bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical tweezer arrays and optical substrates created with diffractive optics
Authors: Dufresne Eric R. , Grier David G.
Published: July 2002

We describe a simple method for creating multiple optical tweezers from a single laser beam using diffractive optical elements. As a demonstration of this technique, we have implemented a 4×4 square array of optical tweezers—the hexadeca tweezer. Not only will diffractively generated optical tweezers facilitate many new experiments in pure and applied physics, but they also will be useful for fabricating nanocomposite materials and devices, including photonic bandgap materials and optical circuit elements.
Direct bonding of piezoelectric crystal onto silicon
Authors: Namba Akihiko , Sugimoto Masato , Ogura Tetsuyoshi , Tomita Yoshihiro , Eda Kazuo
Published: July 2002

A method for bonding a piezoelectric crystal directly onto silicon, without any bonding agents, is reported. The interface microstructure, procedures of fabricating a lithium tantalate (LiTaO3■- on-silicon resonator, and its resonant characteristics are described. This technique is very promising for miniaturizing electroacoustic integrated devices.
Scanning probe optical microscopy of evanescent fields
Authors: Taylor R. S. , Leopold K. E. , Wendman M. , Gurley G. , Elings V.
Published: July 2002

Two new methods for probing evanescent fields using a Dimension™ 3000 atomic force microscope (AFM) from Digital Instruments are described. The first method uses a fiber-optic pickup probe to collect light generated by a commercial silicon AFM probe, which perturbs the evanescent field. The pickup probe is mounted directly onto the AFM cantilever probe holder so that it tracks with the AFM probe tip as it scans a sample but is positioned in such a manner as to permit the use of conventional laser deflection distance regulation. The second method uses a novel bent optical fiber probe with a chemically etched conical quartz tip to perturb the evanescent field together with a metallized cladding to collect the scattered light.
New method for measuring the differential capacity in electrochemistry
Authors: Lecoeur J. , Koehler C. , Bellier J. P.
Published: July 2002

Electrical behavior of the ideally polarizable metal–solution interface is similar to a RC series circuit. The dc polarization, E, of the interface is potentiostatically controlled and differential capacity, C, measurements are carried out with a linear variation of E versus time. A precise measurement method of C is described in the case where the time constant of the circuit is rather high (≈10−2 s). The principle of this method is to impose on the interface an ac current perturbation, Iω, and to measure the ac potential response, Eω. A system composed of a low bandwidth potentiostat (<1 Hz) and a galvanostat controls the dc potential, E, and produces the ac current, Iω. In- and out-of-phase components of the ac potential response, Eω, are analyzed by means of a lock-in amplifier. An ohmic drop compensation technique with suppression of the residual common mode is used to improve the determination of the Eω(90°). Using a dummy cell, comparison between the new method and the classic potentiostatic technique is carried out. Results show that it is possible to measure C with a relative error less than 1% in a frequency range up to 2 kHz whereas with the classic potentiostatic technique the frequency range is limited to around 100 Hz.
Calorimetric apparatus for alternating current loss measurements on high-temperature superconductors
Authors: Magnusson N. , Hörnfeldt S.
Published: July 2002

The use of high-temperature superconductors in electric power components requires the knowledge of their alternating current (ac) losses. Methods are therefore needed to characterize the conductors with respect to their ac losses under applicationlike conditions. In this article we describe a calorimetric setup for ac loss measurements on long length high-temperature superconductors carrying ac transport currents in ac external magnetic fields at variable temperatures. The variable temperature is achieved by a thermal connection between the sample and a cooling machine. Current in copper coils generates the magnetic field parallel to the plane of the tape and perpendicular to the transport current. This current can be induced in the coil-formed sample. Two slightly different methods are used to determine the ac losses, one in which the temperature rise of the sample, caused by the ac losses, is compared to the temperature rise caused by a reference heater and another in which the increase in power dissipation of the sample is compensated for by a reduction of the power dissipation in the heater. Typical results of the ac loss measurements are presented.
Mass analysis of negative ions in etching plasma
Authors: Mizutani Naoki , Nagata Yasushi , Kubo Akira , Hayashi Toshio
Published: July 2002

Negative ions in etching plasma were extracted from a plasma chamber and mass spectra were measured. For the extraction of the negative ions, the plasma sheath was broken by a cone-shaped extractor electrode which had an orifice on the tip. To avoid disturbing the plasma, the tip of the extractor electrode was slightly stuck out of an electrically earthed wall. To remove electrons from the extracted negative charged flux, a magnetic field was applied to the flux. By using the extractor electrode and the magnetic field for the removal of the electrons, the negative ions could be extracted efficiently and the mass spectra could be measured with low noise.
Proposed neutron diagnostics for Wendelstein 7-X stellarator
Authors: Elevant T. , Wolle B. , Weller A.
Published: July 2002

Deuterium plasmas in the Wendelstein 7-X stellarator are estimated to generate 1012–1016 neutrons per second. At this level, information on ion velocity distributions, ion densities, reaction fluctuations, and thermal reaction fractional contribution can be revealed from the neutron emission rate and energy distribution. A system of neutron counters, activation system, neutron spectrometer, and a profile monitor, as well as computer codes for interpretation and analysis are envisaged.
Special absorber neutron detector moderator assembly: A new detector system for flux measurements of collimated 2.5 MeV neutrons
Authors: Wolle B. , Bätzner R. , Baloui T. , Gonda G. , Klein H. , Wiegel B. , Wittstock J.
Published: July 2002

