Monoatomic Wires Research Articles

Monoatomic Nickel Wires via Columnar Self-Assembly of Tribenzocyclyne Nickel Complexes

Monoatomic Nickel Wires via Columnar Self-Assembly of Tribenzocyclyne Nickel Complexes

Formation of Fe nanowires on Cu(1 0 0) vicinal surfaces

The current paper describe the formation of Fe nanowires on Cu(1 0 0) vicinal surfaces via Kinetic Monte-Carlo (KMC) simulations based on the solid-on-solid model to determine optimum growth parameters, such as substrate temperature T, deposition rate F and coverage rate θ. The heteroepitaxial growth of mono-atomic wires on a Cu surface is performed over a large range of temperature, varying between 50 K and 550 K. We found that ‘perfect’ mono-atomic wires are formed at the step-edge of Cu vicinal surface in the temperature range [400–510 K]. The existence of an optimal temperature and deposition flux for the formation of the ordered Fe nanowires on stepped Cu(1 0 0) surface is found. We also discussed how the magnitude of the Ehrlich-Schwoebel barrier (ES) and inverse Ehrlich-Schwoebel barrier (ESi) affects the filling rate and the uniformity of Fe nanowires.

Kinetic Monte Carlo simulation of Ni nanowires on Cu(1 0 0) stepped surfaces

Abstract In this paper we use Kinetic Monte-Carlo (KMC) simulations based on the solid-on-solid model to determine optimum growth parameters, such as deposition rate F, substrate temperature T and coverage rate θ for growing “perfect” Ni nanowires on Cu(1 0 0) vicinal surfaces. The heteroepitaxial growth of mono-atomic wires on a Cu surface is performed over a large range of temperature, varying between 50 K and 560 K. We found that ‘perfect’ mono-atomic wires are formed at the step-edge of Cu vicinal surface in the temperature range [400 K−500 K]. Different atomistic mechanisms may intervene in favoring adatom attachment to surface steps, thus allowing nanowires growth. We discussed how the magnitude of the Ehrlich-Schwoebel barrier affects the filling rate and the uniformity of Ni nanowires. Our results were compared to the available experimental and theoretical results and seem advantageous for a better understanding of the nanowires formation.

Formation of Ag and Co nanowires at the step of the Cu(100) vicinal surfaces: A kinetic Monte Carlo study

We use Kinetic Monte-Carlo (KMC) simulations based on the solid-on-solid model [Phys. Rev. B 95 (2017) 085404] to determine optimum growth parameters, deposition rate F and substrate temperature T for growing “perfect” Co and Ag nanowires on Cu(100) vicinal surfaces. The heteroepitaxial growth of mono-atomic wires on a Cu surface is performed over a large range of temperature, varying between 50 K and 575 K. We found different temperature ranges where ‘perfect’ mono-atomic wires are formed at the step-edge of Cu vicinal surface, such as [200 K575 K] for Ag/Cu and [425 K525 K] for Co/Cu. Different atomistic mechanisms may intervene in favoring adatom attachment to surface steps, thus allowing nanowires growth. Here we have focused on the effect of the Ehrlich-Schwoebel barrier; a physical property that determines the mobility of adatomes across surfaces kinks and steps. We discussed how the magnitude of this barrier affects the filling rate and the uniformity of Ag and Co nanowires.

Impact of surface strain on the spin dynamics of deposited Co nanowires

Tailoring the magnetic properties at atomic-scale is essential in the engineering of modern spintronics devices. One of the main concerns in the novel nanostructured materials design is the decrease of the paid energy in the way of functioning, but allowing to switch between different magnetic states with a relative low-cost energy at the same time. Magnetic anisotropy (MA) energy defines the stability of a spin in the preferred direction and is a fundamental variable in magnetization switching processes. Transition-metal wires are known to develop large, stable spin and orbital magnetic moments together with MA energies that are orders of magnitude larger than in the corresponding solids. Different ways of controlling the MA have been exploited such as alloying, surface charging, and external electrical fields. Here we investigate from a first-principle approach together with dynamic calculations, the surface strain driven mechanism to tune the magnetic properties of deposited nanowires. We consider as a prototype system, the monoatomic Co wires deposited on strained Pt(111) and Au(111) surfaces. Our first-principles calculations reveal a monotonic increase/decrease of MA energy under compressive/tensile strain in supported Co wire. Moreover, the spin dynamics studies based on solving the Landau-Lifshitz-Gilbert equation show that the induced surface-strain leads to a substantial decrease of the required external magnetic field magnitude for magnetization switching in Co wire.

