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Sep 2003

Volume 74, Issue 9, pp. 3909-4222

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back to top CONDENSED MATTER; MATERIALS

Setup for in situ surface investigations of the liquid/glass transition with (coherent) x rays

Tilo Seydel, Anders Madsen, Michael Sprung, Metin Tolan, Gerhard Grübel, and Werner Press

Rev. Sci. Instrum. 74, 4033 (2003); http://dx.doi.org/10.1063/1.1599068 (8 pages) | Cited 11 times

Online Publication Date: 20 August 2003

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A dedicated setup comprising an efficient cryogenic device for the in situ preparation of large surface areas of prototypical organic glass formers in a wide temperature range (170–340 K) is presented. This setup provides the necessary temperature and vibrational stability for surface x-ray and neutron scattering experiments, including the extremely sensitive technique of x-ray photon correlation spectroscopy (XPCS). XPCS is an emerging method which is made possible by the high coherent photon flux produced by third-generation synchrotrons. We demonstrate that microscopic motion at the surface can be studied in a direct way in the liquid and supercooled state using XPCS. In addition, we have used a charge-coupled-device detector to record two-dimensional images of static speckle patterns forming on surfaces in the glassy state. © 2003 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
78.70.Ck X-ray scattering
68.35.Rh Phase transitions and critical phenomena

High-resolution grazing-incidence scattering using a combination of analyzer crystal and linear detector

Detlef M. Smilgies

Rev. Sci. Instrum. 74, 4041 (2003); http://dx.doi.org/10.1063/1.1602938 (7 pages) | Cited 1 time

Online Publication Date: 20 August 2003

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Mesoscopic structures on length scales of 10–1000 nm are of high interest for the study of nanostrucured surfaces and thin films. Such structures can be analyzed with the help of high-resolution x-ray scattering using crystal optics. In order to improve the speed of data collection, it is convenient to combine the analyzer crystal with a linear detector. A simple analytical theory in angular space is presented, how to correct distortions in intensity maps obtained this way, and how to optimize the accessible angular range. The anisotropic resolution that can be achieved with this combination—high-resolution scattering in the sample plane, large scattering range normal to the surface—is useful for grazing-incidence small-angle scattering and high-resolution grazing-incidence diffraction from surfaces and thin films, on both solid substrates as well as at the air–water interface. © 2003 American Institute of Physics.
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41.50.+h X-ray beams and x-ray optics
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cp X-ray diffraction
07.85.-m X- and γ-ray instruments
78.70.Ck X-ray scattering

Diffractometer for soft x-ray resonant magnetic scattering

J. Grabis, A. Nefedov, and H. Zabel

Rev. Sci. Instrum. 74, 4048 (2003); http://dx.doi.org/10.1063/1.1602932 (4 pages) | Cited 38 times

Online Publication Date: 20 August 2003

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We report on the design and construction of a new diffractometer for soft x-ray resonant magnetic scattering which has been built at the Ruhr-University Bochum. The ultrahigh vacuum-compatible diffractometer comprises a two-circle goniometer and works in horizontal scattering geometry. Rotation of the detector and sample is realized by two differentially pumped rotating platforms with motors and gears external to the vacuum. The sample environment consists of a closed-cycle He cryostat that allows heating up to 600 K and applying a magnetic field of ±2.5 kOe. All functions of the experimental setup have been extensively tested at the BESSY II Synchrotron (beamline PM3). The experimental results demonstrate the performance of the instrument. © 2003 American Institute of Physics.
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07.85.Jy Diffractometers
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
07.55.Db Generation of magnetic fields; magnets
61.05.cf X-ray scattering (including small-angle scattering)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Recirculation cell for the small-angle neutron scattering investigation of polymer melts in flow

Julian F. Bent, Randal W. Richards, and Tim D. Gough

Rev. Sci. Instrum. 74, 4052 (2003); http://dx.doi.org/10.1063/1.1602939 (6 pages) | Cited 5 times

