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Feb 2013

Volume 84, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 84, 021101 (2013); http://dx.doi.org/10.1063/1.4789314 (14 pages)

Alexey Goncharov

Typical permanent magnet electrostatic plasma lens, characteristically about 15 cm long and 10 cm inner diameter. The magnets are shown in black between grey spacers. A set of cylindrical ring electrodes are located within the magnetic field region, with field lines connecting ring electrode pairs symmetrically about the lens midplane.

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back to top Nuclear Physics, Fusion and Plasmas

Pure ion current collection in ion sensitive probe measurement with a metal mesh guard electrode for evaluation of ion temperature in magnetized plasma

Tung-Yuan Hsieh, Eiichirou Kawamori, and Yasushi Nishida

Rev. Sci. Instrum. 84, 023502 (2013); http://dx.doi.org/10.1063/1.4790175 (4 pages) | Cited 1 time

Online Publication Date: 6 February 2013

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This paper presents a new design of ion sensitive probe (ISP) that enables collection of pure ion current for accurate measurement of the perpendicular ion temperature in magnetized plasmas. The new type of ISP resolves a longstanding issue widely observed in ISP type measurements, namely, that the current-voltage characteristic is smeared by an unexpected electron current in the standard ISP model. The new ISP is equipped with a fine scale metal mesh on the sensor entrance to prevent electrons from flowing to the sensor, a phenomenon considered to be caused by the space-charge effect. The new ISP successfully measured the ion temperature of electron cyclotron resonance plasmas.
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52.70.Ds Electric and magnetic measurements
07.20.Dt Thermometers

Core-ion temperature measurement of the ADITYA tokamak using passive charge exchange neutral particle energy analyzer

Santosh P. Pandya, Kumar Ajay, Priyanka Mishra, Rajani D. Dhingra, and J. Govindarajan

Rev. Sci. Instrum. 84, 023503 (2013); http://dx.doi.org/10.1063/1.4791998 (9 pages)

Online Publication Date: 20 February 2013

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Core-ion temperature measurements have been carried out by the energy analysis of passive charge exchange (CX) neutrals escaping out of the ADITYA tokamak plasma (minor radius, a = 25 cm and major radius, R = 75 cm) using a 45° parallel plate electrostatic energy analyzer. The neutral particle analyzer (NPA) uses a gas cell configuration for re-ionizing the CX-neutrals and channel electron multipliers (CEMs) as detectors. Energy calibration of the NPA has been carried out using ion-source and ΔE/E of high-energy channel has been found to be ∼10%. Low signal to noise ratio (SNR) due to VUV reflections on the CEMs was identified during the operation of the NPA with ADITYA plasma discharges. This problem was rectified by upgrading the system by incorporating the additional components and arrangements to suppress VUV radiations and improve its VUV rejection capabilities. The noise rejection capability of the NPA was experimentally confirmed using a standard UV-source and also during the plasma discharges to get an adequate SNR (>30) at the energy channels. Core-ion temperature Ti(0) during flattop of the plasma current has been measured to be up to 150 eV during ohmically heated plasma discharges which is nearly 40% of the average core-electron temperature (typically Te(0) ∼ 400 eV). The present paper describes the principle of tokamak ion temperature measurement, NPA's design, development, and calibration along with the modifications carried out for minimizing the interference of plasma radiations in the CX-spectrum. Performance of the NPA during plasma discharges and experimental results on the measurement of ion-temperature have also been reported here.
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52.70.-m Plasma diagnostic techniques and instrumentation
52.25.Ya Neutrals in plasmas
52.55.Fa Tokamaks, spherical tokamaks
07.20.Ka High-temperature instrumentation; pyrometers
07.20.Dt Thermometers

Identification and control of plasma vertical position using neural network in Damavand tokamak

H. Rasouli, C. Rasouli, and A. Koohi

Rev. Sci. Instrum. 84, 023504 (2013); http://dx.doi.org/10.1063/1.4791925 (12 pages)

Online Publication Date: 21 February 2013

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In this work, a nonlinear model is introduced to determine the vertical position of the plasma column in Damavand tokamak. Using this model as a simulator, a nonlinear neural network controller has been designed. In the first stage, the electronic drive and sensory circuits of Damavand tokamak are modified. These circuits can control the vertical position of the plasma column inside the vacuum vessel. Since the vertical position of plasma is an unstable parameter, a direct closed loop system identification algorithm is performed. In the second stage, a nonlinear model is identified for plasma vertical position, based on the multilayer perceptron (MLP) neural network (NN) structure. Estimation of simulator parameters has been performed by back-propagation error algorithm using Levenberg–Marquardt gradient descent optimization technique. The model is verified through simulation of the whole closed loop system using both simulator and actual plant in similar conditions. As the final stage, a MLP neural network controller is designed for simulator model. In the last step, online training is performed to tune the controller parameters. Simulation results justify using of the NN controller for the actual plant.
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52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation
07.05.Dz Control systems
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

