bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic emissions from penny-shaped cracks in glass. II. Moment tensor and source-time function
Authors: Kim Kwang Yul , Sachse Wolfgang
Published: July 2002

In the second part of this paper we describe both epicentral and off-epicentral responses corresponding to the acoustic emission (AE) source of a Mode I type penny-shaped crack generated by the indentation technique. The characteristics of the source are described in terms of the components of the moment tensor and its time function which were recovered from the waveforms coupled with an analysis of the AE radiation pattern described in Part I of this paper [J. Appl. Phys. 59, 2704 (1986)]. The recovered source characteristics indicate that the dominant contribution to the AE source of the penny-shaped crack comes from a single dipole acting normal to the crack plane whose temporal characteristics resemble those of a terminated parabolic ramp function.
Self-consistent domain theory in soft-ferromagnetic media. II. Basic domain structures in thin-film objects
Authors: van den Berg H. A. M.
Published: July 2002

A construction method for determining the domain structure in ideally soft-ferromagnetic cylindrical objects with plane-parallel top and bottom surfaces of arbitrary shape is presented. The self-consistent theory is confined to two-dimensional solenoidal dipole distributions in which the dipoles are parallel to the top and bottom surfaces. It is proved that the basic domain structure is uniquely defined in simply connected objects, while an extra criterion has to be added in order to guarantee the uniqueness in the multiply connected ones. The treatment is based on differential geometrical principles. The object edge is partitioned into segments, in which each segment is situated in between two adjacent edge points where the radii of curvature of convex edge segments are locally minimal. To each edge segment, a region is attributed, in which M is uniquely specified by the course of M along that edge segment. In the cross section of regions corresponding to different edge segments, domain walls provide an adequate separation of the dipole distribution imposed by these segments. The extremities of these domain walls are found in the singular points of the evolute corresponding to the extremities of the edge segments and in the points where a number of walls meet. It is proved that the basic domain structure is the locus of centers of all circles inside the object that touch the object edge at at least two points. A number of experimentally observed basic structures are given, and the relevance of the definition of basic structures in multiply connected objects is examined. OFF
Morphology and structure of a one-dimensional graphite polymer, poly-peri-naphthalene
Authors: Murakami Mutsuaki , Iijima Sumio , Yoshimura Susumu
Published: July 2002

Very fine fibers of 3,4,9,10-perylenetetracarboxylicdianhydride heated above 520 °C in argon (Ar) or argon/hydrogen (Ar/H2) gas were grown on pressed pellets. The fibers synthesized in Ar had a rectangular cross section of about 0.1–0.4 μm on a side with lengths up to 10 mm. By contrast, the fibers synthesized in Ar/H2 had a flat-ribbon like morphology with dimensions of 0.1–0.2 μm on one side and 0.4–2.0 μm on the side. Transmission electron microscopy revealed that component molecules roughly stacked parallel to the fiber axis. Infrared spectra of the fibers synthesized at around 520–550 °C exhibited aromatic C–H and C■C absorptions. The IR and laser–Raman spectra of the fibers can reasonably be explained by theoretically estimated vibrational modes of a poly-peri-naphthalene (PPN) structure. From these results together with elemental analysis data, we conclude that the fibers essentially consist of PPN molecules.
Electrical, gasdynamic, and radiative properties of planar surface discharges
Authors: Beverly III R. E.
Published: July 2002

An investigation was undertaken of the electrical, gasdynamic, and radiative properties of surface discharges intended as intense optical pump sources for lasers. Large-area (≂20–300 cm2), short-pulse (∼1 μs) planar surface discharges were produced across various ceramic and polymer substrates and operated in all of the rare gases, N2, and air at absolute pressures up to 4 atm. Parametric studies of the electrical circuitry and discharge dimensions demonstrate the importance of proper source-driver impedance matching to short-pulse operation and efficient electrical-to-optical energy conversion. Characteristic times for establishment of a conductive discharge gap in the heavy rare gases are consistent with breakdown by the single-stroke leader mechanism. The electrical strength of the gap following discharge remains low for a time which is much greater than the current duration. The delay in recovery is believed to be controlled by continued substrate ablation occurring after the discharge rather than to mechanisms related to plasma expansion or recombination. A shock wave is launched in a direction perpendicular to the dielectric surface while the plasma remains tightly pressed against the substrate. Measured wave velocities can be correlated with the theory of a Chapman–Jouguet detonation despite the fact that the physical processes in a surface discharge depart significantly from those in an optical detonation. Planar surface discharges radiate as Lambertian sources characterized by effective brightness temperatures ≂10 000–20 000 K (visible wavelengths) for specific input energies of ≂1–4 J/cm2. The plasma is not opaque and does not radiate as an ideal blackbody, but shows considerable structure due to line emission from neutral and singly ionized species originating from the gas atmosphere and vaporized substrate material. Line transitions from excited substrate species can greatly enhance the UV radiative output, especially for discharges across perovskite ceramic substrates.

