In this paper, we report our study on gold (Au) films with different thicknesses deposited on single layer graphene (SLG) as surface enhanced Raman scattering (SERS) substrates for the characterization of rhodamine (R6G) molecules. We find that an Au film with a thickness of ~7 nm deposited on SLG is an ideal substrate for SERS, giving the strongest Raman signals for the molecules and the weakest photoluminescence (PL) background. While Au films effectively enhance both the Raman and PL signals of molecules, SLG effectively quenches the PL signals from the Au film and molecules. The former is due to the electromagnetic mechanism involved while the latter is due to the strong resonance energy transfer from Au to SLG. Hence, the combination of Au films and SLG can be widely used in the characterization of low concentration molecules with relatively weak Raman signals.
We report a study of long-range MoS2-substrate interaction using resonant Raman imaging. We observed a strong thickness-dependent peak shift of a Raman-forbidden mode that can be used as a new method of determining the thickness of multilayered MoS2 flakes. In addition, dependence of the Raman scattering intensity on thickness is explained by the interference enhancement theory. Finally, the resonant Raman spectra on different substrates are analysed.
We have investigated ten standard single crystal substrates of complex oxides on the account of their applicability in the Raman spectroscopy based thin film research. In this study we suggest a spectra normalization procedure that utilizes a comparison of the substrate Raman spectra to those of well-established Raman reference materials. We demonstrate that MgO, LaGaO3, (LaAlO3)_0.3(Sr2AlTaO6)_0.7 (LSAT), DyScO3, YAlO3, and LaAlO3 can be of potential use for a Raman based thin film research. At the same time TiO2 (rutile), NdGaO3, SrLaAlO4, and SrTiO3 single crystals exhibit multiple phonon m…
Gold nanoflowers are known for their use as efficient host for surface enhanced Raman scattering of organic dye molecules. In this article, gold nanoflowers have been synthesised and rhodamine 6 G (R6G) molecules have been used as probe molecules. It is found that the gold nanoflowers can detect the presence of R6G molecules upto 10^{-10} M. The petals of these nanoflowers play an important role for the enhancement of Raman signals, and the intensity of Raman signals is enhanced many folds in presence of gold nanoflowers - the enhancement factor is of the order of 10^6. This is explained in te…
We investigated 10 to 200 nm thick black phosphorus flakes on SiO2/Si and polyimide substrates by Angle-resolved Polarized Raman spectra (ARPRS) using 442 nm excitation wavelength. The results revealed that ARPRS with 442 nm excitation can provide unambiguous, convenient, non-destructive and fast determination of BP's crystallographic orientation. The substrate and thickness dependencies of Raman spectra and Raman tensor elements were studied. These dependencies were shown to be influenced by Raman excitation laser heating effect. By comparing with in-situ Raman measurements at elevated temper…
The fabrication of epitaxial graphene (EG) on SiC substrate by annealing has attracted a lot of interest as it may speed up the application of graphene for future electronic devices. The interaction of EG and the SiC substrate is critical to its electronic and physical properties. In this work, Raman spectroscopy was used to study the structure of EG and its interaction with SiC substrate. All the Raman bands of EG blue shift from that of bulk graphite and graphene made by micromechanical cleavage, which was attributed to the compressive strain induced by the substrate. A model containing 13 x…
The on-surface synthesis of graphene nanoribbons (GNRs) allows for the fabrication of atomically precise narrow GNRs. Despite their exceptional properties which can be tuned by ribbon width and edge structure, significant challenges remain for GNR processing and characterization. In this contribution, we use Raman spectroscopy to characterize different types of GNRs on their growth substrate and to track their quality upon substrate transfer. We present a Raman-optimized (RO) device substrate and an optimized mapping approach that allows for acquisition of high-resolution Raman spectra, achiev…
In this work, ZnO nanowire arrays decorated with titanium nitride (TiN) nanoparticles as surface enhanced Raman scattering (SERS) substrates is demonstrated. ZnO nanowires were grown by hydrothermal synthesis while ~100 nm TiN nanoparticles were obtained by grinding commercial powders for several hours. They were then decorated on the ZnO nanowire arrays using acetone as the medium. Scanning electron microscopy confirmed the presence of TiN nanoparticles on the ZnO nanowires. TiN nanoparticles exhibited localized surface plasmon resonances at 430, 520 and 600 nm. SERS experiments using Nile Bl…
Atomically thin boron nitride (BN) nanosheets have been found an excellent substrate for noble metal particles enabled surface enhanced Raman spectroscopy (SERS), thanks to their good adsorption of aromatic molecules, high thermal stability and weak Raman scattering. Faceted gold (Au) nanoparticles have been synthesized on BN nanosheets by a simple but controllable and reproducible sputtering and annealing method. The size and density of the Au particles can be controlled by sputtering time, current and annealing temperature etc. Under the same sputtering and annealing conditions, the Au parti…
Nanoscale step structures have attracted recent interest owing to their importance in both fundamental and applied research, for example in adsorption, in catalysis, and in directing nanowire growth. Here, we used a template-stripping method to obtain vicinal-like surface structures on grains of polycrystalline gold and investigated the effect of annealing temperature on the formation of these surfaces.
