Study Of Nitrogen Effect On The Growth Of Diamond Films

Diamond is an important material for many applications because of its excellent properties in mechanical, optical, thermal and electrical. As the study of nanodiamond attracts more and more interest, the application field of diamond was expended a lot.Because of its effect on the morphology and properties of diamond, Nitrogen is often added during the growth of CVD diamond using hydrocarbon–hydrogen gas chemistries. For many years, the effect of Nitrogen has being studied and there are lots of findings.In this thesis, we prepared diamond films in the methane–hydrogen gas with different contents of Nitrogen. By comparing the morphology and Raman spectrum of these simples, we study the effect of Nitrogen on the diamond growth.For the growth of diamond films in low CH4 content gas, the addition of small defined quantities of nitrogen to the process gas can lead to higher deposition rates and promote <100> textured growth with coplanar {100} surface facets.But larger concentrations of nitrogen were found to lead to surface deterioration and crystallinity reduction because the N2 introduced tetrahedral amorphous carbon into diamond films. When the condition of N2 was large enough, the films would lose their diamond morphology, though the XRD showed the diamond was still in the films. Comparing the SEM images of the films, we could see that as the nitrogen flow rate rise to 2.5 sccm, the morphology become"cauliflower-like", then, as the nitrogen flow rate rise to 5 sccm and 10 sccm, the cauliflowers became smaller. When there was 20 sccm nitrogen in the process gas,"needle-like"structure was found. Studying the Raman spectrum, we found that the content of tetrahedral amorphous carbon in the films was increased with the increase of nitrogen content until the nitrogen flow rate became 10 sccm. Besides, the degree of the order of amorphous carbon was also increased, but when the nitrogen flow rate was bigger than 5sccm, the degree decreased. We deposited nanodiamond in high CH4 content reacting gas. When no nitrogen introduced, the films were composed of needle-like structures. As the nitrogen flow rate rise, the diameter of the needles became smaller and smaller. As saw from the SEM images, the diameter decreased from 170 nm to 70 nm as the nitrogen flow rate increased from 0 sccm to 20 sccm. The Raman spectrum showed that the nitrogen influence the property of amorphous carbon obviously. The change of the G-peak showed that nitrogen influence the degree of the order of amorphous carbon just like it did in the polycrystalline diamond. Besides, the decrease of the two peaks at 1140 cm-1 and 1480 cm-1 showed the nitrogen suppress the formation of transpolyacetylene in nano-diamond.We also deposited diamond films on p(100) Si wafers, which was ultrasonicated in a slurry consisting of nanodiamond powder and alcohol to get high nucleation ratio. It was found that the films transited from polycrystalline to nanocrystalline diamond films as a small flow rate of nitrogen was added. The cross-sections showed that when no nitrogen added the films grow in the columnar growth mode, but the growth mode was totally different after nitrogen added. PL spectrum showed that as the more nitrogen was added, the more N-related impurity in the films. When nitrogen impurity in the diamond lattice reaches the tolerance limit of lattice imperfections, the diamond lattice collapses and thus the diamond grain cannot grow big or remains small and thus a nanocrystalline diamond film is formed.