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Top 20 Most Read Articles
December 2007
The 20 articles with the most full-text downloads during the month, in descending order.
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Current multiplier to improve generator-to-load coupling for pulse-power generators Rev. Sci. Instrum. 76, 063501 (2005); http://dx.doi.org/10.1063/1.1928450 (5 pages) Online Publication Date: 1 June 2005
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The load inductance, Ld, can be several times smaller than that of the pulsed power generator, L0, limiting the energy transfer efficiency. We define a relatively simple circuit modification, which improves the generator-to-load coupling, multiplying the load current in the case of interest, where L0⪢Ld. The suggested circuit modification operates similarly to an N:1 transformer and it can be designed to operate in vacuum with pulsed-power loads at high currents (many megaamperes). The current multiplier requires an additional volume having high self inductance, L, connected through convolutes to the generator and load. In its simplest configuration, N = 2, a single convolute is required. The presented analysis shows that the efficiency of the proposed current multiplication scheme can theoretically exceed the values for a typical direct load-to-generator circuit. The modified hardware allows an increase of the load current by the factor of Id/Ig = NL/(L+Ld), where Ig represents the generator current and L can be easily made much greater than Ld either with or without the use of magnetic cores. The only uncertainties of this approach are potential convolute losses and the slight increase in load current rise time. Preliminary experimental tests were performed with a scaled down configuration which demonstrated current gain of 1.7 in the frequency range of interest and showed good agreement between analytically predicted and measured currents. The benefit of the scheme is also illustrated by simple circuit simulations for two types of potential applications requiring high power densities in vacuum: isentropic compression studies with Ld = constant loads, and imploding z-pinch research with dynamic [Ld(t)] loads. The proposed device is applicable for improving the characteristics of existing and future pulse power facilities.
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WSXM: A software for scanning probe microscopy and a tool for nanotechnology Rev. Sci. Instrum. 78, 013705 (2007); http://dx.doi.org/10.1063/1.2432410 (8 pages) Online Publication Date: 31 January 2007
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In this work we briefly describe the most relevant features of WSXM, a freeware scanning probe microscopy software based on MS-Windows. The article is structured in three different sections: The introduction is a perspective on the importance of software on scanning probe microscopy. The second section is devoted to describe the general structure of the application; in this section the capabilities of WSXM to read third party files are stressed. Finally, a detailed discussion of some relevant procedures of the software is carried out.
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Rev. Sci. Instrum. 78, 121301 (2007); http://dx.doi.org/10.1063/1.2821148 (15 pages) Online Publication Date: 12 December 2007
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Experimental and theoretical aspects of obtaining the magnetic information carried by laser beams diffracted from an array of micro- or nanosized magnetic objects are reviewed. We report on the fundamentals of vector magneto-optic Kerr effect (MOKE), Bragg-MOKE, and second-order effects in the Kerr signal in longitudinal Kerr geometry as well as on an experimental setup used for vector and Bragg-MOKE experiments. The vector and Bragg-MOKE technique in combination with micromagnetic simulation is a reliable tool for measuring the complete magnetization vector and for characterizing the reversal mechanism of lateral magnetic nanostructures. We discuss the Bragg-MOKE effect for three standard domain configurations during the magnetization reversal process and present the expected behavior of the magnetic hysteresis loops.
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Rev. Sci. Instrum. 78, 113104 (2007); http://dx.doi.org/10.1063/1.2802199 (7 pages) Online Publication Date: 9 November 2007
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Recent progress in high intensity ultrafast laser systems provides the opportunity to produce laser plasma x-ray sources exhibiting broad spectrum and high average x-ray flux that are well adapted to x-ray absorption measurements. In this paper, the development of a laser based x-ray absorption near edge structure (XANES) beamline exhibiting high repetition rate by using the Advanced Laser Light Source (ALLS) facility 100 Hz laser system (100 mJ, 35 fs at 800 nm) is presented. This system is based on a broadband tantalum solid target soft x-ray source and a grazing incidence grating spectrometer in the 1–5 nm wavelength range. To demonstrate the high potential of this laser based XANES technique in condensed matter physics, material science, or biology, measurements realized with several samples are presented: VO2 vanadium L edge, Si3N4 nitrogen K edge, and BPDA/PPD polyimide carbon K edge. The characteristics of this laser based beamline are discussed in terms of brightness, signal to noise ratio, and compared to conventional synchrotron broadband x-ray sources which allow achieving similar measurements. Apart from the very compact size and the relative low cost, the main advantages of such a laser based soft x-ray source are the picosecond pulse duration and the perfect synchronization between this x-ray probe and a laser pulse excitation which open the way to the realization of time resolved x-ray absorption measurements with picosecond range time resolution to study the dynamics of ultrafast processes and phase transition.
