bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the dislocation contribution to the internal friction background of gold
Authors: Baur J. , Benoit W.
Published: July 2002

The dislocation contribution to the internal friction (IF) background is studied in annealed gold samples containing various dilute concentrations of platinum impurities. The measurements are performed in the kHz frequency range in order to determine the loss mechanism responsible for the high IF background observed at these low frequencies. To this end, the IF background was systematically measured as a function of frequency, vibration amplitude, temperature, and impurity concentration. The experimental results show that the high dislocation contribution observed in annealed samples is strain-amplitude independent for amplitudes in the range 10−7 to 2×10−6, but rapidly decreases for amplitudes smaller than 10−7. In particular, the dislocation contribution tends to zero when the strain amplitude tends to zero. Furthermore, this contribution is frequency independent. These observations demonstrate that the dislocation contribution cannot be explained by relaxations. In particular, this contribution cannot be attributed to a viscous damping of the dislocation motion. On the contrary, the experiments show that the IF background due to dislocations must be explained by hysteretic and athermal motions of dislocations interacting with point defects. However, these hysteretic motions are not due to breakaway of dislocations from pinning points distributed along their length. The experimental results can be explained by the presence of point defects close to the dislocations, but not on them. The mechanical energy loss is attributed to hysteretic motions of dislocations between potential minima created by point defects.
Conductance transient spectroscopy of metal-semiconductor field effect transistors
Authors: Harrang J. P. , Tardella A. , Rosso M. , Alnot P. , Peray J. F.
Published: July 2002

We have performed conductance deep-level transient spectroscopy experiments on planar gate structure GaAs MESFETs (metal-semiconductor field-effect transistors) using positive and negative filling pulses and, in some cases, under light exposure. We present a simple surface model which accurately describes the main features of the experimental data. We discuss the differences between the predictions of the model and the experimental results.
Strain-induced current leakage in InSb photovoltaic detectors
Authors: Maniv S. , Shamay M. , Sinai Y.
Published: July 2002

Gate-controlled diode devices have been used to study the influence of external strain on the current leakage of InSb p+/n photovoltaic infrared detectors. Equivalence between external strain and the gate electrode in their effect on the current-voltage (I-V) characteristic has been empirically confirmed. By introducing an explicit analytical relationship between the applied gate voltage and the induced charge-carrier density near the p+/n junction and using the technique of simultaneous measurement of the I-V characteristic under a gate voltage and suitable strain at LN2 temperature, the local induced surface and bulk charge-carrier densities equivalent to a given strain are obtained. A discussion of the location of the current leakage induced by the gate voltage or by strain in the piezoelectric-semiconductor device is given.
Structural properties of heteroepitaxial Ge films on a Si(100)-2×1 surface
Authors: Kataoka Y. , Ueba H. , Tatsuyama C.
Published: July 2002

Structural and electrical properties of epitaxial Ge films grown on a Si(100)-2×1 surface have been studied by means of low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), x-ray diffraction, and Raman scattering. The attempt has been made to find the growth conditions, such as the substrate temperature TSi and Ge thickness dGe, for the single-crystalline Ge (100) on the Si surface. The sharp (2×1) LEED pattern of Ge (100) accompanied by the absence of any AES signals from the Si substrate is unambiguous evidence for the growth of single-crystalline Ge films. The structural quality of the Ge films was examined by the peak position and width of the Ge(400) Bragg line in x-ray diffraction. From these results, we found that more than 1000-Å Ge thickness is required to grow the high-quality epitaxial Ge films on the Si substrate at elevated temperatures. This is due to island formation at the initial stage of Ge deposition. Therefore, we also studied the role of thin Ge buffer layers fabricated at low temperatures below TSi=200 °C to grow thinner epitaxial Ge films without island formation. It was found that the amorphous buffer layers are poorly crystallized during the rapid increase in TSi up to 400–500 °C, prior to subsequent Ge deposition on the buffer layer. Consequently, single-crystalline Ge films are grown at relatively thin dGe in such a way that the underlying buffer layers accommodate the strains or misfit dislocations near the Si-Ge interface. The single-crystalline Ge films with and without the buffer layers thus grown on the Si substrates were also characterized by the line shape of the phonon Raman scattering spectra. Depending on the details of sample preparation, the spectra exhibited a characteristic change in shape including peak position and width. Having estimated the probing depth of the Raman scattering, we were able to gain deep insight into not only the Ge–Ge bond strength, but also the inhomogeneity of the Ge films and the extent of the strains into the Ge films, which were not accessible by LEED or x-ray diffraction.
Multiple valued floating potentials of Langmuir probes
Authors: Nam Cheol-Hee , Hershkowitz N. , Cho M. H. , Intrator T. , Diebold D.
Published: July 2002

It is shown that Langmuir probes can have three different floating potentials in plasmas produced by a hot filament discharge in a multi-dipole device when the primary and secondary electron currents are comparable. The measured floating potential depends on the probe’s initial condition—the most negative and the least negative potentials are found to be stable and the in-between value is found to be unstable. Results are compared to a simple theoretical model.
The axial dipole moment of two intersecting spheres of equal radii
Authors: McAllister I. W.
Published: July 2002

