Spatially Bandgap-Graded Mo S2（1-x）Se2x Homojunctions for Self-Powered Visible–Near-Infrared Phototransistors

Ternary transition metal dichalcogenide alloys with spatially graded bandgaps are an emerging class of two-dimensional materials with unique features,which opens up new potential for device applications.Here,visible–near-infrared and self-powered phototransistors based on spatially bandgap-graded MoS2(1−x)Se2x alloys,synthesized by a simple and controllable chemical solution deposition method,are reported.The graded bandgaps,arising from the spatial grading of Se composition and thickness within a single domain,are tuned from 1.83 to 1.73 eV,leading to the formation of a homojunction with a builtin electric field.Consequently,a strong and sensitive gate-modulated photovoltaic effect is demonstrated,enabling the homojunction phototransistors at zero bias to deliver a photoresponsivity of 311 mA W−1,a specific detectivity up to^10^11 Jones,and an on/off ratio up to^10^4.Remarkably,when illuminated by the lights ranging from 405 to 808 nm,the biased devices yield a champion photoresponsivity of 191.5 A W−1,a specific detectivity up to^1012 Jones,a photoconductive gain of 10^6–10^7,and a photoresponsive time in the order of^50 ms.These results provide a simple and competitive solution to the bandgap engineering of two-dimensional materials for device applications without the need for p–n junctions.

Microbially-mediated formation of Ca-Fe carbonates during dissimilatory ferrihydrite reduction:Implications for the origin of sedimentary ankerite

The origin of sedimentary dolomite has become a long-standing problem in the Earth Sciences.Some carbonate minerals like ankerite have the same crystal structure as dolomite,hence their genesis may provide clues to help solving the dolomite problem.The purpose of this study was to probe whether microbial activity can be involved in the formation of ankerite.Bio-carbonation experiments associated with microbial iron reduction were performed in batch systems with various concentrations of Ca^(2+)(0–20 mmol/L),with a marine iron-reducing bacterium Shewanella piezotolerans WP3 as the reaction mediator,and with lactate and ferrihydrite as the respective electron donor and acceptor.Our biomineralization data showed that Ca-amendments expedited microbially-mediated ferrihydrite reduction by enhancing the adhesion between WP3 cells and ferrihydrite particles.After bioreduction,siderite occurred as the principal secondary mineral in the Ca-free systems.Instead,Ca-Fe carbonates were formed when Ca^(2+)ions were present.The CaCO_(3) content of microbially-induced Ca-Fe carbonates was positively correlated with the initial Ca2+concentration.The Ca-Fe carbonate phase produced in the 20 mmol/L Ca-amended biosystems had a chemical formula of Ca_(0.8)Fe_(1.2)(CO_(3))_(2),which is close to the theoretical composition of ankerite.This ankeritelike phase was nanometric in size and spherical,Ca-Fe disordered,and structurally defective.Our simulated diagenesis experiments further demonstrated that the resulting ankerite-like phase could be converted into ordered ankerite under hydrothermal conditions.We introduced the term“proto-ankerite”to define the Ca-Fe phases that possess near-ankerite stoichiometry but disordered cation arrangement.On the basis of the present study,we proposed herein that microbial activity is an important contributor to the genesis of sedimentary ankerite by providing the metastable Ca-Fe carbonate precursors.

Integrated Stratigraphy and Mineralogy of the Doushantuo Formation in Weng’an,South China,and Implications for Ediacaran Phosphogenesis

The Ediacaran–Cambrian Phosphogenic Episode is the Earth’s first true phosphogenic event and resulted in worldwide phosphate deposits,which occurred during the processes of the Neoproterozoic Oxygenation Event.The Ediacaran Doushantuo Formation(ca.635–551 Ma)of Weng’an area in central Guizhou,South China,contains two economic phosphorite beds(the Lower and Upper Phosphorite Beds).This paper presents a detailed stratigraphic,sedimentological and mineralogical study of multiple outcrop and drill core sections of the Doushantuo Formation across the Weng’an area,and identified 11 lithofacies and 4 types of phosphatic grains.Significant differences in lithofacies and grain types between the upper and lower phosphate deposits are observed,indicating that the two sets of phosphate deposits are the products of two distinct phosphogenic processes.The Lower Phosphorite Bed mainly consists of banded and laminated phosphorites,contains micro-oncoids formed by microbially-mediated precipitation and peloids formed by in-situ chemically oscillating reactions,indicating a biochemical and chemical enrichment of phosphorus to sediments during the Early Ediacaran Period.The Upper Phosphorite Bed is mainly composed of carbonaceous,massive,and stromatolitic phosphorites,contains bioclasts(phosphatized spheroidal fossils),and intraclasts formed by hydrodynamic agitation,suggesting that the major accesses of phosphorus to sediments were the remineralization of organic P.Deposition of the two economic phosphorite beds was controlled by two sea-level cycles.Such differences have also been documented in contemporaneous phosphate-bearing successions in Brazil and Mangolia,indicating a significant shift in global phosphogenic mechanism during the early and middle Ediacaran,which may be due to the changes in redox conditions in seawater,associated with the Neoproterozoic Oxygenation Event.These regional active P-cycle processes could produce more free oxygen,which may have contributed to the upcoming Phanerozoic global oxidation.

