Supplementary document for Terahertz transmissive half-wave metasurface with enhanced bandwidth - 5321532.pdf

Supplemental Documen

Strain Modulation of Optoelectronic Properties in Nanolayered Black Phosphorus: Implications for Strain-Engineered 2D Material Systems

Strain engineering is an exciting direct approach to control the key intrinsic properties of two-dimensional (2D) materials. However, fabrication complexities arising from weak van der Waals interaction-induced slippage, coupled with mechanical breakdown of metal electrodes, have prevented fundamental investigations into strain effects on electrical and optoelectronic characteristics of these material systems. To overcome this limitation, we report a simple prestretch fabrication technique that allowed us to demonstrate a functional multilayer black phosphorus (BP)-based device on a stretchable elastomeric platform. By applying a uniaxial compressive strain of up to 10%, we reveal that mechanical strain can be effectively used to modulate the electronic and optical properties of nanolayered BP. This simple strategy can be extended well-beyond BP to other 2D materials, creating opportunities for fundamental investigations into strain effects in 2D material systems and potential applications in strain-engineered sensors for optical synapse applications

Reconfigurable Image Processing Metasurfaces with Phase-Change Materials

Optical metasurfaces have been enabling reduced footprint and power consumption, as well as faster speeds, in the context of analog computing and image processing. While various image processing and optical computing functionalities have been recently demonstrated using metasurfaces, most of the considered devices are static and lack reconfigurability. Yet, the ability to dynamically reconfigure processing operations is key for metasurfaces to be able to compete with practical computing systems. Here, we demonstrate a passive edge-detection metasurface operating in the near-infrared regime whose image processing response can be drastically modified by temperature variations smaller than 10{\deg} C around a CMOS-compatible temperature of 65{\deg} C. Such reconfigurability is achieved by leveraging the insulator-to-metal phase transition of a thin buried layer of vanadium dioxide which, in turn, strongly alters the nonlocal response of the metasurface. Importantly, this reconfigurability is accompanied by performance metrics - such as high numerical aperture, high efficiency, isotropy, and polarization-independence - close to optimal, and it is combined with a simple geometry compatible with large-scale manufacturing. Our work paves the way to a new generation of ultra-compact, tunable, passive devices for all-optical computation, with potential applications in augmented reality, remote sensing and bio-medical imaging

Media 1: Dielectric resonator nanoantennas at visible frequencies

Originally published in Optics Express on 14 January 2013 (oe-21-1-1344

Solution-Processed VO₂ Nanoparticle/Polymer Composite Films for Thermochromic Applications

Thin films composed of vanadium dioxide (VO2), a well-known thermochromic material with reversible insulator-to-metal-transition near room temperature, are intriguing for intelligent and energy-efficient heat-blocking applications. However, the conventional vacuum-based deposition methods often involve a high-temperature annealing process, and oxidation of VO2 under air exposure further limits their practical applications. In this work, we demonstrate a room-temperature solution process to prepare VO2-based thermochromic thin films using a smart ink composed of crystalline VO2 nanoparticles. To enhance their chemical stability against oxidation and assist in the uniform deposition of the VO2 thin films, polymers were used as both capping agents and for surface modification of the VO2 nanocrystals. Specifically, the concentration of VO2 nanocrystals, the type of polymers, and the molar ratio between VO2 and polymers are systematically tailored, and their effects on the thermochromic performance are also explored. It is revealed that the inclusion of optimum polymers enhanced the thermochromic performance with an almost 4-fold increase in IR switching with a visible luminous transmittance of 86% and a solar modulation of 17.61%. In addition, the inks are compatible with an array of scalable manufacturing processes. We demonstrate uniform films on different substrates, both rigid and flexible, by dip coating, drop casting, and screen printing, offering great feasibility for further scaling up

Surface Morphology Induced Localized Electric Field and Piezoresponse Enhancement in Nanostructured Thin Films

Nanostructured piezoelectric and ferroelectric thin films are being increasingly used in sensing and actuating microdevices. In this work, we report the experimental discovery of localized electric field enhancement in nanocolumnar piezoelectric thin films and its significant impact on piezoresponse. The magnitude of electric field enhancement is associated with nonflat surface morphologies and is in agreement with theoretical and finite element models. The influence of this surface morphology induced enhancement on piezoresponse is demonstrated using phase field simulations, which also illustrates surface morphology induced strain enhancement. The observed enhancement can be effectively harnessed to improve the sensitivity of related piezoelectric thin film applications

Synthesis of Self-Assembled Island-Structured Complex Oxide Dielectric Films

A self-assembly driven process to synthesize island-structured dielectric films is presented. An intermetallic reaction in platinized silicon substrates provides preferential growth sites for the complex oxide dielectric layer. Microscopy and spectroscopy analyses have been used to propose a mechanism for this structuring process. This provides a simple and scalable process to synthesize films with increased surface area for sensors, especially those materials with a complex chemistry. The ability of these island-structured dielectric films to improve sensitivity by a factor of 100 compared to continuous films in applications as substrates for surface-enhanced Raman scattering (SERS) is demonstrated

Dual Selective Gas Sensing Characteristics of 2D α‑MoO_3–<i>x</i> via a Facile Transfer Process

Metal oxide-based gas sensor technology is promising due to their practical applications in toxic and hazardous gas detection. Orthorhombic α-MoO3 is a planar metal oxide with a unique layered structure, which can be obtained in a two-dimensional (2D) form. In the 2D form, the larger surface area-to-volume ratio of the material facilitates significantly higher interaction with gas molecules while exhibiting exceptional transport properties. The presence of oxygen vacancies results in nonstoichiometric MoO3 (MoO3–x), which further enhances the charge carrier mobility. Here, we study dual gas sensing characteristics and mechanism of 2D α-MoO3–x. Herein, conductometric dual gas sensors based on chemical vapor deposited 2D α-MoO3–x are developed and demonstrated. A facile transfer process is established to integrate the material into any arbitrary substrate. The sensors show high selectivity toward NO2 and H2S gases with response and recovery rates of 295.0 and 276.0 kΩ/s toward NO2 and 28.5 and 48.0 kΩ/s toward H2S, respectively. These gas sensors also show excellent cyclic endurance with a variation in ΔR ∼ 112 ± 1.64 and 19.5 ± 1.13 MΩ for NO2 and H2S, respectively. As such, this work presents the viability of planar 2D α-MoO3–x as a dual selective gas sensor