bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and characterization of ZnTe films grown on GaAs, InAs, GaSb, and ZnTe
Authors: Rajakarunanayake Y. , Cole B. H. , McCaldin J. O. , Chow D. H. , Söderström J. R. , McGill T. C. , Jones C. M.
Published: July 2002

We report the successful growth of ZnTe on nearly lattice-matched III-V buffer layers of InAs (0.75%), GaSb (0.15%), and on GaAs and ZnTe by molecular beam epitaxy. In situ reflection high-energy electron diffraction measurements showed the characteristic streak patterns indicative of two-dimensional growth. Photoluminescence measurements on these films show strong and sharp features near the band edge with no detectable luminescence at longer wavelengths. The integrated photoluminescence intensity from the ZnTe layers increased with better lattice match to the buffer layer. The ZnTe epilayers grown on high-purity ZnTe substrates exhibited stronger luminescence than the substrates. We observe narrow luminescence linewidths (full width at half maximum ≊1–2 Å) indicative of uniform high quality growth. Secondary-ion mass spectroscopy and electron microprobe measurements, however, reveal substantial outdiffusion of Ga and In for growths on the III-V buffer layers.
Characterization of crystalline quality of diamond films by Raman spectroscopy
Authors: Yoshikawa M. , Katagiri G. , Ishida H. , Ishitani A. , Ono M. , Matsumura K.
Published: July 2002

We have measured Raman spectra of diamond films prepared by a hot-filament method and found that diamond layers on Si substrates are under compressive strain. The degree of the strain is found to increase with increasing nondiamond component in the diamond films. It is shown that Raman spectroscopy is a powerful method to estimate the crystalline quality, especially the strain in the diamond films.
Broadband optical detection of ultrasound by optical sideband stripping with a confocal Fabry–Perot
Authors: Monchalin J.-P. , Héon R. , Bouchard P. , Padioleau C.
Published: July 2002

A method which allows broadband optical detection of ultrasound with large étendue from a scattering surface is presented. The wave scattered by the surface interferes with a reference wave which is derived from the scattered wave after stripping it from its optical sidebands by a confocal resonator. Simple implementation by a confocal Fabry–Perot used in reflection is explained and demonstrated experimentally.
Simultaneous measurement of lateral and normal forces with an optical-beam-deflection atomic force microscope
Authors: Meyer Gerhard , Amer Nabil M.
Published: July 2002

An atomic force microscope capable of measuring, simultaneously yet separately, lateral (‘‘frictional’’) and normal forces is described. A direction-dependent feature, absent in topological images, is found when scanning stepped surfaces of NaCl (001) in ultrahigh vacuum. A simple model is presented to account for this observation.
Measurements of noncritically phase-matched second-harmonic generation in a LiB3O5 crystal
Authors: Ukachi T. , Lane R. J. , Bosenberg W. R. , Tang C. L.
Published: July 2002

The characteristic properties of noncritically phase-matched second-harmonic generation in lithium triborate (LiB3O5, LBO) are investigated. Using a LBO crystal grown in our laboratory, we demonstrate that temperature-tuned noncrictical phase-matched second-harmonic generation from 1.025 to 1.253 μm is achieved in a temperature range from 190 to −3 °C. The noncritical phase-matching temperature for 1.064 μm radiation is found to be 148.0±0.5 °C with a temperature acceptance bandwidth of 3.9 °C cm.
Direct visual observation of powder dynamics in rf plasma-assisted deposition
Authors: Howling A. A. , Hollenstein Ch. , Paris P.-J.
Published: July 2002

Contamination due to particles generated and suspended in silane rf plasmas is investigated. Powder is rendered visible by illumination of the reactor volume. This simple diagnostic for global, spatio-temporal powder dynamics is used to study particle formation, trapping, and powder reduction by power modulation.
High-quality GaAs on sawtooth-patterned Si substrates
Authors: Ismail K. , Legoues F. , Karam N. H. , Carter J. , Smith Henry I.
Published: July 2002

We report a novel technique for growing GaAs on Si substrates with a low density of threading dislocations. The process involves patterning a 200 nm period sawtooth grating on (100) Si using a combination of holographic lithography and wet chemical etching. The GaAs layers grown by metalorganic chemical vapor deposition on such substrates exhibit a dramatic reduction in the density of threading misfit dislocations, even when the grown layers are thin. Twins and stacking faults are also reduced dramatically by either in situ thermal-cycle growth or ex situ rapid thermal annealing.
Long-term annealing study of midgap interface-trap charge neutrality
Authors: Fleetwood D. M.
Published: July 2002

Non-radiation-hardened metal-oxide-semiconductor (MOS) devices were irradiated to doses from 30 to 90 krad(SiO2) and baked at 100 °C under positive bias for 2.75 yr. Threshold-voltage shifts due to radiation-induced oxide- and interface-trap charge were estimated via the subthreshold current-voltage technique of McWhorter and Winokur [Appl. Phys. Lett. 48, 133 (1986)], which depends on the assumption that radiation-induced interface traps are neutral at midgap surface potential. The oxide-trap charge inferred via this technique asymptotically approached zero ∼9 months after irradiation and remained constant for the next 2 yr, despite large changes in the subthreshold current-voltage characteristics caused by changes in interface-trap density (which increased during the first 4–9 months of 100 °C annealing, then decreased during the remaining 2–2.5 yr). This strongly reinforces the often controversial idea that radiation-induced interface traps are charge-neutral at midgap. Finally, a new figure of merit is developed to assess the self-consistency of interface-trap charge measurements on irradiated MOS devices.
Characterization of epitaxial and oxidation-induced stacking faults in silicon: The influence of transition-metal contamination
Authors: Higgs V. , Goulding M. , Brinklow A. , Kightley P.
Published: July 2002

Photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and defect etching have been used to characterize epitaxial stacking faults (ESF) in silicon epilayers grown by low-pressure chemical vapor deposition (LPCVD) and oxidation-induced stacking faults (OISF) in high-purity float-zone (FZ) Si. No dislocation-related luminescence was observed from either ESFs or OISFs grown under clean conditions. Deliberate surface contamination, followed by annealing with Cu, Fe, Ni, Ag, or Au in the range 4×1012–2×1016 atoms cm−2 introduced dislocation luminescence features, with a maximum intensity at ≊4×1012 atoms cm−2. TEM examination revealed that there was no evidence for precipitation at low levels of contamination but as the contamination level increased metal-related precipitates were observed on the bounding partial dislocations.
Growth kinetics and properties of heteroepitaxial ZnTe films grown by metalorganic molecular beam epitaxy
Authors: Rajavel D. , Zinck J. J.
Published: July 2002

High quality (001) ZnTe films have been grown on (001) GaAs by metalorganic molecular beam epitaxy using thermally precracked diethylzinc and diethyltellurium. Reflection high-energy electron diffraction intensity oscillations were measured during the growth of ZnTe and were used to determine the growth kinetics as a function of substrate temperature and II/VI flux ratio. X-ray rocking curves with full widths at half maximum of approximately 200 arcsec have been measured for ZnTe films grown at 385 °C under Zn-rich conditions. Secondary ion mass spectrometric analysis indicated that carbon contamination in the films was minimal. The photoluminescence spectra of the ZnTe layers measured at 5 K were dominated by features associated with free and bound excitons and exhibited weak deep level emission.
Broadband second-harmonic generation in SrxBa1−xNb2O6 by spread spectrum phase matching with controllable domain gratings
Authors: Horowitz Moshe , Bekker Alexander , Fischer Baruch
Published: July 2002

We have demonstrated, for the first time to our knowledge, second-harmonic generation for a broad input wavelength range of 750–1064 nm in SrxBa1−xNb2O6 crystals, with a controllable spread spectrum of quasiphase matching. Second-harmonic conversion efficiencies of up to ∼1% were observed. This was done without any temperature or angular tuning of the crystal. The phase matching was obtained by inducing alternating ferroelectric domains in the crystal in real time, using a novel fixing process which is based on screening. The broadband capability of the conversion is allowed by a spread in the range of the domain widths.
Strain and charge distribution in GaN-AlN-GaN semiconductor-insulator-semiconductor structure for arbitrary growth orientation
Authors: Bykhovski Alexei , Gelmont Boris , Shur Michael
Published: July 2002

We demonstrate that, in a GaN-AlN-GaN semiconductor-insulator-semiconductor structure, the strain-induced electric fields across the interface depend on the angle, θ, between the c axis and the growth direction. The magnitude of the strain induced polarization has a maximum in (0001) crystallographic direction (θ=0°) and a subsidiary maximum near θ=70°. This angular dependence is a unique feature of wurtzite-type structures. Considering θ as an independent parameter for device design, one can obtain structures with flat band voltage shift from 0 to 1.5 V for 30 Å AlN film, with different positions of accumulation-depletion regions, and with electron (hole) charge varying from 0 to more than 1012 cm−2.
Nonlinear excited state absorption in cadmium texaphyrin solution
Authors: Si Jinhai , Yang Miao , Wang Yuxiao , Zhang Lei , Li Chunfei , Wang Duoyuan , Dong Shiming , Sun Wenfang
Published: July 2002

Nonlinear absorption at 532 nm in a cadmium texaphyrin solution has been studied using 8 ns and 23 ps laser pulses. The experiments show that reverse saturable absorption occurs in the nanosecond case. For picosecond pulses, reverse saturable absorption occurs only at low fluences, and the transmission increases with increasing incident fluence at high fluences. A six-level model is presented to explain these nonlinear absorption effects. Several photophysical parameters for cadmium texaphyrin, such as absorption cross sections at 532 nm and lifetimes, have been evaluated by theoretical simulations of the experimental results.
Melt processing for obtaining NdBa2Cu3Oy superconductors with high T
c and large J
c
Authors: Yoo S. I. , Sakai N. , Takaichi H. , Higuchi T. , Murakami M.
Published: July 2002

A reduced oxygen atmosphere during melt processing turned out to be critical for the fabrication of NdBa2Cu3Oy (Nd123) superconductors possessing high superconducting transition temperature (Tc) with a sharp transition and large critical current density (Jc) at 77 K. In a dc magnetization measurement, Nd123 superconductors melt processed in flowing a mixture gas of 1% O2 in Ar exhibited the Tc of about 95 K and the transition width of 1.5 K with the applied field of 10 Oe. A four-probe measurement showed the zero resistive transition Tc (R=0) of about 95 K. An anomalous peak effect in the magnetization hysteresis (M-H) loops was commonly observed and lead to large magnetic Jc of 2×104 A/cm2 at 77 K and 2 T for the applied field H parallel to the c axis of a sample (H∥c). This achievement is attributable to a preferential formation of high Tc phase (x<0.1) among the Nd1+xBa2−xCu3Oy solid solutions in a reduced oxygen atmosphere.
Temporal magnification and reversal of 100 Gb/s optical data with an up-conversion time microscope
Authors: Bennett C. V. , Scott R. P. , Kolner B. H.
Published: July 2002

