bluuebunny/crossref_metadata_2025 huggingface dataset:
Epitaxial all-perovskite ferroelectric field effect transistor with a memory retention
Authors: Watanabe Yukio
Published: July 2002

All-perovskite ferroelectric field effect transistors (FET) are proposed, and switching behaviors of the prototype devices having a (Pb,La)(Zr,Ti)O3 as a gate insulator and a La1.99Sr0.01CuO4 as a channel layer were demonstrated. Marked improvements in device performances were obtained as compared with the previous ferroelectric FETs. Namely, the present device was written and erased at an operating voltage of 7 V with a pulse width of less than 1 ms, yielding resistance modulation up to about 10% and retaining its memory for more than 10 days at room temperature. Examinations show that the switching speed was limited by a delay constant and can therefore be improved up to 1 μs, and that the memory retention may not be limited by an intrinsic ferroelectric instability as previously suggested.
PbTiO3 thin films prepared by metalorganic chemical vapor deposition on LaAlO3
Authors: Chen Yan-Feng , Yu Tao , Chen Jian-Xie , Shun Li , Li Peng , Ming Nai-Ben
Published: July 2002

High-quality PbTiO3 thin films have been grown on LaAlO3 substrates by metalorganic chemical vapor deposition, using purified metalorganic precursors titanium-iso-propoxide and tetra-ethyl-lead. The results of the cross-section scanning electron microscopy and x-ray diffraction (XRD), including theta and phi scan, show that the films are epitaxy, and a domains and c domains may align alternately in the thin films. The experiments of high-temperature XRD reveal the nature of the phase transition of grown PbTiO3 thin films from tetragonal to cubic phase. The transition temperature is around 460 °C which is far lower than that of bulk PbTiO3 and the thin films deposited on fused quartz substrates.
Periscope-camera system for visible and infrared imaging diagnostics on TFTR
Authors: Medley S. S. , Dimock D. L. , Hayes S. , Long D. , Lowrance J. L. , Mastrocola V. , Renda G. , Ulrickson M. , Young K. M.
Published: July 2002

An optical diagnostic consisting of a periscope which relays images of the torus interior to an array of cameras is used on the Tokamak Fusion Test Reactor (TFTR) to view plasma discharge phenomena and inspect the vacuum vessel internal structures in both the visible and near-infrared wavelength regions. Three periscopes view through 20-cm-diam fused-silica windows which are spaced around the torus midplane to provide a viewing coverage of approximately 75% of the vacuum vessel internal surface area. The periscopes have  f/8 optics and motor-driven controls for focusing, magnification selection (5°, 20°, and 60° field of view), elevation and azimuth setting, mast rotation, filter selection, iris aperture, and viewing port selection. The four viewing ports on each periscope are equipped with multiple imaging devices which include: (1) an inspection eyepiece, (2) standard (RCA TC2900) and fast (RETICON) framing rate television cameras, (3) a PtSi CCD infrared imaging camera, (4) a 35-mm Nikon F3 still camera, or (5) a 16-mm Locam II movie camera with variable framing rate up to 500 fps. Operation of the periscope-camera system is controlled either locally or remotely through a computer-CAMAC interface. A description of the equipment and examples of its application are presented.
Optical wideband high-voltage measurement system
Authors: Hertz H. M. , Thomsen P.
Published: July 2002

A wideband fiber-optic system for the measurement of ac high voltages is presented. The system is based on a capacitively coupled Pockels cell which works as a passive voltage sensor. The lower frequency limit is a few Hz and the upper is 150–230 MHz depending on the application. Other system characteristics are excellent electrical noise suppression, large voltage range, high input impedance, and ability to perform differential measurements separated from ground potential. Furthermore, the low cost, rugged design, and ease of operation make it suitable for measurements in a variety of high-voltage applications.
Many body effects in the temperature dependence of threshold in a vertical-cavity surface-emitting laser
Authors: Chow W. W. , Corzine S. W. , Young D. B. , Coldren L. A.
Published: July 2002

The temperature dependence of the threshold in a vertical-cavity surface-emitting laser is investigated. Comparison of theory with experiment indicates that many-body Coulomb interactions play an important role.
Broadband (up to 10 GHz) electron-paramagnetic-resonance spectrometer: cw implementation with direct detection
Authors: Rubinson Kenneth A.
Published: July 2002

The design principles for a broadband (up to 10 GHz) electron-paramagnetic-resonance (EPR) spectrometer are presented. The upper frequency limit is determined by the losses in the coaxial cables. The sample is inserted along the central conductor at the end of a short-circuited coaxial line that has an air dielectric. An adequate H1 field is generated near the surface of the central conductor and is proportional to the rf current therein. The short circuit of the cable serves to separate the E and H microwave fields with the sample predominately in the H-field portion. The instrument is currently operated in the cw mode in absorption with direct detection. The changes in the standing wave due to the resonance absorption are monitored through an E-field probe set at the first E node away from the truncation. A similar geometry is expected to be usable for broadband Fourier transform (FT) EPR spectrometry through the addition of appropriate pulse-generation equipment and signal-capture hardware. Also, obtaining frequency-swept spectra with or without frequency modulation is possible.
Acoustic levitation in a free-jet wind tunnel
Authors: Seaver Mark , Galloway Andrew , Manuccia T. J.
Published: July 2002

