How small nanodiamonds can be? MD study of the stability against graphitization

• Published in: Diamond and related materials Vol. 33; pp. 78 - 84
• Main Authors: Kaviani, Moloud, Deák, Peter, Aradi, Bálint, Köhler, Thomas, Frauenheim, Thomas
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-03-2013; Elsevier
• Subjects: Annealing; Carbon; Clusters; Composition and phase identification; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Graphitization; Materials science; Molecular dynamics; Nanocomposites; Nanodiamond; Nanomaterials; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Other topics in nanoscale materials and structures; Physics; Specific materials; Stability; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Tight-binding density functional theory; Molecular dynamics; Tight-binding density functional theory; Nanodiamond; Graphitization; Annealing; Phase transformations; Synthetic diamond; Molecular dynamics method; Theoretical study; Thermodynamic stability; Etching; Carbon; Polycrystalline diamond; Experimental design; Density functional method; Nanostructured materials; Medical application
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/j.diamond.2013.01.002

How small nanodiamonds can be is a crucial question for biomedical applications. To answer this question, we present here molecular dynamic simulations of the annealing of very small diamond clusters (diameter between 0.3 and 1.3nm) of various shape in vacuum and in the presence of oxygen. Isothermal cycles of 30ps were carried out at 500, 1000, 1500, and 2000K with 10ps ramps between them. Predominantly {100} faceted diamond clusters as small as 1nm (~250 atoms) survive these short anneals up to 1500K. Longer anneals at 1500K, as well “accelerated” MD at very high temperatures, indicate that the diamond core is still preserved when thermal equilibration is reached. The primary effect of oxygen seems to be the saturation of threefold-coordinated surface carbon atoms and the etching of lower coordinated ones. Oxygen accelerates the graphitization somewhat but does not affect the critical size. Our result means that nanodiamonds with a core of only 0.8nm can be kinetically stable up to 1500K. This is significantly less than the lower limit of the thermodynamic stability (~1.9nm).
► We used DFTB based Molecular dynamic to study the stability of nanodiamond clusters. ► Cube or cuboctahedral clusters with over ~250atoms can survive long term annealing. ► Oxygen saturate surface carbon atoms and etchthe graphitic part. ► Oxygen accelerate the graphitization somewhat but does not affect the critical size. ► Nanodiamonds with a core of only 0.8nm can be kinetically stable up to 1500K.