bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion implantation induced defects in SiO2: The applicability of the positron probe
Authors: Fujinami M. , Chilton N. B.
Published: July 2002

Boron ion implantation-induced defects in SiO2 were investigated using slow positron annihilation spectroscopy and electron spin resonance (ESR). The defects caused by ion implantation are manifest as a particularly low S parameter in the region of the SiO2 layer in which B implantation damage occurs. The annealing behavior of the defect responsible for positron trapping was studied. The defect to which the positron is sensitive is found to be unobservable in ESR measurements. The defect is suggested to be dissolved O2 or a charged Frenkel defect, such as the negative nonbridging-oxygen hole center (≡Si—O−).
On the doping efficiency of nitrogen in hydrogenated amorphous germanium
Authors: Chambouleyron I. , Zanatta A. R.
Published: July 2002

This letter reports on the doping efficiency of nitrogen in a-Ge:H films of electronic quality. It has been found that nitrogen is an effective dopant in the a-Ge:H network, its doping efficiency being similar to the one corresponding to phosphorus in a-Si:H. The concentration of active nitrogen atoms decreases with impurity content following a square root dependence on total nitrogen. This behavior is similar to the one determined for column V dopants in a-Si:H films of electronic quality.
Intrinsic superconducting radiation detector
Authors: Flik M. I. , Zhang Z. M. , Goodson K. E.
Published: July 2002

A novel radiation detector, the Intrinsic Superconducting Radiation Detector (ISRD), is proposed. It employs the temperature dependence of the critical current of high Tc superconducting films to determine the detector temperature change caused by incident radiation and operates almost exclusively in the superconducting state. The ISRD has the potential to be a phonon-noise-limited thermal detector.
Reverse saturable absorption in solid xerogel matrices
Authors: Bentivegna Florian , Canva Michael , Georges Patrick , Brun Alain , Chaput Frédéric , Malier Laurent , Boilot Jean-Pierre
Published: July 2002

Aluminophthalocyanine (APC) and fullerene carbon 60 (C60) have been studied encaged in different silica matrices. The reverse saturable absorption properties of these doped xerogels have been compared to those of reference solutions of APC and C60. We show that reverse saturable absorber molecules retain their properties even when they are enclosed in the pores of a solid xerogel matrix.
Electrical picosecond measurements of the photoresponse in YBa2Cu3O7−x
Authors: Ghis A. , Villegier J. C. , Pfister S. , Nail M. , Gibert Ph.
Published: July 2002

Ultrafast transient voltage pulses (rise time 12 ps, width 29 ps) have been observed at 50 K across a current-biased very thin YBa2Cu3O7−x epitaxial film (thickness 30 nm) when illuminated by short laser pulses. The accuracy of the present measures shows the system reaction during the first tens of picoseconds. Such very narrow photosignals can be described as related to nonequilibrium phenomena. The measured decay times corroborate the biexponential escape of the deposited energy described by other authors.
High contrast Fabry–Perot optical modulator using quantum confined Stark effect tuning in InGaAs-GaAs multiple quantum well cavity
Authors: Cheung S. , Jain F. , Sacks R. , Cullen D. , Ball G. , Grudkowski T.
Published: July 2002

Tunable Fabry–Perot modulators, consisting of strained InGaAs-GaAs multiple quantum well (MQW) layers, have been shown to yield a contrast over 1200:1. Tuning is achieved by varying the index of refraction of the MQW layers forming the cavity using a quantum confined Stark effect. The mirrors are realized by AlAs-GaAs quarter wave λ/4 dielectric stacks having 12 and 15.5 periods, respectively. The device has the potential of achieving even higher tunable contrast ratios when the number of periods of the λ/4 mirrors are increased. A contrast ratio of 6000:1 has been achieved for a nontunable structure. Measured data on optical transmission and contrast ratio are presented for various wavelengths as a function of applied bias. Results of simulation of transmitted output are also discussed.
Noncontact characterization for grown-in defects in Czochralski silicon wafers with a laser/microwave photoconductance method
Authors: Ikeda Naoki , Buczkowski Andrzej , Shimura Fumio
Published: July 2002

Minority-carrier recombination lifetime mapping has been performed with a noncontact laser/microwave photoconductance method for as-polished wafers containing a ring-shaped distribution of embryonic defects which form stacking faults during subsequent heat treatment. Using an algorithm for the separation of bulk and surface components of the recombination lifetime, four regions, which cannot be distinguished with other techniques such as x-ray topography and preferential chemical etching, were clearly observed in the maps as those with different lifetimes. The result can be attributed to the inhomogeneous distribution of grown-in defects, most likely intrinsic point defects and/or oxygen related defects. Moreover, the lifetime was correlated to the surface microroughness of the polished wafers.
Radius tailoring of an intense relativistic electron beam using a fast rise-time focusing coil
Authors: Weidman D. J. , Rhee M. J. , Schneider R. F. , Nguyen K. T. , Stark R. A.
Published: July 2002

A ‘‘radius-tailored’’ electron beam, which is tapered with a larger head and a smaller tail, has been generated. This has been accomplished by injecting the electron beam into a fast rise-time magnetic focusing coil, so that the beam head expands while the beam body and tail are confined by the axial magnetic field. Time-resolved beam radius measurements indicate that a beam radius tailoring on the order of 3 to 1 has been achieved. This result is also in agreement with computer simulations.
Effect of thermal self-defocusing of degenerate four wave mixing in absorbing media
Authors: Tomov I. V. , Rentzepis P. M.
Published: July 2002

