Geometric regulation of collective cell tangential ordering migration

Collective cell migration is a coordinated movement of multi-cell systems essential for various processes throughout life.The collective motions often occur under spatial restrictions,hallmarked by the collective rotation of epithelial cells confined in circular substrates.Here,we aim to explore how geometric shapes of confinement regulate this collective cell movement.We develop quantitative methods for cell velocity orientation analysis,and find that boundary cells exhibit stronger tangential ordering migration than inner cells in circular pattern.Furthermore,decreased tangential ordering movement capability of collective cells in triangular and square patterns are observed,due to the disturbance of cell motion at unsmooth corners of these patterns.On the other hand,the collective cell rotation is slightly affected by a convex defect of the circular pattern,while almost hindered with a concave defect,also resulting from different smoothness features of their boundaries.Numerical simulations employing cell Potts model well reproduce and extend experimental observations.Together,our results highlight the importance of boundary smoothness in the regulation of collective cell tangential ordering migration.

Regulation of actin cytoskeleton via photolithographic micropatterning

Actin cytoskeleton plays crucial roles in various cellular functions.Extracellular matrix(ECM)can modulate cell morphology by remodeling the internal cytoskeleton.To define how geometry of ECM regulates the organization of actin cytoskeleton,we plated individual NIH 3T3 cells on micropatterned substrates with distinct shapes and sizes.It was found that the stress fibers could form along the nonadhesive edges of T-shaped pattern,but were absent from the opening edge of V-shaped pattern,indicating that the organization of actin cytoskeleton was dependent on the mechanical environment.Furthermore,a secondary actin ring was observed on 50μm circular pattern while did not appear on 30μm and 40μm pattern,showing a size-dependent organization of actin cytoskeleton.Finally,osteoblasts,MDCK and A549 cells exhibited distinct organization of actin cytoskeleton on T-shaped pattern,suggesting a cell-type specificity in arrangement of actin cytoskeleton.Together,our findings brought novel insight into the organization of actin cytoskeleton on micropatterned environments.

The real-time dynamic holographic display of LN:Bi,Mg crystals and defect-related electron mobility

Holographic display has attracted widespread interest because of its ability to show the complete information of the object and bring people an unprecedented sense of presence. The absence of ideal recording materials has hampered the realization of their commercial applications. Here we report that the response time of a bismuth and magnesium codoped lithium niobate(LN:Bi,Mg) crystal is shortened to 7.2 ms and a sensitivity as high as 646 cm/J. The crystal was used to demonstrate a real-time holographic display with a refresh rate of 60 Hz, as that of the popular high-definition television. Moreover, the first-principles calculations indicate that the electron mobility while Bi occupying Nb-site is significantly greater than that in Li-site, which directly induces the fast response of LN:Bi,Mg crystals when the concentration of Mg is above its doping threshold.

Structural and functional studies of erythrocyte membrane-skeleton by single-cell and single-molecule techniques

As the indispensable oxygen-transporting cells,erythrocytes exhibit extreme deformability and amazing stability as they are subject to huge reversible shear stress and extrusion force during massive circulation in the body.The unique architecture of spectrin-actin-based membraneskeleton is considered to be responsible for such excellent mechanical properties of erythrocytes.Although erythrocytes have been recognized for more than 300 years,myriad questions about membrane-skeleton constantly attract people's attention.Here,we summarize the kinds of distinctive single-cell and single-molecule techniques that were used to investigate the structure and function of erythrocyte membrane-skeleton at macro and micro levels.

Deep-learning-empowered synthetic dimension dynamics:morphing of light into topological modes

Synthetic dimensions(SDs)opened the door for exploring previously inaccessible phenomena in high-dimensional space.However,construction of synthetic lattices with desired coupling properties is a challenging and unintuitive task.Here,we use deep learning artificial neural networks(ANNs)to construct lattices in real space with a predesigned spectrum of mode eigenvalues,and thus to validly design the dynamics in synthetic mode dimensions.By employing judiciously chosen perturbations(wiggling of waveguides at desired frequencies),we show resonant mode coupling and tailored dynamics in SDs.Two distinct examples are illustrated:one features uniform synthetic mode coupling,and the other showcases the edge defects that allow for tailored light transport and confinement.Furthermore,we demonstrate morphing of light into a topologically protected edge mode with modified Su-Schrieffer-Heeger photonic lattices.Such an ANN-assisted construction of SDs may advance toward“utopian networks,”opening new avenues for fundamental research beyond geometric limitations as well as for applications in mode lasing,optical switching,and communication technologies.

