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Top 20 Most Read Articles
January 2007
The 20 articles with the most full-text downloads during the month, in descending order.
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Phase modulation atomic force microscope with true atomic resolution Rev. Sci. Instrum. 77, 123703 (2006); http://dx.doi.org/10.1063/1.2405361 (5 pages) Online Publication Date: 21 December 2006
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We have developed a dynamic force microscope (DFM) working in a novel operation mode which is referred to as phase modulation atomic force microscopy (PM-AFM). PM-AFM utilizes a fixed-frequency excitation signal to drive a cantilever, which ensures stable imaging even with occasional tip crash and adhesion to the surface. The tip-sample interaction force is detected as a change of the phase difference between the cantilever deflection and excitation signals and hence the time response is not influenced by the Q factor of the cantilever. These features make PM-AFM more suitable for high-speed imaging than existing DFM techniques such as amplitude modulation and frequency modulation atomic force microscopies. Here we present the basic principle of PM-AFM and the theoretical limit of its performance. The design of the developed PM-AFM is described and its theoretically limited noise performance is demonstrated. Finally, we demonstrate the true atomic resolution imaging capability of the developed PM-AFM by imaging atomic-scale features of mica in water.
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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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Rev. Sci. Instrum. 77, 123701 (2006); http://dx.doi.org/10.1063/1.2400024 (5 pages) Online Publication Date: 1 December 2006
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The spectroscopic resolution of tunneling measurements performed with a scanning tunneling microscope is ultimately limited by the temperature at which the experiment is performed. To take advantage of the potential high spectroscopic resolution associated with operating a scanning tunneling microscope in a dilution refrigerator we have designed a room-temperature tunnel current amplifier having very small back action on the tunnel contact and allowing to nearly reach the predicted energy resolution. This design is a modification of the standard operational amplifier based tip-biasing current-voltage converter which implements differential voltage sensing and whose back action on the tip voltage is only ∼ 2 μV rms for a 14 MV/A transimpedance and 22 kHz bandwidth.
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Novel probe for the in situ measurement of particle size distributions Rev. Sci. Instrum. 77, 123704 (2006); http://dx.doi.org/10.1063/1.2405388 (8 pages) Online Publication Date: 29 December 2006
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The development of a novel instrument for the in situ measurement of particle size distributions in the size range of 3–200 μm is presented. The system uses high magnification optics, housed in a stainless steel probe, which can be inserted into a process stream or vessel, where images of the dispersed phase particles are recorded. A pulsed light source is used to freeze the motion of the particles in the field of view and present an image of the dispersion onto a charge-coupled device camera chip. The images are digitized and stored for later processing. Automated image analysis routines have been developed for extracting particle size information from the acquired images. An extensive validation of the instrument has been performed for spherical particles, which has produced several important findings. First, a size bias in the depth of field (DOF) exists which favors larger particles. An experiment procedure was developed for the direct measurement of DOF size biases. Additionally, the behavior of the instrument is dependent on the environmental conditions, such as dispersed phase concentration and the difference in index of refraction between continuous phase and dispersed phase.
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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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Design and construction of a compact vacuum furnace for scientific research Rev. Sci. Instrum. 77, 125104 (2006); http://dx.doi.org/10.1063/1.2402910 (5 pages) Online Publication Date: 20 December 2006
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The design, construction, and measurement of a compact vacuum furnace are reported. This type of furnace has many scientific applications in material processing and growth research. One example is the fluxless bonding process, where elevated temperature is needed to melt the solder and vacuum environment is required to inhibit solder oxidation. The primary objective of the furnace design is to keep the vacuum enclosure cool using only natural convection while allowing the heating platform to reach high temperature. This characteristic is necessary to enable us to seal the vacuum chamber using O-rings. To achieve this, the platform was designed to be thermally isolated from the chamber enclosure. Heat losses from the platform by conduction, convection, and radiation were analyzed. The dominating loss was found to be caused by the blackbody radiation, which can thus be used to estimate the relationship between platform temperature and the drive power needed. With a graphite platform of 75×75×25 mm3, only 270 W of power is needed to drive the platform to 400 °C. At this temperature, the temperature of the furnace enclosure is below 55 °C, allowing O-rings to be used to seal the vacuum chamber. Using a mechanical pump, the furnace can be pumped down to 40 mTorr, which is low enough for our fluxless bonding processes. With a temperature controller, the platform temperature can be controlled within 1%. The heat-up time to 400 °C is only 7 min.
