Formation of Two-Dimensional AgTe Monolayer Atomic Crystal on Ag(111) Substrate

We report on the formation of two-dimensional monolayer AgTe crystal on Ag(111) substrates. The samples are prepared in ultrahigh vacuum by deposition of Te on Ag(111) followed by annealing. Using a scanning tunneling microscope(STM) and low electron energy diffraction(LEED), we investigate the atomic structure of the samples.The STM images and the LEED pattern show that monolayer AgTe crystal is formed on Ag(111). Four kinds of atomic structures of AgTe and Ag(111) are observed:(i) flat honeycomb structure,(ii) bulked honeycomb,(iii)stripe structure,(iv) hexagonal structure. The structural analysis indicates that the formation of the different atomic structures is due to the lattice mismatch and relief of the intrinsic strain in the AgTe layer. Our results provide a simple and convenient method to produce monolayer AgTe atomic crystal on Ag(111) and a template for study of novel physical properties and for future quantum devices.

Structured mirror array for two-dimensional collimation of a chromium beam in atom lithography

Direct-write atom lithography,one of the potential nanofabrication techniques,is restricted by some difficulties in producing optical masks for the deposition of complex structures.In order to make further progress,a structured mirror array is developed to transversely collimate the chromium atomic beam in two dimensions.The best collimation is obtained when the laser red detunes by natural line-width of transition 7S3 → 7P40 of the chromium atom.The collimation ratio is 0.45 vertically（in x axis）,and it is 0.55 horizontally（in y axis）.The theoretical model is also simulated,and success of our structured mirror array is achieved.

Two-dimensional atom localization via probe absorption in a four-level atomic system

We have investigated the two-dimensional （2D） atom localization via probe absorption in a coherently driven four-level atomic system by means of a radio-frequency field driving a hyperfine transition. It is found that the detecting probability and precision of 2D atom localization can be significantly improved via adjusting the system parameters. As a result, our scheme may be helpful in laser cooling or the atom nano-lithography via atom localization.

High-precision two-dimensional atom localization via probe absorption in an M-scheme atomic system

In the present paper, we investigate the behavior of two-dimensional atom localization in a five-level M-scheme atomic system driven by two orthogonal standing-wave fields. We find that the precision and resolution of the atom localization depends on the probe field detuning significantly. And because of the effect of the microwave field, an atom can be located at a particular position via adjusting the system parameters.

Atomic coherent states as energy eigenstates of a Hamiltonian describing a two-dimensional anisotropic harmonic potential in a uniform magnetic field

In this paper we find that a set of energy eigenstates of a two-dimensional anisotropic harmonic potential in a uniform magnetic field is classified as the atomic coherent states ｜τ） in terms of the spin values of j in the Schwinger bosonic realization. The correctness of the above conclusions can be verified by virtue of the entangled state 〈η｜ representation of the state ｜τ）.

Two-Dimensional Talbot Effect with Atomic Density Gratings

We report the experimental observation of two-dimensional Talbot effect when a resonance plane wave interacts with a two-dimensional atomic density grating generated by standing wave manipulation of ultracold Bose gases. Clear self-images of the grating and sub-images with reversed phase or fractal patterns are observed. By calculating the autocorrelation functions of the images, the behavior of periodic Talbot images is studied. The Talbot effect with two-dimensional atomic density grating expands the applications of the Talbot effect in a wide variety of research fields.

Coupled Two-Dimensional Atomic Oscillation in an Anharmonic Trap

In atomic dynamics, oscillation Mong different axes can be studied separately in the harmonic trap. When the trap is not harmonic, motion in different directions may couple together. In this work, we observe a two- dimensional oscillation by exciting atoms in one direction, where the atoms are transferred to an anharmonic region. Theoretical calculations are coincident to the experimental results. These oscillations in two dimensions not only can be used to measure trap parameters but also have potential applications in atomic interferometry and precise measurements.

