Adsorption Of Transition Metal Atoms Research Articles

First-principles study of adsorption of 3d and 4d transition metal atoms on aluminene

Using the first principles calculations based on density functional theory, we study the structural, electronic, and magnetic properties of composite systems of first and second row transition metal (TM) atoms adsorbed aluminene. This study aims to probe the stability of the system as a result of adsorption of TM atoms on the two-dimensional (2D) surface of planar aluminene. We also study the same for two other well-known 2D single-atom-monolayer (SAML) structures, namely, silicene and arsenene, and we compare the results with those of aluminene. The TM atoms are adsorbed on these 2DSAML structures in three different crystallographically inequivalent sites, namely, the hollow (H), the top (T) and the bridge (Br) sites. The stability of the composite systems, which are a combination of a 2D monolayer structure and a TM atom each, is systematically analyzed in terms of binding energy per atom, for eighteen different TM atoms, with 3 d or 4 d electrons in their valence shell. We compare the results of optimized geometry and stability of the above-mentioned 2D structures when the TM atoms are adsorbed at the H, T and Br sites. We further analyze the interaction energy to discuss about and compare the ease of adsorption of various TM atoms on the three different 2DSAML structures. Interestingly, in most of the cases, adsorption of TM atoms typically yields higher interaction energy in case of aluminene when compared with silicene and arsenene systems. Among all the TM adatoms, few atoms have been identified to have higher interaction energy compared to the others. From our calculations of the density of states and band structure of the composite systems, almost all the composite systems have been found to be metallic, except the composite system of Sc atom and silicene, which exhibits a half-metallic state. Further, though all the three 2DSAML structures are non-magnetic in pristine form, a few composite systems are found to be magnetic in nature.

Adsorption of 3d transition-metal atom on InSe monolayer: A first-principles study

The adsorption of 3d transition metal (TM) atoms (from Sc to Zn) on the InSe monolayer is studied by using density functional theory. The most preferable adsorption site is on top of In atoms for Sc, Ti, and V atoms, while the other seven 3d TM atoms (from Cr to Zn) are found to prefer the hollow adsorption site of InSe monolayer. The sizable adsorption energies are obtained for these systems except Zn-InSe system. The electrons are transferred from the adsorbed TM atoms to the support, thus a n-doping effect is achieved in the InSe monolayer by the TM atoms adsorption. The interesting magnetic properties are exhibited in those TM-InSe systems for TM from Sc to Co, which can be understood based on the orbital alignments and occupations of adsorbed TM atoms. The spin configurations are listed for each system. Our results indicate that great potential exists in these systems for 2D InSe utilization in nanoelectronics and spintronics.

Adsorption of 3d, 4d, and 5d transition-metal atoms on single-layer boron nitride

The adsorption of 3d, 4d, and 5d transition-metal (TM) atoms on single-layer boron nitride (SLBN) sheets was systematically studied through comparison of structural and magnetic properties determined using first-principles calculations. We found that the majority of TM atoms were chemically adsorbed on SLBN with adsorption energies larger than 0.5 eV, whereas some TM atoms in d5 or d10 configuration were physically adsorbed on SLBN with adsorption energies lower than 0.5 eV. The charge density difference indicated that the main contribution to the adsorption energy was the interaction between the TM and the nearest B atoms rather than N atoms. Moreover, TM adatoms from Sc (Y, La) to Co (Rh, Ir) and Cu (Ag, Au) displayed nonzero magnetic moments arising from the d-orbital occupation of TM atoms. Our results provide fundamental knowledge of TM atom adsorption on SLBN, which will be useful for not only spintronics applications but also the development of magnetic nanostructures.

Adsorption of 3d transition metal atoms on graphene-like gallium nitride monolayer: A first-principles study

We study the structural, electronic and magnetic properties of 3d transition metal (TM) atoms (Cr, Mn, Fe, Co, Ni and Cu) adsorbed GaN monolayer (GaN-ML) using first-principles calculations. The results show that, for 6 different TM adatoms, the most stable adsorption sites are the same. The adsorption of TM atoms results in significant lattice distortions. A covalent chemical bonding character between TM adatom and GaN-ML is found in TM adsorbed systems. Except for Ni adsorbed system, all TM adsorbed systems show spin polarization implying that the adsorption of TM induces magnetization. The magnetic moments of the adsorbed systems are concentrated on the TM adatoms and the nearest-neighbor N atoms of the adsorption site contributed slightly. Our analysis shows that the GaN-ML properties can be effectively modulated by TM adsorption, and exhibit various electronic and magnetic properties, such as magnetic metals (Fe adsorption), half-metal (Co adsorption), and spin gapless semiconductor (Cu adsorption). These present properties of TM adsorbed GaN-ML may be of value in electronics and spintronics applications.

