bluuebunny/crossref_metadata_2025 huggingface dataset:
Low cost high resolution thermoluminescence spectrometer
Authors: Rhodes M. W. , Wanwilairat S. , Vilaithong T. , Hoffmann W.
Published: July 2002

A high-resolution thermoluminescence dosimetry (TLD) spectroscopy reader has been developed in order to perform detailed quantitative studies of the kinetics of TLD materials. The key features of this system are high wavelength resolution (1.3 nm), low cost, and compact size. In addition, the spectrometer is fiber optic coupled to the sample material isolating the system from thermal influences and electrical noise generated by the heating system. Temperature rate control can be computer set with a heat rate accuracy of better than 0.12% and a temperature readout accuracy of 1 °C or better. Analysis of all three parameters: temperature, wavelength, and intensity, is easily visualized with integrated 2D/3D analysis software. Preliminary analysis on TLD300 samples irradiated with Co60 from 5 to 60 Gy show temperature peaks and wavelength locations consistent with other published measurements. Details of the hardware system and software are discussed along with sample results.
Precise and direct determination of the elastic constants of a cylinder with a length equal to its diameter
Authors: Nieves F. J. , Gascón F. , Bayón A.
Published: July 2002

A cylinder made of a homogeneous isotropic material and with a length equal to its diameter is excited by axial percussion. Its axial displacement is detected by speckle interferometry. The two lowest frequencies, the first symmetric mode and first antisymmetric mode, are compared with the corresponding nondimensional natural frequencies, calculated to six significant figures using the Ritz method for 51 values of Poisson’s ratio. The values of both dynamic elastic constants (shear modulus and Poisson’s ratio) are found based on the quotient of the measured frequencies by using a table that is given. The method requires only one experiment and a simple calculator. The origin of the uncertainties is analyzed to improve the method’s precision. The systematic uncertainty of the results shows relative values of 0.23% for shear modulus and 0.59% for Poisson’s ratio. The values of the elastic constants calculated for a stainless steel test piece are compared with the values obtained by other methods.
A pulser for medium-frequency modulated direct-current reactive sputter deposition of insulators
Authors: Kiehne G. T. , Lin M. Z. , Wang G. , Xiang W. H. , Cao H. , Ketterson J. B.
Published: July 2002

We present the circuit design of a unit for medium-frequency modulated direct-current (dc) reactive sputter deposition of electrical insulators. The unit is connected in series between a commercial dc sputtering power supply and a sputtering cathode (target). It modulates the voltage applied to the sputtering cathode in a pulsed, asymmetric bipolar fashion. The pulsing effectively eliminates the problem of arcing at the target surface. The simple circuit is a low-cost, flexible alternative to commercially available units. To demonstrate its utility, we deposited a film of 5 SiO2/TiO2 bilayers, forming a highly reflective dielectric optical mirror with a stop band centered near a wavelength in air of 600 nm.
An innovative linear response time-to-digital converter with a branched propagation delay chain
Authors: Chang Chih-Yao , Sun Wan-Li , Wang Nai-Chueh , Leung Chung-Yee
Published: July 2002

Utilizing the propagation delay in a chain of logic elements to digitize short time intervals has a high potential in various applications because the method has an ultrashort measurement “dead time” and its complete timing circuit can be easily integrated in a single semiconductor chip. However, the existing single-lined chain suffers from serious nonlinearity due to the longer path lengths at the foldings which are unavoidable when the number of delay elements is large as high time resolution requires. We propose a new configuration in which the delay chain is branched. The delay elements of each branch evenly subdivide the corresponding larger folding path so all units have the same delay time. The proposed time-to-digital converter with an 81-delay-unit branched chain and a built-in calibration circuit has been implemented on a commercial programmable logic device. It is used to interpolate different time durations within the 100 ns period of a standard 10 MHz clock. The digital time deviates less than 0.3 ns throughout the entire range. A similar single-lined delay chain, constructed for comparison, exhibits timing error up to 32.7 ns. A major improvement in linearity has been achieved by our device.
Single-layer white light-emitting organic electroluminescent devices based on dye-dispersed poly(N-vinylcarbazole)
Authors: Kido J. , Shionoya H. , Nagai K.
Published: July 2002

Bright single-layer white light-emitting organic electroluminescent devices were developed by using dye-dispersed poly(N-vinylcarbazole) (PVK). The active layer consists only of one polymer layer that is simply sandwiched between two electrodes, indium-tin oxide, and Mg:Ag. In order to achieve bipolarity in the single polymer emitter layer, PVK was molecularly dispersed with electron-transporting additives such as 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole. In addition, several fluorescent dyes, having different emission colors, were dispersed as emitting centers. By adjusting the concentration of the fluorescent dyes, white light with a maximum luminescence of 4100 cd/m2 was obtained, which is the brightest white light ever observed for organic electroluminescent devices.
Phononic band structure in a mass chain
Authors: Parmley Samantha , Zobrist Tom , Clough Terry , Perez-Miller Anthony , Makela Mark , Yu Roger
Published: July 2002

The vibrational properties of a finite one-dimensional string-mass chain are studied experimentally and theoretically. In the experiment both normal mode analysis and pulse analysis are used to obtain the eigenfrequencies of the string-mass chain. The theoretical predictions are made based upon the numerical solution to the wave equation. The phononic band structure for a periodically massed string as well as Anderson localized gap modes for a disordered system are found. The theoretical and experimental results match satisfactorily well.
Enhanced hydrogenation and acceptor passivation in Si by pressurized water boiling
Authors: Ohmura Y. , Otomo Y. , Tago Y. , Terakado N. , Satoh T.
Published: July 2002