We have developed an up-conversion time microscope capable of expanding ultrafast optical wave forms to a time scale accessible to ordinary sampling oscilloscopes. In this system, a 100 Gb/s optical word is magnified (slowed down) to a rate of 8.55 Gb/s with a time lens placed between two dispersive delay lines. The time lens is a nonlinear crystal which mixes the dispersed data with a linearly chirped pump pulse thus imparting a linear frequency sweep to the unconverted wave form. A second dispersive delay line completes the arrangement and forms the temporal analog of a single lens spatial imaging system resulting in a time reversed wave form with a magnification M=−11.7.
Magnetron sputter epitaxy of SimGen/Si(001) strained-layer superlattices
Authors: Sutter P. , Schwarz C. , Müller E. , Zelezny V. , Goncalves-Conto S. , von Känel H.
Published: July 2002

Epitaxial growth of SimGen/Si(001) strained-layer superlattices by magnetron sputter epitaxy is reported. Films of excellent crystal quality resulted from low-temperature sputter growth at TS=350 °C, as is evidenced by Rutherford backscattering spectrometry minimum channeling yields χmin=3%. The absence of relaxation was demonstrated by Raman spectroscopy. Raman results on the first-order longitudinal-optical Ge–Ge phonon proved pure Ge to be present in a Si30Ge6 superlattice, which indicates an interface broadening of the order of 2 monolayers. High resolution transmission electron microscopy confirmed the formation of smooth and well-defined interfaces between subsequent Si and Ge layers.
Filament activated chemical vapor deposition of boron carbide coatings
Authors: Deshpande Sadanand V. , Gulari Erdogan , Harris Stephen J. , Weiner Anita M.
Published: July 2002

In this study, we have demonstrated that boron carbide, an extremely hard and wear-resistant material, can be deposited with hot filament-activated chemical vapor deposition (HFCVD). There are several benefits to using a hot filament system, including a high deposition rate and a relatively low substrate temperature with a process that is not line-of-sight. High purity, apparently amorphous boron carbide films were obtained by the use of a chlorine based precursor (which is less toxic than diborane). This indicates that either the hot filament helps in complete decomposition of BCl3 or the presence of high concentration of atomic hydrogen in a HFCVD environment helps in scavenging the chlorine.
Time-resolved Balmer-alpha emission from fast hydrogen atoms in low pressure, radio-frequency discharges in hydrogen
Authors: Radovanov S. B. , Dzierżȩga K. , Roberts J. R. , Olthoff J. K.
Published: July 2002

Doppler-broadened Hα emission (656.28 nm) detected from a 13.56 MHz, parallel-plate, radio-frequency discharge in hydrogen indicates the presence of fast excited H atoms throughout the discharge volume. Time and spatially resolved measurements of the Doppler-broadened emission indicate that the fast H atoms are formed primarily at the surface of the powered electrode with kinetic energies exceeding 120 eV.
Measurement of amplified spontaneous emission at 200 A (invited; abstract)
Authors: Ceglio N. M.
Published: July 2002

Recent interest in the production of laser radiation at soft x-ray wavelengths makes appropriate the discussion of diagnostic considerations and techniques for the measurement of same. A source of soft x-ray ASE has a number of characteristics which drive the design of diagnostic instruments: (1) The anisotropy of the ASE makes target alignment a critical part of the diagnosis, and couples collection solid angle to S/N considerations in the measurement. (2) The narrow linewidth of the amplified emission and its long wavelength put a high S/N premium on spectroscopic instrumentation of high spectral resolution and good higher-order discrimination. (3) The specialized plasma conditions required to produce gain are typically short lived, requiring time-resolved or at least time-discriminating spectroscopy. (4) The nonlinear nature of the threshold processes involved in ASE requires instrumentation of large dynamic range, broad angular acceptance, and large field of view and depth of focus. Of the many possible methods for gain verification of the x-ray source, five are discussed: (1) Probe amplification; (2) spatial coherence measurement (as a function of gain length); (3) output intensity measurement (absolute measurement and nonlinear variation with gain length); (4) divergence measurement; and (5) cavity formation. In addition, recent soft x-ray laser experiments at LLNL are discussed along with descriptions of the instruments used to measure the ASE. Diagnostic design suggestions for future soft x-ray laser experiments are also presented.
A contactless method for measurement of the critical current density and critical temperature of superconducting films
Authors: Claassen J. H. , Reeves M. E. , Soulen R. J.
Published: July 2002

