Experimental Determination of Single CdSe Nanowire Absorption Cross Sections through Photothermal Imaging

Abstract

Absorption cross sections (σabs) of single branched CdSe nanowires (NWs) have been measured by photothermal heterodyne imaging (PHI). Specifically, PHI signals from isolated gold nanoparticles (NPs) with known cross sections were compared to those of individual CdSe NWs excited at 532 nm. This allowed us to determine average NW absorption cross sections at 532 nm of σabs = (3.17 ± 0.44) × 10−11 cm2/μm (standard error reported). This agrees well with a theoretical value obtained using a classical electromagnetic analysis (σabs = 5.00 × 10−11 cm2/μm) and also with prior ensemble estimates. Furthermore, NWs exhibit significant absorption polarization sensitivities consistent with prior NW excitation polarization anisotropy measurements. This has enabled additional estimates of the absorption cross section parallel (σabs∥) and perpendicular (σabs⊥) to the NW growth axis, as well as the corresponding NW absorption anisotropy (ρabs). Resulting values of σabs∥ = (5.6 ± 1.1) × 10−11 cm2/μm, σabs⊥ = (1.26 ± 0.21) × 10−11 cm2/μm, and ρabs = 0.63 ± 0.04 (standard errors reported) are again in good agreement with theoretical predictions. These measurements all indicate sizable NW absorption cross sections and ultimately suggest the possibility of future direct single NW absorption studies