scholarly journals DFT and TB-mBJLDA studies of structural, electronic and optical properties of Hg1-xCdxTe and Hg1-xZnxTe

2021 ◽  
Vol 67 (6 Nov-Dec) ◽  
Author(s):  
N. Aouail ◽  
M. Noureddine Belkaid ◽  
A. Oukebdane ◽  
M. Hocine Tedjini

In this paper, the fundamental semiconductor properties of Hg1-xCdxTe and Hg1-xZnxTe are investigated by ab initio calculations based on the FP-LAPW method.   Structural properties have been calculated using LDA and GGA approximations. The electronic properties are studied using the LDA and GGA approximations, and the potential TB-mBJLDA coupled with the lattice parameters aLDA and aGGA. The optical properties are determined from the optimal gap energies based on the TB-mBJLDA potential. Lattice parameters aLDA obtained by the LDA calculations predict values that are in good agreement with the experimental results and are better than those results obtained by the GGA calculations.  The use of TB-mBJLDA potential coupled with the lattice parameter aGGA gives gap energy values in good agreement with the experimental results for all alloys except  Hg1-xZnxTe (x=0.5, 0.75) where the (TB-mBJ LDA+aLDA) is more suitable. Optical constants are calculated from the dielectric function in the energy range (0-30 eV).  The spectrum of real and imaginary parts of the dielectric function, the energy loss function, the refractive index, the extinction coefficient, the absorption coefficient, and the reflectivity show that optical properties of Hg1-xCdxTe are comparable to those of  Hg1-xZnxTe. Our results are found to be in reasonable agreement with existing data reported in the literature.

1990 ◽  
Vol 195 ◽  
Author(s):  
S. Berthier ◽  
K. Driss-Khodja

ABSTRACTIn order to take into account the actual morphology of the inhomogeneous media, we have developed, effective medium models based on a 2D and 3D position space renormalization /1,2/. These models predict the dipolar resonance and the percolation transition with critical exponents in good agreement with theoretical values and fairly reproduce most of the experimental results, whatever the concentration is. Further more, this allows a valuable comparison of the predictions of our models when applied on different lattices like real digitized TEM of cermet films or randomly occupied lattices.


2001 ◽  
Vol 693 ◽  
Author(s):  
N.V. Edwards ◽  
O.P.A. Lindquist ◽  
L.D. Madsen ◽  
S. Zollner ◽  
K. Järrehdahl ◽  
...  

AbstractAs a first step toward enabling the in-line metrology of III-V nitride heterostructure and materials, we present the optical constants of the two common substrate materials over an unprecendented spectral range. Vacuum Ultraviolet spectroscopic ellipsometry (VUVSE) was used to obtain the optical constants for Al2O3 and the ordinary and extra-ordinary component of the dielectric function for both 4H- and 6H-SiC. The results are discussed in the context of anisotropy, polytypism, bandstructure, optical transitions, and preparation/characterization of abrupt surfaces, where appropriate.


2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Carl M. Sangan ◽  
Oliver J. Pountney ◽  
Kunyuan Zhou ◽  
J. Michael Owen ◽  
Mike Wilson ◽  
...  

Part I of this two-part paper presented experimental results for externally-induced (EI) ingress, where the ingestion of hot gas through the rim seal into the wheel-space of a gas turbine is controlled by the circumferential variation of pressure in the external annulus. In Part II, experimental results are presented for rotationally-induced (RI) ingress, where the ingestion is controlled by the pressure generated by the rotating fluid in the wheel-space. Although EI ingress is the common form of ingestion through turbine rim seals, RI ingress or combined ingress (where EI and RI ingress are both significant) is particularly important for double seals, where the pressure asymmetries are attenuated in the annular space between the inner and outer seals. In this paper, the sealing effectiveness was determined from concentration measurements, and the variation of effectiveness with sealing flow rate was compared with theoretical curves for RI ingress obtained from an orifice model. Using a nondimensional sealing parameter Φ0 the data could be collapsed onto a single curve, and the theoretical variation of effectiveness with Φ0 was in very good agreement with the data for a wide range of flow rates and rotational speeds. It was shown that the sealing flow required to prevent RI ingress was much less than that needed for EI ingress, and it was also shown that the effectiveness of a radial-clearance seal is significantly better than that for an axial-clearance seal for both EI and RI ingress.


