Tip Enhanced Raman Spectroscopy

An instrument that combines the analytical power of Raman spectroscopy with the spatial resolution of the Atomic Force Microscope ͑AFM͒ is presented. This instrument is capable of resolving 50 nm scale spectral features or better by using surface enhanced Raman scattering at the AFM tip. The localized spectrochemical information allows the interpretation of the concurrently acquired friction or phase contrast AFM images. This instrument has a unique combination of features including side illumination of the tip-sample interface that permits opaque samples. As a result of precise focusing of a laser at the AFM tip-sample interface this instrument is also capable of laser beam profiling and studying optical trapping at the probe tip. Applications of this versatile instrument include chemical analysis of nanometer scale phenomena, chemical separation, and the potential for targeted single molecule spectroscopy.

An atomic force microscope (AFM) tip has been used to selectively produce surface enhanced Raman scattering (SERS) for localized Raman spectroscopy. Spectra of thin films, undetectable with a Raman microprobe spectrometer alone, were readily acquired in contact with a suitably gold-coated AFM tip. Similarly, an AFM tip was used to remove sample layers at the nanometer scale and subsequently served as a SERS substrate for ultratrace analysis. This work demonstrates the interface of an AFM with a Raman spectrometer that provides increased sensitivity, selectivity, and spatial resolution over a conventional Raman microprobe. An AFM guiding the SERS effect has the potential for targeted single molecule spectroscopy.

The biological membrane plays an important role in numerous cellular processes and is linked to various diseases. Many of its biological functions have been shown to depend on local environments with specific compositions. Self-assembled nanoscale compartments enriched in sphingolipids, cholesterol and proteins called “lipid rafts” are believed to be a locus for biochemical reactions taking place on the cell membrane. Investigation of such domains with nanometer resolution is still a very challenging task, especially when it is done in their native environment. Model membrane systems have been developed to study biophysical processes occurring at the cell membrane in a controlled fashion. Solid supported lipid bilayers are a prominent example because of their accessibility for various surface-specific analytical techniques.

In order to combine the advantages of fluorescence and surface-enhanced Raman spectroscopy (SERS) on the same chip platform, a nanostructured gold surface with a unique design, allowing both the sensitive detection of fluorescence light together with the specific Raman fingerprint of the fluorescent molecules, was established. This task requires the fabrication of plasmonic arrays that permit the binding of molecules of interest at different distances from the metallic surface. The most efficient SERS enhancement is achieved for molecules directly adsorbed on the metallic surface due to the strong field enhancement, but where, however, the fluorescence is quenched most efficiently. Furthermore, the fluorescence can be enhanced efficiently by careful adjustment of the optical behavior of the plasmonic arrays. In this article, the simultaneous application of SERS and fluorescence, through the use of various gold nanostructured arrays, is demonstrated by the realization of a DNA detect...

A method using microfabricated resist masks as highly homogenous and sensitive substrates for surface enhanced Raman spectroscopy (SERS) is introduced. Our approach combines e-beam lithography for a polymer (PMMA) mask preparation, atomic layer deposition of aluminum-oxide as protection layer for the PMMA mask and silver evaporation for the SERS-active metal film. Compared to our former investigations on silver deposited etched quartz SERS-substrates these polymer based SERS substrates are easier to fabricate while showing the same reproducible signal enhancement across the whole grating area. The presented method provides high potential as it uses low-cost imprint techniques to pave the way towards low-cost SERS substrates in the future.

Raman spectroscopy is a valuable tool in various research fields. The technique yields structural information from all kind of samples often without the need for extensive sample preparation. Since the Raman signals are inherently weak and therefore do not allow one to investigate substances in low concentrations, one possible approach is surface-enhanced (resonance) Raman spectroscopy. Here, rough coin metal surfaces enhance the Raman signal by a factor of 10 4 -10 15 , depending on the applied method. In this review we discuss recent developments in SERS spectroscopy and their impact on different research fields.

In order to increase the inherent weak but molecular specific Raman signature the exceptional optical properties of plasmonic nanostructures are used. This technique is termed as surface enhanced Raman spectroscopy (SERS) and combines the fingerprint specificity with potential single molecule sensitivity. However, the non-application of SERS in routine analytics is often linked with the low reproducibility of metallic nanostructures or metallic surfaces. Within this contribution, the fabrication of innovative plasmonic arrays with homogenous signal enhancement is introduced, which is an important contribution towards powerful SERS diagnostics. Here, the application of plasmonic arrays for DNA sensing is demonstrated.

