bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards a Microscopic Description of Friction
Authors: Porto Markus , Zaloj Veaceslav , Urbakh Michael , Klafter Joseph
Published: April 2011

We investigate the response of an embedded system subject to an external drive using a microscopic model. The shear is shown to excite “shearons”, which are collective modes of the embedded system with well defined spatial and temporal patterns that dominate the frictional properties of the driven system. We demonstrate that the slip relaxation in stick-slip motion and memory effects are well described in terms of the creation and/or annihilation of shearons.
Propagation Dynamics of a Particle Phase in a Single-File Pore.
Authors: Lacasta A.M. , Sancho J.M. , Sagues F. , Oshanin G.
Published: April 2011

We study propagation dynamics of a particle phase in a single-file pore connected to a reservoir of particles (bulk liquid phase). We show that the total mass M(t) of particles entering the pore up to time t grows as (Mt) = 2m(J,ρF) √D0t, where D0 is the “bare” di usion coeffcient and the prefactor m(J,ρF) is a non-trivial function of the reservoir density ρF and the amplitude J of attractive particle-particle interactions. Behavior of the dynamic density pro les is also discussed.
207Pb NMR of PbZrO3 and PbZr1-xTixO3 Solid Solutions
Authors: Rossi Paolo , Dvorak Matthew R. , Harbison Gerard S.
Published: April 2011

PbZrO3 undergoes a phase transition to a paraelectric phase at 230°C. During this phase transition the unit cell changes from orthorhombic to cubic. Structural changes of PbZrO3 have been monitored using solid state NMR by measuring the variation in the 207Pb chemical shielding tensor as a function of temperature. The two distinct lead sites show rather different behavior as a function of temperature. The less shielded lead maintains an almost constant asymmetry parameter η = 0.2 from 0°C to 200°C while the more shielded lead resonance becomes more axially symmetric as the temperature is raised going from η = 0.24 at 0°C to [.eta] = 0.08 at 200°C. Powder pattern singularities become less distinct near the phase transitions, but the temperature dependence of the chemical shift tensor principal values remains continuous, and there is no evidence of an intervening higher-symmetry phase. At the phase transition, both resonances collapse into a single narrow line characteristic of a nucleus at a high-symmetry site. Results of a preliminary study of the PbZr1−xTixO3 solid solutions by 207Pb solid state NMR are also presented.
Fine-Tuning the Physical Properties of Perovskite Related La-Ti-Oxides by Merely Altering the Oxygen Stoichiometry
Authors: Becker Olav , Ebbinghaus Stefan , Renner Bernd , Reller Armin
Published: April 2011

The isostructural oxides LaTiO3.5, SrNbO3.5 and CaNbO3.5 adopt layered structures made up of perovskite related slabs intermitted by layers of non-linking BO6-octahedra (B=Ti, Nb). In these phases the transition metals Ti and Nb are in their highest oxidation states +IV and +V, respectively. They are insulators, in the case of the Ti phase a ferroelectric insulator with the highest known Tc (above 1700°C). By changing the oxygen stoichiometry, i.e. by controlled reduction or re-oxidation processes in the range of 2ABO3.5 ø 2ABO3 + ½ O2 (A=La or Sr, B=Ti or Nb) mixed valence phases are obtained. Accordingly, the physical properties of the different phases alter from insulating to semiconducting or to conducting. Detailed studies on the structural changes reveal, however, that the sublattice of the metal cations is basically conserved. In principle the reduction corresponds to a condensation of the perovskite layers leading to intermediate phases such as the semiconducting LaTiO3.4, in which five TiO6-octahedra thick perovskite slabs constitute the structural framework and 20% of the Ti+IV cations are reduced to Ti+III. Conductivity measurements using single crystals of the corresponding Ti and Nb phases reveal that these mixed valence oxides must be considered as one-dimensional conductors. The fully reduced phases La+IIITi+IIIO3 and Sr+IINb+IVO3 adopt distorted perovskite structures. Extensive high resolution electron microscopic and light microscopic investigations have been carried out in order to characterize the structural mechanism of the reversible, highly topotactic reduction and re-oxidation processes. Thermogravimetric measurements in reducing and oxidizing atmospheres have been performed for the identification of the temperature ranges wherein the decisive mass changes take place. The results of the described experiments support that the properties of such metal oxides can be finely and reversibly tuned by merely changing the oxygen stoichiometries.
A Structural Analysis Method for Graphite Intercalation Compounds
Authors: Nakazawa Tatsuo , Oshida Kyoichi , Miyazaki Takashi , Endo Morinobu , Dresselhaus Mildred S.
Published: April 2011

