bluuebunny/crossref_metadata_2025 huggingface dataset:
Progress in Oxide-Based Electrochromics: Towards Roll-to-Roll Manufacturing
Authors: Granqvist Claes G.
Published: September 2011

Electrochromics is a key “green” technology for massive energy savings in the built environment jointly with indoor comfort. This paper surveys basic electrochromic (EC) device designs, useful oxide materials and their nanostructures, and elements of a theoretical description of the EC phenomenon. It also outlines critical manufacturing technologies and their pros and cons. Focus is on EC foil technology, which is shown capable of mass fabrication via roll-to-roll web coating and continuous lamination.
Deposition of Zinc Oxide Thin Films Using a Surface Reaction on Platinum Nanoparticles
Authors: Yasui Kanji , Miura Hitoshi , Nishiyama Hiroshi
Published: September 2011

A new chemical vapor deposition method for the growth of ZnO films using the reaction between dimethylzinc (DMZn) and thermally excited H2O produced by a Pt-catalyzed H2–O2 reaction was investigated. The thermally excited H2O molecules formed by the exothermic reaction of H2 and O2 on the catalyst were ejected from a fine nozzle into the reaction zone and allowed to collide with DMZn ejected from another fine nozzle. The ZnO films were grown directly on a-plane (11-20) sapphire substrates at substrate temperatures of 773-873 K with no buffer layer. X-ray diffraction patterns exhibited intense (0002) and (0004) peaks from the ZnO(0001) index plane. The smallest full width at half maximum (FWHM) value of the ω- rocking curve of ZnO(0002) was less than 0.1º. The largest Hall mobility and the smallest residual carrier concentration of the ZnO films were 169 cm2V−1s−1 and 1.7×1017 cm−3, respectively. Photoluminescence (PL) spectra at room temperature exhibited a band edge emission at 3.29 eV, with a FWHM of 104 meV. Green luminescence from deeper levels was generally about 1.5% of the band edge emission intensity. PL spectra at 5 K showed a strong emission peak at 3.3603 eV, attributed to the neutral donor-bound exciton Dºx. The FWHM was as low as 1.0 meV. Free exciton emissions also appeared at 3.3757 eV (FXA, n=1) and 3.4221 eV (FXA, n=2).
Visible ITO Pattern in Capacitive Touch Lens: Cause and Countermeasure
Authors: Kim Duk Su , Lee Gyeong-Geun , Yang Jacob , Shin Dong Hyuk
Published: September 2011

Market demand for touch panel/lens has been exceptionally high for the recent years due to smartphones, tablet PCs, etc. Among the available technologies to envision touch functionality, capacitive touch screen has received the great attention due to the various superiorities over the competing ones. Capacitive touch screen features two transparent conductive electrodes, such as ITO (indium tin oxide). However, the difference in refractive indices of ITO, substrate, and air, ITO pattern is clearly visible if there is no proper countermeasure. Most of touch screen makers and ITO substrate supplier utilize “index-matching technology” to prevent this phenomenon.

Even though of the attempts to minimize visible ITO pattern in final product, there are many technical and process challenges. In this study, the causes around visible ITO pattern were investigated to understand and provide the proper countermeasures.

One of the possible causes for visible ITO pattern was improper annealing process in ITO especially for film substrate. According to XPS (X-ray photoelectron spectroscopy)/ESCA (electron spectroscopy for chemical analysis) and other analysis results, ITO, which is normally deposited through sputtering, is not fully transformed to oxidized state. After aligning and adjusting annealing condition, acknowledged visible ITO pattern was disappeared.

Other causes for visible patterns were also discussed in detail, and the relevant countermeasures were provided.
High Mobility ZnO thin film transistors using the novel deposition of high-k dielectrics
Authors: Ngwashi D. K. , Cross R. B. M. , Paul S. , Milanov Andrian P. , Devi Anjana
Published: September 2011

In order to investigate the performance of ZnO-based thin film transistors (ZnO-TFTs), we fabricate devices using amorphous hafnium dioxide (HfO2) high-k dielectrics. Sputtered ZnO was used as the active channel layer, and aluminium source/drain electrodes were deposited by thermal evaporation, and the HfO2 high-k dielectrics are deposited by metal-organic chemical vapour deposition (MOCVD). The ZnO-TFTs with high-k HfO2 gate insulators exhibit good performance metrics and effective channel mobility which is appreciably higher in comparison to SiO2-based ZnO TFTs fabricated under similar conditions. The average channel mobility, turn-on voltage, on-off current ratio and subthreshold swing of the high-k TFTs are 31.2 cm2V-1s-1, -4.7 V, ~103, and 2.4 V/dec respectively. We compared the characteristics of a typical device consisting of HfO2 to those of a device consisting of thermally grown SiO2 to examine their potential for use as high-k dielectrics in future TFT devices.
Influence of the annealing atmosphere on solution based zinc oxide thin film transistors
Authors: Busch C. , Theissmann R. , Bubel S. , Schierning G. , Schmechel R.
Published: September 2011

