Broadband Tunable Mid-infrared Plasmon Resonances in Cadmium Oxide Nanocrystals Induced by Size-Dependent Nonstoichiometry
Zeke Liu,1,2,# Yaxu Zhong,2,# Ibrahim Shafei,2 Soojin Jeong,2 Liguang Wang,3 Hoai T. Nguyen,3 Cheng-Jun Sun,4 Tao Li,*3,4 Jun Chen,2 Lei Chen,1,2 Yaroslav Losovyj,2 Xinfeng Gao,2 Wanli Ma,*1 Xingchen Ye*2
1Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, 215123, Jiangsu, China.
2Department of Chemistry, Indiana University Bloomington, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, USA.
3Department of Chemistry and Biochemistry, Northern Illinois University, 1425 W. Lincoln Hwy., DeKalb, IL, 60115, USA.
4X-ray Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, USA.
A central theme of nanocrystal (NC) research involves synthesis of dimension-controlled NCs and study of size-dependent scaling laws governing their optical, electrical, magnetic, and thermodynamic properties. Here, we describe the synthesis of monodisperse CdO NCs that exhibit high quality-factor (up to 5.5) midinfrared (MIR) localized surface plasmon resonances (LSPR) and elucidate the inverse scaling relationship between carrier concentration and NC size. The LSPR wavelength is readily tunable between 2.4 and ～6.0 μm by controlling the size of CdO NCs. Structural and spectroscopic characterization provide strong evidence that free electrons primarily originate from self-doping due to NC surface-induced nonstoichiometry. The ability to probe and to control NC stoichiometry and intrinsic defects will pave the way toward predictive synthesis of doped NCs with desirable LSPR characteristics.