Showing papers in "Review of Scientific Instruments in 1978"
TL;DR: A pulsed gas valve is described which produces very intense supersonic molecular beam pulses of about 10 micros duration for light gases such as H2 and He, and of somewhat longer duration for heavier gases.
Abstract: We describe a pulsed gas valve which we have developed for use as a molecular beam source. In order to observe the performance of the pulsed beam source, we also have developed an ionization detector with a rise time of about 1 μs. The pulsed valve produces very intense supersonic molecular beam pulses of about 10 μs duration for light gases such as H2 and He, and of somewhat longer duration for heavier gases. As a new tool for the study of molecular collisions, the pulsed beam technique offers substantial advantages over the conventional continuous‐beam method for experiments which are limited by the signal‐to background ratio for scattered products.
256 citations
TL;DR: A micropositioning stage was developed for use with optical and electron microscopes in the accurate measurement of fine lines used by the microelectronics industry and microscopic objects such as biological cells, air pollution particles, and asbestos fibers.
Abstract: A micropositioning stage has been developed for use with optical and electron microscopes in the accurate measurement of fine lines used by the microelectronics industry and microscopic objects such as biological cells, air pollution particles, and asbestos fibers. The stage combines a piezoelectric driving element and flexure pivoted lever arms to achieve a compact, vacuum compatible device with a resolution of 0.001 μm or less over a range of 50 μm.
178 citations
TL;DR: A quadrupole-based secondary ion mass spectrometer designed for depth profiling is described which combines ultrahigh vacuum construction with high sputtering rate, detection sensitivity, depth resolution, mass spectral purity, and abundance sensitivity.
Abstract: A quadrupole‐based secondary ion mass spectrometer designed for depth profiling is described which combines ultrahigh vacuum construction with high sputtering rate, detection sensitivity, depth resolution, mass spectral purity, and abundance sensitivity. Impurities such as B and Al implanted in Si can be profiled to levels below one part per million atomic (ppma), at a depth resolution equal to that obtained by commercial ion microprobes. The primary beam consists of 5‐keV, mass‐analyzed 40Ar+ ions, focused to about 70 μm in diameter. Its high current density (≳25mA/cm2) permits adequate beam rastering and electronic signal‐gating to optimize depth resolution. A secondary ion extraction lens and spherical energy filter are responsible for achieving abundance sensitivities of five to six orders of magnitude on the low mass side of a matrix peak. The ultrahigh vacuum environment of the sample dramatically reduces molecular peaks containing H, C, and O, allowing even hydrogen to be profiled to concentrations below 10 ppma. Because large amounts of data are generated by multi‐element depth profiling, means for automated instrument control and data acquisition have been developed.
135 citations
TL;DR: Modifications to photometric polarimeter and ellipsometer systems are described that greatly reduce nonlinearity, component drift, and digital noise effects and allow measurements to be made in the presence of ambient scattered light, at high sample temperatures, or using solid-state detectors for which the zero reference is not well defined.
Abstract: We describe simple modifications to photometric polarimeter and ellipsometer systems that greatly reduce nonlinearity, component drift, and digital noise effects. A photomultiplier feedback circuit is described and analyzed that varies the effective system linearity by means of a single control. Linearity to 5×10−4 over more than three orders of magnitude of incident light intensity is obtained. Effective double‐beam stability to 5×10−5 is achieved by blocking the source intensity over part of an extended measurement cycle. These refinements permit photometric instruments to approach accuracy capabilities compatible with their precision capabilities, and also allow measurements to be made in the presence of ambient scattered light, at high sample temperatures, or using solid‐state detectors for which the zero reference is not well defined. As an example, we give the dielectric function of Ge measured from 1.5 to 5.8 eV at a sample temperature of 800° C.
92 citations
TL;DR: A novel means of generating and detecting surface waves at liquid-gas interfaces has been successfully developed using Electrocapillarity through specular reflection of a laser beam from the fluid surface to a position sensitive photodiode.
Abstract: A novel means of generating and detecting surface waves at liquid–gas interfaces has been successfully developed. Electrocapillarity is used to generate the waves which are detected via specular reflection of a laser beam from the fluid surface to a position sensitive photodiode. Such a scheme is compact, sensitive, and does not mechanically touch the fluid surface. A preliminary study of highly damped waves on the magnetically oriented liquid crystal MBBA is reported.