It has been shown that a pressurized water boiling (PWB) at 2 atmospheric pressures and 120 °C in an autoclave vessel accelerates significantly hydrogenation and neutralization of B acceptors in Si. Compared with boiling at atmospheric pressure, PWB reduces more the free-hole IR absorption and increases more the sheet resistivity in B implanted p+ layer on n-type substrate. An IR absorption of B–H stretching vibration (∼1907 cm−1) has been detected at 16 K for a p+ layer which was PWB processed for only 6 h. Concentration increase of H-related species in water and faster diffusion of H in Si at higher temperature may be the cause. In contrast with other hydrogenation techniques, water boiling hardly passivates donors in Si even for 10 h PWB.
Observation of double cyclotron resonance in modulation-δ-doped In0.52Al0.48As/In0.53Ga0.47As heterostructure by optical detection
Authors: Chen Y. F. , Dai Y. T. , Lo I.
Published: July 2002

We report an investigation of optical and electronic properties of a two-subband populated electron gas confined at a δ-doped Al0.48In0.52As/Ga0.47In0.53As heterostructure by the technique of far-infrared optically detected cyclotron resonance (ODCR). Oscillatory characteristics are observed in the ODCR spectrum, and interpreted in terms of the crossing between the Landau levels of the two-dimensional electron gas and the Fermi level from which the electron concentration and effective mass of the first and second subbands can be determined. Quite different effective masses associated with these subbands are obtained, reflecting the strong effects of conduction band nonparabolicity as well as polaron coupling in Ga0.47In0.53As quantum well.
Growth of HgBa2Ca2Cu3O8+δ thin films on LaAlO3 substrates using fast temperature ramping Hg-vapor annealing
Authors: Yun S. H. , Wu J. Z. , Tidrow S. C. , Eckart D. W.
Published: July 2002

The fast temperature ramping Hg-vapor annealing (FTRA) process has been used for growth of superconducting Hg-based cuprate thin films on (100) LaAlO3 substrates. The film/substrate interface chemical reactions and the formation of a CaHgO2 impurity phase have been effectively reduced with adoption of the FTRA process. A zero-resistance superconducting transition temperature of 128 K and critical current densities of up to 1.4×106 A/cm2 at 77 K and 2.5×105 A/cm2 at 110 K and zero field have been obtained.
Strain-induced phase separation in annealed low-temperature grown Al0.3Ga0.7As
Authors: Hsieh K. C. , Hsieh K. Y. , Hwang Y. L. , Zhang T. , Kolbas R. M.
Published: July 2002

Data are presented to show that the hydrostatic strain in a metastable Al0.3Ga0.7As film grown at low temperatures induces a one-dimensional compositional modulation upon annealing at 600 °C, a direct evidence of the existence of a miscibility gap in strained AlxGa1−xAs. A strain-driven vacancy-assisted mechanism is proposed to account for the compositional modulation and segregation of As clusters.
Investigation of the nucleation mechanism in bias-enhanced diamond deposition
Authors: Reinke P. , Kania P. , Oelhafen P. , Guggenheim R.
Published: July 2002

Polycrystalline diamond films were deposited in a MW-PECVD reactor employing bias-enhanced nucleation as pretreatment to promote the subsequent diamond nucleation. The substrate temperature during the bias-enhanced nucleation was varied between 600° and 760 °C by external heating, while the other deposition parameters namely the microwave input power were kept constant. Likewise, the deposition parameters were not changed in the subsequent diamond growth period throughout the experiment. The films formed during the bias-enhanced nucleation were analyzed employing electron energy loss spectroscopy (EELS) and scanning electron microscopy (SEM). The nuclei density (ND) obtained for good quality diamond crystals after the nucleation step and an additional growth period increases considerably from 1×106 cm−2 or less to 1×1010 cm−2 in a narrow temperature range between 670 and 700 °C. For temperatures exceeding 700 °C continuous films are formed. The structure of the pretreatment deposit also undergoes considerable changes: the intensity of the diamond plasmon increases with the substrate temperature, which is indicative of an increase in the concentration of diamond crystallites embedded in an otherwise amorphous carbon matrix. Our experiments suggest that diamond crystallites formed during the pretreatment serve as nucleation centers for the subsequent diamond growth. We can also conclude that the variation in the substrate temperature rather than the changes in the microwave input power or, respectively, plasma chemistry, drive the observed structural changes and increase in ND.
Interface roughness and alloy-disorder scattering contributions to intersubband transition linewidths
Authors: Campman K. L. , Schmidt H. , Imamoglu A. , Gossard A. C.
Published: July 2002

We report measurements of intersubband absorption in single semiconductor quantum wells of different well widths and alloy compositions. The well width dependence of the intersubband absorption linewidth is consistent with broadening dominated by interface roughness. The linewidth, however, is found to be relatively unaffected by alloy composition in the quantum well, making alloying an effective tool in the design of quantum well optical devices relying on intersubband transitions.
A method for synthesizing large quantities of carbon nanotubes and encapsulated copper nanowires
Authors: Setlur A. A. , Lauerhaas J. M. , Dai J. Y. , Chang R. P. H.
Published: July 2002

