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Oct 2005

Volume 76, Issue 10, Articles (10xxxx)

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Instrument techniques for rheometry

Ying Y. Hou and Hamida O. Kassim

Rev. Sci. Instrum. 76, 101101 (2005); http://dx.doi.org/10.1063/1.2085048 (19 pages) | Cited 7 times

Online Publication Date: 25 October 2005

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This article presents a review of some latest advances in rheology measuring techniques. Consideration is given to the modification and approaches in conventional measuring techniques and also to the development of specialty instruments. A number of sensing technologies such as nuclear-magnetic-resonance imaging and ultrasonic pulse Doppler mapping have recently been adopted to produce viscoelastic measurements for both Newtonian and non-Newtonian materials. The working principles of these technologies and their applications are described. Other recent developments in modifications of conventional rheometers for performance enhancement and for complex material characterizations have been thoroughly discussed. Some instrument designs and their special applications, such as interfacial rheometers, extensional rheometers, and high-pressure rheometers, have also been evaluated in detail.
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47.80.-v Instrumentation and measurement methods in fluid dynamics
83.85.Jn Viscosity measurements
83.85.Fg NMR/magnetic resonance imaging
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
47.50.-d Non-Newtonian fluid flows
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High flux source of cold rubidium atoms

Christopher Slowe, Laurent Vernac, and Lene Vestergaard Hau

Rev. Sci. Instrum. 76, 103101 (2005); http://dx.doi.org/10.1063/1.2069651 (10 pages) | Cited 13 times

Online Publication Date: 3 October 2005

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We report on the production of a continuous, slow, and cold beam of math atoms with an extremely high flux of 3.2×1012 atoms/s, a transverse temperature of 3 mK, and a longitudinal temperature of 90 mK. We describe the apparatus created to generate the atom beam. Hot atoms are emitted from a rubidium candlestick atomic beam source and transversely cooled and collimated by a 20 cm long atomic collimator section, boosting overall beam flux by a factor of 50. The Rb atomic beam is then decelerated and longitudinally cooled by a 1 m long Zeeman slower.
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37.20.+j Atomic and molecular beam sources and techniques
37.10.De Atom cooling methods
37.10.Gh Atom traps and guides

Proposed precision laser spectrometer for trapped, highly charged ions

M. Vogel, D. F. A. Winters, D. M. Segal, and R. C. Thompson

Rev. Sci. Instrum. 76, 103102 (2005); http://dx.doi.org/10.1063/1.2069742 (7 pages) | Cited 12 times

Online Publication Date: 3 October 2005

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We propose a type of precision laser spectrometer for trapped, highly charged ions nearly at rest. It consists of a cylindrical, open-endcap Penning trap in which an externally produced bunch of highly charged ions can be confined and investigated by means of laser spectroscopy. The combination of confinement, cooling, and compression of a dense ion cloud will allow the ground-state hyperfine splitting in highly charged ions to be measured with an accuracy three orders of magnitude better than in any previous experiment. A systematic study of different charge states and different isotopes of the same element allows for highly sensitive tests of bound-state quantum electrodynamics and for a precision determination of nuclear properties. Apart from stable isotopes, radioactive species with half-lives longer than about 1 hour also can be investigated.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
37.20.+j Atomic and molecular beam sources and techniques
32.30.Rj X-ray spectra
12.20.Fv Experimental tests
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Generation of programmable near-Fourier-transform-limited pulses of narrow-band laser radiation from the near infrared to the vacuum ultraviolet

R. Seiler, Th. Paul, M. Andrist, and F. Merkt

Rev. Sci. Instrum. 76, 103103 (2005); http://dx.doi.org/10.1063/1.2081891 (10 pages) | Cited 17 times

