3D photonic crystals for direct applications in light emitting devices

In this paper, we present IP-Dip polymer-based Photonic Crystals (PhCs), which are more and more attractive for photonic devices. These structures offer simple and cheap solutions, how to improve optical properties of these devices. In our experiment, we used Direct Laser Writing (DLW) lithography to create a three dimensional (3D) PhCs. We fabricated two types of PhC structure. The first structure was prepared from IP-Dip polymer and used for modification of the radiation pattern of the optical fiber. The second PhC structure was filled with liquid polymer PolyDiMethylSiloxane (PDMS) and directly placed on the LED chip. Quality of the prepared structures was confirmed by a confocal microscope. The modification of the far-field radiation patterns of LED and optical fiber was measured by a goniophotometer

Mulliken occupation as the indicator of transition to superconducting state in SrFe2As2 and BaFe2As2

Basing on the ab initio calculations performed within full potential local orbital minimum basis method, the Mulliken occupation of the Sr 5s (n5s) and Ba 6p (n6p) states can serve as an indicator of transition to the superconducting state in doped SrFe2As2 and BaFe2As2 compounds where the iron was substituted with cobalt or in the pristine compounds under pressure. The estimated pressure, at which both compounds exhibit superconductivity based on Sr 5s and Ba 6p occupation is in good agreement with the recently published experimental data

Lanthanide Contraction in RENi 5 (RE = La, Ce, Nd, Sm, Eu, Gd, Tb, Yb) compounds studied with band structure calculations

Full potential linearized augmented plane wave band structure calculations were performed for hexagonal RENi5 (RE = rare earth) compounds in order to investigate reproducibility of lanthanide contraction by ab initio studies. The a and c parameters were optimised using a paraboloid t, starting from the same initial values for all compounds studied. The trend in lattice parameters across the RE series obtained from the calculations was found to be in general agreement with experimental data. A comparison of results obtained by generalized gradient approximation and generalized gradient approximation with additional Coulomb correlations calculations is presented for several double counting schemes

“DistorX” program for analysis of structural distortions affecting X-ray diffraction patterns

For the purposes of research on strongly correlated electronic systems (SCES), a computer program, DistorX (Distortion or X-ray diffraction patterns), was created. The program is an interactive Jupyter notebook for simulating the effects of structural distortions on X-ray diffraction patterns. The program is designed to be universal, in that it may be successfully applied to a variety of structures. In previous reports, a structural transition from a cubic phase of Yb3Rh4Sn13 – type to the superlattice variantwas been observed at 160 K for a series of skutterudite-related Ce3M4Sn13 compounds, where M = Co, Ru or Rh. In this work, we use a specialized build of DistorX to simulate the low-temperature X-ray diffraction patterns of a distorted unit cell. The method described here obtains simulated XRD patterns from the atomic positions and permits investigation of crystal structure without imposed symmetry operations. We further indicate the crystallographic plane in which the distortion occurs, and explain the possible origin of CDW in these materials

Electronic structure and transport properties of CeNi9In2

We investigated CeNi9In2 compound, which has been considered as a mixed valence (MV) system. Electrical resistivity vs. temperature variation was analysed in terms of the model proposed by Freimuth for systems with unstable 4f shell. At low temperature the resistivity dependence is consistent with a Fermi liquid state with a contribution characteristic of electron-phonon interaction. Ultraviolet photoemission spectroscopy (UPS) studies of the valence band did not reveal a Kondo peak down to 14 K. A difference of the spectra obtained with photon energies of low and high photoionization cross sections for Ce 4f electrons indicated that 4f states are located mainly close to the Fermi energy. The peaks related to f_{5/2}^1 and f_{7/2}^1 final states cannot be resolved but form a plateau between -0.3 eV and the Fermi energy. X-ray photoemission spectroscopy (XPS) studies were realized for the cerium 3d level. The analysis of XPS spectra within the Gunnarsson-Sh\"onhammer theory yielded a hybridization parameter of 104 meV and non-integer f level occupation, being close to 3. Calculations of partial densities of states were realized by a full potential local orbital (FPLO) method. They confirm that the valence band is dominated by Ni 3d states and are in general agreement with the experiment except for the behavior of f-electrons.Comment: 10 pages, 5 figure

