First-principles studies of BN sheets with absorbed transition metal single atoms or dimers: stabilities, electronic structures, and magnetic properties

BN sheets with absorbed transition metal (TM) single atoms, including Fe, Co, and Ni, and their dimers have been investigated by using a first-principles method within the generalized gradient approximation. All of the TM atoms studied are found to be chemically adsorbed on BN sheets. Upon adsorption, the binding energies of the Fe and Co single atoms are modest and almost independent of the adsorption sites, indicating the high mobility of the adatoms and isolated particles to be easily formed on the surface. However, Ni atoms are found to bind tightly to BN sheets and may adopt a layer-by-layer growth mode. The Fe, Co, and Ni dimers tend to lie (nearly) perpendicular to the BN plane. Due to the wide band gap of the pure BN sheet, the electronic structures of the BN sheets with TM adatoms are determined primarily by the distribution of TM electronic states around the Fermi level. Very interesting spin gapless semiconductors or half-metals can be obtained in the studied systems. The magnetism of the TM atoms is preserved well on the BN sheet, very close to that of the corresponding free atoms and often weakly dependent on the adsorption sites. The present results indicate that BN sheets with adsorbed TM atoms have potential applications in fields such as spintronics and magnetic data storage due to the special spin-polarized electronic structures and magnetic properties they possess.     

表面吸附对单层黑磷砷结构、电子性质和磁性调控的第一性原理研究

基于第一性原理，系统研究了11种不同原子吸附在单层AsP上的几何结构、吸附能、磁矩和电子结构性质. 使用的吸附原子包括轻质非金属(C、N、O)原子，第三周期金属原子(Na、Mg、Al)和过渡金属原子(Ti、V、Cr、Mn和Fe). 研究结果表明，吸附原子引起了AsP多样的结构、磁性和电子性质改变. AsP与所研究的吸附原子都能紧密结合，并且所有系统的吸附能都比吸附原子在石墨烯、SiC、BN以及MoS₂上的吸附能强得多. AsP的半导体特性受到吸附原子的影响，其可以诱导产生中间能隙态或引起n型掺杂. 此外，表面吸附产生了不同的自旋电子特性，具体而言，吸附N、Ti和Fe的AsP成为双极半导体；Mn修饰的AsP成为双极自旋无间隙半导体.     

Identification of species formed after pyridine adsorption on iron,cobalt, nickel and silver electrodes by SERS and theoretical calculations

The adsorption of pyridine (py) on Fe, Co, Ni and Ag electrodes was studied using surface‐enhanced Raman scattering (SERS) to gain insight into the nature of the adsorbed species. The wavenumber values and relative intensities of the SERS bands were compared to the normal Raman spectrum of the chemically prepared transition metal complexes. Raman spectra of model clusters M₄(py) (four metal atoms bonded to one py moiety) and M₄(α‐pyridil) where M = Ag, Fe, Co or Ni were calculated by density functional theory (DFT) and used to interpret the experimental SERS results. The similarity of the calculated M₄(py) spectra with the experimental SERS spectra confirm the molecular adsorption of py on the surface of the metallic electrodes. All these results exclude the formation of adsorbed α‐pyridil species, as suggested previously. Copyright © 2009 John Wiley & Sons, Ltd.     

Orbital moments of 3d adatoms and Co nanostructures on Cu(0 0 1) surfaces

We use ab initio calculations to investigate spin and orbital moments of 3d transition-metal adatoms and Co nanostructures on Cu(0 0 1) surfaces. For Fe and Co adatoms on Cu(0 0 1) we predict extremely large orbital moments, comparable to the spin moments at these sites. For Mn and Cr adatoms the orbital moments are extremely small and can be neglected in face of their rather large spin moments. Ni adatoms on Cu(0 0 1) were found to be non-magnetic. Our investigations for adsorbed flat clusters of Co on Cu(0 0 1) address the persistence and extent of these large orbital moments in the clusters as a function of their size. We find that, the average orbital moment (M_orb) per Co atom is strongly correlated with the coordination number, decreasing drastically and monotonically as the average number of first Co neighbors around the sites in the cluster (N_Co) is increased.     

