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May 2013

Volume 84, Issue 5 (partial)

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back to top Optics; Atoms and Molecules; Spectroscopy; Photon Detectors

Fiber-optic Fourier transform infrared spectroscopy for remote label-free sensing of medical device surface contamination

Moinuddin Hassan, Xin Tan, Elissa Welle, and Ilko Ilev

Rev. Sci. Instrum. 84, 053101 (2013); http://dx.doi.org/10.1063/1.4803182 (4 pages)

Online Publication Date: 7 May 2013

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As a potential major source of biochemical contamination, medical device surfaces are of critical safety concerns in the clinical practice and public health. The development of innovative sensing methods for accurate and real-time detection of medical device surface contamination is essential to protect patients from high risk infection. In this paper, we demonstrate an alternative fiber-optic Fourier Transform Infrared (FTIR) spectroscopy based sensing approach for remote, non-contact, and label-free detection of biochemical contaminants in the mid-infrared (mid-IR) region. The sensing probe is designed using mid-IR hollow fibers and FTIR measurements are carried out in reflection mode. Bovine Serum Albumin (BSA) and bacterial endotoxin of different concentrations under thoroughly dry condition are used to evaluate the detection sensitivity. The devised system can identify ≤0.0025% (≤4 × 1011 molecules) BSA and 0.5% (0.5 EU/ml) endotoxin concentration. The developed sensing approach may be applied to detect various pathogens that pose public health threats.
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87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.81.Pa Sensors, gyros
87.14.E- Proteins
87.15.R- Reactions and kinetics
87.64.km Infrared

A seven-crystal Johann-type hard x-ray spectrometer at the Stanford Synchrotron Radiation Lightsource

D. Sokaras, T.-C. Weng, D. Nordlund, R. Alonso-Mori, P. Velikov, D. Wenger, A. Garachtchenko, M. George, V. Borzenets, B. Johnson, T. Rabedeau, and U. Bergmann

Rev. Sci. Instrum. 84, 053102 (2013); http://dx.doi.org/10.1063/1.4803669 (8 pages)

Online Publication Date: 7 May 2013

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We present a multicrystal Johann-type hard x-ray spectrometer (∼5–18 keV) recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The instrument is set at the wiggler beamline 6-2 equipped with two liquid nitrogen cooled monochromators – Si(111) and Si(311) – as well as collimating and focusing optics. The spectrometer consists of seven spherically bent crystal analyzers placed on intersecting vertical Rowland circles of 1 m of diameter. The spectrometer is scanned vertically capturing an extended backscattering Bragg angular range (88°–74°) while maintaining all crystals on the Rowland circle trace. The instrument operates in atmospheric pressure by means of a helium bag and when all the seven crystals are used (100 mm of projected diameter each), has a solid angle of about 0.45% of 4π sr. The typical resolving power is in the order of math ∼ 10 000. The spectrometer's high detection efficiency combined with the beamline 6-2 characteristics permits routine studies of x-ray emission, high energy resolution fluorescence detected x-ray absorption and resonant inelastic x-ray scattering of very diluted samples as well as implementation of demanding in situ environments.
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07.85.Nc X-ray and γ-ray spectrometers

Optical design of the short pulse x-ray imaging and microscopy time-angle correlated diffraction beamline at the Advanced Photon Source

R. Reininger, E. M. Dufresne, M. Borland, M. A. Beno, L. Young, K.-J. Kim, and P. G. Evans

Rev. Sci. Instrum. 84, 053103 (2013); http://dx.doi.org/10.1063/1.4804197 (7 pages)

Online Publication Date: 10 May 2013

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The short pulse x-ray imaging and microscopy beamline is one of the two x-ray beamlines that will take full advantage of the short pulse x-ray source in the Advanced Photon Source (APS) upgrade. A horizontally diffracting double crystal monochromator which includes a sagittally focusing second crystal will collect most of the photons generated when the chirped electron beam traverses the undulator. A Kirkpatrick-Baez mirror system after the monochromator will deliver to the sample a beam which has an approximately linear correlation between time and vertical beam angle. The correlation at the sample position has a slope of 0.052 ps/μrad extending over an angular range of 800 μrad for a cavity deflection voltage of 2 MV. The expected time resolution of the whole system is 2.6 ps. The total flux expected at the sample position at 10 keV with a 0.9 eV energy resolution is 5.7 × 1012 photons/s at a spot having horizontal and vertical full width at half maximum of 33 μm horizontal by 14 μm vertical. This new beamline will enable novel time-dispersed diffraction experiments on small samples using the full repetition rate of the APS.
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41.85.Si Particle beam collimators, monochromators
07.85.-m X- and γ-ray instruments

Improving the accuracy of optical rotation measurement based on optical null methods by curve-fitting

