Showing papers in "Review of Scientific Instruments in 1993"
TL;DR: In this article, the authors describe a simple, nondestructive procedure for measuring the force constant, resonant frequency, and quality factor of an AFM cantilever spring and the effective radius of curvature of an AU tip.
Abstract: Images and force measurements taken by an atomic‐force microscope (AFM) depend greatly on the properties of the spring and tip used to probe the sample’s surface. In this article, we describe a simple, nondestructive procedure for measuring the force constant, resonant frequency, and quality factor of an AFM cantilever spring and the effective radius of curvature of an AFM tip. Our procedure uses the AFM itself and does not require additional equipment.
3,975 citations
TL;DR: The spring constant of microfabricated cantilevers used in scanning force microscopy (SFM) can be determined by measuring their resonant frequencies before and after adding small end masses as mentioned in this paper.
Abstract: The spring constant of microfabricated cantilevers used in scanning force microscopy (SFM) can be determined by measuring their resonant frequencies before and after adding small end masses These masses adhere naturally and can be easily removed before using the cantilever for SFM, making the method nondestructive The observed variability in spring constant—almost an order of magnitude for a single type of cantilever—necessitates calibration of individual cantilevers in work where precise knowledge of forces is required Measurements also revealed that the spring constant scales with the cube of the unloaded resonant frequency, providing a simple way to estimate the spring constant for less precise work
1,635 citations
TL;DR: This article reviews the beam modifying devices and associated dosimetric equipment developed specifically for controlling and monitoring the clinical beams.
Abstract: Clinical trials using accelerated heavy charged‐particle beams for treating cancer and other diseases have been performed for nearly four decades. Recently there have been worldwide efforts to construct hospital‐based medically dedicated proton or light‐ion accelerator facilities. To make such accelerated heavy charged‐particle beams clinically useful, specialized instruments must be developed to modify the physical characteristics of the particle beams in order to optimize their biological and clinical effects. This article reviews the beam modifying devices and associated dosimetric equipment developed specifically for controlling and monitoring the clinical beams.
410 citations
TL;DR: A diamond anvil cell (DAC) was designed and built for conducting research in fluids at pressures to 2.5 GPa and temperatures from −190 to 1200 C.
Abstract: A new style of diamond anvil cell (DAC) has been designed and built for conducting research in fluids at pressures to 2.5 GPa and temperatures from −190 to 1200 °C. The new DAC has been used for optical microscope observations and synchrotron x‐ray diffraction studies. Fringes produced by interference of laser light reflected from top and bottom anvil faces and from top and bottom sample faces provide a very sensitive means of monitoring the volume of sample chamber and for observing volume and refractive index changes in samples that have resulted from transitions and reactions. X‐ray diffraction patterns of samples under hydrothermal conditions have been made by the energy dispersive method using synchrotron radiation. The new DAC has individual heaters and individual thermocouples for the upper and lower anvils that can be controlled and can maintain temperatures with an accuracy of ±0.5 °C. Low temperatures are achieved by introducing liquid nitrogen directly into the DAC. The equation of state of H2O...
379 citations
TL;DR: In this article, it was demonstrated that sub-micrometer focused ion beams can be produced with current densities greater than 1 A ǫ cm−2 using a liquid-metal ion source.
Abstract: The technology of high‐resolution focused ion beams has advanced dramatically in the past 15 years as focusing systems have evolved from laboratory instruments producing minuscule current densities to high current density tools which have sparked an important new process: direct micromachining at the micrometer level. This development has been due primarily to the exploitation of field emission ion sources and in particular the liquid‐metal ion source. Originally developed in the early 1960’s as a byproduct of the development of electrostatic rocket engines, the liquid‐metal ion source was adapted for focused beam work in the late 1970’s, when it was demonstrated that submicrometer focused ion beams could be produced with current densities greater than 1 A cm−2. Ions can be produced with liquid‐metal ion sources from elements including Al, As, Au, B, Be, Bi, Cs, Cu, Ga, Ge, Fe, In, Li, P, Pb, Pd, Si, Sn, and Zn. In the past decade, focused ion beam systems with liquid‐metal ion sources have had a signific...
