bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring temperatures in the presence of external radiation by flash assisted multiwavelength pyrometry
Authors: Tschudi H. R. , Schubnell M.
Published: July 2002

A novel multiwavelength analysis of the radiation emitted by a hot Lambertian surface is presented allowing a reliable measurement of its surface temperature even in the presence of interfering external light sources. For the separation of thermally emitted and reflected external radiation, an accurate knowledge of the spectral emittance/reflectance of the sample is required. In our procedure, this quantity is determined in situ by performing a second measurement with additional light, e.g., from a strong electric flash. The strength of the flash and the relative spectrum of the interfering external radiation are probed with a cooled Lambertian reflectance reference near the sample. In a first step, the spectral reflectance of the sample is determined from spectra recorded with and without flash. The temperature and the total incoming irradiance are then obtained from a least-square fit of the input spectra with an analytical model of the emitted thermal plus the superimposed reflected external radiation. The method delivers also estimates for the statistical accuracy of the measured temperature and irradiance values. It causes no problem to measure temperatures through a window of sufficient optical quality and effects of absorbing gases or vapors may be minimized by an appropriate choice of the spectral intervals used for the analysis. In order to indicate statistical and systematic errors of the method under different operating conditions, extensive numerical simulations were performed. They reveal that a good statistical accuracy of the recorded spectra is crucial for a proper separation of the emitted from the reflected external radiation if one part dominates. In contrast, this separation is not affected by an erroneous calibration of the optical detection system. Finally, the question is discussed if one can dispense with the flash. Without external radiation, the “no-flash” method is equivalent to quotient pyrometry and subject to the same principal limitations. With external radiation, reasonably accurate temperatures can be expected only if thermal radiation clearly dominates or if emittance values are available from other sources.
Photoluminescence of residual transition metal impurities in GaN
Authors: Baur J. , Kaufmann U. , Kunzer M. , Schneider J. , Amano H. , Akasaki I. , Detchprohm T. , Hiramatsu K.
Published: July 2002

A large number of epitaxial GaN samples as well as AlN ceramics have been studied by photoluminescence (PL) and PL excitation spectroscopy. In addition to the PL of residual iron, two new bands with zero-phonon-lines at 0.931 and 1.193 eV have been observed frequently in GaN. An analysis of the PL bands indicates that they arise from internal transitions within the 3d shell of residual vanadium and chromium impurities. The chromium PL has also been observed in polycrystalline AlN ceramics.
A unique optical arrangement for obtaining spectrally resolved confocal images
Authors: Stimson Michael J. , Haralampus-Grynaviski Nicole , Simon John D.
Published: July 2002

The design for a confocal beam-scanning microscope with a unique optical configuration for the rapid acquisition of spectrally resolved images is presented. The novel aspect of the optical configuration is the location of the detection device, which is placed in an intermediate position between fully descanned detection and nondescanned detection (direct projection). This placement allows for the practical implementation of spectrally resolved confocal imaging. The device is demonstrated by the spectral resolution of a sample of fluorescently labeled microbeads.
Kelvin probe liquid-surface potential sensor
Authors: Peterson I. R.
Published: July 2002

The design of a surface potential sensor is described in detail. It uses the Kelvin vibrating-probe principle and is specifically designed to characterize organic overlayers on poorly conducting liquid substrates. A novel manual compensation control allows the systematic measurement offsets originating in the electronics to be nulled. The head is based on a commercially available piezo-driven tuning-fork assembly with a 6 mm diameter gold-plated electrode, and includes a high-gain low-noise preamplifier to maximize sensitivity and minimize parasitic coupling. The input stage of the preamplifier uses balanced junction field-effect transistors mounted in a transimpedance configuration, giving low noise and minimizing phase shifts of the Maxwell-offset signal related to low substrate conductivity. The reproducibility of the measured surface potential is ±1 mV.
Effect of temperature errors on accuracy of deep traps parameters obtained from transient measurements
Authors: Pawlowski Michal
Published: July 2002

The procedure of determination of deep traps parameters by both deep level transient capacitance spectroscopy (DLTS) and photoinduced transient spectroscopy (PITS) is based on Arrhenius plot illustrating the dependence of thermal emission rates as a function of temperature. In this article the effect of temperature measurement inaccuracy on the values of activation energy and capture cross- section obtained from the Arrhenius plot is analyzed. The inaccurate values of temperature involve both a change of slope and shift of the Arrhenius plots along vertical axis. The practical application of the analysis is exemplified by estimation of the temperature errors responsible for the shift of Arrhenius plots related to the center A in irradiated silicon. This article addresses the issue of temperature errors in DLTS and PITS measurements from the metrological point of view.
A compact electron beam evaporator for carbon doping in solid source molecular beam epitaxy
Authors: Reuter D. , Wieck A. D. , Fischer A.
Published: July 2002

A new type of carbon source using the electron evaporator principle to generate a molecular beam is presented. The electrons are extracted from a hot tungsten filament which is biased negatively up to 1500 V versus the carbon target (ground potential), made from ultrapure pyrolytic graphite. The emission current at a fixed high voltage is controlled via a feedback loop and used to tune the carbon flux. In this way, a flux reproducibility of ±5% is achieved over a working period of 5 months. Flux rates up to 6.1×1011 cm−2 s−1 at a source–sample distance of 250 mm have been achieved. The source design is very compact so it was possible to build it onto a flange with a inner diameter of 40 mm (CF40 flange) which saves mounting space. Using this source it was possible to prepare two dimensional hole gases with hole mobilities up to 160 000 cm2 V−1 s−1 at 1 K. No memory effect was observed.
Systematic and random error suppression in instrumentation for stripping (chrono)potentiometry
Authors: Št’astný Miloslav , Lepší Pavel
Published: July 2002

