Controlled growth of single-walled carbon nanotubes for unique nanodevices.

The controlled growth of bent and horizontally aligned single-walled carbon nanotubes (SWNTs) is demonstrated in this study. The bent SWNTs growth is attributed to the interaction between van der Waals force with substrate and aerodynamic force from gas flow. The curvature of bent SWNTs can be tailored by adjusting the angle between gas flow and step-edge direction.

Curvature-induced D-band Raman scattering in folded graphene.

Micro-Raman scattering from folds in single-layer graphene sheets finds a D-band at the fold for both incommensurate and commensurate folding, while the parent single-layer graphene lacks a D-band. A coupled elastic-continuum/tight-binding calculation suggests that this D-band arises from the spatially inhomogeneous curvature around a fold in a graphene sheet. The polarization dependence of the fold-induced D-band further reveals that the inhomogeneous curvature acts as a very smooth, ideal one-dimensional defect along the folding direction.

Polarized Rayleigh back-scattering from individual semiconductor nanowires.

A complete understanding of the interaction between electromagnetic radiation and semiconductor nanowires (NWs) is required in order to further develop a new generation of opto-electronic and photonic devices based on these nanosystems. The reduced dimensionality and high aspect ratio of nanofilaments can induce strong polarization dependence of the light absorption, emission and scattering, leading in some cases to the observation of optical antenna effects. In this work we present the first systematic study of polarized Rayleigh back-scattering from individual crystalline semiconductor NWs with known crystalline structure, orientation and diameters.

Cavity-enhanced stimulated raman scattering from short GaP nanowires.

We report the first observation of stimulated Raman scattering (SRS) from semiconductor nanowires (SNWs). Using continuous wave (CW) excitation (514.5 nm), very strong nonlinear SRS was observed in backscattering from short segments of crystalline GaP NWs with diameter d = 210 nm when the wire length L < 1.

Adsorption of ammonia on graphene.

We report on experimental studies of NH3 adsorption/desorption on graphene surfaces. The study employs bottom-gated graphene field effect transistors supported on Si/SiO2 substrates. Detection of NH3 occurs through the shift of the source-drain resistance maximum ('Dirac peak') with the gate voltage.

Encapsulation of organic molecules in calcium phosphate nanocomposite particles for intracellular imaging and drug delivery.

Encapsulation of imaging agents and drugs in calcium phosphate nanoparticles (CPNPs) has potential as a nontoxic, bioresorbable vehicle for drug delivery to cells and tumors. The objectives of this study were to develop a calcium phosphate nanoparticle encapsulation system for organic dyes and therapeutic drugs so that advanced fluoresence methods could be used to assess the efficiency of drug delivery and possible mechanisms of nanoparticle bioabsorption. Highly concentrated CPNPs encapsulating a variety of organic fluorophores were successfully synthesized.

Near-infrared emitting fluorophore-doped calcium phosphate nanoparticles for in vivo imaging of human breast cancer.

Early detection is a crucial element for the timely diagnosis and successful treatment of all human cancers but is limited by the sensitivity of current imaging methodologies. We have synthesized and studied bioresorbable calcium phosphate nanoparticles (CPNPs) in which molecules of the near-infrared (NIR) emitting fluorophore, indocyanine green (ICG), are embedded. The ICG-CPNPs demonstrate exceptional colloidal and optical characteristics.

n-Type behavior of graphene supported on Si/SiO(2) substrates.

Results are presented from an experimental and theoretical study of the electronic properties of back-gated graphene field effect transistors (FETs) on Si/SiO(2) substrates. The excess charge on the graphene was observed by sweeping the gate voltage to determine the charge neutrality point in the graphene. Devices exposed to laboratory environment for several days were always found to be initially p-type.

Probing graphene edges via Raman scattering.

We present results of a Raman scattering study from the region near the edges of n-graphene layer films. We find that a Raman band (D) located near 1344 cm(-1) (514.5 nm excitation) originates from a region next to the edge with an apparent width of approximately 70 nm (upper bound).

Catalytic polymerization and facile grafting of poly(furfuryl alcohol) to single-wall carbon nanotube: preparation of nanocomposite carbon.

A nanocomposite carbon was prepared by grafting a carbonizable polymer, poly(furfuryl alcohol) (PFA), to a single-wall carbon nanotube (SWNT). The SWNT was first functionalized with arylsulfonic acid groups on the sidewall via a method using a diazonium reagent. Both Raman and FTIR spectroscopies were used to identify the functional groups on the nanotube surface.

Electromagnetic interference (EMI) shielding of single-walled carbon nanotube epoxy composites.

Single-walled carbon nanotube (SWNT)-polymer composites have been fabricated to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) of SWNTs. Our results indicate that SWNTs can be used as effective lightweight EMI shielding materials. Composites with greater than 20 dB shielding efficiency were obtained easily.

Raman and IR spectroscopy of chemically processed single-walled carbon nanotubes.

IR and Raman spectroscopy has been used to study the evolution of the vibrational spectrum of bundled single-walled carbon nanotubes (SWNTs) during the purification process needed to remove metal catalyst and amorphous carbon present in arc-derived SWNT soot. We have carried out a systematic study to define the different outcomes stemming from the purification protocol (e.g.

Mechanical properties of ZnS nanobelts.

Mechanical properties of ZnS nanobelts were measured at room temperature by direct nanoindentation experiments. It was found that the ZnS nanobelts achieve 79% increase in hardness but 52% decrease in elastic modulus compared to bulk ZnS. The nanobelts were found to exhibit creep under indentation.

Atom collision-induced resistivity of carbon nanotubes.

We report the observation of unusually strong and systematic changes in the electron transport in metallic single-walled carbon nanotubes that are undergoing collisions with inert gas atoms or small molecules. At fixed gas temperature and pressure, changes in the resistance and thermopower of thin films are observed that scale as roughly M(1/3), where M is the mass of the colliding gas species (He, Ar, Ne, Kr, Xe, CH4, and N2). Results of molecular dynamics simulations are also presented that show that the maximum deformation of the tube wall upon collision and the total energy transfer between the colliding atom and the nanotube also exhibit a roughly M(1/3) dependence.

Debundling and dissolution of single-walled carbon nanotubes in amide solvents.

Wet chemical methods involving ultrasound and amide solvents were used to purify and separate large bundles of single-walled carbon nanotubes (SWNTs) into individual nanotubes that could then be transported to silicon or mica substrates. The SWNTs studied were produced by the arc-discharge process. Dry oxidation was used in an initial step to remove amorphous carbon.

Raman spectroscopic investigation of H2, HD, and D2 physisorption on ropes of single-walled, carbon nanotubes.

We have observed the S- and Q-branch Raman spectra of H2, HD, and D2 adsorbed at 85 K and pressures up to 8 atm on single-walled, carbon nanotubes (SWNT). Comparative data for H2 on graphite and C60 were also collected. Frequency-downshifted and upshifted features were observed in the Q-branch spectra of H2 on C60 and SWNT.