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Mar 2008

Volume 79, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 79, 031301 (2008); http://dx.doi.org/10.1063/1.2897133 (11 pages)

L. Yang, C. R. Brome, J. S. Butterworth, S. N. Dzhosyuk, C. E. H. Mattoni, D. N. McKinsey, R. A. Michniak, J. M. Doyle, R. Golub, E. Korobkina, C. M. O’Shaughnessy, G. R. Palmquist, P.-N. Seo, P. R. Huffman, K. J. Coakley, et al.
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Perspective: Magnetic traps for nearly untrappable particles: “Development of high field superconducting Ioffe traps” [ Rev. Sci. Instrum. 79, 031301 (2008) ]

J. G. E. Harris

Rev. Sci. Instrum. 79, 030901 (2008); http://dx.doi.org/10.1063/1.2902121 (2 pages)

Online Publication Date: 25 March 2008

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74.20.-z Theories and models of superconducting state
74.25.Ha Magnetic properties including vortex structures and related phenomena
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Invited Article: Development of high-field superconducting Ioffe magnetic traps

L. Yang, C. R. Brome, J. S. Butterworth, S. N. Dzhosyuk, C. E. H. Mattoni, D. N. McKinsey, R. A. Michniak, J. M. Doyle, R. Golub, E. Korobkina, C. M. O’Shaughnessy, G. R. Palmquist, P.-N. Seo, P. R. Huffman, K. J. Coakley, et al.

Rev. Sci. Instrum. 79, 031301 (2008); http://dx.doi.org/10.1063/1.2897133 (11 pages) | Cited 1 time

Online Publication Date: 25 March 2008

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We describe the design, construction, and performance of three generations of superconducting Ioffe magnetic traps. The first two are low current traps, built from four racetrack shaped quadrupole coils and two solenoid assemblies. Coils are wet wound with multifilament NbTi superconducting wires embedded in epoxy matrices. The magnet bore diameters are 51 and 105 mm with identical trap depths of 1.0 T at their operating currents and at 4.2 K. A third trap uses a high current accelerator-type quadrupole magnet and two low current solenoids. This trap has a bore diameter of 140 mm and tested trap depth of 2.8 T. Both low current traps show signs of excessive training. The high current hybrid trap, on the other hand, exhibits good training behavior and is amenable to quench protection.
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84.71.Ba Superconducting magnets; magnetic levitation devices
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Phase-perturbation-free measurement of electro-optic effect based on Mach–Zehnder interferometer

Tomo Iwamura, Xin Yi Liu, Shota Suka, and Shinsuke Umegaki

Rev. Sci. Instrum. 79, 033101 (2008); http://dx.doi.org/10.1063/1.2869144 (5 pages) | Cited 1 time

Online Publication Date: 4 March 2008

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A novel method of evaluating the electro-optic (EO) effect is proposed based on a Mach–Zehnder interferometer, where the interference fringes are perturbed by air turbulence and/or other mechanical vibrations of an optical bench. The method enables the practical and industrial measurement of the EO coefficient in any environment. It also provides the continuous or repetitive measurement, leading to evaluation of temporal change of an EO coefficient or orientation relaxation of an EO-chromophore containing polymer poled by an electric field.
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78.20.Jq Electro-optical effects

Accurate miscut angle determination for spherically bent Bragg crystals

D. S. Covita, M. Ay, S. Schlesser, D. Gotta, L. M. Simons, E.-O. Le Bigot, and J. M. F. dos Santos

Rev. Sci. Instrum. 79, 033102 (2008); http://dx.doi.org/10.1063/1.2884149 (3 pages) | Cited 3 times

Online Publication Date: 5 March 2008

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Spherically bent crystals are used as analyzers in high-resolution spectroscopy, in particular, in low count-rate applications such as exotic-atom research. The focal conditions are determined not only by the bending radius and the Bragg angle but also by the crystal cut angle between its surface and the reflecting crystal planes, along with their orientation with respect to the direction of dispersion. We describe a simple but precise method for measuring the cut angle and its orientation for mounted spherically bent crystals, by combining x-ray diffraction and laser optical alignment, which can be easily performed with standard x-ray laboratory equipment.
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61.50.-f Structure of bulk crystals
78.20.-e Optical properties of bulk materials and thin films
61.05.cp X-ray diffraction