Molecular dynamics simulations of the formation of 1D spin-valves from stretched Au-Co and Pt-Co nanowires

We have performed molecular dynamics (MD) simulations of stretched Aux-Co1 − x and Ptx-Co1 − x nanowires to investigate the formation of bimetallic monoatomic wires between two electrodes. We have considered nanowires with two concentrations x = 0.2 and 0.8, aspect ratio of 13, a cross section of 1 nm2 and a wide range of temperatures (from 10 to 400 K). For the MD simulations we have used a semi-empirical interatomic potential based on the second moment approximation (SMA) of the density of states to the tight-binding Hamiltonian.For Au-Co alloys, Au atoms tends to migrate towards the narrowed region to form almost pure Au wires. In the PtCo case the formed chains usually consist of Pt enriched alternating structures. The most striking result is probably the Au0.2-Co0.8 alloy where pure monoatomic Au chains form between two Co electrodes constituting a potential 1D spin valve. Despite the known ease with which the 5d metals (Pt, Ir, and Au) form monoatomic chains (MACS), our results show that in the presence of Co (x = 0.2), the percentage of chain formation is higher than in the Pt and Au rich cases (x = 0.8).

Electric conductance of a mechanically strained molecular junction from first principles: Crucial role of structural relaxation and conformation sampling

Density functional theory (DFT) based molecular dynamics simulations have been performed of a 1,4-benzenedithiol molecule attached to two gold electrodes. To model the mechanical manipulation in typical break junction and atomic force microscopy experiments, the distance between two electrodes was incrementally increased up to the rupture point. For each pulling distance, the electric conductance was calculated using the DFT nonequilibrium Green's-function approach for a statistically relevant sample of configurations extracted from the simulation. With increasing mechanical strain, the formation of monoatomic gold wires is observed. The conductance decreases by three orders of magnitude as the initial twofold coordination of the thiol sulfur to the gold is reduced to a single S--Au bond at each electrode and the order in the electrodes is destroyed. Independent of the pulling distance, the conductance was found to fluctuate by at least two orders of magnitude depending on the instantaneous junction geometry.

Structural, magnetic and conduction properties of 3d-metal monoatomic wires

From density functional theory calculations, we study the structure, magnetism and conduction properties of monoatomic wires made of all the 3d elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu). Wires with equidistant and alternating bond lengths are considered. Both magnetism and structure are found to play an important role for the conduction properties of the wires. Ferromagnetic wires are found to present a spin filtering effect which is not directly related with the magnitude of their magnetic moment. On the other hand, the main effect of bond length alternation is to partially destroy the transmission around the Fermi level, especially from the d bands. Ni wires are found to present particularly interesting spin filtering properties, meanwhile Cr wires present promising magnetoresistive effects.

Electronic stability and electron transport properties of atomic wires anchored on the MoS2 monolayer.

The stability, electronic structure, and electron transport properties of metallic monoatomic wires anchored on the MoS2 monolayer are investigated within the density functional theory. The anchoring of the atomic wires on the semiconducting monolayer significantly modifies its electronic properties; the metallic characteristics of the assembled monolayers appear in the density of states and band structure of the system. We find that Cu, Ag and Au wires induce the so-called n-type doping effect, whereas Pt wires induce a p-type doping effect in the monolayer. The distinctly different behavior of Pt-MoS2 compared to the rest of the metallic wires is reflected in the calculated current-voltage characteristics of the assembled monolayers with a highly asymmetric behavior of the out-of-the-plane tunneling current with respect to the polarity of the external bias. The results of the present study are likely to extend the functionality of the MoS2 monolayer as a candidate material for the novel applications in the areas of catalysis and optoelectronic devices.

