Single Pb Atoms Research Articles

Boosting photocatalytic overall water splitting performance by dual-metallic single Ni and Pd atoms decoration of MoS2: A DFT study

Herein, we propose a novel MoS2 supported single Ni and Pb atoms catalyst (Ni/Pd@MoS2), on which the enhanced efficiency of water splitting is confirmed by quantitative density functional theory (DFT) calculations. The Bader charge, electron density difference (EDD) and projected density of state (PDOS) analysis demonstrates that the moderate electron transfer is reached by the synergy of the Ni atom and the Pd atom. As extra channel for excited carrier migration, the present of defect states obviously prolongs the carrier lifetime (143.45 ps). The unique electronic environment contributes to the electronic synergy and spatially separated of the effective active sites, leading the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) happen smoothly on the Pd and S site, respectively. Our research presents a novel idea for the development of highly efficient diatomic catalysts towards overall water splitting.

The impact of lead on structural, electronic, and vibrational properties of pristine C36 and its boron, nitrogen-dopant C36 on pentagonal and hexagonal rings

In this work, lead's impacts on the structural, electronic, and vibrational characteristics of pure C36 and C36 doped with boron and nitrogen on pentagonal and hexagonal rings are calculated using the DFT method. We provide an in-depth examination of these characteristics and how lead affects them. The adsorption energy, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and electrostatic potentials at the isosurface (EPI) have been studied in detail. Assess the ring dependence of the lead adsorption energy for the hexagonal and pentagonal rings of pristine C36 and B and N impurities at the substitutional site. The adsorption energy for the Pb on pristine C36 is endothermic; however, it is exothermic for the Pb on NB-doped C36 but has different values on the pentagonal and hexagonal rings. The results demonstrate that nitrogen and boron doping significantly increased the Pb atom's adsorption energy when the dopants occupied pentagonal sites. In addition, the bond lengths surrounding the impurity and the bond lengths of Pb atoms placed on pristine C36, BN-doped hexagonal ring, and BN-doped pentagonal ring in C36 are investigated. The electrostatic potential isosurface (EPI) surrounding the BN-doped hexagonal and pentagonal rings of C36 is described. The Mulliken charge transfer analysis demonstrates that the interaction between NB-doped C36 fullerene and lead (Pb) has a substantial effect on the charge transfer process and the reactivity of the doped system towards lead. However, the quantity of charge transmitted depends on the impurity's location on the hexagonal and pentagonal rings. These findings aid in the atomistic understanding of the interaction between a single Pb atom on the surface of C36 and BN-doped C36 at various rings. Our findings not only shed light on the complex interplay between lead and C36 but also offer valuable insights into potential applications in materials engineering and environmental remediation.

Diode effect in Josephson junctions with a single magnetic atom

Current flow in electronic devices can be asymmetric with bias direction, a phenomenon underlying the utility of diodes1 and known as non-reciprocal charge transport2. The promise of dissipationless electronics has recently stimulated the quest for superconducting diodes, and non-reciprocal superconducting devices have been realized in various non-centrosymmetric systems3–10. Here we investigate the ultimate limits of miniaturization by creating atomic-scale Pb–Pb Josephson junctions in a scanning tunnelling microscope. Pristine junctions stabilized by a single Pb atom exhibit hysteretic behaviour, confirming the high quality of the junctions, but no asymmetry between the bias directions. Non-reciprocal supercurrents emerge when inserting a single magnetic atom into the junction, with the preferred direction depending on the atomic species. Aided by theoretical modelling, we trace the non-reciprocity to quasiparticle currents flowing by means of electron–hole asymmetric Yu–Shiba–Rusinov states inside the superconducting energy gap and identify a new mechanism for diode behaviour in Josephson junctions. Our results open new avenues for creating atomic-scale Josephson diodes and tuning their properties through single-atom manipulation.

