| 51. |
- Björklund, Sebastian, et al.
(författare)
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Humidity scanning quartz crystal microbalance with dissipation monitoring setup for determination of sorption-desorption isotherms and rheological changes
- 2015
-
Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 86:5
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Tidskriftsartikel (refereegranskat)abstract
- A new method to determine water sorption-desorption isotherms with high resolution in the complete range of water activities (relative humidities) is presented. The method is based on quartz crystal microbalance with dissipation monitoring (QCM-D). The QCM-D is equipped with a humidity module in which the sample film is kept in air with controlled humidity. The experimental setup allows for continuous scanning of the relative humidity from either dry to humid conditions or vice versa. The amount of water sorbed or desorbed from the sample is determined from the resonance frequencies of the coated quartz sensor, via analysis of the overtone dependence. In addition, the method allows for characterization of hydration induced changes of the rheological properties from the dissipation data, which is closely connected to the viscoelasticity of the film. The accuracy of the humidity scanning setup is confirmed in control experiments. Sorption-desorption isotherms of pig gastric mucin and lysozyme, obtained by the new method, show good agreement with previous results. Finally, we show that the deposition technique used to coat the quartz sensor influences the QCM-D data and how this issue can be used to obtain further information on the effect of hydration. In particular, we demonstrate that spin-coating represents an attractive alternative to obtain sorption-desorption isotherms, while drop-coating provides additional information on changes of the rheological properties during hydration.
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| 52. |
- Blahins, J., et al.
(författare)
-
Operating a cesium sputter source in a pulsed mode
- 2020
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 91:2
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Tidskriftsartikel (refereegranskat)abstract
- A scheme is presented for pulsing of a cesium sputter negative ion source by periodically switching on and off the high voltage driving the sputtering process. We demonstrate how the pulsed ion beam can be used in combination with a pulsed laser (6 ns pulse length) that has a 10 Hz repetition rate to study the photodetachment process, where a negative ion is neutralized due to the absorption of a photon. In such experiments, where the ion beam is used only for a small fraction of the time, we show that the pulsed mode operation can increase the lifetime of a cathode by two orders of magnitude as compared with DC operation. We also investigate how the peak ion current compares with the ion current obtained when the source is run in a DC mode. We find that the peak current in the pulsed mode is strongly dependent on the ion species. In some cases, we observed a strong enhancement, whereas others showed only a moderate enhancement, or even a decrease, in the peak current. We conclude that the pulsed mode operation can be of great value when the negative ion to be investigated requires cathodes that have short lifetimes, expensive materials, or those with relatively small ion beam yields, in the latter case limited to elements with large enhancement factors. Published under license by AIP Publishing.
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| 53. |
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| 54. |
- Bohm, P., et al.
(författare)
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Edge Thomson scattering diagnostic on COMPASS tokamak : Installation, calibration, operation, improvements
- 2014
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 85:11, s. 11E431-
-
Tidskriftsartikel (refereegranskat)abstract
- The core Thomson scattering diagnostic (TS) on the COMPASS tokamak was put in operation and reported earlier. Implementation of edge TS, with spatial resolution along the laser beam up to similar to 1/100 of the tokamak minor radius, is presented now. The procedure for spatial calibration and alignment of both core and edge systems is described. Several further upgrades of the TS system, like a triggering unit and piezo motor driven vacuum window shutter, are introduced as well. The edge TS system, together with the core TS, is now in routine operation and provides electron temperature and density profiles.
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| 55. |
- Bondza, Saskia, et al.
(författare)
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A simple experimental method for measuring the thermal sensitivity of single-mode fibers
- 2020
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 91:10
-
Tidskriftsartikel (refereegranskat)abstract
- We present a simple technique to experimentally determine the optical-path length change with temperature for optical single-mode fibers. Standard single-mode fibers act as natural low-finesse cavities, with the Fresnel reflection of the straight cleaved surfaces being ∼3%, for the laser light coupled to them. By measuring the intensity variations due to interference of light reflected from the fiber front and end surfaces, while ramping the ambient temperature, the thermal sensitivity of the optical-path length of the fiber can be derived. Light was generated by a narrow linewidth, low drift laser. With our fairly short test fibers, we found that it was possible to reach a relative precision of the temperature sensitivity, compared to a reference fiber, on the 0.4%-2% scale and an absolute precision of 2%-5%, with the potential to improve both by an order of magnitude. The results for single-acrylate, dual-acrylate, and copper- and aluminum-coated fibers are presented. Values are compared with analytic models and results from a finite element method simulation. With the aid of these measurements, a simple fiber-interferometer, which is insensitive to thermal drifts, could be constructed.