The stripping potentiometer based on the potentiometric and current-controlled stripping analysis (PSA/CSA) was improved with respect to hardware simplicity, data acquisition rate, and elimination of the effect of nonlinearity of the analog-to-digital converter. The effects of systematic, random, and frequency noise on the observed signal were studied and discussed. It was found that the Savitzky–Golay polynomial filtering can only be successfully applied to smooth out PSA/CSA records if both the random and frequency noise-to-signal ratio are suppressed to a level of a few percent by a suitable hardware arrangement (not only by software filters) and if the analog-to-digital converter error is eliminated. If this is not the case and a large portion of the original normally distributed random noise is present, digital smoothing does not yield the correct values and records are convoluted with a Gaussian function, which restrains both the sensitivity (peak heights) and resolution (by peak widening) of the PSA/CSA method.
Repetitively sampled time-of-flight mass spectrometry for gas-phase kinetics studies
Authors: Fockenberg Christopher , Bernstein Herbert J. , Hall Gregory E. , Muckerman James T. , Preses Jack M. , Sears Trevor J. , Weston Ralph E.
Published: July 2002

An apparatus has been constructed to study radical–radical reactions in the gas phase. It consists of a tubular quartz reactor in which radicals are produced by flash photolysis using an excimer laser as light source. The composition of the gas mixture is analyzed in situ by photoionizing sampled gases using the vacuum ultraviolet emission of a hollow cathode lamp and subsequent time-of-flight mass spectrometry. A simple arrangement of grids at the entrance to the flight tube is used to interrupt the constant flux of ions by application of a combination of constant and pulsed voltages. Individual mass spectra can be taken at a repetition rate of around 20 kHz following each photolysis event. Signal counts from a specified number of consecutive mass spectra are fed into a 2 GHz multiscaler and accumulated as a sampling-time-indexed series of mass spectra. This allows simultaneous observation of the concentrations of multiple transient or stable species on a millisecond time scale. To achieve a suitable signal-to-noise ratio, signals were typically accumulated over several tens of thousands of laser shots at a pulse rate of 10–15 Hz.
Electron trapping materials for use in a picosecond infrared streak camera
Authors: Fan Wenhui , Hou Xun , Du Li , Niu Lihong , Zhao Wei , Zhang Xiaoqiu
Published: July 2002

We describe our research on the employment of an infrared upconversion screen made of electron trapping material (ETM) in combination with the high sensitivity of the S-20 photocathode responsive to visible radiation to produce a streak camera arrangement capable of viewing and recording infrared incident pulses. The ETM-based upconversion screen converts 800–1600 nm infrared radiation to visible light which is viewed or recorded by the S-20 photocathode. The peak values of the upconversion efficiency are located at 1165 nm for CaS:Eu, Sm and 1060 nm for CaS:Ce, Sm. The present experiment showed time resolution was 12.3 ps for a CaS:Eu, Sm screen and 8.4 ps for a CaS:Ce, Sm screen. The minimum detectability is 4.8×10−9 J/mm2 (minimum detectability of the coupled visible streak camera is 8.3×10−10 J/mm2). Other parameters, such as spatial resolution and dynamic range, have also been measured and analyzed. The results show ETM can be used in the measurement of infrared ultrafast phenomena up to picosecond time domain. In consideration of the limited number of trapped electrons in ETM, the infrared-sensitive streak camera consisting of an ETM-based upconversion screen is suitable to operate in the single shot mode.
The double-diamond anvil cell, the poor-man’s megabar pressure cell
Authors: Silvera Isaac F.
Published: July 2002

We present a new configuration for diamond anvils used in high pressure research. We show how to make a gasketed diamond indentor cell (DIC) in a conventional diamond anvil cell (DAC). Moreover, diamond anvils an order of magnitude smaller than those currently used can easily be mounted, with minor modification. These configurations are called DIC-DACs and double DACs (D-DACs). D-DACs have been tested to a megabar and appear to have the same range as a conventional DAC. D-DACs can lower the cost of diamonds for high pressure research by more than an order of magnitude.
Noise investigation of a high precision digital multimeter model HP3457A or HP3458A for microvolt level dc voltage measurements
Authors: Ueda Ryuzo , Takajo Hiroaki , Kazihara Kazunori
Published: July 2002

This article examines noise characteristics of a high precision digital multimeter HP3457A or HP3458A by presenting a conceptual but useful model for the generation of zero voltage error under short-circuited input terminals. Two setting states, auto-zero on (AZ-ON) and off (AZ-OFF) are tested and one important conclusion derived is that the state of AZ-OFF has a more extensive potential of performing to the full specifications for measurements of μV level dc voltage than that of AZ-ON.
Comment on “Noise averaging and measurement resolution” [Rev. Sci. Instrum. 70, 2038–2040 (1999)]
Authors: Sloman A. W.
Published: July 2002

