bluuebunny/crossref_metadata_2025 huggingface dataset:
The novel surface science instrument: Double reflection electron emission microscope
Authors: Grzelakowski Krzysztof
Published: July 2002

A universal UHV instrument, the double reflection electron emission microscope (DREEM), for surface imaging, diffraction, and local (1 μm resolution) measurements is presented. DREEM consists of three fully electrostatic lens systems: electron gun column, immersion objective lens, and imaging column. The novel illumination system incorporates an electron microreflector in the back focal plane of the objective, where the perpendicular optical axes of the electron gun and imaging column cross. The electron microreflector consists of the tip of a (001)-oriented single-crystalline W wire with a face of area 200 μm2. The primary electrons of energy from 1 to 6 keV elastically reflect from the W tip surface and are decelerated between the objective and grounded sample to the desired impact energy from 0 eV to 5 keV. Numerous contrast mechanisms are expected for image formation with DREEM including topographic, magnetic, chemical (Auger, core level), phase shift, and work function. The instrument is capable of operating in low energy electron diffraction, mirror electron microscopy, low energy electron emission microscope, and photoelectron emission microscope modes. The first results obtained with the DREEM are presented.
Versatile cell for complex permittivity measurements on liquids
Authors: Halalay Ion C.
Published: July 2002

A disk type guarded measurement cell is described, which permits the determination of the complex permittivity of liquids with an accuracy of 0.5% or better. The cell has small residual circuit elements (4 nH and 20 mΩ) and behaves like an ideal capacitor for radius-to-electrode spacing ratios ranging from 15 to 135. Ruggedness and ease of use are achieved through a split cell design with a minimal number of parts and threads for assembly, as well as the attachment of fluid lines and electrical connections.
Low-noise, low drift, high precision linear bipolar (±10 V) voltage supply/reference for cryogenic front-end apparatus
Authors: Pessina Gianluigi
Published: July 2002

A very simple linear bipolar (±10 V) voltage supply/reference (VS/R) featuring very low noise has been implemented. The noise is about 1 μVpp in a 0.1–10 Hz bandwidth, becoming, for the −10 V supply only, 1.3 μVpp at 1.5 A. The VS/R is based on commercial devices and has been designed to face the stringent requirement of very low drift systems. It features very good line regulation, less than 10 mV over 10 V at 1.5 A supply current, and very low drift, between 3 and 8 ppm/°C; it also shows large power supply rejection ratio (PSRR), >120 dB. The VS/R presented includes also safety circuits, to protect itself and the electronic equipment to be supplied in an actual experimental condition. It is protected against inversion of polarity and against under and over voltage at its inputs, and has a foldback current limiting circuit which shuts down the whole system if the current absorption lasts for some time. These protecting circuits acts on both outputs (±10 V), to maintain always the symmetry. From an analysis made on the data extracted from the measured noise spectra, it was possible to measure the dynamic output impedance, found mainly inductive, with a value of the order of 1 mH. The dc PSRR has been improved by about 20 dB with respect to the performances of the devices used, thanks to a very simple circuit solution.
High-precision hydraulic Stewart platform
Authors: van Silfhout Roelof G.
Published: July 2002

We present a novel design for a Stewart platform (or hexapod), an apparatus which performs positioning tasks with high accuracy. The platform, which is supported by six hydraulic telescopic struts, provides six degrees of freedom with 1 μm resolution. Rotations about user defined pivot points can be specified for any axis of rotation with microradian accuracy. Motion of the platform is performed by changing the strut lengths. Servo systems set and maintain the length of the struts to high precision using proportional hydraulic valves and incremental encoders. The combination of hydraulic actuators and a design which is optimized in terms of mechanical stiffness enables the platform to manipulate loads of up to 20 kN. Sophisticated software allows direct six–axis positioning including true path control. Our platform is an ideal support structure for a large variety of scientific instruments that require a stable alignment base with high-precision motion.
Low-temperature atomic force microscope using piezoresistive cantilevers
Authors: Thomson R. E.
Published: July 2002

This article describes the design of an easy-to-operate low-temperature atomic force microscope (AFM) that incorporates piezoresistive cantilevers. The instrument is easier to build and to operate at cryogenic temperatures than AFMs based on laser deflection schemes or interferometers because no mechanical adjustments of the instrument are necessary after a change of temperature. The effects of thermal expansion on the AFM’s tip-to-sample distance are minimized by the use of a double tube scanner assembly. The design includes a simple mechanism that locks the sample holder in place as the temperature is lowered. This AFM is compact and rigid, enabling it to be used in a conventional cryogenic liquid-storage Dewar. All of the materials used in the construction of the AFM are ultra-high-vacuum compatible.
A micromechanical detector for molecular beams
Authors: Wicki Adrian , Marsico Vittorio , Kuhnke Klaus , Kern Klaus , Paratte Lionel , Schweizer Sandra , Renaud Philippe
Published: July 2002

We demonstrate the detection of a molecular beam by means of a micromechanical momentum transfer detector operated in vibrational resonance. With a sensitive surface area of 0.5×0.3 mm2 the small paddle allows us to detect a beam with 6.5×107 He atoms hitting the surface per second. The detector response time equals the damping time of the paddle oscillation of about 1 s. The detector is sensitive enough to measure intensities in molecular beam scattering experiments. The novel detection scheme has the potential to allow the development of a position sensitive molecular beam detector.
A novel method to characterize photorefractive damage in quasiphase-matched wavelength converters
Authors: Xu C. Q. , Okayama H. , Ogawa Y.
Published: July 2002