Nanofibers functionalized by metal nanostructures and particles are exploited as effective flexible substrates for SERS analysis. Their complex three-dimensional structure may provide Raman signals enhanced by orders of magnitude compared to untextured surfaces. Understanding the origin of such improved performances is therefore very important for pushing nanofiber-based analytical technologies to their upper limit. Here we report on polymer nanofiber mats which can be exploited as substrates for enhancing the Raman spectra of adsorbed probe molecules. The increased surface area and the scatte…
Chemically synthesized single-crystalline gold microplates have been attracting increasing interests because of their potential as high-quality gold films for nanotechnology. We present the growth of tens of nanometer thick and tens of micrometer large single-crystalline gold plates directly on solid substrates by solution-phase synthesis. Compared to microplates deposited on substrates from dispersion phase, substrate-grown plates exhibit significantly higher quality by avoiding severe small-particle contamination and aggregation. Substrate-grown gold plates also open new perspec-tives to stu…
Raman studies of nanocomposite SiCN thin film by sputtering showed that with an increase of substrate temperature from room temperature to 500oC, a transition from mostly sp2 graphitic phase to sp3 carbon took place which was observed from the variation of ID/IG ratio and the peak shifts. This process resulted in the growth of C3N4 and Si3N4 crystallites in the amorphous matrix which led to an increase in hardness and modulus obtained through nanoindentation. However, at a further higher temperature of 600oC, again an increase of sp2 C concentration in the film was observed and the H and E val…
We study the optical properties of a single, semiconducting single-walled carbon nanotube (CNT) that is partially suspended across a trench and partially supported by a SiO2-substrate. By tuning the laser excitation energy across the E33 excitonic resonance of the suspended CNT segment, the scattering intensities of the principal Raman transitions, the radial breathing mode (RBM), the G-mode and the D-mode show strong resonance enhancement of up to three orders of magnitude. In the supported part of the CNT, despite a loss of Raman scattering intensity of up to two orders of magnitude, we reco…
We synthesized three-dimensional nanoporous graphene films by a chemical vapor deposition method with nanoporous copper as a catalytic substrate. The resulting nanoporous graphene has the same average pore size as the underlying copper substrate. Our surface-enhanced Raman scattering (SERS) investigation indicates that the nanoporosity of graphene significantly improves the SERS efficiency of graphene as a substrate as compared to planar graphene substrates.
