bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase and composition depth distribution analyses of low energy, high flux N implanted stainless steel
Authors: Öztürk Orhan , Williamson D. L.
Published: July 2002

The phase and composition depth distributions of a low-energy (0.7 keV), high-flux (2.5 mA/cm2) N implanted fcc AISI 304 stainless steel held at 400 °C have been investigated by step-wise Ar+ beam sputter removal in conjunction with conversion electron Mössbauer spectroscopy and x-ray diffraction (XRD). A metastable, fcc, high-N phase (γN), with both magnetic and paramagnetic characteristics, was found to be distributed in the N implanted layer generated by the low-energy, elevated temperature, implantation conditions. The magnetic γN was found to be ferromagnetic and was distributed in the highest N concentration region of the implanted layer (the top 0.5 μm) while the paramagnetic γN becomes predominant below 0.5 μm, where the N content is only slightly lower. The ferromagnetic state is linked to large lattice expansions due to high N contents (∼30 at.%) as determined by XRD and electron microprobe. The relatively uniform XRD N distribution to a depth of ∼1 μm suggests a sensitive dependence of the magnetic γN phase stability on N concentration and degree of lattice expansion. The XRD results also show that the N contents and depths depend on the polycrystalline grain orientation relative to the ion beam direction. The N was found to diffuse deeper in the (200) oriented polycrystalline grains compared to the (111) oriented grains and the N contents were significantly higher in the (200) planes relative to the (111) planes. The effect of compressive residual stresses (∼2 GPa) is considered. The scanning electron microscopy (SEM) analysis reveals quite clearly the uniform nature of the γN layers with a reasonably well defined interface between the γN layer and the substrate, suggesting uniform N contents with uniform layer thicknesses within a given grain. However, they also show significant variations in the γN layer thickness from one grain to the next along the N implanted layer, clearly supporting the XRD findings of the variation in N diffusivity with grain orientation.
High-density thermomagnetic recording method using a scanning tunneling microscope
Authors: Nakamura J. , Miyamoto M. , Hosaka S. , Koyanagi H.
Published: July 2002

A new thermomagnetic recording method using tunneling current in a scanning tunneling microscope as a heating source is proposed. In the experiment, pulse voltage of from 2–8 V with a pulse width of 1 ms is applied to the sample, while the probe position is kept at a bias voltage of 0.2 V and a tunneling current of 0.3 nA. As a result, we have demonstrated that thermally recorded magnetic domains are formed in a Pt/Co multilayered film and minimum domains as small as 0.2 μm in diameter are observed using a polarized optical microscope.
Nonlinear stability analysis of the diffusional spheroidization of rods
Authors: Choy Jun-Ho , Hackney Stephen A. , Lee Jong K.
Published: July 2002

Experimental observations have revealed a significant scatter in the spheroidization wavelength in solid rods and rod-shaped inclusions. Using a finite difference method, the role of multiharmonic initial conditions, where the wavelength and amplitude vary with position, is investigated as a cause of the scatter. When the initial amplitude of the radius perturbation is small relative to the radius of the perturbation, the waves with their wavelengths at the maximum growth rate are shown to evolve with little scatter. As the initial amplitude increases, however, a large magnitude of scatter in the growing wavelength is observed due to wave/wave interactions. A simplified, analytical model is also proposed to describe the nonlinear wave/wave interaction between two waves. Based on this model, it is found that the stability of one wave can be affected by the other, and that a new wave can be generated. A wave stability diagram is constructed to predict the stability of a given wave.
Electronic passivation of GaAs surfaces by electrodeposition of organic molecules containing reactive sulfur
Authors: Asai K. , Miyashita T. , Ishigure K. , Fukatsu S.
Published: July 2002

A scheme for the surface passivation of GaAs is demonstrated by using electrolytically deposited organic thin molecular layers with terminating reactive sulfur (-S−) atoms. This method has an advantage, as a way of fabricating insulator on GaAs, that it is essentially free from surface layer damage which would otherwise be produced when conventional energetic processes are employed to make up insulating layers. Steady-state photoluminescence, Raman scattering, and x-ray photoelectron spectroscopy were used to characterize electronic properties of the passivated surface. Significant reduction both in the surface recombination rate and the adverse band bending due to surface states is shown by implementing an insulator layer created with a simplified process.
An analytical model for short-channel organic thin-film transistors
Authors: Torsi L. , Dodabalapur A. , Katz H. E.
Published: July 2002

An analytical model that describes the operation of α-hexathienylene (α-6T) thin-film-transistors (TFTs) is presented. The current-voltage characteristics of TFTs with channel lengths ranging from 1.5 to 25 μm have been calculated after modifying the equations that describe the characteristics of conventional enhancement mode p-channel metal-oxide-semiconductor field-effect-transistors. The calculated current-voltage characteristics are compared with the experimental data. The model takes into account the non-inversion-mode operation of α-6T TFTs as well as short channel effects such as series parasitic resistance, channel length shortening, apparent threshold voltage, and apparent field-effect mobility. Furthermore, the field-effect mobility is observed to depend on longitudinal electric fields which are higher than 105 V/cm, and this effect is also included in the model. The highest field-effect mobility measured is 0.03 cm2/V s. From an analysis of measured data, the carrier mobility of field-induced positive carriers in α-6T is estimated to be at least as high as 0.08 cm2/V s.
High sensitivity magnetization measurements of nanoscale cobalt clusters
Authors: Wernsdorfer W. , Hasselbach K. , Benoit A. , Wernsdorfer W. , Barbara B. , Mailly D. , Tuaillon J. , Perez J. P. , Dupuis V. , Dupin J. P. , Guiraud G. , Perex A.
Published: July 2002