The use of a finite number of image charges to solve electrostatic problems associated with two conducting spheres intersecting at an angle of π/n (n an integer) has been known for over a century. If, however, only spheres of equal radii are considered, it is possible to extend the permissible angles of intersection to 2π/n. This condition is discussed with reference to the evaluation of the axial dipole moment.
Compaction and sintering behaviors of a Nd-Fe-B permanent magnet alloy
Authors: Chin T.S. , Hung M.P. , Tsai D.S. , Wu K.F. , Chang W.C.
Published: July 2002

Extensive x-ray diffraction (XRD) and magnetic measurements were done on Nd15 Fe77 B8 magnet alloy green compacts after cold isostatic pressing following a pulsed 2-T field (CIP) and die-pressing under a static 1.2-T perpendicular field (DP1) or parallel field (DP2), and on those after sintering. An alignment factor F, through the calculation of the integrated diffraction intensity ratio of the XRD patterns, was adopted as the effectiveness of magnetic alignment. At the green compact state, DP1 has the best alignment while CIP the worst. However, after sintering the alignment factor was such that CIP>DPI>DP2, the same order as the magnetic properties. Three mechanisms were proposed for the evolution of the alignment factor at different stages of sintering, i.e., that both the appearance of a liquid phase at low temperatures and preferred grain growth at high temperatures enhance F, while recrystallization at intermediate temperatures deteriorates F. CIP results in less-defect green compact, hence less recrystallization, leading to better resultant alignment
Neutron irradiation study of Nd-Fe-B permanent magnets made from melt-spun ribbons
Authors: Brown R. D. , Cost J. R. , Meisner G. P. , Brewer E. G.
Published: July 2002

Radiation-induced changes in the magnetization of sintered Nd-Fe-B permanent magnets are known to vary widely among specimens produced by different manufacturers. Samples of Nd-Fe-B MAGNEQUENCH magnets, which are made from melt-spun ribbons, have not been studied and show a much reduced sensitivity to neutron irradiation than do sintered Nd-Fe-B magnets. All melt-spun ribbon-based MAGNEQUENCH magnets, i.e., epoxy-bonded, hot-pressed, and die-upset magnets, show essentially the same slow decrease in magnetic remanence with neutron dose. Measurements of the open-circuit remanence Br/Br 0 at various times during the irradiation show a decay of only 1.5% of the preirradiated value for the MAGNEQUENCH magnets after 1 h of irradiation, or a dose of 1.4×1016 neutrons/cm2, compared to a 4.6% drop in remanence for the best sintered Nd-Fe-B magnet (Sumitomo 30H) with the same irradiation dose. Moreover, after 5.3 h of irradiation, the remanence drops by only 3% for the MAGNEQUENCH magnets. Magnets made from melt-spun ribbons are thus the least sensitive to neutron irradiation so far measured for Nd-Fe-B permanent magnets, but are somewhat more sensitive than samarium-cobalt magnets.
Coupled ac photocurrent and photothermal reflectance response theory of semiconducting p-n junctions. I
Authors: Mandelis Andreas
Published: July 2002

A formalism involving the ac photocurrent and photothermal reflectance (PTR) spectroscopic response of a semiconducting p-n junction device is presented. The differential equations for the photovoltaic and PTR signals are solved explicitly and special limits of use in experimental applications [J. Appl. Phys. 66, ⧠ ⧠ ⧠ ⧠ (1989), part II] are considered. The dependence of the photocurrent and PTR signal modulation frequency response on electronic transport parameters is identified and the suitability of ac PTR as a noncontact diagnostic technique is assessed in comparison with the more conventional ac photocurrent method.
Measurement of adhesion of thin polymer coatings by indentation
Authors: Ritter J. E. , Lardner T. J. , Rosenfeld L. , Lin M. R.
Published: July 2002

A microindentation technique was developed to measure the adhesive shear strength of thin polymer coatings on glass substrates. Indentation-induced debonding of the coating was observed to occur under three different conditions: Type I was with the deformations underneath the indenter being essentially elastic; Type II was with the deformations underneath the indenter being plastic; and Type III was after the indenter penetrated the substrate. Stress analyses to calculate the interfacial shear stress for the indentation-induced debonding of thin coatings are presented for the three types of debonding. All three stress analyses are based upon the linear, elastic analysis of the contact stresses arising from indentation of a soft coating on a rigid substrate. These analyses provide a basis for using controlled indentation debonding as a quantitative measure of the interfacial shear strength of thin coatings to rigid substrates.
Enthalpy of formation of antisite defects and antistructure pairs in III-V compound semiconductors
Authors: Dobson T. W. , Wager J. F.
Published: July 2002

A formulation for estimating the enthalpy of formation of neutral, isolated antisite defects in III-V compound semiconductors is presented, in which it is assumed that the formation enthalpy is comprised of disorder and electronic contributions. The disorder contribution was previously calculated by Van Vechten [J. Electrochem. Soc. 122, 423 (1975); Handbook on Semiconductors, edited by S. P. Keller (North-Holland, Amsterdam, 1989), Vol. 3, Chap. 1]. The electronic contribution is equal to the difference of the donor (acceptor) levels with the valence-band maximum (conduction-band minimum). The enthalpy of formation of neutral, singly, and doubly ionized, isolated antisites is estimated for GaAs and InP. The enthalpy of formation of neutral antistructure pairs in wide band-gap III-V semiconductors is calculated assuming that the binding energy is given by the electrostatic energy of a doubly ionized nearest-neighbor pair of antisites separated by a normal lattice site. The enthalpy of formation of neutral antistructure pairs in the narrow band-gap III-V semiconductors InAs and InSb is estimated assuming the binding energy is twice the band-gap energy.
GaAs/AlGaAs quantum-well intermixing using shallow ion implantation and rapid thermal annealing
Authors: Elman B. , Koteles Emil S. , Melman P. , Armiento C. A.
Published: July 2002