A novel two-beam method is proposed and applied for the first time, to characterize photorefractive damage (PRD) in a LiNbO3 quasiphase-matched (QPM) wavelength converter. In the proposed method, irradiation light from a Ti sapphire laser and a broadband probe beam from an erbium-doped fiber amplifier are coupled into a LiNbO3 QPM waveguide. The PRD effect caused by the irradiation is studied by monitoring the generated second-harmonic light spectrum of the probe light. It is shown that PRD in the LiNbO3 QPM waveguide can be qualitatively characterized by the proposed method, and relevant information relating to the QPM wavelength conversion can be extracted directly.
Lossless beam combiners for nearly equal laser frequencies
Authors: Haubrich D. , Dornseifer M. , Wynands R.
Published: July 2002

We discuss three ways to combine two laser beams with equal linear polarizations and very closely spaced frequencies into a single output beam containing up to 100% of the input power of each beam. One setup, a modified Mach–Zehnder interferometer, is examined in detail; it allows to adjust the combined output power electronically with the help of a simple servo loop. With off-the-shelf optical components we obtained a 98% efficiency.
Pulsed magnetic quadrupole lenses for high rigidity beams
Authors: Li G. , Czok U. , Kalimov A. , Winkler M. , Wollnik H.
Published: July 2002

New pulsed magnetic quadrupole lenses have been developed that can be used to focus pulsed ion beams of high rigidity. To reach sufficiently high flux densities we built such quadrupole lenses as optimized steel-free devices. Up to now a flux density of ≈ 12 T has been reached in a quadrupole of 22 mm aperture with a sufficient field quality. This value is higher than or comparable to values reached in superconducting quadrupole lenses or in pulsed plasma lenses.
Continuous heatable Langmuir probe for flowing afterglow measurements
Authors: Laubé Sylvain , Mostefaoui Toufik , Rowe Bertrand
Published: July 2002

A heatable Langmuir probe consisting of a continuous dc-heating-current loop of tungsten wire is presented. This technique is efficient to keep the probe surface clean for flowing afterglow measurements. In our experimental conditions, the perturbations on the electron density determination can be considered as very small. The measurement of the well-known rate for the dissociative recombination of O2+ shows that the gas surrounding the probe is not heated for estimated probe temperature up to 700 K.
A simple technique for height calibration for z piezo with Angstrom resolution of scanning probe microscopes
Authors: Pal S. , Banerjee S.
Published: July 2002

We present a simple method of preparing a “calibration standard” of nanometer order for the height calibration of z piezo scanner used in scanning probe microscopes. The calibration standard can be accurately characterized using the grazing incidence x-ray reflectivity technique. This method enables one to calibrate displacement/voltage (Å/V) of the z piezo scanner with Angstrom resolution.
Large-area ion source combining microwaves with inductively coupled plasma
Authors: Okuji S. , Sakudo N. , Hayashi K. , Okada M. , Onogawa T. , Maesaka T. , Nishiyama Y. , Toyoda K. , Yashima S. , Ishida T.
Published: July 2002

The semiconductor industry is growing rapidly and requires high technologies for nano-structure devices. Ion sources for manufacturing the next-generation semiconductor devices have been studied from the viewpoint of applications to material processing, such as ion beam assisted deposition, ion beam etching, and ion implantation. Recently, large-area ion sources which extract broad ion beams with multiapertures have come to be required not only for processing the size-growing wafers but also for industrial applications to nonsemiconductor materials. However, the uniformity of plasma density over the multiaperture electrodes has not met the requirements yet. We suggest a new method to improve the uniformity by superposing microwaves to an inductively coupled plasma source. Distributions of ion species in the plasma are measured with a quadrupole mass spectrometer which can be moved in vacuum perpendicularly to the beam extraction. The distributions of both plasma density and ion species in the source plasma as well as their properties over a large area are being studied and discussed.
Criterion for decrease of electric field at ionization point of liquid-metal ion sources
Authors: Gotoh Y. , Tsuji H. , Ishikawa J.
Published: July 2002

Criterion for decrease of electric field at the ionization point of liquid-metal ion sources has been derived. The argument is based on the equation of space-charge limited current with small charge approximation and the balance of electric field stress, with liquid flow and surface tension stress. The result was such that it is possible to decrease the electric field with an increase in the applied voltage, that is, the source current, under the condition of weaker dependence of current density on the electric field than that in the conventional low temperature field evaporation theory. The dependence of the ion current density on the electric field was calculated from the dependence of the angular current intensity on the electric field, assuming postionization theory. The result indicated that the dependence became almost proportional, which is surprisingly weak for field ion emission.
Theoretical analysis of the embedded layer formed by high-energy Au implantation into Si(II)
Authors: Nakagawa S. T. , Nakano S. , Ogiso H. , Iwaki M. , Hashimoto M. , Eckstein W.
Published: July 2002

