Trinaphthyl-triazines: towards persistent room temperature columnar mesomorphic matrices

A series of para substituted trans-4-n-alkylcyclohexylbenzylamines was prepared and examined for mesomorphic properties. The n-pentyl derivative 5b showed monotropic smectic behavior while the n-heptyl derivative 5c was an enantiotropic smectic. 5b and 5c are the first examples of low temperature liquid crystals incorporating an amino functionality. While the p-(trans-4-n-alkylcyclohexyl)anilines were not liquid crystalline, N-alkyl substituted-p-(trans-4-n-alkylcyclohexyl) anilines such as N-(n-butyl)-p-(trans-4-n-pentylcyclohexyl)aniline 12a exhibit low temperature mesophases. A strong tendency to spontaneous homeotropic alignment was found in the nematic members of this series.

A homologous series of new thioalkylated double-decker cerium phthalocyanine complexes, [(CnH2n+1S)8Pc]2Ce, were synthesised and their mesomorphisms were clarified by DSC, polarized optical microscopy and X-ray diffraction. Unlike other lanthanide phthalocyanines, these double-decker cerium compounds were found by spectroscopy and X-ray crystallography to be neutral complexes. A hexagonal columnar mesophase (Colh) was exhibited by all homologues prior to melting to the isotropic liquid. Interestingly, the columnar mesophases of these compounds showed strong tendencies for spontaneous homeotropic alignment on non-treated glass substrates or ITO coated glass. The hole mobility in the Colh mesophase of the longer chain homologue was successfully measured by a TOF technique as having a value of 7 × 10−3 cm2 V−1 s−1.

An unidentified phase X of 1,4-dialkyl-1,4-diazoniabicyclo[2.2.2]octane dibromides reported by Nogami et al. in 1985 was reinvestigated by differential scanning calorimetry, polarizing microscopy and temperature-dependent X-ray diffraction. The X phase was thus established as a smectic tetragonal (ST) mesophase which shows spontaneous homeotropic alignment.

Template-assisted interfacial self-assembly of amphiphilic poly(ethylene oxide)–poly(propylene oxide)-based triblock copolymers for automatic control of molecular alignment

We investigate the reflectance of a dielectric plate coated with a graphene sheet which possesses the nonzero energy gap and chemical potential at any temperature. The general formalism for the reflectance using the polarization tensor is presented in the framework of Dirac model. It allows calculation of the reflectivity properties for any material plate coated with real graphene sheet on the basis of first principles of quantum electrodynamics. Numerical computations of the reflectance are performed for the graphene-coated SiO2 plate at room, liquid-nitrogen, and liquid-helium temperatures. We demonstrate that there is a nontrivial interplay between the chemical potential, energy gap, frequency, and temperature in their joint action on the reflectance of a graphene-coated plate. Specifically, it is shown that at the fixed frequency of an incident light an increase of the chemical potential and the energy gap affect the reflectance in opposite directions by increasing and decreasing it, respectively. According to our results, the reflectance approaches unity at sufficiently low frequencies and drops to that of an uncoated plate at high frequencies for any values of the chemical potential and energy gap. The impact of temperature on the reflectance is found to be more pronounced for graphene coatings with smaller chemical potentials. The obtained results could be applied for optimization of optical detectors and other devices exploiting graphene coatings.

Characterization and photocatalytic activity of TiO 2 thin films prepared by RF magnetron sputtering

We use transmission spectroscopy to determine the energy gap for the AlxIn1−xSb alloy system in the Al concentration range from 0% to 25% from cryogenic to room temperature. The samples are epitaxial layers grown by molecular beam epitaxy on GaAs substrates. Our room temperature results are compared to those from two earlier studies. In our Al concentration range, we find a linear change of energy gap with alloy lattice constant.

Optical and photoemission studies of DLC films prepared with a systematic variation of the sp3:sp2 composition

An optical-optical double resonance procedure is used to compare the relative populations of e/f spin components of the $^{2}\mathrm{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$(v=7) rotational manifold resulting from the collision-induced electronic transitions in ${\mathrm{N}}_{2}^{+}$ for the cases of large and small energy gaps. Rotational levels of the $^{2}\mathrm{\ensuremath{\Pi}}_{\mathrm{ui}}$(v=3 or 4) vibrational state of ${\mathrm{N}}_{2}^{+}$ are selectively populated with a pump laser. Transitions to rotational levels of the $^{2}\mathrm{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$(v=7) level due to collisions with bath gas helium atoms at room temperature are monitored by scanning the lines of the B-X(5,7) band with a second, probe laser. The relaxation pathways A(v=3)\ensuremath{\rightarrow}X(v=7) and A(v=4)\ensuremath{\rightarrow}X(v=7) traverse energy gaps (\ensuremath{\Delta}E) of \ensuremath{\sim}0 and \ensuremath{\sim}1760 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively. Perturbation of the rotational levels of the ${\mathit{B}}^{2}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{u}}^{+}$(v=5) state by the ${\mathit{A}}^{2}$${\mathrm{\ensuremath{\Pi}}}_{\mathrm{u}1/2}$(v=17) manifold allows for the e/f, spin-rotation splitting of the lines of the B-X(5,7) probe laser scan to be resolved. The effects of these perturbations on the relative intensities of the B-X(5,7) lines have been taken into account. The intensity patterns for collision-induced transitions across the two widely different energy gaps are nearly identical, indicating that the propensities for this case have an insignificant energy-gap dependence. These detailed propensities from selectively excited rotational levels of the A(v=4 or 3) level to the individual, nearly degenerate rotational levels of the X(v=7) manifold are compared with theoretical models for inelastic scattering between $^{2}\mathrm{\ensuremath{\Pi}}$ and $^{2}\mathrm{\ensuremath{\Sigma}}$ electronic states.