Radiated energy for the rare gases is almost directly proportional to the atomic weight of the gas. Open-shutter photography, performed both perpendicular and parallel to the discharge plane, is used to develop criteria for obtaining uniform, coalesced discharges.
Electrical conduction in thin chromium films
Authors: Mehanna El Sayed A. , Arajs Sigurds , Helbig Herbert F. , Aidun Rashid , Kattan Nagah A. El.
Published: July 2002

We have prepared thin (50–1500 Å) polycrystalline films of Cr by vacuum (10−8 Torr) evaporation methods using the deposition rate on Corning glass 7059 and its temperature as experimental parameters. Electrical resistivity (ρ) of these films has been studied in situ as a function of temperature (T), film thickness (t), and the above preparation variables. Our films exhibit well-definied anomalies at the Néel temperature which is strongly dominated by internal stresses. The ρ vs T curves are briefly compared with those of other investigators.
Magnetic and crystallographic properties of Y2(Fe1−x Tx)14B (T=Al, Ti, Cr, Mn, and Ni)
Authors: Lin Chin , Lan Jian , Xu Xiao-Feng
Published: July 2002

Y2(Fe1−xTx)14B (T=Al, Ti, Cr, Mn, and Ni) compounds have been studied by x-ray diffraction and magnetic measurements. Lattice constants increase with increasing the content of Ti, and decrease with the contents of Al, Cr, Mn, and Ni. Saturation magnetizations and magnetocrystalline anisotropies were measured with a field up to 70 kOe over the temperature range from 1.5 to 290 K. The composition dependences of Curie temperatures are also given. Saturation magnetizations and Curie temperatures both decrease monotonically with increasing the contents of T except Ni. When Fe is substituted by Ni, the Curie temperature increases slightly, but the saturation magnetization decreases linearly. In contrast with Y2Fe14B, magnetocrystalline anisotropies decrease with increasing temperature in the substituted Y2(Fe1−xTx)14B compounds. The results are discussed in terms of site preference and distance dependence of magnetic interactions.
15-cm hybrid ion diode on PBFA-I
Authors: Mendel C. W. , Quintenz J. P. , Mix L. P. , Zagar D. M. , Noack R. L. , Grasser T. , Webb J. A.
Published: July 2002

Diode experiments on the PBFA-I pulser using a magnetically insulated ion diode are described. The insulating magnetic field is supplied by self-field due to the ion current plus the field generated by a series field coil. In the experiments described here, the diode operated at the 10-TW, 2.5-MV level with over 300 kJ going to the diode on many shots. The operation of the diode, the dielectric anode, and the proton beam focusing are described.
Relative lattice parameter measurement of submicron quaternary (InGaAsP) device structures grown on InP substrates
Authors: Twigg M. E. , Chu S. N. G. , Joy D. C. , Maher D. M. , Macrander A. T. , Chin A. K.
Published: July 2002

With x-ray diffraction techniques, it is possible to routinely measure lattice parameters to several parts in 104 for thin-film samples. However, measurements of lattice parameter changes for quaternary device structures several microns in width are not usually feasible with x-ray diffraction techniques. For this reason, transmission electron microscopy has been used to determine the position of higher-order Laue zone lines within convergent-beam electron diffraction patterns from thin foil cross sections of planar quaternary layers grown on InP substrates. A calibration curve has been generated which describes the position of higher-order Laue zone lines as a function of the lattice parameter determined from x-ray diffraction measurements. For the active quaternary region of an elecro-optical device structure, it is shown that ths calibration procedure may be sensitive to a relative change in lattice parameter as small as ±2 parts in 104.
Metastable atoms in a Mg beam: Excitation dynamics and velocity distribution
Authors: Giusfredi G. , Godone A. , Bava E. , Novero C.
Published: July 2002

We describe the realization of a source of Mg atoms in the metastable triplet 3s3p3P and we report a theoretical model describing the dynamic process of production of metastable atoms via electron impact excitation. Experimental results concerning atomic flux and velocity distribution are reported and compared with the theoretical model; the efficiency of production of metastable atoms was 40%, in good agreement with the computed value, and the velocity distribution showed a dependence from the discharge current close to the theoretical prediction.
X-ray scattering study of the magnetic phase transformation in GdB6
Authors: Galera R. M. , Osterman D. P. , Axe J. D. , Kunii S. , Kasuya T.
Published: July 2002

Gadolinium hexaboride is thought to have at least two magnetic phases in zero magnetic field. The structure of these phases, however, is still unknown. Due to the high neutron absorption of both Gd and B, studies by neutron scattering are not easy to do. We therefore used the alternative technique of x-ray magnetic scattering. Experiments were performed with a rotating anode x-ray source and CuKα radiation at temperatures down to 6 K. At the lowest temperatures two sets of superlattice reflections of the form (h/2,k,l) and/or (h,k/2,l) and (h/2,k/2,l) were observed. The intensity of both types of reflection remains roughly constant until 10 K. At this temperature the intensities of the (h/2,k,l) and (h,k/2,l) reflections increase sharply and reach a maximum around 11.5 K, while the (h/2,k/2,l) reflections rapidly disappear. At 12 K, only the former reflections are observed and they disappear discontinuously at TN =15.85±0.5 K. The results confirm the existence of two magnetic phase transitions in GdB6 and suggest a complex multi-q magnetic structure.
The shapes of first-stage sinters
Authors: Amar Francois , Bernholc J. , Berry R. Stephen , Jellinek Julius , Salamon Peter
Published: July 2002