In this article we describe a laboratory device which provides stable acoustic levitation in the free-jet working section of a horizontal wind tunnel. This apparatus combination provides a covenient means for conducting experiments while maintaining a wall-less environment and relative motion between particle(s) and gas. This facility has been calibrated against the known evaporation of pure water. Applications of this facility to studies of the evaporation of volatile nonideal liquid mixtures, the condensation of water vapor onto an evaporating drop of 1-butanol and the remote thermometry of water drops using laser-induced fluorescence are described. We have successfully levitated drops of liquid ranging in diameter from ∼150 μm to ∼3 mm in laminar air streams whose velocities span the range from 25 to 350 cm/s. The lower limit in size is air speed dependent. Measurements of the evaporation of water agree exactly with literature predictions illustrating the lack of perturbations due to the acoustic field.
Spectroscopic ellipsometry with synchrotron radiation
Authors: Johnson R. L. , Barth J. , Cardona M. , Fuchs D. , Bradshaw A. M.
Published: July 2002

The design, construction, and performance of an automatic photometric ellipsometer with rotating analyzer for the VUV region (5–30 eV) is described. The use of a synchrotron radiation source and triple-reflection polarizers makes this new spectral region accessible to spectroscopic ellipsometry. New dielectric function data are presented for InP(110), YBa2Cu3O7, and epitaxial CaF2/Si(111).
Instrumentation for the stable operation of laser diodes
Authors: Bradley C. C. , Chen J. , Hulet Randall G.
Published: July 2002

We have developed a constant current supply and a temperature control circuit that can be used for frequency-stable operation of laser diodes. These instruments can stabilize laser diode injection current and temperature to better than ±1 μA and ±0.3 mK, respectively, over time periods exceeding 1 h. We have excited the Li(2S↔2P) transition with a red-light-emitting laser diode and find that our instrumentation stabilizes the laser frequency to within ±10 MHz over a period exceeding 1 h.
Crossed horizontal dipoles configured as top-loaded vertical dipoles transmitting high-frequency radiation in the ground plane
Authors: Parkinson Murray , Whitehead David , Wilson John
Published: July 2002

A simple method of configuring center-fed crossed dipoles as either horizontal dipoles emitting circularly polarized radiation toward zenith or top-loaded dipoles forcing vertically polarized radiation along the ground plane is outlined. Either mode of operation was selected by a simple interchange of impedance matching circuits at the base of antenna masts. The radiation distribution of the top-loaded vertical dipoles is analogous to that produced by the alternating displacement current between capacitor plates.
Implementation of the α-CHERS diagnostic for D–T operation of TFTR
Authors: McKee G. R. , Fonck R. J. , Thorson T. A. , Stratton B. C.
Published: July 2002

The α-CHERS diagnostic is a high throughput charge exchange recombination spectroscopy diagnostic designed to measure the density profile and time evolution of 0–500 keV alpha particles during D–T operation of the Tokamak Fusion Test Reactor (TFTR). Following successful tests with a prototype α-CHERS system, an improved, multichannel system has been installed for D–T operation. Three spatial channels may be observed simultaneously, and the spectral resolution of 0.5 nm permits increased alpha energy resolution and improved impurity line identification. More efficient coupling optics between the spectrometer and charge coupled device (CCD) detectors have increased the light throughput, and radiation shielding has been installed around the detectors and spectrometers to eliminate the neutron/gamma-ray noise observed in high power D–D plasmas.
Determination of the density in the gas phase with a computer-controlled measuring system of the dielectric constant
Authors: St-Arnaud J. M. , Hourri A. , Okambawa R. , Bélanger M.
Published: July 2002

A computer-controlled measuring system (CCMS) of the dielectric constant (ε) in the gas phase as a function of pressure (P) and temperature (T) is described. The automated experimental setup is capable of performing the necessary measurements for the determination of the first three dielectric virial coefficients. Combining the value of ε with these dielectric virial coefficients, it is possible to calculate the density and, hence, the compressibility factor of the gas. The CCMS is as accurate as the best methods for the determination of ρ and has the ability to produce numerous experimental data in a short period of time.
A low-energy electron diffraction data acquisition system for very low electron doses based upon a slow scan charge coupled device camera
Authors: Held G. , Uremović S. , Stellwag C. , Menzel D.
Published: July 2002

We have developed a video low-energy electron diffraction (LEED) system on the basis of a slow scan charge coupled device (CCD) camera which is capable of collecting LEED IV data at very low electron doses quickly and therefore enables us to study extremely beam sensitive surface structures which have not been accessible to LEED IV analysis before. The slow scan CCD camera allows separating the relatively short data acquisition process from the more lengthy digitizing, storage, and data analysis processes. Typical total effective exposure times can therefore be reduced to about 200–300 s (1 s per energy point) at a primary beam current of 100 nA which corresponds to a total dose of about 12 e per adsorbate particle; further decrease is possible. The total measurement time for collecting a complete set of LEED images is of the order of 30–40 min which assures the exclusion of contamination effects, even for sensitive layers. The IV curves are then extracted from the digitally stored images off-line which allows collecting the intensities of all visible spots simultaneously with a high reliability in tracing beams, even for very dense LEED patterns.
Thermoacoustic amplification of photoacoustic signal
Authors: Bijnen F. G. C. , Dongen J. v. , Reuss J. , Harren F. J. M.
Published: July 2002

