Nature of Dielectric Properties, Electric Modulus and AC Electrical Conductivity of Nanocrystalline ZnIn2Se4 Thin Films

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Attia, A. A.; Ali, H. A. M.; Salem, G. F.; Ismail, M. I.

2018-02-01

The structural characteristics of thermally deposited ZnIn2Se4 thin films were indexed utilizing x-ray diffraction as well as scanning electron microscopy techniques. Dielectric properties, electric modulus and AC electrical conductivity of ZnIn2Se4 thin films were examined in the frequency range from 42 Hz to 106 Hz. The capacitance, conductance and impedance were measured at different temperatures. The dielectric constant and dielectric loss decrease with an increase in frequency. The maximum barrier height was determined from the analysis of the dielectric loss depending on the Giuntini model. The real part of the electric modulus revealed a constant maximum value at higher frequencies and the imaginary part of the electric modulus was characterized by the appearance of dielectric relaxation peaks. The AC electrical conductivity obeyed the Jonscher universal power law. Correlated barrier hopping model was the appropriate mechanism for AC conduction in ZnIn2Se4 thin films. Estimation of the density of states at the Fermi level and activation energy, for AC conduction, was carried out based on the temperature dependence of AC electrical conductivity.

Quantum-dot light-emitting diodes utilizing CdSe /ZnS nanocrystals embedded in TiO2 thin film

NASA Astrophysics Data System (ADS)

Kang, Seung-Hee; Kumar, Ch. Kiran; Lee, Zonghoon; Kim, Kyung-Hyun; Huh, Chul; Kim, Eui-Tae

2008-11-01

Quantum-dot (QD) light-emitting diodes (LEDs) are demonstrated on Si wafers by embedding core-shell CdSe /ZnS nanocrystals in TiO2 thin films via plasma-enhanced metallorganic chemical vapor deposition. The n-TiO2/QDs /p-Si LED devices show typical p-n diode current-voltage and efficient electroluminescence characteristics, which are critically affected by the removal of QD surface ligands. The TiO2/QDs /Si system we presented can offer promising Si-based optoelectronic and electronic device applications utilizing numerous nanocrystals synthesized by colloidal solution chemistry.

Piezo-phototronic effect on electroluminescence properties of p-type GaN thin films.

PubMed

Hu, Youfan; Zhang, Yan; Lin, Long; Ding, Yong; Zhu, Guang; Wang, Zhong Lin

2012-07-11

We present that the electroluminescence (EL) properties of Mg-doped p-type GaN thin films can be tuned by the piezo-phototronic effect via adjusting the minority carrier injection efficiency at the metal-semiconductor (M-S) interface by strain induced polarization charges. The device is a metal-semiconductor-metal structure of indium tin oxide (ITO)-GaN-ITO. Under different straining conditions, the changing trend of the transport properties of GaN films can be divided into two types, corresponding to the different c-axis orientations of the films. An extreme value was observed for the integral EL intensity under certain applied strain due to the adjusted minority carrier injection efficiency by piezoelectric charges introduced at the M-S interface. The external quantum efficiency of the blue EL at 430 nm was changed by 5.84% under different straining conditions, which is 1 order of magnitude larger than the change of the green peak at 540 nm. The results indicate that the piezo-phototronic effect has a larger impact on the shallow acceptor states related EL process than on the one related to the deep acceptor states in p-type GaN films. This study has great significance on the practical applications of GaN in optoelectronic devices under a working environment where mechanical deformation is unavoidable such as for flexible/printable light emitting diodes.

Characterizing superconducting thin films using AC Magnetic Susceptibility

NASA Astrophysics Data System (ADS)

Mahoney, C. H.; Porzio, J.; Sullivan, M. C.

2014-03-01

We present our work on using ac magnetic susceptibility to determine the critical temperature of superconducting thin films. In ac magnetic susceptibility, the thin film is placed between two coils. One coil carries an ac signal, creating a varying external magnetic field. We measure the voltage induced in the pick-up coil on the opposite side of the sample and measure how the sample magnetization changes as the temperature changes. We will present our work to use ac susceptibility to determine critical temperature and superconducting volume fraction. Using our own analysis program, we are able to accurately locate the critical temperatures of the samples and determine the transition width. For the superconducting volume fraction, we etch samples in order to control the thicknesses of the sample and measure how much of the material grown on the surface is superconducting. Supported by NFS grant DMR-1305637.

AC impedance analysis of polypyrrole thin films

NASA Technical Reports Server (NTRS)

Penner, Reginald M.; Martin, Charles R.

1987-01-01

The AC impedance spectra of thin polypyrrole films were obtained at open circuit potentials from -0.4 to 0.4 V vs SCE. Two limiting cases are discussed for which simplified equivalent circuits are applicable. At very positive potentials, the predominantly nonfaradaic AC impedance of polypyrrole is very similar to that observed previously for finite porous metallic films. Modeling of the data with the appropriate equivalent circuit permits effective pore diameter and pore number densities of the oxidized film to be estimated. At potentials from -0.4 to -0.3 V, the polypyrrole film is essentially nonelectronically conductive and diffusion of polymer oxidized sites with their associated counterions can be assumed to be linear from the film/substrate electrode interface. The equivalent circuit for the polypyrrole film at these potentials is that previously described for metal oxide, lithium intercalation thin films. Using this model, counterion diffusion coefficients are determined for both semi-infinite and finite diffusion domains. In addition, the limiting low frequency resistance and capacitance of the polypyrrole thin fims was determined and compared to that obtained previously for thicker films of the polymer. The origin of the observed potential dependence of these low frequency circuit components is discussed.

Optical Properties of Hybrid Inorganic/Organic Thin Film Encapsulation Layers for Flexible Top-Emission Organic Light-Emitting Diodes.

PubMed

An, Jae Seok; Jang, Ha Jun; Park, Cheol Young; Youn, Hongseok; Lee, Jong Ho; Heo, Gi-Seok; Choi, Bum Ho; Lee, Choong Hun

2015-10-01

Inorganic/organic hybrid thin film encapsulation layers consist of a thin Al2O3 layer together with polymer material. We have investigated optical properties of thin film encapsulation layers for top-emission flexible organic light-emitting diodes. The transmittance of hybrid thin film encapsulation layers and the electroluminescent spectrum of organic light-emitting diodes that were passivated by hybrid organic/inorganic thin film encapsulation layers were also examined as a function of the thickness of inorganic Al203 and monomer layers. The number of interference peaks, their intensity, and their positions in the visible range can be controlled by varying the thickness of inorganic Al2O3 layer. On the other hand, changing the thickness of monomer layer had a negligible effect on the optical properties. We also verified that there is a trade-off between transparency in the visible range and the permeation of water vapor in hybrid thin film encapsulation layers. As the number of dyads decreased, optical transparency improved while the water vapor permeation barrier was degraded. Our study suggests that, in top-emission organic light-emitting diodes, the thickness of each thin film encapsulation layer, in particular that of the inorganic layer, and the number of dyads should be controlled for highly efficient top-emission flexible organic light-emitting diodes.

Deposition of zinc sulfide thin films by chemical bath process

NASA Astrophysics Data System (ADS)

Oladeji, Isaiah O.; Chow, Lee

1996-11-01

Deposition of high quality zinc sulfide (ZnS) thin film over a large area is required if it is to be effectively used in electroluminescent devices, solar cells, and other optoelectronic devices. Of all deposition techniques, chemical bath deposition (CBD) is the least costly technique that meets the above requirements. Recently it is found that the growth of ZnS film, of thickness less than 100 nm in a single dip, by CBD is facilitated by the use of ammonia and hydrazine as complexing agents. Here we report that the thickness of the deposited ZnS film can be increased if ammonium salt is used as a buffer. We also present an analytical study to explain our results and to further understand the ZnS growth process in CBD.

Confining metal-halide perovskites in nanoporous thin films

PubMed Central

Demchyshyn, Stepan; Roemer, Janina Melanie; Groiß, Heiko; Heilbrunner, Herwig; Ulbricht, Christoph; Apaydin, Dogukan; Böhm, Anton; Rütt, Uta; Bertram, Florian; Hesser, Günter; Scharber, Markus Clark; Sariciftci, Niyazi Serdar; Nickel, Bert; Bauer, Siegfried; Głowacki, Eric Daniel; Kaltenbrunner, Martin

2017-01-01

Controlling the size and shape of semiconducting nanocrystals advances nanoelectronics and photonics. Quantum-confined, inexpensive, solution-derived metal halide perovskites offer narrowband, color-pure emitters as integral parts of next-generation displays and optoelectronic devices. We use nanoporous silicon and alumina thin films as templates for the growth of perovskite nanocrystallites directly within device-relevant architectures without the use of colloidal stabilization. We find significantly blue-shifted photoluminescence emission by reducing the pore size; normally infrared-emitting materials become visibly red, and green-emitting materials become cyan and blue. Confining perovskite nanocrystals within porous oxide thin films drastically increases photoluminescence stability because the templates auspiciously serve as encapsulation. We quantify the template-induced size of the perovskite crystals in nanoporous silicon with microfocus high-energy x-ray depth profiling in transmission geometry, verifying the growth of perovskite nanocrystals throughout the entire thickness of the nanoporous films. Low-voltage electroluminescent diodes with narrow, blue-shifted emission fabricated from nanocrystalline perovskites grown in embedded nanoporous alumina thin films substantiate our general concept for next-generation photonic devices. PMID:28798959

Spectral focusing of broadband silver electroluminescence in nanoscopic FRET-LEDs

NASA Astrophysics Data System (ADS)

Puchert, Robin P.; Steiner, Florian; Plechinger, Gerd; Hofmann, Felix J.; Caspers, Ines; Kirschner, Johanna; Nagler, Philipp; Chernikov, Alexey; Schüller, Christian; Korn, Tobias; Vogelsang, Jan; Bange, Sebastian; Lupton, John M.

2017-07-01

Few inventions have shaped the world like the incandescent bulb. Edison used thermal radiation from ohmically heated conductors, but some noble metals also exhibit 'cold' electroluminescence in percolation films, tunnel diodes, electromigrated nanoparticle aggregates, optical antennas or scanning tunnelling microscopy. The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Nanoparticle electroluminescence is particularly intriguing because it involves localized surface-plasmon resonances with large dipole moments. Such plasmons enable very efficient non-radiative fluorescence resonance energy transfer (FRET) coupling to proximal resonant dipole transitions. Here, we demonstrate nanoscopic FRET-light-emitting diodes which exploit the opposite process, energy transfer from silver nanoparticles to exfoliated monolayers of transition-metal dichalcogenides. In diffraction-limited hotspots showing pronounced photon bunching, broadband silver electroluminescence is focused into the narrow excitonic resonance of the atomically thin overlayer. Such devices may offer alternatives to conventional nano-light-emitting diodes in on-chip optical interconnects.

Spectral focusing of broadband silver electroluminescence in nanoscopic FRET-LEDs.

PubMed

Puchert, Robin P; Steiner, Florian; Plechinger, Gerd; Hofmann, Felix J; Caspers, Ines; Kirschner, Johanna; Nagler, Philipp; Chernikov, Alexey; Schüller, Christian; Korn, Tobias; Vogelsang, Jan; Bange, Sebastian; Lupton, John M

2017-07-01

Few inventions have shaped the world like the incandescent bulb. Edison used thermal radiation from ohmically heated conductors, but some noble metals also exhibit 'cold' electroluminescence in percolation films, tunnel diodes, electromigrated nanoparticle aggregates, optical antennas or scanning tunnelling microscopy. The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Nanoparticle electroluminescence is particularly intriguing because it involves localized surface-plasmon resonances with large dipole moments. Such plasmons enable very efficient non-radiative fluorescence resonance energy transfer (FRET) coupling to proximal resonant dipole transitions. Here, we demonstrate nanoscopic FRET-light-emitting diodes which exploit the opposite process, energy transfer from silver nanoparticles to exfoliated monolayers of transition-metal dichalcogenides. In diffraction-limited hotspots showing pronounced photon bunching, broadband silver electroluminescence is focused into the narrow excitonic resonance of the atomically thin overlayer. Such devices may offer alternatives to conventional nano-light-emitting diodes in on-chip optical interconnects.

Interface-Free Area-Scalable Self-Powered Electroluminescent System Driven by Triboelectric Generator

PubMed Central

Yan Wei, Xiao; Kuang, Shuang Yang; Yang Li, Hua; Pan, Caofeng; Zhu, Guang; Wang, Zhong Lin

2015-01-01

Self-powered system that is interface-free is greatly desired for area-scalable application. Here we report a self-powered electroluminescent system that consists of a triboelectric generator (TEG) and a thin-film electroluminescent (TFEL) lamp. The TEG provides high-voltage alternating electric output, which fits in well with the needs of the TFEL lamp. Induced charges pumped onto the lamp by the TEG generate an electric field that is sufficient to excite luminescence without an electrical interface circuit. Through rational serial connection of multiple TFEL lamps, effective and area-scalable luminescence is realized. It is demonstrated that multiple types of TEGs are applicable to the self-powered system, indicating that the system can make use of diverse mechanical sources and thus has potentially broad applications in illumination, display, entertainment, indication, surveillance and many others. PMID:26338365

Multilayer organic based structures with enhanced hole transport

NASA Astrophysics Data System (ADS)

Mladenova, D.; Sinigersky, V.; Budurova, D.; Dobreva, T.; Karashanova, D.; Dimov, D.; Zhivkov, I.

2010-11-01

Multilayer Organic Based Devices (OBDs) were constructed by subsequent casting of organic films (from polymers, soluble in the same organic solvent). The problem with dissolution of the underlying layer was avoided by using electrophoretic deposition technique. Optimized conditions for electrophoretic deposition (EPD) of thin films with homogeneous and smooth surfaces, as confirmed by SEM, were found. The EPD, carried out at constant current, requires continuous increase of the voltage between the electrodes. In this way the decreased deposition rate caused by the decreased concentration of the material in the suspension and the increased thickness of the film deposited is compensated. The SEM images and the current voltage characteristics recorded, show that the hole transport polyvinylcarbazole (PVK) underlayer survive the treatment with the suspension used for the electrophoretic deposition of the active poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene vinylene] electroluminescent layer. The PVK hole transport layer increases the device current, as confirmed by the current-voltage measurements. The results obtained demonstrate the possibility of OBDs preparation for electroluminescent and photovoltaic applications.

Oxygen surface exchange kinetics measurement by simultaneous optical transmission relaxation and impedance spectroscopy: Sr(Ti,Fe)O3-x thin film case study.

PubMed

Perry, Nicola H; Kim, Jae Jin; Tuller, Harry L

2018-01-01

We compare approaches to measure oxygen surface exchange kinetics, by simultaneous optical transmission relaxation (OTR) and AC-impedance spectroscopy (AC-IS), on the same mixed conducting SrTi 0.65 Fe 0.35 O 3-x film. Surface exchange coefficients were evaluated as a function of oxygen activity in the film, controlled by gas partial pressure and/or DC bias applied across the ionically conducting yttria-stabilized zirconia substrate. Changes in measured light transmission through the film over time (relaxations) resulted from optical absorption changes in the film corresponding to changes in its oxygen and oxidized Fe (~Fe 4+ ) concentrations; such relaxation profiles were successfully described by the equation for surface exchange-limited kinetics appropriate for the film geometry. The k chem values obtained by OTR were significantly lower than the AC-IS derived k chem values and k q values multiplied by the thermodynamic factor (bulk or thin film), suggesting a possible enhancement in k by the metal current collectors (Pt, Au). Long-term degradation in k chem and k q values obtained by AC-IS was also attributed to deterioration of the porous Pt current collector, while no significant degradation was observed in the optically derived k chem values. The results suggest that, while the current collector might influence measurements by AC-IS, the OTR method offers a continuous, in situ , and contact-free method to measure oxygen exchange kinetics at the native surfaces of thin films.

Oxygen surface exchange kinetics measurement by simultaneous optical transmission relaxation and impedance spectroscopy: Sr(Ti,Fe)O3-x thin film case study

PubMed Central

Perry, Nicola H.; Kim, Jae Jin; Tuller, Harry L.

2018-01-01

Abstract We compare approaches to measure oxygen surface exchange kinetics, by simultaneous optical transmission relaxation (OTR) and AC-impedance spectroscopy (AC-IS), on the same mixed conducting SrTi0.65Fe0.35O3-x film. Surface exchange coefficients were evaluated as a function of oxygen activity in the film, controlled by gas partial pressure and/or DC bias applied across the ionically conducting yttria-stabilized zirconia substrate. Changes in measured light transmission through the film over time (relaxations) resulted from optical absorption changes in the film corresponding to changes in its oxygen and oxidized Fe (~Fe4+) concentrations; such relaxation profiles were successfully described by the equation for surface exchange-limited kinetics appropriate for the film geometry. The kchem values obtained by OTR were significantly lower than the AC-IS derived kchem values and kq values multiplied by the thermodynamic factor (bulk or thin film), suggesting a possible enhancement in k by the metal current collectors (Pt, Au). Long-term degradation in kchem and kq values obtained by AC-IS was also attributed to deterioration of the porous Pt current collector, while no significant degradation was observed in the optically derived kchem values. The results suggest that, while the current collector might influence measurements by AC-IS, the OTR method offers a continuous, in situ, and contact-free method to measure oxygen exchange kinetics at the native surfaces of thin films. PMID:29511391

Oxide-free aC/Zr0.65Al0.075Cu0.275/aC phase plates for transmission electron microscopy.

PubMed

Dries, M; Obermair, M; Hettler, S; Hermann, P; Seemann, K; Seifried, F; Ulrich, S; Fischer, R; Gerthsen, D

2018-06-01

Thin-film phase plates (PP) have become a valuable tool for the imaging of organic objects in transmission electron microscopy (TEM). The thin film usually consists of amorphous carbon (aC), which undergoes rapid aging under intense illumination with high-energy electrons. The limited lifetime of aC film PPs calls for alternative PP materials with improved material stability. This work presents thin-film PPs fabricated from the metallic glass alloy Zr 0.65 Al 0.075 Cu 0.275 (ZAC), which was identified as a promising PP material with beneficial properties, such as a large inelastic mean free path. An adverse effect of the ZAC alloy is the formation of a surface oxide layer in ambient air, which reduces the electrical conductivity and causes electrostatic charging in the electron beam. To avoid surface oxidation, the ZAC alloy is enclosed by thin aC layers. The resulting aC/ZAC/aC layer system is used to fabricate Zernike and Hilbert PPs. Phase-contrast TEM imaging is demonstrated for a sample of carbon nanotubes, which show strong contrast enhancement in PP TEM images. Copyright © 2018 Elsevier B.V. All rights reserved.

A chlorine precursor route (CPR) to poly(p-phenylene vinylene) light emitting diodes

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

Heieh, B.R.; Antoniadis, H.; Bland, D.C.

1995-12-01

We use a chlorine precursor route (CPR) to fabricate PPV based electroluminescent (EL) devices. 1,4- Bis(chloromethyl)-2,3-diphenylbenzene was polymerized with one equivalent amount of potassium t-butoxide (t-BuOK) to give the corresponding chlorine precursor polymer with very high molecular weights. This polymer is soluble in common organic solvents and is highly stable in the solid state and in solution. Thin films of the precursor polymer were spin cast on indiumtin-oxide (ITO) coated glass substrates followed by thermal conversion at 300{degrees}C for 2 h to give DP-PPV thin films. We found that CPR is more convenient and reliable than sulfonium precursor route formore » the fabrication of PPV thin film EL devices. Efficient emission of green light (500 nm) was observed for Mg/DP-PPV/ITO and Al/DP-PPV/ITO single layer devices.« less

Precursor-route ZnO films from a mixed casting solvent for high performance aqueous electrolyte-gated transistors.

PubMed

Althagafi, Talal M; Algarni, Saud A; Al Naim, Abdullah; Mazher, Javed; Grell, Martin

2015-12-14

We significantly improved the performance of precursor-route semiconducting zinc oxide (ZnO) films in electrolyte-gated thin film transistors (TFTs). We find that the organic precursor to ZnO, zinc acetate (ZnAc), dissolves more readily in a 1 : 1 mixture of ethanol (EtOH) and acetone than in pure EtOH, pure acetone, or pure isopropanol. XPS and SEM characterisation show improved morphology of ZnO films converted from a mixed solvent cast ZnAc precursor compared to the EtOH cast precursor. When gated with a biocompatible electrolyte, phosphate buffered saline (PBS), ZnO thin film transistors (TFTs) derived from mixed solvent cast ZnAc give 4 times larger field effect current than similar films derived from ZnAc cast from pure EtOH. The sheet resistance at VG = VD = 1 V is 30 kΩ □(-1), lower than for any organic TFT, and lower than for any electrolyte-gated ZnO TFT reported to date.

Inorganic Halide Perovskites for Efficient Light-Emitting Diodes.

PubMed

Yantara, Natalia; Bhaumik, Saikat; Yan, Fei; Sabba, Dharani; Dewi, Herlina A; Mathews, Nripan; Boix, Pablo P; Demir, Hilmi Volkan; Mhaisalkar, Subodh

2015-11-05

Lead-halide perovskites have transcended photovoltaics. Perovskite light-emitting diodes (PeLEDs) emerge as a new field to leverage on these fascinating semiconductors. Here, we report the first use of completely inorganic CsPbBr3 thin films for enhanced light emission through controlled modulation of the trap density by varying the CsBr-PbBr2 precursor concentration. Although pure CsPbBr3 films can be deposited from equimolar CsBr-PbBr2 and CsBr-rich solutions, strikingly narrow emission line (17 nm), accompanied by elongated radiative lifetimes (3.9 ns) and increased photoluminescence quantum yield (16%), was achieved with the latter. This is translated into the enhanced performance of the resulting PeLED devices, with lower turn-on voltage (3 V), narrow electroluminescence spectra (18 nm) and higher electroluminescence intensity (407 Cd/m(2)) achieved from the CsBr-rich solutions.

Method for Aluminum Oxide Thin Films Prepared through Low Temperature Atomic Layer Deposition for Encapsulating Organic Electroluminescent Devices

PubMed Central

Li, Hui-Ying; Liu, Yun-Fei; Duan, Yu; Yang, Yong-Qiang; Lu, Yi-Nan

2015-01-01

Preparation of dense alumina (Al2O3) thin film through atomic layer deposition (ALD) provides a pathway to achieve the encapsulation of organic light emitting devices (OLED). Unlike traditional ALD which is usually executed at higher reaction n temperatures that may affect the performance of OLED, this application discusses the development on preparation of ALD thin film at a low temperature. One concern of ALD is the suppressing effect of ambient temperature on uniformity of thin film. To mitigate this issue, the pumping time in each reaction cycle was increased during the preparation process, which removed reaction byproducts and inhibited the formation of vacancies. As a result, the obtained thin film had both high uniformity and density properties, which provided an excellent encapsulation performance. The results from microstructure morphology analysis, water vapor transmission rate, and lifetime test showed that the difference in uniformity between thin films prepared at low temperatures, with increased pumping time, and high temperatures was small and there was no obvious influence of increased pumping time on light emitting performance. Meanwhile, the permeability for water vapor of the thin film prepared at a low temperature was found to reach as low as 1.5 × 10−4 g/(m2·day) under ambient conditions of 25 °C and 60% relative humidity, indicating a potential extension in the lifetime for the OLED. PMID:28787960

Flexible, polymer gated, AC-driven organic electroluminescence devices

NASA Astrophysics Data System (ADS)

Xu, Junwei; Carroll, David L.

2017-08-01

Comparing rigid inorganic layer, polymeric semiconducting gate layer exhibits superior flexibility as well as efficient carrier manipulation in high frequency AC cycles. Mechanism of the carrier manipulation at the gate in forward and reversed bias of AC cycle is studied. The flexible PET-based AC-OEL device with poly[(9,9-bis(3'-((N,N-dimethyl)-Nethylammonium)- propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN-Br) gate shows a stable electroluminescent performance in frequency sweep with a color rendering index (CRI) over 81 at 2800K color temperature.

[Preparation and transmissivity of ZnS nanocolumn thin films with glancing angle deposition technology].

PubMed

Lu, Li-Fang; Xu, Zheng; Zhang, Fu-Jun; Zhao, Su-Ling; Song, Dan-Dan; Li, Jun-Ming; Wang, Yong-Sheng; Xu, Xu-Rong

2010-02-01

Nanocrystalline ZnS thin films were fabricated by glancing angle deposition (GLAD) technology in an electron beam evaporation system. Deposition was carried out in the custom vacuum chamber at a base pressure 3 x 10(-4) Pa, and the deposition rate was fixed at 0.2 nm x s(-1). ZnS films were deposited on pieces of indium tin oxide (ITO) substrates when the oblique angle of the substrate relative to the incoming molecular flux was set to 0 degrees, 80 degrees and 85 degrees off the substrate normal respectively. X-ray diffraction (XRD) spectra and scanning electron microscope (SEM) images showed that ZnS nanocrystalline films were formed on the substrates at different oblique angle, but the nanocolumn structure was only formed under the situation of alpha = 80 degrees and 85 degrees. The dynamics during the deposition process of the ZnS films at alpha = 0 degrees, 80 degrees and 85 degrees was analyzed. The transmitted spectra of ZnS thin films deposited on ITO substrates showed that the ZnS nanocolumn thin films could enhance the transmissivity in visible range. The ZnS nanocolumn could be used into electroluminescence device, and it would enhance the luminous efficiency of the device.

Evidence for Space Charge in Atomic Layer Epitaxy ZnS:Mn Alternating- Current Thin-Film Electroluminescent Devices,

DTIC Science & Technology

1993-01-01

exists wior with ra hho agop io model within the bulk portion of the phosphor layer. Although tAon to obtin alteratinbilarplses with mp del this...field region within the ZnS. emission with a peak at 460 nm and which exhibited ther- Postulating the existence of such a low-field region mal

AC electrical conductivity and dielectric relaxation studies on n-type organic thin films of N, N‧-Dimethyl-3,4,9,10-perylenedicarboximide (DMPDC)

NASA Astrophysics Data System (ADS)

Qashou, Saleem I.; Darwish, A. A. A.; Rashad, M.; Khattari, Z.

2017-11-01

Both Alternating current (AC) conductivity and dielectric behavior of n-type organic thin films of N, N‧-Dimethyl-3,4,9,10-perylenedicarboximide (DMPDC) have been investigated. Fourier transformation infrared (FTIR) spectroscopy is used for identifying both powder and film bonds which confirm that there are no observed changes in the bonds between the DMPDC powder and evaporated films. The dependence of AC conductivity on the temperature for DMPDC evaporated films was explained by the correlated barrier hopping (CBH) model. The calculated barrier height using CBH model shows a decreasing behavior with increasing temperature. The mechanism of dielectric relaxation was interpreted on the basis of the modulus of the complex dielectric. The calculated activation energy of the relaxation process was found to be 0.055 eV.

Detection of microstructural defects in chalcopyrite Cu(In,Ga)Se2 solar cells by spectrally-filtered electroluminescence

NASA Astrophysics Data System (ADS)

Skvarenina, L.; Gajdos, A.; Macku, R.; Skarvada, P.

2017-12-01

The aim of this research is to detect and localize microstructural defects by using an electrically excited light emission from a forward/reverse-bias stressed pn-junction in thin-film Cu(In; Ga)Se2 solar cells with metal wrap through architecture. A different origin of the local light emission from intrinsic/extrinsic imperfections in these chalcopyrite-based solar cells can be distinguished by a spectrally-filtered electroluminescence mapping. After a light emission mapping and localization of the defects in a macro scale is performed a micro scale exploration of the solar cell surface by a scanning electron microscope which follows the particular defects obtained by an electroluminescence. In particular, these macroscopic/microscopic examinations are performed independently, then the searching of the corresponding defects in the micro scale is rather difficult due to a diffused light emission obtained from the macro scale localization. Some of the defects accompanied by a highly intense light emission very often lead to a strong local overheating. Therefore, the lock-in infrared thermography is also performed along with an electroluminescence mapping.

Ultraviolet electroluminescence from hybrid inorganic/organic ZnO/GaN/poly(3-hexylthiophene) dual heterojunctions.

PubMed

Chen, Yungting; Shih, Hanyu; Wang, Chunhsiung; Hsieh, Chunyi; Chen, Chihwei; Chen, Yangfang; Lin, Taiyuan

2011-05-09

Based on hybrid inorganic/organic n-ZnO nanorods/p-GaN thin film/poly(3-hexylthiophene)(P3HT) dual heterojunctions, the light emitting diode (LED) emits ultraviolet (UV) radiation (370 nm - 400 nm) and the whole visible light (400 nm -700 nm) at the low injection current density. Meanwhile, under the high injection current density, the UV radiation overwhelmingly dominates the room-temperature electroluminescence spectra, exponentially increases with the injection current density and possesses a narrow full width at half maximum less than 16 nm. Comparing electroluminescence with photoluminescence spectra, an enormously enhanced transition probability of the UV luminescence in the electroluminescence spectra was found. The P3HT layer plays an essential role in helping the UV emission from p-GaN material because of its hole-conductive characteristic as well as the band alignment with respect to p-GaN. With our new finding, the result shown here may pave a new route for the development of high brightness LEDs derived from hybrid inorganic/organic heterojuctions.

Low-temperature metal-oxide thin-film transistors formed by directly photopatternable and combustible solution synthesis.

PubMed

Rim, You Seung; Lim, Hyun Soo; Kim, Hyun Jae

2013-05-01

We investigated the formation of ultraviolet (UV)-assisted directly patternable solution-processed oxide semiconductor films and successfully fabricated thin-film transistors (TFTs) based on these films. An InGaZnO (IGZO) solution that was modified chemically with benzoylacetone (BzAc), whose chelate rings decomposed via a π-π* transition as result of UV irradiation, was used for the direct patterning. A TFT was fabricated using the directly patterned IGZO film, and it had better electrical characteristics than those of conventional photoresist (PR)-patterned TFTs. In addition, the nitric acid (HNO3) and acetylacetone (AcAc) modified In2O3 (NAc-In2O3) solution exhibited both strong UV absorption and high exothermic reaction. This method not only resulted in the formation of a low-energy path because of the combustion of the chemically modified metal-oxide solution but also allowed for photoreaction-induced direct patterning at low temperatures.

Converse magnetoelectric coupling in NiFe/Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–PbTiO{sub 3} nanocomposite thin films grown on Si substrates

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

Feng, Ming; Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University, Siping 136000; Hu, Jiamian

2013-11-04

Multiferroic NiFe (∼30 nm)/Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–PbTiO{sub 3}(PMN–PT, ∼220 nm) bilayered thin films were grown on common Pt/Ti/SiO{sub 2}/Si substrates by a combination of off-axis magnetron sputtering and sol-gel spin-coating technique. By using AC-mode magneto-optical Kerr effect technique, the change in the Kerr signal (magnetization) of the NiFe upon applying a low-frequency AC voltage to the PMN–PT film was in situ acquired at zero magnetic field. The obtained Kerr signal versus voltage loop essentially tracks the electromechanical strain curve of the PMN–PT thin film, clearly demonstrating a strain-mediated converse magnetoelectric coupling, i.e., voltage-modulated magnetization, in the NiFe/PMN–PT nanocomposite thin films.

Air-stable electrical conduction in oxidized poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylene vinylene] thin films

NASA Astrophysics Data System (ADS)

Hossein-Babaei, F.; Shabani, P.; Azadinia, M.

2013-11-01

Oxidation-caused electroluminescence and electrical conduction deteriorations in poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) have prevented the material from being used in applications requiring air exposure. Here, we report air-stable electrical conduction in oxidized MEH-PPV layers produced by room temperature annealing of MEH-PPV thin films in air. Oxidized layers exhibit lower, but stable, conductivities. As the process is irreversible, the final conductivity is retained in vacuum, inert gas, hydrogen, and oxygen. The oxidation rates recorded at different conditions for layers of varied thickness and electrode configuration are described by a surface oxidation model. Potentials of the oxidized MEH-PPV layers in sensor technology are demonstrated.

Characterization of the electro-optic effect in styrylpyridinium cyanine dye thin-film crystals by an ac modulation method

NASA Astrophysics Data System (ADS)

Yoshimura, Tetsuzo

1987-09-01

The electro-optic effect in styrylpyridinium cyanine dye (SPCD) thin-film crystals is characterized by a newly developed ac modulation method that is effective in characterizing thin-film materials of small area. SPCD thin-film crystals 3-10 μm thick were grown from a methanol solution of SPCD. The crystal shows strong dichroism and anisotropy of refractive index, indicating that molecular dipole moments align along a definite direction (z axis). When an electric field is applied along the z axis, SPCD thin-film crystals show a large figure of merit of electro-optic phase retardation of 6.5×10-10 m/V, which is 5 times as large as in LiNbO3 crystal, 2 times that in 2-methyl-4-nitroaniline (MNA) crystal, and is the largest ever reported in organic solids. The electro-optic coefficient r33 of SPCD crystals is estimated to be approximately 4.3×10-10 m/V, which is 6 times larger than that of an MNA crystal. This value is consistent with that expected from second-harmonic generation measurements.

Multilevel organization in hybrid thin films for optoelectronic applications.

PubMed

Vohra, Varun; Bolognesi, Alberto; Calzaferri, Gion; Botta, Chiara

2009-10-20

In this work we report two simple approaches to prepare hybrid thin films displaying a high concentration of zeolite crystals that could be used as active layers in optoelectronic devices. In the first approach, in order to organize nanodimensional zeolite crystals of 40 nm diameter in an electroactive environment, we chemically modify their external surface and play on the hydrophilic/hydrophobic forces. We obtain inorganic nanocrystals that self-organize in honeycomb electroluminescent polymer structures obtained by breath figure formation. The different functionalizations of the zeolite surface result in different organizations inside the cavities of the polymeric structure. The second approach involving soft-litography techniques allows one to arrange single dye-loaded zeolite L crystals of 800 nm of length by mechanical loading into the nanocavities of a conjugated polymer. Both techniques result in the formation of thin hybrid films displaying three levels of organization: organization of the dye molecules inside the zeolite nanochannels, organization of the zeolite crystals inside the polymer cavities, and micro- or nanostructuration of the polymer.

Purely hopping conduction in c-axis oriented LiNbO3 thin films

NASA Astrophysics Data System (ADS)

Shandilya, Swati; Tomar, Monika; Sreenivas, K.; Gupta, Vinay

2009-05-01

Dielectric constant and ac conductivity of highly c-axis oriented LiNbO3 thin film grown by pulsed laser deposition were studied in a metal-insulator-metal configuration over a wide temperature (200 to 450 K) and frequency (100 Hz to 1 MHz) range. The preferred oriented Al (1%) doped ZnO film with electrical conductivity 1.1×103 Ω-1 cm-1 was deposited for dual purpose: (1) to serve as nucleating center for LiNbO3 crystallites along preferred c-axis growth direction, and (2) to act as a suitable bottom electrode for electrical studies. The room temperature dc conductivity (σdc) of LiNbO3 film was about 5.34×10-10 Ω-1 cm-1 with activation energy ˜0.3 eV, indicating extrinsic conduction. The ac conductivity σac was found to be much higher in comparison to σdc in the low temperature region (<300 K) and exhibits a power law behavior due to the hopping of charge carriers. In higher temperature region (>300 K), σac shows a weak frequency dependence, whereas dielectric constant exhibits a strong frequency dispersion. The dielectric dispersion data has been discussed in the light of theoretical models based on Debye type mixed conduction and purely hopping conduction. The dominant conduction in c-axis oriented LiNbO3 thin film is attributed to the purely hopping where both σdc and σac arise due to same mechanism.

Resistivity behavior of optimized PbTiO3 thin films prepared by spin coating method

NASA Astrophysics Data System (ADS)

Nurbaya, Z.; Wahid, M. H.; Rozana, M. D.; Alrokayan, S. A. H.; Khan, H. A.; Rusop, M.

2018-05-01

Th is study presents the resistivity behavior of PbTiO3 thin films which were prepared towards metal-insulator-metal capacitor device fabrication. The PbTiO3 thin films were prepared through sol-gel spin coating method that involved various deposition parameters that is (1) different molar concentration of PbTiO3 solutions, (2) various additional PbAc-content in PbTiO3 solutions, and (3) various annealing temperature on PbTiO3 thin films. Hence, an electrical measurement of current versus voltage was done to determine the resistivity behavior of PbTiO3 thin films.

Electroluminescence in CdSe/PVA nanocomposites

NASA Astrophysics Data System (ADS)

Kumari, Sarita; Ramrakhiani, M.; Khare, P. K.

2018-05-01

The synthesis of II-VI nanocrystal into the polymer matrix to form nanocomposites with adjustable nanocrystal is of great interest size is a big challenge to the scientific community. In present work semiconducting CdSe/PVA thin film were synthesized by single step solution method with different concentration of CdSe. The as-prepared products were characterized by UV-Visible absorption spectra and FESEM. Absorption spectra of CdSe/PVA nanocomposites indicated that the position of absorption edge shifts to smaller wavelength by increasing the concentration of CdSe. For Electroluminescence a turn on voltage is required for light emission and brightness increases with voltage. Turn on voltage is found to decrease as CdSe concentration is increased. The voltage-current curve represents ohmic nature for all EL cells.

Single n-GaN microwire/p-Silicon thin film heterojunction light-emitting diode.

PubMed

Ahn, Jaehui; Mastro, Michael A; Klein, Paul B; Hite, Jennifer K; Feigelson, Boris; Eddy, Charles R; Kim, Jihyun

2011-10-24

The emission and waveguiding properties of individual GaN microwires as well as devices based on an n-GaN microwire/p-Si (100) junction were studied for relevance in optoelectronics and optical circuits. Pulsed photoluminescence of the GaN microwire excited in the transverse or longitudinal direction demonstrated gain. These n-type GaN microwires were positioned mechanically or by dielectrophoretic force onto pre-patterned electrodes on a p-type Si (100) substrate. Electroluminescence from this p-n point junction was characteristic of a heterostructure light-emitting diode. Additionally, waveguiding was observed along the length of the microwire for light originating from photoluminescence as well as from electroluminescence generated at the p-n junction. © 2011 Optical Society of America

Controlled electroluminescence of n-ZnMgO/p-GaN light-emitting diodes

NASA Astrophysics Data System (ADS)

Goh, E. S. M.; Yang, H. Y.; Han, Z. J.; Chen, T. P.; Ostrikov, K.

2012-12-01

Effective control of room-temperature electroluminescence of n-ZnMgO/p-GaN light-emitting diodes (LEDs) over both emission intensity and wavelength is demonstrated. With varied Mg concentration, the intensity of LEDs in the near-ultraviolet region is increased due to the effective radiative recombination in the ZnMgO layer. Furthermore, the emission wavelength is shifted to the green/yellow spectral region by employing an indium-tin-oxide thin film as the dopant source, where thermally activated indium diffusion creates extra deep defect levels for carrier recombination. These results clearly demonstrate the effectiveness of controlled metal incorporation in achieving high energy efficiency and spectral tunability of the n-ZnMgO/p-GaN LED devices.

Thin-Film Photoluminescent Properties and the Atomistic Model of Mg2TiO4 as a Non-rare Earth Matrix Material for Red-Emitting Phosphor

NASA Astrophysics Data System (ADS)

Huang, Chieh-Szu; Chang, Ming-Chuan; Huang, Cheng-Liang; Lin, Shih-kang

2016-12-01

Thin-film electroluminescent devices are promising solid-state lighting devices. Red light-emitting phosphor is the key component to be integrated with the well-established blue light-emitting diode chips for stimulating natural sunlight. However, environmentally hazardous rare-earth (RE) dopants, e.g. Eu2+ and Ce2+, are commonly used for red-emitting phosphors. Mg2TiO4 inverse spinel has been reported as a promising matrix material for "RE-free" red light luminescent material. In this paper, Mg2TiO4 inverse spinel is investigated using both experimental and theoretical approaches. The Mg2TiO4 thin films were deposited on Si (100) substrates using either spin-coating with the sol-gel process, or radio frequency sputtering, and annealed at various temperatures ranging from 600°C to 900°C. The crystallinity, microstructures, and photoluminescent properties of the Mg2TiO4 thin films were characterized. In addition, the atomistic model of the Mg2TiO4 inverse spinel was constructed, and the electronic band structure of Mg2TiO4 was calculated based on density functional theory. Essential physical and optoelectronic properties of the Mg2TiO4 luminance material as well as its optimal thin-film processing conditions were comprehensively reported.

Tentative anatomy of ZnS-type electroluminescence

NASA Astrophysics Data System (ADS)

Bringuier, E.

1994-05-01

The paper reviews the electrical and optical mechanisms at work in sulfide-based thin-film electroluminescence display devices within the framework of general semiconductor physics. The electrical problem is twofold: (i) charge carriers are sourced at high electric field in a nominally insulating material, the carrier density increasing by almost eight orders of magnitude; (ii) the carriers are transported at high field, with an average energy largely exceeding the thermal one. (i) Carrier sourcing is best understood from direct-current-driven ZnS films, and is ascribed to partly filled deep donors transferring electrons to the conduction band by Fowler-Nordheim tunneling. The deep donors also act as carrier sinkers, and evidence for space charge is afforded by small-signal impedance analysis disclosing a markedly inductive behavior. The conduction picture obtained from dc-driven films is then used to clarify the operation of alternating-current electroluminescence structures where the sulfide is sandwiched between two blocking oxide layers. The electrostatics of the ac structure is investigated in detail including space charge and field nonuniformity, and external observables are related to internal quantities. The simple model of interfacial carrier sourcing and sinking is examined. (ii) High-field electronic transport is controlled by the electron-phonon interaction, and the modeling resorts to numerical simulations or the lucky-drift concept. At low electron energies the interaction with phonons is predominantly polar, while at optical energies it proceeds via deformation potential scattering. In spite of the uncertainties in transport models in that range, it is likely that ˜50% of the electrons overtake 2 eV at the usual operating fields in ZnS. Light emission is associated with impurity luminescence centers embedded in the sulfide host. They are excited while current is flowing, and the ensuing relaxation is partly radiative. We describe the two ways in which an impurity may be excited electrically, namely, impact excitation (internal promotion of the center to a state of higher energy) or impact ionization (with an electron released to the host conduction band). The actual excitation mechanism depends on the position of the impurity excited level relative to the host energy bands. A calculation of the excitation yield (number of excited centers per transferred electron) is detailed in the case of impact excitation. Lastly, a phenomenological description of the various relaxation channels is given in terms of formal kinetics, and the relative importance of radiative relaxation is assessed by means of the deexcitation yield (fraction of centers decaying radiatively), which is defined in the case of the impulse response.

Influence of stress on the structural and dielectric properties of rf magnetron sputtered zinc oxide thin film

NASA Astrophysics Data System (ADS)

Menon, Rashmi; Sreenivas, K.; Gupta, Vinay

2008-05-01

Highly c axis oriented zinc oxide (ZnO) thin films have been prepared on 1737 Corning glass substrate by planar rf magnetron sputtering under varying pressure (10-50mTorr) and different oxygen percentage (40%-100%) in reactive gas mixtures. The as-grown ZnO thin films were found to have stress over a wide range from -6×1010to-9×107dynes/cm2. The presence of stress depends strongly on processing conditions, and films become almost stress free under a unique combination of sputtering pressure and reactive gas composition. The studies show a correlation of stress with structural and electrical properties of the ZnO thin film. The stressed films possess high electrical conductivity and exhibits strong dielectric dispersion over a wide frequency (1kHz-1MHz). The dielectric constant ɛ'(ω) of stress free ZnO film was almost frequency independent and was close to the bulk value. The measured value of dc conductivity, σdc(ω) and ac conductivity σac(ω) of stress free ZnO film was 1.3×10-9 and 6.8×10-5Ω-1cm-1, respectively. The observed variation in the structural and electrical properties of ZnO thin film with stress has been analyzed in the light of growth kinetics.

High Photoluminescence Quantum Yields in Organic Semiconductor-Perovskite Composite Thin Films.

PubMed

Longo, Giulia; La-Placa, Maria-Grazia; Sessolo, Michele; Bolink, Henk J

2017-10-09

One of the obstacles towards efficient radiative recombination in hybrid perovskites is a low exciton binding energy, typically in the orders of tens of meV. It has been shown that the use of electron-donor additives can lead to a substantial reduction of the non-radiative recombination in perovskite films. Herein, the approach using small molecules with semiconducting properties, which are candidates to be implemented in future optoelectronic devices, is presented. In particular, highly luminescent perovskite-organic semiconductor composite thin films have been developed, which can be processed from solution in a simple coating step. By tuning the relative concentration of methylammonium lead bromide (MAPbBr 3 ) and 9,9spirobifluoren-2-yl-diphenyl-phosphine oxide (SPPO1), it is possible to achieve photoluminescent quantum yields (PLQYs) as high as 85 %. This is attributed to the dual functions of SPPO1 that limit the grain growth while passivating the perovskite surface. The electroluminescence of these materials was investigated by fabricating multilayer LEDs, where charge injection and transport was found to be severely hindered for the perovskite/SPPO1 material. This was alleviated by partially substituting SPPO1 with a hole-transporting material, 1,3-bis(N-carbazolyl)benzene (mCP), leading to bright electroluminescence. The potential of combining perovskite and organic semiconductors to prepare materials with improved properties opens new avenues for the preparation of simple lightemitting devices using perovskites as the emitter. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Differential AC chip calorimeter for in situ investigation of vapor deposited thin films

NASA Astrophysics Data System (ADS)

Ahrenberg, Mathias; Schick, Christoph; Huth, Heiko; Schoifet, Evgeni; Ediger, Mark; Whitaker, Katie

2012-02-01

Physical vapor deposition (PVD) can be used to produce thin films with particular material properties like extraordinarily stable glasses of organic molecules. We describe an AC chip calorimeter for in-situ heat capacity measurements of as-deposited nanometer thin films of organic glass formers. The calorimetric system is based on a differential AC chip calorimeter which is placed in the vacuum chamber for physical vapor deposition. The sample is directly deposited onto one calorimetric chip sensor while the other sensor is protected against deposition. The device and the temperature calibration procedure are described. The latter makes use of the phase transitions of cyclopentane and the frequency dependence of the dynamic glass transition of toluene and ethylbenzene. Sample thickness determination is based on a finite element modeling (FEM) of the sensor sample arrangement. A layer of toluene was added to the sample sensor and its thickness was varied in an iterative way until the model fits the experimental data.

Ga flux dependence of Er-doped GaN luminescent thin films

NASA Astrophysics Data System (ADS)

Lee, D. S.; Steckl, A. J.

2002-02-01

Er-doped GaN thin films have been grown on (111) Si substrates with various Ga fluxes in a radio frequency plasma molecular beam epitaxy system. Visible photoluminescence (PL) and electroluminescence (EL) emission at 537/558 nm and infrared (IR) PL emission at 1.5 μm from GaN:Er films exhibited strong dependence on the Ga flux. Both visible and IR PL and visible EL increase with the Ga flux up to the stoichiometric growth condition, as determined by growth rate saturation. Beyond this condition, all luminescence levels abruptly dropped to the detection limit with increasing Ga flux. The Er concentration, measured by secondary ion mass spectroscopy and Rutherford backscattering, decreases with increasing Ga flux under N-rich growth conditions and remains constant above the stoichiometric growth condition. X-ray diffraction indicated that the crystalline quality of the GaN:Er film was improved with increasing Ga flux up to stoichiometric growth condition and then saturated. Er ions in the films grown under N-rich conditions appear much more optically active than those in the films grown under Ga-rich conditions.

Conductive polymer-based material

DOEpatents

McDonald, William F [Utica, OH; Koren, Amy B [Lansing, MI; Dourado, Sunil K [Ann Arbor, MI; Dulebohn, Joel I [Lansing, MI; Hanchar, Robert J [Charlotte, MI

2007-04-17

Disclosed are polymer-based coatings and materials comprising (i) a polymeric composition including a polymer having side chains along a backbone forming the polymer, at least two of the side chains being substituted with a heteroatom selected from oxygen, nitrogen, sulfur, and phosphorus and combinations thereof; and (ii) a plurality of metal species distributed within the polymer. At least a portion of the heteroatoms may form part of a chelation complex with some or all of the metal species. In many embodiments, the metal species are present in a sufficient concentration to provide a conductive material, e.g., as a conductive coating on a substrate. The conductive materials may be useful as the thin film conducting or semi-conducting layers in organic electronic devices such as organic electroluminescent devices and organic thin film transistors.

Nonlinear optical properties of Nd3+-Li+ co-doped ZnS-PVP thin films

NASA Astrophysics Data System (ADS)

Talwatkar, S. S.; Sunatkari, A. L.; Tamgadge, Y. S.; Muley, G. G.

2018-04-01

The nonlinear optical properties of Nd3+-Li+ co-doped ZnS-PVP nanocomposite were studied using a continuous wave (CW) He-Ne laser (λ = 632.8 nm)by z-scan technique. The nonlinear refractive index (n2), absorption coefficient (β) and third order nonlinear susceptibility (χ(3)) of PVP thin films embedded with Nd3+-Li+ co-doped ZnS NPs was found in the order of 10-7 cm2/W, 10-6 cm/W and 10-7 esu respectively. The nonlinearity found increasing with Nd3+-Li+ co-dopant concentration. Based on the results, it is proposed that this material is a new class of luminescent material suitable in optoelectronics devices application, especially in light-emitting devices, electroluminescent devices, display devices, etc.

PECASE: Nanostructure Hybrid Organic/Inorganic Materials for Active Opto-Electronic Devices

DTIC Science & Technology

2011-01-03

FWHM= 30 nm), green-emitting core–shell material ( 4 nm in diameter) suitable for QD- LED display applications (Figure 1b). An alloyed material for...electroluminescence (EL) that can be of use in fields as diverse as optical communications, spectroscopy, and environmental and industrial sensing. The RC structure...variety of QD size distributions (of Gaussian size profile). Such QD monoalyers have already been utilized in a number of thin-film applications , QD

Synthesis and electrochemical property of LiCoO 2 thin films composed of nanosize compounds synthesized via nanosheet restacking method

NASA Astrophysics Data System (ADS)

Quan, Zhen; Iwase, Kosuke; Sonoyama, Noriyuki

LiCoO 2 thin films with nanosize particles were synthesized on Au substrates by nanosheet restacking method and subsequent hydrothermal reaction which needs less cost than the vacuum deposition methods. The grain size of LiCoO 2 films estimated by XRD reflection was about 15 nm that was independent of the thickness of precursor cobalt hydroxide film. Comparing the rate performance of the thin films with various thickness, the optimum performance was obtained by the thin film with 5 min deposition time: 62% of the capacity was held at 400 C-rate compared with that at 20 C-rate. The results of AC-impedance analysis of electrode reaction indicate that the high rate capability of the LiCoO 2 film is obtained by the small grain size and large surface area of LiCoO 2 thin film with nano size particles.

Photo- and electroluminescence of new organic semiconductors

NASA Astrophysics Data System (ADS)

Samsonova, L. G.; Degtyarenko, K. M.; Gadirov, R. M.; Odod, A. V.; Kopylova, T. N.; Begimova, A.; Krasnikova, S. S.; Yakuschenko, I. K.; Gadomsky, S. Y.; Kaplunov, M. G.

2018-04-01

The results of investigation of the luminescence under photo- and electroexcitation for four new compounds are presented. The spectral properties and photoluminescence are studied in ethanol, chloroform solutions and in films formed by thermovacuum deposition (TVD). The phosphorescence of compounds is investigated in ethanol at 77K temperature. The phosphorescence times of molecules are given. The electroluminescence is obtained in multilayered structure ITO/PEDOT/NPD/L /Ca/Al. It is shown, that spectral region of the photoluminescence of TVD films and electroluminescence coincide. Relations of electroluminescence efficiency with molecule structure, photoluminescence quantum yield and possibility of thermally activated delayed fluorescence are discussed.

The effect of the thicknesses of the various layers on the colour emitted by an organic electroluminescent device

NASA Astrophysics Data System (ADS)

Jolinat, P.; Clergereaux, R.; Farenc, J.; Destruel, P.

1998-05-01

Organic electroluminescent diodes based on thin organic layers are one of the most promising next-generation systems for the backlighting of the liquid crystal screens. Among other methods to obtain white light, three-layer luminescent devices with each layer emitting one of the three fundamental colours have been studied here. Red, green and blue light were produced by 0022-3727/31/10/018/img1 doped with Nile red, 0022-3727/31/10/018/img1 and TPD layers respectively. A fourth thin film of TAZ has been inserted between TPD and 0022-3727/31/10/018/img1 to control injection of electrons into the TPD. The effect of the layers' thicknesses on the spectral emission of the device has been examined. Results show that the thicknesses of TAZ and doped 0022-3727/31/10/018/img1 layers have to be controlled to within a precision of better than 5 Å. The discussion turns on the possibility of applying this technology to screen backlighting.

Luminescence in Sulfides: A Rich History and a Bright Future

PubMed Central

Smet, Philippe F.; Moreels, Iwan; Hens, Zeger; Poelman, Dirk

2010-01-01

Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl2S4:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu2+-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles.

Enhanced Optical and Electrical Properties of Polymer-Assisted All-Inorganic Perovskites for Light-Emitting Diodes.

PubMed

Ling, Yichuan; Tian, Yu; Wang, Xi; Wang, Jamie C; Knox, Javon M; Perez-Orive, Fernando; Du, Yijun; Tan, Lei; Hanson, Kenneth; Ma, Biwu; Gao, Hanwei

2016-10-01

Highly bright light-emitting diodes based on solution-processed all-inorganic perovskite thin film are demonstrated. The cesium lead bromide (CsPbBr 3 ) created using a new poly(ethylene oxide)-additive spin-coating method exhibits photoluminescence quantum yield up to 60% and excellent uniformity of electrical current distribution. Using the smooth CsPbBr 3 films as emitting layers, green perovskite-based light-emitting diodes (PeLEDs) exhibit electroluminescent brightness and efficiency above 53 000 cd m -2 and 4%: a new benchmark of device performance for all-inorganic PeLEDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis and optical characterization of ternary chalcogenide Cu3BiS3 thin film by spin coating

NASA Astrophysics Data System (ADS)

Rawal, Neha; Hadi, Mohammed Kamal; Modi, B. P.

2017-05-01

In this work, ternary Chalcogenide Cu3BiS3(CBS) thin films have been prepared and modified by using spin coating technique. Lucratively, spin coating technique is easy going and simple though it hasn't given an enclosure and extensive focus of researches for Cu3BiS3 thin films formation. The surface smoothness and the homogeneity of the obtained thin films have been optimized throughout varying the annealing temperature, concentration and rotation speed. It had been found that as prepared films the value of the energy band gap is 1.4 eV, the absorption coefficient 105 cm-1. Each values of the EBG (Energy Band Gap) and AC (Absorption coefficient) was found in quite agreement with the published work of CBS thin film formation by other methods as CBD, dip coating etc. It signifies that Cu3BiS3 films can be used as an absorber layer for thin film solar cell.

Preparation Of Copper Indium Gallium Diselenide Films For Solar Cells

DOEpatents

Bhattacharya, Raghu N.; Contreras, Miguel A.; Keane, James; Tennant, Andrew L. , Tuttle, John R.; Ramanathan, Kannan; Noufi, Rommel

1998-08-08

High quality thin films of copper-indium-gallium-diselenide useful in the production of solar cells are prepared by electrodepositing at least one of the constituent metals onto a glass/Mo substrate, followed by physical vapor deposition of copper and selenium or indium and selenium to adjust the final stoichiometry of the thin film to approximately Cu(In,Ga)Se.sub.2. Using an AC voltage of 1-100 KHz in combination with a DC voltage for electrodeposition improves the morphology and growth rate of the deposited thin film. An electrodeposition solution comprising at least in part an organic solvent may be used in conjunction with an increased cathodic potential to increase the gallium content of the electrodeposited thin film.

Effect of substitution group on dielectric properties of 4H-pyrano [3, 2-c] quinoline derivatives thin films

NASA Astrophysics Data System (ADS)

H, M. Zeyada; F, M. El-Taweel; M, M. El-Nahass; M, M. El-Shabaan

2016-07-01

The AC electrical conductivity and dielectrical properties of 2-amino-6-ethyl-5-oxo-4-(3-phenoxyphenyl)-5,6-dihydro-4H-pyrano[3, 2-c]quinoline-3-carbonitrile (Ph-HPQ) and 2-amino-4-(2-chlorophenyl)-6-ethyl-5-oxo-5,6-dihydro-4H-pyrano [3, 2-c] quinoline-3-carbonitrile (Ch-HPQ) thin films were determined in the frequency range of 0.5 kHz-5 MHz and the temperature range of 290-443 K. The AC electrical conduction of both compounds in thin film form is governed by the correlated barrier hopping (CBH) mechanism. Some parameters such as the barrier height, the maximum barrier height, the density of charges, and the hopping distance were determined as functions of temperature and frequency. The phenoxyphenyl group has a greater influence on those parameters than the chlorophenyl group. The AC activation energies were determined at different frequencies and temperatures. The dielectric behaviors of Ph-HPQ and Ch-HPQ were investigated using the impedance spectroscopy technique. The impedance data are presented in Nyquist diagrams for different temperatures. The Ch-HPQ films have higher impedance than the Ph-HPQ films. The real dielectric constant and dielectric loss show a remarkable dependence on the frequency and temperature. The Ph-HPQ has higher dielectric constants than the Ch-HPQ.

Theoretical and material studies on thin-film electroluminescent devices

NASA Technical Reports Server (NTRS)

Summers, C. J.; Goldman, J. A.; Brennan, K.

1988-01-01

During this report period work was performed on the modeling of High Field Electronic Transport in Bulk ZnS and ZnSe, and also on the surface cleaning of Si for MBE growth. Some MBE growth runs have also been performed in the Varian GEN II System. A brief outline of the experimental work is given. A complete summary will be done at the end of the next reporting period at the completion of the investigation. The theoretical studies are included.

Cr:ZnSe planar waveguide mid-IR laser

NASA Astrophysics Data System (ADS)

Willimas, J. E.; Martyshkin, D. V.; Fedorov, V. V.; Moskalev, I. S.; Camata, R. P.; Mirov, S. B.

2011-02-01

Middle infrared (mid-IR) chromium-doped zinc selenide (Cr:ZnSe) bulk lasers have attracted a lot of attention due to their unique combination of optical and laser properties facilitating a wide range of potential scientific, industrial, and medical applications. Utilization of thin film waveguide geometry enabling good thermal management and control of beam quality is a viable pathway for compact chip-integrated optical laser design. Cr:ZnSe thin films are also promising as saturable absorbers and mode-lockers of the cavities of solid state lasers operating over 1.3-2.1 μm. We recently reported the first successful demonstration of mid-IR Cr:ZnSe planar waveguide lasing at 2.6 μm under gain-switched short-pulse (5 ns) 1.56 μm excitation as well as the passive Q-switching of the cavity of a fiber-pumped Er:YAG laser operating at 1645 nm using a highly doped Cr:ZnSe thin film. PLD grown Cr:ZnSe waveguide were fabricated on sapphire substrates (Cr:ZnSe/sapphire) with chromium concentration of 1018-1019 cm-3. Further development of mid-IR lasing in the Cr:ZnSe planar waveguide under continuous wave excitation were investigated. In addition, deposition of Cr:ZnSe-based thin film structures on n-type GaAs substrates were also investigated for possible mid-IR electroluminescence.

Light-emitting nanolattices with enhanced brightness

NASA Astrophysics Data System (ADS)

Ng, Ryan C.; Mandal, Rajib; Anthony, Rebecca J.; Greer, Julia R.

2017-02-01

Three-dimensional (3D) photonic crystals have potential in solid state lighting applications due to their advantages over conventional planar thin film devices. Periodicity in a photonic crystal structure enables engineering of the density of states to improve spontaneous light emission according to Fermi's golden rule. Unlike planar thin films, which suffer significantly from total internal reflection, a 3D architectured structure is distributed in space with many non-flat interfaces, which facilitates a substantial enhancement in light extraction. We demonstrate the fabrication of 3D nano-architectures with octahedron geometry that utilize luminescing silicon nanocrystals as active media with an aluminum cathode and indium tin oxide anode towards the realization of a 3D light emitting device. The developed fabrication procedure allows charge to pass through the nanolattice between two contacts for electroluminescence. These initial fabrication efforts suggest that 3D nano-architected devices are realizable and can reach greater efficiencies than planar devices.

Piezoelectric response of a PZT thin film to magnetic fields from permanent magnet and coil combination

NASA Astrophysics Data System (ADS)

Guiffard, B.; Seveno, R.

2015-01-01

In this study, we report the magnetically induced electric field E 3 in Pb(Zr0.57Ti0.43)O3 (PZT) thin films, when they are subjected to both dynamic magnetic induction (magnitude B ac at 45 kHz) and static magnetic induction ( B dc) generated by a coil and a single permanent magnet, respectively. It is found that highest sensitivity to B dc——is achieved for the thin film with largest effective electrode. This magnetoelectric (ME) effect is interpreted in terms of coupling between eddy current-induced Lorentz forces (stress) in the electrodes of PZT and piezoelectricity. Such coupling was evidenced by convenient modelling of experimental variations of electric field magnitude with both B ac and B dc induction magnitudes, providing imperfect open circuit condition was considered. Phase angle of E 3 versus B dc could also be modelled. At last, the results show that similar to multilayered piezoelectric-magnetostrictive composite film, a PZT thin film made with a simple manufacturing process can behave as a static or dynamic magnetic field sensor. In this latter case, a large ME voltage coefficient of under B dc = 0.3 T was found. All these results may provide promising low-cost magnetic energy harvesting applications with microsized systems.

Giant surfactants of poly(ethylene oxide)- b-polystyrene-(molecular nanoparticle): nanoparticle-driven self-assembly with sub-10-nm nanostructures in thin films

NASA Astrophysics Data System (ADS)

Hsu, Chih-Hao; Lin, Zhiwei; Dong, Xue-Hui; Hsieh, I.-Fan; Cheng, Stephen Z. D.

2014-03-01

Giant surfactants are built upon precisely attaching shape- and volume-persistent molecular nanoparticles (MNP) to polymeric flexible tails. The unique class of self-assembling materials, giant surfactants, has been demonstrated to form self-assembled ordered nanostructures, and their self-assembly behaviors are remarkably sensitive to primary chemical structures. In this work, two sets of giant surfactants with functionalized MNP attached to diblock copolymer tails were studied in thin films. Carboxylic acid-functionalized [60]fullerene (AC60) tethered with PEO- b-PS (PEO-PS-AC60) represents an ABA' (hydrophilic-hydrophobic-hydrophilic) giant surfactant, and fluoro-functionalized polyhedral oligomeric silsesquioxane (FPOSS) tethered with PEO- b-PS (PEO-PS-FPOSS) represents an ABC (hydrophilic-hydrophobic-omniphobic) one. The dissimilar chemical natures of the MNPs result in different arrangement of MNPs in self-assembled structures, the dispersion of AC60 in PEO domain and the single domain of FPOSS. Moreover, the chemically bonded MNPs could induce the originally disordered small molecular PEO- b-PS to form ordered cylindrical and lamellar structure, as evidenced by TEM and GISAXS, leading to sub-10-nm nanostructures of copolymer in the thin film state.

Morphological, elemental, and optical characterization of plasma polymerized n-butyl methacrylate thin films

NASA Astrophysics Data System (ADS)

Nasrin, Rahima; Hossain, Khandker S.; Bhuiyan, A. H.

2018-05-01

Plasma polymerized n-butyl methacrylate (PPnBMA) thin films of varying thicknesses were prepared at room temperature by AC plasma polymerization system using a capacitively coupled parallel plate reactor. Field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), energy-dispersive X-ray (EDX) analysis, and ultraviolet-visible (UV-Vis) spectroscopic investigation have been performed to study the morphological, elemental, and optical properties of the PPnBMA thin films, respectively. The flat and defect-free nature of thin films were confirmed by FESEM and AFM images. With declining plasma power, average roughness and root mean square roughness increase. Allowed direct transition ( E gd) and indirect transition ( E gi) energy gaps were found to be 3.64-3.80 and 3.38-3.45 eV, respectively, for PPnBMA thin films of different thicknesses. Values of E gd as well as E gi increase with the increase of thickness. The extinction coefficient, Urbach energy, and steepness parameter were also determined for these thin films.

Electroluminescence and cathodoluminescence from polyethylene and polypropylene films: Spectra reconstruction from elementary components and underlying mechanisms

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

Qiao, B.; Teyssedre, G.; Laurent, C.

The mechanisms of electroluminescence from large band gap polymers used as insulation in electric components are still under debate. It becomes important to unravel the underlying physics of the emission because of increasing thermo-electric stress and a possible relationship between electroluminescence and field withstand. We report herein on the cathodoluminescence spectra of polyethylene and polypropylene films as a way to uncover the nature of its contributions to electroluminescence emission. It is shown that spectra from the two materials are structured around four elementary components, each of them being associated with a specific process contributing to the overall emission with differentmore » weights depending on excitation conditions and on materials. The cathodoluminescence and electroluminescence spectra of each material are reconstructed from the four spectral components and their relative contribution are discussed. It is shown that electroluminescence from polyethylene and polypropylene has the same origin pointing towards generic mechanisms in both.« less

Structural, optical and ac electrical characterization of CBD synthesized NiO thin films: Influence of thickness

NASA Astrophysics Data System (ADS)

Das, M. R.; Mukherjee, A.; Mitra, P.

2017-09-01

We have studied the electrical conductivity, dielectric relaxation mechanism and impedance spectroscopy characteristics of nickel oxide (NiO) thin films synthesized by chemical bath deposition (CBD) method. Thickness dependent structural, optical and ac electrical characterization has been carried out and deposition time was varied to control the thickness. The material has been characterized using X-ray diffraction and UV-VIS spectrophotometer. Impedance spectroscopy analysis confirmed enhancement of ac conductivity and dielectric constant for films deposited with higher deposition time. Decrease of grain size in thicker films were confirmed from XRD analysis and activation energy of the material for electrical charge hopping process was increased with thickness of the film. Decrease in band gap in thicker films were observed which could be associated with creation of additional energy levels in the band gap of the material. Cole-Cole plot shows contribution of both grain and grain boundary towards total resistance and capacitance. The overall resistance was found to decrease from 14.6 × 105 Ω for 30 min deposited film ( 120 nm thick) to 2.42 × 105 Ω for 120 min deposited film ( 307 nm thick). Activation energy value to electrical conduction process evaluated from conductivity data was found to decrease with thickness. Identical result was obtained from relaxation time approach suggesting hopping mechanism of charge carriers.

Shielding superconductors with thin films as applied to rf cavities for particle accelerators

DOE PAGES

Posen, Sam; Transtrum, Mark K.; Catelani, Gianluigi; ...

2015-10-29

Determining the optimal arrangement of superconducting layers to withstand large-amplitude ac magnetic fields is important for certain applications such as superconducting radio-frequency cavities. In this paper, we evaluate the shielding potential of the superconducting-film–insulating-film–superconductor (SIS') structure, a configuration that could provide benefits in screening large ac magnetic fields. After establishing that, for high-frequency magnetic fields, flux penetration must be avoided, the superheating field of the structure is calculated in the London limit both numerically and, for thin films, analytically. For intermediate film thicknesses and realistic material parameters, we also solve numerically the Ginzburg-Landau equations. As a result, it is shownmore » that a small enhancement of the superheating field is possible, on the order of a few percent, for the SIS' structure relative to a bulk superconductor of the film material, if the materials and thicknesses are chosen appropriately.« less

In situ conductance measurements of copper phthalocyanine thin film growth on sapphire [0001].

PubMed

Murdey, Richard; Sato, Naoki

2011-06-21

The current flowing through a thin film of copper phthalocyanine vacuum deposited on a single crystal sapphire [0001] surface was measured during film growth from 0 to 93 nm. The results, expressed as conductance vs. nominal film thickness, indicate three distinct film growth regions. Conductive material forms below about 5 nm and again above 35 nm, but in the intermediate thicknesses the film conductance was observed to decrease with increasing film thickness. With the aid of ac-AFM topology images taken ex situ, the conductance results are explained based on the Stranski-Krastanov (2D + 3D) film growth mechanism, in which the formation of a thin wetting layer is followed by the growth of discrete islands that eventually coalesce into an interpenetrating, conductive network. © 2011 American Institute of Physics

The role of thin MgO(100) epilayer for polarized charge injection into top-emitting OLED

NASA Astrophysics Data System (ADS)

Kim, Tae Hee; Jong Lee, Nyun; Bae, Yu Jeong; Cho, Hyunduck; Lee, Changhee; Ito, Eisuke

2012-02-01

A new top-emitting OLED (TOLED) structure, which is formed on an Si(100) substrate and an epitaxial MgO(100)/Fe(100)/MgO(100) bottom electrode, was investigated. Our TOLED design included a semi-transparent cathode Al, a stack of conventional organic electroluminescent layers (α-NPD/Alq3/LiF) and a thin Cu-Phthalocyanine (CuPc) film to enhance the hole injection into the luminescent layers. At room temperature (RT), magnetoluminescence of ˜5 % was observed in low magnetic field up to 1 Tesla , which is obviously larger than that of the OLEDs with epitaxial and polycrystalline Fe anodes without MgO(100) covering layer. Our results indicate that the magnetic field effect on the electroluminescence could be strongly related to the magnetic properties of bottom electrode, more precisely the interfacial properties between CuPc layer and the anode. Therefore, we focused on understanding interface electronic states and energy alignment by using x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy. Our results showed that the use of appropriate oxide layers could represent a new interface engineering technique for improving reliability and functionality in organic semiconductor devices.

