Experimental results are presented which shed light on the properties of th
in discontinuous metal films as chemical sensing elements. They demonstrate
further some interesting differences between hydrophilic and hydrophobic s
ensing structures. Two different methods are used to study the migration of
charges out onto the oxide surface outside the metal gate of metal-oxide-s
emiconductor capacitors after treatment of the surface with hydrochloric ac
id. The charge migration is observed tither as a time dependent increase of
the inversion capacitance or as a possibility to generate a photocapacitiv
e current by a chopped light beam hitting the oxide surface at a distance f
rom the contact. It is concluded that the charge migration occurs only if t
he surface was hydrophilic before the HCl-treatment. For a hydrophobic surf
ace neither the inversion capacitance nor the photocapacitive current chang
ed upon ion-treatment, An explanation for an observed increase of the capac
itance level of hydrophilic structures immnersed in electrolytes is also gi
ven. (C) 1999 Elsevier Science S.A. All rights reserved.