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Feb 2009

Volume 80, Issue 2, Articles (02xxxx)

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Announcement: Multimedia capability added to Review of Scientific Instruments

Mark M. Cassar

Rev. Sci. Instrum. 80, 020201 (2009); http://dx.doi.org/10.1063/1.3098976 (1 page)

Online Publication Date: 26 February 2009

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01.60.+q Biographies, tributes, personal notes, and obituaries
01.10.Cr Announcements, news, and awards
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Design and estimated performance of a new neutron guide system for the NCNR expansion project

J. C. Cook

Rev. Sci. Instrum. 80, 023101 (2009); http://dx.doi.org/10.1063/1.3077144 (10 pages) | Cited 6 times

Online Publication Date: 11 February 2009

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An integral part of the National Institute of Standards and Technology Center for Neutron Research (NCNR) expansion project is the addition of five cold neutron guide tubes serving multiple experimental stations in an expanded guide hall. The guides have curved-straight arrangements in the horizontal plane, employing horizontally or vertically defocusing and focusing sections in some cases to improve transmission efficiency or for beam reshaping. The horizontally curved sections eliminate direct lines of sight between the source and the experimental stations, and the outer (concave) surfaces generally have higher critical angles than the inner (convex) surfaces. These features result in well-filtered cold neutron beams with no intensity losses at shorter wavelengths with respect to curved guides having the higher critical angle coatings on both surfaces. For all guides the critical angle of the outer coating of the curved section is selected to achieve a desirable characteristic wavelength, consistent with the instrument requirements. On guides where the scattering-plane beam divergence must be strictly limited, the inner radial coatings of the curved sections and the side coatings and lengths of the final straight sections are chosen to produce the desired beam divergence while the outer radial coating is selected so as to obtain a spatial-angular uniformity of the transmitted beam that is not achievable using a curved guide alone. The long-wavelength transmission of such guides tends to exceed that of equivalent straight guides using crystal filters.
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28.50.Dr Research reactors
03.75.Be Atom and neutron optics

A versatile electron-ion coincidence spectrometer for photoelectron momentum imaging and threshold spectroscopy on mass selected ions using synchrotron radiation

Gustavo A. Garcia, Héloïse Soldi-Lose, and Laurent Nahon

Rev. Sci. Instrum. 80, 023102 (2009); http://dx.doi.org/10.1063/1.3079331 (12 pages) | Cited 33 times

Online Publication Date: 13 February 2009

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We present a photoelectron-photoion coincidence (PEPICO) spectrometer named DELICIOUS II which combines a velocity map imaging apparatus with a Wiley–McLaren time of flight analyzer for the study of gas phase samples in interaction with the synchrotron radiation (SR). This versatile system is capable of providing photoelectron images on mass-selected compounds with kinetic energy resolutions of ΔE/E = 5% and a 17 eV bandwidth, as well as threshold photoelectron spectra with a measured resolution of 0.8 meV, as demonstrated on the 3p−1 ionization of argon. This instrument is also employed for threshold PEPICO experiments, allowing the selection of the parent ion’s internal state with sub-meV resolution for light masses (<40 amu) and with typically 2 meV resolution for a mass of 100 amu and with a mass resolving power above 200. The continuous operation of the extraction fields and the independence from the electron’s time of flight are well adapted to the quasicontinuous multibunch mode of the SR. This, together with the high transmission of both the electron and ion detection, allows a high coincidence counting rate and facilitates the subtraction of false coincidences. We illustrate the spectrometer’s coincidence principle of operation with examples from the valence photoionization of an Ar+Xe mixture and of CF4.
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07.81.+a Electron and ion spectrometers
07.75.+h Mass spectrometers

2E1 Ar17+ decay and conventional radioactive sources to determine efficiency of semiconductor detectors

Emily Lamour, Christophe Prigent, Benjamin Eberhardt, Jean Pierre Rozet, and Dominique Vernhet

Rev. Sci. Instrum. 80, 023103 (2009); http://dx.doi.org/10.1063/1.3077284 (7 pages) | Cited 4 times

