bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanometer Lithography for Quantum Scale Devices
Authors: Cook Charles F. , Kwiatkowski Joseph H. , Smith Doran D. , Berkowitz Harry L. 
Published: March 2011

ABSTRACTElectron-beam lithography that has the capability of writing high-resolution nanometer features in semiconductors will be required to fabricate next-generation quantum scale devices, such as nanometer gate mini-FET's, lateral quantum-well arrays, or metal grid radiators,which have feature sizes from 100 nm (1000 A) to 15 nm (150 A). A Philips EM 420T scanning transmission, electron microscope (STEM) has been modified to write nanometersize features in gallium arsenide. For this STEM we have developed a high-speed beam blanker and pattern generator (PG) that is resist speed limited. The maximum writing field size is 100 by 100 micrometers; within this field size, the smallest addressable step is approximately 1.8 nm (18 A). A HP-9845 is used to supply data for the PG and for computer-aided design of the devices to be written. Pattern transfer from the resist to GaAs is completed by using the liftoff method. As a result of this capability, we have patterned more than one million dots in a prototype 80 by 80 micrometer solid state radiator. The dots have diameters down to 15 nm (150 A), which requires an e-beam writing time of less than 30 minutes.
Microfabrication of Field Emission Devices for Vacuum Integrated Circuits using Orientation Dependent Etching
Authors: Campisi G. J. , Gray H. F. 
Published: March 2011

ABSTRACTVacuum integrated circuits and field emission (FE) devices with geometries on the micron and submicron scale have been discussed as alternatives to solid state devices for high speed and hostile environment application as well as for miniature electron sources for CRTs. These miniaturized vacuum devices have been developed on the basis of the advances in micromachining technology, i.e. orientation-dependent etching (ODE) of lithographically patterned silicon. This paper describes the ODE methods used to fabricate pyramidal electron emitter points 1.5 μm high, with radius of curvature of 20 to 100 nm from <100> silicon. In order to reduce operating voltages, an integral extraction electrode (grid) was fabricated by a self-aligned technique. With a single gate mask level the extraction and planar collector structures were fabricated on chip, to form a planar vacuum triode. The final mask step provided the flexibility for fabricating a variety of planar vacuum integrated circuit elements.
Scanning Tunneling Microscopy and Spectroscopy of Semiconductor Surfaces
Authors: Demuth J. E. , Hamers R. J. , Tromp R. M. 
Published: March 2011

ABSTRACTThe principles of scanning tunneling microscopy and its application to study silicon surfaces are briefly reviewed. Scanning tunneling microscopy “topographs” contain both geometric information about the locations of atoms at the surface as well as about the charge densities of surface localized states. We describe procedures by which these two components can be distinguished so as to produce images of the surface electronic states with atomic resolution. This ability to spatially resolve the surface electronic structure provides new information to understand the local structure and nature of bonding, and in some cases can be used as a means to chemically image specific features of the surface.
Hot Electron Relaxation in Quantum Wells
Authors: Lyon S. A. 
Published: March 2011

ABSTRACTHot electron relaxation in bulk semiconductors has been studied for several decades, but only through recent advances in crystal growth has it become possible to investigate the ther-malization of hot quasi-two-dimensional carriers in quantum wells. These same advances have opened the possibility of constructing various semiconductor devices which rely on hot electrons for their operation. We discuss experimental results on the energy relaxation of hot electrons in GaAs/AlGaAs quantum wells. The experiments make use of optical spectroscopy for determining the carrier distribution. In particular, steady-state hot photoluminescence measurements have been employed with modulation-doped quantum wells in order to minimally perturb the system by the photoexcited carriers. Both the relaxation of very energetic electrons and the cooling of a hot thermalized carrier distribution are considered. The quantum well results are compared to results from similar experiments with bulk GaAs.
Theoretical Considerations on the Growth of Metallic Crystalline Superlattices
Authors: Van Der Merwe J. H. , Braun M. W. H. 
Published: March 2011

