The quantitative evaluation of the carbon hybridization state by x-ray photoelectron spectroscopy (XPS) has been a surface-analysis problem for the last three decades due to the challenges associated with the unambiguous identification of the characteristic binding energy values for ${\mathrm{sp}}^2$- and ${\mathrm{sp}}^3$-bonded carbon. Here, we computed the binding energy values of C(1s) core electrons on the absolute energy scale for model structures of amorphous carbon (a-C) using density functional theory (DFT). The DFT calculations show that in the case of hydrogen-free a-C, the C(1s) binding energy for ${\mathrm{sp}}^3$ carbon atoms is a distribution found approximately 1 eV higher than the binding energy distribution of ${\mathrm{sp}}^2$-hybridized carbons. However, the introduction of hydrogen in the a-C network reduces the distance between the characteristic signals of ${\mathrm{sp}}^3$- and ${\mathrm{sp}}^2$-bonded carbon due to the increased ability to screen the core hole by neighboring hydrogen atoms as compared to carbon atoms. This effect hinders the unambiguous quantification of the carbon hybridization state on the basis of C(1s) XPS data alone. This work can assist surface scientists in the use of XPS for the accurate characterization of carbon-based materials.

It is well known that thermal and mechanical properties are the key physical parameters of deep-ultraviolet (DUV) light sources materials, and play critical roles in practical applications. In this work, the thermal conductivity, thermal expansion coefficient, and mechanical performance of newly predicted DUV materials are systematically investigated by means of neuroevolution potential (NEP) combined molecular dynamics (MD) simulation. Both equilibrium molecular dynamics (EMD) and homogeneous nonequilibrium molecular dynamics (HNEMD) calculations demonstrate that the ${\mathrm{BeGeN}}_2$ hosts the best thermal transport performance with $39.4{\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$ at room temperature, among the five DUV light-emitting candidates (i.e., ${\mathrm{BeGeN}}_2, {\mathrm{Mg}}_3{\mathrm{NF}}_3,{\mathrm{KCaBr}}_3$, KHS, and RbHS). Significant boosted thermal conductivity (about 104 ${\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$) could be further observed in compressive ${\mathrm{BeGeN}}_2$ with $3\%$ strain, implying the ability of ${\mathrm{BeGeN}}_2$ to address the severe heat dissipation issue in DUV optoelectronic devices. By performing phonon spectral energy density analysis, we reveal that such enhancement of thermal conductivity mainly originates from the increased phonon lifetime in the low-frequency region. Meanwhile, our calculations also show that the coefficient of thermal expansion of ${\mathrm{BeGeN}}_2$ is merely $25.87\times {10}^{-6}/\mathrm{K}$, the corresponding Pugh modulus ratio (G/B), and the Vickers hardness are, respectively, 0.719 and 22.239 GPa. The findings presented in this work authenticate that the ${\mathrm{BeGeN}}_2$ possesses a high thermal conductivity and stable mechanical properties, foreshowing the great potential in DUV light-emitting field applications.

