bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Structural Analysis Method for Graphite Intercalation Compounds
Authors: Nakazawa Tatsuo , Oshida Kyoichi , Miyazaki Takashi , Endo Morinobu , Dresselhaus Mildred S. 
Published: April 2011

ABSTRACTStudy of the microstructure of electronic materials can be enhanced by using high resolution transmission electron microscopy (TEM) combined with the technique of digitized image analysis. We show here a practical image analysis method for the microstructures of acceptor graphite intercalation compounds (GICs) with CuCl2 and FeCl3 intercalates. The two dimensional fast Fourier transform (2D-FFT) was used for the frequency analysis of the TEM pictures. It is found that the lattice images of CuCl2-GICs consist of different frequency images corresponding to specific frequencies. The detailed features of the stage-1 structure of the FeCl3-GICs is extracted quantitatively by this method from a relatively indistinct TEM picture. The stage structure of the CuCl2- and FeCl3-GICs are further investigated by analyzing the reconstruction of the TEM images by means of the two dimensional inverse FFT (2D-IFFT).
Synthesis of CoFe2O4 Nanoparticles via the Ferrihydrite Route
Authors: Manivannan A. , Constantinescu A. M. , Seehra M. S. 
Published: April 2011

ABSTRACTNanoparticles of CoFe2O4 in the size range of 5 nm to 36 nm have been synthesized by first producing two-line Co-doped ferrihydrite and annealing it at temperatures between 573 and 1073 K. Co-doped ferrihydrite is produced by reacting appropriate amounts of FeCl3/CoCl2 solutions with NH4OH at pH = 7. Thermogravimetric measurements provide evidence for the ferrihydrite to CoFe2O4 conversion between 500 and 700 K and x-ray diffraction is used to confirm the transformation to CoFeO4 and determine the particle size. The lattice constant increases initially with the increase in particle size approaching a constant value above 20 nm. The measured Tc equals 788 K for the 36 nm particles. Measurements of magnetization as a function of temperature and magnetic field confirm that the precursor Co-ferrihydrite is a superparamagnet with T ≃ 40 K, whereas for the 30 nm CoFe2O4, the coercivity Hc ≃ 7 kOe at 20 K, decreasing to Hc ≃ 800 Oe with Ms ≃ 60 emu/g at 300 K.
Disordered mesoporous silicates formed by templation of a liquid crystal (L3)
Authors: Malik Abds-Sami , Dabbs Daniel M. , Aksay Ilhan A. , Katz Howard E. 
Published: April 2011

ABSTRACTFor a wide range of technological applications the need for optically transparent, monolithic, mesoporous silicates is readily apparent. Potential areas of utility include filtration, catalysis, and optoelectronics among many others. This laboratory has previously reported on the synthesis of such materials thatare formed through the addition of tetramethoxysilane to a liquid crystal solution of hexanol, cetylpyridinium chloride, and 0.2 M hydrochloric acid, and our investigation into the properties of these materials is a continuing process. We have achieved defect and fracture free material of suitable size (0.5 cm × 3 cm diameter disks) via supercritical drying of the silicate under ethanol or CO2. The dried materials are remarkably similar to ordinary glass in strength, texture, and clarity. They possess pore volumes of ca. 1.0 cm3/g, with BET surface areas >1000 m2/g. We can re-infiltrate thedried monolith with hydroxyethylacrylate, a photo-polymerizable monomer, to create an inorganic/organic nanocomposite. There is fracturing upon re-infiltration, but preliminary tests show that the polymerization proceeds despite the mechanical failure. These findings suggest many possible applications for these unique nanocomposites.
Chemical Synthesis and Properties of Layered Co1-yNiyO2-δOxides (0≤y≤1)
Authors: Manthiram A. , Chebiam R. V. , Prado F. 
Published: April 2011

ABSTRACTLayered Co1-yNiyO2-δ oxides with 0≤y≤1 have been synthesized by chemically extracting lithium from LiNi1-yCoyO2 with NO2PF6 at ambient temperature. The samples have been characterized by X-ray diffraction, wet-chemical analyses, infrared spectroscopy, and magnetic susceptibility measurements. While NiO2-δ retains the initial O3 (CdCl2 structure) layer structure of LiNiO2, CoO2-δ consists of a mixture of P3 and O1 (CdI2 structure) phases that are formed by a sliding of the oxide ions in the initial O3 structure. CoO2-δ and NiO2-δ have oxygen contents of, respectively, 1.67 and 1.95 and the oxygen content increases with increasing Ni content, y, in Co1-yNiyO2-δ. While CoO2-δ exhibits metallic conductivity as revealed by theabsence of absorption bands in the infrared spectrum, NiO2-δ exhibits semiconducting behavior due to a completely filled t2g band. Magnetic data reveal a transition from antiferromagnetic to ferromagnetic correlations as the Ni content in Co1-yNiyO2-δ increases.
Forms of Hydrogen and Hydrogen Diffusion in Realistic Models of a-Si:H
Authors: Fedders P. A. 
Published: April 2011

