scholarly journals Bloch Waves in Bubbly Crystal Near the First Band Gap: A High-Frequency Homogenization Approach

2019 ◽  
Vol 51 (1) ◽  
pp. 45-59 ◽  
Author(s):  
Habib Ammari ◽  
Hyundae Lee ◽  
Hai Zhang
Keyword(s):  
Band Gap ◽  
High Frequency ◽  
Bloch Waves ◽  
Homogenization Approach

Theoretical study of modified electron band dispersion and density of states due to high frequency phonons in graphene-on-substrates

2018 ◽  
Vol 07 (04) ◽  
pp. 1850024
Author(s):  
Sivabrata Sahu ◽  
G. C. Rout
Keyword(s):  
Band Gap ◽  
Density Of States ◽  
High Frequency ◽  
Vibrational Energy ◽  
Harmonic Approximation ◽  
Coulomb Energy ◽  
Electron Band ◽  
Band Dispersion ◽  
Energy Formula ◽  
Sublattice Site

We propose here a theoretical model for the study of band gap opening in graphene-on- polarizable substrate taking the effect of electron–electron and electron–phonon (EP) interactions at high frequency phonon vibrations. The Hamiltonian consists of hopping of electrons upto third nearest- neighbors and the effect substrate, where A sublattice site is raised by energy [Formula: see text] and B sublattice site is suppressed by energy [Formula: see text], hence producing a band gap energy of [Formula: see text]. Further, we have considered Hubbard type electron–electron repulsive interactions at A and B sublattices, which are considered within Hartree–Fock meanfield approximation. The electrons in the graphene plane interact with the phonon’s present in the polarized substrate in the presence of phonon vibrational energy within harmonic approximation. The temperature-dependent electron occupancies are computed numerically and self-consistently for both spins at both the sublattice sites. By using these electron occupancies, we have calculated the electron band dispersion and density of states (DOS), which are studied for the effects of EP interaction, high phonon frequency, Coulomb energy and substrate induced gap.

Tuning of 2-D Silicon Photonic Crystals

2002 ◽  
Vol 722 ◽  
Author(s):  
H. M. van Driel ◽  
S.W. Leonard ◽  
J. Schilling ◽  
R.B. Wehrspohn
Keyword(s):  
Band Gap ◽  
High Frequency ◽  
Optical Band Gap ◽  
Photonic Band Gap ◽  
Macroporous Silicon ◽  
Optically Pumped ◽  
Electron Hole ◽  
Silicon Photonic ◽  
Induced Changes ◽  
Photonic Band

AbstractWe demonstrate two ways in which the optical band-gap of a 2-D macroporous silicon photonic crystal can be tuned. In the first method the temperature dependence of the refractive index of an infiltrated nematic liquid crystal is used to tune the high frequency edge of the photonic band gap by up to 70 nm as the temperature is increased from 35 to 59°C. In a second technique we have optically pumped the silicon backbone using 150 fs, 800 nm pulses, injecting high density electron hole pairs. Through the induced changes to the dielectric constant via the Drude contribution we have observed shifts up to 30 nm of the high frequency edge of a band-gap.

MODELING OF NOISE BEHAVIOR OF GRADED BAND GAP CHANNEL MOSFET AT GHz FREQUENCIES

2007 ◽  
Vol 07 (04) ◽  
pp. L507-L517
Author(s):  
ALI ABOU-ELNOUR ◽  
OSSAMA ABO-ELNOR ◽  
HAMDY ABDELHAMEED ◽  
ADEL EL-HENAWY
Keyword(s):  
Band Gap ◽  
High Frequency ◽  
Noise Figure ◽  
Low Noise ◽  
Noise Model ◽  
Superior Performance ◽  
Model Parameters ◽  
Short Channel ◽  
Suggested Structure ◽  
Graded Band Gap

A novel graded band gap channel Si - SiGe MOSFET structure has been suggested and its characteristics have been investigated. The investigations indicated that the suggested structure reduces the short-channel effects, increases the cut-off frequency, and hence makes its usage at high frequency and Low noise applications possible. To show the superior performance of the suggested structure at GHz frequencies, and as an example, the noise behavior of the structure is determined. First the device noise model parameters are calculated from D.C. and A.C. characteristics. The extracted noise model parameters are then used to determine the minimum noise figure at GHz frequencies. The effects of the different device parameters on the noise performance are determined. Finally, the results are compared with those of conventional MOSFET structure to show the superior performance of graded band gap Si - SiGe MOSFETs at high frequency ranges.

scholarly journals Vibration Attenuation Investigations on a Distributed Phononic Crystals Beam for Rubber Concrete Structures

