Condensed Matter

Open AccessArticle

Atomic Structure of Mn-Doped CoFe₂O₄ Nanoparticles for Metal–Air Battery Applications

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Condens. Matter 2023, 8(2), 49; https://doi.org/10.3390/condmat8020049 - 24 May 2023

Abstract

We discuss the atomic structure of cobalt ferrite nanoparticles doped with Mn via an analysis based on combining atomic pair distribution functions with high energy X-ray diffraction and high-resolution transmission electron microscopy measurements. Cobalt ferrite nanoparticles are promising materials for metal–air battery applications. [...] Read more.

We discuss the atomic structure of cobalt ferrite nanoparticles doped with Mn via an analysis based on combining atomic pair distribution functions with high energy X-ray diffraction and high-resolution transmission electron microscopy measurements. Cobalt ferrite nanoparticles are promising materials for metal–air battery applications. Cobalt ferrites, however, generally show poor electronic conductivity at ambient temperatures, which limits their bifunctional catalytic performance in oxygen electrocatalysis. Our study reveals how the introduction of Mn ions promotes the conductivity of the cobalt ferrite electrode. Full article

(This article belongs to the Special Issue Feature Papers from Condensed Matter Editorial Board Members)

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Open AccessArticle

A Positron Implantation Profile Estimation Approach for the PALS Study of Battery Materials

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Condens. Matter 2023, 8(2), 48; https://doi.org/10.3390/condmat8020048 - 22 May 2023

Abstract

Positron annihilation spectroscopy is a powerful probe to investigate the interfaces in materials relevant for energy storage such as Li-ion batteries. The key to the interpretation of the results is the positron implantation profile, which is a spatial function related to the characteristics [...] Read more.

Positron annihilation spectroscopy is a powerful probe to investigate the interfaces in materials relevant for energy storage such as Li-ion batteries. The key to the interpretation of the results is the positron implantation profile, which is a spatial function related to the characteristics of the materials forming the battery. We provide models for the positron implantation profile in a cathode of a Li-ion battery coin cell. These models are the basis for a reliable visualization of multilayer geometries and their interfaces in thin cathodes of lithium-ion batteries. Full article

(This article belongs to the Special Issue New Advances in Condensed Matter Physics)

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Open AccessArticle

Thermodynamics in Stochastic Conway’s Game of Life

by

Krzysztof Pomorski

and

Dariusz Kotula

Condens. Matter 2023, 8(2), 47; https://doi.org/10.3390/condmat8020047 - 19 May 2023

Abstract

Cellular automata can simulate many complex physical phenomena using the power of simple rules. The presented methodological platform expresses the concept of programmable matter, of which Newton’s laws of motion are an example. Energy is introduced as the equivalent of the “Game of [...] Read more.

Cellular automata can simulate many complex physical phenomena using the power of simple rules. The presented methodological platform expresses the concept of programmable matter, of which Newton’s laws of motion are an example. Energy is introduced as the equivalent of the “Game of Life” mass, which can be treated as the first level of approximation. The temperature presence and propagation was calculated for various lattice topologies and boundary conditions, using the Shannon entropy measure. This study provides strong evidence that, despite the principle of mass and energy conservation not being fulfilled, the entropy, mass distribution, and temperature approach thermodynamic equilibrium. In addition, the described cellular automaton system transitions from a positive to a negative temperature, which stabilizes and can be treated as a signature of a system in equilibrium. The system dynamics is presented for a few species of cellular automata competing for maximum presence on a given lattice with different boundary conditions. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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Open AccessReview

Superconductors with a Topological Gap

by

Maria Cristina Diamantini

Condens. Matter 2023, 8(2), 46; https://doi.org/10.3390/condmat8020046 - 16 May 2023

Abstract

I review a new superconductivity mechanism in which the gap is opened through a topological mechanism and not through the Landau mechanism of spontaneous symmetry breaking. As a consequence, the low-energy effective theory which describes these new superconductors is not the Landau–Ginzburg theory, [...] Read more.

