先进原子力显微术在表征二维材料物性中的应用

二维材料及其范德华异质结构具有极其丰富的力学、电学、光学、磁学等新奇物性,呈现出丰富的物理内涵并具有潜在的应用.二维材料中掺杂、转角、缺陷态等内在状态以及介电常数、应力、电磁场等外在环境通常具有纳米尺度的不均匀性,并能深刻影响其物性及相应纳米器件的性能,故而深入探测二维材料的新奇物性并揭示背后的物理起因,往往需要纳米尺度的表征手段.原子力显微镜及衍生的各种力学、电学、光学和磁学等先进原子力显微技术能够在纳米尺度测量二维材料的结构和物性并探究构效关系.本文首先介绍了基于原子力显微镜的纳米力学、纳米电学、纳米光学、纳米磁学和纳米加工模式的基本原理,然后总结了这些先进原子力显微术在表征二维材料新奇物性中的应用研究进展,最后展望了未来先进原子力显微术的革新方向和发展潜力.

CFD simulation for reduction of pyrolusite in fluidized beds

In this study,a CFD model coupled with heterogeneous flow structure,mass transfer equations,and chemical reaction kinetics is established to forecast the pyrolusite reduction reaction behavior.Compared with the previous studies which ignore the volume change of solids phase,the influence of volume shrinkage on reaction and flow behavior is explored in this research.Volume shrinkage of pyrolusite is proved to be non-negligible in predicting the conversion rate.The negligence of volume shrinkage leads to the overestimation of conversion rate for its inaccurate estimation of surface area for reaction.Besides,the influence of volume shrinkage on the reaction is found smaller in the scaled-up reactor.

Transient spectral and dynamic properties of magic-size Cd_(3)P_(2) nanoclusters in the limit of strong confinement

Both semiconductor nanocrystals and organic molecules are important photofunctional materials for an array of applications.It is interesting to examine the intermediate regime between these two families,which can be interpreted as the strong-confinement limit of the nanocrystals or alternatively as the large-size limit of molecules.Here,we choose Cd_(3)P_(2) magic-size clusters(MSCs)as a unique platform and apply time-resolved spectroscopy to investigate their spectral and dynamic properties.We find that these small clusters display molecular-like vibronic progression on their absorption and emission spectra and a large Stokes shift,which leads to well-separated transient absorption bleach and stimulated emission signals distinct from typical nanocrystals.On the other hand,such small size MSCs can still accommodate biexciton states,and the strongly enhanced Coulombic interactions lead to very fast dephasing of the biexciton resonance as well as rapid biexciton Auger annihilation(1.5 ps).Further,temperature-dependent measurements provide evidence for the transformation of band-edge excitons to localized excitons,with the localization likely driven by the softened lattice in these small-size clusters.These collective results demonstrate that strongly-confined nanoclusters indeed bridge the gap between nanocrystals and molecules,and can be a unique library to search for exotic excited state properties.

Five-wavelength optical-resolution photoacoustic microscopy of blood and lymphatic vessels

Optical-resolution photoacoustic microscopy(OR-PAM)has been developed for anatomical,functional,and molecular imaging but usually requires multiple scanning for different contrasts.We present five-wavelength OR-PAM for simultaneous imaging of hemoglobin concentration,oxygen saturation,blood flow speed,and lymphatic vessels in single raster scanning.We develop a five-wavelength pulsed laser via stimulated Raman scattering.The five pulsed wavelengths,i.e.,532,545,558,570,and 620∕640 nm,are temporally separated by several hundreds of nanoseconds via different optical delays in fiber.Five photoacoustic images at these wavelengths are simultaneously acquired in a single scanning.The 532-and 620∕640-nm wavelengths are used to image the blood vessels and dye-labeled lymphatic vessels.The blood flow speed is measured by a dual-pulse method.The oxygen saturation is calculated and compensated for by the Grüneisen-relaxation effect.In vivo imaging of hemoglobin concentration,oxygen saturation,blood flow speed,and lymphatic vessels is demonstrated in preclinical applications of cancer detection,lymphatic clearance monitoring,and functional brain imaging.

