Phosphorus‐Mediated MoS2 Nanowires as a High‐Performance Electrode Material for Quasi‐Solid‐State Sodium‐Ion Intercalation Supercapacitors

Molybdenum disulfide (MoS₂) is a promising electrode material for electrochemical energy storage owing to its high theoretical specific capacity and fascinating 2D layered structure. However, its sluggish kinetics for ionic diffusion and charge transfer limits its practical applications. Here, a promising strategy is reported for enhancing the Na⁺‐ion charge storage kinetics of MoS₂ for supercapacitors. In this strategy, electrical conductivity is enhanced and the diffusion barrier of Na⁺ ion is lowered by a facile phosphorus‐doping treatment. Density functional theory results reveal that the lowest energy barrier of dilute Na‐vacancy diffusion on P‐doped MoS₂ (0.11 eV) is considerably lower than that on pure MoS₂ (0.19 eV), thereby signifying a prominent rate performance at high Na intercalation stages upon P‐doping. Moreover, the Na‐vacancy diffusion coefficient of the P‐doped MoS₂ at room temperatures can be enhanced substantially by approximately two orders of magnitude (10^?6–10^?4 cm² s^?1) compared with pure MoS₂. Finally, the quasi‐solid‐state asymmetrical supercapacitor assembled with P‐doped MoS₂ and MnO₂, as the positive and negative electrode materials, respectively, exhibits an ultrahigh energy density of 67.4 W h kg^?1 at 850 W kg^?1 and excellent cycling stability with 93.4% capacitance retention after 5000 cycles at 8 A g^?1.     

Energetics and interdiffusion at the Cu/Ru(0001) interface: density functional calculations

Density functional theory calculations were performed on the energetics of an adatom and adlayer of Cu on a Ru(0001) slab and on the interdiffusion of Cu or Ru at the interface of Cu/Ru(0001) slab. The total energy calculations showed the equal possibilities of both pseudomorphic hcp- and fcc-adlayers of Cu on the Ru(0001) slab. The formation energies of mono-vacancy at the Cu/Ru(0001) interface and the barrier energies of the vacancy-mediated interdiffusion were calculated. The formation energies of mono-vacancy at the Cu/Ru(0001) interface were determined to be 1.31 eV for Cu atom and 1.83 eV for Ru atom, respectively. The diffusion of Ru atom into the vacancy of Cu across the Cu/Ru(0001) interface required energy increase of 0.98 eV, and the barrier energy was substantially high, 1.80 eV. On the other hand, the diffusion of Cu atom into the vacancy of Ru across the Ru/Cu(0001) interface was favored with the energy reduction of 0.35 eV. However, under this most favorable situation, the barrier energy is 0.52 eV. The calculation results imply that, as far as energetics is concerned, the diffusion of both Cu and Ru atoms via the vacancy-mediated diffusion mechanism at the Cu/Ru(0001) interface seems rather restricted unless considerable thermal activation is provided.     

Point defect redistribution in Si1−x Ge x alloys

Using high resolution secondary ion mass spectrometry (SIMS) measurements we have studied the effects of germanium content on antimony diffusion in strained Si_1–x Ge _x layers. Samples were molecular beam epitaxy (MBE) grown Si_1–x Ge _x buried layers incorporating in situ doped antimony delta-layers. These were annealed for a variety of times and temperatures, following which SIMS profiles were taken and from these diffusivities were calculated. The results of a diffusivity versus germanium content study and a diffusivity versus time study are presented; equilibrium antimony diffusion coefficients in alloys of up to 30% germanium are given along with possible transient effects. Changes in antimony diffusivity with composition are attributed to changes in the vacancy population and the vacancy enthalpy of migration. Comparison with the diffusivity of boron versus germanium content in silicon-germanium alloys leads to the proposal that, in silicon-rich alloys, boron diffuses predominantly via the interstitialcy mechanism. The dependence of diffusivity on germanium content for boron is different from that of antimony and it is proposed that the boron diffusion mechanism changes from largely interstitialcy in silicon to vacancy in germanium—the change occurring at around 40% germanium.     

