Structural and Chemical Characterizations of Thin Films on Surfaces

The characterization of thin films hinges critically upon the exploration of nanostructures and chemistry at interfaces governed by intricate interactions and chemical environments due to their reduced dimensions. This work presents a practice utilizing various techniques to conduct structural and chemical characterization of thin films. Scanning tunneling microscopy (STM) offers atomic-scale imaging to study the topography of localized structures, such as heterogeneity of the substrate, defects, and adsorption of molecules. While STM is a potent tool in its own right, chemical information that cannot be directly obtained from STM can be accessed through complementary techniques such as X-ray photoelectron spectroscopy (XPS) or Auger electron spectroscopy (AES). On the other hand, Raman spectroscopy delves into the highly sensitive vibrational fingerprints of a broad range of materials, including two-dimensional (2D) materials synthesized via top-down approaches. In the first project, the self-assembly of an antiaromatic molecule on metal surfaces is investigated. STM and density functional theory (DFT) calculations prove different structures and self-assembled islands of N,N-diphenylquinodimethyl thioamide (Ph2QDM) formed on different substrates based on distinct molecule-substrate interactions. Importantly, desulfurization is observed on Ag(100) surfaces after depositing Ph2QDM, indicating silver-assisted carbon-sulfur double bond activation. The second project entails the design of an ultra-high vacuum (UHV) STM system, facilitating a comprehensive investigation of the nanostructure topography and chemical environment through the integration of multiple techniques. Finally, the third project involves the design of a micro-Raman system. Several experiments have been conducted with this system, showing the capabilities to investigate the chemical information of various samples. The cooperative application of various techniques allows for a comprehensive understanding of the structural and chemical information of thin films on surfaces can be obtained.