Preparation of cuxinygazsen (X=0-2, Y=0-2, Z=0-2, N=0-3) precursor films by electrodeposition for fabricating high efficiency solar cells

DOEpatents

Bhattacharya, Raghu N.; Contreras, Miguel A.; Keane, James; Tennant, Andrew L.; Tuttle, John R.; Ramanathan, Kannan; Noufi, Rommel

1998-03-24

High quality thin films of copper-indium-gallium-diselenide useful in the production of solar cells are prepared by electrodepositing at least one of the constituent metals onto a glass/Mo substrate, followed by physical vapor deposition of copper and selenium or indium and selenium to adjust the final stoichiometry of the thin film to approximately Cu(In,Ga)Se.sub.2. Using an AC voltage of 1-100 KHz in combination with a DC voltage for electrodeposition improves the morphology and growth rate of the deposited thin film. An electrodeposition solution comprising at least in part an organic solvent may be used in conjunction with an increased cathodic potential to increase the gallium content of the electrodeposited thin film.

Differential alternating current chip calorimeter for in situ investigation of vapor-deposited thin films

NASA Astrophysics Data System (ADS)

Ahrenberg, M.; Shoifet, E.; Whitaker, K. R.; Huth, H.; Ediger, M. D.; Schick, C.

2012-03-01

Physical vapor deposition can be used to produce thin films with interesting material properties including extraordinarily stable organic glasses. We describe an ac chip calorimeter for in situ heat capacity measurements of as-deposited nanometer thin films of organic glass formers. The calorimetric system is based on a differential ac chip calorimeter which is placed in the vacuum chamber for physical vapor deposition. The sample is directly deposited onto one calorimetric chip sensor while the other sensor is protected against deposition. The device and the temperature calibration procedure are described. The latter makes use of the phase transitions of cyclopentane and the frequency dependence of the dynamic glass transition of toluene and ethylbenzene. Sample thickness determination is based on a finite element modeling of the sensor sample arrangement. In the modeling, a layer of toluene was added to the sample sensor and its thickness was varied in an iterative way until the model fit the experimental data.

Semiconducting Properties of Nanostructured Amorphous Carbon Thin Films Incorporated with Iodine by Thermal Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Kamaruzaman, Dayana; Ahmad, Nurfadzilah; Annuar, Ishak; Rusop, Mohamad

2013-11-01

Nanostructured iodine-post doped amorphous carbon (a-C:I) thin films were prepared from camphor oil using a thermal chemical vapor deposition (TCVD) technique at different doping temperatures. The structural properties of the films were studied by field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), Raman, and Fourier transform infrared (FTIR) studies. FESEM and EDS studies showed successful iodine doping. FTIR and Raman studies showed that the a-C:I thin films consisted of a mixture of sp2- and sp3-bonded carbon atoms. The optical and electrical properties of a-C:I thin films were determined by UV-vis-NIR spectroscopy and current-voltage (I-V) measurement respectively. The optical band gap of a-C thin films decreased upon iodine doping. The highest electrical conductivity was found at 400 °C doping. Heterojunctions are confirmed by rectifying the I-V characteristics of an a-C:I/n-Si junction.

Dielectric and Raman spectroscopy of TlSe thin films

NASA Astrophysics Data System (ADS)

Ozel, Aysen E.; Deger, Deniz; Celik, Sefa; Yakut, Sahin; Karabak, Binnur; Akyüz, Sevim; Ulutas, Kemal

2017-12-01

In this report, the results of Dielectric and Raman spectroscopy of TlSe thin films are presented. The films were deposited in different thicknesses ranging from 290 Å to 3200 Å by thermal evaporation method. The relative permittivity (dielectric constant εr‧) and dielectric loss (εr″) of TlSe thin films were calculated by measuring capacitance (C) and dielectric loss factor (tan δ) in the frequencies ranging between 10-2 Hz-107 Hz and in the temperature ranging between 173 K and 433 K. In the given intervals, both the dielectric constant and the dielectric loss of TlSe thin films decrease with increasing frequency, but increase with increasing temperature. This behavior can be explained as multicomponent polarization in the structure. The ac conductivity obeys the ωs law when s (s < 1). The dielectric constant of TlSe thin films is determined from Dielectric and Raman spectroscopy measurements. The results obtained by two different methods are in agreement with each other.

Electrodeposition of CdTe thin film from acetate-based ionic liquid bath

NASA Astrophysics Data System (ADS)

Waldiya, Manmohansingh; Bhagat, Dharini; Mukhopadhyay, Indrajit

2018-05-01

CdTe being a direct band gap semiconductor, is mostly used in photovoltaics. Here we present, the synthesis of CdTe thin film on fluorine doped tin oxide (FTO) substrate potentiostatically using 1-butyl-3-methylimidazolium acetate ([Bmim][Ac]) ionic liquid (IL) bath at 90 °C. Major advantages of using electrodeposition involves process simplicity, large scalability & economic viability. Some of the benefits offered by IL electrolytic bath are low vapour pressure, wide electrochemical window, and good ionic mobility. Cd(CH3COO)2 (anhydrous) and TeO2 were used as the source precursors. The IL electrolytic bath temperature was kept at 90 °C for deposition, owing to the limited solubility of TeO2 in [Bmim][Ac] IL at room temperature. Cathodic electrodeposition was carried out using a three electrode cell setup at a constant potential of -1.20 V vs. platinum (Pt) wire. The CdTe/FTO thin film were annealed in argon (Ar) atmosphere. Optical study of nanostructured CdTe film were done using UV-Vis-IR and Raman spectroscopy. Raman analysis confirms the formation of CdTe having surface optics (SO) mode at 160.6 cm-1 and transverse optics (TO) mode at 140.5 cm-1. Elemental Te peaks at 123, 140.5 and 268 cm-1 were also observed. The optical band gap of Ar annealed CdTe thin film were found to be 1.47 eV (absorbance band edge ˜ 846 nm). The optimization of deposition parameters using acetate-based IL electrolytic bath to get nearly stoichiometric CdTe thin film is currently being explored.

Evolution of structural distortion in BiFeO3 thin films probed by second-harmonic generation

NASA Astrophysics Data System (ADS)

Jin, Kuijuan; Wang, Jiesu; Gu, Junxing; L03 Group in Institute of Physics, Chinese Academy of Sciences Team

BiFeO3 thin films have drawn much attention due to its potential applications for novel magnetoelectric devices and fundamental physics in magnetoelectric coupling. However, the structural evolution of BiFeO3 films with thickness remains controversial. Here we use an optical second-harmonic generation technique to explore the phase-related symmetry evolution of BiFeO3 thin films with the variation of thickness. The crystalline structures for 60 and 180-nm-thick BiFeO3 thin films were characterized by high-resolution X-ray diffractometry reciprocal space mapping and the local piezoelectric response for 60-nm-thick BiFeO3 thin films was characterized by piezoresponse force microscopy. The present results show that the symmetry of BiFeO3 thin films with a thickness below 60 nm belongs to the point group 4mm. We conclude that the disappearance of fourfold rotational symmetry in SHG s-out pattern implies for the appearance of R-phase. The fact that the thinner the film is, the closer to 1 the tensor element ratio χ31/ χ15 tends, indicates an increase of symmetry with the decrease of thickness for BiFeO3 thin films. email: kjjin@iphy.ac.cn

Highly Efficient Spectrally Stable Red Perovskite Light-Emitting Diodes.

PubMed

Tian, Yu; Zhou, Chenkun; Worku, Michael; Wang, Xi; Ling, Yichuan; Gao, Hanwei; Zhou, Yan; Miao, Yu; Guan, Jingjiao; Ma, Biwu

2018-05-01

Perovskite light-emitting diodes (LEDs) have recently attracted great research interest for their narrow emissions and solution processability. Remarkable progress has been achieved in green perovskite LEDs in recent years, but not blue or red ones. Here, highly efficient and spectrally stable red perovskite LEDs with quasi-2D perovskite/poly(ethylene oxide) (PEO) composite thin films as the light-emitting layer are reported. By controlling the molar ratios of organic salt (benzylammonium iodide) to inorganic salts (cesium iodide and lead iodide), luminescent quasi-2D perovskite thin films are obtained with tunable emission colors from red to deep red. The perovskite/polymer composite approach enables quasi-2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi-2D perovskite counterparts. Electrically driven LEDs with emissions peaked at 638, 664, 680, and 690 nm have been fabricated to exhibit high brightness and external quantum efficiencies (EQEs). For instance, the perovskite LED with an emission peaked at 680 nm exhibits a brightness of 1392 cd m -2 and an EQE of 6.23%. Moreover, exceptional electroluminescence spectral stability under continuous device operation has been achieved for these red perovskite LEDs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Microfabricated multijunction thermal converters

NASA Astrophysics Data System (ADS)

Wunsch, Thomas Franzen

2001-12-01

In order to develop improved standards for the measurement of ac voltages and currents, a new thin-film fabrication technique for the multijunction thermal converter has been developed. The ability of a thermal converter to relate an rms ac voltage or current to a dc value is characterized by a quantity called `ac-dc difference' that is ideally zero. The best devices produced using the new techniques have ac-dc differences below 1 × 10-6 in the range of frequencies from 20 Hz to 10 kHz and below 7.5 × 10-6 in the range of frequencies from 20 kHz to 300 kHz. This is a reduction of two orders of magnitude in the lower frequency range and one order of magnitude in the higher frequency range over devices produced at the National Institute of Standards and Technology in 1996. The performance achieved is competitive with the best techniques in the world for ac measurements and additional evaluation is therefore warranted to determine the suitability of the devices for use as national standards that form the legal basis for traceable rms voltage measurements of time varying waveforms in the United States. The construction of the new devices is based on thin-film fabrication of a heated wire supported by a thermally isolated thin-film membrane. The membrane is produced utilizing a reactive ion plasma etch. A photoresist lift- off technique is used to pattern the metal thin-film layers that form the heater and the multijunction thermocouple circuit. The etching and lift-off allow the device to be produced without wet chemical etches that are time consuming and impede the investigation of structures with differing materials. These techniques result in an approach to fabrication that is simple, inexpensive, and free from the manual construction techniques used in the fabrication of conventional single and multijunction thermoelements. Thermal, thermoelectric, and electrical models have been developed to facilitate designs that reduce the low- frequency error. At high frequencies, from 300 kHz to 1 MHz, the performance of the device is degraded by a capacitive coupling effect that produces an ac-dc difference of approximately -90 × 10-6 at 1 MHz. A model is developed that explains this behavior. The model shows that an improvement in performance in the high-frequency range is possible through the use of very high or very low resistivity silicon substrates.

Unidirectional oxide hetero-interface thin-film diode

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

Park, Youngmin; Lee, Eungkyu; Lee, Jinwon

2015-10-05

The unidirectional thin-film diode based on oxide hetero-interface, which is well compatible with conventional thin-film fabrication process, is presented. With the metal anode/electron-transporting oxide (ETO)/electron-injecting oxide (EIO)/metal cathode structure, it exhibits that electrical currents ohmically flow at the ETO/EIO hetero-interfaces for only positive voltages showing current density (J)-rectifying ratio of ∼10{sup 5} at 5 V. The electrical properties (ex, current levels, and working device yields) of the thin-film diode (TFD) are systematically controlled by changing oxide layer thickness. Moreover, we show that the oxide hetero-interface TFD clearly rectifies an AC input within frequency (f) range of 10{sup 2} Hz < f < 10{sup 6} Hz, providing amore » high feasibility for practical applications.« less

The function of an In0.17Al0.83N interlayer in n-ZnO/In0.17Al0.83N/p-GaN heterojunctions

NASA Astrophysics Data System (ADS)

Wang, Xiao; Gan, Xuewei; Zhang, Guozhen; Su, Xi; Zheng, Meijuan; Ai, Zhiwei; Wu, Hao; Liu, Chang

2017-01-01

ZnO thin films were deposited on p-type GaN with a thin In0.17Al0.83N interlayer, forming double heterostructural diodes of n-ZnO/In0.17Al0.83N/p-GaN. The crystalline quality of the ZnO films was improved and its orientation was kept along < 70 7 bar 4 > that was perpendicular to (10 1 bar 1) plane. The reverse leakage current was reduced by introducing the In0.17Al0.83N interlayer. The electroluminescence spectra of the n-ZnO/In0.17Al0.83N/p-GaN heterojunctions were dominated by p-GaN emissions under forward biases and n-ZnO emissions under reverse biases. The valence-band offset and conduction-band offset between the ZnO and In0.17Al0.83N were determined to be -0.72 and 1.95 eV, respectively.

Disorder induced spin coherence in polyfluorene thin film semiconductors

NASA Astrophysics Data System (ADS)

Miller, Richard G.; van Schooten, Kipp; Malissa, Hans; Waters, David P.; Lupton, John M.; Boehme, Christoph

2014-03-01

Charge carrier spins in polymeric organic semiconductors significantly influence magneto-optoelectronic properties of these materials. In particular, spin relaxation times influence magnetoresistance and electroluminescence. We have studied the role of structural and electronic disorder in polaron spin-relaxation times. As a model polymer, we used polyfluorene, which can exist in two distinct morphologies: an amorphous (glassy) and an ordered (beta) phase. The phases can be controlled in thin films by preparation parameters and verified by photoluminescence spectroscopy. We conducted pulsed electrically detected magnetic resonance (pEDMR) measurements to determine spin-dephasing times by transient current measurements under bipolar charge carrier injection conditions and a forward bias. The measurements showed that, contrary to intuition, spin-dephasing times increase with material disorder. We attribute this behavior to a reduction in hyperfine field strength for carriers in the glassy phase due to increased structural disorder in the hydrogenated side chains, leading to longer spin coherence times. We acknowledge support by the Department of Energy, Office of Basic Energy Sciences under Award #DE-SC0000909.

Dynamical analysis of relaxation luminescence in ZnS:Er3+ thin film devices

NASA Astrophysics Data System (ADS)

Wang, Yu-Jiang; Wu, Chen-Xu; Chen, Mou-Zhi; Huang, Mei-Chun

2003-06-01

The relaxation luminescence of ZnS:Er3+ thin film devices fabricated by thermal evaporation with two boats is studied. The dynamical processes of the luminescence of Er3+ in ZnS are described in terms of a resonant energy transfer model, assuming that the probability of collision excitation of injected electrons with luminescence centers is expressed as a Gaussian function. It is found that the frequency distribution depends on the Lorentzian function by considering the emission from excited states as a damped oscillator. Taking into consideration the energy storing effect of traps, an expression is obtained to describe a profile that contains multiple relaxation luminescence peaks using the convolution theorem. Fitting of experimental results shows that the relaxation characteristics of the electroluminescence are related to the carriers captured by bulk traps as well as by interface states. The numerical calculation carried out agrees well with the dynamical characteristics of relaxation luminescence obtained by experiments.

Synthesis of Ag and Au nanoparticles embedded in carbon film: Optical, crystalline and topography analysis

NASA Astrophysics Data System (ADS)

Gholamali, Hediyeh; Shafiekhani, Azizollah; Darabi, Elham; Elahi, Seyed Mohammad

2018-03-01

Atomic force microscopy (AFM) images give valuable information about surface roughness of thin films based on the results of power spectral density (PSD) through the fast Fourier transform (FFT) algorithms. In the present work, AFM data are studied for silver and gold nanoparticles (Ag NPs a-C: H and Au NPs a-C: H) embedded in amorphous hydrogenated carbon films and co-deposited on glass substrate via of RF-Sputtering and RF-Plasma Enhanced Chemical Vapor Deposition methods. Here, the working gas is acetylene and the targets are Ag and Au. While time and power are constant, the only variable parameter in this study is initial pressure. In addition, the crystalline structure of Ag NPs a-C: H and Au NPs a-C: H are studied using X-ray diffraction (XRD). UV-visible spectrophotometry will also investigate optical properties and localized surface plasmon resonance (LSPR) of samples.

Jeremy Dunklin | NREL

Science.gov Websites

;In Situ Reduction of Gold Nanoparticles on Liquid Exfoliated Tungsten Disulfide Nanosheets," ;Asymmetric reduction of gold nanoparticles into thermoplasmonic polydimethylsiloxane thin films," ACS

Planar electroluminescent panel techniques

NASA Technical Reports Server (NTRS)

Kerr, C.; Kell, R. E.

1973-01-01

Investigations of planar electroluminescent multipurpose displays with latch-in memory are described. An 18 x 24 in. flat, thin address panel with elements spacing of 0.100 in. was constructed which demonstrated essentially uniform luminosity of 3-5 foot lamberts for each of its 43200 EL cells. A working model of a 4-bit EL-PC (electroluminescent photoconductive) electrooptical decoder was made which demonstrated the feasibility of this concept. A single-diagram electroluminescent display device with photoconductive-electroluminescent latch-in memory was constructed which demonstrated the conceptual soundness of this principle. Attempts to combine these principles in a single PEL multipurpose display with latch-in memory were unsuccessful and were judged to exceed the state-of-the-art for close-packed (0.10 in. centers) photoconductor-electroluminescent cell assembly.

TOPICAL REVIEW: Electrical transport modelling in organic electroluminescent devices

NASA Astrophysics Data System (ADS)

Walker, A. B.; Kambili, A.; Martin, S. J.

2002-10-01

Organic electroluminescent devices (OEDs) emit light when an electric current is applied to a thin film section. They arise from two main technology branches - small molecules and light emitting polymers. Apart from the insight offered into the fundamentals of their physics, which is relevant to topics such as electrical transport in biological systems and molecular computers, understanding how the mobilities in these systems vary with morphology and composition enables the design of improved materials for technological requirements, e.g. fast switching speeds for active matrix displays and polymer field effect transistors. In this review, we have focussed on the models of transport in OEDs that address the unusual nature of this transport and underpin device design. The review concludes with the following point: as new materials for use in OEDs continue to appear, modelling is essential for the prediction of their transport properties, which in turn leads to the establishment of fundamental trends in the behaviour of devices employing them.

Single-Layer Halide Perovskite Light-Emitting Diodes with Sub-Band Gap Turn-On Voltage and High Brightness.

PubMed

Li, Junqiang; Shan, Xin; Bade, Sri Ganesh R; Geske, Thomas; Jiang, Qinglong; Yang, Xin; Yu, Zhibin

2016-10-03

Charge-carrier injection into an emissive semiconductor thin film can result in electroluminescence and is generally achieved by using a multilayer device structure, which requires an electron-injection layer (EIL) between the cathode and the emissive layer and a hole-injection layer (HIL) between the anode and the emissive layer. The recent advancement of halide perovskite semiconductors opens up a new path to electroluminescent devices with a greatly simplified device structure. We report cesium lead tribromide light-emitting diodes (LEDs) without the aid of an EIL or HIL. These so-called single-layer LEDs have exhibited a sub-band gap turn-on voltage. The devices obtained a brightness of 591 197 cd m -2 at 4.8 V, with an external quantum efficiency of 5.7% and a power efficiency of 14.1 lm W -1 . Such an advancement demonstrates that very high efficiency of electron and hole injection can be obtained in perovskite LEDs even without using an EIL or HIL.

Electroluminescence from InGaN/GaN multi-quantum-wells nanorods light-emitting diodes positioned by non-uniform electric fields.

PubMed

Park, Hyunik; Kim, Byung-Jae; Kim, Jihyun

2012-11-05

We report that the nanorod light-emitting diodes (LEDs) with InGaN/GaN multi-quantum-wells (MQWs) emitted bright electroluminescence (EL) after they were positioned and aligned by non-uniform electric fields. Firstly, thin film LED structures with MQWs on sapphire substrate were coated with SiO(2) nanospheres, followed by inductively-coupled plasma etch to create nanorod-shapes with MQWs, which were transferred to the pre-patterned SiO(2)/Si wafer. This method allowed us to obtain nanorod LEDs with uniform length, diameter and qualities. Dielectrophoretic force created by non-uniform electric field was very effective at positioning the processed nanorods on the pre-patterned contacts. After aligned by non-uniform electric field, we observed bright EL from many nanorods, which had both cases (p-GaN/MQWs/n-GaN or n-GaN/MQWs/p-GaN). Therefore, bright ELs at different locations were observed under the various bias conditions.

Effect of solution combusted TiO2 nanopowder within commercial BaTiO3 dielectric layer on the photoelectric properties for AC powder electroluminescence devices.

PubMed

Park, Sung; Choi, Gil Rak; Kim, Youn Cheol; Lee, Jae Chun; Lee, Ju Hyeon

2013-05-01

A unique synthesis method was developed, which is called solution combustion method (SCM). TiO2 nanopowder was synthesized by this method. This SCM TiO2 nanopowder (-35 nm) was added to the dielectric layer of AC powder electroluminescence (EL) device. The dielectric layer was made of commercial BaTiO3 powder (-1.2 microm) and binding polymer. 0, 5, 10 and 15 wt% of SCM TiO2 nanopowder was added to the dielectric layer during fabrication of AC powder EL device respectively. Dielectric constant of these four kinds of dielectric layers was measured. The brightness and current density of AC powder EL device were also measured. When 10 wt% of SCM TiO2 nanopowder was added, dielectric constant and brightness were increased by 30% and 101% respectively. Furthermore, the current density was decreased by 71%. This means that the brightness was double and the power consumption was one third.

Kinetically driven self-assembly of a binary solute mixture with controlled phase separation via electro-hydrodynamic flow of corona discharge.

PubMed

Jung, Hee Joon; Huh, June; Park, Cheolmin

2012-10-21

This feature article describes a new and facile process to fabricate a variety of thin films of non-volatile binary solute mixtures suitable for high performance organic electronic devices via electro-hydrodynamic flow of conventional corona discharge. Both Corona Discharge Coating (CDC) and a modified version of CDC, Scanning Corona Discharge Coating (SCDC), are based on utilizing directional electric flow, known as corona wind, of the charged uni-polar particles generated by corona discharge between a metallic needle and a bottom plate under a high electric field (5-10 kV cm(-1)). The electric flow rapidly spreads out the binary mixture solution on the bottom plate and subsequently forms a smooth and flat thin film in a large area within a few seconds. In the case of SCDC, the static movement of the bottom electrode on which a binary mixture solution is placed provides further control of thin film formation, giving rise to a film highly uniform over a large area. Interesting phase separation behaviors were observed including nanometer scale phase separation of a polymer-polymer binary mixture and vertical phase separation of a polymer-organic semiconductor mixture. Core-shell type phase separation of either polymer-polymer or polymer-colloidal nanoparticle binary mixtures was also developed with a periodically patterned microstructure when the relative location of the corona wind was controlled to a binary solution droplet on a substrate. We also demonstrate potential applications of thin functional films with controlled microstructures by corona coating to various organic electronic devices such as electroluminescent diodes, field effect transistors and non-volatile polymer memories.

Kinetically driven self-assembly of a binary solute mixture with controlled phase separation via electro-hydrodynamic flow of corona discharge

NASA Astrophysics Data System (ADS)

Jung, Hee Joon; Huh, June; Park, Cheolmin

2012-09-01

This feature article describes a new and facile process to fabricate a variety of thin films of non-volatile binary solute mixtures suitable for high performance organic electronic devices via electro-hydrodynamic flow of conventional corona discharge. Both Corona Discharge Coating (CDC) and a modified version of CDC, Scanning Corona Discharge Coating (SCDC), are based on utilizing directional electric flow, known as corona wind, of the charged uni-polar particles generated by corona discharge between a metallic needle and a bottom plate under a high electric field (5-10 kV cm-1). The electric flow rapidly spreads out the binary mixture solution on the bottom plate and subsequently forms a smooth and flat thin film in a large area within a few seconds. In the case of SCDC, the static movement of the bottom electrode on which a binary mixture solution is placed provides further control of thin film formation, giving rise to a film highly uniform over a large area. Interesting phase separation behaviors were observed including nanometer scale phase separation of a polymer-polymer binary mixture and vertical phase separation of a polymer-organic semiconductor mixture. Core-shell type phase separation of either polymer-polymer or polymer-colloidal nanoparticle binary mixtures was also developed with a periodically patterned microstructure when the relative location of the corona wind was controlled to a binary solution droplet on a substrate. We also demonstrate potential applications of thin functional films with controlled microstructures by corona coating to various organic electronic devices such as electroluminescent diodes, field effect transistors and non-volatile polymer memories.

Preparation of copper-indium-gallium-diselenide precursor films by electrodeposition for fabricating high efficiency solar cells

DOEpatents

Bhattacharya, Raghu N.; Hasoon, Falah S.; Wiesner, Holm; Keane, James; Noufi, Rommel; Ramanathan, Kannan

1999-02-16

A photovoltaic cell exhibiting an overall conversion efficiency of 13.6% is prepared from a copper-indium-gallium-diselenide precursor thin film. The film is fabricated by first simultaneously electrodepositing copper, indium, gallium, and selenium onto a glass/molybdenum substrate (12/14). The electrodeposition voltage is a high frequency AC voltage superimposed upon a DC voltage to improve the morphology and growth rate of the film. The electrodeposition is followed by physical vapor deposition to adjust the final stoichiometry of the thin film to approximately Cu(In.sub.1-n Ga.sub.x)Se.sub.2, with the ratio of Ga/(In+Ga) being approximately 0.39.

Blue light emitting thiogallate phosphor

DOEpatents

Dye, Robert C.; Smith, David C.; King, Christopher N.; Tuenge, Richard T.

1998-01-01

A crystalline blue emitting thiogallate phosphor of the formula RGa.sub.2 S.sub.4 :Ce.sub.x where R is selected from the group consisting of calcium, strontium, barium and zinc, and x is from about 1 to 10 atomic percent, the phosphor characterized as having a crystalline microstructure on the size order of from about 100 .ANG. to about 10,000 .ANG. is provided together with a process of preparing a crystalline blue emitting thiogallate phosphor by depositing on a substrate by CVD and resultant thin film electroluminescent devices including a layer of such deposited phosphor on an ordinary glass substrate.

Si based GeSn light emitter: mid-infrared devices in Si photonics

NASA Astrophysics Data System (ADS)

Yu, S. Q.; Ghetmiri, S. A.; Du, W.; Margetis, J.; Zhou, Y.; Mosleh, A.; Al-Kabi, S.; Nazzal, A.; Sun, G.; Soref, R. A.; Tolle, J.; Li, B.; Naseem, H. A.

2015-02-01

Ge1-xSnx/Ge thin films and Ge/Ge1-xSnx/Ge n-i-p double heterostructure (DHS) have been grown using commercially available reduced pressure chemical vapor deposition (RPCVD) reactor. The Sn compositional material and optical characteristics have been investigated. A direct bandgap GeSn material has been identified with Sn composition of 10%. The GeSn DHS samples were fabricated into LED devices. Room temperature electroluminescence spectra were studied. A maximum emission power of 28mW was obtained with 10% Sn LED under the injection current density of 800 A/cm2.

Electroluminescence of thin-film CdTe solar cells and modules

NASA Astrophysics Data System (ADS)

Raguse, John Michael

Thin-film photovoltaics has the potential to be a major source of world electricity. Mitigation of non-uniformities in thin-film solar cells and modules may help improve photovoltaic conversion efficiencies. In this manuscript, a measurement technique is discussed in detail which has the capability of detecting such non-uniformities in a form useful for analysis. Thin-film solar cells emit radiation while operating at forward electrical bias, analogous to an LED, a phenomena known as electroluminescence (EL). This process relatively is inefficient for polycrystalline CdTe devices, on the order of 10-4%, as most of the energy is converted into heat, but still strong enough for many valuable measurements. A EL system was built at the Colorado State University Photovoltaics Laboratory to measure EL from CdTe cells and modules. EL intensity normalized to exposure time and injection current density has been found to correlate very well with the difference between ideal and measured open-circuit voltage from devices that include a GaAs cell, an AlGaAs LED, and several CdTe cells with variations in manufacturing. Furthermore, these data points were found to be in good agreement when overlaid with calibrated data from two additional sources. The magnitude of the inverse slope of the fit is in agreement with the thermal voltage and the intercept was found to have a value near unity, in agreement with theory. The expanded data set consists of devices made from one of seven different band gaps and spans eight decades of EQELED efficiencies. As expected, cells which exhibit major failure of light-dark J-V superposition did not follow trend of well-behaved cells. EL images of selected defects from CdTe cells and modules are discussed and images are shown to be highly sensitive to defects in devices, since the intensity depends exponentially on the cells' voltages. The EL technique has proven to be a useful high-throughput tool for screening of cells. In addition to EL images, other opto-electronics characterization techniques were used to analyze defects in cells and modules such as weak-diode areas, cell delineation near substrate edge, non-uniform chlorine passivation, holes in back contact, high-resistance foreign layer, high back-contact sheet resistance, a discontinuous P3 line scribe (intercell shunt) and shunt through a cell (intracell shunt). Although EL images are proficient at illustrating the location and severity of defects with potentially high spatial resolution and short measurement times, their ability to identify the cause of such defects is limited. EL in concert with Light-Beam-Induced Current (LBIC), however, makes for a powerful ensemble as LBIC can probe different film layers at arbitrary voltage bias conditions, albeit with increased measurement times and potentially reduced spatial resolution.

Effects of electrode modification using calcium on the performance of alternating current field-induced polymer electroluminescent devices

NASA Astrophysics Data System (ADS)

Xia, Yingdong; Chen, Yonghua; Smith, Gregory M.; Li, Yuan; Huang, Wenxiao; Carroll, David L.

2013-06-01

In this work, the effects of electrode modification by calcium (Ca) on the performance of AC field induced polymer electroluminescence (FIPEL) devices are studied. The FIPEL device with Ca/Al electrode exhibits 550 cd m-2, which is 27.5 times higher than that of the device with only an Al electrode (20 cd m-2). Both holes and electrons are injected from one electrode in our FIPEL device. We found that the electron injection can be significantly enhanced by a Ca modification on the Al electrode without greatly affecting the hole injection. Therefore, the electrons and holes can be effectively recombined in the emissive layer to form more excitons under the AC voltage, leading to effective light emission. The device emitted much brighter light than other AC-based organic EL devices. This result provides an easy and effective way to improve FIPEL performance.

Organic Light Emitting Diodes with Opal Photonic Crystal Layer and Carbon Nanotube Anode

NASA Astrophysics Data System (ADS)

Ovalle Robles, Raquel; Del Rocio Nava, Maria; Williams, Christopher; Zhang, Mei; Fang, Shaoli; Lee, Sergey; Baughman, Ray; Zakhidov, Anvar

2007-03-01

We report electroluminescence intensity and spectral changes in light emission from organic light emitting diode (OLEDs) structures, which have thin transparent films of opal photonic crystal (PC). The anode in such PC-OLED is laminated on opal layer from free standing optically transparent multiwall carbon nanotubes (T-CNT) sheets made by dry spinning from CVD grown forests. Silica and polystyrene opal films were grown on glass substrates by vertical sedimentation in colloids in thermal baths and the particle size of opal spheres ranges from 300 nm to 450 nm. The use of T-CNTs, (coated by PEDOT-PSS to avoid shorting) as hole injector, allows to eliminate the use of vacuum deposition of metals and permits to achieve tunneling hole injection regime from CNT tips into Alq^3 emission layer

Role of flexoelectric coupling in polarization rotations at the a-c domain walls in ferroelectric perovskites

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

Cao, Ye; Chen, Long-Qing; Kalinin, Sergei V.

Ferroelectric and ferroelastic domain walls play important roles in ferroelectric properties. However, their couplings with flexoelectricity have been less understood. Here, we applied phase-field simulation to investigate the flexoelectric coupling with ferroelectric a/c twin structures in lead ziconate titanate thin films. Local stress gradients were found to exist near twin walls that created both lateral and vertical electric fields through the flexoelectric effect, resulting in polarization inclinations from either horizontal or normal orientation, polarization rotation angles deviated from 90°, and consequently highly asymmetric a/c twin walls. Furthermore, by tuning the flexoelectric strengths in a reasonable range from first-principles calculations, wemore » found that the transverse flexoelectric coefficient has a larger influence on the polarization rotation than longitudinal and shear coefficients. And as polar rotations that commonly occur at compositional morphotropic phase boundaries contribute to the piezoelectric enhancement, this work calls for further exploration of alternative strain-engineered polar rotations via flexoelectricity in ferroelectric thin films.« less

Role of flexoelectric coupling in polarization rotations at the a-c domain walls in ferroelectric perovskites

DOE PAGES

Cao, Ye; Chen, Long-Qing; Kalinin, Sergei V.

2017-05-16

Ferroelectric and ferroelastic domain walls play important roles in ferroelectric properties. However, their couplings with flexoelectricity have been less understood. Here, we applied phase-field simulation to investigate the flexoelectric coupling with ferroelectric a/c twin structures in lead ziconate titanate thin films. Local stress gradients were found to exist near twin walls that created both lateral and vertical electric fields through the flexoelectric effect, resulting in polarization inclinations from either horizontal or normal orientation, polarization rotation angles deviated from 90°, and consequently highly asymmetric a/c twin walls. Furthermore, by tuning the flexoelectric strengths in a reasonable range from first-principles calculations, wemore » found that the transverse flexoelectric coefficient has a larger influence on the polarization rotation than longitudinal and shear coefficients. And as polar rotations that commonly occur at compositional morphotropic phase boundaries contribute to the piezoelectric enhancement, this work calls for further exploration of alternative strain-engineered polar rotations via flexoelectricity in ferroelectric thin films.« less

Alternating current characterization of nano-Pt(II) octaethylporphyrin (PtOEP) thin film as a new organic semiconductor

NASA Astrophysics Data System (ADS)

M, Dongol; M, M. El-Nahass; A, El-Denglawey; A, A. Abuelwafa; T, Soga

2016-06-01

Alternating current (AC) conductivity and dielectric properties of thermally evaporated Au/PtOEP/Au thin films are investigated each as a function of temperature (303 K-473 K) and frequency (50 Hz-5 MHz). The frequency dependence of AC conductivity follows the Jonscher universal dynamic law. The AC-activation energies are determined at different frequencies. It is found that the correlated barrier hopping (CBH) model is the dominant conduction mechanism. The variation of the frequency exponent s with temperature is analyzed in terms of the CBH model. Coulombic barrier height W m , hopping distance R ω , and the density of localized states N(E F) are valued at different frequencies. Dielectric constant ɛ 1(ω,T) and dielectric loss ɛ 2(ω,T) are discussed in terms of the dielectric polarization process. The dielectric modulus shows the non-Debye relaxation in the material. The extracted relaxation time by using the imaginary part of modulus (M″) is found to follow the Arrhenius law.

Microwave a.c. conductivity of domain walls in ferroelectric thin films

DOE PAGES

Tselev, Alexander; Yu, Pu; Cao, Ye; ...

2016-05-31

Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphologicalmore » roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. Finally, this demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale.« less

Microwave a.c. conductivity of domain walls in ferroelectric thin films

PubMed Central

Tselev, Alexander; Yu, Pu; Cao, Ye; Dedon, Liv R.; Martin, Lane W.; Kalinin, Sergei V.; Maksymovych, Petro

2016-01-01

Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphological roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. This demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale. PMID:27240997

RuO2/Activated Carbon Composite Electrode Prepared by Modified Colloidal Procedure and Thermal Decomposition Method

NASA Astrophysics Data System (ADS)

Li, Xiang; Zheng, Feng; Gan, Weiping; Luo, Xun

2016-01-01

RuO2/activated carbon (AC) composite electrode was prepared by a modified colloidal procedure and a thermal decomposition method. The precursor for RuO2/AC was coated on tantalum sheet and annealed at 150°C to 190°C for 3 h to develop thin-film electrode. The microstructure and morphology of the RuO2/AC film were characterized by thermogravimetric analysis (TGA), x-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). The TGA results showed the maximum loss of RuO2/AC composite film at 410°C, with residual RuO2 of 23.17 wt.%. The amorphous phase structure of the composite was verified by XRD analysis. SEM analysis revealed that fine RuO2 particles were dispersed in an activated carbon matrix after annealing. The electrochemical properties of RuO2/AC electrode were examined by cycling voltammetry, galvanostatic charge-discharge, and cyclic behavior measurements. The specific capacitance of RuO2/AC electrode reached 245 F g-1. The cyclic behavior of RuO2/AC electrode was stable. Optimal annealing was achieved at 170°C for 3 h.

High Performance Piezoelectric Actuators and Wings for Nano Air Vehicles

DTIC Science & Technology

2012-08-26

we designed and fabricated the LionFly, a flapping wing prototype actuated by a PZT -5H bimorph actuator. Several LionFly prototypes were fabricated...in the literature, using PZT thin film actuators directly coupled to a 2.5 mm SiO2/Si3N4/T i-Au wing that produces large flapping angle at resonance...for larger scale mechanisms [17, 9]. For PAVs, linear electromagnetic ac- tuation [21] and bulk PZT bimorph actuators [8], and thin film PZT unimorph

Study of electrostatically self-assembled thin films of CdS and ZnS nanoparticle semiconductors

NASA Astrophysics Data System (ADS)

Suryajaya

In this work, CdS and ZnS semiconducting colloid nanoparticles coated with organic shell, containing either SO[3-] or NH[2+] groups, were deposited as thin films using the technique of electrostatic self-assembly. The films produced were characterized with UV-vis spectroscopy and spectroscopic ellipsometry - for optical properties; atomic force microscopy (AFM) - for morphology study; mercury probe - for electrical characterisation; and photon counter - for electroluminescence study. UV-vis spectra show a substantial blue shift of the main absorption band of both CdS and ZnS, either in the form of solutions or films, with respect to the bulk materials. The calculation of nanoparticles' radii yields the value of about 1.8 nm for both CdS and ZnS.The fitting of standard ellipsometry data gave the thicknesses (d) of nanoparticle layers of around 5 nm for both CdS and ZnS which corresponds well to the size of particles evaluated from UV-vis spectral data if an additional thickness of the organic shell is taken into account. The values of refractive index (n) and extinction coefficient (k) obtained were about 2.28 and 0.7 at 633 nm wavelength, for both CdS and ZnS.Using total internal reflection (TIRE), the process of alternative deposition of poly-allylamine hydrochloride (PAH) and CdS (or ZnS) layers could be monitored in-situ. The dynamic scan shows that the adsorption kinetic of the first layer of PAH or nanoparticles was slower than that of the next layer. The fitting of TIRE spectra gavethicknesses of about 7 nm and 12 nm for CdS and ZnS, respectively. It supports the suggestion of the formation of three-dimensional aggregates of semiconductor nanoparticles intercalated with polyelectrolyte.AFM images show the formation of large aggregates of nanoparticles, about 40-50 nm, for the films deposited from original colloid solutions, while smaller aggregates, about 12-20 nm, were obtained if the colloid solutions were diluted.Current-voltage (I-V) and capacitance-frequency (C-f) measurements of polyelectrolyte/nanoparticles (CdS or ZnS) films suggest the tunnelling behaviour in the films while capacitance- voltage (C-V) and conductance-voltage (G-V) measurements suggest that these nanoparticles are conductive. The electroluminescence was detected in sandwich structures of (PAH/CdS/PAH)[N] using a photon counting detector, but not in the case of ZnS films.

A molecular dynamics analysis of ion irradiation of ultrathin amorphous carbon films

NASA Astrophysics Data System (ADS)

Qi, J.; Komvopoulos, K.

2016-09-01

Molecular dynamics (MD) simulations provide insight into nanoscale problems where continuum description breaks down, such as the modeling of ultrathin films. Amorphous carbon (a-C) films are commonly used as protective overcoats in various contemporary technologies, including microelectromechanical systems, bio-implantable devices, optical lenses, and hard-disk drives. In all of these technologies, the protective a-C film must be continuous and very thin. For example, to achieve high storage densities (e.g., on the order of 1 Tb/in.2) in magnetic recording, the thickness of the a-C film used to protect the magnetic media and the recording head against mechanical wear and corrosion must be 2-3 nm. Inert ion irradiation is an effective post-deposition method for reducing the film thickness, while preserving the mechanical and chemical characteristics. In this study, MD simulations of Ar+ ion irradiated a-C films were performed to elucidate the effects of the ion incidence angle and ion kinetic energy on the film thickness and structure. The MD results reveal that the film etching rate exhibits a strong dependence on the ion kinetic energy and ion incidence angle, with a maximum etching rate corresponding to an ion incidence angle of ˜20°. It is also shown that Ar+ ion irradiation mainly affects the structure of the upper half of the ultrathin a-C film and that carbon atom hybridization is a strong function of the ion kinetic energy and ion incidence angle. The results of this study elucidate the effects of important ion irradiation parameters on the structure and thickness of ultrathin films and provide fundamental insight into the physics of dry etching.

Hydrogen effects on the electroluminescence of n-ZnO nanorod/p-GaN film heterojunction light-emitting diodes.

PubMed

Fang, Fang; Zhao, Dongxu; Li, Binghui; Zhang, Zhenzhong; Shen, Dezhen

2010-07-07

Through a facile low-temperature solution process, vertically n-type ZnO nanorod arrays were grown on a GaN film to form a n-ZnO nanorod/p-GaN film heterojunction. A study of the electroluminescence (EL) characteristics of the heterojunction in air and in air with 2000 ppm hydrogen revealed the sensitivity of such a device to the surrounding atmosphere. The additional hydrogen shallow donors increased the effective electron concentration in ZnO nanorods and the EL recombination zone changed from the ZnO nanorods to the GaN film, which can be identified visually from the color change.

Transient photocurrent responses in amorphous Zn-Sn-O thin films

NASA Astrophysics Data System (ADS)

Kim, Ju-Yeon; Oh, Sang-A.; Yu, Kyeong Min; Bae, Byung Seong; Yun, Eui-Jung

2015-04-01

In this study we characterized the transient photocurrent responses in solution-processed amorphous zinc-tin-oxide (a-ZTO) thin films measured under light illumination with a wavelength of 400 nm at different temperatures. By using the temperature-dependent photoconductivities of a-ZTO thin films, we extracted the activation energies (E ac ) of photo-excitation and dark relaxation through an extended stretched exponential analysis (SEA). The SEA was found to describe well the dark relaxation characteristics as well as the photo-excitation processes. The SEA also indicates that the dark relaxation process reveals a dispersive transient photoconductivity with a broader distribution of the E ac while the photo-excitation process shows non-dispersive characteristics. Samples exposed by light at temperatures less than 373 K possess the fast processes of photo-excitation and dark relaxation. This suggests that a fast process, for example, a generation/recombination of charged carriers related to a band-to-band transition and/or shallow/deep oxygen-vacancy (V o ) sub-gap donor states, is dominant in the case of light illumination at low temperatures of less than 373 K. The SEA indicates, however, that a much slower process due mainly to the delay of the onset of ionization/neutralization of the deep V o states by multiple-trapping is dominant for samples under light illumination at a high temperature of 373 K. Based on the experimental results, for the dark relaxation process, we conclude that the process transitions from a fast recombination of electrons through band-to-band transitions and/or shallow/deep V o donor states to a slow neutralization of the ionized V o states occurs due to enhanced carrier multiple-trapping by relatively deep V o trap states when the temperature becomes greater than 363 K. An energy band diagram of a-ZTO thin films was proposed in terms of the temperature and the E ac distribution to explain these observed results.

Thin Film Phase Transition Materials Development Program

DTIC Science & Technology

1985-04-01

and ̂ from f are consistent with a real, positive film thickness d. These conditions are written IP( td /4) = 0, d > 0, (49) where IP denotes...surface of the substrate of the form . aAC(a) + bBD (a) >< cAB(a) + dCD(a) where (a) represents a phase adsorbed on the substrate surface, and the

Capillary trapping of particles in thin-film flows

NASA Astrophysics Data System (ADS)

Dressaire, Emilie; Gomez, Michael; Colnet, Benedicte; Sauret, Alban

2017-11-01

When a thin layer of suspension flows over a substrate, some particles remain trapped on the solid surface. When the thickness of the liquid layer is comparable to the particle size, the particles deform the liquid interface, which leads to local interactions. These effects modify the transport of particles and the dynamics of the liquid films. Here, we characterize how capillary interactions affect the transport and deposition of non-Brownian particles moving in thin liquid films and the resulting loss of transported material. We focus on gravitational drainage flows, in which the film thickness becomes comparable to the particle size. Depending on the concentration of particles, we find that the drainage dynamics exhibits behavior that cannot be captured with a continuum model, due to the deposition of particles on the substrate. ANR-16-CE30-0009 & CNRS-PICS-07242 & ACS-PRF 55845-ND9.

Preparation of epitaxial TlBa2Ca2Cu3O9 high Tc thin films on LaAlO3 (100) substrates

NASA Astrophysics Data System (ADS)

Piehler, A.; Reschauer, N.; Spreitzer, U.; Ströbel, J. P.; Schönberger, R.; Renk, K. F.; Saemann-Ischenko, G.

1994-09-01

Epitaxial TlBa2Ca2Cu3O9 high Tc thin films were prepared on LaAlO3 (100) substrates by a combination of laser ablation and thermal evaporation of thallium oxide. X-ray diffraction patterns of θ-2θ scans showed that the films consisted of highly c axis oriented TlBa2Ca2Cu3O9. φ scan measurements revealed an epitaxial growth of the TlBa2Ca2Cu3O9 thin films on the LaAlO3 (100) substrates. Ac inductive measurements indicated the onset of superconductivity at 110 K. At 6 K, the critical current density was 4×106 A/cm2 in zero magnetic field and 6×105 A/cm2 at a magnetic field of 3 T parallel to the c axis.

Optical and electrical properties of TiOPc doped Alq3 thin films

NASA Astrophysics Data System (ADS)

Ramar, M.; Suman, C. K.; Tyagi, Priyanka; Srivastava, R.

2015-06-01

The Titanyl phthalocyanine (TiOPc) was doped in Tris (8-hydroxyquinolinato) aluminum (Alq3) with different concentration. The thin film of optimized doping concentration was studied extensively for optical and electrical properties. The optical properties, studied using ellipsometry, absorption and photoluminescence. The absorption peak of Alq3 and TiOPc was observed at 387 nm and 707 nm and the photo-luminescence intensity (PL) peak of doped thin film was observed at 517 nm. The DC and AC electrical properties of the thin film were studied by current density-voltage (J-V) characteristics and impedance over a frequency range of 100 Hz - 1 MHz. The electron mobility calculated from trap-free space-charge limited region (SCLC) is 0.17×10-5 cm2/Vs. The Cole-Cole plots shows that the TiOPc doped Alq3 thin film can be represented by a single parallel resistance RP and capacitance CP network with a series resistance RS (10 Ω). The value of RP and CP at zero bias was 1587 Ω and 2.568 nF respectively. The resistance RP decreases with applied bias whereas the capacitance CP remains almost constant.

Carrier injection and recombination processes in perovskite CH3NH3PbI3 solar cells studied by electroluminescence spectroscopy

NASA Astrophysics Data System (ADS)

Handa, Taketo; Okano, Makoto; Tex, David M.; Shimazaki, Ai; Aharen, Tomoko; Wakamiya, Atsushi; Kanemitsu, Yoshihiko

2016-02-01

Organic-inorganic hybrid perovskite materials, CH3NH3PbX3 (X = I and Br), are considered as promising candidates for emerging thin-film photovoltaics. For practical implementation, the degradation mechanism and the carrier dynamics during operation have to be clarified. We investigated the degradation mechanism and the carrier injection and recombination processes in perovskite CH3NH3PbI3 solar cells using photoluminescence (PL) and electroluminescence (EL) imaging spectroscopies. By applying forward bias-voltage, an inhomogeneous distribution of the EL intensity was clearly observed from the CH3NH3PbI3 solar cells. By comparing the PL- and EL-images, we revealed that the spatial inhomogeneity of the EL intensity is a result of the inhomogeneous luminescence efficiency in the perovskite layer. An application of bias-voltage for several tens of minutes in air caused a decrease in the EL intensity and the conversion efficiency of the perovskite solar cells. The degradation mechanism of perovskite solar cells under bias-voltage in air is discussed.

Visible electroluminescence from a ZnO nanowires/p-GaN heterojunction light emitting diode.

PubMed

Baratto, C; Kumar, R; Comini, E; Faglia, G; Sberveglieri, G

2015-07-27

In the current paper we apply catalyst assisted vapour phase growth technique to grow ZnO nanowires (ZnO nws) on p-GaN thin film obtaining EL emission in reverse bias regime. ZnO based LED represents a promising alternative to III-nitride LEDs, as in free devices: the potential is in near-UV emission and visible emission. For ZnO, the use of nanowires ensures good crystallinity of the ZnO, and improved light extraction from the interface when the nanowires are vertically aligned. We prepared ZnO nanowires in a tubular furnace on GaN templates and characterized the p-n ZnO nws/GaN heterojunction for LED applications. SEM microscopy was used to study the growth of nanowires and device preparation. Photoluminescence (PL) and Electroluminescence (EL) spectroscopies were used to characterize the heterojunction, showing that good quality of PL emission is observed from nanowires and visible emission from the junction can be obtained from the region near ZnO contact, starting from onset bias of 6V.

Analysis of electroluminescence images in small-area circular CdTe solar cells

NASA Astrophysics Data System (ADS)

Bokalič, Matevž; Raguse, John; Sites, James R.; Topič, Marko

2013-09-01

The electroluminescence (EL) imaging process of small area solar cells is investigated in detail to expose optical and electrical effects that influence image acquisition and corrupt the acquired image. An approach to correct the measured EL images and to extract the exact EL radiation as emitted from the photovoltaic device is presented. EL images of circular cadmium telluride (CdTe) solar cells are obtained under different conditions. The power-law relationship between forward injection current and EL emission and a negative temperature coefficient of EL radiation are observed. The distributed Simulation Program with Integrated Circuit Emphasis (SPICE®) model of the circular CdTe solar cell is used to simulate the dark J-V curve and current distribution under the conditions used during EL measurements. Simulation results are presented as circularly averaged EL intensity profiles, which clearly show that the ratio between resistive parameters determines the current distribution in thin-film solar cells. The exact resistance values for front and back contact layers and for CdTe bulk layer are determined at different temperatures, and a negative temperature coefficient for the CdTe bulk resistance is observed.

Enhancement of electroluminescence from embedded Si quantum dots/SiO2multilayers film by localized-surface-plasmon and surface roughening.

PubMed

Li, Wei; Wang, Shaolei; Hu, Mingyue; He, Sufeng; Ge, Pengpeng; Wang, Jing; Guo, Yan Yan; Zhaowei, Liu

2015-07-03

In this paper, we prepared a novel structure to enhance the electroluminescence intensity from Si quantum dots/SiO2multilayers. An amorphous Si/SiO2 multilayer film was fabricated by plasma-enhanced chemical vapor deposition on a Pt nanoparticle (NP)-coated Si nanopillar array substrate. By thermal annealing, an embedded Si quantum dot (QDs)/SiO2 multilayer film was obtained. The result shows that electroluminescence intensity was significantly enhanced. And, the turn-on voltage of the luminescent device was reduced to 3 V. The enhancement of the light emission is due to the resonance coupling between the localized-surface-plasmon (LSP) of Pt NPs and the band-gap emission of Si QDs/SiO2 multilayers. The other factors were the improved absorption of excitation light and the increase of light extraction ratio by surface roughening structures. These excellent characteristics are promising for silicon-based light-emitting applications.

Enhancement of electroluminescence from embedded Si quantum dots/SiO2multilayers film by localized-surface-plasmon and surface roughening

PubMed Central

Li, Wei; Wang, Shaolei; Hu, Mingyue; He, Sufeng; Ge, Pengpeng; Wang, Jing; Guo, Yan Yan; Zhaowei, Liu

2015-01-01

In this paper, we prepared a novel structure to enhance the electroluminescence intensity from Si quantum dots/SiO2multilayers. An amorphous Si/SiO2 multilayer film was fabricated by plasma-enhanced chemical vapor deposition on a Pt nanoparticle (NP)-coated Si nanopillar array substrate. By thermal annealing, an embedded Si quantum dot (QDs)/SiO2 multilayer film was obtained. The result shows that electroluminescence intensity was significantly enhanced. And, the turn-on voltage of the luminescent device was reduced to 3 V. The enhancement of the light emission is due to the resonance coupling between the localized-surface-plasmon (LSP) of Pt NPs and the band-gap emission of Si QDs/SiO2 multilayers. The other factors were the improved absorption of excitation light and the increase of light extraction ratio by surface roughening structures. These excellent characteristics are promising for silicon-based light-emitting applications. PMID:26138830

Extremely low amplified spontaneous emission threshold and blue electroluminescence from a spin-coated octafluorene neat film

NASA Astrophysics Data System (ADS)

Kim, D.-H.; Sandanayaka, A. S. D.; Zhao, L.; Pitrat, D.; Mulatier, J. C.; Matsushima, T.; Andraud, C.; Ribierre, J. C.; Adachi, C.

2017-01-01

We report on the photophysical, amplified spontaneous emission (ASE), and electroluminescence properties of a blue-emitting octafluorene derivative in spin-coated films. The neat film shows an extremely low ASE threshold of 90 nJ/cm2, which is related to its high photoluminescence quantum yield of 87% and its large radiative decay rate of 1.7 × 109 s-1. Low-threshold organic distributed feedback semiconductor lasers and fluorescent organic light-emitting diodes with a maximum external quantum efficiency as high as 4.4% are then demonstrated, providing evidence that this octafluorene derivative is a promising candidate for organic laser applications.

Fabrication of periodical surface structures by picosecond laser irradiation of carbon thin films: transformation of amorphous carbon in nanographite

NASA Astrophysics Data System (ADS)

Popescu, C.; Dorcioman, G.; Bita, B.; Besleaga, C.; Zgura, I.; Himcinschi, C.; Popescu, A. C.

2016-12-01

Thin films of carbon were synthesized by ns pulsed laser deposition in vacuum on silicon substrates, starting from graphite targets. Further on, the films were irradiated with a picosecond laser source emitting in visible at 532 nm. After tuning of laser parameters, we obtained a film surface covered by laser induced periodical surface structures (LIPSS). They were investigated by optical, scanning electron and atomic force microscopy. It was observed that changing the irradiation angle influences the LIPSS covered area. At high magnification it was revealed that the LIPSS pattern was quite complex, being composed of other small LIPSS islands, interconnected by bridges of nanoparticles. Raman spectra for the non-irradiated carbon films were typical for a-C type of diamond-like carbon, while the LIPSS spectra were characteristic to nano-graphite. The pristine carbon film was hydrophilic, while the LIPSS covered film surface was hydrophobic.

Flux pinning enhancement in thin films of Y3 Ba5 Cu8O18.5 + d

NASA Astrophysics Data System (ADS)

Aghabagheri, S.; Mohammadizadeh, M. R.; Kameli, P.; Salamati, H.

2018-06-01

YBa2Cu3O7 (Y123) and Y3Ba5Cu8O18 (Y358) thin films were deposited by pulsed laser deposition method. XRD analysis shows both films grow in c axis orientation. Resistivity versus temperature analysis shows superconducting transition temperature was about 91.2 K and 91.5 K and transition width for Y358 and Y123 films was about 0.6 K and 1.6 K, respectively. Analysis of the temperature dependence of the AC susceptibility near the transition temperature, employing Bean's critical state model, indicates that intergranular critical current density for Y358 films is more than twice of intergranular critical current density of Y123 films. Thus, flux pining is stronger in Y358 films. Weak links in the both samples is of superconductor-normal-superconductor (SNS) type irrespective of stoichiometry.

In-situ spectro-microscopy on organic films: Mn-Phthalocyanine on Ag(100)

NASA Astrophysics Data System (ADS)

Al-Mahboob, Abdullah; Sadowski, Jerzy T.; Vescovo, Elio

2013-03-01

Metal phthalocyanines are attracting significant attention, owing to their potential for applications in chemical sensors, solar cells and organic magnets. As the electronic properties of molecular films are determined by their crystallinity and molecular packing, the optimization of film quality is important for improving the performance of organic devices. Here, we present the results of in situ low-energy electron microscopy / photoemission electron microscopy (LEEM/PEEM) studies of incorporation-limited growth of manganese-phthalocyanine (MnPc) on Ag(100) surfaces. MnPc thin films were grown on both, bulk Ag(100) surface and thin Ag(100)/Fe(100) films, where substrate spin-polarized electronic states can be modified through tuning the thickness of the Ag film. We also discuss the electronic structure and magnetic ordering in MnPc thin films, investigated by angle- and spin-resolved photoemission spectroscopy. Research carried out at the Center for Functional Nanomaterials and National Synchrotron Light Source, Brookhaven National Laboratory, which are supported by the U.S. Dept. of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

Activated carbon/manganese dioxide hybrid electrodes for high performance thin film supercapacitors

NASA Astrophysics Data System (ADS)

Jang, Yunseok; Jo, Jeongdai; Jang, Hyunjung; Kim, Inyoung; Kang, Dongwoo; Kim, Kwang-Young

2014-06-01

We combine the activated carbon (AC) and the manganese dioxide (MnO2) in a AC/MnO2 hybrid electrode to overcome the low capacitance of activated carbon and MnO2 by exploiting the large surface area of AC and the fast reversible redox reaction of MnO2. An aqueous permanganate (MnO4 -) is converted to MnO2 on the surface of the AC electrode by dipping the AC electrode into an aqueous permanganate solution. The AC/MnO2 hybrid electrode is found to display superior specific capacitance of 290 F/g. This shows that supercapacitors classified as electric double layer capacitors and pseudocapacitors can be combined together.

Hard TiCx/SiC/a-C:H nanocomposite thin films using pulsed high energy density plasma focus device

NASA Astrophysics Data System (ADS)

Umar, Z. A.; Rawat, R. S.; Tan, K. S.; Kumar, A. K.; Ahmad, R.; Hussain, T.; Kloc, C.; Chen, Z.; Shen, L.; Zhang, Z.

2013-04-01

Thin films of TiCx/SiC/a-C:H were synthesized on Si substrates using a complex mix of high energy density plasmas and instability accelerated energetic ions of filling gas species, emanated from hot and dense pinched plasma column, in dense plasma focus device. The conventional hollow copper anode of Mather type plasma focus device was replaced by solid titanium anode for synthesis of TiCx/SiC/a-C:H nanocomposite thin films using CH4:Ar admixture of (1:9, 3:7 and 5:5) for fixed 20 focus shots as well as with different number of focus shots with fixed CH4:Ar admixture ratio 3:7. XRD results showed the formation of crystalline TiCx/SiC phases for thin film synthesized using different number of focus shots with CH4:Ar admixture ratio fixed at 3:7. SEM results showed that the synthesized thin films consist of nanoparticle agglomerates and the size of agglomerates depended on the CH4:Ar admixture ratio as well as on the number of focus shots. Raman analysis showed the formation of polycrystalline/amorphous Si, SiC and a-C for different CH4:Ar ratio as well as for different number of focus shots. The XPS analysis confirmed the formation of TiCx/SiC/a-C:H composite thin film. Nanoindentation results showed that the hardness and elastic modulus values of composite thin films increased with increasing number of focus shots. Maximum values of hardness and elastic modulus at the surface of the composite thin film were found to be about 22 and 305 GPa, respectively for 30 focus shots confirming the successful synthesis of hard composite TiCx/SiC/a-C:H coatings.

Fabrication and Characterization of Flexible Organic Light Emitting Diodes Based on Transparent Flexible Clay Substrates

NASA Astrophysics Data System (ADS)

Venkatachalam, Shanmugam; Hayashi, Hiromichi; Ebina, Takeo; Nakamura, Takashi; Nanjo, Hiroshi

2013-03-01

In the present work, transparent flexible polymer-doped clay (P-clay) substrates were prepared for flexible organic light emitting diode (OLED) applications. Nanocrystalline indium tin oxide (ITO) thin films were prepared on P-clay substrates by ion-beam sputter deposition method. The structural, optical, and electrical properties of as-prepared ITO/P-clay showed that the as-prepared ITO thin film was amorphous, and the average optical transparency and sheet resistance were around 84% and 56 Ω/square, respectively. The as-prepared ITO/P-clay samples were annealed at 200 and 270 °C for 1 h to improve the optical transparency and electrical conductivity. The average optical transparency was found to be maximum at an annealing temperature of 200 °C. Finally, N,N-bis[(1-naphthyl)-N,N '-diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPB), tris(8-hydroxyquinoline) aluminum (Alq3) thin films, and aluminum (Al) electrode were prepared on ITO/P-clay substrates by thermal evaporation method. The current density-voltage (J-V) characteristic of Al/NPB/ITO/P-clay showed linear Ohmic behaviour. In contrast, J-V characteristic of Al/Alq3/NPB/ITO/P-clay showed non-linear Schottky behaviour. Finally, a very flexible OLED was successfully fabricated on newly fabricated transparent flexible P-clay substrates. The electroluminescence study showed that the emission intensity of light from the flexible OLED device gradually increased with increasing applied voltage.

Tunable Affinity and Molecular Architecture Lead to Diverse Self-Assembled Supramolecular Structures in Thin Films

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

Hsu, Chih-Hao; Dong, Xue-Hui; Lin, Zhiwei

2015-12-03

The self-assembly behaviors of specifically designed giant surfactants are systematically studied in thin films using grazing incident X-ray and transmission electron microscopy (TEM), focusing on the effects of head surface functionalities and molecular architectures on nanostructure formation. Two molecular nanoparticles (MNPs) with different affinities, i.e., hydrophilic carboxylic acid functionalized [60]fullerene (AC60) and omniphobic fluorinated polyhedral oligomeric silsesquioxane (FPOSS), are utilized as heads of the giant surfactants. By covalently tethering these functional MNPs onto the chain end or the junction point of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer, linear and star-like giant surfactants possess distinct molecular architectures are constructed. With fixed lengthmore » of the PEO block, the molecular weight change of the PS block originates the phase formation and transition. Due to the distinct affinity, the AC60-based giant surfactants form two-component morphologies, while three-component morphologies are found in the FPOSS-based ones. A PS block stretching parameter is introduced to characterize the PS chain conformation in different morphologies. The highly diverse self-assembly behaviors and the tunable dimensions in thin films suggest the giant surfactants could be a promising and robust platform for nanolithography applications.« less

Polarized emission from light-emitting electrochemical cells using uniaxially oriented polymer thin films of poly(9,9-dioctylfluorene-co-bithiophene)

NASA Astrophysics Data System (ADS)

Miyazaki, Masumi; Sakanoue, Tomo; Takenobu, Taishi

2018-03-01

Uniaxially oriented poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) films were prepared on rubbed polyimide substrates and applied to emitting layers of light-emitting electrochemical cells (LECs). The layered structure of the uniaxially oriented F8T2 film and ionic liquid electrolytes enabled us to demonstrate LEC operations with high anisotropic characteristics both in emission and charge transport. Polarized electroluminescence (EL) from electrochemically induced p-n junctions in the uniaxially oriented F8T2 was obtained. The dichroic ratios of EL were the same as those of photoluminescence, suggesting that the doping process into the oriented F8T2 did not interrupt the polymer ordering. This indicates the usefulness of the layered structure of the polymer/electrolyte for the fabrication of LECs based on highly oriented polymer films. In addition, uniaxially oriented F8T2 was found to show reduced threshold energy in optically pumped amplified spontaneous emission. These demonstrations suggest the advantage of uniaxially oriented polymer-based LECs for potential application in future electrically pumped lasers.

Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains

NASA Astrophysics Data System (ADS)

Harmon, N. J.; Wohlgenannt, M.; Flatté, M. E.

2016-12-01

We predict very large changes in the room-temperature electroluminescence of thermally-activated delayed fluorescence organic light emitting diodes near patterned ferromagnetic films. These effects exceed the changes in a uniform magnetic field by as much as a factor of two. We describe optimal ferromagnetic film patterns for enhancing the electroluminescence. A full theory of the spin-mixing processes in exciplex recombination and how they are affected by hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is introduced. These spin-mixing processes are used to describe the effect of magnetic domain structures on the luminescence in various regimes. This provides a method of enhancing light emission rates from exciplexes and also a means of efficiently coupling information encoded in the magnetic domains to organic light emitting diode emission.

Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains

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

Harmon, N. J.; Wohlgenannt, M.; Flatté, M. E.

We predict very large changes in the room-temperature electroluminescence of thermally-activated delayed fluorescence organic light emitting diodes near patterned ferromagnetic films. These effects exceed the changes in a uniform magnetic field by as much as a factor of two. We describe optimal ferromagnetic film patterns for enhancing the electroluminescence. A full theory of the spin-mixing processes in exciplex recombination and how they are affected by hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is introduced. These spin-mixing processes are used to describe the effect of magnetic domain structures on the luminescence in various regimes. This provides a method ofmore » enhancing light emission rates from exciplexes and also a means of efficiently coupling information encoded in the magnetic domains to organic light emitting diode emission« less

Manipulation of the electroluminescence of organic light-emitting diodes via fringe fields from patterned magnetic domains

DOE PAGES

Harmon, N. J.; Wohlgenannt, M.; Flatté, M. E.

2016-12-12

We predict very large changes in the room-temperature electroluminescence of thermally-activated delayed fluorescence organic light emitting diodes near patterned ferromagnetic films. These effects exceed the changes in a uniform magnetic field by as much as a factor of two. We describe optimal ferromagnetic film patterns for enhancing the electroluminescence. A full theory of the spin-mixing processes in exciplex recombination and how they are affected by hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is introduced. These spin-mixing processes are used to describe the effect of magnetic domain structures on the luminescence in various regimes. This provides a method ofmore » enhancing light emission rates from exciplexes and also a means of efficiently coupling information encoded in the magnetic domains to organic light emitting diode emission« less

AC-electric field dependent electroformation of giant lipid vesicles.

PubMed

Politano, Timothy J; Froude, Victoria E; Jing, Benxin; Zhu, Yingxi

2010-08-01

Giant vesicles of larger than 5 microm, which have been of intense interest for their potential as drug delivery vehicles and as a model system for cell membranes, can be rapidly formed from a spin-coated lipid thin film under an electric field. In this work, we explore the AC-field dependent electroformation of giant lipid vesicles in aqueous media over a wide range of AC-frequency from 1 Hz to 1 MHz and peak-to-peak field strength from 0.212 V/mm to 40 V/mm between two parallel conducting electrode surfaces. By using fluorescence microscopy, we perform in-situ microscopic observations of the structural evolution of giant vesicles formed from spin-coated lipid films under varied uniform AC-electric fields. The real-time observation of bilayer bulging from the lipid film, vesicle growth and fusing further examine the critical role of AC-induced electroosmotic flow of surrounding fluids for giant vesicle formation. A rich AC-frequency and field strength phase diagram is obtained experimentally to predict the AC-electroformation of giant unilamellar vesicles (GUVs) of l-alpha-phosphatidylcholine, where a weak dependence of vesicle size on AC-frequency is observed at low AC-field voltages, showing decreased vesicle size with a narrowed size distribution with increased AC-frequency. Formation of vesicles was shown to be constrained by an upper field strength of 10 V/mm and an upper AC-frequency of 10 kHz. Within these parameters, giant lipid vesicles were formed predominantly unilamellar and prevalent across the entire electrode surfaces. Copyright 2010 Elsevier B.V. All rights reserved.

Crystal orientation dependence of the dielectric properties for epitaxial BaZr0.15Ti0.85O3 thin films

NASA Astrophysics Data System (ADS)

Miao, J.; Yuan, J.; Wu, H.; Yang, S. B.; Xu, B.; Cao, L. X.; Zhao, B. R.

2007-01-01

Epitaxial Ba0.15Zr0.85TiO3 (BZT) ferroelectric thin films with (001), (011), and (111) orientations were, respectively, grown on La0.67Sr0.33MnO3 (LSMO) buffered LaAlO3 substrates by pulsed laser deposition method. The dc electric-field dependence of permittivity and dielectric loss of (001)-, (011)-, and (111)-oriented BZT/LSMO heterostructures obeys the Johnson formula, and the ac electric-field dependence of that obeys the Rayleigh law under the subswitching field region. The anisotropic dielectric properties are attributed to the higher mobility of the charge carriers, the concentration of mobile interfacial domain walls, and boundaries in the (111)-oriental films than in the (110)- and (100)-oriented films.

Surfactant modified SnO2 nanostructured thin film for improved sensing performance of LPG and ammonia

NASA Astrophysics Data System (ADS)

Kumari, K. Prasanna; Thomas, Boben

2017-05-01

SnO2 nanostructured thin films have been successfully synthesized by way of spray pyrolysis from surfactant added solution. The X-ray diffraction pattern discloses the tetragonal rutile phase of the deposited SnO2 films, which experience a grain size reduction from 35 nm to 19 nm, on the addition of PVP surfactant in precursor. Gas sensing investigations on the surfactant modified film show considerable LPG and NH3 response at a lower operating temperature of 150°C. Quick response (˜20s) and fast recovery (˜30s) are the main features of these sensors. The measurement of AC conductivity of the sample allows understanding the conduction mechanism and sensing action for to enhance the detection sensitivity greatly.