The paper presents a superficial analysis, based on computer simulation, of a subject which has already been discussed at some length and for which analytic results have been presented. The authors appears to use “uniform dither” where several authors recommend “triangular dither” which gives 50% more quantization noise, but makes the quantization noise independent of signal level. The author also fails to mention the possibility of using “subtractive dither” which is technically difficult, but justifiable in expensive systems.
Comment on “Direct measurement of refractive-index dispersion using a time-delayed technique” [Rev. Sci. Instrum. 69, 1472–1475 (1998)]
Authors: Delbarre H. , Przygodzki C. , Boucher D.
Published: July 2002

In the article on which we comment, the authors have in fact only determined the group index of the materials.
Influence of electron injection on electron cyclotron resonance plasma properties and reflected mode electrons (abstract)
Authors: Ovsyannikov V. P. , Ullmann F. , Zschornack G.
Published: July 2002

The injection of an additional strong focused electron beam from a special designed electron gun into a magnetic electron cyclotron resonance (ECR) confinement field is studied. The electron gun uses a cathode with a long lifetime and resistiveness providing high emission current densities with electron currents up to 50 mA and voltages up to 4 keV. A sequence of aluminum foils is used to investigate the trajectories of the electrons in the magnetic field without plasma. The high density electron beam passes through the foils, welds them, and prints its image into the foils. Details of this technique are described in Ref. 1. Using this technique we see that before the electrons enter the sextupole region the beam moves along the magnetic straight lines preserving its structure. Only a central beam passes through the sextupole region, thereby changing its form due to the interaction with radial components of the magnetic field. A new operation method at our 14.5 GHz ECR ion source is based on so-called reflection mode electrons (RMEs) analogous to a known electron beam ion source operation regime.2 The basic idea is that electrons, which traveling from the cathode in a strong axial field, meet an anticathode potential, are reflected from it, move back to the cathode, and will be reflected again and so on. It can be supposed that the electrons will make reflections up to the moment when the anode aperture of the gun is fulfilled and the electrons will be collected on the anode electrode. Investigations are performed extracting nitrogen ions using the RME beam. As a result we got a clear increase in the beam current of the extracted ions (e.g., at 10 mA electron injection an increase of the current of N5+ ions up to 400%) and a shift of the measured ion charge state distribution to higher mean ionization stages. Measured x-ray spectra from a neon loaded plasma show for the case of RME operation increasing energy shifts to the high energy side of the spectra, i.e., the mean ionization degree of the ions in the plasma increases. They also increase the intensity of the neon K x rays (more than 100% increase for RME injection of Ee=4 keV and Ie=10 mA) indicating that for the same operation parameters the mean density of energetic electrons rises at RME injection, i.e., there are more electrons with energies high enough to ionize K-shell electrons in neon.
Calibration of the Galileo microchannel plates with the Xe2+–Xe13+ and C2+–C6+ ions in the energy range from 0.5 to 150 keV/q (abstract)
Authors: Mróz W. , Stöckli M. P. , Fry D. , Prokopiuk A. , Walch B.
Published: July 2002

The procedure of calibration of the detector assembly consisting of the two Galileo microchannel plates (MCPs) operated in a chevron configuration is described. The current gains and the analog particle gains of MCPs for Xe ions with charge states from q=3+ to q=13+ and C ions, with charge states from q=1+ to q=6+ and ion impact energies to charge state ratios from 0.5 to 150 keV/q have been measured. These results were compared to the earlier results obtained of calibration of this detector assembly with Xe ions with the charge states from q=7+ to q=43+ and ion impact energies to charge state ratios from 2 to 154 keV/q. We have shown the areas of ion parameters in which the secondary ion-electron emission coefficient of the investigated MCPs was dominated by kinetic or potential emission.
Development and evaluation of an electrically detected magnetic resonance spectrometer operating at 900 MHz
Authors: Sato Toshiyuki , Yokoyama Hidekatsu , Ohya Hiroaki , Kamada Hitoshi
Published: July 2002

An optimized design for an electrically detected magnetic resonance (EDMR) spectrometer is described. The bias and detection circuits were fabricated according to this design. The noise generated in the instrument was calculated from theory and by performing experiment. It was shown that the instrument noise was reduced to a level similar to that was generated by a sample itself. Because the electron spin resonance frequency was set at 900 MHz, a larger sample space, which was available to measure a whole semiconductor device, was obtained. Due to a small skin effect, a semiconductor material that had high conductivity was effectively measured. EDMR spectra of a photoexcited silicon crystal and commercially available silicon diodes were measured. Due to the optimized construction of the instrument, various EDMR spectra with different g values or line shapes were clearly observed.
Phase-sensitive multichannel detection system for chemical and biosensor arrays and fluorescence lifetime-based imaging
Authors: Rabinovich Emmanuil , O’Brien Michael J. , Brueck Steven R. J. , Lopez Gabriel P.
Published: July 2002