2D divertor heat flux distribution using a 3D heat conduction solver in National Spherical Torus Experiment

K. F. Gan, J-W. Ahn, J.-W. Park, R. Maingi, A. G. McLean, T. K. Gray, X. Gong, and X. D. Zhang

Rev. Sci. Instrum. 84, 023505 (2013); http://dx.doi.org/10.1063/1.4792595 (8 pages)

Online Publication Date: 21 February 2013

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The divertor heat flux footprint in tokamaks is often observed to be non-axisymmetric due to intrinsic error fields, applied 3D magnetic fields or during transients such as edge localized modes. Typically, only 1D radial heat flux profiles are analyzed; however, analysis of the full 2D divertor measurements provides opportunities to study the asymmetric nature of the deposited heat flux. To accomplish this an improved 3D Fourier analysis method has been successfully applied in a heat conduction solver (TACO) to determine the 2D heat flux distribution at the lower divertor surface in the National Spherical Torus Experiment (NSTX) tokamak. This advance enables study of helical heat deposition onto the divertor. In order to account for heat transmission through poorly adhered surface layers on the divertor plate, a heat transmission coefficient, defined as the surface layer thermal conductivity divided by the thickness of the layer, was introduced to the solution of heat conduction equation. This coefficient is denoted as α and a range of values were tested in the model to ensure a reliable heat flux calculation until a specific value of α led to the constant total deposited energy in the numerical solution after the end of discharge. A comparison between 1D heat flux profiles from TACO and from a 2D heat flux calculation code, THEODOR, shows good agreement. Advantages of 2D heat flux distribution over the conventional 1D heat flux profile are also discussed, and examples of 2D data analysis in the study of striated heat deposition pattern as well as the toroidal degree of asymmetry of peak heat flux and heat flux width are demonstrated.
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28.52.Fa Materials
52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation
02.30.Nw Fourier analysis

Performance of an inverted ion source

M. C. Salvadori, F. S. Teixeira, L. G. Sgubin, W. W. R. Araujo, R. E. Spirin, E. M. Oks, and I. G. Brown

Rev. Sci. Instrum. 84, 023506 (2013); http://dx.doi.org/10.1063/1.4793377 (5 pages)

Online Publication Date: 27 February 2013

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Whereas energetic ion beams are conventionally produced by extracting ions (say, positive ions) from a plasma that is held at high (positive) potential, with ion energy determined by the potential drop through which the ions fall in the beam formation electrode system, in the device described here the plasma and its electronics are held at ground potential and the ion beam is formed and injected energetically into a space maintained at high (negative) potential. We refer to this configuration as an “inverted ion source.” This approach allows considerable savings both technologically and economically, rendering feasible some ion beam applications, in particular small-scale ion implantation, that might otherwise not be possible for many researchers and laboratories. We have developed a device of this kind utilizing a metal vapor vacuum arc plasma source, and explored its operation and beam characteristics over a range of parameter variation. The downstream beam current has been measured as a function of extraction voltage (5–35 kV), arc current (50–230 A), metal ion species (Ti, Nb, Au), and extractor grid spacing and beamlet aperture size (3, 4, and 5 mm). The downstream ion beam current as measured by a magnetically-suppressed Faraday cup was up to as high as 600 mA, and with parametric variation quite similar to that found for the more conventional metal vapor vacuum arc ion source.
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52.50.Dg Plasma sources
29.25.Ni Ion sources: positive and negative

Development of a polarization resolved spectroscopic diagnostic for measurements of the vector magnetic field in the Caltech coaxial magnetized plasma jet experiment

T. Shikama and P. M. Bellan

Rev. Sci. Instrum. 84, 023507 (2013); http://dx.doi.org/10.1063/1.4793403 (7 pages)

Online Publication Date: 28 February 2013

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In the Caltech coaxial magnetized plasma jet experiment, fundamental studies are carried out relevant to spheromak formation, astrophysical jet formation/propagation, solar coronal physics, and the general behavior of twisted magnetic flux tubes that intercept a boundary. In order to measure the spatial profile of the magnetic field vector for understanding the underlying physics governing the dynamical behavior, a non-perturbing visible emission spectroscopic method is implemented to observe the Zeeman splitting in emission spectra. We have designed and constructed a polarization-resolving optical system that can simultaneously detect the left- and right-circularly polarized emission. The system is applied to singly ionized nitrogen spectral lines. The magnetic field strength is measured with a precision of about ±13 mT. The radial profiles of the azimuthal and axial vector magnetic field components are resolved by using an inversion method.
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52.75.-d Plasma devices
07.55.Ge Magnetometers for magnetic field measurements
back to top Microscopy and Imaging

