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Top 20 Most Read Articles
October 2006
The 20 articles with the most full-text downloads during the month, in descending order.
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Superconducting quantum interference device instruments and applications Rev. Sci. Instrum. 77, 101101 (2006); http://dx.doi.org/10.1063/1.2354545 (45 pages) Online Publication Date: 11 October 2006
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Superconducting quantum interference devices (SQUIDs) have been a key factor in the development and commercialization of ultrasensitive electric and magnetic measurement systems. In many cases, SQUID instrumentation offers the ability to make measurements where no other methodology is possible. We review the main aspects of designing, fabricating, and operating a number of SQUID measurement systems. While this article is not intended to be an exhaustive review on the principles of SQUID sensors and the underlying concepts behind the Josephson effect, a qualitative description of the operating principles of SQUID sensors and the properties of materials used to fabricate SQUID sensors is presented. The difference between low and high temperature SQUIDs and their suitability for specific applications is discussed. Although SQUID electronics have the capability to operate well above 1 MHz, most applications tend to be at lower frequencies. Specific examples of input circuits and detection coil configuration for different applications and environments, along with expected performance, are described. In particular, anticipated signal strength, magnetic field environment (applied field and external noise), and cryogenic requirements are discussed. Finally, a variety of applications with specific examples in the areas of electromagnetic, material property, nondestructive test and evaluation, and geophysical and biomedical measurements are reviewed.
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Tip characterizer for atomic force microscopy Rev. Sci. Instrum. 77, 103704 (2006); http://dx.doi.org/10.1063/1.2356855 (4 pages) Online Publication Date: 9 October 2006
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A tip characterizer for atomic force microscopy (AFM) was developed based on the fabrication of multilayer thin films. Comb-shaped line and space (LS) and wedge-shaped knife-edge structures were fabricated on a GaAs substrate. GaAs/InGaP superlattices were used to control the width of the structures precisely, and selective chemical etching was used to form sharp edges on the nanostructures. The minimum size of the LS structure was designed to be 10 nm, and the radius of the knife edge was less than 5 nm. These nanostructures were used as a well-defined tip characterizer to measure the shape of a tip on a cantilever from line profiles of AFM images.
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Method of characterizing electrical contact properties of carbon nanotube coated surfaces Rev. Sci. Instrum. 77, 095105 (2006); http://dx.doi.org/10.1063/1.2349300 (3 pages) Online Publication Date: 25 September 2006
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We present a method for electromechanical characterization of carbon nanotube (CNT) films grown on silicon substrates as potential electrical contacts. The method includes measuring the sheet resistance of a tangled CNT film, measuring the contact resistance between two tangled CNT films, and investigating the dependence on applied force and postgrowth annealing. We also characterize Au-CNT film contact resistance by simultaneous measurement of applied force and resistance. We measure a contact resistance as low as 0.024 Ω/mm2 between two films of tangled single-wall carbon nanotubes grown on a polished silicon substrate and observe an electromechanical behavior very similar to that predicted by classical contact theory.
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Design and performance of a beetle-type double-tip scanning tunneling microscope Rev. Sci. Instrum. 77, 093701 (2006); http://dx.doi.org/10.1063/1.2336112 (5 pages) Online Publication Date: 12 September 2006
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A combination of a double-tip scanning tunneling microscope with a scanning electron microscope in ultrahigh vacuum environment is presented. The compact beetle-type design made it possible to integrate two independently driven scanning tunneling microscopes in a small space. Moreover, an additional level for coarse movement allows the decoupling of the translation and approach of the tunneling tip. The position of the two tips can be controlled from the millimeter scale down to 50 nm with the help of an add-on electron microscope. The instrument is capable of atomic resolution imaging with each tip.
