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May 2010

Volume 81, Issue 5, Articles (05xxxx)

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back to top Condensed Matter; Materials

Highly sensitive parylene membrane-based ac-calorimeter for small mass magnetic samples

A. F. Lopeandia, E. André, J.-L. Garden, D. Givord, and O. Bourgeois

Rev. Sci. Instrum. 81, 053901 (2010); http://dx.doi.org/10.1063/1.3422247 (8 pages) | Cited 3 times

Online Publication Date: 17 May 2010

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We report the microfabrication and operation of a highly sensitive ac-calorimeter designed to characterize small mass magnetic systems operating at very low frequencies (from 0.1 to 5 Hz) in a temperature range from 20 to 300 K. The calorimetric cell is built in the center of a 500 nm thick polymeric membrane of parylene C held up by a Cu frame. On both sides of the membrane defining a three layer structure, electrical leads, heater, and thermometer are deposited as thin film layers of NbNx, with different nitrogen contents, taking benefit of the poor thermal conductance of niobium nitride to thermally isolate the system. This suspended structure ensures very low heat capacity addenda with values in the μJ/K over the 1 mm2 area of the measurement cell. The structuring of the membrane along with suspending of the sensing part only by the parylene bridges leads to a highly reduced thermal link. The calorimeter has been characterized as a function of frequency, temperature, and magnetic field. The thermal link measured is really small reaching values well below 10−8 W/K at 50 K. With these characteristics the frequency of adiabaticity is typically around few hertz and energy exchanges as small as 1 pJ can be detected. Measurements have been performed on Co/Au thin films and on the GdAl2 microcrystal where the ferromagnetic phase transition is clearly evidenced.
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07.20.Fw Calorimeters
07.10.Cm Micromechanical devices and systems
07.20.Dt Thermometers

Miniaturized transportable evaporator for molecule deposition inside cryogenic scanning probe microscopes

K. Lämmle, A. Schwarz, and R. Wiesendanger

Rev. Sci. Instrum. 81, 053902 (2010); http://dx.doi.org/10.1063/1.3428621 (5 pages)

Online Publication Date: 20 May 2010

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Here, we present a very small evaporator unit suitable to deposit molecules onto a sample in a cryogenic environment. It can be transported in an ultrahigh vacuum system and loaded into Omicron-type cantilever stages. Thus, molecule deposition inside a low temperature force microscope is possible. The design features an insulating base plate with two embedded electrical contacts and a crucible with low power consumption, which is thermally well isolated from the surrounding. The current is supplied via a removable power clip. Details of the manufacturing process as well as the used material are described. Finally, the performance of the whole setup is demonstrated.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

A simple external resistance heating diamond anvil cell and its application for synchrotron radiation x-ray diffraction

Dawei Fan, Wenge Zhou, Shuyi Wei, Yonggang Liu, Maining Ma, and Hongsen Xie

Rev. Sci. Instrum. 81, 053903 (2010); http://dx.doi.org/10.1063/1.3430069 (5 pages) | Cited 1 time

Online Publication Date: 21 May 2010

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A simple external heating assemblage allowing diamond anvil cell experiments at pressures up to 34 GPa and temperatures up to 653 K was constructed. This cell can be connected to the synchrotron radiation conveniently. The design and construction of this cell are fully described, as well as its applications for x-ray diffraction. Heating is carried out by using an external-heating system, which is made of NiCr resistance wire, and the temperature was measured by a NiCr–NiSi or PtRh–Pt thermocouple. We showed the performance of the new system by introducing the phase transition study of cinnabar (α-HgS) and thermal equation of state study of almandine at high pressure and temperature with this cell.
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07.85.Qe Synchrotron radiation instrumentation
05.70.Ce Thermodynamic functions and equations of state
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
FREE

A high-efficiency spin-resolved photoemission spectrometer combining time-of-flight spectroscopy with exchange-scattering polarimetry

C. Jozwiak, J. Graf, G. Lebedev, N. Andresen, A. K. Schmid, A. V. Fedorov, F. El Gabaly, W. Wan, A. Lanzara, and Z. Hussain

