Bias-assisted Reactive Ion Etching Research Articles

Effects of Substrate Bias on the Diamond Nanostructure by Reactive Ion Etching

Dense and uniform diamond nanocone arrays on titanium substrate were constructed by using bias-assisted reactive ion etching (RIE) of diamond films in a microwave plasma chemical vapor deposition (MPCVD) system. A hydrogen/argon mixture was employed as work gas with ratio of 3/1. The formation of nanocone structure was generated the lengthways physical bombardment/sputtering by argon ions, and selective chemical reaction of graphite and disordered carbons by hydrogen atoms and ions. The structure, size, and density depended on the substrate bias. The surface morphology of diamond film and nanostructures were characterized by field emission scanning electron microscope (FESME), and the composition of diamond film and nanostructures were characterized by Raman spectra. The Stopping and Range of Trons in Matter (SRIM) software was used to simulate the bombardment effect of the diamond film on different Ar+ ion incident angles during the etching process. The experimental results showed substrate bias at −180 V and −210 V was beneficial to the formation of high density, small size and sharp nanocones, meanwhile larger bias contributed to the formation of large size nanocones. Besides, as-prepared nanocones still maintained significant diamond phase.

Bactericidal activity of biomimetic diamond nanocone surfaces.

The formation of biofilms on implant surfaces and the subsequent development of medical device-associated infections are difficult to resolve and can cause considerable morbidity to the patient. Over the past decade, there has been growing recognition that physical cues, such as surface topography, can regulate biological responses and possess bactericidal activity. In this study, diamond nanocone-patterned surfaces, representing biomimetic analogs of the naturally bactericidal cicada fly wing, were fabricated using microwave plasma chemical vapor deposition, followed by bias-assisted reactive ion etching. Two structurally distinct nanocone surfaces were produced, characterized, and the bactericidal ability examined. The sharp diamond nanocone features were found to have bactericidal capabilities with the surface possessing the more varying cone dimension, nonuniform array, and decreased density, showing enhanced bactericidal ability over the more uniform, highly dense nanocone surface. Future research will focus on using the fabrication process to tailor surface nanotopographies on clinically relevant materials that promote both effective killing of a broader range of microorganisms and the desired mammalian cell response. This study serves to introduce a technology that may launch a new and innovative direction in the design of biomaterials with capacity to reduce the risk of medical device-associated infections.

Fabrication of obliquely-aligned single crystalline diamond nanostructures and their arrays

The polycrystalline diamond film on silicon substrates is used as a starting material to fabricate three different single crystalline nanostructures by employing the bias-assisted reactive ion etching technique in hydrogen plasma. The gold layer was sputtered on the top of the films as an etching mask to produce the high-density arrays of nanocones, nanopillars and nanofibers. The well-aligned nanostructures are uniformly distributed over large surface areas, and have a tilted angle of 60° to the substrate. Meanwhile, Raman measurement confirms that no stress is introduced into the nanostructures during the etching process. The nanostructures with the unique morphologies have potential applications in various diamond-based devices.

Effective improvement in the distribution of single crystalline diamond nanorods fabricated from the randomly-oriented polycrystalline films

By using the bias-assisted reactive ion etching technique and the etching masks of Au nanodots, the high-density single crystalline diamond nanorods have been obtained from the polycrystalline diamond films with randomly-oriented grains grown on silicon substrates. The inhomogenous distribution of the nanorods mainly results from the existence of grain boundaries in the films, and can be effectively improved by adding the graphite sheet under the substrate. Furthermore, the fabrication mechanism of the nanorod array is carefully investigated in this paper. The morphological evolution is observed by using a scanning electron microscopy technique. Raman measurements are carried out to monitor the phase change during the etching process. It is found that the non-diamond phases are present during the experimental process, and then are completely removed away in the end.

A diamond nanocone array for improved osteoblastic differentiation.

Efficient delivery of biomolecules to cells is of great importance in biology and medicine. To achieve this, we designed a novel type of densely packed diamond nanocone array to conveniently transport molecules to the cytoplasm of a great number of cells. The nanocone array was fabricated by depositing a thin layer of diamond film on a silicon substrate followed by bias-assisted reactive ion etching. The height of the diamond nanocones varied from 200 nm to 1 μm with tip radii of approximately 10 nm. Our fluorescein and propidium iodide staining results clearly demonstrated that dramatically enhanced delivery of fluorescein into cells was realized without leading to noticeable cell death with the aid of nanocone treatment. As a test case of the drug delivery application of the device, MC-3T3 cells in differentiation medium were applied to the nanocone array for enhanced intracellular delivery of the medium. This was confirmed by the fact that nanocone treated cells experienced much higher differentiation ability at an early stage in comparison with untreated cells. Overall, the results indicate that the diamond nanocone array provides a very simple but yet very effective approach to achieve delivery of molecules to a large number of cells.

