bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of very thin semiconductor layer thickness by a photothermal method
Authors: Yacoubi N. , Alibert C.
Published: July 2002

A photothermal method for the determination of very thin GaInAs layer thickness of the InP/GaInAs/InP heterostructure was described. This method was based on the Fernelius’ theoretical model [J. Appl. Phys. 51, 650 (1980)] and derived from the phase measurement of the photothermal signal phase in the vicinity of the InP energy gap.
Measurement of InP/In0.53Ga0.47As and In0.53Ga0.47As/In0.52Al0.48As heterojunction band offsets by x-ray photoemission spectroscopy
Authors: Waldrop J. R. , Kraut E. A. , Farley C. W. , Grant R. W.
Published: July 2002

X-ray photoemission spectroscopy (XPS) has been used to measure the valence-band offset ΔEv for the lattice-matched InP/ In0.53Ga0.47As and In0.53Ga0.47As/ In0.52Al0.48As heterojunction interfaces. The heterojunctions were formed by molecular-beam epitaxy. We obtain values of ΔEv (InP/In0.53Ga0.47As) =0.34 eV (ΔEc/ ΔEv=43/57) and ΔEv (In0.53Ga0.47As/ In0.52Al0.48As) =0.22 eV (ΔEc/ ΔEv =68/32) for the respective interfaces. By combining these measurements with available XPS ΔEv (InP/ In0.52Al0.48As) data we find that band offset transitivity is satisfied. Accordingly, the band offsets for heterojunction pairs formed from InP, In0.53Ga0.47As, and In0.52Al0.48As are not influenced by interface specific effects.
Phenomenology of the normal and superconducting states of a marginal Fermi liquid (invited)
Authors: Littlewood P. B. , Varma C. M.
Published: July 2002

A metal with scattering from a flat frequency spectrum of particle-hole pairs is a ‘‘marginal’’ Fermi liquid, with infinite quasiparticle lifetime but a logarithmically vanishing spectral weight. In the superconducting state, the scattering spectrum should acquire a gap, and the quasiparticle character will be restored at low energies. Unless the scattering spectrum results from interband processes, the Drude-like component of the optical conductivity will then have an onset at 4Δ in the clean limit, twice the superconducting gap. Other experimental ramifications, in particular for tunnelling, NMR relaxation rate, thermal conductivity, and photoemission spectra are considered.
Magnetization and magnetostriction of MnAs0.7Sb0.3 in the paramagnetic temperature region
Authors: Ido H. , Yasuda S. , Kido G.
Published: July 2002

Magnetization and forced magnetostriction have been measured for MnAs0.7Sb0.3 in the paramagnetic temperature region under a high-pulse magnetic field. The experimental results are discussed together with the data of temperature variations of magnetization and lattice parameters for MnAs0.7Sb0.3. Analysis of the data implies that MnAs0.7Sb0.3 has a special paramagnetic state having an instability for a ferromagnetic state in the paramagnetic temperature region near the Curie temperature. The magnetization curves in the paramagnetic region are nicely reproduced by an equation H=ασ+βσ3+γσ5, where H is the magnetic field and σ the specific magnetization. The forced magnetostrictions are found to be proportional to σ2.
Shear cell experiments of snow and ice friction
Authors: Casassa Gino , Narita Hideki , Maeno Norikazu
Published: July 2002

Snow and ice friction was investigated with a shear cell in which two surfaces of annular snow and/or ice samples were in contact and sheared by rotation. The temperature ranged from 0 to −25 °C, normal stress from 205 to 1292 Pa, and velocity from 0.9 to 25.3 m/s. The total friction coefficients measured by friction of two hard sintered snow plates ranged roughly from 0.2 to 0.8, which were separated into velocity-independent dry friction and linearly dependent viscous friction; only at velocities larger than 15 m/s did friction increase parabolically, evidence of turbulent friction. The dry friction coefficient (μD) was found to consist of Coulomb friction and adhesion, both of which were strongly dependent on temperature and hardness of snow; μD decreased linearly with lowering temperature from 0.47 at 0 °C to 0.22 at −25 °C. Viscosity was found to be dependent on snow type (grain characteristics) but independent of temperature; the average kinematic viscosity was roughly 5×10−5 m2/s for snow of density around 350 kg/m3. The total friction coefficient for ice-ice friction was an order of magnitude smaller than that of snow-snow friction, typically less than 0.04; its magnitude increased with velocity but at lower temperatures (e.g., −35 °C) it decreased exponentially with velocity. The minimum Coulomb friction coefficient as small as 0.008 was observed at −11 °C. All the friction coefficients for snow-snow, snow-ice, and ice-ice friction were summarized in temperature-velocity diagrams, which conveniently show the overall behaviors of snow and ice friction.
A one-dimensional collisional model for plasma-immersion ion implantation
Authors: Vahedi V. , Lieberman M. A. , Alves M. V. , Verboncoeur J. P. , Birdsall C. K.
Published: July 2002

Plasma-immersion ion implantation (also known as plasma-source ion implantation) is a process in which a target is immersed in a plasma and a series of large negative-voltage pulses are applied to it to extract ions from the plasma and implant them into the target. A general one-dimensional model is developed to study this process in different coordinate systems for the case in which the pressure of the neutral gas is large enough that the ion motion in the sheath can be assumed to be highly collisional.
Interfacial reactions of nickel thin films on BF+2-implanted (001)Si
Authors: Chen W. J. , Chen L. J.
Published: July 2002