Quaternary oxychlorides derived from Ruddlesden–Popper $3d$ transition metal oxides offer a route to cleavable crystals with bulk antiferromagnetic ordering temperatures reaching at least 550 K. Here, we study the magnetic, optical, and mechanical behavior of ${\mathrm{Sr}}_2{\mathrm{FeO}}_3\mathrm{Cl}$, ${\mathrm{Ca}}_2{\mathrm{FeO}}_3\mathrm{Cl}$, ${\mathrm{Ca}}_3{\mathrm{Fe}}_2{\mathrm{O}}_5{\mathrm{Cl}}_2$, and ${\mathrm{Sr}}_3{\mathrm{Fe}}_2{\mathrm{O}}_5{\mathrm{Cl}}_2$. Through optical absorption measurements, we show that these antiferromagnetic semiconductors have optical band gaps of $\approx 2.1\left(1\right)\mathrm{eV}$. The magnetic ordering symmetries and temperatures were probed by neutron powder diffraction and Mössbauer spectroscopy on polycrystalline samples, demonstrating Néel temperatures $\left(T_{\mathrm{N}}\right)$ near room temperature in the single layer ${\mathrm{Sr}}_2{\mathrm{FeO}}_3\mathrm{Cl}$ $(T_{\mathrm{N}}\approx 311\mathrm{K})$ and ${\mathrm{Ca}}_2{\mathrm{FeO}}_3\mathrm{Cl}$ $(T_{\mathrm{N}}\approx 360\mathrm{K})$, and the double-layer compound ${\mathrm{Sr}}_3{\mathrm{Fe}}_2{\mathrm{O}}_5{\mathrm{Cl}}_2$ has $T_{\mathrm{N}}\approx 545\mathrm{K}$. The high-spin moments of ${\mathrm{Fe}}^{3+}$ lie within the basal plane and the magnetic structures are compensated within each magnetic layer and characterized by magnetic propagation vectors $\mathit{k}=\left(\frac{1}{2}\frac{1}{2}0\right)$. Magnetization results demonstrate the quasi-2D nature of the magnetism, with a broad maximum in the susceptibility near $2T_{\mathrm{N}}$ for ${\mathrm{Sr}}_2{\mathrm{FeO}}_3\mathrm{Cl}$. Scotch tape tests and mechanical exfoliation onto ${\mathrm{SiO}}_2$ confirm the micaceous nature of these crystals with cleavage down to a single unit cell (two magnetic layers) achieved for ${\mathrm{Sr}}_3{\mathrm{Fe}}_2{\mathrm{O}}_5{\mathrm{Cl}}_2$. This paper highlights strong antiferromagnetic interactions, semiconducting band gaps, and cleavability of quaternary Fe-based oxychlorides and motivates future work on crystals and exfoliated flakes of these and related oxyhalide systems.

Intermetallic compounds have shown promising catalytic properties, exhibiting better selectivity and thermal stability than their metallic counterparts. Understanding their surface properties is crucial for optimizing catalytic performance. Here, we present an investigation of the atomic structure, chemical composition, and oxidation behavior of the previously unexplored binary intermetallic catalyst, ${\mathrm{Ni}}_2{\mathrm{In}}_3$, using various complementary techniques, including low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and low-energy ion scattering (LEIS), which provides elemental information from the topmost surface layer. We also calculated the surface energy of several possible bulk-terminated surfaces by density functional theory (DFT) to investigate surface stability. The ${\mathrm{Ni}}_2{\mathrm{In}}_3$(100) surface was prepared by ion bombardment and annealing under ultrahigh vacuum conditions. We find that ion bombardment preferentially removes indium (In), while annealing promotes In segregation to the surface. After annealing, the surface exhibits a $(1\times 1)$ LEED pattern. The surface develops a three-domain $\mathrm{c}(2\sqrt{3}\times 4)$ rectangular structure upon exposure to ambient hydrogen present in the experimental chamber or hydrogen dosed from an external source, as evidenced by both STM and LEED. Both nickel (Ni) and In oxidize upon exposure to molecular oxygen. Based on STM and LEIS results along with surface energy calculations, we reveal that the surface planes contain In atoms bonded with Ni, the catalytically active constituent, suggesting that the surface may be stabilized by intermetallic bonding.

The alleged existence of sluggish diffusion in high-entropy alloys has drawn controversy. In high-entropy alloys and, in general, in all solids, transport properties are controlled by point defect concentration, which must be known before performing atomistic simulations to compute transport coefficients. In this work, we present a general Langmuir-like model for defect concentration in an arbitrarily complex solid solution and apply this model to generate expressions for concentrations of vacancies and small interstitial atoms. We then calculate the vacancy concentration as a function of temperature in the equiatomic CoNiCrFeMn and FeAl alloys with modified embedded-atom-method potentials for various chemical orderings, showing there is no clear correlation between vacancy thermodynamics and chemical ordering in the CoNiCrFeMn alloy, but clear systematic patterns for FeAl. We believe this is due to the high stability of disordered, random, and ordered intermetallic phases, respectively, in the CoNiCrFeMn and FeAl systems. This work provides future avenues to the prediction of thermal interstitials and vacancies in solid solutions, which is necessary for models of nonequilibrium behavior of solid solutions.

