bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of magnetic order in single-crystalline UPdSn
Authors: Robinson R. A. , Lynn J. W. , Lawson A. C. , Nakotte H.
Published: July 2002

The noncollinear hexagonal antiferromagnet UPdSn exhibits two magnetic phase transitions, at 35.5 and 23 K. The first transition is from a hexagonal paramagnetic state to a noncollinear antiferromagnetic state with a doubled unit cell (phase I). The second 23-K transition is to a monoclinic magnetic structure (phase II). Ever since these transitions were discovered, the question has been whether the moments simply rotate at 23 K, or whether the y and z components of the moment order at 35.5 K while the x component orders out of incipient fluctuations at the lower 23-K transition. While previous powder studies were rather inconclusive on this point, in this study new single-crystal neutron-diffraction results are presented that show the second picture to be correct. In addition, the structural distortions that accompany the change in symmetry are discussed and show that there is phase-II type magnetic short-range order between 23 and 35.5 K.
Easy-axis transition in SmMn2Ge2 (abstract)
Authors: van Dover R. B. , Gyorgy E. M. , Cava R. J. , Krajewski J. E. , Peck W. F. , Felder R. J.
Published: July 2002

SmMn2Ge2 is a layered ferromagnet with unusual magnetic and electrical properties. In some regards it is a natural analog to artifically layered thin film materials, and its study can provide valuable insights. SmMn2Ge2 is ferromagnetic from 0 to 90 K, with easy axes parallel to the (110) directions (FM1 state). Between 90 and 150 K it is antiferromagnetic, and from 150 K to Tc (340 K) it is again ferromagnetic, with an easy axis parallel to the (001) direction (FM2 state). We have used a continuous recording torque magnetometer to monitor the energy surface of SmMn2Ge2 as a function of temperature. We have found that the moments are parallel to (110) in the AFM state, and that the anisotropy constant varies continuously, i.e., that K→0 at the easy-axis transition, which is found to be at essentially the same temperature as the zero-field AFM/FM2 transition. The FM1/AFM and AFM/FM2 transition temperatures can be varied over a wide range by substitution on the various sites. Substitution of Y or Gd on the Sm site increases TAFM/FM2 strongly, and is found to increase the temperature of the easy axis transition, but not by precisely the same factor. Substitution of a small amount of Cr on the Mn site decreases TAFM/FM2 but appears to have no effect on the easy-axis transition. M-H curves and M-T curves taken in a vibrating sample magnetometer and in a SQUID magnetometer provide corroborating evidence for these conclusions.
Relaxation measurements and particle size determination in Co–Ag heterogeneous alloy films
Authors: Slade S. B. , Parker F. T. , Berkowitz A. E.
Published: July 2002

Magnetic properties of dilute Co–Ag heterogeneous alloy films are investigated to test the Néel model of magnetic relaxation. The static properties indicate a narrow particle size distribution for each sample. Dynamic susceptibility measurements indicate a frequency dependence for the susceptibility peak that is not consistent with the Néel model.
Magnetization reversal in compositionally modulated Tb/Fe multilayers (abstract)
Authors: Kirby Roger D. , Shen J. X. , Sellmyer D. J.
Published: July 2002

We have prepared compositionally modulated Tb(X Å)/Fe(5 Å) thin film multilayers with X ranging from 3.5 to 7 Å by magnetron sputtering on glass substrates. Magnetization measurements using SQUID and alternating gradient force magnetometers show that these samples have uniaxial anisotropies (Ku) up to 107 erg/cm3 and saturation magnetizations (Ms) between 50 and 350 emu/cm3. Constant field magnetization reversal measurements at room temperature show that these samples reverse by slow nucleation followed by relatively rapid domain wall motion. The samples with larger uniaxial anisotropies and smaller saturation magnetizations reverse completely for applied fields less than the coercivity, while those samples on the other end of the spectrum do not. The magnetization reversal curves are correlated with the shapes of the hysteresis loops, and the experimental results are interpreted using a recently developed uniaxial anisotropy model of magnetization reversal.
Oscillation of the interlayer coupling in Co/Au(111)/Co
Authors: de Vries J. J. , de Jonge W. J. M. , Johnson M. T. , aan de Stegge J. , Reinders A.
Published: July 2002

An oscillatory interlayer coupling in Co/Au(111)/Co has been obtained from polar Kerr hysteresis loop measurements on a molecular-beam-epitaxy-grown 50 Å Au/2 Å Co/0–40 Å Au wedge/7 Å Co/20 Å Au sample deposited on a Cu(111) single crystal. The period of the coupling is seen to increase from 11 to 14 Å with increasing Au thickness, indicating a preasymptotic behavior. The asymptotic period of 14±1 Å is larger than the theoretically expected period of 11.4 Å. The observation of coupling up to 40 Å Au will be discussed in relation to the general absence of coupling in evaporated Co/Cu(111)/Co samples.
Computer simulation of the dynamic process of mark formation for magneto-optical memory
Authors: Hasegawa Motoko , Moroga Katsumi , Okada Mitsuya , Okada Osamu , Hidaka Yasuharu
Published: July 2002

A computer simulation method, based on the Landau–Lifshitz–Gilbert equation was developed in order to investigate the dynamics of magneto-optical recording and the mark writing process for the rare earth-transition metal amorphous magneto-optical layer was subsequently analyzed. It was found that the writing process depends sensitively on the spot radius of the irradiation laser. This result is discussed considering the reverse magnetized domain shrinking force, due to radial direction variation of wall energy density in a cylindrical domain model and the characteristics of the magnetic parameters. The writing process is especially affected by the temperature dependence of parameters in the region near the Curie temperature.
Nuclear pumped XeBr* fluorescence
Authors: Williams W. H. , Miley G. H.
Published: July 2002