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Feedforward control of a closed-loop piezoelectric translation stage for atomic force microscope Rev. Sci. Instrum. 78, 013702 (2007); http://dx.doi.org/10.1063/1.2403839 (8 pages) Online Publication Date: 11 January 2007
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Simple feedforward ideas are shown to lead to a nearly tenfold increase in the effective bandwidth of a closed-loop piezoelectric positioning stage used in scanning probe microscopy. If the desired control signal is known in advance, the feedforward filter can be acausal: the information about the future can be used to make the output of the stage have almost no phase lag with respect to the input. This keeps in register the images assembled from right and left scans. We discuss the design constraints imposed by the need for the feedforward filter to work robustly under a variety of circumstances. Because the feedforward needs only to modify the input signal, it can be added to any piezoelectric stage, whether closed or open loop.
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High-reflectivity Cr/Sc multilayer condenser for compact soft x-ray microscopy Rev. Sci. Instrum. 77, 123101 (2006); http://dx.doi.org/10.1063/1.2400665 (6 pages) Online Publication Date: 6 December 2006
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The condenser is a critical component in compact water-window x-ray microscopes as it influences the exposure time via its efficiency and the resolution via its numerical aperture. Normal-incidence multilayer mirrors can reach large geometrical collection efficiencies and match the numerical aperture of the zone plate but require advanced processing for high total reflectivity. In the present article we demonstrate large-diameter normal-incidence spherical Cr/Sc multilayer condensers with high and uniform reflectivity. Dc-magnetron sputtering was used to deposit 300 bilayers of Cr/Sc with a predetermined d-spacing matching the λ = 3.374 nm operating wavelength on spherical substrates. The mirrors show a uniform reflectivity of ∼ 3% over the full 58 mm diameter condenser area. With these mirrors an improvement in exposure time by a factor of 10 was achieved, thereby improving the performance of the compact x-ray microscope significantly.
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Cross-talk correction in atomic force microscopy Rev. Sci. Instrum. 78, 016101 (2007); http://dx.doi.org/10.1063/1.2424448 (3 pages) Online Publication Date: 5 January 2007
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Commercial atomic force microscopes usually use a position-sensitive photodiode to detect the motion of the cantilever via laser beam deflection. This readout technique makes it possible to measure bending and torsion of the cantilever separately. A slight angle between the orientation of the photodiode and the plane of the readout laser beam, however, causes false signals in both readout channels. This cross-talk may lead to misinterpretation of the acquired data. We demonstrate this fault with images recorded in contact mode on periodically poled ferroelectric crystals and present a simple electronic circuit to compensate for it. This circuit can correct for cross-talk with a bandwidth of ∼ 1 MHz suppressing the the false signal to ⪡1%.
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In situ mechanical testing of templated carbon nanotubes Rev. Sci. Instrum. 77, 125101 (2006); http://dx.doi.org/10.1063/1.2400212 (6 pages) Online Publication Date: 13 December 2006
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A new microelectromechanical system (MEMS)-based tensile testing stage (with integrated actuator, direct load sensing beam, and electrodes for controlled assembly of an individual nanostructure) was developed and used for in situ tensile loading of a templated carbon nanotube (T-CNT) inside a scanning electron microscope (SEM). Specifically, an increasing tensile load was applied to the T-CNT by actuating the device and high-resolution scanning electron microscopy images were acquired at different loads. The load (from the bending of the direct force-sensing beam), the elongation of the specimen during loading, and the specimen geometry were all obtained from analysis of SEM images. The stress versus strain curve and Young’s modulus were thus obtained. A model is presented for the tensile loading experiment, and the fit value of Young’s modulus from this model is compared to values obtained by an independent method. The results of this experiment on a T-CNT suggest the use of this device for loading other nanostructures and also for designing other MEMS-based systems, such as a compressive testing stage.
