Understanding the dynamics of photoexcited carriers is essential for advancing photoelectronic device design.Photon absorption generates electron–hole pairs,and subsequent scatterings can induce ultrafast thermalizat...Understanding the dynamics of photoexcited carriers is essential for advancing photoelectronic device design.Photon absorption generates electron–hole pairs,and subsequent scatterings can induce ultrafast thermalization within a picosecond,forming a quasi-equilibrium distribution with overheated electrons.The high-energy tail of this distribution enables carriers to overcome energy barriers,thereby enhancing quantum efficiency—a phenomenon known as photothermionic emission(PTE).Despite its importance,the onset and mechanisms of PTE remain under debate.Using real-time timedependent density functional theory(rt-TDDFT),we investigate ultrafast carrier thermalization in two-dimensional(2D)materials graphene and PtTe2,and the results reveal distinct differences.In graphene,both electrons and holes thermalize into Fermi–Dirac distributions with good agreement to experiment,while PtTe2exhibits anomalous high-energy tails for both electrons and holes,deviating significantly from Fermi–Dirac behavior.We attribute this anomaly to differences in orbital coupling between the two materials,from which we derive design principles for identifying optimal PTE candidates and,ultimately,improving photodetector performance.展开更多
We report a study on the electronic structure and chemical bonding of the PB and AsB diatomic molecules using high-resolution photoelectron imaging of cryogenically-cooled PB^(−)and AsB^(−)anions.The electron affiniti...We report a study on the electronic structure and chemical bonding of the PB and AsB diatomic molecules using high-resolution photoelectron imaging of cryogenically-cooled PB^(−)and AsB^(−)anions.The electron affinities of PB and AsB are measured to be 2.751(1)and 2.600(1)eV,respectively.The ground states of the PB^(−)and AsB−anions are determined to be ^(2)Σ^(+) with a σ^(1)π^(4) valence electron configuration.The ground states of neutral PB and AsB are found to be ^(3)Π_(2) with a σ^(1)π^(3) electron configuration.The spin-orbit excited states(^(3)Π_(1) and ^(3)Π_(0)),as well as two low-lying singlet excited states(^(1)Σ^(+)and ^(1)Π),are observed.Unusual spectroscopic characteristics are observed in the ^(3)Π_(2) ground state of AsB,probably due to state mixing with a higher-lying ^(1)Δ_(2) state.The current work provides extensive electronic and spectroscopic information for the PB and AsB molecules.展开更多
Nano-scale chemical inhomogeneity in surface oxide films formed on a V-and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron-based hard X-ra...Nano-scale chemical inhomogeneity in surface oxide films formed on a V-and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron-based hard X-ray Photoelectron emission spectroscopy(HAXPES)and microscopy(HAXPEEM)as well as microscopic X-ray absorption spectroscopy(μ-XAS)techniques.The results reveal the inhomogeneity in the oxide films on the micron-sized Cr_(2)N-and VN-type particles,while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600℃.The oxide film formed on Cr_(2)N-type particles is rich in Cr_(2)O_(3) compared with that on the martensite matrix and VN-type particles.With the increase of tempering temperature,Cr_(2)O_(3) formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.展开更多
Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications.The microstructure and corrosion behavior of AZ31Mn-xEr(x=0.1,0.5,1.2)alloys were systematicall...Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications.The microstructure and corrosion behavior of AZ31Mn-xEr(x=0.1,0.5,1.2)alloys were systematically investigated using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray photoelectron spectroscopy(XPS),combined with Tafel polarization and electrochemical impedance spectroscopy(EIS)analyses.The findings showed that the alloying element Er refined the grain structure during solidification by increasing the nucleation rate and forming a secondary phase of Al_(3)Er with Al.The Er and Mg in the matrix co-oxidize to form a dense MgO/Er_(2)O_(3)composite oxide,preventing the formation of loose magnesium hydroxide/basic magnesium carbonate.The trace alloying element Mn interacts with impurities Fe in the magnesium matrix to form an AlFeMn second phase,reducing micro-galvanic corrosion driving force.Electrochemical testing in a 3.5%NaCl solution demonstrated a marked reduction in corrosion rate from 10.46 mm/a(AZ 31 Mn alloy)to 0.44 mm/a(AZ31Mn-1.2Er alloy).This research offers a reference for searching for corrosion-resistant magnesium alloy and degradable medical magnesium alloy materials.展开更多
The corrosion behaviors of an as-cast FeCoNiAl_(0.75)Cr_(1.25)high-entropy alloy(HEA)in acidic Na_(2)SO_(4)solution with different pH values were investigated.The results indicate that the as-cast FeCoNiAl_(0.75)Cr_(1...The corrosion behaviors of an as-cast FeCoNiAl_(0.75)Cr_(1.25)high-entropy alloy(HEA)in acidic Na_(2)SO_(4)solution with different pH values were investigated.The results indicate that the as-cast FeCoNiAl_(0.75)Cr_(1.25)HEA is mainly composed of face-centered cubic phase,body-centered cubic(BCC1)phase(Co–Cr–Fe)and ordered BCC(B2)phase(Ni–Al),in which BCC1 phase and B2 phase have a eutectic microstructure.Moreover,the corrosion of B2 phase occurs preferentially in a 0.05 mol/L SO_(4)^(2−)acidic solution.The electrochemical measurement results show that the corrosion resistance of the investigated HEA significantly changes as the solution pH increases from 2 to 2.5.This indicates that there is a critical pH in the range of 2–2.5 that affects the corrosion of HEA.In addition,the results of X-ray photoelectron spectroscopy prove that the surface film of FeCoNiAl_(0.75)Cr_(1.25)in SO_(4)^(2−)solution is formed with Al_(2)O_(3)and Cr_(2)O_(3)as the main components,and The content of Al2O3 and Cr_(2)O_(3)increases with increasing solution pH.展开更多
In the present work,the effects of neodymium(Nd)on micro structure,mechanical performance,and corrosion behavior of powder metallurgy Mg-2Si-xNd(x=0.05 wt%,0.15 wt%,and 0.20 wt%)alloys were investigated.Microstructure...In the present work,the effects of neodymium(Nd)on micro structure,mechanical performance,and corrosion behavior of powder metallurgy Mg-2Si-xNd(x=0.05 wt%,0.15 wt%,and 0.20 wt%)alloys were investigated.Microstructures were examined by optical and scanning electron microscopes combined with an energy-dispersive spectrometer.Hardness and compressive tests were used to study the mechanical properties of alloys.Potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),Mott-Schottky analysis,and the hydrogen evolution test were applied to characterize the corrosion behavior of alloys in Hanks'solution.The microstructure of Mg-2Si-xNd alloys mainly consists ofα-Mg matrix,Mg2Si,and MgNd phases.The increase in Nd content tends to decrease the aspect ratio ofα-Mg grains,which leads to the enhancement of the ultimate-compressive strengths and hardness of the alloys.Potentiodynamic polarization shows that increasing Nd content leads to a lower corrosion current density in the Mg-2Si-xNd alloys.The EIS results confirm that a higher addition of Nd suppresses the dissolution kinetics of the alloys due to the increasing charge transfer resistance.Mott-Schottky analysis reveals the formation of an n-type semiconductive passive film on the alloy surfaces,where the interstitial and oxygen vacancies predominate over the metal vacancies.The X-ray photoelectron spectroscopy(XPS)reveals that a mixture of Mg(OH)_(2),MgO,MgCO_(3),and Nd_(2)O_(3)has formed as the corrosion products on the Mg-2Si-xNd alloy surfaces after a longer immersion time in Hanks'solution.展开更多
