scholarly journals Controlling the energy gap of graphene by Fermi velocity engineering

2015 ◽  
Vol 379 (3) ◽  
pp. 179-182 ◽  
Author(s):  
Jonas R.F. Lima
Keyword(s):  
Energy Gap ◽  
Fermi Velocity

An experimental determination of the Fermi surface in copper

1957 ◽  
Vol 250 (979) ◽  
pp. 325-357 ◽  
Keyword(s):  
Fermi Surface ◽  
Energy Gap ◽  
Skin Resistance ◽  
Pure Copper ◽  
Fermi Velocity ◽  
Zone Boundary ◽  
Electron Model ◽  
Small Areas ◽  
Free Electron Model ◽  
Geometrical Form

Measurements have been made of the variation with crystal orientation of the anomalous skin resistance of plane surfaces of pure copper at low temperatures and at a frequency of 22700 Mc/s. The resistance is related to the geometrical form of the Fermi surface, and a surface is determined which has the correct shape to account for the experimental results. It is believed that there is no other solution which would give equally good agreement. As determined, the surface, which holds one electron per atom, will not quite fit into the Brillouin zone, overlapping in the (111) directions where the zone boundary is closest to the origin. From an examination of simple models it is concluded that probably there is contact with the zone boundary over small areas around these points, and the energy gap across these boundaries is estimated to be about 71/2 eV. Apart from extension to the boundaries in the (111) directions the Fermi surface is more or less spherical. An estimate is made of the Fermi velocity and its variations over the surface, from which it is concluded that the electronic specific heat should lie between 1.7 and 1.9 times that of a free-electron model of copper. The experimental value is 1.38, and it is tentatively suggested that the discrepancy may find an explanation in the theory of Bohm & Pines. Various transport phenomena are briefly discussed, but no reliable evidence is discovered bearing directly on the shape of the Fermi surface. It is concluded that the method, though laborious in interpretation, may be applied with advantage to other simple metals such as silver and gold.

Effect of Magnetic Breakdown on the Magnetoconductivity of Cadmium

1975 ◽  
Vol 53 (11) ◽  
pp. 1060-1070 ◽  
Author(s):  
R. J. Douglas ◽  
W. R. Datars
Keyword(s):  
Relaxation Time ◽  
Path Integral ◽  
Integral Method ◽  
Energy Gap ◽  
Relaxation Times ◽  
Breakdown Field ◽  
Fermi Velocity ◽  
Spin Orbit ◽  
Magnetic Breakdown ◽  
Path Integral Method

The magnetoconductivity and magnetoresistivity tensors of cadmium have been calculated by the path integral method for magnetic fields in the [Formula: see text] and [Formula: see text] directions. A uniform relaxation time and a modified nearly free electron Fermi surface were used. Magnetic breakdown across the HAL spin–orbit energy gap vitiated Kohler's rule and necessitated separate calculations for different relaxation times. Even with open orbits, cadmium was found to be a 'compensated' metal in that the Hall terms never dominated the conductivity tensor determinant. A single breakdown field was found to be inadequate to describe magnetic breakdown on the sheaf of orbits which touch the HAL plane. A range of breakdown fields was calculated across the sheaf of open orbits. From an explanation of induced torque data, it was found that the ratio of the spin–orbit energy gap in the HAL plane to the Fermi velocity is 1.4 × 10−8 eV s cm−1. The resulting field dependences of the magnetoconductivity and magnetoresistivity tensor components are presented and discussed. The use of the path integral technique when there is magnetic breakdown is also presented.

scholarly journals Топологические поверхностные состояния фермионов Дирака в термоэлектриках n-Bi-=SUB=-2-=/SUB=-Te-=SUB=-3-y-=/SUB=-Se-=SUB=-y-=/SUB=-

2019 ◽  
Vol 53 (5) ◽  
pp. 654
Author(s):  
Л.Н. Лукьянова ◽  
И.В. Макаренко ◽  
О.А. Усов ◽  
П.А. Дементьев
Keyword(s):  
Dirac Point ◽  
Energy Gap ◽  
Surface States ◽  
Surface Concentration ◽  
Scanning Tunneling ◽  
Fermi Velocity ◽  
Dirac Fermions ◽  
Tunneling Microscopy ◽  
Topological Surface ◽  
Local Distortions