The thermoacoustic effect is used to amplify the photoacoustic signal induced by trace gas absorption of CO2 laser radiation. The acoustic wave pattern in a thermoacoustic amplifier coupled to a photoacoustic cell is represented in terms of electric transmission lines. Predictions of this model have resulted in a prototype thermoacoustic–photoacoustic (TAPA) detector to get a better understanding of this combination. The photoacoustic signal strength of the TAPA cell was linear with the trace gas density in the cell. Within this study we observed for the TAPA cell a higher PA signal than generated by a normal PA cell. Design criteria for better thermoacoustic amplification of photoacoustic signal are discussed.
A beam line for highly charged ions
Authors: Pikin A. I , Morgan C. A. , Bell E. W. , Ratliff L. P. , Church D. A. , Gillaspy J. D.
Published: July 2002

The design and operation of a beam line for transporting and charge-to-mass selecting highly charged ions extracted from the National Institute of Standards and Technology electron beam ion trap (EBIT) are described. This beam line greatly extends the range of experiments possible at this facility. Using the transport system, pure beams of low-energy, highly charged ions up to Xe44+ have been produced with substantially higher fluxes than previously reported from an EBIT source. Design choices and computer modeling for the various components of the beam line are explained in detail.
A spinning-stage, total electron-yield detector for the elimination of diffraction peaks in x-ray absorption spectra
Authors: Harris V. G.
Published: July 2002

A primary problem in collecting and analyzing x-ray absorption fine structure (XAFS) from crystalline samples, including thin films grown on crystalline substrates, is the contamination of the x-ray absorption spectrum by diffraction events. To address this limitation, a total electron-yield detector equipped with a spinning stage was developed. Samples of (MnZn)Fe2O4, grown on single crystal (100) MgO substrates, were used to illustrate its effectiveness as an electron-yield detector and in eliminating diffraction-related contamination from the XAFS. The design and performance characteristics of this detector are presented and discussed.
Quasidistributed fluorescence-based optical fiber temperature sensor system
Authors: Sun T. , Zhang Z. Y. , Grattan K. T. V. , Palmer A. W.
Published: July 2002

The use of multiple material fluorescence-based sensors, where each is optimized to a particular temperature range yet is pumped by the same light source, emitting over the same spectral region, makes for a very simple, convenient and promising optical arrangement which can be applied in real-time, quasidistributed temperature sensor systems. The fluorescence lifetime approach, which is an important technique to enable fluorescence emission to be exploited for thermometry, is adopted in the system discussed. An analysis scheme using Prony’s method has been reported which enables exponential decays from either single-material or two material and quasidistributed sensors to be deconvolved and thus data and associated measurand information encoded in each individual signal to be recovered. In this work, in the development of quasidistributed temperature sensor algorithms based on Prony’s method are used for the estimation of exponential time constants of a convolved triple exponential fluorescence decay, each corresponding to a different-point temperature. Experimental results obtained are presented to justify their use in practical multiexponential fluorescence decay analysis and show a comparison of the Prony method to the Marquardt nonlinear least-squares approximation algorithm to achieve the deconvolution. The computational time for Prony’s approach is approximately one-thousandth that of the Marquardt technique while the accuracy achieved using Prony’s method is still high enough for practical use.
New electron cyclotron emission diagnostic for measurement of temperature based upon the electron Bernstein wave
Authors: Efthimion P. C. , Hosea J. C. , Kaita R. , Majeski R. , Taylor G.
Published: July 2002

Most magnetically confined plasma devices cannot take advantage of standard electron cyclotron emission (ECE) diagnostics to measure temperature. They either operate at high density relative to their magnetic field (e.g., ωp≫Ωc in spherical tokamaks) or they do not have sufficient density and temperature to reach the blackbody condition (τ>2). The standard ECE technique measures the electromagnetic waves emanating from the plasma. Here we propose to measure electron Bernstein waves (EBW) to ascertain the local electron temperature in these plasmas. The optical thickness of EBW is extremely high because it is an electrostatic wave with a large ki. For example, the National Spherical Torus Experiment (NSTX) will have an optical thickness τ≈3000 and CDX-U will have τ≈300. One can reach the blackbody condition with a plasma density ≈1011 cm−3 and Te≈1 eV. This makes it attractive to most plasma devices. The serious issue with using EBW is the wave accessibility for the emission measurement. Simple accessibility arguments indicate the wave may be accessible by either direct coupling or mode conversion through an extremely narrow layer (≈1–2 mm). EBW experiments on the Current Drive Experiment-Upgrade (CDX-U) will test the accessibility properties of the spherical tokamak configuration.
High-sensitivity inductive magnetometer for pulsed magnetic fields
Authors: Kapustin G. A.
Published: July 2002

A magnetometer is described for measurements in pulsed magnetic fields up to 43 T. The compensation system allows removal of pickups produced both by the longitudinal and transverse components of the pulsed field. The compensation level achieves 10−6 (of the signal from the working coil with an inner diameter 1.4 or 1.75 mm) for the longitudinal and 10−4 for the transverse components. Sensitivity of the magnetometer is about 10−4 emu for the fields up to 10 T and decreases down to 10−3 emu at the pulse amplitude of 35 T. A deviation of the compensation is below 2×10−4 for the temperature increase from 77 up to 300 K and below 5×10−5 after the sample replacement. The sample temperature is controlled by a fast-acting temperature control system in the range from 6 up to 300 K with accuracy of 0.3–0.05 K.
Performance of the advanced photon source 1-BM beamline optics
Authors: Lang J. C. , Srajer G. , Wang J. , Lee P. L.
Published: July 2002