Online Publication Date: 17 February 2009

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Although reliable models may predict the detection efficiency of semiconductor detectors, measurements are needed to check the parameters supplied by the manufacturers, namely, the thicknesses of dead layer, beryllium window, and crystal active area. The efficiency of three silicon detectors has been precisely investigated in their entire photon energy range of detection. In the zero to a few keV range, we developed a new method based on the detection of the 2E1 decay of the metastable Ar17+ 2s→1s transition. Very good theoretical knowledge of the energetic distribution of the 2E1 decay mode enables precise characterization of the absorbing layers in front of the detectors. In the high-energy range (>10 keV), the detector crystal thickness plays a major role in the detection efficiency and has been determined using a 241Am source.
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29.40.Gx Tracking and position-sensitive detectors
29.40.Wk Solid-state detectors
29.25.Rm Sources of radioactive nuclei
23.20.Lv γ transitions and level energies
27.40.+z 39 ≤ A ≤ 58

Principle, calibration, and application of the in situ alkali chloride monitor

Christer Forsberg, Markus Broström, Rainer Backman, Elin Edvardsson, Shahriar Badiei, Magnus Berg, and Håkan Kassman

Rev. Sci. Instrum. 80, 023104 (2009); http://dx.doi.org/10.1063/1.3081015 (4 pages) | Cited 7 times

Online Publication Date: 20 February 2009

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The extended use of biomass for heat and power production has caused increased operational problems with fouling and high-temperature corrosion in boilers. These problems are mainly related to the presence of alkali chlorides (KCl and NaCl) at high concentrations in the flue gas. The in situ alkali chloride monitor (IACM) was developed by Vattenfall Research and Development AB for measuring the alkali chloride concentration in hot flue gases (≲650 °C). The measurement technique is based on molecular differential absorption spectroscopy in the UV range. Simultaneous measurement of SO2 concentration is also possible. The measuring range is 1–50 ppm for the sum of KCl and NaCl concentrations and 4–750 ppm for SO2. This paper describes the principle of the IACM as well as its calibration. Furthermore, an example of its application in an industrial boiler is given.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
89.60.-k Environmental studies
84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Chromatic-free spatially resolved optical emission spectroscopy diagnostics for microplasma

Li-Guo Zhu, Wen-Cong Chen, Xi-Ming Zhu, Yi-Kang Pu, and Ze-Ren Li

Rev. Sci. Instrum. 80, 023105 (2009); http://dx.doi.org/10.1063/1.3079379 (4 pages) | Cited 3 times

Online Publication Date: 27 February 2009

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A chromatic-free spatially resolved diagnostic system for microplasma measurement is proposed and demonstrated, which consists of an optical chromatic-free microscope mirror system, an electron multiplying charge coupled device (EMCCD), and bandpass filters. The diagnostic system free of chromatic aberrations with a spatial resolution of about 6 μm is achieved. The factors that limit the resolution of this diagnostic system have been analyzed, which are optical diffraction, the pixel size of the EMCCD, and the thickness of the microplasma. In this paper, the optimal condition for achieving a maximum resolution power has been analyzed. With this diagnostic system, we revealed the spatial nonuniformity of a microwave atmospheric-pressure argon microplasma. Furthermore, the spatial distribution of the time-averaged effective electron temperature has been estimated from the intensity distributions of 750.4 and 415.8 nm emissions.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Improved plasma uniformity in a discharge system with electron injection

A. V. Vizir, A. V. Tyunkov, and M. V. Shandrikov

Rev. Sci. Instrum. 80, 023301 (2009); http://dx.doi.org/10.1063/1.3069291 (4 pages) | Cited 2 times