A method using a hydrogen arc for synthesizing large quantities of carbon nanotubes filled with pure copper is reported. The interaction of small copper clusters with polycyclic aromatic hydrocarbons (PAHs) is shown to form carbon nanotubes and encapsulated copper nanowires. The effectiveness of this model is demonstrated by showing that no copper filled nanotubes are formed in a helium arc that does not generate PAHs. A direct proof of this model is demonstrated by using pyrene, a PAH molecule, to grow carbon nanotubes and encapsulated copper nanowires.
Effects of finite drain voltage and finite temperature on coherent resonant transport in single electron tunneling regime
Authors: Wang T. H. , Tarucha S.
Published: July 2002

Effects of a finite drain voltage and a finite temperature on coherent transport in the single electron tunneling regime are investigated for a novel quantum dot structure defined by two shallow etched trenches and two line Schottky gates. A regular amplitude modulation of Coulomb blockade oscillations is observed and attributed to coherent resonant transport. Increasing drain voltage disturbs the amplitude modulation more significantly than raising the temperature. This is explained in terms of the effects of nonmonochromatic electrons on the interference condition.
The effect of carbon on strain relaxation and phase formation in the Ti/Si1−x−yGexCy/Si contact system
Authors: Eyal A. , Brener R. , Beserman R. , Eizenberg M. , Atzmon Z. , Smith David J. , Mayer J. W.
Published: July 2002

We report the first study of interfacial reactions of a metal with Si1−x−yGexCy epitaxially grown on Si. The Ti/Si1−x−yGexCy/Si (0<y<1.7%) contact system was studied after isochronal heat treatments from 500 to 800 °C. The results for Ti/Si1−xGex phase formation agree with recent published works. However, C incorporation in the epilayer causes a dramatic decrease in strain relaxation during the Ti reaction with the epilayer, a delay in the appearance of the C54 phase, a decreased Ge concentration in the silicide–germanide phases, and carbon accumulation (probably in the form of TiC) at the silicide–germanide/epilayer interface. Also, at high annealing temperatures, a roughing of the silicide–germanide/epilayer interface was detected for the C-containing samples. A possible explanation for the reduced strain relaxation is based on mobility of dislocations.
Subwavelength Raman spectroscopy
Authors: Grausem J. , Humbert B. , Burneau A. , Oswalt J.
Published: July 2002

Near-field Raman spectroscopy has been performed on liquid CCl4. The spectrum, obtained through an aperture significantly smaller (λ/10) than the exciting wavelength (514.5 nm) with a good signal-to-noise ratio, presents polarization effects that are different from the far-field spectrum. The tip is shown to be polarized at 99.9% by the Raman near field. If the probe is modeled as a single dielectric sphere, the estimated Raman near-field amplitude amounts to about 103 V m−1. The frustration of the Raman near field by the probe allows to record the Raman spectrum of only 0.4 attomol, or 240 000 mol.
Tunable interminiband infrared emission in superlattice electron transport
Authors: Scamarcio Gaetano , Capasso Federico , Faist Jerome , Sirtori Carlo , Sivco Deborah L. , Hutchinson Albert L. , Cho Alfred Y.
Published: July 2002

The observation of infrared emission between superlattice conduction minibands is reported. Electrons resonantly injected into the first excited state miniband by an applied electric field make a radiative transition to the ground state miniband. The spectra are dominated by direct high oscillator strength transitions at the mini-Brillouin zone edge and the peak wavelength can be tailored over a broad infrared range by designing the superlattice minigap. At high bias, the spectra extend to wavelengths corresponding to transitions from high lying states near the mini-Brillouin zone center. Experiments in AlInAs/GaInAs superlattices have demonstrated peak luminescence wavelengths of λ=5 and 7 μm. At high currents, the spectra broaden to shorter wavelengths (down to 3 μm) as electrons are tunnel injected high into the second miniband.
Microcavity effects in GaN epitaxial films and in Ag/GaN/sapphire structures
Authors: Billeb A. , Grieshaber W. , Stocker D. , Schubert E. F. , Karlicek R. F.
Published: July 2002

Luminescence spectra of GaN epitaxial layers grown on sapphire display a strong intensity modulation of the below-band gap transitions and on the low-energy side of the near-band gap transition. The intensity modulation is attributed to a microcavity formed by the semiconductor–air and semiconductor–substrate interface. The microcavity effect is enhanced by using metallic reflectors which increase the cavity finesse. It is shown that microcavity effects can be used to determine the refractive index of the microcavity active material. Using this method, the GaN refractive index is determined and expressed analytically by a Sellmeir fit.
Free-space transient magneto-optic sampling
Authors: Riordan J. A. , Sun F. G. , Lu Z. G. , Zhang X.-C.
Published: July 2002

We demonstrate a free-space magneto-optic sampling system to measure the transient magnetic component of a freely propagating terahertz beam. Preliminary results using two magneto-optic sensors are presented. A detection sensitivity of 10−7 T of the picosecond magnetic field in a standard pump/probe configuration is obtained. In the current orthogonal geometry, a 13 ps risetime of the free-space magneto-optic signal is measured. A temporal resolution limited only by the material spin relaxation time in a velocity-matched geometry is anticipated.
Microstructure of GaN layers grown on (001) GaAs by plasma assisted molecular-beam epitaxy
Authors: Ruvimov Sergei , Liliental-Weber Zuzanna , Washburn Jack , Drummond Timothy J. , Hafich Michael , Lee Stephen R.
Published: July 2002