Study 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

Nanoparticles 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

For 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

Layered 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

Using 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

We 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

The 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

We 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

Previous 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

Substitution 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

This 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

We 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

We 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

Microcrystalline 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

Thin 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

High 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

High 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

CuGaSe2 (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

ZnO 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

The 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.
CdS and CdTe Large Area Thin Films Processed by Radio-Frequency Planar-Magnetron Sputtering
Authors: Hernández-Contreras H. , Contreras-Puente G. , Aguilar-Hernández J. , Morales-Acevedo A. , Vidal-Larramendi J. , Vigil-Galan O.
Published: April 2011

The processing of large area thin films solar cells represents a challenge, mainly due to the need for optimal setting of the critical growth parameters for scaling-up of the processes that guarantee homogeneous properties in the sub-minimodule architecture. We have been working with a Radio-Frequency Planar Magnetron Sputtering (RF-PMS) system, processing 450 cm2 areas of CdS and CdTe thin films grown on soda lime glasses and conducting glasses (SnO2:F-7ω/ ) for CdS, using for it a 6” balanced gun. The films have been processed with substrate temperatures (Ts) of 250°C, Ar chamber-pressure of 20 mTorr, and radio frequency power of 300 watts. The films were characterized by morphological, optical and electrical techniques, presenting in this work the corresponding measurements. Our results show that the better polycrystalline perfection, adherence and pinhole free films are obtained at substrate temperatures of 250°C.
Deep centers and fill factor losses in the CIGS devices
Authors: Igalson M. , Kubiaczyk A. , Zabierowski P.
Published: April 2011

The influence of non-equilibrium space charge distributions on the fill factor of ZnO/CdS/Cu(In,Ga)Se2 photovoltaic devices has been investigated. Metastable changes of the amount of charge captured in deep levels have been produced by red or white illumination. Subsequent characterization by current-voltage, capacitance-voltage and admittance spectroscopy has been conducted at low temperature. The fill factor increases after a white light soaking and decreases after illumination of the reverse-biased device with red light at low temperature. This effect has been attributed to the metastable change of net doping concentration in the p+ layer of absorber close to interface. Blue light, absorbed in CdS provides holes to that region neutralizing the negative charge and thus improving the fill factor. The defects responsible for the interface-related metastability are in our opinion the same as those causing the persistent increase of the net doping concentration in the bulk of Cu(In,Ga)Se2 and seem to be related to selenium vacancies.
Direct Formation of C54 Phase on the Basis of C40 TiSi2 and Its Applications in Deep Sub-Micron Technology
Authors: Chen S. Y. , Shen Z. X. , Xu S. Y. , See A. K. , Chan L. H. , Li W. S.
Published: April 2011

A simple and novel salicidation process applying pulsed laser annealing as the first annealing step was used to induce TiSi2 formation. Both Raman spectroscopy and transmission electron microscope results confirm the formation of a new phase of Ti disilicide, the pure C40 TiSi2 after laser irradiation. Direct C54 phase growth on the basis of C40 template bypassing the C49 phase is accomplished at the second annealing temperature as low as 600°C. Line width independent formation of the C54 phase was observed on patterned wafers using this salicidation process and “fine line effect” is thus eliminated.
Electrical and Structural Properties of Catalytic-Nitrided SiO2 Films
Authors: Izumi Akira , Sato Hidekazu , Matsumura Hideki
Published: April 2011

This paper reports structural and electrical properties of catalytic-nitrided silicon dioxide (SiO2) films. The surface of SiO2/Si(100) was nitrided at temperatures below 573 K. It was found that the incorporated N atoms are bound to Si atoms and O atoms and located on the top-surface of SiO2. Catalytic-nitrided SiO2 films have small amounts of Si-OH bonds and adequate resistance to boron (B) penetration.
TEM Study of strain states in III-V semiconductor epitaxial layers.
Authors: ROCHER André , PONCHET Anne , BLANC Stéphanie , FONTAINE Chantal
Published: April 2011

The strain states induced by a lattice mismatch in epitaxial systems have been studied by Transmission Electron Microscopy (TEM) using the moiré fringe technique on plane view samples. For the GaSb/(001)GaAs system, moiré patterns suggest that the GaSb layer is free of stress and homogeneously relaxed by a perfect square array of Lomer dislocations. A 10 nm thick layer of GaInAs (20% In concentration) grown on (001)GaAs does not give any moiré fringes for all low-index Bragg reflections: this result indicates that the effective misfit strain does not correspond to the theoretical one described by the elastic theory. Segregation effects are expected to play an important role in the relaxation of the misfit strain.
Anodic Bond Quality and impact on Pressure Sensor Long-Term Stability
Authors: Allen Henry , Ramzan Kamrul , Knutti Jim , Ross Carl , Milliman Tim , Frye Jeff
Published: April 2011

Silicon pressure sensors have historically been fabricating by bonding a glass wafer to a micro-machined silicon wafer. The sensor may be sealed as an absolute pressure sensor by using planar glass and can then be used for detection of barometric pressure changes.

