Showing papers in "Review of Scientific Instruments in 1997"

Velocity map imaging of ions and electrons using electrostatic lenses: Application in photoelectron and photofragment ion imaging of molecular oxygen

Abstract: The application of electrostatic lenses is demonstrated to give a substantial improvement of the two-dimensional (2D) ion/electron imaging technique. This combination of ion lens optics and 2D detection makes “velocity map imaging” possible, i.e., all particles with the same initial velocity vector are mapped onto the same point on the detector. Whereas the more common application of grid electrodes leads to transmission reduction, severe trajectory deflections and blurring due to the non-point source geometry, these problems are avoided with open lens electrodes. A three-plate assembly with aperture electrodes has been tested and its properties are compared with those of grid electrodes. The photodissociation processes occurring in molecular oxygen following the two-photon 3dπ(3Σ1g −)(v=2, N=2)←X(3Σg −) Rydberg excitation around 225 nm are presented here to show the improvement in spatial resolution in the ion and electron images. Simulated trajectory calculations show good agreement with experiment and ...

Measuring ultrashort laser pulses in the time-frequency domain using frequency-resolved optical gating

Abstract: We summarize the problem of measuring an ultrashort laser pulse and describe in detail a technique that completely characterizes a pulse in time: frequency-resolved optical gating. Emphasis is placed on the choice of experimental beam geometry and the implementation of the iterative phase-retrieval algorithm that together yield an accurate measurement of the pulse time-dependent intensity and phase over a wide range of circumstances. We compare several commonly used beam geometries, displaying sample traces for each and showing where each is appropriate, and we give a detailed description of the pulse-retrieval algorithm for each of these cases.

Remote thermometry with thermographic phosphors: Instrumentation and applications

Abstract: The temperature-dependent characteristics of fluorescence of several rare-earth-doped ceramic phosphors has made these materials the focus of a major effort in the field of noncontact thermometry over the past few decades. These “thermographic phosphors,” e.g., Y2O3:Eu, have been used for remote measurements of the temperatures of both static and moving surfaces, and have performed many other tasks that standard sensors (thermocouples, thermistors, etc.) cannot. The range of usefulness of this class of materials extends from cryogenic temperatures to those approaching 2000 °C. The instrumentation needed for this type of thermometry has followed many different lines of development, and this evolution has produced a wide variety of both field- and laboratory-grade systems that are now described in the literature. In general, the technique offers high sensitivity (≈0.05 °C), robustness (e.g., stability of the sensor sample in harsh environments), and NIST traceability. In addition, such systems have been suc...

Contrast and resolution in imaging with a microfocus x-ray source

Abstract: A simple general treatment of x-ray image formation by Fresnel diffraction is presented; the image can alternatively be considered as an in-line hologram Particular consideration is given to phase-contrast microscopy and imaging using hard x rays The theory makes use of the optical transfer function in a similar way to that used in the theory of electron microscope imaging Resolution and contrast are the criteria used to specify the visibility of an image Resolution in turn depends primarily on the spatial coherence of the illumination, with chromatic coherence of lesser importance Thus broadband microfocus sources can give useful phase-contrast images Both plane- and spherical-wave conditions are explicitly considered as limiting cases appropriate to macroscopic imaging and microscopy, respectively, while intermediate cases may also be of practical interest Some results are presented for x-ray images showing phase contrast

Review of high-power microwave source research

Abstract: This article reviews the state-of-the-art in high-power microwave source research. It begins with a discussion of the concepts involved in coherent microwave generation. The main varieties of microwave tubes are classified into three groups, according to the fundamental radiation mechanism involved: Cherenkov, transition, or bremsstrahlung radiation. This is followed by a brief discussion of some of the technical fundamentals of high-power microwave sources, including power supplies and electron guns. Finally, the history and recent developments of both high-peak power and high-average power sources are reviewed in the context of four main areas of application: (1) plasma resonance heating and current drive; (2) rf acceleration of charged particles; (3) radar and communications systems; and (4) high-peak power sources for weapons-effect simulation and exploratory development.