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Thermal conductivity measurement from 30 to 750 K: the 3ω method Rev. Sci. Instrum. 61, 802 (1990); http://dx.doi.org/10.1063/1.1141498 (7 pages)
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An ac technique for measuring the thermal conductivity of dielectric solids between 30 and 750 K is described. This technique, the 3ω method, can be applied to bulk amorphous solids and crystals as well as amorphous films tens of microns thick. Errors from black‐body radiation are calculated to be less than 2% even at 1000 K. Data for a‐SiO2, Pyrex 7740, and Pyroceram 9606 are compared to results obtained by conventional techniques. |
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Calibration of rectangular atomic force microscope cantilevers Rev. Sci. Instrum. 70, 3967 (1999); http://dx.doi.org/10.1063/1.1150021 (3 pages)
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A method to determine the spring constant of a rectangular atomic force microscope cantilever is proposed that relies solely on the measurement of the resonant frequency and quality factor of the cantilever in fluid (typically air), and knowledge of its plan view dimensions. This method gives very good accuracy and improves upon the previous formulation by Sader et al. [Rev. Sci. Instrum. 66, 3789 (1995)] which, unlike the present method, requires knowledge of both the cantilever density and thickness. © 1999 American Institute of Physics. |
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Methods of single-molecule fluorescence spectroscopy and microscopy Rev. Sci. Instrum. 74, 3597 (2003); http://dx.doi.org/10.1063/1.1589587 (23 pages) Online Publication Date: 23 July 2003
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Optical spectroscopy at the ultimate limit of a single molecule has grown over the past dozen years into a powerful technique for exploring the individual nanoscale behavior of molecules in complex local environments. Observing a single molecule removes the usual ensemble average, allowing the exploration of hidden heterogeneity in complex condensed phases as well as direct observation of dynamical state changes arising from photophysics and photochemistry, without synchronization. This article reviews the experimental techniques of single-molecule fluorescence spectroscopy and microscopy with emphasis on studies at room temperature where the same single molecule is studied for an extended period. Key to successful single-molecule detection is the need to optimize signal-to-noise ratio, and the physical parameters affecting both signal and noise are described in detail. Four successful microscopic methods including the wide-field techniques of epifluorescence and total internal reflection, as well as confocal and near-field optical scanning microscopies are described. In order to extract the maximum amount of information from an experiment, a wide array of properties of the emission can be recorded, such as polarization, spectrum, degree of energy transfer, and spatial position. Whatever variable is measured, the time dependence of the parameter can yield information about excited state lifetimes, photochemistry, local environmental fluctuations, enzymatic activity, quantum optics, and many other dynamical effects. Due to the breadth of applications now appearing, single-molecule spectroscopy and microscopy may be viewed as useful new tools for the study of dynamics in complex systems, especially where ensemble averaging or lack of synchronization may obscure the details of the process under study. © 2003 American Institute of Physics. |
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Rev. Sci. Instrum. 77, 123702 (2006); http://dx.doi.org/10.1063/1.2400015 (6 pages) Online Publication Date: 6 December 2006
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In this article we present a complete laser scanning microscope designed for simultaneous spectral and lifetime measurements from every point of the specimen located within the field of view. The pulsed laser source used for two-photon excitation provides good spatial resolution with minimal invasivity. In addition, the detection module was optimized for minimal photon loss, allowing laser power minimization and further reduction of cells photodamage. Analysis of biological samples illustrates the performances of this configuration, particularly when applied to fluorescent resonance energy transfer (FRET) measurements. Indeed, multiparametric acquisition is particularly useful to discriminate between FRET and artifactual response due to acquisition invasivity or cell heterogeneity. Combined with adapted homemade driving software, this system is stable, portable, and optimized for living cell studies.
