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Dec 2008

Volume 79, Issue 12, Articles (12xxxx)

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Improvement of temporal resolution for three-dimensional continuous-wave electron paramagnetic resonance imaging

Hideo Sato-Akaba, Hirotada Fujii, and Hiroshi Hirata

Rev. Sci. Instrum. 79, 123701 (2008); http://dx.doi.org/10.1063/1.3033161 (7 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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This paper describes improved temporal resolution for three-dimensional (3D) continuous-wave electron paramagnetic resonance (EPR) imaging. To improve temporal resolution, the duration of magnetic filed scanning that is used to obtain an EPR spectrum for each projection was reduced to 40 ms. The Helmholtz coil pair for field scanning was driven by triangular waves. The uniform distribution of projections was also used to reduce the number of projections for 3D image reconstruction. The reduction reaction of 4-hydroxy-2,2,6,6-tetramethyl-piperidinooxy with ascorbic acid was visualized by improved 3D EPR imaging techniques with a temporal resolution of 5.8 s.
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87.61.Tg Clinical applications
87.57.cf Spatial resolution
87.57.nf Reconstruction
07.05.Pj Image processing
87.14.Pq Vitamins
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Development of new in situ observation system for dynamic study of lubricant molecules on metal friction surfaces by two-dimensional fast-imaging Fourier-transform infrared-attenuated total reflection spectrometer

Keiji Sasaki, Naruhiko Inayoshi, and Kohji Tashiro

Rev. Sci. Instrum. 79, 123702 (2008); http://dx.doi.org/10.1063/1.2987685 (7 pages) | Cited 3 times

Online Publication Date: 2 December 2008

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To observe the time-dependent two-dimensional (2D) images of spatial distribution of chemically/physically modified lubricant molecules on the metal surface during friction motion, a new in situ technique has been developed by combining the 2D fast-imaging Fourier-transform infrared-attenuated total reflection spectrometer with the temperature-controlled friction equipment containing lubricant agent. Using this new instrument, the time-dependent changes in lubricant molecules, for example, cis-trans isomerization, stress-induced molecular deformation, etc., can be detected successfully. The characteristic features of this instrument have been demonstrated in a detailed and concrete manner by demonstrating the experimental data measured for oleic acid and tricresyl phosphate.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.30.-d Imaging and optical processing
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Photothermal excitation and laser Doppler velocimetry of higher cantilever vibration modes for dynamic atomic force microscopy in liquid

Shuhei Nishida, Dai Kobayashi, Takeo Sakurada, Tomonori Nakazawa, Yasuo Hoshi, and Hideki Kawakatsu

Rev. Sci. Instrum. 79, 123703 (2008); http://dx.doi.org/10.1063/1.3040500 (4 pages) | Cited 11 times

Online Publication Date: 12 December 2008

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The authors present an optically based method combining photothermal excitation and laser Doppler velocimetry of higher cantilever vibration modes for dynamic atomic force microscopy in liquid. The frequency spectrum of a silicon cantilever measured in water over frequencies ranging up to 10 MHz shows that the method allows us to excite and detect higher modes, from fundamental to fifth flexural, without enhancing spurious resonances. By reducing the tip oscillation amplitude using higher modes, the average tip-sample force gradient due to chemical bonds is effectively increased to achieve high-spatial-resolution imaging in liquid. The method’s performance is demonstrated by atomic resolution imaging of a mica surface in water obtained using the second flexural mode with a small tip amplitude of 99 pm; individual atoms on the surface with small height differences of up to 60 pm are clearly resolved.
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07.79.Lh Atomic force microscopes
06.30.Gv Velocity, acceleration, and rotation
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
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Single-sided radio-frequency field gradient with two unsymmetrical loops: Applications to nuclear magnetic resonance

Laouès Guendouz, Sébastien Leclerc, Alain Retournard, Ahcène Hedjiedj, and Daniel Canet

Rev. Sci. Instrum. 79, 123704 (2008); http://dx.doi.org/10.1063/1.3042276 (8 pages) | Cited 1 time

