The resulting diffraction patterns are recorded by a multi channel plate-detector and a cooled CCD camera. This means that approximately 0. S Wagner et al New J. Received 9 June Published 22 December From equation 1 , the temporal evolution of the film temperature T f can be derived as follows:.
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Panels c and d show the 2PC on a logarithmic timescale for clarity. Buy this article in print.
Yet the high-energetic electrons after excitation with a shorter wavelength can couple more efficiently to certain unoccupied adsorbate resonances e. Buy this article in print.
In addition, total reflection may occur for waves with incident angles larger than a critical angle max because the speed of sound in Bi is less than in Silicon. B Krenzer et al New J. The f s are the corresponding complete partition functions.
Zoom In Zoom Out Reset image size. Thus, on the much longer time scale of the film cooling the optical and acoustic phonons are in equilibrium. It supports the sharing of ideas and thoughts within the scientific community, fosters physics teaching and would also like to open a window to physics for all those with a healthy curiosity.
Kramers H A Physica 7 Crossref.
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As a model system, we studied ultrathin epitaxial Bi films on Silicon with an abrupt interface and a low defect density. Metals are often investigated as model substrates since the interaction of the adsorbed reaction partners with the substrate may cause a favourable energy landscape, e.
However, the experimentally measured values of the thermal boundary conductance were up to two orders of magnitude larger than expected from the two models.
Dotted lines indicate a linear relationship. We therefore conclude that the thermal properties of the thin Bi film are similar to bulk Bismuth.
This means that despite the seemingly qualitative agreement in the fluence dependence and two-pulse correlation, no quantitative agreement is found for a purely phonon-driven energy transfer. The key questions one would like to address with investigations on ultrashort-laser-induced surface chemistry are the following; what is the driving force, the mechanism of a certain reaction pathway?
The exponential intensity decay is described by the Debye—Waller effect with a surface Debye temperature of solid line. Finally, the energy transfer to nuclear degrees of freedom during the C—O association process on the Ru surface has been studied with time-of-flight measurements.
The solid lines in black represent single-exponential fits to the experimental data. Small deviations, especially at low coverages, most likely arise from difficulties in determining the correct ratio winvows the LT- and HT-TDS peaks in these overlapping TD features. However, within the framework of the AMM, phonon modes with an angle of incidence smaller than the angle of the critical cone are rapidly depopulated.
In equation 2it was assumed that the substrate temperature T s at the interface is constant during the experiment. Menzel D Surf. In conclusion, we studied the heat transport from a thin epitaxial Bi-film gd-eu001 a Si -substrate as a model system for ideal, abrupt hetero interfaces.
Thermal boundary conductance in heterostructures studied by ultrafast electron diffraction
A rather broad two-pulse correlation is observed, which is usually thought to be indicative of adiabatic, i. Repopulation of those depopulated states by the scattering of phonons creates a bottleneck which slows down the cooling of the hetero film.
Frischkorn C and Wolf M Chem. It has a wjndows membership of around 50 comprising physicists from all sectors, as well as those with an interest in physics. With the temperature transients G-dru001 el and T ph determined by the two-temperature model, the adsorbate temperature T ads can be derived, which characterizes the amount of energy transferred to the adsorbate mode usually considered as a one-dimensional 1D problem which is relevant to the reaction of interest.
However, one has to keep in mind winxows this vibrational damping of the nascent N 2 molecule relates to locations on the ground state PES beyond the transition state, whereas the nonadiabatic coupling in the excitation step of the fs-laser induced CO association corresponds to the ascending side of the desorption barrier.
B Crossref. One might expect that due to the location of the barrier along the vibrational coordinate, excitation of the interatomic distance d will facilitate the CO associative desorption more than it does excitation of widows distance coordinate z between the C—O and the Ru surface.