ABSTRACT
XRD spectrum of the as-deposited alumina thin films, which are amorphous in nature [1]. Figure 40.1b shows the transmittance and reflectance spectra of alumina on quartz and bare quartz. A high transmittance value of about 93% was found for bare quartz substrate, while after alumina coating, the transmittance value had dropped only slightly to ≈89% [1]. The reflectance behaviors for both cases were found to be in correspondence with each other. Thus, it is proven that the present alumina thin films can retain almost all of the optical properties of the quartz substrate. For the purpose of measuring nanoindentation, we grew alumina for several hours and got a thicker film. The idea behind using the higher thickness film was to avoid the influence of the substrate’s mechanical properties on the measured nanomechanical properties of the alumina thin films. The implication of substrate effect in nanoindentation-based measurement is explained in greater depth in Chapter 51. Of course, one can ask about the transmittance value for such a thick (≈1.2 μm) coating. Actually, we have also measured the transmittance value of codeposited alumina on quartz. The data showed around ≈85% transmittance [2]. So, the main objective to retain the optical properties of the substrate was indeed achieved to a reasonable level of satisfaction.