The optical transmission of CuGeO3 single crystals was measured at different temperatures in the 250 to 900 nm spectral range. Two spectral regions were analyzed corresponding to the optical absorption edge and crystal field excitation. The energy gap values at room temperature of 3.18 and 3.54 eV as well as the energy gap temperature coefficients of 0.3 and 0.1 meV/K were determined along and perpendicular to the GeO4 chains, respectively. In the crystal field spectral region, lowering of temperature leads to the appearance of three absorption maxima from the broad spectral feature centered at 1.76 eV at room temperature. We assign these low-energy excitations to the crystal field splitting of 3d9 energy levels of Cu2+ ions in CuO6 octahedra.

The optical energy gap of Ge1−xSnx alloys (x⩽0.14) grown on Ge substrates has been determined by performing transmittance measurements at 4K using a fast fourier transform infrared interferometer. The direct energy gap transitions in Ge1−xSnx alloys behave following a nonlinear dependence on the Sn concentration, expressed by a quadratic equation, with a so called bowing parameter b0 that describes the deviation from a simple linear dependence. Our observations resulted in b0RT=2.30±0.10eV and b04K=2.84±0.15eV, at room temperature and 4K, respectively. The validity of our fit is limited for Sn concentrations lower than 15%.

Six novel octakis(dialkoxyphenoxy)phthalocyaninatocopper(II) complexes (abbreviated as [(CnO)2PhO]8PcCu (n = 9–14)) have been synthesized. It was found that these derivatives exhibit rich mesophases; Colh, Colr1, Colr2, Colr3, Coltet and Cub phases. These mesophases were characterized by microscopic observation, DSC measurements and temperature-dependent X-ray diffraction measurements. Temperature-dependent electronic spectra for the thin films of these complexes revealed that roof-top-shaped dimers in the column gradually change into cofacial dimers as the temperature is increased from rt to their clearing points. Furthermore, the phthalocyanine derivatives for n = 11–14 exhibited spontaneous uniform homeotropic alignment for the Coltet mesophase, which is the first example in discotic liquid crystalline phthalocyanine compounds.

Cadmium sulphide CdS films with 200 nm have been prepared by thermal evaporation technique on glass substrate at substrate room temperature under vacuum of 10-5mbar.In this paper, the effect of Dielectric Barrier Discharge plasma on the optical properties of the CdS film. The prepared films were exposed to different time intervals (0, 3, 5, 8) min. For every sample, the Absorption A, absorption coefficient α , energy gap Eg ,extinction coefficient K and dielectric constant ε were studied. It is found that the energy gap were decreased with exposure time, and absorption , Absorption coefficient, refractive index, extinction coefficient, dielectric constant increased with time of exposure to the plasma. Our study considers the first investigation of the effect of cold atmospheric plasma on the optical properties of CdS film.

The resistivity, Hall coefficient, and Seebeck coefficient of single crystals of PbTe were investigated in the range from 77° to 900°K using a capsuling arrangement which prevented tellurium loss from the specimens at elevated temperatures. The low temperature properties obtained agree with the data reported in the literature. The thermal energy gap obtained from the high temperature measurements cannot, however, be brought into agreement with the energy gap determined from room temperature absorption measurements by considering solely the excitation of electron-hole pairs across the energy gap at elevated temperatures. Rather, it is necessary to include the carriers generated by defect formation at elevated temperatures. Both Schottky-Wagner and Frenkel defects are present, the activation energies for formation of the two types of defects being related by the equation EF=½ES+0.55 ev≃0.7 ev.

The current study describes the synthesis of anAg-CoFe2O4/rGO nanocomposite as a photocatalyst via a hydrothermal process that involves the attachment of silver and cobalt ferrite (CoFe2O4) nanoparticles to the surface of reduced graphene oxide. Various analytical techniques are used to investigate the effect of Ag and reduced graphene oxide (rGO) on the structure, optical, magnetic, photocatalytic, and electrochemical performance of CoFe2O4. The results show that the graphene sheets are exfoliated and decorated with well-dispersed Ag and CoFe2O4 nanoparticles. UV-visible spectra show a gradual shift in the absorption edge towards higher wavelengths with the addition of Ag ions, indicating variation in the samples' energy gap. The photoluminescence results show that graphene can reduce electron-hole recombination and improve the photocatalytic activity of the Ag-CoFe2O4/rGO nanocomposite. In this sense, theAg-CoFe2O4/rGO sample exhibits superior catalytic activity to the CoFe2O4 and Ag-CoFe2O4 photocatalysts for the degradation of methylene blue (MB) dye, indicating that rGO plays an important role in the Ag-CoFe2O4/rGO nanocomposite. The deterioration rate of the samples is found in the order of CoFe2O4(78.03%) <Ag-CoFe2O4(83.04%) < Ag-CoFe2O4/rGO(93.25%) in 100 min for MB dye respectively, under visible light irradiation. M-H hysteresis loop measurements confirm the samples' room temperature ferromagnetic behaviour. Overall, the Ag-CoFe2O4/rGO nanocomposite appears to be a strong magnetic photocatalyst for the treatment of contaminated wastewater. The electrochemical performance of all samples was examined using cyclic voltammetry (CV), which reveals that the Ag-CoFe2O4/rGO nanocomposite outperforms the other samples in terms of rate performance and cycle stability.