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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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Simple setup to measure electrical properties of polymeric films Rev. Sci. Instrum. 77, 126106 (2006); http://dx.doi.org/10.1063/1.2403937 (3 pages) Online Publication Date: 20 December 2006
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A simple method to measure electrical conductivity of conducting organic films has been described. A setup, based on four-probe technique, is specifically designed and fabricated for nondestructive electrical conductivity measurements of freestanding thin films. The current-voltage and temperature dependent characteristics of thin films of polyethylenedioxythiophene and polypyrrole and thick wafers of germanium have been used to test the setup. The results obtained are highly reproducible and are in good agreement with the reported values in the literature, employing different techniques.
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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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Measuring activity in ant colonies Rev. Sci. Instrum. 77, 126102 (2006); http://dx.doi.org/10.1063/1.2400215 (3 pages) Online Publication Date: 12 December 2006
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Ants, as paradigm of social insects, have become a recurrent example of efficient problem solvers via self-organization. In spite of the simple behavior of each individual, the colony as a whole displays “swarm intelligence:” the organization of ant trails for foraging is a typical output of it. But conventional techniques of observation can hardly record the amount of data needed to get a detailed understanding of self-organization of ant swarms in the wild. Here we are presenting a measurement system intended to monitor ant activity in the field comprising massive data acquisition and high sensitivity. A central role is played by an infrared sensor devised specifically to monitor relevant parameters to the activity of ants through the exits of the nest, although other sensors detecting temperature and luminosity are added to the system. We study the characteristics of the activity sensor and its performance in the field. Finally, we present massive data measured at one exit of a nest of Atta insularis, an ant endemic to Cuba, to illustrate the potential of our system.
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Compact high current generator for x-ray radiography Rev. Sci. Instrum. 77, 123501 (2006); http://dx.doi.org/10.1063/1.2400667 (5 pages) Online Publication Date: 12 December 2006
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We report here a design of the portable high current generator, which can be used for a row of experiments and applications, including, but not limited to, X pinch, plasma focus, vacuum spark, etc. The X generator consists of the capacitor bank, multigap spark switch, load chamber, and built-in high voltage triggering generator. The capacitor bank consists of 12 General Atomics 35404 type capacitors (20 nF, 25 nH, 0.2 Ω, 100 kV). It stores ∼ 0.8 kJ at 80 kV charging voltage. Each three capacitors are commuted to a load by the multigap spark switch, which is able to commute by eight parallel channels. Switches operate in ambient air at atmospheric pressure. At 76 kV charging voltage the generator provides ∼ 260 kA with 120 ns rise time and 5 nH inductive load and ∼ 220 kA with 145 ns rise time and 10 nH. Delay of output pulse relative to high voltage triggering pulse is ∼ 65 ns with 5 ns jitter. The dimensions of the generator are 1240×1240×225 mm3 and the weight is ∼ 250 kg, and only one high voltage power supply is required as additional equipment for the generator. The generator with a pumping system is placed on area about 0.5 m2. Operation and handling are very simple, because no oil nor purified gases are required for the generator. The X generator has been successfully employed for experiments on the Ni X pinch load. X-ray pulse duration (full width at half maximum above 1 keV) was about 5 ns. Radiation yield Wr ≥ 500 mJ was observed in the 1.2–1.5 KeV range and Wr ≥ 20 mJ in the 3–5 keV energy range, which is comparable to results, obtained on the nanosecond accelerators. Clearly resolved images of 6 μm wire indicate micron level size of hot spot. These results demonstrate possibility of this generator for application for x-ray backlighting.
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Lock-in amplifier error prediction and correction in frequency sweep measurements Rev. Sci. Instrum. 78, 014701 (2007); http://dx.doi.org/10.1063/1.2428269 (7 pages) Online Publication Date: 4 January 2007
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This article proposes an analytical algorithm for predicting errors in lock-in amplifiers (LIAs) working with time-varying reference frequency. Furthermore, a simple method for correcting such errors is presented. The reference frequency can be swept in order to measure the frequency response of a system within a given spectrum. The continuous variation of the reference frequency produces a measurement error that depends on three factors: the sweep speed, the LIA low-pass filters, and the frequency response of the measured system. The proposed error prediction algorithm is based on the final value theorem of the Laplace transform. The correction method uses a double-sweep measurement. A mathematical analysis is presented and validated with computational simulations and experimental measurements.
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