Adatom Vacancy Research Articles

Symmetry-Breaking Sites for Activating Linear Carbon Dioxide Molecules.

ConspectusCO2 is not only a greenhouse gas but also a pivotal carbon source as a promising supplement to fossil fuels. Both the environment and energy crises have compelled the researchers to explore how to efficiently transform CO2 into liquid fuels and value-added chemicals. As the industrialized approach nowadays, heterogeneous CO2 hydrogenation driven by thermal energy represents a potential strategy to help mitigate the greenhouse effect and reduce the reliance on fossil fuels. However, as the prerequisite for CO2 hydrogenation, CO2 activation is difficult due to the thermodynamic stability and chemical inertness of CO2 molecules. It is not proper to activate CO2 by directly increasing the reaction temperature, because CO2 hydrogenation into liquid products is an exothermic process where elevating the temperature decreases both the balanced conversion of CO2 and the balanced selectivity for target products. Therefore, the key scientific issue for CO2 hydrogenation lies in how to design catalysts which enable efficient activation of CO2. Up to date, a vast variety of active sites have been constructed for effective activation of CO2. These active sites including step sites, alloys, interface, substitution, vacancies, etc. are generally symmetry-breaking rather than perfect flat surfaces.Herein, we propose a catalyst design principle of constructing symmetry-breaking sites to activate nonpolar CO2 molecules. From the perspective of electronic properties, there is a prominent charge density gradient in a symmetry-breaking center, resulting in perturbing electronic structures of nonpolar CO2 and polarizing the adsorbed species. From the perspective of adsorption configuration, a symmetry-breaking site gives a local torque which enables more effective overlapping of atomic orbitals and thus more facilely bending of linear CO2 molecules, compared with symmetric sites. In this Account, we categorize the modes of CO2 activation and put forward the design principle of constructing symmetry-breaking sites. Moreover, we illustrate how to construct symmetry-breaking sites from the perspectives of local and global structures. Strategies to break the symmetry of local structures include surface substitution, surface adatom, and surface vacancy. Strategies to break the symmetry of global structures comprise surface modification with ligands, high-index surface, and phase reconstruction. In the future, further improvements, such as quantified descriptors, function for C-C coupling, and applicability to other nonpolar molecules, are necessary.

Dirac half-metallicity of Thin PdCl3 Nanosheets: Investigation of the Effects of External Fields, Surface Adsorption and Defect Engineering on the Electronic and Magnetic Properties

PdCl3 belongs to a novel class of Dirac materials with Dirac spin-gapless semiconducting characteristics. In this paper based, on first-principles calculations, we have systematically investigated the effect of adatom adsorption, vacancy defects, electric field, strain, edge states and layer thickness on the electronic and magnetic properties of PdCl3 (palladium trichloride). Our results show that when spin-orbital coupling is included, PdCl3 exhibits the quantum anomalous Hall effect with a non-trivial band gap of 24 meV. With increasing number of layers, from monolayer to bulk, a transition occurs from a Dirac half-metal to a ferromagnetic metal. On application of a perpendicular electrical field to bilayer PdCl3, we find that the energy band gap decreases with increasing field. Uniaxial and biaxial strain, significantly modifies the electronic structure depending on the strain type and magnitude. Adsorption of adatom and topological defects have a dramatic effect on the electronic and magnetic properties of PdCl3. In particular, the structure can become a metal (Na), half-metal (Be, Ca, Al, Ti, V, Cr, Fe and Cu with, respective, 0.72, 9.71, 7.14, 6.90, 9.71, 4.33 and 9.5 μB magnetic moments), ferromagnetic-metal (Sc, Mn and Co with 4.55, 7.93 and 2.0 μB), spin-glass semiconductor (Mg, Ni with 3.30 and 8.63 μB), and dilute-magnetic semiconductor (Li, K and Zn with 9.0, 9.0 and 5.80 μB magnetic moment, respectively). Single Pd and double Pd + Cl vacancies in PdCl3 display dilute-magnetic semiconductor characteristics, while with a single Cl vacancy, the material becomes a half-metal. The calculated optical properties of PdCl3 suggest it could be a good candidate for microelectronic and optoelectronics devices.