I review a new superconductivity mechanism in which the gap is opened through a topological mechanism and not through the Landau mechanism of spontaneous symmetry breaking. As a consequence, the low-energy effective theory which describes these new superconductors is not the Landau–Ginzburg theory, formulated in terms of a local-order parameter, but a topological-field theory formulated in terms of emerging gauge fields. This new mechanism is realized as global superconductivty in Josephson junction arrays and in thin superconducting films with thicknesses comparable to the superconducting coherence length, which exhibits emergent granularity. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

Open AccessArticle

Strong-Coupling Behavior of the Critical Temperature of Pb/Ag, Pb/Cu and Pb/Al Nanocomposites Explained by Proximity Eliashberg Theory

by

Giovanni Alberto Ummarino

Condens. Matter 2023, 8(2), 45; https://doi.org/10.3390/condmat8020045 - 12 May 2023

Abstract

The experimental critical temperature of the systems of superconducting (

P b

) and normal (

A g

,

C u

and

A l

) nanoparticles, with a random distribution and sizes less than their respective coherence lengths, is governed by the proximity [...] Read more.

The experimental critical temperature of the systems of superconducting (

P b

) and normal (

A g

,

C u

and

A l

) nanoparticles, with a random distribution and sizes less than their respective coherence lengths, is governed by the proximity effect, as shown by the experimental data. At first glance, the behavior of the variation in the critical temperature in function of the ratio of volume fractions of the superconducting and the normal metal components seems to suggest a weak coupling behavior for the superconductor. In reality, upon a more careful analysis, using Eliashberg’s theory for the proximity effect, the system instead shows a strong coupling nature. The most interesting thing is that the theory has no free parameters and perfectly explains the behavior of the experimental data just with the assumption in the case of the nanoparticles

A g

and

C u

, that the value of the density of states at the Fermi level of silver and copper is equal to the value of lead. Full article

(This article belongs to the Section Superconductivity)

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Open AccessArticle

Quadriexciton Binding Energy in Electron–Hole Bilayers

by

Cesare Malosso

,

Gaetano Senatore

and

Stefania De Palo

Condens. Matter 2023, 8(2), 44; https://doi.org/10.3390/condmat8020044 - 10 May 2023

Abstract

Excitonic condensation and superfluidity have recently received a renewed attention, due to the fabrication of bilayer systems in which electrons and holes are spatially separated and form stable pairs known as indirect excitons. Dichalcogenides- and graphene-based bilayers are nowadays built and investigated, giving [...] Read more.

Excitonic condensation and superfluidity have recently received a renewed attention, due to the fabrication of bilayer systems in which electrons and holes are spatially separated and form stable pairs known as indirect excitons. Dichalcogenides- and graphene-based bilayers are nowadays built and investigated, giving access to systems with (i) only spin degeneracy and (ii) spin and valley degeneracy. Simulation studies performed in the last decades at

T = 0

for simple, model electron–hole bilayers, as function of the interlayer distance and in-layer carrier density, have revealed in case (i) the formation of biexcitons in a tiny region of the parameter space and in case (ii) the formation of stable compounds made of four electrons and four holes (quadriexcitons) in a sizable region of the parameter space. Of some interest is the relation of the properties of isolated biexcitons (quadriexcitons) and those of their finite-density counterpart. In fact, the isolated biexciton has been repeatedly studied in the last years with simulations and other techniques. No simulations, instead, are available to our knowledge for the isolated quadriexciton, for which we present here results of the first quantum Monte Carlo (QMC) study. Stability with respect to the dissociation into biexcitons and the pair correlations while varying the interlayer distance d are discussed. Full article

(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors VII)

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Open AccessArticle

Optical Properties of Magnetic Monopole Excitons

by

Junhui Cao

and

Alexey Kavokin

Condens. Matter 2023, 8(2), 43; https://doi.org/10.3390/condmat8020043 - 09 May 2023

Abstract

Here we consider theoretically an exciton-like dipole formed by a magnetic monopole and a magnetic antimonopole. This type of quasiparticles may be formed in a magnetic counterpart of a one dimensional semiconductor crystal. We use the familiar Lorentz driven damped harmonic oscillator model [...] Read more.