ABSTRACTUsing ab initio density functional calculations we investigate the energetics of hydrogen in a-Si:H starting from a basic supercell that contains 142 atoms and is completely free of defects. The study includes isolated H atoms bonded to dangling bonds, H atoms bonded to dangling bonds in regions of clustered H, bond centered hydrogen, and molecular hydrogen. In particular, the difference between clustered and isolated hydrogen has been largely ignored in the past. Energetics of doped as well as undoped cells are considered. The results are discussed with particular emphasis on H diffusion and the replacement of atoms in molecular hydrogen with those bonded.
Illumination- and Annealing-Induced Changes in the Infrared and Raman Spectra of a-Si:H
Authors: Arsenault L.-F. , Lebiba S. , Sacher E. , Yelon A. 
Published: April 2011

ABSTRACTWe have investigated the changes, produced by light-soaking, in both the IR and Raman responses of the Si-Hn stretching peaks in the 2000-2100 cm−1 range. Our observations of the IR response are in qualitative agreement with those of Kong and co-workers [1]: that is, short-term light soaking produces an increase in the intensity of the signal and a simultaneous shift to lower frequency. In contrast, short-term light soaking decreases the total intensity of the Raman signal in the 2000-2100 cm−1 range, when normalized to the TO phonon peak at about 480 cm−1. In both cases, these modifications are reversed on annealing at 200° C. We suggest that these changes are attributable to alterations in the environments of the Si-Hn bonds, with the resultant transfer of intensity between IR and Raman matrix elements. Details of the evolution of the components of the Raman spectrum in the 2000-2100 cm−1 range are presented, and compared with IR changes in the same range.
Thin Film a-Si/poly-Si Multibandgap Tandem Solar Cells With Both Absorber Layers Deposited by Hot Wire Cvd
Authors: Schropp R.E.I. , Werf C.H.M. Van Der , Veen M.K. Van , Veenendaal P.A.T.T. Van , Zambrano R. Jimenez , Hartman Z. , Löffler J. , Rath J.K. 
Published: April 2011

ABSTRACTThe first competitive a-Si/poly-Si multibandgap tandem cells have been made in which the two intrinsic absorber layers are deposited by Hot Wire Chemical Vapor Deposition (HWCVD). These cells consist of two stacked n-i-p type solar cells on a plain stainless steel substrate using plasma deposited n- and p-type doped layers and Hot-Wire deposited intrinsic (i) layers, where the i-layer is either amorphous (band gap 1.8 eV) or polycrystalline (band gap 1.1 eV). In this tandem configuration, all doped layers are microcrystalline and the two intrinsic layers are made by decomposing mixtures of silane and hydrogen at hot filaments in the vicinity of the substrate. For the two layers we used individually optimized parameters, such as gas pressure, hydrogen dilution ratio, substrate temperature, filament temperature, and filament material. The solar cells do not comprise an enhanced back reflector, but feature a natural mechanism for light trapping, due to the texture of the (220) oriented poly-Si absorber layer and the fact that all subsequent layers are deposited conformally. The deposition rate for the throughput limiting step, the poly-Si i-layer, is ≍ 5-6 Å/s. This layer also determines the highest substrate temperature required during the preparation of these tandem cells (500 °C). The initial efficiency obtained for these tandem cells is 8.1 %. The total thickness of the silicon nip/nip structure is only 1.1 µm.
Design and Modeling of Optical Sensors in Multi-Channel Technology
Authors: Knipp D. , Stiebig H. , Herzog P.G. 
Published: April 2011