The distortion of a phase conjugate wave produced by degenerate four wave mixing as a consequence of thermal self-defocusing is reported. The thermally induced refractive index changes cause modulation in the phase of the phase conjugate wave. The thermal self-defocusing effect may impose a limiting factor in high repetition rate nonlinear devices.
Element specific magnetic domain imaging from an antiferromagnetic overlayer system
Authors: Kachel T. , Gudat W. , Holldack K.
Published: July 2002

Magnetic circular dichroism in resonant photoemission combined with a space resolving photoelectron spectrometer has been applied to measure magnetic domain structures with a spatial resolution of ≊10 μm. The tunability of the photon energy and the kinetic energy of photoelectrons provides a high degree of element specifity and magnetic contrast. We have applied the technique to 1 monolayer Gd on Fe(100) which allowed to measure magnetic domains in the Gd overlayer independently from the domains of the Fe substrate. Due to the antiferromagnetic coupling between Fe and Gd and because of the element specifity we could observe inverted domain images for the substrate and the overlayer.
Characterization of process-induced strains in GaAs/Ga0.7Al0.3As quantum dots using room-temperature photoreflectance
Authors: Qiang H. , Pollak Fred H. , Tang Y.-S. , Wang P. D. , Sotomayor Torres C. M.
Published: July 2002

Using contactless photoreflectance at 300 K, we have studied several GaAs/Ga0.7Al0.3As quantum dot arrays fabricated by reactive-ion etching using SiCl4. The spectrum from a control sample that had no dots also was recorded. From the observed shifts of the fundamental conduction to heavyand of the process-induced strain in the dots.
Stress-induced leakage current in ultrathin SiO2 films
Authors: Patel N. K. , Toriumi A.
Published: July 2002

A detailed study of the phenomena of high field stress-induced leakage current in thin oxide (5.0–8.0 nm) metal-oxide-semiconductor capacitors has been undertaken. The dependence of the stress leakage on the stressing electric field and the oxide thickness were obtained. The results show that the stressing voltage, rather than the electric field, is the dominant factor for determining stress-induced leakage. Furthermore, a threshold exists for the stressing voltage, below which no stress-induced leakage occurs. Since the voltage is directly related to the electron energy, these findings are consistent with a model where electrons of energy above a threshold are required to produce the observed stress leakage.
Microstructure study of a degraded pseudomorphic separate confinement heterostructure blue-green laser diode
Authors: Hua G. C. , Otsuka N. , Grillo D. C. , Fan Y. , Han J. , Ringle M. D. , Gunshor R. L. , Hovinen M. , Nurmikko A. V.
Published: July 2002

The microstructure of a degraded II-VI blue-green laser diode based on the ZnCdSe/ZnSSe/ ZnMgSSe pseudomorphic separate confinement heterostructure has been examined by transmission electron microscopy. Triangular nonluminescent dark defects observed in the laser stripe region by electroluminescence microscopy have been identified to be dislocation networks developed at the quantum-well region. The dislocation networks have been observed to be nucleated at threading dislocations originating from pairs of V-shaped stacking faults which are nucleated at or near the II-VI/GaAs interface and extending into the n-ZnMgSSe lower cladding layer.
Growth rate enhancement using ozone during rapid thermal oxidation of silicon
Authors: Kazor A. , Gwilliam R. , Boyd Ian W.
Published: July 2002

Rapid thermal oxidation of Si in a mixed oxygen and ozone ambient in the temperature range of 600–1200 °C is reported. Between 600 and 800 °C a large enhancement in oxidation is observed compared with conventional oxide growth in a pure oxygen ambient. For temperatures above 950 °C conventional thermal oxidation dominates and no significant enhancement is found.
Voltage tunable potential wells for wire confinement of excitons
Authors: Yater J. A. , Kash K. , Chan Winston K. , Ravi T. S. , Gmitter Thomas J. , Florez Leigh T. , Harbison James P.
Published: July 2002

We use applied voltage to modulate lateral strain in a quantum well, thereby achieving tunable confinement of excitons. A capacitor structure is fabricated by attaching a flexible film containing a quantum well and a conducting layer to a doped Si substrate patterned with raised ribs. The film conforms to the ribs, creating a potential well for excitons where the quantum well is in tension. The film is pulled toward the substrate through electrostatic force, increasing the confinement. Modulation of strain confinement by over 50% is reported. The effect is reversible with voltage and polarity independent, as expected for electrostatic attraction.
Superconducting quantum interference device magnetometry during ultrahigh vacuum growth
Authors: Pappas D. P. , Prinz G. A. , Ketchen M. B.
Published: July 2002

An in situ study of the absolute magnetic moment of thin ferromagnetic films grown in ultrahigh vacuum (UHV) is described. The moments are measured using a newly innovated technique, rotating sample superconducting quantum interference device (SQUID) magnetometry (RSSM), in which the sample is spun at low frequency close to an ex situ second derivative superconducting pickup loop structure coupled to a rf SQUID. The sensitivity of the measurements is ≊10−6 emu, which corresponds to 1/10 of an atomic layer of Fe over a 0.5 cm2 area, and the geometry of the pickup loops makes the magnetometer very insensitive to background laboratory noise. The moment of Cr grown on Fe was measured. It was determined that the first two layers of Cr have an average moment of 0.75 μB per atom, and are antiferromagnetically aligned to the Fe film moment. The simplicity of RSSM and the fact that the absolute moment is measured makes this a powerful new approach for characterization of magnetic samples in UHV.
Photorefractive polymer composite with net gain and subsecond response at 633 nm
Authors: Malliaras G. G. , Krasnikov V. V. , Bolink H. J. , Hadziioannou G.
Published: July 2002

