bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective ionization of group I elements from laser ablated plumes of Rb⋅Ga⋅Sb, K3Ga3As4, and K4In4As6
Authors: Panayotov Valentin , Hamar Kyle , Red Clarence , Birdwhistell Teresa L. T. , Koplitz Brent
Published: July 2002

Experimental results are reported on the I–III–V Zintl compounds Rb⋅Ga⋅Sb, K3Ga3As4, and K4In4As6 with respect to laser ablation and subsequent laser ionization/removal processes. The approach takes advantage of the low ionization potentials of the group I elements to achieve selectivity and exert a measure of control over neutral mixtures. A 308 nm laser pulse is used to ablate a I–III–V Zintl compound, while a second laser is used to selectively ionize the ejected species within the extraction region of a time-of-flight mass spectrometer. With the second laser operating at 248 nm (in the case of Rb⋅Ga⋅Sb) and at 266 nm (in the case of K3Ga3As4 and K4In4As6), selective gas-phase ionization and removal of the group I elements is clearly demonstrated.
Magnetic properties of amorphous Sm–Fe and Sm–Fe–B thin films fabricated by radio-frequency magnetron sputtering
Authors: Choi Y. S. , Lee S. R. , Han S. H. , Kim H. J. , Lim S. H.
Published: July 2002

Magnetic properties of giant magnetostrictive Sm–Fe and Sm–Fe–B thin films are systematically investigated over a wide composition range from 14.1 to 71.7 at. % Sm. The amount of B added ranges from 0.3 to 0.8 at. %. The microstructure mainly consists of an amorphous phase in the intermediate Sm content range from 20 to 45 at. %. Together with an amorphous phase, crystalline phases of Fe and Sm also exist at low and high ends of the Sm content, respectively. Well-developed in-plane anisotropy is formed over the whole composition range, except for the low Sm content below 15 at. % and the high Sm content above 55 at. %. As the Sm content increases, the saturation magnetization decreases linearly and the coercive force tends to increase, with the exception of the low Sm content where very large magnitudes of the saturation magnetization and the coercive force are observed due to the existence of the crystalline α-Fe phase. The coercive force is affected rather substantially by the B addition, resulting in lower values of the coercive force in the practically important Sm content range of 30–40 at. %.
Experimental evidence of pressure-induced magnetic phase transition in Fe72Pt28 Invar alloy
Authors: Odin S. , Baudelet F. , Itié J. P. , Polian A. , Pizzini S. , Fontaine A. , Giorgetti Ch. , Dartyge E. , Kappler J. P.
Published: July 2002

X-ray magnetic circular dichroism (XMCD) measurements have been performed under high pressure and used to study the disordered Fe72Pt28 Invar alloy in conjunction with x-ray diffraction. The high spin to low spin state transition is observed by both techniques and is compared with previous work. Furthermore, XMCD gives the first evidence of the complete disappearance of the magnetic moment at high pressure in this alloy. It also proves the existence of an hysteresis cycle due to the pressure-dependent magnetic moment.
Plausible d-wave cuprate superconductivity: Muon-spin-relaxation studies of RBa2Cu3O7−δ vortex states
Authors: Boekema C. , Ruiz E. J. , Pobre Z. C. , Punjabi S. R. , Kong F. , Vera O. , Cooke D. W.
Published: July 2002

The rare-earth (R) magnetism and grain-size dependencies of magnetic field distributions in RBa2Cu3O7−δ (RBCO) vortex states have been studied. A maximum-entropy technique has been applied to transverse field muon-spin-relaxation data of several polycrystalline cuprate superconductors. The main vortex signals for R=Er, Gd, and Ho reveal signs of two peaks in the field distribution below the applied field (Bext=1 kOe) as predicted for d-wave superconductivity. For the RBCO (R=Er, Gd, Ho, Eu, Y) vortex states, we have confirmed low-field tails in the field distributions well below Bext. The low-field tail may be caused by magnetic frustration in the vortex state or possible CuO-chain superconductivity below 25 K. Any interpretation of these (magnetic) vortex anomalies should comprise unconventional non-Bardeen–Cooper–Schrieffer-like fundamental properties of the cuprate vortex states.
Micromachined YBaCuO capacitor structures as uncooled pyroelectric infrared detectors
Authors: Butler Donald P. , Çelik-Butler Zeynep , Jahanzeb Agha , Gray John E. , Travers Christine M.
Published: July 2002

Uncooled pyroelectric infrared detectors based on semiconducting Y–Ba–Cu–O have been investigated. Samples with four different structures were characterized. Two of the pyroelectric detectors were thermally isolated from the substrate by micromachining techniques for high optical sensitivity. Pyroelectricity was observed by the methods of optical illumination and direct substrate heating. A wide range of the values of pyroelectric coefficients was obtained with the maximum close to 20 μC/cm2 K in one device. Detectivities up to 108 cm Hz1/2/W were measured. The temperature dependence of these pyroelectric sensors was investigated. It was found that one device showed a fairly constant optical response with respect to temperature over a wide range around 300 K. However, responsivity of another device of a different geometry decreased sharply at ∼304 K. The spectral study of these devices showed that the wavelength-dependent response decreased when the silicon transmission increased. In addition, frontside illumination evoked a much stronger response than backside illumination. This is attributed to the enhancing effect of the microcavity under the bridge and the transmission properties of the silicon substrate.
Effects of post-growth treatment and coating with ultrathin metal layers on the band bending and field electron emission of diamond films
Authors: Polyakov V. I. , Rossukanyi N. M. , Rukovishnikov A. I. , Pimenov S. M. , Karabutov A. V. , Konov V. I.
Published: July 2002

