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Mar 2007

Volume 78, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 78, 031101 (2007); http://dx.doi.org/10.1063/1.2709758 (20 pages)

Thomas F. Kelly and Michael K. Miller
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Perspective: From field-ion microscopy of single atoms to atom-probe tomography: A journey: “Atom-probe tomography” [ Rev. Sci. Instrum. 78, 031101 (2007) ]

David N. Seidman

Rev. Sci. Instrum. 78, 030901 (2007); http://dx.doi.org/10.1063/1.2716503 (3 pages) | Cited 7 times

Online Publication Date: 30 March 2007

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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
01.65.+g History of science
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Atom probe tomography

Thomas F. Kelly and Michael K. Miller

Rev. Sci. Instrum. 78, 031101 (2007); http://dx.doi.org/10.1063/1.2709758 (20 pages) | Cited 173 times

Online Publication Date: 30 March 2007

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The technique of atom probe tomography (APT) is reviewed with an emphasis on illustrating what is possible with the technique both now and in the future. APT delivers the highest spatial resolution (sub-0.3-nm) three-dimensional compositional information of any microscopy technique. Recently, APT has changed dramatically with new hardware configurations that greatly simplify the technique and improve the rate of data acquisition. In addition, new methods have been developed to fabricate suitable specimens from new classes of materials. Applications of APT have expanded from structural metals and alloys to thin multilayer films on planar substrates, dielectric films, semiconducting structures and devices, and ceramic materials. This trend toward a broader range of materials and applications is likely to continue.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
42.30.Wb Image reconstruction; tomography
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Artificial submicron or nanometer speckle fabricating technique and electron microscope speckle photography

Zhanwei Liu, Huimin Xie, Daining Fang, Fulong Dai, Weining Wang, and Yan Fang

Rev. Sci. Instrum. 78, 033101 (2007); http://dx.doi.org/10.1063/1.2709742 (6 pages) | Cited 1 time

Online Publication Date: 9 March 2007

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In this article, a novel artificial submicro- or nanometer speckle fabricating technique is proposed by taking advantage of submicro or nanometer particles. In the technique, submicron or nanometer particles were adhered to an object surface by using ultrasonic dispersing technique. The particles on the object surface can be regarded as submicro or nanometer speckle by using a scanning electronic microscope at a special magnification. In addition, an electron microscope speckle photography (EMSP) method is developed to measure in-plane submicron or nanometer deformation of the object coated with the artificial submicro or nanometer speckles. The principle of artificial submicro or nanometer speckle fabricating technique and the EMSP method are discussed in detail in this article. Some typical applications of this method are offered. The experimental results verified that the artificial submicro or nanometer speckle fabricating technique and EMSP method is feasible.
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07.60.Ly Interferometers
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
43.35.Yb Ultrasonic instrumentation and measurement techniques

Quasi-Fourier-transform limited, scannable, high energy titanium-sapphire laser source for high resolution spectroscopy

Patrick Dupré and Terry A. Miller

Rev. Sci. Instrum. 78, 033102 (2007); http://dx.doi.org/10.1063/1.2670804 (12 pages) | Cited 10 times

Online Publication Date: 9 March 2007

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A tunable injection seeded Ti:sapphire laser source has been developed and tested. Slave-master tandem cavity and ramp-lock-and-fire concepts have been implemented and fully controlled by a digital signal processor. A Fourier-transform-based analysis, as well as direct measurements, have demonstrated spectral linewidths in the range of 3.5–15 MHz (HWHM), with potential tunability over the entire Ti:sapphire lasing range. A quasi-Fourier-transform limited spectral linewidth is demonstrated assuming a secant hyperbolic shape of the electromagnetic field. Output energies >100 mJ have been reached with ∼ 300 mJ of pump energy. The highest spectral purity is obtained using the quadruple pumping scheme.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
07.60.Rd Visible and ultraviolet spectrometers
42.72.-g Optical sources and standards

