Monatomic Chains Research Articles

Single molecule capture by a doped monatomic carbon chain

A B-doped monatomic carbon chain has fine molecular capture ability for H2O and especially for NO2, which is better than that of other doped monatomic carbon chains. At 300 K and 1 atm, the capture probability of a B-doped monatomic carbon chain is appreciable even in a NO2 concentration of 1 ppm, and the influence of the adsorbate on the quantum transport is notable for the detection. In contrast, a pure monatomic carbon chain shows its invulnerability to N2, O2, H2O, NO2, CO and CO2, and is incapable of molecule capture due to having too low adsorption ability and weak response to quantum conductance. In the investigation of these issues, a statistic mechanical model (Lin et al 2011 Europhys. Lett. 94 40002; 2012 Chin. Phys. Lett. 29 080504) was extended to predict the adsorption and desorption rates of molecules on nanodevices. The theoretical foundation of this model was further discussed and its accuracy was verified by molecular dynamics simulations.

First-Principles Study of the Structural, Electronic, and Magnetic Properties of Cu-Fe, Cu-Co, and Cu-Ni Linear and Zigzag Nanowires

By using first-principles calculations, we have systematically investigated the equilibrium structure, electronic, and magnetic properties of free-standing Cu-Fe, Cu-Co, and Cu-Ni bimetallic linear and zigzag nanowires, and a comparison was carried out with the corresponding monatomic chains. It was found that all the bimetallic linear and zigzag chains have stable ferromagnetic (FM) states, and the total energies of all the considered zigzag chains are lower than those of the corresponding linear chains. The equilibrium bond lengths of the bimetallic Cu-Fe, Cu-Co, and Cu-Ni nanowires lie in between the values of the corresponding monatomic systems. The magnetic moments in linear nanowires are generally larger than the ones of the corresponding zigzag nanowires, and the Fe, Co, and Ni atoms in bimetallic nanowires have quite high local magnetic moments. The calculations suggest that there is hybridization between the Cu-3d and Fe (Co or Ni) 3d states, which leads to lower cohesive energies of the bimetallic nanowires than those of the corresponding monatomic nanowires. The bimetallic Cu-Fe and Cu-Co nanowires also have high spin polarizations and may be good potential materials for spintronic devices.

EfficientDFT+Ucalculations of ballistic electron transport: Application to Au monatomic chains with a CO impurity

An efficient method for computing the Landauer-Buettiker conductance of an open quantum system within DFT+U is presented. The Hubbard potential is included in electronic structure and transport calculations as a simple renormalization of the non-local pseudopotential coefficients by restricting the integration for the on-site occupations within the cutoff spheres of the pseudopotential. We apply the methodology to the case of an Au monatomic chain in presence of a CO molecule adsorbed on it. We show that the Hubbard U correction removes the spurious magnetization in the pristine Au chain at the equilibrium spacing, as well as the unphysical contribution of d electrons to the conductance, resulting in a single (spin-degenerate) transmission channel and a more realistic conductance of 1 G_0 . We find that the conductance reduction due to CO adsorption is much larger for the atop site than for the bridge site, so that the general picture of electron transport in stretched Au chains given by the local density approximation remains valid at the equilibrium Au-Au spacing within DFT+U.

Predicting the chemical stability of monatomic chains

A simple model for evaluating the thermal atomic transfer rates in nanosystems (Lin Z.-Z. et al., EPL, 94 (2011) 40002) was developed to predict the chemical reaction rates of nanosystems with small gas molecules. The accuracy of the model was verified by MD simulations for molecular adsorption and desorption on a monatomic chain. By the prediction, a monatomic carbon chain should survive for 1.2 × 102 years in the ambient of 1 atm O2 at room temperature, and it is very invulnerable to N2, H2O, NO2, CO and CO2, while a monatomic gold chain quickly ruptures in vacuum. It is worth noting that since the model can be easily applied via common ab initio calculations, it could be widely used in the prediction of chemical stability of nanosystems.

Atomistic simulations of highly conductive molecular transport junctions under realistic conditions

We report state-of-the-art atomistic simulations combined with high-fidelity conductance calculations to probe structure-conductance relationships in Au-benzenedithiolate (BDT)-Au junctions under elongation. Our results demonstrate that large increases in conductance are associated with the formation of monatomic chains (MACs) of Au atoms directly connected to BDT. An analysis of the electronic structure of the simulated junctions reveals that enhancement in the s-like states in Au MACs causes the increases in conductance. Other structures also result in increased conductance but are too short-lived to be detected in experiment, while MACs remain stable for long simulation times. Examinations of thermally evolved junctions with and without MACs show negligible overlap between conductance histograms, indicating that the increase in conductance is related to this unique structural change and not thermal fluctuation. These results, which provide an excellent explanation for a recently observed anomalous experimental result [Bruot et al., Nat. Nanotechnol., 2012, 7, 35-40], should aid in the development of mechanically responsive molecular electronic devices.