Oxidation Resistance of In Situ Reaction/Hot Pressing Synthesized Ti_(2)AlC-20%TiB_(2) Composite at 600-900℃in Air

The oxidation behavior and kinetics of Ti_(2)AlC-20vol.%TiB_(2) composite at 600-900℃ in air were investigated.The results showed that the oxidation kinetics of the composite followed a logarithmic law within the given temperature range,which indicated that the composites had excellent oxidation resistance.The selective oxidation of Al in Ti_(2)AlC was greatly enhanced,which facilitated the formation of a continuous and dense protective layer of Al_(2)O_(3).Meanwhile,the existence of molten B_(2)O_(3) inhibited the outward diffusion of Ti and inward diffusion of oxygen,which prevented the growth of anatase TiO_(2) at 600℃ and rutile TiO_(2) at 700-900℃.Therefore,the incorporation of TiB_(2) completely inhibited the abnormally rapid oxidation of bulk Ti_(2)AlC at 600℃ and improved its oxidation resistance at 700-900℃.

Efficient second and third harmonic generation in dual-layer lithium niobate microdisk resonator

Lithium niobate thin film frequency doubler has extensive applications in the preparation of classical and quantum sources.In this study,we successfully fabricated microdisk resonators with a quality factor of 2.2×10^(5) in reverse-polarization dual-layer x-cut lithium niobate for the first time.Based on the modal phase matching condition,efficient second harmonic generation with a record normalized conversion efficiency of~56000%W-1 and cascaded third harmonic generation with an efficiency of~6500%W-2 were obtained in the microdisk resonator.Compared with the periodically poled lithium niobate microcavity,the complex domain structure preparation processes are avoided.Our work provides a scheme for achieving highly efficient second-order nonlinear effects in non-periodically poled microcavities.

Advances in lithium niobate thin-film lasers and amplifiers: a review

Lithium niobate(LN)thin film has received much attention as an integrated photonic platform,due to its rich and great photoelectric characteristics,based on which various functional photonic devices,such as electro-optic modulators and nonlinear wavelength converters,have been demonstrated with impressive performance.As an important part of the integrated photonic system,the long-awaited laser and amplifier on the LN thin-film platform have made a series of breakthroughs and important progress recently.In this review paper,the research progress of lasers and amplifiers realized on lithium niobate thin film platforms is reviewed comprehensively.Specifically,the research progress on optically pumped lasers and amplifiers based on rare-earth ions doping of LN thin films is introduced.Some important parameters and existing limitations of the current development are discussed.In addition,the implementation scheme and research progress of electrically pumped lasers and amplifiers on LN thin-film platforms are summarized.The advantages and disadvantages of optically and electrically pumped LN thin film light sources are analyzed.Finally,the applications of LN thin film lasers and amplifiers and other on-chip functional devices are envisaged.

Realization of photonic p-orbital higher-order topological insulators

The orbital degrees of freedom play a pivotal role in understanding fundamental phenomena in solid-state materials as well as exotic quantum states of matter including orbital superfluidity and topological semimetals.Despite tremendous efforts in engineering synthetic cold-atom,as well as electronic and photonic lattices to explore orbital physics,thus far high orbitals in an important class of materials,namely,higher-order topological insulators(HOTIs),have not been realized.Here,we demonstrate p-orbital corner states in a photonic HOTI,unveiling their underlying topological invariant,symmetry protection,and nonlinearity-induced dynamical rotation.In a Kagome-type HOTI,we find that the topological protection of p-orbital corner states demands an orbital-hopping symmetry in addition to generalized chiral symmetry.Due to orbital hybridization,nontrivial topology of the p-orbital HOTI is“hidden”if bulk polarization is used as the topological invariant,but well manifested by the generalized winding number.Our work opens a pathway for the exploration of intriguing orbital phenomena mediated by higher-band topology applicable to a broad spectrum of systems.

Highly efficient on-chip erbium–ytterbium co-doped lithium niobate waveguide amplifiers

The ability to amplify optical signals is of paramount importance in photonic integrated circuits(PICs). Recently,lithium niobate on insulator(LNOI) has attracted increasing interest as an emerging PIC platform. However, the shortage of efficient active devices on the LNOI platform limits the development of optical amplification. Here,we report an efficient waveguide amplifier based on erbium and ytterbium co-doped LNOI by using electron beam lithography and an inductively coupled plasma reactive ion etching process. We have demonstrated that signal amplification emerges at a low pump power of 0.1 mW, and the net internal gain in the communication band is 16.52 dB/cm under pumping of a 974 nm continuous laser. Benefiting from the efficient pumping facilitated by energy transfer between ytterbium and erbium ions, an internal conversion efficiency of 10% has been achieved, which is currently the most efficient waveguide amplifier under unidirectional pumping reported on the LNOI platform, to our knowledge. This work proposes an efficient active device for LNOI integrated optical systems that may become an important fundamental component of future lithium niobate photonic integration platforms.