By combining the well-known photoconductor poly(N-vinyl carbazole) sensitized with 2,4,7 trinitro-9-fluorenone and the electrooptic molecule N,N, diethyl-substituted para-nitroaniline, which is transparent at 633 nm, a photorefractive polymer composite suitable for applications with He-Ne lasers was developed. Net gain of 18 cm−1 and 400 ms response time were measured on a 65-μm-thick sample.
Precipitation in Fe- or Ni-implanted and annealed GaAs
Authors: Chang J. C. P. , Otsuka N. , Harmon E. S. , Melloch M. R. , Woodall J. M.
Published: July 2002

We report the formation of metal/semiconductor composites by ion implantation of Fe and Ni into GaAs and a subsequent anneal to nucleate clusters. Electron diffraction experiments and high resolution transmission electron microscopy images indicate that these precipitates are probably hexagonal and metallic Fe3GaAs or Ni3GaAs with orientation relationship to GaAs of (101̄0)pp∥(422̄)m, (0002)pp∥(111̄)m, and [12̄10]pp∥[011]m. Correlation of the electrical and structural properties of the samples annealed at different temperatures shows that the buried Schottky-barrier model has general applicability.
Enhanced negative ion formation in ultraviolet-laser irradiated silane: Implications for plasma deposition of amorphous silicon
Authors: Pinnaduwage Lal A. , Martin Madhavi Z. , Christophorou Loucas G.
Published: July 2002

Observation of enhanced electron attachment to ArF-excimer-laser irradiated silane is reported. Evidence is presented that highly excited electronic states of silane or its photofragments are responsible for the observed enhanced electron attachment. Since such electronically excited states may be produced in silane plasmas (by direct electron impact or by excitation transfer via metastable states of rare gases that are commonly used in silane discharges), the possible significance of this electron attachment process for negative ion formation in silane plasmas is indicated.
Monolithic strained-InGaAsP multiple-quantum-well lasers with integrated electroabsorption modulators for active mode locking
Authors: Sato Kenji , Wakita Koichi , Kotaka Isamu , Kondo Yasuhiro , Yamamoto Mitsuo , Takada Atsushi
Published: July 2002

Active mode locking by monolithic lasers with integrated electroabsorption modulators using strained-InGaAsP multiple quantum wells is described. The electroabsorption modulator acts as a short optical gate when a sinusoidal voltage is driven at a deep bias point. Pulse widths as short as 2 ps have been obtained at a repetition rate of 16.3 GHz for a 2.5-mm-long monolithic laser.
Damage induced by plasma etching: On the correlation of results from photoluminescence and transport characterization techniques
Authors: Linke H. , Maximov I. , Hessman D. , Emanuelsson P. , Qin Wang , Samuelson L. , Omling P. , Meyer B. K.
Published: July 2002

Plasma dry etching, used for the fabrication of low-dimensional structures, is known to create defects in the material which affect both the optical and the transport properties of the sample. We compare the results obtained from three different methods of characterizing the damage induced by electron cyclotron resonance metalorganic reactive ion etching to the two-dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructures: photoluminescence, transport measurements, and electron paramagnetic resonance. Etching impairs the quality of luminescence and decreases the single-particle relaxation time, while the concentration of a surface related paramagnetic defect (probably dangling bonds) is increased. However, detailed experiments show no correlation between the density of defects and transport or luminescence properties, nor between transport and luminescence properties. In particular, hydrogen passivation, which improves the luminescence properties after etching, leads to deteriorated transport properties.
Very low resistance nonalloyed ohmic contacts using low-temperature molecular beam epitaxy of GaAs
Authors: Patkar M. P. , Chin T. P. , Woodall J. M. , Lundstrom M. S. , Melloch M. R.
Published: July 2002

Ex situ nonalloyed ohmic contacts were made to n- and p-type GaAs using low-temperature molecular beam epitaxy. For n-type GaAs, Ag, and Ti/Au nonalloyed contacts displayed specific contact resistitivities of mid 10−7 Ω cm2. For p-type GaAs, nonalloyed Ti/Au contacts with specific contact resistivities of about 10−7 Ω cm2 were obtained.
Picosecond all-optical switching in a Fabry–Perot cavity containing polydiacetylene
Authors: Quintero-Torres R. , Thakur M.
Published: July 2002

Off-resonant nonlinear optical measurements have been made in a Fabry–Perot cavity containing a polydiacetylene (PTS) single crystal. The cavity length was controlled to select specific bias points on the Fabry-Perot fringe and the measurements were made by a pump-probe technique using 90 ps pulses at 1.06 μm wavelength. The changes in transmission at selected bias points were measured as a function of time delay between the pump and the probe. The measured response time was found to be pulse-width limited and the maximum changes in transmission were as large as 50% at low optical intensities (∼10 MW/cm2). The sign of n2 was determined from the direction of the fringe shift and was found to be negative. All-optical switching (82 MHz) at a picosecond time scale is demonstrated for an organic material.
Gettering of nickel to cavities in silicon introduced by hydrogen implantation
Authors: Mohadjeri B. , Williams J. S. , Wong-Leung J.
Published: July 2002