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Chao Li ◽  
Sifeng Zhang ◽  
Liyong Gao ◽  
Wei Huang ◽  
Zhaoxin Liu
Keyword(s):  
Band Gap ◽  
Frequency Band ◽  
High Frequency ◽  
Concrete Beam ◽  
Vibration Isolation ◽  
Civil Engineering ◽  
Low Frequency ◽  
Band Gaps ◽  
Spring Force ◽  
Rubber Concrete

Locally resonant phononic crystals (LRPCs) beam is characterized by the band gaps; some frequency ranges within which flexural waves cannot propagate freely. So, the LRPCs beam can be used for noise or vibration isolation. In this paper, a LRPCs beam with distributed oscillators is proposed, and the general formula of band gaps and transmission spectrum are derived by the transfer matrix method (TMM) and spectrum element method (SEM). Subsequently, the parameter effects on band gaps are investigated in detail. Finally, a rubber concrete beam is designed to demonstrate the application of distributed LRPCs beam in civil engineering. Results reveal that the distributed LRPCs beam has multifrequency band gaps and the number of the band gaps is equal to that of the oscillators. Compared with others, the distributed LRPCs beam can reduce the stress concentration when subjected to vibration. The oscillator interval has no effect on the band gaps, which makes it more convenient to design structures. Individual changes of oscillator mass or stiffness affect the band gap location and width. When the resonance frequency of oscillator is fixed, the starting frequency of the band gap remains constant, and increasing oscillator mass of high-frequency band gap widens the high-frequency band gap, while increasing oscillator mass of low-frequency gap widens both high-frequency and low-frequency band gaps. External loads, such as the common uniform spring force provided by foundation in civil engineering, are conducive to the band gap, and when the spring force increases, all the band gaps are widened. Taken together, a configuration of LRPCs rubber concrete beam is designed, and it shows good isolation on the vibration induced by the railway. By the presented design flow chart, the research can serve as a reference for vibration isolation of LRPCs beams in civil engineering.

HIGH FREQUENCY, HIGH TEMPERATURE FIELD-EFFECT TRANSISTORS FABRICATED FROM WIDE BAND GAP SEMICONDUCTORS

1995 ◽  
Vol 06 (01) ◽  
pp. 211-236 ◽  
Author(s):  
R.J. TREW ◽  
M.W. SHIN
Keyword(s):  
High Temperature ◽  
Band Gap ◽  
Microwave Power ◽  
High Frequency ◽  
Field Effect ◽  
Field Effect Transistors ◽  
Wide Band ◽  
Superior Performance ◽  
Wide Band Gap ◽  
Wide Band Gap Semiconductors

Electronic and optical devices fabricated from wide band gap semiconductors have many properties ideal for high temperature, high frequency, high power, and radiation hard applications. Progress in wide band gap semiconductor materials growth has been impressive and high quality epitaxial layers are becoming available. Useful devices, particularly those fabricated from SiC, are rapidly approaching the commercialization stage. In particular, MESFETs (MEtal Semiconductor Field-Effect Transistors) fabricated from wide band gap semiconductors have the potential to be useful in microwave power amplifier and oscillator applications. In this work the microwave performance of MESFETs fabricated from SiC, GaN and semiconducting diamond is investigated with a theoretical simulator and the results compared to experimental measurements. Excellent agreement between the simulated and measured data is obtained. It is demonstrated that microwave power amplifiers fabricated from these semiconductors offer superior performance, particularly at elevated temperatures compared to similar components fabricated from the commonly employed GaAs MESFETs.

High‐gain, high‐frequency AlGaAs/GaAs graded band‐gap base bipolar transistors with a Be diffusion setback layer in the base

1985 ◽  
Vol 46 (6) ◽  
pp. 600-602 ◽  
Author(s):  
R. J. Malik ◽  
F. Capasso ◽  
R. A. Stall ◽  
R. A. Kiehl ◽  
R. W. Ryan ◽  
...  
Keyword(s):  
Band Gap ◽  
High Frequency ◽  
High Gain ◽  
Bipolar Transistors ◽  
Graded Band Gap

Computational investigations of Dienes defect- and vacancy-induced changes in the electronic and vibrational properties of carbon fiber structural units

2021 ◽  
Author(s):  
Sara B. Isbill ◽  
Ashley E. Shields ◽  
Roger J. Kapsimalis ◽  
J. L. Niedziela
Keyword(s):  
Carbon Fiber ◽  
Band Gap ◽  
High Frequency ◽  
Vibrational Properties ◽  
Structural Units ◽  
Electronic Band ◽  
Electronic Band Gap ◽  
Induced Changes

Inclusion of monovacancy and Dienes defects leads to notable changes in the electronic and vibrational properties of graphitic materials, particularly changing the electronic band gap and high-frequency phonon bands.

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