Wyniki wyszukiwania - BazTech

1

Wave Propagation in a LRPC Composite Double Panel Structure with Periodically Attached Pillars and Etched Holes

Qian D.

Archives of Acoustics

|

2018

|

Vol. 43, No. 4

717--725

EN

The locally resonant phononic crystal (LRPC) composite double panel structure (DPS) made of a twodimensional periodic array of a two-component cylindrical LR pillar connected between the upper and lower composite plates is proposed. The plates are composed of two kinds of materials and periodically etched holes. In order to reveal the bandgap properties of structure theoretically, the band structures, displacement fields of eigenmodes and transmission power spectrums of corresponding 8 × 8 finite structure are calculated and displayed by using finite element method (FEM). Numerical results and further analysis demonstrate that if the excitation and response points are picked on different sides of the structure, a wide band gap with low starting frequency is opened, which can be treated as the coupling between dominant vibrations of pillars and plate modes. In addition, the influences of filled-in rubber, etched hole and viscidity of soft material on band gap are studied and understood with the help of “base-spring-mass” simplified model.

2

Struktura pasmowa i wzmocnienie optyczne studni kwantowych GeSn/Ge

Mączko H., Gładysiewicz M., Kudrawiec R.

Przegląd Elektrotechniczny

|

2017

|

R. 93, nr 8

13--16

PL

W niniejszej pracy zaprezentowano wyniki obliczeń struktury pasmowej i widm wzmocnienia optycznego dla studni kwantowych Ge/Ge1-xSnx/Ge. Dokonano optymalizacji składu x i grubości studni d do zastosowań w laserach półprzewodnikowych, w wyniku której uzyskano propozycje korzystnych wartości parametrów studni kwantowej: 0,15 < x < 0,17, d ~ 12 mm.

EN

In this work band structure and optical gain was calculated for Ge/Ge1-xSnx/Ge quantum wells. Ottomanization of x composition and the thickness of the well d were made for use in semiconductor lasers. As a result of optimization achieved the optimum parameter values of quantum wells: 0.15 < x < 0.17, d ~ 12 nm.

3

The study of structural, elastic, electronic and optical properties of CsYx I(1 − x)(Y = F, Cl, Br) using density functional theory

Mian S. A., Muzammil M., Rahman G., Ahmed E.

Materials Science Poland

|

2017

|

Vol. 35, No. 1

197--210

EN

The structural, electronic, elastic and optical properties of CsYx I(1 − x)(Y = F, Cl, Br) are investigated using full potential linearized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA). The ground state properties such as lattice constant (ao) and bulk modulus (K) have been calculated. The mechanical properties including Poisson’s ratio (σ), Young’s modulus (E), anisotropy factor (A) and shear modulus (G) were also calculated. The results of these calculations are comparable with the reported experimental and theoretical values. The ductility of CsYx I(1 − x) was analyzed using Pugh’s rule (B/G ratio) and Cauchy’s pressure (C12−C44). Our results revealed that CsF is the most ductile among the CsYx I(1 − x) (Y = F, Cl, Br) compounds. The incremental addition of lighter halogens (Yx) slightly weakens the strength of ionic bond in CsYx I(1 − x). Moreover, the optical transitions were found to be direct for binary and ternary CsYx I(1 − x). We hope that this study will be helpful in designing binary and ternary Cs halides for optoelectronic applications.

4

Electronic structure and effective masses of TlInSe2 under pressure

Orudzhev G.S., Ismayilova N .A., Jafarova V. N.

Materials Science Poland

|

2017

|

Vol. 35, No. 4

857--860

EN

We have studied the band structure and the band gap closure of TlInSe2 under pressure in the range of 0 GPa to 21 GPa, by employing the first-principles method based on the density functional theory. We discuss the possible metallic transition in the tetragonal phase of TlInSe2 crystal. Our calculation results show that the value of the pressure at the crossover from the direct to the indirect gap is found to be 8 GPa. The “semiconductor-metal” transition is determined to occur at 14 GPa. The study of the pressure effect on the effective masses for semiconductor state shows that with increasing pressure, the effective masses of holes and electrons decrease and the anisotropy of effective masses of holes is weakening.

5

Bandgap properties in locally resonant phononic crystal double panel structures with periodically attached pillars

Qian D., Shi Z.