High resolution electron microscopy has been applied to characterize the structure of β-GaN epilayers grown on (001) GaAs substrates by plasma-assisted molecular-beam epitaxy. An rf plasma source was used to promote chemically active nitrogen. An exposure of the layer surface to the As flux during the growth of the first few monolayers was shown to result in remarkably flat GaN–GaAs interface. The best quality GaN layers were achieved by near-stoichiometric nucleation with optimal Ga-to-N ratio. Deviation from these nucleation conditions leads to interface roughening and formation of the wurtzite phase within the GaN layer. All the layers contained a high density of stacking faults near the interface which sharply decreases toward the surface. Stacking faults were anisotropically distributed within the GaN layer probably due to different properties of α compared to β dislocations in cubic GaN. The majority of stacking faults intersect the interface along lines parallel to the major flat of the GaAs wafer. The stacking faults are often associated with atomic steps at the GaN–GaAs interface.
Fabrication of single-crystal lithium niobate films by crystal ion slicing
Authors: Levy M. , Osgood R. M. , Liu R. , Cross L. E. , Cargill G. S. , Kumar A. , Bakhru H.
Published: July 2002

We report on the implementation of crystal ion slicing in lithium niobate (LiNbO3). Deep-ion implantation is used to create a buried sacrificial layer in single-crystal c-cut poled wafers of LiNbO3, inducing a large etch selectivity between the sacrificial layer and the rest of the sample. 9-μm-thick films of excellent quality are separated from the bulk and bonded to silicon and gallium arsenide substrates. These single-crystal films have the same room-temperature dielectric and pyroelectric characteristics, and ferroelectric transition temperature as single-crystal bulk. A stronger high-temperature pyroelectric response is found in the films.
Computer simulations on near-field scanning optical microscopy: Can subwavelength resolution be obtained using uncoated optical fiber probes?
Authors: von Freymann G. , Schimmel Th. , Wegener M. , Hanewinkel B. , Knorr A. , Koch S. W.
Published: July 2002

Recent experiments claim that subwavelength resolution can be obtained with an optical scanning microscope using uncoated optical fiber probes. In these experiments, linearly polarized light is sent down the fiber which is reflected and depolarized in the tip-sample region. The internally reflected signal in the orthogonal polarization is detected. Here, numerical solutions of the vector Maxwell equations for a model are discussed. In this model, subwavelength resolution can indeed be obtained in the above mode, while this is not possible without polarization sensitivity. The influence of parameters such as polarization, different scanning modes and tip-sample distance is discussed.
Abnormal temperature dependence of intrinsic coercivity in Sm(Co, Fe, Cu, Zr)z powder materials
Authors: Liu J. F. , Chui T. , Dimitrov D. , Hadjipanayis G. C.
Published: July 2002

The intrinsic coercivity Hci in Sm(CobalCuxFe0.1Zr0.033)z powder materials was found to increase with increasing temperature when Cu content x=0.048, but to decrease when Cu content x⩾0.068. This abnormal behavior, which is also reversible, was found in a series of samples with various ratios z. The field dependence of the intrinsic coercivity suggests that the bonded magnets were fully saturated with an applied field of 20 kOe. The exposure to higher temperatures did not change the room temperature value of coercivity. This indicates that the microstructure does not change during the measurement from 573 to 773 K. The change of coercivity mechanism was found to be responsible for this abnormal temperature behavior. Monte Carlo simulation showed that the coercivity increases (decreases) with increasing temperature for the repulsive (attractive) cell boundary, which is consistent with the experimental results.
Large tunneling magnetoresistance enhancement by thermal anneal
Authors: Sousa R. C. , Sun J. J. , Soares V. , Freitas P. P. , Kling A. , da Silva M. F. , Soares J. C.
Published: July 2002

Spin tunnel junctions with tunneling magnetoresistance of 36.5%±0.5%, resistance-area product of 35±6 kΩ×μm2, and junction area between 6 and 75 μm2 were fabricated. The barrier height is 2.5±0.3 eV and the barrier thickness is 7.7±0.3 Å. Large tunneling magnetoresistance (TMR) values are obtained by vacuum anneal (at temperatures from 100 to 240 °C for over 5 h) of junctions prepared with as-deposited TMR of 21%±1.7%, and an as-deposited resistance-area product of 25±6 kΩ×μm2. Two regimes occur during anneal. The first one occurs for anneals up to 200 °C where TMR and junction resistance increase, but the barrier parameters are unaltered. The second occurs above 200 °C, where TMR increases faster, together with an increase in barrier height. At 240 °C, TMR starts to decrease. Rutherford backscattering analysis indicates an asymmetry in the oxygen distribution in the as-deposited barrier. The oxygen distribution becomes homogeneous for anneals above 150 °C.
Discontinuous phase elements for transverse mode selection in laser resonators
Authors: Oron Ram , Danziger Yochay , Davidson Nir , Friesem Asher A. , Hasman Erez
Published: July 2002

Discontinuous phase elements can be inserted into laser resonators so that the lasers will operate with only one desired high order transverse mode. These elements introduce sharp discontinuous phase changes so as to result in minimal losses for a desired transverse mode but high losses to others. The basic principles, along with experimental results with Nd:yttrium–aluminum–garnet and CO2 lasers, illustrating improved output powers with a high beam quality of low divergence, are presented.
Formation of a buried oxide film at the damage peak induced by oxygen implantation into a Si substrate
Authors: Ogura Atsushi
Published: July 2002