The dualism between adatom- and vacancy-based single crystal growth models

In homoepitaxial crystal growth, four basic growth morphologies (idealized growth modes) have been established that describe the deposition of atoms on single crystal surfaces: step-flow, layer-by-layer, mound formation, and random/self-affine growth. Mound formation leads to nano-scale surface patterning. However, the formation of (nano)-islands, patterns, and roughness occurs also during ion bombardment, electrochemical etching and oxidation/reduction cycling. Here we show, in analogy to many particle/anti-particle formalisms in physics, the existence of the dualism between individual adatom and single vacancy growth modes. We predict that all standard adatom growth modes do exist also in their counter, vacancy version. For the particular case of mound formation, we derive the theoretical equations and show the inverse similarity of the solution. We furthermore treat simultaneous growth by adatoms and vacancies, and derive the analytical solution of the growth shape evolution of the mounds. Finally, we present an experimental verification, in which both adatom and vacancy mound formation are active. The theoretically predicted mound shape nicely fits the experimental observation.

Determining the Jahn-Teller stabilization energy of adatom vacancies on a Si(111)- 3×3 :B surface

A charged vacancy on the Si surface, which generates deep levels within the band gap to accommodate multiple charge states, becomes increasingly important with the device scaling. Yet its characteristics have not been addressed as comprehensively as the bulk vacancy in Si. Here we generate the adatom vacancies on a heavily B doped Si(111) surface and measure their structural and electronic properties by using scanning tunneling microscopy. We find that they are Jahn-Teller distorted in the ground state but undergo the symmetry-restoring transition when gated by the external bias. We also determine the stabilization energy of the Jahn-Teller transition as well as the hopping energy between the dangling bonds of the adatom vacancy quantitatively.

Impact of single atomic defects and vacancies on the magnetic anisotropy energy of CoPt thin films

The impact of surface vacancies and single adatoms on the magnetic properties of tetragonal L10 CoPt thin films is investigated from first principles. We consider Co and Fe single adatoms deposited on a Pt-terminated thin film while a Pt adatom is assumed to be supported by a Co-terminated film. The vacancy is injected in the top-surface layer of the films with both types of termination. After finding the most stable location of the defects, we discuss their magnetic properties tied to those of the substrate and investigate the magnetocrystalline anisotropy energy (MAE). Previous simulations (Brahimi et al 2016 J. Phys.: Condens. Matter 28 496002) predicted a large out-of-plane surface MAE for the Pt-terminated CoPt films (4 meV per f.u.) in contrast to in-plane surface MAE for Co-terminated films (−1 meV per f.u.). Here, we find that the surface MAE is significantly modified upon the presence of the atomic defects. All investigated defects induce an in-plane MAE, which is large enough for Fe adatom and Pt vacancy to switch the surface MAE from out-of-plane to in-plane for the Pt-terminated films. Interestingly, among the investigated defects Pt vacancy has the largest effect on the MAE in contrast to Co vacancy, which induced the smallest but still significant effect. This behavior is explained in terms of the orbital moment anisotropy of the thin films.

Writing monolithic integrated circuits on a two-dimensional semiconductor with a scanning light probe

The development of complex electronics based on two-dimensional (2D) materials will require the integration of a large number of 2D devices into circuits. However, a practical method of assembling such devices into integrated circuits remains elusive. Here we show that a scanning visible light probe can be used to directly write electrical circuitry onto the 2D semiconductor molybdenum ditelluride (2H-MoTe2). Laser light illumination over metal patterns deposited onto 2D channels of 2H-MoTe2 can convert the channels from an n-type semiconductor to a p-type semiconductor, by creating adatom–vacancy clusters in the host lattice. With this process, diffusive doping profiles can be controlled at the submicrometre scale and doping concentrations can be tuned, allowing the channel sheet resistance to be varied over four orders of magnitudes. Our doping method can be used to assemble both n- and p-doped channels within the same atomic plane, which allows us to fabricate 2D device arrays of n–p–n (p–n–p) bipolar junction transistor amplifiers and radial p–n photovoltaic cells. A laser can be used to locally dope two-dimensional molybdenum ditelluride channels, allowing both n- and p-doped channels to be assembled within the same atomic plane and for device arrays of n–p–n bipolar junction transistor amplifiers and radial p–n photovoltaic cells to be fabricated.