Thermal Rupture of Monatomic Metal Nanowires

The present study deals with the problem of thermal stability and rupture of metal nanowires, considered here as a monatomic chain located on an atomically smooth crystalline substrate. Based on a recently developed Monte Carlo computational model, the simulation results reveal a scenario of nanowire breaking via formation of atomic vacancies. Depending on temperature, the fluctuations in the positions of the nanowire atoms generate wave-shaped nanowire configurations with specific active sites for breaking. This process is followed by formation of one-atom vacancies in the nanowire. Their overgrowth into vacancies of two, three and more atoms leads to permanent nanowire rupture and, hence, to loss of the nanowire electronic and other physical properties. The time evolution of the atomic-scale nanowire morphology and breaking mechanism are discussed in detail. The proposed model of nanowire rupture sheds light on the general problem of thermal stability of artificial atomic structures on crystal surfaces and their application to electronic and other devices with exotic physical features.

Electronic structure and transport properties of monatomic Fe chains in a vacuum and anchored to a graphene nanoribbon

The electronic structure and transport properties of monatomic Fe wires of different characteristics are studied within the density functional theory. In both equidistant and dimerized (more stable) isolated wires, magnetism plays an important role since it leads to different shapes of the transmission coefficients for each spin component. In equidistant wires, electron localization around the Fermi level leads to symmetry breaking between dxy and dx2−y2 bands. The main effect of the structural dimerization is to decrease the number of channels available for the minority spin component. When anchored to the edges of a graphene nanoribbon, the dimerization of the chain is preserved, despite the hybridization of the d states of Fe with the C atoms which gives way to a reduction in the number of d channels around the Fermi level. Most conduction is then led by an electronic channel from the ribbon and the spz bands from the Fe wires. Suggestions to improve the spintronic ability of Fe wires are proposed.

ChemInform Abstract: Magnetic Nanochains: A Review

AbstractReview: 124 refs.

Negative differential resistance behavior of silicon monatomic chain encapsulated in carbon nanotubes

Using nonequilibrium Green's functions in combination with density-functional theory (DFT), we investigated the electronic transport properties of the silicon monatomic chains (SiMCs) with different geometries which were induced by the encapsulation of the carbon nanotubes (CNTs). The encapsulated SiMCs, which were put inside (5,5), (6,6), (7,7) and (8,8) hydrogenated armchair CNTs, were coupled to two Au (1 0 0) nanoscale electrodes. The electronic transport property of an isolated finite SiMC was also studied to serve as a reference to our calculations. As the diameter of CNTs increases, the geometry structures of SiMCs changed. Calculated results show that the current-voltage (I-V) characteristics depend sensitively on the geometry structures of SiMCs and can be controlled by the size-selective encapsulation. Negative differential resistance (NDR) phenomena were observed within certain bias voltage ranges. A detailed analysis of the origin of NDR was carried out with the transmission spectrum, the spatial distribution of frontier molecular orbitals and the molecular projected self-consistent Hamiltonian (MPSH) states taken into consideration. These results indicated that the size-selective encapsulation of SiMCs in CNTs can become a possible candidate for designing the silicon-based nanoelectronic devices.

Laser-Induced Distortions and Disturbance Propagation of Delocalized Electronic States in Monatomic Carbon Chains

Tight-binding electron-ion dynamics of carbon chains pumped by intense laser pulses are performed to study the interactions between monatomic carbon chains and lasers. Laser-induced distortions of carbon chains, which are enhanced by a long wavelength laser, are investigated. The carbon chains with a strong laser beam focused on one terminal are simulated to study the disturbance of electronic states. By the superposition of delocalized π band states, the disturbance propagates from the illuminated area to the non-illuminated area in a velocity of about 106 m/s at 0 K, and this velocity is weakened at room temperature due to the localization effect of thermal fluctuation.

Understanding formation mechanism of ZnO diatomic chain and multi-shell structure using physical mechanics: Molecular dynamics and first-principle simulations?

In this paper, the possibility of the monatomic chain (MC) formation for ZnO material was studied by molecular dynamics (MD) simulation. The process of MC formation and the effects of temperature, strain rate and size were studied extensively. The tensile process can be divided to be five stages and the ZnO diatomic chain (DC) can be found. The MD results show that most atoms in MC came from the original surface of ZnO nanowires (NWs). Temperature and strain rate are two important factors affecting the process, and both high temperature and low strain rate in a certain range would be beneficial to the formation of DC. Moreover, the effects of strain rate and temperature could attribute to the Arrhenius model and the energy release mechanism. Furthermore, multi-shell structure was found for the samples under tensile strain and the layer-layer distance was about 3 Å. Our studies based on density functional theory showed that the most stable structure of ZnO DC was confirmed to be linear, and the I–V curve was also got using ATK.

