Chapter 1 Scanning Tunneling Microscopy for Self-Assembled Monolayers

Abstract

Publisher Summary Among all the different types of surface imaging techniques, the scanning tunneling microscope (STM) presents the best spatial resolution and versatility. In fact, atoms and molecules can be literally touched one by one, thus opening new ways for investigating them. The first and most amazing ability of the STM is to provide three-dimensional images of individual molecules and their environment at the atomic level. However, many other experiments can be conducted with an STM—for example, manipulating particles, performing local spectroscopy, and even chemically modifying the sample. The basic principle of scanning tunneling microscopy (STM) is based on the tunneling current between a metallic tip, which is sharpened to a single atom point, and a conducting material. A small bias voltage (mV to V) is applied between an atomically sharp tip and the sample. Although the initial applications of STM have been focused on the imaging of semiconductor, inorganic, and metal surfaces, it has recently become possible to study physisorbed organic molecules, immobilized by the formation of densely packed two-dimensional layers, at the solid–liquid interface. In 1990, McGonigal et al. published the first direct STM images of a self-adsorbed monolayer of long-chain alkanes at the solid–liquid interface. Though this kind of system had already been studied using different methods, it was the first direct observation of the true ordering of these adsorbed layers. However, they found that the apparent atomic resolution is related to graphite lattice substrate and the organic molecules only locally enhance the tunneling current.