scholarly journals Spectrum of localized states in fermionic chains with defect and adiabatic charge pumping

2022 ◽  
Vol 2022 (1) ◽  
pp. 013102
Author(s):  
Filiberto Ares ◽  
José G Esteve ◽  
Fernando Falceto
Keyword(s):  
Energy Gap ◽  
The Other ◽  
Localized States ◽  
Topological Phases ◽  
Zero Energy ◽  
Important Ingredient ◽  
Open Chain ◽  
Translational Invariance ◽  
Conduction Bands ◽  
Roots Of A Polynomial

Abstract In this paper, we study the localized states of a generic quadratic fermionic chain with finite-range couplings and an inhomogeneity in the hopping (defect) that breaks translational invariance. When the hopping of the defect vanishes, which represents an open chain, we obtain a simple bulk-edge correspondence: the zero-energy modes localized at the ends of the chain are related to the roots of a polynomial determined by the couplings of the Hamiltonian of the bulk. From this result, we define an index that characterizes the different topological phases of the system and can be easily computed by counting the roots of the polynomial. As the defect is turned on and varied adiabatically, the zero-energy modes may cross the energy gap and connect the valence and conduction bands. We analyze the robustness of the connection between bands against perturbations of the Hamiltonian. The pumping of states from one band to the other allows the creation of particle–hole pairs in the bulk. An important ingredient for our analysis is the transformation of the Hamiltonian under the standard discrete symmetries, C, P, T, as well as a fourth one, peculiar to our system, that is related to the existence of a gap and localized states.

scholarly journals Modeling Energy Efficiency Performance and Cost-Benefit Analysis Achieving Net-Zero Energy Building Design: Case Studies of Three Representative Offices in Thailand

2021 ◽  
Vol 13 (9) ◽  
pp. 5201
Author(s):  
Kittisak Lohwanitchai ◽  
Daranee Jareemit
Keyword(s):  
High Efficiency ◽  
Energy Gap ◽  
Cost Benefit ◽  
Building Design ◽  
Energy Performance ◽  
Office Buildings ◽  
Zero Energy ◽  
Zero Energy Building ◽  
Investment Cost ◽  
High Investment

The concept of a zero energy building is a significant sustainable strategy to reduce greenhouse gas emissions. The challenges of zero energy building (ZEB) achievement in Thailand are that the design approach to reach ZEB in office buildings is unclear and inconsistent. In addition, its implementation requires a relatively high investment cost. This study proposes a guideline for cost-optimal design to achieve the ZEB for three representative six-story office buildings in hot and humid Thailand. The energy simulations of envelope designs incorporating high-efficiency systems are carried out using eQuest and daylighting simulation using DIALux evo. The final energy consumptions meet the national ZEB target but are higher than the rooftop PV generation. To reduce such an energy gap, the ratios of building height to width are proposed. The cost-benefit of investment in ZEB projects provides IRRs ranging from 10.73 to 13.85%, with payback periods of 7.2 to 8.5 years. The energy savings from the proposed designs account for 79.2 to 81.6% of the on-site energy use. The investment of high-performance glazed-windows in the small office buildings is unprofitable (NPVs = −14.77–−46.01). These research results could help architects and engineers identify the influential parameters and significant considerations for the ZEB design. Strategies and technical support to improve energy performance in large and mid-rise buildings towards ZEB goals associated with the high investment cost need future investigations.

a-Si:H/a-SiC:H Heterostructure for Bias-Controlled Photodetectors

1994 ◽  
Vol 336 ◽  
Author(s):  
G. De Cesare ◽  
F. Irrera ◽  
F. Lemmi ◽  
F. Palma ◽  
M. Tucci
Keyword(s):  
Applied Voltage ◽  
Energy Gap ◽  
The Other ◽  
Time Response ◽  
Wavelength Selection ◽  
Load Impedance ◽  
Amorphous Si ◽  
Hydrogenated Amorphous ◽  
High Rejection

ABSTRACTWe present a novel family of photodetectors based on hydrogenated amorphous Si/SiC p-i-n-i-p heterostructures. Front p-i-n and rear n-i-p diodes work one as a detector and the other as a load impedance, depending on the polarity of the applied voltage. Due to different absorption at different wavelengths, the devices operate as bias-controlled light detectors in either the blue or the red regions. The energy gap and the thickness of the two intrinsic layers have been optimized to obtain a sharp wavelength selection (centered at 430 and 630 nm) with high rejection-ratios and good quantum efficiencies. The I-V characteristics and the device time response are investigated and simulated by SPICE.

