| 1. |
- Berlind, Torun, 1965-, et al.
(författare)
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Spectroscopic ellipsometry characterization of amorphous carbon and amorphous,graphitic and fullerene-like carbon nitride thin films
- 2009
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 517:24, s. 6652-6658
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride (CNx) and amorphous carbon (a-C) thin films are deposited by reactive magnetron sputtering onto silicon (001) wafers under controlled conditions to achieve amorphous, graphitic and fullerene-like microstructures. As-deposited films are analyzed by Spectroscopic Ellipsometry in the UV–VIS–NIR and IR spectral ranges in order to get further insight into the bonding structure of the material. Additional characterization is performed by High Resolution Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy. Between eight and eleven resonances are observed and modeled in the ellipsometrically determined optical spectra of the films. The largest or the second largest resonance for all films is a feature associated with C–N or C–C modes. This feature is generally associated with sp3 C–N or sp3 C–C bonds, which for the nitrogen-containing films instead should be identified as a three-fold or two-fold sp2 hybridization of N, either substituted in a graphite site or in a pyridine-like configuration, respectively. The π→πlow asterisk electronic transition associated with sp2 C bonds in carbon films and with sp2 N bonds (as N bonded in pyridine-like manner) in CNx films is also present, but not as strong. Another feature present in all CNx films is a resonance associated with nitrile often observed in carbon nitrides. Additional resonances are identified and discussed and moreover, several new, unidentified resonances are observed in the ellipsometric spectra.
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| 2. |
- 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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| 3. |
- Broitman, E, et al.
(författare)
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Letter: Electrical properties of carbon nitride thin films : Role of morphology and hydrogen content
- 2002
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Ingår i: Journal of Electronic Materials. - 0361-5235 .- 1543-186X. ; 31:9, s. 957-961
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The influence of hydrogen content and ambient humidity on the electrical properties of carbon nitride (CNX) films deposited by reactive magnetron sputtering from a graphite target in Ar discharges mixed with N-2 and H-2 at a substrate temperature of 350degreesC have been investigated. Carbon films deposited in pure Ar exhibit a dark resistivity at room temperature of similar to4 X 10(-2) Omegacm, while the resistivity is one order of magnitude lower for CN0.25 films deposited in pure N-2, due to their denser morphology. The increasing H-2 fraction in the discharge gas leads to an increased resistivity for all gas mixtures. This is most pronounced for the nitrogen-free films deposited in an Ar/H-2 mixture, where the resistivity increases by over four orders of magnitude. This can be related to a decreased electron mobility as H inhibits the formation of double bonds. After exposure to air, the resistivity increases with time through two different diffusion regimes. The measured electrical properties of the films are related to the apparent film microstructure, bonding nature, and ambient humidity.
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| 4. |
- Broitman, E., et al.
(författare)
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Water adsorption on lubricated fullerene-like CNx films
- 2006
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:3, s. 979-983
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Tidskriftsartikel (refereegranskat)abstract
- Humidity influences the tribological performance of the head–disk interface in magnetic data storage devices. In this work we compare the uptake of water of amorphous hydrogenated carbon (a-CHy) and carbon nitride (a-CNx) films, widely used as protective overcoats in computer disk drive systems, with two types of amorphous non-hydrogenated carbon (a-C and a-Csp2) films, and fullerene-like carbon nitride (FL-CNx) films. Carbon films were deposited on quartz crystal substrates by reactive dc magnetron sputtering in Ar/N2 discharges. After deposition, some of the films were coated with a 2-nm-thick layer of Z-tetraol, a lubricant used in hard disk devices. A quartz crystal microbalance placed in a vacuum chamber was used to measure the adsorption of water at room temperature and at pressures of water corresponding to relative humidities in the range RH = 0 to 90%. Water adsorption and desorption is fast, indicating that equilibrium with ambient humidity is reached on time scales of minutes, much faster than the time scales for fluctuations in ambient humidity. The amount of water adsorbed on the non-lubricated amorphous carbon films is significantly higher than that on the fullerene-like films. The presence of the lubricant influences water adsorption but its impact differs on different carbon films.
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| 5. |
- Brunell, I.F., et al.