A highly integrated FPGA-based nuclear magnetic resonance spectrometer

Kazuyuki Takeda

Rev. Sci. Instrum. 78, 033103 (2007); http://dx.doi.org/10.1063/1.2712940 (6 pages) | Cited 20 times

Online Publication Date: 14 March 2007

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The digital circuits required for a nuclear magnetic resonance (NMR) spectrometer, including a pulse programmer, a direct digital synthesizer, a digital receiver, and a PC interface, have been built inside a single chip of the field-programmable gate-array (FPGA). By combining the FPGA chip with peripheral analog components, a compact, laptop-sized homebuilt spectrometer has been developed, which is capable of a rf output of up to 400 MHz with amplitude-, phase-, frequency-, and pulse-modulation. The number of rf channels is extendable up to three without further increase in size.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
84.30.Sk Pulse and digital circuits

Feedback system for improving the performance of extended x-ray absorption fine structure measurements

Togo Kudo and Hajime Tanida

Rev. Sci. Instrum. 78, 033104 (2007); http://dx.doi.org/10.1063/1.2713436 (4 pages) | Cited 1 time

Online Publication Date: 14 March 2007

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A rapid fine energy tuning method for a double-crystal monochromator (DCM) is developed by combining a feedback control system with a phase sensitive detector. This method maintains both a parallel angle between the first and second crystals of the DCM and the peak of the rocking curve. The method is used to perform a continuous energy scan of the DCM without readjustment of the angle between the two crystals. The time taken by this method to measure the extended x-ray absorption fine structure is 60% of that taken by a conventional procedure.
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07.85.Nc X-ray and γ-ray spectrometers
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

A precise method to determine the angular distribution of backscattered light to high angles

P. Gross, M. Störzer, S. Fiebig, M. Clausen, G. Maret, and C. M. Aegerter

Rev. Sci. Instrum. 78, 033105 (2007); http://dx.doi.org/10.1063/1.2712943 (6 pages) | Cited 8 times

Online Publication Date: 15 March 2007

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We present an approach to measure the angular dependence of the diffusely scattered intensity of a multiple scattering sample in backscattering geometry. Increasing scattering strength give rise to an increased width of the coherent backscattering and sets higher demands on the angular detection range. This is of particular interest in the search for the transition to Anderson localization of light. To cover a range of −60° to +85° from direct back-reflection, we introduced a new parallel intensity recording technique. This allows one-shot measurements, with fast alignment and short measuring time, which prevents the influence of illumination variations. Configurational average is achieved by rotating the sample and singly scattered light is suppressed with the use of circularly polarized light up to 97%. This implies that backscattering enhancements of almost two can be achieved. In combination with a standard setup for measuring small angles up to ±3°, a full characterization of the coherent backscattering cone can be achieved. With this setup we are able to accurately determine transport mean free paths as low as 235 nm.
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42.25.Fx Diffraction and scattering

Dead-time optimized time-correlated photon counting instrument with synchronized, independent timing channels

Michael Wahl, Hans-Jürgen Rahn, Ingo Gregor, Rainer Erdmann, and Jörg Enderlein

Rev. Sci. Instrum. 78, 033106 (2007); http://dx.doi.org/10.1063/1.2715948 (6 pages) | Cited 15 times

Online Publication Date: 23 March 2007

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Time-correlated single photon counting is a powerful method for sensitive time-resolved fluorescence measurements down to the single molecule level. The method is based on the precisely timed registration of single photons of a fluorescence signal. Historically, its primary goal was the determination of fluorescence lifetimes upon optical excitation by a short light pulse. This goal is still important today and therefore has a strong influence on instrument design. However, modifications and extensions of the early designs allow for the recovery of much more information from the detected photons and enable entirely new applications. Here, we present a new instrument that captures single photon events on multiple synchronized channels with picosecond resolution and over virtually unlimited time spans. This is achieved by means of crystal-locked time digitizers with high resolution and very short dead time. Subsequent event processing in programmable logic permits classical histogramming as well as time tagging of individual photons and their streaming to the host computer. Through the latter, any algorithms and methods for the analysis of fluorescence dynamics can be implemented either in real time or offline. Instrument test results from single molecule applications will be presented.
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06.60.Jn High-speed techniques (microsecond to femtosecond)
78.47.-p Spectroscopy of solid state dynamics
42.79.-e Optical elements, devices, and systems

