bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of High-Quality Ion-Beam Deposited Cubic Oxide Template Films on Meter-Length Substrates
Authors: Arendt P. N. , Groves J. R. , Foltyn S. R. , Jia Q. X. , Peterson E. J. , Depaula R. F. , Dowden P. C. , Coulter J. Y. , Ma M.
Published: April 2011

Ion-beam assisted deposition was used to fabricate biaxially aligned cubic zirconia on flexible metal substrates. These films were used as templates for heteroepitaxially deposited YBa2Cu3O7-δ (YBCO) films. The quality of the crystalline texture of the template films has a direct influence on the superconducting properties of the final YBCO films. We describe our efforts to fabricate high-quality cubic zirconia templates on short-length substrates processed in stationary mode and meter-long substrates processed in continuous mode. Our best phi scan FWHM values for the films on the meter-long tapes were 12.6 degrees for the template and 6.1 degrees for the overcoated YBCO. This meter-long tape had a self-field, 75 K, superconducting critical current of 122 amps.
Analytical High-Resolution TEM Study on Au/TiO2 Catalysts
Authors: Akita T. , Tanaka K. , Tsubota S. , Haruta M.
Published: April 2011

HRTEM(High-Resolution Transmission Electron Microscope), HAADF-STEM (High Angle Annular Dark Field Scanning Transmission Electron Microscope) and EELS(Electron Energy Loss Spectroscopy) techniques were applied for the characterization of Au/TiO2 catalysts. HAADFSTEM provides precise size distributions for Au particles smaller than ∼2nm in diameter. It was observed that many small particles under 2nm were supported on anatase TiO2 having a large surface area. The HAADF-STEM method was examined as a way to measure the shape of Au particles. EELS measurements were also used to examine the interface between Au and TiO2 support to study electronic structure effects.
LEEM Investigations of bcc Metals Grown Heteroepitaxially on Sapphire
Authors: Swiech W. , Ondrejcek M. , Appleton R.S. , Durfee C.S. , Mundschau M. , Flynn C.P.
Published: April 2011

We describe studies of refractory metals Mo and Nb, grown heteroepitaxially in the (011) orientation on sapphire (1120), using low energy electron microscopy (LEEM). A wide variety of structural and dynamical phenomena are observed and recorded as video sequences. These are organized here in five categories as follows. First are surface impurity phases identified by LEED. It is an important point, established here for Mo, that almost ideally clean surfaces with mainly single stepped terraces, can be prepared on thin films for use in surface science. Second, surface reconstruction phenomena can also be identified by diffraction. This is illustrated here by a reconstruction of the Nb surface, with two equivalent domains that form a stripe phase, owing to competing long and short range interactions. Detailed studies of nucleation, fluctuations and the equilibrium of these variants are described. The third area is surface topography, illustrated here by almost ideal stepped surfaces of Mo and Nb at high temperatures, and by nanofaceting by step edge coalescence to form {110} facets on Nb at lower temperatures. The phase diagram for nanofaceting is discussed. Fourth are processes at the internal Al2O3-metal interface, as interfacial dislocations, misorientation steps and defects become visible in the LEEM image through the displacement fields they cause. The final category includes bulk process where the observed dynamics of threading screw and edge dislocations and accompanying slip traces reveal their release at high temperatures from Cottrell atmospheres. The kinetics are tracked as surface diffusion smooths dislocation slip traces, and the interactions among dislocations and surface steps are measured.
SEM/EDX Spectrum Imaging and Statistical Analysis of a Metal/Ceramic Braze
Authors: Kotula Paul G. , Keenan Michael R. , Anderson Ian M.
Published: April 2011

Energy dispersive x-ray (EDX) spectrum imaging has been performed in a scanning electron microscope (SEM) on a metal/ceramic braze to characterize the elemental distribution near the interface. Statistical methods were utilized to extract the relevant information (i.e., chemical phases and their distributions) from the spectrum image data set in a robust and unbiased way. The raw spectrum image was over 15 Mbytes (7500 spectra) while the statistical analysis resulted in five spectra and five images which describe the phases resolved above the noise level and their distribution in the microstructure
The Vibrational Density-of-States of Nanobundles of Single Wall Carbon Nanotubes: An Inelastic Neutron Scattering Study
Authors: Rols S. , Benes Z. , Sauvajol J.L. , Papanek P. , Anglaret E. , Coddens G. , Dianoux A.J. , Fischer J.E.
Published: April 2011

The phonon density of states of single-wall carbon nanotubes (SWNT) was measured by inelastic neutron scattering (INS) in a large energy range (0 to 120 meV). New information on the vibrational dynamics of SWNT is reported and compared with calculated density-of-sates. At lower frequencies (< 12 meV) we observe a peculiar energy dependence which we attribute to contributions from inter-tube modes in the 2D lattice of SWNT bundles, and also from effects of intertube coupling on the intra-tube excitations.
Purification and Characterization of Single-Walled Carbon Nanotubes
Authors: Kim H.Y. , Choi W.B. , Lee N.S. , Chung D.S. , Kang J.H. , Han I.T. , Kim J.M. , Moon M.H. , Kim J.S.
Published: April 2011

