by considering local field theory. Then the variation of optical absorption coefficient hybrid structure is calculated. The results show that the presence of MNP near MSQD enhances the optical absorption coefficient. Also, by changing the distance between MNP and MSQD and radius of MNP, variation of optical absorption coefficient and refractive index changes are introduced.

  15. Manipulating Thermal Conductivity by Interfacial Modification of Misfit-Layered Cobaltites Ca3Co4O9

    NASA Astrophysics Data System (ADS)

    Fujii, Susumu; Yoshiya, Masato

    2016-03-01

    The phonon thermal conductivities of misfit-layered Ca3Co4O9, Sr3Co4O9, and Ba3Co4O9 were calculated using the perturbed molecular dynamics method to clarify the impact of lattice misfit on the phonon thermal conduction in misfit-layered cobaltites. Substitution of Sr and Ba for Ca substantially modified the magnitude of the lattice misfit between the CoO2 and rock salt (RS) layers, because of the different ionic radii, increasing overall phonon thermal conductivity. Further analyses with intentionally changed atomic masses of Ca, Sr, or Ba revealed that smaller ionic radius at the Ca site in the RS layer, instead of heavier atomic mass, is a critical factor suppressing the overall thermal conductivity of Ca3Co4O9, since it determines not only the magnitude of lattice misfit but also the dynamic interference between the two layers, which governs the phonon thermal conduction in the CoO2 and RS layers. This concept was demonstrated for Sr-doped Ca3Co4O9 as an example of atomistic manipulation for better thermoelectric properties. Phonon thermal conductivities not only in the RS layer but also in the CoO2 layer were reduced by the substitution of Sr for Ca. These results provide another strategy to improve the thermal conductivity of this class of misfit cobaltites, that is, to control the thermal conductivity of the CoO2 layer responsible for electronic and thermal conductivity by atomistic manipulation in the RS layer adjacent to the CoO2 layer.

  16. Calculation of metamorphic two-dimensional quantum energy system: Application to wetting layer states in InAs/InGaAs metamorphic quantum dot nanostructures

    SciTech Connect

    Seravalli, L.; Trevisi, G.; Frigeri, P.

    2013-11-14

    In this work, we calculate the two-dimensional quantum energy system of the In(Ga)As wetting layer that arises in InAs/InGaAs/GaAs metamorphic quantum dot structures. Model calculations were carried on the basis of realistic material parameters taking in consideration their dependence on the strain relaxation of the metamorphic buffer; results of the calculations were validated against available literature data. Model results confirmed previous hypothesis on the extrinsic nature of the disappearance of wetting layer emission in metamorphic structures with high In composition. We also show how, by adjusting InGaAs metamorphic buffer parameters, it could be possible: (i) to spatially separate carriers confined in quantum dots from wetting layer carriers, (ii) to create an hybrid 0D-2D system, by tuning quantum dot and wetting layer levels. These results are interesting not only for the engineering of quantum dot structures but also for other applications of metamorphic structures, as the two design parameters of the metamorphic InGaAs buffer (thickness and composition) provide additional degrees of freedom to control properties of interest.

  17. Nanocrystalline-Si-dot multi-layers fabrication by chemical vapor deposition with H-plasma surface treatment and evaluation of structure and quantum confinement effects

    SciTech Connect

    Kosemura, Daisuke Mizukami, Yuki; Takei, Munehisa; Numasawa, Yohichiroh; Ogura, Atsushi; Ohshita, Yoshio

    2014-01-15

    100-nm-thick nanocrystalline silicon (nano-Si)-dot multi-layers on a Si substrate were fabricated by the sequential repetition of H-plasma surface treatment, chemical vapor deposition, and surface oxidation, for over 120 times. The diameter of the nano-Si dots was 5–6 nm, as confirmed by both the transmission electron microscopy and X-ray diffraction analysis. The annealing process was important to improve the crystallinity of the nano-Si dot. We investigated quantum confinement effects by Raman spectroscopy and photoluminescence (PL) measurements. Based on the experimental results, we simulated the Raman spectrum using a phenomenological model. Consequently, the strain induced in the nano-Si dots was estimated by comparing the experimental and simulated results. Taking the estimated strain value into consideration, the band gap modulation was measured, and the diameter of the nano-Si dots was calculated to be 5.6 nm by using PL. The relaxation of the q ∼ 0 selection rule model for the nano-Si dots is believed to be important to explain both the phenomena of peak broadening on the low-wavenumber side observed in Raman spectra and the blue shift observed in PL measurements.

  18. Effect of surface pretreatment on interfacial chemical bonding states of atomic layer deposited ZrO{sub 2} on AlGaN

    SciTech Connect

    Ye, Gang; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Wang, Hong; Liu, Zhi Hong

    2015-09-15

    Atomic layer deposition (ALD) of ZrO{sub 2} on native oxide covered (untreated) and buffered oxide etchant (BOE) treated AlGaN surface was analyzed by utilizing x-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy. Evidenced by Ga–O and Al–O chemical bonds by XPS, parasitic oxidation during deposition is largely enhanced on BOE treated AlGaN surface. Due to the high reactivity of Al atoms, more prominent oxidation of Al atoms is observed, which leads to thicker interfacial layer formed on BOE treated surface. The results suggest that native oxide on AlGaN surface may serve as a protecting layer to inhibit the surface from further parasitic oxidation during ALD. The findings provide important process guidelines for the use of ALD ZrO{sub 2} and its pre-ALD surface treatments for high-k AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors and other related device applications.

  19. MgO-hybridized TiO{sub 2} interfacial layers assisting efficiency enhancement of solid-state dye-sensitized solar cells

    SciTech Connect

    Sakai, Nobuya; Ikegami, Masashi; Miyasaka, Tsutomu

    2014-02-10

    Interfacial modification of a thin TiO{sub 2} compact layer (T-CL) by hybridization with MgO enhanced the quantum conversion efficiency of solid-state dye-sensitized solar cells (ssDSSCs) comprising a multilayer structure of transparent electrode/T-CL/dye-sensitized mesoporous TiO{sub 2}/hole conductor/metal counter electrode. The Mg(CH{sub 3}COO){sub 2} treatment was employed to introduce a MgO-TiO{sub 2} CL (T/M-CL), which enhanced the physical connection and conduction between the CL and mesoporous semiconductor layer as a consecutive interface, owing to the dehydration reaction of Mg(CH{sub 3}COO){sub 2}. The photocurrent density of ssDSSC was increased 33% by the T/M-CL compared with the T-CL, using an equivalent amount of adsorbed dye. The ssDSSC with the T/M-CL yielded the highest efficiency of 4.02% under irradiation at 100 mW cm{sup −2}. The electrical impedance spectroscopy showed that the charge-transfer resistance (R{sub ct}) of the photoelectrode with T/M-CL was reduced by 300 Ω from the reference non-treated T-CL electrode. Characterized by the intrinsically low R{sub ct} of the compact layer, the T/M-CL is capable of improving the photovoltaic performance of solid-state sensitized mesoscopic solar cells.

  20. Electrochemiluminescence detection of reduced and oxidized glutathione ratio by quantum dot-layered double hydroxide film.

    PubMed

    Yu, Yingchang; Shi, Jingjing; Zhao, Xiaocen; Yuan, Zhiqin; Lu, Chao; Lu, Jun

    2016-05-23

    The ratio of reduced and oxidized glutathione (GSH/GSSG ratio) is a greater first indication of disease risk than the total concentration of GSH. However, the interferences from thiolated biomolecules, especially cysteine (Cys), make the accurate detection of GSH/GSSG ratio a technical problem. In this work, we successfully used a mixture of quantum dots (QDs) and ZnAl-LDH nanosheets to fabricate a high electrochemiluminescence resonance energy transfer (ERET) efficiency sensor for GSH from the disturbances of amino acids, especially Cys and GSSG. The mechanisms of high ERET efficiency and selectivity were well investigated with spectroscopy analysis and theoretical calculation. The results showed that the interaction force between ZnAl-LDH nanosheets and molecules proved a long-range-ordered space and selective transmission for molecules. On the basis of these interesting phenomena, we successfully measured the GSH/GSSG ratio in whole blood and serum samples. PMID:27109740

  1. Color tone and interfacial microstructure of white oxide layer on commercially pure Ti and Ti-Nb-Ta-Zr alloys

    NASA Astrophysics Data System (ADS)

    Miura-Fujiwara, Eri; Mizushima, Keisuke; Watanabe, Yoshimi; Kasuga, Toshihiro; Niinomi, Mitsuo

    2014-11-01

    In this study, the relationships among oxidation condition, color tone, and the cross-sectional microstructure of the oxide layer on commercially pure (CP) Ti and Ti-36Nb-2Ta-3Zr-0.3O were investigated. “White metals” are ideal metallic materials having a white color with sufficient strength and ductility like a metal. Such materials have long been sought for in dentistry. We have found that the specific biomedical Ti alloys, such as CP Ti, Ti-36Nb-2Ta-3Zr-0.3O, and Ti-29Nb-13Ta-4.6Zr, form a bright yellowish-white oxide layer after a particular oxidation heat treatment. The brightness L* and yellowness +b* of the oxide layer on CP Ti and Ti-36Nb-2Ta-3Zr-0.3O increased with heating time and temperature. Microstructural observations indicated that the oxide layer on Ti-29Nb-13Ta-4.6Zr and Ti-36Nb-2Ta-3Zr-0.3O was dense and firm, whereas a piecrust-like layer was formed on CP Ti. The results obtained in this study suggest that oxide layer coating on Ti-36Nb-2Ta-3Zr-0.3O is an excellent technique for dental applications.

  2. Perovskite photovoltaics featuring solution-processable TiO2 as an interfacial electron-transporting layer display to improve performance and stability

    NASA Astrophysics Data System (ADS)

    Yu, Yang-Yen; Chiang, Rih-Sheng; Hsu, Hsiang-Lin; Yang, Chun-Chen; Chen, Chih-Ping

    2014-09-01

    In this study we used solution-processable crystalline TiO2 nanoparticles as an interfacial modified layer between the active layer and aluminum cathode to fabricate CH3NH3PbI3/PCBM-based planar heterojunction perovskite photovoltaic (PPV) devices. We optimized the performance of the PPV device prepared without TiO2 by varying the preheating temperature of the indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT) substrate, obtaining a power conversion efficiency (PCE) of 6.3% under simulated AM 1.5 G irradiation (100 mW cm-2). After incorporating the TiO2 layer, we obtained a much higher PCE of 7.0%. The TiO2-containing PPV device exhibited extremely high stability (retaining ~96% of its PCE after 1000 h) under long-term storage in a dark N2-filled glove box; the unencapsulated device retained approximately 80% of its original efficiency (T80) after 1 week under ambient conditions (ISOS-D-1; defined as 23 °C/50% RH). In contrast, the normal device was sensitive to ambient conditions with a value of T80 at only 3 h. We attributed the improved device performance (PCE, stability) to the enhanced electron transporting, hole blocking, and barrier properties arising from the presence of the TiO2 layer.In this study we used solution-processable crystalline TiO2 nanoparticles as an interfacial modified layer between the active layer and aluminum cathode to fabricate CH3NH3PbI3/PCBM-based planar heterojunction perovskite photovoltaic (PPV) devices. We optimized the performance of the PPV device prepared without TiO2 by varying the preheating temperature of the indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT) substrate, obtaining a power conversion efficiency (PCE) of 6.3% under simulated AM 1.5 G irradiation (100 mW cm-2). After incorporating the TiO2 layer, we obtained a much higher PCE of 7.0%. The TiO2-containing PPV device exhibited extremely high stability (retaining ~96% of its PCE after 1000 h) under long-term storage in a dark N2-filled

  3. Single step deposition of an interacting layer of a perovskite matrix with embedded quantum dots

    NASA Astrophysics Data System (ADS)

    Ngo, Thi Tuyen; Suarez, Isaac; Sanchez, Rafael S.; Martinez-Pastor, Juan P.; Mora-Sero, Ivan

    2016-07-01

    Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and electroluminescence experiments. The radiative exciplex relaxation is centered in the near infrared region (NIR), ~1200 nm, which corresponds to lower energies than the corresponding band gap of both perovskite (PS) and QDs. Our approach allows the fabrication of multi-wavelength light emitting diodes (LEDs) based on a PS matrix with embedded QDs, which show considerably low turn-on potentials. The presence of the exciplex state of PS and QDs opens up a broad range of possibilities with important implications in both LEDs and solar cells.Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and

  4. Enhancement of recombination process using silver and graphene quantum dot embedded intermediate layer for efficient organic tandem cells.

    PubMed

    Ho, Nhu Thuy; Tien, Huynh Ngoc; Jang, Se-Joeng; Senthilkumar, Velusamy; Park, Yun Chang; Cho, Shinuk; Kim, Yong Soo

    2016-01-01

    High performance of organic tandem solar cell is largely dependent on transparent and conductive intermediate layer (IML). The current work reports the design and fabrication of an IML using a simple solution process. The efficiency of a homo-tandem device with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester as an active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylenimine) as an IML was initially found to be 3.40%. Further enhancement of the cell efficiency was achieved using silver nanoparticles (Ag-NPs) of different sizes and graphene quantum dot embedded IML. A maximum efficiency of 4.03% was achieved using 7 nm Ag-NPs that contribute to a better recombination process. Also, the performance of the tandem cell was solely based on the electrical improvements indicated by the current - voltage measurements, external quantum efficiency and impedance analysis. The use of Ag-NPs in the IML has been shown to lengthen the life time of electron-hole pairs in the device. This study thus paves way to develop such efficient IMLs for more efficient tandem solar cells. PMID:27453530

  5. Enhancement of recombination process using silver and graphene quantum dot embedded intermediate layer for efficient organic tandem cells

    PubMed Central

    Ho, Nhu Thuy; Tien, Huynh Ngoc; Jang, Se-Joeng; Senthilkumar, Velusamy; Park, Yun Chang; Cho, Shinuk; Kim, Yong Soo

    2016-01-01

    High performance of organic tandem solar cell is largely dependent on transparent and conductive intermediate layer (IML). The current work reports the design and fabrication of an IML using a simple solution process. The efficiency of a homo-tandem device with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester as an active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylenimine) as an IML was initially found to be 3.40%. Further enhancement of the cell efficiency was achieved using silver nanoparticles (Ag-NPs) of different sizes and graphene quantum dot embedded IML. A maximum efficiency of 4.03% was achieved using 7 nm Ag-NPs that contribute to a better recombination process. Also, the performance of the tandem cell was solely based on the electrical improvements indicated by the current - voltage measurements, external quantum efficiency and impedance analysis. The use of Ag-NPs in the IML has been shown to lengthen the life time of electron-hole pairs in the device. This study thus paves way to develop such efficient IMLs for more efficient tandem solar cells. PMID:27453530

  6. Enhancement of recombination process using silver and graphene quantum dot embedded intermediate layer for efficient organic tandem cells

    NASA Astrophysics Data System (ADS)

    Ho, Nhu Thuy; Tien, Huynh Ngoc; Jang, Se-Joeng; Senthilkumar, Velusamy; Park, Yun Chang; Cho, Shinuk; Kim, Yong Soo

    2016-07-01

    High performance of organic tandem solar cell is largely dependent on transparent and conductive intermediate layer (IML). The current work reports the design and fabrication of an IML using a simple solution process. The efficiency of a homo-tandem device with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester as an active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylenimine) as an IML was initially found to be 3.40%. Further enhancement of the cell efficiency was achieved using silver nanoparticles (Ag-NPs) of different sizes and graphene quantum dot embedded IML. A maximum efficiency of 4.03% was achieved using 7 nm Ag-NPs that contribute to a better recombination process. Also, the performance of the tandem cell was solely based on the electrical improvements indicated by the current - voltage measurements, external quantum efficiency and impedance analysis. The use of Ag-NPs in the IML has been shown to lengthen the life time of electron-hole pairs in the device. This study thus paves way to develop such efficient IMLs for more efficient tandem solar cells.

  7. Polyethylenimine Interfacial Layers in Inverted Organic Photovoltaic Devices: Effects of Ethoxylation and Molecular Weight on Efficiency and Temporal Stability.

    PubMed

    Courtright, Brett A E; Jenekhe, Samson A

    2015-12-01

    We report a comparative study of polyethylenimine (PEI) and ethoxylated-polyethylenimine (PEIE) cathode buffer layers in high performance inverted organic photovoltaic devices. The work function of the indium-tin oxide (ITO)/zinc oxide (ZnO) cathode was reduced substantially (Δφ = 0.73-1.09 eV) as the molecular weight of PEI was varied from 800 g mol(-1) to 750 000 g mol(-1) compared with the observed much smaller reduction when using a PEIE thin film (Δφ = 0.56 eV). The reference inverted polymer solar cells based on the small band gap polymer PBDTT-FTTE (ITO/ZnO/PBDTT-FTTE:PC70BM/MoO3/Ag), without a cathode buffer layer, had an average power conversion efficiency (PCE) of 6.06 ± 0.22%. Incorporation of a PEIE cathode buffer layer in the same PBDTT-FTTE:PC70BM blend devices gave an enhanced performance with a PCE of 7.37 ± 0.53%. In contrast, an even greater photovoltaic efficiency with a PCE of 8.22 ± 0.10% was obtained in similar PBDTT-FTTE:PC70BM blend solar cells containing a PEI cathode buffer layer. The temporal stability of the inverted polymer solar cells was found to increase with increasing molecular weight of the cathode buffer layer. The results show that PEI is superior to PEIE as a cathode buffer layer in high performance organic photovoltaic devices and that the highest molecular weight PEI interlayer provides the highest temporal stability. PMID:26550983

  8. Anode modification of polymer light-emitting diode using graphene oxide interfacial layer: The role of ultraviolet-ozone treatment

    NASA Astrophysics Data System (ADS)

    Jiang, Xiao-Chen; Li, Yan-Qing; Deng, Yan-Hong; Zhuo, Qi-Qi; Lee, Shuit-Tong; Tang, Jian-Xin

    2013-08-01

    A simple and efficient method has been developed to modify the anode interface of polymer light-emitting diode by incorporating solution-processable graphene oxide as hole transport layer. Interface engineering of ultraviolet-ozone treatment on graphene oxide is demonstrated to dramatically enhance the electrical properties, leading to 15% increase in efficiency compared to that with a traditionally used poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) layer. As determined by photoelectron spectroscopy and impedance spectroscopy, an optimized ultraviolet-ozone treatment results in a more favorable energy level alignment and a decrease in series resistance, which can subsequently facilitate charge injection at the anodic interface.

  9. Interfacial effect on the electrochemical properties of the layered graphene/metal sulfide composites as anode materials for Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Lv, Yagang; Chen, Biao; Zhao, Naiqin; Shi, Chunsheng; He, Chunnian; Li, Jiajun; Liu, Enzuo

    2016-09-01

    The layered graphene/metal sulfide composites exhibit excellent electrochemical properties as anode materials for lithium ion battery, due to the synergistic effect between metal sulfide and graphene which still needs to be further understood. In this study, Li adsorption and diffusion on MoS2 and SnS2 monolayers and Li2S surface, as well as at their interfaces with graphene, are systematically investigated through first-principles calculations. The analysis of charge density difference, Bader charge, and density of states indicates that the adsorbed Li atoms interact with both the S atoms at metal sulfide surfaces and C atoms in graphene, resulting in larger Li adsorption energies at the interfaces compared with that on the corresponding surfaces, but with almost no enhancement of the energy barriers for Li atom diffusion. The enhanced Li adsorption capability at Li2S/G interface contributes to the extra storage capacity of graphene/metal sulfide composites. Furthermore, the synergistic mechanism between metal sulfide and graphene is revealed. Moreover, band structure analysis shows the electronic conductivity is enhanced with the incorporation of graphene. The results corroborate the interfacial pseudocapacity-like Li atom storage mechanism, and are helpful for the design of layered graphene/metal sulfide composites as anode materials for lithium ion batteries.

  10. Interfacial chemical reaction and multiple gap state formation on three layer cathode in organic light-emitting diode: Ca/BaF{sub 2}/Alq{sub 3}

    SciTech Connect

    Kim, Tae Gun; Kim, Jeong Won; Lee, Hyunbok; Yi, Yeonjin; Lee, Seung Mi

    2015-07-14

    A three layer cathode is a promising stack structure for long lifetime and high efficiency in organic light-emitting diodes. The interfacial chemical reactions and their effects on electronic structures for alkaline-earth metal (Ca, Ba)/Alq{sub 3} [tris(8-hydroxyquinolinato)aluminum] and Ca/BaF{sub 2}/Alq{sub 3} are investigated using in-situ X-ray and ultraviolet photoelectron spectroscopy, as well as molecular model calculation. The BaF{sub 2} interlayer initially prevents direct contact between Alq{sub 3} and the reactive Ca metal, but it is dissociated into Ba and CaF{sub 2} by the addition of Ca. As the Ca thickness increases, the Ca penetrates the interlayer to directly participate in the reaction with the underlying Alq{sub 3}. This series of chemical reactions takes place irrespective of the BaF{sub 2} buffer layer thickness as long as the Ca overlayer thickness is sufficient. The interface reaction between the alkaline-earth metal and Alq{sub 3} generates two energetically separated gap states in a sequential manner. This phenomenon is explained by step-by-step charge transfer from the alkaline-earth metal to the lowest unoccupied molecular orbital states of Alq{sub 3}, forming new occupied states below the Fermi level.

  11. Enhanced ultraviolet electroluminescence and spectral narrowing from ZnO quantum dots/GaN heterojunction diodes by using high-k HfO{sub 2} electron blocking layer

    SciTech Connect

    Mo, Xiaoming; Long, Hao; Wang, Haoning; Chen, Zhao; Wan, Jiawei; Liu, Yuping; Fang, Guojia; Li, Songzhan; Feng, Yamin; Ouyang, Yifang

    2014-08-11

    We demonstrated the capability of realizing enhanced ZnO-related UV emissions by using the low-cost and solution-processable ZnO quantum dots (QDs) with the help of a high-k HfO{sub 2} electron blocking layer (EBL) for the ZnO QDs/p-GaN light-emitting diodes (LEDs). Full-width at half maximum of the LED devices was greatly decreased from ∼110 to ∼54 nm, and recombinations related to nonradiative centers were significantly suppressed with inserting HfO{sub 2} EBL. The electroluminescence of the ZnO QDs/HfO{sub 2}/p-GaN LEDs demonstrated an interesting spectral narrowing effect with increasing HfO{sub 2} thickness. The Gaussian fitting revealed that the great enhancement of the Zn{sub i}-related emission at ∼414 nm whereas the deep suppression of the interfacial recombination at ∼477 nm should be the main reason for the spectral narrowing effect.

  12. Single step deposition of an interacting layer of a perovskite matrix with embedded quantum dots.

    PubMed

    Ngo, Thi Tuyen; Suarez, Isaac; Sanchez, Rafael S; Martinez-Pastor, Juan P; Mora-Sero, Ivan

    2016-08-14

    Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and electroluminescence experiments. The radiative exciplex relaxation is centered in the near infrared region (NIR), ≈1200 nm, which corresponds to lower energies than the corresponding band gap of both perovskite (PS) and QDs. Our approach allows the fabrication of multi-wavelength light emitting diodes (LEDs) based on a PS matrix with embedded QDs, which show considerably low turn-on potentials. The presence of the exciplex state of PS and QDs opens up a broad range of possibilities with important implications in both LEDs and solar cells. PMID:27437778

  13. Interfacial reactions between titanium and borate glass

    SciTech Connect

    Brow, R.K.; Saha, S.K.; Goldstein, J.I.

    1992-12-31

    Interfacial reactions between melts of several borate glasses and titanium have been investigated by analytical scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). A thin titanium boride interfacial layer is detected by XPS after short (30 minutes) thermal treatments. ASEM analyses after longer thermal treatments (8--120 hours) reveal boron-rich interfacial layers and boride precipitates in the Ti side of the interface.

  14. Spin scattering asymmetric coefficients and enhanced specific interfacial resistance of fully epitaxial current-perpendicular-to-plane giant magnetoresistance spin valves using alternate monatomic layered [Fe/Co]n and a Ag spacer layer

    NASA Astrophysics Data System (ADS)

    Jung, J. W.; Shiozaki, R.; Doi, M.; Sahashi, M.

    2011-04-01

    Using current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) measurement, we have evaluated the bulk and interface spin scattering asymmetric coefficients, βF and γF/N and the specific interfacial resistance, AR*F/N, for exchange-biased spin-valves consisting of artificially ordered B2 structure Fe50Co50 and Ag spacer layer. Artificially epitaxial ordered Fe50Co50 superlattices have been successfully fabricated on MgO (001) substrate by alternate monatomic layer (AML) deposition at a substrate temperature of 75 °C. The structural properties of the full epitaxial trilayer, AML[Fe/Co]n/Ag/AML[Fe/Co]n, on the Ag electrode have been confirmed by in situ reflection high-energy electron diffraction and transmission electron diffraction microscopy. A considerably large resistance-area product change and MR ratio (ΔRA > 3 mΩμm2 and MR ratio ˜5%) were confirmed even at thin AML[Fe/Co]n layer at room temperature (RT) in our spin-valve elements. The estimated values of βF and γF/N were 0.80 and 0.84 ± 0.02, respectively, from the Valet-Fert theory analysis of ΔRA as a function of thickness of the ferromagnetic layer (3, 4, and 5 nm) on the basis of the two-current model.

  15. Current-perpendicular-to-the-plane magnetoresistance from large interfacial spin-dependent scattering between Co50Fe50 magnetic layer and In-Zn-O conductive oxide spacer layer

    NASA Astrophysics Data System (ADS)

    Nakatani, T. M.; Childress, J. R.

    2015-06-01

    We have investigated electrically conductive indium-zinc-oxide (IZO) deposited by magnetron sputtering as spacer layer for current-perpendicular-to-the-plane giant magnetoresistance sensor devices. Spin-valves with a Co50Fe50/IZO/Co50Fe50 trilayer showed resistance-area product (RA) ranging from 110 to 250 mΩ μm2, significantly larger than all-metal structures with Ag or Cu spacers (˜40 mΩ μm2). Magnetoresistance ratios (ΔR/R) of 2.5% to 5.5% depending on the IZO spacer thickness (1.5-6.0 nm), corresponding to ΔRA values from 3 to 13 mΩ μm2, were obtained. The values of ΔRA with the IZO spacers and Co50Fe50 magnetic layers were significantly larger than those with conventional metal spacers and Co50Fe50 magnetic layers (˜1-2 mΩ μm2). The dependence of ΔRA on the magnetic layer thickness suggests that the larger ΔRA obtained with IZO spacer is due to a large interfacial spin-dependent scattering caused by the large specific resistance at the Co50Fe50/IZO interface. From structural characterization by TEM and the observed dependence of the RA dispersion on device size, the electric current flowing through the IZO spacer is thought to be laterally uniform, similar to normal metal spacers.

  16. Probing interfacial electronic structures in atomic layer LaMnO{sub3} and SrTiO{sub 3} superlattices.

    SciTech Connect

    Shah, A. B.; Ramasse, Q. M.; Zhai, X.; Wen, J. G.; May, S. J.; Petrov, I.; Bhattacharya, A.; Abbamonte, P.; Eckstein, J. N.; Zuo, J.-M.; Univ. of Illinois; LBNL

    2010-01-01

    The interfacial electronic structure characterization of a m x (LaMnO{sub 3})/n x (SrTiO{sub 3}) superlattice based on scanning transmission electron microscopy and electron energy loss spectroscopy. Evidence of interfacial band alignment and electron transfer are presented based on the observation of O K edge of individual transition metal and oxygen atomic columns. Electron probe aberration correction was essential for the high spatial resolution mapping of interfacial electronic states.

  17. Mechanism for interfacial adhesion strength of an ion beam mixed Cu/polyimide with a thin buffer layer

    NASA Astrophysics Data System (ADS)

    Chang, G. S.; Chae, K. H.; Whang, C. N.; Kurmaev, E. Z.; Zatsepin, D. A.; Winarski, R. P.; Ederer, D. L.; Moewes, A.; Lee, Y. P.

    1999-01-01

    A Cu (400 Å)/Al (50 Å)/polyimide system showed larger adhesion strength than that of Cu (400 Å)/polyimide after N2+ ion beam mixing. X-ray emission spectroscopy was performed to elucidate the mechanism of adhesion enhancement of the ion beam mixed Cu (400 Å)/polyimide with a thin Al buffer layer. Cu L2,3 x-ray emission spectra showed the formation of a CuAl2O4 layer which is strongly correlated with the large adhesion strength of a Cu/Al/polyimide. A decrease in adhesion strength at an ion dose higher than 5×1015cm-2 was also explained by the formation of an amorphous carbon. This was understood by investigating C Kα x-ray emission spectra. The overall spectroscopic results were in accordance with the behavior of quantitative adhesion strength.

  18. Improved Performance of Organic Light-Emitting Field-Effect Transistors by Interfacial Modification of Hole-Transport Layer/Emission Layer: Incorporating Organic Heterojunctions.

    PubMed

    Song, Li; Hu, Yongsheng; Zhang, Nan; Li, Yantao; Lin, Jie; Liu, Xingyuan

    2016-06-01

    Organic heterojunctions (OHJs) consisting of a strong electron acceptor 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) and an electron donor N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) were demonstrated for the first time that they can be implemented as effective modification layers between hole transport layer (HTL) and emission layer in the heterostructured organic light-emitting field effect transistors (OLEFETs). The influence of both HAT-CN/NPB junction (npJ) and NPB/HAT-CN junction (pnJ) on the optoelectronic performance of OLEFETs were conscientiously investigated. It is found that both the transport ability of holes and the injection ability of holes into emissive layer can be dramatically improved via the charge transfer of the OHJs and that between HAT-CN and the HTL. Consequently, OLEFETs with pnJ present optimal performance of an external quantum efficiency (EQE) of 3.3% at brightness of 2630 cdm(-2) and the ones with npJs show an EQE of 4.7% at brightness of 4620 cdm(-2). By further utilizing npn OHJs of HAT-CN/NPB/HAT-CN, superior optoelectronic performance with an EQE of 4.7% at brightness of 8350 cdm(-2) and on/off ratio of 1 × 10(5) is obtained. The results demonstrate the great practicality of implementing OHJs as effective modification layers in heterostructured OLEFETs. PMID:27215694

  19. Rapid thermal annealing of InAs/GaAs quantum dots with a low-temperature-grown InGaP cap layer

    SciTech Connect

    Jiang, W.H.; Thompson, D.A.; Hul'ko, O.; Robinson, B.J.; Mascher, P.

    2006-05-15

    A single layer of self-assembled InAs quantum dots was grown on a GaAs (001) substrate by gas source molecular-beam epitaxy. The quantum dots were overgrown with 65 nm GaAs, 25 nm InGaP, and a 10 nm GaAs etch-stop layer. This was either uncapped or capped with 100 nm of low-temperature (LT)-grown, lattice-matched InGaP (LT-InGaP) or with a SiO{sub 2} layer or Al{sub 2}O{sub 3} layer. Photoluminescence (PL) measurements were made on samples before and after rapid thermal annealing at 550-900 deg.C and for 15-120 s at 650 deg.C. Samples capped with LT-InGaP showed a significant blueshift of the PL peak wavelength for anneals above 575 deg.C. By comparison, for the SiO{sub 2}-capped and uncapped samples, the net blueshift only becomes significant for anneals >700 deg.C, while an Al{sub 2}O{sub 3} cap actually reduces the blueshift and suppresses the intermixing. It appears that the best conditions for spatially controlling the quantum dot intermixing occur with annealing at low temperatures (600-650 deg.C)

  20. Interfacial material for solid oxide fuel cell

    DOEpatents

    Baozhen, Li; Ruka, Roswell J.; Singhal, Subhash C.

    1999-01-01

    Solid oxide fuel cells having improved low-temperature operation are disclosed. In one embodiment, an interfacial layer of terbia-stabilized zirconia is located between the air electrode and electrolyte of the solid oxide fuel cell. The interfacial layer provides a barrier which controls interaction between the air electrode and electrolyte. The interfacial layer also reduces polarization loss through the reduction of the air electrode/electrolyte interfacial electrical resistance. In another embodiment, the solid oxide fuel cell comprises a scandia-stabilized zirconia electrolyte having high electrical conductivity. The scandia-stabilized zirconia electrolyte may be provided as a very thin layer in order to reduce resistance. The scandia-stabilized electrolyte is preferably used in combination with the terbia-stabilized interfacial layer. The solid oxide fuel cells are operable over wider temperature ranges and wider temperature gradients in comparison with conventional fuel cells.

  1. Linearised theory for surface and interfacial waves interacting with freely floating bodies in a two-layer fluid

    NASA Astrophysics Data System (ADS)

    Cal, Filipe S.; Dias, Gonçalo A. S.; Nazarov, Serguei A.; Videman, Juha H.

    2015-04-01

    We derive a linear system of equations governing the interaction of water waves with partially or totally submerged freely floating structures in a two-layer fluid. We establish conditions for the stability of equilibrium and, by considering time-harmonic motions, rewrite the problem as a spectral boundary-value problem consisting of a differential equation and an algebraic system, coupled through boundary conditions. We give also a suitable variational formulation for the problem and provide examples of configurations where the problem admits only the trivial solution.

  2. Dielectric properties of the interfacial layer on n-CuInSe/sub 2/ in photoelectrochemical solar cells

    SciTech Connect

    Shen, W.; Aurian-Blajeni, B.; Tomkiewicz, M.

    1986-05-01

    The authors report on the properties of n-CuInSe/sub 2/ single crystals, whose surface has been modified by thermal treatment. Frequency dispersion and electron beam induced current (EBIC) measurements show that the oxidic phase formed at the surface has a porous structure. Comparisons between thermally treated CuInSe/sub 2/ in liquid and solid junction devices confirm that the superficial layer alone is a rather poor conductor and that its electric properties change upon immersion in the electrolyte. The implications of this on the photovoltaic performance of thermally oxidized CuInSe/sub 2/ are discussed.

  3. Interfacial effects of the Cu2O nano-dots decorated Co3O4 nanorods array and its photocatalytic activity for cleaving organic molecules

    NASA Astrophysics Data System (ADS)

    Qiu, X. P.; Yu, J. S.; Xu, H. M.; Chen, W. X.; Hu, W.; Chen, G. L.

