scholarly journals Excitons and optical absorption on the surface of a strong topological insulator with a magnetic energy gap

2011 ◽  
Vol 84 (4) ◽  
Author(s):  
Ion Garate ◽  
M. Franz
Keyword(s):  
Optical Absorption ◽  
Topological Insulator ◽  
Energy Gap ◽  
Magnetic Energy

NONLINEAR OPTICAL DEVICES: PROPERTIES OF POLYANILINE BASED CONDUCTING POLYMERS

2003 ◽  
Vol 12 (01) ◽  
pp. 39-43 ◽  
Author(s):  
SUDHIR KUMAR SHARMA ◽  
S. C. K. MISRA ◽  
K. N. TRIPATHI
Keyword(s):  
Optical Properties ◽  
Optical Absorption ◽  
Conducting Polymers ◽  
Spectral Range ◽  
Nonlinear Optical ◽  
Energy Gap ◽  
Optical Devices ◽  
Molecular Architecture ◽  
Nonlinear Optical Devices ◽  
Backbone Structure

We report on the investigation of a series of polyaniline based conducting polymers with rather different backbone structure and energy gap in order to explore the effect of their molecular architecture on nonlinear optical properties. In particular, we report on the dispersion of x(3)(-ω;ω, -ω, ω) in the spectral range covering the rising slope of the optical absorption as well as in off resonance conditions.

Transport Properties of Topological Insulator Bi0.83Sb0.17 Nanowires

2015 ◽  
Vol 1785 ◽  
pp. 1-6
Author(s):  
L.A. Konopko ◽  
A.A. Nikolaeva ◽  
T.E. Huber ◽  
J.P. Ansermet
Keyword(s):  
Magnetic Field ◽  
Single Crystal ◽  
Transport Properties ◽  
Topological Insulator ◽  
Energy Gap ◽  
Oscillation Amplitude ◽  
Glass Capillary ◽  
Wire Axis ◽  
Temperature Dependences ◽  
The Wire

ABSTRACTWe have investigated the transport properties of topological insulator based on single-crystal Bi0.83Sb0.17 nanowires. The single-crystal nanowire samples in the diameter range 200 nm – 1.1 μm were prepared by the high frequency liquid phase casting in a glass capillary using an improved Ulitovsky technique; they were cylindrical single-crystals with (1011) orientation along the wire axis. In this orientation, the wire axis makes an angle of 19.5o with the bisector axis C1 in the bisector-trigonal plane. Bi0.83Sb0.17 is a narrow gap semiconductor with energy gap at L point of Brillouin zone ΔE= 21 meV. In accordance with the measurements of the temperature dependence of the resistivity of the samples resistance increases with decreasing temperature, but at low temperatures decrease in the resistance is observed. This effect, decrease in the resistance, is a clear manifestation of the interesting properties of topological insulators - the presence on its surface of a highly conducting zone. The Arrhenius plot of resistance R in samples with diameter d=1.1 µm and d=200 nm indicates a thermal activation behavior with an activation gap ΔE= 21 and 35 meV, respectively, which proves the presence of the quantum size effect in these samples. We found that in the range of diameter 1100 nm - 200 nm when the diameter decreases the energy gap is growing as 1/d. We have investigated magnetoresistance of Bi0.83Sb0.17 nanowires at various magnetic field orientations. From the temperature dependences of Shubnikov de Haas oscillation amplitude for different orientation of magnetic field we have calculated the cyclotron mass mc and Dingle temperature TD for longitudinal and transverse (B||C3 and B||C2) directions of magnetic fields, which equal 1.96*10-2m0, 9.8 K, 8.5*10-3m0 , 9.4 K and 1.5*10-1m0 , 2.8 K respectively. The observed effects are discussed.

scholarly journals Optical absorption property of oxidized free-standing porous silicon films

2000 ◽  
Vol 72 (1-2) ◽  
pp. 237-243 ◽  
Author(s):  
Dongsheng Xu ◽  
Guolin Guo ◽  
Linlin Gui ◽  
Youqi Tang ◽  
G. G. Qin
Keyword(s):  
Optical Absorption ◽  
Thermal Oxidation ◽  
Quantum Confinement ◽  
Oxidation Process ◽  
Energy Gap ◽  
Quantum Confinement Effect ◽  
Bond Formation ◽  
Confinement Effect ◽  
Transmission Curve ◽  
Free Standing

We have systematically studied the evolution of the optical absorption of free-standing PS films during thermal oxidation at 200°C in air. Our experiment results show the evolution of transmission curve is quite complicated, which red-shifts first and then blue-shifts during thermal oxidation. At the same time, the transmission at the low energy decreases first and then increases. We propose an explanation as follows: (1) the energy gap associated with each crystallite should increase during thermal oxidation process, due to the quantum confinement effect; (2) the energy gap should decrease with an increase in oxygen termination atoms. Both the increasing of the gap due to the quantum confinement effect and the decreasing of the gap due to the Si-O bond formation cause a complicated evolution of optical absorption.