Fluorescence lifetime-based sensors are attractive candidates to satisfy the demand for chemical detection and monitoring in medical, pharmaceutical, and environmental applications. In many cases it is desirable not only to monitor one particular chemical or biological species, but several simultaneously. In this work, we have focused our efforts on the development of a detection platform for multianalyte sensor arrays that is able to monitor changes in the fluorescence lifetimes corresponding to the presence of many analytes of interest in real time. We describe a new version of the multichannel, phase-sensitive electronic detection system employing a multianode photomultiplier tube, light emitting diodes, laser diodes, custom-built detection electronics, and a software package. This system utilizes the frequency-domain method of time-resolved spectroscopy. The present 16-channel prototype of the device is compact and assembled from inexpensive, off-shelf components. Future detection systems may be expected to monitor simultaneously at least up to 63 signals from separate chemical and biosensors. The system is also suitable for lifetime-based imaging. The capabilities of this system are demonstrated with several examples, including a pH-sensitive sensor array measurement and lifetime-based imaging of spatially distributed chemical reactions.
Eddy current testing probe with dual half-cylindrical coils
Authors: Bae Byung-Hoon , Choi Jung-Mi , Kim Soo-Yong
Published: July 2002

We have developed a new eddy current probe composed of a dual half-cylindrical (2HC) coil as an exciting coil and a sensing coil that is placed in the small gap of the 2HC coil. The 2HC coil induces a linear eddy current on the narrow region within the target medium. The magnitude of eddy current has a maximum peak with the narrow width, underneath the center of the exciting 2HC coil. Because of the linear eddy current, the probe can be used to detect not only the existence of a crack but also its direction in conducting materials. Using specimen with a machined crack, and varying the exciting frequency from 0.5 to 100 kHz, we investigated the relationships between the direction of crack and the output voltage of the sensing coil.
Two-dimensional finite element model for a long rectangular eddy current surface coil
Authors: Ptchelintsev Andrei , de Halleux Benoit
Published: July 2002

An eddy current model for predicting the electrical impedance variation of a long rectangular surface coil due to a surface breaking defect in layered conductors is reported. The method is based on transforming a three-dimensional eddy current problem into the spatial frequency domain and solving the transformed diffusion problem for a limited number of the spatial spectrum components. The transformed problem has been assumed to be quasitwo dimensional (2D) for a long rectangular surface coil and formulated in terms of a two-component transformed vector magnetic potential Ā and scalar electric potential φ̄. The 2D problems have been solved with the finite element method using triangle elements. The system of algebraic equations was obtained using the Galerkin weak formulation and solved with the Gaussian elimination method. A high accuracy solution with ten spatial frequency components takes around 4 min on a Pentium 200 MHz PC. The accuracy of the solution has been tested experimentally at 200 kHz on coated stainless steel samples using a rectangular surface coil with the length-to-width ratio around 6. Agreement between theory and experiment is excellent. Discrepancies between the theory and experiment are within 15% and typically less. The method is useful for eddy current nondestructive evaluation and modeling, and can be also applied for the case of buried defects and for general multilayer coatings’ problem.
On the use of magnetic buckets for ion beam profile tailoring
Authors: MacGill R. A. , Vizir A. , Brown I. G.
Published: July 2002

Magnetic multipole plasma confinement geometries employing permanent magnet “buckets” are used extensively for a range of laboratory plasma applications. Among the several consequences for plasma confinement is the important result that the plasma can acquire a more-or-less flat density profile, which when embodied in an ion source, can also lead to a flat profile for the extracted ion beam. For many applications a uniform ion beam current density profile is quite advantageous, for example, for carrying out large-area ion implantation. There are, however, inherent limitations on the extent to which this approach to beam “homogenization” can be utilized, and even for a perfectly flat profile in the immediate postextraction region, the beam will evolve toward Gaussian as it propagates downstream. Here we describe the rare-earth permanent magnet bucket that we have incorporated into our broad-beam vacuum arc ion source, and its effect on the beam profile at the extractor and downstream. The experimental results are compared with a simple model for the beam profile evolution with axial distance. We find that the beam loses memory of its initially flat profile and relaxes to a more-or-less Gaussian shape in a relatively short axial distance ∼w/4θ, where w is the initial width of the flat beam profile and θ is the beamlet divergence half angle.
An investigation into the mechanism of pseudospark producing metal ion beams
Authors: Cai C. G. , Zhao W. J. , Yan S. , Le X. Y. , Han B. X. , Xue J. M. , Wang Y. G. , Jiang X. L.
Published: July 2002

A multiplate pseudospark chamber, whose electrodes were fabricated with different metal materials, was designed and tested as a metal ion source. The ion beam implantation combined with Rutherford backscattering (RBS) measurement was used to understand whether these ion beams come from the anode plasma or the cathode plasma. The RBS measurements have demonstrated the following results: (1) pseudospark produced metal ion beams mainly consist of ions from the cathode materials; (2) the ion beam current increases rapidly with the pseudospark discharge voltage first and then saturates; and (3) the energy of the extracted metal ions is much less than the voltage between the anode and the cathode, therefore the high discharge voltage does not correspond to the high ion energy. A possible mechanism of pseudospark producing metal ion beams is discussed.
Magnetic field profile dependence of zirconium flux in sputtering ion sources
Authors: Suzuki T. , Kawai Y. , Saburi T. , Fujii Y. , Kitayama N.
Published: July 2002

