Rev. Sci. Instrum. - Review of Scientific Instruments

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Detection of nanosecond-scale, high power THz pulses with a field effect transistor

S. Preu, H. Lu, M. S. Sherwin, and A. C. Gossard

Rev. Sci. Instrum. 83, 053101 (2012); http://dx.doi.org/10.1063/1.4705986 (6 pages)

Online Publication Date: 1 May 2012

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We demonstrate detection and resolution of high power, 34 ns free electron laser pulses using a rectifying field effect transistor. The detector remains linear up to an input power of 11 ± 0.5 W at a pulse energy of 20 ± 1 μJ at 240 GHz. We compare its performance to a protected Schottky diode, finding a shorter intrinsic time constant. The damage threshold is estimated to be a few 100 W. The detector is, therefore, well-suited for characterizing high power THz pulses. We further demonstrate that the same detector can be used to detect low power continuous-wave THz signals with a post detection limited noise floor of 3.1 μW/ math

. Such ultrafast, high power detectors are important tools for high power and high energy THz facilities such as free electron lasers.

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41.60.Cr	Free-electron lasers
42.60.-v	Laser optical systems: design and operation

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Realization of autofocusing system for laser direct writing on non-planar surfaces

Jianbo Luo, Yiyong Liang, and Guoguang Yang

Rev. Sci. Instrum. 83, 053102 (2012); http://dx.doi.org/10.1063/1.4709407 (5 pages)

Online Publication Date: 2 May 2012

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This paper presents an autofocusing system for laser direct writing on non-planar surfaces, including focus error signal detection and focusing control. The focus error signal detection is based on modified confocal techniques, which features easy implementation, independence of the tilt angles of non-planar surfaces, and excellent suppression of common-mode noise or variable system factors. We also present a macro/micro dual-drive mechanism and its synchronous operation for focusing control on non-planar surfaces. Finally, a performance evaluation of the autofocusing system is presented. The uniform line width of 2.1 μm for a pattern on a convex spherical substrate with a curvature radius of 100 mm shows the autofocusing system performs well.

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42.62.-b

Laser applications

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Enhancing photocurrent transient spectroscopy by electromagnetic modeling

H. Diesinger, M. Panahandeh-Fard, Z. Wang, D. Baillargeat, and C. Soci

Rev. Sci. Instrum. 83, 053103 (2012); http://dx.doi.org/10.1063/1.4710996 (6 pages)

Online Publication Date: 3 May 2012

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The shape and duration of photocurrent transients generated by a photoconductive switch depend on both the intrinsic response of the active material and the geometry of the transmission line structure. The present electromagnetic model decouples both shape forming contributions. In contrast to previously published work, it accounts for the particular operating mode of transient spectroscopy. The objective is to increase the time resolution by two approaches, by optimizing structural response and by deconvolving it from experimental data. The switch structure is represented by an effective transimpedance onto which the active material acts as current generator. As proof of concept, the response of a standard microstrip switch is modeled and deconvolved from experimental data acquired in GaAs, yielding a single exponential material response and hence supporting the validity of the approach. Beyond compensating for the response deterioration by the structure, switch architectures can be a priori optimized with respect to frequency response. As an example, it is shown that a microstrip gap that can be deposited on materials incompatible with standard lithography reduces pulse broadening by an order of magnitude if it is provided with transitions to coplanar access lines.

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41.20.Jb	Electromagnetic wave propagation; radiowave propagation
07.57.-c	Infrared, submillimeter wave, microwave and radiowave instruments and equipment
11.55.-m	S-matrix theory; analytic structure of amplitudes

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An in situ set up for the detection of CO₂ from catalytic CO oxidation by using planar laser-induced fluorescence

J. Zetterberg, S. Blomberg, J. Gustafson, Z. W. Sun, Z. S. Li, E. Lundgren, and M. Aldén

Rev. Sci. Instrum. 83, 053104 (2012); http://dx.doi.org/10.1063/1.4711130 (5 pages)

Online Publication Date: 4 May 2012

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We report the first experiment carried out on an in situ setup, which allows for detection of CO₂ from catalytic CO oxidation close to a model catalyst under realistic reaction conditions by the means of planar laser-induced fluorescence (PLIF) in the mid-infrared spectral range. The onset of the catalytic reaction as a function of temperature was followed by PLIF in a steady state flow reactor. After taking into account the self-absorption of CO₂, a good agreement between the detected CO₂ fluorescence signal and the CO₂ mass spectrometry signal was shown. The observed difference to previously measured onset temperatures for the catalytic ignition is discussed and the potential impact of IR-PLIF as a detection technique in catalysis is outlined.

