Electronic Structures of Halogenated Polysilanes

1997 ◽  
Vol 486 ◽  
Author(s):  
Hideshi Motoyama ◽  
Kyozaburo Takeda ◽  
Kenji Shiraishi
Keyword(s):  
Band Gap ◽  
Electronic Structures ◽  
Visible Range ◽  
Energy Position ◽  
Unoccupied State ◽  
Valence Electrons ◽  
Orbital Mixing ◽  
Valence Bands ◽  
Halogen Species ◽  
Valence Band Splitting

AbstractThe electronic structures of halogenated polysilanes (PSi), whose side chains are replaced by halogen (X) atoms, have been theoretically investigated based on the firstprinciples calculations. It was found that non-bonding (n) electrons localizing at the X atom produce an important orbital mixing with the u valence electrons delocalized in the direction of the PSi skeleton (a-n mixing). This a-n mixing splits the top of the valence bands, and creates unoccupied states in the band gap. This valence-band-splitting effectively narrows the band gap to the visible range, and the unoccupied state in the band gap has the potential to be an electron acceptor. Moreover, we also investigated several replacement patterns as well as the kind of replaced halogen species (X=F, Cl, Br, I). The dispersion and energy position of the unoccupied state(s) can be artificially tuned by these chemical modifications. Thus, halogenation can change PSi into optelectronic polymers with visible photoluminescence.

Electronic structures and optical properties of α-Fe2O3-xSex alloys for solar absorber

2015 ◽  
Vol 29 (12) ◽  
pp. 1550050 ◽  
Author(s):  
Congxin Xia ◽  
Yu Jia ◽  
Qiming Zhang
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
First Principles ◽  
Electronic Structures ◽  
Visible Range ◽  
Optical Absorption Edge ◽  
Band Structures ◽  
Solar Absorber ◽  
Direct Band ◽  
Gap Values

The band structures and optical properties of α- Fe 2 O 3-x Se x alloys are studied by means of first-principles methods, considering different Se contents x. Numerical results show that Se content has an obvious influence on band structures and optical properties of α- Fe 2 O 3-x Se x alloys. The band gap values of α- Fe 2 O 3-x Se x alloys decrease monotonically when Se concentrations increase, resulting in an obvious increase of the optical absorption edge in the visible range. In particular, our results show that α- Fe 2 O 3-x Se x alloys have the direct band gap properties with band gap values when Se content x ≈ 0.17, which is beneficial to solar cell applications.

scholarly journals Comparative Study on Electronic Structure and Optical Properties of α-Fe2O3, Ag/α-Fe2O3 and S/α-Fe2O3

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 424
Author(s):  
Cuihua Zhao ◽  
Baishi Li ◽  
Xi Zhou ◽  
Jianhua Chen ◽  
Hongqun Tang
Keyword(s):  
Optical Properties ◽  
Optical Absorption ◽  
Electronic Structures ◽  
Density Functional ◽  
Peak Strength ◽  
Visible Range ◽  
High Symmetry ◽  
Functional Theory ◽  
Optical Absorption Peak ◽  
Calculation Results

The electronic structures and optical properties of pure, Ag-doped and S-doped α-Fe2O3 were studied using density functional theory (DFT). The calculation results show that the structure of α-Fe2O3 crystal changes after Ag and S doping, which leads to the different points of the high symmetry of Ag-doped and S-doped α-Fe2O3 with that of pure α-Fe2O3 in the energy band, as well as different Brillouin paths. In addition, the band gap of α-Fe2O3 becomes smaller after Ag and S doping, and the optical absorption peak shifts slightly toward the short wavelength, with the increased peak strength of S/α-Fe2O3 and the decreased peak strength of Ag/α-Fe2O3. However, the optical absorption in the visible range is enhanced after Ag and S doping compared with that of pure α-Fe2O3 when the wavelength is greater than 380 nm, and the optical absorption of S-doped α-Fe2O3 is stronger than that of Ag-doped α-Fe2O3.

