K.J. Plucinski

SiON films deposited on Si(111) substrates—new promising materials for nonlinear optics

Abstract Experimental measurements of the phototransparency stimulated by the YAG–Nd laser (λ=1.06 μm) in the SiON films deposited on the Si crystalline surfaces show essential dependence on the ratio between the nitrogen and oxygen (N/O) content. Dependencies of the phototransparency on the chemical content, delaying time, pressure and temperature demonstrate essential sensitivity to the N/O ratio. All of the data show that the photoinduced changes in the SiON–Si are caused by both linear and nonlinear optical response function contributions and can be used for non-destructive diagnostic of the film content and thickness. To understand the physics of the observed phenomena, we perform detailed theoretical ab initio molecular dynamic simulations on the ground of the norm-conserving non-local pseudopotential method that give possibility to explain the observed dependencies and to predict the possible changes of the optical constants in the desired directions.

Band structure of large-sized SiC nanocomposites

Abstract The and energy structure of large-sized SiC nanocomposites (above 10 nm) was calculated. We used self-consistent norm-conserving pseudopotential method and molecular dynamics simulations of the nanocrystallite interface geometry. Essential changes of the band energy parameters versus the nanocrystallite sizes have been observed. Molecular dynamics structural simulations allowed to find a relation between the degree of hexagonality H (relative presence of hexagonal-like phase) and the sizes. Evaluated size-dependent behavior of the energy gap is compared with the experimentally obtained results. Theoretical data have been compared also with experimental optical spectroscopy and X-ray diffraction measurements. The experimental data are in a good agreement with theoretically calculated data.

Non-linear optical effects and transport phenomena of magnetic semiconductors Pb1−xPrxTe near the semiconductor–metal phase transformation

Measurements of transport and non-linear optical (NLO) properties of the new, synthesized semiconductor Pb0.9835Pr0.0165Te in the vicinity of low-temperature metal–semiconductor phase transformations were performed. A correlation between the temperature behaviour of transport properties near the phase transition and NLO susceptibilities of second- and third-order was observed. FTIR spectra show the substantial role played by the Pr3+ localized levels in the observed anomalies.Among the transport properties, the resistivity, Seebeck coefficient and specific heat were measured. The presence of the minimum at about in the temperature dependence of the resistivity ρ(T) is due to the metal–semiconductor transition in Pb1−xPrxTe and the low-temperature upturn observed in the resistivity is well fitted by the Mott law. Substitution of PbTe by other rare earths shows the crucial role played by Pr in the observed dependences.Experimental temperature measurements using photo-induced NLO (pumped by a UV-laser as well as by second harmonics of the YAG–Nd lasers) and a probing YAG–Nd (at λ = 1.06 µm) laser, show the existence of two maxima in the photo-induced second harmonic generation (PISHG) at temperatures 17 and 30 K, the behaviours of which substantially depend on the wavelength of the pump beam. At the same time the third-order two-photon absorption possesses maxima near 50 K, i.e. at about . Such discrepancies in the positions of the temperature maxima are caused by the difference in contributions of the photo-induced anharmonic phonons near the surfaces PISHG and the bulk. Varying the penetration depth of the photo-inducing light one can operate with the output NLO properties.

Polyimide-fullerene nanostructured materials for nonlinear optics and solar energy applications

Based on the model polyimide systems the principal nonlinear optical features, such as laser induced refractive indices changes, nonlinear refraction and third order susceptibility have been established during their doping with fullerenes, shungites, carbon nanotubes, carbon nanofibers, quantum dots, etc. The evidence of the correlation between laser induced refractive indices and charge carrier mobility has been obtained. The features of new nanocomposites for their possible optoelectronics, laser techniques and solar energy applications have been considered.

Control of the plasmon absorption of gold nanoparticles with a two-color excitation

Substantial photoinduced changes of ultraviolet (UV) -visible (UV-vis) optical spectra were observed for the Au nanoparticles prepared by a “touch” seed-mediated growth technique on the surface of indium-tin-oxide substrate. The phototreatment was performed by two-color coherent laser beams with a wavelength of 1060 nm (fundamental beam) and double frequency 530 nm (writing beam). The maximal photoinduced changes of the UV-vis spectra were observed for the surfaces possessing low resistivity (about 4Ω∕sq). Those of higher resistivity (about 50Ω∕sq) demonstrate only slight shifts of the main Au particle surface-plasmon resonance maxima at λ=570nm. The effect observed is a consequence of a superposition of optically induced surface plasmon resonance, scattering on optically induced grating and electron-phonon relaxation.