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07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.65.+r	Surface and interface chemistry; heterogeneous catalysis at surfaces
42.62.-b	Laser applications

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Response of large area avalanche photodiodes to low energy x rays

T. R. Gentile, M. Bales, U. Arp, B. Dong, and R. Farrell

Rev. Sci. Instrum. 83, 053105 (2012); http://dx.doi.org/10.1063/1.4714348 (9 pages)

Online Publication Date: 8 May 2012

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For an experiment to study neutron radiative beta-decay, we operated large area avalanche photodiodes (APDs) near liquid nitrogen temperature to detect x rays with energies between 0.2 keV and 20 keV. Whereas there are numerous reports of x ray spectrometry using APDs at energies above 1 keV, operation near liquid nitrogen temperature allowed us to reach a nominal threshold of 0.1 keV. However, due to the short penetration depth of x rays below 1 keV, the pulse height spectrum of the APD become complex. We studied the response using monochromatic x ray beams and employed phenomenological fits of the pulse height spectrum to model the measurement of a continuum spectrum from a synchrotron. In addition, the measured pulse height spectrum was modelled using a profile for the variation in efficiency of collection of photoelectrons with depth into the APD. The best results are obtained with the collection efficiency model.

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85.60.Gz	Photodetectors (including infrared and CCD detectors)
85.60.Dw	Photodiodes; phototransistors; photoresistors
07.85.Nc	X-ray and γ-ray spectrometers

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Fourier transform infrared spectroscopy approach for measurements of photoluminescence and electroluminescence in mid-infrared

Y. G. Zhang, Y. Gu, K. Wang, X. Fang, A. Z. Li, and K. H. Liu

Rev. Sci. Instrum. 83, 053106 (2012); http://dx.doi.org/10.1063/1.4717673 (7 pages)

Online Publication Date: 11 May 2012

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An improved Fourier transform infrared spectroscopy approach adapting to photoluminescence and electroluminescence measurements in mid-infrared has been developed, in which diode-pumped solid-state excitation lasers were adopted for photoluminescence excitation. In this approach, three different Fourier transform infrared modes of rapid scan, double modulation, and step scan were software switchable without changing the hardware or connections. The advantages and limitations of each mode were analyzed in detail. Using this approach a group of III–V and II–VI samples from near-infrared extending to mid-infrared with photoluminescence intensities in a wider range have been characterized at room temperature to demonstrate the validity and overall performances of the system. The weaker electroluminescence of quantum cascade lasers in mid-infrared band was also surveyed at different resolutions. Results show that for samples with relatively strong photoluminescence or electroluminescence out off the background, rapid scan mode is the most preferable. For weaker photoluminescence or electroluminescence overlapped with background, double modulation is the most effective mode. To get a better signal noise ratio when weaker photoluminescence or electroluminescence signal has been observed in double modulation mode, switching to step scan mode should be an advisable option despite the long data acquiring time and limited resolution.

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07.57.Ty	Infrared spectrometers, auxiliary equipment, and techniques
42.70.Hj	Laser materials
78.30.Fs	III-V and II-VI semiconductors
78.55.Cr	III-V semiconductors
78.55.Et	II-VI semiconductors
78.60.Fi	Electroluminescence

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A versatile and reconfigurable setup for all-terahertz time-resolved pump-probe spectroscopy

A. Y. Elezzabi and P. Maraghechi

Rev. Sci. Instrum. 83, 053107 (2012); http://dx.doi.org/10.1063/1.4717732 (6 pages)