Origin of n-type conductivity in two-dimensional InSe: In atoms from surface adsorption and van der Waals gap

Recently, two-dimensional (2D) InSe nanosheet becomes a promising material for electronic and optoelectronic nano-devices due to its excellent electron transport, wide bandgap tunability and good metal contact. The inevitable native point defects are essential in determining its characteristics and device performance. Here we investigate the defect formation energy and thermodynamic transition levels for the most important native defects and clarify the physical origin of n-type conductivity in unintentionally doped 2D InSe by using the powerful first-principles calculations. We find that both surface In adatom and Se vacancy are the key defects, and the In adatom, donated 0.65 electrons to the host, causes the n-type conductivity in monolayer InSe under In-rich conditions. For bilayer or few-layer InSe, the In interstitial within the van der Waals gap, transferred 0.68 electrons to InSe, is found to be the most stable donor defect, which dominates the n-type character. Our results are significant for understanding the defect nature of 2D InSe and improving the related nano-device performance.

Anisotropic Mg Electrodeposition and Alloying with Ag-based Anodes from Non-Coordinating Mixed-Metal Borohydride Electrolytes for Mg Hybrid Batteries

A highly anisotropic electrodeposition was observed using the hybrid battery electrolyte Mg(BH4)2 with LiBH4 in diglyme. At low overpotentials high aspect ratio platelet morphologies are observed with a strong fiber texture composed of a {10-10} and a {11-20} component, the first evidence of behavior of this kind in magnesium battery electrolytes. At high overpotentials the deposit aspect ratio is indistinguishable but the texture is shown to be primarily composed of a {11-20} fiber texture. The kinetic parameters relative to the relevant crystallographic faces are extracted from electron microscopy images and compared with the observed bulk rate extracted from the electrochemical data. The use of polycrystalline Ag foil substrates with little preferred orientation at the surface allowed highly polycrystalline nucleation at lower overpotentials than that of platinum, likely due to Ag alloying with Mg. Characterization using focused ion beam (FIB) cross-sections with Auger Electron Spectroscopy (AES) elemental analysis confirm that the deposits are primarily Mg although Mg‐Ag alloys of various compositions were observed. It is proposed that the orientation at slow rates of growth is due to the underlying kinetics of adatom diffusion on Mg and that higher rates diminish the phenomenon due to decreased time for adatom diffusion and instead are governed by the rates of adatom formation or more specifically the adatom vacancy formation on the different low-index planes of Mg.

Magnetism and magnetocrystalline anisotropy in vacancy doped and (non)metal adsorbed single-layer PtSe2

The single-layer (1L) transition-metal dichalcogenides (TMDs) have attracted great attentions over the past years. However, most of previous work focus on the Mo(W) TMDs and the pristine 1L-TMDs are often diamagnetic. Recent experimental progress has sparked renewed interest in Pt(Pd) TMDs. Here, using first-principles calculations, we study the functionalization of the newly synthesized 1L-PtSe2 through adatom adsorption and vacancy defect creation. It is found the 1L-PtSe2 with Pt vacancy (VPt) has large magnetocrystalline anisotropy energy (30.4meV/VPt), which is comparable with that of IrCo dimer adsorbed graphene. Except for the magnetism induced by the magnetic Fe(Co) adatom, the metal-free magnetism is introduced by the B(F) adatom, and the 1L-PtSe2 shows stronger adsorption capability to nonmetal atoms (H, B, C, N, F) than that of the 1L-MoS2(1L-MoSe2). In contrast to the case of 1L-MoS2(1L-MoSe2), significant reconstructions of surfaces are found for the H, B, C and N adsorbed 1L-PtSe2. Moreover, the semiconducting behaviors and spintronic features are modified: Fe(N) adatom causes n(p)-type doping, F adsorbed 1L-PtSe2 becomes bipolar semiconductor.

Li ion diffusion dynamics on Li oxides and peroxides surfaces

Li ion diffusion in the discharge products of the Li-O2 batteries is relevant to the performance of the battery. In this paper, Li ad-atom and Li-vacancy diffusion at the Li2O and Li2O2 surfaces are studied from first principles calculations. Li diffusion are considered on the energetically most favorable surfaces Li2O-(111) and Li2O2 (112̅0), which are obtained from calculating the surface energies of low index surfaces. Results show that Li diffusion on the Li2O-(111) is very slow at room temperature with energy barriers of 0.45eV and 0.98eV for Li ad-atom migration and vacancy migration, respectively. On the other hand, Li diffusion on Li2O2 (112̅0) surface is even more difficult. Li-vacancy migration energy barrier is 0.75eV, while Li ad-atom migration is prohibited with an energy barrier of 1.87eV. These results give explanations to the poor rate performance of the Li-O2 batteries and also suggest a possible Li2O phase formation mechanism at the Li2O2 surface.

