Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Host: A. Kölker
Monday, February 10, 2020, 11:00 am
All are invited to meet around 10:40 am for a chat with coffee & cookies.
PC Seminar Room, G 2.06, Faradayweg 4
Dr. Georg Gramse
Local Nanoscale Electrical Properties from DC to GHz Frequencies
From functional dopant profiling on semiconductors to electrical
properties of 2D materials and nano-electrochemistry
The outstanding electrical properties of nanostructured materials are the key for many new applications ranging from quantum computing over 2D-material-based (opto)electronics or organic electronics to electrochemical energy storage systems.
The SPM techniques Scanning Microwave Microscopy and broadband Electrostatic Force Microscopy, developed in our laboratory, allow us to probe these intrinsic electrical properties in a wide frequency range from DC to 30 GHz. Additionally, we can work in the time domain and probe the temporal evolution of an electrical property upon a sharp optical or electrical excitation.
The overall focus of our research is on elucidating the local and dynamic electrical properties of our system of investigation. Here, I will give an overview on the scientific results we obtained with our techniques in a wide range of applications starting from solid state physics to nano-electrochemistry. As examples I will talk about 5 topics which will cover the following fields:
1) Semiconductor physics where we pinpoint non-invasively the precise 3D location of buried atomic scale n-type and p-type dopant structures for quantum devices with 1 nm vertical and 10 nm lateral resolution and determine their electrical characteristics by SMM and bb-EFM.
2) 2D materials where we images calibrated capacitance and conductance of graphene, hBN and MoS2. The number of layers, sheet resistance and the quantum capacitance are then derived from the impedance images. By applying a DC tip bias, we utilize the tip a local gate and study the capacitance and conductance of graphene and MoS2 layers, probing mobility, charge carrier density, bandgap energy and doping. Trap and carrier dynamics is investigated by bb-EFM.
3) Organic solar cells (perovskites) where we investigate time resolved photoelectric charge relaxation by operating the EFM in pump-probe mode. We optically excite the solar cell sample with a laser pulse and can locally investigate the various mechanisms of charge carrier relaxation in a time frame from seconds to nano-seconds.
4) Local dipole dynamics in protein membranes and its interplay with surface water where we investigate the nanoscale dipole mobility of proteins in a wide frequency range from 3 kHz to 10 GHz. Measurements on bacteriorhodopsin reveal Debye relaxations with time constants being characteristic for the dipole moments of the bR retinal, the a-helices and the entire molecule, respectively.
5) High frequency nano-electrochemistry where we do first steps for investigation of fast electrochemical processes of electron transfer through metallo-organic SAMs and in future battery surfaces.