(författare)
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In-situ stress measurement during the deposition of CN x thin films by unbalanced magnetron sputtering; formation of high levels of stress with 28 eV ion irradiation
- 2004
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 84:6, s. 395-403
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Tidskriftsartikel (refereegranskat)abstract
- Stress development during growth of CN x films by unbalanced magnetron sputtering has been investigated with an in-situ laser deflection technique. The stress is initially tensile, then it becomes compressive, reaching a maximum of as much as 7 GPa. These are anomalously high stress levels compared with pure carbon, considering the low ion energies (28 eV) and ion-to-neutral arrival rate ratio (<1) employed. This phenomenon is explained by the formation of a fullerene-like microstructure and nitrogen substitution at the growth surface. An accompanying increased reactivity of carbon atoms promotes sp3 bonding or other cross-linking of curved basal planes with resulting film densification.
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| 6. |
- Czigany, Zs., et al.
(författare)
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Growth of fullerene-like carbon nitride thin solid films consisting of cross-linked nano-onions
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:16, s. 2639-2641
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Tidskriftsartikel (refereegranskat)abstract
- Fullerene-like CNx (x˜0.12) thin solid films were deposited by reactive magnetron sputtering of graphite in a nitrogen and argon discharge on cleaved NaCl and Si(001) substrates at 450°C. As-deposited films consist of 5 nm diam CNx nano-onions with shell sizes corresponding to Goldberg polyhedra determined by high-resolution transmission electron microscopy. Electron energy loss spectroscopy revealed that N incorporation is higher in the core of the onions than at the perimeter. N incorporation promotes pentagon formation and provides reactive sites for interlinks between shells of the onions. A model is proposed for the formation of CNx nano-onions by continuous surface nucleation and growth of hemispherical shells. © 2001 American Institute of Physics.
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| 7. |
- Czigany, Zs., et al.
(författare)
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Imaging of fullerene-like structures in CNx thin films by electron microscopy, Sample preparation artefacts due to ion-beam milling
- 2003
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Ingår i: Ultramicroscopy. - 0304-3991 .- 1879-2723. ; 94:3-4, s. 163-173
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of CNx thin films, deposited by reactive magnetron sputtering, was investigated by transmission electron microscopy (TEM) at 200kV in plan-view and cross-sectional samples. Imaging artefacts arise in high-resolution TEM due to overlap of nm-sized fullerene-like features for specimen thickness above 5nm. The thinnest and apparently artefact-free areas were obtained at the fracture edges of plan-view specimens floated-off from NaCl substrates. Cross-sectional samples were prepared by ion-beam milling at low energy to minimize sample preparation artefacts. The depth of the ion-bombardment-induced surface amorphization was determined by TEM cross sections of ion-milled fullerene-like CNx surfaces. The thickness of the damaged surface layer at 5° grazing incidence was 13 and 10nm at 3 and 0.8keV, respectively, which is approximately three times larger than that observed on Si prepared under the same conditions. The shallowest damage depth, observed for 0.25keV, was less than 1nm. Chemical changes due to N loss and graphitization were also observed by X-ray photoelectron spectroscopy. As a consequence of chemical effects, sputtering rates of CNx films were similar to that of Si, which enables relatively fast ion-milling procedure compared to carbon compounds. No electron beam damage of fullerene-like CNx was observed at 200kV. © 2002 Elsevier Science B.V. All rights reserved.
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| 8. |
- 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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| 9. |
- 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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| 10. |
- Garcia, I.A., et al.
(författare)
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How hard is fullerene-like CNx? Some observations from the nanoindentation response of a magnetron-sputtered coating
- 2002
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Ingår i: Philosophical magazine. A. Physics of condensed matter. Defects and mechanical properties. - : Informa UK Limited. - 0141-8610. ; 82:10 SPEC., s. 2133-2147
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Tidskriftsartikel (refereegranskat)abstract
- Thin fullerene-like CNx coatings deposited on hard substrates (e.g. SiC) show very shallow residual impressions when investigated by nanoindentation at displacements less than the coating thickness. The low work of indentation (i.e. the small area enclosed by the loading and unloading curves) of these materials implies a large amount of recovery of indent depth which is often associated with materials of high hardness. However, analysis of the unloading curves by the Oliver-Pharr method generates hardness values which are usually less than that of silicon. Detailed analysis of the loading curve shows three distinct regimes of behaviour corresponding to behaviour controlled by surface roughness, elastic deformation and plasticity. Measurements of Young's modulus from the elastic part of the loading curve, from the Oliver-Pharr method and from elastic wave measurements are all consistently low. This implies that the material behaves like a very hard rubber which undergoes considerable elastic recovery on unloading but does not have a very high resistance to penetration on loading. The very high H/E values for fullerene-like CNx confirms this view.