Zhenhao Yang and Hongzhi Jia

Rev. Sci. Instrum. 84, 053104 (2013); http://dx.doi.org/10.1063/1.4804596 (4 pages)

Online Publication Date: 13 May 2013

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An optical rotation measuring system using optical null methods is set up. The system is based on a step-motor rotating stage structure and a modulated laser, which both are controlled by digital signal processor. By introducing a curve-fitting method, the optical rotation angle is obtained from the step difference between the crossed positions in light signal curves with or without sample. The principle of this method is studied, and the system performance is investigated experimentally. We achieved an accuracy of the order of 10−3 degree in at least ±45° range, which is an improvement compared with the resolution of 0.01° for step-motor rotation stage.
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07.60.-j Optical instruments and equipment
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
02.60.Ed Interpolation; curve fitting
42.60.Fc Modulation, tuning, and mode locking
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
07.68.+m Photography, photographic instruments; xerography

Modified Fabry-Perot interferometer for displacement measurement in ultra large measuring range

Chung-Ping Chang, Pi-Cheng Tung, Lih-Horng Shyu, Yung-Cheng Wang, and Eberhard Manske

Rev. Sci. Instrum. 84, 053105 (2013); http://dx.doi.org/10.1063/1.4803672 (8 pages)

Online Publication Date: 14 May 2013

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Laser interferometers have demonstrated outstanding measuring performances for high precision positioning or dimensional measurements in the precision industry, especially in the length measurement. Due to the non-common-optical-path structure, appreciable measurement errors can be easily induced under ordinary measurement conditions. That will lead to the limitation and inconvenience for in situ industrial applications. To minimize the environmental and mechanical effects, a new interferometric displacement measuring system with the common-optical-path structure and the resistance to tilt-angle is proposed. With the integration of optomechatronic modules in the novel interferometric system, the resolution up to picometer order, high precision, and ultra large measuring range have been realized. For the signal stabilization of displacement measurement, an automatic gain control module has been proposed. A self-developed interpolation model has been employed for enhancing the resolution. The novel interferometer can hold the advantage of high resolution and large measuring range simultaneously. By the experimental verifications, it has been proven that the actual resolution of 2.5 nm can be achieved in the measuring range of 500 mm. According to the comparison experiments, the maximal standard deviation of the difference between the self-developed Fabry-Perot interferometer and the reference commercial Michelson interferometer is 0.146 μm in the traveling range of 500 mm. With the prominent measuring characteristics, this should be the largest dynamic measurement range of a Fabry-Perot interferometer up till now.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.60.Ly Interferometers

Absolute photo-destruction and photo-fragmentation cross section measurements using an electrostatic ion beam trap

O. Aviv, B. Kafle, V. Chandrasekaran, O. Heber, M. L. Rappaport, H. Rubinstein, D. Schwalm, D. Strasser, Y. Toker, and D. Zajfman

Rev. Sci. Instrum. 84, 053106 (2013); http://dx.doi.org/10.1063/1.4804646 (10 pages)

Online Publication Date: 15 May 2013

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We describe a technique to measure absolute photo-induced cross sections for cluster anions stored in an electrostatic ion beam trap (EIBT) with a central deflector. The setup allows determination of total photo-destruction cross sections as well as partial cross sections for fragmentation and electron detachment. The unique properties of this special EIBT setup are investigated and illustrated using small Al n− clusters.
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33.80.Eh Autoionization, photoionization, and photodetachment
37.10.Ty Ion trapping
36.40.Wa Charged clusters
36.40.Qv Stability and fragmentation of clusters
back to top Particle Sources, Optics and Acceleration; Particle Detectors

Generation of first hard X-ray pulse at Tsinghua Thomson Scattering X-ray Source

Yingchao Du (杜应超), Lixin Yan (颜立新), Jianfei Hua (华剑飞), Qiang Du (杜强), Zhen Zhang (张振), Renkai Li (李任恺), Houjun Qian (钱厚俊), Wenhui Huang (黄文会), Huaibi Chen (陈怀璧), and Chuanxiang Tang (唐传祥)

Rev. Sci. Instrum. 84, 053301 (2013); http://dx.doi.org/10.1063/1.4803671 (7 pages)

Online Publication Date: 8 May 2013

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Tsinghua Thomson Scattering X-ray Source (TTX) is the first-of-its-kind dedicated hard X-ray source in China based on the Thomson scattering between a terawatt ultrashort laser and relativistic electron beams. In this paper, we report the experimental generation and characterization of the first hard X-ray pulses (51.7 keV) via head-on collision of an 800 nm laser and 46.7 MeV electron beams. The measured yield is 1.0 × 106 per pulse with an electron bunch charge of 200 pC and laser pulse energy of 300 mJ. The angular intensity distribution and energy spectra of the X-ray pulse are measured with an electron-multiplying charge-coupled device using a CsI scintillator and silicon attenuators. These measurements agree well with theoretical and simulation predictions. An imaging test using the X-ray pulse at the TTX is also presented.
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07.85.-m X- and γ-ray instruments
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
41.75.Ht Relativistic electron and positron beams
42.55.Vc X- and γ-ray lasers
85.30.Tv Field effect devices