The shape of first-stage sinters is derived within a framework in which a solid skeleton is wetted by a mobile‘‘liquid’’ pool. Several lattices are considered as possible solid skeletons, corresponding to various degrees of surface versus grain boundary and volume transport; the effect of a nonzero dihedral angle at the interface between crystal faces is also treated. In some cases, significant differences exist between shapes calculated by minimizing the free energy and the shapes assumed by previous workers.
Measurement of ultrasound attenuation by laser ultrasonics
Authors: Aussel J.-D. , Monchalin J.-P.
Published: July 2002

Laser ultrasonics is a technique which uses lasers to generate and detect ultrasound. Determination of the absolute ultrasonic attenuation is difficult since the diffraction corrections cannot be precisely calculated because of the poor knowledge of the laser beam’s intensity distributions. We show that there are two cases where this knowledge is not generally required, which allows precise determination of the attenuation. When the spherical wave approximation holds, i.e., for small laser spot sizes, thick samples, or low ultrasonic frequencies, the diffraction corrections can be precisely calculated. When the plane wave approximation holds, i.e., large laser spot sizes, thin samples, or high ultrasonic frequencies, the diffraction corrections are negligible. Both cases are illustrated with experimental data taken on ceramic and steel samples.
Application of isothermal current deep level transient spectroscopy to solar cells
Authors: Rancour D. P. , Pierret R. F. , Lundstrom M. S. , Melloch M. R.
Published: July 2002

The utility of isothermal current deep level transient spectroscopy (DLTS) techniques in directly probing solar cells is described and illustrated. A modified approach to processing the isothermal DLTS data is also presented. Specifically, it is pointed out that properly normalized isothermal data, whether derived from a current or capacitance transient, should conform to a single, temperature-independent curve.
Optical transitions in a step quantum well
Authors: Yuh P. F. , Wang K. L.
Published: July 2002

We have theoretically studied the field-dependent optical properties of a step quantum-well structure, which consists of a small well inside a big well. The wave functions of the small and big wells overlap and their eigenenergies have different field dependencies. The transition from a small-well state to a big well state thus gives a large Stark shift at low applied field without degrading the oscillator strength. Another advantage is to allow optical transitions that are forbidden in simple single-well structures. This relaxation of the selection rule makes it possible to provide optical pumping for intersubband lasing. Also, since the step well is asymmetric, many nonlinear properties are expected.
Study of brittle fracture by acoustic emission from indentation cracks
Authors: Kim Kwang Yul , Sachse Wolfgang
Published: July 2002

This paper describes a novel approach for investigating the fracture of brittle solids by combining a theory of acoustic emission (AE) with the Dugdale–Barenblatt model. An example is provided with indentation-produced, half-penny-shaped cracks that were generated by pressing a Vickers indenter onto the surface of a glass plate and that produced AE signals. These were detected using four capacitive displacement transducers, one at epicenter and the other three at off-epicentral positions. Assuming that a mode I type of crack was generated and using indentation fracture mechanics, a mode I stress intensity factor KIc=7.44×105 N/m3/2 was obtained. Both dipole strength and source-time function associated with crack formation were determined from the AE theory. Assuming that an effective gauge length can be interpreted equal to a dipole linkage distance and using the Dugdale–Barenblatt model for the fracture of brittle solids, it is shown that all the other important parameters on crack formation can be determined. Included are the critical rupture stress σc=8.94 GPa, the crack tip opening displacement of 1.62 nm, the effective microstructural gauge length equal to 13.2 nm, and the time-dependent crack velocity as a function of a crack front radius.
Construction and performance of a high-temperature-superconductor composite bolometer
Authors: Brasunas J. C. , Moseley S. H. , Lakew B. , Ono R. H. , McDonald D. G. , Beall J. A. , Sauvageau J. E.
Published: July 2002

A high-Tc superconducting bolometer has been constructed using a YBa2Cu3Ox thin-film meander line 20 μm wide and 76 000 μm long, deposited on a SrTiO3 substrate. Radiation is absorbed by a thin film of Bi with well-characterized absorption properties deposited on a Si substrate in contact with the SrTiO3. At 1.8 Hz the measured bolometer response to a 500-K blackbody is 5.2 V/W (820 V/W extrapolated to dc), and the NEP is 5.7×10−8 W/(Hz)1/2 . The impact of apparent nonohmic behavior at the transition is discussed, as are ways of reducing the observed 1/f noise. The response time is 32 s and is dominated by the heat capacity of the SrTiO3 substrate.
Photostimulation mechanisms of x-ray-irradiated RbBr:Tl
Authors: von Seggern H. , Meijerink A. , Voigt T. , Winnacker A.
Published: July 2002

The physical mechanism of photostimulated luminescence (PSL) of RbBr:Tl, resulting from x-ray irradiation, has been investigated. Spectroscopic methods have been utilized to identify the bromine F center as the occupied electron trap. By means of absorption studies the charge state of the dopant Tl was found to be monovalent. The spectral emission showed the characteristic Jahn–Teller splitting of the 3P1 state of the Tl+ and its known temperature dependence. PSL lifetime and efficiency experiments have been conducted in the temperature regime from liquid helium to 500 K to understand the charge transport from the F center to the activator and have been compared with corresponding data obtained from direct optical excitation into the A band of the Tl+. The observed temperature dependencies of both lifetimes could be explained by the properties of the s2 ion Tl+. As a resulting model for the PSL process a tunneling from the relaxed excited state of the F center to an excited state of the Tl2+ ion following photostimulation is suggested. The temporal, thermal, and spectral behavior of the subsequent radiative fraction of the deexcitation process is solely determined by the properties of the Tl+ ion in the RbBr matrix.
Chemically prepared amorphous Fe-B particles: Influence of pH on the composition
Authors: Linderoth S. , Mo/rup S.
Published: July 2002