Online Publication Date: 10 October 2005

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Fourier-transform-limited pulses of programmable length and shape have been generated in the range λ = 720–825 nm from the continuous-wave output of a Ti3+-doped sapphire (Ti:Sa) ring laser using a pulsed acousto-optic modulator (AOM). The minimal rise time of the pulses amounts to 10 ns and is limited by the size of the cw laser beam in the active medium of the AOM. Amplification of the radiation pulses in Nd:YAG-pumped Ti:Sa crystals into intense pulses of near-infrared (NIR) radiation with pulse energies of up to 15 mJ was demonstrated at a repetition rate of 25 Hz. Frequency upconversion into the ultraviolet (UV) by frequency doubling (νUV = 2νNIR) or by mixing the fundamental NIR radiation with the doubled radiation (νUV = 3νNIR) in nonlinear crystals was achieved under conditions where the pulse shapes could be preserved. The pulse energies amounted to up to 1 mJ for the doubled radiation and 100 μJ for the tripled radiation for NIR pulses of 30 ns duration. Vacuum ultraviolet (VUV) radiation pulses of 108–109 photons/pulse at 120 000 cm−1 were generated by two-photon resonance-enhanced third-harmonic generation in a pulsed gas beam of xenon. The VUV pulse length could be adjusted between 10 and 20 ns, and double pulses of VUV radiation separated by a variable delay of up to 100 ns could be generated. Frequency chirps arising in the AOM and the pulsed amplification were found to be negligible, but a frequency shift of −5 MHz was determined. The bandwidth of the generated radiation was estimated to be 35 MHz in the UV at a wave number of ≈ 40 000 cm−1 and 55 MHz in the VUV at a wave number of ≈ 120 000 cm−1 in a Doppler-free measurement of the (5p)6 math→(5p)56p[1/2](J = 0) two-photon resonance of xenon. The absolute accuracy of the wave-number calibration is limited by uncertainties in the positions of NIR lines of I2 taken as reference standard.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Hp Optical processors, correlators, and modulators
42.79.Jq Acousto-optical devices
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Partially ferromagnetic electromagnet for trapping and cooling neutral atoms to quantum degeneracy

M. Fauquembergue, J-F. Riou, W. Guerin, S. Rangwala, F. Moron, A. Villing, Y. Le Coq, P. Bouyer, A. Aspect, and M. Lécrivain

Rev. Sci. Instrum. 76, 103104 (2005); http://dx.doi.org/10.1063/1.2090407 (7 pages) | Cited 4 times

Online Publication Date: 19 October 2005

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We have developed a compact partially ferromagnetic electromagnet to produce an Ioffe-Pritchard trap for neutral atoms. Our structure permits strong magnetic confinement with low power consumption. Compared to the previous iron-core electromagnet [ B. Desruelle, V. Boyer, P. Bouyer, G. Birkl, M. Lécrivain, F. Alves, C. Westbrook, and A. Aspect, Eur. Phys. J. D 1, 255 (1998) ], it allows for easy compensation of remnant fields and very high stability, along with cost-effective realization and compactness. We describe and characterize our apparatus and demonstrate trapping and cooling of math atoms to quantum degeneracy. Pure Bose-Einstein condensates containing 106 atoms are routinely realized on a half-minute cycle. In addition we test the stability of the magnetic trap by producing atom lasers.
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37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
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Technique for increasing dynamic range of space-borne ion composition instruments

J. L. Burch, G. P. Miller, A. De Los Santos, C. J. Pollock, S. E. Pope, P. W. Valek, and D. T. Young

Rev. Sci. Instrum. 76, 103301 (2005); http://dx.doi.org/10.1063/1.2084867 (4 pages)

