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Jul 2006

Volume 77, Issue 7, Articles (07xxxx)

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MAXIMA: A balloon-borne cosmic microwave background anisotropy experiment

B. Rabii, C. D. Winant, J. S. Collins, A. T. Lee, P. L. Richards, M. E. Abroe, S. Hanany, B. R. Johnson, P. Ade, A. Balbi, J. J. Bock, J. Borrill, R. Stompor, A. Boscaleri, E. Pascale, et al.

Rev. Sci. Instrum. 77, 071101 (2006); http://dx.doi.org/10.1063/1.2219723 (25 pages) | Cited 5 times

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 μKmath. 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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95.55.Jz Radio telescopes and instrumentation; heterodyne receivers
95.55.Rg Photoconductors and bolometers
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
98.70.Vc Background radiations
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Apparatus for the imaging of infrared photoluminescence, transmittance, and phototransmittance with high spatial and spectral resolutions

Robert Furstenberg, Julio A. Soares, and Jeffrey O. White

Rev. Sci. Instrum. 77, 073101 (2006); http://dx.doi.org/10.1063/1.2214931 (5 pages)

Online Publication Date: 5 July 2006

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Photoluminescence is a widely used tool for the characterization of wide-gap semiconductor materials. However, most narrow-gap, infrared materials exhibit very weak, hard to detect photoluminescence. We report on the development of a sensitive, Fourier transform infrared (FTIR)-based apparatus capable of measuring and spatial imaging of weak infrared photoluminescence with diffraction limited resolution. The apparatus is also capable of measuring transmittance and phototransmittance. This is, to our knowledge, the first report of measuring infrared phototransmittance using an FTIR spectrometer.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
78.55.Et II-VI semiconductors

Noncontact tissue oxygenation measurement using near-infrared spectroscopy

Masatsugu Niwayama, Hideaki Murata, and Shigenobu Shinohara

Rev. Sci. Instrum. 77, 073102 (2006); http://dx.doi.org/10.1063/1.2219732 (4 pages) | Cited 5 times

Online Publication Date: 7 July 2006

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Here, we present a noncontact tissue oxygenation monitor that uses near-infrared spectroscopy (NIRS). We examined changes in sensitivity of tissue oxygenation measurement due to changes in the distance between the optical probe and the skin surface using a Monte Carlo simulation and in vivo tests. We also examined the effects of skin and fat layer thickness. Photon migration was analyzed in a model consisting of the skin, fat, and muscle layers. The relationship between measurement sensitivity and the probe-tissue distance was obtained from the results of the simulation and was used for correction of measurements. A noncontact tissue oximeter was used to perform the in vivo tests and measure oxygen consumption of the forearm muscle. The value of corrected oxygen consumption was 0.12±0.03 ml/(100 g min), which is consistent with previously reported values obtained using contact NIRS measurement and magnetic resonance spectroscopy. Quantitative measurement of oxygenation using noncontact NIRS is potentially useful for novel applications such as quantification of inflammation.
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87.64.K- Spectroscopy
87.19.Ff Muscles

Lens-coupled liquid core waveguide for ultraviolet-visible absorption spectroscopy

Tony Robles, David Paige, and Cort Anastasio

Rev. Sci. Instrum. 77, 073103 (2006); http://dx.doi.org/10.1063/1.2219973 (4 pages) | Cited 1 time

Online Publication Date: 18 July 2006

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We have developed and characterized a modular liquid core waveguide (LCW) assembly for use in a commercial spectrophotometer to measure very low light absorbance values for dilute aqueous solutions in both the ultraviolet and visible wavelengths. The sample cell in this assembly is composed of a ∼ 1 m, pure Teflon® AF 2400 tube that is coupled to the spectrophotometer light path with a quartz lens and windows. Spectrophotometric absorbance measurements of test solutions (e.g., dilute sodium nitrate and hydrogen peroxide) produce clear and distinct spectra that exhibit a lower limit of detection of 3 mAU between 240 and 640 nm. At absorbances above 10 mAU our LCW system produces spectra from multiple independent injections that have a relative standard deviation of less than 10% and average absorbances within 5% of calculated values based on published molar absorptivities.
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42.79.Gn Optical waveguides and couplers
42.79.Bh Lenses, prisms and mirrors
07.60.Rd Visible and ultraviolet spectrometers
07.60.Dq Photometers, radiometers, and colorimeters
42.79.Ci Filters, zone plates, and polarizers

