Near-edge X-ray absorption fine structure spectroscopy of diamondoid thiol monolayers on gold.
Diamondoids, hydrocarbon molecules with cubic-diamond-cage structures, have unique properties with potential value for nanotechnology. The availability and ability to selectively functionalize this special class of nanodiamond materials opens new possibilities for surface modification, for high-efficiency field emitters in molecular electronics, as seed crystals for diamond growth, or as robust mechanical coatings. The properties of self-assembled monolayers (SAMs) of diamondoids are thus of fundamental interest for a variety of emerging applications. This paper presents the effects of thiol substitution position and polymantane order on diamondoid SAMs on gold using near-edge X-ray absorption fine structure spectroscopy (NEXAFS) and X-ray photoelectron spectroscopy (XPS). A framework to determine both molecular tilt and twist through NEXAFS is presented and reveals highly ordered diamondoid SAMs, with the molecular orientation controlled by the thiol location. C 1s and S 2p binding energies are lower in adamantane thiol than alkane thiols on gold by 0.67 +/- 0.05 and 0.16 +/- 0.04 eV, respectively. These binding energies vary with diamondoid monolayer structure and thiol substitution position, consistent with different degrees of steric strain and electronic interaction with the substrate. This work demonstrates control over the assembly, in particular the orientational and electronic structure, providing a flexible design of surface properties with this exciting new class of diamond nanoparticles.
Willey
Trevor M
TM
Materials Science and Technology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA. willey1@llnl.gov
Fabbri
Jason D
JD
Lee
Jonathan R I
JR
Schreiner
Peter R
PR
Fokin
Andrey A
AA
Tkachenko
Boryslav A
BA
Fokina
Nataliya A
NA
Dahl
Jeremy E P
JE
Carlson
Robert M K
RM
Vance
Andrew L
AL
Yang
Wanli
W
Terminello
Louis J
LJ
van Buuren
Tony
T
Melosh
Nicolas A
NA