Fabrication and Characterization of Light Emitting Porous Silicon and Polymer Nanocomposites
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(1)
where, d (mm) is the mean diagonal length (of the diamond shaped indent) and PL (0Kgf= 9.8N) is the applied load. The measurements were performed by a Tukon 300BM microhardness indenter at ambient laboratory conditions. Individual Vickers hardness (H,) values were calculated as a weighted mean over 3 identically prepared samples and ten indentations per 473
Mat. Res. Soc. Symp. Proc. Vol. 452 ©1997 Materials Research Society
sample. The applied load was 0.49 N and the film thicknesses were about 2 gtm. The intrinsic hardness 4of the film was determined by eliminating the contribution of the underlying silicon substrate. The thermal conductivity (TC) of the samples was measured using the thermal comparator technique developed by Lambropolous et al. 9 This enables rapid, non-destructive TC measurement, and can be applied to samples in a conventional film-on-substrate geometry. The conductivity is determined normal to the film surface. The apparatus consists of an environmentally controlled sample chamber enclosing a sample stage, a control and readout module, and signal processing equipment. The detector is a thermocouple junction sensing tip which is maintained in contact with the sample surface, by applying a load of 5 g. The average EMF generated by the temperature difference between the sensing tip and a reference junction is proportional to the apparent conductivity (kapp) of the sample. The TC values were then determined based on a calibration curve, which was generated using bulk materials of known conductivity. The apparent conductivity measured is that of the film, interface and substrate combined. A detailed modeling of the heat flow is required in order to extract the intrinsic conductivity of the film (kf).9 First, the effective film conductivity (keff) is determined, which also includes any contribution due to the interfaces between the film and the substrate, and the film and the probe tip: (keff)-I = (n/4) (a/t) (kapp-1 - ks-1)
(2)
where a is the heat flow radius, t is the film thickness and k, is the substrate conductivity. The above equation is valid only if keff
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