Protein Conformational Change Based on a Two-dimensional Generalized Langevin Equation

A two-dimensional generalized Langevin equation is proposed to describe the protein conformational change, compatible to the electron transfer process governed by atomic packing density model. We assume a fractional Gaussian noise and a white noise through bond and through space coordinates respectively, and introduce the coupling effect coming from both fluctuations and equilibrium variances. The general expressions for autocorrelation functions of distance fluctuation and fluorescence lifetime variation are derived, based on which the exact conformational change dynamics can be evaluated with the aid of numerical Laplace inversion technique. We explicitly elaborate the short time and long time approximations. The relationship between the two-diraensional description and the one-dimensional theory is also discussed.

Generating two-dimensional quantum gases with high stability

Quantum gas microscopy has enabled the study on intriguing properties of ultracold atoms in optical lattices.It provides the cutting-edge technology for manipulating quantum many-body systems.In such experiments,atoms have to be prepared into a two-dimensional(2D)system for being resolved by microscopes with limited depth of focus.Here we report an experiment on slicing a single layer of the atoms trapped in a few layers of pancake-shaped optical traps to create a 2D system.This technique is implemented with a microwave“knife”,i.e.,a microwave field with a frequency defined by the resonant condition with the Zeeman-shifted atomic levels related to a gradient magnetic field.It is crucial to keep a stable preparation of the desired layer to create the 2D quantum gas for future experimental applications.To achieve this,the most important point is to provide a gradient magnetic field with low noises and slow drift in combination with a properly optimized microwave pulse.Monitoring the electric current source and the environmental magnetic field,we applied an actively stabilizing circuit and realized a field drift of 0.042(3)mG/hour.This guarantees creating the single layer of atoms with an efficiency of 99.92(3)%while atoms are hardly seen in other layers within 48 hours,satisfying future experimental demands on studying quantum many-body physics.

Two-Dimensional Organometallic TM3–C12S12 Monolayers for Electrocatalytic Reduction of CO2

Organometallic nanosheets are a versatile platform for design of efficient electrocatalyst materials due to their high surface area and uniform dispersion of metal active sites.In this paper,we systematically investigate the electrocatalytic performance of the first transition metal series TM3–C12S12 monolayers on CO2 using spin-polarized density functional theory.The calculations show that M3–C12S12 exhibits excellent catalytic activity and selectivity in the catalytic reduction in CO2.The main reduction products of Sc,Ti,and Cr are CH4.V,Mn,Fe and Zn mainly produce HCOOH,and Co produces HCHO,while CO is the main product for Ni and Cu.For Sc,Ti,and Cr,the overpotentials are>0.7 V,while for V,Mn,Fe,Co,Ni,Cu,Zn,the overpotentials are very low and range from 0.27 to 0.47 V.Therefore,our results indicate that many of the M3–C12S12 monolayers are expected to be excellent and efficient CO2 reduction catalysts.

Integrating single Ni site and PtNi alloy on two-dimensional porous carbon nanosheet for efficient catalysis in fuel cell

The performance of catalyst depends on the intrinsic activity of active sites and the structural characteristics of the support.Here,we simultaneously integrate single nickel(Ni)sites and platinum-nickel(PtNi)alloy nanoparticles(NPs)on a two-dimensional(2D)porous carbon nanosheet,demonstrating remarkable catalytic performance in the oxygen reduction reaction(ORR).The single Ni sites can activate the oxygen molecules into key oxygen-containing intermediate that is further efficiently transferred to the adjacent PtNi alloy NPs and rapidly reduced to H_(2)O,which establishes a relay catalysis between active sites.The porous structure on the carbon nanosheet support promotes the transfer of active intermediates between these active sites,which assists the relay catalysis by improving mass diffusion.Remarkably,the obtained catalyst demonstrates a half-wave potential of up to 0.942 V,a high mass activity of 0.54 A·mgPt^(−1),and negligible decay of activity after 30,000 cycles,which are all superior to the commercial Pt/C catalysts with comparable loading of Pt.The theoretical calculation results reveal that the obtained catalyst with defect structure of carbon support presents enhanced relay catalytic effect of PtNi alloy NPs and single Ni sites,ultimately realizing improved catalytic performance.This work provides valuable inspiration for developing low platinum loading catalyst,integrating single atoms and alloy with outstanding performance in fuel cell.

