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The metal/graphene interface has been one of the most important research topics with regard to charge screening, charge transfer, contact resistance, and solar cells. Chemical bond formation of metal and graphene can be deduced from the defect induced D-band and its second-order mode, 2D band, measured by Raman spectroscopy, as a simple and nondestructive method. However, a phonon mode located at ∼1350 cm–1, which is normally known as the defect-induced D-band, is intriguing for graphene deposited with noble metals (Ag, Au, and Cu). We observe anomalous K-point phonons in nonreactive noble metal/graphene heterostructures. The intensity ratio of the midfrequency mode at ∼1350 cm–1 over G-band (∼1590 cm–1) exhibits nonlinear but resonant behavior with the excitation laser wavelength, and more importantly, the phonon frequency–laser energy dispersion is ∼10–17 cm–1 eV–1, which is much less than the conventional range. These phonon modes of graphene at nonzero phonon wave vector (q ≠ 0) around K points are ac...

Using a stabilizing agent-assisted co-assembly method, a novel nanocomposite of mesoporous carbon embedded with uniform tungsten oxide nanorods is obtained, which is converted into carbon-sheathed tungsten oxide nanoparticles by delicate calcination and further reduction. Through optimization of tungsten content, it is found that highly crystalline tungsten oxide nanoparticles are uniformly coated with an ultra-thin carbon layer. When applied into electrochemical charge-storage electrodes for supercapacitor and lithium-ion battery, an excellent average capacitance (129 F g−1, above 400 F cm−3), higher rate performance and significantly advanced cycle stability are observed. These improved charge storage properties are attributed to improved electrical conductivity and enhanced structural stability, which is induced by uniform carbon coating on partially reduced tungsten oxide nanoparticles.

Graphene derivatives have immense potential in stem cell research. Here, we report a three-dimensional graphene/arginine-glycine-aspartic acid (RGD) peptide nanoisland composite effective in guiding the osteogenesis of human adipose-derived mesenchymal stem cells (ADSCs). Amine-modified silica nanoparticles (SiNPs) were uniformly coated onto an indium tin oxide electrode (ITO), followed by graphene oxide (GO) encapsulation and electrochemical deposition of gold nanoparticles. A RGD–MAP–C peptide, with a triple-branched repeating RGD sequence and a terminal cysteine, was self-assembled onto the gold nanoparticles, generating the final three-dimensional graphene–RGD peptide nanoisland composite. We generated substrates with various gold nanoparticle–RGD peptide cluster densities, and found that the platform with the maximal number of clusters was most suitable for ADSC adhesion and spreading. Remarkably, the same platform was also highly efficient at guiding ADSC osteogenesis compared with other substrates, based on gene expression (alkaline phosphatase (ALP), runt-related transcription factor 2), enzyme activity (ALP), and calcium deposition. ADSCs induced to differentiate into osteoblasts showed higher calcium accumulations after 14–21 days than when grown on typical GO-SiNP complexes, suggesting that the platform can accelerate ADSC osteoblastic differentiation. The results demonstrate that a three-dimensional graphene–RGD peptide nanoisland composite can efficiently derive osteoblasts from mesenchymal stem cells.

We investigate the effect of surface area of the lithium manganese spinel (LMO) cathode on the high-temperature storage performance of lithium-ion pouch cells. Using ~200 mAh design capacity, pouch cells were fabricated and their storage performance at high temperature was investigated according to changes in the LMO surface area. Cell performance and electrode analysis revealed that LMO with a large surface area exhibited a poor storage with a large decrease in capacitance and a more severe increase in resistance. This was mostly attributed to the change in surface morphology of anodes in each cell, indicative of the fast growth of a solid electrolyte interface film caused by high dissolution of Mn2+ ions in the high-surface-area LMO.

