Metal Monolayers Research Articles

Efficient Discovery of Room Temperature Magnetic Transition Metal Monolayers Assisted by Artificial Neural Network

Efficient Discovery of Room Temperature Magnetic Transition Metal Monolayers Assisted by Artificial Neural Network

Tunable and enhanced Goos–Hänchen shifts in a monolayer graphene-based metallic grating structure

The Goos–Hänchen (GH) effect, a lateral displacement of the reflection beam, enables rich applications in sensors and detectors. Metallic grating structures have gained great attention due to their unique properties, such as enhanced optical transmission and surface enhanced Raman scattering. Here, instead of using the dielectric grating, we demonstrate an enhanced GH shift in the structure with the metallic grating layer, monolayer graphene, dielectric spacer, and metallic substrate. We find that the amplitude of the GH shift is as high as 3616 times of the incident wavelength at the specific working frequency. This enhancement can be understood from the generation of the coupled surface plasmon polaritons between two surfaces of the dielectric space layer. Furthermore, we show efficient control of the GH shift by modulating the geometric parameters of the proposed structure and chemical potential of the monolayer graphene. Our result establishes an alternative metallic grating structure for tunable and enhanced GH shifts in graphene-based nanostructures.

Synthesis and Characterization of Metallic Janus MoSH Monolayer.

Janus transition-metal dichalcogenides (TMDCs) are emerging as special 2D materials with different chalcogen atoms covalently bonded on each side of the unit cell, resulting in interesting properties. To date, several synthetic strategies have been developed to realize Janus TMDCs, which first involves stripping the top-layer S of MoS2 with H atoms. However, there has been little discussion on the intermediate Janus MoSH. It is critical to find the appropriate plasma treatment time to avoid sample damage. A thorough understanding of the formation and properties of MoSH is highly desirable. In this work, a controlled H2-plasma treatment has been developed to gradually synthesize a Janus MoSH monolayer, which was confirmed by the TOF-SIMS analysis as well as the subsequent fabrication of MoSSe. The electronic properties of MoSH, including the high intrinsic carrier concentration (∼2 × 1013 cm-2) and the Fermi level (∼ - 4.11 eV), have been systematically investigated by the combination of FET device study, KPFM, and DFT calculations. The results demonstrate a method for the creation of Janus MoSH and present the essential electronic parameters which have great significance for device applications. Furthermore, owing to the metallicity, 2D Janus MoSH might be a potential platform to observe the SPR behavior in the mid-infrared region.

Magnetic properties of 3d, 4d, and 5d transition-metal atomic monolayers in Fe/TM/Fe sandwiches: Systematic first-principles study

Previous studies have accurately determined the effect of transition metal point defects on the properties of bcc iron. The magnetic properties of transition metal monolayers on the iron surfaces have been studied equally intensively. In this work, we investigated the magnetic properties of the 3d, 4d, and 5d transition-metal (TM) atomic monolayers in Fe/TM/Fe sandwiches using the full-potential local-orbital (FPLO) scheme of density functional theory. We prepared models of Fe/TM/Fe structures using the supercell method. We selected the total thickness of our system so that the Fe atomic layers furthest from the TM layer exhibit bulk iron-bcc properties. Along the direction perpendicular to the TM layer, we observe oscillations of spin and charge density. For Pt and W we obtained the largest values of perpendicular magnetocrystalline anisotropy and for Lu and Ir the largest values of in-plane magnetocrystalline anisotropy. All TM layers, except Co and Ni, reduce the total spin magnetic moment in the generated models, which is in good agreement with the Slater-Pauling curve. Density of states calculations showed that for Ag, Pd, Ir, and Au monolayers, a distinct van Hove singularity associated with TM/Fe interface can be observed at the Fermi level.

