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Apr 2008

Volume 79, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 79, 041101 (2008); http://dx.doi.org/10.1063/1.2908445 (29 pages)

Ralf Meckenstock
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Perspective: Local ferromagnetic resonance measurement techniques: “Invited Review Article: Microwave spectroscopy based on scanning thermal microscopy: Resolution in the nanometer range” [Rev. Sci. Instrum. 79, 041101 (2008)]

Nan Mo and Carl E. Patton

Rev. Sci. Instrum. 79, 040901 (2008); http://dx.doi.org/10.1063/1.2911921 (2 pages) | Cited 1 time

Online Publication Date: 24 April 2008

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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.70.Gq Microwave and radio-frequency interactions
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Invited Review Article: Microwave spectroscopy based on scanning thermal microscopy: Resolution in the nanometer range

Ralf Meckenstock

Rev. Sci. Instrum. 79, 041101 (2008); http://dx.doi.org/10.1063/1.2908445 (29 pages) | Cited 7 times

Online Publication Date: 24 April 2008

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Scanning thermal microscope-detected ferromagnetic resonance (SThM-FMR) combines a thermal near-field microscope with a FMR spectrometer and detects the thermal response due to resonant microwave absorption by measuring the resistivity change in the thermal nanoprobe. The advantage of this technique is to provide imaging capabilities at fixed resonance conditions as well as local microwave spectroscopy at the nanoscale. A technique that uses the same setup but detects the thermoelastic response of the sample is the scanning thermoelastic microscope-detected FMR (SThEM-FMR). This latter technique is advantageous when FMR spectra of single nanostructures have to be recorded at a fixed position. The experimental setups and the signal generation processes of SThM/SThEM-FMR are described in detail. With the SThM-FMR setups a temperature resolution of 1 mK and a local resolution of 30 nm are actually achieved. With SThEM-FMR the obtained local resolution is 10 nm. The detection limits of both techniques can be as low as 106 spins. To demonstrate the potential of these new techniques SThM/SThEM-FMR investigations of local magnetic anisotropies, magnetization dynamics of single nanodots and inhomogeneous FMR excitations due to finite size effects are presented. Simultaneously, information on the magnetic parameters, the topography, and the thermal properties is provided. To describe the further potential of this recently developed SThM-FMR technique, combined magnetoresistance and FMR investigations are presented and an outlook on possible future applications is given.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.79.Fc Near-field scanning optical microscopes
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Gw Magnetic anisotropy
81.40.Jj Elasticity and anelasticity, stress-strain relations
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Precise measurements of the total concentration of atmospheric CO2 and 13CO2/12CO2 isotopic ratio using a lead-salt laser diode spectrometer

Laurence Croizé, Didier Mondelain, Claude Camy-Peyret, Marc Delmotte, and Martina Schmidt

Rev. Sci. Instrum. 79, 043101 (2008); http://dx.doi.org/10.1063/1.2902829 (9 pages) | Cited 4 times

Online Publication Date: 3 April 2008

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We have developed a tunable diode laser spectrometer, called SIMCO (spectrometer for isotopic measurements of CO2), for determining the concentrations of 12CO2 and 13CO2 in atmospheric air, from which the total concentration of CO2 and the isotopic composition (expressed in delta units) δ13CO2 are calculated. The two concentrations are measured using a pair of lines around 2290.1 cm−1, by fitting a line profile model, taking into account the confinement narrowing effect to achieve a better accuracy. Using the Allan variance, we have demonstrated (for an integration time of 25 s) a precision of 0.1 ppmv for the total CO2 concentration and of 0.3‰ for δ13CO2. The performances on atmospheric air have been tested during a 3 days campaign by comparing the SIMCO instrument with a gas chromatograph (GC) for the measurement of the total CO2 concentration and with an isotopic ratio mass spectrometer (MS) for the isotopic composition. The CO2 concentration measurements of SIMCO are in very good agreement with the GC data with a mean difference of Δ(CO2) = 0.16±1.20 ppmv for a comparison period of 45 h and the linearity of the concentration between the two instruments is also very good (slope of correlation: 0.9996±0.0003) over the range between 380 and 415 ppmv. For δ13CO2, the comparison with the MS data shows a larger mean difference of Δ(δ13CO2) = (−1.9±1.2)‰, which could be partly related to small residual fluctuations of the overall SIMCO instrument response.
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42.68.Kh Effects of air pollution
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.62.Fi Laser spectroscopy
93.85.Pq Remote sensing in exploration geophysics
82.80.Bg Chromatography
82.80.Dx Analytical methods involving electronic spectroscopy
07.60.Rd Visible and ultraviolet spectrometers

