[[abstract]]Microwave-plasma-chemical-vapor-deposition method was used to diamond films on silicon substrate with the size from 5 nm to 1μm. The different grain size diamond films has been synthesized by microwave plasmas fed with CH4/Ar/N2 and CH4/H2 mixtures by varying the proportion of gas mixtures and the growth time. Scanning electron microscope is used to determine the grain size of the grown diamond film. These diamond films have been examined by using ultraviolet (UV,325 nm) and visible (514nm) micro-Raman spectroscopy. Both the Raman intensity of amorphous sp2-bonded carbon and the strength of the 1332 cm-1 sp3-bonded diamond phonon are found to vary considerably as functions of the grain size of diamond film and the incident photon energy. The 1332 cm-1 diamond peak can be found in micro diamond and cannot be observed for grain size under 500nm in visible Raman spectroscopy. Visible Raman spectroscopy is more sensitive to sp2 sites,as visible photons preferentially excite their π states. UV Raman spectroscopy, with its higher photon energy, excites both the π and the σ states and so is able to probe both the sp2 and sp3 sites, allowing a direct probe of the sp3 bonding. After chemical acid cleaning procedure, oxygen ions were absorbed on the surface of diamond films. The oxygen adsorption caused the surface workfunction of diamond films down bending. The work function also shows a strong correlation with the grain size of diamond films.
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