Resonant Auger Electron Research Articles

Angle-resolved resonant Auger electron spectroscopy of CO after vibrationally resolved C 1s nl excitations

Angle-resolved resonant electron spectra following vibrationally resolved C 1s nl ( = 0,1) excitations in CO have been measured. The observed groups of resonant Auger lines exhibit great similarity in shape to the C-KVV group of non-resonant Auger lines and the observed angular distribution behaviour reflects the symmetry-dependent anisotropies of the excitation process. The molecular progressions in the C 1s* resonant Auger spectrum could be clearly identified due to their different angular distribution behaviour. Furthermore, it could be shown that the screening energies for spectator electrons over binding energy have a linear dependence between 3p, 4p and threshold as was expected for the higher p-symmetry Rydberg orbitals.

Dynamically Induced Spin Polarization of Resonant Auger Electrons

Resonant Anger electrons from the decay of the atomic Xe 4d(5/2)(-1)6p(J = 1) state excited with linearly polarized light are shown to have a strong spin polarization. The core hole states are not oriented in this case. We found polarization values ranging from -0.46 to 0.57. For the decay to the 5p(4)(D-1(2))6p(P-2(1/2)) state the ratio of the radiationless decay matrix elements and their relative phase, including its sign, are derived.

The resonant Auger electron spectrum of core-excited ethylene:

We present measurements and calculations of the electronic decay of core-excited states in gas-phase ethylene. We have studied the decay of C 1s→π* core-to-valence resonances and the decay of the 1s→3s, 1s→3p, and 1s→4p Rydberg states. In addition, ab initio calculations are presented for the final states from the decay of the 1s→π* resonantly-excited state. The final states are calculated using configuration interaction wave functions for the intermediate (core-excited) state, and for the final state. The calculated spectrum compares well with the experimental spectrum and all final states may be identified. The method used for the calculation therefore seems very promising for other alkene molecules.

Resonant Auger Electron Spectra at Si-, P-, S-, and Cl-1s Thresholds of Condensed Molecules

Resonant Auger electron spectra were measured for several condensed molecules (Si(CH 3 ) 3 Cl, SiCl 4 , PCl 3 , C 3 H 7 SH and CCl 4 ) around Si-, P-, S-, and Cl-1s edges. It was commonly found that the most frequent decay channel after the excitation was a KL 2 , 3 L 2 , 3 transition. As predicted by a resonant inelastic scattering theory, the phenomenon known as the Auger resonant Raman effect was observed in this transition. Namely, resonant (spectator) Auger peaks exhibited both linear energy dispersion and width sharpening. Only Si- and Cl-KL 2 , 3 L 2,3 transitions in Si(CH 3 ) 3 Cl were found to exhibit complicated dispersion profiles, probably due to two different excitations in each edge. Intensity plots of the spectator and normal Auger peaks revealed that Si- 3 p* and Cl-3p* orbitals in this molecule have different natures, i.e., the former and the latter consist mainly of localized and delocalized components, respectively.

Resonant Auger Electron Spectra at Si-, P-, S-, and Cl-1s Thresholds of Condensed Molecules

Resonant Auger electron spectra were measured for several condensed molecules (Si(CH3)3Cl, SiCl4, PCl3, C3H7SH and CCl4) around Si-, P-, S-, and Cl-1s edges. It was commonly found that the most frequent decay channel after the excitation was a KL2,3L2,3 transition. As predicted by a resonant inelastic scattering theory, the phenomenon known as the Auger resonant Raman effect was observed in this transition. Namely, resonant (spectator) Auger peaks exhibited both linear energy dispersion and width sharpening. Only Si- and Cl-KL1,3L2,3 transitions in Si(CH3)3Cl were found to exhibit complicated dispersion profiles, probably due to two different excitations in each edge. Intensity plots of the spectator and normal Auger peaks revealed that Si-3p* and Cl-3p* orbitals in this molecule have different natures, i.e., the former and the latter consist mainly of localized and delocalized components, respectively.

Apparatus for studying decay and dissociation of core excited molecules

We have constructed an experimental apparatus which allows us to perform various types of non-coincidence experiments such as angle-resolved photo-electron, photoion and resonance Auger electron spectroscopy, as well as coincidence experiments for investigating the angular correlation between two energy-selected charged particles (electrons and/or ions). Their design and performance are described in this paper.