Scanning heterodyne Kerr-effect microscope for imaging of magnetic tracks

Vladimir V. Protopopov, Sukwon Lee, Youngkun Kwon, Sunghoon Cho, Hyuk Kim, and Jonggyn Chae

Rev. Sci. Instrum. 77, 073104 (2006); http://dx.doi.org/10.1063/1.2220519 (5 pages)

Online Publication Date: 18 July 2006

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Design and performance of a new type of Kerr microscope based on heterodyne cross-polarized technique is presented. Weak depolarization of the probe beam due to longitudinal magneto-optical Kerr effect is detected by means of heterodyne mixing of the two cross-polarized and frequency shifted waves generated by Zeeman-type He–Ne laser. In comparison with the traditional homodyne method the proposed technique has better sensitivity and spatial resolution. Experimental results of imaging service magnetic tracks on real samples of magnetic disks are presented, showing better contrast and spatial resolution with respect to the images obtained from commercial devices available in the market.
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07.60.Pb Conventional optical microscopes
07.79.-v Scanning probe microscopes and components
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
78.20.Ls Magneto-optical effects
42.15.Eq Optical system design

Optimizing spectral phase interferometry for direct electric-field reconstruction

Gero Stibenz and Günter Steinmeyer

Rev. Sci. Instrum. 77, 073105 (2006); http://dx.doi.org/10.1063/1.2221511 (9 pages) | Cited 20 times

Online Publication Date: 18 July 2006

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Spectral phase interferometry for direct electric-field reconstruction has become a standard technique for the measurement and characterization of extremely short laser pulses. Here we describe an improved setup that employs a planar geometry, uses an interferometrically stable pulse-splitting scheme, and is suitable for broadband pulse characterization up to one optical octave bandwidth and beyond. We devote particular attention to optimization of parameters for the few-cycle regime, resulting in an instrument with an order-of-magnitude sensitivity improvement and a higher spectral resolution than in previous work.
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07.60.Ly Interferometers
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Fm Reflectors, beam splitters, and deflectors

Accumulator for the production of intense positron pulses

D. B. Cassidy, S. H. M. Deng, R. G. Greaves, and A. P. Mills

Rev. Sci. Instrum. 77, 073106 (2006); http://dx.doi.org/10.1063/1.2221509 (8 pages) | Cited 24 times

Online Publication Date: 19 July 2006

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An intense pulsed positron source has been developed using a buffer gas trap to accumulate large numbers of positrons and create a dense plasma, which may then be bunched and spatially focused. Areal densities of more than 3×1010 e+ cm−2 have been achieved in a subnanosecond pulse producing an instantaneous positron current of more than 10 mA. We describe various aspects of the device including a detection technique specifically developed for use with intense positron pulses. Two applications are also described as well as future experiments such as the formation of positronium molecules and the positronium Bose-Einstein condensate.
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29.25.Bx Electron sources
07.77.Ka Charged-particle beam sources and detectors
52.50.Dg Plasma sources

Low temperature cell for cavity ring down absorption studies

Ernest K. Lewis, Craig J. Moehnke, Juan G. Navea, and Carlos E. Manzanares

Rev. Sci. Instrum. 77, 073107 (2006); http://dx.doi.org/10.1063/1.2222085 (9 pages) | Cited 4 times

Online Publication Date: 21 July 2006

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Phase shift cavity ring down is a technique that due to its long optical path length is an ideal method to detect weak absorptions. Coupling the method to a custom fitted cryostat allows gas phase molecules to be studied at cryogenic temperatures in a thermally isolated vacuum chamber. A novel design is described to construct the complete instrument. With optical cavities of length 10 ⩽ ℓ ⩽ 43 cm, optical path lengths between 200 m and 6 km have been achieved. High vibrational overtones C–H (Δυ = 5) are measured at 130 K (methane), 150 K (ethylene), and 155 K (ethane). Oscillator strengths of each molecule calculated at different temperatures are in excellent agreement. The experimental setup can be used to study kinetics and spectroscopy of atmospheric molecules, planetary atmospheres, and molecular complexes in the gas phase. Low temperatures can be obtained using liquid He or liquid N2 as cryogens.
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07.60.Rd Visible and ultraviolet spectrometers
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Configurable-bandwidth imaging spectrometer based on an acousto-optic tunable filter

