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The mechanism of ballas like nano crystalline diamond formation (NCD) stillremains elusive, and this work attempts to analyze its formation in theframework of activation energy ($E_\text{a}$) of NCD films grown fromH$_\text{2}$/CH$_\text{4}$ plasma in a 2.45 GHz chemical vapor depositionsystem. The $E_\text{a}$ is calculated using the Arrhenius equationcorresponding to the thickness growth rate while using substrate temperature($\sim1000-1300$ K) in all the calculations. While the calculated values matchwith the $E_\text{a}$ for nano diamond formation throughout the literature,these values of $\sim$10 kcal/mol are lower compared to $\sim$15 -- 25 kcal/molfor standard single crystal diamond (SCD) formation, concluding thus far, thatthe energetics and processes involved are different. In this work, To furtherinvestigate this, the substrate preparation and sample collection method aremodified while keeping the growth parameters constant. Unseeded Si substratesare physically separated from the plasma discharge by a molybdenum plate with apinhole drilled in it. Small quantities of a sample substance are collected onthe substrates. The sample is characterized by electron microscopy and Ramanspectroscopy confirming it to be nano diamond, thus, suggesting that nanodiamond self nucleates in the plasma and flows to the substrate which acts as amere collection plate. It is hypothesized then, if nano diamond nucleates ingas phase, gas temperature has to be used in the Arrhenius analysis. The$E_\text{a}$ values for all the nano diamond films are re-calculated using thesimulated gas temperature ($\sim1500-2000$ K) obtained from a simpleH$_\text{2}$/CH$_\text{4}$ plasma model, giving values within the rangecharacteristic to SCD formation. A unified growth mechanism for NCD and SCD isproposed concluding that the limiting reactions for NCD and SCD formation arethe same.

Evidence of Gas Phase Nucleation of Nano Diamond in Microwave Plasma Assisted Chemical Vapor Deposition