Paper NS-ThA8
Combined Scanning Tunnelling Microscopy & Stress Measurements to Elucidate the Origins of Surface Forces

Thursday, October 18, 2007, 4:20 pm, Room 616

The concept of surface stress has been discussed extensively in terms of its role in controlling single crystal reconstruction and the growth morphology of thin films. In contrast, much less is known about the role of surface stress in surface chemical reactions, where differences in atomic size, electronegativity, and the incorporation of surface vacancies are likely to be of great importance, particularly in the case of nanoscale systems where surface effects are expected to dominate. In order to address the role of stress in surface chemical reactivity, we have developed a novel measurement system capable of investigating the underlying origins of surface stress in the context of atomic surface structure.¹ This system combines for the first time two distinct measurement capabilities: (i) measurement of surface stress based on the displacement of a large (50x10x0.28mm) silicon cantilever sample; and (ii) atomic resolution observation of the surface structure of the same cantilever sample. The former measurement incorporates a capacitive detection method capable of detecting energy changes with meV/atom resolution, while the latter measurement incorporates a scanning tunnelling microscope (STM) capable of observing structural changes occurring on the surface of the cantilever sample. Although non-trivial, the development of this combined measurement system was accomplished through careful electrical and mechanical design, accompanied by the incorporation of a novel sample heating method permitting localized heating of the cantilever sample. The system is also equipped with a device capable of applying external mechanical stress to the cantilever sample, thus enabling investigation of the effects of artificially induced stress on surface-based chemical reactions. The combined application of these two measurement capabilities yields detailed information regarding the atomic-scale structure, dynamics and interactions of the surface under investigation, which will ultimately be used to elucidate the origins of surface forces, and contribute to a deeper understanding of atomic-scale phenomena. Here, we present an introduction to the measurement system, a discussion on the challenges encountered during the development process, followed by a demonstration of the capabilities of the system itself.

¹ T. Narushima, N. T. Kinahan, J. J. Boland, Rev. Sci. Instrum. 78, 053903 (2007).