Joan Vila-Francés, Javier Calpe-Maravilla, Jordi Muñoz-Mari, Luis Gómez-Chova, Julia Amorós-López, Emilio Ribes-Gómez, and Vicente Durán-Bosch

Rev. Sci. Instrum. 77, 073108 (2006); http://dx.doi.org/10.1063/1.2221542 (10 pages) | Cited 2 times

Online Publication Date: 28 July 2006

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This article presents a new imaging spectrometer called autonomous tunable filtering system. The instrument acquires sequential images at different spectral wavelengths in the visible and near infrared range of the electromagnetic spectrum. The spectral selection is performed by an acousto-optic tunable filter (AOTF), which is driven by a custom radio-frequency (rf) generator based on a direct digital synthesizer (DDS). The DDS allows a high flexibility in terms of acquisition speed and bandwidth selection. The rf power is dynamically controlled to drive the AOTF with the optimum value for each wavelength. The images are formed through a carefully designed optical layout and acquired with a high performance digital camera. The application software controls the instrument and acquires the raw spectral images from the camera. This software optionally corrects the image for the AOTF nonidealities, such as diffraction efficiency variations, spatial nonuniformity, and chromatic aberration, and generates a single multiband image file. Moreover, the software can calculate the reflectance or transmittance of the acquired images. The instrument has been calibrated to give precise and repetitive measurements and has been validated against a high performance point spectrometer. As a case example, the instrument has been successfully used for the mapping of chlorophyll content of plant leaves from their multispectral reflectance images.
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07.60.Rd Visible and ultraviolet spectrometers
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.79.Jq Acousto-optical devices
42.79.Ci Filters, zone plates, and polarizers
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Modeling of nanofabricated paddle bridges for resonant mass sensing

N. Lobontiu, B. Ilic, E. Garcia, T. Reissman, and H. G. Craighead

Rev. Sci. Instrum. 77, 073301 (2006); http://dx.doi.org/10.1063/1.2221560 (9 pages) | Cited 4 times

Online Publication Date: 28 July 2006

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The modeling of nanopaddle bridges is studied in this article by proposing a lumped-parameter mathematical model which enables structural characterization in the resonant domain. The distributed compliance and inertia of all three segments composing a paddle bridge are taken into consideration in order to determine the equivalent lumped-parameter stiffness and inertia fractions, and further on the bending and torsion resonant frequencies. The approximate model produces results which are confirmed by finite element analysis and experimental measurements. The model is subsequently utilized to quantify the amount of mass which attaches to the bridge by predicting the modified resonant frequencies in either bending or torsion.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
06.30.Dr Mass and density
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Multiple-gap spark gap switch

Z. Liu, K. Yan, G. J. J. Winands, A. J. M. Pemen, E. J. M. Van Heesch, and D. B. Pawelek

Rev. Sci. Instrum. 77, 073501 (2006); http://dx.doi.org/10.1063/1.2216792 (4 pages) | Cited 5 times

Online Publication Date: 5 July 2006

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A triggered multiple-gap spark gap switch has been developed and tested under atmosphere. By means of an LCR trigger circuit, the multiple-gap switch can be used very reliably. For the same switching voltage (35.5 kV), with increasing the number of gaps from 2 to 6, the switching current rise time is reduced from 13.5 to 6 ns, and the energy efficiency is increased from 87% to 92%. An eight-gap switch was also tested, and the switching current rise time is much smaller than the usable rise time of the current probe (3.5 ns). One interesting application of the multiple-gap switch is to improve the switching performance in the multiple-switch and transmission lines based pulsed power circuit. To verify this application, a six-gap switch was tested. In contrast to a single-gap switch, the output current rise time was improved from 21 to 11 ns by the six-gap switch.
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52.75.Kq Plasma switches (e.g., spark gaps)
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
84.30.Sk Pulse and digital circuits

Exploration of the yield-ratio method at Shenguang II laser facility

Zongqing Zhao, Jiabin Chen, Yongkun Ding, Ming Chen, and Yikang Pu

Rev. Sci. Instrum. 77, 073502 (2006); http://dx.doi.org/10.1063/1.2213169 (4 pages) | Cited 3 times