A comparative analysis of the vibrational and structural properties of nearly incommensurate overlayer systems

Using molecular dynamics simulations based on embedded atom method potentials, we have investigated the vibrational properties of the following three systems of nearly hexagonal noble metal monolayers adsorbed on substrates of square symmetry: Ag on Cu(001), Ag on Ni(001) and Au on Ni(001). The corresponding local phonon density of states, mean square amplitudes, and substrate interlayer relaxation of the above systems are compared to identify similarities and differences. A key finding is that the Ag monolayers have a stronger influence on both phonon spectra and vibrational amplitudes of the topmost layer of the Cu(001) surface than that of the nickel substrates. Furthermore, the vibrational amplitudes of the overlayer atoms are shown to be anisotropic and dominant along the incommensurate direction for the three systems. Temperature effects on the vibrational and structural properties are also discussed.

Contacts between monolayer black phosphorene and metal electrodes: Ohmic, Schottky, and their regulating strategy

Two-dimensional black phosphorene (BP) has attracted much interest for application in electronic devices. Contacts between BP and metal electrodes are critical components of BP-based devices and can dramatically affect device performances. In this paper, we adopted first-principles calculations to explore binding energies, electronic structures, and potential distribution for interface systems of Al-, Au-, Cu-, Ni-, and Ti-monolayer BP in surface contact and edge contact (EC) types. Moreover, we also used density functional theoretical coupled with the nonequilibrium Green’s function method to investigate contact resistances and Schottky barrier heights (SBHs) for transport systems of monolayer BP with Al, Au, Cu, Ni, and Ti electrodes. Our calculated results indicate that the contact type between BP and metals may greatly affect electrical properties of BP–metal contacts. Changing contact type between metal electrodes and BP channel can change the type of Schottky barrier of metal–BP contacts. The contact barrier of metal–BP depends on the metal material. Selecting an appropriate contact type and metal can effectively regulate the contact barrier of metal–BP. Specifically exciting, our estimated lateral SBHs for the Ni–BP system in EC-type agree well with the experimental results. We have provided a new strategy on choosing an appropriate contact type to achieve low contact resistance for the metal–BP interface.

Prediction of two-dimensional M2As (M = Mn, Fe) with high Curie temperature and large perpendicular magnetic anisotropy

Recently, with the miniaturization of electronic devices, there is an urgent need to use two-dimensional (2D) ferromagnetic materials with outstanding properties (such as high conductivity, better stability, etc.) and high Curie temperature (TC) in spintronic devices. By first-principles calculations based on density functional theory, we predict two new ferromagnetic metal monolayers M2As (M = Mn, Fe) with hight dynamic and thermal stabilities. Caculation results show that M2As monolayers possess high spin polarization ratio (27.3% for Mn2As and 52.6% for Fe2As), obvious out-of-plane magnetic anisotropy and large magnetic perpendicular anisotropy (101 μeV/Mn for Mn2As and 84 μeV/Fe for Fe2As). In addition, we found that the Mn2As monolayer exhibit high temperature ferromagnetism (TC = 450 K); while for the Fe2As monolayer, a high Curie temperature of 251 K was predicted. Moreover, we applied biaxial strain to the material to examine the changes in its magnetic properties and found that under a certain biaxial strain, Mn2As monolayer will have a ferromagnetic-antiferromagnetic phase transition, while Fe2As monolayer may exhibit a higher TC. Our findings render M2As (M = Mn, Fe) monolayers potential candidates for future spintronics and pave the way for exploring novel 2D magnetism in arsenic-based magnetic materials.

Micro-patterned deposition of MoS2 ultrathin-films by a controlled droplet dragging approach

Micropatterning of transition metal dichalcogenide (TMDC) ultrathin-films and monolayers has been demonstrated by various multi-step approaches. However, directly achieving a patterned growth of TMDC films is still considered to be challenging. Here, we report a solution-based approach for the synthesis of patterned MoS2 layers by dragging a precursor solution droplet with variable velocities across a substrate. Utilizing the pronounced shearing velocity dependence in a Landau-Levich deposition regime, MoS2 films with a spatially modulated thickness with alternating mono/bi- and few-layer regions are obtained after precursor annealing. Generally, the presented facile methodology allows for the direct preparation of micro-structured functional materials, extendable to other TMDC materials and even van der Waals heterostructures.