Single-walled carbon nanotubes (SWNTs) were purified and cut into short length by the liquid phase oxidation using the typical oxidants such as HNO3, H2SO4 and their mixture. The SWNTacid solutions were refluxed at high temperature, filtered on poly tetra-fluoro ethylene (PTFE) filter paper. rinsed with distilled water, and then dried at room temperature. In order to find optimum purifying condition, acid solutions were made by mixing nitric / sulfuric acid by the different volume ratio. The reaction time was also varied from 1h to 6h. Through this method, purified SWNTs with the length of less than 2μm were successfully obtained, which was confirmed by scanning electron microscopy (SEM). From transmission electron microscopy (TEM) analysis, it was verified that SWNTs were purified with little damage on surface and metal catalysts were efficiently removed when sulfuric acid was mixed, which was also confirmed by energy disperse spectrum analysis (EDS). Moreover, size distribution of the purified SWNTs was characterized with Field Flow-Fractionation (FFF) method.
Density and sp3 Content in Diamond-Like Carbon Films by X-ray Reflectivity and Electron Energy Loss Spectroscopy
Authors: Libassi A. , Ferrari A. C. , Stolojan V. , Tanner B. K. , Robertson J. , Brown L. M.
Published: April 2011

Grazing angle x-ray reflectivity (XRR) is used to study density, thickness, internal layering and roughness of a variety of carbon samples, with and without hydrogen and nitrogen. The bulk mass density of optimised tetrahedral amorphous carbon (ta-C) is 3.26 g/cm2, for which Electron Energy Loss Spectroscopy (EELS) found a sp3 fraction of 85%. Combining XRR and EELS we benchmark the dependence of sp3 fraction on density for hydrogen-free carbons. Hydrogenated ta-C (ta-C:H) deposited by electron cyclotron wave resonance (ECWR) reactor from acetylene gas, has a density of 2.35 g/cm3, 75% sp3 and ∼30% hydrogen. These data provide a similar validation for density and sp3 EELS data for hydrogenated DLCs. XRR can also reveal internal layering in films, and indeed less dense layers may be found at the surface or interface of ta-C films, but no such layers are found in ta-C:H films.
Micro-Wear Scan Test on the Carbon Overcoats as Thin as 6 nm or Less
Authors: Wu T.W. , Scharf Thomas W. , Zhang Hong , Barnard John A.
Published: April 2011

Nitrogen-doped carbon (CNx) overcoats, ranging from I to 6nm in thickness, were deposited on magnetic recording disks by a DC-sputtering process. A critical load, based on the first occurrence of coating damage, was used as a semi-quantitative measure of the mechanical strength of these overcoats. It was found that the critical load decreased in a nearly linear manner with the CNx thickness from 6nm down to ∼2nm regime. However, the lnm thick CNx coating deviated from this trend with a significant decrease in critical load. High-resolution SEM was employed to find the critical loads as well as to reveal the details of the coating wear morphology and the CNx failure mechanism
An Auger and XPS Study on CVD and Natural Diamonds
Authors: Howe Jane Y. , Jones Linda E. , Braski David N.
Published: April 2011

CVD diamond films, ET 100 of Norton Diamond Film, were treateds in ultrahigh purity O2 from 420 to 575°C at 95 kPa. Auger and x-ray photoelectron spectra were collected from CVD and natural diamond surfaces. The Auger KVV line shapes of the CVD diamond with various surface conditions were compared to those of natural diamonds and sp2-bound graphite (HOPG) and glassy carbon. Comparisons were made on the peak shape of A1, which is the major satellite peak of carbon KVV. Auger KVV line shaped of oxidized CVD diamonds were more similar to that of natural diamond than either HOPG or glassy carbon. XPS is more sensitive to the change of surface chemisorbed species. The C Is binding energy of oxygenated and oxidized CVD diamonds (287.3 eV) was higher than that of natural diamond (285.7 eV), graphite (283.0 eV) and glassy carbon (284.2 eV). Auger and XPS findings indicated that when treated in O2 from 420 to 575°C at 95 kPa, direct oxidation of CVD diamond occurred without graphitization
Diameter Control in the Formation of Single-Wall Carbon Nanotubes
Authors: Sen Rahul , Ohtsuka Y. , Ishigaki T. , Kasuya D. , Suzuki S. , Kataura H. , Achiba Y.
Published: April 2011

Single-wall carbon nanotubes (SWNTs) have been synthesized by laser ablation of Ni/Co catalyzed graphite target at 1200°C in argon gas. Raman spectroscopy has been used to study the effect of target position in the furnace and flow rate of argon gas on the diameter distribution of SWVNTs. It was found that yield of smaller diameter SWNTs relatively increases as target is placed away from the hot zone of the furnace. The relative yield of smaller diameter SWNTs decreases with increase in flow rate of the argon gas.
Amorphous Carbon-Silicon Alloys Prepared by a High Plasma Density Source
Authors: Ferrari A. C. , Racine B. , Morrison N. A. , Hutchings I. , Milne W. I. , Robertson J.
Published: April 2011

The addition of silicon to hydrogenated amorphous carbon can have the advantageous effect of lowering the compressive stress, improving the thermal stability of its hydrogen and maintaining a low friction coefficient up to high humidity. Most experiments to date have been on a-C1-xSix:H alloys deposited by RF plasma enhanced chemical vapour deposition (PECVD). This method gives alloys with considerable hydrogen content and only moderate hardness. Here, we use a high plasma density source, the electron cyclotron wave resonance (ECWR) source, to prepare films with a high deposition rate. The composition and bonding in the alloys is determined by XPS, visible and UV Raman and FTIR spectroscopy. We find that it is possible to produce hard, low stress, low friction, almost humidity insensitive a-Cl. xSix:H alloys with a good optical transparency and a band gap over 2 eV.
In Situ Conductivity of Poly(3,4-Ethylenedioxythiophene) Electrosynthesized in Aqueous Solutions in the Presence of Large Anions
Authors: Ahonen H. J. , Lukkari J. , Kankare J.
Published: April 2011