Zinc oxide layers with a thickness of less than 10 nanometers have been synthesized from an aqueous solution for the application as active layer in thin film transistors. They have been conditioned by applying different oxidizing and reducing atmospheres during an annealing process at a temperature of 125°C. It is shown that the charge carrier mobility and threshold voltage is strongly influenced by the annealing atmosphere. Samples annealed in 10% forming gas (H2 in N2 - reducing atmosphere) show the highest field-effect-mobility of 0.6 cm2V-1s-1, but no saturation of the drain current, due to a high free carrier concentration. Samples treated under oxygen (strongest oxidizing atmosphere) show significantly lower mobilities. Subsequently, the samples have been exposed to synthetic air, with varying exposure times. Samples which have been annealed under hydrogen atmospheres show a pronounced decay of the drain current if exposed to synthetic air, whereas all samples conditioned under hydrogen-free atmospheres are significantly more stable under synthetic air. This enhanced sensitivity against oxygen after hydrogen treatment is attributed to residual hydrogen content in the sample that supports the formation of OH-groups which act as electron acceptors.
Refractive Index Engineering of Polymer Nanocomposites Prepared by End-grafted Polymer Chains onto Inorganic Nanoparticles
Authors: Tao Peng , Viswanath Anand , Li Yu , Rungta Atri , Benicewicz Brian C. , Siegel Richard W. , Schadler Linda S.
Published: September 2011

Transparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto TiO2 nanoparticles. Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to prepare poly(methyl methacrylate) (PMMA) polymer brushes grafted from TiO2 nanoparticles. The refractive index of the hybrid material increased from 1.49 for neat PMMA to 1.6 by increasing the loading of TiO2 to 40 weight percent. UV-vis spectra showed that grafted particles had a transparency of more than 90% in the visible light range. The hybrid particles can be processed into transparent, high refractive index coatings and self-standing films. The grafted TiO2 nanoparticles can also be easily dispersed into a polymer matrix forming thick, robust transparent polymer nanocomposites.
Outstanding Radiation Performance of an All-carbon Nanotube Patch
Authors: Stollberg David W. , Urbani Fabio , Verma Amit
Published: September 2011

We report the fabrication and characterization of a microstrip patch antenna composed entirely out of multi-walled carbon nanotubes on a silicon substrate. The antenna showed excellent response in the X-band, for which it was designed. In addition, an observed left-shift resonance effect points towards significant potential for miniaturization. The antenna also showed very promising reliability under different operating conditions. Such antennas may therefore have significant promise for system-on-chip, space application, and other specialized applications.
Photo-electrical Effect of Pristine and Functionalized Graphene Grown by Chemical Vapor Deposition
Authors: Lin Jian , Zhong Jiebin , Reiber Kyle Jennifer , Penchev Miroslav , Ozkan Mihrimah , Ozkan Cengiz S.
Published: September 2011

In this poster we will present the photo-electrical effect of pristine and nitric acid treated graphene field effect transistors made by chemical vapor deposition (CVD). The results of the decreased electrical conductance and shift of Dirac point arise from the molecular photodesorption from graphene. When post treated with nitric acid the photodesorption efficiency was decrease from 52% to 21%, which was proposed to be caused by the passivation of oxygen-bearing functionalities to CVD graphene structural defects. This result provides a new strategy of stabilizing the electrical performance of CVD graphene which is promising candidate as highly conductively photoelectrical material.
Electronic Structure of O-vacancy in High-kDielectrics and Oxide Semiconductors
Authors: Chang Kee Joo , Ryu Byungki , Noh Hyeon-Kyun , Bang Junhyeok , Choi Eun-Ae
Published: September 2011

First-principles density functional calculations are performed to investigate the electronic properties of O-vacancy defects in high-kHfO2, Si/HfO2interface, and amorphous oxide semiconductors. The role of O-vacancy in device performance is discussed by comparing the results of the GGA, hybrid density functional, and quasiparticle energy calculations.
Effect of thickness of thin film SnO2 based LPG sensors
Authors: Haridas Divya , Sreenivas K. , Gupta Vinay
Published: September 2011

This paper reports the response characteristics of rf-sputtered SnO2 thin films (of varying thickness) for LPG detection. To monitor and precisely measure leakages, the development of a reliable LPG sensor with improved sensitivity is crucial in preventing fatal accidents. In the present study, thin film of SnO2 is used as the sensing element for LPG sensor. The thickness of a thin film is a very important parameter and determines their main operating characteristics, such as sensor response, rate of response, and working temperature. In the present study, thickness of SnO2 film is varied between 30 nm to 180 nm. The structure, composition and optical properties of SnO2 thin films have been examined by XRD, SEM, AFM and UV-Vis. The crystallite size for 90 nm thin film (for (110) plane) is found to be the smallest ~4-5 nm. Sensor response $(S = \left( {{{R_a - R_g } \over {R_a }}} \right) \times 100\% )$ increases with thickness of the sensing film, with a highest sensor response (~67%) observed for 90 nm thin film and thereafter it decreases. The structural and optical properties clearly support the observed enhanced sensor response for 90 nm thin film.
ZnBeMgO thin films based UV Detectors by Spin Coating
Authors: Panwar Neeraj , Liriano J. , Katiyar Ram S.
Published: September 2011

Be and Mg co-doped ZnO films Zn1-x-yBexMgyO (0 ≤ x ≤ 0.10, 0 ≤y ≤ 0.20) have been deposited for the first time by novel chemical deposition or spin coating method. From the x-ray diffraction patterns it is noticed that the pristine ZnO film exhibits wurtzite polycrystalline structure, however, co-doped films are (0002) preferentially oriented. The (0002) peak intensity also increases with the corresponding increase in dopants concentrations. The systematic decrease in the c-axis lattice parameter value in the co-doped films as compared to pure ZnO film suggests the incorporation of smaller ions Be+2/Mg+2 at Zn+2 site. From the optical transmittance measurement it is noticed that all the films exhibited almost 80% transmittance in the visible region with sharp and single absorption edges in the UV region. The cut-off wavelength shifts from 375nm for the ZnO film to 330nm with 10 Be and 20% Mg co-doped film. The bandgap calculations revealed an increase in bandgap from 3.26eV (ZnO) to 3.60eV (Zn0.7Be0.1Mg0.2O) film. Such an increase in the co-doped films fabricated by a much simpler and cheaper process is very useful in the realization of UV radiation detection without having little interference from the visible light.
A Study of Increased Resistivity of FTO Back Contact for CZTS Based Absorber Material Grown by Electrodeposition-Annealing Route
Authors: Sarswat Prashant K. , Free Michael L. , Tiwari Ashutosh
Published: September 2011