Calibration of liquid crystal ultrafast pulse shaper with common-path spectral interferometry and application to coherent control with a covariance matrix adaptation evolutionary strategy

Jesse W. Wilson, Philip Schlup, Monte Lunacek, Darrell Whitley, and Randy A. Bartels

Rev. Sci. Instrum. 79, 033103 (2008); http://dx.doi.org/10.1063/1.2839919 (5 pages) | Cited 5 times

Online Publication Date: 7 March 2008

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An ultrafast pulse shaper for coherent control applications is described, complete with a simple, reliable calibration technique and an advanced learning control algorithm. The calibration technique makes use of a common-path interferometer, producing less noisy measurements than a conventional Mach–Zehnder interferometer. A covariance matrix adaptation evolutionary strategy (ES) is demonstrated to perform better than a traditional ES for high-dimensional search landscapes.
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78.47.-p Spectroscopy of solid state dynamics
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

Design of a double-pass shear mode acousto-optic modulator

Chih-Hao Chang, R. K. Heilmann, M. L. Schattenburg, and P. Glenn

Rev. Sci. Instrum. 79, 033104 (2008); http://dx.doi.org/10.1063/1.2894210 (5 pages) | Cited 1 time

Online Publication Date: 12 March 2008

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The design of a compact double-pass shear mode acousto-optic modulator for high power operation in the UV is presented. Using a spherical mirror retroreflector in the second pass to correct for beam deflection, changes in beam position and angle during frequency tuning can be eliminated. The use of the shear mode acousto-optic interaction offers several key advantages, but the strain-induced birefringence creates significant levels of spectral leakage in the system. These effects and the polarization of the beams are analyzed to minimize leakage. Using a heterodyne interferometry scheme, two double-pass acousto-optic modulators with offset acoustic frequency inputs are set up to measure the leakage intensity. The designed double-pass shear mode acousto-optic modulator was tested with λ = 351.1 nm and demonstrated a peak double-pass efficiency of 42.6% and a bandwidth of 28 MHz. Over this bandwidth the spectral leakage was reduced to ∼ 0.01%–0.04% relative intensity.
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42.79.Jq Acousto-optical devices
42.79.Hp Optical processors, correlators, and modulators
42.15.Eq Optical system design
42.79.Bh Lenses, prisms and mirrors
42.25.Lc Birefringence

A simple yet effective multipass reflector for vibrational excitation in molecular beams

Jens Riedel, Shannon Yan, Hiroshi Kawamata, and Kopin Liu

Rev. Sci. Instrum. 79, 033105 (2008); http://dx.doi.org/10.1063/1.2894211 (4 pages) | Cited 5 times

Online Publication Date: 12 March 2008

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The fraction of molecules that can be vibrationally excited is often the limiting factor in many infrared laser excitation experiments, in particular, when using weak absorption bands. Reported here is a simple multipass reflector designed to overcome that obstacle. Its enhancement in pumping efficiency is demonstrated in a crossed-beam scattering experiment on the Cl+CH2D2(v1 or v6 = 1) reactions. Compared to a double-pass arrangement, the effective laser fluence for excitation is also characterized.
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37.20.+j Atomic and molecular beam sources and techniques
33.15.Mt Rotation, vibration, and vibration-rotation constants

Broadband optical absorbance spectroscopy using a whispering gallery mode microsphere resonator

Sarah L. Westcott, Jiangquan Zhang, Robert K. Shelton, Nellie M. K. Bruce, Sachin Gupta, Steven L. Keen, Jeremy W. Tillman, Lara B. Wald, Brian N. Strecker, A. T. Rosenberger, Roy R. Davidson, Wei Chen, Kevin G. Donovan, and John V. Hryniewicz

