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Apr 2012

Volume 83, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 83, 041101 (2012); http://dx.doi.org/10.1063/1.3697599 (19 pages)

Michael A. Duncan

The laser vaporization cluster source in the "cutaway" configuration. The sample rod is mounted from above with a flexible nylon screw in a holding block. The pulsed gas valve is mounted in the stainless steel can (left) and the skimmer is mounted on the opposite wall.

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back to top Microscopy and Imaging

Stereoscopic high-speed imaging using additive colors

Georgy N. Sankin, David Piech, and Pei Zhong

Rev. Sci. Instrum. 83, 043701 (2012); http://dx.doi.org/10.1063/1.3697747 (3 pages)

Online Publication Date: 6 April 2012

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multimedia

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An experimental system for digital stereoscopic imaging produced by using a high-speed color camera is described. Two bright-field image projections of a three-dimensional object are captured utilizing additive-color backlighting (blue and red). The two images are simultaneously combined on a two-dimensional image sensor using a set of dichromatic mirrors, and stored for off-line separation of each projection. This method has been demonstrated in analyzing cavitation bubble dynamics near boundaries. This technique may be useful for flow visualization and in machine vision applications.
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47.80.Jk Flow visualization and imaging
47.55.dp Cavitation and boiling
47.55.D- Drops and bubbles

Three-dimensional transport imaging for the spatially resolved determination of carrier diffusion length in bulk materials

K. E. Blaine, D. J. Phillips, C. L. Frenzen, C. Scandrett, and N. M. Haegel

Rev. Sci. Instrum. 83, 043702 (2012); http://dx.doi.org/10.1063/1.3698090 (7 pages)

Online Publication Date: 6 April 2012

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A contact-free optical technique is developed to enable a spatially resolved measurement of minority carrier diffusion length and the associated mobility-lifetime (μτ) product in bulk semiconductor materials. A scanning electron microscope is used in combination with an internal optical microscope and imaging charge-coupled device (CCD) to image the bulk luminescence from minority carrier recombination associated with one-dimensional excess carrier generation. Using a Green's function to model steady-state minority carrier diffusion in a three-dimensional half space, non-linear least squares analysis is then applied to extract values of carrier diffusion length and surface recombination velocity. The approach enables measurement of spatial variations in the μτ product with a high degree of spatial resolution.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Dual resonance excitation system for the contact mode of atomic force microscopy

M. Kopycinska-Müller, A. Striegler, R. Schlegel, N. Kuzeyeva, B. Köhler, and K.-J. Wolter

Rev. Sci. Instrum. 83, 043703 (2012); http://dx.doi.org/10.1063/1.3702799 (8 pages)

Online Publication Date: 12 April 2012

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We propose an improved system that enables simultaneous excitation and measurements of at least two resonance frequency spectra of a vibrating atomic force microscopy (AFM) cantilever. With the dual resonance excitation system it is not only possible to excite the cantilever vibrations in different frequency ranges but also to control the excitation amplitude for the individual modes. This system can be used to excite the resonance frequencies of a cantilever that is either free of the tip-sample interactions or engaged in contact with the sample surface. The atomic force acoustic microscopy and principally similar methods utilize resonance frequencies of the AFM cantilever vibrating while in contact with the sample surface to determine its local elastic modulus. As such calculation demands values of at least two resonance frequencies, two or three subsequent measurements of the contact resonance spectra are necessary. Our approach shortens the measurement time by a factor of two and limits the influence of the AFM tip wear on the values of the tip-sample contact stiffness. In addition, it allows for in situ observation of processes transpiring within the AFM tip or the sample during non-elastic interaction, such as tip fracture.
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07.79.Lh Atomic force microscopes
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Electrical capacitance tomography using an accelerated proximal gradient algorithm

Qian Xue, Huaxiang Wang, Ziqiang Cui, and Chengyi Yang

Rev. Sci. Instrum. 83, 043704 (2012); http://dx.doi.org/10.1063/1.3703306 (7 pages)