Journal of Theoretical and Applied Mechanics

|

2017

|

Vol. 55 nr 4

1167--1179

EN

The locally resonant (LR) phononic crystal double panel structure made of a two-dimensional periodic array of a two-component cylindrical LR pillar connected between the upper and lower plates is proposed, and the bandgap properties of the structure are investigated theoretically in this paper. The band structures, displacement fields of eigenmodes and transmission power spectrums of the corresponding 8×8 finite structure are calculated by the finite element method. Numerical results and further analysis demonstrate that a band gap with a low starting frequency and a wide band width is opened by the coupling between dominant vibrations of the pillars and plate modes of the upper and lower plates when the vibration source and the receiver are considered on different sides of the structure. By comparing the band structures and displacement fields of the double panel and those of the single plate with the same parameters, many common characteristics are displayed. Then, the influence of geometrical parameters on the band gap are studied and understood with the help of a simple ‘spring-mass’ model.

6

Using PWE/FE Method to Calculate the Band Structures of the Semi-Infinite PCs : Periodic in x-y Plane and Finite in z–direction

Qian D., Shi Z.

Archives of Acoustics

|

2017

|

Vol. 42, No. 4

735--742

EN

This paper introduces the concept of semi-infinite phononic crystal (PC) on account of the Infinite periodicity in x-y plane and finiteness in z-direction. The plane wave expansion and finite element methods are coupled and formulized to calculate the band structures of the proposed periodic elastic composite structures based on the typical geometric properties. First, the coupled plane wave expansion and finite element (PWE/FE) method is applied to calculate the band structures of the Pb/rubber, steel/epoxy and steel/aluminum semi-infinite PCs with cylindrical scatters. Then, it is used to calculate the band structure of the Pb/rubber semi-infinite PC with cubic scatter. Last, the band structure of the rubbercoated Pb/epoxy three-component semi-infinite PC is calculated by the proposed method. Besides, all the results are compared with those calculated by the finite element (FE) method implemented by adopting COMSOL Multiphysics. Numerical results and further analysis demonstrate that the proposed PWE/FE method has strong applicability and high accuracy.

7

Structural determination of Co/TiO2 nanocomposite: XRD technique and simulation analysis

Mostaghni F., Abed Y

Materials Science Poland

|

2016

|

Vol. 34, No. 3

534--539

EN

Synthesis and complex theoretical and experimental studies of Co/TiO2 anatase have been reported. The preparation of Co/TiO2 was carried out by sol-gel method. Distribution of cations among the two tetrahedral and octahedral sites was estimated by analyzing the powder X-ray diffraction patterns by employing Rietveld refinement technique, and the results revealed the existence of tetragonal structure. Band structure and density of states calculations were performed using the first-principles methods. The structural and electronic properties of Co/TiO2 were calculated in the general gradient approximation (GGA). An additional comparison with pure TiO2 anatase allowed us to clarify cobalt doping effect on the electronic structure and the band gap. The band gap of Co/TiO2 was decreased by broadening the valence band as a result of the overlap among Co 3d, Ti 3d, and O 2p states, which made it respond better to visible and solar light.

8

First principle calculation of structural, electronic and elastic properties of rare earth nitride

Bhardwaj P., Singh S.

Materials Science Poland

|

2016

|

Vol. 34, No. 4

715--720

EN

First principle calculation of the electronic and elastic properties of CeN nitride, which crystallizes in the rock-salt structure, is reported in the present paper. The ground state properties, such as lattice constant (a0), bulk modulus (B) and its pressure derivative (B′) are reported. These results show good agreement with the experimental and other theoretical results. Besides, we have studied the Murnaghan’s equation of state, and used it to fit the theoretical electronic ground state energy and obtain thermodynamic quantities such as the bulk modulus. Furthermore the electronic band structure, total density of states and partial density of states of CeN are also discussed.

9

Decisiveness of the spectral gaps of periodic Schrodinger operators on the Dumbbell-like metric graph

Niikuni H.

Opuscula Mathematica

|

2015

|

Vol. 35, no. 2

199--234

EN

In this paper, we consider periodic Schrodinger operators on the dumbbell-like metric graph, which is a periodic graph consisting of lines and rings. Let one line and two rings be in the basic period. We see the relationship between the structure of graph and the band-gap spectrum.