A new method is described for measuring the critical current density and transition temperature of a superconducting film without making contact to it or modifying it in any way. This technique is particularly well suited for use with high transition temperature oxide films which are notoriously irreproducible and sensitive to patterning. It consists of positioning a flat, multiturn coil near the film surface and driving the coil with an audio frequency sine-wave current. Induced shielding currents flow in the film. We have calculated the radial dependence of the induced currents and show that the induced current density is zero at the coil center, rises to a maximum near the mean radius of the drive coil, and then falls off rapidly as the radius continues to increase. A measurement of the critical current per length can be obtained by monitoring the development of odd harmonic voltage components across the coil as the drive current is increased. We find that this measure of nonlinearity in the coil–film system increases abruptly when the maximum induced current equals the critical current. The critical current obtained by this inductive measurement has been demonstrated to give nearly the same value as that obtained by a transport measurement. Other advantages to this inductive measurement approach include: sensitivity only to intergranular critical current, and an ability to accommodate large substrates. Finally, with only minor modification to the electronics used to measure Jc, the superconducting transition temperature of the sample may be measured as well.
A vector impedance meter digitally controlled
Authors: Caranti Giorgio M. , Ré Miguel A.
Published: July 2002

As with most similar equipment, the method consists in applying a sinusoidal voltage to an unknown impedance and measuring the current through it. The advantage of the developed equipment is that it allows independent and simultaneous measurement of the resistive and reactive components of the current through the sample impedance, thus making possible the determination of impedances in magnitude and phase. The measurements can be controlled with a computer using a digital interface. The instrument may also be controlled with a computer using a digital interface. The instrument may also be controlled manually from a front panel. The apparatus was designed to operate in the audio range 1 Hz–100 kHz for currents even below 1 μA. The analog outputs may either be connected to an X-Y recorder or the data can be acquired with a computer through an analog-to-digital converter. The laboratory tests have shown a good performance according to the design specifications. These tests have been carried out using discrete circuits made of calibrated components.
High-power pulse-burst generation by magnetically segmented transmission lines
Authors: Ikezi H. , de Grassie J. S. , Lin-Liu Y. R. , Drake J.
Published: July 2002

We present a new technique to generate a high-power pulse burst with a repetition rate of greater than 107 pulses per second. The circuit consists of transmission lines segmented by saturable inductors or ferrite-filled coaxial cables in which an electromagnetic shock wave is driven. Small scale experiments have demonstrated that a burst of ten pulses can be easily generated.
Two-frequency dye laser with accurately controllable frequency difference
Authors: Handerek V. A. , Ahmed S. U. , Rogers A. J.
Published: July 2002

A modification carried out inside a dye laser cavity in order to obtain simultaneous oscillation at two frequencies is described. The frequency difference is accurately tunable from zero to beyond 200 GHz and the system places no restriction on the operating wavelength (which is determined by the type of dye used).
Two-frequency displacement measurement interferometer based on a double-heterodyne technique
Authors: Chien Pie-Yau
Published: July 2002

A two-frequency laser heterodyne interferometer has been implemented for small displacement measurement. The displacement signal is detected by using a double-heterodyne technique. Vibration amplitudes at 1 kHz on the order of 1 nm and smaller can be detected.
A flat array large telescope concept for use on the moon, earth, and in space
Authors: Woodgate Bruce E.
Published: July 2002

An astronomical optical telescope concept is described which can provide very large collecting areas, of order 1000 m2. This is an order of magnitude larger than the new generation of telescopes now being designed and built. Multiple gimballed flat mirrors direct the beams from a celestial source into a single telescope of the same aperture as each flat mirror. Multiple images of the same source are formed at the telescope focal plane. A beam combiner collects these images and superimposes them into a single image, onto a detector or spectrograph aperture. This telescope could be used on the earth, the moon, or in space.
Mechanical arcless dc circuit breaker by current zero operation
Authors: Yamaguchi S. , Sasao H. , Hasegawa H. , Ikeda K. , Tukamoto T.
Published: July 2002

A mechanical arcless dc circuit breaker is proposed and has been constructed. A rectifying device is used to block the reverse current of the breaker, allowing the breaker to open under zero current condition created by the discharge of a commutation circuit. A diode and a saturable reactor are used as the rectifying device, with a leakage current of ∼1 and ∼10 A, respectively. The duration of mechanical motion is about 20 ms, and its jitter is 2 ms, which is too long to make an economical system using a commutation capacitor. In order to avoid the dead time, the commutation circuit is started after the breaker kicks in and the final jitter is reduced to 20 μs. Arcless current interruption is achieved at 10 kA and 9.1 kV. Since a strong arc plasma is not generated between the contacts, a long lifetime of the breaker can be expected and a disconnecting switch can be used instead of a circuit breaker, reducing the size of the switch. These characteristics of the new breaker can be expanded for many applications.
Direct visualization of the focal parameters of a high power CO2 laser beam
Authors: Rogozinski K. , Scott S. W. C. , Seguin H. J. J.
Published: July 2002

A diagnostic method for high power CO2 laser beams is presented. The technique features imaging of high intensity infrared radiation via the thermally induced luminosity of high velocity charcoal particles contained within an air stream. The method is particularly convenient for determination of focal position, depth of field, beam diameter, and spot size. Variations of these parameters with power level are easily observed utilizing this charcoal powder imaging method. Using this ‘‘real-time’’ technique, focal spot size and location accuracy are ±0.1 and ±1 mm, respectively. Results are shown to be independent of micro-particle size within specified limits. As a result, periodic, fine laser-workpiece adjustment is now cost effective when working with high power lasers.
Work function measurements using an improved thermionic projection microscope
Authors: Hinrichs C. H. , Mackie W. A. , Cohen Ira , Alin Jack , Schnitzler Don , Noel Ian
Published: July 2002