360 citations
TL;DR: In this paper, the authors describe the physical architecture and performance of a quantitative three-dimensional atom probe recently constructed using a 10×10 anode array placed behind a two microchannel plate assembly in a chevron arrangement.
Abstract: The physical architecture and the performance of a quantitative three‐dimensional atom probe recently constructed are described. The development of such an instrument relies on the design of a multi‐impact position sensitive detector. The multidetection system that we have developed is based on the use of a 10×10 anode array placed behind a two microchannel plate assembly in a chevron arrangement. The spread of charge between the microchannel plate and the multianode is used to derive the position of ion striking the detector. Spatial coordinates can be calculated for multiple and simultaneous time‐of‐flight events. The procedure used for the derivation of ion positions from charge measurements is given. Specific experiments were carried out in order to determine the intrinsic spatial resolution of the multidetector. Three‐dimensional reconstruction of two‐phase materials are provided and illustrate the performance of this new apparatus. The reconstructed images demonstrate that atoms are positioned with a precision of a few tenths of a nanometer. The mass resolution M/ΔM (FWHM) of the apparatus is close to 200.
343 citations
TL;DR: In this paper, the electrostatic levitator (ESL) has been used for containerless processing of metals and alloys in vacuum and superheating-undercooling-recalescence cycles which can be repeated while maintaining good positioning stability.
Abstract: This article discusses recent developments in high-temperature electrostatic levitation technology for containerless processing of metals and alloys. Presented is the first demonstration of an electrostatic levitation technology which can levitate metals and alloys (2–4 mm diam spheres) in vacuum and of superheating-undercooling-recalescence cycles which can be repeated while maintaining good positioning stability. The electrostatic levitator (ESL) has several important advantages over the electromagnetic levitator. Most important is the wide range of sample temperature which can be achieved without affecting levitation. This article also describes the general architecture of the levitator, electrode design, position control hardware and software, sample heating, charging, and preparation methods, and operational procedures. Particular emphasis is given to sample charging by photoelectric and thermionic emission. While this ESL is more oriented toward ground-based operation, an extension to microgravity applications is also addressed briefly. The system performance was demonstrated by showing multiple superheating-undercooling-recalescence cycles in a zirconium sample (Tm=2128 K). This levitator, when fully matured, will be a valuable tool both in Earth-based and space-based laboratories for the study of thermophysical properties of undercooled liquids, nucleation kinetics, the creation of metastable phases, and access to a wide range of materials with novel properties.
310 citations
TL;DR: In this paper, a four-grid electrostatic energy analyzer for measurements of the ion velocity distribution and the emission of secondary electrons on the electrodes of low-pressure radio frequency glow discharge systems has been conceived.
Abstract: A four‐grid electrostatic energy analyzer for measurements of the ion velocity distribution and the emission of secondary electrons on the electrodes of low‐pressure radio frequency glow‐discharge systems has been conceived. Problems arising from poor analyzer design are discussed and the performance of the presented analyzer is shown for measurements of the ion velocity distribution in pure hydrogen, helium, and argon discharges. Moreover, the secondary electron yields on aluminium, stainless steel, copper, and amorphous silicon exposed to radio frequency argon, helium, and hydrogen plasmas are determined in situ, for the first time to our knowledge. In parallel‐plate radio frequency discharges secondary electron emission involves the contributions of ions, fast neutrals, metastables, and photons impinging on the electrode surfaces. Therefore, secondary electron emission must be considered as a global phenomenon. Global secondary electron emission can be up to ten times larger than only ion‐induced secon...
247 citations
TL;DR: The magnetospheric plasma analyzer (MPA) as mentioned in this paper is a low-power, light-weight, and low power particle analyzer that can be used for measuring the plasma environments of spacecraft with constrained resources.