Ab initio modeling study of boron diffusion in silicon

We present investigations of boron diffusion in crystalline silicon using ab initio calculations (W. Windl et al., Phys. Rev. Lett. 83 (1999) 4345). Based on these results, a new mechanism for B diffusion mediated by Si self-interstitials was proposed. Rather than kick-out of B into a mobile channel-interstitial, one- or two-step diffusion mechanisms have been found for the different charge states. The predicted activation energy of 3.5–3.8 eV, migration barrier of 0.4–0.7 eV, and diffusion-length exponent of −0.6 to −0.2 eV are in excellent agreement with experiment. We also present results of ab initio calculations for the structure and energetics of boron-interstitial clusters in Si. We show how these first-principles results can be used to create a physical B diffusion model within a continuum simulator which has strongly enhanced predictive power in comparison to traditional diffusion models.     

Investigation of vacancy in C54 TiSi2 using ab initio method

Investigated by ab initio plane-wave ultrasoft pseudopotential method based on generalized gradient approximation (GGA), it has been found that the formation energies of the vacancies in C54 TiSi₂ largely depend on the atomic chemical potentials of Ti and Si. In Si-rich limit, the formation energies of the Si and Ti vacancy are 2.39 eV and 2.40 eV while they are 1.53 eV and 4.07 eV in Ti-rich limit, respectively. The introduction of Si or Ti vacancy only slightly changes total density of states (DOS) and it also causes no considerable charge transfer.     

Dopant diffusion and activation induced by sub-melt laser anneal within the co-implanted p+ polycrystalline silicon gate used in CMOS technologies

Due to the continuous CMOS transistor scaling requirements, highly doped shallow junctions with improved activation have been widely investigated in recent CMOS technologies. In this scope, sub-melt millisecond laser annealing has been introduced in the integration flows to enhance dopant activation, without any additional detrimental diffusion. This MSA step impacts not only the transistor junction properties, but also the polysilicon gate depletion. This paper is devoted to the study of the MSA influence on boron and germanium co-implanted polysilicon films. A sensitive boron diffusion occurring during the laser anneal step, with or without an initial spike annealing step, has been observed. The activation energy of the boron diffusivity extracted from SIMS profiles in the laser only sequence has been found equal to 4.05 eV. In addition, it was shown that either a high temperature laser anneal sequence or a spike anneal followed by a laser anneal sequence can reach the same activation levels.     

Interaction of C with vacancy in W: A first-principles study

We provide a vacancy trapping mechanism of C in W by investigating structure, stability, and diffusion properties of C in W using a first-principles method. C easily bonds onto the internal-surface of vacancy. A monovacancy is capable of trapping as many as 4 C atoms to form C_nV (n = 1, 2, 3, 4) complexes. Single C atom prefers to interact with neighboring W at vacancy with the trapping energy of ?1.93 eV. With the C atoms added, both of them are preferred to bind with each other to form covalent-like bond despite the metallic W environment. For the C_nV complexes, C₂V is the major one due to its largest average trapping energy (?1.97 eV). Kinetically, formation of the C_nV complexes can be ascribed to the interstitial mechanism due to the lower activation energy barrier of 1.46 eV for the interstitial C than 1.66 eV for the vacancy.     

Formation and reversion of G-P zones in Al-1.3 at. % Ag alloy

The kinetics of clustering and reversion of G-P zones in an Al-1.3 at. % Ag alloy have been investigated by resistivity measurements, with special attention to the initial parts of reversion. From an analysis of clustering kinetics, vacancy formation, solute migration and solute-vacancy binding energies have been deduced to be 0.70, 0.53 and 0.10 eV respectively.The activation energy for reversion, which is identified as the activation energy for solute atom diffusion, is found to vary from 0.98 to 1.46 eV with increasing reversion time. This is attributed to variations in the vacancy concentration in equilibrium with small dislocation loops.     

