Zn Adatoms Research Articles

Engineering ideal helical topological networks in stanene via Zn decoration

The xene family of topological insulators plays a key role in many proposals for topological electronic, spintronic, and valleytronic devices. These proposals rely on applying local perturbations, including electric fields and proximity magnetism, to induce topological phase transitions in xenes. However, these techniques lack control over the geometry of interfaces between topological regions, a critical aspect of engineering topological devices. We propose adatom decoration as a method for engineering atomically precise topological edge modes in xenes. Our first-principles calculations show that decorating stanene with Zn adatoms exclusively on one of two sublattices induces a topological phase transition from the quantum spin Hall (QSH) to quantum valley Hall (QVH) phase and confirm the existence of spin-valley polarized edge modes propagating at QSH/QVH interfaces. We conclude by discussing technological applications of these edge modes that are enabled by the atomic precision afforded by recent advances in adatom manipulation technology.

Sustainable interface regulation enabled by a bismuth solid-state surfactant effect for Zn-free anodes

This study introduces a novel application of Bi as a solid-state surfactant in Zn electrodes, where the arriving Zn adatoms tend to migrate below Bi and nucleate locally instead of diffusing laterally and forming protruding structures.

Sharp ballistic p–n junction at room temperature using Zn metal doping of graphene

Ballistic graphene p–n junctions (GPNJs) are uniquely suited to develop electrical counterparts of optical circuits as the large transparency enables a better carrier modulation in their interfaces than the diffusive junctions. Here we demonstrate a low-cost and scalable method for the fabrication of ballistic planar GPNJs based on the deposition of physisorbed Zn adatoms. A detailed study of spatially resolved Raman spectroscopy through a quartz transparent substrate enables the accurate mapping of the charge doping and strain across the graphene/Zn interface and underneath the metal layer. At the same time, the electrical measurements of transistor structures with varying channel length, i.e. transfer length electrical measurements, and their modeling reveal the ballistic nature of the charge transport up to room temperature.

Stable Zn Metal Anodes Enabled by Restricted Self‐Diffusion Via Succinimide Surfactant

AbstractDespite its merits of high specific capacity and intrinsic safety for aqueous zinc‐ion batteries (AZIBs), Zn metal as anode suffers from dendritic growth and severe corrosion during battery operation. Here, an electrolyte surfactant of succinimide (SI) that occupies the compact region of the electrical double layer (EDL) at the Zn/electrolyte interface, which protects the Zn surface from the parasitic corrosion in aqueous electrolytes is reported. More importantly, both theoretical calculation and electrochemical analysis demonstrate that the occupation of SI at the EDL can restrict the self‐diffusion of Zn adatoms and tune interfacial reaction kinetics during Zn deposition, thereby promoting small and dense nuclei rather than large Zn dendrites. Accordingly, SI surfactants enable a high Coulombic efficiency of 99.95% and a long cumulative plated capacity over 6800 mAh cm−2at 20 mA cm−2for 10 mAh cm−2. Moreover, the feasibility of SI is also demonstrated on a long‐term cycling stability in Zn‐VS2batteries.

Surfactant-assisted hierarchical silver coating enhances the anode surface stability toward zinc stripping/plating

Rechargeable aqueous zinc (Zn) batteries are promising for large energy storage due to their low cost, high safety, and environmental compatibility, but their commercialization is hindered by the severe irreversibility of Zn metal anodes as exemplified by water-induced side reactions (H2 evolution and Zn corrosion) and dendrite growth. In this work, hierarchical layered silver-coated zinc anode under the assistance of anionic surfactant (trisodium citrate) was prepared for long-time cycle stabilities of zinc stripping and plating, where Ag coating has a strong affinity to Zn adatoms and hierarchical structure exhibits a positive role in inducing the (002) plane preferred-orientation growth of Zn phase. Benefiting from these features, hierarchical Ag-coated zinc anode was able to operate stability for more than 1200 cycles compared with the pure zinc anode at 2 mA/cm2 for 1 mAh/cm2, and an asymmetric cell shows superior Coulombic efficiency of ∼99.6% over 800 cycles at a current density of 1 mA/cm2 and 0.5 mAh/cm2, as well as a long cycling stability of 500 cycles with capacity of 115 mAh/g in MnO2||H–Zn@Ag full batteries. This work provides a new insight to improve the performance of Zn-metal batteries.

