Chemically resolved electrical measurements in organic self-assembled molecular layers

The spectroscopy of charged particles, e.g. X-ray photoelectron spectroscopy (XPS), proposes unique capabilities for electrical studies of nanometric heterostructures. By turning the problem of surface charging into a consistent and general method for chemically resolved electrical measurements (CREM), selected surface and sub-surface regions can be probed in a non-contact manner, with useful advantages over standard electrical tools. When applied to organic systems, CREM can read electrical information out of atomic sites within molecular assemblies, and hence, map the electrostatic potential variations under external stimuli, approaching atomic resolution. This paper reviews CREM studies of self-assembled monolayers (SAMs), with an emphasis on questions regarding the surface charge distribution. Surprising observations in work function changes under self-assembly of dipolar molecules are presented, as well as the direct detection of sub-molecular polarization effects, and photo-induced charge redistribution across SAMs that are situated between semiconducting media. The review concludes by suggesting future applications of CREM and further challenges that may arise.