Bending magnet beamlines at third-generation synchrotron sources combined with well-designed optics offer unique capabilities for providing high x-ray fluxes into relatively small focal spots. This article provides a description of the x-ray optics used in the Advanced Photon Source 1-BM beamline. The performance of these optics in terms of the delivered flux ( 9×1011 ph/s/100 mA at 10 keV), energy resolution [ΔE/E≈1.5×10−4 with Si(111)], and focusing properties (spot size ≈0.25×0.60 mm) is compared with that expected from ideally reflecting and shaped optics.
Accurate measurements of the electro-optic coefficients and birefringence changes using an external modulation signal
Authors: Aillerie M. , Abdi F. , Fontana M. D. , Théofanous N. , Abarkan E.
Published: July 2002

We propose a new method to measure within a high accuracy both the electro-optic properties and the birefringence changes in bulk crystals. This technique is based upon the frequency doubling electro-optic modulation (FDEOM) method in which an external modulator is inserted in the experimental Sénarmont setup. We present a complete analysis of the optical response of a Sénarmont setup within Jones formulation. The FDEOM method possesses as main advantages a high accuracy and sensitivity in the measurements due to a direct determination of the electric field-induced phase retardation in the crystal under study. The measurements are recorded with an adjustment of the shape of the output beam at a frequency double the frequency of the ac applied voltage. The external modulation version of this method allows us to perform measurements with a higher modulation depth and to avoid any additional dynamical perturbation in the electro-optic crystal under study. Therefore, even small values of the electro-optic coefficients can be accurately measured. Moreover, the new method is able to measure with a high accuracy the variations of the birefringence in any crystal, even if it does not present an electro-optic effect. Some significative results in LiNbO3 point out the large advantages of the method.
Radiation effects on n-channel polycrystalline silicon thin-film transistors
Authors: Yang Chien Kuo , Lee Chung Len , Lei Tan Fu , Chern Horng Nan
Published: July 2002

The radiation effect on the n-channel polycrystalline silicon (polysilicon) thin-film transistors has been investigated. It is found that for an unhydrogenated device, the irradiation of Co60 with a total dose of 1 Mrads caused a negative threshold-voltage (Vth) shift and a slight subthreshold-swing (S) degradation, while for a hydrogenated n-channel device, the same irradiation results in a positive Vth shift and a serious S degradation. It is also found that the radiation hardness of the hydrogenated devices can be improved somewhat by a simple irradiation-then-hydrogenation treatment.
Coexistence of incommensurate antiferroelectric and relaxorlike ferroelectric orderings in high Zr-content La-modified lead zirconate titanate ceramics
Authors: Xu Z. , Dai Xunhu , Li Jie-Fang , Viehland Dwight
Published: July 2002

Lanthanum modified lead zirconate titanate (PLZT) ceramics with a Zr/Ti ratio of 85/15 were investigated as a function of La content by dielectric spectroscopy, Sawyer–Tower polarization techniques, and electron microscopy. Tweedlike structures were found to evolve from normal μm-sized ferroelectric domains with increasing La content above 4 at. %. For a composition with 6 at. % La, an incommensurate antiferroelectric state was found to coexist with a polar nanodomain state, where the size of the nanodomains was approximately equal to the value of the incommensurate modulation wavelength. For this composition, P–E studies revealed double hysteresis characteristics, whereas dielectric investigations revealed relaxorlike ferroelectric behavior.
Open air plasma chemical vapor deposition of highly dielectric amorphous TiO2 films
Authors: Ha Hyun-Kwon , Yoshimoto Mamoru , Koinuma Hideomi , Moon Bum-Ki , Ishiwara Hiroshi
Published: July 2002

By using the cold plasma torch we developed, TiO2 films were deposited on substrates exposed to air by feeding Ti(OEt)4 into the plasma. XPS and x-ray analyses revealed that all films were stoichiometric and amorphous TiO2, but Raman spectra indicated the existence of short-range crystallinity in films deposited above 350 °C. The short range structure changed from anatase to rutile by admixing of hydrogen to the plasma. The rutile containing TiO2 film had a higher breakdown electric field as well as a higher dielectric constant than the anatase containing film.
Oxynitride films formed by low energy NO+ implantation into silicon
Authors: Diniz J. A. , Tatsch P. J. , Pudenzi M. A. A.
Published: July 2002

Oxynitride (SiOxNy) insulators have been obtained by low-energy nitric oxide ion (NO+) implantation in Si substrates prior to thermal oxidation. Characterization by Fourier transform infrared (FTIR) and secondary ion mass spectrometry (SIMS) analyses reveal the presence of Si–O, Si–N, and Si–N–O bonds in the high quality 37 nm silicon oxynitride films. The dielectric constant=5.5, effective charge density=7×1010 cm−2 and breakdown E-fields of 3 MV/cm were determined by capacitance–voltage (C–V) and current–voltage (I–V) measurements, respectively, indicating that the SiOxNyfilms formed are suitable gate insulators for metal-oxide-semiconductor (MOS) devices.
Failure phenomena and mechanisms of polymeric light-emitting diodes: Indium–tin–oxide damage
Authors: Chao Ching-Ian , Chuang Kuen-Ru , Chen Show-An
Published: July 2002