    2016-09-01

    A heterogeneous nanocomposite catalyst constructed by the Co3O4 nanorods decorated with the Cu2O quantum dots (QDs) were successfully synthesized via a simple hydrothermal method followed by an oxidation-reduction processing. The fabricated Cu2O/Co3O4 nanocomposite was characterized by the SEM, TEM, XPS, XRD, UV-vis and PL, and the (2 2 0) and (3 1 1) facets of the Co3O4 were exposed. Compared with the original Co3O4 nanorods with an average diameter of 350 nm, a substantial decrease in the band gap was observed after doping the nanorods with the Cu2O QDs (average diameter of 5 nm). Such a dramatic decrease in the band gap indicated a significant enhancement of the photocatalytic activities under visible light. The methylene blue (MB) dye and the phenol were used as model organic pollutants, and the Cu2O/Co3O4 nanocomposite catalyst exhibited both high catalytic activity and good recycling stability. The catalytic activities of the Cu2O/Co3O4/potassium monopersulfate triple salt (PMS) system for cleaving the MB and the phenol were dependent on the dosages of the Cu2O QDs, and the calculated degradation rates achieved by 7.0 wt% Cu2O/Co3O4 nanocomposite catalyst were about 11.3 and 1.8 times than that of the pristine Co3O4 nanorod catalyst for the MB and the phenol, respectively. The reactive species of rad O2- and the holes were determined to be the main active species for the phenol photocatalytic degradation by the 7 wt% Cu2O/Co3O4/PMS system and the 7 wt% Cu2O/Co3O4/H2O2 system, respectively.

  4. Electric field-induced nonlinearity enhancement in strained semi-spheroid-shaped quantum dots coupled to wetting layer

    SciTech Connect

    Sabaeian, Mohammad Shahzadeh, Mohammadreza; Farbod, Mansoor

    2014-12-15

    In this work, the effects of vertical electric field on the electronic and optical properties of strained semi-spheroid-shaped InAs/GaAs quantum dot (QD) coupled to its wetting layer (WL) aimed to enhance the nonlinear optical properties were investigated. The dependence of energy eigenvalues of S- and P- states and intersubband P-to-S transition energy on applied electric field was studied. A ∼∓10 meV Stark shift in the intersubband P-to-S transition energy was calculated for a semi-spheroid-shaped QD with height of 5 nm and base-length of 20 nm when bias voltage was varied from 0 V to ±0.8V. The dependence of transition dipole moment and linear and nonlinear optical properties of the system on bias voltage was also studied. It was concluded that increasing the bias voltage from -0.8V to +0.8V leads to increase in figure of merit of the system from ∼0.153 to ∼0.198.

  5. Studies of the Origins of Half-Loop Arrays and Interfacial Dislocations Observed in Homoepitaxial Layers of 4H-SiC

    NASA Astrophysics Data System (ADS)

    Wang, H.; Dudley, M.; Wu, F.; Yang, Y.; Raghothamachar, B.; Zhang, J.; Chung, G.; Thomas, B.; Sanchez, E. K.; Mueller, S. G.; Hansen, D.; Loboda, M. J.

    2015-05-01

    Synchrotron x-ray topography and KOH etching studies have been carried out on n-type 4H-SiC offcut substrates before and after homoepitaxial growth to study defect replication and strain relaxation processes and identify the nucleation sources of both interfacial dislocations (IDs) and half-loop arrays (HLAs), which are known to have a deleterious effect on device performance. Two cases are reported. In one, they nucleate from short segments of edge-oriented basal plane dislocations (BPDs) in the substrate which are drawn into the epilayer. In the other, they form from segments of half-loops of BPD that are attached to the substrate surface prior to growth which glide into the epilayer. The significance of these findings is: (1) It is demonstrated that it is not necessary for a BPD to intersect the substrate surface in order for it to be replicated into the homoepitaxial layer and take part in nucleation of IDs and HLAs; (2) The conversion of the surface intersections of a substrate BPD half-loop into threading edge dislocations (TEDs) does not prevent it from also becoming involved in nucleation of IDs and HLAs. This means that, while BPD to TED conversion can eliminate most of the BPD transfer into the epilayer, further mitigation may only be possible by continued efforts to reduce the BPD density in substrates by control of temperature-gradient- induced stresses during their physical vapor transport (PVT) growth.

  6. Chemical compatibility issues related to use of copper as an interfacial layer for SiC fiber reinforced Ti3Ai+Nb composite

    NASA Technical Reports Server (NTRS)

    Misra, Ajay K.

    1991-01-01

    The reaction of Cu, a potential interfacial compliant layer for the Ti3Al plus Nb/SiC composite, with SiC, SCS-6 fiber, and the Ti3Al plus Nb matrix was examined at two temperatures: 1223 and 1273 K. Reaction of Cu with SiC resulted in the formation of a CuSi solution and free carbon, the reaction product being molten at 1273 K. Hot pressing the SCS-6 fiber in a Cu matrix at 1273 K resulted in cracking and delamination of the outer carbon-rich coating, thus allowing the Cu to penetrate to the SiC-carbon coating interface and react with SiC. In contrast, no such damage to the outer coating was observed at 1223 K. There was excessive reaction between Cu and the Ti3Al plus Nb matrix, the reaction product being molten both at 1223 and 1273 K. An interlayer of Nb between Cu and Ti3Al plus Nb matrix prevented the reaction between the two.

  7. Low interfacial trap density and high-temperature thermal stability in atomic layer deposited single crystal Y2O3/n-GaAs(001)

    NASA Astrophysics Data System (ADS)

    Lin, Yen-Hsun; Fu, Chien-Hua; Lin, Keng-Yung; Chen, Kuan-Hsiung; Chang, Tsong-Wen; Raynien Kwo, J.; Hong, Minghwei

    2016-08-01

    A low interfacial trap density (D it) of 2.2 × 1011 eV‑1 cm‑2 has been achieved with an atomic layer deposited (ALD) single crystal Y2O3 epitaxially on n-GaAs(001), along with a small frequency dispersion of 10.3% (2.6%/decade) at the accumulation region in the capacitance–voltage (C–V) curves. The D it and frequency dispersion in the C–V curves in this work are the lowest among all of the reported ALD-oxides on n-type GaAs(001). The D it was measured using the conductance–voltage (G–V) and quasi-static C–V (QSCV) methods. Moreover, the heterostructure was thermally stable with rapid annealing at 900 °C under various durations in He and N2, which has not been achieved in the heterostructures of ALD-Al2O3 or HfO2 on GaAs.

  8. Tuning indium arsenide quantum dot electronic structure using (indium aluminum gallium)arsenide capping layers and application to infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Kim, Eui-Tae

    This dissertation contributes to the subjects of (i) molecular beam epitaxical growth and characterization of strain-driven self-assembled InAs/GaAs coherent island based quantum dots (QDs), (ii) manipulation of such InAs QD electronic states and associated transitions utilizing AlxGa 1-xAs, InxGa1-xAs, or InxAl yGa1-x-yAs capping layers, and (iii) application of such InAs/(InAlGa)As QDs to infrared photodetectors (QDIPs). A slow-growth-rate (at 0.054 ML/sec) QD formation is introduced to realize high-quality uniform InAs/(InAlGa)As QDs. Such QDs are characterized utilizing photoluminescence (PL), PL excitation spectroscopy, atomic force microscopy, and transmission electron microscopy. The QD growth kinetics is discussed by comparing with commonly employed relatively fast-growth-rate (at 0.22 ML/sec) QD formation. To manipulate electronic states and associated transitions of such InAs/GaAs QDs, part of the GaAs capping layer is replaced with AlxGa 1-xAs, InxGa1-xAs, or InxAlyGa1-x-yAs layers. Al xGa1-xAs insertions result in blueshifted inter- and intraband transition wavelengths (with respect to those of InAs/GaAs QDs) because of the enhanced confinement potential. By contrast, InxGa 1-xAs insertions allow redshifted inter- and intraband transition wavelengths because of overall lowering of the confinement potential via strain relief and chemical difference effects. Moreover, the InxGa 1-xAs layer regions between the InAs QDs act as a quantum well (QW) having its own energy states. Indeed, we find that the long-wavelength IR (LWIR) photoresponse involves QD intraband transitions to final states that are likely coupled to the QW electron energy states. To further the objective of controlled manipulation of the electronic states in InAs QDs, we introduce the notion of a lateral potential confinement layer (LPCL) whose judicious placement during island capping allows selective impact on ground and excited electron and hole states. Finally, as an application of self

  9. Heat-induced transformation of CdSe-CdS-ZnS core-multishell quantum dots by Zn diffusion into inner layers.

    PubMed

    Yalcin, Anil O; Goris, Bart; van Dijk-Moes, Relinde J A; Fan, Zhaochuan; Erdamar, Ahmet K; Tichelaar, Frans D; Vlugt, Thijs J H; Van Tendeloo, Gustaaf; Bals, Sara; Vanmaekelbergh, Daniël; Zandbergen, Henny W; van Huis, Marijn A

    2015-02-25

    In this work, we investigate the thermal evolution of CdSe-CdS-ZnS core-multishell quantum dots (QDs) in situ using transmission electron microscopy (TEM). Starting at a temperature of approximately 250 °C, Zn diffusion into inner layers takes place together with simultaneous evaporation of particularly Cd and S. As a result of this transformation, CdxZn1-xSe-CdyZn1-yS core-shell QDs are obtained. PMID:25431813

  10. Exchange bias properties of 140 nm-sized dipolarly interacting circular dots with ultrafine IrMn and NiFe layers

    NASA Astrophysics Data System (ADS)

    Spizzo, F.; Tamisari, M.; Chinni, F.; Bonfiglioli, E.; Gerardino, A.; Barucca, G.; Bisero, D.; Fin, S.; Del Bianco, L.

    2016-02-01

    We studied the exchange bias effect in an array of IrMn(3 nm)/NiFe(3 nm) circular dots (size ~140 nm and center-to-center distance ~200 nm, as revealed by microscopy analyses), prepared on a large area (3×3 mm2) by electron beam lithography and lift-off, using dc sputtering deposition. Hysteresis loops were measured by SQUID magnetometer at increasing values of temperature T (in the 5-300 K range) after cooling from 300 K down to 5 K in zero field (ZFC mode) and in a saturating magnetic field (FC mode). The exchange bias effect disappears above T~200 K and, at each temperature, the exchange field HEX measured in ZFC is substantially lower than the FC one. Micromagnetic calculations indicate that, at room temperature, each dot is in high-remanence ground state, but magnetic dipolar interactions establish a low-remanence configuration of the array as a whole. Hence, at low temperature, following the ZFC procedure, the exchange anisotropy in the dot array is averaged out, tending to zero. However, even the FC values of HEX and of the coercivity HC are definitely smaller compared to those measured in a reference continuous film with the same stack configuration (at T=5 K, HEX~90 Oe and HC~180 Oe in the dots and HEX~1270 Oe and HC~860 Oe in the film). Our explanation is based on the proven glassy magnetic nature of the ultrathin IrMn layer, implying the existence of magnetic correlations among the spins, culminating in a collective freezing below T~100 K. We propose, also by the light of micromagnetic simulations, that the small dot size imposes a spatial constraint on the magnetic correlation length among the IrMn spins so that, even at the lowest temperature, their thermal stability, especially at the dot border, is compromised.

  11. Photoluminescence study of InAs quantum dots embedded in GaNAs strain compensating layer grown by metalorganic-molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhang, X. Q.; Ganapathy, Sasikala; Kumano, Hidekazu; Uesugi, Kasturi; Suemune, Ikuo

    2002-12-01

    Self-assembled InAs quantum dots (QDs) embedded in GaN0.007As0.993 strain compensating layers have been grown by metalorganic-molecular-beam epitaxy on a GaAs (001) substrate with a high density of 1×1011 cm-2. The photoluminescence properties have been studied for two periods of InAs quantum dots layers embedded in GaN0.007As0.993 strain compensating layers. Four well-resolved excited-state peaks in the photoluminescence spectra have been observed from these highly packed InAs QDs embedded in the GaN0.007As0.993 strain compensating layers. This indicates that the InAs QDs are uniformly formed and that the excited states in QDs due to the quantum confinement effect are well defined. This is explained by tensile strain in GaNAs layers instead of the usual GaAs layers to relieve the compressive strain formed in InAs QDs to keep the total strain of the system at a minimum.

  12. Bio-sensing based on plasmon-coupling caused by rotated sub-micrometer gratings in metal-dielectric interfacial layers

    NASA Astrophysics Data System (ADS)

    Csete, M.; Sipos, Á.; Szalai, A.; Mathesz, A.; Deli, M. A.; Veszelka, Sz.; Schmatulla, A.; Kőházi-Kis, A.; Osvay, K.; Marti, O.; Bor, Zs.

    2007-09-01

    Novel plasmonic sensor chips are prepared by generating sub-micrometer periodic patterns in the interfacial layers of bimetal-polymer films via master-grating based interference method. Poly-carbonate films spin-coated onto vacuum evaporated silver-gold bimetallic layers are irradiated by the two interfering UV beams of a Nd:YAG laser. It is proven by pulsed force mode AFM that periodic adhesion pattern corresponds to the surface relief gratings, consisting of sub-micrometer droplet arrays and continuous polymer stripes, induced by p- and s-polarized beams, respectively. The characteristic periods are the same, but more complex and larger amplitude adhesion modulation is detectable on the droplet arrays. The polar and azimuthal angle dependence of the resonance characteristic of plasmons is studied by combining the prism- and grating-coupling methods in a modified Kretschmann arrangement, illuminating the structured metal-polymer interface by a frequency doubled Nd:YAG laser through a semi-cylinder. It is proven that the grating-coupling results in double-peaked plasmon resonance curves on both of the droplet arrays and line gratings, when the grooves are rotated to an appropriate azimuthal angle, and the modulation amplitude of the structure is sufficiently large. Streptavidin seeding is performed to demonstrate that small amount of protein can be detected monitoring the shift of the secondary resonance minima. The available high concentration sensitivity is explained by the promotion of protein adherence in the structure's valleys due to the enhanced adhesion. The line-shaped polymer gratings resulting in narrow resonance peaks are utilized to demonstrate the effect of therapeutic molecules on Amyloid-Β peptide, a pathogenic factor in Alzheimer disease.

  13. Growth control and design principles of self-assembled quantum dot multiple layer structures for photodetector applications

    NASA Astrophysics Data System (ADS)

    Asano, Tetsuya

    Self-assembled quantum dots (SAQDs) formed by lattice-mismatch strain-driven epitaxy are currently the most advanced nanostructure-based platform for high performance optoelectronic applications such as lasers and photodetectors. While the QD lasers have realized the best performance in terms of threshold current and temperature stability, the performance of QD photodetectors (QDIPs) has not surpassed that of quantum well (QW) photodetectors. This is because the requirement of maximal photon absorption for photodetectors poses the challenge of forming an appropriately-doped large number of uniform multiple SAQD (MQD) layers with acceptable structural defect (dislocation etc.) density. This dissertation addresses this challenge and, through a combination of innovative approach to control of defects in MQD growth and judicious placement of SAQDs in a resonant cavity, shows that SAQD based quantum dot infrared photodetectors (QDIPs) can be made competitive with their quantum well counterparts. Specifically, the following major elements were accomplished: (i) the molecular beam epitaxy (MBE) growth of dislocation-free and uniform InAs/InAlGaAs/GaAs MQD strained structures up to 20-period, (ii) temperature-dependent photo- and dark-current based analysis of the electron density distribution inside the MQD structures for various doping schemes, (iii) deep level transient spectroscopy based identification of growth procedure dependent deleterious deep traps in SAQD structures and their reduction, and (iv) the use of an appropriately designed resonant cavity (RC) and judicious placement of the SAQD layers for maximal enhancement of photon absorption to realize over an order of magnitude enhancement in QDIP detectivity. The lattermost demonstration indicates that implementation of the growth approach and resonant cavity strategy developed here while utilizing the currently demonstrated MIR and LWIR QDIPs with detectivities > 10 10 cmHz1/2/W at ˜ 77 K will enable RC

  14. Gas-solid interfacial modification of oxygen activity in layered oxide cathodes for lithium-ion batteries

    DOE PAGESBeta

    Qiu, Bao; Zhang, Minghao; Wu, Lijun; Wang, Jun; Xia, Yonggao; Qian, Danna; Liu, Haodong; Chen, Yan; An, Ke; Zhu, Yimei; et al

    2016-07-01

    Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. Here, we report the design of a gas–solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high asmore » 301 mAh g–1 with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g–1 still remains without any obvious decay in voltage. Lastly, this study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries.« less

  15. Gas-solid interfacial modification of oxygen activity in layered oxide cathodes for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Qiu, Bao; Zhang, Minghao; Wu, Lijun; Wang, Jun; Xia, Yonggao; Qian, Danna; Liu, Haodong; Hy, Sunny; Chen, Yan; An, Ke; Zhu, Yimei; Liu, Zhaoping; Meng, Ying Shirley

    2016-07-01

    Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. Here, we report the design of a gas-solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g-1 with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g-1 still remains without any obvious decay in voltage. This study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries.

  16. Exact Solution to Stationary Onset of Convection Due to Surface Tension Variation in a Multicomponent Fluid Layer With Interfacial Deformation

    NASA Technical Reports Server (NTRS)

    Skarda, J. Raymond Lee; McCaughan, Frances E.

    1998-01-01

    Stationary onset of convection due to surface tension variation in an unbounded multicomponent fluid layer is considered. Surface deformation is included and general flux boundary conditions are imposed on the stratifying agencies (temperature/composition) disturbance equations. Exact solutions are obtained to the general N-component problem for both finite and infinitesimal wavenumbers. Long wavelength instability may coexist with a finite wavelength instability for certain sets of parameter values, often referred to as frontier points. For an impermeable/insulated upper boundary and a permeable/conductive lower boundary, frontier boundaries are computed in the space of Bond number, Bo, versus Crispation number, Cr, over the range 5 x 10(exp -7) less than or equal to Bo less than or equal to 1. The loci of frontier points in (Bo, Cr) space for different values of N, diffusivity ratios, and, Marangoni numbers, collapsed to a single curve in (Bo, D(dimensional variable)Cr) space, where D(dimensional variable) is a Marangoni number weighted diffusivity ratio.

  17. Gas-solid interfacial modification of oxygen activity in layered oxide cathodes for lithium-ion batteries.

    PubMed

    Qiu, Bao; Zhang, Minghao; Wu, Lijun; Wang, Jun; Xia, Yonggao; Qian, Danna; Liu, Haodong; Hy, Sunny; Chen, Yan; An, Ke; Zhu, Yimei; Liu, Zhaoping; Meng, Ying Shirley

    2016-01-01

    Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. Here, we report the design of a gas-solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g(-1) with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g(-1) still remains without any obvious decay in voltage. This study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries. PMID:27363944

  18. Interfacial charge-induced polarization switching in Al2O3/Pb(Zr,Ti)O3 bi-layer

    NASA Astrophysics Data System (ADS)

    Kim, Yu Jin; Park, Min Hyuk; Jeon, Woojin; Kim, Han Joon; Moon, Taehwan; Lee, Young Hwan; Kim, Keum Do; Hyun, Seung Dam; Hwang, Cheol Seong

    2015-12-01

    Detailed polarization switching behavior of an Al2O3/Pb(Zr,Ti)O3 (AO/PZT) structure is examined by comparing the phenomenological thermodynamic model to the experimental polarization-voltage (P-V) results. Amorphous AO films with various thicknesses (2-10 nm) were deposited on the polycrystalline 150-nm-thick PZT film. The thermodynamic calculation showed that the transition from the ferroelectric-like state to the paraelectric-like state with increasing AO thickness occurs at ˜3 nm thickness. This paraelectric-like state should have exhibited a negative capacitance effect without permanent polarization switching if no other adverse effects are involved. However, experiments showed typical ferroelectric-like hysteresis loops where the coercive voltage increased with the increasing AO thickness, which could be explained by the carrier injection through the thin AO layer and trapping of the carriers at the AO/PZT interface. The fitting of the experimental P-V loops using the thermodynamic model considering the depolarization energy effect showed that trapped charge density was ˜±0.1 Cm-2 and critical electric field at the Pt electrode/AO interface, at which the carrier transport occurs, was ˜±10 MV/cm irrespective of the AO thickness. Energy band model at each electrostatic state along the P-V loop was provided to elucidate correlation between macroscopic polarization and internal charge state of the stacked films.

  19. Gas–solid interfacial modification of oxygen activity in layered oxide cathodes for lithium-ion batteries

    PubMed Central

    Qiu, Bao; Zhang, Minghao; Wu, Lijun; Wang, Jun; Xia, Yonggao; Qian, Danna; Liu, Haodong; Hy, Sunny; Chen, Yan; An, Ke; Zhu, Yimei; Liu, Zhaoping; Meng, Ying Shirley

    2016-01-01

    Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. Here, we report the design of a gas–solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g−1 with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g−1 still remains without any obvious decay in voltage. This study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries. PMID:27363944

  20. Effect of high-pressure H{sub 2}O treatment on elimination of interfacial GeO{sub X} layer between ZrO{sub 2} and Ge stack

    SciTech Connect

    Huang, Chen-Shuo; Liu, Po-Tsun

    2011-08-22

    This investigation demonstrates the effect of high-pressure H{sub 2}O treatment on the elimination of the interfacial germanium suboxide (GeO{sub X}) layer between ZrO{sub 2} and Ge. The formation of GeO{sub X} interlayer increases the gate-leakage current and worsen the controllability of the gate during deposition or thermal cycles. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy reveal that high-pressure H{sub 2}O treatment eliminates the interfacial GeO{sub X} layer. The physical mechanism involves the oxidation of non-oxidized Zr with H{sub 2}O and the reduction of GeO{sub X} by H{sub 2}. Treatment with H{sub 2}O reduces the gate-leakage current of a ZrO{sub 2}/Ge capacitor by a factor of 1000.

  1. A Resonance-Shifting Hybrid n-Type Layer for Boosting Near-Infrared Response in Highly Efficient Colloidal Quantum Dots Solar Cells.

    PubMed

    Baek, Se-Woong; Song, Jung Hoon; Choi, Woong; Song, Hyunjoon; Jeong, Sohee; Lee, Jung-Yong

    2015-12-22

    A new configuration of a plasmonic quantum dots solar structure is proposed. Gold-silver core-shell metal nanoparticles (Au@Ag NCs) are incorporated into the TiO2 layer (Au@Ag NCs-HL) of PbS-based solar cells. The TiO2 layer enables the Au@Ag NCs to have broad plasmonic responses and the external quantum efficiency and absorption of the plasmonic devices are significantly enhanced. The electrical performance of the solar cells is also improved. PMID:26523933

  2. Current-perpendicular-to-the-plane magnetoresistance from large interfacial spin-dependent scattering between Co{sub 50}Fe{sub 50} magnetic layer and In-Zn-O conductive oxide spacer layer

    SciTech Connect

    Nakatani, T. M. Childress, J. R.

    2015-06-28

    We have investigated electrically conductive indium-zinc-oxide (IZO) deposited by magnetron sputtering as spacer layer for current-perpendicular-to-the-plane giant magnetoresistance sensor devices. Spin-valves with a Co{sub 50}Fe{sub 50}/IZO/Co{sub 50}Fe{sub 50} trilayer showed resistance-area product (RA) ranging from 110 to 250 mΩ μm{sup 2}, significantly larger than all-metal structures with Ag or Cu spacers (∼40 mΩ μm{sup 2}). Magnetoresistance ratios (ΔR/R) of 2.5% to 5.5% depending on the IZO spacer thickness (1.5–6.0 nm), corresponding to ΔRA values from 3 to 13 mΩ μm{sup 2}, were obtained. The values of ΔRA with the IZO spacers and Co{sub 50}Fe{sub 50} magnetic layers were significantly larger than those with conventional metal spacers and Co{sub 50}Fe{sub 50} magnetic layers (∼1–2 mΩ μm{sup 2}). The dependence of ΔRA on the magnetic layer thickness suggests that the larger ΔRA obtained with IZO spacer is due to a large interfacial spin-dependent scattering caused by the large specific resistance at the Co{sub 50}Fe{sub 50}/IZO interface. From structural characterization by TEM and the observed dependence of the RA dispersion on device size, the electric current flowing through the IZO spacer is thought to be laterally uniform, similar to normal metal spacers.

  3. Use of Surface Photovoltage Spectroscopy to Measure Built-in Voltage, Space Charge Layer Width, and Effective Band Gap in CdSe Quantum Dot Films.

    PubMed

    Zhao, Jing; Nail, Benjamin A; Holmes, Michael A; Osterloh, Frank E

    2016-09-01

    Surface photovoltage spectroscopy (SPS) was used to study the photochemistry of mercaptoethanol-ligated CdSe quantum dot (2.0-4.2 nm diameter) films on indium doped tin oxide (ITO) in the absence of an external bias or electrolyte. The n-type films generate negative voltages under super band gap illumination (0.1-0.5 mW cm(-2)) by majority carrier injection into the ITO substrate. The photovoltage onset energies track the optical band gaps of the samples and are assigned as effective band gaps of the films. The photovoltage values (-125 to -750 mV) vary with quantum dot sizes and are modulated by the built-in potential of the CdSe-ITO Schottky type contacts. Deviations from the ideal Schottky model are attributed to Fermi level pinning in states approximately 1.1 V negative of the ITO conduction band edge. Positive photovoltage signals of +80 to +125 mV in films of >4.0 nm nanocrystals and in thin (70 nm) nanocrystal films are attributed to electron-hole (polaron) pairs that are polarized by a space charge layer at the CdSe-ITO boundary. The space charge layer is 70-150 nm wide, based on thickness-dependent photovoltage measurements. The ability of SPS to directly measure built-in voltages, space charge layer thickness, sub-band gap states, and effective band gaps in drop-cast quantum dot films aids the understanding of photochemical charge transport in quantum dot solar cells. PMID:27505130

  4. Effect of passivation layer grown by atomic layer deposition and sputtering processes on Si quantum dot superlattice to generate high photocurrent for high-efficiency solar cells

    NASA Astrophysics Data System (ADS)

    Maksudur Rahman, Mohammad; Higo, Akio; Sekhar, Halubai; Erman Syazwan, Mohd; Hoshi, Yusuke; Usami, Noritaka; Samukawa, Seiji

    2016-03-01

    The effect of passivation films on a Si quantum dot superlattice (QDSL) was investigated to generate high photocurrent in solar-cell applications. Three types of passivation films, sputter-grown amorphous silicon carbide (a-SiC), hydrogenated a-SiC (a-SiC:H), and atomic-layer-deposited aluminum oxide (ALD-Al2O3), were used to passivate the Si QDSLs containing a stack of four 4 nm Si nanodisks (NDs) and 2 nm silicon carbide (SiC) films fabricated by neutral beam etching (NBE). Because of the high surface-to-volume ratio typically present in quantum Si-NDs formed in the top-down NBE process, there is a tendency to form larger surface dangling bonds on untreated Si-ND surfaces as well as to have short distance (<10 nm) between high-aspect-ratio nanopillars of stacked 4 nm Si-NDs/2 nm SiC films, which conventionally sputter SiC films cannot uniformly cover. Therefore, we optimized the passivation techniques with an ALD-Al2O3 film. Scanning electron microscopy (SEM) analysis helped to explain the surface morphology before and after the passivation of the QDSLs. After the completion of the passivation process, the quality of the top surface films of the QDSLs was analyzed from the surface roughness by atomic force microscopy (AFM) analysis, which revealed that ALD-Al2O3 passivated films had the smallest roughness (RMS) of 1.09 nm with respect to sputter-grown a-SiC (RMS: 1.75 nm) and a-SiC:H (RMS: 1.54 nm) films. Conductive atomic force microscopy (CAFM) revealed that ALD-Al2O3 passivation decreased the surface-leakage current as a result of proper passivation of side-wall surface defects in the QDSLs. The carrier transport characteristics were extracted from the QDSLs using the photovoltaic (PV) properties of p++/i/n+ solar cells, where the QDSLs consisted of different passivation layers acting as intermediate layers (i-layers) between the high-doping-density p++ Si (1 × 1020 cm-3) and n+ Si (1 × 1019 cm-3) substrates. High-doping-density p++ Si acted as a hole

  5. Understanding the interfacial phenomena of a 4.7 V and 55 °C Li-ion battery with Li-rich layered oxide cathode and grap2hite anode and its correlation to high-energy cycling performance

    NASA Astrophysics Data System (ADS)

    Pham, Hieu Quang; Hwang, Eui-Hyung; Kwon, Young-Gil; Song, Seung-Wan

    2016-08-01

    Research progress of high-energy performance and interfacial phenomena of Li1.13Mn0.463Ni0.203Co0.203O2 cathode and graphite anode in a 55 °C full-cell under an aggressive charge cut-off voltage to 4.7 V (4.75 V vs. Li/Li+) is reported. Although anodic instability of conventional electrolyte is the critical issue on high-voltage and high-temperature cell operation, interfacial phenomena and the solution to performance improvement have not been reported. Surface spectroscopic evidence revealed that structural degradation of both cathode and anode materials, instability of surface film at cathode, and metal-dissolution from cathode and -deposition at anode, and a rise of interfacial resistance with high-voltage cycling in 55 °C conventional electrolyte are resolved by the formation of a stable surface film with organic/inorganic mixtures at cathode and solid electrolyte interphase (SEI) at anode using blended additives of fluorinated linear carbonate and vinylene carbonate. As a result, significantly improved cycling stability of 77% capacity retention delivering 227-174 mAhg-1 after 50 cycles is obtained, corresponding to 819-609 Wh per kg of cathode active material. Interfacial stabilization approach would pave the way of controlling the performance and safety, and widening the practical application of Li-rich layered oxide cathode materials and high-voltage electrolyte materials in various high-energy density Li-ion batteries.

  6. Highly Enhanced Photoelectrochemical Water Oxidation Efficiency Based on Triadic Quantum Dot/Layered Double Hydroxide/BiVO4 Photoanodes.

    PubMed

    Tang, Yanqun; Wang, Ruirui; Yang, Ye; Yan, Dongpeng; Xiang, Xu

    2016-08-01

    The water oxidation half-reaction is considered to be a bottleneck for achieving highly efficient solar-driven water splitting due to its multiproton-coupled four-electron process and sluggish kinetics. Herein, a triadic photoanode consisting of dual-sized CdTe quantum dots (QDs), Co-based layered double hydroxide (LDH) nanosheets, and BiVO4 particles, that is, QD@LDH@BiVO4, was designed. Two sets of consecutive Type-II band alignments were constructed to improve photogenerated electron-hole separation in the triadic structure. The efficient charge separation resulted in a 2-fold enhancement of the photocurrent of the QD@LDH@BiVO4 photoanode. A significantly enhanced oxidation efficiency reaching above 90% in the low bias region (i.e., E < 0.8 V vs RHE) could be critical in determining the overall performance of a complete photoelectrochemical cell. The faradaic efficiency for water oxidation was almost 90%. The conduction band energy of QDs is ∼1.0 V more negative than that of LDH, favorable for the electron injection to LDH and enabling a more efficient hole separation. The enhanced photon-to-current conversion efficiency and improved water oxidation efficiency of the triadic structure may result from the non-negligible contribution of hot electrons or holes generated in QDs. Such a band-matching and multidimensional triadic architecture could be a promising strategy for achieving high-efficiency photoanodes by sufficiently utilizing and maximizing the functionalities of QDs. PMID:27419597

  7. Improved conversion efficiency of Ag2S quantum dot-sensitized solar cells based on TiO2 nanotubes with a ZnO recombination barrier layer

    PubMed Central

    2011-01-01

    We improve the conversion efficiency of Ag2S quantum dot (QD)-sensitized TiO2 nanotube-array electrodes by chemically depositing ZnO recombination barrier layer on plain TiO2 nanotube-array electrodes. The optical properties, structural properties, compositional analysis, and photoelectrochemistry properties of prepared electrodes have been investigated. It is found that for the prepared electrodes, with increasing the cycles of Ag2S deposition, the photocurrent density and the conversion efficiency increase. In addition, as compared to the Ag2S QD-sensitized TiO2 nanotube-array electrode without the ZnO layers, the conversion efficiency of the electrode with the ZnO layers increases significantly due to the formation of efficient recombination layer between the TiO2 nanotube array and electrolyte. PMID:21777458

  8. Impact of Copper-Doped Titanium Dioxide Interfacial Layers on the Interface-State and Electrical Properties of Si-based MOS Devices

    NASA Astrophysics Data System (ADS)

    Akin, Seçkİn; Sönmezoğlu, Savaş

    2015-09-01

    The current study presents the interface-state and electrical properties of silicon (Si)-based metal-oxide-semiconductor (MOS) devices using copper-doped titanium dioxide (Cu:TiO2) nanoparticles for possible applications as an interfacial layer in scaled high-k/metal gate MOSFET technology. The structural properties of the Cu:TiO2 nanoparticles have been obtained by means of X-ray diffraction (XRD), UV-Vis-NIR spectrometry, atomic force microscopy, and scanning electron microscopy measurements; they were compared with pure TiO2 thin film. With the incorporation of Cu, rutile-dominated anatase/rutile multiphase crystalline was revealed by XRD analysis. To understand the nature of this structure, the electronic parameters controlling the device performance were calculated using current-voltage ( I- V), capacitance-voltage ( C- V), and conductance-voltage ( G- V) measurements. The ideality factor ( n) was 1.21 for the Al/Cu:TiO2/ p-Si MOS device, while the barrier height ϕ b was 0.75 eV with semi-log I- V characteristics. This is in good agreement with 0.78 eV measured by the Norde model. Possible reasons for the deviation of the ideality factor from unity have been addressed. From the C- V measurements, the values of diffusion potential, barrier height, and carrier concentration were extracted as 0.67, 0.98 eV, and 8.73 × 1013 cm-3, respectively. Our results encourage further work to develop process steps that would allow the Cu-doped TiO2 film/Si interface to play a major role in microelectronic applications.

  9. Intercalation of aliphatic amines into the layered structure of vanadyl(IV) hydrogen phosphate hemihydrate (VOHPO[sub 4][center dot]0. 5H[sub 2]O)

    SciTech Connect

    Guliants, V.V.; Benziger, J.B.; Sundaresan, S. )

    1994-04-01

    The vanadyl(IV) hydrogen phosphate hemihydrate, VOHPO[sub 4][center dot]0.5H[sub 2]O, is a pyrolytic precursor of the vanadyl(IV) pyrophosphate phase, (VO)[sub 2]P[sub 2]O[sub 7], generally believed to be the active phase in the selective oxidation of n-butane into maleic anhydride. Pyrolytic transformation into the pyrophosphate phase occurs with conservation of a morphology of the material. VOHPO[sub 4][center dot]0.5H[sub 2]O is a layered hydrogen phosphate, where -POH groups form interlayer hydrogen bonds with the water molecules shared by two face-linked vanadyl octahedra. The structure of the hemihydrate is similar to that of [alpha]-zirconium hydrogen phosphate ([alpha]-ZrP), where hydrogen bonds are within the same layer and -POH groups are also pointed into the interlayer space. In contrast to [alpha]-ZrP, where extensive data exist, intercalation chemistry of the layered vanadyl(IV) hydrogen phosphate hemihydrate at present is a terra incognita. This paper reports the results of the first systematic study of VOHPO[sub 4][center dot]0.5H[sub 2]O intercalation with aliphatic amines as a new route to novel vanadyl(IV) phosphate phases. N-Alkylamines have been commonly known as excellent intercalation agents for testing the intracrystalline reactivity of layered oxides. Intercalated alkylamines may also facilitate introduction of thermostable guest molecules, or [open quotes]pillars[close quotes], by ion exchange producing microporous materials which can modify catalytic and sorptive properties. 9 refs., 6 figs., 2 tabs.