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Spectral shaping of a 10 W diode laser-Yb-fiber amplifier system Rev. Sci. Instrum. 77, 093101 (2006); http://dx.doi.org/10.1063/1.2337092 (4 pages) Online Publication Date: 8 September 2006
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We describe a continuous-wave master-oscillator power-amplifier system based on a distributed Bragg reflection diode laser and an Yb doped fiber amplifier. The observed optical spectrum of the amplified seed source can be tailored to arbitrary shapes and widths between 30 MHz and greater than 1 GHz by controlling the radio frequency modulation wave form of the injection current.
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Rev. Sci. Instrum. 77, 103901 (2006); http://dx.doi.org/10.1063/1.2356856 (11 pages) Online Publication Date: 2 October 2006
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This article describes a versatile instrument capable of probing magnetic domain-wall dynamics in microstructured thin films. The instrument combines a state-of-the-art scanning magneto-optic Kerr effect polarimeter that incorporates high-bandwidth signal detection, an integrated broadband magnet system, and a microwave probe station. Together, these subsystems enable a broad range of studies of field and current-driven domain-wall dynamics in submicrometer magnetic structures and devices. Domain-wall motion can be probed with ≈ 2 μm spatial resolution and less than 2 ns temporal resolution. That motion can be driven by magnetic fields of up to ≈ 100 Oe amplitude with sinusoidal (>20 MHz) or user-defined wave forms (20 ns rise time) or by electric currents from dc to ≈ 10 GHz. A detailed description of the instrument is provided as well as several experiments highlighting its capabilities, including hysteresis loop shape and magnetic energy loss measurements spanning ten decades of drive frequency; spatially and temporally resolved measurements of domain-wall propagation in submicrometer magnetic wires; and mobility measurements of field- and current-driven domain-wall motion.
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Rev. Sci. Instrum. 77, 103702 (2006); http://dx.doi.org/10.1063/1.2354569 (5 pages) Online Publication Date: 2 October 2006
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This article reports a new approach for probe manufacturing, which is the key component in scanning near-field optical microscope (SNOM). The wet-etching process, to create the tip at the apex of a tapered fiber, has been optimized. Typical tip features are short tapers, large cone angles (30°), and very small diameters (<50 nm). Next process steps are performed in an original arrangement of plasma device, based on a modified hollow cathode discharge. It is used for both, to remove the dust particles or the etching residues from the tip surface and to coat the tapered region with a metallic ultrathin and compact film. To complete the probe’s fabrication, the tips are opened by dry electrolytic erosion. These probes have been successfully tested for SNOM applications.
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Rev. Sci. Instrum. 77, 093703 (2006); http://dx.doi.org/10.1063/1.2349599 (7 pages) Online Publication Date: 25 September 2006
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An instrument that incorporates two scanning tunneling microscope (STM) tips which can have their tunnel junctions as close together as a few nanometers was designed and built. The sample is fixed and can be imaged simultaneously and independently with both STM tips. The tips and sample can be positioned and angled to image the same surface or perpendicular surfaces. The entire STM head is cooled with liquid helium to about 4 K while in an ultrahigh vacuum environment. Macroscopic positioning of the tips is accomplished using piezoelectric “stick-slip” coarse motion stages, whereas atomic positioning is accomplished with piezoelectric tube scanners. This instrument addresses the critical need to locally characterize individual nanostructures and heterostructures.
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Simple interferometer for space and time resolved density measurements of laser produced plasmas Rev. Sci. Instrum. 77, 093106 (2006); http://dx.doi.org/10.1063/1.2349596 (4 pages) Online Publication Date: 25 September 2006
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A lateral shearing interferometer has been set up and coupled to an S-20 optical streak camera to obtain time resolved spatial electron density profiles of laser produced plasmas in a single shot. The electron density profiles are recorded with a temporal resolution of 70 ps for a continuous time duration of 15 ns. Performance of the system is demonstrated by recording temporal evolution of one dimensional density profiles of an expanding laser produced aluminum plasma. The system can be especially useful in characterization of expanding plasma for thin film deposition using laser ablated plumes.
