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Surface-enhanced Raman scattering (SERS) is a very promising detection/diagnostic technique at trace levels as the molecules exhibit a significant increase in their Raman signals when they are attached or are in proximity to plasmonic structures. In this study, a numerical design of SERS substrate as a probe has been demonstrated for detection and diagnosis of blood, water and urea samples. The proposed nanospiral design is polarization independent, and it offers the enhancement of the electric field strength ~ 109. The substrate design is based on 3D finite difference time domain simulations and is robust, versatile and sensitive even at low concentrations of the analyte. It works equally well when used in the reflection mode. In this study, the cavity quantum electrodynamics (CQED) Purcell factor has also been transposed to plasmonics. The Purcell factor in corroboration with CQED has been used to achieve efficient light–matter interaction at nanoscale by providing a more realistic result. It takes into account the randomness of incident wave polarizations and arbitrary orientations of interacting molecules. This gives a deeper insight into electromagnetic Raman gain in SERS and can be used to design novel SERS substrates.

Surface-enhanced Raman spectroscopy (SERS) is a surface sensitive technique which gives enhanced Raman signal intensity of the molecules by roughening metal surfaces. It can be used to detect trace amounts of analysts including heavy metals, pesticides, explosives, proteins and different biological and chemical contaminants. In this paper, we report a facile approach to synthesise highly nano-crystalline and homogeneous plasmonic wave guide of silver nanowires (Ag-NWs) by polyol method. Morphology of the synthesised Ag-NWs has been characterised using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques and suggests the homogenous formation of nanowires with an average diameter of 400–450 nm and 15–25 µm of length. Surface-enhanced Raman spectroscopy (SERS) of single-walled carbon nanotube (SWNT) when it is coupled with Ag-NW suggests that the enhancement factor is as high as ~ 103 and ~ 102 for the characteristic Raman signals (G-peak and radial breathing modes, respectively). Using numerical method of finite difference time domain (FDTD), it is shown that the enhancement depends on the orientation of the SWNTs with respect to the Ag-NWs and is maximum (~ 107) when they are at 45° to each other. The proposed approach provides an effective, reproducible and facile method for preparing high-quality SERS substrates for remote optical excitation in plasmonic devices.

Surface-enhanced Raman scattering (SERS) has emerged as a sensitive and established spectroscopic technique for trace detection in various fields including chemistry, material science, biochemistry, and life sciences. With the rapid progress in nano-fabrication scheme, design of SERS substrate has immensely contributed in the development of biological and biomedical sensors, detectors for explosives and narcotics, besides other applications. The electromagnetic enhancement, which majorly contributes to the SERS phenomena, is enabled by the fabrication of nanostructured substrates with high enhancement factor. The enhancement factor depends on the shape, size, and orientation of the nanostructure pattern. Here, we present a new design that ensures high enhancement factor (~ 107), is polarization independent, robust with respect to various geometrical parameters and excitation wavelength. It can be easily implemented in reflection mode configuration and is spread over a hotspot region of ~ 3200 nm2 (in each periodic unit of the array), yielding an overall emission efficiency of 0.12%. The proposed design can be realized for various SERS applications due to ease of its fabrication using standard techniques.

Raman spectroscopy technique is potentially utilized to identify the chemical bonding in molecules or solids and doping in semiconducting materials. Even different forms of carbon materials could also be identified by this technique. Raman Spectroscopy helps in determining the size and conductivity of nanoscale system with high precision. The contents of this chapter include as follows: Sect. 11.2 describes the sample preparation method and instrumentation of confocal scanning microscopy which deals with the recording of Raman spectra of individual nanostructures. Section 11.3 discusses the geometrical structure, electronic band structure, phonon properties, and Raman spectra of single-walled carbon nanotubes (SWNTs). The Raman scattering of multi-walled carbon nanotubes (MWNTs) has also been discussed in Sect. 11.3. Section 11.3 presents the discussion on phonon properties and Raman scattering of graphene. In Sect. 11.5, the basic mechanism of surface-enhanced Raman spectroscopy (SERS) and its application to probe individual molecules are given. In Sect. 11.4, the momentum mapping of Raman scattering of individual nanostructures in the presence of optical nanoantenna is presented. Finally, in Sect. 11.7, summary and future aspects of this chapter is elaborated for the upcoming developments in the field of Raman scattering of nanostructures.