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| 11. |
- 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
-
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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| 12. |
- Gueorguiev, G.K., et al.
(författare)
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First-principles calculations on the role of CN precursors for the formation of fullerene-like carbon nitride
- 2005
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 401:1-3, s. 288-295
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Tidskriftsartikel (refereegranskat)abstract
- First-principles calculations were utilized to study the formation mechanisms of the fullerene-like structure in carbon nitride compounds in the context of aligned incorporation of CN precursors along edges of evolving sheets during vapor phase synthesis. The incorporation of CN dimers and cyanogen molecules promotes an initial stabilization of pentagon defects, necessary for the observed bending of graphene multilayers in these compounds. The theoretical results corroborate recent experimental findings suggesting that preformed CxNy species, besides C and N atoms and ions, play an important role during the growth of FL CNx thin films by reactive magnetron sputtering. © 2004 Elsevier B.V. All rights reserved.
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| 13. |
- Hultman, Lars, et al.
(författare)
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Cross-linked nano-onions of carbon nitride in the solid phase : Existence of a novel C48N12 aza-fullerene
- 2001
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 87:22, s. art. no.-225503
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Tidskriftsartikel (refereegranskat)abstract
- We report a new fullerenelike material consisting of cross-linked nano-onions of C and N. Growth of the onion shells takes place atom by atom on a substrate surface and yields thin solid films during magnetron sputter deposition. Electron microscopy and energy loss spectroscopy show that the core shell contains up to 20 at. % N corresponding to C48N12 aza-fullerene composition. Nanoindentation of this nanostructured material gives high resilience with hardness 7 GPa, Young's modulus 37 GPa, and complete elastic recovery after loading with 0.5 mN to a depth of 75 nm. Total energy calculations show the stability Of C60-2nN2n aza-fullerenes and suggest the existence of a novel C48N12 molecule.
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| 14. |
- Hultman, Lars, et al.
(författare)
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Fullerene-like carbon nitride : A resilient coating material
- 2003
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Ingår i: MRS bulletin. - 0883-7694 .- 1938-1425. ; 28:3, s. 194-202
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride is an emerging material for wear-resistant coatings. The fullerene-like CNx compounds generally exhibit extreme elasticity in combination with a low work of indentation hardness. Yet CNx shows a low-to-moderate resistance to penetration, depending on deposition conditions. Since the deformation energy is predominantly stored elastically, the material possesses an extremely resilient character. This new class of materials consists of sp(2)-coordinated basal planes that are buckled from the incorporation of-pentagons and cross-linked at sp(3)-hybridized C sites, both of which are caused by structural incorporation of nitrogen. Carbon nitride thus deforms elastically due to bending of the structural units. The orientation, radius of curvature of the basal planes, and the degree of cross-linking between them defines the structure and properties of the material. Due to the unique deformation behavior, the hardness requires special care to assess, but can be very high for films with a large degree of cross-linking. This article is a review of the research on CNx films deposited by reactive magnetron sputtering, with examples from our recent work. The findings are significant for the design of fracture-tough materials.
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| 15. |
- 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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| 16. |
- Neidhardt, Jörg, et al.
(författare)
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Beyond ?- C3 N4 -Fullerene-like carbon nitride : A promising coating material
- 2007
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 25:4, s. 633-644
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Tidskriftsartikel (refereegranskat)abstract
- Even though the synthesis of super-hard-crystalline ?- C3 N4 remains elusive, noncrystalline C Nx compounds are of increasing importance owing to their competitive properties. Especially the fullerene-like allotrope of C Nx exhibits outstanding elasticity in combination with low work of indentation. This new class of thin solid film materials is characterized by a microstructure of bent and intersecting basal planes. Substitutional incorporation of nitrogen into the predominantly s p2 hybridized graphitic layer triggers the formation of curvature-inducing pentagons and interplanar cross-links at a much lower energy cost as compared to carbon-only materials. The term "fullerene- like" was coined to reflect the nanometer scale of curved structural units. Thus, fullerene-like C Nx deforms by bond angle deflection and compression of the graphitic interplanar lattice spacing, whereas the superior strength of the s p2 bonds inhibits plastic deformation giving the material an extremely resilient character. The orientation, radius of curvature of basal planes, and density of cross-linking can be adjusted by the synthesis conditions. Here, the existence of significant numbers of precursor molecules is a determining factor. The inherent resiliency of the material in combination with the carbon-based beneficial friction promises to give rise to numerous tribological applications. © 2007 American Vacuum Society.