Interface Engineering by Hydrophilic and Zincophilic Aluminum Hydroxide Fluoride for Anode‐Free Zinc Metal Batteries at Low Temperature

AbstractAnode‐free batteriesgreatly promote overall energy density, but they require an extremely high Coulombic efficiency (CE, >99.7%) to function normally. It becomes very challenging in aqueous batteries, because of water‐related parasitic reactions and dendrite growth on Zn anodes. Herein, aluminum hydroxide fluoride coated on Cu foils (Cu@AOF) is used to realize the anode‐free aqueous batteries. AOF exhibits a high adsorption affinity to H2O and a low diffusion energy barrier for Zn adatoms, promoting the desolvation process and surface migration. Meanwhile, the strong interaction between AOF and Zn2+ enables it to regulate the Zn2+ flux and benefit lateral growth. Then, the anode‐free full cells of Cu@AOF||Zn0.5VO2 exhibit a record‐high cycle life of 2000 cycles at 1 A g−1 with an ultra‐high average CE of 99.95%. More impressively, the full cell shows a long cycle life of 400 cycles with a high CE of 99.94% at −20 °C. This work provides sheds light on the rational engineering of the electrode interfaces to obtain excellent performance at low temperatures.

Effect of Li+ Addition during Initial Stage of Electrodeposition Process on Nucleation and Growth of Zn

Zn negative electrodes are expected to be used in next-generation batteries. However, irregular shape evolution, such as mossy structures, limits its practical applications. Cationic additive species are useful in suppressing this, and Li+ is a promising species. To identify the effect of Li+ on the nucleation and growth of Zn, this study analyzed the Zn aggregation behavior during electrodeposition with Li+ at the initial stage via experimental methods and theoretical calculations using density functional theory and kinetic Monte Carlo simulations. The results suggest that Li+ affected the surface diffusion of Zn adatoms, changing the nucleation and growth during the initial stage of deposition. Li+ allows Zn adatoms to diffuse rapidly owing to the mitigation of the solvation effect on surface diffusion by forming rigid solvation of Li+ in the vicinity of the surface. This results in two-dimensional nucleation of the Zn(0001) facet, which is supported by the X-ray diffraction measurements. Li+ mitigates protrusion as the initial structure of the mossy structure. This analysis provides valuable insight into the control of the behavior of Zn adatoms and their nucleation and growth.

Elucidation of Cu-Zn Surface Alloying on Cu(997) by Machine-Learning Molecular Dynamics.

The Cu-Zn surface alloy has been extensively involved in the investigation of the true active site of Cu/ZnO/Al2O3, the industrial catalyst for methanol synthesis which remains under controversy. The challenge lies in capturing the interplay between the surface and reaction under operating conditions, which can be overcome given that the explicit dynamics of the system is known. To provide a better understanding of the dynamic of Cu-Zn surface at the atomic level, the structure and the formation process of the Cu-Zn surface alloy on Cu(997) were investigated by machine-learning molecular dynamics (MD). Gaussian process regression aided with on-the-fly learning was employed to build the force field used in the MD. The simulation reveals atomistic details of the alloying process, that is, the incorporation of deposited Zn adatoms to the Cu substrate. The surface alloying is found to start at upper and lower terraces near the step edge, which emphasize the role of steps and kinks in the alloying. The incorporation of Zn at the middle terrace was found at the later stage of the simulation. The rationalization of alloying behavior was performed based on statistics and barriers of various elementary events that occur during the simulation. It was observed that the alloying scheme at the upper terrace is dominated by the confinement of Zn step adatoms by other adatoms, highlighting the importance of step fluctuations in the alloying process. On the other hand, the alloying scheme at the lower terrace is dominated by direct exchange between the Zn step adatom and the Cu atom underneath. The alloying at the middle terrace is dominated by the wave deposition mechanism and deep confinement of Zn adatoms. The short propagation of alloyed Zn in the middle terrace was observed to proceed by means of indirect exchange instead of local exchange as proposed in the previous scanning tunneling microscopy (STM) observation. The comparison of migration rate and activation energies to the result of STM observation is also made. We have found that at a certain distance from the surface, the STM tip significantly affects the elementary events such as vacancy formation and direct exchange.