It has generally been assumed that as long as the glass and silicon are reasonable clean, then the silicon-glass seal is good and the part becomes a reliable, stable sensor. This paper addresses a low-level drift that was identified in such an absolute pressure sensor. A Zero drift in the range of 0.1% FS was detectable under humidity stresses. The stress always caused drift in the same direction, indicating an effective increased pressure in the sealed cavity.

The impact of various cleaning processes in reducing drift are reported. The improved process assure reliable product for applications such as automotive and altimeter applications.
Gettering Control at Bonding Interface in ELTRAN®
Authors: Momoi Kazutaka , Ito Masataka , Sato Nobuhiko , Honma Noriaki , Yonehara Takao
Published: April 2011

ABSTRUCT:

Heavy metal gettering capability on ELTRAN® was studied by controlling surface treatments for handle wafer prior to wafer bonding. Hydrophobic bonding pre-treatments wafer had much higher heavy metal gettering capability at bonding interface than hydrophilic wafer. In the case of hydrophilic bonding pre-treatments, atomically flat bonding interface was observed by cross-sectional TEM. On the other hand, in the case of hydrophobic bonding pre-treatments, “nano gaps” were observed at bonding interface. We concluded that these differences in the structure at the bonding interface caused the difference in the gettering capability. It is possible to control gettering capability by no additional steps in SOI wafer process.
Anomalies in the Behavior of Mo Field Emitter Arrays in Inert Gases and Some Insights into the Degradation Mechanisms
Authors: Reuss Robert H. , Chalamala Babu R.
Published: April 2011

Field emission displays can be seriously limited by the rapid current degradation of Mo field emitter arrays primarily due to poor vacuum conditions inside their thin vacuum packages. There have been a number of studies to understand the interaction mechanisms. However, we find that models that have been proposed so far are not consistent with observed device behavior in a variety of gas ambients including inert gases and hydrogen. In this paper, we present a summary of our results on residual gases inside a large number of field emission displays, and the effects of these gases on emission behavior. We describe how these issues and the inter-electrode spacing leading to local pressure buildup impact device life. We present an alternate model based on shallow ion implant to explain the observed device behavior.
Study on the Polycrystalline Silicon Films Deposited by Inductively Coupled Plasma Chemical Vapor Deposition
Authors: Moon Byeong Y. , Youn Jae H. , Won Sung H. , Jang Jin , Pietruszko Stanislaw M.
Published: April 2011

Polycrystalline silicon thin films have been deposited by an inductively coupled plasma chemical vapor deposition using SiH4/H2 mixtures. The quality of poly-Si can be improved by increasing RF power and hydrogen dilution ratio. The poly-Si deposited at a RF power of 1000 W with an addition of H2, showed a Raman polycrystalline volume fraction of 85.7 %, FWHM of 6.4 cm−1, deposition rate of 9.64 Å/s and SEM grain size of ∼3000 Å.
Relaxed Silicon-Germanium on Insulator (SGOI)
Authors: Cheng Zhiyuan , Currie Matthew T. , Leitz Chris W. , Taraschi Gianni , Lee Minjoo L. , Pitera Arthur , Hoyt Judy L. , Antoniadis Dimitri. A. , Fitzgerald Eugene A.
Published: April 2011

We have fabricated high quality SGOI substrates and demonstrated high mobility enhancement in strained-Si MOSFET's fabricated on the relaxed SGOI substrates with a Ge content of 25%. The substrates were fabricated by wafer bonding. The initial relaxed Si1−xGex layers were grown on Si donor substrates by a graded epitaxial growth technology using ultrahigh vacuum chemical vapor deposition (UHVCVD). The SiGe wafers were then bonded to oxidized silicon handle wafers. Two different approaches have been developed to fabricate SGOI substrates: an etch-back process utilizing a 20% Ge layer as a natural etch stop, and a hydrogen-induced wafer delamination process using H+ implantion. The resultant SiGe film quality was compared among the different approaches. Large-area strained-Si MOSFET's were then fabricated on the SGOI substrates. Epitaxial regrowth was used to produce the upper portion of the relaxed SiGe and the surface strained Si layer. The measured electron mobility shows significant enhancement over both the universal mobility and that of co-processed bulk-Si MOSFET's. This SGOI process has a low thermal budget and thus is compatible with a wide range of Ge contents in Si1−xGex layer.
Enhanced Mobility in 100 nm Strained SiGe Vertical P-MOSFETs Fabricated by UHVCVD
Authors: Jayanarayanan Sankaran , Prins Freek , Chen Xiangdong , Banerjee Sanjay
Published: April 2011