High-resolution photoelectron spectra of cryogenically cooled TiO_(2)CH_(3)OH^(−)anions obtained with slow electron velocity-map imaging are reported and used to explore the reactions of TiO_(2)^(−/0)with methanol.The...High-resolution photoelectron spectra of cryogenically cooled TiO_(2)CH_(3)OH^(−)anions obtained with slow electron velocity-map imaging are reported and used to explore the reactions of TiO_(2)^(−/0)with methanol.The highly structured spectra were compared with results from DFT calculations to determine the dominant structure to be cis-CH_(3)OTi(O)OH^(−),a dissociative adduct in which CH3OH is split by TiO_(2)^(−).The experiment yields an electron affinity of 1.2152(7)eV for TiO_(2)CH^(3)OH as well as several vibrational frequencies for the neutral species.Comparison to Franck−Condon(FC)simulations shows that while most experimental features appear in the simulations,several are not and are assigned to FC-forbidden transitions involving non-totally symmetric vibrational modes.The FC-allowed and forbidden transi-tions also exhibit different photoelectron angular distributions.The FC-forbidden transitions are attributed to Herzberg−Teller(HT)coupling with the A^(2)A″excited state of the anion.The results are compared to previous cryogenic slow electron velocity-map imaging(cryo-SE-Ⅵ)studies of bare TiO_(2)^(−)and the water-split adduct TiO_(3)H_(2)^(−).展开更多
The structure and electronic properties of Co_(2)Ge_(10)^(-)anion and its neutral counterpart were investigated by anion photoelectron spectroscopy and theoretical calculations.The experimental vertical detachment ene...The structure and electronic properties of Co_(2)Ge_(10)^(-)anion and its neutral counterpart were investigated by anion photoelectron spectroscopy and theoretical calculations.The experimental vertical detachment energy of Co_(2)Ge_(10)^(-)was measured to be 2.86±0.08 eV.The lowest-energy isomer of Co_(2)Ge_(10)^(-)is in a doublet state and has a cage-like structure with Cs symmetry,which can be constructed by a tetragonal bipyramid on top of a pentagonal bipyramid and these two bipyramid structures share a common Co atom.The most stable structure of neutral Co_(2)Ge_(10)resembles its anionic counterpart and it is in a triplet state.The natural population analysis showed that the inner Co atom of both the anionic and neutral Co_(2)Ge_(10)acquires negative charge from the neighboring Ge atoms.The outer Co atom has a larger spin moment than the inner Co atom,indicating that the magnetic moments of Co_(2)Ge_(10)^(-/0)are mainly contributed by the outer Co atom.Analyses of the density of states and molecular orbitals indicated that there are a few highly delocalized molecular orbitals in Co_(2)Ge_(10)^(-),which are mainly contributed by Ge 4s atomic orbitals.展开更多
MgATP is a stable complex formed by the chelation of Mg^(2+)with deprotonated adenosine-5'-triphosphate(ATP).In the cellular environment,MgATP plays a critical role in ATP hydrolysis,releasing substantial energy t...MgATP is a stable complex formed by the chelation of Mg^(2+)with deprotonated adenosine-5'-triphosphate(ATP).In the cellular environment,MgATP plays a critical role in ATP hydrolysis,releasing substantial energy to support essential biological functions.To understand the structure and stabilization mechanism of MgATP,we conducted a joint negative ion photoelectron spectroscopic and computational study of the[ATP^(4-)·Mg^(2+)]^(2-)complex dianion,using[ATP^(4-)·2H^(+)]^(2-)as a reference.The experimentally determined adiabatic and vertical detachment energies(ADE and VDE)of[ATP^(4-)·Mg^(2+)]^(2-)at 20 K are 3.51±0.05 eV and 3.82±0.05 eV,respectively.The major spectral features of[ATP^(4-)·Mg^(2+)]^(2-)are attributed to two theoretically identified isomers with unfolded geometries,which are stabilized primarily by electrostatic interactions between Mg^(2+)and the triphosphate and ribose groups,with four deprotonated oxygens forming a pseudo-tetrahedral coordination.In contrast,[ATP^(4-)·2H^(+)]^(2-)exhibits a fundamentally different stabilization mechanism.Although most of the fifteen identified[ATP^(4-)·2H^(+)]^(2-)isomers also adopt unfolded geometries,they are primarily stabilized by intramolecular hydrogen bonds within the triphosphate group and between triphosphate and ribose groups.The interaction between ATP^(4-)and two protons is found to be much weaker than that with Mg^(2+),and[ATP^(4-)·2H^(+)]^(2-)exhibits substantial structural flexibility compared to[ATP^(4-)·Mg^(2+)]^(2-)due to the conformational constraint of the triphosphate chain by Mg^(2+).Thirteen[ATP^(4-)·2H^(+)]^(2-)isomers with unfolded geometries likely account for the major high-EBE(electron-binding-energy)spectral features.Notably,for the first time,a low EBE and temperature-dependent spectral feature is observed and attributed to two folded isomers of[ATP^(4-)·2H^(+)]^(2-),which exist at 20 K but disappear at room temperature.This study provides valuable molecular-level insights into cellular MgATP that resides within the hydrophobic pockets of proteins.展开更多
The vibrational resolved spectra of MO_(2)^(-)/MO_(2)(M=Ti,Zr,and Hf)are reported by using photoelectron imaging and theoretical calculations.The results indicate that all the ground states of anionic and neutral MO_(...The vibrational resolved spectra of MO_(2)^(-)/MO_(2)(M=Ti,Zr,and Hf)are reported by using photoelectron imaging and theoretical calculations.The results indicate that all the ground states of anionic and neutral MO_(2)(M=Ti,Zr,and Hf)compounds are formed in bent insertion structures.The observed ground-state adiabatic detachment energy(ADE)is measured to be 1.597±0.003,1.651±0.003,and 2.119±0.003 eV for TiO_(2)^(-),ZrO_(2)^(-),and HfO_(2)^(-),respectively.The vibrational frequencies of the anionic and neutral MO_(2)are also determined from the experimental spectra.The results of theoretical calculations show that the electronic configurations of MO_(2)^(-)are^(2)A_(1)with C_(2v)point group.Bond order analysis indicates that the two M-O bonds are all multiple characters.展开更多
The corrosion behavior of CoCrCu_(0.1)FeMoNi high entropy alloy(HEA)in 0.5 mol/L NaOH solution was investigated using X-ray photoelectron spectroscopy,X-ray diffraction,scanning electron microscopy,potentiodynamic pol...The corrosion behavior of CoCrCu_(0.1)FeMoNi high entropy alloy(HEA)in 0.5 mol/L NaOH solution was investigated using X-ray photoelectron spectroscopy,X-ray diffraction,scanning electron microscopy,potentiodynamic polarization measurement,and electrochemical impedance spectroscopy.The results showed that the microstructure of this HEA displayed a dendritic morphology along with inter-dendritic regions.At the applied potential of–0.3,0,and 0.1 V vs.saturated calomel electrode(SCE),no significant damage to the surface of the alloy was observed.At the applied potentials of 0.15 and 0.2 V vs.SCE,selective detachment and tearing of the microstructure on the alloy surface were observed,attributed to micro-galvanic corrosion.HEA demonstrates typical spontaneous passivation behavior and exhibits capacitance at all five applied potentials.The energy dispersive spectroscopy results indicate significant elemental segregation within HEA,with a decrease in the content of Cr_(2)O_(3)in the passive film as the applied potential increases.Consequently,the protective efficacy of the passive film over the substrate in 0.5 mol/L NaOH solution was compromised.展开更多
