Laser-assisted solid-state synthesis of carbon nanotube/silicon core/shell structures

A single-step solid-state synthetic approach was developed for the synthesis of silicon-coated carbon nanotube (CNT) core/shell structures. This was achieved through laser-induced melting and evaporation of CNT-deposited Si substrates using a continuous wavelength CO2 laser. The synthesis location of the CNT/Si structures was defined by the laser-irradiated spots. The thickness of the coating was controlled by tuning the laser power and synthesis time during the coating process. This laser-based synthetic technique provides a convenient approach for solid-state, controllable, gas-free, simple and cost-effective fabrication of CNT/Si core/shell structures.

Plasmonic-enhanced carbon nanotube infrared bolometers

Plasmonic nanoantennas show significant potential in photodetection applications, but the extent to which their full potential can be realized is dictated by the volume and location of the active materials within the plasmonic structure. Carbon nanotubes (CNTs) have been used as a novel material in photodetection application due to their excellent electronic and optoelectronic properties. However, difficulties in the integration of CNTs in the gaps of nanoantennas have limited the investigation of antenna-coupled CNT detectors. Here, we demonstrate a unique plasmonic approach for selectively growing CNTs in the gap of nanoantenna arrays for fabrication of plasmonic infrared bolometers operating at room temperature. Strong concentration of light at the tips of nanoantennas was utilized for localized heating and growth of CNTs. Moreover, interaction of this strong optical field with the small volume of CNTs enhanced the photoresponse of the bolometers. Consequently, a high responsivity of about 800 V W(-1) was achieved at room temperature.

Surface-enhanced Raman spectroscopy using gold-coated horizontally aligned carbon nanotubes

Gold-coated horizontally aligned carbon nanotube (Au-HA-CNT) substrates were fabricated for surface-enhanced Raman spectroscopy (SERS). The Au-HA-CNT substrates, which are granular in nature, are easy-to-prepare with large SERS-active area. Enhancement factors (EFs) of ∼10(7) were achieved using the Au-HA-CNTs as substrates for rhodamine 6G (R6G) molecules. Maximum enhancement was found when the polarization direction (E-field) of the incident laser beam was parallel to the aligned direction of the HA-CNTs. Simulations using the finite-difference time-domain (FDTD) method were carried out for the granular Au-HA-CNT samples. Enhancement mechanisms and determination of EFs were analyzed. Biological samples, including (13)C- and deuterium (D)-labeled fatty acids and Coccomyxa sp. c-169 microalgae cells, were also measured using this SERS substrate. The limits of detection (LODs) of D- and (13)C-labeled fatty acids on the SERS substrate were measured to be around 10 nM and 20 nM, respectively. Significantly enhanced Raman signals from the microalgae cells were acquired using the SERS substrate.

Diameter modulation by fast temperature control in laser-assisted chemical vapor deposition of single-walled carbon nanotubes

Diameter modulation by fast temperature control in laser-assisted chemical vapor deposition (LCVD) was successfully achieved to tune the diameters of single-walled carbon nanotubes (SWNTs) in different segments. Due to the inverse relationship between the SWNT diameter and the growth temperature, SWNTs with ascending diameters were obtained by reducing the LCVD temperature from high to low. The diameter-modulated SWNTs were integrated in electrodes to form field-effect transistors (FETs) and to investigate their electronic transport properties. The SWNTs in the FET structures have electronic properties similar to Schottky diodes, indicating clear evidence of different bandgap structures at the two ends of the SWNTs. Raman spectroscopy, transmission electron microscopy, and electronic transport characteristics were studied to investigate the influence of temperature variation on the structural and electronic characteristics of the SWNTs.

Towards carbon-nanotube integrated devices: optically controlled parallel integration of single-walled carbon nanotubes

Where it starts and where it goes? Controlled integration of single-walled carbon nanotubes (SWNTs) into pre-designed nano-architectures is one of the major challenges to be overcome for extensive scientific research and technological applications. Various serial assembly techniques have been proposed and developed. However, they are still a long way from practical applications due to the drawbacks on reliability, yield and cost. Here we demonstrate a laser-based strategy to achieve parallel integration of SWNTs into pre-designed nano-architectures through an optically controlled in situ growth process. Optical driving forces originated from tip-induced optical near-field enhancement and laser beam polarization were applied in this study to realize the controlled placement of SWNTs at designated sites following wanted orientations on the nanometer scale. Parallel integration of SWNT arrays was achieved by adjusting laser beam diameter to cover interested nano-architectures. The laser-based process suggests an efficient and cost-effective approach for fabricating and integrating SWNT-based devices and circuits.

Laser induced selective removal of metallic carbon nanotubes

Distinguishing between carbon nanotubes (CNTs) according to their individual electronic properties is of significant importance for developing CNT-based electronics and devices. In this study, selective removal of metallic CNTs from CNT mixtures on silicon substrates was investigated using controlled laser irradiation. Free electron movement and eddy currents are induced within the metallic CNTs by the strong electric field and optical near-field effects caused by the laser irradiation. Selective heating of metallic CNTs in air results in selective removal of metallic CNTs when the laser fluence and wavelength are properly selected. Through this process, metallic nanotubes are successfully removed from the CNT mixtures. This technique provides an efficient single-step approach for selective removal of metallic CNTs from CNT mixtures.

Self-aligned growth of single-walled carbon nanotubes using optical near-field effects

Self-aligned growth of ultra-short single-walled carbon nanotubes (SWNTs) was realized by utilizing optical near-field effects in a laser-assisted chemical vapor deposition (LCVD) process. By introducing the optical near-field effects, bridge structures containing single suspended SWNT channels were successfully fabricated through the LCVD process at a relatively low substrate temperature. Raman spectroscopy and I-V analyses have been carried out to characterize the SWNT-bridge structures. Numerical simulations using a high-frequency structure simulator revealed that significant enhancement of local heating occurs at metallic electrode tips under laser irradiation; it is about one order of magnitude higher than that in the rest of the electrodes. This technique suggests a novel approach to in situ low-temperature fabrication of SWNT-based devices in a precisely controlled manner, based on the nanoscale heating enhancement induced by the optical near-field effects.