Online Publication Date: 5 February 2009

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We present the results of experiments leading to improvement in bulk plasma uniformity of a constricted-arc discharge system with electron injection. The steady-state discharge was in argon, at a gas pressure of 0.5 mTorr, and operated with a main discharge voltage between 20 and 100 V and current between 3 and 15 A. The radial plasma distribution was measured with a movable Langmuir probe. We find that geometric modification of the intermediate electrode exit aperture and the main discharge cathode add little to the plasma uniformity. Improved bulk plasma uniformity is observed when a special distributing grid electrode is used and the main discharge voltage is less than 20–30 V. The application of a weakly divergent magnetic field in the region of the intermediate electrode exit aperture decreases the plasma nonuniformity from 20% to 14% over a radial distance of 30 cm. The plasma uniformity was further improved by compensating the magnetic self-field of the injected electron beam by a reverse magnetic field produced with a special electrode compensator. It is shown that an increase in discharge current causes a proportional increase in back current in the distributing electrode. The approach allows a decrease in plasma nonuniformity from 20% to 13% over a radial distance of 30 cm.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.70.Ds Electric and magnetic measurements

A picosecond time-resolved electron energy spectrometer based on Čerenkov radiation

Lee N. Elberson, Yuan Ping, Ronnie L. Shepherd, Pravesh K. Patel, Andrew J. Mackinnon, and Wendell T. Hill, III

Rev. Sci. Instrum. 80, 023302 (2009); http://dx.doi.org/10.1063/1.3080555 (4 pages)

Online Publication Date: 13 February 2009

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The energy spectrum of relativistic electrons is an important characterization of high intensity laser-matter interactions. We present a technique that utilizes Čerenkov radiation to measure the time-resolved energy distribution of electrons. Electrons escaping from targets irradiated by high-intensity laser pulses were measured, demonstrating the feasibility of such a novel diagnostic. Limitations on the time resolution of this diagnostic are also discussed.
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29.30.Aj Charged-particle spectrometers: electric and magnetic
29.30.Ep Charged-particle spectroscopy
29.40.Ka Cherenkov detectors

Robust, easily shaped, and epoxy-free carbon-fiber-aluminum cathodes for generating high-current electron beams

Lie Liu, Limin Li, Jianchun Wen, and Hong Wan

Rev. Sci. Instrum. 80, 023303 (2009); http://dx.doi.org/10.1063/1.3086728 (4 pages) | Cited 3 times

Online Publication Date: 24 February 2009

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This paper presents the construction of carbon-fiber-aluminum (CFA) cathode by squeezing casting and its applications for generating high-current electron beams to drive high-power microwave sources. The fabrication process avoided using epoxy, a volatile deteriorating the vacuum system. These cathodes had a higher hardness than conventional aluminum, facilitating machining. After surface treatment, carbon fibers became the dominator determining emission property. A multineedle CFA cathode was utilized in a triode virtual cathode oscillator (vircator), powered by a ∼ 450 kV, ∼ 400 ns pulse. It was found that 300–400 MW, ∼ 250 ns microwave was radiated at a dominant frequency of 2.6 GHz. Further, this cathode can endure high-current-density emission without detectable degradation in performance as the pulse shot proceeded, showing the robust nature of carbon fibers as explosive emitters. Overall, this new class of cold cathodes offers a potential prospect of developing high-current electron beam sources.
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84.47.+w Vacuum tubes
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
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Digital I/Q demodulation for KSTAR ion cyclotron range of frequency system

S. J. Wang, J. G. Kwak, and C. K. Hwang

Rev. Sci. Instrum. 80, 023501 (2009); http://dx.doi.org/10.1063/1.3077281 (4 pages)

Online Publication Date: 2 February 2009

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An ion cyclotron range of frequency system requires rf diagnostics for a rf-plasma coupling or for maintaining a correct operation. A detector based on a digital I/Q demodulation technique collects the rf amplitude and phase at the same time without errors from the I/Q imbalance inherent in an analog counterpart. The theory of such a detector was studied and implemented for the first campaign of the KSTAR tokamak. Experimental results of the rf and other diagnostics are presented and discussed.
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52.70.Gw Radio-frequency and microwave measurements
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.55.Fa Tokamaks, spherical tokamaks