ABSTRACTWe deliberate on the conditions favorable to the growth of metallic crystalline superlattices (MCS) with (111) f.c.c./(110) b.c.c. interfaces. We use, with some motivation, equilibrium criteria (i) to justify the occurrence of the Kurdjumov-Sachs (KS) and Nishiyama-Wassermann (NW) orientations, and to show with analyses which also allow for elastic relaxation, that only the NW orientation that occurs at n.n. distance ratios in the interval 0.8 ≲ bf.c.c / ab.c.c ≲ 1.0 can yield the regular orientational relationships required for high quality MCS; ahd(ii) to show that, for the acquisition of the required smoothness of the interfaces, which is mainly determined by the growth mode - monolayer-by-monolayer (FM = Frank-van der Merwe) or island nucleation and growth (VW ≊ Volmer-Weber) mode - it is desirable to use material combinations with small surface free energy mismatch. Only then can VW growth (which inevitably occurs in each superlattice period) at relatively high supersaturation be FM-like and with low density of defects.
Structure Studies of Thin Amorphous Films by Synchrotron X-Ray Absorption and Analytical Electron Microscopy.
Authors: Heald S. M. , Tafto J. 
Published: March 2011

ABSTRACTWe combine the techniques of EXAFS and XANES using synchrotron x-rays, and the corresponding techniques using electron energy loss spectroscopy (EXELFS and ELNES) to characterize and study the local atomic arrangement in thin amorphous films. These probes are complementary in that x-rays are best suited for absorption edges above 3 keV and electron energy loss spectroscopy for low energy edges, and thus this combination is very useful for amorphous materials containing both low and high Z elements. We use in addition transmission electron microscopy, electron diffraction, and electron energy loss spectroscopy in the low energy loss region. Results from amorphous T1O2 and amorphous SnO2 made by reactive sputtering are presented.
Anomalous Magneto-Optical and Magnetic Behavior in a Two-Dimensional Magnetic Semiconductor Superlattice MnSe/ZnSe
Authors: Lee D. , Chang S.-K. , Nakata H. , Nurmikko A. V. , Kolodziejski L. A. , Gunshor R. L. 
Published: March 2011

ABSTRACTThe growth by molecular beam epitaxy (MBE) of ultrathin layer II-VI compound semiconductors with magnetic constituents has opened new possibilities in the study of both lower dimensional electronic and magnetic phenomena. Some aspects of the latter are presented here with the zincblende MnSe/ZnSe superlattice as the test system. Initial indicators suggest that interfaces play a key role in determining the magnetic character of the heterostructure.
Photo Effects in Doping Modulated Amorphous Semiconductors
Authors: Fritzsche H. 
Published: March 2011

ABSTRACTThe persistent photoconductivity (PPC) observed between 200 and 400K in npnp doping modulated hydrogenated silicon (a-Si:H) having individual layer thicknesses between 200 and 600Å iS compared with similar effects in compensated a-Si:H and in amorphous silicon/silicon nitride multilayers. The thermal activation barrier against creation of PPC in these materials, the low quantum efficiency, and the very slow recombination at 300K and higher temperatures suggest the presence of special traps that are spatially or energetically removed from the excess majority carriers. The PPC is accompanied by strongly nonohmic effects which exhibit similar metastabilities and long decay times.
Effects of Indium on the Properties of N-Type CdS Thin Films Deposited by Spray Pyrolysis
Authors: Kim Y. T. , Park S. C. , Chung S. K. 
Published: March 2011

ABSTRACTEffects of the doping level of indium impurity on electrical and optical properties of the CdS thin films, prepared with solution-sprayed method have been studied. The density of free carriers can be raised to an order of magnitude higher than that of non-doped case by increasing doping level of indium up to 0.01mole-% while indium doping does not significantly change the mobility from its value in non-doped samples. The optical energy gap is decreased with increasing indium content while the thermal activation energy remains unchanged. The experimental results are discussed in terms of the self compensation and radiative recombination phenomena.
Optical Properties of Pseudomorphic InxGa1−xAs Quantum Wells
Authors: Anderson N. G. , Lo Y. C. , Kolbas R. M. 
Published: March 2011