Indium–tin–oxide (ITO) coated on a glass plate as the transparent electrode in polymeric light-emitting diodes (LEDs) generates some volcano-like patterns during use especially at a higher applied electric field strength. Such an ITO damage phenomenon is independent of Joule heat, conjugation structure of the polymer, and light-emission process, but only dependent on the applied electric field strength. The ITO damage, which results from a self-decomposition reaction, can cause a reduction of lifetime of the device.
Si:SiGe quantum wells grown on (118) substrates: Surface morphology and transport properties
Authors: Thornton T. J. , Fernández J. M. , Kaya S. , Green P. W. , Fobelets K.
Published: July 2002

We have grown strained Si quantum wells on relaxed Si0.7Ge0.3 buffer layers using vicinal (118) silicon substrates. Compared to conventional (001) substrates the surface is tilted by 10° towards the [110] direction resulting in terraces with step edges which run parallel to [11̄0]. The surface morphology of the layers shows “cross-hatching” characteristic of relaxed SiGe films grown on Si substrates. However, the cross-hatching is not orthogonal but aligns along directions in which (111) planes intersect the (118) surface. We have measured the low temperature transport properties of the two-dimensional electron gas confined within the strained Si channel. When measured with current flowing parallel to the step edges the electron mobility is approximately four times larger than that measured in a perpendicular direction showing the strong elastic scattering associated with the step edges. In contrast the single particle relaxation time is almost identical for the two different orientations.
Generalized magneto-optical ellipsometry
Authors: Berger A. , Pufall M. R.
Published: July 2002

A complete magneto-optical characterization of any material requires the measurement of both, the magneto-optical and the conventional optical constants. We have developed the method of generalized magneto-optical ellipsometry (GME), which enables us to determine these material constants simultaneously in a single setup. In addition, GME even allows the determination of the magnetization orientation. The experimental setup is very simple, using only two rotatable polarizers as polarization sensitive elements. Our experimental results for permalloy demonstrate the validity of our approach and the feasibility of GME as a practical measurement technique.
Schottky barrier heights and conduction-band offsets of In1−xGaxAs1−yPy lattice matched to GaAs
Authors: Lee Jong-Kwon , Cho Yong-Hoon , Choe Byung-Doo , Kim K. S. , Jeon H. I. , Lim H. , Razeghi M.
Published: July 2002

The Schottky barrier heights of Au/In1−xGaxAs1−yPy contacts have been determined as a function of y by the capacitance–voltage and temperature dependent current–voltage characteristics measurements. The barrier height is observed to increase as y is increased for both n- and p-type materials, with a more rapid increase for the p-type material. The compositional variation of the barrier heights for Au/n-In1−xGaxAs1−yPy is found to be identical to that of the conduction-band offsets in In1−xGaxAs1−yPy/GaAs heterojunctions. A possible cause of this phenomenon is also discussed.
Switchable diffractive cholesteric gratings
Authors: Subacius D. , Bos P. J. , Lavrentovich O. D.
Published: July 2002

Electrically switchable diffractive gratings based on cholesteric liquid crystals are suggested. An electric field switches the cholesteric cell between three states: two with a uniform in-plane director and one with a periodic in-plane director modulation. The modulated state produces a Raman–Nath diffractive effect. Characteristic time of switching is of the order of 10 ms. Diffractive properties depend on the polarization of the incident beam and the direction of surface orientation.
Formation of carbon-induced germanium dots
Authors: Schmidt O. G. , Lange C. , Eberl K. , Kienzle O. , Ernst F.
Published: July 2002

A very small amount of pre-deposited C on a Si substrate causes island formation after epitaxial growth of less than 2 monolayers Ge. These C-induced Ge dots can be as small as 10 nm in lateral size and 1 nm in height. Their areal density is 1011 cm−2. Intense photoluminescence signal from these small Ge quantum dots is observed reaching a maximum for 2.1±0.3 monolayers of Ge. In the initial stages of island formation, the optical transition of the wetting layer is blue-shifted by strain compensation effects. We propose spatially indirect mechanisms of radiative recombination between electrons confined in the underlying wetting layer and holes confined in the Ge islands.
Is the c(4×4) reconstruction of Si(001) associated with the presence of carbon?
Authors: Miki Kazushi , Sakamoto Kunihiro , Sakamoto Tsunenori
Published: July 2002

With the increasing annealing temperature in ultrahigh vacuum, hydrogen-terminated Si(001) surface exhibit a (1×2) reconstruction around 500 °C, c(4×4) in the narrow range of 580–750 °C, and a weak SiC transmission pattern above 750 °C. The simultaneous disappearance of c(4×4) and the appearance of the SiC pattern suggest that the c(4×4) reconstruction is associated with carbon contamination. The carbon concentration of 2.5×1018 atoms/cm3 is insufficient for carbon atoms to be a component of the c(4×4) structure, and therefore the carbon must be having another effect. A consequence of this conclusion is that carbon is not responsible for C-type defects.
Enhanced cluster mobilities on Pt(111) during film growth from the vapor phase
Authors: Chirita V. , Münger E. P. , Sundgren J.-E. , Greene J. E.
Published: July 2002