Thermoelectric properties of Ca2Sn/Ca3SnO

This type of materials was first synthesized in 1961 (Eckerlin), and its structure was determined by XRD measurements [1]. There are little experimental studies of thermodynamic and electrical properties of these compounds [2–4], as even in the first paper it was observed that these materials within a very short time turn into black powder after exposure to air. That powder contains mainly oxidation products. Recently, these materials were studied using ab-initio calculations and they were predicted to possess very promising thermopower [5–10]. Its real crystal structure is also a matter of debate [3, 8, 9]. The usability of thermoelectric material for thermoelectric applications depend on figure of merit, where high thermopower, small thermal conductivity and low resistivity is expected from a prospective material [11, 12]. Due to recent ab-initio studies we decided to revisit Ca2Sn, and measure its thermoelectric properties[…

Diffraction Properties and Application of 3D Polymer Woodpile Photonic Crystal Structure

We present a new technique for modification of diffraction and optical properties of photonic devices by surface application of polymer Three-Dimensional (3D) woodpile Photonic Crystal (PhC) structure. Woodpile structure based on IP-Dip polymer was designed and fabricated by Direct Laser Writing (DLW) lithography method based on nonlinear Two-Photon Absorption (TPA). At first, we investigated diffraction properties of woodpile structure with a period of 2 μm. The structure was placed on a glass substrate, and diffraction patterns were measured using laser sources with different wavelengths. After diffraction properties investigation, the fabricated structures were used in optoelectronic devices by their surface application. Our polymer 3D PhC woodpile structures were used for radiation properties modification of light emitting devices - optical fiber and Light Emitting Diode (LED) and for angular photoresponse modification of InGaAsN-based photodiode. The modification of the far-field radiation patterns of optical fiber and LED and spatial modulation of light coupling into photodiode chip with applied structures were measured by goniophotometer. Quality of fabricated structures was analyzed by a Scanning Electron Microscope (SEM)

Studies of electronic structure across a quantum phase transition in CeRhSb_{1-x}Sn_{x}

We study an electronic structure of CeRhSb1xSnx system, which displays quantum critical transition from a Kondo insulator to a non-Fermi liquid at x = 0:13. We provide ultraviolet photoelectron spectra of valence band obtained at 12.5 K. A coherent peak at the Fermi level is not present in the data, but a signal related to 4f1 7=2 nal state is detected. Spectral intensity at the Fermi edge has a general tendency to grow with Sn content. Theoretical calculations of band structure are realized with full-potential local-orbital minimum-basis code using scalar relativistic and full relativistic approach. The calculations reveal a depletion of density of states at the Fermi level for CeRhSb. This gap is shifted above the Fermi energy with increasing Sn content and thus a rise of density of states at the Fermi level is re ected in the calculations. It agrees with metallic properties of compounds with larger x. The calculations also yield another important e ect of Sn substitution. Band structure is displaced in a direction corresponding to hole doping, although with deviations from a rigid band shift scenario. Lifshitz transitions modify a topology of the Fermi surface a few times and a number of bands crossing the Fermi level increases

Thermoelectric properties of heavy fermion compound Ce3Co4Sn13

The heavy fermion compound Ce3Co4Sn13 was studied in terms of its thermoelectric properties. To enhance its gure of merit we milled the solid sample and then pressed to obtain a consistent granulated material. The main properties, such as the Seebeck coe cient, thermal conductivity and electronic resistivity were measured at low (< 300 K) temperatures for both, the solid and the granulated sample. Thermal conductivity was diminished and the Seebeck coe cient was slightly enhanced, while the resistivity of produced material was increased. We explain it by strong electron scattering on defects and grain boundaries present in the sample. The resulting gure of merit ZT was found to be enhanced almost across the whole measured T region