Rev. Sci. Instrum. 81, 053904 (2010); http://dx.doi.org/10.1063/1.3427223 (15 pages) | Cited 6 times

Online Publication Date: 24 May 2010

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We describe a spin-resolved electron spectrometer capable of uniquely efficient and high energy resolution measurements. Spin analysis is obtained through polarimetry based on low-energy exchange scattering from a ferromagnetic thin-film target. This approach can achieve a similar analyzing power (Sherman function) as state-of-the-art Mott scattering polarimeters, but with as much as 100 times improved efficiency due to increased reflectivity. Performance is further enhanced by integrating the polarimeter into a time-of-flight (TOF) based energy analysis scheme with a precise and flexible electrostatic lens system. The parallel acquisition of a range of electron kinetic energies afforded by the TOF approach results in an order of magnitude (or more) increase in efficiency compared to hemispherical analyzers. The lens system additionally features a 90° bandpass filter, which by removing unwanted parts of the photoelectron distribution allows the TOF technique to be performed at low electron drift energy and high energy resolution within a wide range of experimental parameters. The spectrometer is ideally suited for high-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES), and initial results are shown. The TOF approach makes the spectrometer especially ideal for time-resolved spin-ARPES experiments.
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79.60.-i Photoemission and photoelectron spectra
75.30.Ds Spin waves
78.66.-w Optical properties of specific thin films

Accuracy and precision in photonic Doppler velocimetry

D. H. Dolan

Rev. Sci. Instrum. 81, 053905 (2010); http://dx.doi.org/10.1063/1.3429257 (7 pages) | Cited 9 times

Online Publication Date: 27 May 2010

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While photonic Doppler velocimetry (PDV) is becoming a common diagnostic in dynamic compression research, its limiting accuracy and precision are not well understood. Velocity resolution is known to be inversely proportional to the time resolution, but resolution estimates differ by one to two orders of magnitude. Furthermore, resolution varies with the number of recorded signals and how these signals are analyzed. Numerical simulations reveal factors that affect accuracy and precision in PDV, and the results may be extended to a broad class of measurements. After systematic effects are eliminated, the limiting velocity uncertainty in a PDV measurement is governed by the sampling rate, the signal noise fraction, and the analysis time duration.
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06.30.Gv Velocity, acceleration, and rotation
07.60.-j Optical instruments and equipment

An amplified femtosecond laser system for material micro-/nanostructuring with an integrated Raman microscope

Othman H. Y. Zalloum, Matthew Parrish, Alexander Terekhov, and William Hofmeister

Rev. Sci. Instrum. 81, 053906 (2010); http://dx.doi.org/10.1063/1.3430073 (7 pages) | Cited 6 times

Online Publication Date: 27 May 2010

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In order to obtain new insights into laser-induced chemical material modifications, we introduce a novel combined approach of femtosecond pulsed laser-direct writing and in situ Raman microscopy within a single experimental apparatus. A newly developed scanning microscope, the first of its kind, provides a powerful tool for micro-/nanomachining and characterization of material properties and allows us to relate materials’ functionality with composition. We address the issues of light delivery to the photomodification site and show the versatility of the system using tight focusing. Amplified femtosecond pulses are generated by a Ti:sapphire laser oscillator and a chirped-pulse regenerative amplifier, both pumped by a diode-pumped frequency doubled neodymium-doped yttrium orthovanadate (Nd:YVO4) laser operating at 532 nm. Results of Raman spectroscopy and scanning electron microscopy images of femtosecond laser micro-/nanomachining on the surface and in the bulk of single-crystal diamond obtained from first trials of this instrument are also presented. This effective combination could help to shed light on the influence of the local structure fluctuations on controllability of the laser processing and the role of the irradiation in the ablation processes ruling out possible imprecisions coming from the use of the two independent techniques.
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42.62.Cf Industrial applications
42.65.Lm Parametric down conversion and production of entangled photons
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