Resonant Auger electron spectroscopy for analysis of the chemical state of phosphorus segregated at SiO 2/Si interfaces

A new method to characterize the chemical state or environment of phosphorus segregated or piled up at theSiO 2/Si interface has been developed by utilizing the resonant Auger decay process. It is found from synchrotron radiation photoelectron spectroscopy of P 1 s that phosphorus atoms exist not in the oxidized state, but in the elemental P 0 or Si P chemical state. Resonant Auger electron spectroscopy revealed that phosphorus atoms exist not in the silica side, but in the silicon side of the interface, since no spectator Auger spectra are observed from the segregated phosphorus.

Electron emission from PH 2 produced via fast dissociation of core-excited PH 3

We have observed resonant Auger electron emission following P 2p → 3e (σ *) excitation of PH 3 and, with the help of ab initio calculations, assigned some fine structure to the emission from the P 2p core-excited PH 2 fragment produced via fast dissociation.

Electronic structures of phosphates studied by TEY-XANES and resonant AES

The electronic structures of Cr(PO 4)·6H 2O and Zn 3(PO 4) 2·4H 2O have been studied by using total-electron-yield X-ray absorption near-edge structure (TEY-XANES) and resonant Auger electron spectroscopy (AES). In P K edge XANES spectra. which are associated with the electron transition from P 1 s to P3 p-dominant states, a pre-edge peak followed by a main peak is observed for Cr(PO 4)·6H 2O but not for Zn 3(PO 4) 2·4H 2O. The main peaks have different energies. The energy differences between P KL 2,3 L 2,3 normal and spectator Auger peaks at specific photon energies are larger for Zn 3(PO 4) 2·4H 2O than for Cr(PO 4)·6H 2O. These are associated with differences between the hybridization of P3 p-dominant states and the3 d and4 s states of the cations. The sampling depth of TEY-XANES has also been estimated on the basis of simple specimen current measurements. The sampling depth measured by using silicon substrates covered with aluminium overlayers exceeds 100 nm. This value is determined by the penetration length of Auger electrons excited by the X-rays and the inelastic mean free path of secondary electrons excited by inelastically scattered Auger electrons.

Photon stimulated ion desorption of condensed acetonitrile molecules induced by core excitation

Photon stimulated ion desorption (PSID) of condensed acetonitrile molecules induced by carbon and nitrogen core excitation has been examined to elucidate the Auger process following resonant core excitation and the ion desorption mechanism related to this Auger process using total electron yield, total ion yield, resonant Auger electron spectra. Resonant Auger electron spectra show a strong dependence on the character of excitation. In particular, these Auger spectra are drastically changed between the carbon 1s to theπ * CN excitation and that of the C H * excitation. The spectrum of the total ion yield divided by the total electron yield shows that the desorption efficiency is largely increased at the resonant excitation of carbon 1s electron in the CH 3 group to C H * orbital. The results of the resonant Auger spectra and the Auger electron-photoion coincidence (AEPICO) measurements at various resonant excitations are discussed in relation to the bonding/anti-bonding character and localized character of the excited state and the Auger final state.

Resonant Auger spectra of open shell rubidium atom

Resonant Auger electron spectra of atomic rubidium have been measured using selected photon energies to excite the 3d electrons to 5p Rydberg orbitals. The structures of the spectra were investigated by comparing the observed intensity distributions with the results of multiconfiguration Dirac-Fock calculations. The theoretical profiles were calculated taking into account the population of the initial states.

Theoretical analysis of Resonant Auger Electron Spectra produced by isolated resonances

Line profiles of Resonant Auger Electron Spectra produced by isolated resonances are analyzed by separating the contributions due to the direct, resonant and interference terms and taking explicitly into account the effects due to the finite bandwidth of the incident radiation. The mean kinetic energy of the emitted electron and the spectral width of the Auger lines are also studied as functions of the parameters characteristic of the incident radiation. The general expressions derived by the theory are applied to the analysis of the lineshapes produced by a specific electronic transition taken from the autoionization spectrum of the CO molecule.

Assignment of fine structure in the HBr absorption spectrum at the Br3d→Rydberg resonances using the Auger resonant Raman effect

High-resolution resonant Auger electron spectra of HBr are reported at the Br $3d\ensuremath{\rightarrow}5p$ and Br $3d\ensuremath{\rightarrow}4d$ resonances. Subnatural linewidths of \ensuremath{\sim}40 meV, due to the Auger resonance Raman effect, reveal complex multiplet features. By recording spectra at closely spaced energies, the resonant Auger spectra from the resonantly excited core Br $3d$ to $4d,$ $5p\ensuremath{\sigma},$ and $5p\ensuremath{\pi}$ Rydberg states are obtained. The well-resolved resonant Auger spectra are used to confirm the assignments of the complex unresolved Br $3d\ensuremath{\rightarrow}$Rydberg photoabsorption spectrum.

