A Knudsen cell for controlled deposition of L-cysteine and L-methionine on Au(111)

Abstract

This thesis details the development of expertise and tools required for the study of amino acids deposited on Au(111), with a primary focus on the design and testing of a Knudsen cell for controlled deposition of L-cysteine and L-methionine. An ultra-high vacuum preparation chamber designed by Dr. Katie Mitchell and built by Torrovap Industries Inc. was installed. This chamber is connected to the existing scanning tunneling microscopy chamber via a gate valve, and both chambers can operate independently. Various instruments such as a mass spectrometer, quartz crystal microbalance, ion source, and sample manipulator were installed on the preparation chamber. Scanning tunneling microscopy was performed on both homemade and commercial Au(111) thin films. High resolution images of "herringbone" reconstruction and individual atoms were obtained on the commercial thin films, and optimal tunneling conditions were determined. A Knudsen cell was designed to be mounted on the preparation chamber. The Knudsen cell operates over the temperature range 300-400K, with temperatures reproducible to ±0.5K, and stable to ±0.1K over a five minute period. Reproducible deposition rates of less than 0.2Ǻ/s were obtained for both L-cysteine and L-methionine. Electron impact mass spectrometry and heat of sublimation measurements were performed to characterize the effusion of L-cysteine and L-methionine from the Knudsen cell. The mass spectrometry results suggest that L-cysteine was decomposing at 403K while L-methionine was stable during effusion. Heats of sublimation of 168.3±33.2kJ/mol and 156.5±10.1kJ/mol were obtained for L-cysteine and L-methionine respectively.