Raman spectroscopy, X-ray diffraction (XRD), magnetization hysteresis loop, synchrotron X-ray absorption spectroscopy, and photovoltaic effects have been measured in (Bi 1− x Sr x )FeO 3− δ (BFO100 x Sr) ceramics for x =0.0, 0.05, 0.10, and 0.15. Raman spectra and XRD reveal a rhombohedral R3c structure in all compounds. A-site Sr 2+ doping increases fluctuations in cation-site occupancy and causes broadening in Raman modes. BFO15Sr exhibits a strong ferromagnetic feature due to reduction of Fe O Fe bond angle evidenced by the extended synchrotron X-ray absorption fine structure. The heterostructure of indium tin oxide (ITO) film/(Bi 1− x Sr x )FeO 3− δ ceramic/Au film exhibit clear photovoltaic (PV) responses under blue illumination of λ =405 nm. The maximal power-conversion efficiency and external quantum efficiency in ITO/BFO5Sr/Au are about 0.004% and 0.2%, respectively. A model based on optically excited charges in the depletion region between ITO and (Bi 1− x Sr x )FeO 3− δ can well describe open-circuit voltage and short-circuit current as a function of illumination intensity.

We have investigated phosphate adsorption on the Au surface by in situ electrochemical surface-enhanced Raman spectroscopy to assess the possible use of Au-based alloys as catalysts for the oxygen reduction reaction (ORR) in high-temperature proton exchange membrane fuel cells. Compared with its strong adsorption in neutral or basic electrolytes, the adsorption of phosphate species on the Au surface were significantly altered in acidic electrolyte. Thus, Pt x Au 100-x catalysts of various compositions were prepared by electrodeposition and exhibited better ORR activities than pure Pt in phosphoric acid electrolyte, which can be explained in terms of alloying effects and the different phosphate adsorption behavior.

The photoresponse in graphene has drawn significant attention for potential applications owing to its gapless linear electronic band structure. To enhance both the spectral selectivity and responsivity in graphene, we demonstrate a novel but versatile and simple method of introducing surface plasmons. We utilize block copolymers to fabricate different nanostructured metal nanoparticle arrays on a single graphene surface. The plasmonic resonances could be tuned using Ag, Au, and Cu metal nanoparticles. By extending the synthetic route for the metallic particles, dual surface plasmonic bands from a single material were also successfully realized. Furthermore, enhanced photoresponsivity through the entire visible spectra could be achieved by mixing metallic nanoparticles and by controlling their shapes. Owing to its all-band transition characteristics, the ultrabroad band photocurrent generation in graphene can be tailored for an arbitrary photoresponse, which could be utilized in flexible CMOS image sensors...

To develop novel multifunctional magnetic nanoparticles (MNPs) with good magnetic properties, biocompatibility, and anticancer activities by photodynamic therapy (PDT), we synthesized multifunctional cobalt ferrite (CoFe2O4) nanoparticles (CoFe2O4-HPs-FAs) functionalized by coating them with hematoporphyrin (HP) for introducing photo-functionality and by conjugating with folic acid (FA) for targeting cancer cells. We evaluated the activities of the CoFe2O4-HPs-FAs by checking magnetic resonance imaging (MRI) in vitro, its biocompatibility, and photodynamic anticancer activities on FA receptor (FR)-positive and FR-negative cancer cell lines, Hela, KB, MCF-7, and PC-3 cells, to use for clinical applications. In this study, we have demonstrated that the CoFe2O4-HPs-FAs have good MRI and biocompatibility with non-cytotoxicity, and remarkable photodynamic anticancer activities at very low concentrations regardless of cell types. Particularly, the photo-killing abilities in 3.13 μg/mL of CoFe2O4-HPs-FAs were measured to be 91.8% (p < 0.002) for Hela, 94.5% (p < 0.007) for KB, 79.1% (p < 0.003) for MCF-7, and 71.3% (p < 0.006) for PC-3. The photodynamic anticancer activities in 6.25 and 12.5 μg/mL of CoFe2O4-HPs-FAs were measured to be over 95% (p < 0.004) to almost 100% regardless of cell types. The newly developed multifunctional CoFe2O4-HPs-FAs are effective for PDT and have potential as therapeutic agents for MRI-based PDT, because they have a high saturation value of magnetization and superparamagnetism.

