bluuebunny/crossref_metadata_2025 huggingface dataset:
Substitutional versus interstitial carbon incorporation during pseudomorphic growth of Si1−yCy on Si(001)
Authors: Osten H. J. , Kim Myeongcheol , Pressel K. , Zaumseil P.
Published: July 2002

Molecular beam epitaxial growth of Si1−yCy alloys pseudomorphically strained on the (2×1) reconstructed Si(001) has been investigated as a function of growth conditions. An important question concerns the relation between substitutional and interstitial carbon incorporation, which has a large impact on electrical and optical properties of these layers. We show that the interstitial-to-substitutional carbon ratio is strongly influenced by the growth conditions, such as growth temperature and Si growth rate. Both reduction in growth temperature and increase of the overall growth rate lead to an increase in the substitutional-to-interstitial carbon ratio. However, these changes in growth conditions can also cause some deterioration in crystal quality. The carbon incorporation behavior is well described by first order kinetics.
Time-resolved optical waveguide study of the reorientation in a nematic liquid crystal under applied electric field
Authors: Mitsuishi M. , Ito S. , Yamamoto M. , Fischer T. , Knoll W.
Published: July 2002

The reorientation behavior of nematic liquid crystal molecules induced by an electric pulsed field was investigated by means of time-resolved optical waveguide spectroscopy (TROWS) which was developed to observe transient changes in dielectric constants and to measure the thickness of a thin dielectric medium. Time evolution of the waveguide mode patterns was successfully obtained by using TROWS, which records the reflectivity as both functions of the incident angle of laser light and the time from switching-on or -off of the external electric field. The transient dielectric tensor profile in the 4′-pentyl-4-cyanobiphenyl (5CB) layer both after switching-on and -off of the electric field could be precisely determined in a three-dimensional coordinate system by using Deuling’s theory which treats the orientational deformation induced by an external electric field. Theoretical analysis of TROWS data clearly indicated that half of the 5CB molecules rotate clockwise in the plane defined by the rubbing direction and the substrate normal, and the other half rotates counter-clockwise in the same plane. The counter rotation compensates the effect of birefringence observed in the direction parallel and perpendicular to the rubbing direction and the reorientation kinetics could be well described by the Ericksen–Leslie equation. Relaxation behavior from homeotropic to planar orientation could be treated as an orientation diffusion process by applying a Gaussian distribution function to the maximum tilting angle at the middle of the cell. We report the usefulness of TROWS which provided more detailed information about the dynamics of the 5CB molecules.
Growth, structure and electrical properties of epitaxial thulium silicide thin films on silicon
Authors: Travlos A. , Salamouras N. , Boukos N.
Published: July 2002

Thulium silicide thin films were grown on (100) and (111) Si by evaporation of Tm metal and Si layers and annealing in a vacuum. Electron microscopy and x-ray diffraction results showed that the TmSi2−x layers are of high crystalline quality grown epitaxially on Si. Electrical resistivity measurements showed that TmSi2−x layers are metallic exhibiting magnetic ordering below 3 K.
Perpendicular conductance and magnetic coupling in epitaxial Fe/MgO/Fe(100) trilayers
Authors: Keavney D. J. , Fullerton E. E. , Bader S. D.
Published: July 2002

A series of Fe/MgO/Fe(100) trilayer structures with MgO thicknesses ranging from 12 to 1000 Å was grown at 75 °C by molecular beam epitaxy. The structures are all epitaxial, and for MgO thicknesses below 75 Å, the Fe layers are ferromagnetically coupled. The MgO spacer thickness dependence of the coupling energy shows a change in slope at 25 Å, suggesting a change in growth morphology. Perpendicular transport measurements show ohmic current-voltage characteristics with high conductance up to 1000 Å MgO interlayer thicknesses, indicating that the coupling is not due to spin-dependent tunneling. Investigations of the growth morphology reveal the existence of ferromagnetic bridges across the MgO layer.
Electric field induced domain rearrangement in potassium niobate thin films studied by in situ second harmonic generation measurements
Authors: Gopalan Venkatraman , Raj Rishi
Published: July 2002

We report a sensitive technique to study domain rearrangement in ferroelectric thin films using in situ second harmonic generation (SHG) measurements. The following film system on a MgO substrate was studied: KNbO3(110)‖120 Å SrTiO3(100)‖MgO(100). From x-ray diffraction, four possible domain variants in the film growth plane were determined to be KNbO3[11̄0]‖SrTiO3 and MgO[001], [001̄], [010], or [01̄0] denoted as variants X+, X−, Y+ and Y−, with area fractions AX+, AX−, AY+ and AY−, respectively, in the film growth plane. The SHG signal (532 nm) from the films generated by a transmitted fundamental beam of 1064 nm was measured and theoretically correlated to the area fractions of different domain variants in the film. The magnitude and signs of net area fractions (AX+−AX−) and (AY+−AY−) were determined as a function of external field applied along the MgO〈001〉 direction in the film growth plane. No remnant poling was observed in KNbO3 films after application and removal of external fields up to 10 kV/cm at room temperature. We propose mechanisms to correlate this behavior to the pinning of domain wall motion by low angle grain boundaries in KNbO3.
CF2 kinetics and related mechanisms in the presence of polymers in fluorocarbon plasmas
Authors: Tserepi A. D. , Derouard J. , Booth J. P. , Sadeghi N.
Published: July 2002