Gradient-induced long-range optical pulling force based on photonic band gap

Optical pulling provides a new degree of freedom in optical manipulation.It is generally believed that long-range optical pulling forces cannot be generated by the gradient of the incident field.Here,we theoretically propose and numerically demonstrate the realization of a long-range optical pulling force stemming from a self-induced gradient field in the manipulated object.In analogy to potential barriers in quantum tunnelling,we use a photonic band gap design in order to obtain the intensity gradients inside a manipulated object placed in a photonic crystal waveguide,thereby achieving a pulling force.Unlike the usual scattering-type optical pulling forces,the proposed gradient-field approach does not require precise elimination of the reflection from the manipulated objects.In particular,the Einstein-Laub formalism is applied to design this unconventional gradient force.The magnitude of the force can be enhanced by a factor of up to 50 at the optical resonance of the manipulated object in the waveguide,making it insensitive to absorption.The developed approach helps to break the limitation of scattering forces to obtain longrange optical pulling for manipulation and sorting of nanoparticles and other nano-objects.The developed principle of using the band gap to obtain a pulling force may also be applied to other types of waves,such as acoustic or water waves,which are important for numerous applications.

Topological transformation and free-space transport of photonic hopfions

Structured light fields embody strong spatial variations of polarization,phase,and amplitude.Understanding,characterization,and exploitation of such fields can be achieved through their topological properties.Three-dimensional(3D)topological solitons,such as hopfions,are 3D localized continuous field configurations with nontrivial particle-like structures that exhibit a host of important topologically protected properties.Here,we propose and demonstrate photonic counterparts of hopfions with exact characteristics of Hopf fibration,Hopf index,and Hopf mapping from real-space vector beams to homotopic hyperspheres representing polarization states.We experimentally generate photonic hopfions with on-demand high-order Hopf indices and independently controlled topological textures,including Néel-,Bloch-,and antiskyrmionic types.We also demonstrate a robust free-space transport of photonic hopfions,thus showing the potential of hopfions for developing optical topological informatics and communications.

Reliability of organic light-emitting diodes in low-temperature environment

Organic light-emitting diode(OLED)is an electroluminescent technology that relies on charge-carrier dynamics and is a potential light source for variable environmental conditions.Here,by exploiting a self-developed low-temperature testing system,we investigated the characteristics of hole/electron transport,electro-optic conversion efficiency,and operation lifetime of OLEDs at low-temperature ranging from-40℃to 0℃and room temperature(25℃).Compared to devices operating at room temperature,the carrier transport capability is significantly decreased with reducing temperature,and especially the mobility of the hole-transporting material(HTM)and electron-transporting material(ETM)at-40℃decreases from 1.16×10-6 cm2/V·s and 2.60×10-4 cm2/V·s to 6.91×10-9 cm2/V·s and 1.44×10-5 cm2/V·s,respectively.Indeed,the temperature affects differently on the mobilities of HTM and ETM,which favors unbalanced charge-carrier transport and recombination in OLEDs,thereby leading to the maximum current efficiency decreased from 6.46 cd·A-1 at 25℃to 2.74 cd·A-1 at-40℃.In addition,blue fluorescent OLED at-20℃has an above 56%lifetime improvement(time to 80%of the initial luminance)over the reference device at room temperature,which is attributed to efficiently dissipating heat generated inside the device by the low-temperature environment.