Theoretical analysis of line shapes in resonant Auger electron spectra

General expressions for predicting line shapes in resonant Auger electron spectra are derived. These formulas take into account explicitly the interference effects due to the presence of several resonances embedded in the continua of different final states having finite lifetimes and include also the effects due to the finite bandwidth of the incident radiation and the finite resolving power of the electron spectrometer. The characteristic features of the Auger resonant Raman effect are derived analytically. The theory is applied to the analysis of high resolution resonant Auger spectra recently measured at the VUV beam line at Elettra, Sincrotrone Trieste.

Angular distributions of resonant and non-resonant Auger electrons as a test case for the validity of the spectator model: the argon case

Resonant Auger spectra following Ar selective excitation with synchrotron radiation are reported with low- and high-photon resolution. The angular distribution of the resonant Auger lines, in particular the Ar excitation, was analysed in order to test the validity of the spectator model in its various forms. It is shown that this model in its strict form holds well for the Ar excitation and in its `shake modified' gross form also for the nd excitations in the case of n > 3.

Theoretical analysis of line shapes in resonant Auger electron spectra

General expressions for predicting line shapes in resonant Auger electron spectra are derived. These formulas take into account explicitly the interference effects due to the presence of several resonances embedded in the continua of different final states having finite lifetimes and include also the effects due to the finite bandwidth of the incident radiation and the finite resolving power of the electron spectrometer. The characteristic features of the Auger resonant Raman effect are derived analytically. The theory is applied to the analysis of high resolution resonant Auger spectra recently measured at the VUV beam line at Elettra, Sincrotrone Trieste.

Low contact resistance of n + -Si/Ti/WN x /Al submicron contact structures

-Si/Ti/WNx/Al multi-layer metallization scheme. The contact resistance has been strongly related to the plasma nitridation of the Ti surface because the contact resistance of n+-Si/Ti/WNx/Al with contact size of 0.49 μm2 about 100–130 Ω, whereas without the nitridation of the Ti surface the contact resistance rises up to 200–390 Ω. 19F (p,αγ) nuclear resonance analysis and Auger electron spectroscopy reveal that F adatoms on the Ti surface are successfully removed by the 30 s nitridation and as a result, the low contact resistance can be achieved.

Core-to-Rydberg excitations and their Auger decay in the HCl and DCl molecules.

The resonant Auger electron spectra of the HCl and DCl molecules have been measured at the first core-to-Rydberg resonances. The low binding energy region of the spectra has been decomposed into transitions to different bound states and their vibrational progressions. Several transitions have been assigned using the strict spectator model. The total ion yield spectrum of HCl in the energy region of the core-to-Rydberg resonances has been recorded and its assignment refined with the help of the Auger electron and chlorine 2{ital p} photoelectron spectra. {copyright} {ital 1996 The American Physical Society.}

Auger decay of resonantly excited states in atomic Rb

Resonance Auger electron spectra of atomic Rb are studied both experimentally and theoretically. Experiments were carried out using synchrotron radiation from the positron storage ring of the Photon Factory at the National Laboratory for High Energy Physics. The electron spectra were recorded at selected photon energies corresponding to the strongest 3 d → 5 p excitation resonances. Photoexcitation and subsequent Auger decay rates were predicted by multiconfiguration Dirac-Fock (MCDF) calculations. Main features in experiment were found to be fairly well reproduced by MCDF calculations.

Features of the Auger resonant Raman effect in experimental spectra.

The influence of the photon bandwidth on the line shapes of the resonant Auger electron spectra has been studied. The observed features have been explained as due to the Auger resonant Raman effect, which has been extended to cover the cases of nonmonochromatic excitation. Changes in the line shapes and also several specific effects, connected with detuned excitation, have been demonstrated by experimental examples, matched with model calculations. The lifetime interference phenomenon, appearing in the decay of several close-lying resonance states to the same final state, is regarded together with the influence of the limited photon bandwidth. Special attention is paid to the problems of data handling. \textcopyright{} 1996 The American Physical Society.