Naigui Shang

Self-Assembled Growth, Microstructure, and Field-Emission High-Performance of Ultrathin Diamond Nanorods

We report the growth of ultrathin diamond nanorods (DNRs) by a microwave plasma assisted chemical vapor deposition method using a mixture gas of nitrogen and methane. DNRs have a diameter as thin as 2.1 nm, which is not only smaller than reported one-dimensional diamond nanostructures (4-300 nm) but also smaller than the theoretical value for energetically stable DNRs. The ultrathin DNR is encapsulated in tapered carbon nanotubes (CNTs) with an orientation relation of (111)diamond//(0002)graphite. Together with diamond nanoclusters and multilayer graphene nanowires/nano-onions, DNRs are self-assembled into isolated electron-emitting spherules and exhibit a low-threshold, high current-density (flat panel display threshold: 10 mA/cm2 at 2.9 V/microm) field emission performance, better than that of all other conventional (Mo and Si tips, etc.) and popular nanostructural (ZnO nanostructure and nanodiamond, etc.) field emitters except for oriented CNTs. The forming mechanism of DNRs is suggested based on a heterogeneous self-catalytic vapor-solid process. This novel DNRs-based integrated nanostructure has not only a theoretical significance but also has a potential for use as low-power cold cathodes.

Irradiation enhanced paramagnetism on graphene nanoflakes

We have studied the magnetization of vertically aligned graphene nanoflakes irradiated with nitrogen ions of 100 KeV energy and doses in the range 1011–1017 ions/cm2. The non-irradiated graphene nanoflakes show a paramagnetic contribution, which is increased progressively by ion irradiation at low doses up to 1015/cm2. However, further increase on implantation dose reduces the magnetic moment which coincides with the onset of amorphization as verified by both Raman and x-ray photoelectron spectroscopic data. Overall, our results demonstrate the absence of ferromagnetism on either implanted or unimplanted samples from room temperature down to a temperature of 5 K.

Radial textured carbon nanoflake spherules

A unique type of carbon structure, radial textured carbon nanoflake spherules, has been synthesized by a microwave plasma assisted chemical vapor deposition method. The spherules with a diameter of 1.2–35μm consist of a number of radially distributed carbon nanoflakes growing from a common core. The constituent nanoflakes are interlaced and perpendicular to the surface of spherules, forming a large amount of open edge planes. Thus, the carbon nanoflake spherules are isotropic graphite with a larger surface area and higher surface activity, which can be demonstrated by Raman scattering spectroscopy with two characteristic peaks of 860 and 1140cm−1.

Large-sized tubular graphite cones with nanotube tips

Tubular graphite cones (TGCs) have been grown on planar steel substrates by microwave plasma-assisted chemical vapor deposition with a high concentration of methane and at a high substrate temperature. The largest TGCs can reach 110μm in length and 10μm in diameter at the root. Unique TGCs terminated in long extruding carbon nanotube tips are realized. Scanning micro-Raman spectroscopy of individual TGCs shows a high crystallinity of the tips and more disordered structure of the roots. A possible growth mechanism of TGCs is presented.

X-ray propagation in carbon nanotubes

The maintenance of the growth of the multibillion-dollar semiconductor industry requires the development of techniques for the fabrication and characterisation of nanoscale devices. Consequently, there is great interest in photolithography techniques such as extreme UV and x-ray. Both of these techniques are extremely expensive and technologically very demanding. In this paper we describe research on the feasibility of exploiting x-ray propagation within carbon nanotubes (CNTs) for the fabrication and characterisation of nanoscale devices. This work discusses the parameters determining the design space available. To demonstrate experimentally the feasibility of x-ray propagation, arrays of carbon nanotubes have been grown on silicon membranes. The latter are required to provide structural support for the CNTs while minimising energy loss. To form a waveguide metal is deposited between the nanotubes to block x-ray transmission in this region at the same time as cladding the CNTs. The major challenge has been to fill the spaces between the CNTs with material of sufficient thickness to block x-ray transmission while maintaining the structural integrity of the CNTs. Various techniques have been employed to fill the gaps between the nanotubes including electroplating, sputtering and evaporation. This work highlights challenges encountered in optimising the process.

Fabrication and mechanical property of carbon nanotube/metal composites

In this work, we report the fabrication of aligned CNT/Ni/W composite materials. The vertically aligned CNTs are grown on Si by plasma enhanced chemical vapour deposition using Ni films as catalysts. The Ni-W alloys are then filled into the gaps between the CNT forests by electroplating, forming a dense, low-stress composite film. Their mechanical properties are investigated by nanoindentation technique. Results show that CNTs play a critical role in reducing the stress and improving the mechanical property of NiW alloy films.

Synthesis and high activity of vertical graphene nanoflake films for detecting biomolecules

In this work, we report an efficient method of chemical vapour deposition, without use of any metal catalysts, for the successful synthesis of vertical graphene nanoflake films (GNFs) on Si substrate. Effects of the growth condition on the surface morphology, microstructure, and chemical composition of GNFs are characterized by using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. The constituent nanoflakes have a highly graphitized knife-edge structure with a 2 - 3 nm thick sharp edge and show a preferentially vertical orientation with respect to the Si substrate. This leads to the surface of the GNFs being terminated with a large amount of active edge planes. Their electrocatalytic property is studied by using cyclic voltammetry and differential pulse voltammetry. They demonstrated excellent activity for electrooxidating various biomolecules such as dopamine and ascorbic acid and well distinguish them when they co-exist, much better than other solid electrodes. This work will pave the way to the development of highly sensitive, highly selective graphene based biosensors for our community.