Reduced Photoconductivity Observed by Time-Resolved Terahertz Spectroscopy in Metal Nanofilms with and without Adhesion Layers.
Non-contact, optical time-resolved terahertz spectroscopy (TRTS) has been used to study the transient photoconductivity of nanometer-scale metallic films deposited on fused quartz substrates. Samples of 8 nm thick gold or titanium show an instrument-limited (ca.0.5 ps) decrease in conductivity following photoexcitation due to electron-phonon coupling and subsequent increased lattice temperatures which increases charge carrier scattering. In contrast, for samples of 8 nm gold with a 4 nm adhesion layer of titanium or chromium, a ca. 70 ps rise time for the lattice temperature increase is observed. These results establish the increased transient terahertz transmission sign change of metallic compared to semiconductor materials. The results also suggest nanoscale gold films that utilize an adhesion material do not consist of distinct layers.
Radiation Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA.
Brian G
BG
Alberding
Optical Sciences Division, US Naval Research Laboratory, Washington, DC 20375, USA.
Gary P
GP
Kushto
Optical Sciences Division, US Naval Research Laboratory, Washington, DC 20375, USA.
Paul A
PA
Lane
Radiation Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA.
Edwin J
EJ
Heilweil
Chromium; Gold; Metal nanofilms; Time-resolved Terahertz Spectroscopy; Titanium; adhesion layer; alloy; carrier dynamics; electron-phonon coupling