Thomson spectrometer–microchannel plate assembly calibration for MeV-range positive and negative ions, and neutral atoms

R. Prasad, F. Abicht, M. Borghesi, J. Braenzel, P. V. Nickles, G. Priebe, M. Schnürer, and S. Ter-Avetisyan

Rev. Sci. Instrum. 84, 053302 (2013); http://dx.doi.org/10.1063/1.4803670 (6 pages)

Online Publication Date: 9 May 2013

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We report on the absolute calibration of a microchannel plate (MCP) detector, used in conjunction with a Thomson parabola spectrometer. The calibration delivers the relation between a registered count numbers in the CCD camera (on which the MCP phosphor screen is imaged) and the number of ions incident on MCP. The particle response of the MCP is evaluated for positive, negative, and neutral particles at energies below 1 MeV. As the response of MCP depends on the energy and the species of the ions, the calibration is fundamental for the correct interpretation of the experimental results. The calibration method and arrangement exploits the unique emission symmetry of a specific source of fast ions and atoms driven by a high power laser.
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42.79.Pw Imaging detectors and sensors
06.20.fb Standards and calibration
29.40.Gx Tracking and position-sensitive detectors
29.30.-h Spectrometers and spectroscopic techniques
back to top Nuclear Physics, Fusion and Plasmas

Development of the gas-puff imaging diagnostic in the TEXTOR tokamak

I. Shesterikov, Y. Xu, M. Berte, P. Dumortier, M. Van Schoor, M. Vergote, B. Schweer, and G. Van Oost

Rev. Sci. Instrum. 84, 053501 (2013); http://dx.doi.org/10.1063/1.4803934 (11 pages)

Online Publication Date: 9 May 2013

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Gas puff imaging (GPI) [S. J. Zweben, D. P. Stotler et al., Phys. Plasmas 9, 1981 (2002)10.1063/1.1445179; R. J. Maqueda, G. A. Wurden et al., Rev. Sci. Instrum. 74, 2020 (2003)10.1063/1.1535249] is a powerful diagnostic that permits a two-dimensional measurement of turbulence in the edge region of a fusion plasma and is based on the observation of the local emission of a neutral gas, actively puffed into the periphery of the plasma. The developed in-vessel GPI telescope observes the emission from the puffed gas along local (at the puff) magnetic field lines. The GPI telescope is specially designed to operate in severe TEXTOR conditions and can be treated as a prototype for the GPI systems on next generation machines. Also, the gas puff nozzle is designed to have a lower divergence of the gas flow than previous GPI diagnostics. The resulting images show poloidally and radially propagating structures, which are associated with plasma blobs. We demonstrate that the local gas puff does not disturb plasma properties. Our results indicate also that the neutral gas emission intensity is more sensitive to the electron density than the electron temperature. Here, we present implementation details of the GPI system on TEXTOR and discuss some design and diagnostic issues related to the development of GPI systems in general.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.55.Fa Tokamaks, spherical tokamaks
52.35.Ra Plasma turbulence

Data processing and analysis of the imaging Thomson scattering diagnostic system on HT-7 tokamak

Xiaofeng Han, Chunqiang Shao, Xiaoqi Xi, Junyu Zhao, Zang Qing, Jianhua Yang, Xingxing Dai, and Kado Shinichiro

Rev. Sci. Instrum. 84, 053502 (2013); http://dx.doi.org/10.1063/1.4804161 (5 pages)

Online Publication Date: 15 May 2013

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A high spatial resolution imaging Thomson scattering diagnostic system was developed in ASIPP (Institute of Plasma Physics, Chinese Academy of Sciences). After about one month trial running on the superconducting HT-7 (Hefei Tokamak-7) tokamak, the system was proved to be capable of measuring plasma electron temperature. The system setup and data calibration are described in this paper and then the instrument function is studied in detail, as well as the measurement capability, an electron temperature of 50 eV to 2 keV and density beyond 1 × 1019 m−3. Finally, the data processing method and experimental results are presented.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.55.Fa Tokamaks, spherical tokamaks
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.-b Plasma properties

Hard x-ray tomographic studies of the destruction of an energetic electron ring

Y. Wang, W. Gekelman, and P. Pribyl

Rev. Sci. Instrum. 84, 053503 (2013); http://dx.doi.org/10.1063/1.4804354 (10 pages)

