Thermoelastic study of nanolayered structures using time-resolved x-ray diffraction at high repetition rate

We investigate the thermoelastic response of a nanolayered sample composed of a metallic SrRuO3 (SRO) electrode sandwiched between a ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT) film with negative thermal expansion and a SrTiO3 substrate. SRO is rapidly heated by fs-laser pulses with 208 kHz repetition rate. Diffraction of x-ray pulses derived from a synchrotron measures the transient out-of-plane lattice constant c of all three materials simultaneously from 120 ps to 5 mus with a relative accuracy up to Delta c/c = 10^-6. The in-plane propagation of sound is essential for understanding the delayed out of plane expansion.Comment: 5 pages, 3 figure

Investigation of Cu poor and Cu rich Cu In,Ga Se2 CdS interfaces using hard X ray photoelectron spectroscopy

Cu poor and Cu rich Cu In,Ga Se2 CIGSe absorbers were used as substrates for the chemical bath deposition of ultrathin CdS buffer layers in the thickness range of a few nanometers in order to make the CIGSe CdS interface accessible by hard X ray photo emission spectroscopy. The composition of both, the absorber and the buffer layer as well as the energetics of the interface was investigated at room temperature and after heating the samples to elevated temperatures 200 C, 300 C and 400 C . It was found that the amount of Cd after the heating treatment depends on the near surface composition of the CIGSe absorber. No Cd was detected on the Cu poor surface after the 400 C treatment due to its diffusion into the CIGSe layer. In contrast, Cd was still present on the Cu rich surface after the same treatment at 400

Large acoustic transients induced by nonthermal melting of InSb.

We have observed large-amplitude strain waves following a rapid change in density of InSb due to nonthermal melting. The strain has been measured in real time via time-resolved x-ray diffraction, with a temporal resolution better than 2 ps. The change from the solid to liquid density of the surface layer launches a high-amplitude strain wave into the crystalline material below. This induces an effective plane rotation in the asymmetrically cut crystal leading to deflection of the diffracted beam. The uniform strain in the layer below the molten layer is 2.0(+/-0.2)%. A strain of this magnitude develops within 5 ps of the incident pulse showing that the liquid has reached the equilibrium density within this time frame. Both the strain amplitude and the depth of the strained material in the solid can be explained by assuming a reduction in the speed of sound in the nonequilibrium liquid compared to measured equilibrium values

Nanoscale heat transport studied by high resolution time resolved X ray diffraction

We report on synchrotron-based high-repetition rate ultrafast x-ray diffraction (UXRD) experiments monitoring the transport of heat from an epitaxial La0.7Sr0.3MnO3/SrTiO3 superlattice (SL) into the substrate on timescales from 100 ps to 4 mu s. Transient thermal lattice expansion was determined with an accuracy of 10(-7), corresponding to a sensitivity to temperature changes down to 0.01 K. We follow the heat flow within the SL and into the substrate after the impulsive laser heating leads to a small temperature rise of Delta T = 6 K. The transient lattice temperature can be simulated very well using the bulk heat conductivities. This contradicts the interpretation of previous UXRD measurements, which predicted a long-lasting expansion of SrRuO3 for more than 200 ps. The disagreement could be resolved by assuming that the heat conductivity changes in the first hundred picoseconds

Direct time domain sampling of subterahertz coherent acoustic phonon spectra in SrTiO3 using ultrafast x ray diffraction

We synthesize sub-THz longitudinal quasi-monochromatic acoustic phonons in a SrTiO$_3$ single crystal using a SrRuO$_3$/SrTiO$_3$ superlattice as an optical-acoustic transducer. The generated acoustic phonon spectrum is determined using ultrafast X-ray diffraction. The analysis of the generated phonon spectrum in the time domain reveals a k-vector dependent phonon lifetime. It is observed that even at sub-THz frequencies the phonon lifetime agrees with the 1/$\omega^2$ power law known from Akhiezer's model for hyper sound attenuation. The observed shift of the synthesized spectrum to the higher $q$ is discussed in the framework of non-linear effects appearing due to the high amplitude of the synthesized phonons