The influence of hydrogen on the electronic and magnetic structures of TM(0 0 1) (TM=Fe, Co, Ni, and Cu) surfaces and interfaces: Ab-initio calculations

We present ab-initio investigation of the electronic and magnetic structure of TM(0 0 1) surfaces and TM/Cu(0 0 1) systems (TM=Fe, Co, Ni, Cu) with and without hydrogen adsorbed layer. The adsorption energy of hydrogen atom is found to be energetically more stable above the surface layer of Ni(0 0 1) surface than other TM(0 0 1) surfaces. The adsorption energies of hydrogen on TM/Cu(0 0 1) systems are larger than those on TM(0 0 1) surfaces. The relaxed geometries show that hydrogen has a strong influence on the interlayer distance. Furthermore, a marked reduction of Fe, Co, and Ni surface magnetic moments to 2.54, 1.41 and 0.25 μ_B, respectively, is obtained due to the presence of hydrogen.     

Comparison of O–H and C–H activation of methanol on Ni-based cluster: a DFT investigation

Using the density functional theory, the initial dehydrogenation of methanol on Ni_xM_y (M?=?Ni, Co, Fe, Mn, Cr, x?+?y?=?4, y?=?1, 2) clusters is investigated. Two adsorption and dehydrogenation mechanisms of methanol are studied: one proceeds along the C–H scission and another begins with the breaking of the O-H bond. The adsorption sites of methanol on the Ni or M sites of the Ni_xM_y clusters are considered. The adsorption of methanol on Ni₄ cluster is stronger than those on bimetallic clusters, while the initial dehydrogenation barriers on Ni_xM_y clusters are lower than that on Ni₄ cluster. The comparable energy barriers of two pathways (O–H or C–H dissociation) on Ni-based clusters indicate that these two paths are quite competitive. In addition, the Ni₂M₂ clusters show superior activation performance compared with the Ni₃M clusters, especially for Ni₂Mn₂ and Ni₂Cr₂ clusters. The effects of alloyed metal on the catalytic activity of Ni for methanol initial dehydrogenation, including the adsorption energy, O–H or C–H bond scission barrier and frontier molecular orbital levels, are discussed. It can be concluded that the addition of Co, Fe, Mn and Cr to Ni catalyst is able to enhance the activity of the methanol dehydrogenation reaction.     

Synthesis,Spectral Characterization,DNA Binding Studies and Antimicrobial Activity of Co(II), Ni(II), Zn(II), Fe(III) and VO(IV) Complexes with 4-Aminoantipyrine Schiff Base of Ortho-Vanillin

A series of transition metal complexes of Co(II), Ni(II), Zn(II), Fe(III) and VO(IV) have been synthesized involving the Schiff base, 2,3-dimethyl-1-phenyl-4-(2-hydroxy-3-methoxy benzylideneamino)-pyrazol-5-one(L), obtained by condensation of 4-aminoantipyrine with 3-methoxy salicylaldehyde. Structural features were obtained from their FT-IR, UV–vis, NMR, ESI Mass, elemental analysis, magnetic moments, molar conductivity and thermal analysis studies. The Schiff base acts as a monovalent bidentate ligand, coordinating through the azomethine nitrogen and phenolic oxygen atom. Based on elemental and spectral studies six coordinated geometry is assigned to Co(II), Ni(II), Fe(III) and VO(IV) complexes and four coordinated geometry is assigned to Zn(II) complex. The interaction of metal complexes with Calf thymus DNA were carried out by UV–VIS titrations, fluorescence spectroscopy and viscosity measurements. The binding constants (K_b) of the complexes were determined as 5?×?10⁵ M^?1 for Co(II) complex, 1.33?×?10⁴ M^?1 for Ni(II) complex, 3.33?×?10⁵ M^?1 for Zn(II) complex, 1.25?×?10⁵ M^?1 for Fe(III) complex and 8?×?10⁵ M^?1 for VO(IV) complex. Quenching studies of the complexes indicate that these complexes strongly bind to DNA. Viscosity measurements indicate the binding mode of complexes with CT DNA by intercalation through groove. The ligand and it’s metal complexes were screened for their antimicrobial activity against bacteria. The results showed the metal complexes to be biologically active, while the ligand to be inactive.     