Online Publication Date: 15 May 2013

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A tomography system was designed and built at the Large Plasma Device to measure the spatial distribution of hard x-ray (100 KeV-3 MeV) emissivity. The x-rays were generated when a hot electron ring was significantly disrupted by a shear Alfvén wave. The plasma is pulsed at 1 Hz (1 shot/s). A lead shielded scintillator detector with an acceptance angle defined by a lead pinhole is mounted on a rotary gimbal and used to detect the x-rays. The system measures one chord per plasma shot using only one detector. A data plane usually consists of several hundred chords. A novel Dot by Dot Reconstruction (DDR) method is introduced to calculate the emissivity profile from the line integrated data. In the experiments, there are often physical obstructions, which make measurements at certain angles impossible. The DDR method works well even in this situation. The method was tested with simulated data, and was found to be more effective than previously published methods for the specific geometry of this experiment. The reconstructed x-ray emissivity from experimental data by this method is shown.
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07.85.Tt X-ray microscopes
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
back to top Microscopy and Imaging

Simultaneous immersion Mirau interferometry

Oleksandra V. Lyulko, Gerhard Randers-Pehrson, and David J. Brenner

Rev. Sci. Instrum. 84, 053701 (2013); http://dx.doi.org/10.1063/1.4803181 (6 pages)

Online Publication Date: 3 May 2013

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A novel technique for label-free imaging of live biological cells in aqueous medium that is insensitive to ambient vibrations is presented. This technique is a spin-off from previously developed immersion Mirau interferometry. Both approaches utilize a modified Mirau interferometric attachment for a microscope objective that can be used both in air and in immersion mode, when the device is submerged in cell medium and has its internal space filled with liquid. While immersion Mirau interferometry involves first capturing a series of images, the resulting images are potentially distorted by ambient vibrations. Overcoming these serial-acquisition challenges, simultaneous immersion Mirau interferometry incorporates polarizing elements into the optics to allow simultaneous acquisition of two interferograms. The system design and production are described and images produced with the developed techniques are presented.
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87.64.M- Optical microscopy
07.60.Ly Interferometers
42.25.Ja Polarization

Wide-area scanner for high-speed atomic force microscopy

Hiroki Watanabe, Takayuki Uchihashi, Toshihide Kobashi, Mikihiro Shibata, Jun Nishiyama, Ryohei Yasuda, and Toshio Ando

Rev. Sci. Instrum. 84, 053702 (2013); http://dx.doi.org/10.1063/1.4803449 (10 pages)

Online Publication Date: 3 May 2013

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multimedia

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High-speed atomic force microscopy (HS-AFM) has recently been established. The dynamic processes and structural dynamics of protein molecules in action have been successfully visualized using HS-AFM. However, its maximum scan ranges in the X- and Y-directions have been limited to ∼1 μm and ∼4 μm, respectively, making it infeasible to observe the dynamics of much larger samples, including live cells. Here, we develop a wide-area scanner with a maximum XY scan range of ∼46 × 46 μm2 by magnifying the displacements of stack piezoelectric actuators using a leverage mechanism. Mechanical vibrations produced by fast displacement of the X-scanner are suppressed by a combination of feed-forward inverse compensation and the use of triangular scan signals with rounded vertices. As a result, the scan speed in the X-direction reaches 6.3 mm/s even for a scan size as large as ∼40 μm. The nonlinearity of the X- and Y-piezoelectric actuators’ displacements that arises from their hysteresis is eliminated by polynomial-approximation-based open-loop control. The interference between the X- and Y-scanners is also eliminated by the same technique. The usefulness of this wide-area scanner is demonstrated by video imaging of dynamic processes in live bacterial and eukaryotic cells.
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07.79.Lh Atomic force microscopes

Differential interference contrast microscopy using light-emitting diode illumination in conjunction with dual optical traps

C. Battle, L. Lautscham, and C. F. Schmidt

Rev. Sci. Instrum. 84, 053703 (2013); http://dx.doi.org/10.1063/1.4804597 (5 pages)

Online Publication Date: 16 May 2013

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Differential interference contrast (DIC) microscopy is a common mode of biological light microscopy used to achieve maximal resolution and contrast with label-free, weakly absorbing specimens such as cells. Maintaining the polarization state of the illuminating light is essential for the technique, and this requirement can conflict with optical trapping. We describe how to optimize DIC imaging using a light-emitting diode illumination source in a microscope while integrating a dual optical trap into the set up. Every time a polarized light beam reflects off or transmits through a dichroic mirror in the beam path, its polarization state will change if it is not polarized exactly parallel (p) or perpendicular (s) to the plane of incidence. We observe wavelength-dependent optical rotation and depolarization effects in our illumination light upon reflection from/transmission through dichroic mirrors in the beam path, resulting in significant degradation of image quality. We describe a method to compensate for these effects by introducing quarter-waveplates and a laser clean-up filter into the imaging pathway. We show that this approach achieves a full recovery of image quality.
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87.80.Cc Optical trapping
07.60.Pb Conventional optical microscopes
87.64.M- Optical microscopy
42.79.Ci Filters, zone plates, and polarizers

