Nanocluster Carbon Research Articles

Indigenous design and development of the cathodic arc system for the growth of nanocarbon thin Films

Carbon based thin films in its various forms is becoming very attractive for a wide range of applications ranging from simple protective coatings to biocompatible coatings and even conformal coatings. Cathodic arc is emerging as a viable technology for a wide range of applications especially low temperature coating. Presented in this paper is some of the initial results of low temperature nanocarbon thin films and nanocluster carbon (NC) grown using cathodic arc process. The films were deposited on aluminium foil and glass substrates. The process and growth parameters were varied to establish the material properties and presented in this paper are the surface morphological, compositional and electrical properties of the nanocarbons thin films and possible correlation to the process parameters. The surface morphology and composition were studied using SEM (SU-1500 HITACHI), Raman Spectroscopy & AFM, NSOM (ALPHA 100RAS), and the electrical and electronic properties were measured using Kiethly Semiconductor device analyzer.

Effect of electron irradiation on morphological, compositional and electrical properties of nanocluster carbon thin films grown using room temperature based cathodic arc process for large area microelectronics

The influence of 8MeV electron beam bombardment on room temperature grown nanocluster carbon using cathodic arc process has been studied here. Atomic force microscopy (AFM) study shows that surface roughness varies with varying electron doses. High doses of electrons could causes thermal induce graphitization and morphological changes in the films. Raman spectroscopy analysis reveals that G-peak vary from 1555cm−1 to 1570cm−1 and D-peak varying from 1361cm−1 to 1365cm−1 indicating the disorderness and presence of both graphitic and diamond-like phases. Room temperature conductivity changes by two to three orders in magnitude. The conductivity in the films could be due to conduction of charge carriers through neighboring islands of conductive chains. Defect states calculated using the differential technique varies from 8×1017cm−3eV−1 to 1.5×1019cm−3eV−1. Irradiation of nanocluster carbon thin films could be helpful to tune the electrical properties and defect densities of the nanocluster carbon films for various large area, flexible electronic and nano electronic applications.

Raman spectroscopy and conductivity variation of nanocluster carbon thin films grown using a room temperature based cathodic arc process

Nanocluster Carbon (NC) thin films grown at room temperature, using a cathodic arc process, under varying deposition conditions, exhibit interesting electrical and opto-electronic properties. These films are mixed phase material containing both sp2 (graphite-like) and sp3 (diamond-like) bonding. A Raman G-peak has been observed between 1585 and 1595 cm−1, which indicates graphite-like bonding. A Raman D-peak has been observed between 1355 and 1365 cm−1, which indicates disorderliness in the carbon structure of the films. The Raman spectra of the films were deconvoluted using Breit–Wigner–Fano line shapes. The Raman parameters, including intensity ratios, peak positions, Full-Width Half Maxima (FWHM) and coupling coefficients obtained from both line shapes, were described and compared with varying Helium partial pressures. The dependence on temperature of the conductivity, showing two regions of electronic transport, is explained based on a thermal-assisted tunneling process. The electrical conductivity varies from 1×10−4 S/cm to 1.66×10−5 S/cm with respect to varying deposition parameters, such as arc current, DC bias and throw distance.

DETERMINATION OF DENSITY-OF-STATES OF NANOCLUSTER CARBON THIN FILMS MIS STRUCTURE USING CAPACITANCE–VOLTAGE TECHNIQUE

Nanocluster carbon thin films (NC) were deposited at room temperature by cathodic arc process. These films were clustered, amorphous and disordered in nature which is verified using Raman spectroscopy. Density of defect states (DOS), which influences electronic and optical properties, were determined from the capacitance–voltage (C–V) characteristic of Al / NC / c - Si metal–insulator–semiconductor (MIS) structure near the Fermi level of undoped samples. Dielectric constant of the films was also estimated using the same technique. The DOS were found to be varying from 5.68 × 1016 to 4.9 × 1019 cm-3. The dielectric constant varied between 2.76 to 11.8.