Laser-induced fluorescence was used to characterize the fluorocarbon plasma that was used to modify the wettability of hexatriacontane (HTC), a polymer model. The plasma volume downstream from a microwave plasma source was examined by monitoring the CF2 concentration as well as the CF2 decay rate (in the afterglow of a pulsed discharge) during treatment of the polymer surface (in 20–100 mTorr CF4). In parallel, the behavior of F atoms was monitored by means of actinometric optical emission. Pulsed modulation of the discharge allowed the effects of variations in the loss and production rates for CF2 to be distinguished, in the presence of hexatriacontane. Our observations are consistent with enhanced production of CF2, possibly by an ion-assisted surface mechanism, in the presence of HTC.
Fiber coupled ultrafast scanning tunneling microscope
Authors: Keil Ulrich D. , Jensen Jacob R. , Hvam Jo/rn M.
Published: July 2002

We report on a scanning tunneling microscope with a photoconductive gate in the tunneling current circuit. The tunneling tip is attached to a coplanar transmission line with an integrated photoconductive switch. The switch is illuminated through a fiber which is rigidly attached to the switch substrate. By using a firmly attached fiber we achieve an excellent reproducibility and unconstrained positioning of the tip. We observe a transient signal with 2.9 ps pulse width in tunneling mode and 5 ps in contact mode. The instrument is applied to investigating the mode structure on a coplanar waveguide. The measurements show that the probe works as a transient voltage detector in contact and a capacitively coupled transient field detector in tunneling mode. We do not measure the transient voltage change in the ohmic tunneling current. In this sense, the spatial resolution for propagating electrical pulses is better in contact mode than in tunneling mode.
Roughness of the porous silicon dissolution interface
Authors: Lérondel G. , Romestain R. , Barret S.
Published: July 2002

We present a study of the fluctuations in the dissolution front observed during the formation of porous silicon, leading finally to layer thickness inhomogeneities. Two types of fluctuations were revealed, one at the millimeter scale (waviness) and the other one at the micrometer scale (roughness). Root mean square amplitudes are comparable. In both cases fluctuations of the dissolution velocity can be invoked and we discuss their dependence on the current density and viscosity of the solution. The large scale fluctuations are attributed to planar resistivity fluctuations in the wafer. The second type of fluctuation displays a typical spatial periodicity comparable to the wavelength of the light so that a statistical characterization can be performed by optical measurements. The Davies–Bennett model quantitatively describes the induced light scattering. Remarkably, these fluctuations increase linearly with the layer thickness up to a critical value where a saturation regime is observed. In order to explain this behavior, we show the importance of the initial surface state of the wafer and of the porous medium.
Exciton-induced tunneling effect on the current-voltage characteristics of resonant tunneling diodes
Authors: Cao S. M. , Willander M.
Published: July 2002

Tunneling transport assisted by the Coulomb interaction of Wannier–Mott exciton is investigated within the framework of the sequential tunneling formalism. The exciton-assisted tunneling (EAT) probability is derived from Bardeen’s transfer Hamiltonian. The EAT-induced current-voltage (I-V) characteristics are evaluated using a set of three-particle rate equations for double-barrier and triple-barrier tunneling structures. We found that the EAT results in additional current at low bias voltages with respect to the resonant tunneling (RT) current. Their offset in the I-V spectra is associated to the exciton binding energy. The current intensity of the electron EAT is dependent on the quantum-well hole density as well as the exciton Bohr radius. Calculated I-V characteristics of electron tunneling via the heavy-hole excitonic states are presented and discussed for typical AlxGa1−xAs/GaAs nanostructures. In particular, the line shape of the EAT I-V spectra is shown to have a fingerprint distinguishable from that of the RT at low temperature.
Electronic structure of FM|semiconductor|FM spin tunneling structures
Authors: Butler W. H. , Zhang X.-G. , Wang Xindong , van Ek Jan , MacLaren J. M.
Published: July 2002

We have calculated the electronic structure of the spin-dependent tunneling structures, Fe|Ge|Fe and Fe|GaAs|Fe, using first principles techniques. We find that there is a large charge transfer from the metal layer to the semiconductor layer; 0.21 electrons are transferred from Fe to Ge and 0.27 electrons are transferred from Fe to GaAs at each interface. The density of states of the interfacial metal layer is dramatically different from the other metal layers; there is a large peak in the density of states at the Fermi energy for the minority electrons. The electronic structure of the semiconductor layer is quite different for the majority and the minority spins although its total magnetic moment is negligible. Our results suggest that the theory of spin-dependent tunneling using the simple model of a potential barrier or a model based on densities of states taken from bulk band structures may not apply to these systems.
Magnetization change due to stress change in a constant magnetic field on amorphous ribbons
Authors: Yamamoto Ken-ichi , Sasaki Tadashi , Yamashiro Yasumasa
Published: July 2002

Magnetization changes due to stress change in a constant magnetic field on amorphous ribbons are investigated. The magnetization change due to stress is divided into reversible and irreversible components. These occur simultaneously, and can be observed in the domain structure. The reversible magnetization change occurs with rotations in the magnetization vector due to stress, and a corresponding change in the domain structure. The irreversible magnetization change occurs mainly in the small stress regime. The magnetization change results from a stress induced anisotropy field which is calculated from the magnetoelastic energy, which was reduced by an amount of energy associated with the reversible magnetization change. Calculated values show good agreement with experimental results.
Effect of bar width on magnetoresistance of nanoscale nickel and cobalt bars
Authors: Jia Yong Qiang , Chou Stephen Y. , Zhu Jian-Gang
Published: July 2002