Simple active method for reducing magnetic interference in a thermoelectrically cooled photomultiplier tube

Petri Kärhä and Teemu Jaakkola

Rev. Sci. Instrum. 79, 043102 (2008); http://dx.doi.org/10.1063/1.2906317 (3 pages)

Online Publication Date: 9 April 2008

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We present a simple modification for thermoelectrically cooled photomultiplier tube (PMT) assemblies that eliminates the magnetic interference between the peltier element and the PMT. An active compensation is accomplished by forming current loops of the wires of the peltier element and placing them in such a way that they eliminate the interfering magnetic field. It is demonstrated that the improved system reduces measurement errors of the order of 1% to statistical noise at the level of 0.07%.
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85.60.Ha Photomultipliers; phototubes and photocathodes

Twin optical traps for two-particle cross-correlation measurements: Eliminating cross-talk

M. Atakhorrami, K. M. Addas, and C. F. Schmidt

Rev. Sci. Instrum. 79, 043103 (2008); http://dx.doi.org/10.1063/1.2898407 (5 pages) | Cited 8 times

Online Publication Date: 18 April 2008

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The correlated motions of two micron-sized particles reflect the (micro-) rheological properties of a fluid and can be conveniently detected using two optical traps in combination with interferometric displacement detection. When the correlations become small, cross-talk between the two beams becomes important. We have used dual optical traps created by either two orthogonally polarized laser beams derived from one laser source, or by two independent lasers of different wavelengths for microrheology experiments. High numerical aperture lenses (objective and condenser) in the optical path can introduce depolarization, and polarizing beam splitters are not perfect, both of which can lead to optical cross-talk. We have characterized the cross-talk in our setup and demonstrate that the use of two independent laser eliminates cross-talk entirely.
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47.57.Qk Rheological aspects
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
07.60.Ly Interferometers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Background removal in scanning tunneling spectroscopy of single atoms and molecules on metal surfaces

P. Wahl, L. Diekhöner, M. A. Schneider, and K. Kern

Rev. Sci. Instrum. 79, 043104 (2008); http://dx.doi.org/10.1063/1.2907533 (4 pages) | Cited 3 times

Online Publication Date: 21 April 2008

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Scanning tunneling spectroscopy has developed into a powerful spectroscopic technique that has found wide application in the atomic scale characterization of the electronic properties of clean surfaces as well as adsorbates and defects at surfaces. However, it still lacks the standard methods for data treatment and removal of artifacts in spectra as they are, e.g., common in photoemission spectroscopy. The properties of the atomic scale tip apex—the probe of the instrument—tend to introduce spurious background signals into tunneling spectra. We present and discuss two methods which permit to extract tip-independent information from low temperature tunneling spectra acquired on single atoms and molecules on single crystal surfaces by background subtraction. The methods rely on a characterization of the tip on the clean metal surface. The performance of both methods is demonstrated and compared for simulated and experimental tunneling spectra.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
79.60.Dp Adsorbed layers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states

Angle-resolving time-of-flight electron spectrometer for near-threshold precision measurements of differential cross sections of electron-impact excitation of atoms and molecules

M. Lange, J. Matsumoto, A. Setiawan, R. Panajotović, J. Harrison, J. C. A. Lower, D. S. Newman, S. Mondal, and S. J. Buckman

Rev. Sci. Instrum. 79, 043105 (2008); http://dx.doi.org/10.1063/1.2912824 (9 pages) | Cited 3 times