Strained SiGe vertical PMOSFETs with a channel length of 100 nm have been fabricated without sophisticated lithography and the whole process is compatible with a regular CMOS process. The source, channel and drain layers with in situ doping were grown by ultrahigh vacuum chemical vapor deposition (UHVCVD) at 500 °C. Atomic force microscopy (AFM) of the SiGe and silicon sample surfaces shows the RMS roughness to be 0.18 nm. X-ray diffraction (XRD) rocking curves of the Si (004) plane demonstrate that the SiGe layers do result in compressive strain. The drive current for the vertical SiGe PMOSFET was enhanced by as much as 80% as compared with the silicon control device, in both the forward and reverse modes of operation.
Future Silicon Nanocrystal Nonvolatile Memory Technology
Authors: Ostraat Michele L. , Blauwe Jan W. De
Published: April 2011

A great deal of research interest is being invested in the fabrication and characterization of nanocrystal structures as charge storage memory devices. In these flash memory devices, it is possible to measure threshold voltage shifts due to charge storage of only a few electrons per nanocrystal at room temperature. Although a variety of methods exist to fabricate nanocrystals and to incorporate them into device layers, control over the critical nanocrystal dimensions, tunnel oxide thickness, and interparticle separation and isolation remains difficult to achieve. This control is vital to produce reliable and consistent devices over large wafer areas. To address these control issues, we have developed a novel two-stage ultra clean reactor in which the Si nanocrystals are generated as single crystal, nonagglomerated, spherical aerosol particles from silane decomposition at 950°C at concentrations exceeding 108 cm−3 at sizes below 10 nm. Using existing aerosol instrumentation, it is possible to control the particle size to approximately 10% on diameter. In the second reactor, particles are passivated with a high quality oxide layer with shell thickness controllable from 0.7 to 2.0 nm. The two-stage aerosol reactor is integrated to a 200 mm wafer deposition chamber such that controlled particle densities can be deposited thermophoretically. With nanocrystal deposits of 1013 cm−2, contamination of transition metals and other elements can be controlled to less than 1010 atoms cm−2.

We have fabricated 0.2 μm channel length aerosol nanocrystal floating gate memory devices using conventional MOS ULSI processing on 200 mm wafers. The aerosol nanocrystal memory devices exhibit normal transistor characteristics with drive current 30 μA/μm, subthreshold slope 200 mV/dec, and drain induced barrier lowering 100 mV/V, typical values for thick gate dielectric high substrate doped nonvolatile memory devices. Uniform Fowler-Nordheim tunneling is used to program and erase these memory devices. Despite 5 nm tunnel oxides, threshold voltage shifts > 2 V have been achieved with microsecond program and millisecond erase times at moderate operating voltages. The aerosol devices also exhibit excellent endurance cyclability with no window closure observed after 105 cycles. Furthermore, reasonable disturb times and long nonvolatility are obtained, illustrating the inherent advantage of discrete nanocrystal charge storage. No drain disturb was detected even at drain biases of 4V, indicating that little or no charge conduction occurs in the nanocrystal layer. We have demonstrated promise for aerosol nanocrystal memory devices. However, numerous issues exist for the future of nanocrystal devices. These technology issues and challenges will be discussed as directions for future work.
Electrofluidic Assembly of Nanoelectromechanical Systems
Authors: Evoy Stephane , Hailer Ben , Duemling Martin , Martin Benjamin R. , Mallouk Thomas E. , Kratochvilova Irena , Mayer Theresa S.
Published: April 2011

Recent advances in surface nanomachining have allowed the fabrication of mechanical structures with dimensions reaching 20 nm, and resonant frequencies in the 100s of MHz. Structural issues prevent the “top-down” surface machining of high-quality NEMS resonators. Such systems are alternatively to be bestowed by “bottom-up” manufacturing technologies. We report the surface assembly of RF-range NEMS. Using electrofluidic assembly, we have successfully positioned Rh mechanical beams onto specific sites of a silicon circuit. With diameters as small as 250 nm and lengths varying from 2 to 3 [.proportional]m, preliminary results show mechanical resonances ranging from 5 MHz to 80 MHz, and quality factors reaching 500. We also report the development of nanostructured NEMS for sensor applications, and present strategies for their deployment in integrative nanosystems.
Surface Micromachined Polysilicon Components Containing Continuous Hinges and Microrivets Used to Realize Three-Dimensional MEMS Structures
Authors: Kolesar Edward S. , Ruff Matthew D. , Odom William E. , Ko Simon Y. , Howard Jeffery T. , Allen Peter B. , Wilks Richard J. , Wilken Josh M. , Bosch Jorge E. , Boydston Noah C.
Published: April 2011