We use molecular dynamics simulations to follow the dynamics of small two-dimensional Pt clusters on Pt(111) at 1000 K. While close-packed Pt7 heptamers are extremely stable structures, the addition of a single cluster vacancy or an on-top adatom immediately results in intracluster bond breaking, reconfigurations, rotations, the introduction of stacking faults, and greatly enhanced cluster diffusion rates. Mapping center-of-mass motion for total simulation times >145 ns revealed increases in cluster velocities by more than an order of magnitude with cluster migration occurring primarily by concerted motion and a novel diffusion mechanism involving double shearing of dimers/trimers. Contrary to some previous reports, edge-atom diffusion plays only a minor role.
Probing molecular ordering at a liquid-solid interface with a magnetically oscillated atomic force microscope
Authors: Han Wenhai , Lindsay S. M.
Published: July 2002

We have demonstrated the ability of an atomic force microscope operated in the magnetic a/c mode to determine the layered structure of liquids at interfaces with high accuracy and reproducibility. Oscillations in surface stiffness were found for octamethylcyclotetrasiloxane (OMCTS) and mesitylene close to a graphite surface and the period of oscillation allowed us to determine the molecular packing to sub-Angstrom precision. The Young’s modulus, measured at the peak stiffness of each layer, decreased exponentially with distance from the interface with a decay length of 8.8 Å for OMCTS and 6.5 Å for mesitylene.
p-n
junction peripheral current analysis using gated diode measurements
Authors: Czerwinski A. , Simoen E. , Claeys C.
Published: July 2002

A modified method for analysis of the current–voltage characteristics of a gated diode structure is proposed and validated in order to investigate the peripheral reverse current in a silicon p-n junction diode. The peripheral generation current in modern p-n diodes is attributed fully to surface generation underneath the thick field oxide surrounding the structure, which typically contains a high density of interface traps. For a gated diode structure, the current region observed for large gate voltages, VG, is linked to the generation associated with the depletion at the Si-thick SiO2 interface. It will be shown that, compared to the classical analysis, this current step is a better alternative to assess the peripheral generation. The 25 times higher sensitivity of gated diode measurements in this mode allows one to reduce the test device perimeter and dimensions, without penalizing the measurement resolution for interface states. The main advantage of the proposed method is related to the fact that for the peripheral current extraction, only the measurement of one diode is needed instead of the tedious measurements and analyses of a set of diodes.
Field emission from aligned high-density graphitic nanofibers
Authors: Chen Yan , Patel Sushil , Ye Yagu , Shaw David T. , Guo Liping
Published: July 2002

Field emission data from aligned graphitic nanofibers have been obtained. The aligned nanofibers are 50–100 nm in diameter and 6–10 μm in length, with a density of 109–1010/cm2. The fibers were grown on polycrystalline nickel substrate by plasma-assisted hot filament chemical vapor deposition using a gas mixture of nitrogen and acetylene. The onset of emission current in microampere level was detected at about 1.8 V/μm with an emission area of 1 mm2. The Fowler–Nordheim model was used to analyze the data obtained. The field emission current required for flat panel display can be easily achieved at 2.5 V/μm.
Time-resolved photoluminescence measurements of InGaN light-emitting diodes
Authors: Pophristic M. , Long F. H. , Tran C. , Ferguson I. T. , Karlicek R. F.
Published: July 2002

We have used time-resolved photoluminescence (PL) to examine light-emitting diodes made of InGaN/GaN multiple quantum wells (MQWs) before the final stages of processing. The time-resolved photoluminescence from a dim MQW was quenched by nonradiative recombination centers. The PL kinetics from a bright MQW were not single exponential but stretched exponential, with the stretch parameter β=0.59±0.05. The emission lifetime varied with energy, within error β was independent of the emission energy. the stretched exponential kinetics are consistent with significant disorder in the material. We attribute the disorder to spatial fluctuations of the local indium concentration.
Growth of highly oriented carbon nanotubes by plasma-enhanced hot filament chemical vapor deposition
Authors: Huang Z. P. , Xu J. W. , Ren Z. F. , Wang J. H. , Siegal M. P. , Provencio P. N.
Published: July 2002

Highly oriented, multiwalled carbon nanotubes were grown on polished polycrystalline and single crystal nickel substrates by plasma enhanced hot filament chemical vapor deposition at temperatures below 666 °C. The carbon nanotubes range from 10 to 500 nm in diameter and 0.1 to 50 μm in length depending on growth conditions. Acetylene is used as the carbon source for the growth of the carbon nanotubes and ammonia is used for dilution gas and catalysis. The plasma intensity, acetylene to ammonia gas ratio, and their flow rates, etc. affect the diameters and uniformity of the carbon nanotubes.
High-performance GaInAs/GaAs quantum-dot lasers based on a single active layer
Authors: Schäfer F. , Reithmaier J. P. , Forchel A.
Published: July 2002

GaInAs/GaAs quantum-dot lasers were fabricated by self-organized growth in a molecular beam epitaxy system. By using a single active layer, lasers with low-threshold current densities (Jth=144 A/cm2 for a 2 mm long device) and high internal quantum efficiencies (>90%) were obtained. Ground-state lasing of the quantum dots was observed up to a device temperature of 214 °C.
Structural and optical characteristics of InxGa1−xN/GaN multiple quantum wells with different In compositions
Authors: Kwon Yong-Hwan , Gainer G. H. , Bidnyk S. , Cho Y. H. , Song J. J. , Hansen M. , DenBaars S. P.
Published: July 2002