A new detector system has been developed for time resolved flux measurements of collimated D-D neutrons in large magnetic confinement fusion experiments. The novel detection concept, called the special absorber neutron detector moderator assembly, is to place a scatterer behind a collimator and to detect the scattered neutrons in a small Bonner sphere. The system has been optimized by means of the Monte Carlo neutron photon transport code (MCNP) simulations and is capable to be extended for a neutron profile camera. First tests and calibration measurements of a system using a 3 in. Bonner sphere have been carried out in the 2.5 MeV neutron field at the accelerator facility of the Physikalisch-Technische Bundesanstalt in Braunschweig. The numerical and experimental results are presented. The measurements differ from the calculated values by a factor of about 1.09. It is questionable if these discrepancies can be explained by differences in the shielding, moderator and detector characteristics employed in the experiment and those assumed in the calculation. This is highlighting the importance of experimentally validating numerical MCNP response function calculations wherever possible.
Microwave beam steerers for electronically scanned reflectometers (abstract)
Authors: Hsia R. P. , Zhang W.-M. , Jiang F. , Domier C. W. , Luhmann N. C.
Published: July 2002

One of the problems encountered in the application of reflectometry to fusion plasmas is that the transmit antenna must be aligned such that the reflected wave form is successfully collected by a suitably arranged receive antenna. This task is made even more difficult in the case of shaped plasmas, or when plasma motion is such that the incident wave is no longer normal to the plasma surface. One would ideally like to have antennas which may be steered in real time to compensate for changes in plasma shape and/or position. A program has been initiated at U.C. Davis to address this problem, and microwave beam steerers suitable for electronically scanned reflectometers have been developed. The approach taken has been to develop phased antenna array (PAA) concepts which operate over broad bandwidths. Laboratory test results of a proof-of-principle PAA system will be presented, along with a description of ongoing research activities by U.C. Davis in this field.
Neutron penumbral aperture images of inertial confinement fusion targets achieve 60 μm resolution (abstract)
Authors: Lerche R. A. , Ress D. , Ellis R. J. , Lane S. M.
Published: July 2002

Images formed by 14 MeV neutrons emitted from the core of inertial confinement fusion targets demonstrate 60 μm resolution for the penumbral aperture imaging system used in our 1988 experiments. Hohlraums containing deuterium–tritium filled capsules were irradiated at the Nova Laser Facility and produced images with detector limited resolution. Neutron yields ranged from 5×1010 to 2×1011. The results imply that convolution of the aperture point spread function with the neutron emitting region of the target core is less than 40 μm. Images produced by the indirect-drive hohlraum targets are compared with previously reported images of high-yield (1×1013) exploding-pusher targets that show 150 μm (full width half maximum) diameters for the emitting region.
Measurements of charged-particle fusion yields and ratios from Omega (abstract)
Authors: Li C. K. , Hicks D. G. , Seguin F. H. , Petrasso R. D. , Soures J. , Knauer J. P. , Phillips T. W. , Sangster T. C. , Cable M. D. , Bernat T.
Published: July 2002

We have recently conducted a series of experiments on Omega in which we utilized a charged-particle spectrometer. It consists of a 7.6 kG magnet, CR-39 track for particle detection, and an assortment of range filters to either discriminate against or emphasize certain particles. Because of excellent particle selectivity and energy resolution, the spectrometer can accurately measure the ratios of various fusion products from a single shot. Among other uses, these ratios will be used to determine ion temperatures.
An automated, externally heated opposed anvil high pressure–high temperature system for electrical resistivity studies
Authors: Mondal T. K. , Murugavel S. , Asokan S.
Published: July 2002

A simple, externally heated opposed (Bridgman) anvil system has been developed for electrical resistivity measurements up to 8 GPa pressure and 400 °C. The whole system is automated, in which the application and measurement of pressure and heating of the sample are undertaken using an IBM PC and associated electronic and mechanical hardware. The system developed has a pressure control of about ±1% and temperature control better than ±2%. The setup has been calibrated using the high pressure–high temperature transitions in the electrical resistivity of Bi and Yb. The usefulness of the system developed has been demonstrated, by studying the resistivity behavior of glassy chalcogenide semiconductors at high pressure and high temperature.
Precision of quasi-optical null-balanced bridge techniques for transmission and reflection coefficient measurements
Authors: Hadjiloucas S. , Bowen J. W.
Published: July 2002

The precision of quasioptical null-balanced bridge instruments for transmission and reflection coefficient measurements at millimeter and submillimeter wavelengths is analyzed. A Jones matrix analysis is used to describe the amount of power reaching the detector as a function of grid angle orientation, sample transmittance/reflectance and phase delay. An analysis is performed of the errors involved in determining the complex transmission and reflection coefficient after taking into account the quantization error in the grid angle and micrometer readings, the transmission or reflection coefficient of the sample, the noise equivalent power of the detector, the source power and the post-detection bandwidth. For a system fitted with a rotating grid with resolution of 0.017 rad and a micrometer quantization error of 1 μm, a 1 mW source, and a detector with a noise equivalent power 5×10−9 W Hz−1/2, the maximum errors at an amplitude transmission or reflection coefficient of 0.5 are below ±0.025.
Readout electronics for position-sensitive gas filled detectors at the European Synchrotron Radiation Facility
Authors: Hervé Christian , Caër Thierry Le
Published: July 2002

