Micro-Raman spectroscopy on a-C:H nanoparticles

We present the Raman spectra of amorphous hydrogenated carbon nanoparticles prepared in an Ar–CH4 hydrocarbon plasma. The measured Raman spectra are compared with that of both soft polymerlike and hard diamondlike a-C:H films deposited from pure CH4 plasma. The film properties were studied by Rutherford backscattering and spectroscopic ellipsometry. It is shown that the plasma characteristics are continuously changed from a “precursor-rich” state to a “precursor” state during the particle formation process. As a result, the net flux of the carbon atoms to the surface of the nanoparticles (growth rate) decreases linearly as a function of time as the nanoparticles are growing up. Also, the hydrogen content in nanoparticles increases as a function of nanoparticle size. The particle growth process is then examined by a simple ballistic model. It is found that the volume polymerization process, i.e., the growth of the nanoparticles at a large particle size (⩾100nm), is essentially the same as the surface polymerization process occurring at a surface of a substrate.