Fe-B alloys have been prepared by reduction of Fe ions by NaBH4 in aqueous solutions. The boron content was found to vary with pH. For pH between 5 and 7, amorphous Fe72B28 powders were produced. Outside this pH range also α-Fe appeared in the samples. However, for pH=8 amorphous Fe86B14 was formed, constituting about 90% of the sample.
Carrier lifetimes in highly injected silicon
Authors: Misiakos K. , Park Ju-Sung , Neugroschel A.
Published: July 2002

The recombination lifetime under high-injection conditions in the base of n+/p−/p+ diode was investigated on the basis of the relation between electroluminescence and terminal current. For carrier plasma densities up to 1017 cm−3 the relation between the electroluminescence signal and the current through the device is linear and dominated by the heavily doped region recombination. This relation becomes sublinear for higher carrier density due to Auger recombination in the bulk of the p− base. The Auger recombination coefficient is extracted by fitting the experimental sublinearity with numerical solutions that express the electroluminescence signal as a function of the terminal current. In the 1017–6×1017 cm−3 carrier plasma density, the Auger coefficient was found to be 1.77×10−30 (±10%) cm6 s−1 at room temperature.
Efficient calculation of ionization coefficients in silicon from the energy distribution function
Authors: Goldsman Neil , Wu Yu-Jen , Frey Jeffrey
Published: July 2002

A method for calculating impact ionization coefficients by solving the Boltzmann transport equation is presented. The distribution function is taken to be expressible as a Legendre polynomial expansion, which is substituted into a Boltzmann equation that incorporates the effects of nonparabolic band structure, deformation-potential phonon scattering, and impact ionization. The resulting Boltzmann equation can be expressed in a linear form, and solved using sparse-matrix difference-differential methods. Ionization coefficients are obtained directly from the distribution function. Calculated values for the ionization coefficients agree very well with experiment for electrons in silicon.
Dependent scattering of an obliquely incident plane wave by a collection of parallel cylinders
Authors: Lee Siu-Chun
Published: July 2002

Scattering of an obliquely incident electromagnetic wave by an arbitrary configuration of parallel, nonoverlapping infinite cylinders is considered in this study. The incident wave is plane polarized with either of the field vectors parallel to the axes of the cylinders. The solution to the scalar wave equations is obtained by using the boundary value method. The total wave potentials in the vicinity of a cylinder is constructed by including the contributions from the primary incident wave and the scattered waves from all the cylinders. Expressions for the coefficients of the scattered wave potentials are obtained in terms of those for independent scattering. Numerical results are presented to illustrate the effect of dependent scattering by an assembly of cylinders.
Refractive index gratings in rare-earth-doped alkaline earth glasses
Authors: French Valentina A. , Powell Richard C. , Blackburn Douglas H. , Cranmer David C.
Published: July 2002

Four-wave-mixing techniques were used to produce permanent laser-induced refractive index gratings in Eu3+ -doped silicate glasses. These gratings are associated with a thermally induced change in the local glass structure at the site of the Eu3+ ions, leading to a double-minimum potential well for the electronic energy levels of the Eu3+ ions. The effects on the characteristics of the permanent laser-induced gratings produced by changing the divalent modifier ions of the glass host are reported and a theoretical model is presented to explain the physical origin of the change in the refractive index of the material.
Low-temperature epitaxial growth of cerium dioxide layers on (111) silicon substrates
Authors: Inoue T. , Osonoe M. , Tohda H. , Hiramatsu M. , Yamamoto Y. , Yamanaka A. , Nakayama T.
Published: July 2002

The temperature dependence of the epitaxial growth of cerium dioxide (CeO2) layers on (111) silicon substrates was studied using ultra-high-vacuum evaporation, varying the substrate temperature in the range between 150 and 900 °C. Characterization using Rutherford backscattering spectrometry and reflection high-energy electron diffraction proved that a CeO2 layer on (111) silicon has considerably good crystalline quality in the range between 200 and 850 °C. It is clarified that the epitaxy can be attained even at surprisingly low temperatures (less than 200 °C). A substrate temperature above 850 °C leads to rather poor crystallinity due to an exponential increase of residual gas pressure. Refractive indices of the epitaxial layers were measured by ellipsometry to be in the range of 2.19–2.79.
Noise characteristics of barium ferrite particulate rigid disks
Authors: Kodama Naoki , Inoue Hitoshi , Spratt Geoffrey , Uesaka Yasutaro , Katsumoto Masayuki
Published: July 2002