10

Point Defects in GaAs Photonic Crystals

Dissanayake S. E., Wijewardena Gamalath K. A. I. L.

International Letters of Chemistry, Physics and Astronomy

|

2015

|

Vol. 43

91--102

EN

Applying plane wave expansion method to one dimensional multilayer system formed from alternating layers of GaAs and air, a defect mode was artificially introduced by removing a GaAs layer at the centre of a supercell and the band structures and mode field distributions were obtained. The defect mode normalized frequency was 0.28. The parameters for developing a Febry-Perot filter in the visible frequencies are given. The point defects in a two dimensional square lattice formed from GaAs rods of radius 0.16a in air was created by removing one GaAs rod at the centre of a supercell and also by increasing the centre GaAs rod radius to 0.5a. The removal of the rod folded the band structure 25 times creating a localized evanescent defect mode. The increment of the centre GaAs rod radius led to five defect bands inside the band gap with one degenerate state creating a monopole, two quadrupoles and two hexapoles. Evolution of the defect modes with the variation of the radius of GaAs rod is also presented.

11

Simulation of optical spectra of novel Tl4CdI6 and Tl4HgI6 optoelectronic crystals

Franiv V, Bovgyra O, Kushnir O, Franiv A, Plucinski K J

Optica Applicata

|

2014

|

Vol. 44, nr 2

317--326

EN

The results of calculations using local density approximation and generalized gradient approximation: the total energy depending on the volume of the unit cell, the distribution of the total density of states and the partial contributions of electronic orbitals in the band structure of Tl4CdI6 and Tl4HgI6 crystals are shown in this paper. The spectra of the real part of the dielectric permittivity, the spectra of the imaginary part of permittivity, the reflection spectra and the absorption coefficient of both crystals are obtained using the Kramers–Kronig method. A comparative analysis of theoretical calculations with experimental data is carried out. Substantial influence of electron–phonon broadening is shown.

12

Transmission of polarized light in LHM and RHM materials with periodic refractive index

Garus S., Garus J., Nabiałek M., Błoch K., Szota M.

Journal of Achievements in Materials and Manufacturing Engineering

|

2014

|

Vol. 65, nr 2

79--85

EN

Purpose: The paper presents the implementation of the Transfer Matrix Method algorithm using Mathematica and the impact of the structure discretization steps number on the filters transmission. Tested materials were made with periodically varying refractive index. Design/methodology/approach: The properties of the filter transmission made of a materials having a periodically varying refractive index were analyzed. The study used a Transfer Matrix Method algorithm. The materials have a thickness of one micrometer. The refractive index of the analyzed material changed sinusoidally with a wavelength of 500nm. Sinusoid quantizing was performed each for 8, 16, 32, 50 and 60 layers. Findings: Maps show the nature of the transmission bands. Band structure of RHM materials (positive refractive index) is similar to the structure of the filter constructed of LHM material, characterized by a negative refractive index. Transmission band in a left-handed material has less width at half maximum. Thirty two layers discretization stabilizes the simulations of the tested materials filtration properties. Research limitations/implications: The paper had not been analyzed for materials with extinction coefficient different from zero. It would be worthwhile to conduct research for materials with variable refractive index of a different nature, for example a triangular or saw tooth shape. Practical implications: Analysis of the filter materials for a variety of photonic structures allows the prediction and design of materials with specified properties. These tests allow to design filters and mirrors for with very good applications parameters. Originality/value: The influence of the discretization level of continuous medium with periodically changing material properties on the transmission map stability was analyzed.

13

Wpływ składu chemicznego fazy ciekłej na własności niedomieszkowanych kryształów Bi2Se3

Hruban A., Materna A., Strzelecka S., Piersa M., Orłowski W., Jurkiewicz-Wegner E., Diduszko R., Romaniec M., Dalecki W., Wołoś A.

