Dielectric properties of organic monolayers directly bonded on silicon probed by current sensing atomic force microscope

The dielectric properties of alkyl monolayers with various chain lengths $[{\mathrm{CH}}_3({\mathrm{CH}}_2{)}_{\text{n−1}}$ - $\text{(n=12,}$ 14, 16, and 18)] covalently bonded to a hydrogen terminated $n$ -type silicon (111) surface in a nanoscale region were evaluated using current sensing atomic force microscopy (AFM). A reliable electrical contact between the alkyl monolayers and the metal-coated AFM tip was achieved under slight stress. At a force less than 2 nN, current sharply increased as the bias was scanned over a critical value, showing that breakdown took place. The breakdown voltage linearly depended on the chain length of the alkyl monolayers and the dielectric strength of 2.0 GV/m was derived from the slope of this relation.