A quantitative thermionic projection microscope, employing computer image processing, is described. In this system, thermionic emission from a single-crystal hemispherical cathode is projected onto a phosphor screen and the resulting image is digitized by means of a video camera. Single-plane effective work functions for the highest emitting planes of the cathode may be measured to within a tenth of an electron volt.
A contactless method for measuring the bulk resistance of II–VI compound semiconductors
Authors: Wheeler Edward D. , Boone Jack L. , Drewniak James L.
Published: July 2002

A radio frequency measurement technique for measuring the bulk resistivity of II–VI compound semiconductors is described. Wafers of n-type CdS are used to demonstrate the technique. An equivalent circuit model is introduced which predicts a frequency dependence for the CdS wafer impedance which agrees well with the experiment. The model assumes a broad distribution of relaxation times associated with the polarization. The radio frequency method gives values for the resistivity within 15% of four point probe measurements for the lower resistivity wafers, and within 5% for the higher resistivity wafers.
High-temperature ovens (1700 °C) for a wide range of oxygen gas pressures (10−6–2×103 bar): A new two-chamber autoclave
Authors: Genoud J.-Y. , Graf T. , Triscone G. , Naula A.
Published: July 2002

We describe the construction of four different systems used for annealing samples in oxygen. The gas pressure can be controlled over nine decades (10−6–2×103 bar). The maximum temperature, 1700 °C, is limited by the ceramic materials used for thermal insulation and for the crucibles. The low-pressure furnaces (10−6–1 bar) have an external heating system and incorporate an active regulation of a small gas flow. The intermediate pressure furnaces (1–150 bar) are heated either by a special resistive wire or by rf heating with a Pt-20%Rh susceptor, both in the pressurized gas chamber. Quenching is possible in the latter. For the kbar range, we designed a double-chamber autoclave with separate heater and sample spaces, filled with Ar and O2. The gas pressures are balanced in a cold, separate vessel by means of a silicon hose. The temperature is measured with a thermocouple feeding into the hot, pressurized oxygen environment very close to the sample. The construction problems of this new autoclave have been solved with particular emphasis on the safety requirements.
Goddard Space Flight Center astronomical Fabry–Pérot imaging camera
Authors: Brown Larry W. , Woodgate Bruce E. , Ziegler Michael M. , Kenny Peter J. , Oliversen Ronald J.
Published: July 2002

An astronomical camera is described which consists of a scanning Fabry–Pérot Interferometric (FPI) system coupled to a charge coupled detector (CCD) imaging system. The Fabry–Pérot etalon equipment consists of a commercially available Queensgate system. The CCD equipment is a commercially available Photometrics system employing one of the early developmental CCD chips of the Space Telescope Imaging Spectrograph (STIS) project. The camera is controlled by a Digital Equipment Corporation Microvax II computer. Control of a filter wheel system and other housekeeping duties are done through a Kinetic Systems Camac controller commanded by the computer.
Spin-resolved time-of-flight electron spectroscopy following excitation with circularly polarized synchrotron radiation (abstract)
Authors: Snell G. , Kuntze R. , Müller N. , Heinzmann U. , Hergenhahn U. , Viefhaus J. , Wehlitz R. , Becker U.
Published: July 2002

A new type of spectrometer for the spin-polarization sensitive analysis of electrons has been developed. This instrument allows for multichannel detection by employing a retarding-field Mott polarimeter along with a time-of-flight analyzer for the energy selection of the incoming electrons. This method is particularly advantageous for spectra with many lines spread over a wide range of energies, as the whole spectrum can be recorded simultaneously. Such conditions are common for most cases of inner-shell photoionization, where in addition to the photolines a large variety of corresponding Auger lines occurs. The spectrometer was particularly designed to study such processes. First measurements were taken at the crossed-field undulator beamline U2 at BESSY. We obtained results for the Xe 5p photoelectrons in the photon energy range between 42 and 60 eV and for Xe 4d photoelectrons and the following NOO Auger decay at 95 eV.
Mössbauer coherent inelastic scattering of synchrotron radiation in perfect crystals (abstract)
Authors: Belyakov V. A.
Published: July 2002

A dynamical theory of coherent inelastic (accompanied by the creation or absorption of phonons in the crystal lattice) Mössabauer scattering of synchrotron radiation (SR) is developed. General equations describing an inelastic Mössbauer scattering are formulated, analyzed for the general case, and solved analytically for the cases permitting separation of polarizations. Detailed analysis of the solutions was performed for thick samples in the case of pure nuclear reflections. It is found that some qualitatively new effects compared with the case of elastic Mössbauer scattering [V. A. Belyakov, Diffraction Optics of Complex Structured Periodic Media (Springer, New York, 1992), Chap. 3] reveal themselves in the inelastic Mössbauer scattering of SR. They are, for example, different number of frequencies in the pendelosung beats versus a sample thickness, different fine structure of the angular distribution inside the region of strong diffraction, and effectively increased transparency of samples for the resonant component in the primary and diffraction directions.
Dispersive x-ray standing wave measurements
Authors: Gog T. , Hille A. , Bahr D. , Materlik G.
Published: July 2002

