Debdulal Roy

Growth process conditions of vertically aligned carbon nanotubes using plasma enhanced chemical vapor deposition

The growth of vertically aligned carbon nanotubes using a direct current plasma enhanced chemical vapor deposition system is reported. The growth properties are studied as a function of the Ni catalyst layer thickness, bias voltage, deposition temperature, C2H2:NH3 ratio, and pressure. It was found that the diameter, growth rate, and areal density of the nanotubes are controlled by the initial thickness of the catalyst layer. The alignment of the nanotubes depends on the electric field. Our results indicate that the growth occurs by diffusion of carbon through the Ni catalyst particle, which rides on the top of the growing tube.

Characterisation of carbon nano-onions using Raman spectroscopy

Characteristics of the Raman spectrum from carbon onions have been identified in terms of the position of the G peak and appearance of the transverse optic phonon peaks. Five new peaks were observed in the low wavenumber region, at about 1100, 861, 700, 450 and 250 cm−1. The origins of these peaks are discussed in terms of the phonon density of states (PDOS) and phonon dispersion curves of graphite. The curvature of the graphene planes is invoked to explain the relaxation of the Raman selection rules and the appearance of the new peaks. The Raman spectrum of carbon onions is compared with that of highly oriented pyrolytic graphite (HOPG). The strain of graphene planes due to curvature has been estimated analytically and is used to account for the downward shift of the G peak.

Multifunctional Nanoprobes for Nanoscale Chemical Imaging and Localized Chemical Delivery at Surfaces and Interfaces

Double take: Double-barrel carbon nanoprobes with integrated distance control for simultaneous nanoscale electrochemical and ion conductance microscopy can be fabricated with a wide range of probe sizes in less than two minutes. The nanoprobes allow simultaneous noncontact topographical (left image) and electrochemical imaging (right) of living neurons, as well as localized K+ delivery and simultaneous neurotransmitter detection.

Growth of high-quality single-wall carbon nanotubes without amorphous carbon formation

We report an alternative way of preparing high-quality single-wall carbon nanotubes (SWCNTs). Using a triple-layer thin film of Al/Fe/Mo (with Fe as a catalyst) on an oxidized Si substrate, the sample is exposed to a single short burst (5 s) of acetylene at 1000 °C. This produced a high yield of very well graphitized SWCNTs, as confirmed by transmission electron microscopy and Raman spectroscopy. We believe that the high temperature is responsible for the high crystallinity/straightness of the nanotubes, and the rapid growth process allows us to achieve a clean amorphous carbon (a-C) free deposition which is important for SWCNT device fabrication. The absence of a-C is confirmed by Auger electron spectroscopy, Raman spectroscopy, and electrical measurements.

The European nanometrology landscape

This review paper summarizes the European nanometrology landscape from a technical perspective. Dimensional and chemical nanometrology are discussed first as they underpin many of the developments in other areas of nanometrology. Applications for the measurement of thin film parameters are followed by two of the most widely relevant families of functional properties: measurement of mechanical and electrical properties at the nanoscale. Nanostructured materials and surfaces, which are seen as key materials areas having specific metrology challenges, are covered next. The final section describes biological nanometrology, which is perhaps the most interdisciplinary applications area, and presents unique challenges. Within each area, a review is provided of current status, the capabilities and limitations of current techniques and instruments, and future directions being driven by emerging industrial measurement requirements. Issues of traceability, standardization, national and international programmes, regulation and skills development will be discussed in a future paper.

Ag nanoparticle induced surface enhanced Raman spectroscopy of chemical vapor deposition diamond thin films prepared by hot filament chemical vapor deposition

Surface enhanced Raman spectroscopy was performed by depositing Ag particles by dc sputtering on thin diamond films prepared by hot filament chemical vapor deposition. Enhancement of Raman signal by a factor up to 100 could be obtained by controlling the Ag particle size. Raman spectra from different locations through the thickness of diamond films indicate a variation in the carbon structures. Phonon density of states of diamond and graphite are considered along with previously reported observations, to analyze the additional bands which appear in the SERS scattering as a consequence of the presence of the Ag particles.

Visualizing graphene edges using tip-enhanced Raman spectroscopy

The edges of a single layer graphene (SLG) flake play important roles in determining the electronic transport properties of graphene devices. Accurate determination of the phase-breaking lengths (Lσ) near the edges remains to be a significant challenge for near field optical measurements. This article presents an image of graphene edges using high resolution tip-enhanced Raman spectroscopy (TERS) of mechanically exfoliated SLG and reports the value of Lσ (4.2 ± 0.5 nm). The current near-field measurements verify the theoretical value of Lσ and highlight the potential of TERS in characterizing graphene at the nanoscale.

Fabrication of gold tips suitable for tip-enhanced Raman spectroscopy

The authors report on a simple method of fabricating gold tips, suitable for use in a shear-force mode atomic force microscope for tip-enhanced Raman spectroscopy (TERS). The proposed electrochemical method is highly optimized and offers five advantages: produces a low-aspect ratio tip that can withstand the lateral force at the end of the tip during scanning, produces a sharp tip end to generate good Raman enhancements for TERS, a self-terminating process that makes the etching process easy, use of inexpensive electronic systems so that it can be adopted by any laboratory, and less time consuming (takes less than 20s to fabricate a single tip). This article demonstrates TERS imaging using such tips.

Novel methodology for estimating the enhancement factor for tip-enhanced Raman spectroscopy

Enhancement factor and spatial resolution are two of the most important metrological parameters defining the quality of a tip-enhanced Raman spectrometer. A high degree of variability in the reported values of enhancement factor is highlighted in this work, and the possible reasons for the discrepancies are discussed. A methodology for estimating enhancement factor in tip-enhanced Raman imaging using a one-dimensional nanostructure such as single wall carbon nanotube is suggested. This methodology is verified using tip-enhanced Raman images from our laboratory, and an image from another group published previously.

Single-molecule reconstruction of oligonucleotide secondary structure by atomic force microscopy.

Based on soft-touch atomic force microscopy, a method is described to reconstruct the secondary structure of single extended biomolecules, without the need for crystallization. The method is tested by accurately reproducing the dimensions of the B-DNA crystal structure. Importantly, intramolecular variations in groove depth of the DNA double helix are resolved, which would be inaccessible for methods that rely on ensemble-averaging.