Qualification of a fluorescence spectrometer for measuring true fluorescence spectra

Paul C. DeRose, Edward A. Early, and Gary W. Kramer

Rev. Sci. Instrum. 78, 033107 (2007); http://dx.doi.org/10.1063/1.2715952 (12 pages) | Cited 8 times

Online Publication Date: 26 March 2007

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New analytical methods using fluorescence detection are becoming increasingly quantitative and require easy-to-use material standards for fluorometer qualification and method validation. NIST is responding to this need by developing and producing such standards. Reported here is the first step in this process, which is to qualify a research-grade fluorescence spectrometer for measuring true fluorescence spectra of reference material candidates. “True” spectra are defined here as those with fluorescence intensity, either relative or absolute as required, and wavelength both being reported with high accuracy and known precision, after wavelength has been calibrated and corrections for excitation intensity and detection system response have been applied. The uncertainties determined in relative and absolute intensity-corrected fluorescence spectra using both calibrated source (CS)- and calibrated detector (CD)-based methods were compared. The CS-based method gave uncertainties, typically about ±5% for relative spectral correction, that were about half that of the CD-based method for determining both relative and absolute spectral correction factors. Absolute spectral correction factors can be determined using either method without knowing the optical geometry of the instrument. The absolute spectral correction factors were found to have much larger uncertainties than the corresponding relative correction factors with uncertainties for the CS-based method of ±10% to ±15% being typical and ±20% or more not being uncommon, particularly for excitation and emission wavelengths below 400 nm. Uncertainties arising from detection system nonlinearity and instrument polarization ratios were also explored.
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07.60.-j Optical instruments and equipment
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Mega-ampere submicrosecond generator GIT-32

B. M. Kovalchuk, A. V. Kharlov, V. N. Kiselev, E. V. Kumpyak, V. B. Zorin, V. V. Chupin, and A. V. Morozov

Rev. Sci. Instrum. 78, 033501 (2007); http://dx.doi.org/10.1063/1.2712800 (5 pages) | Cited 1 time

Online Publication Date: 13 March 2007

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The GIT-32 current generator was developed for experiments with current carrying pulsed plasma. The main parts of the generator are capacitor bank, multichannel multigap spark switches, low inductive current driving lines, and central load part. The generator consists of four identical sections, connected in parallel to one load. The capacitor bank is assembled from 32 IEK-100-0.17 (0.17 μF, 40 nH, 100 kV) capacitors, connected in parallel. It stores ∼ 18 kJ at 80 kV charging voltage. Each two capacitors are commuted to a load by a multigap spark switch with eight parallel channels. Switches operate in ambient air at atmospheric pressure. The GIT-32 generator was tested with 10, 15, and 20 nH inductive loads. At 10 nH load and 80 kV of charging voltage it provides 1 MA of current amplitude and 490 ns rise time with 0.8 Ω damping resistors in discharge circuit of each capacitor and 1.34 MA/530 ns without resistors. The net generator inductance without a load was optimized to be as low as 12 nH, which results in extremely low self-impedance of the generator ( ∼ 0.05 Ω). It ensures effective energy coupling with low impedance loads like Z pinch. The generator operates reliably without any adjustments in 40–80 kV range of charging voltage. Maximum jitter (relative to a triggering pulse) at 40 kV charging voltage is about 7 ns and lower at higher charging voltages. Operation and handling are very simple, because no oil and no purified gases are required for the generator. The GIT-32 generator has dimensions of 3200×3200×400 mm3 and total weight of about 2500 kg, thus manifesting itself as a simple, robust, and cost effective apparatus.
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52.50.Dg Plasma sources
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.75.Kq Plasma switches (e.g., spark gaps)
52.25.Fi Transport properties
52.58.Lq Z-pinches, plasma focus, and other pinch devices
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Langmuir probe system for dusty plasmas under microgravity