A zirconium sputtering ion source was studied. The argon plasma discharged by electron cyclotron resonance was used as the sputtering working plasma. A cylindrical-type target was used as the sputter target. The zirconium flux is evaluated at the downstream side of the ion source by varying the magnetic field profile of the ion source. And a magnetic profile dependence of the zirconium flux was observed. Zirconium ions and argon ions were detected by a quadrupole mass spectrometer. From the zirconium flux and the ion current, the ionization efficiency was evaluated.
A negative ion beam application to artificial formation of neuron network in culture
Authors: Tsuji Hiroshi , Sato Hiroko , Baba Takahiro , Gotoh Yasuhito , Ishikawa Junzo
Published: July 2002

A negative ion beam modification of the biocompatibility of polystyrene surface was investigated for the artificial formation of neuron network in culture with respect to negative ion species. Negative ions of silver, copper or carbon were implanted in nontreated polystyrene (NTPS) dishes at conditions of 20 keV and 3×1015 ions/cm2 through a mask with many slits of 60 μm in width. For the surface wettability, the contact angle of ion-implanted NTPS was about 75° for silver-negative ions, which was lower than 86° of the original NTPS. For carbon implantation, on the contrary, the contact angles did not change from the original value. In culture experiment using neuron cells of PC-12h (rat adrenal pheochromocytoma), the cells cultured with serum medium in two days showed the cell attachment and growth in number only at the ion-implanted region on NTPS for all ion species. In another two days in culture with nonserum medium including a nerve growth factor, the outgrowth of neural protrusions was also observed only at the ion-implanted region for all ion species. There was a difference in number of attached cells for ion species. The silver-negative ion-implanted NTPS had a large effect for cell attachment compared with other two ion species. This reason is considered to be due to the lowest contract angles among them.
Status of vacuum arc ion sources (invited) (abstract)
Authors: Brown Ian
Published: July 2002

Vacuum arc ion sources have been developed and used in a growing number of laboratories around the world. Beams have been produced from most of the solid metals of the periodic table as well as alloys and mixtures, with ion energy up to several hundred keV and beam current up to several A. Typically the source is repetitively pulsed with a pulse length on the order of a millisecond and duty cycle of 1%, and dc operation has been demonstrated also. The main application has evolved for ion implantation, primarily for metallurgical, ceramic, and polymer surface modification (i.e., nonsemiconductor applications), but also for semiconductor implantation in some special cases; the source is also used for heavy ion injection into particle accelerators. This kind of high-current metal ion source has provided a valuable addition to the spectrum of ion sources available to the experimenter. Here the source fundamentals are briefly reviewed and the source performance and beam characteristics summarized. We survey some of the vacuum arc ion source development that has been accomplished over the past decade at many laboratories around the world, applications to which the source has been put, and recent progress in source innovations that has been accomplished by the community.
Numerical simulation of cesium cooling effects in H− ion source
Authors: Morishita T. , Ogasawara M. , Hatayama A.
Published: July 2002

Cesium volume reactions are included in a two-point model numerical code for a high power hydrogen negative ion source. The energy balance equation for the electron temperature and rate equations of Cs and Cs+ are included in our code to investigate the electron cooling and volume effects by cesium seeding. Cesium density in the ion source is taken as a variable for the calculation. Cesium is ionized over 95% in the driver region of the ion source. The electron temperature begins to decrease at cesium density 1011 cm−3 and the electron density increases because of the ionization of cesium.
Energetic-multiple-charged-ion sources on short-laser-pulse irradiated foils
Authors: Zhidkov A. , Sasaki A. , Tajima T.
Published: July 2002

The emission of multi-MeV multiple-charged ions from a thin metallic target irradiated by a short pulse laser in the range of intensity 1016–20 W/cm2 is investigated via a full kinetic particle-in-cell simulations including transient plasma ionization. Ions over MeV energy are accelerated from non-low-Z matter with up to a 10% conversion from laser energy. The anisotropy of the electron velocity distribution is found to enhance the ion energy and improve the emittance.
Profile control of the large area ribbon beam ion source using 500 MHz ultrahigh frequency discharge
Authors: Sakai Shigeki , Takahashi Masato , Tanjyo Masayasu
Published: July 2002

This article is concerned with the method of controlling the large area ribbon beam profile produced by the same extraction electrode size ion source. We used a bucket type large area ion source with 500 MHz ultrahigh frequency (UHF) discharge for the plasma production. The size of the ion source is comparable to one wavelength of 500 MHz rf. As the UHF wave propagates in the plasma, electrons are accelerated by the rf fields along the multicusp magnetic field produced by the peripheral permanent magnets set on the outer surface of the plasma chamber. We used several entrances of the UHF wave around the plasma chamber. We can control the ion beam profile by adjusting the size of the entrance hole. With this control, less than 2% of uniformity of the large area ion beam of 120 mm×220 mm is achieved for the source gases such as diborane, phosphine, and arsine.
Time resolving diagnostic of the compensation process of pulsed ion beams at high-intensity light ion source
Authors: Jakob A. , Beauvais P-Y. , Gobin R. , Klein H. , LeMaire J-L. , LeRoy P-A. , Pozimski J.
Published: July 2002