CZTS (Copper zinc tin sulfide) thin films have been synthesized on transparent conducting oxide (TCO) back contacts on a glass substrate, allowing sun light to pass through the entire solar cell. Aqueous solution based co-electrodeposition followed by elevated temperature sulfurization, was used to grow CZTS on transparent fluorinated tin oxide. Loss in conductivity of FTO is observed after sulfurization, causing reduced device efficiency. Increased resistivity of the FTO is likely due to outdiffusion process. A systematic study of resistivity of back contact at various sulfurization temperatures and times is discussed. Various remedial measures for improved conductivity of back contact were proposed and conducted.
Thermal Conductivity of Amorphous Indium Zinc Oxide Thin Films
Authors: Endoh Ryo , Hirano Takayuki , Takeda Masaaki , Oishi Manabu , Oka Nobuto , Shigesato Yuzo
Published: September 2011

The thermal conductivity of amorphous indium zinc oxide (IZO) thin films was measured by the 3ω method. Three IZO films were prepared by dc magnetron sputtering method on Si substrate under different O2 flow ratios (O2 / [Ar+O2]) of 0%, 1%, and 5%. The thermal conductivity of IZO films decreases with an increase in O2 flow ratio, the values of the thermal conductivity were 3.4, 3.1 and 1.2 W m-1 K-1 for O2 flow ratios of 0%, 1%, and 5%, respectively. To investigate relationships among the thermal conductivity, the structure and other physical properties, we were carried out nanoindentation, Rutherford back scattering (RBS), electron spin resonance (ESR). The result of ESR measurements indicated that the amount of conduction electron in the IZO film decreases with increasing O2 flow ratio. Increase of O2 flow ratio reduces the amount of oxygen vacancies for providing free electrons. Therefore, decreasing thermal conductivity with an increase in O2 flow ratio is attributed to decreasing conduction electrons as thermal carrier. On the other hand, the chemical composition of IZO films is independent of O2 flow ratio. Furthermore, density, Young’s modulus and hardness also show little changes with increasing O2 flow ratio. Density, Young’s modulus and hardness are strongly associated with the internal structure. It is probable that influence of oxygen vacancies on the internal structure of IZO film is negligibly small.
Encapsulation of Luminescent Silicon Nanocrystals within Mesoporous Silica Nanospheres: Synthesis and Effect on Photoluminescence
Authors: Regli Sarah , Kelly Joel A. , Veinot Jonathan G.C.
Published: September 2011

Silicon nanocrystals (Si-NCs) are of significant research interest owing to their quantum confined photoluminescent (PL) properties and biological inertness. A promising application of these NCs is as the luminescent component in multifunctional biomedical technologies. In this report, we demonstrate the encapsulation of alkyl terminated Si-NCs within a mesoporous silica shell as a multifunctional imaging and drug delivery architecture. The Si-NC concentration was found to critically impact the nanoshell morphology. The impact of the encapsulation process on the Si-NC PL was studied, showing a blue-shift and decrease in intensity attributed to the oxidation of Si-NCs under basic conditions.
Low Field Magnetoresistance at Room Temperature in CrO2 Doped Polyvinyl Alcohol Films
Authors: Biswas S. , Ram S.
Published: September 2011

Ferromagnetic CrO2 nanoparticles embedded in a diamagnetic matrix of polyvinyl alcohol (PVA) presents an example of granular giant magnetoresistance (GMR) in a diluted magnetic composite structure. Usefully significant MR occurs at room temperature, viz. -6.8% in 3.0 wt% CrO2-PVA, at field as small as 1.1 kOe. We suggest that the system is a natural analogue to dilute ferro-fluid structures composed of nanoscale magnetic particles in a viscous organic fluid (diamagnetic as well as an electrical insulator), i.e., this material displays a GMR effect without an introduction of chemical interfaces. It has great potential in various applications and can also facilitate studies of magnetotransport properties in GMR materials.
Second-Harmonic Generation Spectroscopy from Time-Dependent Density-Functional Theory
Authors: Luppi E. , Hübener H. , Bertocchi M. , Degoli E. , Ossicini S. , Véniard V.
Published: September 2011

We developed an ab initio formalism based on Time-Dependent Density-Functional Theory for the calculation of the second-order susceptibility Χ(2) (Luppi et al. J. Chem. Phys. 132, 241104(2010)). We apply this formalism to the calculation of second-harmonic generation spectra of hexagonal SiC polytypes, ZnGeP2 (ZGP) and GaP. Starting from the independent-particle approximation, we include manybody effects, such as quasiparticle via the scissors operator, crystal local fields and excitons. We consider two different types of kernels: the ALDA and the “long-range” kernel. We analyze the effects of the different electron-electron descriptions in the spectra, finding good agreement with experiments.
Roll-to-roll manufacture of pentacene-based thin film transistors with a flash-evaporated polymer dielectric cured with an e-beam
Authors: Abbas Gamal A. W. , Cheng Donna , Mallik Kanad , Assender Hazel E.
Published: September 2011

We report our fabrication of pentacene field effect transistors (FETs) based on a vacuum processed and e-beam cured polymer electrolyte (i.e., tripropylene glycol diacrylate (TRPGDA)) as a gate dielectric layer on flexible wide web substrates. The deposition of the semiconductor and gate insulator layers is carried out in Oxford's roll-to-roll vacuum web processing facility and could be combined in-line with roll-to-roll pattern metallization. The aim of the work is to demonstrate the ability to create all-evaporated transistors, exploiting the kind of technologies at present extensively used in the food packaging industry, for example, in which all layers can be deposited at high web speeds. Ours is a room temperature and a solvent-free method with an ultrahigh deposition rate (web speeds in excess of 100 m/min are possible).