Rev. Sci. Instrum. 79, 033106 (2008); http://dx.doi.org/10.1063/1.2894307 (9 pages) | Cited 6 times

Online Publication Date: 13 March 2008

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We demonstrate the ability to excite and monitor many whispering gallery modes (WGMs) of a microsphere resonator simultaneously in order to make broadband optical absorbance measurements. The 340 μm diameter microsphere is placed in a microfluidic channel. A hemispherical prism is used for coupling the WGMs into and out of the microsphere. The flat surface of the prism seals the microfluidic channel. The slight nonsphericity in the microsphere results in coupling to precessed modes whose emission is spatially separated from the reflected excitation light. The evanescent fields of the light trapped in WGMs interact with the surrounding environment. The change in transmission observed in the precessed modes is used to determine the absorbance of the surrounding environment. In contrast to our broadband optical absorbance measurements, previous WGM sensors have used only a single narrow mode to measure properties such as refractive index. With the microfluidic cell, we have measured the absorbance of solutions of dyes (lissamine green B, sunset yellow, orange G, and methylene blue), aromatic molecules (benzylamine and benzoic acid), and biological molecules (tryptophan, phenylalanine, tyrosine, and o-phospho-L-tyrosine) at visible and ultraviolet wavelengths. The microsphere surface was reacted with organosilane molecules to attach octadecyl groups, amino groups, and fluorogroups to the surface. Both electrostatic and hydrophobic interactions were observed between the analytes and the microsphere surface, as indicated by changes in the measured effective pathlength with different organosilanes. For a given analyte and coated microsphere, the pathlength measurement was repeatable within a few percent. Methylene blue dye had a very strong interaction with the surface and pathlengths of several centimeters were measured. Choosing an appropriate surface coating to interact with a specific analyte should result in the highest sensitivity detection.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.60.-q Optoelectronic devices

A source of a reference spherical wave based on a single mode optical fiber with a narrowed exit aperture

N. I. Chkhalo, A. Yu. Klimov, V. V. Rogov, N. N. Salashchenko, and M. N. Toropov

Rev. Sci. Instrum. 79, 033107 (2008); http://dx.doi.org/10.1063/1.2900561 (5 pages) | Cited 4 times

Online Publication Date: 21 March 2008

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A new type of a reference spherical wave source (SWS) based on a single mode optical fiber with a narrowed down up to the submicrometer size exit aperture is proposed. It is intended for the precision point diffraction interferometers as a source of a reference wave. Systematic experimental errors which influence the measurement accuracy of the quality of the wave fronts generated by the SWSs are considered. Experimental data on wave front deformations are given. The combined root-mean-square (rms) wave deformation for a couple of the SWSs measured in a numerical aperture of NA = 0.27 reaches the value of rms = 0.36 nm that corresponds to rms = 0.25 nm of a single SWS or about λ/2500 for the red He–Ne laser.
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42.81.-i Fiber optics

A soft x-ray beamline capable of canceling the performance impairment due to power absorbed on its optical elements

Ruben Reininger, Ken Kriesel, S. L. Hulbert, Cecilia Sánchez-Hanke, and D. A. Arena

Rev. Sci. Instrum. 79, 033108 (2008); http://dx.doi.org/10.1063/1.2897587 (6 pages) | Cited 2 times

Online Publication Date: 21 March 2008

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We present an entrance slitless beamline design capable of maintaining its very high performance in terms of energy resolution (>104) and spot size (4×4 μm2) at the sample position despite being exposed to more than 2.15 kW of undulator radiation and a maximum power density on the optics of more than 0.9 W/mm2. Ray tracing simulations of this beamline under the worst-case thermal deformations of the optical element surfaces verify that appropriate focusing corrections are able to cancel the deleterious effects of these deformations. One of the necessary conditions for this cancellation is to illuminate the optical elements with a larger solid angle than the undulator’s central cone, which contains the usable photons but is considerably smaller than the angular power distribution.
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41.50.+h X-ray beams and x-ray optics

Characterization of a polarization-resolved high spectral resolution UV-visible spectrometer