High quality single crystalline CuV2O6 (CVO) nanowires were successfully grown on the silicon substrates by simple thermal annealing of spin coated film in air. The synthesized nanowires have an average diameter of 100 nm, and length ranges between 1 and 5 μm, with growth direction along . We found that growth temperature play a vital role in controlling the phase and the diameter of nanowires in this process. We propose a growth mechanism based on the experimental results. Field emission properties were revealed to be strongly morphology dependent. The nanowires in small diameter and high aspect ratio exhibited the best FE performance showing excellent field emission current densities 1.2 mA cm−2 with a low turn-on field of ∼1.2 V μm−1. The experimental results show that CVO nanowires are promising candidate in realizing high performance field emission display.

Here we report the role of ion irradiation in the field emission characteristics of aligned multiwalled carbon nanotubes (MWNTs). Aligned MWNTs show improvement in field emission characteristics under low dose 70 Mev Ni6+ ion irradiation. But field emission current density reduces for the higher dose due to adsorption of amorphous carbon and melting as well damage of carbon nanotubes (CNTs). High resolution transmission electron microscopic (HRTEM) analysis has been carried out to find the morphological changes due to ion irradiation leading to modifications in field emission characteristics. At low dose formation of dangling bond, cross-linking between different layers, exposure of buried emission sites and reduction of mutual shielding are responsible for the enhancement in field emission characteristics.

SWCNT was synthesized by catalytic thermal CVD using Fe–Mo and Co–Mo bimetallic catalysts supported by MgO . The nanotubes were studied by SEM and HRTEM microscopy, thermogravimetric analysis, and Raman spectroscopy. The chiralities of the tubes were established from their Raman spectra using Kataura plot. The Raman shifts for the Co-catalyzed nanotubes were found to lie in the semiconducting region.

Nanostructures based on multiwalled carbon nanotubes (MWNTs) are fabricated using plasma of the mixture of hydrogen and nitrogen gases. The plasma-sharpened tips of nanotubes contain only a few tubes at the apex of the structure and lead to the dramatic enhancement in the emission current density by a factor >10(6) with the onset field as low as 0.16 V/mu m. We propose that the nature of the tunneling barrier changes significantly for a nanosize tip at very high local electric field and may lead to the saturation in the emission current density.

We report here, a detailed study of the parameter window of the deposition pressures to grow the diamond films on GaN coated quartz substrates using microwave plasma deposition technique. Hexagonal GaN films of 5 µm coated on quartz are used as substrates for diamond deposition in the pressure range of 80–140 Torr, using microwave plasma chemical vapor deposition (MPCVD) technique. The diamond films are characterized by scanning electron microscopy, XRD, photoluminescence and Raman spectroscopy. Scanning electron microscope image shows that the nucleation density of the films is high and we can deposit a continuous film for a deposition time ranging for 6–8 h. Oriented growth of diamond has been observed at higher pressure.

The nitrogen doped multiwalled carbon nanotubes (MWNTs) were synthesized by microwave plasma chemical vapor deposition (MPCVD) technique. In this paper, we report the results of FTIR, Raman, and TGA studies to confirm the presence of N-doping inside carbon nanotubes. Fourier transform infrared (FTIR) studies were carried out in the range 400-4000 cm(-1) to study the attachment of nitrogen impurities on carbon nanotubes. FTIR spectra of the virgin sample of MWNTs show dominant peaks which are corresponding to Si-O, C-N, N-CH3, CNT, C-O, and C-Hx, respectively. The Si-O peak has its origin in silicon substrate whereas the other peaks are due to the precursor gases present in the gas mixture. The peaks are sharp and highly intense showing the chemisorption nature of the dipole bond. The intensity of the peaks due to N-CH3, C-N, and C-H reduces after annealing. It is interesting to note that these peaks vanish on annealing at high temperature (900 degrees C). The presence of C-N peak may imply the doping of the MWNTs with N in substitution mode. The position of this intense peak is in agreement with the reported peak in carbon nitride samples prepared by plasma CVD process, since the Raman modes are also expected to be delocalized over both carbon and nitrogen sites it was found that the intensity ratio of the D and G peaks, I(D)/I(G), varies as a function of ammonia concentration. The TGA measurements, carried out under argon flow, show that the dominant weight loss of the sample occurs in the temperature range 400-600 degrees C corresponding to the removal of the impurities and amorphous carbon.