Cation‐Structure Effects on Zinc Electrodeposition and Crystallographic Orientation in Ionic Liquids

AbstractThe electrochemical behavior of Zn deposition in room temperature ionic liquids consisting of bis(trifluoromethanesulfonyl)amide (TFSA−) combined with N‐propyl‐N‐methylpyrrolidinium (Pyr1,3+) or 1‐ethyl‐3‐methylimidazolium (EMI+) was investigated in terms of their physicochemical properties and dissolved Zn2+ species. The effect of cation structure was examined not only on the macroscopic morphologies, but also on the microscopic aspects of crystallographic orientation of Zn deposits obtained from [Zn(TFSA)2]0.1[Cation‐TFSA]0.9. Electron backscattered diffraction revealed that the crystal grains grown in Pyr1,3‐TFSA at the current density of 0.5 mA cm−2 were much finer, compared with the sizes of those in EMI‐TFSA. This is probably because Pyr1,3 cations inhibit the surface diffusion of Zn adatoms, thus preventing growth in a specific plane direction. It was found that higher reversibility on Zn stripping needs larger crystal grains rather than polycrystalline with fine grains. The obtained results will contribute greatly to the realization of longer life batteries using Zn without resource constraints.

Site-Selective Adsorption on ZnF2/Ag Coated Zn for Advanced Aqueous Zinc-Metal Batteries at Low Temperature.

Metallic Zn as a promising anode material of aqueous batteries suffers from severe parasitic reactions and notorious dendrite growth. To address these issues, the desolvation and nucleation processes need to be carefully regulated. Herein, Zn foils coated by ZnF2-Ag nanoparticles (ZnF2-Ag@Zn) are used as a model to modulate the desolvation and nucleation processes by hybrid surfaces, where Ag has a strong affinity to Zn adatoms and ZnF2 shows an intense adsorption to H2O. This selective adsorption of different species on ZnF2 and Ag reduces the mutual interference between two species. Therefore, ZnF2-Ag@Zn exhibits the electrochemical performance much better than ZnF2@Zn or Ag@Zn. Even at -40 °C, the full cells using ZnF2-Ag@Zn demonstrate an ultralong lifespan of 5000 cycles with a capacity retention of almost 100%. This work provides new insights to improve the performance of Zn metal batteries, especially at low temperatures.

Synthesis of mono- and few-layered n-type WSe2 from solid state inorganic precursors.

Tuning the charge transport properties of two-dimensional transition metal dichalcogenides (TMDs) is pivotal to their future device integration in post-silicon technologies. To date, co-doping of TMDs during growth still proves to be challenging, and the synthesis of doped WSe2, an otherwise ambipolar material, has been mainly limited to p-doping. Here, we demonstrate the synthesis of high-quality n-type monolayered WSe2 flakes using a solid-state precursor for Se, zinc selenide. n-Type transport has been reported with prime electron mobilities of up to 10 cm2 V-1 s-1. We also demonstrate the tuneability of doping to p-type transport with hole mobilities of 50 cm2 V-1 s-1 after annealing in air. n-Doping has been attributed to the presence of Zn adatoms on the WSe2 flakes as revealed by X-ray photoelectron spectroscopy (XPS), spatially resolved time of flight secondary ion mass spectroscopy (SIMS) and angular dark-field scanning transmission electron microscopy (AD-STEM) characterization of WSe2 flakes. Monolayer WSe2 flakes exhibit a sharp photoluminescence (PL) peak at room temperature and highly uniform emission across the entire flake area, indicating a high degree of crystallinity of the material. This work provides new insight into the synthesis of TMDs with charge carrier control, to pave the way towards post-silicon electronics.