Correlation between electron-irradiation defects and applied stress in graphene: A molecular dynamics study

Molecular dynamics (MD) simulations are performed to study the correlation between electron irradiation defects and applied stress in graphene. The electron irradiation effect is introduced by the binary collision model in the MD simulation. By applying a tensile stress to graphene, the number of adatom-vacancy (AV) and Stone–Wales (SW) defects increase under electron irradiation, while the number of single-vacancy defects is not noticeably affected by the applied stress. Both the activation and formation energies of an AV defect and the activation energy of an SW defect decrease when a tensile stress is applied to graphene. Applying tensile stress also relaxes the compression stress associated with SW defect formation. These effects induced by the applied stress cause the increase in AV and SW defect formation under electron irradiation.

Catalytic Consequences of Chemisorbed Oxygen during Methanol Oxidative Dehydrogenation on Pd Clusters

Surface oxygen contents and thermodynamic activities of nanosized Pd clusters and their connection to the reactivities for methanol oxidative dehydrogenation are established from rate measurements in the kinetically controlled regime and oxygen uptake studies at chemical equilibrium. First-order rate coefficients for methanol oxidative dehydrogenation (turnover rates divided by CH3OH pressure) are single-valued functions of the oxygen-to-methanol ratio in the contacting gas phase because this ratio determines the oxygen coverages, the relative abundance of chemisorbed oxygen and unoccupied Pd sites, and in turn, the identities of the kinetically relevant steps at Pd cluster surfaces. As the oxygen-to-methanol ratio increases, the most abundant surface intermediates on Pd clusters vary from uncovered to saturated with chemisorbed oxygen; in response to this shift in coverages, the kinetically relevant step concomitantly varies from oxygen dissociation, to CH3OH activation on oxygen adatom and oxygen vacancy pairs (O*–*), and then to CH3OH activation on oxygen adatom pairs (O*–O*), during which the first-order rate coefficients initially increase and then reach a maximum value before decreasing to a constant value that does not vary with the oxygen-to-methanol ratio. These dependencies reflect the dual catalytic functionality of chemisorbed oxygen, first promoting the methanol conversion as the oxygen coverages increase and then inhibiting the reaction at near O* saturation, as oxygen displaces the unoccupied Pd sites, thus removing the O*–* centers while replacing them with less reactive O*–O* centers for CH3OH activation. Methanol acts as a surface oxygen scavenger that reduces the oxygen chemical potential at Pd cluster surfaces during its catalytic turnovers. The oxygen-scavenging step by methanol increases with temperature to a larger extent than the O2 activation step. As a result of more effective oxygen removal (by reactions) at higher temperatures, the critical oxygen coverage required for the transition of regimes from *–* to O*–* as the predominant surface sites occurs at higher oxygen-to-methanol ratios. Larger Pd clusters are more reactive for methanol oxidative dehydrogenation than smaller clusters in all regimes because cluster dimension influences the relative abundance of chemisorbed oxygen and unoccupied Pd sites, the oxygen binding strengths, and their reactivities. The direct connection of first-order rate coefficient and oxidant-to-reductant ratio appears to be general for methanol oxidative dehydrogenation on other transition metals and for oxidation catalysis, for which the reductant scavenges the chemisorbed oxygen effectively, thus dictating their coverages and thermodynamic activities.

Force-Driven Single-Atom Manipulation on a Low-Reactive Si Surface for Tip Sharpening.

A single atomic manipulation on the delta-doped B:Si(111)-(√3x√3)R30° surface using a low temperature dynamic atomic force microscopy based on the Kolibri sensor is investigated. Through a controlled vertical displacement of the probe, a single Si adatom in order to open a vacancy is removed. It is shown that this process is completely reversible, by accurately placing a Si atom back into the vacancy site. In addition, density functional theory simulations are carried out to understand the underlying mechanism of the atomic manipulation in detail. This process also rearranges the atoms at the tip apex, which can be effectively sharpened in this way. Such sharper tips allow for a deeper look into the Si adatom vacancy site. Namely, high-resolution images of the vacancy showing subsurface Si dangling bond triplets, which surround the substitutional B dopant atom in the first bilayer, are achieved.