Confocal visible/NIR photoacoustic microscopy of tumors with structural, functional, and nanoprobe contrasts

Distinguishing early-stage tumors from normal tissues is of great importance in cancer diagnosis.We report fiberbased confocal visible/near-infrared(NIR)optical-resolution photoacoustic microscopy that can image tumor microvasculature,oxygen saturation,and nanoprobes in a single scanning.We develop a cost-efficient single laser source that provides 532,558,and 1064 nm pulsed light with sub-microseconds wavelength switching time.Via dual-fiber illumination,we can focus the three beams to the same point.The optical and acoustic foci are confocally aligned to optimize the sensitivity.The visible and NIR wavelengths enable simultaneous tumor imaging with three different contrast modes.Results show obvious angiogenesis,significantly elevated oxygen saturation,and accumulated nanoparticles in the tumor regions,which offer comprehensive information to detect the tumor.This approach also allows us to identify feeding and draining vessels of the tumor and thus to determine local oxygen extraction fraction.In the tumor region,the oxygen extraction fraction significantly decreases along with tumor growth,which can also assist in tumor detection and staging.Fiber-based confocal visible/NIR photoacoustic microscopy offers a new tool for early detection of cancer.

Altered Energy Metabolism During Early Optic Nerve Crush Injury:Implications of Warburg-Like Aerobic Glycolysis in Facilitating Retinal Ganglion Cell Survival

Neurons,especially axons,are metabolically demanding and energetically vulnerable during injury.However,the exact energy budget alterations that occur early after axon injury and the effects of these changes on neuronal survival remain unknown.Using a classic mouse model of optic nerve-crush injury,we found that traumatized optic nerves and retinas harbor the potential to mobilize two primary energetic machineries,glycolysis and oxidative phosphorylation,to satisfy the robustly increased adenosine triphosphate(ATP) demand.Further exploration of metabolic activation showed that mitochondrial oxidative phosphorylation was amplified over other pathways,which may lead to decreased retinal ganglion cell(RGC) survival despite its supplement to ATP production.Gene set enrichment analysis of a microarray(GSE32309) identified significant activation of oxidative phosphorylation in injured retinas from wild-type mice compared to those from mice with deletion of phosphatase and tensin homolog(PTEN),while PTEN-/-mice had more robust RGC survival.Therefore,we speculated that the oxidation-favoring metabolic pattern after optic nervecrush injury could be adverse for RGC survival.After redirecting metabolic flux toward glycolysis(magnifying the Warburg effect) using the drug meclizine,we successfully increased RGC survival.Thus,we provide novel insights into a potential bioenergetics-based strategy for neuroprotection.

Consideration of climate change impacts will improve the efficiency of protected areas on the Qinghai-Tibet Plateau

The protection of migratory birds and their habitats is important to the ecological stability of the Qinghai-Tibet Plateau(QTP).Currently protected areas(PAs)were designed in accordance with species distribution patterns under current climatic conditions,thus ignoring climate change will lead to a decrease in the protection efficiency of PAs.In this study,using the flagship species Grus nigricollis,as an example,we used the maximum entropy(MaxEnt)model to simulate the distributions and conservation status of G.nigricollis and optimized the existing PA boundaries.The results showed that(1)suitable habitat-for G.nigricollis accounts for 12.48%of the QTP area,and the PAs established under current climatic conditions cover 17.84%of this suitable habitat area;(2)future climate changes will influence the distribution and quality of G.nigricollis habitats,and the average protection efficiency of the current PAs in four climatic scenarios will decrease from 17.84%to 15.31%;and(3)through optimization,the efficiency of existing PAs can be increased by 0.75 times and reach 28.37%,indicating PA planning must consider not only current climate conditions but also the effects of climate changes.Our results aim to address shortcomings in the conservation efficiency of PAs and provide an example for resolving mismatched PA boundaries and habitat changes for species.