The anisotropic magnetoresistance (AMR) of nickel and cobalt bars of 1 μm length, 35 nm thickness, and width varying from 50 to 500 nm is studied. As the bar width is reduced from 500 to 50 nm, longitudinal MR change decreases from 0.8% to 0.2% and transverse MR change increases from 1.3% to 1.8% for the Ni bars; longitudinal MR change is zero and transverse MR change is constant at 1.6% for the Co bars. The zero longitudinal MR is attributed to a single-domain magnetization. The AMR value indicates that the electron scattering from bar edges has little effect on AMR even in a 50 nm width. Furthermore, strong, repeatable Barkhausen noise is observed in the Co bars with a width larger than 200 nm, which can be explained by a micromagnetic model.
Large deformation and geometric instability of substrates with thin-film deposits
Authors: Finot M. , Blech I. A. , Suresh S. , Fujimoto H.
Published: July 2002

Experimental and theoretical results are presented on the evolution of large elastic deformation, non-uniform curvature, shape changes and geometric instability in substrates of Si wafers with metal films. The critical diameter and thickness of the Si wafer, for which large deformation and shape instability occur, are identified, as functions of the line tension in the film (which is the product of the biaxial stress in the film and the film thickness). Observations of the curvature and shape variations along the wafer diameter and geometry-dependence of the shape instability compare favorably with those predicted by detailed finite element analyses.
Effect of grain size, cluster size, and crystallographic orientation upon simulation of longitudinal recording media
Authors: Nolan T. P. , Hara M. , Yoshida K. , Futamoto M.
Published: July 2002

Simulations of hexagonal magnetic particles with uniform exchange energy and random c-axis in-plane orientation do not reproduce real media magnetic properties. Simulation software was thus modified to model four experimentally observed Co-alloy microstructures, to distinguish the effects of grain size, cluster size, exchange decoupling, and cluster substructure; and to more accurately model real media behavior. Results include: (1) Clusters of isolated uniaxial particles act like single grains having the cluster size. Exchange decoupling on a size scale smaller than the crystallographic grain size has little effect upon hysteresis loops or media noise. (2) The magnetic properties of clustered bicrystal and randomly oriented media depend on the exchange interactions within and between clusters of grains. Media hysteresis loops and recorded tracks are well simulated using exchange energies within randomly oriented or bicrystal grain clusters up to ten times larger than those used in the standard model.
Semiclassical electrical current expressions for materials with position-dependent band structure in the near equilibrium approximation
Authors: Marshak Alan H. , Van Vliet Carolyne M.
Published: July 2002

Electrical current density expressions for electrons and holes for materials with position-dependent band structure are presented. This includes materials with nonuniform composition and devices with highly doped regions. Changes in the energy-band edges due to spatial variations in electron affinity and band gap, and spatial variations in the local kinetic energy produce terms in the current-density equations in addition to those for the homogeneous case. These new terms are derived and discussed. The development proceeds from the Boltzmann transport equation. The focus will be on the conceptual framework and the limitations in the underlying theory. Errors in the literature are noted where appropriate. The results are relevant to semiconductor device physics and analysis.
Hall effect in semiconducting epitaxial and amorphous Y-Ba-Cu-O thin films
Authors: Shan Pao-Chuan , Jahanzeb Agha , Butler Donald P. , Çelik-Butler Zeynep , Kula Witold , Sobolewski Roman
Published: July 2002

An experimental study of the Hall effect in nonmetallic Y-Ba-Cu-O thin films is reported. Both epitaxial crystalline YBa2Cu3O6+x (x⩽0.5) and multiphase/amorphous Y-Ba-Cu-O thin films were studied. The structure of the samples was measured by x-ray diffraction and Raman microprobe. The amorphous Y-Ba-Cu-O samples were found to have a grain size of about 100 Å. The conduction properties were studied and analyzed for the two types of samples over a wide temperature range including room temperature. The Hall effect measurements showed positive charge carriers with a concentration ranging from 1017 to 1020 cm−3 at room temperature. The mobility was found to decrease with higher Hall carrier concentration. The empirical relationship for the mobility dependence on impurity concentration agreed with the relationship between mobility and the experimental Hall carrier concentration, suggesting that the same localized states were responsible for both providing the carriers and reducing the mobility through scattering. It was also observed that the mobility values for both amorphous and crystalline samples followed the same empirical curve, a result which showed that the conduction mechanisms in the epitaxial (tetragonal) and amorphous Y-Ba-Cu-O materials are very likely to be similar despite the differences in the composition and structure of the films. The similarity is consistent with other work that concludes that the conduction mechanism occurs along the copper oxide planes. Our work implies that the conduction mechanism operates over a short range, less than the 100 Å grain size of the amorphous, such that the lack of order in the amorphous samples was essentially irrelevant to the charge transport.
Electron attachment to excited states of silane: Implications for plasma processing discharges
Authors: Pinnaduwage Lal A. , Datskos Panos G.
Published: July 2002