J. Kim and D. Kim

Rev. Sci. Instrum. 79, 033109 (2008); http://dx.doi.org/10.1063/1.2898704 (5 pages)

Online Publication Date: 24 March 2008

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To measure the degree of polarization of a plasma emission, a polarization-resolved UV-visible Czerny–Turner-type spectrometer was designed and constructed. For a high spectral resolution, F = 1 m mirrors were used as a focusing and collimating mirrors and the incidence angles to the mirrors were determined to eliminate coma. The effect of astigmatism was reduced by designing the incidence angles to the mirrors to be as small as possible. The flat focal plane condition proposed by Reader [J. Opt. Soc. Am. 59, 1189 (1969) ] was used to determine the grating position. The measured spatial resolution was 170 μm. To simultaneously measure the intensities with two perpendicular polarizations, a calcite crystal was placed after the entrance slit of the spectrometer. The change in the imaging property of the spectrometer due to the calcite crystal was measured and minimized. The spectral resolution was experimentally measured with a laser produced plasma to be 0.05 nm at 348 nm. The resolving power measured is 6600.
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07.60.Rd Visible and ultraviolet spectrometers
42.15.Fr Aberrations
42.15.Eq Optical system design
42.79.Bh Lenses, prisms and mirrors

Wave-dispersive x-ray spectrometer for simultaneous acquisition of several characteristic lines based on strongly and accurately shaped Ge crystal

Kouichi Hayashi, Kazuo Nakajima, Kozo Fujiwara, and Susumu Nishikata

Rev. Sci. Instrum. 79, 033110 (2008); http://dx.doi.org/10.1063/1.2898406 (6 pages) | Cited 3 times

Online Publication Date: 31 March 2008

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Si and Ge are widely used as analyzing crystals for x-rays. Drastic and accurate shaping of Si or Ge gives significant advance in the x-ray field, although covalently bonded Si or Ge crystals have long been believed to be not deformable to various shapes. Recently, we developed a deformation technique for obtaining strongly and accurately shaped Si or Ge wafers of high crystal quality, and the use of the deformed wafer made it possible to produce fine-focused x-rays. In the present study, we prepared a cylindrical Ge wafer with a radius of curvature of 50 mm, and acquired fluorescent x-rays simultaneously from four elements by combining the cylindrical Ge wafer with a position-sensitive detector. The energy resolution of the x-ray fluorescence spectrum was as good as that obtained using a flat single crystal, and its gain was over 100. The demonstration of the simultaneous acquisition of high-resolution x-ray fluorescence spectra indicated various possibilities of x-ray spectrometry, such as one-shot x-ray spectroscopy and highly efficient wave-dispersive x-ray spectrometers.
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07.85.Nc X-ray and γ-ray spectrometers
29.40.Wk Solid-state detectors
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
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Absolute calibration of image plates for electrons at energy between 100 keV and 4 MeV

Hui Chen, Norman L. Back, Teresa Bartal, F. N. Beg, David C. Eder, Anthony J. Link, Andrew G. MacPhee, Yuan Ping, Peter M. Song , Alan Throop, and Linn Van Woerkom

Rev. Sci. Instrum. 79, 033301 (2008); http://dx.doi.org/10.1063/1.2885045 (4 pages) | Cited 11 times

Online Publication Date: 10 March 2008

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We measured the absolute response of image plate (Fuji BAS SR2040) for electrons at energies between 100 keV and 4 MeV using an electron spectrometer. The electron source was produced from a short pulse laser irradiated on solid density targets. This paper presents the calibration results of image plate photon stimulated luminescence per electron at this energy range. The Monte Carlo radiation transport code MCNPX results are also presented for three representative incident angles onto the image plates and corresponding electron energy depositions at these angles. These provide a complete set of tools that allows extraction of our absolute calibration to other spectrometer setting at this electron energy range.
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29.25.Bx Electron sources
29.30.Aj Charged-particle spectrometers: electric and magnetic
29.30.Ep Charged-particle spectroscopy
07.77.Ka Charged-particle beam sources and detectors
06.20.fb Standards and calibration