Experimental and theoretical results are presented on the nuclear pumping of XeBr*. Measurements under 10B and 3He pumping showed fluorescence efficiencies of 1%±0.5% for the B-X emission. Detailed time-dependent kinetic modeling was not in agreement, with predicted efficiencies of order 8%–9%.
Tracer diffusion of Ag in Bi2Sr2Can−1CunO2n+4
Authors: Fang Y. , Routbort J. L.
Published: July 2002

Tracer diffusion of Ag in the c direction of single crystal Bi2Sr2CaCu2Ox (2212), and in dense polycrystalline Bi2Sr2CuOx (2201) and (Bi,Pb)2Sr2Ca2Cu3Ox (2223) has been investigated. Concentration profiles were measured by secondary-ion mass spectrometry and by a radiotracer serial-sectioning technique for the single and polycrystals, respectively. The diffusion coefficients of Ag in the c direction of 2212 at 500 and 600 °C at one atmosphere of oxygen are approximately four orders of magnitude smaller than those previously measured in 2212 polycrystals by [Y. Fang, S. Danyluk, K. C. Goretta, N. Chen, M. Runde, S. J. Rothman, and J. L. Routbort, Appl. Phys. Lett. 60, 2291 (1992)]. The volume diffusivity of 110Ag in 2223 is given by D=6.7×107 exp[(−334±12 kJ/mol/RT] cm2/s at temperatures from 600 to 817 °C, and is not very sensitive to oxygen partial pressure between 103 and 105 Pa at 760 °C. The diffusion coefficient of 110Ag in 2201 is described by D=155 exp[(−196±6 kJ/mol)/RT].
Generation and minority-carrier leakage along GaAs surfaces
Authors: Mayer T. S. , Ling Z. G. , Cooper J. A. , Melloch M. R.
Published: July 2002

We describe electrical measurement on exposed surfaces of n- and p-type GaAs. The n-type surface exhibits substantial electron-hole pair generation and the subsequent escape of generated holes by leakage along the surface. In contrast, the surface of p-type GaAs does not exhibit measurable leakage of minority electrons. These results are significant for all GaAs devices and circuits which are sensitive to small leakage currents, and may provide important clues to the physical and electrical nature of exposed GaAs surfaces.
A study of 2H trapping in YBa2Cu2O7−δ /LaAlO3 〈100〉 samples under 2H+ irradiation
Authors: Li Yupu , Kilner J. A. , Tate T. J. , Lee M. J. , Saba F. M. , Cohen L. F. , Caplin A. D. , Quincey P. G.
Published: July 2002

A c-axis oriented YBa2Cu3O7−δ film, 180–230 nm thick, deposited onto 〈100〉 LaAlO3 by dc sputtering was irradiated at room temperature with 50 keV 2H+ (deuterium) ions to a dose of 1×1016 cm−2. Secondary-ion-mass spectroscopy analysis shows that after implantation the implanted 2H is trapped in both the film and the substrate. For example, when the thickness of the YBCO film is equal to ∼180 nm, it contains about 4.5% of the retained dose. The as-implanted 2H distribution is essentially Gaussian-like and the depth (R̂p) of maximum 2H concentration is ∼485 nm. It is obvious that the target crystallinity has to be taken into account for the range data, since the experiment values (R̂p,R̄p, and ΔRp) are obviously larger than the corresponding values from the transport of ions in matter code. This implantation makes the YBa2Cu3O7−δ film more granular. Within the irradiated LaAlO3 substrate, a damaged band was observed by cross-sectional transmission electron microscopy, which was centered at about 85% of R̂p(exp).
Nitrogen-doped ZnSe with selenium-rich growth by low-pressure organometallic chemical vapor deposition
Authors: Lee M. K. , Yeh M. Y. , Guo S. J. , Huang H. D.
Published: July 2002

A high-quality nitrogen-doped p-type ZnSe epilayer on (100) GaAs substrate was obtained under selenium-rich growth conditions by low-pressure organometallic chemical vapor deposition. Ammonia was used as the dopant source. The resistivity (0.5 Ω cm) and the free-carrier concentration (p=8.8×1017 cm−3) of as-grown ZnSe:N were derived from Hall measurements. With selenium-rich growth conditions, we can reduce the concentration of compensation defects (VSe-Zn-NSe which acts as a donor in ZnSe). Nitrogen is found to incorporate in ZnSe as a shallow level, which is examined by the dependence of free-to-acceptor emission on the NH3/H2Se molar ratio. The carrier concentration of as-grown ZnSe:N seems to change insignificantly within a wide range of growth temperatures. That is thought to be useful for device fabrication due to uniformity considerations.
Index of refraction and its temperature coefficient in CdSe0.18Te0.82 at 10.2 μm wavelength
Authors: Cohen S. , Weil R. , Muranevich E.
Published: July 2002

The index of refraction and its temperature dependence were measured at 10.22 μm on CdSe0.18Te0.82 grown by the Bridgman technique. The results are n=2.67±0.02 (different than the value expected from Vegard’s law), and (1/n)(dn/dt)=(3.89±0.07)10−5 °C−1. The absorption coefficient of the sample has also been measured, α=(0.79±0.05) cm−1.
Application of low temperature scanning electron microscopy for the investigation of single-electron tunneling circuits
Authors: Ustinov A. V. , Lemke S. , Doderer T. , Huebener R. P. , Kuzmin L. S. , Pashkin Yu. A.
Published: July 2002