M. Klindworth, O. Arp, and A. Piel

Rev. Sci. Instrum. 78, 033502 (2007); http://dx.doi.org/10.1063/1.2714036 (7 pages) | Cited 15 times

Online Publication Date: 14 March 2007

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This article describes a fully automated 2D-scanning Langmuir probe system for dusty plasmas under microgravity. The design combines necessary features such as random sampling, radio frequency compensation, and a compact mechanical design. The various aspects of the probe implementation and the contamination problem in the dusty plasma environment are discussed and the functionality of the system is demonstrated by measurements performed on parabolic flights.
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52.70.Ds Electric and magnetic measurements
52.27.Lw Dusty or complex plasmas; plasma crystals

Main characteristics of the fast disruption mitigation valve

S. A. Bozhenkov, K.-H. Finken, M. Lehnen, and R. C. Wolf

Rev. Sci. Instrum. 78, 033503 (2007); http://dx.doi.org/10.1063/1.2712798 (7 pages) | Cited 12 times

Online Publication Date: 15 March 2007

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The article presents a detailed investigation of the fast disruption mitigation valve developed at FZJ Juelich. The essence of this study is the novel direct observation of the piston motion by means of a fast framing camera. The piston stroke and the injection duration are shown to strongly depend on the operational pressure and the used gas. The same is true for the valve throughput. The analysis revealing the leading contribution of the injection duration in this modification is given. The knowledge of the injection duration is also used to reconstruct the characteristic pressure decay rates and the gas outflow rates. The means to increase the gas outflow are discussed. The main found valve characteristics are: (1) valve reaction time, i.e., the delay between the application of the trigger signal and the achievement of reliably observable opening 0.5 mm, is about 0.3 ms; (2) the maximum achieved throughput is 7.5 bar l for argon and 9.5 bar l for helium; (3) the maximum delivery rates are 500 bar l s−1 for Ar and 1500 bar l s−1 for He.
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89.20.Bb Industrial and technological research and development
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Modeling magnetic fields measured by surface probes embedded in a cylindrical flux conserver

R. P. Golingo

Rev. Sci. Instrum. 78, 033504 (2007); http://dx.doi.org/10.1063/1.2713435 (5 pages)

Online Publication Date: 19 March 2007

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Calculating magnetic fields at the surface of a flux conserver, perfect conductor, for displaced plasma currents is useful for understanding modes of a Z-pinch. The magnetic fields measured at the flux conserver are a sum of the magnetic fields from the plasma current and the eddy currents which form in the walls to keep the flux constant. While the magnetic field at the wall from the plasma current alone is easily calculated using the Biot–Savart law, finding the eddy currents in the flux conserver which satisfy the boundary conditions can be a tedious process. A simple method of calculating the surface magnetic field for a given Z-pinch displacement off-axis is derived for a cylindrical flux conserver. This relationship does not require the explicit calculation of the eddy currents, saving time when analyzing surface magnetic probe measurements. Analytic expressions can be used to describe the surface magnetic field which increase the understanding of the magnetic probe measurements.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.40.Hf Plasma-material interactions; boundary layer effects

Measurement of the Dα spectrum produced by fast ions in DIII-D

Y. Luo, W. W. Heidbrink, K. H. Burrell, D. H. Kaplan, and P. Gohil

Rev. Sci. Instrum. 78, 033505 (2007); http://dx.doi.org/10.1063/1.2712806 (11 pages) | Cited 26 times