  10. Nitride passivation reduces interfacial traps in atomic-layer-deposited Al2O3/GaAs (001) metal-oxide-semiconductor capacitors using atmospheric metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Aoki, T.; Fukuhara, N.; Osada, T.; Sazawa, H.; Hata, M.; Inoue, T.

    2014-07-01

    Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al2O3. This AlN passivation incorporated nitrogen at the Al2O3/GaAs interface, improving the capacitance-voltage (C-V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C-V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (Dit). The Dit was reduced over the entire GaAs band gap. In particular, these devices exhibited Dit around the midgap of less than 4 × 1012 cm-2eV-1, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.

  11. Investigation of the energy spectra and the electron-hole alignment of the InAs/GaAs quantum dots with an ultrathin cap layer

    NASA Astrophysics Data System (ADS)

    Gorshkov, Alexey P.; Volkova, Natalia S.; Istomin, Leonid A.; Zdoroveishev, Anton V.; Levichev, Sergey

    2016-08-01

    The effects of indium composition and the thickness of the combined InGaAs/GaAs thin cap layer on the energy spectra and relative electron-hole alignment of InAs quantum dots (QDs) grown by metal organic vapor phase epitaxy (MOVPE) are investigated by photoelectrical spectroscopy in a semiconductor/electrolyte system. In structures with InAs QDs and an InGaAs strain reducing layer, the shift of the hole's wave function to the QDs' top was revealed, which indicates In enrichment of the area near the top of QD'. In structures with an ultrathin GaAs cap layer a change of the sign of the built-in dipole moment was observed. This is explained by coupling effects of quantum-confined electrons with surface states.

  12. Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming; Chacon, Rebecca; Uhl, David; Yang, Rui

    2005-01-01

    In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 microns or more near room temperature. InAs quantum dots self-assemble, as a consequence of the lattice mismatch, during epitaxial deposition of InAs on ln0.53Ga0.47As/lnP. In the unmodified devices, the quantum dots as thus formed are typically nonuniform in size. Strainenergy relaxation in very large quantum dots can lead to poor laser performance, especially at wavelengths near 2 microns, for which large quantum dots are needed. In the modified devices, the thin layers of GaAs added to the active regions constitute potential-energy barriers that electrons can only penetrate by quantum tunneling and thus reduce the hot carrier effects. Also, the insertion of thin GaAs layer is shown to reduce the degree of nonuniformity of sizes of the quantum dots. In the fabrication of a batch of modified InAs quantum-dot lasers, the thin additional layer of GaAs is deposited as an interfacial layer in an InGaAs quantum well on (001) InP substrate. The device as described thus far is sandwiched between InGaAsPy waveguide layers, then further sandwiched between InP cladding layers, then further sandwiched between heavily Zn-doped (p-type) InGaAs contact layer.

  13. Lifetime-applied stress response in air of a SiC-based Nicalon-fiber-reinforced composite with a carbon interfacial layer: Effects of temperature (300 to 1150 C)

    SciTech Connect

    Becher, P.F.; Lin, Hua-Tay; More, K.L.

    1998-07-01

    The lifetimes in air as a function of applied flexure stress and temperature (300--1,150 C) are described for a Si-O-C based (Nicalon) fiber plain-weave cloth reinforced SiC-matrix composite ({approximately}7% closed porosity) with an {approximately}0.3 {micro}m thick carbon interfacial layer. The measured lifetimes of both samples with and without an external SiC seal coating were similar and decreased with applied flexural stress (for stresses greater than {approximately}90 MPa) and with temperature. At temperatures of {ge}600 C, the external CVD SiC coating had negligible effect on the lifetimes; however, at 425 C, a detectable improvement in the lifetime was observed with an external SiC coating. When the applied stress was decreased below an apparent threshold stress (e.g., {approximately}90 MPa) for tests conducted at temperatures {le}950 C, no failures were observed for times of {ge}1,000 H. Electron microscopy observations show that the interfacial carbon layer is progressively removed during tests at 425 and 600 C. In these cases, failure is associated with fiber failure and pull-out. At 950 and 1,150 C, the carbon interface layer is eliminated and replaced by a thick silica layer due to the oxidation of the Nicalon fiber and the SiC matrix. This results in embrittling the composite.

  14. Interfacial structure in thin water layers formed by forced dewetting on self-assembled monolayers of omega-terminated alkanethiols on Ag.

    PubMed

    Tiani, Domenic J; Yoo, Heemin; Mudalige, Anoma; Pemberton, Jeanne E

    2008-12-01

    A method for the spectroscopic characterization of interfacial fluid molecular structure near solid substrates is reported. The thickness and interfacial molecular structure of residual ultrathin D20 films remaining after forced dewetting on alkanethiolate self-assembled monolayers (SAMs) of 11 1-mercaptoundecanoic acid (11-MUA), 11-mercaptoundecanol (11-MUD), and undecanethiol (UDT) on Ag are investigated using ellipsometry and surface Raman spectroscopy. The residual film thickness left after withdrawal is greater on hydrophilic SAMs than on hydrophobic SAMs. This behavior is rationalized on the basis of differing degrees of fluid slip within the interfacial region due to different interfacial molecular structure. The v(O-D) regions of surface Raman spectra clearly indicate unique interfacial molecular properties within these films that differ from bulk D20. Although the residual films are created by shear forces and Marangoni flow at the three-phase line during the forced dewetting process, the nature of the films sampled optically must also be considered from the standpoint of thin film stability after dewetting. Thus, the resulting D20 films exist in vastly different morphologies depending on the nature of the water-SAM interactions. Residual D20 is proposed to exist as small nanodroplets on UDT surfaces due tospontaneous rupture of the film after dewetting. In contrast, on 11-MUD and 11-MUA surfaces, these films exist in a metastable state that retains their conformal nature on the underlying modified surface. Analysis of the peak intensity ratios of the so-called "ice-like" to "liquid-like" v(O-D) modes suggests more ice-like D20 character near 11-MUD surfaces, but more liquid-like character near 11-MUA and UDT surfaces. The creation of residual ultrathin films by forced dewetting is thus demonstrated to be a powerful method for characterizing interfacial molecular structure of fluids near a solid substrate under ambient conditions of temperature and

  15. IR spectroscopy of lattice vibrations and comparative analysis of the ZnTe/CdTe quantum-dot superlattices on the GaAs substrate and with the ZnTe and CdTe buffer layers

    SciTech Connect

    Kozyrev, S. P.

    2009-07-15

    A comparative analysis of multiperiod ZnTe/CdTe superlattices with the CdTe quantum dots grown by molecular beam epitaxy on the GaAs substrate with the ZnTe and CdTe buffer layers is carried out. The elastic-stress-induced shifts of eigenfrequencies of the modes of the CdTe- and ZnTe-like vibrations of materials forming similar superlattices but grown on different buffer ZnTe and CdTe layers are compared. The conditions of formation of quantum dots in the ZnTe/CdTe superlattices on the ZnTe and CdTe buffer layers differ radically.

  16. Tunable Interfacial Thermal Conductance by Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Shen, Meng

    We study the mechanism of tunable heat transfer through interfaces between solids using a combination of non-equilibrium molecular dynamics simulation (NEMD), vibrational mode analysis and wave packet simulation. We investigate how heat transfer through interfaces is affected by factors including pressure, interfacial modulus, contact area and interfacial layer thickness, with an overreaching goal of developing fundamental knowledge that will allow one to tailor thermal properties of interfacial materials. The role of pressure and interfacial stiffness is unraveled by our studies on an epitaxial interface between two Lennard-Jones (LJ) crystals. The interfacial stiffness is varied by two different methods: (i) indirectly by applying pressure which due to anharmonic nature of bonding, increases interfacial stiffness, and (ii) directly by changing the interfacial bonding strength by varying the depth of the potential well of the LJ potential. When the interfacial bonding strength is low, quantitatively similar behavior to pressure tuning is observed when the interfacial thermal conductance is increased by directly varying the potential-well depth parameter of the LJ potential. By contrast, when the interfacial bonding strength is high, thermal conductance is almost pressure independent, and even slightly decreases with increasing pressure. This decrease can be explained by the change in overlap between the vibrational densities of states of the two crystalline materials. The role of contact area is studied by modeling structures comprised of Van der Waals junctions between single-walled nanotubes (SWCNT). Interfacial thermal conductance between SWCNTs is obtained from NEMD simulation as a function of crossing angle. In this case the junction conductance per unit area is essentially a constant. By contrast, interfacial thermal conductance between multiwalled carbon nanotubes (MWCNTs) is shown to increase with diameter of the nanotubes by recent experimental studies [1

  17. Tunable Interfacial Thermal Conductance by Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Shen, Meng

    We study the mechanism of tunable heat transfer through interfaces between solids using a combination of non-equilibrium molecular dynamics simulation (NEMD), vibrational mode analysis and wave packet simulation. We investigate how heat transfer through interfaces is affected by factors including pressure, interfacial modulus, contact area and interfacial layer thickness, with an overreaching goal of developing fundamental knowledge that will allow one to tailor thermal properties of interfacial materials. The role of pressure and interfacial stiffness is unraveled by our studies on an epitaxial interface between two Lennard-Jones (LJ) crystals. The interfacial stiffness is varied by two different methods: (i) indirectly by applying pressure which due to anharmonic nature of bonding, increases interfacial stiffness, and (ii) directly by changing the interfacial bonding strength by varying the depth of the potential well of the LJ potential. When the interfacial bonding strength is low, quantitatively similar behavior to pressure tuning is observed when the interfacial thermal conductance is increased by directly varying the potential-well depth parameter of the LJ potential. By contrast, when the interfacial bonding strength is high, thermal conductance is almost pressure independent, and even slightly decreases with increasing pressure. This decrease can be explained by the change in overlap between the vibrational densities of states of the two crystalline materials. The role of contact area is studied by modeling structures comprised of Van der Waals junctions between single-walled nanotubes (SWCNT). Interfacial thermal conductance between SWCNTs is obtained from NEMD simulation as a function of crossing angle. In this case the junction conductance per unit area is essentially a constant. By contrast, interfacial thermal conductance between multiwalled carbon nanotubes (MWCNTs) is shown to increase with diameter of the nanotubes by recent experimental studies [1

  18. Effects of ozone post deposition treatment on interfacial and electrical characteristics of atomic-layer-deposited Al2O3 and HfO2 films on GaSb substrates

    NASA Astrophysics Data System (ADS)

    Zhao, Lianfeng; Tan, Zhen; Wang, Jing; Xu, Jun

    2014-01-01

    Atomic-layer-deposited Al2O3 and HfO2 films on GaSb substrates were treated by in-situ ozone post deposition treatment (PDT). The effects of ozone PDT on the interfacial and electrical properties of Al2O3 and HfO2 gate dielectric films on GaSb substrates were investigated carefully. It is found that the dielectric quality and the interfacial properties of the Al2O3 and HfO2 films are improved by ozone PDT. After in-situ ozone PDT for 5 min, the Al2O3 and HfO2 films on GaSb substrates exhibit improved electrical and interfacial properties, such as reduced frequency dispersion, gate leakage current, border traps and interface traps. Interface trap density is reduced by ∼24% for the Al2O3/GaSb stacks and ∼27% for the HfO2/GaSb stacks. In-situ ozone PDT is proved to be a promising technique in improving the quality of high-k gate stacks on GaSb substrates.

  19. Investigation of interfacial roughness of In sub x Ga sub 1 minus x As epitaxial layers on GaAs and InP substrates by soft x-ray reflectivity

    SciTech Connect

    Krol, A.; Resat, H.; Sher, C.J.; Woronick, S.C.; Ng, W.; Kao, Y.H. ); Cole, T.L.; Green, A.K.; Lowe-Ma, C.K.; Nee, T.; Rehn, V. )

    1991-01-15

    The grazing incidence x-ray reflectivity is a nondestructive and sensitive technique for probing the depth profile of electron density in layered structures. This method has been utilized in the soft x-ray regime to determine the roughness of interfaces, and the epilayer thickness in In{sub {ital x}}Ga{sub 1{minus}{ital x}}As/InP and In{sub {ital x}}Ga{sub 1{minus}{ital x}}As/GaAs heterostructures, for {ital x}=0.57 and {ital x}=0.60, grown by molecular beam epitaxy. By fitting the experimental results to our model, assuming uncorrelated interfacial roughness, we conclude that the top surface roughness does not depend on the type of the substrate or presence of stress in the epilayer, and is always smaller than interfacial roughness. The main factors which control the interfacial roughness are the quality of substrate and/or growth conditions rather than strain or lattice mismatch.

  20. CdS/CdSe quantum dots and ZnPc dye co-sensitized solar cells with Au nanoparticles/graphene oxide as efficient modified layer.

    PubMed

    Chen, Cong; Cheng, Yu; Jin, Junjie; Dai, Qilin; Song, Hongwei

    2016-10-15

    Co-sensitization by using two or more sensitizers with complementary absorption spectra to expand the spectral response range is an effective approach to enhance device performance of quantum dot sensitized solar cells (QDSSCs). To improve the light-harvesting in the visible/near-infrared (NIR) region, organic dye zinc phthalocyanine (ZnPc) was combined with CdS/CdSe quantum dots (QDs) for co-sensitized solar cells based on ZnO inverse opals (IOs) as photoanode. The resulting co-sensitized device shows an efficient panchromatic spectral response feature to ∼750nm and presents an overall conversion efficiency of 4.01%, which is superior to that of the individual ZnPc-sensitized solar cells and CdS/CdSe-sensitized solar cells. Meanwhile, an Au nanoparticles/graphene oxide (Au NPs/GO) composite layer was successfully prepared to modify Cu2S counter electrode for the co-sensitized solar cells. Reducing the carrier recombination process by GO and catalytic process of Au NPs leads to increased power conversion efficiency(PCE) from 4.01 to 4.60% and sustainable stability remains ∼85% of its original value after 60min light exposure. In this paper, introduction of the organic dyes as co-sensitizer and Au NPs/GO as counter electrode modified layer has been proved to be an effective route to improve the performance of QDSSCs. PMID:27399618

  1. Synthesis of crystalline Si quantum dots by millisecond laser irradiation of SiO{sub x}N{sub y} layers

    SciTech Connect

    Mannino, Giovanni; Spinella, Corrado; Bongiorno, Corrado; Nicotra, Giuseppe; Mercorillo, Flora; Privitera, Vittorio; Franzo, Giorgia; Piro, Alberto Maria; Grimaldi, MariaGrazia; Di Stefano, Maria Ausilia; Di Marco, Silvestra

    2010-01-15

    We demonstrated that the timescale for Si quantum dot (Si-QD) formation in a SiO{sub x}N{sub y} layer is a few milliseconds by IR laser irradiation. The amount of Si agglomerated into QD in a laser irradiated SiO{sub x}N{sub y} layer is comparable to that calculated after furnace annealing at 1250 deg. C for 30 min. However, we found that crystalline Si-QD can be formed by laser only if the amount of Si atoms in excess is as high as 1x10{sup 22}/cm{sup 3}. The Si-QD contains impurities like N and O that prevent luminescence at 900 nm. The photoluminescence (PL) signal is recorded only after an additional annealing after laser irradiation at temperatures above 1000 deg. C when diffusion-assisted replacement of N and O occurs.

  2. Influence of the active layer nanomorphology on device performance for ternary PbS(x)Se(1-x) quantum dots based solution-processed infrared photodetector.

    PubMed

    Song, Taojian; Cheng, Haijuan; Fu, Chunjie; He, Bo; Li, Weile; Xu, Junfeng; Tang, Yi; Yang, Shengyi; Zou, Bingsuo

    2016-04-22

    In this paper, the influence of the active layer nanomorphology on device performance for ternary PbS(x)Se(1-x) quantum dot-based solution-processed infrared photodetector is presented. Firstly, ternary PbS(x)Se(1-x) quantum dots (QDs) in various chemical composition were synthesized and the bandgap of the ternary PbS(x)Se(1-x) QDs can be controlled by the component ratio of S/(S + Se), and then field-effect transistor (FET) based photodetectors Au/PbS0.4Se0.6:P3HT/PMMA/Al, in which ternary PbS0.4Se0.6 QDs doped with poly(3-hexylthiophene) (P3HT) act as the active layer and poly(methyl methacrylate) (PMMA) as the dielectric layer, were presented. By changing the weight ratio of P3HT to PbS0.4Se0.6 QDs (K = M(P3HT):M(QDs)) in dichlorobenzene solution, we found that the device with K = 2:1 shows optimal electrical property in dark; however, the device with K = 1:2 demonstrated optimal performance under illumination, showing a maximum responsivity and specific detectivity of 55.98 mA W(-1) and 1.02 × 10(10) Jones, respectively, at low V(DS) = -10 V and V(G) = 3 V under 980 nm laser with an illumination intensity of 0.1 mW cm(-2). By measuring the atomic force microscopy phase images of PbS0.4Se0.6:P3HT films in different weight ratio K, our experimental data show that the active layer nanomorphology has a great influence on the device performance. Also, it provides an easy way to fabricate high performance solution-processed infrared photodetector. PMID:26963474

  3. Influence of the active layer nanomorphology on device performance for ternary PbS x Se1-x quantum dots based solution-processed infrared photodetector

    NASA Astrophysics Data System (ADS)

    Song, Taojian; Cheng, Haijuan; Fu, Chunjie; He, Bo; Li, Weile; Xu, Junfeng; Tang, Yi; Yang, Shengyi; Zou, Bingsuo

    2016-04-01

    In this paper, the influence of the active layer nanomorphology on device performance for ternary PbS x Se1-x quantum dot-based solution-processed infrared photodetector is presented. Firstly, ternary PbS x Se1-x quantum dots (QDs) in various chemical composition were synthesized and the bandgap of the ternary PbS x Se1-x QDs can be controlled by the component ratio of S/(S + Se), and then field-effect transistor (FET) based photodetectors Au/PbS0.4Se0.6:P3HT/PMMA/Al, in which ternary PbS0.4Se0.6 QDs doped with poly(3-hexylthiophene) (P3HT) act as the active layer and poly(methyl methacrylate) (PMMA) as the dielectric layer, were presented. By changing the weight ratio of P3HT to PbS0.4Se0.6 QDs (K = MP3HT:MQDs) in dichlorobenzene solution, we found that the device with K = 2:1 shows optimal electrical property in dark; however, the device with K = 1:2 demonstrated optimal performance under illumination, showing a maximum responsivity and specific detectivity of 55.98 mA W-1 and 1.02 × 1010 Jones, respectively, at low V DS = -10 V and V G = 3 V under 980 nm laser with an illumination intensity of 0.1 mW cm-2. By measuring the atomic force microscopy phase images of PbS0.4Se0.6:P3HT films in different weight ratio K, our experimental data show that the active layer nanomorphology has a great influence on the device performance. Also, it provides an easy way to fabricate high performance solution-processed infrared photodetector.

  4. Interfacial behavior of polymer electrolytes

    SciTech Connect

    Kerr, John; Kerr, John B.; Han, Yong Bong; Liu, Gao; Reeder, Craig; Xie, Jiangbing; Sun, Xiaoguang

    2003-06-03

    Evidence is presented concerning the effect of surfaces on the segmental motion of PEO-based polymer electrolytes in lithium batteries. For dry systems with no moisture the effect of surfaces of nano-particle fillers is to inhibit the segmental motion and to reduce the lithium ion transport. These effects also occur at the surfaces in composite electrodes that contain considerable quantities of carbon black nano-particles for electronic connection. The problem of reduced polymer mobility is compounded by the generation of salt concentration gradients within the composite electrode. Highly concentrated polymer electrolytes have reduced transport properties due to the increased ionic cross-linking. Combined with the interfacial interactions this leads to the generation of low mobility electrolyte layers within the electrode and to loss of capacity and power capability. It is shown that even with planar lithium metal electrodes the concentration gradients can significantly impact the interfacial impedance. The interfacial impedance of lithium/PEO-LiTFSI cells varies depending upon the time elapsed since current was turned off after polarization. The behavior is consistent with relaxation of the salt concentration gradients and indicates that a portion of the interfacial impedance usually attributed to the SEI layer is due to concentrated salt solutions next to the electrode surfaces that are very resistive. These resistive layers may undergo actual phase changes in a non-uniform manner and the possible role of the reduced mobility polymer layers in dendrite initiation and growth is also explored. It is concluded that PEO and ethylene oxide-based polymers are less than ideal with respect to this interfacial behavior.

  5. Study of ethanolamine surface treatment on the metal-oxide electron transport layer in inverted InP quantum dot light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Jang, Ilwan; Kim, Jiwan; Park, Chang Jun; Ippen, Christian; Greco, Tonino; Oh, Min Suk; Lee, Jeongno; Kim, Won Keun; Wedel, Armin; Han, Chul Jong; Park, Sung Kyu

    2015-11-01

    The present work shows the effect of ethanolamine surface treatment on inverted InP quantum dot light-emitting diodes (QD-LEDs) with inorganic metal oxide layers. In the inverted structure of ITO/ZnO/InP QDs/CBP/MoO3/Al, a sol-gel derived ZnO film was used as an electron transport layer (ETL) and MoO3 was used as a hole injection layer (HIL). First, ethanolamine was treated as a surface modifier on top of the ZnO electron transport layer. The optical performance of the QD-LED device was improved by the ethanolamine surface treatment. Second, low temperature annealing (<200°C) was performed on the ZnO sol-gel electron transport layer, followed by an investigation of the effect of the ZnO annealing temperature. The efficiency of the inverted QD-LEDs was significantly enhanced (more than 3-fold) by optimization of the ZnO annealing temperature. [Figure not available: see fulltext.

  6. Effects of matrix layer composition on the structural and optical properties of self-organized InGaN quantum dots

    NASA Astrophysics Data System (ADS)

    Li, Z. C.; Liu, J. P.; Feng, M. X.; Zhou, K.; Zhang, S. M.; Wang, H.; Li, D. Y.; Zhang, L. Q.; Sun, Q.; Jiang, D. S.; Wang, H. B.; Yang, H.

    2013-09-01

    Self-organized InGaN quantum dots (QDs) with emission wavelength from green to red range have been grown on GaN templated c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The effects of matrix layer composition on the structural and optical properties of InGaN QDs have been investigated. A continued growth of QDs is observed during the growth of In0.1Ga0.9N matrix layer, which results in an increase of the QDs' size. By using In0.1Ga0.9N matrix layer instead of GaN one, the annealing induced blue-shift in emission energy of the InGaN QDs can be suppressed. After the growth of top GaN cap layer, a larger red-shift caused by the quantum confined Stark effect is observed in the sample with In0.1Ga0.9N matrix layer. Employing this method, InGaN QD sample emitting at 615 nm with an internal quantum efficiency of 24.3% has been grown. The significance of this method is that it allows a higher growth temperature of InGaN QDs with emission wavelength in the green range to improve the crystalline quality, which is beneficial to enhance the efficiency of green InGaN QD light-emitting-diodes and laser diodes.

  7. Study of GaAsSb/GaAs type-II quantum well with top InAs quantum dot layer using complementary spectroscopy techniques

    NASA Astrophysics Data System (ADS)

    Hsu, Hung-Pin; Wu, Jiun-De; Lin, Yan-Jih; Huang, Ying-Sheng; Lin, You-Ru; Lin, Hao-Hsiung

    2015-09-01

    The optical characterization of GaAsSb/GaAs type-II quantum wells (QWs) with top InAs quantum dot (QD) layer composite structures was carried out using the complementary surface photovoltage (SPV) and photoluminescence (PL) spectroscopies. The obtained SPV and PL spectra revealed that the features originated from InAs QDs, modulated potential wells in GaAsSb QWs, the wetting layer (WL) as well as the GaAs cap layer/barrier at room temperature. The optical transition from the modulated potential wells in GaAsSb QWs in the composite structures showed a redshift when the spacer layer was narrowed from 10 to 5 nm. This is attributed to the lower modulated potential minimum in GaAsSb QWs caused by the strain exerted by InAs QDs in the composite structures with the narrower spacer layer. The power-dependent PL measurement showed that the luminescences from the GaAsSb/GaAs heterostructure blue-shifted with increasing excitation power owing to the type-II band alignment. These results demonstrated that SPV and PL are useful techniques for the nondestructive optical characterization of GaAsSb QWs with top InAs QD composite structures.

  8. Highly Efficient and Low Turn-On Voltage Quantum Dot Light-Emitting Diodes by Using a Stepwise Hole-Transport Layer.

    PubMed

    Ji, Wenyu; Lv, Ying; Jing, Pengtao; Zhang, Han; Wang, Jia; Zhang, Hanzhuang; Zhao, Jialong

    2015-07-29

    Highly efficient red quantum dot light-emitting diodes (QD-LEDs) with a very high current efficiency of 16 cd/A were demonstrated by adopting stepwise hole-transport layers (HTLs) consisting of 4,4'-N,N'-dicarbazole-biphenyl (CBP) combined with N,N'-dicarbazolyl-3,5-benzene (mCP). The mCP layer plays two important roles in this kind of QD-LEDs. One is that it can block the electron to leak into the HTL due to its higher LUMO (LUMO = the lowest unoccupied molecular orbital) energy level than that of CBP; and the other is it can separate the carrier accumulation zone from the exciton formation interface, which is attributed to the stepwise hole-transport layer structure. Moreover, the lower HOMO (HOMO = the highest occupied molecular orbital) energy level of mCP decreases the hole-injection barrier from the HTL to the QD emitting layer, which improves the charge carrier balance injected into the QD layer, reducing the turn-on voltage of QD-LEDs fabricated with the stepwise HTL structure. PMID:26137935

  9. Interfacial and near interfacial crack growth phenomena in metal bonded alumina

    SciTech Connect

    Kruzic, Jamie Joseph

    2002-03-01

    Metal/ceramic interfaces can be found in many engineering applications including microelectronic packaging, multi-layered films, coatings, joints, and composite materials. In order to design reliable engineering systems that contain metal/ceramic interfaces, a comprehensive understanding of interfacial and near interfacial failure mechanisms is necessary.

  10. Origin of Enhanced Hole Injection in Organic Light-Emitting Diodes with an Electron-Acceptor Doping Layer: p-Type Doping or Interfacial Diffusion?

    PubMed

    Zhang, Lei; Zu, Feng-Shuo; Deng, Ya-Li; Igbari, Femi; Wang, Zhao-Kui; Liao, Liang-Sheng

    2015-06-10

    The electrical doping nature of a strong electron acceptor, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN), is investigated by doping it in a typical hole-transport material, N,N'-bis(naphthalen-1-yl)-N,N'-diphenylbenzidine (NPB). A better device performance of organic light-emitting diodes (OLEDs) was achieved by doping NPB with HATCN. The improved performance could, in principle, arise from a p-type doping effect in the codeposited thin films. However, physical characteristics evaluations including UV-vis absorption, Fourier transform infrared absorption, and X-ray photoelectron spectroscopy demonstrated that there was no obvious evidence of charge transfer in the NPB:HATCN composite. The performance improvement in NPB:HATCN-based OLEDs is mainly attributed to an interfacial modification effect owing to the diffusion of HATCN small molecules. The interfacial diffusion effect of the HATCN molecules was verified by the in situ ultraviolet photoelectron spectroscopy evaluations. PMID:25970499

  11. Role of interfacial carbon layer in the thermal diffusivity/conductivity of silicon carbide fiber-reinforced reaction-bonded silicon nitride matrix composites

    NASA Technical Reports Server (NTRS)

    Bhatt, Hemanshu; Donaldson, Kimberly Y.; Hasselman, D. P. H.; Bhatt, Ramakrishna T.

    1992-01-01

    Experiments were carried out on samples of reaction-bonded silicon nitride uniaxially reinforced by SiC monofilaments with and without a 3-micron-thick carbon-rich coating. It is found that a combination of a carbon coatings on the fibers and an interfacial gap due to the thermal expansion mismatch in the composite can significantly (by a factor of 2) lower the effective thermal diffusivity in the direction transverse to the fiber. At atmospheric pressure, gaseous conduction across the interfacial gap makes a significant contribution to the heat transfer across the interface, indicated by significantly lower values of the effective thermal diffusivity under vacuum than in nitrogen or helium at atmospheric pressure.

  12. Ground-state energy trends in single and multilayered coupled InAs/GaAs quantum dots capped with InGaAs layers: Effects of InGaAs layer thickness and annealing temperature

    SciTech Connect

    Shah, S.; Ghosh, K.; Jejurikar, S.; Mishra, A.; Chakrabarti, S.

    2013-08-01

    Graphical abstract: - Highlights: • Investigation of ground state energy in single and multi-layered InAs/GaAs QD. • Strain reducing layer (InGaAs) prevents the formation of non-radiative. • Strain reducing layer (InGaAs) is responsible for high activation energy. • Significant deviation from the Varshni model, E(T) = E − αT{sup 2}/T + β. - Abstract: Vertically coupled, multilayered InAs/GaAs quantum dots (QDs) covered with thin InGaAs strain-reducing layers (SRLs) are in demand for various technological applications. We investigated low temperature photoluminescence of single and multilayered structures in which the SRL thickness was varied. The SRL layer was responsible for high activation energies. Deviation of experimental data from the Varshni (1967) model, E(T) = E − ∞ T{sup 2}/T + β, suggests that the InAs-layered QDs have properties different from those in bulk material. Anomalous ground-state peak linewidths (FWHM), especially for annealed multilayer structures, were observed. A ground-state peak blue-shift with a broadened linewidth was also observed. Loss of intensity was detected in samples annealed at 800 °C. Presence of SRLs prevents formation of non-radiative centers under high temperature annealing. The results indicate the potential importance of such structures in optoelectronic applications.

  13. Light-emitting diodes based on solution-processed nontoxic quantum dots: oxides as carrier-transport layers and introducing molybdenum oxide nanoparticles as a hole-inject layer.

    PubMed

    Bhaumik, Saikat; Pal, Amlan J

    2014-07-23

    We report fabrication and characterization of solution-processed quantum dot light-emitting diodes (QDLEDs) based on a layer of nontoxic and Earth-abundant zinc-diffused silver indium disulfide (AIZS) nanoparticles as an emitting material. In the QDLEDs fabricated on indium tin oxide (ITO)-coated glass substrates, we use layers of oxides, such as graphene oxide (GO) and zinc oxide (ZnO) nanoparticles as a hole- and electron-transport layer, respectively. In addition, we introduce a layer of MoO3 nanoparticles as a hole-inject one. We report a comparison of the characteristics of different device architectures. We show that an inverted device architecture, ITO/ZnO/AIZS/GO/MoO3/Al, yields a higher electroluminescence (EL) emission, compared to direct ones, for three reasons: (1) the GO/MoO3 layers introduce barriers for electrons to reach the Al electrode, and, similarly, the ZnO layers acts as a barrier for holes to travel to the ITO electrode; (2) the introduction of a layer of MoO3 nanoparticles as a hole-inject layer reduces the barrier height for holes and thereby balances charge injection in the inverted structure; and (3) the wide-bandgap zinc oxide next to the ITO electrode does not absorb the EL emission during its exit from the device. In the QDLEDs with oxides as carrier inject and transport layers, the EL spectrum resembles the photoluminescence emission of the emitting material (AIZS), implying that excitons are formed in the quaternary nanocrystals and decay radiatively. PMID:24983915

  14. Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using in situ X-ray diffraction

    SciTech Connect

    Shimomura, Kenichi; Ohshita, Yoshio; Kamiya, Itaru; Suzuki, Hidetoshi; Sasaki, Takuo; Takahasi, Masamitu

    2015-11-14

    Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures.

  15. Impact of stress relaxation in GaAsSb cladding layers on quantum dot creation in InAs/GaAsSb structures grown on GaAs (001)

    SciTech Connect

    Bremner, S. P.; Ban, K.-Y.; Faleev, N. N.; Honsberg, C. B.; Smith, D. J.

    2013-09-14

    We describe InAs quantum dot creation in InAs/GaAsSb barrier structures grown on GaAs (001) wafers by molecular beam epitaxy. The structures consist of 20-nm-thick GaAsSb barrier layers with Sb content of 8%, 13%, 15%, 16%, and 37% enclosing 2 monolayers of self-assembled InAs quantum dots. Transmission electron microscopy and X-ray diffraction results indicate the onset of relaxation of the GaAsSb layers at around 15% Sb content with intersected 60° dislocation semi-loops, and edge segments created within the volume of the epitaxial structures. 38% relaxation of initial elastic stress is seen for 37% Sb content, accompanied by the creation of a dense net of dislocations. The degradation of In surface migration by these dislocation trenches is so severe that quantum dot formation is completely suppressed. The results highlight the importance of understanding defect formation during stress relaxation for quantum dot structures particularly those with larger numbers of InAs quantum-dot layers, such as those proposed for realizing an intermediate band material.

  16. Effect of InxGa1-XAs Underlying Layer and Growth Mode on the Surface Morphology of In0.5Ga0.5As/GaAs Quantum Dots

    NASA Astrophysics Data System (ADS)

    Ismail, A. K.; Aryanto, D.; Othaman, Z.; Ameruddin, A. S.

    2010-07-01

    Single layer of In0.5Ga0.5As quantum dots (QDs) was grown using self-assembled Stranski-Krastanow on a thin InxGa1-xAs underlying layer and on a reference GaAs wafer by metal-organic chemical vapour deposition (MOCVD). The effect of different indium composition in the underlying layer and the duration of arsine (AsH3) flow during cooling-down period of the growth process were investigated and characterized using atomic force microscopy (AFM). The growth of the thin underlying layer has significant influence on the formation of the QDs on the top surface. The dots density increases with increasing indium composition in the underlying layer. AsH3 flow during the period was found to influence the nucleation process of In0.5Ga0.5As QDs. A shorter period of AsH3 flow promotes smaller dots size and therefore increases the dots density.

