self-assembled thin films of thiocyanate and selenocyanate bithiophenes
abstract
presented herein is the organic synthesis and thin film (tf) assembly of six alkyl-substituted
thiocyante and selenocyante bithiophene molecules: ncse-t2-hx, ncs-t2-hx, ncs-hx-t2-hx, ncse-
hx-t2-hx, ncs-hx-t2-hx-scn and ncse-hx-t2-hx-secn. tfs assembled from these thio and
selenocyanates were characterized by six different techniques: electrochemical capacitance (cp)
measurements, scanning electron microscopy (sem), energy dispersive x-ray spectroscopy (edx),
atomic force microscopy (afm), x-ray photoelectron spectroscopy (xps) and time-of-flight secondary
ion mass spectrometry (tof-sims). cp experiments were used to confirm the development of tfs on an
amorphous au surface using ethanol or hexanes as a reaction solvent. a sputtered au surface was
observed by sem/edx to be an inappropriate surface for tf assembly. tfs assembled onto epitaxially
grown au were characterized by multiple techniques. large crystallites were observed on tfs assembled
from ncse-t2-hx and ncse-hx-t2-hx-secn. chemical maps of these crystallites were obtained
through sem/edx. the presence of a covalent au-s or au-se bond on the surface was confirmed by
xps signals from the s 2p3/2 and se 3d5/2/3d3/2 regions respectively. xps signals of ~ 399 ev in the n 1s
region were observed in all assemblies characterized by this technique, indicating the presence of residual
gold-bound cyanide (au(cn)ads) on the surface. tof-sims chemical intensity maps confirmed the
presence of expected tf fragments on the surface of all tfs characterized by this technique. tof-sims
results suggested that tfs connected to the au surface through an aromatically bound s or se atom
produced tfs with higher surface coverage.