bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of ion bombardment on in-plane texture, surface morphology, and microstructure of vapor deposited Nb thin films
Authors: Ji Hong , Was Gary S. , Jones J. Wayne , Moody Neville R.
Published: July 2002

Niobium films were deposited by physical vapor deposition (PVD) and ion-beam-assisted deposition (IBAD) using ion energies of 0, 250, 500 and 1000 eV, and R ratios (ion-to-atom arrival rate ratio) of 0, 0.1, and 0.4 on (100) silicon, amorphous glass, and (0001) sapphire substrates of thickness 50–1000 nm. Besides a {110} fiber texture, an in-plane texture was created by orienting the ion beam with respect to the substrate. The in-plane texture as measured by the degree of orientation was strongly dependent on both ion-beam energy and the R ratio. In fact, the degree of orientation in the films followed a linear relationship with the energy per deposited atom, En. The grain structure was columnar and the column width increased with normalized energy. The surface morphology depended on both the normalized energy of the ion beam and the film thickness. All films had domelike surface features that were oriented along the ion-beam incident direction. The dimension of these features increased with normalized energy and film thickness. Surface roughness also increased with normalized energy and film thickness, with the root-mean-square roughness increasing from 1.6 nm for the PVD sample (100 nm thick) to 36.7 nm for the IBAD film (1000 eV, R=0.4, 800 nm thick). Both the surface morphology evolution and in-plane texture development in these films were the result of the different ion sputter rates among differently oriented grains.
Effect of chemical oxide layers on platinum-enhanced oxidation of silicon
Authors: Namba K. , Yuasa T. , Nakato Y. , Yoneda K. , Kato H. , Kobayashi H.
Published: July 2002

Si oxidation promoted by a platinum (Pt) overlayer has been investigated using x-ray photoelectron spectroscopy and synchrotron radiation ultraviolet photoelectron spectroscopy. Heat treatments of the specimens with 〈∼5-nm-Pt/0.5–1-nm-chemical oxide/Si(100)〉 structure at 300–400 °C increase the oxide thickness to 4–5 nm. The amounts of the suboxide species, a(Si+), a(Si2+), and a(Si3+), in the chemical oxide layers formed in hydrochloric acid (HCl) plus hydrogen peroxide (H2O2) are in the order of a(Si+)>a(Si2+)>a(Si3+), while those for the oxide layers formed in nitric acid (HNO3) have an order of a(Si3+)>a(Si2+)≈a(Si+). The amounts of the suboxide species in the former oxide layers are much higher than those in the latter oxide layers. These results indicate that the HNO3 oxide layers are more highly oxidized, probably resulting in a higher atomic density and a lower defect density. Although the initial chemical oxide layers formed in HCl+H2O2 are thinner than those grown in HNO3, the former oxide layers become thicker than the latter after the Pt deposition and the heat treatments below 200 °C. This result is attributed to the lower atomic density and the higher defect density of the chemical oxide layers produced in HCl+H2O2, which enhance the diffusion of oxidizing species. It is suggested that the variation in the atomic density of the chemical oxide layers cause the different energy distribution of interface states in the Si band gap.
Structure and magnetic properties of R2Fe15Si2Cy (R=Nd, Sm, Gd, and Er)
Authors: Li Z. W. , Morrish A. H.
Published: July 2002

A new series, R2Fe15Si2Cy (R=Nd, Sm, Gd, and Er), has been prepared by heating powders of their corresponding parents in CH4 gas at 700 °C instead of about 500 °C. For these carbides, the carbon concentrations are close to the theoretical value of y=3 and the 2:17 structure is still retained up to 900 °C. The Curie temperatures are 620–650 K and the saturation magnetizations are 71–113 and 67–129 emu/g at T=300 and 80 K, respectively. The anisotropy fields are larger than 70 and 110 kOe at T=300 and 80 K, respectively, for Sm2Fe15Si2Cy.
Determination of interface roughness cross correlation of thin films from spectroscopic light scattering measurements
Authors: Rönnow D.
Published: July 2002

Diffuse reflectance and transmittance spectra collected in different scattering angle intervals have been analyzed in order to determine the interface roughness cross correlation of thin films. Different angle intervals correspond to different roughness length scales; the cross correlation as a function of length scale can hence be determined. Sputter deposited ZrO2 films were analyzed. The transition from correlated to uncorrelated film interfaces was found to occur at longer length scales, when the film thickness increased.
Analytical model for the refractive index in quantum wells derived from the complex dielectric constant of Wannier excitons in noninteger dimensions
Authors: Tanguy Christian , Lefebvre Pierre , Mathieu Henry , Elliott R. J.
Published: July 2002

Absorption spectra of low-dimensional structures such as quantum wells or wires have been strikingly well reproduced by expressions based on solutions of the Schrödinger equation for the Coulomb potential in noninteger dimensions, which require much less computational effort than more elaborate calculations. The compact and analytical complex dielectric constant of Wannier excitons in d dimensions is given, and included in a simple model of the refractive index in quantum well structures in the vicinity of the absorption threshold.
Electron paramagnetic resonance imaging of the distribution of the single substitutional nitrogen impurity through polycrystalline diamond samples grown by chemical vapor deposition
Authors: Talbot-Ponsonby D. F. , Newton M. E. , Baker J. M.
Published: July 2002

