University of Cambridge > > Physics of Medicine (PoM) Seminar Series > Nanostructured-Enhanced Raman Spectroscopy (NERS) for Surface Science and Molecular Electronics

Nanostructured-Enhanced Raman Spectroscopy (NERS) for Surface Science and Molecular Electronics

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Cancelled, sorry for short notice

Surface-enhanced Raman scattering (SERS) stems from surface plasmon resonance (SPR) which takes place on various nanostructures with suitable dielectric constant, shape and scale. It had been very difficult to apply conventional SERS to study probed molecules adsorbed at atomically-flat single-crystal surfaces and surface components of diverse materials because they cannot effectively support SPR . Based on the borrowing SERS activity strategy, we have utilized some nanostructures to expand SERS studies to Pt and Si single crystal surfaces and various molecules adsorbed on surfaces as diverse as those of platinum, yeast cells or citrus fruits. The latest progress made in our group is a new method named as Shelled-Isolated Nanoparticle-Enhanced Raman Spectroscopy (SHINERS) [1]. We chemically synthesized Au nanoparticles coated with ultra-thin shells (ca. two to four nanometers) of chemically inert silica and alumina, respectively. About monolayer of such nanoparticles is spread over the surface that is to be probed. The ultrathin coating keeps the nanoparticles from agglomerating, separates them from direct contact with the probed substance and allows the nanoparticles to conform to different contours of substrates. High-quality Raman spectra were obtained on various molecules adsorbed at Pt and Au single-crystal surfaces and from Si surfaces with hydrogen monolayers. These measurements and our studies on yeast cells and citrus fruits with pesticide residues illustrate that our method significantly expands the flexibility of SERS for wide applications in surface, materials and life sciences, as well as for the inspection of food safety. In molecular electronics, individual molecules with unique properties serve as the basic electrical components. Various methods have been established to construct electron-transport junctions, which serve as the basic investigative tool in molecular electronics, and to characterise different properties of the active region. Very recently we have introduced a “fishing mode” scanning tunneling microscopy (FM-STM) method which can reliably measure single-molecule conductance on the time scale of seconds (currently existing methods require tens of minutes to hours). We then combine our FM-STM method with tip-enhanced Raman spectroscopy (TERS) to create a second technique, one that allows mutually-verifiable single-molecule conductance and single-molecule Raman to be acquired simultaneously under ambient conditions. We call it “fishing-mode” TERS (FM-TERS). Density functional theory (DFT) calculations reveal a good correlation between the single-molecule conductance and single-molecule TERS , and they yield fresh insights into the non-linear nature of voltage-dependent conductance. The correlated data obtained by FM-TERS will allow molecular structure during the electron-transport process to be understood in a way that has never been possible before: by use of vibrational information obtained exclusively from the single molecule in the junction. Reference: 1. J.F. Li, et. al., Nature 2010, 464, 392.

This talk is part of the Physics of Medicine (PoM) Seminar Series series.

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