Effects of perfluoroalkylsilane molecular assembly on flow induced voltage generated by doped silicon wafers

Abstract

We report the effects of surface modifications on (i) Seebeck coefficients and (ii) flow induced voltage generations of the n-type (n-Si) and p-type (p-Si) silicon wafers. The surfaces of n-Si and p-Si wafers were coated with 1H,1H,2H,2H- perfluorooctyltrichlorosilane (FOTS) molecules. The surface modified n-Si and p-Si of size 12 mm×4 mm were mounted on the π/4 angle inclined experimental mount, and nitrogen gas was flown over the inclined surface at the subsonic velocities, 5.3, 10.61, 15.91, 21.22, and 26.52 ms−1, and the voltage difference between the lead and rear ends of pristine and surface modified n-Si and p-Si was measured. The experimental results and theoretical relations are presented. The flow induced voltage generation is caused by the interplay between the Bernoulli flow and Seebeck effect. The flow-voltage response results show that the half coated and full coated n-Si and p-Si wafers generate more voltage than that of the uncoated at a given velocity. The band theory reveals that the flow of nitrogen gas accumulates charge carriers at the FOTS self assembled monolayer (SAM)—silicon interfaces, which resulted in the more voltage generation by full and half coated ni-Si and p-Si surfaces than that of the pristine surface. The enhanced voltage generations and high sensitivities are caused by an effective increase of the gradient of Fermi Energy (EF) (Seebeck coefficient) due to FOTS SAM coatings. Because of that the FOTS SAM modified n-Si and p-Si are become highly sensitive to nitrogen gas flow.