Today, the rapid advancement of nanoscience and nanotechnology requires atomic-scale optical spectroscopy due to nanofabrication of electronic devices reaching a single nanometer scale (10-9 m). To characterize atomistic structures that will affect the properties and functions of these electronic devices, scientists must first enhance sensitivity.
Researchers at the Institute for Molecular Science utilized state-of-the-art low-temperature tip-enhanced Raman spectroscopy to obtain the vibrational spectra from a silicon surface. During the study, the international team, headed by Takashi Kumagai, discovered a huge enhancement of Raman scattering mediated by a formation of an atomic point contact between a plasmonic silver tip and a Si(111)-7x7 reconstructed surface. Furthermore, researchers determined that the atomic point contact Raman spectroscopy (APCRS) resolves the atomic-scale structures of a silicon surface. The study was published in the journal Nano Letters.
According to the researchers, the discovered enhancement mechanism of Raman scattering will open the possibility of atomic-scale ultrasensitive vibrational spectroscopy to investigate surface structures of semiconductors. In addition, the developed atomic-scale optical microscopy will pave the way for exploring atomic-scale light-matter interactions, leading to a new discipline in light science and technology.
Prior to the study, a plasmonic nanogap typically requiring a metal substrate was deemed necessary to obtain ultrahigh sensitivity in tip-enhanced Raman spectroscopy. The study’s results suggest atomic scale structures play a key role in metal-semiconductor hybrid nano systems, affecting their optoelectronic properties. Additionally, the discovery of the APCRS will expand the potential of atomic-scale vibrational spectroscopy and mitigate limitations on measurable samples in the future.
Photo: Figure 1 (A) Illustration of the experiment. (B) Scanning electron micrograph of an Ag tip (top) and scanning tunneling microscopy image of the Si(111)-7x7 surface. (C) Atomic point contact Raman spectra. Credit: NINS/IMS.