Studies of physico-chemical properties of self-assembled monolayers and carbon nanotube devices by scanning probe microscopy

Abstract

Current trend of miniaturization requires new methodologies to be developed and put to use. One, and perhaps the most important of them is scanning probe microscopy (SPM), which has been evolving in tandem with nanoscience and nanotechnology. In this work, we use various SPM methods to investigate structures and characteristics of low-dimensional nanostructures: a molecular self-assembled monolayer (SAM) and carbon nanotube field-effect transistor (CNFET). Specifically, structures of pyrrolyl-terminated alkanethiol SAMs on gold are studied by STM, and gate hysteresis and its local inhomogeneity in CNFET are studied by scanning surface potential microscopy (SSPM) and scanning gate microscopy (SGM). Chapter 1 is devoted to introduction of backgrounds and current knowledge of relevant research fields that are needed to understand and appreciate the results given in Chapters 3. Details on experiments such as sample preparation methods and analysis methods are given in Chapter 2. Experimental results and discussion for each topic are given in Chapter 3, and their conclusions are given in Chapter 4. In Section 3.1, molecular ordering of pyrrolyl-terminated alkanethiol $(PyC_nSH, n = 11 or 12)$ SAMs on Au(111) substrates is investigated by STM and other spectroscopic methods. The SAMs, which are formed in a disordered state at room temperature, can be ordered either globally by thermal annealing at $70^\circ C$ or locally via stimulation with repetitive STM scans. The ordered phase is characterized by small domains of molecular rows formed along $<11\bar2> $ directional set with an inter-row corrugation period close to 1.44 nm, in which defects are abundant. Based on the experimental results, the molecular arrangement in the ordered $PyC_nSH$ SAM is proposed to be a (5×√3)rect structure with a molecular deficiency ≥ 10%. While mechanical interactions between molecules and scanning probe tips has been pointed out as the major cause of scan-induced phase transiti...