Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

/pdf/diamond-like-amorphous-carbon-3pczopr0z7.pdf

Diamond-like amorphous carbon

A general framework for the interpretation of infrared and Raman spectra of amorphous carbon nitrides is presented. In the first part of this paper we examine the infrared spectra. The peaks around 1350 and 1550 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ found in the infrared spectrum of amorphous carbon nitride or hydrogenated and hydrogen-free amorphous carbon are shown to originate from the large dynamic charge of the more delocalized \ensuremath{\pi} bonding which occurs in more ${\mathrm{sp}}^{2}$ bonded networks. The IR absorption decreases strongly when the \ensuremath{\pi} bonding becomes localized, as in tetrahedral amorphous carbon. Isotopic substitution is used to assign the modes to $\mathrm{C}=\mathrm{C}$ skeleton modes, even those modes around 1600 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ which become strongly enhanced by the presence of hydrogen. The infrared spectrum of carbon nitride may resemble the Raman spectrum at some excitation energy, but the infrared activity does not primarily result from nitrogen breaking the symmetry. In the second part we examine the Raman spectra. A general model is presented for the interpretation of the Raman spectra of amorphous carbon nitrides measured at any excitation energy. The Raman spectra can be explained in terms of an amorphous carbon based model, without need of extra peaks due to CN, NN, or NH modes. We classify amorphous carbon nitride films in four classes, according to the corresponding N-free film: $a\ensuremath{-}\mathrm{C}:\mathrm{N},$ $a\ensuremath{-}\mathrm{C}:\mathrm{H}:\mathrm{N},$ $ta\ensuremath{-}\mathrm{C}:\mathrm{H}:\mathrm{N},$ and $ta\ensuremath{-}\mathrm{C}:\mathrm{N}.$ We analyze a wide variety of samples for the four classes and present the Raman spectra as a function of N content, ${\mathrm{sp}}^{3}$ content, and band gap. In all cases, a multiwavelength Raman study allows a direct correlation of the Raman parameters with the N content, which is not generally possible for single wavelength excitation. The G peak dispersion emerges as a most informative parameter for Raman analysis. UV Raman enhances the ${\mathrm{sp}}^{1}$ CN peak, which is usually too faint to be seen in visible excitation. As for N-free samples, UV Raman also enhances the C-C ${\mathrm{sp}}^{3}$ bonds vibrations, allowing the ${\mathrm{sp}}^{3}$ content to be quantified.

/pdf/interpretation-of-infrared-and-raman-spectra-of-amorphous-4qk3s6kov2.pdf

Interpretation of infrared and Raman spectra of amorphous carbon nitrides

A review of the preparation of carbon nitride films

Mesoporous carbon nitrides (MCN) are fascinating materials with unique semiconducting and basic properties that are useful in many applications including photocatalysis and sensing. Most syntheses of MCN focus on creating theoretically predicted C3N4 stoichiometry with a band gap of 2.7 eV using a nano-hard templating approach with triazine-based precursors. However, the performance of the MCN in semiconducting applications is limited to the MCN framework with a small band gap, which would be linked with the addition of more N in the CN framework, but this remains a huge challenge. Here, we report a precursor with high nitrogen content, 3-amino-1,2,4-triazole, that enables the formation of new and well-ordered 3D MCN with C3N5 stoichiometry (MCN-8), which has not been predicted so far, and a low-band-gap energy (2.2 eV). This novel class of material without addition of any dopants shows not only a superior photocatalytic water-splitting performance with a total of 801 μmol of H2 under visible-light irradiation for 3 h but also excellent sensing properties for toxic acids.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.201702386

Highly Ordered Nitrogen-Rich Mesoporous Carbon Nitrides and Their Superior Performance for Sensing and Photocatalytic Hydrogen Generation.

Carbon-based thin films possess unique and adjustable combination of properties such as high hardness and wear resistance, chemical resistance and good tribological performances Among critical variables to tailor a-C film’s properties for specific application is the distribution of the carbon hybridization states (sp 1 , sp 2 and sp 3 bonds), the atomic H content, the content in dopants such as Si, F, N, B and O Here we focus on: (i) a-C and hydrogenated amorphous carbon (a-C:H) films with a mixture of sp 2 and sp 3 bonding, highly sp 3 -boned material (ta-C) and sp 2 -bonded carbon, (ii) carbon nitride (CN x ) coatings and (iii) metal/amorphous carbon (a-C:M) composite films The study is focused on the review of the nanomechanical properties and analysis of the nanoscratching processes at low loads to obtain quantitative analysis, the comparison of their elastic/plastic deformation response, and nanotribological behavior of the a-C, ta-C, a-C:H, CN x , and a-C:M films For ta-C and a-C:M films new data are presented and discussed