We quantitatively study the Raman and photoluminescence (PL) emission from single layer molybdenum disulfide (MoS2) on dielectric (SiO2, hexagonal boron nitride, mica and the polymeric dielectric Gel-Film) and conducting substrates (Au and few-layer graphene). We find that the substrate can affect the Raman and PL emission in a twofold manner. First, the absorption and emission intensities are strongly modulated by the constructive/destructive interference within the different substrates. Second, the position of the A1g Raman mode peak and the spectral weight between neutral and charged excito…
The interaction of thioglycolic acid with the Au(111) surface is investigaged, and it is found that at the low coverage the molecule lies down on the substrate. If the mercaptan-hydrogen atom is eliminated, the resulting SCH_2COOH molecule is randomly oriented on the surface. If the carboxylic acid group in the HSCH_2COOH molecule is deprotonated instead, the HSCH_2COO^ molecule lies down on the surface. However, when the mercaptan-hydrogen atom in the HSCH_2COO^- molecule is removed, the resulting SCH_2COO^- molecule rises up to a certain level on the substrate. The calculated Raman vibration…
Synthesis and characterization of high-quality single-crystal WSe2 films on highly-insulating substrate is presented. We demonstrate for the first time that the presence of gold nanoparticles in the basal plane of a WSe2 film can enhance its Raman scattering intensity. The experimentally observed enhancement ratio in the Raman signal correlates well with the simulated electric field intensity using a three-dimensional electromagnetic software and theoretical calculation. This work provides guidelines for the use of two-dimensional WSe2 films as a SERS substrate.
In this paper we used Raman spectroscopy to investigate the optical properties of vanadium dioxide (VO2) thin films during the thermally induced insulating to metallic phase transition. We observed a significant difference in transition temperature in similar VO2 films grown on quartz and sapphire substrates: the film grown on quartz displayed the phase transition at a lower temperature (Tc=50C) compared a film grown on sapphire (Tc=68C). We also investigated differences in the detected Raman signal for different wavelengths and polarizations of the excitation laser. We found that for either s…
We demonstrate the possibility in quantifying the Raman intensities for both specimen and substrate layers in a common stacked experimental configuration and, consequently, propose a general and rapid thickness identification technique for atomic-scale layers on dielectric substrates. Unprecedentedly wide-range Raman data for atomically flat MoS2 flakes are collected to compare with theoretical models. We reveal that all intensity features can be accurately captured when including optical interference effect. Surprisingly, we find that even freely suspended chalcogenide few-layer flakes have a…
The room-temperature Raman signatures from graphene layers on sapphire and glass substrates were compared with those from graphene on GaAs substrate and on the standard Si/SiO2 substrate, which served as a reference. It was found that while G peak of graphene on Si/SiO2 and GaAs is positioned at 1580 cm-1 it is down-shifted by ~5 cm-1 for graphene-on-sapphire (GOS) and, in many cases, splits into doublets for graphene-on-glass (GOG) with the central frequency around 1580 cm-1. The obtained results are important for graphene characterization and its proposed graphene applications in electronic …
Trisoctahedral (TOH) shaped Au nanocrystals (NCs) have emerged as a new class of metal nanoparticles (MNP) due to its superior catalystic and SERS activities caused by the presence of high density atomic steps and dangling bonds on their high index facets. We examine the radiative localized surface plasmon resonance (LSPR) modes of an isolated single TOH Au NC using cathodoluminescence (CL), with high resolution spatial information of the local density of optical states (LDOS) across the visible spectral range. Further we show pronounced enhancement factor in the Raman scattering by performing…
Gold is widely used as the substrate material in many graphene devices, due to its superior optoelectronic properties and chemical stability. However, there has been little experimental investigation on the optical contrast of graphene films on Au substrates. Here we report accurate measurement of the optical contrast spectra of few-layer graphene flakes on bulk Au. We used a high-resolution optical microscopy with a 100x magnification objective, accurately determining the thickness of flakes as small as one micrometer in lateral size, which are highly desired in many applications. The results…
