Surface charge transfer doping for two-dimensional semiconductor-based electronic and optoelectronic devices

Doping of semiconductors,i.e.,accurately modulating the charge carrier type and concentration in a controllable manner,is a key technology foundation for modern electronics and optoelectronics.However,the conventional doping technologies widely utilized in silicon industry,such as ion implantation and thermal diffusion,always fail when applied to two-dimensional(2D)materials with atomically-thin nature.Surface charge transfer doping(SCTD)is emerging as an effective and non-destructive doping technique to provide reliable doping capability for 2D materials,in particular 2D semiconductors.Herein,we summarize the recent advances and developments on the SCTD of 2D semiconductors and its application in electronic and optoelectronic devices.The underlying mechanism of STCD processes on 2D semiconductors is briefly introduced.Its impact on tuning the fundamental properties of various 2D systems is highlighted.We particularly emphasize on the SCTD-enabled high-performance 2D functional devices.Finally,the challenges and opportunities for the future development of SCTD are discussed.

From protonation & Li-rich contamination to grain-boundary segregation: Evaluations of solvent-free vs. wet routes on preparing Li_(7)La_(3)Zr_(2)O_(12) solid electrolyte

Garnet-type Li_(7)La_(3)Zr_(2)O_(12)(LLZO) has been recognized as a candidate solid electrolyte for high-safety Lianode based solid-state batteries because of its electro-chemical stability against Li-metal and high ionic conductivity. Solvent(e.g., isopropanol(IPA)) has been commonly applied for preparing LLZO powders and ceramics. However, the deterioration of the proton-exchange between LLZO and IPA/absorbed moisture during the mixing and tailoring route has aroused less attention. In this study, a solvent-free dry milling route was developed for preparing the LLZO powders and ceramics. For orthogonal four categories of samples prepared using solvent-free and IPA-assisted routes in the mixing and tailoring processes, the critical evaluation was conducted on the crystallinity, surficial morphology, and contamination of ascalcinated and as-tailored particles, the cross-sectional microstructure of green and sintered pellets,the morphology and electro-chemical properties of grain boundaries in ceramics, as well as the interfacial resistance and performance of Li anode based symmetric batteries. The wet route introduced Li-rich contaminations(e.g., Li OH·H)_(2)O and Li)_(2)CO)_(3)) onto the surfaces of LLZO particles and Li-Ta-O segregations at the adjacent and triangular grain boundaries. The LLZO solid electrolytes prepared through dry mixing in combination with the dry tailoring route without the use of any solvent were found to the optimal performance. The fundamental material properties in the whole LLZO preparation process were found, which are of guiding significance to the development of LLZO powder and ceramic production craft.

Giant Goos–Hnchen shifts of waveguide coupled long-range surface plasmon resonance mode

A hybrid structure based on a planar waveguide （PWG） mode coupling a long-range surface plasmon resonance （LRSPR） mode is proposed to enhance the GH shift. Both the PWG mode and LRSPR mode can be in strong resonance, and these two modes can be coupled together due to the normal-mode splitting. The largest GH shift of PWG-coupled LRSPR structure is 4156 times that of the incident beam, which is 23 times and 3.6 times that of the surface plasmon resonance （SPR） structure and the LRSPR structure, respectively. As a GH shift sensor, the highest sensitivity of 4.68 x 107 λ is realized in the coupled structure. Compared with the sensitivity of the traditional SPR structure, the sensitivity of our structure is increased by more than 2 orders, which theoretically indicates that the proposed configuration can be applied to the field of high-sensitivity sensors in the future.

Carbon Supported MoO_(2) Spheres Boosting Ultra-Stable Lithium Storage with High Volumetric Density

As important ingredients in lithium-ion battery,the Coulombic efficiency and power density greatly impact the electrochemical performances.Although recent literatures have reported nano-porous materials to enhance the specific capacities,intrinsic drawbacks such as poor initial Coulombic efficiency and low volumetric capacity could not be avoided.Herein,we propose a strategy to prepare carbon supported MoO_(2)spheres used for lithium-ion battery with high volumetric capacity density.A high initial Coulombic efficiency of 76.5%is obtained due to limited solid electrolyte interface film formed on the exposed surface.Meantime,the sample with an optimal carbon content and a proper structural strength reveals a higher reversible capacity of 956 mA h g^(-1)than the theoretical capacity of crystalline Mo O_(2)(838 mA h g^(-1))and a high capacity retention ratio of 96.4%after 100 cycles at 0.5 A g^(-1).And an effective compaction capacity density(under 5 MPa)of 670 mA h cm^(-3)of the spheres proves its potential value in practical applications.