Magnetic field effects in hybrid perovskite devices

NASA Astrophysics Data System (ADS)

Zhang, C.; Sun, D.; Sheng, C.-X.; Zhai, Y. X.; Mielczarek, K.; Zakhidov, A.; Vardeny, Z. V.

2015-05-01

Magnetic field effects have been a successful tool for studying carrier dynamics in organic semiconductors as the weak spin-orbit coupling in these materials gives rise to long spin relaxation times. As the spin-orbit coupling is strong in organic-inorganic hybrid perovskites, which are promising materials for photovoltaic and light-emitting applications, magnetic field effects are expected to be negligible in these optoelectronic devices. We measured significant magneto-photocurrent, magneto-electroluminescence and magneto-photoluminescence responses in hybrid perovskite devices and thin films, where the amplitude and shape are correlated to each other through the electron-hole lifetime, which depends on the perovskite film morphology. We attribute these responses to magnetic-field-induced spin-mixing of the photogenerated electron-hole pairs with different g-factors--the Δg model. We validate this model by measuring large Δg (~ 0.65) using field-induced circularly polarized photoluminescence, and electron-hole pair lifetime using picosecond pump-probe spectroscopy.

Optimisation of growth of epitaxial Tl 2Ba 2Ca 1Cu 2O 8 superconducting thin films for electronic device applications

NASA Astrophysics Data System (ADS)

Michael, Peter C.; Johansson, L.-G.; Bengtsson, L.; Claeson, T.; Ivanov, Z. G.; Olsson, E.; Berastegui, P.; Stepantsov, E.

1994-12-01

Epitaxial thin films of Tl 2Ba 2Ca 1Cu 2O 8 (Tl-2212) superconductor have been grown on single crystal (100) lanthanum aluminate (LaAlO 3) substrates by a two stage process: laser ablation of a BaCaCuO (0212) sintered target and post-deposition anneal ex-situ in a thallium environment. The films are c-axis oriented with in-plane epitaxy as determined by x-ray diffraction (XRD θ-2θ and φ-scans). Superconducting transition temperatures as high as 105.5K have been obtained both from four-probe resistance and a.c. magnetic susceptibility measurements. Film morphology and chemical composition have been assessed by scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX). Sensitivity of the precursor film to environmental exposure has proven to be a determining factor in the reproducibility of film growth characteristics. The effect of oxygen partial pressure and substrate temperature used in the precursor film synthesis, as well as the thallium annealing temperature and duration, on the growth of Tl-2212 thin films is reported.

Dielectric relaxation in AC powder electroluminescent devices

NASA Astrophysics Data System (ADS)

Zhang, Shuai; Su, Haibin; Tan, Chuan Seng; Wong, Terence Kin Shun; Teo, Ronnie Jin Wah

2017-01-01

The dielectric properties of AC powder electroluminescent devices were measured and analyzed using complex impedance spectroscopy to determine the relaxation processes occurring within the devices. The relaxation processes identified were ascribed to the electrode polarization caused by ion accumulation at the electrode/resin interfaces, the Maxwell-Wagner-Sillars effects at the (ZnS or BaTiO3) particle/resin interfaces, and the dipolar reorientation of polymer chains in the resin matrix. Each relaxation process was represented by its corresponding equivalent circuit component. Space charge polarization at the electrodes were represented by a Warburg element, a resistor, and a constant phase element. The resin matrix, ZnS/resin and BaTiO3/resin interfaces could each be modeled by a resistor and a capacitor in parallel. The simulated equivalent circuits for three different printed structures showed good fitting with their experimental impedance results.

A fluorescent stilbenoid dendrimer for solution-processed blue light emitting diodes

NASA Astrophysics Data System (ADS)

Coya, C.; Álvarez, A. L.; Ramos, M.; de Andrés, A.; Zaldo, C.; Gómez, R.; Segura, J. L.; Seoane, C.

2008-04-01

We report a solution processed blue stilbenoid dendrimer based on a 1, 3, 5 - benzene core and endowed with a periphery of electron donating and solubilizing alkoxy chains. Raman analysis it is revealed as a helpful tool to investigate changes from the pristine material to the material in the OLED structure, explaining the differences between the dendrimer single layer thin film photoluminescence (PL) and the electroluminescence (EL) dendrimer active layer emission in the device. We report a blue EL emission (439 nm) and a very promising effective mobility value of 2.55 × 10 -5 cm2/(V•s) suggesting good transport properties for non doped blue OLEDs that use air stable Al as the cathode.

Tunable blue organic light emitting diode based on aluminum calixarene supramolecular complex

NASA Astrophysics Data System (ADS)

Legnani, C.; Reyes, R.; Cremona, M.; Bagatin, I. A.; Toma, H. E.

2004-07-01

In this letter, the results of supramolecular organic light emitting diodes using a calix[4] arene complex thin film as emitter and electron transporting layer are presented. The devices were grown onto glass substrates coated with indium-tin-oxide layer and aluminum thick (150nm) cathode. By applying a dc voltage between the device electrodes in forward bias condition, a blue light emission in the active area of the device was observed. It was found that the electroluminescent emission peak can be tuned between 470 and 510nm changing the applied voltage bias from 4.3 to 5.4V. The observed tunable emission can be associated with an energy transfer from the calixarene compound.

Defect-related electroluminescence from metal-oxide-semiconductor devices with ZrO2 films on silicon

NASA Astrophysics Data System (ADS)

Lv, Chunyan; Zhu, Chen; Wang, Canxing; Li, Dongsheng; Ma, Xiangyang; Yang, Deren

2016-11-01

Defect-related electroluminescence (EL) from ZrO2 films annealed under different atmosphere has been realized by means of electrical pumping scheme of metal-oxide-semiconductor (MOS) devices. At the same injection current, the acquired EL from the MOS device with the vacuum-annealed ZrO2 film is much stronger than that from the counterpart with the oxygen-annealed ZrO2 film. This is because the vacuum-annealed ZrO2 film contains more oxygen vacancies and Zr3+ ions. Analysis on the current-voltage characteristic of the ZrO2-based MOS devices indicates the P-F conduction mechanism dominates the electron transportation at the EL-enabling voltages under forward bias. It is tentatively proposed that the recombination of the electrons trapped in multiple oxygen-vacancy-related states with the holes in the defect level pertaining to Zr3+ ions brings about the EL emissions.

Correlation study of nanocrystalline carbon doped thin films prepared by a thermionic vacuum arc deposition technique

NASA Astrophysics Data System (ADS)

Dinca-Balan, Virginia; Vladoiu, Rodica; Mandes, Aurelia; Prodan, Gabriel

2017-11-01

The synthesis of Ag, Mg and Si nanocrystalline, embedded in a hydrogen-free amorphous carbon (a-C) matrix, deposited by a high vacuum and free buffer gas technique, were investigated. The films with compact structures and extremely smooth surfaces were prepared using the thermionic vacuum arc method in one electron gun configuration, on glass and silicon substrates. The surface morphology and wettability of the obtained multifunctional thin films were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and free surface energy (FSE) by See System. The results from the TEM measurements show how the Ag, Mg and Si interacted with carbon and the influence these materials have on the thin film structure formation and the grain size distribution. SEM correlated with EDX results reveal a very precise comparative study, regarding the quantity of the elements that morphed into carbides nanostructures. Also, the FSE results prove how different materials in combination with carbon can make changes to the surface properties.

MATERIAL AND PROCESS DEVELOPMENT LEADING TO ECONOMICAL HIGH-PERFORMANCE THIN-FILM SOLID OXIDE FUEL CELLS

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

Jie Guan; Atul Verma; Nguyen Minh

2003-04-01

This document summarizes the technical progress from September 2002 to March 2003 for the program, Material and Process Development Leading to Economical High-Performance Thin-Film Solid Oxide Fuel Cells, contract number DE-AC26-00NT40711. The causes have been identified for the unstable open circuit voltage (OCV) and low performance exhibited by the anode-supported lanthanum gallate based cells from the earlier development. Promising results have been obtained in the area of synthesis of electrolyte and cathode powders, which showed excellent sintering and densification at low temperatures. The fabrication of cells using tapecalendering process for anode-supported thin lanthanum gallate electrolyte cells and their performance optimizationmore » is in progress.« less

Droplet manipulation by an external electric field for crystalline film growth.

PubMed

Komino, Takeshi; Kuwabara, Hirokazu; Ikeda, Masaaki; Yahiro, Masayuki; Takimiya, Kazuo; Adachi, Chihaya

2013-07-30

Combining droplet manipulation by the application of an electric field with inkjet printing is proposed as a unique technique to control the surface wettability of substrates for solution-processed organic field-effect transistors (FETs). With the use of this technique, uniform thin films of 2,7-dioctyl[1]benzothieno[2,3,-b][1]benzothiopene (C8-BTBT) could be fabricated on the channels of FET substrates without self-assembled monolayer treatment. High-speed camera observation revealed that the crystals formed at the solid/liquid interface. The coverage of the crystals on the channels depended on the ac frequency of the external electric field applied during film formation, leading to a wide variation in the carrier transport of the films. The highest hole mobility of 0.03 cm(2) V(-1) s(-1) was obtained when the coverage was maximized with an ac frequency of 1 kHz.

SQUIDs De-fluxing Using a Decaying AC Magnetic Field

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

Matlashov, Andrei Nikolaevich; Semenov, Vasili Kirilovich; Anderson, Bill

Flux trapping is the Achilles’ heel of all superconductor electronics. The most direct way to avoid flux trapping is a prevention of superconductor circuits from exposure to magnetic fields. Unfortunately this is not feasible if the circuits must be exposed to a strong DC magnetic field even for a short period of time. For example, such unavoidable exposures take place in superparamagnetic relaxation measurements (SPMR) and ultra-low field magnetic resonance imaging (ULF MRI) using unshielded thin-film SQUID-based gradiometers. Unshielded SQUIDs stop working after being exposed to DC magnetic fields of only a few Gauss in strength. In this paper wemore » present experimental results with de-fluxing of planar thin-film LTS SQUID-based gradiometers using a strong decaying AC magnetic field. We used four commercial G136 gradiometers for SPMR measurements with up to a 10 mT magnetizing field. Strong 12.9 kHz decaying magnetic field pulses reliably return SQUIDs to normal operation 50 ms after zeroing the DC magnetizing field. This new AC de-fluxing method was also successfully tested with seven other different types of LTS SQUID sensors and has been shown to dissipate extremely low energy.« less

Bias-polarity-dependent UV/visible transferable electroluminescence from ZnO nanorod array LED with graphene oxide electrode supporting layer

NASA Astrophysics Data System (ADS)

Liu, Weizhen; Wang, Wei; Xu, Haiyang; Li, Xinghua; Yang, Liu; Ma, Jiangang; Liu, Yichun

2015-09-01

A simple top electrode preparation process, employing continuous graphene oxide films as electrode supporting layers, was adopted to fabricate a ZnO nanorod array/p-GaN heterojunction LED. The achieved LED demonstrated different electroluminescence behaviors under forward and reverse biases: a yellow-red emission band was observed under forward bias, whereas a blue-UV emission peak was obtained under reverse bias. Electroluminescence spectra under different currents and temperatures, as well as heterojunction energy-band alignments, reveal that the yellow-red emission under forward bias originates from recombinations related to heterointerface defects, whereas the blue-UV electroluminescence under reverse bias is ascribed to transitions from near-band-edge and Mg-acceptor levels in p-GaN.

Reverse-bias-driven dichromatic electroluminescence of n-ZnO wire arrays/p-GaN film heterojunction light-emitting diodes

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

Jeong, Junseok; Choi, Ji Eun; Hong, Young Joon, E-mail: yjhong@sejong.ac.kr

Position-controlled n-ZnO microwire (MW) and nanowire-bundle (NW-B) arrays were fabricated using hydrothermal growth of ZnO on a patterned p-GaN film. Both the wire/film p–n heterojunctions showed electrical rectification features at reverse-bias (rb) voltages, analogous to backward diodes. Dichromatic electroluminescence (EL) emissions with 445- and 560-nm-wavelength peaks displayed whitish-blue and greenish-yellow light from MW- and NW-B-based heterojunctions at rb voltages, respectively. The different dichromatic EL emission colors were studied based on photoluminescence spectra and the dichromatic EL peak intensity ratios as a function of the rb voltage. The different EL colors are discussed with respect to depletion thickness and electron tunnelingmore » probability determined by wire/film junction geometry and size.« less

Reverse-bias-driven dichromatic electroluminescence of n-ZnO wire arrays/p-GaN film heterojunction light-emitting diodes

NASA Astrophysics Data System (ADS)

Jeong, Junseok; Choi, Ji Eun; Kim, Yong-Jin; Hwang, Sunyong; Kim, Sung Kyu; Kim, Jong Kyu; Jeong, Hu Young; Hong, Young Joon

2016-09-01

Position-controlled n-ZnO microwire (MW) and nanowire-bundle (NW-B) arrays were fabricated using hydrothermal growth of ZnO on a patterned p-GaN film. Both the wire/film p-n heterojunctions showed electrical rectification features at reverse-bias (rb) voltages, analogous to backward diodes. Dichromatic electroluminescence (EL) emissions with 445- and 560-nm-wavelength peaks displayed whitish-blue and greenish-yellow light from MW- and NW-B-based heterojunctions at rb voltages, respectively. The different dichromatic EL emission colors were studied based on photoluminescence spectra and the dichromatic EL peak intensity ratios as a function of the rb voltage. The different EL colors are discussed with respect to depletion thickness and electron tunneling probability determined by wire/film junction geometry and size.

Investigations of the drift mobility of carriers and density of states in nanocrystalline CdS thin films

NASA Astrophysics Data System (ADS)

Singh, Baljinder; Singh, Janpreet; Kaur, Jagdish; Moudgil, R. K.; Tripathi, S. K.

2016-06-01

Nanocrystalline Cadmium Sulfide (nc-CdS) thin films have been prepared on well-cleaned glass substrate at room temperature (300 K) by thermal evaporation technique using inert gas condensation (IGC) method. X-ray diffraction (XRD) analysis reveals that the films crystallize in hexagonal structure with preferred orientation along [002] direction. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) studies reveal that grains are spherical in shape and uniformly distributed over the glass substrates. The optical band gap of the film is estimated from the transmittance spectra. Electrical parameters such as Hall coefficient, carrier type, carrier concentration, resistivity and mobility are determined using Hall measurements at 300 K. Transit time and mobility are estimated from Time of Flight (TOF) transient photocurrent technique in gap cell configuration. The measured values of electron drift mobility from TOF and Hall measurements are of the same order. Constant Photocurrent Method in ac-mode (ac-CPM) is used to measure the absorption spectra in low absorption region. By applying derivative method, we have converted the measured absorption data into a density of states (DOS) distribution in the lower part of the energy gap. The value of Urbach energy, steepness parameter and density of defect states have been calculated from the absorption and DOS spectra.

Activation of electrocatalytic properties of a-C films by doping with MoSe x clusters

NASA Astrophysics Data System (ADS)

Grigoriev, S. N.; Fominski, V. Y.; Romanov, R. I.; Volosova, M. A.; Fominski, D. V.

2017-12-01

Nanocomposite a-C(Mo/MoSe x ) thin films containing amorphous carbon matrix a-C, nano-Mo and MoSe x ≥2 clusters were obtained by pulsed laser co-deposition of carbon and MoSe2. The deposition was carried out at room temperature onto a graphite substrate. Atomic content of the MoSe x≥2 phase did not exceed 25%. The use of a buffer gas at a pressure of 10 Pa allowed to obtain the maximum Se/Mo ratio in the films and to increase the concentration of sp2-hybridized C atoms for high conductivity realization. The formation of MoSe x≥2 cluster inclusions was the essential factor for activation of hydrogen evolution reaction (HER) in 0.5 M H2SO4 aqueous solution. These clusters also promoted cathodic deposition of Pt nanoparticles on the surface of a-C(Mo/MoSe x ) in a H2SO4/KCl solution when a Pt anode was used as a source of Pt. Hybrid Pt/a-C(Mo/MoSe x ) thin-film coatings with a low Pt loading (~6 μg/cm2) exhibit excellent HER property, which noticeably exceeds that of relatively thick Pt coating prepared on a graphite substrate by pulsed laser deposition.

Over-current carrying characteristics of rectangular-shaped YBCO thin films prepared by MOD method

NASA Astrophysics Data System (ADS)

Hotta, N.; Yokomizu, Y.; Iioka, D.; Matsumura, T.; Kumagai, T.; Yamasaki, H.; Shibuya, M.; Nitta, T.

2008-02-01

A fault current limiter (FCL) may be manufactured at competitive qualities and prices by using rectangular-shaped YBCO films which are prepared by metal-organic deposition (MOD) method, because the MOD method can produce large size elements with a low-cost and non-vacuum technique. Prior to constructing a superconducting FCL (SFCL), AC over-current carrying experiments were conducted for 120 mm long elements where YBCO thin film of about 200 nm in thickness was coated on sapphire substrate with cerium oxide (CeO2) interlayer. In the experiments, only single cycle of the ac damping current of 50 Hz was applied to the pure YBCO element without protective metal coating or parallel resistor and the magnitude of the current was increased step by step until the breakdown phenomena occurred in the element. In each experiment, current waveforms flowing through the YBCO element and voltage waveform across the element were measured to get the voltage-current characteristics. The allowable over-current and generated voltage were successfully estimated for the pure YBCO films. It can be pointed out that the lower n-value trends to bring about the higher allowable over-current and the higher withstand voltage more than tens of volts. The YBCO film having higher n-value is sensitive to the over-current. Thus, some protective methods such as a metal coating should be employed for applying to the fault current limiter.

Electroluminescence and Photoluminescence from a Fluorescent Cobalt Porphyrin Grafted on Graphene Oxide

NASA Astrophysics Data System (ADS)

Janghouri, Mohammad

2017-10-01

A new graphene oxide-cobalt porphyrin (GO-CoTPP) hybrid material has been used as an emissive layer in organic light-emitting diodes (OLEDs). Devices with fundamental structure of indium-doped tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, 45 nm)/polyvinylcarbazole (PVK):2-(4-biphenyl)-5-(4- t-butylphenyl)-1,3,4-oxadiazole (PBD):GO-CoTPP (70 nm)/1,3,5-tris( N-phenylbenzimidazol-2-yl)-benzene (TPBI, 20 nm)/Al (150 nm) were fabricated. A red electroluminescence (EL) was obtained from thin-film PVK:PBD:CoTPP at 70 nm thickness. When CoTPP was covalently grafted on graphene oxide (GO) sheets, near-white EL was obtained. The white emission, which was composed of bluish green and red, is attributed to electroplex formation at the GO-CoTPP/PBD interface. Such electroplex emission between electrons and holes is a reason for the low turn-on voltage of the GO-CoTPP-based OLED. Maximum luminance efficiency of 1.43 cd/A with Commission International de l'Eclairage coordinates of 0.33 and 0.40 was achieved at current of 0.02 mA and voltage of 14 V.

Organic solution-processible electroluminescent molecular glasses for non-doped standard red OLEDs with electrically stable chromaticity

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

Bi, Xiaoman; Zuo, Weiwei; Liu, Yingliang, E-mail: liuylxn@sohu.com

Highlights: • The D–A–D electroluminescent molecular glasses are synthesized. • Non-doped red electroluminescent film is fabricated by spin-coating. • Red OLED shows stable wavelength, luminous efficiency and chromaticity. • CIE1931 coordinate is in accord with standard red light in PAL system. - Abstract: Organic light-emitting molecular glasses (OEMGs) are synthesized through the introduction of nonplanar donor and branched aliphatic chain into electroluminescent emitters. The target OEMGs are characterized by {sup 1}H NMR, {sup 13}C NMR, IR, UV–vis and fluorescent spectra as well as elemental analysis, TG and DSC. The results indicated that the optical, electrochemical and electroluminescent properties of OEMGsmore » are adjusted successfully by the replacement of electron-donating group. The non-doped OLED device with a standard red electroluminescent emission is achieved by spin-coating the THF solution of OEMG with a triphenylamine moiety. This non-doped red OLED device takes on an electrically stable electroluminescent performance, including the stable maximum electroluminescent wavelength of 640 nm, the stable luminous efficiency of 2.4 cd/A and the stable CIE1931 coordinate of (x, y) = (0.64, 0.35), which is basically in accord with the CIE1931 coordinate (x, y) = (0.64, 0.33) of standard red light in PAL system.« less

Recent developments of truly stretchable thin film electronic and optoelectronic devices.

PubMed

Zhao, Juan; Chi, Zhihe; Yang, Zhan; Chen, Xiaojie; Arnold, Michael S; Zhang, Yi; Xu, Jiarui; Chi, Zhenguo; Aldred, Matthew P

2018-03-29

Truly stretchable electronics, wherein all components themselves permit elastic deformation as the whole devices are stretched, exhibit unique advantages over other strategies, such as simple fabrication process, high integrity of entire components and intimate integration with curvilinear surfaces. In contrast to the stretchable devices using stretchable interconnectors to integrate with rigid active devices, truly stretchable devices are realized with or without intentionally employing structural engineering (e.g. buckling), and the whole device can be bent, twisted, or stretched to meet the demands for practical applications, which are beyond the capability of conventional flexible devices that can only bend or twist. Recently, great achievements have been made toward truly stretchable electronics. Here, the contribution of this review is an effort to provide a panoramic view of the latest progress concerning truly stretchable electronic devices, of which we give special emphasis to three kinds of thin film electronic and optoelectronic devices: (1) thin film transistors, (2) electroluminescent devices (including organic light-emitting diodes, light-emitting electrochemical cells and perovskite light-emitting diodes), and (3) photovoltaics (including organic photovoltaics and perovskite solar cells). We systematically discuss the device design and fabrication strategies, the origin of device stretchability and the relationship between the electrical and mechanical behaviors of the devices. We hope that this review provides a clear outlook of these attractive stretchable devices for a broad range of scientists and attracts more researchers to devote their time to this interesting research field in both industry and academia, thus encouraging more intelligent lifestyles for human beings in the coming future.

Scanning AC Nanocalorimetry and Its Applications

NASA Astrophysics Data System (ADS)

Xiao, Kechao

This thesis presents an AC nanocalorimetry technique that enables calorimetry measurements on very small quantities of materials over a wide range of scanning rates (from isothermal to 3x10. 3 K/s), temperatures(up to 1200 K), and environments. Such working range bridges the gap between traditional scanning calorimetry of bulk materials and nanocalorimetry. The method relies on a micromachined nanocalorimeter with negligible thermal lags between heater, thermometer, and sample. The ability to perform calorimetry measurements over such a broad range of scanning rates makes it an ideal tool to characterize the kinetics of phase transformations, reactions at elevated temperatures or to explore the behavior of materials far from equilibrium. We demonstrate the technique by performing measurements on thin-film samples of Sn, In, and Bi with thicknesses ranging from 100 to 300 nm. The experimental heat capacities and melting temperatures agree well with literature values. The measured heat capacities are insensitive to the applied AC frequency, scan rate, and heat loss to the environment over a broad range of experimental conditions. The dynamic range of scanning AC nanocalorimetry enables the combination of nanocalorimetry with in-situ x-ray diffraction (XRD) to facilitate interpretation of the calorimetry measurements. Time-resolved XRD during in-situ operation of nanocalorimetry sensors using intense, high-energy synchrotron radiation allows unprecedented characterization of thermal and structural material properties. We demonstrate this experiment with detailed characterization of the melting and solidification of elemental Bi, In and Sn thin-film samples, using heating and cooling rates up to 300 K/s. By combining scanning DC and AC nano-calorimetry techniques, we study the nucleation behavior of undercooled liquid Bi at cooling rates ranging from 10. 1 to 10. 4 K/s. Upon initial melting, the Bi thin-film sample breaksup into isolated islands. The number of islands in a typical sample is sufficiently large that highly repeatable nucleation behavior is observed, despite the stochastic nature of the nucleation process. We establish a data reduction technique to evaluate the nucleation rate from DC and AC calorimetry results. The results show that the driving force for the nucleation of melted Bi is well described by classical nucleation theory over a wide range of cooling rates. The proposed technique provides a unique and efficient way to examine nucleation kinetics with cooling rates over several orders of magnitude. The technique is quite general and can be used to evaluate reaction kinetics in other materials. Lastly, we apply the scanning AC nanocalorimetry technique to study solid-gas phase reactions by measuring the change in heat capacity of a sample during reaction. We apply this approach to evaluate the oxidation kinetics of thin-film samples of zirconium in air. The results confirm parabolic oxidation kinetics with an activation energy of 0.59+/-0.03 eV. The nano-calorimetry measurements were performed using a device that contains an array of micromachined nano-calorimeter sensors in an architecture designed for combinatorial studies. We demonstrate that the oxidation kinetics can be quantified using a single sample, thus enabling high-throughput mapping of the composition-dependence of the reaction rate.

Ultra-thin and smooth transparent electrode for flexible and leakage-free organic light-emitting diodes

PubMed Central

Ok, Ki-Hun; Kim, Jiwan; Park, So-Ra; Kim, Youngmin; Lee, Chan-Jae; Hong, Sung-Jei; Kwak, Min-Gi; Kim, Namsu; Han, Chul Jong; Kim, Jong-Woong

2015-01-01

A smooth, ultra-flexible, and transparent electrode was developed from silver nanowires (AgNWs) embedded in a colorless polyimide (cPI) by utilizing an inverted film-processing method. The resulting AgNW-cPI composite electrode had a transparency of >80%, a low sheet resistance of 8 Ω/□, and ultra-smooth surfaces comparable to glass. Leveraging the robust mechanical properties and flexibility of cPI, the thickness of the composite film was reduced to less than 10 μm, which is conducive to extreme flexibility. This film exhibited mechanical durability, for both outward and inward bending tests, up to a bending radius of 30 μm, while maintaining its electrical performance under cyclic bending (bending radius: 500 μm) for 100,000 iterations. Phosphorescent, blue organic light-emitting diodes (OLEDs) were fabricated using these composites as bottom electrodes (anodes). Hole-injection was poor, because AgNWs were largely buried beneath the composite's surface. Thus, we used a simple plasma treatment to remove the thin cPI layer overlaying the nanowires without introducing other conductive materials. As a result, we were able to finely control the flexible OLEDs' electroluminescent properties using the enlarged conductive pathways. The fabricated flexible devices showed only slight performance reductions of <3% even after repeated foldings with a 30 μm bending radius. PMID:25824143

RESEARCH ON THE ELECTRONIC AND OPTICAL PROPERTIES OF POLYMER AND OTHER ORGANIC MOLECULAR THIN FILMS

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

ALEXEI G. VITUKHNOVSKY; IGOR I. SOBELMAN - RUSSIAN ACADEMY OF SCIENCES

1995-09-06

Optical properties of highly ordered films of poly(p-phenylene) (PPP) on different substrates, thin films of mixtures of conjugated polymers, of fullerene and its composition with polymers, molecular J-aggregates of cyanine dyes in frozen matrices have been studied within the framework of the Agreement. Procedures of preparation of high-quality vacuum deposited PPP films on different substrates (ITO, Si, GaAs and etc.) were developed. Using time-correlated single photon counting technique and fluorescence spectroscopy the high quality of PPP films has been confirmed. Dependence of structure and optical properties on the conditions of preparation were investigated. The fluorescence lifetime and spectra of highlymore » oriented vacuum deposited PPP films were studied as a function of the degree of polymerization. It was shown for the first time that the maximum fluorescence quantum yield is achieved for the chain length approximately equal to 35 monomer units. The selective excitation of luminescence of thin films of PPP was performed in the temperature range from 5 to 300 K. The total intensity of luminescence monotonically decreases with decreasing temperature. Conditions of preparation of highly cristallyne fullerene C{sub 60} films by the method of vacuum deposition were found. Composites of C{sub 60} with conjugated polymers PPV and polyacetylene (PA) were prepared. The results on fluorescence quenching, IR and resonant Raman spectroscopy are consistent with earlier reported ultrafast photoinduced electron transfer from PPV to C{sub 60} and show that the electron transfer is absent in the case of the PA-C{sub 60} composition. Strong quenching of PPV fluorescence was observed in the PPV-PA blends. The electron transfer from PPV to PA can be considered as one of the possible mechanisms of this quenching. The dynamics of photoexcitations in different types of J-aggregates of the carbocyanine dye was studied at different temperatures in frozen matrices. The optical properties of relatively simple J-aggregates with pure intrasegment relaxation, which they have found, may clarify the problem of the relationship between intrasegment and intersegment processes in the formation of luminescent states in more complicated conjugated polymers, which is important for construction of electroluminescence and photosensitive devices.« less

Optical and electrical properties of TiOPc doped Alq{sub 3} thin films

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

Ramar, M.; Suman, C. K., E-mail: sumanck@nplindia.org; Tyagi, Priyanka

2015-06-24

The Titanyl phthalocyanine (TiOPc) was doped in Tris (8-hydroxyquinolinato) aluminum (Alq3) with different concentration. The thin film of optimized doping concentration was studied extensively for optical and electrical properties. The optical properties, studied using ellipsometry, absorption and photoluminescence. The absorption peak of Alq{sub 3} and TiOPc was observed at 387 nm and 707 nm and the photo-luminescence intensity (PL) peak of doped thin film was observed at 517 nm. The DC and AC electrical properties of the thin film were studied by current density-voltage (J-V) characteristics and impedance over a frequency range of 100 Hz - 1 MHz. The electron mobility calculated from trap-free space-chargemore » limited region (SCLC) is 0.17×10{sup −5} cm{sup 2}/Vs. The Cole-Cole plots shows that the TiOPc doped Alq{sub 3} thin film can be represented by a single parallel resistance R{sub P} and capacitance C{sub P} network with a series resistance R{sub S} (10 Ω). The value of R{sub P} and C{sub P} at zero bias was 1587 Ω and 2.568 nF respectively. The resistance R{sub P} decreases with applied bias whereas the capacitance C{sub P} remains almost constant.« less

Facile One-Pot Synthesis of Flower Like Cobalt Oxide Nanostructures on Nickel Plate and Its Supercapacitance Properties.

PubMed

Kandasamy, N; Venugopal, T; Kannan, K

2018-06-01

A flower like cobalt oxide nanostructured thin film (Co2O3) on Nickel (Ni) plate as have been successfully developed via alcoholic Seed Layer assisted chemical bath Deposition (SLD) process. Through the controlled alkaline electrolytes, the flower and paddles like Co2O3 nanoarchitectures were formed. The prepared thin film was characterized by X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray (SEM and EDX), Atomic Force Microscope (AFM), Raman spectroscopy techniques. Electron micrograph reveals the flower and paddles like nanostructured Co2O3 thin film deposited on Ni plates. The electrochemical characteristics were investigated using cyclic voltammetry (CV), charge-discharge and AC impedance spectroscopy in different aqueous electrolytes such as NaOH, KOH, and LiOH. The maximum specific capacitance of 856 Fg-1 was attained with 2 M KOH electrolyte with 2 mVs-1 of the Co2O3 thin film coated Ni plate at 80 °C using SLD method. The capacitance values obtained with various electrolytes are in the order of KOH > NaOH > LiOH. The results indicate that the present method is economical and the material is ecofriendly with enhanced capacitance property.

Electroluminescence from completely horizontally oriented dye molecules

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

Komino, Takeshi; Center for Organic Photonics and Electronics Research, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395; Japan Science and Technology Agency, ERATO, Adachi Molecular Exciton Engineering Project, 744 Motooka, Nishi, Fukuoka 819-0395

2016-06-13

A complete horizontal molecular orientation of a linear-shaped thermally activated delayed fluorescent guest emitter 2,6-bis(4-(10Hphenoxazin-10-yl)phenyl)benzo[1,2-d:5,4-d′] bis(oxazole) (cis-BOX2) was obtained in a glassy host matrix by vapor deposition. The orientational order of cis-BOX2 depended on the combination of deposition temperature and the type of host matrix. Complete horizontal orientation was obtained when a thin film with cis-BOX2 doped in a 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host matrix was fabricated at 200 K. The ultimate orientation of guest molecules originates from not only the kinetic relaxation but also the kinetic stability of the deposited guest molecules on the film surface during film growth. Utilizing the ultimatemore » orientation, a highly efficient organic light-emitting diode with the external quantum efficiency of 33.4 ± 2.0% was realized. The thermal stability of the horizontal orientation of cis-BOX2 was governed by the glass transition temperature (T{sub g}) of the CBP host matrix; the horizontal orientation was stable unless the film was annealed above T{sub g}.« less

Ultrastrong light-matter coupling in electrically doped microcavity organic light emitting diodes

NASA Astrophysics Data System (ADS)

Mazzeo, M.; Genco, A.; Gambino, S.; Ballarini, D.; Mangione, F.; Di Stefano, O.; Patanè, S.; Savasta, S.; Sanvitto, D.; Gigli, G.

2014-06-01

The coupling of the electromagnetic field with an electronic transition gives rise, for strong enough light-matter interactions, to hybrid states called exciton-polaritons. When the energy exchanged between light and matter becomes a significant fraction of the material transition energy an extreme optical regime called ultrastrong coupling (USC) is achieved. We report a microcavity embedded p-i-n monolithic organic light emitting diode working in USC, employing a thin film of squaraine dye as active layer. A normalized coupling ratio of 30% has been achieved at room temperature. These USC devices exhibit a dispersion-less angle-resolved electroluminescence that can be exploited for the realization of innovative optoelectronic devices. Our results may open the way towards electrically pumped polariton lasers.

Improvement of electroluminescence performance by integration of ZnO nanowires and single-crystalline films on ZnO/GaN heterojunction

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

Shi, Zhifeng; Zhang, Yuantao, E-mail: zhangyt@jlu.edu.cn; Cui, Xijun

2014-03-31

Heterojunction light-emitting diodes based on n-ZnO nanowires/ZnO single-crystalline films/p-GaN structure have been demonstrated for an improved electroluminescence performance. A highly efficient ultraviolet emission was observed under forward bias. Compared with conventional n-ZnO/p-GaN structure, high internal quantum efficiency and light extraction efficiency were simultaneously considered in the proposed diode. In addition, the diode can work continuously for ∼10 h with only a slight degradation in harsh environments, indicating its good reliability and application prospect in the future. This route opens possibilities for the development of advanced nanoscale devices in which the advantages of ZnO single-crystalline films and nanostructures can be integrated together.

Supercapacitive properties of hybrid films of manganese dioxide and polyaniline based on active carbon in organic electrolyte

NASA Astrophysics Data System (ADS)

Zou, Wu-yuan; Wang, Wei; He, Ben-lin; Sun, Ming-liang; Yin, Yan-sheng

This is the first report about supercapacitive performance of hybrid film of manganese dioxide (MnO 2) and polyaniline (PANI) in an organic electrolyte (1.0 M LiClO 4 in acetonitrile). In this work, a high surface area and conductivity of active carbon (AC) electrode is used as a substrate for PANI/MnO 2 film electro-codeposition. The redox properties of the coated PANI/MnO 2 thin film exhibit ideal capacitive behaviour in 1 M LiClO 4/AN. The specific capacitance (SC) of PANI/MnO 2 hybrid film is as high as 1292 F g -1 and maintains about 82% of the initial capacitance after 1500 cycles at a current density of 4.0 mA cm -2, and the coulombic efficiency (η) is higher than 95%. An asymmetric capacitor has been developed with the PANI/MnO 2/AC positive and pure AC negative electrodes, which is able to deliver a specific energy as high as 61 Wh kg -1 at a specific power of 172 W kg -1 in the range of 0-2.0 V. These results indicate that the organic electrolyte is a promising candidate for PANI/MnO 2 material application in supercapacitors.

Influence of inert gases on the reactive high power pulsed magnetron sputtering process of carbon-nitride thin films

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

Schmidt, Susann; Czigany, Zsolt; Greczynski, Grzegorz

2013-01-15

The influence of inert gases (Ne, Ar, Kr) on the sputter process of carbon and carbon-nitride (CN{sub x}) thin films was studied using reactive high power pulsed magnetron sputtering (HiPIMS). Thin solid films were synthesized in an industrial deposition chamber from a graphite target. The peak target current during HiPIMS processing was found to decrease with increasing inert gas mass. Time averaged and time resolved ion mass spectroscopy showed that the addition of nitrogen, as reactive gas, resulted in less energetic ion species for processes employing Ne, whereas the opposite was noticed when Ar or Kr were employed as inertmore » gas. Processes in nonreactive ambient showed generally lower total ion fluxes for the three different inert gases. As soon as N{sub 2} was introduced into the process, the deposition rates for Ne and Ar-containing processes increased significantly. The reactive Kr-process, in contrast, showed slightly lower deposition rates than the nonreactive. The resulting thin films were characterized regarding their bonding and microstructure by x-ray photoelectron spectroscopy and transmission electron microscopy. Reactively deposited CN{sub x} thin films in Ar and Kr ambient exhibited an ordering toward a fullerene-like structure, whereas carbon and CN{sub x} films deposited in Ne atmosphere were found to be amorphous. This is attributed to an elevated amount of highly energetic particles observed during ion mass spectrometry and indicated by high peak target currents in Ne-containing processes. These results are discussed with respect to the current understanding of the structural evolution of a-C and CN{sub x} thin films.« less

Dynamic Field and Current Distributions in Multifilamentary YBa2Cu3O7-delta Thin Films with Magnetic Coupling (POSTPRINT)

DTIC Science & Technology

2010-03-01

INTRODUCTION The separation of high-temperature superconducting HTS tapes into filaments is a viable approach to reduce ac and hysteretic losses in...generation HTS coated conductors. However, ac losses of finely striated tapes can still be larger than desired as predicted by analytical expressions.6...necessitates an in-depth understanding of the flux and current dynamics in multifilamentary HTS structures as both depend strongly on temperature and history of

A Piezoelectroluminescent Fiber-Optical Sensor for Diagnostics of the 3D Stress State in Composite Structures

NASA Astrophysics Data System (ADS)

Pan'kov, A. A.

2018-05-01

The mathematical model of a piezoelectroluminescent fiber-optical sensor is developed for diagnostics of the 3D stress state of composite structures. The sensor model is a coaxial sector-compound layered cylinder consisting of a central optical fiber with electroluminescent and piezoelectric layers and an external uniform elastic buffer layer. The electroluminescent and piezoelectric layers are separated by radial-longitudinal boundaries, common for both layers, into geometrically equal six "measuring elements" — cylindrical two-layered sectors. The directions of 3D polarization of the piezoelectric phases and the frequencies of luminous efficacy of the electroluminescent phases are different in each sector. In the sensor, a thin translucent "internal" controlling electrode is located between the optical fiber and the electroluminescent layer, and the piezoelectric layer is coated by a thin "external" controlling electrode. The results of numerical modeling of the nonuniform coupled electroelastic fields of the piezoelectroluminescent fiber-optical sensor in the loaded "representative volume" of a composite, taking into account the action of the controlling voltage on the internal and external electrodes, of a numerical calculation of "informative and controlling coefficients" of the sensor, and of testing of an arbitrary 3D stress of state of a unidirectional glass-fiber plastic by the finite-element method are presented.

High-frequency applications of high-temperature superconductor thin films

NASA Astrophysics Data System (ADS)

Klein, N.

2002-10-01

High-temperature superconducting thin films offer unique properties which can be utilized for a variety of high-frequency device applications in many areas related to the strongly progressing market of information technology. One important property is an exceptionally low level of microwave absorption at temperatures attainable with low power cryocoolers. This unique property has initiated the development of various novel type of microwave devices and commercialized subsystems with special emphasis on application in advanced microwave communication systems. The second important achievement related to efforts in oxide thin and multilayer technology was the reproducible fabrication of low-noise Josephson junctions in high-temperature superconducting thin films. As a consequence of this achievement, several novel nonlinear high-frequency devices, most of them exploiting the unique features of the ac Josephson effect, have been developed and found to exhibit challenging properties to be utilized in basic metrology and Terahertz technology. On the longer timescale, the achievements in integrated high-temperature superconductor circuit technology may offer a strong potential for the development of digital devices with possible clock frequencies in the range of 100 GHz.

A novel electroluminescent PPV copolymer and silsesquioxane nanocomposite film for the preparation of efficient PLED devices.

PubMed

Venegoni, Ivan; Carniato, Fabio; Olivero, Francesco; Bisio, Chiara; Pira, Nello Li; Lambertini, Vito Guido; Marchese, Leonardo

2012-11-02

Polymer light-emitting diodes (PLEDs) have attracted growing interest in recent years for their potential use in displays and lighting fields. Nevertheless, PLED devices have some disadvantages in terms of low optoelectronic efficiency, high cost, short lifetimes and low thermal stability, which limit their final applications. Huge efforts have been made recently to improve the performances of these devices. The addition of inorganic or hybrid organic-inorganic nanoparticles to the light-emitting polymers, for example, allows their thermal stability and electroluminescent efficiency to be increased. Following this approach, novel PLED devices based on composite films of PPV-derivative copolymer (commercial name Super Yellow, SY) and octaisobutil POSS, were developed in this study. The device containing Super Yellow loaded with 1 wt% of POSS showed higher efficiency (ca. +30%) and improved lifetime in comparison to PLED prepared with the pure electroluminescent polymer. The PLED devices developed in this study are suitable candidates for automotive dashboards and, in general, for lighting applications.

Enhanced polarization and dielectric properties of Pb(Zr1-xTix)O3 thin films

NASA Astrophysics Data System (ADS)

Ortega, N.; Kumar, Ashok; Katiyar, R. S.

2008-10-01

We report the fabrication of PbZr0.57Ti0.43O3 (PZT) thin films with preferential growth along (111) and random crystalline orientation on the platinized silicon substrates using pulsed laser deposition technique. X-ray diffraction patterns and surface morphology indicate increase in grain size and nucleation, which support better perovskite matrix with increase in annealing temperature. We observed large dielectric constant (˜4000) and enhanced remanent polarization 70 μC/cm2 at room temperature attributed to grain growth and intermetallic Pt-Pb transient phase. Frequency dependent polarization showed minor reduction in polarization above 10 kHz frequencies. Normalized fatigue characteristic of PZT thin films showed minimal 25% degradation in remanent polarization after 109 cycles, which may be useful for memory devices. ac conductivity spectra illustrated that anomaly near the phase transition temperature with activation energy (Ea˜0.60-0.75 eV) supports the intrinsic nature of ferroelectric phase transition.

Preparation and evaluation of thin-film sodium tungsten bronzes

NASA Technical Reports Server (NTRS)

Kautz, H. E.; Fielder, W. L.; Singer, J.; Fordyce, J. S.

1974-01-01

Thin films of sodium tungsten bronze (NaxWO3) were investigated as reversible sodium ion electrodes for solid electrolytes. The films were made by electron beam evaporation of the three phases, W metal, Na2WO4, and WO3, followed by sintering. The substrates were sodium beta alumina disks and glass slides. X-ray diffraction analyses of the films showed that sintering in dry nitrogen with prior exposure to air lead to mixed phases. Sintering in vacuum with no air exposure produced tetragonal I bronze with a nominal composition of Na0.31WO3, single phase within the limits of X-ray diffraction detectability. The films were uniform and adherent on sodium beta alumina substrates. The ac and dc conductivities of the beta alumina were measured with the sodium tungsten bronze films as electrodes. These experiments indicated that the tetragonal I bronze electrodes were not completely reversible. This may have resulted from sodium ion blocking within the bronze film or at the bronze beta alumina interface. Methods for attempting to make more completely reversible electrodes are suggested.

Determining the Mechanism of Low Temperature Graphene Growth

DTIC Science & Technology

2014-05-27

layer graphene over cobalt film crystallized on sapphire. ACS Nano, 2010. 4: p. 7407-7414. 8. Sutter, P.W., J. I. Flege and E. A. Sutter, Epitaxial...111). Journal of Physics, 2009. 11: p. 1-25. 15. Sukhdeo, D., Large area CVD of graphene over thin films of cobalt . 2009, Columbia University. p...B.R. Luo, W.P. Hu, G. Yu, Y.Q. Liu, Low Temperature Growth of Highly Nitrogen- doped Single Crystal Graphene Arrays by Chemical Vapor Deposition

Strong visible electroluminescence from silicon nanocrystals embedded in a silicon carbide film

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

Huh, Chul, E-mail: chuh@etri.re.kr; Kim, Tae-Youb; Ahn, Chang-Geun

2015-05-25

We report the strong visible light emission from silicon (Si) nanocrystals (NCs) embedded in a Si carbide (SiC) film. Compared to Si NC light-emitting diode (LED) by employing the Si nitride (SiN{sub x}) film as a surrounding matrix, the turn-on voltage of the Si NC LED with the SiC film was significantly decreased by 4 V. This was attributed to a smaller barrier height for injecting the electrons into the Si NCs due to a smaller band gap of SiC film than a SiN{sub x} film. The electroluminescence spectra increases with increasing forward voltage, indicating that the electrons are efficiently injectedmore » into the Si NCs in the SiC film. The light output power shows a linear increase with increasing forward voltage. The light emission originated from the Si NCs in a SiC film was quite uniform. The power efficiency of the Si NC LED with the SiC film was 1.56 times larger than that of the Si NC LED with the SiN{sub x} film. The Si NCs in a SiC film show unique advantages and are a promising candidate for application in optical devices.« less

Enhancing light emission in flexible AC electroluminescent devices by tetrapod-like zinc oxide whiskers.

PubMed

Wen, Li; Liu, Nishuang; Wang, Siliang; Zhang, Hui; Zhao, Wanqiu; Yang, Zhichun; Wang, Yumei; Su, Jun; Li, Luying; Long, Fei; Zou, Zhengguang; Gao, Yihua

2016-10-03

Flexible alternating current electroluminescent devices (ACEL) are more and more popular and widely used in liquid-crystal display back-lighting, large-scale architectural and decorative lighting due to their uniform light emission, low power consumption and high resolution. However, presently how to acquire high brightness under a certain voltage are confronted with challenges. Here, we demonstrate an electroluminescence (EL) enhancing strategy that tetrapod-like ZnO whiskers (T-ZnOw) are added into the bottom electrode of carbon nanotubes (CNTs) instead of phosphor layer in flexible ACEL devices emitting blue, green and orange lights, and the brightness is greatly enhanced due to the coupling between the T-ZnOw and ZnS phosphor dispersed in the flexible polydimethylsiloxane (PDMS) layer. This strategy provides a new routine for the development of high performance, flexible and large-area ACEL devices.

Frequency dispersion of nonlinear response of thin superconducting films in the Berezinskii-Kosterlitz-Thouless state

DOE PAGES

Dietrich, Scott; Mayer, William; Byrnes, Sean; ...

2015-02-20

The effects of microwave radiation on transport properties of atomically thin La 2-xSr xCuO₄ films were studied in the 0.1-20 GHz frequency range. Resistance changes induced by microwaves were investigated at different temperatures (8–15 K) near the superconducting transition. A strong decrease of the nonlinear response is observed within a few GHz of a cutoff frequency ν cut ≈ 2GHz. The expected frequency dependence vastly underestimates the sharpness of this drop. Numerical simulations that assume ac response to follow dc V-I characteristics of the films reproduce well the low frequency behavior, but fail above ν cut. Thus, high-frequency radiation ismore » much less effective in inducing vortex-antivortex dissociation in the oscillating superconducting condensate.« less

Tribochemistry of contact interfaces of nanocrystalline molybdenum carbide films

NASA Astrophysics Data System (ADS)

Kumar, D. Dinesh; Kumar, N.; Panda, Kalpataru; Kamalan Kirubaharan, A. M.; Kuppusami, P.

2018-07-01

Transition metal carbides (TMC) are known for their improved tribological properties and are sensitive to the tribo-atmospheric environment. Nanocrystalline molybdenum carbide (MoC) thin films were deposited by DC magnetron sputtering technique using reactive CH4 gas. The friction and wear resistance properties of MoC thin films were significantly improved in humid-atmospheric condition as compared to high-vacuum tribo-condition. A comprehensive chemical analysis of deformed contact interfaces was carried out by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX) and Raman spectroscopy. XPS and Raman spectroscopy showed the formation of stable molybdenum-oxide (MoO), molybdenum carbide (MoC) and amorphous carbon (a-C) tribo-phases. Moreover, during the sliding in humid-atmospheric condition, these phases were extensively deposited on the sliding steel ball counter body which significantly protected against undesirable friction and wear.

Electroluminescence from ZnCuInS/ZnS quantum dots/poly(9-vinylcarbazole) multilayer films with different thicknesses of quantum dot layer

NASA Astrophysics Data System (ADS)

Dong, Xiaofei; Xu, Jianping; Shi, Shaobo; Zhang, Xiaosong; Li, Lan; Yin, Shougen

2017-05-01

We report tunable electroluminescence (EL) from solution-processed ZnCuInS/ZnS (ZCIS/ZnS) quantum dots (QDs)/poly(9-vinlycarbazole) multilayer films. The EL spectra exhibit a red shift as the QD layer thickness increases. By analyzing the dependence of the applied voltage and the ZCIS/ZnS QD layer thickness on the EL spectra, the origin of the red shift is associated with the increased trap density of QDs that induces the injected electrons to be trapped in the deep donor level. The current conduction mechanism based on the current density-voltage curves at different voltage regions was discussed.

Localized Surface Plasmon-Enhanced Electroluminescence in OLEDs by Self-Assembly Ag Nanoparticle Film

NASA Astrophysics Data System (ADS)

He, Xiaoxiao; Wang, Wenjun; Li, Shuhong; Wang, Qingru; Zheng, Wanquan; Shi, Qiang; Liu, Yunlong

2015-12-01

We fabricated Ag nanoparticle (NP) film in organic light emission diodes (OLEDs), and a 23 times increase in electroluminescence (EL) at 518 nm was probed by time-resolved EL measurement. The luminance and relative external quantum efficiency (REQE) were increased by 5.4 and 3.7 times, respectively. There comes a new energy transport way that localized surface plasmons (LSPs) would absorb energy that corresponds to the electron-hole pair before recombination, promoting the formation of electron-hole pair and exciting local surface plasmon resonance (LSPR). The extended lifetime of Alq3 indicates the existence of strong interaction between LSPR and exciton, which decreases the nonradiative decay rate of OLEDs.

Magnetic properties of epitaxial hexagonal HoFeO3 thin films

NASA Astrophysics Data System (ADS)

Wang, Xiao; Xiao, Zhuyun; Xu, Xiaoshan; Wang, Wenbin; Keavney, David; Liu, Yaohua; Cheng, X. M.

2014-03-01

Multiferroic materials exhibit multiple ferroic orders simultaneously and thus have great potential applications in information technology, sensing and actuation. Epitaxial hexagonal HoFeO3 (h-HFO) films are very promising candidates as multiferroic materials with room temperature ferromagnetism, because magnetic Ho3+ ions are expected to have stronger exchange interactions with Fe3+ ions than the well-studied h-LuFeO3 films. We report study of magnetic properties of epitaxial h-HFO thin films deposited using laser molecular beam epitaxy on Yttria-stabilized zirconia (YSZ) substrates. X-ray diffraction measurements confirmed the epitaxial registry and six-fold symmetry of the film. Temperature dependence of magnetization of the film measured by a Quantum Design SQUID magnetometer shows dominating paramagnetic characteristic. Element specific x-ray magnetic circular dichroism measurements performed at beamline 4-ID-C of the Advanced Photon Source show a ferromagnetic ordering of Fe and an exchange coupling between Ho3+ and Fe3+ ions. Work at BMC is supported by NSF Career award (DMR 1053854). Work at ANL is supported by US-DOE, Office of Science, BES (No. DE-AC02-06CH11357).

Color-Pure Violet-Light-Emitting Diodes Based on Layered Lead Halide Perovskite Nanoplates

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

Liang, Dong; Peng, Yuelin; Fu, Yongping

Violet electroluminescence is rare in both inorganic and organic light-emitting diodes (LEDs). Low-cost and room- temperature solution-processed lead halide perovskites with high- efficiency and color-tunable photoluminescence are promising for LEDs. Here, we report room-temperature color-pure violet LEDs based on a two-dimensional lead halide perovskite material, namely, 2-phenylethylammonium (C 6H 5CH 2CH 2NH 3 +, PEA) lead bromide [(PEA) 2PbBr 4]. The natural quantum confinement of two-dimen- sional layered perovskite (PEA) 2PbBr 4 allows for photoluminescence of shorter wavelength (410 nm) than its three-dimensional counterpart. By converting as-deposited polycrystalline thin films to micrometer-sized (PEA) 2PbBr 4 nanoplates using solvent vapor annealing,more » we successfully integrated this layered perovskite material into LEDs and achieved efficient room-temperature violet electroluminescence at 410 nm with a narrow bandwidth. This conversion to nanoplates significantly enhanced the crystallinity and photophysical properties of the (PEA) 2PbBr 4 samples and the external quantum efficiency of the violet LED. Finally, the solvent vapor annealing method reported herein can be generally applied to other perovskite materials to increase their grain size and, ultimately, improve the performance of optoelectronic devices based on perovskite materials.« less

2-(2-Hydroxyphenyl)benzimidazole-based four-coordinate boron-containing materials with highly efficient deep-blue photoluminescence and electroluminescence.

PubMed

Zhang, Zhenyu; Zhang, Houyu; Jiao, Chuanjun; Ye, Kaiqi; Zhang, Hongyu; Zhang, Jingying; Wang, Yue

2015-03-16

Two novel four-coordinate boron-containing emitters 1 and 2 with deep-blue emissions were synthesized by refluxing a 2-(2-hydroxyphenyl)benzimidazole ligand with triphenylborane or bromodibenzoborole. The boron chelation produced a new π-conjugated skeleton, which rendered the synthesized boron materials with intense fluorescence, good thermal stability, and high carrier mobility. Both compounds displayed deep-blue emissions in solutions with very high fluorescence quantum yields (over 0.70). More importantly, the samples showed identical fluorescence in the solution and solid states, and the efficiency was maintained at a high level (approximately 0.50) because of the bulky substituents between the boron atom and the benzimidazole unit, which can effectively separate the flat luminescent units. In addition, neat thin films composed of 1 or 2 exhibited high electron and hole mobility in the same order of magnitude 10(-4), as determined by time-of-flight. The fabricated electroluminescent devices that employed 1 or 2 as emitting materials showed high-performance deep-blue emissions with Commission Internationale de L'Eclairage (CIE) coordinates of (X = 0.15, Y = 0.09) and (X = 0.16, Y = 0.08), respectively. Thus, the synthesized boron-containing materials are ideal candidates for fabricating high-performance deep-blue organic light-emitting diodes.

Color-Pure Violet-Light-Emitting Diodes Based on Layered Lead Halide Perovskite Nanoplates

DOE PAGES

Liang, Dong; Peng, Yuelin; Fu, Yongping; ...

2016-06-23

Violet electroluminescence is rare in both inorganic and organic light-emitting diodes (LEDs). Low-cost and room- temperature solution-processed lead halide perovskites with high- efficiency and color-tunable photoluminescence are promising for LEDs. Here, we report room-temperature color-pure violet LEDs based on a two-dimensional lead halide perovskite material, namely, 2-phenylethylammonium (C 6H 5CH 2CH 2NH 3 +, PEA) lead bromide [(PEA) 2PbBr 4]. The natural quantum confinement of two-dimen- sional layered perovskite (PEA) 2PbBr 4 allows for photoluminescence of shorter wavelength (410 nm) than its three-dimensional counterpart. By converting as-deposited polycrystalline thin films to micrometer-sized (PEA) 2PbBr 4 nanoplates using solvent vapor annealing,more » we successfully integrated this layered perovskite material into LEDs and achieved efficient room-temperature violet electroluminescence at 410 nm with a narrow bandwidth. This conversion to nanoplates significantly enhanced the crystallinity and photophysical properties of the (PEA) 2PbBr 4 samples and the external quantum efficiency of the violet LED. Finally, the solvent vapor annealing method reported herein can be generally applied to other perovskite materials to increase their grain size and, ultimately, improve the performance of optoelectronic devices based on perovskite materials.« less

Effects of co-dopants on the microstructure and electroluminescence of ZnS:Mn thin film phosphors

NASA Astrophysics Data System (ADS)

Zhai, Qing

The objective of this study is to investigate the effects of the co-dopants of KCl and Ga2S3 and post-deposition annealing on the microstructure and electroluminescence (EL) properties of ZnS:Mn thin film phosphors. ZnS:Mn thin films are deposited by radio frequency (RF) magnetron sputtering from ZnS and Mn targets onto pre-deposited indium tin oxide (ITO) and aluminum titanium oxide (ATO) layers on Corning 7059 glass. Argon at 20mTorr is the sputtering ambient. The substrates are held at 180°C during deposition. Co-dopants are thermally evaporated after the ZnS:Mn films, and diffused into the ZnS:Mn films by ex situ annealing between 600°C and 800°C for 5 minutes in a nitrogen ambient. Brightness versus the applied voltage, luminous efficiency, and photoluminescence (PL) are used to characterize the EL devices. The figures of merit are the threshold voltage Vth, at which luminescence is first detected, B40 and eta40, the brightness and efficiency at 40V above the threshold voltage, respectively. In the as-deposited ZnS:Mn phosphor, the microstructure is heavily defected with two different grain morphologies: a roughly 100nm layer of equiaxed fine grains at the insulator/phosphor interface and columnar grains with an average diameter of 89nm in the rest of the film. The EL properties of as-deposited films are poor, with a Vth of 125V, B40 of 48.7nits, and a eta40 of 0.2275lm/W. Annealing at 700°C for 5 minutes raises B40 to 99.6nits and eta40 to 0.4463lm/W, with little change in Vth. In KCl doped ZnS:Mn samples, after 5 minutes of annealing at 700°C, SIMS indicates a uniform distribution of K and a complete diffusion of Cl throughout the phosphor. KCl co-doping enhances grain growth by improving dislocation motion, and the columnar grain size increases from 132nm to 187nm. EL properties are improved, with a B40 of 252nits and eta 40 of 0.9879lm/W. A slight increase in Vth is observed. In ZnS:Mn samples with Ga2S3, the grain growth is less than that in undoped ZnS:Mn. Energy dispersive spectrometry (EDS) data show Ga segregation to grain boundaries and triple points. Decreases of 40V in Vth and 10nits in B40 are observed from ZnS:Mn,Ga 2S3 samples annealed at 800°C. It is postulated that Ga2S3 creates a range of shallow donor states at the interface close to the conduction band, which causes lower threshold voltages and "leaky" turn-on properties. The low EL brightness is attributed to the low threshold voltage. The lack of reduction of the defects in the microstructure of ZnS:Mn,Ga2S3 during anneal is another reason for the poor EL properties. When samples are doped with Ga2S3 first followed by KCl, much better EL properties are observed than from samples doped with KCl first followed by Ga2S3 (B40 of 120nits versus 64.2nits). (Abstract shortened by UMI.)

Progress in Emission Efficiency of Organic Light-Emitting Diodes: Basic Understanding and Its Technical Application

NASA Astrophysics Data System (ADS)

Tsutsui, Tetsuo; Takada, Noriyuki

2013-11-01

The technical history of when and how the basic understanding of the emission efficiency of organic light-emitting diodes (OLEDs) was established over the last 50 years is described. At first, our understanding of emission efficiency in single-crystal and thin-film electroluminescence (EL) devices in the early stages before the Eastman-Kodak breakthrough, that is, the introduction of the concept of multilayer structures, is examined. Then our contemplation travels from the Eastman-Kodak breakthrough towards the presently widely accepted concept of emission efficiency. The essential issues concerning the emission efficiency of OLEDs are summarized to help readers to obtain a common understanding of OLED efficiency problems, and detailed discussions on the primary factors that determine emission efficiency are given. Finally, some comments on remaining issues are presented.

Effects of Starting Precursor Ratio on Optoelectrical Properties and Blue Emission of Nanostructured C-ZnS Thin Films Prepared by Spin Coating

NASA Astrophysics Data System (ADS)

Rahimzadeh, N.; Ghodsi, F. E.; Mazloom, J.

2018-02-01

Nanocrystalline cubic zinc sulfide (C-ZnS) thin films have been elaborated by sol-gel spin-coating of Zn(Ac)/thiourea starting precursors at different molar ratios, and their structural, morphological, compositional, optical, electrical, and photoluminescence properties comprehensively investigated. x-ray diffraction results showed that the samples had dominant cubic structure and their crystallinity improved with increasing S content. Morphological characterization of the C-ZnS thin films was carried out by field-emission scanning electron microscopy (FESEM), revealing that the films were smooth with spherical grains included in clusters. Energy-dispersive x-ray and Fourier-transform infrared spectra of ZnS compounds did not show any evidence of impurities. Optical characterization revealed increases of the average optical transmittance and bandgap (from 3.2 eV to 3.56 eV) with increasing S content. The refractive index in the visible region increased with the S content, while the extinction coefficient decreased. The compositional dependence of the optical dispersion parameters (oscillator and dispersion energy), dielectric constant, and surface energy loss function of the films was evaluated. Electrical characterization of the films was carried out using Hall-effect measurements. The ZnS thin films exhibited n-type conductivity, and the electrical resistivity decreased with increasing carrier concentration and mobility due to enhanced crystallite size and reduced structural disorder. Photoluminescence (PL) measurements indicated a blue-shift of the near-band-edge emission. The blue emission peaks centered at about 438 nm and 487 nm were enhanced due to transitions involving interstitial S atoms, surface states, and zinc vacancies.

Green electroluminescence from Tb{sub 4}O{sub 7} films on silicon: Impact excitation of Tb{sup 3+} ions by hot carriers

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

Zhu, Chen; Jiang, Miaomiao; Zhou, Junwei

2016-02-01

We report on green electroluminescence (EL) due to the intra-4f transitions of the trivalent terbium (Tb{sup 3+}) ions inherent in a Tb{sub 4}O{sub 7} film that is sandwiched between the ITO film and heavily phosphorous- or boron-doped silicon (n{sup +}-Si or p{sup +}-Si) substrate, thus forming the so-called metal-oxide-semiconductor (MOS) device. The onset voltage of such EL is below 10 V. From the current-voltage characteristic and voltage-dependent EL spectra of the aforementioned MOS device, it is derived that the Tb-related green EL results from the impact excitation of Tb{sup 3+} ions by the hot electrons (holes), which stem from the electric-fieldmore » acceleration of the electrons (holes) injected from the n{sup +}-Si (p{sup +}-Si) substrate via the trap-assisted tunneling mechanism.« less

Deposition of amorphous carbon thin films by aerosol-assisted CVD method

NASA Astrophysics Data System (ADS)

Fadzilah, A. N.; Dayana, K.; Rusop, M.

2018-05-01

This paper reports on the deposition of amorphous carbon (a-C) by Aerosol-assisted Chemical Vapor Deposition (AACVD) using natural source of camphor oil as the precursor material. 4 samples were deposited at 4 different deposition flow rate from 15 sccm to 20 sccm, with 5 sccm interval for each sample. The analysis includes the electrical, optical and structural analysis of the data. The a-C structure which came from the manipulation of synthesis parameter was characterized by the solar simulator system, UV-VIS-NIR, Raman spectroscope and AFM. The properties of a-C are highly dependent on the deposition techniques and deposition parameters; hence the influences of gas flow rate were studied.

Preparation of TlBa2Ca2Cu3O9±δ high Tc thin films by laser ablation in combination with thermal evaporation of thallium oxide

NASA Astrophysics Data System (ADS)

Piehler, A.; Löw, R.; Betz, J.; Schönberger, R.; Renk, K. F.

1993-11-01

TlBa2Ca2Cu3O9±δ high Tc thin films were prepared on MgO <100> surfaces by a combination of laser ablation from a stoichiometric Ba2Ca2Cu3Ox target and the thermal evaporation of thallium oxide. X-ray diffraction measurements showed that the films consisted of predominantly c axis oriented TlBa2Ca2Cu3O9±δ, and scanning electron microscopy revealed that the surfaces had a flat, platelike morphology. The ac inductive measurements indicated that the onset of superconductivity occurred at 117 K with a transition width (10%-90%) of ˜3 K. Zero resistivity was reached at 120 K. The critical current density was ˜3×104 A/cm2 at 110 K.

Antisite disorder induced spin glass and exchange bias effect in Nd2NiMnO6 epitaxial thin film

NASA Astrophysics Data System (ADS)

Singh, Amit Kumar; Chauhan, Samta; Chandra, Ramesh

2017-03-01

We report the observation of the exchange bias effect and spin glass behaviour at low temperature in a ferromagnetic Nd2NiMnO6 epitaxial thin film. Along with the ferromagnetic transition at ˜194 K, an additional transition is observed at lower temperature (˜55 K) as seen from M-T curves of the sample. A shift in the ac susceptibility peak with frequency has been observed at low temperature, which is a signature of a glassy phase within the sample. The detailed investigation of the memory effect and time dependent magnetic relaxation measurements reveals the presence of a spin glass phase in the Nd2NiMnO6 thin film. The exchange bias effect observed at low temperature in the sample has been associated with an antisite disorder induced spin glass phase, which results in a ferromagnetic/spin glass interface at low temperature. The exchange bias behaviour has been further confirmed by performing cooling field and temperature dependence of exchange bias along with training effect measurements.

A digital output piezoelectric accelerometer using a Pb(Zr, Ti)O3 thin film array electrically connected in series

NASA Astrophysics Data System (ADS)

Kobayashi, T.; Okada, H.; Masuda, T.; Maeda, R.; Itoh, T.

2010-10-01

A digital output piezoelectric accelerometer is proposed to realize an ultra-low power consumption wireless sensor node. The accelerometer has patterned piezoelectric thin films (piezoelectric plates) electrically connected in series accompanied by CMOS switches at the end of some of the piezoelectric plates. The connected piezoelectric plates amplify the output voltage without the use of amplifiers. The CMOS switches turn on when the output voltage of the piezoelectric plates is higher than the CMOS threshold voltage. The piezoelectric accelerometer converts the acceleration into a number of on-state CMOS switches, which can be called the digital output. The proposed digital output piezoelectric accelerometer, using Pb(Zr, Ti)O3 (PZT) thin films as the piezoelectric material, was fabricated through a microelectromechanical system (MEMS) microfabrication process. The output voltage was found to be amplified by the number of connected piezoelectric plates. The DC output voltage obtained by using an AC to DC conversion circuit is proportional to the number of connections. The results show the potential for realizing the proposed digital output piezoelectric accelerometer.

EDITORIAL: Atomic layer deposition Atomic layer deposition

NASA Astrophysics Data System (ADS)

Godlewski, Marek

2012-07-01

The growth method of atomic layer deposition (ALD) was introduced in Finland by Suntola under the name of atomic layer epitaxy (ALE). The method was originally used for deposition of thin films of sulphides (ZnS, CaS, SrS) activated with manganese or rare-earth ions. Such films were grown for applications in thin-film electroluminescence (TFEL) displays. The ALE mode of growth was also tested in the case of molecular beam epitaxy. Films grown by ALD are commonly polycrystalline or even amorphous. Thus, the name ALE has been replaced by ALD. In the 80s ALD was developed mostly in Finland and neighboring Baltic countries. Deposition of a range of different materials was demonstrated at that time, including II-VI semiconductors (e.g. CdTe, CdS) and III-V (e.g. GaAs, GaN), with possible applications in e.g. photovoltaics. The number of publications on ALD was slowly increasing, approaching about 100 each year. A real boom in interest came with the development of deposition methods of thin films of high-k dielectrics. This research was motivated by a high leakage current in field-effect transistors with SiO2-based gate dielectrics. In 2007 Intel introduced a new generation of integrated circuits (ICs) with thin films of HfO2 used as gate isolating layers. In these and subsequent ICs, films of HfO2 are deposited by the ALD method. This is due to their unique properties. The introduction of ALD to the electronics industry led to a booming interest in the ALD growth method, with the number of publications increasing rapidly to well above 1000 each year. A number of new applications were proposed, as reflected in this special issue of Semiconductor Science and Technology. The included articles cover a wide range of possible applications—in microelectronics, transparent electronics, optoelectronics, photovoltaics and spintronics. Research papers and reviews on the basics of ALD growth are also included, reflecting a growing interest in precursor chemistry and growth processes. Summarizing, this special issue of Semiconductor Science and Technology reflects the rapidly growing interest in the ALD growth method and demonstrates the wide range of possible practical applications of ALD-grown materials, not only of high-k dielectrics, but also of a range of different materials (e.g. ZnO). Finally, I would like to thank the IOP editorial staff, in particular Alice Malhador, for their support and efforts in making this special issue possible.

Pyroelectric response of lead zirconate titanate thin films on silicon: Effect of thermal stresses

NASA Astrophysics Data System (ADS)

Kesim, M. T.; Zhang, J.; Trolier-McKinstry, S.; Mantese, J. V.; Whatmore, R. W.; Alpay, S. P.

2013-11-01

Ferroelectric lead zirconate titanate [Pb(ZrxTi1-xO)3, (PZT x:1-x)] has received considerable interest for applications related to uncooled infrared devices due to its large pyroelectric figures of merit near room temperature, and the fact that such devices are inherently ac coupled, allowing for simplified image post processing. For ferroelectric films made by industry-standard deposition techniques, stresses develop in the PZT layer upon cooling from the processing/growth temperature due to thermal mismatch between the film and the substrate. In this study, we use a non-linear thermodynamic model to investigate the pyroelectric properties of polycrystalline PZT thin films for five different compositions (PZT 40:60, PZT 30:70, PZT 20:80, PZT 10:90, PZT 0:100) on silicon as a function of processing temperature (25-800 °C). It is shown that the in-plane thermal stresses in PZT thin films alter the out-of-plane polarization and the ferroelectric phase transformation temperature, with profound effect on the pyroelectric properties. PZT 30:70 is found to have the largest pyroelectric coefficient (0.042 μC cm-2 °C-1, comparable to bulk values) at a growth temperature of 550 °C; typical to what is currently used for many deposition processes. Our results indicate that it is possible to optimize the pyroelectric response of PZT thin films by adjusting the Ti composition and the processing temperature, thereby, enabling the tailoring of material properties for optimization relative to a specific deposition process.