Adsorption of lead on the surfaces of pristine and B, Si and N-doped graphene

The efficacy of graphene and graphene doped with B, Si and N surfaces for the removal of Pb atom is examined by utilising density functional theory calculations. The results show that the binding energy of a single Pb atom on pristine graphene surface is −0.71 eV with the charge transfer of 0.42 electros from Pb to the surface. There is a significant enhancement observed in the binding on the surfaces of B-doped graphene (−1.46 eV) and Si-doped graphene (−2.37 eV) with the transfer of 1.48 and 1.92 electrons to their respective surfaces. The binding energy for the N-doped graphene is endothermic (+0.42 eV) due to negligible charge transfer between the Pb and the doped surface. The intense binding nature between Pb and pristine as well as the doped graphene structures is introduced, analysed and discussed in terms of bond distances, binding energies, Bader charges and electronic structures.

Effect of surface vacancies on the adsorption of Pd and Pb on MgO(100)

Theoretical quantum mechanical calculations have been carried out to establish the effect of surface vacancies on the adsorption of Pd and Pb atoms on the defective MgO(100) surface. The investigated defects included neutral, singly and doubly charged O and Mg vacancies on the (100) surface of MgO. These vacancies played the role of Fsn+ and Vsn− (n = 0, 1, 2) adsorption centers for a single Pd or Pb atom. From the results of calculations, it is clear that the Pd- and Pb-atom adsorption at the Fsn+ and Vsn− centers shows different characteristics than at the regular O2− and Mg2+ centers. Drastic changes in geometric, energetic, and electronic parameters are evident in Pd/Vsn− and Pb/Vsn−. The effect of Fs0 and Fs+, which in practice are the most important vacancies, is smaller, yet the adsorption of Pd and Pb at these centers is more energetically favorable than at the regular O2− center. Of the two metals studied, the atom of Pd is bound by the Fs0 and Fs+ centers with higher adsorption energies.Graphical abstract

Structural and electronic properties of lead sulfide quantum dots from screened hybrid density functional calculations including spin–orbit coupling effects

We present in this work density functional theory calculations of the structural and electronic properties of (PbS)n nanoparticles with n = 4–32. Particular care has been taken on the correct description of their electronic structure by using a hybrid functional including the spin–orbit coupling effects. We demonstrate that the bonding in PbS nanoparticles is quite different from bulk PbS as the six Pb–S bonds around a single Pb atom are found to have a different character while in bulk PbS all Pb–S distances are equivalent. We also relate the geometric structure to the evolution of the HOMO–LUMO gaps and show how the computed electronic properties strongly depend on the functional used. Finally, based on an extrapolation of our results, we predict that to obtain the onset of absorption in the infrared region of the spectrum a cubic nanoparticle of ~1.96 nm side length is needed, a result that is in agreement with existing experimental information.

Plasticity of single-atom Pb junctions

A low-temperature scanning tunneling microscope was used to fabricate atomic contacts on Pb(111). Conductance characteristics of the junctions were simultaneously recorded with forming and subsequent breaking of the contacts. A pronounced hysteresis effect in conductance traces was observed from junctions comprising the clean Pb(111) surface. The hysteretic behavior was less profound in contacts to single Pb atoms adsorbed to Pb(111). Density-functional calculations reproduced the experimental results by performing a full ab initio modeling of plastic junction deformations. A comprehensive description of the experimental findings was achieved by considering different atomic tip apex geometries.

A feasibility study of unconventional planar ligand spacers in chalcogenide nanocrystals.