One- or two-dimensional gas filled detectors based on the space-time conversion by the delay line readout principle are in use at several European Synchrotron Radiation Facility (ESRF) beam lines. Presented is a description of the building blocks of the readout electronics, which rely on a comprehensive set of boards developed at ESRF. Those boards are compliant with the VME industrial standard. In particular a new VME time-to-digital converter is detailed. It features a bin size of 400 ps (250 ps on sorted out components), a measurement range of 14 bits, a fast throughput of 2×106 event/s and a sophisticated built-in pile-up rejection logic. A VME histogramming module, closely coupled to the time-to-digital converter, works at a sustained acquisition rate of 2×106 event/s. Those electronics are operating reliably at several ESRF beam lines.
Linewidth measurements of the JET energetic ion and alpha particle collective Thomson scattering diagnostic gyrotron
Authors: Machuzak John S. , Woskov Paul P. , Fessey John A. , Hoekzema J. A. , Egedal Jan , Bindslev Henrik , Roberts Peter , Stevens Andrew , Davies Paul , Gatcombe Christopher , Hughes Thomas P.
Published: July 2002

Spectral purity of the transmitter source of a collective Thomson scattering (CTS) system is vitally important to insure that measured signals only originate from the plasma and not from stray source light. A number of high power (up to 500 kW), 140 GHz gyrotron tubes used with the Joint European Torus (JET) CTS system have been found to have one or more spurious modes and many harmonics in the output spectrum. The CTS diagnostic receiver system was used to make measurements of the gyrotron spectrum. It was comprised of a homodyne part from MIT for frequency sidebands <500 MHz, and a heterodyne part constructed at JET for frequency sidebands from 0.1 to 6 GHz. One tube at high power produced a strong 25 MHz mode and its harmonics to large frequency offsets, unsuitable for CTS measurements. Only at reduced power of approximately 100 kW was this tube’s spectrum sufficiently clean for CTS. Another tube at JET operated at 500 kW output power with only low level parasitic modes, indicating that higher power gyrotrons may be available for future alpha particle measurements. The main receiver was tested with a low power test setup which simulated the gyrotron stray source light, the thermal ion feature and plasma electron cyclotron emission.
An improved surface plasmon resonance imaging apparatus
Authors: Lyon L. Andrew , Holliway William D. , Natan Michael J.
Published: July 2002

The design, construction, and initial use of an improved surface plasmon resonance imaging instrument are described. The instrument construction allows for introduction of large samples (50×50 mm) and is arranged with a unique horizontal sample geometry. This horizontal geometry provides for the eventual introduction of standard robotics both for substrate handling and liquid delivery, as with other commercialized analytical imaging techniques. The versatile optical train makes the instrument ideal for a wide range of sample sizes and provides for variable lateral resolution. Very small variations in colloidal Au coverage are detected on a patterned substrate, thereby demonstrating the utility of colloidal Au as a surface plasmon resonance imaging contrast reagent.
Variation of the thermovoltage across a vacuum tunneling barrier: Copper islands on Ag(111)
Authors: Rettenberger A. , Baur C. , Läuger K. , Hoffmann D. , Grand J. Y. , Möller R.
Published: July 2002

If there is a temperature difference between tip and sample of a scanning tunneling microscope a thermovoltage is generated which is very sensitive to the electronic states involved in the tunneling process. This has been used, e.g., to distinguish between different metals of a heterogeneous metallic surface. To demonstrate the capability of this method it has been applied to copper islands on a Ag(111) surface. Knowing the thermopower for chemically homogeneous silver and copper surfaces of −45 and −15 μV/K, respectively, islands of copper on the silver substrate can be well identified with a lateral resolution of 1 nm.
Surface ripples, crosshatch pattern, and dislocation formation: Cooperating mechanisms in lattice mismatch relaxation
Authors: Albrecht M. , Christiansen S. , Michler J. , Dorsch W. , Strunk H. P. , Hansson P. O. , Bauser E.
Published: July 2002

We study the interplay of elastic and plastic strain relaxation of SiGe/Si(001). We show that the formation of crosshatch patterns is the result of a strain relaxation process that essentially consists of four subsequent stages: (i) elastic strain relaxation by surface ripple formation; (ii) nucleation of dislocations at the rim of the substrate followed by dislocation glide and deposition of a misfit dislocation at the interface; (iii) a locally enhanced growth rate at the strain relaxed surface above the misfit dislocations that results in ridge formation. These ridges then form a crosshatch pattern that relax strain elastically. (iv) Preferred nucleation and multiplication of dislocations in the troughs of the crosshatch pattern due to strain concentration. The preferred formation of dislocations again results in locally enhanced growth rates in the trough and thus leads to smoothing of the growth surface.
Electron beam ion sources and traps (invited)
Authors: Becker Reinard
Published: July 2002

The electron beam method of stepwise ionization to highest charge states has found applications in electron beam ion sources (EBISs) for accelerators and atomic physics collision experiments as well as in electron beam ion traps (EBITs) for x-ray and mass spectroscopy. A dense and almost monoenergetic electron beam provides a unique tool for ionization, because radiative recombination by slow electrons is negligible and charge exchange is almost avoided in ultrahigh vacua. These are essential differences to electron cyclotron resonance ion sources with inevitable low energy electrons and comparatively high gas pressure. The distinction between EBIS and EBIT as genuine devices has become meaningless, because EBISs may work as traps and almost all EBITs are feeding beamlines for external experiments. More interesting is to note the diversification of these devices, which demonstrates that a matured technology is finding dedicated answers for different applications. At present we may distinguish six major lines of development and application: high current EBISs for upcoming hadron colliders, super EBITs in the energy range above 300 keV for quantum electrondynamics tests, inexpensive and small EBISTs for atomic physics studies, a highly efficient EBIS with oscillating electrons, MEDEBIS for tumor therapy with C6+, and charge breeding in facilities for exotic radioactive beams.
High-current microwave ion source for wide-energy-range O+ ion implantation
Authors: Tokiguchi K. , Seki T. , Ito J. , Sato T. , Mera K.
Published: July 2002

