Electron Energy Shift Research Articles

From Micro to Macro: A Relativistic Treatment of the Chiral Energy Shifts Caused by Static Electromagnetic Effects on Free Electrons.

Free electron systems are ubiquitous in nature and have demonstrated intriguing effects in their collective interactions with weak electric and magnetic fields, especially in aqueous environments. Starting from the Dirac Hamiltonian, a fully relativistic expression is derived for the electron energy shift in the presence of a spatiotemporally constant, weak electromagnetic field. The expectation value of this energy shift is then computed explicitly using the Fourier transforms of the fermionic fields. To first order in the electromagnetic fields, the average relativistic energy shift is found to be completely independent of the electron spin-polarization coefficients. This effect is also considerably larger than that predicted in quantum mechanics by the analogous Zeeman shift. Finally, in the non-relativistic limit, it is shown how to discriminate between achiral and completely polarized states, which leads to a concluding discussion of possible mesoscopic and macroscopic manifestations of electron spin states across many orders of magnitude in the physical world, with stark implications for biological and other complex systems.

Theory of Shaping Electron Wavepackets with Light

We present the quantum theory governing the interaction between short laser pulses and relativistic free electrons and reveal intrinsic conservation laws for such quantum interactions. Through the judicious design of the amplitude and phase of a laser pulse, we propose the complete shaping of the electron temporal wavepacket and energy spectrum. To exemplify the prospects and limitations of the shaping process, we optimize laser pulses that can reduce the energy spread of an electron beam. We also find attosecond laser pulse trains that generate electron combs with record short attosecond features that push the lowest limits of electron temporal duration. We propose to utilize the quantum shaping of the electron energy spectrum for a new kind of light–matter interaction: Matching the shaped electron energy shift to a target material excitation. This way we can transfer the electron coherent state into a new coherent material excitation, allowing access to states that are forbidden with optical excitations. Our formalism generalizes all the previous theoretical models in the area of photon-induced nearfield electron microscopy (PINEM); our formalism can fit experiments in the field that cannot be modeled by the conventional PINEM theory. Altogether, our new formalism of shaping quantum electron-laser interactions in the dimension of time/energy has prospects for novel phenomena in attosecond science, for new techniques in electron microscopy, and for their potential marriage in ultrafast quantum electron optics.

In Situ Grown Epitaxial Heterojunction Exhibits High-Performance Electrocatalytic Water Splitting.

Electrocatalytic performance can be enhanced by engineering a purposely designed nanoheterojunction and fine-tuning the interface electronic structure. Herein a new approach of developing atomic epitaxial in-growth in Co-Ni3 N nanowires array is devised, where a nanoconfinement effect is reinforced at the interface. The Co-Ni3 N heterostructure array is formed by thermal annealing NiCo2 O4 precursor nanowires under an optimized condition, during which the nanowire morphology is retained. The epitaxial in-growth structure of Co-Ni3 N at nanometer scale facilitates the electron transfer between the two different domains at the epitaxial interface, leading to a significant enhancement in catalytic activities for both hydrogen and oxygen evolution reactions (10 and 16 times higher in the respective turn-over frequency compared to Ni3 N-alone nanorods). The interface transfer effect is verified by electronic binding energy shift and density functional theory (DFT) calculations. This nanoconfinement effect occurring during in situ atomic epitaxial in-growth of the two compatible materials shows an effective pathway toward high-performance electrocatalysis and energy storages.

Contribution of resonance excitation on ionization of OCS molecules in strong laser fields

Photoelectron images from single ionization of OCS molecules are measured at 800 nm or 400 nm linearly polarized laser pulses (∼50 fs) using velocity-map imaging techniques. The resonant ionization of the molecules has been studied by tracing the electron energy shift in the photoelectron energy spectra at different laser intensities, and the contributions of three excited states at certain laser intensities and wavelengths are identified. During the ionization of OCS molecules, two excited states (1Δ and 1∏) are shifted into resonance at different 800 nm laser intensities, and the Rydberg state 4pσ ∏ is involved in the resonance for a 400 nm laser. The demonstration of resonant excitation contribution experimentally will help further the understanding of OCS ionization in strong laser fields.

