Diamond single crystal growth in hot filament CVD J. Hirmke ⁎ , S. Schwarz, C. Rottmair, S.M. Rosiwal, R.F. Singer Lehrstuhl für Werkstoffkunde und Technologie der Metalle (WTM), Universität Erlangen-Nürnberg, Martensstr. 5, D-91058 Erlangen, Germany Available online 20 February 2006 Abstract The synthesis of diamond crystals is of particular interest due to the material's outstanding physical and mechanical properties. In hot filament CVD (HFCVD) we found a new process parameter window where the growth of single diamond volume crystals can be stabilized without the use of monocrystalline substrates. These CVD parameters are far beyond growth conditions for HFCVD diamond coating processes. Extremely low methane contents in the feed gas along with high substrate temperatures allow single diamond nuclei of a sufficiently large size to grow stabile. Crystals up to 80 μm in diameter were successfully synthesized. The morphology of the crystals is cubo-octaedric. According to our proposed growth model [S. Schwarz, C. Rottmair, J. Hirmke, S. Rosiwal, R.F. Singer, J. Cryst. Growth 271 (2004) 425.], the observed growth defects are primarily caused by the gas phase conditions during the CVD process. The aim of this work was to exclude a further possible formation of growth defects due to the employed diamond seed particles. The early growth stage was investigated by tracking distinct monocrystalline diamond seeds. It is shown that cubo-octaedric crystals with CVD typical smooth faces of high quality can be grown from micrometer-sized particles. Seed imperfections are therefore not considered as a major reason for growth defects of the larger crystals. © 2006 Elsevier B.V. All rights reserved. Keywords: Hot filament CVD; Single crystal growth; Nucleation; Diamond crystal 1. Introduction Diamond single crystals are in great demand for mechanical and electrical applications. Various techniques for synthesizing high quality diamond of well defined material properties are pursued by numerous research groups. Regarding large single diamond crystals for mechanical purposes, where impurities are of minor interest, high pressure – high temperature (HPHT) synthesis [2] is currently the only reasonable alternative to natural diamond. Concerning electronic applications, where single crystallinity, high purity and the possibility for doping is demanded, diamond synthesis by CVD layer growth is pursued [3]. In this field, synthesis by plasma CVD has prevailed. The trend in this method is clearly towards employing higher and higher process pressures along with increasing methane contents in order to increase growth rate [4,5]. This high growth rate synthesis, however, can lead to stacking faults [6]. Moreover, in plasma CVD, alike at the HPHT method, reactor sizes are limited and such is the amount of diamond that can be synthesized in a single process. In Ref. [1] we reported on a possible way to grow single diamond volume crystals in hot filament CVD (HFCVD). With this CVD method, the size of the reactor is virtually unlimited. Large area deposition of homogenous polycrystalline diamond coatings is already industrial state of the art. Therefore we intend to get a broader understanding of our observed single crystal growth in order to be able to evaluate the possibility for upscaling this process. Upscaling would allow growing scores of diamond crystals on large deposition areas simultaneously. This could highlight a new way of economic diamond crystal production even under the HFCVD typical moderate growth rates. These moderate growth rates are moreover considered less likely to cause stacking faults, a high diamond material quality is therefore expected. As reported in [1], in first experiments crystals up to 100 μm have successfully been synthesized (Fig. 1). An advanced growth model regarding stable growth of volume crystals instead of layer growth and regarding the obtained morphology was given. Our further work aims towards revealing the causes for growth defects such as excrescences on the {100}-faces and defective island growth with increased sp 2 ratios on the {111}-surfaces (Fig. 1). In this work, the particular influence of the employed seed crystals on growth defects such as the applicability of different seed types is investigated. As elucidated in [1], our applied CVD growth conditions of low Diamond & Related Materials 15 (2006) 536 – 541 www.elsevier.com/locate/diamond ⁎ Corresponding author. Tel.: +49 9131 8527520; fax: +49 9131 8527515. E-mail address: joachim.hirmke@ww.uni-erlangen.de (J. Hirmke). 0925-9635/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2006.01.003