Malgorzata Makowska-Janusik

Vibrational density of states in silicon carbide nanoparticles: experiments and numerical simulations

The vibrational properties of silicon carbide nanoparticles (np-SiC) were investigated as function of the nanocrystal size (5-25 nm) and the features of their outermost surfaces. Raman experiments and numerical methods were conjugated to characterize the signatures from the active SiC normal modes and the vibrational density of states (VDOS). The Raman spectra of the nanopowders were marked by VDOS signals which correlate with the SiC amorphous fractions favoured by the high specific surfaces of the nanoparticles and their surface reconstruction. Quantitative interpretation of the experimental VDOS features, IR absorption and Raman scattering properties in nanosized SiC were carried out by means of numerical methods developed on SiC clusters with suitable structures and sizes.

Vibrational and electronic peculiarities of NiTiO3 nanostructures inferred from first principle calculations

Structural, electronic and vibrational properties of nanostructured (NiTiO3)n clusters were calculated by numerical models based on DFT and semi-empirical quantum chemistry codes. The clusters were built by using the initial atomic positions of crystalline ilmenite, which were relaxed to ensure stable and energetically favourable geometries. For the electronic properties, the semi-empirical PM6 parameterisation method was used to evaluate the HOMO–LUMO energy differences versus nanocrystal sizes. The quantum confinement effect was induced with cluster size reduction. Theoretical UV-Vis absorption and Raman spectroscopy showed the drastic influence of the surface characteristics on the electronic and the vibrational properties of the nanoclusters. Theoretically, it was proved that powder NiTiO3 exhibits a patchwork of the properties of the bulk ilmenite material, amorphous Ni–Ti–O structures and atoms located at the surface of the investigated cluster.

Corrosion inhibition of mild steel in 1M HCl by D-glucose derivatives of dihydropyrido [2,3-d:6,5-d′] dipyrimidine-2, 4, 6, 8(1H,3H, 5H,7H)-tetraone

D-glucose derivatives of dihydropyrido-[2,3-d:6,5-d′]-dipyrimidine-2, 4, 6, 8(1H,3H, 5H,7H)-tetraone (GPHs) have been synthesized and investigated as corrosion inhibitors for mild steel in 1M HCl solution using gravimetric, electrochemical, surface, quantum chemical calculations and Monte Carlo simulations methods. The order of inhibition efficiencies is GPH-3 > GPH-2 > GPH-1. The results further showed that the inhibitor molecules with electron releasing (-OH, -OCH3) substituents exhibit higher efficiency than the parent molecule without any substituents. Polarization study suggests that the studied compounds are mixed-type but exhibited predominantly cathodic inhibitive effect. The adsorption of these compounds on mild steel surface obeyed the Langmuir adsorption isotherm. SEM, EDX and AFM analyses were used to confirm the inhibitive actions of the molecules on mild steel surface. Quantum chemical (QC) calculations and Monte Carlo (MC) simulations studies were undertaken to further corroborate the experimental results.

Solid-State NMR Correlation Experiments and Distance Measurements in Paramagnetic Metalorganics Exemplified by Cu-Cyclam

We show how to record and analyze solid-state NMR spectra of organic paramagnetic complexes with moderate hyperfine interactions using the Cu-cyclam complex as an example. Assignment of the (13)C signals was performed with the help of density functional theory (DFT) calculations. An initial assignment of the (1)H signals was done by means of (1)H-(13)C correlation spectra. The possibility of recording a dipolar HSQC spectrum with the advantage of direct (1)H acquisition is discussed. Owing to the paramagnetic shifting the resolution of such paramagnetic (1)H spectra is generally better than for diamagnetic solid samples, and we exploit this advantage by recording (1)H-(1)H correlation spectra with a simple and short pulse sequence. This experiment, along with a Karplus relation, allowed for the completion of the (1)H signal assignment. On the basis of these data, we measured the distances of the carbon atoms to the copper center in Cu-cyclam by means of (13)CR2 relaxation experiments combined with the electronic relaxation determined by EPR.

Electron–phonon contribution to electrooptical coefficient in Ca4GdO(BO3)3 single crystals

Abstract Electrooptical r222 coefficient in new synthesized (Ca4GdO(BO3)3) (GdCOB) single crystals has been measured at room and liquid nitrogen temperature. To separate electronic and phonon contributions we carry out experimental measurements and theoretical calculations. To determine electronic contributions we have used experimental measurements for the SHG (λ=1.06 μm). We also measured electrooptics tensor coefficients at λ=0.694 μm as well for the IR spectral region within the 1.2–2.45 μm. From temperature dependencies within the 77–295 K we evaluate phonon harmonic and electron–phonon anharmonic contributions. Using ab initio norm-conserving pseudopotential calculations and Green function evaluations of electron–phonon contributions we estimate quantitatively electron–phonon contributions. A good agreement between the experimental and theoretical data is achieved. The presented approach can be proposed for another complex crystals in order to receive an information concerning the origin of the observed phenomena.

First principle calculations of the electronic and vibrational properties of the 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole molecule.

