Advanced Optical Materials最新文献

The fabrication of plasmonic metasurfaces on large surfaces is the next challenge to adapt them to augmented reality systems. The optical properties of a self-assembled hexagonal plasmonic metasurface, realized with a large-area compatible approach, are compared at different levels and a correlated-disorder plasmonic metasurface fabricated by electron-beam lithography and considered here as the reference: the contribution of plasmonic nanostructure arrangements is studied using the structure factor, physical properties are assessed by optical transmission and reflection measurements, and finally the entire metasurfaces are tested macroscopically in a head-up display system.

Selectively Functionalized Spirofluorene-Bridged N-Heterotriangulene

The cover page visualizes the cyanated spirofluorene-bridged N-heterotriangulenes surrounded by a mesmerizing aurora borealis, whose vibrancy symbolizes the dynamic nature of the photoinduced charge-transfer process occurring in the compounds synthesized by Milan Kivala and co-workers (see article number 2401656). Highlighted are the tripod-like shapes and the strategic placement of the cyano groups, which are crucial for tuning the optoelectronic properties. The Earth with a glimpse of the Sun illustrates the relevance of the authors' findings in the context of future energy-efficient applications to mitigate society's impact on the environment and climate.

Living Optical Networks in Orchid Leaves

This cover image shows the living optical network observed in the Macodes petola jewel orchid. The unusual convergence of shape, uniformity in size, and cell packing into a short-range hexagonal lattice enable light redistribution across the plane of the leaf. Such plant-based living optical networks could provide inspiration for materials that efficiently harvest, control, and process light. For further information on this approach, see article 2401729 by Giulia Guidetti and Fiorenzo G. Omenetto.

Gold nanoclusters (Au NCs) capped with a small biomolecule, namely (+)-norephedrine, (Au@Nore) display exceptional performance as fluorescent pH sensors. They display high emission quantum yield (Φ_PL of ≈33% in strongly basic media); absence of nanocluster (NC) aggregation and/or induced rigidification of the organic shell; a linear dependency of their emission on the pH in the 8.2–9.5 range; and reversible pH sensing. In addition, excitation at 310 nm, where both the NC and the ligand absorb, enables ratiometric sensing. Studies on the fungus Candida albicans and bacterium Bacillus subtilis demonstrate that while Au@Nore do not cause any impact on the growth of the fungus, it inhibited the growth of the Bacillus, showing the lowest cell viability of 18% at the highest pH values via a mechanism of action involving the disruption of the bacterial wall.

Space-time coding metasurfaces (STCMs) have gained a great deal of achievements in the fields of radar and communication, but they have rarely been explored in the field of electronic jamming. The existing researches use time-varying surface or phase-switched screens to realize electronic deceptions, but the deceptions are completely passive and are limited in the time-frequency domain. Here, a mechanism of STCM-based deceptions is presented in the space and the time-frequency domains, and precise designs of the STCM-based deceptions are achieved by performing shifting operations on the space-time coding sequences of the STCM. Moreover, STCM-based DOA (direction-of-arrival) estimation is integrated with the deception procedure to achieve trackable electronic deception which cannot be realized by completely passive electronic jamming. A prototype system of the STCM-based deception is built to verify the deception performance, and the experimental results agree well with the numerical simulations. This work extends the research and the applications of the STCMs, hence showing great scientific and engineering significance.