Online Publication Date: 14 May 2012

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A versatile optical setup for all-terahertz (THz) time resolved pump-probe spectroscopy was designed and tested. By utilizing a dual THz pulse generator emitter module, independent and synchronized THz radiation pump and probe pulses were produced, thus eliminating the need for THz beam splitters and the limitations associated with their implementation. The current THz setup allows for precise control of the electric fields splitting ratio between the THz radiation pump and probe pulses, as well as in-phase, out-of-phase, and polarization dependent pump-probe spectroscopy. Since the present THz pump-probe setup does not require specialized THz radiation optical components, such as phase shifters, polarization rotators, or wide bandwidth beam splitters, it can be easily implemented with minimal alterations to a conventional THz time domain spectroscopy system. The present setup is valuable for studying the time dynamics of THz coherent phenomena in solid-state, chemical, and biological systems.

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07.57.Pt	Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.79.Fm	Reflectors, beam splitters, and deflectors

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Experimental investigation on focusing characteristics of a He-Ne laser using circular Fresnel zone plate for high-precision alignment of linear accelerators

Tsuyoshi Suwada, Masanori Satoh, Souichi Telada, and Kaoru Minoshima

Rev. Sci. Instrum. 83, 053301 (2012); http://dx.doi.org/10.1063/1.4709497 (9 pages)

Online Publication Date: 3 May 2012

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We experimentally investigate the focusing characteristics of a He–Ne laser at the focal region for the high-precision alignment of long-distance linear accelerators using a circular Fresnel zone plate. The laser wave passing through the Fresnel zone plate having a focal length of 66.7 m propagates for a 268-m-long distance at atmospheric pressure. A new laser-based alignment system using Fresnel zone plates as the alignment targets is discussed. The transverse displacement of the focused spot of the laser is measured as a function of the displacement of the target by a detector installed at the focal point. Systematic studies on the focusing characteristics and alignment precision have been successfully conducted in this experiment. The experimental results are in good agreement with theoretical calculations, and the alignment precision of the target is determined to be less than ±30 μm. In this study, we perform a detailed experimental investigation on the laser propagation and focusing characteristics using the circular Fresnel zone plate at the focal region along with theoretical calculations.

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29.20.Ej	Linear accelerators
42.55.Lt	Gas lasers including excimer and metal-vapor lasers
42.79.Ci	Filters, zone plates, and polarizers

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Central electron temperature estimations of TJ-II neutral beam injection heated plasmas based on the soft x ray multi-foil technique

D. Baião, F. Medina, M. Ochando, K. McCarthy, F. Tabarés, I. Pastor, and C. Varandas

Rev. Sci. Instrum. 83, 053501 (2012); http://dx.doi.org/10.1063/1.4714340 (5 pages)

Online Publication Date: 8 May 2012

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The core electron temperature (T_e0) of neutral beam heated plasmas is determined in TJ-II stellarator by using soft x ray detectors with beryllium filters of different thickness, based on the method known as the foil absorption technique. T_e0 estimations are done with the impurity code IONEQ, making use of complementary information from the TJ-II soft x ray tomography and the VUV survey diagnostics. When considering the actual electron density and temperature profile shapes, an acceptable agreement is found with Thomson scattering measurements for 8 different magnetic configurations. The impact of the use of both neutral beam injectors on the T_e0 measurements is addressed. Also, the behaviour of T_e0 during spontaneous profile transitions is presented.

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52.55.Jd	Magnetic mirrors, gas dynamic traps
52.70.La	X-ray and γ-ray measurements
52.25.Vy	Impurities in plasmas
52.50.Gj	Plasma heating by particle beams

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Quantitative measurement of hard x-ray spectra for high intensity laser produced plasma

Z. Zhang, H. Nishimura, T. Namimoto, S. Fujioka, Y. Arikawa, M. Nishikino, T. Kawachi, A. Sagisaka, H. Hosoda, S. Orimo, K. Ogura, A. Pirozhkov, A. Yogo, Y. Okano, H. Kiriyama, et al.

