Energieverlustmessungen an III–V-Verbindungen

Energy loss measurements with 55 keV electrons were made on the III–V compounds GaP, GaAs, GaSb, InAs and InSb. Retardation effects become important, because for these substances the condition for Cerenkov radiation is fulfilled. These produce an additional peak in the energy loss spectrum; its angular distribution and its dependance on the foil thickness were measured. The experimental results are in good agreement with the energy loss probability calculated by Kröger taking into account the retardation. Retardation- and surface effects vanish for scattering anglesθ≧0.6; 0.6 mrad. Then it is possible to determine the energy loss function Im(1/?). By means of the KramersKronig analysis the optical constants? ₁ and? ₂ were computed. The values are in agreement with data obtained from optical measurements.     

Bestimmung von optischen Konstanten an Palladium und Silber aus Energieverlustmessungen im Energiebereich von 2 bis 90 eV

The energy loss functions Im (?1/?) of Silver and Palladium are determined from energy loss experiments with 60 keV electrons. The influence of surface effects and multiple losses is discussed and the values of Im (?1/?) are corrected for them. By means of Kramers-Kronig analysis the optical constants? ₁ and? ₂ are calculated from the energy loss function and found to be in good agreement with data derived from optical experiments by various authors.     

Messungen von Äquivalentbreiten in homogenen Magnetfeldern II. Na—D2-Typus

Magnetooptical measurements of the equivalent width of the Na—D₂-line as a function of the magnetic field and the optical depth agree with theoretical predictions in all essential details. These results are typical for spectral lines of atoms withS _1/2?P _3/2-transitions and nuclear spinI=3/2 and are very important for any multiple diffusion of radiation in magnetized metal vapours.     

Study of the optically diffused reflectance and thermal-microstructure for the phase transformation of AgNO3

Optical, microstructural, and thermal properties of the investigated silver nitrate samples were characterized by various techniques, such as X-ray analysis, scanning electron microscopy, UV–Vis–NIR absorption and differential scanning calorimetry (DSC). The presence of structural phase transition [orthorhombic structure (phase II) to rhombohedral structure (phase I)] was checked by DSC and X-ray analysis measurements. The thermal energy required for such transformation is found to be 11.6 J/g. The optical band gaps of AgNO₃ are 1.4 and 2.02 eV for phase II and phase I, respectively, at the low-energy region. But at high-energy region, the optical band gaps are 3.41 and 3.43 eV for phase II and phase I, respectively. Characteristic peaks for AgNO₃ corresponding to (2 1 1), (0 0 4) and (3 5 1) for phase II and (0 0 4), (3 1 1) and (0 2 4) for phase I have been observed. The average crystalline size for AgNO₃ samples and the values of dislocation density δ and the strain ε for the planes of two phases II and I are calculated and also the texture coefficient is determined. Such information can considerably aid in understanding the process of phase transformations in AgNO₃.     

Energieverlustmessungen mit 60 keV Elektronen an amorphem und polykristallinem Selen und Tellur und Bestimmung optischer Konstanten

The energy loss functions Im—(1/?) of amorphous and polycrystalline Selenium and Tellurium are determined from energy loss spectra of 60 keV electrons in the energy range up to 30 eV. The optical constants ?₁ and ?₂ are calculated from the energy loss function by Kramers Kronig analysis. The energy difference in the position of the volume plasma loss of amorphous and polycrystalline foils is compared with the calculated change in free electron plasma energy resulting from density change. Characteristic structure dependence of the optical constants are found to be similar for Selenium and Tellurium. They are discussed in terms of the results of band structure calculations.     

Energieverlustspektren der Alkalihalogenide und der Metalle Cu,Ag und Au und Vergleich mit optischen Messungen

Energy loss spectra of 50 keV electrons have been measured in transmission of the alkali halides and of Cu, Ag, and Au at zero scattering angle. These spectra are compared with the quantity ?Im(1/ε) determined from optical measurements. The general agreement is good, especially in the low energy loss region. In the case that the foil thicknesses could be measured, the absolute intensity of ?Im(1/ε) is found to be equal or up to three times larger than from optical data. In addition to the sharp low energy peaks (excitons), characteristic sharp peaks are found at higher energies: 60 eV for the Li-halides, 33 eV for the Na-halides, and 20 eV, 17 eV, and 13 eV for the K-, Rb-, and Cs-halides respectively. These peaks are very little shifted by the different anions in the crystal lattice and may be due to excitons caused by alkali band transitions. We have further examined several peaks in the loss spectra of LiF, KCl, KBr and the Na-halides: 1. The angular dependence of the loss intensity is in agreement with theory. 2. The dispersion of the peaks is much smaller than for plasma losses. 3. The temperature dependence of the peak energy has been found quite different for different peaks.     