Online Publication Date: 3 October 2005

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The dynamic range of ion composition spectrometers is limited by several factors, including saturation of particle counters and spillover of signals from highly dominant species into channels tuned to minor species. Instruments designed for composition measurements of hot plasmas in space can suffer greatly from both of these problems because of the wide energy range required and the wide disparity in fluxes encountered in various regions of interest. In order to detect minor ions in regions of very weak fluxes, geometry factors need to be as large as possible within the mass and volume resources available. As a result, problems with saturation by the dominant fluxes and spillover to minor-ion channels in plasma regions with intense fluxes become especially acute. This article reports on a technique for solving the dynamic-range problem in the few eV to several keV energy/charge range that is of central importance for space physics research where the dominant ion is of low mass/charge (typically H+), and the minor ions are of higher mass/charge (typically O+). The technique involves employing a radio-frequency modulation of the deflection electric field in the back section of an electrostatic analyzer in a time-of-flight instrument. This technique is shown to reduce H+ counts by a controllable amount of up to factors of 1000 while reducing O+ counts by only a few percent that can be calibrated.
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07.87.+v Spaceborne and space research instruments, apparatus, and components (satellites, space vehicles, etc.)
94.80.+g Instrumentation for space plasma physics, ionosphere, and magnetosphere
07.75.+h Mass spectrometers
52.70.Nc Particle measurements
95.30.Qd Magnetohydrodynamics and plasmas

Development of a 27.12 MHz radio frequency driven ion source with 3 mTorr operation pressure for neutron generators

Ximan Jiang, Ye Chen, Lili Ji, Qing Ji, and Ka-Ngo Leung

Rev. Sci. Instrum. 76, 103302 (2005); http://dx.doi.org/10.1063/1.2113782 (4 pages) | Cited 3 times

Online Publication Date: 19 October 2005

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An inductively coupled rf plasma ion source has been developed for neutron generators. The ion source configuration has been optimized for low pressure operation. Both 13.56 and 27.12 MHz rf powers have been used to generate hydrogen plasma. Experimental results show that 27.12 MHz operation is more efficient than 13.56 MHz in a low pressure region. The ion source can also be operated in pulsed mode. Current density higher than 30 mA/cm2 can be extracted from a 2-mm-diam aperture at 2 kW rf input power and 3 mTorr operation pressure.
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29.25.Ni Ion sources: positive and negative
29.25.Dz Neutron sources
52.50.Dg Plasma sources
52.75.-d Plasma devices
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Gated x-ray intensifier for large format simultaneous imaging

T. McCarville, S. Fulkerson, R. Booth, J. Emig, B. Young, S. Anderson, and B. Heeter

Rev. Sci. Instrum. 76, 103501 (2005); http://dx.doi.org/10.1063/1.2090328 (6 pages) | Cited 7 times

Online Publication Date: 10 October 2005

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Some applications of gated x-ray imagers, pulsed x-ray spectroscopy, for example, benefit if image capture is simultaneous and gain is uniform over the frame. Simultaneity and uniformity are both improved when the voltage gate pulse propagation distance is as short as practical across the micro-channel-plate. This article describes a micro-channel-plate intensifier that captures a 40×100 mm2 image in <300 ps. A simple transmission line loss model is proposed to explain voltage loss across the micro-channel-plate. The voltage loss exponent was measured to be 0.05/cm±20%, and used to predict spatial and temporal gain dependence. The spatial and temporal gain profile was measured in detail by capturing images of ∼ 1 ps x-ray bursts created with a short pulse laser. The measured profile is consistent with that predicted using the loss model.
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07.85.Nc X-ray and γ-ray spectrometers
52.70.La X-ray and γ-ray measurements
42.79.Ls Scanners, image intensifiers, and image converters

Three-dimensional observation system for pellet ablation traveling in the high-temperature plasmas

Ryuichi Sakamoto and Hiroshi Yamada

Rev. Sci. Instrum. 76, 103502 (2005); http://dx.doi.org/10.1063/1.2093770 (4 pages) | Cited 3 times

Online Publication Date: 10 October 2005

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In order to investigate the ablation of a solid hydrogen pellet, which is injected into a high-temperature plasma with high speed ( ∼ 1 km/s) for the plasma refueling, a three-dimensional observation system using a fast camera has been developed. A stereo method has been employed to obtain the three-dimensional information of the pellet ablation. A pair of the stereo images, which have been taken from different locations, has been focused onto a single fast camera by using a bifurcated fiber scope to ensure the simultaneity of both images. The projection matrix, which is used for stereo reconstruction, is calibrated by taking images of a model plane of known coordinates from the actual camera positions. The measuring error of the stereo observation is within 2% in the depth direction.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
07.68.+m Photography, photographic instruments; xerography
07.05.Pj Image processing
42.30.Va Image forming and processing

