Although π–π interactions have been studied for several decades, the quantification of the strength of π–π interactions in a macromolecule remains a big challenge. Herein, we utilize single-molecule atomic force microscopy and steered molecular dynamics simulations to study the π–π interactions in polystyrene (PS). It is found that in high vacuum, the single-chain mechanics of PS differs largely from that of polyethylene (PE). Accordingly, the strength of intrachain π–π interactions in PS is estimated to be 0.7 kcal/(mol stack), which is much lower than that in a small-molecule system (benzene dimer, 2–3 kcal/(mol stack)). Further study shows that in high vacuum, there are two types of π–π stacking in the single PS chain, i.e., the every-other-moiety (E) type and the adjacent-moiety (A) type. Upon force stretching, a transition from E-type to A-type π–π stacking can be observed.

Orogenic belts have been among the most important locations to investigate the growth of continental crust (CC). The Eastern Kunlun Orogenic Belt (EKOB), which contains widespread Permian-Triassic granitoids, is volumetrically comparable to the Cenozoic Gangdese magmatic belt in the Tibetan Plateau and is an ideal region to investigate the mechanism of the Paleozoic-Mesozoic CC growth in this region. The Gouli batholith at the eastern end of the EKOB consists of the synchronous Xiangride granodiorite, Asiha quartz diorite (ca. 242 Ma) and adamellite. The granodiorite and quartz diorite, both of which contain magmatic enclaves, show medium-high K, calc-alkalic and metaluminous signatures and have similar rare earth element and trace element patterns to those of bulk CC. Besides, the Xiangride granodiorite displays distinct adakitic signatures (average Sr/Y of 47). The Sr-Nd isotopic values for the different types of rocks are roughly similar ((87 Sr/ 86 Sr) i = 0.708167-0.713553, ε Nd (t) =-6.8 to-5.3), while Hf isotopes are distinguishable, with ε Hf (t) granodiorite = 0.3 to 5.1 and ε Hf (t) diorite =-1.6 to 0.7. These geochemical and petrographic signatures suggest that the granodiorite originated from the partial melting of subducting oceanic crust and terrigenous sediments, and the quartz diorite and enclaves formed via the mixing of slab-derived magma and enriched mantle-derived melt. Further comprehensive analyses of the spatial and temporal distribution of regional magmatic rocks, metamorphism and sedimentary facies reveal that the Gouli batholith and most of the Permian-Triassic granitoids in the EKOB formed during the subduction of the Paleo-Tethys Ocean instead of subsequent syn-collision setting. Thus, we contend that the Permian-Triassic CC growth of the EKOB occurred in a slab

No abstract

The scaling down of switching media encounters high leakage current in the traditional oxide material based memristors, resulting in high power consumption of chips. Two-dimensional (2D) materials promise an ultimate device scaling down to atomic layer thickness. Herein, black phosphorus (BP) and its self-assembly phosphorous oxide (BP) memristors are constructed, which leverages the high on/off ratio operation of oxides and low leakage current of 2D materials with high performance. The memristors exhibit reproducible and reliable switching characteristics with the on/off ratio >107 and data retention >104 s. Depending on the high reproducibility, basic “AND” and “OR” gates have been constructed on flexible substrates. Moreover, on the basis of the symmetry and linearity of conductance in the devices, the neural network simulation for supervised learning presents an online learning accuracy of 91.4%. This work opens an avenue for future flexible electronics.

We report the giant optical nonlinear absorption and refraction of Sb2Te3 phase change materials at low laser irradiation intensities. The nonlinear absorption and refraction coefficients reach up to −6.63×10−2 m/W and 2.606×10−9 m2/W, respectively. The first principles calculation indicates that the giant nonlinear absorption stems from the band filling effect of the photon induced free carriers under laser irradiation. The band-gap shrinking results in a positive thermo-optic coefficient, thus the giant nonlinear refraction. The numerical results are generally correlated with the experimental findings from z-scan and temperature-variable ellipsometric measurements.

The AgInSbTe phase change thin films are very important as optical recording and the super-resolution mask materials in high density optical information storage. In this work, the effective nonlinear absorption coefficients of amorphous and crystalline AgInSbTe thin films were measured by the open-mode Z-scan method and no evidence of nonlinear refraction was found in the closed-mode Z-scan measurement. The effective nonlinear absorption coefficient βeff of amorphous AgInSbTe thin films is 7.53×10−3 m/W and the effective photon-absorption number n is 1.722; βeff of crystalline AgInSbTe thin films is 3.5×10−2 m/W, which is of an order lager than that of amorphous state, and the n value is 1.7011. The giant nonlinearity of AgInSbTe results from the free carrier absorption in the nanosecond time scale and this characteristic should be responsible for the mechanism of optical recording as well as the readout of super-resolution disk.

No abstract

We proposed a method to design a ternary optical element in order to achieve a needle of super-resolution longitudinally polarized beam with ultra-long depth of focus, and obtained a beam with a size of 0.3995λ and depth of focus of 12.83λ after focusing a ternary optical element modulated, radially polarized Bessel-Gaussian beam with an aplanatic lens of numerical aperture 0.95. The algorithm we used to design the ternary optical element is based on axial uniformity in the focal region, which allows rapid searching speeds and excellent performance. The ratio of pupil radius to the beam waist was set as 0.57, making the peak intensity of the incident beam occur at the rim of the lens aperture, which maximized the possible resolution of the focused beam.