Online Publication Date: 21 March 2007

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Fast ions are produced by neutral beam injection and ion cyclotron heating in toroidal magnetic fusion devices. As deuterium fast ions orbit around the device and pass through a neutral beam, some deuterons neutralize and emit Dα light. For a favorable viewing geometry, the emission is Doppler shifted away from other bright interfering signals. In the 2005 campaign, we built a two channel charge-coupled device based diagnostic to measure the fast-ion velocity distribution and spatial profile under a wide variety of operating conditions. Fast-ion data are acquired with a time resolution of ∼ 1 ms, spatial resolution of ∼ 5 cm, and energy resolution of ∼ 10 keV. Background subtraction and fitting techniques eliminate various contaminants in the spectrum. Neutral particle and neutron diagnostics corroborate the Dα measurement. Examples of fast-ion slowing down and pitch angle scattering in quiescent plasma and fast-ion acceleration by high harmonic ion cyclotron heating are presented.
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52.70.Nc Particle measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.55.Fa Tokamaks, spherical tokamaks
52.50.Gj Plasma heating by particle beams
52.50.Sw Plasma heating by microwaves; ECR, LH, collisional heating
52.20.Dq Particle orbits

Particle positioning techniques for dusty plasma experiments

Yuriy Ivanov and André Melzer

Rev. Sci. Instrum. 78, 033506 (2007); http://dx.doi.org/10.1063/1.2714050 (7 pages) | Cited 12 times

Online Publication Date: 21 March 2007

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Video microscopy is a widely applied diagnostic to investigate the structure and the dynamics of particles in dusty plasmas. Reliable algorithms are required to accurately recover particle positions from the camera images. Here, four different particle positioning techniques have been tested on artificial and experimental data of dusty plasma situations. Two methods that rely on pixel-intensity thresholds were found to be strongly affected by pixel-locking errors and by noise. Two other methods—one applying spatial bandpass filters and the other fitting polynomials to the intensity pattern—yield subpixel resolution under various conditions. These two methods have been shown to be ideally suited to recover particle positions even from small-scale fluctuations that are used to derive the normal mode spectra of finite dust clusters.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
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Development of a microlateral force sensor and its evaluation using lateral force microscopy

Yasuhisa Ando and Naoki Shiraishi

Rev. Sci. Instrum. 78, 033701 (2007); http://dx.doi.org/10.1063/1.2714038 (8 pages) | Cited 2 times

Online Publication Date: 19 March 2007

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A microlateral force sensor (MLFS) was developed and evaluated using atomic force microscopy (AFM). The sensor was attached to a sensing table supported by a suspension system. The lateral motion of the sensing table was activated by a comb actuator. The driving voltage to the comb actuator was controlled to maintain a constant position of the sensing table by detecting the tunneling current at a detector, which consisted of two electrodes where the bias voltage was applied. An AFM was used to apply a lateral force to the sensing table of the sensor. When the probe of a cantilever was pressed against the sensing table and a raster scanning was conducted, the driving voltage of the comb actuator changed to compensate the friction force between the probe and sensing table. AFM measurements of an asperity array on the sensing table were conducted, and a lateral force microscopy image (LFM) was obtained from the change in driving voltage. The image by MLFS was very similar to the LFM image that was conventionally obtained from torsion of the cantilever. The LFM image strongly correlated with the gradient image calculated from the AFM topographic image. The force sensitivity of the MLFS was determined by comparing the LFM image obtained by using the MLFS with the tangential force derived from the gradient of the AFM image.
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07.10.Pz Instruments for strain, force, and torque
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Compact flashlamp-based fluorescence imager for use under ambient-light conditions

Frederick Lanni, David A. Pane, Shmuel J. Weinstein, and Alan S. Waggoner

Rev. Sci. Instrum. 78, 033702 (2007); http://dx.doi.org/10.1063/1.2669831 (6 pages) | Cited 2 times

