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Transient Grating Studies of Femtosecond Processes in Ultra‐Thin Layers of PTCDA
Author(s) -
Karki Khadga,
Helms Gesa,
Namboodiri Mahesh,
Wagner Veit,
Fritz Jürgen,
Materny Arnulf
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100854
Subject(s) - femtosecond , materials science , exciton , thin film , graphene , grating , ultrashort pulse , optoelectronics , quantum dot , semiconductor , nanotechnology , chemical physics , laser , optics , chemistry , condensed matter physics , physics
Elementary processes like energy transfer, charge transport, and exciton diffusion in thin films occur on time scales of femtoseconds. Time‐resolved photo‐electron spectroscopy,1, 2 a technique limited to ultra‐high vacuum environment and the proper choice of a substrate, has been used to study ultrafast processes in sub‐nanometer thin films so far. Herein we show that a transient (population) grating3 created by the interference of laser pulses can be used to study ultrafast processes in such films under ambient conditions. Our investigations of exciton dynamics in 1.4±0.2 nm and 0.4±0.2 nm thin films, formed by nanocrystals of 3,4,9,10‐Perylenetetracarboxylic dianhydride (PTCDA) on glass and mica, show that the dynamics differ with the crystal size, possibly due to the confinement induced changes in the electronic structure. The technique is sensitive enough to investigate the dynamics in systems, where only 20 % of the surface is covered by nano‐crystals. We expect such an optical technique that is sensitive enough to study dynamics in few to sub‐nanometer thin layers under ambient conditions to become important in investigating ultrafast dynamics on surfaces, interfaces, functionalized materials, organic semiconductors, and quantum phenomena in ordered structures of reduced dimensions, such as quantum dots and graphene sheets.