The distribution of the single substitutional nitrogen impurity (NS0) through the thickness of diamond films grown by chemical vapor deposition has been studied using Electron Paramagnetic Resonance imaging. The design of an Electron Paramagnetic Resonance imaging probe is described. With this probe we have measured mean bulk concentrations down to a few parts per billion carbon atoms or equivalently ∼1014 cm−3 in diamond samples with dimensions 4.5×10×0.5 mm and achieved a through film spatial resolution of the NS0 distribution of 20 μm.
Strain effects on optical phonons in 〈111〉 GaAs layers analyzed by Raman scattering
Authors: Puech Pascal , Landa Georges , Carles Robert , Fontaine Chantal
Published: July 2002

Strain and thermal effects on longitudinal and transverse optical (LO) and (TO) phonon frequencies and on associated electron–phonon interactions have been analyzed in GaAs. We focus separately on these effects to treat each one thoroughly. By using lattice-mismatched 〈111〉 Si or CaF2 substrates, GaAs layers with highly tensile or compressive strain have been analyzed. We show that the LO/TO Raman scattering efficiency ratio, i.e., the electro-optic versus the atomic displacement electron-phonon mechanisms, varies with the built-in strain and hence its induced piezoelectric field. The Raman selection rules are valid in this process. The increase and decrease of this ratio compared to a reference suggest an interference effect. We discuss this phenomenon on the basis of strain-induced Raman scattering.
Indirect transitions, free and impurity-bound excitons in gallium phosphide: A revisit with modulation and photoluminescence spectroscopy
Authors: Alawadhi H. , Vogelgesang R. , Ramdas A. K. , Chin T. P. , Woodall J. M.
Published: July 2002

The momentum conserving indirect excitonic transitions, from the Γ15 valence band maximum to the conduction band minima close to the X1 point in the Brillouin zone have been measured for GaP in piezo-modulated transmission. At 6 K, excitonic signatures due to phonon emission are observed at Egx+ℏωph for TA(X), LA(X), and TO(X) phonons (Egx=free exciton band gap), whereas at 120 K signatures for both absorption and emission of LA(X) and TA(X) phonons appear. These observations yield Egx=2.3301(4) eV at 6 K. In several GaP specimens, signatures A and/or C for excitons bound to sulfur (S) and/or nitrogen (N) impurities, respectively, are observed in the piezo-modulated transmission. A parallel investigation of the spectra of recombination radiation reveals emission lines for excitons bound to S and N as well as their phonon sidebands. The phonon replicas of N consist of sharp lines in combination with the zone center optical phonons observed in the first order Raman spectrum (LOΓ and TOΓ). In addition, broader replicas are observed for the A line in combination with acoustic and optical phonon branches (A-LA, A-TA, A-X). The phonon energies obtained from both piezo-modulation and photoluminescence experiments are compared with those reported in the literature. Finally, the suppression of S diffusion from a GaP substrate into a GaP epilayer achieved with an intervening GaP/AlGaP superlattice is demonstrated in both modulation and photoluminescence experiments.
Transport of plasmas produced by pulsed laser ablation of HgCdTe
Authors: Man B. Y. , Wang X. T. , Liu A. H.
Published: July 2002

A time- and space-resolved diagnostic technique was used to investigate the emission spectra from the plasmas produced by pulsed laser-ablated HgCdTe targets at different pressures. According to the time-of-flight curves of the excited atoms, the propagation distances and velocities of species in the plasma were measured. To investigate the propagation of the plasma, a shock wave model considering ejected HgCdTe mass was established. The propagation distances and velocities of the plasmas were calculated by using the model. The calculated results were consistent with the experimental results.
Contactless electroreflectance study of strained Zn0.79Cd0.21Se/ZnSe double quantum wells
Authors: Tu R. C. , Su Y. K. , Lin D. Y. , Li C. F. , Huang Y. S. , Lan W. H. , Tu S. L. , Chang S. J. , Chou S. C. , Chou W. C.
Published: July 2002

We have studied various excitonic transitions of strained Zn0.79Cd0.21Se/ZnSe double quantum wells, grown by molecular beam epitaxy on (100) GaAs substrates, using contactless electroreflectance (CER) at 15 and 300 K. A number of intersub-band transitions in the CER spectra from the sample have been observed. An analysis of the CER spectra has led to the identification of various excitonic transitions, mnH(L), between the mth conduction band state and the nth heavy (light)-hole band state. The conduction-band offset Qc is used as an adjustable parameter to study the band offset in the strained Zn0.79Cd0.21Se/ZnSe system. The value of Qc is determined to be 0.67±0.03.
A new two-dimensional theory for vibrations of piezoelectric crystal plates with electroded faces
Authors: Lee P. C. Y. , Yu J. D. , Lin W. S.
Published: July 2002

A system of two-dimensional (2-D) governing equations for piezoelectric plates with general crystal symmetry and with electroded faces is deduced from the three-dimensional (3-D) equations of linear piezoelectricity by expansion in series of trigonometric functions of thickness coordinate. The essential difference of the present derivation from the earlier studies by trigonometrical series expansion is that the antisymmetric in-plane displacements induced by gradients of the bending deflection (the zero-order component of transverse displacement) are expressed by the linear functions of the thickness coordinate, and the rest of displacements are expanded in cosine series of the thickness coordinate. For the electric potential, a sine-series expansion is used for it is well suited for satisfying the electrical conditions at the faces covered with conductive electrodes. A system of approximate first-order equations is extracted from the infinite system of 2-D equations. Dispersion curves for thickness shear, flexure, and face-shear modes varying along x1 and those for thickness twist and face shear varying along x3 for AT-cut quartz plates are calculated from the present 2-D equations as well as from the 3-D equations, and comparison shows that the agreement is very close without introducing any corrections. Predicted frequency spectra by the present equations are shown to agree closely with the experimental data by Koga and Fukuyo [J. Inst. Elec. Comm. Engrs. of Japan 36, 59 (1953)] and those by Nakazawa, Horiuchi, and Ito [Proceedings of 1990 IEEE Ultrasonics Symposium (IEEE, New York, 1990)].
The role of internal dissipation and process average temperature in chiller performance and diagnostics
Authors: Ng K. C. , Chua H. T. , Tu K. , Gordon J. M. , Kashiwagi T. , Akisawa A. , Saha B. B.
Published: July 2002