Giant photonic spin Hall effect in momentum space in a structured metamaterial with spatially varying birefringence

The photonic spin Hall effect(SHE)in the reflection and refraction at an interface is very weak because of the weak spin-orbit interaction.Here,we report the observation of a giant photonic SHE in a dielectric-based metamaterial.The metamaterial is structured to create a coordinate-dependent,geometric Pancharatnam–Berry phase that results in an SHE with a spin-dependent splitting in momentum space.It is unlike the SHE that occurs in real space in the reflection and refraction at an interface,which results from the momentum-dependent gradient of the geometric Rytov–Vladimirskii–Berry phase.We theorize a unified description of the photonic SHE based on the two types of geometric phase gradient,and we experimentally measure the giant spin-dependent shift of the beam centroid produced by the metamaterial at a visible wavelength.Our results suggest that the structured metamaterial offers a potential method of manipulating spin-polarized photons and the orbital angular momentum of light and thus enables applications in spin-controlled nanophotonics.

Oxygen-induced controllable p-type doping in 2D semiconductor transition metal dichalcogenides

Exposure to oxygen alters the physical and chemical properties of two-dimensional(2D)transition metal dichalcogenides(TMDs).In particular,oxygen in the ambient may influence the device stability of 2D TMDs over time.Engineering the doping of 2D TMDs,especially hole doping is highly desirable towards their device function.Herein,controllable oxygen-induced p-type doping in a range of hexagonal(MoTe2,WSe2,MoSe2 and PtSe2)and pentagonal(PdSe2)2D TMDs are demonstrated.Scanning tunneling microscopy,electrical transport and X-ray photoelectron spectroscopy are used to probe the origin of oxygen-derived hole doping.Three mechanisms are postulated that contribute to the hole doping in 2D TMDs,namely charge transfer from absorbed oxygen molecules,surface oxides,and chalcogen atom substitution.This work provides insights into the doping effects of oxygen,enabling the engineering of 2D TMDs properties for nanoelectronic applications.

Broadband ultrafast nonlinear optical response of few-layers graphene: toward the mid-infrared regime

Gapless linear energy dispersion of graphene endows it with unique nonlinear optical properties, including broadband nonlinear absorption and giant nonlinear refractive index. Herein, we experimentally observed that fewlayers graphene has obvious nonlinear absorption and large nonlinear refraction, as investigated by the Z-scan technique in the mid-infrared（mid-IR） regime. Our study may not only, for the first time to our knowledge, verify the giant nonlinear refractive index of graphene(～10-7cm2∕W) at the mid-IR, which is 7 orders of magnitude larger than other conventional bulk materials, but also provide some new insights for graphene-based mid-IR photonics,potentially leading to the emergence of several new conceptual mid-IR optoelectronics devices.

Improved common-path spectral interferometer for single-shot terahertz detection

To seek high signal-to-noise ratio(SNR) is critical but challenging for single-shot intense terahertz(THz)coherent detection. This paper presents an improved common-path spectral interferometer for single-shot THz detection with a single chirped pulse as the probe for THz electro-optic(EO) sampling. Here, the spectral interference occurs between the two orthogonal polarization components with a required relative time delay generated with only a birefringent plate after the EO sensor. Our experiments show that this interferometer can effectively suppress the noise usually suffered in a non-common-path interferometer. The measured single-shot SNR is up to 88.85, and the measured THz waveforms are independent of the orientation of the used Zn Te EO sensor, so it is easy to operate and the results are more reliable. These features mean that the interferometer is quite qualified for applications where strong THz pulses, usually with single-shot or low repetition rate, are indispensable.

Stepwise-Nanocavity-Assisted Transmissive Color Filter Array Microprints

Visible-light color flters using patterned nanostructures have attracted much interest due to their various advantages such as compactness,enhanced stability,and environmental friendliness compared with traditional pigment or dye-based optical flters.While most existing studies are based on planar nanostructures with lateral variation in size,shape,and arrangement,the vertical dimension of structures is a long-ignored degree of freedom for the structural colors.Herein,we demonstrate a synthetic platform for transmissive color flter array by coordinated manipulations between height-varying nanocavities and their lateral flling fractions.Te thickness variation of those nanocavities has been fully deployed as an alternative degree of freedom,yielding vivid colors with wide gamut and excellent saturation.Experimental results show that the color-rendering capability of the pixelated nanocavities can be still retained as pixels are miniaturized to 500 nm.Crosstalk between closely spaced pixels of a Bayer color flter arrangement was calculated,showing minimal crosstalk for 1μm2 square subpixels.Our work provides an approach to designing and fabricating ultracompact color flter arrays for various potential applications including stained-glass microprints,microspectrometers,and high-resolution image sensing systems.