Materiały Elektroniczne

|

2013

|

T. 41, nr 3

27--39

PL

W pracy przedstawione są wyniki badań dotyczących otrzymania dużych kryształów Bi2Se3 (L ~ 140 mm) typu n o obniżonej koncentracji nośników prądu. Materiał taki jest niezbędny do otrzymania kryształów Bi2Se3 domieszkowanych Ca na typ p, dla których możliwe są obserwacje elektronów z topologicznej, metalicznej powierzchni. Kryształy wzrastały zmodyfikowaną metoda Bridgmana. Własności fizyczne otrzymanych kryształów oceniano przy zastosowaniu następujących metod: parametry elektryczne przez pomiar rezystywności i efektu Halla w temperaturze pokojowej i w funkcji temperatury w zakresie (10 – 320 )K, pomiar składu atomowego metodą EDX, składu chemicznego metodą XRD, jakość struktury oceniano przez obserwację w mikroskopie optycznym, skaningowym i AFM. Otrzymano kryształy typu n o koncentracji nośników w zakresie 2 x 1019 cm-3 – 3 x 1017 cm-3. W obszarach o koncentracji n < 5 x 1018 cm-3 obserwuje się wytrącenia Se. Duże zagęszczenie wydzieleń obserwuje się w końcowej części hodowanych kryształów powyżej 0,9 ich długości. Na próbkach o koncentracji nośników ~ 3 x 1017 cm-3 w pomiarach rezystywności w funkcji temperatury w obszarze T < 30 K obserwuje się wzrost rezystywności ze spadkiem temperatury, wskazujący na półprzewodnikowe własności tego materiału.

EN

In this paper the results of the investigation into growth of n – type Bi2Se3 crystals with decreased carrier concentration are presented. Such a material is used for obtaining Ca – doped p – type Bi2Se3, in the case of which the observation of electrons from the metallic topological surface is possible. Crystals were grown by the Vertical Bridgman method (VB). For the evaluation of their physical properties the following methods were applied: resistivity and Hall effect measurements at room temperature and as a function of temperature in the (10 – 320) K range, EDX (atomic composition of compounds), XRD (chemical composition), Nomarski microscopy, scanning microscopy and AFM. Crystals with n – type conductivity and carrier concentration in the range between 2 x 1019 cm-3 and 3 x 1017 cm-3 were grown. In the material with carrier concentration n < 5 x 1018 cm-3 the precipitates of metallic Se were observed. A high concentration of Se inclusions as detecteded in the tail part of the crystals, above 0.9 of their length, when the Se excess in the melt was significantly raised. For the samples with carrier concentration n ~ 3 x 1017 cm-3, an increase in resistivity when decreasing the temperature was observed, which indicates semiconducting properties of the material.

14

The Electronic Properties of New Fe-Based Superconductors

Kruchinin S., Antonchenko V., Zolotovsky A.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2011

|

Vol. 15, No 2

203-208

EN

We investigate the band structure of Fe-based superconductors using the first-principle method of density-functional theory. We calculated the band structure and the density of states at the Fermi level for ReFeAsO (Re = Sm, Dy, Ho, Er) superconductors. Our calculations indicate that the maximum critical superconducting transition temperature Tc will be observed for compounds with Sm and Er. We predict that Tc=60K for ErFeAsO.

15

Band Structure of Ruthenate Superconductors

Dow J., Zolotovsky A.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2011

|

Vol. 15, No 1

99-105

EN

We investigate the band structure of ruthenates using the first-principles method of density functional theory (DFT). We calculated the band structure and density of states at the Fermi level for superconductors Ba2YRuO6 and Sr2YRuO6. Our calculations show that the maximum critical superconducting transition temperature Tc=93K can be obtained for Ba2YRuO6.

16

Nanostructure model and optical properties of InAs/GaAs quantum dot in vertical cavity surface emitting lasers

Chen J., Fan W. J., Ding Y., Xu Q., Zhang X. W., Xu D. W., Yoon S. F., Zhang D. H.

Opto-Electronics Review

|

2011

|

Vol. 19, No. 4

449-453

EN

We apply 8.band k.p model to study InAs/GaAs quantum dots (QDs). The strain was calculated using the valence force field (VFF) model which includes the four nearest.neighbour interactions. For the optical properties, we take into account both homogeneous and non.homogeneous broadening for the optical spectrum. Our simulation result is in good agreement with the experimental micro.photoluminescence (µm-PL) result which is from InAs/GaAs QD vertical cavity surface emitting lasers (VCSELs) structure wafer at room temperature. Accordingly, our simulation model is used to predict the QD emission from this QD.VCSELs structure wafer at different temperature ranging from 200–400 K. The simulation results show a decrease of 41 meV of QDground state (GS) transition energy from 250–350 K. The changes ofQDGS transition energy with different temperature indicate the possible detuning range for 1.3.µm wave band QD-VCSELs applications without temperature control. Furthermore, QD differential gain at 300 K is computed based on this model, which will be useful for predicting the intrinsic modulation characteristics of QD-VCSELs.