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| 17. |
- Neidhardt, Jörg, et al.
(författare)
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Correlated high resolution transmission electron microscopy and X-ray photoelectron spectroscopy studies of structured CNx (0 < x < 0.25) thin solid films
- 2004
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 42:Dec-13, s. 2729-2734
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Tidskriftsartikel (refereegranskat)abstract
- Structured carbon nitride (CNx), thin solid films, also known as fullerene-like, consist of, upon nitrogen substitution, bent and cross-linked graphene planes. They were synthesized by unbalanced reactive magnetron sputtering and analyzed by high-resolution transmission electron microscopy (HRTEM) in combination with X-ray photoelectron spectroscopy (XPS). The microstructure evolution in terms of plane alignment, extension and cross-linking can be controlled by adjusting the synthesis conditions, such as growth temperature, N-2 fraction in the discharge gas and ion energy. HRTEM on plan-view samples was used to examine the structural changes depending on growth temperature and N-2 fraction. The problem of projection artifacts for imaging the structural features was partially overcome by selected area electron diffraction analysis, where it is shown that diffraction corresponding to 3.5 Angstrom is associated with the formation of structured CNx. The incorporation of N is crucial for the evolution of heavily bent and frequently cross-linked basal planes, since it triggers pentagon formation and cross-linking at much lower energies compared to pure carbon films. Therefore, the two spectral features in the nitrogen Is core electron spectra as examined by XPS were correlated to the microstructure evolution. (C) 2004 Elsevier Ltd. All rights reserved.
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| 18. |
- 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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| 19. |
- Neidhardt, Jörg, et al.
(författare)
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Diagnostics of a N2/Ar direct current magnetron discharge for reactive sputter deposition of fullerene-like carbon nitride thin films
- 2003
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 94:11, s. 7059-7066
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Tidskriftsartikel (refereegranskat)abstract
- Composition and energetic conditions of the ion flux of a direct current, N2/Ar, unbalanced magnetron sputtering plasma in front of ionized film-forming species were investigated. Plasma probe measurements and energy selective mass spectrometry were used. The results show that the total number of C-containing ions strongly depends on the N2 fraction in the discharge. It was also found that C and N atoms and ions are important during growth of fullerene-like (FL) carbon nitride (CNx) thin films.
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| 20. |
- 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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| 21. |
- Neidhardt, Jörg
(författare)
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Fullerene-like carbon nitride thin solid films
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this thesis is to establish synthesis-structure-property- performance relations for nano structured carbon nitride thin solid films. This material consists of bent and frequently intersecting nitrogen-containing graphite basal planes, where nitrogen plays an important role for the initiation of inter-planar cross-links and the induction of curvature via pentagon formation, much like in Buckminster Fullerenes - hence, the terminology "fullerene-like carbon nitride". The work presented establishes the existence of a substantial number of preformed CxNy species as a key requirement for the fullerene-like structure evolution. These species are stabilised upon aligned incorporation into evolving sheets against subsequent desorption via C2N2, which has a selective effect for the formation of planar structures. It is shown that besides the existence of precursors, the morphology of the sheet-like structures in terms of plane alignment and extension depends strongly on the selectivity of the etching process and, thus, is defined by the formation probability of C2N2. This is determined by the reaction pathways and, thus, the number and complexity of the arriving CxNy species and the ad-atom (molecule) mobility as given by substrate temperature and ion assist energy. Reactive magnetron sputtering of carbon in a nitrogen-containing atmosphere is shown to comply with the requirements for the fullerene-like structure evolution. Thus, the dependence of the resulting structures in terms of plane extension, alignment and cross-linking on the variation in chemistry and flux of preformed species (N2 fraction in the discharge) as well as ad-atom mobility (substrate temperature, ion flux and energy) was established. Fullerene-like CNx is a predominantly sp2-hybridised material with 20-25 at% nitrogen structurally incorporated either substitutional in a graphite sheet or in a pyridine-like manner, which initiates curvature and cross-linking, respectively. This structure in turn retains the extraordinary in-plane strength of the hexagonal carbon network and extends it into three dimensions via buckling and inter-planar cross-linking. It is shown in this thesis that the fullerene-like microstructure gives rise to an outstanding mechanical behaviour, with a high compliance due to the high compressibility of the inter planar lattice spacing, but a low tendency to plastic deformation due to strong intra and inter-planar bonds. Thus, this class of materials deforms by reversible buckling and compression of sheets via bond angle deflection and rotation rather than bond breaking, whereas the mechanical response is defined by the extension, alignment and crosslinking of sheets. The high compliance and low plasticity alongside with the low coefficient of friction provides for a promising thin film material for tribological applications.
