The theoretical simplicity of sp2 carbons, owing to their having a single atomic type per unit cell, makes these materials excellent candidates in quantum chemical descriptions of vibrational and electronic energy levels. Theoretical discoveries, associated with sp2 carbons, such as the Kohn anomaly, electron-phonon interactions, and other exciton-related effects, may be transferred to other potential 2D materials. The information derived from the unique Raman bands from a single layer of carbon atoms also helps in understanding the new physics associated with this material, as well as other two-dimensional materials. The following chapter describes our studies of the G, D, and G′ bands of graphene and graphite, and the characteristic information provided by each material. The G-band peak located at ~1586 cm−1, common to all sp2 carbons, has been used extensively by us in the estimation of thermal conductivity and thermal expansion characteristics of the sp2 nanocarbon associated with single walled carbon nanotubes (SWCNT). Scanning electron microscope (SEM) images of functionalized graphene nanoplatelet aggregates doped with argon (A), carboxyl (B), oxygen (C), ammonia (D), fluorocarbon (E), and nitrogen (F), have also been recorded and analyzed using the Gwyddion software.

The sp2 carbonaceous molecules possess a single atomic type per unit cell, which makes these materials very good candidates for quantum mechanical studies associated with their vibrational and electronic energy levels. Significant findings, such as the Kohn anomaly, electron-phonon interactions, and other exciton-related effects, associated with these molecules can be transported to other 2-D materials. Information derived from the distinctive Raman bands from a single layer of carbon atoms also aids in gaining insight into new physics from such materials and other graphitic nanomaterials. The present paper focuses on our investigations of the G, D, and G′ bands of graphene and graphite, and the specific information provided by each. The G-band peak located at ~1586 cm−1, shared by all sp2 carbons, has been used by us extensively in the estimation of thermal conductivity and thermal expansion characteristics linked to single-walled carbon nanotubes. In addition, we have investigated functionalized graphene nanoplatelets. For all three materials (graphene, graphite, and functionalized graphene nanoplatelets), we made use of the relationship discovered by Tuinstra and Koenig based on the relative intensities of the D and G Raman bands. In addition to the analysis based on Raman spectroscopy of the nanomaterial samples, SEM visualization/dimensional analysis was also performed on the graphene nanoplatelet samples. The bulk macroscopic 3-D character of graphite was clearly apparent, in contrast to the 2-D nature of graphene. However, the graphene nanoplatelets exhibited both 2-D and 3-D characteristics, without one dimension dominating the other.

This chapter showcases some of the versatility of Raman spectroscopic data as applied to the characterization of single (SWNT) and multi-walled (MWNT) carbon nanotubes, few layer graphene and functionalized graphene nanoplatelets, with an emphasis on gas-sensing applications. Specifically, water vapor and a variety of toxic gases (NO, NO2, and SO2 at 500 ppm in gaseous nitrogen) have been targeted for detection over the temperature range 24–200°C. The structure of sp2-hybridized carbon allotropes is reviewed and scanning electron microscopy (SEM) imagery utilized in conjunction with Raman spectroscopy to physically and spectrally characterize the various graphitic nanomaterials studied. A Kataura plot analysis associated with the Radial Breathing Mode (RBM) vibrations of SWNT has been used to identify possible chiralities in the graphitic samples employing 455, 532 and 780 nm laser excitation wavelengths to record the Raman spectra. The effect of temperature on the various Raman vibrational modes (RBM, G+ and G−) has been investigated, along with a determination of the thermal conductivity of SWNT samples and correlation between the purity of the sample and the variation of the slope of the G+ band with increasing laser power.

The thermal characterization of single-walled carbon nanotubes (SWCNTs) and tungsten oxide (WO3)-based nanomaterials through the use of Raman spectroscopy is the primary aim of this study, and is focused mainly on the applications of SWCNTs for energy storage and WO(3)for toxic gas sensing, respectively. In the case of SWCNTs, the properties relevant to their performance obtained via resonant Raman spectroscopy were thermal expansion and thermal conductivity through the exploitation of the latter property's relationship to the thermal behavior of the Raman G(+)-band of SWCNTs. In the case of the tungsten oxide-based nanomaterials, the responses of the various Raman signature peaks to different external stimuli, such as temperature variation, humidity changes, and toxic gas exposure, under controlled conditions were investigated.