Controlling phase transition in monolayer metal diiodides XI2 (X: Fe, Co, and Ni) by carrier doping

We applied the generalized Bloch theorem to verify the ground state (most stable state) in monolayer metal diiodides 1T-XI2 (X: Fe, Co, and Ni), a family of metal dihalides, using the first-principles calculations. The ground state, which can be ferromagnetic, antiferromagnetic, or spiral state, was specified by a wavevector in the primitive unit cell. While the ground state of FeI2 is ferromagnetic, the spiral state becomes the ground state for CoI2 and NiI2. Since the multiferroic behavior in the metal dihalide can be preserved by the spiral structure, we believe that CoI2 and NiI2 are promising multiferroic materials in the most stable state. When the lattice parameter increases, we also show that the ground state of NiI2 changes to a ferromagnetic state while others still keep their initial ground states. For the last discussion, we revealed the phase transition manipulated by the hole–electron doping due to the spin–spin competition between the ferromagnetic superexchange and the antiferromagnetic direct exchange. These results convince us that metal diiodides have many benefits for future spintronic devices.

Stabilization of dense metallic Pb monolayer by decorating step edges with Au atoms on Si(111)

Under specific conditions, the sequential growth of Au and Pb on Si(111) results in a huge modification of the surface structure which neither Au/Si nor Pb/Si growths provoke separately. Initially atomically flat 7x7 Si(111) substrate breaks into a terraced-hill structure containing up to 10 atomic terraces of a typical width 10-50 nm. Terraces are covered by a dense monolayer of Pb (nominal coverage 1.2 to 1.33 ML); their step edges are decorated by double rows of Au atoms. This could open a route for constructing superconducting Josephson devices on atomic scale.

Reversibly Tailoring Optical Constants of Monolayer Transition Metal Dichalcogenide MoS2 Films: Impact of Dopant-Induced Screening from Chemical Adsorbates and Mild Film Degradation

The refractive index for pristine monolayer MoS2 in the near-infrared is predicted to be ≥4. However, experimental literature reports n can decrease by ∼2 at energies below the band edge. In this work, we show variability in the optical response can correspond to changes in oscillator amplitude and dielectric polarizability of all measured excitons—suggesting exemplary charge transfer and local dielectric media effects discussed here are significant contributors in quantum nanophotonic interactions. Monolayer metal organic chemical vapor deposited MoS2 films are evaluated herein using spectroscopic ellipsometry to assess changes in the refractive index (n) and extinction coefficient (k) due to dopant-induced screening effects from chemical adsorbates and mild film degradation. Notably, large reversible changes in the refractive index (Δn ≈ 2.2) are observed by varying n- and p-type chemical adsorbates. The extent of tailorable dopant-induced screening of MoS2 optical constants illustrated in this work is also shown to be highly dependent on film quality. This suggests a dominant role of pre-existing structural defects on the optical properties of reported films to date. The tailoring of semiconducting transition metal dichalcogenide optical constants in a reversible manner is expected to have broad implications in the development of quantum optical and optoelectronic devices (e.g., high-precision engineered excitonic effects, electroabsorption modulators, and high-efficiency semiconductor nanophotonic technologies).

Controllable vdW Contacts between the Ferroelectric In2Se3 Monolayer and Two-Dimensional Metals

Developing low dimensional multifunctional devices becomes more and more important as the scale of the field-effect transistors decreases. Although van der Waals (vdW) contacts between two-dimensio...

Stable Metallicity of Low Dimentional WCrC Derivatives: A First‐Principles Study

AbstractThe rapid development of 2D material MXenes family brings new opportunities for the application and development of materials science. Here, the structural and electronic properties of WCrC monolayer and its nanoribbons, and the effects of add‐atom adsorption in combination with strain engineering are presented by using first‐principles calculation. The result reveals that pristine WCrC monolayer is always dynamically stable and exhibits metallicity. Within a certain coverage range, the metallic WCrC monolayer can be transformed into semi‐metallic WCrCO2 with dual narrow band gap by adsorbing O atoms, but adsorbed H and Cl atoms cannot change its metal behavior. Moreover, the spin‐splitting of WCrC monolayer is obvious, but when the compressive strain increases to 8%, the energy bands of WCrC monolayer achieve a singular behavior of spin degeneracy. However, neither compressive strain nor tensile strain changes the metallicity of WCrC monolayer. Meanwhile, WCrC nanoribbons with diverse boundaries configurations and edge‐terminated atoms are all metallic, which indicates that boundary configurations and edge‐terminated atoms are not the key factors affecting the metallicity of WCrC nanoribbons. These results suggest that WCrC derivatives are mainly metallic materials, which are expected to be applied in the field of spintronics and may provide new opportunities for the development of metal ion battery electrodes.