  17. Temperature dependence of Coulomb oscillations in a few-layer two-dimensional WS2 quantum dot

    PubMed Central

    Song, Xiang-Xiang; Zhang, Zhuo-Zhi; You, Jie; Liu, Di; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guo-Ping

    2015-01-01

    Standard semiconductor fabrication techniques are used to fabricate a quantum dot (QD) made of WS2, where Coulomb oscillations were found. The full-width-at-half-maximum of the Coulomb peaks increases linearly with temperature while the height of the peaks remains almost independent of temperature, which is consistent with standard semiconductor QD theory. Unlike graphene etched QDs, where Coulomb peaks belonging to the same QD can have different temperature dependences, these results indicate the absence of the disordered confining potential. This difference in the potential-forming mechanism between graphene etched QDs and WS2 QDs may be the reason for the larger potential fluctuation found in graphene QDs. PMID:26538164

  18. Intermixing of InGaAs/GaAs quantum wells and quantum dots using sputter-deposited silicon oxynitride capping layers

    SciTech Connect

    McKerracher, Ian; Fu Lan; Hoe Tan, Hark; Jagadish, Chennupati

    2012-12-01

    Various approaches can be used to selectively control the amount of intermixing in III-V quantum well and quantum dot structures. Impurity-free vacancy disordering is one technique that is favored for its simplicity, however this mechanism is sensitive to many experimental parameters. In this study, a series of silicon oxynitride capping layers have been used in the intermixing of InGaAs/GaAs quantum well and quantum dot structures. These thin films were deposited by sputter deposition in order to minimize the incorporation of hydrogen, which has been reported to influence impurity-free vacancy disordering. The degree of intermixing was probed by photoluminescence spectroscopy and this is discussed with respect to the properties of the SiO{sub x}N{sub y} films. This work was also designed to monitor any additional intermixing that might be attributed to the sputtering process. In addition, the high-temperature stress is known to affect the group-III vacancy concentration, which is central to the intermixing process. This stress was directly measured and the experimental values are compared with an elastic-deformation model.

  19. Long-wavelength room-temperature luminescence from InAs/GaAs quantum dots with an optimized GaAsSbN capping layer

    PubMed Central

    2014-01-01

    An extensive study on molecular beam epitaxy growth conditions of quaternary GaAsSbN as a capping layer (CL) for InAs/GaAs quantum dots (QD) was carried out. In particular, CL thickness, growth temperature, and growth rate were optimized. Problems related to the simultaneous presence of Sb and N, responsible for a significant degradation of photoluminescence (PL), are thereby solved allowing the achievement of room-temperature (RT) emission. A particularly strong improvement on the PL is obtained when the growth rate of the CL is increased. This is likely due to an improvement in the structural quality of the quaternary alloy that resulted from reduced strain and composition inhomogeneities. Nevertheless, a significant reduction of Sb and N incorporation was found when the growth rate was increased. Indeed, the incorporation of N is intrinsically limited to a maximum value of approximately 1.6% when the growth rate is at 2.0 ML s−1. Therefore, achieving RT emission and extending it somewhat beyond 1.3 μm were possible by means of a compromise among the growth conditions. This opens the possibility of exploiting the versatility on band structure engineering offered by this QD-CL structure in devices working at RT. PACS 81.15.Hi (molecular beam epitaxy); 78.55.Cr (III-V semiconductors); 73.21.La (quantum dots) PMID:24438542

  20. Intermixing of InGaAs/GaAs quantum wells and quantum dots using sputter-deposited silicon oxynitride capping layers

    NASA Astrophysics Data System (ADS)

    McKerracher, Ian; Fu, Lan; Hoe Tan, Hark; Jagadish, Chennupati

    2012-12-01

    Various approaches can be used to selectively control the amount of intermixing in III-V quantum well and quantum dot structures. Impurity-free vacancy disordering is one technique that is favored for its simplicity, however this mechanism is sensitive to many experimental parameters. In this study, a series of silicon oxynitride capping layers have been used in the intermixing of InGaAs/GaAs quantum well and quantum dot structures. These thin films were deposited by sputter deposition in order to minimize the incorporation of hydrogen, which has been reported to influence impurity-free vacancy disordering. The degree of intermixing was probed by photoluminescence spectroscopy and this is discussed with respect to the properties of the SiOxNy films. This work was also designed to monitor any additional intermixing that might be attributed to the sputtering process. In addition, the high-temperature stress is known to affect the group-III vacancy concentration, which is central to the intermixing process. This stress was directly measured and the experimental values are compared with an elastic-deformation model.

  1. GaNAs as Strain Compensating Layer for 1.55 μm Light Emission from InAs Quantum Dots

    NASA Astrophysics Data System (ADS)

    Ganapathy, Sasikala; Zhang, Xi Qing; Suemune, Ikuo; Uesugi, Katsuhiro; Kumano, Hidekazu; Kim, B. J.; Seong, Tae-Yeon

    2003-09-01

    GaNAs strain-compensating layers (SCLs) are applied to bury InAs quantum dots (QDs) grown on GaAs substrates. The main idea is the compensation of the compressive strain induced by InAs QDs with the tensile strain in the GaNAs SCLs to keep the total strain of the system minimum. The application of the GaNAs SCLs resulted in a systematic shift of photoluminescence (PL) peaks of the InAs QDs toward the longer wavelengths with the increase of the nitrogen (N) composition in GaNAs, and luminescence at a wavelength of 1.55 μm has been achieved from the InAs QDs for the N composition of 2.7% in the GaNAs SCL. This result is promising for the application of GaNAs SCL for InAs-QDs-based long-wavelength light sources for optical-fiber communication systems.

  2. Effect of wetting-layer density of states on the gain and phase recovery dynamics of quantum-dot semiconductor optical amplifiers

    NASA Astrophysics Data System (ADS)

    Kim, Jungho; Yu, Bong-Ahn

    2015-03-01

    We numerically investigate the effect of the wetting-layer (WL) density of states on the gain and phase recovery dynamics of quantum-dot semiconductor optical amplifiers in both electrical and optical pumping schemes by solving 1088 coupled rate equations. The temporal variations of the ultrafast gain and phase recovery responses at the ground state (GS) are calculated as a function of the WL density of states. The ultrafast gain recovery responses do not significantly depend on the WL density of states in the electrical pumping scheme and the three optical pumping schemes such as the optical pumping to the WL, the optical pumping to the excited state ensemble, and the optical pumping to the GS ensemble. The ultrafast phase recovery responses are also not significantly affected by the WL density of states except the optical pumping to the WL, where the phase recovery component caused by the WL becomes slowed down as the WL density of states increases.

  3. Color stability of white organic light emitting devices with a color conversion layer utilizing CdSe/ZnS quantum dots and phosphors dispersed in polymethylmethacrylate.

    PubMed

    Kwon, W J; Kim, S H; Lee, K S; Choo, D C; Kim, S W; Kim, S W; Yoo, T W; Kwon, M S; Yoo, K H; Kim, T W

    2013-06-01

    White organic light-emitting devices (WOLEDs) were fabricated by combining a blue emitting organic light-emitting devices (OLEDs) and a color conversion layer made of yttrium aluminum garnet phosphors and CdSe/ZnS quantum dots (QDs) embedded into polymethylmethacrylate. When the ratio of phosphors and QDs changed, a good color balance was achieved at a ratio of 1:5, and the maximum luminance of 18.21 cd/m2 was obtained. As the applied voltage varied from 12 to 16 V, Commission Internationale de l'Eclairage coordinates shifted only slightly from (0.32, 0.34) to (0.30, 0.33), indicating a good color stability. PMID:23862508

  4. Ammonia reduced graphene oxides as a hole injection layer for CdSe/CdS/ZnS quantum dot light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Lou, Qing; Ji, Wen-Yu; Zhao, Jia-Long; Shan, Chong-Xin

    2016-08-01

    In this study, we report quantum-dot light-emitting devices (QD-LEDs) using ammonia reduced graphene oxide (rGO) as a hole injection layer (HIL). Compared with pristine GO, QD-LEDs employing rGO as a HIL show higher maximum luminance (936 cd m‑2 versus 699 cd m‑2) and lower turn-on voltage (V th, 5.0 V versus 7.5 V). The improved performance can be attributed to the synergistic effect of the improved conductivity (1.27 μS cm‑1 versus 0.139 μS cm‑1) and decreased work function (5.27 eV versus 5.40 eV) of the GO after the reduction process. The above results indicate that ammonia functionalized graphene may be a promising hole injection material for QD-LEDs.

  5. Ammonia reduced graphene oxides as a hole injection layer for CdSe/CdS/ZnS quantum dot light-emitting diodes.

    PubMed

    Lou, Qing; Ji, Wen-Yu; Zhao, Jia-Long; Shan, Chong-Xin

    2016-08-12

    In this study, we report quantum-dot light-emitting devices (QD-LEDs) using ammonia reduced graphene oxide (rGO) as a hole injection layer (HIL). Compared with pristine GO, QD-LEDs employing rGO as a HIL show higher maximum luminance (936 cd m(-2) versus 699 cd m(-2)) and lower turn-on voltage (V th, 5.0 V versus 7.5 V). The improved performance can be attributed to the synergistic effect of the improved conductivity (1.27 μS cm(-1) versus 0.139 μS cm(-1)) and decreased work function (5.27 eV versus 5.40 eV) of the GO after the reduction process. The above results indicate that ammonia functionalized graphene may be a promising hole injection material for QD-LEDs. PMID:27347655

  6. Electrical Bistabilities and Conduction Mechanisms of Nonvolatile Memories Based on a Polymethylsilsesquioxane Insulating Layer Containing CdSe/ZnS Quantum Dots

    NASA Astrophysics Data System (ADS)

    Ma, Zehao; Ooi, Poh Choon; Li, Fushan; Yun, Dong Yeol; Kim, Tae Whan

    2015-10-01

    Nonvolatile memory (NVM) devices based on a metal-insulator-metal structure consisting of CdSe/ZnS quantum dots embedded in polymethylsilsesquioxane dielectric layers were fabricated. The current-voltage ( I- V) curves showed a bistable current behavior and the presence of hysteresis. The current-time ( I- t) curves showed that the fabricated NVM memory devices were stable up to 1 × 104 s with a distinct ON/OFF ratio of 104 and were reprogrammable when the endurance test was performed. The extrapolation of the I- t curve to 105 s with corresponding current ON/OFF ratio 1 × 105 indicated a long performance stability of the NVM devices. Schottky emission, Poole-Frenkel emission, trapped-charge limited-current and Child-Langmuir law were proposed as the dominant conduction mechanisms for the fabricated NVM devices based on the obtained I- V characteristics.

  7. Magnesium effects on CdSe self-assembled quantum dot formation on Zn xCd yMg 1-x-ySe layers

    NASA Astrophysics Data System (ADS)

    Noemi Perez-Paz, M.; Lu, Hong; Shen, Aidong; Jean Mary, F.; Akins, Daniel; Tamargo, Maria C.

    2006-09-01

    Optical and morphological studies are used to investigate the effects of chemical composition and, in particular, the magnesium content of the Zn xCd yMg 1-x-ySe barrier layers on the size, density and uniformity of CdSe self-assembled quantum dots (QDs). A reduction of the uncapped QD size, as well as a blue shift of the capped QD photoluminescence peak position by increasing Mg concentration in the Zn xCd yMg 1-x-ySe barrier has been demonstrated by changing the Mg cell temperature during growth. In addition, a more uniform and more densely packed QD layer has been observed with an increase of the MgSe fraction in the Zn xCd yMg 1-x-ySe barrier layer using three-dimensional topographic atomic force microscopy images of the surface of uncapped QDs. Results point to Mg as a chemical factor that induces QD formation, either by increasing the density of atomic steps or/and by changing the energy of the Zn xCd yMg 1-x-ySe surface.

  8. A comparative study on the electrical parameters of Au/n-Si Schottky diodes with and without interfacial (Ca1.9Pr0.1Co4Ox) layer

    NASA Astrophysics Data System (ADS)

    Kaya, A.; Çetinkaya, H. G.; Altındal, Ş.; Uslu, I.

    2016-05-01

    In order to compare the main electrical parameters such as ideality factor (n), barrier height (BH) (ΦI-V), series (Rs) and shunt (Rsh) resistances and energy density distribution profile of surface states (Nss), the Au/n-Si (MS) Schotthy diodes (SDs), with and without interfacial (Ca1.9Pr0.1Co4Ox) layer were obtained from the current-voltage (I-V ) measurements at room temperature. The other few electrical parameters such as Fermi energy level (EF), BH (ΦC-V), Rs and voltage dependence of Nss profile were also obtained from the capacitance-voltage (C-V ) measurements. The voltage dependence of Nss profile has two distinctive peaks in the depletion region for two diodes and they were attributed to a particular distribution of Nss located at metal-semiconductor (MS) interface. All of these results have been investigated at room temperature and results have been compared with each other. Experimental results confirmed that interfacial (Ca1.9Pr0.1Co4Ox) layer enhanced diode performance in terms of rectifier rate (RR = IF/IR at ± 3.4V), Nss (at 0.5eV) and Rsh (‑3.4V) with values of 265, 5.38 × 1013eV‑1 ṡcm‑2 and 7.87 × 104Ω for MS type Schottky barrier diode and 2.56 × 106, 1.15 × 1013eV‑1 ṡcm‑2 and 7.50 × 108Ω for metal-insulator-semiconductor (MIS) type SBD, respectively. It is clear that the rectifying ratio of MIS type SBD is about 9660 times greater than MS type SBD. The value of barrier height (BH) obtained from C-V data is higher than the forward bias I-V data and it was attributed to the nature of measurements. These results confirmed that the interfacial (Ca1.9Pr0.1Co4Ox) layer has considerably improved the performance of SD.

  9. TEM Characterization of InAs/GaAs Quantum Dots Capped by a GaSb/GaAs Layer

    SciTech Connect

    Beltran, AM; Ben, Teresa; Sanchez, AM; Sales Lerida, David; Chisholm, Matthew F; Varela del Arco, Maria; Pennycook, Stephen J; Galindo, Pedro; Ripalda, JM; Molina Rubio, Sergio I

    2008-01-01

    It is well known that there is intense interest in expanding the usable wavelength for electronic devices. This is one of the reasons to study new self-assembled semiconductor nanostructures. Telecommunication applications use InGaAsP/InP emitting at 1.3 and 1.55 m. Research efforts are dedicated to develop GaAs technology in order to achieve emission at the same range as InP, so GaAs could be used for optical fibre communications. Ga(As)Sb on InAs/GaAs quantum dots (QDs) is a promising nanostructure to be used in telecommunications. The introduction of antimony during or after the QDs growth is an effective solution to obtain a red shift in the emission wavelength, even at room temperature.

  10. Use of Mixed CH3-/HC(O)CH2CH2-Si(111) Functionality to Control Interfacial Chemical and Electronic Properties During the Atomic-Layer Deposition of Ultrathin Oxides on Si(111).

    PubMed

    O'Leary, Leslie E; Strandwitz, Nicholas C; Roske, Christopher W; Pyo, Suyeon; Brunschwig, Bruce S; Lewis, Nathan S

    2015-02-19

    Silicon surfaces terminated with a mixed monolayer containing both a propyl aldehyde functionality and methyl groups were prepared and used to control the interfacial chemical and electronic properties of Si(111) surfaces during atomic-layer deposition (ALD) of Al2O3 or MnO. Si(111) surfaces functionalized only with the aldehyde moiety exhibited surface recombination velocities, S, of 2500 ± 600 cm s(-1) whereas the mixed CH3-/HC(O)CH2CH2-Si(111) surfaces displayed S = 25 ± 7 cm s(-1). During the ALD growth of either Al2O3 or MnO, both the HC(O)CH2CH2-Si(111) and CH3-/HC(O)CH2CH2-Si(111) surfaces produced increased metal oxide deposition at low cycle number, relative to H-Si(111) or CH3-Si(111) surfaces. As detected by X-ray photoelectron spectroscopy after the ALD process, the CH3- and mixed CH3-/HC(O)CH2CH2- functionalized Si(111) surfaces exhibited less interfacial SiOx than was observed for ALD of metal oxides on H-Si(111) substrates. PMID:26262493

  11. Nitride passivation reduces interfacial traps in atomic-layer-deposited Al{sub 2}O{sub 3}/GaAs (001) metal-oxide-semiconductor capacitors using atmospheric metal-organic chemical vapor deposition

    SciTech Connect

    Aoki, T. Fukuhara, N.; Osada, T.; Sazawa, H.; Hata, M.; Inoue, T.

    2014-07-21

    Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al{sub 2}O{sub 3}. This AlN passivation incorporated nitrogen at the Al{sub 2}O{sub 3}/GaAs interface, improving the capacitance-voltage (C–V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C–V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (D{sub it}). The D{sub it} was reduced over the entire GaAs band gap. In particular, these devices exhibited D{sub it} around the midgap of less than 4 × 10{sup 12} cm{sup −2}eV{sup −1}, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.

  12. Atomic layer deposition in nanostructured photovoltaics: tuning optical, electronic and surface properties

    NASA Astrophysics Data System (ADS)

    Palmstrom, Axel F.; Santra, Pralay K.; Bent, Stacey F.

    2015-07-01

    Nanostructured materials offer key advantages for third-generation photovoltaics, such as the ability to achieve high optical absorption together with enhanced charge carrier collection using low cost components. However, the extensive interfacial areas in nanostructured photovoltaic devices can cause high recombination rates and a high density of surface electronic states. In this feature article, we provide a brief review of some nanostructured photovoltaic technologies including dye-sensitized, quantum dot sensitized and colloidal quantum dot solar cells. We then introduce the technique of atomic layer deposition (ALD), which is a vapor phase deposition method using a sequence of self-limiting surface reaction steps to grow thin, uniform and conformal films. We discuss how ALD has established itself as a promising tool for addressing different aspects of nanostructured photovoltaics. Examples include the use of ALD to synthesize absorber materials for both quantum dot and plasmonic solar cells, to grow barrier layers for dye and quantum dot sensitized solar cells, and to infiltrate coatings into colloidal quantum dot solar cell to improve charge carrier mobilities as well as stability. We also provide an example of monolayer surface modification in which adsorbed ligand molecules on quantum dots are used to tune the band structure of colloidal quantum dot solar cells for improved charge collection. Finally, we comment on the present challenges and future outlook of the use of ALD for nanostructured photovoltaics.

  13. Comparison of interfacial and electrical properties between Al2O3 and ZnO as interface passivation layer of GaAs MOS device with HfTiO gate dielectric

    NASA Astrophysics Data System (ADS)

    Shuyan, Zhu; Jingping, Xu; Lisheng, Wang; Yuan, Huang; Wing Man, Tang

    2015-03-01

    GaAs metal-oxide-semiconductor (MOS) capacitors with HfTiO as the gate dielectric and Al2O3 or ZnO as the interface passivation layer (IPL) are fabricated. X-ray photoelectron spectroscopy reveals that the Al2O3 IPL is more effective in suppressing the formation of native oxides and As diffusion than the ZnO IPL. Consequently, experimental results show that the device with Al2O3 IPL exhibits better interfacial and electrical properties than the device with ZnO IPL: lower interface-state density (7.2 × 1012 eV-1 cm-2), lower leakage current density (3.60 × 10-7 A/cm2 at Vg = 1 V) and good C-V behavior. Project supported by the National Natural Science Foundation of China (Nos. 61176100, 61274112).

  14. GaAsSb/GaAsN short-period superlattices as a capping layer for improved InAs quantum dot-based optoelectronics

    SciTech Connect

    Utrilla, A. D.; Ulloa, J. M. Guzman, A.; Hierro, A.

    2014-07-28

    The application of a GaAsSb/GaAsN short-period superlattice capping layer (CL) on InAs/GaAs quantum dots (QDs) is shown to be an option for providing improved luminescence properties to this system. Separating both GaAsSb and GaAsN ternaries during the growth in 2 monolayer-thick phases solves the GaAsSbN immiscibility-related problems. Strong fluctuations in the CL composition and strain field as well as in the QD size distribution are significantly reduced, and a more regular CL interface is also obtained. Room-temperature (RT) photoluminescence (PL) is obtained for overall N contents as high as 3%, yielding PL peak wavelengths beyond 1.4 μm in samples with a type-II band alignment. High external quantum efficiency electroluminescence and photocurrent from the QD ground state are also demonstrated at RT in a single QD-layer p-i-n device. Thus, it becomes possible to combine and transfer the complementary benefits of Sb- and N-containing GaAs alloys to InAs QD-based optoelectronics.

  15. Highly efficient hybrid light-emitting device using complex of CdSe/ZnS quantum dots embedded in co-polymer as an active layer.

    PubMed

    Kang, Byoung-Ho; Seo, Jun-Seon; Jeong, Sohee; Lee, Jihye; Han, Chang-Soo; Kim, Do-Eok; Kim, Kyu-Jin; Yeom, Se-Hyuk; Kwon, Dae-Hyuk; Kim, Hak-Rin; Kang, Shin-Won

    2010-08-16

    We propose a highly efficient hybrid light-emitting device (LED) with a single active layer where CdSe/ZnS quantum dots (QDs) are dispersed as a guest material in a conjugated polymer (co-polymer) matrix used for a host material. In our structure, the QDs act on light-emitting chromophores by trapping the migrating excitons in the co-polymer matrix via Förster energy transfer, and improve the charge balance within the co-polymer by trapping the injected electron carriers. Experimental results show that the electroluminescent properties highly depend on the doping density of the QDs within the co-polymer matrix, where the luminance as well as the external current efficiency are initially enhanced with increasing the concentration of the dispersed QDs in the co-polymer solution, and then such properties are degraded due to aggregation of the QDs. We can get the maximum brightness of 9,088 cd/m(2) and the maximum external current efficiency of 7.5 cd/A in mixing ratio of the QDs by 1.0 wt%. The external current efficiency is enhanced by over 15 times and the turn-on voltage is reduced in comparison with the corresponding values for a reference device that uses only a co-polymer as an active layer. PMID:20721223

  16. Effect of spacer layer thickness on structural and optical properties of multi-stack InAs/GaAsSb quantum dots

    SciTech Connect

    Kim, Yeongho; Ban, Keun-Yong Honsberg, Christiana B.; Boley, Allison; Smith, David J.

    2015-10-26

    The structural and optical properties of ten-stack InAs/GaAsSb quantum dots (QDs) with different spacer layer thicknesses (d{sub s} = 2, 5, 10, and 15 nm) are reported. X-ray diffraction analysis reveals that the strain relaxation of the GaAsSb spacers increases linearly from 0% to 67% with larger d{sub s} due to higher elastic stress between the spacer and GaAs matrix. In addition, the dislocation density in the spacers with d{sub s} = 10 nm is lowest as a result of reduced residual strain. The photoluminescence peak energy from the QDs does not change monotonically with increasing d{sub s} due to the competing effects of decreased compressive strain and weak electronic coupling of stacked QD layers. The QD structure with d{sub s} = 10 nm is demonstrated to have improved luminescence properties and higher carrier thermal stability.

  17. A layer-nanostructured assembly of PbS quantum dot/multiwalled carbon nanotube for a high-performance photoswitch

    NASA Astrophysics Data System (ADS)

    Feng, Wei; Qin, Chengqun; Shen, Yongtao; Li, Yu; Luo, Wen; An, Haoran; Feng, Yiyu

    2014-01-01

    A layered nanostructure of a lead sulfide (PbS) quantum dot (QD)/multi-walled carbon nanotube (MWNT) hybrid was prepared by the electrostatic assembly after the phase transfer of PbS QDs from an organic to an aqueous phase. Well-crystallized PbS QDs with a narrow diameter (5.5 nm) was mono-dispersed on the sidewalls of MWNT by the electrostatic adsorption. Near-infrared absorption of PbS/MWNT nanostructures was improved and controlled by the packing density of PbS QDs. Efficient charge transfer between PbS and MWNT at the interface resulted in a remarkable quenching of photoluminescence up to 28.6% and a blue-shift of emission band by 300 nm. This feature was facilitated by band energy levels based on the intimate contact through the electrostatic interaction. Two-terminal devices using PbS/MWNT nanostructures showed an excellent on/off switching photocurrent and good stability during 20 cycles under light illumination due to electron transfer from PbS to MWNT. The photoswitch exhibited a high photo sensitivity up to 31.3% with the photocurrent of 18.3 μA under the light of 3.85 mW/cm2, which outperformed many QD/carbon-based nanocomposites. Results indicate that the electrostatic layered assembly of QD/MWNT nanostructure is an excellent platform for the fabrication of high-performance optoelectronic devices.

  18. High temperature interfacial superconductivity

    SciTech Connect

    Bozovic, Ivan; Logvenov, Gennady; Gozar, Adrian Mihai

    2012-06-19

    High-temperature superconductivity confined to nanometer-scale interfaces has been a long standing goal because of potential applications in electronic devices. The spontaneous formation of a superconducting interface in bilayers consisting of an insulator (La.sub.2CuO.sub.4) and a metal (La.sub.1-xSr.sub.xCuO.sub.4), neither of which is superconducting per se, is described. Depending upon the layering sequence of the bilayers, T.sub.c may be either .about.15 K or .about.30 K. This highly robust phenomenon is confined to within 2-3 nm around the interface. After exposing the bilayer to ozone, T.sub.c exceeds 50 K and this enhanced superconductivity is also shown to originate from a 1 to 2 unit cell thick interfacial layer. The results demonstrate that engineering artificial heterostructures provides a novel, unconventional way to fabricate stable, quasi two-dimensional high T.sub.c phases and to significantly enhance superconducting properties in other superconductors. The superconducting interface may be implemented, for example, in SIS tunnel junctions or a SuFET.

  19. Reduction of Cu-rich interfacial layer and improvement of bulk CuO property through two-step sputtering for p-CuO/n-Si heterojunction solar cell

    NASA Astrophysics Data System (ADS)

    Masudy-Panah, Saeid; Dalapati, Goutam Kumar; Radhakrishnan, K.; Kumar, Avishek; Tan, Hui Ru

    2014-08-01

    Copper-rich interfacial-layer (Cu-rich IL) is formed during sputter deposition of cupric oxide (CuO) layer on silicon (Si). It has significant impact on the performance of p-CuO/n-Si heterojunction solar cells. In this report, CuO films deposited on Si at different RF-power levels using single and two-step RF-sputtering techniques and p-CuO/n-Si heterojunction solar cells have been investigated. Systematic characterization using XPS, AFM, XRD, Raman, and HR-TEM reveal that two-step RF-sputtering technique offers better crystal quality CuO film with thinner Cu-rich IL layer. Photovoltaic (PV) properties with an open-circuit voltage (Voc) of 421 mV, short circuit current (Jsc) of 4.5 mA/cm2, and a photocurrent of 8.3 mA/cm2 have been achieved for the cells prepared using two-step sputtering method, which are significantly higher than that for the solar cells fabricated using a single-step sputtering. The PV properties were further improved by depositing CuO films at higher working pressure with nitrogen doping. The efficiency of the best device achieved is approximately 1.21%, which is the highest value reported for p-CuO/n-Si heterojunction based solar cells.

  20. High color rendering index of remote-type white LEDs with multi-layered quantum dot-phosphor films and short-wavelength pass dichroic filters

    NASA Astrophysics Data System (ADS)

    Yoon, Hee Chang; Oh, Ji Hye; Do, Young Rag

    2014-09-01

    This paper introduces high color rendering index (CRI) white light-emitting diodes (W-LEDs) coated with red emitting (Sr,Ca)AlSiN3:Eu phosphors and yellowish-green emitting AgIn5S8/ZnS (AIS/ZS) quantum dots (QDs) on glass or a short-wavelength pass dichroic filter (SPDF), which transmit blue wavelength regions and reflect yellow wavelength regions. The red emitting (Sr,Ca)AlSiN3:Eu phosphor film is coated on glass and a SPDF using a screen printing method, and then the yellowish-green emitting AIS/ZS QDs are coated on the red phosphor (Sr,Ca)AlSiN3:Eu film-coated glass and SPDF using the electrospray (e-spray) method.To fabricate the red phosphor film, the optimum amount of phosphor is dispersed in a silicon binder to form a red phosphor paste. The AIS/ZS QDs are mixed with dimethylformamide (DMF), toluene, and poly(methyl methacrylate) (PMMA) for the e-spray coating. The substrates are spin-coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to fabricate a conductive surface. The CRI of the white LEDs is improved through inserting the red phosphor film between the QD layer and the glass substrate. Furthermore, the light intensities of the multi-layered phosphor films are enhanced through changing the glass substrate to the SPDF. The correlated color temperatures (CCTs) vary as a function of the phosphor concentration in the phosphor paste. The optical properties of the yellowish-green AIS/ZS QDs and red (Sr,Ca)AlSiN3:Eu phosphors are characterized using photoluminescence (PL), and the multi-layered QD-phosphor films are measured using electroluminescence (EL) with an InGaN blue LED (λmax = 450 nm) at 60 mA.

  1. Interfacial structure of multi-layered thin-films produced by pulsed laser deposition for use in small-scale ceramic capacitors

    NASA Astrophysics Data System (ADS)

    Araki, Takao; Hino, Takanori; Ohara, Masahiro

    2014-08-01

    The aim of this study was to develop thin film capacitors with superior properties that could provide an alternative to materials currently used in conventional multi-layer ceramic capacitors fabricated by sintering. To this end, an artificial dielectric super lattice technique, incorporating pulsed laser deposition, was applied to improving the dielectric properties of thin film capacitors. This method permits the A-site atoms of a perovskite ABO3 structure to be selected layer by layer at a nanoscopic scale; consequently, multi-layer BaTiO3- SrTiO3 thin films were produced on Pt(111)/Ti/SiO2/Si(100) and SrTiO3(111) substrates. Hetero-epitaxial grain growth was observed between BaTiO3 and SrTiO3, with the lattice mismatch between them introducing a compressive residual strain at the interface. The dielectric properties of these multi-layer thin-film capacitors were found to be superior to those of conventional solid-solution thin films once the thickness of the layers and the ratio of the two oxides were optimized.

  2. Improving charge transport of P3HT:PCBM organic solar cell using MoO3 nanoparticles as an interfacial buffer layer

    NASA Astrophysics Data System (ADS)

    Kim, Jae-Hyoung; Park, Eung-Kyu; Kim, Ji-Hwan; Cho, Hyeong Jun; Lee, Dong-Hoon; Kim, Yong-Sang

    2016-05-01

    In this work, P3HT:PCBM based organic solar cells (OSCs) were fabricated. We investigated the protection of PEDOT:PSS from active layer using the solution processed molybdenum oxide nanoparticles layer (MoO3 NPs, ≤100 nm). The device structure was ITO/ZnO/P3HT: PCBM/MoO3/PEDOT:PSS/Ag. A thin film MoO3 NPs was spin-coated and it acts as a hole transporting layer between the active layer and PEDOT:PSS. The MoO3 NPs based device showed an improved short circuit current compared without MoO3 NP layer. The pristine OSCs showed short circuit current density ( J sc ) of 11.56 mA/cm2 and PCE of 3.70% under AM 1.5G (100 mW/cm2). MoO3 NPs based device showed an increased PCE of 4.11% with J sc of 12.74 mA/cm2. MoO3 NPs also decreased the charge recombination and resistance of the OSCs. [Figure not available: see fulltext.

  3. Impact of electrically formed interfacial layer and improved memory characteristics of IrOx/high-κx/W structures containing AlOx, GdOx, HfOx, and TaOx switching materials

    PubMed Central

    2013-01-01

    Improved switching characteristics were obtained from high-κ oxides AlOx, GdOx, HfOx, and TaOx in IrOx/high-κx/W structures because of a layer that formed at the IrOx/high-κx interface under external positive bias. The surface roughness and morphology of the bottom electrode in these devices were observed by atomic force microscopy. Device size was investigated using high-resolution transmission electron microscopy. More than 100 repeatable consecutive switching cycles were observed for positive-formatted memory devices compared with that of the negative-formatted devices (only five unstable cycles) because it contained an electrically formed interfacial layer that controlled ‘SET/RESET’ current overshoot. This phenomenon was independent of the switching material in the device. The electrically formed oxygen-rich interfacial layer at the IrOx/high-κx interface improved switching in both via-hole and cross-point structures. The switching mechanism was attributed to filamentary conduction and oxygen ion migration. Using the positive-formatted design approach, cross-point memory in an IrOx/AlOx/W structure was fabricated. This cross-point memory exhibited forming-free, uniform switching for >1,000 consecutive dc cycles with a small voltage/current operation of ±2 V/200 μA and high yield of >95% switchable with a large resistance ratio of >100. These properties make this cross-point memory particularly promising for high-density applications. Furthermore, this memory device also showed multilevel capability with a switching current as low as 10 μA and a RESET current of 137 μA, good pulse read endurance of each level (>105 cycles), and data retention of >104 s at a low current compliance of 50 μA at 85°C. Our improvement of the switching characteristics of this resistive memory device will aid in the design of memory stacks for practical applications. PMID:24011235

  4. Impact of electrically formed interfacial layer and improved memory characteristics of IrOx/high-κx/W structures containing AlOx, GdOx, HfOx, and TaOx switching materials

    NASA Astrophysics Data System (ADS)

    Prakash, Amit; Maikap, Siddheswar; Banerjee, Writam; Jana, Debanjan; Lai, Chao-Sung

    2013-09-01

    Improved switching characteristics were obtained from high-κ oxides AlOx, GdOx, HfOx, and TaOx in IrOx/high-κx/W structures because of a layer that formed at the IrOx/high-κx interface under external positive bias. The surface roughness and morphology of the bottom electrode in these devices were observed by atomic force microscopy. Device size was investigated using high-resolution transmission electron microscopy. More than 100 repeatable consecutive switching cycles were observed for positive-formatted memory devices compared with that of the negative-formatted devices (only five unstable cycles) because it contained an electrically formed interfacial layer that controlled `SET/RESET' current overshoot. This phenomenon was independent of the switching material in the device. The electrically formed oxygen-rich interfacial layer at the IrOx/high-κx interface improved switching in both via-hole and cross-point structures. The switching mechanism was attributed to filamentary conduction and oxygen ion migration. Using the positive-formatted design approach, cross-point memory in an IrOx/AlOx/W structure was fabricated. This cross-point memory exhibited forming-free, uniform switching for >1,000 consecutive dc cycles with a small voltage/current operation of ±2 V/200 μA and high yield of >95% switchable with a large resistance ratio of >100. These properties make this cross-point memory particularly promising for high-density applications. Furthermore, this memory device also showed multilevel capability with a switching current as low as 10 μA and a RESET current of 137 μA, good pulse read endurance of each level (>105 cycles), and data retention of >104 s at a low current compliance of 50 μA at 85°C. Our improvement of the switching characteristics of this resistive memory device will aid in the design of memory stacks for practical applications.