Presented is a novel high sensitivity magnetometer allowing us to measure the magnetization reversal of about 104 μB corresponding to a sensitivity of about 10−16 emu. The detector is a niobium micro-bridge DC superconducting quantum interference device (SQUID), fabricated using electron-beam lithography. It is operational in the temperature range of 0–7 K. Furthermore, we present a method to deposit on the SQUID loop a small number of Co clusters of about 2–5 nm in diameter. The first results obtained on these samples show that there is still a ferromagnetic coupling between the clusters and the magnetization reversal takes place by small avalanches.
Neutron diffraction study of lattice changes in Nd2Fe17−xSix(Cy)
Authors: Yelon W. B. , Hu Z. , Singleton E. W. , Hadjipanayis G. C.
Published: July 2002

Neutron diffraction has been used to determine the location and concentration of C in Nd2Fe17 and in a Si substituted alloy. The results indicate that two carbide phases exist. One contains nearly three C atoms per formula unit, while the other has a much lower concentration. The high C phase contains C only on the 9e sites, but the low C phase appears to contain C on the tetrahedral 18g site. The changes in interatomic distances and cell volume are associated with the different site occupancies.
Gas dynamics and radiation heat transfer in the vapor plume produced by pulsed laser irradiation of aluminum
Authors: Ho J. R. , Grigoropoulos C. P. , Humphrey J. A. C.
Published: July 2002

The interaction of pulsed laser irradiation of nanosecond duration with a metal surface is studied by numerical simulation. The heat transfer in the solid substrate and the melted liquid is modeled as one-dimensional transient heat conduction using the enthalpy formulation for the solution of phase change problems. A discontinuity layer is assumed just above the liquid surface. Mass, momentum, and energy conservation are expressed across this layer, while the vapor across the discontinuity is modeled as an ideal gas. The compressible gas dynamics is computed numerically by solving the system of Euler equations for mass, momentum, and energy, supplemented with an isentropic equation of state in a two-dimensional axisymmetric system of coordinates. The excimer laser-beam absorption and radiation transport in the vapor phase are modeled using the discrete ordinates method. The rates for ionization are computed using the Saha–Eggert equation assuming conditions of local thermal equilibrium. The inverse bremsstrahlung mechanism is considered as the main mechanism of plasma absorption. Results show that a thin, submicron vapor layer is formed above the target surface in the duration of laser pulse while thermal radiation plays the key role for plume cooling during the period of strong absorption by the plasma. The release of a very strong shock wave, propagating with a speed of 104 m/s, is observed in the evaporating plume.
The role of diluents in electronegative fluorinated gas discharges
Authors: Langan J. G. , Beck S. E. , Felker B. S. , Rynders S. W.
Published: July 2002

To study the role of diluents in NF3 plasma processing we have correlated SiO2 and plasma chemical vapor deposition silicon nitride (SiN) etch rate measurements with rf electrical impedance analysis. A series of rare gas (He, Ar) and molecular (N2, O2, N2O) mixing gases were added to NF3 plasmas at different pressures to understand the effect of diluents on the chemical and physical properties of NF3 discharges. The etch rate experiments show that for NF3 plasmas the choice of mixing gas can have a profound effect on the etch rates of SiO2 and SiN with 25 mol % NF3 in Ar yielding the highest rates and 25 mol % NF3 in N2O the lowest. The electrical measurements revealed that the diluents have a profound effect on the plasma impedance and actual power dissipated in the discharge. NF3 plasmas diluted with Ar exhibited the lowest impedances and highest real power dissipation at higher pressures while N2O diluted plasmas had the highest impedances and lowest power dissipation levels. These results indicate that the diluents which result in the highest power dissipation in the discharge, at high pressures, result in the highest etch rates. We propose that the dominant role of the diluent in NF3 plasmas is to control the electronegativity of the discharge, and thus to control real power dissipation. This function is in contrast to the role of diluents in plasmas based on other fluorinated gases, where the diluents are seen as primarily affecting the concentrations of reactive species which deposit or remove materials from the surface of the thin film being processed.
Characterization of the noise in secondary ion mass spectrometry depth profiles
Authors: Chu D. P. , Dowsett M. G. , Cooke G. A.
Published: July 2002

The noise in the depth profiles of secondary ion mass spectrometry (SIMS) is studied using different samples under various experimental conditions. Despite the noise contributions from various parts of the dynamic SIMS process, its overall character agrees very well with the Poissonian rather than the Gaussian distribution in all circumstances. The Poissonian relation between the measured mean-square error and mean can be used to describe our data in the range of four orders. The departure from this relation at high counts is analyzed and found to be due to the saturation of the channeltron used. Once saturated, the detector was found to exhibit hysteresis between rising and falling input flux and output counts.
Formation of nitrogen doped carbon during arc-discharge of carbon rods in the presence of pyrrole
Authors: Glenis S. , Nelson A. J. , Labes M. M.
Published: July 2002