Interfacial reactions of nickel thin films on BF+2-implanted (001)Si annealed at 200–900 °C for various periods of time have been studied by both cross-sectional and plan-view transmission electron microscopy as well as by sheet resistance measurement. Drastic difference in NiSi2 formation was found between samples with implanted amorphous and regrown substrates. In samples with implanted amorphous substrates, polycrystalline NiSi2 was found to be the stable phase after annealing at 400–900 °C. In contrast, although epitaxial NiSi2 was formed on implanted regrown samples at a temperature as low as 250 °C, the dominant phase was NiSi in samples annealed at 400–700 °C. The presence of B and/or F atoms in silicon was found to be essential for the formation of epitaxial NiSi2 on crystalline silicon at low temperatures. The final structure of the silicide layer was found to depend critically on the thickness of starting Ni overlayer and the annealing temperature. In addition, the amorphicity of the substrate apparently played an important role in promoting the formation of polycrystalline NiSi2 at low temperatures. From a comparison with Si+ implanted amorphous samples, the growth of laterally uniform NiSi2 and resistance to islanding at high temperature in BF+2-implanted amorphous samples are attributed to the retardation of the growth of NiSi2 grains by the presence of B and/or F atoms at the grain boundaries. Sheet resistance data were found to correlate well with the microstructures of the systems.
An air breakdown kinetic model
Authors: Rodríguez A. E. , Morgan W. L. , Touryan K. J. , Moeny W. M. , Martin T. H.
Published: July 2002

A kinetic model is developed for the glow phase of a spark gap in air. The model includes heavy-particle collisions leading to thermal ionization and electron-collision processes. Rates for the latter are calculated by a computer program that solves the electron Boltzmann equation, verified using empirical measurements. These rates include attachment and ionization, excitation followed by ionization of the excited species, and dissociation followed by ionization of the atomic species; molecular-impact detachment was found to be necessary to match experimental closing times. With those processes, the model predicts closing times well, over a wide range of voltages above and below the dc breakdown voltage.
Structural properties of polycrystalline silicon films prepared at low temperature by plasma chemical vapor deposition
Authors: Kakinuma H. , Mohri M. , Sakamoto M. , Tsuruoka T.
Published: July 2002

Evolution with thickness of the structure of the polycrystalline silicon (poly-Si) films prepared at 300 °C has been studied by plasma decomposition of SiF4/SiH4/H2 source gases. The poly-Si films with varied thickness are characterized mainly by Raman spectroscopy, x-ray diffraction (XRD), and supplementarily by reflection high-energy electron diffraction, transmission electron microscopy, Fourier-transform infrared (FT-IR) spectroscopy, electron-spin resonance (ESR), and secondary-ion-mass spectroscopy (SIMS) measurements. The crystalline fraction of the film was calculated to be 87% by deconvoluting the Raman spectra. The grains indicated a strong 〈110〉 preferred orientation by XRD. The thickness (d) dependence of the diffracted (220) intensity is divided into three regions: an incubation region (d<200 nm, region 1), a linear region (200 nm ≤d<300–500 nm, region 2) where the deposition parameter (SiF4 flow rate, substrate temperature, and rf power) dependence is weak, and a linear region with steeper (or more moderate) slopes (300–500 nm≤d, region 3) where the deposition parameter dependence is large. The measurements of the angular distribution of the 〈110〉 grains reveal that they contain slanting ones by more than 4° in region 2, while they disappear in region 3. The FT-IR and SIMS measurements for typical samples (Ts = 300 °C, 300 Pa) indicate that the grain boundaries are passivated by hydrogen in the bonding configurations of Si—Hn (n=1–3) and its concentration is approximately 3 at. %. The residual fluorine in the film is found to be much fewer (6×1019 cm−3) than hydrogen. It is found that the density of unpassivated dangling bonds indicates a low value of 1.1×1017 cm−3 for the film with d=280 nm by ESR measurements. The origin of the preferred orientation is also discussed on the basis of a model in which nucleation, ledge formation, and etching processes are considered.
Extended defects of ion-implanted GaAs
Authors: Jones K. S. , Allen E. L. , Robinson H. G. , Stevenson D. A. , Deal M. D. , Plummer J. D.
Published: July 2002

Ion-implantation-induced extended defect formation and annealing processes have been studied in GaAs. Mg, Be, Si, Ge, and Sn ions were implanted between 40 and 185 keV over the dose range of 1×1013–1×1015/cm2. Furnace annealing after capping with Si3N4 was performed between 700 and 900 °C for times between 5 min and 10 h. Plan-view and cross-sectional transmission electron microscopy results were correlated with secondary-ion-mass spectroscopy profiles. The results indicate subthreshold (type-I) defect formation occurs at a dose of 1×1014/cm2 for high-energy, light (Mg, Be) ions but not for heavier ions (Si, Ge, Sn) at shallower projected ranges (<500 Å). Si and Ge implants at a dose of 1×1015/cm2 both show extended defect formation upon annealing that is believed to be precipitation related (type-V defects). For Si implants, these dislocation loops are eliminated after 10 h at 900 °C. Upon annealing 1×1015/cm2 Sn implants, unusual precipitate motion both toward the surface and into the crystal was observed. Type-II defects are observed but only in the as-implanted cross section. In addition, a layer of dislocation loops formed at a depth much greater than the type-II defect layer. These defects appear to be a new type of defect possibly related to either the different binary recoil distributions of Ga and As or differences in vacancy and interstitial diffusivities. It is shown that, with modifications to account for the binary nature of the target, the classification scheme developed for extended defects in silicon can be applied to implantation of gallium arsenide.
Magnetic study of SmCo5, PrCo5, SmCo4B, and Sm3Co11B4 under pulse high field
Authors: Ido H. , Konno K. , Ogata H. , Sugiyama K. , Hachino H. , Date M. , Maki K.
Published: July 2002