The formation of a buried oxide layer in a Si substrate by oxygen implantation and subsequent high-temperature annealing is examined. The oxide precipitation, growth, and coalescence processes are enhanced by increasing the oxygen concentration in the annealing atmosphere. These processes are enhanced more effectively at the damage peak, where the implantation damage is at a maximum, than at the concentration peak. Therefore, the buried oxide layer can be formed at the damage peak instead of at the concentration peak by choosing an appropriate ramping rate for the annealing and Ar/O2 ratio in the annealing atmosphere. Double buried oxide layers, with a layer at both the damage peak and the concentration peak, can also be fabricated by using a single sequence of oxygen implantation and high-temperature annealing. In both cases, oxygen atoms introduced from the atmosphere through the surface, as well as the implanted oxygen, contribute to the formation of the buried oxide layers.
Growth of a single-wall carbon nanotube in the gap of scanning tunneling microscope
Authors: Yamashita J. , Hirayama H. , Ohshima Y. , Takayanagi K.
Published: July 2002

Single-wall carbon nanotubes (SWNTs) were grown in the tunneling gap of a scanning tunneling microscope (STM). We could observe their growth processes in situ by operating the STM in a transmission electron microscope. The STM tip and sample were covered by graphite layers. The tip was lightly touched to the sample and subsequently retracted. Occasionally, a carbon nanobridge was generated between the tip and the sample. The bridge had the shape of SWNT at the tip side.
Resonant-tunneling diodes with emitter prewells
Authors: Boykin Timothy B. , Bowen R. Chris , Klimeck Gerhard , Lear Kevin L.
Published: July 2002

Resonant-tunneling diodes (RTDs) incorporating an emitter prewell structure are studied both theoretically and experimentally in order to investigate the utility of the emitter region as a device design parameter. The experiments show a tendency for peak bias, current, and the peak-to-valley ratio to increase for wider prewells, behavior likewise seen in both very simple and detailed calculations. Both the simple and more complete models point to interactions between states associated with the prewell and the main quantum well as the reasons for the increase in peak current. These results suggest design guidelines to affect peak bias, current, or the peak-to-valley ratio of RTDs.
Effect of niobium doping on the microstructure and electrical properties of strontium titanate thin films for semiconductor memory application
Authors: Gopalan Sundararaman , Wong Chun-Hui , Balu Venkatasubramani , Lee Jian-Hung , Han Jeong H. , Mohammedali Razak , Lee Jack C.
Published: July 2002

Niobium doped strontium titanate [Sr(Ti1−xNbx)O3] thin films (≅40 nm) were deposited on Ir substrates using rf magnetron sputtering. The effect of Nb content (x=0, 0.001, 0.01, and 0.05) on the microstructure, dielectric constant, dielectric dispersion, and leakage current was studied. It was found that with increasing Nb content the dielectric constant decreased, probably owing to an observed decrease in grain size. The dielectric dispersion of all the Nb-doped ST films was lower than that of undoped ST film deposited at the same temperature and pressure. For the case of x=0.01, dispersion as low as 0.425% per decade was observed. The leakage current was found to increase slightly for x=0.001 and x=0.01, and drastically for the x=0.05 case.
Electron-induced crosslinking of aromatic self-assembled monolayers: Negative resists for nanolithography
Authors: Geyer W. , Stadler V. , Eck W. , Zharnikov M. , Gölzhäuser A. , Grunze M.
Published: July 2002

We have explored the interaction of self-assembled monolayers of 1,1′-biphenyl-4-thiol (BPT) with low energy electrons. X-ray photoelectron, infrared, and near edge x-ray absorption fine structure spectroscopy showed that BPT forms well-ordered monolayers with the phenyl rings tilted ∼15° from the surface normal. The films were exposed to 50 eV electrons and changes were monitored in situ. Even after high (∼10 mC/cm2) exposures, the molecules maintain their preferred orientation and remain bonded on the gold substrate. An increased etching resistance and changes in the infrared spectra imply a crosslinking between neighboring phenyl groups, which suggests that BPT can be utilized as an ultrathin negative resist. This is demonstrated by the generation of patterns in the underlying gold.
Energy spectrum of surface states of lattice-matched In0.52Al0.48As surface intrinsic-n+ structure
Authors: Hwang J. S. , Hwang W. C. , Yang Z. P. , Chang G. S. , Chyi J. I. , Yeh N. T.
Published: July 2002

This work uses photoreflectance to investigate the band gap, built-in electric field, and surface Fermi level of a series of lattice-matched In0.52Al0.48As surface intrinsic-n+ structures having different undoped layer thickness. Experimental results indicate that the surface Fermi level is weakly pinned. By converting the dependence of the built-in electric field on undoped layer thickness into the dependence of surface state density on the surface Fermi level, this study defines the energy spectrum of the surface state density of InAlAs surface using a Gaussian distribution function.
A visible–near infrared range photonic crystal made up of Si nanopillars
Authors: Poborchii Vladimir V. , Tada Tetsuya , Kanayama Toshihiko
Published: July 2002

We studied a two-dimensional square lattice of Si nanopillars (SQLN) perspective for applications in waveguides. Reflection spectra of SQLN with the period of 270 nm were studied for different surrounding media, namely air and water. SQLN is shown to display photonic band gap (PBG) behavior in the visible–infrared spectral range. The energy positions and widths of the experimentally observed reflection bands are found to be in agreement with calculated PBG.
Enhancement of electromechanical coupling coefficient by proton exchange in Z-cut LiNbO3
Authors: Čiplys D. , Rimeika R. , Korkishko Yu. N. , Fedorov V. A.
Published: July 2002