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Invited Article: An improved double-toroidal spectrometer for gas phase (e,2e) studies Rev. Sci. Instrum. 78, 111301 (2007); http://dx.doi.org/10.1063/1.2813014 (20 pages) Online Publication Date: 27 November 2007
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A new spectrometer is described for measuring the momentum distributions of scattered electrons arising from electron-atom and electron-molecule ionization experiments. It incorporates and builds on elements from a number of previous designs, namely, a source of polarized electrons and two high-efficiency electrostatic electron energy analyzers. The analyzers each comprise a seven-element retarding-electrostatic lens system, four toroidal-sector electrodes, and a fast position-and-time-sensitive two-dimensional delay-line detector. Results are presented for the electron-impact-induced ionization of helium and the elastic scattering of electrons from argon and helium which demonstrate that high levels of momentum resolution and data-collection efficiency are achieved. Problematic aspects regarding variations in collection efficiency over the accepted momentum phase space are addressed and a methodology for their correction presented. Principles behind the present design and previous designs for electrostatic analyzers based around electrodes of toroidal-sector geometry are discussed and a framework is provided for optimizing future devices.
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BaHigh-force magnetic tweezers with force feedback for biological applications Rev. Sci. Instrum. 78, 114301 (2007); http://dx.doi.org/10.1063/1.2804771 (6 pages) Online Publication Date: 9 November 2007
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Magnetic micromanipulation using magnetic tweezers is a versatile biophysical technique and has been used for single-molecule unfolding, rheology measurements, and studies of force-regulated processes in living cells. This article describes an inexpensive magnetic tweezer setup for the application of precisely controlled forces up to 100 nN onto 5 μm magnetic beads. High precision of the force is achieved by a parametric force calibration method together with a real-time control of the magnetic tweezer position and current. High forces are achieved by bead-magnet distances of only a few micrometers. Applying such high forces can be used to characterize the local viscoelasticity of soft materials in the nonlinear regime, or to study force-regulated processes and mechanochemical signal transduction in living cells. The setup can be easily adapted to any inverted microscope.
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Rev. Sci. Instrum. 78, 081101 (2007); http://dx.doi.org/10.1063/1.2754076 (8 pages) Online Publication Date: 6 August 2007
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Cantilevers with single micro- or nanoparticle probes have been widely used for atomic force microscopy surface force measurements and apertureless scanning near-field optical microscopy applications. In this article, I critically review the particle attachment and modification techniques currently available, to help researchers choose the appropriate techniques for specific applications.
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Femtosecond pulse shaping using spatial light modulators Rev. Sci. Instrum. 71, 1929 (2000); http://dx.doi.org/10.1063/1.1150614 (32 pages)
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We review the field of femtosecond pulse shaping, in which Fourier synthesis methods are used to generate nearly arbitrarily shaped ultrafast optical wave forms according to user specification. An emphasis is placed on programmable pulse shaping methods based on the use of spatial light modulators. After outlining the fundamental principles of pulse shaping, we then present a detailed discussion of pulse shaping using several different types of spatial light modulators. Finally, new research directions in pulse shaping, and applications of pulse shaping to optical communications, biomedical optical imaging, high power laser amplifiers, quantum control, and laser-electron beam interactions are reviewed. © 2000 American Institute of Physics. |
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Rev. Sci. Instrum. 76, 061101 (2005); http://dx.doi.org/10.1063/1.1927327 (12 pages) Online Publication Date: 26 May 2005
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Nanoelectromechanical systems (NEMS) are drawing interest from both technical and scientific communities. These are electromechanical systems, much like microelectromechanical systems, mostly operated in their resonant modes with dimensions in the deep submicron. In this size regime, they come with extremely high fundamental resonance frequencies, diminished active masses,and tolerable force constants; the quality (Q) factors of resonance are in the range Q ∼ 103–105—significantly higher than those of electrical resonant circuits. These attributes collectively make NEMS suitable for a multitude of technological applications such as ultrafast sensors, actuators, and signal processing components. Experimentally, NEMS are expected to open up investigations of phonon mediated mechanical processes and of the quantum behavior of mesoscopic mechanical systems. However, there still exist fundamental and technological challenges to NEMS optimization. In this review we shall provide a balanced introduction to NEMS by discussing the prospects and challenges in this rapidly developing field and outline an exciting emerging application, nanoelectromechanical mass detection.