Online Publication Date: 28 April 2008

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This article presents a new type of low-energy crossed-beam electron spectrometer for measuring angular differential cross sections of electron-impact excitation of atomic and molecular targets. Designed for investigations at energies close to excitation thresholds, the spectrometer combines a pulsed electron beam with the time-of-flight technique to distinguish between scattering channels. A large-area, position-sensitive detector is used to offset the low average scattering rate resulting from the pulsing duty cycle, without sacrificing angular resolution. A total energy resolution better than 150 meV (full width at half maximum) at scattered energies of 0.5–3 eV is achieved by monochromating the electron beam prior to pulsing it. The results of a precision measurement of the differential cross section for electron-impact excitation of helium, at an energy of 22 eV, are used to assess the sensitivity and resolution of the spectrometer.
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07.81.+a Electron and ion spectrometers
34.80.Dp Atomic excitation and ionization
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Time-of-flight spectroscopy of the energy distribution of laser-ablated atoms and ions

A. Buchsbaum, G. Rauchbauer, P. Varga, and M. Schmid

Rev. Sci. Instrum. 79, 043301 (2008); http://dx.doi.org/10.1063/1.2901607 (8 pages) | Cited 3 times

Online Publication Date: 4 April 2008

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The growth of ultrathin films, deposited by laser ablation, crucially depends on the energy of the ablated species. Therefore, a time-of-flight (TOF) spectrometer has been constructed and measurements have been carried out in order to determine the energy distribution of laser-ablated Fe and Pt atoms and ions in the plasma created by nanosecond pulses of a frequency-doubled neodymium doped yttrium aluminum garnet laser. The experiments have been performed in ultrahigh vacuum at relatively low laser power. For measuring the spectra of the neutrals, a cross-beam electron source for postionization and electric as well as magnetic fields for repelling the ions are employed. Nevertheless, measurements of neutral particles are restricted to low plasma densities due to electrostatic shielding within the plasma, leading to an inefficient deflection of charged particles by electrostatic and magnetic fields. Test measurements have been performed by utilizing the TOF spectrometer as a pressure gauge and also by chopping the electron beam, running the TOF spectrometer as a residual gas mass spectrometer. The spectra of the laser-ablated plasmas have shown plasma conditions with a Debye length of approximately 10−4 m, densities of 1015–1016 m−3 and ion energies up to 150 eV. Neutral spectra have shown an unexpectedly low fraction of neutrals (10−3–10−4) and hyperthermal energies up to several 10 eV, possibly contributed by recombination of ions and electrons in the plasma. Even though gas spectra had demonstrated the expected sensitivity of the TOF spectrometer for low-energy neutrals, no thermally evaporated neutral atoms could be found.
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07.75.+h Mass spectrometers
52.38.Mf Laser ablation
81.15.Fg Pulsed laser ablation deposition

An accelerator based fusion-product source for development of inertial confinement fusion nuclear diagnostics

S. C. McDuffee, J. A. Frenje, F. H. Séguin, R. Leiter, M. J. Canavan, D. T. Casey, J. R. Rygg, C. K. Li, and R. D. Petrasso

Rev. Sci. Instrum. 79, 043302 (2008); http://dx.doi.org/10.1063/1.2904452 (6 pages) | Cited 6 times

Online Publication Date: 14 April 2008

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A fusion-product source, utilizing a 150 kV Cockraft–Walton linear accelerator, has been refurbished to provide a reliable nuclear diagnostic development tool to the national inertial confinement fusion (ICF) research program. The accelerator is capable of routinely generating DD reaction rates at ∼ 107/s when using a 150 kV, 150 μA deuterium (D) beam onto an erbium (Er) or titanium (Ti) target doped with D, and D3He reaction rates at ∼ 5×105/s when using a using a 120 kV, ∼ 100 μA D beam onto a Er or Ti target doped with 3He. The new accelerator is currently being used in a number of projects related to the national ICF program at the OMEGA Laser Fusion Facility [ T. R. Boehly et al., Opt. Commun. 133, 495 (1997) ], which includes the wedge range filter charged-particle spectrometry program [ F. H. Seguin et al., Rev. Sci Instrum. 75, 3520 (2004) ] and the magnetic recoil neutron spectrometer [ J. A. Frenje et al., Rev. Sci. Instrum. 72, 854 (2001) ].
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52.57.-z Laser inertial confinement
52.70.Nc Particle measurements
28.52.Cx Fueling, heating and ignition
28.52.Lf Components and instrumentation
29.20.Ej Linear accelerators

