| 1. |
- Broitman, Esteban, et al.
(författare)
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Fullerene-like carbon nitride - A new form of DLC solid lubricant coatings
- 2008
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Ingår i: Tribology of diamondlike carbon films: fundamentals and applications. - Berlin : Springer. - 9780387302645 - 9780387498911 ; , s. -664
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This book highlights some of the most important structural, chemical, mechanical and tribological characteristics of DLC films. It is particularly dedicated to the fundamental tribological issues that impact the performance and durability of these coatings. The book provides reliable and up-to-date information on available industrial DLC coatings and includes clear definitions and descriptions of various DLC films and their properties.
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| 2. |
- Gago, R, et al.
(författare)
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Correlation between bonding structure and microstructure in fullerenelike carbon nitride thin films
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:12, s. 125414-
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Tidskriftsartikel (refereegranskat)abstract
- The bonding structure of highly ordered fullerenelike (FL) carbon nitride (CNx) thin films has been assessed by x-ray absorption near-edge spectroscopy (XANES). Samples with different degrees of FL character have been analyzed to discern spectral signatures related to the FL microstructure. The XANES spectra of FL-CNx films resemble that of graphitic CN x, evidencing the sp2 hybridization of both C and N atoms. The FL structure is achieved with the promotion of N in threefold positions over pyridinelike and cyanidelike bonding environments. In addition, the relative p* / σ* XANES intensity ratio at the C(1s) edge is independent of the FL character, while it decreases ∼40% at the N(1s) edge with the formation of FL arrangements. This result indicates that there is no appreciable introduction of C-sp3 hybrids with the development of FL structures and, additionally, that a different spatial localization of π electrons at C and N sites takes place in curved graphitic structures. The latter has implications for the elastic properties of graphene sheets and could, as such, explain the outstanding elastic properties of FL-CNx.
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| 3. |
- Gago, R., et al.
(författare)
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Synthesis of carbon nitride thin films by low-energy ion beam assisted evaporation : On the mechanisms for fullerene-like microstructure formation
- 2005
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 483:1-2, s. 89-94
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride (CNx) thin films were grown at different substrate temperatures by low-energy (<100 eV) ion beam assistance deposition (LE-IBAD) in order to discern possible formation mechanisms of a fullerene-like (FL) microstructure. The samples are compared to those of well-structured FL-CNx films synthesized by reactive magnetron sputtering (MS). The comparison yields similar trends for both techniques, such as limitation of the nitrogen content at 20–25 at.%, dominance of sp2 hybrids, as well as thermally activated chemical desorption of CxNy species from the substrate during growth. However, CNx films produced by LE-IBAD are amorphous. The lack of FL structural features correlates with a lower degree of sp2 clustering, attributed to the promotion of nitrile groups. Therefore, low-energy ion bombardment is shown not to be a sufficient condition for the growth of FL-CNx. This result reinforces the eventual relevance of pre-formed CxNy species at the sputtering target in MS for the introduction and/or evolution of FL arrangements.
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| 4. |
- Gueorguiev, Gueorgui Kostov, 1968-, et al.
(författare)
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First-principles calculations on the curvature evolution and cross-linkage in carbon nitride
- 2005
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 410:4-6, s. 228-234
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Tidskriftsartikel (refereegranskat)abstract
- First-principles calculations were utilized to study the formation mechanisms and structural features of fullerene-like carbon nitride (FL CN x). Cohesive energy comparisons reveal the energy cost for different defects arising from substitution of C for N as a function of the nitrogen concentration. In FL CNx, combinations of pentagons and heptagons compete in causing graphene sheet curvature during the addition of CN-precursors and single species. Also, cross-linkage between graphene layers in FL CNx can be explained by the bond rotation due to incorporated N atoms. The computational results agree with recent experimental observations from the growth of FL CNx thin films. © 2005 Elsevier B.V. All rights reserved.
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| 5. |
- Neidhardt, Jörg, 1976-, et al.
