Emerging classical and quantum device concepts demand precise spatial control over the optoelectronic properties of two-dimensional (2D) materials, but deterministic engineering via local multiaxial strain distributions remains challenging. Using Ga_2Se_2, we demonstrate a material-agnostic platform in which nanostructure geometry deterministically prescribes in-plane strain profiles in suspended van der Waals membranes. We first use hyperspectral photoluminescence mapping and experimentally-constrained finite element analysis to quantify the experimental biaxial and uniaxial strain gauge factors that relate strain to the change in bandgap. We next show that a two-component analytical model can predict, with less than 12

Vanadium dioxide (VO2) is a phase transition material that experiences significant shifts in electrical, optical, and mechanical properties near its transition temperature. Among various methods for depositing VO2 thin films, pulsed laser deposition (PLD) provides precise stoichiometric control, good versatility, and high consistency. In this work, we introduce an optimized PLD-based method for depositing high-quality polycrystalline VO2 thin films. Experimental results demonstrate a resistance change of over four orders of magnitude during the phase transition, accompanied by high uniformity, with a thickness variation of less than 2% across a 100 mm wafer, and reliable reproducibility over time.

Local strain engineering is a promising technique to tune the properties of two-dimensional materials at the nanoscale. However, many existing methods are static and limit the systematic exploration of strain-dependent material behavior. Here, we demonstrate dynamic and reversible control of local strain distributions in suspended trilayer tungsten disulfide (WS_2) via nanoindentation using a micro-mechanical spring patterned with nanoscale probes. Micro-photoluminescence measurements reveal that indentation using a ring-shaped probe induces a nearly uniform biaxial strain distribution accompanied by a reversible redshift of the neutral exciton peak, consistent with simulated strain magnitudes. We further show that the in-plane strain distribution is spatially programmable by engineering the probe geometry and present designs for inducing point-like, uniaxial, biaxial, and triaxial strain distributions. The presented platform enables substrate-free, repeatable local strain engineering in suspended 2D materials and provides a versatile tool for streamlining the investigation of strain-dependent phenomena.

Local strain engineering is a promising technique to tune the properties of two-dimensional materials at the nanoscale. However, many existing methods are static and limit the systematic exploration of strain-dependent material behavior. Here, we demonstrate dynamic and reversible control of local strain distributions in suspended trilayer tungsten disulfide (WS2) via nanoindentation using a micromechanical spring patterned with nanoscale probes. Microphotoluminescence measurements reveal that indentation using a ring-shaped probe induces a nearly uniform biaxial strain distribution accompanied by a reversible redshift of the neutral exciton peak, consistent with simulated strain magnitudes. We further show that the in-plane strain distribution is spatially programmable by engineering the probe geometry and present designs for inducing point-like, uniaxial, biaxial, and triaxial strain distributions. The presented platform enables substrate-free, repeatable local strain engineering in suspended 2D materials and provides a versatile tool for streamlining the investigation of strain-dependent phenomena.

This study introduces a reconfigurable metasurface that achieves transmission control across a broadband terahertz (THz) frequency range by leveraging the phase transition property of vanadium dioxide (VO2) to enable precise beam steering. Designed with a single-layer metasurface composed of VO2 split-ring resonator (SRR) unit structures, this device offers switchable THz beam steering upon actuation with a global temperature change. At high temperatures corresponding to the "ON" state, the metasurface exhibits frequency-dependent THz beam steering at large angles for crosspolarized THz transmission, as demonstrated both numerically and experimentally. At room temperature and in the "OFF" state, it achieves near-perfect ordinary transmission for the incident THz light, without distorting the incoming light. The reconfigurable metasurface demonstrates an average modulation depth of 95% with a maximum value of 99.8% at the designed deflection angles. This innovative approach indicates the potential advanced applications in THz technology, including communications, imaging, and sensing, which require high-performance, efficient, and reconfigurable THz deflectors.