The performance of the pentacene and the polymer dielectric materials within devices was investigated, demonstrating (1) the ability to deposit good quality pentacene layers in the roll-to-roll environment and (2) the importance of the e-beam curing conditions of the dielectric layer on the performance of the organic FET devices. This deposition route creates a smooth, pin-hole-free dielectric layer as it is deposited onto the substrate as a monomeric liquid, before curing, and there is no mass-loss such as in solvent-based deposition processes. These devices have a 250 μm channel length and an aspect ratio of 16. No self-assembled monolayer (SAM) or other surface modification had been applied to the insulator layer to achieve these properties.

The tuning of the transistors' operating voltage and output characteristics was feasible through the ease of control of the polymer dielectric thickness achieving a threshold voltage of less than 10 V. On/off ratio in excess of 103, and mobility = 0.1 cm2V-1s-1 have been achieved.

The ability to integrate such a high deposition rate polymer process, into a single step, multilayer, vacuum deposition process with conventional vacuum deposition sources provides a possible route to low cost and large area electronic device processing.
Large Area Graphene on Polymer Films for Transparent and Flexible Field Emission Device
Authors: Verma Ved Prakash , Das Santanu , Lahiri Indranil , Choi WonBong
Published: September 2011

Large scale fabrication of graphene over transparent flexible polymer, Polyethelyne tetrapthalate (PET), and its application in flexible field emission display is reported here. We used Cu foil (~160 mm x 60 mm) to grow graphene by thermal chemical vapor deposition process and transfer the graphene over a polymer using a straightforward hot press lamination technique. The fabrication method is facile as there is no rigorous chemical process involved and the process is also applicable towards the fabrication of large scale graphene over a wide range of transparent flexible substrates for foldable micro-electronics applications. Further, we demonstrate the application of graphene/PET polymer film as anode of transparent flexible field emission display device. The device shows low turn-on voltage ~ 1.75V/μm and high current density of ~ 65μA/cm2 with field enhancement factor (β) ~1000.
Annealing Effects of Microstructure in Thin-film Silicon Solar Cell Materials Measured by Effusion of Implanted Rare Gas Atoms
Authors: Beyer W. , Lennartz D. , Prunici P. , Stiebig H.
Published: September 2011

In thin film silicon solar cell technology, annealing (heat treatment) effects are of interest since (i) annealing of underlying films often cannot be avoided during deposition and (ii) heat treatment (e.g. by laser) may be actively used for improvement of as-deposited material. Changes in the microstructure of several thin film silicon solar cell materials like hydrogenated amorphous silicon, microcrystalline silicon and zinc oxide by heat treatment were investigated by effusion measurements of hydrogen and implanted helium. Densification is observed for all materials studied, i.e. interconnected voids disappear or are transformed to isolated voids. We attribute the observed annealing effects primarily to an incomplete polymerization during growth. Important for solar cell processing is the result that the annealing effects involving structural changes set in at temperatures close to the temperature of deposition.
Atomistic Simulations of the Silicon Surface Structure at the Interface of Silver Thick Film Contacts on n-Type Silicon
Authors: Kontermann Stefan , Ruf Alexander , Preu Ralf
Published: September 2011

Nanoscale silver crystals at the interface of silver thick film contacts on n-type silicon carry the current across the contact and therefore control the contact resistance, which is a main performance limiting parameter for semiconductor devices. The silver crystals are located in pits at the silicon surface. The shape of the pits is different on Si-(111) and Si-(100). During contact formation, these pits form before the silver crystals. Hence they determine the crystal size and shape. Consequently, the pits with the crystals influence the contact resistance. We investigate these pits experimentally by scanning electron microscopy. We are the first to simulate the mechanism of pit formation at a contact interface by considering a model that is based on the removal probability of silicon surface atoms. This model leads to good agreement between experimental and simulated data. It enables the prediction of pit formation for arbitrary process parameters like temperature and duration for silver thick film contact formation on silicon.
High deposition rate of low resistive and transparent ZnO:Al on glass with an industrial moving belt APCVD reactor
Authors: Illiberi A. , Kniknie B. , Steijvers H.L.A.H. , Habets D. , Simons P.J.P.M. , Beckers E.H.A. , Van Deelan J.
Published: September 2011

Aluminum doped ZnOx (ZnOx:Al) films have been deposited on glass in an in-line industrialtype reactor by a metalorganic chemical vapor deposition process at atmospheric pressure. ZnOx:Al films can be grown at very high deposition rates of ~ 14 nm/s for a substrate speed from 150 mm/min to 500 mm/min. ZnOx:Al films are highly conductive (R < 9 Ohm/sq, for a film thickness above 1300 nm) and transparent in the visible range (> 80%). Amorphous silicon p-i-n solar cells have been grown on as deposited ZnOx:Al films, without optimizing the surface texturing of ZnOx:Al films to enhance light scattering. An initial efficiency of approximately 8% has been achieved.
High Efficiency Sputtered CdS/CdTe Cells without CdCl2 Activation
Authors: Paudel N.R. , Wieland K.A. , Compaan A.D.
Published: September 2011

