Computations of isomeric fullerenes are performed at semiempirical and ab initio quantum-chemical levels: C36, C72, C88. C36 fullerenes and quasi-fullerenes are computed at the SAM1 level, and then at the B3LYP/6-31G* level. Altogether 598 cages are considered. The SAM1 method is also applied to C72, i.e., the solitary isolated-pentagon-rule (IPR) structure and several non-IPR isomers. Finally, the complete set of thirty five topologically different IPR isomers of C88 is computed. In all the cases, energetics is combined with entropy contributions based on the harmonic-oscillator and rigid-rotator model. Considerable temperature effects on the relative stabilities in the systems are found. Relationships to available observed data are discussed throughout and a good agreement is found.

An individual single-walled carbon nanotube (SWNT) has been shown [1-4] to exhibit remarkable electronic properties which depend on its diameter and chirality. In this work, the 13C nuclear magnetic resonance technique is used to measure quantitatively the electronic density-of-state (DOS) at the Fermi level in a bulk SWNT sample. Two types of 13C nuclear spins are observed with drastically different nuclear spin-lattice relaxation time (Tl). About onethird of the 13C nuclear spins with shorter Tl, are identified to reside at the metallic SWNTs and two-thirds can be associated with the semiconducting SWNTs. For the metallic SWNTs, the DOS at the Feimi level is measured quantitatively, which is about 0.022 states/(eV·atom·spin). The measured electronic DOS at the Fermi level agrees with the theoretical prediction for metallic tubes. This study also found that the semiconducting SWNTs in bundles, in fact, possess weak metallic characters. This indicates that tube-tube interactions within SWNT bundles could change the electronic properties.

We present the results of a large-scale molecular dynamics investigation of addimers on strained carbon nanotubes. We find that addimers induce a new set of transformations that lead to the formation of extended defects that are actually short segments of tubes of altered helicity. As these defects wrap themselves about the circumference of the nanotube, this suggests that the combination of addimers and strain may well lead to the formation of nanotube-based quantum dots. The formation of these quantum dots is most favorable for the (n.O) zigzag tubes. For these tubes, addimers induce plastic transformations in tubes that normally display brittle behavior.

We report the use of high power ultrasonic agitation to create inelastic deformations in multiwalled carbon nanotubes. Using STM coupled with TEM we show that this damage can range from kinking to breaking of continuous tube walls into segments. Such deformed tubes provide an insight into the role of re-hybridization in the electrical and mechanical properties of tubes.

We study the electronic structure of potassium-doped crystalline lattice of so-called (10.10) carbon nanotubes in the framework of the density-finctional theory. Tie stoichiometrv of the material studied is K2C80 which was originally proposed in designing the superconducting doped nanotube material based on tile size of dopants and the charge transfer being favorable for superconductivity. Electronic band dispersions obtained are actually found to be very similar to those of the pristine (10,10) nanotube lattice with the upward shift of the Fermi energy by 1 eV above the second conduction-band miinimum. Tie system therefore possesses higher Fermi-level density of states than the pristine material with rather sinmple charge transfer from K to C sites, and is confirned to be a good candidate for a naxiotube superconductor.

Amorphous hydrogen-free carbon films (sp2-dominated a-C) were deposited under ultrahigh vacuum conditions between room temperature and 800°C. These films served as matrices for the in-situ incorporation of alkali-metal atoms (Li, Na). In-situ sample characterization was performed by photoelectron spectroscopy with both x-ray and ultraviolet excitation (XPS, UPS). While the clean metal-containing samples were prepared with metal contents of about 10 at%, a strong oxidation driven accumulation of metal atoms on the film surface exceeding 50 at% was observed upon exposure to molecular oxygen. Work-function measurements by UPS reflected the changes within the electronic structure of the material. Metal incorporation considerably decreased the work-function, but only after oxidation we observed work-functions below the values given for pure alkali metals.

Single wall nanotubes have been made by arc-discharge method. Residual impurities (fullerenes, amorphous carbon, catalyst metals…) have been removed by tangential filtration process followed by high temperature annealing under vacuum (1200 °C). In this work we present results on the influence of the surrounding gas nature (N2, H2, CO2, H2O…) on the electrical resistivity of carefully outgassed mat of such samples.

In particular, we have observed that the sample resistance exhibits a strong dependence on water contamination during the transfer to the measurement reactor.

The elastic behavior and structural changes of single-walled carbon nanotubes under hydrostatic pressure produced by a gasketed diamond anvil cell has been studied using in situ synchrotron x-ray diffraction. The compaction of the raft-like bundles of single-walled carbon nanotube showed a linear behavior up to 1.5 GPa pressure and the volume compressibility deduced from the experimental data is 0.024 GPa−1. The elastic deformation is attributed to the combination of a reduction in the inter-tubular distance and the polygonization of the otherwise circular nanotube sections.

