Delayed fracture of silicon. Silicon sheet growth development for the Large Area Silicon Sheet Task of the Low Cost Silicon Solar Array Project. Final report

Bar specimens were cut from ingots of single crystal silicon, and acid-etched prior to testing. Artificial surface flaws were introduced in specimens by indentation with a Knoop hardness tester. The specimens were loaded in four-point bending to 95% of the nominal fracture stress, while keeping the surface area, containing the flaw, wet with test liquids. No evidence of delayed fracture, and, therefore stress corrosion, of single crystal silicon was observed for liquid environments including water, acetone and aqueous solutions of NaCl, NH/sub 4/OH, and HNO/sub 3/, when tested with a flaw parallel to a (110) surface. The fracture toughness was calculated to be K/sub IC/ = 0.591 x 10/sup 6/ N/m/sup 3/2/.