Interplay between strong correlation and adsorption distances: Co on Cu(001)

Adsorbed transition metal atoms can have partially filled $d$- or $f$-shells due to strong on-site Coulomb interaction. Capturing all effects originating from electron correlation in such strongly correlated systems is a challenge for electronic structure methods. It requires a sufficiently accurate description of the atomistic structure (in particular bond distances and angles), which is usually obtained from Kohn-Sham density functional theory (DFT), which due to the approximate nature of the exchange-correlation functional may provide an unreliable description of strongly correlated systems. To elucidate the consequences of this popular procedure, we apply a combination of DFT with the Anderson impurity model (AIM), as well as DFT+U for a calculation of the potential energy surface along the Co/Cu(001) adsorption coordinate, and compare the results with those obtained from DFT. The adsorption minimum is shifted towards larger distances by applying DFT+AIM, or the much cheaper DFT+U method, compared to the corresponding spin-polarized DFT results, by a magnitude comparable to variations between different approximate exchange-correlation functionals (0.08 to 0.12 Angstrom). This shift originates from an increasing correlation energy at larger adsorption distances, which can be traced back to the Co 3$d_{xy}$ and 3$d_{z2}$ orbitals being more correlated as the adsorption distance is increased.

Anchoring transition metal elements on graphene-like ZnO monolayer by CO molecule to obtain spin gapless semiconductor

Graphene-like zinc oxide monolayer (g-ZnO) is a newfound two-dimensional material. Here we utilize the transition metal (TM) elements (Cr, Mn, Fe, Co, Ni, and Cu) to functionalize the g-ZnO with the aim of designing novel spintronics materials by using first-principles calculations. Our results show that although the adsorption of TM atoms can endow g-ZnO with magnetization and impurity states in the bandgap, the interaction between TM elements and g-ZnO is weak. We found that the attachment of CO molecule on TM is able to stabilize the TM elements on g-ZnO based on the ‘donation and back-donation’ mechanism. As a result, the adsorption energy of the CO-TM complex on g-ZnO is as high as 1.41–2.11eV. Furthermore, the incorporation of CO molecule modulates the magnetic and electronic properties of the TM-decorated g-ZnO. In particular, the CO-Mn-g-ZnO is predicted to be a spin gapless semiconductor.

Electronic and magnetic properties of TM atoms adsorption on 2D silicon carbide by first-principles calculations

Abstract The magnetic properties of different transition-metal (TM) atoms (TM=Co, Cu, Mn, Fe, and Ni) adsorption on SiC monolayer are investigated using density functional theory (DFT). Magnetism appears in the cases of Co, Cu, Mn, and Fe. Among all the magnetic cases, the Co-adsorbed system has the most stable structure. Therefore, we further study the interaction in the two-Co-adsorbed system. Our results show that the interaction between two Co atoms is always FM and the p–d hybridization mechanism results in such ferromagnetic states. However, the FM interaction is obviously depressed by the increasing Co-Co distance, which could be well explained by the Zener-RKKY theory. Moreover, different magnetic behavior is observed in the two-Mn-adsorbed system and a long-range AFM state is showing. Such multiple magnetic properties may suggest promising applications of TM-adsorbed SiC monolayer in the future.

Density functional theory calculations on transition metal atoms adsorbed on graphene monolayers

Transition metal atom adsorption on graphene monolayers has been elucidated using periodic density functional theory under hybrid and generalized gradient approximation functionals. More specifically, we examined the adsorption of Cu, Fe, Zn, Ru, and Os on graphene monolayers by calculating, among others, the electronic density-of-states spectra of the adatom-graphene system and the overlap populations of the adatom with the nearest adsorbing graphene carbon atoms. These calculations reveal that Cu form primarily covalent bonds with graphene atoms via strong hybridization between the adatom orbitals and the sp band of the graphene substrate, whereas the interaction of the Ru and Os with graphene also contain ionic parts. Although the interaction of Fe with graphene atoms is mostly covalent, some charge transfer to graphene is also observed. The interaction of Zn with graphene is weak. Mulliken population analysis and charge contour maps are used to elucidate charge transfers between the adatom and the substrate. The adsorption strength is correlated with the metal adsorption energy and the height of the metal adatom from the graphene plane for the geometrically optimized adatom-graphene system. Our analysis shows that show that metal adsorption strength follows the adatom trend Ru≈Os>Fe>Cu>Zn, as verified by corresponding changes in the adsorption energies. The increased metal-carbon orbital overlap for the Ru relative to Os adatom is attributed to hybridization defects.