A cryogenic scattering-type scanning near-field optical microscope

Honghua U. Yang, Erik Hebestreit, Erik E. Josberger, and Markus B. Raschke

Rev. Sci. Instrum. 84, 023701 (2013); http://dx.doi.org/10.1063/1.4789428 (6 pages)

Online Publication Date: 1 February 2013

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Scattering-type scanning near-field optical microscopy (s-SNOM) provides few nanometer optical spatial resolution and is compatible with nearly any form of linear and nonlinear optical spectroscopy. We have developed a versatile s-SNOM instrument operating under cryogenic and variable temperature (∼20–500 K) and compatible with high magnetic fields (up to 7 T). The instrument features independent tip and sample scanning and free-space light delivery with an integrated off-axis parabolic mirror for tip-illumination and signal collection with a numerical aperture of N.A. = 0.45. The optics operate from the UV to THz range allowing for continuous wave, broadband, and ultrafast s-SNOM spectroscopy, including different variants of tip-enhanced spectroscopy. We discuss the instrument design, implementation, and demonstrate its performance with mid-infrared Drude response s-SNOM probing of the domain formation associated with the metal-insulator transitions of VO2 (TMIT ≃ 340 K) and V2O3 (TMIT ≃ 150 K). This instrument enables the study of mesoscopic order and domains of competing quantum phases in correlated electron materials over a wide range of controlled electric and magnetic fields, strain, current, and temperature.
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07.79.Fc Near-field scanning optical microscopes
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
42.79.Bh Lenses, prisms and mirrors

Design of a high-speed electrochemical scanning tunneling microscope

Y. I. Yanson, F. Schenkel, and M. J. Rost

Rev. Sci. Instrum. 84, 023702 (2013); http://dx.doi.org/10.1063/1.4779086 (9 pages)

Online Publication Date: 5 February 2013

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In this paper, we present a bottom-up approach to designing and constructing a high-speed electrochemical scanning tunneling microscope (EC-STM). Using finite element analysis (FEA) calculations of the frequency response of the whole mechanical loop of the STM, we analyzed several geometries to find the most stable one that could facilitate fast scanning. To test the FEA results, we conducted measurements of the vibration amplitudes using a prototype STM setup. Based on the FEA analysis and the measurement results, we identified the potentially most disturbing vibration modes that could impair fast scanning. By modifying the design of some parts of the EC-STM, we reduced the amplitudes as well as increased the resonance frequencies of these modes. Additionally, we designed and constructed an electrochemical flow-cell that allows STM imaging in a flowing electrolyte, and built a bi-potentiostat to achieve electrochemical potential control during the measurements. Finally, we present STM images acquired during high-speed imaging in air as well as in an electrochemical environment using our newly-developed EC-STM.
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07.79.Cz Scanning tunneling microscopes
02.70.Dh Finite-element and Galerkin methods
07.10.-h Mechanical instruments and equipment

Calibration of measurement sensitivities of multiple micro-cantilever dynamic modes in atomic force microscopy using a contact detection method

Zhen Liu, Younkoo Jeong, and Chia-Hsiang Menq

Rev. Sci. Instrum. 84, 023703 (2013); http://dx.doi.org/10.1063/1.4790194 (9 pages)

Online Publication Date: 6 February 2013

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An accurate experimental method is proposed for on-spot calibration of the measurement sensitivities of multiple micro-cantilever dynamic modes in atomic force microscopy. One of the key techniques devised for this method is a reliable contact detection mechanism that detects the tip-surface contact instantly. At the contact instant, the oscillation amplitude of the tip deflection, converted to that of the deflection signal in laser reading through the measurement sensitivity, exactly equals to the distance between the sample surface and the cantilever base position. Therefore, the proposed method utilizes the recorded oscillation amplitude of the deflection signal and the base position of the cantilever at the contact instant for the measurement sensitivity calibration. Experimental apparatus along with various signal processing and control modules was realized to enable automatic and rapid acquisition of multiple sets of data, with which the calibration of a single dynamic mode could be completed in less than 1 s to suppress the effect of thermal drift and measurement noise. Calibration of the measurement sensitivities of the first and second dynamic modes of three micro-cantilevers having distinct geometries was successfully demonstrated. The dependence of the measurement sensitivity on laser spot location was also experimentally investigated. Finally, an experiment was performed to validate the calibrated measurement sensitivity of the second dynamic mode of a micro-cantilever.
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06.20.fb Standards and calibration
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Kirkpatrick-Baez microscope for hard X-ray imaging of fast ignition experiments

H. Friesen, H. F. Tiedje, D. S. Hey, M. Z. Mo, A. Beaudry, R. Fedosejevs, Y. Y. Tsui, A. Mackinnon, H. S. McLean, and P. K. Patel

