Derivation of Physical Parameters from Raman Spectra of Hard Carbon Films

A typical spectrum of a hard carbon film.

Figure 1: Raman spectrum of Carbon Film recorded and band-fit on the DiskRAM.

The Raman spectra of elemental carbon materials are known to be sensitive to polymorphy. For hard carbon films, the spectra of amorphous and diamond-like carbons can be band-fit to separate the contributions of the “graphitic carbon» (G band) from the «disordered carbon» (D band). Figure 1 shows a typical spectrum of a hard carbon film. The spectral behaviour of carbon films has been empirically correlated with thin film physical properties such as hardness, durability, optical transparency, electrical conductivity, thermal conductivity and corrosion resistance, and can be of use for prediction of these properties without extensive alternative testing.

In recent years the computer hard disc manufacturing industry has implemented hard carbon coatings on all disc media as a means of protecting the magnetic media with hard, non-brittle films.  The coatings provide wear protection against head sliders repeatedly dragging and slapping on the disk surface during the start and stop cycles of normal operation.

The DiskRam has been engineered to facilitate and significantly accelerate the acquisition of the Raman spectra of hard carbon overcoats on disk media. Subsequent data reduction automates the derivation of the physical properties of interest.  Curve-fitting the spectrum with two carbon bands (the D and G bands), additional nitrogen bands if required, and a baseline achieves these goals.  The methodology used for the spectral reduction will be reviewed in this note.

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