Type: Process Essays
Sample donated: Cesar Ross
Last updated: August 11, 2019
Introduction DLNconsists of two interpenetrating networks, one is atomicscale diamond like (carbon network) a-C:H, another is quartz like (siliconnetwork) a-Si:O. In carbon network, mainly consist of sp3 hybridization, i.e.diamond like bonds and chemically stabilized by “H” atoms. In silicon network,Si atoms are chemically stabilized by “O” atoms 1.
Fourier transform–infra red (FT–IR) spectroscopy, transmission electronmicroscopy (TEM) and X-ray diffraction (XRD) reveal the structuralcharacterization of DLN. Due to the presence of Quartz like Oxygenated Siliconnetwork (a-Si:O), it is found that DLN has good adhesion property compare toits predecessor DLC and hence it is suitable to coat almost any type ofmaterials 2. Due to the interpenetrating network of hydrogenated carbon andoxygenated silicon, the internal stress is reduced and thus DLN composite showsgood tribological performance over its predecessor Diamond-like carbon or DLC. Diamond-likeor graphait-like are the umbrella termswhich refer to different forms of amorphous carbon that exhibit some of theunique properties of natural diamonds or graphit and that can be synthesized inthe lab environment. Diamond-like carbon or DLC is a amorphous hydrogenatedcarbon which is a blend of sp2 bonded carbon atoms into sp3bonded carbon clusters. In DLC atomic structure, hydrogen can be present with an atomic concentration rangesfrom 0% – 50%.
DLC acronym was first used by Aisenberg and Chabot 3 who forthe first time synthesized amorphous carbon films exhibiting some of the uniquecharacteristics of natural diamond. Beauty ofthe DLC film is that, its properties canbe tailored based on the concentartionof sp2 – sp3 bonded carbon atoms and hydrogenconcentration. Due to the room temperature deposition possibility, almost allmaterials those are compatible with vacuum environment can be coated with DLCfilms. Unique and tunable properties of DLC are: material hardness, lowfriction and high wear resistance, chemical inertness, optical transparency (visible light – infraredlight), thermal conductivity, electrical resistivity, radiation resistance etc.Most of the present industrial applications of DLC films are protectitvecoating but this application can be extended upto ” data to beer storage” 4, 5.Properties of DLC films can be controlled further bydoping them with different chemical elements or compunds.
Thus a new class of amorphous hydrogenatedcarbon is formed whose atomic morphology complies with crystalline diamond andwisely termed as Diamond-like nanocomposites. In this process, someproperties of DLN films are improved even further than DLC films. DLN coating have been in existance since early 1990s.V.F. Dorfman first reported and synthesized this unique class of material 1.Later on Bekaert Advanced Coating Technologies (formerly known as AdvancedRefractories Technologies) and Russian and American scientists patented DLNcoatings for various protective coatings applications 6, 7, 8, 9, 10, 11, 12,13, 14, 15. DLN coatings also have been used in micro-electromechanicalsystems (MEMS) applications like LIGA (German acronym for Lithographie,Galvanoformung und Abformung) structures 16 and more 17.
Bekaert AdvancedCoating Technologies, Belgium have used plasma enhanced chemical vapordeposition (PECVD) method for growing such composite films. Chinese researchershave successfully used ion beam technology for growing DLN films 18. SouthKorean researchers have reported thermally activated CVD process for growth ofDLN films 19. Moreover Diamond-like carbon/nanosilica composite films havebeen deposited on silicon substrates, making use of the electrolysis ofmethanol– dimethylethoxydisilane (DDS) solution at low temperature 20. DLNwas deposited with same type of reactor, used by Bekaert Advanced CoatingsTechnology, Belgium by a research groupto deposit the thin film over Co-Cr alloy based knee implant of complex shape2. Various researchers haverecorded various unique characteristic of DLN thin film since its inception.They have focussed different properties in their research works 21, 22, 23,24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42.DLN coating have excellent bulk and surface property as well as thermalstability.
This can be used as tribological coatings, chemical protectivecoatings 43, 44, 45, 46, 47, 48 and abrasion resistant coatings. It hasoptical transparency over a wide bandwidth which includes visible light andinfrared. Due to this reason, DLN coating is used as antireflection coatingover the solar cell to enhance the over all efficiency of the system.
Due to low residual stress DLN coating hasexcellent adhesion to variety of substrate materials 31, 33. Researchers atDepartment of Cardiology, University Hospitals Leuven, Belgium 49 reported the biocompatibility of DLN filmresulting in decreased thrombogenicity and decreased neointimal hyperplasia.Awadesh Kr Mallik et al reported that deposition of DLN coating by PECVD methodover different substrate used as load bearing orthopedic implant and the resultwas satisfactory 2. Since its inception, DLNfilms are being received huge attention due to its attractive electricalmechanical optical and tribological properties such as reduced stress level,increased thermal stability, high hardness, low friction etc, Visible andinfrared transparency etc.
Dielectric permittivity and refractive index of DLNis lower than the DLC, whereas opticaltransparency is higher than the DLC films. In this paper deposition, structure, chemical compositionas well as mechanical, optical, electrical, properties of DLN composite filmare elaborated and industrial and prospective applications of DLN films arediscussed.