Rev. Sci. Instrum. 84, 023704 (2013); http://dx.doi.org/10.1063/1.4776670 (8 pages)

Online Publication Date: 7 February 2013

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A Kirkpatrick-Baez X-ray microscope has been developed for use on the Titan laser facility at the Lawrence Livermore National Laboratory in Fast Ignition experiments. It was developed as a broadband alternative to narrow band Bragg crystal imagers for imaging Kα emission from tracer layers. A re-entrant design is employed which allows for alignment from outside the chamber. The mirrors are coated with Pt and operate at a grazing incident angle of 0.5° providing higher resolution than an equal brightness pinhole and sufficient bandwidth to image thermally shifted characteristic Kα emission from heated Cu tracer layers in Fast Ignition experiments. The superpolished substrates (<1 Å rms roughness) had a final visible wavelength roughness of 1.7 Å after coating, and exhibited a reflectivity corresponding to an X-ray wavelength roughness of 7 ± 1 Å. A unique feature of this design is that during experiments, the unfiltered direct signal along with the one-dimensional reflections are retained on the detector in order to enable a live indication of alignment and incident angle. The broad spectral window from 4 to 9 keV enables simultaneous observation of emission from several spectral regions of interest, which has been demonstrated to be particularly useful for cone-wire targets. An experimentally measured resolution of 15 μm has been obtained at the center of the field of view.
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52.70.La X-ray and γ-ray measurements
41.50.+h X-ray beams and x-ray optics
42.79.Bh Lenses, prisms and mirrors
42.79.Wc Optical coatings

Diagonal control design for atomic force microscope piezoelectric tube nanopositioners

B. Bhikkaji, Y. K. Yong, I. A. Mahmood, and S. O. R. Moheimani

Rev. Sci. Instrum. 84, 023705 (2013); http://dx.doi.org/10.1063/1.4790474 (8 pages)

Online Publication Date: 12 February 2013

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Atomic Force Microscopes (AFM) are used for generating surface topography of samples at micro to atomic resolutions. Many commercial AFMs use piezoelectric tube nanopositioners for scanning. Scanning rates of these microscopes are hampered by the presence of low frequency resonant modes. When inadvertently excited, these modes lead to high amplitude mechanical vibrations causing the loss of accuracy, while scanning, and eventually to break down of the tube. Feedback control has been used to damp these resonant modes. Thereby, enabling higher scanning rates. Here, a multivariable controller is designed to damp the first resonant mode along both the x and y axis. Exploiting the inherent symmetry in the piezoelectric tube, the multivariable control design problem is recast as independent single-input single-output (SISO) designs. This in conjunction with integral resonant control is used for damping the first resonant mode.
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45.80.+r Control of mechanical systems
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
89.20.Kk Engineering
02.30.Rz Integral equations
02.30.Yy Control theory
FREE

A near-field scanning microwave microscope based on a superconducting resonator for low power measurements

S. E. de Graaf, A. V. Danilov, A. Adamyan, and S. E. Kubatkin

Rev. Sci. Instrum. 84, 023706 (2013); http://dx.doi.org/10.1063/1.4792381 (7 pages) | Cited 1 time

Online Publication Date: 21 February 2013

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We report on the design and performance of a cryogenic (300 mK) near-field scanning microwave microscope. It uses a microwave resonator as the near-field sensor, operating at a frequency of 6 GHz and microwave probing amplitudes down to 100 μV, approaching low enough photon population (N ∼ 1000) of the resonator such that coherent quantum manipulation becomes feasible. The resonator is made out of a miniaturized distributed fractal superconducting circuit that is integrated with the probing tip, micromachined to be compact enough such that it can be mounted directly on a quartz tuning-fork, and used for parallel operation as an atomic force microscope (AFM). The resonator is magnetically coupled to a transmission line for readout, and to achieve enhanced sensitivity we employ a Pound-Drever-Hall measurement scheme to lock to the resonance frequency. We achieve a well localized near-field around the tip such that the microwave resolution is comparable to the AFM resolution, and a capacitive sensitivity down to 6.4 × 10−20 F/math, limited by mechanical noise. We believe that the results presented here are a significant step towards probing quantum systems at the nanoscale using near-field scanning microwave microscopy.
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07.79.Fc Near-field scanning optical microscopes
85.25.-j Superconducting devices
84.40.Az Waveguides, transmission lines, striplines

A new adaptive light beam focusing principle for scanning light stimulation systems

L. A. Bitzer, M. Meseth, N. Benson, and R. Schmechel

Rev. Sci. Instrum. 84, 023707 (2013); http://dx.doi.org/10.1063/1.4791795 (4 pages)

