Ionization energies of liquids from energy distribution,quantum yield and second derivative curves

The energies of the lowest ionization band of eight liquids of low vapor pressure are determined from energy distribution curves (EDC), quantum yield spectra (collected electrons per incident photon as a function of photon energy), and second derivative curves (SDC) of retarding potential curves. Threshold energies from EDCs and quantum yield spectra agree if one takes into account a 0.15 e V shift caused by the spectrometer's rather low resolution and a small difference (0.15 eV or less) resulting from the use of approximate extrapolation methods. Threshold energies from EDCs and SDCs agree to within 0.1 eV after correction for the half-width of the high-energy branch of SDCs. Multiple ionization bands are exhibited by the SDCs of some of the liquids, and the observed splittings agree well with the results from gas-phase UPS spectra. A new spectrometer for the measurement of EDCs of liquids is described. The liquids studied are 6-chloro-1-hexanol, 2-ethyl-1-hexanol, ethylene cyanohydrin, ethylene glycol, 1,5-pentanediol, tetraglyme, triethylene glycol and tetraethylene glycol.     

Variation of electron energy loss spectra of Ni (100) with increasing primary energy

Electron energy loss spectra of clean Ni(1 0 0) show for the first time a 17 eV peak, which is attributed to an interband transtiion. All the observed peaks are shifted to higher energies as the primary electron energy E_p increases from 102 to 2045 eV. This shift is explained by a continuous decay in energy of the primary electrons inside the crystal. At E_p ? 700 eV, the decay takes place in the surface region of the crystal, while at E_p > 700 eV it takes place mainly in the bulk. The rate of decay increases with increasing temperature of the crystal between 300 and 900 K.     

Influence of 2p-2h excitations in the41Sc-41Ca Coulomb energy shift

The influence of 2p-2h core excitations on the⁴¹Sc-⁴¹Ca Coulomb energy difference is studied. A simple parametrization of the main wave function components shows that the calculated energy shift could only agree with experiment for rather unrealistic values of the amplitudes. Using an effective interaction appropriate for this region, we find that when this kind of excitations is included, the calculated Coulomb energy shift is increased by 105keV.     

Oxygen isotope effect in optimally doped Bi2Sr2CaCu2O8+δ studied by low-energy ARPES

Using angle-resolved photoemission spectroscopy (ARPES) with low-energy tunable photons, we studied the oxygen isotope effect in optimally doped Bi₂Sr₂CaCu₂O_8+δ (Bi2212). We found the oxygen isotope shift in the real part of the electron self-energies [ReΣ(ω)s] along the nodal direction derived not only from the momentum distribution curves (MDCs) but also from the energy distribution curves (EDCs). Present results indicate straightforwardly the coupling between the nodal electrons and the phonons.     

Coulomb energy of nuclei

The density functional determining the Coulomb energy of nuclei is calculated to the first order in e ². It is shown that the Coulomb energy includes three terms: the Hartree energy; the Fock energy; and the correlation Coulomb energy (CCE), which contributes considerably to the surface energy, the mass difference between mirror nuclei, and the single-particle spectrum. A CCE-based mechanism of a systematic shift of the single-particle spectrum is proposed. A dominant contribution to the CCE is shown to come from the surface region of nuclei. The CCE effect on the calculated proton drip line is examined, and the maximum charge Z of nuclei near this line is found to decrease by 2 or 3 units. The effect of Coulomb interaction on the effective proton mass is analyzed.     

Directed energy transfer due to orientational broadening of energy levels in photosynthetic pigment solutions

The directed non-radiative energy transfer through monomeric molecules of chlorophyll “a” and pheophytin “a” at high concentrations (c~10^-2 M) in a rigid matrix of polyvinylbutyral has been found by using the nanosecond laser spectrofluorimeter. The phenomenon is caused by orientational broadening of pigment molecular spectra owing to its interaction with a solvent. The observed temporal shift of the luminescence spectrum to the red region in a nanosecond time scale as well as the red shift of the time integrated spectrum at a high concentration of pigment molecules and the monotonic growth of the luminescence lifetime with a shift to the red region of the spectrum served as indications of the directed energy transfer in the sample. The non-radiative energy transfer from monomeric molecules towards aggregates is also directly demonstrated by the deformation of instantaneous luminescence spectra in the long-wavelength range (λ>700 nm). The role and the possibility of the directed energy transfer between molecules with orientationally broadened spectra in the biological systens are discussed.     

