D. N. Batchelder

Direct observation of sp3 bonding in tetrahedral amorphous carbon using ultraviolet Raman spectroscopy

The vibrational modes of the sp3 sites in tetrahedral amorphous carbon (ta-C) thin films are revealed directly using ultraviolet Raman spectroscopy at 244 nm excitation and are shown to produce a Raman peak centered around 1100 cm−1. In addition, the main Raman peak associated with sp2 vibrational modes is shifted upward in frequency by 100 cm−1 relative to its position in spectra excited at 514 nm. The spectra are interpreted in terms of the bonding in ta-C.

Confocal Raman Microspectroscopy Using a Stigmatic Spectrograph and CCD Detector

Confocal Raman microspectroscopy has previously used pinholes placed at the back focal plane of the microscope to provide depth resolution along the optical axis. The process of optimizing the pinhole alignment can often be difficult and time-consuming. We demonstrate a different approach to setting up a confocal Raman microscope using a stigmatic spectrograph and a CCD detector. This arrangement is easy to use and provides a depth resolution of ∼2 μm.

Transformation of nanodiamond into carbon onions: A comparative study by high-resolution transmission electron microscopy, electron energy-loss spectroscopy, x-ray diffraction, small-angle x-ray scattering, and ultraviolet Raman spectroscopy

The structural properties of both nanodiamond particles synthesized by detonation and the products of their transformation into carbon onions via vacuum annealing at 1000 and 1500°C have been studied using high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy, x-ray diffraction (XRD), small-angle x-ray scattering (SAXS), and Raman spectroscopy. The advantages of UV Raman spectroscopy over visible Raman spectroscopy for the analysis of these carbon nanomaterials are demonstrated. It was found that the synthesized nanodiamond particles have a composite core-shell structure comprising an ordered diamond core covered by a disordered (amorphous) outer shell formed by the mixed sp2∕sp3 bonding of carbon atoms. The observed structure of the nanodiamond particles are comparable with the structure of the bucky diamond clusters comprising a diamond core and a reconstructed surface which stabilizes the cluster at the average diameter of ∼30A, as predicted recently from theoretic...

Confocal Raman Microspectroscopy through a Planar Interface

We have developed a model to describe the effect of refraction through a planar interface on the collection efficiency and depth of focus when performing confocal Raman microspectroscopy. The planar interface introduces spherical aberration, which can substantially degrade the performance of the microscope, especially for large-numerical-aperture microscope objectives. This spherical aberration will increase the range of focal depths spanned by the paraxial and marginal rays of the illuminating laser beam within the sample. In the collection path, it will also distort the scattering volume defined by the confocal aperture; this results in a dramatic fall in the collected light intensity with increasing depth. We demonstrate that there is an optimum numerical aperture for collected light intensity at a given depth. The prediction of this theoretical model is compared to empirical results obtained by mapping the stress distribution within the diamond anvil of a high-pressure cell. Both the collected Raman intensity and the effective depth of focus are compared to the predictions from the theory.

Submicron resolution measurement of stress in silicon by near-field Raman spectroscopy

A scanning near-field optical microscope (SNOM) has been constructed that is capable of recording Raman spectra with a spatial resolution of ∼150 nm. The SNOM has been used to produce a combined topological and Raman map of a plastically deformed area of a silicon wafer. The variation of the frequency of the 520 cm−1 Raman band with position has been used to estimate the residual stresses associated with the deformation. The measurements demonstrate the feasibility of nondestructive, submicron stress measurement in semiconductors by near-field Raman spectroscopy.

In Situ Detection and Identification of Trace Explosives by Raman Microscopy

The innovative design of the newly developed Renishaw Raman Microscope system and its application to the in situ detection and identification of plastic explosives contained in fingerprint samples are presented. Raman microscopy is a nondestructive inspection method. Our experimental results show that Raman spectra and Raman band images can be obtained from explosive particles as small as 1 µm3 in size or 1 picogram in mass. After exploring the full potential of the Raman microscopic technique, the aim of this research is to develop a real-time and field-deployable plastic explosive detection system.

A theoretical study of the structure and vibrations of 2,4,6-trinitrotolune

Abstract Theoretical calculations of the structure, internal rotations and vibrations of 2,4,6-trinitrotolune, TNT, in the gas phase were performed at the B3LYP/6-31G* and B3LYP/6-311+G** levels of theory. Two genuine energy minimum structures were found. In both structures the 4-nitro group is planar to the phenyl ring, while the 2,6-nitro groups are slightly out of plane with the phenyl ring due to steric interaction with the methyl group. The two structures are related by internal rotations of the methyl and 2, or 6-nitro group. The lowest energy route for interconversion between them is a concerted motion of the methyl group and 2 or 6 nitro group in a ‘cog wheel’ type of mechanism. The geometry of the low energy structure A is closest to that observed in the crystal structures of TNT, where all three nitro groups are out of plane with the phenyl ring. FTIR and Raman spectra of solid TNT and 13C, 15N enriched TNT are presented and assigned with the help of the B3LYP/6-311+G** calculations on A. The lower level B3LYP/6-31G* calculation fails to predict the correct vibrational coupling between the nitro and phenyl groups. The B3LYP/6-311+G** calculation gives a good prediction of the nitro vibrations and the isotopic shifts observed for TNT isotopomers.

Combining high resolution and tensorial analysis in Raman stress measurements of silicon

We present the development of a Raman spectroscopy technique for the measurement of the tensorial nature of stress in silicon on a micrometric scale. After the detailed description of the theoretical bases of the experiment, we measure the stress tensor of a silicon surface close to a scratch. Then, we apply this method to discern which models are suitable for the description of the stress tensor in shallow trench isolations for microelectronics.

UV-Excited Resonance Raman Spectroscopy of Narcotics and Explosives

A 244 nm excitation Raman microspectroscope has been developed and successfully used to investigate a range of narcotics and explosives, both pure and contaminated. The instrument is quick and simple to operate and effective in identifying these compounds. The wavelength was chosen to exploit the resonance Raman effect, thereby enhancing the band intensities beyond the normal v4 enhancement associated with the shorter wavelength excitation. Another advantage over visibly excited Raman spectroscopy is the complete lack of any fluorescence background, even with heavily contaminated samples. The simplification of spectra caused by resonance allowed the easy identification of species contained in complex mixtures.

Development of a scanning near-field optical probe for localised Raman spectroscopy

Abstract The scanning near-field optical probe technique has made it possible to perform conventional optical spectroscopies with unprecedented spatial resolution. We present the development of an instrument for scanning near-field Raman spectroscopy and present near-field Raman linescans and spectra of a range of materials with subwavelength resolution.