Magnetization curves and hysteresis loops for field-oriented powders of Smn+1Co3n+5B2n (n=0, 1, and 3) and PrCo5 were measured at T=4.2 K and partly at 77 K, under a strong pulsed field up to 36 T. Magnetic measurements for Smn+1Co3n+1B2n (n=1, 2, and 3) compounds were also performed. Huge anisotropy fields of 120 T for SmCo4B and of 130 T for Sm2Co7B3 were obtained. The Sm sublattice anisotropy of SmCo4B was found to be larger than that of SmCo5. To explain this, the Sm f-electron state for n≥ (R18)2 of Smn+1Co3n+5B2n has been expected to change from that for n≤1. Huge coercivities of 8 T and 27.5 T were observed at T=4.2 K for SmCo4B and for Sm2Co7B3 respectively. Magnetization processes for field-oriented PrCo5 at T=4.2 K were found to be similar to those of Nd2Fe14B at T=4.2 K.
Effect of nitrogen on the structural and magnetic properties of intermetallic compounds with the ThMn12 structure
Authors: Wang Y. Z. , Hadjipanayis G. C.
Published: July 2002

The effects of nitrogen uptake on the structural and magnetic properties of RFe12−xTx alloys have been studied. Several interstitial nitrides with composition RFe12−xTxNy (R=Nd and Sm and T=Ti and V) were prepared by heat treating fine powders of RFe12−xTx alloys in N2 gas. Preliminary results show the following observations: (1) The ThMn12 structure of the original compounds is retained with the addition of nitrogen but with increased lattice constants (a and c). (2) The Curie temperature is greatly enhanced by about 150–175 K. (3) The character of magnetic anisotropy is changed from ‘‘weak uniaxial’’ type to ‘‘strong uniaxial’’ type for NdFe12−xTxNy and from ‘‘uniaxial’’ to ‘‘planar’’ for SmFe12−xTxNy.
Ion-implanted optical waveguides in KTaO3
Authors: Wong J. Y. C. , Zhang L. , Kakarantzas G. , Townsend P. D. , Chandler P. J. , Boatner L. A.
Published: July 2002

Optical waveguides have been formed by helium-ion implantation in KTaO3. The implantation forms a confinement barrier near the projected range of the ion by decreasing the refractive index as much as 16% for ion doses of 4×1016 ions/cm2. This is the highest refractive-index change yet reported for ion-implanted crystalline planar waveguides. Guiding modes (with moderately low loss) are produced without the need for annealing out of color centers. During annealing studies, the index change reduces during an anneal stage near 400 °C, but waveguiding is maintained even after anneals to 900 °C. Loss measurements indicate a planar-waveguide loss of <1 dB/cm after a 400 °C anneal.
Improved performance of magnetically tunable GaAs and InP far-infrared detectors
Authors: Knap W. , Lusakowski J. , Karpierz K. , Orsal B. , Robert J. L.
Published: July 2002

Properties of GaAs and InP magnetically tunable far-infrared (FIR) detectors based on transitions between 1s-2p(+/0/−) shallow donor states, were studied in magnetic fields up to 8 T. Repeatable low background radiation conditions were obtained by using cyclotron emission from InSb and GaAs as a FIR source. Signal and noise dependence on the temperature, electric, and magnetic fields was investigated. Physical mechanisms responsible for the signal and noise dependencies on the temperature, electric, and magnetic fields are discussed. Local generation-recombination instabilities are proposed as a physical mechanism causing appearance of the low frequency noise in high magnetic fields.
Photoluminescence linewidths in metalorganic vapor phase epitaxially grown ordered and disordered InAlGaP alloys
Authors: Schneider R. P. , Jones E. D. , Lott J. A. , Bryan R. P.
Published: July 2002

The dependence of the photoluminescent properties of In0.48(AlyGa1−y)0.52P alloys (0≤y≤0.5) on growth temperature and substrate misorientation off GaAs(100) has been studied. Samples were grown using low-pressure metalorganic vapor phase epitaxy. By studying the dependence of ordering behavior in InGaP as a function of substrate misorientation and growth temperature simultaneously, a very large range in low-temperature photoluminescence emission energy—135 meV—has been obtained. The photoluminescence linewidth exhibits a strong, continuous dependence on the extent of atomic ordering (the emission energy) in the alloys. The results indicate that inhomogeneity in the microstructure of the material (i.e., between ‘‘ordered’’ domains and the ‘‘disordered’’ matrix) is the dominant photoluminescence broadening mechanism. This investigation has allowed a significant optimization of the optical properties of these materials, including the narrowest low-temperature photoluminescent linewidths reported for all of the In(AlyGa1−y)P alloys exhibiting direct band gaps (4.2 meV for InGaP).
Analysis of the resonance characteristics of a cantilever vibrated photothermally in a liquid
Authors: Inaba Seiki , Akaishi Kenya , Mori Takahiro , Hane Kazuhiro
Published: July 2002

The resonance characteristics of stainless-steel cantilevers vibrated photothermally in a liquid have been investigated using an optical detection system. Resonance frequencies of vibrating cantilevers in liquids are lower than those in air as a result of the action of reaction forces in the liquid. It is shown that experimental values of the resonance frequencies for several types of cantilevers in water agree well with those calculated. The half power width at resonance broadens with increasing viscosity of the liquid. The possibility for using this photothermal vibration method as an optical sensing system for the density or viscosity of liquids is described.
Spatiotemporal optical emission spectroscopy of rf discharges in SF6
Authors: Petrović Zoran Lj. , Tochikubo Fumiyoshi , Kakuta Shigeru , Makabe Toshiaki
Published: July 2002

