scholarly journals Modeling the electronic structure and stability of three aluminum nitride phases

2021 ◽  
Vol 67 (3 May-Jun) ◽  
pp. 343
Author(s):  
J. Ruiz-González ◽  
G. H. Cocoletzi ◽  
L. Morales de la Garza
Keyword(s):  
Aluminum Nitride ◽  
Rock Salt ◽  
Ground State ◽  
Energy Gap ◽  
Ground State Structure ◽  
Cohesion Energy ◽  
Wurtzite Phase ◽  
Zinc Blende ◽  
External Pressures ◽  
Indirect Band Gap

Phase transitions in aluminum nitride (AlN) were investigated by first principles total energy calculations. Three AlN crystal structures were considered: rock salt (NaCl), zinc blende and wurtzite. The cohesion energy was calculated within both GGA and LDA formalisms. According to the cohesion energy results, the ground state corresponds to the hexagonal wurtzite phase, in agreement with experimental evidence. However, the zinc blende and NaCl phases may be formed as metastable structures. To determine the energy gap the modified Becke-Johnson pseudopotential was applied, with results showing good agreement with the experimental data. The ground state structure exhibits direct electronic transitions. However, the zinc blende and NaCl phases show indirect band gap. Provided that external pressures may induce transitions from wurtzite to zinc blende or rock salt, these transitions were also investigated. Estimation of the pressure at the phase transition indicates that small pressures are needed to achieve such transitions.

scholarly journals First-principles calculations of elastic and optical properties of Aluminum Nitride (AlN) in cubic and hexagonal phase

2021 ◽  
Vol 49 (1) ◽  
Author(s):  
Burhan Ahmed ◽  
◽  
B. Indrajit Sharma ◽  
Keyword(s):  
Optical Properties ◽  
Energy Range ◽  
Rock Salt ◽  
Density Functional ◽  
High Energy ◽  
Wurtzite Phase ◽  
Metallic Behavior ◽  
Zinc Blende ◽  
Good Agreement ◽  
Three Phases

Investigation of elastic and optical properties of AlN in rock salt, zinc blende, and wurtzite phase is done under the framework of Density Functional Theory (DFT) with modified Becke Johnson Generalised Gradient Approximation (mBJ-GGA) as exchange-correlation functional. Elastic properties conclude the bonding nature of the AlN in the rock salt phase is covalent and stiffest, while the bonding nature in the zinc blende and wurtzite phase is found to be ionic and less stiff. The ratio of bulk modulus to shear modulus indicates AlN is brittle in all three phases. The calculated Debye temperature in all three phases is in good agreement with the available theoretical and experimental works. The optical properties calculation shows the AlN is transparent in the low energy range and it has the metallic behavior in the energy range 7.5eV to 10 eV. At the same time, the compound loses its transparency at the high energy range. Our calculated value of the refractive index of AlN in the rock salt, zinc blende, and wurtzite phases is in good agreement with the available experimental and theoretical works.

Structural and Optical Properties of ZnS:Mn Films Grown by Pulsed Laser Deposition

2001 ◽  
Vol 667 ◽  
Author(s):  
K. M. Yeung ◽  
S. G. Lu ◽  
C. L. Mak ◽  
K. H. Wong
Keyword(s):  
Optical Properties ◽  
Substrate Temperature ◽  
Pulsed Laser Deposition ◽  
Energy Gap ◽  
Pulsed Laser ◽  
Laser Deposition ◽  
Yellow Emission ◽  
Wurtzite Phase ◽  
Zinc Blende ◽  
Zinc Blende Structure

ABSTRACTHigh-quality manganese-doped zinc sulfide (ZnS:Mn) thin films have been deposited on various substrates using pulsed laser deposition (PLD). Effects of back-filled Ar pressure and substrate temperature on the structural as well as optical properties of ZnS:Mn films were studied. Structural properties of these films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Photoluminescence (PL) and optical transmittance were used to characterize the optical properties of these films. Our results reveal that ZnS:Mn films were polycrystalline with a mixed phase structure consisting of both wurtzite and zinc-blende structure. The ratio of these two structures was strongly depended on the change of substrate temperature. Low substrate temperature facilitated the formation of zinc-blende structure while the wurtzite phase became dominant at high substrate temperature. ZnS:Mn films with preferred wurtzite structure were obtained at a substrate temperature as low as 450°C. An orange-yellow emission band was observed at ∼590 nm. As the substrate temperature increased, the peak of this PL band shifted to a shorter wavelength. Furthermore, shifts in the absorption edge and the energy gap due to the change in substrate temperature were also observed. The variation in these optical properties will be correlated to their structural change.

Zur Berechnung der chemischen Verschiebung unter besonderer Berücksichtigung des paramagnetischen Terms / Attempts to the Calculation of the Chemical Shift with Especial Consideration of the Paramagnetic Term

1977 ◽  
Vol 32 (12) ◽  
pp. 1541-1543
Author(s):  
H. Sterk ◽  
J. J. Suschnigg
Keyword(s):  
Chemical Shift ◽  
Excited States ◽  
Ground State ◽  
Energy Gap

Abstract Attempts to the Calculation of the Chemical Shift with Especial Consideration of the Paramagnetic Term The calculation of the paramagnetic term according to the Pople formalism of the chemical shift is expanded. The hitherto constant value of the energy gap between the ground state and the excited states is replaced by the value of the lowest lying excitation. This leads to a remarkably better differentiation of the paramagnetic terms of different compounds. The influence is shown on ethane, ethene and ethine.

scholarly journals A high-spin ground-state donor-acceptor conjugated polymer

2019 ◽  
Vol 5 (5) ◽  
pp. eaav2336 ◽  
Author(s):  
A. E. London ◽  
H. Chen ◽  
M. A. Sabuj ◽  
J. Tropp ◽  
M. Saghayezhian ◽  
...  
Keyword(s):  
Organic Semiconductors ◽  
High Spin ◽  
Ground State ◽  
Conjugated Polymer ◽  
Organic Materials ◽  
Energy Gap ◽  
Light Element ◽  
Paramagnetic Resonance ◽  
Practical Applications ◽  
Polymer Semiconductor

Interest in high-spin organic materials is driven by opportunities to enable far-reaching fundamental science and develop technologies that integrate light element spin, magnetic, and quantum functionalities. Although extensively studied, the intrinsic instability of these materials complicates synthesis and precludes an understanding of how fundamental properties associated with the nature of the chemical bond and electron pairing in organic materials systems manifest in practical applications. Here, we demonstrate a conjugated polymer semiconductor, based on alternating cyclopentadithiophene and thiadiazoloquinoxaline units, that is a ground-state triplet in its neutral form. Electron paramagnetic resonance and magnetic susceptibility measurements are consistent with a high-to-low spin energy gap of 9.30 × 10−3 kcal mol−1. The strongly correlated electronic structure, very narrow bandgap, intramolecular ferromagnetic coupling, high electrical conductivity, solution processability, and robust stability open access to a broad variety of technologically relevant applications once thought of as beyond the current scope of organic semiconductors.

Electronic Absorption and Ground State Structure of Carotenoid Molecules

2013 ◽  
Vol 117 (38) ◽  
pp. 11015-11021 ◽  
Author(s):  
Maria M. Mendes-Pinto ◽  
Elodie Sansiaume ◽  
Hideki Hashimoto ◽  
Andrew A. Pascal ◽  
Andrew Gall ◽  
...  
Keyword(s):  
Electronic Absorption ◽  
Ground State ◽  
Ground State Structure ◽  
State Structure
Sign in / Sign up

Export Citation Format

Share Document