Band bending formation on thin nanocrystalline diamond films and field electron emission after post-growth treatments was investigated. It was found that treatment of the diamond surface with hydrogen plasma substantially decreases the density of point defects, forms the downward band bending and enhances the field electron emission from the films. In the case of an argon plasma treated diamond surface, new point defects were induced and their energy distribution was changed. Nevertheless, the downward band bending was formed and the field electron emission was enhanced similar to the H–plasma-treated diamond surface with minor density of defects. These effects were interpreted in terms of the electrical dipole formation on the plasma treated diamond surfaces. Coating the diamond films with ultrathin metal (Ni, Ti) layers revealed the dependence of the band bending and field emission behavior on the type and thickness of the metal used. The deposition of a few monolayers of Ni on the diamond surface was found to raise the position of the Fermi level relative to the valence band maximum and cause the downward band bending, reducing the field emission threshold. It was suggested that the charge of the surface dipoles on the metal coated diamond surfaces (as in the case of the H and Ar plasma treatments) plays a key role in the band bending formation.
Electrode phenomena and current distribution in a radial multichannel pseudospark switch
Authors: Bergmann K. , Kiefer J. , Gavrilescu C. , Neff W. , Lebert R.
Published: July 2002

The microscopic structure and the spatial distribution of the cathode spots in a radial multichannel pseudospark switch have been investigated by means of scanning electron microscopy. Current pulses of about 15 μs duration and peak amplitudes up to 340 kA have been applied. When using stainless steel and copper as electrode material cathode spots of type I and type II are observed. These cathode spots appear in groups (macrospots) with a diameter of several 100 μm. Assuming that the lifetime of the macrospots corresponds to the half period time of the current pulse the distribution of the cathode spots within the macrospots can be explained by a retrograde motion of the spots with a velocity of several 100 m/s in the self-magnetic field of the discharge current. Furthermore, the spatial distribution of the cathode spots within the macrospots can be interpreted by assuming a splitting and a repulsion of the cathode spots. The electrode phenomena show that the discharge current is distributed over a large area which is prerequisite for low erosion and long lifetime operation of the switch.
Ga
2+
hole centers and photostimulated luminescence in the x-ray storage phosphor RbBr:Ga+
Authors: Rogulis U. , Schweizer S. , Assmann S. , Spaeth J.-M.
Published: July 2002

It was previously shown that RbBr doped with Ga+ is an efficient x-ray storage phosphor with a figure of merit comparable to that of the commercially used BaFBr:Eu2+. The paramagnetic hole centers generated upon x-irradiation involved in the storage and read-out process were investigated by measuring the magnetic circular dichroism of the optical absorption (MCDA), the MCDA-detected electron paramagnetic resonance (MCDA-EPR) and the photostimulated luminescence (PSL). Two different Ga2+ hole centers with a hyperfine interaction with 69Ga of 69A = 8.2 GHz and 69A=6.0GHz, respectively, were found. No superhyperfine interaction was resolved. Therefore, the structural difference between the two Ga2+ centers could not be established from EPR. The PSL effect is correlated only to one of the two Ga2+ centers, namely that with A=8.2 GHz. The generation mechanism of the two hole centers is investigated. It is proposed that the PSL-active Ga2+ center is an isolated Ga2+ on a Rb+ site, whereas the other center is a Ga2+-cation vacancy complex.
Analysis of multiple-tunnel junctions and their application to bidirectional electron pumps
Authors: Jalil M. B. A. , Ahmed H. , Wagner M.
Published: July 2002

A quantitative analysis is performed of a bidirectional electron pump circuit that incorporates multiple-tunnel junctions (MTJs), with special emphasis on stability diagrams. The number of electrons transferred per cycle is calculated to be in general agreement with experimental data. The frequency and temperature conditions under which the circuit deviates from ideal pumping operation are evaluated, which suggests that the prospect for a metrological application is not improved by the presence of ultrasmall capacitances in the MTJs.
AC loss analysis on high-temperature superconductors with finite thickness and arbitrary magnetic field dependent voltage–current relation
Authors: Yazawa T. , Rabbers J. J. , ten Haken B. , ten Kate H. H. J. , Maeda H.
Published: July 2002

A numerical model is developed for the current distribution in high-temperature superconductors (HTS conductors) subjected to self and applied field. This analysis is based on the two-dimensional Poisson equation for the vector potential. The vector potential is rewritten into an equation of motion for the current density J. The finite thickness of the conductor and the n-power law electric field-current density relations (E-J relations) of the conductor are included in the model. The magnetic field dependence of critical current density Jc is also included in this E-J relation. The self-field loss obtained with this analysis has good agreement with experimental data. Also the effects of aspect ratio and n value on ac loss are pointed out to be important on the ac loss.
Field-dependent surface impedance of a bilayer film with an antisymmetric bias magnetization
Authors: Makhnovskiy D. P. , Antonov A. S. , Lagar’kov A. N. , Panina L. V.
Published: July 2002