Theoretical and experimental study on two-stage-imaging microscopy using ellipsometric contrast for real-time visualization of molecularly thin films

Y. Kajihara, K. Fukuzawa, S. Itoh, R. Watanabe, and H. Zhang

Rev. Sci. Instrum. 84, 053704 (2013); http://dx.doi.org/10.1063/1.4804633 (9 pages)

Online Publication Date: 16 May 2013

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A two-stage-imaging ellipsometric-contrast microscope (TIEM) has been developed to measure the distribution of film thickness over a wide area of molecularly thin liquid films with a high lateral resolution, wide field of view, high thickness resolution, and high-speed. Moreover, this ellipsometric microscope enables us to achieve simultaneous measurements with other measurement apparatuses. We present the principle used to parallelize an object image to an imaging sensor and to reduce the incident angle entering the imaging sensor. In addition, we discuss the characteristic shape deformation of the object image due to oblique observation. The performance of the actual setup for TIEM was experimentally studied. A lateral resolution of about 1 μm was obtained by measuring the modulation transfer function of the TIEM. We also found that the shape deformation approximately agreed with that from theory. Furthermore, for molecularly thin films, we confirmed linearity between the film thickness and the light intensity measured with TIEM, which enables us to quantify the thickness of the films. TIEM can open up a new field of real-time imaging of thin films such as visualization of a liquid lubricant film under shear.
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07.60.Fs Polarimeters and ellipsometers
07.60.Pb Conventional optical microscopes
42.79.Pw Imaging detectors and sensors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.30.Lr Modulation and optical transfer functions
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
back to top Condensed Matter; Materials

Relaxation calorimeter for hydrogen thermoporometry

E. Van Cleve, M. A. Worsley, and S. O. Kucheyev

Rev. Sci. Instrum. 84, 053901 (2013); http://dx.doi.org/10.1063/1.4803180 (6 pages)

Online Publication Date: 3 May 2013

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A relaxation calorimeter for measuring the heat capacity of hydrogen isotopes in nanoporous solids is described. Apparatus’ features include (i) cooling by a pulse tube refrigerator, (ii) a modular design, allowing for rapid reconfiguration and sample turn around, (iii) a thermal stability of ≲1 mK, and (iv) a bottom temperature of ∼5 K. The calorimeter is tested on effective heat capacity measurements of H2 in Vycor (silica) nanoporous glass, yielding a very detailed pore size distribution analysis with an effectively sub-Angstrom resolution.
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07.20.Fw Calorimeters
61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Quantum state-resolved gas/surface reaction dynamics probed by reflection absorption infrared spectroscopy

Li Chen, Hirokazu Ueta, Régis Bisson, and Rainer D. Beck

Rev. Sci. Instrum. 84, 053902 (2013); http://dx.doi.org/10.1063/1.4803933 (9 pages)

Online Publication Date: 9 May 2013

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We report the design and characterization of a new molecular-beam/surface-science apparatus for quantum state-resolved studies of gas/surface reaction dynamics combining optical state-specific reactant preparation in a molecular beam by rapid adiabatic passage with detection of surface-bound reaction products by reflection absorption infrared spectroscopy (RAIRS). RAIRS is a non-invasive infrared spectroscopic detection technique that enables online monitoring of the buildup of reaction products on the target surface during reactant deposition by a molecular beam. The product uptake rate obtained by calibrated RAIRS detection yields the coverage dependent state-resolved reaction probability S(θ). Furthermore, the infrared absorption spectra of the adsorbed products obtained by the RAIRS technique provide structural information, which help to identify nascent reaction products, investigate reaction pathways, and determine branching ratios for different pathways of a chemisorption reaction. Measurements of the dissociative chemisorption of methane on Pt(111) with this new apparatus are presented to illustrate the utility of RAIRS detection for highly detailed studies of chemical reactions at the gas/surface interface.
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07.77.Gx Atomic and molecular beam sources and detectors
02.50.Cw Probability theory
81.70.Fy Nondestructive testing: optical methods

Numerical simulation and experiment on multilayer stagger-split die

Zhiwei Liu, Mingzhe Li, Qigang Han, Yunfei Yang, Bolong Wang, and Zhou Sui

Rev. Sci. Instrum. 84, 053903 (2013); http://dx.doi.org/10.1063/1.4804159 (6 pages)

