Confocal Raman spectromicroscopy for tin-core/carbon-shell nanowire heterostructure

High density heterostructures of carbon nanotubes encapsulated single crystalline tin nanowires have been characterized by Raman spectromicroscopy. The morphology, composition and structure of the synthesized nanoheterostructures were examined by using scanning electron microscopy, transmission electron microscopy. The Raman spectra obviously manifest the crystalline nano-graphite within amorphous carbon walls in the heterostructures. The Raman image reproduces the pristine heterostructures of the CNTs as seen in SEM image, which illustrate the single nanowires oriented uniformly grown on micro-graphitic fibers. It was found that the resultant heterostructures are luminescent which was attributed to crystalline nano-graphite embedded in the amorphous carbon matrix, which is a consequence of excitons localization within an increasing number of sp² rich clusters. The contrast in the Raman image reflects nonuniform distribution of the graphite cluster size which acts as the radiative centers. The luminescent property was reviewed. The enhanced Raman spectra and luminescent property by the well-defined tin nanowires inside the heterostructures was revealed.     

Selective growth, characterization, and field emission performance of single-walled and few-walled carbon nanotubes by plasma enhanced chemical vapor deposition

Single-walled carbon nanotubes (SWCNTs) and few-walled carbon nanotubes (FWCNTs) have been selectively synthesized by plasma enhanced chemical vapor deposition at a relative low temperature (550 °C) by tuning the thickness of iron catalyst. The parametric study and the optimization of the nanotube growth were undertaken by varying inductive power, temperature, catalyst thickness, and plasma to substrate distance. When an iron film of 3-5 nm represented the catalyst thickness for growing FWCNT arrays, SWCNTs were synthesized by decreasing the catalyst thickness to 1 nm. The nanotubes were characterized by field emission scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. Electron field emission properties of the nanotubes indicate that the SWCNTs exhibit lower turn-on field compared to the FWCNTs, implying better field emission performance.     

Hydrogen-free spray pyrolysis chemical vapor deposition method for the carbon nanotube growth: Parametric studies

Spray pyrolysis chemical vapor deposition (CVD) in the absence of hydrogen at low carrier gas flow rates has been used for the growth of carbon nanotubes (CNTs). A parametric study of the carbon nanotube growth has been conducted by optimizing various parameters such as temperature, injection speed, precursor volume, and catalyst concentration. Experimental observations and characterizations reveal that the growth rate, size and quality of the carbon nanotubes are significantly dependent on the reaction parameters. Scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy techniques were employed to characterize the morphology, structure and crystallinity of the carbon nanotubes. The synthesis process can be applied to both semiconducting silicon wafer and conducting substrates such as carbon microfibers and stainless steel plates. This approach promises great potential in building various nanodevices with different electron conducting requirements. In addition, the absence of hydrogen as a carrier gas and the relatively low synthesis temperature (typically 750 °C) qualify the spray pyrolysis CVD method as a safe and easy way to scale up the CNT growth, which is applicable in industrial production.