bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of plasma parameters and electric fields in a microwave-rf hybrid plasma
Authors: Fujita Hiroharu , Okuno Yoshihiro , Ohtsu Yasunori , Yagura Shinya
Published: July 2002

Control of electron energy and electric field in a low-pressure argon plasma produced by a hybrid (2.45 GHz microwave and 13.56 MHz rf) discharge was studied for thin-film preparation. The hybrid plasma was found to be useful over a wide range of magnetic field strengths, unlike conventional microwave plasma. A novel probe measurement revealed that the electron temperature and density were effectively controllable by the microwave power and the magnetic field strength, rather than the rf power, and the potential profile describing the electric field was controllable by the magnetic field strength. The control of an ion beam injected from the microwave into the rf plasma is described.
Negative hydrogen ion densities and drift velocities in a multicusp ion source
Authors: Eenshuistra P. J. , Gochitashvilli M. , Becker R. , Kleyn A. W. , Hopman H. J.
Published: July 2002

We have determined densities of negative hydrogen ions in a discharge by a laser detachment technique. We measured the electron density, the electron temperature, and the positive ion density using a Langmuir probe. We also performed extraction measurements. Combination of H− density measurements and extraction measurements yields information about the H− drift velocity. It was found that the velocity scaled with the square root of the electron temperature. All measurements were done as a function of discharge voltage, discharge current, and gas pressure. The densities are compatible with a semiquantitative model in which H− is produced by dissociative attachment of plasma electrons to vibrationally excited molecules and destroyed by wall collisions at very low pressure and collisions with H atoms, positive ions and/or hot thermal electrons at higher pressure.
Different spin and lattice temperatures observed by spin-polarized photoemission with picosecond laser pulses
Authors: Vaterlaus A. , Guarisco D. , Lutz M. , Aeschlimann M. , Stampanoni M. , Meier F.
Published: July 2002

The spin polarization of the photoelectrons emitted from Sn and Fe during picosecond (ps) and nanosecond (ns) laser pulses is measured as function of the laser intensity. For Sn the optically induced spin polarization is defined through the lattice symmetry. No difference is found between ps and ns heating. From this it is concluded that the melting of a metal like tin occurs on a time scale which is short compared to the duration of a 70 ps laser pulse. In Fe the spin polarization probes the magnetic order. It is found that Fe cannot be demagnetized within the duration of a 30 ps laser pulse, even if the melting point is reached in the laser focus. During a ns laser pulse the spin system and the lattice are in thermal equilibrium.
Temperature and time dependence of B and P diffusion in Si during surface oxidation
Authors: Packan P. A. , Plummer J. D.
Published: July 2002

Diffusion of B and P in silicon during surface oxidation in dry O2 has been measured as a function of time and temperature. The diffusion coefficients were measured for oxidations at 900, 1000, and 1100 °C for times ranging from 5 min to 4 h. For a 30-min oxidation at 900 °C, the measured P diffusion was 15 times greater than diffusion in an inert ambient. The diffusion enhancements for B and P decreased as the temperature was increased. Increasing oxidation times at a given temperature resulted in a decrease in the diffusion enhancement. The time and temperature dependence of the interstitial component of B and P diffusion are analyzed. By using P diffusion as an interstitial monitor, the fraction of boron diffusion which occurs through the interstitial mechanism is calculated to be 0.8 at 1100 °C.
Composition-dependent ferroelectric Curie temperature of Pb5(Cr1−xAlx)3F19 from 555 to 280 K and of Pb5 (Cr1−xFex)3F19 from 555 to 725 K for 0≤x≤1
Authors: Ravez J. , Simon A. , Andriamampianina V. , Grannec J. , Hagenmuller P. , Abrahams S. C.
Published: July 2002

Ferroelectric Pb5Cr3F19 forms a complete series of solid solutions both with Pb5Al3F19 and Pb5Fe3F19. The end and intermediate compositions are isostructural with the ferroelectric A5M3F19 family previously reported [J. Appl. Phys. 62, 4299 (1987)]. The a and c axial lengths in Pb5(Cr0.2Al0.8)3F19 undergo discontinuities of +0.5% and −0.8%, respectively on heating through the Curie temperature (Tc =325 K), and exhibit a hysteresis of about 40 K between the phase transition temperature on heating and on cooling, characteristic of a first-order phase change. The value of Tc may be varied continuously between 555 and 280 K for the solid solution Pb5(Cr1−xAlx) 3F19, and between 555 and 725 K for Pb5(Cr1−xFex) 3F19, by increasing x from 0 to 1. The entropy change at the phase transition in Pb5Fe3F19, Pb5Cr3F19, and Pb5(Cr0.8Al0.2)3 F19 is high, at about Rln8. The maximum dielectric permittivity in Pb5Cr3F19 is about 2000.
Holographic recording in photorefractive crystals with simultaneous electron-hole transport and two active centers
Authors: Zhivkova S. , Miteva M.
Published: July 2002

A theoretical model of the formation and behavior of holographic gratings in photorefractive crystals, based on the assumption of two types of active centers being involved and simultaneous electron-hole transport, is derived. A diffusion mechanism of recording is discussed. It is demonstrated that a photorefractive grating can change its phase by 180° during recording and erasure. At large angles between the recording beams, after a long recording or fixing the grating in darkness at room temperature, the grating decay is much slower than in the case when it is formed by diffusion and trapping of one type of carrier.
Charge exchange of low-energy ions in thin carbon foils
Authors: Bürgi Alfred , Oetliker Michael , Bochsler Peter , Geiss Johannes , Coplan Michael A.
Published: July 2002