Thick poly(3,4-ethylenedioxythiophene) films incorporating various anion dopants were anodically deposited from aqueous solutions. In situ AC conductometry was applied during the electropolymerisation and the conductivity values obtained in different electrolyte systems were compared. The results indicate that 3,4-ethylenedioxythiophene can be polymerised also from relatively dilute aqueous solutions containing various types of electrolytes and that the most conducting films are obtained using large organic anions.
High Dielectric Constant Polymer Ceramic Composites
Authors: Bai Y. , Bharti V. , Cheng Z.-Y. , Xu H. S. , Zhang Q. M.
Published: April 2011

A new polymer-ceramic composite, using the newly developed relaxor ferroelectric polymer that has a high room temperature dielectric constant as the matrix, is reported. Different kinds of ceramic powders were studied and homogeneous composite thin films (20μm) were fabricated. It was observed that the increase of the dielectric constant of the composites with the ceramic content could be described quite well by the expression developed by Yamada et al., when the ceramic content is below 60% by volume. The experimental data shows that the relative dielectric constant of composites using PMN-PT powders can reach more than 250 with weak temperature dependence (i.e., the dielectric constant changes little in a broad temperature range). In addition to high permittivity, the composite prepared in clean environment also has high breakdown field strength (120MV/m), which yields an energy storage density more than 14J/cm3. The dielectric behavior of the composite at various frequencies was also studied and the results show that the material is promising for high frequency applications.
Synthesis and Electric Property of VDF/TrFE/HFP Terpolymers
Authors: Petchsuk A. , Chung T. C.
Published: April 2011

This paper focuses on the molecular structure-electric property relationships of VDF/TrFE/HFP terpolymers, containing vinylidene difluoride (VDF), trifluoroethylene (TrFE) and hexafluoropropene (HFP) units. Several terpolymers were synthesized and evaluated with the corresponding VDF/TrFE copolymers. In general, a small amount of bulky HFP units in the polymer chain prevents the long sequence of crystallization and results in smaller ferroelectric (polar) micro-domains, which show the improved electric properties. The resulting terpolymer possesses a interesting combined properties with good processibility, low Curie transition temperature and high dielectric constant, narrow polarization hysteresis loop, and high strain response (2.5%) at relatively low electric field (50 MV/m).
Superplastic Dome Forming of Machined Sheets
Authors: Akkus Nihat , Usugi Toshihiro , Kawahara Masanori , Manabe Ken-ichi , Nishimura Hisashi
Published: April 2011

An experimental work on the superplastic bulge forming of machined sheets is presented in this study. Unlike the previously employed incremental-iterative method, a reverse deformation model was used to estimate the initial thickness distribution of the machined sheets from which a constant final thickness can be obtained when the shape of the bulged sheet is hemisphere. The reverse deformation modci was obtained by modifying previously-known models, which were based on the axisymmetric membrane and the incremental strain theory.

Bulge forming experiments were conducted on machined sheets of Al alloy, A5083, at about 530°C under constant pressure control mode. The result of this simulation to estimate the final constant thickness distribution agreed well with the experiment, and confirmed that the reverse deformation model can be successfully applied in optimizing the thickness distribution of the starting sheets in order to obtain the desired final thickness distribution of the free bulged hemispherical product.
Effect of SN Additions on Superplasticity in Al-Mg-Mn-Sc Alloys
Authors: Henager C. H. , Vetrano J. S. , Gertsman V. Y. , Bruemmer S. M.
Published: April 2011

Identical Al-Mg-Mn-Sc alloys without and with 0.034-wt% Sn additions were fabricated, heat-treated, and tensile tested in a fine-grain (d < 6 pm) condition at four strain rates from 10−2to 10−4s−1and at temperatures from 723K to 823K. Alloys with Sn additions exhibited reduced failure strains at 723K but higher failure strains at 823K for the slowest strain rates. The effect of Sn on flow stress, activation energy for flow stress, and strain rate exponent was explored and was found to be small. The main effect of Sn was suggested to be in reducing cavitation by allowing a redistribution of stress at critical hetero-junctions in the alloys.
Superplasticity of Nickel-Based Alloys with Micro- and Sub-Microcrystalline Structures
Authors: Valitov V.A. , Bewlay B.P. , Mukhtarov Sh. Kh. , Kaibyshev O.A. , Gigliotti M.F.X.
Published: April 2011

This paper will describe the generation of micro- and sub-microcrystalline structures in two Ni-based alloys that are typically strengthened by phases, such as γ′ and γ″+δ. The relationship between the superplastic behavior and microstructure will be discussed. High strain deformation processing in the temperature range of 0.9 Tm to 0. 6Tm results in reduction of the initial coarse-grained structure (>100 µm) to a range of structures including microcrystalline (MC) (grain size <10 µm) and sub-microcrystalline (SMC) (grain size <1 µm) with increasing deformation. The influence of alloy chemistry and constituent phases on dynamic and static recrystallization is considered, and their effect on grain refinement is described. Low-temperature and high strain rate superplasticity can be observed in dispersionstrengthened alloys with SMC structures. It was established that in dispersion-hardened Ni alloys with SMC structures, superplasticity can be observed at temperatures 200-250°C lower than in alloys with MC structure.
Formation and Characterization of Single Crystal Ni2MnGa Thin Films
Authors: Dong J. W. , Chen L. C. , Mckernan S. , Xie J. Q. , Figus M. T. , James R. D. , Palmstrøm C. J.
Published: April 2011