The characterization of graphitic and metal oxide nanomaterials through the use of Resonant Raman Spectroscopy at multiple laser excitations is the primary aim of this research. Raman spectroscopic techniques can help characterize the vibrational phonon modes of nanomaterials with little in the way of sample preparation, making it an ideal tool for device characterization. The Stokes Raman spectra of carbon nanotubes and tungsten oxide were recorded with a DXR Smart Raman spectrometer over a temperature range of 27-200 degrees Celsius. The Raman spectra of SWCNTs were used to demonstrate the bond softening and resultant red-shifting of the various Raman peaks of SWCNTs. The thermal changes in the spectra were used to characterize the nanomaterial samples with an eye to future applications for energy storage (using carbon nanotubes) and for toxic gas sensing (using tungsten oxide). The observed and modeled redshifting of the Raman frequencies and broadening of the peak widths are being used to better understand the thermomechanical response of the nanomaterials for potential device applications at elevated temperatures.

Graphitic nanomaterials, such as graphene and carbon nanotubes, have been of particular interest in the development of applications such as supercapacitors, nanoprobes, drug delivery, biochemical sensors, and storage materials. This chapter will discuss the importance of researching these graphitic nanomaterials through Raman spectroscopy and molecular dynamics simulations. This chapter will also discuss results relating to thermal analysis of purified single-walled carbon nanotubes and the effects of increasing temperature on the Raman features of these materials. Finally, this chapter discusses the results of molecular dynamics simulations based on the Raman spectra thermal analysis results.

Carbon Nanotubes (CNTs) are honey-combed lattices rolled up into cylinders with nanometer-sized diameters and lengths on the order of microns. Actively studied for over thirty years, and with now greater availability, single-walled nanotubes are predicted to significantly impact semi-conductor physics, owing to their unique electronic properties and reduced dimensionality. Some of the semi-conductor technologies in which CNTs are expected to hold significant promise are in super-capacitors, hydrogen storage materials, nanoprobes, and bio-chemical sensors. Necessary to many future CNT applications is a clear understanding of their thermal properties, as nano-devices based on single-walled and/or multi-walled nanotubes may have to experience high temperatures during the manufacturing process while being operated. This, in turn, affects the reliability due to thermal expansion and the ensuing strain in the electronic devices. The coefficient of thermal expansion (CTE) of CNTs is a key property for nano-electronic applications. In this paper we will present Raman Spectroscopy measurements of single-walled carbon nanotubes as a function of temperature in the range 25-200 degrees C, as well as Molecular Dynamics (MD) simulations that incorporate current state-ofthe-art models of Carbon-Carbon interactions associated with the thermal expansion of carbon nanotubes.

Metal oxides are suitable for detecting, through conductive measurements, a variety of reducing and oxidizing gases in environmental and sensing applications. Metal-oxide gas sensors can be developed with the goal of sensing gases under specific conditions and, as a whole, are heavily dependent on the manufacturing process. Tungsten oxide (WO3) is a promising metal-oxide material for gas-sensing applications. The purpose of this paper is to determine the existence of a correlation between thermal effects and the changes in the Raman spectra for multiple WO3 structures. We have obtained results utilizing Raman spectroscopy for three different structures of WO3 (monoclinic WO3 on Si substrate, nanopowder, and nanowires) that have been subjected to temperatures in the range of 30-160 °C. The major vibrational modes of the WO3:Si and the nanopowder samples, located at ~807, ~716, and ~271 cm(-1), correspond to the stretching of O-W-O bonds, the stretching of W-O, and the bending of O-W-O, respectively; these are consistent with a monoclinic WO3 structure. However in the nanowires sample only asymmetric stretching of the W-O bonds occurs, resulting in a 750 cm(-1) band, and the bending of the O-W-O mode (271 cm(-1)) is a stretching mode (239 cm(-1)) instead, suggesting the nanowires are not strictly monoclinic. The most notable effect of increasing the temperature of the samples is the appearance of the bending mode of W-OH bonds in the approximate range of 1550-1150 cm(-1), which is related to O-H bonding caused by humidity effects. In addition, features such as those at 750 cm(-1) for nanowires and at 492 and 670 cm(-1) for WO3:Si disappear as the temperature increases. A deeper understanding of the effect that temperature has on the Raman spectral characteristics of a metal oxide such as WO3 has helped to extend our knowledge regarding the behavior of metal oxide-gas interactions for sensing applications. This, in turn, will help to develop theoretical models for the identification of specific metal oxide-gas relationships.