[The role of BCP in electroluminescence of multilayer organic light-emitting devices].

PubMed

Deng, Zhao-Ru; Yang, Sheng-Yi; Lou, Zhi-Dong; Meng, Ling-Chuan

2009-03-01

As a hole-blocking layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is usually used in blue and white light electroluminescent devices. The ability of blocking holes of BCP layer depends on its thickness, and basically holes can tunnel through thin BCP layer. In order to know the role of BCP layer in electroluminescence (EL) of multilayer organic light-emitting diodes (OLEDs), in the present paper, the authors designed a multilayer OLED ITO/NPB/BCP/Alq3 : DCJTB/Alq3/Al and investigated the influence of thickness of BCP on the EL spectra of multilayer OLEDs at different applied voltages. The experimental data show that thin BCP layer can block holes partially and tune the energy transfer between different emissive layers, and in this way, it is easy to obtain white emission, but its EL spectra will change with the applied voltages. The EL spectra of multilayer device will remain relatively stable when BCP layer is thick enough, and the holes can hardly tunnel through when the thickness of BCP layer is more than 15 nm. Furthermore, the stability of EL spectra of the multilayer OLED at different applied voltages was discussed.

Floquet spectrum and driven conductance in Dirac materials: Effects of Landau-Zener-Stuckelberg-Majorana interferometry

NASA Astrophysics Data System (ADS)

Rodionov, Yaroslav; Kugel, Kliment; Nori, Franco

Using the Landau-Zener-Stückelberg-Majorana-type (LZSM) semiclassical approach, we study both graphene and a thin film of a Weyl semimetal subjected to a strong ac electromagnetic field. The spectrum of quasienergies in the Weyl semimetal turns out to be similar to that of a graphene sheet. It has been predicted qualitatively that the transport properties of strongly irradiated graphene oscillate as a function of the radiation intensity. Here we obtain rigorous quantitative results for a driven linear conductance of graphene and a thin film of a Weyl semimetal. The exact quantitative structure of oscillations exhibits two contributions. The first one is a manifestation of the Ramsauer-Townsend effect, while the second contribution is a consequence of the LZSM interference defining the spectrum of quasienergies.

Supramolecular luminescence from oligofluorenol-based supramolecular polymer semiconductors.

PubMed

Zhang, Guang-Wei; Wang, Long; Xie, Ling-Hai; Lin, Jin-Yi; Huang, Wei

2013-11-13

Supramolecular luminescence stems from non-covalent exciton behaviors of active π-segments in supramolecular entities or aggregates via intermolecular forces. Herein, a π-conjugated oligofluorenol, containing self-complementary double hydrogen bonds, was synthesized using Suzuki coupling as a supramolecular semiconductor. Terfluorenol-based random supramolecular polymers were confirmed via concentration-dependent nuclear magnetic resonance (NMR) and dynamic light scattering (DLS). The photoluminescent spectra of the TFOH-1 solution exhibit a green emission band (g-band) at approximately ~520 nm with reversible features, as confirmed through titration experiments. Supramolecular luminescence of TFOH-1 thin films serves as robust evidence for the aggregates of g-band. Our results suggest that the presence of polyfluorene ketone defects is a sufficient condition, rather than a sufficient-necessary condition for the g-band. Supramolecular electroluminescence will push organic devices into the fields of supramolecular optoelectronics, spintronics, and mechatronics.

Radiometric calibration of optical microscopy and microspectroscopy apparata over a broad spectral range using a special thin-film luminescence standard

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

Valenta, J., E-mail: jan.valenta@mff.cuni.cz; Greben, M.

2015-04-15

Application capabilities of optical microscopes and microspectroscopes can be considerably enhanced by a proper calibration of their spectral sensitivity. We propose and demonstrate a method of relative and absolute calibration of a microspectroscope over an extraordinary broad spectral range covered by two (parallel) detection branches in visible and near-infrared spectral regions. The key point of the absolute calibration of a relative spectral sensitivity is application of the standard sample formed by a thin layer of Si nanocrystals with stable and efficient photoluminescence. The spectral PL quantum yield and the PL spatial distribution of the standard sample must be characterized bymore » separate experiments. The absolutely calibrated microspectroscope enables to characterize spectral photon emittance of a studied object or even its luminescence quantum yield (QY) if additional knowledge about spatial distribution of emission and about excitance is available. Capabilities of the calibrated microspectroscope are demonstrated by measuring external QY of electroluminescence from a standard poly-Si solar-cell and of photoluminescence of Er-doped Si nanocrystals.« less

Molybdenum oxide and molybdenum oxide-nitride back contacts for CdTe solar cells

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

Drayton, Jennifer A., E-mail: drjadrayton@yahoo.com; Geisthardt, Russell M., E-mail: Russell.Geisthardt@gmail.com; Sites, James R., E-mail: james.sites@colostate.edu

2015-07-15

Molybdenum oxide (MoO{sub x}) and molybdenum oxynitride (MoON) thin film back contacts were formed by a unique ion-beam sputtering and ion-beam-assisted deposition process onto CdTe solar cells and compared to back contacts made using carbon–nickel (C/Ni) paint. Glancing-incidence x-ray diffraction and x-ray photoelectron spectroscopy measurements show that partially crystalline MoO{sub x} films are created with a mixture of Mo, MoO{sub 2}, and MoO{sub 3} components. Lower crystallinity content is observed in the MoON films, with an additional component of molybdenum nitride present. Three different film thicknesses of MoO{sub x} and MoON were investigated that were capped in situ in Ni.more » Small area devices were delineated and characterized using current–voltage (J-V), capacitance–frequency, capacitance–voltage, electroluminescence, and light beam-induced current techniques. In addition, J-V data measured as a function of temperature (JVT) were used to estimate back barrier heights for each thickness of MoO{sub x} and MoON and for the C/Ni paint. Characterization prior to stressing indicated the devices were similar in performance. Characterization after stress testing indicated little change to cells with 120 and 180-nm thick MoO{sub x} and MoON films. However, moderate-to-large cell degradation was observed for 60-nm thick MoO{sub x} and MoON films and for C/Ni painted back contacts.« less

In Situ Preparation of Metal Halide Perovskite Nanocrystal Thin Films for Improved Light-Emitting Devices.

PubMed

Zhao, Lianfeng; Yeh, Yao-Wen; Tran, Nhu L; Wu, Fan; Xiao, Zhengguo; Kerner, Ross A; Lin, YunHui L; Scholes, Gregory D; Yao, Nan; Rand, Barry P

2017-04-25

Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelectronic applications, such as photovoltaics, light-emitting diodes, and lasers. Perovskite nanocrystals are of particular interest, where electrons and holes can be confined spatially, promoting radiative recombination. However, nanocrystalline films based on traditional colloidal nanocrystal synthesis strategies suffer from the use of long insulating ligands, low colloidal nanocrystal concentration, and significant aggregation during film formation. Here, we demonstrate a facile method for preparing perovskite nanocrystal films in situ and that the electroluminescence of light-emitting devices can be enhanced up to 40-fold through this nanocrystal film formation strategy. Briefly, the method involves the use of bulky organoammonium halides as additives to confine crystal growth of perovskites during film formation, achieving CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 perovskite nanocrystals with an average crystal size of 5.4 ± 0.8 nm and 6.4 ± 1.3 nm, respectively, as confirmed through transmission electron microscopy measurements. Additive-confined perovskite nanocrystals show significantly improved photoluminescence quantum yield and decay lifetime. Finally, we demonstrate highly efficient CH 3 NH 3 PbI 3 red/near-infrared LEDs and CH 3 NH 3 PbBr 3 green LEDs based on this strategy, achieving an external quantum efficiency of 7.9% and 7.0%, respectively, which represent a 40-fold and 23-fold improvement over control devices fabricated without the additives.

Unexpected behavior of ultra-thin films of blends of polystyrene/poly(vinyl methyl ether) studied by specific heat spectroscopy

NASA Astrophysics Data System (ADS)

Madkour, Sherif; Szymoniak, Paulina; Schick, Christoph; Schönhals, Andreas

2017-05-01

Specific heat spectroscopy (SHS) employing AC nanochip calorimetry was used to investigate the glassy dynamics of ultra-thin films (thicknesses: 10 nm-340 nm) of a polymer blend, which is miscible in the bulk. In detail, a Poly(vinyl methyl ether) (PVME)/Polystyrene (PS) blend with the composition of 25/75 wt. % was studied. The film thickness was controlled by ellipsometry while the film topography was checked by atomic force microscopy. The results are discussed in the framework of the balance between an adsorbed and a free surface layer on the glassy dynamics. By a self-assembling process, a layer with a reduced mobility is irreversibly adsorbed at the polymer/substrate interface. This layer is discussed employing two different scenarios. In the first approach, it is assumed that a PS-rich layer is adsorbed at the substrate. Whereas in the second approach, a PVME-rich layer is suggested to be formed at the SiO2 substrate. Further, due to the lower surface tension of PVME, with respect to air, a nanometer thick PVME-rich surface layer, with higher molecular mobility, is formed at the polymer/air interface. By measuring the glassy dynamics of the thin films of PVME/PS in dependence on the film thickness, it was shown that down to 30 nm thicknesses, the dynamic Tg of the whole film was strongly influenced by the adsorbed layer yielding a systematic increase in the dynamic Tg with decreasing the film thickness. However, at a thickness of ca. 30 nm, the influence of the mobile surface layer becomes more pronounced. This results in a systematic decrease in Tg with the further decrease of the film thickness, below 30 nm. These results were discussed with respect to thin films of PVME/PS blend with a composition of 50/50 wt. % as well as literature results.

Integrated fuses for OLED lighting device

DOEpatents

Pschenitzka, Florian [San Jose, CA

2007-07-10

An embodiment of the present invention pertains to an electroluminescent lighting device for area illumination. The lighting device is fault tolerant due, in part, to the patterning of one or both of the electrodes into strips, and each of one or more of these strips has a fuse formed on it. The fuses are integrated on the substrate. By using the integrated fuses, the number of external contacts that are used is minimized. The fuse material is deposited using one of the deposition techniques that is used to deposit the thin layers of the electroluminescent lighting device.

Characterizations of low-temperature electroluminescence from ZnO nanowire light-emitting arrays on the p-GaN layer.

PubMed

Lu, Tzu-Chun; Ke, Min-Yung; Yang, Sheng-Chieh; Cheng, Yun-Wei; Chen, Liang-Yi; Lin, Guan-Jhong; Lu, Yu-Hsin; He, Jr-Hau; Kuo, Hao-Chung; Huang, JianJang

2010-12-15

Low-temperature electroluminescence from ZnO nanowire light-emitting arrays is reported. By inserting a thin MgO current blocking layer in between ZnO nanowire and p-GaN, high-purity UV light emission at wavelength 398 nm was obtained. As the temperature is decreased, contrary to the typical GaN-based light emitting diodes, our device shows a decrease of optical output intensity. The results are associated with various carrier tunneling processes and frozen MgO defects.

A New Kind of Blue Hybrid Electroluminescent Device.

PubMed

Wang, Junling; Li, Zhuan; Liu, Chunmei

2016-04-01

Bright blue Electroluminescence come from a ITO/BBOT doped silica (6 x 10(-3) M) made by a sol-gel method/Al driven by AC with 500 Hz at different voltages and Gaussian analysis under 55 V showed that blue emission coincidenced with typical triple emission from BBOT. This kind of device take advantage of organics (BBOT) and inorganics (silica). Electroluminescence from a single-layered sandwiched device consisting of blue fluorescent dye 2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene (BBOT) doped silica made by sol-gel method was investigated. A number of concentrations of hybrid devices were prepared and the maxium concentration was 6 x 10(-3) M. Blue electroluminescent (EL) always occurred above a threshold field 8.57 x 10(5) V/cm (30 V) at alternating voltage at 500 HZ. The luminance of the devices increased with the concentration of doped BBOT, but electroluminescence characteristics were different from a single molecule's photoluminescence properties of triple peaks. When analyzing in detail direct-current electroluminescence devices of pure BBOT, a single peak centered at 2.82 eV appeared with the driven voltage increase, which is similar to the hybrid devices. Comparing Gaussian decomposition date between two kinds of devices, the triple peak characteristic of BBOT was consistent. It is inferred that BBOT contributed EL of the hybrid devices mainly and silica may account for a very small part. Meanwhile the thermal stability of matrix silica was measured by Thermal Gravity-Mass Spectroscopy (TG-MS). There is 12 percent weight loss from room temperature to 1000 °C and silica has about 95% transmittance. So the matric silica played an important role in thermal stability and optical stability for BBOT. In addition, this kind of blue electroluminescence device can take advantages of organic materials BBOT and inorganic materials silica. This is a promising way to enrich EL devices, especially enriching inorganic EL color at a low cost.

Improved Emergency Egress Lighting System for the ISS

NASA Technical Reports Server (NTRS)

Eaton, Leslie L.; Barr, Don A.

2005-01-01

Emergency lights provide illumination in corridors, stairwells, ramps, escalators, aisles, and exit passageways during power failures. Safety and visibility are critical during a power outage. If emergency lights fail to operate properly, the building occupants can become disoriented. Four documents in a collection discuss different topics relating to a proposed improved emergency egress lighting system (EELS) for the International Space Station (ISS). While the present EELS is designed around rows of green-light-emitting diodes, the proposed system contains strips of electroluminescent tape using different colors for each egress path. The proposed EELS can be powered by the same battery currently used by the present EELS, but would require an inverter because electroluminescent devices require AC. Electroluminescent devices also require significantly less current and, depending on the color, would emit 3 to 8 times the light of the present EELS. In addition, they could operate for up to 75 hours (versus .20 minutes for the present system). The first document contains a one-page summary of the proposal and an evaluation of technical merit. The second document summarizes the motivation for, and the design of, the proposed EELS. The third document addresses relevant aspects of the measurement of spectral sensitivity and the psychophysics of perception of light. The fourth document presents additional background information and technical specifications for the electroluminescent tapes.

Highly stretchable electroluminescent skin for optical signaling and tactile sensing.

PubMed

Larson, C; Peele, B; Li, S; Robinson, S; Totaro, M; Beccai, L; Mazzolai, B; Shepherd, R

2016-03-04

Cephalopods such as octopuses have a combination of a stretchable skin and color-tuning organs to control both posture and color for visual communication and disguise. We present an electroluminescent material that is capable of large uniaxial stretching and surface area changes while actively emitting light. Layers of transparent hydrogel electrodes sandwich a ZnS phosphor-doped dielectric elastomer layer, creating thin rubber sheets that change illuminance and capacitance under deformation. Arrays of individually controllable pixels in thin rubber sheets were fabricated using replica molding and were subjected to stretching, folding, and rolling to demonstrate their use as stretchable displays. These sheets were then integrated into the skin of a soft robot, providing it with dynamic coloration and sensory feedback from external and internal stimuli. Copyright © 2016, American Association for the Advancement of Science.

The nature of trapping sites and recombination centres in PVK and PVK-PBD electroluminescent matrices seen by spectrally resolved thermoluminescence

NASA Astrophysics Data System (ADS)

Glowacki, Ireneusz; Szamel, Zbigniew

2010-07-01

Two electroluminescent polymer matrices poly(N-vinylcarbazole) (PVK) and PVK with 40 wt% of 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) were studied using spectrally resolved thermoluminescence (SRTL) in the temperature range 15-325 K. The comparison of the SRTL results with the electroluminescence (EL) spectra has allowed identification of the localized (trapping) sites and the radiative recombination centres present in the investigated matrices. In the neat PVK films deep traps with a depth about 200 meV, related to triplet excimers dominate, while in the PVK-PBD (40 wt%) blend films the traps that are related to triplet exciplexes formed by the carbazole groups and the PBD molecules dominate. Depth of the traps in the PVK-PBD blend is somewhat lower than that in the neat PVK. An analysis of the EL spectra shows that in the PVK and in the PVK-PBD blend the dominant radiative centres are singlet excimers and singlet exciplexes, respectively. However, in the neat PVK some contributions of the triplet monomer and the triplet excimer states in the EL were also detected.

Contact angle hysteresis and oil film lubrication in electrowetting with two immiscible liquids

NASA Astrophysics Data System (ADS)

Gao, J.; Mendel, N.; Dey, R.; Baratian, D.; Mugele, F.

2018-05-01

Electrowetting (EW) of water drops in ambient oil has found a wide range of applications including lab-on-a-chip devices, display screens, and variable focus lenses. The efficacy of all these applications is dependent on the contact angle hysteresis (CAH), which is generally reduced in the presence of ambient oil due to thin lubrication layers. While it is well-known that AC voltage reduces the effective contact angle hysteresis (CAH) for EW in ambient air, we demonstrate here that CAH for EW in ambient oil increases with increasing AC and DC voltage. Taking into account the disjoining pressure of the fluoropolymer-oil-water system, short range chemical interactions, viscous oil entrainment, and electrostatic stresses, we find that this observation can be explained by progressive thinning of the oil layer underneath the drop with increasing voltage. This exposes the droplet to the roughness of the underlying solid and thereby increases hysteresis.

Temperature dependence of the distribution of the thermally activated energy barriers in Tl2Ba2CaCu2O8 film

NASA Astrophysics Data System (ADS)

Ren, C.; Lin, F. Y.; Ding, S. Y.; Li, Z. M.; Aruna, S. A.; Qiu, L.; Yao, X. X.; Yan, S. L.; Si, M. S.

1999-06-01

The effects of frequency and ac amplitude on ac susceptibility have been measured for a thin Tl2Ba2CaCu2O8 film in the range 100 Hz-100 kHz in magnetic field 0.52 T. A phenomenological equation with an asymmetrical distribution of thermally activated energy barriers has been used to analyse these frequency and amplitude dependences of the ac susceptibility icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/>(icons/Journals/Common/omega" ALT="omega" ALIGN="TOP"/>,hac) in the vicinity of the peak temperature of icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/>´´. We obtain the effective energy barrier U against amplitude hac (current density j): Uicons/Journals/Common/propto" ALT="propto" ALIGN="TOP"/> hac-0.38. This U(j) relationship shows that the flux lines are in the 3D collective creep regime. Therefore, we conclude that the effective energy barrier is in fact an average of the barrier's distribution, and the distribution function is a distinguished asymmetrical one in this 3D collective creep regime.

Low-voltage polariton electroluminescence from an ultrastrongly coupled organic light-emitting diode

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

Gubbin, Christopher R.; Maier, Stefan A.; Kéna-Cohen, Stéphane, E-mail: s.kena-cohen@polymtl.ca

2014-06-09

We demonstrate electroluminescence from Frenkel molecular excitons ultrastrongly coupled to photons of a metal-clad microcavity containing a 2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene emissive layer. Thin layers of molybdenum oxide and 4,7-diphenyl-1,10-phenanthroline are used as hole and electron injection layers, respectively. The fabricated devices exhibit an electroluminescence threshold of 3.1 V, a value that is below the bare exciton energy. This result is found to be independent of detuning and consistent with a two-step process for polariton formation. Moreover, we investigate the quantum efficiency of carrier to polariton to photon conversion and obtain an external quantum efficiency of 0.1% for the fabricated structures, an improvement ofmore » 5 orders of magnitude over previous reports.« less

Influence of deposition temperature and amorphous carbon on microstructure and oxidation resistance of magnetron sputtered nanocomposite Crsbnd C films

NASA Astrophysics Data System (ADS)

Nygren, Kristian; Andersson, Matilda; Högström, Jonas; Fredriksson, Wendy; Edström, Kristina; Nyholm, Leif; Jansson, Ulf

2014-06-01

It is known that mechanical and tribological properties of transition metal carbide films can be tailored by adding an amorphous carbon (a-C) phase, thus making them nanocomposites. This paper addresses deposition, microstructure, and for the first time oxidation resistance of magnetron sputtered nanocomposite Crsbnd C/a-C films with emphasis on studies of both phases. By varying the deposition temperature between 20 and 700 °C and alternating the film composition, it was possible to deposit amorphous, nanocomposite, and crystalline Crsbnd C films containing about 70% C and 30% Cr, or 40% C and 60% Cr. The films deposited at temperatures below 300 °C were X-ray amorphous and 500 °C was required to grow crystalline phases. Chronoamperometric polarization at +0.6 V vs. Ag/AgCl (sat. KCl) in hot 1 mM H2SO4 resulted in oxidation of Crsbnd C, yielding Cr2O3 and C, as well as oxidation of C. The oxidation resistance is shown to depend on the deposition temperature and the presence of the a-C phase. Physical characterization of film surfaces show that very thin C/Cr2O3/Crsbnd C layers develop on the present material, which can be used to improve the oxidation resistance of, e.g. stainless steel electrodes.

Adventitious Carbon on Primary Sample Containment Metal Surfaces

NASA Technical Reports Server (NTRS)

Calaway, M. J.; Fries, M. D.

2015-01-01

Future missions that return astromaterials with trace carbonaceous signatures will require strict protocols for reducing and controlling terrestrial carbon contamination. Adventitious carbon (AC) on primary sample containers and related hardware is an important source of that contamination. AC is a thin film layer or heterogeneously dispersed carbonaceous material that naturally accrues from the environment on the surface of atmospheric exposed metal parts. To test basic cleaning techniques for AC control, metal surfaces commonly used for flight hardware and curating astromaterials at JSC were cleaned using a basic cleaning protocol and characterized for AC residue. Two electropolished stainless steel 316L (SS- 316L) and two Al 6061 (Al-6061) test coupons (2.5 cm diameter by 0.3 cm thick) were subjected to precision cleaning in the JSC Genesis ISO class 4 cleanroom Precision Cleaning Laboratory. Afterwards, the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy.

Defect engineering and luminescence characterization in bulk and thin film polycrystalline silicon

NASA Astrophysics Data System (ADS)

Koshka, Yaroslav

The passivation of recombination centers and the monitoring of passivation efficiency are critical for successful utilization of polycrystalline silicon (poly-Si) in solar cells and in thin-film transistors. Two important classes of poly-Si-thin films and bulk wafers-can respond differently to passivation processes (hydrogenation efficiency, possibilities of extrinsic and intrinsic gettering, etc.) and demand different approaches to their characterization. The effect of photoluminescence (PL) enhancement using ultrasound treatment (UST) was studied in poly-Si and amorphous-Si films on glass. In addition to the previously documented growth of the 0.7 eV oxygen related band in poly-Si films, generation and dramatic enhancement of a new luminescence maximum at about 0.98 eV occurs in films containing a superposition of poly-Si and alpha-Si phases. A model of ultrasound stimulated hydrogen detrapping followed by hydrogen diffusion and passivation of non-radiative centers was developed. Room temperature photoluminescence (PL) mapping was used to monitor improvement of recombination properties in bulk photovoltaic poly-Si during solar cell fabrication. Analysis of the statistical distribution of the values of PL enhancement shows that the contribution of individual processing steps to the increasing PL are different in nature. A correlation between PL mapping and minority carrier diffusion length was performed and quantitatively described. A method of obtaining separate information about the recombination properties of the bulk and the p/n junction regions of solar cells was developed. The method is based on measurements of PL distribution under different biases applied to solar cells and under different intensities of the excitation light. A PL study at 0.8 eV spectral maximum and comparison with the band-to-band PL was performed. Influence of the defects responsible for the 0.8 eV defect band was insignificant in as-grown wafers. It was revealed, however, that these defects start to determine non-homogeneity of recombination properties in poly-Si after the solar cell processing. Room-T electroluminescence (EL) mapping is shown to be a complimentary approach to characterize the bulk and the p/n junction regions of poly-Si solar cells. The major advantage of the EL approach is the possibility of instantaneous mapping of solar-grade poly-Si.

Transcending the slow bimolecular recombination in lead-halide perovskites for electroluminescence

PubMed Central

Xing, Guichuan; Wu, Bo; Wu, Xiangyang; Li, Mingjie; Du, Bin; Wei, Qi; Guo, Jia; Yeow, Edwin K. L.; Sum, Tze Chien; Huang, Wei

2017-01-01

The slow bimolecular recombination that drives three-dimensional lead-halide perovskites' outstanding photovoltaic performance is conversely a fundamental limitation for electroluminescence. Under electroluminescence working conditions with typical charge densities lower than 1015 cm−3, defect-states trapping in three-dimensional perovskites competes effectively with the bimolecular radiative recombination. Herein, we overcome this limitation using van-der-Waals-coupled Ruddlesden-Popper perovskite multi-quantum-wells. Injected charge carriers are rapidly localized from adjacent thin few layer (n≤4) multi-quantum-wells to the thick (n≥5) multi-quantum-wells with extremely high efficiency (over 85%) through quantum coupling. Light emission originates from excitonic recombination in the thick multi-quantum-wells at much higher decay rate and efficiency than bimolecular recombination in three-dimensional perovskites. These multi-quantum-wells retain the simple solution processability and high charge carrier mobility of two-dimensional lead-halide perovskites. Importantly, these Ruddlesden-Popper perovskites offer new functionalities unavailable in single phase constituents, permitting the transcendence of the slow bimolecular recombination bottleneck in lead-halide perovskites for efficient electroluminescence. PMID:28239146

Transcending the slow bimolecular recombination in lead-halide perovskites for electroluminescence.

PubMed

Xing, Guichuan; Wu, Bo; Wu, Xiangyang; Li, Mingjie; Du, Bin; Wei, Qi; Guo, Jia; Yeow, Edwin K L; Sum, Tze Chien; Huang, Wei

2017-02-27

The slow bimolecular recombination that drives three-dimensional lead-halide perovskites' outstanding photovoltaic performance is conversely a fundamental limitation for electroluminescence. Under electroluminescence working conditions with typical charge densities lower than 10 15  cm -3 , defect-states trapping in three-dimensional perovskites competes effectively with the bimolecular radiative recombination. Herein, we overcome this limitation using van-der-Waals-coupled Ruddlesden-Popper perovskite multi-quantum-wells. Injected charge carriers are rapidly localized from adjacent thin few layer (n≤4) multi-quantum-wells to the thick (n≥5) multi-quantum-wells with extremely high efficiency (over 85%) through quantum coupling. Light emission originates from excitonic recombination in the thick multi-quantum-wells at much higher decay rate and efficiency than bimolecular recombination in three-dimensional perovskites. These multi-quantum-wells retain the simple solution processability and high charge carrier mobility of two-dimensional lead-halide perovskites. Importantly, these Ruddlesden-Popper perovskites offer new functionalities unavailable in single phase constituents, permitting the transcendence of the slow bimolecular recombination bottleneck in lead-halide perovskites for efficient electroluminescence.

In Situ Nanocalorimetric Investigations of Plasma Assisted Deposited Poly(ethylene oxide)-like Films by Specific Heat Spectroscopy.

PubMed

Madkou, Sherif; Melnichu, Iurii; Choukourov, Andrei; Krakovsky, Ivan; Biederman, Hynek; Schönhals, Andreas

2016-04-28

In recent years, highly cross-linked plasma polymers have started to unveil their potential in numerous biomedical applications in thin-film form. However, conventional diagnostic methods often fail due to their diverse molecular dynamics conformations. Here, glassy dynamics and the melting transition of thin PEO-like plasma assisted deposited (ppPEO) films (thickness 100 nm) were in situ studied by a combination of specific heat spectroscopy, utilizing a pJ/K sensitive ac-calorimeter chip, and composition analytical techniques. Different cross-linking densities were obtained by different plasma powers during the deposition of the films. Glassy dynamics were observed for all values of the plasma power. It was found that the glassy dynamics slows down with increasing the plasma power. Moreover, the underlying relaxation time spectra broaden indicating that the molecular motions become more heterogeneous with increasing plasma power. In a second set of the experiment, the melting behavior of the ppPEO films was studied. The melting temperature of ppPEO was found to decrease with increasing plasma power. This was explained by a decrease of the order in the crystals due to formation of chemical defects during the plasma process.

Electrical conduction mechanism and dielectric characterization of MnTPPCl thin films

NASA Astrophysics Data System (ADS)

Meikhail, M. S.; Oraby, A. H.; El-Nahass, M. M.; Zeyada, H. M.; Al-Muntaser, A. A.

2018-06-01

The AC conductivity and dielectric properties of MnTPPCl sandwich structure as Au/MnTPPCl/Au were studied. The conductivity of the MnTPPCl thin films have been interpreted by the correlated barrier hopping (CBH) model. The dominant conduction process have found to be the single polaron hopping conduction. The values of the hopping distance, Rω, barrier height, W, and the localized-state density, N, are estimated at different frequencies. The behavior of dielectric constant and dielectric loss was discussed as a function of temperature and frequency. The dielectric constant was described in terms of polarization mechanism in materials. The spectral behavior of dielectric loss is interpreted on the basis of the Giuntini et al. model [1]. The value of WM is obtained as 0.32 eV. A non-Debye relaxation phenomenon was observed from the dielectric relaxation mechanism.

A comparative study of n-channel low temperature poly-Si thin-film transistors with a body terminal or a lightly-doped-drain structure

NASA Astrophysics Data System (ADS)

Wu, Yanwen; Wang, Mingxiang; Wang, Huaisheng; Zhang, Dongli

2018-02-01

Hot-carrier (HC) induced degradation is a critical reliability issue of n-channel low temperature poly-Si thin-film transistors (TFTs) in TFT-based circuits. In this work, a kind of four-terminal TFT, which has an additional p+-doped lateral body terminal connecting to the floating channel, is systematically compared to conventional n-channel TFT and lightly-doped-drain (LDD) TFT. We demonstrate that the four-terminal TFT can provide similar advantages to that of the LDD TFT such as kink current suppression and DC HC degradation immunity, much superior immunity to the dynamic HC degradation, but without any tradeoffs in device performance and process complexity of the LDD TFT. It has high performance, as well as excellent reliability under both DC and AC conditions.

Thin film colossal dielectric constant oxide La2-xSrxNiO4: Synthesis, dielectric relaxation measurements, and electrode effects

NASA Astrophysics Data System (ADS)

Podpirka, Adrian; Ramanathan, Shriram

2011-01-01

We have successfully synthesized the colossal dielectric constant oxide La2-xSrxNiO4 in thin film form by reactive cosputtering from metallic targets and careful annealing protocols. Composition and phase purity was determined through energy dispersive spectra and x-ray diffraction, respectively. The dielectric constant exceeds values of over 20 000 up to 1 kHz and the activation energy for the frequency-independent conductivity plateau was extracted to be approximately 155 meV from 300 to 473 K, both in agreement with measurements conducted on bulk single crystals. However, unlike in single crystals, we observe early onset of relaxation in thin films indicating the crucial role of grain boundaries in influencing the dielectric response. ac conductivity at varying temperatures is analyzed within the framework of the universal dielectric law leading to an exponent of approximately 0.3, dependent on the electrode material. Impedance spectroscopy with electrodes of different work function (Pt, Pd, and Ag) was further carried out as a function of temperature and applied bias to provide mechanistic insights into the nature of the dielectric response.

Energy Transfer Between Coherently Delocalized States in Thin Films of the Explosive Pentaerythritol Tetranitrate (PETN) Revealed by Two-Dimensional Infrared Spectroscopy

NASA Astrophysics Data System (ADS)

Ostrander, Joshua; Knepper, Robert; Tappan, Alexander; Kay, Jeffery; Zanni, Martin; Farrow, Darcie

2017-06-01

Pentaerythritol tetranitrate (PETN) is a common secondary explosive and has been used extensively to study shock initiation and energy propagation in energetic materials. We report 2D IR measurements of PETN thin films that resolve vibrational energy transfer and relaxation mechanisms. Ultrafast anisotropy measurements reveal a sub-500 fs reorientation of transition dipoles in thin films of vapor-deposited PETN that is absent in solution measurements, consistent with intermolecular energy transfer. The anisotropy is frequency dependent, suggesting spectrally heterogeneous vibrational relaxation. Cross peaks are observed in 2D IR spectra that resolve a specific energy transfer pathway with a 2 ps time scale. Measurements of the transition dipole strength indicate that these vibrational modes are coherently delocalized over at least 15-30 molecules. We discuss the implications of vibrational relaxation between coherently delocalized eigenstates for mechanisms relevant to explosives. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Thin-film Rechargeable Lithium Batteries

DOE R&D Accomplishments Database

Bates, J. B.; Gruzalski, G. R.; Dudney, N. J.; Luck, C. F.; Yu, X.

1993-11-01

Rechargeable thin films batteries with lithium metal anodes, an amorphous inorganic electrolyte, and cathodes of lithium intercalation compounds have been fabricated and characterized. The cathodes include TiS{sub 2}, the {omega} phase of V{sub 2}O{sub 5}, and the cubic spinel Li{sub x}Mn{sub 2}O{sub 4} with open circuit voltages at full charge of about 2.5 V, 3.7 V, and 4.2 V, respectively. The development of these robust cells, which can be cycled thousands of times, was possible because of the stability of the amorphous lithium electrolyte, lithium phosphorus oxynitride. This material has a typical composition of Li{sub 2.9}PO{sub 3.3}N{sub 0.46} and a conductivity at 25 C of 2 {mu}S/cm. Thin film cells have been cycled at 100% depth of discharge using current densities of 2 to 100 {mu}A/cm{sup 2}. The polarization resistance of the cells is due to the slow insertion rate of Li{sup +} ions into the cathode. Chemical diffusion coefficients for Li{sup +} ions in the three types of cathodes have been estimated from the analysis of ac impedance measurements.

Carbon Nanotube-Based Supercapacitors with Excellent ac Line Filtering and Rate Capability via Improved Interfacial Impedance.

PubMed

Rangom, Yverick; Tang, Xiaowu Shirley; Nazar, Linda F

2015-07-28

We report the fabrication of high-performance, self-standing composite sp(2)-carbon supercapacitor electrodes using single-walled carbon nanotubes (CNTs) as conductive binder. The 3-D mesoporous mesh architecture of CNT-based composite electrodes grants unimpaired ionic transport throughout relatively thick films and allows superior performance compared to graphene-based devices at an ac line frequency of 120 Hz. Metrics of 601 μF/cm(2) with a -81° phase angle and a rate capability (RC) time constant of 199 μs are obtained for thin carbon films. The free-standing carbon films were obtained from a chlorosulfonic acid dispersion and interfaced to stainless steel current collectors with various surface treatments. CNT electrodes were able to cycle at 200 V/s and beyond, still showing a characteristic parallelepipedic cyclic votammetry shape at 1 kV/s. Current densities are measured in excess of 6400 A/g, and the electrodes retain more than 98% capacity after 1 million cycles. These promising results are attributed to a reduction of series resistance in the film through the CNT conductive network and especially to the surface treatment of the stainless steel current collector.

Supramolecular Luminescence from Oligofluorenol-Based Supramolecular Polymer Semiconductors

PubMed Central

Zhang, Guang-Wei; Wang, Long; Xie, Ling-Hai; Lin, Jin-Yi; Huang, Wei

2013-01-01

Supramolecular luminescence stems from non-covalent exciton behaviors of active π-segments in supramolecular entities or aggregates via intermolecular forces. Herein, a π-conjugated oligofluorenol, containing self-complementary double hydrogen bonds, was synthesized using Suzuki coupling as a supramolecular semiconductor. Terfluorenol-based random supramolecular polymers were confirmed via concentration-dependent nuclear magnetic resonance (NMR) and dynamic light scattering (DLS). The photoluminescent spectra of the TFOH-1 solution exhibit a green emission band (g-band) at approximately ~520 nm with reversible features, as confirmed through titration experiments. Supramolecular luminescence of TFOH-1 thin films serves as robust evidence for the aggregates of g-band. Our results suggest that the presence of polyfluorene ketone defects is a sufficient condition, rather than a sufficient-necessary condition for the g-band. Supramolecular electroluminescence will push organic devices into the fields of supramolecular optoelectronics, spintronics, and mechatronics. PMID:24232455

Eddy current imaging for electrical characterization of silicon solar cells and TCO layers

NASA Astrophysics Data System (ADS)

Hwang, Byungguk; Hillmann, Susanne; Schulze, Martin; Klein, Marcus; Heuer, Henning

2015-03-01

Eddy Current Testing has been mainly used to determine defects of conductive materials and wall thicknesses in heavy industries such as construction or aerospace. Recently, high frequency Eddy Current imaging technology was developed. This enables the acquirement of information of different depth level in conductive thin-film structures by realizing proper standard penetration depth. In this paper, we summarize the state of the art applications focusing on PV industry and extend the analysis implementing achievements by applying spatially resolved Eddy Current Testing. The specific state of frequency and complex phase angle rotation demonstrates diverse defects from front to back side of silicon solar cells and characterizes homogeneity of sheet resistance in Transparent Conductive Oxide (TCO) layers. In order to verify technical feasibility, measurement results from the Multi Parameter Eddy Current Scanner, MPECS are compared to the results from Electroluminescence.

Band Gap Tuning of CH₃NH₃Pb(Br(1-x)Clx)₃ Hybrid Perovskite for Blue Electroluminescence.

PubMed

Kumawat, Naresh K; Dey, Amrita; Kumar, Aravindh; Gopinathan, Sreelekha P; Narasimhan, K L; Kabra, Dinesh

2015-06-24

We report on the structural, morphological and optical properties of AB(Br(1-x)Cl(x))3 (where, A = CH3NH3(+), B = Pb(2+) and x = 0 to 1) perovskite semiconductor and their successful demonstration in green and blue emissive perovskite light emitting diodes at room temperature. The bandgap of perovskite thin film is tuned from 2.42 to 3.16 eV. The onset of optical absorption is dominated by excitonic effects. The coulomb field of the exciton influences the absorption at the band edge. Hence, it is necessary to explicitly account for the enhancement of the absorption through the Sommerfield factor. This enables us to correctly extract the exciton binding energy and the electronic bandgap. We also show that the lattice constant varies linearly with the fractional chlorine content satisfying Vegards law.

Display technologies; Proceedings of the Meeting, National Chiao Tung Univ., Hsinchu, Taiwan, Dec. 17, 18, 1992

NASA Astrophysics Data System (ADS)

Chen, Shu-Hsia; Wu, Shin-Tson

1992-10-01

A broad range of interdisciplinary subjects related to display technologies is addressed, with emphasis on high-definition displays, CRTs, projection displays, materials for display application, flat-panel displays, display modeling, and polymer-dispersed liquid crystals. Particular attention is given to a CRT approach to high-definition television display, a superhigh-resolution electron gun for color display CRT, a review of active-matrix liquid-crystal displays, color design for LCD parameters in projection and direct-view applications, annealing effects on ZnS:TbF3 electroluminescent devices prepared by RF sputtering, polycrystalline silicon thin film transistors with low-temperature gate dielectrics, refractive index dispersions of liquid crystals, a new rapid-response polymer-dispersed liquid-crystal material, and improved liquid crystals for active-matrix displays using high-tilt-orientation layers. (No individual items are abstracted in this volume)

Low-frequency dielectric properties of intrinsic and Al-doped rutile TiO{sub 2} thin films grown by the atomic layer deposition technique

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

Kassmi, M.; LMOP, El Manar University, Tunis 2092; Pointet, J.

2016-06-28

Dielectric spectroscopy is carried out for intrinsic and aluminum-doped TiO{sub 2} rutile films which are deposited on RuO{sub 2} by the atomic layer deposition technique. Capacitance and conductance are measured in the 0.1 Hz–100 kHz range, for ac electric fields up to 1 MV{sub rms}/cm. Intrinsic films have a much lower dielectric constant than rutile crystals. This is ascribed to the presence of oxygen vacancies which depress polarizability. When Al is substituted for Ti, the dielectric constant further decreases. By considering Al-induced modification of polarizability, a theoretical relationship between the dielectric constant and the Al concentration is proposed. Al doping drastically decreasesmore » the loss in the very low frequency part of the spectrum. However, Al doping has almost no effect on the loss at high frequencies. The effect of Al doping on loss is discussed through models of hopping transport implying intrinsic oxygen vacancies and Al related centers. When increasing the ac electric field in the MV{sub rms}/cm range, strong voltage non-linearities are evidenced in undoped films. The conductance increases exponentially with the ac field and the capacitance displays negative values (inductive behavior). Hopping barrier lowering is proposed to explain high-field effects. Finally, it is shown that Al doping strongly improves the high-field dielectric behavior.« less

The dynamics and stability of lubricating oil films during droplet transport by electrowetting in microfluidic devices.

PubMed

Kleinert, Jairus; Srinivasan, Vijay; Rival, Arnaud; Delattre, Cyril; Velev, Orlin D; Pamula, Vamsee K

2015-05-01

The operation of digital microfluidic devices with water droplets manipulated by electrowetting is critically dependent on the static and dynamic stability and lubrication properties of the oil films that separate the droplets from the solid surfaces. The factors determining the stability of the films and preventing surface fouling in such systems are not yet thoroughly understood and were experimentally investigated in this study. The experiments were performed using a standard digital microfluidic cartridge in which water droplets enclosed in a thin, oil-filled gap were transported over an array of electrodes. Stable, continuous oil films separated the droplets from the surfaces when the droplets were stationary. During droplet transport, capillary waves formed in the films on the electrode surfaces as the oil menisci receded. The waves evolved into dome-shaped oil lenses. Droplet deformation and oil displacement caused the films at the surface opposite the electrode array to transform into dimples of oil trapped over the centers of the droplets. Lower actuation voltages were associated with slower film thinning and formation of fewer, but larger, oil lenses. Lower ac frequencies induced oscillations in the droplets that caused the films to rupture. Films were also destabilized by addition of surfactants to the oil or droplet phases. Such a comprehensive understanding of the oil film behavior will enable more robust electrowetting-actuated lab-on-a-chip devices through prevention of loss of species from droplets and contamination of surfaces at points where films may break.

The dynamics and stability of lubricating oil films during droplet transport by electrowetting in microfluidic devices

PubMed Central

Kleinert, Jairus; Srinivasan, Vijay; Rival, Arnaud; Delattre, Cyril; Velev, Orlin D.; Pamula, Vamsee K.

2015-01-01

The operation of digital microfluidic devices with water droplets manipulated by electrowetting is critically dependent on the static and dynamic stability and lubrication properties of the oil films that separate the droplets from the solid surfaces. The factors determining the stability of the films and preventing surface fouling in such systems are not yet thoroughly understood and were experimentally investigated in this study. The experiments were performed using a standard digital microfluidic cartridge in which water droplets enclosed in a thin, oil-filled gap were transported over an array of electrodes. Stable, continuous oil films separated the droplets from the surfaces when the droplets were stationary. During droplet transport, capillary waves formed in the films on the electrode surfaces as the oil menisci receded. The waves evolved into dome-shaped oil lenses. Droplet deformation and oil displacement caused the films at the surface opposite the electrode array to transform into dimples of oil trapped over the centers of the droplets. Lower actuation voltages were associated with slower film thinning and formation of fewer, but larger, oil lenses. Lower ac frequencies induced oscillations in the droplets that caused the films to rupture. Films were also destabilized by addition of surfactants to the oil or droplet phases. Such a comprehensive understanding of the oil film behavior will enable more robust electrowetting-actuated lab-on-a-chip devices through prevention of loss of species from droplets and contamination of surfaces at points where films may break. PMID:26045729

Electroluminescent Yb2O3:Er and Yb2Si2O7:Er nanolaminate films fabricated by atomic layer deposition on silicon

NASA Astrophysics Data System (ADS)

Ouyang, Zhongtao; Yang, Yang; Sun, Jiaming

2018-06-01

Atomic layer doped Yb2O3:Er and Yb2Si2O7:Er nanolaminate films are fabricated on silicon by atomic layer deposition, and ∼1530 nm electroluminescence (EL) is obtained from the metal-oxide-semiconductor light-emitting devices (MOSLEDs) based on these films. The Yb2O3 films transfer to Yb2Si2O7 phase after annealing above 1000 °C. Intense photoluminescence from Yb2Si2O7 film confirms high efficiency and energy transfer under optical excitation, but the limited electron conduction restricts the EL performance. EL from the Yb2O3:Er MOSLED outperforms, presenting an external quantum efficiency up to 8.5% and the power efficiency of 1 × 10-3. The EL is derived to result from the impact excitation of Er3+ ions by hot electrons, which stem from Fowler-Nordheim tunneling mechanism under sufficient bias voltage. The critical distance for the cross relaxation of doped Er3+ ions in nanolaminate Yb2O3 matrix is experimentally determined to be ∼3 nm. Such devices manifest the technological potential of Er-doped Yb-oxides for applications in silicon-based optoelectronics.

Dielectric and transport properties of thin films precipitated from sols with silicon nanoparticles

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

Kononov, N. N., E-mail: nnk@kapella.gpi.ru; Dorofeev, S. G.; Ishchenko, A. A.

2011-08-15

Dielectric properties of thin films precipitated on solid substrates from colloidal solutions containing silicon nanoparticles (average diameter is 10 nm) are studied by optical ellipsometry and impedance-spectroscopy. In the optical region, the values of real {epsilon} Prime and imaginary {epsilon} Double-Prime components of the complex permittivity {epsilon} vary within 2.1-1.1 and 0.25-0.75, respectively. These values are significantly lower than those of crystalline silicon. Using numerical simulation within the Bruggeman effective medium approximation, we show that the experimental {epsilon} Prime and {epsilon} Double-Prime spectra can be explained with good accuracy, assuming that the silicon film is a porous medium consisting ofmore » silicon monoxide (SiO) and air voids at a void ratio of 0.5. Such behavior of films is mainly caused by the effect of outer shells of silicon nanoparticles interacting with atmospheric oxygen on their dielectric properties. In the frequency range of 10-10{sup 6} Hz, the experimentally measured {epsilon} Prime and {epsilon} Double-Prime spectra of thin nanoscale silicon films are well approximated by the semi-empirical Cole-Cole dielectric dispersion law with the term related to free electric charges. The experimentally determined power-law frequency dependence of the ac conductivity means that the electrical transport in films is controlled by electric charge hopping through localized states in the unordered medium of outer shells of silicon nanoparticles composing films. It is found that the film conductivity at frequencies of {<=}2 Multiplication-Sign 10{sup 2} Hz is controlled by proton transport through Si-OH groups on the silicon nanoparticle surface.« less

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

NASA Astrophysics Data System (ADS)

Basel, Tek Prasad

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

Exciplex electroluminescence and photoluminescence spectra of the new organic materials based on zinc complexes of sulphanylamino-substituted ligands.

PubMed

Kaplunov, Mikhail G; Krasnikova, Svetlana S; Nikitenko, Sergey L; Sermakasheva, Natalia L; Yakushchenko, Igor K

2012-04-03

We have investigated the electroluminescence spectra of the electroluminescent devices based on the new zinc complexes of amino-substituted benzothiazoles and quinolines containing the C-N-M-N chains in their chelate cycles. The spectra exhibit strong exciplex bands in the green to yellow region 540 to 590 nm due to interaction of the excited states of zinc complexes and triaryl molecules of the hole-transporting layer. For some devices, the intrinsic luminescence band of 460 nm in the blue region is also observed along with the exciplex band giving rise to an almost white color of the device emission. The exciplex band can be eliminated if the material of the hole-transporting layer is not a triarylamine derivative. We have also found the exciplex emission in the photoluminescence spectra of the films containing blends of zinc complex and triphenylamine material.

Exciplex electroluminescence and photoluminescence spectra of the new organic materials based on zinc complexes of sulphanylamino-substituted ligands

PubMed Central

2012-01-01

We have investigated the electroluminescence spectra of the electroluminescent devices based on the new zinc complexes of amino-substituted benzothiazoles and quinolines containing the C-N-M-N chains in their chelate cycles. The spectra exhibit strong exciplex bands in the green to yellow region 540 to 590 nm due to interaction of the excited states of zinc complexes and triaryl molecules of the hole-transporting layer. For some devices, the intrinsic luminescence band of 460 nm in the blue region is also observed along with the exciplex band giving rise to an almost white color of the device emission. The exciplex band can be eliminated if the material of the hole-transporting layer is not a triarylamine derivative. We have also found the exciplex emission in the photoluminescence spectra of the films containing blends of zinc complex and triphenylamine material. PMID:22471942

Measurement and modeling of dielectric properties of Pb(Zr,Ti)O3 ferroelectric thin films.

PubMed

Renoud, Raphaël; Borderon, Caroline; Gundel, Hartmut W

2011-09-01

In this study, the real and imaginary parts of the complex permittivity of lead zirconate titanate ferroelectric thin films are studied in the frequency range of 100 Hz to 100 MHz. The permittivity is well fitted by the Cole-Cole model. The variation of the relaxation time with the temperature is described by the Arrhenius law and an activation energy of 0.38 eV is found. Because of its nonlinear character, the dielectric response of the ferroelectric sample depends on the amplitude of the applied ac electric field. The permittivity is composed of three different contributions: the first is due to intrinsic lattice, the second is due to domain wall vibrations, and the third is due to domain wall jumps between pinning centers. This last contribution depends on the electric field, so it is important to control the field amplitude to obtain the desired values of permittivity and tunability.

Floquet spectrum and driven conductance in Dirac materials: Effects of Landau-Zener-Stückelberg-Majorana interferometry

NASA Astrophysics Data System (ADS)

Rodionov, Ya. I.; Kugel, K. I.; Nori, Franco

2016-11-01

Using the Landau-Zener-Stückelberg-Majorana-type (LZSM) semiclassical approach, we study both graphene and a thin film of a Weyl semimetal subjected to a strong ac electromagnetic field. The spectrum of quasienergies in the Weyl semimetal turns out to be similar to that of a graphene sheet. It has been predicted qualitatively that the transport properties of strongly irradiated graphene oscillate as a function of the radiation intensity [S. V. Syzranov et al., Phys. Rev. B 88, 241112 (2013)], 10.1103/PhysRevB.88.241112. Here we obtain rigorous quantitative results for a driven linear conductance of graphene and a thin film of a Weyl semimetal. The exact quantitative structure of oscillations exhibits two contributions. The first one is a manifestation of the Ramsauer-Townsend effect, while the second contribution is a consequence of the LZSM interference defining the spectrum of quasienergies.

Direct Determination of Field Emission across the Heterojunctions in a ZnO/Graphene Thin-Film Barristor.

PubMed

Mills, Edmund M; Min, Bok Ki; Kim, Seong K; Kim, Seong Jun; Kang, Min-A; Song, Wooseok; Myung, Sung; Lim, Jongsun; An, Ki-Seok; Jung, Jongwan; Kim, Sangtae

2015-08-26

Graphene barristors are a novel type of electronic switching device with excellent performance, which surpass the low on-off ratios that limit the operation of conventional graphene transistors. In barristors, a gate bias is used to vary graphene's Fermi level, which in turn controls the height and resistance of a Schottky barrier at a graphene/semiconductor heterojunction. Here we demonstrate that the switching characteristic of a thin-film ZnO/graphene device with simple geometry results from tunneling current across the Schottky barriers formed at the ZnO/graphene heterojunctions. Direct characterization of the current-voltage-temperature relationship of the heterojunctions by ac-impedance spectroscopy reveals that this relationship is controlled predominantly by field emission, unlike most graphene barristors in which thermionic emission is observed. This governing mechanism makes the device unique among graphene barristors, while also having the advantages of simple fabrication and outstanding performance.

Surface modification of an amorphous Si thin film crystallized by a linearly polarized Nd:YAG pulse laser beam

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

Horita, Susumu; Kaki, Hirokazu; Nishioka, Kensuke

2007-07-01

Amorphous Si films of 60 and 10 nm thick on glass substrates were irradiated by a linearly polarized Nd:YAG pulse laser with the wavelength {lambda}=532 nm at the incident angle {theta}{sub i}=0. The surface of the irradiated 60-nm-thick film had both periodic ridges perpendicular to the electric field vector E and aperiodic ridges roughly parallel to E, where the spatial period of the periodic ridges was almost {lambda}. From the continuous 10-nm-thick film, the separate rectangular Si islands were formed with a periodic distance of {lambda}, with the edges parallel or perpendicular to E. When {theta}{sub i} was increased frommore » normal incidence of the s-polarized beam for a 60-nm-thick film, the aperiodic ridges were reduced while the periodic ridges were still formed. For a 10-nm-thick film, the Si stripes were formed perpendicular to E, using the s-polarized beam at {theta}{sub i}=12 deg. In order to investigate the mechanisms of the surface modifications of, in particular, aperiodic ridges, islands, and stripes, we improved the previous theoretical model of the periodic distribution of the beam energy density (periodic E-D) generated by irradiation of the linearly polarized laser beam, taking account of the multireflection effect in the Si film which is semitransparent for {lambda}. Further, the calculated E-D was corrected with respect to the thermal diffusion in the irradiated Si film. The calculation results show that the two-dimensional E-D consists of a constant or a dc term and a sinusoidal or an ac term which contains various spatial periods. The multireflection effect strongly influences the amplitude and phase of every ac term, which means that the amplitude and phase depend on the film thickness. The thermal diffusion during the heating of the irradiated film greatly reduces the amplitudes of the ac terms with periods below the thermal diffusion length. The theoretical calculation showed that, by increasing {theta}{sub i}, the temperature distribution in the irradiated Si film was changed from two-dimensional toward one-dimensional, which can explain the above experimental results reasonably.« less

2-(2-Hydroxyphenyl)imidazole-based four-coordinate organoboron compounds with efficient deep blue photoluminescence and electroluminescence.

PubMed

Zhang, Zhenyu; Zhang, Zuolun; Zhang, Hongyu; Wang, Yue

2017-12-19

Two new four-coordinate organoboron compounds with 2-(2-hydroxyphenyl)imidazole derivatives as the chelating ligands have been synthesized. They possess high thermal stability and are able to form an amorphous glass state. Crystallographic analyses indicate that the differences in ligand structure cause the change of ππ stacking character. The CH 2 Cl 2 solutions and thin films of these compounds display bright blue emission, and these compounds have appropriate HOMO and LUMO energy levels for carrier injection in OLEDs. By utilizing the good thermal and luminescent properties, as well as the proper frontier orbital energy levels, bright non-doped OLEDs with a simple structure have been realized. Notably, these simple devices show deep blue electroluminescence with the Commission Internationale de l'Éclairage (CIE) coordinate of ca. (0.16, 0.08), which is close to the CIE coordinate of (0.14, 0.08) for standard blue defined by the National Television System Committee. In addition, one of the devices exhibits good performance, showing brightness, current efficiency, power efficiency and external quantum efficiency up to 2692 cd m -2 , 2.50 cd A -1 , 1.81 lm W -1 and 3.63%, respectively. This study not only provides good deep-blue emitting OLED materials that are rarely achieved by using four-coordinate organoboron compounds, but also allows a deeper understanding of the structure-property relationship of 2-(2-hydroxyphenyl)imidazole-based boron complexes, which benefits the further structural design of this type of material.

2D Semiconductors for Valley-Polarized LEDs and Photodetectors

NASA Astrophysics Data System (ADS)

Yu, Ting

The recently discovered two-dimensional (2D) semiconductors, such as transitional-metal-dichalcogenide monolayers, have aroused great interest due to the underlying quantum physics and the appealing optoelectronic applications like atomically thin light-emitting diodes (LEDs) and photodetectors. On the one hand, valley-polarized electroluminescence and photocurrent from such monolayers have not caused enough attention but highly demanded as building blocks for the new generation valleytronic applications. On the other hand, most reports on these devices are based on the mechanically exfoliated small samples. Considering real applications, a strategy which could offer mass-product and high compatibility to the current planar processes is greatly demanded. Large-area samples prepared by chemical vapour deposition (CVD) are perfect candidates towards such a goal. Here, we report electrically tunable valley-polarized electroluminescence and the selective spin-valley-coupled photocurrent in optoelectronic devices based on monolayer WS2 and MoS2 grown by CVD, exhibiting large electroluminescence and photocurrent dichroisms of 81% and 60%, respectively. The controllable valley polarization and emission components of the electroluminescence have been realized by varying electrical injection of carriers. For the observed helicity-dependent photocurrent, the circular photogalvanic effect at resonant excitations has been found to take the dominant responsibility.

Modeling the Voltage Dependence of Electrochemical Reactions at Solid-Solid and Solid-Liquid Interfaces in Batteries

NASA Astrophysics Data System (ADS)

Leung, Kevin

2015-03-01

Electrochemical reactions at electrode/electrolyte interfaces are critically dependent on the total electrochemical potential or voltage. In this presentation, we briefly review ab initio molecular dynamics (AIMD)-based estimate of voltages on graphite basal and edge planes, and then apply similar concepts to solid-solid interfaces relevant to lithium ion and Li-air batteries. Thin solid films on electrode surfaces, whether naturally occuring during power cycling (e.g., undesirable lithium carbonate on Li-air cathodes) or are artificially introduced, can undergo electrochemical reactions as the applied voltage varies. Here the onset of oxidation of lithium carbonate and other oxide thin films on model gold electrode surfaces is correlated with the electronic structure in the presence/absence of solvent molecules. Our predictions help determine whether oxidation first occurs at the electrode-thin film or electrolyte-thin film interface. Finally, we will critically compare the voltage estimate methodology used in the fuel cell community with the lithium cohesive energy calibration method broadly applied in the battery community, and discuss why they may yield different predictions. This work was supported by Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DESC0001160. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Deparment of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

A new LTPS TFT AC pixel circuit for an AMOLED

NASA Astrophysics Data System (ADS)

Yongwen, Zhang; Wenbin, Chen

2013-01-01

This work presents a new voltage programmed pixel circuit for an active-matrix organic light-emitting diode (AMOLED) display. The proposed pixel circuit consists of six low temperature polycrystalline silicon thin-film transistors (LTPS TFTs), one storage capacitor, and one OLED, and is verified by simulation work using HSPICE software. Besides effectively compensating for the threshold voltage variation of the driving TFT and OLED, the proposed pixel circuit offers an AC driving mode for the OLED, which can suppress the degradation of the OLED. Moreover, a high contrast ratio can be achieved by the proposed pixel circuit since the OLED does not emit any light except for the emission period.

Single- and Multilayered Nanostructures via Laser-Induced Block Copolymer Self-Assembly

NASA Astrophysics Data System (ADS)

Majewski, Pawel; Yager, Kevin; Rahman, Atikur; Black, Charles

We present a novel method of accelerated self-assembly of block copolymer thin films utilizing laser light, called Laser Zone Annealing (LZA). In our approach, steep temperature transients are induced in block copolymer films by rastering narrowly focused laser line over the light-absorbing substrate. Extremely steep temperature gradients accelerate the process of self-assembly by several orders-of-magnitude compared to conventional oven annealing, and, when coupled to photo-thermal shearing, lead to global alignment of block copolymer domains assessed by GISXAS diffraction studies and real-space SEM imaging. We demonstrate monolithic alignment of various block-copolymer thin films including PS-b-PMMA, PS-b-PEO, PS-b-P2VP, PS-b-PI and observe different responsiveness to the shearing rate depending on the characteristic relaxation timescale of the particular material. Subsequently, we use the aligned polymeric films as templates for synthesis of single- and multi-layered arrays of inorganic, metallic or semiconducting nanowires and nanomeshes and investigate their anisotropic electro-optical properties. Research carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

Supramolecular structures and assembly and luminescent properties of quinacridone derivatives.

PubMed

Ye, Kaiqi; Wang, Jia; Sun, Hui; Liu, Yu; Mu, Zhongcheng; Li, Fei; Jiang, Shimei; Zhang, Jingying; Zhang, Hongxing; Wang, Yue; Che, Chi-Ming

2005-04-28

The synthesis and single-crystal X-ray structures of two quinacridone derivatives, N,N'-di(n-butyl)quinacridone (1) and N,N'-di(n-butyl)-1,3,8,10-tetramethylquinacridone (2), are reported, and the 1H NMR, absorption, photoluminescent (PL), and electroluminescent (EL) characteristics are presented. Both these crystal structures are characterized by intermolecular pi...pi and hydrogen bonding interactions. The intermolecular pi...pi interactions lead to the formation of molecular columns in the solids of 1 and 2, and the interplanar contact distances between two adjacent molecules are 3.48 and 3.55 angstroms, respectively. Crystals of 1 display shorter intermolecular pi...pi contacts and higher density than 2. These results suggest that tighter intermolecular interactions exist in 1. The 1H NMR, absorption, and PL spectra of 1 and 2 in solutions exhibit concentration-dependent properties. The PL quantum yields of 1 in solutions decrease more quickly with the increase of concentration compared to that of 2 in solutions. For solid thin films of Alq3:1 (Alq3 = tris(8-hydroxyquinolinato)aluminum), emission intensities dramatically decrease and obvious red shifts are observed when the dopant concentration is above 4.2%, while for films of Alq3:2, a similar phenomenon occurs when the concentration is above 6.7%. EL devices with Alq3:1 as emitting layer only show high efficiencies (20.3-14.5 cd/A) within the narrow dopant concentration range of 0.5-1.0%. In contrast, high efficiencies (21.5-12.0 cd/A) are achieved for a wider dopant concentration range of 0.5-5.0% when Alq3:2 films are employed as emitting layer. The different PL and EL concentration-dependent properties of the solid thin films Alq3:1 and Alq3:2 are attributed to their different molecular packing characteristics in the solid state.

Fifth-year response to thinning in a water oak plantation in north Louisiana

Treesearch

James S. Meadows; J.C.G. Goelz

2001-01-01

A 21 ac, 28-yr-old water oak (Quercus nigra L.) plantation, on an old-field loessial site in north Louisiana, was subjected to three thinning treatments during the winter of 1987-1988: (1) no thinning, (2) light thinning to 180 dominant and codominant trees/ac, and (3) heavy thinning to 90 dominant and codominant trees/ac. Prior to thinning...

Strong enhancement of the luminescence decay time of isoelectronic centers in GaP:N at low temperatures

NASA Astrophysics Data System (ADS)

St-Jean, Philippe; Ethier-Majcher, Gabriel; Bergeron, Alaric; Francoeur, Sebastien

2013-03-01

We report (i)- results from ac impedance measurements obtained for intrinsic indium oxide films, grown under O2-rich conditions, (ii)- current-voltage (I-V) curves for p-n homojunctions fabricated by sequential growth of a 200 nm thick p-type In2O3 layer on a 400 nm thick n-type In2O3, and (iii)- capacitance-voltage (C-V) curves for these junctions. Impedance as well as I-V and C-V measurements were performed under UV irradiation and in darkness. We find two distinct contributions to the ac conductivity. One of them is brought about by grain boundaries, and the other one by inversion layers, which are on grain surfaces. In addition, we have found that photocurrents relax extremely slowly in these films. All of this fits consistently within a model in which mobile holes in inversion layers are responsible for p-type dc conductivity in intrinsic indium oxide films grown under O2-rich conditions. Such mechanism might be important in other polycrystalline thin films which have a large number of oxidizing defects at grain boundaries. We acknowledge support from grant MAT2012-38213-C02-01, from the Ministerio de Economia y Competividad, Spain.

Residual ferroelectricity in barium strontium titanate thin film tunable dielectrics

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

Garten, L. M., E-mail: lmg309@psu.edu; Trolier-McKinstry, S.; Lam, P.

2014-07-28

Loss reduction is critical to develop Ba{sub 1−x}Sr{sub x}TiO{sub 3} thin film tunable microwave dielectric components and dielectric energy storage devices. The presence of ferroelectricity, and hence the domain wall contributions to dielectric loss, will degrade the tunable performance in the microwave region. In this work, residual ferroelectricity—a persistent ferroelectric response above the global phase transition temperature—was characterized in tunable dielectrics using Rayleigh analysis. Chemical solution deposited Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} films, with relative tunabilities of 86% over 250 kV/cm at 100 kHz, demonstrated residual ferroelectricity 65 °C above the ostensible paraelectric transition temperature. Frequency dispersion observed in the dielectric temperature response wasmore » consistent with the presence of nanopolar regions as one source of residual ferroelectricity. The application of AC electric field for the Rayleigh analysis of these samples led to a doubling of the dielectric loss for fields over 10 kV/cm at room temperature.« less

Scalable planar fabrication processes for chalcogenide-based topological insulators

NASA Astrophysics Data System (ADS)

Sharma, Peter; Henry, M. David; Douglas, Erica; Wiwi, Michael; Lima Sharma, Ana; Lewis, Rupert; Sugar, Joshua; Salehi, Maryam; Koirala, Nikesh; Oh, Seongshik

Surface currents in topological insulators are expected to have long spin diffusion lengths, which could lead to numerous applications. Experiments that show promising transport properties were conducted on exfoliated flakes from bulk material, thin films on substrates of limited dimensions, or bulk material, with limited yield. A planar thin film-based technology is needed to make topological insulator devices at scale and could also lead to new device designs. We address two problems related to fabricating chalcogenide-based topological insulator devices on 3'' wafers in the Sandia Microfabrication Facility using Bi2Te3 films. (2) Implantation damage and its subsequent mitigation through annealing is characterized. (2) The degradation in dielectric layers used to manipulate surface potential for elucidating topological surface state transport is characterized under different processing conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000. Funded by the Office of Naval Research (N0001416IP00098-0).

Emission Behavior of Crystalline 1,4-Bis(4-phenylthiophene-2-yl)benzene Film Under Optical Excitation with Ultra Short Pulses.

PubMed

Mochizuki, Hiroyuki; Kawaguchi, Yoshizo; Sasaki, Fumio; Hotta, Shu

2016-04-01

We evaluated emission behaviors of crystallized films of 1,4-bis(5-phenylthiophene-2-yl)benzene (AC5) in detail which was a representative thiophene/phenylene co-oligomer. The crystallized AC5 films were prepared by vapor deposition onto a substrate and thermal treatment. The AC5 films consisted of a crystalline domain with the size of several tens of micrometers. We used femtosecond laser pulses for the excitation of the AC5 films. As a result, the femtosecond laser pulses did not induce re-absorption above excitation energy densities of their laser threshold. The obtained gain value for AC5 crystallized film was large, over 150 cm-1. Furthermore, the emission cross section of the crystallized AC5 film was nearly 10(-16) cm2.

Critical frequency for coalescence of emulsions in an AC electric field

NASA Astrophysics Data System (ADS)

Liu, Zhou; Ali, Faizi Hammad; Shum, Ho Cheung

2017-11-01

Applying an electric field to trigger the coalescence of emulsions has been applied in various applications which include crude oil recovery, emulsion stability characterization as well as pico-injection and droplet-based chemical reaction in microfluidics. In this work, we systematically investigated the responses of surfactant-stabilized emulsions to a controlled AC electric field using a customer-built chip. At a given amplitude of the AC voltage, we found a critical frequency beyond which the emulsions remain stable. When the frequency is decreased to below the critical value, emulsions coalesce immediately. Such critical frequency is found to be dependent of amplitude of the AC voltage, viscosity of the fluids, concentration and type of the surfactant as well as the electric conductivity of the droplet phase. Using a model based on the drainage of thin film, we have explored the mechanism behind and interpret this phenomenon systematically. Our work extends the understanding of the electro-coalescence of emulsions and can be beneficial for any applications involve the coalescence of droplets in an AC electric field.

Preparation, characterization and electroluminescence studies of ZnO nanorods for optoelectronic device applications

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

Singh, Anju, E-mail: singh-nk24@yahoo.com; Vishwakarma, H. L., E-mail: horilal5@yahoo.com

2015-07-31

In this work, ZnO nanorods were achieved by a simple chemical precipitation method in the presence of capping agent Poly Vinyl Pyrrolidone (PVP) at room temperature. X-Ray Diffraction (XRD) result indicates that the synthesized undoped ZnO nanorods have wurtzite hexagonal structure without any impurities. It has been seen that the growth orientation of the prepared ZnO nanorods were (101). XRD analysis revealed that the nanorods having the crystallite size 49 nm. The Scanning Electron Microscopy (SEM) image confirmed the size and shape of these nanorods. The diameter of nanorods has been found that 1.52 µm to 1.61 µm and the lengthmore » of about 4.89 µm. It has also been found that at room temperature Ultra Violet Visible (UV-VIS) absorption band is around 355 nm (blue shifted as compared to bulk). Electroluminescence (EL) studies show that emission of light is possible at very small threshold voltage and increases rapidly with increasing applied voltage. It is seen that smaller ZnO nanoparticles give higher electroluminescence brightness starting at lower threshold voltage. The brightness is also affected by increasing the frequency of AC signal.« less

Strain Phase Diagram of SrTiO3 Thin Films

NASA Astrophysics Data System (ADS)

He, Feizhou; Shapiro, S. M.

