We investigate the initial stages of oxidation in siligene, a two-dimensional nanomaterial made of silicon (Si) and germanium (Ge) honeycomb lattice systems, using first-principles calculations. Our results show that a single oxygen atom preferentially adsorbs at epoxy sites between Si and Ge atoms, independent of whether the surface is Si- or Ge-terminated. When an oxygen molecule interacts with siligene, the dissociation into two separate O atoms is energetically favored. In the most stable configuration, oxygen atoms remain in epoxy positions but bond to the same Si atom with one O atom on each side of the siligene sheet. Furthermore, we explore the formation of an oxidized siligene 2D system by considering various oxygen coverages and structural arrangements. Among the tested configurations, two of them were found to be stable. They consist of bilayers of SiO3Ge, coupled with and without O atoms, forming Si2O8Ge2 and Si2O6Ge2 structures, respectively. The electronic properties of these siligene oxide 2D systems show large band gaps and therefore can be applied in power electronics, optoelectronics, high-frequency communications, and radiation-resistant devices due to their ability to operate at higher temperatures, voltages, and frequencies than silicon. Furthermore, the atomic elements and structural cavities in siligene oxides make them promising candidates for trapping ions and small molecules for next-generation sensing materials applications.

The oxygen reduction reaction (ORR) is a key process in energy conversion and storage technologies, and graphene-based materials have emerged as promising alternatives to platinum-based catalysts. In this work, density functional theory (DFT) is employed to investigate the effects of atomic vacancies, pentagonal rings, and nitrogen doping on the ORR mechanism in graphene. A toolkit of twenty-four graphene pore models is constructed to explore a range of pore sizes and assess their structural stability. From this set, three representative models are selected for an in-depth analysis of the ORR mechanism, focusing on their reactivity during oxygen adsorption, dissociation, and subsequent hydrogenation processes. Our results show that vacancies and pentagonal rings promote O2 adsorption and facilitate its dissociation, while increasing pore size reduces structural stability. In contrast, nitrogen doping primarily stabilizes the graphene framework but suppresses O2 chemisorption due to electronic effects. These findings provide atomistic insights into the role of defect engineering in graphene and contribute to the rational design of carbon-based electrocatalysts.

N‐doped carbon nanostructures have gained attention as an alternative electrocatalyst for diverse reactions. They are making attractive the scalable methods to achieve enough material. However, optimizing the appropriate nitrogen species in the N‐doped graphitic electrocatalysts is critical. Here, the N‐doping process to obtain N‐doped graphene starting from graphene oxide (GO) as the precursor to contributing toward this goal is explored. The role of doping temperatures and doping times on nitrogen incorporation into the graphene sheets, the subsequent desorption, and the influence of the oxygen (O) species from the GO during the N‐doping process are analyzed. The experimental evidence is combined with first‐principles density functional theory calculations to understand key characteristics of the N‐doping process, particularly emphasizing the proportion of N species obtained. Finally, the critical sensitivity to N species proportions present in the electrocatalysts is illustrated by evaluating the activity and selectivity for the oxygen reduction reaction with a set of three different samples designed.

This study investigates the influence of transition metal magnetic moments on the adsorption and reactivity of molecular oxygen (O2) in nitrogen-doped graphene-supported single-atom catalyst systems using density functional theory calculations. We demonstrate that metals with higher magnetic moments, such as Cr and Mn, exhibit enhanced affinity and stabilization of O2 adsorption. In contrast, metals with lower or null magnetic moments, like Ni and Cu, show diminished capability to adsorb O2 effectively. Our analysis of adsorption energies, Morse potential depths, and reaction force underscores the critical role of transition metal magnetic moments in dictating catalytic performance and characterizing the nature of the chemical bond between the metal center and oxygen. It has been found that the strength of the oxygen-metal bond as well as its electronic activity are crucial elements that can be used to enhance the catalytic effect in capturing O2. This provides insights for optimizing single-atom catalysts (SACs) in oxygen reduction reactions and other energy conversion applications.

Janus monolayers are two-dimensional materials with distinct chemical compositions on their opposing sides, leading to unique properties and potential applications in various fields. Based on density functional theory (DFT) calculations, we have explored the dynamic stability of a family of Janus monolayers with the general formula TMCSe (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn). Only two explored systems were dynamically and thermal stable: CrCSe and MnCSe, as evidenced by their phonon dispersion curves and molecular dynamics calculations. Their electronic properties and magnetic character have been investigated using their corresponding density of states. The CrCSe monolayer is a 0.4 eV indirect semiconductor, and the magnetic MnCSe monolayer is spin-up metallic and a spin-down semimetal. Electrostatic potential isosurfaces are used to assess the reactivity of the stable monolayers. They indicate that the surfaces of the TMCSe structures are polarized, with the C side exhibiting a strong negative potential and the Se side displaying a more neutral character. This property may lead to applications in many fields, such as Li storage or toxic molecule trapping.