Spectroscopic Analysis and Synthesis of Wide Band Gap CdS Quantum Dots Using Colloidal Synthesis Technique at Low Temperature

2009 ◽  
Vol 67 ◽  
pp. 191-196 ◽  
Author(s):  
Lubna Hashmi ◽  
M.S. Qureshi ◽  
R.N. Dubey ◽  
M.M. Malik ◽  
Ishrat Alim ◽  
...  
Keyword(s):  
Low Temperature ◽  
Band Gap ◽  
Spectroscopic Analysis ◽  
Quantum Confinement Effect ◽  
Wide Band ◽  
Colloidal Synthesis ◽  
Visible Range ◽  
Wide Band Gap ◽  
Synthesis Technique ◽  
Analysis And Synthesis

A broad range of II-VI materials has been investigated in order to produce light in the full visible range for optoelectronic applications. The present investigation was carried out for the spectroscopic analysis and synthesis of wide band gap cadmium sulfide nanoparticles. Large-band gap semiconductors have the added advantage in that; they can support higher electric field before breaking down, which means that they can be used for high-power electronic devices.Synthesis has been carried out using colloidal synthesis technique at low temperature. The size, stabilization and optical properties were studied using UV-vis Spectrophotometer and Spectroflourometer. Further, the structural studies of synthesized powder were carried out using X-ray diffraction technique; which also confirms the formation of desired product. The capping ligand and the impurities present in the sample were characterized by Fourier transform infra red spectroscopy. Synthesized CdS powder dispersed in aqueous media gave the value of 193 nm for the onset wavelength using UV-vis spectrophotometer, which is significantly blue-shifted compared to bulk CdS and shows the quantum confinement effect. From the onset wavelength the radius of CdS quantum dot calculated using the Brus equation was found to be ca. 0.7 nm.

First-Principles Calculations of Titanium Dopants in Alumina

2005 ◽  
Vol 475-479 ◽  
pp. 3095-3098
Author(s):  
Katsuyuki Matsunaga ◽  
Teruyasu Mizoguchi ◽  
Atsutomo Nakamura ◽  
Takahisa Yamamoto ◽  
Yuichi Ikuhara
Keyword(s):  
Band Gap ◽  
First Principles ◽  
Electronic Structures ◽  
First Principles Calculations ◽  
Pseudopotential Calculations ◽  
Formation Energies

First-principles pseudopotential calculations were performed to investigate atomic and electronic structures of titanium (Ti) dopants in alumina (Al2O3). It was found that a substitutional Ti3+ defect induced an extra level occupied by one electron within the band gap of Al2O3. When two or more substitutional Ti3+ defects were located closely to each other, the defect-induced levels exhibited strong bonding interactions, and their formation energies decreased with increasing numbers of Ti3+ defects. This indicates that association and clustering of substitutional Ti3+ defects in Al2O3 can take place due to the interaction of the defect-induced levels.

Tunable band gap of graphyne-based homo- and hetero-structures by stacking sequences, strain and electric field

2018 ◽  
Vol 20 (42) ◽  
pp. 26934-26946 ◽  
Author(s):  
Jiangni Yun ◽  
Yanni Zhang ◽  
Yanbing Ren ◽  
Manzhang Xu ◽  
Junfeng Yan ◽  
...  
Keyword(s):  
Electric Field ◽  
Band Gap ◽  
Electronic Structures ◽  
Vertical Electric Field ◽  
Tunable Band Gap ◽  
External Strain

Stacking sequences, external strain and a vertical electric field can be used to effectively modulate the electronic structures of graphyne-based homo- and hetero-structures.

scholarly journals Study of Band Gap of Silver Nanoparticles—Titanium Dioxide Nanocomposites

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
P. Barone ◽  
F. Stranges ◽  
M. Barberio ◽  
D. Renzelli ◽  
A. Bonanno ◽  
...  
Keyword(s):  
Silver Nanoparticles ◽  
Band Gap ◽  
Chemical Properties ◽  
Photoelectrochemical Cells ◽  
Visible Range ◽  
X Ray ◽  
Optical Absorbance ◽  
Laser Ablation Process ◽  
Uv Visible ◽  
And Chemical Properties

The optical and chemical properties of Ag/TiO2nanocomposites were investigated to explore the possibilities of incorporating these new materials in Gratzel photoelectrochemical cells. The nanocomposites were obtained doping TiO2, in both allotropic species anatase and rutile, with silver nanoparticles (grown by laser ablation process). X-ray photoelectron data indicate the absence of Ag-Ti chemical bonds, while measurements of photoluminescence and optical absorbance in UV-visible range show a quench in photoluminescence emission of about 50% and an increase in visible absorbance of about 20%. Measurements of optical band gap, obtained by Tauc’s equation, indicate a variation of about 1.6 eV.