微生物异化还原水铁矿介导的Ca-Fe碳酸盐矿物形成:对铁白云石成因的启示

白云石的成因机制至今仍是地球科学领域的一个谜题(“白云石问题”).铁白云石等碳酸盐矿物具有类白云石晶体结构,因此研究这些矿物的形成机制可为解答“白云石问题”提供新线索.本研究利用一株海洋异化铁还原菌(Shewanella piezotolerans WP3),在不同钙离子浓度(0~20mmol/L)条件下,通过氧化乳酸盐诱导水铁矿还原转化为次生碳酸盐矿物,以此评估微生物在铁白云石形成过程中的作用.实验结果表明,加入Ca^(2+)可以增强S.piezotolerans WP3细胞与水铁矿颗粒之间的黏附作用,从而提高反应体系中Fe(Ⅲ)还原速率.在不同Ca^(2+)浓度条件下,菌株WP3诱导生成的次生碳酸盐矿物类别有所差异:在0mmol/L Ca^(2+)体系中生成菱铁矿,而含钙体系中则为Ca-Fe碳酸盐固溶体,且这些固溶体的钙离子含量与反应体系中初始的Ca^(2+)浓度呈正相关关系.值得注意的是,在20mmol/L Ca^(2+)体系中生成的Ca-Fe碳酸盐固溶体化学组成为Ca0.8Fe1.2(CO3)2,与铁白云石类似.此外,这些微生物成因的“类铁白云石”具有纳米晶粒的形态,晶体结构中钙和铁元素呈无序分布,并且发育较多晶体缺陷.进一步成岩模拟实验证明,“类铁白云石”可以在水热条件下转化为有序铁白云石.基于成分类比性和转化规律,微生物成因的“类铁白云石”可能是沉积物(岩)中铁白云石的重要前驱体,可以被定义为“原铁白云石”.以上新发现对理解微生物在铁白云石乃至白云石形成中的贡献具有重要的启示意义.

Nanoscale control of Ag nanostructures for plasmonic fluorescence enhancement of near-infrared dyes

为各种各样的疾病的早察觉和诊断的蛋白质的潜在的利用在基于蛋白质的察觉技术的发展拉了可观的兴趣。导致的荧光改进为在临床的应用增加蛋白质察觉的敏感的可能性提供的金属。我们为荧光改进报导悦耳的 plasmonic 银 nanostructures 的使用一在红外线附近(NIR ) 染料(Alexa Fluor 790 ) 。2 个数量级的广泛的荧光改进被 Ag nanostructure 尺寸和 interparticle 距离的 nanoscale 控制获得。这些 Ag nanostructures 也与很高的量产量从染料提高了荧光(为 Alexa Fluor 488 的 7.8 褶层，量效率(Qy )= 0.92 ) 。极大地提高的刺激和增加的放射的腐烂率的联合，导致量效率的联系改进导致大改进。这些结果作为金属显示出 Ag nanostructures 的潜力为在 NIR 生物窗户以及可见区域中的染料的导致的荧光改进(MIFE ) 底层。胶体的平版印刷术制作的 Ag nanostructured 数组因此为 NIR 基于染料的 biosensing 应用显示出大潜力。

Tetraphenylethylene-BODIPY aggregation-induced emission luminogens for near-infrared polymer light-emitting diodes

The aggregation-induced emission(AIE) phenomenon provides a new direction for the development of organic light-emitting devices. Here, we present a new class of emitters based on 4,4-difluoro-4-bora-3 a,4 a-diaza-s-indacene(BODIPY), functionalized at different positions with tetraphenylethylene(TPE), which is one of the most famous AIE luminogens. Thanks to this modification, we were able to tune the photoluminescence of the BODIPY moiety from the green to the near-infrared(NIR)spectral range and achieve PL efficiencies of ~50% in the solid state. Remarkably, we observed an enhancement of the AIE and up to ~100% photoluminescence efficiencies by blending the TPE-substituted BODIPY fluorophores with a poly[(9,9-di-noctylfluorene-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,7-diyl)](F8 BT) matrix. By incorporating these blends in organic lightemitting diodes(OLEDs), we obtained electroluminescence peaked in the range 650–700 nm with up to 1.8% external quantum efficiency and ~2 m W/cm2 radiance, a remarkable result for red/NIR emitting and solution-processed OLEDs.