Low-energy As+-ion implantation followed by rapid thermal annealing (RTA) was utilized to modify exciton transition energies of GaAs/AlGaAs quantum wells (QW). A variety of structures were irradiated at an energy low enough that the disordered region was spatially separated from the QWs. After RTA, exciton energies showed large increases which were dependent on QW widths and the implantation fluence with no significant increases in peak linewidths. The observed energy shifts were interpreted as resulting from the modification of the shapes of the as-grown QWs due to enhanced Ga and Al interdiffusion at heterointerfaces in irradiated areas. These results are consistent with the model of enhanced intermixing of Al and Ga atoms in depth of the material due to diffusion of vacancies generated near the surface.
Direct determination of cobalt site preferences at infinite dilution in iron-based intermetallic compounds (invited)
Authors: Ryan D. H. , Altounian Z. , Liao L. X. , Ström-Olsen J. O. , Muir W. B.
Published: July 2002

Extremely low doping levels (∼1 ppm) and unambiguous interpretation combine to make the Mössbauer-source technique an ideal method for determining cobalt site preferences in intermetallic compounds. Data on Gd2Fe17 and Nd2Fe14B are presented and compared with earlier work using Mössbauer spectroscopy, NMR, and neutron diffraction.
The theory of the photoconductance under the presence of a small photocarrier grating
Authors: Balberg I.
Published: July 2002

Recently, responding to the need for the determination of the minority-carrier diffusion length in noncrystalline materials and devices, Ritter, Zeldov, and Weiser suggested a new photocarrier grating technique that became very popular among researchers of these materials. In this paper we present the first closed-form solutions for the photoconductance of the corresponding physical system. This system consists of a photoconductor that is subjected to both a uniform illumination and a periodically varying illumination of much lower intensity. The present analysis, which considers the effect of trapping, enables the evaluation of the conditions under which the experimental results can be uniquely translated into the value of the ambipolar diffusion length and thus into the mobility-lifetime (μτ) product of the minority carriers. In particular it is shown that the larger the shallow trapping the more justified the above translation.
Increase of electrical activation and mobility of Si-doped GaAs, grown at low substrate temperatures, by the migration-enhanced epitaxy method
Authors: Tadayon Bijan , Tadayon Saied , Spencer M. G. , Harris G. L. , Griffin J. , Eastman L. F.
Published: July 2002

Si-doped GaAs layers were grown by the migration-enhanced epitaxy (MEE) method and by the conventional molecular-beam epitaxy (MBE) method, for the substrate temperatures between 220 and 670 °C. For the layers grown below 400 °C, the Si activation and mobility of the MEE layers are significantly higher than those of the MBE layers. For substrate temperatures above 400 °C, the MEE and MBE layers have roughly similar Si activation and mobility. The Raman and 4-K photoluminescence spectra of the layers are consistent with the measured electron concentrations. This work suggests that for Si doping in GaAs at low substrate temperatures (below 400 °C), the MEE method is a very desirable alternative to the conventional MBE method.
Temperature dependence of the frequency-dependent negative photoconductivity and photodielectric effects in proustite
Authors: Yang S. R. , Taylor K. N. R.
Published: July 2002

An exhaustive study of the photodielectric response of proustite at various temperatures over the frequency range 10−2–103 Hz has revealed an extremely complex series of changes. These involve both negative and positive photoeffects which appear to arise from competing processes in the sample. A model based on a two-layer dielectric system, in which one of the layers is established by space-charge buildup at the electrode, appears to explain most of the observed results.
Hall effect of sputtered NiZr and CoZr metallic glasses near the critical magnetic concentration
Authors: Morel R. , Abadli L. , Cochrane R. W.
Published: July 2002

With increasing 3d component, the 3d transition-metal Zr amorphous alloys undergo a transition to ferromagnetism at xc=88 at. % Ni, 62 at. % Co, and 38 at. % Fe, respectively. The first two compositions are outside the range of stable melt-spun glasses, but can be prepared by sputtering. In this paper, we present Hall data for sputtered NiZr and CoZr alloys in the vicinity of the critical magnetic composition. For the ferromagnetic glasses, x>xc, the alloys are magnetically soft. Although the NiZr alloys are quite weak magnetically [μ0M(T=0)=0.15 T at 90 at. %], the extraordinary Hall coefficient is very large (Rs=−0.67×10−7 m3/C for the same alloy). In the Co glasses, Rs is positive, but of the same magnitude even though the magnetism is considerably stronger. In the paramagnetic range x<xc, the rapid change in ordinary Hall coefficient close to the critical concentration for ferromagnetism indicates the presence of spin fluctuations, as has been found for the melt-spun FeZr glasses.
Organometallic vapor-phase epitaxy growth and characterization of Bi-containing III/V alloys
Authors: Ma K. Y. , Fang Z. M. , Cohen R. M. , Stringfellow G. B.
Published: July 2002

