Nanomaterials

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10 pages, 536 KiB

Open AccessEditor’s ChoiceArticle

Cone-Shell Quantum Structures in Electric and Magnetic Fields as Switchable Traps for Photoexcited Charge Carriers

by Christian Heyn, Leonardo Ranasinghe, Ahmed Alshaikh and Carlos A. Duque

Nanomaterials 2023, 13(10), 1696; https://doi.org/10.3390/nano13101696 - 22 May 2023

Viewed by 887

Abstract

The optical emission of cone-shell quantum structures (CSQS) under vertical electric (F) and magnetic (B) fields is studied by means of simulations. A CSQS has a unique shape, where an electric field induces the transformation of the hole probability [...] Read more.

The optical emission of cone-shell quantum structures (CSQS) under vertical electric (F) and magnetic (B) fields is studied by means of simulations. A CSQS has a unique shape, where an electric field induces the transformation of the hole probability density from a disk into a quantum-ring with a tunable radius. The present study addresses the influence of an additional magnetic field. A common description for the influence of a B-field on charge carriers confined in a quantum dot is the Fock-Darwin model, which introduces the angular momentum quantum number l to describe the splitting of the energy levels. For a CSQS with the hole in the quantum ring state, the present simulations demonstrate a B-dependence of the hole energy which substantially deviates from the prediction of the Fock-Darwin model. In particular, the energy of exited states with a hole

l_{h} >

0 can become lower than the ground state energy with

l_{h} =

0. Because for the lowest-energy state the electron

l_{e}

is always zero, states with

l_{h} >

0 are optically dark due to selection rules. This allows switching from a bright state (

l_{h} =

0) to a dark state (

l_{h} >

0) or vice versa by changing the strength of the F or B field. This effect can be very interesting for trapping photoexcited charge carriers for a desired time. Furthermore, the influence of the CSQS shape on the fields required for the bright to dark state transition is investigated. Full article

(This article belongs to the Special Issue Photoemission and Excitation Properties of Nanomaterials by Computational Methods)

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14 pages, 1330 KiB

Open AccessArticle

Multipole Excitations and Nonlocality in 1d Plasmonic Nanostructures

by Anatoliy V. Goncharenko and Vyacheslav M. Silkin

Nanomaterials 2023, 13(8), 1395; https://doi.org/10.3390/nano13081395 - 18 Apr 2023

Cited by 2 | Viewed by 833

Abstract

Efficient simulation methods for taking nonlocal effects in nanostructures into account have been developed, but they are usually computationally expensive or provide little insight into underlying physics. A multipolar expansion approach, among others, holds promise to properly describe electromagnetic interactions in complex nanosystems. [...] Read more.

Efficient simulation methods for taking nonlocal effects in nanostructures into account have been developed, but they are usually computationally expensive or provide little insight into underlying physics. A multipolar expansion approach, among others, holds promise to properly describe electromagnetic interactions in complex nanosystems. Conventionally, the electric dipole dominates in plasmonic nanostructures, while higher order multipoles, especially the magnetic dipole, electric quadrupole, magnetic quadrupole, and electric octopole, can be responsible for many optical phenomena. The higher order multipoles not only result in specific optical resonances, but they are also involved in the cross-multipole coupling, thus giving rise to new effects. In this work, we introduce a simple yet accurate simulation modeling technique, based on the transfer-matrix method, to compute higher-order nonlocal corrections to the effective permittivity of 1d plasmonic periodic nanostructures. In particular, we show how to specify the material parameters and the arrangement of the nanolayers in order to maximize or minimize various nonlocal corrections. The obtained results provide a framework for guiding and interpreting experiments, as well as for designing metamaterials with desired dielectric and optical properties. Full article

(This article belongs to the Special Issue Photoemission and Excitation Properties of Nanomaterials by Computational Methods)

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19 pages, 4787 KiB

Open AccessArticle

Acoustic Plasmons in Nickel and Its Modification upon Hydrogen Uptake

by Yury M. Koroteev, Igor V. Silkin, Ivan P. Chernov, Evgueni V. Chulkov and Vyacheslav M. Silkin

Nanomaterials 2023, 13(1), 141; https://doi.org/10.3390/nano13010141 - 28 Dec 2022

Viewed by 1429

Abstract

In this work, we study, in the framework of the ab initio linear-response time-dependent density functional theory, the low-energy collective electronic excitations with characteristic sound-like dispersion, called acoustic plasmons, in bulk ferromagnetic nickel. Since the respective spatial oscillations in slow and fast charge [...] Read more.