Rev. Sci. Instrum. 83, 053502 (2012); http://dx.doi.org/10.1063/1.4717677 (5 pages)

Online Publication Date: 10 May 2012

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X-ray line spectra ranging from 17 to 77 keV were quantitatively measured with a Laue spectrometer, composed of a cylindrically curved crystal and a detector. Either a visible CCD detector coupled with a CsI phosphor screen or an imaging plate can be chosen, depending on the signal intensities and exposure times. The absolute sensitivity of the spectrometer system was calibrated using pre-characterized laser-produced x-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an open code for x-ray diffraction. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer agency for specific x-ray line emissions, is derived as a consequence of this work.

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52.25.Os	Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm	Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.59.Px	Hard X-ray sources
52.70.La	X-ray and γ-ray measurements

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Experimental and simulation study of undesirable short-period deformation in piezoelectric deformable x-ray mirrors

Hiroki Nakamori, Satoshi Matsuyama, Shota Imai, Takashi Kimura, Yasuhisa Sano, Yoshiki Kohmura, Kenji Tamasaku, Makina Yabashi, Tetsuya Ishikawa, and Kazuto Yamauchi

Rev. Sci. Instrum. 83, 053701 (2012); http://dx.doi.org/10.1063/1.4709499 (6 pages)

Online Publication Date: 3 May 2012

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To construct adaptive x-ray focusing optics whose optical parameters can be varied while performing wavefront correction, ultraprecise piezoelectric deformable mirrors have been developed. We computationally and experimentally investigated undesirable short-period deformation caused by piezoelectric actuators adhered to the substrate during mirror deformation. Based on the results of finite element method analysis, shape measurements, and the observation of x-ray reflection images, a guideline is developed for designing deformable mirrors that do not have short-period deformation errors.

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41.50.+h	X-ray beams and x-ray optics
42.79.Bh	Lenses, prisms and mirrors
07.07.Tw	Servo and control equipment; robots

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Development of a pulse programmer for magnetic resonance imaging using a personal computer and a high-speed digital input–output board

Seitaro Hashimoto, Katsumi Kose, and Tomoyuki Haishi

Rev. Sci. Instrum. 83, 053702 (2012); http://dx.doi.org/10.1063/1.4711132 (6 pages)

Online Publication Date: 7 May 2012

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We have developed a pulse programmer for magnetic resonance imaging (MRI) using a personal computer and a commercially available high-speed digital input–output board. The software for the pulse programmer was developed using C/C++ and .NET Framework 2.0 running under the Windows 7 operating system. The pulse programmer was connected to a digital MRI transceiver using a 32-bit parallel interface, and 128-bit data (16 bits × 8 words) for the pulse sequence and the digitally detected MRI signal were transferred bi-directionally every 1 μs. The performance of the pulse programmer was evaluated using a 1.0 T permanent magnet MRI system. The acquired MR images demonstrated the usefulness of the pulse programmer. Although our pulse programmer was developed for a specially designed digital MRI transceiver, our approach can be used for any MRI system if the interface for the transceiver is properly designed. Therefore, we have concluded that our approach is promising for MRI pulse programmers.

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07.57.Pt	Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
84.30.Ng	Oscillators, pulse generators, and function generators

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Retrofitting an atomic force microscope with photothermal excitation for a clean cantilever response in low Q environments

Aleksander Labuda, Kei Kobayashi, Yoichi Miyahara, and Peter Grütter

Rev. Sci. Instrum. 83, 053703 (2012); http://dx.doi.org/10.1063/1.4712286 (8 pages)

Online Publication Date: 10 May 2012

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It is well known that the low-Q regime in dynamic atomic force microscopy is afflicted by instrumental artifacts (known as “the forest of peaks”) caused by piezoacoustic excitation of the cantilever. In this article, we unveil additional issues associated with piezoacoustic excitation that become apparent and problematic at low Q values. We present the design of a photothermal excitation system that resolves these issues, and demonstrate its performance on force spectroscopy at the interface of gold and an ionic liquid with an overdamped cantilever (Q < 0.5). Finally, challenges in the interpretation of low-Q dynamic AFM measurements are discussed.