2D Transition‐Metal Silicides as Analogs of MXenes: A First‐Principles Exploration

The family of 2D transition metal carbides, carbonitrides, and nitrides (MXenes) has aroused scientific research due to their unique electrical, optical, and chemical properties and their versatile applications. Based on first‐principles calculations, ten transition metal silicide (M2Si, M = Sc, Ti, V, Cr, Mn, Co, Zn, Y, Nb, and Mo) monolayers are studied. Three stable 2D M2Si (M = Mn, Co, and Y) crystals are identified through the investigation of thermodynamic, dynamical, and thermal perspectives. Among them, Y2Si monolayer is a nonmagnetic metal, whereas Mn2Si and Co2Si monolayers are antiferromagnetic metals. The three monolayers are chemically inert to H2 and N2, but highly active to O2, and only Y2Si with its surface functionalized by oxygen exhibits good thermal stability, whose magnetic and electronic properties retain its pristine counterpart. In addition, it is found that the Y2Si shows good electrocatalytic performance in hydrogen evolution reaction (HER). These stable 2D M2Si monolayers have potential in the fields of electronics and electrocatalysis.

Grinding performance and wear of metal bond super-abrasive tools in grinding of Zr-based bulk metallic glass

Bulk metallic glass (BMG) is the new class of promising materials with exceptional mechanical properties and corrosion resistance. BMG parts need grinding to obtain high dimension precision and surface finish. In present research work, Zr-BMG was ground by mono-layer metal bond super-abrasive grinding tools with different abrasive (diamond, CBN) and bond (Ni electroplated, NiCr and Cu-Sn-Ti brazed). The grinding force, surface roughness, surface crystallization status, wear of tools in grinding of BMG with different tools were examined and compared. The specific grinding energy of Zr-BMG was also compared with SS304 steel. The results showed that diamond tool produces lower grinding forces than that of CBN. Ni electroplated tools own lower grinding force than that of brazed ones. Zr based BMG produce higher grinding force and specific grinding energy than SS304 steel. Ni electroplated tools obtain lower surface roughness of Zr-BMG than that of brazed ones. A severe adhesion of Zr-BMG dominates the wear of super-abrasive grinding tools. Ni-electroplated tools produce less adhesion than the brazed tools.

A theoretical study of the ability of 2D monolayer Au (111) to activate gas molecules

The adsorption and activation of gas molecules are investigated substantially in solid-gas heterogeneous catalysis. Here we investigated the interaction between gas molecules and unique two-dimensional monolayer Au (111) structure using density functional theory. It is found that CO2, H2O, N2 and CH4 molecules are weakly adsorbed on the surface with the adsorption energies between −0.150 and −0.250 eV due to van der Waals interaction. While CO, NO, NO2, and NH3 molecules are adsorbed more stably with the adsorption energies between −0.300 and −0.470 eV. Especially, the bond length of CO is stretched by 0.038 Å and the bond angle of NO2 is obviously enlarged by 10.460°. The activation originates from the rearrangement of molecule orbitals and the orbitals hybridization between the partial orbitals of gas molecules and Au-5d orbitals. The fundamental analyses of adsorption mechanism and electronic properties may provide guidance for the applications of two-dimensional monolayer metal catalysis.PACSnumbers 73.22.-f, 73.61.-r

One- and two-dimensional electrical contacts and transport properties in monolayer black phosphorene–Ni interface

