bluuebunny/crossref_metadata_2025 huggingface dataset:
Micron-sized Hall probes on a Si/SiGe heterostructure as a tool to study vortex dynamics in high-temperature superconducting crystals
Authors: van Veen R. G. , Verbruggen A. H. , van der Drift E. , Radelaar S. , Anders S. , Jaeger H. M.
Published: July 2002

We describe the fabrication of micron-sized Hall probes from a Si/SiGe heterostructure. The magnetic field response of the Hall probes shows a very high sensitivity of ∼60 Ω/kG. Below a temperature of 80 K, the Hall probes exhibit a highly linear field dependence of the Hall resistance. The onset of the quantum Hall effect at very low temperatures and high magnetic fields causes only small deviations from the linear field response. We demonstrate the performance of the device as a sensitive local magnetization probe in high-temperature superconducting crystals of Bi2Sr2CaCu2O8. With a linear array of Hall probes we track both the spatial and temporal evolution of the magnetization profile across the crystal. In this way surface and bulk contributions to the overall magnetization can be delineated.
A metal plasma source ion implantation and deposition system
Authors: Liu Bin , Li B. , Sun M. , Jiang B. Y. , Ren Y. F. , Yang Si-Ze
Published: July 2002

This article presents a metal plasma source ion implantation and deposition system, which is a qualitative extension of plasma source ion implantation by combining pulsed metal plasma and steady-state gas plasma. The pulsed metal plasma is produced by pulsed cathodic arc discharge and the steady-state gas plasma by magnetic multipole filament discharge. The existence of gas plasma greatly facilitates the breakdown of the pulsed cathodic arc plasma source, which does not need the conventional trigger system. Some operation characteristics of this system were measured. It was shown that the cathodic arc plasma parameters depend strongly on gas pressure. 0.45% C steel was modified in nitrogen plasma and pulsed aluminum plasma. The corrosion resistance ability of the treated 0.45% C steel sample was increased by about 30 times over that of the untreated sample. AlN/Al2O3/Al composite film was deposited on 0.45% C steel using a glow-arc technique.
A 6 kV–150 A, 8 ns rise time pulse generator for excitation of ferroelectric cathodes
Authors: Boscolo I. , La Torre S.
Published: July 2002

A pulse generator with the following characteristics is presented: the voltage ranges in the interval 0.1–6 kV, the maximum delivered current is 150 A, the pulse length ranges within the interval 100–300 ns, the rise time and the decay times are, respectively, 10 and 25 ns on 50 Ω resistive load and the repetition rate is higher than 1 MHz. The circuit has a source capacitor of 10 nF charged at the needed voltage, the capacitor feeds the load through a parallel of two fast and high voltage solid state switches. The nanosecond rise time and the square fashion of the pulse have been accomplished arranging all the components in cylindrical symmetry. A bipolar pulse is obtained coupling two circuits with opposite polarity.
Two-dimensional toroidal electron analyzer for energy and angular dispersive measurements
Authors: Danjo A. , Kato Y. , Kobayashi N. , Matsumoto J. , Shimizu H. , Tanuma H. , Wang Z. , Wu W. , Yamazaki K. , Yoshino M.
Published: July 2002

A toroidal electrostatic analyzer with a two-dimensional position-sensitive electron detector has been developed for the measurement of differential excitation cross sections in electron-ion collisions. The electron position is resolved simultaneously in the energy and angular dispersive directions of the analyzer. The present electron analyzer is specially designed with a narrow curved entrance slit and a wide exit slit coupled with an exit lens system after the toroidal deflector, which can give a wide energy dispersed range of 20% of the mean pass energy and a large angular range extending from 30° to 120°. The performance of the spectrometer has been studied by measuring the scattered electrons from Ar atoms and from a highly oriented pyrolytic graphite surface, indicating the usefulness of the present analyzer in electron spectroscopy. A brief description of the method for a spectrum transformation from Cartesian coordinates to polar coordinates is also presented.
Noise averaging and measurement resolution (or “A little noise is a good thing”)
Authors: Potzick James
Published: July 2002

When a continuous quantity is measured with a digital instrument or digitized for further processing, a measurement uncertainty component is incurred from quantization of the continuous variable. This uncertainty can be reduced by oversampling and averaging multiple measurements, but only if there is some noise on the measurand. In this article the optimum noise level is determined, and the subsequent improvement in measurement uncertainty calculated.
Production of microwave plasma in narrow cross sectional tubes: Effect of the shape of cross section
Authors: Bhattacharjee Sudeep , Amemiya Hiroshi
Published: July 2002

A microwave plasma is produced in a conducting tube with a cross section smaller than the cutoff value. Waves of 2.45 GHz are launched perpendicularly to the multicusp magnetic field formed by permanent magnets surrounding the tube. Circular and square cross sectional tubes are tested. Overdense plasmas with a density of (0.8–2.0)×1011 cm−3 are obtained in the range of 10−4 Torr for powers of 200–360 W. The electron temperature is 6–12 eV. Under the same experimental conditions, the plasma density and the electron temperature are higher for the circular cross section.
A variable cryogenic temperature near-field scanning optical microscope
Authors: Gray Matthew H. , Hsu J. W. P.
Published: July 2002