2005-03-01

SrTiO3 thin films were used as a model system to study the effects of strain and epitaxial constraint on structural phase transitions of oxide films. The basic phenomena revealed will apply to a variety of important structural transitions including the ferroelectric transition. Highly strained, epitaxial films of SrTiO3 were grown on different substrates. The structural phase transition temperature Tc increases from 105 K in bulk STO to 167 K for films under tensile strain and 330 K for films with compressive strain. The measured temperature-strain phase diagram is qualitatively consistent with theory [1], however the increase in Tc is much larger than predicted in all cases. The symmetry of the phases involved in the transition is different from the corresponding bulk structures largely because of epitaxial constraint, the clamping effect. Thus the shape of the STO unit cell is tetragonal at all temperatures. The possibility exists of a very unique low temperature phase with orthorhombic symmetry (Cmcm) but tetragonal unit cell shape. More generally, we have characterized at least three different manifestations of the clamping effect, showing it is much more subtle than usually recognized. This work is supported through NSF DMR-0239667, DMR-0132918, by the Research Corp, and at BNL by the US DOE DE-AC02-98CH10886. [1] N. A. Pertsev, A. K. Tagantsev and N. Setter, Phys. Rev. B61, R825 (2000).

Plasmonic Ag nanostructures on thin substrates for enhanced energy harvesting

NASA Astrophysics Data System (ADS)

Osgood, R. M.; Giardini, S. A.; Carlson, J. B.; Gear, C.; Diest, K.; Rothschild, M.; Fernandes, G. E.; Xu, J.; Kooi, S.; Periasamy, P.; O'Hayre, R.; Parilla, P.; Berry, J.; Ginley, D.

2013-09-01

Nanoparticles and nanostructures with plasmonic resonances are currently being employed to enhance the efficiency of solar cells. Ag stripe arrays have been shown theoretically to enhance the short-circuit current of thin silicon layers. Such Ag stripes are combined with 200 nm long and 60 nm wide "teeth", which act as nanoantennas, and form vertical rectifying metal-insulator-metal (MIM) nanostructures on metallic substrates coated with thin oxides, such as Nb/NbOx films. We characterize experimentally and theoretically the visible and near-infrared spectra of these "stripeteeth" arrays, which act as microantenna arrays for energy harvesting and detection, on silicon substrates. Modeling the stripe-teeth arrays predicts a substantial net a.c. voltage across the MIM diode, even when the stripe-teeth microrectenna arrays are illuminated at normal incidence.

Fabrication and evaluation of plasmonic light-emitting diodes with thin p-type layer and localized Ag particles embedded by ITO

NASA Astrophysics Data System (ADS)

Okada, N.; Morishita, N.; Mori, A.; Tsukada, T.; Tateishi, K.; Okamoto, K.; Tadatomo, K.

2017-04-01

Light-emitting diodes (LEDs) have been demonstrated with a thin p-type layer using the plasmonic effect. Optimal LED device operation was found when using a 20-nm-thick p+-GaN layer. Ag of different thicknesses was deposited on the thin p-type layer and annealed to form the localized Ag particles. The localized Ag particles were embedded by indium tin oxide to form a p-type electrode in the LED structure. By optimization of the plasmonic LED, the significant electroluminescence enhancement was observed when the thickness of Ag was 9.5 nm. Both upward and downward electroluminescence intensities were improved, and the external quantum efficiency was approximately double that of LEDs without the localized Ag particles. The time-resolved photoluminescence (PL) decay time for the LED with the localized Ag particles was shorter than that without the localized Ag particles. The faster PL decay time should cause the increase in internal quantum efficiency by adopting the localized Ag particles. To validate the localized surface plasmon resonance coupling effect, the absorption of the LEDs was investigated experimentally and using simulations.

Field emission from amorphous carbon films grown by electrochemical deposition using methanol liquid

NASA Astrophysics Data System (ADS)

Kiyota, H.; Higashi, M.; Kurosu, T.; Iida, M.

2006-05-01

The field emission from an amorphous carbon (a-C) film grown by electrochemical deposition has been studied. The deposition of the a-C film was accomplished by applying a direct-current potential to a substrate that was immersed in methanol. Both scanning electron microscopy and Raman results indicate that smooth and homogeneous a-C films are grown on specific substrates such as Ti and Al. Field emission measurements demonstrate excellent emission properties such as threshold fields as low as 5 V/μm. Enhancement factors are estimated to be in the range of 1300-1500; these are attributed to local field enhancements around sp2 carbon clusters that are embedded in the a-C films. Emission properties of a-C films grown on Si exhibit a current saturation under higher applied fields. These saturation characteristics are explained by effects of a potential barrier at the interface between the a-C film and the substrate. The interface barrier is reduced by formation of the Ti interfacial layer, suggesting that the formation of TiC decreases the contact resistance between the substrate and the a-C film. Therefore, an approach to use carbide formation at the interface is verified as useful to improve the emission properties of a-C films.

Dispenser printed electroluminescent lamps on textiles for smart fabric applications

NASA Astrophysics Data System (ADS)

de Vos, Marc; Torah, Russel; Tudor, John

2016-04-01

Flexible electroluminescent (EL) lamps are fabricated onto woven textiles using a novel dispenser printing process. Dispenser printing utilizes pressurized air to deposit ink onto a substrate through a syringe and nozzle. This work demonstrates the first use of this technology to fabricate EL lamps. The luminance of the dispenser printed EL lamps is compared to screen-printed EL lamps, both printed on textile, and also commercial EL lamps on polyurethane film. The dispenser printed lamps are shown to have a 1.5 times higher luminance than the best performing commercially available lamp, and have a comparable performance to the screen-printed lamps.

Growth and physical investigations of sprayed ZnMoO4 thin films along with wettability tests

NASA Astrophysics Data System (ADS)

Askri, Besma; Mhamdi, Ammar; Mahdhi, Noureddine; Amlouk, Mosbah

2018-06-01

Ternary oxides based on zinc and molybdenum elements have known as semiconductor oxides with large band gap energies. With the focus mainly on their synthesis by cost-effective process as thin films, the aspect of their stability and reactivity as transparent layers against both UV radiation and oxidation under wet medium due to their oxygen deficiency has so far not been investigated. This work covers the synthesis as well as the structural, electrical and the wettability properties of ZnMoO4 thin films which have been prepared by the spray pyrolysis method on glass substrates at 460 °C. First, X-ray diffraction analysis shows that this oxide crystallizes in triclinic structure with the space group P-1. The thickness value of ZnMoO4 thin film of about 1.5 μm was estimated by spectroscopic ellipsometry (SE). Moreover, a special emphasis has been focused on the photoluminescence properties of such films to reach possible presence of defaults and oxygen vacancy. Second, the electrical conductivity, conduction mechanism, relaxation model of these films were indeed studied using impedance spectroscopy technique in the frequency range 10-1-106 Hz at various temperatures (25-300 °C). At high temperature, σAC conductivity obeys to the power law established by Jonscher. Besides, the variation of σDC with the inverse of the temperature follows Arrhenius law. This evolution suggests that the conduction process is thermally activated and the activation energy of this process is equal to 0.97 eV. Finally, the wettability tests reveal that zinc molybdates loses its hydrophobic character during aging under UV radiation to become completely hydrophilic. All these physical investigations demonstrated that such ternary oxide contains oxygen deficiency which may be of interest for photocatalytic purposes and pave the way for various sensitivity applications like gas and bio-sensors.

Carbon Nanotubes/Nanofibers by Plasma Enhanced Chemical Vapour Deposition

NASA Technical Reports Server (NTRS)

Teo, K. B. K.; Hash, D. B.; Bell, M. S.; Chhowalla, M.; Cruden, B. A.; Amaratunga, G. A. J.; Meyyappan, M.; Milne, W. I.

2005-01-01

Plasma enhanced chemical vapour deposition (PECVD) has been recently used for the production of vertically aligned carbon nanotubedfibers (CN) directly on substrates. These structures are potentially important technologically as electron field emitters (e.g. microguns, microwave amplifiers, displays), nanoelectrodes for sensors, filter media, superhydrophobic surfaces and thermal interface materials for microelectronics. A parametric study on the growth of CN grown by glow discharge dc-PECVD is presented. In this technique, a substrate containing thin film Ni catalyst is exposed to C2H2 and NH3 gases at 700 C. Without plasma, this process is essentially thermal CVD which produces curly spaghetti-like CN as seen in Fig. 1 (a). With the plasma generated by biasing the substrate at -6OOV, we observed that the CN align vertically during growth as shown in Fig. l(b), and that the magnitude of the applied substrate bias affects the degree of alignment. The thickness of the thin film Ni catalyst was found to determine the average diameter and inversely the length of the CN. The yield and density of the CN were controlled by the use of different diffusion barrier materials under the Ni catalyst. Patterned CN growth [Fig. l(c)], with la variation in CN diameter of 4.1% and 6.3% respectively, is achieved by lithographically defining the Ni thin film prior to growth. The shape of the structures could be varied from very straight nanotube-like to conical tip-like nanofibers by increasing the ratio of C2H2 in the gas flow. Due to the plasma decomposition of C2H2, amorphous carbon (a-C) is an undesirable byproduct which could coat the substrate during CN growth. Using a combination of depth profiled Auger electron spectroscopy to study the substrate and in-situ mass spectroscopy to examine gas phase neutrals and ions, the optimal conditions for a-C free growth of CN is determined.

Amorphous carbon for photovoltaics

NASA Astrophysics Data System (ADS)

Risplendi, Francesca; Grossman, Jeffrey C.

2015-03-01

All-carbon solar cells have attracted attention as candidates for innovative photovoltaic devices. Carbon-based materials such as graphene, carbon nanotubes (CNT) and amorphous carbon (aC) have the potential to present physical properties comparable to those of silicon-based materials with advantages such as low cost and higher thermal stability.In particular a-C structures are promising systems in which both sp2 and sp3 hybridization coordination are present in different proportions depending on the specific density, providing the possibility of tuning their optoelectronic properties and achieving comparable sunlight absorption to aSi. In this work we employ density functional theory to design suitable device architectures, such as bulk heterojunctions (BHJ) or pn junctions, consisting of a-C as the active layer material.Regarding BHJ, we study interfaces between aC and C nanostructures (such as CNT and fullerene) to relate their optoelectronic properties to the stoichiometry of aC. We demonstrate that the energy alignment between the a-C mobility edges and the occupied and unoccupied states of the CNT or C60 can be widely tuned by varying the aC density to obtain a type II interface.To employ aC in pn junctions we analyze the p- and n-type doping of a-C focusingon an evaluation of the Fermi level and work function dependence on doping.Our results highlight promising features of aC as the active layer material of thin-film solar cells.

Patterning of a-C DLC films: exploration of an aqueous electro-oxidative mechanism

NASA Astrophysics Data System (ADS)

Mühl, Thomas; Myhra, Sverre

2007-06-01

Conducting ion-beam assisted CVD deposited a-C type DLC films can be patterned electro-oxidatively by masked and maskless probe-induced STM-based lithography. The former constitutes a parallel rapid processing technology, with the tip acting as a distant stationary electrode. The latter is a higher spatial resolution serial technology, with the tip defining a travelling local electro-chemical cell. The mechanism is based on electro-oxidative conversion of solid carbon to gaseous CO or CO2 in the presence of an aqueous phase, either as a bulk fluid or as a thin adsorbed film. The process is constrained kinetically in the early stages by limitations on charge transport through the surface barrier at the fluid-to-solid interface and subsequently by the availability of oxidants and by their transport to reactive sites. The as-received surface is terminated by chemisorbed oxygen, leading to the formation of an insulating surface barrier. The threshold potential for initiation of conversion depends on the width of the barrier. The results may have implications for new technologies exploiting the properties of carbon-based materials, but may also add to the present understanding of the electrochemistry of carbon solids.

A Rapid Deposition of Fluorine Doped Zinc Oxide Using the Atmospheric Pressure Chemical Vapour Deposition Method

NASA Astrophysics Data System (ADS)

Najafi, Navid; Rozati, S. M.

2018-03-01

Fluorine-doped zinc oxide (FZO) (ZnO:F) thin films were manufactured by atmospheric pressure chemical vapor deposition (APCVD) on glass substrates using zinc acetate dihydrate [C4H6O4Zn·2H2O, ZnAc] and ammonium fluoride (NH4F) as the source of fluorine with deposition duration of only 120 s for each sample. The effects of different amounts of fluorine as the dopant on the structural, electrical and optical properties of FZO thin films were investigated. The results show a polycrystalline structure at higher temperatures compared to amorphous structure at lower temperatures. The x-ray diffraction patterns of the polycrystalline films were identified as a hexagonal wurtzite structure of zinc oxide (ZnO) with the (002) preferred orientation. Also, the sheet resistance decreased from 17.8 MΩ/□ to 28.9 KΩ/□ for temperatures 325°C to 450°C, respectively. In order to further decrease the sheet resistance of the undoped ZnO thin films, fluorine was added using NH4F as the precursor, and again a drastic change in sheet resistance of only 17.7 Ω/□ was obtained. Based on the field emission scanning electron microscopy images, the fluorine concentration in CVD source is an important factor affecting the grain size and modifies electrical parameters. Ultraviolet-visible measurements revealed reduction of transparency of the layers with increasing fluorine as the dopant.

Preparation and characterisation of crystalline tris(acetylacetonato)Fe(III) films grown on p-Si substrate for dielectric applications

NASA Astrophysics Data System (ADS)

Dakhel, A. A.; Ali-Mohamed, A. Y.

2007-02-01

Thin tris(acetylacetonato)iron(III) films were prepared by sublimation in vacuum on glass and p-Si substrates. Then comprehensive studies of X-ray fluorescence (XRF), X-ray diffraction (XRD), optical absorption spectroscopy, AC-conductivity, and dielectric permittivity as a function of frequency and temperature have been performed. The prepared films show a polycrystalline of orthorhombic structure. The optical absorption spectrum of the film was identical with that of the bulk powder layer. For electrical measurements of the complex as insulator, sample in form of metal insulator semiconductor (MIS) structure was prepared and characterised by the measurement of the capacitance and AC-conductance as a function of gate voltage. From those measurements, the state density Dit at insulator/semiconductor interface and the density of the fixed charges in the complex film were determined. It was found that Dit was of order 1010 eV-1/cm2 and the surface charge density in the insulator film was of order 1010 cm-2. The frequency dependence of the electrical conductivity and dielectric properties of MIS structures were studied at room temperature. It was observed that the experimental data follow the correlated barrier-hopping (CBH) model, from which the fundamental absorption edge, the cut off hopping distance, and other parameters of the model were determined. It was found that the capacitance of the complex increases as temperature increases. Generally, the present study shows that the tris(acetylacetonato)iron(III) films grown on p-Si is a promising candidate for low-k dielectric applications, it displays low-k value around 2.0.

Electroluminescence from metal-oxide-semiconductor devices with erbium-doped CeO{sub 2} films on silicon

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

Lv, Chunyan; Department of Chemistry, Huzhou University, Zhejiang, Huzhou 313000; Zhu, Chen

2015-04-06

We report on erbium (Er)-related electroluminescence (EL) in the visible and near-infrared (NIR) from metal-oxide-semiconductor (MOS) devices with Er-doped CeO{sub 2} (CeO{sub 2}:Er) films on silicon. The onset voltage of such EL under either forward or reverse bias is smaller than 10 V. Moreover, the EL quenching can be avoidable for the CeO{sub 2}:Er-based MOS devices. Analysis on the current-voltage characteristic of the device indicates that the electron transportation at the EL-enabling voltages under either forward or reverse bias is dominated by trap-assisted tunneling mechanism. Namely, electrons in n{sup +}-Si/ITO can tunnel into the conduction band of CeO{sub 2} host viamore » defect states at sufficiently high forward/reverse bias voltages. Then, a fraction of such electrons are accelerated by electric field to become hot electrons, which impact-excite the Er{sup 3+} ions, thus leading to characteristic emissions. It is believed that this work has laid the foundation for developing viable silicon-based emitters using CeO{sub 2}:Er films.« less

Acetate Salts as Nonhalogen Additives To Improve Perovskite Film Morphology for High-Efficiency Solar Cells.

PubMed

Wu, Qiliang; Zhou, Pengcheng; Zhou, Weiran; Wei, Xiangfeng; Chen, Tao; Yang, Shangfeng

2016-06-22

A two-step method has been popularly adopted to fabricate a perovskite film of planar heterojunction organo-lead halide perovskite solar cells (PSCs). However, this method often generates uncontrollable film morphology with poor coverage. Herein, we report a facile method to improve perovskite film morphology by incorporating a small amount of acetate (CH3COO(-), Ac(-)) salts (NH4Ac, NaAc) as nonhalogen additives in CH3NH3I solution used for immersing PbI2 film, resulting in improved CH3NH3PbI3 film morphology. Under the optimized NH4Ac additive concentration of 10 wt %, the best power conversion efficiency (PCE) reaches 17.02%, which is enhanced by ∼23.2% relative to that of the pristine device without additive, whereas the NaAc additive does not lead to an efficiency enhancement despite the improvement of the CH3NH3PbI3 film morphology. SEM study reveals that NH4Ac and NaAc additives can both effectively improve perovskite film morphology by increasing the surface coverage via diminishing pinholes. The improvement on CH3NH3PbI3 film morphology is beneficial for increasing the optical absorption of perovskite film and improving the interfacial contact at the perovskite/spiro-OMeTAD interface, leading to the increase of short-circuit current and consequently efficiency enhancement of the PSC device for NH4Ac additive only.

Electroluminescence and Photocurrent Generation from Atomically Sharp WSe2/MoS2 Heterojunction p–n Diodes

PubMed Central

2015-01-01

The p–n diodes represent the most fundamental device building blocks for diverse optoelectronic functions, but are difficult to achieve in atomically thin transition metal dichalcogenides (TMDs) due to the challenges in selectively doping them into p- or n-type semiconductors. Here, we demonstrate that an atomically thin and sharp heterojunction p–n diode can be created by vertically stacking p-type monolayer tungsten diselenide (WSe2) and n-type few-layer molybdenum disulfide (MoS2). Electrical measurements of the vertically staked WSe2/MoS2 heterojunctions reveal excellent current rectification behavior with an ideality factor of 1.2. Photocurrent mapping shows rapid photoresponse over the entire overlapping region with a highest external quantum efficiency up to 12%. Electroluminescence studies show prominent band edge excitonic emission and strikingly enhanced hot-electron luminescence. A systematic investigation shows distinct layer-number dependent emission characteristics and reveals important insight about the origin of hot-electron luminescence and the nature of electron–orbital interaction in TMDs. We believe that these atomically thin heterojunction p–n diodes represent an interesting system for probing the fundamental electro-optical properties in TMDs and can open up a new pathway to novel optoelectronic devices such as atomically thin photodetectors, photovoltaics, as well as spin- and valley-polarized light emitting diodes, on-chip lasers. PMID:25157588

Optoelectronic characteristics of MEH-PPV + BT blend thin films in polymer light emitting diodes

NASA Astrophysics Data System (ADS)

Massah Bidgoli, M.; Mohsennia, M.; Akbari Boroumand, F.; Mohsen Nia, A.

2015-06-01

Due to the unique optical and electronic properties of conjugated polymers, much research has been conducted to study the effect of the incorporation of electron-transporting materials on the polymer blends’ compatibility and their capability for use in optoelectronic devices. In this work, to characterize the optoelectronic properties of blend thin films of poly [2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with benzothiadiazole (BT), polymer light- emitting diodes (PLEDs) with single-emission layers of MEH-PPV + BT blends have been fabricated. The influence of MEH-PPV + BT blend weight ratios over ITO/PEDOT:PSS/MEH-PPV + BT/Al PLEDs performances, e.g., lifetime, turn-on voltage, and current density-voltage (J-V) characteristics, has been studied. According to the obtained results, the turn-on voltage of the devices successfully decreased with the addition of the BT as an electronic transportation material. At an optimum condition, we obtained a turn-on voltage as low as 5 V and a lifetime of about 190 h for a device incorporating 65% BT. The logarithmic plots of the J-V characteristics of the fabricated devices showed a power law behavior (J ∝ Vk+1) with three distinct regions. The J-V characteristics have been explained by the Fowler-Nordheim (FN) tunneling model. It was found that the hole-injection barrier height decreases with increasing BT content in the range of 0-65%. According to the obtained results, in all of our investigations, the electroluminescence (EL) originated exclusively from the MEH-PPV material, even for the high BT contents.

A study of effects of electrode contacts on performance of organic-based light-emitting field-effect transistors

NASA Astrophysics Data System (ADS)

Kim, Dae-Kyu; Choi, Jong-Ho

2018-02-01

Herein is presented a comparative performance analysis of heterojunction organic-based light-emitting field-effect transistors (OLEFETs) with symmetric (Au only) and asymmetric (Au and LiF/Al) electrode contacts. The devices had a top source-drain contact with long-channel geometry and were produced by sequentially depositing p-type pentacene and n-type N,N‧-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13) using a neutral cluster beam deposition apparatus. The spectroscopic, structural and morphological properties of the organic thin films were examined using photoluminescence (PL) spectroscopy, X-ray diffraction (XRD) method, laser scanning confocal and atomic force microscopy (LSCM, AFM). Based upon the growth of high-quality, well-packed crystalline thin films, the devices demonstrated ambipolar field-effect characteristics, stress-free operational stability, and light emission under ambient conditions. Various device parameters were derived from the fits of the observed characteristics. The hole mobilities were nearly equal irrespective of the electrode contacts, whereas the electron mobilities of the transistors with LiF/Al drain electrodes were higher due to the low injection barrier. For the OLEFETs with symmetric electrodes, electroluminescence (EL) occurred only in the vicinity of the hole-injecting electrode, whereas for the OLEFETs with asymmetric electrodes, the emission occurred in the vicinity of both hole- and electron-injecting electrodes. By tuning the carrier injection and transport through high- and low-work function metals, the hole-electron recombination sites could be controlled. The operating conduction and light emission mechanism are discussed with the aid of EL images obtained using a charge-coupled device (CCD) camera.

BIMOS transistor solutions for ESD protection in FD-SOI UTBB CMOS technology

NASA Astrophysics Data System (ADS)

Galy, Philippe; Athanasiou, S.; Cristoloveanu, S.

2016-01-01

We evaluate the Electro-Static Discharge (ESD) protection capability of BIpolar MOS (BIMOS) transistors integrated in ultrathin silicon film for 28 nm Fully Depleted SOI (FD-SOI) Ultra Thin Body and BOX (UTBB) high-k metal gate technology. Using as a reference our measurements in hybrid bulk-SOI structures, we extend the BIMOS design towards the ultrathin silicon film. Detailed study and pragmatic evaluations are done based on 3D TCAD simulation with standard physical models using Average Current Slope (ACS) method and quasi-static DC stress (Average Voltage Slope AVS method). These preliminary 3D TACD results are very encouraging in terms of ESD protection efficiency in advanced FD-SOI CMOS.

Simultaneous dual-functioning InGaN/GaN multiple-quantum-well diode for transferrable optoelectronics

NASA Astrophysics Data System (ADS)

Shi, Zheng; Yuan, Jialei; Zhang, Shuai; Liu, Yuhuai; Wang, Yongjin

2017-10-01

We propose a wafer-level procedure for the fabrication of 1.5-mm-diameter dual functioning InGaN/GaN multiple-quantum-well (MQW) diodes on a GaN-on-silicon platform for transferrable optoelectronics. Nitride semiconductor materials are grown on (111) silicon substrates with intermediate Al-composition step-graded buffer layers, and membrane-type MQW-diode architectures are obtained by a combination of silicon removal and III-nitride film backside thinning. Suspended MQW-diodes are directly transferred from silicon to foreign substrates such as metal, glass and polyethylene terephthalate by mechanically breaking the support beams. The transferred MQW-diodes display strong electroluminescence under current injection and photodetection under light irradiation. Interestingly, they demonstrate a simultaneous light-emitting light-detecting function, endowing the 1.5-mm-diameter MQW-diode with the capability of producing transferrable optoelectronics for adjustable displays, wearable optical sensors, multifunctional energy harvesting, flexible light communication and monolithic photonic circuit.

Integration of transmissible organic electronic devices for sensor application

NASA Astrophysics Data System (ADS)

Tam, Hoi Lam; Wang, Xizu; Zhu, Furong

2013-09-01

A high performance proximity sensor that integrates a front semitransparent organic photodiode (OPD) and an organic light-emitting diode (OLED) is demonstrated. A 0.3-nm-thick plasma-polymerized fluorocarbon film (CFX)-modified thin silver interlayer, serving simultaneously as a semitransparent cathode for the OPD and an anode for OLED, is used to vertically connect the functional organic electronic components. A microcavity OLED is formed between a semitransparent Ag/CFX interlayer and the rear Al cathode enhancing the forward electroluminescence emission in the integrated device. The semitransparent-OPD/OLED stack is designed using an optical admittance analysis method. In the integrated sensor, the front semitransparent OPD component enables a high transmission of light emitted by the integrated OLED unit and a high absorption when light is reflected from objects, thereby to increase the signal/noise ratio. The design and fabrication flexibility of an integrated semitransparent-OPD/OLED device also has cost benefit, making it possible for application in organic proximity sensors.

Polymers Containing Diphenylvinyl-Substituted Indole Rings as Charge-Transporting Materials for OLEDs

NASA Astrophysics Data System (ADS)

Grigalevicius, S.; Zostautiene, R.; Sipaviciute, D.; Stulpinaite, B.; Volyniuk, D.; Grazulevicius, J. V.; Liu, L.; Xie, Z.; Zhang, B.

2016-02-01

Monomers and polymers containing electronically isolated diphenylvinyl-substituted indole rings were synthesized and characterized by nuclear magnetic resonance (NMR) and mass spectroscopies as well as by gel permeation chromatography. The polymers represent amorphous materials with glass transition temperatures of 91-109°C and thermal decomposition starting above 307°C. Electron photoemission spectra of thin films of the synthesized polymers revealed ionization potentials of 5.54-5.58 eV. The synthesized polymers were tested as hole-transporting materials in simple electroluminescent organic light-emitting diode (OLED) devices with tris(quinolin-8-olato)aluminium (Alq3) as an emitter as well as an electron-transporting layer. A green OLED device containing a hole-transporting layer of poly[1-(2,3-epithiopropyl)-2-methyl-3-(2,2-diphenylvinyl)índole] exhibited the best overall performance with a driving voltage of 4.0 V, maximum photometric efficiency of 2.8 cd/A and maximum brightness of about 4200 cd/m2.

Tunneling Spectroscopy of MoN and NbxTi1-xN Thin Films Grown by Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Cao, Chaoyue; Groll, Nickolas; Klug, Jeffrey; Becker, Nicholas; Altin, Serdar; Proslier, Thomas; Zasadzinski, John

2014-03-01

Tunneling I(V) and dI/dV vs. V are reported on superconducting thin films of MoN and NbxTi1-xN using a point contact method with a Au tip. The films are grown by the chemical process of atomic layer deposition (ALD) onto various substrates (Si, quartz, sapphire) held at 450 C. Resistively measured superconducting Tc values up to 12K and 13K are found for the MoN and NbxTi1-xN respectively. Artificial tunnel barriers (1-3 nm thick) of Al2O3, also grown by ALD, are shown to provide much improved tunneling characteristics compared to the native oxides. Relatively high quality gap features are observed with zero-bias conductance values as low as ~ 10% of the high bias values. Gap parameters Δ ~ 2.0meV are found for the MoN and Δ ~ 2.0-2.4 meV for the NbxTi1-xN which follow the BCS temperature dependence and close near the measured film Tc indicating bulk superconductivity at the surface. The suitability of such conformal ALD grown films for potential superconducting devices is discussed. This work was supported by the U.S. Department of Energy, Office of Science under contract No. DE-AC02-06CH11357.

Subatomic deformation driven by vertical piezoelectricity from CdS ultrathin films.

PubMed

Wang, Xuewen; He, Xuexia; Zhu, Hongfei; Sun, Linfeng; Fu, Wei; Wang, Xingli; Hoong, Lai Chee; Wang, Hong; Zeng, Qingsheng; Zhao, Wu; Wei, Jun; Jin, Zhong; Shen, Zexiang; Liu, Jie; Zhang, Ting; Liu, Zheng

2016-07-01

Driven by the development of high-performance piezoelectric materials, actuators become an important tool for positioning objects with high accuracy down to nanometer scale, and have been used for a wide variety of equipment, such as atomic force microscopy and scanning tunneling microscopy. However, positioning at the subatomic scale is still a great challenge. Ultrathin piezoelectric materials may pave the way to positioning an object with extreme precision. Using ultrathin CdS thin films, we demonstrate vertical piezoelectricity in atomic scale (three to five space lattices). With an in situ scanning Kelvin force microscopy and single and dual ac resonance tracking piezoelectric force microscopy, the vertical piezoelectric coefficient (d 33) up to 33 pm·V(-1) was determined for the CdS ultrathin films. These findings shed light on the design of next-generation sensors and microelectromechanical devices.

Time-of-flight Measurement Of Hole-tunneling Properties And Emission Color Control In Organic Light-emitting Diodes

NASA Astrophysics Data System (ADS)

Kurata, K.; Kashiwabara, K.; Nakajima, K.; Mizoguchi, Y.; Ohtani, N.

2011-12-01

Hole transport properties of organic light-emitting diodes (OLEDs) with a thin hole-blocking layer (HBL) were evaluated by time-of-flight measurement. Electroluminescence (EL) spectra of OLEDs with various HBL thicknesses were also evaluated. The results clearly show that the time-resolved photocurrent response and the emission color strongly depend on HBL thickness. This can be attributed to hole-tunneling through the thin HBL. We successfully fabricated a white OLED by controlling the thickness of HBL.

Design of optimal buffer layers for CuInGaSe2 thin-film solar cells(Conference Presentation)

NASA Astrophysics Data System (ADS)

Lordi, Vincenzo; Varley, Joel B.; He, Xiaoqing; Rockett, Angus A.; Bailey, Jeff; Zapalac, Geordie H.; Mackie, Neil; Poplavskyy, Dmitry; Bayman, Atiye

2016-09-01

Optimizing the buffer layer in manufactured thin-film PV is essential to maximize device efficiency. Here, we describe a combined synthesis, characterization, and theory effort to design optimal buffers based on the (Cd,Zn)(O,S) alloy system for CIGS devices. Optimization of buffer composition and absorber/buffer interface properties in light of several competing requirements for maximum device efficiency were performed, along with process variations to control the film and interface quality. The most relevant buffer properties controlling performance include band gap, conduction band offset with absorber, dopability, interface quality, and film crystallinity. Control of an all-PVD deposition process enabled variation of buffer composition, crystallinity, doping, and quality of the absorber/buffer interface. Analytical electron microscopy was used to characterize the film composition and morphology, while hybrid density functional theory was used to predict optimal compositions and growth parameters based on computed material properties. Process variations were developed to produce layers with controlled crystallinity, varying from amorphous to fully epitaxial, depending primarily on oxygen content. Elemental intermixing between buffer and absorber, particularly involving Cd and Cu, also is controlled and significantly affects device performance. Secondary phase formation at the interface is observed for some conditions and may be detrimental depending on the morphology. Theoretical calculations suggest optimal composition ranges for the buffer based on a suite of computed properties and drive process optimizations connected with observed film properties. Prepared by LLNL under Contract DE-AC52-07NA27344.

High-κ TiO{sub 2} thin film prepared by sol-gel spin-coating method

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

Kumar, Arvind; Mondal, Sandip; Rao, K. S. R. Koteswara, E-mail: ksrkrao@physics.iisc.ernet.in

2015-06-24

High-k TiO{sub 2} thin film on p-type silicon substrate was fabricated by a combined sol-gel and spin coating method. Thus deposited titania film had anatase phase with a small grain size of 16 nm and surface roughness of ≅ 0.6 nm. The oxide capacitance (C{sub ox}), flat band capacitance (C{sub FB}), flat band voltage (V{sub FB}), oxide trapped charge (Q{sub ot}), calculated from the high frequency (1 MHz) C-V curve were 0.47 nF, 0.16 nF, − 0.91 V, 4.7x10{sup −12} C, respectively. As compared to the previous reports, a high dielectric constant of 94 at 1 MHz frequency was observedmore » in the devices investigated here and an equivalent oxide thickness (EOT) was 4.1 nm. Dispersion in accumulation capacitance shows a linear relationship with AC frequencies. Leakage current density was found in acceptable limits (2.1e-5 A/cm{sup 2} for −1 V and 5.7e-7 A/cm{sup 2} for +1 V) for CMOS applications.« less

Performance analysis of resistive switching devices based on BaTiO3 thin films

NASA Astrophysics Data System (ADS)

Samardzic, Natasa; Kojic, Tijana; Vukmirovic, Jelena; Tripkovic, Djordjije; Bajac, Branimir; Srdic, Vladimir; Stojanovic, Goran

2016-03-01

Resitive switching devices, memristors, have recenty attracted much attention due to promising performances and potential applications in the field of logic and memory devices. Here, we present thin film BaTiO3 based memristor fabricated using ink-jet printing technique. Active material is a single layer barium titanate film with thickness of ̴100 nm, sandwitched between metal electodes. Printing parameters were optimized aiming to achieve stable drop flow and uniform printed layer. Current-voltage characteristics show typical memristive behavior with pinched hysteresis loop crossed at the origin, with marked differences between High Resistive State (HRS) and Low Resistive State (LRS). Obtained resistive states are stable during numerous switching processes. The device also shows unipolar switching effect for negative voltage impulses. Variable voltage impulse amplitudes leads to the shifting of the energy levels of electode contacts resulting in changing of the overall current through the device. Structural charcterization have been performed using XRD analysis and SEM micrography. High-temperature current-voltage measurements combined with transport parameter analysis using Hall efect measurement system (HMS 3000) and Impedance Analyzer AC measurements allows deeper insigth into conduction mechanism of ferroelectric memristors.

Luminescence and electroluminescence of bis (2-(benzimidazol-2-yl) quinolinato) zinc. Exciplex formation and energy transfer in mixed film of bis (2-(benzimidazol-2-yl) quinolinato) zinc and N,N‧-bis-(1-naphthyl)-N,N‧-diphenyl-1,1‧-biphenyl-4,4‧-diamine

NASA Astrophysics Data System (ADS)

Chen, Tsun-Ren

2005-02-01

The absorption and emission properties of benzimidazol-2-yl-quinoline (BIQ) and bis (2-(benzimidazol-2-yl) quinolinato) zinc (ZnBIQ) a new emitter used for organic light emitting device (OLED) were reported. Exciplexes are observed for ZnBIQ with N, N'-bis-(1-naphthyl)- N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) system, in both electro- and photoluminescent processes. The identification of exciplex emission in co-evaporated and multi-layer ZnBIQ thin film was reported for the first time. The optical formation of the exciplex involves the excitation of a single molecule, followed by the relaxation of that exciton into a lower energy exciplex state. Both BIQ and ZnBIQ possess very high thermal stabilities and can be purified by subliming under the high vacuum condition. Devices consisting of ZnBIQ as the emitting layer have been fabricated, and the emission spectra of ZnBIQ-base devices gave a voltage-dependent spectrum, with the red emission observed (3-7 V), switching over to strong white emission as the bias was raised.

Control of mobility in molecular organic semiconductors by dendrimer generation

NASA Astrophysics Data System (ADS)

Lupton, J. M.; Samuel, I. D.; Beavington, R.; Frampton, M. J.; Burn, P. L.; Bässler, H.

2001-04-01

Conjugated dendrimers are of interest as novel materials for light-emitting diodes. They consist of a luminescent chromophore at the core with highly branched conjugated dendron sidegroups. In these materials, light emission occurs from the core and is independent of generation. The dendron branching controls the separation between the chromophores. We present here a family of conjugated dendrimers and investigate the effect of dendron branching on light emission and charge transport. We apply a number of transport measurement techniques to thin films of a conjugated dendrimer in a light-emitting diode configuration to determine the effect of chromophore spacing on charge transport. We find that the mobility is reduced by two orders of magnitude as the size of the molecule doubles with increased branching or dendrimer generation. The degree of branching allows a unique control of mobility by molecular structure. An increase in chromophore separation also results in a reduction of intermolecular interactions, which reduces the red emission tail in film photoluminescence. We find that the steady-state charge transport is well described by a simple device model incorporating the effect of generation, and use the materials to shed light on the interpretation of transient electroluminescence data. We demonstrate the significance of the ability to tune the mobility in bilayer devices, where a more balanced charge transport can be achieved.

Highly Modified Cellulose Nanocrystals and Formation of Epoxy-CNC Nanocomposites.

PubMed

Abraham, Eldho; Kam, Doron; Nevo, Yuval; Slattegard, Rikard; Rivkin, Amit; Lapidot, Shaul; Shoseyov, Oded

2016-10-05

This work presents an environmentally friendly, iodine-catalysed chemical modification method to generate highly hydrophobic, optically active cellulose nanocrystals (CNC). The high degree of ester substitution (DS=2.18), hydrophobicity, crystalline behaviour and optical activity of the generated acetylated CNC (Ac-CNC) were quantified by TEM, FTIR, solid 13C NMR, contact angle, XRD and POM analyses. Ac-CNC possessing substantial enhancement in thermal stability (16.8%) and forms thin films with interlayer distance of 50-150 nm, presenting cavities suitable for entrapping nano and micro particles. Generated Ac-CNC proved as an effective reinforcing agent in hydrophobic polymer matrices for fabricating high performance nanocomposites. When integrated at a very low weight percentage (0.5%) in an epoxy matrix, Ac-CNC provided for a 73% increase in tensile strength and a 98% increase in modulus, demonstrating its remarkable reinforcing potential and effective stress transfer behaviour. The method of modification and the unique properties of the modified CNC (hydrophobicity, crystallinity, reinforcing ability and optical activity) render them a novel bionanomaterial for a range of multipurpose applications.

Current distribution and ac susceptibility response of a thin superconducting disc in an axial field: a theoretical approach

NASA Astrophysics Data System (ADS)

Aruna, S. A.; Zhang, P.; Lin, F. Y.; Ding, S. Y.; Yao, X. X.

2000-04-01

Within the framework of the thermally activated process of the flux line or flux line bundles, and by time integration of the 1D equation of motion of the circulating current density icons/Journals/Common/vecJ" ALT="vecJ" ALIGN="TOP"/> (icons/Journals/Common/rho" ALT="rho" ALIGN="TOP"/> ,t ), which is suitable for thin superconducting films (R >>d ,icons/Journals/Common/le" ALT="le" ALIGN="TOP"/> icons/Journals/Common/lambda" ALT="lambda" ALIGN="TOP"/> ), we present numerical calculations of the current profiles, magnetization hysteresis loops and ac susceptibility icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> n = icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> ´n +iicons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> ´´n for n = 1, 3 and 5 of a thin disc immersed in an axial time-dependent external magnetic field Ba (t ) = Bdc +Bac cos(2icons/Journals/Common/pi" ALT="pi" ALIGN="TOP"/> icons/Journals/Common/nu" ALT="nu" ALIGN="TOP"/> t ). Our calculated results are compared with those of the critical state model (CSM) and found to prove the approximate validity of the CSM below the irreversibility field. The differences between our computed results and those of the CSM are also discussed.

Direct Observation of the Thickness-Induced Crystallization and Stress Build-Up during Sputter-Deposition of Nanoscale Silicide Films.

PubMed

Krause, Bärbel; Abadias, Gregory; Michel, Anny; Wochner, Peter; Ibrahimkutty, Shyjumon; Baumbach, Tilo

2016-12-21

The kinetics of phase transitions during formation of small-scale systems are essential for many applications. However, their experimental observation remains challenging, making it difficult to elucidate the underlying fundamental mechanisms. Here, we combine in situ and real-time synchrotron X-ray diffraction (XRD) and X-ray reflectivity (XRR) experiments with substrate curvature measurements during deposition of nanoscale Mo and Mo 1-x Si x films on amorphous Si (a-Si). The simultaneous measurements provide direct evidence of a spontaneous, thickness-dependent amorphous-to-crystalline (a-c) phase transition, associated with tensile stress build-up and surface roughening. This phase transformation is thermodynamically driven, the metastable amorphous layer being initially stabilized by the contributions of surface and interface energies. A quantitative analysis of the XRD data, complemented by simulations of the transformation kinetics, unveils an interface-controlled crystallization process. This a-c phase transition is also dominating the stress evolution. While stress build-up can significantly limit the performance of devices based on nanostructures and thin films, it can also trigger the formation of these structures. The simultaneous in situ access to the stress signal itself, and to its microstructural origins during structure formation, opens new design routes for tailoring nanoscale devices.

Electroluminescent TCC, C3dg and fB/Bb epitope assays for profiling complement cascade activation in vitro using an activated complement serum calibration standard.

PubMed

van Vuuren, B Jansen; Bergseth, G; Mollnes, T E; Shaw, A M

2014-01-15

Electroluminescent assays for epitopes on the complement components C3dg, terminal complement complex (TCC) and factor B/Bb (fB/Bb) have been developed with capture and detection antibodies to produce detection limits C3dg=91±9ng/mL, TCC=3±0.1ng/mL and fB=55.7±0.1ng/mL. The assay performance was assessed against a series of zymosan and heat aggregated IgG (HAIgG) in vitro activations of complement using a calibrated activated complement serum (ACS) as calibration standard. The ACS standard was stable within 20% accuracy over a 6-month period with freeze-thaw cycles as required. Differential activation of the complement cascade was observed for TCC showing a pseudo-first order formation half-life of 3.5h after activation with zymosan. The C3dg activation fragment indicates a 10% total activation for both activation agents. The kinetic-epitope analysis for fB indicates that the capture epitope is on the fB/Bb protein fragment which can then become covered by the formation of C3bBb or C3bBbP complexes during the time course of the cascade. Copyright © 2013 Elsevier B.V. All rights reserved.

Reactive polymer multilayers fabricated by covalent layer-by-layer assembly: 1,4-conjugate addition-based approaches to the design of functional biointerfaces.

PubMed

Bechler, Shane L; Lynn, David M

2012-05-14

We report on conjugate addition-based approaches to the covalent layer-by-layer assembly of thin films and the post-fabrication functionalization of biointerfaces. Our approach is based on a recently reported approach to the "reactive" assembly of covalently cross-linked polymer multilayers driven by the 1,4-conjugate addition of amine functionality in poly(ethyleneimine) (PEI) to the acrylate groups in a small-molecule pentacrylate species (5-Ac). This process results in films containing degradable β-amino ester cross-links and residual acrylate and amine functionality that can be used as reactive handles for the subsequent immobilization of new functionality. Layer-by-layer growth of films fabricated on silicon substrates occurred in a supra-linear manner to yield films ≈ 750 nm thick after the deposition of 80 PEI/5-Ac layers. Characterization by atomic force microscopy (AFM) suggested a mechanism of growth that involves the reactive deposition of nanometer-scale aggregates of PEI and 5-Ac during assembly. Infrared (IR) spectroscopy studies revealed covalent assembly to occur by 1,4-conjugate addition without formation of amide functionality. Additional experiments demonstrated that acrylate-containing films could be postfunctionalized via conjugate addition reactions with small-molecule amines that influence important biointerfacial properties, including water contact angles and the ability of film-coated surfaces to prevent or promote the attachment of cells in vitro. For example, whereas conjugation of the hydrophobic molecule decylamine resulted in films that supported cell adhesion and growth, films treated with the carbohydrate-based motif D-glucamine resisted cell attachment and growth almost completely for up to 7 days in serum-containing media. We demonstrate that this conjugate addition-based approach also provides a means of immobilizing functionality through labile ester linkages that can be used to promote the long-term, surface-mediated release of conjugated species and promote gradual changes in interfacial properties upon incubation in physiological media (e.g., over a period of at least 1 month). These covalently cross-linked films are relatively stable in biological media for prolonged periods, but they begin to physically disintegrate after ≈ 30 days, suggesting opportunities to use this covalent layer-by-layer approach to design functional biointerfaces that ultimately erode or degrade to facilitate elimination.

Conduction in In 2O 3/YSZ heterostructures: Complex interplay between electrons and ions, mediated by interfaces

DOE PAGES

Veal, B. W.; Eastman, J. A.

2017-03-01

Thin film In 2O 3/YSZ heterostructures exhibit significant increases in electrical conductance with time when small in-plane electric fields are applied. Contact resistances between the current electrodes and film, and between current electrodes and substrate are responsible for the behavior. With an in-plane electric field, different field profiles are established in the two materials, with the result that oxygen ions can be driven across the heterointerface, altering the doping of the n-type In 2O 3. Furthermore, a low frequency inductive feature observed in AC impedance spectroscopy measurements under DC bias conditions was found to be due to frequency-dependent changes inmore » the contact resistance.« less

The Role of Ambient Gas and Pressure on the Structuring of Hard Diamond-Like Carbon Films Synthesized by Pulsed Laser Deposition

PubMed Central

Popescu, Andrei C.; Stan, George E.; Duta, Liviu; Nita, Cristina; Popescu, Camelia; Surdu, Vasile-Adrian; Husanu, Marius-Adrian; Bita, Bogdan; Ghisleni, Rudy; Himcinschi, Cameliu; Craciun, Valentin

2015-01-01

Hard carbon thin films were synthesized on Si (100) and quartz substrates by the Pulsed Laser Deposition (PLD) technique in vacuum or methane ambient to study their suitability for applications requiring high mechanical resistance. The deposited films’ surface morphology was investigated by scanning electron microscopy, crystalline status by X-ray diffraction, packing and density by X-ray reflectivity, chemical bonding by Raman and X-ray photoelectron spectroscopy, adherence by “pull-out” measurements and mechanical properties by nanoindentation tests. Films synthesized in vacuum were a-C DLC type, while films synthesized in methane were categorized as a-C:H. The majority of PLD films consisted of two layers: one low density layer towards the surface and a higher density layer in contact with the substrate. The deposition gas pressure played a crucial role on films thickness, component layers thickness ratio, structure and mechanical properties. The films were smooth, amorphous and composed of a mixture of sp3-sp2 carbon, with sp3 content ranging between 50% and 90%. The thickness and density of the two constituent layers of a film directly determined its mechanical properties.

Structural and interfacial defects in c-axis oriented LiNbO3 thin films grown by pulsed laser deposition on Si using Al : ZnO conducting layer

NASA Astrophysics Data System (ADS)

Shandilya, Swati; Tomar, Monika; Sreenivas, K.; Gupta, Vinay

2009-05-01

Highly c-axis oriented LiNbO3 films are deposited using pulsed laser deposition on a silicon substrate using a transparent conducting Al doped ZnO layer. X-ray diffraction and Raman spectroscopic analysis show the fabrication of single phase and oriented LiNbO3 films under the optimized deposition condition. An extra peak at 905 cm-1 was observed in the Raman spectra of LiNbO3 film deposited at higher substrate temperature and higher oxygen pressure, and attributed to the presence of niobium antisite defects in the lattice. Dielectric constant and ac conductivity of oriented LiNbO3 films deposited under the static and rotating substrate modes have been studied. Films deposited under the rotating substrate mode exhibit dielectric properties close to the LiNbO3 single crystal. The cause of deviation in the dielectric properties of the film deposited under the static substrate mode, in comparison with the bulk, are discussed in the light of the possible formation of an interdiffusion layer at the interface of the LiNbO3 film and the Al : ZnO layer.

Luminescence properties of Ce{sup 3+} and Tb{sup 3+} co-doped SiO{sub x}N{sub y} thin films: Prospects for color tunability in silicon-based hosts

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

Ramírez, J. M., E-mail: joan-manel.ramirez@u-psud.fr; Ruiz-Caridad, A.; Estradé, S.

2016-03-21

In this work, the role of the nitrogen content, the annealing temperature, and the sample morphology on the luminescence properties of Ce{sup 3+} and Tb{sup 3+} co-doped SiO{sub x}N{sub y} thin films has been investigated. An increasing nitrogen atomic percentage has been incorporated in the host matrix by gradually replacing oxygen with nitrogen during fabrication while maintaining the Si content unaltered, obtaining a sequential variation in the film composition from nearly stoichiometric SiO{sub 2} to SiO{sub x}N{sub y}. The study of rare earth doped single layers has allowed us to identify the parameters that yield an optimum optical performance frommore » Ce{sup 3+} and Tb{sup 3+} ions. Ce{sup 3+} ions proved to be highly sensitive to the annealing temperature and the nitrogen content, showing strong PL emission for relatively low nitrogen contents (from 0 to 20%) and moderate annealing temperatures (800–1000 °C) or under high temperature annealing (1180 °C). Tb{sup 3+} ions, on the other hand, displayed a mild dependence on those film parameters. Rare earth co-doping has also been investigated by comparing the luminescence properties of three different approaches: (i) a Ce{sup 3+} and Tb{sup 3+} co-doped SiO{sub x}N{sub y} single layer, (ii) a bilayer composed of two SiO{sub x}N{sub y} single layers doped with either Ce{sup 3+} or Tb{sup 3+} ions, and (iii) a multilayer composed of a series of either Tb{sup 3+} or Ce{sup 3+}-doped SiO{sub x}N{sub y} thin films with interleaved SiO{sub 2} spacers. Bright green emission and efficient energy transfer from either Ce{sup 3+} ions or Ce silicates to Tb{sup 3+} ions has been observed in the co-doped single layer as a consequence of the strong ion-ion interaction. On the other hand, independent luminescence from Ce{sup 3+} and Tb{sup 3+} ions has been observed in the Ce{sup 3+} and Tb{sup 3+} co-doped bilayer and multilayer, providing a good scenario to develop light emitting devices with wide color tunability by varying the number of deposited films that contain each rare earth dopant. Moreover, the optoelectronic properties of Ce{sup 3+}- and/or Tb{sup 3+}-doped thin films have been studied by depositing transparent conductive electrodes over selected samples. An electroluminescence signal according to the rare earth transitions is obtained in all cases, validating the excitation of Ce{sup 3+} and Tb{sup 3+} ions upon electron injection. Also, the main charge transport of injected electrons has been evaluated and correlated with the layer stoichiometry. Finally, a simple reliability test has allowed disclosing the origin of the early breakdown of test devices, attributed to the excessive joule heating at filament currents that occur around a region close to the polarization point.« less

Transparent Conductive Ink for Additive Manufacturing

NASA Technical Reports Server (NTRS)

Patlan, X. J.; Rolin, T. D.

2017-01-01

NASA analyzes, tests, packages, and fabricates electrical, electronic, and electromechanical (EEE) parts. Nanotechnology is listed in NASA's Technology Roadmap as a key area to invest for further development.1 This research project focused on using nanotechnology to improve electroluminescent lighting in terms of additive manufacturing and to increase energy efficiency. Specifically, this project's goal was to produce a conductive but transparent printable ink that can be sprayed on any surface for use as one of the electrodes in electroluminescent device design. This innovative work is known as thick film dielectric electroluminescent (TDEL) technology. TDEL devices are used for "backlighting, illumination, and identification due to their tunable color output, scalability, and efficiency" (I.K. Small, T.D. Rolin, and A.D. Shields, "3D Printed Electroluminescent Light Panels," NASA Fiscal Year 2017 Center Innovation Fund Proposal, unpublished data, 2017). These devices use a 'front-to-back' printing method, where the substrate is the transparent layer, and the dielectric and phosphor are layered on top. This project is a first step in the process of creating a 3D printable 'back-to-front' electroluminescent device. Back-to-front 3D-printed devices are beneficial because they can be printed onto different substrates and embedded in different surfaces, and the substrate is not required to be transparent, all because the light is emitted from the top surface through the transparent conductor. Advances in this area will help further development of printing TDEL devices on an array of different surfaces. Figure 1 demonstrates the layering of the two electrodes that are aligned in a parallel plate capacitor structure (I.K. Small, T.D. Rolin, and A.D. Shields, "3D Printed Electroluminescent Light Panels," NASA Fiscal Year 2017 Center Innovation Fund Proposal, unpublished data, 2017). Voltage is applied across the device, and the subsequent electron excitation results in light emission at the top layer.

A comparative physical evaluation of four X-ray films.

PubMed

Egyed, M; Shearer, D R

1981-09-01

In this study, four general purpose radiographic films (Agfa Gevaert Curix RP-1, duPont Cronex 4, Fuji RX, and Kodak XRP-1) were compared using three independent techniques. By examining the characteristic curves for the four films, film speed and contrast were compared over the diagnostically useful density range. These curves were generated using three methods: (1) irradiation of a standard film cassette lined with high-speed screens, covered by a twelve-step aluminum wedge; (2) direct exposure of film strips to an electro-luminescent sensitometer; and (3) direct irradiation of a standard film cassette lined with high-speed screens. The latter technique provided quantitative values for film speed and relative contrast. All three techniques provided virtually properly identical results and indicate that under properly controlled conditions simplified methods of film testing can give results equivalent to those obtained by more sophisticated techniques.

Nanoscale deformation mechanism of TiC/a-C nanocomposite thin films

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

Chen, C. Q.; Pei, Y. T.; Shaha, K. P.

2009-06-01

This paper concentrates on the deformation behavior of amorphous diamondlike carbon composite materials. Combined nanoindentation and ex situ cross-sectional transmission electron microscopy investigations are carried out on TiC/a-C nanocomposite films, with and without multilayered structures deposited by pulse dc magnetron sputtering. It is shown that by controlling the distribution of nanocrystallites forming nanoscale multilayers, the system can be used as a 'microstructural ruler' that is able to distinguish various deformation patterns, which can be hardly detected otherwise in a homogeneous structure. It is shown that rearrangement of nanocrystallites and displacement of a-C matrix occur at length scales from tens ofmore » nanometer down to 1 nm. At submicrometer scale homogeneous nucleation of multiple shear bands has been observed within the nanocomposites. The multilayered structure in the TiC/a-C nanocomposite film contributes to an enhanced toughness.« less

Subatomic deformation driven by vertical piezoelectricity from CdS ultrathin films

PubMed Central

Wang, Xuewen; He, Xuexia; Zhu, Hongfei; Sun, Linfeng; Fu, Wei; Wang, Xingli; Hoong, Lai Chee; Wang, Hong; Zeng, Qingsheng; Zhao, Wu; Wei, Jun; Jin, Zhong; Shen, Zexiang; Liu, Jie; Zhang, Ting; Liu, Zheng

2016-01-01

Driven by the development of high-performance piezoelectric materials, actuators become an important tool for positioning objects with high accuracy down to nanometer scale, and have been used for a wide variety of equipment, such as atomic force microscopy and scanning tunneling microscopy. However, positioning at the subatomic scale is still a great challenge. Ultrathin piezoelectric materials may pave the way to positioning an object with extreme precision. Using ultrathin CdS thin films, we demonstrate vertical piezoelectricity in atomic scale (three to five space lattices). With an in situ scanning Kelvin force microscopy and single and dual ac resonance tracking piezoelectric force microscopy, the vertical piezoelectric coefficient (d33) up to 33 pm·V−1 was determined for the CdS ultrathin films. These findings shed light on the design of next-generation sensors and microelectromechanical devices. PMID:27419234

Electroluminescence of organic light-emitting diodes consisting of an undoped (pbi)2Ir(acac) phosphorescent layer

NASA Astrophysics Data System (ADS)

Lei, Xia; Yu, Junsheng; Zhao, Juan; Jiang, Yadong

2011-11-01

The electroluminescence (EL) characteristics of phosphorescent organic light-emitting diodes (OLEDs) with an undoped bis(1,2-dipheny1-1H-benzoimidazole) iridium (acetylacetonate) [(pbi)2Ir(acac)] emissive layer (EML) of various film thicknesses were studied. The results showed that the intensity of green light emission decreased rapidly with the increasing thickness of (pbi)2Ir(acac), which was relevant to the triplet excimer emission. It suggested that the concentration quenching of monomer emission in the undoped (pbi)2Ir(acac) film was mainly due to the formation of triplet excimer and partly due to the triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA). A green OLED with a maximum luminance of 26,531 cd/m2, a current efficiency of 36.2 cd/A, and a power efficiency of 32.4 lm/W was obtained, when the triplet excimer emission was eliminated. Moreover, the white OLED with low efficiency roll-off was realized due to the broadened recombination zone and reduced quenching effects in the EML when no electron blocking layer was employed.

Domain wall effects on the magnetoresistance in epitaxial nanostructures

NASA Astrophysics Data System (ADS)

Perason, David; Zambano, Antonio; Lukaszew, R. Alejandra

2004-03-01

It has been postulated that adiabatic magneto-transport in sufficiently small contacts in nano-bridges should exhibit significant magnetoresistance at room temperature.[1] In order to study this phenomenon we have patterned nano-bridges on epitaxial ferromagnetic thin films using e-beam lithography. We have tested (001) and (111) oriented Ni films, as well as (001) and (011) CrO2 films. We have patterned bridges with different geometric orientations with respect to the crystallographic axes in the samples. We will show magnetic force microscopy images of the devices and will compare them with OOMMF simulations of the magnetization dynamics during reversal. The magneto-transport was studied using 4-point probe with AC current and Lock-In techniques. We notice here that the size of the observed effect is inversely proportional to the width of the nano-contact. The typical MR observed was 1-2at room temperature. We will show a comparison of MR effects observed in the various films and geometries described. [1]. P. Bruno, Phys. Rev. Lett. 83, 2425, (1999).

Cross-tie walls and magnetic singularities on the surface of permalloy films (abstract)

NASA Astrophysics Data System (ADS)

Lee, Y.; Kueny, A.; Koymen, A. R.

1997-04-01

An understanding of the surface magnetic microstructure of thin polycrystalline permalloy films is important for the development of improved magnetoresistive sensors. Scanning electron microscopy with polarization analysis (SEMPA) was used to image the surface magnetic domain structure of permalloy films in ultrahigh vacuum. The SEMPA system uses a compact Mott electron spin polarimeter with a Th foil (operating at 25 keV) that has been attached to the back of a hemispherical energy analyzer. Two orthogonal in-plane components of the electron spin polarization were measured to obtain magnetic domain images with excellent contrast. 350 Å Ni83Fe17 films, deposited by Honeywell-Micro Switch using dc magnetron sputtering, were studied. The samples were demagnetized along the easy axis by an ac magnetic field with decreasing amplitude. Using SEMPA, zigzag domain walls separating two large approximately head-on domains were observed. Cross-tie walls were observed with a periodic vortex structure along the straight edges of the zigzag domain walls. The cross-tie walls occur at the points where the magnetization is reversed by 180° across the straight edges of the wall. At high magnification, the elliptical and hyperbolic singularities at the cross-tie walls were clearly observed. In addition, the Néel part and the Bloch part of the cross-tie were distinguished This is a detailed study of cross-tie walls on sputter deposited thin permalloy films using SEMPA and our results are in good agreement with theoretical calculations.

High conductivity a-C:N thin films prepared by electron gun evaporation

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

Rebollo-Plata, B.; Lozada-Morales, R.; Palomino-Merino, R.

2007-08-15

By employing electron beam evaporation, amorphous carbon nitride (a-C:N) thin films, with a low nitrogen content ({approx} 1%), were prepared on Si(110) and glass substrates at about 150 deg. C. The source was a graphite target and an ambient of N{sub 2} was introduced into the growing chamber. The source-substrate distance (SSD) was the main parameter that was intentionally varied. Electron dispersion spectroscopy measurements indicate the nitrogen concentration in the layer as {approx} 1%. The dark electrical conductivity ({sigma}) of layers was very sensitive to SSD variation, changing up to six orders of magnitude when this parameter was varied frommore » 10.5 to 23.5 cm. A maximum value of {sigma} = 1 x 10{sup 3} {omega}{sup -1} cm{sup -1} at room temperature was obtained when the SSD was equal to 15.5 cm. We have deduced that, in accordance with the Ferrari-Robertson model (FRM), our samples are localized in the second stage of the amorphization trajectory of FRM. When the SSD increases the C atoms have more probability to collide with N{sub 2} molecules, and the content of nitrogen in the a-C film increases. The amorphization trajectory followed by the films with an SSD increase is from nanocrystalline graphite to amorphous carbon. The changes in the amorphization are due to the nitrogen content in the layers.« less

Room-temperature giant magneto-mechanical-electric cross-coupling in Si-integrated PbZr0.52Ti0.48O3/Ni50Mn35In15 multiferroic heterostructures

NASA Astrophysics Data System (ADS)

Singh, Kirandeep; Kaur, Davinder

2017-04-01

The current study reports the strong magnetoelectric coupling (M-E) in silicon (Si)-integrated ferromagnetic shape memory alloy-based PZT/Ni-Mn-In thin-film multiferroic heterostructure. The strain-mediated nature of converse M-E coupling is reflected from the butterfly-shaped normalized magnetization (M/M s) versus electric field plots. The direct M-E properties of the heterostructure were measured with a frequency of AC magnetic field, bias magnetic field, as well as with temperature. A maximum direct M-E coupling in the bilayered thin-film multiferroic heterostructures occurred at resonance frequencies around the first-order structural transitional temperature of the bottom Ni-Mn-In layer. It was observed that the measuring temperature remarkably affects the direct M-E characteristic of the heterostructure. A large direct ME effect and converse ME effect coefficient α DME  ~  894 mV cm-1.Oe and α CME ~ 2.7  ×  10-5 s m-1, respectively, were achieved in the bilayer at room temperature. The mechanism of direct as well as converse M-E effects in the thin-film multiferroic heterostructures is discussed. The electrically driven angular dependence of normalized magnetization (M/M s) reveals the twofold symmetric magnetic anisotropy of the heterostructure, with the drastic shifting of the magnetic hard axis at E  >  E c (coercivity of PZT).

Dangling bond energetics in carbon nitride and phosphorus carbide thin films with fullerene-like and amorphous structure

NASA Astrophysics Data System (ADS)

Gueorguiev, G. K.; Broitman, E.; Furlan, A.; Stafström, S.; Hultman, L.

2009-11-01

The energy cost for dangling bond formation in Fullerene-like Carbon Nitride (FL-CN x) and Phosphorus carbide (FL-CP x) as well as their amorphous counterparts: a-CN x, a-CP x, and a-C has been calculated within the framework of Density Functional Theory and compared with surface water adsorption measurements. The highest energy cost is found in the FL-CN x (about 1.37 eV) followed by FL-CP x compounds (0.62-1.04 eV).

Radiological Defense. Volume 4. An Introduction to Radiological Instruments for Military Use

DTIC Science & Technology

1950-01-01

alpha admission. Thin mica and stretched nylon walls with nonmetals of low atomic number and and rubber hydrochloride films about 5 microns writing...individual pulse. This process is called qu •,cIh1ng and can be ac- R, 5ME.OH, , • .. complished by using external electronic methods ’-""::_:-:Ž-:- " or...counter tubes field survey work. Mica windows down to 0.5 )resentliy employed in survey meters are " inch in mg/cm 2 are available, although in normal

Electrohydrodynamic controlled assembly and fracturing of thin colloidal particle films confined at drop interfaces

NASA Astrophysics Data System (ADS)

Rozynek, Z.; Dommersnes, P.; Mikkelsen, A.; Michels, L.; Fossum, J. O.

2014-09-01

Particles can adsorb strongly at liquid interfaces due to capillary forces, which in practice can confine the particles to the interface. Here we investigate the electrohydrodynamic flow driven packing and deformation of colloidal particle layers confined at the surface of liquid drops. The electrohydrodynamic flow has a stagnation point at the drop equator, leading to assembly of particles in a ribbon shaped film. The flow is entirely controlled by the electric field, and we demonstrate that AC fields can be used to induce hydrodynamic "shaking" of the colloidal particle film. We find that the mechanical properties of the film is highly dependent on the particles: monodisperse polystyrene beads form packed granular monolayers which "liquefies" upon shaking, whereas clay mineral particles form cohesive films that fracture upon shaking. The results are expected to be relevant for understanding the mechanics and rheology of particle stabilized emulsions. Supplementary material in the form of a pdf file available from the Journal web page at http://dx.doi.org/10.1140/epjst/e2014-02231-x

Effects of gas residence time of CH4/H2 on sp2 fraction of amorphous carbon films and dissociated methyl density during radical-injection plasma-enhanced chemical vapor deposition

NASA Astrophysics Data System (ADS)

Sugiura, Hirotsugu; Jia, Lingyun; Kondo, Hiroki; Ishikawa, Kenji; Tsutsumi, Takayoshi; Hayashi, Toshio; Takeda, Keigo; Sekine, Makoto; Hori, Masaru

2018-06-01

Quadruple mass spectrometric measurements of CH3 density during radical-injection plasma-enhanced chemical vapor deposition to consider the sp2 fraction of amorphous carbon (a-C) films were performed. The sp2 fraction of the a-C films reached a minimum of 46%, where the CH3 density was maximum for a residence time of 6 ms. The sp2 fraction of the a-C films was tailored with the gaseous phase CH3 density during the deposition. This knowledge is useful for understanding the formation mechanism of bonding structures in the a-C films, which enables the precise control of their electronic properties.

Spin-glass behaviors in carrier polarity controlled Fe{sub 3−x}Ti{sub x}O{sub 4} semiconductor thin films

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

Yamahara, H., E-mail: yamahara@bioxide.t.u-tokyo.ac.jp; Seki, M.; Adachi, M.

2015-08-14

Carrier-type control of spin-glass (cluster spin-glass) is studied in order to engineer basic magnetic semiconductor elements using the memory functions of spin-glass. A key of carrier-polarity control in magnetite is the valence engineering between Fe(II) and Fe(III) that is achieved by Ti(IV) substitution. Single phases of (001)-oriented Fe{sub 3−x}Ti{sub x}O{sub 4} thin films have been obtained on spinel MgAl{sub 2}O{sub 4} substrates by pulsed laser deposition. Thermoelectric power measurements reveal that Ti-rich films (x = 0.8) show p-type conduction, while Ti-poor films (x = 0.6–0.75) show n-type conduction. The systematic Fe(III) reduction to Fe(II) followed by Ti(IV) substitution in the octahedral sublattice is confirmedmore » by the X-ray absorption spectra. All of the Fe{sub 3−x}Ti{sub x}O{sub 4} films (x = 0.6–0.8) exhibit ferrimagnetism above room temperature. Next, the spin-glass behaviors of Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film are studied, since this magnetically diluted system is expected to exhibit the spin-glass behaviors. The DC magnetization and AC susceptibility measurements for the Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film reveal the presence of the spin glass phase. Thermal- and magnetic-field-history memory effects are observed and are attributed to the long time-decay nature of remanent magnetization. The detailed analysis of the time-dependent thermoremanent magnetization reveals the presence of the cluster spin glass state.« less

Electrochemical impedance spectroscopy analysis of a thin polymer film-based micro-direct methanol fuel cell

NASA Astrophysics Data System (ADS)

Schulz, Tobias; Weinmüller, Christian; Nabavi, Majid; Poulikakos, Dimos

A single cell micro-direct methanol fuel cell (micro-DMFC) was investigated using electrochemical impedance spectroscopy. The electrodes consisted of thin, flexible polymer (SU8) film microchannel structures fabricated in-house using microfabrication techniques. AC impedance spectroscopy was used to separate contributions to the overall cell polarization from the anode, cathode and membrane. A clear distinction between the different electrochemical phenomena occurring in the micro-DMFC, especially the distinction between double layer charging and Faradaic reactions was shown. The effect of fuel flow rate, temperature, and anode flow channel structure on the impedance of the electrode reactions and membrane/electrode double layer charging were investigated. Analysis of impedance data revealed that the performance of the test cell was largely limited by the presence of intermediate carbon monoxide in the anode reaction. Higher temperatures increase cell performance by enabling intermediate CO to be oxidized at much higher rates. The results also revealed that serpentine anode flow microchannels show a lower tendency to intermediate CO coverage and a more stable cell behavior than parallel microchannels.

Engineering Graphene Films from Coal

NASA Astrophysics Data System (ADS)

Vijapur, Santosh H.

Graphene is a unique material with remarkable properties suitable for a wide array of applications. Chemical vapor deposition (CVD) is a simple technique for synthesis of large area and high quality graphene films on various metal substrates. Among the metal substrates, copper has been shown to be an excellent support for the growth of graphene films. Traditionally, hydrocarbon gases are used for the graphene synthesis via CVD. Unconventional solid carbon sources such as various polymers and food waste have also shown great potential for synthesis of graphene films. Coal is one such carbon enriched and abundantly available unconventional source. Utilization of coal as a carbon source to synthesize large area, transparent, and high quality few-layer graphene films via CVD has been demonstrated in the present work. Hydrocarbon gases are released as products of coal pyrolysis at temperatures ≥400 °C. This study hypothesized that, these hydrocarbon gases act as precursors for the synthesis of graphene films on the copper substrate. Hence, atmospheric pressure CVD and low temperature of 400 °C were utilized initially for the production of graphene films. These conditions were suitable for the formation of amorphous carbon (a-C) films but not crystalline graphene films that were the objective of this work. The synthesized a-C films on the copper substrate were shown to be uniform and transparent with large surface area. The thickness and surface roughness of the a-C films were determined to have typical values of 5 nm and 0.55 nm, respectively. The a-C film has >95 % optical transmittance and sheet resistivity of 0.6 MO sq-1. These values are comparable to other carbon thin films synthesized at higher temperatures. Further, the a-C films were transferred onto any type of substrate such as silicon wafer and titanium foil, and can be utilized for diverse applications. However, crystalline graphene films were not produced by implementing atmospheric pressure CVD and low temperature operation. Annealing of copper support was required to remove the oxide layer present on its surface and low pressure operation was demonstrated to be suitable for crystalline graphene film formation. The CVD system and the synthesis procedure were modified to address these issues. This was done by increasing the synthesis temperature, incorporating a vacuum pump for low pressure operation, and implementing two step procedure of annealing the copper substrate followed by subsequent coal pyrolysis for the synthesis of crystalline graphene films. The synthesized few layer graphene films were uniform and continuous with thickness in the range of 3-7 nm. The optical transmittance and electrical conductivity measurements demonstrated that the graphene films have >95 % transparency and sheet resistivity of 5.0 kO sq-1, respectively. An investigation of growth mechanism of coal derived graphene films synthesized via CVD was conducted utilizing spectroscopy, microscopy, and chromatography techniques. Gas collection was performed at the graphene synthesis conditions utilizing the CVD reactor without vacuum in operation. Various gases released as products of coal pyrolysis in the CVD reactor were collected and analyzed using gas chromatography. The analysis showed the presence of methane, ethane, ethene, propane, propene, carbon monoxide, and carbon dioxide as coal pyrolysis products. The hydrocarbon gases act as precursors for graphene growth. Raman spectroscopy, selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS) confirmed the formation of crystalline graphene films at 1055 °C and 18-30 min synthesis. The growth mechanism involves copper catalyzed reaction to produce amorphous carbon film within the first few minutes of synthesis. Raman spectroscopy and SAED validated that lower synthesis times (6-12 min) produced hybrid amorphous carbon films. This is followed by hydrogen catalyzed graphitization of the underlying carbon film to form graphene domains. Optical microscopy and Raman spectra demonstrated the formation of these oval shaped graphene domains as synthesis time was increased (18-30 min). The graphene films are formed by growth and merging of these graphene domains on the copper substrate. The growth mechanism of coal derived crystalline graphene films is presented in the current work.

