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Room temperature pseudodielectric function spectra (?) = 1(?) + i2(?) of the ordered defects compounds Cu2In4Se7, CuGa3Se5and CuGa5Se8have been measured by spectroscopic ellipsometry. The values of refractive index nand extinction coefficient kare given. The structures observed in (?) spectra have been analysed using different methods, including fitting the numerically differentiated experimental spectrum (second derivative) to analytical line shapes. As a result, the energies corresponding to the fundamental gap (E0) and higher critical points have been determined. A linear correlation of the fundamental gap values with Ga/Cu atomic ratio contents in CuGaxSeysamples is deduced. [ABSTRACT FROM AUTHOR]

A multilayer nanocomposite consisting of Au nanoparticles separated by layers of amorphous Al2O3 was prepared by pulsed laser deposition. The laser energy density used to deposit the Al2O3 layers was varied to investigate the effects on the resulting microstructure. When Al2O3 is deposited on the Au it results in resputtering and interfacial mixing of the Au nanoparticles into the Al2O3 matrix being deposited onto them. This leads to a reshaping of the nanoparticles, elongating them in the growth direction and in some cases forming cavities in the nanoparticles. These effects become more pronounced with increasing laser energy density. The high kinetic energies of the species involved also result in implantation of Au into the Al2O3 where it forms nanoparticles of about 1 nm mean diameter. [ABSTRACT FROM AUTHOR]

The formation of gratings on the surface of a silicon wafer by nanosecond laser irradiation through a phase mask using an ArF laser emitting at 193 nm is studied. The phase mask along with some focusing optics is capable to generate via interference a periodic intensity distribution, which can be used for surface patterning. The surface patterning strongly depends on the laser energy density and on the number of pulses, as revealed by atomic force microscopy (AFM). The results show that irradiation even with a single laser pulse produces periodic depth modulations on the surface. The spatial surface modulation is in the micrometer (1.7 µm) range while the depth modulation is in the nanometer regime (1–20 nm). With an increasing number of pulses (1–100), the depth modulation amplitude increases smoothly. Increasing the number of pulses further results in the progressive destruction of the grating, vanishing completely after ~5000 pulses. This evolution is also monitored in situ by measuring the intensity of the first order-diffracted probe beam and the behavior is in accordance with what is observed by AFM. Finally, we qualitatively explain the results invoking thermally induced effects in the melted Si: these physical processes involved are probably thermocapillary and/or Marangoni effects inducing material displacement as the surface melts. [ABSTRACT FROM AUTHOR]

The resistive switching properties of silicon-aluminium oxynitride (SiAlON) based devices have been studied. Electrical transport mechanisms in both resistance states were determined, exhibiting an ohmic behaviour at low resistance and a defect-related Poole−Frenkel mechanism at high resistance. Nevertheless, some features of the Al top-electrode are generated during the initial electroforming, suggesting some material modifications. An in-depth microscopic study at the nanoscale has been performed after the electroforming process, by acquiring scanning electron microscopy and transmission electron microscopy images. The direct observation of the devices confirmed features on the top electrode with bubble-like appearance, as well as some precipitates within the SiAlON. Chemical analysis by electron energy loss spectroscopy has demonstrated that there is an out-diffusion of oxygen and nitrogen ions from the SiAlON layer towards the electrode, thus forming silicon-rich paths within the dielectric layer and indicating vacancy change to be the main mechanism in the resistive switching. [ABSTRACT FROM AUTHOR]

In this work, we report on the production of regular (SiGe/SiO2)20 multilayer structures by conventional RF-magnetron sputtering, at 350 °C. Transmission electron microscopy, scanning transmission electron microscopy, raman spectroscopy, and x-ray reflectometry measurements revealed that annealing at a temperature of 1000 °C leads to the formation of SiGe nanocrystals between SiO2 thin layers with good multilayer stability. Reducing the nominal SiGe layer thickness (tSiGe) from 3.5–2 nm results in a transition from continuous SiGe crystalline layer (tSiGe ∼ 3.5 nm) to layers consisting of isolated nanocrystals (tSiGe ∼ 2 nm). Namely, in the latter case, the presence of SiGe nanocrystals ∼3–8 nm in size, is observed. Spectroscopic ellipsometry was applied to determine the evolution of the onset in the effective optical absorption, as well as the dielectric function, in SiGe multilayers as a function of the SiGe thickness. A clear blue-shift in the optical absorption is observed for tSiGe ∼ 2 nm multilayer, as a consequence of the presence of isolated nanocrystals. Furthermore, the observed near infrared values of n = 2.8 and k = 1.5 are lower than those of bulk SiGe compounds, suggesting the presence of electronic confinement effects in the nanocrystals. The low temperature (70 K) photoluminescence measurements performed on annealed SiGe/SiO2 nanostructures show an emission band located between 0.7–0.9 eV associated with the development of interface states between the formed nanocrystals and surrounding amorphous matrix. [ABSTRACT FROM AUTHOR]