Measurement of incident position of hypervelocity particles on piezoelectric lead zirconate titanate detector

Seiji Takechi, Toshiyuki Onishi, Shigeyuki Minami, Takashi Miyachi, Masayuki Fujii, Nobuyuki Hasebe, Ken-ichi Nogami, Hideo Ohashi, Sho Sasaki, Hiromi Shibata, Takeo Iwai, Eberhard Grün, Ralf Srama, and Nagaya Okada

Rev. Sci. Instrum. 79, 043303 (2008); http://dx.doi.org/10.1063/1.2908206 (4 pages) | Cited 1 time

Online Publication Date: 29 April 2008

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A cosmic dust detector for use onboard a satellite is currently being developed by using piezoelectric lead zirconate titanate (PZT). The characteristics of the PZT detector have been studied by bombarding it with hypervelocity iron (Fe) particles supplied by a Van de Graaff accelerator. One central electrode and four peripheral electrodes were placed on the front surface of the PZT detector to measure the impact positions of the incident Fe particles. It was demonstrated that the point of impact on the PZT detector could be identified by using information on the time at which the first peak of the output signal obtained from each electrode appeared.
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96.50.Dj Interplanetary dust and gas
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
29.40.Gx Tracking and position-sensitive detectors
95.55.-n Astronomical and space-research instrumentation
29.20.Ba Electrostatic accelerators

Simulating ion beam extraction from a single aperture triode acceleration column: A comparison of the beam transport codes IGUN and PBGUNS with test stand data

A. Patel, J. S. C. Wills, and W. T. Diamond

Rev. Sci. Instrum. 79, 043304 (2008); http://dx.doi.org/10.1063/1.2908170 (6 pages) | Cited 2 times

Online Publication Date: 30 April 2008

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Ion beam extraction from two different ion sources with single aperture triode extraction columns was simulated with the particle beam transport codes PBGUNS and IGUN. For each ion source, the simulation results are compared to experimental data generated on well-equipped test stands. Both codes reproduced the qualitative behavior of the extracted ion beams to incremental and scaled changes to the extraction electrode geometry observed on the test stands. Numerical values of optimum beam currents and beam emittance generated by the simulations also agree well with test stand data.
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29.25.-t Particle sources and targets
52.50.Dg Plasma sources
52.65.-y Plasma simulation
41.75.-i Charged-particle beams
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Direct coupling of pulsed radio frequency and pulsed high power in novel pulsed power system for plasma immersion ion implantation

Chunzhi Gong, Xiubo Tian, Shiqin Yang, Ricky K. Y. Fu, and Paul K. Chu

Rev. Sci. Instrum. 79, 043501 (2008); http://dx.doi.org/10.1063/1.2906220 (5 pages) | Cited 2 times

Online Publication Date: 11 April 2008

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A novel power supply system that directly couples pulsed high voltage (HV) pulses and pulsed 13.56 MHz radio frequency (rf) has been developed for plasma processes. In this system, the sample holder is connected to both the rf generator and HV modulator. The coupling circuit in the hybrid system is composed of individual matching units, low pass filters, and voltage clamping units. This ensures the safe operation of the rf system even when the HV is on. The PSPICE software is utilized to optimize the design of circuits. The system can be operated in two modes. The pulsed rf discharge may serve as either the seed plasma source for glow discharge or high-density plasma source for plasma immersion ion implantation (PIII). The pulsed high-voltage glow discharge is induced when a rf pulse with a short duration or a larger time interval between the rf and HV pulses is used. Conventional PIII can also be achieved. Experiments conducted on the new system confirm steady and safe operation.
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52.77.Dq Plasma-based ion implantation and deposition
52.25.Jm Ionization of plasmas
52.80.Hc Glow; corona
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New surface forces apparatus using two-beam interferometry

Hiroshi Kawai, Hiroshi Sakuma, Masashi Mizukami, Takashi Abe, Yasuhiro Fukao, Haruo Tajima, and Kazue Kurihara

Rev. Sci. Instrum. 79, 043701 (2008); http://dx.doi.org/10.1063/1.2903404 (5 pages) | Cited 8 times

