DIAMOND NANOWIRES GROWN INSIDE CARBON NANOTUBES UPON
CHEMICAL VAPOR DEPOSITION: THERMODYNAMIC AND KINETIC
APPROACH
C. X. Wang, P. Liu, H. Cui, G. W. Yang
State key laboratory of optoelectronic materials and technologies, School of Physics Science & Engineering,
Zhongshan University, Guangzhou 510275, P. R. China
Keywords: diamond nanowire, thermodynamics, kinetics, nucleation, growth
Abstract
One-dimensional nanostructures such as wires, rods, belts, and tubes have become the focus of intensive
research owing to their unique applications in mesoscopis physics and fabrication of nanoscale devices. Due to
several unique properties including extreme high hardness, very high thermal conductivity, large band gap, and
chemical inertness, etc., diamonds are expected to be an important semiconductor material for high-temperature and
high-power microelectronics device, and UV-light emitting optoelectronics. Very recently, one-dimensional
nanostructures of diamond have received increasing interesting in theoretical. For example, due to stronger than
fullerene nanotubes, diamond nanorods are expected to be an important and viable target structure for synthesis.
Barnar“s studies indicate that the energy band gap of diamond nanowires (DNWs) is significantly reduced, due to
the contributions from occupied and unoccupied surface states. However, up to date, any successful syntheses of
diamond nanowires have not been found in the literature yet, to our best knowledge. On the other hand, carbon
nanotubes (CNTs) have many potential applications as molecular sieves, membranes, and ”nanopipes„ for precise
delivery of gases or liquid. Furthermore, some studies focused their attentions on transport, adsorbed, and condensed
phases of gases inside CNTs. Especially, the transport rates of CH4 and H2 gases in CNTs were suggested to be
exceptionally high. Interestingly, CH4 and H2 gases are just two typical reactive gases that are employed to deposit
diamond films upon chemical vapor deposition (CVD). These studies mentioned above naturally imply that CNTs
could be expected to be a possible path to fabricate DNWs by CVD. In this study, we propose a nano-scaled
thermodynamic nucleation and growth kinetic approach in theoretical, with respect to the effect of nanosize-induced
surface tension, for the formation of DNWs inside CNTs upon CVD. Thermodynamic analyses show that the
diamond nucleation inside a CNT would be preferable to that on the flat surface of silicon substrate due to the effect
of surface tension induced by the nanosize curvature of CNTs. Meanwhile, the capillary effect of the nanosize
curvature of diamond nuclei could drive the metastable phase region of diamond nucleation into a new stable phase
region in the carbon thermodynamic equilibrium phase diagram. Kinetic analyses indicate that the growing rate of
DNWs would go to much high once nuclei formed inside CNTs, due to the same nanosize-induced effect.
Eventually, we predict that CNTs could be an effective route to grow DNWs by CVD.