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| 56. |
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| 57. |
- Borgani, Riccardo, et al.
(författare)
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Intermodulation spectroscopy as an alternative to pump-probe for the measurement of fast dynamics at the nanometer scale
- 2019
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 90:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present an alternative approach to pump-probe spectroscopy for measuring fast charge dynamics with an atomic force microscope (AFM). Our approach is based on coherent multifrequency lock-in measurement of the intermodulation between a mechanical drive and an optical or electrical excitation. In response to the excitation, the charge dynamics of the sample is reconstructed by fitting a theoretical model to the measured frequency spectrum of the electrostatic force near resonance of the AFM cantilever. We discuss the time resolution, which in theory is limited only by the measurement time, but in practice is of order 1 ns for standard cantilevers and imaging speeds. We verify the method with simulations and demonstrate it with a control experiment, achieving a time resolution of 30 ns in ambient conditions, limited by thermal noise.
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| 58. |
- Bottyán, L., et al.
(författare)
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GINA—A polarized neutron reflectometer at the Budapest Neutron Centre
- 2013
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics. - 0034-6748 .- 1089-7623. ; 84:1
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Tidskriftsartikel (refereegranskat)abstract
- The setup, capabilities, and operation parameters of the neutron reflectometer GINA, the recently installed “Grazing Incidence Neutron Apparatus” at the Budapest Neutron Centre, are introduced. GINA, a dance-floor-type, constant-energy, angle-dispersive reflectometer is equipped with a 2D position-sensitive detector to study specular and off-specular scattering. Wavelength options between 3.2 and 5.7 Å are available for unpolarized and polarized neutrons. Spin polarization and analysis are achieved by magnetized transmission supermirrors and radio-frequency adiabatic spin flippers. As a result of vertical focusing by a five-element pyrolytic graphite monochromator, the reflected intensity from a 20 × 20 mm2 sample has been doubled. GINA is dedicated to studies of magnetic films and heterostructures, but unpolarized options for non-magnetic films, membranes, and other surfaces are also provided. Shortly after its startup, reflectivity values as low as 3 × 10−5 have been measured by the instrument. The instrument capabilities are demonstrated by a non-polarized and a polarized reflectivity experiment on a Si wafer and on a magnetic film of [62Ni/natNi]5 isotope-periodic layer composition. The facility is now open for the international user community. Its further development is underway establishing new sample environment options and spin analysis of off-specularly scattered radiation as well as further decreasing the background.
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| 59. |
- Bowman, Lawrence E., et al.
(författare)
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A single photon timing instrument that covers a broad temporal range in the reversed timing configuration
- 1993
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 64:2, s. 338-341
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Tidskriftsartikel (refereegranskat)abstract
- A versatile single-photon timing instrument based on the reversed timing configuration has been constructed. Unlike similar instruments, the apparatus described here is capable of recording a broad range of excited-state decay times owing to a switched fiber optic delay. This allows the user to readily collect time-resolved luminescence data over a variable time window in the reversed-timing configuration. With proper adjustment of the appropriate components, one can acquire a luminescence decay over a variable time range from less than 1 ns to nearly 1 μs. The full width at half-maximum of the instrument response function is 42 ps. The utility of a switched fiber optic delay is discussed and the device's construction is described.
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| 60. |
- Boye, Shawn A., et al.
(författare)
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Precise magnetoresistance and Hall resistivity measurements in the diamond anvil cell
- 2004
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 75:11, s. 5010-5015
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Tidskriftsartikel (refereegranskat)abstract
- An experimental system in combination with a technique for creating samples has been developed for conducting magnetotransport measurements of 3d ferromagnets as a function of temperature and pressure. Polycrystalline Ni0.985O0.015 thin film samples have been manufactured for experiments at zero pressure and in the diamond anvil cell (DAC) such that the contacts are of a predetermined size. This ensures that the placement of the leads in the pressure chamber of the DAC does not affect the quality of the measurement. Magnetoresistance and Hall resistivity measurements are preformed using the van der Pauw technique and the constant current method. The performance of the experimental apparatus is demonstrated by magnetotransport measurements of Ni0.985O0.015 thin films between 285 and 455 K in applied magnetic fields up to 10 T. The change in magnetic resistivity measured in the transverse configuration at zero pressure in the DAC, −0.0162(2) μΩ cm T−1 at 297 K, is observed to be negative and linear up to the maximum applied field. The extraordinary Hall coefficient measured at zero pressure and 297 K is found to be RE = −30.4(1)×10−10 m3 C−1.
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