The conventional dip coating techinques, as it is used for flat surfaces, cannot be applied to deposit homogeneous coatings in optical quality inside tubes. The resulting coatings exhibit large variations in thickness and roughness over the length of the tube and show a morphology with a network of cracks. The main reason for these problems seem to be a delayed and restricted solvent evaporation due to the impediment of a laminar flow and the progressive saturation of the atmosphere in the tube. A modified dip coating technique was therefore developed to allow forced flow conditions inside the tubes by an additional exhausting tube. By means of this modification transparent conducting coatings of sol-gel SnO₂:Sb (antimony-doped tin oxide - ATO) could be deposited on both sides of borosilicate glass tubes (300 mm, inner diamters down to 11 mm) with excellent thickness uniformity and low roughness (Ra≈1nm). After a heat treatment at temperatures up to 500°C, the prepared ATO coatings are mechanically stable and highly transparent (>85% transmission) with a sheet resistance down to 10 kΩ. The coatings can be used as electrodes for electronic devices and electrical heaters or to give antistatic properties to the substrate.

Date Published: 23 October 2002
PDF: 8 pages
Proc. SPIE 4804, Sol-Gel Optics VI, (23 October 2002); doi: 10.1117/12.453905

Published in SPIE Proceedings Vol. 4804:
Sol-Gel Optics VI
Edward J. A. Pope; Helmut K. Schmidt; Bruce S. Dunn; Shuichi Shibata, Editor(s)