Ab initio study of magnetic properties in the adsorption of transition-metal atoms on arsenene

The magnetic properties of adsorption of different transition-metal (TM) atoms (Co, Cu, Mn, Fe, and Ni) on arsenene are investigated using density functional theory (DFT). Magnetism appears in the cases of Co, Mn, and Fe. Among all the magnetic cases, the TM atom prefers the same adsorption site. Then, we further study the interaction in two-TM-adsorbed system and different magnetic states are observed. Our results show that both nonmagnetic and ferromagnetic states exist in two-Co-adsorbed system and the p-d hybridization mechanism results in its ferromagnetic state. However, for two Mn and two Fe adsorbed systems, an AFM interaction is found, which could be reasonably explained by the superexchange mechanism. Such multiple magnetic properties may suggest promising applications of TM-adsorbed arsenene in the future.

Spin-filtering in graphene junctions with Ti and Co adsorbates

The accurate theoretical modeling of a nanojunction made of a single graphene sheet with regularly adsorbed Ti or Co atoms is presented in the context of spintronic applications. Our calculations show that the adsorption of transition metal atoms on graphene induces the opening of a gap in the transmission function in one spin channel only. Charge carriers flowing through the nanojunction in Ti@graphene belong almost entirely to the minority spin component, and the spin polarization of the current is almost 100%. The opposite is found in Co@graphene, where the charge carriers belonging to the majority spin component are dominant. The analysis of the non equilibrium electron density distribution indicates that a spin separation between the left and the right portions of the device occurs. This strong spin asymmetry suggests that transition metal adatoms have the potential of turning graphene into an efficient spin-filtering device.

Giant magnetic anisotropy in doped single layer molybdenum disulfide and fluorographene

Stable monolayer materials based on existing, well known and stable two-dimensional crystal fluorographene and molybdenum disulfide are predicted to exhibit a huge magnetocrystalline anisotropy when functionalized with adsorbed transition metal atoms at vacant sides. Ab initio calculations within the density-functional theory formalism were performed to investigate the adsorption of the transitional metals in a single S (or F) vacancy of monolayer molybdenum disulfide (or fluorographene). We found strong bonding of the transitional metal atoms to the vacant sites with binding energies ranging from 2.5 to 5.2 eV. Our calculations revealed that these systems with adsorbed metal atoms exhibit a magnetic anisotropy, specifically the structures including Os and Ir show a giant magnetocrystalline anisotropy energy of 31–101 meV. Our results demonstrate the possibility of obtaining stable monolayer materials with huge magnetocrystalline anisotropy based on preexisting, well known and stable two-dimensional crystals: fluorographene and molybdenum disulfide. We believe that the results obtained here are useful not only for deeper understanding of the origin of magnetocrystalline anisotropy but also for the design of monolayer optoelectronic devices with novel functionalities.

Study of interaction between transition metal atoms and bigraphene monovacancy by means of quantum chemistry

First-row transition metal atoms adsorption on bigraphene monovacancy was studied within the framework of DFT in periodic boundary conditions. Electronic and magnetic properties of composites were analyzed and their potential utilization in spintronics was discussed. Barriers of metal atoms migration from bigraphene surface to the interlayer space through the vacancy were estimated in order to consider both thermodynamic and kinetic aspects of composites experimental preparation. Formation of metal atoms inner-sorbed on bigraphene was found to demand harsh synthesis conditions; whereas outer-sorbed composites demonstrate significantly higher degree of spin polarization which makes them perspective for usage in spintronic devices.