For potential infrared detector applications, single-crystalline InAsBi and InAsSbBi have been grown by atmospheric pressure organometallic vapor-phase epitaxy. The precursors used were trimethylindium, trimethylantimony, trimethylbismuth, and arsine at growth temperatures of 375 and 400 °C. Good quality epilayers with smooth surface morphologies were obtained by properly controlling the key growth parameter, the V/III ratio. The variation of lattice constant with solid composition for the InAs1−xBix system, a=6.058+0.966x, provides evidence that Bi atoms indeed incorporate substitutionally into the As sites of the sublattice in the InAs zinc-blende structure. An extrapolated lattice parameter for the hypothetical zinc-blende InBi is 7.024 Å. Thermodynamic calculations of the InAs-InBi and InSb-InBi pseudobinary phase diagrams were carried out using the delta-lattice-parameter model using the lattice constant for zinc-blende InBi of 7.024 Å. The results agree well with experimental data. The calculations predict that the solid solubility limit of Bi in InAs is less than 0.025 at. %. The calculated maximum solubility limit is 2.1 at. % for Bi in InSb at the eutectic temperature of 132 °C. Thus, tremendously large miscibility gaps exist in both alloy systems. The critical temperature was predicted to be 2569 °C for the InAs-InBi system and 496 °C for the InSb-InBi system. The miscibility gap is the major factor limiting Bi incorporation into the InAsSb alloys. Nevertheless, metastable InAsBi and InAsSbBi alloys were grown with concentrations far exceeding the solubility limit. For example 3.1 at. % Bi was incorporated into InAs. Infrared photoluminescence measurements show a decrease of peak energy with increasing Bi concentration in the alloys, with dEg/dx=−55 meV/at. %Bi.
Non-steady-state photo-electromotive-force induced by dynamic gratings in partially compensated photoconductors
Authors: Petrov M. P. , Sokolov I. A. , Stepanov S. I. , Trofimov G. S.
Published: July 2002

This paper gives a thorough treatment of a new effect of non-steady-state photo-electromotive-force (emf). The effect consists of an alternating electric current arising in a short-circuited bulk sample of a photoconductor illuminated by a vibrating sinusoidal pattern. As a detailed theoretical analysis shows, the frequency transfer function of the effect is identical with that of a differentiating RC circuit having a time constant equal to the characteristic time of a space-charge grating formation within the sample volume τsc. For high excitation frequencies (ω≳τ−1sc), the photo-emf signal peaks at spatial frequency K=L−1D (LD is the mean diffusion length of photoinduced carriers) and the photovoltage amplitude in an open-circuit sample can be as high as kBT/e times the number of fringes of the interference pattern in the interelectrode spacing. The basic conclusions of the theoretical analysis of the effect are supported by the experimental evidence obtained for cubic photoconducting Bi12SiO20 crystals.
Size and surface effect in nematic-isotropic phase transition of a liquid crystal
Authors: Barbero G. , Miraldi E. , Stepanescu A.
Published: July 2002

The size and surface effects on the nematic-isotropic phase transition of a liquid crystal are analyzed using a functional form of the surface energy proportional to the square of the scalar order parameter. The evaluated temperature shift agrees with the published experimental observations. This form seems confirmed by experimental data of the anchoring energy versus temperature, determined by means of the Freedericksz technique. The obtained formula for the temperature shift is similar to the well-known Thomson formula, usually considered in the classical phase transitions.
Hole drift mobility and chemical structure of charge-transporting hydrazone compounds
Authors: Kitamura Takashi , Yokoyama Masaaki
Published: July 2002

The hole drift mobility of several hydrazone compounds dispersed in a polymer binder was correlated with their chemical structure. The mobility of hydrazone compounds having the same basic skeleton, i.e., aminophenylhydrazone, varied over about two orders of magnitude by systematic change of the substituents on the N atoms. The variety of the hole mobility was discussed on the basis of the concept of polyfunctionality and intramolecular mobility. From molecular orbital calculations, the importance of the positive charge distribution on a molecule in the cation radical state was emphasized for the molecular design of high-mobility charge-transporting compounds.
Theory of origins of the photorefractive and photoconductive effects in Bi12SiO20
Authors: Attard Alfred E.
Published: July 2002

We have observed modulation of the dark current in Bi12SiO20 (BSO) as a function of prior irradiation, and a time-varying absorption of radiation that is dependent upon prior irradiation. As a result of these observations and the previously reported observations of photoconductivity, photorefractivity, photosensitivity, and mobility modulation, a model theory of transport has been developed that requires multiple sources of defect/impurity energy levels. A hopping band exists in the forbidden energy gap where these levels coincide. Transport via exchange of charge is possible here, analogous to conduction via hopping in the presence of impurity bands or dense concentrations of defects. Traps capable of containing immobile charge carriers occur where these various levels do not coincide. Large mobility variations can occur as a result of photon-induced modulation of the Fermi level. Much of the phenomena observed in BSO can be explained through interaction between the multiple defect/impurity energy levels.
Linear and nonlinear intersubband electroabsorptions in a modulation-doped quantum well
Authors: Roan E. J. , Chuang S. L.
Published: July 2002

The linear and nonlinear optical-absorption coefficients and changes in refractive indices due to intersubband optical transitions in a modulation-doped quantum well with an applied electric field are derived theoretically based on the density-matrix formalism. The calculations of electron energy levels and envelope wave functions in a double-confinement quantum-well structure are discussed with electric-field and screening effects. The electric-field, screening, and tunneling effects on the electronic properties (electron energy levels and envelope wave functions) and optical properties (linear and nonlinear optical-absorption coefficients and changes in refractive indices) are discussed with detailed numerical results. The comparisons between theoretical results and the corresponding experimental data show good agreement. The results presented here will be useful for high-speed intersubband infrared photodetectors and electro-optical modulators.
Excimer laser melting of GaAs: Real-time optical study
Authors: Solis J. , Afonso C. N. , Piqueras J.
Published: July 2002