Online Publication Date: 20 August 2003

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A small-scale flow cell has been developed and used for small-angle neutron scattering (SANS) investigations of polymer melts in Poiseuille flow through a 4:1 contraction. The cell enables the investigation of polymer melt flow subject to a volumetric flow rate of up to 6 cm3 s−1, at pressures up to 10 MPa, temperatures up to 230 °C, and a melt viscosity up to 65 000 Pa s. The cell has recirculating flow path and a relatively small capacity (circa 200 g of polymer) so that polymers with novel and well-defined molecular architectures may be investigated. The details of its construction and operation are described. When two walls of the cell are composed of zero order birefringent sapphire, both small-angle neutron scattering and birefringence studies can be undertaken in the same cell providing a link between macroscopic and molecular level descriptions of the influence of melt flow. Both birefringence and the first melt flow SANS data for a monodisperse, linear polystyrene are presented. These demonstrate the capability and potential of the apparatus to provide data which provide a crucial test for molecular theories of the rheology of entangled polymer melts. However, the use of sapphire windows limits the maximum flow rate that can be used and higher flows necessitated an all aluminum flow cell to cope with the higher pressures developed in flow. Clear evidence of a stretching of the molecule in the direction of the melt flow and a contraction perpendicular to the flow direction has been provided. © 2003 American Institute of Physics.
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83.85.Hf X-ray and neutron scattering
83.80.Sg Polymer melts
47.80.-v Instrumentation and measurement methods in fluid dynamics
61.05.fg Neutron scattering (including small-angle scattering)
61.25.H- Macromolecular and polymers solutions; polymer melts
47.60.-i Flow phenomena in quasi-one-dimensional systems
78.20.Fm Birefringence
83.50.Ha Flow in channels

An improved continuous compositional-spread technique based on pulsed-laser deposition and applicable to large substrate areas

H. M. Christen, C. M. Rouleau, I. Ohkubo, H. Y. Zhai, H. N. Lee, S. Sathyamurthy, and D. H. Lowndes

Rev. Sci. Instrum. 74, 4058 (2003); http://dx.doi.org/10.1063/1.1602962 (5 pages) | Cited 10 times

Online Publication Date: 20 August 2003

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A method for continuous compositional-spread (CCS) thin-film fabrication based on pulsed-laser deposition (PLD) is introduced. This approach is based on a translation of the substrate heater and the synchronized firing of the excimer laser, with the deposition occurring through a slit-shaped aperture. Alloying is achieved during film growth (possible at elevated temperature) by the repeated sequential deposition of submonolayer amounts. Our approach overcomes serious shortcomings in previous in situ implementation of CCS based on sputtering or PLD, in particular the variation of thickness across the compositional spread and the differing deposition energetics as a function of position. While moving-shutter techniques are appropriate for PLD approaches yielding complete spreads on small substrates (i.e., small as compared to distances over which the deposition parameters in PLD vary, typically ≈1 cm), our method can be used to fabricate samples that are large enough for individual compositions to be analyzed by conventional techniques, including temperature-dependent measurements of resistivity and dielectric and magnetic properties (i.e., superconducting quantum interference device magnetometry). Initial results are shown for spreads of (Sr1−xCax)RuO3. © 2003 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition

Patterning of particulate films using Faraday waves

P. H. Wright and J. R. Saylor

Rev. Sci. Instrum. 74, 4063 (2003); http://dx.doi.org/10.1063/1.1602936 (8 pages) | Cited 6 times