The thermodynamic behavior of conventional chillers (generalized air conditioning and refrigeration systems) is acutely sensitive to internal dissipation. Previous chiller analyses have excluded entropy production in the evaporator and condenser heat exchangers, on the assumption of its being negligible. With experimental measurements from a commercial chiller, we demonstrate that heat exchanger internal dissipation is not inconsequential, and that ignoring its contribution can lead to substantial errors in chiller diagnostics and in the prediction of chiller performance curves. To evaluate the impact of this dissipation on chiller efficiency, one needs to define a proper process average temperature (PAT). In addition to discussing the fundamental significance of the correct PAT, we will show that earlier conventional definitions of PAT, where internal irreversibilities in chiller heat exchangers have been overlooked, result in inaccurate and sometimes unphysical predictions.
Numerical calculations of the temperature distribution and the cooling speed in the laser-heated diamond anvil cell
Authors: Morishima H. , Yusa H.
Published: July 2002

Numerical calculations have been done to reveal temperature distributions and cooling speeds of laser-heated samples in a diamond anvil cell. The distributions were calculated for variable experimental parameters including the diameter of the laser beam, anvil gap, and sample. The results show that the radial temperature distribution in all samples is Gaussian. The axial temperature gradient is ∼10 K/μm in samples heated by a broad laser beam of 100 μm diameter, and is ∼102 K/μm when a narrow laser beam of 10 μm diameter is used. The broad beam can generate a less extreme temperature gradient in both radial and axial directions as compared with the narrow beam, whereas the temperature gradient strongly depends on the anvil gap, although this is minimized when a narrow beam is used. When the narrow beam is used to heat samples, the surface temperature of the anvil culet can be kept below 400 K; thus, the narrow beam is suitable for heating samples under high pressure while keeping anvil temperatures low. Cooling speeds of the laser-heated samples were found to be from 100 to 102 K/μs. The discrepancy between actual sample temperature and measured temperature was also evaluated. To measure the peak temperature of a sample heated by a laser with a Gaussian power distribution within 5% accuracy, radiation from a circular area of less than (1/2)σ of the Gaussian must be observed.
The mechanism of nanocrystallization driven by the Fe/Si ratio in Fe73.5Cu1Nb3Si22.5−xBx alloys
Authors: Pradell T. , Zhu J. , Clavaguera N. , Clavaguera-Mora M. T.
Published: July 2002

The kinetics of nanocrystallization were studied in two amorphous Fe–Cu–Nb–Si–B based alloys with different Fe/Si ratios. Differential scanning calorimetry and transmission Mössbauer spectroscopy data were collected in a range of time-temperature space. Nanocrystallization is preceded by a relaxation of the amorphous phase that appears to involve changes in its short range order (SRO) parameters [T. Pradell, N. Clavaguera, J. Zhu, and M. T. Clavaguera-Mora, J. Phys.: Condens. Matter 7, 4129 (1995)] which are consistent with Cu-clustering. This process is followed by formation of Fe(Si) embryos with ∼20 at. % Si, regardless of alloy composition. Nanocrystals with DO3 structure grow, and change composition via a diffusion controlled process that is stopped by soft impingement [D. Crespo, T. Pradell, M. T. Clavaguera-Mora, and N. Clavaguera, Phys. Rev. B 55, 3435 (1997)]. The rate of this process depends on both temperature and alloy composition. Nanocrystallization is enhanced by prior annealing at conditions which induce SRO relaxation, however, prior annealing at an intermediate temperature (where crystal nucleation occurs) will retard nanocrystallization.
Single photon detection at visible and x-ray wavelengths with Nb–Al superconducting tunnel junctions
Authors: Verhoeve P. , Rando N. , Peacock A. , van Dordrecht A. , Poelaert A. , Goldie D. J. , Venn R.
Published: July 2002

Photon counting experiments at wavelengths ranging from near infrared to x-ray with niobium based superconducting tunnel junctions with aluminum trapping layers are presented. Single photons can be detected up to a wavelength of 1 μm. The response in the ultraviolet to near-infrared region is characterized by a good energy linearity (<2.5%), a capability to handle event rates up to ∼3 kHz, and moderate energy resolving power (E/ΔE≈7 for E=4 eV). The x-ray response at 6 keV is characterized by anomalously high signals compared to the low energy response, a severe energy nonlinearity and a relatively poor energy resolution of ∼140 eV, full width at half maximum.
Superconductivity in the new quaternary ruthenium borocarbide Y–Ru–B–C system
Authors: Hsu Y. Y. , Chiang H. C. , Ku H. C.
Published: July 2002