Space-charge effects in the catcher gas cell of a rf ion guide

A. Takamine, M. Wada, Y. Ishida, T. Nakamura, K. Okada, Y. Yamazaki, T. Kambara, Y. Kanai, T. M. Kojima, Y. Nakai, N. Oshima, A. Yoshida, T. Kubo, S. Ohtani, K. Noda, et al.

Rev. Sci. Instrum. 76, 103503 (2005); http://dx.doi.org/10.1063/1.2090290 (6 pages) | Cited 13 times

Online Publication Date: 24 October 2005

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Slow radioactive ion beams have been produced with an overall efficiency of 4% by thermalizing energetic ions produced by a projectile fragment separator in a He-gas cell and guiding them to a vacuum vessel by dc and rf fields. Space charge was observed to have a limiting effect. Since the ionization of He atoms by energetic ions creates a region of high space charge, many thermalized ions of interest are pushed toward the walls of the gas cell. Such losses have been investigated for different incoming ion intensities.
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29.25.Ni Ion sources: positive and negative
41.75.-i Charged-particle beams
41.85.-p Beam optics
29.30.Aj Charged-particle spectrometers: electric and magnetic

X-ray flux from filtered arrays of detectors without unfolding

D. L. Fehl, W. A. Stygar, G. A. Chandler, M. E. Cuneo, and C. L. Ruiz

Rev. Sci. Instrum. 76, 103504 (2005); http://dx.doi.org/10.1063/1.2090468 (10 pages) | Cited 5 times

Online Publication Date: 24 October 2005

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A simple computational method is proposed for estimating the time-dependent flux F[ΔE](t) of an x-ray spectrum S(E,t) over domain [ΔE] from data Dk(t)(k = 1,…,N) obtained by an N-channel array of filtered detectors. It is assumed that the data are related to the spectrum by a discrete, inhomogeneous, first-kind Fredholm integral equation Dk = ∫ S(E,t)Rk(E)dE, where Rk(E) is the known response function for each detector channel of the diagnostic. The proposed method constructs a spectral sensitivity HLS(E) for the diagnostic array as a linear combination ∑k = 1NakRk(E) of the responses, where the coefficients ak are obtained by a least-squares criterion plus a constraint. The ak values, once determined, apply as long as the responses are valid. The flux estimate is then simply FLS(t) = ∑k = 1NakDk(t), without a spectral unfold of the data. The method is useful for quick analyses of time-dependent data, for comparisons with other flux-measuring diagnostics, and for the experimental design of filtered-detector arrays. The method is applied to a five-channel array of filtered photoemissive x-ray detectors [ G. A. Chandler et al., Rev. Sci. Instrum. 70, 561 (1999) ], used for z-pinch measurements at the Z-accelerator facility [ R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998) ]. Comparisons with unfold results are made, and a first-order analysis of error propagation into FLS(t) is presented.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.70.La X-ray and γ-ray measurements
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
02.60.Nm Integral and integrodifferential equations
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A versatile instrument for in situ combination of scanning probe microscopy and time-of-flight mass spectrometry

A. Wetzel, A. Socoliuc, E. Meyer, R. Bennewitz, E. Gnecco, and C. Gerber

Rev. Sci. Instrum. 76, 103701 (2005); http://dx.doi.org/10.1063/1.2082004 (6 pages) | Cited 5 times