  5. Synchrotron radiation photoemission study of interfacial electronic structure of HfO{sub 2} on In{sub 0.53}Ga{sub 0.47}As(001)-4 × 2 from atomic layer deposition

    SciTech Connect

    Pi, T. W. E-mail: gkwer@verizon.net E-mail: mhong@phys.ntu.edu.tw; Lin, T. D.; Chang, Y. C.; Hong, M. E-mail: gkwer@verizon.net E-mail: mhong@phys.ntu.edu.tw; Lin, H. Y.; Kwo, J. E-mail: gkwer@verizon.net E-mail: mhong@phys.ntu.edu.tw; Wertheim, G. K. E-mail: gkwer@verizon.net E-mail: mhong@phys.ntu.edu.tw

    2014-01-27

    The growth of a passivating layer on a In{sub 0.53}Ga{sub 0.47}As(001)-4 × 2 surface by atomic-layer deposition of tetrakis[ethylmethylamino]Hafnium (TEMAHf)) followed by the water pulse was investigated by synchrotron radiation photoemission. The Hf atoms maintain four-fold coordination, both after the initial TEMAHf deposition and the subsequent water pulse. The Hf atoms initially bond to the As dangling bonds of the surface As atom located on the edges of the raised ridges. One EMA ligand is removed in this process. Subsequent water exposure substitutes OH ligand for one or more remaining EMA ligands. These in turn react with TEMAHf to form Hf-O-Hf bonds allowing the hafnium oxides to grow. The surface In atoms on the terrace of the raised ridges were partially removed, but none bonded of the precursor atoms. Correlations between the interfacial electronic structure and the electric performance are discussed.

  6. Bulk- and layer-heterojunction phototransistors based on poly [2-methoxy-5-(2'-ethylhexyloxy-p-phenylenevinylene)] and PbS quantum dot hybrids

    NASA Astrophysics Data System (ADS)

    Song, Xiaoxian; Zhang, Yating; Wang, Ran; Cao, Mingxuan; Che, Yongli; Wang, Jianlong; Wang, Haiyan; Jin, Lufan; Dai, Haitao; Ding, Xin; Zhang, Guizhong; Yao, Jianquan

    2015-06-01

    The responsivity (R) of a thin film photodetector is proportional to the product of its photo-induced carrier density (n) and mobility (μ). However, when choosing between layer heterojunction (LH) and bulk heterojunction (BH) field-effect phototransistors (FEpTs), it is still unclear which of the two device structures is more conducive to photodetection. A comparison study is performed on the two structures based on polymer and PbS quantum dot hybrids. Both devices exhibit ambipolar behavior, with μE ≈ μH = 3.7 cm2 V-1 s-1 for BH-FEpTs and μH = 36 cm2 V-1 s-1 and μE = 52 cm2 V-1 s-1 for LH-FEpTs. Because of the improvements in μ and the channel order degree (α), the responsivity of LH-FEpTs is as high as 101 A/W, which is as much as two orders of magnitude higher than that of BH-FEpTs (10-1A/W) under the same conditions. Although the large area of the BH improves both the exciton separation degree (β) and n in the BH-FEpT, the lack of an effective transport mechanism becomes the main constraint on high device responsivity. Therefore, LH-FEpTs are better candidates for use as photo detectors, and a "three-high" principle of high α, β, and μ is found to be required for high responsivity.

  7. Effect of sodium acetate additive in successive ionic layer adsorption and reaction on the performance of CdS quantum-dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Liu, I.-Ping; Chen, Liang-Yih; Lee, Yuh-Lang

    2016-09-01

    Sodium acetate (NaAc) is utilized as an additive in cationic precursors of the successive ionic layer adsorption and reaction (SILAR) process to fabricate CdS quantum-dot (QD)-sensitized photoelectrodes. The effects of the NaAc concentration on the deposition rate and distribution of QDs in mesoporous TiO2 films, as well as on the performance of CdS-sensitized solar cells are studied. The experimental results show that the presence of NaAc can significantly accelerate the deposition of CdS, improve the QD distribution across photoelectrodes, and thereby, increase the performance of solar cells. These results are mainly attributed to the pH-elevation effect of NaAc to the cationic precursors which increases the electrostatic interaction of the TiO2 film to cadmium ions. The light-to-energy conversion efficiency of the CdS-sensitized solar cell increases with increasing concentration of the NaAc and approaches a maximum value (3.11%) at 0.05 M NaAc. Additionally, an ionic exchange is carried out on the photoelectrode to transform the deposited CdS into CdS1-xSex ternary QDs. The light-absorption range of the photoelectrode is extended and an exceptional power conversion efficiency of 4.51% is achieved due to this treatment.

  8. Highly efficient quantum-dot light-emitting diodes with DNA-CTMA as a combined hole-transporting and electron-blocking layer.

    PubMed

    Sun, Qingjiang; Subramanyam, Guru; Dai, Liming; Check, Michael; Campbell, Angela; Naik, Rajesh; Grote, James; Wang, Yongqiang

    2009-03-24

    Owing to their narrow bright emission band, broad size-tunable emission wavelength, superior photostability, and excellent flexible-substrate compatibility, light-emitting diodes based on quantum dots (QD-LEDs) are currently under intensive research and development for multiple consumer applications including flat-panel displays and flat lighting. However, their commercialization is still precluded by the slow development to date of efficient QD-LEDs as even the highest reported efficiency of 2.0% cannot favorably compete with their organic counterparts. Here, we report QD-LEDs with a record high efficiency (approximately 4%), high brightness (approximately 6580 cd/m(2)), low turn-on voltage (approximately 2.6 V), and significantly improved color purity by simply using deoxyribonucleic acid (DNA) complexed with cetyltrimetylammonium (CTMA) (DNA-CTMA) as a combined hole transporting and electron-blocking layer (HTL/EBL). This, together with controlled thermal decomposition of ligand molecules from the QD shell, represents a novel combined, but simple and very effective, approach toward the development of highly efficient QD-LEDs with a high color purity. PMID:19309174

  9. Atomic layer deposition effect on the electrical properties of Al{sub 2}O{sub 3}-passivated PbS quantum dot field-effect transistors

    SciTech Connect

    So, Hye-Mi; Shim, Hyung Cheoul; Choi, Hyekyoung; Lee, Seung-Mo; Jeong, Sohee; Chang, Won Seok

    2015-03-02

    We have investigated the effect of atomic layer deposition (ALD) on the electrical properties of colloidal PbS quantum dot field-effect transistors (PbS QD-FETs). Low-temperature Al{sub 2}O{sub 3} ALD process was used to fill up the pore spaces of PbS QD films containing 1, 2-ethanedithiol ligands. Upon deposition of Al{sub 2}O{sub 3} on PbS film, the PbS QD-FETs showed ambipolar behavior. The treated film retained this property for over 2 months, despite of exposure to air. This change in the electrical properties of the PbS QD-FETs is attributed to the formation of electron channels in the Al{sub 2}O{sub 3}-passivated PbS film. We conclude that these electron transport channels in the Al{sub x}O{sub y}-PbS film are formed due to substitution of the Pb sites by Al metal and chemical reduction of Pb{sup 2+} ions, as determined by an analysis of the depth profile of the film using secondary ion mass spectrometry and X-ray photoelectron spectroscopy.

  10. Modification of ZnS-inserting layer in the TiO2 inverse opal-based photoanode to enhance the efficiency of quantum dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Deng, Fei; Wan, Xiangyu; Mei, Xingan; Fan, Runzhou; Yan, Xuemin; Wan, Li; Shi, Dean; Xiong, Yan

    2016-07-01

    Modification of ZnS-inserting layer in the titanium dioxide (TiO2) inverse opal-based photoanode was investigated, and it is an effective and easy approach to enhance the efficiency of quantum dot-sensitized solar cells (QDSSCs). The introduction of ZnS between TiO2 and quantum dots (QDs) not only enhanced the light harvesting of QDs on its top, but also lessened the charge-transfer resistances at the TiO2/QD/electrolyte interfaces. The TiO2 inverse opal-based QDSSCs increased the energy conversion efficiency by modifying the ZnS-inserting layer in the photoanode, particularly the CdS/CdSe QD co-sensitized solar cells which attained 79% rate of increase in cell efficiency.

  11. Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tartakovskii, Alexander

    2012-07-01

    Part I. Nanostructure Design and Structural Properties of Epitaxially Grown Quantum Dots and Nanowires: 1. Growth of III/V semiconductor quantum dots C. Schneider, S. Hofling and A. Forchel; 2. Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. Bakkers and V. Zwiller; 3. Atomic scale analysis of self-assembled quantum dots by cross-sectional scanning tunneling microscopy and atom probe tomography J. G. Keizer and P. M. Koenraad; Part II. Manipulation of Individual Quantum States in Quantum Dots Using Optical Techniques: 4. Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton; 5. Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atature; 6. Coherent control of quantum dot excitons using ultra-fast optical techniques A. J. Ramsay and A. M. Fox; 7. Optical probing of holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente; Part III. Optical Properties of Quantum Dots in Photonic Cavities and Plasmon-Coupled Dots: 8. Deterministic light-matter coupling using single quantum dots P. Senellart; 9. Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vukovic; 10. Photon statistics in quantum dot micropillar emission M. Asmann and M. Bayer; 11. Nanoplasmonics with colloidal quantum dots V. Temnov and U. Woggon; Part IV. Quantum Dot Nano-Laboratory: Magnetic Ions and Nuclear Spins in a Dot: 12. Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette; 13. Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaitre; 14. Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie; Part V. Electron Transport in Quantum Dots Fabricated by

  12. A layer-nanostructured assembly of PbS quantum dot/multiwalled carbon nanotube for a high-performance photoswitch

    PubMed Central

    Feng, Wei; Qin, Chengqun; Shen, Yongtao; Li, Yu; Luo, Wen; An, Haoran; Feng, Yiyu

    2014-01-01

    A layered nanostructure of a lead sulfide (PbS) quantum dot (QD)/multi-walled carbon nanotube (MWNT) hybrid was prepared by the electrostatic assembly after the phase transfer of PbS QDs from an organic to an aqueous phase. Well-crystallized PbS QDs with a narrow diameter (5.5 nm) was mono-dispersed on the sidewalls of MWNT by the electrostatic adsorption. Near-infrared absorption of PbS/MWNT nanostructures was improved and controlled by the packing density of PbS QDs. Efficient charge transfer between PbS and MWNT at the interface resulted in a remarkable quenching of photoluminescence up to 28.6% and a blue-shift of emission band by 300 nm. This feature was facilitated by band energy levels based on the intimate contact through the electrostatic interaction. Two-terminal devices using PbS/MWNT nanostructures showed an excellent on/off switching photocurrent and good stability during 20 cycles under light illumination due to electron transfer from PbS to MWNT. The photoswitch exhibited a high photo sensitivity up to 31.3% with the photocurrent of 18.3 μA under the light of 3.85 mW/cm2, which outperformed many QD/carbon-based nanocomposites. Results indicate that the electrostatic layered assembly of QD/MWNT nanostructure is an excellent platform for the fabrication of high-performance optoelectronic devices. PMID:24445285

  13. (In,Mn)As multilayer quantum dot structures

    SciTech Connect

    Bouravleuv, Alexei; Sapega, Victor; Nevedomskii, Vladimir; Khrebtov, Artem; Samsonenko, Yuriy; Cirlin, George

    2014-12-08

    (In,Mn)As multilayer quantum dots structures were grown by molecular beam epitaxy using a Mn selective doping of the central parts of quantum dots. The study of the structural and magneto-optical properties of the samples with three and five layers of (In,Mn)As quantum dots has shown that during the quantum dots assembly, the out-diffusion of Mn from the layers with (In,Mn)As quantum dots can occur resulting in the formation of the extended defects. To produce a high quality structures using the elaborated technique of selective doping, the number of (In,Mn)As quantum dot layers should not exceed three.

  14. Science and technology of thin films and interfacial layers in ferroelectric and high-dielectric constant heterostructures and application to devices.

    SciTech Connect

    Auciello, O.; Materials Science Division

    2006-01-01

    The fabrication of the next generation of complex oxide thin film-based micro and nanoscale devices, such as, for example, low and high density nonvolatile ferroelectric random access memories (FeRAMS), high-dielectric constant (K) high-frequency devices, and the next generation of complimentary metal oxide semiconductor (CMOS) nanoscale devices based on high-K dielectrics, require understanding and control of film growth and interface processes as well as development of materials integration strategies with atomic scale control. In recent years, we developed and applied a unique combination of integrated film synthesis/in situ characterization and ex situ analytical techniques capable of providing information about thin film surface and interface processes at the atomic scale as required for the development of the devices mentioned above. These techniques are also useful for establishing composition-microstructure-property relationships critical for the integration of oxide thin films with semiconductor device platforms for the development of a whole new generation of micro and nanodevices based on film technologies beyond semiconductors and specifically silicon. Our recent work has been focused on developing diffusion barrier layers and heterostructured bottom electrodes that play a critical role in high-density FeRAM integration. We demonstrated that TiAl layers can be used as a material with a double diffusion barrier/bottom electrode functionality for integration of ferroelectric capacitors CMOS devices for fabrication of FeRAMs. We also demonstrated that control of interfaces is critical to the integration of high-K dielectric films with appropriate substrates for the fabrication of high-performance high-frequency devices, and here again a diffusion barrier such as the TiAl layer developed by our group is critical for such integration. These studies revealed that when properly oxidized, nanoscale thick amorphous Ti-Al-O layers exhibit properties that make

  15. Influence of microstructure and interfacial strain on the magnetic properties of epitaxial Mn3O4/La0.7Sr0.3MnO3 layered-composite thin films

    NASA Astrophysics Data System (ADS)

    Mukherjee, Devajyoti; Bingham, Nicholas; Hordagoda, Mahesh; Phan, Manh-Huong; Srikanth, Hariharan; Witanachchi, Sarath; Mukherjee, Pritish

    2012-10-01

    Epitaxial Mn3O4/La0.7Sr0.3MnO3 (Mn3O4/LSMO) bilayer thin films were grown on lattice-matched single crystal substrates of SrTiO3 (STO) (100) and MgO (100), with Mn3O4 as the top layer, using a pulsed laser deposition technique. X-ray diffraction (XRD) patterns revealed the single crystalline nature and epitaxial relationship between the layers. A detailed analysis of strains using XRD asymmetric/symmetric scans indicated an increasing in-plane compressive strain in the LSMO layer with increasing thicknesses of the Mn3O4 layer, resulting in a tetragonal distortion of the LSMO lattice in the Mn3O4/LSMO films in comparison to the tensile strains in LSMO single-layer films grown on both STO and MgO substrates. Cross-sectional high resolution transmission electron microscope (HRTEM) images showed atomically sharp interfaces in all films. However, as opposed to a flat interface between LSMO and STO, the Mn3O4 and LSMO interface was undulating and irregular in the bilayer films. Magnetic measurements revealed that relative to LSMO, the presence of Mn3O4 in Mn3O4/LSMO reduced the saturation magnetization at T > 50 K (the ferrimagnetic ordering temperature of Mn3O4) but enhanced it at T < 50 K. The decrease of the saturation magnetization in Mn3O4/LSMO for T > 50 K was associated with the appearance and increase of the compressive strain with the increase in Mn3O4 thickness. These observations point to the importance of a ferromagnetic-ferrimagnetic interfacial coupling between the LSMO and Mn3O4 layers in enhancing the surface magnetism of LSMO in the Mn3O4/LSMO bilayers. Our study provides useful information regarding the development of manganite composite thin films with improved magnetic properties for a wide range of technological applications, such as in spintronics and sensor devices.

  16. Enhanced heteroepitaxial growth of CoCrPt-SiO{sub 2} perpendicular magnetic recording media on optimized Ru intermediate layers

    SciTech Connect

    Srinivasan, Kumar; Piramanayagam, S. N.

    2008-01-15

    The crystallographic growth, interfacial roughness, and magnetic properties of CoCrPt-SiO{sub 2} perpendicular magnetic recording media prepared on various types of Ru intermediate growth layers were systematically investigated based on high angle and omega offset x-ray diffraction scans, rocking curve scans, synchrotron radiation based grazing incidence reflectivity scans, and magneto-optical Kerr hysteresis loops. For samples that make use of one Ru growth layer, voltage bias applied on the Ru layer was seen to have two observable effects: (1) the dispersion in the Ru(00{center_dot}2) perpendicular texture increased, but that of the Co(00{center_dot}2) remained unchanged, leading to identical layered growth and (2) the in-plane a-lattice parameter of the Ru decreased leading to enhanced heteroepitaxy with the Co. There was no significant change in the Ru-Co interfacial roughness with changing the bias on the Ru layer. The bias effect can be used to optimize the design of the Ru intermediate layers. A scheme that makes use of two Ru growth layers consisting of a bottom Ru layer prepared under zero bias, which is inserted below a second Ru layer prepared under biased conditions, is shown to lead to significant benefits such as improved texture without affecting the magnetic properties. This is due to the different functional roles ascribed to each of the Ru growth layers.

  17. On-chip high density droplet-on-template (DOT) array

    NASA Astrophysics Data System (ADS)

    Kim, Jitae; Song, Simon

    2015-01-01

    In this report, we present a new method for generating a high-density (2D) droplet array using double-layered polydimethylsiloxane (PDMS) templates containing honeycomb microwells. Without external flow control, a droplet-on-template (DOT) was created by utilizing capillary forces associated with the interfacial tension between the aqueous and oil phases. The DOT process involved three simple steps: (1) vacuum-assisted filling of microwells; (2) excess water removal; and (3) covering the droplet array with oil. To demonstrate the concept of the DOT, we generated spherical water droplets 147, 191, 238, 326 and 405 μm in diameter from corresponding microwells with lengths of 200, 300, 400, 600 and 800 μm, respectively and a height of 76 μm (up to ~10,000 droplets on a template 25  ×  25 mm). Two important factors, including the aspect ratio (height-to-length ratio) of the microwell and the interfacial tension of the two phases, were investigated to understand how those factors affect the shape of the droplets (‘sphere’ or ‘dome’). All the droplets were spherical up to an aspect ratio of 0.55. The droplets were dome-shaped for aspect ratios above 0.82. For a 1 mM sodium dodecyl sulfate (SDS) solution, the use of mineral oil (which had the highest interfacial tension studied) produced spherical droplets, but dome-shaped droplets were produced by corn oil and oleic acid.

  18. Quantum dot-layer-encapsulated and phenyl-functionalized silica spheres for highly luminous, colour rendering, and stable white light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Yoo, Hyein; Jang, Ho Seong; Lee, Kwangyeol; Woo, Kyoungja

    2015-07-01

    Although the quantum efficiencies of quantum dots (QDs) are approaching unity through advances in the synthesis of QD materials, their luminescence efficiencies after mixing with resin and thermal curing for white light-emitting diodes (LEDs) are seriously lowered because of aggregation and oxidation of QDs and poor adhesion of QDs to the resin. To overcome these problems, QD-layer-encapsulated and phenyl-functionalized silica (SQSPh) spheres were synthesized and applied for white LEDs, whereby the QDs were homogeneously distributed at radial equidistance from the center and near the surface of approximately 100 nm-sized silica spheres and the surface was functionalized with phenylethyl groups. The inter-core distances of QDs were over ~14 nm, which is over the limit (<10 nm) for Förster resonance energy transfer (FRET) that leads to photoluminescence (PL) reduction. This hierarchical nanostructure excludes a chance of FRET between QDs and provides the QDs a gradually refractive index matching environment, which yields ~4-fold enhanced PL in SQSPh. More importantly, the SQSPh acquired a highly adhesive property to silicone resin due to their phenyl functional group matching, which resulted in remarkably improved light extraction in white LEDs. When incorporated along with a yellow-emitting Y3Al5O12:Ce3+ (YAG:Ce) phosphor and silicone resin on blue LED chips, the SQSPh spheres presented significantly improved performance [luminous efficiency (LE) = 58.2 lm W-1 colour rendering index Ra = 81.8; I/I0 = 0.98 after 60 h operation] than their original QDs (LE = 39.6 lm W-1 Ra = 78.1; I/I0 = 0.91 after 60 h operation) under a forward bias current of 60 mA.Although the quantum efficiencies of quantum dots (QDs) are approaching unity through advances in the synthesis of QD materials, their luminescence efficiencies after mixing with resin and thermal curing for white light-emitting diodes (LEDs) are seriously lowered because of aggregation and oxidation of QDs and poor

  19. HfO2-based InP n-channel metal-oxide-semiconductor field-effect transistors and metal-oxide-semiconductor capacitors using a germanium interfacial passivation layer

    NASA Astrophysics Data System (ADS)

    Kim, Hyoung-Sub; Ok, I.; Zhang, M.; Zhu, F.; Park, S.; Yum, J.; Zhao, H.; Lee, Jack C.; Majhi, Prashant

    2008-09-01

    In this letter, we present our experimental results of HfO2-based n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) and metal-oxide-semiconductor capacitors (MOSCAPs) on indium phosphide (InP) substrates using a thin germanium (Ge) interfacial passivation layer (IPL). We found that MOSCAPs on n-InP substrates showed good C-V characteristics such as a small capacitance equivalent thickness (14Å ), a small frequency dispersion (<10% and <200mV), and a low dielectric leakage current (˜5×10-4A/cm2 at Vg=1.5V), whereas MOSCAPs on p-InP exhibited poor characteristics, implying severe Fermi level pinning. It was also found that InP was more vulnerable to a high temperature process such that C-V curves showed a characteristic "bump" and inversion capacitance at relatively high frequencies. From n-channel MOSFETs on a semi-insulating InP substrate using Ge IPL, HfO2, and TaN gate electrodes, excellent electrical characteristics such as a large transconductance (9.3mS /mm) and large drain currents (12.3mA/mm at Vd=2V and Vg=Vth+2V) were achieved, which are comparable to other works.

  20. White-light-exciting, layer-by-layer-assembled ZnCdHgSe quantum dots/polymerized ionic liquid hybrid film for highly sensitive photoelectrochemical immunosensing of neuron specific enolase.

    PubMed

    Yu, Xiangyang; Wang, Yanying; Chen, Xuemin; Wu, Kangbing; Chen, Danchao; Ma, Ming; Huang, Zhenjia; Wu, Wangze; Li, Chunya

    2015-04-21

    ZnCdHgSe quantum dots (QDs) functionalized with N-acetyl-l-cysteine were synthesized and characterized. Through layer-by-layer assembling, the ZnCdHgSe QDs was integrated with a polymerized 1-decyl-3-[3-pyrrole-1-yl-propyl]imidazolium tetrafluoroborate (PDPIT) ionic liquid film modified indium tin oxide (ITO) electrode to fabricated a photoelectrochemical interface for the immobilization of rabbit antihuman neuron specific enolase (anti-NSE). After being treated with glutaraldehyde vapor and bovine serum albumin successively, an anti-NSE/ZnCdHgSe QDs/PDPIT/ITO sensing platform was established. Simplely using a white-light LED as an excitation source, the immunoassay of neuron specific enolase (NSE) was achieved through monitoring the photocurrent variation. The polymerized ionic liquid film was demonstrated to be an important element to enhance the photocurrent response of ZnCdHgSe QDs. The anti-NSE/ZnCdHgSe QDs/PDPIT/ITO based immunosensor presents excellent performances in neuron specific enolase determination. The photocurrent variation before and after being interacted with NSE exhibits a good linear relationship with the logarithm of its concentration (log cNSE) in the range from 1.0 pg mL(-1) to 100 ng mL(-1). The limit of detection of this immunosensor is able to reach 0.2 pg mL(-1) (S/N = 3). The determination of NSE in clinical human sera was also demonstrated using anti-NSE/ZnCdHgSe QDs/PDPIT/ITO electrode. The results were found comparable with those obtained by using enzyme-linked immunosorbent assay method. PMID:25790014

  1. Capping layer growth rate and the optical and structural properties of GaAsSbN-capped InAs/GaAs quantum dots

    SciTech Connect

    Ulloa, J. M. Utrilla, A. D.; Guzman, A.; Hierro, A.

    2014-10-07

    Changing the growth rate during the heteroepitaxial capping of InAs/GaAs quantum dots (QDs) with a 5 nm-thick GaAsSbN capping layer (CL) strongly modifies the QD structural and optical properties. A size and shape transition from taller pyramids to flatter lens-shaped QDs is observed when the CL growth rate is decreased from 1.5 to 0.5 ML/s. This indicates that the QD dissolution processes taking place during capping can be controlled to some extent by the GaAsSbN CL growth rate, with high growth rates allowing a complete preservation of the QDs. However, the dissolution processes are shown to have a leveling effect on the QD height, giving rise to a narrower size distribution for lower growth rates. Contrary to what could be expected, these effects are opposite to the strong blue-shift and improvement of the photoluminescence (PL) observed for higher growth rates. Nevertheless, the PL results can be understood in terms of the strong impact of the growth rate on the Sb and N incorporation into the CL, which results in lower Sb and N contents at higher growth rates. Besides the QD-CL band offsets and QD strain, the different CL composition alters the band alignment of the system, which can be transformed to type-II at low growth rates. These results show the key role of the alloyed CL growth parameters on the resulting QD properties and demonstrate an intricate correlation between the PL spectra and the sample morphology in complex QD-CL structures.

  2. Quantum dot-layer-encapsulated and phenyl-functionalized silica spheres for highly luminous, colour rendering, and stable white light-emitting diodes.

    PubMed

    Yoo, Hyein; Jang, Ho Seong; Lee, Kwangyeol; Woo, Kyoungja

    2015-08-14

    Although the quantum efficiencies of quantum dots (QDs) are approaching unity through advances in the synthesis of QD materials, their luminescence efficiencies after mixing with resin and thermal curing for white light-emitting diodes (LEDs) are seriously lowered because of aggregation and oxidation of QDs and poor adhesion of QDs to the resin. To overcome these problems, QD-layer-encapsulated and phenyl-functionalized silica (SQS(Ph)) spheres were synthesized and applied for white LEDs, whereby the QDs were homogeneously distributed at radial equidistance from the center and near the surface of approximately 100 nm-sized silica spheres and the surface was functionalized with phenylethyl groups. The inter-core distances of QDs were over ∼14 nm, which is over the limit (<10 nm) for Förster resonance energy transfer (FRET) that leads to photoluminescence (PL) reduction. This hierarchical nanostructure excludes a chance of FRET between QDs and provides the QDs a gradually refractive index matching environment, which yields ∼4-fold enhanced PL in SQS(Ph). More importantly, the SQS(Ph) acquired a highly adhesive property to silicone resin due to their phenyl functional group matching, which resulted in remarkably improved light extraction in white LEDs. When incorporated along with a yellow-emitting Y3Al5O12:Ce(3+) (YAG:Ce) phosphor and silicone resin on blue LED chips, the SQS(Ph) spheres presented significantly improved performance [luminous efficiency (LE) = 58.2 lm W(-1); colour rendering index Ra = 81.8; I/I0 = 0.98 after 60 h operation] than their original QDs (LE = 39.6 lm W(-1); Ra = 78.1; I/I0 = 0.91 after 60 h operation) under a forward bias current of 60 mA. PMID:26156214

  3. Bulk- and layer-heterojunction phototransistors based on poly [2-methoxy-5-(2′-ethylhexyloxy-p-phenylenevinylene)] and PbS quantum dot hybrids

    SciTech Connect

    Song, Xiaoxian; Zhang, Yating Wang, Ran; Cao, Mingxuan; Che, Yongli; Wang, Jianlong; Wang, Haiyan; Jin, Lufan; Ding, Xin; Zhang, Guizhong; Yao, Jianquan; Dai, Haitao

    2015-06-22

    The responsivity (R) of a thin film photodetector is proportional to the product of its photo-induced carrier density (n) and mobility (μ). However, when choosing between layer heterojunction (LH) and bulk heterojunction (BH) field-effect phototransistors (FEpTs), it is still unclear which of the two device structures is more conducive to photodetection. A comparison study is performed on the two structures based on polymer and PbS quantum dot hybrids. Both devices exhibit ambipolar behavior, with μ{sub E} ≈ μ{sub H} = 3.7 cm{sup 2} V{sup −1} s{sup −1} for BH-FEpTs and μ{sub H} = 36 cm{sup 2} V{sup −1} s{sup −1} and μ{sub E} = 52 cm{sup 2} V{sup −1} s{sup −1} for LH-FEpTs. Because of the improvements in μ and the channel order degree (α), the responsivity of LH-FEpTs is as high as 10{sup 1 }A/W, which is as much as two orders of magnitude higher than that of BH-FEpTs (10{sup −1}A/W) under the same conditions. Although the large area of the BH improves both the exciton separation degree (β) and n in the BH-FEpT, the lack of an effective transport mechanism becomes the main constraint on high device responsivity. Therefore, LH-FEpTs are better candidates for use as photo detectors, and a “three-high” principle of high α, β, and μ is found to be required for high responsivity.

  4. Surface and interfacial reaction study of half cycle atomic layer deposited HfO{sub 2} on chemically treated GaSb surfaces

    SciTech Connect

    Zhernokletov, D. M.; Dong, H.; Brennan, B.; Kim, J.; Yakimov, M.; Tokranov, V.; Oktyabrsky, S.; Wallace, R. M.

    2013-04-01

    An in situ half-cycle atomic layer deposition/X-ray photoelectron spectroscopy (XPS) study was conducted in order to investigate the evolution of the HfO{sub 2} dielectric interface with GaSb(100) surfaces after sulfur passivation and HCl etching, designed to remove the native oxides. With the first pulses of tetrakis(dimethylamido)hafnium(IV) and water, a decrease in the concentration of antimony oxide states present on the HCl-etched surface is observed, while antimony sulfur states diminished below the XPS detection limit on sulfur passivated surface. An increase in the amount of gallium oxide/sulfide is seen, suggesting oxygen or sulfur transfers from antimony to gallium during antimony oxides/sulfides decomposition.

  5. Effect of graphene layer thickness and mechanical compliance on interfacial heat flow and thermal conduction in solid-liquid phase change materials.

    PubMed

    Warzoha, Ronald J; Fleischer, Amy S

    2014-08-13

    Solid-liquid phase change materials (PCMs) are attractive candidates for thermal energy storage and electronics cooling applications but have limited applicability in state-of-the-art technologies due to their low intrinsic thermal conductivities. Recent efforts to incorporate graphene and multilayer graphene into PCMs have led to the development of thermal energy storage materials with remarkable values of bulk thermal conductivity. However, the full potential of graphene as a filler material for the thermal enhancement of PCMs remains unrealized, largely due to an incomplete understanding of the physical mechanisms that govern thermal transport within graphene-based nanocomposites. In this work, we show that the number of graphene layers (n) within an individual graphene nanoparticle has a significant effect on the bulk thermal conductivity of an organic PCM. Results indicate that the bulk thermal conductivity of PCMs can be tuned by over an order of magnitude simply by adjusting the number of graphene layers (n) from n = 3 to 44. Using scanning electron microscopy in tandem with nanoscale analytical techniques, the physical mechanisms that govern heat flow within a graphene nanocomposite PCM are found to be nearly independent of the intrinsic thermal conductivity of the graphene nanoparticle itself and are instead found to be dependent on the mechanical compliance of the graphene nanoparticles. These findings are critical for the design and development of PCMs that are capable of cooling next-generation electronics and storing heat effectively in medium-to-large-scale energy systems, including solar-thermal power plants and building heating and cooling systems. PMID:24983698

  6. Smart interfacial bonding alloys

    SciTech Connect

    R. Q. Hwang; J. C. Hamilton; J. E. Houston

    1999-04-01

    The goal of this LDRD was to explore the use of the newly discovered strain-stabilized 2-D interfacial alloys as smart interface bonding alloys (SIBA). These materials will be used as templates for the heteroepitaxial growth of metallic thin films. SIBA are formed by two metallic components which mix at an interface to relieve strain and prevent dislocations from forming in subsequent thin film growth. The composition of the SIBA is determined locally by the amount of strain, and therefore can react smartly to areas of the highest strain to relieve dislocations. In this way, SIBA can be used to tailor the dislocation structure of thin films. This project included growth, characterization and modeling of films grown using SIBA templates. Characterization will include atomic imaging of the dislocations structure, measurement of the mechanical properties of the film using interface force microscopy (IFM) and the nanoindenter, and measurement of the electronic structure of the SIBA with synchrotron photoemission. Resistance of films to sulfidation and oxidation will also be examined. The Paragon parallel processing computer will be used to calculate the structure of the SIBA and thin films in order to develop ability to predict and tailor SIBA and thin film behavior. This work will lead to the possible development of a new class of thin film materials with properties tailored by varying the composition of the SIBA, serving as a buffer layer to relieve the strain between the substrate and the thin film. Such films will have improved mechanical and corrosion resistance allowing application as protective barriers for weapons applications. They will also exhibit enhanced electrical conductivity and reduced electromigration making them particularly suitable for application as interconnects and other electronic needs.

  7. L{sub g} = 100 nm In{sub 0.7}Ga{sub 0.3}As quantum well metal-oxide semiconductor field-effect transistors with atomic layer deposited beryllium oxide as interfacial layer

    SciTech Connect

    Koh, D. E-mail: Taewoo.Kim@sematech.org; Kwon, H. M.; Kim, T.-W. E-mail: Taewoo.Kim@sematech.org; Veksler, D.; Gilmer, D.; Kirsch, P. D.; Kim, D.-H.; Hudnall, Todd W.; Bielawski, Christopher W.; Maszara, W.; Banerjee, S. K.

    2014-04-21

    In this study, we have fabricated nanometer-scale channel length quantum-well (QW) metal-oxide-semiconductor field effect transistors (MOSFETs) incorporating beryllium oxide (BeO) as an interfacial layer. BeO has high thermal stability, excellent electrical insulating characteristics, and a large band-gap, which make it an attractive candidate for use as a gate dielectric in making MOSFETs. BeO can also act as a good diffusion barrier to oxygen owing to its small atomic bonding length. In this work, we have fabricated In{sub 0.53}Ga{sub 0.47}As MOS capacitors with BeO and Al{sub 2}O{sub 3} and compared their electrical characteristics. As interface passivation layer, BeO/HfO{sub 2} bilayer gate stack presented effective oxide thickness less 1 nm. Furthermore, we have demonstrated In{sub 0.7}Ga{sub 0.3}As QW MOSFETs with a BeO/HfO{sub 2} dielectric, showing a sub-threshold slope of 100 mV/dec, and a transconductance (g{sub m,max}) of 1.1 mS/μm, while displaying low values of gate leakage current. These results highlight the potential of atomic layer deposited BeO for use as a gate dielectric or interface passivation layer for III–V MOSFETs at the 7 nm technology node and/or beyond.

