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Mar 2013

Volume 84, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 84, 033701 (2013); http://dx.doi.org/10.1063/1.4774387 (7 pages)

E. Nazaretski, Jungdae Kim, H. Yan, K. Lauer, D. Eom, D. Shu, J. Maser, Z. Pešić, U. Wagner, C. Rau, and Y. S. Chu

Computer aided design (CAD) model of the multilayer Laue lenses (MLL) based scanning fluorescence microscope. The inset shows schematic of the MLL setup used to perform scanning fluorescence experiments. The background represents thermal image of the horizontal MLL assembly.

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Coupling a Knudsen reactor with the short lived radioactive tracer 13N for atmospheric chemistry studies

S. Schreiber, M. Kerbrat, T. Huthwelker, M. Birrer, and M. Ammann

Rev. Sci. Instrum. 84, 035101 (2013); http://dx.doi.org/10.1063/1.4793405 (13 pages)

Online Publication Date: 4 March 2013

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A Knudsen cell flow reactor was coupled to an online gas phase source of the short-lived radioactive tracer 13N to study the adsorption of nitrogen oxides on ice at temperatures relevant for the upper troposphere. This novel approach has several benefits over the conventional coupling of a Knudsen cell with a mass spectrometer. Experiments at lower partial pressures close to atmospheric conditions are possible. The uptake to the substrate is a direct observable of the experiment. Operation of the experiment in continuous or pulse mode allows to retrieve steady state uptake kinetics and more details of adsorption and desorption kinetics.
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92.60.hf Tropospheric composition and chemistry, constituent transport and chemistry
93.85.-q Instruments and techniques for geophysical research: Exploration geophysics
68.43.Nr Desorption kinetics
47.45.-n Rarefied gas dynamics
68.43.Mn Adsorption kinetics

Design and fabrication of a bending rotation fatigue test rig for in situ electrochemical analysis during fatigue testing of NiTi shape memory alloy wires

Lakshman Neelakantan, Jenni Kristin Zglinski, Matthias Frotscher, and Gunther Eggeler

Rev. Sci. Instrum. 84, 035102 (2013); http://dx.doi.org/10.1063/1.4793488 (5 pages)

Online Publication Date: 5 March 2013

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The current investigation proposes a novel method for simultaneous assessment of the electrochemical and structural fatigue properties of nickel-titanium shape memory alloy (NiTi SMA) wires. The design and layout of an in situ electrochemical cell in a custom-made bending rotation fatigue (BRF) test rig is presented. This newly designed test rig allows performing a wide spectrum of experiments for studying the influence of fatigue on corrosion and vice versa. This can be achieved by performing ex situ and/or in situ measurements. The versatility of the combined electrochemical/mechanical test rig is demonstrated by studying the electrochemical behavior of NiTi SMA wires in 0.9% NaCl electrolyte under load. The ex situ measurements allow addressing various issues, for example, the influence of pre-fatigue on the localized corrosion resistance, or the influence of hydrogen on fatigue life. Ex situ experiments showed that a pre-fatigued wire is more susceptible to localized corrosion. The synergetic effect can be concluded from the polarization studies and specifically from an in situ study of the open circuit potential (OCP) transients, which sensitively react to the elementary repassivation events related to the local failure of the oxide layer. It can also be used as an indicator for identifying the onset of the fatigue failure.
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81.05.Bx Metals, semimetals, and alloys
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
62.20.fg Shape-memory effect; yield stress; superelasticity
62.20.me Fatigue

An electric stimulation system for electrokinetic particle manipulation in microfluidic devices

M. S. Lopez-de la Fuente, H. Moncada-Hernandez, V. H. Perez-Gonzalez, B. H. Lapizco-Encinas, and S. O. Martinez-Chapa

Rev. Sci. Instrum. 84, 035103 (2013); http://dx.doi.org/10.1063/1.4793559 (7 pages)

Online Publication Date: 6 March 2013

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Microfluidic devices have grown significantly in the number of applications. Microfabrication techniques have evolved considerably; however, electric stimulation systems for microdevices have not advanced at the same pace. Electric stimulation of micro-fluidic devices is an important element in particle manipulation research. A flexible stimulation instrument is desired to perform configurable, repeatable, automated, and reliable experiments by allowing users to select the stimulation parameters. The instrument presented here is a configurable and programmable stimulation system for electrokinetic-driven microfluidic devices; it consists of a processor, a memory system, and a user interface to deliver several types of waveforms and stimulation patterns. It has been designed to be a flexible, highly configurable, low power instrument capable of delivering sine, triangle, and sawtooth waveforms with one single frequency or two superimposed frequencies ranging from 0.01 Hz to 40 kHz, and an output voltage of up to 30 Vpp. A specific stimulation pattern can be delivered over a single time period or as a sequence of different signals for different time periods. This stimulation system can be applied as a research tool where manipulation of particles suspended in liquid media is involved, such as biology, medicine, environment, embryology, and genetics. This system has the potential to lead to new schemes for laboratory procedures by allowing application specific and user defined electric stimulation. The development of this device is a step towards portable and programmable instrumentation for electric stimulation on electrokinetic-based microfluidic devices, which are meant to be integrated with lab-on-a-chip devices.
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47.85.Np Fluidics
47.61.-k Micro- and nano- scale flow phenomena