90 citations
TL;DR: A T-format, photon-counting polarization photometer was constructed to facilitate precise polarization measurements at low signal-to-noise ratios and several examples of the instrument's performance are given.
Abstract: A T‐format, photon‐counting polarization photometer was constructed to facilitate precise polarization measurements at low signal‐to‐noise ratios. The instrument optics and electronics are described. Several examples of the instrument’s performance are given, including measurements on picomolar fluorescein solutions at low excitation resolution and the excitation polarization spectrum of indole (2×10−4M) at a resolution of 5 A.
86 citations
TL;DR: An optical probe with a controlled tip geometry developed and developed can be used to determine both local void fractions and interface velocities in liquid-vapor two-phase flows.
Abstract: In view of the importance of obtaining unsteady local void fraction and interface velocities in liquid–vapor two‐phase flows, an optical probe with a controlled tip geometry was developed and is described. In order to minimize the disturbances caused to the flow field by the presence of the probe, its dimensions have been miniaturized. The electronic and hydrodynamic responses of the probe were investigated experimentally. The probe was found to be sensitive to both the interface velocities and the phase present at the probe tip. A possible explanation for the behavior of the probe is presented. Within the velocity range checked and with proper calibration, the optical probe described can be used to determine both local void fractions and interface velocities.
80 citations
TL;DR: The Ar(+) laser pumped tunable dye laser can be operated in three timing configurations: acousto-optically mode locked, cavity dumped, and cavity dumped-mode locked and the system stability is sufficient to accurately determine exponential decays as short as 50 psec.
Abstract: We present several laser based methods to improve the technique of time-correlated photon counting. Our Ar(+) laser pumped tunable dye laser can be operated in three timing configurations: acousto-optically mode locked, cavity dumped, and cavity dumped-mode locked. Performance characteristics of the laser system in various operational modes are described along with measurement techniques for both gas and liquid phase. The subnanosecond pulses generated by mode locking are extremely stable and they maintain identical pulse shapes over a 6-h period, as shown via photon counting measurements at a 15-psec channel resolution. Our RCA C31034 photomultiplier with a red sensitive GaAs photocathode provides wavelength-independent response to detected fluorescence in both the visible and ultraviolet. The present limit of our apparatus is controlled by the accuracy of deconvoluting fluorescence decay from the finite response width caused by photomultiplier transit time dispersion (0.8 nsec FWHM). Our system stability is sufficient to accurately determine exponential decays as short as 50 psec. Furthermore, we can successfully analyze dual exponential decays such as those arising from solution reorientation times of 390 psec competing with a fluorescence lifetime of 725 psec. Examples of the laser performance are selected from a variety of measurements in the gas phase and from the fluorescent dye rose bengal in the liquid phase.
80 citations
TL;DR: A hollow tube cathode using lanthanum hexaboride as the electron emitter has been designed and constructed and tests in both argon and hydrogen indicate that this cathode is capable of producing over 800 A of electron current continuously.
Abstract: A hollow tube cathode using lanthanum hexaboride as the electron emitter has been designed and constructed. Tests in both argon and hydrogen indicate that this cathode is capable of producing over 800 A of electron current continuously, corresponding to over 25 A/cm2 from the LaB6. The cathode has been operated for over 300 h and exposed to air more than 100 times with no deterioration in emission. Projected lifetime is in excess of 3500 h for the sintered LaB6 piece tested in this configuration. Construction details, performance characteristics, and discussions of space charge limits on emission are described.
77 citations
TL;DR: Subnanosecond fluorescence lifetimes of Rhodamine B with KI as a quencher have been determined by deconvolution of photons counted versus elapsed time using the method of moments; the shortest lifetime measured was 68 ps.
Abstract: A synchronously pumped tunable dye laser has been constructed and interfaced with a modified Ortec 9200 photon counting system for the purpose of measuring subnanosecond relaxation phenomena. The dye laser excitation pulse, which has an intrinsic 35‐ps FWHM for Rhodamine 6G, is 350 ps when measured by time‐correlated single photon counting. This value appears to be characteristic of the transit time jitter in the RCA 8850 photomultiplier tube. Subnanosecond fluorescence lifetimes of Rhodamine B with KI as a quencher have been determined by deconvolution of photons counted versus elapsed time using the method of moments; the shortest lifetime measured was 68 ps. Various technical aspects of the system are discussed with emphasis on applications to biophysical problems.