An organic radical polymer (ORP) was prepared by radical polymerization and following oxidation into nitroxyl radical. Two different oxidation methods were employed and their radical concentrations were measured using electroparamagnetic resonance spectroscopy (EPR) and UV-visible absorption (UV-vis) spectroscopy. From these measurements, H2O2-Na2WO4 oxidation method exhibited a complete oxidation, which resulted in 97.6% spin concentration. Also, it was revealed that convenient and cheap UV-vis measurement was useful for preliminary radical concentration comparison. After applied as a cathode material in lithium ion batteries, ORP electrode showed a high initial capacity (110 mAh g), a good initial efficiency (96%), a very high rate performance (70% charging during 1.2 min) and stable cycle performance.

In this paper, we have synthesized multifunctional magnetic particles (MNPs) using by two different ferrite submicrometer paticles (Fe 3 O 4 @HP and CoFe 2 O 4 @HP) with different surface properties. Two different multifunctional particles have the same particle sizes within the error tolerance of 4.5%. The concentration measurement of the hematoporphyrin (HP) molecule indicates that the weight of HP molecules bonded to the surface of the Fe 3 O 4 particles is smaller than that of the CoFe 2 O 4 particles. Moreover, we have evaluated their biocompatibilities and photodynamic anticancer activities on mammalian cells. The two MNPs have demonstrated that they both have good biocompatibilities without any cytotoxicity and anticancer activities in the concentration range of 0-50 μg/mL. Specifically, photodynamic-killing activities of both MNPs were measured to be 100% for CoFe 2 O 4 @HP, and were measured to be 37.9 ± 3.5% and 9.2 ± 2.5% for Fe 3 O 4 @HP in 25 and 50 μg/mL of both MNPs. These results suggest that both MNPs can be safely used to for clinical photodynamic cancer therapy, although the CoFe 2 O 4 @HP showed a slightly better photo-killing efficacy compared with the Fe 3 O 4 @HP in prostate cancer.

The authors present an external cavity diode laser with high spectral purity for tunable laser Raman spectroscopy. To achieve high spectral purity required for Raman spectroscopy, a laser cavity utilizing a volume phase holographic grating, which has very low stray light, is developed and the first-order diffracted beam from the grating is taken as the output. Raman signals can be obtained from common samples with only a commercial laser rejection filter, greatly simplifying a tunable Raman instrument.

Unlike conventional two-dimensional (2D) planar structures, signal or power is supplied through through-silicon via (TSV) in three-dimensional (3D) integration technology to replace wires for binding the chip/wafer. TSVs have becomes an essential technology, as they satisfy Moore's law. This 3D integration technology enables system and sensor functions at a nanoscale via the implementation of a highly integrated nano-semiconductor as well as the fabrication of a single chip with multiple functions. Thus, this technology is considered to be a new area of development for the systemization of the nano-bio area. In this review paper, the basic technology required for such 3D integration is described and methods to measure the bonding strength in order to measure the void occurring during bonding are introduced. Currently, CMOS image sensors and memory chips associated with nanotechnology are being realized on the basis of 3D integration technology. In this paper, we intend to describe the applications of high-performance nano-biosensor technology currently under development and the direction of development of a high performance lab-on-a-chip (LOC).

In vitro bone tissue development requires mimicking the in vivo bone environment, as well as a suitable combination of cells and scaffold for optimal results. We developed heterogeneous multilayered gelatin scaffolds with diverse compositions of porous structures by using a stacking procedure in which each layer had a different pore size depending on the gelatin concentration used. We then used these gelatin scaffolds to investigate the in vitro effect of varying porous structural compositions on the diffusion characteristics and cellular activity of MC3T3-E1 cells. We have shown that multilayered scaffolds with a larger pore size on the outer layers exhibited enhanced diffusion characteristics such as the diffusion coefficient compared to other scaffolds, including single-layered scaffolds with single pore size and multilayered scaffolds with a smaller pore size on the outer layers. Moreover, multilayered scaffolds with a larger pore size on the outer layers promoted cell adhesion, proliferation, and differentiation of MC3T3-E1 preosteoblast cells by providing a favorable environment for the cells within the tissue-engineered scaffold. Open image in new window