Online Publication Date: 9 May 2013

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A novel ultra-high pressure device, multilayer stagger-split die, has been constructed based on the principle of “dividing dies before cracking.” Multilayer stagger-split die includes an encircling ring and multilayer assemblages, and the mating surfaces of the multilayer assemblages are mutually staggered between adjacent layers. In this paper, we investigated the stressing features of this structure through finite element techniques, and the results were compared with those of the belt type die and single split die. The contrast experiments were also carried out to test the bearing pressure performance of multilayer stagger-split die. It is concluded that the stress distributions are reasonable and the materials are utilized effectively for multilayer stagger-split die. And experiments indicate that the multilayer stagger-split die can bear the greatest pressure.
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07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
02.70.Dh Finite-element and Galerkin methods

Sensitive thermal transitions of nanoscale polymer samples using the bimetallic effect: Application to ultra-thin polythiophene

O. Ahumada, M. M. Pérez-Madrigal, J. Ramirez, D. Curcó, C. Esteves, A. Salvador-Matar, G. Luongo, E. Armelin, J. Puiggalí, and C. Alemán

Rev. Sci. Instrum. 84, 053904 (2013); http://dx.doi.org/10.1063/1.4804395 (8 pages)

Online Publication Date: 15 May 2013

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A sensitive nanocalorimetric technology based on microcantilever sensors is presented. The technology, which combines very short response times with very small sample consumption, uses the bimetallic effect to detect thermal transitions. Specifically, abrupt variations in the Young's modulus and the thermal expansion coefficient produced by temperature changes have been employed to detect thermodynamic transitions. The technology has been used to determine the glass transition of poly(3-thiophene methyl acetate), a soluble semiconducting polymer with different nanotechnological applications. The glass transition temperature determined using microcantilevers coated with ultra-thin films of mass = 10−13 g is 5.2 °C higher than that obtained using a conventional differential scanning calorimeter for bulk powder samples of mass = 5 × 10−3 g. Atomistic molecular dynamics simulations on models that represent the bulk powder and the ultra-thin films have been carried out to provide understanding and rationalization of this feature. Simulations indicate that the film-air interface plays a crucial role in films with very small thickness, affecting both the organization of the molecular chains and the response of the molecules against the temperature.
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64.70.pj Polymers
61.43.Bn Structural modeling: serial-addition models, computer simulation
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.25.-g Mechanical properties of nanoscale systems
68.60.Bs Mechanical and acoustical properties

Development and application of an instrument for spatially resolved Seebeck coefficient measurements

Andriy Zakutayev, Frank J. Luciano, IV, Vincent P. Bollinger, Ajaya K. Sigdel, Paul F. Ndione, John D. Perkins, Joseph J. Berry, Philip A. Parilla, and David S. Ginley

Rev. Sci. Instrum. 84, 053905 (2013); http://dx.doi.org/10.1063/1.4804634 (9 pages)

Online Publication Date: 17 May 2013

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The Seebeck coefficient is a key indicator of the majority carrier type (electrons or holes) in a material. The recent trend toward the development of combinatorial materials research methods has necessitated the development of a new high-throughput approach to measuring the Seebeck coefficient at spatially distinct points across any sample. The overall strategy of the high-throughput experiments is to quickly identify the region of interest on the sample at some expense of accuracy, and then study this region by more conventional techniques. The instrument for spatially resolved Seebeck coefficient measurements reported here relies on establishing a temperature difference across the entire compositionally graded thin-film and consecutive mapping of the resulting voltage as a function of position, which facilitates the temperature-dependent measurements up to 400 °C. The results of the designed instrument are verified at ambient temperature to be repeatable over 10 identical samples and accurate to within 10% versus conventional Seebeck coefficient measurements over the −100 to +150 μV/K range using both n-type and p-type conductive oxides as test cases. The developed instrument was used to determine the sign of electrical carriers of compositionally graded Zn–Co–O and Ni–Co–O libraries prepared by combinatorial sputtering. As a result of this study, both cobalt-based materials were determined to have p-type conduction over a broad single-phase region of chemical compositions and small variation of the Seebeck coefficient over the entire investigated range of compositions and temperature.
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07.20.Dt Thermometers
back to top Gravity; Geophysics; Astronomy and Astrophysics

Dedicated vertical wind tunnel for the study of sedimentation of non-spherical particles

G. H. Bagheri, C. Bonadonna, I. Manzella, P. Pontelandolfo, and P. Haas

Rev. Sci. Instrum. 84, 054501 (2013); http://dx.doi.org/10.1063/1.4805019 (12 pages)