The solar cell efficiency of chalcogenide nanocrystals (quantum dots) has been limited in the past by the insulation between neighboring quantum dots caused by intervening, often long-chain, aliphatic ligands. We have conducted a computationally based feasibility study to investigate the use of ultra-thin, planar, charge-conducting ligands as an alternative to traditional long passive ligands. Not only might these radically unconventional ligands decrease the mean distance between adjacent quantum dots, but, since they are charge-conducting, they have the potential to actively enhance charge migration. Our ab initio studies compare the binding energies, electronic energy gaps, and absorption characteristics for both conventional and unconventional ligands, such as phthalocyanines, porphyrins and coronene. This comparison identified these unconventional ligands with the exception of titanyl phthalocyanine, that bind to themselves more strongly than to the surface of the quantum dot, which is likely to be less desirable for enhancing charge transport. The distribution of finite energy levels of the bound system is sensitive to the ligand's binding site and the levels correspond to delocalized states. We also observed a trap state localized on a single Pb atom when a sulfur-containing phenyldithiocarbamate (PTC) ligand is attached to a slightly off-stoichiometric dot in a manner that the sulfur of the ligand completes stoichiometry of the bound system. Hence, this is indicative of the source of trap state when thio-based ligands are bound to chalcogenide nanocrystals. We also predict that titanyl phthalocyanine in a mix with chalcogenide dots of diameter ∼1.5 Å can form a donor-acceptor system.

Bis(μ-4-hydroxybenzoato-κ2O:O′)bis[(2,9-dimethyl-1,10-phenanthroline-κ2N,N′)(4-hydroxybenzoato-κ2O,O′)lead(II)

In the centrosymmetric binuclear title complex, [Pb2(C7H5O3)4(C14H12N2)2], each PbII ion is coordinated by two N atoms from a 2,9-dimethyl-1,10-phenanthroline (dmphen) ligand and four O atoms from three 4-hydroxy­benzoate anions in a distorted octa­hedral environment. The 4-hydroxy­benzoate groups coordinate to each PbII atom in two different ways. Two 4-hydroxy­benzoate ions behave as chelating ligands to a single Pb atom, and the other two form bridges between the two Pb atoms, forming a centrosymmetric eight-membered ring in the binuclear structure. Mol­ecules are linked into a two-dimensional framework by O—H⋯O hydrogen bonds. The packing is further stabilized by π–π inter­actions between the dmphen rings of neighboring mol­ecules, with a distance of 3.327 A between the planes of the dmphen ligands.

Morphology and electronic structure of submonolayer Pb on Si(111)–( [formula omitted])Au

The electronic structure and the morphology of Pb adsorbed on the Si(111)–( 6 × 6 )Au substrate in the coverage range from 0.025 up to 1 monolayer are investigated with ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling microscopy (STM). The UPS measurements reveal two distinct peaks in the spectra. Correlation with the STM images allows us to associate one of them with single Pb atoms. The second peak emerges at coverage of 0.075 ML and is identified as a localized quantum well state. An evolution of these states as a function of the Pb coverage is determined.

Experimental and theoretical studies of single Pb atom dynamics in one Si(1 1 1)-(7 × 7) unit cell

The theoretical simulation of single Pb atom motion in faulted and unfaulted halves of a Si(1 1 1)-(7 × 7) surface were performed using the kinetic Monte Carlo method. Modifying diffusion barriers within the unit cell, the results were fitted to STM observations over a wide temperature range between 50 and 300 K. The average activation energy of a single atom jump was estimated to be approximately 0.1–0.2 eV, giving a diffusion coefficient of ≈3 × 10 −5 cm 2 s −1 at 300 K inside the Si(1 1 1)-(7 × 7) unit cell.

Si(1 1 1)-(6 × 6)Au surface morphology and nucleation of Pb at low temperature

The morphologies of the Si(1 1 1)-(6 × 6)Au surface and the nucleation of Pb have been investigated at temperatures below room temperature using scanning tunnelling microscopy (STM). The STM scans of the clean Si(1 1 1)-(6 × 6)Au surface revealed exceptionally rich and strongly bias-dependent details within the unit cell. After deposition of about 0.01 ML of Pb(1 1 1), at temperatures above 180 K, the single Pb atoms formed a two-dimensional mesh with (6 × 6)-Au periodicity. In this early stage of deposition, the Pb atoms occupied predominantly one specific site of the (6 × 6) unit cell. The local symmetry of this site determined the further growth of the Pb layer. As a consequence, the structure of the Pb layer on Si(1 1 1)-(6 × 6)Au is rotated of 30° relative to that of the Pb layer on Si(1 1 1)-(7 × 7).