Online Publication Date: 12 December 2008

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Magnetic field gradients are nowadays indispensable to most nuclear magnetic resonance experiments and are at the basis of magnetic resonance imaging (MRI). Most of the time, gradients of the static magnetic field are employed. Gradients of the radio-frequency (rf) field may constitute an interesting alternative. Until now, they were produced by a single loop. We demonstrate in this paper how two unsymmetrical series loops can be optimized to produce rf gradients of much better performances. This optimization is based on a thorough theoretical approach and the gradient uniformity is studied through accurate simulations. Two prototypes were devised: one for a 2.34 T horizontal magnet (used in MRI), and the other for a 4.7 T vertical magnet (used for pure spectroscopic applications). These two-loop systems were designed for proton resonance frequencies (100 and 200 MHz, respectively). Performances of both systems were verified (versus theoretical predictions) by means of experiments employing gradients in view of the determination of the self-diffusion coefficients of liquids.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
66.10.cg Mass diffusion, including self-diffusion, mutual diffusion, tracer diffusion, etc.
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Digital control of force microscope cantilevers using a field programmable gate array

Jonathan P. Jacky, Joseph L. Garbini, Matthew Ettus, and John A. Sidles

Rev. Sci. Instrum. 79, 123705 (2008); http://dx.doi.org/10.1063/1.3043432 (11 pages) | Cited 1 time

Online Publication Date: 12 December 2008

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This report describes a cantilever controller for magnetic resonance force microscopy based on a field programmable gate array, along with the hardware and software used to integrate the controller into an experiment. The controller is assembled from a low-cost commercially available software defined radio device and libraries of open-source software. The controller includes a digital filter comprising two cascaded second-order sections (“biquads”), which together can implement transfer functions for optimal cantilever controllers. An appendix in this report shows how to calculate filter coefficients for an optimal controller from measured cantilever characteristics. The controller also includes an input multiplexer and adder used in calibration protocols. Filter coefficients and multiplexer settings can be set and adjusted by control software while an experiment is running. The input is sampled at 64 MHz; the sampling frequency in the filters can be divided down under software control to achieve a good match with filter characteristics. Data reported here were sampled at 500 kHz, chosen for acoustic cantilevers with resonant frequencies near 8 kHz. Inputs are digitized with 12 bit resolution, and outputs are digitized with 14 bits. The experiment software is organized as a client and server to make it easy to adapt the controller to different experiments. The server encapsulates the details of controller hardware organization, connection technology, filter architecture, and number representation. The same server could be used in any experiment, while a different client encodes the particulars of each experiment.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
84.30.Sk Pulse and digital circuits
07.05.Dz Control systems
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
84.30.Vn Filters
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Nanoscale lithography with frequency-modulation atomic force microscopy

Masayuki Hamada, T. Eguchi, K. Akiyama, and Y. Hasegawa

Rev. Sci. Instrum. 79, 123706 (2008); http://dx.doi.org/10.1063/1.3043435 (4 pages) | Cited 2 times

Online Publication Date: 12 December 2008

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A lithographic method to draw nanoscale structures by repetitive depositions of the tip material by field evaporation has been developed based on frequency-modulation atomic force microscopy (FM-AFM). Because of high stiffness of quartz tuning forks, a force sensor in the AFM, unwanted mechanical contact of the AFM tip with the substrate was prevented. Precise control of the tip-substrate gap distance with FM-AFM and a gold tip sharpened with focused ion beam enable us to deposit gold dots as small as ∼ 20 nm in size and construct nanoscale patterns.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
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Microbeam-integrated multiphoton imaging system

Alan W. Bigelow, Charles R. Geard, Gerhard Randers-Pehrson, and David J. Brenner

Rev. Sci. Instrum. 79, 123707 (2008); http://dx.doi.org/10.1063/1.3043439 (6 pages) | Cited 2 times