The non-ionizing and penetrative characteristics of terahertz (THz) radiation have recently led to its adoption across a variety of applications. To effectively utilize THz radiation, modulators with precise control are imperative. While most recent THz modulators manipulate the amplitude, frequency, or phase of incident THz radiation, considerably less progress has been made toward THz polarization modulation. Conventional methods for polarization control suffer from high driving voltages, restricted modulation depth, and narrow band capabilities, which hinder device performance and broader applications. Consequently, an ideal THz modulator that offers high modulation depth along with ease of processing and operation is required. In this paper, we propose and realize a THz metamaterial comprised of microelectromechanical systems (MEMS) actuated by the phase-transition material vanadium dioxide (VO2). Simulation and experimental results of the three-dimensional metamaterials show that by leveraging the unique phase-transition attributes of VO2, our THz polarization modulator offers notable advancements over existing designs, including broad operation spectrum, high modulation depth, ease of fabrication, ease of operation condition, and continuous modulation capabilities. These enhanced features make the system a viable candidate for a range of THz applications, including telecommunications, imaging, and radar systems.

The patterning of silicon and silicon oxide nanocones onto the surfaces of devices introduces interesting phenomena such as anti-reflection and super-transmissivity. While silicon nanocone formation is well-documented, current techniques to fabricate silicon oxide nanocones either involve complex fabrication procedures, non-deterministic placement, or poor uniformity. Here, we introduce a single-mask dry etching procedure for the fabrication of sharp silicon oxide nanocones with smooth sidewalls and deterministic distribution using electron beam lithography. Silicon oxide films deposited using plasma-enhanced chemical vapor deposition are etched using a thin alumina hard mask of selectivity > 88, enabling high aspect ratio nanocones with smooth sidewalls and arbitrary distribution across the target substrate. We further introduce a novel multi-step dry etching technique to achieve ultra-sharp amorphous silicon oxide nanocones with tip diameters of 10 nm. The processes presented in this work may have applications in the fabrication of amorphous nanocone arrays onto arbitrary substrates or as nanoscale probes.

Cavity-mediated strong coupling is an essential element for quantum photonic technologies, but there are multiple challenges to creating scalable device platforms in which multiple matter-based qubits can be strongly coupled to a single cavity. Among these challenges is the inherent inhomogeneity in ensembles of matter-based qubits, which necessitates independent tuning of each qubit into resonance with the mode of the cavity. We present a new design for a photonic crystal split cavity that enables independent electric field tuning of two distinct qubits based on indium arsenide quantum dots in a gallium arsenide heterostructure. Using finite difference time domain simulations, we alter the cavity geometry and the local arrangement of photonic crystal holes to optimize the cavity quality factor. We achieve a simulated quality factor of 20,000, which is comparable to values that have been used to demonstrate strong coupling. We further show that distinct electric fields can be applied to the two qubits with negligible cross talk. The result demonstrates the viability of a new approach to coupling multiple qubits to a single cavity and opens the door for both further numerical optimization and experimental realization of this new paradigm.

Dynamic THz modulations with adaptive metamaterials have been demonstrated. By utilizing the significant volume shrinkage during the phase-transition of phase-transition materials, a specially designed chiral structure performs drastically structural deformation. The rapid geometrical change modulating the polarization of the incident THz wave is fully designable, continuously tunable, and reversible. Large azimuth rotation angle and ellipticity angle changes have been observed. The metamaterials are actuated by either global heating or Joule heating, providing an efficient way to modulate THz waves with high modulation depth. This brings us a prosperous future of broader THz applications such as radar, communications, and imaging systems.

In this paper, we show theoretically that the spin-dependent transverse shift of the transmitted photonic spin Hall effect (SHE) through layered structure cannot exceed half of the incident beam waist. Exact conditions for obtaining the upper limit of the transmitted SHE are clarified in detail. In addition, different from the popular view in many investigations, we find that there is no positive correlation between the spin-dependent transverse displacement and the ratio between the Fresnel transmission coefficients (tp, ts). In contrast, the optimal transmission ratio is determined by the incident angle and the beam waist. Moreover, two conventional transmission structures are selected and studied in detail. The characteristics of the transverse displacements obtained are in very good agreement with our theoretical conclusions. These findings provide a deeper insight into the photonic spin Hall phenomena and offer a guide for future related research.