Vacancy formation on C60/Pt (111): unraveling the complex atomistic mechanism

The interaction of fullerenes with transition metal surfaces leads to the development of an atomic network of ordered vacancies on the metal. However, the structure and formation mechanism of this intricate surface reconstruction is not yet understood at an atomic level. We combine scanning tunneling microscopy, high resolution and temperature programmed-x-ray photoelectrons spectroscopy, and density functional theory calculations to show that the vacancy formation in C60/Pt(111) is a complex process in which fullerenes undergo two significant structural rearrangements upon thermal annealing. At first, the molecules are physisorbed on the surface; next, they chemisorb inducing the formation of an adatom–vacancy pair on the side of the fullerene. Finally, this metastable state relaxes when the adatom migrates away and the vacancy moves under the molecule. The evolution from a weakly-bound fullerene to a chemisorbed state with a vacancy underneath could be triggered by residual H atoms on the surface which prevent a strong surface-adsorbate bonding right after deposition. Upon annealing at about 440 K, when all H has desorbed, the C60 interacts with the Pt surface atoms forming the vacancy-adatom pair. This metastable state induces a small charge transfer and precedes the final adsorption structure.

Identification of Surface Defects and Subsurface Dopants in a Delta-Doped System Using Simultaneous nc-AFM/STM and DFT

We have studied the near surface defects of the delta-doped B:Si(111)-(√3 × √3)R30° system using a combination of scanning tunneling microscopy, non-contact atomic force microscopy, Kelvin probe force spectroscopy, total energy DFT, and STM theoretical simulations. We positively identify and characterize two near surface defects: the adatom vacancy and a B substitutional defect located in the second Si bilayer. We also confirm the assignment of the dangling-bond defect. Additionally, the influence that the subsurface B dopants have on the surface electronic structure, the modulation of the surface potential and the chemical activity of the surface is investigated.

Gert Ehrlich

Gert Ehrlich, who made important contributions to surface science, especially in the area of atomic interactions on solid surfaces, died of leukemia on 10 August 2012 in Urbana, Illinois. Up to five weeks before his death, he worked tirelessly as a professor in the materials science department at the University of Illinois at Urbana-Champaign. He coauthored more than 200 scientific articles and the book Surface Diffusion: Metals, Metal Atoms, and Clusters (Cambridge University Press, 2010).Gert was born on 22 June 1926 in Vienna. After Germany annexed Austria in 1938, Gert and his father, who was Jewish (his mother was Catholic), were detained for questioning but, luckily, released. His father immediately departed for the US, and in May 1939 Gert and his sister, Dorothy, arrived unescorted in New York on the T.S.S. Veendam and were reunited with their father. What might have been a harrowing voyage had become a grand adventure: Gert had investigated all aspects of the ship’s operation and explored the ship from top to bottom. His mother joined the family several months later.In 1944 Gert enrolled at Columbia University. He served in the US Army from 1945 to 1947 and then returned to graduate from the university with honors in chemistry in 1948. He obtained his PhD in chemistry from Harvard University in 1952 under adviser Paul Doty; his thesis title was “Studies on synthetic polyampholytes.” Gert remained at Harvard for a year as a National Institutes of Health fellow. He then served a year as a research associate in the University of Michigan physics department, where he worked with Gordon Sutherland on IR spectroscopy of macromolecules.In 1953 Gert accepted a full-time appointment at the General Electric Research Laboratory in Schenectady, New York, where he studied the kinetics of gas–solid interactions. He developed temperature-programmed, or flash, desorption techniques for quantitative kinetic studies at the gas–solid interface and demonstrated the importance of distinct binding sites in chemisorption phenomena.The field ion microscope, invented in 1951 by Erwin Müller, enabled Gert to probe the underlying atomic details of his macroscopic observations. Gert made unique chemisorption studies on single-crystal surfaces and the first quantitative observations of individual atoms diffusing on a metal surface. His resulting 1966 article with Frank Hudda in the Journal of Chemical Physics has been cited more than 1000 times.Gert accepted a professorship at the University of Illinois in 1968. Leading a small group of graduate students and postdocs, he expanded his research toward surface studies on an atomic scale. Using an atom-probe field ion microscope, Gert and his group made the first direct observation of an adatom exchange mechanism. They observed and characterized numerous aspects of surface diffusion, including interior step-edge barriers, reflective plane-edge barriers, adatom–vacancy interactions, temperature-dependent long jumps, and adatom cluster motion. Gert and his group used a variety of theoretical and experimental methods to study atomic behavior and transformed the apparently hopelessly complicated subject of surface diffusion at the atomic scale into one much more understandable and explainable.Among the several honors Gert received were the 1979 Medard W. Welch Award from the American Vacuum Society and the 1982 American Chemical Society Award in Colloid and Surface Chemistry. Through a 1992 research award from the German Alexander von Humboldt Foundation, he worked on boundary layer chemistry and interfacial chemistry at the Fritz Haber Institute in Berlin with Gerhard Ertl and Jochen Block.Gert was an extremely careful and extraordinarily attentive researcher, with the highest achievable vacuum and precise timing and temperature controls. Gert also was merciless in the proper statistical analysis of data—no small task in the early slide-rule days when access to a computer meant a time-sharing connection on a teletype at 10 characters per second.Perhaps Gert’s most endearing characteristic was his concern for students. His door was always open. When a student would stop by with a question, Gert usually answered with another question to challenge the student. He established a mentoring system in which current students taught the necessary know-how and unpublished techniques to incoming students. When not in the lab, he could easily be found: As he wandered the halls, he would produce a low, enigmatic, warbling whistle, usually his unique rendering of a classical opera aria.Gert was a curious scientist, and his precise work on the behavior of atoms on surfaces was foundational to modern nanoscience and technology. He also was an excellent teacher who compulsively prepared every lecture, even on material he had previously taught. On receiving news about the success of a former student, he would sport a generous grin and his eyes would sparkle.Gert EhrlichPPT|High resolution© 2013 American Institute of Physics.