Online Publication Date: 20 August 2003

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Faraday waves were used to create a patterned particulate film on the surface of a glass substrate. The process involves deposition of a thin liquid film on the substrate, where the liquid is comprised of water and a concentrated suspension of particles. Faraday waves were created on the surface of the liquid film by subjecting the substrate and film to a vertical oscillation. Because the films are thin, the standing waves create velocity fluctuations that are not negligible near the substrate surface. As the particles in the liquid settled to the bottom, the flow field caused by the waves caused preferential particle deposition organized in a pattern determined by the Faraday wave field. Subsequent evaporation of the liquid film left a particulate film on the solid substrate that retained the pattern of the original wave field. We refer to these particulate films as Faraday films. The length scale of the patterns in these films was on the order of millimeters in the experiments described here. Use of higher frequency oscillations could permit the formation of Faraday films having smaller spatial scales. © 2003 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
47.35.-i Hydrodynamic waves
47.55.Kf Particle-laden flows
47.54.-r Pattern selection; pattern formation

Characterization of laser ablation as a means for doping helium nanodroplets

P. Claas, S.-O. Mende, and F. Stienkemeier

Rev. Sci. Instrum. 74, 4071 (2003); http://dx.doi.org/10.1063/1.1602943 (6 pages) | Cited 15 times

Online Publication Date: 20 August 2003

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Helium nanodroplets are doped with metal atoms by means of laser evaporation. The material is evaporated directly in front of the helium nozzle by a pulsed laser. In comparison with conventional pickup from an oven we deduce that the droplets can be loaded with more than one atom per droplet on average. Conditions and efficiencies for loading are evaluated. Furthermore, metal ions can be attached to helium droplets by this method, allowing isolation of charged particles at temperatures below 1 K. In this way we can directly measure size distributions of helium nanodroplets which are compared to results using other techniques. © 2003 American Institute of Physics.
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47.55.D- Drops and bubbles
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
52.38.Mf Laser ablation
47.60.-i Flow phenomena in quasi-one-dimensional systems

Magnetomechanical testing machine for ferromagnetic shape-memory alloys

T. W. Shield

Rev. Sci. Instrum. 74, 4077 (2003); http://dx.doi.org/10.1063/1.1599072 (12 pages) | Cited 16 times

Online Publication Date: 20 August 2003

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Recently, a new class of active materials, known as ferromagnetic shape-memory alloys, has shown promise as actuator and sensor materials. These alloys, such as Ni2MnGa and Fe3Pd, are ferromagnetic and undergo a reversible diffusionless structural phase transformation giving rise to shape-memory behavior. In order to explore the behavior of these materials it is necessary to combine both mechanical materials testing, magnetic field application, and magnetization measurements. To accomplish this, an apparatus called a magnetomechanical testing machine (MMTM) has been constructed. The MMTM combines a screw driven mechanical load frame with a dual-dipole electromagnet to load specimens both mechanically and magnetically. The pair of magnets allows the magnetic field to point in any direction in the plane containing the uniaxial loading axis of the mechanical test frame. In addition, the specimen temperature is controlled and the surface is observed microscopically. This apparatus is described and some preliminary measurements are reported. Saturation magnetization measurements for Fe3Pd made with the MMTM are found to be within 2% of previously reported values. © 2003 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

A novel spectrometer for spin-polarized electron energy-loss spectroscopy

H. Ibach, D. Bruchmann, R. Vollmer, M. Etzkorn, P. S. Anil Kumar, and J. Kirschner

Rev. Sci. Instrum. 74, 4089 (2003); http://dx.doi.org/10.1063/1.1597954 (7 pages) | Cited 12 times

Online Publication Date: 20 August 2003

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By making use of advanced methods for the calculation of electron trajectories in the presence of space charge fields we have designed and built a novel electron energy-loss spectrometer for the purpose of measuring spin flip excitations at surfaces. The measurement of the spin asymmetry requires a deflection angle between the photocathode and the sample position which amounts to 90° in total. That deflection angle is not provided by standard electron deflectors, or by a combination of those. We show that a 90° deflection angle can be realized by a combination of two novel deflectors with 90° and 180° deflection angles each. The performance of the new spectrometer matches the performance of the best electron spectrometers developed for surface vibration spectroscopy. © 2003 American Institute of Physics.
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07.81.+a Electron and ion spectrometers
68.49.Jk Electron scattering from surfaces
79.20.Uv Electron energy loss spectroscopy
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