Online Publication Date: 9 April 2008

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We designed a new surface forces apparatus for measuring the interactions between two nontransparent substrates and/or in nontransparent liquids. The small displacement of a surface, the bottom one in this study, was measured by the two-beam (twin path) interferometry technique using the phase difference between the laser light reflected by the fixed mirror and that by the mirror on the back of the bottom surface unit. It is possible to determine the distance with a resolution of 1 nm in the working range of 5 μm. This apparatus was successfully applied to measure the forces between mica surfaces in pure water and aqueous KBr solutions.
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07.60.Ly Interferometers
06.30.-k Measurements common to several branches of physics and astronomy
68.08.-p Liquid-solid interfaces

A charge coupled device camera with electron decelerator for intermediate voltage electron microscopy

Kenneth H. Downing and Paul E. Mooney

Rev. Sci. Instrum. 79, 043702 (2008); http://dx.doi.org/10.1063/1.2902853 (10 pages) | Cited 4 times

Online Publication Date: 18 April 2008

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Electron microscopists are increasingly turning to intermediate voltage electron microscopes (IVEMs) operating at 300–400 kV for a wide range of studies. They are also increasingly taking advantage of slow-scan charge coupled device (CCD) cameras, which have become widely used on electron microscopes. Under some conditions, CCDs provide an improvement in data quality over photographic film, as well as the many advantages of direct digital readout. However, CCD performance is seriously degraded on IVEMs compared to the more conventional 100 kV microscopes. In order to increase the efficiency and quality of data recording on IVEMs, we have developed a CCD camera system in which the electrons are decelerated to below 100 kV before impacting the camera, resulting in greatly improved performance in both signal quality and resolution compared to other CCDs used in electron microscopy. These improvements will allow high-quality image and diffraction data to be collected directly with the CCD, enabling improvements in data collection for applications including high-resolution electron crystallography, single particle reconstruction of protein structures, tomographic studies of cell ultrastructure, and remote microscope operation. This approach will enable us to use even larger format CCD chips that are being developed with smaller pixels.
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42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.07.Hj Display and recording equipment, oscilloscopes, TV cameras, etc.
07.68.+m Photography, photographic instruments; xerography
84.30.Sk Pulse and digital circuits
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
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A new advanced experimental setup for in-depth study of the interfacial reaction during reactive wetting

Sascha Frenznick, Martin Stratmann, and Michael Rohwerder

Rev. Sci. Instrum. 79, 043901 (2008); http://dx.doi.org/10.1063/1.2901539 (9 pages) | Cited 6 times

Online Publication Date: 3 April 2008

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Reactive wetting plays a crucial role in many technical processes, from soldering in microelectronics, production of metal/ceramic composites, to hot dip galvanizing in mass production of zinc coated steel sheet. In all these cases the wetting behavior of metal melts on different surfaces plays a crucial role in material joining and coating. In all these processes the formation of the interfacial reaction layer has to occur within as short a time as possible in order to ensure a fast overall production speed. As the interfacial layer determines the stability of the formed composites, detailed knowledge of its growth mechanisms is required for a directed process optimization. However, the investigation of the processes occurring at the buried interface between substrate and wetting phase is difficult, especially for the case of liquid metal wetting metallic or ceramic solid substrates at high temperatures. Here, a novel advanced technique for the investigation of high temperature wetting processes up to a temperature of 1100 K is presented. It is based on the sessile drop technique but, in addition, allows spinning off the droplet at any chosen wetting time, thus providing direct access to the interfacial reaction layer. Since the experimental setup is integrated into a UHV compatible reaction chamber, not only excellent control of the composition of the atmosphere is ensured, but also direct transfer to surface analytical tools such as scanning electron microscope or electron spectroscopy for chemical analysis without intermediate exposure to air is realized. As will be shown for the case of hot dip galvanising of steel, this is an outstanding advance compared to existing methods.
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68.08.Bc Wetting
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.81.+a Electron and ion spectrometers
82.80.Bg Chromatography
81.65.-b Surface treatments

Laser powered heating stage in a scanning electron microscope for microstructural investigations at elevated temperatures