In order to calibrate a time-of-flight mass spectrometer which is to be flown in the solar wind we have investigated the charge exchange properties of low-energy ions in thin carbon foils. We have used incident ions of He, C, N, O, Ne, and Ar with energies in the range 0.5–2 keV/nucleon to measure charge-state distribution, residual energy, and angular distribution after transmission through thin (1–6 μg/cm2 ) carbon foils. Within such foils an equilibrium between ionization and recombination of the projectile is rapidly established and, consequently, the charge state of the emerging particle depends essentially on its residual velocity. A comparison of the charge exchange properties of 22 Ne with 2 0 Ne demonstrates that indeed the velocity (and not the energy) of the emerging particle determines its final charge. Comparing properties of different elements one observes an indication of an electron shell effect. Predictions for the energy loss of ions within the carbon foils made with the trim code [J. F. Ziegler, computer code trim-88 (IBM-Research, Yorktown, NY, 1987)] are in good agreement with the experimental results presented in this paper.
High-brightness electron-beam generation and transport
Authors: Hughes Thomas P. , Carlson Randolph L. , Moir David C.
Published: July 2002

Experimental results for a high-brightness electron-beam source are compared to results of numerical and analytic calculations. The 4-MV, 5-kA beam is generated from a velvet cathode and focused by a solenoidal magnet. Data for the diode impedance and the beam focusing length and spot size agree well with numerical simulations. The minimum spot size is consistent with a normalized Lapostolle emittance of 0.12 cm rad, yielding a brightness of 3.5×108 A/m2  rad2 . Transverse beam oscillations are observed in streak photographs and are thought to be caused by electromagnetic dipole modes in the diode cavity. The oscillation amplitude is significantly reduced by making the current rise more slowly.
Electronic properties of semiconducting FeSi2 films
Authors: Dimitriadis C. A. , Werner J. H. , Logothetidis S. , Stutzmann M. , Weber J. , Nesper R.
Published: July 2002

Polycrystalline iron disilicide thin films are prepared by furnace annealing of electron-beam deposited iron layers. As substrates we use single-crystal silicon wafers, epitaxial silicon thin films on sapphire substrates, and low-pressure chemical vapor deposited polycrystalline silicon thin films on oxidized silicon wafers. X-ray diffraction indicates that orthorhombic β-FeSi2 is obtained for growth temperatures in the range 800–900 °C. Photothermal deflection spectroscopy reveals a direct band-gap of 0.85 eV. Optical transitions at energies above 1.4 eV are investigated by spectroscopic ellipsometry. Measurements of the subgap defect absorption, photoluminescence, conductivity, and of the Hall mobility suggest that lower growth temperatures yield material of better quality.
The influence of substrate topography on ion bombardment in plasma etching
Authors: Ingram S. G.
Published: July 2002

The reactive ion etching of small features in a planar substrate produces a wide range of profiles which depend on many factors. Of underlying importance is the energetic positive ion flux incident on any substrate exposed to the plasma. Therefore, the nature of this directed ion flux is of interest when trying to understand the microscopic nature of dry etching where ion-enhanced surface chemistry and physical sputtering contribute to the etching performance. This paper uses a simple model to examine the influence of the local electric fields at the substrate on ion trajectories. It is found that the presence of trenches in the substrate distorts the local electric field, and the nature of this field is such that positive ions arriving normal to the substrate surface are deflected towards the sidewalls of the trench. The deflection is largest for those ions arriving near the trench sidewalls, the magnitude of which is calculated to be a few degrees. From the results of this investigation a new technique is proposed where in principle the positive ion flux can be influenced by externally applied potentials in an attempt to control the ion trajectories.
Foil focusing of electron beams
Authors: Fernsler R. F. , Hubbard R. F. , Slinker S. P.
Published: July 2002

Thin conducting foils focus charged particle beams through image charges induced on the foils. Such focusing has led to the suggestion that foils be used to transport intense, relativistic electron beams in high-energy accelerators. This paper examines some of the limitations of foil focusing including sensitivity to the beam parameters, emittance growth from anharmonic focusing, and beam stability in multifoil transport. The analysis is based on a thin-lens electrostatic treatment of paraxial beams.
Investigation of the creation process in dc pulsed discharges
Authors: Dengra A. , Ballesteros J. , Hernández M. A. , Colomer V.
Published: July 2002

In this paper we study the creation process of a cylindrical pulsed argon plasma. A new numerical model to simulate the plasma evolution during the creation process has been developed. This model is based on the solution of the continuity equations for ions and electrons together with the Poisson’s equation. The good agreement obtained between numerical and experimental results of electron density as a function of the time confirms the validity of the hypothesis made in the model proposed.
Eddy-current induction in a uniaxially anisotropic plate
Authors: Burke S. K.
Published: July 2002