Polycrystalline thin-film CdS/CdTe PV cells nearly always require “activation” with vapors containing chlorine and oxygen near 400 oC in order to realize the highest cell performance, even when growth occurs near 600 oC. In this study we have used film growth near 270 oC by magnetron sputtering in an oxygen-free ambient and have studied the effects of post-deposition heat treatments for 20 minutes at 400, 425 and 450 oC without CdCl2 in a dry air ambient. The heat treatments enhanced grain growth and produced re-crystallization of the CdTe film at all three temperatures, but 450 oC was required to reach the best electrical performance. Grain size increased from a couple of hundred nanometers to more than a micron as the preferred (111) growth orientation decreased. Efficiencies up to 11.6% were achieved with no CdCl2 compared to ~13% with activation at 387 oC in the presence of CdCl2 vapors. X-ray diffraction and quantum efficiency measurements show interdiffusion of CdS and CdTe at 450 oC comparable with a standard CdCl2 treatment at 387 oC. The results are discussed in terms of CdSTe alloy gradients and minority-carrier diffusion lengths.
Enhanced Light Emission at Self-assembled GaN Inversion Domain Boundary
Authors: Liu Mei-Chun , Cheng Yuh-Jen , Chang Jet-Rung , Chang Chun-Yen
Published: September 2011

We report the fabrication of GaN lateral polarity inversion heterostructure with self assembled crystalline inversion domain boundaries (IDBs). The sample was fabricated by two step molecular-beam epitaxy (MBE) with microlithography patterning in between to define IDBs. Despite the use of circular pattern, hexagonal crystalline IDBs were self assembled from the circular pattern during the second MBE growth. Both cathodoluminescent (CL) and photoluminescent (PL) measurements show a significant enhanced emission at IDBs and in particular at hexagonal corners. The ability to fabricate self assembled crystalline IDBs and its enhanced emission property can be useful in optoelectronic applications.
Kesterites and Chalcopyrites: A Comparison of Close Cousins
Authors: Repins Ingrid , Vora Nirav , Beall Carolyn , Wei Su-Huai , Yan Yanfa , Romero Manuel , Teeter Glenn , Du Hui , To Bobby , Young Matt , Noufi Rommel
Published: September 2011

Chalcopyrite solar cells based on CuInSe2 and associated alloys have demonstrated high efficiencies, with current annual shipments in the hundreds of megawatts (MW) range and increasing. Largely due to concern over possible indium (In) scarcity, a related set of materials, the kesterites, which comprise Cu2ZnSnS4 and associated alloys, has received increasing attention. Similarities and differences between kesterites and chalcopyrites are discussed as drawn from theory, depositions, and materials characterization. In particular, we discuss predictions from density functional theory, results from vacuum co-evaporation, and characterization via x-ray diffraction, scanning electron microscopy, electron beam-induced current, quantum efficiency, secondary ion mass spectroscopy, and luminescence.
Photostimulable Fluorescent Nanoparticles for Biological Imaging
Authors: Osvet Andres , Milde Moritz , Dembski Sofia , Rupp Sabine , Gellermann Carsten , Batentschuk Miroslaw , Brabec Christoph J. , Winnacker Albrecht
Published: September 2011

Spherical monodisperse core/shell-type nanoparticles, comprising an amorphous SiO2 core coated with a luminescent phosphor layer were synthesized by the modified Pechini processes. The sol-gel method allows covering the 50 – 500 nm core particles with different inorganic phosphor layers of about 10 nm thickness, doped with rare-earth or transition metal ions which determine the luminescent properties. Particles comprising a Zn2SiO4 shell, doped with Mn2+ ions, are not only fluorescent under UV irradiation (260 nm), but store the activation energy by trapping electrons/holes at lattice defects. This energy is released as phosphorescence in the time scale of seconds and minutes, or as photostimulated luminescence under the excitation of red light (650 nm). Traps related to these processes are different, and their concentration is affected by the preparation conditions of the particles.
Electronic Structure Calculations Using A Modified Thomas-Fermi Approximation
Authors: Dente Gregory C. , Tilton Michael
Published: September 2011

We have recently developed an accurate and easily implemented approach to many-electron calculations, based on a modified Thomas-Fermi approximation. Specifically, we derived an electron density approximation, the first term of which is the Thomas-Fermi result, while the remaining terms substantially corrected the density near the nucleus. In a first application, we used the new density to accurately calculate the details of the self-consistent ion cores, as well as the ionization potentials for the outer s-orbital bound to the closed-shell ion core of the Group III, IV and V elements. Next, we demonstrated that the new density expression allows us to separate closed-shell core electron densities from valence electron densities. When we calculated the valence kinetic energy density, we showed that it separated into two terms: the first exactly cancelled the potential energy due to the ion core in the core region; the second was the residual kinetic energy density resulting from the envelopes of the valence electron orbitals. These features allowed us to write a functional for the total valence energy dependant only on the valence density. This equation provided the starting point for a large number of electronic structure calculations. Here, we used it to calculate the band structures of several Group IV and Group III-V semiconductors. We emphasize that this report only provides a summary; detailed derivations of all results are in Reference 5.
Influence of Process Condition on the Dielectric Properties of CCTO-P(VDF-TrFE) 0-3 Composites
Authors: Shan Xiaobing , Zhang Lin , Cheng Z.-Y.
Published: September 2011