We performed a high-energy and high-fluence ion implantation, expecting to fabricate micromachines. (100) Si was bombarded by 3.1 MeV Au2+ ion with a fluence of 1017/cm2 at 95 K. Then an embedded layer was extracted after chemical etching (30% KOH, at 333 K). The stoichiometric change was evaluated by both experiments and simulation using TRIDYN. The experiments showed, although qualitatively, that Au clustering occurred even at a temperature lower than had ever been reported. From a critical ion fluence, which is necessary to extract a material after etching, we estimate a local concentration to be 1.0–1.2 at. %, which caused a physicochemical change by Au doping. A probable model for the clustering is proposed. It is a nonthermal atomic transfer mechanism following the electronic excitation. Here the electronic stopping power just beneath the surface is 140 eV/Å, which is large enough to ionize valence electrons of Si. Also, a wide amorphized region supports an unstable electrostatic field, which should be produced by many odd-number member rings made of host(Si) atoms. Both ionization of Si and the unstable electrostatic field may most likely trigger the Au clustering.
New improvements on the Kansas State University cryogenic electron beam ion source, a user facility for low energy, highly charged ions
Authors: Stockli M. P. , Carnes K. , Cocke C. L. , DePaola B. D. , Ehrenreich T. , Fehrenbach C. , Fry D. , Gibson P. E. , Kelly S. , Lehnert U. , Needham V. , Reiser I. , Richard P. , Tipping T. N. , Walch B. , Cuquemelle A. , Doudna C. , Eastman B. , Kentsch U. , Schedler R. , Kobayashi N. , Matsumoto J. , Madzunkov S.
Published: July 2002

The Kansas State University cryogenic electron beam ion source supplies low energy ion beams to users of the Department of Energy user facility for highly charged ions. The ions escape the source with an initial energy between 1.6 and 5 kV per charge and are analyzed in a 90° dipole magnet located on the high voltage platform. When leaving the platform the ions can be accelerated by up to 160 kV per charge or can be decelerated to about 20% of their initial energy, covering 2.5 orders of magnitude. We are in the process of adding another order of magnitude to the range of available ion energies as a newly installed lens allows for deceleration down to a very few percent of the initial energy. In addition we present the current microbunching and chopping system which has been substantially improved over the past 2 yr.
Production of Ce negative ions in a Cs sputter ion source
Authors: Saitoh Y. , Yotsombat B. , Mizuhashi K. , Tajima S.
Published: July 2002

We have developed a new technique for stable production of lanthanide negative ions in a cesium sputter ion source without damage to the ionizer. Lanthanide elements sticking to a cesium ionizer deteriorate an ionization efficiency of the ionizer because of their characteristics such as low vapor pressures and low work functions. We have resolved the problem to make a sputter cathode that has a predrilled double layer structure. Cerium oxide powder pressed in the cathode pellet was covered by tungsten and drilled. Using this cathode, we achieved smaller solid angle emission of the sputtered lanthanide elements from the bottom of the drilled hole, and most of them could pass through the center hole of the ionizer. As a result, damage to the ionizer decreased, and stable operation of the ion source was successfully achieved with a cerium oxide beam current of 600 nA for 24 h continuous operation. The technique was applied for production of other rare earth ions.
Compact injector with alternating phase focusing–interdigital H-mode linac and superconducting electron cyclotron resonance ion source for heavy ion cancer therapy
Authors: Hayashizaki Noriyosu , Hattori Toshiyuki , Matsui Shinjiro , Tomizawa Hiromitsu , Yoshida Toru , Isokawa Katsushi , Kitagawa Atsushi , Muramatsu Masayuki , Yamada Satoru , Okamura Masahiro
Published: July 2002

We have researched a compact medical accelerator with low investment and running cost for the popularization of heavy ion cancer therapy. As the first step, the compact injector system has been investigated for a Heavy Ion Medical Accelerator in Chiba at National Institute of Radiological Sciences. The proposed new injector system consists of a 6 MeV/u interdigital H-mode (IH) linac of 3.1 m long and a 18 GHz superconducting electron cyclotron resonance (ECR) (SC–ECR) ion source. The IH linac with high power efficiency is appropriate to a medical and industrial injector system. Its beam trajectory was simulated and a prototype has been constructed. The SC–ECR ion source has been designed to realize lightweight and low power consumption and the mirror field distribution was estimated.
Preparation of giant magnetostrictive thin film by magnetron and ion beam sputtering processes
Authors: Nakazato K. , Hashimoto M. , Uchida H. , Matsumura Y.
Published: July 2002

Thin films of giant magnetostrictive materials were formed by dc magnetron sputtering and ion beam sputtering processes. A systematic investigation was made to examine the effect of these deposition processes on the magnetic properties and magnetostriction of TbFe2 and (Tb, Dy)Fe2 thin films. The magnetostriction of the films formed by dc sputtering was in the range from 200 to 400 ppm at a magnetic field H=15 kOe, whereas the films formed by the ion beam sputtering exhibited a slightly higher magnetostriction. For both processes, the increase in Ar partial pressure in the deposition processes strongly changed magnetic anisotropy from perpendicular to in plane, and increased magnetostriction and magnetostrictive response at low magnetic fields. However, the mixture of Xe gas into Ar gas in the dc sputtering lowered magnetization and gave almost no effect on magnetic anisotropy.
Effects of indirect ionization on the charge state distributions observed with highly charged ion sources
Authors: Stockli M. P. , Lehnert U. , Becker R. , Delferriere O. , Gebel Th. , Ullmann F. , Kobayashi N. , Matsumoto J.
Published: July 2002