Forty-five terawatt vortex ultrashort laser pulses from a chirped-pulse amplification system

We report on a vortex laser chirped-pulse amplification(CPA)system that delivers pulses with a peak power of 45 TW.A focused intensity exceeding 1019 W/cm2 has been demonstrated for the first time by the vortex amplification scheme.Compared with other schemes of strong-field vortex generation with high energy flux but narrowband vortex-converting elements at the end of the laser,an important advantage of our scheme is that we can use a broadband but size-limited q-plate to realize broadband mode-converting in the front end of the CPA system,and achieve high-power amplification with a series of amplifiers.This method is low cost and can be easily implemented in an existing laser system.The results have verified the feasibility to obtain terawatt and even petawatt vortex laser amplification by a CPA system,which has important potential applications in strong-field laser physics,for example,generation of vortex particle beams with orbital angular momentum,fast ignition for inertial confinement fusion and simulation of the extreme astrophysical environment.

Controlling phase transition in WSe_(2) towards ideal n-type transistor

Two-dimensional(2D)transition metal dichalcogenides(TMDs)have been rapidly established as promising building blocks for versatile atomic scale circuits and multifunctional devices.However,the high contact resistance in TMDs based transistors seriously hinders their applications in complementary electronics.In this work,we show that an Ohmic homojunction n-type tungsten diselenide(WSe_(2))transistor is realized through spatially controlling cesium(Cs)doping region near the contacts.We find that the remarkable electron doping effect of Cs stimulates a semiconductor to metal(2H to 1T')phase transition in WSe_(2),and hence the formation of 2H-1T’hetero-phase contact.Our method significantly optimizes the WSe_(2) transport behavior with a perfect low subthreshold swing of-61 mV/dec and ultrahigh current on/off ratio exceeding-10^(9).Meanwhile,the electron mobility is enhanced by nearly 50 times.We elucidate that the ideal n-type behavior originates from the negligible Schottky barrier height of~19 meV and low contact resistance of-0.9Ωk·μm in the 2H-1T’homojunction device.Moreover,based on the Ohmic hetero-phase configuration,a WSe_(2) inverter is achieved with a high gain of~270 and low power consumption of-28 pW.Our findings envision Cs functionalization as an effective method to realize ideal Ohmic contact in 2D WSe_(2) transistors towards high performance complementary electronic devices.

Recent progress in multi-wavelength fiber lasers:principles,status,and challenges

In recent years,multi-wavelength fiber lasers play a significant role in plenty of fields,ranging from optical communications to mechanical processing and laser biomedicine,owing to their high beam quality,low cost,and excellent heat dissipation properties.Benefitting from increasing maturity of optical elements,the multi-wavelength fiber laser has made rapid developments.In this review,we summarize and analyze diverse implementation methods covering continuous wave and pulsed fiber lasers at room temperature conditions:inserting an optical filter device and intensity-dependent loss structure in the resonant cavity,and applying ultrafast nonlinear optical response of materials and a dual-cavity structure.Finally,future challenges and perspectives of the multi-wavelength fiber laser are discussed and addressed.

Aqueous Zn^(2+)/Na^(+) dual-salt batteries with stable discharge voltage and high Coulombic efficiency by systematic electrolyte regulation

While aqueous Zn-Na hybrid batteries have garnered widespread attention because of their low cost and high safety,it is still challenging to achieve long cycle-life and stable discharge-voltage due to sluggish reaction kinetics,zinc dendrite formation,and side reactions.Herein,we design a Zn^(2+)/Na^(+) dual-salt battery,in which sodiation of the NVP cathode favors zinc intercalation under an energy threshold,leading to decoupled redox reactions on the cathode and anode.Systematic investigations of the electrolyte effects show that the ion intercalation mechanism and the kinetics in the mixture of triflate-and acetate-based electrolytes are superior to those in the common acetate-only electrolytes.As a result,we have achieved fast discharging capability,suppressed zinc dendrites,a stable discharge voltage at 1.45 V with small polarization,and nearly 100%Coulombic efficiency in the dual-salt mixture electrolyte with optimized concentration of 1 M Zn(OAc)_(2)+1 M NaCF_(3)SO_(3).This work demonstrates the importance of electrolyte regulation in aqueous dual-salt hybrid batteries for the energy storage.

Sb掺杂的CaZnOS层状半导体中的宽带多模发射

力致发光(ML)智能材料由于其独特的机械能-光能转换特性,有望用于应力传感器、新型显示和先进的柔性光电器件.然而,单一材料的窄波长范围ML发射特性限制了它们的应用范围.在这项工作中,我们报道了Sb掺杂的Ca Zn OS层状半导体中的宽带多模态发射.使用高温固相法合成了一系列具有不同Sb^(3+)掺杂浓度的Ca Zn OS层状结构粉末.Ca Zn OS:Sb^(3+)荧光粉实现了400–900 nm ML的宽谱发光范围,可调光致发光,两个发射峰位于465和620 nm,我们还系统研究了X射线诱导发光特性.我们还实现了Sb^(3+)和Bi^(3+)共掺杂样品的超宽暖白光ML发射.因此,这些ML荧光粉将有望用于智能照明、显示、可见应力传感器以及X射线成像和检测.