Using ab initio calculations, we have investigated the adsorption of both S-cis and S-trans isomers of acrolein, crotonaldehyde, and cinnamaldehyde on the Pt(111) surface at low and high surface coverages and for five types of coordinations. Emphasis was placed on identifying trends by highlighting the similarities and differences in the adsorption of all three molecules. Adsorption was found to depend on coverage: the most stable adsorption geometry at low coverages is flat, in either eta(3) or eta(4) coordinations with most atoms bonded to the surface, whereas a more tilted arrangement involving fewer atoms, in a eta(2)-C2C3 coordination mode, prevails at high coverages. The extra methyl group in crotonaldehyde was determined to lead to a destabilization of the multiply coordinated adsorbates at high coverages, whereas the aromatic ring in cinnamaldehyde was found to be able to bind itself to the Pt surface, at least at low coverages, and thus increase the absolute value of the adsorption energy by about 0.5 eV. Additional calculations using a noncovalent interaction index provided further insights into the variations in bonding to the surface across the three molecules versus coverage in terms of both covalent and noncovalent attractive and repulsive interactions.

The advancement of atomic layer deposition (ALD) techniques for the controlled growth of transition metals thin films is hindered by the current scarcity of organometallic (OM) precursors capable of facilitating...

The advancement of atomic layer deposition (ALD) techniques for the controlled growth of transition metal thin films is constantly growing due to the design and synthesis of novel organometallic (OM) precursors capable of facilitating precise deposition and clean film growth. In this context, acetamidinates have emerged as a highly promising family of OM precursors due to their exceptional attributes, including outstanding stability, favorable volatility, and reactivity at low evaporation and deposition temperatures. These unique properties make them a sought-after candidate for enabling ALD processes. Here we conducted an atomic-scale study to get an in-depth understanding of the first ALD partial reaction, which involves the adsorption and dissociation process of the silver acetamidinate on the Ag(110) surface. Our research sheds light on the multistep adsorption and breaking mechanism of the novel silver(i)-N,N '-dimethylacetamidinate precursor employed as the silver source. Since the difference in energy between the monomer and dimer phases of the precursor is only 1.92 eV, we have explored the adsorption states of both phases. The monomer adsorbs on the surface by occupying hollow (H) sites; after that, it dissociates and loses its ligand, adopting a perpendicular geometry via the formation of new Ag-N bonds with the pair of N atoms at the top sites of the surface. On the other hand, the dimer adsorbs on long-bridge sites (LB) with the pair of N atoms occupying top sites with the silver atoms from the surface. Next, the dimer loses a pair of N-Ag bonds on each ligand, reaching a more stable state of partial cleavage with a relative energy of -0.38 eV. After overcoming an energy barrier of 0.41 eV, the dimer loses the remaining pair of N-Ag bonds, and the silver atoms diffuse towards H sites. Finally, the ligands diffuse toward the adjacent channel in the [100] direction of the surface. A charge distribution analysis of the adsorption stages shows the evolution of the silver atoms from precursor to the metallic state.

The thin films of c -plane dominated hexagonal (- phase Mn 2 N were successfully grown on a cubic MgO (001) substrate directly using plasma -assisted molecular beam epitaxy. The surface was comprehensively studied through experimental and theoretical approaches. Reflection high energy electron diffraction revealed two pseudo -cubic domains along [100] MgO and [110] MgO , and one hexagonal domain, which is 30 degrees apart from the [100] MgO direction. Scanning tunneling microscopy was used to image and resolve the high quality surface, revealing a distorted hexagonal surface structure. Furthermore, atomic resolution of the hexagonal domain with a 2 x 2 reconstructed surface is presented. For the c -plane surface, theoretical investigations were carried out using first -principle studies to determine the surface formation energy for various reconstructed surfaces. The theoretical study shows that the nitrogen terminated 2 x 2 structure with a manganese adatom on the surface is the most stable reconstruction that reproduces the experimental results. A corresponding simulated scanning tunneling microscopy model is also presented, providing strong support for the experimentally observed inplane lattice structures. The manganese:nitrogen stoichiometry within the bulk and surface is in good agreement with the expected ratio of 2:1.