ABSTRACTWe have realized color sensors based on vertically integrated thin film structures to overcome color moiré or color aliasing effects. The complete color information of the color aliasing free sensors can be detected at the same position of a sensor array without optical filters. The color separation is realized by the wavelength dependent absorption of amorphous silicon and its alloys. The sensors consist of three amorphous silicon pin diodes. The spectral sensitivity of the sensors can be controlled by the optical and optoelectronic properties of the materials on one hand and the design of the devices on the other hand. In order to investigate the optical wave propagation within the device and to optimize the color separation we have developed an analytical optical model, which takes the optical properties of the materials and the device design into account. The optical model has been combined with a colorimetrical model, which facilitates the benchmarking of the color sensors and the reduction of the color error of the sensors. The analytical colorimetric/optical model and an improved device design will be presented.
Fast light-induced change in ellipsometry spectra of hydrogenated amorphous silicon measured through a transparent substrate upon bias light illumination
Authors: Hata N. , Fortmann C. M. , Matsuda A. 
Published: April 2011

ABSTRACTPrevious ellipsometric studies of the stability of amorphous silicon (a-Si:H) found reversible changes in the pseudo-dielectric functions. These changes were slow to generate and slow to anneal away. These slow changes are associated with a dangling bond related structural change. Since any light-induced change in the dielectric function is useful for photonic engineering, we undertook the present more detailed study of light induced optical effects in a-Si:H. The optical pseudo-dielectric functions of hydrogenated amorphous silicon (a-Si:H) were measured using spectroscopic ellipsometry (SE) and the “through-the-substrate” measurement technique as a function of measurement temperature and bias light illumination. For the first time we report a light-induced change in a-Si:H materials that is fast, bias-light-dependent, reversible, and temperature dependent. This effect, while not completely understood, offers exciting new prospects for photonic engineering.
Surface Derivatization of Amorphous Silicon by Grignard Reagents
Authors: Ehara Takashi , Maruyama Arata 
Published: April 2011

ABSTRACTSubstitution reactions of surface hydrogen in amorphous silicon at room temperature have been studied. After wet treatment of hydrogenated amorphous silicon thin films with Grignard reagent, surface hydrogen atoms have been substituted by organic groups. Wet treatment of amorphous silicon thin films in CH3(CH2)9-MgBr ether solution followed by quenching by diluted HCl changes infrared absorption spectra. After the treatment, new three peaks of C–H have been observed. In addition, the peaks did not disappeared after rising by hydrofluoric acid or various kinds of organic solvent. The spectra indicate that the Grignard reagent is enough reactive to form new covariant bonding of C and Si at the amorphous silicon surface by substitution reaction.
Sensitization of the Holes Lifetime by the Addition of Dangling Bonds in a-Si:H
Authors: Fonseca L.F. , Weisz S. Z. , Balberg I. 
Published: April 2011

ABSTRACTThis paper is concerned with the phenomenon of the increase of the holes lifetime with the increase of the dangling bond concentration in a-Si:H. This rather surprising phenomenon that was observed, but not discussed, previously is shown to be a non-trivial effect which is based on the charged nature of the dangling bonds and a special scenario of the concentrations of the various defect states in the material. The most important implication of our study is that the charged dangling bonds can sensitize the valence band tail states, in contrast with the accepted roles of these types of states. The present understanding suggests that many new interesting phototransport phenomena can be found in a-Si:H.
Correlation between film and cell properties for DC plasma deposited amorphous silicon
Authors: Heath Jennifer , Iyer Suman B. , Lubianiker Yoram , Cohen J. David , Ganguly Gautam 
Published: April 2011

ABSTRACTWe have carried out measurements to try to correlate amorphous silicon film properties with companion solar cell device performance. The dc plasma deposited intrinsic films were prepared with various hydrogen dilution levels, and increasing power levels to increase growth rate. The electronic properties were determined using admittance spectroscopy and drive-level capacitance profiling (DLCP) techniques as well as transient photocapacitance and photocurrent spectroscopy. Cell and film performance were explored in both as-grown and light-soaked states. We observed that, although cell performance decreased systematiclly with increasing growth rate, it depended on factors other than the deep defect density in the matched films. On the other hand, we did observe that increases in defect density caused by the light-induced degradation led to fairly predictable decreases in the cell fill factors.
Guiding Principle to Develop Intrinsic Microcrystalline Silicon Absorber Layer For Solar Cell By Hot-Wire Cvd
Authors: Middya A. R. , Weber U. , Mukherjee C. , Schroeder B. 
Published: April 2011