When the arc vaporization of carbon rods in a helium atmosphere is conducted in the presence of small amounts of pyrrole, not only does one form nitrogen-doped fullerenes, but also the surface of the carbon rods becomes coated with a layer of a nitrogen-doped carbon. X-ray diffraction indicates d spacing expansion, and x-ray photoelectron spectroscopy confirms that nitrogen doping has occurred at a level of 2.3%. N1s spectra reveal a nonuniformity in the distribution of nitrogen atoms relative to carbon. These data are consistent with a model in which substitution of nitrogen occurs at the domain boundaries of the graphitic particles. A consequence of this doping is a twofold increase in the electrical conductivity of the carbon. The x-ray photoemission results indicate that N incorporation induces a shift of the valence band toward the Fermi level.
Low fluence laser sputtering of gold at 532 nm
Authors: Elam Jeffrey W. , Levy Donald H.
Published: July 2002

Angle velocity distributions of 532 nm laser sputtered gold atoms are measured. No emission is seen at low fluence unless melt structure is first induced on the gold surface. Following melting, the velocity distribution at 1.4 J/cm2 is Boltzmann at 6500 K and the angular distribution is cosine. At 4.9 J/cm2 the angle velocity distribution shows collisional modification. These data contradict thermal sputtering but may result from surface plasmon excitation.
Surface relaxation during plasma-enhanced chemical vapor deposition of hydrocarbon films, investigated by in situ ellipsometry
Authors: von Keudell A. , Jacob W.
Published: July 2002

The ion–thin-film interaction during plasma-enhanced chemical vapor deposition of hydrocarbon films (C:H films) from a methane electron cyclotron resonance plasma was investigated by means of in situ ellipsometry. Films were deposited with varying rf bias, resulting in a dc self-bias ranging from floating potential up to 100 V. The ion bombardment during plasma-enhanced chemical vapor deposition of hydrocarbon films leads to a disturbed surface layer, which becomes apparent in the in situ ellipsometric results by optical constants which are higher than those for the bulk material. The optical constants of the modified surface layer increase with ion energy during deposition, but decrease with the addition of hydrogen to the source gas. When using acetylene instead of methane for the deposition we also find a higher value for the optical constants. After switching off the plasma, the increased optical constants of the surface layer relax to its equilibrium state. The sources of this modified film surface and the mechanisms for its relaxation are discussed in this article. The change of the optical constants of the film surface is compared to the dependence of the film properties on the gas composition and the ion bombardment during deposition.
Structure, chain orientation, and properties in thin films of aromatic polyimides with various chain rigidities
Authors: Ree M. , Kim K. , Woo S. H. , Chang H.
Published: July 2002

Several high temperature polyimides, as model polymers with various chain rigidities and chain orders, were synthesized through the polycondensation of p-phenylene diamine (PDA) with five different aromatic dianhydrides [i.e., pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA), benzophenonetetracarboxylic dianhydride (BTDA), and 4,4′-hexafluoroisopropylidenediphthalic anhydride (6F)], and investigated in terms of structure and properties. Both fully rodlike PMDA-PDA and ether-linked ODPA-PDA polyimides showed excellent orientation and poor ordering of chain in x-ray diffraction patterns, whereas both biphenyl-linked (BPDA-PDA) and carbonyl-linked (BTDA-PDA) polyimides exhibited excellent orientation and high ordering of chain. However, hexafluoroisopropylidene-linked 6F-PDA polyimide is structureless. The coherence length along the chain axis, which is a measure of chain rigidity and ordering, was estimated from (00l) peaks of x-ray diffraction patters: 6F-PDA (could not be measured) <ODPA-PDA (95 Å)<BTDA-PDA (98 Å)<BPDA-PDA (104 Å)<PMDA-PDA (130 Å). In films prepared on substrates, all polyimides were preferentially oriented in the film plane. However, the degree of molecular in-plane orientation strongly depended on the coherence length. Higher coherence length, i.e., higher chain rigidity and ordering, caused higher in-plane orientation of chains. However, the chain rigidity is more critically responsible for molecular in-plane orientation, in comparison to the chain ordering. Higher in-plane orientation of chains led to larger anisotropies of refractive indices and dielectric constants, higher in-plane modulus, lower in-plane thermal expansion coefficient, and lower residual stress.
Breakdown characteristics in InP/InGaAs avalanche photodiode with p-i-n multiplication layer structure
Authors: Hyun Kyung-Sook , Park Chan-Yong
Published: July 2002

We report on the breakdown voltages in InP/InGaAs avalanche photodiode (APD) experimentally and theoretically, based on the parameters of electric field distribution, carrier concentrations, thicknesses, and temperatures. According to the calculation, the breakdown voltage has its minimum point, w0, at each carrier concentration in charge plate and avalanche photodiode with very thin multiplication layer width will provide high gain bandwidth product. The devices having different multiplication layer width showed different breakdown voltages and temperature behaviors. We introduced newly defined temperature coefficient, γ, and found that γ’s are linearly dependent on breakdown voltages at each temperature. From these results, the empirical formula which effectively describes the temperature dependence of breakdown voltages was obtained.
Silicon carbide formation by annealing C60 films on silicon
Authors: Moro L. , Paul A. , Lorents D. C. , Malhotra R. , Ruoff R. S. , Lazzeri P. , Vanzetti L. , Lui A. , Subramoney S.
Published: July 2002