The electromechanical coupling coefficient K for surface acoustic waves (SAWs) in proton-exchanged Z-cut X-propagation lithium niobate has been experimentally investigated by the method of evaporating a thin metal film and measuring in situ the SAW attenuation. The enhancement in K2 value by as much as two times caused by the proton exchange has been observed. It is attributed to the redistribution of electric potential of the acoustic wave due to formation of a HxLi1−xNbO3 layer at the surface. The change of electromechanical coupling coefficient in samples fabricated under different conditions depends on the acoustic wavelength–layer thickness product kd. The K2 value attains a maximum of about 0.8×10−2 at kd≈0.4, whereas it is equal to 0.46×10−2 in nonexchanged lithium niobate. The increase in electromechanical coupling coefficient can be applied for enhancement of the SAW interdigital transducer efficiency.
Transient-enhanced diffusion of boron implanted at ultralow energies in silicon: Localization of the source
Authors: Schroer E. , Privitera V. , Priolo F. , Napolitani E. , Carnera A.
Published: July 2002

We have investigated the location of the defects causing the transient-enhanced diffusion (TED) of boron implanted at very low energies in Si. The localization was done by removing the surface layer of the silicon implanted with boron (1 and 0.5 keV, 1×1014/cm−2) by repeated native-oxide growth and removal. Subsequent annealing revealed the diffusion behavior. The fast and ultrafast processes of TED that where discriminated in an earlier work by Napolitani et al. [Appl. Phys. Lett. 75, 1869 (1999)] are found to be generated by defects located at different depths. The defects responsible for the fast tail shift are found to be located closer to the surface than the defects leading to the ultrafast tail shift. The nature of the two defect classes is discussed.
On the SU(2) Kepler problem
Authors: Lévay Péter
Published: July 2002

Using the idea that the symmetry generators commuting with a Landau-like Hamiltonian containing non-Abelian gauge fields will be matrix-valued differential operators, we reconsider the eigenvalue problem of the five-dimensional (5-D) Kepler problem on a SU(2) instanton background. We quickly reproduce the result of Pletyukhov and Tolkachev [J. Math. Phys. 40, 93–100 (1999)], obtained for the energy spectrum. The eigenstates can be expressed in terms of the SU(2) monopole harmonics. The relevance of the theory of induced representations for solving similar problems is emphasized.
Fractional statistic
Authors: Bergère M. C.
Published: July 2002

We improve Haldane’s formula which gives the number of configurations for N particles on d states in a fractional statistic defined by the coupling g=l/m. Although nothing is changed in the thermodynamic limit, the new formula makes sense for finite N=pm+r with the p integer and 0<r⩽m. A geometrical interpretation of fractional statistic is given in terms of “composite particles.”
Diffusion properties of Al in ZnTe substrates
Authors: Hanafusa M. , Sato K. , Noda A. , Arakawa A. , Matsuda Y. , Oda O.
Published: July 2002

In order to fabricate intrinsic pn junctions in p-type ZnTe substrates for realizing pure-green light-emitting diodes, Al was used as the diffusion species. We found that the Al diffusion region is observed as a dark region image by scanning electron microscopy. Al was diffused over a wide range of annealing temperatures and times. It was found that the activation energies of Al diffusion into p-type ZnTe substrates were 1.9±0.1 eV and the diffusion coefficient was given by D=20 exp(−1.9/kT) cm2/s.
Properties of anisotropic piezoactive polycrystals
Authors: Aleshin Valeri
Published: July 2002

The equations are presented that relate electric and elastic fields inside and outside a spherical inclusion located in the anisotropic piezoactive medium. A case of the medium with the axial symmetry of properties has been considered in greater detail. A technique has been described for calculating effective constants of an anisotropic piezoactive polycrystal from the constants of the crystallites that compose it. A comparison is made with a similar procedure in which the anisotropy of properties is neglected.
Improved Ni based composite Ohmic contact to n-SiC for high temperature and high power device applications
Authors: Cole M. W. , Joshi P. C. , Hubbard C. W. , Wood M. C. , Ervin M. H. , Geil B. , Ren F.
Published: July 2002

Ni/WSi/Ti/Pt Ohmic contacts to n-SiC were investigated as a function of annealing temperatures up to 1000 °C. Annealing at temperatures between 950 and 1000 °C yielded excellent Ohmic behavior. At these temperatures the contact–SiC interface was smooth, defect free, and characterized by a narrow Ni2Si reaction region. The annealed contacts possessed atomically smooth surface morphologies and exhibited minimal contact expansion. The residual carbon, resultant from SiC decompositon and reaction with Ni to form Ni2Si, was constrained by reaction with the WSi and Ti layers forming carbide phases of W and Ti spatially distant from the metal semiconductor interface. Our results demonstrate that the Ni/WSi/Ti/Pt composite Ohmic contact maintains the desirable electrical properties associated with Ni contacts and possesses excellent interfacial, compositional, and surface properties which are required for reliable high power and high temperature device operation.
Satake diagrams and Iwasawa decomposition of twisted Kac–Moody algebras
Authors: Pati K. C. , Das B.
Published: July 2002