We report on the systematic studies of the parameters governing the integrity of graphene film during general “wet” transfer from a thermodynamic point of view. We chose polystyrene (PS) as a test carrier material and attempted to use eight different solvents to find optimal conditions for the graphene transfer from a catalyst film to a desired substrate without defects. When parameterizing the conventional chemical properties of solvents, the boiling points and surface tension were found to be critical in determining the quality of the transferred graphene. During the formation step of a conformal PS film on a graphene surface before catalyst etching, a solvent with a boiling point over ∼140 °C was essential. During the following PS film removal step, a solvent with surface tension higher than approximately 29 dyn/cm led to the formation of a continuous graphene film without cracks and holes. In addition, a high spin-coating velocity and lower concentration of PS in the solvent enhanced the quality of a transferred graphene film. The UV treatment of Si/SiO2 (100 nm) was also found to improve the adhesion of the graphene on substrates. By electrical characterization, morphological differences were found to affect the electrical properties markedly.

NiCu alloy catalysts for alkaline water electrolysis were prepared by an electrodeposition method varying the alloy composition. When the deposition potential became more positive, the bulk and surface Cu content in NiCu alloys as well as the catalyst particle size gradually increased, which were confirmed by various spectroscopic and electrochemical techniques. The surface coverage of the catalysts was found to be a function of the deposition potential, as well. The catalytic activities of the prepared NiCu alloys to hydrogen evolution reaction (HER) were investigated with cyclic voltammetry in a 6.0 M KOH electrolyte at 298 K, and the mass activities of NiCu alloys were correlated with bulk and surface Cu contents to investigate the Cu alloying effect.

The activities of Au-modified Cu electrodes toward glucose oxidation are evaluated according to their fabrication conditions and physico-chemical properties. The Au-modified Cu electrodes are fabricated by the galvanic displacement of Au on a Cu substrate and the characteristics of the Au particles are controlled by adjusting the displacement time. From the glucose oxidation tests, it is found that the Au modified Cu has superior activity to the pure Au or Cu film, which is evidenced by the negative shift in the oxidation potential and enhanced current density during the electrochemical oxidation. Though the activity of the Au nanoparticles is a contributing factor, the enhanced activity of the Au-modified Cu electrode is due to the increased oxidation number of Cu through the electron transfer from Cu to more electronegative Au. The depletion of electron in Cu facilitates the oxidation of glucose. The stability of the Au-modified Cu electrode was also studied by chronoamperometry.

We determined that the use of densification, sacrificial oxidation, gate oxidation and source/drain implantation has the capability to reduce the dislocation. A dislocation-free process is proposed, and its mechanism presented in embedded flash memory. The dislocation decreased when n-type ions were implanted at a low energy level for source and drain. A dry oxidation process using only oxygen without hydrogen and oxidation for logic gates led to the formation of a sacrificial oxide on the rapid thermal oxidation (RTP) methods without densification after gap-filling as reducing dislocation processes. These methods dramatically reduced the standby leakage current.

We have shown the enhanced piezoelectricity by electrostatic effects on a textile based platform. The electrostatic and piezoelectric effects were hybridized by integrating piezoelectric ZnO nanowires and a charged dielectric film on a wearable textile substrate. The hybrid textile nanogenerator produced an output voltage of 8 V and an output current of 2.5 μA. Using a simple AC-DC converter circuit, we operated the green organic light-emitting diode and a liquid crystal display panel using a 100 dB sonic wave. © 2012 The Royal Society of Chemistry.

Graphene nanoribbons can exhibit either quasi-metallic or semiconducting behavior, depending on the atomic structure of their edges. Thus, it is important to control the morphology and crystallinity of these edges for practical purposes. We demonstrated an efficient edge-reconstruction process, at the atomic scale, for graphitic nanoribbons by Joule heating. During Joule heating and electron beam irradiation, carbon atoms are vaporized, and subsequently sharp edges and step-edge arrays are stabilized, mostly with either zigzag- or armchair-edge configurations. Model calculations show that the dominant annealing mechanisms involve point defect annealing and edge reconstruction.