We describe a novel variable (cryogenic) temperature near-field scanning optical microscope (VT-NSOM) designed specifically for submicron imaging of materials and devices over a temperature range of 12–300 K. In high vacuum, we cool only the sample stage of the compact NSOM, thereby maintaining a large scan area (35 μm×35 μm) at low temperatures and enabling rapid (∼30 min) temperature changes. With incorporation into an external conventional optical microscope, the VT-NSOM is capable of imaging a single submicron feature over the entire temperature range. We demonstrate the performance of the instrument by examining the photoresponse of threading dislocation defects in relaxed GeSi films.
A novel capacitive wave form transformer
Authors: Paul B. C. , Satyam M. , Selvarajan A.
Published: July 2002

This article describes a new method of wave form transformation through the use of a nonlinear capacitor. Two specific examples, the transformation of a sinusoidal wave form to a triangular wave form and vice versa are discussed in detail. A method of obtaining this nonlinear capacitor, by having a suitable doping profile in a metal–oxide–semiconductor capacitor is also described.
Fast low-cost phase detection setup for tapping-mode atomic force microscopy
Authors: Stark M. , Guckenberger R.
Published: July 2002

A fast low-cost device to detect the phase shift between the excitation and the response of a cantilever in tapping-mode atomic force microscopy is described. For cantilever signals with a good signal to noise ratio, as is commonly found, the device presented can replace a lock-in amplifier. The setup is based on indirect time measurements realized by a combination of commonly used analog and digital integrated circuits. Phase measurement can already be achieved within one cycle. Signal output rates up to 100 kHz allow the use of the phase shift as an auxiliary imaging channel. Cantilever frequencies may range from 6 to more than 500 kHz. The principle of the setup is illustrated together with technical data. Images of a hydrophobic–hydrophilic structured silicon surface obtained in air and of purple membrane obtained in fluid are presented.
True near-field optical characters of a GaAlAs semiconductor laser diode
Authors: Chen Sy-Hann , Tsai Din Ping , Chen Yung-Fu , Ong Pang-Ming
Published: July 2002

In this research we have taken advantage of near-field scanning optical microscopy, a recently developed technique, to test the optical nature of GaAlAs semiconductor laser diodes working at 780 nm. With this method, both the images of the topographic and the near-field intensity of the laser diodes can be simultaneously obtained. With the obtained results, we can analyze the variety of the geometric structure, the local near-field optical intensity, the propagating modes, and the near-field mode-field diameter at different working states of the laser diodes. Hereby, we can find the factors that affected the radiation cavity of the laser diode and explore its alive state.
Spectrophotometers intercomparison for spectrocolorimetric scale harmonization
Authors: Soares Olivério D. D. , Costa José L. C.
Published: July 2002

An in situ comparison of spectrophotometer scales of wavelength, spectral bandwidth, and regular spectral transmittance was made in 1997/98 towards the harmonization of spectrocolorimetric scales for the measurements in transmittance mode. It used a set of three neutral density glass filter standards and a crystal with sharp absorption bands as wavelength and spectral bandwidth standard. Measurements by 22 laboratories with a great diversity of instrumentation constituted a good testing reference data to examine the aspects in scale harmonization. The intercomparison reflects a widespread misunderstanding about levels of accuracy achieved and a generalized lack of use of service standard coverage in checking uncertainty levels along the range of the concerned metrological scales. The spectral bandwidth scale is usually not taken in appropriated attention. It is demonstrated that relative small discrepancies in the spectral bandwidth setting lead to large uncertainties in the measurements that may overexceed computed uncertainty values derived from wavelength and spectral transmittance scale uncertainties.
Simultaneous energy distribution and ion fraction measurements using a linear time-of-flight analyzer with a floatable drift tube
Authors: Morozov V. A. , Meyer F. W.
Published: July 2002

A technique for simultaneous energy distribution and ion fraction measurements using a linear time-of-flight analyzer with a floatable drift tube is described. Analytical expressions for the relative collection efficiency and viewing region of the apparatus are developed as functions of the analyzed particle reduced energy and dimensionless apparatus parameters. The method was applied to studies of large-angle scattering of singly charged oxygen ions incident on Au(110), and carried out at the Oak Ridge National Laboratory’s Multicharged Ion Research Facility. Energy distributions of the scattered projectiles and the negative ion fraction are presented as a function of scattered projectile energy. As a by-product of the measurements, the relative ion detection efficiency of the particle detector was reconstructed as a function of ion impact energy on the detector.
Single-ion detection using nuclear track detector CR-39 plastic
Authors: Hara Ken-ichi , Koh Meishoku , Matsukawa Takashi , Tanii Takashi , Ohdomari Iwao
Published: July 2002

We have developed a technique for detecting single-ions that uses CR-39 plastic. Chemical etching of the plastic enables us to visualize both the incident sites and the existence of the single-ion incidences as etch pits. Using this technique, we obtained a singularity rate of 88.3%.
The use of a special work station for in situ measurements of highly reactive electrochemical systems by atomic force and scanning tunneling microscopes
Authors: Cohen Yair , Aurbach Doron
Published: July 2002

In this article, we describe a special homemade workstation in which highly reactive electrochemical systems, such as lithium electrodes in polar aprotic systems, can be measured in situ by both atomic force microscopy and scanning tunneling microscopy (STM). The workstation includes an evacuable glovebox that maintains a pure atmosphere in which the microscopes are located, thus enabling measurements in a highly pure argon atmosphere. The system is based on a compact and functional evacuable glovebox which is placed in a special construction which provides full protection against vibrations. This is obtained by suspending the box by flexible cords during the experiments, while all the piping connections are removed. The concept of an evacuable glovebox, which can be back-filled by a pure atmosphere, enables measurements to be performed under a pure inert atmosphere, eliminating the need for noisy gas purification systems. Pure solutions and highly reactive electrode materials are introduced into this glovebox by the use of a transfer method, based on a hermetically sealed transfer vessel and a special vacuum chamber in the glovebox. Preliminary results demonstrated that high-quality imaging of reactive electrochemical systems can be obtained using this system. A procedure for the preparation of STM tips is also described.
Electron quantum wires in type II single heterostructures on nonplanar substrates
Authors: Türck V. , Stier O. , Heinrichsdorff F. , Grundmann M. , Bimberg D.
Published: July 2002

