Narrow Results

The reverse Monte Carlo (RMC) technique has been used to generate atomic structures of amorphous carbon based on the radial distribution functions and the fraction of differently coordinated sites measured on experimental samples. The resulting structures have been subsequently relaxed via a Tight Binding Molecular Dynamics simulation (TBMD). The radial distribution function, the energy and the fraction of 2-, 3- and 4-fold coordinated sites, evaluated on the relaxed structures, have been compared to those calculated for atomic systems generated on the basis of the "conventional" numerical melt-quench technique. We thus suggest the possibility of using RMC modeling as a useful and convenient tool for generating amorphous structures to be used as initial configurations in Molecular Dynamics simulations.

Two sets of amorphous carbon materials prepared at different routes are irradiated with swift (145 MeV) heavy ion (Ne⁶⁺). The structural parameters like the extent of local ordering along the c and a axis i.e., L_c and L_a, the average spacing of the crystallographic planes (002) i.e., d₀₀₂ and the fraction of the amorphous phase of the unirradiated and the irradiated samples are estimated by X-ray diffraction technique. The fraction of the amorphous phase is generally found to increase with the irradiation dose for both sets of the samples. The estimated d₀₀₂ values are found to be almost unaffected by irradiation but L_c and L_a are decreased slightly with irradiation. The estimated values of L_c and L_a corroborate with the increase of disorder in both sets of the samples with the increasing dose of irradiation.

Nitrogen incorporated hydrogenated amorphous carbon (a-C:N:H) thin films have been deposited by microwave surface-wave plasma chemical vapor deposition on silicon and quartz substrates, using helium, methane and nitrogen (N₂) as plasma source. The deposited a-C:N:H films were characterized by their optical, structural and electrical properties through UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current-voltage characteristics. The optical band gap decreased gently from 3.0 eV to 2.5 eV with increasing N₂ concentration in the films. The a-C:N:H film shows significantly higher electrical conductivity compared to that of N₂-free a-C:H film.

The influence of methane gas (CH₄) pressure on the optical, electrical and structural properties of the nitrogenated amorphous carbon nitride (a-C:N) films grown by microwave surface wave plasma chemical vapor deposition (SWP-CVD) on quartz and silicon (100) substrates have been studied. The a-C:N films are deposited with varying CH₄ gas ranging from 5 to 20 ml/min. To incorporate nitrogen in the film, we have introduced nitrogen gas (N) at 5 ml/min in the chamber. The effects of CH₄ gas pressure on the surface morphology, composition, structure, and electrical properties of the N-incorporated camphoric carbon thin films have been investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES), UV-visible spectroscopy and four-probe resistance measurement. We have succeed in growing a-C:N thin films using SWP-CVD at room temperature and found that the amorphous structure of a-C films can be changed and is strongly dependent on the CH₄ gas source.

The n-type conductivity nitrogen-doped amorphous carbon (n-C) films have been grown by surface wave microwave chemical vapor deposition (SWP-CVD) on plastic and quartz substrates. The bonding, electrical and photovoltaic properties have been studied. The Tauc plot of UV-Visible measurement have shown that n-C films deposited on plastic have smaller optical band gaps compared to the films grown on quartz substrate at the same parameters. Temperature dependence and photoresponse measurements also have shown that the properties of n-C thin films deposited on plastic have higher photoelectrical response. Our experimental results have shown that the flexible polytetrafluoroethene plastic substrate is a reliable candidate for future photovoltaic applications.