Graphene has extraordinary mechanical and electronic properties, making it a promising material for membrane based nanoelectromechanical systems (NEMS). Here, chemical-vapor-deposited graphene is transferred onto target substrates to suspend it over cavities and trenches for pressure-sensor applications. The development of such devices requires suitable metrology methods, i.e., large-scale characterization techniques, to confirm and analyze successful graphene transfer with intact suspended graphene membranes. We propose fast and noninvasive Raman spectroscopy mapping to distinguish between fr…
Raman spectra of LCMO films grown on LAO (001), STO (001), and MgO (001) substrates were studied at different temperatures. The effect of temperature, doping level and strain on Raman spectra are discussed in detail. With decreasing temperature, the changes of Raman spectra are correlated with the disorder-order transition, shuch as: paramagnetism to ferromagnetism, and charge-ordering. The strain induced by lattice-substrate mismatch affects the Raman spectra strongly. The mode induced by disorder of oxygen defects is apparently observed in $La_{0.67}Ca_{0.33}MnO_3$ film on STO due to the lar…
A simple, non-invasive method using Raman spectroscopy for the estimation of the thickness of graphene layers grown epitaxially on silicon carbide (SiC) is presented, enabling simultaneous determination of thickness, grain size and disorder using the spectra. The attenuation of the substrate Raman signal due to the graphene overlayer is found to be dependent on the graphene film thickness deduced from X-ray photoelectron spectroscopy and transmission electron microscopy of the surfaces. We explain this dependence using an absorbing overlayer model. This method can be used for mapping graphene …
Surface-enhanced Raman spectroscopy (SERS) demands reliable, high enhancement substrates in order to be used in different fields of application. Here, we introduce freestanding porous gold membranes (PAuM) as easy to produce, scalable, mechanically stable, and effective SERS substrates. We fabricate large-scale sub-30 thick PAuM, that form freestanding membranes with varying morphologies depending on the nominal gold thickness. These PAuM are mechanically stable for pressures up to $>3$ bar, and exhibit surface-enhanced Raman scattering with local enhancement factors of $10^4$ to $10^5$, which…
The graphene-enhanced Raman scattering of Rhodamine 6G molecules on pristine, fluorinated and 4-nitrophenyl functionalized graphene substrates was studied. The uniformity of the Raman signal enhancement was studied by making large Raman maps. The relative enhancement of the Raman signal is demonstrated to be dependent on the functional groups, which was rationalized by the different doping levels of pristine, fluorinated and 4-nitrophenyl functionalized graphene substrates. The impact of the Fermi energy of graphene and the phonon energy of the molecules was considered together for the first t…
The responsive behavior of methanethiol and methylthiolate molecules on the Au(111) surface with an applied electrical potential is studied, and it is shown how the sulfur adsorption site, the S-H bond orientation and the interacting energy change with an external electric field strength. The electron charge density corresponding to an electric field minus that obtained in zero field, with zero-field optimal geometry, is calculated to explain the responsive behavior. The interacting energy for the intact methanethiol adsorption is larger than that for the dissociative one, showing that an exte…
Raman spectroscopic studies of graphene have attracted much interest. The G-band Raman intensity of a single layer graphene on Si substrate with 300 nm SiO2 capping layer is surprisingly strong and is comparable to that of bulk graphite. To explain this Raman intensity anomaly, we show that in addition to the interference due to multiple reflection of the incident laser, the multiple reflection of the Raman signal inside the graphene layer must be also accounted for. Further studies of the role of SiO2 layer in the enhancement Raman signal of graphene are carried out and an enhancement factor …
We show the evolution of Raman spectra with number of graphene layers on different substrates, SiO$_{2}$/Si and conducting indium tin oxide (ITO) plate. The G mode peak position and the intensity ratio of G and 2D bands depend on the preparation of sample for the same number of graphene layers. The 2D Raman band has characteristic line shapes in single and bilayer graphene, capturing the differences in their electronic structure. The defects have a significant influence on the G band peak position for the single layer graphene: the frequency shows a blue shift upto 12 cm$^{-1}$ depending on th…
Graphene was deposited on a transparent and flexible substrate and tensile strain up to ~0.8% was loaded by stretching the substrate in one direction. Raman spectra of strained graphene show significant redshifts of 2D and G band (-27.8 cm^-1 and -14.2 cm^-1per 1% strain, respectively), because of the elongation of the carbon-carbon bonds. This indicates that uniaxial strain has been successfully applied on graphene. We also proposed that by applying uniaxial strain on graphene, tunable bandgap at K point can be realized. First principle calculations predicted a bandgap opening of ~300 meV for…