Two new quaternary borocarbide phases were discovered in the Y–Ru–B–C system: the (1111) YRuBC phase of the LuNiBC-type structure with tetragonal lattice parameters a=3.625–3.630 Å and c=7.775–7.874 Å, and the (1221) YRu2B2C phase of the LuNi2B2C-type structure with tetragonal lattice parameters a=3.742–3.787 Å and c=10.278–10.453 Å. Bulk superconductivity of 9.7 K was observed from transport and magnetic measurements for the annealed YRu2B2C sample with a short Ru–Ru bond length d(Ru–Ru)=√2 a/2=2.646 Å.
Magnetostatic critical point phenomena of ErIGa garnet
Authors: Tanaka Toshiro , Miyatani Kazuo
Published: July 2002

The magnetostatic critical point phenomena of an ErIGa garnet, Er3(Fe0.8Ga0.2)5O12, single crystal sphere were investigated by a computer controlled vibrating sample magnetometer. Subtracting the induced large spin paramagnetic moment of Er3+ from the measured values, allowed the Fe-sublattice magnetization Msub(H,T) to be extracted. Msub data were used to analyze the critical phenomena by eliminating the low field data to avoid the effect of the magnetic inhomogeneity. The spontaneous magnetization and the zero-field susceptibility were obtained from the Arrot plot. The critical temperature and critical indices were obtained to be Tc=463.64 K, β=0.48±0.03, γ=1.1±0.1, and δ=3.1±0.1. These results agree well with the predicted values from the molecular field theory. The plot of the critical equation of states ψ(H,M) showed the same function as that found for Fe. Thus, Msub(H,T) was shown to satisfy the second-order phase transition based on the molecular field theory.
Modeling the effect of dislocations on the minority carrier diffusion length of a semiconductor
Authors: Donolato C.
Published: July 2002

An analysis is given of the minority carrier diffusion and collection in a semiconductor with a surface junction, in the presence of a periodic array of straight dislocations perpendicular to the surface. A dislocation is characterized by its line recombination velocity and is attributed a finite cross section. An approximate solution is obtained for the three-dimensional charge collection probability φ(r) in the unit cell of the array. The integral of φ over the unit cell is used to introduce a new definition of effective diffusion length and to give its analytical expression. It is shown that the relative reduction of diffusion length produced by the dislocation array coincides with the fractional decrease of the total number of junction-injected carriers. This result establishes a connection between the efficiency of charge collection and luminescence of a sample containing dislocations. The analysis is extended to the case of a thin sample, and is compared to previous discussions of the same problem. The consequences of the theory are illustrated by numerical examples and applications to published experimental data.
Cross-sectional transmission electron microscopy study of 1.5 MeV Kr+ irradiation-induced amorphization in α-quartz
Authors: Gong W. L. , Wang L. M. , Ewing R. C.
Published: July 2002

Cross-sectional and high-resolution transmission electron microscopy (XTEM and HRTEM, respectively) have been used to characterize ion-beam-induced amorphization of α-quartz irradiated with 1.5 MeV Kr+ ions at room temperature. The accumulation of damage and the growth of the amorphous layers in quartz were studied as a function of ion fluence up to 1.7×1014 ions/cm2. An amorphous band was first observed at the peak displacement damage range, and this region increased in width with increasing ion fluence. These results demonstrate that direct displacement damage by nuclear collision is more efficient than ionization processes in inducing amorphization in quartz. At lower fluences (⩽1.7×1013 ions/cm2), the damage profile observed by XTEM is in excellent agreement with the distribution of displacement damage predicted by TRIM calculations. At higher fluences, the range of the amorphous band measured by XTEM exceeds the depth predicted by TRIM.
Effective energy of nonlinear elastic and conducting composites: Approximations and cross-property bounds
Authors: Gibiansky Leonid , Torquato Salvatore
Published: July 2002

By using similar techniques that were employed in an earlier article on nonlinear conductivity [L. V. Gibiansky and S. Torquato, J. Appl. Phys. 84, 301 1998], we find approximations for the effective energy of nonlinear, isotropic, elastic dispersions in arbitrary space dimension d. We apply our results for incompressible dispersions with rigid or liquid inclusions and, more generally, with a power-law-type shear energy. It is shown that the new approximations lie within the best available rigorous upper and lower bounds on the effective energy. We also develop bounds on the effective energy of nonlinear conducting media with voids or cracks, purely in terms of the effective and phase elastic moduli of the media.
p-type conductivity control of ZnSe with insertion of ZnTe:Li submonolayers in metalorganic molecular-beam epitaxy
Authors: Hirose J. , Uesugi K. , Hoshiyama M. , Numai T. , Suemune I. , Machida H. , Shimoyama N.
Published: July 2002

p-type ZnSe with periodic insertion of ZnTe:Li submonolayers was grown by metalorganic molecular-beam epitaxy. The net acceptor concentration, NA–ND, up to 2×1017–5×1018 cm−3 was observed. However, under higher Li doping, reduction of the growth rate was observed and the growth direction of the islands on the surface changed from the [01̄1] to [011] direction. This resulted in samples not uniformly doped along the growth direction especially for higher Li doping. This reduction of the growth rate was attributed to the adsorption of Li to the B steps, and this phenomenon was suppressed by a periodic Zn purge to the growing surface. By this method, we could keep the growth rate constant and succeeded in obtaining samples which are doped uniformly along the growth direction for higher Li doping. NA–ND up to 4.5×1017 cm−3 was measured in this way. The photoluminescence peaks were blueshifted and discrete peaks were observed with increasing Li doping. This interesting behavior was explained with a ZnTe quantum box model.
Deep level transient spectroscopy of synthetic type IIb diamond
Authors: Zeisel R. , Nebel C. E. , Stutzmann M.
Published: July 2002