Dirk M. Kirch, Arndt Ziemons, Thomas Burlet, Ingo Lischewski, Xenia Molodova, Dmitri A. Molodov, and Günter Gottstein

Rev. Sci. Instrum. 79, 043902 (2008); http://dx.doi.org/10.1063/1.2908434 (8 pages) | Cited 2 times

Online Publication Date: 15 April 2008

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A laser powered heating stage designed for application in high vacuum environment of a scanning electron microscope (SEM) is presented. It was developed to observe and characterize microstructural changes in crystalline materials at elevated temperatures up to 1000 °C. The approach utilizes the power output of a commercial infrared diode laser in order to heat up specimens without interference with the electronic system of the SEM. The heating stage can be used in combination with any standard characterization technique applicable for SEMs—electron backscatter diffraction, orientation contrast imaging, x-ray energy dispersive spectrometry, etc. The results of test measurements are presented.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
42.62.-b Laser applications

Vacuum ellipsometry as a method for probing glass transition in thin polymer films

Mikhail Yu. Efremov, Shauheen S. Soofi, Anna V. Kiyanova, Claudio J. Munoz, Peter Burgardt, Franco Cerrina, and Paul F. Nealey

Rev. Sci. Instrum. 79, 043903 (2008); http://dx.doi.org/10.1063/1.2901601 (10 pages) | Cited 7 times

Online Publication Date: 17 April 2008

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A vacuum ellipsometer has been designed for probing the glass transition in thin supported polymer films. The device is based on the optics of a commercial spectroscopic phase-modulated ellipsometer. A custom-made vacuum chamber evacuated by oil-free pumps, variable temperature optical table, and computer-based data acquisition system was described. The performance of the tool has been demonstrated using 20–200 nm thick poly(methyl methacrylate) and polystyrene films coated on silicon substrates at 10−6–10−8 torr residual gas pressure. Both polymers show pronounced glass transitions. The difficulties in assigning in the glass transition temperature are discussed with respect to the experimental challenges of the measurements in thin polymer films. It is found that the experimental curves can be significantly affected by a residual gas. This effect manifests itself at lower temperatures as a decreased or even negative apparent thermal coefficient of expansion, and is related to the uptake and desorption of water by the samples during temperature scans. It is also found that an ionization gauge—the standard accessory of any high vacuum system—can cause a number of spurious phenomena including drift in the experimental data, roughening of the polymer surface, and film dewetting.
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61.41.+e Polymers, elastomers, and plastics
64.70.pj Polymers
68.55.am Polymers and organics
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
68.43.Nr Desorption kinetics

Rapid qualitative phase analysis in highly textured thin films by x-ray diffraction

Cesare Borgia, Sven Olliges, and Ralph Spolenak

Rev. Sci. Instrum. 79, 043904 (2008); http://dx.doi.org/10.1063/1.2907534 (6 pages) | Cited 6 times

Online Publication Date: 17 April 2008

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Phase analysis of highly out-of-plane textured specimens using x-ray diffraction is usually complicated due to the disappearance of most of the x-ray peaks in a common θ/2θ diffraction geometry. In this paper, we propose a technique, where powderlike spectra of textured samples are obtained by multiaxial x-ray diffraction scans. This technique is a simple, yet powerful method which allows for significant improvement in thin film characterization and provides several types of information about the samples, such as the rapid qualitative identification of phases using common powder x-ray diffraction spectra databases, texture distribution, and quantitative residual stress analysis.
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68.55.jm Texture
68.60.Bs Mechanical and acoustical properties
68.55.Nq Composition and phase identification

Novel in situ setup to study the formation of nanoparticles in the gas phase by small angle x-ray scattering

I. Shyjumon, M. Rappolt, B. Sartori, H. Amenitsch, and P. Laggner

Rev. Sci. Instrum. 79, 043905 (2008); http://dx.doi.org/10.1063/1.2908436 (5 pages) | Cited 4 times