This paper discusses the relationship between the noise characteristics and magnetic properties of longitudinal barium ferrite (Ba-F) rigid disks with different switching field distributions (SFD). The magnetomotive force dependencies of reverse dc-erase (RDC) noise are measured and compared with SFD values. Coated disks with acicular magnetic particles have dips and thin-film disks peaks in the RDC. In Ba-F disks, both cases are observed depending on the SFD values, though the depths or heights of the RDC noise are much smaller than those of coated disks with acicular particles or thin-film disks. Disks with small SFD values have peaks, and disks with large SFD values have dips. In order to find the relationship between noise properties and magnetic properties, interparticle interactions in Ba-F disks are investigated. Reverse dc remanence Id(H) and ac-demagnetized isothermal remanence Ir(H) are measured. Both are normalized by the saturation remanence. The deviation from the noninteracting system, ΔM = Id(H) − [1ΔM=Id(H)−[1− 2Ir(H)] and an interaction field factor (IFF) given by (H′r − Hr)/Hc, are derived from these remanent properties. Here, H′r is the field corresponding to 50% of the remanent magnetization, Hr is remanence coercivity. In Ba-F disks, ΔM shows positive interactions, and the peak heights of ΔM increase and IFF decrease with decreasing SFD values. Positive interactions between Ba-F particles seem to be caused by particle stacking. Therefore, particle stacking results in small SFD values and peak-type RDC noise.
Study of semitransparent palladium contacts on mercuric iodide by photoluminescence spectroscopy and thermally stimulated current measurements
Authors: Bao X. J. , Schlesinger T. E. , James R. B. , Gentry G. L. , Cheng A. Y. , Ortale C.
Published: July 2002

Semitransparent palladium contacts on mercuric iodide were studied by low temperature photoluminescence spectroscopy and thermally stimulated conductivity. These contacts were deposited either by thermal evaporation or by plasma sputtering. Changes due to palladium deposition were found in the photoluminescence spectra and were attributed to modifications in the stoichiometry within the palladium/mercuric iodide interfacial region. Thermally stimulated conductivity measurements revealed two dominant traps with activation energies of 0.010 and 0.54 eV. The importance of these traps in the application of nuclear detection is discussed.
Calculation of the base current components and determination of their relative importance in AlGaAs/GaAs and InAlAs/InGaAs heterojunction bipolar transistors
Authors: Liou J. J.
Published: July 2002

The base current density JB is an important parameter in determining the common-emitter current gain β of heterojunction bipolar transistors (HBTs). To develop an analytical β model with which a circuit designer can quickly estimate the current gain in a HBT, it is also important to identify the dominant component of JB so that minimum computations are required. Based on heterojunction device physics, the three components of JB have been calculated, namely, the recombination current density in the base JRB, the recombination current density in the space-charge region JSCR, and the injection current density from the base to the emitter JRE, and have determined their relative importance to JB for abrupt AlGaAs/GaAs and InAlAs/InGaAs HBTs under normal bias conditions. It is found that relative importance of the three current densities depends strongly on the bias condition, strongly on the density of states NtI at the emitter-base heterointerface, but weakly on the density of trapping states NtB in the bulk of the emitter-base space-charge region. Also, JB is relatively insensitive to device makeup such as doping concentration and layer thickness. Depending on NtI and on the bias condition, either JSCR or JRE is the dominant component for AlGaAs/GaAs HBTs and either JSCR or JRB is the dominant component for InAlAs/InGaAs HBTs. Effects of base and heterojunction grading on the present findings are also addressed.
Si—O bond structure in slow-ion deposited SiO2 films
Authors: Baek D. H. , Kim B. O. , Jeong J. I. , Kim C. Y. , Chung J. W.
Published: July 2002

By impinging a beam of O+2 ions of energy 150 eV<E<1 keV on a Si(100) surface, we produced oxide films of varying thickness at room temperature. We find that the Si—O bond features of the films are quite similar to those of a thermally prepared vitreous SiO2 glass. We further observe that an intermediate range order in the form of n-member ring clusters with n=4 and n=6 exists in the resulting films.
Velocity distributions and photodissociation of neutral C60 and C70 clusters
Authors: Wurz Peter , Lykke Keith R. , Pellin Michael J. , Gruen Dieter M.
Published: July 2002

Purified samples of C60 and C70 are synthesized according to recently published procedures. Desorption with 308 nm laser light from solid C60 and C70 samples is used as a neutral cluster source to study the ionization and concurrent fragmentation in the gas phase by interaction with intense laser radiation. According to a well-known classification scheme, the ionization/fragmentation behavior of C60 and C70 clusters is clearly identified as of class A type. Also, the laser desorption process itself has been investigated by measuring the velocity distributions of laser desorbed neutral C60 and C70 clusters. Good agreement of the experimental data with a Maxwell-Boltzmann distribution is found. We conclude that at the applied laser fluences, C60 and C70 clusters are desorbed by evaporation induced by the incident radiation, providing no fragmentation in the desorption process.
The plasma waveguide with a finite thickness of cladding
Authors: Shen Hao-Ming , Pao Hsueh-Yuan
Published: July 2002

The properties of the plasma waveguide of finite thickness (plasma tube) have been studied. The analysis indicates that, in the case of finite thickness, most of the properties for the plasma waveguide with infinite thickness are retained. At high frequencies, such a plasma tube is still a nondispersive waveguide system. The losses due to the finite thickness of the cladding and the conductivity of the plasma are both small. The decay coefficient decreases with the thickness exponentially. With a thickness equal to the radius of the central core, the attenuation can be as low as 0.1 dB/km.
A Monte Carlo study of the dipolar ferromagnetic transition
Authors: Bouchaud J. P. , Zérah P. G.
Published: July 2002

