Department of Physics, University of California, Santa Barbara, Santa Barbara, California, United States of America.|California NanoSystems Institute, University of California, Santa Barbara, Santa Barbara, California, United States of America.|Department of Mechanical Engineering, University of California, Santa Barbara, Santa Barbara, California, United States of America.|Department of Mechanical Engineering, University of California, Santa Barbara, Santa Barbara, California, United States of America.|Department of Molecular, Cell and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, United States of America.|California NanoSystems Institute, University of California, Santa Barbara, Santa Barbara, California, United States of America.