ANALYSIS OF CLUSTER DIMENSION AND MORPHOLOGY OF ROOM TEMPERATURE GROWN NANOCARBON USING CATHODIC ARC AND ITS INFLUENCE ON FIELD ASSISTED ELECTRON EMISSION

Low temerpatuere grown nanocluster carbon thin films grown using a continuous cathodic arc process at room temperature are found to be interesting material for wide range of and nanoelectronic application. Reported is the study of the influence of background gases such as helium and nitrogen on the nanoclsuter dimension and morphology and a possible influence of the -4 same to field assisted electron emission properties. The Helium partial pressure was changed from 5x10 to 50 Torr under two -4 -3 different nitrogen partial pressure conditions namely 1x10 Torr and 1x10 Torr respectively. Raman and SEM data for these samples were used to estimate the cluster dimension structural and morphological properties. The surface morphology of the films grown, varied from atomic smooth surface to clusters with varying sizes (50–200 nm). A methodology for the estimation of cluster dimension from the Raman data was established and the estimated data compared with dimensions derived from SEM images. Effort was made to look at the possible correlation of between process parameters, estimated parameters and field assisted electron emission data. The curve fitting analysis and the observed correlation, indicates possibility of establishing Raman Spectroscopy as an instantaneous characterization approach for the evaluation of nanocarbons.

Electron transport in semiconducting nanoparticle and nanocluster carbon–polymer composites

The electron transport properties of two types of carbon–polyimide (C–PI) nanocomposite thin films have been evaluated. Conductive nanocomposites formed by incorporation of 30 nm carbon particles prior to polymer cross linking (ex situ formation) has been compared to high energy ion beam irradiation in situ formation of nanoscale carbon clusters within the polymer composite. Addition of carbon nanoparticles were able to reduce the resistivity by 13 orders of magnitude for 8 vol% carbon content. The irradiated in situ formed film showed a comparable resistivity to this 8% C–PI film. All the films exhibited negative temperature coefficient of resistance (NTCR) behaviour. While in the ex situ films the NTCR decreased progressively with increasing temperature above 350 K, the in situ film exhibited a constant NTCR value at ambient as well as elevated temperatures indicating that films formed by ion beam irradiation eliminate possible clustering of nanoparticles prior to crosslinking seen in the ex situ films. The optimum hop energies for the ex situ films ranged from 23.1 to 8.05 meV when carbon content increased from 1 to 8 vol% and the corresponding value for the in situ formed film was 34.94 meV. These films had appreciable NTCR values, and were evaluated for their thermistor behaviour as a class of material with potential for temperature sensing devices.

Fundamental and applied directions of field emission electronics using nanocluster carbon materials

Fundamental and applied directions of field emission electronics on the base of carbon nanocluster materials are considered. The emission properties of thin films composed of nanotube and nanocluster carbon structures are described. Potentials for their improvement on the path to apply them in various electronic devices are discussed.

Field emission from nano-cluster carbon films

Abstract Field emission has been reported to occur at much lower fields in carbon based thin film systems than from any other material systems. The emission has been shown to depend on the various material parameters, but whichever carbon based system is used, it is found that emission occurs at localised sites rather than uniformly over the entire surface. Carbon films with mixed sp 3 /sp 2 bonding, like nanocrystalline diamond and nanocluster graphitic films emit at lower fields with a higher emission site density than single-phase films. The sp 2 cluster size in any carbon film can be altered during deposition, but it is easier to control nanocluster size by post-deposition annealing. Annealing increases the sp 2 cluster size embedded in a sp 3 matrix until the sp 3 matrix disappears completely and the film transforms into nanocrystalline graphite. To distinguish the effects of the sp 2 cluster size from other material parameters, a series of different carbon films were annealed post-deposition and the sp 2 cluster size was measured using visible Raman. Field emission was then measured at a vacuum of 10 −8 mbar on all films using a parallel plate configuration. It was found that the field emission for all films tested depended upon the clustering of the sp 2 phase and this effect dominates the effects of the other parameters, such as chemical composition, surface termination, sp 3 content or conductivity. The optimum size of the sp 2 was of the order of 1 nm for all systems tested. We believe that field emission occurs form the localised conducting, predominantly sp 2 bonded regions, which provideds the large field enhancement required for effective emission.