Space- and time-resolved emission spectroscopy was applied to obtain information on the kinetics of radio-frequency (rf) discharges for 100 kHz, 800 kHz, and 13.56 MHz in SF6. Emission lines of fluorine and SFx radical were used, but particularly useful were the second positive (2+) and the first negative (1−) bands of nitrogen. The two nitrogen bands gave an opportunity to separate, respectively, the behavior of middle-energy (11–20 eV) and higher-energy (above 20 eV) electrons. Development of double layers was studied from the excess emission close to the anode due to an increased electric field. Also observed were the emission from the bulk and emission due to the electrons accelerated in the instantaneous cathode sheath. The development of these features was followed as a function of the pressure, frequency, and power.
Orientation relationship between chemical vapor deposited diamond and graphite substrates
Authors: Li Zhidan , Wang Long , Suzuki Tetsuya , Argoitia Alberto , Pirouz Pirouz , Angus John C.
Published: July 2002

Diamond was deposited on synthetic graphite, highly oriented pyrolytic graphite and on substrates covered with graphite powder. Scanning electron microscopy and transmission electron microscopy were used to examine the samples. A strong preference for nucleation of diamond on the edges of the graphite sheets was observed. The graphite and the diamond have a preferential orientation relationship in which the diamond (111) plane is parallel to the graphite (0001) plane, and the diamond [11̄0] direction is parallel to the graphite [112̄0] direction. This orientation means that the puckered hexagons in the diamond (111) plane retain the same orientation as the flat hexagons in the original graphite sheet. We conclude that the diamond can nucleate with an epitaxial relationship to the graphite. Some of the edges of the graphite sheets may have been converted to diamond by the atomic hydrogen.
Ultraviolet optical absorptions of semiconducting copper phosphate glasses
Authors: Bae Byeong-Soo , Weinberg Michael C.
Published: July 2002

Ultraviolet optical absorptions of semiconducting copper phosphate glasses with batch compositions of 40%, 50%, and 55% CuO have been examined as a function of [Cu2+]/[Cutotal] in the glasses. The optical energy gap, Eopt, obtained from the fundamental absorption edge depends upon both glass composition and the ratio [Cu2+]/[Cutotal] in the glass. Eopt increases as CuO content and [Cu2+]/[Cutotal] in the glass are raised. This trend is explained by speculating upon the energy band structure of copper phosphate glass. However, the Urbach energy, ΔE, obtained from the tail of the optical absorption edge is affected solely by [Cu2+]/[Cutotal] in the glass. An absorption band of Cu1+ (in its crystal field) occurs in the vicinity of the absorption tail and is responsible for the increase of ΔE with reducing [Cu2+]/[Cutotal] in the glass.
Acoustic shear wave propagation in Paratellurite with reduced spreading
Authors: Kastelik J. C. , Gazalet M. G. , Bruneel C. , Bridoux E.
Published: July 2002

An original configuration of propagation of acoustic shear wave in Paratellurite slightly off the [110] axis in the (001) plane is described. It allows greatly reducing the spreading of the acoustic energy. The main characteristics of an acousto-optic interaction with this acoustic shear wave are then discussed. An experimental validation based on the schlieren method is finally proposed. It shows the effective reduction of the acoustic beam diffraction of the shear wave propagating with a 5° angular tilt. It is compared with the acoustic diffraction obtained for a shear wave propagating in TeO2 along the [110] axis without angular tilt.
Argon incorporation in Si(100) by ion bombardment at 15–100 eV
Authors: Lau W. M. , Bello I. , Huang L. J. , Feng X. , Vos M. , Mitchell I. V.
Published: July 2002

Argon incorporation in Si(100) by low energy ion bombardment has been studied by polar angle dependent x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. The bombardment was performed at 15, 20, and 100 eV in an ultrahigh vacuum chamber where a mass-separated argon ion beam with an energy spread of less than 1 eV was directed to the target. Both the argon penetration depth and incorporation probability were found to increase with bombardment energy. With a fluence of 2×1017/cm2, most of the incorporated argon was located within 20 Å of the target surface for the 100 eV bombardment and within 10 Å for the 15 eV bombardment. In all cases, the argon depth distribution reached a maximum and then declined. At this fluence, the incorporation probabilities were 0.0015 and 0.0004 for the 100 and 15 eV bombardment, respectively. When the amount of incorporated argon was measured as a function of fluence, it increased with fluence at low fluences, reached a quasisaturation at about 1×1016/cm2, but became fluence dependent again above 1×1018/cm2. The retained argon was stable at room temperature but showed at least two stages of thermal desorption in the temperature range 25–500 °C.
Electrical and structural properties of dislocations confined in a InGaAs/GaAs heterostructure
Authors: Uchida Y. , Kakibayashi H. , Goto S.
Published: July 2002