Abstract: A light‐weight, low‐power, plasma analyzer is described that can be used for measuring the plasma environments of spacecraft with constrained resources. A unique system using a single electrostatic analyzer coupled to a single array of channel electron multipliers allows measurement of the three‐dimensional energy per charge distributions of both ions and electrons over E/q ranges from ∼1 eV/q to ≳40 keV/q. Particles selected by the analyzer are post‐accelerated into the multipliers to maintain sensitivity for the lowest energy particles. An instrument using this concept called the magnetospheric plasma analyzer (MPA) is described. Presently, three MPAs are in geosynchronous orbits (GEO) aboard spacecraft with International Designators of 1989‐046, 1990‐095, and 1991‐080. The MPA and its response characteristics are described, and examples of on‐orbit data showing some of the MPA capabilities are presented.
238 citations
TL;DR: In this article, the frequency response of the optical-detection electronics of an atomic-force microscope cantilever was corrected for a high frequency cut-off, which, in our case, was higher than the resonant frequency of the cantilevers.
Abstract: In our calibration of atomic-force microscope cantilevers, we neglected to correct for the frequency response of the optical-detection electronics. The response to cantilever vibrations will have a high-frequency cut-off, which, in our case, was higher than the resonant frequency of the cantilever. Our results were not affected, but for higher resonant frequencies, one should calibrate the detector response. We thank V. Croquette for raising this point.
220 citations
TL;DR: In this paper, the authors describe a new experimental setup for photoluminescence spectroscopy on van der Waals clusters, which consists of a molecular beam apparatus with a cluster beam installed behind a high intensity vacuum ultraviolet synchrotron radiation beamline.
Abstract: We describe a new experimental setup for photoluminescence spectroscopy on van der Waals clusters. It consists of a molecular beam apparatus with a cluster beam installed behind a high intensity vacuum ultraviolet synchrotron radiation beamline. Special emphasis was given to the design of a very intense cluster source which can also be used for the preparation of quantum clusters (He,H2). For the determination of the cluster size a time‐of‐flight mass spectrometer can be attached to the setup. In addition, an atomic cross jet is installed in the experimental chamber which can be used for mass separation or for doping of the clusters. The luminescence light can be recorded with several different detectors or spectrally analyzed with a secondary monochromator which is equipped with a position sensitive detector. The pulsed nature of synchrotron radiation provides the basis for time‐resolved measurements in the regime 100 ps–3 μs.
TL;DR: In this paper, a modified high-pressure, stopped-flow apparatus was developed to enable kinetic experiments to be monitored spectrophotometrically to 200 MPa, with efficient mixing of the reactant solutions.
Abstract: A modified high‐pressure, stopped‐flow apparatus has been developed to enable kinetic experiments to be monitored spectrophotometrically to 200 MPa, with efficient mixing of the reactant solutions. This apparatus is compact, relatively inexpensive to construct, and the solutions are only exposed to inert materials, such as Kel‐F, Teflon, quartz (low‐pressure windows), and glass or Viton. The drive‐syringe pistons are propelled by a step motor housed on top of the stopped‐flow unit inside the pressure vessel, resulting in a dead time for the system of ∼10 ms at 25 °C.
TL;DR: In this article, a single photon avalanche photodiode in a passively quenched circuit is used with time correlated single photon counting modules to achieve sub-nanosecond time response together with high quantum efficiency and low dark noise.
Abstract: A commercially available single photon avalanche photodiode in a passively quenched circuit is used with time‐correlated single photon counting modules to achieve subnanosecond time response together with high quantum efficiency and low dark noise. These characteristics are required for experiments in single molecule detection and spectroscopy in which time‐gated detection schemes are used. By tightly focusing the input light onto the active area, a quantum efficiency of over 50% and a single photon timing jitter of 168 ps full width at half‐maximum are achieved. In addition, the full width at one‐hundredth maximum, which is of greater importance for time gating, is 790 ps, comparable to that from a microchannel plate photomultiplier. Measurements of the detector dead time, and the quantum efficiency, dark counts, time response, and pulse height distribution for different operating conditions are also reported.
TL;DR: In this paper, the authors describe a new diode laser current controller which features low current noise, excellent dc stability, and the capacity for high speed modulation, and compare favorably with the best presently available commercial diode current controllers.