The existence of electronic quantum wires in the center of homogeneously doped single type II heterojunctions in V grooves is predicted. No additional structural confinement is needed. The valence and conduction band edges in such structures are calculated by solving the 2D-Poisson and 2D-Schrödinger equations self-consistently. As a prototype system we consider a realistic n-InP/n-InAlAs heterostructure in a V groove along [011̄] with a finite curvature. The band bending is found to depend on the position along the heterojunction, inducing two-dimensionally confined bound states for electrons which can serve as 1D conducting channels. Using proper doping conditions a ground state below the Fermi energy can be achieved. The subband separation is strongly dependent on the radius of curvature of the groove center and amounts to about 15 meV.
Waveguide version of an asymmetric Fabry–Perot modulator
Authors: Pezeshki B. , Kash J. A. , Agahi F.
Published: July 2002

We show that the high contrast property of vertical cavity asymmetric Fabry–Perot modulators can also be obtained in a waveguide geometry. Increasing the absorption in one arm of a waveguide directional coupler causes the transmission through the other arm to decrease, go to zero, and then increase again. Thus, by adjusting the coupling length and the absorption, an infinite contrast ratio can theoretically be obtained with a low insertion loss. The waveguide geometry is not only more convenient than normal incidence for fiber-based devices, but also provides a larger optical bandwidth. We present the design equations and provide a first order model of device operation.
Low-noise electrometer and its low-noise cryogenic probe with completely guarded sample chamber
Authors: Yao Jie , Yoon Jongsoo
Published: July 2002

We describe a low-noise cryogenic probing system capable of measuring currents at the femtoAmpere (fA) level with integration time ⩽1 s and current noise spectra at the 1 fA/√Hz level with the sample cooled to cryogenic temperatures. The system consists of a low-noise electrometer and a low-noise cryogenic probe with completely guarded sample chamber. The low-noise electrometer has amplification of 0.1 V/1 pA with f3 dB=70 Hz, 1.1 V/pA with f3 dB=20 Hz, and/or 10.1 V/pA with f3 dB=1.4 Hz, and input current noise power density of 0.4 fA/√Hz rms and input voltage noise power density of ≈0.3 μV/√Hz rms at 1 Hz frequency. With the cryogenic probe, the entire measurement system has input current noise of 0.8 fA/√Hz rms at 1 Hz. The completely guarded sample chamber reduces parasitic conductance to <10−16 S and parasitic capacitance to ⩽15 fF between pairs of pins for current–voltage measurements. With this instrumentation, we are able to characterize the current and current noise of quantum well infrared photodetectors for sensitive zero-background applications.
Pulsed technique for observing infrared emissions from ionic gas phase reactions at low reactant ion concentrations
Authors: Williams T. L. , Decker B. K. , Babcock L. M. , Adams N. G. , Harland P. W.
Published: July 2002

A technique has been developed to detect infrared emissions from the products of ionic reactions in plasmas. The technique employs dual-phase digital lock-in amplification and cold filtering to permit the detection of the weak infrared chemiluminescence (IRCL) with a solid-state detector. A novel method of cleanly modulating plasma chemiluminescence by the pulsed introduction of reagent gases has been developed and implemented. This new technique has been tested by studying the well-characterized H-atom reactions, H+Cl2→HCl(v=0–4)+Cl and H+NO2→OH(v=0–3)+NO. Rotational and vibrational distributions have been measured for these two reactions and are presented and compared with previous determinations. Additionally, the associative electron detachment reaction, H+Cl−→HCl(v=0–2)+e, has been studied, demonstrating that IRCL can be collected from reactions occurring at a low number density approaching that of the plasma ionization (∼4×1010 cm−3). The resolution, and hence, the information content of the collected emissions from this reaction have been greatly improved over previous work, with which our data are compared.
Double layers of single domains formed by rapid thermal annealing of proton-exchanged LiTaO3
Authors: Zhao Cangsang , Engelmann Reinhart
Published: July 2002

A double layer of single domains with opposing polarizations has been formed on both c faces by rapid thermal annealing of proton-exchanged z-cut LiTaO3 at above the Curie temperature. The formed top single-domain layers have inward-directed polarization and the single-domain layers underneath have outward-directed polarization. The domain structure development for an annealing range from 2 s to 10 min has been investigated. The results are discussed in relation to recently proposed models for the domain-inversion mechanisms in LiTaO3 and LiNbO3.
Sidegating effect improvement of GaAs metal–semiconductor field effect transistor by multiquantum barrier structure
Authors: Lee Ching-Ting , Tsai Chang-Da , Wang Chi-Yu , Shiao Hung-Pin , Nee Tzer-En , Shen Jia-Nan
Published: July 2002

The sidegating effect in a GaAs metal–semiconductor field effect transistor is significantly suppressed by the use of a multiquantum barrier (MQB) structure as a buffer layer. The enhancement of potential barrier height of the MQB buffer layer is confirmed from the comparison with a heterostructure buffer layer device.
Thin-film transistors with multistep deposited amorphous silicon layers
Authors: Kuo Yue
Published: July 2002