Observation of enhanced negative-ion formation in ArF–excimer–laser irradiated silane was reported in a recent paper [L. A. Pinnaduwage, M. Z. Martin, and L. G. Christophorou, Appl. Phys. Lett. 65, 2571 (1994)]. In that paper, preliminary evidence was presented to show that highly excited electronic states of silane or its photofragments could be responsible for the observed enhanced negative-ion formation. In the present paper, we report evidence, obtained using a new experimental technique, that the electron attaching species are high-Rydberg (HR) states of silane indirectly populated via laser irradiation and show that an absolute lower bound for the corresponding electron attachment rate constant is ∼4×10−7 cm3 s−1. The initial capture of the electron by the HR states is likely to be a diabatic process and the large polarizabilities associated with the HR states appear to be responsible for the observed large electron attachment rate constants. We also measured electron attachment to thermally excited vibrational states of the ground electronic state of silane, which showed no measurable electron attachment up to 750 K. Implications of these observations in modeling of silane discharges used for plasma processing of amorphous silicon are discussed. It is also pointed out that large negative ion formation observed in many “weakly electronegative” plasma processing gas discharges could be due to enhanced electron attachment to HR states: such states could be populated via direct electron impact and/or via excitation transfer from the metastable states of rare gases that are commonly used in these processing discharges.
Effect of surface anisotropy on the coercive field of small magnetic particles
Authors: Zianni X. , Trohidou K. N. , Blackman J. A.
Published: July 2002

Monte Carlo calculations were used to study the coercive behavior of small spherical ferromagnetic particles as a function of particle size and temperature. The influence of the surface anisotropy on the coercive field is discussed. Enhancement of the coercive field compared to its bulk value is observed in particles surrounded by a spherical cell with enhanced anisotropy while in the pure ferromagnetic particles an enhanced surface anisotropy with the easy axis normal to the surface does not give such enhancement. These results are in agreement with experimental findings.
Permeability spectra of hole arrays defined on single layer Permalloy thin films
Authors: Grimes Craig A. , Trouilloud Philip L. , Lumpp Janet K. , Bush Gary C.
Published: July 2002

Although considerable work has been done investigating the properties of arrays of magnetic elements, there have been few investigations on the reverse geometry, i.e., an array of nonmagnetic regions defined within a magnetic thin film. The 10 Hz BH loops, 10–500 MHz permeability spectra, and domain patterns of homogeneous, single layer 100 nm radio frequency (rf) sputtered Ni81Fe19 thin films with arrays of 23-, 50-, and 100-μm-diam holes defined by laser ablation were measured. The holes were defined in a grid along the hard and easy axes of the sample. Letting (x,y) represent, respectively, the hole spacing parallel to the easy and hard axes, the point to point spacing of the ablated circular regions was varied from (5, 2 mm) to (0.1, 0.1 mm).
Surface plasmon scanning near-field optical microscopy
Authors: Kryukov A. E. , Kim Y.-K. , Ketterson J. B.
Published: July 2002

We have constructed a surface plasmon scanning near-field optical microscope. Surface plasmons (SP) are excited by laser light at the silver–air interface in the Kretschmann attenuated total reflection geometry. A scanning tunneling microscope or atomic force microscope tip penetrates the evanescent electromagnetic field and serves as a scatterer of the SP’s which, in turn, radiate conical electromagnetic waves. The conical radiation is collected on a photodiode by an annular mirror or a fiber-optic bundle. It is shown that the SP’s are predominantly scattered in the forward direction. The conical radiation intensity is recorded as a function of the tip position, creating an optical image of the silver surface. It is demonstrated that the technique’s spatial resolution is determined by the tip size, rather than the wavelength of light, though the interference of the scattered SP’s creates interference patterns that may present a problem.
Fowler–Nordheim tunneling current oscillations at metal/oxide/Si interfaces
Authors: Hebert K. J. , Irene E. A.
Published: July 2002

Fowler–Nordheim tunneling current oscillations are used to investigate two metal/oxide/Si interfaces: n+ polysilicon/oxide and oxide/p-Si interfaces on the same samples for p-Si substrate metal–oxide–semiconductor devices. Electron injection from the p-Si substrate is facilitated by the application of visible light during the I–V measurement in order to create and inject sufficient carriers into the SiO2 conduction band. We compare the interfaces of thermal with rapid thermal silicon oxides prepared with nitrogen. We find that these two processes yield the same quality of interfaces. An analysis of the magnitude of the current oscillations indicates that the oxide/Si interface is superior to the polysilicon/oxide interface. Oxide thicknesses are determined from the oscillations at each interface for devices fabricated on the same wafer, and the requirement of constant film thickness enables the (uncertain) value of the barrier at the p-Si injecting electrode to be approximated at 2.80±0.1 eV.
Photoluminescence processes in Si1−xGex/Si disordered superlattices grown on Si(001) substrate
Authors: Wakahara Akihiro , Kuramoto Kyosuke , Hasegawa Toshimichi , Noda Susumu , Sasaki Akio
Published: July 2002