We present the first experimental results on a spatially-resolved investigation of a SET (single-electron tunneling) circuit using the method of low temperature scanning electron microscopy. The new technique can be operated with short electron beam pulses down to 1 μs and small beam current below 1 pA, which gives the value of the charge per pulse as low as one elementary charge. By recording the circuit voltage response to the modulated electron beam irradiation as a function of the beam coordinates on the circuit, we were able to image the potentials of different parts of the circuit. For a SET-transistor which displayed the Coulomb blockade we found evidence of memory-effects due to charge trapping in the vicinity of one of the junctions. Further possible applications of our method for the spatially resolved study of single-electron circuits are suggested.
Indirect exchange interaction for zero-gap semiconductors in the Kane model
Authors: Iordanskii S. V. , Pikus F. G. , Pikus G. E.
Published: July 2002

The magnetic susceptibility of a gapless semimagnetic semiconductor have been calculated. The susceptibility is determined by the exchange interaction between the localized magnetic ions, caused by virtual electron transitions from occupied valence bands to the empty one. The band structure of the semiconductor was described in the framework of the four-band Kane model. Unlike the previous works, the general equations for the exchange integral have been derived, taking into account the transitions from all three occupied bands into the empty ‘‘light-hole’’ band. The susceptibility for Hg1−xMgxTe with x=0.01 and x=0.016 and within the temperature range from 5 to 250 K have been calculated. numerically In the numerical calculations, the transitions from the spin-orbit band have been neglected. The experimental values of the exchange interaction energies for the closest ion pairs (those within one Bravais cell) have been used. The sign of the exchange interaction constant does not change for all distances larger than between those pairs. In the calculations of the susceptibility the general formula has been used, which takes into account the possibility of a ‘‘freeze-out’’ of the close ion pairs. It is shown that the temperature dependence of the magnetic susceptibility can be described approximately by the expression χ−1=AT/n+BT1/4, where n is the magnetic ion concentration.
Ultrasonic measurement of Young’s modulus in dog-bone-shaped samples subjected to a tensile stress
Authors: Cutard T. , Fargeot D. , Gault C. , Huger M.
Published: July 2002

Thermostructural applications of fibrous ceramic composites require the knowledge of their behavior in severe service conditions (high temperature, high stress, oxidizing atmosphere). Previous results have shown that ultrasonic measurements of Young’s modulus are particularly suitable to monitor oxidation mechanisms at high temperature in these materials. Such measurements in materials subjected to tensile stress are possible by modeling the ultrasonic wave propagation in ‘‘dog-bone’’ specimens. The tensile specimens are modeled as a ‘‘slender bar’’ with two heads assumed to be thin plates (thickness less than the wave length). The frequency analysis of the signal allowed the determination of the optimal dimensions of the specimen and the calculation of time corrections in order to evaluate the real ultrasonic propagation time t0 in the material. The ultrasonic wave velocity and the Young’s modulus are then derived from the knowledge of t0.
Synchrotron radiation studies of diamond nucleation and growth on Si
Authors: Simons J. K. , Duevel R. V. , Frigo S. P. , Taylor J. W. , Rosenberg R. A.
Published: July 2002

Valence-band as well as Si(2p) and C(1s) core-level photoemission, Auger, and near-edge x-ray-absorption fine-structure spectroscopies were used to follow the surface chemistry associated with diamond film deposition with a filament-assisted chemical-vapor-deposition reactor on atomically clean and diamond polished Si(100) and Si(111) surfaces. Raman spectroscopy and atomic force microscopy (AFM) were also used ex situ to characterize the deposited films. Within 3 min of deposition, a carbon-rich SiC layer, at least 13 Å thick, was observed to develop. At early stages of growth (<10 min of deposition), no differences were observed between the clean and diamond-polished surfaces. With additional deposition, a 20–30-Å-thick amorphous carbon overlayer was deposited on the clean Si surfaces: The amorphous carbon layer did not promote diamond nucleation. Deposition of an a-C:H layer on top of the amorphous carbon layer also did not promote diamond nucleation. In contrast, ∼500 Å diamond films were deposited within 45–60 min on the diamond-polished surfaces. Two types of nuclei were observed following 20 min of deposition by atomic force microscopy: (1) large (200–300 nm in diameter) nuclei, randomly distributed on the surface; and (2) smaller (50–100 nm) nuclei that show a preference for forming along the scratches. Atomic force micrographs of the originally clean surface show the formation of sharp relief structures on the surface. These structures, combined with the amorphous carbon overlayer, may be responsible for the few sites that do nucleate diamond on unpolished Si surfaces.
Electron biprism operation of split-gate heterostructures having a single impurity within the channel
Authors: Bulutay Ceyhun , Günalp Nilgün , Tomak Mehmet
Published: July 2002

In the phase-coherent transport regime the possibility of a solid-state electron biprism employing an intentionally implanted impurity in a split-gate heterostructure is theoretically studied. The impurity-assisted interference phenomenon has been investigated under several impurity profiles and positions within the constriction. The effect of gate width on quenching the interference has also been considered. A quantitative explanation is offered which is based on the Fourier analysis of the wave function at the aperture and the guided-mode dynamics within the constriction.
Optical characteristics of SiO2 formed by plasma-enhanced chemical-vapor deposition of tetraethoxysilane
Authors: Ishii Keisuke , Ohki Yoshimichi , Nishikawa Hiroyuki
Published: July 2002