  8. Impact of post-deposition annealing on interfacial chemical bonding states between AlGaN and ZrO{sub 2} grown by atomic layer deposition

    SciTech Connect

    Ye, Gang; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Wang, Hong; Liu, Zhi Hong

    2015-03-02

    The effect of post-deposition annealing on chemical bonding states at interface between Al{sub 0.5}Ga{sub 0.5}N and ZrO{sub 2} grown by atomic layer deposition (ALD) is studied by angle-resolved x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It has been found that both of Al-O/Al 2p and Ga-O/Ga 3d area ratio decrease at annealing temperatures lower than 500 °C, which could be attributed to “clean up” effect of ALD-ZrO{sub 2} on AlGaN. Compared to Ga spectra, a much larger decrease in Al-O/Al 2p ratio at a smaller take-off angle θ is observed, which indicates higher effectiveness of the passivation of Al-O bond than Ga-O bond through “clean up” effect near the interface. However, degradation of ZrO{sub 2}/AlGaN interface quality due to re-oxidation at higher annealing temperature (>500 °C) is also found. The XPS spectra clearly reveal that Al atoms at ZrO{sub 2}/AlGaN interface are easier to get oxidized as compared with Ga atoms.

  9. Interfacial charge-induced polarization switching in Al{sub 2}O{sub 3}/Pb(Zr,Ti)O{sub 3} bi-layer

    SciTech Connect

    Kim, Yu Jin; Park, Min Hyuk; Jeon, Woojin; Kim, Han Joon; Moon, Taehwan; Lee, Young Hwan; Kim, Keum Do; Hyun, Seung Dam; Hwang, Cheol Seong

    2015-12-14

    Detailed polarization switching behavior of an Al{sub 2}O{sub 3}/Pb(Zr,Ti)O{sub 3} (AO/PZT) structure is examined by comparing the phenomenological thermodynamic model to the experimental polarization–voltage (P-V) results. Amorphous AO films with various thicknesses (2–10 nm) were deposited on the polycrystalline 150-nm-thick PZT film. The thermodynamic calculation showed that the transition from the ferroelectric-like state to the paraelectric-like state with increasing AO thickness occurs at ∼3 nm thickness. This paraelectric-like state should have exhibited a negative capacitance effect without permanent polarization switching if no other adverse effects are involved. However, experiments showed typical ferroelectric-like hysteresis loops where the coercive voltage increased with the increasing AO thickness, which could be explained by the carrier injection through the thin AO layer and trapping of the carriers at the AO/PZT interface. The fitting of the experimental P-V loops using the thermodynamic model considering the depolarization energy effect showed that trapped charge density was ∼±0.1 Cm{sup −2} and critical electric field at the Pt electrode/AO interface, at which the carrier transport occurs, was ∼±10 MV/cm irrespective of the AO thickness. Energy band model at each electrostatic state along the P-V loop was provided to elucidate correlation between macroscopic polarization and internal charge state of the stacked films.

  10. Interfacial insertion of a poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) layer between the poly(3-hexyl thiophene) semiconductor and cross-linked poly(vinyl alcohol) insulator layer in organic field-effect transistors

    NASA Astrophysics Data System (ADS)

    Cruz-Cruz, Isidro; Tavares, Ana C. B.; Reyes-Reyes, Marisol; López-Sandoval, Román; Hümmelgen, Ivo A.

    2014-02-01

    The role of a thin layer of conductive poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT : PSS), inserted between the gate dielectric and the active layer in poly(3-hexylthiophene)-based transistors was investigated. The devices were fabricated in the bottom-gate top-contact geometry by using cross-linked poly(vinyl alcohol) as the dielectric, whereas the PEDOT : PSS layer was prepared by using an aged aqueous dispersion with addition of different amounts of dimethyl sulfoxide (DMSO) as a secondary dopant. Under these conditions, both a significant reduction in the number of electrically active traps at the interface with the semiconductor and an improvement in the field-effect mobility were obtained, whereas the low power consumption was preserved. The threshold voltage was also displaced by approximately -1 V.

  11. Oxidation-resistant interfacial coatings for fiber-reinforced ceramic composites

    SciTech Connect

    Lara-Curzio, Edgar; More, Karren L.; Lee, Woo Y.

    1999-04-22

    A ceramic-matrix composite having a multilayered interfacial coating adapted to protect the reinforcing fibers from long-term oxidation, while allowing these to bridge the wake of advancing cracks in the matrix, is provided by selectively mismatching materials within adjacent layers of the interfacial coating, the materials having different coefficients of thermal expansion so that a low toughness interface region is created to promote crack deflection either within an interior layer of the mismatched interfacial coating or between adjacent layers of the mismatched interfacial coating.

  12. Interfacial engineering of microstructured materials

    NASA Astrophysics Data System (ADS)

    Poda, Aimee

    The tribological behavior of octadecyltrichlorosilane self assembled monolayers (OTS-SAMs) has been successfully exploited to reduce energy losses and to produce adequate adhesion barrier properties on many MEMS surfaces. Unfortunately, performance discrepancies are reported in the literature between films produced on smooth surfaces as compared to typical MEMS surfaces maintaining topographical roughness. Rational explanations in terms of reproducibility issues, production considerations, and the scale of measurement technique have been introduced to account for some of the variation. The tribological phenomena at the micro-scale are complicated by the fact that rather than inertial effects, the forces associated with the surface become dominant factors influencing the mechanical behavior of contacting components. In MEMS, real mechanical contacts typically consist of a few nanometer scale asperities. Furthermore, various surface topographies exist for MEMS device fabrication and their corresponding asperity profiles can vary drastically based on the production process. This dissertation presents research focusing on the influence of topographical asperities on OTS film properties of relevance for efficient tribological improvement. A fundamental approach has been taken to carefully examine the factors that contribute to high quality film formation, specifically formation temperature and the role of interfacial water layer associated with the sample surface. As evidenced on smooth surfaces, the characteristics for successful tribological performance of OTS films are strongly dependent on the lateral packing density and molecular orientation of the monolayer. Limited information is available on how monolayers associate on topographical asperities and whether these topographical asperities influence the interfacial reactivity of MEMS surfaces. A silica film produced from a low temperature, vapor-phase hydrolysis of tetrachlorosilane with a tunable topography is

  13. Investigation of GaInAs strain reducing layer combined with InAs quantum dots embedded in Ga(In)As subcell of triple junction GaInP/Ga(In)As/Ge solar cell.

    PubMed

    Li, Senlin; Bi, Jingfeng; Li, Mingyang; Yang, Meijia; Song, Minghui; Liu, Guanzhou; Xiong, Weiping; Li, Yang; Fang, Yanyan; Chen, Changqing; Lin, Guijiang; Chen, Wenjun; Wu, Chaoyu; Wang, Duxiang

    2015-01-01

    The InAs/GaAs quantum dots structure embedded in GaInP/Ga(In)As/Ge triple junction solar cell with and without Ga0.90In0.10As strain reducing layer was investigated. Conversion efficiency of 33.91% at 1,000 suns AM 1.5D with Ga0.90In0.10As strain reducing layer was demonstrated. A 1.19% improvement of the conversion efficiency was obtained via inserting the Ga0.90In0.10As strain reducing layer. The main contribution of this improvement was from the increase of the short-circuit current, which is caused by the reduction of the Shockley-Read-Hall recombination centers. Consequently, there was a decrease in open circuit voltage due to the lower thermal activation energy of confined carriers in Ga0.9In0.1As than GaAs and a reduction in the effective band gap of quantum dots. PMID:25852406

  14. Rheology of interfacial protein-polysaccharide composites

    NASA Astrophysics Data System (ADS)

    Fischer, P.

    2013-05-01

    The morphology and mechanical properties of protein adsorption layers can significantly be altered by the presence of surfactants, lipids, particles, other proteins, and polysaccharides. In food emulsions, polysaccharides are primarily considered as bulk thickener but can under appropriate environmental conditions stabilize or destabilize the protein adsorption layer and, thus, the entire emulsion system. Despite their ubiquitous usage as stabilization agent, relatively few investigations focus on the interfacial rheology of composite protein/polysaccharide adsorption layers. The manuscript provides a brief review on both main stabilization mechanisms, thermodynamic phase separation and electrostatic interaction and discusses the rheological response in light of the environmental conditions such as ionic strength and pH.

  15. Emulsions for interfacial filtration.

    SciTech Connect

    Grillet, Anne Mary; Bourdon, Christopher Jay; Souza, Caroline Ann; Welk, Margaret Ellen; Hartenberger, Joel David; Brooks, Carlton, F.

    2006-11-01

    We have investigated a novel emulsion interfacial filter that is applicable for a wide range of materials, from nano-particles to cells and bacteria. This technology uses the interface between the two immiscible phases as the active surface area for adsorption of targeted materials. We showed that emulsion interfaces can effectively collect and trap materials from aqueous solution. We tested two aqueous systems, a bovine serum albumin (BSA) solution and coal bed methane produced water (CBMPW). Using a pendant drop technique to monitor the interfacial tension, we demonstrated that materials in both samples were adsorbed to the liquid-liquid interface, and did not readily desorb. A prototype system was built to test the emulsion interfacial filter concept. For the BSA system, a protein assay showed a progressive decrease in the residual BSA concentration as the sample was processed. Based on the initial prototype operation, we propose an improved system design.

  16. TiO2 quantum dots as superb compact block layers for high-performance CH3NH3PbI3 perovskite solar cells with an efficiency of 16.97%

    NASA Astrophysics Data System (ADS)

    Tu, Yongguang; Wu, Jihuai; Zheng, Min; Huo, Jinghao; Zhou, Pei; Lan, Zhang; Lin, Jianming; Huang, Miaoliang

    2015-12-01

    A compact TiO2 layer is crucial to achieve high-efficiency perovskite solar cells. In this study, we developed a facile, low-cost and efficient method to fabricate a pinhole-free and ultrathin blocking layer based on highly crystallized TiO2 quantum dots (QDs) with an average diameter of 3.6 nm. The surface morphology of the blocking layer and the photoelectric performance of the perovskite solar cells were investigated by spin-coating with three different materials: colloidal TiO2 QDs, titanium precursor solution, and aqueous TiCl4. Among these three treatments, the perovskite solar cell based on the TiO2 QD compact layer offered the highest power conversion efficiency (PCE) of 16.97% with a photocurrent density of 22.48 mA cm-2, a photovoltage of 1.063 V and a fill factor of 0.71. The enhancement of PCE mainly stems from the small series resistance and the large shunt resistance of the TiO2 QD layer.A compact TiO2 layer is crucial to achieve high-efficiency perovskite solar cells. In this study, we developed a facile, low-cost and efficient method to fabricate a pinhole-free and ultrathin blocking layer based on highly crystallized TiO2 quantum dots (QDs) with an average diameter of 3.6 nm. The surface morphology of the blocking layer and the photoelectric performance of the perovskite solar cells were investigated by spin-coating with three different materials: colloidal TiO2 QDs, titanium precursor solution, and aqueous TiCl4. Among these three treatments, the perovskite solar cell based on the TiO2 QD compact layer offered the highest power conversion efficiency (PCE) of 16.97% with a photocurrent density of 22.48 mA cm-2, a photovoltage of 1.063 V and a fill factor of 0.71. The enhancement of PCE mainly stems from the small series resistance and the large shunt resistance of the TiO2 QD layer. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05563f

  17. Increasing optical density of single-layer multi-polymer bulk-heterojunction OPVs using CdSe(ZnS) core(shell) quantum dots

    NASA Astrophysics Data System (ADS)

    Bump, Buddy J.; Olson, Grant T.; Savage, Richard; Echols, Robert S.

    2014-10-01

    Photovoltaic technology has powerful implications from commercial and national security standpoints. Due to the high material cost of silicon solar devices, inexpensive and lightweight polymer based solar is desirable to meet the demand for decentralized electrical power production in traditionally "off-grid" areas. Using a blend of Poly(3-hexylthiophene- 2,5-diyl) (P3HT), Phenyl-C61-butyric acid methyl ester (PCBM), and the low band-gap polymer Poly[2,6-(4,4-bis-(2- ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), we have fabricated devices with a wide spectral response and 3% power conversion efficiency in AM 1.5 conditions. Due to low absorptivity in the peak of the solar spectra (500nm), we have blended this previous polymer system with CdSe(ZnS) core (shell) quantum dots to improve absorption, and thus power conversion efficiencies. Devices were prepared with quantum dots having a peak absorbance at 560nm and an emission wavelength of 577nm, with device loading ranging from 0% to 2.7% by weight. The relationship between quantum dot concentration and device performance is discussed, along with the impact of quantum dot concentration on thermal resistance to morphology changes.

  18. Organic electrophosphorescence device having interfacial layers

    DOEpatents

    Choulis, Stelios A.; Mathai, Mathew; Choong, Vi-En; So, Franky

    2010-08-10

    Techniques are described for forming an organic light emitting diode device with improved device efficiency. Materials having at least one energy level that is similar to those of a phosphorescent light emitting material in the diode are incorporated into the device to directly inject holes or electrons to the light emitting material.

  19. Probing Interfacial Water on Nanodiamonds in Colloidal Dispersion.

    PubMed

    Petit, Tristan; Yuzawa, Hayato; Nagasaka, Masanari; Yamanoi, Ryoko; Osawa, Eiji; Kosugi, Nobuhiro; Aziz, Emad F

    2015-08-01

    The structure of interfacial water layers around nanoparticles dispersed in an aqueous environment may have a significant impact on their reactivity and on their interaction with biological species. Using transmission soft X-ray absorption spectroscopy in liquid, we demonstrate that the unoccupied electronic states of oxygen atoms from water molecules in aqueous colloidal dispersions of nanodiamonds have a different signature than bulk water. X-ray absorption spectroscopy can thus probe interfacial water molecules in colloidal dispersions. The impacts of nanodiamond surface chemistry and concentration on interfacial water electronic signature are discussed. PMID:26267179

  20. Interfacial bonding stability

    NASA Technical Reports Server (NTRS)

    Boerio, J.

    1984-01-01

    Interfacial bonding stability by in situ ellipsometry was investigated. It is found that: (1) gamma MPS is an effective primer for bonding ethylene vinyl acetate (EVA) to aluminum; (2) ellipsometry is an effective in situ technique for monitoring the stability of polymer/metal interfaces; (3) the aluminized back surface of silicon wafers contain significant amounts of silicon and may have glass like properties.

  1. Molecular dynamics studies of interfacial water at the alumina surface.

    SciTech Connect

    Argyris, Dr. Dimitrios; Ho, Thomas; Cole, David

    2011-01-01

    Interfacial water properties at the alumina surface were investigated via all-atom equilibrium molecular dynamics simulations at ambient temperature. Al-terminated and OH-terminated alumina surfaces were considered to assess the structural and dynamic behavior of the first few hydration layers in contact with the substrates. Density profiles suggest water layering up to {approx}10 {angstrom} from the solid substrate. Planar density distribution data indicate that water molecules in the first interfacial layer are organized in well-defined patterns dictated by the atomic terminations of the alumina surface. Interfacial water exhibits preferential orientation and delayed dynamics compared to bulk water. Water exhibits bulk-like behavior at distances greater than {approx}10 {angstrom} from the substrate. The formation of an extended hydrogen bond network within the first few hydration layers illustrates the significance of water?water interactions on the structural properties at the interface.

  2. Photoconductivity of Er-doped InAs quantum dots embedded in strain-relaxed InGaAs layers with 1.5 µm cw and pulse excitation

    NASA Astrophysics Data System (ADS)

    Murakumo, Keisuke; Yamaoka, Yuya; Kumagai, Naoto; Kitada, Takahiro; Isu, Toshiro

    2016-04-01

    We fabricated a photoconductive antenna structure utilizing Er-doped InAs quantum dot layers embedded in strain-relaxed In0.35Ga0.65As layers on a GaAs substrate. Mesa-shaped electrodes for the antenna structure were formed by photolithography and wet etching in order to suppress its dark current. We measured the photocurrent with the excitation of ∼1.5 µm cw and femtosecond pulse lasers. Compared with the dark current, the photocurrent was clearly observed under both cw and pulse excitation conditions and almost linearly increased with increasing excitation power in a wide range of magnitudes from 10 W/cm2 to 10 MW/cm2 order.

  3. Investigation of single-layer/multilayer self-assembled InAs quantum dots on GaAs{sub 1-x}Sb{sub x}/GaAs composite substrates

    SciTech Connect

    Tang, Dinghao; Kim, Yeongho Faleev, Nikolai; Honsberg, Christiana B.; Smith, David J.

    2015-09-07

    The structure-performance properties of single-layered and multi-layered InAs/GaAs{sub 1−x}Sb{sub x} quantum dot (QD) system, grown by molecular beam epitaxy on GaAs (001) substrates, have been investigated as a function of Sb concentration. Electron microscopy observations showed no significant crystalline defects for the single-layered InAs QDs (Sb 20%). X-ray diffraction analysis revealed that the increase of Sb concentration from 7.3% to 10.2% for the multi-layered QDs increased the strain relaxation from 0% to ∼23% and the dislocation density of GaAsSb layers went up to 3.6 × 10{sup 9 }cm{sup −2}. The peak energy of QD luminescence was red-shifted with increasing Sb concentration due to reduced strain inside QDs. Moreover, the carrier lifetime of the QDs was highly improved from 1.7 to 36.7 ns due to weak hole confinement as the Sb concentration was increased from 7.3% to 10.2%. These structures should be highly promising as the basis for photovoltaic solar-cell applications. Finally, the increased Sb concentration increased the thermal activation energy of electrons confined in the QDs from 163.7 to 206.8 meV, which was indicative of the improved thermal stability with Sb concentration.

  4. TiO2 quantum dots as superb compact block layers for high-performance CH3NH3PbI3 perovskite solar cells with an efficiency of 16.97.

    PubMed

    Tu, Yongguang; Wu, Jihuai; Zheng, Min; Huo, Jinghao; Zhou, Pei; Lan, Zhang; Lin, Jianming; Huang, Miaoliang

    2015-12-28

    A compact TiO(2) layer is crucial to achieve high-efficiency perovskite solar cells. In this study, we developed a facile, low-cost and efficient method to fabricate a pinhole-free and ultrathin blocking layer based on highly crystallized TiO(2) quantum dots (QDs) with an average diameter of 3.6 nm. The surface morphology of the blocking layer and the photoelectric performance of the perovskite solar cells were investigated by spin-coating with three different materials: colloidal TiO(2) QDs, titanium precursor solution, and aqueous TiCl(4). Among these three treatments, the perovskite solar cell based on the TiO(2) QD compact layer offered the highest power conversion efficiency (PCE) of 16.97% with a photocurrent density of 22.48 mA cm(-2), a photovoltage of 1.063 V and a fill factor of 0.71. The enhancement of PCE mainly stems from the small series resistance and the large shunt resistance of the TiO(2) QD layer. PMID:26585357

  5. Nb and Ta layer doping effects on the interfacial energetics and electronic properties of LaAlO3/SrTiO3 heterostructure: first-principles analysis.

    PubMed

    Nazir, Safdar; Behtash, Maziar; Cheng, Jianli; Luo, Jian; Yang, Kesong

    2016-01-28

    The two-dimensional electron gas (2DEG) formed at the n-type (LaO)(+1)/(TiO2)(0) interface in the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) has emerged as a prominent research area because of its great potential for nanoelectronic applications. Due to its practical implementation in devices, desired physical properties such as high charge carrier density and mobility are vital. In this respect, 4d and 5d transition metal doping near the interfacial region is expected to tailor electronic properties of the LAO/STO HS system effectively. Herein, we studied Nb and Ta-doping effects on the energetics, electronic structure, interfacial charge carrier density, magnetic moment, and the charge confinements of the 2DEG at the n-type (LaO)(+1)/(TiO2)(0) interface of LAO/STO HS using first-principles density functional theory calculations. We found that the substitutional doping of Nb(Ta) at Ti [Nb(Ta)@Ti] and Al [Nb(Ta)@Al] sites is energetically more favorable than that at La [Nb(Ta)@La] and Sr [Nb(Ta)@Sr] sites, and under appropriate thermodynamic conditions, the changes in the interfacial energy of HS systems upon Nb(Ta)@Ti and Nb(Ta)@Al doping are negative, implying that the formation of these structures is energetically favored. Our calculations also showed that Nb(Ta)@Ti and Nb(Ta)@Al doping significantly improve the interfacial charge carrier density with respect to that of the undoped system, which is because the Nb(Ta) dopant introduces excess free electrons into the system, and these free electrons reside mainly on the Nb(Ta) ions and interfacial Ti ions. Hence, along with the Ti 3d orbitals, the Nb 4d and Ta 5d orbitals also contribute to the interfacial metallic states; accordingly, the magnetic moments on the interfacial Ti ions increase significantly. As expected, the Nb@Al and Ta@Al doped LAO/STO HS systems show higher interfacial charge carrier density than the undoped and other doped systems. In contrast, Nb@Ti and Ta@Ti doped systems may

  6. Improved performance of CuInS2 quantum dot-sensitized solar cells based on a multilayered architecture.

    PubMed

    Chang, Jia-Yaw; Lin, Jie-Mo; Su, Li-Fong; Chang, Chia-Fu

    2013-09-11

    This article describes a CuInS2 quantum dot (QD)-sensitized solar cell (QDSSC) with a multilayered architecture and a cascaded energy-gap structure fabricated using a successive ionic-layer adsorption and reaction process. We initially used different metal chalcogenides as interfacial buffer layers to improve unmatched band alignments between the TiO2 and CuInS2 QD sensitizers. In this design, the photovoltaic performance, in terms of the short-circuit current density (JSC), open-circuit voltage (VOC), fill factor (FF), and power conversion efficiency (PCE), was significantly improved. Both JSC and VOC were improved in CuInS2-based QDSSCs in the presence of interfacial buffer layers because of proper band alignment across the heterointerface and the negative band edge movement of TiO2. The PCE of CuInS2-based QDSSCs containing In2Se3 interfacial buffer layers was 1.35%, with JSC=5.83 mA/cm2, VOC=595 mV, and FF=39.0%. We also examined the use of alternative CdS and CdSe hybrid-sensitized layers, which were sequentially deposited onto the In2Se3/CuInS2 configuration for creating favorable cascaded energy-gap structures. Both JSC (11.3 mA cm(-2)) and FF (47.3%) for the CuInS2/CdSe hybrid-sensitized cells were higher than those for CuInS2-based cells (JSC=5.83 mA cm(-2) and FF=39.0%). In addition, the hybrid-sensitized cells had PCEs that were 1.3 times those of cells containing identically pretreated In2Se3 interfacial buffer layers. Additionally, we determined that ZnSe served as a good passivation layer on the surface of CuInS2/CdSe hybrid-sensitized QDs, prevented current leakage from the QDs to electrolytes, and lowered interfacial charge recombination. Under simulated illumination (AM 1.5, 100 mW cm(-2)), multilayered QDSSCs with distinct architectures delivered a maximum external quantum efficiency of 80% at 500 nm and a maximum PCE of 4.55%, approximately 9 times that of QDSSCs fabricated with pristine CuInS2. PMID:23937511

  7. Interfacial behavior of asphaltenes.

    PubMed

    Langevin, Dominique; Argillier, Jean-François

    2016-07-01

    We review the existing literature on asphaltenes at various types of interfaces: oil-water, air-water, gas-oil and solid-liquid, with more emphasis on the oil-water interfaces. We address the role of asphaltene aggregation, recently clarified for asphaltenes in bulk by the Yen-Mullins model. We discuss the questions of adsorption reversibility and interfacial rheology, especially in connection with emulsion stability. PMID:26498501

  8. A new method to disperse CdS quantum dot-sensitized TiO2 nanotube arrays into P3HT:PCBM layer for the improvement of efficiency of inverted polymer solar cells

    PubMed Central

    2014-01-01

    We report that the efficiency of ITO/nc-TiO2/P3HT:PCBM/MoO3/Ag inverted polymer solar cells (PSCs) can be improved by dispersing CdS quantum dot (QD)-sensitized TiO2 nanotube arrays (TNTs) in poly (3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) layer. The CdS QDs are deposited on the TNTs by a chemical bath deposition method. The experimental results show that the CdS QD-sensitized TNTs (CdS/TNTs) do not only increase the light absorption of the P3HT:PCBM layer but also reduce the charge recombination in the P3HT:PCBM layer. The dependence of device performances on cycles of CdS deposition on the TNTs was investigated. A high power conversion efficiency (PCE) of 3.52% was achieved for the inverted PSCs with 20 cyclic depositions of CdS on TNTs, which showed a 34% increase compared to the ITO/nc-TiO2/P3HT:PCBM/MoO3/Ag device without the CdS/TNTs. The improved efficiency is attributed to the improved light absorbance and the reduced charge recombination in the active layer. PMID:24936158

  9. Scalable quantum computer architecture with coupled donor-quantum dot qubits

    DOEpatents

    Schenkel, Thomas; Lo, Cheuk Chi; Weis, Christoph; Lyon, Stephen; Tyryshkin, Alexei; Bokor, Jeffrey

    2014-08-26

    A quantum bit computing architecture includes a plurality of single spin memory donor atoms embedded in a semiconductor layer, a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, wherein a first voltage applied across at least one pair of the aligned quantum dot and donor atom controls a donor-quantum dot coupling. A method of performing quantum computing in a scalable architecture quantum computing apparatus includes arranging a pattern of single spin memory donor atoms in a semiconductor layer, forming a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, applying a first voltage across at least one aligned pair of a quantum dot and donor atom to control a donor-quantum dot coupling, and applying a second voltage between one or more quantum dots to control a Heisenberg exchange J coupling between quantum dots and to cause transport of a single spin polarized electron between quantum dots.

  10. Quantum-dot-in-perovskite solids.

    PubMed

    Ning, Zhijun; Gong, Xiwen; Comin, Riccardo; Walters, Grant; Fan, Fengjia; Voznyy, Oleksandr; Yassitepe, Emre; Buin, Andrei; Hoogland, Sjoerd; Sargent, Edward H

    2015-07-16

    Heteroepitaxy-atomically aligned growth of a crystalline film atop a different crystalline substrate-is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned 'dots-in-a-matrix' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics. PMID:26178963

  11. Quantum-dot-in-perovskite solids

    NASA Astrophysics Data System (ADS)

    Ning, Zhijun; Gong, Xiwen; Comin, Riccardo; Walters, Grant; Fan, Fengjia; Voznyy, Oleksandr; Yassitepe, Emre; Buin, Andrei; Hoogland, Sjoerd; Sargent, Edward H.

    2015-07-01

    Heteroepitaxy--atomically aligned growth of a crystalline film atop a different crystalline substrate--is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned `dots-in-a-matrix' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

  12. Design principles of interfacial thermal conductance

    NASA Astrophysics Data System (ADS)

    Polanco, Carlos; Rastgarkafshgarkolaei, Rouzbeh; Zhang, Jingjie; Le, Nam; Norris, Pamela; Ghosh, Avik

    We explore fundamental principles to design the thermal conductance across solid interfaces by changing the composition and disorder of an intermediate matching layer. In absence of phonon-phonon interactions, the layer addition involves two competing effects that influence the conductance. The layer can act as an impedance matching 'bridge' to increase the mode-averaged phonon transmission. However, it also reduces the relevant modes that conserve their momenta transverse to the interface, so that the net result depends on features such as the overlap of conserving modes and the dispersivity of the transverse subbands. Moving into the interacting anharmonic regime, we find that the added layer aids conductance when the decreased resistances at the contact-layer boundaries compensate for the layer resistance. In fact, we show that the maximum conductance corresponds to an exact matching of the two separate contact-layer resistances. For instance, if we vary just the atomic mass across layers, then maximum conductance happens when the intervening layer mass is the geometric mean of the contact masses. We conjecture that the best interfacial layer is one that is compositionally graded into many geometric means - in other words, an exponential variation in thermal impedance.

  13. High-Throughput Screening and Optimization of Binary Quantum Dots Cosensitized Solar Cell.

    PubMed

    Yuan, Ding; Xiao, Lina; Luo, Jianheng; Luo, Yanhong; Meng, Qingbo; Mao, Bing-Wei; Zhan, Dongping

    2016-07-20

    Quantum dots (QDs) are considered as the alternative of dye sensitizers for solar cells. However, interfacial construction and evaluation of photocatalytic nanomaterials still remains challenge through the conventional methodology involving demo devices. We propose here a high-throughput screening and optimizing method based on combinatorial chemistry and scanning electrochemical microscopy (SECM). A homogeneous TiO2 catalyst layer is coated on a FTO substrate, which is then covered by a dark mask to expose the photocatalyst array. On each photocatalyst spot, different successive ionic layer adsorption and reaction (SILAR) processes are performed by a programmed solution dispenser to load the binary PbxCd1-xS QDs sensitizers. An optical fiber is employed as the scanning tip of SECM, and the photocatalytic current is recorded during the imaging experiment, through which the optimized technical parameters are figured out. To verify the validity of the combinatorial SECM imaging results, the controlled trials are performed with the corresponding photovoltaic demo devices. The harmonious accordance proved that the methodology based on combinatorial chemistry and SECM is valuable for the interfacial construction, high-throughput screening, and optimization of QDSSCs. Furthermore, the PbxCd1-xS/CdS QDs cosensitized solar cell optimized by SECM achieves a short circuit current density of 24.47 mA/cm(2), an open circuit potential of 421 mV, a fill factor of 0.52, and a photovoltaic conversion efficiency of 5.33%. PMID:27355523

  14. Estimating interfacial thermal conductivity in metamaterials through heat flux mapping

    SciTech Connect

    Canbazoglu, Fatih M.; Vemuri, Krishna P.; Bandaru, Prabhakar R.

    2015-04-06

    The variability of the thickness as well as the thermal conductivity of interfaces in composites may significantly influence thermal transport characteristics and the notion of a metamaterial as an effective medium. The consequent modulations of the heat flux passage are analytically and experimentally examined through a non-contact methodology using radiative imaging, on a model anisotropic thermal metamaterial. It was indicated that a lower Al layer/silver interfacial epoxy ratio of ∼25 compared to that of a Al layer/alumina interfacial epoxy (of ∼39) contributes to a smaller deviation of the heat flux bending angle.

  15. Interfacial phase-change memory.

    PubMed

    Simpson, R E; Fons, P; Kolobov, A V; Fukaya, T; Krbal, M; Yagi, T; Tominaga, J

    2011-08-01

    Phase-change memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating or some other excitation process. For example, switching the composite Ge(2)Sb(2)Te(5) (GST) alloy from its covalently bonded amorphous phase to its resonantly bonded metastable cubic crystalline phase decreases the resistivity by three orders of magnitude, and also increases reflectivity across the visible spectrum. Moreover, phase-change memory based on GST is scalable, and is therefore a candidate to replace Flash memory for non-volatile data storage applications. The energy needed to switch between the two phases depends on the intrinsic properties of the phase-change material and the device architecture; this energy is usually supplied by laser or electrical pulses. The switching energy for GST can be reduced by limiting the movement of the atoms to a single dimension, thus substantially reducing the entropic losses associated with the phase-change process. In particular, aligning the c-axis of a hexagonal Sb(2)Te(3) layer and the 〈111〉 direction of a cubic GeTe layer in a superlattice structure creates a material in which Ge atoms can switch between octahedral sites and lower-coordination sites at the interface of the superlattice layers. Here we demonstrate GeTe/Sb(2)Te(3) interfacial phase-change memory (IPCM) data storage devices with reduced switching energies, improved write-erase cycle lifetimes and faster switching speeds. PMID:21725305

  16. ‘Green’-synthesized near-infrared PbS quantum dots with silica-PEG dual-layer coating: ultrastable and biocompatible optical probes for in vivo animal imaging

    NASA Astrophysics Data System (ADS)

    Wang, D.; Qian, J.; Cai, F.; He, S.; Han, S.; Mu, Y.

    2012-06-01

    In this paper, PbS semiconductor quantum dots (QDs) with near-infrared (NIR) photoluminescence were synthesized in oleic acid and paraffin liquid mixture by using an easily handled and ‘green’ approach. Surface functionalization of the QDs was accomplished with a silica and polyethylene glycol (PEG) phospholipid dual-layer coating and the excellent chemical stability of the nanoparticles is demonstrated. We then successfully applied the ultrastable PbS QDs to in vivo sentinel lymph node (SLN) mapping of mice. Histological analyses were also carried out to ensure that the intravenously injected nanoparticles did not produce any toxicity to the organism of mice. These experimental results suggested that our ultrastable NIR PbS QDs can serve as biocompatible and efficient probes for in vivo optical bioimaging and has great potentials for disease diagnosis and clinical therapies in the future.

  17. Interfacial solvation thermodynamics.

    PubMed

    Ben-Amotz, Dor

    2016-10-19

    Previous studies have reached conflicting conclusions regarding the interplay of cavity formation, polarizability, desolvation, and surface capillary waves in driving the interfacial adsorptions of ions and molecules at air-water interfaces. Here we revisit these questions by combining exact potential distribution results with linear response theory and other physically motivated approximations. The results highlight both exact and approximate compensation relations pertaining to direct (solute-solvent) and indirect (solvent-solvent) contributions to adsorption thermodynamics, of relevance to solvation at air-water interfaces, as well as a broader class of processes linked to the mean force potential between ions, molecules, nanoparticles, proteins, and biological assemblies. PMID:27545849

  18. Role of InxGa1-xAs Layer Composition in Modifying Strain Fields and Carrier Confinement Potentials in a Close-stacked InAs/GaAs Quantum Dot System

    NASA Astrophysics Data System (ADS)

    Lee, Woong; Yoo, Yo-Han; Shin, Hyunho; Myoung, Jae-Min

    2005-05-01

    Role of the composition of InxGa1-xAs strain-relief layer (SRL) in controlling the strain fields and consequent modification of band structures in a close-stacked multi-layer InAs/GaAs quantum dot (QD) system was investigated within the framework of continuum elasticity and model solid theory. It was predicted that strains in the QDs are significantly relieved in proportion to the In concentration in the InxGa1-xAs SRLs between InAs QD and GaAs cap layer. The relaxation of strains caused substantial shift of the conduction band edge in the QDs mainly by the relief of hydrostatic strain component resulting in narrower bandgap within the QDs with increasing In concentration. It is interpreted that such strain relaxation and subsequent band structure modifications are responsible for the experimentally observed redshift of photo-luminescence (PL) spectra elsewhere. Therefore, together with existing experimental work, it is confirmed that conduction band edges of QD systems can be tailored by the control of the SRL composition allowing more flexibility in bandgap engineering.