ABSTRACTWe report on ways to develop device quality microcrystalline silicon (μc-Si:H) intrinsic layer with high growth rate by hot-wire chemical vapor deposition (HWCVD). With combine approach of controlling impurities and moderate H-dilution [H2/SiH4 ͌ 2.5], we developed, for the first time, highly photosensitive (103 μc-Si:Hfilms with high growth rate (>1 nm/s); the microstructure of the film is found to be close to amorphous phase (fc ͌ 46 ̻± 5%). The photosensitivity systematically decreases with fc and saturates to 10 for fc> 70%. On application of these materials in non-optimized pin [.proportional]c-Si:H solar cell structure yields 700 mV open-circuit voltage however, surprisingly low fill factor and short circuit current. The importance of reduction of oxygen impurities [O], adequate passivation of grain boundary (GB) as well as presence of inactive GB of (220) orientation to achieve efficient [.proportional]c-Si:H solar cells are discussed.
Preparation Temperature Effects in Microcrystalline Silicon Thin Film Solar Cells
Authors: Vetterl O. , Dasgupta A. , Lambertz A. , Stiebig H. , Finger F. , Wagner H. 
Published: April 2011

ABSTRACTMicrocrystalline silicon solar cells were prepared at various substrate temperatures using a plasma enhanced chemical vapor deposition technique at 95 MHz. Devices in superstrate configuration, i.e. prepared on transparent glass/ZnO substrates with deposition sequence p-i-n, suffer from a reduction of short wavelength response upon increasing substrate temperature. As underlying mechanism adverse effects on the p-i interface region are discussed. For devices in substrate configuration (deposition sequence n-i-p on Ag/ZnO back-reflectors) a pronounced efficiency maximum with a highest value of 8.7 % is observed at substrate temperatures of about 250 °C. Comparing the dark J-V characteristics obtained for different device thicknesses at substrate temperatures of 200 °and 250 °C, respectively, improved i-layer material and transport properties are suggested in the latter case. The results illustrate the sensitivity ofmicrocrystalline silicon devices with respect to the employed substrate temperature by effects on the absorber layer material properties on the one hand and by effects related to the device design, e.g. the specific deposition sequence of the individual layers, on the other hand.
CW Argon-ion Laser Crystallization of a-Si:H Thin Films
Authors: Sunda-Meya A. , Gracin D. , Dutta J. , Vlahovic B. , Nemanich R.J. 
Published: April 2011

ABSTRACTThin a-Si:H films, with a thickness of 1 µm, with different hydrogen concentrations, prepared by hot wire deposition were crystallized by 514.5 nm cw Ar ion laser radiation, with a power density between 150 and 270 kW/cm2. The crystallization was continuously monitored by Raman spectroscopy for exposures up to hours. The analysis of crystallization process using Johnson-Mehl phenomenological equations showed an apparent crystallization energy of around 0.5 eV and low dimensional crystal growth. The mean value of the crystal size decreases with increasing irradiation energy and initial hydrogen content and varies between 3 and 6 nm.
High Quality Amorphous Silicon Germanium Alloy Solar Cells Made by Hot-wire CVD at 10 Å/s
Authors: Wang Qi , Iwaniczko Eugene , Yang Jeffrey , Lord Kenneth , Guha Subhendu 
Published: April 2011

ABSTRACTHigh quality amorphous silicon germanium (a-SiGe:H) alloys have been obtained using the hot wire chemical vapor deposition (HWCVD) from a gas mixture of SiH4, GeH4, and H2 at a deposition rate of ∼10 Å/s. Solar cells in a SS/n-i-p/ITO configuration are evaluated in which the n- and i-layers are deposited by HWCVD at NREL and the microcrystalline p-layer by conventional RF glow discharge in a separate reactor by United Solar. Effects of hydrogen dilution and step-wise bandgap profile have been studied and optimized. The best cell has an average optical bandgap of 1.6 eV and incorporates multi-bandgap steps where the narrow-most bandgap is near the p-i interface. J-V characteristics are measured under AM 1.5 illumination with a λ>530 nm filter. The best initial power output obtained exceeds 4 mW/cm2, which is usually used as an indicator for a good quality middle-gap cell. Double-junction cells are made on textured Ag/ZnO back reflectors. The bottom cell uses the optimized a-SiGe:H alloy cell by HWCVD, and the top cell uses an optimized a-Si:H cell near the amorphous-to-microcrystalline transition by PECVD at ∼1 Å/s. The best double-junction cell made to date exhibits an initial AM 1.5 active-area efficiency of 11.7%, and a stable efficiency after 1000 hours of one sun light soaking of 9.6%.
Electronic and optical properties of high quality low bandgap amorphous (Ge, Si) alloys
Authors: Sheng S.R. , Braunstein R. , Dalal V.L. 
Published: April 2011