High-resolution ion mobility measurements

Abstract: Gas phase ion mobility measurements can resolve structural isomers for polyatomic ions and provide information about their geometries. A new experimental apparatus for performing high-resolution ion mobility measurements is described. The apparatus consists of a pulsed laser vaporization/desorption source coupled through an ion gate to a 63-cm-long drift tube. The ion gate is a critical component that prevents the diffusion of neutral species from the source into the drift tube. Ions travel along the drift tube under the influence of a uniform electric field. At the end of the drift tube some of the ions exit through a small aperture. They are focused into a quadrupole mass spectrometer, where they are mass analyzed, and then detected by an off-axis collision dynode and by dual microchannel plates. The apparatus is operated with a drift voltage of up to 14 000 V and a helium buffer gas pressure of around 500 Torr. The resolving power for ion mobility measurements is over an order of magnitude higher than has been achieved using conventional injected-ion drift tube techniques. Examples of the application of the new apparatus in resolving isomers of laser desorbed metallofullerenes, in studying silicon clusters generated by laser vaporization, and in following the isomerization of small nanocrystalline (NaCl)nCl− clusters as a function of temperature, are presented.

Impulse excitation apparatus to measure resonant frequencies, elastic moduli, and internal friction at room and high temperature

Abstract: This paper presents a new apparatus to measure elastic properties and internal friction of materials. The apparatus excites the test specimen by a light mechanical impact (impulse excitation) and performs a software-based analysis of the resulting vibration. The resonant frequencies fr of the test object are determined and, in the case of isotropic and regular shaped specimens, the elastic moduli are calculated. The internal friction value (Q−1) is determined for each fr as Q−1=k/(πfr) with k the exponential decay parameter of the vibration component of frequency fr. A furnace was designed and equipped with automated impulse excitation and vibration detection devices, thus allowing computer-controlled measurements at temperatures up to 1750 °C. The precision of the measured fr depends on the size and stiffness of the specimen, and varies from the order of 10−3 (that is ±1 Hz at 1 kHz) in soft, high damping materials or light specimens, to values as precise as 10−5 (that is ±0.1 Hz at 10 kHz) in larger or ...

Measurement of heat capacity by fitting the whole temperature response of a heat-pulse calorimeter

Abstract: A new method that fits the whole temperature response of a heat-pulse calorimeter for heat capacity is developed. Analyzing the thermal response of a heat-pulse calorimeter on a model that was used by the relaxation method, the authors derived some useful relations and further utilized the numeric method of the general linear least squares to determine the heat capacity of a sample. Absolute accuracy of the proposed method was verified by determining the heat capacity of a 0.249 76 g copper sample (purity 99.999%) on a self-designed and fully automated calorimetric system from 4.5 to 80 K. Comparing the result with the literature, the deviation in average was 1.2% from 4.5 to 20 K and 2.0% from 20 to 80 K. It is found that the proposed method is capable of measuring heat capacity regardless if the sample is adiabatically or nonadiabatically isolated. The size of the specimen is not critical for the application of the method and the temperature range of measurement can be expanded. It also deals with the τ...

Chemical reactivity of size-selected supported clusters: An experimental setup

Abstract: We describe an experimental setup for the investigation of the chemical reactivity of size-selected, supported clusters. The clusters are generated by a high frequency laser vaporization source. After mass selection and energy control the clusters are deposited under ultrahigh-vacuum conditions and with low kinetic energy onto thin oxide films grown on metal single crystals. Such films are ideal in their function as supports for size-selected deposited metal clusters. Measured currents of mass-selected niobium cluster ions were of the order of 1 nA and are high enough for fast deposition rates. Adsorbed molecules used on the one hand as probes to characterize the supported clusters and on the other hand for studying chemical reactions on these clusters are investigated in situ by Fourier transform infrared spectroscopy, temperature desorption spectroscopy, and Auger electron spectroscopy. The performance of these analytical tools is illustrated with CO adsorbed on Ni atoms supported on thin MgO(100) films...