Simultaneous nanometer-scale measurements of the strain and surface undulation distributions of strained Si (s-Si) layers on strain-relief quadruple-Si 1Àx Ge x -layer buffers, using a combined atomic force microscopy (AFM) and tip-enhanced Raman spectroscopy (TERS) system, clarify that an s-Si sample formed by our previously proposed sputter epitaxy method has a smoother and more uniformly strained surface than an s-Si sample formed by gas-source molecular beam epitaxy. The TERS analyses suggest that the compositional fluctuation of the underlying Si 1Àx Ge x buffer layer is largely related to the weak s-Si strain fluctuation of the sputtered sample.

Experimental studies on the conductive properties of molecular systems led to the discovery and characterization of two essential elements of molecular electronics: a molecularwire and a single electron switch. The synthesis and cyclic current versus voltage (I/V) measurements of intrinsically conductive linear chain [-Ag-S-BP-S-]n polymers determined their relatively large conductivity and suggested that mobile Ag adatoms on the roughened Ag surface catalyzed the polymerization. On the other hand, the single electron switch was determined to be controlled by the spin-vibronic density of an odd electron on a single molecule. Analysis of the two-level telegraphic conductance switching produced effective wiring diagrams to control the switch’s frequency, amplitude, polarity, and duty-cycle. Furthermore, it gave insight into the molecule’s governing vibronic Hamiltonian.

We have developed an optofluidic device that can significantly improve the sensitivity, efficiency and reproducibility of the surface enhanced Raman spectroscopy (SERS). This device has demonstrated the capalibity of detecting molecules of interest at ultra-low concentration and is able to identify fingerprint signals from multiple analytes. This device can potentially be used for the definitive early stage diagnostics of disease associated with protein conformation change such as Alzheimer's disease (AD) or Bovine Spongiform Encephalopathy (BSE) .

We have developed an optofluidic device that improves the sensitivity of surface enhanced Raman spectroscopy (SERS) when compared to other SERS approaches. This device has a pinched and step microchannel-nanochannel junction that can trap and assemble nanoparticles/target molecules into optically enhanced SERS active clusters by using capillary force. These SERS active clusters provide an electromagnetic enhancement factor of y10 8 . In addition, due to the continuous capillary flow that can transport nanoparticles/target molecules into the junction sites, the numbers of nanoparticles/target molecules and SERS active sites are increased. As a result, the detection limit of SERS for adenine molecules was better than 10 pM.

Surface-enhanced Raman scattering (SERS) coupled with micro-or nanofluidics integrated into optofluidic devices offer many advantages over conventional SERS conducted under static conditions. Higher reproducibility, larger intensity, as well as greater enhancement can be achieved by efficient mixing of analytes and SERS enhancers under a continuous flow. Progress and advances in the past 10 years, including the design of channels and efficient mixing conditions, assemblies of SERS substrates for optimal enhancement, and advantages of optofluidic-SERS analysis, are reviewed. Recent results show that optofluidic-SERS effectively overcomes many of the difficulties and limitations plaguing conventional SERS and the novel technique has enormous application potential.

Raman spectroscopy is a valuable tool in various research fields. The technique yields structural information from all kind of samples often without the need for extensive sample preparation. Since the Raman signals are inherently weak and therefore do not allow one to investigate substances in low concentrations, one possible approach is surface-enhanced (resonance) Raman spectroscopy. Here, rough coin metal surfaces enhance the Raman signal by a factor of 10 4-10 15 , depending on the applied method. In this review we discuss recent developments in SERS spectroscopy and their impact on different research fields.

Tip-enhanced Raman spectroscopy is considered a promising technique for imaging with nanoscale lateral resolution. However, its developments and use face many problems. In this paper we provide insight into the level of sample heating by the laser light in the presence of a metal-coated atomic force microscope (AFM) tip. The heating is attributed to the presence of an optical field enhanced by the tip. Sample temperatures were estimated using measurements of the ratio of the Stokes and anti-Stokes signals from a thin 50-nm sample on an Al substrate. A correlation between the heating and optical properties of the tips is established. The results demonstrate significant tip-induced heating (100 K and more) even at very low laser power. Copyright

By tuning substrate temperatures in a thermal deposition process, Au nanostructures with different morphologies, such as polygons, dendrites, irregular islands and dense clusters have been obtained on graphene surface. The surface-enhanced Raman scattering (SERS) of graphene caused by gold decoration is systematically investigated. The enhancement factor of graphene G band and the extent of G band splitting are found to be dependent on the morphologies of gold clusters. A maximum enhancement factor as high as $270 is obtained for polygonal gold film deposited on monolayer graphene. Furthermore, as a SERS substrate, graphene combined with polygonal gold shows the highest Raman enhancing efficiency for crystal violet (CV) molecules. The mechanisms for the above results are discussed.