Shallow impurity states and the free exciton binding energy in gallium phosphide

A new set of donor and acceptor ionization energies in GaP is deduced from photoexcitation spectra. Energy spectrum of donor states confirms an existence of the “camel's back” with a conduction band minima displacement ≈ 0.08(2π/a) from the X, and the corresponding energy shift ≈ 3meV. The free exciton binding energy in GaP is correctly determined: E_ex = 21 ± 2 meV.     

Electron energy loss for two transition metal-transition metal glasses

Electron energy loss data are reported for metallic glasses Fe_0.92Zr_0.08 and Ni_0.5Zr_0.5. These data document the sensitivity of the spectra to sample thickness and suggest studies of metallic glasses require samples that are nearly $\text{1}\text{2}$ an order of magnitude “thinner” than crystalline alloys. Each electron energy loss spectrum has a dominant loss near 23–25 eV which is similar to the loss function of the pure 3-d metal. This lack of a shift in the location of the dominant loss challenges any simple model of plasmon behavior. The M₂₃ core losses are visible in the “thinner” samples and, in agreement with earlier studies on metal-metalloid glasses, no measureable chemical shift is observed.     

Potential energy shift for a screened Coulomb potential

Utilizing Hartree-Fock self-consistent field wave functions, accurate values of the potential energy shift at the nucleus due to atomic electrons have been determined for a large number of atoms. An extensive numerical table of values of the shift,V ₀, is given and comparison is made with earlier approximate results obtained from the Thomas-Fermi and Thomas-Fermi-Dirac statistical models and with estimates fromK binding energy data. In the calculation of screening corrections to Fermi functions, the Hartree-Fock results present a considerable improvement over earlier estimates from the aforementioned methods.     

Exciton binding energy in a double quantum well: effect of the barrier shift

We have calculated the exciton binding energy in an Al _xGa_1 − x As  / GaAs double quantum well by a variational envelope function procedure using a simple two-band model. The influence of the shift of the AlAs separating barrier, introducing an asymmetry into the system, on the value of the exciton binding energy has been analysed. It has been observed that this shift induces significant changes of the exciton binding energy—even several meVs in the case of very thin barriers.     

The transverse energy distribution in hadron-lead collisions

The transverse energy cross-sectiondσ/dE _T has been measured in the pseudorapidity region 0.6<η<2.4 for hadron-lead collisions at 200 GeV/c incident hadron momentum. TheE _T distribution extends to 40 GeV, which is twice the kinematic limit forp-p collisions at the same incident beam momentum. The distribution ofE _T is found to shift towards low pseudorapidities with increasing total transverse energy.     

Photoinduced absorption in Trans-(CD)x; isotope energy shifts

Steady state photoinduced absorption in trans (CD)_x is reported for energies of 0.1–2.1 eV. All induced infrared active vibrations as well as the photoinduced electronic bands show an energy down shift compared to those of (CH)_x. The change in the induced vibrations spectrum is fully understood and it results from different bare-phonons in the two isotopes. The origin of the isotope shift observed in the electronic bands is discussed.     