Elliptical flexure hinges

Abstract: This paper presents closed form equations based on a modification of those originally derived by Paros and Weisbord in 1965, for the mechanical compliance of a simple monolithic flexure hinge of elliptic cross section, the geometry of which is determined by the ratio e of the major and minor axes. It is shown that these equations converge at e=1 to the Paros and Weisbord equations for a hinge of circular section and at e ⇒∞ to the equations predicted from simple beam bending theory for the compliance of a cantilever beam. These equations are then assessed by comparison with results from finite element analysis over a range of geometries typical of many hinge designs. Based on the finite element analysis, stress concentration factors for the elliptical hinge are also presented. As a further verification of these equations, a number of elliptical hinges were manufactured on a CNC milling machine. Experimental data were produced by applying a bending moment using dead weight loading and measuring subsequent ...

Pt resistor thermometry and pressure calibration in a clamped pressure cell with the medium, Daphne 7373

Abstract: Calibration of a Pt resistance thermometer (Netsushin) in magnetic fields and under pressure in the range of 1.5–300 K and below 1.5 GPa is presented. With the pressure medium, olefin olygomers, Daphne 7373, the pressure is continuous at its solidification and the pressure drop from 300 to 4.2 K by 0.15–0.17 GPa is constant, irrespective of the initial clamped pressure at 300 K. The applicability of the thermometer and the medium for precise study in field and pressure at low temperature is discussed.

Performance of the vacuum ultraviolet high-resolution and high-flux beamline for chemical dynamics studies at the Advanced Light Source

Abstract: At the Advanced Light Source an undulator beamline, with an energy range from 6 to 30 eV, has been constructed for chemical dynamics experiments. The higher harmonics of the undulator are suppressed by a novel, windowless gas filter. In one branchline high-flux, 2% bandwidth radiation is directed toward an end station for photodissociation and crossed molecular-beam experiments. A photon flux of 1016 photon/s has been measured at this end station. In a second branchline a 6.65 m off-plane Eagle monochromator delivers narrow bandwidth radiation to an end station for photoionoization studies. At this second end station a peak flux of 3×1011 was observed for 25 000 resolving power. This monochromator has achieved a resolving power of 70 000 using a 4800 grooves/mm grating, one of the highest resolving powers obtained by a vacuum ultraviolet monochromator.

Energetic neutral atom imaging of space plasmas

Abstract: Experimental techniques and instrumentation for space plasma imaging in fluxes of energetic neutral atoms (ENAs) are reviewed. ENAs are born in charge exchange collisions between space plasma energetic ions and background neutral gas. ENAs are ubiquitous in the space environment and their energies are in the range from a few eV up to >100 keV. Contrary to charged particles, ENAs can travel large distances through space with minimal disturbance, and by recording ENA fluxes as a function of observational direction, one can reconstruct a global image of a planetary magnetosphere or the heliosphere. Plasma ion energy distribution and ion composition can be remotely established by measuring ENA energies and masses. ENA imaging opens a new window on various phenomena in space plasmas with a promise to qualitatively improve our understanding of global magnetospheric and heliospheric processes. At first we review ENA fluxes in space and their properties, and present a brief history of ENA experimental studies and...