Graphene can be used as a starting material for the synthesis of useful nano-complexes for flexible, transparent electrodes, therapeutic, bio-diagnostics and bio-sensing. In order to apply graphene in the medical field, chemical vapor deposition (CVD) method has been mainly utilized considering its large and near-homogenious carbon constituents. Especially, the less degree of perturbation of graphene monolayer (GM), which is followed by the underneath catalytic Cu surface morphology, is very crucial in terms of providing the suspended GM and relatively fluent lateral carrier mobility with lower sheet resistance value. In this work, we can suggest a surface-Enhanced Raman Spectroscopic (SERS) indicator in a quantitative way on the status of z-directional morphological corrugation of a CVD–grown GM (CVD-GM) by applying a Nanoparticle-on-Mirror (NPoM) system composed of Au nanoparticle (NP) / CVD-GM / Au thin film (TF) plasmonic junction structure. A new (or enhanced) Radial Breathing ...

We carried out the tip-enhanced Raman scattering (TERS) with a tip that is functionalized with a Aunanoparticle (AuNP, with a diameter of 250 nm). The AuNP tip is fabricated by a direct mechanical pickup of a AuNP from a flat substrate, and the TERS signal from the AuNP tip-organic monolayer-Au thin film (thickness of 10 nm) is recorded. We find that such a AuNP-tip interacting with a thin film routinely yields signal enhancement larger than ~10 4 , which is sufficient not only for local (with detection area of ~200 nm 2) Raman spectroscopy, but also the nanometric imaging of organic monolayers within a reasonable acquisition time (~20 minutes/image).

The spatial resolution and high sensitivity of tip-enhanced Raman spectroscopy allows the characterization of surface features on a nano-scale. This technique is used to visualize silicon-based structures, which are similar in width to the transistor channels in present leading-edge CMOS devices. The reduction of the intensive far-field background signal is crucial for detecting the weak near-field contributions and requires beside a careful alignment of laser polarization and tip axis also the consideration of the crystalline sample orientation. Despite the chemical identity of the investigated sample surface, the structures can be visualized by the shift of the Raman peak positions due to the patterning induced change of the stress distribution within lines and substrate layer. From the measured peak positions the intrinsic stress within the lines is calculated and compared with results obtained by finite element modeling. The results demonstrate the capability of the tip-enhanced Raman technique for strain analysis on a sub-50 nm scale.

Developed multidisciplinary and multinational vertical teams including faculty, postdocs, graduate and undergraduate students to internationalize engineering education at graduate level  Collaborated with partners at Technical University of Braunschweig (TU-BS) to find innovative strategies for integrating research and education  Built on success of our undergraduate International Engineering Program (IEP) to create new dual-degree masters and doctoral programs  Impacted other curricula at URI and at TUBS to explore multidisciplinary dual-degree concept  Offered a model for other institutions of higher education to adopt  Enhanced the development of students through mentoring and career development  Provided graduate students with multidisciplinary and international research experiences to increase their abilities to compete in global market Prototyping and Testing Equipment Lens-less

Through geological time, cyanobacterial picoplankton have impacted the global carbon cycle by sequestrating CO2 and forming authigenic carbonate minerals. Various studies have emphasized the cyanobacterial cell envelopes as nucleation sites for calcium carbonate formation. Little is known, however, about how environmental conditions (e.g., nutrient content) trigger a cell surface and its properties and, consequently, influence biomineralization. Our study aims to understand how phosphorus (P) concentration impacts the properties of cell surfaces and cell–mineral interactions. Changes to the surface properties of marine Synechococcus strains grown under various P conditions were characterized by potentiometric titrations, X-ray photoelectron spectroscopy (XPS), and tip-enhanced Raman spectroscopy (TERS). Biomineralization experiments were performed using cyanobacterial cells, which were grown under different P concentrations and exposed to solutions slightly oversaturated with respec...

