| 1. |
- Allaf Navirian, Hengameh, et al.
(author)
-
Acoustically driven ferroelastic domain switching observed by time-resolved x-ray diffraction
- 2010
-
In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 81:2
-
Journal article (peer-reviewed)abstract
- Domain polarization switching in potassium dihydrogen phosphate (KH2PO4, KDP) induced by a propagating strain wave has been observed with time-resolved x-ray diffraction. A pulsed electric field with amplitude of 6 kV/cm and duration of 1 mu s was applied along the crystallographic c axis. The field-induced strain waves emanating from the sample surfaces are the result of the converse piezoelectric effect. In the center of the probed surface two waves interfered constructively inducing ferroelastic domain switching, in the absence of an external electric field, at a delay of 3 mu s, corresponding to acoustic propagation at a velocity found to be 1500 m/s.
|
|
| 2. |
- Enquist, Henrik, et al.
(author)
-
Subpicosecond hard x-ray streak camera using single-photon counting.
- 2010
-
In: Optics Letters. - 1539-4794. ; 35:19, s. 3219-3221
-
Journal article (peer-reviewed)abstract
- We have developed and characterized a hard x-ray accumulating streak camera that achieves subpicosecond time resolution by using single-photon counting. A high repetition rate of 2 kHz was achieved by use of a readout camera with built-in image processing capabilities. The effects of sweep jitter were removed by using a UV timing reference. The use of single-photon counting allows the camera to reach a high quantum efficiency by not limiting the divergence of the photoelectrons.
|
|
| 3. |
- Gaudin, J., et al.
(author)
-
Time-resolved investigation of nanometer scale deformations induced by a high flux x-ray beam
- 2011
-
In: Optics Express. - 1094-4087. ; 19:16, s. 15516-15524
-
Journal article (peer-reviewed)abstract
- We present results of a time-resolved pump-probe experiment where a Si sample was exposed to an intense 15 keV beam and its surface monitored by measuring the wavefront deformation of a reflected optical laser probe beam. By reconstructing and back propagating the wavefront, the deformed surface can be retrieved for each time step. The dynamics of the heat bump, build-up and relaxation, is followed with a spatial resolution in the nanometer range. The results are interpreted taking into account results of finite element method simulations. Due to its robustness and simplicity this method should find further developments at new x-ray light sources (FEL) or be used to gain understanding on thermo-dynamical behavior of highly excited materials. (C) 2011 Optical Society of America
|
|
| 4. |
- Harb, Maher, et al.
(author)
-
Picosecond dynamics of laser-induced strain in graphite
- 2011
-
In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 84:4
-
Journal article (peer-reviewed)abstract
- We report on the use of grazing-incidence time-resolved x-ray diffraction to investigate the evolution of strain in natural graphite excited by femtosecond-laser pulses in the fluence range of 6-35 mJ/cm(2). Strains corresponding to up to similar to 2.8% c-axis expansion were observed. We show that the experimental data is in good agreement with calculations based on the Thomsen strain model in conjunction with dynamical diffraction theory. Furthermore we find no evidence of nonthermal lattice expansion as reported in recent ultrafast electron-diffraction studies of laser-excited graphite conducted under comparable excitation conditions.
|
|
| 5. |
- Jurgilaitis, Andrius, et al.
(author)
-
Measurements of light absorption efficiency in InSb nanowires
- 2014
-
In: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 1:1
-
Journal article (peer-reviewed)abstract
- We report on measurements of the light absorption efficiency of InSb nanowires. The absorbed 70 fs light pulse generates carriers, which equilibrate with the lattice via electron-phonon coupling. The increase in lattice temperature is manifested as a strain that can be measured with X-ray diffraction. The diffracted X-ray signal from the excited sample was measured using a streak camera. The amount of absorbed light was deduced by comparing X-ray diffraction measurements with simulations. It was found that 3.0(6)% of the radiation incident on the sample was absorbed by the nanowires, which cover 2.5% of the sample. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
|
|
| 6. |
- Jurgilaitis, Andrius, et al.
(author)
-
Time-Resolved X-ray Diffraction Investigation of the Modified Phonon Dispersion in InSb Nanowires
- 2014
-
In: Nano letters (Print). - Washington, DC : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 14:2, s. 541-546
-
Journal article (peer-reviewed)abstract
- The modified phonon dispersion is of importance for understanding the origin of the reduced heat conductivity in nanowires. We have measured the phonon dispersion for 50 nm diameter InSb (111) nanowires using time-resolved X-ray diffraction. By comparing the sound speed of the bulk (3880 m/s) and that of a classical thin rod (3600 m/s) to our measurement (2880 m/s), we conclude that the origin of the reduced sound speed and thereby to the reduced heat conductivity is that the C44 elastic constant is reduced by 35% compared to the bulk material. © 2014 American Chemical Society.
|
|
| 7. |
- Jurgilaitis, Andrius, et al.
(author)
-
Time resolved X-ray studies in semiconductor nanostructures
- 2012
-
In: 2012 Conference on Lasers and Electro-Optics (Cleo). - 9781557529336
-
Conference paper (peer-reviewed)abstract
- Time resolved X-ray diffraction has been used to study acoustic oscillations in InAs/Sb nanowires with diameters of 80 nm and 40 nm in order to determine the speed of sound in the wires.
|
|
| 8. |
- Jurgilaitis, Andrius, et al.