Silicon carbide films were grown on (100) silicon substrates by deposition of 200-nm-thick C60 films, followed by annealing. The predeposited C60 is progressively destroyed by annealing, and carbon reacts with silicon to produce SiC. The reaction starts at the interface and continues by diffusion of silicon through the already formed SiC. At the lower temperatures (700 °C), the reaction is localized at the interface. Diffusion of silicon and formation of stoichiometric SiC requires annealing at 800 °C for t⩾100 min and at 900 °C for t⩾25 min. The stoichiometric films are uniform with a grain size of 20–40 nm. A diffusion coefficient of silicon in SiC of 4×10−15 cm2/s at 900 °C was determined. Because the diffusion of silicon is faster through preferential paths in the SiC film, such as grain boundaries and other crystalline defects, pits and voids are produced in the silicon substrate when the C60 predeposited film covers larger areas.
Magnetic phase transitions in Mn5−xTxSi3 alloys
Authors: Al-Kanani H. J. , Booth J. G.
Published: July 2002

The magnetic properties of a series of the intermetallic compound Mn5−xTxSi3 with T=3d transition metal Ti, V, Cr, and Ni have been examined as a function of the magnetic field (0–12 T) and temperature (2–300 K). The alloys have the same hexagonal D88 crystal structure as Mn5Si3 with very little change in lattice spacing. The magnetization measurements show that the substitutional elements produce a variety of effects, dramatically altering the field and temperature dependence of the AF1/AF2 and AF2/paramagnetic transitions. It is assumed that since the Mn–Mn distances in the parent alloy are all near critical values for instability the substitution on to Mn sites interferes significantly in the Mn–Mn interactions.
Static magnetic and microwave properties of Li-ferrite films prepared by pulsed laser deposition
Authors: Cadieu F. J. , Rani R. , Mendoza W. , Peng B. , Shaheen S. A. , Hurben M. J. , Patton C. E.
Published: July 2002

Highly textured Li-ferrite films have been synthesized by pulsed laser deposition from bulk targets onto c-plane sapphire substrates. For substrate temperatures approaching 1000 °C the growth mode was predominantly (333). A similar growth mode was recently reported for Ni-ferrite films grown onto c-plane sapphire substrates. The films were 4–8 μm thick and were grown at deposition rates of 3–5 Å/s at oxygen partial pressures of 200–400 mTorr. Magnetic measurements were made by SQUID and 9.5 GHz ferromagnetic resonance (FMR) on the as deposited films. Textured Li-ferrite films with x-ray diffractometer intensity ratios of I(333)/I(311)=10.3 for films made in 200 mTorr oxygen and 14.5 for films made in 400 mTorr oxygen exhibited room temperature in-plane intrinsic coercivities of <100 Oe for SQUID magnetometer measurements. Highly (333) textured Li-ferrite films made in 400 mTorr oxygen exhibited clean symmetric FMR absorption lines with a derivative peak-to-peak linewidth of 335 Oe for the in-plane static field configuration. The FMR profiles for the perpendicular-to-plane field configuration were highly distorted. The magnetization versus field measurements and the in-plane FMR field position yielded saturation flux density 4πMs and effective saturation flux density 4πMeff values of 3.6–4.0 kG and 3.56–3.70 kG, respectively. These values are in the same range as for bulk Li-ferrite. The in-plane FMR linewidths were significantly larger than expected for bulk single crystals or large grain size, dense polycrystals.
Oxygen as a surfactant in the growth of giant magnetoresistance spin valves
Authors: Egelhoff W. F. , Chen P. J. , Powell C. J. , Stiles M. D. , McMichael R. D. , Judy J. H. , Takano K. , Berkowitz A. E.
Published: July 2002

We have found a novel method for increasing the giant magnetoresistance (GMR) of Co/Cu spin valves with the use of oxygen. Surprisingly, spin valves with the largest GMR are not produced in the best vacuum. Introducing 5×10−9 Torr (7×10−7 Pa) into our ultrahigh vacuum deposition chamber during spin-valve growth increases the GMR, decreases the ferromagnetic coupling between magnetic layers, and decreases the sheet resistance of the spin valves. It appears that the oxygen may act as a surfactant during film growth to suppress defects and to create a surface which scatters electrons more specularly. Using this technique, bottom spin valves and symmetric spin valves with GMR values of 19.0% and 24.8%, respectively, have been produced. These are the largest values ever reported for such structures.
Metal deposition into a porous silicon layer by immersion plating: Influence of halogen ions
Authors: Tsuboi Takashi , Sakka Tetsuo , Ogata Yukio H.
Published: July 2002

Metal deposition into a porous silicon (PS) layer by immersion plating has been studied. Ag and Cu were found to deposit on PS, while Ni was found not to deposit. The dependence of the amount of Cu deposition on Cu2+ concentration, halogen ion concentration, and immersion time was investigated using chelatometric titration. Copper deposition from halide solutions exhibited an unusual behavior; the amount increased with increasing concentration, then decreased, and no copper deposited at high concentration. This is because adsorption of chloride and bromide ions inhibits the copper deposition process. We have also discussed the metal deposition mechanism on the basis of x-ray diffraction, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy measurements. They revealed that metal deposition occurred simultaneously with the oxidation of silicon to SiO2. Copper crystals 30–80 nm in diameter deposited on the oxidized PS surface rather than on the unoxidized PS surface.
Analytical approach to calculate the flux dependent current–voltage characteristics of dc superconducting quantum interference devices
Authors: Maruyama Emi , Kuriki Shinya , Kurisu Yoshiyuki , Matsuda Mizushi
Published: July 2002