Online Publication Date: 11 July 2006

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In inertial confinement fusion implosion experiments with the primary-neutron yield as low as 107, the method of yield ratio is proposed to diagnose the areal density 〈ρR〉 at Shenguang II laser facility. Considering the detection efficiency and the time response, a new detector for detecting the secondary-neutron signal is developed, which locates 50 cm away from the target. According to Monte Carlo N-particle simulation, 5-cm-thick lead shield was placed in front of the detector to shield x rays. In the 2004 experiments, the highest primary-neutron yield is 3.18×106, which is an order lower than expected. Inspite of this fact, a secondary-neutron signal is measured for the first time at the Shenguang II laser facility, which proves the method’s feasibility. The method will be used in the experiments at the prototype of Shenguang III laser facility.
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52.70.Nc Particle measurements
28.52.Cx Fueling, heating and ignition
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.50.Lp Plasma production and heating by shock waves and compression
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.65.Pp Monte Carlo methods

Technique for measuring D2 pellet mass loss through a curved guide tube using two microwave cavity detectors

S. K. Combs, J. B. O. Caughman, and J. B. Wilgen

Rev. Sci. Instrum. 77, 073503 (2006); http://dx.doi.org/10.1063/1.2219748 (6 pages) | Cited 2 times

Online Publication Date: 13 July 2006

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Two microwave cavity mass detectors have been used to measure the mass loss of deuterium (D2) pellets transported through a curved guide tube. The test tube was a mock-up of the pellet injection guide tube for the proposed ITER experiment, which will be used to transport pellets, including deuterium-tritium (D-T), from the pellet acceleration device to the inner wall (or magnetic high-field side) of the large tokamak for pellet injection and core fueling of plasmas. An accurate estimate of the mass loss is particularly important for D-T injection, because the inventory of the radioactive isotope (T) for ITER is limited and accountability and recycling will be crucial issues. In the laboratory, frozen cylindrical D2 pellets of nominal 5.3-mm diameter were shot through the stainless steel test tube ( ≈ 10 m in length and 10-mm inside diameter), with each end equipped with a microwave cavity. As the pellet passes through each tuned microwave cavity, the peak output signal from the electronics is directly proportional to the pellet mass. An absolute calibration of the cavities, which can be problematic, is not needed for the nondestructive technique described here. Instead, a cross calibration of the two cavities with pellets of varying masses provides the relationship to determine mass loss more precisely than any other technique previously reported. In addition, the individual output signals from the cavities can be used to identify intact pellets (a single signal peak) or broken pellets (multiple signal peaks). For the pellet speed range tested in this study (100–500 m/s), the mass loss for intact pellets was directly dependent on the pellet speed, with ≈ 10% mass loss at 300 m/s. The microwave cavities and the associated electronics, as well as some basic theory, are described; calibration and experimental data are presented and discussed.
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52.70.Gw Radio-frequency and microwave measurements
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
52.40.Hf Plasma-material interactions; boundary layer effects
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
06.20.fb Standards and calibration

Debye size microprobes for electric field measurements in laboratory plasmas

P. Pribyl, W. Gekelman, M. Nakamoto, E. Lawrence, F. Chiang, J. Stillman, J. Judy, N. Katz, P. Kintner, and P. Niknejadi

Rev. Sci. Instrum. 77, 073504 (2006); http://dx.doi.org/10.1063/1.2198730 (8 pages) | Cited 1 time

Online Publication Date: 21 July 2006

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Microelectromechanical systems (MEMS) have led to the development of a host of tiny machines and sensors over the past decade. Plasma physics is in great need of small detectors for several reasons. First of all, very small detectors do not disturb a plasma, and secondly some detectors can only work because they are very small. We report on the first of a series of small (sub-Debye length) probes for laboratory plasmas undertaken at the basic Plasma Science Facility at UCLA. The goal of the work is to develop robust and sensitive diagnostic probes that can survive in a plasma. The probes must have electronics packages in close proximity. We report on the construction and testing of probes that measure the electric field.
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52.70.Ds Electric and magnetic measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
06.30.Ka Basic electromagnetic quantities
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Real-time recovery of the electron density from interferometric measurements affected by fringe jumps

A. Murari, L. Zabeo, A. Boboc, D. Mazon, and M. Riva

Rev. Sci. Instrum. 77, 073505 (2006); http://dx.doi.org/10.1063/1.2219731 (9 pages) | Cited 3 times

