Changes in the Fermi surface of CuNi and AgMn random alloys deduced from studies of the photoemission from (111) surface states

AbstractThe electronic states at the Fermi surface determine diverse properties such as magnetism, chemical bonding, and phonon-electron coupling. Using a conventional hemispherical analyzer at the ultraESCA beamline 7.0 of the Advanced Light Source, we have measured Fermi contours of the bulk and surface states of Cu(001) and Ag(001). For bulk states, we used uniform sampling in k-space by varying both the electron takeoff angle as well as the photon energy. Three-dimensional plots (in k-space) of bulk and surface states at the Fermi level can easily be achieved within one or two synchrotron shifts. Surface states, whose momentum is independent of k-perpendicular, are easily mapped if sufficiently dense angular sampling is performed. The states crossing the Fermi level at X in the surface Brillouin Zone of Cu(100) and Ag(100) are presented as examples.

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Surface levels of organic conductors in a tilted in-plane magnetic field

Zeitschrift für Naturforschung A ◽

10.1515/zna-2021-0093 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Danica Krstovska ◽

Aleksandar Skeparovski

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Fermi Surface ◽

Tilt Angle ◽

Experimental Studies ◽

Surface States ◽

Organic Conductors ◽

Magnetic Field Direction ◽

Two Dimensional ◽

Tilted Magnetic Field

Abstract Surface quantum states in quasi-two dimensional organic conductors induced by an external magnetic field tilted in the plane of the layers are obtained and analyzed. In tilted magnetic fields, these states arise from the transitions of the electrons between the closed orbits on the sides of the Fermi surface determined by the electron momentum along the magnetic field direction p B and the coordinate of the center of electron revolution Z. By far, in organic conductors, the surface states have not been studied for tilted magnetic fields. In this work, we have performed detail analyses of the surface states in a tilted in-plane magnetic field by calculating the surface energy spectrum and surface wave functions in order to address their properties and features. We find that, in a tilted magnetic field, the surface levels have higher energies compared to those at zero tilt angle but can be observed only up to a certain tilt angle. The resonant magnetic field and angular values at which the peaks in the surface oscillations should be observed are obtained. Further theoretical and new experimental studies of the surface states in a tilted magnetic field might give new insights into the surface properties of quasi-two dimensional organic conductors. Additionally, they may reveal new information about the parameters of the Fermi surface of organic conductors necessary for its reconstruction.

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Photoemission study of surface states on the (111) faces of Ag and Ag-Mn random alloys

Journal of Physics C Solid State Physics ◽

10.1088/0022-3719/16/16/005 ◽

1983 ◽

Vol 16 (16) ◽

pp. L529-L534 ◽

Cited By ~ 12

Author(s):

R G Jordan ◽

G S Sohal

Keyword(s):

Surface States ◽

Random Alloys ◽

Photoemission Study

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Bandgap atomistic calculations on hydrogen-passivated GeSi nanocrystals

Scientific Reports ◽

10.1038/s41598-021-92936-z ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Ovidiu Cojocaru ◽

Ana-Maria Lepadatu ◽

George Alexandru Nemnes ◽

Toma Stoica ◽

Magdalena Lidia Ciurea

Keyword(s):

Density Functional ◽

Surface States ◽

Published Data ◽

Atomic Concentration ◽

Simulation Data ◽

Functional Theory ◽

Sensor Applications ◽

Atomistic Calculations ◽

Random Alloys ◽

Effect Of Surface

AbstractWe present a detailed study regarding the bandgap dependence on diameter and composition of spherical Ge-rich GexSi1−x nanocrystals (NCs). For this, we conducted a series of atomistic density functional theory (DFT) calculations on H-passivated NCs of Ge-rich GeSi random alloys, with Ge atomic concentration varied from 50 to 100% and diameters ranging from 1 to 4 nm. As a result of the dominant confinement effect in the DFT computations, a composition invariance of the line shape of the bandgap diameter dependence was found for the entire computation range, the curves being shifted for different Ge concentrations by ΔE(eV) = 0.651(1 − x). The shape of the dependence of NCs bandgap on the diameter is well described by a power function 4.58/d1.25 for 2–4 nm diameter range, while for smaller diameters, there is a tendency to limit the bandgap to a finite value. By H-passivation of the NC surface, the effect of surface states near the band edges is excluded aiming to accurately determine the NC bandgap. The number of H atoms necessary to fully passivate the spherical GexSi1−x NC surface reaches the total number atoms of the Ge + Si core for smallest NCs and still remains about 25% from total number of atoms for bigger NC diameters of 4 nm. The findings are in line with existing theoretical and experimental published data on pure Ge NCs and allow the evaluation of the GeSi NCs behavior required by desired optical sensor applications for which there is a lack of DFT simulation data in literature.

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