Online Publication Date: 22 February 2013

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In this article a novel principle to achieve optimal focusing conditions or rather the smallest possible beam diameter for scanning light stimulation systems is presented. It is based on the following methodology: First, a reference point on a camera sensor is introduced where optimal focusing conditions are adjusted and the distance between the light focusing optic and the reference point is determined using a laser displacement sensor. In a second step, this displacement sensor is used to map the topography of the sample under investigation. Finally, the actual measurement is conducted, using optimal focusing conditions in each measurement point at the sample surface, that are determined by the height difference between camera sensor and the sample topography. This principle is independent of the measurement values, the optical or electrical properties of the sample, the used light source, or the selected wavelength. Furthermore, the samples can be tilted, rough, bent, or of different surface materials. In the following the principle is implemented using an optical beam induced current system, but basically it can be applied to any other scanning light stimulation system. Measurements to demonstrate its operation are shown, using a polycrystalline silicon solar cell.
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42.79.Pw Imaging detectors and sensors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Three-dimensional imaging of copper pillars using x-ray tomography within a scanning electron microscope: A simulation study based on synchrotron data

N. Martin, J. Bertheau, P. Bleuet, J. Charbonnier, P. Hugonnard, D. Laloum, F. Lorut, and J. Tabary

Rev. Sci. Instrum. 84, 023708 (2013); http://dx.doi.org/10.1063/1.4792377 (5 pages)

Online Publication Date: 25 February 2013

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While microelectronic devices are frequently characterized with surface-sensitive techniques having nanometer resolution, interconnections used in 3D integration require 3D imaging with high penetration depth and deep sub-micrometer spatial resolution. X-ray tomography is well adapted to this situation. In this context, the purpose of this study is to assess a versatile and turn-key tomographic system allowing for 3D x-ray nanotomography of copper pillars. The tomography tool uses the thin electron beam of a scanning electron microscope (SEM) to provoke x-ray emission from specific metallic targets. Then, radiographs are recorded while the sample rotates in a conventional cone beam tomography scheme that ends up with 3D reconstructions of the pillar. Starting from copper pillars data, collected at the European Synchrotron Radiation Facility, we build a 3D numerical model of a copper pillar, paying particular attention to intermetallics. This model is then used to simulate physical radiographs of the pillar using the geometry of the SEM-hosted x-ray tomography system. Eventually, data are reconstructed and it is shown that the system makes it possible the quantification of 3D intermetallics volume in copper pillars. The paper also includes a prospective discussion about resolution issues.
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85.40.Ls Metallization, contacts, interconnects; device isolation
07.85.Tt X-ray microscopes
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Atomic force microscope infrared spectroscopy on 15 nm scale polymer nanostructures

Jonathan R. Felts, Hanna Cho, Min-Feng Yu, Lawrence A. Bergman, Alexander F. Vakakis, and William P. King

Rev. Sci. Instrum. 84, 023709 (2013); http://dx.doi.org/10.1063/1.4793229 (6 pages)

Online Publication Date: 27 February 2013

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We measure the infrared spectra of polyethylene nanostructures of height 15 nm using atomic force microscope infrared spectroscopy (AFM-IR), which is about an order of magnitude improvement over state of the art. In AFM-IR, infrared light incident upon a sample induces photothermal expansion, which is measured by an AFM tip. The thermomechanical response of the sample-tip-cantilever system results in cantilever vibrations that vary in time and frequency. A time-frequency domain analysis of the cantilever vibration signal reveals how sample thermomechanical response and cantilever dynamics affect the AFM-IR signal. By appropriately filtering the cantilever vibration signal in both the time domain and the frequency domain, it is possible to measure infrared absorption spectra on polyethylene nanostructures as small as 15 nm.
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07.79.Lh Atomic force microscopes
07.60.-j Optical instruments and equipment
back to top Condensed Matter; Materials

Synchrotron radiation-based far-infrared spectroscopic ellipsometer with full Mueller-matrix capability

T. N. Stanislavchuk, T. D. Kang, P. D. Rogers, E. C. Standard, R. Basistyy, A. M. Kotelyanskii, G. Nita, T. Zhou, G. L. Carr, M. Kotelyanskii, and A. A. Sirenko

Rev. Sci. Instrum. 84, 023901 (2013); http://dx.doi.org/10.1063/1.4789495 (15 pages)