Online Publication Date: 21 July 2006

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Optical interferometers are normally used in magnetically confined plasmas to measure the refractive index of the plasma by comparing the phase shift variation between a reference and a probe laser beam, from which the line-integrated electron density can be derived. Unfortunately, interferometric measurements are affected by fringe jumps, which are basically the erroneous phase difference determination due to the loss of signals or a phase difference bigger than 2π. The multiple causes include the refraction, wavelength of the laser radiation used, sensitivity, and time resolution of the measurements. On the other hand, the plasma density has become an essential piece of information for many real-time control schemes, which can therefore be completely jeopardized by fringe jumps. To overcome this problem at JET two main approaches can be adopted. The first approach consists of performing a real-time correction of the affected chords, eliminating the spurious effect of the fringe jumps, and providing a corrected line integral of acceptable quality. This is done at JET by complex algorithms that have inputs of various interferometry and polarimetry measurements.
A second approach can be adopted based on the observation that, for many real-time experiments, an approximate estimate of the density profile is sufficient. In JET, it was demonstrated that the density profile of the vast majority of configurations could be determined with sufficient accuracy by using only the line-integrated density profile provided by two chords; one external and one internal. The various solutions were tested and results compared in order to verify the most suitable one for the various plasma configurations and operational scenarios. A “general purpose” version of the correction algorithm was implemented and is now normally running during JET operation.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.55.Fa Tokamaks, spherical tokamaks
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)

Optimized method of producing washers of titanium hydride for plasma gun using occluded hydrogen gas

H. Himura, Y. Saito, A. Sanpei, S. Masamune, N. Takeuchi, and T. Shiono

Rev. Sci. Instrum. 77, 073506 (2006); http://dx.doi.org/10.1063/1.2227648 (5 pages)

Online Publication Date: 25 July 2006

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An optimized way of producing washers of titanium hydride for the application to a plasma gun using the occluded gas is presented. The amount of H2 gas (equivalently, gas pressure p) is entirely preadjusted in a gas reservoir of a simple instrument. The temperature T of a furnace is completely feedback controlled. Data show that when p is the order of 1 atm, T needs to be higher than about 450 °C in order to successfully produce washers of titanium hydride. Results on compressive strength of the loaded washers suggest that an appropriate ratio of atoms of hydrogen to titanium is less than H:Ti ∼ 0.85:1.
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84.60.Ve Energy storage systems, including capacitor banks
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
52.50.Dg Plasma sources
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Electronic linearization of piezoelectric actuators and noise budget in scanning probe microscopy

G. Aloisi, A. Santucci, M. Carlà, D. Dolci, and L. Lanzi

Rev. Sci. Instrum. 77, 073701 (2006); http://dx.doi.org/10.1063/1.2213214 (6 pages) | Cited 4 times

Online Publication Date: 5 July 2006

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The maximum resolution achievable with a scanning probe microscope is limited by the probe size, by the mechanism of interaction with the sample, as is widely known, and by the electronic noise in the instrument. The evaluation of this noise for the three motion axes of a linearized high resolution scanning electrochemical microscope has been carried through and the intrinsic maximum resolution is discussed.
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07.79.-v Scanning probe microscopes and components
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Quantitative mapping of switching behavior in piezoresponse force microscopy

Stephen Jesse, Ho Nyung Lee, and Sergei V. Kalinin

Rev. Sci. Instrum. 77, 073702 (2006); http://dx.doi.org/10.1063/1.2214699 (10 pages) | Cited 43 times

Online Publication Date: 7 July 2006

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The application of ferroelectric materials for nonvolatile memory and ferroelectric data storage necessitates quantitative studies of local switching characteristics and their relationship to material microstructure and defects. Switching spectroscopy piezoresponse force microscopy (SS-PFM) is developed as a quantitative tool for real-space imaging of imprint, coercive bias, remanent and saturation responses, and domain nucleation voltage on the nanoscale. Examples of SS-PFM implementation, data analysis, and data visualization are presented for epitaxial lead zirconate titanate (PZT) thin films and polycrystalline PZT ceramics. Several common artifacts related to the measurement method, environmental factors, and instrument settings are analyzed.
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07.79.-v Scanning probe microscopes and components
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Fm Switching phenomena

Modified atomic force microscopy cantilever design to facilitate access of higher modes of oscillation

S. Sadewasser, G. Villanueva, and J. A. Plaza

Rev. Sci. Instrum. 77, 073703 (2006); http://dx.doi.org/10.1063/1.2219738 (5 pages) | Cited 2 times

