Structure formation in diamond powder during chemical infiltration from the gas phase

In this paper was investigated effect of pumping a mixture of methane and hydrogen in a microwave discharge through layers of diamond powder on structure formation sediment during chemical infiltration from the gas phase. The infiltration process was implemented on the conditions of gas pumping through the layers of diamond powder, in the presence of a plasma discharge over the samples. It is established that in contempt of the size of the diamond powder, the growth of diamond from the gas phase occurs on the surface of the first layer, the growth of diamond from the gas phase stops when the second layer starts, and different allotropic modifications of carbon start to grow, in particular nanocrystalline graphite, carbon nanotubes, and graphite. Such a rapid transition between diamond growth and the growth of various allotropic carbon modifications is related with the screening of the plasma discharge by the first layer of diamond powder. Thus, the absence of direct contact of the microwave plasma discharge with the formed molecular hydrogen during its recombination leads to the fact that the concentration of atomic hydrogen is low to maintain the growth of diamond from the gas phase inside the layer of diamond powder.