Detection of Electronic Coherence via Two-Dimensional Electronic Spectroscopy in Condensed Phase

Two dimensional Fourier transforrn electronic spectroscopy （2DES） in the visible region enables direct observation of complex dynamics of molecules including quantum coherence in the condensed phase. This review aims to provide a bridge between the principles and intuitive physical description of 2DES for tutorial purpose. Special emphasis is laid upon how 2DES circumvents the restrictions from both uncertainty principle and the wave-packet collapse during the coherent detection, leading to the successful detection of the coherence in terms of energy difference between the eigenstates showing as the quantum beats; then upon the possible mixing among the pure electronic transition, single-rnode and multi-mode coupled vibronic transition leading to the observed beating phenomena. Finally, recent ad- vances in experimentally distinguishing between the electronic coherence and the vibrational coherence are briefly discussed.

Fe−C micro-alloying effect on properties of Zr_(53)Al_(11.6)Ni_(11.7)Cu_(23.7)bulk metallic glass

(Zr_(53)Al_(11.6)Ni_(11.7)Cu_(23.7))_(1−x)(Fe_(77.1)C_(22.9))_(x)(x=0−2.2,at.%)bulk metallic glasses(BMGs)were prepared by copper mold suction casting method.Their glass forming ability and physical and chemical properties were systematically investigated.The glass forming ability is firstly improved with increasing x,and then decreased when x exceeds 0.44 at.%.Both glass transition temperature and crystallization temperature are increased,while the supercooled liquid region is narrowed,with Fe−C micro-alloying.The hardness,yielding and fracture strength,and plasticity firstly increase and then decrease when x reaches up to 1.32 at.%.The plasticity of the BMG(x=1.32 at.%)is six times that of the Fe-free and C-free BMG.In addition,by the Fe−C micro-alloying,the corrosion potential is slightly decreased,while the corrosion current density increases.The pitting corrosion becomes increasingly serious with the increase of Fe and C content.

Effect of the degree of dispersion of Pt over MgAl_2O_4 on the catalytic hydrogenation of benzaldehyde

One of the central tasks in the field of heterogeneous catalysis is to establish structure‐function relationships for these catalysts,especially for precious metals dispersed on the sub‐nanometer scale.Here,we report the preparation of MgAl2O4‐supported Pt nanoparticles,amorphous aggregates and single atoms,and evaluate their ability to catalyze the hydrogenation of benzaldehyde.The Pt species were characterized by N2adsorption,X‐ray diffraction(XRD),aberration‐corrected transmission electron microscopy(ACTEM),CO chemisorption and in situ Fourier transform infrared spectroscopy of the chemisorbed CO,as well as by inductively coupled plasma atomic emission spectroscopy.They existed as isolated or neighboring single atoms on the MgAl2O4support,and formed amorphous Pt aggregates and then nanocrystallites with increased Pt loading.On the MgAl2O4support,single Pt atoms were highly active in the selective catalytic hydrogenation of benzaldehyde to benzyl alcohol.The terrace atoms of the Pt particles were more active but less selective;this was presumably due to their ability to form bridged carbonyl adsorbates.The MgAl2O4‐supported single‐atom Pt catalyst is a novel catalyst with a high precious atom efficiency and excellent catalytic hydrogenation ability and selectivity.

Direct Observation of Electron-Vibration Coupling at MXene-Solvent Interface

MXenes,a new family of two-dimensional(2D)materials,have received extensive interest due to their fascinating physicochemical properties,such as outstandinglight-to-heat conversion efficiency.However,the photothermal conversion mechanism of MXenes is still poorly understood.Here,by using femtosecond visible and mid-infrared transient absorption spectroscopy,the electronic energy dissipation dynamics of MXene(Ti_(3)C_(2)T_(x))nanosheets dispersed in various solvents are carefully studied.Our results indicate that the lifetime of photoexcited MXene is strongly dependent on the surrounding environment.Especially,the interfacial electron-vibration coupling between the MXene nanosheets and the adjacent solvent molecules is directly observed following the ultrafast photoexcitation of MXene.It suggests that the interfacial interactions at the MXene-solvent interface play a critical role in the ultrafast energy transport dynamics of MXene,which offers a potentially feasible route for tailoring the light conversion properties of 2D systems.

Unveiling Defect-Mediated Carrier Dynamics in Few-Layer MoS2 Prepared by Ion Exchange Method via Ultrafast Vis-NIR-MIR Spectroscopy

Defect-mediated processes in two-dimensional transition metal dichalcogenides have a significant influence on their carrier dynamics and transport properties,however,the detailed mechanisms remain poorly understood.Here,we present a comprehensive ultrafast study on defect-mediated carrier dynamics in ion exchange prepared few-layer MoS2 by femtosecond time-resolved Vis-NIR-MIR spectroscopy.The broadband photobleaching feature observed in the near-infrared transient spectrum discloses that the mid-gap defect states are widely distributed in few-layer MoS2 nanosheets.The processes of fast trapping of carriers by defect states and the following nonradiative recombination of trapped carriers are clearly revealed,demonstrating the mid-gap defect states play a significant role in the photoinduced carrier dynamics.The positive to negative crossover of the signal observed in the mid-infrared transient spectrum further uncovers some occupied shallow defect states distributed at less than0.24 e V below the conduction band minimum.These defect states can act as effective carrier trap centers to assist the nonradiative recombination of photo-induced carriers in few-layer MoS2 on the picosecond time scale.

Ab Initio Calculation on Spectroscopic Properties and Radiative Lifetimes of Low-Lying Excited States of NaK

We performed high-level ab initio calculations on electronic structure of Na K. The potential energy curves (PECs) of 10 Λ-S states correlated with the three lowest dissociation limits have been calculated. On the basis of the calculated PECs, the spectroscopic constants of the boundΛ-S states are obtained, which are in good agreement with experimental results. The maximum vibrational quantum numbers of the singlet ground state X^1Σ^+ and the triplet ground state a^3Σ^+ have been analyzed with the semiclassical scattering theory. Transition properties including transition dipole moments, Franck-Condon factors, and radiative lifetimes have been investigated. The research results indicate that such calculations can provide fairly reliable estimation of parameters for the ultracold alkali diatomic molecular experiment.

物理学中的女性:记述制约与受限

一份对全球15000名物理学家新近完成的调查显示,女物理学家在获得事业提升所需的资源和机遇方面还没有与她们的男同事享有同等的机会.

接近于零色散的色散平坦光子晶体光纤的数值模拟与分析

基于标量近似理论利用有效折射率方法对低空气填充率的光子晶体光纤 (PCF)的色散特性进行了数值模拟。发现通过调节光纤包层的空气穴节距或空气穴大小可以有效地调节光子晶体光纤的色散特性 ,可以实现光子晶体光纤零色散波长向短波方向 (小于石英材料的零色散波长 1 2 7μm)移动 ,甚至在光通信波段出现两个零色散波长 ;可以设计在光通信波段接近于零色散的色散平坦光子晶体光纤 ,其色散系数D的绝对值在 1 2～ 1 7μm波长范围小于 2 0 ps·km-1·nm-1,其色散斜率D′的绝对值小于 0 0 2 ps·km-1·nm-2 。