Electrical activation and structural defects in lattice-mismatched InGaAs/GaAs heterostructures are studied using the capacitance-voltage method, deep-level transient spectroscopy, and cross-sectional transmission electron microscopy. Confinement of structural defects is observed in an In0.2Ga0.8As/GaAs heterostructure with a relaxed InGaAs layer thicker than the thickness of the critical layer. When In composition is 0.2, where the lattice mismatch is 1.4% between InGaAs and GaAs, a two-dimensional growth mode dominates. Misfit dislocations are formed and conduction electrons are depleted only near the InGaAs/GaAs interface. Carrier depletion is related to an electron trap with an activation energy of 0.395 eV and a capture cross section of 1×10−16 cm2 induced by deformation. Electrical evaluations show that electrical activity in the InGaAs layer does not degrade by interfacial dislocations. Therefore, a good-quality InGaAs layer is provided though the thin layer near the interface is of poor quality. These results indicate that elastic strain is not large enough in this system for dislocations to rise to the surface. In an In0.4Ga0.6As/In0.2Ga0.8As/GaAs heterostructure, however, dislocation confinement is imperfect in spite of similar lattice mismatches between each of the interfaces. In this structure, threading dislocations rise into the epitaxial layer not only from the In0.4Ga0.6As/In0.2Ga0.8As interface but also from the In0.2Ga0.8As/GaAs interface. This indicates that dislocations can be generated in the layer that had already been formed during the growth of an upper layer.
Low-band-gap Ga0.5In0.5P grown on (511)B GaAs substrates
Authors: Kurtz Sarah R. , Olson J. M. , Arent D. J. , Bode M. H. , Bertness K. A.
Published: July 2002

The band gap and microstructure of Ga0.5In0.5P have been shown to vary with deposition conditions. However, growth on (511)B GaAs substrates has been reported to give Ga0.5In0.5P with band gaps close to that of disordered material. It is shown here, that with appropriate selection of the growth parameters, Ga0.5In0.5P can be grown with low band gap and significant ordering on even the (511)B substrates, implying that surface steps play an important role in the ordering process. For the lattice-matched composition, a band gap of 1.83 eV was obtained using low growth temperature (575 °C), low growth rate (0.55 μm/h), and high phosphine pressure (5 Torr).
Optical and electrical properties of rare earth (Yb,Er) doped GaAs grown by molecular beam epitaxy
Authors: Seghier D. , Benyattou T. , Kalboussi A. , Moneger S. , Marrakchi G. , Guillot G. , Lambert B. , Guivarc’h A.
Published: July 2002

Electrical and optical properties of erbium-doped and ytterbium-doped GaAs are reported in this article. The studied samples are semi-insulating and have been grown by molecular beam epitaxy. The Yb and Er concentrations in the GaAs epitaxial layers measured by secondary ion mass spectroscopy are 2–3×1017 cm−3. The photoluminescence of Yb intra-4f shell has not been observed, while that of Er has been widely reported. Photoinduced current transient spectroscopy measurements (PICTS) reveal that the Yb doping (Er doping) creates a level in the gap with an activation energy of 0.65 eV (0.67 eV). The depth of such levels may be responsible for the absence of Yb 4f photoluminescence in GaAs:Yb. Moreover, photoconductivity experiments show the presence of rare earth related traps. The energies of these traps correspond exactly to the difference between the gap energy and the corresponding activation energy found by PICTS. These observations confirm the excitation model based on the energy transfer from recombination to the rare earth transitions.
Broadband ultrafast superconducting NbN detector for electromagnetic radiation
Authors: Gousev Yu. P. , Gol’tsman G. N. , Semenov A. D. , Gershenzon E. M. , Nebosis R. S. , Heusinger M. A. , Renk K. F.
Published: July 2002

An ultrafast detector that is sensitive to radiation in a broad spectral range from submillimeter waves to visible light is reported. It consists of a structured NbN thin film cooled to a temperature below Tc (∼11 K). Using 20 ps pulses of a GaAs laser, we observed signal pulses with both rise and decay time of about 50 ps. From the analysis of a mixing experiment with submillimeter radiation we estimate an intrinsic response time of the detector of ∼12 ps. The sensitivity was found to be similar for the near-infrared and submillimeter radiation. Broadband sensitivity and short response time are attributed to a quasiparticle heating effect.
Low-temperature luminescent properties of degenerate p-type GaAs grown by low-pressure metalorganic chemical vapor deposition
Authors: Chen H. D. , Feng M. S. , Chen P. A. , Lin K. C. , Wu C. C.
Published: July 2002

Low-temperature (20 K) luminescent properties of heavily carbon- and zinc-doped GaAs grown by low-pressure metalorganic chemical vapor deposition were investigated. The luminescence linewidth became broader at low temperatures when p≳4×1019 cm−3 due to the appearance of a shoulder peak. The main peak shifted to low energy when the dopant concentration was increased; however, the shoulder peak was at around 1.485 eV and was nearly independent of the dopant concentration. The peak of the band-to-acceptor transition occurred at low temperature and dominated the emission spectra of degenerate GaAs. The peak energy of Zn-doped samples was lower than that of C-doped samples because of the existence of defects. The excitation power intensity was varied to investigate the behavior of the shoulder peak for both types of dopants. The shoulder peak was a part of the main peak because of the recombination between the conduction band and the bottom of the impurity band.
Magnetic properties of Gd(Fe1−xCox)9Ti2 alloys
Authors: Suharyana  , Cadogan J. M. , Li Hong-Shuo , Bowden G. J.
Published: July 2002

Four samples of Gd(Fe1−xCox)9Ti2 with x=0.0, 0.1, 0.2, and 0.3 were prepared by conventional arc melting followed by annealing at 1000 °C for 3 days. Powder-x-ray-diffraction patterns of these samples show that all of the samples have a dominant phase with the tetragonal CeMn6Ni5 structure. Traces of TiFe2 are also present. 57Fe Mössbauer spectra have been collected at 80 and 295 K. X-ray-diffraction patterns and Mössbauer spectra on magnetically aligned samples indicate that the easy axis of magnetization is the crystallographic c axis. The Curie temperature increases monotonically with increasing cobalt concentration. The average hyperfine field at 80 K reaches a maximum of 26.8(5) T for x≊0.2.
Effects of barrier layer and annealing on abnormal grain growth in copper thin films
Authors: Zielinski E. M. , Vinci R. P. , Bravman J. C.
Published: July 2002