Fast-growing multifunctional ZnMoO4 protection layer enable dendrite-free and hydrogen-suppressed Zn anode

Metallic zinc has become one of the most potential anodes for aqueous zinc-ion batteries (ZIBs) due to its high capacity and safety. However, uneven Zn deposition and hydrogen evolution at zinc anode severely limit the development and commercialization of aqueous ZIBs. Here, we directly formed a uniform ridge-like ZnMoO4 layer on the Zn anode (denoted as Zn@ZnMoO4) within 20 s by chemical deposition. Due to its special structure and strong binding energy to Zn adatoms, the modified layer can induce uniform zinc nucleation and inhibit dendrite growth. In addition, ZnMoO4 can significantly increase the adsorption free energy of H adatoms (ΔG(H*)), suppressing the evolution of hydrogen. With this synergy effect, Zn@ZnMoO4 delivers strong hydrogen suppression capability that increases the hydrogen evolution overpotential from 27 mV to 137 mV, achieves exciting cycling stability for 10,000 cycles at a high current density of 10 mA cm−2. Meanwhile, the capacity retention rate of the Zn@ZnMoO4/α-MnO2 full battery reaches 87% after 1000 cycles under 1A g − 1.

An In Situ and Real-Time Plasmonic Approach of Seed/Adhesion Layers: Chromium Buffer Effect at the Zinc/Alumina Interface

The effect of additives on metal/oxide interfaces is explored in situ and in real time on evaporated films by a combination of surface science techniques, among which a very flexible optical method shows a unique ability to scrutinize the growth and wetting properties of supported clusters that involve several elements. The study focuses on Cr at the Zn/α-Al2O3(0001) interface at 300 K. A particular interest of the present interface is that Zn does not stick at all on bare alumina. The sticking and morphology of both Cr and Zn films during their growth are analyzed from sub-monolayer to multilayer thicknesses. After an initial oxidation reaction with residual OH groups, shown to be detrimental to Zn adhesion, Cr growth proceeds through the formation of high aspect ratio particles that percolate around an average thickness of 10 Å. With regard to Zn growth on a Cr deposit, two very distinct stages can be distinguished. In the sub-monolayer thickness range, Cr forms a seed layer that drastically increases the Zn sticking coefficient from 0 to nearly 1 due to a diffusion length of physisorbed Zn adatoms before desorption larger than Cr island separation; Zn clusters are anchored on the Cr seeds that they encapsulate, but their wetting behavior is dictated by the interaction with alumina. In a second stage, as soon as the Cr film percolates, it forms an adhesion layer on which Zn grows in a nearly two-dimensional mode. In all cases, Cr films are stable upon annealing. On Cr-covered alumina, the Zn desorption energy is enhanced as compared to bare surfaces, which, in line with atomistic simulations, is assigned to the formation of more favorable Cr–Al2O3 and Cr–Zn than Zn–Al2O3 bonds. Generally speaking, the ability demonstrated herein of small amounts of additives to dramatically increase the adhesion of films is of great practical interest. It shows that noncontinuous and partially oxidized films of additives, closer to realistic cases of application, can strongly enhance the sticking of films. Also, anchoring a functional film by discrete predeposited seeds can keep its properties intact.

Unveiling the adsorption properties of 3d, 4d, and 5d metal adatoms on the MoS2 monolayer: A DFT-D3 investigation

