Radosław Belka

The Phase Transitions in Ferroelectric Crystals of A 2 MX 4 and AMX 3 Type

Investigations of characteristics the ferroelectric crystals of A 2 MX 4 and AMX 3 type with incommensurate phases are very interesting both from a scientific and practical point of view. Some aspects of behaviour phase transitions of these crystals are discussed. Special attention is paid to the temperature dependence of series of different type phase transitions. Analysis of the literature data and results of our research let us to consider potential possibilities of practical applications of these materials for optoelectronic devices. Observed temperature hysteresis of birefringence and absorption coefficient in incommensurate phases are especially important for application as optical memories.

Raman studies of Pd-C nanocomposites

The results of studying palladium-carbon (Pd-C) nanocomposites using Raman spectroscopy are presented. This method has been used for studying samples having various palladium content, prepared by a one-step Physical Vapour Deposition (PVD) process and a Chemical Vapour Deposition (two-step PVD/CVD) process using different process parameters. For samples obtained by PVD, the vibration bands characteristic of C60 fullerene molecules were observed in the spectra, whereas for layers obtained by PVD/CVD, the Raman spectra displayed mainly D and G bands characteristic solely of the prescence of graphite-like layers’ vibrations. The analysis of the obtained Raman spectra reveals that its shape is affected by many parameters including type of substrate, temperature, and the percentage content of Pd in the studied layer. The quantitative analysis of spectra for layers obtained using the PVD/CVD process shows a difference in the relative intensity of bands D and G, reflecting the different degrees of amorphisation in the investigated nanocomposites.

The optical study of nanoporous C-Pd thin films

In this paper, the preliminary results for thin carbon-palladium (C-Pd) nanocomposites obtained by PVD/CVD method, carried out using optical methods are presented. Raman studies reveal the dominance of graphite-like structures. The optical transmittance measurement shows an exceptionally low value of the effective extinction coefficient when compared to amorphous graphite. The carbon structure porosity impact on the transmission properties of the studied layers is discussed.

Raman study of TiO2 coatings modified by UV pulsed laser

The TiO2 coatings were prepared by simple sol-gel method and modified by UV pulsed laser. TiO2, also know as titania, is a ceramic compound, existing in numerous polymorphic forms, mainly as tetragonal rutile and anatase, and rhomboidal brookite. Rutile is the most stable form of titanium dioxide, whereas anatase is a metastable form, created in lower temperatures than rutile. Anatase is marked with higher specific surface area, porosity and a higher number of surface hydroxyl groups as compared to rutile. The unique optical and electronic properties of TiO2 results in its use as semiconductors dielectric mirrors, sunscreen and UV-blocking pigments and especially as photocatalyst. In this paper, the tetraisopropoxide was used as Ti precursor according to sol-gel method. An organic base was applied during sol preparation. Prepared gel was coated on glass substrates and calcined in low temperature to obtain amorphous phase of titania. Prepared coatings were modified by UV picosecond pulse laser with different pulse repetition rate and pulse power. Physical modification of the coatings using laser pulses was intended in order change the phase content of the produced material. Raman spectroscopy (RS) method was applied to studies of modified coatings as it is one of the basic analytical techniques, supporting the identification of compounds and obtaining information about the structure. Especially, RS is a useful method for distinguishing the anatase and rutile phases. In these studies, anatase to rutile transformation was observed, depending on laser parameters.

Analysis of optical properties of fullerene-palladium nanostructures using effective medium theory

In this paper an influence of the content of palladium on optical properties of fullerene-palladium nanocomposite was discussed, based on Effective Medium Theory (EMT). Since the complex refractive index of Pd is clearly different from the refractive index of fullerene, even a small admixture of metal leads to significant changes in value of effective index and consequently to change the reflection coefficient of the layer.

Properties of the carbon-palladium nanocomposites studied by Raman spectroscopy method

In this paper, the results for thin carbon-palladium (C-Pd) nanocomposites obtained by PVD (Physical Vapour Deposition) and PVD/CVD (Chemical Vapour Deposition) method, carried out using Raman spectroscopy method are presented. Studies reveal the dominance of fullerene-like structure for PVD samples and graphite-like structures for CVD samples. The type of substrate and metal content have great impact on spectra shapes.

Some aspects of using of A2MX4 crystals in optoelectronic measurements of temperature

In this paper a concept of a non-contact method of temperature and humidity measurements based on the thermooptic and higroscopic effects of A2MX4 crystals is presented. Temperature and humidity influences on optical properties of some crystals were investigated. Possibilities of application of the A2MX4 crystals as a temperature and humidity sensors were discussed.

Nonlinear phenomena in A2MX4 type crystals with incommensurate phases

Investigations of the nonlinear phenomena in A2MX4 type crystals (A, organic cation or alkaline metal ion; M, metal ion; X, halogen ion) with incommensurate phases are very interesting from both a scientific and a practical point of view. In the crystals many interesting nonlinear phenomena are observed, e.g., thermal hysteresis of birefringence and absorption coefficient, piezooptic effect, electrooptic effect. Different anomalies (e.g., a discontinuity or change of sign of the briefringence coefficient, a distinct increase of the value of piezooptic and electrooptic coefficients) exist in the phase transition regions. They are especially distinct for a transition from the incommensurate phase to the commensurate phase. Some possibilities of detection and recognition of the existence of incommensurate phases by optical methods are suggested.

Possibilities and limitations of A2MX4 and AMX3 crystal growth

Materials with non-linear properties such as thermal hysteresis of birefringence, electrooptic, thermooptic, piezooptic and thermochromic phenomena are very interesting both from scientific and practical points of view. They can be applied to photonic technology as optical memories, optical modulators, temperature and stress sensors. The examples of such materials are A2MX4 and AMX3 crystals (where A organic cation, M transition metal, X halogens). Possibilities and limitation of the A2MX4 and AMX3 crystals growth from water and organic solution have been discussed in order to determine the optimal parameters of the growth.

Features of crystals with incommensurate phases

The main features of crystals with incommensurate phases are reviewed. Special attention is paid to optical properties of ferroelectric crystals of the A2MX4 type. Some aspects of practical application of these materials in optoelectronics is also discussed.