Conventional x-ray standing wave (XSW) measurements are performed in a ‘‘nondispersive’’ mode, generating interference fields with matched phases at any wavelength involved. In dispersive setups a mixing of XSW phases leads to broadened, less pronounced XSW yields and rocking curves which are reminiscent of the angular distribution of intensity in the incident x-ray beam. Nevertheless, even in extreme dispersive setups meaningful XSW measurements are feasible. These will benefit greatly from an increased initial collimation at high-brilliance, third generation synchrotron sources.
First inelastic x-ray scattering spectroscopy measurements of the dynamic structure factor S(q,ω) of electrons in a solid noble gas (He)
Authors: Schülke W. , Kaprolat A. , Gabriel K.-J. , Schell N. , Burkel E. , Simmons R. O.
Published: July 2002

Inelastic x-ray scattering spectroscopy measurements on hcp single crystal solid He with q∥c axis and q=0.45, 0.97, and 1.24 a.u. are presented. The crystals were grown in situ under a pressure of 600 bar at 5–7 K within a Be hollow cylinder. By subtracting a measurement on the empty Be cylinder, pure solid He spectra are obtained and discussed in terms both of the hcp He band structure and of excitonic excitation. The existence of an exciton at 21.8 eV above the 1s core level could unambiguously be settled. Clear evidence is found that the bottom of the conduction band is at 27 eV.
Soft x-ray emission spectrometer equipped with a multilayer rotating analyzer for study of the polarized emission
Authors: Yanagihara Mihiro , Goto Yoshinori , Miyata Noboru , Furudate Minaji
Published: July 2002

A soft x-ray emission spectrometer equipped with a multilayer rotating analyzer has been made. The spectrometer covers an energy range of 50–500 eV with a resolution power of about 300. Using the rotating analyzer we have measured the polarization of the B K emission of h-BN, and have found that it is dominantly polarized perpendicularly to the c-axis, which agrees well with the experimental result.
A multielement Ge detector with complete spectrum readout for x-ray fluorescence microprobe and microspectroscopy (abstract)
Authors: Rivers Mark L. , Sutton Stephen R. , Rarback Harvey
Published: July 2002

Multielement Ge and Si(Li) detectors have been used in recent years to improve the increase count rate capability and to improve the solid-angle efficiency in fluorescence x-ray absorption spectroscopy (XAS). Such systems have typically been equipped with one or more single-channel analyzers (SCAs) for each detector element. Such SCA-based electronics are sufficient when only the counts in one or two well-resolved peaks are of interest. For the fluorescence (XRF) microprobe at beamline X-26A at the NSLS, SCA-based electronics were not a satisfactory solution for two reasons: (1) for XRF experiments, the entire fluorescence spectrum is required; (2) for micro-XAS studies of trace elements in complex systems, the fluorescence peak often sits on a significant background or partially overlaps another fluorescence peak, requiring software background subtraction or peak deconvolution. An electronics system which permits collection of the entire fluorescence spectrum from each detector element has been designed. The system is made cost-effective by the use of analog multiplexors, reducing the number of analog-to-digital converters (ADCs) and multichannel analyzers (MCAs) required. The system was manufactured by Canberra Industries and consists of: (1) a 13 element Ge detector (11 mm diameter detector elements), (2) 13 NIM spectroscopy amplifiers with programmable gains, (3) four analog multiplexors with maximum of eight inputs each, (4) four ADCs with programmable offsets and gains and 800 ns conversion time, and (5) two MCAs with Ethernet communications ports and two ADC inputs each.

The amplifiers have shaping times which are adjustable from 0.5 to 12 μs. The analog multiplexors were modified to perform pileup rejection. The analog multiplexing does not significantly reduce the count rate capability of the system, even at the shortest amplifier shaping times. The average detector resolution is 170 eV at 12 μs shaping time and 200 eV at 4 μs shaping time. The maximum aggregate count rate is 400 kHz with 0.5 μs shaping time. The system is controlled by software based upon a package from Canberra and another commercial package (IDL), both running on a VAXstation 4000/90. The software automatically adjusts the gains of the amplifiers and offsets of the ADCs so that the spectra from each detector have identical calibrations and can be added channel for channel. The overhead to read a 1024 channel spectrum from each of the 13 elements and sum them is about 2 s. The software allows a range of options for data storage, from saving the complete spectrum for each of the 13 detectors elements (≳50 000 bytes/point) to saving only the net counts under a single fluorescence peak summed over all the detector elements (4 bytes/point). These data can be stored at each pixel in an elemental map or at each point in a monochromator scan. The system has been commissioned and is being used for XRF and micro-XAS studies.
Development of a circularly polarizing microscope with a polarizing undulator
Authors: Yamada Toru , Yuri Masatada , Onuki Hideo , Ishizaka Shozo
Published: July 2002

A circularly polarizing microscope by which we intend to obtain images with CD (circular dichroism) or CIDS (circular intensity differential scattering) in order to observe the structure and distribution of biomolecules has been constructed by using a polarizing undulator as the polarizing light source. The polarizing undulator with crossed and retarded magnetic field having fifteen periods was installed in the electron storage ring NIJI-II in the Electrotechnical Laboratory. A Schwarzschild-type mirror system combined with a convex mirror was developed in order to focus the undulator radiation to a microbeam keeping the quality of polarization of the radiation from the undulator. The beam size was from 0.66 μm (at wavelength 200 nm) to 0.96 μm (at 400 nm). Using a scanning sample stage and a photomultiplier which was positioned in the back of the sample, some images with transmitted and scattered light from fibrous DNA have been obtained. Attempts have also been made at obtaining images with CD and CIDS from the alternation between right- and left-handed circularly polarized radiation from the undulator.
Ultrahigh vacuum diffractometer for grazing-angle x-ray standing-wave experiments at a vertical-wiggler source
Authors: Sakata O. , Hashizume H.
Published: July 2002