The adsorption of metal (M) adatoms on two-dimensional (2D) transition-metal dichalcogenides (TMDs) monolayers have been used to tune the physical-chemical properties of 2D TMDs such as MoS2, however, our atomistic understanding of the binding mechanism, site preference, charge transfer, diffusion barriers, etc., of metal adatoms on MoS2 is far from satisfactory. Thus, we report spin-polarized density functional theory calculations within the D3 van der Waals (vdW) correction to characterize the adsorption properties of 15 metal adatoms (3d, 4d, 5d) on MoS2 at low-coverage limit. All adatoms can be separated into two groups, namely, Fe, Co, Ni, Ru, Rh, Os, Ir, and Pt bind covalently to the MoS2 monolayer on the topMo site, where the binding mechanism can be explained by the combination of two factors, namely, (i) distortions within the MoS2 monolayers, which breaks the degeneracy of the electronic states and reduces their magnitude near the valence band maximum, and (ii) strong hybridization between the partially unoccupied d- and Mo dz2-states. In contrast, Pd has a strong preference for the hollow site compared with the topMo site, however, Cu, Zn, Ag, Cd, and Hg adatoms bind to the topMo and hollow sites with nearly the same energy (differences less than 0.10eV) due to the weak hybridization of the fully occupied metal d-states, while Au binds preferentially on the topS site. Thus, the M-MoS2 interactions are dominated by covalent and van der Waals interactions, which shows strong and weak dependence on the adsorption site preference, respectively.

Dendrite-free Zn electrodeposition triggered by interatomic orbital hybridization of Zn and single vacancy carbon defects for aqueous Zn-based flow batteries

Highly reversible aqueous zinc anodes are demonstrated via suppressing surface diffusion of Zn adatoms from strong orbital hybridization of the Zn adatoms and single vacancy defects.

Electronic and magnetic properties of graphene densely decorated with 3d metallic adatoms—the effect of structure privilege and spin–orbit interaction

The electronic properties of graphene decorated with Ni, Co, Cu and Zn adatoms in the presence of the spin–orbit interaction are studied using the density functional theory approach. We focus on the case when the indicated 3d metallic adatoms form a perfect, close-packed single-atomic layer above the graphene surface. The two configurations are examined, namely the adatoms in the on-top, and the hollow positions on graphene. We show that despite relatively small values of the binding energies, suggesting rather a physisorbtion of the adatomic layers on graphene, the p − d orbital hybridization at the graphene-adatomic layer interface arises. The arisen orbital hybridization results in the charge transfer that takes place from the adatomic layer to the graphene, and in a consequence the graphene becomes n-doped. The proximity of metallic adatoms modifies also the magnetic state of graphene. This effect is especially pronounced for the decoration with magnetic atoms, when the magnetic moments of the considerable values are induced on the graphene sublattices. The analysis of the band structure demonstrates that the charge transfer, as well as the related induced magnetism on graphene, modify the graphene electronic properties, especially near high symmetry points and importantly the Dirac cones. The presence of the metallic adatoms breaks the graphene symmetry and splits the bands due to the exchange coupling. We show that for the hollow configuration the gap opening arises at the point due to the Rashba-like spin–orbit interaction, while in the case of the on-top configuration the energy gap opens mainly due to the staggered potential. We also mapped the parameters of an effective Hamiltonian on the results obtained with the density functional theory approach.

Tuning the Surface Morphologies and Properties of ZnO Films by the Design of Interfacial Layer

Wurtzite ZnO films were grown on MgO(111) substrates by plasma-assisted molecular beam epitaxy (MBE). Different initial growth conditions were designed to monitor the film quality. All the grown ZnO films show highly (0001)-oriented textures without in-plane rotation, as illustrated by in situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD). As demonstrated by atomic force microscopy (AFM) images, “ridge-like” and “particle-like” surface morphologies are observed for the ZnO films grown in a molecular O2 atmosphere with and without an initial deposition of Zn adatoms, respectively, before ZnO growth with oxygen plasma. This artificially designed interfacial layer deeply influences the final surface morphology and optical properties of the ZnO film. From room-temperature photoluminescence (PL) measurements, a strong defect-related green luminescence band appears for the ZnO film with a “particle-like” morphology but was hardly observed in the films with flat “ridge-like” surface morphologies. Our work suggests that the ZnO crystallinity can be improved and defect luminescence can be reduced by designing interfacial layers between substrates and epilayers.