Controlling spin off state by gas molecules adsorption on metal-phthalocyanine molecular junctions and its possibility of gas sensor

Employing Green's function (GF) technique in combination with spin-polarized density functional theory (DFT), we study the electronic structure and magnetic properties of metal phthalocyanine (MPc) (M?=?Mn, Fe, Co, Ni, Cu, Zn) with or without four different gas molecules (NO, CO, O₂ and NO₂) adsorbing on the M atom of MPc molecule. The corresponding stable adsorption structural configurations and transport properties of MPc molecular junctions are also investigated. Our results indicate that the magnetic moment of MPc for M?=?Mn, Fe and Co can be modified by the specific gas molecule adsorption, which is mainly ascribed to competitive relation of HOMO-LUMO Gap and Hund's rules. However, for M?=?Ni, Cu and Zn, it is difficult to detect gas molecule because the interaction of M atom and these gases is most of weak van der Waals interaction. Remarkably, the spin of MPc molecule can be switched to a magnetic off-state by specific gas absorption, giving rise to a potential application on controllable spintronic devices. In addition, CO, NO, O₂ and NO₂ gas molecules can be detected selectively by measuring spin filter efficiency of these MPc molecular junctions. On the basis of our results, MPc (M?=?Mn, Fe, Co) molecular junctions can be considered as a promising nanosensor device to detect individual gas molecules.     

Adsorption of H<Subscript>2</Subscript>S,HS, S,and H on a stepped Fe(310) surface

Using periodic density functional theory we studied adsorption of H₂S, HS, S and H on the Fe(310) stepped surface, comparing our results with those on Fe(100). H₂S is predicted to weakly adsorb on all high-symmetry sites, with the bridge site at the step edge as preferred one, oriented perpendicularly to the (100) terraces with the two H atoms pointing out of the surface. Adsorption of HS, S, and H is more stable on the bridge, four-fold hollow, and three-fold hollow sites, respectively. The detailed analysis of the computed local density of states show common trends with the behavior of adsorption energies and is able to account for energy differences of all species adsorbed on Fe(100) and Fe(310).     

Structural,electronic,and magnetic properties of transition-metal atom adsorbed two-dimensional GaAs nanosheet

By using first-principles calculations within the framework of density functional theory,the electronic and magnetic properties of 3d transitional metal(TM) atoms(from Sc to Zn) adsorbed monolayer Ga As nanosheets(Ga As NSs) are systematically investigated.Upon TM atom adsorption,Ga As NS,which is a nonmagnetic semiconductor,can be tuned into a magnetic semiconductor(Sc,V,and Fe adsorption),a half-metal(Mn adsorption),or a metal(Co and Cu adsorption).Our calculations show that the strong p–d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the Ga As NSs with Sc,V,and Fe adsorption.However,the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit,resulting in a stronger exchange interaction.Our results may be useful for electronic and magnetic applications of Ga As NS-based materials.     

Vibrational Spectroscopic Studies of 3,4-Lutidine Metal (II) Tetracyanonickelate Complexes

Infrared and Raman spectra of seven new metal (II) 3,4-lutidine tetracyanonickelate complexes, M(3,4 L)₂ Ni(CN)₄ [where 3,4 L = 3,4 - dimethyl-pyridine or 3,4-lutidine; M = Mn, Fe, Co, Zn, Ni, Cu or Cd] (abbreviated to M - Ni - 3,4 L) have been investigated. Spectroscopic and magnetic susceptibility measurements indicate that the compounds have the structure of Hofmann-type complexes. The copper complex has spectral features different from the other compounds.     