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Calibration of atomic‐force microscope tips Rev. Sci. Instrum. 64, 1868 (1993); http://dx.doi.org/10.1063/1.1143970 (6 pages)
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Images and force measurements taken by an atomic‐force microscope (AFM) depend greatly on the properties of the spring and tip used to probe the sample’s surface. In this article, we describe a simple, nondestructive procedure for measuring the force constant, resonant frequency, and quality factor of an AFM cantilever spring and the effective radius of curvature of an AFM tip. Our procedure uses the AFM itself and does not require additional equipment. |
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A hyperspectral fluorescence lifetime probe for skin cancer diagnosis Rev. Sci. Instrum. 78, 123101 (2007); http://dx.doi.org/10.1063/1.2818785 (7 pages) Online Publication Date: 4 December 2007
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The autofluorescence of biological tissue can be exploited for the detection and diagnosis of disease but, to date, its complex nature and relatively weak signal levels have impeded its widespread application in biology and medicine. We present here a portable instrument designed for the in situ simultaneous measurement of autofluorescence emission spectra and temporal decay profiles, permitting the analysis of complex fluorescence signals. This hyperspectral fluorescence lifetime probe utilizes two ultrafast lasers operating at 355 and 440 nm that can excite autofluorescence from many different biomolecules present in skin tissue including keratin, collagen, nicotinamide adenine dinucleotide (phosphate), and flavins. The instrument incorporates an optical fiber probe to provide sample illumination and fluorescence collection over a millimeter-sized area. We present a description of the system, including spectral and temporal characterizations, and report the preliminary application of this instrument to a study of recently resected (<2 h) ex vivo skin lesions, illustrating its potential for skin cancer detection and diagnosis.
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A low temperature scanning tunneling microscope for electronic and force spectroscopy Rev. Sci. Instrum. 78, 113705 (2007); http://dx.doi.org/10.1063/1.2804165 (5 pages) Online Publication Date: 9 November 2007
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In this article, we describe and test a novel way to extend a low temperature scanning tunneling microscope with the capability to measure forces. The tuning fork that we use for this is optimized to have a high quality factor and frequency resolution. Moreover, as this technique is fully compatible with the use of bulk tips, it is possible to combine the force measurements with the use of superconductive or magnetic tips, advantageous for electronic spectroscopy. It also allows us to calibrate both the amplitude and the spring constant of the tuning fork easily, in situ and with high precision.
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Rev. Sci. Instrum. 78, 120901 (2007); http://dx.doi.org/10.1063/1.2821150 (2 pages) Online Publication Date: 12 December 2007
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Manufacturing a thin wire electrostatic trap for ultracold polar molecules Rev. Sci. Instrum. 78, 113108 (2007); http://dx.doi.org/10.1063/1.2815338 (4 pages) Online Publication Date: 30 November 2007
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We present a detailed description on how to build a thin wire electrostatic trap (TWIST) for ultracold polar molecules. It is the first design of an electrostatic trap that can be superimposed directly onto a magneto-optical trap (MOT). We can thus continuously produce ultracold polar molecules via photoassociation from a two species MOT and instantaneously trap them in the TWIST without the need for complex transfer schemes. Despite the spatial overlap of the TWIST and the MOT, the two traps can be operated and optimized completely independently due to the complementary nature of the utilized trapping mechanisms.
