Bottom–Up Evolution of Diamond–Graphite Hybrid Two‐Dimensional Nanostructure: Underlying Picture and Electrochemical Activity

Abstract

It recently culminated as the nitrogen-included ultrananocrystalline diamond (N-UNCD), which was reported to be the only successful form of diamond for neural stimulation and recording. [14] The N-UNCD is fabricated through the intriguing bottom-up evolution of the diamond-graphite hybrid nanostructure under chemical vapor deposition (CVD). [4][5][6][7][8][9] While the material is indeed outstanding in the neural stimulation and recording, there's still an important issue to be resolved: their performance for the simultaneous electrochemical detection of the neural transmitter, for example, dopamine (DA) in presence of ascorbic acid (AA) and uric acid (UA) is still far from satisfactory, [26,27] as compared to that of the nanocarbon-powder-based porous thin films. [28] Furthermore, the detection of AA in presence of interference from DA and UA, which is inevitable in many biological samples, [29] is particularly challenging, relative to those of DA and UA, which might be attributed to the lack of π-π molecular bonding route of AA absorption on carbon electrode. [30,31] Such challenging situation was persistent until recently despite the decade-long presence of the diamond-graphite hybrid nanostructured thin film, and one might attribute it to the lack of the fundamental understanding of the bottom-up evolution mechanism of the hybrid film, which is essential for a proper optimization of materials performance throughThe diamond-graphite hybrid thin film with low-dimensional nanostructure (e.g., nitrogen-included ultrananocrystalline diamond (N-UNCD) or the alike), has been employed in many impactful breakthrough applications. However, the detailed picture behind the bottom-up evolution of such intriguing carbon nanostructure is far from clarified yet. Here, the authors clarify it, through the concerted efforts of microscopic, physical, and electrochemical analyses for a series of samples synthesized by hotfilament chemical vapor deposition using methane-hydrogen precursor gas, based on the hydrogen-dependent surface reconstruction of nanodiamond and on the substrate-temperature-dependent variation of the growth species (atomic hydrogen and methyl radical) concentration near substrate. The clarified picture provides insights for a drastic enhancement in the electrochemical activities of the hybrid thin film, concerning the detection of important biomolecule, that is, ascorbic acid, uric acid, and dopamine: their limits of detections are 490, 35, and 25 nm, respectively, which are among the best of the all-carbon thin film electrodes in the literature. This work also enables a simple and effective way of strongly enhancing AA detection.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202105087.

Two-Dimensional Diamond Formation Drivers in Chemical Vapor Deposition: Planar Defects and Graphite

“…It is noteworthy that the NCD 2 layer, with increased graphite proportion, plays a vital role as the “seeding layer” in giving birth to the diamond nanoplatelet, as shown in Figure k. Lee et al also noticed that diamond nanoplatelets are always embedded in the predeposited diamond matrix . However, insight into the microstructure is still limited.…”

“…Lee et al also noticed that diamond nanoplatelets are always embedded in the predeposited diamond matrix. 27 However, insight into the microstructure is still limited. In the following sections, thorough microstructural investigations will be carried out so as to clarify how the diamond nanoplatelet is developed from the NCD 2 layer.…”