Abnormal (100) grain growth has been characterized in predominantly (111)-textured Cu thin films as a function of deposition temperature, annealing temperature and the presence of a Ta or W underlayer. For films deposited at room temperature, bimodal grain size distributions are observed at annealing temperatures at or above 150 °C for Cu on Ta and 100 °C for Cu on W. Suppression of (100) abnormal grain growth was achieved by depositing Cu on either barrier layer at 150 °C. A bimodal grain size distribution was still observed for the film deposited on W at 150 °C but the large grains forming this distribution were found to be (111) oriented. These results are explained as the result of competition between strain energy minimization and surface and interface energy minimization. The (100) growth is shown to be driven by a reduction of the orientation-dependent strain energy that builds up due to the elastic anisotropy of Cu. Films deposited at higher temperatures have a lower yield stress which limits the achievable strain energy driving force, thereby suppressing the (100) growth. Surface energy minimization drives the (111) abnormal growth.
A new, optical-lever based atomic force microscope
Authors: Hansma P. K. , Drake B. , Grigg D. , Prater C. B. , Yashar F. , Gurley G. , Elings V. , Feinstein S. , Lal R.
Published: July 2002

A new optical-lever based atomic force microscope is described in which the cantilever scans and is accurately tracked by a scanning focused spot. It can operate at forces below one nanoNewton over image areas greater than 100 μ×100 μ. It can be combined with optical microscopes of high numerical aperture and operated with the sample and cantilever in fluids. As examples of its applications, images of living cells in Petri dishes and a 6 in. (15.24 mm) silicon wafer are included.
Optical constants of sapphire (α-Al2O3) single crystals
Authors: Harman Alang Kasim , Ninomiya Susumu , Adachi Sadao
Published: July 2002

Spectroscopic ellipsometry has been used to measure the dielectric functions of synthetic sapphire (α-Al2O3) single crystals. The measurements have been made on the (112̄0) surfaces of sapphire in the near-infrared–near-ultraviolet spectral region (1.2–5.4 eV) at room temperature. These data and the literature values are used for the modeling of the optical constants of sapphire crystals over the 0–30 eV photon-energy range. By using damped harmonic oscillators as a basis of the model, the causality, linearity, reality, and Kramers–Kronig requirements, compulsory properties of the dielectric function ε(E)=ε1(E)+iε2(E), can be satisfied automatically. It is found that the damped harmonic oscillator model provides satisfactory fits to the experimental ε2(E), but does not yield good fits to ε1(E) in the higher-photon-energy region (E≳7 eV). As a byproduct of this analysis, we obtain the static and high-frequency dielectric constants of sapphire crystals as ε∞=3.064 and εs=8.90 for the ordinary ray (E⊥c) and ε∞=3.038 and εs=11.11 for the extraordinary ray (E∥c), respectively.
Resonance reflection and transmission of shear elastic waves in multilayered piezoelectric structures
Authors: Alshits V. I. , Shuvalov A. L.
Published: July 2002

Inclined incidence of a shear horizontal elastic wave on a periodic structure of piezoelectric layers with metallized interfaces is considered. The layers are supposed to be made from the identical crystal of hexagonal symmetry but have alternating widths d1,d2. Due to the condition of fixed electropotential, each interface provides the reflection proportional to the parameter of electromechanical coupling q2. The interference of the reflected waves in the periodic structure causes the existence of the Bragg resonances in the reflection-transmission spectrum so that ‖R‖max≊1 for a sufficiently large number of layers. Since q2≪1, the considered reflection spectrum exhibits some specific features such as high selectivity, modulation of the heights of the Bragg maximums depending on the value d1/(d1+d2), and the extinction effect.
Experimental study of continuous CO2 laser welding at subatmospheric pressures
Authors: Verwaerde A. , Fabbro R. , Deshors G.
Published: July 2002

A comparison between laser welding under vacuum and atmospheric pressure conditions was performed. By measuring plasma size, electron density, and electron temperature, plasma suppression at low pressure (below 20 Torr) is observed, associated with an electron density and temperature decrease with reduction of pressure. These microscopic parameters were then correlated to the ambient pressure according to Saha’s law. The electron density in the plasma plume is controlled by the ambient pressure. The influence of the plasma suppression on the welded seam was also studied. New information concerning the energy deposition process inside the keyhole was obtained: Under reduced pressure conditions, the laser light is mainly absorbed by Fresnel reflection and a constant energy deposition per unit length occurs. At atmospheric pressure the laser is absorbed by a combination of Fresnel effect and inverse bremsstrahlung plasma process. The power deposition can be approximated by an inverse exponential law.
Laser power dependence of particulate formation on pulse laser deposited films
Authors: Watanabe Yukio , Tanamura M. , Matsumoto S. , Seki Y.
Published: July 2002

The density and the size of particulates in films laser-deposited at room temperature using various target materials were observed to depend strongly on the target material and the laser power density. However, loose universal relations between the deposition rates and the particulate density as well as the particulate size were found, where the latter corresponds approximately to the ratio of the laser power density to the ablation threshold. Furthermore, particulates consisting of only some of the target elements such as CuOx were found. Additionally, an acceptably high deposition rate was obtained by using halide and sulfide targets. These materials offer a possibility of deposition using a low power laser.
Effect of stoichiometry on the dynamic mechanical properties of LiNbO3
Authors: de Bernabé A. , Prieto C. , de Andrés A.
Published: July 2002