Photoluminescence (PL) properties of Si1−xGex/Si disordered superlattices (d-SLs) are investigated. Two types of d-SLs with various Ge compositions (x<0.55) and various averaged superlattice periods are grown for experiments. The PL intensity ratio I(d-SL)/I(o-SL), the redshift energy, and the characteristic temperature T0 are strongly affected with Ge composition variation but not with averaged superlattice period variation. Small improvement of the ratio of no-phonon (NP)/TO-phonon assisted PL intensities by the Si1−xGex/Si disordered structure suggests that the disorder effect on the increase in NP recombination probability is not as large as expected by other disordered superlattices. The reasons are (1) the weak electron localization and (2) the difference in the directions between momentum ambiguity caused by the localization and the momentum required for recombination. Thus, improved PL properties for SiGe/Si d-SL are mainly owing to the strong hole localization by increased valence-band offset.
Unsteady plane smooth wave fronts of combined growing-attenuating type
Authors: Sano Yukio , Miyamoto Isamu , Arathoon Peter
Published: July 2002

Unsteady plane smooth wave fronts of a combined growing-attenuating type, where the peak of each strain wave is growing, are derived by a qualitative analysis. There are three different modes in this combined type: In mode I, the peak of a particle velocity wave is growing, but that of a stress wave is attenuating; in mode II, the former is attenuating, but the latter is growing; in mode III, both are attenuating. Three possible wave fronts belong to mode I, five to mode II, and three to mode III. Five new elementary waves are found in these eleven wave fronts. The wave fronts near the impacted surface of sandstone detected by the previous quantitative analysis [Sano, J. Appl. Phys. 73, 118 (1993)] are identified with some of the eleven possible wave fronts. As a result, the theoretical existence of several new wave fronts and a new elementary wave is verified. The equation for the stress at the impacted surface indicates that strain acceleration is responsible for the formation of the wave fronts of the combined type, which cause an anomalous response, and hence it should be included in the constitutive relations which describe the response.
SiO
2
aerogel film as a novel intermetal dielectric
Authors: Jo Moon-Ho , Park Hyung-Ho , Kim Dong-Joon , Hyun Sang-Hoon , Choi Se-Young , Paik Jong-Tae
Published: July 2002

A low dielectric constant material for an intermetal dielectric (IMD) is imperative to reduce power dissipation, cross talk, and interconnection delay in the deep submicron device regime. SiO2 aerogel is one of the possible candidate with an inherent low dielectric constant. This article reports on the results of the successful fabrication of a SiO2 aerogel film as well as its material properties and electrical properties. Fundamental physical, chemical, and electrical material properties were evaluated for a SiO2 aerogel film before and after thermal treatment. An inherent low dielectric constant of 2.0 was realized for about 70% porosity of the SiO2 aerogel film and the leakage current density held at a level of 10−7 A/cm2. Preliminary results of the SiO2 aerogel film investigated in our study represent a very positive prospective to IMD applications.
Infrared ellipsometry study of evaporated SiO2 films: Matrix densification, porosity, water sorption
Authors: Brunet-Bruneau A. , Rivory J. , Rafin B. , Robic J. Y. , Chaton P.
Published: July 2002

The dielectric function of SiO2 films deposited by electron-beam evaporation on silicon substrates is determined by infrared ellipsometry between 700 and 5000 cm−1 one month after venting. Analysis of the absorption band associated with the Si–O–Si stretching mode at about 1075 cm−1 and of the water absorption band at about 3300 cm−1 enables the complex structure of the films, modeled as a densified silica matrix with pores partially or fully filled by water, to be characterized. The film density and visible refractive index values, which are estimated from the infrared parameters, are compared with the measured ones. A quantitative analysis of the wide water band, in which the contributions of three vibration modes (H–OH bonds, isolated Si–OH bonds, and neighboring Si–OH bonds) are clearly identified, shows that the Si–OH bond contribution is equal to 50% of the H–OH bond. This value is independent of the deposition parameters and seems to be representative of a particular type of porosity present in porous dielectric thin films.
Limits of different detection schemes used in the optical beam deflection method
Authors: Garcı́a-Valenzuela A.
Published: July 2002

The theoretical performances of a split detector and a lateral effect detector used as a position sensitive device in the optical beam deflection method are compared. It is shown that the limit to the resolution in both cases is essentially equal. The possibility of improving the resolution in angle deflection by reflecting the beam from a cylindrical mirror, as was recently proposed by A. Yarai, Y. Fukunaga, K. Sakamoto, and T. Nakanishi [Jpn. J. Appl. Phys. 33, 3251 (1994)] is also explored. It is shown that using a cylindrical mirror does not result in a smaller theoretical limit to the resolution. However, it does improve the resolution in some cases and may have practical uses.
Channeling and diffusion in dry-etch damage
Authors: Rahman M.
Published: July 2002

At present channeling is accepted to be the primary mechanism causing defects deep within dry-etched material, with diffusion possibly modifying the final defect distribution. In this article detailed analytic expressions are presented incorporating both these mechanisms. The dominant parameter affecting damage depth is found to be the mean channeling length. We show how enhanced diffusion, e.g., by illumination, may increase the observed damage. We also study the effect of damage on depletion depths and suggest how the channeling length may be inferred from the etch-depth dependence of conductance or Raman spectroscopy measurements.
Electron nuclear double resonance of stable Rh centers in solution-grown NaCl single crystals
Authors: Zdravkova M. , Vrielinck H. , Callens F. , Boesman E. , Vercammen H. , Schoemaker D.
Published: July 2002

