Electron vortices generation of photoelectron of H_(2)^(+) by counter-rotating circularly polarized attosecond pulses

Molecular-frame photoelectron momentum distributions(MF-PMDs) of an H_(2)^(+) molecule ion in the presence of a pair of counter-rotating circularly polarized attosecond extreme ultraviolet laser pulses is studied by numerically solving the two-dimensional time-dependent Schrodinger equation within the frozen-nuclei approximation. At small time delay, our simulations show that the electron vortex structure is sensitive to the time delay and relative phase between the counterrotating pulses when they are partially overlapped. By adjusting time delay and relative phase, we have the ability to manipulate the MF-PMDs and the appearance of spiral arms. We further show that the internuclear distance can affect the spiral vortices due to its different transition cross sections in the parallel and perpendicular geometries. The lowest-order perturbation theory is employed to interpret these phenomena qualitatively. It is concluded that the internuclear distancedependent transition cross sections and the confinement effect in diatomic molecules are responsible for the variation of vortex structures in the MF-PMDs.

Study of NdCl_3-FeCl_3-Graphite Intercalation Compounds by X-Ray Photoelectron Spectroscopy

NdCl 3 FeCl 3 graphite intercalation compounds were synthesized by molten salt exchange method. The state of the intercalates and the relative contents of Nd, Fe, Cl, C in the product were determined by X ray photoelectron spectroscopy(XPS). From the XPS data, it is concluded that the binding energy of Fe2p electrons is about 711 20～710 3 eV, the binding energy of Nd3d electrons is about 983 08～983 20 eV, and Fe in the product has two valence states (Fe 3+ and Fe 2+ ).

Modeling the photon counting and photoelectron counting characteristics of quanta image sensors

A signal chain model of single-bit and multi-bit quanta image sensors(QISs)is established.Based on the proposed model,the photoresponse characteristics and signal error rates of QISs are investigated,and the effects of bit depth,quantum efficiency,dark current,and read noise on them are analyzed.When the signal error rates towards photons and photoelectrons counting are lower than 0.01,the high accuracy photon and photoelectron counting exposure ranges are determined.Furthermore,an optimization method of integration time to ensure that the QIS works in these high accuracy exposure ranges is presented.The trade-offs between pixel area,the mean value of incident photons,and integration time under different illuminance level are analyzed.For the 3-bit QIS with 0.16 e-/s dark current and 0.21 e-r.m.s.read noise,when the illuminance level and pixel area are 1 lux and 1.21μm^(2),or 10000 lux and 0.21μm^(2),the recommended integration time is 8.8 to 30 ms,or 10 to21.3μs,respectively.The proposed method can guide the design and operation of single-bit and multi-bit QISs.

Rabi Oscillations and Coherence Dynamics in Terahertz Streaking-Assisted Photoelectron Spectrum

We present an approach,a Terahertz streaking-assisted photoelectron spectrum(THz SAPS),to achieve direct observations of ultrafast coherence dynamics with timescales beyond the pulse duration.Using a 24 fs probe pulse,the THz SAPS enables us to well visualize Rabi oscillations of 11.76 fs and quantum beats of 2.62 fs between the 5S_(1/2) and 5P_(3/2) in rubidium atoms.The numerical results show that the THz SAPS can simultaneously achieve high resolution in both frequency and time domains without the limitation of Heisenberg uncertainty of the probe pulse.The long probe pulse promises sufficiently high frequency resolution in photoelectron spectroscopy allowing to observe Autler-Townes splittings,whereas the streaking THz field enhances temporal resolution for not only Rabi oscillations but also quantum beats between the ground and excited states.The THz SAPS demonstrates a potential applicability for observation and manipulation of ultrafast coherence processes in frequency and time domains.

Response of photoelectron peaks in the Martian ionosphere to solar EUV/X-ray irradiance

An important population of the dayside Martian ionosphere are photoelectrons that are produced by solar Extreme Ultraviolet and X-ray ionization of atmospheric neutrals.A typical photoelectron energy spectrum is characterized by a distinctive peak near 27 eV related to the strong solar HeⅡ emission line at 30.4 nm,and an additional peak near 500 eV related to O Auger ionization.In this study,the extensive measurements made by the Solar Wind Electron Analyzer on board the recent Mars Atmosphere and Volatile Evolution spacecraft are analyzed and found to verify the scenario that Martian ionosphere photoelectrons are driven by solar radiation.We report that the photoelectron intensities at the centers of both peaks increase steadily with increasing solar ionizing flux below 90 nm and that the observed solar cycle variation is substantially more prominent near the O Auger peak than near the HeⅡ peak.The latter observation is clearly driven by a larger variability in solar irradiance at shorter wavelengths.When the solar ionizing flux increases from 1 mW·m^-2 to 2.5 mW·m^-2,the photoelectron intensity increases by a factor of 3.2 at the HeⅡ peak and by a much larger factor of 10.5 at the O Auger peak,both within the optically thin regions of the Martian atmosphere.

