Low-temperature fabrication of superior
nano-/microcrystalline
diamond (NCD/MCD) films is a major thrust in diamond technology. The
widely used seeding techniques applied on the substrate surface are
usually harsh, lead to defect formation, and suffer from the lack
of reproducibility in maintaining homogeneity and uniformity over
nano-/microdimensions. Low-temperature growth of a significant diamond
phase on purely untreated glass substrates is indeed a challenging
task. Using CO2 as the supplementary gas-phase constituent
included in the (CH4 + H2)-plasma and a specific
shadow-mask assembly to generate the diffuse plasma environment above
the growth zone, the present experiment succeeds in the spontaneous
growth of nanocrystalline diamond (NCD), including microcrystalline
diamond (MCD) of an average crystal size of ∼0.9–1.2
μm at ∼300 °C on glass substrates, without any seeding
pretreatment. In the plasma, the shadow mask establishes a virtual
remote plasma configuration in setting the diffuse plasma, protects
the growth surface from a direct bombardment of energetic ions, generates
negative self-bias on the substrate, and, importantly, promotes significant
gas-phase nucleation dominant over typical solid-state nucleation.
The incubation of diamond embryo clusters onto the untreated glass
substrates under the shadow-mask structure and its growth evolution
through the efficient transport of the preferential carbonaceous precursors
proceed within the diffuse plasma. In the course of network modification
under the diffuse plasma, atomic O remains instrumental for efficient
etching of the a-C overlayer on a diamond embryo and atomic H, with
its small physical dimension, conveniently penetrates within the diamond
network and promotes crystallization via transferring its moderate
chemical energy to the diamond lattice. The low-temperature-grown
nanostructured diamond films are up-and-coming for applications in
nanotribology.
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