We performed density-functional calculations to search for adsorption sites and predict maximum hydrogen storage capacity in carbon nanotubes. Our calculations show that the storage capacity of hydrogen, limited by the repulsive forces between H2 molecules inside nanotubes, increases linearly with tube diameters in single-walled nanotubes, whereas this value is independent of tube diameters in multi-walled nanotubes. We predict that H storage capacity in (10,10) nanotubes can exceed 14 wt % (161 kg H2/m3).

We have developed a new synthetic procedure to fabricate mesoporous carbons using mesoporous inorganic materials as templates. Mesoporous carbons with regular 3-dimensionally interconnected ∼ 2 nm pore arrays have been synthesized using aluminum substituted MCM-48 and HMS mesoporous silicas as templates. The polymerization of phenol and formaldehyde inside the nanopores of the mesoporous silica templates generated phenol-resin/luminosilicate nanocomposites. The carbonization followed by the removal of silicate templates generated mesooporous carbons with regular pore dimensions. The mesoporous carbons exhibited excellent performance for electrochemical double layer capacitors (EDLC). They revealed ideal rectangular shaped cyclovoltammograms up to the high scan rate of 20 mV/sec, which is important for the future applications.

The structure and mechanical properties of nanocomposites composed of (10,10) carbon nanotubes in an amorphous polyethylene matrix have been modeled with molecular dynamics simulations. Two systems were studied, an infinite nanotube (via periodic boundaries) and a finite capped nanotube 6 nm in length. In the infinite case the modulus in the direction of the nanotube is given by the upper bound of the rule of mixtures, as expected under isostrain conditions for a well-aligned fiber-reinforced composite. In the finite case, no load transfer is observed at low strain, consistent with the weak nanotube-polymer adhesion and a subcritical nanotube length. The simulations predict that regions of amorphous polymer close to the bulk density remain around the nanotubes at relatively large strains, and that the density decrease during strain results primarily from chain disentanglement and alignment in regions between nanotubes.

Carbon films with variable sp3/sp2 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 N2partial 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 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/cm2 and emission site densities of up to 104 -105/cm2 have been obtained.

A variety of carbon nanotube films have been fabricated and tested as cold cathodes. A spray deposition technique was developed for processing as-grown bulk nanotubes, both single-walled and multi-walled, into films of randomly oriented nanotubes. Films of randomly oriented multi-walled nanotubes were grown using thermal chemical vapor deposition, and arrays of well-aligned multi-walled nanotubes have been fabricated using a microwave plasma enhanced chemical vapor deposition technique. The emission current-voltage (I-V) characteristics of these nanotube cathodes have been measured. Both multi-walled (random and aligned) and single-walled carbon nanotubes exhibit low turn-on fields (∼ 2 V/μm to generate 1 nA) and threshold fields (< 5 V/μm to generate 10 mA/cm2). Significantly, these cathodes were capable of operation at very large current densities (> 1A/cm2), making them candidates for application in a variety of vacuum microelectronic devices.

The results of field emission measurements of various forms of carbon films are reported. It is shown that the films' nanostructure is a crucial factor determining the field emission properties. In particular, smooth, pulsed-laser deposited amorphous carbon films with both high and low sp3 contents are poor field emitters. This is similar to the results obtained for smooth nanocrystalline, sp2 - bonded carbon films. In contrast, carbon films prepared by hot-filament chemical vapor deposition (HF-CVD) exhibit very good field emission properties, including low emission turn-on fields, high emission site density, and excellent durability. HF-CVD carbon films were found to be predominantly sp2 -bonded. However, surface morphology studies show that these films are thoroughly nanostructured, which is believed to be responsible for their promising field emission properties.

Electron field emission measurements have been performed on thin film cold cathode materials grown, on molybdenum, by a modified MPACVD diamond process. Specifically the modification is due to the addition of nitrogen and oxygen, in varying ratios, during the diamond growth phase. Characterization using Raman spectroscopy shows features at 1190, 1330 and 1550 cm−1. A simple triode device was fabricated for electron emission characterization. KAPTON® film is used as the insulating layer and a Mo mesh is used as the extraction gate electrode. The collector is an indium tin oxide (ITO) coated glass plate which is positively biased with respect to the gate electrode. Field emission characteristics have shown current measurements of greater than I microamp for fields of 40 V/micron. Gate currents are typically 1000 times greater than the emitted current. Issues currently being addressed include improvement in the total emitted current, current stability and device failure. We also present field emission measurements on diamond films grown by HFCVD.