Almost complete gettering of Ni in (100) Si was obtained by initially implanting H to a depth of ∼0.9 μm, followed by Ni implantation close to the surface, and subsequent thermal annealing. H-induced cavities, as evidenced by transmission electron microscopy, act as efficient gettering sites for Ni. By performing Ni implantations at various doses and at elevated sample temperature, it was shown that formation of amorphous silicon caused by Ni implantation significantly reduces the gettering efficiency. The results will be discussed taking diffusion and solubility of Ni in Si into account, as well as formation of NiSi2 precipitates.
Photocurrent polarization in long-range ordered Ga0.5In0.5P
Authors: Kita Takashi , Fujiwara Akira , Nakayama Hiroshi , Nishino Taneo
Published: July 2002

Photocurrent polarization properties near the band gap of long-range ordered Ga0.5In0.5P have been investigated. The linearly polarized PC spectra of the ordered Ga0.5In0.5P show an absorption anisotropy for the [110] and [11̄0] directions together with a large band-gap reduction. The anistotropy in the PC spectra is due to a crystal-field splitting at the valence-band maximum in ordered Ga0.5In0.5P. The PC edge of the [110] polarization is lower at about 10 meV than one of the [11̄0]. The polarization spectra defined by (I110−I11̄0)/(I110+I11̄0), where I110 and I11̄0 are the PC signal intensities measured at the [110] and [11̄0], respectively, show a single broad peak. The maximum polarization reaches about 50% at the energy of the transition between Γ6c and Γ4v, Γ5v. With increased sample temperature, the polarization maximum shifts to the lower energy side according to the change of the Γ6c-Γ4v,Γ5v transition energy. Even at room temperature, a clear polarization signal was observed.
Microstructure, thermal, and mechanical properties of nanostructured Cu-9.5Ni-4.0Sn-7.5P
Authors: Li J. , Wang T. M.
Published: July 2002

Nanostructured Cu-9.5Ni-4.0Sn-7.5P samples represent a polycrystal microstructure of nanometer-sized α-Cu and Cu3P crystallites for crystallite sizes less than 20 nm and of nanometer-sized α-Cu, Cu3P, and Ni2P crystallites for crystallite sizes greater than 20 nm. The specific heat values between 300 K and 400 K for the nanostructured sample with crystallite size of 10 nm are about 20% higher than for the amorphous sample and about 40% higher than for the coarse-grained sample. The hardness of the nanostructured sample with crystallite size of 10 nm is 30% higher than that of the amorphous sample and 110% higher than that of the coarse-grained sample. The variation in hardness with the crystallite size for the nanostructured samples follows the Hall-Petch relationship.
Easy-to-use Mössbauer system with simultaneous display
Authors: Wallingford Errol , Bordeleau Claude
Published: July 2002

The Mössbauer interface system described herein offers a unique implementation with distinct advantages over conventional systems that use a time-consuming interrupt mode. These advantages include simultaneous display of all 1024 channels during data accumulation, optional scaling of Mössbauer spectra, software control of drive frequency, alternate use of two counters to provide zero dead time between channel advances, and autoscaling of spectra in the pulse-height analysis (PHA) operation. The present implementation completely avoids the use of an external waveform generator through an efficient design. A sophisticated and fast 16-bit microcomputer is used instead to generate the triangular wave in synchronization with data accumulation and display. The elegant assembly language software which balances all timing operations to the exact clock cycle is essential in achieving high performance. External support hardware is also kept to a minimum. High performance is further achieved by accumulating and storing data in double precision (32 bits) on all 1024 channels.
Technique to determine solute diffusion coefficient and partial pressure simultaneously
Authors: Zee R. H. , Watters J. F. , Davidson R. D.
Published: July 2002

A simple technique to measure simultaneously the diffusion coefficient and the partial vapor pressure of a solute in a homogeneous solid solution is presented. The analysis is based on the mathematical solution of the diffusion equation for a cylindrical system with a solute loss term at the cylinder surface. The magnitude of the loss term is proportional to the solute concentration at the surface. Three zirconium rods, one with 3 at. % Sn, one with 5 at. % Sn, and one with 4 at. % Ti, were treated in vacuum at 1875 K for 7, 5, and 2.5 h, respectively. Results from these specimens indicate that Sn and Ti both diffuse via a vacancy mechanism in β-Zr. Also, the Sn–Zr bonds appear to be much stronger than the Sn–Sn bonds, whereas the Ti–Zr bonds seem to be a little weaker than the Ti–Ti bonds.
Status of the multiply charged heavy-ion source MINIMAFIOS
Authors: Geller R. , Jacquot B. , Pontonnier M.
Published: July 2002

The principles, construction, and performance of the MINIMAFIOS electron cyclotron resonance ion source (ECRIS) are reviewed. The source can operate either pulsed, with pulse width of >50 ms, or cw, with 1011 fully stripped light ions per second and much higher amounts of lower charge state ions. The source has excellent reliability and reproducibility. It has acceptable emittance and energy dispersion. The manner of operation and adjustment of the source is very simple since it depends only on the two parameters: gas feed and rf power injected. In addition, metallic ions can be produced directly. ECRIS is well suited for injection into heavy ion accelerators and for atomic physics. Its high ion fluxes in a quasicontinuous regime are useful for numerous other applications and open new fields for scientific research with multiply charged ions. Thus, more and better sources are desired. New ideas have been proposed and new sources have been built or are under construction. We present the latest performance data of MINIMAFIOS for gaseous elements as a reference for evaluating the performance of new ECRIS in various laboratories. For metallic ions we need more experimental results in order to establish basic data references.
Nondispersive x-ray spectroscopy and imaging of plasmas using a charge−coupled device
Authors: Marsh K. , Joshi C. , Janesick J. , Collins S.
Published: July 2002

