[1] N Carolina State Univ, Dept Mat Sci & Engn, Raleigh, NC 27695 USA
[2] N Carolina State Univ, Dept Phys, Raleigh, NC 27695 USA
[3] N Carolina State Univ, Analyt Instrumentat Facil, Raleigh, NC 27695 USA
[4] Univ N Carolina, Dept Elect & Comp Engn, Charlotte, NC 28223 USA