Light confinement provided by whispering gallery mode (WGM) microresonators is especially useful for integrated photonic circuits. In particular, the tunability of such devices has gained increased attention for active filtering and lasering applications. Traditional lithographic approaches for fabricating such devices, especially Si-based ones, often restrict the device’s tuning due to the material’s inherent properties. Two-photon polymerization (2PP) has emerged as an alternative fabrication technique of sub-diffraction resolution 3D structures, in which compounds can be incorporated to further expand their applications, such as enabling active devices. Here, we exploited the advantageous characteristics of polymer-based devices and produced, via 2PP, acrylic-based WGM hollow microcylinders incorporated with the azoaromatic chromophore Disperse Red 13 (DR13). Within telecommunication range, we demonstrated the tuning of the microresonator’s modes by external irradiation within the dye’s absorption peak (at 514 nm), actively inducing a blueshift at a rate of 1.2 nm/(Wcm−2). Its thermo-optical properties were also investigated through direct heating, and the compatibility of both natural phenomena was also confirmed by finite element simulations. Such results further expand the applicability of polymeric microresonators in optical and photonic devices since optically active filtering was exhibited.
In this study, 4-pyrrolidinopyridine (PPY) and 2,5-diphenyloxazole (DPO) were employed as N-heterocyclic derivatives to synthesize novel picrate salts. These salts were subsequently subjected to characterization using infrared spectroscopy, ultraviolet spectroscopy, and single-crystal X-ray diffraction. Comparison of these structures with entries in the Cambridge Structural Database (CSD) and the application of two multivariate statistical analyses, namely Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA), facilitated the differentiation of salts and co-crystals based on the structural behaviors of the picrate molecule. Additionally, Hirshfield Surface Analysis and 2D fingerprint plots were employed to investigate intermolecular contacts. The fluorescence emission spectra revealed that compound 2 has the potential to serve as a probe for turn-off detection of picric acid (PA).
In this work, we apply a combination of theoretical techniques to characterize a two-dimensional material with formula B2N2O2, featuring a zigzag array of nitrogen atoms. We predict its energetic, thermal, and dynamic stability and determine its electronic properties, including band structure and mobility evaluation for a phonon-mediated mechanism. We show that the compound is a wideband-gap semiconductor, with parabolic band edges and with large electron and hole mobilities within the deformation potential approach. We ascribe this result to the existence of electronic channels defined by the zigzag array of nitrogen bonds, which define the edges of both conduction and valence bands. We also propose a mechanism to synthesize the compound based on oxygen functionalization and application of pressure. Finally, we show that the results can be generalized to represent a family of 2D compounds.
The CO2 reduction by solar means has been discussed as an alternative to emission abatement, a fundamental topic for sustainable, carbon-free production in the future. However, the choice of efficient systems, starting with the catalysts, is still a critical issue, especially due to the poor activity of available options. Polyoxometalates have been extensively studied as promising photocatalysts due to their semiconducting properties. Nevertheless, the synthetic conditions of polyoxoniobate are stringent due to the low reaction activity of Nb species, the lack of soluble precursors, and the narrow pH range. Unlike the literature, in the present study, we report a simple polyoxoniobate synthesis method. This synthesis method has some remarkable features, such as low processing time and temperature and good activity and selectivity in the CO2 photoreduction process. The results revealed an outstanding efficiency for the CO2 reduction reaction with a high selectivity of CO2 to CO conversion (92.5%). Furthermore, C2 compounds (e.g., acetate) were produced in the liquid phase of the reaction system. Our findings are significant for indicating the potential of polyoxoniobate for CO2 photoreduction, which opens a way to control competitive reactions with synthesis, leading to higher selectivity.
Moiré superlattices of two-dimensional heterostructures arose as a new platform to investigate emergent behaviour in quantum solids with unprecedented tunability. To glean insights into the physics of these systems, it is paramount to discover new probes of the moiré potential and moiré minibands, as well as their dependence on external tuning parameters. Hydrostatic pressure is a powerful control parameter, since it allows to continuously and reversibly enhance the moiré potential. Here we use high pressure to tune the minibands in a rotationally aligned MoS2/WSe2 moiré heterostructure, and show that their evolution can be probed via moiré phonons. The latter are Raman-inactive phonons from the individual layers that are activated by the moiré potential. Moiré phonons manifest themselves as satellite Raman peaks arising exclusively from the heterostructure region, increasing in intensity and frequency under applied pressure. Further theoretical analysis reveals that their scattering rate is directly connected to the moiré potential strength. By comparing the experimental and calculated pressure-induced enhancement, we obtain numerical estimates for the moiré potential amplitude and its pressure dependence. The present work establishes moiré phonons as a sensitive probe of the moiré potential as well as the electronic structures of moiré systems.
Natural Language Processing (NLP) makes use of Artificial Intelligence algorithms to extract meaningful information from unstructured texts, i.e., content that lacks metadata and cannot easily be indexed or mapped onto standard database fields. It has several applications, from sentiment analysis and text summary to automatic language translation. In this work, we use NLP to figure out similar structural linguistic patterns among several different languages. We apply the word2vec algorithm that creates a vector representation for the words in a multidimensional space that maintains the meaning relationship between the words. From a large corpus we built this vectorial representation in a 100-dimensional space for English, Portuguese, German, Spanish, Russian, French, Chinese, Japanese, Korean, Italian, Arabic, Hebrew, Basque, Dutch, Swedish, Finnish, and Estonian. Then, we calculated the fractal dimensions of the structure that represents each language. The structures are multi-fractals with two different dimensions that we use, in addition to the token-dictionary size rate of the languages, to represent the languages in a three-dimensional space. Finally, analyzing the distance among languages in this space, we conclude that the closeness there is tendentially related to the distance in the Phylogenetic tree that depicts the lines of evolutionary descent of the languages from a common ancestor.