An 800×800 Texas Instruments virtual phase charge-coupled device (CCD) was used to obtain pinhole images and x-ray spectra of laser-produced, solid target plasmas. With the CCD used in the single-photon counting mode, the spectrum in the energy range 2–10 keV was obtained without a dispersive element. Typical spectra reveal two distinct temperatures: a ‘‘cold’’ component of approximately 200 eV and ‘‘hot’’ component of approximately 5 keV. Also, multiline spectra comprising characteristic line emission (Kα, Kβ) from a multilayer target bombarded by β rays were recorded using a three-phase CCD. The results demonstrate the potential of CCDs as imaging spectrometers with application in space, laboratory, and fusion plasma research.
High-temperature containerless calorimeter
Authors: Robinson Michael B. , Lacy Lewis L.
Published: July 2002

A high-temperature (> 1500 K) containerless calorimeter is described and its usefulness demonstrated. The calorimeter uses the technique of omnidirectional electron bombardment of pendant drops to achieve an isothermal test environment. The small heat input into the sample (i.e., 15–50 W) can be controlled and measured. The apparatus can be used to determine the total hemispherical emissivity, specific heat, heat of fusion, surface tension, and equilibrium melting temperature of small molten drops in the temperature range of 1500 to 3500 K. The total hemispherical emissivity εT and specific heat Cp of pure niobium and two alloys of niobium–germanium have been measured in the temperature range of 1700 to 2400 K. As reported in the literature, εT varied as a function of temperature. However, Cp values for both the pure metal and alloys seem to be independent of temperature. Cp for the liquid alloy phase was also measured and compared to the solid phase.
Small acousto-optic modulation for active mode locking in the iodine photodissociation laser and the effect of supplementary saturable absorber
Authors: Kim Yeong Sik , Lee Sang Soo
Published: July 2002

Active, passive, and active–passive mode locking of the iodine photodissociation laser are investigated. The peak-to-background ratio (PBR) of the acousto-optically mode-locked pulse is 85% for rf power of 5 W. Passive mode locking using BDN dye gives PBR of 75% and has inferior reproducibility. The active–passive mode locking using the two methods simultaneously is useful for the pressure broadened iodine laser line and gives a PBR of 91%. In this case the rf power required for complete mode locking is calculated to be 7 W which is much less than the required power of 11 W in using active mode locking alone.
Electron temperature measurements from induced toroidal current in ELMO Bumpy Torus-Scale
Authors: Uckan Taner
Published: July 2002

We have carried out measurements on ELMO Bumpy Torus Scale (EBT-S) to estimate the electron temperature of the toroidal plasma by inducing a small (∼2 A) fluctuating (5 Hz) ac toroidal current. The modulating frequency used is low enough to minimize the effects of cavity skin time (∼100 ms) and plasma inductance. We have calculated the temperature from the measured values of the current obtained by use of the Rogowsky loop at various fill pressures at 100 kW with 28-GHz operation. The electron temperature has been estimated to be around 80–90 eV with an error of about 10%–25% in the low T mode, which is in good agreement with the Thomson scattering measurements.
Effect of filter frequency response on the uncertainty in measuring statistical estimators of input noise
Authors: Roberts M. J. , Blalock T. V.
Published: July 2002

It is shown that in a system consisting of a bandpass filter followed by an ideal linear detector and then an integrator, with white noise as the system input, the statistical uncertainty of the output of the integrator depends on the shape of the bandpass filter power transfer function. That is, for a constant integration time and a constant equivalent noise bandwidth (defined in the usual sense), the statistical uncertainty of the integrator output is a function of the shape of the bandpass filter power transfer function. A new equivalent noise bandwidth is proposed to account for this variation with filter shape so that the relations derived by Rice for rectangular cutoff bandpass filters can be used.
Application of diode array spectrometers in microscope photometry
Authors: Koch Klaus-P. , Maechler Meinrad , Glueck Franz
Published: July 2002

Multichannel fast scanning diode array spectrometers represent a new class of spectroscopic instruments. They feature a unique combination of novel technologies, speed, comfort in handling, and ease of operation. In a research study the potentials of this powerful instrument in the field of microscope photometry are evaluated. As examples for possible applications the results of typical spectral measurements in absorption and reflection, including film-thickness determination of microstructured semiconductor layers, are presented.
Use of electron beam position modulation in Auger depth profile analysis
Authors: Leung M. S. , Stupian G. W.
Published: July 2002