Determination of Density of Localized States in Amorphous Silicon Alloys From the Low Field Conductance of Thin N-I-N Diodes

1985 ◽  
Vol 49 ◽  
Author(s):  
Michael Shur ◽  
Michael Hack
Keyword(s):  
Temperature Dependence ◽  
Amorphous Silicon ◽  
Bulk Density ◽  
Density Of States ◽  
Energy Gap ◽  
Localized States ◽  
New Technique ◽  
Silicon Alloys ◽  
Low Field ◽  
Density Of Localized States

AbstractWe describe a new technique to determine the bulk density of localized states in the energy gap of amorphous silicon alloys from the temperature dependence of the low field conductance of n-i-n diodes. This new technique allows us to determine the bulk density of states in the centre of a device, and is very straightforward, involving fewer assumptions than other established techniques. Varying the intrinsic layer thickness allows us to measure the,density of states within approximately 400 meV of midgap.We measured the temperature dependence of the low field conductance of an amorphous silicon alloy n-i-n diode with an intrinsic layer thjckness of 0.45 microns and deduced the density of localised states to be 3xlO16cm−3 eV−1 at approximately 0.5 eV below the bottom of the conduction band. We have also considered the high bias region (the space charge limited current regime) and proposed an interpolation formula which describes the current-voltage characteristics of these structures at all biases and agrees well with our computer simulation based on the solution of the complete system of transport equations.

Defect states in amorphous Ge2Sb2Te5 phase change material

2014 ◽  
Vol 92 (7/8) ◽  
pp. 619-622
Author(s):  
N. Qamhieh ◽  
S.T. Mahmoud ◽  
A.I. Ayesh
Keyword(s):  
Fermi Level ◽  
Energy Gap ◽  
Continuous Distribution ◽  
Dark Conductivity ◽  
Localized States ◽  
Defect States ◽  
Thermally Activated ◽  
Level Shifts ◽  
Gap States ◽  
Change Material

Steady-state photoconductivity measurements in the temperature range 100–300 K on amorphous Ge2Sb2Te5 thin film prepared by dc sputtering are analyzed. The dark conductivity is thermally activated with a single activation energy that allocates the position of the Fermi level approximately in the middle of the energy gap relative to the valance band edge. The temperature dependence of the photoconductivity ensures the presence of a maximum normally observed in chalcogenides with low- and high-temperature slopes, which predict the location of discrete sets of localized states (recombination levels) in the gap. The presence of these defect states close to the valence and conduction band edges leaves the quasi Fermi level shifts in a continuous distribution of gap states at high temperatures, as evidenced from the γ values of the lux–ampere characteristics.

Study on Electronic Structure of GaN under Pressure

2014 ◽  
Vol 900 ◽  
pp. 217-221
Author(s):  
Xing Xiang Ruan ◽  
Xian Hui Zhong ◽  
Fu Chun Zhang ◽  
Wei Hu Zhang
Keyword(s):  
Electronic Structure ◽  
Density Functional ◽  
Energy Gap ◽  
Potential Method ◽  
High Energy ◽  
Functional Theory ◽  
Conduction Bands ◽  
The Density Functional Theory ◽  
The Relationship ◽  
Pseudo Potential

A detailed theoretical study of electronic structure and optical properties of GaN under pressure was performed by the first-principles calculations of plane wave ultra-soft pseudo-potential method based on the density functional theory (DFT). The results indicate that Ga-N bond length becomes shorter and the valence bonds shift towards the low energy while the conduction bands towards high energy, the band gap becomes wider with the pressure increasing, and theoretical studies explained the relationship between the band edges, energy gap of GaN and pressure. In addition, the peak in band was cracked slightly, and the Ga 3d-N 2p hybridization was enhanced.

New Evidence for the Second Conduction Band in 4H SiC

2017 ◽  
Vol 897 ◽  
pp. 250-253 ◽  
Author(s):  
Walter Klahold ◽  
Charles Tabachnick ◽  
Gabriel Freedman ◽  
Robert P. Devaty ◽  
Wolfgang J. Choyke
Keyword(s):  
Conduction Band ◽  
Energy Gap ◽  
Free Exciton ◽  
Epitaxial Films ◽  
Energy Separation ◽  
Orbit Splitting ◽  
Conduction Bands ◽  
Spin Orbit Splitting ◽  
New Evidence ◽  
Absorption Measurements

Differential absorption measurements were taken on ultra-pure boule pieces and epitaxial films of 4H SiC. The energy range of particular interest is from 3.40 eV to 3.52 eV. The free exciton energy gap associated with the second lowest conduction band at the M point in the Brillouin zone was determined to be EGX-2 = 3.4107 eV. This value is obtained from phonon assisted free exciton transitions involving the second conduction band measured in transmission with polarization E⊥c. The energy separation of the two lowest conduction bands is determined to be 144 ± 2 meV. Some replica peaks attributable to the spin orbit splitting in the valence band are also seen.