Recent studies of field emission from diamond have focused on the feasibility of growing diamond films on glass substrates, which are the preferred choice for cost-effective, large area flat panel displays. However, diamond growth on glass requires temperatures < 500 °C, which is much lower than the temperature needed for growing conventional microwave plasma chemical vapor deposition (CVD) diamond films. In addition, it is desirable to minimize the deposition time for cost-effective processing. We have grown ultrananocrystalline diamond (UNCD) films using a unique microwave plasma technique that involves CH4-Ar gas mixtures, as opposed to the conventional CH4-H2 plasma CVD method. The growth species in the CH4-Ar CVD method are C2 dimers, resulting in lower activation energies and consequently the ability to grow diamond at lower temperatures than conventional CVD diamond processes. For the work discussed here, the UNCD films were grown with plasma-enhanced chemical vapor deposition (PECVD) at low temperatures on glass substrates coated with Ti thin films. The turn-on field was as low as 3 V/μm for a film grown at 500 °C with a gas chemistry of l%CH4/99%Ar at 100 Torr, and 7 V/μm for a film grown at 350 °C. UV Raman spectroscopy revealed the presence of high quality diamond in the films.

The saddle-field glow discharge is modeled and electron multiplication and energy spectra are presented. The roles of the ion substrate current and ion energy at the substrate on the growth rate, hydrogen content, sp2 content and energy gap are discussed and the effects of atmospheric aging and high temperature annealing are described.

Tetrahedral diamond like carbon (ta-C) films were deposited onto Si substrates using Filtered Cathodic Vacuum Arc (FCVA) process. Stress of deposited films was varied in the range 3.5÷8.5 GPa. The ESR (stationary and pulse) and Raman techniques were used to analyze sp2 related defects in the pseudo-gap of undoped, as deposited 20 – 100 nm thick films. The results are compared with data for direct ion beam deposited from CH4 plasma hydrogenated DLHC films and nature of paramagnetic defects in DLC is discussed.

Optical emission study of ablation plasma plumes from single crystal graphite (SCG) and amorphous carbon (a-C) targets during the preparation of diamond-like carbon (DLC) films by KrF excimer pulsed laser deposition (PLD) has been investigated. The C I emission intensity increases with laser energy density (EL) increase, while the C2 emission changes drastically with EL for both ablated plasma plumes. The C2/C emission intensity ratio for the a-C plume decreases with EL increase, while the C2/C ratio for the SCG plume decreases with EL increase up to 3.0 J/cm2, then increases slightly with further EL increase Nanohardness of the DLC films decreases with the C2/C ratio increase. It is suggested that the C2 molecule in the plasma plume does not play an important role in producing high quality DLC films, and that the C2/C ratio is a good parameter to monitor the PLD process.

A triple Langmuir probe measurement has been implemented to investigate plasma plume character in low fluence (∼ 3.0 J/cm2) pulsed laser evaporation (PLE) discharges and has been found to be an extremely valuable tool. Absolute plasma plume density estimates are found to reside in the range 1.0 × 1013–2.0 × 1014 cm−3 for vacuum pulses. A simple heavy particle streaming model for vacuum pulses allows estimates of the plume ionization fraction of ∼ 10%. This is consistent with typical deposition inventory suggesting that high kinetic energy ions play an important role in DLC film deposition. Electron temperature is found to consistently reside in the range 0.5-3.0 eV, and appears to be uninfluenced by operating conditions and large variations in Ar and N2 fill gas pressure. Consistent with strong plume ion and neutral particle coupling to the background fill, constancy of Te suggests expulsion of background gas by the energetic plume. The leading edge ion plume speed is measured via temporal displacement of spatially separated probe signals on consecutive PLE pulses. Flow speeds as high as 5.0 × 104 m/s are observed, corresponding to ∼ 156 eV in C+. The ion flow speed is found to be a strongly decreasing function of fill pressure from an average high of ∼ 126 eV in vacuum to ∼ 0.24 eV at 600 mTorr N2. Raman scattering spectroscopy indicates DLC film quality also degrades with fill pressure suggesting the importance of high ion kinetic energy in producing good quality films. Optical emission indicates an increase in C2 molecular light intensity with fill gas pressure implying a reduced, if any, role of these species in DLC production. Ion current signal anomalies in high pressure pulses indicate the formation of high mass carbon clusters during plume evolution in the presence of background gas. Mass diffusivity estimates, based on density decay, suggest the presence of under these conditions. Demonstration and control of such cluster formation may provide method(s) for controlling novel advanced materials properties.