The evolution of magneto-impedance (MI) behavior under the effect of an antisymmetric transverse bias field is studied in a bilayer film with in-plane anisotropy directed at an angle ±α with respect to the current flow. By symmetry, this case is similar to MI in a helically magnetized wire, but in contrast to the wire, permits an analytical consideration at any frequencies in terms of the surface impedance tensor ζ̂. The longitudinal diagonal component of ζ̂ contributes to the voltage between the ends of the sample, whereas the off-diagonal component related to the inverse Wiedemann effect indicates that the current flow induces a circular electric field or a coil voltage. A strong skin effect existing at certain high frequencies causes the surface impedance to become an explicit function of the ac permeability and the stable magnetization direction both of which can be sensitive to a dc magnetic field. Without the dc bias, the plots of impedance versus longitudinal field exhibit a symmetric hysteresis. With increasing bias field, the hysteresis area shifts and shrinks, and finally disappears, resulting in highly sensitive asymmetric impedance plots. Such behavior is in line with that reported for a twisted amorphous wire excited by a sharp current pulse involving low and high frequency harmonics.
Application of silver-dispersed AlN thin film to solar control glass
Authors: Nakashima Hiroshi , Yonekura Masaaki , Wakabayashi Hideaki , Kominami Masanobu
Published: July 2002

Solar reflective multilayered films which mainly reflect near-infrared rays in solar radiation but transmit radio waves were prepared by dispersing fine silver particles in an AlN layer of the film. The silver particle-dispersed AlN film was fabricated by heating the film consisting of three layers of AlN, Ag, and AlN. A theoretical equation regarding the reflection–wavelength relationship was derived based on the assumption that the power reflection coefficient of dielectric film, in which metal particles are randomly dispersed, is expressed by the reflection from many domains of different sizes, each domain consisting of periodic conductive square segments. Comparing the theoretical values of reflection for silver-dispersed AlN thin film with the observed ones allows us to estimate the mean size and thickness of silver particle to be 130 and 18 nm, respectively. This suggests that the frequency selective screen which reflects only near-infrared rays can be designed by controlling the size of silver particles.
Characterizations of sol-gel grown (PbLaLi)(Zr0.60Ti0.40)O3
Authors: Shannigrahi S. R. , Choudhary R. N. P. , Acharya H. N. , Sinha T. P.
Published: July 2002

Polycrystalline samples of Pb0.92(La1−zLiz)0.08(Zr0.60Ti0.40)0.98+0.04zO3 (z=0.0, 0.1, 0.3, 0.5, 0.7) have been prepared using the metal-alkoxide sol-gel technique. Differential thermal analysis and x-ray diffraction studies show that the above materials can be formed in a single-phase perovskite structure at 550 °C. The formation of grain structure, particle size, and their distributions have been studied by scanning electron microscopy and transmission electron microscopy, respectively. Systematic studies of compositional dependence of ferroelectric properties [dielectric constant (ε), dielectric loss (tan δ), remanent polarization (Pr), coercive field (Ec), piezoelectric coefficients, and pyroelectric coefficient (pT)] of the compounds have been done. High value of dielectric constant ∼104, remanent polarization (14–24 μC cm−2), pyroelectric coefficient (46–57 nC cm−2 K−1) and small piezoelectric parameters have been observed for all the compounds with z=0.0, 0.1, 0.3, 0.5, and 0.7. The coercive field increased with increasing Li+ concentration to a maximum of 6.98 kV cm−1 for z=0.7.
Hydrogen interaction with implantation induced point defects in p-type silicon
Authors: Fatima S. , Jagadish C. , Lalita J. , Svensson B. G. , Hállen A.
Published: July 2002

Interaction of hydrogen with implantation induced point defects in p-type Si has been monitored using deep level transient spectroscopy. H ions are implanted into p-Si using low doses in the range from 109 to 1010 cm−2. Vacancy and interstitial related defects are observed. Besides irradiation induced defects with levels at Ev+0.19 and Ev+0.35 eV, two additional defect levels at 0.28 and 0.51 eV above the valence band edge (Ev) are resolved. They are identified as hydrogen related after comparison with He, B, and C implanted p-type Si. The generation of these defect levels, in the presence of hydrogen, has been studied as a function of ion dose, sample depth, and impurity content in the as grown Si. The level at Ev+0.19 eV shows a saturation effect for higher hydrogen doses. This is attributed to passivation by mobile hydrogen through the formation of neutral complexes. The level at Ev+0.51 eV has been assigned to be a complex involving H and B interstitials.
Er
3+
:Yb
3+
codoped lead fluoroindogallate glasses for mid infrared and upconversion applications
Authors: de Sousa D. F. , Zonetti L. F. C. , Bell M. J. V. , Lebullenger R. , Hernandes A. C. , Nunes L. A. O.
Published: July 2002

In this work, two sets of lead fluoroindogallate glasses were studied with the aim of using them as active media for laser devices at the mid infrared (∼2.8 μm) and visible (∼0.54 μm) regions. The infrared and upconverted emissions of Er3+ in single and Er3+:Yb3+ codoped samples were analyzed, and it was observed that the best set of samples for 2.8 μm emission was the single doped one, and that as the upconversion (anti-Stokes luminescence) increased as a function of Yb3+ concentration, the infrared emission decreased in the same manner. The results suggest that the codoping with Yb3+ favors only the upconversion processes which depopulate the I11/24 level, reducing the 2.8 μm emission intensity. On the other hand, the Yb3+ codoping will certainly increase the efficiency of an upconversion based device. Quantum efficiencies of infrared emissions and radiative lifetimes were calculated by using the Judd–Ofelt approximation. Er3+–Er3+ and Er3+–Yb3+ energy transfer efficiencies were calculated using the measured lifetimes of the levels involved in the energy transfer processes.
Temperature behavior of specific contact resistance and resistivity on nitrogen implanted 6H-SiC with titanium silicide ohmic contacts
Authors: Schmid U. , Getto R. , Sheppard S. T. , Wondrak W.
Published: July 2002