A theoretical model is presented to describe the time-harmonic electromagnetic induction of eddy currents in a uniaxially anisotropic plate. The model assumes that the plate is nonmagnetic and that the axis of uniaxial anisotropy is horizontal (i.e., lying in a plane parallel to the surface of the plate). The fields and currents induced by a general magnetic source are obtained by formulating the problem in terms of reduced electromagnetic potentials (Hertzian potentials) and making extensive use of integral transforms. Closed-form expressions for the reduced potentials are given explicitly, enabling the induced fields to be calculated in all regions provided the free-space source fields are known. The change in probe-coil impedance ΔZ due to eddy-current induction is considered in detail, and an explicit closed-form expression for ΔZ is derived for the general case. This general theory is illustrated by calculating ΔZ for a cylindrical air-cored coil when (i) the coil axis is normal to the surface of the plate and (ii) the coil axis is tangential to the surface of the plate. The validity of these calculations was established by performing a series of measurements of ΔZ using an aluminum-alloy sheet unidirectionally reinforced with boron fibers. The results of the theoretical calculations are in excellent agreement with experiment. The significance of the results for the nondestructive characterization of metal-matrix composite materials is discussed.
Thermal gas evolution studies on a-C:H:Ta films
Authors: Gerstenberg K. W. , Grischke M.
Published: July 2002

Thermal induced gas evolution studies were performed on a-C:H:Ta films deposited by a sputtering process using a tantalum target and an argon-hydrocarbon gas mixture. Decreasing hydrocarbon concentration of the plasma atmosphere during the deposition results in an increasing tantal carbid (TaC) volume fraction, perceptible by x-ray diffraction measurements, while the a-C:H volume fraction decreases. Gas evolution spectra, similar to those of a-C:H and a-Si:C:N:H films, suggesting the presence of an a-C:H matrix with a void network structure. TaC forms precipitations in this matrix. The degree of crosslinking of the carbon atom network of the a-C:H matrix, which increases with an increasing volume fraction of TaC in the films, determines the thermal gas evolution concerning temperature and amount of hydrocarbons and argon. As shown also by gas effusion measurements, a more crosslinked matrix can also be obtained by reduction of the hydrogen content of the hydrocarbon gas, for instance, by substitution of methane by ethylene. Since the argon effusion temperature does not depend on film thickness, the argon effusion temperature may serve as a material property, which renders the comparison of different a-C:H materials possible, also in two phase systems like a-C:H:metal. The released hydrocarbon molecules were formed during the heating by alkyl group cleavage. Hydrocarbon gas release temperature is found to depend on the volume fraction of TaC, since bonding states of carbon atoms are influenced by the presence of tantalum, as indicated by x-ray-photoelectron-spectroscopy.
Collection efficiency of a-Si:H Schottky barriers: A computer study of the sensitivity to material and device parameters
Authors: McElheny P. J. , Chatterjie P. , Fonash S. J.
Published: July 2002

A comprehensive numerical calculation of the spectral response, or equivalently, collection efficiency behavior of a-Si:H Schottky barrier detector and solar cell structures is presented. This allows, for the first time, for a thorough assessment of the impact of materials property variations as well as of device parameter variations on spectral response. In the case of material parameters, the analysis shows that the spectral response measurement for a-Si:H type materials is not sensitive to the tail-state density or tail-state capture cross sections for the band whose carriers are repelled at the barrier. However, it is sensitive to these quantities for the band tail of the carriers collected at the barrier and it is sensitive, in general, to the midgap states. It is sensitive to the carrier mobilities but again the sensitivity depends on the role of the carrier in barrier formation. This sensitivity does not follow a simple mobility-lifetime product model. Spectral response is also sensitive to the device length and front surface barrier parameters. All of this spectral response behavior is shown to be due to the interplay of three loss mechanisms with certain general features.
‘‘Water window’’ x-ray source produced by a slab glass laser
Authors: Zeng Guan-ming , Daido Hiroyuki , Togawa Takuya , Nakatsuka Masahiro , Nakai Sadao , Aritome Hiroaki
Published: July 2002

X-ray emission in the water window spectral region (2.3–4.4 nm) from materials (carbon, aluminum, titanium, copper, and molybdenum) irradiated by a 5 J/35 ns slab glass laser was recorded with a grazing-incidence spectrometer for microscopy application. Carbon was determined to be the suitable source material for an x-ray microscopy experiment. The absolute spectral brightness of the CVI 1s-2p line and CV 1s2-1s2p line emitted from the carbon plasmas was estimated to be ∼1.0×1016 photons/s/mm2/mrad2 in 0.1% bandwidth. The electron density and electron temperature of the carbon plasmas were derived from the x-ray spectra and the conditions for intense emission are also discussed.
Stability of tungsten/carbon and tungsten/silicon multilayer x-ray mirrors under thermal annealing and x-radiation exposure
Authors: Kortright J. B. , Joksch St. , Ziegler E.
Published: July 2002

The effect of thermal annealing and irradiation in an intense white synchrotron x-ray beam on the x-ray reflectance of tungsten/carbon and tungsten/silicon multilayers is reported. Thermal annealing at 400 °C for two hours produces larger effects than irradiation of cooled multilayers in the white beam of a 20-pole hard x-ray wiggler with 0.94-T peak field on the storage ring DORIS operating at 5.42 GeV and electron currents of 20–36 mA for 40 h. Thermal annealing caused the period and first order reflectance of a W/Si sample to decrease, in contrast to a W/C sample whose period and reflectance increased on annealing. Of five actively cooled samples irradiated, one W/C sample showed significant change in reflectance. Preannealing of this multilayer stabilized it to radiation-induced changes. Irradiation effects also depend on multilayer period and constituent materials. Implications of these results for models describing multilayer reflectance and for multilayer applications in the new generation of synchrotron radiation sources are discussed.
Magnetic and structural properties of rf-sputtered Co/Fe and Co/Cr multilayers
Authors: Houdy Ph. , Boher P. , Giron F. , Pierre F. , Chappert C. , Beauvillain P. , Dang K. Le , Veillet P. , Velu E.
Published: July 2002

