the most widely applied holographic method. [2] Though SLMs possess a huge number of pixels with highly tunable flexibility and fast tuning speed, the pixel size is commonly larger than the working wavelength. Such feature results in unwanted holographic images generated at higher diffraction orders, thus bringing down the efficiency and the field of view. Recently, metasurfaces with unprecedented wavefront engineering ability have gained enormous interest. [3,4] Being composed of specially designed subwavelength structures, metasurfaces control the interfacial abrupt changes of phase, amplitude, and polarization distributions in a flexible manner, thus breaking many limitations in conventional optics. Many intriguing and unique demonstrations beyond their conventional counterparts have been presented using metasurfaces, such as beam deflection, lensing, special beam generation, surface plasmon coupling, etc. [5][6][7][8][9] Besides those with continuous wavefront distributions, metasurfaces are also promising in complex wavefront control, for instance, holography. In particular, the subwavelength resolution of metasurfaces perfectly avoids the problems in SLMs mentioned above. Meanwhile, the capability of synchronously engineering diverse electromagnetic parameters also endows Metasurfaces have drawn enormous attention in both the physics and engineering communities owing to their capabilities of arbitrarily manipulating the electromagnetic waves at subwavelength scale. One of the promising applications of metasurfaces is the realization of high-quality holograms. However, due to the passive response of metasurface resonators, previous demonstrations on meta-holography were mainly limited to generating static images. Seeking new approaches to realize active control over meta-holograms is highly demanded for display applications, such as holographic movies. Here, a broadband active meta-holography which enables temperature-dependent dynamic holographic imaging is experimentally demonstrated. The metahologram consists of two sets of resonators: set 1 is passive, being composed of simple metallic C-shape split-ring resonators (CSRRs) and set 2 is active, being composed of vanadium dioxide (VO 2 ) integrated CSRRs (V-CSRRs). Each set generates certain holographic images with predesigned amplitude and phase distributions. Under external heating, the insulator-to-metal transition property of VO 2 will gradually short out the V-CSRRs and their responses, thus dynamically changing the overall generated holographic image. The proposed approach presents a new way of tunable metasurface design and holds promise for active meta-devices with versatile functionalities.

Etching single-layer graphene to incorporate a high pore density with sub-angstrom precision in molecular differentiation is critical to realize the promising high-flux separation of similar-sized gas molecules, e.g., CO2 from N2. However, rapid etching kinetics needed to achieve the high pore density is challenging to control for such precision. Here, we report a millisecond carbon gasification chemistry incorporating high density (>1012 cm−2) of functional oxygen clusters that then evolve in CO2-sieving vacancy defects under controlled and predictable gasification conditions. A statistical distribution of nanopore lattice isomers is observed, in good agreement with the theoretical solution to the isomer cataloging problem. The gasification technique is scalable, and a centimeter-scale membrane is demonstrated. Last, molecular cutoff could be adjusted by 0.1 Å by in situ expansion of the vacancy defects in an O2 atmosphere. Large CO2 and O2 permeances (>10,000 and 1000 GPU, respectively) are demonstrated accompanying attractive CO2/N2 and O2/N2 selectivities.

Chiral media exhibit optical activity, which manifests itself as differential retardation and attenuation of circularly polarized electromagnetic waves of opposite handedness. This effect can be described by different refractive indices for left-and right-handed waves and yields a negative index in extreme cases. Here, active control of chirality, optical activity, and refractive index is demonstrated. These phenomena are observed in a terahertz metamaterial based on 3D-chiral metallic resonators and achiral vanadium dioxide inclusions. The chiral structure exhibits pronounced optical activity and a negative refractive index at room temperature when vanadium dioxide is in its insulating phase. Upon heating, the insulator-to-metal phase transition of vanadium dioxide effectively renders the structure achiral, resulting in absence of optical activity and a positive refractive index. The origin of the structure's chiral response is traced to magnetic coupling between front and back of the structure, whereas the temperature-controlled chiral-to-achiral transition is found to correspond to a transition from magnetic to electric dipole excitations. The use of a fourfold rotationally symmetric design avoids linear birefringence and dichroism, allowing such a structure to operate as tunable polarization rotator, adjustable linear polarization converter, and switchable circular polarizer.

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Generating pores in graphene by decoupled nucleation and expansion is desired to achieve a fine control over the porosity, and is desired to advance several applications. Herein, epoxidation is introduced, which is the formation of nanosized epoxy clusters on the graphitic lattice as nucleation sites without forming pores. In situ gasification of clusters inside a transmission electron microscope shows that pores are generated precisely at the site of the clusters by surpassing an energy barrier of 1.3 eV. Binding energy predictions using ab initio calculations combined with the cluster nucleation theory reveal the structure of the epoxy clusters and indicate that the critical cluster is an epoxy dimer. Finally, it is shown that the cluster gasification can be manipulated to form Å‐scale pores which then effectively sieve gas molecules based on their size. This decoupled cluster nucleation and pore formation will likely pave the way for an independent control of pore size and density.