In this work we extend the study of the use of Raman spectroscopy to characterize graphitic foams by analyzing the dependence of the G ′ band lineshape on both the excitation laser energy and on the topology of the studied area. The G ′ band lineshape was found to be strongly correlated with the presence of stacking faults. The contribution of the TO + LA combination mode at ∼ 2450 cm −1 to the evaluated skewness includes an excitation energy dependence which needs to be considered. We analyze how to take this effect into consideration, thus obtaining a good evaluation of the dependence of the skewness of the G ′ band on the presence of stacking faults. We also discuss the correlation between the presence of stacking faults and of in plane defects in graphitic foams.

Resonance Raman studies have been carried out on length-sorted single walled carbon nanotubes (SWNTs). For nanotubes much shorter than the wavelength of light, a large increase in Raman intensity is observed for several features in the intermediate frequency mode (IFM) region. The changes in IFM intensities are found to be highly dependent on the laser excitation energies, the (n, m) indices, and the specific Raman features. A direct correlation is found between the amount of IFM intensity increase as a function of the average nanotube length, as well as the symmetry of the physical origin for the specific IFM feature.

The electrical and optical properties of single-walled carbon nanotubes (SWNTs) have been shown to be sensitive to their environment. Therefore it is very important to understand and exploit the environmental effect on the properties of nanotubes, especially for individual SWNTs. We report herein a systematic investigation of the Raman spectra variation of 15 individual SWNTs partially suspended on trench-contained substrates. Our experiments are conducted with low laser power to exclude possible heating effects. Most SWNTs show enhanced Raman signals for their suspended segment compared with their segment sitting on the SiO2 substrate, with several exceptions exhibiting either similar Raman intensity or a reverse result. Apart from this distinct intensity contrast, moderate radial breathing mode (RBM) frequency variations are observed for some nanotubes, which can be attributed to nanotube−substrate interactions. By analyzing the behaviors of the RBM full width at half-maximum (fwhm) and the intensity ra...

We have developed a methodology to use resonant Raman spectroscopy with a tunable excitation source to characterize the chirality distribution of a synthesized single-walled carbon nanotube (SWNT) material. Isolated SWNTs are either dispersed or directly grown on substrates with markers. The samples are then placed on an automatic scanning stage of a confocal Raman microscope. Resonant Raman signals from SWNTs are collected while the laser spot scans across the substrate and a two-dimensional mapping is obtained at each laser excitation energy. From the resonant Raman signal the chiralities of the SWNTs can be assigned and a chirality distribution of the material can therefore be obtained by examining hundreds to thousands SWNTs on the substrate.

We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (

Scanning probe microscopy (SPM) is considered one of the most powerful tools for nanoscale studies that are becoming increasingly important, and SPM has shown rapid development. Atomic force microscopy (AFM), in particular, is the widely used SPM system. SPM, and especially AFM, has been used as a new measuring tool for phenomena that were earlier difficult to prove because of the limitations of earlier systems. In addition SPM allows acquiring nanoscale resolution images of the surface of materials. New applications are constantly being developed for SPM, and it is now used actively in material sciences and biological fields. The most important reason why SPM has attracted attention in the biological field is because it can be used in liquids as well. This allows the study of live cells and various other systems in nanoscale. Recently, there have been many advances in nanoscale studies, such as studies of cell interactions, cell changes according to environmental changes, and development of biosensors. This review is focused on applications in nanodevices, as well as on specific biological applications to discuss the development and opportunities of SPM in the biological field.

Especially, nanocompositesbetween transient metal oxides and ordered mesoporouscarbon (OMC) have become more attractive due to theirbeneficial characteristics: i) abundant lithium storage sitesand fast lithium diffusion in nanosized metal oxides andOMC; ii) facile electrolyte penetration owing to orderedmesopores iii) higher electric conductivity through carbonframework.