The tetrahedral carbon (ta-C) and boron doped amorphous carbon (a-C:B) thin films have been grown by pulsed laser deposition. The respective effects of diamond percentages by weight in the target (Dwt%) and boron percentages by weight in the camphoric carbon target (Bwt%), on the tetrahedral (sp³) and trihedral (sp²) bonding properties are discussed. The optical gap E_g and electrical resistivity ρ increase with Dwt%, up to 1.6 eV and 5.63 × 10⁷ Ω cm respectively, for the film deposited using target with 50 Dwt%. We found that the Dwt% has modified the sp³ bonds content and the morphology of the carbon films. On the other hand, the E_g of a-C:B films is almost unchanged at about 0.95 eV up to 10 Bwt% and decreases thereafter to 0.6 eV at 16 Bwt%. The ρ increases initially to 2.29 × 10⁶ Ω cm at 2 Bwt%, and decreases thereafter up to 4.58 × 10⁵ and 1.82 × 10⁴ Ω cm at 10 and 16 Bwt%, respectively. The variation of structural properties, E_g and ρ, can be related to the successful doping of B in the a-C films at low content of Bwt% (up to 10 Bwt%), as the structural properties and E_g remain almost unchanged and the ρ decreased. Since both E_g and ρ decreased sharply with higher Bwt%, this phenomenon can be related to graphitization. In this paper, the dependence of sp³ and sp² impurity content on the growth and growth conditions of the films are also studied.

Nitrogenated diamond-like carbon films have been deposited on glass and p-type Si (100) substrates by radio frequency (r.f.) plasma-enhanced chemical vapor deposition (PECVD) with a frequency of 13.56 MHz at room temperature using CH₄ as precursor of carbon source and H₂ as a carrier gas. The deposition was performed at a different flow rate of nitrogen from 0 to 12 sccm under a constant r.f. power. The effect of nitrogen incorporation on the bonding states and growth kinetics of the deposited films have been investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy and optical properties by UV spectroscopy measurement. Our experimental results show that the incorporation of nitrogen has a considerable effect on the properties of the deposited films. FTIR spectra show that the nitrogen is bonded to carbon and hydrogen as C=N, C≡N, N–H and C–H bonding configurations in the as-deposited film. The incorporation of nitrogen is found to shift the Raman G peak toward the higher wave number and to increase the Raman I_D/I_G ratio demonstrating the graphitic character of the hydrogenated amorphous carbon–nitrogen films. Band gap is found to reduce with the increase in nitrogen concentration.

Nitrogen doped amorphous carbon (a-C:N) thin films were deposited on silicon and quartz substrates by microwave surface-wave plasma chemical vapor deposition (SWMP-CVD) technique at low temperatures (<100°C). We used argon (Ar), camphor dissolved in alcohol, and nitrogen (N) as carrier, source, and dopant gases, respectively. Optical band gap (E_g) decreased from 4.1 to 2.4 eV when the N gas concentration increased from 0% to 4.5%. The films were annealed at different temperatures ranging from 150°C to 450°C in Ar gas environment to investigate the optical and electrical properties of the films before and after annealing. Both E_g and electrical resistivity (ρ) decreased dramatically up to 0.95 eV and 57×10³ Ω cm at 450°C annealing. The structural modifications of the films leading them to become more graphitized as a function of the annealing temperature were confirmed by the characterization of Raman spectra.

A carbon precursor film was formed on a titanium plate by a hydrothermal method using glucose, and an amorphous film was obtained by carbonization at 400^∘C under an Ar atmosphere. The morphology and composition of the surface was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), and the interface contact resistance (ICR) under different pressures by simulating the working mode of the fuel cell. The corrosion resistance of amorphous carbon coatings was tested by simulating the proton exchange membrane fuel cells (PEMC). The amorphous coating showed excellent interfacial conductivity and great corrosion resistance, with high potential application in bipolar plates of PEMFCs

A novel memristor device using platinum (Pt)/amorphous carbon (a-C)/MXene (Ti₃C₂)/silver (Ag) structure was proposed and experimentally fabricated. Its electrical measurements clearly indicated that in comparison with the device without MXene capping, the proposed device exhibited lower “SET” voltage, longer endurance, and better stability. This can be attributed to the lower formation energy of Ag nanoclusters inside the MXene layer, derived from the first-principles calculations. Numerous device conductances were also obtained by choosing appropriate “SET” and “RESET” pulses, and thus enabled the imitation of synaptic potentiation/depression and pair-pulse facilitation. This implied its potential for in-memory computing and neuromorphic computing applications.