G. Kordas

Study of Antibacterial Composite Cu/SiO2 Thin Coatings

In the present work, composite copper containing silicate thin coatings (Cu/SiO2) were prepared on glass substrates by the sol-gel route. The preparation process included hydrolysis and subsequent polycondensation of corresponding alkoxide under refluxing and addition of soluble salt of antibacterial metal to the resulting sol. The coatings deposited by dipping process, were thermally treated in oxidative and reductive conditions up to 500°C for metal nanoparticles formation. The coating structure and the nanoparticles formation were studied by the X-ray Diffraction (XRD), UV-VIS and Heavy Ion Rutherford Backscattering (HIRBS) Spectroscopies. The antibacterial activity against Escherichia Coli was examined by the so-called antibacterial-drop test. The possible correlation between the layer interdiffusion after the thermal treatment and the antibacterial activity was considered and analyzed. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the metal concentration and was decreased with the increase of temperature of thermal treatment and metal nanoparticles formation.

Nanodesigned magnetic polymer containers for dual stimuli actuated drug controlled release and magnetic hyperthermia mediation

Novel magnetic, pH and redox sensitive microcontainers have been prepared using a sacrificial template-directed synthesis procedure, followed by chemical deposition of magnetic nanocrystals via co-precipitation. The fabricated magnetic microcontainers exert operative pH responsiveness, gradual and controlled collapse, once met with highly reducing environment, and efficient magnetic response.

Preparation effects on the UV optical properties of GeO2 glasses

The fusion temperature (Tφ), the oxygen partial pressure (PO2) during melting and the quenching rate from Tφ all influence the optical absorption in the 5.06‐eV (245‐nm) region. These observations are consistent with the assumption that the defect responsible for the optical absorption is an oxygen vacancy or complex of vacancies. The activation energy for the formation of the defect in GeO2 glasses which is repsonsible for the optical absorption is 2.3 eV which is larger than the activation energy for oxygen diffusion (∼1 eV).

Electron spin resonance studies of radiation damage in silicate glasses

Radiation-induced defects in silicate glasses were studied by the ESR-method. Two types of paramagnetic centers, whose ESR signals show a strong overlap, have been observed. A separation of the spectra was necessary for an exact characterization of these centers. Here, we took advantage of the effect that different centers disappear at different temperatures. By studying the behavior of the single spectra, both as a function of the temperature and of the composition, two types of paramagnetic centers could be isolated, which were called HI- and HII-centers. We developed new models for these centers on the basis of the data obtained from the experiments, computer-simulations and the literature.

Tailoring the particle size of sol–gel derived silver nanoparticles in SiO2

Abstract Metallic silver nanoparticles were prepared by the sol–gel method in amorphous SiO2 matrix. The process includes complexation of an appropriate silicon alkoxide with AgNO3, hydrolysis, polycondensation, and subsequent thermal treatment of the resulting powder. The thermal treatment conditions were optimized by differential thermal analysis (DTA) and differential thermal gravimetry (DTG) measurements. The size of the particles were determined by transmission electron microscopy (TEM) study. The metal particles were monodispersed in size and their mean diameters varied between 1 and 10 nm, depending upon the processing conditions. The particle size distributions were log-normal showing that the dominant particle growth mechanism is the coalescence. The effect of the oxidation temperature, the duration of oxidation, and the metal concentration on the particle size distribution was studied.

Sol-gel processing of Y1Ba2Cu3O7-x using alkoxide precursors: two systems yielding high degrees of thin film orientation and crystal growth

Abstract An alkoxide sol-gel chemistry has been developed to form superconducting Y 1 Ba 2 Cu 3 O 7− x thin films and bulk powders. The Cu(II) ethoxide synthesis and processing steps used to obtain a homogeneous Y-Ba-Cu sol are specifically outlined. Sols were produced using two different solvent systems: toluene and methoxyethanol/methylethylketone. Both systems promote complexation of insoluble Cu(II) ethoxide with the barium and yttrium precursors allowing the formation of nanometer-sized sols. Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to characterize the gel decomposition and oxide formation processes. The toluene system produced gels having a crystallization temperature of 425°C while the methoxyethanol/methylethylketone processed gel crystallized at 500°C. The methoxyethanol/methylethylketone gel had essentially complete organic by-product oxidation by 475°C. Films produced on single-crystal SrTiO 3 (for both systems) showed a high degree of orientation and crystal growth.

Highly oriented superconducting thin films derived from the sol‐gel process

Highly oriented YBa2Cu3O6+x superconducting thin films have been developed via sol‐gel processing. Film deposition involved spin coating a ‘‘partially hydrolyzed’’ metal‐alkoxide stock solution onto single‐crystal [100] SrTiO3 substrates. Although scanning electron microscopy revealed the film consisted of oriented polycrystallites, from the broad statistical x‐ray diffraction data the 1000 A film ‘‘appeared’’ to be single crystal with moderate mosaic spread (i.e., full width at half‐maximum was 0.3° in θ at a 2θ of 55°). No twinning of the crystal was found in any of the three orthogonal directions (2θ, φ, χ). The onset temperature Tc for the film was 55 K while the critical current density Jc was found to be 102 A/cm2.

Size distribution and EPR of silver nanoparticles in SiO2 matrix

Abstract Metallic silver nanoparticles were prepared by the sol–gel method in a SiO 2 matrix. The process includes complexation of silicon alkoxides with metal salts, hydrolysis, polycondensation, formation of powder, and subsequent thermal treatment first in oxidizing and second in reducing atmosphere. The sizes of metallic particles were determined both by X-ray diffraction and transmission electron microscopy. These measurements revealed sizes of metallic particles between 1 and 20 nm, depending upon processing conditions. The magnetic properties were investigated using the electron paramagnetic resonance spectroscopy in the temperature range between 4 and 300 K. The variation of the intensity of the resonance line with the temperature can be approximated by the Curie law indicative for the quantum size effect.

High-temperature ceramic superconductors derived from the sol-gel process

Abstract X-ray diffraction, four-probe electrical resistance and susceptibility measurements have been performed on class I and II ceramic superconductors produced by the sol-gel process. The onset temperature T c was 91 and 23 K for YBa 2 Cu 3 O 6 + x (class II) and La 1.9 Ba 0.1 CuO 4 (class I) respectively. The diamagnetic transition of each sample was consistent with its resistive transition.

Electron-spin-resonance (ESR) study of sol-gel glasses

Abstract The 9.5 GHz ESR-spectra of gamma-ray irradiated SiO 2 vacuum dried gels, produced with 2, 4, 8 and 16 mol. of water per mol. tetraethylorthosilicate (TEOS) and gels heat treated at temperatures between 400°C and 1000°C were recorded at 77 K and 300 K. A broad asymmetric line ( ΔH pp = 20.5 G, g eff = 2.006) dominated the room temperature spectra of the dried gels. The ESR-spectra of these gels recorded at 77 K consist of a well resolved characterized by g 1 = 2.004, g 2 = 2.01 and g 3 = 2.04. We tentatively attribute this resonance to O 2 − -ions. The resonance of this O 2 − -specie dominates the spectra of the gels treated up to 500°C. The spectrum of the vacuum dried gel heat treated at 900°C exhibits the resonance of the E 1 ′ -center and non-bridging oxygens. The spectrum of the gel heat treated at 1000°C is composed of several lines attributed to O 2 − radicals having different ligand fields.