Inverted, staggered thin-film transistors (TFTs), in which the a-Si:H layer is deposited stepwise, using different rf powers, were prepared and studied. Using identically prepared top and bottom interface silicon layers, the multilayer a-Si:H TFT characteristics can be better or worse than those of a single-layer a-SiH TFT, depending on the rf power used to deposit the middle layer and the total number of layers added. The result can be explained by considering the mechanism of the SiH4 plasma deposition process. For example, the extra hydrogen generated in the high power plasma can passivate dangling bonds, which enhances the transistor performance. The high intensity plasma radiation source can generate defects at the film/film interface as well as in the bulk of the film, which deteriorates the transistor.
Hysteresis effect in microwave power transmission of high temperature superconducting coplanar transmission lines
Authors: Gao F. , Zhou Z. , Feng M. , Scharen M. , Cardona A. , Forse R.
Published: July 2002

We have observed an unusual hysteresis loop in rf power dependence of high-temperature superconductor (HTS) coplanar transmission lines. At 77 K and 1 GHz, the signal transmission was linear (insertion loss <0.1 dB) until the input power (Pin) reached a critical value of Pc=0.4 W. An abrupt drop by ∼37 dB in the transmitted power (Pout) was observed at Pin=Pc followed by a slow increase (Pout∝Pin0.62) for Pin≳ Pc. As Pm was then decreased, it retraced the previous curve only until Pin=Pc. However, as Pin was reduced further Pout did not rise until Pin=158 mW, at which Pout started to increase rapidly and returned to the linear regime for Pin<71 mW. Such a sharp transition and a strong hysteresis effect were unique to the HTS line whereas a gold line with an identical structure did not exhibit these characteristics. This behavior may be utilized for potential applications of new HTS microwave power (current) limiters and switches. Several possible origins for the hysteresis effect are proposed and discussed.
Space-charge-limited injection in n+-i-n+ structures fabricated by a focused ion beam
Authors: Hwang S. W. , Lezec H. J. , Sakamoto T. , Nakamura N. , Pak J. H.
Published: July 2002

Transport characteristics of n+-i-n+ structures fabricated on a GaAs/AlGaAs HEMT wafer are presented. An insulating strip (i) between two-dimensional electron gases (n+) is created by a single line scan of a focused ion beam. At sufficiently large biases, the current–voltage (I–V) characteristics of the n+-i-n+ structures display highly linear increases of the currents as a function of the biases. The observed I–V’s are quantitatively explained by the space-charge-limited injection into the insulating region when the bias is large enough for the flatband condition. The charged defect density and the length of the insulating region are obtained from the I–V characteristics.
Single-gate multichannel amorphous silicon thin-film transistors
Authors: Kuo Yue
Published: July 2002

A redundant thin-film transistor (TFT), which has multiple sub-TFTs sharing one gate, is presented and studied. This transistor can be fabricated with two photomasks. It has transfer characteristics similar to those of a conventional single-channel TFT, except for (1) the negative-direction shift of the curve in the low drain current range, (2) the two-stage turn-on mechanism in the high drain current range, and (3) the high photoleakage current at the high drain voltage. The first phenomenon is due to the inclusion of electron accumulation interfaces in the semiconductor layer. The second phenomenon is caused by the sequential turn-on of various sub-TFTs at various gate voltages. The last phenomenon can be explained by the photoresistor characteristics of the top a-Si:H layer.
Photoconductivity of Si/Ge structures
Authors: Arndt M. , Koschinski W. , Dettmer K. , Kessler F. R. , Kriks H. J.
Published: July 2002

Photoconductivity (PC) spectroscopy is used to determine the optical absorption and behavior of free carriers of Si/Ge structures and (Si6Ge4)100 superlattices grown on Si0.4Ge0.6 alloys. Negative photoconductivity is observed at a temperature of 67 K. Some samples are additionally doped by nuclear transmutation. These samples exhibit a strong negative PC signal even at room temperature, which cannot be suppressed by a bias illumination.
Raman scattering from vibrational modes in metalorganic molecular beam epitaxy grown carbon doped InP: spectroscopic search for the carbon donor
Authors: Ramsteiner M. , Kleinert P. , Ploog K. H. , Oh J. , Konagai M. , Takahashi Y.
Published: July 2002

Vibrational modes of carbon doped InP have been investigated by Raman scattering and cluster-Bethe-lattice calculations. In contrast to other carbon doped III–V semiconductors, the InP samples grown by metalorganic molecular beam epitaxy (MOMBE) show n-type conductivity. Raman spectra from such samples reveal a vibrational mode at 220 cm−1. The frequency of this mode lies in the gap between the acoustic and optical branches of the phonon dispersion (gap mode). Cluster-Bethe-lattice calculations predict such a gap mode only for the carbon donor on the In site and not for the carbon acceptor on the P site.
Plasma assisted conversion of carbon fibers to diamond
Authors: Ismat Shah S. , Walls D. J. , Waite Matthew M. , Guerin D.
Published: July 2002

Pitch based carbon fibers have been converted to diamond through exposure to a pure hydrogen microwave plasma. The conversion depends strongly on the process pressure. At low pressure only part of the surface of the fiber was converted to diamond, however under optimum conditions a thick continuous diamond layer could be obtained. The carbon conversion efficiency to form diamond at the high pressure was at least an order of magnitude higher than is obtained in a regular CH4+H2 plasma assisted diamond deposition.
Metallization to asymmetric cladding separate confinement heterostructure lasers
Authors: Smith G. M. , Forbes D. V. , Lammert R. M. , Coleman J. J.
Published: July 2002

