[en] 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.

[en] 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. (paper)

[en] The influence of resonant vibrational excitation of ethylene molecules in combustion chemical vapor deposition of diamond was investigated. Resonant vibrational excitation of the CH₂-wagging mode (a type c fundamental band, υ_7, at 949.3 cm⁻¹) in ethylene molecules was achieved by using a wavelength-tunable CO₂ laser with a matching wavelength at 10.532 µm. By comparing to laser irradiation at off-resonance wavelengths, an on-resonance vibrational excitation is more efficient in energy coupling, increasing flame temperatures, accelerating the combustion reactions, and promoting diamond deposition. An enhanced rate of 5.7 was achieved in terms of the diamond growth rate with an improved diamond quality index at a high flame temperature under a resonant excitation of the CH₂-wagging mode. This study demonstrates that a resonant vibrational excitation is an effective route for coupling energy into the gas phase reactions and promoting the diamond synthesis process. (letter)

[en] The interaction between an iron atom and graphene containing a single Stone-Wales (SW) defect has been investigated by ab initio density functional calculations. The top site on the core defective bond-rotated carbon atom turns out to be the most favorable for iron atom adsorption. The local magnetic moment of the iron atom is 2.24 μ_B in this adsorbed system, and it can be interpreted by an effective Fe 3d⁸4s⁰ configuration caused by the strong interaction between the adatom and the core defective bond-rotated carbon atom. The defect minimizes the binding energy with respect to the adsorption of iron atoms on defect-free graphene and consequently makes the adsorbed systems more stable. Additionally, the adsorption of iron atoms on the defective graphene induces the adsorbed structures to be distorted evidently along the direction perpendicular to the graphene sheet. In particular, the band structures of these adsorbed systems, with some spin-polarized gap states lying between the π and π^* bands, are modulated by Fe 3d states in the vicinity of the Fermi level, and the gap between the valence band maximum and conduction band minimum is decreased to almost zero due to the interaction of Fe 3d states with C 2p states.

[en] 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.

[en] 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.

[en] A catalyst-free and highly efficient synthetic method for growing carbon nano-onions (CNOs) in open air has been developed through the laser resonant excitation of a precursor molecule, ethylene, in a combustion process. Highly concentric CNO particles with improved crystallinity were obtained at a laser wavelength of 10.532 μm through the resonant excitation of the CH₂ wagging mode of the ethylene molecules. A higher growth rate up to 2.1 g h^-1 was obtained, compared with that without a laser (1.3 g h^-1). Formation of the CNOs with ordered graphitic shells is ascribed to the decomposition of polycyclic aromatic hydrocarbons (PAHs) into C₂ species. The optical limiting performances of the CNOs grown by the combustion processes were investigated. CNOs grown at 10.532 μm laser excitation demonstrated improved optical limiting properties due to the improved crystallinity.

[en] 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.

[en] Branched nickel monosilicide (NiSi) nanowires (NWs), for the first time, have been synthesized on Ni foams by laser-assisted chemical vapor deposition using disilane precursor molecules. Studies indicate that 600 deg. C is the threshold temperature for the growth of a large number of branched NiSi NWs with 100-500 nm long branches extending from the main stems. Below the threshold temperature, unbranched NiSi NWs were obtained. The density of the branched NiSi NWs is relatively higher in comparison to that of the unbranched ones. The growth rate of the branched NiSi NWs at 700 deg. C is estimated up to 10 μm min^-1. High-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy of the branched NiSi NWs suggest that the formation of these branched nanostructures is ascribed to the Ni-dominant diffusion process. These NiSi NWs with branched nanostructures could bring them new opportunities in nanodevices.

[en] Rapid single-step fabrication of graphene patterns was developed using laser-induced chemical vapor deposition (LCVD). A laser beam irradiates a thin nickel foil in a CH₄ and H₂ environment to induce a local temperature rise, thereby allowing the direct writing of graphene patterns in precisely controlled positions at room temperature. Line patterns can be achieved with a single scan without pre- or postprocesses. Surprisingly, the growth rate is several thousand times faster than that of general CVD methods. The discovery and development of the LCVD growth process provide a route for the rapid fabrication of graphene patterns for various applications.