Unlike the photographically important silver halides, large NaCl single crystals can be grown from solution. In such NaCl crystals, with doping comparable to practical AgCl and AgBr microcrystals, three stable Rh centers were detected and studied by electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR). The primary center was identified as a nonlocally compensated [RhCl6]4− complex, at variance with earlier reported EPR work. By lack of sufficient EPR and/or ENDOR evidence, the identity of the two other Rh related centers with orthorhombic and isotropic symmetry respectively, remains rather speculative.
Temperature dependent optical resonances of quantum confined CuCl nanocrystals in borosilicate glasses
Authors: Yoon Y. K. , Han W.-T.
Published: July 2002

The optical density change of the CuCl-doped borosilicate glasses (2 wt% CuCl +52.5SiO2−40B2O3−7.5Na2O(wt%)) heat treated at 550 °C for 0–10 hrs was measured with temperature at spectral vicinity of the CuCl resonant absorption and the effect of size and distribution of CuCl precipitate particles on the optical spectra was investigated. The optical absorption spectrum obtained during heating and cooling cycle showed a typical hysteresis loop because of the melting and solidification of the CuCl particles embedded in the glass matrix. The shape of the optical absorption curve measured at 375 nm with temperature upon melting of CuCl particles was dependent on the size and the distribution of the CuCl particles. While the average size of the CuCl particles increased with heat treatment time, the size difference of the precipitated CuCl particles was found to be decreased with time before 1 h and then increased. The optical absorption spectra of the CuCl doped glass was also predicted theoretically and the predicted spectra curve was found to be in good agreement with experimental data. It is proposed that if the semiconducting particles embedded in an optically transparent matrix and the melting point of semiconductor is lower than that of the matrix material, the average size and size distribution of the particles can be estimated by the optical absorption measurements with temperature.
Effects of dopant concentration, crystallographic orientation, and crystal morphology on secondary electron emission from diamond
Authors: Miller John B. , Brandes George R.
Published: July 2002

Secondary electron emission properties from crystalline and polycrystalline diamond films containing different boron concentrations were measured. The secondary electron yields δ were high. Yields were independent of incident beam angle and crystallographic orientation. The secondary electron yields were greatest for boron concentrations of 1019 – 1020 cm-3. The angular distribution was peaked about the surface normal with a half width at half maximum of 37±7°. The secondary electron yield decreased with prolonged energetic electron beam bombardment. The energy distribution of the emitted electrons contained a large, relatively narrow, low energy peak that disappeared with extended electron beam bombardment. The large secondary electron yields and narrow energy distributions of the emitted electrons were consistent with nearly thermalized electron emission from negative electron affinity states.
Microstructure of Co–Al–O granular thin films
Authors: Ohnuma M. , Hono K. , Abe E. , Onodera H. , Mitani S. , Fujimori H.
Published: July 2002

We have investigated the microstructures of Co–Al–O granular thin films, which were prepared by the sputter-deposition technique with various oxygen partial pressures. The constituent phases, grain sizes of granular particles, and width of insulating channels have been evaluated quantitatively. The specimen with the optimum giant magnetoresistance (GMR) is composed of nanoscale Co particles, and these are completely isolated by amorphous aluminum oxide channels. The GMR behavior observed in the Co–Al–O films has a close correlation with the width of the insulating channel and the grain size of the magnetic particles, which is consistent with the spin-dependent tunneling conduction mechanism of GMR
Finite element analysis of the effects of geometry and microstructure on electromigration in confined metal lines
Authors: Liu Yongkun , Cox C. L. , Diefendorf R. J.
Published: July 2002

A simple mathematical model based on atomic drift and diffusion is advanced to describe electromigration-induced stress in confined metal lines. Using a finite element approach, a MATLAB program was developed to simulate stress evolution in lines with variable geometry and microstructure under different boundary conditions. The simulation results show that the contact pads connected to the line end in the National Institute of Standards and Technology (NIST) test structure postpone the stress buildup in a microstructurally homogeneous line and the time to reach a certain stress is proportional to the pad sizes when the pads are much wider than the line. Subtractive defects are not the preferred failure sites when the defects fall on a wide polycrystalline line or a bamboo structure line. In a narrow polycrystalline conductor with a distribution of grain size, a subtractive defect may result in an abrupt change in the effective diffusion coefficient (blocking effect) along the line and quick buildup of the stress at the defect site. The stress at a center blocking site in a 190 μm line reaches maximum in 146 h, under 1 MA/cm2 and at 200 °C. Electromigration lifetime is most sensitive to distribution of grain size and variation of the linewidth when the linewidth is a few times average grain size. For a near bamboo structure line, the evolution of the stress after local quasisteady state is affected by line end conditions as well as by distribution of the polygranular clusters. Under a constant source boundary condition, the maximum stress at final steady state depends on the length and distribution of individual polygranular clusters in a line. Under blocking end conditions, the stress distribution in final global steady state (if it exists) is determined by electrical current density and is independent of microstructure of a line. The cluster/bamboo juncture is the most severely stressed site in the early stages, and the blocking line end will finally become the most severely stressed site if the line does not fail at an early time. The magnitude of the maximum stress at the cluster/bamboo juncture at the local steady state depends on the ratio of the effective diffusivity of the cluster to that of the bamboo segment, Dg/Db, as well as on the cluster length and current density.
1/f
noise investigations in small channel length amorphous silicon thin film transistors
Authors: Rhayem J. , Valenza M. , Rigaud D. , Szydlo N. , Lebrun H.
Published: July 2002

