High-resolution Energy Spectra Research Articles

Investigation of complex ionization amplitudes in cadmium by (e,2e) spectroscopy.

High-resolution (e,2e) energy spectra are presented which enable the isolation of interference effects between J=0,1,2 multipoles in electron-impact ionization of cadmium. It is found that both resonant and nonresonant processes are important. Relative magnitudes and phases of ionization amplitudes are obtained which disagree with plane-wave Born approximation calculations.

Spin conservation in single-electron capture by N2+ in He, Ne, and Ar.

High-resolution translational energy spectra (0.2 eV at full width at half maximum) have been obtained for single-electron capture by 4-keV N[sup 2+] ions in collision with He, Ne, and Ar. Seven capture channels have been unambiguously identified for each of the He and Ne spectra, many of which have not been previously reported. This allows clarification of earlier studies. Twelve reaction channels have been identified for capture by N[sup 2+] in Ar, three of which involve excitation of the target product Ar[sup +] ion. All the observed channels are spin conservative. Competing channels which violate spin conservation are seen to be rigorously suppressed.

Shallow-acceptor spectral-line fine structure in germanium.

A controlled-accuracy, high-resolution energy spectrum of the 4\ifmmode\times\else\texttimes\fi{}4 Kohn-Luttinger Hamiltonian with a screened Coulomb impurity potential has been obtained. The calculated and measured spectra were adjusted using selected line positions. An identification of the boron spectrum reveals a complex structure for most of the lines. The identification yields the splittings in the multiplets and chemical shifts of the odd-parity excited states. An estimated splitting in the C triplet of 53 \ensuremath{\mu}eV is in fair agreement with the reported separation for Ge(B), Ge(Al), and Ge(In). New data on the spectroscopic values of the ground-state binding energies for nine experimentally studied acceptors are presented.

Copper by XPS

High energy resolution spectra of high purity Cu foil that was scraped in situ are presented. The experimental width (16%–84% measurement) of the Fermi level of nickel obtained under identical experimental conditions was 0.32 ± 0.02 eV. The binding energy scale calibration is based on the position of the Au 4f7/2 line which is taken to be 83.98 eV [see M. T. Anthony and M. P. Seah, Surf. Interface Anal. 6, 95 (1984)]. The Auger spectra are presented primarily to provide information on the detailed structure of the line at high energy resolution and accurate measurements of the relative separations between the transitions contained within the line. Since the kinetic energy of a photoelectron depends upon the photon energy and the kinetic energy of an Auger electron does not, the position of the Auger electron on the binding energy scale is a function of the photon energy. For nonmonochromatic x-ray excitation, the positions of the photoelectron lines and Auger lines are fixed relative to one another because the natural x-ray line has a defined centroid. However, for monochromatic Al Kα radiation, the exact photon energy can deviate from the centroid energy by as much as 0.3 eV. Thus, there can be systematic deviations in the binding energies of the Auger lines as recorded with instruments using monochromatic radiation as compared to those using nonmonochromatic x-ray sources. Comparison of the L3M4,5M4,5 line position with other published work [see M. P. Seah, G. C. Smith, and M. T. Anthony, Surf. Interface. Anal. 15, 293 (1990)] suggests that our photon energy is 1486.73 eV, and that all of the Auger line positions recorded in the table are systematically displaced by 0.15 eV.

A new Monte Carlo model for the calculation of MEIS energy spectra

A Monte Carlo model for the simulation of the interaction of medium energy ions with crystalline solids is presented. In the simulations all energy loss events are taken into account to obtain simulated ion backscattering energy spectra. The inelastic energy loss in the ion-atom interactions is calculated using either one of three distinct models: (1) a continuous or impact parameter independent model; (2) the Oen and Robinson model; and (3) the dielectric response model of Lindhard. Calculated and measured spectra of medium energy He + -ions scattered from Cu(100) are compared. It is concluded that both the continuous model and the dielectric response model underestimate the impact parameter dependence of the inelastic energy loss. A good fit between simulated and experimental results is obtained for the Oen and Robinson model. The Monte Carlo simulations are used to analyze high energy resolution spectra of 100 keV H + backscattered from NiSi 2 /Si(111). It is shown that the relaxation of the outermost atomic layer can be determined by comparing measured with simulated energy losses.

Secondary electron spectra from a tantalum surface by multiply charged ions

The kinetic energy spectra of secondary electrons from a Ta surface induced by multiply charged ions with keV incident energies, are observed. The spectral profiles are measured as a function of the incident charge state and the incident energy of the projectiles. Low energy electrons below 10 eV are found to be dominant and their intensities increase as the incident charge state as well as the incident energy increase. These low energy electrons are understood to be due to the kinetic emission. On the other hand, secondary electrons by the potential emission are also observed in high resolution energy spectra. It is found that the resonant neutralization followed by the Auger de-excitation and/or the autoionization plays an important role in the potential emission processes.

