Sharali Malik

Single-wall carbon nanotubes with diameters approaching 6 nm obtained by laser vaporization

Abstract Single-wall carbon nanotubes (SWNTs) with large diameters from 2 to 5.6 nm were prepared by pulsed laser vaporization of carbon rods doped with Co, Ni and FeS in an atmosphere of Ar:H2. The SWNT material was characterized by SEM, HRTEM, Raman, IR, UV–VIS–NIR absorption spectroscopy and thermogravimetric analysis.

Preparation, characterization and applications of free-standing single walled carbon nanotube thin films

A method for the reliable fabrication of less than 200 nm thick, free-standing purified-SWNT films having large surface areas exceeding several cm2 is described. Films were characterized using a variety of optical, microscopic and spectroscopic methods. The procedure was also used to prepare thin films of as-prepared, acid-cut and octadecylamine (ODA) functionalized SWNTs. Such samples allow facile transmission measurements of SWNT derived solids.

Reversible modification of the absorption properties of single-walled carbon nanotube thin films via nitric acid exposure

Exposure of thin films of as-prepared single-walled carbon nanotubes (SWNT) to nitric acid induces dramatic bleaching of the first and second interband transitions of semiconducting tubes (S1 and S2). These near-IR absorption features can be restored by annealing of treated SWNT films to elevated temperatures. Annealing may also be accomplished by visible laser irradiation thus allowing for spatially resolved modifications to SWNT thin film optical absorption.

High purity graphenes prepared by a chemical intercalation method

A simple method of fabricating pristine few-layer and single-layer graphene which could be used for production on a gram scale is described.

Debundling, selection and release of SWNTs using fluorene-based photocleavable polymers

Photocleavable polymers based on 9,9-dialkylfluorene backbone and o-nitrobenzylether were designed and synthesized to obtain stable (n,m) enriched suspensions of semiconducting SWNTs in toluene. Photoirradiation of the suspensions triggered the precipitation of the SWNTs and TEM images indicate close packing of SWNTs pointing at partial removal of the coating polymer.

Failure mechanism of free standing single-walled carbon nanotube thin films under tensile load

The mechanical properties of free standing films of as prepared and acid purified single-walled carbon nanotubes were studied by means of tensile stress measurements as well as electron microscopy. Films appear to fail by crack propagation involving rupture or matrix pull-out of bridging nanotube bundles.

Nanostructuring the graphite basal plane by focused ion beam patterning and oxygen etching

Ga+ focused ion beam (FIB) patterning was used to structure highly oriented pyrolytic graphite surfaces with square, periodic arrays of amorphous carbon defects (mesh sizes: 300 nm–2 µm). Controlled oxygen etching of these arrays leads to matrices of uniform, orientationally aligned, nm-sized, hexagonal holes. The properties of the resulting hole assembly (hole depths and lateral hole dimensions) have been investigated by means of atomic force microscopy, scanning electron microscopy and FIB sectioning. The hole dimensions and uniformity both depend on the FIB parameters and etching conditions. Etching temperatures from 500 to 700 °C were applied. Initial etch rates of up to 106 C s−1 per individual hole were observed when using oxygen pressures of 200 mbar. For an etch temperature of 590 °C the rate of etching of individual holes was found to depend measurably on the inter-hole separation. This confirms that the associated reaction kinetics is mediated by the finite diffusion length of reactive oxygen species along the graphite basal plane. Prolonged etching results in hole–hole contact and generation of mesa arrays of controllable size and shape.

Sequence-Specifically Addressable Hairpin DNA−Single-Walled Carbon Nanotube Complexes for Nanoconstruction

Single-walled carbon nanotubes (SWCNTs) are attractive building blocks for molecular electronics and novel materials. Generating functional architectures with SWCNTs requires methodologies for dispersing, purifying, and binding these highly insoluble quasi one-dimensional molecules. We have previously shown that unstructured DNA strands bind to carbon nanotubes so tightly that it is difficult to address them with complementary strands. Here we show that hairpin oligonucleotides give SWCNT suspensions more concentrated than those obtainable with previously optimized DNA sequences. Further, hairpin-forming oligonucleotides and (6,5)-SWCNTs form complexes that are addressable with complementary, triplex-forming oligonucleotides. As proof of principle, we show that DNA-SWCNT complexes can be bound sequence-specifically with oligonucleotides featuring fluorophores or quantum dots. The new method brings SWCNTs of exquisite purity into the realm of DNA-based nanostructuring.

Nanostructured arrays of stacked graphene sheets.

Molecular oxygen etching of HOPG surfaces prepatterned by Ga(+) focused-ion-beam irradiation (FIB) has been used to generate large-area arrays of nanometer-sized graphite blocks. AFM and SEM imaging show that structures with lateral sizes down to ~100 nm and heights of between 30 and 55 nm can be routinely fabricated. The trenches separating the graphite blocks form in the early oxidation stages via preferential gasification (into CO and CO(2)) of the gridlike amorphized carbon regions written by FIB. In the later oxidative etching stages, gasification of the graphite nanoprism faces laterally terminating the graphite blocks becomes the major reaction channel. Correspondingly, graphite blocks are (further) reduced in lateral extent while the trenches in between are widened. Raman and photoionization spectroscopies indicate that the quality of the topmost nG sheet(s) covering the blocks also decreases with increasing etching time-as the size and lateral density of defect-mediated etch pits increases. nG block arrays are useful substrates with which to probe the size-dependent properties of nanographene, as they comprise large numbers of uniform sheets (ca. 4 × 10(10) cm(-2) for an array of 0.5 × 0.5 μm(2)) thus allowing for the application of area-integrating spectroscopic methods. We demonstrate this by examining the Raman features of nG block arrays which include a graphene-rim-region fingerprint mode. Individual nG sheets can be exfoliated from nG stacks by means of electron-irradiation-induced charging. We have explored a number of printing/manipulation strategies aimed at controllable electromechanical transfer of nG sheet arrays to silicon wafers.

Free‐Standing Single‐Wall Carbon Nanotube Thin Films

A method for the reliable fabrication of less than 200 nm thick, free‐standing as‐prepared, purified, acid‐cut and octadecylamine (ODA) functionalized SWNTs films having large surface areas exceeding several cm2 is described. Films were characterized using a variety of optical, microscopic and spectroscopic methods.