Annealed and nonannealed p-contact metallization for asymmetric cladding separate confinement heterostructure lasers with a thin p-cladding layer is reported. Ti–Au and annealed Ti–Pt–Au p-type contacts are demonstrated to improve the adhesion over a pure gold contact and allow annealing of the metallization to thin p-cladding laser structures at the expense of an increase in the optical loss. The increased optical loss is due to the decreased conductivity of titanium and platinum as compared to gold. As little as 10 Å of titanium is adequate for an adhesion layer and only increases the optical loss by 1.6 cm −1 over a pure gold metallization which has an optical loss of 10.0 cm−1. A metallization of 15 Å Ti−15 Å Pt−1500 Å Au is adequate for an anneal at 410 °C for 10 s and increases the optical loss by 7.0 cm −1.
Importance of channeled implantation to the synthesis of erbium silicide layers
Authors: Wu M. F. , Vantomme A. , Pattyn H. , Langouche G.
Published: July 2002

166Er atoms were implanted with an energy of 70 to 90 keV and doses of 0.8 to 2.0×1017/cm2 into Si(111) substrates at temperatures ranging from 450 to 530 °C. We found that using conventional nonchanneled implantation at energies of ∼90 keV, it is impossible to form a continuous ErSi1.7 layer. At best, after annealing, a discontinuous ErSi1.7 layer with poor crystalline quality (χmin=40%) is obtained. On the contrary, using channeled implantation, a continuous epitaxial ErSi1.7 layer with very good crystalline quality can be formed; a lowest χmin value of 1.5% for a surface ErSi1.7 layer has been obtained. The origin of this different behavior is explained. Our results show that for synthesizing continuous ErSi1.7 layers with good quality using ion beam synthesis at energies around 90 keV, channeled implantation is indispensable.
2000 h stable operation in 0.87 μm light-emitting diode using stress-free InGaP/GaAs/Si
Authors: Egawa T. , Jimbo T. , Dong J. , Matsumoto K. , Umeno M.
Published: July 2002

We have grown Al-free reliable 877 nm In0.49Ga0.51P/GaAs light-emitting diodes (LEDs) on Si substrates by metalorganic chemical vapor deposition. The conventional Al-containing Al0.3Ga0.7As/GaAs LEDs on Si substrates exhibit rapid degradations because of the formation of dark-line defects (DLDs). On the contrary, the In0.49Ga0.51P layer on the GaAs/Si substrate exhibited a 300 K electron mobility of 950 cm2/V s with the carrier concentration of 3.8×1017 cm−3, no residual stress and a lower surface recombination velocity. The In0.49Ga0.51P/GaAs LED on Si shows the stable operation for more than 2000 h, which results from the suppression of the formation of DLDs.
Dislocation behavior in InGaAs step- and alternating step-graded structures: Design rules for buffer fabrication
Authors: Araújo D. , González D. , García R. , Sacedón A. , Calleja E.
Published: July 2002

A comparison between compositionally stepped and alternating step-graded structures used in the production of a relaxation buffer layer is carried out by means of transmission electron microscopy. The latter shows higher efficiency in relieving the strain. A simple balance force model permits us to understand the reason for a higher generation of threading dislocations observed in the alternating step-graded structures. The presented results can be applied as new design rules for buffer fabrication that contrast in some key points with previous published rules as, for example, the ‘‘zero-net-strain’’ precept [D. Dunstan, P. Kidd, P. F. Fewster, N. L. Andrew, L. González, Y. González, A. Sacedón, and F. González-Sanz, Appl. Phys. Lett. 65, 845 (1994)].
Subthreshold slope in polycrystalline silicon thin-film transistors and effect of the gate oxide on the subthreshold characteristics
Authors: Dimitriadis C. A.
Published: July 2002

A simple expression for the inverse subthreshold slope in polycrystalline silicon thin-film transistors (TFTs) is derived as a function of the gate voltage and with parameters the trapping states at the grain boundaries, the grain size, and the gate oxide. Comparison with the experimental results verifies the validity of the derived expression. We show that in polysilicon TFTs, even with high trapping states density and small grain size, excellent subthreshold characteristics can be obtained by scaling down the SiO2 thickness to 10 nm. Further improvement in the subthreshold characteristics can be achieved using as gate oxide a Si3N4/SiO2 bilayer of thickness 10 nm which has higher dielectric constant, exhibits good interface properties with polysilicon and serves as a diffusion barrier to avoid penetration effects of impurities through the oxide.
Laser-induced modification of transport properties of Y–Ba–Cu–O step-edge weak links
Authors: Adam R. , Kula W. , Sobolewski Roman , Murduck J. M. , Pettiette-Hall C.
Published: July 2002

We report on the laser-induced permanent changes of the critical current (Ic) and normal resistance (Rn) of YBa2Cu3O7−x (YBCO) step-edge Josephson junctions. The 2- to 20-μm-wide junctions were prepared from a 200-nm-thick YBCO film deposited by a pulsed KrF excimer laser onto 300-nm-high steps etched in the LaAlO3 substrate. The laser modification experiments were performed by illuminating the junctions at 50 K with a focused Ar-ion laser beam of various intensities. Depending on the illumination power density, either increase or decrease of the junction Ic has been observed. In particular, after illumination at the 0.6×105 W/cm2 power level, a 75% enhancement of Ic and increase of the IcRn product up to 25% were obtained without a measurable change in the junction critical temperature. The laser-induced modifications were very reproducible and remained unchanged even after a subsequent room-temperature/helium thermal cycling of the sample. Photoassisted, thermally activated oxygen redistribution in the YBCO grain boundary region is proposed to explain the observed behavior.
Improved atomic force microscopy imaging using carbon-coated probe tips
Authors: Doris Bruce B. , Hegde Rama I.
Published: July 2002