ABSTRACTThe luminescence properties of MBE-grown pseudomorphic InxGa1−xAs—GaAs quantum-well structures are examined as a function of photoexcitation intensity and temperature. The structures examined consist of single In0.28Ga0.72As or (isolated) multiple In0.16Ga0.84As pseudomorphic wells sandwiched between thick, unstrained GaAs confining layers. Low-temperature photoluminescence spectra for these samples, which range in quantum-well thickness from 17 Å to 50 Å, consist of a single feature attributable to transitions associated with n = 1 electron and j = 3/2, Mj = 3/2 > - hole states. Spectral widths of these peaks are very narrow (7–11 meV), even for a heavily spike-doped sample (Si, ND ∼ 1018 spike-doped at well center). Emission intensities for the quantum-well structures are studied as a function of excitation intensity over the range 3 × 102 ≤ Pex ≤ 6 x 1O4 W/cm2, and one of the samples (x = 0.16, 50 Å undoped wells) prepared as a laser structure is shown to support stimulated emission at an excitation intensity < 104 W/cm2. The excellent luminescence properties of these structures are shown to degrade rapidly with increasing temperature, with radiative efficiencies dropping more than two orders of magnitude over the temperature range 20K – 180K. One possible explanation for this behavior is proposed.
Properties of Gold Films on Aluminum Alloy Substrates Prepared by Ionized Cluster Beam Deposition Process
Authors: Hashimoto Yoichi , Maeyama Yoshitaka , Machida Kazumichi 
Published: March 2011

ABSTRACTThe deposition of gold film onto aluminum alloy substrate was attempted by the Ionized Cluster Beam(ICB) deposition process. The adhesive strength, reflectivity, and geometrical accuracy(conformance to specifications) were evaluated for the films deposited under various acceleration voltages and substrate temperatures. The film-substrate interface was examined by Auger electron spectroscopy and x-ray diffraction. A gold film with reflectivity of 99.2 % and an adhesive strength of over 4–0 N/mm2 was obtained by ICB deposition at room temperature. It was established that a high adhesive strength can be achieved by ICB deposition even if a surface oxide layer on the substrate remains.
Defects in Superlattices Under Pressure
Authors: Hong Run-Di , Jenkins David W. , Ren S. Y. , Dow John D. 
Published: March 2011

ABSTRACTWe report theoretical calculations of deep levels in GaAs/AlxGa1−xAs superlattices under hydrostatic pressure. We predict phase diagrams for DX centers: for a given composition x there is a function p(a), which relates pressure p and GaAs quantum-well width a, and defines a phase boundary between two regions: one in which DX is a deep trap in the fundamental band gap and another in which the DX deep level lies in the conduction band.
The Effects of Surface and Interface Depletion Regions on the Photoconductivity of a-Si:H in Surface Cell Structures
Authors: Parsons GN , Kusano C , Lucovsky G 
Published: March 2011

ABSTRACTWe have studied the optical, electrical and photoelectronic properties of a-Si:H thin films in surface cell structures. We have concluded that upward band bending in the form of depletion layers at the film surface and film oxide glass interface causes the electrical properties to display a thickness dependence. We find that the measured values of the quantum efficiency, mobility, lifetime product, hereafter nuT, also displays a thickness dependence. We show how the limiting bulk values for nuT and other electronic properties can be determined.
The Growth of Silicon Oxide Films by Remote Plasma Enhanced CVD
Authors: Tsu DV , Lucovsky G 
Published: March 2011

ABSTRACTWe have grown films of silicon oxide by remote Plasma Enhanced CVD (remote PECVD). By changing the fraction of O3 in a plasma excited O3/He mixture that is mixed with a fixed flow of SiH4 diluted with Ar, we can deposit films which are either Si-rich, stoichiometric or Si-deficient. These changes are accompanined by differences in the incorporation of bonded hydrogen which occurs in SiH groups in Si-rich films and SiOH groups in Si-deficient films.
Enhancement of Photocarrier Lifetime Due to Charge Separation in a-Si:H/a-Ge:H Superlattices
Authors: Wronski C. R. , Tiedje T. , Abeles B. 
Published: March 2011

ABSTRACTThe lifetime of photogenerated electrons in a-Ge:H/a-Si:H multilayer structures with layers about 100Å thick, is enhanced by two orders of magnitude above the value in bulk a-Ge:H. This lifetime enhancement effect is explained by charge separation produced by layers, due to the assymmetry in the conduction and valence band offsets at the interfaces. The peak in the electron lifetime as a function of superlattice periodicity is determined by a trade-off between the electron tunneling rate into the a-Si:H barriers and electrostatic repulsion of holes due to photo-induced space charge.
Photoacoustic Measurement of a-Si:H/a-SiNx:H Superlattice Films
Authors: Xiaomei Feng , Hsiangna Liu , Zhichao Wang , Shuye Qiu , Yuliang He 
Published: March 2011