A novel medium-entropy(TiVNb)_(2)AlC MAX phase:Fabrication,microstructure,and properties

Medium-or high-entropy materials have great potential for applications due to their diverse compo-sitions and unexpected physicochemical properties.Herein,a novel medium-entropy(TiVNb)_(2)AlC was synthesized via hot pressing at 1400℃from three individual M_(2)AlC(M=Ti,V,Nb)MAX phases.The microstructure of(TiVNb)_(2)AlC was characterized from the microscale to the atomic scale by scanning electron microscope microscopy(SEM),scanning transmission electron microscopy(STEM),and energy dispersive spectroscopy(EDS).The results showed that Ti,V,and Nb atoms were fully solid-soluble in the M-sites of the M_(2)AlC MAX phase.Compared with three individual MAX phases,the thermal conduc-tivity of(TiVNb)_(2)AlC was reduced greatly in the temperature range of 293-1473 K,and its mechanical properties(including Young’s modulus,Vickers hardness,and bending strength)were all increased due to the solid solution strengthening and electronic mechanism.

High-spatial-resolution composition analysis of micro/nanostructures with a nanoscale compositional variation

The composition of materials in a micro-/nano-devices plays a key role in determining their mechanical,physical,and chemical properties.Especially,for devices with a compositional change on nanoscale which can often be achieved by point-by-point direct writing technology using a focused ion beam(FIB),electron beam(EB),or laser beam(LB),but so far,nanoscale composition analysis of a large-area micro/nano structures with a variation composition remains a big challenge in cost,simpleness,and flexibility.Here we present a feasible route to realize large-area composition analysis with nanoscale spatial resolution by using Raman spectroscopy.We experimentally verified the capability of this method by analyzing a complex Sn-SnOx system of a microscale grayscale mask with nanoscale spatial resolution of composition.Further analyses using Auger electron spectroscopy,transmission electron microscopy,and atomic force microscopy indicated the effectiveness and practicality of our method.This work opens up a way to analyze the composition of a large-area complex system at a nanoscale spatial resolution,and the method can be extended to many other material systems.

Li^(+)doping induced zero-thermal quenching in Cs_(3)Zn_(6-x-y)B_(9)O_(21):xEu^(3+),yLi^(+)(0≤x≤0.10,0.06≤y≤0.16)

Thermal stability is a crucial index to assess application value of high-power LEDs,which is related to lattice defects.Herein,an effective structure-engineering strategy is proposed to achieve excellent properties.Under the 394 nm excitation,Cs_3Zn_(5.94)B_9O_(21):0.06Eu^(3+)possesses two characteristic emissions peaked at 591 and 612 nm with limited thermal stability.By introducing Li^(+)ions into the lattice,the sample exhibits high color purity and excellent zero-thermal quenching because the defect contents of the phosphor can be effectively modulated via charge-compensation effect.Then,under the stimulus of high temperature,the corresponding trap levels with a suitable depth(E=1.27 eV)will release electrons to recombine with the luminescent centers,compensating for the energy loss.The study provides a meaningful guide for optimizing and designing novel functional photoluminescent materials.

Advances in on-chip photonic devices based on lithium niobate on insulator

Crystalline lithium niobate(LN)is an important optical material because of its broad transmission window that spans from ultraviolet to mid-infrared and its large nonlinear and electro-optic coefficients.Furthermore,the recent development and commercialization of LN-on-insulator(LNOI)technology has opened an avenue for the realization of integrated on-chip photonic devices with unprecedented performances in terms of propagation loss,optical nonlinearity,and electro-optic tunability.This review begins with a brief introduction of the history and current status of LNOI photonics.We then discuss the fabrication techniques of LNOI-based photonic structures and devices.The recent revolution in the LN photonic industry has been sparked and is still being powered by innovations of the nanofabrication technology of LNOI,which enables the production of building block structures,such as optical microresonators and waveguides of unprecedented optical qualities.The following sections present various on-chip LNOI devices categorized into nonlinear photonic and electro-optic tunable devices and photonic-integrated circuits.Some conclusions and future perspectives are provided.