A high-current microwave ion source which is used for O+ ion implantation in separation by implanted oxygen (SIMOX) wafer fabrication is presented. The source consists of a new transform waveguide which efficiently propagates a 2.45 GHz microwave power into the ion source, a cylindrical plasma chamber of 90 mm in diameter, and a multiaperture extraction electrode system. The extracted beams are mass separated and then postaccelerated up to 200 keV. Ion source operates stably for a long time and the microwave absorption efficiency is as high as 80%. A total extraction current of 240 mA is obtained at the extraction voltage of 50–60 kV and the mass-separated O+ current reaches about 100 mA at the same extraction voltage. The data show that the ion source has a good potential to provide 100 mA-class O+ ion beams stably in the wide energy range demanded for SIMOX ion implantation.
A 13.56 MHz multicusp ion source for high intensity Ar beam
Authors: Boonyawan D. , Chirapatpimol N. , Sanguansak N. , Vilaithong T.
Published: July 2002

A 13.56 MHz radio frequency (rf) inductively coupled multicusp ion source has been developed for producing an intense argon beam with current density in excess of 30 mA cm−2. The source chamber is a 10 cm diam aluminum cylinder surrounded by 20 rows of 3.5 kG Sm–Co5 magnets which form a longitudinal line-cusp field configuration. The rf antenna coil, placed inside the source chamber, is made of a braided wire threaded through a two turn pyrex tube 6 cm in diameter to prevent electrical leakage and ion sputtering. A 10:1 turns-ratio matching transformer is used to match the 50 Ω output impedance of the rf generator to the impedance of the plasma load. Preliminary measurements were carried out with a single- and four-hole aperture extracting system using argon gas. For single-hole extraction with pressure at 5 mTorr and rf power at 500 W, the ion current density was 27 mA cm−2. Under the same operating condition, a four-hole extracting system could achieve almost the same amount of current density of 25 mA cm−2.
Extreme ultraviolet–vacuum ultraviolet spectrum detection using image plates
Authors: Ben-Kish A. , Fisher A. , Cheifetz E. , Schwob J. L.
Published: July 2002

A new detection system for extreme ultraviolet (XUV) and vacuum ultraviolet (VUV) spectroscopic measurements, in the energy range of 7–2500 eV, is demonstrated. A photonstimulated luminescence mechanism in BaFBr:Eu2+, previously used in image plates (IPs) for hard x rays and particle beam detection, is used for detecting the XUV–VUV spectra. The IP detection system proved to be one to two orders of magnitude more sensitive than conventional photographic glass plates. The measured dynamic range of the IP system (four to five orders of magnitude) is wider than any other available XUV recording media. The internal resolution of the IP system (50 μm) is slightly lower than photographic glass plate resolution, restricted by scattering processes in the IP during their readout procedure. Theoretically, much higher resolution (∼5 μm) could be obtained in the XUV–VUV region by using thinner IPs with better scanning systems. Image plates are flexible, easy to handle, and reusable. No dark room loading and developing conditions are needed and good reproducibility is obtained. All these characteristics make the image plate a very suitable recording medium for XUV–VUV spectroscopy.
Emissivity of B-implanted and annealed silicon
Authors: Takeuti D. F. , Timans P. J. , Ahmed H.
Published: July 2002

Isothermal electron beam heating has been used to anneal ion-implanted silicon samples and the changes in the spectral ε(λ,T) and total hemispherical εTot(T) emissivities caused by damage annealing and dopant activation have been monitored in situ. Free carrier absorption effects have been observed after annealing of a B-implanted sample, resulting in an increase of ε(λ,T) in the semitransparent region and an increase of εTot(T). An increase of normalized emissivity at 800 °C was also observed.
Measurement of the ac power loss of (Bi,Pb)2Sr2Ca2Cu3Ox composite tapes using the transport technique
Authors: Fleshler S. , Cronis L. T. , Conway G. E. , Malozemoff A. P. , Pe T. , McDonald J. , Clem J. R. , Vellego G. , Metra P.
Published: July 2002

The transport self-field ac loss voltages of (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) multifilamentary tapes depend strongly on the voltage lead configuration. We have measured the loss voltage as a function of the measuring circuit loop size defined by the voltage leads and the tapes for well-defined lead geometries. The loss signal was found to reach a limiting value when the length of the loop transverse to the tape was several times the tape width. This limiting voltage represents the ‘‘true’’ self-field ac loss as predicted by new theoretical analysis.
Room-temperature photoluminescence of erbium-doped hydrogenated amorphous silicon
Authors: Bresler M. S. , Gusev O. B. , Kudoyarova V. Kh. , Kuznetsov A. N. , Pak P. E. , Terukov E. I. , Yassievich I. N. , Zakharchenya B. P. , Fuhs W. , Sturm A.
Published: July 2002