Multilayers alternating cobalt with different spacers such as iron and chromium at nanometric scale have been deposited by rf diode sputtering. The structures have been characterized in situ by kinetic ellipsometry and ex situ by grazing x-ray reflection, x-ray diffraction, Auger profile analysis, and transmission electron microscopy. Nuclear magnetic resonance (NMR) and high-field SQUID magnetometry have been used to determine the magnetic properties. In Co/Fe multilayers the structure strongly depends on the cobalt thickness tCo. For tCo below 2 nm, the cobalt layers exhibit a bcc crystalline structure, and the crystalline coherence extends over many periods. For tCo above 2 nm, for Co a mixed fcc-hcp phase has been observed. In this case the crystalline coherence is destroyed from one iron layer to the other. The NMR frequency (198 MHz), and the magnetic moment (1.58 μB/atom) of bcc cobalt have been evaluated. A similar behavior is observed in Co/Cr multilayers, the bcc phase disappearing around tCo=1.5 nm. Moreover, interdiffusion is observed at the Cr-on-Co interface: The samples have zero magnetization up to tCo=0.7 nm. Preliminary experiments show some antiferromagnetic coupling between Co layers. 
Optical characterization of Si-doped InAs1−xSbx grown on GaAs and GaAs-coated Si by molecular-beam epitaxy
Authors: Dobbelaere W. , De Boeck J. , Van Mieghem P. , Mertens R. , Borghs G.
Published: July 2002

Epitaxial layers of Si-doped InAs1−xSbx have been grown by molecular-beam epitaxy on GaAs and GaAs-coated Si substrates. The absorption coefficient was measured in the 3–12 μm wavelength range and the experimental data was fit using an analytical expression that was derived from the Kane band model. The fitted value of the Fermi level was used to calculate the electron concentration and the results were compared with doping levels obtained from secondary ion mass spectroscopy and Hall measurements.
Characterization of ion implanted waveguides in Nd:YAG
Authors: Zhang L. , Chandler P. J. , Townsend P. D. , Field S. J. , Hanna D. C. , Shepherd D. P. , Tropper A. C.
Published: July 2002

Ion implantation into Nd:YAG has been used to produce waveguides which are capable of supporting laser action. The refractive index profiles have been characterized as a function of ion dose and energy, implant temperature, and subsequent thermal annealing. Transmission losses down to 1.2 dB/cm have been obtained in the optimized waveguides. There is a temperature independent index enhancement of ∼0.15% in the electronic stopping (guiding) region. The nuclear collision damage is temperature dependent, and shows an initial index increase (∼0.3% for dose 1 × 1016 ions/cm2), but a subsequent decrease of up to several percent, which forms an optical barrier, as has been observed in many other crystalline materials. The best mode confinement and attenuation is obtained by utilizing the low dose nuclear index enhancement produced by several equally spaced implants (multiple energy) to give a broad well with Δn∼0.25%. Several unusual features of the profiles are reported and discussed.
Oxygen desorption from YBa2Cu3O7−x and Bi2CaSr2Cu2O8+δ superconductors
Authors: Mesarwi A. , Levenson L. L. , Ignatiev A.
Published: July 2002

Oxygen desorption experiments from YBa2Cu3O7−x (YBCO) and Bi2CaSr2Cu2O8+δ (BSCCO) superconductors were carried out using a quadrupole mass spectrometer for monitoring the desorbing species and x-ray photoemission spectroscopy for surface characterization. Molecular oxygen was found to desorb from both superconductors following photoirradiation with ultraviolet/optical radiation and subsequent heating at over 150 °C. Both YBCO and BSCCO were found to have similar oxygen desorption rates and similar activation energies (1012–1013 molecules/cm2 s and ∼1.5 eV/molecule, respectively). The desorption data as well as the x-ray photoemission data indicate that the oxygen desorption is not intrinsic to the superconductors but rather due to molecular oxygen entrapped in the material.
Poor intergrain connectivity of PbMo6S8 in sintered Mo-sheathed wires and the beneficial effect of hot-isostatic-pressing treatments on the transport critical current density
Authors: Yamasaki H. , Umeda M. , Kosaka S. , Kimura Y. , Willis T. C. , Larbalestier D. C.
Published: July 2002

The microstructure of Mo-sheathed Chevrel-phase superconducting wires was investigated by high-resolution scanning electron microscopy (SEM). Excess Pb forms small nodules (10–30 nm) on the Chevrel-phase grains or wetting layers between the Chevrel grains. The critical current density Jc is strongly reduced when wetting layers are present. However, second-phase Mo exists as islands as large as 2–10 μm and has little harmful effect on Jc. Although some Mo-sheathed wires sintered at 700 °C show relatively high Jc ( ≥ 2 × 108 A/m2 at 8 T), the Chevrel phase in these wires has a very porous microstructure, and the Jc values measured with a magnetic field parallel to the current, Jc(∥), were only about 10% higher than the Jc values measured with a field perpendicular to the current, Jc(⊥). This clearly suggests that the transport current flows percolatively in these wires. Much denser microstructures were obtained by hot-isostatic-pressing (HIP) treatments at 1200 °C, and very high Jc values, ≳ 5 × 108 A/m2 at 8 T and 9.3 × 107 A/m2 at 23 T, which are of the order of the highest Jc values so far reported, were observed. High-resolution SEM observations of HIP’ed wires demonstrate that the interconnectivity between the Chevrel grains was much improved.
Ferroelectric-paraelectric phase transitions in Pb5M3F19 with M=Al, Ti, V, Cr, Fe, Ga
Authors: Ravez J. , Andriamampianina V. , Simon A. , Grannec J. , Abrahams S. C.
Published: July 2002

