Photoionization of the Ne-like Si4+ ion in ground and metastable states in the 110–184-eV photon energy range

We present measurements of the absolute photoionization cross section of the neonlike Si4+ ion over the 110–184 eV photon energy range. The measurements were performed using two independent merged-beam setups at the super-ACO and ASTRID synchrotron-radiation facilities, respectively. Signals produced in the photoionization of the 2p subshell of the Si4+ ion both from the 2p6 1S0 ground state and the 2p53s 3P0,2 metastable levels were observed. Calculations of the 2p photoionization cross sections were carried out using a multi-configuration Dirac-Fock code. They give results in good agreement with the measured spectra. Comparison with other available theoretical results is also presented

Absolute photoionization cross sections and resonance structure of doubly ionized silicon in the region of the 2p-1 threshold: experiment and theory

We present the absolute photoionization cross section of doubly ionized silicon as a function of photon energy. These were obtained by merging a Si2+ ion beam generated in an electron cyclotron resonance source with monochromatized synchrotron radiation from an undulator. The photoion yield measurements were carried out in the photon energy range between 95 eV and 170 eV, i.e., the region corresponding to the excitation followed by the ionization (threshold ∼133.8eV) of an inner-subshell 2p electron. Resonance structure due to 2p excitation in the 2p63s3p3P metastable state was also observed with its contribution to the total cross section not exceeding 3%. Calculation of the 2p photoionization continuum cross section as a function of photon energy was carried out using the relativistic random-phase approximation (RRPA) and agreed very well with the corresponding measurements. The resonance structure in the 3s cross section below the 2p threshold was found to be in good agreement with the multiconfiguration atomic structure calculations of Sayyad et al. [J. Phys. B 28, 1715 (1995)], while the corresponding RRPA-RMQDT (relativistic multi-channel quantum-defect theory) calculations proved less successful

Fabrication of patterned porous silicon using high-energy ion irradiation

Abstract P-type silicon has been patterned using highenergy protons beam prior to electrochemical etching in hydrofluoric acid. The ion beam selectively damages the silicon lattice, resulting in an increase in the local resistivity of the irradiated regions. It is found that the photoluminescence intensity of the irradiated regions increases with proton irradiation into a 0.02 .cm resistivity p-type silicon. By immersing the etched sample into potassium hydroxide, the porous silicon is removed to reveal the underlying three-dimensional structure of the patterned area

State-resolved valence shell photoionization of Be-like ions: experiment and theory

High-resolution photoionization experiments were carried out using beams of Be-like C$^{2+}$, N$^{3+}$, and O$^{4+}$ ions with roughly equal populations of the $^1$S ground-state and the $^3$P$^o$ manifold of metastable components. The energy scales of the experiments are calibrated with uncertainties of 1 to 10 meV depending on photon energy. Resolving powers beyond 20,000 were reached allowing for the separation of contributions from the individual metastable $^3$P$^o_0$, $^3$P$^o_1$, and $^3$P$^o_2$ states. The measured data compare favourably with semi-relativistic Breit-Pauli R-matrixComment: 23 figures and 3 table

Absolute cross sections for

Absolute photoionization cross sections for the ions N2+, N3+, O3+, O4+, F3+, F4+ and Ne4+ are measured using the merged-beam technique, combining the synchrotron radiation from an undulator at the storage ring ASTRID with ions produced by an ECR ion source. The spectral structures and the development of the cross sections along iso-electronic sequences are discussed. The experimental data are compared with R-matrix calculations from the Opacity Project and other sources, MCDF calculations, as well as the model functions provided by verner et al. (1996). In general, good agreement between experiment and calculations is observed for the magnitude of the continuum cross sections whereas very significant discrepancies are present for the resonance structures. The experimental data are also available in electronic form at the CDS

Thermal hysteresis measurement of the VO 2 dielectric function for its metal-insulator transition by visible-IR ellipsometry

International audienceThe real and imaginary parts of the dielectric function of VO2 thin films, deposited on r-plane sapphire via pulsed laser deposition, are measured by means of visible-infrared ellipsometry for wavelengths ranging from 0.4 to 15 μm and temperatures within its phase transition. For both the insulator-to-metal (heating) and metal-to-insulator (cooling) transitions, it is shown that the two ellipsometric signals exhibit three temperature-driven behaviors, which are well described by appropriate combinations of the Tauc-Lorentz, Gaussian, and Drude oscillator models. By fitting Bruggeman's effective medium model for the dielectric function to the corresponding measured experimental values, using the volumetric fraction of the VO2 metallic domains as a fitting parameter for different temperatures within the VO2 phase transition, we have found that this model is suitable for describing the dielectric function in visible and near-infrared wavelengths (∼0.4 to ∼3.0 μm), but it generally fails for longer infrared ones. Furthermore, the hysteresis loop of the VO2 emissivity averaged over a relevant interval of wavelengths is determined and shown to vary from ∼0.49, in the insulator phase, to ∼0.16, in the metallic one. These values, based on the VO2 dielectric function, are consistent with previous measurements reported in the literature, and therefore, our measured data are expected to be useful for describing the behavior of VO2 films involved in optical and radiative applications