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| 22. |
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| 23. |
- 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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| 24. |
- 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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| 25. |
- Neidhardt, Jörg, et al.
(författare)
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Superelastic fullerene-like carbon nitride coatings synthesised by reactive unbalanced magnetron sputtering
- 2003
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Ingår i: Surface Engineering. - 0267-0844 .- 1743-2944. ; 19:4, s. 299-303
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Tidskriftsartikel (refereegranskat)abstract
- The present paper presents the results of in depth process characterisation and microstructural investigation of fullerene-like carbon nitride (FL - CNx) coatings combined with deformation analysis, such as indentation testing, in order to assess its performance. Unbalanced reactive magnetron sputtering of graphite in a nitrogen containing atmosphere is essential for the growth of FL - CNx structures chic to CxNy molecules, which are preformed in the process and may act as precursors or growth templates. The deposition process is best described as a hybrid of plasma vapour deposition and chemical vapour deposition. The fullerene-like (FL) structure leads to extraordinary mechanical properties which are assessed by nanoindentation. It exhibits a low work of indentation (usually a property associated with superhard materials) and also a low to moderate resistance to penetration. Therefore, deformation energy is predominantly stored elastically and released after unload giving it a tough and resilient character. In addition, the relatively low modulus leads to a spreading of the contact stresses over a larger volume and consequently to low, stress gradients at the substratelfilm interface. This hinders substratelfilm delamination under load and therefore results in a high load bearing capability, while the coating asperities behave elastically with 110 tendency to brittle fracture in tribological contact. This characteristic combined with the low coefficient of fraction reveals a coating which may be suitable for many tribological applications. (C) 2003 IoM Communications Ltd. Published by Maney for the Institute of Materials, Minerals and Mining.
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| 26. |
- Palacio, JF, et al.
(författare)
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Nanoindentation response of high perfonnance fullerene-like CNx
- 2006
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 494:01-Feb, s. 63-68
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous carbon nitride (CNx) coatings are now being developed for a range of applications, e.g. as a protective top layer for hard disks or as a coating to reduce the friction between synthetic joints in the human body. The purpose of this work is to assess the mechanical properties of the latest generation of fullerene-like CNx deposited on different substrates in order to expand the number of potential applications. Samples of CNx on four different substrates have been studied using quasistatic nanoindentation with a wide range of peak loads, from 500 mu N to 500 mN and dynamic nanoindentation for peak loads from 100 mu N to up to 10 mN. Improved deposition techniques generate samples with extremely high values of hardness/Young's modulus, in some cases greater than 0.4 which is not achieved by any other hard material. Adhesion and fracture resistance are comparable to or better than that of traditional high hardness coatings, such as SiC and TiN, on similar substrates. The sample of CNx on titanium showed differences in hardness and Young's modulus at low loads, where the influence of the substrate is negligible, compared to coatings deposited on other substrates. This arises due to the fact that Ti from the substrate may have diffused into the coating in the deposition process creating a sort of C-N-Ti high hardness layer which would have some advantages of both the fullerene-like and traditional hard coating systems. (c) 2005 Elsevier B.V. All rights reserved.
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| 27. |
- Palmquist, J.-P., et al.
(författare)
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Magnetron sputtered W-C films with C60 as carbon source
- 2003
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 444:1-2, s. 29-37
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Tidskriftsartikel (refereegranskat)abstract
- Thin films in the W–C system were prepared by magnetron sputtering of W with coevaporated C60 as carbon source. Epitaxial deposition of different W–C phases is demonstrated. In addition, nanocrystalline tungsten carbide film growth is also observed. At low C60/W ratios, epitaxial growth of α-W with a solid solution of carbon was obtained on MgO(001) and Al2O3(001) at 400 °C. The carbon content in these films (10–20 at.%) was at least an order of magnitude higher than the maximum equilibrium solubility and gives rise to an extreme hardening effect. Nanoindentation measurements showed that the hardness of these films increased with the carbon content and values as high as 35 GPa were observed. At high C60/W ratios, films of the cubic β-WC1−x (x=0–0.6) phase were deposited with a nanocrystalline microstructure. Films with a grain size <30 Å were obtained and the hardness of these films varied from 14 to 24 GPa. At intermediate C60/W ratios, epitaxial films of hexagonal W2C were deposited on MgO(111) at 400 °C. Polycrystalline phase mixtures were obtained on other substrates and hexagonal WC could be deposited as minority phase at 800 °C.