Measurement of the high energy component of the x-ray spectra in the VENUS electron cyclotron resonance ion source

D. Leitner, J. Y. Benitez, C. M. Lyneis, D. S. Todd, T. Ropponen, J. Ropponen, H. Koivisto, and S. Gammino

Rev. Sci. Instrum. 79, 033302 (2008); http://dx.doi.org/10.1063/1.2821137 (6 pages) | Cited 9 times

Online Publication Date: 27 March 2008

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High performance electron cyclotron resonance (ECR) ion sources, such as VENUS (Versatile ECR for NUclear Science), produce large amounts of x-rays. By studying their energy spectra, conclusions can be drawn about the electron heating process and the electron confinement. In addition, the bremsstrahlung from the plasma chamber is partly absorbed by the cold mass of the superconducting magnet, adding an extra heat load to the cryostat. Germanium or NaI detectors are generally used for x-ray measurements. Due to the high x-ray flux from the source, the experimental setup to measure bremsstrahlung spectra from ECR ion sources is somewhat different from that for the traditional nuclear physics measurements these detectors are generally used for. In particular, the collimation and background shielding can be problematic. In this paper, we will discuss the experimental setup for such a measurement, the energy calibration and background reduction, the shielding of the detector, and collimation of the x-ray flux. We will present x-ray energy spectra and cryostat heating rates depending on various ion source parameters, such as confinement fields, minimum B-field, rf power, and heating frequency.
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07.77.Ka Charged-particle beam sources and detectors
29.25.-t Particle sources and targets

The Thomson deflectometer: A novel use of the Thomson spectrometer as a transient field and plasma diagnostic

S. Ter–Avetisyan, M. Schnürer, P. V. Nickles, T. Sokollik, E. Risse, M. Kalashnikov, W. Sandner, and G. Priebe

Rev. Sci. Instrum. 79, 033303 (2008); http://dx.doi.org/10.1063/1.2901579 (5 pages) | Cited 4 times

Online Publication Date: 31 March 2008

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Laser accelerated proton beams have been used for field characterization in expanding plasmas. The Thomson parabola spectrometer, as a charged particles analyzer, also allows precise measurement of the charged particles’ trajectories. The proton’s deflections by fast changing plasma fields can be measured with the new design of the Thomson parabola spectrometer and, therefore, it can be applied for proton deflectometry. It is shown that from resulting spectrograms the plasma field dynamics can be reconstructed with high temporal resolution. In a proof-of-principle experiment, a weakly relativistic plasma expansion is studied as an example.
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52.70.Nc Particle measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.27.Ny Relativistic plasmas
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Volume measurement of cryogenic deuterium pellets by Bayesian analysis of single shadowgraphy images

T. Szepesi, S. Kálvin, G. Kocsis, P. T. Lang, and C. Wittmann

Rev. Sci. Instrum. 79, 033501 (2008); http://dx.doi.org/10.1063/1.2870089 (10 pages) | Cited 2 times

Online Publication Date: 5 March 2008

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In situ commissioning of the Blower-gun injector for launching cryogenic deuterium pellets at ASDEX Upgrade tokamak was performed. This injector is designed for high repetitive launch of small pellets for edge localised modes pacing experiments. During the investigation the final injection geometry was simulated with pellets passing to the torus through a 5.5 m long guiding tube. For investigation of pellet quality at launch and after tube passage laser flash camera shadowgraphy diagnostic units before and after the tube were installed. As indicator of pellet quality we adopted the pellet mass represented by the volume of the main remaining pellet fragment. Since only two-dimensional (2D) shadow images were obtained, a reconstruction of the full three-dimensional pellet body had to be performed. For this the image was first converted into a 1-bit version prescribing an exact 2D contour. From this contour the expected value of the volume was calculated by Bayesian analysis taking into account the likely cylindrical shape of the pellet. Under appropriate injection conditions sound pellets with more than half of their nominal mass are detected after acceleration; the passage causes in average an additional loss of about 40% to the launched mass. Analyzing pellets arriving at tube exit allowed for deriving the injector’s optimized operational conditions. For these more than 90% of the pellets were arriving with sound quality when operating in the frequency range 5–50 Hz.
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52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.70.-m Plasma diagnostic techniques and instrumentation
28.52.Fa Materials