Contacts between black phosphorene (BP) and metal electrodes are critical components of BP-based devices and can dramatically affect device performance. In this paper, we adopted first-principles calculations to explore binding energies, electronic structures, spatial potential distribution of monolayer BP–Ni interfaces in surface contact and edge contact types, and used density functional theoretical coupled with nonequilibrium Green’s function method to investigate the electrical transport properties for transport systems of monolayer BP with Ni electrodes. Our calculated results indicate that contact type between monolayer BP and metal Ni electrodes may much affect the transport properties of monolayer BP–Ni devices. Interfacial interaction between Ni and monolayer BP in edge contact type is stronger than that in surface contact type. The potential distributions indicate that edge contact type is more beneficial for reducing contact resistance of monolayer BP–Ni contacts and conducive to improve the performance of BP–Ni electrode device.

Planar Iron Hydride Nanoclusters: Combined Spectroscopic and Theoretical Insights into Structures and Building Principles

The controlled assembly of well‐defined planar nanoclusters from molecular precursors is synthetically challenging and often plagued by the predominant formation of 3D‐structures and nanoparticles. Herein, we report planar iron hydride nanoclusters from reactions of main group element hydrides with iron(II) bis(hexamethyldisilazide). The structures and properties of isolated Fe4, Fe6, and Fe7 nanoplatelets and calculated intermediates enable an unprecedented insight into the underlying building principle and growth mechanism of iron clusters, metal monolayers, and nanoparticles.

Ab InitioStudy of Adsorption of Fission Gas Atoms Xe and Kr on MoS2Monolayer Functionalized with 3d Transition Metals

It is well known that a nuclear reactor generates various fission products including radioactive fission gases made of isotopes of Xe and Kr. The separation of Xe and Kr isotopes and their entrapment are important tasks for efficient operation of nuclear reactors and fuel-reprocessing plants. Two-dimensional materials are known to have a large surface-to-volume ratio; this makes them prospective candidates as gas adsorbent materials. Motivated by this, we carry out ab initio density functional theory-based calculations to explore the reactivity and selectivity of a monolayer of pristine and 3d transition metal (TM)-functionalized MoS2 toward the fission gas atoms Xe and Kr. To this end, we first study and analyze the adsorption of the TM adatoms on the monolayer of MoS2 at different inequivalent crystallographic sites. Further, we calculate partial atomic charges and atom-projected density of states of the functionalized composite systems to understand the bonding mechanism of TM adatoms with the monolayer of MoS2. We predict the coexistence of both ionic and covalent bonding between the TM atoms and the surface atoms. Subsequently, we probe the adsorption of Xe and Kr atoms on both the pristine and the TM-functionalized MoS2 surfaces. Our calculated results indicate that the adsorption energies for Xe (Kr) gas atoms on the functionalized MoS2 are enhanced up to a maximum of 2.77 (2.86) times of adsorption energy found in case of the pristine surface. We find that the adsorption energy of Xe and Kr gas atoms over different TM atom-functionalized MoS2 follows the order Ti > V > Co > Ni > Fe > Sc > Mn > Cr > Cu. Charge density difference analyses indicate that the polarization of Xe/Kr adatoms is enhanced in the case of functionalized surfaces, which leads to the strengthened interaction between the noble gas (NG) atoms and the functionalized surfaces, compared to the adsorption of NG on the pristine MoS2 surface. This polarization has direct one-to-one correspondence with the adsorption energy of these gas atoms on the surface. Moreover, our calculated results suggest that both the pristine and the functionalized MoS2 surfaces show selectivity for Xe atom over Kr atom. The present study predicts that the TM atom-functionalized MoS2 surfaces may have great potential for adsorption and selective separation of Xe and Kr atoms, which may have important implication in the field of spent nuclear fuel management.

Электронный спектр капсулированных монослоев: аналитические результаты

Green’s function method is used to find the dispersion low for a monolayer (ML) placed be-tween two crystalline slabs. Weak- and strong-coupling regimes are considered in details. For the systems graphene, hBN – metallic ML – SiC polytypes analytical expressions for the ML electron effective masses are obtained. It is shown that the effective mass decreases with the increase of the SiC polytype energy gap.