Abstract
Diamond properties down to the quantum-size region are still poorly understood. High-pressure high-temperature (HPHT) synthesis from chloroadamantane molecules allows precise control of nanodiamond size. Thermal stability and optical properties of nanodiamonds with sizes spanning range from <1 to 8 nm are investigated. It is shown that the existing hypothesis about enhanced thermal stability of nanodiamonds smaller than 2 nm is incorrect. The most striking feature in IR absorption of these samples is the appearance of an enhanced transmission band near the diamond Raman mode (1332 cm). Following the previously proposed explanation, we attribute this phenomenon to the Fano effect caused by resonance of the diamond Raman mode with continuum of conductive surface states. We assume that these surface states may be formed by reconstruction of broken bonds on the nanodiamond surfaces. This effect is also responsible for the observed asymmetry of Raman scattering peak. The mechanism of nanodiamond formation in HPHT synthesis is proposed, explaining peculiarities of their structure and properties.
Highlights
Accepted: 17 January 2022Current methods of mass production of nanodiamonds (detonation method, chemical vapor deposition, milling of high pressure high temperature (HPHT) microcrystals) do not allow simultaneous control of the size distribution of obtained samples and preservation of the structural and chemical state of the nanodiamond (ND) surfaces
In the current paper we present a study of the size-dependent thermal stability/graphitization and optical properties of nanodiamonds synthesized in the growth medium comprising C-H-Cl
In samples synthesized at temperature of 1300 ◦ C EDX analysis reveals only Cl at
Summary
Current methods of mass production of nanodiamonds (detonation method, chemical vapor deposition, milling of high pressure high temperature (HPHT) microcrystals) do not allow simultaneous control of the size distribution of obtained samples and preservation of the structural and chemical state of the nanodiamond (ND) surfaces. These difficulties are especially pronounced in the ultra-small (or quantum) size range of 1–3 nm and significantly hinder study and understanding of the size dependence of the properties of NDs [1–5]. It was reported by Butenko et al [11] and Xu et al [12] that small nanoparticles (
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