Magnesium(Mg)alloys have attracted considerable attention as promising implant materials for biodegradable medical devices.In this study,we focused on investigating the effect of macroscopic environmental heterogeneit...Magnesium(Mg)alloys have attracted considerable attention as promising implant materials for biodegradable medical devices.In this study,we focused on investigating the effect of macroscopic environmental heterogeneity due to the degradation of Mg on its corrosion behavior.The immersion experiments using pure Mg plates,which were placed vertically in a culture medium(Dulbecco’s Modified Eagle’s Medium(DEME)+10%fetal bovine serum(FBS))for 1,5,and 10 days,were conducted.Surface analyses for the corrosion product layers and the measurements of the pH values and concentrations of eluted ions in the immersion medium around the upper and lower areas of the Mg plate were performed.The significant effect of the macroscopic environmental heterogeneity derived from Mg degradation on the corrosion behavior was demonstrated by in vitro tests.Additionally,the in vivo tests were carried out by implanting the pure Mg plates in the femur of rabbits.The in vivo results exhibited macroscopically heterogeneous Mg degradation,with areas of more severe corrosion compared to the in vitro test;it is especially noticeable during the early stage of degradation,even though the average corrosion rate was lower.展开更多
We have performed a comparative study of the photoelectron spectra adopting different initial states(2s or 2_(p0))of hydrogen atoms in a near-infrared laser pulse by using the full three-dimensional time-dependent Sch...We have performed a comparative study of the photoelectron spectra adopting different initial states(2s or 2_(p0))of hydrogen atoms in a near-infrared laser pulse by using the full three-dimensional time-dependent Schr?dinger equation.It is demonstrated that the atomic photoelectron spectra oscillate out of step as a function of electron kinetic energies for different initial states(2s or 2_(p0)),which is well reproduced by the simulations based on strong field approximation,and the above distinct feature is ascribed to the different interferences from the partial electron wave packets detached by positive and negative electric fields for different initial states of 2s and 2_(p0).展开更多
In order to investigate the effect of different doping types on the band alignment of heterojunctions,we prepared PtSe_(2)/n-GaN,PtSe_(2)/p-GaN,and PtSe_(2)/u-GaN heterojunctions by wet transfer technique.The valence ...In order to investigate the effect of different doping types on the band alignment of heterojunctions,we prepared PtSe_(2)/n-GaN,PtSe_(2)/p-GaN,and PtSe_(2)/u-GaN heterojunctions by wet transfer technique.The valence band offsets(VBO)of the three heterojunctions were measured by x-ray photoelectron spectroscopy(XPS),while the PtSe_(2)/n-GaN is 3.70±0.15 eV,PtSe_(2)/p-GaN is 0.264±0.15 eV,and PtSe_(2)/u-GaN is 3.02±0.15 eV.The conduction band offset(CBO)of the three heterojunctions was calculated from the material bandgap and VBO,while the PtSe_(2)/n-GaN is 0.61±0.15 eV,PtSe_(2)/p-GaN is 2.83±0.15 eV,and PtSe_(2)/u-GaN is 0.07±0.15 eV.This signifies that both PtSe_(2)/u-GaN and PtSe_(2)/p-GaN exhibit type-Ⅰband alignment,but the PtSe_(2)/n-GaN heterojunction has type-Ⅲband alignment.This signifies that the band engineering of PtSe_(2)/GaN heterojunction can be achieved by manipulating the concentration and type of doping,which is significantly relevant for the advancement of related devices through the realization of band alignment and the modulation of the material properties of the PtSe_(2)/GaN heterojunction.展开更多
A series of heteronuclear yttrium-nickel monoxide carbonyl complexes YNiO(CO)_(n)^(-)(n=1-5)were generated in a pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectrosco...A series of heteronuclear yttrium-nickel monoxide carbonyl complexes YNiO(CO)_(n)^(-)(n=1-5)were generated in a pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectroscopy combined with theoretical calculations.CO ligand-mediated reactivity in CO oxidation of yttrium-nickel monoxide carbonyl complexes was experimentally and theoretically identified.During the consecutive CO adsorption,aμ^(2)-O linear structure was most favorable for YNiO(CO)_(n)^(-)(n=1,2),then a structure in which the terminal O was bonded to the Y atom became favored for YNiO(CO)_(3)^(-),and finally a structure bearing a CO_(2)moiety was most favorable for YNiO(CO)_(n)^(-)(n=4,5).Theoretical calculations indicated that the Ni atom acted as an electron acceptor and accumulated electron density at n≤3,and then served as an electron donor along with the Y atom to contribute electron density in the rearrangement that accompanied CO oxidation at n>3.展开更多
We propose a method to characterize the features of a cold strontium cloud in a magneto-optical trap(MOT)through the photoionization of cold Sr atoms in a custom-designed reaction microscope.Sr atoms in the dark state...We propose a method to characterize the features of a cold strontium cloud in a magneto-optical trap(MOT)through the photoionization of cold Sr atoms in a custom-designed reaction microscope.Sr atoms in the dark state of 5s5p3P2 populated via the cascade transition 5s5p^(1)P_(1)→5s4d^(1)D_(2)→5s5p^(3)P_(2)accumulate a significant fraction,giving a long lifetime of 520 s.These atoms in the dark state are subsequently trapped by the gradient magnetic field of the MOT.By scanning the Sr+momentum distributions ionized with an 800 nm infrared femtosecond laser,we are able to outline the size of~0.55 mm in radius and the temperature of~0.40 mK for the dark-state atoms,which is significantly cooler than the MOT temperature of 3.3 mK trapped in the 461 nm.The size of MOT exhibits an oblate spheroidal distribution with a radius of approximately 0.35 mm and 0.55 mm,extracted with momenta of photoion and absorption imaging,respectively.The results using the photoion momenta are consistent with the expected results from absorption imaging,which confirms the method's reliability.The advantage of this method is the ability to simultaneously characterize the distribution information of atoms in different initial states within the cold atomic cloud.展开更多