Chemical state of cobalt doped in and adsorbed on α-(Fe1-x Cr x )2O3 by emission Mössbauer spectroscopy

Mössbauer parameters (internal magnetic field, quadrupole splitting and isomer shift) of both α-(Fe_1-x Cr _x )₂O₃ (x=0, 0.2 and ≈1.0) doped and undoped with⁵⁷Co are in good agreement at room temperature and 77 K, except internal magnetic fields of both α-Cr₂O₃ doped with⁵⁷Co and enriched⁵⁷Fe. It is thus concluded that⁵⁷Fe produced from⁵⁷Co occupies the octahedral sites as Fe³⁺ with small distortion from cubic symmetry. Different internal magnetic field of doped α-Cr₂O₃ may be explained by the difference of canting of the spin against the [111] axis. By adding zinc ions, the adsorption of Co²⁺ ions on α-Fe₂O₃ particles in aqueous solution is decreased considerably in the pH range of 6.5–9.5 at 303 K, but the internal magnetic field of⁵⁷Co adsorbed on α-Fe₂O₃ does not change, although the internal magnetic fields of both samples with and without zinc ions are smaller than that of bulk α-Fe₂O₃ doped with⁵⁷Co. This suggests that densities of⁵⁷Co ions on the surface of α-Fe₂O₃ may be decreased by the addition of zinc ions and⁵⁷Co ions adsorbed on α-Fe₂O₃ are weakly bound on the substrate.     

Structural,electronic and catalytic performance of single-atom Fe anchored 3Si-doped graphene

By density functional theory (DFT) calculations, it is found that the single-atom Fe anchored three Si modified defective graphene (3Si-graphene-Fe) exhibits the high stability, and this system is semiconducting property and has non-magnetic moment. Besides the most stable configurations, electronic structures and magnetic properties of adsorbed species (O₂, CO, 2CO and CO/O₂) on 3Si-graphene-Fe systems are comparably discussed. The adsorption of O₂ is more stable than that of CO molecule and the coadsorption of 2CO and CO/O₂ has the larger adsorption energy than that of the isolated one. The adsorbed O₂, CO and CO/O₂ can induce the change in magnetic properties of 3Si-graphene-Fe system, and the coadsorbed CO/O₂ on system exhibits the metallic property. Among the reaction mechanisms, the CO oxidation reactions through Eley–Rideal (ER) reactions have lower energy barriers (<0.5?eV) than those of the Langmuir–Hinshelwood (LH) and new termolecular Eley–Rideal (TER) mechanisms, indicating that the ER reaction as starting step is an energetically favourable process. These results provide an important guidance on validating the catalytic activity of single atom on graphene-based materials.     

First-principles study of transition metal linear monoatomic chains adsorption on boron nitride nanotube

Structural, electronic and magnetic properties of six 3d transition metals (TM=V, Cr, Mn, Fe, Co and Ni) linear monoatomic chains adsorbed on the (5,5) boron nitride nanotube (BNNT) at five different sites have been investigated by first-principle calculations. The results indicate all TM chains can be spontaneously adsorbed on the outer surface of the BNNT. The stable adsorption sites are different for different TM chains. All TM chains can be adsorbed on the N site, while the adsorption on the Z site is unstable. The dispersion character occurs in energy band curves of stable TM/BNNT systems and bring about the band gap disappearance in comparison with that of pure (5,5) BNNT. Interestingly, the TM/BNNT systems with nearly half-filled 3d metals V and Cr at H and N sites, as well as Mn at A site show a half-metal character and are usable in spintronics devices. The different electronic properties of BNNT can also be achieved through decorations of the same TM chain on different sites. The TM chain adsorbed BNNT systems exhibit high stability, promising electronic properties and high magnetic moments, which may be useful for a wide variety of next-generation nanoelectronic device components.     