A high dielectric constant was observed in 0-3 composites using P(VDF-TrFE) copolymer as matrix and CaCu3TiO4 (CCTO) ceramic powders as fillers with a composition of 50 vol% CCTO. CCTO-P(VDF-TrFE) 0-3 composites with a CCTO content from 0 to 50 vol% were prepared and their dielectric properties, including frequency dependence and temperature dependence of the dielectric constant and loss, were characterized. It was experimentally observed that the hot-press process, inlcuding the configuration and hot-press time, has a strong influence on the dielectric properties of the composites. Additionally, the influence of the CCTO partice size on the dielectric properties of the composites was studied.
Electrochromic performance of WO3 thin films with solvent-free viscous electrolytes based on polyethylene glycol-titanium oxide nanocomposites
Authors: Mendoza Narcizo , Hechavarría Liliana , Paraguay-Delgado Francisco , Hu Hailin
Published: September 2011

Polymeric nanocomposites of polyethylene glycol (PEG) with titanium oxide compound, PEG-Ti, have been prepared by sol-gel method from liquid PEG and titanium isopropoxide in acidic medium. Lithium salt (LiX) has been added into PEG-Ti to form PEG-Ti-LiX polymeric electrolytes. Electrochromic devices based on tungsten oxide thin films and PEG-Ti-LiX electrolyte may show excellent optical transmittance transient, however it depends on the type of lithium salt used during the sol-gel process. With LiI, the color change speed of the devices is very fast but they show a yellow color at bleaching state. The use of LiClO4 makes the devices totally transparent in visible region but the optical contrast is small. Possible molecular structure model of these polymeric electrolytes have been analyzed to explain the relation between electrochromic performance of tungsten oxide and electrolyte chemical composition.
Methods of Faience Manufacture in Antiquity: Investigation of Colorants and Technological Processes
Authors: Frame Lesley , DeSordao Donna Bright , Chiang Yuan-Chi , Vandiver Pamela
Published: September 2011

Faience production methods include efflorescence, direct glaze application, and cementation glazing. However, similar processing has been used with a variety of other materials, such as glazed monolithic quartz, ground and re-fired faience, and steatite bodies. Furthermore, faience technology has been linked by similar processing to glass, synthetic pigment and glazing technologies. Here we reinforce these cross-craft relationships by comparing the range of similar functioning chemical elements in faience and glazed artifacts from a variety of archaeological sites that range from the Indus Valley to the Mediterranean. This broad comparative method based primarily on x-ray fluorescence analysis reveals trends in faience production, relationships with metallurgical technologies, and aspects of processing that provide areas of study that may be considered more closely in the future.
Effect of Bandgap Grading on the Performance of a-Si1-xGex:H Single-Junction Thin-Film Solar Cells
Authors: Hsu H. J. , Wang C. M. , Hsu C. H. , Tsai C. C.
Published: September 2011

In this work, the effect of bandgap grading of hydrogenated amorphous silicon germanium (a-Si1-xGex:H) absorber near the p/i and the i/n interfaces was investigated. The a-Si1-xGex:H single-junction solar cells were improved by applying both p/i grading and i/n grading. Our results showed that both the p/i and the i/n grading can increase the open-circuit voltage (VOC) as compared to the cell without grading. The i/n grading can further improve the FF. Presumably the potential gradient created by the i/n grading can facilitate the hole transport thus it can improve the FF. However, the JSC decreased as the i/n grading width increased. The reduction of JSC was due to the loss in the red response, which can be attributed to the replacement of lower bandgap material by the larger ones. Combining the effects of VOC, JSC and FF, a suitable thickness of the p/i and the i/n grading was 20 nm and 45 nm, respectively. Finally, the grading structures accompanied with further optimization of doped layers were integrated to achieve a cell efficiency of 8.59 %.
Formation of Light-weight Low-density Materials via Gas Phase Aerosol Gelation
Authors: Sorensen Christopher M. , Dhaubhadel Rajan , Gerving Corey S. , Chakrabarti Amitabha
Published: September 2011

We have demonstrated that gas phase explosive combustion can lead to nanoparticle aerosols with sufficiently large volume fraction to cause a volume spanning gel to form on the order of ten’s of seconds. The term “aerosol gel” was coined to name these materials. So far we have made aerosol gels of carbon and silica. These aerosol gels are similar to well-known, liquid-phase, sol-gel synthesized aerogels.
Impact of rapid thermal annealing and hydrogenation on the doping concentration and carrier mobility in solid phase crystallized poly-Si thin films
Authors: Kumar A. , Widenborg P.I. , Hidayat H. , Zixuan Qiu , Aberle A.G.
Published: September 2011

The effect of the rapid thermal annealing (RTA) and hydrogenation step on the electronic properties of the n+ and p+ solid phase crystallized (SPC) poly-crystalline silicon (poly-Si) thin films was investigated using Hall effect measurements and four-point-probe measurements. Both the RTA and hydrogenation step were found to affect the electronic properties of doped poly-Si thin films. The RTA step was found to have the largest impact on the dopant activation and majority carrier mobility of the p+ SPC poly-Si thin films. A very high Hall mobility of 71 cm2/Vs for n+ poly-Si and 35 cm2/Vs for p+ poly-Si at the carrier concentration of 2×1019 cm-3 and 4.5×1019 cm-3, respectively, were obtained.
Excimer-Laser-Induced Melting and Solidification of PECVD a-Si films under Partial-Melting Conditions
Authors: Hu Q. , Lee Catherine S. , Li T. , Deng Y. , Chung U.J. , Limanov A. B. , Chitu A. M. , Thompson M.O. , Im James S.
Published: September 2011