(författare)
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Arrhenius-type temperature dependence of the chemical desorption processes active during deposition of fullerene-like carbon nitride thin films
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 569:1-3
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Tidskriftsartikel (refereegranskat)abstract
- The chemical desorption of carbon and nitrogen-containing species from the growth surface was investigated for the deposition of fullerene-like carbon nitride (FL CNx) thin solid films by reactive magnetron sputtering of a carbon target in a N2-containing atmosphere. The desorption of mainly C2N2 was suppressed by decreasing the substrate temperature for various N2 fractions in the discharge stepwise from 873 K down to cryogenic temperatures of 153 K. This approach enabled us to quantify the film-forming flux by determining the carbon and nitrogen incorporation rates by elastic recoil detection. The incorporation of both, carbon and nitrogen, was found to increase substantially at lower substrate temperatures, whereas this effect is most pronounced for the higher N 2 fractions. In turn, a modified Arrhenius-type rate equation was applied to extrapolate the total flux of the elements as well as their respective activation energies of desorption for the series at higher N 2 fractions. The reasonable fit indicates that the desorption process is mainly determined by the surface diffusion rate of adsorbed C xNy species as well as their structure and total number. The extrapolated fluxes of carbon and nitrogen atoms arriving as preformed species at the growth surface scaled strongly with the availability of N 2 in the discharge, while the obtained activation energies of 0.05-0.17 eV point towards a saturation of the process at elevated temperatures. Furthermore, the constant C/N ratio found in the film-forming flux leads to the notion that most of the nitrogen incorporated originates from preformed species instead of N atoms or ions. The FL structure evolution has to be seen as a sensitive interplay between the type and magnitude of preformed C xNy species in the deposition flux and the selectiveness of the preferential etching by means of the chemical desorption. © 2004 Elsevier B.V. All rights reserved.
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| 6. |
- Neidhardt, Jörg, 1976-, et al.
(författare)
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Cryogenic deposition of carbon nitride thin solid films by reactive magnetron sputtering, Suppression of the chemical desorption processes
- 2005
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 478:1-2, s. 34-41
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured fullerene-like carbon nitride (FL CNx) is commonly grown by reactive magnetron sputtering of carbon in a nitrogen-containing atmosphere. The film structure formation for this technique is presumably due to the existence of preformed molecular CxNy (x,y≤2) species in the deposition flux, which act as growth templates and enhance the selectivity of chemical desorption processes. In the present study, the extent of the desorption processes and the implications on the resulting film have been investigated in detail, addressing in particular the structure evolution and the origin of the incorporated nitrogen. This was studied by varying the N2-fraction in the discharge from 0 to 1 and the substrate temperature from 600 °C (873 K) down to minus 130 °C (143 K). The results show that the incorporation rate of carbon and nitrogen into the film increases substantially with an increased N2-content in the plasma and decreasing substrate temperature, thus indicating that the chemistry and magnitude of the arriving flux is substantially altered with the N2-fraction in the discharge. It is concluded that the chemically activated desorption in conjunction with the varying chemistry of the film-forming flux affects the sensitive structural balance, determined by incorporation and desorption of film forming CxNy (x,y≤2) species.
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| 7. |
- Neidhardt, Jörg, 1976-, et al.
(författare)
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Fullerene-like carbon nitride - A new thin film material
- 2006
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Ingår i: Wide Band Gap Materials and New Developments 2006. - Trivandrum : Research Signpost. - 8130800926 - 9788130800929 ; , s. -208
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Neidhardt, Jörg, 1976-
(författare)
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Materials science of magnetron sputtered fullerene-like carbon nitride thin films
- 2002
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon nitride (CNx) is a promising compound thin film material for a variety of applications. The nano-structured fullerene-like allotrope in particular exhibits outstanding mechanical proper ties. such as extreme elasticity and toughness. due to a unique microstructure of curved and crosslinked basal planes. Relations between growth. film microstructure and properties of fullerene-like CNx thin solid films have been studied. The material was synthesised by dual. w1balanced. reactive. direct current. magnetron sputtering at a substrate temperature of 450 °C, to provide for sufficient ad-atom mobility. while the total pressure of an argon and nitrogen mixture was kept constant at 0.4 Pa. to avoid gas-phase reactions. In order to study the effect of ionised species bombarding the growing film, the gas composition was varied from aN2-fraction of 0 to L while ion energy was set either to 25 or 40 eV. The deposition process was extensively characterised regarding the type and energy of ionised species arriving at the substrate by plasma probe based techniques and energy selective mass spectrometry. It is shown that the ion flux consists predominantly of multi-atomic CxNy(2 ≥ x, y) species and that their total number scales with the N2-fraction. Elastic recoil detection revealed a nitrogen concentration in the different films of approximately 14 to 18 at%. The nitrngen content exhibits only a minor dependence on the ion energy and gas composition. due to the effect of temperature enhanced chemical desorption of volatile. mainly nitrogen-containing. species from the growth surface. This points towards a rather complicated growth process. where besides the preferential etching by chemical desorption. the structural orientation of multi-atomic species upon incorporation might provide the key for a better understanding of the fullerene-like structure evolution. The material consist of predominantly sp2-coordinated carbon basal planes. which curve and cross-link upon nitrogen incorporation. The radius of curvature and alignment of planes. as well as the crosslinking between them can be controlled by the deposition parameters and define the mechanical properties. as determined by nanoindentation. Fullerene-like CNx in general deforms predominantly elastic by buckling of sheets. bond deflection and rotation rather than breaking. due to the large inter-planar lattice spacing and the strength of the carbon sp2 bond. Fullerene-like CNx exhibits an extremely low tendency to plastic deformation. usually connected to highhardness materials. Yet. it has a low to moderate resistance to penetration. which results in a compliant and fracture-to ugh material.