74 citations
TL;DR: Two low-noise differential input amplifiers designed for voltage and current fluctuation measurements in epithelia are described and performance is demonstrated with Na(+) current power density spectra obtained from frog skin with the transistor-input stage.
Abstract: Two low‐noise differential input amplifiers designed for voltage and current fluctuation measurements in epithelia are described. The first one uses a matched pair of low‐noise transistors and is particularly suited for low‐frequency current and voltage noise measurements in frog skin and other preparations with impedances below 1 kΩ. The second one is designed around a matched pair of JFETs and can also be used for higher source impedance. Performance is demonstrated with Na+ current power density spectra obtained from frog skin with the transistor‐input stage.
TL;DR: The viscosity of liquids can be measured in the diamond-anvil pressure cell utilizing a falling-solid sphere method and the ruby technique for pressure measurement to 70 kilobars.
Abstract: The viscosity of liquids can be measured in the diamond‐anvil pressure cell utilizing a falling‐solid sphere method and the ruby technique for pressure measurement. The pressure dependence of the viscosity of a 4:1 mixture (by volume) of methanol–ethanol was determined to 70 kilobars. The accuracy of the method is estimated from measurements made on a fluid of known viscosity.
TL;DR: In this article, an instrument was proposed to detect and measure stratospheric water mixing ratios utilizing H2O photodissociation by Ly α (1216 A) light and detecting OH(A2J+X2Π) emission.
Abstract: Photodissociation of polyatomic molecules by vacuum‐uv light often results in the formation of electronically excited diatomic molecular fragments. Based on this, instruments that measure mixing ratios or densities of selected polyatomic species in the stratosphere and higher troposphere can be constructed. This is demonstrated by an instrument to detect and measure stratospheric water mixing ratios utilizing H2O photodissociation by Ly α (1216 A) light and detecting OH(A2J+X2Π) emission. Also, detectors for H2O2, HNO3, and NO2 are discussed.
TL;DR: The properties of a steady-state, dc discharge multidipole ion source have been investigated and different schemes to reduce the loss of ions to the chamber wall are described.
Abstract: The properties of a steady‐state, dc discharge multidipole ion source have been investigated. The plasma density in the source depends on the magnet geometries, the discharge voltage, and the bias voltage on the first extraction grid. Different schemes to reduce the loss of ions to the chamber wall are described. Hydrogen ion species in the extracted beam are studied by a mass analyzer.
TL;DR: A long-life, high-current, microwave ion source for an electromagnetic mass separator that operates under low pressure (10(-2)-10(-3) Torr) and with high power efficiency.
Abstract: A long‐life, high‐current, microwave ion source for an electromagnetic mass separator is described. Ionization takes place due to the 2.45‐GHz microwave discharge at a magnetic field intensity which is higher than the electron cyclotron resonance magnetic field. The discharge chamber is a ridged circular waveguide. The discharge region is restricted to a rectangular volume between the ridged electrodes by filling the remaining portions with dielectric. This source operates under low pressure (10−2–10−3 Torr) and with high power efficiency. The incident microwave power is only several hundred watts at maximum output. When PH3 gas is introduced, the total extracted current is about 40 mA with a 2×40‐mm extraction slit. A P+ ion implantation current of more than 10 mA is obtained by combining the source with a 40‐cm radius, 60° deflection magnetic mass separator.
TL;DR: The troublesome spurious ringing phenomenon found in pulsed nuclear magnetic resonance probes is explained in terms of the electromagnetic generation and detection of ultrasonic waves.
Abstract: The troublesome spurious ringing phenomenon found in pulsed nuclear magnetic resonance probes is explained in terms of the electromagnetic generation and detection of ultrasonic waves. A few techniques for eliminating this problem are discussed.
TL;DR: An optical heterodyne interferometer utilizing a fiber optic target probe and a digital phase compensation system and the effect of background motions on output is described.
Abstract: An optical heterodyne interferometer utilizing a fiber optic target probe and a digital phase compensation system is described. Optical performance and the effect of background motions on output are described. Maximum sensitivity for a simulated biological target in aqueous medium is 0.05 A Hz−1/2 for a signal‐to‐noise ratio of unity.
TL;DR: A laser flash method developed for the measurement of thermal conductivity of solids was applied to liquids of low thermal Conductivity, and thermal conductivities of water and toluene near room temperature were measured with a mean deviation of 2.6%.