Angular Distribution of Photoelectrons During Irradiation of Metal Surface by HElectromagnetic Waves

Angular distribution of photoelectrons is investigated during the inner photoemissive effect for two variants: quantum of light basically reveals wave and basically corpuscular properties interacting with orbital electron. Distinction in angular distribution of photoelectrons for these variants is demonstrated. Angular distribution in the second variant is investigated for the nonrelativistic and relativistic cases.

Bidirectional electron conic observations for photoelectrons in the Martian ionosphere

Electron pitch angle distributions similar to bidirectional electron conics(BECs)have been reported at Mars in previous studies based on analyses of Mars Global Surveyor measurements.BEC distribution,also termed“butterfly”distribution,presents a local minimum flux at 90°and a maximum flux before reaching the local loss cone.Previous studies have focused on 115 eV electrons that were produced mainly via solar wind electron impact ionization.Here using Solar Wind Electron Analyzer measurements made onboard the Mars Atmosphere and Volatile Evolution spacecraft,we identify 513 BEC events for 19-55 eV photoelectrons that were generated via photoionization only.Therefore,we are investigating electrons observed in regions well away from their source regions,to be distinguished from 115 eV electrons observed and produced in the same regions.We investigate the spatial distribution of the 19-55 eV BECs,revealing that they are more likely observed on the nightside as well as near strong crustal magnetic anomalies.We propose that the 19-55 eV photoelectron BECs are formed due to day-to-night transport and the magnetic mirror effect of photoelectrons moving along cross-terminator closed magnetic field lines.

Photoelectron pitch angle distribution near Mars and implications on cross terminator magnetic field connectivity

The photoelectron peak at 22 27 eV, a distinctive feature of the energetic electron distribution in the dayside Martian ionosphere, is a useful diagnostic of solar extreme ultraviolet (EUV) and X-ray ionization as well as of large-scale transport along magnetic field lines. In this work, we analyze the pitch angle distribution (PAD) of energetic electrons at 22 27 eV measured during several representative Mars Atmosphere and Volatile Evolution (MAVEN) orbits, based on the electron spectra gathered by MAVEN’s Solar Wind Electron Analyzer (SWEA) instrument. On the dayside, most photoelectron spectra show an isotropic PAD as is expected from production via solar EUV/X-ray ionization. The photoelectron spectra occasionally observed on the nightside show instead a strongly anisotropic PAD, indicative of cross-terminator transport along ambient magnetic field lines. This would in turn predict the presence of dayside photoelectrons, also with a strongly anisotropic PAD, which was indeed revealed in SWEA data. Comparison with magnetic field measurements made by the MAVEN Magnetometer suggests that on average the photoelectrons with anisotropic PAD stream away from Mars on the dayside and towards Mars on the nightside, further supporting the scenario of day-to-night transport. On both sides, anisotropic photoelectrons tend to be observed above the photoelectron exobase at ~160 km where photoelectron transport dominates over local production and energy degradation.

Photoelectron imaging of resonance-enhanced multiphoton ionization and above-threshold ionization of ammonia molecules in a strong 800-nm laser pulse

In this work, we mainly investigate the NH3 molecular multiphoton ionization process by using the photoelectron velocity map imaging technique. Under the condition of femtosecond laser(wavelength at 800 nm), the photoelectron images are detected. The channel switching and above-threshold ionization(ATI) effect are also confirmed. The kinetic energy spectrum(KES) and the photoelectron angular distributions(PADs) are obtained through the anti-Abel transformation from the original images, and then three ionization channels are confirmed successfully according to the Freeman resonance effect in a relatively low laser intensity region. In the excitation process, the intermediate resonance Rydberg states are C^1 A 1(6 + 2 photons process), B^1 E(6 + 2 photons process) and C^1 A 1(7 + 2 photons process), respectively. At the same time, we also find that the photoelectron angular distributions are independent of laser intensity. In addition, the electrons produced by different processes interfere with each other and they can produce a spider-like structure. We also find ac-Stark movement according to the Stark-shift-induced resonance effect when the laser intensity is relatively high.

Energy band alignment at ferroelectric/electrode interface determined by photoelectron spectroscopy

The most important interface-related quantities determined by band alignment are the barrier heights for charge transport, given by the Fermi level position at the interface. Taking Pb(Zr,Ti)O3(PZT) as a typical ferroelectric material and applying X-ray photoelectron spectroscopy(XPS), we briefly review the interface formation and barrier heights at the interfaces between PZT and electrodes made of various metals or conductive oxides. Polarization dependence of the Schottky barrier height at a ferroelectric/electrode interface is also directly observed using XPS.