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| 9. |
- Neidhardt, Jörg, 1976-, et al.
(författare)
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Structural, mechanical and tribological behavior of fullerene-like and amorphous carbon nitride coatings
- 2004
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Ingår i: Diamond and related materials. - : Elsevier BV. - 0925-9635 .- 1879-0062. ; 13:10, s. 1882-1888
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical and tribological properties of fullerene-like (FL) and amorphous carbon nitride (CNX) coatings synthesized by reactive unbalanced magnetron sputtering were analyzed and compared to carbon coatings deposited without N2. Elastic recoil detection analysis (ERDA) was used to determine the amount of incorporated nitrogen while X-ray photoelectron spectroscopy (XPS) was used to study the local bonding environment. Nano-indentation revealed a large spread in hardness, elastic modulus and elastic recovery. The tribological performance of the coatings was tested with a reciprocating sliding tribometer that allowed in situ visualization of the sliding contact. Tests were performed with a sapphire hemisphere sliding at 4 mm/s in dry and ambient humidity air. Friction coefficients of the FL-CN X coatings in both humidities were slightly higher than those of diamond-like carbon coatings (DLC), the values were between 0.1 and 0.25, dropping as the bias voltage increased. FL-CNX coatings had higher wear resistance than amorphous CNX, DLC and graphite coatings in sliding contact although the hardnesses of the coatings were comparable. Wear rates of the FL-CNX coatings in ambient air were lower than in dry air and orders of magnitude lower than the other carbon coatings. Furthermore, the most wear-resistant high-temperature FL-CNX coating had the highest hardness, but the shortest wear life of the three high-temperature FL-CN X coatings. In situ visualization indicated films transferred from the coating to the sapphire hemisphere, the transfer film isolated the hemisphere from the coating, thereby controlling both the friction coefficient and the wear behavior. Effects of deposition conditions, structure and hardness on wear and friction behavior are discussed. © 2004 Elsevier B.V. All rights reserved.
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| 10. |
- Rester, M., et al.
(författare)
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Annealing studies of nanocomposite Ti-Si-C thin films with respect to phase stability and tribological performance
- 2006
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 429:1-2, s. 90-95
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Tidskriftsartikel (refereegranskat)abstract
- Nanocomposite Ti-Si-C thin films were deposited by dc magnetron sputtering from a Ti3SiC2 target onto Si(1 0 0) and high-speed steel substrates at 300 °C. The as-deposited films consisted of nanocrystalline (nc-) TiCx and amorphous (a-) SiCx, as determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Annealing in vacuum up to 1450 °C resulted in improved crystallinity and a decreased volume fraction of the amorphous phase. Additionally, differential scanning calorimetry (DSC) was used to monitor heat flows connected to the respective reactions in the material, where a broad exothermic peak attributed to grain growth of crystalline TiCx appeared, while an exothermic reaction related to the formation of Ti3SiC2 was not detected. Tribological testing in a ball-on-disk setup was conducted at room temperature, 500 and 700 °C against an alumina counterpart. The room temperature measurement resulted in a coefficient of friction value of 0.8, at elevated temperatures the coefficient of friction decreased to 0.4. © 2006 Elsevier B.V. All rights reserved.
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