Optical characteristics of thin SiO2 films deposited from tetraethoxysilane by the plasma-enhanced chemical-vapor-deposition method were studied using synchrotron radiation. When the deposition temperature is 600 °C, 7.6 eV absorption and 4.4 eV luminescence with a small decay constant (<3 ns) due to the oxygen vacancy (≡Si-Si≡) are observed. The decay curve of the 4.4 eV luminescence has the appearance of a stretched-exponential function. This indicates that the decay constant consists of widely distributed components, reflecting structural distortion of the film.
Effect of doping and structural nonuniformities on reflectivity spectrum of AlxGa1−xAs distributed Bragg reflector
Authors: Heinämäki A. , Kapovits A.
Published: July 2002

The effect of doping and structural nonuniformities in AlxGa1−xAs distributed Bragg reflectors is investigated theoretically. The reflectors appear to be quite resistant to random fluctuations in thickness. Depending on the structure of the mirror, doping and small variations in composition may change the reflectivity spectrum essentially, indicating the importance of including doping in the mirror design. Only p-type doping is analyzed. The different role of variations in the thickness or refractive index is studied analytically.
Effect on magnetoresistance and magnetic properties of Co/Cu/Co/CoO films with a thin Co layer inserted within the Cu layer
Authors: McGuire T. R. , Plaskett T. S.
Published: July 2002

We find that sandwich films of the form Co50 Å/Cu (t)/Co50 Å with a CoO overlayer have large negative magnetoresistance [(MR)—up to 15% at T=4.2 K] for Cu thickness t≳10 Å. The MR correlates with a plateau in the magnetization curve which indicates antiparallel magnetization directions of the Co layers as caused by exchange coupling from the antiferromagnetic CoO overlayer. The addition of Co layers 2 or 4 Å thick inserted midway in the Cu spacer can increase or decrease the MR depending on Cu spacer thickness. When comparing sandwich films with and without the insert layer, MR agrees in magnitude if 1/2 the total Cu thickness is used for the insert film. This means that it is only necessary to have a 2 or 4 Å Co layer to scatter spin polarized electrons and implies that interface scattering at a boundary between Co and Cu may dominate over bulk scattering. For films with or without Co insert layers, a metallic Cu overlayer of 20 Å thickness, causes the magnetization plateau to disappear and reduces the MR to less than 1%.
Re-emission of deuterium from graphite as a function of D+ flux density
Authors: Davis J. W. , Pitcher C. S. , Haasz A. A.
Published: July 2002

An experiment was performed in order to determine whether a first-order or second-order mechanism governs the re-emission of deuterium molecules from graphite during D+ bombardment. The order of the release mechanism should be reflected in the dependence of the re-emission on the incident flux density. No flux density dependence was observed, indicating a first-order process, in agreement with a hydrogen transport model where the rate of molecule release is determined by a first-order process involving H diffusion within graphite crystallites.
Structure and formation of porous Si layers as studied by infrared absorption and Raman scattering
Authors: Sasaki Y. , Kitahara M.
Published: July 2002

The microscopic structure and formation processes of porous Si layers (PSLs) have been studied by infrared absorption and Raman scattering. How the concentration of HF used during formation affects the vibrational spectra of PSLs has been examined. The IR spectra of as-anodized PSL in the Si-Hx vibration region are quite similar to those of Si(111) or (100) surfaces etched in HF solutions of pH∼2. The amount of dihydrogen adsorbed on the surface increases for lower HF concentrations relative to that of monohydrogen. Fluorine and oxygen are found on PSLs anodized for a long period. The size of the Si particle (or column) is a few nanometers for samples anodized with the solution of HF:H2O=1:1 as estimated from Raman data, and it decreases with a decrease in the HF concentration. No Si nanostructures are detected in the Raman data for the case of HF:H2O:ethanol=1:1:8. The HF concentration dependence of the IR spectra is explained in terms of the change in the size of columns or particles in the PSL. The Si—Si back bond for the surface Si atom terminated by dihydrogen is more stable against oxidation in air than the bond for the atom terminated by monohydrogen. The HF concentration dependence of the electrochemical process is discussed in connection with the relative contribution of electropolishing and pore formation processes. The relation between the photoluminescence intensity and the surface structure is also discussed.
Influence of ultraviolet irradiation on excitation efficiency and space charge in ZnS thin-film electroluminescent devices
Authors: Zeinert A. , Benalloul P. , Benoit J. , Barthou C. , Gumlich H.-E.
Published: July 2002

Alternating current driven ZnS thin-film electroluminescent devices (ACTFELDs) have been investigated under continuous-wave ultraviolet (UV) irradiation. Under specific experimental conditions, UV irradiation can erase the residual polarization between two electric pulses which is caused by stored charges in the semiconductor and the semiconductor-insulator interfaces. No photodielectric effects have been observed. The reduction of the residual polarization allows one to investigate the role of the space charge in ACTFELDs, by comparing the excitation efficiencies with and without UV irradiation.
Importance of heat flux for stable operation of submicron gallium arsenide field-effect transistors
Authors: Jyegal J. , DeMassa T. A.
Published: July 2002