In situ real-time reflectivity measurements have been made in GaAs under ArF excimer laser (λ=193 nm) irradiation. The results obtained provide a reflectivity value for the solid material at the melting temperature of 0.44 and for the liquid of 0.63, both at 633 nm. The reflectivity values obtained for fluences just above the melting threshold (E=225 mJ/cm2) show that melting proceeds inhomogeneously, the near-surface region being formed by a mixture of solid and liquid phases. The comparison of these results to those obtained previously for irradiation of single-crystalline Si and Ge shows that inhomogeneous melting can be a general phenomenon at least in semiconductors. Higher fluences (E≳300 mJ/cm2) are necessary to induce an homogeneous melted layer on the surface of the irradiated material.
A technique for measuring residual stress in SiC whiskers within an alumina matrix through Raman spectroscopy
Authors: DiGregorio J. F. , Furtak T. E. , Petrovic J. J.
Published: July 2002

We measured the Raman spectrum associated with the transverse optical (TO) phonon of cubic SiC (β-SiC) whiskers as a function of stress using a diamond anvil cell (for hydrostatic stress, X) and an individual whisker microtension apparatus (for uniaxial stress along [111], P). These experiments were used to calibrate the shift and the splitting of the TO phonon mode with applied stress. The results of the calibration experiments were used to evaluate the residual stress in an Al2O3/SiC(w) composite (30% SiC by volume). The Raman spectra from the composite shows that residual stress in the SiC near the surface of the composite is (X+P/3)=−1050±100 MPa.
Cathode heating mechanisms in pseudospark plasma switches
Authors: Sommerer Timothy J. , Pak Hoyoung , Kushner Mark J.
Published: July 2002

Pseudosparks, and the back-lighted thyratron (BLT) in particular, are finding increasing application as pulse power switches. An attractive feature of BLTs is that high current densities (≥ tens of kA cm−2) can be sustained from metal cathodes without auxiliary heating. The source of this current is believed to be electric-field-enhanced thermionic emission resulting from heating of the cathode by ion bombardment during commutation which ultimately melts the surface of the cathode. It is proposed that a photon-driven ionization mechanism in the interelectrode gap of the BLT is responsible for initiating the observed patterns of cathode surface melting and electron emission. A 21/2-dimensional computer model is presented that incorporates a photo-induced ionization mechanism to spread the plasma into the interelectrode gap. It predicts a melting of the cathode in a pattern similar to that which is experimentally observed, and predicts a rate of field-enhanced thermionic electron emission that is sufficient to explain the high BLT conduction current density. In the absence of these mechanisms, the model does not predict the observed large-area melting of the face of the cathode. The cathode heating rate during the BLT switching phase is maximum for operating parameters that are very close to the limit for which the switch will close (that is, the smallest possible pressure-electrode spacing product and smallest possible electrode holes).
Melting kinetics of Sb under nanosecond UV laser irradiation
Authors: Serna R. , Solís J. , Afonso C. N.
Published: July 2002

Real time reflectivity measurements at the HeNe laser wavelength (λ=632.8 nm) have been performed in crystalline Sb under pulsed UV laser irradiation (λ=193 nm). For energy densities above 100 mJ cm−2, a transient low-reflectivity phase is observed, which is related to surface melting. The change of reflectivity of the solid material upon heating is small, and a maximum variation of −0.02 relative to the room-temperature value (RSb,rt) is determined for the solid material at the melting point. The value of the reflectivity of the liquid material is determined to be 0.94RSb,rt(632.8 nm)=0.67, which is lower than that of the solid and it is associated with a decrease of the absorption coefficient upon phase change. The analysis of reflectivity transients at energy densities just above the melting threshold suggests that melting nucleation proceeds inhomogeneously.
Application of microwave detection of the Shubnikov–de Haas effect in two-dimensional systems
Authors: Linke H. , Omling P. , Ramvall P. , Meyer B. K. , Drechsler M. , Wetzel C. , Rudeloff R. , Scholz F.
Published: July 2002

Microwave detection of the Shubnikov–de Haas (SdH) effect as a contact-free characterization technique for different types of two-dimensional semiconductor structures is explored in the low magnetic field region. The detection technique and the data analysis are described. The character and relevance of the single-particle relaxation time that can be detected by this technique are distinguished from the usual transport scattering time. The measured values of the carrier concentration and single-particle relaxation time agree with electrical measurements, while the problem of making contacts on the structure is avoided. Uncertainties in the analysis for the single-particle relaxation time are discussed. Cyclotron resonance, optically detected cyclotron resonance, and magneto-photoluminescence are applied as other contact-free techniques on the same samples. The results and suitability of these techniques are compared with the microwave detection of the SdH effect.
Local structural and polar Kerr effect measurements on an ultrathin epitaxial Co wedge grown on Pd(111)
Authors: Purcell S. T. , Johnson M. T. , McGee N. W. E. , de Vries J. J. , Zeper W. B. , Hoving W.
Published: July 2002