The development of an analytical method for determining the properties of quantum dots(QDs)is crucial for improving the optical performance of QD-based displays.Therefore,synchrotron-based X-ray photoelectron spectros...The development of an analytical method for determining the properties of quantum dots(QDs)is crucial for improving the optical performance of QD-based displays.Therefore,synchrotron-based X-ray photoelectron spectroscopy(XPS)is designed here to accurately characterize the chemical and structural differences between different QDs.This method enables the determination of the reason for the minimal differences between the optical properties of different QDs depending on the synthesis process,which is difficult to determine using conventional methods alone.Combined with model simulations,the XPS spectra obtained at different photon energies reveal the internal structures and chemical-state distributions of the QDs.In particular,the QD synthesized under optimal conditions demonstrates a relatively lower degree of oxidation of the core and more uniformly stacked ZnSe/ZnS shell layers.The internal structures and chemical-state distributions of QDs are closely related to their optical properties.Finally,the synchrotron-based XPS proposed here can be applied to compare nearly equivalent QDs with slightly different optical properties.展开更多
Over the past few decades,angle-resolved photoemission spectroscopy(ARPES)has been one of the important tools to study electronic structure of crystals.In recent years,the spatial resolution of around 150 nm has been ...Over the past few decades,angle-resolved photoemission spectroscopy(ARPES)has been one of the important tools to study electronic structure of crystals.In recent years,the spatial resolution of around 150 nm has been reached through tight focusing of the light spot(nano-ARPES).At present,the lower limit of the spot size of the light on the sample has been reached.Another way to further improve the spatial resolution is through using apertures to only let electrons from a small area of the sample pass.With both back-focal plane and image apertures,the size of the selected area can be as small as 20 nm.Yet,without aberration correction,the maximum opening angle at the sample for 20 nm spatial resolution is usually smaller than 3°,making this method not suitable for nano-ARPES.As shown in this paper,a conventional aberration corrector,which corrects chromatic and third-order spherical aberrations,is not enough either.Only when the fifth-order spherical aberration is also corrected,the opening angle at the sample is large enough for nano-ARPES.In this paper,the design of a time-of-fight PEEM/ARPES/nano-ARPES instrument,which is currently under development at the Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area,is presented.The main point of innovation is a fiveelectrode electron mirror corrector,which is used to correct simultaneously chromatic,third-order and fifth-order spherical aberrations,resulting in 1 nm spatial resolution with~230 mrad aperture angle in PEEM mode.This makes feasible the method of using apertures to improve the spatial resolution of the nano-ARPES mode.A new design of the magnetic prism array(MPA)is also presented,which preserves the rotational symmetry better than the existing designs.展开更多
A plasma injection ion source has been de-veloped for the photoelectron velocity imag-ing studies of metal-containing anions.The source employs a pulse discharge nozzle for generating a plasma beam that perpendicu-lar...A plasma injection ion source has been de-veloped for the photoelectron velocity imag-ing studies of metal-containing anions.The source employs a pulse discharge nozzle for generating a plasma beam that perpendicu-larly crosses the master supersonic jet beam from a home-made pulsed piezo valve.The discharge nozzle is designed for high voltage gas discharge with efficient metal sputtering of the cathode,and thus plays a role in met-al atom and ion source.Supersonically jet-cooled anions can be produced in the master gas jet via reactions of the plasma products.The source is integrated into a photoelectron ve-locity imaging spectrometer.Test mass spectrometry experiments show that the ion source can efficiently produce transition metal containing anions,such as FeO_(m)^(-),CuO_(m)^(-),CuC_(n)^(-),CuC_(n)O_(m)^(-).The photoelectron imaging results by photodetachment of O-show that the pho-toelectron energy resolution of the whole instrument isΔE/E≈2.3%,and the results of FeO^(-)indicate that internal temperatures of anions from the source could be efficiently cooled down.展开更多
The alignment-dependent photoelectron spectrum is a valuable tool for mapping out the electronic structure of molecular orbitals.However,this approach may not be applicable to all molecules,such as CO_(2),as the ioniz...The alignment-dependent photoelectron spectrum is a valuable tool for mapping out the electronic structure of molecular orbitals.However,this approach may not be applicable to all molecules,such as CO_(2),as the ionization process in a linearly polarized laser field involves contributions from orbitals other than the highest occupied molecular orbital(HOMO).Here,we conducted a theoretical investigation into the ionization process of N_(2) and CO_(2) in near-circularly polarized laser field using the Coulomb-corrected strong-field approximation(CCSFA)method for molecules.In particular,we introduced a generalized dressed state into the CCSFA method in order to account for the impact of the laser field on the molecular initial state.The simulated alignment-dependent photoelectron momentum distribution(PMD)of the two molecules exhibited markedly disparate behaviors,which were in excellent agreement with the previous experimental observations reported in[Phys.Rev.A 102,013117(2020)].Our findings indicate that under a near-circularly polarized laser field,the alignment-dependent PMD of molecules is primarily sourced from the HOMO,in contrast to the situation under a linearly polarized laser field.Moreover,a satisfactory correlation between the alignment-dependent angular distribution and the orbital symmetry was observed,which suggests an effective approach for molecular orbital imaging.展开更多
基金Project supported by the Natural Science Foundation of Chongqing of China(Grant No.CSTB2023NSCQ-LZX0087)the National Natural Science Foundation of China(Grant Nos.62074021 and 12174380)。
文摘Understanding the dynamics of photoexcited carriers is essential for advancing photoelectronic device design.Photon absorption generates electron–hole pairs,and subsequent scatterings can induce ultrafast thermalization within a picosecond,forming a quasi-equilibrium distribution with overheated electrons.The high-energy tail of this distribution enables carriers to overcome energy barriers,thereby enhancing quantum efficiency—a phenomenon known as photothermionic emission(PTE).Despite its importance,the onset and mechanisms of PTE remain under debate.Using real-time timedependent density functional theory(rt-TDDFT),we investigate ultrafast carrier thermalization in two-dimensional(2D)materials graphene and PtTe2,and the results reveal distinct differences.In graphene,both electrons and holes thermalize into Fermi–Dirac distributions with good agreement to experiment,while PtTe2exhibits anomalous high-energy tails for both electrons and holes,deviating significantly from Fermi–Dirac behavior.We attribute this anomaly to differences in orbital coupling between the two materials,from which we derive design principles for identifying optimal PTE candidates and,ultimately,improving photodetector performance.