The effects of electron heat conduction upon the drain characteristics predicted for submicron gallium arsenide metal-semiconductor field-effect transistors (GaAs MESFETs) are analyzed by a numerical study. It is shown that, for submicron devices, the predicted drain characteristics are sensitively affected by electron heat conduction and are largely changed depending upon numerical approximations for the heat flux vector. It is shown that if the heat flux is taken into account incorrectly, then pronounced nonphysical negative differential resistance (NDR) drain characteristics are predicted instead of pentode-like drain characteristics normally observed experimentally. On the other hand, if the heat flux is neglected completely, Gunn oscillation drain characteristics can be produced at large applied drain voltages. It is found that the heat flux also plays a very important role in electron transport in the channel of a submicron GaAs MESFET and hence cannot be neglected for physically reasonable simulation results. It is observed that neglecting nonstationary relaxation effects tends to produce NDR drain characteristics whereas neglecting heat conduction effects tends to produce Gunn oscillation drain characteristics.
Forward tunneling current in HgCdTe photodiodes
Authors: Sarusi G. , Zemel A. , Sher Ariel , Eger D.
Published: July 2002

Current voltage characteristics of narrow-gap Hg1−xCdxTe photodiodes, fabricated on liquid phase epitaxy and metalorganic chemical vapor deposition grown layers, have been investigated. It is shown that the tunneling-recombination process is the dominant mechanism that determines the dark current at forward and at low reverse bias. This mechanism also determines the junction zero-bias resistance.
Ponderomotive forces in liquid conductors with macroscopic solid inclusions
Authors: Dolinsky Yu. , Elperin T.
Published: July 2002

This work studies the ponderomotive forces occurring in liquid conductors with macroscopic inclusions. It is shown that if the electric conductivity of inclusions is higher than the electric conductivity of the host medium then the inclusions are attracted to the axis of a conductor. In the opposite case the ponderomotive forces repel the inclusions towards the surface of a conductor. It is shown that if a certain relation between an amplitude and a frequency of an electric current is satisfied, the parametric resonance in the oscillations of the inclusions with electric conductivity higher than that in the bulk of the conductor can occur. The moments of the ponderomotive forces exerted on a particle of a nonspherical shape are determined. It is shown that the direction of the moment of a ponderomotive force alternates depending upon the sign of the difference between the electric conductivity of an inclusion and of the host medium.
Dynamic instabilities in the power spectrum of deeply modulated semiconductor lasers
Authors: Vurgaftman Igor , Singh Jasprit
Published: July 2002

Semiconductor lasers under large-signal direct modulation by a square waveform are found to exhibit a transition from a power spectrum characterized by a fundamental frequency and FM sidebands to a continuous spectrum with a catastrophically broadened linewidth of the order of several GHz. The interesting feature of the phenomenon is that the photon output remains periodic apart from noise-induced fluctuations, and the broadening of the power spectrum is attributed to the sensitivity of the phase of the optical field to a large difference in the relaxation oscillation frequencies in the on and off states as well as the coupling between motions at the intrinsic resonance frequency of the system and the externally-imposed modulation frequency. It is shown that under deep modulation by a periodic injection current, the optical phase becomes aperiodic generating a wide range of new frequencies in the power spectrum. It is also demonstrated that by confining the excursions of the injection current to the region of almost-linear optical response, linewidth broadening may be avoided. Quantitative criteria for determining the boundary of the broadened-linewidth region are presented for several modulation frequencies.
Strained film deposition on thin substrates: Resulting internal strains with an application to prestrained and preshaped multilayered membranes for a soft-x-ray window
Authors: Mutikainen R.
Published: July 2002

When a strained film is deposited on a thin substrate or membrane able to relax laterally, the film induces strains into the substrate. Accordingly, the continuing relaxation of the film-substrate system during deposition generates a nonuniform strain field in the film itself. In this study, the substrate shrinkage or expansion and nonuniform strain distributions within the deposited film are derived. Also, the induced strains due to the pressurization of initially strained and buckled multilayered membranes are analyzed. The lateral expansion of a thin membrane by a compressively strained coating is applied to increase the pressure endurance of the membrane-coating system. An experimental comparison of pressure endurance is presented for polyimide-based soft-x-ray windows of about a thickness of 200 nm, with thin coatings in various stress states. The strains within the window membrane are calculated by applying the derived formulae successively to the supporting grid and to the membrane cells.
Structural and optical properties of porous silicon at different porosities
Authors: Di Francia G. , Turchini S. , Prosperi T. , Martelli F. , Amato G. , De Santis M.
Published: July 2002

In this article we report on the Si atomic environment, investigated by near edge x-ray absorption fine structure (NEXAFS) measurements, and on the optical properties of porous silicon samples having different porosity values (30%, 60%, 80%), the sample with the lowest porosity not being luminescent. On the high porosity samples, time resolved photoluminescence measurements have been performed as a function of the temperature in the 10 K≤T≤300 K. The comparison between structural and optical properties shows that the NEXAFS measurements are consistent with the appearance of a large number of passivating Si-H groups on the surface of the highest porosity samples.
Raman ‘‘fingerprinting’’ of amorphous carbon films
Authors: Tamor M. A. , Vassell W. C.
Published: July 2002