Online Publication Date: 21 March 2007

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A low-power, lightweight, multiwavelength fluorescence imager based on the use of a compact xenon flashlamp, bandpass filters, gated charge-coupled device camera, and digital image processing was developed for use on an autonomous rover vehicle. The imager discriminates against ambient light by use of microsecond excitation pulses along with synchronized camera operation to limit the time period in which ambient-light photocounts are accumulated, and digital image subtraction to remove background counts. In a 10 cm square field of view, weak fluorescence, equivalent to 0.05 pmol fluorescein/mm2, can be quantified against a white-light background equivalent to shaded sunlight. For application in autonomous search for organisms in extreme environments such as in situ desert rock or soil, the instrument was equipped with a set of fluorescence excitation filters (380, 450, 545, and 600 nm) and emission filters (460, 510, 620, and 740 nm) suitable for detection of chlorophyll, applied stains for protein, DNA, lipid and carbohydrate, and autofluorescence. True-color images were obtained through red-green-blue imaging filters (630, 535, and 470 nm) used with white-light flashes. Automated focusing on ground features was based on the R-band image and was carried out prior to fluorescence image acquisition.
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42.79.Pw Imaging detectors and sensors
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.30.Sy Pattern recognition
42.30.Va Image forming and processing
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

In situ azimuthal rotation device for linear dichroism measurements in scanning transmission x-ray microscopy

D. Hernández-Cruz, A. P. Hitchcock, T. Tyliszczak, M.-E. Rousseau, and M. Pézolet

Rev. Sci. Instrum. 78, 033703 (2007); http://dx.doi.org/10.1063/1.2716502 (6 pages) | Cited 4 times

Online Publication Date: 26 March 2007

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A novel miniature rotation device used in conjunction with a scanning transmission x-ray microscope is described. It provides convenient in situ sample rotation to enable measurements of linear dichroism at high spatial resolution. The design, fabrication, and mechanical characterization are presented. This device has been used to generate quantitative maps of the spatial distribution of the orientation of proteins in several different spider and silkworm silks. Specifically, quantitative maps of the dichroic signal at the C 1s→π*amide transition in longitudinal sections of the silk fibers give information about the spatial orientation, degree of alignment, and spatial distribution of protein peptide bonds. A new approach for analyzing the dichroic signal to extract orientation distributions, in addition to magnitudes of aligned components, is presented and illustrated with results from Nephila clavipes dragline spider silk measured using the in situ rotation device.
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87.80.-y Biophysical techniques (research methods)
87.14.E- Proteins
87.15.M- Spectra of biomolecules
87.15.B- Structure of biomolecules
33.55.+b Optical activity and dichroism
33.57.+c Magneto-optical and electro-optical spectra and effects

X-ray imaging with grazing-incidence microscopes developed for the LIL program

R. Rosch, J. Y. Boutin, J. P. le Breton, D. Gontier, J. P. Jadaud, C. Reverdin, G. Soullié, G. Lidove, and R. Maroni

Rev. Sci. Instrum. 78, 033704 (2007); http://dx.doi.org/10.1063/1.2715865 (6 pages) | Cited 4 times

Online Publication Date: 28 March 2007

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This article describes x-ray imaging with grazing-incidence microscopes, developed for the experimental program carried out on the Ligne d’Intégration Laser (LIL) facility [ J. P. Le Breton et al., Inertial Fusion Sciences and Applications 2001 (Elsevier, Paris, 2002), pp. 856–862 ] (24 kJ, UV—0.35 nm). The design includes a large target-to-microscope (400–700 mm) distance required by the x-ray ablation issues anticipated on the Laser MégaJoule facility [ P. A. Holstein et al., Laser Part. Beams 17, 403 (1999) ] (1.8 MJ) which is under construction. Two eight-image Kirkpatrick-Baez microscopes [ P. Kirkpatrick and A. V. Baez J. Opt. Soc. Am. 38, 766 (1948) ] with different spectral wavelength ranges and with a 400 mm source-to-mirror distance image the target on a custom-built framing camera (time resolution of ∼ 80 ps). The soft x-ray version microscope is sensitive below 1 keV and its spatial resolution is better than 30 μm over a 2-mm-diam region. The hard x-ray version microscope has a 10 μm resolution over an 800-μm-diam region and is sensitive in the 1–5 keV energy range. Two other x-ray microscopes based on an association of toroidal/spherical surfaces (T/S microscopes) produce an image on a streak camera with a spatial resolution better than 30 μm over a 3 mm field of view in the direction of the camera slit. Both microscopes have been designed to have, respectively, a maximum sensitivity in the 0.1–1 and 1–5 keV energy range. We present the original design of these four microscopes and their test on a dc x-ray tube in the laboratory. The diagnostics were successfully used on LIL first experiments early in 2005. Results of soft x-ray imaging of a radiative jet during conical shaped laser interaction are shown.
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07.85.Tt X-ray microscopes
41.50.+h X-ray beams and x-ray optics
07.85.-m X- and γ-ray instruments
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Implementation of diffractive optical element in four-wave mixing scheme for ex situ characterization of hydride vapor phase epitaxy-grown GaN layers

