Heating and cooling at the nanoscale

Samenvatting

Semiconductor nanocrystals are promising building-blocks for next-generation devices. Their cheap and facile processing, synthetic variability, and size-dependent optoelectronic and catalytic properties will enable cheap and efficient solar cells, LEDs, broadcasting screens, photocatalytic and thermoelectric devices. Much of the recent progress is based on the great number of studies investigating charge transfer and charge transport properties in nanocrystals. In contrast, little is known about their thermal properties. This is surprising, considering that commercialization demands sophisticated nanoscale thermal management: the safe and efficient operation of solar cells or LEDs requires maximum heat dissipation from the nanocrystal, whereas in thermoelectric devices heat dissipation should be minimized. Furthermore, many loss-related electronic processes in nanocrystals (e.g. intraband relaxation and charge trapping) seem intrinsically coupled to thermal (i.e. nuclei) motion, calling for insights into vibrational phenomena. I propose to close these knowledge gaps via state-of-the-art ultrafast spectroscopy techniques which (1) monitor electronic and vibrational properties in real-time, (2) are non-invasive, circumventing the need for electrical contacts, (3) cover device-relevant time-scales, from ~100 femtoseconds to milliseconds. My approach is to exploit the dissimilar optical, electrical, and thermal properties of the nanocrystal core, ligand shell, and surrounding. First, I will selectively photo-excite the core; then, by tracing vibrational fingerprints, I will directly observe heat generation and annihilation inside the core, and subsequent interfacial heat transfer to ligands and surrounding; finally, observing the vibration move from one nanocrystal to its nearest neighbour will reveal the rate and mechanism of heat transport in a film (i.e. device-relevant) environment.
Insights from my research establishes guidelines for thermal management at the nanoscale and directly facilitates the search for materials and interfaces with engineered (device-specific) thermal functionality. In a broader context, my research fuels the development of ‘holistic’ theories for phenomena of coupled electronic-vibrational nature, such as nonradiative processes at nanocrystal surfaces.

Kenmerken

Projectnummer

722.017.011

Hoofdaanvrager

Dr. S.C. Boehme

Verbonden aan

Vrije Universiteit Amsterdam, Faculteit der Exacte Wetenschappen, Afdeling Natuurkunde & Sterrenkunde

Looptijd

01/11/2017 tot 31/10/2020