Spatially homogeneous elemental distributions in vapor-liquid-solid or catalyst-free III-V ternary nanowires based on group III intermix is the exception rather than the rule. Herein, we develop the nanowire growth theory by combining the material transport equations and the minimum energy principle for the liquid-solid or vapor-solid growth on the top facet of III-V ternary nanowires $A_x{B}_{1-x}C$. These considerations lead to a general vapor-solid distribution whose governing parameters depend on the nanowire length and radius due to surface diffusion of group III adatoms. We reveal the two competing effects on the vapor-solid distribution. One effect is related to different diffusion lengths of group III adatoms A and B, and it favors incorporation of an element A with a longer diffusion length (for example, In in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ or Ga in ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$) toward the nanowire top. The other effect originates from gradually decreasing the effective V/III ratio of fluxes entering a catalyst droplet, and it favors near-equilibrium vapor-solid distributions. Length-dependent surface diffusion of group III adatoms decreases the effective V/III ratios in nanowires based on group III intermix and increases it in nanowires based on group V intermix. Consequently, the compositional trends in such nanowires are very different. The model fits well a wide range of data on the elemental distributions in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$, ${\mathrm{Al}}_{1-x}{\mathrm{Ga}}_x\mathrm{As}$ and ${\mathrm{In}}_{1-x}{\mathrm{Sb}}_x\mathrm{As}$ nanowires. The simple analytic vapor-solid distribution may be used for the compositional tuning of different nanowires. The concept of a single ternary nucleus forming at the minimum free energy for a given size generalizes the earlier models of the nucleation-limited composition, and it may be useful in the compositional modeling of a wide range of nanostructures.

The binary manganese aluminum (MnAl) alloy with $\mathrm{L}{1}_0$ crystal structure is a promising rare earth (RE) element-free permanent magnetic material because of its exceptional magnetic properties. However, experimentally synthesizing it in a stable bulk form is extremely challenging. Here, an alternative method of stabilizing the material, a pathway for experimental synthesis and validation, is proposed and theoretically verified. This is done by partially substituting Mn and Al sites with Fe and Ni and identifying its enhanced phase stability, saturation magnetization density, magnetic anisotropy, and coercivity from density functional theory (DFT), machine learning (ML) crystal graph convolution neural network (CGCNN), and micro-magnetic modeling. When considering a fixed $50\%$ Ni, the magnetic anisotropy increases with the increasing Fe content but decreases the formation energy. The calculated formation energies, elastic constants, and phonon frequencies demonstrate that the binary and quaternary compositions are stable. Most importantly, in $50\%$ Fe and Ni-substituted-equiatomic phase, magnetic anisotropy constants and saturation magnetization density increase by 56% and 23% as compared to the MnAl. Further, the coercivity of the equiatomic phase predicted with micro-magnetic modeling is higher by 17% than the parent compound.

The structural, electronic, and magnetic properties of one-dimensional (1D) $\mathrm{Mo}{X}_3$ ($X=\mathrm{Br}$,I) atomic chains (ACs), as well as their sensitivity to strain, carrier doping, and optical excitation, were comprehensively investigated using first-principles calculations and the tight-binding approximation. These 1D $\mathrm{Mo}{X}_3$ ACs, characterized by alternating Mo-Mo dimers, exhibit semiconducting behavior and a staggered antiferromagnetic (AFM) state, arising from the robust AFM direct exchange. The magnetocrystalline anisotropy energies are 1.079 meV/Mo for $\mathrm{Mo}{\mathrm{Br}}_3$ and 1.031 meV/Mo for $\mathrm{Mo}{\mathrm{I}}_3$. Fully noncollinear magnetic calculations reveal that magnetic spirals with helical angles $\theta =2\pi /n(n=\pm 2,\pm 3,\pm 4,\cdots ,\pm \infty$) possess higher energy than the collinear AFM state, confirming the AFM state as the ground state. Under tensile strain, structural transitions occur at 12% for $\mathrm{Mo}{\mathrm{Br}}_3$ and 6.5% for $\mathrm{Mo}{\mathrm{I}}_3$, with remarkable superelasticity up to 36% for $\mathrm{Mo}{\mathrm{Br}}_3$ and 38% for $\mathrm{Mo}{\mathrm{I}}_3$ before structural failure. Furthermore, carrier doping facilitates an AFM-to-FM phase transition, enabling 100% spin polarization. The lowest energy excitation involves domain walls with an energy of $\sim 0.17$ eV, readily achievable through moderate doping of optically excited electron-hole pairs. These findings provide profound insights into the electronic and magnetic characteristics of 1D $\mathrm{Mo}{X}_3$ ACs, highlighting their significant potential for applications in spintronic and wearable flexible electronic devices.