First-Principles Calculations of Adatom–Vacancy Pairs on the Graphene

First-Principles Calculations of Adatom–Vacancy Pairs on the Graphene

First-Principles Calculations of Adatom–Vacancy Pairs on the Graphene

By using first-principles calculation, we study adatom–vacancy pairs on graphenes. We found that the healing barrier of the adatom–vacancy pair is very small (0.06 eV) when the adatom is bonded to a nearest carbon atom of the mono-vacancy. Therefore, this pair is easily healed. On the contrary, when the adatom is located 4.26–5.54 Å far from the vacant site, the healing barrier becomes high (0.24–0.32 eV), but these barriers are lower than that of the adatom diffusion. It is therefore expected that these adatom–vacancy pairs are healed in low temperature range where the adatom does not diffuse.

First-principles study on the reconstruction induced by the adsorption of C60 on Pt(111)

The adsorption of C60 on a Pt(111) surface and the origins of the √13 × √13R13.9° or 2√3 × 2√3R30° reconstruction of the C60/Pt(111) system have been investigated by means of first-principles calculations. In agreement with the experimental observations, our calculations reveal that the C60 molecule binds covalently on the Pt(111) surface. The C60 molecule adsorbs on the Pt(111) surface with the center of a hexagonal ring located on top of a surface Pt atom. The surface Pt atom can be removed easily, forming a Pt vacancy upon the adsorption of C60 molecule. Our calculation results show that the strong covalent bonds between C60 and the Pt(111) surface and the formation of adatom-vacancy pairs in the C60/Pt(111) system may be the main driving forces promoting the substrate reconstructing pattern observed in experiments.

Functionalization of Single-Layer MoS2 Honeycomb Structures

Based on first-principles plane-wave calculations, we studied the functionalization of the two-dimensional single-layer MoS2 structure through adatom adsorption and vacancy defect creation. Minimum-energy adsorption sites were determined for 16 different adatoms, each of which gives rise to diverse properties. Bare, single-layer MoS2, which is normally a nonmagnetic, direct-band-gap semiconductor, attains a net magnetic moment upon adsorption of specific transition-metal atoms, as well as silicon and germanium atoms. The localized donor and acceptor states in the band gap expand the utilization of MoS2 in nanoelectronics and spintronics. Specific adatoms, such as C and O, attain significant excess charge upon adsorption onto single-layer MoS2, which might be useful for tribological applications. Each MoS2 triple vacancy created in a single layer of MoS2 gives rise to a net magnetic moment, whereas other vacancy defects related to Mo and S atoms do not influence the nonmagnetic ground state. The present results are also relevant for the surface of graphitic MoS2.