Valency-Conserved Doping in Infrared Plasmonic Nanocrystals for Supersonic Shock-Resistant Multi-Level Cell Modulation

Indium tin oxide (Sn/In₂O₃) is a degenerately doped semiconductor nanocrystal (NC) that exhibits localized surface plasmon resonance (LSPR) in the short-wavelength infrared electromagnetic spectral range. Alternative to metals, the tunability of LSPR is possible in doped semiconductor NCs by controlling the dopant type, doping level, and opto-electrochemical modulation. In this study, dopant oxidation valency in carrier density and LSPR peaks (Sn(IV): 1.04 × 10²⁰ cm^-3, 4826 cm^-1, Sn(II): 1.05 × 10²⁰ cm^-3, 4854 cm^-1) is observed to be conserved using differing dopant precursor Sn oxidation states. The robustness and surface oxidation stability were evaluated after extreme shock environment exposure. A synthesized NC-coated substrate was exposed to multicycle supersonic shockwaves at Mach 1.7, pressure 2 MPa, and temperature 864 K, under 5 cycles. Postshock exposed NCs were fabricated into a silicon-on-glass device and LSPR was electrochemically modulated (2 V to -2 V) to reveal multilevel cell (MLC) states through surface-depleted red-shift LSPR spectra. We observe that the device MLC operation, induced by the surface depletion effect, is more apparent in Sn(II) dopant precursor NCs. This is attributed to the delayed incorporation of free carrier donating Sn(IV) toward the NC surface, where the Sn(II) precursor oxidation state undergoes delayed activation into an n-type aliovalent substitutional dopant Sn(IV) during NC growth.