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Bistable electrical conductivity switching behavior and write‐once, read‐many‐times (WORM) memory effects have been demonstrated in Al/polymer/ITO sandwich devices. These devices were constructed from two poly(N‐vinylcarbazole) derivatives with pendant donor–trap–acceptor (D‐T‐A) structures. The observed electrical bistability can be attributed to the field‐induced charge‐transfer interaction between the carbazole electron‐donor unit and the terminal electron‐acceptor unit, and subsequent charge trapping at the intermediate azobenzene chromophores. The charge‐transfer and trapping processes are further stabilized by the conformational relaxation of the total energy of the D‐T‐A system through donor–acceptor electrostatic interaction. The proposed switching and conduction mechanism is supported by density functional theory calculations, UV/Visible absorption spectra, core‐level X‐ray photoelectron spectra, and high‐resolution transmission electron microscopy images of the polymer thin films. The influence of the charge‐trapping effect of the azobenzene mediator is further explored by studying the electronic properties of two other poly(N‐vinylcarbazole) derivatives as the control samples, in which nitro or cyano acceptor groups are directly bonded to the carbazole electron‐donor moieties.

New soluble MoS2 nanosheets covalently functionalized with poly(N-vinylcarbazole) (MoS2-PVK) were in situ synthesized for the first time. In contrast to MoS2 and MoS2 /PVK blends, both the solution of MoS2 -PVK in DMF and MoS2-PVK/poly(methyl methacrylate) (PMMA) film show superior nonlinear optical and optical limiting responses. The MoS2-PVK/PMMA film shows the largest nonlinear coefficients (βeff) of about 917 cm GW(-1) at λ=532 nm (cf. 100.69 cm GW(-1) for MoS2/PMMA and 125.12 cm GW(-1) for MoS2/PVK/PMMA) and about 461 cm GW(-1) at λ=1064 nm (cf. -48.92 cm GW(-1) for MoS2/PMMA and 147.56 cm GW(-1) for MoS2/PVK/PMMA). A larger optical limiting effect, with thresholds of about 0.3 GW cm(-2) at λ=532 nm and about 0.5 GW cm(-2) at λ=1064 nm, was also achieved from the MoS2-PVK/PMMA film. These values are among the highest reported for MoS2-based nonlinear optical materials. These results show that covalent functionalization of MoS2 with polymers is an effective way to improve nonlinear optical responses for efficient optical limiting devices.

Accurate cotton maps are crucial for monitoring cotton growth and precision management. The paper proposed a county-scale cotton mapping method by using random forest (RF) feature selection algorithm and classifier based on selecting multi-features, including spectral, vegetation indices, and texture features. The contribution of texture features to cotton classification accuracy was also explored in addition to spectral features and vegetation index. In addition, the optimal classification time, feature importance, and the best classifier on the cotton extraction accuracy were evaluated. The results showed that the texture feature named the gray level co-occurrence matrix (GLCM) is effective for improving classification accuracy, ranking second in contribution among all studied spectral, VI, and texture features. Among the three classifiers, the RF showed higher accuracy and better stability than support vector machines (SVM) and artificial neural networks (ANN). The average overall accuracy (OA) of the classification combining multiple features was 93.36%, 7.33% higher than the average OA of the single-time spectrum, and 2.05% higher than the average OA of the multi-time spectrum. The classification accuracy after feature selection by RF can still reach 92.12%, showing high accuracy and efficiency. Combining multiple features and random forest methods may be a promising county-scale cotton classification method.

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In the past decades, significant effort has been invested into the research and development of optical limiting materials and processes in order to develop practical solutions for the protection from laser beams. In this study, a new soluble graphene oxide based material (GO-Cz) has been synthesized through the covalent modification of graphene oxide (GO) with a carbazole derivative (Cz). The formation of an amido bond between the Cz group and GO has been confirmed by X-ray photoelectron and Fourier transform infrared spectroscopy. At the same concentration, both the nonlinear extinction coefficient and the imaginary third-order susceptibility were increased by a factor of ≈6.93 at 532 nm and ≈6.07 at 1064 nm relative to those of GO, as a result of the covalent grafting of the Cz moieties onto the GO surface. The GO-Cz dispersions exhibit a much better optical limiting performance than GO and GO/Cz blends at both 532 and 1064 nm due to the possible intramolecular electron-transfer between the GO and Cz moieties and the effective combination of the different nonlinear optical mechanisms.

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