In this paper, molecular beam epitaxial growth of Ni2MnGa single crystal layers on GaAs (001) using a NiGa interlayer is reported. X-ray diffraction and transmission electron microscopy confirmed an epitaxial relationship of Ni2MnGa [100]“010] // GaAs [100] [010] and a tetragonal structure of the film (a = b = 5.79 Å, c = 6.07 Å). Magnetic measurements using vibrating sample and superconducting quantum interference device magnetometers revealed an in-plane magnetization of ∼200 emu/cm3at room temperature and a Curie temperature of ∼350 K. The martensitic phase transformation was observed to occur at ∼250 K
Effects of Electric Fields on the Bending Behavior of Piezoelectric Composite Laminates
Authors: Cheng J.Q , Zhang T.Y. , Zhao M.H. , Qian C.F. , Lee S. W. R. , Tong P.
Published: April 2011

This Paper investigates the bending behavior of piezoelectric laminates under combined mechanical and electrical loading. The laminate has a PZT - 5H ceramic core sandwiched by graphite/epoxy plates. Three-point bending tests and in-situ acoustic emission measurements were conducted on the PZT-5H laminates preloaded by an applied electric field. The results show that the PZT-5H core fractures first and then delaminaton occurs along the tensile stressed interface between the PZT ceremic and the graphite/epoxy layer. Finite element analysis was performed to analyze stresses in the sandwich structure under combined mechanical and electrical loading. Consequently, the bending strength of the PZT core was evaluated from the experiment data. The electric field, either positive or negative, reduces the fracture strength of the pzt core.
Considerations in the Development of a Piezoelectric Transducer Cochlear Implant
Authors: Mukherjee N. , Roseman R. D.
Published: April 2011

Sensorineural hearing loss results from the inability of the inner ear cochlear organ of Corti to transduce mechanical energy incident in the cochlea to electrical signals in auditory nerve fibers. Cochlear implant devices are used to alleviate this condition. Piezoelectric materials offer the unique scope of functioning as cochlear implants, possibly enabling simplification of the process of electrical stimulation and enhancing knowledge of the workings of both the healthy and artificially stimulated inner ear. The requirements imposed on such a device are discussed. It is believed that flexible piezoelectric PVDF and ceramic-polymer composites are best suited for this application. The design of a device which utilizes the bending piezoelectric mode, and results of testing the same in air are presented. Present work is aimed at understanding the fundamental dynamic piezoelectric properties in this mode and is expected to result in a device suitable forin vitroandin vivotesting.
Characterization of Low Temperature, Wafer-Level Gold-Gold Thermocompression Bonds
Authors: Tsau Christine H. , Schmidt Martin A. , Spearing S. Mark
Published: April 2011

Low temperature, wafer-level bonding offers several advantages in MEMS packaging, such as device protection during aggressive processing/handling and the possibility of vacuum sealing. Although thermocompression bonding can be achieved with a variety of metals, gold is often preferred because of its acceptance in die bonding [1] and its resistance to oxidation. This study demonstrates that the simultaneous application of moderate pressure (0.5 MPa) and temperature (300°C) produces strong wafer-level bonds. A four-point benddelamination technique was utilized to quantify bond toughness. Test specimens exhibited constant load versus displacement behavior during steady state crack propagation. Two distinct fracture modes were observed: cohesive failure within the Au and adhesive failure at the Ti-Si interface. The strain energy release rate for Au-Au fracture was found to be higher than that associated with Ti-Si fracture, consistent with the greater plastic deformation that occurs in the metal during fracture.
Fracture Behavior of Micro-Sized Ni-P Amorphous Alloy Specimens
Authors: Ichikawa Y. , Maekawa S. , Takashima K. , Shimojo M. , Higo Y. , Swain M. V.
Published: April 2011

Fracture behavior of micro-sized Ni-P Amorphous alloy specimens has been investigated using a newly developed mechanical testing machine. Specimens with dimensions of 10 × 12 × 50 μm were prepared by focused ion beam machining. Two types of specimens with different crack geometries were prepared. One specimen has a notch with root radius is 0.25 μtm and the other has a fatigue pre-crack. The shapes of the loaddisplacement curves are different for each type of specimen. The fracture strength of the specimens with a notch is higher than that with a fatigue pre-crack and the fracture surfaces of the specimens are also different for each type of specimen. This may be due to the difference in stress concentration at the crack (notch) tip, and indicates that even a notch with a root radius of 0.25 μm is not able to be regarded as a crack for micro-sized specimens. Therefore, the introduction of a fatigue pre-crack is essential for the evaluation of fracture toughness for such micro-sized specimens.
Low Temperature Thermal Chemical Vapor Deposition of Silicon Nitride Thin Films for Microelectronics Applications
Authors: Skordas Spyridon , Sirinakis George , Yu Wen , Wu Di , Efstathiadis Haralabos , Kaloyeros Alain E.
Published: April 2011

Silicon nitride technology has been incorporated in ultra-large scale integration (ULSI) microchip fabrication, thin film transistors (TFT), solar cells, and many other applications in a rapidly expanding market. Nevertheless, silicon nitride technologies currently in use face considerable limitations. Low pressure chemical vapor deposition (LPCVD) occurs at relatively high temperature (>700 °C) and plasma enhanced chemical vapor deposition (PECVD), although occurring at temperatures below 300 °C, produces hydrogen-rich films and could be self-limiting in terms of conformality and damage to the devices due to ion bombardment. In the present work, successful low temperature thermal chemical vapor deposition (LTCVD) of silicon nitride is reported on 8” silicon wafers. The use of a halide-based silicon precursor, tetraiodosilane (SiI4) has led to the deposition of high quality silicon nitride thin films at temperatures as low as 300 °C.