基金supported by the National Science Foundation (Grant No.CHE-2403841)。
文摘We report a study on the electronic structure and chemical bonding of the PB and AsB diatomic molecules using high-resolution photoelectron imaging of cryogenically-cooled PB^(−)and AsB^(−)anions.The electron affinities of PB and AsB are measured to be 2.751(1)and 2.600(1)eV,respectively.The ground states of the PB^(−)and AsB−anions are determined to be ^(2)Σ^(+) with a σ^(1)π^(4) valence electron configuration.The ground states of neutral PB and AsB are found to be ^(3)Π_(2) with a σ^(1)π^(3) electron configuration.The spin-orbit excited states(^(3)Π_(1) and ^(3)Π_(0)),as well as two low-lying singlet excited states(^(1)Σ^(+)and ^(1)Π),are observed.Unusual spectroscopic characteristics are observed in the ^(3)Π_(2) ground state of AsB,probably due to state mixing with a higher-lying ^(1)Δ_(2) state.The current work provides extensive electronic and spectroscopic information for the PB and AsB molecules.
基金supported by the Vinnova(project number 2020-03778)supported by the Swedish Research Council(Vetenskapsradet,project number 2021-04157).
文摘Nano-scale chemical inhomogeneity in surface oxide films formed on a V-and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron-based hard X-ray Photoelectron emission spectroscopy(HAXPES)and microscopy(HAXPEEM)as well as microscopic X-ray absorption spectroscopy(μ-XAS)techniques.The results reveal the inhomogeneity in the oxide films on the micron-sized Cr_(2)N-and VN-type particles,while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600℃.The oxide film formed on Cr_(2)N-type particles is rich in Cr_(2)O_(3) compared with that on the martensite matrix and VN-type particles.With the increase of tempering temperature,Cr_(2)O_(3) formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.
基金Projects(82171030,81870678)supported by the National Natural Science Foundation of China。
文摘Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications.The microstructure and corrosion behavior of AZ31Mn-xEr(x=0.1,0.5,1.2)alloys were systematically investigated using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray photoelectron spectroscopy(XPS),combined with Tafel polarization and electrochemical impedance spectroscopy(EIS)analyses.The findings showed that the alloying element Er refined the grain structure during solidification by increasing the nucleation rate and forming a secondary phase of Al_(3)Er with Al.The Er and Mg in the matrix co-oxidize to form a dense MgO/Er_(2)O_(3)composite oxide,preventing the formation of loose magnesium hydroxide/basic magnesium carbonate.The trace alloying element Mn interacts with impurities Fe in the magnesium matrix to form an AlFeMn second phase,reducing micro-galvanic corrosion driving force.Electrochemical testing in a 3.5%NaCl solution demonstrated a marked reduction in corrosion rate from 10.46 mm/a(AZ 31 Mn alloy)to 0.44 mm/a(AZ31Mn-1.2Er alloy).This research offers a reference for searching for corrosion-resistant magnesium alloy and degradable medical magnesium alloy materials.
基金supported by Key Laboratory of Research on Hydraulic and Hydro-Power Equipment Surface Engineering Technology of Zhejiang Province(20240304).
文摘The corrosion behaviors of an as-cast FeCoNiAl_(0.75)Cr_(1.25)high-entropy alloy(HEA)in acidic Na_(2)SO_(4)solution with different pH values were investigated.The results indicate that the as-cast FeCoNiAl_(0.75)Cr_(1.25)HEA is mainly composed of face-centered cubic phase,body-centered cubic(BCC1)phase(Co–Cr–Fe)and ordered BCC(B2)phase(Ni–Al),in which BCC1 phase and B2 phase have a eutectic microstructure.Moreover,the corrosion of B2 phase occurs preferentially in a 0.05 mol/L SO_(4)^(2−)acidic solution.The electrochemical measurement results show that the corrosion resistance of the investigated HEA significantly changes as the solution pH increases from 2 to 2.5.This indicates that there is a critical pH in the range of 2–2.5 that affects the corrosion of HEA.In addition,the results of X-ray photoelectron spectroscopy prove that the surface film of FeCoNiAl_(0.75)Cr_(1.25)in SO_(4)^(2−)solution is formed with Al_(2)O_(3)and Cr_(2)O_(3)as the main components,and The content of Al2O3 and Cr_(2)O_(3)increases with increasing solution pH.
基金Project supported by National Research and Innovation Agency of the Republic of Indonesia(Badan Riset dan Inovasi Nasional-BRIN)through the Grant of Rumah Program Organisasi Riset Nanoteknologi dan Material(RP-ORNM)No.20/Ⅲ.10/HK/2024。
文摘In the present work,the effects of neodymium(Nd)on micro structure,mechanical performance,and corrosion behavior of powder metallurgy Mg-2Si-xNd(x=0.05 wt%,0.15 wt%,and 0.20 wt%)alloys were investigated.Microstructures were examined by optical and scanning electron microscopes combined with an energy-dispersive spectrometer.Hardness and compressive tests were used to study the mechanical properties of alloys.Potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),Mott-Schottky analysis,and the hydrogen evolution test were applied to characterize the corrosion behavior of alloys in Hanks'solution.The microstructure of Mg-2Si-xNd alloys mainly consists ofα-Mg matrix,Mg2Si,and MgNd phases.The increase in Nd content tends to decrease the aspect ratio ofα-Mg grains,which leads to the enhancement of the ultimate-compressive strengths and hardness of the alloys.Potentiodynamic polarization shows that increasing Nd content leads to a lower corrosion current density in the Mg-2Si-xNd alloys.The EIS results confirm that a higher addition of Nd suppresses the dissolution kinetics of the alloys due to the increasing charge transfer resistance.Mott-Schottky analysis reveals the formation of an n-type semiconductive passive film on the alloy surfaces,where the interstitial and oxygen vacancies predominate over the metal vacancies.The X-ray photoelectron spectroscopy(XPS)reveals that a mixture of Mg(OH)_(2),MgO,MgCO_(3),and Nd_(2)O_(3)has formed as the corrosion products on the Mg-2Si-xNd alloy surfaces after a longer immersion time in Hanks'solution.
