Radiation damage to alkyl chain monolayers on semiconductor substrates investigated by electron spectroscopy.
Monolayers of alkyl chains, attached through direct Si-C bonds to Si(111), via phosphonates to GaAs(100) surfaces, or deposited as alkyl-silane monolayers on SiO2, are investigated by ultraviolet and inverse photoemission spectroscopy and X-ray absorption spectroscopy. Exposure to ultraviolet radiation from a He discharge lamp, or to a beam of energetic electrons, leads to significant damage, presumably associated with radiation- or electron-induced H-abstraction leading to carbon-carbon double-bond formation in the alkyl monolayer. The damage results in an overall distortion of the valence spectrum, in the appearance of (occupied) states above the highest occupied molecular orbital of the alkyl molecule, and in a characteristic (unoccupied state) pi resonance at the edge of the carbon absorption peak. These distortions present a serious challenge for the interpretation of the electronic structure of the monolayer system. We show that extrapolation to zero damage at short exposure times eliminates extrinsic features and allows a meaningful extraction of the density of state of the pristine monolayer from spectroscopy measurements.
Amy
Fabrice
F
Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Chan
Calvin K
CK
Zhao
Wei
W
Hyung
Jaehyung
J
Ono
Masaki
M
Sueyoshi
Tomoki
T
Kera
Satoshi
S
Nesher
Guy
G
Salomon
Adi
A
Segev
Lior
L
Seitz
Oliver
O
Shpaisman
Hagay
H
Schöll
Achim
A
Haeming
Marc
M
Böcking
Till
T
Cahen
David
D
Kronik
Leeor
L
Ueno
Nobuo
N
Umbach
Eberhard
E
Kahn
Antoine
A