Progress on mechanical and tribological characterization of 2D materials by AFM force spectroscopy

Two-dimensional(2D)materials are potential candidates for electronic devices due to their unique structures and exceptional physical properties,making them a focal point in nanotechnology research.Accurate assessment of the mechanical and tribological properties of 2D materials is imperative to fully exploit their potential across diverse applications.However,their nanoscale thickness and planar nature pose significant challenges in testing and characterizing their mechanical properties.Among the in situ characterization techniques,atomic force microscopy(AFM)has gained widespread applications in exploring the mechanical behaviour of nanomaterials,because of the easy measurement capability of nano force and displacement from the AFM tips.Specifically,AFM-based force spectroscopy is a common approach for studying the mechanical and tribological properties of 2D materials.This review comprehensively details the methods based on normal force spectroscopy,which are utilized to test and characterize the elastic and fracture properties,adhesion,and fatigue of 2D materials.Additionally,the methods using lateral force spectroscopy can characterize the interfacial properties of 2D materials,including surface friction of 2D materials,shear behaviour of interlayers as well as nanoflake-substrate interfaces.The influence of various factors,such as testing methods,external environments,and the properties of test samples,on the measured mechanical properties is also addressed.In the end,the current challenges and issues in AFM-based measurements of mechanical and tribological properties of 2D materials are discussed,which identifies the trend in the combination of multiple methods concerning the future development of the in situ testing techniques.

Atomic crystals resistive switching memory

Facing the growing data storage and computing demands, a high accessing speed memory with low power and non- volatile character is urgently needed. Resistive access random memory with 4F2 cell size, switching in sub-nanosecond, cycling endurances of over 1012 cycles, and information retention exceeding 10 years, is considered as promising next- generation non-volatile memory. However, the energy per bit is still too high to compete against static random access memory and dynamic random access memory. The sneak leakage path and metal film sheet resistance issues hinder the further scaling down. The variation of resistance between different devices and even various cycles in the same device, hold resistive access random memory back from commercialization. The emerging of atomic crystals, possessing fine interface without dangling bonds in low dimension, can provide atomic level solutions for the obsessional issues. Moreover, the unique properties of atomic crystals also enable new type resistive switching memories, which provide a brand-new direction for the resistive access random memory.

Constructing two-dimensional interfacial ice-like water at room temperature for nanotribology

Water/solid interfaces play crucial roles in a wide range of physicochemical and technological processes.However,our microscopic understanding of the interfacial water under ambient temperature is relatively primitive.Herein,we report the direct experimental construction of two-dimensional(2D)ice-like water layer on hydrophilic surface at room temperature by using environment-controlled atomic force microscopy.In contrast to the prevailing view that nanoscale confinement is needed for the formation of 2D ice-like water,we find that 2D ice-like water can form on mica surface at temperatures above the freezing point without confinement.The 2D ice-like water layer shows epitaxial relation with the underlying mica lattice and good thermostability.In addition,the growth of ice-like water layer can be well controlled by the mechanical force from the scanning tip.Furthermore,the friction properties of 2D ice-like water layer are also probed by friction force microscopy.It is found that the icelike water layer can dramatically reduce the friction.These results provide deep understanding of 2D ice-like water formation on solid surfaces without nanoscale confinement and suggest means of growing 2D ices on surfaces at room temperature.

Two-dimensional novel optical lattices with multi-well traps for cold atoms or molecules

We propose some new schemes to constitute two-dimensional （2D） array of multi-well optical dipole traps for cold atoms （or molecules） by using an optical system consisting of a binary 7r-phase grating and a 2D array of rectangle microlens. We calculate the intensity distribution of each optical well in 2D array of multi-well traps and its geometric parameters and so on. The proposed 2D array of multi-well traps can be used to form novel 2D optical lattices with cold atoms （or molecules）, and form various novel optical crystals with cold atoms （or molecules）, or to perform quantum computing and quantum information processing on an atom chip, even to realize an array of all-optical multi-well atomic （or molecular） Bose- Einstein condensates （BECs） on an all-optical integrated atom （or molecule） chip.