Nanomechanical and nanotribological properties of carbon-based thin films: A review

The effect of nitrogen addition on the structural and electronic properties of hydrogenated amorphous carbon (a-C:H) films has been characterized in terms of its composition, sp3 bonding fraction, infrared and Raman spectra, optical band gap, conductivity, and paramagnetic defect. The variation of conductivity with nitrogen content suggests that N acts as a weak donor, with the conductivity first decreasing and then increasing as the Fermi level moves up in the band gap. Compensated behavior is found at about 7 at. % N, for the deposition conditions used here, where a number of properties show extreme behavior. The paramagnetic defect density and the Urbach tailwidth are each found to decrease with increasing N content. It is unusual to find alloy additions decreasing disorder in this manner.

Nitrogen modification of hydrogenated amorphous carbon films

Fluorinated amorphous-carbon films (a-C:F:H) were deposited by low-power rf capacitively coupled plasma-enhanced chemical-vapor deposition using CH4–CF4 gas mixtures. Different series of films were deposited, changing one parameter at a time: the CF4 partial pressure from 0% to 100%, the self-bias voltage from −50 to −700 V, and the total deposition pressure from 5 to 15 Pa. The composition was determined by ion-beam analysis (IBA): Rutherford backscattering spectrometry, elastic recoil detection analysis, and nuclear reaction analysis. The atomic density of the films was evaluated by combining the IBA results with the thickness value measured by stylus profilometry. Film structure was investigated by infrared transmission and Raman scattering spectroscopies. The internal stress and Vickers hardness were also measured. For a fixed self-bias, the increase of the CF4 partial pressure leads to a higher fluorine incorporation and the decrease of both hardness and internal stress. The film microstructure chang...

Structural and mechanical characterization of fluorinated amorphous-carbon films deposited by plasma decomposition of CF4–CH4 gas mixtures

Hard amorphous hydrogenated carbon-nitrogen films obtained by PECVD in methane-ammonia atmospheres

Amorphous hydrogenated carbon–nitrogen films, a-C(N):H, were deposited by plasma enhanced chemical vapor deposition using acetylene–nitrogen mixtures. Film composition and density were determined by means of ion beam techniques being the film microstructure studied by infrared and Raman spectroscopies. Films were obtained with nitrogen content up to 22 at. %. As for films obtained using other gas mixtures, the deposition rate showed a strong decrease upon nitrogen incorporation, although with a smaller rate. The film growth kinetic is discussed and some specific features of acetylene–nitrogen precursor gas mixtures are pointed out. A remarkable decrease on the C atom sp3 fraction was inferred for nitrogen contents higher than 10 at. %, and was correlated to the film density behavior. The mechanical hardness and internal stress were relatively insensitive to low nitrogen incorporation, with a systematic decreasing behavior for nitrogen contents above 10 at. %.

Growth kinetics and relationship between structure and mechanical properties of a-C(N):H films deposited in acetylene–nitrogen atmospheres

Amorphous carbon nitride thin films (a-CNx) have been deposited onto Si (100) substrates by using a rf diode sputtering system. The films were deposited in reactive nitrogen-argon atmospheres. The partial pressure of nitrogen ranged from 0% to 100% at two different deposition pressures (Pd=2 Pa and Pd=8 Pa). The film composition was determined by ion beam techniques: Rutherford backscattering spectrometry and nuclear reaction analysis. The relative amount of carbon and nitrogen in the films is nearly independent of the nitrogen partial pressure in the reactive plasma. The maximum nitrogen content is 48 at. %. The structural characterization was performed by means of Raman and infrared spectroscopies. Raman spectra revealed the presence of the D and G bands, typical of disordered carbon based materials, and a third band, at about 680 cm−1, also attributed to film disorder. Infrared spectroscopy results showed the D and G Raman bands, IR allowed due to the nitrogen incorporation in the carbon network, the p...

D. F. Franceschini

Papers

Nitrogen modification of hydrogenated amorphous carbon films

Structural and mechanical characterization of fluorinated amorphous-carbon films deposited by plasma decomposition of CF4–CH4 gas mixtures

Hard amorphous hydrogenated carbon-nitrogen films obtained by PECVD in methane-ammonia atmospheres

Growth kinetics and relationship between structure and mechanical properties of a-C(N):H films deposited in acetylene–nitrogen atmospheres

Carbon nitride thin films prepared by reactive sputtering: Elemental composition and structural characterization