We have studied analytical expressions for the voltage of Josephson junctions in dc superconducting quantum interference devices (SQUIDs). Assuming sinusoidal oscillating currents of the junctions for simplicity and easy computation and using a four-terminal network circuit of the SQUID loop, the junction voltage was calculated analytically for zero external flux and half the flux quantum. The current–voltage characteristics obtained at 0 and 77 K for a SQUID consisting of lump elements were in reasonable agreement with those calculated by using a numerical method solving nonlinear differential equations. The analytical method proved helpful for estimating the characteristics of high-Tc SQUIDs, which have distributed impedance due to the interaction between the high-Tc film and dielectric substrate.
Magnetic and superconducting properties of Pr in La1−xPrxBaCaCu3O7 system with 0.0⩽x⩽1.0
Authors: Awana V. P. S. , Dou S. X. , Singh Rajvir , Narlikar A. V. , Malik S. K. , Yelon W. B.
Published: July 2002

We report the results on structural aspects, magnetic, and superconducting properties of the La1−xPrxBaCaCu3O7 system. Both x-ray and neutron diffraction studies reveal that Pr substitutes isostructurally in the tetragonal LaBaCaCu3O7 (La:1113) system until the complete replacement of La by Pr. The superconducting transition temperature, Tc, determined from ac susceptibility measurements decreases, with increasing x. The relative Tc depression due to Pr in the LaBaCaCu3O7 superconductor is less in comparison to that found for La-site Pr substituted LaBa2Cu3O7 (La:123). While the critical Pr concentration (xcr) to completely suppress the superconductivity in the former is around 70 at. % of Pr at La site, the same is reported as only 30 at. % for the latter. For nonsuperconducting samples, i.e., for x=0.70 and 1.0, possible antiferromagnetic ordering with Neel temperatures, TN, of 4 and 8 K, respectively, are observed from both dc magnetic and heat capacity measurements. Interestingly in the La1−xPrx:1113 system the xcr of Pr is 0.70, and TN of Pr:1113 is 8 K, while for the La1−xPrx:123 system xCr is 0.30 and TN of Pr:123 is 17 K. The results are explained on the basis of distribution of Pr at both RE and Ba sites in the RE:1113 structure. This leads to a lower TN and a less deleterious effect of Pr on superconductivity of La:1113 compared to La:123.
Ferromagnetic resonance linewidth in thin films coupled to NiO
Authors: McMichael R. D. , Stiles M. D. , Chen P. J. , Egelhoff W. F.
Published: July 2002

The out-of-plane angular dependence of the ferromagnetic resonance linewidth, ΔH, has been measured for thin magnetic films coupled to NiO and for uncoupled control films. In the control films, ΔH is described by nearly angle-independent damping parameters. In the NiO-coupled films, however, the damping was found to depend strongly on magnetization orientation, with linewidth values comparable to the control samples at normal orientation, but several times larger when the magnetization lies in plane. The additional linewidth in the NiO-coupled films follows the angular dependence of the number of nearly degenerate spin wave modes, in agreement with the predictions of a two-magnon scattering model of damping which incorporates a spin wave dispersion relation suitable for ultrathin films.
Study of DX center in Cd0.8Zn0.2Te:Cl by positron annihilation
Authors: Fung S. , Shan Y. Y. , Deng A. H. , Ling C. C. , Beling C. D. , Lynn K. G.
Published: July 2002

Variable energy positron beam and positron annihilation lifetime experiments have been carried out to study the DX center in Cd0.8Zn0.2Te:Cl at 50 K. A short positron effective diffusion length of 275±25 Å and a large intensity of 79.0%±0.3% for the long lifetime component indicate a strong trapping effect at DX centers. A trapping rate of κ=1.53±0.05×109 s−1 and a positron lifetime of 335±2 ps at the DX center were obtained. The concentration of DX centers is found to be 5.9±0.7×1016 cm−3, which is in good agreement with the results obtained using Hall effect and thermo-electric effect measurements.
Influence of geometry and passivation on noise in GaInP/GaAs heterojunction bipolar transistors
Authors: Delseny C. , Mourier Y. , Pascal F. , Jarrix S. , Lecoy G.
Published: July 2002

First order and low-frequency noise measurements are performed on GaInP/GaAs heterojunction bipolar transistors. The base current is decomposed into different components. Passivated transistors exhibit higher gain values, hence the passivation layer limits recombinations on the extrinsic device. Noise is measured in the 1 Hz–100 kHz frequency range on common-emitter-mounted transistors. The 1/f component is analyzed. The emitter series resistances are extracted. The proximity of the base contact on the smaller devices lead to a higher noise level due to enhanced recombinations. Extrinsic and intrinsic phenomena are put forward with the help of noise analysis versus base current and collector current density. An attempt is made to locate the 1/f noise sources. Unlike first order measurements, noise characterization shows that the passivation layer can be at the origin of recombination-type phenomena.
A photoelectron spectroscopy study of Ti/Cu interfaces
Authors: Geng J. , Schüler A. , Reinke P. , Oelhafen P.
Published: July 2002

Reactions at Ti/Cu interfaces were investigated by ultraviolet and x-ray photoelectron spectroscopy (UPS, XPS). For Ti deposition onto copper substrates at ambient temperature, our measurements strongly suggest that at the interface an amorphous alloy is formed. This idea is supported by the comparison of our UPS data to the ones of bulk glassy CuxTi1−x. The thickness of this amorphous interlayer which is built up onto the polycrystalline Cu substrate corresponds to a nominal Ti coverage of about 10 monolayers. At a substrate temperature of 300 °C, however, the interface reaction is still present at nominal Ti coverages over a hundred monolayers. Presumably the crystalline phase Cu3Ti2 is formed.
The electronic structure and optical properties of intermixed GaAs/AlGaAs double quantum wells
Authors: Ke Maolong , Helmy A. Saher , Bryce A. C. , Marsh J. H. , Davidson J. , Dawson P.
Published: July 2002

