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HL: Fachverband Halbleiterphysik

HL 7: "New" Materials and New Physics in "Old" Materials I

HL 7.5: Vortrag

Montag, 26. März 2012, 10:30–10:45, EW 015

Switchable nanothermochromic VO₂ diffraction gratings defined by site selective ion implantation — •Johannes Zimmer, Hubert Krenner, Helmut Karl, and Achim Wixforth — Institut für Physik, Universität Augsburg, Universitätsstr. 2, 86159 Augsburg

The metal-insulator transition (MIT) of vanadium dioxide has been studied in great detail over the past 50 years, showing both structural and electronic phase changes. The bulk materials electric conductivity rises drastically at T=68^∘C, when heated from the isolating phase at room temperature to the metallic phase. Additionally optical properties of VO₂ exhibit significant changes during the MIT on sub-picosecond timescales. We examined the near-infrared thermochromic behaviour of VO₂ nanocrystals, which were synthesised by high-dose ion implantation through optically structured masks. Fused silica was chosen as matrix material for the fabrication of the diffractive optical elements, leaving the VO₂ crystals inert to structural degradation when undergoing the MIT. Two different processes were used to define diffraction gratings containing VO₂ nanocrystals. The first was direct implantation of VO₂ through masks into the host material and the second was site-selective bombardement of already synthesised nanocrystals, with argon ions in order to suppress the metallic phase in those regimes. While undergoing the phase transition, the gratings showed switching in diffraction efficiencies by factors of 3 for the directly synthesised gratings and more than one order of magnitude for the Ar-deactivated gratings. All gratings show broad thermal hysteresis extending down to room temperature.