An ultrahigh vacuum (UHV) diffractometer has been designed for studies of surface structures using the grazing-angle x-ray standing-wave method. The design is featured by a horizontal plane of diffraction for use at a vertical-wiggler source of synchrotron radiation. A sample is horizontally mounted in an UHV chamber (4×10−7 Pa) placed on crossed swivels, which control the glancing-incidence angle of x rays on the sample surface with a 50-μrad accuracy. The chamber accepts a sample from a transportation vessel under high vacuum. A beryllium window allows x-ray fluorescence to reach a semiconductor detector at short access. The whole assembly sits on a high-precision rotary table, regulating the sample Δθ angle with a reproducibility of better than 0.5 μrad required for control of the x-ray field profile. The system has been successfully applied to an accurate determination of the in-plane ordering of As atoms on a Si(111) surface with a 1×1 structure.
Design of a monochromatic ellipsometer for studies at the solid–liquid interface
Authors: Pai-Panandiker R. S. , Dorgan J. R.
Published: July 2002

A new design for a monochromatic ellipsometer used for studies at the solid–liquid interface is described. The design of the ellipsometer incorporates two novel features—a special optical glass cell and a thermally controlled sample oven. The ellipsometer design allows for in situ kinetic studies through use of the optical glass cell. Furthermore, the apparatus is modified to allow thermal equilibration over a range of temperatures. The temperature response of the cell assembly is presented and the response time is seen to be approximately 1 h. Data on the adsorption of a diblock copolymer [poly(ethylene oxide)–block–polystyrene] are presented; the analyzed data agree with previous studies on the same system.
Antenna decoupling requirements in a gyrotron collective Thomson scattering diagnostic (CTS)a)
Authors: Orsitto F. , Tartari U.
Published: July 2002

The required rejection ratio of the stray light in a CTS, respect to the launching power is investigated, for obtaining useful signal-to-noise ratio. This problem is faced considering the central gyrotron frequency f0, as well as the in-band stray light raising from the spurious mode of the gyrotron and amplified cyclotron emission (the so-called gyrotron noise), falling into the scattered light spectrum. The statistical nature of the gyrotron noise in the scattering band is important because the required decoupling is obtained using the S/N formula where the fluctuation of the plasma radiation and the gyrotron noise fluctuation appears. It turns out that the total decoupling required at f0 is of the order of or greater than 80 dB, while in the scattering band could be less than 40 dB.
Microwave scattering diagnostic on the Advanced Toroidal Facility torsatrona)
Authors: Shats M. G. , Likin K. M. , Wilgen J. B. , Harris J. H. , Sarksyan K. A. , Baylor L. R. , Bell J. D. , Bigelow T. S. , Dunlap J. L. , Goldfinger R. C. , Ma C. H.
Published: July 2002

A 2 mm scattering diagnostic used to study density fluctuations of the electron cyclotron resonance heated plasma in the Advanced Toroidal Facility is described. A four-channel flexible antenna design was chosen to monitor fluctuations within the wave number range of 3<k⊥<20 cm−1 and to locate the scattering volume anywhere in the stellarator minor cross section. Special attention was paid to the system calibration and to the normalization of the k spectra. Analysis of the diagnostic noise showed that the main source of spurious signal was a scattering from high-level edge turbulence driven by the second-harmonic radiation from the gyrotron used for plasma heating. This spurious signal was suppressed using waveguide filters and rearrangement of the microwave circuit elements. Evidence in support of direct scattering from a well-defined plasma volume was found. Good correlation of the scattered waves’ intensity with the density scale length was observed. Use of a dual-homodyne circuit configuration made is possible to determine that the plasma density fluctuations were propagating in the electron diamagnetic direction.
Diffraction of high-energy synchrotron radiation (invited) (abstract)
Authors: Brückel Th. , Bouchard R. , Köhler T. , Lippert M. , Neumann H.-B. , Poulsen H. F. , Rütt U. , Schmidt T. , Schneider J. R. , von Zimmermann M.
Published: July 2002

Diffraction of high-energy synchrotron radiation at energies above 100 keV combines advantages of conventional x-ray diffraction and neutron diffraction. For hard x rays absorption in matter is weak with typical mean free paths of several millimeters. Bulk properties are studied on large samples. With a three-crystal diffractometer an excellent k-space resolution of about 10−5 Å−1 transversal and 10−4 Å−1 longitudinal is achieved. In this contribution the particularities of hard x rays, the instrumental setup, and the k-space resolution are discussed and presented. The potential of the new method will be demonstrated on two examples: magnetic diffraction from MnF2 and the structural phase transition of SrTiO3.
Simple computer-controlled scanning for a coherent Stokes Raman scattering spectrometer
Authors: Rodriguez R. , Hackworth R. J. , Wells F. V. , Warner D.
Published: July 2002

Synchronous wave number-shift scanning of a Nd:YAG pumped dye laser and the detection monochromator for a coherent Stokes Raman scattering (CSRS) system were realized using an inexpensive analog to digital board. With this improvement the CSRS spectrometer may be used to scan over a large wave number shift range and/or may be used at relatively high resolution using a photomultiplier tube as the detector. This is especially useful in the probing of luminous systems.
Sub-kHz precision voltage-controlled-oscillator system for laser frequency control: An application in atom optics
Authors: Littler I. C. M. , Eschner J. H. , Bachor H.-A.
Published: July 2002

