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| Home/Research areas |
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| 1. Nano-structured DLC films with low friction and long durability (click here for detail) |
| "Fullerene-like" DLC films
Carbon-based thin films have been subject of extensive research over the last decade due to their excellent properties, such as low friction coefficient, chemical inertness, infrared transparency, and high hardness. The hardness of carbon-based films is usually linked to the presence of sp3 C-C bonds and these films are called diamond-like carbon. Recently, it was shown that some nonhydrogenated carbon and carbon nitride films containing a high number of sp2 bonds exhibit superior mechanical properties-high hardness (up to 55 GPa) and extreme elasticity (elastic recovery of 85%). To bestow material good hardness and good elasticity at the same time has been attributed to a "fullerene-like" nanostructure. The fullerene-like carbon materials composed of intersecting graphene sheets, together with amorphous structures have been already synthesized by different physical vapor deposition techniques, e.g. carbon arc synthesized pure elastic carbon films, magnetron sputtering and pulsed laser deposition synthesized elastic carbon nitride films. Here we show that hard, elastic hydrogenated carbon films can also be fabricated by plasma chemical vapor deposition—pulsed glow discharge. Curved graphite particles and multi-shelled carbon nanoparticles consisting of prolate and tapered spheroids embedded in an amorphous matrix were observed by high-resolution electron microscopy (HREM). Furthermore our central result is that this film exhibits ultra-low friction in 20% relative humidity in ambient air condition.
Noncrystal/nanocrystal network structure DLC films
The DLC films consisting of crystalline carbides, transition metal dichalcogenides, and amorphous diamond-like carbon were fabricated. Various mechanisms were activated to achieve surface self-adaptation and supertough characteristics. These mechanisms were demonstrated by TiC/DLC and TiC/DLC/MoS2 films deposited by magnetron sputtering. The TiC/DLC composite films survived 2 millions of sliding cycles in air and exhibited excellent wear-resistant. The friction coefficient of the TiC/DLC/MoS2 film was below 0.03 in vacuum and demonstrated having good wear-resistant comparing with pure MoS2.
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| 2. The electrochemistry deposition of DLC films in liquid phase (click here for detail) |
| Diamond-like nanocomposite (DLN) is a class of modified diamond-like carbon (DLC) coatings.For prepareing DLN films, various chemical and physical vapor deposition techniques have been developed. Our research work is to develop the new technology, novel method and theory for the preparation of the functional DLN films. Taking advantage of the liquid deposition techniques, such as availability for large area deposition on irregular shape substrates, low deposition temperature, low cost and simplicity of the setup, DLN films doped with functional nano-metal, nano-nonmetal and nano-semiconductor particls will be prepared through the addition of compounds with optimum composition and structure in the liquid reaction systems. This work is conducted to investigate the influence of particle kind, particle size, particle shape and the nano-composite structure of DLN films on the properties of optics, electronics, magnetic functions, as well as to explore the potential applications of functional DLN films in fluorescence, electro field emission, electrochemistry and magnetism. This work will also provide technique and theory foundation for the applications of the functional DLN films in the fields of microelectronics, optical devices, magnetic record devices, chemical sensors, catalysis, aviation and spaceflight. Our group has successfully prepared a-CNx, DLC/SiO2 nanocomposite, low-dielectric Au-a-C:H and hydrophobic a-C:F films with liquid deposition techniques.
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| 3. The correlation between intrinsic structure and wettability/tribology of organic thin films (click here for detail) |
| Self-assembled monolayers (SAMs) have potential applications in the field of surface modification, boundary lubricant, sensor, photoelectronics, and functional bio-membrane modeling, etc. On the basis of the surface chemical reaction and synthetic approaches, the chemical structures of SAMs can be manipulated easily both at the individual molecular and at the material levels. As a potential lubricant for controlling stiction and friction in micro-electromechanical systems (MEMS), the nano-tribological properties of SAMs are closely related to their intrinsic chemical composition and structures.
For example, the frictional behaviors of SAMs are chain length and terminal group dependent. SAMs with longer chains are generally densely packed, while the shorter-chain ones are not. With the same terminal groups, loosely packed SAMs generally possess higher friction force due to the larger energy dissipation during the sliding, and higher adhesive force as well due to the liquidlike disordered structure. On the other hand, SAMs with more polarized groups generally possess higher surface energy and a relatively strong interaction during the sliding, and therefore higher adhesion and more energy loss are expected, which leads to a higher friction force.
Co-deposition of molecules with different terminal groups or alkyl chain lengths to form mixed SAMs is also extensively studied, which allows an in-depth understanding of the relationship between structure and performance of SAMs.
Introducing a functional group, such as diacetylene, peptide, and sulfone, into straight hydrocarbon chains to construct robust SAMs is another alternative way to improve their tribological properties. It is hypothesized that, within the SAMs, the functional groups interact laterally taking the form of hydrogen bonding, dipole interaction, π-stacking, or covalent attachment, which may enhance the mechanical integrity and stability.
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| 4. Electroplating process of Cr(III) and alloy to replace Cr(VI) process (click here for detail) |
| Possessing excellent wear and corrosion resistances, chromium coatings have been widely used in aerospace, automotive, manufacture industries. The conventional Cr coatings electrodeposited from chromium (VI) have been utilized for more than 120 years. However, the chromium (VI) plating process needs to be substituted by more environmental friendly technologies because of its intense toxicity and carcinogenicity. U.S. Environmental Protection Agency (EPA) identifies the chromium (VI) as one of seventeen kinds of high hazardous and toxic substances. European Union has passed the “WEEE” and “ROHS” directives to restrict chromium (VI) plating in electrical and electronic equipment since July 1, 2006. It's sure that under the pressure of protecting environment the whole chromium (VI) plating will be forbidden in near future. Among many potential alternatives, trivalent chromium electroplating is considered as a very promising technology to replace conventional Cr electroplating due to the fact that no matter chromium (III) plating process or chromium (VI) plating process, the final plating substances are identical, zero valent chromium. Our group has prepared a 50μm thick hard Cr coatings, which can be used for anti-wear purpose successfully, from chromium (III) bath.
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| 5. Formation mechanisms for nanocrystals and symmetry breaking at mesoscopic-scale
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| In recent years, with the developments of quantum field theory, string theory and theory of elementary particles, symmetry and symmetry breaking have been realized to be more and more important, and have been introduced in many other fields, including those researches at micro-scale or cosmoscopic-scale. Yet at meso-scale, little study focusing on symmetry and symmetry breaking has been done till now. On the other hand, the study of nanocrystal is an interdisciplinary field crossing materials, crystallography and physics at meso-scale. If theories of symmetry and symmetry breaking could be introduced into the investigation of nanocrystals, epochal results would be drawn out to check the generality of the theories about symmetry and symmetry breaking. Whatever the outcome is, it will be a scientific method innovation to introduce symmetry breaking into exploring the mechanism for nanocrystals.
ZnO nanocrystals with different morphologies and MgO nanowires along <110> direction have been obtained in our experiments. Based on deep theoretical analyses and experiment results support, it can be concluded that symmetry breaking dictated the formation of these nanocrystals. Thus, not only the spontaneous symmetry breaking, but also the dynamical symmetry breaking have been proved to play their roles in crystalliation of nanocyrstals. Two new mechanisms have been proposed to explain the formation of ZnO nanocrystals and MgO nanowires, respectively. Some puzzling structures of nanocrystals have been explained reasonably by these mechanisms based on symmetry and symmetry breaking.
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