An enhanced Raman signal is observed from individual suspended single-wall carbon nanotubes (SWNTs) and from isolated SWNTs grown on an n-doped polycrystalline silicon film used in standard silicon processing. The radial breathing modes of the Raman spectra taken from suspended SWNTs exhibit narrow linewidths, which indicate a relatively unperturbed environment for suspended SWNTs. Clear Raman signals from intermediate frequency modes in the frequency range from 520to1200cm−1 are presented, which might allow a detailed study of the phonon band structure of individual SWNTs.

We performed Raman spectroscopy experiments on undoped and boron-doped double walled carbon nanotubes DWNTs that exhibit the “coalescence inducing mode” as these DWNTs are heat treated to temperatures between 1200 ° C and 2000 ° C. The fact that boron doping promotes DWNT coalescence at lower temperatures allowed us to study in greater detail the behavior of first- and second-order Raman modes as a function of temperature with regard to the coalescence process. Furthermore, by using various excitation laser energies we probed DWNTs with different metallic M and semiconducting S inner and outer tubes. We find that regardless of their M and S configurations, the smaller diameter nanotubes disappear at a faster rate than their larger diameter counterparts as the heat treatment temperature is increased. We also observe that the frequency of the G band is mostly determined by the diameter of the semiconducting layer of those DWNTs that are in resonance with the laser excitation energy. Finally, we explain the contributions to the G band from the inner and outer layers of a DWNT.

In this work, we carried out electroluminescence (EL) measurements on metallic single-walled carbon nanotubes (SWNTs) and compared the light emission from the suspended section with the on-substrate section along the same SWNT. In addition to the lowest excitonic emission for metallic SWNTs (M(11)), a side peak was observed at an energy of 0.17-0.20 eV lower than the M(11) peak, which is attributed to a phonon-assisted sideband. Interestingly, this side peak was only observed from on-substrate sections but not from suspended sections. This is likely due to the higher electric field used in the EL measurement of on-substrate sections and the asymmetric surroundings for on-substrate SWNT sections. When the drain voltage is increased, either a blue shift or a red shift of the M(11) emission (up to +/-20 meV) was observed in different suspended SWNTs. The red shift can be explained by the temperature-dependence of the M(11) transition energy, whereas the blue shift is surprising and has never been observed before. Some possible mechanisms for the blue shift are discussed.

In this work we present a low cost and scalable technique, via ambient pressure chemical vapor deposition (CVD) on polycrystalline Ni films, to fabricate large area ( approximately cm2) films of single- to few-layer graphene and to transfer the films to nonspecific substrates. These films consist of regions of 1 to approximately 12 graphene layers. Single- or bilayer regions can be up to 20 mum in lateral size. The films are continuous over the entire area and can be patterned lithographically or by prepatterning the underlying Ni film. The transparency, conductivity, and ambipolar transfer characteristics of the films suggest their potential as another materials candidate for electronics and opto-electronic applications.

In this work, we performed a detailed study of the Raman spectra of double-wall carbon nanotube (DWNT) bucky paper samples. The effects of ${\mathrm{H}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ doping on the electronic and vibrational properties of the DWNTs are analyzed and compared to the corresponding effects on single-wall carbon nanotubes (SWNTs). Analysis of the radial breathing mode (RBM) Raman spectra indicates that the resonance condition for the outer wall nanotubes and the SWNTs are almost the same, indicating that the effect of the inner-outer wall interaction on the transition energies of the outer walls is weak compared to the width of the resonance window for the RBM peaks. The effect of ${\mathrm{H}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ on the RBM frequencies of the outer wall of the DWNTs is stronger for larger diameter nanotubes. In the case of the inner walls, only the metallic nanotubes were affected by the acid treatment, while the RBM peaks for the inner semiconducting nanotubes remained almost unchanged in both frequency and intensity. The ${G}^{+}$ band was seen to upshift in frequency with ${\mathrm{H}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ doping for both DWNTs and SWNTs. However, the effect of the acid treatment on the ${G}^{\ensuremath{-}}$ band frequency for DWNTs was opposite to that of SWNTs in the $2.05--2.15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ range, for which the acid treatment causes a ${\ensuremath{\omega}}_{{G}^{\ensuremath{-}}}$ upshift for SWNTs and a downshift for DWNTs. The ${G}^{\ensuremath{'}}$ band line shape of the DWNTs is explained in terms of four contributions from different components which are in resonance with the laser excitation. Two of these peaks are more related to the inner wall nanotube while the other two are more related to the outer wall.