The electrical characteristics of TiSix contacts to nitrogen implanted 6H-SiC are investigated using linear transmission line method structures at temperatures up to 673 K. Nitrogen is implanted into a p-type (NA≈1×1016 cm−3) 6H-SiC epilayer at 500 °C and activated at 1700 °C, resulting in an activated donor concentration of ND=5×1019 cm−3 to a depth of 300 nm with a reduced electrically active surface concentration of about ND≈5×1018 cm−3. Sputtered titanium silicide is used as contact metallization. Five different contact formation temperatures TA ranging from 900 to 1150 °C are applied to the samples in order to investigate the specific contact resistance ρc. Whereas an anneal of at least 950 °C is necessary to achieve an ohmic contact behavior, samples annealed at 1150 °C show specific contact resistance of 7×10−6 Ω cm2 at room temperature, which decreases monotonically to 4×10−6 Ω cm2 at 673 K. The sheet resistance Rs (resistivity ρs) of the n+-implanted layer is 521 Ω/□ (15.6×10−3 Ω cm) at 303 K. Up to 573 K, Rs declines to 354 Ω/□ (10.6×10−3 Ω cm) as the incomplete ionization of the nitrogen dopants dominates the temperature behavior. Above 573 K, the reduction of the electron mobility via phonon scattering dominates, and Rs increases to 363 Ω/□ (10.9×10−3 Ω cm) at 673 K. From the resistivity as a function of temperature, the low field mobility μ0 is 149 cm2/V s at 300 K, and the temperature exponent α=1.62 of the power law dependence can be deduced.
An experimental study of light modulator using magnetic fluid
Authors: Seo Jong-Wook , Park Sang Ju , Jang Kyeong Oh
Published: July 2002

A type of light modulator using light-absorbing magnetic fluid has been studied experimentally. The basic operation principle and design of the modulator are addressed. It is shown that the luminance of the device can be modulated by applying a moderate level of electric current to a light-reflecting metal electrode. A high contrast ratio comparable to that of printed material was obtained using a kerosene-base magnetite magnetic fluid with a saturation magnetization of 196 G and a thickness of around 20 μm. Doubling of the luminance from a minimum level takes about 200 ms for a driving current of 80 mA. The operation speed of the cell was found to increase almost exponentially with driving current, suggesting the possibility of motion picture applications.
Physical parameters of Au–n-InP structures
Authors: Touhami R. , Ravelet S.
Published: July 2002

An approach suitable for determining the physical parameters of Au-oxide–n-InP structures is presented in this article. This approach consists in describing the Au-oxide–n-InP structures by a modified current–voltage model in which both least squares and Newton–Raphson methods are used in the parameter determination. The Au-oxide–n-InP samples under study are either oxidized by air or treated with oxygen plasma. The ideality factor, the series resistance, the effective Richardson constant, and the effective barrier height of these structures are computed by means of the current voltage model. A better estimation of these parameters is obtained when we consider another definition of the Richardson constant, namely, the correct value of the Richardson constant. Physical parameters such as the barrier lowering at zero bias due to the image force, the barrier height at 0 K, the correct value of the Richardson constant, and the tunnel coefficient are then simulated. The values of these parameters obtained for Au-oxide–n-InP structures are in good agreement with those published in the literature.
Structural properties of InN on GaN grown by metalorganic vapor-phase epitaxy
Authors: Yamaguchi Shigeo , Kariya Michihiko , Nitta Shugo , Takeuchi Tetsuya , Wetzel Christian , Amano Hiroshi , Akasaki Isamu
Published: July 2002

InN has been expected to be a suitable material for electronic devices such as high mobility transistors because of its small effective mass compared to other nitrides. Heteroepitaxial InN films were grown by metalorganic vapor-phase epitaxy. The films have been structurally characterized by triple-axis x-ray diffraction (XRD) analysis in terms of lattice-mismatch dependence and InN film thickness dependence, and Hall measurements have been performed. In the XRD measurement, ω and ω–2θ scans were used, and the degree of tilting (the linewidth of x-ray signal, Δωc) [(0002) reflection] and that of twisting (Δωa) [(101̄0) reflection] have been separated. In addition, the degree of distribution of lattice constant c (Δ2θc) [(0002) reflection] of InN films has been assessed. For study of the lattice-mismatch dependence, growth of InN films on GaN, AlN and directly on sapphire substrates was performed, and accordingly, Δωc was found to range from about 500 to 4000 arcsec, and Δ2θc from about 400 to 700 arcsec. Among those three kinds of samples, InN films grown on GaN showed the smallest Δωc and Δ2θc values. Observation of c- and a-lattice parameters has shown that the InN on GaN is affected by the residual strain. On the other hand, InN thickness dependence of XRD showed that Δωc was changed from about 700 to 500 arcsec, and Δ2θc from about 600 to 300 arcsec with increasing InN thickness from 400 to 2400 Å. In accordance with the thickness of InN, Δωa was found to change from about 2500 to 1700 arcsec. Moreover, it was found that the InN film less than 1200 Å thick is composed of grain islands with different crystalline orientation and that the growth mode changes at a thickness of about 1200 Å—and screw dislocations occur. It is found that the residual strain in InN films over 1200 Å thick is gradually released, resulting in almost the same orientation. This is reflected in the reduction of the mosaicity, the proceeding of relaxation and the surface morphology. Selection of GaN for the underlying layer of the InN film has been shown to lead to structural improvement of the epitaxial InN film. In fact, InN film with a thickness of 2400 Å grown on GaN has a Hall mobility of about 700 cm2/V s even at an electron carrier concentration of 5×1019 cm−3. This value corresponds to that for GaAs at the same impurity concentration.
Low temperature heat capacity of Ti3SiC2
Authors: Ho J. C. , Hamdeh H. H. , Barsoum M. W. , El-Raghy T.
Published: July 2002