Abstract: We describe a new diode laser current controller which features low current noise, excellent dc stability, and the capacity for high‐speed modulation. While it is simple and inexpensive to construct, the controller compares favorably with the best presently available commercial diode laser current controllers.
TL;DR: In this article, the authors describe an AFM probe where forces rather than displacements are applied to the tip of the probe, which allows absolute determination of contact compliance and hence p...
Abstract: The mechanical properties of very small volumes of material can vary greatly from bulk properties. These modified properties are of interest in many areas including the operation of atomic force microscopy (AFM), the study of adhesion and fracture, and the evaluation of electrical contact response. Despite the importance of these properties, AFM has not yet been successfully utilized for their investigation. Most existing AFMs still rely on the control and monitoring of displacements, with forces being inferred from spring constants. This would be fine if other interactions, such as those between the tip and the surface, were minor perturbations. However, this is frequently not the case, particularly for contact mode AFM. Hence very little is known about the forces applied in the contact and their affect on both the tip and the sample. In this article we describe an AFM probe where forces rather than displacements are applied to the tip. This allows absolute determination of contact compliance and hence p...
TL;DR: In this article, a method for disentangling the various noise components in semiconductor radiation detector-amplifier systems is described and experimentally tested using a charge amplification scheme.
Abstract: In this paper a method for disentangling the various noise components in semiconductor radiation detector–amplifier systems is described and experimentally tested. A charge amplification scheme is adopted for the measurements. It is shown how an accurate estimate of the series and parallel white noise, 1/f series noise, and f parallel noise can be quickly obtained through a multiparameter least‐squares interpolation of the equivalent noise charge data of the system.
TL;DR: In this article, the authors describe techniques to accurately set, maintain, and measure the temperature of a small sample (typically a single crystal disk of about 1 cm in diameter and 1 mm thick) in a strongly nonisothermal surrounding in ultrahigh vacuum, in the temperature range from at least 6.5 K up.
Abstract: On the basis of detailed considerations of the relevant effects and parameters, we describe techniques which have been developed to accurately set, maintain, and measure the temperature of a small sample (typically a single‐crystal disk of about 1 cm in diameter and 1 mm thick) in a strongly nonisothermal surrounding in ultrahigh vacuum, such as required by surface science experiments, in the temperature range from at least 6.5 K up. The resettability and resolution are 30–70 mK and the absolute error is estimated as about 0.7 K at 10 K and about 1.5 K at 100 K. Controlled linear heating with rates from 10−2 to 50 K/s and high constancy (deviations below 0.1 K up to 5 K/s and below 0.5 K up to 50 K/s), and stepwise heating (≳100 K/s) without measurable overshoot can be carried out in this whole cryogenic range.
TL;DR: Pellet injection is the leading technology for deep fueling of magnetically confined, hot plasmas for controlled thermonuclear fusion research as discussed by the authors, where frozen macroscopic (millimeter-size) pellets composed of the isotopes of hydrogen are formed, accelerated, and transported to the plasma for fueling.
Abstract: During the last 10 to 15 years, significant progress has been made worldwide in the area of pellet injection technology. This specialized field of research originated as a possible solution to the problem of depositing atoms of fuel deep within magnetically confined, hot plasmas for refueling of fusion power reactors. Using pellet injection systems, frozen macroscopic (millimeter‐size) pellets composed of the isotopes of hydrogen are formed, accelerated, and transported to the plasma for fueling. The process and benefits of plasma fueling by this approach have been demonstrated conclusively on a number of toroidal magnetic confinement configurations; consequently, pellet injection is the leading technology for deep fueling of magnetically confined plasmas for controlled thermonuclear fusion research. Hydrogen pellet injection devices operate at very low temperatures (≂10 K) at which solid hydrogen ice can be formed and sustained. Most injectors use conventional pneumatic (light gas gun) or centrifuge (mechanical) acceleration concepts to inject hydrogen or deuterium pellets at speeds of ≂1–2 km/s. Pellet injectors that can operate at quasi‐steady state (pellet delivery rates of 1–40 Hz) have been developed for long‐pulse fueling. The design and operation of injectors with the heaviest hydrogen isotope, tritium, offer some special problems because of tritium’s radioactivity. To address these problems, a proof‐of‐principle experiment was carried out in which tritium pellets were formed and accelerated to speeds of 1.4 km/s. Tritium pellet injection is scheduled on major fusion research devices within the next few years. Several advanced accelerator concepts are under development to increase the pellet velocity. One of these is the two‐stage light gas gun, for which speeds of slightly over 4 km/s have already been reported in laboratory experiments with deuterium ice. A few two‐stage pneumatic systems (single‐shot) have recently been installed on tokamak experiments. This article reviews the equipment and instruments that have been developed for pellet injection with emphasis on recent advances. Prospects for future development are addressed, as are possible applications of this technology to other areas of research.