Online Publication Date: 18 July 2006

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The detection of higher modes of oscillation in atomic force microscopy can provide additional information on sample properties. However, the limited bandwidth of the photodiode in the beam deflection detection technique often limits the detectable frequency range. We present a novel cantilever design, which allows lowering the frequency of higher modes of oscillation, maintaining the frequency of the fundamental resonance. Simulations by finite element methods show that the ratio between the second mode and the fundamental resonance frequency can be adjusted between 2 and 10, compared to 6.3 for the regular rectangular cantilever design. Even stronger changes are observed for the third oscillation mode, corresponding to a torsional cantilever oscillation. Cantilevers with modified geometry were fabricated using silicon micromachining processes and subsequently tested, confirming the results from the simulation.
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07.79.Lh Atomic force microscopes
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Single-particle levitation system for automated study of homogeneous solute nucleation

Adam P. Olsen, Richard C. Flagan, and Julia A. Kornfield

Rev. Sci. Instrum. 77, 073901 (2006); http://dx.doi.org/10.1063/1.2212945 (7 pages) | Cited 3 times

Online Publication Date: 5 July 2006

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We present an instrument that addresses two critical requirements for quantitative measurements of the homogeneous crystal nucleation rate in supersaturated aqueous solution. First, the need to perform repeated measurements of nucleation incubation times is met by automating experiments to enable programmable cycling of thermodynamic conditions. Second, the need for precise and robust control of the chemical potential in supersaturated aqueous solution is met by implementing a novel technique for regulating relative humidity. The apparatus levitates and weighs micron-sized samples in an electric field, providing access to highly supersaturated states. We report repeated observations of the crystal nucleation incubation time in a supersaturated aqueous sodium chloride droplet, from which we infer the nucleation rate.
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07.68.+m Photography, photographic instruments; xerography
64.60.Q- Nucleation
81.10.Dn Growth from solutions
65.40.G- Other thermodynamical quantities

Three-dimensional magnetic spin-echo small-angle neutron scattering and neutron depolarization: A comparison

M. Theo Rekveldt, Niels H. van Dijk, Serguei V. Grigoriev, Wicher H. Kraan, and Wim G. Bouwman

Rev. Sci. Instrum. 77, 073902 (2006); http://dx.doi.org/10.1063/1.2204579 (10 pages) | Cited 3 times

Online Publication Date: 7 July 2006

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The recently developed magnetic spin-echo small-angle neutron scattering (SANS) technique provides unique information about the distance correlation of the local vector magnetization as a function of the spin-echo length within a magnetic material. The technique probes the magnetic correlations on a length scale from 10 nm up to 10 μm within the bulk of a magnetic material by evaluating the Larmor precession of a polarized neutron beam in a spin-echo setup. The characteristics of the spin-echo SANS technique are discussed and compared to those of the more conventional neutron depolarization technique. Both of these techniques probe the average size of the magnetic inhomogeneities and the local magnetic texture. The magnetic spin-echo SANS technique gives information on the size distribution of these magnetic inhomogeneities perpendicular to the beam and, in principle, independent on the local magnetic induction. This information is not accessible by the neutron depolarization technique that gives the average size parallel to the beam multiplied with the square of the local magnetic induction. The basic possibilities of the magnetic spin-echo SANS technique are demonstrated by experiments on samples with a strong magnetic texture.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.05.fg Neutron scattering (including small-angle scattering)

Facility for combined in situ magnetron sputtering and soft x-ray magnetic circular dichroism

N. D. Telling, G. van der Laan, M. T. Georgieva, and N. R. S. Farley

Rev. Sci. Instrum. 77, 073903 (2006); http://dx.doi.org/10.1063/1.2219719 (6 pages) | Cited 2 times

Online Publication Date: 18 July 2006

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An ultrahigh vacuum chamber that enables the in situ growth of thin films and multilayers by magnetron sputtering techniques is described. Following film preparation, x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements are performed by utilizing an in vacuum electromagnet. XMCD measurements on sputtered thin films of Fe and Co yield spin and orbital moments that are consistent with those obtained previously on films measured in transmission geometry and grown in situ by evaporation methods. Thin films of FeN prepared by reactive sputtering are also examined and reveal an apparent enhancement in the orbital moment for low N content samples. The advantages of producing samples for in situ XAS and XMCD studies by magnetron sputtering are discussed.
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07.30.-t Vacuum apparatus
81.15.Cd Deposition by sputtering
78.66.Bz Metals and metallic alloys
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.30.Cr Saturation moments and magnetic susceptibilities