Vacancy formation enthalpies of high-entropy FeCoCrNi alloy via first-principles calculations and possible implications to its superior radiation tolerance

Because atoms in high-entropy alloys(HEAs) coordinate in very different and distorted local environments in the lattice sites, even for the same type of constituent, their point defects could highly vary.Therefore, theoretical determination of the thermodynamic quantities(i.e., defect formation enthalpies)of various point defects is rather challenging because each corresponding thermodynamic quantity of all involve constituents is not unique. The knowledge of these thermodynamic quantities is prerequisite for designing novel HEAs and understanding the mechanical and physical behaviors of HEAs. However,to date there has not been a good method to theoretically derive the defect formation enthalpies of HEAs. Here, using first-principles calculations within the density functional theory(DFT) in combination of special quasi-random structure models(SQSs), we have developed a general method to derive corresponding formation enthalpies of point defects in HEAs, using vacancy formation enthalpies of a four-component equiatomic fcc-type FeCoCrNi HEA as prototypical and benchmark examples. In difference from traditional ordered alloys, the vacancy formation enthalpies of FeCoCrNi HEA vary in a highly wide range from 0.72 to 2.89 eV for Fe, 0.88–2.90 eV for Co, 0.78–3.09 eV for Cr, and 0.91–2.95 eV for Ni due to high-level site-to-site lattice distortions and compositional complexities. On average, the vacancy formation enthalpies of 1.58 eV for Fe, 1.61 eV for Cr, 1.70 eV for Co and 1.89 eV for Ni are all larger than that(1.41 eV) of pure fcc nickel. This fact implies that the vacancies are much more difficult to be created than in nickel, indicating a reasonable agreement with the recent experimental observation that FeCoCrNi exhibits two orders of amplitudes enhancement of radiation tolerance with the suppression of void formation at elevated temperatures than in pure nickel.     

Electrostatic Control of Structure in Self‐Assembled Membranes

Self‐assembling peptide amphiphiles (PAs) can form hierarchically ordered membranes when brought in contact with aqueous polyelectrolytes of the opposite charge by rapidly creating a diffusion barrier composed of filamentous nanostructures parallel to the plane of the incipient membrane. Following this event, osmotic forces and charge complexation template nanofiber growth perpendicular to the plane of the membrane in a dynamic self‐assembly process. In this work, we show that this hierarchical structure requires massive interfacial aggregation of PA molecules, suggesting the importance of rapid diffusion barrier formation. Strong PA aggregation is induced here through the use of heparin‐binding PAs with heparin and also with polyelectrolytes of varying charge density. Small angle X‐ray scattering shows that in the case of weak PA‐polyelectrolyte interaction, membranes formed display a cubic phase ordering on the nanoscale that likely results from clusters of PA nanostructures surrounded by polyelectrolyte chains.     

第一原理研究LuPO4中氧空位的性质

磷酸结构的晶体在掺杂二价阳离子后容易形成产生焦磷酸结构(P₂O₇) ^4-, 这种含有焦磷酸结构的氧化物材料十分适合做质子导体、燃料电池、气体传感器以及陶瓷膜等。本文利用第一性原理研究了LuPO₄晶体中氧空位的结构性质, 结果显示当氧空位带二价正电时, 会引发氧空位周围原子奇特的畸变, 形成焦磷酸结构。为了解释这种结构畸变的机理, 本文利用过渡态搜索计算了结构变化过程中势能面的变化情况, 正一价氧空位形成焦磷酸 结构需要越过2.4 eV的势垒, 而正二价氧空位形成焦磷酸结构则不需要越过任何势垒, 因此很容易形成焦磷酸 结构。最后给出氧空位不同带电态的晶格结构、电子态密度以及电荷密度分布等基本物理性质, 氧空位处于正二价态结构下, 氧空位附近的P原子与O原子成键, 又由于O原子有较强的电负性, P的s轨道电子向O的p轨道转 移。P的s、p轨道在禁带中出现了与总态密度对应的缺陷能级, 结果表明带正二价氧空位的晶体性质发生了明显变化。     