Results of first principle quantum chemical calculations of electronic and vibrational properties of the push-pull 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) molecule are reported and discussed. The structure of DCNP was optimized with HF/6-311G methodology and found to be planar. On the basis of obtained geometry, infrared absorption and Raman spectra were computed within the HF/6-311++G** formalism. They allow to conclude that the changes of molecule dipole moment and variation of its polarizability appear at the same vibrational mode and affect the optical properties of the DCNP. Four different methodologies: time-dependent HF and time-dependent DFT method with B3LYP, LC-BLYP, and CAM-B3LYP potentials were used to compute the optical absorption spectra of DCNP. Influence of solvent on molecular electronic structure was studied within the C-PCM model. It predicts the DFT/B3LYP methodology as the best one to compute the NLO properties of the DCNP. The computed HOMO and LUMO orbitals show evidence that the ground state of the molecule is located at its aromatic part. The discussion of charge transfer during the excitation process for the transition S0-S1 was performed. The charge transfer parameter calculated in vacuum and in solvent gives the evidence that the solvent environment weakly enhance the molecular charge transfer. It confirms the tendency of an occurrence of the intermolecular charge transfer in DCNP which is crucial for its hyperpolarizability magnitude. It was proved that the second-order susceptibility corresponding to SHG may be calculated for host-guest polymer/DCNP composite using the simple oriented gas model and the rigorous local field approach should not necessarily be applied.

Some fundamental and applicative properties of (polymer/nano-SiC) hybrid nanocomposites

Hybrid nanocomposites which combine polymer as host matrix and nanocrystals as active elements are promising functional materials for electronics, optics or photonics. In these systems, the physical response is governed by the nanocrystal features (size, surface and defect states), the polymer properties and the polymer-nanocrystal interface. This work reviews some selective nanostructured architectures based on active elements such as silicon carbide (SiC) nanocrystals and polymer host matrices. Beyond an overview of some key properties of the nanocrystals, a main part will be devoted to the electro-optical (EO) properties of SiC based hybrid systems where SiC nanocrystals are embedded in polymer matrices of different chemical nature such as poly-(methylmethacrylate) (PMMA), poly-vinylcarbazole (PVK) or polycarbonate. Using this approach, the organic-inorganic interface effects are emphasised with regard to the dielectric or hole transporting behaviour of PMMA and PVK respectively. These effects are illustrated through different EO responses associated with hybrid composites based on PMMA or PVK.

Photoinduced nonlinear optics in Sb2Se3–BaCl2–PbCl2 glasses

Abstract Photoinduced structural transformations in amorphous Sb2Se3–BaCl2–PbCl2 glasses were studied using a differential IR spectroscopy Fourier technique in the spectral region between 100 and 300 cm−1. A stage of the reversible photodarkening is realized in the Sb2Se3 fragments after the first cycle of photoexposure and thermoannealing. The whole scheme of the photo- and thermoinduced transformations in the amorphous system may be explained as a coordination of formation and annihilation of defects. The vibrational density of states calculated using quantum chemical solid state methods confirms our experimental results and their interpretation. Photoinduced photodarkening changes using a CO2 pulse laser (λ=10.6 μm) in new synthesized Sb2Se3–BaCl2–PbCl2 glasses were investigated. At the same time we have studied photoinduced second harmonic generation (SHG) and two-photon absorption (TPA). The possibility of using this glass as perspective materials for IR optoelectronics and nonlinear optics was shown.

Electronic, optical and vibrational features of BiVO4 nanostructures investigated by first-principles calculations

Numerical models based on DFT and semi-empirical methods were developed on bulk and nano-sized BiVO4 semiconducting oxide. Two different approaches were implemented to calculate the electronic properties of the bulk BiVO4 crystal. One approach used the X-ray specified atomic positions with the defined lattice parameters involved in the monoclinic crystalline structure of BiVO4, for which geometry optimization was performed before the electronic properties calculations. The second approach considered the atomic positions of the scheelite structure, which was maintained frozen without any lattice rearrangement. The obtained data were considered as a guideline to choose appropriate methodology to calculate the physical properties of (BiVO4)n nanoparticles. A semi-empirical method with the PM6 parameterization was applied to calculate the electronic and vibrational properties of (BiVO4)n nanostructures versus their sizes. The quantum confinement effect was shown for the clusters through a blue-shift of the optical absorption bands compared to an infinite system. It was demonstrated that the optical and vibrational properties of the nanoparticles are determined by the internal atoms keeping their positions as in the crystalline structure and also that they feel surface reconstruction effects according to the environmental interactions. The above mentioned behaviors were analyzed (using UV-vis absorption, IR and Raman features), theoretically predicted and then compared with the experimental results. The performed analyses underlines the evolution of the electronic density of states and the optical absorption peculiarities between a bulk infinite system and nano-sized objects dedicated to realize visible-light-driven photocatalysts.

Experimental and Quantum Chemical Calculations of Imidazolium Appended Naphthalene Hybrid in Different Biomimicking Aqueous Interfaces

The effect of solvent polarity and micellar headgroup on a newly designed imidazolium based ionic liquid (IL) conjugated with naphthalene, 1,2-dimethyl-3-((6-(octyloxy)naphthalen-2-yl)methyl)-1H-imidazol-3-ium chloride (IN-O8-Cl), was studied using steady state and time-resolved fluorescence techniques. We observed that the dipole moment in the excited state is remarkably higher than the ground state. The effect of micellar surface charge on the photophysics of IN-O8-Cl in aqueous phase at room temperature was investigated. Formation of premicellar aggregates in sodium dodecylsulfate (SDS) was perceived; further the microenvironment of IN-O8-Cl was examined using steady-state fluorescence spectroscopy. Micropolarity of the micellar environment of SDS was found to be lower than that of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) following the order SDS < TX-100 < CTAB. The binding constant (Kb) and edge excitation red shift (EERS) from the emission maximum suggest that the probe binds strongly to the micelles. Multiexponential behavior was observed in time-resolved fluorescence lifetime studies in all micellar environments. We have observed an increase in rotational correlation time as we move from pure aqueous phase to solution containing surfactants of different head charge. Varieties of spectral parameters were used to justify the region in which the probe is present. The experimentally obtained dipole moment data were justified and explained by the DFT calculations of the electronic properties of IN-O8-Cl molecules in gas phase and in selected solvents.