The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

/pdf/present-and-future-of-surface-enhanced-raman-scattering-34aqgcm385.pdf

Present and Future of Surface-Enhanced Raman Scattering

In the mid-1970s, surface-enhanced Raman scattering (SERS) was discovered which impacted on surface science and spectroscopy because of its extremely high surface sensitivity. However, SERS had not developed as many people had hoped to be a powerful surface diagnostic technique that can be widely used because of some obstacles. For example, only three noble metals Au, Ag, and Cu could provide large enhancement, severely limiting the widespread applications involving other metallic materials of both fundamental and practical importance. In this article, emphasis is put on the recent work of our group to directly generate SERS on net transition metals (e.g., Pt, Ru, Rh, Pd, Fe, Co, Ni, and their alloys) by developing various roughening procedures and optimizing the performance of the confocal Raman microscope. An approach of replacing the randomly roughened surface with ordered nanorod arrays of transition metals is introduced as a promising class of highly SERS-active substrates. The surface enhancement fa...

Surface-Enhanced Raman Scattering: From Noble to Transition Metals and from Rough Surfaces to Ordered Nanostructures

Iron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earth's crust, is the structural backbone of our modern infrastructure. It is therefore ironic that as a nanoparticle, iron has been somewhat neglected in favor of its own oxides, as well as other metals such as cobalt, nickel, gold, and platinum. This is unfortunate, but understandable. Iron's reactivity is important in macroscopic applications (particularly rusting), but is a dominant concern at the nanoscale. Finely divided iron has long been known to be pyrophoric, which is a major reason that iron nanoparticles have not been more fully studied to date. This extreme reactivity has traditionally made iron nanoparticles difficult to study and inconvenient for practical applications. Iron however has a great deal to offer at the nanoscale, including very potent magnetic and catalytic properties. Recent work has begun to take advantage of iron's potential, and work in this field appears to be blossoming.

Synthesis, Properties, and Applications of Iron Nanoparticles

Blue luminescent nanocrystals (NCs) were prepared electrochemically from multiwalled carbon nanotubes (MWCNTs) for the first time. The carbon NCs were characterized by UV−vis, photoluminescence, Raman, XRD spectroscopy, and high-resolution transmission electron microscopy. The structure evolution of the MWCNTs during electrochemical treatments was monitored by SEM ex situ. Since the MWCNTs were formed with scrolled graphene layers, we propose that tetrabutyl ammonium (TBA) cations most probably intercalate into the gaps and the defects during electrochemical cycling and break the tubes near the defects.

An Electrochemical Avenue to Blue Luminescent Nanocrystals from Multiwalled Carbon Nanotubes (MWCNTs)

CuO nanostructures: Synthesis, characterization, growth mechanisms, fundamental properties, and applications

The microemulsion method is employed to synthesize iron nanoparticles with an average size of ∽3 nm using
 trioctyl phosphine oxide (TOPO) as a stabilizing agent. The morphology, structure, and composition of
 the nanoparticles are studied by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–VIS spectroscopy. The iron nanoparticles show a remarkable surface-enhanced Raman scattering (SERS) activity, and the scheme of iron nanoparticle-on-electrode is successfully used in the in situ SERS study of adsorbed molecules. Electrocatalysis over the iron nanoparticles is demonstrated in the highly efficient and selective reduction of H2O2 in the presence of oxygen.

Iron nanoparticles: Synthesis and applications in surface enhanced Raman scattering and electrocatalysis

The thermal behavior of Cu2S nanowires has been studied in the presence of N2 and O2. The nanowires are stable in N2 at the highest temperature we have studied (320 °C), but they are oxidized by O2 to Cu2O above 260 °C and to CuO at even higher temperatures. At the highest temperature we have studied (400 °C), the S atoms in the Cu2S nanowires are completely removed by O2, forming CuxO wires mainly with x = 2. Although the Cu1,2O wires are polycrystalline and are much thicker than Cu2S nanowires, they are remarkably uniform. This represents a new template method for the synthesis of mesoscopic Cu1,2O wires.

Thermal oxidation of Cu2S nanowires: A template method for the fabrication of mesoscopic CuxO (x = 1,2) wires

Metal nanoparticles-on-smooth-electrode (NOSE) was used as the substrate in a potential-dependent surface-enhanced hyper-Raman(SEHRS), hyper-Rayleigh(SEHRyS) and Raman (SERS) study of adsorbed molecules of pyridine, pyrazine and benzene. The three molecules are chosen because they are known to adsorb in different orientations on an Ag surface, thus allowing us to examine the sensitivity of SEHRS and SERS signals to the orientation of adsorbed molecules on the NOSE substrate. A computational subroutine is developed and interfaced with Gaussian-98 to calculate the numeric infrared, Raman and hyper-Raman intensities, as well as their projections along any molecular-fixed orientation axis at the level of finite perturbation theory. In this study, we tried to make four types of systematic comparisons. First, we compared the performance of Agn|Ag NOSE substrate with that of traditional substrates such as a randomly roughened Ag electrode or a randomly aggregated Ag sol in SEHRS and SERS. Secondly, we tried to compare between infrared, Raman and hyper-Raman spectra, which represent the parity-differentiated one-photon, two-photon and three-photon processes, respectively, with the aim of examining the complementarity between SEHRS and SERS as well as between SEHRS and infrared absorption. Thirdly, we compared isotropic normal spectra with surface-enhanced spectra (SEHRS and SERS), with the aim of examining the effect of surface adsorption on the selectivity and enhancement. Lastly, we made a systematic comparison between the observed and calculated spectra for both isotropic and surface spectra, which allowed us to assign and interpret the observed data and to infer the most likely orientation of the adsorbed molecules. The NOSE method can be generalized easily to other metal nanoparticles dispersed on a smooth inert metal electrode. The rapid development in the synthesis of metal nanoparticles of various sizes, shapes and crystalline states makes the NOSE method a much more flexible and versatile substrate in the study and applications of SERS and SEHRS techniques. Copyright © 2005 John Wiley & Sons, Ltd.

Surface-enhanced hyper-Raman and surface-enhanced Raman scattering from molecules adsorbed on nanoparticles-on-smooth-electrode (NOSE) substrate - I. Pyridine, pyrazine and benzene

Qunjian Huang

Papers

Iron nanoparticles: Synthesis and applications in surface enhanced Raman scattering and electrocatalysis

Thermal oxidation of Cu2S nanowires: A template method for the fabrication of mesoscopic CuxO (x = 1,2) wires

Surface-enhanced hyper-Raman and surface-enhanced Raman scattering from molecules adsorbed on nanoparticles-on-smooth-electrode (NOSE) substrate - I. Pyridine, pyrazine and benzene

Adsorption behavior of C60 fullerene on golden crystal nanoparticles

Blue-green photoluminescence from pyridine-C60 adduct