Computational investigations of Cu-embedded MoS<Subscript>2</Subscript> sheet for CO oxidation catalysis

Elevated amount of CO levels in the atmosphere poses serious health and environmental hazards. Oxidation of CO using suitable catalysts is one of the methods to control it. By means of DFT calculations, single Cu atom doped in S vacancy of MoS₂ nanosheet is studied for CO oxidation catalysis. Cu atom is strongly confined at the S-defective site of the MoS₂ sheet, possessing high energy barrier for the diffusion to its neighboring sites. Adsorption energy, charge transfer and orbital hybridization of CO and O₂ molecules adsorbed Cu-doped MoS₂ sheet reveal that O₂ is relatively more strongly adsorbed than CO. High adsorption energy of O₂ (??2.115 eV) and large charge transfer between O₂ and Cu–MoS₂ sheet (0.493e), compared to CO, make O₂ adsorption more favorable, which extenuates CO poisoning and hence helps in the efficient CO oxidation process. The complete oxidation of CO takes place in two steps: \( {\text{CO}} + {\text{O}}_{2} \to {\text{OOCO}} \) with activation energy of 0.201 eV, succeeded by \( {\text{OOCO}} + {\text{CO}} \to 2{\text{CO}}_{2} \) without any energy barrier. Our results show that the basal plane of MoS₂ sheet gets activated by embedding it with Cu metal, which can catalyze CO oxidation reaction effectively and without poisoning issues. The high activity, stability and low cost features can possibly encourage fabricating MoS₂-based catalysts for CO oxidation reaction.     

Vacancy mediated substitutional diffusion in binary crystalline solids

We describe a formalism to predict diffusion coefficients of substitutional alloys from first principles. The focus is restricted to vacancy mediated diffusion in binary substitutional alloys. The approach relies on the evaluation of Kubo-Green expressions of kinetic-transport coefficients and fluctuation expressions of thermodynamic factors for a perfect crystal using Monte Carlo simulations applied to a cluster expansion of the configurational energy. We make a clear distinction between diffusion in a perfect crystal (i.e. no climbing dislocations and grain boundaries that can act as vacancy sources) and diffusion in a solid containing a continuous distribution of vacancy sources that regulate an equilibrium vacancy concentration throughout. A variety of useful metrics to characterize intermixing processes and net vacancy fluxes that can result in the Kirkendall effect are described and are analyzed in the context of thermodynamically ideal but kinetically non-ideal model alloys as well as a realistic thermodynamically non-ideal alloy. Based on continuum simulations of diffusion couples using self-consistent perfect-crystal diffusion coefficients, we show that the rate and mechanism of intermixing in kinetically non-ideal alloys is very sensitive to the density of discrete vacancy sources.     

Clustering and solute-vacancy binding energies in Al-4.4% Zn alloy with 0.01% ternary additions

Isochronal and isothermal ageing experiments have been carried out to determine the influence of 0.01 at. % addition of a second solute on the clustering rate in the quenched Al-4,4 a/o Zn alloy. The influence of quenching and ageing temperatures has been interpreted to obtain the apparent vacancy formation and vacancy migration energies in the various ternary alloys. Using a vacancy-aided clustering model the following values of binding free energy have been evaluated: Ce-0.18; Dy-0.24; Fe-0.18; Li-0.25; Mn-0.27; Nb-0.18; Pt-0.23; Sb-0.21; Si-0.30; Y-0.25; and Yb-0.23 (± 0.02 eV). These binding energy values refer to that between a solute atom and a single vacancy. The values of vacancy migration energy (c. 0.4 eV) and the experimental activation energy for solute diffusion (c. 1.1 eV) are unaffected by the presence of the ternary atoms in the Al-Zn alloy.     