A Pd/Co double layer has been grown epitaxially in ultrahigh vacuum on a Pd(111) single crystal, with the Co in the shape of a wedge of thickness varying from 0 to 10 monolayers (ML). The polar magneto-optical Kerr effect has been used to make a nearly continuous set of measurements of the magnetic properties as a function of Co thickness tCo. The coercive fields Hc and nucleation fields Hn show large, well-defined maxima at tCo∼2.3 ML. Between 4 and 9 ML, we find that Hc falls with increasing thickness according to a tCo−5/2 dependence. The Kerr ellipticity and Kerr rotation depend linearly on Co thickness above ∼2 ML Co, but show appreciable offsets when extrapolated to tCo=0. These offsets are clear evidence of the polarization of Pd near the interfaces. Extensive in situ growth studies of the structure of the films are also reported.
The role of boron in Rn+1Con+5B2n systems (R=Y, Sm, Dy; n=0, 1, 2, 3, and ∞)
Authors: Ogata H. , Ido H. , Yamauchi H.
Published: July 2002

Magnetic measurements have been made for the systems of Rn+1Co3n+5B2n (R=Y, Sm, Dy; n=1, 2, 3, 4, and ∞) in wide temperature region. The Curie temperature decreases drastically between n=0 and n=1, and slowly with n larger than 1, for all above systems. Three kinds of Co sites with different magnetic moments are proposed. The estimated Sm- and Dy-atomic moments are found to be smaller than the free ion moments in the Dy system with n≥1 and in the Sm system. Magnetic anisotropy constants K1(Co) and K2(Co) have been determined at various temperatures for the Y system, and the Sm-sublattice anisotropy constants K1(Sm) have been estimated and found to take the maximum value at n=1 and decrease with n≥1 in the Sm system. Magnetic anisotropy in the Dy system is found to be planar at all temperatures below the Curie temperature.
Fractional-dimensional calculation of exciton binding energies in semiconductor quantum wells and quantum-well wires
Authors: Christol Philippe , Lefebvre Pierre , Mathieu Henry
Published: July 2002

We propose a fractional-dimensional approach of excitonic characteristics in semiconductor quantum wells and quantum-well wires with cylindrical or rectangular cross sections. This type of approach has proved to provide accurate and convenient methods for extracting excitonic binding energies, either from optical spectroscopy experiments, or from simple envelope function calculations. In this paper, we first try and extend the simple description previously developed for single quantum wells and superlattices. Next, we show how the accuracy of the model is dramatically improved by invoking microscopic considerations, in order to describe the anisotropy of the relative motion of confined electron-hole pairs. This original approach allows a rather simple and quick determination of eigenenergies of confined excitons, whatever the quantum numbers of the conduction and valence subbands, and whatever the shape of the confining medium. The results of our calculations compare favorably to those of available variational theories and to experimental findings.
A 150–600 GHz step-tunable gyrotron
Authors: Hong K. D. , Brand G. F. , Idehara T.
Published: July 2002

An account of the operation of a step-tunable, low-power, continuous-wave gyrotron, GYROTRON V, at the fundamental and second harmonic of the electron cyclotron frequency is presented. The design of this gyrotron was especially optimized for the second harmonic. The gyrotron operating frequency at the fundamental can be tuned from 150 to 300 GHz and extended by second-harmonic operation to above 600 GHz. Under normal operating conditions where the accelerating voltage is 10 kV and the beam current is 50 mA, power levels in excess of 20 W are obtained at the fundamental and hundreds of milliwatts at the second harmonic. The paper includes observations of single mode operation at the second harmonic and mode competition between second harmonic and fundamental.
Homojunction diode of CuInSe2 thin film fabricated by nitrogen implantation
Authors: Nishitani M. , Negami T. , Kohiki S. , Terauchi M. , Wada T. , Hirao T.
Published: July 2002

Rectifying homojunction have been fabricated in polycrystalline CuInSe2 thin film. The p-n junction diode was obtained by short annealing in nitrogen atmosphere at 450 °C following the ion implantation of nitrogen with the energy and the dose of 50 keV and 1×1015 cm−2, respectively. The properties of the near surface region in the films implanted have been studied by the Raman scattering spectroscopy. The secondary ion mass spectroscopy depth profile of the nitrogens in the CuInSe2 film and the capacitive-voltage characteristics of the rectifying diode have been measured to characterize the junction properties. The photovoltaic characteristics in AM 1.0, 100 mW/cm2 are shown with the efficiency of 0.35%.
Investigation of interaction mechanisms in melt-quenched NdFeB
Authors: Folks L. , Street R. , Woodward R.
Published: July 2002

Investigation of the magnetization processes in melt-quenched Nd2Fe14B materials has been made by analysis of measurements of the time dependence of the magnetizing curves (after thermal demagnetization) and demagnetizing curves at room temperature. The quantities S (the magnetic viscosity parameter) and χirri (the intrinsic irreversible susceptibility) have been determined for the commercially available materials MQI (isotropic, resin bonded), MQII (slightly anisotropic, hot pressed), and MQIII (anisotropic, hot formed) produced by Delco Remy, U.S. In addition δM(H), which compares the fraction of irreversible processes occurring at a particular field in the magnetizing mode with those occurring at the same field in the demagnetizing mode, has been determined as a function of internal field, and the results are interpreted in terms of interactions between grains. From these results it is shown that although the magnetization and demagnetization behavior of these materials differ substantially, this may be attributed to differences in the domain structure. There is no evidence that the mechanism for hardening is different from that of the sintered materials.
Deformation of Si(100) wafers during rapid thermal annealing
Authors: Jongste J. F. , Oosterlaken T. G. M. , Bart G. C. J. , Janssen G. C. A. M. , Radelaar S.
Published: July 2002