Resonance Raman spectra of individual strained ultralong single-wall carbon nanotubes (SWNTs) are studied. Torsional and uniaxial strains are introduced by atomic force microscopy manipulation. Torsional strain strongly affects the Raman spectra, inducing a large downshift in the E2 symmetry mode in the G+ band, but a slight upshift for the rest of the G modes and also an upshift in the radial breathing mode (RBM). Whereas uniaxial strain has no effect on the frequency of either the E2 symmetry mode in the G+ band or the RBM, it downshifts the rest of the G modes. The Raman intensity change reflects the effect of these strains on the SWNT electronic band structure.

We have studied the line shape and frequency of the $G$ band Raman modes in individual metallic single walled carbon nanotubes (M-SWNTs) as a function of Fermi level (${ϵ}_{F}$) position, by tuning a polymer electrolyte gate. Our study focuses on the data from M-SWNTs where explicit assignment of the ${G}^{\ensuremath{-}}$ and ${G}^{+}$ peaks can be made. The frequency and line shape of the ${G}^{\ensuremath{-}}$ peak in the Raman spectrum of M-SWNTs is very sensitive to the position of the Fermi level. Within $\ifmmode\pm\else\textpm\fi{}\ensuremath{\hbar}\ensuremath{\omega}/2$ (where $\ensuremath{\hbar}\ensuremath{\omega}$ is the phonon energy) around the band crossing point, the ${G}^{\ensuremath{-}}$ mode is softened and broadened. In contrast, as the Fermi level is tuned away from the band crossing point, a semiconductinglike $G$ band line shape is recovered both in terms of frequency and linewidth. Our results confirm the predicted softening of the $A$-symmetry LO phonon mode frequency due to a Kohn anomaly in M-SWNTs.

We present herein a rational approach to probe the torsional strain-induced electronic transition energy Eii variation of individual SWNTs by resonant Raman spectroscopy (RRS). When a SWNT was manipulated by AFM tip through a path perpendicular to SWNT axis, both torsional and uniaxial strain would be introduced in SWNTs. Under the torsional strain, resonant Raman spectral mapping along a SWNT detected an M-shaped frequency ( ˆ RBM) and W-shaped intensity (IS) variation of radial breathing mode (RBM) spectra, which were induced by the elastic retraction of the nanotubes in combination with the friction after the tip has been removed. The electronic transition energy Eii variation along SWNTs by torsional strain follows a family pattern based on q ) (n - m) mod 3: for semiconducting SWNTs, E33 S increases for q )+ 1, E33 S decreases and E22 S increases for q ) -1, and for metallic SWNTs, E11 M always increases.

Using self-assembled block copolymers as templates, catalytically active nanostructures with controlled size and space have been produced. A self-assembled polystyrene-b-polyferrocenylsilane thin film and monolayer of surface micelles of cobalt-complexed polystyrene-b-poly(2-vinylpyridine) are fully compatible with novolac-based conventional photoresists. Combining bottom-up self-assembly of catalyst-containing block copolymers with top-down microfabrication processing, plateaus covered with arrays of catalytically active nanostructures have been generated. Spatially selective growth of suspended single-walled carbon nanotubes over a large surface area has been achieved. Greatly enhanced Raman signals have been detected from the suspended tubes. This facile method of creating highly ordered catalyst nanostructures on top of posts enables the rational synthesis of suspended carbon nanotubes, thus facilitating the study of CNT properties by optical methods and enabling the fabrication of devices based on suspended CNTs.

The electron-phonon coupling in two-dimensional graphite (graphene sheet) and metallic single-wall carbon nanotubes (SWNTs) is analyzed. In the graphene sheet the G-band phonon mode induces oscillations of the Fermi points, while the G′-band phonon mode opens a dynamical (oscillating with the phonon frequency) band gap, and accordingly, both phonon modes exhibit Kohn anomalies. Similarly, truly metallic armchair SWNTs undergo Peierls transitions driven by the G−- and G′-band phonon modes both of which open a dynamical band gap. In addition, the dynamical band gap induces a non-linear dependence of the phonon frequencies on the doping level and gives rise to strong anharmonic effects in the graphene sheet and metallic SWNTs.