Here we consider theoretically an exciton-like dipole formed by a magnetic monopole and a magnetic antimonopole. This type of quasiparticles may be formed in a magnetic counterpart of a one dimensional semiconductor crystal. We use the familiar Lorentz driven damped harmonic oscillator model to find the eigenmodes of magnetic monopole dipoles strongly coupled to light. The proposed model allows predicting optical signatures of magnetic monopole excitons in crystals. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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Open AccessArticle

Low-Lying Collective Excitations of Superconductors and Charged Superfluids

by

Serghei Klimin

,

Jacques Tempere

and

Hadrien Kurkjian

Condens. Matter 2023, 8(2), 42; https://doi.org/10.3390/condmat8020042 - 03 May 2023

Abstract

We investigate theoretically the momentum-dependent frequency and damping of low-lying collective excitations of superconductors and charged superfluids in the BCS–BEC crossover regime. The study is based on the Gaussian pair-and-density fluctuation method for the propagator of Gaussian fluctuations of the pair and density [...] Read more.

We investigate theoretically the momentum-dependent frequency and damping of low-lying collective excitations of superconductors and charged superfluids in the BCS–BEC crossover regime. The study is based on the Gaussian pair-and-density fluctuation method for the propagator of Gaussian fluctuations of the pair and density fields. Eigenfrequencies and damping rates are determined in a mutually consistent nonperturbative way as complex poles of the fluctuation propagator. Particular attention is paid to new features with respect to preceding theoretical studies, which were devoted to collective excitations of superconductors in the far BCS regime. We find that at a sufficiently strong coupling, new branches of collective excitations appear, which manifest different behavior as functions of the momentum and the temperature. Full article

(This article belongs to the Special Issue Fluctuations and Highly Non-linear Phenomena in Superfluids and Superconductors VII)

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Open AccessArticle

Features of Light-Matter Coupling in Non-Ideal Lattice of Coupled Microcavities Containing Quantum Dots

by

Vladimir V. Rumyantsev

,

Stanislav A. Fedorov

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Konstantin V. Gumennyk

and

Alexey Ye. Rybalka

Condens. Matter 2023, 8(2), 41; https://doi.org/10.3390/condmat8020041 - 02 May 2023

Abstract

In this paper, within the framework of virtual crystal approximation, the mathematical modeling of the dependence of the density of states of polariton excitations in a 1D photonic crystal—a system of pores (tunnel-coupled microresonators) containing quantum dots—on the concentration of structural defects is [...] Read more.

In this paper, within the framework of virtual crystal approximation, the mathematical modeling of the dependence of the density of states of polariton excitations in a 1D photonic crystal—a system of pores (tunnel-coupled microresonators) containing quantum dots—on the concentration of structural defects is performed. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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Open AccessArticle

Investigating the Intrinsic Anisotropy of VO₂(101) Thin Films Using Linearly Polarized Resonant Photoemission Spectroscopy

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Condens. Matter 2023, 8(2), 40; https://doi.org/10.3390/condmat8020040 - 26 Apr 2023

Abstract

VO₂ is one of the most studied vanadium oxides because it undergoes a reversible metal-insulator transition (MIT) upon heating with a critical temperature of around 340 K. One of the most overlooked aspects of VO₂ is the band’s anisotropy in the [...] Read more.

VO₂ is one of the most studied vanadium oxides because it undergoes a reversible metal-insulator transition (MIT) upon heating with a critical temperature of around 340 K. One of the most overlooked aspects of VO₂ is the band’s anisotropy in the metallic phase when the Fermi level is crossed by two bands: π* and d_||. They are oriented perpendicularly in one respect to the other, hence generating anisotropy. One of the parameters tuning MIT properties is the unbalance of the electron population of π* and d_|| bands that arise from their different energy position with respect to the Fermi level. In systems with reduced dimensionality, the electron population disproportion is different with respect to the bulk leading to a different anisotropy. Investigating such a system with a band-selective spectroscopic tool is mandatory. In this manuscript, we show the results of the investigation of a single crystalline 8 nm VO₂/TiO₂(101) film. We report on the effectiveness of linearly polarized resonant photoemission (ResPES) as a band-selective technique probing the intrinsic anisotropy of VO₂. Full article

(This article belongs to the Special Issue Superstripes Physics)

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Open AccessArticle

Superconducting Stiffness and Coherence Length of FeSe_0.5Te_0.5 Measured in a Zero-Applied Field

by

Amotz Peri

,

Itay Mangel

and

Amit Keren

Condens. Matter 2023, 8(2), 39; https://doi.org/10.3390/condmat8020039 - 23 Apr 2023

Abstract

Superconducting stiffness

ρ_{s}

and coherence length

ξ

are usually determined by measuring the penetration depth

λ

of a magnetic field and the upper critical field

H_{c 2}

of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could [...] Read more.