ABSTRACTHigh quality low bandgap a-(Ge,Si):H alloys were prepared using low pressure, reactive ECR plasma deposition with high H dilution and subtle (sub-ppm) B-doping. The charge transport and optical properties of these low bandgap materials as a function of alloy composition have been investigated by employing the microwave photomixing technique and optical absorption spectroscopy. From the measurements of electric field dependence of the drift mobility, we have found strong evidence for the existence of long-range potential fluctuations in a-(Ge,Si):H alloys, and determined the depth and range of the potential fluctuations, and subsequently the charged defect density, as a function of alloy composition. It was found that at ∼30% Si in Ge, the photoresponse begins to decrease rapidly with increasing Si content due to the decreases in the mobility and lifetime, and meanwhile, both the charged defect density and the Urbach energy increase significantly. The latter indicates an increase in the compositional disorder. It is the potential fluctuations whose effect can be also enhanced by incorporating Si to the alloy system that result in the deterioration of the electronic properties of a-(Ge,Si):H alloys, similar to the case of the incorporation of Ge at the Si end. This enhanced effect accompanies with an increase in the depth, and a decrease in the range of potential fluctuations, leading to a decrease in the mobility, and consequently in the photoconductivity. Our present results demonstrate that the increased charged scattering centers and compositional disorder upon adding Si to the alloys play an important role in the potential fluctuations.
Significant Compositional Changes and Formation of a Ga-O Phase after Oxygen-annealing of Ga-rich CuGaSe2 Films
Authors: Nishio Akihiko , Yamada Akimasa , Fons Paul. J. , Hunger Ralf , Matsubara Koji , Iwata Kakuya , Niki Shigeru , Nakanishi Hisayuki 
Published: April 2011

ABSTRACTCuGaSe2 (CGS) is a promising material for high efficiency thin film solar cells though predicted device performance has not been realized. Understanding the difference in the chemical nature between CuInSe2 (CIS) and CGS is critical for improving Cu (In, Ga) Se2 solar cells with high Ga concentrations. In this work, we have investigated the effects of oxygen-annealing on Ga-rich CGS epitaxial films focusing on compositional changes and secondary phase formations. The photoluminescence (PL) spectrum of Ga-rich films after oxygen-annealing was observed to always change into a spectrum characteristic of CGS grown under Cu-excess conditions. Electron probe micro-analysis (EPMA) measurements indicate the formation of Ga-O after oxygen-annealing. Selective etching of the Ga-O phase showed the composition of the CGS phase became close to stoichiometric. The oxygen-annealed films showed multiple pits ∼ 100 nm in depth and ∼ 2.5 μm in width. The Ga-O phase is founded in a layer formed on the surface of the CGS phase and in a columnar form rising from the bottom of the pits to the film/substrate interface. The above results suggest that excess Ga in Ga-rich CGS tends to react with oxygen to form Ga-O, thus the composition of the remaining CGS approaches stoichiometry consistent with the changes observed in PL.
Observation of Interdiffusion in ZnO/CuInSe2 Heterostructures and its Effect on Film Properties
Authors: Hunger Ralf , Fons Paul , Iwata Kakuya , Yamada Akimasa , Matsubara Koji , Niki Shigeru , Nakahara Ken , Takasu Hidemi 
Published: April 2011

ABSTRACTZnO films were grown directly on epitaxial CuInSe2 (001) (CIS) by radical-source molecular beam epitaxy (RS-MBE). The substrate-film interdiffusion was investigated dependent on the ZnO growth temperature. Secondary Ion Mass Spectroscopy (SIMS) profiles indicate the mutual temperature-activated diffusion of Zn and In at a growth temperature of 440°C which is absent at 250°C. Zn indiffusion into the CIS substrate leads to characteristic changes in the photoluminescence (PL) properties, whereas the In outdiffusion into the growing ZnO film causes an increased carrier concentration.
Fabrication of Solar-Cell-Quality Cadmium Sulfide Layers Via Laser-Assisted Chemical Vapor Deposition (LCVD)
Authors: Hixson Johnnie L. , Cassidy Christopher S. , Stewart Robert L. , Taylor Robert M. , Matthews Lowell R. , Church Kenneth H. , Mamazza Robert , Ferekides Christos S. 
Published: April 2011

ABSTRACTThe laser-assisted chemical vapor deposition (LCVD) technique has proved to be an effective means of depositing cadmium sulfide layers in a well-controlled manner over select small areas. Observations of favorable conditions for deposition and typical pitfalls in the process are discussed. Analysis of the LCVD CdS layers is presented in conjunction with comparisons to conventionally grown CdS layers. The stoichiometry, thickness, and grain structure of the LCVD CdS layers have been suitably optimized for use in solar-cell applications.