Time-resolved measurements of the compensation process have been performed at the (high-intensity light ion source)-low-energy beam transport test stand (CEA-Saclay) using an 92 kV; 73 mA proton beam. A residual gas ion energy analyzer was used to measure the potential distribution as a function of time. To measure the radial density profile of the ion beam a charge coupled device camera has been used to perform time-resolved measurements and to estimate the rise time of compensation. Both measurements in combination allow an investigation of the space-charge compensation process due to the residual gas ionization and the experimental study of the rise of compensation. A numerical simulation of selfconsistent equilibrium states [J. Pozimski, Il Nuovo Cimento 106, A.N.11 (1993)] of the ion beam has been used to determine plasma parameters such as the density and the temperature of the electrons from the measured data. An interpretation of the acquired data and the achieved results is given.
Beam extraction from a compact Ku-band electron cyclotron resonance ion source with double resonance modes
Authors: Tojyo E. , Oyaizu M. , Jeong S. C. , Ishiyama H. , Ishida Y. , Kawakami H. , Miyatake H. , Katayama I. , Nomura T.
Published: July 2002

Beam extraction tests were carried out using a new compact Ku-band electron cyclotron resonance (ECR) ion source. In the case of a single rf frequency operation, a B2 zone can contribute for increase of single and low charged state ion beams when the gas flow rate is relatively higher than that for the basic ECR mode. The scheme seems, however, not so effective for the production of multicharged state ion beams. A double frequency heating (12 and 14 GHz) is, on the other hand, effective for increase of extracted ion current when the rf power is injected into the chamber from both the axial and the radial ports, as succeeded at the LBL experiment.
Energy distribution of negative carbon ion beam extracted from a plasma-sputter-type negative ion source
Authors: Oomori H. , Kasuya T. , Wada M. , Horino Y. , Tsubouchi N.
Published: July 2002

The energy distributions of C− and C2− beams extracted from a plasma-sputter-type negative ion source with the concave graphite target were measured by a retarding field energy analyzer having 1.5% resolving power. The reduction in energy spread of the energy distribution functions was observed by adding Cs into the discharge. The observed energy spreads of C− beam for 650 V target bias were 15 eV without Cs and 13 eV with Cs, respectively. The shift toward the lower energy due to Cs supply was also observed. The observed negative energy shift was constant at about 3.7 eV for the C beam, the value corresponded to the work function reduction from a pure graphite to Cs covered graphite surface.
Ion bombardment-type high frequency metal ion source for compact ion beam deposition apparatus
Authors: Yamashita Mutsuo
Published: July 2002

A novel metal ion source has been developed for a compact nonmass-separated ion beam deposition apparatus. To produce a dense plasma, a high frequency (hf) antenna coil made of Cu was mounted inside the metallic ionization chamber and a hf power of 300 W (13.56 MHz) was applied to this coil. A Cr rod target 10 mm in diameter was fitted at the center of the hf coil and a dc bias voltage of −600 V was applied to it. The temperature of a tip of the Cr rod target increased locally by means of ion bombardment; the Cr target material vaporized vigorously by sublimation and effectively ionized in the high density plasma. A pure Cr ion current of 400 μA was obtained at an energy of 100 eV without mass separation. Circular Cr thin films of 10 mm in diameter and 500 nm in thickness were deposited on Si substrates at a deposition rate of 30 nm/min at an ion energy of 100 eV. No contamination due to a sputtering of Cu antenna coil was detected by X-ray fluorescence analysis.
Fast Fourier transform of photoreflectance spectroscopy of δ-doped GaAs
Authors: Wang D. P. , Chen C. T.
Published: July 2002

The photoreflectance (PR) spectroscopy of δ-doped or similar structured sample has been observed to exhibit many Franz–Keldysh oscillations (FKOs). The beats are shown in the FKOs and they are attributed to the different frequencies of the FKOs of the transitions from the heavy and light holes. We have applied the fast Fourier transform on the PR spectra to separate the contributions from the heavy and light holes. The electric fields in the undoped layer can be calculated from the frequencies of heavy and light holes, respectively. The result of the heavy hole agrees well with that from the conventional FKOs fittings if the reduced mass=0.055 m0 is used in the conventional fittings.
Molecular beam epitaxy growth of MgZnSSe/ZnSSe Bragg mirrors controlled by in situ optical reflectometry
Authors: Uusimaa P. , Rakennus K. , Salokatve A. , Pessa M. , Aherne T. , Doran J. P. , O’Gorman J. , Hegarty J.
Published: July 2002

In situ optical reflectometry at the wavelength of 488 nm was employed to control the growth of MgZnSSe/ZnSSe Bragg mirror stacks for the blue-green spectral region. 10- and 20-period layer structures of MgZnSSe/ZnSSe were grown on GaAs (100) epilayers by molecular beam epitaxy. A room-temperature peak reflectance of 86% was obtained for the 20-period structure at the central wavelength of 474 nm. The results show that, in general, in situ optical monitoring of growth is a viable and simple method for real-time layer thickness control of MgZnSSe/ZnSSe quarter-wave stacks.
A gas phase chemical etchant for boron nitride films
Authors: Harris Stephen J. , Doll Gary L. , Chance Derek C. , Weiner Anita M.
Published: July 2002

We have demonstrated that boron nitride films deposited on silicon and tantalum can be etched in a hot filament environment with an input gas composition of 1% methane in hydrogen. Etching experiments were carried out at around 800 K on a tantalum foil and at somewhat higher temperatures on silicon substrates. If the etchant is atomic hydrogen or methyl radical, then we estimate etching efficiencies (atoms etched per collision) of ∼10−5 or 10−4 for these species, respectively.
Single-crystalline, single-domain epitaxy of PbTiO3 thin films by metalorganic chemical vapor deposition
Authors: Chen Yan-Feng , Sun Li , Yu Tao , Chen Jian-Xie , Ming Nai-Ben , Ding De-Sheng , Wang Lian-Wei
Published: July 2002