A system design is presented which allows a voltage controlled oscillator (VCO) to be tuned to an arbitrary frequency between 78 and 94 MHz with an accuracy better than 1 kHz (10 ppm). The temperature coefficient is on the order of 1 kHz/K, giving a long-term stability better than 1 kHz in a controlled environment. The slew rate for frequency switching is ≊10 MHz in 50 μs. The system comprises a computer-controlled precision voltage source, a spline interpolation of the voltage versus frequency characteristic, and good isolation of the VCO electronics from the subsequent circuitry. It provides an extremely low-cost alternative to frequency synthesisers. In our application involving the launching of slow atoms at a target, we can achieve atomic velocities as low as 10 cm/s with 1 cm/s precision.
A simple setup to simultaneously measure the resonant frequency and the absolute dissipation factor of a quartz crystal microbalance
Authors: Rodahl Michael , Kasemo Bengt
Published: July 2002

An experimental setup is described that can simultaneously measure the absolute dissipation factor and the resonant frequency of a short-circuited quartz crystal microbalance. The crystal is driven at approximately its resonant frequency by a signal generator which is intermittently disconnected by a relay, causing the crystal oscillation amplitude to decay exponentially. The decay is measured using a ferrite toroid transformer. One of the crystal leads is fed through the center of the ferrite toroid and thereby acts as the primary winding of the transformer. The secondary winding of the transformer is connected to a digitizing oscilloscope which records the decay of the crystal oscillation. From the recorded decay curve, the absolute dissipation factor (calculated from the decay time constant) and the series resonant frequency of the freely oscillating crystal are obtained. Alternatively, the dissipation factor and resonant frequency can be measured for the crystal oscillating under open-circuit conditions, i.e., in the parallel mode. The measurements are automated.
Automated microcoring device using custom core drills and lapidary techniques
Authors: Tucker R. F. , Secco R. A.
Published: July 2002

A simple, automated, fine-control, inexpensive, mechanical apparatus for coring thin samples is described. The apparatus consists of a motor-driven wheel attached to the feed handle of a microdrill press through an adjustable linkage that produces a peck drilling action. Using a Pb–Sn solder-tipped Cu or stainless steel core drill as a lapidary tool, cylindrical samples of ceramics, metals, and minerals with densities in the range 2.3–12.4 g/cm3 and as small as 250 μm in diam and 1.0 mm in length have been cored. Textures on the cored surface depend on sample type, grit size, core drill speed, etc., but surface height variations of 0.05–0.4 μm have been achieved with coring times in the range 1–6 h.
Electronic circuit for sustaining the oscillations of a vibrating element: Application to density measurements
Authors: Herrero-Álvarez J. , González-Gaitano G. , Tardajos G.
Published: July 2002

An electronic circuit has been designed to sustain the oscillations of a vibrating element. It has been applied to density measurements of fluids with a vibrating tube densimeter. The electronic part of the apparatus has been designed to avoid the presence of elements attached to the tube (such as wires or magnets), since the tube itself performs the excitation and the detection, making possible an easy manufacture. The mechanical part permits the best temperature control and a fast thermal response, since it can be totally immersed in a thermostat. The precision has been tested by calibration with pure substances and applied to density measurements of a colloidal solution (sodium decanoate in water). Relative measurements are obtained with a precision of better than 1×10−6 g cm −3, in the temperature range studied (between 293 and 313 K).
New setup for end-fire coupling excitation of planar waveguides at low temperatures
Authors: Marco de Lucas M. C. , Jacquier B. , Lebrasseur E. , Rivoire J. Y. , Varrel B.
Published: July 2002

This work describes a new experimental setup for end-fire coupling excitation of planar waveguides in the 300–10 K temperature range, which allows us to analyze their optical and spectroscopic properties through different techniques such as transmission, luminescence, or waveguide Raman spectroscopy. Two main novelties are relevant in this setup; (1) the use of long working distance microscope objectives, placed out of the cryostat, for both coupling and collecting guided light, and (2) the original set of mirrors, combined with different translation and rotation stages, which allows fine x,y,z,θ displacements of the beam focusing point preserving the laser beam alignment along the optical axis of the coupling objective. The setup has been tested in a series of Nd3+ doped ZBLA (ZrF4-BaF2-LaF3-AlF3) fluoride glass channel waveguides (from 2 to 40 μm width and 2 μm depth) obtained by ion-exchange and photolithography methods. The Nd3+ guided luminescence has been analyzed at low temperatures and compared to the spectra obtained for the bulk substrate.
Sensitivity enhancement in magnetic circular dichroism of absorption-detected electron paramagnetic resonance with a mirror cavity
Authors: Koschnick F. K.
Published: July 2002

A mirror cavity was developed to improve the signal to noise (S/N) ratio of the measurement of the magnetic circular dichroism of the absorption (MCDA) and of the MCDA-detected electron paramagnetic resonance (EPR). In this cavity the measurement light beam passes through the sample several times due to reflections between two mirrors. With our first prototype we improved the S/N ratio of the MCDA of a GaAs sample with five passages through the sample by a factor of approximately 4. MCDA-detected EPR signals were improved by a factor of approximately 3. The gain in sensitivity of the mirror cavity is demonstrated using the well-known EL2+ defect.