A new polysilicon surface micromachining technique for fabricating and assembling three- dimensional structures has been developed. Single-layer polysilicon elements and laminated polysilicon panels incorporating trapped-glass reinforcement ribs have been successfully fabri- cated on a silicon substrate with robust and continuous hinges that facilitate out-of-plane rotation and assembly. To realize a stable three-dimensional structure, one of the device's elevatable panel components is terminated with an array of open windows, and the mating rotatable element has a matched set of protruding arrowheads/microrivets with flexible barbs that readily flex to facilitate their joining and assembly. Because the arrowhead/microrivet barb tip-to-barb tip sepa- ration is larger than the opening in the mating window, the barbs flex inward as they pass through the open window and then expand to their original shape upon exiting the window, re- sulting in a permanently latched joint and a three-dimensional structure. Three novel arrow- head/microrivet designs have been micromachined to facilitate the latching process, including a simple arrowhead, a high-aspect ratio arrowhead, and a rivet-like structure with a hemispherical shaped cap and a flexible split shank.
Fracture Strength of Polysilicon thin Films at Stress Concentrations
Authors: Bagdahn J. , Sharpe W. N.
Published: April 2011

The fracture strengths of 3.5 microns thick and 20 or 50 microns wide polysilicon specimens were measured. One set of specimens was straight in the gage section, another set had a central hole 5.0 microns in diameter, and the third set had symmetric semicircular notches 2.5 microns in radius on each side. The local maximum fracture stresses of the non- uniform specimens, as calculated from the remote fracture stress with a stress concentration factor, were higher than measured in the straight specimens. This indicates a size effect, which is presumably due to the smaller highly stressed volume or area in the non-uniform specimens.
Iron-clad MgB2Superconductor Wires
Authors: Jin S. , Mavoori H. , Bower C. , van Dover R. B.
Published: April 2011

The fabrication of bulk, stoichiometric MgB2wires is a challenge because of the difficulties associated with the volatility and reactivity of magnesium and the brittleness of MgB2. Metal-clad processing of MgB2is a convenient, practical method of overcoming these problems. With such a fabrication approach, iron-clad MgB2superconductor wires exhibiting desirable characteristics with the transport Jcof ∼105 A/cm2at 4.2K have been obtained. In this paper, understanding of the composite wire structures, effect of processing parameters, grain boundary characteristics, and critical current bahavior of the MgB2wires will be described.
Critical Current Properties of Hg(Re)1223 Single Crystals with Various Oxygen Content
Authors: Ueda S. , Shimoyama J. , Sato T. , Horii S. , Otzschi K. , Kishio K.
Published: April 2011

High quality single crystals of Hg(Re)1223 were grown by the flux method using BaZrO3 crucible, which is stable against molten Ba-Cu-O. The maximum size of the obtained crystal was 1 × 1.1 × 0.1mm3 in dimension. X-ray diffraction analysis revealed that grown crystals are of Hg(Re)1223 single phase with c0 = 15.7 å. In the magnetic hysteresis curves for post-annealed Hg(Re)1223 single crystals under H // c, large second peak effect was found with steep increase of magnetization at approximately 2∼3kOe independent of temperature. The peak field systematically increased with a decrease of temperature, suggesting generation of field-induced pinning. Critical current density and irreversibility field of single crystals were dependent on synthesis batch, possibly due to the difference in resulting concentration of Re, while postannealing under various conditions did not affect largely for critical current properties. Irreversibility lines of the Hg(Re)1223 single crystals locate at higher fields than that of Re-free Hg1223. This suggests that electromagnetic anisotropy is reduced by Re-doping, which is consistent with the recent results on the resistive anisotropy in the normal state.
The Nature of Surface Oxides on Magnesium Diboride
Authors: Meegoda Chandana , Paderno Yu. , Trenary Michael
Published: April 2011

Surface oxides present on polycrystalline MgB2 were characterized by high-resolution x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). X-ray diffraction (XRD) measurements were used to determine the MgB2 phases. XRD line broadening analysis reveals a grain size of 40 nm. XPS results show that MgO and B2O3 are the major surface oxides. Auger spectra provide further evidence of the presence of MgO. The B 1s and Mg 2p peaks have been used to quantify the amount of the surface oxides.