A fast scan submillimeter spectroscopic technique

Abstract: A new fast scan submillimeter spectroscopic technique (FASSST) has been developed which uses a voltage tunable backward wave oscillator (BWO) as a primary source of radiation, but which uses fast scan (∼105 Doppler limited resolution elements/s) and optical calibration methods rather than the more traditional phase or frequency lock techniques. Among its attributes are (1) absolute frequency calibration to ∼1/10 of a Doppler limited gaseous absorption linewidth (<0.1 MHz, 0.000 003 cm−1), (2) high sensitivity, and (3) the ability to measure many thousands of lines/s. Key elements which make this system possible include the excellent short term spectral purity of the broadly (∼100 GHz) tunable BWO; a very low noise, rapidly scannable high voltage power supply; fast data acquisition; and software capable of automated calibration and spectral line measurement. In addition to the unique spectroscopic power of the FASSST system, its implementation is simple enough that it has the prospect of impacting a wide range of scientific problems.

Thermal conductivity of thin metallic films measured by photothermal profile analysis

Abstract: Thermal conductivity of nickel and gold films on quartz (thickness 0.4–8 μm) was measured by a modulated thermoreflectance technique recording the surface temperature profile. Model calculations predict an optimum frequency for measuring thermal transport within the film. Measurements on films with various thicknesses reveal a thermal conductivity close to the bulk value for nickel while gold films exhibit a reduced conductivity with decreasing film thickness.

Principles and characteristics of a new generation plasma immersion ion implanter

Abstract: A new generation multipurpose plasma immersion ion implanter (PIII) was custom designed, constructed, and installed in the City University of Hong Kong. The system is designed for general R&D applications in metallurgy, tribology, surface modification, and fabrication of novel materials. Using the new rf ion source in conjunction with the internal antenna system, the plasma density achieves excellent uniformity both laterally and axially. The system also incorporates two metal sources, including four metal arc sources and a sputtering electrode, so that multiple metal deposition and implantation steps can be performed in succession in the same equipment without exposing the samples to air. This capability can be critical to the study of surface properties and corrosion resistance. This article describes the design objectives, the novel features, and the characteristics of this new generation PIII equipment.

Vacuum ultraviolet rare gas excimer light source

Abstract: A dc electron beam at 20 keV is used for the excitation of pure rare gases at pressures up to 1.7 bar. The well known second excimer continua of argon, krypton, and xenon observed under these excitation conditions provide an efficient light source in the vacuum ultraviolet spectral region between 120 and 200 nm. Thin (300 nm) SiNx foils are used as entrance windows for the low energy electron beam. Due to the flexibility of the production process of the thin foils one can consider various shapes and sizes of the light emitting region to be manufactured. Efficiencies of ∼30% are observed for the conversion of electron beam energy into light.

MDSplus data acquisition system

Abstract: MDSplus, a tree based, distributed data acquisition system, was developed in collaboration with the ZTH Group at Los Alamos National Lab and the RFX Group at CNR in Padua, Italy. It is currently in use at MIT, RFX in Padua, TCV at EPFL in Lausanne, and KBSI in South Korea. MDSplus is made up of a set of X/motif based tools for data acquisition and display, as well as diagnostic configuration and management. It is based on a hierarchical experiment description which completely describes the data acquisition and analysis tasks and contains the results from these operations. These tools were designed to operate in a distributed, client/server environment with multiple concurrent readers and writers to the data store. While usually used over a Local Area Network, these tools can be used over the Internet to provide access for remote diagnosticians and even machine operators. An interface to a relational database is provided for storage and management of processed data. IDL is used as the primary data analysis and visualization tool. IDL is a registered trademark of Research Systems Inc.

Evanescent wave cavity ring-down spectroscopy with a total-internal-reflection minicavity

Abstract: A miniature-cavity realization of the cavity ring-down concept, which permits extension of the technique to spectroscopy of surfaces, thin films, liquids, and, potentially, solids, is explored using a wave-optics model. The novel spectrometer design incorporates a monolithic, total-internal-reflection-ring cavity of regular polygonal geometry with at least one convex facet to induce stability. Evanescent waves generated by total-internal reflection probe absorption by matter in the vicinity of the cavity. Optical radiation enters or exits the resonator by photon tunneling, which permits precise control of input and output coupling. The broadband nature of total-internal reflection circumvents the narrow bandwidth restriction imposed by dielectric mirrors in conventional gas-phase cavity ring-down spectroscopy. Following a general discussion of design criteria, calculations are presented for square and octagonal cavity geometries that quantify intrinsic losses and reveal an optimal cavity size for each geo...