Online Publication Date: 12 December 2008

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Multiphoton microscopy has been added to the array of imaging techniques at the endstation for the Microbeam II cell irradiator at Columbia University’s Radiological Research Accelerator Facility (RARAF). This three-dimensional (3D), laser-scanning microscope functions through multiphoton excitation, providing an enhanced imaging routine during radiation experiments with tissuelike samples, such as small living animals and organisms. Studies at RARAF focus on radiation effects; hence, this multiphoton microscope was designed to observe postirradiation cellular dynamics. This multiphoton microscope was custom designed into an existing Nikon Eclipse E600-FN research fluorescence microscope on the irradiation platform. Design details and biology applications using this enhanced 3D-imaging technique at RARAF are reviewed.
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87.64.mn Multiphoton
87.63.lt Laser imaging
87.50.W- Optical/infrared radiation effects
42.62.Be Biological and medical applications
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A scanning Hall probe microscope for high resolution magnetic imaging down to 300 mK

V. V. Khotkevych, M. V. Milošević, and S. J. Bending

Rev. Sci. Instrum. 79, 123708 (2008); http://dx.doi.org/10.1063/1.3046285 (5 pages) | Cited 4 times

Online Publication Date: 12 December 2008

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We present the design, construction, and performance of a low-temperature scanning Hall probe microscope with submicron lateral resolution and a large scanning range. The detachable microscope head is mounted on the cold flange of a commercial 3He-refrigerator (Oxford Instruments, Heliox VT-50) and operates between room temperature and 300 mK. It is fitted with a three-axis slip-stick nanopositioner that enables precise in situ adjustment of the probe location within a 6×6×7 mm3 space. The local magnetic induction at the sample surface is mapped with an easily changeable microfabricated Hall probe [typically GsAs/AlGaAs or AlGaAs/InGaAs/GaAs Hall sensors with integrated scanning tunnel microscopy (STM) tunneling tips] and can achieve minimum detectable fields ≥ 10 mG/Hz1/2. The Hall probe is brought into very close proximity to the sample surface by sensing and controlling tunnel currents at the integrated STM tip. The instrument is capable of simultaneous tunneling and Hall signal acquisition in surface-tracking mode. We illustrate the potential of the system with images of superconducting vortices at the surface of a Nb thin film down to 372 mK, and also of labyrinth magnetic-domain patterns of an yttrium iron garnet film captured at room temperature.
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06.30.Ka Basic electromagnetic quantities
07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ch Domain walls and domain structure
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Direct calibration of colloidal probe cantilevers via Derjaguin, Landau, Verwey, and Overbeek surface forces in electrolyte solution

Xiaoting Hong and Gerold A. Willing

Rev. Sci. Instrum. 79, 123709 (2008); http://dx.doi.org/10.1063/1.3046284 (5 pages)

Online Publication Date: 17 December 2008

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The development of colloidal probe microscopy has made it possible to directly measure the interaction forces between two different surfaces in solution. Cantilever calibration is presently a subject of intense experimental and theoretical interest due to the need for accurate force measurement. We developed a novel and direct calibration method for colloidal probe cantilevers to which a silica microsphere has been previously attached based on fitting experimental force curves for the interaction between the silica sphere and a silica flat in dilute KBr solutions to the theoretical Derjaguin, Landau, Verwey, and Overbeek force curves using the measured zeta potential of the silica surfaces.
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82.45.Gj Electrolytes
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.45.Jn Surface structure, reactivity and catalysis
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Development of a scanning surface probe for nanoscale tip-enhanced desorption/ablation

Kent A. Meyer, Olga Ovchinnikova, Kin Ng, and Douglas E. Goeringer

Rev. Sci. Instrum. 79, 123710 (2008); http://dx.doi.org/10.1063/1.3053200 (4 pages) | Cited 7 times

Online Publication Date: 23 December 2008

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We report on the development of a versatile scanning apparatus for nanoscale surface sampling that utilizes the interaction of laser radiation at a sharp probe tip to effect desorption/ablation on opaque substrates. The process, which currently yields surface craters as small as ∼ 50 nm diameter×5 nm deep, has been demonstrated with both metal-coated and bare silicon tips. Desorption/ablation under the tip occurs at illumination intensities below the corresponding optical far-field threshold, suggesting that the latter process should not degrade the spatial resolution attainable for proposed chemical imaging methods based on the scanning surface probe.
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07.79.-v Scanning probe microscopes and components
79.20.La Photon- and electron-stimulated desorption
79.20.Ds Laser-beam impact phenomena
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