Auger analysis combined with ion etching in the scanning Auger microprobe (SAM) provides ‘‘three-dimensional’’ composition information not readily obtainable from other analytical methods. As this technique is being applied to the analysis of microelectronic devices with increasingly smaller dimensions, two major limitations became evident: (1) features of interest in microelectronic circuits are often comparable in size to the beam diameter of commercial Auger microprobes and (2) the electron beam tends to drift about on the specimen surface because of mechanical instability and differential thermal expansion. We describe a technique that will reduce the error and uncertainty caused by beam instability. In our technique, the analyzing beam is scanned repetitively across the feature to be profiled and the Auger signal is synchronously detected at the scan frequency. This position modulation technique allows a tradeoff between depth resolution and sensitivity on the one hand and drift in spatial position of the analyzing electron beam. Position modulation is particularly suited to the analysis of microelectronic devices (e.g., microwave field effect transistors), where the dimensions of features of interest are comparable to the electron beam diameter.
Measurements of density, surface recombination coefficient, and diffusion coefficient of hydrogen atoms by Lα laser fluorescence spectroscopy
Authors: Kajiwara Toshinori , Inoue Masayuki , Okada Tatsuo , Muraoka Katsunori , Akazaki Masanori , Maeda Mitsuo
Published: July 2002

The technique of laser fluorescence spectroscopy at the Lyman-alpha (Lα) wavelength in hydrogen was used to measure the temporally and spatially resolved atomic density, the surface recombination coefficient γ, and the diffusion coefficient DH,H2 of the atomic hydrogen in molecular hydrogen. At the same time, it revealed a temporal change of γ, probably due to the change of surface number density of trapped hydrogen atoms. The present technique provides a new and powerful means for determinations of values associated with hydrogen atoms by absolute and local measurements of the atoms at the detection limit of extremely low concentrations.
Application of far-infrared, integrated detector arrays to chord-averaged plasma measurements (invited)
Authors: Young P. E.
Published: July 2002

The recent development of linear, monolithic microbolometer detector arrays for the far infrared has led to the construction of active imaging diagnostics for tokamak plasmas. Detector arrays have an advantage over discrete detectors in that the cost per detector is significantly reduced since many detectors are fabricated simultaneously. Also, the plasma can be probed with a higher spatial resolution than conventional discrete-beam systems because of the higher channel density. Another advantage is provided by the increased channel number which is important to chord-averaged measurements since it allows an increase in the accuracy of the calculation of Abel inversions of the measured line density profile which are used to reconstruct the actual electron density distribution. The usefulness of this technique has been demonstrated on the UCLA Microtor tokamak (a=11 cm, BT =20 kG, I=70 kA, ne =5×1013 cm−3) in which a 20-channel heterodyned interferometer at wavelengths of 800 and 1000 μm has been used to study the behavior of the plasma profile. Line density profiles during the startup phase of the tokamak discharge have been obtained, as well as sawtooth fluctuation profiles. The imaging technique can also be applied to Faraday rotation measurements of the poloidal magnetic field in the tokamak. A 20-channel polarimeter has been developed that operates simultaneously with the multichannel interferometer.
Device for computer-controlled potential modulation in electrochemical Fourier transform infrared spectroscopy
Authors: Corrigan Dennis S. , Milner David , Weaver Michael J.
Published: July 2002

A circuit has been designed for the automatic control of potential modulation for subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) using an IBM IR/90 series FTIR spectrometer. This device enables the potential modulation to remain synchronized with the spectral data collection under all conditions.
Novel spatial scanning method for tokamak spectroscopy
Authors: Ramsey Alan T.
Published: July 2002

For spectroscopic diagnostics, the problem of optical access to all poloidal regions of the plasma in a large tokamak is severe. One must scan a large angle through a small window in a high magnetic field, often at elevated temperatures. Moving systems have problems in such an environment. A method is described here which uses only a static, curved mirror at the tokamak window. The rest of the elements (field lenses, a small mirror scanner, and the spectrometer) are in another room. The details of a design for the tokamak fusion test reactor (TFTR) are presented. Scan angles of ±40° are easily achieved, the optics of the spectrometer are filled, and the scan angle in the plasma is linearly proportional to the ramp voltage applied to the scanner.
Preparation and characterization of ultrathin porous silicon films
Authors: von Behren J. , Tsybeskov L. , Fauchet P. M.
Published: July 2002

Light emitting porous silicon thin films with thicknesses from ∼0.1 to ∼100 μm were produced by electrochemical etching and subsequently lifted off the silicon wafer by an electropolishing step. The structural integrity of the thinner layers was maintained by deposition on sapphire windows where they remain attached by van der Waals or electrostatic forces. The procedure for manufacturing high quality layers and their structural and optical properties is discussed.
Precision phase measurement with short tone burst signals in acoustic microscopy
Authors: Liang K. K. , Bennett S. D. , Kino G. S.
Published: July 2002

A new phase measurement system based on a sychronous detection scheme is described. It is capable of yielding high precision phase data with very short tone bursts. A theoretical analysis of the system is given and system performance characteristics are also discussed. This phase measurement technique is especially suited for acoustic microscopy applications. Examples in material characterization and surface topography mapping are presented.
Efficient signal recovery from pulsed lasers
Authors: Kumar D. , Nauman R. V. , McGlynn S. P.
Published: July 2002

This paper is complementary to a recent work [Kumar et al., Rev. Sci. Instrum. 54, 463 (1983)] that described a simple, inexpensive technique for correcting laser-induced, pulsed signals for fluctuations of the individual laser excitation pulses. This inexpensive pulse-by-pulse correction technique, based on analog circuitry, exhibits an improved time-constant characteristic and is applicable to both linear and nonlinear processes. Circuit details are presented here and the versatility of the technique is illustrated by laser optogalvanic spectroscopy of the iodine molecule.
Contactless scanner for photoactive materials using laser-induced microwave absorption
Authors: Beck G. , Kunst M.
Published: July 2002

