Self -assembly on strained metallic interfaces, and, Novel collective excitations on metal surfaces

<p>Recent interest in novel physical properties of reduced dimensional systems is spurred by the advance of investigation methods at the nanoscale. Understanding bottom-up techniques for the growth of nanomaterials with novel physical, chemical, and mechanical properties require specialized investigation tools.</p><p>I am presenting a novel design and performance of an ultra high vacuum scanning tunneling microscope (STM) that allows for large scale (8 mum x 8 mum), fast scanning (3 s for a 100 A x 100 A frame), and atomically resolved studies of reduced dimensional systems on metallic surfaces. The STM proved excellent performance, allowing for variable temperature (100 K to 700 K) and high resolution (&lt; 2 pm at 300 K) structural and dynamical studies on surfaces, as shown by the STM study of the general types of self-assembly processes on strained metallic interfaces.</p><p>With this new instrument, I performed a complete experimental investigation of the misfit dislocation network of one atom thick Ag films on Ru(0001) and of the restructuring induced by molecular sulfur adsorption when S filled Ag vacancy island are formed. The experiments suggest that the mechanism through which hundreds of Ag atoms are rear-ranging themselves following S deposition is driven by a process of threading dislocation pair annihilation and glide. The experimental observations are explained via an atomistic model, which is based on first-principles interaction parameters. I have found that the self-assembly process is driven by stress relaxation in the Ag film.</p><p>While the first part of my thesis is focused on the structural properties of low-dimensional metallic systems and instrumentation methods needed to access the nano-scale, in the secand part I investigated a novel low-energy electronic excitation of a metallic surface. I am presenting the first experimental measurement of an acoustic surface plasmon on metal surfaces. The experiment was performed using electron energy loss spectroscopy on Be(0001). This new mode is a collective excitation of the surface electrons. This discovery goes against the traditional wisdom that on metal surfaces only regular (optical) surface plasmons can exist. First-principles calculations show that this mode is caused by the coexistence of a partially occupied surface state band with the underlying bulk electrons.</p>

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Dissertation

Year

2007

Author dc:creator

• Diaconescu, Bogdan

Contributors dc:contributor

• Karsten Pohl

• Physics
• Condensed Matter

Repository record dc:identifier

https://scholars.unh.edu/dissertation/369

OAI identifier oai:identifier

oai:scholars.unh.edu:dissertation-1368