Characterization of resulting film properties has been performed to determine their dependence on deposition parameters by Auger Electron Spectroscopy (AES), Rutherford Backscattering Spectroscopy (RBS), Fourier Transform Infrared (FTIR), Nuclear Reaction Analysis (NRA), Ellipsometry, Capacitance-Voltage (C-V), and Current-Voltage (I-V) measurements.
Volatile Liquid Precursors for the Chemical Vapor Deposition (CVD) of Thin Films Containing Alkali Metals
Authors: Broomhall-Dillard Randy N. R. , Gordon Roy G. , Wagner Valerie A.
Published: April 2011

The first volatile, liquid compounds of alkali metals were synthesized and used for the CVD of materials containing alkali metals. Amides of the type MNR1(SiMe2R2) and MN(SiMe2R2)2 [M = Li, Na, K; R1= t-butyl, t-amyl; R2= ethyl, n-propyl, i-propyl, n-butyl, i-butyl, n-hexyl, n-octyl] were made and characterized. The lithium amides were prepared via the deprotonation of the parent amine using butyl lithium. The sodium and potassium amides were formed by transamination of sodium amide and potassium bis(trimethylsilyl)amide with the parent amines. For example, lithium bis(ethyldimethylsilyl)amide was prepared from butyl lithium and bis(ethyldimethylsilyl)amine and was distilled as a clear, colorless liquid at 122 °C (0.2 Torr) having a viscosity of 37 cP at 40 °C. These alkali metal amides can be used as convenient liquid sources for CVD of mixed metal oxides containing alkali metals, such as the non-linear optical material lithium niobate, lithium-containing materials for battery electrodes, electrochromic tungsten bronzes, and the pyroelectric and ferroelectric material potassium tantalate.
Chemical Vapor Deposition of Conformal Alumina Thin Films
Authors: Fahlman Bradley D. , Barron Andrew R.
Published: April 2011

Deposition of highly conformal alumina thin films has been carried out by hydrolysis of the liquid alane precursor, AlH3(NMe2Et). Deposition onto Si wafers, quartz and carbon fibers were all carried out utilizing a hot-wall atmospheric pressure chemical vapor deposition (APCVD) system, while deposition onto ceramic particles was accomplished in a simple fluidized-bed APCVD reactor. Films were characterized by SEM, microprobe and electrical conductivity measurements. Growth rates were on the order of 40 - 80 Å.min−1at 165 °C. The conformality of the films was illustrated using silicon wafers that were etched prior to deposition.
Emissivity Compensated Pyrometry of the Substrate Surface During Movpe Growth of InxGa1−xAs1−yPy/InP Materials in Rotating Disc Reactors
Authors: Ramer J. , Patel B. , Patel A. , Boguslavskiy V. , Gurary A.
Published: April 2011

In order to overcome some of the inherent difficulties with applying conventional pyrometry to production scale rotating disc MOVPE reactors, the in-situ technique of emissivity compensated pyrometry has been applied. Due to the extreme temperature sensitivity of epitaxial processes involving InxGa1−xAs1−yPy, this material system provides the optimum proving grounds for this technology. With this temperature measurement technique, we have developed a method for measuring the temperature of the substrate during MOVPE growth in high speed rotating disc reactors that does not require any modification to the reactor hardware. Real world testing, during the growth of complex epitaxial structures involving the highly temperature sensitive InxGa1−xAs1−yPy quaternary, indicates a very strong correlation between the measured temperature of the substrate during growth, and actual epitaxial wafer measurements after growth. This temperature measurement system can be used to maintain the wavelength of the InxGa1−xAs1−yPy quaternary materials within a range of 2 nm.
Recent Progress of Mid-IR Type-II Interband Cascade Lasers
Authors: Lin Chlh-Hsiang , Hwang W.-Y. , Zaitsev S. V. , Urn J. , Kuo C.H. , Delaney A. , Zheng Jun , Murry S. J. , Liu A. , Le H. Q. , Mu Y. , Pei S. S.
Published: April 2011

We report the recent progress in type-II interband cascade (IC) lasers, For the 4.2-pm devices, lasing was observed up to 210 K, and the threshold density was only 95 A/cm2at 90 K and 284 A/cm2at 200 K. For the 4.5-μm lasers, the internal loss was only 11.6 cm−1 and the internal quantum efficiency was 460% at 90 K. We have also demonstrated the first dual-wavelength type-II IC lasers at 4.482 and 4.568 μm.
Native Defect Characterization in ZnGeP2
Authors: Hoffmann A. , Born H. , Näser A. , Gehlhoff W. , Maffetone J. , Perlov D. , Ruderman W. , Zwieback I. , Dietz N. , Bachmann K. J.
Published: April 2011

Electron paramagnetic resonance (EPR) as well as time-resolved and time-integrated photoluminescence (PL) are used to characterize the defect centers in ZnGeP2 bulk crystals. The samples, as-grown, electron-irradiated and annealed, reveal a strong intensity dependence of the VZn-correlated EPR-transitions. Photo-EPR experiments show that this intensity behavior is mainly caused by a recharging of the VZn centers owing to the preparation induced shift of the Fermi-level. The luminescence spectra show a broad infrared emission with peak position at 1.23 eV that exhibits features of classical donor-acceptor recombination. The hyperbolic decay characteristics, investigated in energy range from 1.2 eV up to 1.5eV, suggest that this broad emission band is related to one energetic recombination center. This recombination is interpreted to be between donor-acceptor states related to residual disorder on the cation sublattice that is retained in metastable equilibrium during the formation of the chalcopyrite structure. The emission decay behavior in the energy range from 1.2 eV up to 1.6 eV is characterized by two hyperbolic time constants, and explained as the super-composition of the decays from the broad emission center peaked at 1.2 eV and an additional donor-acceptor recombination centers at 1.4 eV.
Photoresponse of Tellurium Rich TexSe(1−x) Nonlinear Optical Semiconductors
Authors: Brown G. J. , Dennis Cindi L. , Ohmer M. C. , Burger Arnold
Published: April 2011