Wall scanning probe for high-field side plasma measurements on Alcator C-Mod

Noah Smick and Brian LaBombard

Rev. Sci. Instrum. 80, 023502 (2009); http://dx.doi.org/10.1063/1.3069290 (8 pages) | Cited 8 times

Online Publication Date: 4 February 2009

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A new, high-field side scanning probe has been added to Alcator C-Mod’s complement of edge diagnostics. The wall scanning probe is designed to provide all the benefits of a linear plunge, multielectrode scanning probe while working from the confined space of the inner tokamak wall. The drive mechanism is an embedded coil which produces a torque with the ambient toroidal magnetic field when energized, thus allowing the probe to plunge to different preprogramed depths at different times during a plasma discharge. The probe tip is designed for easy replacement and is presently configured to operate as a modified, high heat-flux “Gundestrup-type” probe with four tungsten electrodes. The probe has demonstrated the ability to obtain cross-field profiles for electron temperature, density, floating potential, and plasma flow information (parallel and perpendicular to B) up to a depth of a few millimiters inside the last-closed flux surface in standard C-Mod discharges. The tungsten-tipped probe has proved very robust and shows little or no damage though it routinely handles surface heat fluxes on the order of 100 MW/m2 at peak insertion.
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52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties
52.80.-s Electric discharges
52.55.Fa Tokamaks, spherical tokamaks
52.30.-q Plasma dynamics and flow

Localized measurement of short wavelength plasma fluctuations with the DIII-D phase contrast imaging diagnostic

J. R. Dorris, J. C. Rost, and M. Porkolab

Rev. Sci. Instrum. 80, 023503 (2009); http://dx.doi.org/10.1063/1.3065094 (10 pages) | Cited 2 times

Online Publication Date: 18 February 2009

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A novel rotating mask system has been designed and implemented on the DIII-D phase contrast imaging (PCI) diagnostic to produce the first spatially localized PCI measurements of a tokamak plasma. The localization technique makes use of the variation in the magnetic field component perpendicular to the viewing chord as a function of chord height. This new capability provides measurements in the range of 2<k<30 cm−1, 10 kHz<f<10 MHz, and 0.7<r/a<1. This technique provides a spatial resolution of 10 cm at k = 15 cm−1 and can realistically provide measurements at a rate of 10 profiles/s. Calibration measurements show accurate characterization of the system transfer function making feasible a time dependent analysis that results in improved localization. Initial measurements show turbulence to peak near the plasma edge. This upgrade is part of a broader program to operate the DIII-D PCI at wave numbers up to 40 cm−1 to probe electron scale turbulence in the plasma core.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Gj Fluctuation and chaos phenomena
52.55.Fa Tokamaks, spherical tokamaks
52.35.Ra Plasma turbulence
52.40.Hf Plasma-material interactions; boundary layer effects

Measurement of the energy distribution of an intense electron beam in an external magnetic field

M. C. Myers, S. B. Swanekamp, M. Friedman, and F. Hegeler

Rev. Sci. Instrum. 80, 023504 (2009); http://dx.doi.org/10.1063/1.3082041 (7 pages)

Online Publication Date: 20 February 2009

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An energy analyzer device has been developed which utilizes a series of stacked foils and Rogowski current monitors to the measure time resolved current of an intense electron beam. The energy distribution of the electron beam is unfolded from measured current ratios using computer simulations. This device is particularly useful where electron beams are guided by external magnetic fields which may make other electron energy measurement techniques difficult. This technique was used to determine the energy distribution of a 550 keV, 95 kA electron beam as it propagates in the gas mixture of a high power KrF laser. The resulting energy distributions at various depths in the gas are in agreement with three-dimensional particle-in-cell simulations providing confidence in the measurement technique.
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07.77.Ka Charged-particle beam sources and detectors
41.75.Fr Electron and positron beams
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
06.60.Jn High-speed techniques (microsecond to femtosecond)

Radio-frequency electromagnetic field measurements for direct detection of electron Bernstein waves in a torus plasma

Eiichi Yatsuka, Kiyotake Kinjo, Junji Morikawa, and Yuichi Ogawa

Rev. Sci. Instrum. 80, 023505 (2009); http://dx.doi.org/10.1063/1.3082047 (6 pages)