We report photoluminescence and photoluminescence excitation (PLE) investigations of intermixed GaAs/AlGaAs double quantum wells. The PLE spectra provide energy information about many different transitions, from which the band profile can be more reliably derived. Using the widely assumed error function profile, it was not possible to explain the observed results. Detailed analysis revealed that the as-grown sample had a graded interface which affected the band profile for the intermixed samples.
Effect of Pt layers on the photoelectrochemical properties of a WO3/p-Si electrode
Authors: Yoon Ki Hyun , Seo Dong Kyun , Cho Yong Soo , Kang Dong Heon
Published: July 2002

The effect of Pt deposition on the photoelectrochemical properties of a WO3/p-Si electrode was studied with regard to hydrogen evolution, photocurrent transient, and chemical stability. Deposition of Pt layers made it possible for photocurrent onset potential to be shifted to a more positive value and both the photocurrent density and hydrogen evolution rate were increased. These phenomena can be explained by the fact that Pt loading decreases the overpotentials in the reduction reaction at the electrode/electrolyte interfaces to make electron transfer faster, as well as decrease the recombination rate of carriers. The influences of the Pt layer were confirmed by investigating the photocurrent transient behaviors. In the case of the Pt/WO3/p-Si electrode, particularly high quantum efficiencies were obtained in a wavelength range of 430–700 nm, possibly due to inelastic electron–electron scattering. The Pt/WO3/p-Si electrodes did not show any detectable corrosion after illumination for 5 h according to the observation of surface microstructures.
The density of states in silicon nanostructures determined by space-charge-limited current measurements
Authors: Matsumoto Takahiro , Mimura Hidenori , Koshida Nobuyoshi , Masumoto Yasuaki
Published: July 2002

Space-charge-limited current (SCLC) flow was investigated as a function of applied potential and specimen thickness in nanocrystalline silicon films prepared by electrochemical anodization. From the analysis of the current–voltage (J–V) characteristics in the SCLC regime, the density of states distribution near the Fermi level was determined. The agreement between the experimental J–V characteristics and the theoretical curve strongly implies that the current flow is entirely controlled by localized states situated at the quasi-Fermi level.
Origin of a parasitic surface film on p+ type porous silicon
Authors: Chamard V. , Dolino G. , Muller F.
Published: July 2002

The presence of a parasitic surface film of 80 nm thickness has been observed by x-ray reflectivity on the top of some p+ type porous silicon layers, related to a contamination of the substrate. After testing several methods to clean the substrate and to avoid this film, it was found that a 300 °C thermal annealing of the substrate is sufficient to obtain a homogeneous porous layer. The thickness of the perturbed surface layer is determined by anodic oxidation experiments and the effect of the parasitic surface film on the porous silicon formation is studied by comparing porous layers formed on untreated and on annealed substrates. The hypothesis of a passivation of the boron doping atoms by hydrogen is discussed and we review the observations of nonhomogeneous porous layers which could be related to such a contamination problem.
Macroparticle separation and plasma collimation in positively biased ducts in filtered vacuum arc deposition systems
Authors: Beilis I. I. , Keidar M. , Boxman R. L. , Goldsmith S.
Published: July 2002

The objective of the present work was to determine the influence of positive bias on plasma and macroparticle (MP) flow in curved magnetized plasma ducts. The plasma bulk and sheath regions were analyzed. In the plasma bulk, the current density and electrical field component normal to the wall were obtained and used as boundary conditions for the near wall sheath region. In the sheath, a nonstationary model for MP charging and motion was developed. The solution of the hydrodynamic equations in the plasma when a positive bias is applied to the wall result in a radial electrical current. The electric field in the plasma bulk is generated by the separation between the magnetically confined electrons, and the ions, which are thrown outwards by the centrifugal force. The field increases with increasing positive bias. It was shown that MPs traveling in the sheath accumulate a charge which depends on the potential distribution, in contrast to MP charging in the quasineutral plasma where the charge depends on plasma density and electron temperature. MP trapping in the near-wall sheath was found. MPs may move in the sheath region along the wall by a repetitive process of electrostatic attraction to the wall, mechanical reflection and neutralization, followed by MP charging and attraction, etc. For example, titanium MPs with a radius less than 0.4 μm and with a velocity component normal to the wall of about 20 m/s are trapped if the sheath potential drop exceeds 20 V. It was obtained that the MP transmission fraction through filter decreases by more than few orders of magnitude due to the trapping effect when a bias potential of +100 V is applied between the wall and the plasma.
Theoretical and experimental aspects of three-dimensional infrared photothermal radiometry of semiconductors
Authors: Ikari Tetsuo , Salnick Alex , Mandelis Andreas
Published: July 2002