  19. Effect of nanoscale patterned interfacial roughness on interfacial toughness.

    SciTech Connect

    Zimmerman, Jonathan A.; Moody, Neville Reid; Mook, William M.; Kennedy, Marian S.; Bahr, David F.; Zhou, Xiao Wang; Reedy, Earl David, Jr.

    2007-09-01

    The performance and the reliability of many devices are controlled by interfaces between thin films. In this study we investigated the use of patterned, nanoscale interfacial roughness as a way to increase the apparent interfacial toughness of brittle, thin-film material systems. The experimental portion of the study measured the interfacial toughness of a number of interfaces with nanoscale roughness. This included a silicon interface with a rectangular-toothed pattern of 60-nm wide by 90-nm deep channels fabricated using nanoimprint lithography techniques. Detailed finite element simulations were used to investigate the nature of interfacial crack growth when the interface is patterned. These simulations examined how geometric and material parameter choices affect the apparent toughness. Atomistic simulations were also performed with the aim of identifying possible modifications to the interfacial separation models currently used in nanoscale, finite element fracture analyses. The fundamental nature of atomistic traction separation for mixed mode loadings was investigated.

  20. A direct investigation of photocharge transfer across monomolecular layer between C60 and CdS quantum dots by photoassisted conductive atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Jiang, Xiaohong; Liu, He; Zhang, Xingtang; Cheng, Gang; Wang, Shujie; Du, Zuliang

    2016-04-01

    The composite assembly of C60 and CdS Quantum Dots (QDs) on ITO substrate was prepared by Langmuir-Blodgett (LB) technique using arachic acid (AA), stearic acid (SA) and octadecanyl amine (OA) as additives. Photoassisted conductive atomic force microscopy was used to make point contact current-voltage (I-V) measurements on both the CdS QDs and the composite assembly of C60/CdS. The result make it clear that the CdS, C60/CdS assemblies deposited on ITO substrate showed linear characteristics and the current increased largely under illumination comparing with that in the dark. The coherent, nonresonant tunneling mechanism was used to explain the current occurrence. It is considered that the photoinduced carriers CdS QDs tunneled through alkyl chains increased the current rapidly.

  1. Fluorescent carbon dot (C-dot) nanoclusters

    NASA Astrophysics Data System (ADS)

    Wang, Guan; Pan, Xiaoyong; Gu, Liuqun; Ren, Wei; Cheng, Weiren; Kumar, Jatin N.; Liu, Ye

    2014-09-01

    Fluorescent carbon dot (C-dot) nanoclusters composed of C-dot-loaded hollow silica spheres are obtained via the dehydration of mannose, which is adsorbed onto hollow silica spheres or poly(ethylene glycol)-graft-hollow silica spheres (PEG-g-hollow silica). The structure of C-dot nanoclusters are confirmed using 1H NMR, FTIR, TEM and TGA. C-dot nanoclusters show a redshifted fluorescence emission with an increased excitation wavelength. Passivation with PEG diamines improve the quantum yields to ˜2%. Confocal laser scanning microscopy (CLSM) results reflect the fact that C-dot nanoclusters can provide good cytoplasm imaging of live Hep G2 cells and live MCF-7 cells, and the imaging obtained is brighter and more even than those from free C-dots. With their combination of good photostability and low cytotoxicity, C-dot nanoclusters are promising for the production of higher quality bioimaging.

  2. Interfacial insert for electrical connectors

    NASA Technical Reports Server (NTRS)

    Macavay, D.

    1975-01-01

    The development of interfacial inserts for improved electric connectors is discussed. The inserts were manufactured from epoxy resins. The design features of the inserts and the manufacturing equipment are described. The reliability test program is reported. Drawings of the interfacial inserts are provided.

  3. Lateral excitonic switching in vertically stacked quantum dots

    NASA Astrophysics Data System (ADS)

    Jarzynka, Jarosław R.; McDonald, Peter G.; Shumway, John; Galbraith, Ian

    2016-06-01

    We show that the application of a vertical electric field to the Coulomb interacting system in stacked quantum dots leads to a 90° in-plane switching of charge probability distribution in contrast to a single dot, where no such switching exists. Results are obtained using path integral quantum Monte Carlo with realistic dot geometry, alloy composition, and piezo-electric potential profiles. The origin of the switching lies in the strain interactions between the stacked dots hence the need for more than one layer of dots. The lateral polarization and electric field dependence of the radiative lifetimes of the excitonic switch are also discussed.

  4. Surface and interfacial creases in a bilayer tubular soft tissue

    NASA Astrophysics Data System (ADS)

    Razavi, Mir Jalil; Pidaparti, Ramana; Wang, Xianqiao

    2016-08-01

    Surface and interfacial creases induced by biological growth are common types of instability in soft biological tissues. This study focuses on the criteria for the onset of surface and interfacial creases as well as their morphological evolution in a growing bilayer soft tube within a confined environment. Critical growth ratios for triggering surface and interfacial creases are investigated both analytically and numerically. Analytical interpretations provide preliminary insights into critical stretches and growth ratios for the onset of instability and formation of both surface and interfacial creases. However, the analytical approach cannot predict the evolution pattern of the model after instability; therefore nonlinear finite element simulations are carried out to replicate the poststability morphological patterns of the structure. Analytical and computational simulation results demonstrate that the initial geometry, growth ratio, and shear modulus ratio of the layers are the most influential factors to control surface and interfacial crease formation in this soft tubular bilayer. The competition between the stretch ratios in the free and interfacial surfaces is one of the key driving factors to determine the location of the first crease initiation. These findings may provide some fundamental understanding in the growth modeling of tubular biological tissues such as esophagi and airways as well as offering useful clues into normal and pathological functions of these tissues.

  5. More About Measuring Interfacial Tension Between Liquids

    NASA Technical Reports Server (NTRS)

    Rashidnia, Nasser; Balasubramaniam, R.; Del Signore, David M.

    1995-01-01

    Report presents additional discussion of technique for measuring interfacial tension between two immiscible liquids. Technique described in "Measuring Interfacial Tension Between Immiscible Liquids" (LEW-15855).

  6. Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

    NASA Astrophysics Data System (ADS)

    Lai, Wei-Ting; Yang, Kuo-Ching; Liao, Po-Hsiang; George, Tom; Li, Pei-Wen

    2016-02-01

    We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5‑90 nm), the SiO2 thickness (3‑4 nm), and as well the SiGe-shell thickness (2‑15 nm) has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS) devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5) in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge) MOS nanoelectronic and nanophotonic applications.

  7. Interfacial models of nerve fiber cytoskeleton.

    PubMed Central

    Malev, V V; Gromov, D B; Komissarchik YaYu; Brudnaya, M S

    1992-01-01

    A new approach, basing on a resemblance between cytoskeleton structures associated with plasma membranes and interfacial layers of coexisting phases, is proposed. In particular, a lattice model, similar to those of the theory of surface properties of pure liquids and nonelectrolyte solutions (Ono, S., and S. Kondo. 1960. Handbuch der Physik.), has been developed to describe nerve fiber cytoskeleton. The preliminary consideration of the model shows the existence of submembrane cytoskeleton having increased peripheral densities of microtubules (compared with the bulk density) which is in qualitative agreement with the data in literature. Some additional possibilities of the approach proposed are briefly discussed. Images FIGURE 2 FIGURE 3 FIGURE 4 PMID:1420929

  8. Interfacial chemistry and structure in ceramic composites

    SciTech Connect

    Jones, R.H.; Saenz, N.T.; Schilling, C.H.

    1990-09-01

    The interfacial chemistry and structure of ceramic matrix composites (CMCs) play a major role in the properties of these materials. Fiber-matrix interfaces chemistries are vitally important in the fracture strength, fracture toughness, and fracture resistance of ceramic composites because they influence fiber loading and fiber pullout. Elevated-temperature properties are also linked to the interfacial characteristics through the chemical stability of the interface in corrosive environments and the creep/pullout behavior of the interface. Physical properties such as electrical and thermal conductivity are also dependent on the interface. Fiber-matrix interfaces containing a 1-{mu}m-thick multilayered interface with amorphous and graphitic C to a 1-nm-thick SiO{sub 2} layer can result from sintering operations for some composite systems. Fibers coated with C, BN, C/BC/BN, and Si are also used to produce controlled interface chemistries and structures. Growth interfaces within the matrix resulting from processing of CMCs can also be crucial to the behavior of these materials. Evaluation of the interfacial chemistry and structure of CMCs requires the use of a variety of analytical tools, including optical microscopy, scanning electron microscopy, Auger electron spectroscopy, and transmission electron microscopy coupled with energy dispersive x-ray analysis. A review of the interfacial chemistry and structure of SiC whisker- and fiber-reinforced Si{sub 3}N{sub 4} and SiC/SiC materials is presented. Where possible, correlations with fracture properties and high-temperature stability are made. 94 refs., 10 figs.

  9. Transport through graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Güttinger, J.; Molitor, F.; Stampfer, C.; Schnez, S.; Jacobsen, A.; Dröscher, S.; Ihn, T.; Ensslin, K.

    2012-12-01

    We review transport experiments on graphene quantum dots and narrow graphene constrictions. In a quantum dot, electrons are confined in all lateral dimensions, offering the possibility for detailed investigation and controlled manipulation of individual quantum systems. The recently isolated two-dimensional carbon allotrope graphene is an interesting host to study quantum phenomena, due to its novel electronic properties and the expected weak interaction of the electron spin with the material. Graphene quantum dots are fabricated by etching mono-layer flakes into small islands (diameter 60-350 nm) with narrow connections to contacts (width 20-75 nm), serving as tunneling barriers for transport spectroscopy. Electron confinement in graphene quantum dots is observed by measuring Coulomb blockade and transport through excited states, a manifestation of quantum confinement. Measurements in a magnetic field perpendicular to the sample plane allowed to identify the regime with only a few charge carriers in the dot (electron-hole transition), and the crossover to the formation of the graphene specific zero-energy Landau level at high fields. After rotation of the sample into parallel magnetic field orientation, Zeeman spin splitting with a g-factor of g ≈ 2 is measured. The filling sequence of subsequent spin states is similar to what was found in GaAs and related to the non-negligible influence of exchange interactions among the electrons.

  10. Initial stage growth of GexSi1−x layers and Ge quantum dot formation on GexSi1−x surface by MBE

    PubMed Central

    2012-01-01

    Critical thicknesses of two-dimensional to three-dimensional growth in GexSi1−x layers were measured as a function of composition for different growth temperatures. In addition to the (2 × 1) superstructure for a Ge film grown on Si(100), the GexSi1−x layers are characterized by the formation of (2 × n) reconstruction. We measured n for all layers of Ge/GexSi1−x/Ge heterosystem using our software with respect to the video recording of reflection high-energy electron diffraction (RHEED) pattern during growth. The n reaches a minimum value of about 8 for clear Ge layer, whereas for GexSi1−x films, n is increased from 8 to 14. The presence of a thin strained film of the GexSi1−x caused not only the changes in critical thicknesses of the transitions, but also affected the properties of the germanium nanocluster array for the top Ge layer. Based on the RHEED data, the hut-like island form, which has not been previously observed by us between the hut and dome islands, has been detected. Data on the growth of Ge/GexSi1−x/Ge heterostructures with the uniform array of islands in the second layer of the Ge film have been received. PMID:23043796

  11. Mechanobiology of interfacial growth

    NASA Astrophysics Data System (ADS)

    Ciarletta, P.; Preziosi, L.; Maugin, G. A.

    2013-03-01

    A multiscale analysis integrating biomechanics and mechanobiology is today required for deciphering the crosstalk between biochemistry, geometry and elasticity in living materials. In this paper we derive a unified thermomechanical theory coupling growth processes with mass transport phenomena across boundaries and/or material interfaces. Inside a living system made by two contiguous bodies with varying volumes, an interfacial growth mechanism is considered to force fast but continuous variations of the physical fields inside a narrow volume across the material interface. Such a phenomenon is modelled deriving homogenized surface fields on a growing non-material discontinuity, possibly including a singular edge line. A number of balance laws is derived for imposing the conservation of the thermomechanical properties of the biological system. From thermodynamical arguments we find that the normal displacement of the non-material interface is governed by the jump of a new form of material mechanical-energy flux, also involving the kinetic energies and the mass fluxes. Furthermore, the configurational balance indicates that the surface Eshelby tensor is the tangential stress measure driving the material inhomogeneities on the non-material interface. Accordingly, stress-dependent evolution laws for bulk and interfacial growth processes are derived for both volume and surface fields. The proposed thermomechanical theory is finally applied to three biological system models. The first two examples are focused on stress-free growth problems, concerning the morphogenesis of animal horns and of seashells. The third application finally deals with the stress-driven surface evolution of avascular tumours with heterogeneous structures. The results demonstrate that the proposed theory can successfully model those biological systems where growth and mass transport phenomena interact at different length-scales. Coupling biological, mechanical and geometrical factors, the proposed

  12. Some Aspects of Interfacial Phenomena in Steelmaking and Refining

    NASA Astrophysics Data System (ADS)

    Wang, L. J.; Viswanathan, N. N.; Muhmood, L.; Kapilashrami, E.; Seetharaman, S.

    2016-03-01

    Unique experiments were designed to study the surface phenomena in steelmaking reactions. The concept of surface sulfide capacities and an understanding of the surface accumulation of surface-active species, based on experimental results, are presented. In order to understand the flow phenomenon at slag/metal interface, experiments were designed to measure the interfacial velocity of S on the surface of an iron drop immersed in an aluminosilicate slag using the X-ray sessile drop method. The oscillation of the iron drop in the slag due to the change in the surface concentration of sulfur at the slag-metal interface was monitored by X-ray imaging. From the observations, the interfacial velocity of sulfur was evaluated. Similar experiments were performed to measure the interfacial velocity of oxygen at the interface as well as the impact of oxygen potential on the interfacial velocity of sulfur. The interfacial shear viscosity and the dilatational modulus were also evaluated. In a study of the wetting of alumina base by iron drop at constant oxygen pressure under isothermal condition, the contact angle was found to be decreased with the progress of the reaction leading to the formation of hercynite as an intermediate layer creating non-wetting conditions. In the case of silica substrate, an intermediate liquid fayalite layer was formed.

  13. Some Aspects of Interfacial Phenomena in Steelmaking and Refining

    NASA Astrophysics Data System (ADS)

    Wang, L. J.; Viswanathan, N. N.; Muhmood, L.; Kapilashrami, E.; Seetharaman, S.

    2016-08-01

    Unique experiments were designed to study the surface phenomena in steelmaking reactions. The concept of surface sulfide capacities and an understanding of the surface accumulation of surface-active species, based on experimental results, are presented. In order to understand the flow phenomenon at slag/metal interface, experiments were designed to measure the interfacial velocity of S on the surface of an iron drop immersed in an aluminosilicate slag using the X-ray sessile drop method. The oscillation of the iron drop in the slag due to the change in the surface concentration of sulfur at the slag-metal interface was monitored by X-ray imaging. From the observations, the interfacial velocity of sulfur was evaluated. Similar experiments were performed to measure the interfacial velocity of oxygen at the interface as well as the impact of oxygen potential on the interfacial velocity of sulfur. The interfacial shear viscosity and the dilatational modulus were also evaluated. In a study of the wetting of alumina base by iron drop at constant oxygen pressure under isothermal condition, the contact angle was found to be decreased with the progress of the reaction leading to the formation of hercynite as an intermediate layer creating non-wetting conditions. In the case of silica substrate, an intermediate liquid fayalite layer was formed.

  14. Annealing-induced change in quantum dot chain formation mechanism

    NASA Astrophysics Data System (ADS)

    Park, Tyler D.; Colton, John S.; Farrer, Jeffrey K.; Yang, Haeyeon; Kim, Dong Jun

    2014-12-01

    Self-assembled InGaAs quantum dot chains were grown using a modified Stranski-Krastanov method in which the InGaAs layer is deposited under a low growth temperature and high arsenic overpressure, which suppresses the formation of dots until a later annealing process. The dots are capped with a 100 nm GaAs layer. Three samples, having three different annealing temperatures of 460°C, 480°C, and 500°C, were studied by transmission electron microscopy. Results indicate two distinct types of dot formation processes: dots in the 460°C and 480°C samples form from platelet precursors in a one-to-one ratio whereas the dots in the sample annealed at 500°C form through the strain-driven self-assembly process, and then grow larger via an additional Ostwald ripening process whereby dots grow into larger dots at the expense of smaller seed islands. There are consequently significant morphological differences between the two types of dots, which explain many of the previously-reported differences in optical properties. Moreover, we also report evidence of indium segregation within the dots, with little or no indium intermixing between the dots and the surrounding GaAs barrier.

  15. Annealing-induced change in quantum dot chain formation mechanism

    SciTech Connect

    Park, Tyler D.; Colton, John S.; Farrer, Jeffrey K.; Yang, Haeyeon; Kim, Dong Jun

    2014-12-15

    Self-assembled InGaAs quantum dot chains were grown using a modified Stranski-Krastanov method in which the InGaAs layer is deposited under a low growth temperature and high arsenic overpressure, which suppresses the formation of dots until a later annealing process. The dots are capped with a 100 nm GaAs layer. Three samples, having three different annealing temperatures of 460°C, 480°C, and 500°C, were studied by transmission electron microscopy. Results indicate two distinct types of dot formation processes: dots in the 460°C and 480°C samples form from platelet precursors in a one-to-one ratio whereas the dots in the sample annealed at 500°C form through the strain-driven self-assembly process, and then grow larger via an additional Ostwald ripening process whereby dots grow into larger dots at the expense of smaller seed islands. There are consequently significant morphological differences between the two types of dots, which explain many of the previously-reported differences in optical properties. Moreover, we also report evidence of indium segregation within the dots, with little or no indium intermixing between the dots and the surrounding GaAs barrier.

  16. Impact of La{sub 2}O{sub 3} interfacial layers on InGaAs metal-oxide-semiconductor interface properties in Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks deposited by atomic-layer-deposition

    SciTech Connect

    Chang, C.-Y. Takenaka, M.; Takagi, S.; Ichikawa, O.; Osada, T.; Hata, M.; Yamada, H.

    2015-08-28

    We examine the electrical properties of atomic layer deposition (ALD) La{sub 2}O{sub 3}/InGaAs and Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs metal-oxide-semiconductor (MOS) capacitors. It is found that the thick ALD La{sub 2}O{sub 3}/InGaAs interface provides low interface state density (D{sub it}) with the minimum value of ∼3 × 10{sup 11} cm{sup −2} eV{sup −1}, which is attributable to the excellent La{sub 2}O{sub 3} passivation effect for InGaAs surfaces. It is observed, on the other hand, that there are a large amount of slow traps and border traps in La{sub 2}O{sub 3}. In order to simultaneously satisfy low D{sub it} and small hysteresis, the effectiveness of Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks with ultrathin La{sub 2}O{sub 3} interfacial layers is in addition evaluated. The reduction of the La{sub 2}O{sub 3} thickness to 0.4 nm in Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks leads to the decrease in hysteresis. On the other hand, D{sub it} of the Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs interfaces becomes higher than that of the La{sub 2}O{sub 3}/InGaAs ones, attributable to the diffusion of Al{sub 2}O{sub 3} through La{sub 2}O{sub 3} into InGaAs and resulting modification of the La{sub 2}O{sub 3}/InGaAs interface structure. As a result of the effective passivation effect of La{sub 2}O{sub 3} on InGaAs, however, the Al{sub 2}O{sub 3}/10 cycle (0.4 nm) La{sub 2}O{sub 3}/InGaAs gate stacks can realize still lower D{sub it} with maintaining small hysteresis and low leakage current than the conventional Al{sub 2}O{sub 3}/InGaAs MOS interfaces.

  17. Effects of Interfacial Fluorination on Performance Enhancement of High-k-Based Charge Trap Flash Memory

    NASA Astrophysics Data System (ADS)

    Wang, Chenjie; Huo, Zongliang; Liu, Ziyu; Liu, Yu; Cui, Yanxiang; Wang, Yumei; Li, Fanghua; Liu, Ming

    2013-07-01

    The effects of interfacial fluorination on the metal/Al2O3/HfO2/SiO2/Si (MAHOS) memory structure have been investigated. By comparing MAHOS memories with and without interfacial fluorination, it was identified that the deterioration of the performance and reliability of MAHOS memories is mainly due to the formation of an interfacial layer that generates excess oxygen vacancies at the interface. Interfacial fluorination suppresses the growth of the interfacial layer, which is confirmed by X-ray photoelectron spectroscopy depth profile analysis, increases enhanced program/erase efficiency, and improves data retention characteristics. Moreover, it was observed that fluorination at the SiO-HfO interface achieves a more effective performance enhancement than that at the HfO-AlO interface.

  18. Cold welding of organic light emitting diode: Interfacial and contact models

    NASA Astrophysics Data System (ADS)

    Asare, J.; Adeniji, S. A.; Oyewole, O. K.; Agyei-Tuffour, B.; Du, J.; Arthur, E.; Fashina, A. A.; Zebaze Kana, M. G.; Soboyejo, W. O.

    2016-06-01

    This paper presents the results of an analytical and computational study of the contacts and interfacial fracture associated with the cold welding of Organic Light Emitting diodes (OLEDs). The effects of impurities (within the possible interfaces) are explored for contacts and interfacial fracture between layers that are relevant to model OLEDs. The models are used to study the effects of adhesion, pressure, thin film layer thickness and dust particle modulus (between the contacting surfaces) on contact profiles around impurities between cold-welded thin films. The lift-off stage of thin films (during cold welding) is then modeled as an interfacial fracture process. A combination of adhesion and interfacial fracture theories is used to provide new insights for the design of improved contact and interfacial separation during cold welding. The implications of the results are discussed for the design and fabrication of cold welded OLED structures.

  19. Innovative qPCR using interfacial effects to enable low threshold cycle detection and inhibition relief

    PubMed Central

    Harshman, Dustin K.; Rao, Brianna M.; McLain, Jean E.; Watts, George S.; Yoon, Jeong-Yeol

    2015-01-01

    Molecular diagnostics offers quick access to information but fails to operate at a speed required for clinical decision-making. Our novel methodology, droplet-on-thermocouple silhouette real-time polymerase chain reaction (DOTS qPCR), uses interfacial effects for droplet actuation, inhibition relief, and amplification sensing. DOTS qPCR has sample-to-answer times as short as 3 min 30 s. In infective endocarditis diagnosis, DOTS qPCR demonstrates reproducibility, differentiation of antibiotic susceptibility, subpicogram limit of detection, and thermocycling speeds of up to 28 s/cycle in the presence of tissue contaminants. Langmuir and Gibbs adsorption isotherms are used to describe the decreasing interfacial tension upon amplification. Moreover, a log-linear relationship with low threshold cycles is presented for real-time quantification by imaging the droplet-on-thermocouple silhouette with a smartphone. DOTS qPCR resolves several limitations of commercially available real-time PCR systems, which rely on fluorescence detection, have substantially higher threshold cycles, and require expensive optical components and extensive sample preparation. Due to the advantages of low threshold cycle detection, we anticipate extending this technology to biological research applications such as single cell, single nucleus, and single DNA molecule analyses. Our work is the first demonstrated use of interfacial effects for sensing reaction progress, and it will enable point-of-care molecular diagnosis of infections. PMID:26601245

  20. Innovative qPCR using interfacial effects to enable low threshold cycle detection and inhibition relief.

    PubMed

    Harshman, Dustin K; Rao, Brianna M; McLain, Jean E; Watts, George S; Yoon, Jeong-Yeol

    2015-09-01

    Molecular diagnostics offers quick access to information but fails to operate at a speed required for clinical decision-making. Our novel methodology, droplet-on-thermocouple silhouette real-time polymerase chain reaction (DOTS qPCR), uses interfacial effects for droplet actuation, inhibition relief, and amplification sensing. DOTS qPCR has sample-to-answer times as short as 3 min 30 s. In infective endocarditis diagnosis, DOTS qPCR demonstrates reproducibility, differentiation of antibiotic susceptibility, subpicogram limit of detection, and thermocycling speeds of up to 28 s/cycle in the presence of tissue contaminants. Langmuir and Gibbs adsorption isotherms are used to describe the decreasing interfacial tension upon amplification. Moreover, a log-linear relationship with low threshold cycles is presented for real-time quantification by imaging the droplet-on-thermocouple silhouette with a smartphone. DOTS qPCR resolves several limitations of commercially available real-time PCR systems, which rely on fluorescence detection, have substantially higher threshold cycles, and require expensive optical components and extensive sample preparation. Due to the advantages of low threshold cycle detection, we anticipate extending this technology to biological research applications such as single cell, single nucleus, and single DNA molecule analyses. Our work is the first demonstrated use of interfacial effects for sensing reaction progress, and it will enable point-of-care molecular diagnosis of infections. PMID:26601245

  1. Adhesion and interfacial fracture toughness between hard and soft materials

    NASA Astrophysics Data System (ADS)

    Rahbar, Nima; Wolf, Kurt; Orana, Argjenta; Fennimore, Roy; Zong, Zong; Meng, Juan; Papandreou, George; Maryanoff, Cynthia; Soboyejo, Wole

    2008-11-01

    This paper presents the results of a combined experimental and theoretical study of adhesion between hard and soft layers that are relevant to medical devices such as drug-eluting stents and semiconductor applications. Brazil disk specimens were used to measure the interfacial fracture energies between model parylene C and 316L stainless steel over a wide range of mode mixities. The trends in the overall fracture energies are predicted using a combination of adhesion theories and fracture mechanics concepts. The measured interfacial fracture energies are shown to be in good agreement with the predictions.

  2. Dynamics of interfacial pattern formation

    NASA Technical Reports Server (NTRS)

    Ben-Jacob, E.; Goldenfeld, N.; Langer, J. S.; Schon, G.

    1983-01-01

    A phenomenological model of dendritic solidification incorporating interfacial kinetics, crystalline anisotropy, and a local approximation for the dynamics of the thermal diffusion field is proposed. The preliminary results are in qualitative agreement with natural dendrite-like pattern formation.

  3. Controlling quantum dot energies using submonolayer bandstructure engineering

    SciTech Connect

    Yu, L.; Law, S.; Wasserman, D.; Jung, D.; Lee, M. L.; Shen, J.; Cha, J. J.

    2014-08-25

    We demonstrate control of energy states in epitaxially-grown quantum dot structures formed by stacked submonolayer InAs depositions via engineering of the internal bandstructure of the dots. Transmission electron microscopy of the stacked sub-monolayer regions shows compositional inhomogeneity, indicative of the presence of quantum dots. The quantum dot ground state is manipulated not only by the number of deposited InAs layers, but also by control of the thickness and material composition of the spacing layers between submonolayer InAs depositions. In this manner, we demonstrate the ability to shift the quantum dot ground state energy at 77 K from 1.38 eV to 1.88 eV. The results presented offer a potential avenue towards enhanced control of dot energies for a variety of optoelectronic applications.

  4. Oscillatory interfacial instability between miscible fluids

    NASA Astrophysics Data System (ADS)

    Shevtsova, Valentina; Gaponenko, Yuri; Mialdun, Aliaksandr; Torregrosa, Marita; Yasnou, Viktar

    Interfacial instabilities occurring between two fluids are of fundamental interest in fluid dynamics, biological systems and engineering applications such as liquid storage, solvent extraction, oil recovery and mixing. Horizontal vibrations applied to stratified layers of immiscible liquids may generate spatially periodic waving of the interface, stationary in the reference frame of the vibrated cell, referred to as a "frozen wave". We present experimental evidence that frozen wave instability exists between two ordinary miscible liquids of similar densities and viscosities. At the experiments and at the numerical model, two superimposed layers of ordinary liquids, water-alcohol of different concentrations, are placed in a closed cavity in a gravitationally stable configuration. The density and viscosity of these fluids are somewhat similar. Similar to the immiscible fluids this instability has a threshold. When the value of forcing is increased the amplitudes of perturbations grow continuously displaying a saw-tooth structure. The decrease of gravity drastically changes the structure of frozen waves.

  5. Interfacial Widths of Conjugated Polymer Bilayers

    SciTech Connect

    NCSU; UC Berkeley; UCSB; Advanced Light Source; Garcia, Andres; Yan, Hongping; Sohn, Karen E.; Hexemer, Alexander; Nguyen, Thuc-Quyen; Bazan, Guillermo C.; Kramer, Edward J.; Ade, Harald

    2009-08-13

    The interfaces of conjugated polyelectrolyte (CPE)/poly[2-methoxy-5-(2{prime}-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) bilayers cast from differential solvents are shown by resonant soft X-ray reflectivity (RSoXR) to be very smooth and sharp. The chemical interdiffusion due to casting is limited to less than 0.6 nm, and the interface created is thus nearly 'molecularly' sharp. These results demonstrate for the first time and with high precision that the nonpolar MEH-PPV layer is not much disturbed by casting the CPE layer from a polar solvent. A baseline is established for understanding the role of interfacial structure in determining the performance of CPE-based polymer light-emitting diodes. More broadly, we anticipate further applications of RSoXR as an important tool in achieving a deeper understanding of other multilayer organic optoelectronic devices, including multilayer photovoltaic devices.

  6. Interfacial Engineering of Molecular Photovoltaics

    NASA Astrophysics Data System (ADS)

    Shelton, Steven Wade

    One of the most worthy pursuits in the field of organic solar cells is that of discovering ways to more effectively harvest charge generated by light absorption. The measure of the efficacy of this process is the external quantum efficiency (EQE). It is determined by the efficiency of incident light absorption, exciton diffusion, exciton splitting and charge transfer, and charge collection. Enhanced EQE can be realized by engineering interfaces between materials in the device to allow for smoother charge transfer throughout the extent of the device, which is usually between 10 and 200 nanometers. Improvements in charge transport are vitally important because the photogenerated excitons in electron donating polymers and small molecules typically only diffuse between 5 and 10 nanometers. These excitons must reach the interface between the electron donor and electron acceptor in order to be split so that the resulting electron and hole can be harvested at the cathode and anode, respectively. The aim of much of this dissertation is to describe a method by which the donor-acceptor interfacial area can be augmented using nanoimprint lithography, first with a single donor and then with multiple donors. Nanoimprint lithography is introduced as a simple embossing technique that can create features in a single component donor with dimensions as small as 20 nm. Solution-processable small molecules are of interest for their ease of synthesis and fabrication. I continue the discussion of nanoimprint lithography by offering candidates for a two-component donor combination. A two-component donor can extend the absorption range across a broader portion of the solar spectrum than just one donor to improve energy harvesting. After considering ways of optimizing the donor-acceptor interface, I describe the use of a charge selective layer for better charge transport and collection. When incorporated into a bilayer solar cell and an inverted solar cell, these two molecules markedly

  7. Solid/liquid interfacial free energies in binary systems

    NASA Technical Reports Server (NTRS)

    Nason, D.; Tiller, W. A.

    1973-01-01

    Description of a semiquantitative technique for predicting the segregation characteristics of smooth interfaces between binary solid and liquid solutions in terms of readily available thermodynamic parameters of the bulk solutions. A lattice-liquid interfacial model and a pair-bonded regular solution model are employed in the treatment with an accommodation for liquid interfacial entropy. The method is used to calculate the interfacial segregation and the free energy of segregation for solid-liquid interfaces between binary solutions for the (111) boundary of fcc crystals. The zone of compositional transition across the interface is shown to be on the order of a few atomic layers in width, being moderately narrower for ideal solutions. The free energy of the segregated interface depends primarily upon the solid composition and the heats of fusion of the component atoms, the composition difference of the solutions, and the difference of the heats of mixing of the solutions.

  8. Understanding the electric field control of the electronic and optical properties of strongly-coupled multi-layered quantum dot molecules.

    PubMed

    Usman, Muhammad

    2015-10-21

    Strongly-coupled quantum dot molecules (QDMs) are widely employed in the design of a variety of optoelectronic, photovoltaic, and quantum information devices. An efficient and optimized performance of these devices demands engineering of the electronic and optical properties of the underlying QDMs. The application of electric fields offers a way to realise such a control over the QDM characteristics for a desired device operation. We performed multi-million-atom atomistic tight-binding calculations to study the influence of electric fields on the electron and hole wave function confinements and symmetries, the ground-state transition energies, the band-gap wavelengths, and the optical transition modes. Electrical fields parallel (Ep) and anti-parallel (Ea) to the growth direction were investigated to provide a comprehensive guide for understanding the electric field effects. The strain-induced asymmetry of the hybridized electron states is found to be weak and can be balanced by applying a small Ea electric field, of the order of 1 kV cm(-1). The strong interdot couplings completely break down at large electric fields, leading to single QD states confined at the opposite edges of the QDM. This mimics a transformation from a type-I band structure to a type-II band structure for the QDMs, which is a critical requirement for the design of intermediate-band solar cells (IBSCs). The analysis of the field-dependent ground-state transition energies reveals that the QDM can be operated both as a high dipole moment device by applying large electric fields and as a high polarizability device under the application of small electric field magnitudes. The quantum confined Stark effect (QCSE) red shifts the band-gap wavelength to 1.3 μm at the 15 kV cm(-1) electric field; however the reduced electron-hole wave function overlaps lead to a decrease in the interband optical transition strengths by roughly three orders of magnitude. The study of the polarisation-resolved optical

  9. Understanding the electric field control of the electronic and optical properties of strongly-coupled multi-layered quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad

    2015-10-01

    Strongly-coupled quantum dot molecules (QDMs) are widely employed in the design of a variety of optoelectronic, photovoltaic, and quantum information devices. An efficient and optimized performance of these devices demands engineering of the electronic and optical properties of the underlying QDMs. The application of electric fields offers a way to realise such a control over the QDM characteristics for a desired device operation. We performed multi-million-atom atomistic tight-binding calculations to study the influence of electric fields on the electron and hole wave function confinements and symmetries, the ground-state transition energies, the band-gap wavelengths, and the optical transition modes. Electrical fields parallel () and anti-parallel () to the growth direction were investigated to provide a comprehensive guide for understanding the electric field effects. The strain-induced asymmetry of the hybridized electron states is found to be weak and can be balanced by applying a small electric field, of the order of 1 kV cm-1. The strong interdot couplings completely break down at large electric fields, leading to single QD states confined at the opposite edges of the QDM. This mimics a transformation from a type-I band structure to a type-II band structure for the QDMs, which is a critical requirement for the design of intermediate-band solar cells (IBSCs). The analysis of the field-dependent ground-state transition energies reveals that the QDM can be operated both as a high dipole moment device by applying large electric fields and as a high polarizability device under the application of small electric field magnitudes. The quantum confined Stark effect (QCSE) red shifts the band-gap wavelength to 1.3 μm at the 15 kV cm-1 electric field; however the reduced electron-hole wave function overlaps lead to a decrease in the interband optical transition strengths by roughly three orders of magnitude. The study of the polarisation-resolved optical modes

  10. Protein adsorption and interfacial rheology interfering in dilatational experiment

    NASA Astrophysics Data System (ADS)

    Rühs, P. A.; Scheuble, N.; Windhab, E. J.; Fischer, P.

