Structural and electronic characterization of nanocrystalline diamondlike carbon thin films.

The origin of low threshold field-emission (threshold field 1.25 V/µm) in nanocrystalline diamond-like carbon (nc-DLC) thin films is examined. The introduction of nitrogen and thermal annealing are both observed to change the threshold field and these changes are correlated with changes to the film microstructure. A range of different techniques including micro-Raman and infrared spectroscopy, X-ray diffraction, electron microscopy, energy-dispersive X-ray analysis and time-of-flight-secondary ion mass spectroscopy are used to examine the properties of the films. A comparison of the field emission properties of nc-DLC films with atomically smooth amorphous DLC (a-DLC) films reveals that nc-DLC films have lower threshold fields. Our results show that nc-DLC can be a good candidate for large area field emission display panels and cold cathode emission devices.

Electron transfer from a carbon nanotube into vacuum under high electric fields.

The transfer of an electron from a carbon nanotube (CNT) tip into vacuum under a high electric field is considered beyond the usual one-dimensional semi-classical approach. A model of the potential energy outside the CNT cap is proposed in order to show the importance of the intrinsic CNT parameters such as radius, length and vacuum barrier height. This model also takes into account set-up parameters such as the shape of the anode and the anode-to-cathode distance, which are generically portable to any modelling study of electron emission from a tip emitter. Results obtained within our model compare well to experimental data. Moreover, in contrast to the usual one-dimensional Wentzel-Kramers-Brillouin description, our model retains the ability to explain non-standard features of the process of electron field emission from CNTs that arise as a result of the quantum behaviour of electrons on the surface of the CNT.

Engineering the next generation of large-area displays: prospects and pitfalls.

Considerable effort is currently expounded on the development and improvement of the myriad display technologies that have come to the market place. In this paper, several key questions are addressed in the development of the future generation of large-area field-emission-based displays based on semiconducting amorphous carbon thin films and carbon nanotubes (CNTs). The development of carbon-based cathodes has to date proceeded along empirical lines, with attempts to correlate the variation of field-emission characteristics with changes in deposition or post-deposition processing parameters, often without a full explanation being forthcoming. In addition, there have been incidents of incorrect interpretation of some of the results, due to a lack of appreciation of the significant differences between the different types of amorphous carbon film that exist. It is only recently that a fuller understanding of the different electron-emission mechanisms has begun to emerge through an understanding of the roles played by the electrical and structural inhomogeneity at nanometre level. This 'intrinsic dielectric inhomogeneity' is shown to possess some remarkable electronic properties, which also have important consequences for extrinsic inhomogeneous nanometre systems such as CNT and CNT-polymer-composite-based displays. The future outlook for broad-area displays based on amorphous carbon and CNTs is also addressed.

A case-control study of the factors associated with spontaneous resolution of hepatitis C viremia.

OBJECTIVE: Infection with the hepatitis C virus (HCV) becomes chronic in 85% of the infected individuals. We studied risk factors that may predict clearance of HCV. METHODS: A case-control study compared the association between risk factors and viral clearance. Viral clearance was defined as presence of a positive HCV antibody test plus negative HCV test by polymerase chain reaction (PCR). Forty-four cases and 214 controls with persistent viremia were identified in a database of patients evaluated at the Gastroenterology Clinic of the University of New Mexico. RESULTS: Of all 258 HCV-antibody-positive patients, 17% had a negative test by PCR. The multivariate logistic regression revealed that a history of parenteral exposure and a long time interval since the most recent exposure were both associated with an increased likelihood of persistent viremia, whereas subjects who had been monogamous for longer time periods were more likely to have cleared HCV from their serum. A low serum level of ferritin also conferred protection against persistent viremia. Case and control subjects did not differ with respect to their demographic characteristics, occurrence of comorbid disease, previous medical history, occurrence of sexually transmitted diseases, blood group, and risky health or sexual practices. CONCLUSIONS: These data suggest that route of exposure and time when exposure occurred are important in the development of persistent HCV infection.