The optical properties of TexSe(1−x) were studied for x = 0.8, 0.9, and 1.0. The results for variable temperature, polarization sensitive, spectral photoconductivity measurements on oriented single crystals, as well as the energy band gaps and their temperature dependencies are presented. In all cases, the band gap was found to increase with increasing temperature. Analytical expressions describing the temperature dependent behavior are reported. Furthermore, for the first time the characteristic two peak spectrum of tellurium was separated into its two components for incident radiation polarized parallel and perpendicular to the c-axis as a function of temperature. However, two distinct peaks were not discernible in the alloys, with or without polarization, although the signal intensity was slightly polarization dependent.
Temperature Dependent Hall Measurements on CdGeAs2
Authors: Ptak A.J. , Jain S. , Stevens K.T , Myers T.H. , Schunemann P.G. , Setzler S.D. , Pollak T.M.
Published: April 2011

Seventeen samples of CdGeAs2 have been extensively characterized by temperature-dependent Hall effect and resistivity measurements. Due to the anisotropic nature of the electrical properties, carefully matched sample sets were fabricated with the c-axis either in or out of the plane of the sample. The matched samples allowed determination of carrier concentration and both in-plane and out-of-plane mobilities as a function of temperature. The electrical properties of both undoped and lightly doped samples were dominated by either native defects or residual growth impurities, leading to compensated p-type material. N-type doped material was obtained only with heavy doping. An apparent variation in acceptor activation energy between 110 and 165 meV could be best explained in terms of two deep acceptor levels and at least one shallow donor. Room temperature absorption coefficient data and the relation to background doping is also reported.
Reduction of the Optical Absorption of Zinc Germanium Phosphide Via Post-Growth Thermal Anneal
Authors: Ang How-Ghee , Chng Leng-Leng , Lee Yiew-Wang , Flynn Colin J. , Smith Phil C. , Vere Anthony W.
Published: April 2011

This paper describes the reduction of the near-band-edge absorption of zinc germanium phosphide (ZGP) through thermal annealing. The effects of the annealing time, temperature and vapour atmosphere on the reduction of the optical absorption in the near infrared (NIR) region are reported. Results have shown that the optical absorption at 2µm is reduced by at least 50% upon thermal anneal of ZGP. The optimal annealing temperature was 600'C and the optimal annealing time ranged from 200 - 400 h. Annealing in vacuum yielded a larger reduction in the 2-µm optical absorption compared to annealing in the presence of additional zinc and phosphorus vapours. Re-annealing ZGP further reduced the absorption coefficient at 2-µm. However, the percentage decrease in the 2-µm absorption coefficient was much smaller compared to the first thermal anneal.
Correlation Between Surface/Interface States and the Performance of MIS Structures
Authors: Águas Hugo M. B. , Fortunato Elvira M.C. , Cabrita Ana M. , Silva Vitor , Tonello Pedro M.N. , Martins Rodrigo F.P.
Published: April 2011

In order to understand the kinetics of formation of interface/surface states and its correlation on the final device performance, a preliminary study was performed on MIS structures, before and after surface oxidation/passivation, using different oxidation techniques and oxides: thermal (in air), chemical (in H2O2) and oxygen plasma.

The devices used in this work are based on a glass/Cr/a-Si:H(n+)/a-Si:H(i)/SiOx/Pd structures, where the amorphous silicon intrinsic layer (i a-Si:H) with a photosensitivity of 107was deposited by a modified plasma enhanced chemical vapour deposition (PECVD) triode system.

The electrical properties of a-Si:H MIS structures were investigated by measuring their diode current-voltage characteristics in the dark and under illumination as well as the spectral response, as a function of the various oxidation techniques. Infrared spectroscopy and spectroscopic ellipsometry were used as a complementary tool to characterise the oxidised surface.
Phase Transition in Cr/a-Si:H/V Thin Film Devices
Authors: Hu J. , Snell A.J. , Hajto J. , Rose M.J. , Edmiston W.
Published: April 2011

Experimental results on the electronic properties of conditioned Cr/hydrogenated amorphous silicon (a-Si:H)/V thin film devices are presented. The devices under test were electro-formed, and had resistances in the range from several hundred ohms to several kiloohms. The current of conditioned devices varied non-linearly with the bias at low voltages, but exhibited ‘jumps' at a threshold voltage (Vth) (typically 2∼3V ), leading to a resistance change of 1∼3 orders of magnitude. Above Vth the current increased almost linearly with bias, and the carrier transport changed from a semiconducting behaviour into a more conducting (metallic) state. The threshold voltage Vth was found to decrease with increasing temperature and disappear at 340 ∼ 350K, but recovered on reducing the temperature. The transition at Vth has been analysed in terms of electrothermal mechanism. The calculated turnover temperature is about 346K, close to that for the disappearance of Vth. We suggest that the observed transition could involve vanadium oxides such as VO2.
Measurement of Impurity Profiles in Microcrystalline Silicon Solar Cells by SIMS
Authors: Dasgupta Arup , Zastrow Uwe , Lambertz Andreas , Vetterl Oliver , Finger Friedhelm , Beyer Wolfhard , Ray Swati
Published: April 2011