An automated high throughput tribometer for adhesion, wear, and friction measurements

Vivek Kalihari, Shannon J. Timpe, Lyle McCarty, Matthew Ninke, and Jim Whitehead

Rev. Sci. Instrum. 84, 035104 (2013); http://dx.doi.org/10.1063/1.4794908 (9 pages)

Online Publication Date: 14 March 2013

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Understanding the origin and correlation of different surface properties under a multitude of operating conditions is critical in tribology. Diverse tribological properties and a lack of a single instrument to measure all make it difficult to compare and correlate properties, particularly in light of the wide range of interfaces commonly investigated. In the current work, a novel automated tribometer has been designed and validated, providing a unique experimental platform capable of high throughput adhesion, wear, kinetic friction, and static friction measurements. The innovative design aspects are discussed that allow for a variety of probes, sample surfaces, and testing conditions. Critical components of the instrument and their design criteria are described along with examples of data collection schemes. A case study is presented with multiple surface measurements performed on a set of characteristic substrates. Adhesion, wear, kinetic friction, and static friction are analyzed and compared across surfaces, highlighting the comprehensive nature of the surface data that can be generated using the automated high throughput tribometer.
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46.55.+d Tribology and mechanical contacts
68.35.Np Adhesion

Thin conductive diamond films as beam intensity monitors for soft x-ray beamlines

K. Kummer, A. Fondacaro, F. Yakhou-Harris, V. Sessi, P. Pobedinskas, S. D. Janssens, K. Haenen, O. A. Williams, J. Hees, and N. B. Brookes

Rev. Sci. Instrum. 84, 035105 (2013); http://dx.doi.org/10.1063/1.4794439 (6 pages)

Online Publication Date: 15 March 2013

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Quantitative analysis of X-ray absorption and dichroism data requires knowledge of the beamline photon flux during the measurements. We show that thin conductive (B-doped) diamond thin films can be an alternative to the widely used gold meshes for monitoring the beam intensity of soft X-ray beamlines in situ. Limited by the carbon extended x-ray absorption fine structure oscillations, the diamond films become applicable beginning from about 600 eV photon energy, where the important transition metal edges and the rare-earth edges are found. The 100 nm and 250 nm thick free-standing diamond films were grown and tested against standard gold meshes in real-life dichroism experiments performed at beamline ID08 of the European Synchrotron Radiation Facility, Grenoble, France. Quantitative agreement was found between the two experimental data sets. The films feature an extremely high transmission of about 90% and, at the same time, yield a sufficiently strong and clean reference signal. Furthermore, the thin films do not affect the shape of the transmitted beam. X-rays passing mesh-type monitors are subject to diffraction effects, which widen the beam and become particularly disturbing for small beamsizes in the micrometer range.
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07.85.-m X- and γ-ray instruments
68.55.-a Thin film structure and morphology
78.70.Dm X-ray absorption spectra

A combined matrix isolation spectroscopy and cryosolid positron moderation apparatus

Christopher D. Molek, C. Michael Lindsay, and Mario E. Fajardo

Rev. Sci. Instrum. 84, 035106 (2013); http://dx.doi.org/10.1063/1.4795555 (11 pages)

Online Publication Date: 26 March 2013

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We describe the design, construction, and operation of a novel apparatus for investigating efficiency improvements in thin-film cryogenic solid positron moderators. We report results from solid neon, argon, krypton, and xenon positron moderators which illustrate the capabilities and limitations of our apparatus. We integrate a matrix isolation spectroscopy diagnostic within a reflection-geometry positron moderation system. We report the optical thickness, impurity content, and impurity trapping site structures within our moderators determined from infrared absorption spectra. We use a retarding potential analyzer to modulate the flow of slow positrons, and report positron currents vs. retarding potential for the different moderators. We identify vacuum ultraviolet emissions from irradiated Ne moderators as the source of spurious signals in our channel electron multiplier slow positron detection channel. Our design is also unusual in that it employs a sealed radioactive Na-22 positron source which can be translated relative to, and isolated from, the cryogenic moderator deposition substrate. This allows us to separate the influences on moderator efficiency of surface contamination by residual gases from those of accumulated radiation damage.
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28.20.Gd Neutron transport: diffusion and moderation
29.25.Bx Electron sources
85.60.Ha Photomultipliers; phototubes and photocathodes
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Tungstate sharpening: A versatile method for extending the profile of ultra sharp tungsten probes

R. Stone, M. Rosamond, K. Coleman, M. Petty, O. Kolosov, L. Bowen, V. Dubrovskii, and D. Zeze

Rev. Sci. Instrum. 84, 035107 (2013); http://dx.doi.org/10.1063/1.4797483 (5 pages)

Online Publication Date: 28 March 2013

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The benefits of a new electrochemical etching method for the controlled sharpening of sub-micron tungsten probes are demonstrated. The proposed technique only utilizes the insulating effect of the WO42− by-product which offers more practical ways of controlling the process parameters. The electrosharpening method was fully automated through the analysis of the process current, bulk coulometry, shadowgraphs, and time lapse microscopy. Tip radii smaller than 15 nm were maintained over a wide range of controlled lengths up to 4.5 mm with conic angles of less than 1°.
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81.65.Cf Surface cleaning, etching, patterning
82.80.Fk Electrochemical methods
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