Atomic carbon in magnesium oxide single crystals—depth profiling, temperature-and time-dependent behavior

• Published in: The Journal of physics and chemistry of solids 1982, Vol.43 (1), p.59-71
• Main Authors: Wengeler, H., Knobel, R., Kathrein, H., Freund, F., Demortier, G., Wolff, G.
• Format: Article
• Language: English
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/0022-3697(82)90174-3

Using the 12C d, p) 13C method and ultrahigh vacuum techniques it is shown that MgO single crystals, grown by arc fusion, invariably contain high concentrations of carbon, 250–2500 at.-ppm. The carbon sets up steep concentration gradients in the 0–1μm subsurface zone, disappears and reappears as a function of heat treatments between 300 and 1170 K in ultrahigh vacuum. By heating in O 2 the carbon can be burnt out of the subsurface zone, but upon isothermal annealing at 470 K the carbon starts to diffuse from the bulk back into the subsurface zone within minutes, giving rise to fluctuating concentration variations which lasted for hours with peroidicities of about 45 min. After quenching samples previously heated in O 2 to 80 K and reheating linearly at 2K/min the onset temperature of the carbon mobility was found to be as low as 140 K. From these experiments it is concluded that carbon is atomically dissolved in the MgO. The C atoms probably occupy extrinsic cation vacancies introduced in the MgO by co-dissolved “water”, but at the same time they must also be on interstitial sites where they acquire an extremely high mobility.