Phase transitions have been found in Pb5Al3F19 at Tc = 285 K, Pb5Ti3F19 at 695 K, Pb5V3F19 at 630 K, Pb5Cr3F19 at 545 K (reported previously), Pb5Fe3F19 at 740 K, and Pb5Ga3F19 at 945 K. In striking contrast to the variation of Tc with M atom in Sr5M3F19 and Ba5M3F19 (reported previously), for which materials the phase transition temperature increases with increasing atomic number from M=Ti to M=Cr but with a lower Tc for M=Fe before increasing again, Tc in Pb5M3F19 decreases from M=Ti to M=Cr with a sharp increase for M=Fe before it decreases again. The transition temperature for Pb5Al3F19 is below room temperature, that for isotypic Sr5Al3F19 is not detectable before reaching a dissociation temperature around 1000 K. All phase transitions in the Pb5M3F19 family are first order. Each new material has been fully characterized. Differences between materials with A=Pb, M=Al or Cr, and those with A=Sr, M=Al or Cr have been investigated through the formation of solid solutions. Six separate systems have been studied. Complete solid solutions form between end components with identical A and different M atoms. Partial solid solutions form with different A and different M atoms. Solid solutions do not form with different A and identical M atoms. M atom replacement, hence, appears to be energetically favorable, A atom replacement unfavorable, probably due to the role of the Pb atom lone pair of electrons. Two models outlining this role are presented.
13.4% efficient thin-film CdS/CdTe solar cells
Authors: Chu T. L. , Chu S. S. , Ferekides C. , Wu C. Q. , Britt J. , Wang C.
Published: July 2002

Cadmium telluride is a promising thin-film photovoltaic material as shown by the more than 10% efficient CdS/CdTe heterojunction solar cells. In this work, thin-film CdS/CdTe solar cells have been prepared using CdS films grown from an aqueous solution and p-CdTe films deposited by close-spaced sublimation (CSS). The properties of CdS films deposited from an ammonical solution of a Cd-salt, an ammonium salt, and thiourea have been controlled by optimizing the temperature and composition of the solution. The solution-grown CdS films have a high photoconductivity ratio, and its optical transmission is superior to that of vacuum evaporated CdS films. The properties of p-CdTe films deposited by CSS have been optimized by controlling the temperature and composition of the source material, and the substrate temperature. The properties of CdS/CdTe heterojunctions have been studied; junction photovoltage spectroscopy is used for the qualitative comparison of junction characteristics. Solar cells of 1-cm2 area with an AM 1.5 efficiency of 13.4% are reported.
Ion dose effect in subgap absorption spectra of defects in ion implanted GaAs and Si
Authors: Zammit U. , Gasparrini F. , Marinelli M. , Pizzoferrato R. , Agostini A. , Mercuri F.
Published: July 2002

Subgap optical absorption investigations have been used to study the influence of increasing ion dose on the properties of ion implanted layers of Si and GaAs. Beside the spectral region corresponding to the band edge region, a second region at lower energy, also exhibiting an exponential behavior but with a substantially larger value of the inverse logarithmic slope, has been observed in all the investigated samples. A common trend has been observed for ion implanted Si and GaAs in the dependence of the values of the lower energy region inverse logarithmic slope as a function of the implantation dose, and it depended on the presence or not of amorphous material in the implanted layer. The results are discussed in terms of a possible evolution of gap states responsible for the observed features.
Deep-level transient spectroscopy: Increased accuracy of interpretation of silicon/silicon dioxide interface state data by the assistance of computer simulations
Authors: Ricksand Anders , Engström Olof
Published: July 2002

Computer simulations of small filling pulse deep level transient spectroscopy (DLTS) measurements of Si/SiO2 interface states in metal-oxide semiconductor (MOS) capacitors, demonstrate that the time dependence of the surface potential during emission and capture of charge carriers must be considered for a correct interpretation of DLTS data. It is demonstrated that not only the amplitude but also the shape of DLTS spectra are influenced by the interface state density Nit. Accurate values of Nit and capture cross sections are obtained for exponential as well as nonexponential emission of charge carriers by fitting simulated to experimental data. This solves the problem of nonexponential transients due to a time dependent surface potential for high interface state densities. Measurements on irradiated MOS samples verify that numerical simulations can be used for accurate determination of interface state parameters. An observed discrepancy between the amplitudes of the measured and simulated DLTS signals is explained by surface potential fluctuations and a nonuniform lateral distribution of interface states.
Film synthesis and magnetic properties of ThMn12-type Sm(Fe1−xTx)12, x≤0.12
Authors: Hegde H. , Rani R. , Navarathna A. , Chen K. , Cadieu F. J.
Published: July 2002