Advanced atomic force microscopies and their applications in two-dimensional materials:a review

Scanning probe microscopy(SPM)allows the spatial imaging,measurement,and manipulation of nano and atomic scale surfaces in real space.In the last two decades,numerous advanced and functional SPM methods,particularly atomic force microscopy(AFM),have been developed and applied in various research fields,from mapping sample morphology to measuring physical properties.Herein,we review the recent progress in functional AFM methods and their applications in studies of two-dimensional(2D)materials,particularly their interfacial physical properties on the substrates.This review can inspire more exciting application works using advanced AFM modes in the 2D and functional materials fields.

Recent progress and challenges on two-dimensional material photodetectors from the perspective of advanced characterization technologies

Atomically thin two-dimensional(2D)materials exhibit enormous potential in photodetectors because of novel and extraordinary properties,such as passivated surfaces,tunable bandgaps,and high mobility.High-performance photodetectors based on 2D materials have been fabricated for broadband,position,polarization-sensitive detection,and large-area array imaging.However,the current performance of 2D material photodetectors is not outstanding enough,including response speed,detectivity,and so forth.The way to further promote the development of 2D material photodetectors and their corresponding practical applications is still a tremendous challenge.In this article,these issues of 2D material photodetectors are analyzed and expected to be solved by combining micro-nano characterization technologies.The inherent physical properties of 2D materials and photodetectors can be accurately characterized by Raman spectroscopy,transmission electron microscopy(TEM),and scattering scanning near-field optical microscope(s-SNOM).In particular,the precise probe of lattice defects,doping concentration,and near-field light absorption characteristics can promote the researches of low-noise and high-responsivity photodetectors.Scanning photocurrent microscope(SPCM)can show the overall spatial distribution of photocurrent and analyze the mechanism of photocurrent.Photoluminescence(PL)spectroscopy and Kelvin probe force microscope(KPFM)can characterize the material bandgap,work function distribution and interlayer coupling characteristics,making it possible to design high-performance photodetectors through energy band engineering.These advanced characterization techniques cover the entire process from material growth,to device preparation,and to performance analysis,and systematically reveal the development status of 2D material photodetectors.Finally,the prospects and challenges are discussed to promote the application of 2D material photodetectors.

The influence of two-dimensional organic adlayer thickness on the ultralow frequency Raman spectra of transition metal dichalcogenide nanosheets

Recently, it has been reported that physisorbed adsorbates can be trapped between the bottom surface of twodimensional(2D) materials and supported substrate to form2 D confined films. However, the influence of such 2D confined adsorbates on the properties of 2D materials is rarely explored. Herein, we combined atomic force microscopy(AFM), Kelvin probe force microscopy(KPFM) and Raman spectroscopy especially the ultralow frequency(ULF) Raman spectroscopy to explore the influence of 2D confined organic adlayer thickness on the ULF breathing modes of few-layer MoS2 and WSe2nanosheets. As the thickness of organic adlayers increased, red shift, coexistence of blue and red shifts as well as blue shift of ULF breathing mode was observed. KPFM measurement confirmed the enhanced n-doping and p-doping behaviors of organic adlayers as their thickness increased,respectively. Our results will provide new insights into the interaction between 2D confined adsorbates and bottom surface of 2D nanosheets, which could be useful for modulating properties of 2D materials.

二维氢原子与二维谐振子之间的关系

借助于su( 1 ,1 )代数找出了二维氢原子与二维谐振子之间的能量本征值、能量本征函数的关系 。

Three ultracold fermions in a two-dimensional anisotropic harmonic confinement

We calculate the energy spectrum of three identical fermionic ultracold atoms in two different internal states confined in a two-dimensional anisotropic harmonic trap.Using the solutions of the corresponding two-body problems obtained in our previous work(Chen et al 2020 Phys.Rev.A 101,053624),we derive the explicit transcendental equation for the eigen-energies,from which the energy spectrum is derived.Our results can be used for the calculation of the 3rd Virial coefficients or the studies of few-body dynamics.