Calorimetric measurements between 2 and 10 K have been made on Ti3SiC2. The molar heat capacity, c, data can be fitted to the sum of an electronic and a lattice contribution: c=γT+βT3. The β value of 0.049 mJ/mol K4 yields a Debye temperature of 620 K, typical of high stiffness and hardness ceramic materials such as TiC. This value is significantly higher than the Debye temperature measured from elastic measurements. The γ value of 5.21 mJ/mol K2 is a measure of the density of states at the Fermi level. This value, when normalized to a per Ti atom basis, is higher than that of TiC0.97, but roughly half that of Ti metal, implying that covalent-type bonding induced electron localization increases in going from Ti to Ti3SiC2 to TiC. It also partially explains the excellent electrical and thermal conductivities of Ti3SiC2.
Role of relative tilt on the structural properties of GaInSb epitaxial layers grown on (001) GaSb substrates
Authors: Ehsani H. , Bhat I. , Gutmann R. J. , Charache G. , Freeman M.
Published: July 2002

The extent of relative tilt angle, crystalline quality, and relaxation of GaxIn1−xSb layers grown on (001) GaSb substrates by organometallic vapor phase epitaxy have been investigated, using double-crystal x-ray diffraction and transmission electron microscopy. An unexpectedly large tilt is formed between Ga0.8In0.2Sb epitaxial layers and oriented (001) GaSb substrates which has not been previously reported. Double-crystal x-ray diffraction measurements revealed that the tilt angle between the Ga0.8In0.2Sb epilayers and the substrates increases as the layer thickness increases. A strong correlation has been established between the variation of the tilt angle and the residual strain in the layers. Transmission electron micrographs of Ga0.8In0.2Sb layers revealed that irregular dislocation activities occur in the layer at different distances from the interface which could be related to tilt formation and relaxation. The structural characteristics of the layers as a function of the compositional variation showed that the amount of tilt angle is small when the indium concentration was in the range from 0 to 12%, but increases at higher indium concentrations. Ga1−xInxSb layers with poor crystalline quality and small tilt angle are obtained when the indium concentration was more than 25%. The tilt angle between Ga0.8In0.2Sb epilayers and GaSb substrates grown at temperatures ranging from 560 to 620 °C was essentially identical, indicating that the tilt formation is not a kinetic effect.
Effect of hydrogen partial pressure on optoelectronic properties of indium tin oxide thin films deposited by radio frequency magnetron sputtering method
Authors: Zhang Keran , Zhu Furong , Huan C. H. A. , Wee A. T. S.
Published: July 2002

In this study, indium tin oxide (ITO) films were made from an oxidized target with In2O3 and SnO2 in a weight proportion of 9:1 using the radio frequency magnetron sputtering method. Hydrogen was added to the gas mixture during the preparation of the ITO films. In order to study the effect of hydrogen partial pressure on the structural and optoelectronic properties of the ITO films, we have varied the hydrogen partial pressure in the gas mixture over the range 0–1.6×10−5 Torr and kept the substrate temperature constant at 300 °C during film growth. The x-ray diffraction patterns of ITO films prepared at different hydrogen partial pressures show that the films have (111) and (100) preferred orientations. Hall effect measurements reveal that the addition of hydrogen in the sputtering gas mixture shows an increase in the number of charged carriers in the ITO films. However the carrier mobility did not increase considerably. At optimal conditions, ITO films with resistivity of 2.7×10−4 Ω cm and transparency of over 89% in the visible wavelength region were achieved.
Application of the pressure wave propagation method for adhesion defects detection and quantification in bilayer structures
Authors: Aïnouche Leïla , Alquié Claude
Published: July 2002

The pressure wave propagation method, usually used to study electrical behavior of dielectric materials, is applied here to nondestructive detection and quantification of adhesion defects in a bilayer structure. This method relies on a very simple idea: as an electric field is created in a bilayer dielectric sample placed between short-circuited electrodes, the propagation of a pressure pulse induces an electric signal. If the field distribution is known, the signal leads to the pressure profile all along its propagation through the sample and therefore gives information on the interface. First, we extend the signal expression already established for a monolayer structure to a multilayer structure and consider particularly bilayer structures. After explaining the signal analysis in perfectly bonded and totally disbonded structures, a model is proposed to describe and analyze the signal in a partially disbonded structure and relate it to the percentage of totally disbonded area in the zone being tested by the pressure pulse. To assess this analysis, measurements were carried out on kapton (130 μm)–adhesive (98 μm) transparent samples. Some samples are perfectly bonded, some are totally disbonded and the others are partially disbonded. The pressure pulse is created by the impact of a laser pulse on an absorbing target coupled to the sample. The excellent agreement between the measurements carried out on perfectly bonded and totally disbonded samples and simulations assesses the correctness of the signal expression for a multilayer structure. In the case of partially disbonded structures, the value of the percentage of totally disbonded area, determined by measurement and simulation, is very close to that deduced from a photograph of the sample, only possible for transparent materials. The spatial resolution of the method is related to the spectrum of the pressure pulse, which extends up to 200 MHz. This method presents an excellent spatial resolution. If the transit time of the pressure pulse in each medium is superior to 11 ns, measurements and simulations show that owing to this method, it is possible to detect and localize in the structure submicron gaps and a percentage of totally disbonded area as low as 5% in the tested zone by analyzing the signals in the time domain in a very simple manner.
Combined photoemission/in vacuo transport study of the indium tin oxide/copper phthalocyanine/N,N′-diphenyl-N,N′-bis(l-naphthyl)-1,1′biphenyl-4,4″diamine molecular organic semiconductor system
Authors: Hill I. G. , Kahn A.
Published: July 2002

