Semiconducting phase of amorphous carbon-nickel composite films

Abstract

Amorphous carbon-nickel composite films, which constitute a homogeneously mixed phase of carbon and 10% nickel, are prepared by UV pulsed laser ablation. From the low temperature conductivity study of these films, a nearly activated conduction followed by conductivity saturation below a temperature of 25 K has been identified. This is very different from undoped diamond-like carbon ͑DLC͒ films. The presence of additional density of states at the Fermi level observed in these samples when compared with DLC films, is directly confirmed using valence band spectroscopy. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2216030͔In the past, many attempts have been made to increase electrical conduction in diamond and amorphous diamondlike carbon ͑DLC͒ films by incorporating various light and heavy elements in order to "dope" them and make controllable semiconducting materials. One of the difficulties for substitutional doping of carbon is the formation of unstable graphitic structures, which results in a high defect density of states ͑DOS͒ at the Fermi level ͑E F ͒. Although several examples of conductivity enhancement of amorphous carbon ͑a-C͒ films alloyed with light elements such as nitrogen were found, a true signature of activated or delocalized transport has rarely been demonstrated. 1 In spite of the unique ability of carbon to mix with a large number of heavy elements, synthesis of a homogeneous amorphous phase of metalcarbon remains difficult. 2-5 Nickel has been used for the recrystallization of carbon or the graphitization of carbon at high temperature ͑ϳ500°C͒. 2,3 In the microstructure of metal and carbon multilayers fabricated by ion bombardment or sputtering, the formation of metal and carbon clusters was attributed to non-homogeneous structures in the films. 4 Similarly, when mixed phase materials were attempted by substitutional doping of diamond by metal atoms or preparation of diamond-metal composites, they yielded only metallic films having no signature of activated conduction. 5 Due to the formation of metal clusters and nanostructures, tunneling of electrons was found to dominate the conduction processes even at high temperatures and therefore, an activated conduction, showing a small energy gap at low temperature, was rarely observed. 5 We show that to achieve a homogeneous amorphous phase or embedded nanostructures, laser ablation can be utilized to mix insulators and metals. Metal catalysts mixed with carbon are routinely used for the growth of various nanostructures such as carbon nanotubes, at high temperature, where supersaturation of the vapor phase of carbon and metal is crucial in the formation of a stable metal-free carbon nanostructure. 6 It seems that by controlling the temperature and energy, the degree of supersaturation of the carbon-metal mixture can be achieved, giving rise to a metastable amorphous phase. Keeping in mind that the initial state of carbon is important to transform the film structure, we introduce Ni into highly insulating sp 3 carbon films by laser ablation t...

IR laser‐induced breakdown in tetramethyltin adjacent to Ag or Au: deposition of β‐Sn nanograin‐containing amorphous Au–Sn/C and Ag–Sn/C films

“…Nanocrystalline composites were fabricated by a myriad of techniques, such as solution chemical routes, electrochemical processes, sputtering, rod milling and gas phase depositions and various laser‐induced deposition processes. The laser‐induced processes include ablation of element or alloy targets or organometallic compound, as well as chemical vapor deposition (CVD) or metal ablation in dielectric breakdown of hydrocarbons . The last technique has proved to have potential for fabrication of rare nanocrystalline forms of metals (hcp‐Ag and ambient‐pressure unstable Ga) in amorphous carbonaceous phase.…”

Bioactivity and mechanical properties of nickel‐incorporated hydrogenated carbon nanocomposite thin films

“…In addition to these properties, the biological behavior (bioactivity) of the coating is strongly influenced by the chemical properties at the surface. It has been reported that the biomedical properties of the a‐C:H films can be modified by adding suitable carbide and noncarbide‐forming materials which includes silicon (Si), titanium (Ti), calcium (Ca), phosphorus (P), boron (B), nickel (Ni) and nitrogen (N) 8–16. Among these doping materials, carbide‐forming metals plays a significant role in altering the mechanical and the bioactivity of the coating to a greater extent.…”

“…Our present research interest is mainly focused to study the in vitro bioactivity (bone‐bonding ability) and mechanical properties of pure a‐C:H and Ni/a‐C:H nanocomposite thin films. Several deposition methods such as hybrid reactive magnetron sputtering,13 pulsed laser ablation,14 electrodeposition17 and hybrid plasma enhanced chemical vapor deposition method18 have been employed to synthesize nickel‐incorporated hydrogenated carbon thin films. Biased target ion beam deposition is a new deposition method mainly used for the fabrication of ultrathin (with high adhesion) films.…”

PEMANFAATAN TEKNIK HEM UNTUK PENUMBUHAN CNT DARI GRAFIT MENGGUNAKAN Ni SEBAGAI KATALIS = UTILIZATION OF HEM TECHNIQUE FOR GROWTH OF CNT FROM GRAPHITE POWDERS BY USING Ni AS CATALYST

“…The highest intensity of D band shown in the milling process for 50 hours, which indicates that this milling time produces more graphite-like structure compared to other conditions, and is predicted good for growing CNTs. Keywords CNT telah menjadi perhatian yang menarik bagi peneliti di seluruh dunia karena sifat kimia, elektronik, termal, mekanik, optik dan listriknya yang luar biasa [1][2][3] . Telah banyak aplikasi yang menunjukkan bahan ini memiliki sifat yang luar biasa.…”

“…Berbagai metode telah dikembangkan untuk memproduksi CNT, seperti arc discharge listrik, laser ablation target karbon, dan chemical vapor deposition (CVD), serta sintesis elektrokimia dan pirolisis benzene dengan adanya hidrogen [1][2][3][4] . Namun metodemetode tersebut membutuhkan bahan baku kimia yang banyak dan biaya mahal.…”