Mesoscopic superelasticity, superplasticity, and superrigidity

Atomic-undercoordination-induced local bond contraction, bond strength gain, and the associated temperature (T)-dependent atomic-cohesive-energy and binding-energy-density are shown to originate intrinsically the exotic paradox of superplasticity, superelasticity, and superrigidity demonstrated by solid sizing from monatomic chain to mesoscopic grain. The paradox follows these relationships: $$\left. \begin{gathered} \varepsilon (K,T) \hfill \\ y(K,T) \hfill \\ \sigma (K,T) \hfill \\ \end{gathered} \right\} \propto \left\{ \begin{gathered} \exp \left( {{B \mathord{\left/ {\vphantom {B {\Delta T}}} \right. \kern-\nulldelimiterspace} {\Delta T}}_{mk} } \right), (Plastic strain) \hfill \\ \left( {\eta _1 \Delta T_{mk} } \right)d^{ - 3} , (Elastic modulus) \hfill \\ \left[ {1 + AK^{ - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} \exp \left( {{{\Delta T_{mk} } \mathord{\left/ {\vphantom {{\Delta T_{mk} } T}} \right. \kern-\nulldelimiterspace} T}} \right)} \right]\Delta T_{mk} d^{ - 3} , (Yield stress, IHPR) \hfill \\ \end{gathered} \right. $$ where A, B, η 1, d and ΔT mk = T m (K)−T are size (K)-dependent physical parameters. T m(K) is the melting point. Mechanical work hardening during compressing and self-heating during stretching modulate the measured outcome extrinsically. Superplasticity dominates in the solid-quasimolten-liquid transition state. The competition between the accumulation and annihilation of dislocations activates the inverse Hall-Petch relationship. Therefore, it is essential for one to discriminate the intrinsic competition between the local bond energy density gain and the atomic cohesive energy loss from the extrinsic factors of pressure and temperature in dealing with atomistic mechano-thermo dynamics.

Effect of stretching on the ballistic conductance of Au nanocontacts in presence of CO: A density functional study

CO adsorption on an Au monatomic chain is studied within density functional theory in nanocontact geometries as a function of the contact stretching. We compare the bridge and atop adsorption sites of CO, finding that the bridge site is energetically favored at all strains studied here. Atop adsorption gives rise to an almost complete suppression of the ballistic conductance of the nanocontact, while adsorption at the bridge site results in a conductance value close to 0.6 G0, in agreement with previous experimental data. We show that only the bridge site can qualitatively account for the evolution of the conductance as a function of the contact stretching observed in the experimental conductance traces. The numerical discrepancy between the theoretical and experimental conductance slopes is rationalized through a simple model for the elastic response of the metallic leads. We also verify that our conductance values are not affected by the specific choice of the nanocontact geometry by comparing two different atomistic models for the tips.

Interaction of CO with an Au monatomic chain at different strains: Electronic structure and ballistic transport

We study the energetics, the electronic structure, and the ballistic transport of an infinite Au monatomic chain with an adsorbed CO molecule. We find that the bridge adsorption site is energetically favored with respect to the atop site, both at the equilibrium Au-Au spacing of the chain and at larger spacings. Instead, a substitutional configuration requires a very elongated Au-Au bond, well above the rupture distance of the pristine Au chain. The electronic structure properties can be described by the Blyholder model, which involves the formation of bonding/antibonding pairs of $5\ensuremath{\sigma}$ and $2{\ensuremath{\pi}}^{\ensuremath{\star}}$ states through the hybridization between molecular levels of CO and metallic states of the chain. In the atop geometry, we find an almost vanishing conductance due to the $5\ensuremath{\sigma}$ antibonding states giving rise to a Fano-like destructive interference close to the Fermi energy. In the bridge geometry, instead, the same states are shifted to higher energies and the conductance reduction with respect to pristine Au chain is much smaller. We also examine the effects of strain on the ballistic transport, finding opposite behaviors for the atop and bridge conductances. Only the bridge geometry shows a strain dependence compatible with the experimental conductance traces.

Bias-dependent oscillatory electron transport of monatomic sulfur chains

The bias-dependent oscillatory electron transport of monatomic sulfur chains sandwiched between gold electrodes is investigated with density functional theory and non-equilibrium Green’s function method. At zero bias, in contrast to the typical odd-even oscillations observed in most metallic chains, we find that the conductance oscillates with a period of four atoms. However, as the bias voltage is increased the current displays a two-atom periodicity. This emerges gradually, first for the longer chains and then, at voltages larger than 0.7 V, for lengths. The oscillatory behaviors are analyzed by the density of states and the energy-dependent and bias-dependent transmission coefficients.