In this paper in situ wafer curvature measurements are presented that were performed during rapid thermal annealing of silicon wafers. The wafer curvature due to thermal stress originating from a nonuniform temperature distribution was measured as a function of time for a fixed setting of the illumination source power. The presence of thermal stress was clearly demonstrated. It was found that wafers deform during the complete annealing cycle and moreover that, the deformation is largest during the heating and cooling transients. The influence of various wafer supports on the deformation was investigated. The use of a susceptor and a guard ring reduce the wafer deformation compared to a free-standing wafer by a factor of 6 and 10, respectively.
Postgrowth tuning of quantum-well infrared detectors by rapid thermal annealing
Authors: Steele A. G. , Buchanan M. , Liu H. C. , Wasilewski Z. R.
Published: July 2002

The peak detection wavelength of an operational quantum-well infrared photodetector structure has been red shifted using rapid thermal annealing to partially intermix the well and barrier layers. Successive anneals at 850 °C were used to tune an 8.13 μm detector continuously out to 9.13 μm. All of the fabricated detectors were operational in spite of very long annealing times of up to 300 s. The peak spectral responsivity at a device current of 10 μA dropped from 0.62 to 0.12 A/W after the longest anneal time, but the broadband responsivity only dropped by a factor of 3 due to a simultaneous increase in the detection spectral bandwidth.
Electroacoustic effect in electrolytes
Authors: Tankovsky N.
Published: July 2002

A highly sensitive pulse-modulated technique has been used to verify experimentally the existence of electroacoustic effect in electrolytes. Some insight to the mechanisms involved is obtained by studying the Fourier spectrum of the detected acoustic signal and its dependence on the exciting voltage.
Photoinduced surface deposition of metallic silver in Ag-As-S glasses
Authors: Kawaguchi Takeshi , Maruno Shigeo
Published: July 2002

Detailed characteristics of photoinduced surface deposition (PSD) of metallic Ag have been studied using Ag-As-S bulk glasses to reveal the mechanism. The composition dependence of PSD in the AgxAs60−xS40 (25≤x≤45) system shows that the photosensitivity decreases with a decrease in the Ag content and becomes negligible at x≂25. All the related crystalline materials hardly exhibit the PSD, even if the Ag content is greater than 45 at. %. The size of photodeposited Ag particles and the number per unit area depend on the Ag content and illumination conditions (light intensity, photon energy, and temperature). The PSD phenomenon is induced by light with photon energy higher than the optical band gap, and the photosensitivity shows a maximum at room temperature. PSD can be suppressed by coating over the surface with thin Au film. From these results and other observations it can be suggested that the PSD phenomenon is characteristic of thermodynamically unstable glasses containing excess Ag+ ions and is a kind of photoelectro-ionic chemical reaction.
Short-range ordering in face-centered-cubic Ni3Al
Authors: Okamoto J. K. , Ahn C. C. , Fultz B.
Published: July 2002

Films of fcc Ni3Al with suppressed short-range order (SRO) were prepared by physical vapor deposition of Ni3Al onto room-temperature substrates. Extended electron energy-loss fine-structure spectra were obtained from both Al K and Ni L23 edges. After the samples were annealed for various times at 150 °C, a moderate growth of SRO was observed in the first-nearest-neighbor environments of both the Al and Ni atoms. As prepared, these fcc Ni3Al materials, and presumably others having similar heat evolutions as measured by differential scanning calorimetry, have a high degree of chemical disorder.
Application of Kramers–Krönig analysis to the photoreflectance spectra of heavily doped GaAs/SI-GaAs structures
Authors: Jezierski K. , Markiewicz P. , Misiewicz J. , Panek M. , Ściana B. , Korbutowicz R. , Tl/aczal/a M.
Published: July 2002

The photoreflectance spectra for heavily doped p-type GaAs/SI-GaAs structures have been measured at room temperature for the energies in the vicinity of the GaAs band gap. The complex photoreflectance function is defined and determined by means of a Kramers–Krönig analysis from the measured photoreflectance spectra. The modulus of the complex photoreflectance function gives us the critical point energy whereas the phase of this function can be used for a topographical study of the homogeneity of the internal electric field in the structure.
A high-speed photographic study of cavitation damage
Authors: Bourne N. K. , Field J. E.
Published: July 2002

Cylindrical cavities, viewed through the side as they collapsed onto solid surfaces, were studied using high-speed streak and framing photography. The cavities were collapsed asymmetrically using shock waves of varying amplitude so that the rear surface formed a high-speed jet which crossed the cavity and interacted with the target surface. Schlieren optics were used to visualise waves in the fluid and in the target. Two features of the collapsing bubble affected the damage to the target surface. The first was the impact of the high-speed liquid jet on either the rear wall of the cavity or the target itself. The second was the production of a strong compression wave on the rebound of the bubble after it reached minimum volume. Damage to the targets related to their material properties. Metals, with low compressive but higher tensile strengths, plastically deformed beneath the penetrating jet to form a pit. Brittle materials, with high compressive but low tensile strengths, deformed by cracking. The position of the cavity relative to the surface had a major effect upon the geometry of the damage. With the cavity close to the target, the penetrating jet dominated the damage leaving single pits. With the cavity at some distance, the rebound wave was more important than the jet giving rise to a circular damage mark. This mechanism can be used to re-interpret previous experimental observations [Y. Tomita and A. Shima, J. Fluid Mech. 119, 535 (1986)].
Defect diffusion in ion implanted AlGaAs and InP: Consequences for quantum well intermixing
Authors: Poole P. J. , Charbonneau S. , Aers G. C. , Jackman T. E. , Buchanan M. , Dion M. , Goldberg R. D. , Mitchell I. V.
Published: July 2002

