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Special note, exceptional schedule
Title: Photovoltaics at the molecular scale with an atomic force microscope
Abstract:
Kelvin Probe Force Microscopy (KPFM) is a variant of AFM that yields access to the electrostatic landscape on the surface of a sample at the nanoscale. The applications of KPFM are extremely broad. It is now used by physicists, chemists and biologists to characterise the nanoscale electronic/electrostatic properties of an ever-expanding range of materials, interfaces and devices. Since the early 1990s, a variety of approaches have been implemented to improve the performance of KPFM in terms of spatial, potentiometric and temporal resolution. Several research teams continue to work in this direction and KPFM is still an evolving technique in many aspects. In particular, the development of KPFM-based approaches specifically designed to study photogeneration mechanisms and charge dynamics at the nanoscale in photovoltaic and optoelectronic materials is an active research area.
In this communication, after introducing some basic concepts of ultra-high vacuum non-contact AFM and Kelvin probe microscopy, I will focus on the frequency mixing effects that are at the heart of modern heterodyne KPFM approaches. In particular, I will show how these effects can be exploited to access the dynamics of the surface photovoltage through frequency domain measurements. The power of this intermodulation approach will be illustrated by results obtained on nanosegregated blends of donor-acceptor pi-conjugated moelcules and polymers. Finally, I will show how these results encourage us to implement a cryogenic AFM based on interferometric detection for SPV imaging at the molecular scale.