A comparison of the photoluminescence of Er-doped hydrogenated amorphous silicon and crystalline silicon a-Si:H(Er) and c-Si(Er), is presented. It is shown that a-Si:H(Er) exhibits efficient room-temperature photoluminescence at 1.537 μm which is as strong as the emission from optimized c-Si(Er) at 2 K. Most remarkably, there is practically no temperature quenching of the emission intensity in the range 2–300 K. The experiments suggest that the lifetime connected with the Er-induced emission is considerably shorter in a-Si:H(Er) than in c-Si(Er) which may be responsible for the different dependences of the photoluminescence intensity on the temperature, chopping frequency, and excitation power.
Unified thermodynamic equation-of-state for porous materials in a wide pressure range
Authors: Wu Qiang , Jing Fuqian
Published: July 2002

Assuming that the specific heat at constant pressure CP, is simply dependent on the pressure or remains constant, a new thermodynamic equation-of-state (EOS), which is suitable for the analysis in the isobaric plane, is derived in this letter. Combining with the Rankine–Hugoniot relations, the new EOS can be used to predict the Hugoniot behavior of materials with different initial porosities over a shock pressures range from a few kbar to a few Mbar. The calculated Hugoniots from this model are in good agreement with the reported experimental results.
Subpicosecond electrical pulse generation by edge illumination of silicon and indium phosphide photoconductive switches
Authors: Wang Chia-Chi , Currie Marc , Sobolewski Roman , Hsiang Thomas Y.
Published: July 2002

Using a femtosecond pulsed laser, ultrafast electrical pulses were optoelectronically generated on silicon and indium phosphide by edge illumination of a coplanar transmission line. Backing up theory with experiment, we demonstrate that this pulse-generation method is material independent, thus providing a powerful tool for broadband characterization of devices made on a wide range of semiconductor substrates. We also demonstrate that edge illumination enables the generation of 550 fs electrical pulses on indium phosphide and 800 fs pulses on silicon—the fastest pulses to date on bulk silicon.
Raman scattering of porous structure formed on C+-implanted silicon
Authors: Wu Xing-Long , Yan Feng , Bao Xi-Mao , Li Ning-Sheng , Liao Liang-Sheng , Zhang Ming-Sheng , Jiang Shu-Sheng , Feng Duan
Published: July 2002

Raman spectra of the porous structure with intense blue emission formed on C+-implanted silicon were examined using a 488 nm line of Ar+ laser. A Raman peak with full width at half-maximum of 37 cm−1 was obtained at about 492 cm−1. No Raman signals related to the β-SiC were detected. The experimental result indicates that the porous structure mainly consists of Si nanometer crystallites. The existence of β-SiC precipitates with nanometer sizes may be beneficial to the reduction of crystallite sizes and strengthen the Si skeleton, which will lead to an increase in the energy band gap of Si to the blue light emission. Using a model of phonon confinement, the obtained Raman spectra could be fitted on the basis of Si quantum crystallites and the average crystallite size was estimated to be 1.4 nm.
Oxide mediated epitaxy of CoSi2 on silicon
Authors: Tung R. T.
Published: July 2002

Uniform, single-crystal CoSi2 layers have been grown on Si by the technique of oxide mediated epitaxy (OME). Deposition of a thin layer of cobalt (1–3 nm) onto surfaces covered with a thin silicon oxide layer and annealing at 500–700 °C led to the growth of epitaxial, essentially uniform, CoSi2 layers on the (100), (110), and (111) surfaces of Si. The nucleation and growth of silicide apparently occurred subsurface, leaving the silicon oxide layer largely on the surface of the silicide after the growth. On all surfaces, thicker (10–30 nm), excellent quality, CoSi2 single-crystal thin films have been grown by repeated growth sequences. Experimental results are presented along with a discussion on the possible roles played by the thin oxide layer in promoting the epitaxial growth of silicide.
Probe-surface interaction in near-field optical microscopy: The nonlinear bending force mechanism
Authors: Gregor M. J. , Blome P. G. , Schöfer J. , Ulbrich R. G.
Published: July 2002

The probe-surface interaction underlying the ‘‘shear-force’’ distance control commonly used in near-field microscopy has been studied in detail by measuring dither resonance profiles and approach curves in vacuum and liquid helium. Simulations based on a nonlinear oscillator model considering the probe geometry, its elastic properties, adiabatic short-range probe-surface contact, and the surface tilt angle, are in excellent agreement with the experiments. We prove conclusively that a nonlinear bending force mechanism with parametric mode conversion is responsible for the observed phenomena.
Visible luminescence from nanocrystalline silicon films produced by plasma enhanced chemical vapor deposition
Authors: Edelberg Erik , Bergh Sam , Naone Ryan , Hall Michael , Aydil Eray S.
Published: July 2002

Thin nanocrystalline silicon (nc-Si) films deposited by plasma enhanced chemical vapor deposition (PECVD) exhibited room-temperature photoluminescence in the visible range of the electromagnetic spectrum. High resolution transmission electron microscopy revealed that the films are made of Si crystals with dimensions 2–15 nm. The photoluminescence spectra of the nc-Si films were similar to the spectra observed from porous silicon produced by anodization and electrochemical dissolution of crystalline Si. This similarity suggests that the luminescence mechanism of nc-Si films is similar to the mechanism of light emission from porous silicon. The ability to manufacture luminescent Si films by methods which are compatible with the current Si based technology, such as PECVD, can provide new possibilities in the realization of optoelectronic devices.
Photochromic coloration of WO3 with visible light
Authors: Bechinger C. , Wirth E. , Leiderer P.
Published: July 2002

