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Topological insulators (TI) belong to category of phases which go beyond the theory of spontaneous symmetry breaking, well describing classical phases. TI are materials of strong spin-orbit interaction that leads to the inversed band structure. Thus, they belong to different topological class than surrounding “normal” world. Consequently, these materials behave as insulators in their volume while their surface hosts metallic states, that appear as a result of the need to meet boundary conditions. The metallic states have the unusual spin structure described by the Dirac-type Hamiltonian, with the electron spin locked to its momentum. They are protected by the time reversal symmetry, thus are resistant to non-magnetic disturbances. Introducing magnetic impurities breaks the time reversal symmetry, opening the energy gap at the Dirac point and eventually modifying spin texture. In research of magnetically doped TI there are still many challenges and open questions. Here, I will present results of our recent studies of three-dimensional TI from the Bi2-xSbxTe3-ySey family, doped with Mn ions. I will discuss possible locations of Mn impurity in the crystal host lattice, the influence of doping on the crystal structure and magnetic properties. Ferromagnetism was successfully obtained in Bi2Te3 and BiSbTe3 doped with 1.5-2 at. % of Mn, with the Curie temperature of the order of ~ 15 K. The role of free carriers in ferromagnetic interactions is not clear. Ferromagnetism is observed at diluted Mn concentrations suggesting a need for a medium mediating the long-range ferromagnetic order, but the Tc does not scale with the concentration of free carriers. We would like to acknowledge National Science Center, Poland, grant no 2016/21/B/ST3/02565.

The use of plasmonic inclusions in heterojunction solar cells promises increase of solar-to-electric energy conversion efficiency. Recently, solar cells with ZnO nanorods attracted a lot of attention due to improved efficiency provided by highly scattering ZnO nanostructures on silicon or perovskite. N-type ZnO nanorods are grown on p-Si monocrystalline 180 μm thick substrates among others by means of a hydrothermal technique which requires prior seeding by deposition of thin film of ZnO or noble metals. In the latter case, naturally formed metal islands can also act as plasmonic nanoparticles (NPs). Excitation of plasmonic resonance on the NPs leads to directional scattering of light towards Si layer and electromagnetic field enhancement at their vicinity, close to the ZnO-Si junction, what results in improved energy absorption in the semiconductor layer and thus energy conversion efficiency. In this study, we investigate optimal conditions at which plasmonic phenomenon further improves light trapping in the Si-ZnO solar cells. In simulations performed by means of 3D FDTD method, we calculate light absorption enhancement in the system due to plasmonic NPs used as a seed layer at the ZnO/Si. In the calculations Ag, and Al NPs of different size and geometry close to that achievable in the experiment are analyzed. Finally, numerical results taking into account the granulometry of metal NPs achieved in the experiment are compared with the efficiency of fabricated cells.

The properties of nanocomposite palladium-nickel-multi-walled (Pd-Ni-MWCNT) films deposited on aluminum oxide (Al2O3) substrate have been prepared and investigated. These films were obtained by 3 step process consisted of PVD/CVD/PVD methods. The morphology and structure of the obtained films were characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques at various stages of the film formation. EDX spectrometer was used to measurements of elements segregation in the obtained film. TEM and STEM (Scanning Transmission Electron Microscopy) observations showed MWCNTs decorated with palladium nanoparticles in the film obtained in the last step of film formation (final PVD process). The average size of the palladium nanoparticles observed both on MWCNTs and carbonaceous matrix does not exceed 5 nm. The research was conducted on the use of the obtained films as potential sensors of gases (e.g. H2, NH3, CO2) and bio-sensors or optical sensors.

Structural, topographical and morphological changes of carbonaceous-palladium (C-Pd) films obtained by physical vapor deposition /chemical vapor deposition (PVD/CVD) method were studied. Effect of changes in these properties under the influence of CVD process temperature on the hydrogen sensitivity of these films is discussed. Scanning electron microscopy (SEM) observations were used to investigate the topography and morphology of an initial (PVD) film and the film modified in CVD process (PVD/CVD film) at different temperatures. The changes of film’s morphology after modification performed at various temperatures (500, 550, 600, 650, 700 and 750°C) caused changes in their resistance. The electrical measurements carried out in the presence of gas containing 1vol % of hydrogen showed different sensing characteristics for various films. The highest hydrogen sensitivity and the fastest response were observed for films modified at the temperature of 500°C and 550°C. In SEM images on surface of these films palladium nanograins with different sizes were observed. For films modified at the temperatures higher than 600°C Pd nanograins placed under superficial very thin carbonaceous layer were found.