Ultrafast surface-enhanced Raman spectroscopy

Abstract

Ultrafast surface-enhanced Raman spectroscopy (SERS) with pico- and femtosecond time resolution has the ability to elucidate the mechanisms by which plasmons mediate chemical reactions. Here we review three important technological advances in these new methodologies, and discuss their prospects for applications in areas including plasmon-induced chemistry and sensing at very low limits of detection. Surface enhancement, arising from plasmonic materials, has been successfully incorporated with stimulated Raman techniques such as femtosecond stimulated Raman spectroscopy (FSRS) and coherent anti-Stokes Raman spectroscopy (CARS). These techniques are capable of time-resolved measurement on the femtosecond and picosecond time scale and can be used to follow the dynamics of molecules reacting near plasmonic surfaces. We discuss the potential application of ultrafast SERS techniques to probe plasmon-mediated processes, such as H2 dissociation and solar steam production. Additionally, we discuss the possibilities for high sensitivity SERS sensing using these stimulated Raman spectroscopies.

Surface- and Tip-Enhanced Raman Spectroscopy in Catalysis

“…28,29 With increased control over these SERS substrates, improved Raman signals are obtained with shorter acquisition times, allowing the observation of possible reaction intermediates or even transition states. 30,31 …”

Raman scattering mediated by neighboring molecules

“…To begin, the explicit form of the matrix elements given by (3), (11), (12), (15), (16), (19), (20), (24), and (25) are inserted into Equation (5) for the radiant intensity, I ′ , producing an expression in which the matrix elements are multiplied by their complex conjugates and cross terms occur denoting quantum interference. The resulting 45-term expression then undergoes a 4th rank isotropic rotationalaverage, which can be described by the following tensor expression 30 …”

“…Raman scattering involving individual optical centers is a well-established molecular process used as a spectroscopic [1][2][3] and microscopic tool 4,5 with an ever-increasing range of applications, including surface-enhanced spectroscopy, [6][7][8][9][10][11] sensing, [12][13][14] the detection of environmental pollutants, 15,16 and identification of disease. 17 The theoretical basis for the underlying phenomenon is well-known and established with quantum electrodynamical techniques offering a particularly insightful means of formulation.…”

Laser intensity limits in surface‐enhanced linear and nonlinear Raman micro‐spectroscopy of organic molecule/Au‐nanoparticle conjugates

“…Presently, the investigations are devoted, among other topics, to clarification of physical mechanisms of laser light interaction with SERS‐active surfaces and, in particular, of surface‐enhanced coherent anti‐Stokes Raman scattering (SECARS), as well as to possible applications of SERS in biology, biochemistry and medicine, chemistry, and pharmacy . Special interest in recent years is the development of linear and nonlinear versions of SERS excited by femtosecond and picosecond laser sources . At the same time, it is still important to search for new structures and surfaces that not only promise high electromagnetic field gain and hence high sensitivity for reporter molecules but also provide high reproducibility of their SERS properties, good stability in the surrounding atmosphere, and high resistance to laser power.…”