Presently, most charge state distributions produced with highly charged ion sources are predicted with models that approximate the ionization process with the Lotz formula. The Lotz ionization cross sections decrease approximately geometrically with increasing charge state except for ions with very few vacancies, for ions with very few electrons, and for electron impact energies which barely exceed the ionization energy. The geometrical decrease causes these models to predict a maximum abundance for most of the charge states, which is only weakly dependent on the charge state. Experimental results, however, yield much higher abundances for ions with an empty M shell than ions with a partly filled M shell. This difference is explained with indirect ionization processes that are neglected by the Lotz approximation, and normally can be neglected for the ionization of the L shell, but can dominate the ionization of the M shell.
Medical accelerators in Japan (invited)
Authors: Soga F.
Published: July 2002

Particle accelerators for medical usage are in the main stream in the application of physics and technology in Japan as well as in other parts of the world. It affects directly the social welfare of the people and strong interest has been taken especially in the medical field. The medical application of accelerators of different radiations is described, and the present status of radiotherapy for cancer treatments and future perspective are also given.
Carbon shunting arc and its induced plasma
Authors: Yukimura Ken , Yoshioka Kenji , Tani Yuji
Published: July 2002

A pulsed carbon arc is produced in a low-pressure gas or vacuum without any external trigger source. The arc is initiated around a carbon rod that is heated using a same power source with the arc. This is called a shunting arc and it is characteristic that the arc is self-initiated and its current of over 1000 A with a sinusoidal waveform is easily attained. Spectroscopic measurement shows that the shunting arc induces a new nitrogen plasma in the chamber. Thus, two different plasmas exist in one shunting arc production process. As a preliminary research of plasma-based ion implantation, pulsed carbon ions are extracted from the arc plasma and implanted into a target placed in the chamber by directly applying a pulsed high voltage to the target.
Model for ion extraction from pulsed plasma source for plasma based ion implantation (PBII)
Authors: Masamune Sadao , Yukimura Ken
Published: July 2002

In plasma based ion implantation, the use of a pulsed plasma source may have some advantages over the conventional dc source, in that a pulsed plasma may easily meet the requirement of high density plasma production in low pressure environment. For the purpose of understanding the ion dynamics, we have developed a one-dimensional model for the ion implantation into a target from a pulsed plasma which expands toward the target with finite velocity. The sheath edge evolution equation and the equations of ion motion are solved, to obtain analytic formulas for the implanted ion current and energy distribution on some assumptions. Influence of the vacuum region and plasma expansion velocity will be discussed.
Measurement of the four-dimensional transverse emittance of an ion beam
Authors: Zeinoun Issam , Benveniste Victor , Saadatmand Kourosh , Swenson David
Published: July 2002

A pepper-pot emittance measurement system has been developed for measuring the four-dimensional transverse emittance of an ion beam. The complete emittance can be constructed by stepping a graphite pepper-pot mask through a cross section of the beam and taking two-dimensional profiles of its images. The profiles are measured by moving a set of thin collectors (0.6 mm wide and 0.4 mm apart) stacked vertically on a ceramic board through a cross section of the beam. A high-resolution capability of 1.6 mm by 1.3 mrad has been demonstrated for beam widths of 50 mm and divergence angles up to 75 mrad. An adaptive algorithm has been developed to match the pepper-pot holes to their corresponding images without imposing any bounds on the divergence or direction of the beam.
Measurement of free-space terahertz pulses via long-lifetime photoconductors
Authors: Sun F. G. , Wagoner G. A. , Zhang X.-C.
Published: July 2002

Antennas based on commercially available GaAs as a photoconductor with a subnanosecond photocarrier lifetime have been used to detect subpicosecond free-space electromagnetic radiation (THz pulses). At low optical gating intensities (≤1 mW/100 μm2), GaAs based antennas exhibit a higher responsivity and signal-to-noise ratio than typical antennas based on radiation-damaged silicon-on-sapphire.
Studies on molten glass sealing in diffusion coefficient measurements using shear cell technique
Authors: Yu Jianding , Natsuisaka Makoto , Kato Hirokazu , Matsumoto Satoshi , Kinoshita Kyoichi , Itami Toshio , Yoda Shinichi
Published: July 2002

To develop a shear cell technique for measuring the diffusion coefficient of molten materials with high vapor pressure, molten silica glass was used to seal the vapor leak from the clearance between the cell and the rotating rod. An apparatus was designed to investigate the sealing ability of several molten silica glasses. Using Corning 0211, 7059, and 7740 silica glasses, Ar could be sealed under 150 kPa in the 1100–1500 K temperature range. The corresponding viscosities of the molten silica glasses in the sealing temperature range were 105.3–103.8 Pa s. Based on the results of Ar sealing experiments, the configuration of molten glass sealing was used to seal the As vapor leak in InxGa1−xAs diffusion coefficient measurement experiments. The As vapor leak was successfully sealed and excellent diffusion coefficient measurement data were obtained using the shear cell technique during microgravity experiments carried out on sounding rocket.
Fluorescence measurements on nanotiter plates
Authors: Hessling M. , Ihlemann J. , Marowsky G.
Published: July 2002

Two different highly sensitive and fast but low-cost instruments for fluorescence measurements on nanotiter plates or other high density sample arrays are presented. Both instruments use 635 nm diode lasers for the detection of Cy5 fluorescence. In the first device all cavities of the nanotiter plate are illuminated simultaneously and the fluorescence is detected spatially resolved by a charge-coupled device camera within a few seconds. The second system uses an on-chip microscanner for the sequential illumination of the samples and the fluorescence is detected by a simple photomultiplier tube. Both instruments have originally been developed for environmental analysis by immunochemical labeling but they can also be used for other medical and biological purposes where analyte concentrations have to be determined.
Imaging of liquid crystals using a new scanning near-field optical microscope with microfabricated tips and shear force detection
Authors: Röder Th. , Paelke L. , Held N. , Vinzelberg S. , Kitzerow H.-S.
Published: July 2002