Online Publication Date: 16 May 2013

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A dedicated 4-m-high vertical wind tunnel has been designed and constructed at the University of Geneva in collaboration with the Groupe de compétence en mécanique des fluides et procédés énergétiques. With its diverging test section, the tunnel is designed to study the aero-dynamical behavior of non-spherical particles with terminal velocities between 5 and 27 ms−1. A particle tracking velocimetry (PTV) code is developed to calculate drag coefficient of particles in standard conditions based on the real projected area of the particles. Results of our wind tunnel and PTV code are validated by comparing drag coefficient of smooth spherical particles and cylindrical particles to existing literature. Experiments are repeatable with average relative standard deviation of 1.7%. Our preliminary experiments on the effect of particle to fluid density ratio on drag coefficient of cylindrical particles show that the drag coefficient of freely suspended particles in air is lower than those measured in water or in horizontal wind tunnels. It is found that increasing aspect ratio of cylindrical particles reduces their secondary motions and they tend to be suspended with their maximum area normal to the airflow. The use of the vertical wind tunnel in combination with the PTV code provides a reliable and precise instrument for measuring drag coefficient of freely moving particles of various shapes. Our ultimate goal is the study of sedimentation and aggregation of volcanic particles (density between 500 and 2700 kgm−3) but the wind tunnel can be used in a wide range of applications.
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47.55.Ca Gas/liquid flows
47.57.eb Diffusion and aggregation
47.57.ef Sedimentation and migration
47.80.Jk Flow visualization and imaging
82.70.Kj Emulsions and suspensions
47.40.-x Compressible flows; shock waves
back to top Electronics; Electromagnetic Technology; Microwaves

High-temperature superconducting radiofrequency probe for magnetic resonance imaging applications operated below ambient pressure in a simple liquid-nitrogen cryostat

Simon Lambert, Jean-Christophe Ginefri, Marie Poirier-Quinot, and Luc Darrasse

Rev. Sci. Instrum. 84, 054701 (2013); http://dx.doi.org/10.1063/1.4802947 (7 pages)

Online Publication Date: 2 May 2013

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The present work investigates the joined effects of temperature and static magnetic field on the electrical properties of a 64 MHz planar high-temperature superconducting (HTS) coil, in order to enhance the signal-to-noise ratio (SNR) in nuclear magnetic resonance (NMR) applications with a moderate decrease of the HTS coil temperature (THTS). Temperature control is provided with accuracy better than 0.1 K from 80 to 66 K by regulating the pressure of the liquid nitrogen bath of a dedicated cryostat. The actual temperature of the HTS coil is obtained using a straightforward wireless method that eliminates the risks of coupling electromagnetic interference to the HTS coil and of disturbing the static magnetic field by DC currents near the region of interest. The resonance frequency ( f0) and the quality factor (Q) of the HTS coil are measured as a function of temperature in the 0‑4.7 T field range with parallel and orthogonal orientations relative to the coil plane. The intrinsic HTS coil sensitivity and the detuning effect are then analyzed from the Q and f0 data. In the presence of the static magnetic field, the initial value of f0 in Earth's field could be entirely recovered by decreasing THTS, except for the orthogonal orientation above 1 T. The improvement of Q by lowering THTS was substantial. From 80 to 66 K, Q was multiplied by a factor of 6 at 1.5 T in orthogonal orientation. In parallel orientation, the maximum measured improvement of Q from 80 K to 66 K was a factor of 2. From 80 to 66 K, the improvement of the RF sensitivity relative to the initial value at the Earth's field and ambient pressure was up to 4.4 dB in parallel orientation. It was even more important in orthogonal orientation and continued to increase, up to 8.4 dB, at the maximum explored field of 1.5 T. Assuming that the noise contributions from the RF receiver are negligible, the SNR improvement using enhanced HTS coil cooling in NMR experiments was extracted from Q measurements either with or without the presence of the sample. Notably, the additional cooling in the presence of conductive samples appears more beneficial at higher field strengths and with an orthogonal incidence than with parallel. The temperature range accessible here, involving a relatively straightforward cryogenic design, brings a gain in RF sensitivity that is of great significance to cutting-edge applications with very weakly conducting samples, small biological specimens, or small animals in vivo. This work also demonstrates a better tolerance to thin-film orientation misalignments relative to the magnetic field, and this could eventually play a role in designing effective non-planar HTS coils or coil arrays which include elements of various orientations. Finally, the data provided in this work may help understand some critical aspects in the design of HTS coils for NMR and MRI applications and accounts for the presence of the static magnetic field, particularly regarding the SNR loss due to a decreased quality factor and detuning issues.
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84.71.Ba Superconducting magnets; magnetic levitation devices
85.25.Am Superconducting device characterization, design, and modeling
87.61.Ff Instrumentation
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
84.30.-r Electronic circuits

A digital magnetic resonance imaging spectrometer using digital signal processor and field programmable gate array