Experimental determination of the mechanical strength of monatomic carbon chains

The ultimate tensile strength of monatomic carbon chains has been determined using the method of high-field mechanical loading in a field-ion microscope. The maximum strength of monatomic carbon chains (181 GPa) experimentally observed at 77 K amounts to about 70% of the value calculated for an ideal chain and significantly exceeds the tensile strength of well-known carbon materials, including carbon nanotubes and graphene.

Magnon spectrum of a symmetric-spin nanocontact on a ferromagnetic ultrathin film

A theoretical model is presented for the study of the magnetic properties and the coherent magnon transport via monatomic chains in ultrathin magnetic films. In particular, we studied a finite number of monatomic chains joining two slabs of ferromagnetic material. Each slab consists of five atomic layers of a cubic lattice with magnetically ordered spins coupled by the Heisenberg exchange. The system is supported on a non-magnetic substrate and otherwise considered free from magnetic interactions. The spin dynamics of the ultrathin film is studied by the matching method. The individual and the total magnon transmissions of the ultrathin ferromagnetic film, scattering coherently at the nanojunction zone, and the localized spin states in the boundary domain are calculated and analyzed. The interatomic magnetic exchange is varied on the boundary domain specifically for three cases of magnetic exchange to investigate the consequences of magnetic softening and hardening for the calculated properties. Numerical results show characteristic interference effects between the incident spinwaves and the localized spin states of the nanocontact. The calculated properties are presented for arbitrary incidence of the magnons on the boundary, for all accessible frequencies in the propagating bands, and for the interatomic magnetic exchange of the magnetic film. The localized magnon branches created by the nanocontact domain are observed in the Brillouin zone.

Study of wave propagation in strongly nonlinear periodic lattices using a harmonic balance approach

This paper presents a general harmonic balance method for studying plane wave propagation in strongly nonlinear periodic media. The proposed approach starts by assuming a multi-wavenumber and frequency solution for the unit cell degrees of freedom. A Galerkin projection then transforms the nonlinear differential equations of motion into a set of nonlinear algebraic equations, which are subsequently solved numerically through a Newton-like iteration scheme. These solutions reveal amplitude-dependent dispersion behavior and group velocities. Specific example systems studied include one-dimensional chains and two-dimensional lattices, both formed by a periodic arrangement of spheres interacting under a Hertzian contact law. Amplitude-dependent dispersion is noted in monatomic and diatomic chains, and in hexagonally close-packed two-dimensional lattices. The validity of the presented technique is assessed through direct numerical simulation of the equations governing finite-extent lattices. Strong agreement is documented for results calculated using the harmonic balance approach and the direct numerical simulations.

Effect of Coulomb correlations on one-dimensional monatomic nanowire

The experimental realisation of one–dimensional (1D) monatomic chains of transition elements has opened a new route to study the magnetism in nanostructures in the field of condensed matter physics. We studied a so–called extended Hubbard model which includes all the off–diagonal matrix elements of Coulomb interactions, to explain the phenomenon of ferromagnetism in 1D monatomic chain of itinerant ferromagnets like Fe, Co and Ni. We have used the Green's function equation of motion approach to get energy eigenvalue of quasi–particle. Within the mean field approximation, among the off–diagonal matrix elements, the effect of correlated hopping is very crucial, because the magnitude is larger than exchange interaction. Therefore, in 1D itinerant ferromagnets, the ferromagnetism is driven by combined effect of band splitting and band narrowing/broadening. As a result of it, for the systems with less than half filled band, the up spin band gets broadened and down spin band narrowed down and vice versa for more than half filled band systems. From available Density Functional Theory (DFT) results it can be seen that up spin channel is present for conduction near Fermi level in the systems with less than half filled band and vice versa for more than half filled band systems. This effect is more pronounced in the presence of external magnetic field. Presence of one spin channel is one of the requirements for spintronic devices. The obtained results are in good agreement with existing DFT results.

A one-dimensional extremely covalent material: monatomic carbon linear chain

Polyyne and cumulene of infinite length as the typical covalent one-dimensional (1D) monatomic linear chains of carbon have been demonstrated to be metallic and semiconductor (Eg = 1.859 eV), respectively, by first-principles calculations. Comparing with single-walled carbon nanotubes, the densities are evidently low and the thermodynamic properties are similar below room temperature but much different at the high temperature range. Polyyne possesses a Young's modulus as high as 1.304 TPa, which means it is even much stiffer than carbon nanotubes and to be the superlative strong 1D material along the axial direction. The Young's modulus of cumulene is estimated to be 760.78 GPa. In addition, polyyne is predicted to be as a one-dimensional electronic material with very high mobility.