Ultraviolet photoemission spectroscopy (UPS) was used to study the indium tin oxide/copper phthalocyanine (CuPc) and CuPc/N,N′-diphenyl-N,N′-bis(l-naphthyl)-1,1′biphenyl-1-4,4″diamine interfaces, which are commonly used as an anode/hole injection layer/hole transport layer combination in organic light emitting devices. In order to assess the validity of the transport barriers measured using UPS, in vacuo I–V measurements have been performed on simple devices grown and measured in the same system as the samples studied using UPS. I–V characteristics were modeled using numerical simulations. The parameters used in the simulated curves which best fit the measured I–V characteristics agree quantitatively with the UPS measured barriers.
Dependence of energy gaps and effective masses on atomic positions in hexagonal SiC
Authors: Persson C. , Lindefelt U.
Published: July 2002

We have performed several band structure calculations on 2H–, 4H–, and 6H–SiC, using different lattice constants and basis atom positions in order to investigate the sensitivity of the electronic structure and explain the discrepancies in band structure results between different authors. It is shown that even small changes in the basis atom positions have a strong impact on the crystal-field splitting, whereas the relative changes in the fundamental band gap, the spin-orbit splitting, and the effective electron and hole masses are practically negligible. The computational method was based on the local density approximation within the density functional theory.
Elasticity, shear strength, and equation of state of molybdenum and gold from x-ray diffraction under nonhydrostatic compression to 24 GPa
Authors: Duffy Thomas S. , Shen Guoyin , Shu Jinfu , Mao Ho-Kwang , Hemley Russell J. , Singh Anil K.
Published: July 2002

Lattice strains were measured as a function of the angle ψ between the diffracting plane normal and the stress axis of a diamond anvil cell in a layered sample of molybdenum and gold. The sample was compressed over the range 5–24 GPa and the lattice strains were measured using energy-dispersive x-ray diffraction. As ψ is varied from 0° to 90°, the mean lattice parameter of molybdenum increases by up to 1.2% and that of gold increases by up to 0.7%. A linear relationship between Q(hkl), which is related to the slope of the measured d spacing versus 1−3 cos2 ψ relation, and 3Γ(hkl), a function of the Miller indices of the diffracting plane, is observed for both materials as predicted by theory. The pressure dependence of the uniaxial stress t for gold from this and other recent studies is given by t=0.06+0.015P, where P is the pressure in GPa. The uniaxial stress in molybdenum can be described by t=0.46+0.13P. Using gold as an internal pressure standard, the equation of state of molybdenum depends strongly on ψ. The bulk modulus obtained from a Birch–Murnaghan fit varies from 210 to 348 GPa as ψ varies from 0° to 90°. However, an equation of state in good agreement with shock and ultrasonic isotherms is obtained for ψ=54.7° where the deviatoric contribution to the lattice strain vanishes. Second-order elastic moduli for gold and molybdenum are obtained from the data. The results are generally consistent with an earlier x-ray study and with extrapolations of low-pressure ultrasonic data. The pressure dependence of the shear modulus C44 is smaller for the x-ray data than predicted by extrapolation of ultrasonic data.
The B factor in multilayer thermionic refrigeration
Authors: Vining C. B. , Mahan G. D.
Published: July 2002

The figure of merit for multilayer thermionic refrigeration is discussed in terms of an effective B factor, which has a similar definition as the B factor in thermoelectrics. We show that high efficiencies for cooling or power generation are only obtained with very high values of this B factor. Such high values can only be attained because of the low thermal conductivity of multilayers. The B factor for thermionics is usually less than the one for thermoelectrics.
Phase formation due to high dose aluminum implantation into silicon carbide
Authors: Heera V. , Reuther H. , Stoemenos J. , Pécz B.
Published: July 2002

High doses of 350 keV aluminum (Al) ions were implanted into hexagonal silicon carbide (6H–SiC) single crystals at 500 °C. Phase formation was studied by transmission electron microscopy, secondary-ion mass spectrometry, and Auger electron spectrometry. A critical Al concentration of about 10 at. % was found below which the 6H–SiC structure remains stable. The Al atoms occupy preferentially silicon (Si) sites in the SiC lattice. The replaced Si atoms seem to be mobile under the implantation conditions and diffuse out. At higher Al concentrations the SiC matrix is decomposed and precipitates of Si and aluminum carbide (Al4C3) are formed. The Al4C3 precipitates have a perfect epitaxial orientation to the SiC matrix. The phase transformation is accompanied by atomic redistribution and strong volume swelling. The resulting changes in the atomic depth profiles can be accounted for by a simple chemical reaction model.
Magnetoresistance of constricted ferromagnetic wires
Authors: Adeyeye A. O. , Cowburn R. P. , Welland M. E.
Published: July 2002