Single crystal diamond films of varying quality are deposited using microwave plasma chemical vapor deposition (MPCVD) apparatus. Unpolished natural diamond seeds are used as substrates in the temperature (Ts) range 850–1200 °C. The gas mixture of methane (CH4), hydrogen (H2) and oxygen (O2) is used for the deposition of diamond. The deposition pressure is varied in the range 90 to 150 Torr. The films are characterized using scanning electron microscopy (SEM), Atomic force microscopy (AFM) and Raman spectroscopy techniques. The growth morphology of the films is found to be a sensitive function of the deposition parameters. The crystalline nature of the films change from polycrystalline to single crystal as we increase Ts and for a certain set of parameters the filamentary growth of the diamond crystals can be seen. The films are polycrystalline in the range of substrate temperatures 850–900 °C and oriented grains of diamond crystals are evident as the Ts increases. The single crystal diamond growth is observed to proceed via the step growth mechanism with the evidence of bunching of the steps. Our study explores evolution of the growth of single crystal diamond in a wide range of parameters.

We perform momentum mapping of the Raman scattering of individual single-walled carbon nanotubes (SWNTs) or thin ropes of SWNTs enhanced by surface plasmons sustained by either a linear chain of nanoantennas or flower-shaped nanoparticles. The momentum spectroscopy of Raman scattering of the carbon nanotube (CNT) demonstrates the direct verification of momentum selection rules and identifies the characteristic bands of the molecules or the nanomaterials under scrutiny. The characteristic vibrational signatures of the D, G−, and G bands provide an isotropic response in k-space irrespective of the arrangement of the enhancing platform. However, other dispersive or double resonance bands, such as D−, D+, D′, M, and iTOLA bands appear as a dipolar emission oriented towards the long axis of the CNT regardless of the CNT orientation but strongly depend on the patterning of enhancement of the electromagnetic field.

We investigate charge transport in a chemically reduced graphene oxide (RGO) film of sub-micron thickness. The I-V curve of RGO film shows current switching of the order of ∼10(5) above the threshold voltage. We found that the observed I-V curve is consistent with quantum tunnelling based charge transport. The quantum tunnelling based Simmons generalized theory was used to interpret the charge transport mechanism which shows that the current switching phenomenon is associated with transition from direct to Fowler-Nordheim (F-N) tunneling. The absence of current switching in the I-V curve after stripping away the oxygen functional groups from chemically RGO film confirms that the presence of these groups and reduced interaction between adjacent layers of RGO play a key role in charge transport. Such metal-based current switching devices may find applications in graphene-based electronic devices such as high voltage resistive switching devices.

Detection of explosive residues using portable devices for locating landmine and terrorist weapons must sat- isfy the application criteria of high reproducibility, specificity, sensitivity and fast response time. Vibrational spectroscopies such as Raman and infrared spectroscopies have demonstrated their potential to distinguish the members of the chemical family of more than 30 explosive materials. The characteristic chemical fingerprints in the spectra of these explosives stem from the unique bond structure of each compound. However, these spectroscopies, developed in the early sixties, suffer from a poor sensitivity. On the contrary, MEMS-based chemical sensors have shown to have very high sensitivity lowering the detection limit down to less than 1 picogram, (namely 10 part per trillion) using sensor platforms based on microcantilevers, plasmonics, or surface acoustic waves. The minimum amount of molecules that can be detected depends actually on the transducer size. The selectivity in MEMS sensors is usually realized using chemical modification of the active surface. However, the lack of sufficiently selective receptors that can be immobilized on MEMS sensors remains one of the most critical issues. Microcantilever based sensors offer an excellent opportunity to combine both the infrared photothermal spectroscopy in their static mode and the unique mass sensitivity in their dynamic mode. Optical sensors based on localized plasmon resonance can also take up the challenge of addressing the selectivity by monitoring the Surface Enhanced Raman spectrum down to few molecules. The operating conditions of these promising localized spectroscopies will be discussed in terms of reliability, compactness, data analysis and potential for mass deployment.

We demonstrate here the realization of an integrated, electrically driven, source of surface plasmon polaritons. Light-emitting individual single-walled carbon nanotube field effect transistors were fabricated in a plasmonic-ready platform. The devices were operated at ambient conditions to act as an electroluminescence source localized near the contacting gold electrodes. We show that photon emission from the semiconducting channel can couple to propagating surface plasmons developing in the electrical terminals. Our results show that a common functional element can be operated for two different platforms emphasizing thus the high degree of compatibility between state-of-the-art nano-optoelectronics devices and a plasmonic architecture.

