Great Variety of Man-Made Porous Diamond Structures: Pulsed Microwave Cold Plasma System with a Linear Antenna Arrangement

Abstract

Synthetic diamond films are routinely grown using chemical vapor deposition (CVD) techniques. Due to their extraordinary combination of intrinsic properties, they are used as the functional layers in various bio-optoelectronic devices. It is a challenge to grow the dimensional layers or porous structures that are required. This study reviews the fabrication of various porous diamond-based structures using linear antenna microwave plasma (LAMWP) chemical vapor deposition (CVD), a low-cost technology for growing diamond films over a large area (>1 m 2 ) at low pressure (<100 Pa) and at low temperature (even at 350 °C). From a technological point of view, two different approaches, i.e., templated diamond growth using three different prestructured (macro-, micro-, and nanosized) porous substrates and direct bottom-up growth of ultra-nanoporous diamond (block-stone and dendritelike) films, are successfully employed to form diamond-based structures with controlled porosity and an enhanced surface area. As a bottom-up strategy, the LAMWP CVD system allows diamond growth at as high as 80% CO 2 in the CH 4 /CO 2 /H 2 gas mixture. In summary, the low-pressure and cold plasma conditions in the LAMWP system facilitate the growth on three-dimensionally prestructured substrates of various materials that naturally form porous self-standing diamond structures.

Multifunctional and Mechanically Robust Porous Diamond with Large Electroactive Surfaces via Electrically Conductive and Insulating Templates for 3D Electrode Applications

“…For all fabricated pBDD electrodes, with an increase in the number of the template layers, besides diamond features, a relatively high fraction of nondiamond carbon located within the diamond layer‐coated template elements is evident, resulting from the somewhat inhibited ability of growth species to contribute to formation of sp 3 bonds within the bulk of the porous template during the diamond growth process. [ 15,21 ] Simultaneously, features related to diamond (Fano‐shaped peak at ≈1320 cm −1 ) and boron doping (peaks at ≈500 and 1220 cm −1 ) become more distinctive as the number of template layers increases (see Figure 4a–c), which can be attributed to individual diamond grains developing into thicker layers due to cumulative growth time of the electrode. Overall, the position and intensity of the aforementioned Raman peaks are preserved along the top surface of all pBDD electrodes, thus highlighting the relative homogeneity of the BDD coating.…”

“…inside the pores/atop surface-structures is a necessary requirement for the formation of the homogeneous diamond structure within the entire thickness of the structured/porous electrode. [14,21] Typically, during the synthesis of polycrystalline diamond layers, formation of tight sp 3 carbon bonding is accompanied by the incorporation of nominal fraction of non-sp 3 bonded carbon (e.g., graphite, amorphous, disordered, etc.) in-between individual diamond grains.…”

“…[22] For commercialization of porous diamond for relevant applications (Figure 1), the readiness of the diamond synthesis technology, including the fabrication approach for porous diamond, must be considered. [15,21] Although many of top-down, bottom-up, and template-free strategies are viewed as promising methods for fabrication of structured/porous diamond, manufacturing of etching masks, templates/scaffolds or diamond-templated composites are considered to be difficult to reproduce, complex or time-consuming. Therefore, along with economic aspect, the preferred manufacturing strategy of 3D diamond coatings should be efficient, scalable, free of chemical/ion etching procedures, involve only diamond formation/ growth processes, but most importantly, result in the mechanically robust material, which can be easily handled and operated on the macroscale.…”

Ultrathin Diamond Nanofilms—Development, Challenges, and Applications

“…Self-assembly seeding Spin coating seeding MPCVD [133,29] Germanium Self-assembly seeding MPCVD [134] Ceramic Quartz/silica Self-assembly seeding HFCVD MPCVD [26,24] Glass Spin coating MPCVD [34] Si 3 N 4 Ultrasonic seeding HFCVD MPCVD [135,136] Metal Not forming carbides (i.e., Cu, Au) Self-assembly seeding or polyvinyl alcohol mixed with nanodiamond MPCVD, HFCVD [137][138][139] Forming carbides (Ti, W, Mo) Seeding HFCVD [78,79,84] Multiwall carbon nanotubes (MWCNT) MPCVD [130,131] Kapton (polyimide) Mo interlayer HFCVD [78,79,84] and Si 3 N 4 possess higher Young's moduli than other materials and lower mismatches of their thermal expansion coefficient. Interestingly, the necessity of diamond seeding procedures can be avoided by employing carbon species (carbon nanotubes) as substrate, as the carbon species serve as nuclei.…”

“…For example, such mixtures were employed to enhance the diamond nucleation on foreign substrates like copper and large area porous structures. [138,139] It was suggested that the polymer fibers act as a carbon source, which enhances the diamond nucleation (catchword: chemical nucleation). This approach represents a combination of seeding by DNDs and the so-called chemical nucleation (see next subsection).…”