基金funded by the Air Force Office of Scientific Research (AFOSR) under Grant (No.FA955023-1-0545)。
文摘High-resolution photoelectron spectra of cryogenically cooled TiO_(2)CH_(3)OH^(−)anions obtained with slow electron velocity-map imaging are reported and used to explore the reactions of TiO_(2)^(−/0)with methanol.The highly structured spectra were compared with results from DFT calculations to determine the dominant structure to be cis-CH_(3)OTi(O)OH^(−),a dissociative adduct in which CH3OH is split by TiO_(2)^(−).The experiment yields an electron affinity of 1.2152(7)eV for TiO_(2)CH^(3)OH as well as several vibrational frequencies for the neutral species.Comparison to Franck−Condon(FC)simulations shows that while most experimental features appear in the simulations,several are not and are assigned to FC-forbidden transitions involving non-totally symmetric vibrational modes.The FC-allowed and forbidden transi-tions also exhibit different photoelectron angular distributions.The FC-forbidden transitions are attributed to Herzberg−Teller(HT)coupling with the A^(2)A″excited state of the anion.The results are compared to previous cryogenic slow electron velocity-map imaging(cryo-SE-Ⅵ)studies of bare TiO_(2)^(−)and the water-split adduct TiO_(3)H_(2)^(−).
基金supported by the National Natural Science Foundation of China(Nos.92461313,12074387,and 92161114)the Innovation Capability Support Program of Shaanxi Province(No.2023-CX-TD-49).
文摘The structure and electronic properties of Co_(2)Ge_(10)^(-)anion and its neutral counterpart were investigated by anion photoelectron spectroscopy and theoretical calculations.The experimental vertical detachment energy of Co_(2)Ge_(10)^(-)was measured to be 2.86±0.08 eV.The lowest-energy isomer of Co_(2)Ge_(10)^(-)is in a doublet state and has a cage-like structure with Cs symmetry,which can be constructed by a tetragonal bipyramid on top of a pentagonal bipyramid and these two bipyramid structures share a common Co atom.The most stable structure of neutral Co_(2)Ge_(10)resembles its anionic counterpart and it is in a triplet state.The natural population analysis showed that the inner Co atom of both the anionic and neutral Co_(2)Ge_(10)acquires negative charge from the neighboring Ge atoms.The outer Co atom has a larger spin moment than the inner Co atom,indicating that the magnetic moments of Co_(2)Ge_(10)^(-/0)are mainly contributed by the outer Co atom.Analyses of the density of states and molecular orbitals indicated that there are a few highly delocalized molecular orbitals in Co_(2)Ge_(10)^(-),which are mainly contributed by Ge 4s atomic orbitals.
基金was supported by the U.S.Department of Energy(DOE),Office of Science,Office of Basic Energy Sciences,Division of Chemical Sciences,Geosciences,and Biosciences,Condensed Phase and Interfacial Molecular Science program,FWP 16248.
文摘MgATP is a stable complex formed by the chelation of Mg^(2+)with deprotonated adenosine-5'-triphosphate(ATP).In the cellular environment,MgATP plays a critical role in ATP hydrolysis,releasing substantial energy to support essential biological functions.To understand the structure and stabilization mechanism of MgATP,we conducted a joint negative ion photoelectron spectroscopic and computational study of the[ATP^(4-)·Mg^(2+)]^(2-)complex dianion,using[ATP^(4-)·2H^(+)]^(2-)as a reference.The experimentally determined adiabatic and vertical detachment energies(ADE and VDE)of[ATP^(4-)·Mg^(2+)]^(2-)at 20 K are 3.51±0.05 eV and 3.82±0.05 eV,respectively.The major spectral features of[ATP^(4-)·Mg^(2+)]^(2-)are attributed to two theoretically identified isomers with unfolded geometries,which are stabilized primarily by electrostatic interactions between Mg^(2+)and the triphosphate and ribose groups,with four deprotonated oxygens forming a pseudo-tetrahedral coordination.In contrast,[ATP^(4-)·2H^(+)]^(2-)exhibits a fundamentally different stabilization mechanism.Although most of the fifteen identified[ATP^(4-)·2H^(+)]^(2-)isomers also adopt unfolded geometries,they are primarily stabilized by intramolecular hydrogen bonds within the triphosphate group and between triphosphate and ribose groups.The interaction between ATP^(4-)and two protons is found to be much weaker than that with Mg^(2+),and[ATP^(4-)·2H^(+)]^(2-)exhibits substantial structural flexibility compared to[ATP^(4-)·Mg^(2+)]^(2-)due to the conformational constraint of the triphosphate chain by Mg^(2+).Thirteen[ATP^(4-)·2H^(+)]^(2-)isomers with unfolded geometries likely account for the major high-EBE(electron-binding-energy)spectral features.Notably,for the first time,a low EBE and temperature-dependent spectral feature is observed and attributed to two folded isomers of[ATP^(4-)·2H^(+)]^(2-),which exist at 20 K but disappear at room temperature.This study provides valuable molecular-level insights into cellular MgATP that resides within the hydrophobic pockets of proteins.
基金supported by the National Natural Science Foundation of China(No.22273065)Shandong Energy institute(SEI U202312)"Strategic Priority Research Program"of the Chinese Academy of Sciences(No.XDA02020000).
文摘The vibrational resolved spectra of MO_(2)^(-)/MO_(2)(M=Ti,Zr,and Hf)are reported by using photoelectron imaging and theoretical calculations.The results indicate that all the ground states of anionic and neutral MO_(2)(M=Ti,Zr,and Hf)compounds are formed in bent insertion structures.The observed ground-state adiabatic detachment energy(ADE)is measured to be 1.597±0.003,1.651±0.003,and 2.119±0.003 eV for TiO_(2)^(-),ZrO_(2)^(-),and HfO_(2)^(-),respectively.The vibrational frequencies of the anionic and neutral MO_(2)are also determined from the experimental spectra.The results of theoretical calculations show that the electronic configurations of MO_(2)^(-)are^(2)A_(1)with C_(2v)point group.Bond order analysis indicates that the two M-O bonds are all multiple characters.