Retarding field analyzer for ion energy distribution measurements at a radio-frequency biased electrode

D. Gahan, B. Dolinaj, and M. B. Hopkins

Rev. Sci. Instrum. 79, 033502 (2008); http://dx.doi.org/10.1063/1.2890100 (9 pages) | Cited 27 times

Online Publication Date: 10 March 2008

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A retarding field energy analyzer designed to measure ion energy distributions impacting a radio-frequency biased electrode in a plasma discharge is examined. The analyzer is compact so that the need for differential pumping is avoided. The analyzer is designed to sit on the electrode surface, in place of the substrate, and the signal cables are fed out through the reactor side port. This prevents the need for modifications to the rf electrode—as is normally the case for analyzers built into such electrodes. The capabilities of the analyzer are demonstrated through experiments with various electrode bias conditions in an inductively coupled plasma reactor. The electrode is initially grounded and the measured distributions are validated with the Langmuir probe measurements of the plasma potential. Ion energy distributions are then given for various rf bias voltage levels, discharge pressures, rf bias frequencies—500 kHz to 30 MHz, and rf bias waveforms—sinusoidal, square, and dual frequency.
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52.70.Ds Electric and magnetic measurements
52.80.Pi High-frequency and RF discharges
52.25.-b Plasma properties
52.77.-j Plasma applications

COBRA-STAR, a five frame point-projection x-ray imaging system for 1 MA scale wire-array Z pinches

J. D. Douglass and D. A. Hammer

Rev. Sci. Instrum. 79, 033503 (2008); http://dx.doi.org/10.1063/1.2884707 (4 pages) | Cited 10 times

Online Publication Date: 14 March 2008

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A new imaging system for 1 MA scale wire-array Z-pinch experiments that produces up to five high-resolution x-ray images per experimental pulse has been developed. Calibrated areal density measurements of the Z-pinch plasma can be obtained from each pulse. The system substitutes five molybdenum (Mo) X pinches for the normal copper return-current conductors to provide point sources of x-rays for point-projection radiography. Each backlighting X pinch consists of four Mo wires, the x-ray burst timing of which was controlled by varying the wire diameter (mass) from 10.2 to 30 μm in the five X pinches. Typical images have a 16×8 mm2 field of view at the wire array and a magnification of about 6.5:1 on the x-ray-sensitive film. Titanium (Ti) filters in front of the films transmit continuum radiation in the spectral range of 3–5 keV. Inclusion on the Ti of a step wedge having known thickness increments of the same material as the wires enables the calibrated areal density measurements to be made of the exploding wire plasmas. Here, we used tungsten (W) step wedges with step thicknesses ranging from 0.015 to 1.1 μm to obtain accurate (±10%) areal density measurements of W plasmas from the spatial profile of film exposure. When imaging arrays that produce intense radiation pulses, a plastic monofilament “quencher” is placed on axis to avoid film saturation. Images have subnanosecond temporal resolution and about 7 μm spatial resolution.
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52.59.Qy Wire array Z-pinches
52.59.Px Hard X-ray sources
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
07.85.-m X- and γ-ray instruments

A complex plasma device of large surface area

Y. Nakamura and O. Ishihara

Rev. Sci. Instrum. 79, 033504 (2008); http://dx.doi.org/10.1063/1.2894300 (4 pages) | Cited 4 times

Online Publication Date: 14 March 2008

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A novel complex plasma device (YCOPEX) to create two-dimensional monolayer plasma crystals of a large surface area of 15×90 cm2 is described. The YCOPEX, in which a plasma is produced by a rf discharge of argon gas, is designed to utilize gravitational force to study fundamental physics of complex plasmas. The device may be used for observation of spatial change of a phase state, propagation of waves, and collisions of flowing dust particles with an obstacle. As an example of experiments, neutral drag forces on microspheres are measured using the gravitational force on those particles. The obtained neutral drag force agrees reasonably with the values estimated from Epstein’s formula.
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52.75.-d Plasma devices
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.27.Lw Dusty or complex plasmas; plasma crystals