The involutive automorphism of twisted Kac–Moody algebras of A2(2) and D4(3) are computed from the Satake diagrams of these algebras, which are then used to furnish a general procedure of their Iwasawa decomposition.
Superspace formulation of general massive gauge theories and geometric interpretation of mass-dependent Becchi–Rouet–Stora–Tyutin symmetries
Authors: Geyer B. , Mülsch D.
Published: July 2002

A superspace formulation is proposed for the osp(1,2)-covariant Lagrangian quantization of general massive gauge theories. The superalgebra osp(1,2) is considered as subalgebra of the superalgebra sl(1,2)∼osp(2,2) which may be considered as the algebra of generators of the conformal group in a superspace with two anticommuting coordinates. The mass-dependent (anti)Becchi–Rouet–Stora–Tyutin symmetries of proper solutions of the quantum master equations in the osp(1,2)-covariant formalism are realized in that superspace as invariance under translations combined with mass-dependent special conformal transformations. The Sp(2) symmetry—in particular the ghost number conservation—and the new ghost number conservation are realized in the superspace as invariance under symplectic rotations and dilatations, respectively. The new ghost number conservation is generally broken by the choice of a gauge. The transformations of the gauge fields and the full set of necessarily required (anti)ghost and auxiliary fields under the superalgebra sl(1,2) are determined both for irreducible and first-stage reducible theories with closed gauge algebra.
Quantum paraelectric La1/2Na1/2TiO3 films as capacitor dielectrics for temperature- and electric-field-insensitive applications
Authors: Rao R. M. V. , Munekata H. , Shimada K. , Lippmaa M. , Kawasaki M. , Inaguma Y. , Itoh M. , Koinuma H.
Published: July 2002

Thin films of La1/2Na1/2TiO3 fabricated by pulsed laser deposition show interesting dielectric properties exhibiting quantum paraelectric-type temperature-insensitive dielectric constant below 50 K. The dielectric constant (εr∼180) is also very stable under electric bias up to 4×104 V/cm. These properties indicate that these films coupled with high temperature superconductors have a great potential for microwave applications.
Approximate near-field blast theory: A generalized approach
Authors: Hutchens Gregory J.
Published: July 2002

A method for analyzing strong shock waves in arbitrary one-dimensional geometry is presented. An approximation to classical Taylor–Sedov theory is extended to the near-field case where source mass is not negligible, accounting for differences in the chemical properties of the source mass and ambient medium. Example solution results are given.
Magnetic resonance investigations of defects in Ga14N and Ga15N
Authors: Bayerl M. W. , Reinacher N. M. , Angerer H. , Ambacher O. , Brandt M. S. , Stutzmann M.
Published: July 2002

The influence of the nitrogen nuclear spin on the optically detected magnetic resonance and electron spin resonance signatures of the intrinsic shallow donor and a deep defect causing the characteristic yellow luminescence have been studied on wurtzite GaN epitaxial layers grown by plasma induced molecular beam epitaxy with isotopically pure N14 and N15. In particular, the linewidth of the deep defect signal is observed to be independent of the nitrogen isotope. The missing effect of the different nuclear spin properties of the N14 and N15 isotopes is discussed in view of current microscopic models for the yellow luminescence in GaN.
Comparison of dc and microwave resistivity in polycrystalline La0.7−xYxCa0.3MnO3 samples: Influence of Y at grain boundaries
Authors: Yates K. A. , Cohen L. F. , Watine C. , Tay T-N. , Damay F. , MacManus-Driscoll J. , Freitas R. S. , Ghivelder L. , Haines E. M. , Gehring G. A.
Published: July 2002

A series of polycrystalline La0.7−xYxCa0.3MnO3 samples were studied, where x=0, 0.07, 0.1, 0.15, and 0.2. Measurement of the dc resistivity, microwave surface resistance, ac susceptibility, and dc magnetization were made. As expected, the magnetic state becomes more frustrated as Y is added. It is found that the dc resistivity is approximately two orders of magnitude larger than the 9 GHz resistivity for all samples, however, both increase with Y doping by the same multiplicative factor. From circumstantial evidence and estimation of the grain boundary response time, it is found that the microwave measurement short circuits the grain boundaries. We assume that the dc resistivity is dominated by grain boundary properties and the microwave resistivity reflects intragranular behavior. Analysis of the electrical transport at dc and microwave frequencies is carried out and a phenomenological model proposed which agrees well with observation. The model implies that the influence of Y is modified by the underlying static disorder in which it is placed.
Analysis of the Hall effect device using an anisotropic material
Authors: Shibata Hisashi , Oide Jun-ichi
Published: July 2002

The analysis of the rectangular Hall effect device consists of an anisotropic material, two input-current electrodes, and two output-voltage electrodes is shown. The Hall voltages are numerically analyzed by using an affine transformation and a conformal representation. The voltages are shown in the graphical form. In addition, an approximate formula for Hall voltage is presented with the useful range for the ratio of the sides of the rectangular sample. The measuring method of the Hall constant of anisotropic materials is also shown. The result in this article includes that of a well-known Hall voltage for an isotropic material.
Characteristics of the low energy photoluminescence in μc-Si films
Authors: Yue Guozhen , Han Daxing , McNeil L. E. , Wang Qi
Published: July 2002