International audience; Amplifying local electromagnetic fields by engineering optical interactions between individual constituents of an optical antenna is considered fundamental for efficient nonlinear wavelength conversion in nanometer-scale devices. In contrast to this general statement we show that high field enhancement does not necessarily lead to an optimized nonlinear activity. In particular, we demonstrate that second-harmonic responses generated at strongly interacting optical gap antennas can be significantly suppressed. Numerical simulations are confirming silencing of second-harmonic in these coupled systems despite the existence of local field amplification. We then propose a simple approach to restore and amplify the second-harmonic signal by changing the manner in which electrically-connected optical antennas are interacting in the charge-transfer plasmon regime. Our observations provide critical design rules for realizing optimal structures that are essential for a broad variety of nonlinear surface-enhanced characterizations and for realizing the next generation of electrically-driven optical antennas.

International audience; In this paper, we experimentally show the effect of waveguide discontinuity on the propagation of the surface plasmon in metal stripes and tapered terminations. Dual-plane leakage microscopy and near-field microscopy were performed on Au stripes with varied widths to imag29e the surface plasmon intensity distribution in real and reciprocal spaces. We unambiguously demonstrate that edge diffraction is the limiting process determining the cutoff conditions of the surface plasmon mode. Finally, we determine the optimal tapered geometry leading to the highest transmission.

International audience; Graphene was synthesized on copper foil by thermal chemical vapor deposition technique. To investigate the field electron emission property, planar graphene (PG) and morphologically disordered graphene (MDG) were fabricated on the doped silicon substrate by transfer of as-grown graphene. Incorporation of morphological disorder in graphene creates more emission sites due to the additional defects, edges, and atomic scale ripples. This resulted in (1) a dramatic increase in the maximum current density by a factor of 500, (2) considerable increase in the enhancement factor, and (3) decrease in the turn-on field of MDG compared to PG.

International audience; In this work, we demonstrate propagating surface plasmon polariton (SPP) coupled photoluminescence (PL) excitation of single-walled carbon nanotube (SWNT). SPPs were launched at a few micrometers from individually marked SWNT, and plasmon-coupled PL was recorded to determine the efficiency of this remote in-plane addressing scheme. The efficiency depends upon the following factors: (i) longitudinal and transverse distances between the SPP launching site and the location of the SWNT and (ii) orientation of the SWNT with respect to the plasmon propagation wave vector (k(SPP)). Our experiment explores the possible integration of carbon nanotubes as a plasmon sensor in plasmonic and nanophotonic devices.

Carbon nano structures including fullerenes, nanotubes, nanocones and graphene are gaining a considerable interest for supercapaitors in memory backup devices, electric vehicles, and emergency power supplies. In addition, these structures are utilized to improve resolution and power consumption of field emission displays. The energy density and performance of supercapacitors depend on the choice of electrode and electrolyte materials. Our recent work based on direct modification of grapheme and multiwall carbon nanotubes (MWCNTs) as well as their incorporation in metal oxides shows considerable future potential for improved supercapacitor performance. The structural stability and capacitive performance of MWCNTs and grapheme were investigated at varying Gallium ion doses. It was found that ion irradiation dose of 2×1013 ions/cm2 results in twice the electric double layer capacitance of MWCNT electrodes. The observed dependence of the specific capacitance on the irradiation dose can be explained via defect creation and opening up of CNT caps. The field emission properties of morphologically disordered monolayer graphene improved in terms of turn-on voltages and current density.

Extensive bulk and micro-texture measurements are used to characterize single and polycrystalline diamond thin films of different film thicknesses produced using CVD. With increasing film thickness, texturing improves and in-grain misorientation drops. This is observed for both single and polycrystalline films. Improved texturing in polycrystalline diamond can be rationalized from growth selection/advantage, however explanation(s) on the in-grain misorientation development and its relationship with texturing, if any, remain pending.

Low energy Ar + ion irradiation of aligned multiwalled carbon nanotube and in situ field emission measurement revealed deterioration of field emission current density with the energy of incident ions for high dose irradiation. Defect co-ordination number, calculated through Molecular Dynamics simulations increases for the low energy and finally saturates. The saturation of emission current density follows the same pattern as the defect co-ordination number varies with the energy of the incident ion. Interestingly, both the curves saturate at exactly same energy of Ar + ions which establishes a correlation between the saturation of emission current density and defect co-ordination number.