Thin films of gold were deposited on single crystalline CaF2 substrates of (100) and (111) orientation by thermal evaporation. The resulting film structure was analyzed by means of atomic force microscopy in dependence of substrate temperature and deposition thickness. A marked substrate dependency was found. On CaF2 (100), extended and flat plateaus with diameters of several hundreds of nanometers form in a network-like arrangement for deposition thicknesses between 30 and 45 nm. On CaF2 (111), closed films of small average roughness develop at film thicknesses between 70 and 90 nm. These fil…
Measurements and calculations have shown significant disagreement regarding the sign and variations of the thermal expansion coefficient (TEC) of graphene $α(T)$. Here we report dedicated Raman scattering experiments conducted for graphene monolayers deposited on silicon nitride substrates and over the broad temperature range 150--900~K. The relation between those measurements for the G band and the graphene TEC, which involves correcting the measured signal for the mismatch contribution of the substrate, is analyzed based on various theoretical candidates for $α(T)$. Contrary to calculations …
The pressure evolution of the Raman spectrum of graphene grown by chemical vapour deposition on polycrystalline copper is investigated with the use of a polar and a non-polar pressure transmitting medium (PTM). The G and 2D Raman bands exhibit similar pressure slopes for both PTM irrespectively of any unintentional initial doping and/or strain of the samples. Our analysis suggests that any pressure-induced charge transfer effects are negligibly small to influence the pressure response of graphene. This is determined by the mechanical stress due to the pressure-induced substrate contraction and…
Tip-enhanced Raman spectroscopy (TERS) has reached nanometer spatial resolution for measurements performed at ambient conditions and sub-nanometer resolution at ultra high vacuum. Super-resolution (beyond the tip apex diameter) TERS has been obtained, mostly in the gap mode configuration, where a conductive substrate localizes the electric fields. Here we present experimental and theoretical TERS to explore the field distribution responsible for spectral enhancement. We use gold tips of $40\pm 10 \ \text{nm}$ apex diameter to measure TERS on graphene, a spatially delocalized two-dimensional sa…
GaN-nanorods grown on Si(111) substrates are found strain- and defect-free as characterized by micro Raman spectroscopy, secondary electron (SE) and cathode-luminescence (CL) imaging. The matrix supporting the nanorods bears the brunt of all strains, strain-relaxations, and defect generations, giving the nanorods an ideal environment to grow to perfection. Photo-excitations by the Raman laser source and electron irradiation during CL imaging lead to an increase of non-equilibrium electrons, suggesting an effective approach to photo-emitting or field emitting device applications. The nanorods, …
Under the challenge of growing a single bilayer of Bi oriented in the (111) crystallographic direction over amorphous substrates, we have studied different thicknesses of Bi thermally evaporated onto silicon oxide in order to shed light on the dominant atomic structures and their oxidation. We have employed atomic force microscope, X-ray diffraction, and scanning electron microscope approaches to demonstrate that Bi is crystalline and oriented in the (111) direction for thicknesses over 20 nm. Surprisingly, Raman spectroscopy indicates that the rhombohedral structure is preserved even for ultr…
Graphene has many unique properties that make it an ideal material for fundamental studies as well as for potential applications. Here we review the recent results on the Raman spectroscopy and imaging of graphene. Raman spectroscopy and imaging can be used as a quick and unambiguous method to determine the number of graphene layers. Following, the strong Raman signal of single layer graphene compared to graphite is explained by an interference enhancement model. We have also studied the effect of substrates, the top layer deposition, the annealing process, as well as folding (stacking order) …
Single-walled carbon nanotubes (SWNTs) have been coated with gold and platinum nanoparticles either by microwave treatment or by the click reaction and the Raman spectra of these SWNT-metal nanoparticle composites have been investigated. Analysis of the G bands in the Raman spectra shows an increase in the proportion of metallic SWNTs on attachment with metal nanoparticles. This conclusion is also supported by the changes observed in the RBM bands. Ab-initio calculations reveal that semiconductor-metal transition occurs in SWNTs due to Columbic charge transfer between the metal nanoparticles a…