Abstract: A laser flash method developed for the measurement of thermal conductivity of solids was applied to liquids of low thermal conductivity. The sample liquid was sandwiched in between a small thin metal disk and a sample holder. When the laser beam is absorbed in the front surface of the metal disk, the temperature of the disk quickly rises about 2 K and heat then flows downwards through the sample liquid as one‐dimensional heat flow. The thermal conductivity of liquid can be obtained from the temperature fall of the disk without employing any reference materials and also without measuring the thickness of the sample liquid layer. Thermal conductivities of water and toluene near room temperature were measured by this method with a mean deviation of 2.6%. This laser flash method may be applied to the measurement of the thermal conductivity of liquids such as molten salts at elevated temperatures.
TL;DR: An in-laboratory apparatus utilizing a focusing crystal technique which increases available fluxes two to three orders of magnitude over previous laboratory facilities is developed, so that EXAFS measurements can be carried out quickly and accurately in the laboratory.
Abstract: The EXAFS technique is a powerful new structural tool, particularly useful for studies of disordered or otherwise complex materials for which x-ray diffraction techniques are difficult or unfeasible. At the present time, most EXAFS experiments are carried out at a synchrotron facility because of the larger fluxes available. We have developed an in-laboratory apparatus utilizing a focusing crystal technique which increases available fluxes two to three orders of magnitude over previous laboratory facilities, so that EXAFS measurements can be carried out quickly and accurately in the laboratory. We will discuss the principles of the focusing monochromator and we will also illustrate the experimental method with examples, including studies of chemical solutions, defect crystalline solids, and high-temperature superconductors.
TL;DR: Time-dependent fluorescence processes can be investigated using a phase fluorometer with variable frequency using the high cutoff frequency of 500 MHz leads to a time-resolving power of about 1 ps.
Abstract: Time‐dependent fluorescence processes can be investigated using a phase fluorometer with variable frequency. The high cutoff frequency of 500 MHz leads to a time‐resolving power of about 1 ps.
TL;DR: A sensitive, efficient image intensifier-TV x-ray detector is described that has been optimized for a large class of diffraction studies of biological structures and is particularly well suited for studies utilizing the high fluxes of synchrotron sources.
Abstract: A sensitive, efficient image intensifier‐TV x‐ray detector is described that has been optimized for a large class of diffraction studies of biological structures. All of the major components are commercially available. The system is well suited to measuring the intensity of diffraction patterns that are weak, or changing with time. Because there is no count rate limitation, it is particularly well suited for studies utilizing the high fluxes of synchrotron sources.
TL;DR: The high ion trapping efficiency and open geometry of the analyzer cell make it well suited for studying the interaction of laser radiation with gaseous ions and may also be useful for high-accuracy isotope ration mass spectrometry.
Abstract: A pulsed ion cyclotron resonance mass spectrometer utilizes the cyclotron resonance principle for mass analysis of ions trapped at low pressures by electric and magnetic fields. Both mass analysis and ion trapping are accomplished in a one‐region device called a trapped ion analyzer cell. A pulsing sequence is described which allows for generation of ions by electron impact, reaction with added gases, and mass analysis of the products of ion–molecule reactions. Methods are described for measuring rate constants and equilibrium constants for ion–molecule reactions. The high ion trapping efficiency and open geometry of the analyzer cell make it well suited for studying the interaction of laser radiation with gaseous ions and may also be useful for high‐accuracy isotope ration mass spectrometry.
TL;DR: Al is a better material for a heat switch than the usually used superconductors because of its large k(n) and large Debye temperature (reducing the lattice conductivity k(s).
Abstract: We have measured the thermal conductivity of a 0.1-mm-thick Al foil in the normal and superconducting state down to 58 mK. At this temperature, our data give a ratio for the conductivities of k(n)/k(s)=1600 T(-2). They show that Al is a better material for a heat switch than the usually used superconductors because of its large k(n) and large Debye temperature (reducing the lattice conductivity k(s)). In addition, we describe the design of a heat switch and an excellent performing demountable press-contact between Al and Cu, both gold plated, as joint to the switch.
TL;DR: A computer system was developed at NIH, NCI, to add data acquisition, storage, and processing capability to two different flow microfluorometer/cell separators (FMF).
