Molecular materials have been a subject of interest in fundamental research and applications for decades, and have been studied as bulk crystals, (thin) films and as individual molecules, due to... Show moreMolecular materials have been a subject of interest in fundamental research and applications for decades, and have been studied as bulk crystals, (thin) films and as individual molecules, due to the large variety in their properties. This dissertation explores pentacene crystals near the two-dimensional limit, i.e. in films of one to a few monolayers, primarily using an experimental technique called Low Energy Electron Microscopy (LEEM). We utilize the interaction of low-energy electrons with the molecular layers to learn about the properties of the layers, and also employ low-energy electrons as an external stimulus to create controlled changes in the properties of the sample. We study the real-time dynamics of growth of pentacene layers on various substrates. We study beam irradiation damage to molecular layers due to exposure to low-energy electrons, with implications for technological processes such as electron-beam lithography. We study photoemission and secondary electron emission from the molecular layers and highlight the critical role of unoccupied electronic band structure above the vacuum level in these processes. Finally, we present the design of, as well as the first scientific measurements in, a cryogenic sample chamber for LEEM that enables novel experiments addressing questions in surface science and condensed matter physics. Show less