Superconducting stiffness

ρ_{s}

and coherence length

ξ

are usually determined by measuring the penetration depth

λ

of a magnetic field and the upper critical field

H_{c 2}

of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could lead to erroneous results, since the internal field could be very different from the applied one. To overcome this problem in Fe

_{1 + y}

Se

_{x}

Te

_{1 - x}

with

x \sim 0.5

and

y \sim 0

(FST), we measured both quantities with the Stiffnessometer technique. In this technique, one applies a rotor-free vector potential

A

to a superconducting ring and measures the current density

j

via the ring’s magnetic moment

m

.

ρ_{s}

and

ξ

are determined from London’s equation,

j = - ρ_{s} A

, and its range of validity. This method is particularly accurate at temperatures close to the critical temperature

T_{c}

. We find weaker

ρ_{s}

and longer

ξ

than existing literature reports, and critical exponents which agree better with expectations based on the Ginzburg–Landau theory. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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Open AccessArticle

Anodic Potential and Conversion Chemistry of Anhydrous Iron (II) Oxalate in Na-Ion Batteries

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Condens. Matter 2023, 8(2), 38; https://doi.org/10.3390/condmat8020038 - 23 Apr 2023

Abstract

Anhydrous ferrous (II) oxalate (AFO) outperforms its hydrated form when used as an anode material in Li-ion batteries (LIBs). With the increasing interest in Na-ion batteries (NIBs) in mind, we examine the potential of AFO as the anode in NIBs through first principles [...] Read more.

Anhydrous ferrous (II) oxalate (AFO) outperforms its hydrated form when used as an anode material in Li-ion batteries (LIBs). With the increasing interest in Na-ion batteries (NIBs) in mind, we examine the potential of AFO as the anode in NIBs through first principles calculations involving both periodic and non-periodic structures. Our analysis based on periodic (non-periodic) modeling scheme shows that the AFO anode generates a low reaction potential of 1.22 V (1.45 V) in the NIBs, and 1.34 V (1.24 V) in the LIBs, which is much lower than the potential of NIBs with mixed oxalates. The conversion mechanism in the underlying electrochemical process involves the reduction of Fe

^{2 +}

with the addition of Na or Li. Such conversion electrodes can achieve high capacities through the Fe

^{2 +}

valence states of iron. Full article

(This article belongs to the Special Issue Rechargeable Batteries Studied Using Advanced Spectroscopic and Computational Techniques II)

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Open AccessReview

Advanced Boron Carbide Matrix Nanocomposites Obtained from Liquid-Charge: Focused Review

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Condens. Matter 2023, 8(2), 37; https://doi.org/10.3390/condmat8020037 - 20 Apr 2023

Abstract

Boron carbide is known as a hard material; it possesses a unique complex of physical-mechanical properties and has diverse applications in industries. An expansion of its field of uses stems from the creation of boron carbide matrix nanocomposite materials. In view of this [...] Read more.

Boron carbide is known as a hard material; it possesses a unique complex of physical-mechanical properties and has diverse applications in industries. An expansion of its field of uses stems from the creation of boron carbide matrix nanocomposite materials. In view of this perspective, an effective liquid-charge synthesizing method for their components in nanopowder form has been proposed. This paper provides a focused review on advanced boron carbide matrix ceramic and metal-ceramic nanocomposites recently obtained by the authors using this method. Particular attention is paid to the characterization of boron carbide nanocomposites, including some ceramic borides, metallic alloys and also other metal-ceramic composites. Full article

(This article belongs to the Special Issue Advances in Nanocomposite Materials)

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Open AccessArticle

Superconducting Diode Effect in Topological Hybrid Structures

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Condens. Matter 2023, 8(2), 36; https://doi.org/10.3390/condmat8020036 - 14 Apr 2023

Abstract

Currently, the superconducting diode effect (SDE) is being actively discussed, due to its large application potential in superconducting electronics. In particular, superconducting hybrid structures, based on three-dimensional (3D) topological insulators, are among the best candidates, due to their having the strongest spin–orbit coupling [...] Read more.