Sample probe to measure resistivity and thermopower in the temperature range of 300–1000 K

V. Ponnambalam, S. Lindsey, N. S. Hickman, and Terry M. Tritt

Rev. Sci. Instrum. 77, 073904 (2006); http://dx.doi.org/10.1063/1.2219734 (5 pages) | Cited 13 times

Online Publication Date: 18 July 2006

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We have fabricated and tested a sample probe that can measure resistivity (ρ) and thermopower (α) on either bar or rod shaped samples over a temperature span of 300–1000 K. The design allows us to perform measurements both in vacuum as well as in inert atmosphere and hence suitable for any oxygen sensitive bulk samples. The main feature is the spring assisted pressure contacts between the sample and the two silver blocks, on which the electrical leads as well as thermocouples are mounted. This enables us to establish good thermal contacts over the entire temperature range of measurements between the sample and the thermocouples. To measure the thermopower, a slowly varying temperature difference (ΔT) is generated across the sample by using a small heater. The resulting slope of thermo-emf (ΔV) vs temperature difference (ΔT) plot is used to obtain the thermopower at any temperature. Resistivity is measured in sequence by a linear four-probe method at the same temperature. Hence in a single experiment, both resistivity and thermopower can be measured. Test measurements carried out on Ni and W standards yielded an accuracy of about few percent for both ρ and α.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.20.-n Thermal instruments and apparatus
72.15.Jf Thermoelectric and thermomagnetic effects

Long symmetric high-pressure cell for magnetic measurements in superconducting quantum interference device magnetometer

K. V. Kamenev, S. Tancharakorn, N. Robertson, and A. Harrison

Rev. Sci. Instrum. 77, 073905 (2006); http://dx.doi.org/10.1063/1.2221537 (5 pages) | Cited 9 times

Online Publication Date: 19 July 2006

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We describe a high-pressure cell for magnetic measurements in a magnetic property measurement system superconducting quantum interference device (SQUID) magnetometer. The cell has been developed for studies of weakly magnetic materials and has the operating pressure limit of 1 GPa. Its design is focused on reducing the background signal by making the pressure cell symmetric with respect to the sample in order to provide an integrable SQUID response. The use of an externally loaded cylinder has resulted in the increased strength of the cell and in the provision of a larger sample volume. The optimization of the cell’s length has made it possible to use the approximation of an infinitely long cylinder in the whole range of accessible pressures and to apply the Lamé equation for calculating the change in the diameter of the cell as a function of applied pressure. This enabled us to remove a superconductive manometer from the cell and use the diameter-pressure calibration instead. This has further increased the sensitivity of the measurements at low temperatures which is particularly relevant to studies of weakly magnetic materials. The performance of the cell is illustrated by the results of high-pressure measurements on the molecular antiferromagnet [N(C2H5)4][FeCl4].
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07.55.Ge Magnetometers for magnetic field measurements
85.25.Dq Superconducting quantum interference devices (SQUIDs)
75.50.Xx Molecular magnets
75.50.Ee Antiferromagnetics

System for measuring auto- and cross correlation of current noise at low temperatures

L. DiCarlo, Y. Zhang, D. T. McClure, C. M. Marcus, L. N. Pfeiffer, and K. W. West

Rev. Sci. Instrum. 77, 073906 (2006); http://dx.doi.org/10.1063/1.2221541 (7 pages)

Online Publication Date: 20 July 2006

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We describe the construction and operation of a two-channel noise detection system for measuring power and cross spectral densities of current fluctuations near 2 MHz in electronic devices at low temperatures. The system employs cryogenic amplification and fast Fourier transform based spectral measurement. The gain and electron temperature are calibrated using Johnson noise thermometry. Full shot noise of 100 pA can be resolved with an integration time of 10 s. We report a demonstration measurement of bias-dependent current noise in a gate defined GaAs/AlGaAs quantum point contact.
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07.50.Hp Electrical noise and shielding equipment
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
72.70.+m Noise processes and phenomena
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
73.61.Ey III-V semiconductors
73.63.Rt Nanoscale contacts
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