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07.79.Lh

Atomic force microscopes

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Design and analysis of multi-color confocal microscopy with a wavelength scanning detector

Dukho Do, Wanhee Chun, and Dae-Gab Gweon

Rev. Sci. Instrum. 83, 053704 (2012); http://dx.doi.org/10.1063/1.4717679 (6 pages)

Online Publication Date: 10 May 2012

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Spectral (or multi-color) microscopy has the ability to detect the fluorescent light of biological specimens with a broad range of wavelengths. Currently, the acousto-optic tunable filter (AOTF) is widely used in spectral microscopy as a substitute for a multiple-dichroic mirror to divide excitation and emission signals while maintaining sufficient light efficiency. In addition, systems which utilize an AOTF have a very fast switching speed and high resolution for wavelength selection. In this paper, confocal-spectral microscopy is proposed with a particular spectrometer design with a wavelength-scanning galvano-mirror. This enables the detection of broadband (480–700 nm) fluorescence signals by a single point detector (photomultiplier tube) instead of a CCD pixel array. For this purpose, a number of optical elements were applicably designed. A prism is used to amplify the dispersion angle, and the design of the relay optics matches the signals to the diameter of the wavelength-scanning galvano-mirror. Also, a birefringent material known as calcite is used to offset the displacement error at the image plane depending on the polarization states. The proposed multi-color confocal microscopy with the unique detection body has many advantages in comparison with commercial devices. In terms of the detection method, it can be easily applied to other imaging modalities.

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42.79.Pw	Imaging detectors and sensors
07.60.Pb	Conventional optical microscopes
42.79.Bh	Lenses, prisms and mirrors
42.79.Ci	Filters, zone plates, and polarizers
42.79.Jq	Acousto-optical devices

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Quantitative scheme for full-field polarization rotating fluorescence microscopy using a liquid crystal variable retarder

John F. Lesoine, Ji Youn Lee, Jeffrey R. Krogmeier, Hyeonggon Kang, Matthew L. Clarke, Robert Chang, Dan L. Sackett, Ralph Nossal, and Jeeseong Hwang

Rev. Sci. Instrum. 83, 053705 (2012); http://dx.doi.org/10.1063/1.4717682 (9 pages)

Online Publication Date: 16 May 2012

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We present a quantitative scheme for full-field polarization rotating fluorescence microscopy. A quarter-wave plate, in combination with a liquid crystal variable retarder, provides a tunable method to rotate polarization states of light prior to its being coupled into a fluorescence microscope. A calibration of the polarization properties of the incident light is performed in order to correct for elliptical polarization states. This calibration allows the response of the sample to linear polarization states of light to be recovered. Three known polarization states of light can be used to determine the average fluorescent dipole orientations in the presence of a spatially varying dc offset or background polarization-invariant fluorescence signal. To demonstrate the capabilities of this device, we measured a series of full-field fluorescence polarization images from fluorescent analogs incorporated in the lipid membrane of Burkitts lymphoma CA46 cells. The fluorescent lipid-like analogs used in this study are molecules that are labeled by either a DiI (1,1^′-Dioctadecyl 3,3,3^′,3^′-Tetramethylindocarbocyanine) fluorophore in its head group or a Bodipy (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) molecule in its acyl chain. A spatially varying contrast in the normalized amplitude was observed on the cell surface, where the orientation of the DiI molecules is tangential to the cell membrane. The internally labeled cellular structures showed zero response to changes in linear polarization, and the net linear polarization amplitude for these regions was zero. This instrument provides a low cost calibrated method that may be coupled to existing fluorescence microscopes to perform investigations of cellular processes that involve a change in molecular orientations.

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87.64.M-	Optical microscopy
42.79.Ci	Filters, zone plates, and polarizers
42.79.Kr	Display devices, liquid-crystal devices
87.64.kv	Fluorescence

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A furnace with rotating load frame for in situ high temperature deformation and creep experiments in a neutron diffraction beam line

H. M. Reiche, S. C. Vogel, P. Mosbrucker, E. J. Larson, and M. R. Daymond

Rev. Sci. Instrum. 83, 053901 (2012); http://dx.doi.org/10.1063/1.4708619 (7 pages)

Online Publication Date: 2 May 2012

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A resistive furnace combined with a load frame was built that allows for in situ neutron diffraction studies of high temperature deformation, in particular, creep. A maximum force of 2700 N can be applied at temperatures up to 1000 °C. A load control mode permits studies of, e.g., creep or phase transformations under applied uni-axial stress. In position control, a range of high temperature deformation experiments can be achieved. The examined specimen can be rotated up to 80° around the vertical compression axis allowing texture measurements in the neutron time-of-flight diffractometer HIPPO (High Pressure – Preferred Orientation). We present results from the successful commissioning, deforming a Zr-2.5 wt.% Nb cylinder at 975 °C. The device is now available for the user program of the HIPPO diffractometer at the LANSCE (Los Alamos Neutron Science Center) user facility.