TL;DR: An apparatus and data analysis methodology is described which allows determination of response time to oxygen concentration changes of luminescent oxygen sensor coatings and nonlinear least‐squares and numerical convolution of the luminecent response to the pressure rise allow determination ofresponse times of the oxygen sensor.
Abstract: An apparatus and data analysis methodology is described which allows determination of response time to oxygen concentration changes of luminescent oxygen sensor coatings. Utilizing a solenoid valve, a sample chamber creates a pressure jump from 0.1 to 700 Torr in 600 μs that is followed by 15 ms of ringing. An optical detection system measures the response of porphyrin‐based luminescent oxygen sensors to the pressure jump. The pressure in the chamber is measured simultaneously and independently with a piezoresistive pressure transducer. Data analysis techniques using nonlinear least‐squares and numerical convolution of the luminescent response to the pressure rise allow determination of response times of the oxygen sensor. The response to pressure jumps of several luminescent oxygen sensitive coatings designed for video luminescent barometry are measured with this computer‐controlled instrument. Several coatings were studied with response times of ∼2.5 s, ∼400 ms, 11 ms, 1.5 ms, and <25 μs. Studies of the...
TL;DR: In this article, a Taylor cone array was established on a flat plate counterelectrode to investigate the feasibility of increasing the liquid throughput rate in electrospray atomizers, and it was found that individual Taylor cones could be established on each capillary over a wide range of the capillary radius to spacing ratio.
Abstract: Linear arrays of Taylor cones were established on capillary electrode tubes opposite a slotted flat plate counterelectrode to investigate the feasibility of increasing the liquid throughput rate in electrospray atomizers. It was found that individual Taylor cones could be established on each capillary over a wide range of the capillary radius to spacing ratio R/S. The onset potential Vs required to establish the cones varied directly with R/S, but the liquid flow rate per cone and current per cone were nearly independent of R/S for a given overpotential ratio P=V/Vs. Only six working capillaries were used, but the results per cone are applicable to larger arrays of cones since end effects were minimized.
TL;DR: In this article, a method to measure intensity autocorrelation functions with a CCD camera and a fast computer has been proposed for low-intensity applications like x-ray correlation spectroscopy.
Abstract: We have successfully implemented a method to measure intensity autocorrelation functions with a CCD camera and a fast computer. We report light scattering experiments on solutions of diffusing latex spheres in glycerol and compare our results to those obtained with a conventional hardwired electronic correlator. Averaging allows significant reduction of measurement times and makes this technique suitable for the study of systems with very long time scales. Moreover, the CCD setup allows measurement of two‐time correlation functions under nonequilibrium conditions where conventional correlators which rely on time‐averaging fail. The new method may offer significant advantage for low‐intensity applications like x‐ray correlation spectroscopy.
TL;DR: In this article, an EMAT is excited by a high-power rf burst in the 0.5-20MHz range and generates ultrasonic oscillations in a plate through a Lorentz force mechanism.