Transition metal decorated graphene-like zinc oxide monolayer: A first-principles investigation

Transition metal (TM) atoms have been extensively employed to decorate the two-dimensional materials, endowing them with promising physical properties. Here, we have studied the adsorption of TM atoms (V, Cr, Mn, Fe, and Co) on graphene-like zinc oxide monolayer (g-ZnO) and the substitution of Zn by TM using first-principles calculations to search for the most likely configurations when TM atoms are deposited on g-ZnO. We found that when a V atom is initially placed on the top of Zn atom, V will squeeze out Zn from the two-dimensional plane then substitute it, which is a no barrier substitution process. For heavier elements (Cr to Co), although the substitution configurations are more stable than the adsorption ones, there is an energy barrier for the adsorption-substitution transition with the height of tens to hundreds meV. Therefore, Cr to Co prefers to be adsorbed on the hollow site or the top of oxygen, which is further verified by the molecular dynamics simulations. The decoration of TM is revealed to be a promising approach in terms of tuning the work function of g-ZnO in a large energy range.

Site-dependent magnetism of Ni adatoms on MgO/Ag(001)

We examine the adsorption of a single Ni atom on a monolayer of MgO on a Ag substrate using DFT and $\mathrm{DFT}+U$ computational approaches. We find that the electronic and magnetic properties vary considerably across the three binding sites of the surface. Two of the binding sites are competitive in energy, and the preferred site depends on the strength of the on-site Coulomb interaction $U$. These results can be understood in terms of the competition between bonding and magnetism for surface adsorbed transition metal atoms. Comparisons are made with a recent experimental and theoretical study of Co on MgO/Ag, and implications for scanning tunneling microscopy experiments on the Ni system are discussed.

Adsorption properties of transition metal atoms on strongly correlated NiO(001) surfaces with surface oxygen vacancies

Using first-principles density functional theory combined with on-site Coulomb repulsion U, we have systematically studied the adsorption properties of transition metal (TM) atoms on strongly correlated NiO(001) surfaces with Fs centers (surface O vacancies). For the TM atoms, the adsorption on Fs centers is 1.26–3.18 eV more stable compared to positions near the surface O sites of defect-free NiO(001) surfaces. This indicates that Fs centers play an important role in the binding of TM atoms on O-defective NiO(001) surfaces. An analysis of the electronic structures and the charge redistribution for the adsorption of TM atoms on defective NiO(001) has been performed. The TM atoms are negatively charged, with charges ranging from −0.29 to −0.73 |e|. The TM-related states caused by interactions between TMs and surface defect states are found in the gap region of NiO. These results provide important information about controlling and understanding the adsorption properties of TM atoms on metal-supported ultrathin NiO films with surface defects like Fs centers.

First-principles study of 3d transition metal atom adsorption onto graphene: the role of the extended line defect

A type of extended line defect (ELD) with two pentagons plus an octagon as the basic unit is currently an experimentally available topological defect in the graphene lattice, which brings about some interesting modifications to the electronic properties of graphene. Within the framework of density functional theory (DFT), we perform a systematic calculation to clarify the role of the ELD in 3d-transition metal atom (TMA) adsorption onto the graphene surface. We find that, in contrast to the ordinary lattice position of graphene, the ELD presents a much stronger adsorption for the TMAs(Sc–Cu). Thus, the presence of ELD provides a feasible approach to pattern magnetic impurities onto the graphene surface in a controllable and self-assembled way. In addition, our calculation indicates that as the adatom near the ELD alters from Sc to Cu, the spin moment and the adsorption energy show intricate variations. By means of symmetry analysis, we establish a hybridization picture between the TMA orbitals and the pz orbital of graphene, by which these numerical results are reasonably explained. Finally, by calculating the electronic transport properties based on the DFT and nonequilibrium Green function technique, we find that when the electron tunnels through an ELD with Co or Fe adsorption, the maximum spin-filter efficiency can reach 85% and 97%, respectively, with a bias voltage less than 0.6 V. Therefore, these composite structures of graphene with TMA adsorbed by the ELD can be considered as a prototype of a spin-filter device.

Tunable electronic and magnetic properties in germanene by alkali, alkaline-earth, group III and 3d transition metal atom adsorption.