We report results obtained with a scanning near-field optical microscope which was developed, recently. The scanning head of the device is mounted on an inverted polarizing microscope. The sample is illuminated through a microfabricated tip which is mounted on a single-mode optical wave-guiding fiber. The light transmitted through the sample is collected in the far field by a microscope lens. The distance between the tip and the sample is controlled by shear force detection, using a nonconventional setup. We applied this new equipment successfully in order to investigate birefringent and dichroic liquid crystal films, using polarization modulation or fluorescence detection, respectively. An optical resolution down to ≈200 nm was obtained on the sample of a cholesteric liquid crystal for a wavelength of 488 nm.
Excitonic optical properties in semiconductor thin quantum boxes of intermediate regime between zero and two dimensions
Authors: Gotoh Hideki , Ando Hiroaki , Kanbe Hiroshi
Published: July 2002

We discuss the optical properties in thin quantum boxes based on a theoretical analysis that rigorously treats excitonic confinement effects in the intermediate regime between zero and two dimensions. Our theory can exactly analyze not only the excitonic ground state but also higher energy states, and thus can simulate whole absorption spectra near the band edge region. We also report novel exciton electro-absorption effects found in the intermediate confinement regime.
Domain structure and phase transitions in epitaxial KNbO3 thin films studied by in situ second harmonic generation measurements
Authors: Gopalan Venkatraman , Raj Rishi
Published: July 2002

Epitaxial thin films of KNbO3  were deposited on SrTiO3 (100) substrate by laser ablation. In the orthorhombic phase, the four possible domain variants in the KNbO3 (110) film growth plane were determined to be KNbO3[11̄0]∥SrTiO3[001], [001̄], [010], and [01̄0] denoted as X+, X−, Y+, and Y−, respectively. Using a fundamental beam of 1064 nm transmitted normal to the film, the second harmonic generation (SHG) signal at 532 nm was measured and correlated to the area fractions AX+, AX−, AY+, and AY− of the four domain variants X+, X−, Y+, and Y−, respectively, in the growth plane of the film. At room temperature, the area fractions δAx=AX+−AX− and δAy=AY+−AY− were determined to be ∼3.3% and ∼2.2%, respectively. In-situ SHG measurements revealed the phase transitions to be 210±10 °C for orthorhombic–tetragonal and 450±10 °C for tetragonal–cubic transitions. In the tetragonal phase (between 210 °C and 450 °C) the KNbO3 〈100〉∥SrTiO 3 〈100〉. The use of SHG as a sensitive, non-destructive and real-time probe of phase transitions and evolution of domains in ferroelectric thin films is demonstrated.
High barrier height GaN Schottky diodes: Pt/GaN and Pd/GaN
Authors: Wang Lei , Nathan M. I. , Lim T-H. , Khan M. A. , Chen Q.
Published: July 2002

Platinum (Pt) and palladium (Pd) Schottky diodes on n-type GaN grown by metalorganic chemical vapor deposition were achieved and investigated. Aluminum was used for ohmic contacts. Barrier heights were determined to be as high as ΦB=1.13 eV by the current–voltage (I–V) method and ΦB=1.27 eV by the capacitance–voltage (C–V) method for the Pt/GaN diode, and ΦB=1.11 eV, ΦB=0.96 eV, and ΦB=1.24 eV by I–V, activation energy (I–V–T), and C–V methods for the Pd/GaN diode, respectively. The ideality factors were obtained to be n∼1.10.
Ultra-smooth, highly ordered, thin films of La0.67Ca0.33MnO3±d
Authors: Vas’ko V. A. , Nordman C. A. , Kraus P. A. , Achutharaman V. S. , Ruosi A. R. , Goldman A. M.
Published: July 2002

We report the growth and characterization of ultra-smooth, highly ordered, strained La2/3Ca1/3MnO3±d thin films (approximately 600 Å in thickness). The thin films were deposited by ozone-assisted, block-by-block, molecular beam epitaxy on SrTiO3 (001) substrates without any post-deposition annealing. Scanning tunneling microscopy images showed oriented, unit-cell-high terraces characteristic of a step-flow growth mechanism. The root-mean-square roughness of the surface of an imaged film was determined to be 2 Å. This same film showed negative magnetoresistance values, [R(H=0)−R(Happlied)]/R(H=0), at 150 K of 93% and 5% in applied magnetic fields of 5.12 and 4×10−2 T, respectively.
Laser ablation: Selective unzipping of addition polymers
Authors: Blanchet Graciela B. , Fincher C. R.
Published: July 2002

These studies show that laser ablation, a technique widely used to deposit thin films of inorganic materials is also a simple and highly versatile tool for studying polymer decomposition. The use of laser ablation and fast resistive heating to control the degradation kinetics of vinyl polymers is illustrated here. Although polypropylene and polyvinyl fluoride are commonly believed to pyrolyze via random scission producing little monomer, our results demonstrate that in ablative decomposition they unzip with large monomer yields. We propose heating rate and final temperature to be the controlling factors in determining the thermodynamics and kinetics of decomposition reactions.
Molecular-beam epitaxy of Mn1+xSb thin films and substrate temperature dependence of their magneto-optical properties
Authors: Miyanishi S. , Akinaga H. , Tanaka K.
Published: July 2002