Rapid acquisition, analysis, and display of fluorescence lifetime-resolved images for real-time applications

Abstract: Fluorescence lifetime-resolved imaging (FLI) is a relatively new technique of fluorescence imaging whereby the spatial distribution of fluorescence decay times can be determined directly at every pixel of an image simultaneously The fluorescence decay times of many chromophores can act as sensitive gauges of their molecular environments By employing measurement techniques that are quantitatively related to the radiative dynamics of the dye molecules (in the nanosecond time range), additional physical parameters are available for discerning different fluorophores with disparate lifetimes, or for characterizing a single fluorophore in different surroundings Many physical processes such as molecular aggregation, binding of dyes to macromolecular species, inclusion of chromophores in specific cellular organwelles, fluorescence resonance energy transfer, and dynamic quenching determine the excited-state lifetime of a fluorophore The FLI technique provides a way to measure these processes directly at 103–10

Gas condensation source for production and deposition of size-selected metal clusters

Abstract: We describe the construction and performance of a gas condensation cluster source. The source was designed for deposition of mass-selected metal clusters with controlled landing energy. We have produced clusters of Pbn (n=2–∼300) and Agn (n=∼20–∼300) with sufficient intensity to deposit size-selected clusters to a density of 1012 clusters/cm2 in 10 min. The landing energy of the clusters can be controlled from ∼25 to 800 eV.

A synchrotron x-ray liquid surface spectrometer

Abstract: The design of a synchrotron x-ray liquid surface spectrometer at beamline X19C at the National Synchrotron Light Source is described. This spectrometer is capable of performing the full range of x-ray surface scattering techniques. A few examples of measurements made using this spectrometer are presented, including studies of organic monolayers on the surface of water and of the structure of strongly fluctuating oil–microemulsion interfaces. The measurements discussed illustrate the accuracy, resolution, and capabilities of the spectrometer.

Use of a charge coupled device camera for low-angle elastic light scattering

Abstract: A charge coupled device (CCD) camera has been successfully used to implement a low-angle elastic light scattering setup. A novel optical detection layout brings all the light scattered by the sample directly onto the CCD, optimizing the instrument sensitivity. The detectable angular range covers ∼2 decades, from ∼0.1° to ∼10°. The calibration of the instrument, as well as the estimate of its sensitivity, accuracy, dynamic range and linearity, can be carried out by using single pinholes. Experimental results from pinholes and diluted suspensions of polystyrene spheres are presented.

Description of a single modular optical setup for ellipsometry, surface plasmons, waveguide modes, and their corresponding imaging techniques including Brewster angle microscopy

Abstract: A versatile modular setup is described which incorporates ellipsometry, surface plasmon spectroscopy, waveguide modes, their corresponding imaging techniques and Brewster angle microscopy in a single instrument The important design criteria are discussed with special emphasis given to the requirements imposed by imaging under an oblique angle of incidence Several experimental examples demonstrate the power of the instrument Imaging nullellipsometry of a patterned monolayer on a highly reflecting support demonstrates a lateral resolution of approximately 1 μm and an accuracy in the thickness determination in the sub-nm region The localization of the evanescent field of a surface plasmon was exploited to characterize adsorption layers in turbid and thus highly scattering solutions An example of how an anisotropic sample can be characterized with the aid of waveguide modes is provided

Miniature, high-resolution, quadrupole mass-spectrometer array

Abstract: A minature quadrupole mass-spectrometer array consisting of 16 rods in a 4X4 array is reported.