基金funded by National Key Research and Development Program of China(No.2021YFB3401100)Evaluation Project of Guangdong Provincial Key Laboratory(No.2023B1212060043)+1 种基金Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC001)GDAS'Project of Science and Technology Development(Nos.2023GDASQNRC-0205 and 2024GDASZH-2024010102).
文摘The corrosion behavior of CoCrCu_(0.1)FeMoNi high entropy alloy(HEA)in 0.5 mol/L NaOH solution was investigated using X-ray photoelectron spectroscopy,X-ray diffraction,scanning electron microscopy,potentiodynamic polarization measurement,and electrochemical impedance spectroscopy.The results showed that the microstructure of this HEA displayed a dendritic morphology along with inter-dendritic regions.At the applied potential of–0.3,0,and 0.1 V vs.saturated calomel electrode(SCE),no significant damage to the surface of the alloy was observed.At the applied potentials of 0.15 and 0.2 V vs.SCE,selective detachment and tearing of the microstructure on the alloy surface were observed,attributed to micro-galvanic corrosion.HEA demonstrates typical spontaneous passivation behavior and exhibits capacitance at all five applied potentials.The energy dispersive spectroscopy results indicate significant elemental segregation within HEA,with a decrease in the content of Cr_(2)O_(3)in the passive film as the applied potential increases.Consequently,the protective efficacy of the passive film over the substrate in 0.5 mol/L NaOH solution was compromised.
基金supported by JSPS KAKENHI Grant Number 22K12903.
文摘Magnesium(Mg)alloys have attracted considerable attention as promising implant materials for biodegradable medical devices.In this study,we focused on investigating the effect of macroscopic environmental heterogeneity due to the degradation of Mg on its corrosion behavior.The immersion experiments using pure Mg plates,which were placed vertically in a culture medium(Dulbecco’s Modified Eagle’s Medium(DEME)+10%fetal bovine serum(FBS))for 1,5,and 10 days,were conducted.Surface analyses for the corrosion product layers and the measurements of the pH values and concentrations of eluted ions in the immersion medium around the upper and lower areas of the Mg plate were performed.The significant effect of the macroscopic environmental heterogeneity derived from Mg degradation on the corrosion behavior was demonstrated by in vitro tests.Additionally,the in vivo tests were carried out by implanting the pure Mg plates in the femur of rabbits.The in vivo results exhibited macroscopically heterogeneous Mg degradation,with areas of more severe corrosion compared to the in vitro test;it is especially noticeable during the early stage of degradation,even though the average corrosion rate was lower.
基金Project supported by Li Ka Shing Foundation STUGTIIT Joint Research(Grant No.2024LKSFG02)the STU Scientific Research Foundation for Talents(Grant Nos.NTF22026,NTF23011,NTF23014,and NTF23036T)+1 种基金the National Basic Research Program of China(Grant No.2019YFA0307700)the National Natural Science Foundation of China(Grant Nos.12074239 and 12274300)。
文摘We have performed a comparative study of the photoelectron spectra adopting different initial states(2s or 2_(p0))of hydrogen atoms in a near-infrared laser pulse by using the full three-dimensional time-dependent Schr?dinger equation.It is demonstrated that the atomic photoelectron spectra oscillate out of step as a function of electron kinetic energies for different initial states(2s or 2_(p0)),which is well reproduced by the simulations based on strong field approximation,and the above distinct feature is ascribed to the different interferences from the partial electron wave packets detached by positive and negative electric fields for different initial states of 2s and 2_(p0).
基金Project supported by the National Natural Science Foundation of China(Grant No.61874108)the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2024-04)the Gansu Provincial Scientific and Technologic Planning Program(Grant No.22ZD6GE016).
文摘In order to investigate the effect of different doping types on the band alignment of heterojunctions,we prepared PtSe_(2)/n-GaN,PtSe_(2)/p-GaN,and PtSe_(2)/u-GaN heterojunctions by wet transfer technique.The valence band offsets(VBO)of the three heterojunctions were measured by x-ray photoelectron spectroscopy(XPS),while the PtSe_(2)/n-GaN is 3.70±0.15 eV,PtSe_(2)/p-GaN is 0.264±0.15 eV,and PtSe_(2)/u-GaN is 3.02±0.15 eV.The conduction band offset(CBO)of the three heterojunctions was calculated from the material bandgap and VBO,while the PtSe_(2)/n-GaN is 0.61±0.15 eV,PtSe_(2)/p-GaN is 2.83±0.15 eV,and PtSe_(2)/u-GaN is 0.07±0.15 eV.This signifies that both PtSe_(2)/u-GaN and PtSe_(2)/p-GaN exhibit type-Ⅰband alignment,but the PtSe_(2)/n-GaN heterojunction has type-Ⅲband alignment.This signifies that the band engineering of PtSe_(2)/GaN heterojunction can be achieved by manipulating the concentration and type of doping,which is significantly relevant for the advancement of related devices through the realization of band alignment and the modulation of the material properties of the PtSe_(2)/GaN heterojunction.
基金supported by the Natural Science Foundation of Shandong Province(No.ZR2021QB215)the National Natural Science Foundation of China(Nos.22273101,22125303,92061203,21327901,and 22288201)+2 种基金Dalian Institute of Chemical Physics(No.DICP I202437)the Talent Induction Program for Youth Innovation Teams in Colleges and Universities of Shandong Province(No.2022-2024)the Talent Introduction Research Start-up Funds of Ludong University(No.20212026)。
文摘A series of heteronuclear yttrium-nickel monoxide carbonyl complexes YNiO(CO)_(n)^(-)(n=1-5)were generated in a pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectroscopy combined with theoretical calculations.CO ligand-mediated reactivity in CO oxidation of yttrium-nickel monoxide carbonyl complexes was experimentally and theoretically identified.During the consecutive CO adsorption,aμ^(2)-O linear structure was most favorable for YNiO(CO)_(n)^(-)(n=1,2),then a structure in which the terminal O was bonded to the Y atom became favored for YNiO(CO)_(3)^(-),and finally a structure bearing a CO_(2)moiety was most favorable for YNiO(CO)_(n)^(-)(n=4,5).Theoretical calculations indicated that the Ni atom acted as an electron acceptor and accumulated electron density at n≤3,and then served as an electron donor along with the Y atom to contribute electron density in the rearrangement that accompanied CO oxidation at n>3.
