Correlation between the optical absorption and twisted angle of bilayer graphene observed by high-resolution reflectance confocal laser microscopy

Angle-Resolved Optical Imaging of Interlayer Rotations in Twisted Bilayer Graphene

Twisted bilayer graphene (TBG) is a prototypical layered material whose properties are strongly correlated to interlayer coupling. The two stacked graphene layers with distinct orientations are investigated to generate peculiar optical and electronic phenomena. Thus, the rapid, reliable, and nondestructive twist angle identification technique is of essential importance. Here, we integrated the white light reflection spectra (WLRS), the Raman spectroscopy, and the transmission electron microscope (TEM) to propose a facile RGB optical imaging technique that identified the twist angle of the TBG in a large area intuitively with high efficiency. The RGB technique established a robust correlation between the interlayer rotation angle and the contrast difference in the RGB color channels of a standard optical image. The angle-resolved optical behavior is attributed to the absorption resonance matching with the separation of van Hove singularities in the density of states of the TBG. Our study thus developed a route to identify the rotation angle of stacked bilayer graphene by means of a straightforward optical method, which can be further applied in other stacked van der Waals layered materials.

End-to-end varifocal multiview images coding framework from data acquisition end to vision application end

The emerging data, varifocal multiview (VFMV) has an exciting prospect in immersive multimedia. However, the distinctive data redundancy of VFMV derived from dense arrangements and blurriness differences among views causes difficulty in data compression. In this paper, we propose an end-to-end coding scheme for VFMV images, which provides a new paradigm for VFMV compression from data acquisition (source) end to vision application end. VFMV acquisition is first conducted in three ways at the source end, including conventional imaging, plenoptic refocusing, and 3D creation. The acquired VFMV has irregular focusing distributions due to varying focal planes, which decreases the similarity among adjacent views. To improve the similarity and the consequent coding efficiency, we rearrange the irregular focusing distributions in descending order and accordingly reorder the horizontal views. Then, the reordered VFMV images are scanned and concatenated as video sequences. We propose 4-directional prediction (4DP) to compress the reordered VFMV video sequences. Four most similar adjacent views from the left, upper left, upper and upper right directions serve as reference frames to improve the prediction efficiency. Finally, the compressed VFMV is transmitted and decoded at the application end, benefiting potential vision applications. Extensive experiments demonstrate that the proposed coding scheme is superior to the comparison scheme in objective quality, subjective quality and computational complexity. Experiments on new view synthesis show that VFMV can achieve extended depth of field than conventional multiview at the application end. Validation experiments show the effectiveness of view reordering, the advantage over typical MV-HEVC, and the flexibility on other data types, respectively.

Non-invasive probing of dynamic ion migration in light-emitting electrochemical cells by an advanced nanoscale confocal microscope

In this study, we firstly propose an optical approach to investigate the ion profile of organic films in light-emitting electrochemical cells (LECs) without any invasive sputtering processes. In contrast to previous literatures, this pure optical strategy allows us to record clear and non-destructive ion profile images in the (Ru(dtb-bpy)₃(PF₆)₂) consisted organic layer without interferences of complex collisions from the bombardment of secondary sputter induced ions in a conventional time-of-flight secondary ion mass spectrometry. By using the advanced position sensitive detector (PSD)-based Nanoscale Confocal Microscope, ion distribution profiles were successfully acquired based on the observation of nanoscale optical path length difference by measuring the refractive-index variation while the thickness of the LEC layer was fixed. Dynamic time-dependent ion profile displayed clear ion migration process under a 100 V applied bias at two ends of the LEC. This technique opens up a new avenue towards the future investigations of ion distributions inside organic/inorganic materials, Li-ion batteries, or micro-fluid channels without damaging the materials or disturbing the device operation.