Graphene/MoS2 heterostructure:a robust mid-infrared optical modulator for Er3+-doped ZBLAN fiber laser

We have prepared the graphene∕MoS2 heterostructure by a hydrothermal method, and presented its nonlinear absorption parameters and application as a nonlinear optical modulator in the mid-infrared region.Using the nonlinear optical modulator, stable passively Q-switched operation of an Er^（3＋）-doped ZrF4-BaF2-LaF3-AlF3-NaF（ZBLAN） fiber laser at ~2.8 μm can be obtained. The Q-switched Er^（3＋）-doped ZBLAN fiber laser can yield per-pulse energy up to 2.2 μJ with the corresponding pulse width and pulse repetition rate of 1.9 μs and 45 kHz, respectively. Our results indicate that the graphene∕MoS2 heterostructure can be a robust optical modulator for pulsed lasers in the mid-infrared spectral range.

Chiral self-assembly of terminal alkyne and selenium clusters organic–inorganic hybrid

The on-surface self-assembly of inorganic atomic clusters and organic molecules offers significant opportunities to design novel hybrid materials with tailored functionalities.By adopting the advantages from both inorganic and organic components,the hybrid self-assembly molecules have shown great potential in future optoelectrical devices.Herein,we report the co-deposition of 4,8-diethynylbenzo[1,2-d-4,5-d0]bisoxazole(DEBBA)and Se atoms to produce a motif-adjustable organic–inorganic hybrid self-assembly system via the non-covalent interactions.By controlling the coverage of Se atoms,various chiral molecular networks containing Se,Se_(6),Se_(8),and terminal alkynes evolved on the Ag(111)surface.In particular,with the highest coverage of Se atoms,phase segregation into alternating one-dimensional chains of non-covalently bonded Se_(8) clusters and organic ligands has been noticed.The atom-coverage dependent evolution of self-assembly structures reflects the remarkable structural adaptability of Se clusters as building blocks based on the spontaneous resize to reach the maximum non-covalent interactions.This work has significantly extended the possibilities of flexible control in self-assembly nanostructures to enable more potential functions for broad applications.

Superior optical Kerr effects induced by two-dimensional excitons

Materials with strong optical Kerr effects(OKEs)are crucial for a broad range of applications,such as all-optical data processing and quantum information.However,the underlying OKE mechanism is not clear in 2D materials.Here,we reveal key insights of the OKE associated with 2D excitons.An admirably succinct formalism is derived for predicting the spectra and the magnitude of the nonlinear refractive index(n_(2))of 2D materials.The predicted n_(2)spectra are consistent with reported experimental data and exhibit pronounced excitonic resonances,which is distinctively different from bulk semiconductors.The n_(2) value is predicted to be 3×10^(−10)cm^(2)/W for a 2D layered perovskite at low temperature as 7 K,which is four orders of magnitude larger than those of bulk semiconductors.The superior OKE induced by 2D excitons would give rise to a narrow refractive index-near-zero region for intense laser light.Furthermore,we demonstrate that the 2D layered perovskite should exhibit the best OKE efficiency(W_(FOM)=1.02,T_(FOM)=0.14)at 1550 nm,meeting the material requirements for all-optical switching.Our findings deepen the understanding of the OKE of 2D semiconducting materials and pave the way for highly efficient all-optical excitonic devices.

High-gain amplification for femtosecond optical vortex with mode-control regenerative cavity

Ultra-intense femtosecond vortex pulses can provide an opportunity to investigate the new phenomena with orbital angular momentum(OAM)involved in extreme cases.This paper reports a high gain optical vortex amplifier for intense femtosecond vortex pulses generation.Traditional regeneration amplifiers can offer high gain for Gaussian mode pulses but cannot amplify optical vortex pulses while maintaining the phase singularity because of mode competition.Here,we present a regeneration amplifier with a ring-shaped pump.By controlling the radius of the pump,the system can realize the motivation of the Laguerre–Gaussian[LG0,1(−1)]mode and the suppression of the Gaussian mode.Without seeds,the amplifier has a donut-shaped output containing two opposite OAM states simultaneously,as our prediction by simulation.If seeded by a pulse of a topologic charge of 1 or−1,the system will output an amplified LG0,1(−1)mode pulse with the same topologic charge as the seed.To our knowledge,this amplifier can offer the highest gain as 1.45×106 for optical vortex amplification.Finally,we obtain a 1.8 mJ,51 fs compressed optical vortex seeded from a 2 nJ optical vortex.