Progress in modern science cannot emerge without reliable instruments for characterization of microstructure, physical, and chemical properties of materials, and devices at the micro-, nano-, and atomic (angstrom)-scale levels. Although structural information can be obtained by such established techniques as scanning and transmission electron microscopy, high-resolution examination of local electronic structure, electric potential, and chemical functionality is a much more challenging problem. Local electronic properties became accessible after the development of scanning tunneling microscopy (STM) by Binnig et al. [1] in 1981 at IBM Zurich-an invention that earned its authors the Nobel prize in physics five years later. Based on the quantum mechanical tunneling between an atomically sharp metallic tip and a conductive surface, STM has become the first instrument to generate real-space images of surfaces with atomic resolution and has triggered the development of new classes of STM-related techniques. In 1986, Binnig et al. [2] introduced the atomic force microscope (AFM) based on the mechanical detection of the van der Waals forces between the tip and the surface using a pliable cantilever. It was almost immediately realized that AFM could be extended to map forces of various types, such as magnetic and electrostatic forces, as well as for probing chemical interactions. This dual capability of probing currents and forces at the nanometer and atomic levels has led to a rapid growth of a variety of scanning probe microscopy (SPM) techniques over the past two decades. Techniques such as AFM, magnetic force microscopy, electrostatic force microscopy, scanning capacitance microscopy, near-field scanning optical microscopy, and other methods have emerged to provide users with the capability to access the local electrical, magnetic, chemical, mechanical, optical, and thermal properties of materials at the nanometer scale. It has been demonstrated that SPM not only allows imaging, but it also enables users to control and modify the local structure and material functionality at the nano-and atomic levels. As a consequence, the past two decades have witnessed an explosive growth in application of SPM techniques in a wide spectrum of

fields of science, ranging from condensed matter physics, chemistry, and materials science to medicine and biology. It will not be an exaggeration to say that the rapid development of nanoscience and nanotechnology in the past two decades was strongly stimulated by the availability of SPM techniques, and in turn constantly stimulates development of novel SPM probes. The scanning tunneling microscope (STM) is an atomic tool based on an electric method that measures the tunneling current between a conductive tip and a conductive surface. It can characterize or analyze the electronic nature around surface atoms/molecules. In addition, it can manipulate individual atoms/molecules. Hence, the STM is the first generation of atom/molecule technology. However, STMs can only be used to study surfaces that are electrically conductive to some degree. On the other hand, AFM is a unique atomic tool based on a mechanical method that can deal with even the insulator surface.