InGaAs/GaAs/AlGaAs and InGaAs/InGaAsP/InP laser structures, with InGaAs quantum wells approximately 1.85 μm beneath the surface, were implanted with ions having energies up to 8.6 MeV. Intermixing of the quantum wells, after rapid thermal annealing, was monitored through changes in the energy, linewidth, and intensity of the photoluminescence peak from the quantum wells. Where the defects had to diffuse primarily through Al0.71Ga0.29As, these quantities correlate strongly, for short anneal times, with calculated vacancy generation and ion deposition at the depth of the quantum well prior to annealing. This suggests that the defect diffusion length in the AlGaAs and/or GaAs is quite low. For diffusion primarily through InP, the photoluminescence data correlated well with the calculated total number of vacancies created in the sample, suggesting that defect diffusion is very efficient in InP.
Temperature and strain dependence of the roughening transition in III-V semiconductor and SiGe epitaxial growth
Authors: Bangert U. , Harvey A. J. , Dieker C. , Hartdegen H. , Vescan L. , Smith A.
Published: July 2002

Experimental and theoretical evidence is given for the occurrence of a temperature and strain dependent roughening transition from two dimensional (2-D) monolayer to 3-D island growth in strained III-V compound ternary alloys and GeSi. For sufficiently large strain energy values the shape of the transition curve was found to follow a T∼ε−2f relationship, as predicted from classical nucleation theory arguments, where T is the growth temperature and εf the areal misfit strain energy. The asymptotic behavior in the zero strain energy regime could be reproduced by an empirical curve of a more complex expression. The transition curve appears to separate routes of strain relief in the above systems, which were found to predominantly follow 3-D island formation in the higher, and misfit dislocation formation in the lower growth temperature/strain regime.
Observation of potassium-intercalated carbon nanotubes and their valence-band excitation spectra
Authors: Suzuki S. , Tomita M.
Published: July 2002

Second-stage potassium-intercalated carbon nanotubes were synthesized in a specially designed ultrahigh vacuum analytical electron microscope and their valence-band excitation spectra in the region of the π+σ plasmon were measured by electron energy loss spectroscopy. The carbon nanostructures consisted of graphene sheets. Potassium was deposited in an ultrahigh vacuum at room temperature. As a result, a second stage of intercalated nanotubes was found to be formed close to the surface. The energy loss spectra of the intercalated nanotubes showed humps at about 16, 19, and 22 eV, in addition to those of unintercalated tubes. This suggests that intercalation modified the band structure of the interlayer bands and/or the σ(σ*) bands.
Interface traps in jet-vapor-deposited silicon nitride–silicon capacitors
Authors: Mallik A. , Wang X. W. , Ma T. P. , Cui G. J. , Tamagawa T. , Halpern B. L. , Schmitt J. J.
Published: July 2002

The properties of interface traps in metal–silicon nitride (deposited by jet vapor deposition technique) –silicon (MNS) capacitors have been studied in some detail. In comparison with those in metal–oxide–Si capacitors, the interface traps in our MNS capacitors exhibit the following major differences: (i) ∼2 orders of magnitude higher time constants; (ii) no evidence of two distinguishable defects following irradiation as revealed by the ac conductance measurement; and (iii) absence of latent generation of interface traps following irradiation. On the other hand, the interface-trap transformation process following irradiation is qualitatively similar in silicon nitride and thermal oxide devices.
Effect of SiO2 buffer layers on the structure of SrTiO3 films grown on silicon by pulsed laser deposition
Authors: Tejedor P. , Fuenzalida V. M. , Briones F.
Published: July 2002

Thin films of SrTiO3 were grown by pulsed laser deposition on Si and SiO2/Si at 35 and 650 °C in a 50 mTorr oxygen discharge (300 V). The effect of introducing a SiO2 buffer layer between the Si substrate and the complex oxide on the crystallinity and microstructure of the SrTiO3 films was investigated at both deposition temperatures. All films grown at 35 °C were amorphous. Surface morphology examination by scanning electron microscopy (SEM) showed that these films were continuous and homogeneous when grown on Si, but were porous and had low-density noninterconnecting lines when grown on SiO2/Si. Films prepared at 650 °C were polycrystalline and their x-ray-diffraction patterns exhibited peaks corresponding to the (001), (110), (111), and (002) reflections of the SrTiO3 cubic phase (a=3.904 Å). The films deposited on SiO2/Si were found to grow with a high degree of preferred orientation along the (110) direction. SEM studies on the surface morphology of the films grown at high temperature showed the presence of a ‘‘rosette’’ structure. The mean size of the rosettes was ∼80 nm in 40-nm-thick films grown on Si and ∼100 nm in films of similar thickness grown on SiO2/Si. Additional atomic force microscopy studies on the topography of these samples indicated that the rosettes were constituted by ∼35-nm-diam grains. Typical peak-to-valley surface roughness of these films was 0.5–2 nm.