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| 28. |
- 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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| 29. |
- Riascos, Henry, 1999-, et al.
(författare)
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Structure and properties of pulsed-laser deposited carbon nitride thin films
- 2006
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 497:1-2, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride (CNx) thin films were deposited on silicon (100) and (111) substrates at 300 °C by laser ablation of a graphite target using a pulsed Nd:YAG laser in a nitrogen atmosphere. The composition and structural properties of the films were investigated as functions of gas pressure and laser fluence. X-ray photoelectron spectroscopy (XPS) revealed a strong dependence of the amount of structurally incorporated nitrogen upon gas pressure. A maximum was observed at the highest laser fluence of 10 J/cm2 and at an intermediate pressure of 4 Pa. Further analyses of the XPS N 1s core level spectra of the CNx films, exhibiting the highest elasticity in nanoindentation experiments, revealed a typical double-peak arrangement; most pronounced for the highest laser fluence at low pressures. These two peak components indicate that the nitrogen bonded onto a graphitic structure dominates over the two-fold coordinated pyridine-like bonding configuration. This favors the growth of intersecting corrugated graphene structures that may be considered to have “fullerene-like” microstructures. Additionally, Fourier Transformed Infrared Spectroscopy analyses of films deposited at different pressures show the presence of 2229 and 2273 cm− 1 stretching peaks associated with CN triple bonds (CN) of nitriles and isocyanides, 1640 cm− 1 and 1545 cm− 1 associated with the CC and CN and a peak at 1730 cm− 1, which is connected to the CO carbonyls groups. Films grown at 0.66 Pa revealed the strongest CN peak.
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| 30. |
- Schmidt, Susann
(författare)
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Carbon based Thin Films Prepared by HiPIMS and DCMS
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis focuses on carbon based thin films prepared by high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). The properties of such thin films can be tailored to an extensive variety; the film microstructure, for example, ranges in the presented work from fully amorphous, graphitic films to fullerene like (FL). Consequently, the applications of these films migh be as wide spread as their properties. Carbon nitride (CNx, 0 < x < 0.20) as well as carbon fluoride (CFx 0.16 < x < 0.35)thin films were synthesized in an industrial deposition chamber by reactive sputtering ofgraphite in an Ar/N2 and Ar/CF4 ambient. In order to gain a better understanding of thegrowth processes the C/Ar/N2 and the C/Ar/CF4 plasma was investigated by ion massspectroscopy at room temperature. Further understanding in this context gave thedetailed evaluation of target current and target voltage waveforms, acquired whengraphite was sputtered in HiPIMS mode. First principle calculations were carried out forthe growth of CFx and gave additional grasp about the most probable plasma precursorsas well as structure defining defects. Data gained from these characterisations of thedeposition processes were successfully related to the film properties. In order to linkdifferent process parameters to film properties, the synthesized films werecharacterized with regards to their thickness and deposition rate (secondary electronmicroscopy, SEM), chemical composition (elastic recoil detection analysis, ERDA and xrayphotoelectron spectroscopy, XPS), the chemical bonding (XPS), microstructure (transmission electron spectroscopy, TEM and selected area electron diffraction, SAED).Another part on thin film characterization comprised measurements for possibleapplications. For this, mainly nanoindentation and surface energy measurements wereperformed. Application-related measurements revealed a hardness of up to 23 GPa at high elastic recoveries of ~ 90 % for CNx (x = 0.1) films that exhibited a weakly pronounced fullerene like structure. The hardness correlated with the microstructure and N incorporation rate of the thin film. Evidence by TEM for an increased amount of N intercalations in CNx HiPIMS thin films is supported by ion mass spectroscopic measurements. As expected, higher ion particle energies as well as amounts particularly for C+ and N+ were measured in the reactive HiPIMS plasma. CFx thin films were found to show surface energies equivalent to superhydrophobic material for x > 0.26 while such films were polymeric in nature accounting for hardnesses below 1 GPa. Whereas, an amorphous structure for carbon-based films with fluorine contents ranging between 16 % and 23 % was observed. For such films, the hardness increased with decreasing fluorine content and ranged between 16 GPa and 4 GPa.
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