The controlled growth and stability of transition metal clusters on N-doped materials have become the subject of intense investigation for unveiling comprehension on the cluster growth evolution. In this study, we investigated the growth mechanisms of non-magnetic (copper) and magnetic (iron) clusters on graphene with two atomic vacancies, with and without pyridinic nitrogen (N). Our results determine the role of pyridinic N in the growth and physicochemical properties of the mentioned metal clusters. In an N environment, Cu grows perpendicularly, whereas under N-deficient conditions, the clusters agglomerate. Fe cumulate-type clusters are formed regardless of the presence of N. However, N causes the Fe clusters to rise over one side of the surface without deforming the monolayer; meanwhile, in the absence of N, the Fe clusters protrude from both sides of the monolayer. Remarkably, the presence of N makes it feasible to induce magnetization in the Cun-N4V2 systems and aid in focalizing the magnetic properties on the Fe clusters for the Fen-N4V2 case. These findings offer insights into the role of N in cluster growth, with potential implications for diverse applications, including magnetic and electrocatalytic materials.

Using density functional theory, we have studied a graphene structure with a single C vacancy, doped with three pyridinic N atoms and a single metallic adatom (Fe, Ni, and Cu) as a catalyst for the oxygen reduction reaction (ORR), one of the most critical reactions in electrocatalysis. Nitrogen(N)-doped graphitic structures are promising candidates for the ORR, and the incorporation of metallic adatoms could improve their activity. Previous experimental and theoretical reports indicate that Fe favors the four-electron pathway, resulting in the formation of water molecules. On the other hand, Ni and Cu favor the two-electron pathway, producing hydrogen peroxide molecules. Our calculations show that in the case of a single C vacancy with three pyridinic N atoms, the reaction proceeded via the four-electron pathway for either Fe, Ni, or Cu. This result differs from the case of two C vacancies and four N atoms. Therefore, the chemical environment of single-atom catalysis plays an essential role in the reaction.

The new generation of Li-ion batteries is based on integrating 2D materials into the electrodes to increase the energy density while reducing the charging time and size. The two-dimensional transition metal carbide or nitride (MXene) materials offer ideal electronic properties, such as metallic behavior, low energy barriers for Li-ion diffusion, and structural stability. This study focuses on Nb2C and Nb2CO2 MXenes, which have shown promising Li-storage capacity, especially the oxidized phase. By using density functional theory (DFT) and thermodynamic criteria, we studied the Li intercalation process in both MXenes. The results show that the Li intercalation process in the oxidized phase is more stable. Also, the Li diffusion barriers are 35 and 250 meV for the bare and oxidized phase, due to the strong interaction between Li ions and O functional groups. Nb2C and Nb2CO2 MXenes deliver a maximum gravimetric theoretical capacity of 275 and 233.26 mA h/g, respectively, with a stable performance.

In this work, we propose the construction of a two-dimensional system based on the stable phases previously reported for the 2D arsenic and phosphorus compounds, with hexagonal and orthorhombic symmetries. Therefore, we have modeled one hexagonal and three possible orthorhombic structures. To ensure the dynamical stability, we performed phonon spectra calculations for each system. We found that all phases are dynamically stable. To ensure the thermodynamic and mechanical stabilities, we have calculated cohesive energies and elastic constants. Our results show that the criteria for the stabilities are all fulfilled. For these stable structures, we computed the electronic and optical properties from first-principles studies based on density functional theory. The computation of electronic band gaps was performed by using the GW approximation to overcome the underestimation of the results obtained from standard DFT approaches. To study the optical properties, we have computed the dielectric function imaginary part within the BSE approach, which takes into account the excitonic effects and allows us to calculate the exciton binding energies of each system. The study was complemented by the computation of the absorption coefficient. From our calculations, it can be established that the 2D As-P systems are good candidates for several technological applications.

Spin-polarized first-principles calculations are carried out to study the structural, electronic, and magnetic properties of the MnN growth on the CrN (111) surface. Different magnetic configurations between Mn-deposited atoms and the substrate are considered. The H3 site is the most favorable site for the adoption and incorporation cases and the Mn spins switch from paramagnetic to antiferromagnetic arrangement. The minimum energy pathway for the Mn diffusion is calculated, showing magnetic modifications in the substrate. A structural transition from tetragonal rock-salt to zinc-blende (ZB) structure as the number of MnN deposited layers increases is noticed. Thermodynamic analysis demonstrates that the growth of MnN on CrN is feasible. The density of states for an MnN layer with an extra nitrogen layer shows a half-metallic behavior and the remaining structures exhibit a metallic character. The ZB-MnN structures have an antiferromagnetic behavior with a metallic character. Magnetic anisotropy energies reveal a switching of easy magnetization axis, from in-plane to out-of-plane with the formation of MnN on the surface. These results suggest that the CrN/ZB-MnN system may be employed in antiferromagnetic spintronics applications as the fabrication of perpendicular magnetic tunnel junctions. A magneto-structural transition in MnN is found, in the MnN growth process on CrN (111) surface. The MnN switches from a tetragonal rock-salt structure with a ferromagnetic behavior to zinc blende stacking and an antiferromagnetic arrangement. In addition, the MnN formation produces an exchange in the easy magnetic axis in the system. image