Atomic force microscopy (AFM) images using carbon-coated probe tips are presented for hydrogen-passivated Si and SiO2 surfaces. Tapping mode measurements on these surfaces demonstrate that the image quality and probe tip wear characteristics are dramatically improved for scans performed with the carbon coated tips. The reasons for the improved quality of AFM imaging and reduced tip damage are discussed.
Combined differential amplitude and phase interferometer with a single probe beam
Authors: Suddendorf M. B. , See C. W. , Somekh M. G.
Published: July 2002

A novel interferometer capable of measuring differential amplitude and phase with a single probe beam is presented. Differentiation in any direction can be performed in the detector plane which allows the system transfer function to be modified without altering the optical configuration. Differential amplitude and phase results are given for different detector arrangements and compared with theoretical predictions showing excellent agreement.
What determines the lateral bonding speed in silicon wafer bonding?
Authors: Gösele U. , Hopfe S. , Li S. , Mack S. , Martini T. , Reiche M. , Schmidt E. , Stenzel H. , Tong Q.-Y.
Published: July 2002

In silicon wafer bonding, the initial contact area spreads laterally with a typical speed on the order of 10 mm/s. We observed that this lateral bonding speed increases with decreasing ambient pressure, and is independent of the distance of the contact front to the rim of the wafers and independent of wafer thickness. From these results, we conclude that the lateral bonding speed is mainly determined by pressing the ambient gas out between the two wafers from a very localized area close to the propagating bonding front.
Two-stage nanostructural formation process in Fe–Nb–B soft magnetic alloys
Authors: Suzuki K. , Cadogan J. M. , Dunlop J. B. , Sahajwalla V.
Published: July 2002

The nanostructural formation kinetics in a soft magnetic Fe80Nb6B14 alloy have been investigated by means of differential scanning calorimetry, thermogravimetric analysis and transmission electron microscopy. Unlike nanocrystalline Fe–Zr–B soft magnetic alloys, where the nanocrystallite formation is governed mostly by a nucleation and growth mechanism, the nanostructural formation mechanism in the Fe–Nb–B alloy shows a change in the fraction transformed range 0.1–0.2. The first- and second-stage nanostructural formation processes have been described by the nucleation and growth and grain-growth models, respectively. This two-stage nature in the nanostructural formation kinetics can be attributed to a high population density of the primary bcc nuclei.
Control of quasi-bound states by electron Bragg mirrors in GaAs/Al0.3Ga0.7As quantum wells
Authors: Sung B. , Chui H. C. , Martinet E. L. , Harris J. S.
Published: July 2002

Electron Bragg mirrors grown on both sides of identical quantum wells were used for confining above-barrier states at different energies. By varying the thickness of the electron mirrors, a confined above-barrier state (a quasi-bound state) changed by over 110 meV in a 40 Å wide GaAs/Al0.3Ga0.7As quantum well. Formation of quasi-bound states due to the electron Bragg mirrors was theoretically investigated using the envelope function approximation and semi-infinite superlattice limit of the electron mirror layers. Theoretical calculations for absorption spectra involving quasi-bound states are compared with experimental results.
Initial growth mechanism of a/b-axis oriented YBa2Cu3O7−y film prepared by liquid phase epitaxy
Authors: Kitamura Tasuku , Hirabayashi Izumi , Tanaka Shoji , Sugawara Yoshihro , Ikuhara Yuichi
Published: July 2002

The a/b-axis oriented YBa2Cu3O7−y (YBCO) films were fabricated by liquid phase epitaxy (LPE) on NdGaO3 (110) single-crystalline substrates using a modified top-seeded solution growth method. The x-ray diffraction measurement, and transmission electron microscopic observation showed the epitaxial growth of YBCO film on the substrate. Scanning electron microscopic observation revealed the epitaxy of YBCO on the substrate and an initial growth mechanism of a/b-axis oriented YBCO film by LPE. The film growth consists of the following stages; (1) nucleation and island growth, (2) lateral growth of island, and (3) layer formation due to coalescence of island.
Complete p-type activation in vertical-gradient freeze GaAs co-implanted with gallium and carbon
Authors: Horng S. T. , Goorsky M. S.
Published: July 2002

High-resolution triple-axis x-ray diffractometry and Hall-effect measurements were used to characterize damage evolution and electrical activation in gallium arsenide co-implanted with gallium and carbon ions. Complete p-type activation of GaAs co-implanted with 5×1014 Ga cm−2 and 5×1014 C cm−2 was achieved after rapid thermal annealing at 1100 °C for 10 s. X-ray diffuse scattering was found to increase after rapid thermal annealing at 600–900 °C due to the aggregation of implantation-induced point defects. In this annealing range, there was ∼10%–72% activation. After annealing at higher annealing temperatures, the diffuse scattered intensity decreased drastically; samples that had been annealed at 1000 °C (80% activated) and 1100 °C (∼100% activated) exhibited reciprocal space maps that were indicative of high crystallinity. The hole mobility was about 60 cm2/V s for all samples annealed at 800 °C and above, indicating that the crystal perfection influences dopant activation more strongly than it influences mobility. Since the high-temperature annealing simultaneously increases dopant activation and reduces x-ray diffuse scattering, we conclude that point defect complexes which form at lower annealing temperatures are responsible for both the diffuse scatter and the reduced activation.
Size and volume distributions of thermally induced stress voids in AlCu metallization
Authors: Kordic Srdjan , Engel Jan , Wolters Rob A. M.
Published: July 2002