Contribution of resonance excitation on ionization of OCS molecules in strong laser field

SynopsisThe resonant enhanced multiphoton ionization (REMPI) of OCS molecules has been studied by tracing the electron energy shift with the laser intensity dependent photoelectron energy spectra. We find that two excited states (1Δ and 1Π) have been involved in the ionization of OCS at 800 nm and the REMPI through a certain excited state can be selectively controlled by varying the laser intensity. Furthermore, the REMPI of OCS through 4sσ Rydberg states at 400 nm laser fields has also been identified by angular distribution of electrons.

Dynamics of space-charge acceleration of X-ray generated electrons emitted from a metal surface

The so-called vacuum space-charge acceleration of emitted electrons triggered by absorption of soft X-rays (a few 100eV) under intense near-infrared laser excitation is studied experimentally and theoretically. The influence of high excitation densities on the properties of Auger and photo electrons liberated by a probe X-ray beam is investigated for grazing-incidence photons interacting with an atomically clean Cu (111) surface as a model system. Transient electron spectra have been taken in a pump–probe setup at the BESSY II storage ring using a newly developed compact electrostatic retarding Bessel-box spectrometer. Strong electron-energy shifts have been found and assigned to space-charge acceleration. Model calculations based on experimental input parameters are in good agreement with experimentally obtained energy-gain values indicating ultimate limits of ultrafast X-ray experiments with photo or Auger electrons as a probe.

Asymmetric Stark shift in an impurity doped dome-shaped quantum dot with wetting layer

The effects of vertical electric field and donor impurity on the electronic properties of the dome-shaped InAs/GaAs quantum dot coupled to its wetting layer were investigated. The dependence of the electron density, energy and Stark shift of the S-, P- and WL-states on the applied electric field was studied with and without impurity. The S- and P-states have no significant qualitative changes in the shape of the wave functions with increasing the electric field, except that they become slightly shifted due to the competition between the field action and the quantum confinement. The wave function of the WL-state is strongly modified in polarized structures. Our results reveal that the Stark shift of electron energies can be fitted with a quadratic dependence on the electric field, the linear and quadratic terms corresponding to the dipole moment and static electron polarizability. Their estimated values reasonable agree with those calculated.

Laser-pump/X-ray-probe experiments with electronsejected from a Cu(111) target: space-charge acceleration.

A comprehensive investigation of the emission characteristics for electrons induced by X-rays of a few hundred eV at grazing-incidence angles on an atomically clean Cu(111) sample during laser excitation is presented. Electron energy spectra due to intense infrared laser irradiation are investigated at the BESSY II slicing facility. Furthermore, the influence of the corresponding high degree of target excitation (high peak current of photoemission) on the properties of Auger and photoelectrons liberated by a probe X-ray beam is investigated in time-resolved pump and probe measurements. Strong electron energy shifts have been found and assigned to space-charge acceleration. The variation of the shift with laser power and electron energy is investigated and discussed on the basis of experimental as well as new theoretical results.

Strain‐ and torsion‐induced resonance energy tuning of Raman scattering in single‐wall carbon nanotubes

AbstractRaman excitation profiles for homogeneously deformed single‐walled carbon nanotubes are calculated and systematically analyzed. A number of attractive and apparent effects significant in designing electromechanical devices are caused by torsion and uniaxial strain. The shift of radial breathing mode (RBM) phonon energies due to deformation is negligible. The linear dependence of electronic transition energy shift on deformation is confirmed and it is found that the slope of it is strongly related to the chiral angle of the tube. It is also shown that for some tubes the transition energy shift covers the entire visible‐light interval, making them perfectly tunable light absorbers. Two types of deformation are compared, a relaxed (slow) deformation and an adiabatic (fast) one. It is found that transition energies are more sensitive to adiabatic deformation, which can be useful for optomechanical device designing.Raman excitation profile of a (9,9) nanotube under torsion.

Energy Shift of H-Atom Electrons Due to Gibbons-Hawking Thermal Bath

The electromagnetic shift of energy levels of H-atom electrons is determined by calculating an electron coupling to the Gibbons-Hawking ectromagnetic field thermal bath. Energy shift of electrons in H-atom is determined in the framework of non-relativistic quantum mechanics.