We compare the Raman spectra and other macroscopic properties of nearly one hundred amorphous carbon films deposited at five research laboratories by a total of five different methods in search of correlations useful for both process control and basic understanding of the structure of these materials. For the full range of carbon-hydrogen alloys, including so-called ‘‘amorphous diamond,’’ hydrogenated ‘‘diamondlike’’ carbon, and plasma-polymers, a simple parametrization of the Raman spectrum in the usual 1000 cm−1 to 2000 cm−1 range can be used as a reliable predictor of hydrogenation and other properties (e.g., optical gap, hardness). Raman features in the 200 cm−1 to 1000 cm−1 range, a spectral region not usually reported for carbon films, may also be used as an indicator of hydrogenation. These growth method independent correlations greatly enhance the utility of Raman spectroscopy as a non-destructive characterization and process control tool.
Electrical and optical response of a very high frequency AlGaAs/GaAs heterojunction bipolar transistor
Authors: Martin M. Z. , Oshita F. K. , Matloubian M. , Fetterman H. R. , Ho W. J. , Wang N. L. , Chang F. , Cheung D.
Published: July 2002

The current gain cutoff frequency of very high frequency AlGaAs/GaAs heterojunction bipolar transistors has been measured at 300 and at 20 K using the picosecond optoelectronic technique. These devices showed cutoff frequencies of 72 and 84 GHz at room temperature and at a fixture temperature of 20 K, respectively. Optical response measurements were also obtained at visible and infrared wavelengths. The visible optical response shows a FWHM of 14 and 9.5 ps at 300 and 20 K, respectively. The infrared (λ=850 nm) optical response, corresponding to deeper penetration, showed a FWHM significantly larger (≳50 ps) than the visible optical response.
Optical strength of Si–SixGe1−x direct-band-gap superlattices
Authors: Cole J. Vernon , Lee Hong H.
Published: July 2002

Optical strength is evaluated for various types of Si–SixGe1−x direct-band-gap superlattices. A method for the evaluation is developed that is compatible with a k⋅p method for indirect-band-gap constituent materials, which is more rigorous than the envelope-function approach. The optical matrix elements based on the more rigorous method are found to be an order of magnitude greater than the values previously reported based on the envelope-function approach.
Effect of strain and temperature on the behavior of oxygen ion implanted manganese films
Authors: Rajanna K. , Muralidhar G. K. , Nair K. G. M. , Panchapagesan T. , Nayak M. M. , Mohan S.
Published: July 2002

The strain sensitive and temperature behavior of the oxygen ion implanted manganese films have been studied for their possible application as strain gauges. Films were subjected to different ion dosages and the resistance-strain behavior was studied. Also, the resistance variation of films with temperature was studied and TCR (temperature co-efficient of resistance) values were calculated. The structure and surface morphology of the films were examined using x-ray diffraction and scanning electron microscopy methods, respectively. The TCR value as low as 3.94×10−5/°C has been observed at lower annealing temperatures. It was found that both Mn and MnO2 phases exist in the film after annealing. Observed data indicate that metallic conduction is the predominant mechanism in these films.
A study of Franz–Keldysh oscillations of GaAs/Si/GaAs and AlAs/Si/AlAs heterostructures
Authors: Meléndez-Lira M. , Jiménez-Sandoval S. , López-López M. , Hernández-Calderón I. , Kawai T. , Pak K. , Yonezu H.
Published: July 2002

We have carried out a detailed study of Franz–Keldysh oscillations observed in the photoreflectance spectra of molecular beam epitaxy grown GaAs/Si/GaAs and AlAs/Si/AlAs heterostructures with a Si nominal thickness of two monolayers. The oscillations in the photoreflectance spectra were due to internal electric fields generated by graded p-n junctions created by Si diffusion. The data were analyzed employing the asymptotic Franz–Keldysh theory. It is concluded that different contributions from degenerate heavy and light hole bands, to transitions around the Γ point of the Brillouin zone, must be expected for different heterostructures depending upon the particular characteristics of the internal electric fields present in the sample.
Dynamic conversion of optical modes in magnetic garnet films induced by resonances of periodic stripe domains
Authors: Winkler H. P. , Dötsch H. , Lührmann B. , Sure S.
Published: July 2002

Magnetic garnet films of composition (Y,Bi)3(Fe,Al)5O12 are grown by liquid phase epitaxy on [111] oriented substrates of Gd3Ga5O12. They support periodic lattices of parallel stripe domains. A simple strip antenna is used to excite the domain wall resonance and the two branches of the domain resonance in the frequency range up to 5 GHz. The resonance frequencies and the dynamic components of the magnetization are calculated using a hybridization model. Good agreement between calculated and measured resonance frequencies is obtained if the quality factor of the film is larger than 0.6. Optical modes are coupled into the waveguiding film. The excited domain resonances cause dynamic conversion of transverse electric and transverse magnetic modes by the Faraday and the Cotton–Mouton effects. Mode coupling and conversion are calculated by the perturbation theory. The dynamic conversion efficiencies are measured at the fundamental and the first harmonic frequency and at zero diffraction order as a function of the static induction applied in the film plane parallel to the stripes. Conversion efficiencies up to 18% are achieved at a frequency of 2.8 GHz. From the experimental data the precession angles are derived.
Damage profiles in silicon tilt angles bombarded by high energy Cu ions
Authors: Wang Ke-Ming , Shi Bo-Rong , Wang Zhong-Lie , Liu Xiang-Dong , Ma Shi-Jie , Xu Tian-Bing , Zhu Pei-Ran , Zhao Qing-Tai
Published: July 2002