A theoretical study of the photoelectron spectrum of atomic lithium

The 1s photoelectron spectrum of atomic lithium has been calculated for incident photon energies of 151 and 1487 eV. For this open-shell system there are four possible final-state manifolds for the residual ion, with symmetries ³S, ¹S, ³P^o and ¹P^o. The line energies for the first four members of each manifold have been calculated using relaxed Hartree—Fock or configuration interaction wavefunctions as required. The agreement with available optical data is excellent.The intensity expressions neglecting interchannel coupling have been evaluated to allow a comparison of line intensities between final-state manifolds and hence the synthesis of theoretical spectra. The variation of the spectral profile with photon energy is clearly demonstrated. Conjugate shake-up, as well as shake-up processes are predicted to be important at high photon energy.     

Photonuclear reaction yields from59Co at 35 MeV and 54 MeV

In energy loss measurements with 50 keV electrons the damping of the 15 eV volume plasma loss in Al was investigated by means of its energy half widthΔ E as function of the scattering angle?. For angles smaller than 1.5 · 10^?3 rad a damping is observed, which cannot be explained by former theories. It comes into play when the wavelength of the plasmons is larger than the mean crystal sized. — For large crystal size (d ≧250 Å) the half width of the plasma loss obtained at ?=0 was 0.53 eV.     

Observation of the ABC effect and final-state isospin

Despite the number of inclusive measurements of the pionic fusion reactions, the nature of the ABC effect discovered in 1960 was not completely established. Exclusive measurements of the doublepion-production reactions leading to either fused d, ³He and ⁴He nuclear final states or pp pairs are analyzed. A significant ABC effect—enhancement in the region of low ππ mass—is found only in the isoscalar ππ channel while in the isovector channels it is small or absent. For the reaction with isovector pp final state an ABC effect was not observed even at the special kinematic conditions to reproduce a quasi-bound two-proton state. The total cross sections for the d and 4He fusion reactions show similar resonance-like energy dependence.     

Electron-spectroscopic investigations of Ba and Ba compounds

Electron spectroscopic investigations of barium, barium compounds and barium thin film structures are reported. It is found that the barium 3d photoelectrons from BaO are at lower binding energies than for the case of pure barium metal. This effect is ascribed to relaxation processes. In some cases the compounds studied exhibited charging. In these cases plots of the Auger—Photoelectron energy separations are measured which were found to provide a using means of identifying the chemical environment of the barium atoms. Finally, measurements of the ionization loss spectra, principally the barium 4d lines, and changes in the plasmon energies for this series of barium compounds are reported.     

Optische Eigenschaften des einkristallinen Siliziums aus Elektronenenergieverlustmessungen

Electron energy loss measurements on Si-monocrystals with fast electrons in transmission have been carried out to determine the energy loss function Im—1/. The real and imaginary part of the dielectric constant have been deduced from the Kramers-Kronig relation. The results are compared with those obtained from optical reflectance data. The energy loss function obtained from these energy loss experiments is found to be in good agreement with theoretical calculations.     

Structure of the mirror nuclei21Ne and21Na

Theγ-decay of levels in²¹Ne up to 10 MeV excitation energy has been investigated byn — γ coincidence measurements initiated with the¹⁸O(α, nγ) reaction at 12, 13, 14.5 and 15.4 MeV bombarding energies. Spin(-parity) assignments of excited states are obtained by combining then — γ angular correlation measurements performed atE _α=11, 11.82 and 13.6 MeV with a consideration of lifetimes, neutron penetrabilities of the unbound states, and information from the mirror nucleus²¹Na. The resulting values of E_x[keV]?J ^π are as follows: 4525-5⁺, 4686-3⁺, 5431-7⁺, 5549-3⁺, 5819-7^?, 6175-7⁺, 6268-9⁺, 6550-9, 6639-9, 7006-7⁺, 7041-9, 7356-7 or 9, 7422-11^(?), 7648-7⁺, 7981-11 or (7⁺), 8154-9, 8240-11, 8664-9^? or 11 or 13^?, 9401-13^?, 9867-13^? or 15⁺, 9941-13^? or 15 or 17⁺. The assignment of mirror levels in²¹Ne —²¹Na has been extended to the 6175 keV level of²¹Ne. Excitation energies, electromagnetic properties, Gamow?Teller matrix elements and spectroscopic factors of positive parity states are compared with the results of shell-model calculations which employ a unifieds—d shell Hamiltonian and the unrestricted configuration space of the 0d _5/2 —1s _1/2—0d_3/2 shell. Collective properties contained in shell model wave functions are explored up to the termination of bands atJ=17/2 or 19/2. The spectrum of intruder states in²¹Ne is observed to begin with a 5628 keV,J ^π=7/2⁺ state. The 7422, 8664 and 9401 keV levels are assigned as members of previously established negative-parity rotational bands.     