Online Publication Date: 5 February 2013

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We developed far-IR spectroscopic ellipsometer at the U4IR beamline of the National Synchrotron Light Source in Brookhaven National Laboratory. This ellipsometer is able to measure both, rotating analyzer and full-Mueller matrix spectra using rotating retarders, and wire-grid linear polarizers. We utilize exceptional brightness of synchrotron radiation in the broad spectral range between about 20 and 4000 cm−1. Fourier-transform infrared (FT-IR) spectrometer is used for multi-wavelength data acquisition. The sample stage has temperature variation between 4.2 and 450 K, wide range of θ–2θ angular rotation, χ tilt angle adjustment, and X-Y-Z translation. A LabVIEW-based software controls the motors, sample temperature, and FT-IR spectrometer and also allows to run fully automated experiments with pre-programmed measurement schedules. Data analysis is based on Berreman's 4 × 4 propagation matrix formalism to calculate the Mueller matrix parameters of anisotropic samples with magnetic permeability μ ≠ 1. A nonlinear regression of the rotating analyzer ellipsometry and/or Mueller matrix (MM) spectra, which are usually acquired at variable angles of incidence and sample crystallographic orientations, allows extraction of dielectric constant and magnetic permeability tensors for bulk and thin-film samples. Applications of this ellipsometer setup for multiferroic and ferrimagnetic materials with μ ≠ 1 are illustrated with experimental results and simulations for TbMnO3 and Dy3Fe5O12 single crystals. We demonstrate how magnetic and electric dipoles, such as magnons and phonons, can be distinguished from a single MM measurement without adducing any modeling arguments. The parameters of magnetoelectric components of electromagnon excitations are determined using MM spectra of TbMnO3.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Fs Polarimeters and ellipsometers
41.60.Ap Synchrotron radiation
42.79.Ci Filters, zone plates, and polarizers

Qualitative comparison of bremsstrahlung X-rays and 800 MeV protons for tomography of urania fuel pellets

C. L. Morris, M. Bourke, D. D. Byler, C. F. Chen, G. Hogan, J. F. Hunter, K. Kwiatkowski, F. G. Mariam, K. J. McClellan, F. Merrill, D. J. Morley, and A. Saunders

Rev. Sci. Instrum. 84, 023902 (2013); http://dx.doi.org/10.1063/1.4789947 (7 pages)

Online Publication Date: 11 February 2013

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We present an assessment of x-rays and proton tomography as tools for studying the time dependence of the development of damage in fuel rods. We also show data taken with existing facilities at Los Alamos National Laboratory that support this assessment. Data on surrogate fuel rods have been taken using the 800 MeV proton radiography (pRad) facility at the Los Alamos Neutron Science Center (LANSCE), and with a 450 keV bremsstrahlung X-ray tomography facility. The proton radiography pRad facility at LANSCE can provide good position resolution (<70 μm has been demonstrate, 20 μm seems feasible with minor changes) for tomography on activated fuel rods. Bremsstrahlung x-rays may be able to provide better than 100 μm resolution but further development of sources, collimation, and detectors is necessary for x-rays to deal with the background radiation for tomography of activated fuel rods.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Ag Apertures, collimators

Practical guide for validated memristance measurements

Nan Du, Yao Shuai, Wenbo Luo, Christian Mayr, René Schüffny, Oliver G. Schmidt, and Heidemarie Schmidt

Rev. Sci. Instrum. 84, 023903 (2013); http://dx.doi.org/10.1063/1.4775718 (7 pages)

Online Publication Date: 13 February 2013

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Chua [IEEE Trans. Circuit Theory 18, 507–519 (1971)10.1109/TCT.1971.1083337] predicted rather simple charge-flux curves for active and passive memristors (short for memory resistors) and presented active memristor circuit realizations already in the 1970 s. The first passive memristor has been presented in 2008 [D. B. Strukov, G. S. Snider, and D. R. Williams, Nature (London) 453, 80–83 (2008)10.1038/nature06932]. Typically, memristors are traced in complicated hysteretic current-voltage curves. Therefore, the true essence of many new memristive devices has not been discovered so far. Here, we give a practical guide on how to use normalized charge-flux curves for the prediction of hysteretic current-voltage characteristics of memristors. In the case of memristive BiFeO3 thin film capacitor structures, the normalized charge-flux curves superimpose for different numbers of measurement points Ns and a different measurement time per measurement point Ts. Such normalized charge-flux curves can be used for the prediction of current-voltage characteristics for input signals with arbitrarily chosen Ns and Ts.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
06.30.Ft Time and frequency
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
84.32.Tt Capacitors

Translational diffusion of probe molecules under high pressure: A study by fluorescence recovery after photobleaching technique

Marco Bonetti and Michel Roger

Rev. Sci. Instrum. 84, 023904 (2013); http://dx.doi.org/10.1063/1.4790567 (6 pages)

Online Publication Date: 14 February 2013

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We present fluorescence recovery measurements after photobleaching performed under high pressure in liquids that fill square-section fused silica micro-capillaries. These micro-capillaries withstand pressure up to 2500 bar for a wall thickness of about 140 μm and fit easily on the microscope stage. This technique allows the translational diffusion coefficient of fluorescent molecules in liquids to be measured as a function of pressure. When the liquid sample is far from its glass transition the translational diffusive coefficient is in agreement with the Stokes-Einstein equation. As the glass transition is approached by further increasing the pressure, decoupling of the measured diffusion coefficient from the Stokes-Einstein relation is observed. These are the first measurements that combine the fluorescence recovery technique and high hydrostatic pressures. This experimental setup can also be used either with diamond or sapphire anvil cells in order to span a larger pressure range.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.65.-k Nonlinear optics
78.55.-m Photoluminescence, properties and materials
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells

Demonstration of glass transition temperature shift in thin supported polystyrene films by internal reference method

Mikhail Yu. Efremov, Christopher Thode, and Paul F. Nealey

Rev. Sci. Instrum. 84, 023905 (2013); http://dx.doi.org/10.1063/1.4793226 (6 pages)

Online Publication Date: 26 February 2013

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An internal reference method is used for the first time to clearly demonstrate the glass transition temperature (Tg) depression effect in 5 nm thick polystyrene films spin-cast on silicon wafers. Initially flat films exhibit depressed Tg at approximately 85 °C. Temperature-induced dewetting on hexamethyldisilazane-treated silicon substrates leads to formation of discontinuous films with average effective thickness of 15–30 nm. Dewetted films demonstrate Tg close to the bulk value (≈ 100 °C) and are used as internal references. Data both for continuous and discontinuous films are obtained in the same experimental run for the same sample, which allows direct comparison between datasets. Phase-modulated ellipsometry in vacuum is used to monitor glass transition. Both traditional linear temperature scan method and a novel temperature modulated technique have been employed in the measurements.
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64.70.pj Polymers
07.20.Dt Thermometers
back to top Chemistry

An exchangeable-tip scanning probe instrument for the analysis of combinatorial libraries of electrocatalysts

Eric D. Rus, Hongsen Wang, Anna E. Legard, Nicole L. Ritzert, Robert Bruce Van Dover, and Héctor D. Abruña

Rev. Sci. Instrum. 84, 024101 (2013); http://dx.doi.org/10.1063/1.4776199 (8 pages)

Online Publication Date: 7 February 2013

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A combined scanning differential electrochemical mass spectrometer (SDEMS)-scanning electrochemical microscope (SECM) apparatus is described. The SDEMS is used to detect and spatially resolve volatile electrochemically generated species at the surface of a substrate electrode. The SECM can electrochemically probe the reactivity of the surface and also offers a convenient means of leveling the sample. It is possible to switch between these two different scanning tips and techniques without moving the sample and while maintaining potential control of the substrate electrode. A procedure for calibration of the SDEMS tip-substrate separation, based upon the transit time of electrogenerated species from the substrate to the tip is also described. This instrument can be used in the characterization of combinatorial libraries of direct alcohol fuel cell anode catalysts. The apparatus was used to analyze the products of methanol oxidation at a Pt substrate, with the SDEMS detecting carbon dioxide and methyl formate, and a PtPb-modified Pt SECM tip used for the selective detection of formic acid. As an example system, the electrocatalytic methanol oxidation activity of a sputter-deposited binary PtRu composition spread in acidic media was analyzed using the SDEMS. These results are compared with those obtained from a pH-sensitive fluorescence assay.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
81.15.Cd Deposition by sputtering
82.45.Fk Electrodes
88.30.G- Fuel cell systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.75.+h Mass spectrometers

Scanning droplet cell for high throughput electrochemical and photoelectrochemical measurements

John M. Gregoire, Chengxiang Xiang, Xiaonao Liu, Martin Marcin, and Jian Jin

Rev. Sci. Instrum. 84, 024102 (2013); http://dx.doi.org/10.1063/1.4790419 (6 pages)

Online Publication Date: 12 February 2013

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High throughput electrochemical techniques are widely applied in material discovery and optimization. For many applications, the most desirable electrochemical characterization requires a three-electrode cell under potentiostat control. In high throughput screening, a material library is explored by either employing an array of such cells, or rastering a single cell over the library. To attain this latter capability with unprecedented throughput, we have developed a highly integrated, compact scanning droplet cell that is optimized for rapid electrochemical and photoeletrochemical measurements. Using this cell, we screened a quaternary oxide library as (photo)electrocatalysts for the oxygen evolution (water splitting) reaction. High quality electrochemical measurements were carried out and key electrocatalytic properties were identified for each of 5456 samples with a throughput of 4 s per sample.
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82.80.-d Chemical analysis and related physical methods of analysis
82.45.Fk Electrodes

The influence of laterally inhomogeneous corrosion on electrical and optical calcium moisture barrier characterization

H. Klumbies, L. Müller-Meskamp, T. Mönch, S. Schubert, and K. Leo

Rev. Sci. Instrum. 84, 024103 (2013); http://dx.doi.org/10.1063/1.4791798 (8 pages)

