| 1. |
- Allaf Navirian, Hengameh, et al.
(författare)
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Repetitive ultrafast melting of InSb as an x-ray timing diagnostic
- 2008
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 103:10, s. 6-103510
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Tidskriftsartikel (refereegranskat)abstract
- We have demonstrated the possibility of using repetitive ultrafast melting of InSb as a timing diagnostic in connection with visible-light pump/x-ray probe measurements at high-repetition-rate x-ray facilities. Although the sample was molten and regrown approximately 1x10(6) times, a distinct reduction in time-resolved x-ray reflectivity could be observed using a streak camera with a time resolution of 2.5 ps. The time-resolved x-ray reflectivity displayed this distinct decrease despite the fact that the average reflectivity of the sample had fallen to approximately 50% of its original value due to accumulated damage from the prolonged laser exposure. The topography of the laser-exposed sample was mapped using an optical microscope, a stylus profilometer, photoelectron microscopy, and a scanning tunneling microscope. Although the surface of the sample is not flat following prolonged exposure at laser fluences above 15 mJ/cm(2), the atomic scale structure regrows, and thus, regenerates the sample on a nanosecond timescale. In the fluence range between 15 and 25 mJ/cm(2), the laser power is sufficient to melt the sample, while regrowth occurs with a sufficiently good structure to allow the extraction of timing information via ultrafast time-resolved x-ray measurements. This can be applied for timing purposes at synchrotron radiation and x-ray free-electron laser facilities. It is also noteworthy that we were able to reproduce the fluence dependencies of melting depth and disordering time previously obtained in single-shot, nonthermal melting experiments with higher temporal resolution.
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| 2. |
- Andersson, E, et al.
(författare)
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Coronary angiography using laser plasma sources: X-ray source efficiency and optimization of a bent crystal monochromator
- 2001
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 90:6, s. 3048-3056
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Tidskriftsartikel (refereegranskat)abstract
- A monochromator has been developed for coronary angiography, comprising a single bent crystal of silicon in Laue transmission geometry. K spectra of laser irradiated solid tin and tantalum (Z=50 and 73, respectively) targets were measured. The high resolution crystal spectrometer resolve the Sn and Ta K alpha doublets, allowing in a proof-of-principle experiment the absolute K alpha photon numbers emitted by the source to be determined. The Ta K alpha yield is measured as a function of the laser pulse energy, allowing an assessment to be made of the suitability of such sources for medical applications. (C) 2001 American Institute of Physics.
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| 3. |
- Andresen, SE, et al.
(författare)
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Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface
- 2003
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 94:6, s. 3990-3994
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Tidskriftsartikel (refereegranskat)abstract
- We study the spin-polarized tunneling of electrons from the valence band of GaMnAs into the conduction band of n-type GaAs with Si delta-doping at the interface. The injection of spin-polarized electrons is detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode, corresponding to magneto-optical Kerr effect loops. The angular momentum selection rules are simplified by the strain-induced heavy-hole/light-hole splitting, allowing a direct relation between circular polarization and spin-polarization. Comparison with the influence of Zeeman splitting allow us to conclude a spin-injection from the majority spin-band.
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| 4. |
- Argun, Aykut, et al.
(författare)
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Enhanced force-field calibration via machine learning
- 2020
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- The influence of microscopic force fields on the motion of Brownian particles plays a fundamental role in a broad range of fields, including soft matter, biophysics, and active matter. Often, the experimental calibration of these force fields relies on the analysis of the trajectories of the Brownian particles. However, such an analysis is not always straightforward, especially if the underlying force fields are non-conservative or time-varying, driving the system out of thermodynamic equilibrium. Here, we introduce a toolbox to calibrate microscopic force fields by analyzing the trajectories of a Brownian particle using machine learning, namely, recurrent neural networks. We demonstrate that this machine-learning approach outperforms standard methods when characterizing the force fields generated by harmonic potentials if the available data are limited. More importantly, it provides a tool to calibrate force fields in situations for which there are no standard methods, such as non-conservative and time-varying force fields. In order to make this method readily available for other users, we provide a Python software package named DeepCalib, which can be easily personalized and optimized for specific force fields and applications. This package is ideal to calibrate complex and non-standard force fields from short trajectories, for which advanced specific methods would need to be developed on a case-by-case basis.
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| 5. |
- Bertram, Florian, et al.
(författare)
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In situ anodization of aluminum surfaces studied by x-ray reflectivity and electrochemical impedance spectroscopy
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 116:3
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Tidskriftsartikel (refereegranskat)abstract
- We present results from the anodization of an aluminum single crystal [Al(111)] and an aluminum alloy [Al 6060] studied by in situ x-ray reflectivity, in situ electrochemical impedance spectroscopy and ex situ scanning electron microscopy. For both samples, a linear increase of oxide film thickness with increasing anodization voltage was found. However, the slope is much higher in the single crystal case, and the break-up of the oxide film grown on the alloy occurs at a lower anodization potential than on the single crystal. The reasons for these observations are discussed as are the measured differences observed for x-ray reflectivity and electrochemical impedance spectroscopy.
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| 6. |
- Björn, Lars Olof, et al.
