Coherent optical adaptive technique improves the spatial resolution of STED microscopy in thick samples

Stimulated emission depletion(STED) microscopy is one of far-field optical microscopy techniques that can provide sub-diffraction spatial resolution. The spatial resolution of the STED microscopy is determined by the specially engineered beam profile of the depletion beam and its power. However, the beam profile of the depletion beam may be distorted due to aberrations of optical systems and inhomogeneity of a specimen's optical properties, resulting in a compromised spatial resolution. The situation gets deteriorated when thick samples are imaged. In the worst case, the severe distortion of the depletion beam profile may cause complete loss of the superresolution effect no matter how much depletion power is applied to specimens. Previously several adaptive optics approaches have been explored to compensate aberrations of systems and specimens. However, it is difficult to correct the complicated high-order optical aberrations of specimens. In this report, we demonstrate that the complicated distorted wavefront from a thick phantom sample can be measured by using the coherent optical adaptive technique. The full correction can effectively maintain and improve spatial resolution in imaging thick samples.

The coupling effect characterization for van der Waals structures based on transition metal dichalcogenides

van der Waals(vdW)heterostructures based on two-dimensional(2D)materials holding design-by-demand features offer astonishing opportunities to construct novel electronics and optoelectronics devices due to the vdW force interaction between their stacked components.At the atomically thin confinement,vdW heterostructure not only exhibits unprecedented properties as an entire counterpart,but also provides unique platforms to manipulate the vdW interfacial behaviors.Therefore,developing characterization techniques to comprehensively understand the coupling effect on structure-property-performance relationship of vdW heterostructures is crucial for fundamental science and practical applications.Here,we focus on the most widely studied 2D semiconductor transition metal dichalcogenides(TMDCs)and systematically review significant advances in characterizing the material and interfacial coupling effect of the related vdW heterostructures.Specially,we will discuss microscopy techniques for unveiling the structure-property relationship of vdW heterostructures and optical spectroscopy measurements for analyzing vdW interfacial coupling effect.Finally,we address some promising strategies to optimize characterization technologies for resolving vdW heterostructures,including coupling multiple characterization technologies,improving temporal and spatial resolution,developing fast,efficient,and non-destructive techniques and introducing artificial intelligence.

Effect of precursor thermal history on the formation of amorphous and crystalline calcium carbonate

The role of the thermal history of the precursor was studied for amorphous and crystalline calcium carbon- ate phases synthesized from calcium nitrate. The X-ray diffraction patterns of these phases are influenced by their annealing temperature of 0, 300, 400, and 500 ℃. However, the effect of the precursor thermal history on the X-ray diffraction pattern of the resulting calcium carbonate phase is negligible. Transmis- sion electron microscopy indicates that materials annealed at 400 ℃ consist of amorphous aggregates, irrespective of the precursor thermal history. The crystallite size of crystalline calcium carbonate is influ- enced by the precursor thermal history, and ranges from 23 to 26 rim. Near-edge X-ray absorption fine structure measurements indicate that the annealing temperature plays an important role in determining the local electronic structure. The role of the thermal history of the precursor is also important for the resultinu electronic structure.