The increase in conductance of a gold single atom chain during elastic elongation

The conductance of monoatomic gold wires has been studied using ab initio calculations and the transmission was found to vary with the elastic strain. Counter-intuitively, the conductance was found to increase for the initial stages of the elongation, where the structure has a zigzag shape and the bond angles increase from ≈140° toward ≈160°. After a certain elongation limit, where the angles are relatively high, the bond length elongation associated with a Peierls distortion reverses this trend and the conductance decreases. These simulations are in good agreement with previously unexplained experimental results.

Electronic transport of nitrogen-capped monoatomic carbon wires between lithium electrodes

Nitrogen (N)-capped single-atom carbon wires are chemisorbed onto two identical Li (111) electrodes to construct nanodevices. First-principles calculations predict that devices with even and odd numbers of carbon wires would show dramatically different and unexpected electronic transport properties. An even number of wires shows a metallic-like ballistic transport at low bias, a nonlinear current–voltage characteristic over the whole bias region, and a very striking negative differential resistance (NDR). An odd number of carbon wires shows the exact opposite behavior. Currents are very small and rise extreme slowly with bias, and no NDR is observed. The zero-bias conductance of an even number of carbon wires is rather high and reaches a value of about 20 times larger than that for an odd number of wires. These intriguing phenomena can be attributed to changes in the molecular states due to charge transfer doping.

Modelling the Cu mono-atomic wire formation on Pt vicinal surfaces using kinetic Monte Carlo simulations

Heteroepitaxial growth of the Cu–Pt system is investigated using kinetic Monte Carlo simulations based on a semi-empirical description of metal–metal interactions to interpret recent experiments devoted to the formation of mono-atomic copper wires on the steps of the vicinal Pt surface. We show that step decoration occurs for the narrow temperature range [250, 300] K in agreement with growth experiments. An exchange mechanism leading to interlayer diffusion at step edges which could strongly influence the temperature range for which the perfect Cu wires are observed is also introduced in our model. In addition, we find that an activation barrier higher than 0.6 eV for this exchange process is necessary to reproduce the experimental features observed by Gambardella et al. We also show that this process, when active, is responsible for a modification of the scaling law governing the island density evolution on the step.

Electron transport across a quantum wire in the presence of electron leakage to a substrate

We investigate electron transport through a mono-atomic wire which is tunnel coupled to two electrodes and also to the underlying substrate. The setup is modeled by a tight-binding Hamiltonian and can be realized with a scanning tunnel microscope (STM). The transmission of the wire is obtained from the corresponding Green’s function. If the wire is scanned by the contacting STM tip, the conductance as a function of the tip position exhibits oscillations which may change significantly upon increasing the number of wire atoms. Our numerical studies reveal that the conductance depends strongly on whether or not the substrate electrons are localized. As a further ubiquitous feature, we observe the formation of charge oscillations.

First principles theoretical study of complex magnetic order in transition‐metal nanowires

AbstractThe electronic and magnetic properties of one‐dimensional (1D) transition‐metal (TM) systems are investigated from a first principles theoretical perspective. The development of local magnetic moments and the stability of various collinear and non‐collinear spin arrangements are determined in the framework of a generalized gradient approximation to density‐functional theory (DFT). Two specific complementary problems are considered. The first one concerns the local moment formation in Cu wires doped with Co and Ni impurities. Recent results as a function of wire length, interatomic distances, impurity position within the wire, and total spin polarization $S_{z} $ are reviewed. It is shown that both Co and Ni impurities preserve their magnetic degree of freedom in monoatomic Cu wires by developing almost saturated local moments in all low‐lying total spin configurations ($S_{z} \leq 5/2$). The impurity moments are largely dominated by the d‐electron contributions. In the ground state they couple ferromagnetically with the moments induced at the Cu host atoms. The changes in the spin‐density distribution and in the local densities of electronic states are quantified as a function of the position of the impurity position within the wire. In addition, recent results on the ground‐state magnetic order in V nanowires are reviewed. The stability of ferromagnetic (FM), antiferromagnetic (AF), and spiral non‐collinear (NC) orders is analyzed in terms of the frozen‐magnon spectrum. A remarkable transition from FM to NC order is observed as a function of the nearest‐neighbor (NN) distance a. The dependence of the single‐particle electronic structure of the wire on the wave‐vector of the spin‐density wave (SDW) is demonstrated. Finally, the role of magnetic anisotropy on the stability of NC order is discussed in the framework of a simple classical spin model.