Deep level transient spectroscopy (DLTS) and optically excited DLTS are applied to investigate the defect distribution in IIb synthetic diamond. Two defects at 0.83 and 1.25 eV above the valence band edge are detected. Capacitance–voltage measurements reveal a boron doping density of 7×1015 cm−3 and a trap density at 0.83 eV of ≈1015 cm−3. The results are discussed in comparison with data available in the literature.
Optical control of Larmor precession of Mn2+ moments in CdTe/Cd1−xMnxTe quantum wells
Authors: Akimoto R. , Ando K. , Sasaki F. , Kobayashi S. , Tani T.
Published: July 2002

We demonstrate the control of the Larmor precession of Mn2+ moments in CdTe/Cd1−xMnxTe quantum wells by inputting two successive optical short pulses with duration of 200 fs. It is based on our finding that additional carrier injection induces additional Larmor precession of Mn2+ moments.
Fundamental properties and application of Zn1−XMgXS:Mn thin film electroluminescent devices
Authors: Noma Mikihiro , Tanaka Kouichi , Mikami Akiyoshi , Yoshida Masaru
Published: July 2002

By Mg doping of ZnS, the lattice constants and the band gap of Zn1−XMgXS host material were increased. The emission spectrum of Mn in Zn1−XMgXS shifted to shorter wavelengths than that of ZnS:Mn. The electroluminescent (EL) devices fabricated with the source of X=0.32 show 552 nm peak yellowish–green emission. Deposition conditions for the Zn1−XMgXS:Mn phosphor layer were optimized to obtain bright emission. As a result, the Zn1−XMgXS:Mn EL devices have a luminance of 282–333 cd/m2 which is as high as that of the conventional ZnS:Mn EL devices.
Green’s functions theory of eddy currents and forces for conductors in unsteady motion with application to electrodynamic levitation
Authors: Giovachini Jean-Luc
Published: July 2002

A close-form solution to the problem of the unsteady linear motion of an arbitrary current distribution past materials of constant permeability is presented. The application of Green’s functions technique to the field equations yields to integral representations of the induction, eddy currents, and electromagnetic forces. Due to interface coupling of the boundary conditions along the surface of the conductor and taking into account the initial conditions, Green’s functions are shown to satisfy integral equations. In the case of a slab conductor of finite depth, explicit solutions for the Green’s functions are derived. Applications to electromagnetic levitation of forces on moving coils are derived and discussed. This analysis shows and experiments confirm that forces as a function of velocity may be strongly dependent on acceleration, giving in some cases a sort of hysteresis cycle.
Intersubband infrared detector with optimized valence band quantum wells for 3–5 μm wavelength region
Authors: Liu H. C. , Szmulowicz F. , Wasilewski Z. R. , Buchanan M. , Brown G. J.
Published: July 2002

We present results on a p-type intersubband infrared detector for the 3–5 μm wavelength region with optimal quantum well design. For valence band quantum wells made by the AlGaAs/GaAs heterosystem with negligible strain, the ground state subband is the first heavy hole subband, and a structure with the second light hole subband in resonance with the top of the barrier is optimal for normal incidence. Using this resonance design, the fabricated detector shows good performance with a background limited operating temperature of 100 K. Our experiments also show a clear polarization dependence for different intersubband transitions involving heavy hole to heavy hole and heavy hole to light hole processes.
Wide band gap amorphous silicon thin films prepared by chemical annealing
Authors: Futako Wataru , Yoshino Kunihiko , Fortmann Charles M. , Shimizu Isamu
Published: July 2002

High quality wide gap hydrogenated amorphous silicon films were prepared using a hydrogen chemical annealing technique involving the deposition of thin amorphous silicon films followed by a hydrogen radical (and/or ion) treatment. Thick films were prepared by repeating this process many times. The substrate temperature and the hydrogen treatment time can be used to select optical band gaps ranging from 1.8 to 2.1 eV. Low dangling bond defect densities in the as-deposited films ranging from 3 to 8×1015 cm−3 were measured over the entire optical band gap range. The light induced dangling bond densities were less than those found in standard high quality amorphous silicon. The optical band gap is strongly correlated to the medium range structure characterized by the dihydride density. The electronic transport and stability are correlated with the Si–Si bonding environments and the associated short range order including bond angle and bond length distributions.
Microstructural study on the C49-to-C54 phase transformation in TiSi2 formed from preamorphization implantation
Authors: Okihara M. , Hirashita N. , Tai K. , Kageyama M. , Harada Y. , Onoda H.
Published: July 2002

Microstructural characteristics of C49–TiSi2 in narrow lines have been investigated by transmission electron microscopy. The C49–TiSi2 formed by a preamorphization treatment exhibits small grain size and heavily faulted structures. C54 grains are also observed sporadically in the C49 matrix in spite of relatively low temperature range. Moreover, defects circularly distribute around a less-defective region in the vicinity of the C54 grains. The C49 grains in these regions are well aligned with identical crystallographic orientations. These results indicate two-dimensional growth of C49–TiSi2, and the circular defects are introduced by internal stress associated with the growth process. Also the internal stress is considered to enhance the heterogeneous C54 nucleation.
Intensity dependent transmission dynamics in magnetic fluids
Authors: Du Tengda , Luo Weili
Published: July 2002