Online Publication Date: 18 April 2008

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An in-house built aerosol generator setup for in situ gas phase studies of aerosol and nanoparticles is described. The aerosol generator with an ultrasonic ceramic disk mist maker provides high enough particle concentrations for structural gas phase analysis by synchrotron small angle x-ray scattering (for water ∼ 4×108 droplets/s with a droplet size of ∼ 2.5 μm). The working principle was proved by scattering of gold nanoparticles. For evaporation induced self-assembly studies of nanostructured particles, an additional thermal treatment chamber was included in the setup. The first on-line gas phase data with our setup for mesostructured silica particles are presented for different thermal treatments. Scanning electron microscope imaging revealed the average particle size to be ∼ 1 μm. Furthermore, to quantify their internal nanostructure, diffraction experiments of deposited silica aerosols were carried out and the corresponding electron density map indicates a silica wall thickness of about 1 nm.
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07.85.-m X- and γ-ray instruments
82.80.-d Chemical analysis and related physical methods of analysis
81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly

A fast ramp rate thermally stimulated current technique to quantify electronic charge dynamics in thin films

Connie Lew and Michael O. Thompson

Rev. Sci. Instrum. 79, 043906 (2008); http://dx.doi.org/10.1063/1.2917183 (7 pages) | Cited 2 times

Online Publication Date: 28 April 2008

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Thermally stimulated current (TSC) techniques have been applied to study thermally activated events in many materials. However, the temperature ramp rates in traditional TSC are typically too slow (few degrees per minute) to monitor materials whose properties are strongly time dependent. A fast ramp rate TSC (FR-TSC) technique was developed with ramp rates of 1–5 K/s. This is up to 100 times faster than traditional TSC, so that material changes can be appropriately quantified in the time scale at which they take place. In this paper, the experimental design and challenges to achieve fast and stable ramp rates and to measure the low-level currents are discussed. The fast ramps were attained using a thermoelectric cooler, controlled by a proportional-integral-derivative feedback loop, for both heating and cooling. FR-TSC measurements (1 K/s and 20–100 °C) on poly(vinylidene fluoride-trifluoroethylene) ferroelectric thin films are discussed as an example material. From these measurements, thermally activated currents as well as irreversible and reversible charge dynamics were readily distinguished with multiple thermal cycles. These measurements suggest that this technique holds substantial promise in quantifying charge dynamics in fast response materials.
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73.61.Ph Polymers; organic compounds
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.84.Jd Polymers; organic compounds
77.22.Ej Polarization and depolarization
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
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Kilovolt Blumlein pulse generator with variable pulse duration and polarity

Andrea de Angelis, Juergen F. Kolb, Luigi Zeni, and Karl H. Schoenbach

Rev. Sci. Instrum. 79, 044301 (2008); http://dx.doi.org/10.1063/1.2901609 (4 pages) | Cited 4 times

Online Publication Date: 9 April 2008

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A Blumlein pulse generator which utilizes the superposition of electrical pulses launched from two individually switched pulse forming lines has been designed and tested. By using a power metal-oxide-semiconductor field-effect transistor as a switch on each end of the Blumlein line, we were able to generate pulses with amplitudes of 1 kV across a 100 Ω load. Pulse duration and polarity can be controlled by the temporal delay in the triggering of the two switches. Using this technique, we have demonstrated the generation of pulses with durations between 8 and 60 ns. The lower limit in pulse duration was determined by the switch closing time and the upper limit by the length of the pulse forming line. A further advantage of the concept is that pulse distortions caused by the non-negligible on-resistance of a line with a single switch can be eliminated by using switches with identical characteristics.
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84.30.Ng Oscillators, pulse generators, and function generators
84.30.Jc Power electronics; power supply circuits
84.32.Dd Connectors, relays, and switches

Magnetic microposts for mechanical stimulation of biological cells: Fabrication, characterization, and analysis

Nathan J. Sniadecki, Corinne M. Lamb, Yaohua Liu, Christopher S. Chen, and Daniel H. Reich

Rev. Sci. Instrum. 79, 044302 (2008); http://dx.doi.org/10.1063/1.2906228 (8 pages) | Cited 7 times