Conduction and low-frequency noise are analyzed in hydrogenated amorphous thin film transistors with small channel length. From current–voltage characteristics a set of conduction parameters is extracted pointing out parasitic resistances in series with the active channel. The low-frequency noise behavior is studied by means of the small equivalent circuit of the device. Intrinsic channel noise is separated from access resistance noise. Channel noise variations versus device biases agree with Hooge’s theory (carrier mobility fluctuations) but the noise levels are greater than in crystalline metal-oxide-semiconductor transistors. For high drain current 1/f noise in access series resistances prevails and becomes the main noise source. So, the results show the important part taken by these resistances in conduction and noise. Some comments for the design of thin film transistors are given.
Chromaticity and electroluminescent efficiency of atomic layer epitaxy SrS:Ce thin films
Authors: Warren W. L. , Seager C. H. , Soininen E. , Benalloul P. , Barthou C. , Sun S.-S.
Published: July 2002

We have studied various factors that control the luminous properties of atomic layer epitaxy (ALE) SrS:Ce electroluminescent (EL) devices by using electron paramagnetic resonance, photoluminescent decay, x-ray diffraction, and charge-voltage characterization. EL and PL light is green shifted in ALE SrS:Ce films, compared to powders and thin films prepared with some other techniques. The origin of the green shift is discussed. Moderate heat treatments of as-deposited SrS:Ce devices were found to dramatically improve the EL efficiency. This is due to the removal of defects leading to nonradiative Ce3+ decay and to reduction of Ce4+ to radiative Ce3+. Different heat treatments were found to influence the transferred charge, so that there is an optimal heat treatment temperature between 500 and 750 °C. Heat treatments also induce macroscopic stress in these SrS:Ce films. This was seen to induce a local stress around Ce3+ sites. However, the stresses were not found to directly correlate with the luminous efficiency. The SrS:Ce growth temperature was found to affect the Ce3+ excitation efficiency in EL. Electronic traps in SrS:Ce films are discussed. We suggest that some traps can be beneficial in providing necessary charge for the Ce3+ excitation process and others can be deleterious in that they suppress radiative Ce3+ decay events. To determine the effects of Ce doping, undoped SrS films were also deposited and fully characterized. Finally, we compare the properties of films prepared by ALE to those deposited via rf sputtering.
Mass spectrometric measurement of molecular dissociation in inductively coupled plasmas
Authors: Wang Yicheng , Van Brunt R. J. , Olthoff J. K.
Published: July 2002

The dissociation fraction of molecules in radio frequency, planar, inductively coupled plasmas are measured for mixtures of oxygen, nitrogen, sulfur hexafluoride, and chlorine in argon. A modified gaseous electronics conference rf reference cell with an inductively coupled source is used to produce the discharges, with pressures ranging from 1.3 Pa to 5.3 Pa and applied powers from 100 W to 300 W. Neutrals are sampled from the side of the discharge, and the degree of dissociation is determined mass spectrometrically by comparison of the intensities of the parent ion peaks with the plasma power on and off. Measured dissociation levels of O2 in Ar:O2 mixtures ranged from 0.02 (i.e., 2% of the oxygen molecules were dissociated) to 0.08 (8%), while dissociation levels for Ar:SF6 mixtures ranged from 0.92 to 0.98, depending upon plasma conditions. The degree of dissociation of Cl2 in Ar:Cl2 mixtures ranged from near 0.07 to 0.19, while dissociation levels of N2 in Ar:N2 mixtures were less than 2% for all plasma conditions studied.
X-ray absorption and magnetic resonance spectroscopic studies of LixV6O13
Authors: Stallworth P. E. , Kostov S. , denBoer M. L. , Greenbaum S. G. , Lampe-Onnerud C.
Published: July 2002

Polycrystalline LixV6O13 samples, 0.5⩽x⩽6, were prepared by chemical intercalation in n-butyl lithium and investigated spectroscopically by x-ray absorption, electron paramagnetic resonance (EPR), and Li7 solid state nuclear magnetic resonance (NMR). Both the EPR results and the vanadium K-edge x-ray absorption fine structure spectra show that the average oxidation state of the vanadium decreases with the addition of Li, and the x-ray results provide evidence of lithium deficient and oxygen deficient impurity phases. The local symmetry of the vanadium atoms first decreases with increasing x from 0⩽x⩽1 and then increases with increasing x as the vanadium octahedral environment becomes less distorted. These changes are revealed by both the intensity of the first V-O peak in the radial distribution function and by the decrease in the x-ray absorption pre-edge peak intensity. However, structural correlations beyond the nearest neighbor atoms rapidly decrease with increasing Li content above x=1.5, reflecting increased disorder. The observed increase in the V-O distance implies a modest lattice expansion with intercalated Li, from 1.93 Å at x=0 (in agreement with x-ray diffraction) to 2.11 Å at x=5. Variable temperature Li NMR7 linewidth and spin-lattice relaxation measurements demonstrate that dynamic processes govern the spin-lattice relaxation when 0.5⩽x⩽2, but paramagnetic and homonuclear dipolar interactions reduce the spin-lattice relaxation time as x is increased beyond 2. The Li NMR7 lineshape confirms the presence of impurity phases. Paramagnetic and diamagnetic chemical shifts imply local magnetic ordering accompanying the structural changes on lithium intercalation.
Anodic-oxide-induced interdiffusion in GaAs/AlGaAs quantum wells
Authors: Yuan Shu , Kim Yong , Tan H. H. , Jagadish C. , Burke P. T. , Dao L. V. , Gal M. , Chan M. C. Y. , Li E. H. , Zou J. , Cai D. Q. , Cockayne D. J. H. , Cohen R. M.
Published: July 2002

