The modulation of electrical properties in semiconductor devices can be achieved by molecular surface functionalization. This enables to combine diverse organic molecular synthesis with the benefits of current microelectronic technology to create hybrid devices. For example, self-assembled monolayers are widely used as linkers between semiconductor surfaces and biological molecules.

   A molecular-gated transistor is a device in which a molecular layer is directly adsorbed on the top dielectric of a transistor and affects its current. Adsorption of a polar molecular layer can create a surface dipole, which will change the surface electron affinity, and thus its work function, depending on the dipole orientation and magnitude. However, It should be noted that an ideal polar layer should not, induce any field in the transistor conductive channel, since the electric-field is confined to the layer. Nevertheless, several observations of a correlation between the adsorbed layer net-dipole and the induced field-effect were recently reported.

   In order to determine whether the net-dipole of polar monolayers induces a field-effect in molecular-gated transistors we combine nanoscale potential measurements, using Kelvin probe force microscopy (KPFM), of the transistor's channel with macroscopic current-voltage measurements . Layers having alternating net-dipole direction were self-assembled on the top dielectric layer of the transistors. Non-zero field-effect was observed only with an amine-terminated monolayer and is attributed to the protonation of the amine groups. No correlation between the field-effect and the net-dipole of the molecular layers was found; this effect is discussed and explained.

O. Shaya et al., Appl. Phys. Lett., 97, 053501 (2010).