Titanium nitride (TiN) has recently gained considerable interest because of its remarkable plasmonic properties and for its strong electron–phonon (e–ph) coupling, leading to extremely fast (<100 fs) electron-lattice cooling. Here, the generation of coherent phonons in TiN films is reported, along with their real-time detection by means of broadband transient reflection spectroscopy with sub-15-fs temporal resolution. The measurements show damped oscillations, superimposed to excited state electronic decay. A coherent vibrational mode is revealed, with ≈10 THz frequency ascribed to defect-activated normal modes, consistent with spontaneous Raman scattering data, and a dephasing time of ≈250 fs. Two π-phase flips are also observed located at photon energies corresponding to interband optical transitions (at 3.2 and 2.5 eV), ascribed to selective coupling of the vibrational mode to these transitions; the energy modulation induced by the vibrational coherence is evaluated. It is shown that the displacive excitation of coherent phonons model describes the coherent response in terms of temporal behavior and of spectral amplitude profile. Overall, a comprehensive and detailed analysis of coherent phonons in TiN films, so far undected, is provided and relevant information on TiN photo-physical properties, potentially useful for its applications, is given.

Images captured in inadequate illumination or uneven brightness conditions are prone to suffer from loss of detail and reduced contrast. Self-powered BiOI/WO₃ heterojunction PDs with bidirectionally regulated ultraviolet (UV) and visible dual-band photoresponse characteristics can help to solve the problems. By varying the growth time of BiOI nanoflakes (NFs) on WO₃ nanorod arrays (NRs), different stoichiometric ratios and crystal and band structures of BiOI are achieved. The I⁻ ions migration inside the BiOI controlled by applying a pre-bias voltage can induce the accumulation of polarized charges at the heterojunction interface, then alter the width of the depletion region as well as the height of the interface barrier, which in turn affects the dynamics of photo-generated carriers. Upon applying a positive (negative) pre-bias, the self-powered photocurrent decreases (increases) in the UV band, whereas increases (decreases) in the visible band. Based on BiOI/WO₃ heterojunction PDs, a machine vision imaging system is designed, which enhances image contrast and detail in strong and weak light conditions. This system facilitates rapid feature extraction and recognition, advancing the development of intelligent, real-time digital machine vision systems.

The proposed model structure, featuring a gold (Au) nano-island film (GNIF) integrated with a vertically stacked van der Waals heterojunction and offering an elegant platform for high-performance, efficient, and sensitive photodetection across a broad spectral range, is designated as GNIF-MoS₂/p-Ge(MoS₂ = Molybdenum disulfide, p-Ge = p type germanium). The GNIF is fabricated via ultrathin film deposition, based on the surface dewetting properties of MoS₂. The as-fabricated photodetector (PD), offering ≈20 times reduction in dark current and characterized by wavelength-dependent high responsivity (R(λ)), photoconductive gain (G(λ)), and detectivity (D(λ)), respond to a broad spectral range from visible light (400 nm) to short wave infrared (SWIR) (1600 nm). The ultrahigh transient response (τ_r) is found to be ≈2.5 and 16 µs for the 470 (visible light) and 1550 (SWIR) nm wavelengths, respectively, resulting in 3-dB bandwidths of up to ≈48 kHz, which is considered high for such devices. To understand the inherent mechanisms of broadband detection and the high photoresponse and ultrafast transient response of PDs, a meticulous investigation is conducted on the wavelength-dependent behaviors, depletion width changes, and material properties. The results provide valuable insights and a basis for the construction of suitable PDs based on nanometer-thin metal films, 2D semiconductors, and a 3D hybrid structure.

The ultrafast dynamics of photoexcited charge carriers are studied in micron-scale crystals composed of the inorganic perovskite CsPbBr₃ with time-resolved terahertz spectroscopy. Exciting with photon energy close to the band edge, it is found that a fast (<10 ps) decay emerges in the terahertz photoconductivity with increasing pump fluence and decreasing temperature, dominating the dynamics at 4 K. The fluence-dependent dynamics can be globally fit by a nonlinear recombination model, which reveals that the influence of different nonlinear recombination mechanisms in the studied pump fluence range depends on temperature. Whereas the Auger scattering rate decreases with decreasing temperature from 77 to 4 K, the radiative recombination rate increases by three orders of magnitude. Spectroscopically, the terahertz photoconductivity resembles a Drude response at all delays, yet an additional Lorentz component due to an above-bandwidth resonance is needed to fully reproduce the data.