Two-photon absorption and photoinduced second-harmonic generation in Sb 2 Te 3 –CaCl 2 –PbCl 2 glasses

Photoinduced nonlinear optical phenomena in Sb2Te3–CaCl2–PbCl2 glasses have been studied by experimental and theoretical quantum chemistry and molecular dynamics methods. Additionally, photoinduced two-photon absorption (TPA) and second-harmonic generation (SHG) were measured in the IR region from 5.8 to 18 µm. A CO laser (λ=5.5 µm) and parametrically generated wavelengths (5.7–13.4 µm) were used as a source of pump light. With an increase of the photoinducing power, the SHG signal increased for a probe CO2 laser (with double frequency λ=5.7 µm) and achieved its maximum value at a photoinducing power of 1.65 GW/cm2 per pulse. Absolute values of the SHG intensities were more than 1 order of magnitude less than those of χ222 nonlinear optical tensor components for Ag3AsSe3 single crystals. The SHG signal increases strongly for a temperature decrease from 39 to 26 K. Femtosecond probe–pump measurements indicate a SHG maximum at a pump–probe delay time of ∼18 ps. The spectral positions of the TPA maxima depend strongly on the pump power. Differently from the SHG behavior, the TPA results show at least two time-delayed maxima, namely, at 14–17 and 45 ps. These dependencies are explained within the framework of the quantum-chemistry approach, which takes into account photoinduced anharmonic electron–vibration interactions. The Sb–Te tetrahedral plays a key role in the observed photoinduced nonlinear optics effects. The results clearly show that these effects can be used as powerful tools for investigation of picosecond IR nonlinear optics. In addition, these glasses are promising materials for IR femtosecond quantum electronics.

The structure and electronic properties of silicon oxynitride gate dielectrics

Despite considerable progress achieved over the past few years in understanding ultrathin oxynitrides, several fundamental questions, in particular, the oxynitridation mechanism and the mechanisms behind the beneficial role of nitrogen are still not well understood. To improve understanding of the explanations which have been proposed for the phenomena specific to silicon oxynitride and for the nature of the defects, a study of the electron structure of a MOS system using silicon oxynitrides as the gate oxide and based on a molecular dynamics geometry optimization method, was carried out. Investigations of the band energy parameters versus the SiON film thickness and oxygen to nitrogen ratio were done theoretically as well as experimentally. Theoretical calculations were done by norm-conserving non-local pseudopotentials together with molecular dynamics geometry optimization. Experimental investigations included spectroscopic investigations of the film absorption. Both theoretical and experimental data indicate that the effective band energy gap possess modulated-like dependence versus the film thickness and oxygen/nitrogen ratio. The origin of the observed phenomenon is caused by specific electron-phonon anharmonic interactions between the film and the Si substrate.

X-ray Photoelectron Spectrum and Electronic Properties of a Noncentrosymmetric Chalcopyrite Compound HgGa2S4 : LDA, GGA, and EV-GGA

An all electron full potential linearized augmented plane wave method has been applied for a theoretical study of the band structure, density of states, and electron charge density of a noncentrosymmetric chalcopyrite compound HgGa(2)S(4) using three different approximations for the exchange correlation potential. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Gamma resulting in a direct energy gap of about 2.0, 2.2, and 2.8 eV for local density approximation (LDA), generalized gradient approximation (GGA), and Engel-Vosko (EVGGA) compared to the experimental value of 2.84 eV. We notice that EVGGA shows excellent agreement with the experimental data. This agreement is attributed to the fact that the Engel-Vosko GGA formalism optimizes the corresponding potential for band structure calculations. We make a detailed comparison of the density of states deduced from the X-ray photoelectron spectra with our calculations. We find that there is a strong covalent bond between the Hg and S atoms and Ga and S atoms. The Hg-Hg, Ga-Ga, and S-S bonds are found to be weaker than the Hg-S and Ga-S bonds showing that a covalent bond exists between Hg and S atoms and Ga and S atoms.

Growth, crystal structure, thermal properties and optical anisotropy of Tl4CdI6 single crystals *

We report on the growth and initial thermal and optical characterisation of a single-crystalline ternary halide, Tl4CdI6. The crystal is described by the centrosymmetric tetragonal class P4/mnc at the room temperature. The parameters of linear thermal expansion are studied in the temperature region 330-500 K. The crystal is optically positive and reveals very high optical anisotropy (the birefringence ~ 0.13 at 633 nm). Its optical pseudo-gap value corresponds to wide- gap semiconductors. A broad maximum at 400-410 K found in the temperature dependence of IR radiation-induced second harmonic generation may be indication of a polymorphic phase transformation.

Influence of chromophore dipole moments in parameterts of organic light emitting devices based on phenyl and methyl modified pyrazoloquinoline

Absorption, photo- and electroluminescence spectra of some trityl substituted 1H-pyrazolo[3,4-b]quinolines derivatives (methyl- and phenyl substituted) and fabrication of the single layered organic light emitting diodes are reported. The bulky trityl substituent was introduced to prevent aggregation and crystallization of the dopant in polymer matrix. Role of ground state dipole moments in the observed red Stokes shift, electroluminescent features and photocarrier transport is explored. The maximally achieved brightness about 50Cd/m(2) is observed in the spectral range extending from 443nm up to 462nm. The voltage threshold was varied from 7.8V up to 10V. The brightness-current dependences show an existence of at least two types of carrier injections.