Single adatom adsorption and diffusion onSi(111)−(7×7)surfaces: Scanning tunneling microscopy and first-principles calculations

The adsorption and diffusion of single Pb atoms on $\mathrm{Si}(111)\ensuremath{-}(7\ifmmode\times\else\texttimes\fi{}7)$ surfaces have been studied by scanning tunneling microscopy (STM) and first-principles density functional calculations. STM experiments at temperatures from 100 to 130 K have revealed three regions of preferential adsorption, inside each half-unit cell, as well as real time diffusion events between them. The stable adsorption sites have been determined by first-principles calculations and by comparing simulated and measured STM images. The activation barriers for the motion inside the half-unit cells have been calculated and measured experimentally. A very good agreement between calculations and experiments has been found.

Diffusion mediated film growth on polycrystalline substrates

Mechanisms of island formation and growth are central issues in thin-film deposition. The shape and size as well as the spatial distribution of stable islands in the first phases of growth determine a wide variety of film properties. In an earlier work, the growth mode of sputter-deposited tin (Sn) and lead (Pb) films on polycrystalline Al substrates was analyzed in the framework of the rate-equation theory. This analysis yielded Stranski–Krastanov growth with the size of the critical nucleus in the range from 6 to 20 monomers. The present study is devoted to a detailed experimental investigation of the mechanisms involved in the formation of Sn and Pb islands on polycrystalline aluminum (Al). All thin-film systems treated in this work were deposited on glass substrates by DC magnetron sputtering. They consist of a polycrystalline Al underlayer covered with a 100 Å thick Sn or Pb films. The variation of the mean Sn and Pb island distance was determined as a function of the deposition temperature and of the underlayer thickness. It varied from 0.5 to 20 μm and showed an Arrhenius dependence on the deposition temperature. A rate-equation analysis yielded activation energies for surface diffusion of single Sn and Pb atoms of approximately 0.5 eV. Island size distributions (ISDs) were determined for different deposition temperatures and were mostly found to be monomodal with a global maximum at the mean island size. All these facts indicate that the mechanism of island formation is mediated by surface diffusion of the Sn or Pb monomers on the Al surface in a wide range of deposition temperatures.

Study of Pb diffusion on Si(111)−(7×7) with scanning tunneling microscopy: Low coverage

The diffusion of single Pb atoms and the formation of stable clusters containing two and three Pb atoms on a Si(111)−(7×7) reconstructed surface was studied with variable temperature scanning tunneling microscopy (STM). The numbers of single Pb atoms and Pb atoms in clusters were monitored as a function of time. A new and simple statistical model describing diffusion was developed. This model enables us to estimate the diffusion coefficient and the activation energy of diffusion. The main advantage is the avoidance of questionable counting of jump events in successive STM images. For substrate temperatures of 308, 311, and 313 K we obtained diffusion coefficients of 8.1×10−18, 1.2×10−17, and 1.9×10−17 cm2 s−1, respectively, and the activation energy of diffusion equaled E=0.56±0.07 eV. The energy difference ΔE between the binding energies of single Pb atoms at faulted and unfaulted halves of the Si(111)−(7×7) unit cells was estimated to be 27±9 meV.