(författare)
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Comment on “A proposal for in vitro/GFR molecular erythema action spectrum” [J. Appl. Phys. 104, 034701 (2008)]
- 2009
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 105:11, s. 1-116103
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Tidskriftsartikel (refereegranskat)abstract
- The recent article by de Souza, Lorenzini and Rizzatti J. A. V. de Souza, F. Lorenzini, and M. R. Rizatti, J. Appl. Phys. 104, 034701 2008 in this journal needs corrections and clarifications on several points. The model used by them is not suitable for the study of erythema. © 2009 American Institute of Physics. DOI: 10.1063/1.3124649
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| 7. |
- Cai, Weidong, et al.
(författare)
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Multicolor light emission in manganese-based metal halide composites
- 2022
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- Manganese-based organic-inorganic metal halide composites have been considered as promising candidates for lead-free emitters. However, in spite of their excellent luminescence properties in green and red regions, blue emission-a critical component for white light generation-from pristine manganese-based composites is currently missing. In this work, we successfully achieve blue luminescence center in manganese-based composites through selecting specific organic component methylbenzylamine (MBA). Our approach is fundamentally different from green and red emission in manganese-based composites, which result from manganese-halide frameworks. The coexistence of different luminescence centers in our manganese-based composites is confirmed by photoluminescence (PL) and photoluminescence excitation (PLE) results. As a result of different photoluminescence excitation responses of different emission centers, the resulting emission color can be tuned with selecting different excitation wavelengths. Specifically, a white light emission can be obtained with Commission Internationale de leclairage coordinates of (0.33, 0.35) upon the 330 nm excitation. We further demonstrate the promise of our manganese-based composites in the anti-counterfeiting technology and multicolor lighting. Our results provide a novel strategy for full-spectral emission in manganese-based organic-inorganic metal halide composites and lay a solid foundation for a range of new applications. (C) 2022 Author(s).
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| 8. |
- Chao, Y, et al.
(författare)
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Reactions and luminescence in passivated Si nanocrystallites induced by vacuum ultraviolet and soft-x-ray photons
- 2005
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 98:4
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Tidskriftsartikel (refereegranskat)abstract
- Alkyl-modified silicon nanocrystallites are efficient fluorophores which are of interest for fundamental spectroscopic studies and as luminescent probes in biology because of their stability in aqueous media. In this work we have investigated these particles using scanning tunneling microscopy, synchrotron-radiation excited photoemission, and x-ray excited optical luminescence (XEOL). During the course of illumination with 145-eV photons we have monitored the evolution of the Si2p core level and, in samples which have suffered prolonged atmospheric exposure, observed in real time the growth of an extra Si2p component attributed to in situ photoinduced oxidation of the Si nanocrystallites. XEOL reveals that two emission bands are active upon soft-x-ray photon excitation and that photoluminescence intensity decreases with photon exposure, which is attributed to charge trapping within the film.
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| 9. |
- Chen, W, et al.
(författare)
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Temperature and pressure dependences of the Mn2+ and donor-acceptor emissions in ZnS : Mn2+ nanoparticles
- 2002
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 92:4, s. 1950-1955
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Tidskriftsartikel (refereegranskat)abstract
- Temperature and pressure dependent measurements have been performed on 3.5 nm ZnS:Mn2+ nanoparticles. As temperature increases, the donor-acceptor (DA) emission of ZnS:Mn2+ nanoparticles at 440 nm shifts to longer wavelengths while the Mn2+ emission (T-4(1)-(6)A(1)) shifts to shorter wavelengths. Both the DA and Mn2+ emission intensities decrease with temperature with the intensity decrease of the DA emission being much more pronounced. The intensity decreases are fit well with the theory of thermal quenching. As pressure increases, the Mn2+ emission shifts to longer wavelengths while the DA emission wavelength remains almost constant. The pressure coefficient of the DA emission in ZnS:Mn2+ nanoparticles is approximately -3.2 meV/GPa, which is significantly smaller than that measured for bulk materials. The relatively weak pressure dependence of the DA emission is attributed to the increase of the binding energies and the localization of the defect wave functions in nanoparticles. The pressure coefficient of Mn2+ emission in ZnS:Mn2+ nanoparticles is roughly -34.3 meV/GPa, consistent with crystal field theory. The results indicate that the energy transfer from the ZnS host to Mn2+ ions is mainly from the recombination of carriers localized at Mn2+ ions. (C) 2002 American Institute of Physics.
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| 10. |
- Chen, W, et al.
(författare)
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The origin of x-ray luminescence from CdTe nanoparticles in CdTe/BaFBr : Eu2+ nanocomposite phosphors
- 2006
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 99:3
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Tidskriftsartikel (refereegranskat)abstract
- X-ray luminescence from CdTe nanoparticles is observed when CdTe nanoparticles are encapsulated into BaFBr:Eu2+ phosphors. In contrast, negligible x-ray luminescence is observed from the unencapsulated nanoparticles, either in solution or in solid form. The origin of the x-ray luminescence is attributed to the effective energy transfer from Eu2+ ions to CdTe nanoparticles in the nanocomposite materials. The x-ray luminescence of these nanocomposites is dose dependent and the emission wavelength is size adjustable which may allow use as a type of dosimeter for both in vitro and in vivo applications. (c) 2006 American Institute of Physics.
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