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MAXIMA: A balloon-borne cosmic microwave background anisotropy experiment Rev. Sci. Instrum. 77, 071101 (2006); http://dx.doi.org/10.1063/1.2219723 (25 pages) Online Publication Date: 21 July 2006
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We describe the Millimeter wave Anisotropy eXperiment IMaging Array (MAXIMA), a balloon-borne experiment which measured the temperature anisotropy of the cosmic microwave background (CMB) on angular scales of 10′ to 5°. MAXIMA mapped the CMB using 16 bolometric detectors in spectral bands centered at 150, 240, and 410 GHz, with 10′ resolution at all frequencies. The combined receiver sensitivity to CMB anisotropy was ∼ 40 μK
 . The bolometric detectors, which were cooled to 100 mK, were a prototype of the detectors which will be used on the Planck Surveyor Satellite of the European Space Agency. Systematic parasitic contributions were controlled by using four uncorrelated spatial modulations, thorough cross-linking, multiple independent CMB observations, heavily baffled optics, and strong spectral discrimination. Pointing reconstruction was accurate to 1′, and absolute calibration was better than 4%. Two MAXIMA flights with more than 8.5 h of CMB observations have mapped a total of 300 deg2 of the sky in regions of negligible known foreground emission. MAXIMA results have been released in previous publications and shown to be consistent with the Wilkinson Microwave Anisotropy Probe. MAXIMA I maps, power spectra, and correlation matrices are publicly available at http://cosmology.berkeley.edu/maxima. |
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Rev. Sci. Instrum. 68, 3277 (1997); http://dx.doi.org/10.1063/1.1148286 (19 pages)
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We summarize the problem of measuring an ultrashort laser pulse and describe in detail a technique that completely characterizes a pulse in time: frequency-resolved optical gating. Emphasis is placed on the choice of experimental beam geometry and the implementation of the iterative phase-retrieval algorithm that together yield an accurate measurement of the pulse time-dependent intensity and phase over a wide range of circumstances. We compare several commonly used beam geometries, displaying sample traces for each and showing where each is appropriate, and we give a detailed description of the pulse-retrieval algorithm for each of these cases. © 1997 American Institute of Physics. |
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New method of high-precision thermometry Rev. Sci. Instrum. 77, 094901 (2006); http://dx.doi.org/10.1063/1.2349597 (6 pages) Online Publication Date: 21 September 2006
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Measurements of temperature using infrared radiation have become common in industry. They are used in process control for materials ranging from steel to glass to silicon, in machinery to monitor component temperature and performance, and to predict component failure. We developed a rapid, noncontact method of accurately measuring the temperature and the spectral emissivity of a surface. Inclusion of the emissivity in the measurement makes it possible to achieve high-precision results. In our method, the power spectrum emitted by a surface is measured first by a multichannel spectrometer; the surface is then illuminated by a full-spectrum light source with a known spectrum, and the sum of the emitted and reflected power from the surface is measured. The data from the two measurements and the governing relations for the radiation and reflection processes are then combined to generate a set of curves that intersects near a solution point, which yields the temperature and the emissivity in the range of wavelengths of one of the channels. The emissivity in the other channels is readily calculated and yields the wavelength-dependent emissivity of the surface. The accuracy of the method for very rapid (submicrosecond) measurements is approximately 1% or less. We named this method the spectrum method because it uses the spectrum of both the emitted and reflected light to make the calculation. The method is more accurate than a grey body calculation because the wavelength-dependent emissivity is an integral part of the calculation of the surface temperature. The accuracy of the temperature and emissivity measurements can be calculated for a system containing five or more channels. We discuss the sources of errors and quantitatively assess their effect. Relative as well as absolute values of the channel emissivities have a significant effect on errors in the emissivity and temperature measurements. This temperature diagnostic has been tested on a tabletop device that allows us to make quick and reproducible measurements.