Resonant Tunnelling Behaviour in Multilayered Cold Cathodes Made of Nanoseeded Diamond and Nanocluster Carbon

ABSTRACTMultilayered cold cathodes made of spin coated nanocrystalline diamond and cathodic arc process grown nanocluster carbon films, were studied. The nanocrystalline diamond was first coated on to the substrate. The nanocluster carbon films were then deposited on the seeded nanocrystalline diamond coated substrates using the cathodic arc process at room temperature. Theresultant hetrostructured microcathodes were observed to exhibit electron emission currents of 1μA/cm2 at fields as low as 1.2 V/μm. Further some of the samples seem to exhibit I-V characteristics witha negative differential resistance region at room temperature conditions. This negative differential resistance or the resonant tunneling behaviour was observed to be dependent on the nanoseeded diamond size and concentration for a given nanocluster carbon film.

Field Emission from Novel Room Temperature Grown Carbon Based Multilayered Cathodes

AbstractLow field electron emission from novel room temperature grown multilayered cold cathodes were studied. The cathodes consisted of a layer of nanocrystalline diamond and a layer of nanocluster carbon films. The nanocrystalline diamond was first coated on to the substrate. The nanocluster carbon films and the tetrahedral amorphous carbon films were then deposited on the nanocrystalline diamond coated substrates using the cathodic arc process at room temperature. The heterostructured microcathodes were observed to exhibit electron emission currents of 1µA/cm2 at fields as low as 1 V/µm. The effect of the nanoseeded diamond size and concentration and the properties of different nanocluster carbon films on emission characteristics is presented.

Electron emission from amorphous and nanocluster carbon films grown by the cathodic arc process

Carbon films with variable sp 3/sp 2 bonding ratio can be deposited on a variety of substrates at room temperature, using the cathodic vacuum arc deposition process. The variation in their surface morphology as a function of He and N 2 partial pressure during growth have been investigated and it has been shown that the morphology of the films can be varied from the mirror-like smooth tetrahedrally bonded amorphous carbon (ta-C) films through nanocluster to fibrous-type carbon. This paper reviews the work carried out on Field Emission from these various carbon films. Threshold fields as low as 1 V/μm for emission current densities of 1 μA/cm 2 and emission site densities of up to 10 4–10 5/cm 2 have been obtained.

Low field electron emission from nanoclustered carbon grown by cathodic arc

Abstract Nanocluster carbon films grown using a cathodic arc process at room temperature in the presence of background gases such as helium are found to be good electron emitters. The variation in the surface morphology and the corresponding emission characteristics of the films with change in helium partial pressure (5×10− 4 to 50 Torr) during film growth are reported. The effect of helium partial pressure on clustering was studied for films grown at nitrogen partial pressures of 10−4 and 10−3 Torr. The surface morphology of the films varied from smooth through clusters (with sizes 50–200 nm) to fibrous films. The threshold field varied from 1 to 10 V/μm for an emission current density 1 μA/cm 2.

Low threshold field emission from nanoclustered carbon grown by cathodic arc

Nanocluster carbon films grown using a cathodic arc process at room temperature in the presence of background gases such as He are found to be good electron emitters. The variation in the surface morphology and the corresponding emission characteristics of the films with change in helium partial pressure (5×10−4–50 Torr) during the film growth are reported. The effect of helium partial pressure on clustering was studied for films grown at nitrogen partial pressures of 10−4 and 10−3 Torr. The surface morphology of the films grown, varied from smooth through clusters (with sizes 50–200 nm), to fibrous films. The threshold field varied from 1 to 10 V/μm for an emission current density of 1 μA/cm2. These films exhibit an emission site density of ∼104–105/cm2 at an applied field of 5 V/μm.

Field emission from heterostructured nanoseeded diamond and nanocluster carbon cathodes

ABSTRACTNovel heterostructured cold cathodes made of nanoseeded diamond and cathodic arc process grown nanocluster carbon films, were studied. The nanocrystalline diamond with varying diamond concentration was first coated on to the substrate. The nanocluster carbon films were then deposited on the nanoseeded diamond coated substrates using the cathodic arc process at room temperature. The resultant heterostructured microcathodes were observed to exhibit electron emission currents of 1μA/cm2 at low fields of 1.2 - 5 V/μm. Further some of the samples seem to exhibit I-V characteristics with a negative differential resistance region at room temperature conditions. This negative differential resistance or the resonant tunneling behaviour was observed to be dependent on the nanoseeded diamond concentration.