Nanoscale heat transport from Ge hut, dome, and relaxed clusters on Si(001) measured by ultrafast electron diffraction

Abstract

The thermal transport properties of crystalline nanostructures on Si were studied by ultra-fast surface sensitive time-resolved electron diffraction. Self-organized growth of epitaxial Ge hut, dome, and relaxed clusters was achieved by in-situ deposition of 8 monolayers of Ge on Si(001) at 550 °C under UHV conditions. The thermal response of the three different cluster types subsequent to impulsive heating by fs laser pulses was determined through the Debye-Waller effect. Time resolved spot profile analysis and life-time mapping was employed to distinguish between the thermal response of the different cluster types. While dome clusters are cooling with a time constant of τ = 150 ps, which agrees well with numerical simulations, the smaller hut clusters with a height of 2.3 nm exhibit a cooling time constant of τ = 50 ps, which is a factor of 1.4 slower than expected.

Ultrafast transmission electron microscopy using a laser-driven field emitter: Femtosecond resolution with a high coherence electron beam

“…Ultrafast electron [8][9][10][11][12][13] and x-ray [14][15][16][17] diffraction are wellestablished techniques to track structural relaxation with femtosecond temporal resolution, widely applied to homogeneous and thin film systems. The observation of spatiotemporal relaxation processes in heterogeneous systems [18][19][20][21][22][23], however, such as excitation and energy transfer across functional interfaces, is particularly challenging, requiring simultaneous nanoscale spatial and ultrafast temporal resolutions. To this end, various experimental approaches are pursued very actively at present, including time-resolved variants of scanning tunneling microscopy (STM) [24][25][26] and scanning near-field optical microscopy (SNOM) [27][28][29].…”

Spot profile analysis and lifetime mapping in ultrafast electron diffraction: Lattice excitation of self-organized Ge nanostructures on Si(001)

“…For a more quantitative analysis, temperature dependent numerical simulations of the one dimensional heat diffusion equation were performed 22,50 . The thermal boundary conductance σ tbc was calculated in the framework of the diffuse mismatch model (DMM), 51 including anharmonic inelastic phonon interactions 52 and a real phonon dispersion relation in the [001] crystallographic direction.…”

“…In this paper, we will employ nanoscale heat transport from Germanium (Ge) nanoclusters into a Silicon (Si) substrate 22 to demonstrate the capabilities of time-resolved electron diffraction to observe different transient processes in parallel from the same diffraction experiment. The standard techniques for the determination of the transient temperature evolution of thin films are ultrafast optical methods like time-domain thermoreflectance (TDTR) 23,24 .…”

Precision Plasmonics with Monomers and Dimers of Spherical Gold Nanoparticles: Nonequilibrium Dynamics at the Time and Space Limits

“…In particular, on the nanoscale, size and shape as well as surface and interface effects can play an important role. , The majority of experimental work addressing electron–phonon coupling in NPs makes use of time-resolved optical techniques, for example, femtosecond transient absorption (see the review by Hartland et al and references therein). More recently, ultrafast X-ray or electron diffraction/scattering has also been applied to directly monitor various aspects of the structural response of nanostructured materials upon optical excitation. − …”