Scanning probe microscopy (SPM) is widely used for analysis of structures on substrate surfaces. Particularly, scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) enable real-space observations of solid surfaces at the atomic level with high spatial resolution. However, these microscopic measurement methods still involve difficulties in elemental analysis at the nanoscale for general purposes, although several validated solutions have already been proposed for well-defined cases. This brief review explains issues and their resolution, including topics related to the development of chemical analysis methodologies based on STM/NC-AFM, such as inelastic tunneling spectroscopy (IETS)-STM for spectroscopy of individual molecules, STM combined with synchrotron radiation X-ray sources for elemental analysis of surface structures, and force spectroscopy with atom tracking technology, as well as X-ray-aided noncontact atomic force microscopy (XANAM). Particularly, the review describes details of XANAM including recently obtained results on X-ray energy dependence of force spectroscopy and its twodimensional recording as XANAM imaging, suggesting XANAM offers great potential to contribute to nanoscale investigations of chemical analysis for various purposes.
IntroductionScanning probe microscopy (SPM) is a powerful tool to observe surface structures on substrate surfaces with measurement of physical parameters of different interactions between a tip and a sample surface. Among the SPM techniques, scanning tunneling microscopy (STM) 1 and noncontact atomic force microscopy (NC-AFM) 2,3 enable real-space observations of solid surfaces at the atomic level with high spatial resolution. Actually, STM can visualize surface structures of conductive materials with projection of electron density of states near the Fermi level. A sharpened metal tip is scanned with sensing tunneling current for imaging. Using a tiny tip, NC-AFM can visualize structures even on insulator surfaces by tracing corrugations of substances through sensing weak attractive force interactions. Many books 19 have described experimental and theoretical studies of the development of STM and NC-AFM, and have provided numerous examples of SPM applications in the fields of semiconductor devices, catalysis, sensors, and biochemistry. In addition, an upward trend is apparent in the number of studies in spectroscopy used to examine characteristic features of surfaces at the nanoscale. They have presented important new insights into surface physics and chemistry. Particularly, the identification of chemical characteristics on individual atoms and molecules on surfaces has persistently underlain SPM studies.Studies of the development of such chemically sensitive SPM are classifiable into two approaches: enhancing chemical sensitivity of tipsurface mutual interactions of SPM, and introducing extra probes of light/electron beam sources that can stimulate responses in the tipsurface interactions of SPM. As an example for the former, inelast...