K. Jarasiunas, R. Aleksiejunas, T. Malinauskas, V. Gudelis, T. Tamulevicius, S. Tamulevicius, A. Guobiene, A. Usikov, V. Dmitriev, and H. J. Gerritsen

Rev. Sci. Instrum. 78, 033901 (2007); http://dx.doi.org/10.1063/1.2712788 (4 pages) | Cited 8 times

Online Publication Date: 9 March 2007

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A holographic beam splitter has been integrated into a picosecond four-wave mixing (FWM) scheme. This modification significantly simplified the procedure of dynamic grating recording, thus making the FWM technique an easy-to-use tool for the holographic characterization of wide band gap materials. The novel FWM scheme was applied for characterization of hydride vapor phase epitaxy-grown undoped GaN layers of different thickness. It allowed the determination of carrier lifetime, diffusion coefficient, and carrier diffusion length by optical means, as well as the study of carrier recombination peculiarities with respect to dislocation and excess carrier density.
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42.40.Eq Holographic optical elements; holographic gratings
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Fm Reflectors, beam splitters, and deflectors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.70.Fy Nondestructive testing: optical methods
66.30.-h Diffusion in solids

Computer-controlled susceptometer for investigating the linear and nonlinear dielectric response

S. Miga, J. Dec, and W. Kleemann

Rev. Sci. Instrum. 78, 033902 (2007); http://dx.doi.org/10.1063/1.2712792 (7 pages) | Cited 14 times

Online Publication Date: 13 March 2007

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A fully automatized alternating current (ac) susceptometer is constructed for simultaneous measurements of the phase resolved complex linear and complex nonlinear ac susceptibilities of lossy and dispersive dielectric materials. This relatively simple setup allows measurements over a wide range of experimental variables, such as ac amplitudes up to 40 V, frequencies from 10−2 to 103 Hz, and temperatures from 100 to 600 K utilizing only current/voltage and analog/digital converters and a personal computer. In contrast with the commonly used analysis of the charge accumulated on a standard capacitor in series with the sample our method is based on the analysis of the current flowing directly through the sample. Absence of any capacitive voltage dividers in the measurement circuit eliminates uncontrolled phase shifts. This is why the instrument provides high quality, nonlinear susceptibility data and in particular appears as a very convenient tool for discrimination between continuous and discontinuous phase transitions when determining the sign of the real part of the third order dielectric susceptibility.
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07.68.+m Photography, photographic instruments; xerography
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Portable chamber for the study of UHV prepared electrochemical interfaces by hard x-ray diffraction

Frank Uwe Renner, Yvonne Gründer, and Jörg Zegenhagen

Rev. Sci. Instrum. 78, 033903 (2007); http://dx.doi.org/10.1063/1.2714046 (8 pages) | Cited 11 times

Online Publication Date: 15 March 2007

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We report on a new electrochemical cell setup, combined with a portable UHV chamber, for in situ x-ray diffraction using synchrotron radiation. In contrast to more traditional electrochemical sample preparation schemes, atomically clean and well-ordered surfaces are routinely prepared by UHV methods, even in the case of reactive elements or alloys. Samples can be transferred from larger UHV systems into the portable chamber without exposure to ambient air. They can then be studied successively in UHV, in controlled gas atmospheres, and in contact with electrolyte solutions under applied electrochemical potential. The electrochemical setup employs a droplet geometry, which guarantees good electrochemical conditions during in situ x-ray measurements combined with voltammetry. We present first experimental results of Cu deposition on GaAs(001) and on freshly produced nanometric Pd(001) islands on Cu0.83Pd0.17(001), respectively.
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61.05.cp X-ray diffraction
81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
82.45.Mp Thin layers, films, monolayers, membranes