The concentration profiles of B, P, Zn, and O in the active intrinsic (i) νc-Si:H layer and across the interfaces in p-i-n and n-i-p structures have been measured with SIMS. For the ZnO/νc-p/νc-i sequences, an apparent B and O profile extends over several hundred nanometers into the i-layer, and high levels of Zn can be found well above the ZnO substrate layer. These profiles are not affected by annealing at the deposition temperature. Much lower impurity concentrations are measured for n-i-p deposition sequences, or when the p-layer or the i-layer is amorphous. Ruling out diffusion and intermixing processes, evidence for the presence of pinholes in the material is presented, which explain most of the experimental findings.
Open-Circuit Voltage Physics in Amorphous Silicon Solar Cells
Authors: Jiang L. , Lyou J. H. , Rane S. , Schiff E. A. , Wang Q. , Yuan Q.
Published: April 2011

We have performed computer calculations to explore effects of the p/i interface on the open-circuit voltage in a-Si:H based pin solar cells. The principal conclusions are that interface limitation can occur for values of VOC significantly below the built-in potential VBI of a cell, and that the effects can be understood in terms of thermionic emission of electrons from the intrinsic layer into the p-layer. We compare measurements of VOC and electroabsorption estimates of VBI with the model calculations. We conclude that p/i interface limitation is important for current a-Si:H based cells, and that the conduction band offset between the p and i layers is as important as the built-in potential for future improvements to VOC.
Low Temperature Thin-Film Microelectromechanical Devices on Plastic Substrates
Authors: Boucinha M. , Brogueira P. , Chu V. , Alpuim P. , Conde J. P.
Published: April 2011

Air-gap micromachined structures such as bridges and cantilevers were fabricated on 50 and 125 µm-thick polyethylene terephthalate (PET) plastic substrates. The maximum processing temperature using PET is limited to 110 °C. Two surface micromachining processes on PET which used two different sacrificial layers - photoresist and Al - were developed. Several materials were used as structural layers in the microstructures including Al, TiW, amorphous silicon (a-Si:H) and a bilayer of a-Si:H and Al. The maximum length of free-standing bridges and cantilevers is discussed as a function of the fabrication process. The bridge structures were actuated electrostatically, in a DC switch setup configuration, and the critical voltage as a function of the length was measured. Mechanical actuation and optical detection were used, in an AC mode, for the measurement of the resonance frequency of bridge structures.
Metastable defects by low-intensity pulsed illumination of hydrogenated amorphous silicon
Authors: Heck Stephan , Branz Howard M.
Published: April 2011

Illumination of hydrogenated amorphous silicon (a-Si:H) samples with short (e.g., 40 microsecond) pulses of red light produces a smaller metastable absorption increase in the defect region than continuous illumination of the same intensity for the same integrated exposure time. The defect absorption was measured at 1.3 and 1.4 eV by use of the constant photocurrent method (CPM). This smaller degradation is also observed in the photoconductivity. Careful measurement of the film temperature with several techniques confirm that the film temperature rises by less than 5 °C, under continuous illumination. However, several experiments suggest that the suppressed degradation during pulsed illumination is caused primarily by annealing during the dark time between pulses, even at 15 to 26 °C.
Suppression of Plasma Damage on SnO2 by Means of a Different Surface Chemistry Using Dichlorosilane
Authors: Nakashima T. , Kondo M. , Toyoshima Y. , Matsuda A.
Published: April 2011

We report on that plasma damage on SnO2 can be suppressed by using surface termination by chlorine. It was found that the darkening of SnO2 is decreased and a wider gap p-a-Si material is obtained by using SiH2Cl2 especially at the higher reaction pressure and at the lower substrate temperature. The suppression of darkening of SnO2 and wide optical gap is correlated to chlorine contents in the film. It is demonstrated that SiH2Cl2 is also beneficial for boron-doped material, indicating a suitable material for a window layer of solar cells.
Barrier-Controlled Transport in Doped Microcrystalline Si
Authors: Brehme S. , Kanschat P. , Fuhs W.
Published: April 2011

Thin μc-Si films doped with P and B are grown on glass at temperatures between 300 °C and 400 °C by electron cyclotron resonance chemical vapor deposition (ECR-CVD). Hall mobilities in the films are found to be temperature-activated with activation energies being correlated to the doping concentrations. The in-grain mobility as determined by an electron spin resonance investigation is much higher than the Hall mobility the values of which are typically near 1 cm2/Vs at 300 K. The experimental results suggest that transport is dominated by potential barriers at the grain boundaries. An extended Seto model is used to probe the interface trap distribution. We obtained the best fitting results by assuming band-tail states decaying exponentially from the respective band edges.
Thermal Oxidation of Si Nanoparticles Grown by Plasma-Enhanced CVD
Authors: Das Debabrata , Farjas Jordi , Costa Josep , Roura Pere , Viera Gregorio , Bertran Enric
Published: April 2011

Nanoparticles of amorphous silicon were grown by plasma-enhanced CVD. Their high hydrogen content has a great influence on the oxidation kinetics. Oxidation experiments done in a thermo-balance show that during a heating ramp under oxygen the onset of oxidation shifts to higher temperatures when hydrogen content is reduced by annealing. Apparently this higher oxidation rate of the as-grown particles is due to the great density of dangling bonds that are left behind just after the hydrogen is desorpted. This fact is supported by analyzing the oxidation dynamics under isothermal conditions. At lower temperature, when oxidation takes place just after hydrogen desorption, the oxidation transient begins with a finite slope which indicates that oxidation is not diffusion controlled. On the other hand, at higher temperatures, activation energy of the parabolic rate constant indicates that the oxide layer formed is less protective than the oxide layer formed on crystalline silicon.
Microstructure and Electronic Properties of Thin Film Nanoporous Silica as a Function of Processing and Annealing Methods
Authors: Caragianis-Broadbridge Christine , Miecznikowski John R. , Zhu Wenjuan , Luo Zhijiong , Han Jin-ping , Lehman Ann Hein
Published: April 2011