Abstract: A practical method of acoustoelastic stress measurement based on electromagnetic acoustic resonance is presented. This overcomes fundamental limitations of conventional procedures and exhibits the stress resolution to 0.1 MPa for thin aluminum plates and the spatial resolution to several millimeter square in a noncontacting operation. The proposed method successfully combines an electromagnetic acoustic transducer (EMAT) and a superheterodyne phase‐ sensitive detector. An EMAT is excited by a high‐power rf burst in the 0.5–20‐MHz range and generates ultrasonic oscillations in a plate through a Lorentz force mechanism. The signals in the plate are then received by this same EMAT and analyzed for the amplitude spectrum using swept‐frequency phase‐sensitive detection circuitry. The resonance frequencies can be determined for longitudinal and shear modes simultaneously. To illustrate the resonance spectrum technique, experimental results are shown for the measurement of a two‐dimensional stress field in a thi...
TL;DR: In this paper, the characteristics and formation by electrochemical etching under ac voltage of very sharp metal tips usable in several applications and in particular in scanning probe microscopy [STM] and atomic force microscopy].
Abstract: This article deals with the characteristics and formation by electrochemical etching under ac voltage of very sharp metal tips usable in several applications and in particular in scanning probe microscopy [scanning tunneling microscopy (STM) and atomic force microscopy]. An exhaustive survey of other existing mechanical and physicochemical procedures for producing sharp tips is also included for background comparison. Because tip sharpness is central to the atomic or near‐atomic resolution attainable by STM, yet appears to be so far incompletely studied or documented in the literature, it is argued that high‐resolution evidence is required for proper tip characterization as a prerequisite toward adequate performance in the nanometer range. Although atomic‐resolution imaging of two‐dimensional (flat) surfaces by STM has been possible with tips of ill defined or large apex radii, comparable performance on three‐dimensional (rough) surfaces requires the use of tips with sleek shanks and apex radii smaller th...
TL;DR: The torsion pendulum is not only a mainstay instrument in the world of precision measurement and gravitational physics, but is important in electrical science, biophysics, petrology, metallurgy, and various other fields of endeavor as discussed by the authors.
Abstract: The torsion pendulum is not only a mainstay instrument in the world of precision measurement and gravitational physics, but is important in electrical science, biophysics, petrology, metallurgy, and various other fields of endeavor Whether used in the ‘‘static’’ (deflection) mode, the ‘‘dynamic’’ (oscillating) mode, or in some more complex configuration, instrumentation of this kind enables one to isolate and measure weak effects that would otherwise be difficult if not impossible to observe against the background gravitational field of the earth In this review, we present a brief history of fiber‐suspended apparatus and assess the fundamental limits of performance of the dumbbell pendulum We then inventory the different versions of such systems presently used by gravitational physicists and discuss the various interrogation techniques used to monitor the movement of the suspended test mass Next, we tabulate some of the applications for torsion instruments outside of gravitational physics, and close with a few comments on the direction of research in this area
TL;DR: In this paper, a stand-alone atomic force microscope (AFM) featuring large scan, friction measurement, atomic resolution, and liquid operation is developed, which can be combined with a (confocal) inverted microscope, yielding a versatile setup for biological applications.
Abstract: A stand-alone atomic force microscope (AFM) featuring large scan, friction measurement, atomic resolution, and liquid operation, has been developed. Cantilever displacements are measured using the optical beam deflection method. The laser diode and focusing lens are positioned inside the piezo tube and the cantilever at the end of the piezo tube. Because the laser beam stays on the cantilever during scanning, the scan range is solely determined by the characteristics of the piezo tube. In our case 30 x 30 x 9.5 mum3 (xyz). The optical beam deflection detection method allows simultaneous measurement of height displacements and torsion (induced by lateral forces) of the cantilever. AFM images of dried lymphocytes reveal features in the torsion images, which are only faintly visible in the normal height images. A new way of detecting the nonlinear behavior of the piezo tube is described. With this information the piezo scan is linearized. The nonlinearity in a 30-mum scan is reduced from 40% to about 1%, as is illustrated with images of a compact disk. The stand-alone AFM can be combined with a (confocal) inverted microscope, yielding a versatile setup for biological applications.