A general theoretical model for the infrared photothermal radiometric (PTR) signal from a semiconductor wafer is developed for the case of three-dimensional sample geometry with finite thickness. Carrier diffusion and heat conduction along the radial direction of the sample as well as along the thickness coordinate are taken into account. The simulated results for the modulation frequency dependence of the PTR signal amplitude and phase are applied to experimental data from Si wafers. Good agreement between the theoretical and experimental curves is obtained and several electronic and thermophysical parameters are estimated. This indicates that the three-dimensional PTR measurement is useful to remotely characterize semiconductor wafers patterned for large scale integrated circuits.
Effects of the O2 concentration on the removal efficiency of volatile organic compounds with dielectric barrier discharges in Ar and N2
Authors: Falkenstein Zoran
Published: July 2002

This article presents experimental results on the effects of the O2 concentration on the removal efficiency of two exemplaric volatile organic compounds (VOCs): toluene (TOL) and trichloroethylene (TCE), with dielectric barrier discharges in dry Ar and N2. For both carrier gases, there is an optimal oxygen concentration of 0.3% for the removal efficiency, suggesting optimal utilization of oxygen radicals for VOC attack, rather than ozone production which has slow reaction rates with TOL and TCE. This is manifested by measurements of ozone concentrations in mixtures of Ar/O2/TCE as a function of the oxygen concentration, showing a minimum at maximal removal efficiencies. All results are discussed in terms of changes in the discharge behavior, radical formation, and chemical reaction pathways with changing O2 concentration in the carrier gas.
Exchange-correlation, dipole, and image charge potentials for electron sources: Temperature and field variation of the barrier height
Authors: Jensen K. L.
Published: July 2002

Potential barrier profiles for large applied fields and/or high temperature are developed for the study of field and thermionic emission electron sources intended for radio frequency power tube applications. The numerical implementation provides a fast and flexible method to obtain the barriers which govern current density, and yet allows for complications such as nanoprotrusions, adsorbates, “internal” field emission, the sputtering of low work function emission sites, and so on. The model consists of (i) a modified form of the Wigner Lattice expansion of the electron ground state energy to evaluate the exchange and correlation potential, (ii) a simplified form of the ionic core potential to correct the “Jellium” model, (iii) a triangular representation of the barrier with a single adjustable parameter which enables both the solution of Schrödinger’s equation in terms of Airy functions and thus an exact evaluation of the electron density near the barrier, and (iv) a numerical integration of Poisson’s equation to evaluate the dipole potential and positive background boundary. An iterative calculation is performed such that the barrier used in the solution of Schrödinger’s equation becomes equivalent to the barrier predicted from the exchange-correlation and dipole potentials. As a test of the method, evaluations of the work function of various metals are made. A good correspondence is found between the potential profiles and an “analytic” image charge potential (which contains modifications to the standard image charge model). Modifications to the Richardson–Laue–Dushman and Fowler Nordheim equations, so as to obtain current density estimates, are described. The (only) adjustable parameter used to correlate theory and experimental work functions is the magnitude of the ionic core “radius,” which is often close to the actual radius of the metal ions in the test cases considered. The temperature and field dependence of the work function, which is dependent upon electron penetration of the barrier and its effect on the dipole potential, are investigated. The method is suggested to be suitable for the analysis of more complex potential barrier profiles that are encountered in actual (realistic) thermionic and field emission electron sources. The limitations of the model are discussed and methods to circumvent them are proposed.
Effects of electron confinement on thermionic emission current in a modulation doped heterostructure
Authors: Anwar Amro , Nabet Bahram , Culp James , Castro Fransisco
Published: July 2002

We discuss mechanisms responsible for the reduction of electron thermionic emission current from a Schottky contact to a modulation doped semiconductor compared to a bulk semiconductor. The effects discussed include metal to semiconductor barrier height enhancement due to proposed electron–electron cloud interaction, confined potential of the reduced dimensional systems, and the reduced dimensional nature of the density of states in the semiconductor. These effects describe the observed lowering of the dark current, and hence noise, of a modulation doped heterojunction based photodetector compared to a conventional bulk device.
Effects of barrier height fluctuations and electron tunneling on the reverse characteristics of 6H–SiC Schottky contacts
Authors: Zheng L. , Joshi R. P. , Fazi Christian
Published: July 2002

Analytic calculations of electron transport across a Schottky barrier in 6H–silicon carbide are presented. The treatment includes the effect of barrier height fluctuations and image charge lowering on both the thermionic emission and electron tunneling processes. The results show that barrier height inhomogeneities are very important, and can lead to reverse current densities that are orders of magnitude higher than obtained from a simple theory. Formation of detrimental filamentary currents are predicted. The results are in very good agreement with published experimental data at 300 K. Finally, under forward biasing conditions, the analytical theory yields ideality factors of 1.037 in close agreement with measurements.
Spin-valve heads with synthetic antiferromagnet CoFe/Ru/CoFe/IrMn
Authors: Huai Y. , Zhang J. , Anderson G. W. , Rana P. , Funada S. , Hung C.-Y. , Zhao M. , Tran S.
Published: July 2002

Spin-valve (SV) films Si(100)/Ta30/NiFe50/CoFe20/Cu26/CoFe23/Ru7/CoFe20/IrMn50/Ta30 (in Å) exhibit a room temperature (RT) giant magnetoresitance (GMR) ratio of 8.5% with an effective exchange pinning field (Heex) of ∼1.3 kOe and an antiferromagnetic (AF) saturation field (Hs) of ∼6.0 kOe. The synthetic spin valve shows a GMR ratio of 5.0% at 150 °C with Heex>500 Oe, while a conventional spin valve [Si(100)/Ta50/NiFe50/CoFe20/Cu28/CoFe22/IrMn50/Ta50 in Å] has a GMR ratio of 5.0% with Hex<200 Oe. The synthetic sample also showed a superior thermal stability with a RT GMR value of 6.9% (compared to 6.1% for conventional sample) after an anneal at 250 °C for 10 h. Shielded narrow track synthetic SV readers demonstrated high amplitude, large dynamic range, and excellent magnetic stability, indicating extendibility for ultrahigh density read head applications.
Deposition of amorphous silicon films by hot-wire chemical vapor deposition
Authors: Feenstra K. F. , Schropp R. E. I. , Van der Weg W. F.
Published: July 2002

