Shmuel Barzilai

The effect of internal impurities on the mechanical and conductance properties of gold nanowires during elongation

The conductance and mechanical properties of contaminated gold nanowires (NWs) were studied using first principle calculations. Nanowires containing internal impurities of H2O or O2 were elongated along two different directions. It was found that both impurities interact with the gold atoms and affect the properties of the NWs. From a mechanical viewpoint, the impurities increase the bond strength in their vicinity and, throughout the entire elongation, remain surrounded by gold atoms. The impurities do not migrate to the surface and never end up in the single atom chain. The NW fracture always occurs at an Au–Au bond, far from the impurity. Therefore, the impurities do not affect the fracture strength but do decrease the strain at fracture. A variety of conductance effects were observed depending on the type and location of the impurity, and the O2 has the most significant impact. The O2 reduces the conductance when it is close to the gold atoms in the main pathway. However, at the late stages of the elongation, both impurities are located far from the main pathway and have little influence on the conductance.

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.

Ab initio study of the mechanical and transport properties of pure and contaminated silver nanowires

The mechanical properties and conductance of contaminated and pure silver nanowires were studied using density functional theory (DFT) calculations. Several nanowires containing O2 on their surfaces were elongated along two different directions. All of the NWs thinned down to single atom chains. In most simulations, the breaking force was not affected by the presence of the O2, and similar fracture strengths of ≈1xa0nN were computed for the pure and impure NWs. When the O2 became incorporated in the single atom chain, the fracture occurred at the Ag-O bond and a lower fracture strength was found. All of the simulations showed that the impurity interacted with the silver atoms to reduce the electron density in its nearby vicinity. A variety of conductance effects were observed depending on the location of the impurity. When the impurity migrated during the elongation to the thinnest part of the NW, it reduced the conductance significantly, and an ≈1 G0 conductance (usually associated with a single atom chain) was calculated for three- and two-dimensional structures. When the impurity was adjacent to the single atom chain, the conductance reduced almost to zero. However, when it stayed far from the thinnest part of the NW, the impurity had only a small influence on the conductance.

Structure stability and electronic transport of gold nanowires on a BeO (0 0 0 1) surface

Gold nanowires (NWs) exhibit remarkable structural and electrical properties, making them good candidates for practical nanoelectronic devices. For such engineering applications, ?-wurtzite BeO may be a useful platform for supporting these NWs, because gold atoms are attracted to this surface and the atom separation of the BeO (0?0?0?1) surface is compatible with the Au?Au atom spacing. However, the influence of this substrate on the NW conductivity and structure is not known. Here, the stability and conductance of several Au NW configurations on BeO (0?0?0?1) surfaces are investigated using ab initio simulations. It was found that the beryllium-terminated surface preserves the configuration for most of the NWs while the oxygen-terminated surface changes and even repels most of the NW configurations. The electronic structure and the transmission properties of the stable cases showed small changes in the electronic structure of gold NWs due to the presence of the BeO substrate. These changes do not restrict the conduction of the NWs and even enhance it by increasing the capacity of the existing transmission channels, and forming new conduction paths.

Sensitivity of gold nano conductors to common contaminations ab initio results

Gold nanowire chains are considered a good candidate for nanoelectronic devices because they exhibit remarkable structural and electrical properties. A previous study shows that the beryllium-terminated BeO (0001) surface may be a useful platform for supporting nano gold conductors, since it preserves the nano-wire configuration, does not restrict its conductivity, and even enhances it. However, the influence of contamination on the conductivity of such conductors is unknown. Here, ab initio simulations were performed to determine the effect of commonly adsorbed contaminants (H2O and O2) on the conductivity of gold nano-conductors. We found that the presence of adsorbed impurities does not alter the good conductive ability of the conductors under examination.

Disparate effects of an O2 internal impurity on the elongation and quantum transport of gold and silver nanowires

In this work, we investigated the effects of an internal O2 impurity on the conductance of elongated gold and silver nanowires (NWs) using density functional theory calculations. We found that the O2 interacts with these metallic NWs very differently. In the case of gold NWs, the presence of an internal oxygen molecule locally strengthens the wire, therefore, forcing the phase transformations connected to the thinning process (3D to 2D and 2D to single atom chain) to occur far from the oxygen. As a consequence, towards the end of the elongation, the internal O2 is located far from the main conductance channel and therefore has little influence on the conductance of the NW. In contrast, in silver NWs, the presence of an internal oxygen molecule involves a larger charge transfer from the metallic atoms to the oxygen, therefore, weakening the Ag-Ag binding. During the initial stages of the elongation, several metallic bonds adjacent to the impurity break, so that in most simulations the NW thinning takes pla...

Sensitivity of gold nano-conductors to voids, substitutions, and electric field: ab initio results

AbstractnGold nanowires are good candidates for nano-electronics devices. A previous study has shown that the beryllium-terminated BeO (0001) surface may be a useful platform for supporting gold nano-conductors, since it preserves the nano wire configuration and does not restrict its conductivity. Here, we used ab initio simulations to determine the sensitivity of potential gold nano-conductors to the presence of point defects, O2 substitutions and to an applied perpendicular electric field, as in field effect transistors. We found that the presence of the point defects causes only small changes in the atomic bond lengths of the NW, does not alter the NW configuration, but may affect the overall conductivity. Single or double voids on the same channel reduce the conductance by 28xa0% at most, but when the voids arrange in a way that only one channel remains for conductance, it reduces by factor of two to ≈1 G0 (G0xa0=xa02e2/h). The presence of a single O2 molecule as a substitution reduces the electron availability in the neighboring Au atoms, in most cases reducing the conductance. The perpendicular electric field, which is typical for field effect transistors, affects the electron density distribution, shifts and changes the conductance spectra profile, but does not decrease the conductivity.

Effect of wire configuration and point defects on the conductance of gold nano-conductors

Gold nanowire (NW) chains are considered a good candidate for nano-electronics devices because they exhibit remarkable structural and electrical properties. One promising nano-conductor candidate is called ‘Hexa1’. It has a two-dimensional, one atom thick structure and was found to spontaneously form during simulations of gold NWs elongations. It is stable and a good conductor when adsorbed on a suitable substrate. In this study, we deepened the investigation of such a NW structure, to explore the effect of the NWs length, point defects and NW junctions on its conductance. We found that the conductance is not affected by the NW length, and that conveniently placed point defects can be used to create resistors. We also found that direction changes in circuits produce conductance bottle necks, therefore decreasing the conductance. However, this decrease can be easily overcome by adding a few atoms to the NW junction.