We investigate numerically the dipolar ferromagnetic transition on an fcc lattice. The transition temperature and the critical exponents are determined. In particular, the specific heat is found to diverge at the transition. We find a second transition in the low-temperature phase where the anisotropy field switches from [100] to [111].
Fabricating magnetic Co-Ni-C thin-film alloys by organometallic chemical vapor deposition
Authors: Kim Yoon-Gi , Byun Dongjin , Hutchings C. , Dowben P. A. , Hejase H. , Schröder K.
Published: July 2002

We have deposited CoxNiy-C films with a variety of compositions to verify dependence of the saturation magnetization on the composition. These experiments suggest that we can produce CoxNiy-C films with a variety of magnetic properties. The CoxNiy-C films were fabricated by ultraviolet decomposition of cobaltocene and nickelocene. We demonstrated that the photolytic decomposition of these metallocenes produces cyclopentadienyl (C5H5) species, consistent with recent studies of the energetics of the ligand metal bonds.
Lubricant dynamics in sliding and flying
Authors: Novotny V. J. , Baldwinson M. A.
Published: July 2002

The dynamics of molecularly thin liquid lubricant films in sliding and flying experiments is studied principally by scanning microellipsometry and complemented with both scanning x-ray photoelectron spectroscopy and infrared spectroscopy. Microellipsometric profiling of lubricant thickness is performed in situ, either dynamically or statically on films ranging from 1 to 10 nm. The removal of liquid polyperfluoroether lubricants from sliding and flying tracks, which includes the displacement and loss depends on film thickness, molecular weight, and chemical structure. In flying and sliding, the lubricant removal rate from monolayer films is significantly slower than from multilayer films. In flying, lubricant displacement and loss increase with a decrease in molecular weight.
Probing laser induced metal vaporization by gas dynamics and liquid pool transport phenomena
Authors: DebRoy T. , Basu S. , Mundra K.
Published: July 2002

During laser beam welding of many important engineering alloys, an appreciable amount of alloying element vaporization takes place from the weld pool surface. As a consequence, the composition of the solidified weld pool is often significantly different from that of the alloy being welded. Currently there is no comprehensive theoretical model to predict, from first principles, laser induced metal vaporization rates and the resulting weld pool composition changes. The weld pool heat transfer and fluid flow phenomena have been coupled with the velocity distribution functions of the gas molecules at various locations above the weld pool to determine the rates of the laser induced element vaporization for pure metals. The procedure allows for calculations of the condensation flux based on the equations of conservation of mass, momentum and energy in both the vapor and the liquid phases. Computed values of the rates of vaporization of pure metals were found to be in good agreement with the corresponding experimentally determined values. The synthesis of the principles of gas dynamics and weld pool transport phenomena can serve as a basis for weld metal composition control.
Operational theory of crossed-field devices based on double-box density profiles
Authors: Kaup David J. , Thomas Gary E.
Published: July 2002

Studies of the nonlinear evolution of the electron-density profile in crossed-field devices indicate the classical Brillouin profile to be inadequate for the explanation of the operation of such devices. Instead, the existence of a density plateau at the edge of the electron sheath is found to be essential in the operation of such a device. Such a plateau placed at the edge of a classical Brillouin profile creates a double-box profile. The operational theory for crossed-field devices based on this double-box density profile is presented. It is shown that this profile generates an operating voltage range that agrees quite well with the actual voltage operating range of such devices, except for high magnetic fields.
Effect of electronic strain on the optically induced mechanical moment in silicon microstructures
Authors: Prak Albert , Lammerink Theo S. J.
Published: July 2002

A model for the effect of the presence of photogenerated electron-hole pairs on the optically induced mechanical moment in a silicon cantilever beam has been developed. This effect is twofold and is the consequence of electronic strain on one hand and of the recombination heat of the photogenerated electron-hole pairs on the other. It manifests itself by a deviant phase- frequency relation of the vibrating beam in comparison with a pure thermally excited beam. Experiments have been performed, and the results show excellent agreement with the model.
The thermal conductivity of chemical-vapor-deposited diamond films on silicon
Authors: Graebner J. E. , Mucha J. A. , Seibles L. , Kammlott G. W.
Published: July 2002

The thermal conductivity of chemical-vapor-deposited diamond films on silicon is measured for the case of heat flow parallel to the plane of the film. A new technique uses thin-film heaters and thermometers on a portion of the film which is made to be free standing by etching away the substrate. Effects of thermal radiation are carefully avoided by choosing the length scale properly. Data for several films yield thermal conductivities in the range 2–6 W/cm °C. This is comparable to copper (4 W/cm °C) and is in a range that would be useful as a thin-film dielectric material, provided that the interface thermal resistance can be minimized. The conductivity varies inversely with the growth rate and the Raman linewidth.
Nanosecond photothermal dynamics in colloidal suspension
Authors: Kesavamoorthy R. , Super Mike S. , Asher Sanford A.
Published: July 2002