Online Publication Date: 20 February 2009

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To identify the mode-converted electron Bernstein wave (EBW) in a torus plasma directly, we have developed an interferometry system, in which a diagnostic microwave injected outside of the plasma column was directly detected with the probing antenna inserted into the plasma. In this work, plasma production and heating are achieved with 2.45 GHz, 2.5 kW electron cyclotron heating (ECH), whereas diagnostics are carried out with a lower power (10 W) separate frequency (1–2.1 GHz) microwave. Three components, i.e., two electromagnetic (toroidal and poloidal directions) and an electrostatic (if refractive index is sufficiently higher than unity, it corresponds to radial component), of ECRF electric field are simultaneously measured with three probing antennas, which are inserted into plasma. Selectivities of each component signal were checked experimentally. Excitation antennas have quite high selectivity of direction of linear polarization. As probing antennas for detecting electromagnetic components, we employed a monopole antenna with a length of 35 mm, and the separation of the poloidal (O-wave) and toroidal (X-wave) components of ECRF electric field could be available with this antenna. To detect EBW, which is an electrostatic wave, a small tip (1 mm) antenna was used. As the preliminary results, we detected signals that have three characteristics of EBW, i.e., short wavelength, backward propagation, and electrostatic.
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52.70.Gw Radio-frequency and microwave measurements
52.70.Ds Electric and magnetic measurements
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.50.Sw Plasma heating by microwaves; ECR, LH, collisional heating
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
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Frequency modulation atomic force microscopy in ambient environments utilizing robust feedback tuning

J. I. Kilpatrick, A. Gannepalli, J. P. Cleveland, and S. P. Jarvis

Rev. Sci. Instrum. 80, 023701 (2009); http://dx.doi.org/10.1063/1.3073964 (6 pages) | Cited 9 times

Online Publication Date: 2 February 2009

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Frequency modulation atomic force microscopy (FM-AFM) is rapidly evolving as the technique of choice in the pursuit of high resolution imaging of biological samples in ambient environments. The enhanced stability afforded by this dynamic AFM mode combined with quantitative analysis enables the study of complex biological systems, at the nanoscale, in their native physiological environment. The operational bandwidth and accuracy of constant amplitude FM-AFM in low Q environments is heavily dependent on the cantilever dynamics and the performance of the demodulation and feedback loops employed to oscillate the cantilever at its resonant frequency with a constant amplitude. Often researchers use ad hoc feedback gains or instrument default values that can result in an inability to quantify experimental data. Poor choice of gains or exceeding the operational bandwidth can result in imaging artifacts and damage to the tip and/or sample. To alleviate this situation we present here a methodology to determine feedback gains for the amplitude and frequency loops that are specific to the cantilever and its environment, which can serve as a reasonable “first guess,” thus making quantitative FM-AFM in low Q environments more accessible to the nonexpert. This technique is successfully demonstrated for the low Q systems of air (Q ∼ 40) and water (Q ∼ 1). In addition, we present FM-AFM images of MC3T3-E1 preosteoblast cells acquired using the gains calculated by this methodology demonstrating the effectiveness of this technique.
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87.64.Dz Scanning tunneling and atomic force microscopy
87.18.-h Biological complexity
07.79.Lh Atomic force microscopes

Separation of topographic features from magnetic force images using capacitive coupling effect

Byung I. Kim

Rev. Sci. Instrum. 80, 023702 (2009); http://dx.doi.org/10.1063/1.3077151 (4 pages) | Cited 3 times

Online Publication Date: 5 February 2009

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Separation of topographic features from magnetic images has been an issue for the past two decades in magnetic force microscopy (MFM). The frequent pickups of the topographic features are interpreted as transitions of the tip between bistable states of the tip-sample assembly in the noncontact and tapping regions. MFM using electrostatic force modulation demonstrates the separation of the topographic features from the magnetic images by removing the tapping state from the bistable states through the introduction of a capacitive coupling.
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68.37.Rt Magnetic force microscopy (MFM)
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Thermally actuated tapping mode atomic force microscopy with polymer microcantilevers

