Simply invariant subspaces for antisymmetric finite subdiagonal algebras

An amorphous film (44) of a photoresponsive semi-conducting material such as germanium-telluride deposited upon a thick silicon dioxide layer (40) formed on a silicon chip substrate (38). The silicon chip (38) underlying the central region of the amorphous film (44) is etched through to the silicon dioxide layer (40) to define a trough (48) thermally isolating the central region of the silicon dioxide layer (40).