Determination of sheath potentials in rf plasmas

High resolution energy spectra of ions, accelerated across the sheath at the powered electrode of an rf gas discharge, are presented. The measured profiles are explained by a simple model. Ion energy, ion mass, total ion flux and time averaged sheath thickness are thus obtained. In the presence of a magnetic field fast electrons modify the sheath, resulting in an increased ion flux and a decreased sheath thickness.

Translational energy spectroscopy of CH 2+: First direct evidence of an excited electronic state

High-resolution translational energy spectra are presented of inelastic CH +-He and CH 2+-He collisions. An excited electronic state of CH 2+, of 2Σ + symmetry, is located at an energy of 12.3 eV above the ground electronic state. This excited state is metastable despite the existence of a large number of channels open for rapid decay by predissociation or dipole-allowed photon emission.

Recent X-ray Observations of Supernova Remnants and their Interpretation

AbstractA review is given of recent observations of the X-ray emission from supernova remnants carried out on the Einstein, Tenma and EXOSAT satellites as well as from a few sounding rocket experiments. Our current interpretation of the high resolution images, high resolution energy spectra and the first few spectrally resolved images is discussed.

Nanosecond timing in prompt γ ray analysis of bulk media using fast neutrons

High resolution time and energy spectra of γ rays emitted after inelastic scattering of 14.6 MeV neutrons in a bulk sample of concrete have been observed. The time spectrum suggests that about 90% of γ rays of interest for the prompt γ ray analysis are emitted from the 12 cm thick surface layer in less than 10 ns after the neutrons hit the sample. The decay of the observed γ ray intensity was found to be approximately exponential, yielding the effective fast neutron lifetime of 2.1 ns. The signal-to-background ratio in the high resolution energy spectrum can thus be substantially increased by applying nanosecond timing techniques. In this way we identified all major (abundance ≳ 1%) elements in the sample.

An electron spectrum and profile monitor for the UK free electron laser

A versatile electron spectrum monitor has been developed for the UK free electron laser project. The monitor uses secondary emission from 96 tungsten foils and microprocessor-controlled sampling electronics to produce a high-resolution electron energy spectrum. A 30-channel prototype is currently operating as a beam profile monitor and has been extensively used in emittance measurements at the Kelvin Laboratory linac.

Detachment of very-low-energy electrons from H^{-}

High-resolution energy spectra of electrons detached from ${\mathrm{H}}^{\ensuremath{-}}$ and ${\mathrm{D}}^{\ensuremath{-}}$ upon collisions with He and Ar have been measured at and near ${\ensuremath{\theta}}_{L}=0\ifmmode^\circ\else\textdegree\fi{}$. The measurements reveal some structure previously unseen in the high-energy peak at ${v}_{e}={v}_{i}$. This structure, along with changes in the spectra for ${\ensuremath{\theta}}_{L}g0\ifmmode^\circ\else\textdegree\fi{}$, leads to the assumption that the peak at ${v}_{e}={v}_{i}$ is due to the superposition of a very sharp peak on a broader peak. This very sharp peak has been stripped from the data and transformed to the rest frame of the incident ion. The ejection probabilities for the very-low-energy group of electrons (\ensuremath{\lesssim} 0.10 eV) were found to possess forward-backward symmetry and to be insensitive to the target gas and velocity of the ion.

Ionization of hydrogen and deuterium atoms in thermal energy collisions with state-selected Ne(3s 3 P 2,3 P 0) metastable atoms

High resolution energy spectra of electrons and ions resulting from thermal energy collisions of hydrogen and deuterium atoms with state-selected metastable Ne(Ne(3s 3 P 2,3 P 0) atoms are reported. The electron spectra for Ne(3 P 2)+H(D) are very broad: The high energy part due to formation of NeH+ (NeD+) bound states (associative ionization), amounts to about 30% of the ionizing events, whereas the dominant part of the spectrum including a prominent low-energy peak is due to Penning ionization out of a strongly-attractive entrance potential curve. Comparison of the spectra with quantum mechanical fit calculations yields fairly accurate information on this potential, in particular its well depthD e [Ne(3 P 2)−H,D]= 2.0(1) eV. The spectra for Ne(3 P 0)+H, D are comparatively narrow with much lower cross sections than the one for the Ne(3 P 2) state. The corresponding entrance channel is a weakly bound van der Waals molecule with a well depth below 0.1 eV. A perturbation calculation of the Ne(3s)+H(1s) potential energy curves at large distances explains the observed difference between the Ne(3 P 2)+H(D) and Ne(3 P 0)+H(D) systems. Symmetry arguments are given that the major contribution to the Ne(3 P 2)+H(D) spectra is due to the2 Σ potential.

Einstein observations of hot stars

Surveys with instruments on the Einstein Observatory have shown that essentially all 0 and B main sequence stars are X-ray sources as are many, if not all, 0B supergiants and Wolf-Rayet stars. The X-ray luminosities are sufficient to explain broad lines from the superionization stages seen in the UV spectra of the stars. High energy resolution spectra from the Solid State Spectrometer are shown to place severe constraints on various models for the location of the X-ray sources in the outer atmospheres of the stars. Coronal and embedded shock models for the X-ray emission are discussed and each is found to have some problems in explaining the X-ray emission of 0B stars. X-ray line emission of Si XIII and S XV in ς Ori is discussed and interpreted as arising from magnetically confined loops.