Bhaskar Mitra and Angelo Gaitas

Rev. Sci. Instrum. 80, 023703 (2009); http://dx.doi.org/10.1063/1.3078010 (4 pages) | Cited 3 times

Online Publication Date: 5 February 2009

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This paper demonstrates a thermally actuated tapping mode atomic force microscopy (AFM) with a polymer cantilever. The cantilever (350×250×3 μm3) is made from polyimide and includes an embedded resistive heater for thermal actuation. The oscillation of the cantilever is due to the stress gradient caused by alternating heating and cooling from the periodic ac excitation of the heater. The tip oscillation amplitude is 5–10 nm in air. The oscillation occurs at 2ω and is a linear function of the applied voltage. The maximum oscillation amplitude is seen at 0.8 Hz with a 3dB frequency of 26 Hz. The damping of the oscillation due to tip-sample interaction is used to image the sample without any optomechanical feedback. Scans with a 200 nm tall grating indicate a resolution comparable to deflection signal from the AFM in contact mode.
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07.79.Lh Atomic force microscopes

Application of triangular atomic force microscopy cantilevers to friction measurement with the improved parallel scan method

Yu-Liang Wang and Xue-Zeng Zhao

Rev. Sci. Instrum. 80, 023704 (2009); http://dx.doi.org/10.1063/1.3079685 (7 pages)

Online Publication Date: 12 February 2009

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The atomic force microscopy (AFM) can provide tribological information in micro/nanoscale. However, the general measurement techniques require rigorous value of stiffness and relationship between AFM cantilever deformation and corresponding photodetector response. In this study, triangular AFM cantilevers with different dimensions are applied to quantitatively measure the coefficient of friction with the improved parallel scan method [ Y. L. Wang, X. Z. Zhao, and F. Q. Zhou, Rev. Sci. Instrum. 78, 036107 (2007) ]. An analytical model is first presented with the plan-view geometrical dimensions of cantilevers. Finite element analysis (FEA) models are set up to validate the analytical model. The results show good agreement between analytical calculation and FEA simulation. More importantly, the coefficient of friction obtained with different cantilevers on silicon surface shows a good consistency. At last, the factors which may affect measurement are discussed. The advantage of the model presented here is that the general uncertainties of thickness and Young’s modulus are not necessary to be known for the friction force calibration in AFM application.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
62.20.Qp Friction, tribology, and hardness
68.35.Af Atomic scale friction
07.10.Cm Micromechanical devices and systems
81.40.Pq Friction, lubrication, and wear
07.10.-h Mechanical instruments and equipment

Development of atomic force microscope with wide-band magnetic excitation for study of soft matter dynamics

Masami Kageshima, Takuma Chikamoto, Tatsuya Ogawa, Yoshiki Hirata, Takahito Inoue, Yoshitaka Naitoh, Yan Jun Li, and Yasuhiro Sugawara

Rev. Sci. Instrum. 80, 023705 (2009); http://dx.doi.org/10.1063/1.3080557 (7 pages) | Cited 7 times

Online Publication Date: 13 February 2009

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In order to probe dynamical properties of mesoscopic soft matter systems such as polymers, structured liquid, etc., a new atomic force microscopy apparatus with a wide-band magnetic cantilever excitation system was developed. Constant-current driving of an electromagnet up to 1 MHz was implemented with a closed-loop driver circuit. Transfer function of a commercial cantilever attached with a magnetic particle was measured in a frequency range of 1–1000 kHz in distilled water. Effects of the laser spot position, distribution of the force exerted on the cantilever, and difference in the detection scheme on the obtained transfer function are discussed in comparison with theoretical predictions by other research groups. A preliminary result of viscoelasticity spectrum measurement of a single dextran chain is shown and is compared with a recent theoretical calculation.
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07.79.Lh Atomic force microscopes
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

High sensitivity resonance frequency measurements of individual microcantilevers using fiber optical interferometry