AlCu integrated circuit interconnect lines are stressed at 200 °C for a variable duration of time. The number of stress voids and the total void volume are measured. The number of voids saturates between 0.1 and 1 day of stress, and reaches a constant value. The total void volume continues to rise and saturates between 30 and 100 days of stress at 200 °C. Measurements also show that the void volume and the penetration length of the voids into the lines have a log-normal distribution.
Lateral inhomogeneity in InGaAs–GaAs quantum wire arrays by selective-area metalorganic chemical vapor deposition
Authors: Osowski M. L. , Panepucci R. , Turnbull D. A. , Gu S. Q. , Jones A. M. , Bishop S. G. , Adesida I. , Coleman J. J.
Published: July 2002

We present an experimental characterization of InGaAs–GaAs quantum wire arrays grown by selective-area metalorganic chemical vapor deposition (MOCVD). The wire patterns studied were obtained by high-resolution electron-beam lithography on poly(methylmethacrylate) and wet etching of silicon dioxide. We observe a large nonlinear enhancement of growth inside the wire region. In addition, the results of gas phase diffusion growth simulations on the expected inhomogeneity of the fabricated quantum wires are presented. The degree of inhomogeneity of fabricated quantum wire arrays was studied by spatially resolved photoluminescence. Our results show that a suitable patterning technique, coupled with proper growth conditions, could allow control of the selective growth profile across the wire array.
Femtosecond dynamics of the optical Stark effect in semiconductor-doped glass
Authors: Tsuda Sérgio , Brito Cruz Carlos H.
Published: July 2002

We report the observation of the optical Stark shift in CdSxSe1−x semiconductor-doped glass excited under nonresonant below gap condition and probed with femtosecond optical pulses. An ultrafast and pure light-induced shift of the band edge is observed. The measured dependence of the band edge shift with the pump pulse peak intensity is linear for pump intensities up to 0.3 GW/cm2. Above this value, departure from linearity is observed. For a pump intensity of 3 GW/cm2, the band shifts by 11 meV. The response of the shift tracks the profile of the pumping pulse.
A design of reflection scanning near-field optical microscope and its application to AlGaAs/GaAs heterostructures
Authors: Guttroff G. , Keto J. M. , Shih C. K. , Anselm A. , Streetman B. G.
Published: July 2002

A scanning near-field microscope design using the reflected light intensity as the feedback mechanism is described. Multiple fibers with high numerical apertures provide a high collection efficiency in a reflection geometry. The performance with regard to its response to large spatial variations has been tested by using a Si-grating sample and with regard to variations of local indices of refraction by using GaAs/AlGaAs heterostructure samples. In addition, spatially resolved spectroscopy on GaAs/AlGaAs heterostructures has been obtained.
Pulsed anodic etching: An effective method of preparing light-emitting porous silicon
Authors: Hou Xiao-yuan , Fan Hong-lei , Xu Lei , Zhang Fu-long , Li Min-qian , Yu Ming-ren , Wang Xun
Published: July 2002

A pulsed anodic etching method is developed to prepare light-emitting porous silicon. Under the same equivalent etching condition, pulsed etching can yield a more uniform porous silicon film with stronger photoluminescence intensity than the film prepared by ordinary dc etching. The atomic force microscopic observation shows that the porous silicon surface prepared by pulsed etching contains more widely separated Si columns but with steeper sidewalls, which are believed to result in the improvement of quantum confinement. The thickness of pulse etched porous silicon film is found to be much larger than that of a dc etched sample.
Synthesis of the superconducting thin film of HgBa2Ca2Cu3O8+δ
Authors: Wu X. S. , Shao H. M. , Yao X. X. , Jiang S. S. , Wang D. W. , Wu Z. H. , Cai Y. M. , Shen L. J. , Wu Z.
Published: July 2002

HgBa2Ca2Cu3O8+δ (Hg-1223) superconducting thin films of about 0.3 μm in thickness have been successfully synthesized. The process involves depositing films (∼ 1 μm thickness) of Ba2Ca2Cu3Ox on a SrTiO3 substrate by pulse laser ablation technique and implanting mercury ions into this deposited film, followed by annealing at oxygen atmosphere. The films so obtained show a relatively wide superconducting transition temperature up to 118 K, as determined magnetically, which is similar to that of underdoping bulk Hg-1223.
Growth of 6H–SiC on 6H–SiC(0001) by migration enhanced epitaxy controlled to an atomic level using surface superstructures
Authors: Fissel Andreas , Kaiser Ute , Pfennighaus Kay , Schröter Bernd , Richter Wolfgang
Published: July 2002

Epitaxial growth of 6H–SiC on 6H–SiC(0001) via two-dimensional nucleation was realized at 930 °C by solid-source molecular beam epitaxy using the alternate supply of Si and C. The deposition was controlled to an atomic level by surface superstructures. The growth was started on the (√3×√3)R30° surface which turns into the (1×1) phase upon deposition of about 1 monolayer silicon and recurs after subsequent deposition of about 1 monolayer carbon. Deviations from the monolayer deposition and, moreover, growth around substrate related defects result in the deposition of 3C–SiC.
A tunable microwave signal generator using magnetostatic surface wave modulation instability
Authors: Jun Su
Published: July 2002

