19 research outputs found
Alumina-based nanoparticles obtained by anodic dissolution of Al in electrolytes with alcohol solvents
In the present work, alumina-based nanoparticles were produced by an electrochemical method. Alcohols (methanol, ethanol, and propanol) containing 5 % of water and LiCl were applied as electrolytes. Sizes of the micelles in the obtained solution ranged from 200 nm to over 1 depending on the used alcohol. Measurements performed by ultraviolet and visible light (UV-VIS) spectroscopy indicated a presence of aluminum oxides and hydroxides in the solution. Studies using transmission electron microscopy (TEM) revealed that the obtained nanoparticles are in a form of flakes and membranes and their size is \sim 200 nm for methanol and nm for propanol. The composition of the product was characterized by the Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD). It consists of amorphous Al oxides and hydroxides as well as poorly crystallized aluminates and metallic Al
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
Electronic band structure and surface states in Dirac semimetal
LaAgSb is a Dirac semimetal showing charge density wave (CDW) order. Previous angle-resolved photoemission spectroscopy (ARPES) results suggest the existence of the Dirac-cone-like structure in the vicinity of the Fermi level along the –M direction. This paper is devoted to a complex analysis of the electronic band structure of LaAgSb by means of ARPES and theoretical studies within the ab initio method as well as tight binding model formulation. To investigate the possible surface states, we performed the direct DFT slab calculation and the surface Green function calculation for the (001) surface. The appearance of the surface states, which depends strongly on the surface, points to the conclusion that LaSb termination is realized in the cleaved crystals. Moreover, the surface states predicted by our calculations at the and X points are found by ARPES. Nodal lines, which exist along the X–R and M–A paths due to crystal symmetry, are also observed experimentally. The calculations reveal other nodal lines, which originate from the vanishing of spin–orbit splitting and are located at the X–M–A–R plane at the Brillouin zone boundary. In addition, we analyze the band structure along the –M path to verify whether Dirac surface states can be expected. Their appearance in this region is not confirmed
Valence band of and studied by resonant photoemission spectroscopy and FPLO calculations
This work presents studies of the valence band of two Kondo lattice systems: Ce2Co0.8Si3.2, which is paramagnetic with the Kondo temperature T-K approximate to 50 K and Ce2RhSi3, which is antiferromagnetic below T-N = 4.5 K and exhibits TK approximate to 9 K. The photoemission spectra, which are obtained with photon energy tuned to Ce - 4d 4f resonance, reveal a Kondo peak at the Fermi energy (E-F), its spin orbit splitting partner at 0.24 eV and a broad maximum related to Ce f(0) final state. The spectra indicate that Kondo peak has a higher intensity for Ce2Co0.8Si3.2. The off-resonance photoemission data reveal that a maximum in the 3d electron density of states is shifted towards EF for Ce2Co0.8Si3.2 as compared to Ce2RhSi3. Full-potential local-orbital calculations were realized with local spin density approach +U approach for 213 stoichiometry. They show that a higher density of states near EF is observed for Ce2CoSi3. The calculations also reveal the existing tendencies for antiferromagnetic and ferromagnetic ground states in a case of Ce2RhSi3 and Ce2CoSi3, respectively
The Profile of Polyphenolic Compounds, Contents of Total Phenolics and Flavonoids, and Antioxidant and Antimicrobial Properties of Bee Products
This study aimed to characterize bee products (bee bread, bee pollen, beeswax, and multiflorous honey) with the profile of phenolic compounds, total phenolic (TPC) and flavonoid (TFC) contents, and antioxidant and microbiological properties. The TP and TF contents could be ordered as follows: bee pollen > bee bread > beeswax > honey. The UPLC−PDA−MS/MS analysis allowed identifying 20 polyphenols. Sinapic acid dominated in bee pollen, gallic acid in the bee bread and honey, while pinobanksin was the major compound of beeswax. The data showed that bee pollen and bee bread had a stronger antioxidant potential than honey and beeswax. Moreover, the antibacterial activity of the bee products was studied using 14 bacterial strains. Bee bread’s and bee pollen’s antimicrobial activity was higher towards Gram-negative strains. In comparison, honey was more potent in inhibiting Gram-positive bacteria. Our study indicates that bee products may represent valuable sources of bioactive compounds offering functional properties
Effect of electron doping in FeTe_{1−y} Se_{y} realized by Co and Ni substitution
Angle-resolved photoemission spectroscopy (ARPES) reveals effects of electron
doping, which is realized by Co and Ni substitution for Fe in
FeTeSe (y0.35) superconductor. The data show consistent
band shifts as well as expansion and shrinking of electron and hole Fermi
surface, respectively. Doping of either element leads to a Lifshitz transition
realized as a removal of one or two hole pockets. This explains qualitatively a
complex behavior of Hall coefficient observed before [Bezusyy, et al., Phys.
Rev. B 91, 100502 (2015)], including change of sign with doping, which takes
place only below room temperature. Assuming that Ni substitution should deliver
twice more electrons to the valence band than Co, it appears that such transfer
is slightly more effective in the case of Co. Therefore, charge doping cannot
account for much stronger effect of Ni on superconducting and transport
properties [Bezusyy, et al., Phys. Rev. B 91, 100502 (2015)]. Although overall
band shifts are roughly proportional to the amount of dopant, clear deviations
from a rigid band shift scenario are found. The shape of electron pockets
becomes elliptical only for Ni doping, effective mass of electron bands
increases with doping, strong reduction of effective mass is observed for one
of hole bands of the undoped system. The topology of hole and electron pockets
for superconducting FeTeSe with T=13.6 K
indicates a deviation from nesting. Co and Ni doping causes further departure
from nesting, which accompanies the reduction of critical temperature
Kondo lattice behavior observed in the CeCu_{9}In_{2} compound
We report systematic studies of CeCuIn, which appears to be a new
Kondo lattice system. Electrical resistivity exhibits a logarithmic law
characteristic of Kondo systems with a broad maximum at 45 K
and it obeys the Fermi liquid theory at low temperature. Specific heat of
CeCuIn is well described by the Einstein and Debye models with
electronic part at high temperature. Fitting of the Schottky formula to low
temperature 4f contribution to specific heat yielded crystal field splitting of
50.2 K between a doublet and quasi-quartet. The Schotte-Schotte model estimates
roughly Kondo temperature as 5 K, but does not reproduce well the
data due to a sharp peak at 1.6 K. This structure should be attributed to a
phase transition, a nature of which is possibly antiferromagnetic. Specific
heat is characterized with increased Sommerfeld coefficient estimated as
132 mJ/(moleK). Spectra of the valence band, which
have been collected with ultraviolet photoelectron spectroscopy (UPS), show a
peak at binding energy250 meV, which originates from the Ce 4f
electrons and is related to the 4f final state. Extracted 4f
contribution to the spectral function exhibits also the enhancement of
intensity in the vicinity of the Fermi level. Satellite structure of the Ce 3d
levels spectra measured by X-ray photoelectron spectroscopy (XPS) has been
analyzed within the framework of the Gunnarsson-Sch\"onhammer theory.
Theoretical calculations based on density functional theory (FPLO method with
LDA+U approach) delivered densities of states, band structures and Fermi
surfaces for CeCuIn and LaCuIn. The results indicate that Fermi
surface nesting takes place in CeCuIn