Integrated lithium niobate single-mode lasers by the Vernier effect

Microcavity lasers based on erbium-doped lithium niobate on insulator(LNOI),which are key devices for LNOI integrated photonics,have attracted significant attention recently.In this study,we report the realization of a C-band single-mode laser using the Vernier effect in two coupled erbium-doped LNOI microrings with different radii under the pump of a 980-nm continuous laser.The laser,operating stably over a large range of pumping power,has a pump threshold of about 200μW and a side-mode suppression ratio exceeding 26 dB.The high-performance LNOI single-mode laser will promote the development of lithium niobate integrated photonics.

Microdisk lasers on an erbium-doped lithium-niobite chip

Lithium niobate on insulator(LNOI) provides a platform for the fundamental physics investigations and practical applications of integrated photonics. However, as an indispensable building block of integrated photonics, lasers are in short supply. In this paper, erbium-doped LNOI laser in the 1550-nm band was demonstrated in microdisk cavities with high quality factors fabricated in batches by UV exposure, inductively coupled plasma reactive ion etching, and chemomechanical polishing. The threshold and conversion efficiency of the erbium-doped LNOI microdisk laser were measured to be lower than 1 m W and 6.5×10^(-5)%, respectively. This work will benefit the development of integrated photonics based on LNOI.

On-chip erbium-doped lithium niobate waveguide amplifiers [Invited]

Lithium niobate on insulator(LNOI), as an emerging and promising optical integration platform, faces shortages of on-chip active devices including lasers and amplifiers. Here, we report the fabrication of on-chip erbium-doped LNOI waveguide amplifiers based on electron beam lithography and inductively coupled plasma reactive ion etching. A net internal gain of ~30 d B/cm in the communication band was achieved in the fabricated waveguide amplifiers under the pump of a974 nm continuous laser. This work develops new active devices on LNOI and may promote the development of LNOI integrated photonics.

Periodically poled lithium niobate whispering gallery mode microcavities on a chip

In this study, we investigate the fabrication of periodically poled lithium niobate(PPLN) microdisk cavities on a chip. These resonators are fabricated from a PPLN film with a 16 μm poling period on insulator using conventional microfabrication techniques.The quality factor of the PPLN microdisk resonators with a 40-μm radius and a 700-nm thickness is 6.7×10~5. Second harmonic generation(SHG) with an efficiency of 2.2×10^(-6) mW(-1) is demonstrated in the fabricated PPLN microdisks. The nonlinear conversion efficiency could be considerably enhanced by optimizing the period and pattern of the poled structure and by improving the cavity quality factors.

Second-harmonic generation using d(33)in periodically poled lithium niobate microdisk resonators

A fabrication process allowing for the production of periodically poled lithium niobate(PPLN)photonic devices with any domain pattern and unit size down to 200 nm is developed by combining semiconductor fabrication techniques and piezo-force-microscopy tips polarization.Based on this fabrication process,PPLN microdisk resonators with quality factors of 8×10~4 were fabricated from a Z-cut lithium niobate film.Second-harmonic generation(SHG)utilizing d(33)in the whole cavity was demonstrated in a PPLN microdisk with a 2μm-spatialperiod radial domain pattern.The SHG conversion efficiency was measured to be 1.44×10^(-5)m W^(-1).This work paves the way to fabricate complex PPLN photonic devices and to obtain efficient nonlinear optical effects that have wide applications in both classical and quantum optics.

Nonlinear control of photonic higher-order topological bound states in the continuum

Higher-order topological insulators(HOTIs)are recently discovered topological phases,possessing symmetry-protected corner states with fractional charges.An unexpected connection between these states and the seemingly unrelated phenomenon of bound states in the continuum(BICs)was recently unveiled.When nonlinearity is added to the HOTI system,a number of fundamentally important questions arise.For example,how does nonlinearity couple higher-order topological BICs with the rest of the system,including continuum states?In fact,thus far BICs in nonlinear HOTIs have remained unexplored.Here we unveil the interplay of nonlinearity,higher-order topology,and BICs in a photonic platform.We observe topological corner states that are also BICs in a laser-written second-order topological lattice and further demonstrate their nonlinear coupling with edge(but not bulk)modes under the proper action of both self-focusing and defocusing nonlinearities.Theoretically,we calculate the eigenvalue spectrum and analog of the Zak phase in the nonlinear regime,illustrating that a topological BIC can be actively tuned by nonlinearity in such a photonic HOTI.Our studies are applicable to other nonlinear HOTI systems,with promising applications in emerging topology-driven devices.