Photoreflectance Study of Gan Film Grown by Metalorganic Chemical Vapor Deposition

1996 ◽  
Vol 423 ◽  
Author(s):  
K. Yang ◽  
R. Zhang ◽  
Y. D. Zheng ◽  
L. H. Qin ◽  
B. Shen ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Optical Absorption ◽  
Vapor Deposition ◽  
Metalorganic Chemical Vapor Deposition ◽  
Energy Gap ◽  
Chemical Vapor ◽  
Optical Absorption Edge ◽  
Surface Field ◽  
Gan Film ◽  
Metalorganic Chemical

AbstractPhotoreflectance was used to study the optical properties of single crystal hexagonal GaN film on (0001) sapphire substrate grown by metalorganic chemical vapor deposition. The energy gap of GaN was determined as 3.400 eV, and the possible origin of the PR signal was attributed to the modulation of the surface field and lineshape broadening of defects. Optical absorption and cathodoluminescence of the GaN sample were measured, and the optical absorption edge of 3.39 eV and the cathodoluminescence emission peak of 3.461 eV at low temperature (15.6K) confirmed the results of Photoreflectance.

Synthesis and Optical Studies of the 3,4-dimethoxy Benzaldehyde [5-(2-hydroxyphenyl)-1,3,4-oxadiazol-2-yl]Hydrazone Metal Complexes

2020 ◽  
pp. 95-100
Keyword(s):  
Optical Absorption ◽  
Absorption Coefficient ◽  
Metal Complexes ◽  
Mass Spectra ◽  
Energy Gap ◽  
Planar Geometry ◽  
Optical Absorption Spectra ◽  
Optical Studies ◽  
Tetrahedral Geometry ◽  
Square Planar

The aim of the present study is to synthesize and optical studies of 3,4-dimethoxy benzaldehyde [5-(2-hydroxyphenyl)-1,3,4-oxadiazol-2-yl]hydrazone metal complexes. Firstly, the 3,4-dimethoxybenzaldehyde [5-(2-hydroxyphenyl)-1,3,4-oxadiazol-2-yl] hydra zone was synthesized by the reaction of the 2-(5-hydrazino-1,3,4-oxadiazol-2-yl)phenol with 2,3-dimethoxybenzaldehyde in the ethanol as a solvent . Scondly, its complexes of Cr(III), Fe(III), Co(II) and Ni (II) have been synthesized. The synthesized coumpounds and its metal complexes were characterized by the FTIR, Mass spectra and UV-vis absorption. The results confirmed the suggested square planar geometry of the Ni (II) complex and tetrahedral geometry of the Co(II) complex, while Cr (III), Fe(III) complexes were assigned octahedral geometrics. The optical absorption spectra of those complexes in the wavelength range from 200-900 nm were studied.The results showed that the optical absorption is due to indirect allowed transitions of the compound and its complexes, the energy gap (Eg) of these compounds decreases in the order L> Ni (II)> Fe(III)> Co(II) and > Cr(III), the absorption coefficient (α), real and imaginary parts (ɛr,ɛi), and optical conductivity (σopt)were estimated.

Topological Properties in Strained Monolayer Antimony Iodide

2021 ◽  
Vol 38 (11) ◽  
pp. 117301
Author(s):  
Danwen Yuan ◽  
Yuefang Hu ◽  
Yanmin Yang ◽  
Wei Zhang
Keyword(s):  
Topological Insulator ◽  
Topological Insulators ◽  
Energy Gap ◽  
Square Lattice ◽  
Honeycomb Lattice ◽  
Type I ◽  
Topological Properties ◽  
Dirac Semimetal ◽  
Low Dissipation ◽  
Binary Compounds

Two-dimensional (2D) topological insulators present a special phase of matter manifesting unique electronic properties. Till now, many monolayer binary compounds of Sb element, mainly with a honeycomb lattice, have been reported as 2D topological insulators. However, research of the topological insulating properties of the monolayer Sb compounds with square lattice is still lacking. Here, by means of the first-principles calculations, a monolayer SbI with square lattice is proposed to exhibit the tunable topological properties by applying strain. At different levels of the strain, the monolayer SbI shows two different structural phases: buckled square structure and buckled rectangular structure, exhibiting attracting topological properties. We find that in the buckled rectangular phase, when the strain is greater than 3.78%, the system experiences a topological phase transition from a nontrivial topological insulator to a trivial insulator, and the structure at the transition point actually is a Dirac semimetal possessing two type-I Dirac points. In addition, the system can achieve the maximum global energy gap of 72.5 meV in the topological insulator phase, implying its promising application at room temperature. This study extends the scope of 2D topological physics and provides a platform for exploring the low-dissipation quantum electronics devices.

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