Topological surface states of Dirac fermions in n-Bi2Te3−ySey thermoelectrics L.N. Lukyanova, I.V. Makarenko, O.A. Usov, P.A. Dementev Ioffe Institute, 194021 St. Petersburg, Russia Abstract In n-Bi2Te3 and n-Bi2Te3−ySey thermoelectrics, the surface states of Dirac fermions of the interlayer van der Waals plane (0001) were studied by scanning tunneling microscopy (STM) and spectroscopy. The surface morphology and modulated line profiles of the images in tunneling microscopy is determined by local distortions of the surface electron states density and depend on the composition. The Dirac point ED of the studied compositions is localized in the energy gap, and it shifts to the top of the valence band with increase of Se content in the solid solutions. The dependence between Dirac surface state parameters (the Dirac point position, the Fermi velocity, the fermion surface concentration) and thermoelectric properties (Seebeck coefficient and the power factor) is established for the thermoelectrics studied.

Point contact spectroscopy in oriented La2?x Sr x CuO4 superconductors; energy gap and Fermi velocity

1994 ◽  
Vol 7 (4) ◽  
pp. 763-766 ◽  
Author(s):  
Nir Hass ◽  
Guy Deutscher ◽  
A. Revcolevschi ◽  
G. Dhalenne
Keyword(s):  
Energy Gap ◽  
Point Contact ◽  
Fermi Velocity ◽  
Point Contact Spectroscopy

Anisotropy of the Fermi surface, Fermi velocity, many-body enhancement, and superconducting energy gap in Nb

1987 ◽  
Vol 35 (4) ◽  
pp. 1728-1741 ◽  
Author(s):  
G. W. Crabtree ◽  
D. H. Dye ◽  
D. P. Karim ◽  
S. A. Campbell ◽  
J. B. Ketterson
Keyword(s):  
Fermi Surface ◽  
Energy Gap ◽  
Fermi Velocity ◽  
Many Body ◽  
Superconducting Energy Gap ◽  
Body Enhancement

Formation of high temperature phase in flash-evaporated SnSe films

1990 ◽  
Vol 48 (4) ◽  
pp. 698-699
Author(s):  
J.P.S. Hanjra
Keyword(s):  
Thin Films ◽  
Electrical Properties ◽  
Energy Gap ◽  
Dominant Role ◽  
Fine Powder ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Water Mixture ◽  
Flash Evaporation ◽  
Photovoltaic Applications

Tin mono selenide (SnSe) with an energy gap of about 1 eV is a potential material for photovoltaic applications. Various authors have studied the structure, electronic and photoelectronic properties of thin films of SnSe grown by various deposition techniques. However, for practical photovoltaic junctions the electrical properties of SnSe films need improvement. We have carried out investigations into the properties of flash evaporated SnSe films. In this paper we report our results on the structure, which plays a dominant role on the electrical properties of thin films by TEM, SEM, and electron diffraction (ED).Thin films of SnSe were deposited by flash evaporation of SnSe fine powder prepared from high purity Sn and Se, onto glass, mica and KCl substrates in a vacuum of 2Ø micro Torr. A 15% HF + 2Ø% HNO3 solution was used to detach SnSe film from the glass and mica substrates whereas the film deposited on KCl substrate was floated over an ethanol water mixture by dissolution of KCl. The floating films were picked up on the grids for their EM analysis.

Effect of the structural changes on the mechanical properties of the sintered films

2016 ◽  
Vol 12 (1) ◽  
pp. 4141-4144
Author(s):  
Garima Jain
Keyword(s):  
Crystallite Size ◽  
Lattice Constant ◽  
Structural Changes ◽  
Structural Investigation ◽  
Energy Gap ◽  
Lattice Parameter ◽  
Metal Chalcogenides ◽  
Optical Energy Gap ◽  
Tin Telluride ◽  
Physical Quantities

Polycrystalline films of tin telluride were prepared by sintering technique. The structural investigation of the films with different thicknesses enables to determine lattice parameter, crystallite size and strain existing in the films. The XRD traces showed that strain was tensile in nature. The crystallite size increases with thickness while strain decreases. Higher the value of tensile strain, larger is the lattice constant. The optical energy gap shows a descending nature with increasing strain and so with the lattice constant. Such an attempt made to delve into interdependence of basic physical quantities helps to explore the properties of SnTe and utilize it as an alternative to heavy metal chalcogenides in various technological applications.  