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07.78.+s	Electron, positron, and ion microscopes; electron diffractometers
62.50.-p	High-pressure effects in solids and liquids
64.70.K-	Solid-solid transitions
62.20.Hg	Creep
81.40.Lm	Deformation, plasticity, and creep

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Development of a simultaneous Hugoniot and temperature measurement for preheated-metal shock experiments: Melting temperatures of Ta at pressures of 100 GPa

Jun Li, Xianming Zhou, Jiabo Li, Qiang Wu, Lingcang Cai, and Chengda Dai

Rev. Sci. Instrum. 83, 053902 (2012); http://dx.doi.org/10.1063/1.4716459 (7 pages)

Online Publication Date: 14 May 2012

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Equations of state of metals are important issues in earth science and planetary science. A major limitation of them is the lack of experimental data for determining pressure-volume and temperature of shocked metal simultaneously. By measuring them in a single experiment, a major source of systematic error is eliminated in determining from which shock pressure release pressure originates. Hence, a non-contact fast optical method was developed and demonstrated to simultaneously measure a Hugoniot pressure-volume (P_H-V_H) point and interfacial temperature T_R on the release of Hugoniot pressure (P_R) for preheated metals up to 1000 K. Experimental details in our investigation are (i) a Ni–Cr resistance coil field placed around the metal specimen to generate a controllable and stable heating source, (ii) a fiber-optic probe with an optical lens coupling system and optical pyrometer with ns time resolution to carry out non-contact fast optical measurements for determining P_H-V_H and T_R. The shock response of preheated tantalum (Ta) at 773 K was investigated in our work. Measured data for shock velocity versus particle velocity at an initial state of room temperature was in agreement with previous shock compression results, while the measured shock data between 248 and 307 GPa initially heated to 773 K were below the Hugoniot evaluation from its off-Hugoniot states. Obtained interfacial temperatures on release of Hugoniot pressures (100–170 GPa) were in agreement with shock-melting points at initial ambient condition and ab initio calculations of melting curve. It indicates a good consistency for shock melting data of Ta at different initial temperatures. Our combined diagnostics for Hugoniot and temperature provides an important approach for studying EOS and the temperature effect of shocked metals. In particular, our measured melting temperatures of Ta address the current controversy about the difference by more than a factor of 2 between the melting temperatures measured under shock and those measured in a laser-heated diamond anvil cell at ∼100 GPa.

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07.20.Dt	Thermometers
07.20.Ka	High-temperature instrumentation; pyrometers
42.79.Bh	Lenses, prisms and mirrors
06.30.Bp	Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

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A digitally configurable measurement platform using audio cards for high-resolution electronic transport studies

D. B. Gopman, D. Bedau, and A. D. Kent

Rev. Sci. Instrum. 83, 054701 (2012); http://dx.doi.org/10.1063/1.4709498 (4 pages)

Online Publication Date: 7 May 2012

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We report on a software-defined digitally configurable measurement platform for determining electronic transport properties in nanostructures with small readout signals. By using a high-resolution audio analog-to-digital/digital-to-analog converter in a digitally compensated bridge configuration we significantly increase the measurement speed compared to established techniques and simultaneously acquire large and small signal characteristics. We characterize the performance (16 bit resolution, 100 dB dynamic range at 192 kS/s) and demonstrate the application of this measurement platform for studying the transport properties of spin-valve nanopillars, a two-terminal device that exhibits giant magnetoresistance and whose resistance can be switched between two levels by applied magnetic fields and by currents applied by the audio card. The high resolution and fast sampling capability permits rapid acquisition of deep statistics on the switching of a spin-valve nanopillar and reduces the time to acquire the basic properties of the device – a state-diagram showing the magnetic configurations as function of applied current and magnetic field – by orders of magnitude.