By tuning substrate temperatures in a thermal deposition process, Au nanostructures with different morphologies, such as polygons, dendrites, irregular islands and dense clusters have been obtained on graphene surface. The surface-enhanced Raman scattering (SERS) of graphene caused by gold decoration is systematically investigated. The enhancement factor of graphene G band and the extent of G band splitting are found to be dependent on the morphologies of gold clusters. A maximum enhancement factor as high as $270 is obtained for polygonal gold film deposited on monolayer graphene. Furthermore, as a SERS substrate, graphene combined with polygonal gold shows the highest Raman enhancing efficiency for crystal violet (CV) molecules. The mechanisms for the above results are discussed.

We demonstrate highly sensitive detection of real-world food and water contaminants using a portable and automated optofluidic surface enhanced Raman spectroscopy (SERS) microsystem. The optofluidic SERS device utilizes a porous microfluidic matrix formed by packed silica microspheres to concentrate silver nanoparticles and adsorbed analyte molecules, resulting in greatly improved SERS detection performance. In addition, a passive micromixer that mixes silver nanoparticles into the sample solution is integrated into the device for improved automation. Furthermore, two optical fibers are integrated into the device and aligned to the detection volume to improve the automation as compared to confocal SERS, which requires focusing and alignment. The device exhibits up to 2 orders of magnitude improvement in SERS performance as compared to conventional microfluidic SERS in an open channel. Using the optofluidic SERS device, the food contaminant melamine was detected in low concentrations, with an estimated limit of detection (LOD) of 63 ppb, while the fungicide thiram was detected down to an estimated LOD of 50 ppt. In both cases, the reported results meet the U.S. federal requirements. Additionally, it is shown that the device continues to exhibit excellent performance even when mated to a commercially available portable spectrometer for the trace detection of thiram. This combination of the optofluidic SERS microsystem with a portable spectrometer will lead to highly sensitive and automated sensing systems for on-site detection of food and water contaminants in the field.

We consider $\,R-$modules as functors in the following way: if $\,M\,$ is a (left) $R$-module, let $\,\mathcal M\,$ be the functor of $\,\mathcal R-$modules defined by $\,\mathcal M(S) := S \otimes_R M\,$ for every $\,R-$algebra $\,S$. With the corresponding notion of dual functor, we prove that the natural morphism of functors $\,\mathcal M\to \mathcal M^{**}\,$ is an isomorphism.

Molecular electronics promises a new generation of ultralow-energy information technologies, based around functional molecular junctions. Here, we report optical probing that exploits a gold nanoparticle in a plasmonic nanocavity geometry used as one terminal of a well-defined molecular junction, deposited as a self-assembled molecular monolayer on flat gold. A conductive transparent cantilever electrically contacts individual nanoparticles while maintaining optical access to the molecular junction. Optical readout of molecular structure in the junction reveals ultralow-energy switching of ∼50 zJ, from a nano-electromechanical torsion spring at the single molecule level. Real-time Raman measurements show these electronic device characteristics are directly affected by this molecular torsion, which can be explained using a simple circuit model based on junction capacitances, confirmed by density functional theory calculations. This nanomechanical degree of freedom is normally invisib...

We report the effect of gold nanoparticles (AuNPs) and unwanted sodium citrate residues (UnR) left after deposition of AuNPs by drop-casting method on the Raman spectra of graphene sheets (GS). The AuNPs solution was deposited on three different substrates: 5.0 wt% Yb 3+-doped (Q5) phosphate glass, silica glass (S1), and Si/SiO 2-300 nm (S2) substrates. For Q5 substrate, a slight increase in intensity of the G peak was observed, mostly for thinner layers, which can be attributed to a weak SERS effect shielded by UnR. The combination of the following aspects: a blue shift of the G band position, a slight increase in the FWHM (Full Width at Half Maximum), and a slight increase of the Raman intensities of both G and 2D bands in other GS without UnR supports the argument of shielded SERS effect. On the other hand, the effects of UnR on the S1 and S2 substrates produce a decrease on the Raman intensities of G and 2D bands, opposite to the effect produced by the AuNPs; this result was found more intense for the S2 substrate in relation to S1. This is possibly caused by the greater amount of UnR accumulated on the Si/SiO 2 substrate, due to its higher hydrophilicity in relation to other samples. Additional Raman measurements reveal that the Raman intensity of GS in all substrates is unaffected by the presence of a possible humidity on GS, revealing the effect of UnR. Hence, it is vital to understand how residues influence the salient features of GS/AuNPs.