We have studied the structural and optical properties of InxGa1−xN/GaN multiple quantum wells with different In compositions of 8.8%, 12.0%, and 13.3% by means of high-resolution x-ray diffraction (HRXRD), photoluminescence (PL), PL excitation (PLE), stimulated emission (SE), and time-resolved PL spectroscopy. As the In composition increases, the superlattice peaks in HRXRD measurements and the PLE band edge broaden, indicating the deterioration of interface quality due to the difficulty of uniform In incorporation into the GaN layer. However, the lower room-temperature SE threshold densities of the higher In concentration samples indicate that the effect of In suppressing nonradiative recombination overcomes the drawbacks associated with increasing interface imperfection.
Reconstruction of the charge collection probability in a semiconductor device from the derivative of collection efficiency data
Authors: Donolato C.
Published: July 2002

A method is presented for analyzing the charge collection efficiency data that are obtained by irradiating a semiconductor device with an electron beam at different energies, and measuring the induced current. The procedure uses the numerical derivative of the function Rη(R) (η is the collection efficiency and R the electron range), and allows a direct reconstruction of the depth distribution of the charge collection probability in the device. Examples of application of the method to simulated data and published measurements are described.
Fabricating nanometer-scale Co dot and line arrays on Cu(100) surfaces
Authors: Silva S. L. , Jenkins C. R. , York S. M. , Leibsle F. M.
Published: July 2002

We have templated Cu(100) surfaces with self-assembled arrays of atomic nitrogen islands and then used these islands as masks for Co growth. This method of nanolithography enables the creation of Co dot arrays with dot densities 4×1012 cm−2 (27 teradots/in.2). Adjusting the nitrogen coverage also enabled the creation of arrays of Co lines spaced 10 nm (0.01 μm) apart.
Direct wafer bonding and transfer of 10-μm-thick magnetic garnet films onto semiconductor surfaces
Authors: Izuhara T. , Levy M. , Osgood R. M.
Published: July 2002

Bonding between liquid-phase-epitaxy-grown yttrium iron garnet films and various semiconductors is realized by direct wafer bonding. The semiconductor substrates can serve as a platform for integration or as a “handle” platform for the transfer of mesoscopic garnet films. To effect film transfer, a sacrificial layer is formed in the garnet by deep ion implantation prior to bonding. Shear stress at the garnet/semiconductor interface can be controlled by temperature tuning during the bonding process. A debonding temperature threshold of ∼400 °C is found and related to the interfacial thermal stress due to difference in thermal expansion coefficients of the bonded materials. Film separation is realized by the application of thermally induced stress at the sacrificial layer.
Waveguide ultrasonic force microscopy at 60 MHz
Authors: Inagaki K. , Kolosov O. V. , Briggs G. A. D. , Wright O. B.
Published: July 2002

We present measurements using ultrasonic force microscopy at ∼60 MHz, operating in a “waveguide” mode in which the cantilever base is vibrated and flexural ultrasonic vibrations are launched down the cantilever without exciting any particular cantilever resonance. The nonlinearity of the tip-sample force-distance curve allows the conversion of a modulated ultrasonic frequency into a low frequency vibration of the cantilever, detected in a conventional atomic force microscope. Images of Ge quantum dots on a Si substrate show contrast related to elasticity and adhesion differences, and this is interpreted with the Johnson–Kendall–Roberts model of the force-distance curve.
Spectral diffusion of the exciton transition in a single self-organized quantum dot
Authors: Seufert J. , Weigand R. , Bacher G. , Kümmell T. , Forchel A. , Leonardi K. , Hommel D.
Published: July 2002

We report on reversible spectral shifts in the emission spectra of self-organized CdSe single quantum dots on a time scale of seconds. Energy shifts of up to 3.5 meV have been observed and can be attributed to the Stark effect caused by fluctuating local electric fields. Most surprisingly, the energy shift turns out to be quasi-periodic with time constants between 70 and 190 s.
On the main irradiation-induced defect in GaN
Authors: Polenta L. , Fang Z-Q. , Look D. C.
Published: July 2002

We show that the usual Arrhenius analysis of the main electron-irradiation-induced defect trap in n-type GaN, observed by deep-level transient spectroscopy (DLTS), is not sufficiently accurate. Instead, an exact fitting of the DLTS spectrum for this trap reveals two components, each of which has a thermal energy near 60 meV, not the apparent 140–200 meV, as given in other DLTS studies. This result resolves the discrepancy between Hall-effect and DLTS determinations of the thermal energy of this defect center.
Dielectric constant measurement of thin films by differential time-domain spectroscopy
Authors: Jiang Zhiping , Li Ming , Zhang X.-C.
Published: July 2002

We present a theoretical model and preliminary experimental results on the dielectric constant measurement of thin films by using differential time-domain spectroscopy. This technique greatly reduces the minimum measurable thickness, and it promises the dielectric constant measurement of μm-thick thin films with the frequency range from GHz to THz.
The effect of anisotropic reactivity and interaction potential on the kinetics of diffusion controlled reactions
Authors: Shushin A. I.
Published: July 2002