Curvature-induced bound states and coherent electron transport on the surface of a truncated cone

We study the curvature-induced bound states and the coherent transport properties for a particle constrained to move on a truncated cone-like surface. With longitudinal hard wall boundary condition, the probability densities and spectra energy shifts are calculated, and are found to be obviously affected by the surface curvature. The bound-state energy levels and energy differences decrease as increasing the vertex angle or the ratio of axial length to bottom radius of the truncated cone. In a two-dimensional (2D) GaAs substrate with this geometric structure, an estimation of the ground-state energy shift of ballistic transport electrons induced by the geometric potential (GP) is addressed, which shows that the fraction of the ground-state energy shift resulting from the surface curvature is unnegligible under some region of geometric parameters. Furthermore, we model a truncated cone-like junction joining two cylinders with different radii, and investigate the effect of the GP on the transmission properties by numerically solving the open-boundary 2D Schrödinger equation with GP on the junction surface. It is shown that the oscillatory behavior of the transmission coefficient as a function of the injection energy is more pronounced when steeper GP wells appear at the two ends of the junction. Moreover, at specific injection energy, the transmission coefficient is oscillating with the ratio of the cylinder radii at incoming and outgoing sides.

A computational study on azaazulenes

Abstract All possible aza analogs of azulene, containing from one to three nitrogen atoms in the five-membered ring or from one to five nitrogen atoms in the seven-membered ring, have been theoretically considered to obtain information about their stabilities and aromaticities. Total electronic energy and nucleus independent chemical shift (NICS) data have been used to evaluate stability and aromaticity, respectively. The stabilities of the structures are strongly affected by the positions of the nitrogen atoms. Calculations of azaazulenes show that stability is decreased with close proximity of the nitrogen atoms. When nitrogen in the five-membered ring is adjacent to a ring junction, aromaticity of the cyclopentadienyl anion is reduced and that of the tropylium cation is increased. The number of nitrogen atoms affects the aromaticity of the system.

Independent control of electron energy and density using a rotating magnetic field in inductively coupled plasmas

Effects of a rotating magnetic field (RMF) on the electron energy distribution function (EEDF) and on the electron density are investigated with the aim of controlling the radical composition of inductively coupled plasmas. By adjusting the RMF frequency and generation power, the desired electron density and electron energy shift are obtained. Consequently, the amount and fraction of high-energy electrons, which are mostly responsible for direct dissociation processes of raw molecules, will be controlled externally. This controllability, with no electrode exposed to plasma, will enable us to control radical components and their flux during plasma processing.

Electron distribution function and recombination coefficient in ultracold plasma in a magnetic field

The electron distribution function and diffusion coefficient in energy space have been calculated for the first time for a weakly coupled ultracold plasma in a magnetic field in the range of magnetic fields B = 100−50000 G for various temperatures. The dependence of these characteristics on the magnetic field is analyzed and the distribution function is shown to depend on the electron energy shift in a magnetic field. The position of the “bottleneck” of the distribution function has been found to be shifted toward negative energies with increasing magnetic field. The electron velocity autocorrelators as a function of the magnetic field have been calculated; their behavior suggests that the frequency of collisions between charged particles decreases significantly with increasing magnetic field. The collisional recombination coefficient αB has been calculated in the diffusion approximation for a weakly coupled ultracold plasma in a magnetic field. An increase in magnetic field is shown to lead to a decrease in αB and this decrease can be several orders of magnitude.

Influence of addifion of electronegative gases on the properties of capacitively coupled Ar plasmas

Investigation of electronegative plasmas has now been atrractive due to the advantages of negative-ion assisted etching and charge-free ion implantation in semiconductor manufacture. Langmuir electrostatic probe, as a simple, inexpensive and good spatial resolution diagnosic tool, is popularly used in investigating electronegative plasmas. In this paper, the Langmuir electrostatic probe is proposed to measure the capacitively coupled Ar plasmas with added electronegative gases, such as O2, Cl2 and SF6. The experimental results from the measurements of Ar plasmas with added electronegative gases driven by a 40.68 MHz field indicate that, with increasing flow rate of electronegative gas, high energy peak will occur in electron energy possibility function and shift towards higher energyside. The addition of electronegative gases reduces the electron density significantly as the electron temperature increases. We also calculate the electronegativity of Ar plasmas for the three kinds of electronegative gases. The preliminary interpretations of the above experimental phenomena are presented.

