We demonstrate optical metamaterial design using colloidal gold nanocrystal building blocks. In the solid state, chemically exchanging the nanocrystals' surface-capping molecules provides a tailorable dielectric-to-metal transition exhibiting a 10(10) range in DC conductivity and dielectric permittivity ranging from everywhere positive to everywhere negative throughout the visible-to-near-IR. Direct, wide-area nanoimprinting of subwavelength superstructures at room temperature, on plastic and glass substrates, affords plasmonic resonances ranging from 660 to 1070 nm, in agreement with numerical simulations.

We demonstrate thermally switchable VO2 metamaterials fabricated using solution-processable colloidal nanocrystals (NCs). Vanadium oxide (VOx) NCs are synthesized through a nonhydrolytic reaction and deposited from stable colloidal dispersions to form NC thin films. Rapid thermal annealing transforms the VOx NC thin films into monoclinic, nanocrystalline VO2 thin films that show a sharp, reversible metal-insulator phase transition. Introduction of precise concentrations of tungsten dopings into the colloidal VOx NCs enables the still sharp phase transition of the VO2 thin films to be tuned to lower temperatures as the doping level increases. We fabricate "smart", differentially doped, multilayered VO2 films to program the phase and therefore the metal-insulator behavior of constituent vertically structured layers with temperature. With increasing temperature, we tailored the optical response of multilayered films in the near-IR and IR regions from that of a strong light absorber, in a metal-insulator structure, to that of a Drude-like reflector, characteristic of a pure metallic structure. We demonstrate that nanocrystal-based nanoimprinting can be employed to pattern multilayered subwavelength nanostructures, such as three-dimensional VO2 nanopillar arrays, that exhibit plasmonic dipolar responses tunable with a temperature change.

The development of real-time and sensitive humidity sensors is in great demand from smart home automation and modern public health. We hereby proposed an ultrafast and full-color colorimetric humidity sensor that consists of chitosan hydrogel sandwiched by a disordered metal nanoparticle layer and reflecting substrate. This hydrogel-based resonator changes its resonant frequency to external humidity conditions because the chitosan hydrogels are swollen under wet state and contracted under dry state. The response time of the sensor is ~10 4 faster than that of the conventional Fabry-Pérot design. The origins of fast gas permeation are membrane pores created by gaps between the metal nanoparticles. Such instantaneous and tunable response of a new hydrogel resonator is then exploited for colorimetric sensors, anti-counterfeiting applications, and high-resolution displays.

Lumped circuit elements (i.e., resistors, capacitors, and inductors) provide the basic building blocks of microelectronic devices ubiquitous in information processing, storage, and communications. The use of these modular quasistatic components can be extended to the nanoscale optical regime to achieve high-density, high-speed analogues of these traditional circuits. We reimagine these devices in the near-infrared (NIR) regime, making use of a simple nanorod geometry and plasmonic transparent conducting oxides (TCOs). We evaluate their equivalent impedance as lumped circuit elements and construct bandpass and band-stop filters operating at NIR wavelengths. Through variation in the TCO nanorod geometry and the addition of PbS nanocrystals in between and NiCr on top of the TCO nanorods, we present the first designable NIR lumped nanocircuits with tailorable response. The experimental results agree with both circuit models and full-wave simulations.

Since its discovery almost 70 years ago, the hologram has been considered to reproduce the most realistic three dimensional images without visual side effects. Holographic video has been extensively researched for commercialization, since Benton et al. at MIT Media Lab developed the first holographic video systems in 1990. However, commercially available holographic video displays have not been introduced yet for several reasons: narrow viewing angle, bulky optics and heavy computing power. Here we present an interactive slim-panel holographic video display using a steering-backlight unit and a holographic video processor to solve the above issues. The steering-backlight unit enables to expand the viewing angle by 30 times and its diffractive waveguide architecture makes a slim display form-factor. The holographic video processor computes high quality holograms in real-time on a single-chip. We suggest that the slim-panel holographic display can provide realistic three-dimensional video in office and household environments.