Device-quality a-Si:H films have been deposited by hot-wire chemical vapor deposition (HWCVD). We have investigated the influence of deposition parameters on the film growth and properties. The most important deposition and growth processes that influence the optoelectronic material properties of a-Si:H deposited by HWCVD are clarified. During the deposition process attention must be paid to accurately control the substrate temperature, which is a key parameter to obtain device-quality films. A heat transport model is presented to be able to correct for the heating of the substrate by the filaments. It is found that films deposited at high deposition temperatures are under a high compressive stress. We show how the hydrogen incorporation in the layer is influenced by hydrogenation of subsurface layers by the atomic hydrogen flux that is inherent to the HWCVD process. We further identify the fundamental differences between plasma enhanced CVD and HWCVD material.
New Fe-based amorphous alloys with large magnetostriction and wide supercooled liquid region before crystallization
Authors: Inoue Akihisa , Zhang Wei
Published: July 2002

A glass transition, followed by a supercooled liquid region was found in wide composition ranges of 0–65 at % Co and 1.5–7 at % Ln in Fe80−x−yCoxLnyB20 (Ln=Nd, Sm, Tb, or Dy) amorphous alloys. The supercooled liquid region (ΔTx) shows the largest value of 41 K for the Fe47Co30Sm3B20 alloy. An internal equilibrium state leading to the disappearance of the previous thermal history was achieved within a temperature interval of 15 K. The Fe–Co–Ln–B amorphous alloys exhibit soft ferromagnetism with saturated magnetization (Bs) of 0.84–1.66 T and coercivity (Hc) of 5.0–36 A/m. A high magnetostriction (λs) exceeding 40×10−6 was also observed in the composition range of 0–10 at % Co and 1.5–3 at % Ln (Ln=Sm, Tb, or Dy). The highest λs reaches 58×10−6 for Fe68.5Co10Ln1.5B20 (Ln=Sm or Tb), which is higher than the highest value (44×10−6) for previously reported amorphous alloys. All the Fe68.5Co10Ln1.5B20 amorphous alloys have good bending ductility. The tensile strength, Vickers hardness and Young’s modulus of the Fe68.5Co10Sm1.5B20 alloy are 3220 MPa, 990 and 76.5 GPa, respectively. The combination of high λs, high Bs, low Hc, large ΔTx, good ductility and high mechanical strength is promising a new type of ferromagnetic bulk amorphous alloy.
Scanning capacitance microscope methodology for quantitative analysis of p-n junctions
Authors: Zavyalov V. V. , McMurray J. S. , Williams C. C.
Published: July 2002

Quantification of dopant profiles in two dimensions (2D) for p-n junctions has proven to be a challenging problem. The scanning capacitance microscope (SCM) capability for p-n junction imaging has only been qualitatively demonstrated. No well-established physical model exists yet for the SCM data interpretation near the p-n junction. In this work, the experimental technique and conversion algorithm developed for nonjunction samples are applied to p-n junction quantification. To understand the SCM response in the active p-n junction region, an electrical model of the junction is proposed. Using one-dimensional secondary ion mass spectrometry (SIMS) data, the carrier distribution in the vertical dimension is calculated. The SIMS profile and carrier distribution is then compared with the SCM data converted using a first-order model. It is shown that for a certain class of profiles, the SCM converted dopant profile fits well to the SIMS data in one dimension. Under this condition, it is possible to identify the metallurgical p-n junction position in two dimensions. Examples of 2D metallurgical p-n junction delineation are presented. In addition, the SCM ability to locate the 2D position of the intrinsic point in the p-n junction depletion region is demonstrated. The SCM probe tip size is found to be a major factor limiting the SCM accuracy on shallow profiles. On junctions with shallow profiles, the SCM tip interacts with carriers on both sides of the junction. As a consequence, a decrease in accuracy and spatial resolution is observed using a first-order conversion algorithm.
Kinetic analysis of interfacial diffusion accompanied by intermetallic compound formation
Authors: Kim P. G. , Jang J. W. , Tu K. N. , Frear D. R.
Published: July 2002

In interfacial reactions, a short-circuit diffusion along grain boundaries or interfaces can be accompanied by intermetallic compound formation. The compound penetrates the grain boundaries or the interfaces. This is a generic reliability issue for layered thin film structures because it causes a decrease in adhesion strength of the thin films. We have modified Fisher’s grain boundary diffusion model to include this reactive kinetic process, and an analytical solution was obtained. A t1/4 dependence of penetration is found, the same as Fisher’s model. The important kinetic parameters in the solutions are a diffusion coefficient along the short-circuit path, an intrinsic interdiffusion coefficient in the compound, and a partition coefficient. A comparison between the calculated and measured data from the lateral penetration of eutectic SnPb solder along the interface between electroless Ni and oxysilicon nitride dielectric, accompanied by Ni3Sn4 compound formation, is given.