Enhancement of interdiffusion in GaAs/AlGaAs quantum wells due to anodic oxides was studied. Photoluminescence, transmission electron microscopy, and quantum well modeling were used to understand the effects of intermixing on the quantum well shape. Residual water in the oxide was found to increase the intermixing, though it was not the prime cause for intermixing. Injection of defects such as group III vacancies or interstitials was considered to be a driving force for the intermixing. Different current densities used in the experimental range to create anodic oxides had little effect on the intermixing.
Model for electrostatic imaging of forensic evidence via discharge through Mylar-paper path
Authors: Seward George H.
Published: July 2002

A model for the electrostatic detection apparatus is presented. An electrostatic potential models the effects of indented writing, erasures, and fingerprints. Poole–Frenkel emission from Mylar surface states is employed to model the discharge process. Experimental evidence is provided which supports the model. The role of the Mylar sheet is identified. The electric effect of indented writing is identified as a surface charge created by paper-to-paper friction.
Nanoscale oxidation of GaAs-based semiconductors using atomic force microscope
Authors: Okada Yoshitaka , Amano Shinji , Kawabe Mitsuo , Shimbo Barden N. , Harris James S.
Published: July 2002

Fundamental results obtained in an atomic force microscope (AFM) direct nanoscale oxidation process are presented, which is regarded as a simple method for fabricating nm-scale devices such as single electron tunneling transistors and quantum effect electronic devices. Using Au-coated Si cantilevers, we have succeeded in drawing nm-scale oxide lines in GaAs-based semiconductor surfaces; n+-GaAs(100) and self-assembled InGaAs quantum dots grown by molecular beam epitaxy on GaAs(100) substrates. The effects of AFM drawing parameters such as tip bias voltage and writing speed on oxide linewidth and height have been explored. GaAs oxide lines as narrow as ∼40 nm have been patterned by this technique.
Optimization of double drive pulse pumping in Ne-like Ge x-ray lasers
Authors: Lin J. Y. , Tallents G. J. , Demir A. , Healy S. B. , Pert G. J.
Published: July 2002

Pumping of the Ne-like Ge x-ray laser with two 100 ps duration pulses (a prepulse and main pulse) is investigated using a fluid and atomic physics code coupled to a 3D ray tracing postprocessor code. The modeling predicts the optimum ratio of the irradiance of the two pulses for the maximum x-ray laser output resulting from the balance between the relative lower electron density gradients and wider gain region which is produced with a larger prepulse and the higher peak gain coefficients produced with a small prepulse. With a longer pulse interval between prepulse and main pulse, a relatively lower optimum pulse ratio is found. The threshold irradiance of the main driving pulse with a prepulse required to make an order of magnitude enhancement of laser output compared to irradiation without a prepulse is also found at 3–4×1013 W/cm2 for Ne-like Ge.
Boron diffusion across silicon–silicon germanium boundaries
Authors: Lever R. F. , Bonar J. M. , Willoughby A. F. W.
Published: July 2002

Most boron diffusion studies in Si–Ge have been made in regions of uniform germanium content. In this paper diffusion is observed from a boron-doped epitaxial silicon layer across surrounding Si–Ge layers. Pileup of boron in the Si–Ge layers shows that the activity coefficient for boron in Si–Ge is lower than that for pure silicon. A simple pairing model for Si–B interaction fitted the pileup quite well, with the same equilibrium constant applying to both Si0.9Ge0.1 and Si0.97Ge0.03 layers. The effect of this was simply to immobilize a significant fraction of the boron while retaining its acceptor qualities, the ratio of immobile boron to normal substitutional boron being proportional to the germanium content. Quasielectric field effects at the Si–SiGe interface have a strong effect on the results obtained.
Correlation between photoluminescence and infrared absorption spectra of oxidized nanoscale silicon clusters
Authors: Lowe-Webb Roger R. , Lee Hao , Ewing Jay B. , Collins Sandra R. , Yang Weidong , Sercel Peter C.
Published: July 2002

We report in situ photoluminescence and ex situ Fourier transform infrared spectra of nanoscale silicon clusters exposed to atomic hydrogen, molecular oxygen, and humidified argon. Comparisons between infrared absorption spectra of fresh and aged samples indicate that photoluminescence efficiency is correlated with a stoichiometric oxide shell and the presence of Si dangling bond passivants at the core/oxide interface. Photoluminescence quenching is demonstrated in efficiently luminescing samples upon exposure to atomic hydrogen with recovery of photoluminescence occurring upon subsequent exposure to air. The photoluminescence quenching and recovery is correlated with a partial quenching and recovery of absorption due to interfacial silane groups. The correlations between photoluminescence and infrared absorption spectra, together with the hydrogen quenching results, provide evidence that radiative recombination in these samples is associated with interfacial oxide-related defects.