The Raman scattering spectra of uranium-doped Ca 2 CuO 3 were investigated. The small doping of uranium (≤5%) in this one-dimensional spin 1/2 chain system induced three new first-order scattering bands and two new multiphonon bands in the structure of forbidden phonons. The first-order bands were found to agree well with the existing theoretical results from the ab initio and tight-binding calculation. Among them, the 470 and 665 cm −1 bands appeared as the basic wavenumbers of which the multiphonon overtones were composed. The grain size effect in this strongly anisotropic system was proposed not to originate from the classical phonon confinement but rather as a result of the segmentation of one-dimensional spin chains due to doping, which in turn allowed the new vibrational modes and implied the appearance of higher overtones in the scattering spectra.

We studied how a protection layer influences the performance of an Ag-coated dielectric tip in tip-enhanced Raman spectroscopy using 3D simulations. Two typical chemically inert materials, Au and SiO 2 were considered in this work. Neither of them introduces a significant shift of the resonance frequency; the field enhancement as well as the spatial resolution can also be preserved with a thin protective layer. Surprisingly, a 5 nm layer of SiO 2 can even improve the field enhancement of the tip. This provides a new method to prevent Ag tips from undesired physical and chemical damages without losing their original performance for TERS.

Nowadays, surface plasmon resonance (SPR) induced hot-electron transfer from noble metals to host materials has been a widely used concept in solar energy conversion. On the other hand, the development of graphene-based photocatalytic systems for photocatalytic water reduction has attracted tremendous interest. In the present article, we develop a novel efficient photocatalytic system for clean energy production, i.e., semiconductor-free, solar-light harvesting graphene sensitized Ag/Au-bimetallic plasmonic system, by cost-effective and eco-friendly one-pot in situ green reduction process. Here, graphene oxide (GO) reduced well under the reflux conditions approximately at 90°C with vitamin C, and simultaneously the Ag and Au nanoparticles (NPs) deposited on the graphene sheet. The reduction of GO to graphene and deposition of an alloy of Ag and Au nanoparticles on graphene sheet have been analyzed by UV−vis and PXRD. These results revealed that bimetallic Ag/Au-graphene has all the characteristic peaks of graphene and Ag and Au NPs. Morphological studies (SEM, TEM) clearly show that the alloys of Ag and Au NPs are well orderly deposited on the graphene sheet. The synthesized bimetallic Ag/Au-graphene plasmonic system was applied for photocatalytic water reduction process for the first time, and it affords a superior photocatalytic performance for H 2 evolution from water reduction than Ag-graphene and Au-graphene plasmonic systems under sunlight illumination and further supported by photocurrent experiments. The rate of H 2 evolution of bimetallic Ag/Au-graphene plasmonic system is 1.4-and 2-fold more than that of Au-graphene and Ag-graphene plasmonic systems. For enhanced photocatalytic H 2 evolution, a mechanism has been proposed. Here graphene serves as an electron mediator/acceptor and light absorber, and the Ag and Au NPs alloy serves as reaction center for H 2 evolution.

The interaction of anatase titanium dioxide (TiO 2) nanoparticles with chemical vapour deposited graphene sheets transferred on glass substrates is investigated by using atomic force microscopy, Raman spectroscopy and imaging. Significant electronic interactions between the nanoparticles of TiO 2 and graphene were found. The changes in the graphene Raman peak positions and intensity ratios indicate that charge transfer between graphene and TiO 2 nanoparticles occurred, increasing the Raman signal of the TiO 2 nanoparticles up to five times. The normalized Raman intensity of TiO 2 nanoparticles per their volume increased with the disorder of the graphene structure. The complementary reason for the observed enhancement is that due to the higher density of states in the defect sites of graphene, a higher electron transfer occurs from the graphene to the anatase TiO 2 nanoparticles.

In Tip-Enhanced Raman Spectroscopy (TERS) a metal (or metallized) sharp tip is used to enhance the electromagnetic field by a localized surface-plasmon excitation. Two different modes-atomic force mode (AFM) and scanning tunneling mode (STM)-together with their respective types of probe tips are used in TERS experiments. We have compared the efficiency in enhancing the Raman signal on a thin dye layer for metal-coated AFM tips as well as for electrochemically etched metal STM tips. A much higher enhancement factor and better reproducibility were found when using STM tips. The very different performance is mainly attributed to the more efficient plasmonic excitation when using bulk-metal tips and possibly to the morphological differences in the tip and apex shapes existing between the two tip types.