The programmable assembly of DNA strands is a promising tool for building tailored bottom-up nanostructures. Here, we present a plasmonic nanosystem obtained by the base-pairing mediated aggregation of gold nanoparticles (NPs) which are separately functionalized with two different single-stranded DNA chains. Their controlled assembly is mediated by a complementary DNA "bridge" sequence. We monitor the formation of DNA assembled NP aggregates in solution, and we study their Surface Enhanced Raman Scattering (SERS) response by comparison with the single NP constituents. We interpret the revealed…
We report a joint study, using Raman micro-spectroscopy and molecular dynamics simulations, on the substrate effect on thermal properties of 2D materials and revisit measurement of thermal expansion coefficient (TEC) of supported 2D film. Graphene is employed as a representative. We find that the out-of-plane coupling between graphene and substrate strongly affects the temperature-dependent vibrational modes and TEC of graphene. Density of states for long-wavelength out-of-plane oscillations is significantly reduced when graphene is supported on an alkane substrate. To account for the contribu…
The application of graphene in electronic devices requires large scale epitaxial growth. The presence of the substrate, however, usually reduces the charge carrier mobility considerably. We show that it is possible to decouple the partially sp3-hybridized first graphitic layer formed on the Si-terminated face of silicon carbide from the substrate by gold intercalation, leading to a completely sp2-hybridized graphene layer with improved electronic properties.
Cr2Ge2Te6 has been of interest for decades, as it is one of only a few ferromagnetic insulators. Recently, this material has been revisited due to its potential as a substrate for Bi2Te3, a topological insulator. This enables the possibility of studying the anomalous quantum Hall effect in topological insulators, and a route to novel spintronic devices. To probe the compatibility of these two materials, we use polarized variable temperature Raman microscopy to study Bi2Te3-Cr2Ge2Te6 heterostructure as well as the phonon dynamics of Cr2Ge2Te6. We found the temperature dependence of the Cr2Ge2Te…
We study the role of gold droplets in the initial stage of nanowire growth via the vapor liquid solid method. Apart from serving as a collections center for growth species, the gold droplets carry an additional crucial role that necessarily precedes the nanowire emergence, that is, they assist the nucleation of nanocraters with strongly faceted 111B side walls. Only once these facets become sufficiently large and regular, the gold droplets start nucleating and guiding the growth of nanowires. We show that this dual role of the gold droplets can be detected and monitored by high energy electron…
We present theoretical calculations for the absorption properties of protein-coated gold nanoparticles on graphene and graphite substrates. As the substrate is far away from nanoparticles, numerical results show that the number of protein bovine serum molecules molecules aggregating on gold surfaces can be quantitatively determined for gold nanoparticles with arbitrary size by means of the Mie theory and the absorption spectra. The presence of graphitic substrate near protein-conjugated gold nanoparticles substantially enhances the red shift of the surface plasmon resonances of the nanoparticl…
Graphene devices require electric contacts with metals, particularly with gold. Scanning tunneling spectroscopy studies of electron local density of states performed on mono-, bi- and tri- graphene layer deposited on metallic conductive Au/Cr/SiO2/Si substrate shows that gold substrate causes the Fermi level shift downwards which means that holes are donated by metal substrate to graphene which becomes p-type doped. These experimental results are in good accordance with recently published density function theory calculations. The estimated positions of the Dirac point show that the higher numb…
Enhanced diffusion of gold atoms into silicon substrate has been studied in Au thin films of various thicknesses (2.0, 5.3, 10.9 and 27.5 nm) deposited on Si(111) and followed by irradiation with 1.5 MeV Au2+ at a flux of 6.3x10^12 ions cm-2 s-1 and fluence up to 1x10^15 ions cm-2. The high resolution transmission electron microscopy measurements showed the presence of gold silicide formation for the above-mentioned systems at fluence greater than equal to 1x1014 ions cm-2. The maximum depth to which the gold atoms have been diffused at a fluence of 1x10^14 ions cm-2 for the cases of 2.0, 5.3,…
Two-dimensional (2D) materials, such as graphene and MoS2, have been attracting wide interest in surface enhancement Raman spectroscopy. This perspective gives an overview of recent developments in 2D materials' application in surface enhanced Raman spectroscopy. This review focuses on the applications of using bare 2D materials and metal/2D material hybrid substrate for Raman enhancement. The Raman enhancing mechanism of 2D materials will also be discussed. The progress covered herein shows great promise for widespread adoption of 2D materials in SERS application.