Online Publication Date: 16 April 2008

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Cells use force as a mechanical signal to sense and respond to their microenvironment. Understanding how mechanical forces affect living cells requires the development of tool sets that can apply nanoscale forces and also measure cellular traction forces. However, there has been a lack of techniques that integrate actuation and sensing components to study force as a mechanical signal. Here, we describe a system that uses an array of elastomeric microposts to apply external forces to cells through cobalt nanowires embedded inside the microposts. We first biochemically treat the posts’ surfaces to restrict cell adhesion to the posts’ tips. Then by applying a uniform magnetic field (B<0.3 T), we induce magnetic torque on the nanowires that is transmitted to a cell’s adhesion site as an external force. We have achieved external forces of up to 45 nN, which is in the upper range of current nanoscale force-probing techniques. Nonmagnetic microposts, similarly prepared but without nanowires, surround the magnetic microposts and are used to measure the traction forces and changes in cell mechanics. We record the magnitude and direction of the external force and the traction forces by optically measuring the deflection of the microposts, which linearly deflect as cantilever springs. With this approach, we can measure traction forces before and after force stimulation in order to monitor cellular response to forces. We present the fabrication methods, magnetic force characterization, and image analysis techniques used to achieve the measurements.
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87.19.lt Sensory systems: visual, auditory, tactile, taste, and olfaction
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
87.80.Ek Mechanical and micromechanical techniques
87.18.Mp Signal transduction networks
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A new stereolithography experimental porous flow device

Dustin Crandall, Goodarz Ahmadi, Douglas Leonard, Martin Ferer, and Duane H. Smith

Rev. Sci. Instrum. 79, 044501 (2008); http://dx.doi.org/10.1063/1.2903740 (6 pages) | Cited 5 times

Online Publication Date: 11 April 2008

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A new method for constructing laboratory-scale porous media with increased pore-level variabilities for two-phase flow experiments is presented here. These devices have been created with stereolithography directly on glass, thus improving the stability of the model created with this precision rapid construction technique. The method of construction and improved parameters are discussed in detail, followed by a brief comparison of two-phase drainage results for air invasion into the water-saturated porous medium. Flow through the model porous medium is shown to substantiate theoretical fractal predictions.
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47.56.+r Flows through porous media
47.55.-t Multiphase and stratified flows
47.53.+n Fractals in fluid dynamics
47.80.-v Instrumentation and measurement methods in fluid dynamics
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A switched supply tunable red-green-blue light emitting diode driver

Weifeng Feng, Frank G. Shi, Yongzhi He, and Bin Zhao

Rev. Sci. Instrum. 79, 044701 (2008); http://dx.doi.org/10.1063/1.2894304 (5 pages)

Online Publication Date: 10 April 2008

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This paper presents a new switched supply tunable red-green-blue (RGB) light emitting diode (LED) driver. The RGB LEDs act not only as light emitting devices but also as rectifying diodes in the presented driver circuit. The RGB LED color control is realized by controlling the switched supply voltage amplitude, frequency, and duty cycle. The driver efficiency is high since the only loss in the driver circuit is the switch and can be further reduced by direct alternate current supply.
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84.30.Jc Power electronics; power supply circuits
85.60.Jb Light-emitting devices

Precisely tunable continuous-wave terahertz source with interferometric frequency control

Anselm J. Deninger, Thorsten Göbel, Daniel Schönherr, Thomas Kinder, Axel Roggenbuck, Markus Köberle, Frank Lison, Thomas Müller-Wirts, and Peter Meissner

Rev. Sci. Instrum. 79, 044702 (2008); http://dx.doi.org/10.1063/1.2905033 (6 pages) | Cited 22 times

Online Publication Date: 15 April 2008

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We realized a tunable continuous-wave terahertz source with megahertz frequency resolution. The system is based on optical heterodyning of two near-infrared distributed feedback diode lasers, each laser being stabilized by electronic feedback from a low-finesse quadrature interferometer. The control loop permits precisely linear laser frequency scans over >1200 GHz, and a beat signal linewidth of 1 MHz at 80 ms time scale. Using GaAs photomixers and log-periodic antennae, we achieve a signal-to-noise ratio of the terahertz power of >70 dB at 100 GHz and 100 ms integration time, and still ∼ 30 dB at 1 THz. As an example for high-resolution terahertz spectroscopy, we characterize the transmission properties of a subwavelength metal grating.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
07.60.Ly Interferometers
42.79.Dj Gratings
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