Currently, the superconducting diode effect (SDE) is being actively discussed, due to its large application potential in superconducting electronics. In particular, superconducting hybrid structures, based on three-dimensional (3D) topological insulators, are among the best candidates, due to their having the strongest spin–orbit coupling (SOC). Most theoretical studies on the SDE focus either on a full numerical calculation, which is often rather complicated, or on the phenomenological approach. In the present paper, we compare the linearized and nonlinear microscopic approaches in the superconductor/ferromagnet/3D topological insulator (S/F/TI) hybrid structure. Employing the quasiclassical Green’s function formalism we solve the problem self-consistently. We show that the results obtained by the linearized approximation are not qualitatively different from the nonlinear solution. The main distinction in the results between the two methods was quantitative, i.e., they yielded different supercurrent amplitudes. However, when calculating the so-called diode quality factor the quantitative difference is eliminated and both approaches result in good agreement. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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Open AccessProject Report

Effects of Focused Ion Beam Lithography on La_2−xSr_xCuO₄ Single Crystals

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Condens. Matter 2023, 8(2), 35; https://doi.org/10.3390/condmat8020035 - 13 Apr 2023

Abstract

Focused ion beam (FIB) milling is a mask-free lithography technique that allows the precise shaping of 3D materials on the micron and sub-micron scale. The recent discovery of electronic nematicity in La_2−xSr_xCuO₄ (LSCO) thin films triggered the [...] Read more.

Focused ion beam (FIB) milling is a mask-free lithography technique that allows the precise shaping of 3D materials on the micron and sub-micron scale. The recent discovery of electronic nematicity in La_2−xSr_xCuO₄ (LSCO) thin films triggered the search for the same phenomenon in bulk LSCO crystals. With this motivation, we have systematically explored FIB patterning of bulk LSCO crystals into micro-devices suitable for longitudinal and transverse resistivity measurements. We found that several detrimental factors can affect the result, ultimately compromising the possibility of effectively using FIB milling to fabricate sub-micrometer LSCO devices, especially in the underdoped regime. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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Open AccessArticle

Plasma-Assisted Nitrogen Doping of Langmuir–Blodgett Self-Assembled Graphene Films

by

Tijana Tomašević-Ilić

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Condens. Matter 2023, 8(2), 34; https://doi.org/10.3390/condmat8020034 - 04 Apr 2023

Abstract

Graphene films prepared from solution and deposited by Langmuir–Blodgett self-assembly technique (LBSA) were treated with radio-frequency (13.56 MHz) nitrogen plasma in order to investigate the influence of the time of nitrogen plasma exposure on the work function, sheet resistance, and surface morphology of [...] Read more.

Graphene films prepared from solution and deposited by Langmuir–Blodgett self-assembly technique (LBSA) were treated with radio-frequency (13.56 MHz) nitrogen plasma in order to investigate the influence of the time of nitrogen plasma exposure on the work function, sheet resistance, and surface morphology of LBSA graphene films. Kelvin probe force microscopy and sheet resistance measurements confirm nitrogen functionalization of our films, with the Fermi level shifting in a direction that indicates binding to a pyridinic and/or pyrrolic site. Upon 1 min of nitrogen plasma exposure, the sheet resistance decreases and there is no obvious difference in film morphology. However, plasma exposure longer than 5 min leads to the removal of graphene flakes and degradation of graphene films, in turn, affecting the flake connectivity and increasing film resistance. We show that by changing the exposure time, we can control the work function and decrease sheet resistance, without affecting surface morphology. Controllability of the plasma technique has an advantage for graphene functionalization over conventional doping techniques such as chemical drop-casting. It allows for the controllable tuning of the work function, surface morphology, and sheet resistance of LBSA graphene films, which is substantial for applications in various optoelectronic devices. Full article

(This article belongs to the Section Surface and Interfaces)

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Open AccessArticle

Elucidation of Spin-Correlations, Fermi Surface and Pseudogap in a Copper Oxide Superconductor

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Condens. Matter 2023, 8(2), 33; https://doi.org/10.3390/condmat8020033 - 04 Apr 2023

Abstract

First-principles calculations for underdoped La_2−xSr_xCuO₄ (LSCO) have revealed a Fermi surface consisting of spin-triplet (KS) particles at the antinodal Fermi-pockets and spin-singlet (SS) particles at the nodal Fermi-arcs in the presence of AF local order. By performing [...] Read more.