High energy (MeV) Cu ions were implanted into n-type Si samples at angles of 7°, 30°, 45°, and 60°. The doses were 5×1014 and 2×1014 ions/cm2. The damage profiles in Si(100) were investigated by a Rutherford backscattering/channeling technique with 2.1 MeV He ions. The longitudinal damage straggling and lateral damage spread are estimated for 1.0 MeV Cu+ implanted in Si(100). The values obtained are compared with the trim (transport of ions in matter) code. The results show that the longitudinal damage straggling is found to be in good agreement with the calculated one within 13% by use of the trim code, but the experimental value of the lateral damage spread is higher than the calculated one by about 28% using the trim code. The effect of dose rate, energy, and dose on damage distribution is investigated also.
Multiple low angles of incidence x-ray-diffraction method for nondestructively determining the depth-dependent fraction of a phase in the surface layer
Authors: Mizutani Katsumi , Murata Kazuo , Tanaka Yoshio
Published: July 2002

An x-ray-diffraction technique for nondestructively determining the depth-dependent fraction of a phase in the surface layer of a polycrystalline solid is presented using the data at low angles of incidence above the critical angle for the total reflection of x rays. The fraction, which is expressed as a polynomial in depth, is given by solving the equation of the kinematic diffracted intensity under the ratios of diffracted intensities from the phase to the bulk measured with multiple angles of incidence. The method utilizes the fact that at a lower angle of incidence the diffracted intensity from a deep layer attenuates more steeply and also the degree of the attenuation largely varies depending upon the angle of incidence. An application of the method to ground plates of yttria-doped tetragonal zirconia polycrystals revealed that the fraction of monoclinic phase induced by the machining was maximum (∼0.2) near the surface and decreased gradually in the deeper layer up to a few microns.
Resonance enhanced multiphonon ionization of silicon produced during disilane pyrolysis
Authors: Johannes Justine E. , Ekerdt John G.
Published: July 2002

Gas phase species generated by thermal decomposition of disilane were studied using resonance enhanced multiphoton ionization at disilane pressures ranging from 1–10 Torr and temperatures ranging from 300–1000 K. Atomic Si, mass 28, was observed at 487.9, 417.7, and 416.2 nm. A mass-30 signal was not observed between 494–515 nm. Masses 2, 32, and 60 were observed using multiphonon ionization and were photoionization fragments from higher silanes and silenes. Thermal decomposition reactions were the main source of atomic Si for the mass-28 signal, although ionization of SiH2 and higher silanes followed by fragmentation may have contributed some of the mass-28 signal.
Magnetic recording patterns of obliquely evaporated Co-O thin films observed by using ultrafine Co particles
Authors: Sakurai Tomoaki , Kitakami Osamu , Shimada Yutaka
Published: July 2002

Recording states of obliquely evaporated Co-O thin film media with different noise levels are observed by using ultrafine Co particles fabricated by a sputtering method. Very clear bit patterns with high resolution and high contrast are obtained by the method. This method enables us to estimate the fluctuation of magnetization transitions in the thin film media. It is also experimentally confirmed that the modulation noise level increases as fluctuation in the magnetization transitions become great.
Study of CsNO3 by Brillouin scattering
Authors: Takagi Yasunari , Sasaki Yukihiko , Takeuchi Yoshio
Published: July 2002

The phase transition of CsNO3 has been studied by the Brillouin scattering. Temperature dependence of Brillouin spectra has shown almost similar behavior for acoustic phonons propagating along three directions [001]h, [101]h, and [100]h in hexagonal axes. At Tc, jumps of Brillouin shifts were very large, especially for 45° oblique phonon. This results from the fact that Brillouin shifts were estimated to have a minimum for the phonon propagating along the axial direction [100]c in the cubic phase and the maximum for the same direction in the trigonal phase.
Silver diffusion in a nanometer Ni-B-O amorphous alloy
Authors: Li Xiangyang , Cheng Huansheng , He Wenquan , Yang Fujia
Published: July 2002

Diffusion of Ag in a nanometer Ni-B-O amorphous alloy has been studied by heavy-ion Rutherford backscattering spectroscopy. A significant mass transport was observed at the extremely low anneal temperatures. The values of the diffusion coefficients that were found at 293, 323, and 373 K are 3.5×10−16, 4.3×10−15, and 5.0×10−14 cm2/s, respectively. Moreover, small values for the activation energy, 0.58 eV, and the pre-exponential factor of the diffusion coefficient, 3.9×10−6 cm2/s, were derived from the Arrhenius plot. Finally, a possible free volume controlled diffusion mechanism was discussed.
Lattice relaxation and three-dimensional reflection high-energy electron-diffraction analysis of strained epitaxial Co/Mn superlattices
Authors: Henry Y. , Pierron-Bohnes V. , Vennégues P. , Ounadjela K.
Published: July 2002

In situ observations of reflection high-energy electron diffraction (RHEED) are used to study the structure and growth of epitaxial Co/Mn superlattices on hcp (0001) Ru buffer layers. Mn deposited on fcc (111) or hcp (0001) Co presents a singular growth behavior which can be interpreted as an incoherent growth with compressive stresses perpendicular to the surface. Moreover, the Mn structure is found to switch from a sixfold in-plane symmetric 1×1 structure, which probably corresponds to strained fcc γ-Mn, to a sixfold in-plane symmetric √3×√3−30° structure with in-plane lattice parameter a=4.69 Å. This structural change occurs at a critical thickness of 5–6 monolayers, after the partial relaxation of the Mn in-plane lattice parameter. An analysis of the three-dimensional contribution to the RHEED patterns shows that the √3×√3−30° structure is probably identical to the Cu2Mg Laves phase which in turn closely resembles the α-Mn phase.
Dimensionless solution of the equation describing the effect of surface recombination on carrier decay in semiconductors
Authors: Sproul A. B.
Published: July 2002