Energy band alignment at Cu2O/ZnO heterojunctions characterized by in situ x-ray photoelectron spectroscopy

With the increasing interest in Cu2O-based devices for photovoltaic applications,the energy band alignment at the Cu2O/ZnO heterojunction has received more and more attention.In this work,a high-quality Cu2O/ZnO heterojunction is fabricated on a c-Al2 O3 substrate by laser-molecular beam epitaxy,and the energy band alignment is determined by x-ray photoelectron spectroscopy.The valence band of ZnO is found to be 1.97 eV below that of Cu2O.A type-II band alignment exists at the Cu2O/ZnO heterojunction with a resulting conduction band offset of 0.77 eV,which is especially favorable for enhancing the efficiency of Cu2O/ZnO solar cells.

Photoelectron longitudinal momentum distributions containing nondipole effects

This paper proposes a modified strong field approximation model for evaluating nondipole effects on the ionization of an atom in an intense laser field. The photoelectron longitudinal momentum distributions(PLMD) of a hydrogen-like atom exposed to a mid-infrared laser field is calculated. The theoretical results indicate an obvious asymmetry in the PLMD, and an offset of the PLMD peak appears in the opposite direction of the beam propagation due to nondipole effects. The peak offsets of the PLMD increased with the laser intensity, imposed by the initial state of the hydrogen-like atom.

THE HEI PHOTOELECTRON SPECTROSCOPIC STUDY OF MICROWAVE-DISCHARGED SPECIES OF METHYL IODIDE

The detection of the microwave-discharged species of methyliodide by HeI photoelectron spectroscopy（UPS）is reported for the firsttime.The UPS spectra of I2 and HI molecules clearly appeared in thespectrum of microwave-discharged species of methyl iodide,The mechanismof the change of methyl iodide under microwave discharge wasproposed,The result provides the basis for understanding depletion ofthe ozone shell of the atomsphere by halogenated methane.

Pseudohalide induced tunable electronic and excitonic properties in two-dimensional single-layer perovskite for photovoltaics and photoelectronic applications

Two-dimensional(2D) layered organic-inorganic hybrid perovskites have attracted much more attention for some applications than their three-dimensional(3D) perovskite counterparts due to their promising thermal and moisture stabilities.In particular, the 2D perovskite devices have shown better promise for optoelectronic applications.However, tunability of optoelectronic properties is often demanded to improve the device performance.Herein, we adopt a newly method to tune the electronic properties of 2D perovskite by introducing pseudohalide into the structure.In this work, we designed a pseudohalidesubstituted 2D perovskite by substituting the out-of-plane halide with pseudohalide and studied the electronic and excitonic properties of 2D-BA2MX4 and 2D-BA2MX2Ps2(M=Ge^(2+), Sn^(2+), and Pb^(2+);X=I;Ps=NCO, NCS, OCN, SCN, Se CN).We revealed the dependence of electronic properties including band gaps, composition of band edges, bonding characteristics, work functions, effective masses, and exciton binding energies on different pseudohalides substituted in 2D perovskite.Our results indicate that the substitution of pseudohalide in 2D perovskites is energetically favorable and can significantly affect the bonding characteristics as well as the CBM and VBM that often play major role in determining their performance in optoelectronic devices.It is expected that the pseudohalide substitution will be helpful in developing more advanced optoelectronic device based on 2D perovskite by optimizing band alignment and promoting charge extraction.

THROUGH—SPACE AND THROUGH—BOND INTERACTIONS IN 1,5-CYCLOOCTADIYNE; THE ASSIGNMENT OF ITS PHOTOELECTRON SPECTRA

The through--space and through--bond interactions in 1, 5 -- Cyclooctadiyne arestudied. It is shown, with the assistance of improved MS--X_α method, that the through- spaceinteractions decrease with the distance of the orbitals, and both through--space and through--bondinteractions of 1, 5- Cyclooctadiyne are sizable but those two interactions oppose each othercausing the net splitting to be small for π_z orbital. The calculated ionization potentials are in goodagreement with the experiment of photoelectron spectra.

Landscape of s-triazine molecule on Si(100) by a theoretical x-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectra study

The chemisorbed structure for an aromatic molecule on a silicon surface plays an important part in promoting the development of organic semiconductor material science. The carbon K-shell x-ray photoelectron spectroscopy(XPS) and the x-ray absorption near-edge structure(XANES) spectra of the interfacial structure of an s-triazine molecule adsorbed on Si(100) surface have been performed by the first principles, and the landscape of the s-triazine molecule on Si(100) surface has been described in detail. Both the XPS and XANES spectra have shown their dependence on different structures for the pristine s-triazine molecule and its several possible adsorbed configurations. By comparison with the XPS spectra, the XANES spectra display the strongest structural dependency of all of the studied systems and thus could be well applied to identify the chemisorbed s-triazine derivatives. The exploration of spectral components originated from non-equivalent carbons in disparate local environments has also been implemented for both the XPS and XANES spectra of s-triazine adsorbed configurations.