Conventional laser scanning techniques for the topological characterization of photoactive materials and devices are hampered by the need to apply electrical contacts. We present a technique to overcome this limitation using the relative change of reflected microwave power to probe the conductivity locally induced in the sample. After a discussion of the theoretical background and the limitations of the method the apparatus is described. Application to scan the surface of a semiconductor chip carrying an electrode structure is used to discuss the resolution and linearity.
High-resolution He-scattering apparatus for gas–surface interaction studies
Authors: David Rudolf , Kern Klaus , Zeppenfeld Peter , Comsa George
Published: July 2002

A high-resolution apparatus designed for the study of elastic and inelastic scattering of thermal helium atoms from crystal surfaces is presented. The highly expanded He nozzle beam has an energy spread ΔE/E of about 1.4% and is collimated to 0.2°. The angle subtended by the detector opening as seen from the sample is also 0.2°. Beam intensities as low as 10−6 of the specular beam intensity from a low-temperature clean Pt(111) surface are detectable. Pseudorandom chopping with a resolution of 2.5 μs (flight path 790 mm) is used for time-of-flight (TOF) analysis of the scattered helium. The base pressure in the sample chamber is in the low 10−11 mbar. The capabilities of the apparatus are demonstrated for physisorbed Xe adlayers on Pt(111). The results presented are obtained by using He scattering in various modes: coherent inelastic, coherent elastic, and incoherent (diffuse) elastic. This technique allows for a nondestructive nearly exhaustive characterization of the thermodynamics, structure, and dynamics of physisorbed adlayers on arbitrary substrates.
Simple low-energy sputter ion gun based on a Bayard–Alpert pressure gauge
Authors: Kirschner J.
Published: July 2002

The design and performance of a simple sputter ion gun is given. It uses a commercial Bayard–Alpert ionization gauge. A two-stage extraction and acceleration system provides a variable beam profile as well as high currents at low energies (>1 μA above 200 eV). At a distance of 4 cm from the end of the gun a current density of more than 150 μA/cm2 was obtained at 1.2 keV. A narrow energy distribution may also be obtained (≤1.6 eV FWHM at 1.2 keV).
Measurement of multidimensional ion velocity distributions by optical tomography
Authors: Koslover R. , McWilliams R.
Published: July 2002

We report the development of a new diagnostic capable of measuring plasma ion distributions as a function of all three velocity–space coordinates. The diagnostic makes use of laser-induced fluorescence (LIF) and computer-assisted image reconstruction techniques. LIF yields high-resolution, nonperturbing measurements of one-dimensional distributions that are integrated in two directions through three-dimensional velocity space. Computer tomography allows for the unambiguous determination of the complete ion velocity distribution. In addition to a description of the diagnostic, examples of recovered distributions obtained from experiments are given, and the effects of the major steps in the data processing are discussed.
Simple color center laser optothermal molecular beam spectrometer for high-resolution infrared spectroscopy
Authors: Kyrö E. K. , Shoja-Chaghervand P. , Eliades M. , Danzeiser D. , Bevan J. W.
Published: July 2002

A broadband tunable single-frequency color center laser optothermal molecular beam spectrometer has been constructed. K components have been resolved for P(18) to R(11) rovibrational transitions in ν1 CH3C≡C–H. The observed transition linewidths are demonstrated to be ≤6 MHz and are determined with a relative precision of ≤10 MHz over the 15-cm−1 frequency segment scanned.
Analysis programs and standardization of the neutron activation system at TFTR
Authors: Nieschmidt E. B.
Published: July 2002

The recently installed neutron activation system at the TFTR has been calibrated and the analysis programming largely completed. Data analysis programs are available on an on-line acquisition analysis system or off line on a VAX system. Analysis techniques include random and coincident summing corrections as well as finite source size correction at close geometries. Detector efficiency determinations also use these corrections.
Channel electron multiplier compatibility with Viton and Apiezon-L vacuum grease
Authors: McComas D. J. , Baldonado J. R. , Bame S. J. , Barraclough B. L.
Published: July 2002

Clean Viton and Viton coated with Apiezon-L vacuum grease were tested for their noncontaminating compatibility with channel electron multipliers (CEMs). The test setup and procedure were the same as those used previously in conjunction with CEM compatibility tests of certain epoxies, solder, and fluorocarbon polymer materials useful for construction of spaceflight sensors. While some CEM gain degradation was noted during exposure to Viton and Apiezon-L, the present tests indicate that, at least over instrument lifetimes of ∼2×1012 counts, these materials should be suitable for (1) preflight space sensor testing systems, (2) hermetic seals for CEM-based space sensors, and (3) terrestrial CEM-based instrumentation.
Simultaneous subnanosecond timing information and 2D spatial information from imaging photomultiplier tubes
Authors: McMullan W. G. , Charbonneau S. , Thewalt M. L. W.
Published: July 2002

We have incorporated a resistive anode, microchannel-plate based photon-counting 2D optical imaging detector with standard time-correlated single photon counting circuitry. The result is a very powerful spectroscopic system which combines the very low dark count and parallel collection capabilities typical of this type of detector with simultaneous time resolution of the individual photon counts. The required timing signal can be generated with a very simple addition to the biasing network of the standard detector, and results in temporal resolution of 500-ps FWHM, equivalent to that typically obtainable with moderately fast single channel photomultiplier tubes.
Low voltage electron emission from Pb(ZrxTi1−x)O3-based thin film cathodes
Authors: Auciello O. , Ray M. A. , Palmer D. , Duarte J. , McGuire G. E. , Temple D.
Published: July 2002