Online Publication Date: 3 October 2005

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A scanning probe microscope is combined with a time-of-flight mass spectrometer that analyzes material from the tip of the probe microscope. Chemical analysis on the nanometer scale is achieved by transferring material from surfaces via the probing tip to the mass spectrometer under ultrahigh vacuum conditions. Fast switching between scanning probe and mass analysis operation is implemented by means of a motorized rotatable probe holder. Electrochemically etched tungsten tips are used as probes for the experiments. Thorough characterization of the tips by means of field-emission measurements is crucial for successful experiments. Quartz tuning forks have been applied as force sensors in force microscopy experiments.
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68.37.−d
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
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Cryogenic scanning Hall-probe microscope with centimeter scan range and submicron resolution

Rafael B. Dinner, M. R. Beasley, and Kathryn A. Moler

Rev. Sci. Instrum. 76, 103702 (2005); http://dx.doi.org/10.1063/1.2072438 (11 pages) | Cited 18 times

Online Publication Date: 4 October 2005

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We have constructed a scanning Hall-probe microscope that combines a 1×4 cm scan range with 200 nm positioning resolution by coupling stepper motors to high-resolution drivers and reducing gears. The instrument is uniquely suited for efficient magnetic imaging of mesoscopic devices, media, and materials, operating from 4 K to room temperature with fast turn-around time. Its potential for studying dissipation in coated conductors—high-Tc superconducting tapes—is demonstrated via model systems. We image an entire sample of YBa2Cu3O7−δ, then zoom in to individual fluxons. Flux penetration into a single artificial grain boundary is imaged with 4×10−3 G/math field resolution and 25 μs time resolution by averaging over cycles of ac driving current. Using the resulting magnetic movie, we map out ac power losses.
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07.55.-w Magnetic instruments and components
07.79.-v Scanning probe microscopes and components
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

A fluid cell with integrated acoustic radiation pressure actuator for atomic force microscopy

A. G. Onaran and F. L. Degertekin

Rev. Sci. Instrum. 76, 103703 (2005); http://dx.doi.org/10.1063/1.2069627 (6 pages) | Cited 6 times

Online Publication Date: 11 October 2005

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The development of a fluid cell with an acoustic radiation pressure (ARP) actuator for atomic force microscopy (AFM) is reported. The ARP actuator uses a zinc oxide thin film transducer fabricated on a silicon substrate to generate acoustic waves in the 120–180 MHz range. These waves are coupled to the liquid and are reflected off of the AFM cantilever exerting radiation pressure to move the AFM cantilevers in the dc-MHz frequency range, providing a fast actuation scheme. Since the ARP actuator is remotely located on the fluid cell, it can be used with virtually any type of cantilever. The design, fabrication, and characterization of the AFM fluid cell with an ARP actuator are discussed and the performance of the device is compared with theoretical predictions. ARP actuator electronics and its integration to a commercial AFM system are described. Tapping mode images and molecular adhesion measurements are presented as illustrative examples.
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07.79.Lh Atomic force microscopes
07.07.Mp Transducers

Filtration of micron-sized particles in granular media revealed by x-ray computed tomography

F. A. H. Al-Abduwani, R. Farajzadeh, W. M. G. T. van den Broek, P. K. Currie, and P. L. J. Zitha

Rev. Sci. Instrum. 76, 103704 (2005); http://dx.doi.org/10.1063/1.2103467 (6 pages) | Cited 2 times

Online Publication Date: 19 October 2005

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We investigate the deep-bed filtration of micron-sized hematite particles suspended in distilled water during flow in siliceous granular porous media, where particle retention is mostly due to surface (van der Waals and electrostatic) interactions. We show that x-ray computed tomography enables three-dimensional images of the filtration process to be generated. The one-dimensional filtrate concentration profiles obtained by averaging the images over sections perpendicular to the flow direction are rapidly decaying functions of the distance from the porous medium inlet and slide upward in the course of time, consistently with the filtration model presented by Herzig et al. [Ind. Eng. Chem. 62, 8 (1970)] . Finally, the filtration coefficient is found to decrease rapidly as a function of time: This indicates that the attractive interaction responsible for the retention of the hematite particles is strongly attenuated as the particles accumulate of the pore surfaces.
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47.56.+r Flows through porous media
47.80.-v Instrumentation and measurement methods in fluid dynamics
83.80.Fg Granular solids
45.70.Mg Granular flow: mixing, segregation and stratification
47.55.Kf Particle-laden flows
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids

A highly sensitive atomic force microscope for linear measurements of molecular forces in liquids

Shivprasad Patil, George Matei, Hang Dong, Peter M. Hoffmann, Mustafa Karaköse, and Ahmet Oral

Rev. Sci. Instrum. 76, 103705 (2005); http://dx.doi.org/10.1063/1.2083147 (7 pages) | Cited 9 times

Online Publication Date: 24 October 2005

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We describe a highly improved atomic force microscope for quantitative nanomechanical measurements in liquids. The main feature of this microscope is a modified fiber interferometer mounted on a five axis inertial slider which provides a deflection sensitivity that is significantly better than conventional laser deflection based systems. The measured low noise floor of 572.0 fm/math provides excellent cantilever amplitude resolution. This allows us to operate the instrument far below resonance at extremely small cantilever amplitudes of less than 1 Å. Thus linear measurements of nanomechanical properties of liquid systems can be performed. In particular, we present measurements of solvation forces in confined octamethylcyclotetrasiloxane and water with amplitudes smaller than the size of the respective molecules. In general, the development of the instrument is important in the context of quantitative nanomechanical measurements in liquid environments.
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07.79.Lh Atomic force microscopes
82.30.-b Specific chemical reactions; reaction mechanisms

In situ imaging of micro-organisms in intense magnetic fields

Karine Guevorkian and James M Valles

Rev. Sci. Instrum. 76, 103706 (2005); http://dx.doi.org/10.1063/1.2103427 (3 pages) | Cited 1 time

Online Publication Date: 24 October 2005

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This article describes a setup suitable for the in situ visualization and imaging of swimming unicellular organisms in intense magnetic fields at a constant temperature. It fits within a 31 T maximum field, 50 mm bore resistive magnet at the National High Magnetic Field Laboratory. The main optical component is a 6 mm side view borescope, which provides an optical axis perpendicular to the magnetic field allowing us to monitor the motion of the micro-organisms parallel to the field. The system has a maximum resolution of 20 μm. We will present images of swimming paramecia in magnetic field obtained with this setup and show that the resolution is adequate for tracking purposes.
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87.80.-y Biophysical techniques (research methods)
87.50.C- Static and low-frequency electric and magnetic fields effects
87.17.Jj Cell locomotion, chemotaxis
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Double sublimation system to deposit molecules from solid organic compounds onto a cryogenic substrate: Thymine on solid argon

P. L. Levesque, M. Michaud, and L. Sanche

Rev. Sci. Instrum. 76, 103901 (2005); http://dx.doi.org/10.1063/1.2069519 (6 pages) | Cited 6 times

Online Publication Date: 3 October 2005

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We report on the design, operation, and performance of a double sublimation system for the deposition of a submonolayer up to a few layers of a low-vapor pressure molecular solid compound onto a cryogenic substrate. The system consists of a primary oven (i.e., crucible type) to degas and first sublimate the compound onto the tip of a secondary oven (i.e., finger type), which is then used to transport the purified compound inside an analysis chamber and sublimate it just in front of the cryogenic substrate. The latter is kept at exactly the same position all the time, which is essential for experiments sensitive to target position. Besides, the negligible radiant heat transfer from the tip of the secondary oven allows operation in the presence of a cryogenic substrate consisting of an inert gas solid. The overall performance of the system is studied by EEL spectroscopy for thymine deposited onto a multilayer film of Ar used as an inert cryogenic substrate.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
64.70.Hz Solid-vapor transitions

Modulated-bath ac calorimetry using modified commercial Peltier elements

Rolf Lortz, Satoko Abe, Yuxing Wang, Frédéric Bouquet, Ulrich Tutsch, and Alain Junod