A type of tunable microwave signal generator is described that utilizes the sideband induced by the modulation instability of magnetostatic surface waves propagating in yttrium iron garnet (YIG) films. Using an epitaxial 28-μm-thick and 0.4-cm-wide YIG film and a pair of identical 50-μm-wide microstrip transducers in a delay-line configuration, S-band signals are generated. The generated microwave frequency is tunable by adjustment of external biasing magnetic field. The determination of the device bandwidth is introduced.
Influence of the semi-insulating GaAs Schottky pad on the Schottky barrier in the active layer
Authors: Wu J. , Wang Z. G. , Lin L. Y. , Han C. B. , Zhang M. , Bai S. W.
Published: July 2002

The influence of the sidegate voltage on the Schottky barrier in the ion-implanted active layer via the Schottky pad on the semi-insulating GaAs substrate was observed, and the mechanism for such an influence was proposed.
Superconductivity and transport behavior of laser ablated Au-added YBa2Cu3O7−δ thin films
Authors: Pinto R. , Apte P. R. , Rao M. S. R. , Chandra Ramesh , D’Souza C. P. , Pai S. P. , Gupta L. C. , Vijayaraghavan R. , Gnanasekar K. I. , Sharon M.
Published: July 2002

We report here a systematic investigation of superconducting properties of Au-added YBa2Cu3O7−δ (YBCO) thin films in situ grown by pulsed laser ablation method. Films are highly c-axis oriented while the corresponding bulk samples contain multiphases. The superconducting transition temperature Tc of films remains close to 90 K even for large concentration of Au (up to 10% by weight) and the critical current denisty Jc is about 5×106 A cm−2 at 77 K (in self-field) with higher reproducibility when compared with that of undoped films of YBCO on 〈100〉 LaAlO3. Preliminary investigations indicate that Au gets rejected by the grains and dopes the grain boundaries thus improving the stability of the boundaries and hence of the films. Our result also demonstrates that pulsed laser deposition can be used to grow films of compounds that generally do not form as a single phase in bulk by the conventional solid state methods and hence offers unique possibilities in terms of exploring structure-property relationships in thin films.
Radially and azimuthally oriented liquid crystal alignment patterns fabricated by linearly polarized ultraviolet exposure process
Authors: Chen J. , Johnson D. L. , Bos P. J. , Sprunt S. , Lando J. , Mann J. A.
Published: July 2002

Radially and azimuthally oriented liquid crystal (LC) alignment patterns, which are hard to achieve by conventional LC alignment techniques, have been realized by exposure of polyimide surfaces to linearly polarized ultraviolet radiation. These surfaces can be used to realize some special LC configurations which are useful for LC basic research and applications.
Observation of population inversion in recombining Al plasma by time- and space-resolved x-ray spectroscopy
Authors: Katsuragawa M. , Itatani J. , Orimo S. , Ozaki T. , Kuroda H. , Sasaki A.
Published: July 2002

Time- and/or space-resolved spectra of laser-produced Al plasmas were investigated using a framing crystal x-ray spectrometer. Population inversion was directly observed between the n=4 and n=3 levels in He-like Al, and the correspondent numerical simulation well describes observed characteristics. Plasma evolution and their effects on inversion was shown on a Te–Ne map, and discussions on the optimum conditions based on the experiments and calculations are also given.
Thickness measurements of thin anodic oxides on GaAs using atomic force microscopy, profilometry, and secondary ion mass spectrometry
Authors: Schmuki P. , Buchanan M. , Mason B. F. , Sproule G. I. , Graham M. J.
Published: July 2002

Techniques to determine the thickness of thin (30–200 Å) anodic oxide films on p-GaAs (100) are reported. The layers were grown potentiostatically in 0.3 M NH4H2PO4 (pH 4.4) solution. By lithographic techniques, several series of squares were etched into the oxide and the step height was measured using both atomic force microscopy (AFM) and a stylus surface profiler (Dektak). Secondary ion mass spectrometry (SIMS) profiles of samples prior to and after the photolithographic treatment show that neither the thickness nor composition of the layers are affected by the treatment. The thickness values obtained in the investigated range show standard deviations better than ±9 Å (AFM) and ±22 Å (Dektak) and correlate well in a linear relation to SIMS sputter times to the interface.
Atomic resolution x-ray hologram
Authors: Xu G.
Published: July 2002

Unlike crystals producing sharp peaks under the x-ray diffraction, disordered materials show slowly varying patterns presenting little structural information. This is due to the fact that only the scattering intensity can be recorded, and the loss of the phase information makes the Fourier inversion of the amplitude impossible. However, when an amorphous sample is placed on a crystal, the x-ray intensity diffracted by the assembly can produce a hologram which contains the spatial modulation of both density functions. Therefore, with known crystal structure the electron density of the amorphous specimen can be resolved by holographic technique. Moreover, it is found that only the amorphous scattering data are needed, and the Bragg peak(s) can be dropped. This gives the scheme the same noise tolerance as by the ordinary amorphous diffraction.
Ultrafast transient gain in type II multiple quantum wells
Authors: Mohs G. , Fluegel B. , Giessen H. , Meissner K. , Khitrova G. , Gibbs H. , Peyghambarian N.
Published: July 2002

Gain for less than one picosecond is observed in a type II GaAs/AlAs multiple quantum well and compared to a type I multiple quantum well under the same conditions. A sophisticated three-beam experiment is used to unambiguously determine the internal gain of the samples. This method is capable of measuring very small amounts of gain and applicable to a wide variety of situations. The observations are well explained by a simple carrier scattering model.