The temperature and excitation-intensity dependence of the ∼0.9 eV photoluminescence (PL) band has been studied in several microcrystalline silicon (μc-Si) films with varied crystallinity. When the measurement temperature is increased from 15 to 180 K, the PL peak energy redshifts from 1.0 to 0.83 eV. The PL quenching of the intensity follows a model of carrier thermalization in an exponential band tail with a width of ∼20 meV. The total PL intensity (IPL) as a function of excitation intensity (Iex) obeys a power law of IPL∝Iexγ, where γ≈0.65 or 1 for high or low excitation intensity, respectively. The experimental results suggest that the ∼0.9 eV PL band originates from radiative tail-to-tail transitions in the grain-boundary region in μc-Si.
Temporal and spatial distribution of minority carriers in semiconductors generated by modulated inhomogeneous illumination
Authors: Kabrede H. , Würfel P.
Published: July 2002

The distribution of minority carriers is derived which results from inhomogeneous illumination modulated at arbitrary frequency in a semiconductor sample with surfaces characterized by their surface recombination velocity. Results for a point source are discussed in detail. They are compared with experimental results from photoluminescence and light beam induced currents in solar cells. The method to determine the diffusion length in solar cells from the dependence of the short circuit current on the penetration depth of the light is discussed for arbitrary frequencies and inhomogeneous illumination in the vicinity of grain boundaries in polycrystalline materials. An unexpected phenomenon is found experimentally and is explained theoretically which demonstrates the complex nature of the carrier concentration by an interference effect of carriers with different phases. When a light beam, modulated at high frequencies, is scanned over the surface towards a grain boundary or an edge of the sample the amplitude of excess carriers is observed to increase although the recombination probability is increasing too.
A robust signal processing algorithm for linear displacement measuring optical transmission sensors
Authors: Kim Kyung-Chan , Kim Jong Ahn , Kim Soohyun , Kwak Yoon Keun
Published: July 2002

Optical triangulation sensors fall into a general category of noncontact height or displacement measurement devices and are widely used for their simple structure, high resolution, and long operating range. However, there are several factors that must be taken into account in order to obtain high accuracy and reliability: Measurement errors from inclinations of an object surface, probe signal fluctuations generated by speckle effects, power variation of a light source, electronic noises, and so on. In this article, we propose a signal processing algorithm, named expanded average square difference function (EASDF), for a newly designed optical triangulation sensor which is composed of an incoherent source, a line scan array detector, a specially selected diffuse reflecting surface, and several optical components. The EASDF, which is a modified correlation function, can calculate displacement between the probe and the object surface effectively even if there are inclinations, power fluctuations, and noises. This optical triangulation sensor system with the EASDF shows an 8 mm linear operation range and 1 μm resolution without averaging and the maximum measurement error is 2.4 μm for ±10° inclinations.
Design of a scanning atom probe with improved mass resolution
Authors: Cerezo A. , Godfrey T. J. , Huang M. , Smith G. D. W.
Published: July 2002

A design for a high mass resolution scanning atom probe is described, which utilizes a two-conductor microelectrode held at 10–100 μm from the specimen. Field evaporation pulses are applied to the part of the counter-electrode closest to the specimen, while the output is maintained at ground. If the gap between the two conductors is small, field evaporated ions pass through the microelectrode while the pulse voltage is essentially constant, and thus the resultant spread in ion energies is small and the mass resolution in time-of-flight mass spectrometry is correspondingly improved. Initial results indicate improvements of 4–5 times over the mass resolution obtained with a simple counter electrode.
Electric field dependence of the screening currents in the mixed state of high temperature superconductors investigated by an ac technique
Authors: Eisterer M. , Weber H. W.
Published: July 2002

The influence of the electric field on the shielding currents of melt textured YBa2Cu3O7−δ superconductors was investigated by low frequency ac magnetization measurements. The electric field was varied by changing the amplitude as well as the frequency of the applied ac field. These two dependencies were found to be consistent with each other and allowed to develop a method for the derivation of the E(J) characteristic of the superconductor from these measurements. E(J) was found to follow approximately a power law with an exponent, which decreases monotonically with increasing magnetic dc field. The results are compared with dc magnetization measurements, where the corresponding electric field is lower by up to four orders of magnitude. We find convincing agreement between the dc shielding currents and their relaxation and the current–voltage characteristic derived from the ac technique.
Laser control of molecular photodissociation with use of the complete reflection phenomenon
Authors: Nagaya Kuninobu , Teranishi Yoshiaki , Nakamura Hiroki
Published: July 2002

A new idea of controlling molecular photodissociation branching by a stationary laser field is proposed by utilizing the unusual intriguing quantum-mechanical phenomenon of complete reflection. By introducing the Floquet (or dressed) state formalism, we can artificially create potential curve crossings, which can be used to control molecular processes. Our control scheme presented here is summarized as follows. First, we prepare an appropriate vibrationally excited state in the ground electronic state, and at the same time by applying a stationary laser field of the frequency ω we create two nonadiabatic tunneling (NT) type curve crossings between the ground electronic bound state shifted up by one photon energy ℏω and the excited electronic state with two dissociative channels. In the NT-type of curve crossing where the two diabatic potential curves cross with opposite signs of slopes, it is known that the complete reflection phenomenon occurs at certain discrete energies. By adjusting the laser frequency to satisfy the complete reflection condition at the NT type curve crossing in one channel, the complete dissociation into the other channel can be realized. By taking one- and two-dimensional models which mimic the HOD molecule and using a wave packet propagation method, it is numerically demonstrated that a molecule can be dissociated into any desired channel selectively. Selective dissociation can be realized even into such a channel that cannot be achieved in the ordinary photodissociation because of a potential barrier in the excited electronic state.