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Rev. Sci. Instrum. 78, 123701 (2007); http://dx.doi.org/10.1063/1.2821610 (7 pages) Online Publication Date: 10 December 2007
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We describe the development and the capabilities of an advanced system for nanoscale electrical transport studies. This system consists of a low temperature four-probe scanning tunneling microscope (STM) and a high-resolution scanning electron microscope coupled to a molecular-beam epitaxy sample preparation chamber. The four STM probes can be manipulated independently with subnanometer precision, enabling atomic resolution STM imaging and four-point electrical transport study of surface electronic systems and nanostructured materials at temperatures down to 10 K. Additionally, an integrated energy analyzer allows for scanning Auger microscopy to probe chemical species of nanostructures. Some testing results are presented.
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Microcantilever actuation via periodic internal heating Rev. Sci. Instrum. 78, 126102 (2007); http://dx.doi.org/10.1063/1.2818805 (3 pages) Online Publication Date: 11 December 2007
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This paper reports electrothermal actuation of silicon microcantilevers having integrated resistive heaters. Periodic electrical excitation induced periodic resistive heating in the cantilever, while the cantilever deflection was monitored with a photodetector. Excitation was either at the cantilever resonant frequency, f0, f0/2, or f0/3. When the time averaged maximum cantilever temperature was 174 °C, the cantilever out-of-plane actuation amplitude was 484 nm near the cantilever resonance frequency of 24.9 kHz. This actuation was sufficiently large to operate the cantilever in intermittent contact mode and scan a calibration grating of height of 20 nm.
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A broadband laser plasma x-ray source for application in ultrafast chemical structure dynamics Rev. Sci. Instrum. 78, 115105 (2007); http://dx.doi.org/10.1063/1.2813340 (9 pages) Online Publication Date: 20 November 2007
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A plasma source free from characteristic emission lines is described, based on laser irradiation of a water jet in a helium atmosphere. Various key aspects of the laser interaction are presented along with practical characterization of the observed isotropic ∼ 4–10 keV x-ray emissions, measurements of which indicate subpicosecond duration. Observations are consistent with a vacuum heating plasma mechanism at the helium-water interface and indicate strong potential for in-house ultrafast chemical structure dynamics application when coupled to contemporary detector developments.
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Rev. Sci. Instrum. 78, 113707 (2007); http://dx.doi.org/10.1063/1.2794732 (5 pages) Online Publication Date: 13 November 2007
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Most of studies in protein nanomechanics have used the atomic force microscope (AFM) in its force-measuring mode on immobilized protein repeats (polyproteins) as single-molecule markers. Here, we add imaging capabilities to a standard, state-of-the-art AFM “puller” and integrate the most powerful programs of analysis available for both AFM modes. This unique instrument allows high-resolution, quasi-simultaneous imaging/force spectroscopy in aqueous solution. We demonstrate its capabilities using polyproteins of a model system (titin I27 domain). This tool should greatly facilitate the development of a much needed universal functionalization system for AFM, one that should allow better sample control and an improved efficiency of protein immobilization.
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Cantilever transducers as a platform for chemical and biological sensors Rev. Sci. Instrum. 75, 2229 (2004); http://dx.doi.org/10.1063/1.1763252 (25 pages) Online Publication Date: 21 June 2004
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Since the late 1980s there have been spectacular developments in micromechanical or microelectro-mechanical (MEMS) systems which have enabled the exploration of transduction modes that involve mechanical energy and are based primarily on mechanical phenomena. As a result an innovative family of chemical and biological sensors has emerged. In this article, we discuss sensors with transducers in a form of cantilevers. While MEMS represents a diverse family of designs, devices with simple cantilever configurations are especially attractive as transducers for chemical and biological sensors. The review deals with four important aspects of cantilever transducers: (i) operation principles and models; (ii) microfabrication; (iii) figures of merit; and (iv) applications of cantilever sensors. We also provide a brief analysis of historical predecessors of the modern cantilever sensors. © 2004 American Institute of Physics. |
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Time‐of‐Flight Mass Spectrometer with Improved Resolution Rev. Sci. Instrum. 26, 1150 (1955); http://dx.doi.org/10.1063/1.1715212 (8 pages) Online Publication Date: 29 December 2004
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A new type of ion gun is described which greatly improves the resolution of a nonmagnetic time‐of‐flight mass spectrometer. The focusing action of this gun is discussed and analyzed mathematically. The validity of the analysis and the practicability of the gun are demonstrated by the spectra obtained. The spectrometer is capable of measuring the relative abundance of adjacent masses well beyond 100 amu. |
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