Adsorption and diffusion mechanisms of Pb on Si(111)-(7 × 7) in the initial stages of Pb chemisorption

We present a theoretical study of the adsorption and diffusion mechanisms of Pb on the Si(111)-(7 × 7) surface in the initial stages of Pb chemisorption within the DAS model. In the framework of the crystalline extension of the extended Hückel theory, two adsorption mechanisms are studied: the adsorption of Pb atoms on Si dangling bonds and Pb adsorption with the formation of Pb atom clusters. The second mechanism is found to be more favorable than the first, but the two mechanisms could possibly coexist. Trimers and tetramers of Pb atoms are more likely than pairs. This tendency to agglomeration, in agreement with STM observations for room-temperature deposition, is explained by the strong interaction between Pb atoms which is emphasized in our calculations. The faulted half of the unit cell is preferred by about 0.1 eV. The diffusion paths for Pb on Si(111)-(7 × 7) are then investigated: jumps of Pb atoms between unfaulted and faulted half unit cells are more difficult than jumps inside the same half unit cell. Considering the diffusion of a Pb pair between an adatom and a restatom, we show that the interaction between Pb atoms leads to a significant decrease in the barrier energy as compared to that for the diffusion of a single Pb atom. An interpretation of experimental data obtained for room-temperature deposition at low coverage is proposed.

Adsorption and diffusion of single Pb atoms on Si(111)7 × 7 and Si(111)5 × 5 surfaces studied by scanning tunneling microscopy

We have shown very recently by means of scanning tunneling microscopy (STM) that single Pb atoms are highly mobile at room temperature (RT) when adsorbed on Si(111)7 × 7 surfaces. In the present work we have undertaken a further STM investigation of RT adsorption and diffusion of Pb on another DAS (dimer-adatom-stacking fault) reconstruction. To do so, substrates with large terraces presenting the Si(111)5 × 5 reconstruction were prepared and ultra-low coverage (≈0.01–0.02 ML) of Pb were deposited at RT. The STM results measured on these surfaces show that single Pb atoms are highly mobile at RT inside (5 × 5) half-cells but diffuse at very low rate to neighboring half-cells, as is the case for (7 × 7) substrates. The implications of these findings on the possible adsorption sites are discussed in comparison with the Pb Si 1117 × 7 system.

SURFACE DYNAMICS AND SCANNING TUNNELING MICROSCOPY: DIFFUSION OF Pb ATOMS ON Si(111)-(7×7)

The very early stages of Pb deposition on Si(111)-(7×7) surfaces have been investigated in real time by scanning tunneling microscopy. Variable temperature measurements combined with unusually long periods of imaging time have enabled us to observe that single Pb atoms are highly mobile within each half of the 7×7 unit cell. Individual jumps of single atoms between different half-cells have been resolved as well as the formation of atom pairs as a result. An activation energy of 0.64±0.07 eV has been measured for the diffusion of single atoms between different half-cells. Pb atom pairs are also mobile inside half-cells at much slower rates than single atoms. An activation energy of 0.40±0.04 eV has been measured for this process.

Controlled manipulation of ethen molecules and lead atoms on Cu(211) with a low temperature scanning tunneling microscope

We present results of manipulation experiments for single C2H4 molecules and single Pb atoms and buildup of small nanostructures on a Cu(211) substrate employing our temperature-variable scanning tunneling microscope. We further discuss novel ‘‘indirect’’ lateral manipulation experiments with C2H4 chains and Pb dimers. The latter experiments prove the special stability of Pb dimers. Co-adsorption experiments with CO allow determination of the adsorption sites of C2H4 molecules as well as Pb atoms and Pb dimers.

Real-time observation of the dynamics of single Pb atoms on Si(111)- (7 x 7) by scanning tunneling microscopy.

The very early stages of Pb deposition on $\mathrm{Si}(111)\ensuremath{-}(7\ifmmode\times\else\texttimes\fi{}7)$ surfaces have been investigated in real time by scanning tunneling microscopy. The combination of variable temperature scanning with unusual very long periods of imaging time have enabled us to observe that single Pb atoms are highly mobile within each half $(7\ifmmode\times\else\texttimes\fi{}7)$ unit cell. Individual jumps of single atoms between different half cells have been resolved as well as the formation of atom pairs as a result. An activation energy of $0.64\ifmmode\pm\else\textpm\fi{}0.07\mathrm{eV}$ has been measured for the diffusion of single atoms between different half cells.