Rev. Sci. Instrum. 76, 103902 (2005); http://dx.doi.org/10.1063/1.2069648 (8 pages) | Cited 5 times

Online Publication Date: 5 October 2005

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We developed a type of ac microcalorimeter based on a modulated-bath technique for measuring the specific heat of small microgram samples in the temperature range from 30 to 300 K, and tested it in magnetic fields up to 14 T. The device is built from a modified commercial Peltier element. The temperature of its top plate can be modulated periodically by the Peltier effect, so that the oscillation is symmetrical about the temperature of the main bath. This avoids the problem of dc offsets which plague conventional ac calorimeters. The sample is attached to a thin thermocouple cross, acting as a weak thermal link to a platform. The absence of a heater reduces the background heat capacity (“addenda”) to a minimum. As an illustrative example of the performance of our device, the specific heat in fields up to 14 T of a small single crystal of the high-temperature superconductor Bi2.12Sr1.71Ca1.22Cu1.95Oy is determined.
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07.20.Fw Calorimeters
74.25.F- Transport properties
74.72.-h Cuprate superconductors

A force sensor for atomic point contacts

A. M. C. Valkering, A. I. Mares, C. Untiedt, K. Babaei Gavan, T. H. Oosterkamp, and J. M. van Ruitenbeek

Rev. Sci. Instrum. 76, 103903 (2005); http://dx.doi.org/10.1063/1.2084347 (5 pages) | Cited 9 times

Online Publication Date: 5 October 2005

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We have developed a sensor to study the mechanical stiffness of atomic-size contacts. It consists of a modification of the mechanically controllable break-junction technique, using a quartz tuning fork resonator as force sensor. We present first results of measurements of the force constants in gold atomic contacts. In the formation of chains of single-metal atoms, the folding in of individual atoms from the banks into the chain can be observed. This sensor allows one to measure forces in atomic contacts for a wide variety of metals, as illustrated with the first measurements on platinum.
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07.10.Pz Instruments for strain, force, and torque
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Robotic dipping system for layer-by-layer assembly of multifunctional thin films

Woo-Sik Jang and Jaime C. Grunlan

Rev. Sci. Instrum. 76, 103904 (2005); http://dx.doi.org/10.1063/1.2084447 (4 pages) | Cited 9 times

Online Publication Date: 5 October 2005

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A simple, yet very flexible robotic dipping system for the preparation of functional thin films is presented. These films are deposited onto a substrate using the layer-by-layer assembly technique. The robot alternately dips a substrate into aqueous mixtures containing oppositely charged or otherwise complementary species. Samples can be spray rinsed (a unique feature of this robot relative to others created for thin film deposition) and blow dried after each dip. Dipping, rinsing, and drying times are adjustable and up to twelve mixtures can be deposited in any order. An example 20-bilayer film was prepared using aqueous mixtures of carbon black stabilized with polyethylenimine and poly(acrylic acid). This film exhibits low resistivity (<0.2 Ω∙cm) and is free of the porosity and brittleness that are characteristic of highly filled polymer composites. The robotic dipping system is especially useful for films requiring more than tenbilayers and a variety of different layers.
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07.07.Tw Servo and control equipment; robots
68.55.-a Thin film structure and morphology
73.61.-r Electrical properties of specific thin films
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Reflectron velocity map ion imaging

Brian D. Leskiw, Myung Hwa Kim, Gregory E. Hall, and Arthur G. Suits

Rev. Sci. Instrum. 76, 104101 (2005); http://dx.doi.org/10.1063/1.2075167 (6 pages) | Cited 12 times

Online Publication Date: 3 October 2005

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We report the first demonstration of velocity map ion imaging in a reflectron configuration. Under these conditions, the velocity-resolving capabilities associated with velocity map ion imaging are achieved simultaneously with long flight times and the high mass resolution characteristic of reflectron time-of-flight mass spectrometers. The photodissociation of OCS at 230 nm has been used to characterize the velocity-focusing performance of the instrument. The reflectron geometry provides an increased magnification factor over conventional velocity map ion imaging.
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82.80.Rt Time of flight mass spectrometry
06.30.Gv Velocity, acceleration, and rotation
07.75.+h Mass spectrometers
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.50.Hp Processes caused by visible and UV light