Alcogels, aerogel precursors, were prepared by hydrolysis and condensation of the metal alkoxide tetraethylorthosilicate and were catalyzed by both acids and bases, according to a standard reaction. Alcogel solution was spin coated onto p-type silicon wafers and fluid extraction was achieved in an uncontrolled (room temperature, atmospheric pressure) environment. Film porosity was retained through surface modification and/or low vapor pressure solvent techniques. The microstructure and electronic properties of the resulting films were evaluated using non-contact atomic force microscopy (nc-AFM), cross sectional scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Metal insulator semiconductor (MIS) devices were prepared and current-voltage and capacitance-voltage measurements were obtained from these devices. Annealing studies reveal a dramatic temperature dependent effect on both the microstructure and electronic properties of the porous silica films.
Sputter Deposition of GMR Spin Valves
Authors: Zou W. , Zhou X.W. , Quan J.J. , Yang Y.G. , Wadley H.N.G. , Brownell D. , Wang D. , Ghosal S. , Subhas D. , Kosut Robert , Ebert Jon
Published: April 2011

Radio frequency (RF) diode sputtering has been used for the growth of giant magnetoresistive (GMR) metal multilayers. Control of the atomic-scale structure of the surfaces and interfaces within these films is critical for GMR applications. A systematic series of experiments have been conducted to evaluate the dependence of the magnetotransport properties upon the growth conditions (i.e. background pressure, input power) for NiFeCo/CoFe/CuAgAu spin valves during RF diode sputter deposition. By using computational fluid dynamics, plasma, molecular dynamics, and various Monte Carlo techniques, a multiscale modeling approach has investigated the atomic assembly events during film growth. Energetic metal atoms and inert gas ion fluxes are shown to have very strong effects upon interfacial structures. The insights gained have led to novel deposition strategy propopositions for interface morphology control.
In Situ Analysis Gaseous Species for CVD Diamond Synthesis and the Possible Reaction Model
Authors: Uede Mayu , Takagi Yoshiki
Published: April 2011

For few years, we had been concentrated of developing completely closed diamond synthesizing system aimed for microgravity experiments. Recently we started the new method with graphite as carbon source. With this method, completely closed system is successfully performed.

In-situ gaseous species analyzed with gas chromatographic analysis and possible reaction model will be presented.
Modeling of PVT Growth of Bulk SiC Crystals: General Trends and 2” to 4” Reactor Scaling
Authors: Ramm M.S. , Kulik A.V. , Zhmakin I.A. , Karpov S.Yu. , Bord O.V. , Demina S.E. , Makarov Yu.N.
Published: April 2011

We report on study of a growth system upscaling from 2” to 4” using numerical modeling. The model applied involves heat and mass transfer computations combined with a self-consistent analysis of deposit formation on the reactor walls. General trends in SiC bulk crystal growth originated from upscaling are discussed in detail.
Laser-Induced Liftoff And Laser Patterning Of Large Free-Standing GaN Substrates
Authors: Ambacher O. , Kelly M. K. , Miskys C. R. , Höppel L. , Nebel C. , Stutzmann M.
Published: April 2011

Free-standing GaN crystals are produced from 200-300 µn thick GaN films grown on 2 inch sapphire substrates by hydride vapor phase epitaxy. The GaN films are separated from the growth substrate by laser-induced liftoff, using a pulsed laser to thermally decompose a thin layer of GaN close to the film-substrate interface. The free-standing films are polished and used for the homoepitaxial growth of high quality GaN layers by metalorganic chemical vapor deposition. The structural and optical properties of the homoepitaxial films in comparison to layers grown on sapphire are significantly improved, mainly because of lower dislocation density and surface roughness as low as 5×106 cm2 and 0.2 nm, respectively.

Laser-induced thermal decomposition is also applied to achieve etching of GaN. At exposures of 500 mJ/cm2 with 355 nm light, etch rates of up to 90 nm for one pulse are obtained. Illumination with an interference grating is used to produce trenches as narrow as 100 nm or sinusoidal surface patterns with a period of 260 nm. Such surface morphologies are very useful for the processing of anti-reflection coatings or distributed Bragg reflectors.
Mechanisms Affecting Emission in Rare-Earth-Activated Phosphors
Authors: Tallant David R. , Seager Carleton H. , Simpson Regina L.
Published: April 2011

The relatively poor efficiency of phosphor materials in cathodoluminescence with low accelerating voltages is a major concern in the design of field emission flat panel displays operated below 5 kV. Our research on rare-earth-activated phosphors indicates that mechanisms involving interactions of excited activators have a significant impact on phosphor efficiency. Persistence measurements in photoluminescence (PL) and cathodoluminescence (CL) show significant deviations from the sequential relaxation model. This model assumes that higher excited manifolds in an activator de-excite primarily by phonon-mediated sequential relaxation to lower energy manifolds in the same activator ion. In addition to sequential relaxation, there appears to be strong coupling between activators, which results in energy transfer interactions. Some of these interactions negatively impact phosphor efficiency by nonradiatively de-exciting activators. Increasing activator concentration enhances these interactions. The net effect is a significant degradation in phosphor efficiency at useful activator concentrations, which is exaggerated when low–energy electron beams are used to excite the emission.