Amygdala activity at encoding correlated with long-term, free recall of emotional information.

PubMed

Cahill, L; Haier, R J; Fallon, J; Alkire, M T; Tang, C; Keator, D; Wu, J; McGaugh, J L

1996-07-23

Positron emission tomography of cerebral glucose metabolism in adult human subjects was used to investigate amygdaloid complex (AC) activity associated with the storage of long-term memory for emotionally arousing events. Subjects viewed two videos (one in each of two separate positron emission tomography sessions, separated by 3-7 days) consisting either of 12 emotionally arousing film clips ("E" film session) or of 12 relatively emotionally neutral film clips ("N" film session), and rated their emotional reaction to each film clip immediately after viewing it. Three weeks after the second session, memory for the videos was assessed in a free recall test. As expected, the subjects' average emotional reaction to the E films was higher than that for the N films. In addition, the subjects recalled significantly more E films than N films. Glucose metabolic rate of the right AC while viewing the E films was highly correlated with the number of E films recalled. AC activity was not significantly correlated with the number of N films recalled. The findings support the view derived from both animal and human investigations that the AC is selectively involved with the formation of enhanced long-term memory associated with emotionally arousing events.

Contrasting behavior of covalent and molecular carbon allotropes exposed to extreme ultraviolet and soft x-ray free-electron laser radiation

NASA Astrophysics Data System (ADS)

Toufarová, M.; Hájková, V.; Chalupský, J.; Burian, T.; Vacík, J.; Vorlíček, V.; Vyšín, L.; Gaudin, J.; Medvedev, N.; Ziaja, B.; Nagasono, M.; Yabashi, M.; Sobierajski, R.; Krzywinski, J.; Sinn, H.; Störmer, M.; Koláček, K.; Tiedtke, K.; Toleikis, S.; Juha, L.

2017-12-01

All carbon materials, e.g., amorphous carbon (a-C) coatings and C60 fullerene thin films, play an important role in short-wavelength free-electron laser (FEL) research motivated by FEL optics development and prospective nanotechnology applications. Responses of a-C and C60 layers to the extreme ultraviolet (SPring-8 Compact SASE Source in Japan) and soft x-ray (free-electron laser in Hamburg) free-electron laser radiation are investigated by Raman spectroscopy, differential interference contrast, and atomic force microscopy. A remarkable difference in the behavior of covalent (a-C) and molecular (C60) carbonaceous solids is demonstrated under these irradiation conditions. Low thresholds for ablation of a fullerene crystal (estimated to be around 0.15 eV/atom for C60 vs 0.9 eV/atom for a-C in terms of the absorbed dose) are caused by a low cohesive energy of fullerene crystals. An efficient mechanism of the removal of intact C60 molecules from the irradiated crystal due to Coulomb repulsion of fullerene-cage cation radicals formed by the ionizing radiation is revealed by a detailed modeling.

Contrasting behavior of covalent and molecular carbon allotropes exposed to extreme ultraviolet and soft x-ray free-electron laser radiation

DOE PAGES

Toufarová, M.; Hájková, V.; Chalupský, J.; ...

2017-12-04

All carbon materials, e.g., amorphous carbon (a-C) coatings and C 60 fullerene thin films, play an important role in short-wavelength free-electron laser (FEL) research motivated by FEL optics development and prospective nanotechnology applications. We investigate responses of a-C and C 60 layers to the extreme ultraviolet (SPring-8 Compact SASE Source in Japan) and soft x-ray (free-electron laser in Hamburg) free-electron laser radiation by Raman spectroscopy, differential interference contrast, and atomic force microscopy. A remarkable difference in the behavior of covalent (a-C) and molecular ( C 60 ) carbonaceous solids is demonstrated under these irradiation conditions. Low thresholds for ablation ofmore » a fullerene crystal (estimated to be around 0.15 eV/atom for C 60 vs 0.9 eV/atom for a-C in terms of the absorbed dose) are caused by a low cohesive energy of fullerene crystals. An efficient mechanism of the removal of intact C 60 molecules from the irradiated crystal due to Coulomb repulsion of fullerene-cage cation radicals formed by the ionizing radiation is revealed by a detailed modeling.« less

Contrasting behavior of covalent and molecular carbon allotropes exposed to extreme ultraviolet and soft x-ray free-electron laser radiation

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

Toufarová, M.; Hájková, V.; Chalupský, J.

All carbon materials, e.g., amorphous carbon (a-C) coatings and C 60 fullerene thin films, play an important role in short-wavelength free-electron laser (FEL) research motivated by FEL optics development and prospective nanotechnology applications. We investigate responses of a-C and C 60 layers to the extreme ultraviolet (SPring-8 Compact SASE Source in Japan) and soft x-ray (free-electron laser in Hamburg) free-electron laser radiation by Raman spectroscopy, differential interference contrast, and atomic force microscopy. A remarkable difference in the behavior of covalent (a-C) and molecular ( C 60 ) carbonaceous solids is demonstrated under these irradiation conditions. Low thresholds for ablation ofmore » a fullerene crystal (estimated to be around 0.15 eV/atom for C 60 vs 0.9 eV/atom for a-C in terms of the absorbed dose) are caused by a low cohesive energy of fullerene crystals. An efficient mechanism of the removal of intact C 60 molecules from the irradiated crystal due to Coulomb repulsion of fullerene-cage cation radicals formed by the ionizing radiation is revealed by a detailed modeling.« less

Optical and morphological characterizations of pyronin dye-poly (vinyl alcohol) thin films formed on glass substrates

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

Meral, Kadem, E-mail: kademm@atauni.edu.tr; Arik, Mustafa, E-mail: marik@tatauni.edu.tr; Onganer, Yavuz, E-mail: yonganer@atauni.edu.tr

Thin films of pyronin dye mixed with poly(vinyl alcohol) (PVA) on glass substrate were prepared by using spin-coating technique. The optical and morphological properties of the thin films were studied by UV-Vis., steady-state fluorescence spectroscopies and atomic force microscopy (AFM). The thin films on glass substrate were fabricated at various [PVA]/[dye] (P/D) ratios. Hence, the monomeric and H-aggregates thin films of pyronin dye mixed with PVA were formed as a function of the dye and PVA concentration. It was determined that while the monomeric thin films showed strong fluorescence, the formation of H-aggregates in the thin film caused to decreasingmore » the fluorescence intensity. AFM studies demonstrated that the morphology of the thin film was drastically varied with changing the optical property of the thin film such as monomeric and H-aggregates thin films.« less

Study on copper phthalocyanine and perylene-based ambipolar organic light-emitting field-effect transistors produced using neutral beam deposition method

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

Kim, Dae-Kyu; Oh, Jeong-Do; Shin, Eun-Sol

2014-04-28

The neutral cluster beam deposition (NCBD) method has been applied to the production and characterization of ambipolar, heterojunction-based organic light-emitting field-effect transistors (OLEFETs) with a top-contact, multi-digitated, long-channel geometry. Organic thin films of n-type N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide and p-type copper phthalocyanine were successively deposited on the hydroxyl-free polymethyl-methacrylate (PMMA)-coated SiO{sub 2} dielectrics using the NCBD method. Characterization of the morphological and structural properties of the organic active layers was performed using atomic force microscopy and X-ray diffraction. Various device parameters such as hole- and electron-carrier mobilities, threshold voltages, and electroluminescence (EL) were derived from the fits of the observed current-voltage andmore » current-voltage-light emission characteristics of OLEFETs. The OLEFETs demonstrated good field-effect characteristics, well-balanced ambipolarity, and substantial EL under ambient conditions. The device performance, which is strongly correlated with the surface morphology and the structural properties of the organic active layers, is discussed along with the operating conduction mechanism.« less

Theoretical and material studies on thin-film electroluminescent devices

NASA Technical Reports Server (NTRS)

Summers, C. J.; Brennan, K. F.

1986-01-01

A theoretical study of resonant tunneling in multilayered heterostructures is presented based on an exact solution of the Schroedinger equation under the application of a constant electric field. By use of the transfer matrix approach, the transmissivity of the structure is determined as a function of the incident electron energy. The approach presented is easily extended to many layer structures where it is more accurate than other existing transfer matrix or WKB models. The transmission resonances are compared to the bound state energies calculated for a finite square well under bias using either an asymmetric square well model or the exact solution of an infinite square well under the application of an electric field. The results show good agreement with other existing models as well as with the bound state energies. The calculations were then applied to a new superlattice structure, the variablly spaced superlattice energy filter, (VSSEP) which is designed such that under bias the spatial quantization levels fully align. Based on these calculations, a new class of resonant tunneling superlattice devices can be designed.

Stable Light-Emitting Diodes Using Phase-Pure Ruddlesden-Popper Layered Perovskites.

PubMed

Tsai, Hsinhan; Nie, Wanyi; Blancon, Jean-Christophe; Stoumpos, Constantinos C; Soe, Chan Myae Myae; Yoo, Jinkyoung; Crochet, Jared; Tretiak, Sergei; Even, Jacky; Sadhanala, Aditya; Azzellino, Giovanni; Brenes, Roberto; Ajayan, Pulickel M; Bulović, Vladimir; Stranks, Samuel D; Friend, Richard H; Kanatzidis, Mercouri G; Mohite, Aditya D

2018-02-01

State-of-the-art light-emitting diodes (LEDs) are made from high-purity alloys of III-V semiconductors, but high fabrication cost has limited their widespread use for large area solid-state lighting. Here, efficient and stable LEDs processed from solution with tunable color enabled by using phase-pure 2D Ruddlesden-Popper (RP) halide perovskites with a formula (CH 3 (CH 2 ) 3 NH 3 ) 2 (CH 3 NH 3 ) n -1 Pb n I 3 n +1 are reported. By using vertically oriented thin films that facilitate efficient charge injection and transport, efficient electroluminescence with a radiance of 35 W Sr -1 cm -2 at 744 nm with an ultralow turn-on voltage of 1 V is obtained. Finally, operational stability tests suggest that phase purity is strongly correlated to stability. Phase-pure 2D perovskites exhibit >14 h of stable operation at peak operating conditions with no droop at current densities of several Amperes cm -2 in comparison to mixtures of 2D/3D or 3D perovskites, which degrade within minutes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Single crystalline ZnO radial homojunction light-emitting diodes fabricated by metalorganic chemical vapour deposition

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

Yoo, Jinkyoung; Ahmed, Towfiq; Tang, Wei

ZnO radial p–n junction architecture has the potential for forward-leap of light-emitting diode (LED) technology in terms of higher efficacy and economical production. Here, we report on ZnO radial p–n junction-based light emitting diodes prepared by full metalorganic chemical vapour deposition (MOCVD) with hydrogen-assisted p-type doping approach. The p-type ZnO(P) thin films were prepared by MOCVD with the precursors of dimethylzinc, tert-butanol, and tertiarybutylphosphine. Controlling the precursor flow for dopant results in the systematic change of doping concentration, Hall mobility, and electrical conductivity. Moreover, the approach of hydrogen-assisted phosphorous doping in ZnO expands the understanding of doping behaviour in ZnO.more » Ultraviolet and visible electroluminescence of ZnO radial p–n junction was demonstrated through a combination of position-controlled nano/microwire and crystalline p-type ZnO(P) radial shell growth on the wires. Lastly, the reported research opens a pathway of realisation of production-compatible ZnO p–n junction LEDs.« less

Energy transfer mechanism and optoelectronic properties of (PFO/TiO2)/Fluorol 7GA nanocomposite thin films

NASA Astrophysics Data System (ADS)

Al-Asbahi, Bandar Ali

2017-10-01

Energy transfer between poly (9,9'-di-n-octylfluorenyl-2,7-diyl) (PFO) as a donor in presence of TiO2 nanoparticles (NPs) and Fluorol 7GA as an acceptor with different weight ratios has been investigated by steady-state emission measurements. Based on the absorption and fluorescence measurements, the energy transfer properties, such as quenching rate constant (kSV), energy transfer rate constant (kET), quantum yield (ϕDA), and lifetime (τDA), of the donor in the presence of the acceptor, energy transfer probability (PDA), energy transfer efficiency (η), energy transfer time (τET), and critical distance of the energy transfer (Ro) were calculated. Förster-type energy transfer between the excited donor and ground-state acceptor molecules was the dominant mechanism responsible for the energy transfer as evidenced by large values of kSV, kET, and Ro. Moreover, these composite materials were employed as an emissive layer in organic light-emitting diodes (OLEDs). Additionally, the optoelectronic properties of OLEDs were investigated in terms of current density-voltage characteristics and electroluminescence spectra.

Single crystalline ZnO radial homojunction light-emitting diodes fabricated by metalorganic chemical vapour deposition

DOE PAGES

Yoo, Jinkyoung; Ahmed, Towfiq; Tang, Wei; ...

2017-09-05

ZnO radial p–n junction architecture has the potential for forward-leap of light-emitting diode (LED) technology in terms of higher efficacy and economical production. Here, we report on ZnO radial p–n junction-based light emitting diodes prepared by full metalorganic chemical vapour deposition (MOCVD) with hydrogen-assisted p-type doping approach. The p-type ZnO(P) thin films were prepared by MOCVD with the precursors of dimethylzinc, tert-butanol, and tertiarybutylphosphine. Controlling the precursor flow for dopant results in the systematic change of doping concentration, Hall mobility, and electrical conductivity. Moreover, the approach of hydrogen-assisted phosphorous doping in ZnO expands the understanding of doping behaviour in ZnO.more » Ultraviolet and visible electroluminescence of ZnO radial p–n junction was demonstrated through a combination of position-controlled nano/microwire and crystalline p-type ZnO(P) radial shell growth on the wires. Lastly, the reported research opens a pathway of realisation of production-compatible ZnO p–n junction LEDs.« less

Fully Printed Flexible and Stretchable Electronics

NASA Astrophysics Data System (ADS)

Zhang, Suoming

Through this thesis proposal, the author has demonstrated series of flexible or stretchable sensors including strain gauge, pressure sensors, display arrays, thin film transistors and photodetectors fabricated by a direct printing process. By adopting the novel serpentine configuration with conventional non-stretchable materials silver nanoparticles, the fully printed stretchable devices are successfully fabricated on elastomeric substrate with the demonstration of stretchable conductors that can maintain the electrical properties under strain and the strain gauge, which could be used to measure the strain in desired locations and also to monitor individual person's finger motion. And by investigating the intrinsic stretchable materials silver nanowires (AgNWs) with the conventional configuration, the fully printed stretchable conductors are achieved on various substrates including Si, glass, Polyimide, Polydimethylsiloxane (PDMS) and Very High Bond (VHB) tape with the illustration of the capacitive pressure sensor and stretchable electroluminescent displays. In addition, intrinsically stretchable thin-film transistors (TFTs) and integrated logic circuits are directly printed on elastomeric PDMS substrates. The printed devices utilize carbon nanotubes and a type of hybrid gate dielectric comprising PDMS and barium titanate (BaTiO3) nanoparticles. The BaTiO3/PDMS composite simultaneously provides high dielectric constant, superior stretchability, low leakage, as well as good printability and compatibility with the elastomeric substrate. Both TFTs and logic circuits can be stretched beyond 50% strain along either channel length or channel width directions for thousands of cycles while showing no significant degradation in electrical performance. Finally, by applying the SWNTs as the channel layer of the thin film transistor, we successfully fabricate the fully printed flexible photodetector which exhibits good electrical characteristics and the transistors exhibit good reliability under bending conditions owing to the ultrathin polyimide substrate as well as the superior mechanical flexibility of the gate dielectric and carbon nanotube network. Furthermore, we have demonstrated that by using two types of SWCNT samples with different optical absorption characteristics, the photoresponse exhibits unique wavelength selectivity, as manifested by the good correlation between the responsive wavelengths of the devices with the absorption peaks of the corresponding carbon nanotubes. All the proposed materials above together with the unique direct printing process may offer an entry into more sophisticated flexible or stretchable electronic systems with monolithically integrated sensors, actuators, and displays for real life applications.

Radiation damage to amorphous carbon thin films irradiated by multiple 46.9 nm laser shots below the single-shot damage threshold

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

Juha, L.; Hajkova, V.; Vorlicek, V.

2009-05-01

High-surface-quality amorphous carbon (a-C) optical coatings with a thickness of 45 nm, deposited by magnetron sputtering on a silicon substrate, were irradiated by the focused beam of capillary-discharge Ne-like Ar extreme ultraviolet laser (CDL=capillary-discharge laser; XUV=extreme ultraviolet, i.e., wavelengths below 100 nm). The laser wavelength and pulse duration were 46.9 nm and 1.7 ns, respectively. The laser beam was focused onto the sample surface by a spherical Sc/Si multilayer mirror with a total reflectivity of about 30%. The laser pulse energy was varied from 0.4 to 40 muJ on the sample surface. The irradiation was carried out at five fluencemore » levels between 0.1 and 10 J/cm{sup 2}, accumulating five different series of shots, i.e., 1, 5, 10, 20, and 40. The damage to the a-C thin layer was investigated by atomic force microscopy (AFM) and Nomarski differential interference contrast (DIC) optical microscopy. The dependence of the single-shot-damaged area on pulse energy makes it possible to determine a beam spot diameter in the focus. Its value was found to be equal to 23.3+-3.0 mum using AFM data, assuming the beam to have a Gaussian profile. Such a plot can also be used for a determination of single-shot damage threshold in a-C. A single-shot threshold value of 1.1 J/cm{sup 2} was found. Investigating the consequences of the multiple-shot exposure, it has been found that an accumulation of 10, 20, and 40 shots at a fluence of 0.5 J/cm{sup 2}, i.e., below the single-shot damage threshold, causes irreversible changes of thin a-C layers, which can be registered by both the AFM and the DIC microscopy. In the center of the damaged area, AFM shows a-C removal to a maximum depth of 0.3, 1.2, and 1.5 nm for 10-, 20- and 40-shot exposure, respectively. Raman microprobe analysis does not indicate any change in the structure of the remaining a-C material. The erosive behavior reported here contrasts with the material expansion observed earlier [L. Juha et al., Proc. SPIE 5917, 91 (2005)] on an a-C sample irradiated by a large number of femtosecond pulses of XUV high-order harmonics.« less

Ab Initio Study of Interfacial Structure Transformation of Amorphous Carbon Catalyzed by Ti, Cr, and W Transition Layers.

PubMed

Li, Xiaowei; Li, Lei; Zhang, Dong; Wang, Aiying

2017-11-29

Amorphous carbon (a-C) films composited with transition layers exhibit the desirable improvement of adhesion strength between films and substrate, but the further understanding on the interfacial structure transformation of a-C structure induced by transition layers is still lacked. In this paper, using ab initio calculations, we comparatively studied the interfacial structure between Ti, Cr, or W transition layers and a-C film from the atomic scale, and demonstrated that the addition of Ti, Cr, or W catalyzed the graphitic transformation of a-C structure at different levels, which provided the theoretical guidance for designing a multilayer nanocomposite film for renewed application.

Investigation of coercivity for electroplated Fe-Ni thick films

NASA Astrophysics Data System (ADS)

Yanai, T.; Eguchi, K.; Koda, K.; Kaji, J.; Aramaki, H.; Takashima, K.; Nakano, M.; Fukunaga, H.

2018-05-01

We have already reported Fe-Ni firms with good soft magnetic properties prepared by using an electroplating method. In our previous studies, we prepared the Fe-Ni films from citric-acid-based baths (CA-baths) and ammonium-chloride-based ones (AC-baths), and confirmed that the coercivity for the AC-baths was lower than that for the CA-baths. In the present study, we investigated reasons for the lower coercivity for the AC-baths to further improve the soft magnetic properties. From an observation of magnetic domains of the Fe22Ni78 films, we found that Fe22Ni78 film for AC-bath had a magnetic anisotropy in the width direction, and also found that the coercivity in the width direction was lower than the longitudinal one for the AC-bath. As an annealing for a stress relaxation in the films reduced the difference in the coercivity, we considered that the anisotropy is attributed to the magneto-elastic effect.

Optimization of high quality Cu2ZnSnS4 thin film by low cost and environment friendly sol-gel technique for thin film solar cells applications

NASA Astrophysics Data System (ADS)

Chaudhari, J. J.; Joshi, U. S.

2018-05-01

In this study kesterite Cu2ZnSnS4 (CZTS) thin films suitable for absorber layer in thin film solar cells (TFSCs) were successfully fabricated on glass substrate by sol-gel method. The effects of complexing agent on formation of CZTS thin films have been investigated. X-ray diffraction (XRD) analysis confirms formation of polycrystalline CZTS thin films with single phase kesterite structure. XRD and Raman spectroscopy analysis of CZTS thin films with optimized concentration of complexing agent confirmed formation of kesterite phase in CZTS thin films. The direct optical band gap energy of CZTS thin films is found to decrease from 1.82 to 1.50 eV with increase of concentration of complexing agent triethanolamine. Morphological analysis of CZTS thin films shows smooth, uniform and densely packed CZTS grains and increase in the grain size with increase of concentration of complexing agent. Hall measurements revealed that concentration of charge carrier increases and resistivity decreases in CZTS thin films as amount of complexing agent increases.

Thin film cell development workshop report

NASA Technical Reports Server (NTRS)

Woodyard, James R.

1991-01-01

The Thin Film Development Workshop provided an opportunity for those interested in space applications of thin film cells to debate several topics. The unique characteristics of thin film cells as well as a number of other issues were covered during the discussions. The potential of thin film cells, key research and development issues, manufacturing issues, radiation damage, substrates, and space qualification of thin film cells were discussed.

Composite polymeric film and method for its use in installing a very-thin polymeric film in a device

DOEpatents

Duchane, D.V.; Barthell, B.L.

1982-04-26

A composite polymeric film and a method for its use in forming and installing a very thin (< 10 ..mu..m) polymeric film are disclosed. The composite film consists of a thin film layer and a backing layer. The backing layer is soluble in a solvent in which the thin film layer is not soluble. In accordance with the method, the composite film is installed in a device in the same position in which it is sought to finally emplace the thin film. The backing layer is then selectiely dissolved in the solvent to leave the insoluble thin film layer as an unbacked film. The method permits a very thin film to e successfully installed in devices where the fragility of the film would preclude handling and installation by conventional methods.

Composite polymeric film and method for its use in installing a very thin polymeric film in a device

DOEpatents

Duchane, David V.; Barthell, Barry L.

1984-01-01

A composite polymeric film and a method for its use in forming and installing a very thin (<10 .mu.m) polymeric film are disclosed. The composite film consists of a thin film layer and a backing layer. The backing layer is soluble in a solvent in which the thin film layer is not soluble. In accordance with the method, the composite film is installed in a device in the same position in which it is sought to finally emplace the thin film. The backing layer is then selectively dissolved in the solvent to leave the insoluble thin film layer as an unbacked film. The method permits a very thin film to be successfully installed in devices where the fragility of the film would preclude handling and installation by conventional methods.

Mechanical design of thin-film diamond crystal mounting apparatus with optimized thermal contact and crystal strain for coherence preservation x-ray optics

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

Shu, Deming; Shvydko, Yury; Stoupin, Stanislav

A method and mechanical design for a thin-film diamond crystal mounting apparatus for coherence preservation x-ray optics with optimized thermal contact and minimized crystal strain are provided. The novel thin-film diamond crystal mounting apparatus mounts a thin-film diamond crystal supported by a thick chemical vapor deposition (CVD) diamond film spacer with a thickness slightly thicker than the thin-film diamond crystal, and two groups of thin film thermal conductors, such as thin CVD diamond film thermal conductor groups separated by the thick CVD diamond spacer. The two groups of thin CVD film thermal conductors provide thermal conducting interface media with themore » thin-film diamond crystal. A piezoelectric actuator is integrated into a flexural clamping mechanism generating clamping force from zero to an optimal level.« less

Tunable Optical Polymer Systems (TOPS)

DTIC Science & Technology

2001-05-01

pixelation o1 displays is done. One team member has combined this work with self-assembling layers so that it is possible to make three-dimensional...I THERMOCHROMISM I ELECTROCHEMILUMINESCENCE (ECL) I MAGNETOCHROMISM I TUNABLE ELECTROLUMINESCENCE (EL) PROTONIC BAND GAP (PBG) SELECTIVE...via Selective Reflection • Chiral-nematic liquid crystalline film as a helical stack of quasinematic layers , illustrated below with a LH structure

Efficient luminescent solar cells based on tailored mixed-cation perovskites

PubMed Central

Bi, Dongqin; Tress, Wolfgang; Dar, M. Ibrahim; Gao, Peng; Luo, Jingshan; Renevier, Clémentine; Schenk, Kurt; Abate, Antonio; Giordano, Fabrizio; Correa Baena, Juan-Pablo; Decoppet, Jean-David; Zakeeruddin, Shaik Mohammed; Nazeeruddin, Mohammad Khaja; Grätzel, Michael; Hagfeldt, Anders

2016-01-01

We report on a new metal halide perovskite photovoltaic cell that exhibits both very high solar-to-electric power-conversion efficiency and intense electroluminescence. We produce the perovskite films in a single step from a solution containing a mixture of FAI, PbI2, MABr, and PbBr2 (where FA stands for formamidinium cations and MA stands for methylammonium cations). Using mesoporous TiO2 and Spiro-OMeTAD as electron- and hole-specific contacts, respectively, we fabricate perovskite solar cells that achieve a maximum power-conversion efficiency of 20.8% for a PbI2/FAI molar ratio of 1.05 in the precursor solution. Rietveld analysis of x-ray diffraction data reveals that the excess PbI2 content incorporated into such a film is about 3 weight percent. Time-resolved photoluminescence decay measurements show that the small excess of PbI2 suppresses nonradiative charge carrier recombination. This in turn augments the external electroluminescence quantum efficiency to values of about 0.5%, a record for perovskite photovoltaics approaching that of the best silicon solar cells. Correspondingly, the open-circuit photovoltage reaches 1.18 V under AM 1.5 sunlight. PMID:26767196

Frequency Dependence of Low-Voltage Electrowetting Investigated by Impedance Spectroscopy.

PubMed

Li, Ying-Jia; Cahill, Brian P

2017-11-14

An electrowetting-on-dielectric (EWOD) electrode was developed that facilitates the use of low alternating voltages (≤5 V AC ). This allows online investigation of the frequency dependence of electrowetting by means of impedance spectroscopy. The EWOD electrode is based on a dielectric bilayer consisting of an anodic tantalum pentoxide (Ta 2 O 5 ) thin film (d = 59.35 nm) with a high relative permittivity (ε d = 26.3) and a self-assembled hydrophobic silane monolayer. The frequency dependence of electrowetting was studied using an aqueous μL-sized sessile droplet on the planar EWOD electrode in oil. Experiments using electrochemical impedance spectroscopy and optical imaging indicate the frequency dependence of all three variables in the Young-Lippmann equation: the voltage drop across the dielectric layers, capacitance per unit area, and contact angle under voltage. The electrowetting behavior induced by AC voltages is shown to be well described by the Young-Lippmann equation for AC applications below a frequency threshold. Moreover, the dielectric layers act as a capacitor and the stored electrostatic potential energy is revealed to only partially contribute to the electrowetting.

Permanent laser conditioning of thin film optical materials

DOEpatents

Wolfe, C. Robert; Kozlowski, Mark R.; Campbell, John H.; Staggs, Michael; Rainer, Frank

1995-01-01

The invention comprises a method for producing optical thin films with a high laser damage threshold and the resulting thin films. The laser damage threshold of the thin films is permanently increased by irradiating the thin films with a fluence below an unconditioned laser damage threshold.

Partial characterization of chayotextle starch-based films added with ascorbic acid encapsulated in resistant starch.

PubMed

Martínez-Ortiz, Miguel A; Vargas-Torres, Apolonio; Román-Gutiérrez, Alma D; Chavarría-Hernández, Norberto; Zamudio-Flores, Paul B; Meza-Nieto, Martín; Palma-Rodríguez, Heidi M

2017-05-01

Chayotextle starch was modified by subjecting it to a dual treatment with acid and heating-cooling cycles. This caused a decrease in the content of amylose, which showed values of 30.22%, 4.80%, 3.27% and 3.57% for native chayotextle starch (NCS), starch modified by acid hydrolysis (CMS), and CMS with one (CMS1AC) and three autoclave cycles (CMS3AC), respectively. The percentage of crystallinity showed an increase of 36.9%-62% for NCS and CMS3AC. The highest content of resistant starch (RS) was observed in CMS3AC (37.05%). The microcapsules were made with CMS3AC due to its higher RS content; the total content of ascorbic acid of the microcapsules was 82.3%. The addition of different concentrations of CMS3AC microcapsules (0%, 2.5%, 6.255% and 12.5%) to chayotextle starch-based films (CSF) increased their tensile strength and elastic modulus. The content of ascorbic acid and RS in CSF was ranged from 0% to 59.4% and from 4.84% to 37.05% in the control film and in the film mixed with CMS3AC microcapsules, respectively. Water vapor permeability (WVP) values decreased with increasing concentrations of microcapsules in the films. Microscopy observations showed that higher concentrations of microcapsules caused agglomerations due their poor distribution in the matrix of the films. Copyright © 2017 Elsevier B.V. All rights reserved.

Unexpected resonant response in [Fe(001)/Cr(001)]10/MgO(001) multilayers in a magnetic field.

PubMed

Aliev, F G; Pryadun, V V; Snoeck, E

2009-01-23

We observed unexpected resonant response in [Fe/Cr]10 multilayers epitaxially grown on MgO(100) substrates which exists only when both ac current and dc magnetic field are simultaneously applied. The magnitude of the resonances is determined by the multilayer magnetization proving their intrinsic character. The reduction of interface epitaxy leads to nonlinear dependence of the magnitude of resonances on the alternating current density. We speculate that the existence of the interface transition zone could facilitate the subatomic vibrations in thin metallic films and multilayers grown on bulk insulating substrates.

Thin Film Photovoltaic Partnership Project | Photovoltaic Research | NREL

Science.gov Websites

Thin Film Photovoltaic Partnership Project Thin Film Photovoltaic Partnership Project NREL's Thin Film Photovoltaic (PV) Partnership Project led R&D on emerging thin-film solar technologies in the National Laboratory developed low-cost transparent encapsulation schemes for CIGS cells that reduced power

Permanent laser conditioning of thin film optical materials

DOEpatents

Wolfe, C.R.; Kozlowski, M.R.; Campbell, J.H.; Staggs, M.; Rainer, F.

1995-12-05

The invention comprises a method for producing optical thin films with a high laser damage threshold and the resulting thin films. The laser damage threshold of the thin films is permanently increased by irradiating the thin films with a fluence below an unconditioned laser damage threshold. 9 figs.

Ordered organic-organic multilayer growth

DOEpatents

Forrest, Stephen R.; Lunt, Richard R.

2016-04-05

An ordered multilayer crystalline organic thin film structure is formed by depositing at least two layers of thin film crystalline organic materials successively wherein the at least two thin film layers are selected to have their surface energies within .+-.50% of each other, and preferably within .+-.15% of each other, whereby every thin film layer within the multilayer crystalline organic thin film structure exhibit a quasi-epitaxial relationship with the adjacent crystalline organic thin film.

Ordered organic-organic multilayer growth

DOEpatents

Forrest, Stephen R; Lunt, Richard R

2015-01-13

An ordered multilayer crystalline organic thin film structure is formed by depositing at least two layers of thin film crystalline organic materials successively wherein the at least two thin film layers are selected to have their surface energies within .+-.50% of each other, and preferably within .+-.15% of each other, whereby every thin film layer within the multilayer crystalline organic thin film structure exhibit a quasi-epitaxial relationship with the adjacent crystalline organic thin film.

Low work function, stable thin films

DOEpatents

Dinh, Long N.; McLean, II, William; Balooch, Mehdi; Fehring, Jr., Edward J.; Schildbach, Marcus A.

2000-01-01

Generation of low work function, stable compound thin films by laser ablation. Compound thin films with low work function can be synthesized by simultaneously laser ablating silicon, for example, and thermal evaporating an alkali metal into an oxygen environment. For example, the compound thin film may be composed of Si/Cs/O. The work functions of the thin films can be varied by changing the silicon/alkali metal/oxygen ratio. Low work functions of the compound thin films deposited on silicon substrates were confirmed by ultraviolet photoelectron spectroscopy (UPS). The compound thin films are stable up to 500.degree. C. as measured by x-ray photoelectron spectroscopy (XPS). Tests have established that for certain chemical compositions and annealing temperatures of the compound thin films, negative electron affinity (NEA) was detected. The low work function, stable compound thin films can be utilized in solar cells, field emission flat panel displays, electron guns, and cold cathode electron guns.

Electroluminescence from single-wall carbon nanotube network transistors.

PubMed

Adam, E; Aguirre, C M; Marty, L; St-Antoine, B C; Meunier, F; Desjardins, P; Ménard, D; Martel, R

2008-08-01

The electroluminescence (EL) properties from single-wall carbon nanotube network field-effect transistors (NNFETs) and small bundle carbon nanotube field effect transistors (CNFETs) are studied using spectroscopy and imaging in the near-infrared (NIR). At room temperature, NNFETs produce broad (approximately 180 meV) and structured NIR spectra, while they are narrower (approximately 80 meV) for CNFETs. EL emission from NNFETs is located in the vicinity of the minority carrier injecting contact (drain) and the spectrum of the emission is red shifted with respect to the corresponding absorption spectrum. A phenomenological model based on a Fermi-Dirac distribution of carriers in the nanotube network reproduces the spectral features observed. This work supports bipolar (electron-hole) current recombination as the main mechanism of emission and highlights the drastic influence of carrier distribution on the optoelectronic properties of carbon nanotube films.

Technological development of cylindrical and flat shaped high energy density capacitors. [using polymeric films

NASA Technical Reports Server (NTRS)

Zelik, J. A.; Parker, R. D.

1977-01-01

Cylindrical wound metallized film capacitors rated 2 micron F 500 VDC that had an energy density greater than 0.3 J/g, and flat flexible metallized film capacitors rated at 2 micron F 500 VDC that had an energy density greater than 0.1 J/g were developed. Polysulfone, polycarbonate, and polyvinylidene fluoride (PVF2) were investigated as dielectrics for the cylindrical units. PVF2 in 6.0 micron m thickness was employed in the final components of both types. Capacitance and dissipation factor measurements were made over the range 25 C to 100 C, and 10 Hz to 10 kHz. No pre-life-test burning was performed, and six of ten cylindrical units survived a 2500 hour AC plus DC lift test. Three of the four failures were infant mortality. All but two of the flat components survived 400 hours. Finished energy densities were 0.104 J/g at 500 V and 0.200 J/g at 700 V, the energy density being limited by the availability of thin PVF2 films.

Low stress polysilicon film and method for producing same

NASA Technical Reports Server (NTRS)

Heuer, Arthur H. (Inventor); Kahn, Harold (Inventor); Yang, Jie (Inventor)

2001-01-01

Multi-layer assemblies of polysilicon thin films having predetermined stress characteristics and techniques for forming such assemblies are disclosed. In particular, a multi-layer assembly of polysilicon thin film may be produced that has a stress level of zero, or substantially so. The multi-layer assemblies comprise at least one constituent thin film having a tensile stress and at least one constituent thin film having a compressive stress. The thin films forming the multi-layer assemblies may be disposed immediately adjacent to one another without the use of intermediate layers between the thin films.

Low stress polysilicon film and method for producing same

NASA Technical Reports Server (NTRS)

Heuer, Arthur H. (Inventor); Kahn, Harold (Inventor); Yang, Jie (Inventor)

2002-01-01

Multi-layer assemblies of polysilicon thin films having predetermined stress characteristics and techniques for forming such assemblies are disclosed. In particular, a multi-layer assembly of polysilicon thin film may be produced that has a stress level of zero, or substantially so. The multi-layer assemblies comprise at least one constituent thin film having a tensile stress and at least one constituent thin film having a compressive stress. The thin films forming the multi-layer assemblies may be disposed immediately adjacent to one another without the use of intermediate layers between the thin films.

The temperature and ion energy dependence of deuterium retention in lithium films

NASA Astrophysics Data System (ADS)

Buzi, Luxherta; Koel, Bruce E.; Skinner, Charles H.

2016-10-01

Lithium conditioning of plasma facing components in magnetic fusion devices has improved plasma performance and lowered hydrogen recycling. For applications of lithium in future high heat flux and long pulse duration machines it is important to understand and parameterize deuterium retention in lithium. This work presents surface science studies of deuterium retention in lithium films as a function of surface temperature, incident deuterium ion energy and flux. Initial experiments are performed on thin (3-30 ML) lithium films deposited on a single crystal molybdenum substrate to avoid effects due to grain boundaries, intrinsic defects and impurities. A monoenergetic and mass-filtered deuterium ion beam was generated in a differentially pumped Colutron ion gun. Auger electron spectroscopy and X-ray photoelectron spectroscopy were used to identify the elemental composition and temperature programmed desorption was used to measure the deuterium retention under the different conditions. Support was provided through DOE Contract Number DE-AC02-09CH11466.

Miniature hybrid microwave IC's using a novel thin-film technology

NASA Astrophysics Data System (ADS)

Eda, Kazuo; Miwa, Tetsuji; Taguchi, Yutaka; Uwano, Tomoki

1990-12-01

A novel thin-film technology for miniature hybrid microwave ICs is presented. All passive components, such as resistors and capacitors, are fully integrated on ordinary alumina ceramic substrates using the thin-film technology with very high yield. The numbers of parts and wiring processes were significantly reduced. This technology was applied to the fabrication of Ku-band solid-state power amplifiers. This thin-film technology offers the following advantages: (1) a very high yield fabrication process of thin-film capacitor having excellent electrical characteristics in the gigahertz range (Q = 230 at 12 GHz) and reliability: (2) two kinds of thin-film resistors having different temperature coefficients of resistivity and a lift-off process to integrate them with thin-film capacitors; and (3) a matching method using the thin-film capacitor.

Self-supporting activated carbon/carbon nanotube/reduced graphene oxide flexible electrode for high performance supercapacitor

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

Li, Xing; Tang, Yao; Song, Junhua

A self-supporting and flexible activated carbon/carbon nanotube/reduced graphene oxide (AC/CNT/RGO) film has been rationally designed for constructing high- performance supercapacitor. The AC/CNT/RGO film is prepared by anchoring the AC particles with a 3D and porous framework built by hierarchically weaving the 1 D CNT and 2D RGO using their intrinsic van der Waals force. The CNT network is beneficial for improving the electronic conductivity of the electrode, while the AC particles could effectively suppress the aggregation of RGO and CNT due to their blocking effect. The synergistic effects among the AC, CNT and RGO validate the AC/CNT/RGO as a promisingmore » electrode for supercapacitor, exhibiting greatly enhanced electrochemical performances in comparison with the pure RGO film, pure CNT film and AC electrode. The AC/CNT/RGO electrode delivers a high specific capacitance of 101 F g-1 at the current density of 0.2 A g-1, offering a maximum energy density of 30.0 W h kg-1 in organic electrolyte at the cut-off voltage range of 0.001~3.0 V. The findings of this work open a new avenue for the design of self-supporting electrodes for the development of flexible and light weight energy storage supercapacitor.« less

Use of UO 2 films for electrochemical studies

NASA Astrophysics Data System (ADS)

Miserque, F.; Gouder, T.; Wegen, D. H.; Bottomley, P. D. W.

2001-10-01

UO 2 films have been prepared by dc reactive sputtering of a uranium metal target in an Ar/O 2 atmosphere. We have used the films deposited on gold substrates as working electrodes for electrochemical investigations as simulating the surfaces of fuel pellets. Film composition was determined by photoelectron spectroscopy (XPS and UPS) and X-ray diffraction (XRD). The oxide stoichiometry as a function of deposition conditions was determined and the appropriate conditions for UO 2.0 formation established. AC impedance and cyclic voltammetry measurements were performed. A double RC electrical equivalent circuit was used to fit the data from impedance measurements, similar to those used in unirradiated UO 2 or spent fuel pellets. However due to the porosity or adhesion defects on the thin films that permitted a direct contact between the solution and the gold substrate, we were obliged to add a contribution simulating the water-gold system. Cyclic voltammetry measurements show the influence of pH on the dissolution mechanism. Alkaline solutions permit the formation of an oxidised layer (UO 2.33) which is not present in the acidic solutions. In both pH=2 and pH=6 solutions, a U VI species layer is formed.

Competition between dewetting and cross-linking in poly(N-vinylpyrrolidone)/polystyrene bilayer films.

PubMed

Telford, Andrew M; Thickett, Stuart C; James, Michael; Neto, Chiara

2011-12-06

We investigated the dewetting of metastable poly(N-vinylpyrrolidone) (PNVP) thin films (45 nm) on top of polystyrene (PS) thin films (58 nm) as a function of annealing temperature and molecular weight of PS (96 and 6850 kg/mol). We focused on the competition between dewetting, occurring as a result of unfavorable intermolecular interactions at the PNVP/PS interface, and spontaneous cross-linking of PNVP, occurring during thermal annealing, as we recently reported (Telford, A. M.; James, M.; Meagher, L.; Neto, C. ACS Appl. Mater. Interfaces 2010, 2, 2399-2408). Using optical microscopy, we studied how the dewetting morphology and dynamics at different temperatures depended on the relative viscosity of the top PNVP film, which increased with cross-linking time, and of the bottom PS film. In the PNVP/PS96K system, cross-linking dominated over dewetting at temperatures below 180 °C, reducing drastically nucleated hole density and their maximum size, while above 180 °C the two processes reversed, with complete dewetting occurring at 200 °C. On the other hand, the PNVP/PS6850K system never achieved advanced dewetting stages as the dewetting was slower than cross-linking in the investigated temperature range. In both systems, dewetting of the PNVP films could be avoided altogether by thermally annealing the bilayers at temperatures where cross-linking dominated. The cross-linking was characterized quantitatively using neutron reflectometry, which indicated shrinkage and densification of the PNVP film, and qualitatively through selective removal of the bottom PS film. A simple model accounting for progressive cross-linking during the dewetting process predicted well the observed hole growth profiles and produced estimates of the PNVP cross-linking rate coefficients and of the activation energy of the process, in good agreement with literature values for similar systems. © 2011 American Chemical Society

Development of nanostructured ZnO thin film via electrohydrodynamic atomization technique and its photoconductivity characteristics.

PubMed

Duraisamy, Navaneethan; Kwon, Ki Rin; Jo, Jeongdai; Choi, Kyung-Hyun

2014-08-01

This article presents the non-vacuum technique for the preparation of nanostructured zinc oxide (ZnO) thin film on glass substrate through electrohydrodynamic atomization (EHDA) technique. The detailed process parameters for achieving homogeneous ZnO thin films are clearly discussed. The crystallinity and surface morphology of ZnO thin film are investigated by X-ray diffraction and field emission scanning electron microscopy. The result shows that the deposited ZnO thin film is oriented in the wurtzite phase with void free surface morphology. The surface roughness of deposited ZnO thin film is found to be ~17.8 nm. The optical properties of nanostructured ZnO thin films show the average transmittance is about 90% in the visible region and the energy band gap is found to be 3.17 eV. The surface chemistry and purity of deposited ZnO thin films are analyzed by fourier transform infrared and X-ray photoelectron spectroscopy, conforming the presence of Zn-O in the deposited thin films without any organic moiety. The photocurrent measurement of nanostructured ZnO thin film is examined in the presence of UV light illumination with wavelength of 365 nm. These results suggest that the deposited nanostructured ZnO thin film through EHDA technique possess promising applications in the near future.

Chemical bath deposited and dip coating deposited CuS thin films - Structure, Raman spectroscopy and surface study

NASA Astrophysics Data System (ADS)

Tailor, Jiten P.; Khimani, Ankurkumar J.; Chaki, Sunil H.

2018-05-01

The crystal structure, Raman spectroscopy and surface microtopography study on as-deposited CuS thin films were carried out. Thin films deposited by two techniques of solution growth were studied. The thin films used in the present study were deposited by chemical bath deposition (CBD) and dip coating deposition techniques. The X-ray diffraction (XRD) analysis of both the as-deposited thin films showed that both the films possess covellite phase of CuS and hexagonal unit cell structure. The determined lattice parameters of both the films are in agreement with the standard JCPDS as well as reported data. The crystallite size determined by Scherrer's equation and Hall-Williamsons relation using XRD data for both the as-deposited thin films showed that the respective values were in agreement with each other. The ambient Raman spectroscopy of both the as-deposited thin films showed major emission peaks at 474 cm-1 and a minor emmision peaks at 265 cm-1. The observed Raman peaks matched with the covellite phase of CuS. The atomic force microscopy of both the as-deposited thin films surfaces showed dip coating thin film to be less rough compared to CBD deposited thin film. All the obtained results are presented and deliberated in details.

Synthesis and characterization of cobalt doped nickel oxide thin films by spray pyrolysis method

NASA Astrophysics Data System (ADS)

Sathisha, D.; Naik, K. Gopalakrishna

2018-05-01

Cobalt (Co) doped nickel oxide (NiO) thin films were deposited on glass substrates at a temperature of about 400 °C by spray pyrolysis method. The effect of Co doping concentration on structural, optical and compositional properties of NiO thin films was investigated. X-ray diffraction result shows that the deposited thin films are polycrystalline in nature. Surface morphologies of the deposited thin films were observed by FESEM and AFM. EDS spectra showed the incorporation of Co dopants in NiO thin films. Optical properties of the grown thin films were characterized by UV-visible spectroscopy. It was found that the optical band gap energy and transmittance of the films decrease with increasing Co doping concentration.

Insight into the epitaxial encapsulation of Pd catalysts in an oriented metalloporphyrin network thin film for tandem catalysis.

PubMed

Vohra, M Ismail; Li, De-Jing; Gu, Zhi-Gang; Zhang, Jian

2017-06-14

A palladium catalyst (Pd-Cs) encapsulated metalloporphyrin network PIZA-1 thin film with bifunctional properties has been developed through a modified epitaxial layer-by-layer encapsulation approach. Combining the oxidation activity of Pd-Cs and the acetalization activity of the Lewis acidic sites in the PIZA-1 thin film, this bifunctional catalyst of the Pd-Cs@PIZA-1 thin film exhibits a good catalytic activity in a one-pot tandem oxidation-acetalization reaction. Furthermore, the surface components can be controlled by ending the top layer with different precursors in the thin film preparation procedures. The catalytic performances of these thin films with different surface composites were studied under the same conditions, which showed different reaction conversions. The result revealed that the surface component can influence the catalytic performance of the thin films. This epitaxial encapsulation offers a good understanding of the tandem catalysis for thin film materials and provides useful guidance to develop new thin film materials with catalytic properties.

Generation of low work function, stable compound thin films by laser ablation

DOEpatents

Dinh, Long N.; McLean, II, William; Balooch, Mehdi; Fehring, Jr., Edward J.; Schildbach, Marcus A.

2001-01-01

Generation of low work function, stable compound thin films by laser ablation. Compound thin films with low work function can be synthesized by simultaneously laser ablating silicon, for example, and thermal evaporating an alkali metal into an oxygen environment. For example, the compound thin film may be composed of Si/Cs/O. The work functions of the thin films can be varied by changing the silicon/alkali metal/oxygen ratio. Low work functions of the compound thin films deposited on silicon substrates were confirmed by ultraviolet photoelectron spectroscopy (UPS). The compound thin films are stable up to 500.degree. C. as measured by x-ray photoelectron spectroscopy (XPS). Tests have established that for certain chemical compositions and annealing temperatures of the compound thin films, negative electron affinity (NEA) was detected. The low work function, stable compound thin films can be utilized in solar cells, field emission flat panel displays, electron guns, and cold cathode electron guns.

Exciting transition metal doped dilute magnetic thin films: MgO:Er and ZnO:Er

NASA Astrophysics Data System (ADS)

Ćakıcı, T.; Sarıtaş, S.; Muǧlu, G. Merhan; Yıldırım, M.

2017-02-01

Erbium doped MgO and doped ZnO thin films have reasonably important properties applications in spintronic devices. These films were synthesized on glass substrates by Chemical Spray Pyrolysis (CSP) method. In the literature there has been almost no report on preparation of MgO:Er dilute magnetic thin films by means of CSP. Because doped thin films show different magnetic behaviors, depending upon the type of magnetic material ions, concentration of them, synthesis route and experimental conditions, synthesized MgO:Er and ZnO:Er films were compared to thin film properties. Optical analyses of the synthesized thin films were examined spectral absorption and transmittance measurements by UV-Vis double beam spectrophotometer technique. Structural analysis of the thin films was examined by using XRD, Raman Analysis, FE-SEM, EDX and AFM techniques. Also, magnetic properties of the MgO:Er and ZnO:Er films were investigated by vibrating sample magnetometer (VSM) which show that diamagnetic behavior of the MgO:Er thin film and ferromagnetic (FM) behavior of the ZnO:Er film were is formed.

Tuning emission color of electroluminescence from two organic interfacial exciplexes by modulating the thickness of middle gadolinium complex layer

NASA Astrophysics Data System (ADS)

Li, Mingtao; Li, Wenlian; Chen, Lili; Kong, Zhiguo; Chu, Bei; Li, Bin; Hu, Zhizhi; Zhang, Zhiqiang

2006-02-01

Electroluminescent colors of organic light-emitting diodes (OLEDs) can be tuned by modulating the thickness of gadolinium (Gd) complex layer sandwiched between an electron-transporting layer (ETL) and a hole-transporting layer (HTL). The emission colors, which originate from the two interfacial exciplexes simultaneously, can be tuned from green to orange by increasing the thickness of the Gd-complex layer. The atom force microscope images have proved that there are many gaps in the thinner Gd-complex layers. Therefore, besides the exciplex formation between Gd complex and HTL, the exciplex between ETL and HTL is also formed. The results demonstrate that a simple way of color tuning can be realized by inserting a thin layer of color tuning material between HTL with lower ionization potentials and ETL with higher electron affinities. Moreover, photovoltaic device and white OLED based on the two exciplexes are also discussed.

Color tunable electroluminescence and resistance switching from a ZnO-nanorod-TaOx-p-GaN heterojunction.

PubMed

Zhao, J L; Teo, K L; Zheng, K; Sun, X W

2016-03-18

Well-aligned ZnO nanorods have been prepared on p-GaN-sapphire using a vapor phase transport (VPT) technique. A thin sputtered layer of TaOx is employed as the intermediate layer and an n-ZnO-TaOx-p-GaN heterojunction device has been achieved. The current transport of the heterojunction exhibited a typical resistance switching behavior, which originated from the filament forming and breaking in the TaOx layer. Color controllable electroluminescence (EL) was observed from the biased heterojunction at room temperature. Bluish-white wide band emission is achieved from the forward biased device in both the high resistance and low resistance states, while red emission can only be observed for the reverse biased device in the low resistance state. The correlation between the EL and resistance switching has been analyzed in-depth based on the interface band diagram of the heterojunction.

Thin-film optical initiator

DOEpatents

Erickson, Kenneth L.

2001-01-01

A thin-film optical initiator having an inert, transparent substrate, a reactive thin film, which can be either an explosive or a pyrotechnic, and a reflective thin film. The resultant thin-film optical initiator system also comprises a fiber-optic cable connected to a low-energy laser source, an output charge, and an initiator housing. The reactive thin film, which may contain very thin embedded layers or be a co-deposit of a light-absorbing material such as carbon, absorbs the incident laser light, is volumetrically heated, and explodes against the output charge, imparting about 5 to 20 times more energy than in the incident laser pulse.

Fabrication and etching processes of silicon-based PZT thin films

NASA Astrophysics Data System (ADS)

Zhao, Hongjin; Liu, Yanxiang; Liu, Jianshe; Ren, Tian-Ling; Liu, Li-Tian; Li, Zhijian

2001-09-01

Lead-zirconate-titanate (PZT) thin films on silicon were prepared by a sol-gel method. Phase characterization and crystal orientation of the films were investigated by x-ray diffraction analysis (XRD). It was shown that the PZT thin films had a perfect perovskite structure after annealed at a low temperature of 600 degrees C. PZT thin films were chemically etched using HCl/HF solution through typical semiconductor lithographic process, and the etching condition was optimized. The scanning electron microscopy results indicated that the PZT thin film etching problem was well solved for the applications of PZT thin film devices.

Investigations of Si Thin Films as Anode of Lithium-Ion Batteries

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

Wu, Qingliu; Shi, Bing; Bareño, Javier

Amorphous silicon thin films having various thicknesses were investigated as a negative electrode material for lithium-ion batteries. Electrochemical characterization of the 20 nm thick thin silicon film revealed a very low first cycle Coulombic efficiency, which can be attributed to the silicon oxide layer formed on both the surface of the as-deposited Si thin film and the interface between the Si and the substrate. Among the investigated films, the 100 nm Si thin film demonstrated the best performance in terms of first cycle efficiency and cycle life. Observations from scanning electron microscopy demonstrated that the generation of cracks was inevitablemore » in the cycled Si thin films, even as the thickness of the film was as little as 20 nm, which was not predicted by previous modeling work. However, the cycling performance of the 20 and 100 nm silicon thin films was not detrimentally affected by these cracks. The poor capacity retention of the 1 mu m silicon thin film was attributed to the delamination.« less

Polypyrrole-coated LiCoO2 nanocomposite with enhanced electrochemical properties at high voltage for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Cao, Jingchao; Hu, Guorong; Peng, Zhongdong; Du, Ke; Cao, Yanbing

2015-05-01

A conducting polypyrrole thin film is successfully coated onto the surface of LiCoO2 by a simple chemical polymerization method. The structure and morphology of pristine LiCoO2 and PPy-coated LiCoO2 are investigated by the techniques of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). Energy dispersive X-ray spectroscopy (EDXS), Fourier transform infrared spectrometry (FTIR) and thermogravimetric analysis (TGA) further demonstrate the existence of PPy. The electrochemical properties of the composites are investigated by galvanostatic charge-discharge test and AC impedance measurements, which show that the conductive PPy film on the surface significantly decrease the charge-transfer resistance of LiCoO2. The PPy-coated LiCoO2 exhibits a good electrochemical performance, showing initial discharge capacity of 182 mAh g-1 and retains 94.3% after 170 cycles. However, the retention of pristine LiCoO2 is only 83.5%. The rate capability results show that the reversible capacity retention (10C/0.2C) of LiCoO2 increases from 52.4% to 80.1% after being coated with PPy. The continuously coated thin PPy film is just like a capsule shell, which can protect the core (LiCoO2) from corrosion causing by the HF attacking and greatly reduce the dissolution of Co into electrolyte.

Low-Cost Detection of Thin Film Stress during Fabrication

NASA Technical Reports Server (NTRS)

Nabors, Sammy A.

2015-01-01

NASA's Marshall Space Flight Center has developed a simple, cost-effective optical method for thin film stress measurements during growth and/or subsequent annealing processes. Stress arising in thin film fabrication presents production challenges for electronic devices, sensors, and optical coatings; it can lead to substrate distortion and deformation, impacting the performance of thin film products. NASA's technique measures in-situ stress using a simple, noncontact fiber optic probe in the thin film vacuum deposition chamber. This enables real-time monitoring of stress during the fabrication process and allows for efficient control of deposition process parameters. By modifying process parameters in real time during fabrication, thin film stress can be optimized or controlled, improving thin film product performance.

Compositional ratio effect on the surface characteristics of CuZn thin films

NASA Astrophysics Data System (ADS)

Choi, Ahrom; Park, Juyun; Kang, Yujin; Lee, Seokhee; Kang, Yong-Cheol

2018-05-01

CuZn thin films were fabricated by RF co-sputtering method on p-type Si(100) wafer with various RF powers applied on metallic Cu and Zn targets. This paper aimed to determine the morphological, chemical, and electrical properties of the deposited CuZn thin films by utilizing a surface profiler, atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), UV photoelectron spectroscopy (UPS), and a 4-point probe. The thickness of the thin films was fixed at 200 ± 8 nm and the roughness of the thin films containing Cu was smaller than pure Zn thin films. XRD studies confirmed that the preferred phase changed, and this tendency is dependent on the ratio of Cu to Zn. AES spectra indicate that the obtained thin films consisted of Cu and Zn. The high resolution XPS spectra indicate that as the content of Cu increased, the intensities of Zn2+ decreased. The work function of CuZn thin films increased from 4.87 to 5.36 eV. The conductivity of CuZn alloy thin films was higher than pure metallic thin films.

A thin film nitinol heart valve.

PubMed

Stepan, Lenka L; Levi, Daniel S; Carman, Gregory P

2005-11-01

In order to create a less thrombogenic heart valve with improved longevity, a prosthetic heart valve was developed using thin film nitinol (NiTi). A "butterfly" valve was constructed using a single, elliptical piece of thin film NiTi and a scaffold made from Teflon tubing and NiTi wire. Flow tests and pressure readings across the valve were performed in vitro in a pulsatile flow loop. Bio-corrosion experiments were conducted on untreated and passivated thin film nitinol. To determine the material's in vivo biocompatibility, thin film nitinol was implanted in pigs using stents covered with thin film NiTi. Flow rates and pressure tracings across the valve were comparable to those through a commercially available 19 mm Perimount Edwards tissue valve. No signs of corrosion were present on thin film nitinol samples after immersion in Hank's solution for one month. Finally, organ and tissue samples explanted from four pigs at 2, 3, 4, and 6 weeks after thin film NiTi implantation appeared without disease, and the thin film nitinol itself was without thrombus formation. Although long term testing is still necessary, thin film NiTi may be very well suited for use in artificial heart valves.

The effect of thin film morphology on the electrochemical performance of Cu-Sn anode for lithium rechargeable batteries.

PubMed

Polat, B D; Keleş, O

2014-05-01

We investigate the anode performance of non ordered and ordered nanostructured Cu-Sn thin films deposited via electron beam deposition technique. The ordered nanostructured Cu-Sn thin film having nano-porosities was fabricated using an oblique (co)deposition technique. Our results showed that the nano structured Cu-Sn thin film containing Cu-Sn nanorods had higher initial anodic capacity (790 mA h g(-)) than that of the non ordered thin film (330 mA h g(-)). But the capacity of the ordered nanostructured Cu-Sn thin film diminished after the first cycle and a steady state capacity value around 300 mA h g(-) is sustainable in following up to 80th cycle, which is attributed to the composition and morphology of the thin film. The presence of copper containing Sn nanorods leading to form nano-porosities as interstitial spaces among them, enhanced lithium ions movement within thin film and increased the thin film tolerance against the stress generated because of the drastic volume change occurred during lithiation-delithiation processes; hence, homogenously distributed porosities increased the cycle life of the thin film.

Specific considerations for obtaining appropriate La1-xSrxGa1-yMgyO3-δ thin films using pulsed-laser deposition and its influence on the performance of solid-oxide fuel cells

NASA Astrophysics Data System (ADS)

Hwang, Jaeyeon; Lee, Heon; Lee, Jong-Ho; Yoon, Kyung Joong; Kim, Hyoungchul; Hong, Jongsup; Son, Ji-Won

2015-01-01

To obtain La1-xSrxGa1-yMgyO3-δ (LSGM) thin films with the appropriate properties, pulsed-laser deposition (PLD) is employed, and specific considerations regarding control of the deposition parameters is investigated. It is demonstrated that with a target of stoichiometric composition, appropriate LSGM thin films cannot be produced because of the deviation of the composition from the target to the thin film. Only after adjusting the target composition an LSGM thin film with an appropriate composition and phase can be obtained. The optimized LSGM thin film possesses an electrical conductivity close to that of the bulk LSGM. In contrast, non-optimized thin films do not yield any measurable electrical conductivity. The impact of the optimization of the LSGM thin-film electrolyte on the cell performance is quite significant, in that a solid-oxide fuel cell (SOFC) with an optimized LSGM thin-film electrolyte produces a maximum power density of 1.1 W cm-2 at 600 °C, whereas an SOFC with a non-optimal LSGM thin-film electrolyte is not operable.

Ultrafast Shock Compression Hugoniot Data of beta-CL-20 and TATB Thin Films

NASA Astrophysics Data System (ADS)

Zaug, Joseph; Armstrong, Michael; Grivickas, Paulius; Tappan, Alexander; Kohl, Ian; Rodriguez, Mark; Knepper, Robert; Crowhurst, Jonathan; Stavrou, Elissaios; Bastea, Sorin

2017-06-01

The shock induced initiation threshold of two energetic materials, CL-20 and TATB are remarkably different; CL-20 is a relatively shock sensitive energetic material and TATB is considered an insensitive high explosive (IHE). Here we report ultrafast laser-based shockwave hydrodynamic data on the 100 ps timescale with 10 ps time resolution to further develop density dependent unreacted shock Hugoniot equations of state (UEOS) and to elucidate ultrafast timescale shock initiation processes for these two vastly different HEs. Thin film samples were made by vacuum thermal evaporation of the explosive on a deposited aluminum ablator layer. The deposited explosives were characterized by scanning electron microscopy, surface profilometry, and x-ray diffraction. Our preliminary UEOS results (up range of 1.3 - 1.8 km/s) from shock compressed beta-CL-20 agree reasonably well with extrapolated pseudo-velocities computed from epsilon-CL-20 isothermal diamond-anvil cell EOS measurements. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporati.

Confinement in Melts of Chains with Junction Points, but No Ends

NASA Astrophysics Data System (ADS)

Foster, Mark; He, Qiming; Zhou, Yang; Zhang, Fan; Huang, Chongwen; Narayanan, Suresh

Measurements of surface fluctuations of 4-arm star and ''8-shaped'' analogs of the same polystyrene (PS) chain show that elimination of chain ends is much more important in dictating the fragility in a thin film than is the introduction of a branch point in the molecule. Both the viscosities derived from surface fluctuations and rheological measurements for the 8-shaped PS manifest a lower value than the 4-arm star PS analog, with the discrepancy increasing as the temperature approaches the glass transition temperature, Tg , bulk. Comparison among different chain topologies shows the effect of the number of chain ends and junction point on the viscosity. The viscosity behavior of the 8-shaped PS is quite different from that of the star analog, but similar to that of the simple cycle analog. The fragility of the 8-shaped molecule in the thin film is reduced relative to that in the bulk, manifesting a nanoconfinement effect. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

The role of tortuosity on ion conduction in block copolymer electrolyte thin films

NASA Astrophysics Data System (ADS)

Kambe, Yu; Arges, Christopher G.; Nealey, Paul F.

This talk discusses the role of grain tortuosity on ion conductivity in block copolymer electrolyte (BCE) thin films. In particular, we studied lamellae forming BCEs with both domains oriented perpendicular to the substrate surface and connected directly from one electrode to another - i.e., tortuosity of one. The BCE is composed of ion-conducting, poly(2-vinyl n-methylpyridinium) blocks and non-ionic polystyrene blocks. Prior to creating the BCE, the pristine block copolymer, poly(styrene- b-2-vinyl pyridine), was directly self-assembled (DSA) on topographical or chemical patterns via graphoepitaxy and chemoepitaxy. A chemical vapor infiltration reaction modified the P2VP block into positively charged, fixed quaternary ammonium groups paired with mobile counteranions. The graphoepitaxy process utilized topographical interdigitated gold nanoelectrodes (100s of nanometers spacing between electrodes) created via e-beam lithography. Alternatively, chemical patterns had gold electrodes incorporated into them with 10s to 100s of microns spacing using conventional optical lithography. The interdigitated gold electrodes enabled in-plane ion conductivity measurements of the DSA BCEs to study the role of grain tortuosity on ion conductivity. U.S. Department of Energy Office of Science: Contract No. DE-AC02-06CH11357.

Temperature dependent dielectric properties of Au/ZnO/n-Si heterojuntion

NASA Astrophysics Data System (ADS)

Kocyigit, Adem; Orak, İkram; Turut, Abdulmecit

2018-03-01

Owing to importance of ZnO in electronics, Au/ZnO/n-type Si device was fabricated to investigate its dielectric properties by aid of capacitance-conductance-voltage measurements. While the ZnO thin film layer on the n-type Si was formed by atomic layer deposition (ALD) technique, the rectifying and ohmic contacts were obtained by thermal evaporation. The surface morphology of ZnO thin film was characterized using atomic force microscopy (AFM) to show its compatibility as interfacial layer in the Au/ZnO/n-type Si device. The dielectric properties of the device were examined in terms of dielectric parameters such as dielectric constant (ɛ‧), dielectric loss (ɛ″), loss tangent (tan δ), the real and imaginary parts of electric modulus (M ‧ and M ″) and ac electrical conductivity (σ) depending on applied voltages (from -1 to 2 V) and temperatures (from 140 K to 360 K) ranges. The results have revealed that interfacial polarization and charge carriers are the important parameters to affect the dielectric properties of the device with changing temperature. The device can be used at wide range temperatures for diode applications.

Preparation of nickel oxide thin films at different annealing temperature by sol-gel spin coating method

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

Abdullah, M. A. R., E-mail: ameerridhwan89@gmail.com; Mamat, M. H., E-mail: hafiz-030@yahoo.com; Ismail, A. S., E-mail: kyrin-samaxi@yahoo.com

2016-07-06

Preparation of NiO thin films at different annealing temperature by sol-gel method was conducted to synthesize the quality of the surface thin films. The effects of annealing temperature on the surface topology were systematically investigated. Our studies confirmed that the surface roughness of the thin films was increased whenever annealing temperature was increase. NiO thin films morphology structure analysis was confirmed by field emission scanning electron microscope. Surface roughness of the thin films was investigated by atomic force microscopy.

Thin-film metal coated insulation barrier in a Josephson tunnel junction. [Patent application

DOEpatents

Hawkins, G.A.; Clarke, J.

1975-10-31

A highly stable, durable, and reproducible Josephson tunnel junction consists of a thin-film electrode of a hard superconductor, a thin oxide insulation layer over the electrode constituting a Josephson tunnel junction barrier, a thin-film layer of stabilizing metal over the barrier, and a second thin-film hard superconductive electrode over the stabilizing film. The thin stabilizing metal film is made only thick enough to limit penetration of the electrode material through the insulation layer so as to prevent a superconductive short.

[Spectral emissivity of thin films].

PubMed

Zhong, D

2001-02-01

In this paper, the contribution of multiple reflections in thin film to the spectral emissivity of thin films of low absorption is discussed. The expression of emissivity of thin films derived here is related to the thin film thickness d and the optical constants n(lambda) and k(lambda). It is shown that in the special case d-->infinity the emissivity of thin films is equivalent to that of the bulk material. Realistic numerical and more precise general numerical results for the dependence of the emissivity on d, n(lambda) and k(lambda) are given.

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition.

PubMed

Yoo, Young Jin; Lee, Gil Ju; Jang, Kyung-In; Song, Young Min

2017-08-29

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.  We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.  Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

Effect of Substrate Roughness on Adhesion and Structural Properties of Ti-Ni Shape Memory Alloy Thin Film.

PubMed

Kim, Donghwan; Lee, Hyunsuk; Bae, Joohyeon; Jeong, Hyomin; Choi, Byeongkeun; Nam, Taehyun; Noh, Jungpil

2018-09-01

Ti-Ni shape memory alloy (SMA) thin films are very attractive material for industrial and medical applications such as micro-actuator, micro-sensors, and stents for blood vessels. An important property besides shape memory effect in the application of SMA thin films is the adhesion between the film and the substrate. When using thin films as micro-actuators or micro-sensors in MEMS, the film must be strongly adhered to the substrate. On the other hand, when using SMA thin films in medical devices such as stents, the deposited alloy thin film must be easily separable from the substrate for efficient processing. In this study, we investigated the effect of substrate roughness on the adhesion of Ti-Ni SMA thin films, as well as the structural properties and phase-transformation behavior of the fabricated films. Ti-Ni SMA thin films were deposited onto etched glass substrates with magnetron sputtering. Radio frequency plasma was used for etching the substrate. The adhesion properties were investigated through progressive scratch test. Structural properties of the films were determined via Feld emission scanning electron microscopy, X-ray diffraction measurements (XRD) and Energy-dispersive X-ray spectroscopy analysis. Phase transformation behaviors were observed with differential scanning calorimetry and low temperature-XRD. Ti-Ni SMA thin film deposited onto rough substrate provides higher adhesive strength than smooth substrate. However the roughness of the substrate has no influence on the growth and crystallization of the Ti-Ni SMA thin films.