Low-temperature differential-thermal analysis to measure variations in entropy

A. Schilling and M. Reibelt

Rev. Sci. Instrum. 78, 033904 (2007); http://dx.doi.org/10.1063/1.2712793 (6 pages) | Cited 5 times

Online Publication Date: 23 March 2007

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We describe how we can precisely measure variations in the entropy S of small solid samples below room temperature, as a function the temperature T or the external magnetic field H, respectively. A simple differential-thermal analysis technique allows, in principle, for the measurement of variations in S without any instrumental broadening of the data. The method is particularly well suited for the detection of sharp phase transitions in samples of milligram size.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

An instrument to investigate femtochemistry on metal surfaces in real space

Michael Mehlhorn, Heiko Gawronski, Lorenz Nedelmann, Alexander Grujic, and Karina Morgenstern

Rev. Sci. Instrum. 78, 033905 (2007); http://dx.doi.org/10.1063/1.2432244 (7 pages) | Cited 25 times

Online Publication Date: 26 March 2007

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A newly established combination of a femtosecond laser with a low temperature scanning tunneling microscope is described, which facilitates one to analyze femtochemistry on metal surfaces in real space. The combined instrument enables focusing the laser to some tens of micrometers and guiding it reproducibly into the tunneling gap with the aid of in situ movable mirrors. Furthermore, a method to determine the focus size on the sample is presented. The focus size is used to calculate the electron and phonon temperatures at the surface. Despite the additional noise introduced by laser operation the vertical resolution of the microscope lies below 1 pm. The potential of the instrument is demonstrated on para-chloronitrobenzene clusters adsorbed on Au(111). Single chloronitrobenzene molecules diffuse upon femtosecond laser irradiation; some smaller clusters rotate by multiples of 30°; clusters of less compact form rearrange to close-packed clusters.
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82.53.St Femtochemistry of adsorbed molecules
68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
68.49.-h Surface characterization by particle-surface scattering
82.33.Fg Reactions in clusters
78.47.-p Spectroscopy of solid state dynamics
79.20.Ds Laser-beam impact phenomena

Gravitational capillary viscometer for low-temperature liquids

David K. Hilton and Steven W. Van Sciver

Rev. Sci. Instrum. 78, 033906 (2007); http://dx.doi.org/10.1063/1.2716823 (15 pages)

Online Publication Date: 28 March 2007

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A pressurized gravitational capillary viscometer was developed for subcooled liquefied gases such as oxygen, nitrogen, hydrogen, and methane. It acquires accurate absolute viscosity measurements with an uncertainty of 1% at a 95.5% confidence level, necessary for the demands of aerospace engineering. The viscometer includes a coiled capillary of electroformed nickel that hydraulically connects two reservoirs located at equal heights. Using helium gas to temporarily drive liquid from a third supply reservoir, a level difference is created between the first two reservoirs without the need to tilt or invert the viscometer. Helium gas is then used to pressurize the first two reservoirs equally. Each reservoir holds a capacitive liquid-level sensor that both measure the flow induced by gravity through the capillary more precisely than by visual observations through windows. Viscosity data for liquid oxygen were acquired in the pressure domain from 0.15 to 1.0 MPa and in the temperature domain from the normal boiling point to near the freezing point. Published viscosity data and correlations for subcooled liquid oxygen are not precise nor complete in this density regime. Accordingly, the viscosity data delivered by the viscometer of the present work are superior.
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47.80.-v Instrumentation and measurement methods in fluid dynamics
47.35.Bb Gravity waves
47.55.nb Capillary and thermocapillary flows
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.55.Ca Gas/liquid flows
47.85.Dh Hydrodynamics, hydraulics, hydrostatics
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