This paper reports on new experimental findings and conclusions regarding the pulsed-laser-induced melting-and-solidification behavior of PECVD a-Si films. The experimental findings reveal that, within the partial-melting regime, these a-Si films can melt and solidify in ways that are distinct from, and more complex than, those encountered in microcrystalline-cluster-rich LPCVD a-Si films. Specifically (1) spatially dispersed and temporally stochastic nucleation of crystalline solids occurring relatively effectively at the moving liquid-amorphous interface, (2) very defective crystal growth that leads to the formation of fine-grained Si proceeding, at least initially after the nucleation, at a sufficiently rapidly moving crystal solidification front, and (3) the propensity for local preferential remelting of the defective regions and grain boundaries (while the beam is still on) are identified as being some of the fundamental factors that can participate and affect how these PECVD films melt and solidify.
Investigation of local light scattering properties of thin-film silicon solar cells with subwavelength resolution
Authors: Bittkau K. , Hoffmann A. , Owen J. , Carius R.
Published: September 2011

In order to obtain efficient light trapping within a thin-film silicon solar cell, randomly textured interfaces are used. The texture can be introduced by wet-chemical etching in diluted hyrdofluoric acid (HF). By varying of the HF concentration, a continuous transition to smaller surface structures can be achieved. Near-field scanning optical microscopy is applied to measure scattered light with sub-wavelength resolution. On those different surfaces, using Fourier high-pass filters on the measured near-field images, surface features with a high light trapping potential are identified. Finally, criteria for optimized scattering surfaces are obtained.
Amorphous Silicon Based Particle Detectors
Authors: Wyrsch N. , Franco A. , Riesen Y. , Despeisse M. , Dunand S. , Powolny F. , Jarron P. , Ballif C.
Published: September 2011

Radiation hard monolithic particle sensors can be fabricated by a vertical integration of amorphous silicon particle sensors on top of CMOS readout chip. Two types of such particle sensors are presented here using either thick diodes or microchannel plates. The first type based on amorphous silicon diodes exhibits high spatial resolution due to the short lateral carrier collection. Combination of an amorphous silicon thick diode with microstrip detector geometries permits to achieve micrometer spatial resolution beneficial for high accuracy beam positioning. Microchannel plates based on amorphous silicon were successfully fabricated and multiplication of electrons was observed. This material may solve some of the problems related to conventional microchannel devices. Issues, potential and limits of these detectors are presented and discussed.
Band alignment at amorphous/crystalline silicon hetero-interfaces
Authors: Korte L. , Schulze T. F. , Leendertz C. , Schmidt M. , Rech B.
Published: September 2011

We present an investigation of the band offsets in amorphous/crystalline silicon heterojunctions (a-Si:H/c-Si) using low energy photoelectron spectroscopy, ellipsometry and surface photovoltage data. For a variation of deposition conditions that lead to changes in hydrogen content and the thereby the a-Si:H band gap by ∼180 meV, we find that mainly the conduction band offset ΔEV varies, while ΔEC stays constant within experimental error. This result can be understood in the framework of charge neutrality (CNL) band lineup theory.
Excitation of guided-mode resonances in thin film silicon solar cells
Authors: Haug F.-J. , Söderström K. , Naqavi A. , Ballif C.
Published: September 2011

Thin film silicon solar cells are attractive for photovoltaics; however, the poor charge transport in this material requires that the devices are thinner than the absorption length. Adequate absorption can nevertheless be achieved by light scattering at textured interfaces because light can get trapped inside the absorber layer if it is scattered into angles above the critical angle of total internal reflection. This situation can be identified with the propagation of a guided mode in a waveguide where silicon plays the role of the high index guiding medium and the interface texture serves to couple the incident light to modes via grating coupling. We present an experimental realization of a solar cell structure on a line grating where the enhanced photocurrent can be clearly related to resonant excitation of waveguide modes.
DC and AC Gate-Bias Stability of Nanocrystalline Silicon Thin-Film Transistors Made on Colorless Polyimide Foil Substrates
Authors: Chiu I-Chung , Cheng I-Chun , Chen Jian Z. , Huang Jung-Jie , Chen Yung-Pei
Published: September 2011

Staggered bottom-gate hydrogenated nanocrystalline silicon (nc-Si:H) thin-film transistors (TFTs) were demonstrated on flexible colorless polyimide substrates. The dc and ac bias-stress stability of these TFTs were investigated with and without mechanical tensile stress applied in parallel to the current flow direction. The findings indicate that the threshold voltage shift caused by an ac gate-bias stress was smaller compared to that caused by a dc gate-bias stress. Frequency dependence of threshold voltage shift was pronounced in the negative gate-bias stress experiments. Compared to TFTs under pure electrical gate-bias stressing, the stability of the nc-Si:H TFTs degrades further when the mechanical tensile strain is applied together with an electrical gate-bias stress.
Modeling of Advanced Light Trapping Approaches in Thin-Film Silicon Solar Cells
Authors: Zeman Miro , Isabella Olindo , Jäger Klaus , Babal Pavel , Solntsev Serge , Santbergen Rudi
Published: September 2011