Effects of high temperature and film thicknesses on the texture evolution in Ag thin films

NASA Astrophysics Data System (ADS)

Eshaghi, F.; Zolanvari, A.

2017-04-01

In situ high-temperature X-ray diffraction techniques were used to study the effect of high temperatures (up to 600°C) on the texture evolution in silver thin films. Ag thin films with different thicknesses of 40, 80, 120 and 160nm were sputtered on the Si(100) substrates at room temperature. Then, microstructure of thin films was determined using X-ray diffraction. To investigate the influence of temperature on the texture development in the Ag thin films with different thicknesses, (111), (200) and (220) pole figures were evaluated and orientation distribution functions were calculated. Minimizing the total energy of the system which is affected by competition between surface and elastic strain energy was a key factor in the as-deposited and post annealed thin films. Since sputtering depositions was performed at room temperature and at the same thermodynamic conditions, the competition growth caused the formation of the {122} < uvw \\rangle weak fiber texture in as-deposited Ag thin films. It was significantly observed that the post annealed Ag thin films showed {111} < uvw \\rangle orientations as their preferred orientations, but their preferred fiber texture varied with the thickness of thin films. Increasing thin film thickness from 40nm to 160nm led to decreasing the intensity of the {111} < uvw \\rangle fiber texture.

The Tuning of Optical Properties of Nanoscale MOFs-Based Thin Film through Post-Modification.

PubMed

Yin, Wenchang; Tao, Cheng-An; Zou, Xiaorong; Wang, Fang; Qu, Tianlian; Wang, Jianfang

2017-08-29

Optical properties, which determine the application of optical devices in different fields, are the most significant properties of optical thin films. In recent years, Metal-organic framework (MOF)-based optical thin films have attracted increasing attention because of their novel optical properties and important potential applications in optical and photoelectric devices, especially optical thin films with tunable optical properties. This study reports the first example of tuning the optical properties of a MOF-based optical thin film via post-modification. The MOF-based optical thin film was composed of NH₂-MIL-53(Al) nanorods (NRs) (MIL: Materials from Institute Lavoisier), and was constructed via a spin-coating method. Three aldehydes with different lengths of carbon chains were chosen to modify the MOF optical thin film to tune their optical properties. After post-modification, the structural color of the NH₂-MIL-53(Al) thin film showed an obvious change from purple to bluish violet and cyan. The reflection spectrum and the reflectivity also altered in different degrees. The effective refractive index ( n eff ) of MOFs thin film can also be tuned from 1.292 to 1.424 at a wavelength of 750 nm. The success of tuning of the optical properties of MOFs thin films through post-modification will make MOFs optical thin films meet different needs of optical properties in various optical and optoelectronic devices.

The Tuning of Optical Properties of Nanoscale MOFs-Based Thin Film through Post-Modification

PubMed Central

Zou, Xiaorong; Wang, Fang; Qu, Tianlian; Wang, Jianfang

2017-01-01

Optical properties, which determine the application of optical devices in different fields, are the most significant properties of optical thin films. In recent years, Metal-organic framework (MOF)-based optical thin films have attracted increasing attention because of their novel optical properties and important potential applications in optical and photoelectric devices, especially optical thin films with tunable optical properties. This study reports the first example of tuning the optical properties of a MOF-based optical thin film via post-modification. The MOF-based optical thin film was composed of NH2-MIL-53(Al) nanorods (NRs) (MIL: Materials from Institute Lavoisier), and was constructed via a spin-coating method. Three aldehydes with different lengths of carbon chains were chosen to modify the MOF optical thin film to tune their optical properties. After post-modification, the structural color of the NH2-MIL-53(Al) thin film showed an obvious change from purple to bluish violet and cyan. The reflection spectrum and the reflectivity also altered in different degrees. The effective refractive index (neff) of MOFs thin film can also be tuned from 1.292 to 1.424 at a wavelength of 750 nm. The success of tuning of the optical properties of MOFs thin films through post-modification will make MOFs optical thin films meet different needs of optical properties in various optical and optoelectronic devices. PMID:28850057

Growth temperature modulated phase evolution and functional characteristics of high quality Pb1-x Lax (Zr0.9Ti0.1)O3 thin films

NASA Astrophysics Data System (ADS)

Kumar, Anuj; Pawar, Shuvam; Singh, Kirandeep; Kaur, Davinder

2018-05-01

In this study, we have reported the influence of growth temperature on perovskite phase evolution in sputtered deposited high quality Pb1-x Lax (Zr0.9 Ti0.1)O3 (PLZT) thin films on Pt/Ti/SiO2/Si substrate. PLZT thin films were fabricated at substrate temperature ranging from 400 to 700 °C. We have investigated the structural, dielectric, ferroelectric and leakage current characteristics of these thin films. XRD patterns reveal that 600 °C is the optimized temperature to deposit highly (110) oriented perovskite phase PLZT thin film. The further increase in temperature (700 °) causes reappearance of additional peaks corresponding to lead deficient pyrochlore phase. All PLZT thin films show decrease in dielectric constant with frequency. However, PLZT thin film fabricated at 600 °C displays dielectric constant ˜532 at 1 MHz frequency which is relatively higher than other deposited thin films. The P-E loops of these PLZT thin films exhibit strong dependence on deposition temperature. The pure perovskite PZLT thin film shows saturation polarization of ˜51.2µC/cm2 and coercive field (2Ec) ˜67.85 kV/cm. These high quality PLZT thin films finds their applications in non-volatile memory and nano-electro-mechanical systems (NEMS).

Dewetting of Thin Polymer Films

NASA Astrophysics Data System (ADS)

Dixit, P. S.; Sorensen, J. L.; Kent, M.; Jeon, H. S.

2001-03-01

DEWETTING OF THIN POLYMER FILMS P. S. Dixit,(1) J. L. Sorensen,(2) M. Kent,(2) H. S. Jeon*(1) (1) Department of Petroleum and Chemical Engineering, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, jeon@nmt.edu (2) Department 1832, Sandia National Laboratories, Albuquerque, NM. Dewetting of thin polymer films is of technological importance for a variety of applications such as protective coatings, dielectric layers, and adhesives. Stable and smooth films are required for the above applications. Above the glass transition temperature (Tg) the instability of polymer thin films on a nonwettable substrate can be occurred. The dewetting mechanism and structure of polypropylene (Tg = -20 ^circC) and polystyrene (Tg = 100 ^circC) thin films is investigated as a function of film thickness (25 Åh < 250 Åand quenching temperature. Contact angle measurements are used in conjunction with optical microscope to check the surface homogeneity of the films. Uniform thin films are prepared by spin casting the polymer solutions onto silicon substrates with different contact angles. We found that the stable and unstable regions of the thin films as a function of the film thickness and quenching temperature, and then constructed a stability diagram for the dewetting of thin polymer films. We also found that the dewetting patterns of the thin films are affected substantially by the changes of film thickness and quenching temperature.

Temperature dependence of LRE-HRE-TM thin films

NASA Astrophysics Data System (ADS)

Li, Zuoyi; Cheng, Xiaomin; Lin, Gengqi; Li, Zhen; Huang, Zhixin; Jin, Fang; Wang, Xianran; Yang, Xiaofei

2003-04-01

Temperature dependence of the properties of RE-TM thin films is very important for MO recording. In this paper, we studied the temperature dependence of the magnetic and magneto-optical properties of the amorphous LRE-HRE-TM single layer thin films and LRE-HRE-TM/HRE-TM couple-bilayered thin films. For LRE-HRE-TM single layer thin films, the temperature dependence of the magnetization was investigated by using the mean field theory. The experimental and theoretical results matched very well. With the LRE substitution in HRE-TM thin film, the compensation temperature Tcomp decreased and the curie temperature Tc remained unchanged. Kerr rotation angle became larger and the saturation magnetization Ms at room temperature increased. For LRE-HRE-TM/HRE-TM couple-bilayered thin films, comparisons of the temperature dependences of the coercivities and Kerr rotation angles were made between isolated sublayers and couple-bilayered thin film.

Surface proton transport of fully protonated poly(aspartic acid) thin films on quartz substrates

NASA Astrophysics Data System (ADS)

Nagao, Yuki; Kubo, Takahiro

2014-12-01

Thin film structure and the proton transport property of fully protonated poly(aspartic acid) (P-Asp100) have been investigated. An earlier study assessed partially protonated poly(aspartic acid), highly oriented thin film structure and enhancement of the internal proton transport. In this study of P-Asp100, IR p-polarized multiple-angle incidence resolution (P-MAIR) spectra were measured to investigate the thin film structure. The obtained thin films, with thicknesses of 120-670 nm, had no oriented structure. Relative humidity dependence of the resistance, proton conductivity, and normalized resistance were examined to ascertain the proton transport property of P-Asp100 thin films. The obtained data showed that the proton transport of P-Asp100 thin films might occur on the surface, not inside of the thin film. This phenomenon might be related with the proton transport of the biological system.

Thin film superconductor magnetic bearings

DOEpatents

Weinberger, Bernard R.

1995-12-26

A superconductor magnetic bearing includes a shaft (10) that is subject to a load (L) and rotatable around an axis of rotation, a magnet (12) mounted to the shaft, and a stator (14) in proximity to the shaft. The stator (14) has a superconductor thin film assembly (16) positioned to interact with the magnet (12) to produce a levitation force on the shaft (10) that supports the load (L). The thin film assembly (16) includes at least two superconductor thin films (18) and at least one substrate (20). Each thin film (18) is positioned on a substrate (20) and all the thin films are positioned such that an applied magnetic field from the magnet (12) passes through all the thin films. A similar bearing in which the thin film assembly (16) is mounted on the shaft (10) and the magnet (12) is part of the stator (14) also can be constructed.

Measuring Exciton Diffusion in Conjugated Polymer Films with Super-resolution Microscopy

NASA Astrophysics Data System (ADS)

Penwell, Samuel; Ginsberg, Lucas; Noriega Manez, Rodrigo; Ginsberg, Naomi

2015-03-01

Conjugated polymers are highly tunable organic semiconductors, which can be solution processed to form thin films, making them prime candidates for organic photovoltaic devices. One of the most important parameters in a conjugated polymer solar cell is the exciton diffusion length, which depends on intermolecular couplings, and is typically on the order of 10 nm. This mean exciton migration can vary dramatically between films and within a single film due to heterogeneities in morphology on length scales of 10's to 100's nm. To study the variability of exciton diffusion and morphology within individual conjugated polymer films, we are adapting stimulated emission depletion microscopy. STED is typically used in biology with well-engineered fluorescent labels or on NV-centers in diamond. I will, however, describe how we have demonstrated STED in conjugated polymer films of MEH-PPV and CN-PPV by taking care to first understand the film's photophysical properties. This new approach provides a way to study exciton diffusion by utilizing subdiffraction optical excitation volumes. In this way, we will obtain a spatiotemporal map of exciton distributions that will help to correlate the energetic landscape to film morphology at the nanoscale. This research is supported in part by the Department of Energy Office of Science Graduate Fellowship Program (DOE SCGF), made possible in part by the American Recovery and Reinvestment Act of 2009, administered by ORISE-ORAU under Contract No. DE-AC05-06.

Metal Induced Growth of Si Thin Films and NiSi Nanowires

DTIC Science & Technology

2010-02-25

Zinc Oxide Over MIG Silicon- We have been studying the formation of ZnO films by RF sputtering. Part of this study deals with...about 50 nm. 15. SUBJECT TERMS Thin film silicon, solar cells, thin film transistors , nanowires, metal induced growth 16. SECURITY CLASSIFICATION...to achieve, µc-Si is more desirable than a-Si due to its increased mobility. Thin film µc-Si is also a popular material for thin film transistors

NMR characterization of thin films

DOEpatents

Gerald II, Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

2010-06-15

A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

NMR characterization of thin films

DOEpatents

Gerald, II, Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

2008-11-25

A method, apparatus, and system for characterizing thin film materials. The method, apparatus, and system includes a container for receiving a starting material, applying a gravitational force, a magnetic force, and an electric force or combinations thereof to at least the starting material, forming a thin film material, sensing an NMR signal from the thin film material and analyzing the NMR signal to characterize the thin film of material.

Thermoelectric properties of epitaxial β-FeSi2 thin films grown on Si(111) substrates with various film qualities

NASA Astrophysics Data System (ADS)

Watanabe, Kentaro; Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Suzuki, Takeyuki; Fujita, Takeshi; Nakamura, Yoshiaki

2017-05-01

Si-based epitaxial β-FeSi2 thin films are attractive as materials for on-chip thermoelectric power generators. We investigated the structure, crystallinity, and thermoelectric properties of β-FeSi2 thin films epitaxially grown on Si(111) substrates by using three different techniques: conventional reactive deposition epitaxy followed by molecular beam epitaxy (RDE+MBE), solid phase epitaxy (SPE) based on codeposition of Fe and Si presented previously, and SPE followed by MBE (SPE+MBE) presented newly by this work. Their epitaxial growth temperatures were fixed at 530 °C for comparison. RDE+MBE thin films exhibited high crystalline quality, but rough surfaces and rugged β-FeSi2/Si(111) interfaces. On the other hand, SPE thin films showed flat surfaces and abrupt β-FeSi2/Si(111) interfaces but low crystallinity. We found that SPE+MBE thin films realized crystallinity higher than SPE thin films, and also had flatter surfaces and sharper interfaces than RDE+MBE thin films. In SPE+MBE thin film growth, due to the initial SPE process with low temperature codeposition, thermal interdiffusion of Fe and Si was suppressed, resulting in the surface flatness and abrupt interface. Second high temperature MBE process improved the crystallinity. We also investigated thermoelectric properties of these β-FeSi2 thin films. Structural factors affecting the thermoelectric properties of RDE+MBE, SPE, and SPE+MBE thin films were investigated.

In situ Pulsed Laser Deposition of C-Axis Oriented MgB2 Films and Their Characterization

NASA Technical Reports Server (NTRS)

Shinde, Sanjay; Lakew, Brook; Ogale, S. B.; Kulkarni, V. N.; Kale, S. N.; Venkatesan, T.

2004-01-01

The recent discovery of an intermetallic superconductor MgB2 has renewed interest in the area of superconductivity not only because of fundamental understanding of superconductivity but also due to its potential applicability in devices such as thermal detectors. Considerable amount of research has been devoted to obtain MgB2 films by an all in situ growth technique. We have grown MgB2 thin films by an all in situ pulsed laser deposition process from pure B and Mg targets. Ultrathin layers of B and Mg were deposited in a multilayer configuration. Hundreds of such Mg-B bilayers with a capping Mg layer on the top were deposited on sapphire substrate. These depositions were done in high vacuum (approx. 10(exp -7) Torr) and at room temperature. After deposition, such a configuration was annealed at high temperature for a short time in a forming gas (4% H2 in Ar). The best films, obtained by this procedure, showed superconducting transition temperature approx. 30 K. These films have been characterized by x-ray diffraction, Rutherford Backscattering Spectrometry, AC susceptibility-, resistivity- (with and without magnetic field) and 1/f noise-measurements. The physical properties of these films will be presented and discussed.

Nanostructural characterization of amorphous diamondlike carbon films

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

SIEGAL,MICHAEL P.; TALLANT,DAVID R.; MARTINEZ-MIRANDA,L.J.

2000-01-27

Nanostructural characterization of amorphous diamondlike carbon (a-C) films grown on silicon using pulsed-laser deposition (PLD) is correlated to both growth energetic and film thickness. Raman spectroscopy and x-ray reflectivity probe both the topological nature of 3- and 4-fold coordinated carbon atom bonding and the topographical clustering of their distributions within a given film. In general, increasing the energetic of PLD growth results in films becoming more ``diamondlike'', i.e. increasing mass density and decreasing optical absorbance. However, these same properties decrease appreciably with thickness. The topology of carbon atom bonding is different for material near the substrate interface compared to materialmore » within the bulk portion of an a-C film. A simple model balancing the energy of residual stress and the free energies of resulting carbon topologies is proposed to provide an explanation of the evolution of topographical bonding clusters in a growing a-C film.« less

A general strategy for hybrid thin film fabrication and transfer onto arbitrary substrates.

PubMed

Zhang, Yong; Magan, John J; Blau, Werner J

2014-04-28

The development of thin film-based structures/devices often requires thin films to be transferred onto arbitrary substrates/surfaces. Controllable and non-destructive transfer method, although highly desired, remains quite challenging. Here we report a general method for fabrication and transfer of hybrid (ultra)thin films. The proposed solution-based in-situ transfer method shows not only its robust ability for thin film transfer onto arbitrary substrates but also its highly controlled and non-destructive characteristic. With a hole structure as the support, fully-stretched free-standing thin film is prepared. The successful transfer to a curved surface demonstrates the possibility for production of thin film-coated complex optical components. Ultrathin (35 nm) hybrid film transferred onto PET (50 μm thick) shows high transparency (>90% in visible range), conductivity (1.54 × 10(4) S/m), and flexibility (radius of curvature down to mm scale). The reported transfer method would provide a powerful route towards complex thin film-based structures/devices.

A General Strategy for Hybrid Thin Film Fabrication and Transfer onto Arbitrary Substrates

PubMed Central

Zhang, Yong; Magan, John J.; Blau, Werner J.

2014-01-01

The development of thin film-based structures/devices often requires thin films to be transferred onto arbitrary substrates/surfaces. Controllable and non-destructive transfer method, although highly desired, remains quite challenging. Here we report a general method for fabrication and transfer of hybrid (ultra)thin films. The proposed solution-based in-situ transfer method shows not only its robust ability for thin film transfer onto arbitrary substrates but also its highly controlled and non-destructive characteristic. With a hole structure as the support, fully-stretched free-standing thin film is prepared. The successful transfer to a curved surface demonstrates the possibility for production of thin film-coated complex optical components. Ultrathin (35 nm) hybrid film transferred onto PET (50 μm thick) shows high transparency (>90% in visible range), conductivity (1.54 × 104 S/m), and flexibility (radius of curvature down to mm scale). The reported transfer method would provide a powerful route towards complex thin film-based structures/devices. PMID:24769689

Fabrication of VO2 thin film by rapid thermal annealing in oxygen atmosphere and its metal—insulator phase transition properties

NASA Astrophysics Data System (ADS)

Liang, Ji-Ran; Wu, Mai-Jun; Hu, Ming; Liu, Jian; Zhu, Nai-Wei; Xia, Xiao-Xu; Chen, Hong-Da

2014-07-01

Vanadium dioxide thin films have been fabricated through sputtering vanadium thin films and rapid thermal annealing in oxygen. The microstructure and the metal—insulator transition properties of the vanadium dioxide thin films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and a spectrometer. It is found that the preferred orientation of the vanadium dioxide changes from (1¯11) to (011) with increasing thickness of the vanadium thin film after rapid thermal annealing. The vanadium dioxide thin films exhibit an obvious metal—insulator transition with increasing temperature, and the phase transition temperature decreases as the film thickness increases. The transition shows hysteretic behaviors, and the hysteresis width decreases as the film thickness increases due to the higher concentration carriers resulted from the uncompleted lattice. The fabrication of vanadium dioxide thin films with higher concentration carriers will facilitate the nature study of the metal—insulator transition.

Synthesis, characterization, and photocatalytic properties of nanocrystalline NZO thin films

NASA Astrophysics Data System (ADS)

Aryanto, D.; Hastuti, E.; Husniya, N.; Sudiro, T.; Nuryadin, B. W.

2018-03-01

Nanocrystalline Ni-doped ZnO (NZO) thin films were synthesized on glass substrate using sol-gel spin coating methods. The effect of annealing on the structural and optical properties of nanocrystalline thin film was studied using X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), UV-VIS spectrophotometry, and photoluminescence (PL). The results showed that the annealing temperature strongly influenced the physical properties of nanocrystalline NZO thin films. The photocatalytic properties of nanocrystalline NZO thin films were evaluated using an aqueous solution of Rhodamine-B. The photocatalytic activity of nanocrystalline NZO thin films increased with the increase of annealing temperature. The results indicated that the structure, morphology, and band gap energy of nanocrystalline NZO thin films played an important role in photocatalytic activity.

Metallic Thin-Film Bonding and Alloy Generation

NASA Technical Reports Server (NTRS)

Peotter, Brian S. (Inventor); Fryer, Jack Merrill (Inventor); Campbell, Geoff (Inventor); Droppers, Lloyd (Inventor)

2016-01-01

Diffusion bonding a stack of aluminum thin films is particularly challenging due to a stable aluminum oxide coating that rapidly forms on the aluminum thin films when they are exposed to atmosphere and the relatively low meting temperature of aluminum. By plating the individual aluminum thin films with a metal that does not rapidly form a stable oxide coating, the individual aluminum thin films may be readily diffusion bonded together using heat and pressure. The resulting diffusion bonded structure can be an alloy of choice through the use of a carefully selected base and plating metals. The aluminum thin films may also be etched with distinct patterns that form a microfluidic fluid flow path through the stack of aluminum thin films when diffusion bonded together.

Enhanced luminescence efficiency by surface plasmon coupling of Ag nanoparticles in a polymer light-emitting diode

NASA Astrophysics Data System (ADS)

Chen, Sy-Hann; Jhong, Jhen-Yu

2011-08-01

This study achieved a substantial enhancement in electroluminescence by coupling localized surface plasmons in a single layer of Ag nanoparticles. Thermal evaporation was used to fabricate 20-nm Ag particles sandwiched between a gallium-doped zinc oxide film and a glass substrate to form novel window materials for use in polymer light-emitting diodes (PLEDs). The PLEDs discussed herein are single-layer devices based on a poly(9,9-di-n-octyl-2,7-fluorene) (PFO) emissive layer. In addition to low cost, this novel fabrication method can effectively prevent interruption or degradation of the charge transport properties of the active layer to meet the high performance requirements of PLEDs. Due to the surface-plasmon-enhanced emission, the electroluminescence intensity was increased by nearly 1-fold, compared to that of the same PLED without the interlayer of Ag nanoparticles.

Advances in Thin Film Thermocouple Durability Under High Temperature and Pressure Testing Conditions

NASA Technical Reports Server (NTRS)

Martin, Lisa C.; Fralick, Gustave C.; Taylor, Keith F.

1999-01-01

Thin film thermocouples for measuring material surface temperature have been previously demonstrated on several material systems and in various hostile test environments. A well-developed thin film fabrication procedure utilizing shadow masking for patterning the sensors elements had produced thin films with sufficient durability for applications in high temperature and pressure environments that exist in air-breathing and hydrogen-fueled burner rig and engine test facilities. However, while shadow masking had been a reliable method for specimens with flat and gently curved surfaces, it had not been consistently reliable for use on test components with sharp contours. This work reports on the feasibility of utilizing photolithography processing for patterning thin film thermocouples. Because this patterning process required changes in the thin film deposition process from that developed for shadow masking, the effect of these changes on thin film adherence during burner rig testing was evaluated. In addition to the results of changing the patterning method, the effects on thin film adherence of other processes used in the thin film fabrication procedure is also presented.

Effects of air annealing on CdS quantum dots thin film grown at room temperature by CBD technique intended for photosensor applications

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

Shaikh, Shaheed U.; Desale, Dipalee J.; Siddiqui, Farha Y.

2012-11-15

Graphical abstract: The effect of different intensities (40, 60 100 and 200 W) of light on CdS quantum dots thin film annealed at 350 °C indicating enhancement in (a) photo-current and (b) photosensitivity. Highlights: ► The preparation of CdS nanodot thin film at room temperature by M-CBD technique. ► Study of air annealing on prepared CdS nanodots thin film. ► The optimized annealing temperature for CdS nanodot thin film is 350 °C. ► Modified CdS thin films can be used in photosensor application. -- Abstract: CdS quantum dots thin-films have been deposited onto the glass substrate at room temperature usingmore » modified chemical bath deposition technique. The prepared thin films were further annealed in air atmosphere at 150, 250 and 350 °C for 1 h and subsequently characterized by scanning electron microscopy, ultraviolet–visible spectroscopy, electrical resistivity and I–V system. The modifications observed in morphology and opto-electrical properties of the thin films are presented.« less

Self-supporting activated carbon/carbon nanotube/reduced graphene oxide flexible electrode for high performance supercapacitor

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

Li, Xing; Tang, Yao; Song, Junhua

A self-supporting and flexible activated carbon/carbon nanotube/reduced graphene oxide (AC/CNT/RGO) film has been rationally designed for constructing high-performance supercapacitor. We prepared the AC/CNT/RGO film by anchoring the AC particles with a 3D and porous framework built by hierarchically weaving the 1 D CNT and 2D RGO using their intrinsic van der Waals force. The CNT network is beneficial for improving the electronic conductivity of the electrode, while the AC particles could effectively suppress the aggregation of RGO and CNT due to their blocking effect. The synergistic effects among the AC, CNT and RGO validate the AC/CNT/RGO as a promising electrodemore » for supercapacitor, exhibiting greatly enhanced electrochemical performances in comparison with the pure RGO film, pure CNT film and AC electrode. Furthermore, the AC/CNT/RGO electrode delivers a high specific capacitance of 101 F g -1 at the current density of 0.2 A g -1 offering a maximum energy density of 30.0 W h kg -1 in organic electrolyte at the cut-off voltage range of 0.001–3.0 V. The findings of this work open a new avenue for the design of self-supporting electrodes for the development of flexible and light weight energy storage supercapacitor.« less

Self-supporting activated carbon/carbon nanotube/reduced graphene oxide flexible electrode for high performance supercapacitor

DOE PAGES

Li, Xing; Tang, Yao; Song, Junhua; ...

2017-12-06

A self-supporting and flexible activated carbon/carbon nanotube/reduced graphene oxide (AC/CNT/RGO) film has been rationally designed for constructing high-performance supercapacitor. We prepared the AC/CNT/RGO film by anchoring the AC particles with a 3D and porous framework built by hierarchically weaving the 1 D CNT and 2D RGO using their intrinsic van der Waals force. The CNT network is beneficial for improving the electronic conductivity of the electrode, while the AC particles could effectively suppress the aggregation of RGO and CNT due to their blocking effect. The synergistic effects among the AC, CNT and RGO validate the AC/CNT/RGO as a promising electrodemore » for supercapacitor, exhibiting greatly enhanced electrochemical performances in comparison with the pure RGO film, pure CNT film and AC electrode. Furthermore, the AC/CNT/RGO electrode delivers a high specific capacitance of 101 F g -1 at the current density of 0.2 A g -1 offering a maximum energy density of 30.0 W h kg -1 in organic electrolyte at the cut-off voltage range of 0.001–3.0 V. The findings of this work open a new avenue for the design of self-supporting electrodes for the development of flexible and light weight energy storage supercapacitor.« less

Effect of annealing temperatures on the morphology and structural properties of PVDF/MgO nanocomposites thin films

NASA Astrophysics Data System (ADS)

Rozana, M. D.; Arshad, A. N.; Wahid, M. H. M.; Habibah, Z.; Sarip, M. N.; Rusop, M.

2018-05-01

This study investigates the effect of annealing on the topography, morphology and crystal phases of poly(vinylideneflouride)/Magnesium Oxide (MgO) nanocomposites thin films via AFM, FESEM and ATR-FTIR. The nanocomposites thin films were annealed at temperatures ranging from 70°C to 170°C. The annealed PVDF/MgO nanocomposites thin films were then cooled at room temperature before removal from the oven. This is to restructure the crystal lattice and to reduce imperfection for the PVDF/MgO nanocomposites thin films. PVDF/MgO nanocomposites thin films with annealing temperatures of 70°C, 90°C and 110°C showed uniform distribution of MgO nanoparticles, relatively low average surface roughness and no visible of defects. High application of annealing temperature on PVDF/MgO nanocomposites thin films caused tear-like defects on the thin films surface as observed by FESEM. The PVDF/MgO nanocomposites thin films annealed at 70°C was found to be a favourable film to be utilized in this study due to its enhanced β-crystalites of PVDF as evident in ATR-FTIR spectra.

Determining the Origin of Half-bandgap-voltage Electroluminescence in Bifunctional Rubrene/C60 Devices

PubMed Central

Chen, Qiusong; Jia, Weiyao; Chen, Lixiang; Yuan, De; Zou, Yue; Xiong, Zuhong

2016-01-01

Lowering the driving voltage of organic light-emitting diodes (OLEDs) is an important approach to reduce their energy consumption. We have fabricated a series of bifunctional devices (OLEDs and photovoltaics) using rubrene and fullerene (C60) as the active layer, in which the electroluminescence threshold voltage(~1.1 V) was half the value of the bandgap of rubrene. Magneto-electroluminescence (MEL) response of planner heterojunction diodes exhibited a small increase in response to a low magnetic field strength (<20 mT); however, a very large decay was observed at a high magnetic field strength (>20 mT). When a hole-transport layer with a low mobility was included in these devices, the MEL response reversed in shape, and simultaneously, the EL threshold voltage became larger than the bandgap voltage. When bulk heterojunction device was examined, the amplitude of MEL curves presented an anomalous voltage-dependence. Following an analysis of the MEL responses of these devices, we proposed that the EL of half-bandgap-voltage device originated from bimolecular triplet-triplet annihilation in the rubrene film, rather than from singlet excitons that formed via an interface auger recombination. This work provides critical insight into the mechanisms of OLED emission and will help advance the applications of bifunctional devices. PMID:27142285

Atomic layer deposition of copper thin film and feasibility of deposition on inner walls of waveguides

NASA Astrophysics Data System (ADS)

Yuqing, XIONG; Hengjiao, GAO; Ni, REN; Zhongwei, LIU

2018-03-01

Copper thin films were deposited by plasma-enhanced atomic layer deposition at low temperature, using copper(I)-N,N‧-di-sec-butylacetamidinate as a precursor and hydrogen as a reductive gas. The influence of temperature, plasma power, mode of plasma, and pulse time, on the deposition rate of copper thin film, the purity of the film and the step coverage were studied. The feasibility of copper film deposition on the inner wall of a carbon fibre reinforced plastic waveguide with high aspect ratio was also studied. The morphology and composition of the thin film were studied by atomic force microscopy and x-ray photoelectron spectroscopy, respectively. The square resistance of the thin film was also tested by a four-probe technique. On the basis of on-line diagnosis, a growth mechanism of copper thin film was put forward, and it was considered that surface functional group played an important role in the process of nucleation and in determining the properties of thin films. A high density of plasma and high free-radical content were helpful for the deposition of copper thin films.

Nanocrystal thin film fabrication methods and apparatus

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

Kagan, Cherie R.; Kim, David K.; Choi, Ji-Hyuk

Nanocrystal thin film devices and methods for fabricating nanocrystal thin film devices are disclosed. The nanocrystal thin films are diffused with a dopant such as Indium, Potassium, Tin, etc. to reduce surface states. The thin film devices may be exposed to air during a portion of the fabrication. This enables fabrication of nanocrystal-based devices using a wider range of techniques such as photolithography and photolithographic patterning in an air environment.

Pyrolyzed thin film carbon

NASA Technical Reports Server (NTRS)

Harder, Theodore (Inventor); Konishi, Satoshi (Inventor); Miserendino, Scott (Inventor); Tai, Yu-Chong (Inventor); Liger, Matthieu (Inventor)

2010-01-01

A method of making carbon thin films comprises depositing a catalyst on a substrate, depositing a hydrocarbon in contact with the catalyst and pyrolyzing the hydrocarbon. A method of controlling a carbon thin film density comprises etching a cavity into a substrate, depositing a hydrocarbon into the cavity, and pyrolyzing the hydrocarbon while in the cavity to form a carbon thin film. Controlling a carbon thin film density is achieved by changing the volume of the cavity. Methods of making carbon containing patterned structures are also provided. Carbon thin films and carbon containing patterned structures can be used in NEMS, MEMS, liquid chromatography, and sensor devices.

Preparation of LiMn{sub 2}O{sub 4} cathode thin films for thin film lithium secondary batteries by a mist CVD process

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

Tadanaga, Kiyoharu, E-mail: tadanaga@chem.osakafu-u.ac.jp; Yamaguchi, Akihiro; Sakuda, Atsushi

2014-05-01

Highlights: • LiMn{sub 2}O{sub 4} thin films were prepared by using the mist CVD process. • An aqueous solution of lithium and manganese acetates is used for the precursor solution. • The cell with the LiMn{sub 2}O{sub 4} thin films exhibited a capacity of about 80 mAh/g. • The cell showed good cycling performance during 10 cycles. - Abstract: LiMn{sub 2}O{sub 4} cathode thin films for thin film lithium secondary batteries were prepared by using so-called the “mist CVD process”, employing an aqueous solution of lithium acetate and manganese acetate, as the source of Li and Mn, respectively. The aqueousmore » solution of starting materials was ultrasonically atomized to form mist particles, and mists were transferred by nitrogen gas to silica glass substrate to form thin films. FE-SEM observation revealed that thin films obtained by this process were dense and smooth, and thin films with a thickness of about 750 nm were obtained. The electrochemical cell with the thin films obtained by sintering at 700 °C exhibited a capacity of about 80 mAh/g, and the cell showed good cycling performance during 10 cycles.« less

Magnetite nano-islands on Graphene

NASA Astrophysics Data System (ADS)

Anderson, Nathaniel; Zhang, Qiang; Rosenberg, Richard; Vaknin, David

X-ray magnetic circular dichroism (XMCD) of ex-situ iron nano-islands grown on graphene reveals that iron oxidation spontaneously leads to the formation of magnetite nano-particles - i.e, the formation of the inverse spinel Fe3O4. Fe islands have been grown with two different heights (20 and 75 MLs) on epitaxial graphene and we have determined their magnetic behavior both as function of temperature and applied external field. Our XAS and XMCD at an applied magnetic field of B = 5 T show that the thin film (20 MLs) is totally converted to magnetite whereas the thicker film (75 MLs) exhibits magnetite properties but also those of pure metal iron. For both samples, temperature dependence of the XMCD shows clear transitions at ~120 K consistent with the Verwey transition of bulk magnetite. XMCD at low temperatures shows a weak hysteresis and provide the average spin and angular-momentum moments, the dipolar term, and the total moment . In addition, manipulation and comparison of the XMCD data from both samples allows us to extract information about the pure iron nano-islands from the thicker sample. Ames Laboratory is supported by the U.S. DOE, BES, MSE Contract No. DE-AC02-07CH11358. APS is supported by U.S. DOE Contract No. DE-AC02-06CH11357.

Solution processable 2-(trityloxy)ethyl and tert-butyl group containing amorphous molecular glasses of pyranylidene derivatives with light-emitting and amplified spontaneous emission properties

NASA Astrophysics Data System (ADS)

Zarins, Elmars; Vembris, Aivars; Misina, Elina; Narels, Martins; Grzibovskis, Raitis; Kokars, Valdis

2015-11-01

Small organic molecules with incorporated 4H-pyran-4-ylidene (pyranylidene) fragment as the π-conjugation system which bonds the electron acceptor fragment (A) with electron donor part (D) in the molecule - also well known as derivatives of 4-(dicyano-methylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM) laser dye-have attracted considerable attention of scientists as potential new generation materials for organic photonics and molecular electronics due to their low-cost fabrication possibility, flexibility and low-weight. Six glassy derivatives of 4H-pyran-4-ylidene (pyranylidene) with attached bulky 2-(trityloxy)ethyl and tert-butyl groups are described in this report. Almost all of the synthesized compounds form good optical quality transparent amorphous films from volatile organic solvents and could be obtained in good yields up to 75%. Their light emission in solution and thin solid films is in the range of 600-700 nm, they are thermally stable and show glass transition in the range of 108-158 °C. The amplified spontaneous emission threshold values of the neat films of the glassy pyranylidene derivatives vary from 155 to 450 μJ/cm2 and their HOMO and LUMO energy levels are between of those of tris(8-hydroxy quinolinato) aluminum (Alq3). The photoluminescence quantum yields of the glassy compounds are in the range from 1% to about 7.7% and their electroluminescence properties have been investigated. Therefore, glassy pyranylidene derivatives could be a very potential low-cost solution processable materials for Alq3 hosted light-amplification and light-emitting application studies.

Preparation methodologies and nano/microstructural evaluation of metal/semiconductor thin films.

PubMed

Chen, Zhiwen; Jiao, Zheng; Wu, Minghong; Shek, Chan-Hung; Wu, C M Lawrence; Lai, Joseph K L

2012-01-01

Metal/semiconductor thin films are a class of unique materials that are widespread technological applications, particularly in the field of microelectronic devices. Assessment strategies of fractal and tures are of fundamental importance in the development of nano/microdevices. This review presents the preparation methodologies and nano/microstructural evaluation of metal/semiconductor thin films including Au/Ge bilayer films and Pd-Ge alloy thin films, which show in the form of fractals and nanocrystals. Firstly, the extended version of Au/Ge thin films for the fractal crystallization of amorphous Ge and the formation of nanocrystals developed with improved micro- and nanostructured features are described in Section 2. Secondly, the nano/microstructural characteristics of Pd/Ge alloy thin films during annealing have been investigated in detail and described in Section 3. Finally, we will draw the conclusions from the present work as shown in Section 4. It is expected that the preparation methodologies developed and the knowledge of nano/microstructural evolution gained in metal/semiconductor thin films, including Au/Ge bilayer films and Pd-Ge alloy thin films, will provide an important fundamental basis underpinning further interdisciplinary research in these fields such as physics, chemistry, materials science, and nanoscience and nanotechnology, leading to promising exciting opportunities for future technological applications involving these thin films.

Evaluation of humidity sensing properties of TMBHPET thin film embedded with spinel cobalt ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Zafar, Qayyum; Azmer, Mohamad Izzat; Al-Sehemi, Abdullah G.; Al-Assiri, Mohammad S.; Kalam, Abul; Sulaiman, Khaulah

2016-07-01

In this study, we report the enhanced sensing parameters of previously reported TMBHPET-based humidity sensor. Significant improved sensing performance has been demonstrated by coupling of TMBHPET moisture sensing thin film with cobalt ferrite nanoparticles (synthesized by eco-benign ultrasonic method). The mean size of CoFe2O4 nanoparticles has been estimated to be 6.5 nm. It is assumed that the thin film of organic-ceramic hybrid matrix (TMBHPET:CoFe2O4) is a potential candidate for humidity sensing utility by virtue of its high specific surface area and porous surface morphology (as evident from TEM, FESEM, and AFM images). The hybrid suspension has been drop-cast onto the glass substrate with preliminary deposited coplanar aluminum electrodes separated by 40 µm distance. The influence of humidity on the capacitance of the hybrid humidity sensor (Al/TMBHPET:CoFe2O4/Al) has been investigated at three different frequencies of the AC applied voltage ( V rms 1 V): 100 Hz, 1 kHz, and 10 kHz. It has been observed that at 100 Hz, under a humidity of 99 % RH, the capacitance of the sensor increased by 2.61 times, with respect to 30 % RH condition. The proposed sensor exhibits significantly improved sensitivity 560 fF/ % RH at 100 Hz, which is nearly 7.5 times as high as that of pristine TMBHPET-based humidity sensor. Further, the capacitive sensor exhibits improved dynamic range (30-99 % RH), small hysteresis ( 2.3 %), and relatively quicker response and recovery times ( 12 s, 14 s, respectively). It is assumed that the humidity response of the sensor is associated with the diffusion kinetics of water vapors and doping of the semiconductor nanocomposite by water molecules.

Heavily-doped ZnO:Al thin films prepared by using magnetron Co-sputtering: Optical and electrical properties

NASA Astrophysics Data System (ADS)

Moon, Eun-A.; Jun, Young-Kil; Kim, Nam-Hoon; Lee, Woo-Sun

2016-07-01

Photovoltaic applications require transparent conducting-oxide (TCO) thin films with high optical transmittance in the visible spectral region (380 - 780 nm), low resistivity, and high thermal/chemical stability. The ZnO thin film is one of the most common alternatives to the conventional indium-tin-oxide (ITO) thin film TCO. Highly transparent and conductive ZnO thin films can be prepared by doping with group III elements. Heavily-doped ZnO:Al (AZO) thin films were prepared by using the RF magnetron co-sputtering method with ZnO and Al targets to obtain better characteristics at a low cost. The RF sputtering power to each target was varied to control the doping concentration in fixed-thickness AZO thin films. The crystal structures of the AZO thin films were analyzed by using X-ray diffraction. The morphological microstructure was observed by using scanning electron microscopy. The optical transmittance and the band gap energy of the AZO thin films were examined with an UV-visible spectrophotometer in the range of 300 - 1800 nm. The resistivity and the carrier concentration were examined by using a Hall-effect measurement system. An excellent optical transmittance > 80% with an appropriate band gap energy (3.26 - 3.27 eV) and an improved resistivity (~10 -1 Ω·cm) with high carrier concentration (1017 - 1019 cm -3) were demonstrated in 350-nm-thick AZO thin films for thin-film photovoltaic applications.

Decoding Nucleation and Growth of Zeolitic Imidazolate Framework Thin Films with Atomic Force Microscopy and Vibrational Spectroscopy.

PubMed

Öztürk, Zafer; Filez, Matthias; Weckhuysen, Bert M

2017-08-10

The synthesis of metal-organic framework (MOF) thin films has garnered significant attention during the past decade. By better understanding the parameters governing the nucleation and growth of such thin films, their properties can be rationally tuned, empowering their application as (reactive) membranes. Here, a combined AFM-vibrational spectroscopy research strategy is employed to detail the chemistries governing the nucleation and growth of zeolitic imidazolate framework (ZIF) thin films, in particular isostructural Co-ZIF-67 and Zn-ZIF-8. First, a single step direct synthesis approach is used to investigate the influence of different synthesis parameters -metal/linker ratio, temperature, and metal type- on the thin film nucleation and growth behaviour. While the metal/linker ratio has a pronounced effect on the thin film nucleation rate, the temperature mainly influences the growth kinetics of nuclei forming the thin film. In addition, the nucleation and growth of ZIF thin films is shown to be highly dependent on the electronegativity of the metal type. Thin-film thickness control can be achieved by using a multistep synthesis strategy, implying repetitive applications of single step deposition under identical synthesis conditions, for which a growth mechanism is proposed. This study provides insight into the influence of synthesis parameters on the ZIF thin film properties, using tools at hand to rationally tune MOF thin film properties. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Methods for fabricating thin film III-V compound solar cell

DOEpatents

Pan, Noren; Hillier, Glen; Vu, Duy Phach; Tatavarti, Rao; Youtsey, Christopher; McCallum, David; Martin, Genevieve

2011-08-09

The present invention utilizes epitaxial lift-off in which a sacrificial layer is included in the epitaxial growth between the substrate and a thin film III-V compound solar cell. To provide support for the thin film III-V compound solar cell in absence of the substrate, a backing layer is applied to a surface of the thin film III-V compound solar cell before it is separated from the substrate. To separate the thin film III-V compound solar cell from the substrate, the sacrificial layer is removed as part of the epitaxial lift-off. Once the substrate is separated from the thin film III-V compound solar cell, the substrate may then be reused in the formation of another thin film III-V compound solar cell.

Synthesis and characterization of lithium intercalation electrodes based on iron oxide thin films

NASA Astrophysics Data System (ADS)

Sarradin, J.; Guessous, A.; Ribes, M.

Sputter-deposited iron oxide thin films are investigated as a possible negative electrode for rocking-chair microbatteries. Experimental conditions related to the manufacturing of amorphous thin films suitable to a large number of available intercalation sites are described. Structural and physical properties of the thin layer films are presented. The conductivities of the amorphous thin films were found to be very high compared with those of the respective crystalline forms. Regarding the electrochemical behaviour, Fe 2O 3-based thin films electrodes are able to store and reversibly exchange lithium ions. At a C/2 charge/discharge rate with 100% depth-of-discharge (DOD), the specific capacity of these amorphous thin film electrodes remains almost constant and close to 330 Ah/kg after more than 120 charge/discharge cycles.

Microstructure and thermochromic properties of VOX-WOX-VOX ceramic thin films

NASA Astrophysics Data System (ADS)

Khamseh, S.; Araghi, H.; Ghahari, M.; Faghihi Sani, M. A.

2016-03-01

W-doped VO2 films have been synthesized via oxygen annealing of V-W-V (vanadium-tungsten-vanadium) multilayered films. The effects of middle layer's thickness of V-W-V multilayered film on structure and properties of VOX-WOX-VOX ceramic thin films were investigated. The as-deposited V-W-V multilayered film showed amorphous-like structure when mixed structure of VO2 (M) and VO2 (B) was formed in VOX-WOX-VOX ceramic thin films. Tungsten content of VOX-WOX-VOX ceramic thin films increased with increasing middle layer's thickness. With increasing middle layer's thickness, room temperature square resistance ( R sq) of VOX-WOX-VOX ceramic thin films increased from 65 to 86 kΩ/sq. The VOX-WOX-VOX ceramic thin film with the thinnest middle layer showed significant SMT (semiconductor-metal transition) when SMT became negligible on increasing middle layer's thickness.

Grain-Size-Limited Mobility in Methylammonium Lead Iodide Perovskite Thin Films

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

Reid, Obadiah G.; Yang, Mengjin; Kopidakis, Nikos

2016-09-09

We report a systematic study of the gigahertz-frequency charge carrier mobility found in methylammonium lead iodide perovskite films as a function of average grain size using time-resolved microwave conductivity and a single processing chemistry. Our measurements are in good agreement with the Kubo formula for the AC mobility of charges confined within finite grains, suggesting (1) that the surface grains imaged via scanning electron microscopy are representative of the true electronic domain size and not substantially subdivided by twinning or other defects not visible by microscopy and (2) that the time scale of diffusive transport across grain boundaries is muchmore » slower than the period of the microwave field in this measurement (-100 ps). The intrinsic (infinite grain size) minimum mobility extracted form the model is 29 +/- 6 cm2 V-1 s-1 at the probe frequency (8.9 GHz).« less

Self-Limited Growth in Pentacene Thin Films

PubMed Central

2017-01-01

Pentacene is one of the most studied organic semiconducting materials. While many aspects of the film formation have already been identified in very thin films, this study provides new insight into the transition from the metastable thin-film phase to bulk phase polymorphs. This study focuses on the growth behavior of pentacene within thin films as a function of film thickness ranging from 20 to 300 nm. By employing various X-ray diffraction methods, combined with supporting atomic force microscopy investigations, one crystalline orientation for the thin-film phase is observed, while three differently tilted bulk phase orientations are found. First, bulk phase crystallites grow with their 00L planes parallel to the substrate surface; second, however, crystallites tilted by 0.75° with respect to the substrate are found, which clearly dominate the former in ratio; third, a different bulk phase polymorph with crystallites tilted by 21° is found. The transition from the thin-film phase to the bulk phase is rationalized by the nucleation of the latter at crystal facets of the thin-film-phase crystallites. This leads to a self-limiting growth of the thin-film phase and explains the thickness-dependent phase behavior observed in pentacene thin films, showing that a large amount of material is present in the bulk phase much earlier during the film growth than previously thought. PMID:28287698

Self-Limited Growth in Pentacene Thin Films.

PubMed

Pachmajer, Stefan; Jones, Andrew O F; Truger, Magdalena; Röthel, Christian; Salzmann, Ingo; Werzer, Oliver; Resel, Roland

2017-04-05

Pentacene is one of the most studied organic semiconducting materials. While many aspects of the film formation have already been identified in very thin films, this study provides new insight into the transition from the metastable thin-film phase to bulk phase polymorphs. This study focuses on the growth behavior of pentacene within thin films as a function of film thickness ranging from 20 to 300 nm. By employing various X-ray diffraction methods, combined with supporting atomic force microscopy investigations, one crystalline orientation for the thin-film phase is observed, while three differently tilted bulk phase orientations are found. First, bulk phase crystallites grow with their 00L planes parallel to the substrate surface; second, however, crystallites tilted by 0.75° with respect to the substrate are found, which clearly dominate the former in ratio; third, a different bulk phase polymorph with crystallites tilted by 21° is found. The transition from the thin-film phase to the bulk phase is rationalized by the nucleation of the latter at crystal facets of the thin-film-phase crystallites. This leads to a self-limiting growth of the thin-film phase and explains the thickness-dependent phase behavior observed in pentacene thin films, showing that a large amount of material is present in the bulk phase much earlier during the film growth than previously thought.

Magneto-Optic Laser Beam Steering

DTIC Science & Technology

1975-10-01

Thin Substrates 16 1. Substrate Thinning 16 2. LPE on TMn Substrates 18 3. Statics of BRIG Crystal Films on Thin Substrates... 19 4. Results...6 Garnet Etch Rate 17 7 Thin Substrate: Film Both Sides 20 8 Thin Substrate: Film One Side 21 9 Film with Substrate Both Sides 23 10 Ratio...Robbins et al reported that iron garnet films could be grown on gallium garnet sub- strates by using a coprecipitated slurry. This technique was

Assessment of Chemical Solution Synthesis and Properties of Gd2Zr2O7 Thin Films as Buffer Layers for Second-Generation High-Temperature Superconductor Wires (Postprint)

DTIC Science & Technology

2012-02-01

AC05-00OR22725. REFERENCES 1. D.P. Norton, A. Goyal, J.D. Budai, D.K. Christen, D.M. Kroeger, E.D. Specht , Q. He, B. Saffian, M. Paranthaman, C.E...critical current density. Science 274, 755 (1996). 2. A. Goyal, D.P. Norton, J.D. Budai, M. Paranthaman, E.D. Specht , D.M. Kroeger, D.K. Christen, Q...D.K. Christen, M. Paranthaman, E.D. Specht , J.D. Budai, Q. He, B. Saffian, F.A. List, D.F. Lee, E. Hatfield, P.M. Martin, C.E. Klabunde, J. Mathis

Highly sensitive pseudo-differential ac-nanocalorimeter for the study of the glass transition

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

Laarraj, Mohcine; University Grenoble Alpes, Institut NEEL, F-38042 Grenoble; Laboratoire d’Ingénierie et des Matériaux

2015-11-15

We present a nanocalorimeter designed for the measurement of the dynamic heat capacity of thin films. The microfabricated sensor, the thermal conditioning of the sensor, as well as the highly stable and low noise electronic chain allow measurements of the real and imaginary parts of the complex specific heat with a resolution Δ C/C of about 10{sup −5}. The performances of this quasi-differential nanocalorimeter were tested on a model of polymeric glass-former, the polyvinyl acetate (PVAc). The high stability and low noise of the device are essential for accurate studies on non-equilibrium slow relaxing systems such as glasses.

Atomic layer deposition for fabrication of HfO2/Al2O3 thin films with high laser-induced damage thresholds.

PubMed

Wei, Yaowei; Pan, Feng; Zhang, Qinghua; Ma, Ping

2015-01-01

Previous research on the laser damage resistance of thin films deposited by atomic layer deposition (ALD) is rare. In this work, the ALD process for thin film generation was investigated using different process parameters such as various precursor types and pulse duration. The laser-induced damage threshold (LIDT) was measured as a key property for thin films used as laser system components. Reasons for film damaged were also investigated. The LIDTs for thin films deposited by improved process parameters reached a higher level than previously measured. Specifically, the LIDT of the Al2O3 thin film reached 40 J/cm(2). The LIDT of the HfO2/Al2O3 anti-reflector film reached 18 J/cm(2), the highest value reported for ALD single and anti-reflect films. In addition, it was shown that the LIDT could be improved by further altering the process parameters. All results show that ALD is an effective film deposition technique for fabrication of thin film components for high-power laser systems.

Synthesis and annealing study of RF sputtered ZnO thin film

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

Singh, Shushant Kumar, E-mail: singhshushant86@gmail.com; Sharma, Himanshu; Singhal, R.

2016-05-23

In this paper, we have investigated the annealing effect on optical and structural properties of ZnO thin films, synthesized by RF magnetron sputtering. ZnO thin films were deposited on glass and silicon substrates simultaneously at a substrate temperature of 300 °C using Argon gas in sputtering chamber. Thickness of as deposited ZnO thin film was found to be ~155 nm, calculated by Rutherford backscattering spectroscopy (RBS). These films were annealed at 400 °C and 500 °C temperature in the continuous flow of oxygen gas for 1 hour in tube furnace. X-ray diffraction analysis confirmed the formation of hexagonal wurtzite structuremore » of ZnO thin film along the c-axis (002) orientation. Transmittance of thin films was increased with increasing the annealing temperature estimated by UV-visible transmission spectroscopy. Quality and texture of the thin films were improved with annealing temperature, estimated by Raman spectroscopy.« less

Deposition and characterization of ZnSe nanocrystalline thin films

NASA Astrophysics Data System (ADS)

Temel, Sinan; Gökmen, F. Özge; Yaman, Elif; Nebi, Murat

2018-02-01

ZnSe nanocrystalline thin films were deposited at different deposition times by using the Chemical Bath Deposition (CBD) technique. Effects of deposition time on structural, morphological and optical properties of the obtained thin films were characterized. X-ray diffraction (XRD) analysis was used to study the structural properties of ZnSe nanocrystalline thin films. It was found that ZnSe thin films have a cubic structure with a preferentially orientation of (111). The calculated average grain size value was about 28-30 nm. The surface morphology of these films was studied by the Field Emission Scanning Electron Microscope (FESEM). The surfaces of the thin films were occurred from small stacks and nano-sized particles. The band gap values of the ZnSe nanocrystalline thin films were determined by UV-Visible absorption spectrum and the band gap values were found to be between 2.65-2.86 eV.

Characterisation of Nd2O3 thick gate dielectric for silicon

NASA Astrophysics Data System (ADS)

Dakhel, A. A.

2004-03-01

Thin neodymium films were prepared by the reactive synthesis method on Si (P) substrates to form MOS devices. The oxide films were characterised by UV absorption spectroscopy, X-ray fluorescence (EDXRF) and X-ray diffraction (XRD). The ac conductance and capacitance of the devices were studied as a function of frequency in the range 100 Hz-100 kHz, of temperature in the range 293-473 K and of gate voltage. It was proved that a suitable formalism to explain the frequency dependence of the ac conductivity and capacitance of the insulator is controlled by a universal power law based on the relaxation processes of the hopping or tunnelling of the current carriers between equilibrium sites. The temperature dependence of the ac conductance at the accumulation state shows a small activation energy of about 0.07 eV for a MOS device with amorphous neodymium oxide. The temperature dependence of the accumulation capacitance for a MOS structure with crystalline neodymium oxide shows a maximum at about 390 K; such a maximum was not observed for the structure with amorphous neodymium oxide. The method of capacitance-gate voltage (C-Vg) measurements was used to investigate the effect of annealing in air and in vacuum on the surface density of states (Nss) at the insulator/semiconductor (I/S) interface. It was concluded that the density of surface states in the mid-gap increases by about five times while the density of the trapped charges in the oxide layer decreases by about eight times when the oxide crystallises into a polycrystalline structure.

Multicolor and near-infrared electroluminescence from the light-emitting devices with rare-earth doped TiO{sub 2} films

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

Zhu, Chen; Gao, Zhifei; Wang, Canxing

2015-09-28

We report on multicolor and near-infrared electroluminescence (EL) from the devices using rare-earth doped TiO{sub 2} (TiO{sub 2}:RE) films as light-emitting layers, which are ascribed to the impact excitation of RE{sup 3+} ions, with the EL onset voltages below 10 V. The devices are in the structure of ITO/TiO{sub 2}:RE/SiO{sub 2}/Si, in which the SiO{sub 2} layer is ∼10 nm thick and RE includes Eu, Er, Tm, Nd, and so on. With sufficiently high positive voltage applied on the ITO electrode, the conduction electrons in Si can tunnel into the conduction band of SiO{sub 2} layer via the trap-assisted tunneling mechanism, gainingmore » the potential energy ∼4 eV higher than the conduction band edge of TiO{sub 2}. Therefore, as the electrons in the SiO{sub 2} layer drift into the TiO{sub 2}:RE layer, they become hot electrons. Such hot electrons impact-excite the RE{sup 3+} ions incorporated into the TiO{sub 2} host, leading to the characteristic emissions.« less

Al-/Ga-Doped ZnO Window Layers for Highly Efficient Cu₂ZnSn(S,Se)₄ Thin Film Solar Cells.

PubMed

Seo, Se Won; Seo, Jung Woo; Kim, Donghwan; Cheon, Ki-Beom; Lee, Doh-Kwon; Kim, Jin Young

2018-09-01

The successful use of Al-/Ga-doped ZnO (AGZO) thin films as a transparent conducting oxide (TCO) layer of a Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cell is demonstrated. The AGZO thin films were prepared by radio frequency (RF) sputtering. The structural, crystallographic, electrical, and optical properties of the AGZO thin films were systematically investigated. The photovoltaic properties of CZTSSe thin film solar cells incorporating the AGZO-based TCO layer were also reported. It has been found that the RF power and substrate temperature of the AGZO thin film are important factors determining the electrical, optical, and structural properties. The optimization process involving the RF power and the substrate temperature leads to good electrical and optical transmittance of the AGZO thin films. Finally, the CZTSSe solar cell with the AGZO TCO layer demonstrated a high conversion efficiency of 9.68%, which is higher than that of the conventional AZO counterpart by 12%.

Antimicrobial Activity of Thin Solid Films of Silver Doped Hydroxyapatite Prepared by Sol-Gel Method

PubMed Central

Iconaru, Simona Liliana; Chapon, Patrick; Le Coustumer, Philippe; Predoi, Daniela

2014-01-01

In this work, the preparation and characterization of silver doped hydroxyapatite thin films were reported and their antimicrobial activity was characterized. Silver doped hydroxyapatite (Ag:HAp) thin films coatings substrate was prepared on commercially pure Si disks by sol-gel method. The silver doped hydroxyapatite thin films were characterized by various techniques such as Scanning electron microscopy (SEM) with energy Dispersive X-ray attachment (X-EDS), Fourier transform infrared spectroscopy (FT-IR), and glow discharge optical emission spectroscopy (GDOES). These techniques have permitted the structural and chemical characterisation of the silver doped hydroxyapatite thin films. The antimicrobial effect of the Ag:HAp thin films on Escherichia coli and Staphylococcus aureus bacteria was then investigated. This is the first study on the antimicrobial effect of Ag:HAp thin films obtained by sol-gel method. The results of this study have shown that the Ag:HAp thin films with x Ag = 0.5 are effective against E. coli and S. aureus after 24 h. PMID:24523630

Properties of WO3-x Electrochromic Thin Film Prepared by Reactive Sputtering with Various Post Annealing Temperatures

NASA Astrophysics Data System (ADS)

Kim, Min Hong; Choi, Hyung Wook; Kim, Kyung Hwan

2013-11-01

The WO3-x thin films were prepared on indium tin oxide (ITO) coated glass at 0.7 oxygen flow ratio [O2/(Ar+O2)] using the facing targets sputtering (FTS) system at room temperature. In order to obtain the annealing effect, as-deposited thin films were annealed at temperatures of 100, 200, 300, 400, and 500 °C for 1 h in open air. The structural properties of the WO3-x thin film were measured using an X-ray diffractometer. The WO3-x thin films annealed at up to 300 °C indicated amorphous properties, while those annealed above 400 °C indicated crystalline properties. The electrochemical and optical properties of WO3-x thin films were measured using cyclic voltammetry and a UV/vis spectrometer. The maximum value of coloration efficiency obtained was 34.09 cm2/C for thin film annealed at 200 °C. The WO3-x thin film annealed at 200 °C showed superior electrochromic properties.

Antimicrobial activity of thin solid films of silver doped hydroxyapatite prepared by sol-gel method.

PubMed

Iconaru, Simona Liliana; Chapon, Patrick; Le Coustumer, Philippe; Predoi, Daniela

2014-01-01

In this work, the preparation and characterization of silver doped hydroxyapatite thin films were reported and their antimicrobial activity was characterized. Silver doped hydroxyapatite (Ag:HAp) thin films coatings substrate was prepared on commercially pure Si disks by sol-gel method. The silver doped hydroxyapatite thin films were characterized by various techniques such as Scanning electron microscopy (SEM) with energy Dispersive X-ray attachment (X-EDS), Fourier transform infrared spectroscopy (FT-IR), and glow discharge optical emission spectroscopy (GDOES). These techniques have permitted the structural and chemical characterisation of the silver doped hydroxyapatite thin films. The antimicrobial effect of the Ag:HAp thin films on Escherichia coli and Staphylococcus aureus bacteria was then investigated. This is the first study on the antimicrobial effect of Ag:HAp thin films obtained by sol-gel method. The results of this study have shown that the Ag:HAp thin films with x(Ag) = 0.5 are effective against E. coli and S. aureus after 24 h.

Electrochemical detection of nitrite on poly(pyronin Y)/graphene nanocomposites modified ITO substrate

NASA Astrophysics Data System (ADS)

Şinoforoğlu, Mehmet; Dağcı, Kader; Alanyalıoğlu, Murat; Meral, Kadem

2016-06-01

The present study reports on an easy preparation of poly(pyronin Y)/graphene (poly(PyY)/graphene) nanocomposites thin films on indium tin oxide coated glass substrates (ITO). The thin films of poly(PyY)/graphene nanocomposites are prepared by a novel method consisting of three steps; (i) preparation of graphene oxide (GO) thin films on ITO by spin-coating method, (ii) self-assembly of PyY molecules from aqueous solution onto the GO thin film, (iii) surface-confined electropolymerization (SCEP) of the adsorbed PyY molecules on the GO thin film. The as-prepared poly(PyY)/graphene nanocomposites thin films are characterized by using electroanalytical and spectroscopic techniques. Afterwards, the graphene-based polymeric dye thin film on ITO is used as an electrode in an electrochemical cell. Its performance is tested for electrochemical detection of nitrite. Under optimized conditions, the electrocatalytical effect of the nanocomposites thin film through electrochemical oxidation of nitrite is better than that of GO coated ITO.

Ultrahigh-Performance Cu2ZnSnS4 Thin Film and Its Application in Microscale Thin-Film Lithium-Ion Battery: Comparison with SnO2.

PubMed

Lin, Jie; Guo, Jianlai; Liu, Chang; Guo, Hang

2016-12-21

To develop a high-performance anode for thin-film lithium-ion batteries (TFBs, with a total thickness on the scale of micrometers), a Cu 2 ZnSnS 4 (CZTS) thin film is fabricated by magnetron sputtering and exhibits an ultrahigh performance of 950 mAh g -1 even after 500 cycles, which is the highest among the reported CZTS for lithium storage so far. The characterization and electrochemical tests reveal that the thin-film structure and additional reactions both contribute to the excellent properties. Furthermore, the microscale TFBs with effective footprints of 0.52 mm 2 utilizing the CZTS thin film as anode are manufactured by microfabrication techniques, showing superior capability than the analogous TFBs with the SnO 2 thin film as anode. This work demonstrates the advantages of exploiting thin-film electrodes and novel materials into micropower sources by electronic manufacture methods.

Silk fibroin/chitosan thin film promotes osteogenic and adipogenic differentiation of rat bone marrow-derived mesenchymal stem cells.

PubMed

Li, Da-Wei; He, Jin; He, Feng-Li; Liu, Ya-Li; Liu, Yang-Yang; Ye, Ya-Jing; Deng, Xudong; Yin, Da-Chuan

2018-04-01

As a biodegradable polymer thin film, silk fibroin/chitosan composite film overcomes the defects of pure silk fibroin and chitosan films, respectively, and shows remarkable biocompatibility, appropriate hydrophilicity and mechanical properties. Silk fibroin/chitosan thin film can be used not only as metal implant coating for bone injury repair, but also as tissue engineering scaffold for skin, cornea, adipose, and other soft tissue injury repair. However, the biocompatibility of silk fibroin/chitosan thin film for mesenchymal stem cells, a kind of important seed cell of tissue engineering and regenerative medicine, is rarely reported. In this study, silk fibroin/chitosan film was prepared by solvent casting method, and the rat bone marrow-derived mesenchymal stem cells were cultured on the silk fibroin/chitosan thin film. Osteogenic and adipogenic differentiation of rat bone marrow-derived mesenchymal stem cells were induced, respectively. The proliferation ability, osteogenic and adipogenic differentiation abilities of rat bone marrow-derived mesenchymal stem cells were systematically compared between silk fibroin/chitosan thin film and polystyrene tissue culture plates. The results showed that silk fibroin/chitosan thin film not only provided a comparable environment for the growth and proliferation of rat bone marrow-derived mesenchymal stem cells but also promoted their osteogenic and adipogenic differentiation. This work provided information of rat bone marrow-derived mesenchymal stem cells behavior on silk fibroin/chitosan thin film and extended the application of silk fibroin/chitosan thin film. Based on the results, we suggested that the silk fibroin/chitosan thin film could be a promising material for tissue engineering of bone, cartilage, adipose, and skin.

Evolution of Structural and Electrical Properties of Carbon Films from Amorphous Carbon to Nanocrystalline Graphene on Quartz Glass by HFCVD.

PubMed

Zhai, Zihao; Shen, Honglie; Chen, Jieyi; Li, Xuemei; Jiang, Ye

2018-05-23

Direct growth of graphene films on glass is of great importance but has so far met with limited success. The noncatalytic property of glass results in the low decomposition ability of hydrocarbon precursors, especially at reduced temperatures (<1000 °C), and therefore amorphous carbon (a-C) films are more likely to be obtained. Here, we report the hydrogen influence on the structural and electrical properties of carbon films deposited on quartz glass at 850 °C by hot-filament chemical vapor deposition (HFCVD). The results revealed that the obtained a-C films were all graphitelike carbon films. Structural transition of the deposited films from a-C to nanocrystalline graphene was achieved by raising the hydrogen dilution ratios from 10 to over 80%. On the basis of systematic structural and chemical characterizations, a schematic process with three steps including sp 2 chain aggregation, aromatic ring formation, and sp 3 bond etching was proposed to interpret the structural evolution. The nanocrystalline graphene films grown on glass by HFCVD exhibited good electrical performance with a carrier mobility of 36.76 cm 2 /(V s) and a resistivity of 5.24 × 10 -3 Ω cm over an area of 1 cm 2 . Temperature-dependent electrical characterizations revealed that the electronic transport in carbon films was dominated by defect, localized, and extended states, respectively, when increasing the temperature from 75 to 292 K. The nanocrystalline graphene films presented higher carrier mobility and lower carrier concentration than those of a-C films, which was mainly attributed to their smaller conductive activation energy. The present investigation provides an effective way for direct growth of graphene films on glass at reduced temperatures and also offers useful insights into the understanding of structural and electrical relationship between a-C and graphene.

Growth after thinning a 35-year-old natural stand to different loblolly pine and hardwood basal areas

Treesearch

Michael G. Shelton; Paul A. Murphy

1997-01-01

Growth was monitored for 4 years in a thinned stand in southern Arkansas with three pine basal areas (70, 85, and 100 ft2/ac) and three hardwood basal areas (0, 15, and 30 ft2/ac); pretreatment basal areasaveraged 119 and 33 ft2/ac for pines and hardwoods, respectively.Treatments were arranged in a 3 x 3 factorial...

Study on the Hydrogenated ZnO-Based Thin Film Transistors. Part 1

DTIC Science & Technology

2011-04-30

IGZO film on the performance of thin film transistors 5 Chapter 2. Hydrogenation of a- IGZO channel layer in the thin film transistors 12...effect of substrate temperature during the deposition of a- IGZO film on the performance of thin film transistors Introduction The effect of substrate...temperature during depositing IGZO channel layer on the performance of amorphous indium-gallium-zinc oxide (a- IGZO

Imaging as characterization techniques for thin-film cadmium telluride photovoltaics

NASA Astrophysics Data System (ADS)

Zaunbrecher, Katherine

The goal of increasing the efficiency of solar cell devices is a universal one. Increased photovoltaic (PV) performance means an increase in competition with other energy technologies. One way to improve PV technologies is to develop rapid, accurate characterization tools for quality control. Imaging techniques developed over the past decade are beginning to fill that role. Electroluminescence (EL), photoluminescence (PL), and lock-in thermography are three types of imaging implemented in this study to provide a multifaceted approach to studying imaging as applied to thin-film CdTe solar cells. Images provide spatial information about cell operation, which in turn can be used to identify defects that limit performance. This study began with developing EL, PL, and dark lock-in thermography (DLIT) for CdTe. Once imaging data were acquired, luminescence and thermography signatures of non-uniformities that disrupt the generation and collection of carriers were identified and cataloged. Additional data acquisition and analysis were used to determine luminescence response to varying operating conditions. This includes acquiring spectral data, varying excitation conditions, and correlating luminescence to device performance. EL measurements show variations in a cell's local voltage, which include inhomogeneities in the transparent-conductive oxide (TCO) front contact, CdS window layer, and CdTe absorber layer. EL signatures include large gradients, local reduction of luminescence, and local increases in luminescence on the interior of the device as well as bright spots located on the cell edges. The voltage bias and spectral response were analyzed to determine the response of these non-uniformities and surrounding areas. PL images of CdTe have not shown the same level of detail and features compared to their EL counterparts. Many of the signatures arise from reflections and severe inhomogeneities, but the technique is limited by the external illumination source used to excite carriers. Measurements on unfinished CdS and CdTe films reveal changes in signal after post-deposition processing treatments. DLIT images contained heat signatures arising from defect-related current crowding. Forward- and reverse-bias measurements revealed hot spots related to shunt and weak-diode defects. Modeling and previous studies done on Cu(In,Ga)Se 2 thin-film solar cells aided in identifying the physical causes of these thermographic and luminescence signatures. Imaging data were also coupled with other characterization techniques to provide a more comprehensive examination of nonuniform features and their origins and effects on device performance. These techniques included light-beam-induced-current (LBIC) measurements, which provide spatial quantum efficiency maps of the cell at varying resolutions, as well as time-resolved photoluminescence and spectral PL mapping. Local drops in quantum efficiency seen in LBIC typically corresponded with reductions in EL signal while minority-carrier lifetime values acquired by time-resolved PL measurements correlate with PL intensity.