Thin amorphous films of tungsten oxide (WO3) are well known to change their optical absorption behavior upon light exposure, usually referred to as photochromic effect. Since the formation of color centers is closely related to the optical creation of electron-hole pairs the sensitivity of the photochromic effect in WO3 is limited to energies above its band-gap energy of 3.25 eV, corresponding to the near-ultraviolet range. We will demonstrate that in case of a thin cadmium sulfide (CdS) layer underneath the tungsten oxide film the sensitivity of photochromism is shifted into the visible range. This result is interpreted in terms of charge carrier injection from the CdS into the WO3. Apart from a more detailed understanding of the photochromic effect this may have also relevance for technical applications.
Uniparabolic mirror grading for vertical cavity surface emitting lasers
Authors: Lear K. L. , Schneider R. P.
Published: July 2002

We report details of mirror grading profiles for high efficiency vertical cavity surface emitting lasers. The mirrors provide low vertical resistance in conjunction with improvements in optical reflectivity, thermal conductivity, and lateral electrical conductivity in comparison to earlier grading profiles. The enhancement of these properties is verified by a comparison of thermal resistance and total electrical resistance for lasers of varying size.
Atomistic calculations of ion implantation in Si: Point defect and transient enhanced diffusion phenomena
Authors: Jaraiz M. , Gilmer G. H. , Poate J. M. , de la Rubia T. D.
Published: July 2002

A new atomistic approach to Si device process simulation is presented. It is based on a Monte Carlo diffusion code coupled to a binary collision program. Besides diffusion, the simulation includes recombination of vacancies and interstitials, clustering and re-emission from the clusters, and trapping of interstitials. We discuss the simulation of a typical room-temperature implant at 40 keV, 5×1013 cm−2 Si into (001)Si, followed by a high temperature (815 °C) anneal. The damage evolves into an excess of interstitials in the form of extended defects and with a total number close to the implanted dose. This result explains the success of the ‘‘+1’’ model, used to simulate transient diffusion of dopants after ion implantation. It is also in agreement with recent transmission electron microscopy observations of the number of interstitials stored in (311) defects.
Defect and transport properties of nanocrystalline CeO2−x
Authors: Chiang Y.-M. , Lavik E. B. , Kosacki I. , Tuller H. L. , Ying J. Y.
Published: July 2002

It is shown that unique defect thermodynamics and transport properties result for oxides of a few nanometers crystallite size. Fully-dense CeO2−x polycrystals of ∼10 nm grain size were synthesized, and their electrical properties compared with those of samples coarsened from the same material. The nanocrystals showed reduced grain boundary resistance, 104 higher electronic conductivity, and less than one-half the heat of reduction of its coarse-grained counterpart. These properties are attributed to a dominant role of interfacial defect formation.
Thermal nitridation enhanced diffusion of Sb and Si(100) doping superlattices
Authors: Mogi T. K. , Thompson Michael O. , Gossmann H.-J. , Poate J. M. , Luftman H. S.
Published: July 2002

Depth dependent nitridation enhanced diffusion (NED) of Sb was investigated by annealing Si(100) doping superlattice (DSL) structures in NH3 at 810–910 °C for 15–180 min. These multilayered DSLs consisted of six 10 nm wide Sb doping spikes spaced 100 nm apart. Antimony NED, attributed to vacancy injection, indicated vacancy supersaturation values of 3–5. From the spatial decay of Sb NED, lower bounds for vacancy diffusivities of (7.9±1.4)±10−14, (1.2±0.2)×10−12, and 2.1×10−11 cm2/s were obtained at 810, 860, and 910 °C, respectively. Evidence of trap limited vacancy diffusivity was observed.
Novel spectromicroscopy: Pt–GaP studies by spatially resolved internal photoemission with near-field optics
Authors: Almeida J. , dell’Orto Tiziana , Coluzza C. , Margaritondo G. , Bergossi O. , Spajer M. , Courjon D.
Published: July 2002

The combination of internal photoemission and near-field optics is proposed as a generally applicable approach to study the lateral variations of solid interface properties such as energy barriers and electron-hole recombination rates. A successful test on Pt–GaP is described in which topographic and nontopographic phenomena are revealed, in particular recombination rate variations and small lateral changes of the Schottky barrier height.
Oxygen gettering and precipitation at MeV Si+ ion implantation induced damage in silicon
Authors: Agarwal Aditya , Christensen K. , Venables D. , Maher D. M. , Rozgonyi G. A.
Published: July 2002

The interaction of intrinsic oxygen in Czhochralski silicon with implantation damage induced by 2.0 MeV Si+ ions has been investigated as a function of annealing temperature and time. Four distinct regions of oxygen localization are revealed by secondary ion mass spectrometry following sample annealing. The different regions are correlated with either a near surface vacancy-rich region or the buried layer of extended defects near the projected range. The relative concentration of oxygen in each region depends on the competition between oxygen gettering in each region and out-diffusion to the surface. It has been established, using quasikinematical and dynamical contrast transmission electron microscopy imaging techniques, that the oxygen in regions containing extended dislocations is in the form of fine precipitates. The precipitates decorate both the dislocations and, for faulted loops, the stacking fault planes.
Photoluminescence wandering in single CdSe nanocrystals
Authors: Blanton Sean A. , Hines Margaret A. , Guyot-Sionnest Philippe
Published: July 2002