Single-crystalline and single-domain PbTiO3 films with thickness of 3000 Å have been prepared by metalorganic chemical vapor deposition (MOCVD), using metalorganic precursors of tetra-ethyl-lead and iso-propoxide titanium. The nature of single-crystalline epitaxy and single domain of as-grown films was characterized by x-ray diffraction (XRD), synchrotron radiation (SR), and Rutherford backscattering (RBS). Using atomic force microscopy (AFM), the evidence of layer-by-layer growth was observed. The growth steps on the surface may be attributable to the formation of single-crystalline and single-domain PbTiO3 film with 3000-Å thickness.
Optical investigation of quaternary GaInAsSb/AlGaAsSb strained multiple quantum wells
Authors: Shen W. Z. , Shen S. C. , Tang W. G. , Zhao Y. , Li A. Z.
Published: July 2002

Photoluminescence and absorption measurements were carried out on quaternary Ga0.75In0.25As0.04Sb0.96 /Al0.22Ga0.78As0.02Sb0.93 strained multiple quantum well (MQW) structure grown by molecular-beam epitaxy to investigate its band offsets and subband behavior. Strong luminescence and well-resolved excitonic absorption peaks are observed even at room temperature, which is indicative of good quality of our quaternary sample. By fitting the experimental results with the theoretical calculations, we find that the light holes are in Ga0.75In0.25As0.04Sb0.98 well regions (type I MQW) and the conduction-band offset ratio Qc=0.66±0.01. The transition from type I to type II for light holes may occur for the composition of x≤0.70 in GaxIn1−xAs0.04Sb0.96/ Al0.22Ga0.78As0.02Sb0.98 system.
Rapid single-flux-quantum balanced comparator based on high-T
c bicrystal Josephson junctions
Authors: Oelze B. , Ruck B. , Roth M. , Dömel R. , Siegel M. , Kidiyarova-Shevchenko A. Yu. , Filippov T. V. , Kupriyanov M. Yu. , Hildebrandt G. , Töpfer H. , Ihlmann F. H. , Prusseit W.
Published: July 2002

A balanced current comparator based on high-Tc bicrystal Josephson junctions has been designed, fabricated, and experimentally tested. The operation of the balanced comparator has been demonstrated in the temperature range from 4.2 to 70 K. The correct sequence of switching of the Josephson junctions has been determined by dc measurements for different values of operating frequency and signal current Ix. The threshold uncertainty ΔIx of the balanced comparator, measured at 40 K, was 60 μA at 40 GHz and 300 μA at 240 GHz.
Ion focusing by an expanding, two-dimensional plasma sheath
Authors: Sheridan T. E.
Published: July 2002

The temporal evolution of the collisionless, pulsed plasma sheath around a square bar is studied using a two-dimensional particle-in-cell code. It is found that the incident ion dose is peaked near to, but not on, the corner. This effect is explained physically by considering ion trajectories across the sheath, yielding an estimate for the dose in good agreement with the simulation results. The present results are compared to those from a fluid simulation [T. E. Sheridan and M. J. Alport, Appl. Phys. Lett. 64, 1783 (1994)], and it is found that the fluid simulation erroneously underestimates the ion dose near the corner of the bar.
Threshold investigation of oxide-confined vertical-cavity laser diodes
Authors: Choquette Kent D. , Chow W. W. , Hagerott Crawford M. , Geib K. M. , Schneider R. P.
Published: July 2002

We report an experimental and theoretical analysis of the threshold properties of infrared oxide-confined vertical-cavity surface emitting lasers. We find good agreement between experiment and theory on the wavelength dependencies of the threshold current density and intrinsic voltage. The threshold voltage is shown to equal the sum of the calculated quasi-Fermi energy separation and the ohmic drop arising from a record low 17 to 30 Ω series resistance in these vertical-cavity lasers. Our analysis provides two independent means for determining the material threshold gain. A threshold gain of 500 cm−1 is found for these oxide-confined lasers, which is half that estimated for ion-implanted lasers with inferior electrical and optical confinement.
Nanoparticle deposition in hydrogenated amorphous silicon films during rf plasma deposition
Authors: Tanenbaum D. M. , Laracuente A. L. , Gallagher Alan
Published: July 2002

Particles of 2–14 nm diameter, representing 10−4–10−3 of the film volume, are observed by scanning tunneling microscopy (STM) in thin films of hydrogenated amorphous silicon (a-Si:H) grown by rf-plasma-enhanced deposition using optimized conditions. The particles are produced in the discharge and incorporated in the film during growth, in contradiction to expected particle trapping by discharge sheath fields. The interfaces between the nanoparticles and the homogeneous film can produce low-density regions that form electronic defects in a-Si:H films.
Influence of oxygen on surface morphology of metalorganic vapor phase epitaxy grown GaAs (001)
Authors: Nayak S. , Huang J. W. , Redwing J. M. , Savage D. E. , Lagally M. G. , Kuech T. F.
Published: July 2002