On the nature of energy bands in tetracyanoplatinates

Optical data and band calculations are presented for a series of tetracyanoplatinates with varying Pt—Pt-distance R. The band gap energies decrease according to R^-3 with decreasing R. The energy bands which determine the optical and electrical properties for E6 c originate from (Pt5d_z², 6s) and (Pt6p_z, CNπ¹) hybrid molecular states.     

Nontrivial class of composite U(σ+μ) vector solitons

A mixed problem for the compact U(m) vector nonlinear Schrödinger model with an arbitrary sign of coupling constant is exactly solved. It is shown that a new class of solutions—composite U(σ+μ) vector solitons with inelastic interaction (changing shape without energy loss) at σ>1 and strictly elastic interaction at σ=1— exists for m≥3. These solitons are color structures consisting of σ bright and μ dark solitons (σ+μ=m) and capable of existing in both self-focusing and defocusing media. The N-soliton formula universal for attraction and repulsion is derived by the Hirota method.     

Channeling of protons,pions and deuterons in the GeV region

Strong directional effects have been observed when 1.15 and 1.35 GeV/c protons, π⁺ and π^?, and deuterons penetrate through germanium crystals. Transmission, wide-angle scattering, and an attempt to do blocking distributions are obtained from experiments using position-sensitive drift chambers. Corresponding measurements of energy loss in germanium crystals are also presented. These experimental results are compared to theory for energy loss, and satisfactory agreement is obtained.     

Dispersion relation for the 3.8 eV volume plasmon of silver

The dispersion curve of the 3.8 eV volume plasmon of Ag has been obtained by electron energy loss measurements for wave vectors q in the range $\text{0.1 ?q? 0.35}\text{A}\text{?}{}^{-1}$. Results from the low-q end of this range match well with the optical results of Lindau and Nilsson. The curve can be described by a dispersion constant a = 0.8 ± 0.1 and the intensity of the loss goes like I≈q^-2.9±0.4. A simple model for the longitudinal dielectric function yields results in good agreement with the experimental conclust     

Structural,optical and dispersion characteristics of nanocrystalline GaN films prepared by MOVPE

In this work, nanocrystalline GaN film was grown on a c-plane sapphire substrate by metal-organic vapor phase epitaxy (MOVPE). The structural and optical properties of the nanocrystalline GaN thin film were studied. The morphological and structural properties of GaN film were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. According to the X-ray diffraction spectrum, a GaN film was formed with a wurtzite structure, which is the stable phase. The optical parameters were determined using spectrophotometric measurements of transmittance and reflectance in the wavelength range 200–2500 nm. The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region reveals a direct allowed transition with a band gap of 3.34 eV. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–Didomenico (WD) model. The single oscillator energy (E_o), the dispersion energy (E_d), the high frequency dielectric constant (ε_∞), the lattice dielectric constant (ε_L) and the free charge carrier concentration (N) were estimated. From the optical dielectric analysis, the optical conductivity, volume and surface energy loss functions were calculated. Moreover, the third-order nonlinear optical susceptibility χ⁽³⁾ was also considered.     

Electron—hole liquid in CdS crystals as revealed by non-equilibrium transmission spectroscopy

Transmission measurements in the excitonic region on thin platelets under high N₂ laser excitation showed the disappearance of exciton absorption into a strong absorption continuum. The low energy edge of the latter — about 12 meV below the free exciton A_n=1 — coincides with the high energy edge of the gain spectrum of stimulated emission under similar excitations. These results favour the assumption of electron—hole drop formation with a ground state of the e-h-pair about 12 meV below A_n=1.     

Temperature dependent energy relaxation time in AlGaN/AlN/GaN heterostructures

The two-dimensional (2D) electron energy relaxation in Al_0.25Ga_0.75N/AlN/GaN heterostructures was investigated experimentally by using two experimental techniques; Shubnikov-de Haas (SdH) effect and classical Hall Effect. The electron temperature (T_e) of hot electrons was obtained from the lattice temperature (T_L) and the applied electric field dependencies of the amplitude of SdH oscillations and Hall mobility. The experimental results for the electron temperature dependence of power loss are also compared with the current theoretical models for power loss in 2D semiconductors. The power loss that was determined from the SdH measurements indicates that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. In addition, the power loss from the electrons obtained from Hall mobility for electron temperatures in the range T_e > 100 K is associated with optical phonon emission. The temperature dependent energy relaxation time in Al_0.25Ga_0.75N/AlN/GaN heterostructures that was determined from the power loss data indicates that hot electrons relax spontaneously with MHz to THz emission with increasing temperatures.     

Modern trends in methods of charged particle identification at high energies

The survey is devoted to methods of charged particle identification at high energies that are based on measurements of the angle of Cherenkov radiation (ring imaging Cherenkov counters — RICH), of time of flight (TOF) and propagation (TOP), and of ionization energy loss (dE/dx). As an example, some operating spectrometers are considered (LHCb, ALICE, COMPASS, Belle, and BaBar) together with proposed ones (Belle-2 and PANDA) in which new achievements of recent years are introduced.