Ferromagnetic Mn1+xSb thin films have been grown on (001) GaAs substrates by molecular-beam epitaxy at substrate temperatures (TS) in the range from 50 to 400 °C. The excess Mn composition (x) of the grown films was found to change uniquely depending on TS. The polar magneto-optical Kerr effect measurement demonstrated a strong TS dependence of Kerr rotation and Kerr ellipticity spectra of Mn1+xSb films from the infrared through ultraviolet wavelength region. A possible origin of the TS dependence of the spectra is discussed in connection with the composition of Mn1+xSb films.
High power generation with distributed Josephson-junction arrays
Authors: Booi P. A. A. , Benz S. P.
Published: July 2002

We have experimentally coupled emission from a distributed series array of 1968 wide Josephson junctions to an on-chip 10.8 Ω load and detected 0.16 mW at 240 GHz. This result is achieved by reducing the parasitic inductance associated with shunt resistors so that junctions with critical currents of 23 mA are effectively shunted at the operating frequency. This power is less than the 1.3 mW expected from theory due to the presence of a large impedance mismatch. Optimization of the load design will allow the detection of mW power.
Integrated three-color organic light-emitting devices
Authors: Wu C. C. , Sturm J. C. , Register R. A. , Thompson M. E.
Published: July 2002

We report a demonstration of the integration of individual polymer-based light emitting devices of three different colors on the same substrate. Orange, green, and blue color devices are sequentially fabricated on the same indium–tin oxide (ITO) coated glass substrate coated with a patterned insulator on the ITO, by the spin coating of polymer thin films, the vacuum deposition of top metal contacts, and the patterning of polymer thin film by plasma etching, using the top metal contacts as the self-aligned etching mask. The devices exhibit no degradation of device characteristics due to the integration processing compared to discrete devices on separate substrates. This demonstration shows a new path towards the fabrication of high performance low-cost full-color organic flat panel displays.
Effect of rapid thermal annealing on carrier lifetimes of arsenic-ion-implanted GaAs
Authors: Lin Gong-Ru , Chen Wen-Chung , Ganikhanov Feruz , Chang C.-S. , Pan Ci-Ling
Published: July 2002

Femtosecond time-resolved reflectivity measurements, structural, and electrical analyses have been performed to investigate the effect of rapid thermal annealing (RTA) on GaAs implanted with 200 keV arsenic ions at 1016 ions/cm2. Ultrashort carrier lifetimes from 0.48 fs to 2.3 ps were observed for samples annealed at temperatures between 600 and 800 °C. The time constants are somewhat shorter than those of RTA-annealed low-temperature molecular-beam epitaxy grown material, while following the same trend of longer time constants and recovery of resistance at higher annealing temperatures. Arsenic precipitates were not observed.
p-type GaSb and Ga0.8In0.2Sb layers grown by metalorganic vapor phase epitaxy using silane as the dopant source
Authors: Ehsani H. , Bhat I. , Gutmann R. , Charache G.
Published: July 2002

p-type GaSb and Ga0.8In0.2Sb layers were grown on GaAs substrates by the low pressure metalorganic vapor phase epitaxy technique, using silane as the dopant source. It was found that Si is a well behaved p-type dopant in GaSb and Ga0.8In0.2Sb compounds. Secondary ion mass spectrometry measurements and Van der Pauw Hall measurements indicated that the compensation ratio (defined as Nd/Na) of 2×1018 cm−3 doped p-type Ga0.8In0.2Sb layer is less than 0.25, whereas the compensation ratio is less than 0.1 for layers doped to <5×1017 cm−3. Control of p-type doping level in the mid 1016 cm−3–mid 1018 cm−3 range has been demonstrated. The effects of trimethylantimony mole fraction and the growth temperature on the Si incorporation behavior were also studied.
Unusual enhancement of transient reflecting grating signal under a surface plasmon resonance condition
Authors: Katayama Kenji , Shen Qing , Harata Akira , Sawada Tsuguo
Published: July 2002

Subnanosecond time-resolved transient reflecting grating (TRG) measurements were carried out under resonance conditions of surface plasmon (SP) with a Kretschmann configuration using a 40-nm-thick gold film deposited on a hemicylindrical prism. The TRG was generated and detected with two pump beams and with one probe beam incident from the prism side, the angles of which for incidence and polarization were changed. When the pump beams resonantly excited SPs, the TRG signal amplitude was enhanced as expected. An unusual enhancement was observed when the probe beam excited SPs, i.e., the TRG signal amplitude was also enhanced strongly although reflecting diffraction was probed under the less reflective condition. This enhancement was accompanied by a transient wave form change. The mechanism of these phenomena is discussed.
Advances in ultrafast scanning tunneling microscopy
Authors: Botkin D. , Glass J. , Chemla D. S. , Ogletree D. F. , Salmeron M. , Weiss S.
Published: July 2002

Time resolved tunnel current was measured over 4 orders of magnitude in separation between tip and sample using an ultrafast scanning tunneling microscope (USTM). These measurements reveal two distinct regimes for tip height dependence of the signal. In addition, we report 900 femtosecond temporal resolution with a sensitivity of 20 mV/√Hz in USTM measurements of voltage pulses on a coplanar transmission line, and we show that the microscope operates as a high impedance probe.
Stability of binary logic tunneling phase states in dc-biased and ac-pumped single-electron tunnel junctions
Authors: Ohshima T.
Published: July 2002

