avhandlingar

Disputation i fysik: Alexander Gustafsson

Titel: Theoretical modeling of scanning tunneling microscopy
Ämne: Fysik
Fakultet: Fakulteten för teknik
Datum: Onsdagen den 20 december 2017 kl 10.15
Plats: Sal Newton, hus C, Växjö
Opponent: Staff Senior Researcher Jorge Iribas Cerdá, Spanish National Research Council, Spanien
Betygsnämnd: Professor Mats Persson, University of Liverpool, England
Professor Igor Zozoulenko, Linköpings universitet
Docent Rainer Timm, Lunds universitet
Ordförande: Professor Staffan Carius, Institutionen för fysik och elektroteknik, Linnéuniversitetet
Handledare: Docent Magnus Paulsson, Institutionen för fysik och elektroteknik, Linnéuniversitetet
Examinator: Professor Carlo Canali, Institutionen för fysik och elektroteknik, Linnéuniversitetet
Spikning: Torsdagen den 23 november 2017 kl 13.00 på Universitetsbiblioteket i Växjö och fredagen den 24 november 2017 kl 13.00 på Universitetsbiblioteket i Kalmar

Abstract

The main body of this thesis describes how to calculate scanning tunneling microscopy (STM) images from first-principles methods. The theory is based on localized orbital density functional theory (DFT), whose limitations for large-vacuum STM models are resolved by propagating localized-basis wave functions close to the surface into the vacuum region in real space. A finite difference approximation is used to define the vacuum Hamiltonian, from which accurate vacuum wave functions are calculated using equations based on standard single-particle Green's function techniques, and ultimately used to compute the conductance. By averaging over the lateral reciprocal space, the theory is compared to a series of high-quality experiments in the low-bias limit, concerning copper surfaces with adsorbed carbon monoxide (CO) species and adsorbate atoms, scanned by pure and CO-functionalized copper tips. The theory compares well to the experiments, and allows for further insights into the elastic tunneling regime.

A second significant project in this thesis concerns first-principles calculations of a simple chemical reaction of a hydroxyl (oxygen-deuterium) monomer adsorbed on a copper surface. The reaction mechanism is provided by tunneling electrons that, via a finite electron-vibration coupling, trigger the deuterium atom to flip between two nearly identical configurational states along a frustrated rotational motion. The theory suggests that the reaction primarily occurs via nuclear tunneling for the deuterium atom through the estimated reaction barrier, and that over-barrier ladder climbing processes are unlikely.

 

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