Spectroscopic techniques such as Raman and IR vibrational spectroscopy can be applied to monitor molecular species within the liquid interface or bound directly to the solid surface. Spectral signatures that depend on the external electric field can be monitored and analyzed to infer the electric field properties of the interface. 44-47 X-ray-based techniques, such as X-ray photoelectron spectroscopy can be applied similarly to study the interfacial electrochemical environment. In this case, insight derives from the fact that the electronic energies are sensitive to the value of their local atomic environment or electrostatic potential. These techniques provide specific information about adsorption sites and adsorbate order, adsorbate configurational geometry, and surface band structures. Sum frequency and second-harmonic generation spectroscopy are capable of isolating interfacial signal and have been used to identify changes in spectral properties of interfacial molecules. Devices utilizing a surface force apparatus can be used to provide information about molecular interfacial structure. This type of experiment have provided clear evidence of molecular layering at interfaces, for example as manifest in long-range charge oscillations emerging from solid ionic-liquid interfaces. Simiarly, atomic force microscopy can be used to report on the electrostatic profiles at pristine solid-liquid interfaces. This class of techniques provides concrete evidence of the manifestation of molecular excluded volume effects at interfaces, which are neglected in most standard theories of interfacial electrostatic profiles.