Brain Function: Novel Technologies Driving Novel Understanding - Bioinspired Approaches for Human-Centric Technologies - page 323

Fig. 10.16 Gold nanoantenna with tip radius below 17 nm and Raman spectroscopy of a
benzenethiol (BTH) monolayer chemisorbed on the gold nanoantenna ( red ) compared with a
spectrum of bulk BTH
(EBID; see below), a bottom-up nanofabrication technique (Fig. 10.16 ). The cou-
pling between incident light and SPPs on the nanoantenna was achieved by means
of a photonic crystal produced on the substrate on which the nanoantenna was
fabricated. The authors performed far-field Raman spectroscopy of a benzenethiol
(BTH) monolayer chemisorbed on the gold nanoantenna, acquiring signals from an
estimate of about 200 molecules deposited on the nanoantenna tip. The spectrum of
these few BTH molecules presents the same characteristic peaks and shift positions
as spectra acquired with bulk BTH.
The previous paragraph introduced the use of EBID, which is a specific variant
of chemical vapor deposition (CVD), in which thin and thick layers are grown using
molecular precursors from the gas phase. In CVD the molecular precursors are
decomposed in proximity of the substrate by providing either thermal energy
(thermal CVD) or radiofrequency plasma energy (plasma-enhanced CVD). Once
decomposed, the free radicals may combine with other different radicals to form
new nonvolatile molecules that deposit on the substrate. Alternatively, in the
presence of only one type of molecular precursor, some atoms from the
decomposed molecules deposit directly on the substrate and bind to the preexisting
structure. By carefully adjusting the gas mixture, energy, and pressure/temperature
conditions, several materials can be grown by CVD techniques, including crystal-
line, polycrystalline, and amorphous silicon; silicon compounds (SiO 2 and Si 3 N 4 );
diamond; gallium arsenide; and gallium nitride. Variants of CVD, such as EBID
and ion beam-induced deposition (IBID), make use of electron or ion beams for
locally decomposing the gas molecular precursors on the substrate spot where they
are illuminating; by decomposing the precursors, constituent atoms are deposited
on the substrate surface. An interesting property of EBID and IBID techniques is
that the deposition process takes place in the vertical direction as long as the beam is
illuminating the spot. This combined with the fact that electron and ion beam can be