Surface Nanostructuring of Boron-Doped Diamond Films and Their Electrochemical Performance

Uniform and vertically aligned nanocone and nanopillar arrays were successfully constructed on heavily boron-doped nanocrysatlline diamond films by carrying out bias-assisted reactive ion etching in hydrogen/argon plasmas. The electrochemical properties of the nanostructured boron-doped diamond films were investigated by cyclic voltammetry using 1 mM [Fe(CN)6](3-/4-) as redox couple. Compared to the planar boron-doped nanocrystalline diamond film electrode, the surface nanostructuring of boron-doped diamond film electrodes demonstrate enhanced sensitivity due to their enlarged electro-active surface areas. The results indicated that boron-doped diamond nanocones and nanopillars are promising electrode materials which benefit to improve the efficiency, sensitivity and reproducibility of biomedical and chemical sensors.

Preparation of superhydrophobic nanodiamond and cubic boron nitride films

Superhydrophobic surfaces were achieved on the hardest and the second hardest materials, diamond and cubic boron nitride (cBN) films. Various surface nanostructures of nanocrystalline diamond (ND) and cBN films were constructed by carrying out bias-assisted reactive ion etching in hydrogen/argon plasmas; and it is shown that surface nanostructuring may enhance dramatically the hydrophobicity of ND and cBN films. Together with surface fluorination, superhydrophobic ND and cBN surfaces with a contact angle greater than 150° and a sliding angle smaller than 10° were demonstrated. The origin of hydrophobicity enhancement is discussed based on the Cassie model.

Fabrication of diamond nanopillars and their arrays

High-density, uniform diamond nanopillar arrays were fabricated by employing bias-assisted reactive ion etching in a hydrogen/argon plasma. Gold nanodots were employed as etching masks. The formation of nanopillar structure is associated with the directional physical etching/sputtering by ion bombardment and selective chemical etching of sp2 carbons by reactive hydrogen atoms and ions. The density and geometry of the nanopillars depend on the initial structure of diamond films and reactive ion etching conditions. The nanopillars with high aspect ratio and large surface area may have potential applications in high-efficiency and high-sensitivity diamond-based biomedical and chemical sensors and in mechanical and thermal management.

Fabrication of diamond nanocones and nanowhiskers by bias-assisted plasma etching

Nanodiamond film surfaces were structured into high-aspect-ratio nanodiamond cones and whiskers by utilizing bias-assisted reactive ion etching (RIE) in hydrogen/argon microwave plasmas. The role of Ar addition in the RIE process was investigated by varying the argon concentration in a wide range from 5 to 75% in the plasma. Based on the dependence of the density and the geometrical configuration of cones/whiskers on RIE conditions, the formation mechanism of these nanodiamond structures was discussed. It was found that the formation of the conical/whisker structures was correlated with the original column structure of nanodiamond films. The bias-assisted RIE structuring involves both physical and chemical etching, and the addition of Ar in the plasma is capable of enhancing the physical etching significantly.

Structuring nanodiamond cone arrays for improved field emission

A structuring method capable of producing uniform, large-area cone arrays of diamond films was developed. The technique employs bias-assisted reactive ion etching and is applicable to any structure of diamond films ranging from microcrystalline to nanocrystalline. Variation of the etching conditions enables control of the cone density, geometry, and height. Surface nanostructuring of cone arrays significantly improves the field emission properties of diamond films of all kinds. The turn on field is reduced to 6 and 10 V/μm for nanodiamond and microdiamond films, respectively, (compared to >25 V/μm for as deposited surfaces). Lower cone density yields better field electron emission (lower turn-on electrical field) due to the screening in high-density cone arrays. The field emission properties are determined by both the enhancement factor of the cone array and the emitting properties of the material. The field electron emission properties of nanodiamond arrays are better than cone arrays of single crystalline diamond with a similar cone density and cone geometry.

Oriented single-crystal diamond cones and their arrays

One of the major problems in material science has been the difficulty in modification of the most endurable material, diamond, due to its extreme hardness and chemical inertness. Here, we report the development of a conical structure of diamond by performing bias-assisted reactive ion etching in hydrogen plasma. The diamond cones produced by this method are uniformly distributed over large areas on silicon substrates. Each cone was identified to be a single crystal with an apical angle as small as 28° and a very sharp tip (tip radii ∼2 nm). Their [001] axes are perpendicular to the substrate surface and parallel to each other. Such striking structures of individual single-crystal diamond cones and their arrays, in addition to their scientific value, may lead to a breakthrough in the design of high-performance mechanical and electronic devices.