The manifestation of strongly anisotropic reactivity and interaction potential in the kinetics of diffusion controlled reaction is thoroughly investigated using the method of local analysis (MLA) proposed earlier. The MLA enables one to simplify the problem reducing it to the analysis of the stochastic relative motion of molecules in the vicinity of the reactive orientations. Simple analytical expressions for the reaction rate are derived within the realistic model of reactive hemispheres (MRH) assuming that the reaction occurs upon the overlap of the small reactive hemispheres on the surfaces of molecules. Unlike the conventional model of reactive patches (MRP) the MRH takes into account the “thickness” of the reactive region, which is found to lead to the strong (up to two orders of magnitude) increase of the rate. Within the proposed model of ellipsoidal reactive patch the unified formula for the rate is derived that reproduces the results of both the MRP and the MRH. It is shown that the peculiarities of the local shape of molecules in the vicinity of reactive region manifest themselves fairly strongly. The effects of these peculiarities and as well as the effects of anisotropic potential are discussed.
A fast-response chemical ionization mass spectrometer for in situ measurements of HNO3 in the upper troposphere and lower stratosphere
Authors: Neuman J. A. , Gao R. S. , Schein M. E. , Ciciora S. J. , Holecek J. C. , Thompson T. L. , Winkler R. H. , McLaughlin R. J. , Northway M. J. , Richard E. C. , Fahey D. W.
Published: July 2002

A chemical ionization mass spectrometer instrument has been developed for in situ measurements of nitric acid (HNO3) in the upper troposphere and lower stratosphere from the NASA WB-57 aircraft. Fast and sensitive measurements of HNO3 are achieved by using a low surface area heated Teflon sampling inlet and detection techniques that employ ion-molecule reactions. Sensitivity to HNO3 is determined in flight by adding HNO3 from a calibrated HNO3 permeation source into the sample air flow, and instrument background is measured by displacing ambient air from the sampling inlet with a flow of dry nitrogen in the sampling inlet. Instrument temperatures, pressures, and gas flows are controlled in flight to maintain a constant detection sensitivity in a changing ambient operating environment. The initial performance of this new instrument is evaluated using HNO3 and ozone data obtained between 6 and 19 km during the 1999 NASA Atmospheric Chemistry of Combustion Emissions Near the Tropopause mission. The data reveal a sensitivity of 0.73 Hz/pptv, a detection limit of 30 pptv for 10 s integration times, and a fast time response (<1 s). Further reductions in the background HNO3 signal will improve performance.
Localization of gate oxide integrity defects in silicon metal-oxide-semiconductor structures with lock-in IR thermography
Authors: Huth S. , Breitenstein O. , Huber A. , Lambert U.
Published: July 2002

A technique to image gate oxide integrity (GOI) defects across large gate areas has been developed. First, a low-ohmic bias pulse is used in order to break down nearly all GOI defects in a large area metal-oxide-semiconductor (MOS) structure. Then a periodic bias of typically 2 V is applied and the local heating caused by the leakage current through the broken GOI defects is imaged by infrared (IR) lock-in thermography. This method allows us to detect very small temperature variations down to 10 μK at a lateral resolution down to 10 μm. The determined defect densities in Czochralski silicon materials with various densities of crystal originated particles are in good agreement with charge-to-breakdown measurements of small area MOS capacitors. In conclusion, IR lock-in thermography provides a fast and reliable imaging technique of the lateral GOI defect distribution across the entire wafer area.
Poloidally asymmetric distribution of impurities in Joint European Torus plasmas
Authors: Chen H. , Hawkes N. C. , Ingesson L. C. , von Hellermann M. , Zastrow K.-D. , Haines M. G. , Romanelli M. , Peacock N. J.
Published: July 2002

Poloidally asymmetric distributions of nickel ions have been observed experimentally in Joint European Torus optimized shear tokamak plasmas following nickel laser injection experiments. Two types of asymmetries occur. In the first type of asymmetry, which has earlier been observed in high-confinement mode plasmas, nickel ions accumulate on the outboard side of the poloidal cross section. This can be explained well by fast toroidal plasma rotation driven by neutral beam injection. The second type of asymmetry was opposite in position: In a radio frequency heated optimized shear plasma, nickel ions have been seen to accumulate on the inboard side of the poloidal cross section.
Type-II InAsSb/InAs strained quantum-well laser diodes emitting at 3.5 μm
Authors: Wilk A. , El Gazouli M. , El Skouri M. , Christol P. , Grech P. , Baranov A. N. , Joullié A.
Published: July 2002

Mid-infrared laser diodes with compressively strained InAsSb/InAs type-II slightly coupled quantum wells are reported. These lasers, grown on InAs by molecular-beam epitaxy, have emission wavelength near 3.5 μm. They exhibit pulsed operation up to 220 K, with at 90 K threshold current density of 150 A/cm2. Ridge lasers continuous wave (cw) operated up to 130 K with cw output power of 40 mW/A/facet and a characteristic temperature T0=40 K.
Magnetic rotation molecular spectroscopy using an oscillating field
Authors: Boone C. D. , Dalby F. W. , Ozier I.
Published: July 2002

The high resolution magnetic rotation spectrum of a diatomic molecule is considered. A procedure is described for calculation of the magnetic rotation signal in both first and second harmonic for an oscillating magnetic field in the low-field limit. The procedure is simpler than other methods available in the literature, and a more complete account is taken of the various possible contributions to the signal. Perturbations between electronic states that make it possible to observe magnetic rotation signals for high-J transitions are discussed, along with the associated evolution of line shape that complicates frequency measurements from magnetic rotation spectra. Examples are given from a recent magnetic rotation study of the A 3Π1u–X 1Σg+ system of Br279.