First Principles Investigation of the Magnetic,Magnetoelectric, and Optical Properties of Double Perovskites Containing Ions of Transition Metals LaPbTSbO<Subscript>6</Subscript> (T = Fe,Co, Ni)

Within the first principles approach implemented in the VASP package, a correlation between magnetic, electronic, polarization, and optical properties, on the one hand, and the structural ordering of cations, on the other hand, is investigated in double perovskites LaPbTSbO₆ (T = Fe, Co, Ni). Two types of cation ordering are considered: simultaneous layered (LL) and checkerboard (RR) ordering of both cations. These two types of ordering are chosen due to their significance; namely, the ordering RR is one of the most implementable types of cation ordering in double perovskites, and compounds with layered ordering can be considered as a heterostructure consisting of periodically alternating metal–nonmagnetic metal layers, which is of interest for experimental synthesis and investigation. It is found that the type of cation ordering in compounds with T = Fe and Ni radically changes the magnetic and/or electronic properties of the compound. Moreover, it is found that low-symmetry stable phases are polar for both types of cation ordering, and the values of spontaneous polarization are evaluated.     

The structural,electronic and magnetic properties of Ag4M and Ag4MCO (M = Sc–Zn) clusters

The structures, spectra and electronic and magnetic properties of Ag₄M and Ag₄MCO (M?=?Sc–Zn) clusters have been studied using density functional theory and CALYPSO structure searching method. Structural searches show that M atoms except Zn tend to occupy the highest coordination position in the ground state Ag₄M and Ag₄MCO clusters. Carbon monoxide is most easily adsorbed on Ag atom of Ag₄Zn and M atom of other Ag₄M. Infrared and Raman spectra, photoabsorption spectra and photoelectron spectra of Ag₄M and Ag₄MCO clusters are forecasted and can be used to identify these clusters from experiment. Analysis of electronic properties indicates that the adsorption of CO on Ag₄M clusters changes the zero vibrational energy (ZPVE) and increases stability of the host clusters. Dopant atoms except for Zn improve the stability of silver cluster. The Ag₄Ni cluster shows high chemical activity and maximum adsorption energy for carbon monoxide. Magnetism calculations reveal that the magnetic moment of Ag₄M (M?=?Mn–Ni) cluster adsorbed by carbon monoxide is decreased by 2 μ_B. The change of magnetic moment makes it possible to be used as a nanomaterial for carbon monoxide detection. Simultaneously, it is found that the adsorption of CO on Ag₄Cu cluster is a physical adsorption.     

First-principles study of small palladium clusters on NiAl(1 1 0) alloy surface

Theoretical calculations focused on the geometry, stability, electronic and magnetic properties of small palladium clusters Pd_n (n=1–5) adsorbed on the NiAl(1 1 0) alloy surface were carried out within the framework of density functional theory (DFT). In agreement with the experimental observations, both Ni-bridge and Al-bridge sites are preferential for the adsorption of single palladium atom, with an adsorption energy difference of 0.04 eV. Among the possible structures considered for Pd_n (n=1–5) clusters adsorbed on NiAl(1 1 0) surface, Pd atoms tend to form one-dimensional (1D) chain structure at low coverage (from Pd₁ to Pd₃) and two-dimensional (2D) structures are more stable than three-dimensional (3D) structures for Pd₄ and Pd₅. Furthermore, metal-substrate bonding prevails over metal–metal bonding for Pd cluster adsorbed on NiAl(1 1 0) surface. The density of states for Pd atoms of Pd/NiAl(1 1 0) system are strongly affected by their chemical environment. The magnetic feature emerged upon the adsorption of Pd clusters on NiAl(1 1 0) surface was due to the charge transfer between Pd atoms and the substrate. These findings may shade light on the understanding of the growth of Pd metal clusters on alloy surface and the construction of nanoscale devices.     