In this work, we study, in the framework of the ab initio linear-response time-dependent density functional theory, the low-energy collective electronic excitations with characteristic sound-like dispersion, called acoustic plasmons, in bulk ferromagnetic nickel. Since the respective spatial oscillations in slow and fast charge systems involve states with different spins, excitation of such plasmons in nickel should result in the spatial variations in the spin structure as well. We extend our study to NiH

_{x}

with different hydrogen concentrations x. We vary the hydrogen concentration and trace variations in the acoustic plasmons properties. Finally, at

x = 1

the acoustic modes disappear in paramagnetic NiH. The explanation of such evolution is based on the changes in the population of different energy bands with hydrogen content variation. Full article

(This article belongs to the Special Issue Photoemission and Excitation Properties of Nanomaterials by Computational Methods)

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11 pages, 15361 KiB

Open AccessArticle

One-Step Theory View on Photoelectron Diffraction: Application to Graphene

by Eugene Krasovskii

Nanomaterials 2022, 12(22), 4040; https://doi.org/10.3390/nano12224040 - 17 Nov 2022

Cited by 2 | Viewed by 1231

Abstract

Diffraction of photoelectrons emitted from the core 1s and valence band of monolayer and bilayer graphene is studied within the one-step theory of photoemission. The energy-dependent angular distribution of the photoelectrons is compared to the simulated electron reflection pattern of a low-energy [...] Read more.

Diffraction of photoelectrons emitted from the core 1s and valence band of monolayer and bilayer graphene is studied within the one-step theory of photoemission. The energy-dependent angular distribution of the photoelectrons is compared to the simulated electron reflection pattern of a low-energy electron diffraction experiment in the kinetic energy range up to about 55 eV, and the implications for the structure determination are discussed. Constant energy contours due to scattering resonances are well visible in photoelectron diffraction, and their experimental shape is well reproduced. The example of the bilayer graphene is used to reveal the effect of the scattering by the subsurface layer. The photoemission and LEED patterns are shown to contain essentially the same information about the long-range order. The diffraction patterns of C

1 s

and valence band photoelectrons bear similar anisotropy and are equally suitable for diffraction analysis. Full article

(This article belongs to the Special Issue Photoemission and Excitation Properties of Nanomaterials by Computational Methods)

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11 pages, 2794 KiB

Open AccessArticle

Quasiparticle Self-Consistent GW Study of Simple Metals

by Christoph Friedrich, Stefan Blügel and Dmitrii Nabok

Nanomaterials 2022, 12(20), 3660; https://doi.org/10.3390/nano12203660 - 18 Oct 2022

Cited by 5 | Viewed by 1289

Abstract

The

G W

method is a standard method to calculate the electronic band structure from first principles. It has been applied to a large variety of semiconductors and insulators but less often to metallic systems, in particular, with respect to a self-consistent employment [...] Read more.

The

G W

method is a standard method to calculate the electronic band structure from first principles. It has been applied to a large variety of semiconductors and insulators but less often to metallic systems, in particular, with respect to a self-consistent employment of the method. In this work, we take a look at all-electron quasiparticle self-consistent

G W

(QS

G W

) calculations for simple metals (alkali and alkaline earth metals) based on the full-potential linearized augmented-plane-wave approach and compare the results to single-shot (i.e., non-selfconsistent)

G_{0} W_{0}

calculations, density-functional theory (DFT) calculations in the local-density approximation, and experimental measurements. We show that, while DFT overestimates the bandwidth of most of the materials, the

G W

quasiparticle renormalization corrects the bandwidths in the right direction, but a full self-consistent calculation is needed to consistently achieve good agreement with photoemission data. The results mainly confirm the common belief that simple metals can be regarded as nearly free electron gases with weak electronic correlation. The finding is particularly important in light of a recent debate in which this seemingly established view has been contested. Full article

(This article belongs to the Special Issue Photoemission and Excitation Properties of Nanomaterials by Computational Methods)

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13 pages, 8464 KiB

Open AccessEditor’s ChoiceArticle

RPA Plasmons in Graphene Nanoribbons: Influence of a VO₂ Substrate

by Mousa Bahrami and Panagiotis Vasilopoulos

Nanomaterials 2022, 12(16), 2861; https://doi.org/10.3390/nano12162861 - 19 Aug 2022

Cited by 1 | Viewed by 1593

Abstract

We study the effect of the phase-change material VO

_{2}

on plasmons in metallic arm-chair graphene nanoribbons (AGNRs) within the random-phase approximation (RPA) for intra- and inter-band transitions. We assess the influence of temperature as a knob for the transition from the insulating [...] Read more.