Effect of adsorbed H atoms on magnetism in monoatomic Fe wires at Ir(100)

By means of ab initio calculations based on density-functional theory we demonstrate that magnetism in monoatomic Fe wires deposited on nanostructured Ir(100) surface can be tuned by their functionalization with hydrogen. The pristine monoatomic Fe wires deposited on nanostructured Ir(100) surface partially covered by H atoms are antiferromagnetic. However, the type of exchange interaction between Fe atoms can be changed by increasing H coverage. At fully hydrogenated Ir surface the Fe wires themselves are decorated with hydrogen, which gives rise to the ferromagnetic coupling between adjacent Fe atoms.

Spiral Adsorbate Structures on Monoatomic Nanowire Electrodes

Salty strand: Molecular dynamics simulations suggest that a monoatomic silver wire, immersed in an aqueous solution of NaCl, is covered by a monoatomic salt with spiral structure (see picture). This behaviour is in striking contrast to that of a plane silver electrode, on which Na+ does not adsorb. The difference is caused mainly by steric effects.

Measurements of stretch lengths of gold mono-atomic wires covered with 1,6-hexanedithiol in 0.1 M NaClO 4 with an electrochemical scanning tunneling microscope

Stretch lengths of pure gold mono-atomic wires have been studied recently with an electrochemical scanning tunneling microscope (STM). Here, we will report a study of stretch lengths of gold mono-atomic wires with and without 1,6-hexanedithiol (HDT) using the STM break-junction method. First, the stretch length was measured as a function of electrode potentials of a bare Au(1 1 1) substrate and a gold STM tip in a 0.1 M NaClO 4 aqueous solution. Second, a self-assembled monolayer (SAM) was fabricated on an Au(1 1 1) substrate by dipping the substrate into a 1 mM HDT ethanol solution. At last, we measured the stretch length of gold mono-atomic wires on a substrate covered with the SAM in place of the bare Au(1 1 1) substrate. We compared the electrode potential dependence of the stretch lengths of gold mono-atomic wires covered with and without HDT. We will discuss the effect of the electrode potential on the stretch lengths by taking account of electrocapillarity of gold mono-atomic wires.

Ballistic conductance of oxygen and sulfur-incorporated zigzag Au atomic wires

We study the effects of oxygen and sulfur impurity atoms on the electronic structure and ballistic conductance of zigzag-shaped Au monoatomic wires by a first-principles calculation based on the embedded Green's-function technique. In contrast to the straight wires in which the $\mathrm{O}\phantom{\rule{0.2em}{0ex}}2p$ $(\mathrm{S}\phantom{\rule{0.2em}{0ex}}3p)$ states form doubly degenerate sharp $\ensuremath{\pi}$ resonant levels at the Fermi energy $({E}_{F})$, one of them is broadened due to symmetry lowering accompanied by zigzag deformations, shifts to lower energies, and exhibits a Fano-type resonance dip in the ballistic conductance. The other state, which does not couple with the $\mathrm{Au}\phantom{\rule{0.2em}{0ex}}6s$-like band, remains a sharp resonant peak at ${E}_{F}$ in the density of states and in the conductance. It splits into two peaks corresponding to majority and minority spin electrons when spin polarization is taken into consideration.

Theoretical study of linear monoatomic nanowires, dimer and bulk of Cu, Ag, Au, Ni, Pd and Pt

The binding and electronic properties of monoatomic nanowires, dimers and bulk structures of Cu, Ag, Au and Ni, Pd, Pt have been studied by the projector augmented-wave method (PAW) within the density functional theory (DFT) using the local density approximation (LDA) as well as generalized gradient approximation (GGA) in both Perdew–Wang (PW91) and Perdew–Burke–Ernzerhof (PBE) parameterizations. Our results show that the formation of atomic chains is not equally plausible for all the studied elements. In agreement with experimental observations Pt and Au stand out as most likely elements to form monoatomic wires. Changes in the electronic structure and magnetic properties of metal chains at stretching are analyzed.

Inelastic Electron Transport in Monoatomic Wires

Based on non-equilibrium Green's function theory and density functionaltheory, we investigate the vibrational property and electron–phonon(el–ph) interaction induced inelastic scattering in electron transportthrough metallic monoatomic wires.