基金Project supported by the Natural Science Foundation of Henan(Grant No.252300421304)the National Natural Science Foundation of China(Grant Nos.12204498,12474259+1 种基金12334011)the National Key Research and Development Program of China(Grant No.2022YFA1604302)。
文摘We propose a method to characterize the features of a cold strontium cloud in a magneto-optical trap(MOT)through the photoionization of cold Sr atoms in a custom-designed reaction microscope.Sr atoms in the dark state of 5s5p3P2 populated via the cascade transition 5s5p^(1)P_(1)→5s4d^(1)D_(2)→5s5p^(3)P_(2)accumulate a significant fraction,giving a long lifetime of 520 s.These atoms in the dark state are subsequently trapped by the gradient magnetic field of the MOT.By scanning the Sr+momentum distributions ionized with an 800 nm infrared femtosecond laser,we are able to outline the size of~0.55 mm in radius and the temperature of~0.40 mK for the dark-state atoms,which is significantly cooler than the MOT temperature of 3.3 mK trapped in the 461 nm.The size of MOT exhibits an oblate spheroidal distribution with a radius of approximately 0.35 mm and 0.55 mm,extracted with momenta of photoion and absorption imaging,respectively.The results using the photoion momenta are consistent with the expected results from absorption imaging,which confirms the method's reliability.The advantage of this method is the ability to simultaneously characterize the distribution information of atoms in different initial states within the cold atomic cloud.
基金Advanced Light Source,which is a DOE Office of Science User Facility under contract no.DE-AC02-05CH11231the Basque Government for funding through a PhD Fellowship(Grant no.PRE_2018_2_0285)+1 种基金through Egonlabur Travel Fellowship(Grant no.EP_2018_1_0004)partially supported by an Early Career Award in the Condensed Phase and Interfacial Molecular Science Program,in the Chemical Sciences Geosciences and Biosciences Division of the Office of Basic Energy Sciences of the U.S.Department of Energy under Contract No.DE-AC02-05CH11231.
文摘The development of an analytical method for determining the properties of quantum dots(QDs)is crucial for improving the optical performance of QD-based displays.Therefore,synchrotron-based X-ray photoelectron spectroscopy(XPS)is designed here to accurately characterize the chemical and structural differences between different QDs.This method enables the determination of the reason for the minimal differences between the optical properties of different QDs depending on the synthesis process,which is difficult to determine using conventional methods alone.Combined with model simulations,the XPS spectra obtained at different photon energies reveal the internal structures and chemical-state distributions of the QDs.In particular,the QD synthesized under optimal conditions demonstrates a relatively lower degree of oxidation of the core and more uniformly stacked ZnSe/ZnS shell layers.The internal structures and chemical-state distributions of QDs are closely related to their optical properties.Finally,the synchrotron-based XPS proposed here can be applied to compare nearly equivalent QDs with slightly different optical properties.
基金supported by Shanghai Tech University and Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area,China(Grant No.SZZX2301006)。
文摘Over the past few decades,angle-resolved photoemission spectroscopy(ARPES)has been one of the important tools to study electronic structure of crystals.In recent years,the spatial resolution of around 150 nm has been reached through tight focusing of the light spot(nano-ARPES).At present,the lower limit of the spot size of the light on the sample has been reached.Another way to further improve the spatial resolution is through using apertures to only let electrons from a small area of the sample pass.With both back-focal plane and image apertures,the size of the selected area can be as small as 20 nm.Yet,without aberration correction,the maximum opening angle at the sample for 20 nm spatial resolution is usually smaller than 3°,making this method not suitable for nano-ARPES.As shown in this paper,a conventional aberration corrector,which corrects chromatic and third-order spherical aberrations,is not enough either.Only when the fifth-order spherical aberration is also corrected,the opening angle at the sample is large enough for nano-ARPES.In this paper,the design of a time-of-fight PEEM/ARPES/nano-ARPES instrument,which is currently under development at the Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area,is presented.The main point of innovation is a fiveelectrode electron mirror corrector,which is used to correct simultaneously chromatic,third-order and fifth-order spherical aberrations,resulting in 1 nm spatial resolution with~230 mrad aperture angle in PEEM mode.This makes feasible the method of using apertures to improve the spatial resolution of the nano-ARPES mode.A new design of the magnetic prism array(MPA)is also presented,which preserves the rotational symmetry better than the existing designs.
基金supports from the National Natural Science Foundation of China(No.22173089,No.21827804,and No.22103075)the National Key R&D Program of China(No.2021YFA0716801 and No.2017YFA0303502).
文摘A plasma injection ion source has been de-veloped for the photoelectron velocity imag-ing studies of metal-containing anions.The source employs a pulse discharge nozzle for generating a plasma beam that perpendicu-larly crosses the master supersonic jet beam from a home-made pulsed piezo valve.The discharge nozzle is designed for high voltage gas discharge with efficient metal sputtering of the cathode,and thus plays a role in met-al atom and ion source.Supersonically jet-cooled anions can be produced in the master gas jet via reactions of the plasma products.The source is integrated into a photoelectron ve-locity imaging spectrometer.Test mass spectrometry experiments show that the ion source can efficiently produce transition metal containing anions,such as FeO_(m)^(-),CuO_(m)^(-),CuC_(n)^(-),CuC_(n)O_(m)^(-).The photoelectron imaging results by photodetachment of O-show that the pho-toelectron energy resolution of the whole instrument isΔE/E≈2.3%,and the results of FeO^(-)indicate that internal temperatures of anions from the source could be efficiently cooled down.
基金supported by the National Natural Science Foundation of China(Grant No.12274273).
文摘The alignment-dependent photoelectron spectrum is a valuable tool for mapping out the electronic structure of molecular orbitals.However,this approach may not be applicable to all molecules,such as CO_(2),as the ionization process in a linearly polarized laser field involves contributions from orbitals other than the highest occupied molecular orbital(HOMO).Here,we conducted a theoretical investigation into the ionization process of N_(2) and CO_(2) in near-circularly polarized laser field using the Coulomb-corrected strong-field approximation(CCSFA)method for molecules.In particular,we introduced a generalized dressed state into the CCSFA method in order to account for the impact of the laser field on the molecular initial state.The simulated alignment-dependent photoelectron momentum distribution(PMD)of the two molecules exhibited markedly disparate behaviors,which were in excellent agreement with the previous experimental observations reported in[Phys.Rev.A 102,013117(2020)].Our findings indicate that under a near-circularly polarized laser field,the alignment-dependent PMD of molecules is primarily sourced from the HOMO,in contrast to the situation under a linearly polarized laser field.Moreover,a satisfactory correlation between the alignment-dependent angular distribution and the orbital symmetry was observed,which suggests an effective approach for molecular orbital imaging.