We have investigated the stability of phase states of single-electron tunneling oscillation phase locked by an external ac pump with twice the tunneling frequency using the Monte Carlo method. It has been shown that the lifetime of phase states depends strongly on the temperature, average current, pump amplitude, and dc bias. For a large current, the lifetime is determined by shot noise and decreases drastically with current. For a small current, it is limited by Nyquist noise and increases exponentially with the inverse temperature. Although junctions with a diameter of about 10 nm are required, a lifetime of over 104 cycles at 4.2 K can be estimated. We believe that this is a practical value for use in logic processing using phase bistability.
Photothermal radiometric investigation of implanted silicon: The influence of dose and thermal annealing
Authors: Othonos Andreas , Christofides Constantinos , Mandelis Andreas
Published: July 2002

Photothermal radiometric measurements were performed on phosphorus implanted and annealed silicon wafers. Data were collected over modulation frequencies ranging between 0.1 and 100 kHz with the 488 nm Ar ion laser line as the excitation source. The sensitivity of this technique on implantation dose and annealing temperature is discussed. A semiquantitative analysis of the data is also carried out.
Thermal analysis using a micromechanical calorimeter
Authors: Berger R. , Gerber Ch. , Gimzewski J. K. , Meyer E. , Güntherodt H. J.
Published: July 2002

A fast and extremely sensitive method for reversible thermal analysis of picoliter volumes of solid samples is presented. Using a micromechanical calorimeter based on the deflection of a bimetallic cantilever, enthalpy changes at phase transitions in n-alkanes (paraffins) are determined. The key role of volume changes associated with phase transitions is discussed together with a method to separate thermal and volume-induced stresses associated with these phase transitions.
Optical properties of GaN grown on ZnO by reactive molecular beam epitaxy
Authors: Hamdani F. , Botchkarev A. , Kim W. , Morkoç H. , Yeadon M. , Gibson J. M. , Tsen S.-C. Y. , Smith David J. , Reynolds D. C. , Look D. C. , Evans K. , Litton C. W. , Mitchel W. C. , Hemenger P.
Published: July 2002

High quality wurtzite GaN epilayers have been grown on ZnO(0001) substrates by reactive molecular beam epitaxy. Photoluminescence and reflectivity measurements point to high quality presumably due to the near match of both the crystal lattice parameter and the stacking order between GaN and ZnO. In addition, the good films lack the characteristic yellow photoluminescence band. Any misorientation of the GaN epilayer planes with respect to the ZnO substrate is not detectable with polarized reflectivity. The x-ray double crystal diffraction measurements indicate this misorientation is much smaller than those for GaN epilayers on SiC and Al2O3 .
Passivation of GaAs/AlGaAs heterojunction bipolar transistors by S2Cl2 solution
Authors: Cao Xian-an , Hou Xiao-yuan , Chen Xi-ying , Li Zhe-shen , Su Run-zhou , Ding Xun-min , Wang Xun
Published: July 2002

The diluted S2Cl2 solution has been employed to treat the GaAs/AlGaAs heterojunction bipolar transistors. It is shown that the dc characteristics of the transistor could be improved significantly and the passivation effect is not subject to degradation by heating to 150 °C in atmospheric air and immersing in water. A real-time monitoring technique is proposed which provides good control of the passivation stopping point.
Scanning tunneling spectroscopy of n-type GaAs under laser irradiation
Authors: Takahashi Takuji , Yoshita Masahiro
Published: July 2002

We studied the scanning tunneling spectroscopy of n-type GaAs under laser irradiation. The negative surface photovoltage effects due to the laser irradiation were clearly observed in the differential conductance properties. The photosensitivities depend on the doping density, that is, a lower doped sample has a higher sensitivity. This dependence can be explained by the net surface charge density effect as well as by the carrier lifetime effect.
Near-field scanning optical microscopy studies of Cu(In,Ga)Se2 solar cells
Authors: McDaniel A. A. , Hsu J. W. P. , Gabor A. M.
Published: July 2002

A near-field scanning optical microscope (NSOM) is used to study the local photoresponse of Cu(In,Ga)Se2 thin film solar cells. The grain boundaries of the small grains (<1 μm) show some reduction in photoresponse; however the photoresponse is significantly reduced near most crevices separating large grains (>10 μm). In addition, NSOM images show response variations from grain to grain and areas of reduced photoresponse which have no corresponding topography. Photovoltage imaging of the cleaved side of the solar cells reveals the depth and nonuniformities of the actual p-n junction. It is found that the response of the p-n junction varies on a 0.5 μm length scale.
Optical detection for scanning microdeformation microscopy
Authors: Cretin B. , Vairac P.
Published: July 2002

Scanning microdeformation microscopy is a kind of ac contact force microscopy sensitive to the variations of the local elastic constants of the investigated material. In this letter a new optical interferometer designed for detecting the small displacement of the cantilever is reported. The setup is described and some applications of the laser probe to scanning microdeformation microscopy are demonstrated.
Detection of defect states responsible for leakage current in ultrathin tantalum pentoxide (Ta2O5) films by zero-bias thermally stimulated current spectroscopy
Authors: Lau W. S. , Zhong L. , Lee Allen , See C. H. , Han Taejoon , Sandler N. P. , Chong T. C.
Published: July 2002