TL;DR: In this paper, the authors describe the design and construction of a scanning tunneling microscope (STM), which is contained in a reactor cell and allows in situ operation throughout a wide range of pressures and temperatures.
Abstract: We describe the design and construction of a scanning tunneling microscope (STM), which is contained in a reactor cell and allows in situ operation throughout a wide range of pressures and temperatures. This STM is capable of imaging in pressures ranging from ultrahigh vacuum up to several atmospheres. Samples can also be easily moved in and out of the STM cell in a small separate vacuum transfer chamber for external characterization and treatment. The equilibration time and stability of the microscope after temperature changes was determined at atmospheric pressures, by monitoring the evolution of atomically resolved images of highly oriented pyrolytic graphite at temperatures ranging from 300 to 425 K. We have also examined the stability when flowing gases are used instead of stationary pressures. In preliminary experiments using Pt(111) and (110) crystals, we have observed the effect of atmospheres of H2 and O2 on the structure of these surfaces.
TL;DR: The most important factors contributing to line broadening and background intensity in electron spectra are identified and new design principles for high quality measurements are presented in this article, where it is shown that time-dependent potential gradients in the gas cell are responsible for a large part of the "normal" line widening.
Abstract: The most important factors contributing to line broadening and background intensity in electron spectra are identified and new design principles for high quality measurements are presented. It is shown that time‐dependent potential gradients in the gas cell are responsible for a large part of the ‘‘normal’’ line broadening, while scattering processes inside the gas cell are responsible for a large part of the background intensity. By designing the experiment according to these results, gas‐phase electron spectra can be recorded routinely at an instrument resolution level of better than 5 meV even at comparatively high gas cell pressures necessary to give high intensity for weak lines, and in principle unlimited counting times, at a much improved signal‐to‐background level. The resulting improvements in the spectral quality are demonstrated by spectra of Ar and HBr.
TL;DR: In this article, the phase of the photodeflection signal is used to extend the thermal diffusivity range of measurements using the phase phase of photodeglection signal, and a comparison with computer simulations and experimental results shows good agreement.
Abstract: The photodeflection method when applied to measure the low thermal diffusivity of some materials gives inconsistent results. In this article a way to extend the thermal diffusivity range of measurements using the phase of the photodeflection signal is presented. A comparison with computer simulations and experimental results shows good agreement.
TL;DR: In this article, a high-sensitivity computer-controlled infrared polariscope has been developed to measure a small amount of phase retardation, and the principal axes of birefringence induced by residual strains in commercial III-V compound wafers with standard dimensions.
Abstract: A high‐sensitivity computer‐controlled infrared polariscope has been developed to measure a small amount of phase retardation, and the principal axes of birefringence induced by residual strains in commercial III‐V compound wafers with standard dimensions. In order to check the performance of the polariscope, semi‐insulating LEC‐grown GaAs (100) wafers, currently used for high‐speed integrated circuits, were examined. The residual strain components of ‖Sr−St‖, ‖Syy−Szz‖, and ‖Syz‖ were evaluated from the measured values of the phase retardation and the principal axes of birefringence. It was found that the polariscope developed here was highly sensitive enough to characterize the residual strain components to the order of 10−7 in thin commercial GaAs wafers.
TL;DR: In this paper, a method based on the reciprocity theorem is proposed to evaluate the sensitivity of a tuned coil for NMR signal detection, which is defined as the magnetic field that the coil induces at a given point per unit supplied power.
Abstract: The radio‐frequency coil sensitivity for NMR signal detection can be defined as B1/√P, which is the magnetic field that the coil induces at a given point per unit supplied power. We propose a new method, based on the reciprocity theorem, to quickly evaluate the sensitivity of a tuned coil. The only requirement of the method is a voltage gain measurement with a small dual‐loop probe, without mobilization of the NMR unit. The probe can be used to gauge and map the sensitivity of the coil with good accuracy, while monitoring its tuning frequency ω0 and its quality factor Q. Our method is particularly convenient for development and maintenance of coils for MR imaging, and more generally could be applied to other fields involving radio‐frequency characterization of inductive circuits.