Abstract: A computer system was developed at NIH, NCI, to add data acquisition, storage, and processing capability to two different flow microfluorometer/cell separators (FMF). Data can be collected from either or both cell separators while previously collected data are being simultaneously processed. Measured cell parameters can be accumulated in the computer memory as arrays of cell counts over a range of intensities or stored as raw data in a list mode on magnetic tape. The computer system hardware includes a refresh display, two disks, industry standard magnetic tape, 32K core, an incremental plotter, a link to the central facility, and links to the FMFs. For convenience in program development and to give direct access to additional data analysis resources, a direct 1200 baud link is available to a Central Facility PDP‐10. Programs have been developed to display the data in two dimensions and to create three‐dimensional projections which can be rotated. Two‐dimensional contour maps at user‐selected thresholds a...
TL;DR: A novel type of ion-scattering spectrometer for analyzing the composition of surfaces is described, by means of a specially designed cylindrical mirror analyzer, which allows analyses to be performed using extremely low ion doses.
Abstract: A novel type of ion-scattering spectrometer for analyzing the composition of surfaces is described. By means of a specially designed cylindrical mirror analyzer the sensitivity of the instrument is increased by two or three orders of magnitude as compared with that of equipment used hitherto. The increased sensitivity allows analyses to be performed using extremely low ion doses. Under these conditions, destruction of the surface is negligible. The use of a differential pumping system guarantees UHV conditions at the target, thus minimizing contamination.
TL;DR: An apparatus for the coincident observation of both outgoing electrons in an electron impact ionization, or (e,2e), experiment, which employs ten detectors arranged such that every pair corresponds to a different set of momenta for the outgoing electrons intercepted by that pair.
Abstract: We describe an apparatus for the coincident observation of both outgoing electrons in an electron impact ionization, or (e,2e), experiment. The device employs ten detectors arranged such that every pair corresponds to a different set of momenta for the outgoing electrons intercepted by that pair. By simultaneously monitoring the output from all ten detectors it is possible to perform 25 simultaneous (e,2e) experiments. The results of these experiments can be compared without considering temporal variations of source conditions.
TL;DR: A two-wavelength plasma density interferometer utilizing a CO(2) laser and an HeNe laser is described, being designed for use on Doublet III, a large noncircular cross-section tokamak.
Abstract: A two-wavelength plasma density interferometer utilizing a CO(2) laser and an HeNe laser is described. The interferometer is being designed for use on Doublet III, a large noncircular cross-section tokamak. The use of the two wavelengths allows the distinction between fringe shifts due to plasma density and fringe shifts due to mirror vibrations. Plasma density fringe shifts of 1/10 of a fringe shift can be measured in the presence of mirror vibrations which cause several fringe shifts. A simple digital phase comparing electronic system is used.
TL;DR: The generation and measurement of subpicosecond electron beam pulses by the transverse-longitudinal combination gate system and close agreement has been obtained between the calculated pulse width and the observed one which was measured by the Lissajous's figure method.
Abstract: The generation and measurement of subpicosecond electron beam pulses by the transverse‐longitudinal combination gate system is described. The temporal property of the pulse gate is analyzed with the help of the longitudinal emittance diagram. Close agreement has been obtained between the calculated pulse width and the observed one which was measured by the Lissajous’s figure method. A beam pulse of 0.2 ps (FWHM) was produced.
TL;DR: The Mars viking gas chromatograph-mass spectrometer is described, designed to determine the composition of the Martian atmosphere and detect and identify chemical compounds vaporized or pyrolyzed from the Martian soil.
Abstract: The Mars viking gas chromatograph–mass spectrometer is described. The system is designed to determine the composition of the Martian atmosphere and detect and identify chemical compounds vaporized or pyrolyzed from the Martian soil. Construction details, performance data, data processing methods, and references to manufacturing and test procedures are also provided.
TL;DR: Methods of obtaining quantitative thermometric data with a thermographic camera are discussed, and practical considerations of theromometry are emphasized as opposed to radiometric measurements (such as spectral properties).
Abstract: Methods of obtaining quantitative thermometric data with a thermographic camera are discussed. These include the assessment of errors associated with the camera itself and techniques for calibrating the particular camera. Difficulties arising from the nature of the object to be measured also are considered. These include determining the ’’penetration of depth’’ of infrared radiation emitted by the object (how ’’thick’’ is the surface?), measuring the transmittance of ’’windows’’ in front of th objects, and measuring the object’s emittance under somewhat adverse circumstances. Finally, an example of a temperature measurement is given. Practical considerations of theromometry are emphasized as opposed to radiometric measurements (such as spectral properties). Examples are drawn from measurements involving tissue‐equivalent electromagnetic phantom materials.