Low temperature two-photon fluorescence excitation microscopy was used to obtain fluorescence spectra of single CdSe colloidal nanocrystals or quantum dots. The fluorescence spectra reveal large, 0.02 eV shifts of the peak emission wavelength on times of the order of 100 s were also observed in some instances. We attribute this behavior to excited state coupling to photoinduced changes at the nanocrystal surface.
Epitaxial MnGa/(Mn,Ga,As)/MnGa trilayers: Growth and magnetic properties
Authors: Van Roy W. , Akinaga H. , Miyanishi S. , Tanaka K. , Kuo L. H.
Published: July 2002

Epitaxial ferromagnet/semiconductor/ferromagnet sandwiches with the nominal structure δ Mn60Ga40/GaAs/δ Mn54Ga46 have been grown on GaAs(001) by molecular beam epitaxy, with spacer layer thicknesses ranging from 2 to 19 monolayers (ML) GaAs nominally. A strong antiferromagnetic coupling field μ0Hs=−12 to −39 mT at room temperature is observed for spacer layers of 4–14 ML GaAs nominally, a weaker ferromagnetic coupling of +1 to +7 mT exists outside of this thickness region. Magnetic contamination of the spacer layer and the inclusion of antiferromagnetic Mn2As cannot be ruled out.
Tuning of ZnSe–GaAs band discontinuities in heterojunction diodes
Authors: Pellegrini Vittorio , Börger Marco , Lazzeri Michele , Beltram Fabio , Paggel Jens J. , Sorba Lucia , Rubini Silvia , Lazzarino Marco , Franciosi Alfonso , Bonard Jean-Marc , Ganiére Jean-Daniel
Published: July 2002

The conduction band offset in ZnSe/GaAs n-p heterodiodes was determined from measurements of the low-temperature tunneling current of photoinjected carriers. We found widely different discontinuities for heterojunctions fabricated with different Zn/Se flux ratios, with conduction band offsets as high as 0.75 eV for Se-rich interfaces, and as low as 0.26 eV for Zn-rich interfaces.
Scanning magnetoresistance microscopy
Authors: Yamamoto S. Y. , Schultz S.
Published: July 2002

We have developed a new scanning magnetic microscopy which uses commercial magnetoresistive (MR) record/playback heads as sense probes. Two-dimensional magnetic images are constructed by bringing the MR head into physical contact with the sample, and then acquiring MR voltage while the head is raster scanned using a high resolution (∼1 nm), linearized positioning stage. With currently available MR heads, an upper bound on the spatial resolution is 0.1×2.0 μm. This technique has broad applications beyond the magnetic storage media for which these heads were designed. In addition to magnetic imaging, this instrument can also be used to evaluate contact record and playback processes.
Electroluminescence from Au/Si nitride film/Si with the film prepared by electron cyclotron resonance method
Authors: Li A. P. , Zhang Lidong , Zhang Y. X. , Qin G. G. , Wang Xin , Hu X. W.
Published: July 2002

We use only nitrogen as the reaction gas to deposit on the cleaned Si wafer an extra-thin Si nitride film (∼40 Å) by electron cyclotron resonance method. Electroluminescence (EL) with its peak wavelength at about 7000 Å from the semitransparent Au/extra-thin Si nitride film/p-Si structure has been detected. The effects of forward bias and annealing on the EL have been studied.
Nonlinear optical properties of silicon nanoclusters
Authors: Vijayalakshmi S. , George M. A. , Grebel H.
Published: July 2002

The nonlinear and linear optical responses of Si nanoclusters at λ=355 nm were measured. The nanoclusters were laser ablated on quartz substrates. χ(3) values as high as 2.28×10−5 esu (as measured by the Z-scan technique) and lifetime as long as 143 ns were measured for clusters of an average size of 11 nm. The optical properties were strongly correlated with the clusters’ sizes.
Dual frequency cholesteric light shutters
Authors: Xu Ming , Yang Deng-Ke
Published: July 2002

We developed a dual frequency cholesteric light shutter which utilizes a cholesteric liquid crystal; the dielectric anisotropy of the material changes from positive to negative when the frequency of applied voltage is increased. The shutters are switched to the transparent homeotropic texture by low frequency voltages, and switched to the reflecting planar texture by high frequency voltages. We designed a waveform which reduced the transition time from the homeotropic texture to the planar texture to less than 100 ms.
Temperature measurements using pulsed photothermal radiometry and silver halide infrared optical fibers
Authors: Eyal O. , Scharf V. , Katzir A.
Published: July 2002

A novel technique for measuring temperature, based on pulsed photothermal radiometry and analysis of the spectral and temperature dependence of Planck’s blackbody equation, is described. In this technique a body is irradiated by a laser pulse and its temperature inferred from the time dependence of the emitted infrared signal curve. This technique was used for near ambient temperature measurements using a CO2 laser, an infrared detector, and infrared transmitting silver halide optical fibers. The experimental results are consistent with theory. This technique is independent of changes in emissivity or geometric factors and it will be useful for accurate and fast noncontact temperature measurements.
Influence of Γ-X resonances on Γ1 ground state electron occupation in type-I GaAs/AlAs superlattice
Authors: Hosoda M. , Tominaga K. , Ohtani N. , Mimura H. , Nakayama M.
Published: July 2002

The influence of Γ-X resonances on Γ1 ground state electron occupation in type-I direct-gap GaAs/AlAs superlattices was studied under an applied electric field. Photoluminescence and photocurrent-voltage characteristics showed anomalous behaviors at corresponding Γ-X resonance voltages. The experimental results demonstrate that Γ1-Xn transfer degrades the sweep-out of carriers, while X1-Γ2 transfer promotes it.
Room temperature operation of Si single-electron memory with self-aligned floating dot gate
Authors: Nakajima Anri , Futatsugi Toshiro , Kosemura Kinjiro , Fukano Tetsu , Yokoyama Naoki
Published: July 2002