Xiao Liang, Sun Binghe, Ma Yueping, and Zhao Ruyan

Rev. Sci. Instrum. 84, 054702 (2013); http://dx.doi.org/10.1063/1.4803007 (8 pages)

Online Publication Date: 2 May 2013

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A digital spectrometer for low-field magnetic resonance imaging is described. A digital signal processor (DSP) is utilized as the pulse programmer on which a pulse sequence is executed as a subroutine. Field programmable gate array (FPGA) devices that are logically mapped into the external addressing space of the DSP work as auxiliary controllers of gradient control, radio frequency (rf) generation, and rf receiving separately. The pulse programmer triggers an event by setting the 32-bit control register of the corresponding FPGA, and then the FPGA automatically carries out the event function according to preset configurations in cooperation with other devices; accordingly, event control of the spectrometer is flexible and efficient. Digital techniques are in widespread use: gradient control is implemented in real-time by a FPGA; rf source is constructed using direct digital synthesis technique, and rf receiver is constructed using digital quadrature detection technique. Well-designed performance is achieved, including 1 μs time resolution of the gradient waveform, 1 μs time resolution of the soft pulse, and 2 MHz signal receiving bandwidth. Both rf synthesis and rf digitalization operate at the same 60 MHz clock, therefore, the frequency range of transmitting and receiving is from DC to ∼27 MHz. A majority of pulse sequences have been developed, and the imaging performance of the spectrometer has been validated through a large number of experiments. Furthermore, the spectrometer is also suitable for relaxation measurement in nuclear magnetic resonance field.
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87.61.Ff Instrumentation
02.30.-f Function theory, analysis
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
84.30.Sk Pulse and digital circuits

All solid-state high power microwave source with high repetition frequency

J.-W. B. Bragg, W. W. Sullivan, III, D. Mauch, A. A. Neuber, and J. C. Dickens

Rev. Sci. Instrum. 84, 054703 (2013); http://dx.doi.org/10.1063/1.4804196 (7 pages)

Online Publication Date: 9 May 2013

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An all solid-state, megawatt-class high power microwave system featuring a silicon carbide (SiC) photoconductive semiconductor switch (PCSS) and a ferrimagnetic-based, coaxial nonlinear transmission line (NLTL) is presented. A 1.62 cm2, 50 kV 4H-SiC PCSS is hard-switched to produce electrical pulses with 7 ns full width-half max (FWHM) pulse widths at 2 ns risetimes in single shot and burst-mode operation. The PCSS resistance drops to sub-ohm when illuminated with approximately 3 mJ of laser energy at 355 nm (tripled Nd:YAG) in a single pulse. Utilizing a fiber optic based optical delivery system, a laser pulse train of four 7 ns (FWHM) signals was generated at 65 MHz repetition frequency. The resulting electrical pulse train from the PCSS closely follows the optical input and is utilized to feed the NLTL generating microwave pulses with a base microwave-frequency of about 2.1 GHz at 65 MHz pulse repetition frequency (prf). Under typical experimental conditions, the NLTL produces sharpened output risetimes of 120 ps and microwave oscillations at 2–4 GHz that are generated due to damped gyromagnetic precession of the ferrimagnetic material's axially pre-biased magnetic moments. The complete system is discussed in detail with its output matched into 50 Ω, and results covering MHz-prf in burst-mode operation as well as frequency agility in single shot operation are discussed.
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85.60.-q Optoelectronic devices

Measurement of ultra-low power oscillators using adaptive drift cancellation with applications to nano-magnetic spin torque oscillators

S. Tamaru and D. S. Ricketts

Rev. Sci. Instrum. 84, 054704 (2013); http://dx.doi.org/10.1063/1.4804650 (7 pages)

Online Publication Date: 15 May 2013

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This work presents a technique for measuring ultra-low power oscillator signals using an adaptive drift cancellation method. We demonstrate this technique through spectrum measurements of a sub-pW nano-magnet spin torque oscillator (STO). We first present a detailed noise analysis of the standard STO characterization apparatus to estimate the background noise level, then compare these results to the noise level of three measurement configurations. The first and second share the standard configuration but use different spectrum analyzers (SA), an older model and a state-of-the-art model, respectively. The third is the technique proposed in this work using the same old SA as for the first. Our results show that the first and second configurations suffer from a large drift that requires ∼30 min to stabilize each time the SA changes the frequency band, even though the SA has been powered on for longer than 24 h. The third configuration introduced in this work, however, shows absolutely no drift as the SA changes frequency band, and nearly the same noise performance as with a state-of-the-art SA, thus providing a reliable method for measuring very low power signals for a wide variety of applications.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
84.30.Ng Oscillators, pulse generators, and function generators
07.10.Pz Instruments for strain, force, and torque
85.70.-w Magnetic devices
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
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