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84.40.Ua

Telecommunications: signal transmission and processing; communication satellites

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Development of a continuous testing apparatus for temperature reduction performance of cool coatings

Zhongnan Song, Yunxing Shi, Weidong Zhang, Jianrong Song, Jian Qu, Yanwen Li, and Zhongde Wang

Rev. Sci. Instrum. 83, 054901 (2012); http://dx.doi.org/10.1063/1.4709494 (5 pages)

Online Publication Date: 2 May 2012

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The working principle of a continuous testing apparatus for the temperature reduction performance of cool coatings is presented in this work. The apparatus consists of infrared reflector type lamps, an adiabatic box, and a data acquisition system. It was calibrated with the different conventional reference panels. The tests for dynamic and steady state temperature reduction performances were illustrated with two cool coatings. Results obtained directly from the simultaneous measurement are in good agreement with those calculated from separate measurements, thus confirming this apparatus as a valuable experimental tool for research and development of cool coatings.

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07.05.Hd	Data acquisition: hardware and software
07.20.Dt	Thermometers

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Highly sensitive thermal conductivity measurements of suspended membranes (SiN and diamond) using a 3ω-Völklein method

A. Sikora, H. Ftouni, J. Richard, C. Hébert, D. Eon, F. Omnès, and O. Bourgeois

Rev. Sci. Instrum. 83, 054902 (2012); http://dx.doi.org/10.1063/1.4704086 (7 pages)

Online Publication Date: 8 May 2012

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A suspended system for measuring the thermal properties of membranes is presented. The sensitive thermal measurement is based on the 3ω dynamic method coupled to a Völklein geometry. The device obtained using micro-machining processes allows the measurement of the in-plane thermal conductivity of a membrane with a sensitivity of less than 10 nW/K (+/−5 × 10⁻³ Wm⁻¹ K⁻¹ at room temperature) and a very high resolution (ΔK/K = 10⁻³). A transducer (heater/thermometer) centered on the membrane is used to create an oscillation of the heat flux and to measure the temperature oscillation at the third harmonic using a Wheatstone bridge set-up. Power as low as 0.1 nW has been measured at room temperature. The method has been applied to measure thermal properties of low stress silicon nitride and polycrystalline diamond membranes with thickness ranging from 100 nm to 400 nm. The thermal conductivity measured on the polycrystalline diamond membrane support a significant grain size effect on the thermal transport.

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07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm	Micromechanical devices and systems
07.20.-n	Thermal instruments and apparatus

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A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials

V. Félix, Y. Jannot, and A. Degiovanni

Rev. Sci. Instrum. 83, 054903 (2012); http://dx.doi.org/10.1063/1.4704842 (8 pages)

Online Publication Date: 11 May 2012

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Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10⁻¹ to 10⁵ Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.

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07.20.-n	Thermal instruments and apparatus
06.30.Bp	Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
77.84.-s	Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

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Remote vibration measurement: A wireless passive surface acoustic wave resonator fast probing strategy

J.-M. Friedt, C. Droit, S. Ballandras, S. Alzuaga, G. Martin, and P. Sandoz

Rev. Sci. Instrum. 83, 055001 (2012); http://dx.doi.org/10.1063/1.4705728 (6 pages)

Online Publication Date: 1 May 2012

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Surface acoustic wave (SAW) resonators can advantageously operate as passive sensors which can be interrogated through a wireless link. Amongst the practical applications of such devices, structural health monitoring through stress measurement and more generally vibration characteristics of mechanical structures benefit from the ability to bury such sensors within the considered structure (wireless and battery-less). However, measurement bandwidth becomes a significant challenge when measuring wideband vibration characteristics of mechanical structures. A fast SAW resonator measurement scheme is demonstrated here. The measurement bandwidth is limited by the physical settling time of the resonator (Q/π periods), requiring only two probe pulses through a monostatic RADAR-like electronic setup to identify the sensor resonance frequency and hence stress on a resonator acting as a strain gauge. A measurement update rate of 4800 Hz using a high quality factor SAW resonator operating in the 434 MHz Industrial, Scientific and Medical band is experimentally demonstrated.

