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New mechanism of microcrystalline diamond formation through phase transition in spark discharge

Tetyana V. Semikina 

Institute of Semiconductor Physics, NAS of Ukraine, Kiev, Ukraine (ISP), 45 pr. Nauki, Kyiv 03028, Ukraine


In this report the results of deposition of diamond particles with size 3-5 mm for 10 sec in spark discharge between two graphite rods of special shapes are presented. The process ran in hydrogen atmosphere (100 Torr) with different types of substrates: silicon, Al2O3 ceramics and non-alkaline glass under several variation of geometrical arrangement of substrates and graphite rods: distance between substrate and graphite rods was 5-10 mm with up and down position of substrates to graphite rods. The diamond nature of obtained particles was confirmed by sharp peak 1331 cm-1 in Raman spectrum and particles shape on scanning electron microscope images. Because the obtained growth rate of diamond particles in our process was higher than all known growth rates for process under low pressure we present our physical hypothesis of formation mechanism running in our experiment.

To elucidate the formation mechanisms our substrates were cut along in the place of diamond particles position by focused Ga ion beam. From the obtained scanning ion microscope (SIM) image it is evidence that diamond particle formation doesn’t run on the substrate because the diamond particles are contiguous to surface of substrate only by corner. For comparison the SIM image of diamond particles formation running in chemical vapour deposition (CVD) process confirms that nucleation and follows growth occurs on the substrate surface. We suggest that in our process the diamond particles formation runs in the contact place of graphite rods where the high electric magnetic field and high temperature take place. The next suggestion is that diamond particles formation is not the result of chemical reaction between ionized carbon and hydrogen and their atoms because the reaction time (less than 10 sec) is evidently not enough for growing such big particles as we have (3-5 mm). That is why we decide that obtained diamond particles are the result of new phase transferring such as: solid state graphite rod ® melt carbon ® diamond particles. The hydrogen role in running process is analyzed. For this elucidating some experiments were carried out without hydrogen at pressure ~ 0 Torr. As a result was only graphite and diamond particles were not observed. Hydrogen plays some important role of energy transferring.

The next argument that diamond particles are not the result of chemical reaction is the fact that presence or absence of diamond particles on the substrate depends on graphite shape rods. We get diamond particles only in the case when graphite rods have sharper contact ends that consequently provided the biggest value of electromagnetic field in the contact place.

We conclude that diamond formation is the result of physical process under the conditions of high pressure and temperature that could be realised in local area of spark discharge.

Keywords: Spark Diamond, Spark Discharge, Hydrogen Atmosphere, Physical Formation


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Related papers

Presentation: Poster at Joint Fith International Conference on Solid State Crystals & Eighth Polish Conference on Crystal Growth, by Tetyana V. Semikina
See On-line Journal of Joint Fith International Conference on Solid State Crystals & Eighth Polish Conference on Crystal Growth

Submitted: 2007-01-09 15:29
Revised:   2009-06-07 00:44