Atomic force microscopy has been used to investigate the influence of controlled oxygen incorporation on the surface morphology of GaAs films grown by metalorganic vapor phase epitaxy (MOVPE). Oxygen influences the periodic morphology observed in GaAs surfaces, with concentrations about 1018 cm−3 leading to a breakup of the periodicity. To account for these observations, we propose a model in which oxygen preferentially attaches at steps with a subsequent reduction in step mobility and a concomitant increase in the surface roughness.
Electro-optical structure with high speed and high reflectivity modulation
Authors: Levin M. , Rosenbluh M. , Sandomirsky V.
Published: July 2002

A voltage controlled, multilayer electro-optic structure is proposed. It is constructed from repeated Schottky-like modules, which consist of layers of semiconductor-dielectric-semiconductor. The device reflectivity, in the range of incidence angles corresponding to surface plasmon excitation, is determined by the combined thickness and permittivity of the semiconductor space charge regions of all modules. A structure consisting of many modules allows for a large effective thickness of the voltage controlled space charge region which yields a high reflectivity modulation. Calculations show that fast (response time ∼ 10−10 s) and low-voltage structures with reflectivity modulation depth of more than 80% can be constructed.
Laser focused atomic deposition: A new lithography tool
Authors: Behringer R. E. , Natarajan Vasant , Timp G.
Published: July 2002

We have used the force exerted on a neutral atom by an optical standing wave to focus a neutral atomic beam into a grating structure that is deposited on a substrate. We have made gratings with pitch of 294 nm, linewidths of δ=40–45 nm and contrast ≳10:1, over an area of 7.6 mm2. We discuss the conditions needed to make the narrowest structures, and how these conditions affect the performance of this technique as a lithography tool. We also show depositions that have lower resolution, δ≊80 nm, but could cover an area greater than 3×104 mm2.
Epitaxial film thickness in the low-temperature growth of Si(100) by plasma enhanced chemical vapor deposition
Authors: Varhue W. J. , Rogers J. L. , Andry P. S. , Adams E.
Published: July 2002

The limiting epitaxial thickness of Si films grown at a low substrate temperature by plasma enhanced chemical vapor deposition has been determined. The specific process used was electron cyclotron resonance plasma deposition. The limiting epitaxial thickness was found to decrease with the ratio of energetic ion-to-adatom arrivals on the substrate surface. The measured epitaxial thicknesses are similar to those obtained in previous investigations using molecular beam epitaxy. Hydrogen surface coverage does not appear to be a factor in limiting epitaxial thickness. The maximum epitaxial thickness remains to be determined for this process and substrate temperature range.
Characteristics of Si3N4/Si/n-GaAs metal-insulator-semiconductor interfaces grown on GaAs(111)B substrate
Authors: Park Dae-Gyu , Diatezua Deda M. , Chen Zhi , Mohammad S. Noor , Morkoç Hadis
Published: July 2002

Interfacial properties of Al/Si3N4/Si/n-GaAs metal-insulator-semiconductor (MIS) capacitors grown on GaAs(111)B prepared with a combination of in situ molecular beam epitaxy and chemical vapor deposition techniques are presented. The density of the surface states in the high 1010 eV−1 cm−2 near the GaAs midgap for the GaAs grown at 575 and 625 °C was obtained. The MIS structure with GaAs homoepitaxial layer grown at 625 °C, showing smoother surface morphology than the surface grown at 575 °C, exhibited small hysteresis which was as small as 30 mV under a field excursion of 1.5 MV/cm. The presence of a 1 MHz frequency response at 77 K requires that the traps be within 60 meV of the conduction band edge of GaAs and confirms the unpinned GaAs surface Fermi energy within GaAs band gap.
Detection of terahertz radiation by hot electron effects in coupled quantum well photodiodes
Authors: Stone R. J. , Michels J. G. , Wong S. L. , Foxon C. T. , Nicholas R. J. , Fox A. M.
Published: July 2002

Detection of continuous-wave terahertz (THz) radiation has been demonstrated in GaAs/AlGaAs coupled quantum well p-i-n photodiodes by intrasubband absorption. The sharp interwell tunneling resonances observed in the photocurrent are highly sensitive to temperature, and the carrier temperature increase caused by the absorption of THz radiation is found to affect the photocurrent in a qualitatively similar manner. We find that the effect results in detectivities of THz radiation around 1 mA/W for a photocurrent signal of 100 nA. We discuss the functionality of our device in the context of an ‘‘optical/THz mixer,’’ where the mixing occurs between the modulation frequencies of the applied THz and visible light fields.
Nonoptical tip–sample distance control for scanning near-field optical microscopy
Authors: Chuang Yung-Hui , Wang Chia-Jen , Huang J. Y. , Pan Ci-Ling
Published: July 2002

We propose and demonstrate a novel nonoptical technique for regulation of tip–sample distance in a scanning near-field optical microscope (SNOM). The fiber tip for the SNOM is attached to one prong of a quartz tuning fork. The fork is dithered with a gated sinusoidal signal. The vibration of the freely oscillating fiber tip, which manifests as the induced piezoelectric voltage on the fork electrodes, is monitored during the half-period of the gated sinusoid for which the fork is not driven. The time-multiplexing scheme, thus, allows the tuning fork to serve as a dither and a sensor with high Q factor, simultaneously. The gating technique could also potentially allow the SNOM to be used for the investigation of surface relaxation dynamics with high spatial resolution and submillisecond time resolution.