Not a YC company, but Lonnie Johnson is an excellent example. Inventor of the supersoaker and now developing thin-film lithium air batteries and working with MIT on solid state thermoelectric engines.

http://www.johnsonems.com/

http://www.excellatron.com/

http://www.johnsonrd.com/ie/lj/ljprofile.html

http://www.parc.com/event/713/high-efficiency-solid-state-en...