Online Publication Date: 16 April 2012

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Image reconstruction in electrical capacitance tomography requires a solution of an ill-posed inverse problem. This paper applies an accelerated proximal gradient (APG) singular value thresholding algorithm, which is originally proposed for the matrix completion problem, to image two-phase flow. Aiming to improve the image quality, a nuclear norm-based regularization technique is adopted to treat the ill-posedness of the inverse problem, and a simple updating technique is used to update the sensitivity matrix. Both typical and complicated distributions (e.g., “sun-rise” and cross-shape), have been examined based on a 16-electrode configuration. The results showed that the APG algorithm with updated sensitivity matrix could produce higher quality images when compared to the algorithm based on the typical sensitivity matrix. Both simulation and experiment results indicate that the algorithm developed has been able to achieve good quality reconstructed images with relativity fast computation speed for the cases tested in this paper.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
42.30.Wb Image reconstruction; tomography
02.30.Zz Inverse problems
02.60.-x Numerical approximation and analysis

Compact, low power radio frequency cavity for femtosecond electron microscopy

A. Lassise, P. H. A. Mutsaers, and O. J. Luiten

Rev. Sci. Instrum. 83, 043705 (2012); http://dx.doi.org/10.1063/1.3703314 (10 pages) | Cited 1 time

Online Publication Date: 17 April 2012

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Reported here is the design, construction, and characterization of a small, power efficient, tunable dielectric filled cavity for the creation of femtosecond electron bunches in an existing electron microscope without the mandatory use of femtosecond lasers. A 3 GHz pillbox cavity operating in the TM110 mode was specially designed for chopping the beam of a 30 keV scanning electron microscope. The dielectric material used is ZrTiO4, chosen for the high relative permittivity (ɛr = 37 at 10 GHz) and low loss tangent (tan δ = 2 × 10−4). This allows the cavity radius to be reduced by a factor of six, while the power consumption is reduced by an order of magnitude compared to a vacuum pillbox cavity. These features make this cavity ideal as a module for existing electron microscopes, and an alternative to femtosecond laser systems integrated with electron microscopes.
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42.79.-e Optical elements, devices, and systems
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.60.Jn High-speed techniques (microsecond to femtosecond)

18/20 T high magnetic field scanning tunneling microscope with fully low voltage operability, high current resolution, and large scale searching ability

Quanfeng Li, Qi Wang, Yubin Hou, and Qingyou Lu

Rev. Sci. Instrum. 83, 043706 (2012); http://dx.doi.org/10.1063/1.3703568 (5 pages) | Cited 1 time

Online Publication Date: 17 April 2012

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We present a home-built 18/20 T high magnetic field scanning tunneling microscope (STM) featuring fully low voltage (lower than ±15 V) operability in low temperatures, large scale searching ability, and 20 fA high current resolution (measured by using a 100 GOhm dummy resistor to replace the tip-sample junction) with a bandwidth of 3.03 kHz. To accomplish low voltage operation which is important in achieving high precision, low noise, and low interference with the strong magnetic field, the coarse approach is implemented with an inertial slider driven by the lateral bending of a piezoelectric scanner tube (PST) whose inner electrode is axially split into two for enhanced bending per volt. The PST can also drive the same sliding piece to inertial slide in the other bending direction (along the sample surface) of the PST, which realizes the large area searching ability. The STM head is housed in a three segment tubular chamber, which is detachable near the STM head for the convenience of sample and tip changes. Atomic resolution images of a graphite sample taken under 17.6 T and 18.0001 T are presented to show its performance.
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07.79.Cz Scanning tunneling microscopes

A method to provide rapid in situ determination of tip radius in dynamic atomic force microscopy

Sergio Santos, Li Guang, Tewfik Souier, Karim Gadelrab, Matteo Chiesa, and Neil H. Thomson

Rev. Sci. Instrum. 83, 043707 (2012); http://dx.doi.org/10.1063/1.4704376 (11 pages) | Cited 10 times

Online Publication Date: 24 April 2012

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We provide a method to characterize the tip radius of an atomic force microscopy in situ by monitoring the dynamics of the cantilever in ambient conditions. The key concept is that the value of free amplitude for which transitions from the attractive to repulsive force regimes are observed, strongly depends on the curvature of the tip. In practice, the smaller the value of free amplitude required to observe a transition, the sharper the tip. This general behavior is remarkably independent of the properties of the sample and cantilever characteristics and shows the strong dependence of the transitions on the tip radius. The main advantage of this method is rapid in situ characterization. Rapid in situ characterization enables one to continuously monitor the tip size during experiments. Further, we show how to reproducibly shape the tip from a given initial size to any chosen larger size. This approach combined with the in situ tip size monitoring enables quantitative comparison of materials measurements between samples. These methods are set to allow quantitative data acquisition and make direct data comparison readily available in the community.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.79.Lh Atomic force microscopes