ABSTRACTPhotoacoustic (PAS) and optical transmission spectra were measured on a-Si:H/a-SiNx:H superlattices. The absorption coefficient ∝ in the range 102∼104 cm-1 was obtained by converting the PAS signal to ∝. The enhancement of the PAS peak intensity Qs and the increase in the width of the Urbach edge with decreasing a-Si:H layer thickness are explained as results of quantum size effect in the superlattice structure.
Evaluation of Commercially Available Transformation Toughened Zirconia
Authors: Swab Jeffrey J. 
Published: March 2011

ABSTRACTTransformation toughened zirconia (TTZ) is a material being considered for use in advanced heat engines. However, at elevated temperatures TTZ materials undergo a phase transformation fron tetragonal to the monoclinic with an associated volume increase of approximately 5%.This transformation results in a loss of strength and fracture toughness. Six commercially available Japanese TTZ materials and one experimental domestic grade were examined for the extent and effect of this phasetransformation after exposure to elevated temperatures (1000 to 1200°C) for times of 100 and 500 hours. Tests completed to date show that all the TTZ materials examined transform and lose strength, but to various degrees. Strength losses after heat treatment at 1000°C for 100 and 500 hours, ranged from a high of 60% to as little as 7%. Additional heattreatments of 500 hours at 1100 and 1200°C were carried out on TTZ's whichhad strength losses of 15% or less after exposure to 1000°C.Although the major thrust of this program is to examine the effects of high temperatures on TTZ materials, a preliminary examination of the effects of low temperatures on the properties is also being done. A small number of specimens are undergoing treatments at 200°C and ∼.8 MPa water vapor pressure for 50 hours. Early indications are that strength greatly reduced after this treatment.
Weibull Modulus of Toughened Ceramics
Authors: Kendall Kevin , Alford N. McN , Birchall J. D 
Published: March 2011

ABSTRACTThe influence of toughness on the Weibull modulus of ceramics is discussed. It is shown that an increase in toughness does not give a higher Weibull modulus if the ceramic is truly brittle, following the Griffith criterion of fracture. However, R curve behaviour, such as that shown by tetragonal zirconia, by Dugdale material, or by fibrous ceramic composites, leads to an improved Weibull modulus. Theoretical argument and experimental results support these conclusions.
Erosion of a Silicon Carbide Whisker Reinforced Silicon Nitride
Authors: Morrison C. T. , Routbort J. L. , Scatitergood R. O. 
Published: March 2011

ABSTRACTThe steady-state solid particle erosion behavior of hot-pressed Si3N4 reinforced with 0, 10, and 20 weight percent SiC whiskers has been investigated at room temperature using angular alumina particles (63 to 270 μm diameter) as the erodent. The impact angle was varied from 30 to 90 ° and particle velocities were varied from 80 to 140 m/s. These materials were found to be very erosion resistant. However, there was little effect of the SiC whisker reinforcement on either the absolute erosion rate or on the velocity or particle-size exponents for the rates.The lack of a fiber reinforcement effect occurs even though the fiber additions provide an increase in the fracture toughness at high fiber contents. Results on differently processed Si3Na4 .base materials showed that microstructural variations due to processing history have very significant influence on the erosion resistance of the base (matrix) material. The results substantiate the idea that microstructure plays an important, but not fully understood role in the erosion processes for brittle materials.
On Prevalent Whisker Toughening Mechanisms in Ceramics
Authors: Evans A. G. , Rühle M. , Daigleish B. J. , Thouless M. D. 
Published: March 2011

ABSTRACTSome aspects of whisker toughening are reviewed. It is shown that several important toughened materials have a toughness dominated by the nonlinear bridging of intact whiskers. Such toughening is demonstrated to depend sensitively on the relative fracture resistance properties of the whiskers, the interface and the matrix. It is also shown that, when the interface fracture resistance is low, the frictional sliding behavior of the previously debonded interface and the whisker strength distribution exert a major influence on toughness, in accordance with pull-out phenomena.
Processing and Creep Performance of Silicon Carbide Whisker-Reinforced Silicon Nitride
Authors: Porter John. R. , Lange F. F. , Chokshi A. H. 
Published: March 2011