A comparison study of Co and Cu doped MgO diluted magnetic thin films

NASA Astrophysics Data System (ADS)

Sarıtaş, S.; ćakıcı, T.; Muǧlu, G. Merhan; Kundakcı, M.; Yıldırım, M.

2017-02-01

Transition metal-doped MgO diluted magnetic thin films are appropriate candidates for spintronic applications and designing magnetic devices and sensors. Therefore, MgO:Co and MgO:Cu films were deposited on glass substrates by Chemical Spray Pyrolysis (CSP) method different thin film deposition parameters. Deposited different transition metal doped MgO thin films were compared in terms of optic and structural properties. Comparison optic analysis of the films was investigated spectral absorption and transmittance measurements by UV-Vis double beam spectrophotometer technique. Comparison structural analysis of the thin films was examined by using XRD, Raman Analysis, SEM, EDX and AFM techniques. The transition metal-doped; MgO:Co and MgO:Cu thin films maybe have potential applications in spintronics and magnetic data storage.

Synthesis of cobalt doped BiFeO3 multiferroic thin films on p-Si substrate by sol-gel method

NASA Astrophysics Data System (ADS)

Prasannakumara, R.; Shrisha, B. V.; Naik, K. Gopalakrishna

2018-05-01

Bismuth ferrite (BiFeO3) and cobalt doped BiFeO3 (BiFe1-xCoxO3) nanostructure thin films were grown on p-silicon substrates by sol-gel spin coating method with a sequence of coating and annealing process. The post-annealing of the grown films was carried out under high pure argon atmosphere. The grown nanostructure thin films were characterized using XRD, FESEM, and AFM for the structural, morphological and topological studies, respectively. The elemental compositions of the samples were studied by EDX spectra. The PL spectra of the grown sample shows a narrow emission peak around 559 nm which corresponds to the energy band gap of BFO thin films. The XRD peaks of the BiFeO3 nanostructure thin film reveals the rhombohedral structure and transformed from rhombohedral to orthorhombic or tetragonal structure in Co doped BiFeO3 thin films. The Co substitution in BiFeO3 helped to obtain higher dense nanostructure thin films with smaller grain size than the BiFeO3 thin films.

Structural and electrical transport properties of La2Mo2O9 thin films prepared by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Paul, T.; Ghosh, A.

2017-04-01

We have studied the structure and electrical properties of La2Mo2O9 thin films of different thicknesses prepared by the laser deposition technique at different substrate temperatures. The structural properties of the thin films have been investigated using XRD, XPS, AFM, TEM, SEM, and Raman spectroscopy. The electrical transport properties of the thin films have been investigated in wide temperature and frequency ranges. The cubic nature of the thin films has been confirmed from structural analysis. An enhancement of the oxygen ion conductivity of the films up to five orders of magnitude is obtained compared to that of the bulk La2Mo2O9, suggesting usefulness of the thin films as electrolytes in micro-solid oxide fuel cells. The enhanced dc ionic conductivity of the thin films has been interpreted using the rule of the mixture model, while a power law model has been used to investigate the frequency and temperature dependences of the conductivity. The analysis of the results predicts the three-dimensional oxygen ion conduction in the thin films.

Thin film bismuth iron oxides useful for piezoelectric devices

DOEpatents

Zeches, Robert J.; Martin, Lane W.; Ramesh, Ramamoorthy

2016-05-31

The present invention provides for a composition comprising a thin film of BiFeO.sub.3 having a thickness ranging from 20 nm to 300 nm, a first electrode in contact with the BiFeO.sub.3 thin film, and a second electrode in contact with the BiFeO.sub.3 thin film; wherein the first and second electrodes are in electrical communication. The composition is free or essentially free of lead (Pb). The BFO thin film is has the piezoelectric property of changing its volume and/or shape when an electric field is applied to the BFO thin film.

Applications of Thin Film Thermocouples for Surface Temperature Measurement

NASA Technical Reports Server (NTRS)

Martin, Lisa C.; Holanda, Raymond

1994-01-01

Thin film thermocouples provide a minimally intrusive means of measuring surface temperature in hostile, high temperature environments. Unlike wire thermocouples, thin films do not necessitate any machining of the surface, therefore leaving intact its structural integrity. Thin films are many orders of magnitude thinner than wire, resulting in less disruption to the gas flow and thermal patterns that exist in the operating environment. Thin film thermocouples have been developed for surface temperature measurement on a variety of engine materials. The sensors are fabricated in the NASA Lewis Research Center's Thin Film Sensor Lab, which is a class 1000 clean room. The thermocouples are platinum-13 percent rhodium versus platinum and are fabricated by the sputtering process. Thin film-to-leadwire connections are made using the parallel-gap welding process. Thermocouples have been developed for use on superalloys, ceramics and ceramic composites, and intermetallics. Some applications of thin film thermocouples are: temperature measurement of space shuttle main engine turbine blade materials, temperature measurement in gas turbine engine testing of advanced materials, and temperature and heat flux measurements in a diesel engine. Fabrication of thin film thermocouples is described. Sensor durability, drift rate, and maximum temperature capabilities are addressed.

Sol-gel derived Al-Ga co-doped transparent conducting oxide ZnO thin films

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

Serrao, Felcy Jyothi, E-mail: jyothiserrao@gmail.com; Department of Physics, Karnataka Government Research centre SCEM, Mangalore, 575007; Sandeep, K. M.

2016-05-23

Transparent conducting ZnO doped with Al, Ga and co-doped Al and Ga (1:1) (AGZO) thin films were grown on glass substrates by cost effective sol-gel spin coating method. The XRD results showed that all the films are polycrystalline in nature and highly textured along the (002) plane. Enhanced grain size was observed in the case of AGZO thin films. The transmittance of all the films was more than 83% in the visible region of light. The electrical properties such as carrier concentration and mobility values are increased in case of AGZO compared to that of Al and Ga doped ZnOmore » thin films. The minimum resistivity of 2.54 × 10{sup −3} Ω cm was observed in AGZO thin film. The co-doped AGZO thin films exhibited minimum resistivity and high optical transmittance, indicate that co-doped ZnO thin films could be used in transparent electronics mainly in display applications.« less

Effect of precursor on epitaxially grown of ZnO thin film on p-GaN/sapphire (0 0 0 1) substrate by hydrothermal technique

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

Sahoo, Trilochan; Ju, Jin-Woo; Kannan, V.

2008-03-04

Single crystalline ZnO thin film on p-GaN/sapphire (0 0 0 1) substrate, using two different precursors by hydrothermal route at a temperature of 90 deg. C were successfully grown. The effect of starting precursor on crystalline nature, surface morphology and optical emission of the films were studied. ZnO thin films were grown in aqueous solution of zinc acetate and zinc nitrate. X-ray diffraction analysis revealed that all the thin films were single crystalline in nature and exhibited wurtzite symmetry and c-axis orientation. The thin films obtained with zinc nitrate had a more pitted rough surface morphology compared to the filmmore » grown in zinc acetate. However the thickness of the films remained unaffected by the nature of the starting precursor. Sharp luminescence peaks were observed from the thin films almost at identical energies but deep level emission was slightly prominent for the thin film grown in zinc nitrate.« less

The uniformity study of non-oxide thin film at device level using electron energy loss spectroscopy

NASA Astrophysics Data System (ADS)

Li, Zhi-Peng; Zheng, Yuankai; Li, Shaoping; Wang, Haifeng

2018-05-01

Electron energy loss spectroscopy (EELS) has been widely used as a chemical analysis technique to characterize materials chemical properties, such as element valence states, atoms/ions bonding environment. This study provides a new method to characterize physical properties (i.e., film uniformity, grain orientations) of non-oxide thin films in the magnetic device by using EELS microanalysis on scanning transmission electron microscope. This method is based on analyzing white line ratio of spectra and related extended energy loss fine structures so as to correlate it with thin film uniformity. This new approach can provide an effective and sensitive method to monitor/characterize thin film quality (i.e., uniformity) at atomic level for thin film development, which is especially useful for examining ultra-thin films (i.e., several nanometers) or embedded films in devices for industry applications. More importantly, this technique enables development of quantitative characterization of thin film uniformity and it would be a remarkably useful technique for examining various types of devices for industrial applications.

Investigation of the structural, surface, optical and electrical properties of the Indium doped CuxO thin films deposited by a thermionic vacuum arc

NASA Astrophysics Data System (ADS)

Musaoğlu, Caner; Pat, Suat; Özen, Soner; Korkmaz, Şadan; Mohammadigharehbagh, Reza

2018-03-01

In this study, investigation of some physical properties of In-doped CuxO thin films onto amorphous glass substrates were done. The thin films were depsoied by thermionic vacuum arc technique (TVA). TVA technique gives a thin film with lower precursor impurity according to the other chemical and physical depsoition methods. The microstructural properties of the produced thin films was determined by x-ray diffraction device (XRD). The thickness values were measured as to be 30 nm and 60 nm, respectively. The miller indices of the thin films’ crystalline planes were determined as to be Cu (111), CuO (\\bar{1} 12), CuInO2 (107) and Cu2O (200), Cu (111), CuO (\\bar{1} 12), CuO (\\bar{2} 02), CuInO2 (015) for sample C1 and C2, respectively. The produced In-doped CuO thin films are in polycrystalline structure. The surface properties of produced In doped CuO thin films were determined by using an atomic force microscope (AFM) and field emission scanning electron microscope (FESEM) tools. The optical properties of the In doped CuO thin films were determined by UV–vis spectrophotometer, interferometer, and photoluminescence devices. p-type semiconductor thin film was obtained by TVA depsoition.

Linking Precursor Alterations to Nanoscale Structure and Optical Transparency in Polymer Assisted Fast-Rate Dip-Coating of Vanadium Oxide Thin Films

PubMed Central

Glynn, Colm; Creedon, Donal; Geaney, Hugh; Armstrong, Eileen; Collins, Timothy; Morris, Michael A.; Dwyer, Colm O’

2015-01-01

Solution processed metal oxide thin films are important for modern optoelectronic devices ranging from thin film transistors to photovoltaics and for functional optical coatings. Solution processed techniques such as dip-coating, allow thin films to be rapidly deposited over a large range of surfaces including curved, flexible or plastic substrates without extensive processing of comparative vapour or physical deposition methods. To increase the effectiveness and versatility of dip-coated thin films, alterations to commonly used precursors can be made that facilitate controlled thin film deposition. The effects of polymer assisted deposition and changes in solvent-alkoxide dilution on the morphology, structure, optoelectronic properties and crystallinity of vanadium pentoxide thin films was studied using a dip-coating method using a substrate withdrawal speed within the fast-rate draining regime. The formation of sub-100 nm thin films could be achieved rapidly from dilute alkoxide based precursor solutions with high optical transmission in the visible, linked to the phase and film structure. The effects of the polymer addition was shown to change the crystallized vanadium pentoxide thin films from a granular surface structure to a polycrystalline structure composed of a high density of smaller in-plane grains, resulting in a uniform surface morphology with lower thickness and roughness. PMID:26123117

Nonlinear optical parameters of nanocrystalline AZO thin film measured at different substrate temperatures

NASA Astrophysics Data System (ADS)

Jilani, Asim; Abdel-wahab, M. Sh; Al-ghamdi, Attieh A.; Dahlan, Ammar sadik; Yahia, I. S.

2016-01-01

The 2.2 wt% of aluminum (Al)-doped zinc oxide (AZO) transparent and preferential c-axis oriented thin films were prepared by using radio frequency (DC/RF) magnetron sputtering at different substrate temperature ranging from room temperature to 200 °C. For structural analysis, X-ray Diffraction (XRD) and Atomic Force Electron Microscope (AFM) was used for morphological studies. The optical parameters such as, optical energy gap, refractive index, extinction coefficient, dielectric loss, tangent loss, first and third order nonlinear optical properties of transparent films were investigated. High transmittance above 90% and highly homogeneous surface were observed in all samples. The substrate temperature plays an important role to get the best transparent conductive oxide thin films. The substrate temperature at 150 °C showed the growth of highly transparent AZO thin film. Energy gap increased with the increased in substrate temperature of Al doped thin films. Dielectric constant and loss were found to be photon energy dependent with substrate temperature. The change in substrate temperature of Al doped thin films also affect the non-liner optical properties of thin films. The value of χ(3) was found to be changed with the grain size of the thin films that directly affected by the substrate temperature of the pure and Al doped ZnO thin films.

Thin-Film Thermocouple Technology Demonstrated for Reliable Heat Transfer Measurements

NASA Technical Reports Server (NTRS)

1996-01-01

Exploratory work is in progress to apply thin-film thermocouples to localized heat transfer measurements on turbine engine vanes and blades. The emerging thin-film thermocouple technology shows great potential to improve the accuracy of local heat transfer measurements. To verify and master the experimental methodology of thin-film thermocouples, the NASA Lewis Research Center conducted a proof-of-concept experiment in a controlled environment before applying the thin-film sensors to turbine tests.

Scientific Understanding of Non-Chromated Corrosion Inhibitors Function

DTIC Science & Technology

2013-01-01

deposited Al - Cu thin films (left) and aged Al - Cu thin films (right). 348 Figure 7.8. Pit morphologies developed...under neat epoxy resins applied to “as- deposited ” (left) and aged Al - Cu thin films (right) at different exposure times. 349 Figure 7.9. SEM and EDS...results of “As- deposited ” Al - Cu thin film. 351 Figure 7.10. SEM and EDS results of aged Al - Cu thin films. 352 Figure 7.11. Pit

Piezoelectric thin films and their applications for electronics

NASA Astrophysics Data System (ADS)

Yoshino, Yukio

2009-03-01

ZnO and AlN piezoelectric thin films have been studied for applications in bulk acoustic wave (BAW) resonator. This article introduces methods of forming ZnO and AlN piezoelectric thin films by radio frequency sputtering and applications of BAW resonators considering the relationship between the crystallinity of piezoelectric thin films and the characteristics of the BAW resonators. Using ZnO thin films, BAW resonators were fabricated for a contour mode at 3.58 MHz and thickness modes from 200 MHz to 5 GHz. The ZnO thin films were combined with various materials, substrates, and thin films to minimize the temperature coefficient of frequency (TCF). The minimum TCF of BAW resonators was approximately 2 ppm/°C in the range -20 to 80 °C. The electromechanical coupling coefficient (k2) in a 1.9 GHz BAW resonator was 6.9%. Using AlN thin films, 5-20 GHz BAW resonators with an ultrathin membrane were realized. The membrane thickness of a 20 GHz BAW resonator was about 200 nm, k2 was 6.1%, and the quality factor (Q) was about 280. Q decreased with increasing resonant frequency. The value of k2 is almost the same for 5-20 GHz resonators. This result could be obtained by improving the thickness uniformity, by controlling internal stress of thin films, and by controlling the crystallinity of AlN piezoelectric thin film.

Nanostructured Sublayers for Improved Light Extraction of Top-Emitting and Transparent Organic Electroluminescent Devices

DTIC Science & Technology

2007-05-01

luminous efficiency and wider color gamut . In addition, organic phosphorescent light emitting materials and devices were studied. 15. SUBJECT TERMS...nanostructured Bragg mirrors provided an improved external luminous efficiency and wide color gamut , which will be an essential part of future flat-panel...layers (usually with an ultra-thin shadow mask) or the fabrication of anodes with variable thickness have been used to achieve enhanced color gamut

Electro-thermal control of aluminum-doped zinc oxide/vanadium dioxide multilayered thin films for smart-device applications

PubMed Central

Skuza, J. R.; Scott, D. W.; Mundle, R. M.; Pradhan, A. K.

2016-01-01

We demonstrate the electro-thermal control of aluminum-doped zinc oxide (Al:ZnO) /vanadium dioxide (VO2) multilayered thin films, where the application of a small electric field enables precise control of the applied heat to the VO2 thin film to induce its semiconductor-metal transition (SMT). The transparent conducting oxide nature of the top Al:ZnO film can be tuned to facilitate the fine control of the SMT of the VO2 thin film and its associated properties. In addition, the Al:ZnO film provides a capping layer to the VO2 thin film, which inhibits oxidation to a more energetically favorable and stable V2O5 phase. It also decreases the SMT of the VO2 thin film by approximately 5–10 °C because of an additional stress induced on the VO2 thin film and/or an alteration of the oxygen vacancy concentration in the VO2 thin film. These results have significant impacts on technological applications for both passive and active devices by exploiting this near-room-temperature SMT. PMID:26884225

Effect of substrate temperature and oxygen partial pressure on RF sputtered NiO thin films

NASA Astrophysics Data System (ADS)

Cheemadan, Saheer; Santhosh Kumar, M. C.

2018-04-01

Nickel oxide (NiO) thin films were deposited by RF sputtering process and the physical properties were investigated for varying substrate temperatures and oxygen partial pressure. The variation of the crystallographic orientation and microstructure of the NiO thin films with an increase in substrate temperature were studied. It was observed that NiO thin films deposited at 350 °C shows relatively good crystalline characteristics with a preferential orientation along (111) plane. With the optimum substrate temperature of 350 °C, the NiO thin films were deposited under various oxygen partial pressures at the same experimental conditions. The structural, optical and electrical properties of NiO thin films under varying oxygen partial pressure of 10%–50% were investigated. From XRD it is clear that the films prepared in the pure argon atmosphere were amorphous while the films in oxygen partial pressure exhibited polycrystalline NiO phase. SEM and AFM investigations unveil that the higher substrate temperature improves the microstructure of the thin films. It is revealed that the NiO thin films deposited at oxygen partial pressure of 40% and a substrate temperature of 350 °C, showed higher electrical conductivity with p-type characteristics.

Method and system for constructing a rechargeable battery and battery structures formed with the method

DOEpatents

Hobson, David O.; Snyder, Jr., William B.

1995-01-01

A method and system for manufacturing a thin-film battery and a battery structure formed with the method utilizes a plurality of deposition stations at which thin battery component films are built up in sequence upon a web-like substrate as the substrate is automatically moved through the stations. At an initial station, cathode and anode current collector film sections are deposited upon the substrate, and at another station, a thin cathode film is deposited upon the substrate so to overlie part of the cathode current collector section. At another station, a thin electrolyte film is deposited upon so as to overlie the cathode film and part of the anode current collector film, at yet another station, a thin lithium film is deposited upon so as to overlie the electrolyte film and an additional part of the anode current collector film. Such a method accommodates the winding of a layup of battery components into a spiral configuration to provide a thin-film, high capacity battery and also accommodates the build up of thin film battery components onto a substrate surface having any of a number of shapes.

Research progress of VO2 thin film as laser protecting material

NASA Astrophysics Data System (ADS)

Liu, Zhiwei; Lu, Yuan; Hou, Dianxin

2018-03-01

With the development of laser technology, the battlefield threat of directional laser weapons is becoming more and more serious. The blinding and destruction caused by laser weapons on the photoelectric equipment is an important part of the current photo-electronic warfare. The research on the defense technology of directional laser weapons based on the phase transition characteristics of VO2 thin films is an important subject. The researches of VO2 thin films are summarized based on review these points: the preparation methods of VO2 thin films, phase transition mechanism, phase transition temperature regulating, interaction between VO2 thin films and laser, and the application prospect of vo2 thin film as laser protecting material. This paper has some guiding significance for further research on the VO2 thin films in the field of defense directional laser weapons.

Exciplex-Sensitized Triplet-Triplet Annihilation in Heterojunction Organic Thin-Film.

PubMed

Lin, Bo-Yen; Easley, Connor J; Chen, Chia-Hsun; Tseng, Po-Chen; Lee, Ming-Zer; Sher, Pin-Hao; Wang, Juen-Kai; Chiu, Tien-Lung; Lin, Chi-Feng; Bardeen, Christopher J; Lee, Jiun-Haw

2017-03-29

A new concept for organic light-emitting diodes (OLEDs) is presented, which is called exciplex-sensitized triplet-triplet annihilation (ESTTA). The exciplex formed at the organic heterojunction interface of 4,4',4″-tris(N-3-methyphenyl-N-phenyl-amino) triphenylamine and 9,10-bis(2'-naphthyl) anthracene (ADN) is used to sensitize the triplet-triplet annihilation (TTA) process on the ADN molecules. This results in a turn-on voltage (2.2 V) of the blue emission from the OLED below the bandgap (2.9 eV). From the transient electroluminescence measurement, blue emission totally came from the TTA process without direct recombination on the ADN molecules. The blue singlet exciton from the TTA process can be quenched by energy transfer to the exciplex, as revealed by transient photoluminescence measurements. This can be prevented by blocking the energy transfer path and improving the radiative recombination rate of blue emission. With the insertion of the "triplet diffusion and singlet blocking (TDSB)" layer and the incorporation of the dopant material, an ESTTA-OLED with external quantum efficiency of 5.1% was achieved, which consists of yellow and blue emission coming from the exciplex and ESTTA process, respectively.

Two-dimensional CdS nanosheet-based TFT and LED nanodevices.

PubMed

Ye, Yu; Yu, Bin; Gao, Zhiwei; Meng, Hu; Zhang, Hui; Dai, Lun; Qin, Guogang

2012-05-17

Semiconductor nanosheets have several unique applications in electronic and optoelectronic nanodevices. We have successfully synthesized single-crystalline n-type CdS nanosheets via a chemical vapor deposition (CVD) method in a Cd-enriched ambient. The as-synthesized nanosheets are typically 40-100 nm thick, 10-300 µm wide, and up to several millimeters long. Using the nanosheets, we fabricated for the first time (to our knowledge), nano thin-film transistors (nano-TFTs) based on individual CdS nanosheets. A typical unit of such nanosheet TFTs has a high on-off ratio (∼1.7 ×10(9)) and peak transconductance (∼14.1µS), which to our knowledge are the best values reported so far for semiconductor nano-TFTs. In addition, we fabricated n-CdS nanosheet/p(+)-Si heterojunction light emitting diodes (LEDs) with a top electrode structure. This structure, where the n-type electrode is directly above the junction, has the advantage of a large active region and injection current favorable for high-efficiency electroluminescence (EL) and lasing. Room-temperature spectra of the LEDs consist of only an intense CdS band-edge emission peak (∼507.7 nm) with a full width at half-maximum of about 14 nm.

Chemical vapor deposition of silicon, silicon dioxide, titanium and ferroelectric thin films

NASA Astrophysics Data System (ADS)

Chen, Feng

Various silicon-based thin films (such as epitaxial, polycrystalline and amorphous silicon thin films, silicon dioxide thin films and silicon nitride thin films), titanium thin film and various ferroelectric thin films (such as BaTiO3 and PbTiO3 thin films) play critical roles in the manufacture of microelectronics circuits. For the past few years, there have been tremendous interests to search for cheap, safe and easy-to-use methods to develop those thin films with high quality and good step coverage. Silane is a critical chemical reagent widely used to deposit silicon-based thin films. Despite its wide use, silane is a dangerous material. It is pyrophoric, extremely flammable and may explode from heat, shock and/or friction. Because of the nature of silane, serious safety issues have been raised concerning the use, transportation, and storage of compressed gas cylinders of silane. Therefore it is desired to develop safer ways to deposit silicon-based films. In chapter III, I present the results of our research in the following fields: (1) Silane generator, (2) Substitutes of silane for deposition of silicon and silicon dioxide thin films, (3) Substitutes of silane for silicon dioxide thin film deposition. In chapter IV, hydropyridine is introduced as a new ligand for use in constructing precursors for chemical vapor deposition. Detachement of hydropyridine occurs by a low-temperature reaction leaving hydrogen in place of the hydropyridine ligands. Hydropyridine ligands can be attached to a variety of elements, including main group metals, such as aluminum and antimony, transition metals, such as titanium and tantalum, semiconductors such as silicon, and non-metals such as phosphorus and arsenic. In this study, hydropyridine-containing titanium compounds were synthesized and used as chemical vapor deposition precursors for deposition of titanium containing thin films. Some other titanium compounds were also studied for comparison. In chapter V, Chemical Vapor Depositions (CVD) of many oxide thin films including ferroelectric and high dielectric constant BaTiO3, SrTiO 3 and PbTiO3 films had been carried out under reduced pressure (30 torr--80 torr) using liquid precursors containing beta-diketone ligands. The relative reactivities of Ba(beta-diketonate)2, Sr(beta-diketonate) 2, Pb(beta-diketonate)2, Ti(beta-diketonate)3, TiO(beta-diketonate)2 and Ti(OiPr)2(beta-diketonate) 2 had been studied individually prior to the deposition of BaTiO 3, SrTiO3 and PbTiO3 thin films from the mixtures of corresponding precursors. By using multi-step deposition method, carbon free stoichiometric BaTiO3 thin films uniform in large area have been achieved.

Thermoelectric Properties of Epitaxial β-FeSi2 Thin Films on Si(111) and Approach for Their Enhancement

NASA Astrophysics Data System (ADS)

Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Okuhata, Ryo; Ishibe, Takafumi; Watanabe, Kentaro; Suzuki, Takeyuki; Fujita, Takeshi; Sawano, Kentarou; Nakamura, Yoshiaki

2017-05-01

We have investigated the intrinsic thermoelectric properties of epitaxial β-FeSi2 thin films and the impact of phosphorus (P) doping. Epitaxial β-FeSi2 thin films with single phase were grown on Si(111) substrates by two different techniques in an ultrahigh-vacuum molecular beam epitaxy (MBE) system: solid-phase epitaxy (SPE), where iron silicide films formed by codeposition of Fe and Si at room temperature were recrystallized by annealing at 530°C to form epitaxial β-FeSi2 thin films on Si(111) substrates, and MBE of β-FeSi2 thin films on epitaxial β-FeSi2 templates formed on Si(111) by reactive deposition epitaxy (RDE) at 530°C (RDE + MBE). Epitaxial SPE thin films based on codeposition had a flatter surface and more abrupt β-FeSi2/Si(111) interface than epitaxial RDE + MBE thin films. We investigated the intrinsic thermoelectric properties of the epitaxial β-FeSi2 thin films on Si(111), revealing lower thermal conductivity and higher electrical conductivity compared with bulk β-FeSi2. We also investigated the impact of doping on the Seebeck coefficient of bulk and thin-film β-FeSi2. A route to enhance the thermoelectric performance of β-FeSi2 is proposed, based on (1) fabrication of thin-film structures for high electrical conductivity and low thermal conductivity, and (2) proper choice of doping for high Seebeck coefficient.

Structure disorder degree of polysilicon thin films grown by different processing: Constant C from Raman spectroscopy

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

Wang, Quan, E-mail: wangq@mail.ujs.edu.cn; State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000; Zhang, Yanmin

2013-11-14

Flat, low-stress, boron-doped polysilicon thin films were prepared on single crystalline silicon substrates by low pressure chemical vapor deposition. It was found that the polysilicon films with different deposition processing have different microstructure properties. The confinement effect, tensile stresses, defects, and the Fano effect all have a great influence on the line shape of Raman scattering peak. But the effect results are different. The microstructure and the surface layer are two important mechanisms dominating the internal stress in three types of polysilicon thin films. For low-stress polysilicon thin film, the tensile stresses are mainly due to the change of microstructuremore » after thermal annealing. But the tensile stresses in flat polysilicon thin film are induced by the silicon carbide layer at surface. After the thin film doped with boron atoms, the phenomenon of the tensile stresses increasing can be explained by the change of microstructure and the increase in the content of silicon carbide. We also investigated the disorder degree states for three polysilicon thin films by analyzing a constant C. It was found that the disorder degree of low-stress polysilicon thin film larger than that of flat and boron-doped polysilicon thin films due to the phase transformation after annealing. After the flat polysilicon thin film doped with boron atoms, there is no obvious change in the disorder degree and the disorder degree in some regions even decreases.« less

Temperature Behavior of Thin Film Varactor

DTIC Science & Technology

2012-01-01

Temperature Behavior of Thin Film Varactor By Richard X. Fu ARL-TR-5905 January 2012...Thin Film Varactor Richard X. Fu Sensors and Electron Devices Directorate, ARL...DD-MM-YYYY) January 2012 2. REPORT TYPE Final 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Temperature Behavior of Thin Film Varactor 5a

Electronic Devices Based on Oxide Thin Films Fabricated by Fiber-to-Film Process.

PubMed

Meng, You; Liu, Ao; Guo, Zidong; Liu, Guoxia; Shin, Byoungchul; Noh, Yong-Young; Fortunato, Elvira; Martins, Rodrigo; Shan, Fukai

2018-05-30

Technical development for thin-film fabrication is essential for emerging metal-oxide (MO) electronics. Although impressive progress has been achieved in fabricating MO thin films, the challenges still remain. Here, we report a versatile and general thermal-induced nanomelting technique for fabricating MO thin films from the fiber networks, briefly called fiber-to-film (FTF) process. The high quality of the FTF-processed MO thin films was confirmed by various investigations. The FTF process is generally applicable to numerous technologically relevant MO thin films, including semiconducting thin films (e.g., In 2 O 3 , InZnO, and InZrZnO), conducting thin films (e.g., InSnO), and insulating thin films (e.g., AlO x ). By optimizing the fabrication process, In 2 O 3 /AlO x thin-film transistors (TFTs) were successfully integrated by fully FTF processes. High-performance TFT was achieved with an average mobility of ∼25 cm 2 /(Vs), an on/off current ratio of ∼10 7 , a threshold voltage of ∼1 V, and a device yield of 100%. As a proof of concept, one-transistor-driven pixel circuit was constructed, which exhibited high controllability over the light-emitting diodes. Logic gates based on fully FTF-processed In 2 O 3 /AlO x TFTs were further realized, which exhibited good dynamic logic responses and voltage amplification by a factor of ∼4. The FTF technique presented here offers great potential in large-area and low-cost manufacturing for flexible oxide electronics.

Uniform implantation of CNTs on total activated carbon surfaces: a smart engineering protocol for commercial supercapacitor applications

NASA Astrophysics Data System (ADS)

Jiang, Jian; Li, Linpo; Liu, Yani; Liu, Siyuan; Xu, Maowen; Zhu, Jianhui

2017-04-01

The main obstacles to building better supercapacitors are still trade-offs between energy and power parameters. To promote commercial supercapacitor behaviors, proper optimization toward electrode configurations/architectures may be a feasible and effective way. We herein propose a smart and reliable electrode engineering protocol, by in situ implantation of carbon nanotubes (CNTs) on total activated carbon (AC) surfaces via a mild chemical vapor deposition process at ˜550 °C, using nickel nitrate hydroxide (NNH) thin films and waste ethanol solvents as the catalyst and carbon sources, respectively. The direct and conformal growth of NNH layers onto carbonaceous scaffold guarantees the later uniform implantation of long and high-quality CNTs on total AC outer surfaces. Such fluffy and entangled CNTs preserve ionic diffusion channels, well connect neighboring ACs and function as superhighways for electrons transfer, endowing electrodes with outstanding capacitive behaviors including large output capacitances of ˜230 F g-1 in 1 M Na2SO4 neutral solution and ˜502.5 F g-1 in 6 M KOH using Ni valence state variation, and very negligible capacity decay in long-term cycles. Furthermore, a full symmetric supercapacitor device of CNTs@ACs//CNTs@ACs has been constructed, capable of delivering both high specific energy and power densities (maximum values reaching up to ˜97.2 Wh kg-1 and ˜10.84 kW kg-1), which holds great potential in competing with current mainstream supercapacitors.

Uniform implantation of CNTs on total activated carbon surfaces: a smart engineering protocol for commercial supercapacitor applications.

PubMed

Jiang, Jian; Li, Linpo; Liu, Yani; Liu, Siyuan; Xu, Maowen; Zhu, Jianhui

2017-04-07

The main obstacles to building better supercapacitors are still trade-offs between energy and power parameters. To promote commercial supercapacitor behaviors, proper optimization toward electrode configurations/architectures may be a feasible and effective way. We herein propose a smart and reliable electrode engineering protocol, by in situ implantation of carbon nanotubes (CNTs) on total activated carbon (AC) surfaces via a mild chemical vapor deposition process at ∼550 °C, using nickel nitrate hydroxide (NNH) thin films and waste ethanol solvents as the catalyst and carbon sources, respectively. The direct and conformal growth of NNH layers onto carbonaceous scaffold guarantees the later uniform implantation of long and high-quality CNTs on total AC outer surfaces. Such fluffy and entangled CNTs preserve ionic diffusion channels, well connect neighboring ACs and function as superhighways for electrons transfer, endowing electrodes with outstanding capacitive behaviors including large output capacitances of ∼230 F g -1 in 1 M Na 2 SO 4 neutral solution and ∼502.5 F g -1 in 6 M KOH using Ni valence state variation, and very negligible capacity decay in long-term cycles. Furthermore, a full symmetric supercapacitor device of CNTs@ACs//CNTs@ACs has been constructed, capable of delivering both high specific energy and power densities (maximum values reaching up to ∼97.2 Wh kg -1 and ∼10.84 kW kg -1 ), which holds great potential in competing with current mainstream supercapacitors.

Studies on RF sputtered (WO3)1-x (V2O5)x thin films for smart window applications

NASA Astrophysics Data System (ADS)

Meenakshi, M.; Sivakumar, R.; Perumal, P.; Sanjeeviraja, C.

2016-05-01

V2O5 doped WO3 targets for RF sputtering thin film deposition were prepared for various compositions. Thin films of (WO3)1-x (V2O5)x were deposited on to glass substrates using these targets. Structural characteristics of the prepared targets and thin films were studied using X-ray diffraction. Laser Raman studies were carried out on the thin films to confirm the compound formation.

Application Of Positron Beams For The Characterization Of Nano-scale Pores In Thin Films

NASA Astrophysics Data System (ADS)

Hirata, K.; Ito, K.; Kobayashi, Y.; Suzuki, R.; Ohdaira, T.; Eijt, S. W. H.; Schut, H.; van Veen, A.

2003-08-01

We applied three positron annihilation techniques, positron 3γ-annihilation spectroscopy, positron annihilation lifetime spectroscopy, and angular correlation of annihilation radiation, to the characterization of nano-scale pores in thin films by combining them with variable-energy positron beams. Characterization of pores in thin films is an important part of the research on various thin films of industrial importance. The results of our recent studies on pore characterization of thin films by positron beams will be reported here.

Characterization of aluminum selenide bi-layer thin film

NASA Astrophysics Data System (ADS)

Boolchandani, Sarita; Soni, Gyanesh; Srivastava, Subodh; Vijay, Y. K.

2018-05-01

The Aluminum Selenide (AlSe) bi-layer thin films were grown on glass substrate using thermal evaporation method under high vacuum condition. The morphological characterization was done using SEM. Electrical measurement with temperature variation shows that thin films exhibit the semiconductor nature. The optical properties of prepared thin films have also been characterized by UV-VIS spectroscopy measurements. The band gap of composite thin films has been calculated by Tauc's relation at different temperature ranging 35°C-100°C.

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

NASA Astrophysics Data System (ADS)

Miller, Richards; van Schooten, K. J.; Malissa, H.; Joshi, G.; Jamali, S.; Lupton, J. M.; Boehme, C.

2016-12-01

We have studied the role of spin-dependent processes on conductivity in polyfluorene (PFO) thin films by preforming continuous wave (cw) electrically detected magnetic resonance (EDMR) spectroscopy at temperatures between 10 K and room temperature using microwave frequencies between about 1 GHz and 20 GHz, as well as pulsed EDMR at the X band (10 GHz). Variable frequency EDMR allows us to establish the role of spin-orbit coupling in spin-dependent processes whereas pulsed EDMR allows for the observation of coherent spin motion effects. We used PFO for this study in order to allow for the investigation of the effects of microscopic morphological ordering since this material can adopt two distinct intrachain morphologies: an amorphous (glassy) phase, in which monomer units are twisted with respect to each other, and an ordered (β) phase, where all monomers lie within one plane. In thin films of organic light-emitting diodes, the appearance of a particular phase can be controlled by deposition parameters and solvent vapor annealing, and is verified by electroluminescence spectroscopy. Under bipolar charge-carrier injection conditions, we conducted multifrequency cw EDMR, electrically detected Rabi spin-beat experiments, and Hahn echo and inversion-recovery measurements. Coherent echo spectroscopy reveals electrically detected electron-spin-echo envelope modulation due to the coupling of the carrier spins to nearby nuclear spins. Our results demonstrate that, while conformational disorder can influence the observed EDMR signals, including the sign of the current changes on resonance as well as the magnitudes of local hyperfine fields and charge-carrier spin-orbit interactions, it does not qualitatively affect the nature of spin-dependent transitions in this material. In both morphologies, we observe the presence of at least two different spin-dependent recombination processes. At room temperature and 10 K, polaron-pair recombination through weakly spin-spin coupled intermediate charge-carrier pair states is dominant, while at low temperatures, additional signatures of spin-dependent charge transport through the interaction of polarons with triplet excitons are seen in the half-field resonance of a triplet spin-1 species. This additional contribution arises since triplet lifetimes are increased at lower temperatures. We tentatively conclude that spectral broadening induced by hyperfine coupling is slightly weaker in the more ordered β-phase than in the glassy phase since protons are more evenly spaced, whereas broadening effects due to spin-orbit coupling, which impacts the distribution of g -factors, appear to be somewhat more significant in the β-phase.

Investigation of phase transition properties of ZrO2 thin films

NASA Astrophysics Data System (ADS)

Kumar, Davinder; Singh, Avtar; Kaur, Manpreet; Rana, Vikrant Singh; Kaur, Raminder

2018-05-01

This paper presents the synthesis of transparent thin films of zirconium oxide (ZrO2) deposited on glass substrates by sol-gel dip coating technique. Synthesized films were characterized for different annealing time and withdrawal speed. Change in crystallographic properties of thin films was investigated by using X-ray diffraction. Surface morphology of transparent thin films was estimated by using scanning electron microscope.

Consequence of oxidant concentration on XPS properties of chemically synthesized polythiophene thin films

NASA Astrophysics Data System (ADS)

Kamat, Sandip V.; Chhabra, Jasvinder; Patil, V. S.; Yadav, J. B.; Puri, R. K.; Puri, Vijaya

2018-05-01

The polythiophene thin films were prepared by a wellknown chemical bath deposition technique. The deposited thin films were characterized for structural morphological properties and the adhesion of these thin films were measured by direct pull off (DPO) method, the effect of oxidant concentration on these thin films also studied. The FTIR spectra of chemically deposited polythiophene thin films shows the absorption peak at 836 cm-1 which represents c-s stretching vibrations, shifts to 869 cm-1 as the oxidant concentration increases. The band at 666 cm-1 representing c-s-c ring deformation becomes sharper and appears with a shoulder peak due to increase in oxidant concentration.

Methods of making non-covalently bonded carbon-titania nanocomposite thin films and applications of the same

DOEpatents

Liang, Yu Teng; Vijayan, Baiju K.; Gray, Kimberly A.; Hersam, Mark C.

2016-07-19

In one aspect, a method of making non-covalently bonded carbon-titania nanocomposite thin films includes: forming a carbon-based ink; forming a titania (TiO.sub.2) solution; blade-coating a mechanical mixture of the carbon-based ink and the titania solution onto a substrate; and annealing the blade-coated substrate at a first temperature for a first period of time to obtain the carbon-based titania nanocomposite thin films. In certain embodiments, the carbon-based titania nanocomposite thin films may include solvent-exfoliated graphene titania (SEG-TiO.sub.2) nanocomposite thin films, or single walled carbon nanotube titania (SWCNT-TiO.sub.2) nanocomposite thin films.

Tunnel based spin injection devices for semiconductor spintronics

NASA Astrophysics Data System (ADS)

Jiang, Xin

This dissertation summarizes the work on spin-dependent electron transport and spin injection in tunnel based spintronic devices. In particular, it focuses on a novel three terminal hot electron device combining ferromagnetic metals and semiconductors---the magnetic tunnel transistor (MTT). The MTT has extremely high magnetic field sensitivity and is a useful tool to explore spin-dependent electron transport in metals, semiconductors, and at their interfaces over a wide energy range. In Chap. 1, the basic concept and fabrication of the MTT are discussed. Two types of MTTs, with ferromagnetic single and spin-valve base layers, respectively, are introduced and compared. In the following chapters, the transport properties of the MTT are discussed in detail, including the spin-dependent hot electron attenuation lengths in CoFe and NiFe thin films on GaAs (Chap. 2), the bias voltage dependence of the magneto-current (Chap. 3), the giant magneto-current effect in MTTs with a spin-valve base (Chap. 4), and the influence of non-magnetic seed layers on magneto-electronic properties of MTTs with a Si collector (Chap. 5). Chap. 6 concentrates on electrical injection of spin-polarized electrons into semiconductors, which is an essential ingredient in semiconductor spintronics. Two types of spin injectors are discussed: an MTT injector and a CoFe/MgO tunnel injector. The spin polarization of the injected electron current is detected optically by measuring the circular polarization of electroluminescence from a quantum well light emitting diode. Using an MTT injector a spin polarization of ˜10% is found for injection electron energy of ˜2 eV at 1.4K. This moderate spin polarization is most likely limited by significant electron spin relaxation at high energy. Much higher spin injection efficiency is obtained by using a CoFe/MgO tunnel injector with spin polarization values of ˜50% at 100K. The temperature and bias dependence of the electroluminescence polarization provides insight into spin relaxation mechanisms within the semiconductor heterostructure.

Development of Room Temperature Excitonic Lasing From ZnO and MgZnO Thin Film Based Metal-Semiconductor-Metal Devices

NASA Astrophysics Data System (ADS)

Suja, Mohammad Zahir Uddin

Room temperature excitonic lasing is demonstrated and developed by utilizing metal-semiconductor-metal devices based on ZnO and MgZnO materials. At first, Cu-doped p-type ZnO films are grown on c-sapphire substrates by plasma-assisted molecular beam epitaxy. Photoluminescence (PL) experiments reveal a shallow acceptor state at 0.15 eV above the valence band edge. Hall effect results indicate that a growth condition window is found for the formation of p-type ZnO thin films and the best conductivity is achieved with a high hole concentration of 1.54x1018 cm-3, a low resistivity of 0.6 O cm and a moderate mobility of 6.65 cm2 V -1 s-1 at room temperature. Metal oxide semiconductor (MOS) capacitor devices have been fabricated on the Cu-doped ZnO films and the characteristics of capacitance-voltage measurements demonstrate that the Cu-doped ZnO thin films under proper growth conditions are p-type. Seebeck measurements on these Cu-doped ZnO samples lead to positive Seebeck coefficients and further confirm the p-type conductivity. Other measurements such as XRD, XPS, Raman and absorption are also performed to elucidate the structural and optical characteristics of the Cu-doped p-type ZnO films. The p-type conductivity is explained to originate from Cu substitution of Zn with a valency of +1 state. However, all p-type samples are converted to n-type over time, which is mostly due to the carrier compensation from extrinsic defects of ZnO. To overcome the stability issue of p-type ZnO film, alternate devices other than p-n junction has been developed. Electrically driven plasmon-exciton coupled random lasing is demonstrated by incorporating Ag nanoparticles on Cu-doped ZnO metal-semiconductor-metal (MSM) devices. Both photoluminescence and electroluminescence studies show that emission efficiencies have been enhanced significantly due to coupling between ZnO excitons and Ag surface plasmons. With the incorporation of Ag nanoparticles on ZnO MSM structures, internal quantum efficiency up to 6 times is demonstrated. Threshold current for lasing is decreased by as much as 30% while the output power is increased up to 350% at an injection current of 40 mA. A numerical simulation study reveals that hole carriers are generated in the ZnO MSM devices from impact ionization processes for subsequent plasmon-exciton coupled lasing. Our results suggest that plasmon-enhanced ZnO MSM random lasers can become a competitive candidate of efficient ultraviolet light sources. Semiconductor lasers in the deep ultraviolet (UV) range have numerous potential applications ranging from water purification and medical diagnosis to high-density data storage and flexible displays. Nevertheless, very little success was achieved in the realization of electrically driven deep UV semiconductor lasers to date. In this thesis, we report the fabrication and characterization of deep UV MgZnO semiconductor lasers. These lasers are operated with continuous current mode at room temperature and the shortest wavelength reaches 284 nm. The wide bandgap MgZnO thin films with various Mg mole fractions were grown on c-sapphire substrate using radio-frequency plasma assisted molecular beam epitaxy. Metal-semiconductor-metal (MSM) random laser devices were fabricated using lithography and metallization processes. Besides the demonstration of scalable emission wavelength, very low threshold current densities of 29 33 A/cm2 are achieved. Numerical modeling reveals that impact ionization process is responsible for the generation of hole carriers in the MgZnO MSM devices. The interaction of electrons and holes leads to radiative excitonic recombination and subsequent coherent random lasing.

Effect of Doping Materials on the Low-Level NO Gas Sensing Properties of ZnO Thin Films

NASA Astrophysics Data System (ADS)

Çorlu, Tugba; Karaduman, Irmak; Yildirim, Memet Ali; Ateş, Aytunç; Acar, Selim

2017-07-01

In this study, undoped, Cu-doped, and Ni-doped ZnO thin films have been successfully prepared by successive ionic layer adsorption and reaction method. The structural, compositional, and morphological properties of the thin films are characterized by x-ray diffractometer, energy dispersive x-ray analysis (EDX), and scanning electron microscopy, respectively. Doping effects on the NO gas sensing properties of these thin films were investigated depending on gas concentration and operating temperature. Cu-doped ZnO thin film exhibited a higher gas response than undoped and Ni-doped ZnO thin film at the operating temperature range. The sensor with Cu-doped ZnO thin film gave faster responses and recovery speeds than other sensors, so that is significant for the convenient application of gas sensor. The response and recovery speeds could be associated with the effective electron transfer between the Cu-doped ZnO and the NO molecules.

Spectroscopic ellipsometry investigation of the optical properties of graphene oxide dip-coated on magnetron sputtered gold thin films

NASA Astrophysics Data System (ADS)

Politano, Grazia Giuseppina; Vena, Carlo; Desiderio, Giovanni; Versace, Carlo

2018-02-01

Despite intensive investigations on graphene oxide-gold nanocomposites, the interaction of graphene oxide sheets with magnetron sputtered gold thin films has not been studied yet. The optical constants of graphene oxide thin films dip-coated on magnetron sputtered gold thin films were determined by spectroscopic ellipsometry in the [300-1000] wavelength range. Moreover, the morphologic properties of the samples were investigated by SEM analysis. Graphene oxide absorbs mainly in the ultraviolet region, but when it is dip-coated on magnetron sputtered gold thin films, its optical constants show dramatic changes, becoming absorbing in the visible region, with a peak of the extinction coefficient at 3.1 eV. Using magnetron sputtered gold thin films as a substrate for graphene oxide thin films could therefore be the key to enhance graphene oxide optical sheets' properties for several technological applications, preserving their oxygen content and avoiding the reduction process.

Optical stress generator and detector

DOEpatents

Maris, Humphrey J.; Stoner, Robert J

2001-01-01

Disclosed is a system for the characterization of thin films and interfaces between thin films through measurements of their mechanical and thermal properties. In the system light is absorbed in a thin film or in a structure made up of several thin films, and the change in optical transmission or reflection is measured and analyzed. The change in reflection or transmission is used to give information about the ultrasonic waves that are produced in the structure. The information that is obtained from the use of the measurement methods and apparatus of this invention can include: (a) a determination of the thickness of thin films with a speed and accuracy that is improved compared to earlier methods; (b) a determination of the thermal, elastic, and optical properties of thin films; (c) a determination of the stress in thin films; and (d) a characterization of the properties of interfaces, including the presence of roughness and defects.

Optical stress generator and detector

DOEpatents

Maris, Humphrey J.; Stoner, Robert J.

1998-01-01

Disclosed is a system for the characterization of thin films and interfaces between thin films through measurements of their mechanical and thermal properties. In the system light is absorbed in a thin film or in a structure made up of several thin films, and the change in optical transmission or reflection is measured and analyzed. The change in reflection or transmission is used to give information about the ultrasonic waves that are produced in the structure. The information that is obtained from the use of the measurement methods and apparatus of this invention can include: (a) a determination of the thickness of thin films with a speed and accuracy that is improved compared to earlier methods; (b) a determination of the thermal, elastic, and optical properties of thin films; (c) a determination of the stress in thin films; and (d) a characterization of the properties of interfaces, including the presence of roughness and defects.

Optical stress generator and detector

DOEpatents

Maris, H.J.; Stoner, R.J.

1998-05-05

Disclosed is a system for the characterization of thin films and interfaces between thin films through measurements of their mechanical and thermal properties. In the system light is absorbed in a thin film or in a structure made up of several thin films, and the change in optical transmission or reflection is measured and analyzed. The change in reflection or transmission is used to give information about the ultrasonic waves that are produced in the structure. The information that is obtained from the use of the measurement methods and apparatus of this invention can include: (a) a determination of the thickness of thin films with a speed and accuracy that is improved compared to earlier methods; (b) a determination of the thermal, elastic, and optical properties of thin films; (c) a determination of the stress in thin films; and (d) a characterization of the properties of interfaces, including the presence of roughness and defects. 32 figs.

Optical stress generator and detector

DOEpatents

Maris, Humphrey J.; Stoner, Robert J

2002-01-01

Disclosed is a system for the characterization of thin films and interfaces between thin films through measurements of their mechanical and thermal properties. In the system light is absorbed in a thin film or in a structure made up of several thin films, and the change in optical transmission or reflection is measured and analyzed. The change in reflection or transmission is used to give information about the ultrasonic waves that are produced in the structure. The information that is obtained from the use of the measurement methods and apparatus of this invention can include: (a) a determination of the thickness of thin films with a speed and accuracy that is improved compared to earlier methods; (b) a determination of the thermal, elastic, and optical properties of thin films; (c) a determination of the stress in thin films; and (d) a characterization of the properties of interfaces, including the presence of roughness and defects.

Optical stress generator and detector

DOEpatents

Maris, Humphrey J.; Stoner, Robert J

1999-01-01

Disclosed is a system for the characterization of thin films and interfaces between thin films through measurements of their mechanical and thermal properties. In the system light is absorbed in a thin film or in a structure made up of several thin films, and the change in optical transmission or reflection is measured and analyzed. The change in reflection or transmission is used to give information about the ultrasonic waves that are produced in the structure. The information that is obtained from the use of the measurement methods and apparatus of this invention can include: (a) a determination of the thickness of thin films with a speed and accuracy that is improved compared to earlier methods; (b) a determination of the thermal, elastic, and optical properties of thin films; (c) a determination of the stress in thin films; and (d) a characterization of the properties of interfaces, including the presence of roughness and defects.

Antimicrobial activity of biopolymer-antibiotic thin films fabricated by advanced pulsed laser methods

NASA Astrophysics Data System (ADS)

Cristescu, R.; Popescu, C.; Dorcioman, G.; Miroiu, F. M.; Socol, G.; Mihailescu, I. N.; Gittard, S. D.; Miller, P. R.; Narayan, R. J.; Enculescu, M.; Chrisey, D. B.

2013-08-01

We report on thin film deposition by matrix assisted pulsed laser evaporation (MAPLE) of two polymer-drug composite thin film systems. A pulsed KrF* excimer laser source (λ = 248 nm, τ = 25 ns, ν = 10 Hz) was used to deposit composite thin films of poly(D,L-lactide) (PDLLA) containing several gentamicin concentrations. FTIR spectroscopy was used to demonstrate that MAPLE-transferred materials exhibited chemical structures similar to those of drop cast materials. Scanning electron microscopy data indicated that MAPLE may be used to fabricate thin films of good morphological quality. The activity of PDLLA-gentamicin composite thin films against Staphylococcus aureus bacteria was demonstrated using drop testing. The influence of drug concentration on microbial viability was also assessed. Our studies indicate that polymer-drug composite thin films prepared by MAPLE may be used to impart antimicrobial activity to implants, medical devices, and other contact surfaces.

Characterization of Pb-Doped GaN Thin Films Grown by Thermionic Vacuum Arc

NASA Astrophysics Data System (ADS)

Özen, Soner; Pat, Suat; Korkmaz, Şadan

2018-03-01

Undoped and lead (Pb)-doped gallium nitride (GaN) thin films have been deposited by a thermionic vacuum arc (TVA) method. Glass and polyethylene terephthalate were selected as optically transparent substrates. The structural, optical, morphological, and electrical properties of the deposited thin films were investigated. These physical properties were interpreted by comparison with related analysis methods. The crystalline structure of the deposited GaN thin films was hexagonal wurtzite. The optical bandgap energy of the GaN and Pb-doped GaN thin films was found to be 3.45 eV and 3.47 eV, respectively. The surface properties of the deposited thin films were imaged using atomic force microscopy and field-emission scanning electron microscopy, revealing a nanostructured, homogeneous, and granular surface structure. These results confirm that the TVA method is an alternative layer deposition system for Pb-doped GaN thin films.

A study on micro-structural and optical parameters of InxSe1-x thin film

NASA Astrophysics Data System (ADS)

Patel, P. B.; Desai, H. N.; Dhimmar, J. M.; Modi, B. P.

2018-04-01

Thin film of Indium Selenide (InSe) has been deposited by thermal evaporation technique onto pre cleaned glass substrate under high vacuum condition. The micro-structural and optical properties of InxSe1-x (x = 0.6, 1-x = 0.4) thin film have been characterized by X-ray diffractrometer (XRD) and UV-Visible spectrophotometer. The XRD spectra showed that InSe thin film has single phase hexagonal structure with preferred orientation along (1 1 0) direction. The micro-structural parameters (crystallite size, lattice strain, dislocation density, domain population) for InSe thin film have been calculated using XRD spectra. The optical parameters (absorption, transmittance, reflectance, energy band gap, Urbach energy) of InSe thin film have been evaluated from absorption spectra. The direct energy band gap and Urbach energy of InSe thin film is found to be 1.90 eV and 235 meV respectively.

Large area polysilicon films with predetermined stress characteristics and method for producing same

NASA Technical Reports Server (NTRS)

Heuer, Arthur H. (Inventor); Kahn, Harold (Inventor); Yang, Jie (Inventor); Phillips, Stephen M. (Inventor)

2002-01-01

Multi-layer assemblies of polysilicon thin films having predetermined stress characteristics and techniques for forming such assemblies are disclosed. In particular, a multi-layer assembly of polysilicon thin films may be produced that has a stress level of zero, or substantially so. The multi-layer assemblies comprise at least one constituent thin film having a tensile stress and at least one constituent thin film having a compressive stress. The thin films forming the multi-layer assemblies may be disposed immediately adjacent to one another without the use of intermediate layers between the thin films. Multi-layer assemblies exhibiting selectively determinable overall bending moments are also disclosed. Selective production of overall bending moments in microstructures enables manufacture of such structures with a wide array of geometrical configurations.

Enhancing the color gamut of white displays using novel deep-blue organic fluorescent dyes to form color-changed thin films with improved efficiency

NASA Astrophysics Data System (ADS)

Liu, Wei-Ting; Huang, Wen-Yao

2012-10-01

This study used the novel fluorescence based deep-blue-emitting molecule BPVPDA in an organic fluorescent color thin film to exhibit deep blue color with CIE coordinates of (0.13, 0.16). The developed original organic RGB color thin film technology enables the optimization of the distinctive features of an organic light emitting diode (OLED) and thin-film-transistor (TFT) LCD display. The color filter structure maintains the same high resolution to obtain a higher level of brightness in comparison with conventional organic RGB color thin film. The image-processing engine is designed to achieve a sharp text image for a TFT LCD with organic color thin films. The organic color thin films structure uses an organic dye dopant in a limpid photoresist. With this technology, the following characteristics can be obtained: 1. high color reproduction of gamut ratio, and 2. improved luminous efficiency with organic color fluorescent thin film. This performance is among the best results ever reported for a color-filter used on TFT-LCD or OLED.

Enhancing the color gamut of white displays using novel deep-blue organic fluorescent dyes to form color-changed thin films with improved efficiency

NASA Astrophysics Data System (ADS)

Liu, Wei-ting; Huang, Wen-Yao

2012-06-01

This study used novel fluorescence based deep-blue-emitting molecules, namely BPVPDA, an organic fluorescence color thin film using BPVPDA exhibit deep blue fluorine with CIE coordinates of (0.13,0.16). The developed original Organic RGB color thin film technology enables the optimization of the distinctive features of an organic light emitting diode (OLED) and (TFT) LCD display. The color filter structure maintains the same high resolution to obtain a higher level of brightness, in comparison with conventional organic RGB color thin film. The image-processing engine is designed to achieve a sharp text image for a thin-film-transistor (TFT) LCD with organic color thin films. The organic color thin films structure uses organic dye dopent in limpid photo resist. With this technology , the following characteristics can be obtained: (1) high color reproduction of gamut ratio, and (2) improved luminous efficiency with organic color fluorescence thin film. This performance is among the best results ever reported for a color-filter used on TFT-LCD and OLED.

Fabrication and properties of ZnO/GaN heterostructure nanocolumnar thin film on Si (111) substrate

PubMed Central

2013-01-01

Zinc oxide thin films have been obtained on bare and GaN buffer layer decorated Si (111) substrates by pulsed laser deposition (PLD), respectively. GaN buffer layer was achieved by a two-step method. The structure, surface morphology, composition, and optical properties of these thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, infrared absorption spectra, and photoluminiscence (PL) spectra, respectively. Scanning electron microscopy images indicate that the flower-like grains were presented on the surface of ZnO thin films grown on GaN/Si (111) substrate, while the ZnO thin films grown on Si (111) substrate show the morphology of inclination column. PL spectrum reveals that the ultraviolet emission efficiency of ZnO thin film on GaN buffer layer is high, and the defect emission of ZnO thin film derived from Zni and Vo is low. The results demonstrate that the existence of GaN buffer layer can greatly improve the ZnO thin film on the Si (111) substrate by PLD techniques. PMID:23448090

The effect of Argon pressure dependent V thin film on the phase transition process of (020) VO2 thin film

NASA Astrophysics Data System (ADS)

Meng, Yifan; Huang, Kang; Tang, Zhou; Xu, Xiaofeng; Tan, Zhiyong; Liu, Qian; Wang, Chunrui; Wu, Binhe; Wang, Chang; Cao, Juncheng

2018-01-01

It has been proved challenging to fabricate the single crystal orientation of VO2 thin film by a simple method. Based on chemical reaction thermodynamic and crystallization analysis theory, combined with our experimental results, we find out that when stoichiometric number of metallic V in the chemical equation is the same, the ratio of metallic V thin film surface average roughness Ra to thin film average particle diameter d decreases with the decreasing sputtering Argon pressure. Meanwhile, the oxidation reaction equilibrium constant K also decreases, which will lead to the increases of oxidation time, thereby the crystal orientation of the VO2 thin film will also become more uniform. By sputtering oxidation coupling method, metallic V thin film is deposited on c-sapphire substrate at 1 × 10-1 Pa, and then oxidized in the air with the maximum oxidation time of 65s, high oriented (020) VO2 thin film has been fabricated successfully, which exhibits ∼4.6 orders sheet resistance change across the metal-insulator transition.

Surface-area-controlled synthesis of porous TiO2 thin films for gas-sensing applications

NASA Astrophysics Data System (ADS)

Park, Jae Young; Kim, Ho-hyoung; Rana, Dolly; Jamwal, Deepika; Katoch, Akash

2017-03-01

Surface-area-controlled porous TiO2 thin films were prepared via a simple sol-gel chemical route, and their gas-sensing properties were thoroughly investigated in the presence of typical oxidizing NO2 gas. The surface area of TiO2 thin films was controlled by developing porous TiO2 networked by means of controlling the TiO2-to-TTIP (titanium isopropoxide, C12H28O4Ti) molar ratio, where TiO2 nanoparticles of size ˜20 nm were used. The sensor’s response was found to depend on the surface area of the TiO2 thin films. The porous TiO2 thin-film sensor with greater surface area was more sensitive than those of TiO2 thin films with lesser surface area. The improved sensing ability was ascribed to the porous network formed within the thin films by TiO2 sol. Our results show that surface area is a key parameter for obtaining superior gas-sensing performance; this provides important guidelines for preparing and using porous thin films for gas-sensing applications.

Fabrication and properties of ZnO/GaN heterostructure nanocolumnar thin film on Si (111) substrate.

PubMed

Wei, Xianqi; Zhao, Ranran; Shao, Minghui; Xu, Xijin; Huang, Jinzhao

2013-02-28

Zinc oxide thin films have been obtained on bare and GaN buffer layer decorated Si (111) substrates by pulsed laser deposition (PLD), respectively. GaN buffer layer was achieved by a two-step method. The structure, surface morphology, composition, and optical properties of these thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, infrared absorption spectra, and photoluminiscence (PL) spectra, respectively. Scanning electron microscopy images indicate that the flower-like grains were presented on the surface of ZnO thin films grown on GaN/Si (111) substrate, while the ZnO thin films grown on Si (111) substrate show the morphology of inclination column. PL spectrum reveals that the ultraviolet emission efficiency of ZnO thin film on GaN buffer layer is high, and the defect emission of ZnO thin film derived from Zni and Vo is low. The results demonstrate that the existence of GaN buffer layer can greatly improve the ZnO thin film on the Si (111) substrate by PLD techniques.

Photovoltaic devices comprising cadmium stannate transparent conducting films and method for making

DOEpatents

Wu, Xuanzhi; Coutts, Timothy J.; Sheldon, Peter; Rose, Douglas H.

1999-01-01

A photovoltaic device having a substrate, a layer of Cd.sub.2 SnO.sub.4 disposed on said substrate as a front contact, a thin film comprising two or more layers of semiconductor materials disposed on said layer of Cd.sub.2 SnO.sub.4, and an electrically conductive film disposed on said thin film of semiconductor materials to form a rear electrical contact to said thin film. The device is formed by RF sputter coating a Cd.sub.2 SnO.sub.4 layer onto a substrate, depositing a thin film of semiconductor materials onto the layer of Cd.sub.2 SnO.sub.4, and depositing an electrically conductive film onto the thin film of semiconductor materials.

Domain matched epitaxial growth of (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} thin films on (0001) Al{sub 2}O{sub 3} with ZnO buffer layer

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

Krishnaprasad, P. S., E-mail: pskrishnaprasu@gmail.com, E-mail: mkj@cusat.ac.in; Jayaraj, M. K., E-mail: pskrishnaprasu@gmail.com, E-mail: mkj@cusat.ac.in; Antony, Aldrin

2015-03-28

Epitaxial (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) thin films have been grown by pulsed laser deposition on (0001) Al{sub 2}O{sub 3} substrate with ZnO as buffer layer. The x-ray ω-2θ, Φ-scan and reciprocal space mapping indicate epitaxial nature of BST thin films. The domain matched epitaxial growth of BST thin films over ZnO buffer layer was confirmed using Fourier filtered high resolution transmission electron microscope images of the film-buffer interface. The incorporation of ZnO buffer layer effectively suppressed the lattice mismatch and promoted domain matched epitaxial growth of BST thin films. Coplanar inter digital capacitors fabricated on epitaxial (111) BSTmore » thin films show significantly improved tunable performance over polycrystalline thin films.« less

Synthesis, characterization and oxidation of metallic cobalt (Co) thin film into semiconducting cobalt oxide (Co3O4)thin film using microwave plasma CVD

NASA Astrophysics Data System (ADS)

Rahman Ansari, Akhalakur; Hussain, Shahir; Imran, Mohd; Abdel-wahab, M. Sh; Alshahrie, Ahmed

2018-06-01

The pure cobalt thin film was deposited on the glass substrate by using DC magnetron sputtering and then exposed to microwave assist oxygen plasma generated in microwave plasma CVD. The oxidation process of Co thin film into Co3O4 thin films with different microwave power and temperature were studied. The influences of microwave power, temperature and irradiation time were investigated on the morphology and particle size of oxide thin films. The crystal structure, chemical conformation, morphologies and optical properties of oxidized Co thin films (Co3O4) were studied by using x-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Raman Spectroscopy and UV–vis Spectroscopy. The data of these films showed complete oxidation pure metallic cobalt (Co) into cobalt oxide (Co3O4). The optical properties were studied for calculating the direct band gaps which ranges from 1.35 to 1.8 eV.

Preparation of p-type GaN-doped SnO2 thin films by e-beam evaporation and their applications in p-n junction

NASA Astrophysics Data System (ADS)

Lv, Shuliang; Zhou, Yawei; Xu, Wenwu; Mao, Wenfeng; Wang, Lingtao; Liu, Yong; He, Chunqing

2018-01-01

Various transparent GaN-doped SnO2 thin films were deposited on glass substrates by e-beam evaporation using GaN:SnO2 targets of different GaN weight ratios. It is interesting to find that carrier polarity of the thin films was converted from n-type to p-type with increasing GaN ratio higher than 15 wt.%. The n-p transition in GaN-doped SnO2 thin films was explained for the formation of GaSn and NO with increasing GaN doping level in the films, which was identified by Hall measurement and XPS analysis. A transparent thin film p-n junction was successfully fabricated by depositing p-type GaN:SnO2 thin film on SnO2 thin film, and a low leakage current (6.2 × 10-5 A at -4 V) and a low turn-on voltage of 1.69 V were obtained for the p-n junction.

Electron-beam-evaporated thin films of hafnium dioxide for fabricating electronic devices

DOE PAGES

Xiao, Zhigang; Kisslinger, Kim

2015-06-17

Thin films of hafnium dioxide (HfO 2) are widely used as the gate oxide in fabricating integrated circuits because of their high dielectric constants. In this paper, the authors report the growth of thin films of HfO 2 using e-beam evaporation, and the fabrication of complementary metal-oxide semiconductor (CMOS) integrated circuits using this HfO 2 thin film as the gate oxide. The authors analyzed the thin films using high-resolution transmission electron microscopy and electron diffraction, thereby demonstrating that the e-beam-evaporation-grown HfO 2 film has a polycrystalline structure and forms an excellent interface with silicon. Accordingly, we fabricated 31-stage CMOS ringmore » oscillator to test the quality of the HfO 2 thin film as the gate oxide, and obtained excellent rail-to-rail oscillation waveforms from it, denoting that the HfO 2 thin film functioned very well as the gate oxide.« less

Stretchable, adhesive and ultra-conformable elastomer thin films.

PubMed

Sato, Nobutaka; Murata, Atsushi; Fujie, Toshinori; Takeoka, Shinji

2016-11-16

Thermoplastic elastomers are attractive materials because of the drastic changes in their physical properties above and below the glass transition temperature (T g ). In this paper, we report that free-standing polystyrene (PS, T g : 100 °C) and polystyrene-polybutadiene-polystyrene triblock copolymer (SBS, T g : -70 °C) thin films with a thickness of hundreds of nanometers were prepared by a gravure coating method. Among the mechanical properties of these thin films determined by bulge testing and tensile testing, the SBS thin films exhibited a much lower elastic modulus (ca. 0.045 GPa, 212 nm thickness) in comparison with the PS thin films (ca. 1.19 GPa, 217 nm thickness). The lower elastic modulus and lower thickness of the SBS thin films resulted in higher conformability and thus higher strength of adhesion to an uneven surface such as an artificial skin model with roughness (R a = 10.6 μm), even though they both have similar surface energies. By analyzing the mechanical properties of the SBS thin films, the elastic modulus and thickness of the thin films were strongly correlated with their conformability to a rough surface, which thus led to a high adhesive strength. Therefore, the SBS thin films will be useful as coating layers for a variety of materials.

In-situ ellipsometry: applications to thin film research, development, and production

NASA Astrophysics Data System (ADS)

Kief, M. T.

1999-07-01

Many industries including the optics industry, semiconductor industry, and magnetic storage industry are deeply rooted in the science and technology of thin film materials and thin film based devices. Research in novel thin film systems and the engineering of artificial structures increasingly requires a control on the atomic scale in both thickness and lateral order. Development of the deposition and fabrication processes for these thin film structures requires technical sophistication and efficiency combined with an understanding of the multi-faceted process interactions. The production of these materials necessitates a remarkable degree of control to minimize scrap and assure good performance. Furthermore, in today's industry these operations must occur at an ever accelerating pace. In this article, we will review one technique which can make these challenges more tractable - insitu ellipsometry. This is a very powerful tool which is capable of characterizing thin film processes in real-time. We review the art and illustrate with novel applications to metal thin film growth. In addition, we will illustrate how information obtained with insitu ellipsometry can predict the end use thin film properties such as the transport properties. In conclusion, further advances in insitu ellipsometry and its applications will be discussed in terms of needs and trends as a tool for thin film research, development and production.