The time dependent transmission is observed when a laser beam passes through a thin layer of a magnetic fluid. We found that the transmission reaches a peak at a time that depends on the intensity of the incident beam—the peak position shifts to shorter time when the input intensity is increased. The peak value of transmitted power decreases with increasing magnetic field. A simplified model is provided to explain these complex dynamics.
Canting of exchange coupling direction in spin valve with various pinned layers
Authors: Shimazawa K. , Sano M. , Tsuchiya Y. , Kasahara N. , Araki S. , Morita H. , Matsuzaki M.
Published: July 2002

One of the problems in spin valve (SV) is the thermal stability of exchange coupling between the pinned magnetic layer and the antiferromagnetic (AFM) layer. During operating in actual hard disk drives, the pinned direction tends to cant toward the longitudinal hard magnet direction and as a result, the output voltage drops. In this study we examine the amount of the cant by the heat and field in SV which used different pinned layer material. The sample we used is Ta(5)/NiFe(9)/Co(1)/Cu(2.7)/pinned layer/AFM/Ta(5) unit nanometers. The pinned layer is three kinds—Co(2), Co(1)/NiFe(1.7), NiFe(3.5), and AFM is two kinds of Ru3Rh15Mn(12 nm), Ru3Rh15Mn(8 nm). The pinned-Co–SV has a larger increase of canting degree than the pinned-Co/NiFe–SV and the pinned-NiFe–SV. The longer the SV is exposed to heat and magnetic field, the more the cant increases. It is likely due to the change of the local pinned direction which in turn may be due to the aftereffect in the minute AFM grains during the heating process.
Effect of transverse-longitudinal kinetic energy coupling at heterostructure boundaries on quantum transport under the Wigner function formulation
Authors: Kim Kyoung-Youm , Lee Byoungho
Published: July 2002

At heterostructure boundaries under the effective mass approximation, the transverse momentum conservation results in coupling between the longitudinal and transverse kinetic energies. We discuss the effect of this on quantum transport in the resonant tunneling diode (RTD) under the Wigner function formulation, which causes a considerable change in the peak-to-valley ratio that is a major characteristic of the RTD.
Stripping and cleaning of photoresist using low energy neutrals
Authors: Tang Xianmin , Nichols C. A. , Manos D. M.
Published: July 2002

Experimental studies of a broad-area hyperthermal neutral stream source for photoresist cleaning are reported. Low energy neutrals are generated from a high-density inductively coupled plasma by the surface reflection neutralization method. Rates of removal of photoresist polymers such as polymethyl methacrylate as functions of the hyperthermal translational energy and background neutral pressure are reported. The results demonstrate this low energy neutral source provides controllable fast neutrals for cleaning applications. Ex situ and in situ measurements yield typical removal rates of about 10 Å/s without stream collimation. The removal rates at increasing pressures show a trade-off between creating higher density plasma, leading to a greater initial neutral flux and attenuation of neutrals due to collisions. These observations are in good agreement with previous Monte Carlo simulations. The removal rate increases linearly with rf power and is nearly constant as the neutral energy is varied by varying the reflector bias. One consequence of neutral directionality in collimated stream applications is the presence of unremoved carbon compounds on the sidewalls as indicated by angle-resolved x-ray photoelectron spectroscopy.
Oxygen precipitation and secondary defects in silicon by high energy ion implantation and two-step annealing
Authors: Yoon Sahng-Hyun , Kwack Kae-Dal , Ko Bong-Gyun , Park Jea-Gun , Kim Jun-Yup , Ruh Hyun
Published: July 2002

Intrinsic gettering is usually used to improve wafer quality which is an important factor for reliable ultralarge scale integration devices. The two-step annealing method was adopted to investigate the oxygen precipitates and secondary defects in the aspect of various nucleations and growths for 1.5 MeV, 1×1015 As/cm2 implanted wafers. After two-step annealing, the wafers were cleaved and etched with Wright etchant. Oxygen precipitation density observed by optical microscope in lightly boron doped samples was very low. However, in heavily boron doped samples, the density of oxygen precipitation was the largest at 600 °C in the first annealing, and decreased abruptly until 800 °C. But it increased slightly from 800 to 1000 °C and was independent with the implantation. The location and type of secondary defects were inspected by high resolution transmission electron microscopy. The aligned dislocation was located in the vicinity of the amorphous/crystalline interface in the case of the first annealing temperature of 600 °C. But the dislocations climbed to the surface for the first annealing temperature of 700–1000 °C. The difference indicated that the nucleation might be occurring at the first annealing of 600 °C but growth of defects occurred at 700 °C or above.
Theoretical and experimental responses for a large-aperture broadband spherical transducer probing a liquid–solid boundary
Authors: Zhang J. , Guy P. , Baboux J. C. , Jayet Y.
Published: July 2002

A theoretical analysis of a spherical focusing transducer for broadband acoustic microscopy is proposed. The originality of the present contribution is the particular attention we have paid to describe, as rigorously as possible, the diffraction phenomena. Our analysis starts in the harmonic domain with the well-known angular spectrum method, and then gets into the time domain. A new formulation of the angular spectrum in the focal plane has been obtained and compared to other expressions previously reported. This article is deliberately limited to isotropic semi-infinite plane reflectors in order to carry out the inverse Fourier transform in an analytical way. The analytical approach is helpful for the physical interpretation of particular interesting phenomena observed in the transient analysis. A new kind of contribution to the echographic response has been identified and named “geometrical edge waves.” The weight and the arrival time of each discontinuity of the impulse response is analytically evaluated and the physical meaning of each of them is clearly established with the help of a ray model. In the last part of this article, a broadband polyvinylidene fluoride transducer excited by short pulses is used for the experimental validation of the model. The excellent quantitative agreement observed on the time waveforms confirms the efficiency of our approach both in the time domain and in the harmonic one. The comparison between theory and experiment is limited here to some typical examples, but similar results have been obtained on a wide range of defocus and for a large variety of materials. Applications for the characterization of materials will be discussed in future publications.
The species dependence of inert gas ion incorporation in the ion-induced deposition of tungsten
Authors: McLaren M. G. , Carter G.
Published: July 2002

