Electrically tunable perfect light absorbers as color filters and modulators

Abstract Methods for spectrally controlling light absorption in optoelectronic devices have attracted considerable attention in recent years. It is now well known that a Fabry-Perot nanocavity comprising thin semiconductor and metal films can be used to absorb light at selected wavelengths. The absorption wavelength is controlled by tailoring the thickness of the nanocavity and also by nanostructure patterning. However, the realization of dynamically tuning the absorption wavelength without changing the structural geometry remains a great challenge in optoelectronic device development. Here it is shown how an ultrathin n-type doped indium antimonide integrated into a subwavelength-thick optical nanocavity can result in an electrically tunable perfect light absorber in the visible and near infrared range. These absorbers require simple thin-film fabrication processes and are cost effective for large-area devices without resorting to sophisticated nanopatterning techniques. In the visible range, a 40 nm spectral shift can be attained by applying a reasonable bias voltage to effect the color change. It is also shown that these electrically tunable absorbers may be used as optical modulators in the infrared. The predicted (up to) 95.3% change in reflectance, transforming the device from perfectly absorbing to highly reflective, should make this technology attractive to the telecommunication (switching) industry

Free Atom Like d States in Single Atom Alloy Catalysts

Alloying provides a means by which to tune a metal catalyst’s electronic structure and thus tailor its performance; however, mean-field behaviour in metals imposes limits. To access unprecedented catalytic behaviour, materials must exhibit emergent properties that are not simply interpolations of the constituent components’ properties. Here we show an emergent electronic structure in single-atom alloys, whereby weak wavefunction mixing between minority and majority elements results in a free-atom-like electronic structure on the minority element. This unusual electronic structure alters the minority element’s adsorption properties such that the bonding with adsorbates resembles the bonding in molecular metal complexes. We demonstrate this phenomenon with AgCu alloys, dilute in Cu, where the Cu d states are nearly unperturbed from their free-atom state. In situ electron spectroscopy demonstrates that this unusual electronic structure persists in reaction conditions and exhibits a 0.1 eV smaller activation barrier than bulk Cu in methanol reforming. Theory predicts that several other dilute alloys exhibit this phenomenon, which offers a design approach that may lead to alloys with unprecedented catalytic properties