ABSTRACTSilicon carbide whisker reinforcement can significantly reduce creep rates in polycrystalline alumina [1], but the system SiC/Al2O3 is thermodynamically unstable in air and oxidizes to mullite during creep testing [2]. The system SiC/Si3N4 was investigated as a potentially more stable, high temperature structural composite. Silicon carbide whiskers were successfully incorporated into a silicon nitride matrix doped with alumina and yttria. Processing involved mixing dispersed slurries of silicon carbide and silicon nitride, adding the dopants as a solution of their nitrates and subsequently increasing the pH to precipitate the additive hydroxides. The resulting slurries were filter pressed at room temperature and hot pressed at 1650°C in graphite dies to full density. X-ray diffraction and transmission electron microscopy confirmed the presence of β-Si3N4, α-SiC and trace quantities of α-Si3N4, confirming that the α-β Si3N4 reaction occurred. An additional, as yet unidentified, minor phase was also detected.Whisker reinforcement was shown to increase the room temperature flexural strength and fracture toughness but high temperature creep performance was unaffected by whisker reinforcement.
Displacive Phase Transformations in Zirconia-Based Ceramics
Authors: Muddle B. C. 
Published: March 2011

ABSTRACTA review is presented of experimental observations of the mechanism and crystallography of the martensitic tetragonal to monoclinic transformation occurring both in dispersed tetragonal ZrO2 particles in partially stabilized zirconia and in polycrystalline tetragonal zirconia. Preliinary results of determination of the orientation relationship and habit plane for the stress-activated transformation in a CeO2 –stabilized TZP ceramic are reported and compared with predictions of the crystallographic theory for the transformation. This orientation relationship is such that (100)m//(100)t and [001]m//[001]m, and for this variant of the orientation relationship the habit plane is approximately ( 301 )t. These results are in good agreement with theoretical predictions. Progress in the application of the formal theory of martensitic transformations to the transformations in both types of system is examined critically and implications for theories of transformation toughening are discussed.Attention is also given to tetragonal orthorhombic and orthorhombic monoclinic transformations occurring in Zro2 particles in thin foil specimens of partially stabilized zirconia. Formation of a metastable orthorhombic phase appears a possible, but not essential, intermediate stage in the tetragonal to monoclinic transition. However, present evidence strongly suggests that the orthorhombic structure only occurs in those particles experiencing the relaxed matrix constraints typical of thin foil specimens.
The Stress Induced Transformation by Fracture in Y2 O3 Containing Tetragonal Zirconia Polycrystals
Authors: Katagiri G. , Ishida H. , Ishitani A. , Masaki T. 
Published: March 2011

ABSTRACTThe stress induced transformation in Y2 O3 containing tetra gonal zirconia polycrystals (Y-TZP) by a three-point bending test was studied by Raman microprobe. Transformation zone extends to as large as 100μm in the starting side of the fracture and the transformation zone size becomes smaller in the direction from the starting to the ending side of the fracture. The transformation zone size has no correlation with fracture toughness and Y2O3 content. It is suggested that the transformation plastici y may operate in the initial stage of the fracture. The obtained results have remarkable contrast with the case of the fracture of a pre-indented specimen. The transformation behavior of defect-dominating fracture is also discussed.
Change of D/Tc, Ratio During Heat Treatment of Fe90-xSixB10 Amorphous Alloy
Authors: Minor Wladyslaw 
Published: March 2011

AbstractThe ferromagnetic transition temperature Tc for Fe-Si-B amorphous alloys with iron concentration exceeding 75 atomic percent changes monotonically with the annealing time. This change of Tc is accompanied by a drastic change of the magnetic excitation spectrum measured by means of low angle neutron inelastic scattering. It was observed that a small amount of α-Fe(Si) precipitated in an amorphous matrix during the heat treatment even at relatively low temperatures, leading to a decrease of the spin-wave stiffness constant D. Because at the same time T, increases, the D/Tc ratio (which is about 0.3 for “as quenched” Fe-Si-B system) decreases abruptly.
The Effect of Surface on the Kinetics of Crystallization of Pd-Si Glassy Metals
Authors: Calka A. , Radliński A. P. 
Published: March 2011

IntroductionThe isothermal devitrification by nucleation and growth of metallic glasses is usually analysed using the Johnson-Mehl-Avrami (JMA) equation: where x is the volume fraction crystallized after time t, K is a thermally activated rate constant, τ is the nucleation lag time, and n is the so-called Avrami exponent. If the nucleation conditions and growth morphology remain unchanged during the crystallization then n is a constant. There is ample experimental evidence that for the Pd-Si system the growth process is either eutectic or interface-controlled. Therefore, one expects n=3 for crystallization on pre-existing nuclei (zero nucleation rate) and n=4 for crystallization at constant nucleation rate, both for three-dimensional growth. When the growth dimensionality is decreased by one these values decrease stepwise by one as well.