Defect states responsible for leakage current in ultrathin (physical thickness <10 nm) tantalum pentoxide (Ta2O5) films were measured with a novel zero-bias thermally stimulated current technique. It was found that defect states A, whose activation energy was estimated to be about 0.2 eV, can be more efficiently suppressed by using N2O rapid thermal annealing (RTA) instead of using O2 RTA for postdeposition annealing. The leakage current was also smaller for samples with N2O RTA than those with O2 RTA for postdeposition annealing. Hence, defect states A are quite likely to be important in causing leakage current.
Mapping the confined optical field in a microcavity via the emission from a conjugated polymer
Authors: Lidzey D. G. , Bradley D. D. C. , Pate M. A. , David J. P. R. , Whittaker D. M. , Fisher T. A. , Skolnick M. S.
Published: July 2002

The distribution of a confined optical field within a microcavity was determined using a thin layer of the fluorescent polymer PPV as a probe of the local-field amplitude. It is shown that the photoluminescence emission intensity from the cavity is a function of the axial position of the polymer, and confirms that a microcavity can be used to control spontaneous emission.
Far-infrared spectroscopic, magnetotransport, and x-ray study of athermal annealing in neutron-transmutation-doped silicon
Authors: Donnelly D. W. , Covington B. C. , Grun J. , Hoffman C. A. , Meyer J. R. , Manka C. K. , Glembocki O. , Qadri S. B. , Skelton E. F.
Published: July 2002

We present evidence that the energy introduced by a short laser pulse focused to high intensity on a small spot on the surface of neutron-transmutation-doped silicon electrically activates impurities far away from the focal spot. The activation of the impurities is measured by far-infrared spectroscopy of shallow donor levels and by magnetotransport characterization. Electrical activity is comparable to that obtained with conventional thermal annealing. X-ray rocking curve measurements show strain in the area of the focal spot, but none at large distances from the focal spot.
Self-formed silicon quantum wires on ultrasmooth sapphire substrates
Authors: Yanagiya Shun-ichi , Kamimura Shunsuke , Fujii Masanori , Ishida Makoto , Moriyasu Yoshitaka , Matsui Masahiro , Yoshimoto Mamoru , Ohnishi Tsuyoshi , Yoshida Kenji , Sasaki Kenji , Koinuma Hideomi
Published: July 2002

We have observed step-flow growth of Si on sapphire, for the first time, by gas-source molecular beam epitaxy using ultrasmooth sapphire substrates, and self-formed Si quantum wires were fabricated on the substrates. The wires were aligned along the substrate steps and formed uniformly with 50 nm width and 1 nm height. Visible photoluminescence from the wires was observed at 9 and 300 K. The optical properties of the wires were very similar to those observed in conventional porous silicon and other nanostructured silicon.
Shock-wave generation during rear- and front-side ablation of calcite
Authors: Yavas O. , Maddocks E. L. , Papantonakis M. R. , Haglund R. F.
Published: July 2002

Shock waves generated by rear- and front-side infrared (λ=1.064 μm) laser irradiation of calcite were measured using time-resolved surface-plasmon resonance spectroscopy. The shock waves generated in the two cases are found to be distinctly different: Rear-side ablation gives rise to planar shock waves, while the front-side ablation is more nearly spherical. The observed differences are related to differing material-removal mechanisms at the two surfaces.
Charge compensation study of molecular beam epitaxy grown SrS:Ce
Authors: Tong W. , Zhang L. , Park W. , Chaichimansour M. , Wagner B. K. , Summers C. J.
Published: July 2002

A study is reported of the codoping of SrS:Ce by Ag and Cu in order to achieve charge compensation of the trivalent Ce atom. Both Ag and Cu codoping produced a blue shift in the photoluminescence spectra and much higher electroluminescent device performance. These improvements were attributed to the substitutional incorporation of Ag and Cu onto the Sr lattice site which minimized the vacancy formation and provided charge compensation.
Infrared photothermal radiometric deep-level transient spectroscopy of shallow B+ dopant states in p-Si
Authors: Salnick A. , Mandelis A. , Jean C.
Published: July 2002

Infrared photothermal radiometric deep-level transient spectroscopy (PTR-DLTS) has been applied to noncontact diagnostics of a p-Si wafer. Both negative and positive peaks in the PTR-DLTS signal temperature scans have been detected. A behavior consistent with photoinjected carrier lifetime enhancement due to the thermal filling of B+ dopant levels in the band gap has been observed. The activation energies of 43 meV (negative peaks) and 60 meV (positive peaks) have been extracted from the corresponding Arrhenius plots.
Post growth rapid thermal annealing of GaN: The relationship between annealing temperature, GaN crystal quality, and contact-GaN interfacial structure
Authors: Cole M. W. , Ren F. , Pearton S. J.
Published: July 2002

Microstructure of GaN films grown by metalorganic chemical-vapor-deposition (MOCVD) on c-sapphire substrates has been accessed as a function of post-growth rapid thermal annealing (RTA) temperatures from 600 °C to 800 °C. The influence of the thermally modified, near-surface crystalline quality on sputtered WSi contact to GaN was also evaluated. Similar planar defects were observed in all heat treated samples; only their density differed. Our analyses demonstrated a strong relationship between the improved GaN crystal quality and postgrowth high-temperature thermal processing. The density of the near-surface defects was lowered by 61% as the annealing temperature was raised from 600 °C to 800 °C. Depression of the near-surface defects encouraged development of the β-W2N interfacial phase and promoted metal-semiconductor interface smoothness.