Films of binary SmFe12 and Sm(Fe1−xTx)12 compounds, where x≤0.12, and T=V, V-Ti, and Ti, exhibiting the ThMn12-type tetragonal crystal structure have been successfully synthesized. These films were crystallized by rf sputter deposition onto Al2O3 substrates preheated to 400–550 °C. The lattice parameters of the SmFe12 tetragonal structure, x=0, were determined to be a=8.438±0.005 Å and c=4.805±0.005 Å. The binary SmFe12 and Sm(Fe,T)12 alloys were found to be magnetically uniaxial as confirmed by magnetization measurements, x-ray diffraction, and Mössbauer spectroscopy. Coercivities up to 6 kOe were obtained for these films. For the binary system, room-temperature 4πM values of 14.3±0.2 kG were obtained for magnetization measurements made perpendicular to film plane at applied fields of 90 kOe. For the first time, remnant flux-density values close to the saturation values were obtained for x≤0.08 for films synthesized with an extreme (002) texture. For certain dense films a static energy product of 21 MGOe was measured with the magnetization directed perpendicular to the film plane. The anisotropy field at 293 K of a Sm(Fe0.96Ti0.04)12 sample was estimated from high-field measurements to be 130±10 kOe.
Analysis of magnetic anisotropies in ultrathin films by magnetometry in situ in UHV (invited)
Authors: Elmers H. J. , Furubayashi T. , Albrecht M. , Gradmann U.
Published: July 2002

Magnetic anisotropies of Ni(111) films on Re(0001) and Fe(110) films on W(110) were analyzed using torsion oscillating magnetometry in UHV. They can be decomposed in volume contributions that are independent of thickness and surface state and can be explained as a superposition of shape, magnetocrystalline and residual strain anisotropies, and surface contributions, which scale with 1/d and depend sensitively on the state of the surface. Néel’s phenomenological anisotropy model provides a useful connection between different components of surface anisotropies.
Atomic force microscopy of (100), (110), and (111) homoepitaxial diamond films
Authors: Sutcu L. F. , Chu C. J. , Thompson M. S. , Hauge R. H. , Margrave J. L. , D’Evelyn M. P.
Published: July 2002

We present atomic force microscopy images of diamond films grown by chemical vapor deposition epitaxially on diamond (100), (110), and (111) substrates. The films were grown from 0.2%–1.6% mixtures of CH4 and C2H2 in H2 in a hot-filament reactor at a total pressure of 25 Torr. The substrate and filament temperatures were held at 810–1000 and 2000–2150 °C, respectively. A (100)-oriented diamond film grown with 0.3% CH4 at a substrate temperature of 810 °C was rough on the μm scale, exhibiting pyramidal features, terraces, and penetration twins, while films grown at higher substrate temperatures and hydrocarbon flow rates were smooth on the nm scale and showed evidence of a (2×1) reconstruction. A (110)-oriented film was very rough on the μm scale but nearly atomically smooth on the 0.5–5 nm scale and exhibited local slopes higher than 40° with no evidence of faceting. A film grown on a diamond (111) substrate underwent spontaneous fracture due to tensile stress and exhibited a roughness of ≊10–50 nm on the ≊100 nm lateral scale in regions far away from any cracks. The implications of the morphological features for diamond growth mechanisms are discussed.
Investigation of the photorefractive effect in Bi2TeO5
Authors: Foldvari I. , Liu Huimin , Powell Richard C. , Peter A.
Published: July 2002

Single crystals of Bi2TeO5, both undoped and doped with transition-metal-ion dopants, were grown with high optical quality. Continuous-wave four-wave-mixing experiments on these crystals show a strong photorefractive signal with a multicomponent decay. The photorefractive efficiency was studied as a function of the wavelength, intensity, polarization direction, and crossing angle of the laser write beams, and the sample orientation. Both absorption and phase gratings were observed with their relative strengths dependent on the laser wavelength and sample dopants. The signal evolves in time from a defect population grating, to trapped charge gratings involving two different types of traps, to fixed gratings produced by oxygen ion displacements. The photorefractive effect in this material is found to be of the photoconductive type and it produces a larger diffraction efficiency than that observed in sillenite materials under the same experimental conditions. A mechanism is proposed for the various physical processes leading to the different decay components of the signal.
Densification induced dielectric properties change in amorphous BaTiO3 thin films
Authors: Li P. , McDonald J. F. , Lu T.-M.
Published: July 2002

The properties of amorphous BaTiO3 thin films deposited on Si substrates were studied as functions of annealing temperature. The film thickness decreased monotonically as the annealing temperature increased up to 600 °C. This reduction is believed to correlate with the densification process observed in the amorphous films during annealing. After the 500 °C annealing, a partial crystallization process was observed. It was also found that the dielectric constant and the index of refraction of the film showed significant changes as the annealing temperature increased from 400 to 500 °C. Correlations between the film density, index of refraction, and the dielectric constant are discussed. A severe reaction at the interface between the film and Si substrate was observed in the 750 °C annealed sample.
Regenerative balance in magnetic Ericsson refrigeration cycles
Authors: Dai Wen
Published: July 2002

The coefficient of performance of the refrigeration cycles of ferromagnetic material is derived. It is shown that the Ericsson cycle, using the composite working substance, cannot only possess the condition of perfect regeneration, but also attain to or approach the Carnot coefficient of performance.
On single-photon ultraviolet ablation of polymeric materials
Authors: Cain Stephen R. , Burns F. C. , Otis C. E.
Published: July 2002

