Abstract
Atomic Force Microscopy (AFM) is a technique that allows atomic scale spatial resolution on essentially any material, including insulators and metals, in essentially any environment ranging from ultra high vacuum to liquids, at temperatures of several 100K down to mK. Many properties, such as electrical surface potential, mechanical stress, adhesion or friction can be measured at the same length scale, often as a function of external parameters such as light or electrochemical potential. Completing this ‘nanolab’ is the capability of AFM to manipulate objects. In this presentation I will explore several examples from research in my group to illustrate these capabilities. I will concentrate on three topics:
1. A combined STM/AFM-field ion microscopy (FIM) UHV system allows the creation and investigation of atomically defined contacts. Both contact electrodes can be characterized on an atomic scale, which in combination with state-of-the art transport and MD theory allows deep insights into the conductance of nanoscale metallic contacts.
2. We have used Ultra High Vacuum AFM integrated in a surface science system to understand and control the nucleation and growth of molecules on insulating surfaces. We can generate different molecular packing structures by suitable templating of the insulating substrates. This then allows us to correlate optical properties with structure using Kelvin Probe Force Microscopy, including molecular systems relevant to organic photovoltaics (OPV) by shining light on the sample. Preliminary results indicate that we can observe exciton formation in model OPV systems.
3. AFM can be used to measure the ground state and excited state energy levels of quantum dots, and possibly molecules, by understanding dissipation of the AFM cantilever. AFM techniques can also be used to measure variations in the surface potential on semiconductors and oxide surfaces as well as conductance variations in a graphene Hall bar device. In ‘normal’ oxides on Si as well as InP we map large variation of the surface potential (~250 mV) on length scales of 50nm. Such large potential variations are expected to strongly affect the operation of nanoscale electronic systems or possibly even adsorption of molecular species.
Coffee and tea will be served 20 minutes prior to the seminar.