Tuning band gap and optical properties of SnX2 nanosheets: Hybrid functional studies

2016 ◽  
Vol 30 (10) ◽  
pp. 1650120 ◽  
Author(s):  
P. Guo ◽  
Y. W. Luo ◽  
Y. Jia
Keyword(s):  
Optical Properties ◽  
Optical Absorption ◽  
Band Gap ◽  
Electronic Structures ◽  
Threshold Values ◽  
Hybrid Functional ◽  
Functional Studies ◽  
Quantum Size ◽  
Light Activity ◽  
Optical Applications

Based on hybrid functional calculations, the electronic structures and optical properties are investigated in the monolayer and bilayer tin dichalcogenides SnX2 (X = S and Se) nanosheets. Numerical results show that quantum size effects are obvious on the electronic structures and optical absorption in the SnS2 and SnSe2 nanosheets. The band gap values increase when the nanosheets layer numbers decrease. Moreover, for SnSe2 nanosheet, the optical absorption coefficients are high and its threshold values lie in the visible light activity range. These results are interesting and indicate that SnS2 and SnSe2 nanosheets may serve as the promising candidates for visible optical applications.

Bandfilling and structural stability of trialuminides: YAl3, ZrAl3, and NbAl3

1991 ◽  
Vol 6 (6) ◽  
pp. 1188-1199 ◽  
Author(s):  
Jian-hua Xu ◽  
A.J. Freeman
Keyword(s):  
Transition Metal ◽  
Structural Stability ◽  
Electronic Structures ◽  
Local Density ◽  
Metal Carbides ◽  
Metal Compounds ◽  
Cohesive Properties ◽  
Valence Electrons ◽  
Stable Forms ◽  
Covalent Interactions

The cohesive properties and electronic structures versus the structural stability of transition-metal trialuminides YAl3, ZrAl3, and NbAl3 in their cubic L12, tetragonal DO22, and naturally stable forms (i.e., the DO19 structure for YAl3 and the DO23 structure for ZrAl3) have been investigated using a total energy local-density approach. The variation of structural stability with transition-metal constituent can be simply understood in terms of the bandfilling of the bonding states in the rigid band sense, with the valence electrons gradually filling the bonding states on going from YAl3, ZrAl3 to NbAl3. This leads to a phase transition from the cubic L12 structure (for YAl3) to the tetragonal DO22 structure (for NbAl3). It is argued that this criterion may also apply to explain the variation of the structural stability of other transition-metal compounds (such as transition-metal carbides, nitrides, silicides, etc.) that are dominated by covalent interactions between the transition-metal d and the metalloid p states.

First-principles studies on electronic structures and optical properties of two-dimensional Sn1−xTi(Zr)xS2 alloys

2018 ◽  
Vol 32 (07) ◽  
pp. 1850092 ◽  
Author(s):  
Dandan Li ◽  
Juan Du ◽  
Qian Zhang ◽  
Congxin Xia ◽  
Shuyi Wei
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
First Principles ◽  
Electronic Structures ◽  
Threshold Energy ◽  
Ternary Alloys ◽  
Two Dimensional ◽  
First Principles Calculations ◽  
Experimental Conditions ◽  
Part Formula

Through first-principles calculations we study the electronic structures and optical properties of two-dimensional (2D) Sn[Formula: see text]Ti(Zr)[Formula: see text]S2 alloys. The results indicate that the band gap value of Sn[Formula: see text]Ti(Zr)[Formula: see text]S2 alloys is decreased continuously when Ti(Zr) concentration is increased, which is very beneficial to optoelectronic devices applications. Moreover, the static dielectric constant is increased when the Ti(Zr) concentration is increased in the 2D Sn[Formula: see text]Ti(Zr)[Formula: see text]S2 alloys. In addition, we also calculate the imaginary part [Formula: see text] dispersion of Sn[Formula: see text]Ti(Zr)[Formula: see text]S2 alloys along the plane with different Ti(Zr) concentrations. The threshold energy values decrease with increasing Ti(Zr) concentrations in the Sn[Formula: see text]Ti(Zr)[Formula: see text]S2 ternary alloys. Moreover, the calculations of formation energy also indicate that these 2D alloys can be fabricated under some experimental conditions. These results suggest that Ti(Zr) substituting Sn atom is an efficient way to tune the band gap and optical properties of 2D SnS2 nanosheets.

Band gap energy and valence band splitting of p-CdIn2Te4 crystal by photocurrent spectroscopy

2004 ◽  
Vol 95 (8) ◽  
pp. 4042-4045 ◽  
Author(s):  
S. H. You ◽  
K. J. Hong ◽  
T. S. Jeong ◽  
C. J. Youn ◽  
J. S. Park ◽  
...  
Keyword(s):  
Band Gap ◽  
Valence Band ◽  
Band Gap Energy ◽  
Gap Energy ◽  
Band Splitting ◽  
Photocurrent Spectroscopy ◽  
Valence Band Splitting
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