Algorithm for evaluating layer thickness based on electron average energy shift analysis

Layer thickness estimation method using the average energy shift of electrons passing through the layer is presented. The traditional approach of analyzing the signal electron is extended by using the spectral distribution of the energy shift of the electrons. In this approach, the tendency of the multiple inelastic scattering spectra to increase the average energy shift, depending on the number of inelastic interactions, is utilized to estimate the thickness of a layer. An algorithm that uses this spectral energy shift to evaluate the layer thickness was developed and validated against calculated spectrum from a known materials and thicknesses. The thickness evaluation by this algorithm is in a good agreement with the known thickness.

Enhancement and red shift of photoluminescence (PL) of fresh porous Si under prolonged laser irradiation or ageing: Role of surface vibration modes

We study the effect of a red shift and a considerable enhancement of photoluminescence (PL) intensity from a freshly etched porous Si (PS) thin film after prolonged laser irradiation or after aging in atmosphere. Both effects coincide with the appearance of Si–OH and Si–O–Si vibration modes in the Fourier transform infrared (FTIR) absorption spectra. The red shift is attributed to a pinning of the band gap of the light-emitting Si nanocrystals (NCs) due to the formation of Si–OH and Si–O–Si bonds. Using theoretical calculations, we estimated the electron and hole energy shifts caused by the interaction of the electronic states of the Si NCs with the surface vibrations, and correlated the observed PL enhancement with resonant coupling between the quantized valence sub-levels in the Si NCs and surface vibration modes.

Unconventional quantum-confined Stark effect in a singleGaNquantum dot

We show that a peculiar excitonic effect and a confining potential in self-assembled hexagonal $\mathrm{GaN}∕\mathrm{AlN}$ quantum dots produce an unconventional quantum-confined Stark effect. In contrast to the conventional quantum-confined Stark shift, the emission line from a single $\mathrm{GaN}$ dot under the applied electric field perpendicular to the growth direction blueshifts nearly symmetrically with respect to the direction of the field. The field dependence of the emission lines is reproduced in a charge self-consistent effective mass calculation, taking into account strain, piezoelectric charge, and pyroelectric charge. The unconventional blueshift is attributed to a significant variation of the exciton binding energy, made obvious by a cancellation between the energy shifts of electron and hole confined states.

Charge Migration Mechanism in DNA Strands Elucidated by Electronic Structure Examinations

In order to establish the charge migration mechanism, we examined the electronic structure of bases in DNA strands by means of resonant photoemission spectroscopy near the Fermi level. Because the N atoms are only included in bases in DNA strands, the electronic orbital features of the bases can be specified selectively at the resonant excitation from the N core level to unoccupied states. On the obtained resonant photoemission spectra for both poly(dG) · poly(dC) and poly(dA) · poly(dT) DNAs, we observed a kinetic energy shift of N-KLL Auger electrons and an intensity enhancement of valence electrons. These results clearly show the localized unoccupied electronic states of the bases. Therefore, it is concluded that the charge hopping model is pertinent for the charge migration mechanism in DNA strands, when electrons pass through the unoccupied states.

Electronic structure of bases in DNA duplexes characterized by resonant photoemission spectroscopy near the Fermi level.

The electronic structure of bases in DNA duplexes was investigated by resonant photoemission spectroscopy near the Fermi level, in order to specify charge migration mechanisms. We observed a kinetic energy shift of N-KLL Auger electrons and an intensity enhancement of valence electrons on the resonant photoemission spectra for both poly(dG).poly(dC) and poly(dA).poly(dT) DNAs. These directly show the localized unoccupied states of the bases. We conclude that the charge hopping model is pertinent for electric conduction in a DNA duplex, when electrons pass through the unoccupied states.