Electron emission from ferroelectric thin films (≤1 μm thick) is demonstrated. In addition, electron energy distributions have been measured using an Auger electron spectrometer. The electron emission measurements were performed using ferroelectric cathodes based on this Pb(Zr0.53Ti0.47)O3 (PZT) films and 80–110 μm Pb0.93La0.07(Z0.53Ti0.47)O3 (PLZT) layered capacitors with Pt top and bottom electrodes. Current densities in the range of 0.5–1.5 mA/cm2 were measured from the PLZT cathodes excited with 100–400 V pulses, which produced electrons of about 265 eV with a narrow energy distribution (full width at half-maximum of about 30 eV). On the other hand, current densities in the range 0.07–0.15 μA/cm2 were measured for thin film PZT-based cathodes excited with pulses in the range 10–40 V. The initial results suggest that the electron emission current may depend, among other factors, on the thickness of the ferroelectric layer, the applied excitation voltage, and the interval between the polarizing and switching pulses.
Rapid-scanning autocorrelator with extended scanning span for monitoring short optical pulses
Authors: Watanabe Akira , Saito Hiroshi , Tokizaki Takashi , Ishida Yuzo , Yajima Tatsuo
Published: July 2002

We have developed a low-cost rapid-scanning autocorrelator which enables us to monitor picosecond optical pulses up to almost 100 ps. To achieve wide-scan range, each arm of a Michelson-type interferometer is scanned 180° out of phase by using audio speakers, and also only one-half of a full autocorrelation waveform of the pulses is observed. The present apparatus is usefully used to measure about 80-ps pulses generated from a cw mode-locked Nd:YAG laser.
Double-pass high-resolution vibrational electron energy loss spectrometer
Authors: Nishijima M. , Kubota Y. , Kondo K. , Yoshinobu J. , Onchi M.
Published: July 2002

A double-pass high-resolution vibrational electron energy loss spectrometer of 127° cylindrical electrostatic deflection type has been constructed for surface studies. In the direct mode, an electron current at the detector of 1.3×10−14 A is obtained with the energy spread (full width at half-maximum) of 2.4 meV for electrons whose energy at the sample position is 5 eV.
Method for measurement of viscosity and density of liquid with a slowly rotating column
Authors: Kimura Masatsugu , Shirane Kotaro , Aoki Ichiro , Tokimoto Takayuki
Published: July 2002

The locus of a fine spherical particle in a slowly rotating column filled with liquid is investigated in detail with a fundamental equation of motion, and a method for measurements of viscosity η and density ρ′ of the liquid is proposed. With a particle having the radius a=10−3–10−2 cm from the restriction Re≲1, (Re, Reynolds number) and the density ρ within 1.5ρ′≲ρ<4ρ′ in a column rotating at the angular velocity ω0 within 1.5≲Aω0/V0<2, the particle locus becomes almost a circle with a diameter D that sensitively correlates with η and ρ′ to be measured, where A=A0−a (A0, column radius) and V0 is the speed at free fall. For one particle (a one-particle system), η is universally measurable for almost any kind of liquid with a known ρ′. A two-particle system is also proposed for the continuous measurement of both η and ρ′, and would be applied, for example, at varying temperatures or in the course of a chemical reaction.
Velocity and moving angle measurements of solid surfaces by simple velocimetry
Authors: Okada Eiji , Minamitani Haruyuki , Fukuoka Yutaka
Published: July 2002

A simple laser Doppler velocimeter constructed for measuring the velocity and moving angle of a moving surface simultaneously is described. This instrument accomplished two-component velocity measurement for a solid surface by using the characteristic of specular reflection of the solid surface.
Design and construction of a multipole element control unit
Authors: Webster N. E. , Haider M. , Houf H.
Published: July 2002

We have designed and constructed a new microprocessor-controlled power supply, which is needed to excite the required multipole fields within three magnetic twelve-pole elements. We require the multipole fields to align and focus an electron beam and to correct the aberrations of an electron spectrometer which is mounted on a Cryo-STEM. With this power supply, the strength and orientation of each multipole field can be controlled independently. In order to reduce the number of digital-to-analog converters, we used a dynamic refresh technique to provide the analog output voltages. As an additional benefit of using a microprocessor, the number of front-panel controls could be kept low and extra functions provided, which would be difficult to implement in an analog system. The use of dynamic refreshing to produce analog voltages is not new, but the results obtained from our system indicate that the technique may also be employed where high stability is required.
Improved bolometry system for reversed field pinch research
Authors: Miller G. , Ingraham J. C. , Schrank L. S.
Published: July 2002

A bolometry system for time and spatially resolved energy-loss measurements on the ZT-40M reversed-field pinch is described. This system allows ∼100-μs time resolution with a radiation detection limit of ∼100 mW/cm2 , in particularly noisy electromagnetic environments. The bolometer element fabrication using evaporative techniques and photolithography is discussed. Increased noise rejection is realized by using an oscillator/FM receiver electronics system based on 5-MHz ac excitation of the resistor. An improved oscillator is described. Because resistive sensing is done at 5 MHz, pulsed heating currents may simultaneously be passed through the bolometer resistor and this allows for absolute in situ system calibration. We describe a new method of such calibration that is independent of the resistor geometry.