Milan Vlček

Optical properties of amorphous As-Se and Ge-As-Se thin films

Abstract Amorphous As–Se and Ge–As–Se thin films were prepared by thermal evaporation. From parameters of the Wemple–DiDomenico model, the values of the third-order non-linear susceptibility were estimated using the generalized Millers rule. Measurements of photodarkening at 78 K showed that the optical gap and the slope of the optical absorption edge are intercorrelated. The kinetics of the photoinduced shift of the gap are described using a stretched exponential law. A possible role of the concentration of Se atoms on the rate of photodarkening on one hand and of the network rigidity (measured by the mean coordination number) on the other are briefly discussed.

Mixed Organotin(IV) Chalcogenides: From Molecules to Sn‐S‐Se Semiconducting Thin Films Deposited by Spin‐Coating

Put the right spin on it: Mixed monomeric organotin(IV) chalcogenides of the general formula L(2)Sn(2)EX(2) containing two terminal Sn-X (X = Se, Te) bonds were prepared and were tested as potential single-source precursors for the deposition of semiconducting thin films. Spin-coating deposition of [{2,6-(Me(2)NCH(2))(2)C(6)H(3)}SnSe](2)(μ-S), as the useful single-source precursor, provided amorphous Sn-S-Se semiconducting thin films.

Amorphous Ge–Se thin films prepared by pulsed-laser deposition

Amorphous Ge x Se1− x , x = 0.22–0.28 thin films were prepared by the pulsed-laser deposition technique. The photo-induced and thermally induced changes of structure and optical gap of the films were studied and discussed. The exposure and annealing causes bleaching of the films, and increases. The structure is influenced only a little by exposure; the annealing causes a decrease in the Raman band amplitudes corresponding to Ge–Ge and Se–Se bonds and to structural units similar to (GeSe) n . This can be ascribed to chemical reactions between fragments formed during pulsed-laser deposition.

High-temperature thermoelectric properties of Hg-doped CuInTe2

Polycrystalline samples of composition CuIn1−xHgxTe2 (x = 0–0.21) were synthesized from elements of 5N purity using a solid state reaction. The phase purity of the products was verified by X-ray diffraction. Samples for transport property measurements were prepared using hot-pressing. The samples were characterized by measurement of the electrical conductivity, Hall coefficient, Seebeck coefficient, and thermal conductivity over a temperature range of 300–675 K. All samples show p-type conductivity. We discuss the influence of Hg substitution on the free carrier concentration and thermoelectric performance. The investigation of the thermoelectric properties shows up to a 40% improvement of ZT in the temperature range of 300–600 K.

Crystallization behaviour of Ge17Sb23Se60thin films

The crystallization behaviour of as-prepared and nucleated Ge17Sb23Se60 thin films was studied by means of differential scanning calorimetry, X-ray diffraction analysis and scanning electron microscopy. Detailed analysis of the non-isothermal crystal growth kinetics was performed; the apparent activation energy, kinetic model and value of the pre-exponential factor were determined. The kinetic behaviour was found to be surprisingly close to the ideal Johnson–Mehl–Avrami nucleation-growth process, with the only non-ideality being the prolonged peak end tail (which may be a specificity associated with certain thicknesses of thin layers). This corresponds to the initiation of crystal growth in agreement with the classical nucleation theory, with the amount of mechanical defects and strains being negligible. The value of the kinetic parameter suggests two-dimensional crystal growth, which is consistent with the idea of macroscopic crystallites growing in a sterically restricted thin layer. A similar conclusion can be made on the basis of direct microscopic observation of the crystallites’ morphology.

Toxicity of zinc oxide nanoparticles to the annelid Enchytraeus crypticus in agar-based exposure media