Thomas Duden and Velimir Radmilovic

Rev. Sci. Instrum. 80, 023706 (2009); http://dx.doi.org/10.1063/1.3079686 (4 pages) | Cited 1 time

Online Publication Date: 17 February 2009

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We describe a setup for the resonance frequency measurement of individual microcantilevers. The setup displays both high spatial selectivity and sensitivity to specimen vibrations by utilizing a tapered fiber tip. The high sensitivity to specimen vibrations is achieved by the combination of optical Fabry–Perot interferometry and narrow band rf detection. Wave fronts reflected on the specimen and on the fiber tip end face interfere, thus no reference plane on the specimen is needed, as demonstrated with the example of freestanding silicon nitride microcantilevers. The resulting system is integrated in a DB-235 dual beam focused ion beam (FIB) system, thereby allowing the measurement of microcantilever responses during observation in scanning electron microscopy mode. The FIB was used to modify the optical fiber tip. At this point of our rf system development, the microcantilevers used to characterize the detector were not modified in situ.
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07.60.Ly Interferometers
07.60.Vg Fiber-optic instruments
42.81.Pa Sensors, gyros
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Wideband low-noise optical beam deflection sensor with photothermal excitation for liquid-environment atomic force microscopy

Takeshi Fukuma

Rev. Sci. Instrum. 80, 023707 (2009); http://dx.doi.org/10.1063/1.3086418 (8 pages) | Cited 17 times

Online Publication Date: 24 February 2009

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I developed a wideband low-noise optical beam deflection sensor with a photothermal cantilever excitation system for liquid-environment atomic force microscopy. The developed sensor has a 10 MHz bandwidth and 4.7 fm/math deflection noise density in water. The theoretically limited noise performance (i.e., the noise level limited only by the photodiode shot noise) has been achieved in liquid for the first time. Owing to the wide bandwidth and the replaceable focus lens design, the sensor is applicable to cantilevers with various dimensions. The deflection noise densities of less than 7.8 fm/math have been achieved in water for cantilevers with lengths from 35 to 125 μm. The ideal amplitude and phase versus frequency curves without distortion are obtained with the developed photothermal excitation system. The excitation system is applicable to relatively stiff cantilevers (>20 N/m) in liquid, making it possible to obtain true atomic-resolution images in liquid. True atomic-resolution imaging of mica in water is demonstrated using the developed deflection sensor and the photothermal excitation system.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.79.Lh Atomic force microscopes
42.79.Fm Reflectors, beam splitters, and deflectors

A low-temperature spin-polarized scanning tunneling microscope operating in a fully rotatable magnetic field

S. Meckler, M. Gyamfi, O. Pietzsch, and R. Wiesendanger

Rev. Sci. Instrum. 80, 023708 (2009); http://dx.doi.org/10.1063/1.3086428 (8 pages) | Cited 6 times

Online Publication Date: 25 February 2009

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A new scanning tunneling microscope for spin-polarized experiments has been developed. The microscope is operated at 4.7 K in a superconducting triple axis vector magnet providing the possibility for measurements depending on the direction of the magnetic field. In single axis mode the maximum field is 5 T perpendicular to the sample plane and 1.3 T in the sample plane, respectively. In cooperative mode fields are limited to 3.5 T perpendicular and 1 T in plane. The microscope is operated in an ultrahigh vacuum system providing optimized conditions for the self-assembled growth of magnetic structures at the atomic scale. The available temperature during growth ranges from 10 up to 1100 K. The performance of the new instrument is illustrated by spin-polarized measurements on 1.6 atomic layers Fe/W(110). It is demonstrated that the magnetization direction of ferromagnetic Fe and Gd tips can be adjusted using the external magnetic field. Atomic resolution is demonstrated by imaging an Fe monolayer on Ru(0001).
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.75.-c Magnetic properties of nanostructures
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
07.79.Cz Scanning tunneling microscopes
07.55.-w Magnetic instruments and components

Quantitative analysis of signal transduction in motile and phototactic cells by computerized light stimulation and model based tracking

