Fabrication And Characterization Of Al/Ag Films And Their Effects On Molecular Self-assembly Of C₆₀

Nanotechnology, information technology and bio-technology are known as the threethree leading technologies in the twenty-first century. Low dimensional nanoscalestructures from molecular self-assembly (MSA) into on metallic surface have attracted lotsof research interests due to their excellent physical and chemical properties. C60, due to itsunique cage-like structure with unparalleled stability as well as variable adsorptionorientation and position on metal surfaces, is a prototype molecule to study MAS. Inaddition, black phosphorus as a novel two-dimensional semiconductor material isacknowledged as a promising alternative to graphene for next-generation nano-electronicdevices. The main content of this thesis is:1. Ag thin films were fabricated on mica substrate by molecular beam epitaxy (MBE).An atomically flat surface of Ag thin film with terrace width greater than100nm wasobtained by Ar+sputtering and annealing at500°C. Auger electron spectroscopy (AES)measurement showed no obvious impurity. Low energy electron diffraction (LEED)measurement showed the film was a single crystal with Ag (111) as the surface.2. Al thin films were grown with MBE on Ag single crystal film as substrates holdingat room temperature,250°C and350°C, respectively. Distinct surface structures wererevealed for samples prepared at different substrate temperatures. Aluminum thin film ofnanocrystals was achieved on room temperature Ag substrate. These Al nanocrystalsshowed a (111) surface, which was revealed by LEED measurement. At the250°C and350°C, Al/Ag alloying happened leading to herringbone and polygon structures,respectively. The alloying was confirmed by AES measurement. The structures of thefilms prepared at two lower temperatures (room temperature and250°C) altered while theone prepared at350°C kept stable after annealing treatment.3. C60was deposited on the herringbone structure and polygon structure of Al/Agalloys. It was found that the C60deposited on different structures exhibited differentorientation and MSA structures. C60on herringbone structure of Al tended to attach on the edge of the terrace. High resolution STM images indicated that C60molecules appear“four-leaf” shape. Polygon structure of Al had a strong interaction with C60and themolecules self-assembled into isolated islands on the terraces. High resolution STMimages showed C60molecules exhibited both “four-leaf” and “%”shapes.4. A tape-based mechanical exfoliation method was used to cleave thin blackphosphorus flakes from bulk crystal onto Ag(111) surface. It was found that the surfaceatomic structure of the two-dimensional black phosphorus was identical to that in bulkblack phosphorus. It was also revealed that the contrast of the atoms in two differentpositions of the zigzag chain was unequal in the STM images taken at different biasvoltage, suggesting different electronic properties of these two classes of P atoms in blackphosphorus. Also, P atoms reconstructed obviously where defects occurred due to missingatoms.