Hydrophilic surface modification of PDMS for droplet microfluidics using a simple,quick,and robust method via PVA deposition

Polydimethylsiloxane(PDMS)is a dominant material in the fabrication of microfluidic devices to generate water-in-oil droplets,particularly lipid-stabilized droplets,because of its highly hydrophobic nature.However,its key property of hydrophobicity has hindered its use in the microfluidic generation of oil-in-water droplets,which requires channels to have hydrophilic surface properties.In this article,we developed,optimized,and characterized a method to produce PDMS with a hydrophilic surface via the deposition of polyvinyl alcohol following plasma treatment and demonstrated its suitability for droplet generation.The proposed method is simple,quick,effective,and low cost and is versatile with respect to surfactants,with droplets being successfully generated using both anionic surfactants and more biologically relevant phospholipids.This method also allows the device to be selectively patterned with both hydrophilic and hydrophobic regions,leading to the generation of double emulsions and inverted double emulsions.

Experimental demonstration of linear and spinning Janus dipoles for polarisation-and wavelength-selective near-field coupling

The electromagnetic field scattered by nano-objects contains a broad range of wavevectors and can be efficiently coupled to waveguided modes.The dominant contribution to scattering from subwavelength dielectric and plasmonic nanoparticles is determined by electric and magnetic dipolar responses.Here,we experimentally demonstrate spectral and phase selective excitation of Janus dipoles,sources with electric and magnetic dipoles oscillating out of phase,in order to control near-field interference and directional coupling to waveguides.We show that by controlling the polarisation state of the dipolar excitations and the excitation wavelength to adjust their relative contributions,directionality and coupling strength can be fully tuned.Furthermore,we introduce a novel spinning Janus dipole featuring cylindrical symmetry in the near and far field,which results in either omnidirectional coupling or noncoupling.Controlling the propagation of guided light waves via fast and robust near-field interference between polarisation components of a source is required in many applications in nanophotonics and quantum optics.

Precipitation of High Mg-Calcite and Protodolomite Using Dead Biomass of Aerobic Halophilic Bacteria

The microbial dolomite model has been used to interpret the origin of sedimentary dolomite.In this model,the formation of low-temperature protodolomite,an important precursor to sedimentary dolomite,can be facilitated either by actively metabolizing cells of anaerobic microbes and aerobic halophilic archaea or by their inactive biomass.Aerobic halophilic bacteria are widely distributed in(proto-)dolomite-depositing evaporitic environments and their biomass might serve as a template for the crystallization of protodolomite.To test this hypothesis,carbonation experiments were conducted using dead biomass of an aerobic halophilic bacterium(Exiguobacterium sp.strain JBHLT-3).Our results show that dead biomass of JBHLT-3 can accelerate Mg2+uptake in carbonate mineral precipitates.In addition,the amount of Mg incorporated into Ca-Mg carbonates is proportional to the concentration of biomass.High Mg-calcite is produced with 0.25 or 0.5 g/L biomass,whereas protodolomite forms with 1 g/L biomass.This is confirmed by the main Raman peak of Ca-Mg carbonates,which shifts towards higher wavenumbers with increased Mg substitution.Microbial cells and their imprints are preserved on the surface of high Mg-calcite and protodolomite.Hence,this study furthers our understanding of the dolomitization within buried and dead microbial mats,which provides useful insights into the origin of ancient dolomite.

Resolution-enhanced X-ray fluorescence microscopy via deep residual networks

Multimodal hard X-ray scanning probe microscopy has been extensively used to study functional materials providing multiple contrast mechanisms.For instance,combining ptychography with X-ray fluorescence(XRF)microscopy reveals structural and chemical properties simultaneously.While ptychography can achieve diffraction-limited spatial resolution,the resolution of XRF is limited by the X-ray probe size.Here,we develop a machine learning(ML)model to overcome this problem by decoupling the impact of the X-ray probe from the XRF signal.The enhanced spatial resolution was observed for both simulated and experimental XRF data,showing superior performance over the state-of-the-art scanning XRF method with different nano-sized X-ray probes.Enhanced spatial resolutions were also observed for the accompanying XRF tomography reconstructions.Using this probe profile deconvolution with the proposed ML solution to enhance the spatial resolution of XRF microscopy will be broadly applicable across both functional materials and biological imaging with XRF and other related application areas.