Summary Atomic Force Microscopy of hydrophobic material surfaces in water shows the presence of closely spaced soft domains. The radii of curvature of these features are of the order of 100 nm and their heights above the substrate are in the range 20-30 nm. The consensus interpretation of these features is that they are nanosized gas bubbles formed on the substrate following immersion. Levy et al.1 have shown experimentally that when graphene is stretched to form nanobubbles on a platinum substrate, electrons behave as if they are subject to magnetic fields in excess of 300 Tesla, even though no magnetic field has actually been applied. The ability to make electrons behave as if they were in magnetic fields of 300 Tesla or more - merely by stretching graphene - offers a new approach for important applications relating to modern solid state devices. There still remains the difficulty of explaining the apparent stability of nanobubbles with conventional thermodynamics.2-3 Zhou et al.,4 in their study on interfacial wetting at epitaxial graphene, have extended some of our results. An interesting result from this work, with its combined use of experimental and computational approaches, was that the macroscopic contact angle of water on epitaxial graphene layers is correlated with the number of layers. Based on their results, the small amount of the epitaxial buffer layer of bi-layer graphene that makes direct contact with water helps explain its macroscopic contact angle being close to the value for bulk graphite, that is {}{} . This contact angle value for bulk graphite, independent of the number of graphene layers, n, was also obtained after it was found that the water-exposure coverage of Gn (n-layer graphene) was close to unity. These results agree with ours,5specifically the room temperature contact angle value of water on graphite. On another front, we note that recent experiments have found evidence for phase transitions of gases (e.g. argon and krypton) adsorbed on a single carbon nanotube. In order to understand these observations, classical Grand Canonical Monte Carlo simulations have been performed.3 Intricate and overlapping nanoscale issues relating to the modeling and simulation of wetting phenomena, formation of nanobubbles on nanomaterials, and the adsorption of rare gas atoms in carbon nanotubes, will be compared and discussed.

Industrial applications, such as mixture separation, air purification, and surface coatings, all depend on adsorption phenomena. The significant role of interfaces and the need for a better understanding of both physisorption and chemisorption at the microscopic level over the past few decades has motivated the innumerable theoretical developments of the subject. Almost a quarter century ago, carbon research was given a boost by Richard Smalley’s discovery of fullerenes and buckyballs [1] and Sumio Iijima’s detection of nanotubes [2] the one-dimensional allotrope of carbonin the soot of an arc discharge in an effort to synthesize clusters of fullerene. In contrast to buckyballs and nanotubes, which were observed experimentally twenty five years ago, the one-atom-thick sheet of carbon possessing a honey-comb lattice structure called graphene has been an object of theoretical interest for more than fifty years [3]. The awarding of the 2010 Nobel Prize in Physics to Andre Geim and Konstantin Novoselov for the definitive identification and characterization of graphene recognizes a new chapter in carbon research and is testament to the importance of the field [4]. Graphene exhibits the so-called

Nanobubbles have been found to form at the interface of water and solid surfaces. We examine the conditions for such bubbles to form and estimate the pressure inside the bubble based on thermodynamic considerations. Using a simple model we calculate the contact angle for a wide range of temperatures and hypothetical substrates possessing a continuous range of strengths. We show that as the temperature increases the shape of a bubble changes continuously from a spherical cap with low curvature to a complete sphere. An equivalent effect results from either increasing the strength of the solid or decreasing the surface tension. A model of a substrate formed by layers of materials is proposed to obtain a nanobub- ble with a particular contact angle.