    2013-05-01

    The static and dilatational response of β-lactoglobulin fibrils and native β-lactoglobulin (monomers) at water-air and water-oil interfaces (pH 2) was measured using the pendant drop method. The resulting adsorption behavior and viscoelasticity is dependent of concentration and adsorption time. The interfacial pressure of the β-lactoglobulin fibrils obtained in static measurements was 16-18 mN/m (against air) and 7 mN/m (against oil) for all concentrations. With higher concentrations, faster adsorption kinetics and slightly higher interfacial and surface pressure is achieved but did not lead to higher viscoelastic moduli. The transient saturation of the interface is similar for both the fibril solution and the monomers, however the fibril solution forms a strong viscoelastic network. To evaluate the superimposed adsorption behavior and rheological properties, the formed interfacial layer was subjected to dilatational experiments, which were performed by oscillating the surface area of the drop in sinusoidal and sawtooth (diagonal) deformation manner. The sinusoidal oscillations (time depended area deformation rate) result in a complex interfacial tension behavior against air and oil interfaces and show remarkable differences during compression and expansion as emphasized by Lissajous figures. For diagonal (constant area deformation rate) experiments, a slight bending of the interfacial tension response was observed at low frequencies emphasizing the influence of protein adsorption during rheological measurements.

  11. CuInS2-Sensitized Quantum Dot Solar Cell. Electrophoretic Deposition, Excited-State Dynamics, and Photovoltaic Performance.

    PubMed

    Santra, Pralay K; Nair, Pratheesh V; George Thomas, K; Kamat, Prashant V

    2013-03-01

    Ternary metal chalcogenides such as CuInS2 offer new opportunities to design quantum dot solar cells (QDSC). Chemically synthesized CuInS2 quantum dots (particle diameter, 2.6 nm) have been successfully deposited within the mesoscopic TiO2 film using electrophoretic deposition (150 V cm(-1) dc field). The primary photoinduced process of electron injection from excited CuInS2 into TiO2 occurs with a rate constant of 5.75 × 10(11) s(-1). The TiO2/CuInS2 films are photoactive and produce anodic photocurrent with a power conversion efficiency of 1.14%. Capping the TiO2/CuInS2 film with a CdS layer decreases the interfacial charge recombination and thus offers further improvement in the power conversion efficiency (3.91%). The synergy of using CdS as a passivation layer in the composite film is also evident from the increased external quantum efficiency of the electrode in the red region where only CuInS2 absorbs the incident light. PMID:26281925

  12. Influence of electron irradiation on the electronic transport mechanisms during the conductive AFM imaging of InAs/GaAs quantum dots capped with a thin GaAs layer.

    PubMed

    Troyon, M; Smaali, K

    2008-06-25

    We have used conductive atomic force microscopy (C-AFM) to study the electronic transport mechanisms through InAs quantum dots (QDs) grown by molecular beam epitaxy on an n-type GaAs(001) substrate and covered with a 5 nm thick GaAs cap layer. The study is performed with a conductive atomic force microscope working inside a scanning electron microscope. Electric images can be obtained only if the sample is preliminarily irradiated with an electron probe current sufficiently high to generate strong electron beam induced current. In these conditions holes are trapped in QDs and surface states, so allowing the release of the Fermi level pinning and thus conduction through the sample. The electronic transport mechanism depends on the type of AFM probe used; it is explained for a metal (Co/Cr) coated probe and p-doped diamond coated probe with the aid of energy band diagrams. The writing (charge trapping) and erasing (untrapping) phenomena is conditioned by the magnitude of the electron probe current. A strong memory effect is evidenced for the sample studied. PMID:21828669

  13. Dot-in-Well Quantum-Dot Infrared Photodetectors

    NASA Technical Reports Server (NTRS)

    Gunapala, Sarath; Bandara, Sumith; Ting, David; Hill, cory; Liu, John; Mumolo, Jason; Chang, Yia Chung

    2008-01-01

    Dot-in-well (DWELL) quantum-dot infrared photodetectors (QDIPs) [DWELL-QDIPs] are subjects of research as potentially superior alternatives to prior QDIPs. Heretofore, there has not existed a reliable method for fabricating quantum dots (QDs) having precise, repeatable dimensions. This lack has constituted an obstacle to the development of uniform, high-performance, wavelength-tailorable QDIPs and of focal-plane arrays (FPAs) of such QDIPs. However, techniques for fabricating quantum-well infrared photodetectors (QWIPs) having multiple-quantum- well (MQW) structures are now well established. In the present research on DWELL-QDIPs, the arts of fabrication of QDs and QWIPs are combined with a view toward overcoming the deficiencies of prior QDIPs. The longer-term goal is to develop focal-plane arrays of radiationhard, highly uniform arrays of QDIPs that would exhibit high performance at wavelengths from 8 to 15 m when operated at temperatures between 150 and 200 K. Increasing quantum efficiency is the key to the development of competitive QDIP-based FPAs. Quantum efficiency can be increased by increasing the density of QDs and by enhancing infrared absorption in QD-containing material. QDIPs demonstrated thus far have consisted, variously, of InAs islands on GaAs or InAs islands in InGaAs/GaAs wells. These QDIPs have exhibited low quantum efficiencies because the numbers of QD layers (and, hence, the areal densities of QDs) have been small typically five layers in each QDIP. The number of QD layers in such a device must be thus limited to prevent the aggregation of strain in the InAs/InGaAs/GaAs non-lattice- matched material system. The approach being followed in the DWELL-QDIP research is to embed In- GaAs QDs in GaAs/AlGaAs multi-quantum- well (MQW) structures (see figure). This material system can accommodate a large number of QD layers without excessive lattice-mismatch strain and the associated degradation of photodetection properties. Hence, this material

  14. Martensitic transformation of FeNi nanofilm induced by interfacial stress generated in FeNi/V nanomultilayered structure

    PubMed Central

    2014-01-01

    FeNi/V nanomultilayered films with different V layer thicknesses were synthesized by magnetron sputtering. By adjusting the thickness of the V layer, different interfacial compressive stress were imposed on FeNi layers and the effect of interfacial stress on martensitic transformation of the FeNi film was investigated. Without insertion of V layers, the FeNi film exhibits a face-centered cubic (fcc) structure. With the thickness of V inserted layers up to 1.5 nm, under the coherent growth structure in FeNi/V nanomultilayered films, FeNi layers bear interfacial compressive stress due to the larger lattice parameter relative to V, which induces the martensitic transformation of the FeNi film. As the V layer thickness increases to 2.0 nm, V layers cannot keep the coherent growth structure with FeNi layers, leading to the disappearance of interfacial compressive stress and termination of the martensitic transformation in the FeNi film. The interfacial compressive stress-induced martensitic transformation of the FeNi nanofilm is verified through experiment. The method of imposing and modulating the interfacial stress through the epitaxial growth structure in the nanomultilayered films should be noticed and utilized. PMID:25232296

  15. Exploring interfacial ferromagnetism in manganite-based superlattices

    NASA Astrophysics Data System (ADS)

    Yi, Di; Flint, Charles; Suzuki, Yuri

    Heterointerface of complex oxides provides a rich playground to explore the emergent phenomena that are not found in bulk. In particular, emergent interfacial ferromagnetism has been successfully demonstrated in heterostructures composed of materials which are paramagnetic and antiferromagnetic in bulk. In our previous work, leakage of itinerant electrons from a paramagnetic metal to an antiferromagnetic insulator has been shown to give rise to interfacial ferromagnetism in CaMnO3 based superlattices. However interfacial ferromagnetism in insulating superlattices suggests a more complicated scenario. Therefore a thorough investigation of coupling between charge, lattice and spin degrees of freedom is necessary. In this talk, we focus on the NdNiO3 /CaMnO3 system. By choosing a paramagnetic layer that undergoes a metal-insulator transition, we can explore the role of electron itinerancy in interfacial ferromagnetism in the same sample to eliminate the inconsistencies that may originate from the deposition of multiple samples. We demonstrate that NdNiO3 exhibits a metal-insulator transition as a function of temperature, which can be tuned as a function of film thickness. We have also grown NdNiO3 /CaMnO3 heterostructures with excellent crystallinity. Preliminary transport measurements indicate that the presence of an adjacent CaMnO3 layer also affects the transport in NdNiO3 so that charge transfer from the itinerant layer into the adjacent antiferromagnetic insulating CaMnO3 is likely not the only contribution to interfacial ferromagnetism.

  16. Auger-decay engineering in quantum dots in relation to applications in LEDs and lasers (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Klimov, Victor I.

    2015-09-01

    Multicarrier dynamics in colloidal quantum dots (QDs) are normally controlled by nonradiative Auger recombination wherein the energy of an electron-hole pair is converted not into a photon but instead transferred to a third carrier (an electron or a hole). Auger decay is extremely fast in QDs (time scales of tens-to-hundreds of picoseconds) due to both close proximity between interacting charges and elimination of restrictions imposed by translational momentum conservation. Photoluminescence (PL) quenching by nonradiative Auger processes complicates realization of applications that require high emissivity of multicarrier states such as light-emitting diodes (LEDs) and lasers. Therefore, the development of "Auger-recombination-free" QDs is an important current challenge in the field of colloidal nanostructures. Previous single-dot spectroscopic studies have indicated a significant spread in Auger lifetimes across an ensemble of nominally identical QDs. It has been speculated that in addition to dot-to-dot variation in physical dimensions, this spread is contributed to by variations in the structure of the QD interface, which controls the shape of the confinement potential. Here we directly evaluate the effect of the composition of the core-shell interface on single- and multi-exciton dynamics via side-by-side measurements of individual core-shell CdSe/CdS nanocrystals with a sharp vs. smooth (graded) interface. We observe that while having essentially no effect on single-exciton decay, the interfacial alloy layer leads to a systematic increase in the biexciton lifetime indicating suppression of Auger recombination. We demonstrate that using QDs with "engineered interfaces" we can considerably improve the performance of QD LEDs and lasers.

  17. Interfacial chemistry at p-GaP photoelectrodes

    SciTech Connect

    Ginley, D.S.; Chamberlain, M.B.

    1982-09-01

    P-GaP photoelectrodes are of interest as cathodes in photosynthetic photoelectrochemical devices. The nature of the surface appears crucial to the efficient utilization of this material. In this study we show how an oxide surface layer is present even in the reductive environment at the surface; that this layer appears to be necessary for efficient interfacial charge transport; and that high solution oxygen concentrations increase the stability of this layer and consequently the electrode. Aging experiments with chemical and surface analyses are included that support these surprising results.

  18. Auger recombination of biexcitons and negative and positive trions in individual quantum dots.

    PubMed

    Park, Young-Shin; Bae, Wan Ki; Pietryga, Jeffrey M; Klimov, Victor I

    2014-07-22

    Charged exciton states commonly occur both in spectroscopic studies of quantum dots (QDs) and during operation of QD-based devices. The extra charge added to the neutral exciton modifies its radiative decay rate and also opens an additional nonradiative pathway associated with an Auger process whereby the recombination energy of an exciton is transferred to the excess charge. Here we conduct single-dot spectroscopic studies of Auger recombination in thick-shell ("giant") CdSe/CdS QDs with and without an interfacial alloy layer using time-tagged, time-correlated single-photon counting. In photoluminescence (PL) intensity trajectories of some of the dots, we resolve three distinct states of different emissivities ("bright", "gray", and "dark") attributed, respectively, to the neutral exciton and negative and positive trions. Simultaneously acquired PL lifetime trajectories indicate that the positive trion is much shorter lived than the negative trion, which can be explained by a high density of valence band states and a small hole localization radius (defined by the QD core size), factors that favor an Auger process involving intraband excitation of a hole. A comparison of trion and biexciton lifetimes suggests that the biexciton Auger decay can be treated in terms of a superposition of two independent channels associated with positive- and negative-trion pathways. The resulting interdependence between Auger time constants might simplify the studies of multicarrier recombination by allowing one, for example, to infer Auger lifetimes of trions of one sign based on the measurements of biexciton decay and dynamics of the trions of the opposite sign or, alternatively, estimate the biexciton lifetime based on studies of trion dynamics. PMID:24909861

  19. Structure of droplet-epitaxy-grown InAs/GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Cohen, Eyal; Yochelis, Shira; Westreich, Ohad; Shusterman, Sergey; Kumah, Divine P.; Clarke, Roy; Yacoby, Yizhak; Paltiel, Yossi

    2011-06-01

    We have used a direct x-ray phasing method, coherent Bragg rod analysis, to obtain sub-angstrom resolution electron density maps of the InAs/GaAs dot system. The dots were grown by the droplet heteroepitaxy (DHE) technique and their structural and compositional properties are compared with those of dots grown by the strain-driven Stranski-Krastanov method. Our results show that the Ga diffusion into the DHE-grown dots is somewhat larger; however, other characteristics such as the composition of the dots' uppermost layers, the interlayer spacing, and the bowing of the atomic layers are similar.

  20. Interfacial and electrical characteristics of Al2O3 gate dielectric on fully depleted SiGe on insulator

    NASA Astrophysics Data System (ADS)

    Di, Zengfeng; Zhang, Miao; Liu, Weili; Shen, Qinwo; Luo, Suhua; Song, Zhitang; Lin, Chenglu; Huang, Anping; Chu, Paul K.

    2005-06-01

    The interfacial and electrical characteristics of as-deposited or annealed A2O3 gate dielectric films grown on fully depleted SiGe-on-insulator are investigated. An interfacial layer composed of SiOx and GeOx is observed in the as-grown film. The interfacial silicate formation is effectively suppressed by GeOx formation. However, GeOx is reduced to Ge and extensive silicate formation occurs after annealing. The formation of silicate and disappearance of GeOx after annealing leads to a decrease in the density of the interfacial states.

  1. Wear and interfacial transport of material

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1975-01-01

    Bonding across the interface for two solids in contact and the subsequent transfer of material from one surface to another is a direct result of the interfacial bonds being stronger than the cohesive bonds in either of the two solids. Surface tools such as LEED, Auger emission spectroscopy, field ion microscopy, and the atom probe are used to examine adhesive contacts and to determine the direction, nature, quantity of material transfer and properties of the solids which effect transfer and wear. The electronic nature, cohesive binding energies, surface structure, lattice disregistry and distribution of species in surface layers are all found to effect adhesion and transfer or transport for clean surfaces in solid state contact. The influence of adsorbed and reacted surface films from fractions of a monolayer to multilayer reactive films are considered. It is shown that even fractions of a monolayer of surface active species such as oxygen and sulfur can markedly inhibit adhesion and transport.

  2. Role of the elasticity of pharmaceutical materials on the interfacial mechanical strength of bilayer tablets.

    PubMed

    Busignies, Virginie; Mazel, Vincent; Diarra, Harona; Tchoreloff, Pierre

    2013-11-30

    The effect of the elasticity of various pharmaceutical materials on the interfacial adhesion in bilayer tablets was investigated. The elastic properties of five pharmaceutical products were characterized by their total elastic recovery. To test the interfacial strength of the bilayer tablets a new flexural test was proposed. Thanks to the test configuration, the experimental breaking force is directly correlated with the interfacial layer strength. Depending on the materials, the fracture occurred over the interface or in one of the two layers. In most cases, the highest breaking forces were obtained when the materials had close elastic recovery. On the contrary, for materials with different elastic recovery, the breaking forces were reduced. The observed changes in the interfacial mechanical strength were statistically analyzed. Such an approach has an importance in the growing interest in the Quality by Design (QbD) concept in pharmaceutical industry. PMID:24055440

  3. Numerical simulation of optical feedback on a quantum dot lasers

    SciTech Connect

    Al-Khursan, Amin H.; Ghalib, Basim Abdullattif; Al-Obaidi, Sabri J.

    2012-02-15

    We use multi-population rate equations model to study feedback oscillations in the quantum dot laser. This model takes into account all peculiar characteristics in the quantum dots such as inhomogeneous broadening of the gain spectrum, the presence of the excited states on the quantum dot and the non-confined states due to the presence of wetting layer and the barrier. The contribution of quantum dot groups, which cannot follow by other models, is simulated. The results obtained from this model show the feedback oscillations, the periodic oscillations which evolves to chaos at higher injection current of higher feedback levels. The frequency fluctuation is attributed mainly to wetting layer with a considerable contribution from excited states. The simulation shows that is must be not using simple rate equation models to express quantum dots working at excited state transition.

  4. Avalanche in adhesion. [interfacial separation between two Ni crystals

    NASA Technical Reports Server (NTRS)

    Smith, John R.; Bozzolo, Guillermo; Banerjea, Amitava; Ferrante, John

    1989-01-01

    Consider surfaces being brought into contact. It is proposed that atomic layers can collapse or avalanche together when the interfacial spacing falls below a critical distance. This causes a discontinuous drop in the adhesive binding energy. Avalanche can occur regardless of the stiffness of external supports. A simple understanding of the origin of this phenomenon is provided. A numerical calculation has been carried out for adhesion in Ni. A new wear mechanism due to avalanche is suggested.

  5. Interfacial adsorption of antifreeze proteins: a neutron reflection study.

    PubMed

    Xu, Hai; Perumal, Shiamalee; Zhao, Xiubo; Du, Ning; Liu, Xiang-Yang; Jia, Zongchao; Lu, Jian R

    2008-06-01

    Interfacial adsorption from two antifreeze proteins (AFP) from ocean pout (Macrozoarces americanus, type III AFP, AFP III, or maAFP) and spruce budworm (Choristoneura fumiferana, isoform 501, or cfAFP) were studied by neutron reflection. Hydrophilic silicon oxide was used as model substrate to facilitate the solid/liquid interfacial measurement so that the structural features from AFP adsorption can be examined. All adsorbed layers from AFP III could be modeled into uniform layer distribution assuming that the protein molecules were adsorbed with their ice-binding surface in direct contact with the SiO(2) substrate. The layer thickness of 32 A was consistent with the height of the molecule in its crystalline form. With the concentration decreasing from 2 mg/ml to 0.01 mg/ml, the volume fraction of the protein packed in the monolayer decreased steadily from 0.4 to 0.1, consistent with the concentration-dependent inhibition of ice growth observed over the range. In comparison, insect cfAFP showed stronger adsorption over the same concentration range. Below 0.1 mg/ml, uniform layers were formed. But above 1 mg/ml, the adsorbed layers were characterized by a dense middle layer and two outer diffuse layers, with a total thickness around 100 A. The structural transition indicated the responsive changes of conformational orientation to increasing surface packing density. As the higher interfacial adsorption of cfAFP was strongly correlated with the greater thermal hysteresis of spruce budworm, our results indicated the important relation between protein adsorption and antifreeze activity. PMID:18234809

  6. Relaxations and Interfacial Water Ordering at the Corundum (110) Surface

    SciTech Connect

    Catalano, Jeffrey G.

    2010-09-17

    In situ high resolution specular X-ray reflectivity measurements were used to examine relaxations and interfacial water ordering occurring at the corundum (110)-water interface. Sample preparation affected the resulting surface structure. Annealing in air at 1373 K produced a reconstructed surface formed through an apparently ordered aluminum vacancy. The effect of the reconstruction on in-plane periodicity was not determined. The remaining aluminum sites on the surface maintain full coordination by oxygen and the surface was coated with a layer of physically adsorbed water. Ordering of water further from the surface was not observed. Acid etching of this surface and preparing a surface through annealing at 723 K both produced an unreconstructed surface with identical relaxations and water ordering. Relaxations were confined primarily to the top {approx}4 {angstrom} of the surface and were dominated by an increased distribution width of the fully occupied surface aluminum site and outward relaxation of the oxygen surface functional groups. A layer of adsorbed water fully coated the surface and occurred in two distinct sites. Water above this showed signs of layering and indicated that water ordering extended 7-10 {angstrom} from the surface. Relaxations and the arrangement of interfacial water were nearly identical on both the unreconstructed corundum and isostructural hematite (110) surfaces. Comparison to corundum and hematite (012) suggests that the arrangement of interfacial water is primarily controlled by mineral surface structure.

  7. Three-layer model for exchange anisotropy

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; Azevedo, A.; de Aguiar, F. M.; Fermin, J. R.; Egelhoff, W. F.; Parkin, S. S.

    2002-08-01

    Recent x-ray absorption measurements have indicated that the interface between the antiferromagnetic (AF) and the ferromagnetic (FM) layers in AF/FM bilayers instead of being abrupt, consists of a thin layer with uncompensated spins. Here the effect of an interfacial layer between the AF and FM layers on the ferromagnetic resonance response is investigated using a three-layer model for the exchange anisotropy. The calculated dependence of the resonance field with the azimuthal angle of the in-plane external field agrees quite well with experimental data in several samples, lending support to the existence of the uncompensated interfacial layer.

  8. Inverted colloidal quantum dot solar cells.

    PubMed

    Kim, Gi-Hwan; Walker, Bright; Kim, Hak-Beom; Kim, Jin Young; Sargent, Edward H; Park, Jongnam; Kim, Jin Young

    2014-05-28

    An inverted architecture of quantum dot solar cells is demonstrated by introducing a novel ZnO method on top of the PbS CQD film. Improvements in device characteristics stem from constructive optical interference from the ZnO layer that enhances absorption in the PbS CQD layer. Outstanding diode characteristics arising from a superior PbS/ZnO junction provide a further electronic advantage. PMID:24677118

  9. Interfacial conditions and electrical properties of the SrBi 2Ta 2O 9/ZrO 2/Si (MFIS) structure according to the heat treatment of the ZrO 2 buffer layer

    NASA Astrophysics Data System (ADS)

    Park, Chul-Ho; Kim, Jae-Hyun; Kim, Min-Cheol; Son, Young-Gook; Won, Mi-Sook

    2005-08-01

    The possibility of the ZrO 2 buffer layer as the insulator for the metal-ferroelectric-insulator-semiconductor (MFIS) structure was investigated. ZrO 2 and SrBi 2Ta 2O 9 (SBT) thin films were deposited on the p-type Si(1 1 1) wafer by the rf magnetron-sputtering method. According to the process with and without the post-annealing of the ZrO 2 buffer layer, the diffusion amount of Sr, Bi, Ta elements show slight difference through the glow discharge spectrometer (GDS) analysis. From X-ray photoelectron spectroscopy (XPS) results, we could confirm that the post-annealing process affects the chemical binding condition of the interface between the ZrO 2 thin film and the Si substrate, which results in the chemical stability of the ZrO 2 thin film. The electrical properties of the MFIS structure were relatively improved by the post-annealing ZrO 2 buffer layer. The window memory of the Pt/SBT (260 nm, 800 °C)/ZrO 2 (20 nm) structure increases from 0.75 to 2.2 V. This memory window is sufficient for the practical application of the NDRO-FRAM operating at low voltage.

  10. Intermediate-band photosensitive device with quantum dots embedded in energy fence barrier

    DOEpatents

    Forrest, Stephen R.; Wei, Guodan

    2010-07-06

    A plurality of layers of a first semiconductor material and a plurality of dots-in-a-fence barriers disposed in a stack between a first electrode and a second electrode. Each dots-in-a-fence barrier consists essentially of a plurality of quantum dots of a second semiconductor material embedded between and in direct contact with two layers of a third semiconductor material. Wave functions of the quantum dots overlap as at least one intermediate band. The layers of the third semiconductor material are arranged as tunneling barriers to require a first electron and/or a first hole in a layer of the first material to perform quantum mechanical tunneling to reach the second material within a respective quantum dot, and to require a second electron and/or a second hole in a layer of the first semiconductor material to perform quantum mechanical tunneling to reach another layer of the first semiconductor material.

  11. Liquid metal actuation by electrical control of interfacial tension

    NASA Astrophysics Data System (ADS)

    Eaker, Collin B.; Dickey, Michael D.

    2016-09-01

    By combining metallic electrical conductivity with low viscosity, liquid metals and liquid metal alloys offer new and exciting opportunities to serve as reconfigurable components of electronic, microfluidic, and electromagnetic devices. Here, we review the physics and applications of techniques that utilize voltage to manipulate the interfacial tension of liquid metals; such techniques include electrocapillarity, continuous electrowetting, electrowetting-on-dielectric, and electrochemistry. These techniques lower the interfacial tension between liquid metals and a surrounding electrolyte by driving charged species (or in the case of electrochemistry, chemical species) to the interface. The techniques are useful for manipulating and actuating liquid metals at sub-mm length scales where interfacial forces dominate. We focus on metals and alloys that are liquid near or below room temperature (mercury, gallium, and gallium-based alloys). The review includes discussion of mercury—despite its toxicity—because it has been utilized in numerous applications and it offers a way of introducing several phenomena without the complications associated with the oxide layer that forms on gallium and its alloys. The review focuses on the advantages, applications, opportunities, challenges, and limitations of utilizing voltage to control interfacial tension as a method to manipulate liquid metals.

  12. Quantum dot device tunable from single to triple dot system

    SciTech Connect

    Rogge, M. C.; Haug, R. J.; Pierz, K.

    2013-12-04

    We present a lateral quantum dot device which has a tunable number of quantum dots. Depending on easily tunable gate voltages, one, two or three quantum dots are found. They are investigated in transport and charge detection.

  13. Iridium Interfacial Stack - IrIS

    NASA Technical Reports Server (NTRS)

    Spry, David

    2012-01-01

    Iridium Interfacial Stack (IrIS) is the sputter deposition of high-purity tantalum silicide (TaSi2-400 nm)/platinum (Pt-200 nm)/iridium (Ir-200 nm)/platinum (Pt-200 nm) in an ultra-high vacuum system followed by a 600 C anneal in nitrogen for 30 minutes. IrIS simultaneously acts as both a bond metal and a diffusion barrier. This bondable metallization that also acts as a diffusion barrier can prevent oxygen from air and gold from the wire-bond from infiltrating silicon carbide (SiC) monolithically integrated circuits (ICs) operating above 500 C in air for over 1,000 hours. This TaSi2/Pt/Ir/Pt metallization is easily bonded for electrical connection to off-chip circuitry and does not require extra anneals or masking steps. There are two ways that IrIS can be used in SiC ICs for applications above 500 C: it can be put directly on a SiC ohmic contact metal, such as Ti, or be used as a bond metal residing on top of an interconnect metal. For simplicity, only the use as a bond metal is discussed. The layer thickness ratio of TaSi2 to the first Pt layer deposited thereon should be 2:1. This will allow Si from the TaSi2 to react with the Pt to form Pt2Si during the 600 C anneal carried out after all layers have been deposited. The Ir layer does not readily form a silicide at 600 C, and thereby prevents the Si from migrating into the top-most Pt layer during future anneals and high-temperature IC operation. The second (i.e., top-most) deposited Pt layer needs to be about 200 nm to enable easy wire bonding. The thickness of 200 nm for Ir was chosen for initial experiments; further optimization of the Ir layer thickness may be possible via further experimentation. Ir itself is not easily wire-bonded because of its hardness and much higher melting point than Pt. Below the iridium layer, the TaSi2 and Pt react and form desired Pt2Si during the post-deposition anneal while above the iridium layer remains pure Pt as desired to facilitate easy and strong wire-bonding to the Si

  14. Surface Exchange and Shape Transitions of PbSe Quantum Dots during Overgrowth

    SciTech Connect

    Abtin, L.; Springholz, G.; Holy, V.

    2006-12-31

    Epitaxial overgrowth of PbSe quantum dots is shown to drastically affect their shape and composition due to anion exchange reactions. As shown by scanning tunneling microscopy, for PbTe capping layers this results in a complete truncation of the dots. Introduction of EuTe into the cap layer leads to an effective suppression of the anion exchange process. This preserves the original dot pyramids and induces a large stress concentration on the surface which further alters the overgrowth process.

  15. Energy levels of hybrid monolayer-bilayer graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Mirzakhani, M.; Zarenia, M.; Ketabi, S. A.; da Costa, D. R.; Peeters, F. M.

    2016-04-01

    Often real samples of graphene consist of islands of both monolayer and bilayer graphene. Bound states in such hybrid quantum dots are investigated for (i) a circular single-layer graphene quantum dot surrounded by an infinite bilayer graphene sheet and (ii) a circular bilayer graphene quantum dot surrounded by an infinite single-layer graphene. Using the continuum model and applying zigzag boundary conditions at the single-layer-bilayer graphene interface, we obtain analytical results for the energy levels and the corresponding wave spinors. Their dependence on perpendicular magnetic and electric fields are studied for both types of quantum dots. The energy levels exhibit characteristics of interface states, and we find anticrossings and closing of the energy gap in the presence of a bias potential.

  16. Decimetric radio dot emissions

    NASA Astrophysics Data System (ADS)

    Mészárosová, H.; Karlický, M.; Sawant, H. S.; Fernandes, F. C. R.; Cecatto, J. R.; de Andrade, M. C.

    2008-11-01

    Context: We study a rare type of solar radio bursts called decimetric dot emissions. Aims: In the period 1999-2001, 20 events of decimetric dot emissions observed by the Brazilian Solar Spectroscope (BSS) in the frequency range 950-2640 MHz are investigated statistically and compared with radio fine structures of zebras and fibers. Methods: For the study of the spectral characteristics of the dot emissions we use specially developed Interactive Data Language (IDL) software called BSSView and basic statistical methods. Results: We have found that the dm dot emissions, contrary to the fine structures of the type IV bursts (i.e. zebras, fibers, lace bursts, spikes), are not superimposed on any background burst emission. In the radio spectrum, in most cases the dot emissions form chains that appear to be arranged in zebra patterns or fibers. Because some zebras and fibers, especially those observed with high time and high spectral resolutions, also show emission dots (but superimposed on the background burst emission), we compared the spectral parameters of the dot emissions with the dots being the fine structure of zebras and fibers. For both these dots, similar spectral characteristics were found. Some similarities of the dot emissions can be found also with the lace bursts and spikes. For some events the dot emissions show structural evolution from patterns resembling fibers to patterns resembling zebras and vice versa, or they evolve into fully chaotic patterns. Conclusions: For the first time, we present decimetric dot emissions that appear to be arranged in zebra patterns or fibers. We propose that these emissions are generated by the plasma emission mechanism at the locations in the solar atmosphere where the double resonance condition is fulfilled.

  17. Elastocapillary-mediated interfacial assembly

    NASA Astrophysics Data System (ADS)

    Evans, Arthur

    2015-11-01

    Particles confined to an interface are present in a large number of industrial applications and ubiquitous in cellular biophysics. Interactions mediated by the interface, such as capillary effects in the presence of surface tension, give rise to rafts and aggregates whose structure is ultimately determined by geometric characteristics of these adsorbed particles. A common strategy for assembling interfacial structures relies on exploiting these interactions by tuning particle anisotropy, either by constructing rigid particles with heterogeneous wetting properties or fabricating particles that have a naturally anisotropic shape. Less explored, however, is the scenario where the interface causes the particles to deform. In this talk I will discuss the implications for interfacial assembly using elastocapillary-mediated interactions. The competition between surface energy and elasticity can wrinkle and buckle adsorbed soft particles, leading to complicated (but programmable) aggregates.

  18. Height control of self-assembled quantum dots by strain engineering during capping

    SciTech Connect

    Grossi, D. F. Koenraad, P. M.; Smereka, P.; Keizer, J. G.; Ulloa, J. M.

    2014-10-06

    Strain engineering during the capping of III-V quantum dots has been explored as a means to control the height of strained self-assembled quantum dots. Results of Kinetic Monte Carlo simulations are confronted with cross-sectional Scanning Tunnel Microscopy (STM) measurements performed on InAs quantum dots grown by molecular beam epitaxy. We studied InAs quantum dots that are capped by In{sub x}Ga{sub (1−x)}As layers of different indium compositions. Both from our realistic 3D kinetic Monte Carlo simulations and the X-STM measurements on real samples, a trend in the height of the capped quantum dot is found as a function of the lattice mismatch between the quantum dot material and the capping layer. Results obtained on additional material combinations show a generic role of the elastic energy in the control of the quantum dot morphology by strain engineering during capping.

  19. Photoluminescence efficiency of self-assembled germanium dots

    NASA Astrophysics Data System (ADS)

    Lockwood, D. J.; Rowell, N. L.; Barbagiovanni, E. G.; Goncharova, L. V.; Simpson, P. J.; Berbezier, I.; Amiard, G.; Favre, L.; Ronda, A.; Faustini, M.; Grosso, D.

    2013-10-01

    Under the proviso that the existing tight-binding (TB) and effective mass (EM) theoretical models provide a good description of the Ge dot energy gap versus dot diameter, this work investigates the effect of nanoparticle size and the size distribution on the near infrared PL spectrum obtained from self-assembled Ge dots grown on a thin layer of TiO2 or SiO2 on Si. For the as-grown samples, the dot PL emission occupies a wide near-infrared band between 0.8 and 1 eV. The PL efficiency versus dot size for four samples was obtained in three steps. Firstly, the PL spectrum was converted to an intensity plot versus dot diameter rather than energy by taking the PL emission from each dot to occur at the dot bandgap calculated using the TB or EM model. Secondly, a numerical form for the physical size distribution of that sample was obtained by performing a least-squares fit of a Gaussian to the dot size distribution measured by atomic force microscopy or transmission electron microscopy. Finally, the PL efficiency versus dot size was calculated using the fitted Gaussian dot size distribution to normalize the PL intensity distribution obtained in the first step. Although the absolute intensities of the PL from the samples vary, the calculated curves are all well-fitted by straight lines on a log-log plot with essentially the same slope for all samples, which indicates that under weak confinement there is a universal power-law increase in PL efficiency with decreasing dot size.

  20. Effect of interfacial layer on the crystal structure of InAs/AlAs{sub 0.16}Sb{sub 0.84}/AlSb quantum wells

    SciTech Connect

    Lin, Y. M.; Chen, C. H.; Lee, C. P.

    2014-04-28

    Ion channeling technique using MeV C{sup 2+} ions and high resolution X-ray diffraction were used to study the crystal quality of an InAs/AlSb-based quantum wells. We found that the InAs quality has a strong dependence on the type of the interface used. With the addition of the InSb-like interface, the crystal quality of the InAs channel was greatly improved. The InAs lattice was fully strained and aligned with the lattice of the buffer layer without any lattice relaxation. On the other hand, if the interface was of the AlAs type, the lattice of the InAs quantum well was relaxed and the crystal quality was poor. This explains why a superior InAs quantum well with high electron mobility and good surface morphology can be achieved with the use of the InSb interface.