Fourier transform photoabsorption spectroscopy based on scanning tunneling microscopy

Abstract

A scheme of photoabsorption spectroscopy (PAS) based on scanning tunneling microscopy (STM) applicable to semiconductors has been devised to circumvent experimental difficulties inherent in STM-PAS measurements so far conducted in the conventional lock-in detection scheme. The present scheme uses multiplexed lights from an interferometer for spectroscopic lights and the modulated current flowing through the STM tip for the signal from which the photoabsorption spectrum is deduced by Fourier transformation. The technique under an optimized condition has been applied to Si samples deposited with epitaxially grown Ge1−xSnx nanodots, which proved the spatial resolution of a few nanometers.

Laser-Combined STM and Related Techniques for the Analysis of Nanoparticles/Clusters

“…Clusters ofstructures of the top layers. Individual Pt atoms are clearly identified, especially for (c) Pt (8) and (d) Pt (9), indicating that the geometry of the clusters is atomically resolved and the details can be analyzed with a CNT tip. …”

“…Fourier transform STM-PAS (STM-PAS-FT) based on the Fourier transformation technique was devised to solve such technical problems [9]. This scheme is essentially the same as that used in Fourier transform near-infrared spectroscopy (FT-NIR).…”

“…Compared with the long acquisition time for the LI spectrum, that for a single STM-FT-NIR spectrum is much shorter (1 s), which enables us to avoid acquiring spurious spectra. Figure 2 shows an STM topographic image (a) and a two-dimensional map (b) of Si signals integrated from 1.3 to 1.5 eV in the STM-PAS-FT spectra recorded in the framed area in (a) (8 spectra were measured and averaged at each pixel) [9]. The samples were hemispherical …”

“…Figure 1(b) shows a typical photoabsorption spectrum obtained around the band gap of Si by the STM-PAS-FT scheme (a) and the LI scheme (b). Although it took about 100 min to acquire the spectrum for a single sweep of photon energy from 0.68 to 1.55 eV in the LI scheme, it took only 16 min to obtain a. high quality STM-FT-NIR spectrum in the range of 0.25-1.85 eV (1s for each scan and 1000 scans totally) [9]. Compared with the long acquisition time for the LI spectrum, that for a single STM-FT-NIR spectrum is much shorter (1 s), which enables us to avoid acquiring spurious spectra.…”

Nanoscale-resolved near-infrared photoabsorption spectroscopy and imaging of individual gallium antimonide quantum dots

“…Methods for assessing the optical property of such variable nanoscale structures were limited to a few techniques, such as scanning near-field optical microscopy, 8 until recently, when we developed schemes for nanoscale-resolved photoabsorption spectroscopy (PAS) based on scanning tunneling microscopy (STM). In semiconductor samples, the tip-current (the current flowing in the STM tip is not necessarily the tunneling current) reflects the surface photovoltage (SPV) generated by the optical interband transition under appropriate experimental conditions, 12,15,17 thereby permitting the detection of photoabsorption by the sample. 9,10,13,15 These two schemes have a number of features in common.…”