S. Bastide et al., CONTROLLING THE WORK FUNCTION OF GAAS BY CHEMISORPTION OF BENZOIC-ACID DERIVATIVES, JOURNAL OF PHYSICAL CHEMISTRY B, 101(14), 1997, pp. 2678-2684
Control of the work function of GaAs single crystals, under ambient co
nditions, was achieved by chemisorption of a series of benzoic acid de
rivatives with varying dipole moments. Quantitative Fourier transform
infrared spectroscopy shows that the benzoic acid derivatives bind as
carboxylates, via coordination to oxidized Ga or As atoms, with a surf
ace coverage of about one layer and a binding constant of 2.1 10(4) M(
-1) for benzoic acid. Contact potential difference measurements reveal
that molecules affect the work function by changing the electron affi
nity while band bending is not affected significantly. The direction o
f the electron affinity changes depends on the direction of the dipole
moments, and the extent of the change increases linearly with the dip
ole's magnitude. Investigation of the surface composition by X-ray pho
toelectron spectroscopy shows that the etched surface, onto which the
molecules adsorb, is covered by an oxide layer. This may prevent the m
olecules from affecting band bending.