The nature of uv ablation of organic polymers is discussed in terms of a pseudo-zeroth-order rate law of the form dx/dt = k0e−(Eact/kT), where Eact is assumed to be the strength of the weakest bonds in the polymer and T is the local temperature increase from the incident laser pulse. Equations derived from previous models that assumed nonthermal photodecomposition were duplicated from this photothermal model. Even for the simple case of single-photon absorption, nonideal behavior is affected by radiationless decay, pulse length, and thermal diffusion. These effects were probed. Results indicated that thermal diffusion may have a significant effect on the threshold fluence and to some degree on the shape of the etch depth versus fluence curve. Absorption dynamics (saturation and radiationless decay) appear to be the dominant factor in determining the functional dependence of etch depth on fluence. As a result of competition between absorption saturation and radiationless decay, the penetration depth is intensity dependent. High fluence as well as short temporal pulses (subnanosecond) penetrate more deeply into the polymer than predicted by simple Beer’s law absorption. The apparent existence of an optimum pulse length, for a given absorbing system, is another result of the absorption dynamics.
Annealing of Si-implanted GaAs studied using variable-energy positrons
Authors: Simpson P. J. , Schultz P. J. , Lee S.-Tong , Chen Samuel , Braunstein G.
Published: July 2002

Modification of GaAs by Si+-ion implantation is an important process for selective doping of the material. Defects caused by the implantation process often lead to incomplete electrical activation, and annealing procedures are used to recover the crystal quality. Results are presented of variable-energy positron (VEP) and cross-sectional transmission electron microscopy (XTEM) studies of a series of GaAs samples implanted with moderate to high fluences of 3×1013, 3×1014, and 1×1015 Si+ ions cm−2. Samples were irradiated at room temperature, and studied both before and after thermal annealing for one hour at 850 °C. In all cases XTEM results show a high density of small extrinsic dislocations after implantation, and VEP shows high concentrations of point (vacancy type) defects. Annealing leads to a decrease in the point-defect concentration in the lowest-fluence sample, but both XTEM and VEP confirm the formation of macroscopic (i.e., ≳20 Å diameter) voids following annealing. These data are discussed in the context of microscopic models for defect formation and migration.
Continuum modeling of radio-frequency glow discharges. II. Parametric studies and sensitivity analysis
Authors: Gogolides Evangelos , Sawin Herbert H.
Published: July 2002

A plasma simulator which employs efficient numerical methods is used to do parametric studies on an electropositive (Ar), and an electronegative (SF6) discharge. The effects of pressure and current amplitude variation are studied; the phenomena associated with the transition of the discharge into different operating regimes at low currents, and at high currents, are demonstrated and discussed. Comparison of the model results with experimental data is good. The effect of ion mobility variation with electric field is also studied, and is shown to be important in improving the comparison with experimental data. Finally, a sensitivity analysis on the values of the transport and kinetic parameters is done. The sensitivity analysis and the agreement with experimental data demonstrate the validity of the continuum modeling approach, as long as reasonably accurate experimental data for the model parameters are available.
Laser reflective interferometry for in situ monitoring of diamond film growth by chemical vapor deposition
Authors: Wu Ching-Hsong , Weber W. H. , Potter T. J. , Tamor M. A.
Published: July 2002

A simple laser reflective interferometer has been employed for in situ monitoring of diamond film growth in a hot-filament chemical vapor deposition reactor. This method uses a low power HeNe laser beam reflected at normal incident from the substrate. The high refractive index of the diamond film and the relatively high reflectivity of the Si substrate result in pronounced and easily detected interference oscillations in the reflected beam intensity. The oscillation period provides an accurate and immediate measure of the growth rate. In addition, the variations of the extrema of the oscillations provide an estimate of the quality and surface texture of the diamond films. Significant improvement in research productivity has been realized by using this technique.
Optical ion energy measurements in a radio-frequency-induction plasma source
Authors: O’Neill James A. , Barnes Michael S. , Keller John H.
Published: July 2002

In situ, Fabry–Perot interferometry was used to study the translational dynamics of ions in a magnetically confined, radio-frequency-induction (RFI) plasma reactor. Radial ion motion was characterized through measurements of the Doppler profile of emission from Ar+ ions. Radial ion energies depend on the operating power, pressure, and magnetic-field configuration. In a magnetically confined RFI plasma at 1000 W, ion energies increase from 0.08 to approximately 0.25 eV as the operating pressure is lowered from 13 to 0.18 mTorr. Complementary Langmuir probe studies of the plasma potential as well as its variation across the radius of the reactor illustrate the influence of electric fields on the radial motion of ions in the RFI system. These measurements illustrate that radially directed ion motion in the RFI reactor is significantly less than that reported previously for a divergent-field electron cyclotron resonance system.
Stoichiometry measurement and electric characteristics of thin-film Ta2O5 insulator for ultra-large-scale integration
Authors: Shimizu K. , Katayama M. , Funaki H. , Arai E. , Nakata M. , Ohji Y. , Imura R.
Published: July 2002

Elastic recoil detection and Rutherford backscattering were adapted to a stoichiometric study of thin Ta2O5 films deposited on Si substrates by means of the reactive sputtering (SP) and chemical-vapor-deposition (CVD) method. Before annealing the samples it was observed that (i) the atomic ratio of oxygen to tantalum in the SP films agreed with 5/2 within the experimental accuracy and (ii) the CVD films have less oxygen content than the other samples. The specimens were annealed for 30 min under the following three conditions: (a) in dry oxygen ambient at 800 °C; (b) in ozone atmosphere under ultraviolet irradiation (UV ozone) at 300 °C; and (c) two-step treatment of (a) after the (b) process. Each oxidizing process has shown a certain positive effect on the thin CVD samples. Among them, the two-step treatment has proven to be very effective to restore the stoichiometry of 5/2 in the CVD films. Additionally the thickness of contaminant carbon films on the surface of the samples has been reduced by annealing in the oxidizing atmosphere. The relationship between the chemical composition and the electric properties of the samples is discussed.
Effects of low-temperature annealing on the native oxide of AlxGa1−xAs
Authors: Sugg A. R. , Chen E. I. , Holonyak N. , Hsieh K. C. , Baker J. E. , Finnegan N.
Published: July 2002