Stefan Streif, Wilfried Franz Staudinger, Dieter Oesterhelt, and Wolfgang Marwan

Rev. Sci. Instrum. 80, 023709 (2009); http://dx.doi.org/10.1063/1.3076408 (8 pages) | Cited 1 time

Online Publication Date: 25 February 2009

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To investigate the responses of Halobacterium salinarum to stimulation with light (phototaxis and photokinesis), we designed an experimental setup consisting of optical devices for automatic video image acquisition and computer-controlled light stimulation, and developed algorithms to analyze physiological responses of the cells. Cells are categorized as motile and nonmotile by a classification scheme based on the square displacement of cell positions. Computerized tracking based on a dynamic model of the stochastic cell movement and a Kalman filter-based algorithm allows smoothed estimates of the cell tracks and the detection of physiological responses to complex stimulus patterns. The setup and algorithms were calibrated which allows quantitative measurements and systematic analysis of cellular sensing and response. Overall, the setup is flexible, extensible, and consists mainly of commercially available products. This facilitates modifications of the setup and algorithms for physiological studies of the motility of cells or microorganisms.
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87.17.Aa Modeling, computer simulation of cell processes
87.85.Ng Biological signal processing
87.50.wf Biophysical mechanisms of interaction
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Experimental setup and realization of thin film specimens for microtensile tests

Christophe Malhaire, Cédric Seguineau, Michel Ignat, Charles Josserond, Laurent Debove, Sebastiano Brida, Jean-Michel Desmarres, and Xavier Lafontan

Rev. Sci. Instrum. 80, 023901 (2009); http://dx.doi.org/10.1063/1.3077153 (5 pages) | Cited 3 times

Online Publication Date: 5 February 2009

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This paper describes a microtensile test system and the design as the realization of the samples dedicated to the tensile experiments. Two different technologies for the development of miniaturized specimens are detailed: self-standing tensile samples sustained by silicon frames and metal on polymer specimens obtained by laser cutting. The design of the samples has been optimized by means of finite element simulations. Aluminum beams with very large length on thickness ratio have been released from their silicon substrate using a standard etching process. Stress/strain curves are derived from experimental force/displacement values and discussed in terms of Young’s modulus values and critical parameters (flow and rupture stresses).
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81.70.Bt Mechanical testing, impact tests, static and dynamic loads
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
02.70.Dh Finite-element and Galerkin methods

High resolution in situ magneto-optic Kerr effect and scanning tunneling microscopy setup with all optical components in UHV

A. Lehnert, P. Buluschek, N. Weiss, J. Giesecke, M. Treier, S. Rusponi, and H. Brune

Rev. Sci. Instrum. 80, 023902 (2009); http://dx.doi.org/10.1063/1.3077148 (7 pages) | Cited 5 times

Online Publication Date: 9 February 2009

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A surface magneto-optic Kerr effect (MOKE) setup fully integrated in an ultrahigh vacuum chamber is presented. The system has been designed to combine in situ MOKE and scanning tunneling microscopy. Magnetic fields up to 0.3 T can be applied at any angle in the transverse plane allowing the study of in-plane and out-of-plane magnetization. The setup performance is demonstrated for a continuous film of 0.9 monolayers (ML) Co/Rh(111) with in-plane easy axis and for a superlattice of nanometric double layer Co islands on Au(11,12,12) with out-of-plane easy axis. For Co/Au(11,12,12) we demonstrate that the magnetic anisotropy energies deduced from thermally induced magnetization reversal and from applying a torque onto the magnetization by turning the field are the same. For the presented setup we establish a coverage detection limit of 0.5 ML for transverse and 0.1 ML for polar MOKE. For island superlattices with the density of Co/Au(11,12,12), the latter limit corresponds to islands composed of about 50 atoms. The detection limit can be further reduced when optimizing the MOKE setup for either one of the two Kerr configurations.
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78.20.Ls Magneto-optical effects
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
72.15.Jf Thermoelectric and thermomagnetic effects
68.55.jm Texture
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