Thermal diffusion from a single colloidal sphere suspended in an aqueous medium that is heated by a laser pulse is examined. The temperature field as a function of position and time arising from the cooling of a hot colloidal sphere suspended in an infinitely extended aqueous medium is obtained by solving the heat conduction equation with initial, asymptotic, boundary conditions using a Laplace transform technique. A polymethylmethacrylate sphere of 83 nm diameter is calculated to cool in water within 7 ns. The cooling time is found to decrease quadratically with the particle diameter. We discuss the use of arrays of dyed polymethylmethacrylate spheres suspended in a refractive-index-matched aqueous medium as a fast (ns) optical switching device which acts as an optical monostable.
Aging characteristics of ZnS:Mn electroluminescent films grown by a chemical vapor deposition technique
Authors: Mikami Akiyoshi , Terada Kousuke , Okibayashi Katsushi , Tanaka Kouichi , Yoshida Masaru , Nakajima Shigeo
Published: July 2002

The stability of luminance-voltage characteristics (L-V) has been investigated on ZnS:Mn electroluminescent films grown by chemical vapor deposition. It is found that the aging pattern varies between the positive shift (P shift) and the negative shift (N shift) with the growth temperature. In both cases the L-V curve, the current-voltage relationship, and the symmetry of the light emission with respect to the voltage polarity are strictly cooperative during the aging process. The N shift appears to be dominant when the current is limited by electron injection from the interface, whereas the P shift becomes dominant under the bulk limited conduction, accompanying an excellent symmetry of the emission. A high-field-conduction characteristic in the ZnS layer, which is a decisive factor to determine the aging pattern, is significantly affected by its stoichiometry, grain size, and impurity content. It has been further clarified that the N shift consists of the combination of a softening and a shifting in the L-V relation, which are defined as the effect due to the asymmetric polarization and the band bending in the ZnS layer, respectively. This study demonstrates a stable L-V characteristic without shifting the threshold voltage. The difference between the P shift and the N shift is discussed on the basis of the crystalline property and the carrier transport mechanism.
Excitons in semiconductor quantum wells: A straightforward analytical calculation
Authors: Mathieu Henry , Lefebvre Pierre , Christol Philippe
Published: July 2002

A new and very simple method is presented for calculating exciton binding energies in quantum confined semiconductor structures. The aim of the model calculation, which is developed in the framework of the fractional-dimensional space, is not to compete with the very advanced ones already proposed but, on the contrary, to avoid tedious and expensive calculations to obtain, with a good accuracy, the exciton binding energy in most of the confined structures. Furthermore, in the cases where the 1s and 2s transition energies can be experimentally measured, the method permits one to obtain the exciton binding energy without any hypothesis nor calculation.
bcc cobalt: Metastable phase or forced structure?
Authors: Liu Amy Y. , Singh David J.
Published: July 2002

General potential linearized augmented plane wave calculations of the elastic and magnetic properties of body-centered-cubic (bcc) Co are presented and discussed. Particular attention is given to the nature of the stability of bcc Co films that have been grown epitaxially on GaAs substrates. The bcc structural phase of Co, which is not found in nature, is calculated to be unstable with respect to a tetragonal distortion that transforms it continuously into the face-centered-cubic (fcc) phase. This means that bcc Co is not a true metastable phase of bulk Co. The thinner films of bcc Co that have been synthesized are more properly termed forced structures. We speculate that the few existing thick (up to 357 Å) samples of bcc Co are stabilized by the presence of impurities or other defects. This is further supported by discrepancies between the measured and calculated magnetic moments in bcc Co.
Measurement of ion species ratio in the plasma source ion implantation process
Authors: Tang B. Y. , Fetherston R. P. , Shamim M. , Breun R. A. , Chen A. , Conrad J. R.
Published: July 2002

Ion species and their ratios in nitrogen, oxygen, and argon plasmas in the plasma source ion implantation process have been determined with a simple and low-cost measurement system. The measured ion species ratio in the nitrogen plasma was used as an input parameter for the computer simulation code transport and mixing from ion irradiation to predict the atomic composition-depth profile. Comparison between the code results and data derived from Auger analysis for a nitrogen-implanted Ti-6Al-4V alloy showed good agreement. In this article, the design, performance, and possible future improvements regarding the resolution of this measurement system will be discussed.
Alternate heteroepitaxial growth of vanadyl- and chloroaluminum-phthalocyanines on KBr and KCl
Authors: Morioka Toshiko , Tada Hirokazu , Koma Atsushi
Published: July 2002

Ultrathin films of vanadyl phthalocyanine (VOPc) and chloroaluminum phthalocyanine (AlPcCl) have been grown alternately on cleaved (001) faces of KBr and KCl by molecular-beam epitaxy. Surface structures of the grown films were investigated by reflection high-energy electron diffraction. The arrangements of metal phthalocyanine molecules in the upper layer are found to be strongly influenced by those in the sublayer. As a result, new types of molecular arrangements have been obtained. The multilayered films consisting of VOPc and AlPcCl layers have shown characteristic visible absorption spectra depending on their own structures. The peak positions of intense Q bands shift gradually to longer wavelengths with an increase in the number of the alternation with VOPc and AlPcCl layers on KBr and KCl.
Laser ablative hole formation in amorphous thin films
Authors: Blatter A. , Ortiz C.
Published: July 2002