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Simple method enabling pulse on command from high power, high frequency lasers Rev. Sci. Instrum. 77, 093103 (2006); http://dx.doi.org/10.1063/1.2338284 (5 pages) Online Publication Date: 8 September 2006
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A method for addressing individual laser pulses in high repetition frequency systems using an intracavity optical chopper and novel electronic timing system is reported. This “pulse on command” capability is shown to enable free running and both subharmonic pulse rate and burst mode operation of a high power, high pulse frequency copper vapor laser while maintaining a fixed output pulse energy. We demonstrate that this technique can be used to improve feature finish when laser micromachining metal.
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Derivation of time-dependent two-dimensional velocity field maps for plasma turbulence studies Rev. Sci. Instrum. 77, 103501 (2006); http://dx.doi.org/10.1063/1.2356851 (13 pages) Online Publication Date: 2 October 2006
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Time-resolved two-dimensional (2D) velocity maps have been derived for fluctuation measurements in the edge plasma of the National Spherical Torus Experiment (NSTX). The maps have been derived from time sequences of 2D images recorded with the gas puff imaging diagnostic. A hybrid technique combining optical flow and local pattern matching has been implemented to overcome the individual limitations of each when used with data of limited temporal and/or spatial resolution. Local flow velocities of up to ∼ 8 km/s and average poloidal flow velocities of up to ∼ 5 km/s are found. Results are compared to previous velocity extraction techniques and NSTX results.
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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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Rev. Sci. Instrum. 77, 103706 (2006); http://dx.doi.org/10.1063/1.2358703 (5 pages) Online Publication Date: 11 October 2006
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A new technique based on electrochemical etching for the fabrication of sharp metallic tips for scanning probe microscopes is introduced. In the proposed method, a small Teflon mass is attached to the end of an immersed tungsten wire using an aluminum tape, which leads to a significant enhancement of yield rate of sharp tungsten tips with an apex size below 100 nm to over 60%. The functionality of the tungsten tips fabricated by the proposed method is verified by measuring the topography of a standard sample using a shear-force scanning probe microscope.
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Rev. Sci. Instrum. 77, 103701 (2006); http://dx.doi.org/10.1063/1.2356850 (6 pages) Online Publication Date: 2 October 2006
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A novel closed-loop regulation of a piezoelectric actuator is presented to implement wideband and hysteresis-free motion required for high-speed operation of scanning probe microscopy. Velocity of the actuator’s displacement detected via the induced current and its integration giving the displacement were used to actively compensate the resonances and hysteresis. The validity of the idea was demonstrated using a prototype circuit composed of operational amplifiers and multilayered piezoelectric actuators. The fundamental resonance of the actuator at 260 kHz was completely eliminated from the actuator’s displacement with an appropriate velocity feedback. With an additional displacement feedback the gain error was suppressed within ±5 dB over a frequency range from dc to 1 MHz, while a −45° bandwidth was also maintained as wide as 250 kHz. In addition, intrinsic hysteresis of the actuator measured with an 8 kHz sinusoidal signal was suppressed to below 1%. Responses in displacement of the actuator to burst oscillation and square wave inputs exhibited clear improvement from the uncompensated responses.
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Design and performance of a piezoelectric actuated precise rotary positioner Rev. Sci. Instrum. 77, 105101 (2006); http://dx.doi.org/10.1063/1.2336760 (5 pages) Online Publication Date: 4 October 2006
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Industries including semiconductor, biotechnology, and nanotechnology are seeking compact and reliable nanometer resolution positioning techniques. To address this demand, this article presents a friction-drive rotary stage driven by a piezoelectric transducer (PZT) actuator. This stage includes a multilayer PZT actuator, the Scott-Russell mechanism, an actuation stage, a preload spring, and an output shaft. Its rotary positioning is accomplished by the stick-slip effect between the wire electrodischarge-machining rotary stage and the output shaft. Finite element analysis and Taguchi optimization method were extensively conducted to analyze the displacement, stress, and vibration behavior for optimum design. As shown by the experimental results, the stage achieved a resolution of 0.13 μrad and a speed of 0.15°/h by tuning of the preload spring.
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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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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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