A gantry-based tri-modality system for bioluminescence tomography

Han Yan, Yuting Lin, William C. Barber, Mehmet Burcin Unlu, and Gultekin Gulsen

Rev. Sci. Instrum. 83, 043708 (2012); http://dx.doi.org/10.1063/1.3698295 (8 pages) | Cited 1 time

Online Publication Date: 25 April 2012

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A gantry-based tri-modality system that combines bioluminescence (BLT), diffuse optical (DOT), and x-ray computed tomography (XCT) into the same setting is presented here. The purpose of this system is to perform bioluminescence tomography using a multi-modality imaging approach. As parts of this hybrid system, XCT and DOT provide anatomical information and background optical property maps. This structural and functional a priori information is used to guide and restrain bioluminescence reconstruction algorithm and ultimately improve the BLT results. The performance of the combined system is evaluated using multi-modality phantoms. In particular, a cylindrical heterogeneous multi-modality phantom that contains regions with higher optical absorption and x-ray attenuation is constructed. We showed that a 1.5 mm diameter bioluminescence inclusion can be localized accurately with the functional a priori information while its source strength can be recovered more accurately using both structural and the functional a priori information.
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42.30.Wb Image reconstruction; tomography

Wide-band acousto-optic deflectors for large field of view two-photon microscope

Runhua Jiang, Zhenqiao Zhou, Xiaohua Lv, and Shaoqun Zeng

Rev. Sci. Instrum. 83, 043709 (2012); http://dx.doi.org/10.1063/1.4705972 (5 pages)

Online Publication Date: 26 April 2012

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Acousto-optic deflector (AOD) is an attractive scanner for two-photon microscopy because it can provide fast and versatile laser scanning and does not involve any mechanical movements. However, due to the small scan range of available AOD, the field of view (FOV) of the AOD-based microscope is typically smaller than that of the conventional galvanometer-based microscope. Here, we developed a novel wide-band AOD to enlarge the scan angle. Considering the maximum acceptable acoustic attenuation in the acousto-optic crystal, relatively lower operating frequencies and moderate aperture were adopted. The custom AOD was able to provide 60 MHz 3-dB bandwidth and 80% peak diffraction efficiency at 840 nm wavelength. Based on a pair of such AOD, a large FOV two-photon microscope was built with a FOV up to 418.5 μm (40× objective). The spatiotemporal dispersion was compensated simultaneously with a single custom-made prism. By means of dynamic power modulation, the variation of laser intensity within the FOV was reduced below 5%. The lateral and axial resolution of the system were 0.58–2.12 μm and 2.17–3.07 μm, respectively. Pollen grain images acquired by this system were presented to demonstrate the imaging capability at different positions across the entire FOV.
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42.79.Jq Acousto-optical devices
42.79.Fm Reflectors, beam splitters, and deflectors
07.60.Pb Conventional optical microscopes

Complementary cellophane optic gate and its use for a 3D iPad without glasses

K. Iizuka

Rev. Sci. Instrum. 83, 043710 (2012); http://dx.doi.org/10.1063/1.4705734 (8 pages)

Online Publication Date: 27 April 2012

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A complementary cellophane optic gate was fabricated using a birefringent cellophane sheet. Previous versions of the optic gate required the retardance of the cellophane to be as close to 180° as possible throughout the entire visible wavelength range, which meant it was often difficult to find a cellophane sheet with the right thickness and dispersion characteristics to meet this requirement. The complementary optic gate reported in this paper has no restriction on the thickness, composition, or wavelength range of the cellophane sheet except that the cellophane must have some birefringence. Even with an arbitrary retardance, an extinction ratio of 5 × 10−3 was achieved at λ = 0.63 μm. The optic gate was used to convert an iPad into a 3D display without the need for the observer to wear glasses. The high extinction ratio of the optic gate resulted in a 3D display of supreme quality.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.79.Kr Display devices, liquid-crystal devices
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