We describe a systematic study of magnetoresistance (MR) behavior of individual constricted 25 nm thick Ni80Fe20 wires. The structures consist of a 5 μm support and a narrow wire with width w in the range 100–500 nm. When the field is applied parallel to the wire axis, we observe two switching fields (for w⩽200 nm) corresponding to the distinct coercive fields of the narrow part of the wire and the 5 μm support structure, as compared to one switching field observed for w=500 nm. The MR response to the field applied perpendicular to the wire width is found to be very sensitive to w due to the demagnetizing field. We are able to deduce from the field sequence measurements the spin orientations in the fabricated structures. We have shown that it is possible to laterally control spin orientation for tailor made magnetic devices.
Temperature behavior of multiple tunnel junction devices based on disordered dot arrays
Authors: Cordan A. S. , Leroy Y. , Goltzené A. , Pépin A. , Vieu C. , Mejias M. , Launois H.
Published: July 2002

Nanometer-sized multijunction arrays are expected to exhibit a large Coulomb blockade effect. However, up to now, only highly disordered arrays can be fabricated. In this article, we evaluate the consequences of disorder on the dispersion of the device characteristics. We show that, as observed for regular arrays, the threshold voltage Vth increases with the length of the multijunction array. At very low temperature, the Vth dispersion is small. Conversely, at higher temperature, a large dispersion in Vth is observed. We evidence the importance of the different array parameters with respect to the device characteristics. We show that the crucial parameters are the tunnel resistances and, therefore, for a two-dimensional array, the total resistance of the minimal resistance path is the most relevant parameter.
Reverse annealing, clustering, and electron mobility in arsenic doped silicon
Authors: Solmi S. , Nobili D. , Shao J.
Published: July 2002

The reverse annealing phenomena and the nature of the As clusters were studied on silicon on insulator samples uniformly doped with As at concentrations up to 7.6×1020 cm−3. Carrier concentration and electron mobility were determined by Hall and resistivity measurements after annealing at temperatures in the range 550–800 °C. The amplitude of transient reactivation, which can involve up to 20% of the clustered As, depends on dopant concentration and on the annealing temperatures and times. The results of a detailed study of the influence of these parameters are reported. The occurrence of reverse annealing confirms the existence of different types of As clusters, whose distribution and features depend on the experimental conditions. The effect of clustered As on the electron mobility was measured and a quantitative relationship for this phenomenon is reported. The amplitude of this effect is in agreement with the view that at room temperature As clusters are electrically neutral.
Small particle growth in silane radio-frequency discharges
Authors: Childs M. A. , Gallagher Alan
Published: July 2002

Particle size and number density are measured versus discharge operating time (t) in pure silane, capacitively coupled rf discharges. Discharge conditions are those typically used to produce amorphous silicon devices, except the temperature is 300 K. Particle radii (Rp) from 4 to 25 nm are observed, where Rp is determined from the rate of particle diffusive loss in the plasma afterglow. The scattered light intensity then yields the particle number density. We generally observe a Rp(t) consistent with initial rapid growth to Rp∼2 nm, followed by a constant dRp/dt at a rate consistent with growth due to SiH3 reactions. However, at higher pressures and film growth rates, or rf voltage, the particle growth rate exceeds that due to SiH3, indicating additional growth mechanisms. Particle density increases orders of magnitude when pressure and rf voltage increase by small amounts. Measurement of the particle spatial distribution in the afterglow, when most particles are neutral, shows that they have sufficient sticking probability on the upper electrode to yield essentially equal deposition on both electrodes.
Phase formation and electrical resistivity of ultrahigh vacuum deposited Cu thin films on epitaxial Si–Ge layers on Si and Ge
Authors: Lai J. B. , Chen L. J.
Published: July 2002

The phase formation and the morphological stability of ε1-Cu3Ge and ε1-Cu3(Si1−xGex) in Cu/epitaxial-Ge(e-Ge)/(111)Ge, Cu/(001)Ge, Cu/e-Ge/(111)Si, and Cu/(001)Si–Ge alloys have been investigated by transmission electron microscopy in conjunction with the energy dispersive spectrometry as well as by sheet resistance measurement. Epitaxial Cu and epitaxial ζ-Cu5Ge were found to form in as-deposited Cu/e-Ge/(111)Ge and Cu/e-Ge/(111)Si. On the other hand, textured Cu was found to form in the other systems. Polycrystalline ε1-Cu3Ge and ε1-Cu3(Si1−xGex) were the only phases formed in 150–500 °C annealed Cu/Ge and (Cu/e–Ge/Si and Cu/Si–Ge alloys) systems, respectively. They were found to agglomerate at 550 °C. The room-temperature oxidation of substrate in the presence of Cu3(Si1−xGex) was found only in the Cu/Si0.7Ge0.3 system. From the sheet resistance measurement, ε1-Cu3Ge has the lowest resistivity of 7 μΩ cm after 400 °C annealing. The electrical resistivity was found to decrease with the Ge content.
The field-induced cholesteric-nematic phase transition and its dependence on layer thickness, boundary conditions, and temperature
Authors: Schlangen Luc J. M. , Pashai Alexandre , Cornelissen Hugo J.
Published: July 2002