Structure, Stability and Water Adsorption on Ultra-Thin TiO2 Supported on TiN

2019 ◽  
Author(s):  
Jose Julio Gutierrez Moreno ◽  
Marco Fronzi ◽  
Pierre Lovera ◽  
alan O'Riordan ◽  
Mike J Ford ◽  
...  
Keyword(s):  
Density Functional ◽  
Water Adsorption ◽  
Chemical Potential ◽  
Energy Gap ◽  
Molecular Water ◽  
Structure Stability ◽  
Ambient Conditions ◽  
Rutile Structure ◽  
The Stability ◽  
The One

<p></p><p>Interfacial metal-oxide systems with ultrathin oxide layers are of high interest for their use in catalysis. In this study, we present a density functional theory (DFT) investigation of the structure of ultrathin rutile layers (one and two TiO<sub>2</sub> layers) supported on TiN and the stability of water on these interfacial structures. The rutile layers are stabilized on the TiN surface through the formation of interfacial Ti–O bonds. Charge transfer from the TiN substrate leads to the formation of reduced Ti<sup>3+</sup> cations in TiO<sub>2.</sub> The structure of the one-layer oxide slab is strongly distorted at the interface, while the thicker TiO<sub>2</sub> layer preserves the rutile structure. The energy cost for the formation of a single O vacancy in the one-layer oxide slab is only 0.5 eV with respect to the ideal interface. For the two-layer oxide slab, the introduction of several vacancies in an already non-stoichiometric system becomes progressively more favourable, which indicates the stability of the highly non-stoichiometric interfaces. Isolated water molecules dissociate when adsorbed at the TiO<sub>2</sub> layers. At higher coverages the preference is for molecular water adsorption. Our ab initio thermodynamics calculations show the fully water covered stoichiometric models as the most stable structure at typical ambient conditions. Interfacial models with multiple vacancies are most stable at low (reducing) oxygen chemical potential values. A water monolayer adsorbs dissociatively on the highly distorted 2-layer TiO<sub>1.75</sub>-TiN interface, where the Ti<sup>3+</sup> states lying above the top of the valence band contribute to a significant reduction of the energy gap compared to the stoichiometric TiO<sub>2</sub>-TiN model. Our results provide a guide for the design of novel interfacial systems containing ultrathin TiO<sub>2</sub> with potential application as photocatalytic water splitting devices.</p><p></p>

Molecular Investigations of the Newly Synthesized Azomethines as Antioxidants: Theoretical and Experimental Studies

2019 ◽  
Vol 19 (6) ◽  
pp. 419-433 ◽  
Author(s):  
Siyamak Shahab ◽  
Masoome Sheikhi ◽  
Liudmila Filippovich ◽  
Evgenij Dikusar ◽  
Anhelina Pazniak ◽  
...  
Keyword(s):  
Density Functional ◽  
Energy Gap ◽  
Experimental Studies ◽  
Antioxidant Property ◽  
Nbo Analysis ◽  
Antioxidant Potential ◽  
Functional Theory ◽  
Homo And Lumo ◽  
Intramolecular Hydrogen ◽  
Activity Mechanism

: In this study, the antioxidant property of new synthesized azomethins has been investigated as theoretical and experimental. Methods and Results: Density functional theory (DFT) was employed to investigate the Bond Dissociation Enthalpy (BDE), Mulliken Charges, NBO analysis, Ionization Potential (IP), Electron Affinities (EA), HOMO and LUMO energies, Hardness (η), Softness (S), Electronegativity (µ), Electrophilic Index (ω), Electron Donating Power (ω-), Electron Accepting Power (ω+) and Energy Gap (Eg) in order to deduce scavenging action of the two new synthesized azomethines (FD-1 and FD-2). Spin density calculations and NBO analysis were also carried out to understand the antioxidant activity mechanism. Comparison of BDE of FD-1 and FD-2 indicate the weal antioxidant potential of these structures. Conclusion: FD-1 and FD-2 have very high antioxidant potential due to the planarity and formation of intramolecular hydrogen bonds.

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