We study the effect of the phase-change material VO

_{2}

on plasmons in metallic arm-chair graphene nanoribbons (AGNRs) within the random-phase approximation (RPA) for intra- and inter-band transitions. We assess the influence of temperature as a knob for the transition from the insulating to the metallic phase of VO

_{2}

on localized and propagating plasmon modes. We show that AGNRs support localized and propagating plasmon modes and contrast them in the presence and absence of VO

_{2}

for intra-band (SB) transitions while neglecting the influence of a substrate-induced band gap. The presence of this gap results in propagating plasmon modes in two-band (TB) transitions. In addition, there is a critical band gap below and above which propagating modes have a linear negative or positive velocity. Increasing the band gap shifts the propagating and localized modes to higher frequencies. In addition, we show how the normalized Fermi velocity increases plasmon modes frequency. Full article

(This article belongs to the Special Issue Photoemission and Excitation Properties of Nanomaterials by Computational Methods)

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Review

Jump to: Research

11 pages, 2102 KiB

Open AccessReview

Determination of the Primary Excitation Spectra in XPS and AES

by Nicolas Pauly, Francisco Yubero and Sven Tougaard

Nanomaterials 2023, 13(2), 339; https://doi.org/10.3390/nano13020339 - 13 Jan 2023

Viewed by 1663

Abstract

This paper reviews a procedure that allows for extracting primary photoelectron or Auger electron emissions from homogeneous isotropic samples. It is based on a quantitative dielectric description of the energy losses of swift electrons travelling nearby surfaces in presence of stationary positive charges. [...] Read more.

This paper reviews a procedure that allows for extracting primary photoelectron or Auger electron emissions from homogeneous isotropic samples. It is based on a quantitative dielectric description of the energy losses of swift electrons travelling nearby surfaces in presence of stationary positive charges. The theory behind the modeling of the electron energy losses, implemented in a freely available QUEELS-XPS software package, takes into account intrinsic and extrinsic effects affecting the electron transport. The procedure allows for interpretation of shake-up and multiplet structures on a quantitative basis. We outline the basic theory behind it and illustrate its capabilities with several case examples. Thus, we report on the angular dependence of the intrinsic and extrinsic Al 2s photoelectron emission from aluminum, the shake-up structure of the Ag 3d, Cu 2p, and Ce 3d photoelectron emission from silver, CuO and CeO₂, respectively, and the quantification of the two-hole final states contributing to the L₃M₄₅M₄₅ Auger electron emission of copper. These examples illustrate the procedure, that can be applied to any homogeneous isotropic material. Full article

(This article belongs to the Special Issue Photoemission and Excitation Properties of Nanomaterials by Computational Methods)

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Graphical abstract

34 pages, 771 KiB

Open AccessReview

Methods of Modeling of Strongly Correlated Electron Systems

by Roman Kuzian

Nanomaterials 2023, 13(2), 238; https://doi.org/10.3390/nano13020238 - 05 Jan 2023

Cited by 2 | Viewed by 1532

Abstract

The discovery of high-

T_{c}

superconductivity in cuprates in 1986 moved strongly correlated systems from exotic worlds interesting only for pure theorists to the focus of solid-state research. In recent decades, the majority of hot topics in condensed matter physics (high- [...] Read more.

The discovery of high-

T_{c}

superconductivity in cuprates in 1986 moved strongly correlated systems from exotic worlds interesting only for pure theorists to the focus of solid-state research. In recent decades, the majority of hot topics in condensed matter physics (high-

T_{c}

superconductivity, colossal magnetoresistance, multiferroicity, ferromagnetism in diluted magnetic semiconductors, etc.) have been related to strongly correlated transition metal compounds. The highly successful electronic structure calculations based on density functional theory lose their predictive power when applied to such compounds. It is necessary to go beyond the mean field approximation and use the many-body theory. The methods and models that were developed for the description of strongly correlated systems are reviewed together with the examples of response function calculations that are needed for the interpretation of experimental information (inelastic neutron scattering, optical conductivity, resonant inelastic X-ray scattering, electron energy loss spectroscopy, angle-resolved photoemission, electron spin resonance, and magnetic and magnetoelectric properties). The peculiarities of (quasi-) 0-, 1-, 2-, and 3- dimensional systems are discussed. Full article

(This article belongs to the Special Issue Photoemission and Excitation Properties of Nanomaterials by Computational Methods)

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