Acoustic and optic phonons have been measured by Brillouin and Raman spectroscopies in LiNbO3 samples with different stoichiometries. Consequently, the elastic constants have been determined by Brillouin scattering as a function of the stoichiometry. The C44 elastic constant presents, as a function of the stoichiometry, a clear minimum for the [Li]/[Nb]=1 in the melt sample. This behavior must be related to the existence and competition of two kind of defects, i.e., extended defects induced when growing samples not at the congruent composition, and point defects present in nonstoichiometric samples. The optic phonons seem to be dominated by the point defects. The linear increase of the phonon lifetimes, with respect to an ideal stoichiometric sample, can be due to the scattering by the static imperfections and to an increase of the anharmonic scattering. Several Raman peaks, which appear when the [Li]/[Nb] ratio decreases, are related to the presence of Nb in antisites. The width of some particular phonons can be used to estimate the [Li]/[Nb] ratio whenever a line shape study and a good correction, taking into account the instrumental broadening, is carried out.
Precursor route pentacene metal-insulator-semiconductor field-effect transistors
Authors: Brown A. R. , Pomp A. , de Leeuw D. M. , Klaassen D. B. M. , Havinga E. E. , Herwig P. , Müllen K.
Published: July 2002

Metal-insulator-semiconductor field-effect transistors have been constructed with pentacene as the active semiconductor. The pentacene is processed by spin coating from a soluble precursor. A simple thermal conversion yields transistors with carrier mobilities as high as 9×10−3 cm2 V−1 s−1 and current modulations of the order of 105. Depletion of charge is essential to the device operation. Data for an invertor exhibiting voltage amplification are presented.
Destruction of carbon tetrachloride in a dielectric barrier/packed-bed corona reactor
Authors: Tonkyn R. G. , Barlow S. E. , Orlando T. M.
Published: July 2002

The destruction of low concentrations (<1000 ppm) of gas-phase carbon tetrachloride (CCl4) using a low-temperature, dielectric barrier/packed-bed corona reactor was studied. We compare, in particular, the destruction efficiencies using either borosilicate or zirconia oxide (ZrO2) packing materials in dry and moist air, and nitrogen buffer gases. Measurements of contaminant removal in the effluent gas were made at atmospheric pressure as a function of energy dissipated in the reactor. In dry N2, destruction of CCl4 was most efficient using ZrO2 beads, whereas, in dry air, contaminant removal was approximately equal for borosilicate glass and ZrO2. The presence of water in the gas stream reduced the CCl4 destruction efficiency under all conditions. This reduction was likely a synergistic effect that involves changes in the plasma density, scavenging of low energy secondary electrons, and possible surface passivation. Assuming the primary step in CCl4 destruction is dissociative electron attachment, an estimate of the average density of low energy electrons as a function of input energy was made. We relate the enhancement in CCl4 destruction using the ZrO2 beads in N2 to a slight increase in the number density of low energy secondary electrons. A discussion of the importance of energy density measurements and a useful phenomenological kinetic model consistent with the observed results are presented.
The influence of argon pressure on the structure of sputtered molybdenum: From porous amorphous to a new type of highly textured film
Authors: Klabunde F. , Löhmann M. , Bläsing J. , Drüsedau T.
Published: July 2002

The density of the low-rate (<0.1 nm/s) sputtered molybdenum films can be controlled between 48% and 96% of the bulk material by the variation of argon pressure from 4.7 to 0.45 Pa. Small angle x-ray scattering shows the existence of columnar voids with a typical size of 10 nm, especially in the low-density films, whereas a high concentration of primary voids with a diameter of 1 nm is found independent of the density. The conductivity of the films decreases monotonically with decreasing density from 2.4×104 to 2.1×102 (Ω cm)−1, with a strong decay below a density of 55%. Films of about 30 nm thickness are amorphous or nanocrystalline with a (110) texture for high- and low-pressure sputter deposition, respectively. Upon increasing the film thickness up to 3 μm, the low-density films become nanocrystalline, too, and develop the common (110) fiber texture. In contrast, increasing the thickness of the high-density films results in a turnover of texture from a (110) type to a (211) mosaiclike texture.
Cathodoluminescence image of defects and luminescence centers in ZnS/GaAs(100)
Authors: Mitsui Tadashi , Yamamoto Naoki , Tadokoro Toyoyasu , Ohta Shin-ichi
Published: July 2002

The spatial distributions of the cathodoluminescence (CL) emissions from thin ZnS films on GaAs(100) have been examined by the low-temperature CL measurement system combined with a transmission electron microscope (TEM). The correlation between these CL emissions and structural defects were studied by comparing the monochromatic CL images with the TEM images for both plan-view and cross-sectional observations. It is found that the neutral acceptor–bound exciton associated emission (A0,X) and the free-electron-to-ionized acceptor transition emission (e,A) are affected by the stacking fault distribution. The localization of the emission due to the deep-level emission transition near the interface suggest the diffusion of Ga atoms from the GaAs substrate. The characteristic distributions of the CL emission regions can be explained by considering the competitions among the recombination channels of those radiative processes for each type of an excess carrier, an electron, or a hole.
Proximity and coupling effects in superconductor/ferromagnet multilayers (invited)
Authors: Chien C. L. , Jiang J. S. , Xiao John Q. , Davidovic D. , Reich Daniel H.
Published: July 2002