We have developed an excellent fabrication method for a Si single-electron field effect transistor memory device having a self-aligned floating dot gate. This device demonstrates single electron memory operation at room temperature. The ability to precisely control the size and position of the floating dot gate and the channel indicates the feasibility of practical single-electron memory.
Monolithic carbazole oligomer exhibiting efficient photorefractivity
Authors: Zhang Yadong , Wang Liming , Wada Tatsuo , Sasabe Hiroyuki
Published: July 2002

A multifunctional conjugated carbazole trimer has been designed as a monolithic photorefractive material. The photorefractive properties of this carbazole trimer were demonstrated by a two-beam coupling experiment at a wavelength of 532 nm. An asymmetric energy transfer between the two beams has been observed. A relatively large two-beam coupling net gain coefficient and a four-wave mixing diffraction efficiency have been obtained.
Quantification of magnetic force microscopy using a micronscale current ring
Authors: Kong Linshu , Chou Stephen Y.
Published: July 2002

Metal rings with inner diameters of 1 and 5 μm, fabricated using electron-beam lithography, were used to calibrate magnetic force microscopy (MFM). A MFM tip’s effective magnetic charge, q, and effective magnetic moment along the tip’s long axis, mz, can be determined from the MFM signal of the ring at a different scan height and a different electric current in the ring. The magnetic moments in the directions transverse to the tip’s long axis were estimated by a straight current wire. It was found that for a Si tip coated with 65 nm cobalt on one side, q is 2.8×10−6 emu/cm, mz is 3.8×10−9 emu, and mx and my are in the order of 10−13 emu, which are negligible compared with mz. Furthermore, the MFMs sensitivity to the second derivative of the magnetic field was determined from the minimum ring current for a measurable MFM signal to be 0.1 Oe/nm2.
Amorphous carbon thin films containing benzene rings for use as low-dielectric-constant interlayer dielectrics
Authors: Endo Kazuhiko , Tatsumi Toru
Published: July 2002

The effect on the thermal and dielectric properties of incorporating benzene rings in hydrogenated amorphous carbon (a-C:H) films was investigated. The benzene rings were introduced into a-C:H films by using plasma-enhanced chemical vapor deposition and aromatic source compounds. The a-C:H film that contained benzene rings had thermal stability up to 400 °C and a low-dielectric constant of 3.0. The difference in the dielectric constant and thermal stability of a-C:H films appeared to be due to the hydrogen concentration of the films.
Synthesis of gallium nitride quantum dots through reactive laser ablation
Authors: Goodwin Timothy J. , Leppert Valerie J. , Risbud Subhash H. , Kennedy Ian M. , Lee Howard W. H.
Published: July 2002

Nanocrystalline GaN was synthesized through reactive laser ablation of gallium metal in a N2 atmosphere. X-ray diffraction, selected-area electron diffraction, and transmission electron microscopy measurements show that the GaN crystallites are as small as 2 nm in diameter, and follow a log-normal size distribution with a mean particle diameter of 12 nm. Size-selective photoluminescence and photoluminescence excitation spectroscopy reveal a continuous range of blueshifted band-edge emissions and absorptions starting from the bulk value for gallium nitride and continuing to below 300 nm. These results are consistent with a GaN particle size distribution that encompasses regions above and below the excitonic-Bohr radius of GaN, such that the GaN material shows combined bulk and quantum confined optical properties.
Color variable bipolar/ac light-emitting devices based on conjugated polymers
Authors: Wang Y. Z. , Gebler D. D. , Fu D. K. , Swager T. M. , Epstein A. J.
Published: July 2002

There is increased interest in developing color variable light emitting devices. We report here the fabrication of color variable bipolar/ac light-emitting devices based on conjugated polymers. The devices consist of blends of pyridine-phenylene and thiophene-phenylene based copolymers sandwiched between the emeraldine base form and the sulfonated form of polyaniline. ITO and Al are used as electrodes. The devices operate under either polarity of driving voltage with different colors of light being emitted, red under forward bias, and green under reverse bias. The relative fast time response allows the rapid switching of colors and ac operation.
Blue green stimulated emission from a high gain conjugated polymer
Authors: Zenz C. , Graupner W. , Tasch S. , Leising G. , Müllen K. , Scherf U.
Published: July 2002

An optically pumped waveguide structure has been fabricated with methyl substituted conjugated laddertype poly(paraphenylene) as the active material. The choice of the device parameters allows one to observe a high directionality, a small beam divergence, a complete linear polarization, and a linewidth with an upper limit of 1.7 nm at a considerable low threshold of 3 kW/cm2 at room temperature.
Photovoltaic quantum well infrared photodetectors: The four-zone scheme
Authors: Schneider H. , Schönbein C. , Walther M. , Schwarz K. , Fleissner J. , Koidl P.
Published: July 2002

We have investigated a particular class of photovoltaic quantum well intersubband photodetectors. Each period of the active region in these structures consists of four zones, namely an excitation zone, a drift zone, a capture zone, and a tunneling zone. The devices show pronounced photovoltaic behavior and high detectivities. In particular, the responsivity without external bias is substantially enhanced if resonant carrier capture is achieved due to an appropriate design of the capture zone.