Neutral hydrogen from the foil-induced dissociation of 4HeH +, 3HeH +, and H 2+

High-resolution energy spectra and angular distributions of H 0 from the dissociation of 4HeH +, 3HeH +, and H 2 + in thin carbon foils are presented for incident ion energies ranging from 170 to 1800 keV/amu. For the range of dwell times inside the target foils studied (about 1–10 fs), the dominant mechanism for such dissociation is the Coulomb explosion of the ions inside the target followed by electron capture near the rear surface of the foil. At the shortest of these dwell times, the yield of H 0 for incident ions oriented perpendicular to the beam relative to that for ions aligned with the beam is a factor of two greater than at longer dwell times. These data indicate that, for ion fragments which emerge from the rear surface of the target within a few Å of one another, those in the perpendicular orientation have a greater electron capture probability than those emerging in other orientations.

Inelastic effects in the scattering of low energy helium ions from monocrystalline silicon

High resolution energy spectra of He ions scattered from monocrystalline silicon have been measured at various scattering, azimuthal and incident angles for primary energies in the range 450–1600 eV. In these experiments, it is observed that the maximum of the peak corresponds to an energy significantly lower than predicted by the binary elastic collision model. The dependence of this inelastic loss is investigated as a function of the experimental parameters. Emphasis is placed on the energy dependence at a scattering angle of 30° for four (111) surface planes of differently doped silicon samples. With increasing primary energy, a broadening of the peak is observed and a second peak appears, which is well defined only in a restricted energy range. The relative intensity of both peaks is strongly dependent on the energy and on the incident angle. The experimental results are compared with models of inelastic energy loss by electronic excitation and multiple collisions.

Conjugate photoelectron fluxes observed on Atmosphere Explorer C

High resolution energy spectra of the flux of precipitating photoelectrons which arise from solar illumination of the area near the magnetic conjugate point have been measured with the Photoelectron Spectrometer Experiment on the Atmosphere Explorer C Spacecraft. Conjugate photoelectrons have been observed when the spacecraft was well away from the terminator at local solar zenith angles up to 160°. The shape of the observed electron energy spectrum is almost identical to that reported for high altitude photoelectron spectra from the Atmosphere Explorer E Spacecraft by Doering et al., 1976. Identification of the residual spectral features in the energy spectra of the conjugate photoelectrons shows that to within the experimental uncertainty of ± 1 eV, the photoelectrons from the magnetic conjugate point have not experienced any acceleration. The magnitude of the observed conjugate photoelectron flux varies considerably between passes, but in some cases the 250 km flux has been observed to be as much as half of the magnitude of the escaping photoelectron flux at 300 km near the sunlit conjugate point. Observations of the precipitating and backscattered flux provide a direct measurement of the low energy (10 eV ‐ 60 eV) electron albedo.

Field ionization energy spectra of molecules

Considerations for determination of the partition of internal energy in ion s formed by field ionization are discussed in terms of the distribution of ion energies. Experimental high-resolution energy spectra for the molecular ions produced by field ionization of toluene, cycloheptatriene, phenol, hydrogen and carbon monoxide are shown and discussed. In particular it is concluded that the range of internal energies can be of the order of several electron volts. Implications of the observations for rate predictions are discussed.

The γ annihilation spectrum is temperature independent

In a recent paper (1) it has been discussed the set of measurements performed at 300 ~ and 77 ~ in order to understand the temperature effect on the 2-u positron annihilation in crystals, according to which, by lowering temperature, the area under the angular-distribution curve decreases in single crystals but not in polycrystals. From the experimental data it arose a possible explanation (1) of the effect, as due to positrons annihilating in flight when the temperature decreases in single crystals. In these conditions, positrons would save a fraction of their initial energy because of channeling between lattice planes. This brings to a noncomplete thermalization of the positrons, which consequently annihilate at wide angles spread quite far from the usual range of the angular distribution. In fact, this measurement performed (1) for a Pb single crystal up to 30 mrad did not show any increase, within the experimental errors, on the tails of the curve detected at low temperature. Thus the h lost in the central part of the curve should have a distribution so large in angle that the corresponding mean energy saved has to be detectable on the V spectrum. For this reason we performed high-resolution energy spectra at 300 ~ 77 ~ and 4.2 ~ for the y-radiation of positrons annihilating in a Pb single crystal which was one of the samples with a very large temperatnre effect (1). The experimental apparatus reported in Fig. 1 consisted in a eryostat supplied by the Oxford Instruments, which allowed, by the cold-finger technique, the same experimental conditions at any temperature, and a Ge-Li detector whose resohltion on the 511 keV annihilation gamma line was of 3 kV FWHM, while the electronic chain was stabilized within 100 eV/h by a computer PDP 8/1 working on two leference peaks which went through it, together with the 511 keV annihilation line. For each temperature several spectra have been performed which have been compared with each other, both for the same and for different temperatures.