Negative-electron-affinity diamondoid monolayers as high-brilliance source for ultrashort electron pulses

Diamondoids are nanometer-sized, hydrogen terminated diamond-like molecules consisting of fused adamantane units. The thiolated diamondoid [121] tetramantane-6-thiol shows negative electron affinity behavior, i.e. population of unoccupied states directly leads to spontaneous electron emission. We present time-resolved photoemission data from self-assembled monolayers of [121] tetramantane-6-thiol in order to shed light on the emission process: A photon energy threshold for electron emission of 5.6-5.8 eV was observed, and the electron affinity was estimated to be -0.21 to -0.57 eV for Ag and Au substrates, respectively. Electrons are emitted after excitation in the metal substrate through the molecular orbitals within a few femtoseconds. (C) 2010 Elsevier B.V. All rights reserved.