17

Determination of the electronic band structure of the rutile polymorph of TiO2: a quantum chemical approach

Bardziński P. J.

Materials Science Poland

|

2011

|

Vol. 29, No. 3

223--232

EN

The aim of this work is the investigation of the relationship between the electronic band structure of the TiO2 rutile and the dimensionality of the system. For three dimensional system the bulk form of rutile was considered, while a slab model was chosen in order to represent the titanium (IV) dioxide (110) surface. The influence of changing the number of atomic layers on the bandgap value for the (110) surface was also examined. Density of states referring to the bands from the first valence band up to the bottom of the conduction band was projected on the whole set of atomic orbitals as well as on the significant shells of the titanium and oxygen atoms. Ab initio calculations with a B3LYP functional were carried out. Basis sets used were modified Ti 86-411(d31)G darco unpub and O 8-411 muscat 1999. The results are compared with experimental and computational data already available in the literature. Surface termination problem was discussed and the application of the obtained results as a starting point to obtain the first model of the rutile titania nanotube was proposed. The surface formation energies for rutile planes with a different surface terminations were compared and the modification to the equation needed for surface energy calculation was introduced.

18

Mössbauer effect studies of Dy(Fe0.4-xNixCo0.6)2

Jabłońska A., Suwalski J., Stoch P., Pszczoła J., Guzdek P., Szamański P., Pańta A.

Nukleonika

|

2007

|

Vol. 52, supl. 1

55-58

EN

A consequence of the Fe/Ni substitution in the Dy(Fe0.4Co0.6)2 compound was studied in the present paper. For this purpose the synthesis and X-ray analysis (295 K) of the Dy(Fe0.4 xNixCo0.6)2 series were performed. The cubic, MgCu2-type, Fd3m crystal structure was observed across the series. 57Fe Mössbauer effect spectra for the series were collected at 77 K. The obtained crystallographic data and the hyperfine interaction parameters are presented. The magnetic hyperfine fields form a separate branch of the Slater-Pauling curve known for the Dy(Mn1 xFex)2 and Dy(Fe1 xCox)2 series. The data are qualitatively related to the Stoner model.

19

Mössbauer effect studies of Dy(Fe0.7-xNixCo0.3)2 intermetallics

Jabłońska A., Suwalski J., Pszczoła J., Guzdek P., Stoch P., Pańta A.

Nukleonika

|

2004

|

Vol. 49,suppl.3

85-88

EN

Abstract A consequence of the Fe/Ni substitution in the series of Dy(Fe0.7 xNixCo0.3)2 was studied in the presented paper. The synthesis and X-ray analysis (300 K) of the Dy(Fe0.7 xNixCo0.3)2 system were performed. The cubic, MgCu2-type, Fd3m crystal structure was evidenced for this solid solution. 57Fe Mössbauer effect measurements for the system were carried out at 77 K. The obtained crystallographic lattice parameters and the hyperfine interaction data are presented. The magnetic hyperfine field values form a separate branch of the Slater-Pauling curve situated above the branch corresponding to the Dy(Fe1 xCox)2 intermetallics.

20

Quantum chemical studies of Cl-...HNO comlex in the singlet and triplet electronic states

Latajka Z., Ratajczak H.

Bulletin of the Polish Academy of Sciences. Chemistry

|

2001

|

Vol. 49, No. 2

125-131

EN

The structure and energetics of the hydrogen bonded complex formed between HNO and Cl- in the singlet and triplet states was investigated at the MP2 level with 6-31+ G(d, p) basis set. It is shown that the complex is strongly bound. The binding energy of the complex calculated at the MP4(SDTQ)/6-311++ G(2d,2p) level is -15.42 kcal/mol for the singlet state and —25.75 kcal/mol for the triplet state.