Chiral-nematic liquid-crystal layers which have a short pitch, homeotropic boundary conditions, and bistable properties are investigated with respect to the temperature dependence of their field-induced cholesteric-nematic phase transition. Hereto the threshold field needed for the transition is studied as a function of the layer thickness. This is done for various temperatures. The threshold field hardly depends on the layer thickness. Moreover, it sharply rises below −5 °C. Both the value of the threshold field and its temperature dependence can be fully described in terms of liquid-crystal bulk material parameters, the conditions at the homeotropic boundary layer used do not play a role. From the threshold field data the twist elastic constant is determined as a function of temperature. This temperature dependence is compared to the temperature dependence as determined from the square of the long range order parameter calculated from temperature dependent refractive index data. A good correlation is found between both data sets of the twist elastic constant.
High frequency, small signal MH loops of ferromagnetic thin films
Authors: Grimes Craig A. , Ong Keat Ghee
Published: July 2002

A method is presented for transforming the high frequency bias susceptibility measurements of ferromagnetic thin films into the form of a MH loop with, depending upon the measurement geometry, the y-axis zero crossing giving a measure of the coercive force or anisotropy field. The loops provide a measure of the quantitative and qualitative high frequency switching properties of ferromagnetic thin films.
Co alloy longitudinal thin film media with ultrahigh coercivity
Authors: Wang Jian Ping , Tan Lea Ping , Yan Ming Lang , Chong Tow Chong
Published: July 2002

The effect of CoCrTa intermediate layer and postannealing on the magnetic properties and microstructure of CoCrPt/Cr thin film media has been investigated. Through a postdeposition annealing in a vacuum oven, a tremendous increase of coercivity up to 6000 Oe was observed for these CoCrPt/CoCrTa/Cr films, in which the thickness of CoCrTa intermediate layer is about 2.6 mm. X-ray diffraction results showed that the hexagonal-close-packed crystallographic structure for the cobalt alloy did not show any change for the sample after postannealing. In-plane transmission electron microscope images for the CoCrPt/CoCrTa/Cr films showed no change of the morphology before and after annealing and about 15% increase of the grain size for the films after annealing. Delta M curves and remanent squareness results showed that intergrain diffusion may result in this improvement of magnetic properties. Atomic force microscope images showed that the surface roughness for the sample after annealing was almost the same as that before annealing. After tailoring the thickness of the magnetic layer to 10 nm, the coercivity as high as 5200 Oe and Mrt value as low as 0.24 memu/cm2 were obtained, which may support ultrahigh bit density than current media.
Thickness and process optimization of planetary magnetron sputtered FeMnRh spin valves
Authors: Feng Y. , Pakala M. , Huai Yiming , Anderson G. , Rook K. , Gupta S.
Published: July 2002

Thickness dependence and process optimization of planetary magnetron sputtered FeMnRh-based spin valves (SV) have been investigated in terms of the interrelationship between process conditions, microstructure, and magnetic properties. For the Cu spacer layer, sputtering at low power (0.5–1 kW) and low pressure (1–3 mT) give lower film resistivity. The ΔR/R reaches >9.0% for Cu thickness range of 18–22 Å and drops as Cu thickness increases in spin valves of structure: Ta50/NiFe50/CoFe20/Cu(t)/CoFe22/FeMnRh80/Ta50 Å. From the pinned layer thickness (CoFe) dependence of Hex, an interfacial anisotropy energy (Jk=HexMst) is calculated to be 0.14 erg/cm2 which is larger than the value reported for FeMnRh previously. Both Hex (400–480 Oe) and ΔR/R (7.3%–8.5%) were found to increase with FeMnRh sputtering pressure (3–15 mT) for Ta50/NiFe50/CoFe20/Cu26/CoFe22/FeMnRh110/Ta50 Å films. Two-step depositions (low and high sputtering pressure) of FeMnRh layer suggest that the higher Hex is mainly attributed to the interfacial smoothness at the CoFe/FeMnRh interface rather than the effect of smaller grain size of FeMnRh layer. The blocking temperature (Tb) of these spin valves increases from 160 to 175 °C with increasing FeMnRh thickness from 80 up to 110 Å, after which it decreases to 170 °C at 120 Å.
Grain-boundary room-temperature low-field magnetoresistance in Sr2FeMoO6 films
Authors: Yin H. Q. , Zhou J.-S. , Dass R. , Zhou J.-P. , McDevitt J. T. , Goodenough John B.
Published: July 2002

Thin films of (001)-oriented Sr2FeMoO6 have been epitaxially deposited or LaAlO3 and SrTiO3 (001) substrates by pulsed laser deposition. The deposition conditions were optimized. Single-phase Sr2FeMoO6 was obtained in 100 mTorr 99.999% Ar gas at 825 °C. Transport and magnetic data showed a metallic temperature dependence and a saturation magnetization Ms at 10 K of 3.2μB/f.u. However, the Curie temperature TC≈380 K was reduced from 415 K found for tetragonal polycrystalline best ceramics, which lowers Ms at 300 K in the thin films to 1.5μB/f.u. compared to 2.2μB/f.u. in the ceramics. A low remanence was attributed to the presence of antiphase boundaries. A Wheatstone bridge arrangement straddling a bicrystal boundary was used to verify that spin-dependent electron transfer through a grain boundary and not an antiphase boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below TC.