In Tip-Enhanced Raman Spectroscopy (TERS) a metal (or metallized) sharp tip is used to enhance the electromagnetic field by a localized surface-plasmon excitation. Two different modes-atomic force mode (AFM) and scanning tunneling mode (STM)-together with their respective types of probe tips are used in TERS experiments. We have compared the efficiency in enhancing the Raman signal on a thin dye layer for metal-coated AFM tips as well as for electrochemically etched metal STM tips. A much higher enhancement factor and better reproducibility were found when using STM tips. The very different performance is mainly attributed to the more efficient plasmonic excitation when using bulk-metal tips and possibly to the morphological differences in the tip and apex shapes existing between the two tip types.

The spatial resolution in optical imaging is restricted by so-called diffraction limit, which prevents it to be better than about half of the wavelength of the probing light. Tipenhanced Raman spectroscopy (TERS), which is based on the SPP-induced plasmonic enhancement and confinement of light near a metallic nanostructure, can however, overcome this barrier and produce optical images far beyond the diffraction limit. Here in this article, the basic phenomenon involved in TERS is reviewed, and the high spatial resolution achieved in optical imaging through this technique is discussed. Further, it is shown that when TERS is combined with some other physical phenomena, the spatial resolution can be dramatically improved. Particularly, by including tip-applied extremely localized pressure in TERS process, it has been demonstrated that a spatial resolution as high as 4 nm could be achieved. 4 nm Illustration of local deformation in an isolated carbon nanotube due to the pressure applied through the apex of a nano-tip. By sensing this local deformation by means of Raman shift in TERS, the sample can be imaged with extremely high spatial resolution.

Since the carrier mobility in a strained silicon thin layer is enhanced compared to unstrained layers, strained silicon is finding tremendous attention as a promising material for ultralarge integrated electronic circuits assembled on one substrate. These strained substrates, however, suffer from nanoscale fluctuation of strain distribution, which can strongly affect the performance of devices. Raman spectroscopy is a powerful tool because the optical phonons in the Raman spectra are strongly influenced by strain. However, Raman efficiency of a thin layer is extremely small and is often eclipsed under the Raman scattering of the underlying buffer substrates. Also, the spatial resolution is restricted by the diffraction limits of the probing light. Here, in this article we demonstrate the use of surface enhancement in Raman scattering to overcome both these problems. In the first step, a strained silicon thin layer was covered with a silver layer to invoke surface-enhanced Raman spectroscopy (SERS), and it was found that SERS can effectively enhance the Raman signal originating from the strained silicon layer, so that it stands distinctly apart from the background signal originating from the buffer layer. In the next step, we demonstrate the utilization of the same mechanism for a point surface enhancement, rather than a large surface enhancement. This is done by utilizing a silver-coated sharp tip, just like SERS, but only from the sample region very close to the tip apex. This technique, known as tip-enhanced Raman spectroscopy (TERS), provides nanometric resolution in our measurement. We observed localized strains by utilizing TERS. The TERS spectra revealed clear nanoscale variation in the Raman wavenumber. Micro-Raman measurements, however, show only uniform features because of the averaging effect due to the diffraction limit of light. For further improvement of TERS on silicon materials, we discuss the utilization of shorter wavelength, specialized tip, tip-pressure effect, and depolarization configurations.

Developed multidisciplinary and multinational vertical teams including faculty, postdocs, graduate and undergraduate students to internationalize engineering education at graduate level  Collaborated with partners at Technical University of Braunschweig (TU-BS) to find innovative strategies for integrating research and education  Built on success of our undergraduate International Engineering Program (IEP) to create new dual-degree masters and doctoral programs  Impacted other curricula at URI and at TUBS to explore multidisciplinary dual-degree concept  Offered a model for other institutions of higher education to adopt  Enhanced the development of students through mentoring and career development  Provided graduate students with multidisciplinary and international research experiences to increase their abilities to compete in global market Prototyping and Testing Equipment Lens-less