Data are presented on the effects of low-temperature (∼540 °C) annealing, with and without an As overpressure, on the native oxide of AlxGa1−xAs formed via water vapor oxidation at elevated temperature (∼425 °C). Auger electron spectroscopy data show the Al to be oxidized while the Ga remains unoxidized after the water vapor oxidation of AlxGa1−xAs. Transmission electron microscopy data show a possible composition or phase change upon annealing with an As overpressure. Electron diffraction data indicate that the as-oxidized AlxGa1−xAs is a combination of four possible phases of Al2O3, η, γ, δ, χ, or AlO(OH). Supporting secondary-ion mass spectrometry data are also presented. Ellipsometer measurements indicate an index of refraction n=1.63 (λ=6328 Å) for the native oxide. Ellipsometer measurements of the oxidized and annealed samples show the creation of a region 300–550 Å thick at the oxide-semiconductor interface with n=2.78–2.93.
On the current mechanism in reverse-biased amorphous-silicon Schottky contacts. II. Reverse-bias current mechanism
Authors: Nieuwesteeg K. J. B. M. , van der Veen M. , Vink T. J. , Shannon J. M.
Published: July 2002

The physical mechanisms that determine the current transport in reverse-biased Schottky diodes on undoped ‘‘device-grade’’ hydrogenated amorphous silicon (a-Si:H) are elucidated. The current-voltage (J-V) curves for several Schottky diodes up to reverse-biases of 40 V have been measured at temperatures between 40 and 180 °C. The reverse currents generally increase approximately exponentially with reverse bias. The decrease of the apparent barrier height as obtained from internal photoemission experiments is in good agreement with the decrease of the thermal activation energy with reverse bias. Extra information on the current transport mechanism can be obtained from the bias dependence of the prefactor in the Arrhenius plot. A theoretical model is presented which gives a semiquantitative fit to all the features observed in the experimental data. The model involves quantum-mechanical tunnelling of a thermal distribution of carriers through an image-force lowered triangular potential shape. At low reverse bias, the apparent barrier height decreases due to image-force lowering alone and the prevailing carrier transport mechanism is drift/diffusion or thermionic emission over the barrier, which can be determined from the bias dependence of the conduction prefactor in the Arrhenius plots. At higher fields, the apparent barrier height decreases faster than the image-force lowering. This is due to tunnelling of carriers through (the top of) the potential barrier and the apparent barrier becomes approximately equal to the mean energy at which the carriers move through the barrier. This energy is lowered with increasing reverse bias. The conduction prefactor from the Arrhenius plot now decreases with increasing applied bias and gives an indication of the effective tunnel probability.
Saturation of ZnS:Ag,Al under cathode-ray excitation
Authors: Raue R. , Shiiki M. , Matsukiyo H. , Toyama H. , Yamamoto H.
Published: July 2002

The decrease in efficiency of ZnS:Ag,Al phosphor powders under high cathode-ray excitation densities has been investigated in a wide range of Ag concentrations (18–1560 ppm) with the Al/Ag ratio fixed at 1.5. Two distinct regions have been observed in this saturation behavior. For low Ag concentrations up to some 100 ppm (mol) saturation is due to activator ground-state depletion, which manifests itself in a concentration dependence of saturation. For higher doping levels saturation becomes independent on the Ag concentration. Saturation was found to be temperature independent between 83 and 303 K. Diffuse reflectance measurements revealed an onset of optical absorption near 2.8 eV due to Ag incorporation, which continuously increased with Ag concentration giving no evidence for a change in activator incorporation around 100 ppm. Varying the Al/Ag ratio up to 56.2 had no influence on the saturation behavior, while the efficiency at low excitation densities showed a considerable decrease which could not be reconciled with optical-absorption losses, only. The saturation at high Ag concentration is tentatively attributed to a nonradiative Auger process. The probability of different types of Auger processes is discussed.
Antiferroelectric-ferroelectric switching and induced strains for sol-gel derived lead zirconate thin layers
Authors: Tani Toshihiko , Li Jie-Fang , Viehland Dwight , Payne David A.
Published: July 2002

Lead zirconate (PZ) thin layers were formed by a sol-gel method and crystallized with a pseudocubic (111) or (100) preferred orientation. The field-forced antiferroelectric (AFE)-to-ferroelectric (FE) phase transformation behavior was examined by Sawyer–Tower measurements. Dielectric properties were measured as a function of temperature and frequency, and the field-induced transformational strain was measured by interferometry. Both the high-field hysteresis behavior and the temperature-dependent weak-field dielectric properties were found to be strongly dependent on preferred orientation. An increase in the remanent polarization and dielectric constant was observed under high electric field strengths at room temperature, or for lower field strengths at higher temperature. Strains as large as 0.7% were determined for the field-forced AFE-to-FE transformation. AFE-to-FE switching was demonstrated with full saturation at room temperature for high dielectric strength (100 MV/m) thin layers (300 nm).