Structural, electronic and magnetic properties of Mn, Co, Ni in Gen for (n=1-13)

The structural, electronic and magnetic properties of TMGe_n (TM=Mn, Co, Ni; n=1-13) have been investigated using spin polarized density functional theory. The transition metal (TM) atom prefers to occupy surface positions for n<9 and endohedral positions for n≥9. The critical size of the cluster to form endohedral complexes is at n=9, 10 and 11 for Mn, Co and Ni respectively. The binding energy of TMGe_n clusters increases with increase in cluster size. The Ni doped Ge_n clusters have shown higher stability as compared to Mn and Co doped Ge_n clusters. The HOMO-LUMO gap for spin up and down electronic states of Ge_n clusters is found to change significantly on TM doping. The magnetic moment in TMGe_n is introduced due to the presence of TM. The magnetic moment is mainly localized at the TM site and neighbouring Ge atoms. The magnetic moment is quenched in NiGe_n clusters for all n except for n=2, 4 and 8.     

Synthesis,Thermal Behavior,and Antimicrobial Activity of a Novel Macrocycle and its Transition Metal Complexes Derived from Thiosemicarbazide

The present study reports the synthesis of Co(II), Ni(II), Mn(II), Cu(II), and Zn(II) complexes with a new macrocyclic ligand (L₂)- 1,2,8,9,11,14-hexaazacyclopentadeca-12,13-dioxo-10,15-dithione-2,7-diene. The macrocycle was derived from thiosemicabazone (L₁) and diethyloxalate that were prepared by the reaction of thiosemicarbazide and glutaraldehyde in the ratio of 2:1. The synthesized complexes and ligands were characterized by elemental analysis and molar conductance, magnetic susceptibility, ¹HNMR, IR, electronic, and thermogravimetric analyses. The molar conductance values confirmed that the Ni(II), Cu(II), Zn(II), Mn(II) and Co(II) complexes were 1:2 electrolytes. On the basis of electronic spectral studies and molar conductance measurements, the authors proposed an octahedral structure for Ni(II), Mn(II), and Co(II) complexes, tetrahedral geometry for Zn(II) complex, and square planar geometry for Cu(II) complex. The thermal behavior of the compounds was studied by TGA in a nitrogen atmosphere up to 750°C at the rate of 20°C/min. The TGA results revealed that the complexes had higher thermal stability than the macrocycle. All the synthesized compounds were screened against 4 bacteria (i.e., Streptococcus aureus, Escherichia coli, Bacillus subtillis, Salmonella typhimurium) and 2 fungi (i.e., Fusarium oryzae, Candida albicans). The results showed that the metal complexes inhibited the growth of bacteria to a greater extent as compared to the ligand.     

Interfacial properties of Ce<Subscript>0.75</Subscript>Zr<Subscript>0.25</Subscript>O<Subscript>2</Subscript> supported noble metals (Pd,Pt) from first principles

First-principles electronic structure calculations of noble metals (NM=Pd, Pt)/Ce_0.75Zr_0.25O₂ systems are presented. It is found that: the NM adatoms do not prefer to stay at the atop or the bridge sites of the cations (Ce and Zr), but prefer to be adsorbed at or around the anion sites. The most preferable adsorption sites for both the Pd and Pt adatoms are the O-bridge sites neighboring the Zr dopant. The Pt adatom show much stronger interaction with the Ce_0.75Zr_0.25O₂(111) surface than does the Pd adatom. The interactions of the NM/Ce_0.75Zr_0.25O₂(111) interfaces are stronger than those of the corresponding NM/ceria(111) interfaces. There are some metal induced gap states (MIGS) appeared in the gaps of the NM/Ce_0.75Zr_0.25O₂(111) interfaces, which are important to catalytic properties of the NM/Ce_0.75Zr_0.25O₂(111) catalysts.