We show that hemispherical gold droplets on top of silicon nanowires when grown by the vapor−liquid−solid (VLS) mechanism, can produce a significant enhancement of Raman scattered signals. Signal enhancement for a few or even just single gold droplets is demonstrated by analyzing the enhanced Raman signature of malachite green molecules. For this experiment, trenches (∼800 nm wide) were etched in a silicon-on-insulator (SOI) wafer along 〈110〉 crystallographic directions that constitute sidewalls ({110} surfaces) suitable for the growth of silicon nanowires in 〈111〉 directions with the intention that the gold droplets on the silicon nanowires can meet somewhere in the trench when growth time is carefully selected. Another way to realize gold nanostructures in close vicinity is to attach a silicon nanowire with a gold droplet onto an atomic force microscopy (AFM) tip and to bring this tip toward another gold-coated AFM tip where malachite green molecules were deposited prior to the measurements. In both experiments, signal enhancement of characteristic Raman bands of malachite green molecules was observed. This indicates that silicon nanowires with gold droplets atop can act as efficient probes for tip-enhanced Raman spectroscopy (TERS). In our article, we show that a nanowire TERS probe can be fabricated by welding nanowires with gold droplets to AFM tips in a scanning electron microscope (SEM). TERS tips made from nanowires could improve the spatial resolution of Raman spectroscopy so that measurements on the nanometer scale are possible.

This paper presents an effective Tip-Enhanced Raman Spectrometer (TERS) in backscattering reflection configuration. It combines a tip-probe nanopositioning system with Raman spectroscope. Specific tips were processed by anchoring gold nanoparticles on the apex of tapered optical fibers, prepared by an improved chemical etching method. Hence, it is possible to expose a very small area of the sample (∼20 nm 2) to the very strong local electromagnetic field generated by the lightning rod effect. This experimental configuration was modelled and optimised using the finite element method, which takes into account electromagnetic effects as well as the plasmon resonance. Finally, TERS measurements on single-wall carbon nanotubes were successfully performed. These results confirm the high Raman scattering enhancement predicted by the modelling, induced by our new nano-Raman device.

We show that hemispherical gold droplets on top of silicon nanowires when grown by the vapor−liquid−solid (VLS) mechanism, can produce a significant enhancement of Raman scattered signals. Signal enhancement for a few or even just single gold droplets is demonstrated by analyzing the enhanced Raman signature of malachite green molecules. For this experiment, trenches (∼800 nm wide) were etched in a silicon-on-insulator (SOI) wafer along 〈110〉 crystallographic directions that constitute sidewalls ({110} surfaces) suitable for the growth of silicon nanowires in 〈111〉 directions with the intention that the gold droplets on the silicon nanowires can meet somewhere in the trench when growth time is carefully selected. Another way to realize gold nanostructures in close vicinity is to attach a silicon nanowire with a gold droplet onto an atomic force microscopy (AFM) tip and to bring this tip toward another gold-coated AFM tip where malachite green molecules were deposited prior to the measurements. In both experiments, signal enhancement of characteristic Raman bands of malachite green molecules was observed. This indicates that silicon nanowires with gold droplets atop can act as efficient probes for tip-enhanced Raman spectroscopy (TERS). In our article, we show that a nanowire TERS probe can be fabricated by welding nanowires with gold droplets to AFM tips in a scanning electron microscope (SEM). TERS tips made from nanowires could improve the spatial resolution of Raman spectroscopy so that measurements on the nanometer scale are possible.

The Raman scattering spectra of uranium-doped Ca 2 CuO 3 were investigated. The small doping of uranium (≤5%) in this one-dimensional spin 1/2 chain system induced three new first-order scattering bands and two new multiphonon bands in the structure of forbidden phonons. The first-order bands were found to agree well with the existing theoretical results from the ab initio and tight-binding calculation. Among them, the 470 and 665 cm −1 bands appeared as the basic wavenumbers of which the multiphonon overtones were composed. The grain size effect in this strongly anisotropic system was proposed not to originate from the classical phonon confinement but rather as a result of the segmentation of one-dimensional spin chains due to doping, which in turn allowed the new vibrational modes and implied the appearance of higher overtones in the scattering spectra.

We propose the use of Fabry−Perot cavities as a means to augment the enhancement factor in surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) experiments by optical interference. Using both clean-room and bench-top fabrication approaches, we demonstrate that such a design can be readily realized and provides an additional 12× SERS enhancement and 5× TERS enhancement, in good agreement with expectations from electromagnetic modeling. The mechanism of optical interference enhancement is of far-field nature and is independent of the enhancement mechanisms relying on plasmonic and molecular resonances. Therefore, the Fabry−Perot cavity substrate can be applied generally without material and molecular limitations. The Fabry−Perot cavity structure provides enhancement at large incidence angles away from the surface normal, particularly suitable for low-light Raman measurements with side illumination.