Determination of the electron density in plasma by means of a floating double probe

J. L. Jauberteau and I. Jauberteau

Rev. Sci. Instrum. 79, 033505 (2008); http://dx.doi.org/10.1063/1.2900579 (5 pages) | Cited 2 times

Online Publication Date: 25 March 2008

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Investigations are performed in a microwave plasma expansion containing argon-nitrogen gas mixture. The purpose of this work is to measure accurate electron density values by means of a floating double probe. We check the accuracy of the different methods developed for the double probe under different experimental conditions in Ar–N2 gas mixture, comparing results to single probe measurements. On the basis of previous works, we propose a simple way to determine the electron density without the knowledge of the plasma potential.
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52.80.Pi High-frequency and RF discharges
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.70.Ds Electric and magnetic measurements
52.40.Kh Plasma sheaths
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A heater-integrated scanning probe microscopy probe array with different tip radii for study of micro-nanosize effects on silicon-tip/polymer-film friction

Haifei Bao and Xinxin Li

Rev. Sci. Instrum. 79, 033701 (2008); http://dx.doi.org/10.1063/1.2885682 (8 pages) | Cited 2 times

Online Publication Date: 3 March 2008

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Electric-heated cantilever-tip probes fabricated by micromachining techniques can be used for high-density data storage, nanopatterning, etc., where contact-scanning and thermal-plastic nanowritings are frequently implemented on the surface of a polymer thin-film such as polymethylmethacrylate (PMMA). In such kind of applications, micro-nanofriction effects, e.g., contacting–size and temperature effects of the tip/film friction system, will largely influence the performance of the applications. To elucidate the effects, present research fabricates a monolithically integrated probe array that comprises three scanning probe microscopy cantilever-tip probes with different tip radii of tens of nanometers, submicrometers and microns, respectively. The tip is enabled an electric-heating function by integrating a heating resistors on the tip. Using the tips, the tip/film friction experiment shows an obvious contacting-area effect. Within a wide temperature range, the friction signal and the normal force load exhibit a nonlinear relationship for the nanoradius tip but a linear relationship for the submicron tip. With the heated tips, the experiment directly reveals significant size effects on friction and adhesion behaviors. It is found that the glassy transition of the PMMA film can be characterized using the submicron tip, while the nanotip is suited to detect the secondary β transition process. By fitting the experimental data into a power law with apparent friction coefficient included, the temperature-effect combined size effect of the micronano tip/polymer friction is modeled and discussed.
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62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
68.37.-d Microscopy of surfaces, interfaces, and thin films
68.60.Bs Mechanical and acoustical properties
61.41.+e Polymers, elastomers, and plastics
81.20.Wk Machining, milling

A new sample holder for laser-excited pump-probe magnetic measurements on a Focus photoelectron emission microscope

Jorge Miguel, Matthias Bernien, Daniela Bayer, Jaime Sánchez-Barriga, Florian Kronast, Martin Aeschlimann, Hermann A. Dürr, and Wolfgang Kuch

Rev. Sci. Instrum. 79, 033702 (2008); http://dx.doi.org/10.1063/1.2884709 (3 pages) | Cited 1 time

Online Publication Date: 4 March 2008

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A custom-made Omicron-compatible sample holder for time-resolved photoelectron emission microscopy experiments is presented. It comprises a sample plate with four contacts that hosts a chip carrier where the semiconductor substrate is mounted. Covering the sample holder, a 6 mm diameter mask protects electrostatically the sample from the extractor lens voltage while keeping the imaging quality unperturbed. The improvements are a greater sample lifetime and the ability to withstand much higher currents in the stripline that provides the magnetic pulse to the magnetic microstructure.
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06.60.Ei Sample preparation (including design of sample holders)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Atomically resolved imaging by low-temperature frequency-modulation atomic force microscopy using a quartz length-extension resonator