Gold-mediated exfoliation of MoS2 has attracted considerable interest in the recent years. A strong interaction between MoS2 and Au facilitates preferential production of centimeter-sized monolayer MoS2 with near-unity yield and provides a heterostructure system noteworthy from a fundamental standpoint. However, little is known about the detailed nature of the MoS2-Au interaction and its evolution with the MoS2 thickness. Here, we identify specific vibrational and binding energy fingerprints of such strong interaction using Raman and X-ray photoelectron spectroscopy, which indicate substantial…
The present approach to SERS does not rely on a hihj electrical conductivity substrate or admixture to enable the SERS process. The novelty of our method is to create an artificial periodic electron distribution on a surface by illumination with ultraviolet radiation whose photon energy is above the photoelectric work function of the material.
We have studied electric-field-induced symmetry lowering in the tetragonal (001)-oriented heteroepitaxial (Ba$_{0.8}$Sr$_{0.2}$)TiO$_3$ thin film deposited on (001)MgO substrate. Polarized micro-Raman spectra were recorded from the film area in between two planar electrodes deposited on the film surface. Presence of \textit{c}-domains with polarization normal to the substrate was confirmed from polarized Raman study under zero field, while splitting and hardening of the \textit{E}(TO) soft mode and polarization changes in the Raman spectra suggest monoclinic symmetry under external electric fi…
We report on preparation dependent properties observed in monolayer WS2 samples synthesized via chemical vapor deposition (CVD) on a variety of common substrates (Si/SiO2, sapphire, fused silica) as well as samples that were transferred from the growth substrate onto a new substrate. The as-grown CVD materials (as-WS2) exhibit distinctly different optical properties than transferred WS2 (x-WS2). In the case of CVD growth on Si/SiO2, following transfer to fresh Si/SiO2 there is a ~50 meV shift of the ground state exciton to higher emission energy in both photoluminescence emission and optical r…
The gold-assisted exfoliation is a very effective method to produce large-area ($cm^2$-scale) membranes of molybdenum disulfide ($MoS_2$) for electronics. However, the strong $MoS_2/Au$ interaction, beneficial for the exfoliation process, has a strong impact on the vibrational and light emission properties of $MoS_2$. Here, we report an atomic force microscopy (AFM), micro-Raman ($μ-R$) and micro-Photoluminescence ($μ-PL$) investigation of $MoS_2$ with variable thickness exfoliated on Au and subsequently transferred on an $Al_2O_3/Si$ substrate. The $E_{2g}$ - $A_{1g}$ vibrational modes separa…
We present a graphene/Cu nanoparticle hybrids (G/CuNPs) system as a surface-enhanced Raman scattering (SERS) substrate for adenosine detection. The Cu nanoparticles wrapped around a monolayer graphene shell were directly synthesized on flat quartz by chemical vapor deposition in a mixture of methane and hydrogen. The G/CuNPs showed an excellent SERS enhancement activity for adenosine. The minimum detected concentration of the adenosine in serum was demonstrated as low as 5 nM, and the calibration curve showed a good linear response from 5 to 500 nM. The capability of SERS detection of adenosin…
The use of Raman scattering techniques to study the mechanical properties of graphene films is reviewed here. The determination of Gruneisen parameters of suspended graphene sheets under uni- and bi-axial strain is discussed and the values are compared to theoretical predictions. The effects of the graphene-substrate interaction on strain and to the temperature evolution of the graphene Raman spectra are discussed. Finally, the relation between mechanical and thermal properties is presented along with the characterization of thermal properties of graphene with Raman spectroscopy.
