Zhanbing He

On the mechanisms of precipitation of graphene on nickel thin films

Growth on transition metal substrates is becoming a method of choice to prepare large-area graphene foils. In the case of nickel, where carbon has a significant solubility, such a growth process includes at least two elementary steps: 1) carbon dissolution into the metal, and 2) graphene precipitation at the surface. Here, we dissolve calibrated amounts of carbon in nickel films, using carbon ion implantation, and annealing at 725°C or 900°C. We then use transmission electron microscopy to analyse the precipitation process in detail: the latter appears to imply carbon diffusion over large distances and at least two distinct microscopic mechanisms.

Synthesis of few-layered graphene by ion implantation of carbon in nickel thin films

The synthesis of few-layered graphene is performed by ion implantation of carbon species in thin nickel films, followed by high temperature annealing and quenching. Although ion implantation enables a precise control of the carbon content and of the uniformity of the in-plane carbon concentration in the Ni films before annealing, we observe thickness non-uniformities in the synthesized graphene layers after high temperature annealing. These non-uniformities are probably induced by the heterogeneous distribution/topography of the graphene nucleation sites on the Ni surface. Taken altogether, our results indicate that the number of graphene layers on top of Ni films is controlled by the nucleation process on the Ni surface rather than by the carbon content in the Ni film.

Dual graphene films growth process based on plasma-assisted chemical vapor deposition

Graphene has been given great attention to overcome current physical limits in electronic devices and its synthesis routes are developing rapidly. However, graphene film manufacturing is still hindered by either low throughput or low material quality. Here, we present a low temperature PE-CVD assisted graphene growth process on nickel thin films deposited on silicon oxide. Furthermore, our process leads to the formation of two separated graphene films, one at the nickel surface and the other at the Ni/SiO2 interface. A mixture of methane and hydrogen was employed as carbon precursor and activated by DC plasma. We found that the number of graphene layers on top of nickel can be controlled by carbon exposure time, from 1 to around 10 layers. Further annealing process of samples allowed us to achieve improved graphene films by the dissolution and segregation-crystallization process.

Growth mechanisms of carbon nanostructures with branched carbon nanofibers synthesized by plasma-enhanced chemical vapour deposition

Y- and comb-type carbon nanotrees formed from branched carbon nanofibres grown by plasma-enhanced chemical vapour deposition were studied by transmission electron microscopy. Different growth mechanisms are proposed for the two types of nanotrees based on the observed and reconstituted dynamic transformations of the catalyst particles during synthesis. However, the splitting of large catalyst particles is required for both kinds of nanotrees, whatever the involved growth mechanism. The carbon nanotrees are well crystallized and the connections of the branches are continuous, which might be interesting for future applications in nanoelectronic devices and also composite materials.

Well organized Si nanowires arrays synthesis for electronic devices

In this paper we demonstrate the efficiency of porous anodic alumina (PAA) to confine the growth of silicon nanowires (SiNWs). High-density arrays of parallel, straight and organized SiNWs have been realized, by Hot Wire Chemical Vapor Deposition (HW-CVD) growth process inside PAA templates with electrodeposited copper as catalyst. The PAA was made by the anodization of an aluminium layer, followed by the catalysts electrodeposition at the bottom of the pores. Subsequently, SiNWs were grown in a modified HW-CVD reactor with SiH4 as the precursor gas. The morphology and the structure of the wires have been investigated by SEM and TEM, and their collective electrical behavior has been characterized with a 2-probes device.

Study of Graphene Growth Mechanism on Nickel Thin Films

Since chemical vapor deposition of carbon-containing precursors onto transition metals tends to develop as the preferred growth process for the mass production of graphene films, the deep understanding of its mechanism becomes mandatory. In the case of nickel, which represents an economically viable catalytic substrate, the solubility of carbon is significant enough so that the growth mechanism proceeds in at least two steps: the dissolution of carbon in the metal followed by the precipitation of graphene at the surface. In this work, we use ion implantation to dissolve calibrated amounts of carbon in nickel thin films and grow graphene films by annealing. Observations of those graphene films using transmission electron microscopy , directly on the growth substrate as well as transfered on TEM grids, allowed us to precisely study the mechanisms that lead to their formation.