The Raman spectra of the multi-walled carbon nanotubes are studied with the laser power of 5–20 mW. We observe the Raman bands at not, vert, similar1352, 1581, 1607, and 2700 cm−1 with 5 mW laser power. As the laser power is increased to 10, 15 and 20 mW, the radial breathing modes (RBMs) of the single wall carbon nanotubes (SWNTs) appear in the range 200–610 cm−1. The diameter corresponding to the highest RBM is not, vert, similar0.37 nm, the lowest reported so far. The RBMs are attributed to the local synthesis of the SWNTs at the top surface of the samples at higher laser power., © Elsevier

Employing photoluminescence (PL) spectroscopy, we have carried out a detailed study of the different luminescence center in chemical-vapor- deposited (CVD) single-crystal and poly-crystalline diamond and natural diamonds. In addition to the zero phonon line, the fine structure of the PL emission spectra reveals vibronic bands corresponding to both phonon emission and absorption. At lower temperature, the emission intensity increases and peak position shifts towards higher energy band.

The carbon nanotubes (CNTs) samples are grown using the microwave plasma chemical vapor deposition (MPCVD) and thermal chemical vapor deposition (THCVD) technique on Fe catalyst deposited by thermal evaporation on silicon substrate. The field emission measurements of the samples have been made in a diode assembly at room temperature in a vacuum chamber with a base pressure of 10-7 mbar. The turn-on fields of CNT films grown by THCVD and MPCVD techniques are 0.6 and 1.0 V/mum, respectively.

In a recent report [Sun , Science 312, 1119 (2006)], the partially filled material inside multiwalled carbon nanotubes (MWNTs) was shown to have shrunk and deformed in the axial direction under 300 kV electron irradiation. In this experiment, 100 MeV Au7+ ion irradiation was performed to study the deformation and defects in uniformly nickel filled MWNTs with high-resolution transmission electron microscopy and Raman spectroscopy. We propose that high-pressure induced torsion in confined nickel could possibly result in successive compressions and expansions of the tubes, leading to axial buckling of MWNTs. The tangential Raman G band systematically upshifts as the ion fluence increases, attributed to the torsional strain. In contrast to a square root dependence of the buckling wavelength (lambda) on the radius (r) and thickness (t) of the tubes [lambda=3.5(rt)(1/2)], as predicted by theoretical models, the exponential fit of the data that assumes lambda proportional to e(root(r/t)) also produces an excellent fit.

Chemical vapor deposited diamond films grown on strained gallium nitride-coated quartz substrate are found to display a dominantly hexagonal diamond phase. The phase identification is done using Raman spectroscopy and orientation imaging microscopy (OIM). The presence of a 1324.4 cm(-1) band in the Raman spectra is attributed to a hexagonal diamond symmetry, but the unambiguous signature of the hexagonal phase is confirmed by OIM. A phase map of the sample clearly shows that 88% of the scanned sample area is hexagonal diamond. (c) 2006

Irradiation by 30 keV Ga+ ions was used to create defects in multiwalled carbon nanotubes. Damage to the graphitic structure of the nanotube wall resulting from ion irradiation was observed by a transmission electron microscope which was accompanied by corresponding changes in Raman spectra. It was found that ion irradiation at 2 × 1013 ions/cm2 cumulative dose increases the electric double layer capacitance of a multiwalled carbon nanotube electrode by a factor of 2.3, followed by a decrease and saturation at higher (2 × 1014 and 4 × 1014 ions/cm2) doses. This might be a trade-off between the enhancement caused by the tip opening and lowering of the capacitance due to amorphization of carbon nanotubes.

The field emission of a carbon nanotube (CNT) pillar array has been improved significantly by plasma treatment in a mixture of hydrogen and nitrogen gases. The plasma treatment for 30 s on a pillar array decreased the turn- on electric field from 0.48 to 0.37 V/mu m and increased the field enhancement factor from 6200 to 6900. The emission current density increased by a factor of approximate to 40. We report in this letter the technique of generating nanotips on CNT pillars with an enormous potential to become a tool for the control and manipulation of CNTs and nanostructures. (C) 2008