The local crystallization in nanoscale diamond-like carbon films during annealing

Abstract

The local crystallization during annealing at 600 °C in nanoscale diamond-like carbon coatings films grown by pulsed vacuum-arc deposition method was observed using modem techniques of high-resolution transmission electron microscopy. The crystallites formed by annealing have a face-centred cubic crystal structure and grow in the direction [011 ] as a normal to the film surface. The number and size of the crystallites depend on the initial values of the intrinsic stresses before annealing, which in turn depend on the conditions of film growth. The sizes of crystallites are 10 nm for films with initial compressive stresses of 3 GPa and 17 nm for films with initial compres sive stresses of 12 GPa. Areas of local crystallization arising during annealing have a structure dif ferent from the graphite. Additionally, the investigation results of the structure of nanoscale diamond-like carbon coatings films using Raman spectroscopy method are presented, which are consistent with the transmission electron microscopy research results.[http://dx.doi.Org/10.1063/l.4903803]The negative influence of high intrinsic compressive stresses in diamond-like carbon (DLC) films with a high con tent of sp3-phase, restraining their widespread application in micromechanics, is well known.1,2 However, many research ers use the intrinsic stresses purposefully to form carbon coatings with special properties. In particular, the investiga tion of multilayer carbon-based structures, with different contents of sp3 and sp2-phases, which are characterized by different values of electrical conductivity and the internal stresses, is described.3,4 In this case, the changing accelerat ing potential of the substrate is used. It allows to accelerate carbon ions and forms layers with different properties, which is necessary for the method of vacuum-arc deposition with the filtration of the plasma flow.5The structure and electrical properties of the tetrahedral amorphous carbon (ta-C) films with 70%-88% sp3 content were investigated by atomic force microscopy (AFM), trans mission electron microscopy (ТЕМ), and Raman spectros copy as a function of annealing temperature in the range of 25-1100 °C.6 ТЕМ investigation is confirmed that the clus ters appear not only at the surface of the films but also in the bulk. The growth and the partial orientation of the sp2-bonded nanoclusters in the size range of 1-3 nm are accom panied by a large reduction in the film intrinsic stress, which decreases sharply in the temperature range of 500-600 °C. Therefore, temperature of 600 °C was selected in the present work as the critical temperature at which significant changes in the structure and properties of carbon coatings are beginning.The pulsed vacuum-arc method7 for deposition of DLC films allows to exclude the using of the electrostatic ion acceleration by applying a negative potential to the substrate Author to whom correspondence should be addressed. Electronic mail: kolpakov@bsu. edu.ru and to reduce undesirable heating of the carbon film during the deposition, ...

A ternary phase diagram for amorphous carbon

“…However, it can be shown with Eqs. (8), (9) and (11) that samples with no nc-graphite type of sp 2 clusters (n g = 0) have a fixed point at k 0 = Àðb c À b r Þ=ðk c À k r Þ and x 0 = k r k 0 þ b r for arbitrary n r and n c .…”

“…High-resolution transmission electron microscopy images of nc-graphite have been observed in amorphous carbon samples grown at high substrate temperature [8] or after annealing [9]. Robertson and O'Reilly [4] found that fused aromatic rings are the most stable configuration for the sp 2 phase; Bredas and Street [10] proved that only fused aromatic rings can lead to the 2.0 eV level band gaps observed in amorphous carbon; Matsunuma [11] reproduced Raman spectra from resonant Raman scattering off fused aromatic rings; and Arenall and Liu [12] assigned the Raman peak at 867 cm À1 to vibrations in the clusters of aromatic rings.…”

Nanostructured Coatings Based on Amorphous Carbon and Gold Nanoparticles Obtained by the Pulsed Vacuum-arc Method

“…It was found that the most promising composite coating, which has optimal properties (high wear resistance, low friction coefficient, high electrical conductivity and transmittance) is a coating based on layers (C-C: 25Au-C) with a total thickness of 250-300 nm, C:25Au layer thickness was 200 nm. As a disadvantage, it is necessary to note rather high internal compressive stresses, which can be significantly reduced by annealing in vacuum [16].…”

The effect of vacuum annealing on the structure and properties of the electrically conductive a-CN coating

“…Of particular interest is the comparison with the results obtained in Ref. [15], which describe local crystallization in a diamond-like carbon coating after annealing at 600 • C.…”