The Termination and Aftermath of the Lomagundi -Jatuli Carbon Isotope Excursions in the Paleoproterozoic Hutuo Group, North China

The Lomagundi-Jatuli Event（LJE） is one of the largest and earliest positive carbon isotope excursions preserving δ^（13）C_（carb） values between ＋5 and ＋16‰ in Paleoproterozoic carbonates worldwide. However, the duration, amplitude and patterns of these excursions remain poorly constrained. The 2.14-1.83 Ga Hutuo Group in the North China Craton is a 〉10 km thick volcano-sedimentary sequence, including 〉5 km thick well-preserved carbonates that were deposited in supra-tidal to sub-tidal environments. C-O isotopic and elemental analyses of 152 least altered samples of the carbonates revealed a three-stage δ^（13）C evolution. It began with an exclusively positive δ^（13）C_（carb）（＋1.3 to ＋ 3.4‰） stage in the ~2.1 Ga carbonate in the Dashiling and Qingshicun Formations, followed by a transition from positive values to oscillating positive and negative values in ~3 000 m thick carbonates of the Wenshan, Hebiancun, Jianancun, and Daguandong Formations, and end with exclusively negative δ^（13）C_（carb） values preserved in 〉 500 m thick dolostones of the Huaiyincun and Beidaxing Formations. It appears that much of the LJE, particularly those extremely positive δ^（13）C_（carb） signals, was not recorded in the Hutuo carbonates. The exclusively positive δ^（13）C_（carb） values（＋1.3 to ＋ 3.4‰） preserved in the lower formations likely correspond to the end of the LJE, whereas the subsequent two stages reflect the aftermath of the LJE and the onset of Shunga-Francevillian event（SFE）. The present data point to an increased influence of oxygen on the carbon cycle from the Doucun to the Dongye Subgroups and demonstrate that the termination of the LJE in the North China Craton is nearly simultaneous with those in Fennoscandia and South Africa.

Visible light communication with efficient far-red/near-infrared polymer light-emitting diodes

Visible light communication(VLC)is a wireless technology that relies on optical intensity modulation and is potentially a game changer for internet-of-things(IoT)connectivity.However,VLC is hindered by the low penetration depth of visible light in non-transparent media.One solution is to extend operation into the“nearly(in)visible”near-infrared(NIR,700-1000 nm)region,thus also enabling VLC in photonic bio-applications,considering the biological tissue NIR semitransparency,while conveniently retaining vestigial red emission to help check the link operativity by simple eye inspection.Here,we report new far-red/NIR organic light-emitting diodes(OLEDs)with a 650-800 nm emission range and external quantum efficiencies among the highest reported in this spectral range(>2.7%,with maximum radiance and luminance of 3.5 mW/cm^(2) and 260 cd/m^(2),respectively).With these OLEDs,we then demonstrate a“real-time”VLC setup achieving a data rate of 2.2 Mb/s,which satisfies the requirements for IoT and biosensing applications.These are the highest rates ever reported for an online unequalised VLC link based on solution-processed OLEDs.

Three-dimensional coherent X-ray diffraction imaging via deep convolutional neural networks

As a critical component of coherent X-ray diffraction imaging(CDI),phase retrieval has been extensively applied in X-ray structural science to recover the 3D morphological information inside measured particles.Despite meeting all the oversampling requirements of Sayre and Shannon,current phase retrieval approaches still have trouble achieving a unique inversion of experimental data in the presence of noise.Here,we propose to overcome this limitation by incorporating a 3D Machine Learning(ML)model combining(optional)supervised learning with transfer learning.The trained ML model can rapidly provide an immediate result with high accuracy which could benefit real-time experiments,and the predicted result can be further refined with transfer learning.More significantly,the proposed ML model can be used without any prior training to learn the missing phases of an image based on minimization of an appropriate‘loss function’alone.We demonstrate significantly improved performance with experimental Bragg CDI data over traditional iterative phase retrieval algorithms.

Towards efficient near-infrared fluorescent organic light-emitting diodes

The energy gap law(E_(G)-law)and aggregation quenching are the main limitations to overcome in the design of near-infrared(NIR)organic emitters.Here,we achieve unprecedented results by synergistically addressing both of these limitations.First,we propose porphyrin oligomers with increasing length to attenuate the effects of the E_(G)-law by suppressing the non-radiative rate growth,and to increase the radiative rate via enhancement of the oscillator strength.Second,we design side chains to suppress aggregation quenching.We find that the logarithmic rate of variation in the non-radiative rate vs.E_(G)is suppressed by an order of magnitude with respect to previous studies,and we complement this breakthrough by demonstrating organic light-emitting diodes with an average external quantum efficiency of-1.1%,which is very promising for a heavy-metal-free 850 nm emitter.We also present a novel quantitative model of the internal quantum efficiency for active layers supporting triplet-to-singlet conversion.These results provide a general strategy for designing high-luminance NIR emitters.