Laser ablative hole formation in amorphous Te-Se-I films was studied by microscopy and transient reflectivity measurements. Laser pulses of variable power and length were focused to either 0.8 or 10 μm spots on the films which were deposited on glass and polycarbonate substrates. The important feature of these films was that they did not crystallize upon pulsed laser irradiation. This allowed the examination of dependences on experimental parameters without the complication of phase transitions. The absence of a crystal-melt interface in the films enabled the ablation of holes with exceptionally smooth rims. The experiments confirm that hole formation is by material flow, induced by the laser heating, radially away from the irradiation center. We show that the hole opening is a thermally activated process limited by viscous flow. A barrier of 0.7 eV is derived for the Te-Se-I films. Film viscosity and substrate thermal properties are identified as the key variables by which the dynamics of the process can be affected and the final shape of the hole thereby controlled.
Impression creep of a thin film by vacancy diffusion. I. Straight punch
Authors: Yang Fuqian , Li J. C. M.
Published: July 2002

A closed-form solution for diffusion in two dimensions is obtained for impression creep of a thin film by a straight punch. The results show that for a rigid impermeable substrate the penetration rate is proportional directly to the thickness of the film and inversely to the square of the punch width. Without the substrate the penetration rate is inversely proportional to the thickness of the film and independent of the punch width.
On spinodal decomposition in elastically anisotropic epitaxial films of III-V semiconductor alloys
Authors: Ipatova I. P. , Malyshkin V. G. , Shchukin V. A.
Published: July 2002

The elastic energy associated with alloy composition modulation in the epitaxial film of a III-V semiconductor alloy on the [001]-substrate is calculated in the analytic form. Composition modulation both in the directions parallel to the substrate surface and in the growth direction are taken into account. It is shown that the minimum of the elastic energy corresponds to the modulation along the [100]- (and/or [010]-) direction, the period of the modulation d being small compared to the film thickness h (d≪h). The ‘‘soft mode’’ of composition modulation is exponentially localized near the free surface, the localization length l being l=d/2π. The elastic energy caused by this modulation is less by the factor 1/2c11/(c11+c12) than the elastic energy corresponding to spinodal decomposition in the bulk sample. This factor is ≊1/3 for III-V alloys. Critical temperatures of spinodal decomposition Tc are calculated for a number of epitaxial ternary III-V alloys. The diffusion which occurs only in the very thin subsurface layer (nearly monolayer) is shown to provide exponential amplification of the composition modulation amplitude δc(0)∼exp(Δh/l) at early stages of the subsequent layer-by-layer growth.
Magnetic profile as a function of structural disorder in Fe/Cr superlattices
Authors: Pechan Michael J. , Ankner J. F. , Majkrazk C. F. , Kelly David M. , Schuller Ivan K.
Published: July 2002

Structural disorder has been systematically introduced in an [Fe(30 Å)/Cr(17 Å)]10 superlattice to investigate its effects on the magnetization profile. Low angle x-ray and neutron scattering results indicate progressive structural degradation in samples produced with increased argon pressure (3, 6, and 12 mTorr). The x-ray spectra from the more disordered samples are characterized by a decreased intensity and increased linewidth of the superlattice Bragg peaks, along with a systematic disappearance of the finite size intensity oscillations. Elastic, polarized, low angle, neutron reflectivity data exhibit decreasing superlattice Bragg intensities and increasing linewidths, indicating increased disorder in agreement with x-ray data. Antiferromagnetic alignment of adjacent Fe layers is inferred by the appearance of magnetic peaks between the structural peaks and by the lack of magnetic contribution to the structural superlattice peaks. Interestingly, the magnetic superlattice peak does not exhibit appreciable degradation with increasing disorder in the structure, indicating a magnetic coherence length significantly greater than that of the chemical superlattice structure.
Thermal strain effects on the excitonic states in GaAs/AlxGa1−xAs multiple quantum wells
Authors: Prete P. , Cingolani R. , Rinaldi R. , Ploog K. H.
Published: July 2002

Temperature-dependent absorption experiments have been performed to investigate the effect of thermal strain in GaAs/AlxGa1−xAs multiple quantum wells clad by thick AlGaAs layers. A temperature-dependent splitting of the heavy-hole and light-hole excitons is observed between 10 and 300 K. This is ascribed to the different thermal expansion coefficient of GaAs and AlxGa1−xAs, causing the constituent GaAs layers to be under weak tensile strain during the optical measurements at different temperatures.
Amplification of an electromagnetic wave in the polariton mode of magnetoplasma
Authors: Iida Takashi , Mizushima Yoshihiko
Published: July 2002

The magnetoplasma amplification theory in an ionic semiconductor crystal is further expanded. A new type of a magnetoplasma amplification utilizes the phonon as an oscillator. The Lorentz force in the Voigt configuration causes the interaction between the electrons’ space-charge wave, the optical phonon, and the electromagnetic wave. In the Reststrahlen frequency range, the induced dielectric constant dispersion provides a slow-wave structure and causes a phase shift in the waves, which are combined in drifting synchronization. It results in a traveling wave instability. The new amplifications appear very near the transverse phonon frequency and the longitudinal phonon frequency, respectively, corresponding to the forward-wave coupling and backward-wave coupling.