Nanoscale elemental identification by synchrotron‐radiation‐based scanning tunneling microscopy

Abstract

Scanning tunneling microscopy (STM) combined with synchrotron radiation (SR) enabled elemental analysis on solid surfaces at an anometer scale. The principle of analysis is based on the inner-shell excitation of a specific energy level under STM observation. After first demonstrative results on a semiconductor heterointerface (Ge nanoisland on an Si(111) 7 × 7 surface), a second trial of nanoscale elemental analysis by the SR-STM system was accomplished for Cu nanodomains on a Ge(111) 2 × 8 surface. A key to achieve successful results is to effectively increase the signal to noise (S/N) ratio and to extract the element-specific modulation of the tunneling current, which is derived from the inner-shell excitation. An essential point for signal detection with a high S/N ratio is to construct a total system including lock-in amplifier with an optical chopper for high accuracy, and a real-time control system to check the incident-beam condition by observing the beam-induced current profiles. Using these techniques, it has been shown that the SR-STM system provides new possibilities forn anoscale surface analysis.

X-ray Assisted Scanning Tunneling Microscopy and Its Applications for Materials Science: The First Results on Cu Doped ZrTe3

“…The research team utilized glass-coated W tips [41]. Saito et al showed that Cu islands (>100 nm 2 ) embedded into Ge(111) 2 × 8 surface can be spatially resolved by detecting changes in the tip current (∼10 pA) when scanned laterally [42].…”

Direct Observation of X-ray Induced Atomic Motion Using Scanning Tunneling Microscope Combined with Synchrotron Radiation

“…The details of the apparatus have been presented in our past reports. [5][6][7] The STM controller and scanner were based on a conventional STM system with a UHV chamber having a base pressure of 1 0 × 10 −8 Pa (JEOL Co., Ltd., Tokyo, Japan). The STM tip was made from tungsten wire (0.3 mm in diameter) by electrochemical etching with NaOH solution.…”

“…4 We have recently directly observed the atomic motion caused by X-ray photons in UHV using scanning tunneling microscope (STM) dedicated to in-situ observation at an SR facility. [5][6][7] In this report, we show the details on the X-ray induced atomic motion with its dependence on beam parameters such as incident energy and photon density. Also we report a method to visualize a track of the atomic motion in STM images.…”

X-ray Spectrometry

“…They concluded that quantitative determinations of the elemental and crystal-phase content of each layer is possible by means of a combination of microbeam-based XRF and XRD tomography. Saito et al have attempted to develop a new method of STM combined with SR for elemental analysis of solid surfaces at the nanometer scale (89). They demonstrated this SR-STM system by elemental imaging of a Cu nanodomain.…”