We performed first-principles calculations to study the adsorption characteristics of alkali, alkali-earth, group III, and 3d transition-metal (TM) adatoms on germanene. We find that the adsorption of alkali or alkali-earth adatoms on germanene has minimal effects on geometry of germanene. The significant charge transfer from alkali adatoms to germanene leads to metallization of germanene, whereas alkali-earth adatom adsorption, whose interaction is a mixture of ionic and covalent, results in semiconducting behavior with an energy gap of 17-29 meV. For group III adatoms, they also bind germanene with mixed covalent and ionic bonding character. Adsorption characteristics of the transition metals (TMs) are rather complicated, though all TM adsorptions on germanene exhibit strong covalent bonding with germanene. The main contributions to the strong bonding are from the hybridization between the TM 3d and Ge pz orbitals. Depending on the induced-TM type, the adsorbed systems can exhibit metallic, half-metallic, or semiconducting behavior. Also, the variation trends of the dipole moment and work function with the adsorption energy across the different adatoms are discussed. These findings may provide a potential avenue to design new germanene-based devices in nanoelectronics.

First-principle study of the transition-metal adatoms on B-doped vacancy-defected graphene

The energetic, electronic, and magnetic properties of transition metal (TM) atoms absorbed on modified graphene, including B-dopant, vacancy, and combination of these two, were theoretically investigated using the density functional theory (DFT) method. It was found that the adsorption of TM atoms (V, Mn, Fe and Ni) was significantly enhanced by the presence of vacancy sites. Furthermore, the introduction of B-dopant affected the adsorption process of TM atoms and the band structure of graphene. The results of partial electronic density of states (PDOS) indicated that the influence by B-dopant was due to the interaction between the 2p orbital of B atoms and 3d orbital of TM atoms. Interestingly, the strong hybridization contributed by B-2p and C-2p at vacancy sites enlarged the adsorption energies of TM-adatoms. It is expected that the results could provide useful information to explore application of graphene as spintronic and electronic devices.

Divacancy-assisted transition metal adsorption on the BN graphene and its interaction with hydrogen molecules: a theoretical study

We have performed first-principles calculations to study the chemical functionalization of the BN graphene with divacancy (DV) defect by 12 different transition metal (TM) atoms, including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pt, and Au. The results indicate that the DV defect can assist the adsorption of TM atoms on BN graphene. Moreover, some impurity bands are induced within the band gap of DV-BN graphene, leading to the modification of its electronic properties in various ways. Interestingly, Ti- and Co-adsorbed DV-BN graphenes are found to possess ferromagnetic characteristic, while antiferromagnetic state is preferred for V-, Mn-, and Fe-functionalized DV-BN graphenes, and the paramagnetic state is the ground state for Sc-, Cr-, Ni-, Cu, Zn-, Pt-, and Au-decorated DV-BN graphenes. Finally, aiming at evaluating the potential of these functionalized BN graphenes in hydrogen storage, we study their interaction with H2 molecules. It is found that the dispersed Sc, V, and Cr on DV-BN graphene are able to adsorb up to three H2 molecules as strongly as 0.25–0.58eV/H2, suggesting that the three nanomaterials may be suitable candidates for hydrogen storage.

Catalytically healing the Stone–Wales defects in graphene by carbon adatoms

Graphene with a perfect hexagonal network structure is desirable for various reasons, e.g., mechanical, thermal conductivity and transport properties. Yet, the embedded defects generated either in synthesis or usage stages have posed obstacles for graphene applications. Therefore, removal of the structural defects in graphene has remained an important task. Stone–Wales (SW) defects are one typical topological structure in the carbon nanomaterials. Unfortunately, the SW defects in graphene have to overcome a very high restoration barrier (ca. 6 eV). Very recent theoretical work has shown the promise to reduce the restoration barrier by the adsorbed transition metal atoms down to 2.86 eV (for W) (yet this is still too high). In the present density functional theory (DFT) study, we find that through a mechanically different process, the adsorption of carbon atoms can dramatically reduce the restoration barrier to hitherto the lowest value, i.e., 20.0 kcal mol−1 (0.87 eV), which could make the SW-healing experimentally accessible. Subsequently, the C-adatom can migrate very easily on the graphene surface. As a result, one carbon adatom could principally catalyze the healing of all the SW defects in a cascade mode if no termination steps exist. During the graphene growth, the presently proposed carbon-adatom catalytic mechanism could have played a role in healing the SW defect. Moreover, we propose that in the post-treatment of graphene, adsorption of the carbon adatom could be used as an effective catalyst for the SW-healing. The catalytic role of carbon atoms on the SW defect should be included in the modeling of graphene growth.