We report on the monotonic Raman frequency shift and intensity variation when a laser spot moves along the same single-walled carbon nanotube (SWNT) for both the radial-breathing mode (RBM) and the G-band. Our substrates are Si wafers coated with thermal oxide, and trenches with widths of 1-80 mum are etched in the SiO2 by photolithography and reactive ion etching. SWNTs are grown by chemical vapor deposition and lie on top of the SiO2 and across the trenches. When the laser spot moves from the middle of the trench to the SiO2 region along the nanotube, we observe a clear upshift in the RBM and G-band frequencies and a decrease of intensity. The effect is more significant with large ( approximately 2 nm) diameter nanotubes and appears to be chirality dependent. These studies provide important information about environmental effects on single-walled carbon nanotube resonant Raman spectroscopy.

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A signal detection technique utilising a `lock-in` architecture using the second-order harmonic frequency (2 ω c ) applicable to portable optical-biosensor systems is presented. The properties of frequency synthesis and filtering techniques are used to detect a weak signal concealed in intense background noise, such as thermal noise, 1/ f noise and shot noise. Using the 2 ω c lock-in, the main signal of interest keeps away from the influence of the 1/ f noise, providing a much higher dynamic reserve. In this work, a portable biosensor system using the 2 ω c frequency detection technique is demonstrated. The technique further enhances the minimum detectable range of 20 dB compared to the conventional DC lock-in method under the same conditions.

In this work, electrostatic spray assisted chemical vapor deposition is used to directly deposit single-walled carbon nanotube (SWNT) thin films on a substrate. The catalyst solution was finely dispersed by a strong electrical field and injected into the heated reaction zone (950-1100 degrees C) during the growth. It was found that under optimized growth conditions, the deposited material consists of SWNTs while only small amounts of impurities are observed. The growth at different temperatures results in nanotubes of different length and morphology. The location at which the SWNTs deposit at the downstream end of the growth chamber is found to be affected by the nanotube length and the growth temperature, which can be understood by considering different forces acting on the floating aerosol particles inside the furnace. These results suggest a potential for in situ separation of the SWNTs by applying different forces to the floating SWNTs.

Axial strain is introduced into individual single wall carbon nanotubes (SWCNTs) suspended from a trench-containing Si∕SiO2 substrate by employing the van der Waals interaction between the SWCNT and the substrate. Resonance Raman spectroscopy is used to characterize the strain, and up to 3% axial strain is observed. It is also found that a significant friction between the SWCNT and the substrate, on the order of 10pN∕nm, governs the localization and propagation of the strain in the SWCNTs sitting on the substrate. This method can be applied to introduce strain into materials sitting on a substrate, such as a graphene sheet.

A systematic resonance Raman study has been carried out on DNA-wrapped single walled carbon nanotubes (SWCNTs) of three different average lengths ⟨Ltube⟩ using seven different values of laser excitation energy Elaser. The dependence of the intensity ratio of the D-band and G-band Raman features (ID∕IG) on ⟨Ltube⟩ indicates that nanotube length can be used as an important structural parameter for Raman characterization. By systematically varying Elaser, the ratio ID∕IG is found to be much stronger for metallic than for semiconducting SWCNTs but appears to have the same functional dependence on Elaser and ⟨Ltube⟩ or crystallite size as does nanographite.

Using a confocal micro-Raman system, spectra showing the splitting of optical transitions due to trigonal warping effect are presented for metallic single-wall carbon nanotubes SWNT’s. Our results indicate that the intensity variations between different optical transitions can be attributed primarily to the differences in the magnitude of the electron-phonon coupling matrix elements. Our approach will allow the study of the magnitude of electron-phonon matrix elements as well as quantum interference effects between different transitions in metallic SWNT’s.