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07.10.-h	Mechanical instruments and equipment
07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

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A novel driving principle by means of the parasitic motion of the microgripper and its preliminary application in the design of the linear actuator

Hu Huang, Hongwei Zhao, Zhaojun Yang, Jie Mi, Zunqiang Fan, Shunguang Wan, Chengli Shi, and Zhichao Ma

Rev. Sci. Instrum. 83, 055002 (2012); http://dx.doi.org/10.1063/1.4711869 (6 pages)

Online Publication Date: 4 May 2012

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This paper presents a novel driving principle by means of the parasitic motion of the microgripper. Actuators based on this principle can realize the large displacement range and high speed easily. Also the structure can be simple. A parasitic motion principle linear actuator mainly consisting of two piezoelectric stacks, two microgrippers and a mover was designed. Experimental results indicate that at a low driving frequency of 5 Hz, large velocity over 40 μm/s is obtained with the driving voltage of 100 V. Backward motion was observed and analyzed. Experimental results verify the feasibility of the new principle and it can be used to design new linear or rotary actuators.

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07.07.Tw	Servo and control equipment; robots
85.85.+j	Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

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Tuning of nanogap size in high tensile stress silicon nitride thin films

Anıl Günay-Demirkol and İsmet İ. Kaya

Rev. Sci. Instrum. 83, 055003 (2012); http://dx.doi.org/10.1063/1.4712289 (5 pages)

Online Publication Date: 7 May 2012

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High tensile stress suspended structures are demanded for high mechanical quality factor applications. However, high tensile stress causes distortion of the original shapes by contracting, buckling, and bending the suspended structures. We demonstrate a method to compensate for the shape deformation of suspended structures due to intrinsic tensile stress after they are released. With a new design, the distance between two suspended structures after wet etch can easily be tuned by a single fabrication beyond the lithographic resolution limits. The technique is simulated by finite element analysis and experimentally implemented to demonstrate a gap tuning capability with 2.4 nm standard error.

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68.60.Bs	Mechanical and acoustical properties
62.20.mq	Buckling
81.40.Lm	Deformation, plasticity, and creep
62.20.F-	Deformation and plasticity

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Development of a micro cell compression stimulator for evaluating real-time cellular responses

Y. Nakashima, Y. Yang, and K. Minami

Rev. Sci. Instrum. 83, 055004 (2012); http://dx.doi.org/10.1063/1.4717683 (7 pages)

Online Publication Date: 11 May 2012

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This paper presents a micro cell compression stimulator for evaluating real-time cellular responses to compression stimuli. The device was produced by a micro three-dimensional structure fabrication process using multiple exposures to the photoresist. The device consists of a pressure inlet port, cell inlet ports, a gasket, microchannels, cell culture chambers, and a diaphragm on the culture chamber for applying compressive pressure to cells. Compression stimuli applied to the cells can be controlled by regulating the expansion of the diaphragm via a pressure control. The device permits the observation of cellular responses to compressive pressure in real time because it is made of transparent materials and stimulates the cells without deforming the cell culture surface, when observed by optical microscopy. We demonstrated the validity of the fabrication process, evaluated the performance of the fabricated device, and compared the experimental results with the FEM structural analysis results. We found through operational testing that the diaphragm was deformed quickly by applying negative/positive pressure and that the diaphragm displacement became larger with increasing applied pressure. These results indicate that this device can be used to control the intensity and the cell stimulus profile by regulating the applied pressure. In all cases, the cellular deformation during compression stimulus was successfully observed in real time using an optical microscope. The device is expected to facilitate the control of stem cell differentiation and the clarification of cellular mechanoreceptor mechanisms and signal transduction pathways.

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87.80.Ek	Mechanical and micromechanical techniques
07.10.Cm	Micromechanical devices and systems
87.17.-d	Cell processes
47.60.Dx	Flows in ducts and channels
87.19.lt	Sensory systems: visual, auditory, tactile, taste, and olfaction
87.64.M-	Optical microscopy

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