The structural, electronic, and magnetic properties of the epitaxial growth of zinc-blende CrP onto the AlP (001) surface are investigated by first-principles spin-polarized calculations. Early stages of the epitaxial growth are investigated by the deposit of a Cr monolayer onto the Al and P-terminated surfaces. The results show that the deposit onto the P-T surface is feasible, with the surface acquiring antiferromagnetic characteristics. Once two CrP layers are deposited, the system becomes ferromagnetic. Also, the surface displays a half-metallic property, which is preserved when the interface is well defined. The thermodynamic stability of the initial stages of the epitaxial growth and the subsequent formation of the interface are investigated by the surface and interface formation energy formalisms. Our results show that the interface is stable under Al-rich and Cr-poor conditions. At the same time, five AlP (001) surface reconstructions are stable in the rest of the chemical potential region, as previously reported. We also calculated the Curie temperature, finding a value of 743 K. Our results demonstrate that the epitaxial growth of the zinc-blende CrP onto the AlP (001) substrates is feasible, and the properties of the CrP/AlP(001) system are suitable for implementation in spintronic devices that operate at room temperature.

Using non-collinear spin-polarized first-principles calculations, we have investigated the properties of the hexagonal D019 (0001) Mn3Ga surface. Two different surface terminations were considered: type-1 and type-2, with opposite chiralities. In the case of pristine surfaces, the Kagome triangular AFM character remains on the surface and in inner layers, with a slight increase in the surface magnetic moments due to the low coordination of the surface atoms. An increase in the remnant out-of-plane FM character compared to the bulk is also noticed. The effect of Ga or Mn vacancies on both surfaces was also investigated. Ga vacancies in the 2nd monolayer are more stable than in other layers. Such vacancies distort the triangular AFM configuration of the neighboring layers. Despite this, the AFM layer-by-layer nature remains. Conversely, Mn vacancies stabilize in the most exposed layer. In this case, the neighboring layers completely lose the triangular alignment. However, Mn atoms rearrange to preserve the AFM layer-by-layer character. Upon evaluating the thermodynamic stability of these surfaces, we observe that the pristine Kagome AFM magnetic surfaces are the most stable. Ga vacancies are the least stable configurations because they break down the super-exchange interaction that holds the Kagome magnetic arrangement. Finally, our calculations show that the Kagome magnetic arrangement at the surface is stabilized by both the magnetic (Mn) and non-magnetic (Ga) atoms. Therefore, it is expected that D019-Mn3Ga will not present low-index reconstructions induced by vacancies.

In the present work, we report on a theoretical-computational study of the growth mechanism of the TiO2-Graphene nanohybrid by atomic layer deposition. Hydroxyl groups (OH) are anchoring sites for interacting with the main ALD titanium precursors (Tetrakis (dimethylamino) Titanium, Titanium Tetrachloride, and Titanium Isopropoxide). Results demonstrate that the chemical nature of the precursor directly affects the reaction mechanism in each ALD growth step. Tetrakis(dimethylamino)titanium is the precursor that presents a higher affinity (lower energy barriers for the reaction) to hydroxylated graphene in the growth process. A complete reaction mechanism for each precursor was proposed. The differences between precursors were discussed through the non-covalent interactions index. Finally, the water molecules help reduce the energy barriers and consequently favor the formation of the TiO2-graphene nanohybrid.

The Kagome antiferromagnet Mn3Sn has garnered a lot of attention due to the presence of interesting properties such as anomalous Hall effects and Nernst effects. Until now, few papers have been reported to grow using molecular beam epitaxy with a buffer layer or on other substrates. In this paper, we discuss the synthesis of crystalline Mn3Sn layers, prepared on Al2O3 (0001) without a buffer layer using molecular beam epitaxy. The growth is monitored in-situ using reflection high energy electron diffraction and measured ex-situ using X-ray diffraction, Rutherford back-scattering, and cross-sectional scanning transmission electron microscopy. The samples were deposited at 524 +/- 5 degrees C, with an Mn: Sn atomic flux ratio of 3.2:1 for 90 min. Orientation re- lationships between the Mn3Sn films and the sapphire substrates are determined from in-plane and out-of-plane measurements. Our analysis indicates that the resulting film is predominantly c-plane oriented. Lastly, the samples prepared in this way were found to be discontiguous, showing a 3-dimensional morphology. According to first-principles calculations, the Mn3Sn exhibits a displaced Kagome structure in the very first stages of growth, for 2 ML and 4 ML growth on Al2O3 (0001). This result is corroborated by calculating the surface formation energies and explains the observed RHEED patterns.