Toshu An, Takahiro Nishio, Toyoaki Eguchi, Masanori Ono, Atsushi Nomura, Kotone Akiyama, and Yukio Hasegawa

Rev. Sci. Instrum. 79, 033703 (2008); http://dx.doi.org/10.1063/1.2830937 (6 pages) | Cited 7 times

Online Publication Date: 6 March 2008

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Low-temperature ultrahigh vacuum frequency-modulation atomic force microscopy (AFM) was performed using a 1 MHz length-extension type of quartz resonator as a force sensor. Taking advantage of the high stiffness of the resonator, the AFM was operated with an oscillation amplitude smaller than 100 pm, which is favorable for high spatial resolution, without snapping an AFM tip onto a sample surface. Atomically resolved imaging of the adatom structure on the Si(111)-(7×7) surface was successfully obtained.
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68.37.Ps Atomic force microscopy (AFM)
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Combined low-temperature scanning tunneling/atomic force microscope for atomic resolution imaging and site-specific force spectroscopy

Boris J. Albers, Marcus Liebmann, Todd C. Schwendemann, Mehmet Z. Baykara, Markus Heyde, Miquel Salmeron, Eric I. Altman, and Udo D. Schwarz

Rev. Sci. Instrum. 79, 033704 (2008); http://dx.doi.org/10.1063/1.2842631 (9 pages) | Cited 12 times

Online Publication Date: 6 March 2008

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We present the design and first results of a low-temperature, ultrahigh vacuum scanning probe microscope enabling atomic resolution imaging in both scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) modes. A tuning-fork-based sensor provides flexibility in selecting probe tip materials, which can be either metallic or nonmetallic. When choosing a conducting tip and sample, simultaneous STM/NC-AFM data acquisition is possible. Noticeable characteristics that distinguish this setup from similar systems providing simultaneous STM/NC-AFM capabilities are its combination of relative compactness (on-top bath cryostat needs no pit), in situ exchange of tip and sample at low temperatures, short turnaround times, modest helium consumption, and unrestricted access from dedicated flanges. The latter permits not only the optical surveillance of the tip during approach but also the direct deposition of molecules or atoms on either tip or sample while they remain cold. Atomic corrugations as low as 1 pm could successfully be resolved. In addition, lateral drifts rates of below 15 pm/h allow long-term data acquisition series and the recording of site-specific spectroscopy maps. Results obtained on Cu(111) and graphite illustrate the microscope’s performance.
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07.79.Lh Atomic force microscopes
07.79.Cz Scanning tunneling microscopes

Stripe sensor tomography

Mladen Barbic, Lvcian Vltava, Christopher P. Barrett, Teresa H. Emery, and Axel Scherer

Rev. Sci. Instrum. 79, 033705 (2008); http://dx.doi.org/10.1063/1.2894330 (6 pages)

Online Publication Date: 12 March 2008

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We introduce a general concept of tomographic imaging for the case of an imaging sensor that has a stripelike shape. We first show that there is no difference, in principle, between two-dimensional tomography using conventional electromagnetic or particle radiation and tomography where a stripe sensor is mechanically scanned over a sample at a sequence of different angles. For a single stripe detector imaging, linear motion and angular rotation are required. We experimentally demonstrate single stripe sensor imaging principle using an elongated inductive coil detector. By utilizing an array of parallel stripe sensors that can be individually addressed, two-dimensional imaging can be performed with rotation only, eliminating the requirement for linear motion, as we also experimentally demonstrate with parallel coil array. We conclude that imaging with a stripe-type sensor of particular width and thickness (where the width is much larger than the thickness) is resolution limited only by the thickness (smaller parameter) of the sensor. We give examples of multiple sensor families where this imaging technique may be beneficial such as magnetoresistive, inductive, superconducting quantum interference device, and Hall effect sensors, and, in particular, discuss the possibilities of the technique in the field of magnetic resonance imaging.
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42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)
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