At temperature $T=293\mathrm{K}$, the crystal structure of ${\mathrm{CoIn}}_2$ is characterized by linear chains of equidistant Co atoms, but these chains undergo pairwise dislocation via Peierls distortion at some $T>90\mathrm{K}$ [Z. Kristallogr. 237, 239 (2022)]. Recently published differential scanning calorimetry measurements revealed at least two intervening thermodynamic effects near $T_1=194\left(1\right)\mathrm{K}$ and $T_2=206\left(2\right)\mathrm{K}$ but did not clarify how these features were related to the structural distortion or distortions. In the present paper, we report a suite of measurements on high-quality single crystals of ${\mathrm{CoIn}}_2$. We observe clear signatures of both transitions in $T$-dependent measurements of heat capacity, electrical resistivity, and dc magnetization. Moreover, we find a new crystal structure with polar orthorhombic space group $Fdd2$ to reside between the two transitions at $T=198\left(2\right)\mathrm{K}$. Like the high-$T$ structure, the lattice of this intermediate-$T$ structure remains characterized by a single intrachain Co-Co distance $d_{\mathrm{Co}-\mathrm{Co}}=2.69324\left(10\right)\AA$, but sparse $\mathcal{O}(1\%)$ structural disorder is resolved by the formation of a structural modulation with propagation vector $\mathbf{q}=(0,\delta ,0), \delta =0.23\pm 0.02$ oriented in a direction perpendicular to the Co-Co chains. We discuss the results in light of the potential onset of a charge density wave state above the Peierls distortion.

${\mathrm{CuSn}\left(\mathrm{OH}\right)}_6$ is a quantum spin system from the family of magnetic double perovskite hydroxides, having a frustrated magnetic sublattice. It is also known as the natural mineral mushistonite, whose crystal structure has remained elusive for decades. Here we employ x-ray and neutron powder diffraction to solve the crystal structure of ${\mathrm{CuSn}\left(\mathrm{OH}\right)}_6$ and propose a structure model in the orthorhombic space group $Pnnn$ with correlated proton disorder. The occupation of the hydrogen sites in the structure is constrained by “ice rules” similar to those known for water ice, albeit with only local correlations. The resulting frustration of the hydrogen bonding network is likely to have a complex and interesting interplay with the strong magnetic frustration expected in the face-centered magnetic sublattice. Structural distortions, which are quite pronounced in ${\mathrm{Cu}}^{2+}$ compounds due to the Jahn-Teller effect, partially alleviate both types of frustration. We also show that hydrostatic pressure tends to suppress proton disorder through a sequence of proton-ordering transitions, as some of the split hydrogen sites merge already at 1.75 GPa while others show a tendency toward possible merging at higher pressures.

A novel material consisting of a monolayer of ${\mathrm{C}}_{60}$ buckyballs with hexagonal symmetry has recently been observed experimentally, named graphullerene. In this study, we present a comprehensive ab initio theoretical analysis of the electronic and optical properties of both pristine and impurity-engineered monolayer graphullerene using spin-dependent density functional theory (spin-DFT). Our findings reveal that graphullerene is a direct band gap semiconductor with a band gap of approximately 1.5 eV at the $\mathrm{\Gamma }$ point, agreeing well with experimental data. Notably, we demonstrate that adding impurities, in particular substitutional nitrogen, substitutional boron, or adsorbent hydrogen, to graphullerene results in the formation of spin-dependent deep donor and deep acceptor levels, thereby giving rise to a variety of half-semiconductors. Using an Ising-type Hamiltonian, we attribute the spin-dependent impurity band splittings to a strong exchange interaction of about 0.6 eV for N, 0.8 eV for B, and 1.0 eV for H between the impurity/adatom spin and the total angular momentum of the electrons in the surrounding carbon atoms in graphullerene. All the impurities exhibit a magnetic moment of approximately ${\mu }_B$ per impurity. This impurity engineering enables the tuning of spin-polarized exciton properties in graphullerene, with spin-dependent band gap energies ranging from 0.43 eV ($\lambda \sim 2.9\mu \mathrm{m}$) to 1.5 eV ($\lambda \sim 820$ nm), covering the near-infrared (NIR) and short-wavelength infrared (SWIR) regimes. Our results suggest that both pristine and impurity-engineered graphullerene have significant potential for the development of carbon-based 2D semiconductor spintronic and opto-spintronic devices.