Toxicity of zinc oxide nanoparticle (ZnO-NPs) powder and water soluble salt of Zn (ZnCl2) to the annelid Enchytraeus crypticus was tested in agarose gel. Influence of the spiking method on the resulting size of nanoparticles and on E. crypticus mortality was studied. Two methods of ZnO-NPs powder (mean particle size diameter of 10 nm) introduction into the exposure media were used. In the first method, the nano-powder was initially cryogenically ground with dry agar followed by an addition of water. The second procedure began with re-suspension of nanoparticles in demineralized water containing a dispersant (sodium pyrophosphate decahydrate). The obtained colloid was subsequently mixed with hot agar gel. Relative mortality in worms observed after 96 h of their exposure to the ZnO-NPs concentrations (all in mg of ZnO-NPs per kg of agar) of 50, 100, 200, 500 and 1000 in the cryogenically ground medium ranged between 28.9 % and 34.4 % and it did not exhibit any concentration dependence. When the second method of exposure media preparation was applied, the relative mortality ranged from 0 % to 66.6 % in the same concentration region depending on the concentration. Scanning electron microscopy (SEM) revealed the presence of large agglomerates (1–10 µm in diameter) in the media prepared by cryogenic grinding with the highest concentration of ZnO-NPs. Neither the cryogenically ground media with lower ZnO-NPs concentrations nor any media prepared from colloidal solutions contained agglomerates exceeding 100 nm, detectable by SEM. Hydrodynamic diameters of particles in the colloids used in the second method of agar preparation were measured using dynamic light scattering (DLS) and ranged between 164 nm and 240 nm. The observed toxicity was thus clearly dependent on the size of ZnO-NPs agglomerates and the technique of exposure media preparation. Experimentally detected LC50 value for dissolved Zn2+ was 37.2 mg kg−1 in agar. The same concentration of Zn induced an approximately 30 % mortality of E. crypticus when administered in form of cryogenically ground ZnO-NPs with agar. No observable effects were found at this ZnO-NPs concentration when the exposure medium was prepared from the colloid solution.

Compositional trend of the blue shift of the gap in GexS100−x thin amorphous films induced by annealing and illumination

Abstract The blue shift of the gap in Ge x S 100− x amorphous films (49 ⩽ x ⩽ 26) induced by annealing and illumination has been examined using visible and infrared spectroscopy. It was found that annealing results in a considerable increase of the gap ( E g ) (by about 0.5 eV at around GeS 2 ). The shape of the E g ( x ) dependence of well-annealed films has a very similar form to that for bulk glasses. It is proposed that the magnitude of the blue shift of the gap induced by annealing is enhanced (except for short-range ordering) by an additional contribution associated with the structural phase transition at around composition GeS 2 .

Cryogenic grinding of electrospun poly-ε-caprolactone mesh submerged in liquid media.

In this paper, the treatment of poly-ε-caprolactone (PCL) nano/micro-mesh system by cryogenic grinding and subsequent characterization of obtained product is described. The PCL nano/micro-mesh layer submerged in appropriate liquid was cryogenically ground and obtained particles were characterized employing mainly laser diffraction and scanning electron microscopy (SEM). In the ground sample, different types of particles (fibrous particles, fibrous fragments, agglomerates with and without an internal fibrous structure, lamellae and nanoparticles) were identified, described and quantified. Parameters of cryogenic grinding (weight of sample, type of liquid medium, and influence of sample storage) were optimized to maximize the yield of particles with desired features. The potential of the system for cell scaffolding was demonstrated by cultivation of 3T3 fibroblasts on the produced microparticles.

The preparation and some physical properties of thin amorphous Ge-Bi-S films

Amorphous Ge-Bi-S thin films having n-type conductivity were prepared by thermal evaporation from two boats. The dc electrical conductivity (σ) of these films in the “low”-temperature region only weakly depends on temperature. This indicates (i) the possible presence of an “impurity-like” conduction due to the donor-like band located in the proximity of the conductivity band or (ii) a hopping type conduction due to the variable range hopping. Of interest is the fact that the dc electrical conductivity reaches considerably high values (σ(300 K) = 2.7 Ω−1 cm−1 for Ge18.6Bi25.3S56.1 thin film). Far-infrared transmission spectra of the studied films indicate a typical two-mode behavior due to the Ge-S and Bi-S stretching modes.

Impact of particle size reduction on glaze-melting behaviour

The effect of milling on thermal behaviour of two types of industrial ceramic glazes was investigated by heating microscopy. The Vogel–Fulcher–Tamman equation was used for viscosity calculation of the glaze samples, and the impact of particle size reduction on calculated data has been analysed. The employed model provides a good fit to the general tendencies of viscosity change during melting and can be applied for a comparative description of glaze-melting behaviour. Observed correlations between the viscosity, the contact angle, milling time, glazing temperature and the specular reflection of the glazed tiles help to reveal the optimal physical characteristics for glaze manufacturing and to achieve the desired gloss and smoothness of glazed surface. On its turn, variation of particle size distribution highly affects thermal behaviour of ceramic glazes, and thus, the milling procedure provides the possibility of manipulation of glaze-melting behaviour during heating and allows to change the manufacturing heating cycle when required.