(author)
-
X-ray diffraction from the ripple structures created by femtosecond laser pulses
- 2010
-
In: Applied Physics A: Materials Science & Processing. - : Springer Science and Business Media LLC. - 1432-0630. ; 100:1, s. 105-112
-
Journal article (peer-reviewed)abstract
- In this paper, we present the investigation and characterization of the laser-induced surface structure on an asymmetrically cut InSb crystal. We describe diffraction from the ripple surface and present a theoretical model that can be used to simulate X-ray energy scans. The asymmetrically cut InSb sample was irradiated with short-pulse radiation centred at 800 nm, with fluences ranging from 10 to 80 mJ/cm(2). The irradiated sample surface profile was investigated using optical and atomic force microscopy. We have investigated how laser-induced ripples influence the possibility of studying repetitive melting of solids using X-ray diffraction. The main effects arise from variations in local asymmetry angles, which reduce the attenuation length and increase the X-ray diffraction efficiency.
|
|
| 9. |
- Nüske, Ralf, et al.
(author)
-
Picosecond time-resolved x-ray refectivity of a laser-heated amorphous carbon film
- 2011
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 98:10
-
Journal article (peer-reviewed)abstract
- We demonstrate thin film x-ray reflectivity measurements with picosecond time resolution. Amorphous carbon films with a thickness of 46 nm were excited with laser pulses characterized by 100 fs duration, a wavelength of 800 nm, and a fluence of 70 mJ/cm(2). The laser-induced stress caused a rapid expansion of the thin film followed by a relaxation of the film thickness as heat diffused into the silicon substrate. We were able to measure changes in film thickness as small as 0.2 nm. The relaxation dynamics are consistent with a model which accounts for carrier-enhanced substrate heat diffusivity. (C) 2011 American Institute of Physics. [doi:10.1063/1.3562967]
|
|
| 10. |
- Nüske, Ralf, et al.
(author)
-
Time-resolved x-ray scattering from laser-molten indium antimonide.
- 2010
-
In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 81:1
-
Journal article (peer-reviewed)abstract
- We demonstrate a concept to study transient liquids with picosecond time-resolved x-ray scattering in a high-repetition-rate configuration. Femtosecond laser excitation of crystalline indium antimonide (InSb) induces ultrafast melting, which leads to a loss of the long-range order. The remaining local correlations of the liquid result in broad x-ray diffraction rings, which are measured as a function of delay time. After 2 ns the liquid structure factor shows close agreement with that of equilibrated liquid InSb. The measured decay of the liquid scattering intensity corresponds to the resolidification rate of 1 m/s in InSb.
|
|
| 11. |
- Nüske, Ralf, et al.
(author)
-
Transforming graphite to nanoscale diamonds by a femtosecond laser pulse
- 2012
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:4
-
Journal article (peer-reviewed)abstract
- Formation of cubic diamond from graphite following irradiation by a single, intense, ultra-short laser pulse has been observed. Highly oriented pyrolytic graphite (HOPG) samples were irradiated by a 100 fs pulse with a center wavelength of 800 nm. Following laser exposure, the HOPG samples were studied using Raman spectroscopy of the sample surface. In the laser-irradiated areas, nanoscale cubic diamond crystals have been formed. The exposed areas were also studied using grazing incidence x-ray powder diffraction showing a restacking of planes from hexagonal graphite to rhombohedral graphite. (C) 2012 American Institute of Physics. [doi:10.1063/1.3678190]
|
|
| 12. |
- Nüske, Ralf
(author)
-
X-ray - Based Studies of Structural Dynamics in Solids and Liquids
- 2011
-
Doctoral thesis (other academic/artistic)abstract
- The wavelength of x-ray radiation is much shorter than that of visible light. In fact, it is comparable to the distances between atoms in solids, which is on the order of one tenth of a nanometer. Using light of such a short wavelength, it is possible to study the structure of materials on the atom level. Scattering of x-rays has been developed into an invaluable tool to analyze various characteristics of matter, from the lattice structure of crystals to the structure of large biological molecules. In this way, we found that many of the properties of materials depend on their internal structure. To learn about changes in the structure of materials on the atom-level, time resolved x-ray scattering has proven a powerful technique. A wide variety of processes can be studied: from phase transitions in materials to vibrations in crystal lattices and pathways of chemical reactions. The aim of time-resolved studies is to follow these processes in real time. The timescale for changes in structure varies considerably depending on the underlying mechanism. Processes involving neighboring atoms typically take about 100\,fs. Structure changes involving large groups of atoms or molecules occure on a timescale of picoseconds to nanoseconds. Different mechanisms can be used to trigger changes in structure. Laser pulses with a duration of less than 100\,fs can be produced routinely and are used to initiate ultrafast changes in the structure. Alternatively, short electrical pulses can be used to trigger structural changes in piezo-electric materials. In this work, the main focus has been on experimental studies in order to deepen the understanding of structural changes in matter. The picosecond dynamics involved in the melting and recrystallization of a semiconductor, acoustic and thermal response of laser-excited solids, and the dynamics in the structure of a piezo-electric material have been studied. Additionally, instrumentation required for time-resolved x-ray scattering experiments has been developed.
|
|