The tuning of magnetic properties through electrochemical loading of hydrogen has recently attracted significant interest as a way to manipulate magnetic devices with electric fields. In this paper we investigate quantitatively the magneto-ionic effect of hydrogen uptake on the magnetic properties of rare-earth transition-metal alloy ${\mathrm{Tb}}_x{\mathrm{Co}}_{(100-x)}$ in the composition range of $x=10-39$ at.% using ion implantation. Using this technique we are able to link changes in magnetic behavior to exact concentrations of hydrogen, isolated from the movement of any other ions that would be a factor in electrochemical studies. The composition of the alloy has been varied alongside the hydrogen dose to characterize the effect of progressive hydrogen loading on the full range of $x$ displaying out-of-plane magnetic anisotropy. We find large changes in two important properties: the compensation composition and the Co-rich in-plane to out-of-plane magnetic anisotropy transition composition, both of which move by 6 at.% toward higher Tb concentrations after hydrogen implantation. This shift in composition does not increase with a larger dose. From the changes in magnetization we attribute the change in compensation composition to a significant reduction of the moment on the Tb sublattice.

We have demonstrated the existence of the Morin transition in epitaxially grown hematite thin films exceeding a critical thickness. The Morin transition temperature can be suppressed by magnetic fields applied both parallel and perpendicular to the Dzyaloshinskii-Moriya (DM) vector, exhibiting a distinct anisotropic behavior that is consistent with bulk hematite crystals. Detailed analysis explains the anisotropic behavior and provides a method for determining the DM strength, which remains nearly constant across the sample thickness over four orders of magnitude. Our findings obtained with transport measurements offer a valuable approach for studying antiferromagnetic spin configurations in thin films and nanodevices.

We studied a phase change from a Mott insulating state to a metallic state in the series of ${\mathrm{V}}_{1-x}{\mathrm{Nb}}_x\mathrm{O}$ ($0\le x\le 1$) with an NaCl structure. We found an intermediate state near the insulator-metal phase boundary, which is characterized by a metallic behavior in the resistivity, a Curie-Weiss behavior and a low-temperature ($T<10\mathrm{K}$) anomaly in the magnetic susceptibility, and a small Drude weight in the optical conductivity. Partial ordering of V/Nb and O defects is likely to cause such an intermediate state. We also studied ${\mathrm{V}}_{1-x}{\mathrm{Ti}}_x\mathrm{O}$ ($0\le x\le 0.2$) and found that they exhibit a behavior different from that of ${\mathrm{V}}_{1-x}{\mathrm{Nb}}_x\mathrm{O}$.

High-magnetization ferromagnets play a crucial role in advancing spintronics, magnetic sensing, and high-density data storage technologies. Fe–Co–Ir alloys, previously identified through machine learning to potentially surpass the Slater-Pauling limits for transition-metal magnets, present a valuable platform for uncovering the mechanisms behind their enhanced magnetic properties. This study investigates the influence of Ir doping on the element-specific magnetic moments by high-throughput x-ray magnetic circular dichroism (XMCD) techniques using both soft and hard x-rays on Fe–Co–Ir single-crystal composition-spread thin films. A single-crystal composition-spread thin film of ${\left(\mathrm{F}{\mathrm{e}}_{75}\mathrm{C}{\mathrm{o}}_{25}\right)}_{100-x}\mathrm{I}{\mathrm{r}}_x$ ($x=0\text{–}11$ at%) was fabricated on a MgO(100) substrate using a combinatorial sputtering technique, enabling a systematic analysis of compositional variations. XMCD measurements revealed that Ir doping enhances the magnetic moments of Fe, Co, and Ir, with a particular emphasis on the orbital contribution of Fe and Ir. These experimental findings are supported by ab initio calculations, which highlight increased electron localization and stronger spin-orbit coupling between Ir $5d$ electrons and Fe/Co $3d$ electrons as the primary mechanisms behind the enhanced magnetization. This study provides a deeper understanding of the electronic and magnetic moments in Fe–Co–Ir alloys, offering valuable insights for the development of next-generation ferromagnetic materials optimized for advanced technological applications.