First-principles calculations for underdoped La_2−xSr_xCuO₄ (LSCO) have revealed a Fermi surface consisting of spin-triplet (KS) particles at the antinodal Fermi-pockets and spin-singlet (SS) particles at the nodal Fermi-arcs in the presence of AF local order. By performing a unique method of calculating the electronic-spin state of overdoped LSCO and by measurement of the spin-correlation length by neutron inelastic scattering, the origin of the phase-diagram, including the pseudogap phase in the high temperature superconductor, Sr-doped copper-oxide LSCO, has been elucidated. We have theoretically solved the long-term problem as to why the angle-resolved photoemission spectroscopy (ARPES) has not been able to observe Fermi pockets in the Fermi surface of LSCO. As a result, we show that the pseudogap region is bounded below the characteristic temperature T*(x) and above the superconducting transition temperature T_c(x) in the T vs. x phase diagram, where both the AF order and the KS particles in the Fermi pockets vanish at T*(x), whilst KS particles contribute to d-wave superconductivity below T_c. We also show that the relationship T*(x_c) = T_c(x_c) holds at x_c = 0.30, which is consistent with ARPES experiments. At T*(x), a phase transition occurs from the pseudogap phase to an unusual metallic phase in which only the SS particles exist. Full article

(This article belongs to the Special Issue Spin Dynamics in Magnetic Materials: Spin Resistivity, Spin Waves, Spin-Orbit Coupling, Phase Transition)

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Open AccessArticle

Angle-dependent Magnetoresistance of an Ordered Bose Glass of Vortices in YBa₂Cu₃O_7-δ Thin Films with a Periodic Pinning Lattice

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Condens. Matter 2023, 8(2), 32; https://doi.org/10.3390/condmat8020032 - 27 Mar 2023

Abstract

The competition between intrinsic disorder in superconducting YBa

_{2}

Cu

_{3}

O

_{7 - δ}

(YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples [...] Read more.

The competition between intrinsic disorder in superconducting YBa

_{2}

Cu

_{3}

O

_{7 - δ}

(YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples were created by scanning the focused beam of a helium-ion microscope over the surface of the YBCO thin film to form columns of point defects where superconductivity was locally suppressed. The voltage–current isotherms reveal critical behavior and scale in the vicinity of the second-order glass transition. The latter exhibits a distinct peak in melting temperature (

T_{g}

) vs. applied magnetic field (

B_{a}

) at the magnetic commensurability field, along with a sharp rise in the lifetimes of glassy fluctuations. Angle-dependent magnetoresistance measurements in constant-Lorentz-force geometry unveil a strong increase in anisotropy compared to a pristine reference film where the density of vortices matches that of the columnar defects. The pinning is therefore, dominated by the magnetic-field component parallel to the columnar defects, exposing its one-dimensional character. These results support the idea of an ordered Bose glass phase. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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Open AccessArticle

Pump-Probe X-ray Photoemission Spectroscopy of Free-Standing Graphane

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Condens. Matter 2023, 8(2), 31; https://doi.org/10.3390/condmat8020031 - 27 Mar 2023

Abstract

Free-standing nanoporous graphene was hydrogenated at about 60 at.% H uptake, as determined by the emerging of the sp³ bonding component in the C 1s core level investigated by high-resolution X-ray photoelectron spectroscopy (XPS). Fully unsupported graphane was investigated by XPS under [...] Read more.

Free-standing nanoporous graphene was hydrogenated at about 60 at.% H uptake, as determined by the emerging of the sp³ bonding component in the C 1s core level investigated by high-resolution X-ray photoelectron spectroscopy (XPS). Fully unsupported graphane was investigated by XPS under optical excitation at 2.4 eV. At a laser fluence of 1.6 mJ/cm², a partial irreversible dehydrogenation of the graphane was observed, which could be attributed either to the local temperature increase or to a photo-induced softening of the H-to-C stretching mode. The sub-ns dynamics of the energy shift and peak broadening of the C 1s core level revealed two different decay constants: 210 ps and 130 ps, respectively, the former associated with photovoltage dynamics and the latter with thermal heating on a time scale comparable with the synchrotron temporal resolution. Full article

(This article belongs to the Special Issue Experimental Ideas for Novel FEL Facilities Based on Plasma Acceleration)

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