A study of the deposition rates of W thin films by the simultaneous irradiation of a Si substrate with 20 keV ions of Ne, Ar, Kr, and Xe and a flux of molecular W(CO)6 and measurement of the incorporated fraction of the irradiating ion species is described. It is shown that the measured growth rate contains a contribution due to sputtering of the film and, when this is accounted for, the deposition rate increases with increasing ion mass. The ion incorporation rate, on the other hand, decreases with increasing mass and a simple model is developed to explain this behavior in terms of the ratio of individual ion incorporation probability to the net metal atomic growth rate, which compares favorably with the observations.
A quantitative numerical model of multilayer vapor-deposited organic light emitting diodes
Authors: Staudigel J. , Stößel M. , Steuber F. , Simmerer J.
Published: July 2002

A one-dimensional numerical model for the quantitative simulation of multilayer organic light emitting diodes (OLEDs) is presented. It encompasses bipolar charge carrier drift with field-dependent mobilities and space charge effects, charge carrier diffusion, trapping, bulk and interface recombination, singlet exciton diffusion and quenching effects. Using field-dependent mobility data measured on unipolar single layer devices, reported energetic levels of highest occupied and lowest unoccupied molecular orbitals, and realistic assumptions for experimentally not direct accessible parameters, current density and luminance of state-of-the-art undoped vapor-deposited two- and three-layer OLEDs with maximum luminance exceeding 10000 cd/m2 were successfully simulated over 4 orders of magnitude. For an adequate description of these multilayer OLEDs with energetic barriers at interfaces between two adjacent organic layers, the model also includes a simple theory of charge carrier barrier crossing and recombination at organic–organic interfaces. The discrete nature of amorphous molecular organic solids is reflected in the model by a spatial discretization according to actual molecule monolayers, with hopping processes for charge carrier and energy transport between neighboring monolayers.
Limitations on ultrafast optical switching in a semiconductor laser amplifier operating at transparency current
Authors: Kao Y.-H. , Xia T. J. , Islam M. N. , Raybon G.
Published: July 2002

Ultrafast optical switching in a semiconductor laser amplifier (SLA) at transparency current is studied under a strong pump condition. The switch configuration is a nonlinear optical loop mirror with a SLA as the nonlinear element. We demonstrate optical switching with 2 ps recovery time and 60% nonlinear transmission at switching energy of 9 pJ. We find that the transparency current is pump power dependent and that the transparency current is different for uniform 7-bit input control pulses at 100 Gb/s. We believe these two outcomes are due to significant carrier generation via two photon absorption (TPA) at high pump intensity. To verify our hypothesis, we modify coupled propagation equations by including the carrier generation due to the TPA and solve the equations numerically. Good agreement between the experimental and simulation results is obtained. We conclude that to achieve complete pattern-independent 100 Gb/s optical switching using a SLA at transparency current, we have to avoid TPA or use the SLA with a transit time shorter than the control pulse width.
Electrical characterization of He-ion implantation-induced deep levels in p+n InP junctions
Authors: Quintanilla L. , Pinacho R. , Enrı́quez L. , Peláez R. , Dueñas S. , Castán E. , Bailón L. , Barbolla J.
Published: July 2002

The electrical characterization of He-ion implantation-induced deep levels existing in fully implanted p+n InP junctions isolated by He bombardment is reported in this work. An electron trap located at 0.19 eV below the conduction band and a hole trap located at 0.13 eV above the valence band were detected by deep-level transient spectroscopy (DLTS). Several emission characteristics of these traps were extracted from the correlation between DLTS and the capacitance–voltage transient technique. The experimental determination of trap capture properties was also carried out. In particular, the capture kinetics was found to exhibit a strong temperature dependence for both centers. Two experimental methods—direct recording of capture transients and analysis of DLTS peaks—were used to estimate the capture parameters. Finally, some tentative arguments are proposed in order to correlate the results obtained from the thermal emission and capture measurements.
Stability of amorphous Se/Se100−xTex multilayers: A Raman study
Authors: Nesheva D. , Kotsalas I. P. , Raptis C. , Arsova D.
Published: July 2002

The Raman spectra of amorphous Se/Se100−xTex multilayers (AMLs) of various compositions and sublayer thicknesses have been measured at room and low temperature (38 K) with the aim to assess the thermal and absorption effects of laser illumination on the structural stability of the AMLs. Under thermal treatment at room temperature (mediated by increasing gradually the power of the probing laser line), the AML stability (manifested by the rate of Se crystallization) increases with decreasing Se100−xTex sublayer thickness and with decreasing Te content. However, in single layers (2 μm thickness) of Se100−xTex, we have observed the opposite effect, that is, the stability of single layers increases with increasing Te content. This apparent contradiction is explained in terms of thermodynamic energy considerations stated previously [K. Tanaka et al., Mater. Res. Soc. Symp. Proc. 118, 343 (1988)] and of a higher crystallization temperature of Se sublayers in the AMLs than that of bulk Se of the single layer. In order to eliminate (or, at least, reduce considerably) the thermal effects of laser illumination and study the photoinduced structural changes (due to absorption) in Se/Se100−xTex AMLs, low temperature (38 K) measurements were carried out using the 530.9 nm Kr+ laser line which is strongly absorbed by these AMLs. The rate of photoinduced crystallization increases with increasing Te content, which means that their stability to photoinduced changes is (again) higher, the lower the Te content. This is in agreement with previous results concerning three-dimensional Se100−xTex alloys, implying that the dimensionality change (from 3 in the alloys to 2 in the AMLs) does not affect significantly the Se–Se and Se–Te bond energies.
Adsorption site determination of light elements on heavy substrates by low-energy ion channeling
Authors: Lui K. M. , Kim Y. , Lau W. M. , Rabalais J. W.
Published: July 2002