Online Publication Date: 20 February 2013

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The reaction of calcium thin films with water – monitored optically or electrically – is widely used for evaluating ultrahigh barrier foils for the encapsulation of organic electronic devices. We studied the common optical and the electrical method and compared them with in situ atomic force microscope topography scans. All three methods were applied at the same sample in parallel in a typical test design containing a gas volume for water distribution next to the calcium layer of 60 and 1000 nm thickness, respectively. The common assumption for the interpretation of such measurement data is laterally homogeneous calcium consumption of the layer from top to bottom. In contrast, we observed a significant ratio of laterally inhomogeneous corrosion of the calcium on the micro-scale for both thicknesses. Some areas were strongly or completely corroded through the whole layer while others exhibited less or no corrosion. Furthermore, those corroded spots grew in lateral direction. As a consequence of lateral inhomogeneous calcium corrosion the electrical calcium measurement method underestimates the amount of calcium left; according to our results this does not affect the water vapor transmission rate (WVTR). Optical data evaluated by Lambert-Beer law underestimate the amount of calcium left as well and also underestimate the WVTR. If the data are evaluated, using a linear relationship between transmission and amount of calcium left, the both values are more precise. The scope of this study is to call attention to the existence of lateral inhomogeneity in calcium corrosion and its impact on the calcium permeation measurements. While more investigations would be needed to quantify the effect of this inhomogeneity on the electrical and optical method in general, the discussion sheds light on the way, calcium test data are influenced by lateral inhomogeneous calcium corrosion. Our observations highlight the need for careful interpretation of calcium test results, but also demonstrate its capabilities for precise ultrahigh barrier measurements.
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73.61.At Metal and metallic alloys
78.66.Bz Metals and metallic alloys
81.65.-b Surface treatments
68.37.Ps Atomic force microscopy (AFM)
back to top Biology and Medicine

A high sensitivity fiber optic macro-bend based gas flow rate transducer for low flow rates: Theory, working principle, and static calibration

Emiliano Schena, Paola Saccomandi, and Sergio Silvestri

Rev. Sci. Instrum. 84, 024301 (2013); http://dx.doi.org/10.1063/1.4793227 (7 pages)

Online Publication Date: 26 February 2013

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A novel fiber optic macro-bend based gas flowmeter for low flow rates is presented. Theoretical analysis of the sensor working principle, design, and static calibration were performed. The measuring system consists of: an optical fiber, a light emitting diode (LED), a Quadrant position sensitive Detector (QD), and an analog electronic circuit for signal processing. The fiber tip undergoes a deflection in the flow, acting like a cantilever. The consequent displacement of light spot center is monitored by the QD generating four unbalanced photocurrents which are function of fiber tip position. The analog electronic circuit processes the photocurrents providing voltage signal proportional to light spot position. A circular target was placed on the fiber in order to increase the sensing surface. Sensor, tested in the measurement range up to 10 l min−1, shows a discrimination threshold of 2 l min−1, extremely low fluid dynamic resistance (0.17 Pa min l−1), and high sensitivity, also at low flow rates (i.e., 33 mV min l−1 up to 4 l min−1 and 98 mV min l−1 from 4 l min−1 up to 10 l min−1). Experimental results agree with the theoretical predictions. The high sensitivity, along with the reduced dimension and negligible pressure drop, makes the proposed transducer suitable for medical applications in neonatal ventilation.
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42.81.Pa Sensors, gyros
47.80.-v Instrumentation and measurement methods in fluid dynamics
06.20.fb Standards and calibration
07.07.Mp Transducers
back to top Gravity; Geophysics; Astronomy and Astrophysics

Tracking geomagnetic fluctuations to picotesla accuracy using two superconducting quantum interference device vector magnetometers

S. Henry, E. Pozzo di Borgo, and A. Cavaillou

Rev. Sci. Instrum. 84, 024501 (2013); http://dx.doi.org/10.1063/1.4790715 (6 pages)

Online Publication Date: 15 February 2013

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SQUIDs can be used to monitor the three vector components of the geomagnetic field to a high precision at very low frequencies, yet as they are susceptible to external interference, the accuracy to which they can track changes in the dc field over long periods has been unclear. We have carried out simultaneous measurements of the geomagnetic field recorded using two independent 3-axis SQUID magnetometers at the Laboratoire Souterrain à Bas Bruit (LSBB). We demonstrate a technique to take the difference between a linear transform of the three signals from one magnetometer, and a reference signal from the other, in order to account for any difference in alignment and calibration, and track local signals at a sub-nT level. We confirmed that both systems tracked the same signal with an RMS difference as low as 56pT over a period of 72 h. To our knowledge this is the first such demonstration of the long term accuracy of SQUID magnetometers for monitoring geomagnetic fields.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
06.20.fb Standards and calibration
07.55.Ge Magnetometers for magnetic field measurements
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