Direct Imaging of Dopant Distribution in Polycrystalline ZnO Films

Two fundamental requirements of transparent conductive oxides are high conductivity and low optical absorptance, properties strongly dependent on the free-carrier concentration of the film. The free-carrier concentration is usually tuned by the addition of dopant atoms; which are commonly assumed to be uniformly distributed in the films or partially segregated at grain boundaries. Here, the combination of secondary ion mass spectroscopy at the nanometric scale (NanoSIMS) and Kelvin probe force microscopy (KPFM) allows direct imaging of boron-dopant distribution in polycrystalline zinc oxide (ZnO) films. This work demonstrates that the boron atoms have a bimodal spatial distribution within each grain of the ZnO films. NanoSIMS analysis shows that boron atoms are preferentially incorporated into one of the two sides of each ZnO grain. KPFM measurements confirm that boron atoms are electrically active, locally increasing the free-carrier concentration in the film. The proposed cause of this nonuniform dopant distribution is the different sticking coefficient of Zn adatoms on the two distinct surface terminations of the ZnO grains. The higher sticking coefficient of Zn on the c+ surface restricts the boron incorporation on this side of the grains, resulting in preferential boron incorporation on the c- side and causing the bimodal distribution.

The Effects of Heteroatom Adsorption on the Electronic Properties of Phosphorene

A new 2D material, phosphorene, has several remarkable advantages; various superiorities make phosphorene a research hotspot. This paper provides comprehensive information about the structure and electronic and magnetic properties of phosphorene adsorbed with atoms, including alkali and alkaline-earth metal atoms, nonmetallic atoms, noble metal atoms, and transition-metal atoms. Phosphorene adsorbed with alkali and alkaline-earth metal atoms, such as Li and Na adatoms, becomes an n-type semiconductor, while phosphorene adsorbed with Be and Mg atoms becomes a p-type semiconductor. In view of nonmetallic adatoms (B, C, N, and O), the B adatom decorated phosphorene becomes metallic, the band gap of phosphorene adsorbed with C adatom decreases, and the phosphorene is p-type with N adatom, while the electronic property of O adatom adsorption case is affected slightly. Regarding noble metal adatoms adsorption condition, the Ag adatom makes phosphorene a n-type semiconductor, the Au adatom induces phosphorene to have a magnetism of 1 μB, and the electronic property of phosphorene is changed by adsorbing with Pt adatom. Among transition-metal adatoms, such as Fe, Ni, Co, Cu, and Zn adatoms, the band gap is reduced when Fe/Ni adatom adheres to the surface of phosphorene, The Co adsorbed phosphorene turns into a polar-gapless semiconductor and phosphorene is proved to be n-type with Cu adatom, but it is testified that the Zn atom is not suitable to adsorb on the phosphorene.

Surface electronic structure and evidence of plains-wave superconductivity in(Li0.8Fe0.2)OHFeSe

(Li0.8Fe0.2)OHFeSe is a newly-discovered intercalated iron-selenide superconductor with a Tc above 40 K, which is much higher than the Tc of bulk FeSe (8 K). Here we report a systematic study of (Li0.8Fe0.2)OHFeSe by low temperature scanning tunneling microscopy (STM). We observed two kinds of surface terminations, namely FeSe and (Li0.8Fe0.2)OH surfaces. On the FeSe surface, the superconducting state is fully gapped with double coherence peaks, and a vortex core state with split peaks near EF is observed. Through quasi-particle interference (QPI) measurements, we clearly observed intra- and inter-pocket scatterings in between the electron pockets at the M point, as well as some evidence of scattering that connects gamma and M points. Upon applying magnetic field, the QPI intensity of all the scattering channels are found to behave similarly. Furthermore, we studied impurity effects on the superconductivity by investigating intentionally introduced impurities and intrinsic defects. We observed that magnetic impurities such as Cr adatoms can induce in-gap states and suppress superconductivity. However, nonmagnetic impurities such as Zn adatoms do not induce visible in-gap states. Meanwhile, we show that Zn adatoms can induce in-gap states in thick FeSe films, which is believed to have an (s+-)wave pairing symmetry. Our experimental results suggest it is likely that (Li0.8Fe0.2)OHFeSe is a plain s-wave superconductor, whose order parameter has the same sign on all Fermi surface sections.