Due to the increasing complexity of thin-film silicon solar cells, the role of computer modeling for analyzing and designing these devices becomes increasingly important. The ASA program was used to study two of these advanced devices. The simulations of an amorphous silicon solar cell with silver nanoparticles embedded in a zinc oxide back reflector demonstrated the negative effect of the parasitic absorption in the particles. When using optical properties of perfectly spherical particles a modest enhancement in the external quantum efficiency was found. The simulations of a tandem micromorph solar cell, in which a zinc oxide based photonic crystal-like multilayer was incorporated as an intermediate reflector (IR), demonstrated that the IR resulted in an enhanced photocurrent in the top cell and could be used to optimize the current matching of the top and bottom cell.
Recent progress in transparent conducting materials by use of metallic grids on metaloxides
Authors: van Deelen Joop , Rendering Henk , Hovestad Arjan
Published: September 2011

Alternatives to ITO are under heavy investigation. Organic and inorganic transparent conducting materials are compared based on their transparency versus sheet resistance characteristics. Although graphene has advanced recently, TCOs are still superior in performance and can only be surpassed by the combination of transparent materials with a metal grid. Results on modeling and design optimization using a monolithically integrated CIGS cell configuration as case showed that considerable efficiency enhancement (up to 17% in power output compared to single TCOs) can be achieved for metal grid/TCO combinations. Conductivity improvement has been experimentally verified by four point probe measurements. on both commercial ITO coated PET foil as well as on ZnO coated glass with electrochemically deposited metal grids Sheet resistances as low as 0,1 Ohm/sq were reached and 80 times and 400 times conductivity improvements were obtained at a transparency loss of only 3% and 6%, respectively. It was also found that electrochemical deposition results in more conductive grids than obtained by Ag-ink screen printing due to higher aspect ratios and bulk-like conductivity of the first. Simultaneously, nanopatterning allows optimal grid width of 20 μm, as determined by modeling.
Fabrication of Improved p-AgGaSe2/n-Si Heterojunction Solar Cells on Optimum Quality Thermally Evaporated AgGaSe2 Thin Films
Authors: Das Sandip , Mandal Krishna C.
Published: September 2011

Optimum quality polycrystalline AgGaSe2 thin films were deposited on H-terminated n-Si substrates by controlled thermal evaporation method. The film deposition conditions were varied to optimize the structure and optoelectronic properties of AgGaSe2 thin films. X-ray diffraction (XRD) studies showed that all AgGaSe2 films were of chalcopyrite structure and while the films deposited at room temperature (300 K) had random grain orientation, the films deposited at higher substrate temperature (≥ 450K) showed preferred (112) orientation. The composition of the films were analyzed by electron probe microanalysis (EPMA) deposited at different substrate temperatures. The ultraviolet-visible (UV-Vis) spectra showed the optical bandgap of 1.80 eV, with sharper band edge for the films deposited at higher temperature. The films were p-type and the resistivities of the as deposited films at 300 and 650K were ~5×103 and ~200 Ω.cm respectively. p-AgGaSe2/n-Si heterojunction solar cells, having an active area of 0.18 cm2 without any antireflection coating were designed and fabricated. It was observed that the films deposited at 650K produced heterojunctions with significantly improved photovoltaic properties. The evidence of the barrier height modifications have been provided by C-V measurements. Under solar simulator AM1 illumination, the improved junction exhibited an efficiency of 5.2%, whereas the AgGaSe2 films deposited at 300K showed a lower efficiency of 2.1%.
High Throughput, Low Cost Deposition of Alumina Passivation Layers by Spatial Atomic Layer Deposition
Authors: Vermeer Ad , Roozeboom F. , Poodt P. , Gortzen Roger
Published: September 2011

Atomic Layer Deposition (ALD) is a gas phase deposition technique for depositing very high quality thin films with an unsurpassed conformality. The main drawback of ALD however is the very low deposition rate (~ 1 nm/min). Recently, record deposition rates for alumina of up to 1 nm/s were reached using spatial ALD, while maintaining the typical assets regarding film quality as obtained by conventional, slow ALD [1]. This allows for ALD at high throughput numbers.

One interesting application is passivation of crystalline silicon solar cells. Applying a thin alumina layer is reported to increase solar cell efficiency and enables the use of thinner wafers, thus reducing the main cost factor [2]. In this paper we report on the latest progress made by SoLayTec that delivered a working prototype of a system realizing full area single sided deposition of alumina on 156 x 156 mm2, mono- and multi crystalline silicon wafers for solar cell applications. The alumina layers showed excellent passivation. Based on this concept, a high-throughput ALD deposition tool is being developed targeting throughput numbers of up to 3000 wafers/hr, making ALD ready for mass production. This will bring on new opportunities in other applications.
I-III-VI2 (Copper Chalcopyrite-based) Thin Films for Photoelectrochemical Water-Splitting Tandem-Hybrid Photocathode
Authors: Kaneshiro Jess M. , Deangelis Alexander , Song Xi , Gaillard Nicolas , Miller Eric L.
Published: September 2011

This presentation will investigate various parameters regarding the use of I-III-VI2 Copper Chalcopyrite-based materials for use in tandem-hybrid photocathodes capable of splitting water into hydrogen and oxygen gases in an acidic electrolyte. Constituent parts (fabricated at HNEI) of a proposed monolithically integrated hybrid photovoltaic/photoelectrochemical (PV/PEC) device were characterized separately and combined theoretically using electronic and optical models to simulate tandem operation to first indicate feasibility of matching existing materials. Robust CGSe2 photocathodes were focused on for the PEC cells and CIGSe2 and CISe2 devices were evaluated for the PV cells. Simulation suggested the hybrid PV/PEC system could pass enough light to produce up to 15.87mA/cm2, validating the feasibility and warranting the fabrication of stacked PV/PEC devices.