Density of Deep Bandgap States in Amorphous Silicon From the Temperature Dependence of Thin Film Transistor Current

1994 ◽  
Vol 336 ◽  
Author(s):  
T. Globus ◽  
H. C. Slade ◽  
M. Shur ◽  
M. Hack
Keyword(s):  
Thin Film ◽  
Activation Energy ◽  
Amorphous Silicon ◽  
Conduction Band ◽  
Energy Gap ◽  
Localized States ◽  
Flat Band ◽  
Gate Bias ◽  
Density Of Localized States ◽  
Wide Range

ABSTRACTWe have measured the current-voltage characteristics of amorphous silicon thin film transistors (a-Si TFTs) over a wide range of temperatures (20 to 160°C) and determined the activation energy of the channel current as a function of gate bias with emphasis on the leakage current and subthreshold regimes. We propose a new method for estimating the density of localized states (DOS) from the dependence of the derivative of activation energy with respect to gate bias. This differential technique does not require knowledge of the flat-band voltage (VFB) and does not incorporate integration over gate bias. Using this Method, we have characterized the density of localized states with energies in the range 0.15–1.2 eV from the bottom of the conduction band and have found a wide peak in the DOS in the range of 0.8–0.95 eV below the conduction band. We have also observed that the DOS peak in the lower half of the bandgap increases in magnitude and shifts towards the conduction band as a result of thermal and bias stress. We also measured an overall increase in the DOS in the upper half of the energy gap and an additional peak, centered at 0.2 eV below the conduction band, which appear due to the applied stress. These results are in qualitative agreement with the defect pool Model [1,2].

Evolution of Photoluminescence Mechanisms of Si+-Implanted SiO2 Films with Thermal Annealing

2008 ◽  
Vol 8 (7) ◽  
pp. 3555-3560 ◽  
Author(s):  
L. Ding ◽  
T. P. Chen ◽  
Y. Liu ◽  
C. Y. Ng ◽  
M. Yang ◽  
...  
Keyword(s):  
Band Structure ◽  
Thermal Annealing ◽  
Annealing Temperature ◽  
Energy Gap ◽  
The Other ◽  
Extended Defects ◽  
Band Transition ◽  
Luminescent Centers ◽  
Subsequent Thermal Annealing ◽  
Si Ion Implantation

The information of band structure of silicon nanocrystal (nc-Si) embedded in SiO2 thin films synthesized by Si ion implantation and subsequent thermal annealing at various temperatures has been obtained from spectroscopy ellipsometric (SE) analysis. The indirect band structure and the energy gap of the nc-Si are not affected by the annealing. In contrast, the photoluminescence (PL) spectra show a continuous evolution with the annealing. Six PL bands located at 415, 460, 520, 630, 760, and 845 nm, respectively, have been observed depending on the annealing temperature. The annealing at 1100 °C yields the strongest PL band at 760 nm (∼1.63 eV) with the intensity much higher than that of all the other PL bands. Based on the knowledge of the band structure, the 760 nm-PL band could be attributed to the indirect band-to-band transition of the nc-Si assisted by the Si—O vibration of the nc-Si/SiO2 interface with the stretching frequency of ∼1083 cm−1 (&sim0.13 eV). On the other hand, the first four PL bands mentioned above could originate from different extended defects in the oxide matrix, while the 845-nm PL band could be related to the interface luminescent centers.

scholarly journals Investigation of nitrogen balance in dairy cows and steers nourished by intragastric infusion

1983 ◽  
Vol 50 (1) ◽  
pp. 99-107 ◽  
Author(s):  
E. R. Ørskov ◽  
N. A. MacLeod ◽  
S. T. M. Fahmy ◽  
L. Istasse ◽  
F. D. DeB. Hovell
Keyword(s):  
Fatty Acids ◽  
Dairy Cows ◽  
Energy Supply ◽  
Volatile Fatty Acids ◽  
Energy Content ◽  
The Other ◽  
N Balance ◽  
Zero Energy ◽  
Gross Energy ◽  
Practical Implications

1. Two dairy cows were maintained by intragastric infusion of volatile fatty acids and casein. Except when fasting, the casein-nitrogen was held constant, while total gross energy supply was varied from zero during fasting to 650 kJ/kg body-weight (W)0·75.2. One cow was estimated to attain zero N balance at an energy intake of 255 kJ/kg W0·75and the other at 307 kJ/kg W0·75, which was calculated to be substantially below the estimated energy required for zero energy balance.3. When the cows were later given an N-free infusion for a period preceding the trial, N balance occurred at 98 kJ/kg W0·75for one cow and 115 kJ/kg W0·75for the other.4. Four steers were similarly nourished by intragastric infusion and the energy nutrient increased from 0 at fasting to 450 kJ/kg W0·75. The protein was held constant at 1 g N/kg W0·75except at fasting. The energy level at which N balance occurred was 154 (SE 38) kJ/kg W0·75or approximately equal to the energy content of the protein. The practical implications of these findings are discussed.

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