Paper AS-TuM4
Photovoltage, Photoconductivity and Charging Probed by Dynamical XPS Measurements

Tuesday, October 19, 2010, 9:00 am, Room Cochiti

We have developed a technique for recording the shifts in the positions of the XPS peaks in response to different forms of electrical stimuli for probing dynamics of charging/discharging processes of thin dielectric films, which we have named as Dynamic XPS. Modulation of the electrical signals in the forms of square, sinusoidal and triangular waves at different frequencies enables us to extract some dielectric properties of surface structures, such as effective resistance, and capacitance values in a chemically resolved fashion. We have also introduced photo-illumination as an additional form of the stimuli and have been using this technique for investigating the combined optical + electrical responses of semiconductive (Si and GaAs) as well as photoactive (CdS and TiO₂) materials towards better understanding of the different photo-processes, like photoconductivity and/or photovoltage development, etc. We use our dynamic measurements to help in distinguishing various fundamental processes, by using the frequency dependence as an additional tool. This makes XPS a more powerful technique for characterizing today’s demanded nano or optoelectronic devices. The methodology will be introduced, and several examples will be presented.