The electric field effect on binding energy of hydrogenic impurity in zinc-blende GaN/AlxGa1−xN spherical quantum dot

Within the framework of effective mass approximation, the binding energy of a hydrogenic donor impurity in zinc-blende GaN/Al_xGa_1−xN spherical quantum dot (QD) is investigated using the plane wave basis. The results show that the binding energy is highly dependent on impurity position, QD size, Al content and external field. The binding energy is largest when the donor impurity is located at the centre of the QD and the binding energy of impurity is degenerate for symmetrical positions with respect to the centre of QD without the external electric field. The maximum of the donor binding energy is shifted from the centre of QD and the degenerating energy levels for symmetrical positions with respect to the centre of QD are split in the presence of the external electric field. The binding energy is more sensitive to the external electric field for the larger QD and lower Al content. In addition, the Stark shift of the binding energy is also calculated.     

Effect of energy spread on micro-bunching from shot noise in SASE FELs

The motion of Ne electrons moving along a helical undulator and interacting with each other through Lienard-Wiechert fields is considered. The numerical solution for initially mono-energetic electrons shows the emergence and growth of micro-bunching. For the case of initially non-mono-energetic electrons, calculations show that the presence of energy spread results in partial suppression of the micro-bunching. The calculations also show that the initial energy spread would shift the micro-bunching maximum to deeper positions within the undulator. Analytical treatment of equations of motion demonstrates that the micro-bunching fall and shift is mainly due to the random motion of the interacting electrons.     

Hysteresis effect and surface energy of drops in silicon

We report here the observation of the hysteresis effect of the drop luminescence in silicon at the temperature of 6.6 K. Hysteresis ratios up to 2.1 have been registered. The surface energy σ of drops is deduced from the measurement of the energy shift of the drops luminescence at low pumping level. The results yield: σ = (125±60) × 10^?4ergcm^?2.     

Carrier energy spectrum and lifetime in quantum dots in electric field

The S-matrix formalism is used to perform analytical calculations of the spectrum of quasi-stationary states of charge carriers in a core-shell quantum dot. Analytical expressions are obtained for the second-order perturbative corrections to the position and half-width of a quasi-stationary energy level, and level shifts are calculated numerically for a core-shell quantum dot in the presence of an electrostatic field. The corrections to level half-width due to Stark effect are analyzed as functions of level energy and barrier thickness. It is shown that there exists a level position E _cr such that the correction δΓ to the level half-width changes sign. An analytical expression for the quadratic Stark shift in a dc-biased quantum well is found in semiclassical approximation. It is shown that the corresponding correction δΓ to half-width also changes sign as energy passes through E _cr. As an example, the Stark shift is calculated for a core-shell quantum dot in the electrostatic field of an adjacent protein molecule.     

Double-hole binding energy shifts for the 5d transition metals

Recent experimental M₄₅N₆₇N₆₇ Auger energies for Ta, W, Ir, Pt, Au, Hg and Pb are analyzed in terms of the complete screening picture. For the shift in the double-hole (N₆₇N₆₇) binding energy between the free atom and the metal a good agreement is found between theory and experiment. The variation of the shift throughout the 5d series and beyond reflects different types of screening of the two core holes, i.e. a large shift in the case of d-type screening and a considerably smaller shift for sp-type screening.     

Momentum and energy relaxation of warm carriers in semiconductors

Non-linear microwave optics of semiconductors is influenced by two relaxation times τ _m and τ_? which determine energy and momentum relaxation. In the range of warm carriers τ_? is assumed to be not dependent and τ _m linearly dependent on energy. The simple model of band structure of semiconductors and a monoenergetic energy distribution of carriers are assumed. The calculation yields the frequency dependence of the nonlinearity coefficient β as observed by Seeger with Morgan's experimental arrangement (parallel d.c. and a.c. electric fields) also at high frequencies and low temperatures. Furthermore, the h.f. behaviour of frequency multiplication and harmonic mixing are given.     

Binding energy of an off-center hydrogenic donor in a spherical Gaussian quantum dot

The energy levels of an off-center hydrogenic donor confined by a spherical Gaussian potential have been calculated as a function of the potential radius for different donor position by exact diagonalization method. The results have clearly demonstrated the so-called quantum size effect. The binding energy is dependent on the dot radius R, the impurity ion distance D, and the confining potential depth V₀.