New features in superconductor/ferromagnet multilayers have been observed. A nonmonotonic dependence of the superconducting Tc on the ferromagnetic layer thickness, due to the coupling across a thin magnetic layer, has been observed in both Nb/Gd multilayers and trilayers. The results are consistent with those of the predicted π-phase coupling. Effects on superconductivity due to insulating ferromagnetic layers have been observed in NbN/GdN multilayers, where the main pair-breaking effect is that of the ferromagnetic walls. The insulating ferromagnetic layers also give rise to very large superconducting critical fields.
Magnetization process of iron surface observed by transverse Kerr magnetometry
Authors: Maruyama K. , Namikawa K. , Konno M. , Maruyama H.
Published: July 2002

Transverse magneto-optical Kerr hysteresis loops were observed on pure iron single crystals. They exhibit a steplike behavior of magnetization different from that of the bulk. The hysteresis loop is compared with those magnetization curves which are obtained on the same sample by x-ray resonant magnetic scattering measurement and by the vibrating sample magnetometry. The magnetization process is discussed in terms of the components of magnetization parallel and perpendicular to magnetic field. The nature of the steplike magnetization was revealed to be characterized by the wall displacement of fracturized magnetic domains in the surface region.
On the applicability of the Ivantsov growth equation
Authors: Liu Zi-Kui , Chang Y. Austin
Published: July 2002

The steady state growth equation for a paraboloid of revolution and a parabolic cylinder, taking the interfacial energy into account, is revisited. Although the consideration of the interfacial energy was necessary, the growth equation was much more complicated than the original equation with a zero interfacial energy, since both the thermodynamics and kinetics of the growth are considered in one equation. In the present work, we take advantage of the development in computational thermodynamics and consider the thermodynamics and kinetics of the process in separate equations, but solve them simultaneously. A consistent framework to describe the phenomena and compare it with previous treatment of the interfacial energy will be presented.
A theory of 1/f noise
Authors: Stephany Joseph F.
Published: July 2002

Universal 1/f noise is shown to originate from the variations in the initial velocities of conduction electrons after collisions with defects. Defect atoms, after being struck by conduction electrons, recoil and form an impacted mass of lattice atoms. Conduction electrons emitted after a collision have an average initial velocity which steadily decreases as the impacted mass builds up. It is shown that this process yields a noise spectrum of the form f−n where n is in the vicinity of one and has an amplitude given by the Hooge empirical formula. Variations from the Hooge result are discussed. The model described applies to all semiconductors and metals.
Temperature and injection dependence of the Shockley–Read–Hall lifetime in electron-irradiated p-type silicon
Authors: Keskitalo Niclas , Jonsson Per , Nordgren Kenneth , Bleichner Henry , Nordlander Edvard
Published: July 2002

The Shockley–Read–Hall (SRH) carrier lifetime in electron-irradiated low-doped p-type silicon was measured at different injection levels and various temperatures. The lifetime under high-level injection was determined using the open-circuit carrier decay technique. The reverse recovery technique was used to determine the lifetime under low-level injection. The defect composition was studied using deep-level transient spectroscopy, and according to that the SRH lifetime is calculated. The good agreement between the calculated and the measured lifetimes strongly indicates that the lifetime is controlled by two different deep levels. At low injection levels, the lifetime is mainly controlled by the singly negative charge state of the divacancy center, HC−HT=0.421 eV, and at high injection levels by the vacancy–oxygen complex, HC−HT=0.164 eV. These are the same levels controlling the lifetime in electron-irradiated n-type silicon.
Determination of trapping parameters in poly(p-phenylenevinylene) light-emitting devices using thermally stimulated currents
Authors: Meier M. , Karg S. , Zuleeg K. , Brütting W. , Schwoerer M.
Published: July 2002

Employing thermally stimulated current (TSC) technique, the existence of distinct trap distributions in poly(p-phenylenevinylene) (PPV) light-emitting devices has been established. In devices with an indium tin-oxide (ITO) anode two TSC peaks in the temperature range between 100 and 150 K are observed. They correspond to trap levels with a depth of 0.03–0.06 eV and 0.13–0.18 eV, respectively. The total density of these trap species is of the order of 1016 cm−3 which is in good agreement with the dopant concentration obtained from capacitance-voltage measurements. The investigated peaks in the TSC spectrum do not occur if a Au electrode is used instead of ITO. Hence, the reaction of ITO with the elimination products (mainly HCl) during the conversion of the PPV precursor leads to the formation of these shallow traps. Deeper trap states with energies between 0.6 and 1 eV have been detected, too. The latter trapping levels appear independently of the anode substrate material and are due to the influence of air.
Growth stage of crystalline Y2O3 film on Si(100) grown by an ionized cluster beam deposition
Authors: Cho M.-H. , Ko D.-H. , Jeong K. , Whangbo S. W. , Whang C. N. , Choi S. C. , Cho S. J.
Published: July 2002

We investigated the initial and epitaxial growth stage of Y2O3/Si(100) grown by reactive ionized cluster beam deposition, using x-ray diffraction (XRD), atomic force microscope, and reflection high-energy electron diffraction. We also investigated the crystalline structure of the films using transmission electron microscopy and XRD. The preferred growth direction of Y2O3 grown by an ion beam changed completely from the 〈111〉 to the 〈110〉 orientation in order to minimize the overall energy of the film as the substrate temperature increased. In addition to the kinetic energy of the deposited atoms, oxygen partial pressure and the substrate surface state also bear a relationship to the change in the preferred growth direction. The crystalline growth of Y2O3 film depends on the state of the surface at the initial growth stage, whether the Si surface was first exposed to oxygen or yttrium. In particular, the silicon oxide layer which formed on the Si surface during the initial growth stage played an important role in the epitaxial growth as well as the preferred growth direction of Y2O3 film.