A dimensionless solution is presented for the surface recombination component τs of the effective lifetime τeff of the fundamental mode of excess carrier decay in semiconductors. The case of different surface recombination velocities S1 and S2 is analyzed. As the problem is solved in terms of dimensionless variables, the solution obtained is a general one. A normalized surface lifetime τ *s is plotted as a function of normalized surface recombination velocities S*1 and S*2. This allows rapid calculation and visualization of the influence of surface recombination on τs, for all possible cases of recombination parameters. That is, for any value of S1, S2, W (the width of a sample), and D (the diffusion constant) a solution for the surface lifetime τs can be found from the one graphical solution. It is a useful tool for rapidly interpreting the effect of surface recombination in transient lifetime measurement experiments. For the cases where S=S1=S2, or where S1 or S2 is zero, this approach is an elegant tool for investigating useful approximations for τs.
Self-consistent simulation of quantum transport in dual-gate field-effect transistors
Authors: Bigelow Jeffrey M. , Leburton J.-P.
Published: July 2002

A quantum transport model to investigate lateral resonant tunneling through one-dimensional states in a dual-gate field-effect transistor is presented. A self-consistent scheme based on the iterative extraction orthogonalization method for calculating the electronic properties of two-dimensionally confined carriers is employed. The model successfully reproduces the multiple negative differential resistance in the I-V characteristics; however, it is necessary to invoke nonuniformities and disorder at the heterointerface of the resonant tunneling structure to explain the observation of multiple negative differential resistance in the I-V characteristics.
Distribution of the satellite reflections of the modulation and its thermal stability in single-crystal Bi2Sr2CaCu2Oy
Authors: Wu Wen-Bin , Wang Liang-Bin , Zhu Jing-Sheng , Li Xiao-Guang , Zhou Gui-En , Qian Yi-Tai , Chen Zu-Yao , Zhang Yu-Heng
Published: July 2002

The satellite distribution around the main reflections of the incommensurate modulation in Bi2Sr2CaCu2Oy has been studied by means of x-ray diffraction on a number of single crystals. The presence of the forbidden reflections which are incompatible with a B-centered Bravais lattice is found to be correlated with the spread of the mosaic blocks in the crystal sheet and therefore spurious to the distribution of the satellite reflections in the reciprocal space. Diffraction data collected for a highly oriented crystal annealed in flowing nitrogen at 650 °C for 60 h have shown that the structural modulation is coherent with the Bi2Sr2CaCu2Oy phase and robust to the anneal. Relationships between superconductivity, structural modulation, and oxygen content in the compound are discussed.
X-ray study of the three-dimensional orientation of mixed a/c-oriented YBa2Cu3Ox films on (100)-SrTiO3 substrates by metalorganic chemical vapor deposition
Authors: Sandiumenge F. , Santiso J. , Figueras A.
Published: July 2002

A three-dimensional x-ray diffraction study of films deposited on (100)-SrTiO3 substrates by metalorganic chemical vapor deposition at two substrate temperatures is reported. Films deposited at 740 °C contain domains with either the a, b, or c axes perpendicular to the substrate, while those grown at 810 °C display almost only c-axis orientation. The 〈110〉 in-plane directions of the substrate and the c-axis oriented grains are aligned, while a/b-axes oriented grains have their [001] and [010]/[100] directions aligned with the substrate 〈100〉 ones. The in-plane mosaic spread is smaller for higher deposition temperatures. We demonstrate that the films are densely twinned independently of the orientation of the coexisting domains.
Window layer for current spreading in AlGaInP light-emitting diode
Authors: Chi G. C. , Su Y. K. , Jou M. J. , Hung W. C.
Published: July 2002

The current spreading effect and other characteristics of an AlGaInP double-heterojunction (DH) light-emitting diode (LED) were investigated via numerical calculation and experimental results. The finite difference method was employed to numerically solve the two-dimensional steady-state equations of a semiconductor device. Poisson’s equation and two continuity equations were approximated by a set of equations under the assumption that the hole and electron current components along the mesh lines are constant between two neighboring mesh points. Additionally, the DH structure was modified to a simple p-n junction model, in light of the fact that the former does not contribute significantly to the current spreading effect. Furthermore, a comparison of the measured light intensities from LEDs with the calculated current densities revealed a sufficient correlation. Experimental results indicated that a 10-μm-thick window layer with a carrier concentration at 2×1018 cm−3 would be adequate for an optimum device.
Electrical transport and superconductivity in YBa2Cu3O7−δ -YBa2HfO5.5 percolation system
Authors: Thomas J. K. , Koshy J. , Kurian J. , Yadava Y. P. , Damodaran A. D.
Published: July 2002

Percolation behavior of the normal state resistivity and superconductivity of YBa2Cu3O7−δ-YBa2HfO5.5 composites has been studied by x-ray diffraction and temperature- resistivity measurements. No detectable chemical reactivity was observed between YBa2Cu3O7−δ and a ceramic insulator YBa2HfO5.5 even when the two materials were mixed thoroughly and sintered at 1020 °C. Normal state and superconducting percolation threshold values are ≊23 vol % of YBa2Cu3O7−δ in the composite. The values obtained for the critical exponents describing the normal state transport behavior of the system matched with theoretically expected values for an ideal conductor-insulator percolation system. The implications are discussed.