Ion channeling in the low-keV energy range is demonstrated by means of the technique of time-of-flight scattering and recoiling spectrometry. The predictions of the Lindhard string model of ion channeling are compared with the experimental findings. Qualitative agreement was obtained between the experimentally measured critical angles and the predictions of the model. The technique of low-energy ion channeling is shown to be capable of quantitatively probing the positions of light elements on heavy substrates with analysis by simple geometrical constructs. Classical ion trajectory simulations using the scattering and recoiling imaging code were used to observe the details of the ion trajectories. Quantitative analysis of the Pt(111)-(1×1)-H surface using 5 keV Ne+ shows that the hydrogen atoms preferentially populate the threefold fcc sites with a height of 0.9±0.1 Å above the first-layer Pt atoms and a corresponding Pt–H bond length of 1.9±0.1 Å.
Numerical and experimental studies on synthesis of ultrafine nanosize powders of AlN by ion beam evaporation
Authors: Zhu Qifeng , Jiang Weihua , Yatsui Kiyoshi
Published: July 2002

Synthesis of ultrafine nanosize powders by ion beam evaporation (IBE) has been studied numerically and experimentally. Theoretical models have been developed, which involve such physical processes as beam-target interaction, plasma expansion, and the synthesis of powders. The macroscopic properties of the ultrafine powders have been predicted. As an application of our models, the macroscopic properties of AlN powders synthesized by IBE with an AlN target have been predicted. The energy density, pulse width, and spot size of the ion beam are 20 J/cm2, 70 ns, and 1 cm2, respectively. The main results have shown that the particle size distribution is log normal and that 70% of all particles exist between 20 and 40 nm. The average diameter and the specific surface area are ∼30 nm and ∼50 m2/g, respectively. Experimentally, the ultrafine AlN powders have been successfully synthesized by IBE, which has been verified by x-ray diffraction and transmission electron diffraction. Furthermore, particle size distributions have been obtained by transmission electron microscopy. The experimental results are found to be in a reasonable agreement with the numerical studies.
Amplified spontaneous emission and optical gain spectra from stilbenoid and phenylene vinylene derivative model compounds
Authors: Kretsch Kevin P. , Belton Colin , Lipson Stephen , Blau Werner J. , Henari Fryad Z. , Rost Henning , Pfeiffer Steffen , Teuschel Annett , Tillmann Hartwig , Hörhold Hans-Heinrich
Published: July 2002

We report single-pass optical gain measurement in poly(styrene) waveguides doped with stilbenoid and phenylene vinylene derivative model compounds under picosecond excitation. Using a wavelength dependent model of amplified spontaneous emission, we produce optical gain spectra for these materials. Net optical gains of g=15–20 cm−1 are deduced. The spectra also exhibit features consistent with excited state absorption and fluorescence depletion via stimulated emission. A figure of merit describing the potential of a material for use as a laser medium is presented and comparisons with other recent publications are made. This comparison indicates that organic materials can compete with inorganic semiconductors for optically pumped applications.
Microstructure and electrical resistivity of Cu and Cu3Ge thin films on Si1−xGex alloy layers
Authors: Aboelfotoh M. O. , Borek M. A. , Narayan J.
Published: July 2002

We have studied the reaction between Cu and ε1-Cu3Ge thin films and Si1−xGex (x=0.5) alloy layers epitaxially grown on Si(100) in the temperature range of 250–400 °C. In this temperature range, Cu reacts with the alloy to form a Cu3Si1−xGex ternary phase with an ordered body-centered-cubic crystal structure, and no Ge segregation occurs during the reaction. Unlike ε1-Cu3Ge, the Cu3Si1−xGex films exhibit a high-room-temperature resistivity of ∼150 μΩ cm. However, the Cu3Si1−xGex phase is not observed when Ge is added to Cu to form ε1-Cu3Ge. In contrast to the results reported for films of ε1-Cu3Ge formed on Si(100) substrates, the outdiffusion of Si into the ε1-Cu3Ge films is found to be suppressed when the films are formed on Si0.5Ge0.5 layers at temperatures up to 500 °C, and their resistivity remains low (typically less than 10 μΩ cm at room temperature), indicating the increased stability of ε1-Cu3Ge on Si1−xGex alloys. Furthermore, the ε1-Cu3Ge films form a sharp interface with the Si0.5Ge0.5 layers. These results indicate that ε1-Cu3Ge is an attractive candidate for contacts to SiGe-based devices.
Near-field probing control of optical propagation in bidimensional guiding mesostructures
Authors: Mulin David , Spajer Michel , Courjon Daniel , Carcenac Franck , Chen Yong
Published: July 2002

Scanning near-field optical microscopy is used for analyzing both the interaction of light with mesostructures and the capability of wave transfer between two macrowaveguides coupled by a matrix of periodic mesostructures. A spectral analysis shows the influence of the wavelength in such a configuration.