An improved lamellae drop-off technique for sharp tip preparation in scanning tunneling microscopy

Abstract: A superior lamellae etching drop-off technique is described for the preparation of W tips without the use of CCl4. Sharp tips with an apex of 25 nm or less can be produced routinely. In the case of Pt/Ir wire, the chemical inertness of the material means that it has to be reduced in diameter before being etched to yield a tip. In order to accomplish this, a capillary diameter reduction technique has also been developed for use in combination with the lamellae etching drop-off technique. The apparatus does not require the use of micromanipulators or micromovers. The shapes of tips with apexes as small as 25 nm can be investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This low cost method of producing sharp tips scanning tunneling microscopy is very effective and it would probably be feasible to develop an automatic tip preparation with a little more technical effort. Since it is possible to produce well shaped W tips almost every time after acquiring a little ski...

A low-temperature ultrahigh-vacuum scanning tunneling microscope with rotatable magnetic field

Abstract: We present a new design of a low-temperature ultrahigh-vacuum (UHV) scanning tunneling microscope setup with a combination of a solenoid and a split-pair magnet The scanning tunneling microscope can be operated at temperatures down to 8 K and in a rotatable magnetic field of up to 1 T Magnetic fields of up to 7 T perpendicular and 2 T parallel to the sample surface can be applied The UHV part of the system allows in situ preparation and low energy electron diffraction/Auger analysis of samples First topographic and spectroscopic measurements on p-InAs(110) are presented

A 3-350 k fast automatic small sample calorimeter

Abstract: A description of a fully automated calorimeter for rapid measuring the heat capacity of solids in the temperature region from ∼3 to ∼350 K and in magnetic fields from 0 to 10 T is given. A comprehensive mathematical analysis of the semiadiabatic heat pulse technique for heat capacity measurements on solid materials resulted in the development of the necessary formal algorithms for the complete automatization of the data collection process. Simultaneously a procedure for the on-line evaluation of uncertainties in the measured heat capacity data is developed. An approach which eliminates the need for a separate temperature sensor(s) attached to an adiabatic heat shield(s) used to maintain semiadiabatic conditions during heat pulse heat capacity measurements has been proposed and tested. The sensorless technique provides reliable control of the heat transfer inside a vacuum chamber and results in accurate heat capacity data. The calibration results show that the heat capacity can be measured with an average ...

Pulsed thrust measurements using laser interferometry

Abstract: An optical interferometric proximeter system (IPS) for measuring thrust and impulse bit of pulsed electric thrusters was developed. Unlike existing thrust stands, the IPS-based thrust stand offers the advantage of a single system that can yield electromagnetic interference-free, high accuracy (<2% error) thrust measurements within a very wide range of impulses (100 μN s to above 10 N s) covering the impulse range of all known pulsed plasma thrusters. In addition to pulsed thrusters, the IPS is theoretically shown to be capable of measuring steady-state thrust values as low as 20 μN for microthrusters such as the field emission electric propulsion thruster. The IPS-based thrust stand relies on measuring the dynamic response of a swinging arm using a two-sensor laser interferometer with 10 nm position accuracy. The wide application of the thrust stand is demonstrated with thrust measurements of an ablative pulsed plasma thruster and a quasi-steady magnetoplasmadynamic thruster.

A photoelectron spectrometer for k-space mapping above the Fermi level

Abstract: The setup of an electron spectrometer for angle-resolved photoemission is described. A sample goniometer offers the opportunity for angle scanned photoemission over 2π solid angle above the surface. A monochromatized high flux He discharge photon source is exploited to measure thermally populated electronic states above the Fermi level EF. At energies greater than EF+5kBT the signal from a constant density of states declines below the photoelectron background caused by photons with higher energies than He Iα (21.2 eV). For He IIα (40.8 eV) the residual photoelectron background is lower and photoemission up to 6kBT above EF can be performed. Data showing two cuts through the Fermi surface of silver are presented. Furthermore the dispersion of the Shockley surface state on Ag (111) above the Fermi energy is quantified.