Scanning Tunneling Microscopy Combined with Hard X-ray Microbeam of High Brilliance from Synchrotron Radiation Source

Abstract

In situ scanning tunneling microscopy (STM) with highly brilliant hard X-ray irradiation was enabled at SPring-8. To obtain a good signal-to-noise ratio for elemental analysis, an X-ray beam with a limited size of '10 mm was aligned to a specially designed STM stage in ultrahigh vacuum. Despite various types of noises and a large radiation load around the STM probe, STM images were successfully observed with atomic resolution. The use of a new system for elemental analysis was also attempted, which was based on the modulation of tunneling signals rather than emitted electrons. Among tunneling signals, tunneling current was found to be better than tip height as a signal to be recorded, because the former reduces markedly the error of measurement. On a Ge nanoisland on a clean Si(111) surface, the modulation of tunneling current was achieved by changing the incident photon energy across the Ge absorption edge.

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

“…It should be mentioned here that the tunneling condition should be maintained throughout the measurement [12] to obtain local information against the abundant noise arising from emitted electrons. To obtain a modulation of the tunneling component with high S/N ratio, an incident beam of ϕ 10 µm in diameter was chopped at a frequency of 2.5 kHz, and the tip current was recorded through a lock-in amplifier (SEIKO, Tokyo, Japan) with integration for 5 ms.…”

“…2 to measure a 'tip-current spectrum' were obtained within a mode in which the incident energy is scanned, while the tip is fixed at a position on the surface. [12] Another experimental mode to obtain the element-sensitive STM image is performed by scanning the tip on the surface, while the incident photon is fixed at an energy point, as described later.…”

“…Our main strategy was to extract exclusively, a tunneling current modulation following the core excitation, which should include local information under the tunneling condition. Since newly developed devices and apparatus have been explained in our earlier papers, [11,12] it is worthwhile to describe here the total data acquisition system with its conceptual details, as this has not been presented elsewhere. It was also necessary to develop a special insulator-coated tip that could shut out the electrons that contribute to noise coming from a wide area.…”

Very low thermally induced tip expansion by vacuum ultraviolet irradiation in a scanning tunneling microscope junction

“…8 To have a better control over these correlated properties, new investigation route can be proposed when exploring the use of other irradiation wavelengths. 20,21 In this work, we report an original method of laser-STM combination that allows measuring the photoinduced STMtip expansion when associated with photoelectronic emission. This is performed by exposing the junction of a roomtemperature STM to a pulsed vacuum ultraviolet ͑VUV͒ laser.…”

Imaging of charge trapping in distorted carbon nanotubes by x-ray excited scanning probe microscopy

“…7,8 Unlike other related works, [9][10][11][12][13][14] the SPM used in this study was configured for electrostatic force microscopy ͑EFM͒, [15][16][17][18] and the x-ray photons were produced by synchrotron radiation ͑SR͒. We denote EFM combined with the x-ray source as X-EFM.…”