2012 ◽  
Vol 36 (2) ◽  
pp. 233-240 ◽  
Author(s):  
M R A Bhuiyan ◽  
M A H Miah ◽  
J Begum

Zinc selenide (ZnSe) thin films were deposited on to chemically and ultrasonically cleaned  glass substrates at different substrate temperatures from room temperature to 200°C keeping the  thickness fixed at 300 nm by using thermal evaporation method in vacuum. The structural properties of the films were ascertained by X-ray diffraction (XRD) method utilizing a  diffractometer. The optical properties were measured in the photon wavelength ranging between 300 and 2500 nm by using a UV-VIS-NIR spectrophotometer. The XRD patterns reveal that the  films were polycrystalline in nature exhibiting f.c.c zincblende structure with average lattice parameter, a = 5.6873Å. The grain size, strain and dislocation densities of the films have bee calculated. The optical transmittance and reflectance were utilized to compute the absorption  coefficient, band gap energy and refractive index of the films. The band gap energy of the films  was extracted from the absorption spectra. The direct band gap energy of the films slightly increases with substrate temperature.DOI: http://dx.doi.org/10.3329/jbas.v36i2.12969Journal of Bangladesh Academy of Sciences, Vol. 36, No. 2, 233-240, 2012


RSC Advances ◽  
2015 ◽  
Vol 5 (25) ◽  
pp. 19734-19742 ◽  
Author(s):  
Ling Li ◽  
Xiaoguang Liu

The photoluminescence properties and theoretical analysis of Sm2+ doped MAl2Si2O8 (M = Ca, Sr, Ba) were reported. The theoretical analysis is in good agreement with our experimental results.


2005 ◽  
Vol 12 (03) ◽  
pp. 425-431 ◽  
Author(s):  
F. E. GHODSI

A simple method for determination of optical constants and thickness of semitransparent thin films deposited onto a transparent finite substrate has been developed. The method is based on the analysis of successive interference fringes of transmission spectra created by the films. It is essentially not necessary to obtain the envelope of transmission spectra in this method. The determined values of optical parameters are in good agreement with their true values used to generate transmission data. The accuracy of method in determining refractive index and thickness of the films is better than 1%.


2012 ◽  
Vol 571 ◽  
pp. 292-295
Author(s):  
Ben Hai Yu ◽  
Chao Xu ◽  
Dong Chen

We report ab initio calculations of the structural, elastic and optical properties of the compound LaB6 as a function of pressure. The computation is based on the density functional theory in combination with the generalized gradient approximation functional. The calculated lattice constants and elastic moduli are compared with the theoretical results and a good agreement is found. LaB6 can retain its mechanical stability in the pressure range of 0-20GPa. Besides, the frequency-dependent dielectric function, absorption coefficient and loss function of LaB6 are also obtained. The calculated static dielectric function is 8.8 at 0GPa and 5GPa. The computed results should be testified by experiments.


2014 ◽  
Vol 602-605 ◽  
pp. 2922-2925
Author(s):  
Fu Chun Zhang ◽  
Wei Hu Zhang

The density functional theory based on first-principles plane wave ultrasoft pseudopotential method is adopted to study the electronic structure and the optical linear response function of 21R-SiC. The calculated data include the lattice parameter, the energy band structure, the density of states, the electric charge density, the complex dielectric function and the absorption coefficient, theoretically giving the relationship between the electronic structure and the optical properties of 21R-SiC. The dielectric function and the extinction coefficient of 21R-SiC are investigated by using the calculated energy band structure to provide the theoretical basis for the design and application of 21R-SiC photoelectric material. At the same time, the calculating result also provides the possibility for us to accurately monitor and control the growth process of SiC material.


2018 ◽  
Vol 6 (1) ◽  
pp. 38-43 ◽  
Author(s):  
Serly J. Sekewael ◽  
Karna Wijaya ◽  
Triyono .

The thermal treatment of the silica-zirconia montmorillonite K10 and silica-ferri oxide montmorillonite K10 nanocomposites at 300 and 500 °C has been carried out, respectively as part of a study of their function as the catalyst. The heating effect on the crystallinity and the lattice parameter calculation of both nanocomposites was studied using XRD and FTIR instruments. The results showed that the nanocomposite silica-zirconia montmorillonite K10 has a thermal resistance and the crystallinity better than the silica-ferri oxide montmorillonite K10, and both have values varying lattice parameters.


Author(s):  
Carl M. Sangan ◽  
Kunyuan Zhou ◽  
J. Michael Owen ◽  
Oliver J. Pountney ◽  
Mike Wilson ◽  
...  

Part 1 of this two-part paper presented experimental results for externally-induced (EI) ingress, where the ingestion of hot gas through the rim seal into the wheel-space of a gas turbine is controlled by the circumferential variation of pressure in the external annulus. In Part 2, experimental results are presented for rotationally-induced (RI) ingress, where the ingestion is controlled by the pressure generated by the rotating fluid in the wheel-space. Although EI ingress is the common form of ingestion through turbine rim seals, RI ingress or combined ingress (where EI and RI ingress are both significant) is particularly important for double seals, where the pressure asymmetries are attenuated in the annular space between the inner and outer seals. In this paper, the sealing effectiveness was determined from concentration measurements, and the variation of effectiveness with sealing flow rate was compared with theoretical curves for RI ingress obtained from an orifice model. Using a nondimensional sealing parameter, Φ0, the data could be collapsed onto a single curve, and the theoretical variation of effectiveness with Φ0 was in very good agreement with the data for a wide range of flow rates and rotational speeds. It was shown that the sealing flow required to prevent RI ingress was much less than that needed for EI ingress, and it was also shown that the effectiveness of a radial-clearance seal is significantly better than that for an axial-clearance seal for both EI and RI ingress.


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