We demonstrate electromagnetic field localization and enhancement effects on the non-structured planar surface of a two-dimensional gradient permittivity material. Surface plasmons are excited by a normally-incident Gaussian illumination beam and are confined to subwavelength rings on the surface of the gradient permittivity material. The performance of the surface is programmable by adjusting the permittivity distribution of the material and polarization of incident light. We show that field localization and enhancement effects can be realized at mid-infrared frequencies by conventional semiconductor materials with designed doping distributions. This demonstration suggests a compact and readily accessible platform for materials characterizations with spatially controlled illumination, providing a convenient approach to explore nanospectroscopy and light-matter interactions of nanomaterials, such as quantum dots, nanowires, and organic molecules.

The rise of mid-infrared and terahertz wave technology over the past two decades has led to incredible insights and potential applications for next-generation optoelectronics. Modulators, which control amplitude, phase, and/or polarization of incident light, are widely used in communications, imaging, and sensing and are crucial for further development of technology functioning in the mid-infrared and terahertz frequency regimes. The lack of natural materials with optical responses in these frequency regimes has led to a surge in engineering efforts to create novel devices and architectures for achieving control over the properties of mid-infrared and terahertz radiation. Major efforts in the field have been devoted to studying carrier concentration modulation, liquid crystals, phase-change materials, and micro-electromechanical systems for controlling the light–matter interaction. Although there has been considerable progress in realizing mid-infrared and terahertz modulators, novel approaches are seeking higher modulation speed, more functionality, and miniaturized size. In this perspective, we review the recent advancements of modulators for mid-infrared and terahertz wavelengths. We discuss various modulation mechanisms, along with their relative performance, and consider future architectures to improve upon the current technology for mid-infrared and terahertz modulation.

In this work, bilateral unidirectional transmissions (UDTs) with opposite transmission directions in one hybrid structure are realized using two different resonant mechanisms. The hybrid structure consists of a dielectric grating and a one-dimensional photonic crystal (PC) with a defect sandwiched at its center. One resonant mode is the defect mode of the PC enabling one UDT for one transmission direction. The other resonant mode is the grating guided mode resonance which introduces UDT for the opposite direction. Numerical calculations demonstrate that for each UDT, its transmittance difference, transmittance contrast ratio, and isolation degree can reach 90%, 100%, and 20%, respectively. In addition, the operation wavelength of each UDT as well as the wavelength interval between the two UDTs with opposite transmission directions can be tuned easily by adjusting structural parameters. This novel bilateral UDT creates potential for applications in both free space optics and optical circuits.

A connection between condensed matter physics and basic quantum mechanics is demonstrated as we use the fundamental 3D particle-in-a-box model to explain the optical properties of semiconductor nanocrystals, which are substantially modified due to quantum confinement. We also discuss recent advances in the imaging and measurement capabilities of transmission electron microscopy, which have made it possible to directly image single nanocrystals while simultaneously measuring their characteristic absorption energies. We introduce the basic theory of nanocrystals and derive a simplified expression to approximate the optical bandgap energy of an orthorhombic nanocrystal. CsPbBr3 perovskite nanocrystals are used to demonstrate this model due to their cubic crystal structure, large absorption cross-section, and favourable dielectric properties, which make them ideal for exploring the applications of this simple classroom problem. Various orthorhombic shapes are explored, and the predicted values of the optical bandgap energies using the proposed model are shown to be in good agreement with the experimentally determined values.

We present density functional theory based results on the interaction of size-selected gold nanoclusters, Au-10 and Au-20, with dopamine molecule. The gold clusters interact strongly with the nitrogen site of dopamine, thereby forming stable gold-dopamine complexes. Our calculations further show that there is no site specificity on the planar Au-10 cluster with all the edge gold atoms equally preferred. On the other hand, in the pyramidal Au-20 cluster, the vertex metal atom is the most active site. As the size increased from Au-10 to Au-20, the interaction strength has shown a declining trend. The effect of aqueous environment on the interaction strengths were also studied by solvation model. It is found that the presence of solvent water stabilizes the interaction between the metal cluster and dopamine molecule, even though for Au-10 cluster the energy ordering of the isomers changed from that of the gas-phase.