We describe the fabrication of self-aligned split gate electrodes on suspended multiwalled carbon nanotube structures. A suspended multiwalled carbon nanotube structure was used as an evaporation mask for the deposition of metal electrodes resulting in the formation of discontinuous wire deposition. The metal deposits on the nanotubes are removed with lift-off due to the poor adhesion of metal to the nanotube surface. Using Al sacrificial layers, it was possible to fabricate self-aligned contact electrodes and control electrodes nanometers from the suspended carbon nanotubes with a single lithography step. It was also shown that the fabrication technique may also be used to form nano-gaped contact electrodes. The technique should prove useful for the fabrication of nano-electromechanical systems.

In order to utilise the full potential of carbon nanotubes/nanofibers, it is necessary to be able to synthesize well aligned nanotubes/nanofibres at desired locations on a substrate. This paper examines the preferential growth of aligned carbon nanofibres by PECVD using lithographically patterned catalysts. In the PECVD deposition process, amorphous carbon is deposited together with the nanotubes due to the plasma decomposition of the carbon feed gas, in this case, acetylene. The challenge is to uniformly nucleate nanotubes and reduce the unwanted amorphous carbon on both the patterned and unpatterned areas. An etching gas (ammonia) is thus also incorporated into the PECVD process and by appropriately balancing the acetylene to ammonia ratio, conditions are obtained where no unwanted amorphous carbon is deposited. In this paper, we demonstrate high yield, uniform, ‘clean’ and preferential growth of vertically aligned nanotubes using PECVD.

Highly tetrahedral amorphous carbon thin films have exceptional mechanical properties that make them ideal for many challenging wear applications such as protective overcoats for orthopaedic prostheses and aerospace components. However, the use of ta–C in many wear applications is limited due to the poor adhesion and the inability to grow thick films because of the large compressive stress. Here we report on a simple modification of the substrate growth surface by 1-keV ion bombardment using a cathodic vacuum arc (CVA) plasma prior to deposition of ta–C films at 100 eV. The 1-keV C+ ion bombardment created a thin intermixed layer consisting of substrate and carbon atoms. The generation of the intermixed carbide layer improved the adhesion and allowed the growth of thick (several μm) ta–C layers on metallic substrates.

We have deposited carbon nitride (CNx) films by magnetron sputtering at varying nitrogen pressures and substrate temperatures. The films were deposited on silicon and quartz substrates simultaneously. The incoming ion energy was controlled by a radio frequency power supply. A magnet in front of the substrate holder was used to enhance the plasma density. The films deposited at room temperature (RT) were found to have nitrogen content of ≥ 40%. These films were semiconducting with an optical bandgap of greater than 2 eV and a RT resistivity of 1012 Ω-cm. Films deposited at low nitrogen pressure (< 7 mtorr), at RT and in the presence of a 15 mtesla magnetic field were found to be hard and also exhibited extremely high elastic recovery. The most interesting result we found was that the hard and elastic CN films were also semiconducting with an optical band gap of 1.7 eV, RT resistivity of 107 Ω-cm and an activation energy of 0.8 eV. In all cases the CN films were almost entirely sp2 bonded.

The incorporation of carbon nanoparticles in the forms of nanotubes and bucky onions have shown to improve the mechanical properties of amorphous carbon (a-C) thin films. In this paper we report on the change in the optical properties of a-C films containg nanoparticles. The optical band gap, index of refraction and extinction coefficient are studied. The optical band gap in highly tetrahedral amorphous carbon (ta-C) is found to be around 2 eV. It decreases almost linearly with the sp2 fraction. It is theorized that the clustering of the sp2 sites leads to a reduction in the band gap. In this paper, we study the influence of large sp2 clusters in forms of graphitic nanoparticles on the optical of ta-C. We find that the optical gap remains around 1.8 eV even with the large inclusions of clustered nanoparticles. Furthermore, the gap remains close to 1.8 eV even when the sp2 fraction in the amorphous matrix is increased. The index of refraction however is found to decrease with the sp2 fraction indicating a reduction in density.

The properties of a highly sp3 bonded form of amorphous carbon denoted ta-C deposited from a filtered cathodic vacuum arc (FCVA) are described as a function of ion energy and deposition temperature. The sp3 fraction depends strongly on ion energy and reaches 85% at an ion energy of 100 eV. Other properties such as density and band gap vary in a similar fashion, with the optical gap reaching a maximum of 2.3 eV. These films are very smooth with area roughness of order 1 nm. The sp3 fraction falls suddenly to almost zero for deposition above about 200°C.

The low electron affinity of a-C:H is related to that of diamond surfaces and is studied using a chemical bonding model. The electron field emission from hydrogenated amorphous carbon (a-C:H) and nitrogen modified a-C:H showing low turn on fields are described. Nitrogen improves the field emission, apparently by raising the Fermi level.

Thin C films deposited from a CH4/Ar plasma on Si substrates kept at 20C are shown to be semiconducting. The semiconducting properties are associated with the poly-crystalline diamond grains present within the films. Diode type I-V characteristics observed from AVC/Si verticle structures are explained by the action of a C-Si heterojunction. A band gap of 2eV, a resistivity of 106Ω.cm and an electrical breakdown strength of 5.106 V/cm are estimated for the C.

Rapid thermal annealing of arsenic and boron difluoride implants, such as those used for source/drain regions in CMOS, has been carried out using a scanning electron beam annealer, as part of a study of transient diffusion effects. Three types of e-beam anneal have been performed, with peak temperatures in the range 900-1200°C; the normal isothermal e-beam anneals, together with sub-second fast anneals and ‘dual-pulse’ anneals, in which the sample undergoes an isothermal pre-anneal followed by rapid heating to the required anneal temperature in less than O.5s.

The diffusion occuring during these anneal cycles has been modelled using SPS−1D, an implant and diffusion modelling program developed by one of the authors. This has been modified to incorporate simulated temperature vs. time cycles for the anneals. Results are presented applying the usual equilibrium clustering model, a transient point-defect enhancement to the diffusivity proposed recently by Fair and a new dynamic clustering model for arsenic. Good agreement with SIMS measurements is obtained using the dynamic clustering model, without recourse to a transient defect model.

Defects remaining in diodes fabricated with the forementioned implants after these anneal cycles have been studied using DLTS techniques. Trap densities for the three types of e-beam anneal are comparable to those for furnace annealed diodes, as are the reverse leakage currents measured (typically 2–5nA for a 0.85mm2 diode at -5V).