Regensburg 2013 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 24: Graphene: Electronic properties and transport (O, jointly with HL, TT)

HL 24.4: Talk

Monday, March 11, 2013, 16:45–17:00, H17

Probing Hot Electron Distributions in Graphene on Ni(111) with High Harmonic Radiation — •Carsten Winter¹, Thorben Haarlammert¹, Luca Bignardi², Petra Rudolf², and Helmut Zacharias¹ — ¹Physikalisches Institut, Westfälische Wilhelms-Universität, Münster — ²Zernike Institute for Advanced Materials, University of Groningen

Theoretical calculations and experimental observations of hot electron distributions in graphene show an initial ultrafast carrier relaxation accompanied by a population of optical phonons, which decay on a picosecond time scale. In this talk we present an experimental set-up suited to measure the lifetime of excited electrons and their relaxation dynamics via time-resolved 2PPE. Through frequency conversion by High Harmonic Generation coherent radiation at 39 eV photon energy is generated and subsequently used as the probe pulse in two-photon photoemssion.

A graphene sheet was produced by decomposition of ethylene on a Ni(111) substrate. Hot electron distributions were generated in graphene on Ni(111) by applying 800nm pulses. The energy dependent lifetimes of these distributions have been measured. The lifetimes have been determined to 20-50 fs in the lower energy parts of the distribution (E-E_F < 1eV) and show a strong Ni-like behavior. In the upper energy parts lifetimes of 10-20 fs have been measured and a graphite-like behavior dominates.