We show that hemispherical gold droplets on top of silicon nanowires when grown by the vapor−liquid−solid (VLS) mechanism, can produce a significant enhancement of Raman scattered signals. Signal enhancement for a few or even just single gold droplets is demonstrated by analyzing the enhanced Raman signature of malachite green molecules. For this experiment, trenches (∼800 nm wide) were etched in a silicon-on-insulator (SOI) wafer along 〈110〉 crystallographic directions that constitute sidewalls ({110} surfaces) suitable for the growth of silicon nanowires in 〈111〉 directions with the intention that the gold droplets on the silicon nanowires can meet somewhere in the trench when growth time is carefully selected. Another way to realize gold nanostructures in close vicinity is to attach a silicon nanowire with a gold droplet onto an atomic force microscopy (AFM) tip and to bring this tip toward another gold-coated AFM tip where malachite green molecules were deposited prior to the measurements. In both experiments, signal enhancement of characteristic Raman bands of malachite green molecules was observed. This indicates that silicon nanowires with gold droplets atop can act as efficient probes for tip-enhanced Raman spectroscopy (TERS). In our article, we show that a nanowire TERS probe can be fabricated by welding nanowires with gold droplets to AFM tips in a scanning electron microscope (SEM). TERS tips made from nanowires could improve the spatial resolution of Raman spectroscopy so that measurements on the nanometer scale are possible.

An ultrathin aluminum oxide (Al 2 O 3) coating improves significantly the stability of plasmonic structures used in tip enhanced Raman spectroscopy (TERS). The coating does not alter the favorable optical properties of metallic structures yet improves wear resistance and inhibits degradation, so that signal enhancement remains constant over 40 days for structures with a 3 nm thick protective coating. Most unprotected structures show substantial losses in enhancement over periods as short as 10 days when stored and used in ambient conditions.

Resonant excitation of surface plasmons of a metal or metal-coated tip is crucial for achieving high enhancement of an optical signal with apertureless near-field optics. However, it remains a challenge to measure the optical spectrum of a tip with sub-wavelength dimensions. We present a technique based on total internal reflection microscopy to measure the optical properties of tips. A dependence of the optical resonance on the metal deposited is shown for silver-coated and gold-coated tips. These tips were also used to measure the tip-enhanced Raman spectra of silicon and a polymer blend of poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonate) (PEDOT/PSS) at 514.5 and 647 nm incident wavelengths. Qualitative agreement was observed between the tip-enhanced Raman spectra and the optical resonance of the tip measured with the technique developed.

This article, a part of the larger research project of Surface-Enhanced Raman Scattering (SERS), describes an advanced study focusing on the shapes and materials of Tip-Enhanced Raman Scattering (TERS) designated to serve as part of a novel imager device. The initial aim was to define the optimal shape of the “probe”: tip or cavity, round or sharp. The investigations focused on the effect of shape (hemi-sphere, hemispheroid, ellipsoidal cavity, ellipsoidal rod, nano-cone), and the effect of material (Ag, Au, Al) on enhancement, as well as the effect of excitation wavelengths on the electric field. Complementary results were collected: numerical simulations consolidated with analytical models, based on solid assumptions. Preliminary experimental results of fabrication and structural characterization are also presented. Thorough analyses were performed around critical parameters, such as the plasmonic metal—Silver, Aluminium or Gold—using Rakic model, the tip geometry—sphere, spheroid...

Structure of 4-biphenylthiolate on Au nanoparticle surfaces has been studied by UV-Vis absorption spectroscopy, transmission electron microscopy and surface-enhanced Raman scattering (SERS). 4-Biphenylthiolate is found to have a standing geometry on Au from the presence of the benzene ring CH stretching band identified at ∼3060 cm −1. The n 8a band at 1597 cm −1 in the ordinary Raman spectrum was found to split clearly into two features at 1599 and 1585 cm −1. This result suggests that orientation of the phenyl rings in 4-biphenylthiolate may be quite different and should not lie in the same plane on Au nanoparticle surfaces. On the basis of the electromagnetic enhancement factor, the dihedral angle could be estimated with a reported value of the tilt angle.