ZnO and Zn1-xMnxO Minicrystal by CVT and Temporal Process of Photoelectrons

The ZnO and Zn1-xMnxO minicrystal were synthesized by chemical vapor transport (CVT). The electron trap structure (donor level) and process on the temporal behavior of photoelectrons of materials were respectively studied by thermo-luminescence and microwave absorption dielectric spectrometry. There are two peaks in the thermo-luminescence spectra in pure ZnO, one is -183 ℃ and the other is -127 ℃, which shows two kinds of electron trap energy level produced by the intrinsic defects in ZnO;but obtain very low thermo-luminescence that only equals to ten percent of pure ZnO in Zn1-xMnxO, which shows that its intensity of electron trap is less. The studies of microwave absorption dielectric spectrometry show that conduction band photoelectrons are two-step exponential decay process in ZnO, the lifetime of rapid process is 83 ns, while slow process is 828 ns, the reason of delay is relaxation effects of electron trap to conduction band photoelectrons. The intensity of electron trap is less in Zn1-xMnxO minicrystal, the relaxation effects of conduction band photoelectrons from electron trap is little, so electrons disappeared quickly at conduction band, and the decay process of photoelectrons is only 10～20 ns.

Strategies for enhancing conductivity of colloidal nanocrystals and their photoelectronic applications

Semiconductor colloidal nanocrystals(NCs)have size-and shape-dependent optoelectronic properties due to the quantum confinement effect,and are considered to be promising optoelectronic materials.Among them,Ⅱ-Ⅵ(CdSe,CdS,CdTe,etc.)andⅣ-Ⅵ(PbSe,PbTe,PbS,etc.)have been widely studied as representative colloidal NCs.However,the surfactant used in its synthesis progress results in the NCs surface covered by an insulating shell,which greatly affects the exciton separation and carrier transport of colloidal NCs-based photovoltaic devices.Therefore,how to design high-efficiency optoelectronic devices by improving the transport performance of carriers has been a great challenge.The key issues in the research ofⅡ-Ⅵ(CdSe,CdS,CdTe,etc.)andⅣ-Ⅵ(PbSe,PbTe,PbS,etc.)colloidal NCs were summarized,including synthesis strategy,morphology/size adjustment,surface ligand design,improvement of conductivity and their optoelectronic properties.The influence of surface ligands on the stability and dispersion of NCs was firstly introduced,and then strategies of improving electrical conductivity of NCs were discussed,such as ligands exchange,doping,self-assembly and plasmons,which provided a good foundation for the subsequent preparation of optoelectronic devices.The future development direction of NCs optoelectronic devices is expounded from the aspects of materials composition,comprehensive preparation and flexible processing of colloidal NCs.

High Energy Inner Shell Photoelectron Diffraction in CO_(2)

Photoelectron diffraction is an effective tool to probe the structures of molecules.The higher the photoelectron kinetic energy is,the higher order the diffraction pattern is disclosed in.Up to date,either the multi-atomic molecule with the photoelectron kinetic energy below 150 e V or the diatomic molecule with 735 eV photoelectron has been experimentally reported.In this study,we measured the diffraction pattern of C 1 s and O 1 s photoelectrons in CO_(2)with 319.7 and 433.5 eV kinetic energies,respectively.The extracted C–O bond lengths are longer than the C–O bond length at the ground state,which is attributed to the asymmetric fragmentation that preferentially occurs at the longer chemical bond side during the zero-energy asymmetric vibration.

Manipulation of Resonance-Enhanced Multiphoton-Ionization Photoelectron Spectroscopy by Two Time-Delayed Femtosecond Laser Pulses

We theoretically demonstrate that the(2+1)resonance-enhanced multiphoton-ionization(REMPI)photoelectron spectrum in a cesium(Cs)atom can be effectively manipulated by two time-delayed femtosecond laser pulses,involving its photoelectron spectral structure and photoelectron energy.We show that the photoelectron spectrum exhibits interference fringes and the fringe spacing is determined by the time delay of the two laser pulses,and the photoelectron energy is periodically modulated and the modulation period is determined by the two-photon transition frequency of the excited state.Finally,we utilize the power spectrum of the two time-delayed laser pulses and the two-photon transition probability of the excited state to respectively explain the modulations of the photoelectron spectrum and photoelectron energy.