Controlled growth of helium nanodroplets from a pulsed source

Shengfu Yang, Scott M. Brereton, and Andrew M. Ellis

Rev. Sci. Instrum. 76, 104102 (2005); http://dx.doi.org/10.1063/1.2093766 (4 pages) | Cited 15 times

Online Publication Date: 11 October 2005

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Factors affecting the size of liquid-helium droplets produced by a pulsed nozzle are described. The shape of the nozzle orifice is found to be important in allowing control of the size of the droplets. With an appropriate choice of nozzle geometry, the average droplet size is shown to be continuously variable over nearly two orders of magnitude by adjustment of the helium gas stagnation pressure and/or temperature. A scaling law similar to, but not identical with, that found for helium droplets produced by continuous supersonic expansion sources is found for the pulsed source. The pulsed nozzle described in this article has been used to make helium droplets ranging in size from a few thousand atoms up to nearly 105 helium atoms.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
47.60.-i Flow phenomena in quasi-one-dimensional systems
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A simple setup for the study of microvolume frozen samples using Raman spectroscopy

Marco Kriek, Cameron Neylon, Peter L. Roach, Ian P. Clark, and Anthony W. Parker

Rev. Sci. Instrum. 76, 104301 (2005); http://dx.doi.org/10.1063/1.2054486 (3 pages)

Online Publication Date: 5 October 2005

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A method for obtaining resonance Raman spectra from microvolume (2–5 μl) frozen samples is described. The procedure involves trapping and freezing a microdroplet in a specially designed sample holder using a cryostream. The method makes it possible to prepare numerous low-volume air-sensitive samples in a suitable environment for spectroscopic studies. We have demonstrated the potential of the setup measuring the resonance Raman spectra of 4-thiouracil and horse heart myoglobin.
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87.64.K- Spectroscopy
87.14.E- Proteins
87.15.M- Spectra of biomolecules
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Aspirated capacitor measurements of air conductivity and ion mobility spectra

K. L. Aplin

Rev. Sci. Instrum. 76, 104501 (2005); http://dx.doi.org/10.1063/1.2069744 (6 pages) | Cited 5 times

Online Publication Date: 19 October 2005

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Measurements of ions in atmospheric air are used to investigate atmospheric electricity and particulate pollution. Commonly studied ion parameters are (1) air conductivity, related to the total ion number concentration, and (2) the ion mobility spectrum, which varies with atmospheric composition. The physical principles of air ion instrumentation are long established. A recent development is the computerized aspirated capacitor, which measures ions from (a) the current of charged particles at a sensing electrode, and (b) the rate of charge exchange with an electrode at a known initial potential, relaxing to a lower potential. As the voltage decays, only ions of higher and higher mobility are collected by the central electrode and contribute to the further decay of the voltage. This enables extension of the classical theory to calculate ion mobility spectra by inverting voltage decay time series. In indoor air, ion mobility spectra determined from both the voltage decay inversion, and an established voltage switching technique, were compared and shown to be of similar shape. Air conductivities calculated by integration were: 5.3±2.5 and 2.7±1.1 fSm−1, respectively, with conductivity determined to be 3 fSm−1 by direct measurement at a constant voltage. Applications of the relaxation potential inversion method include air ion mobility spectrum retrieval from historical data, and computation of ion mobility spectra in planetary atmospheres.
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93.85.-q Instruments and techniques for geophysical research: Exploration geophysics
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
84.32.Tt Capacitors
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
92.60.Pw Atmospheric electricity, lightning
82.33.Tb Atmospheric chemistry
92.60.H- Atmospheric composition, structure, and properties
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
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