Shibing Tian

Robust adhesion of flower-like few-layer graphene nanoclusters

Nanostructured surface possessing ultrahigh adhesion like “gecko foot” or “rose petal” can offer more opportunities for bionic application. We grow flower-like few-layer graphene on silicon nanocone arrays to form graphene nanoclusters, showing robust adhesion. Their contact angle (CA) is 164° with a hysteresis CA of 155° and adhesive force for a 5 μL water droplet is about 254 μN that is far larger than present reported results. We bring experimental evidences that this great adhesion depends on large-area plentiful edges of graphene nanosheets tuned by conical nanostructure and intrinsic wetting features of graphene. Such new hierarchical few-layer graphene nanostructure provides a feasible strategy to understand the ultra-adhesive mechanism of the “gecko effect” or “rose effect” and enhance the wettability of graphene for many practical applications.

Floral-clustered few-layer graphene nanosheet array as high performance field emitter

Graphene sheet is expected to be a highly efficient field emitter due to its unique electrical properties and open surface with sharp edges. However, it is still a tremendous technical challenge to grow and align a graphene sheet in one particular direction to protrude its sharp edges for good field emission. Here, we report an ideal graphene field emitter of flower-like graphene nanosheets grown on a silicon nanocone array, wherein nanocone array guides the alignment of vertical nanosheets and produces high-density sharp edge protrusions on the conical tip. We observe high performance and stable field emission with low turn-on fields from floral-clustered graphene nanosheets. Protrusive sharp edges on the nanocone tip and optimized spacing between clusters both appear to locally enhance the electric field and dramatically increase field emission. Our new graphene emitter design provides a robust approach to the prospect for development of practical electron sources and advanced devices based on graphene field emitters.

Large-scale ordered silicon microtube arrays fabricated by Poisson spot lithography

A novel approach based on the Poisson spot effect in a conventional optical lithography system is presented for fabricating large-scale ordered ring patterns at low cost, in which the pattern geometries are tuned by controlling the exposure dose and deliberate design of the mask patterns. Following this by cryogenic deep etching, the ring patterns are transferred into Si substrates, resulting in various vertical tubular Si array structures. Microscopic analysis indicates that the as-fabricated Si microtubes have smooth interior and exterior surfaces that are uniform in size, shape and wall-thickness, which exhibit potential applications as electronic, biological and medical devices.

Single-crystal SnO2 nanoshuttles: shape-controlled synthesis, perfect flexibility and high-performance field emission

Vertically aligned single-crystal SnO(2) nanoshuttle arrays with uniform morphology and a relatively high aspect ratio were synthesized by a simple hot-wall chemical vapor deposition (CVD) method. It was found that regulating the growth temperature gradient could change the shape of the SnO(2) nanostructure from nanoshuttles to nanochisels and nanoneedles, and a self-catalyzing growth process was responsible for tunable morphologies of SnO(2) nanostructures. The as-synthesized SnO(2) nanoshuttles showed ultrahigh flexibility and strong toughness with a large elastic strain of ∼ 6.2, which is much higher than reported for Si and ZnO nanowire as well as most crystalline metallic materials. The field emitter fabricated using SnO(2) nanoshuttle arrays has a low turn-on electric field of around 0.6 V µm(-1), and a high field emission current density of above 10 mA cm(-2), which is comparable with the highest emission current density of carbon nanotube and nanowire field emitters.

Morphology Modulating the Wettability of a Diamond Film

Control of the wetting property of diamond surface has been a challenge because of its maximal hardness and good chemical inertness. In this work, the micro/nanoarray structures etched into diamond film surfaces by a maskless plasma method are shown to fix a surfaces wettability characteristics, and this means that the change in morphology is able to modulate the wettability of a diamond film from weakly hydrophilic to either superhydrophilic or superhydrophobic. It can be seen that the etched diamond surface with a mushroom-shaped array is superhydrophobic following the Cassie mode, whereas the etched surface with nanocone arrays is superhydrophilic in accordance with the hemiwicking mechnism. In addition, the difference in cone densities of superhydrophilic nanocone surfaces has a significant effect on water spreading, which is mainly derived from different driving forces. This low-cost and convenient means of altering the wetting properties of diamond surfaces can be further applied to underlying wetting phenomena and expand the applications of diamond in various fields.

General fabrication of ordered nanocone arrays by one-step selective plasma etching

One-step selective direct current (DC) plasma etching technology is employed to fabricate large-area well-aligned nanocone arrays on various functional materials including semiconductor, insulator and metal. The cones have nanoscale apexes (∼2 nm) with high aspect ratios, which were achieved by a selective plasma etching process using only CH4 and H2 in a bias-assisted hot filament chemical vapor deposition (HFCVD) system without any masked process. The CH(3)(+) ions play a major role to etch the roughened surface into a conical structure under the auxiliary of H(+) ions. Randomly formed nano-carbon may act as an original mask on the smooth surface to initiate the following selective ions sputtering. Physical impinging of energetic ions onto the concave regions is predominant in comparison with the etching of convex parts on the surface, which is identified as the key mechanism for the formation of conical nanostructures. This one-step maskless plasma etching technology enables the universal formation of uniform nanocone structures on versatile substrates for many promising applications.

Reducing edge effect of temperature-field for large area thin film deposition in hot filament chemical vapor deposition system

The uniformity in temperature-field of the hot filament chemical vapor deposition (HFCVD) system is of great importance since it is a critical parameter that determines the quality of the deposited films. In fact, the temperature-field is mainly filament distribution dependent. In conventional analysis method, the filament array usually has an equal-space distribution, which leads to a remarkable edge effect and consequently unable to obtain large area uniformity in temperature-field in HFCVD for high-quality thin film deposition. Here, we proposed theoretically an asymmetrical filament distribution to reduce the edge-effect of temperature field. The adjacent filament distance was optimized by using numerical simulation based on heat-transfer theory. Based the optimized condition, temperature difference as low as 13 K between the center and edge region of the filament arrays can be achieved in 100-mm substrate, which is only one tenth of the temperature difference of that in the case that the filaments were evenly distributed. Thus unequal-space distribution can be employed to enhance the uniformity in temperature field of the HFVCD system in favor of the growth of high quality thin films in large area. Copyright