Large variation of vacancy formation energies in the surface of crystalline ice

Resolving the atomic structure of the surface of ice particles within clouds, over the temperature range encountered in the atmosphere and relevant to understanding heterogeneous catalysis on ice, remains an experimental challenge. By using first-principles calculations, we show that the surface of crystalline ice exhibits a remarkable variance in vacancy formation energies, akin to an amorphous material. We find vacancy formation energies as low as ~0.1-0.2 eV, which leads to a higher than expected vacancy concentration. Because a vacancy's reactivity correlates with its formation energy, ice particles may be more reactive than previously thought. We also show that vacancies significantly reduce the formation energy of neighbouring vacancies, thus facilitating pitting and contributing to pre-melting and quasi-liquid layer formation. These surface properties arise from proton disorder and the relaxation of geometric constraints, which suggests that other frustrated materials may possess unusual surface characteristics.     

A New Route to Low Resistance Contacts for Performance‐Enhanced Organic Electronic Devices

The barrier to charge carrier injection across the semiconductor/electrode interface is a key parameter in the performance of organic transistors and optoelectronic devices, and the work function of the electrode material plays an important role in determining the size of this barrier. We present a new, chemical route for making metal surfaces with low work functions, by functionalizing gold surfaces with self‐assembled monolayers of n,n‐dialkyl dithiocarbamates. Ultraviolet photoemission spectroscopy measurements show that work functions of 3.2 eV ± 0.1 eV can be achieved using this surface modification. Electronic structure calculations reveal that this low work function is a result of the packing‐density, polarization along the N‐C bond, and charge rearrangement associated with chemisorption. We demonstrate that electrodes functionalized with these monolayers significantly improve the performance of organic thin‐film transistors and can potentially be employed in charge selective contacts for organic photovoltaics.     

Atomistic simulation of boron diffusion with charged defects and diffusivity in strained Si/SiGe

We discuss the boron diffusion in a biaxial tensile strained {001} Si and SiGe layer with kinetic Monte Carlo (KMC) method. We created a strain in silicon by adding a germanium mole fraction in silicon in order to perform a theoretical analysis. The generation of a strain in silicon influences in the diffusivity as well as the penetration profile during the implantation. The strain energy for the charged defects has been calculated from the ab-initio calculation while the diffusivity of boron was extracted from the Arrhenius formula. Hereby, the influence of the germanium content on the dopant diffusivity was estimated. Our KMC study revealed that the diffusion of the B atoms was retarded with increasing Germanium mole fraction in a strained silicon layer. Furthermore, we derived a functional dependence of the in-plane strain as well as the out-of-plane strain on the germanium mole fraction, which lies in the distribution of equivalent stresses along the Si/SiGe interface.     

Quantitative nanoscale tracking of oxygen vacancy diffusion inside single ceria grains by in situ transmission electron microscopy

Oxygen vacancy formation and migration in ceria is critical to its electrochemical and catalytic properties in systems for chemical and energy transformation, but its quantification is rather challenging especially at atomic-scale because of disordered distribution. Here we report a rational approach to track oxygen vacancy diffusion in single grains of pure and Sm-doped ceria at −20 °C to 160 °C using in situ (scanning) transmission electron microscopy ((S)TEM). To create a gradient in oxygen vacancy concentration, a small region (∼30 nm in diameter) inside a ceria grain is reduced to the C-type CeO_1.68 phase by the ionization or radiolysis effect of a high-energy electron beam. The evolution in oxygen vacancy concentration is then mapped through lattice expansion measurement using scanning nano-beam diffraction or 4D STEM at a spatial resolution better than 2 nm; this allows direct determination of local oxygen vacancy diffusion coefficients in a very small domain inside pure and Sm-doped ceria at different temperatures. Further, the activation energies for oxygen transport are determined to be 0.59, 0.66, 1.12, and 1.27 eV for pure CeO₂, Ce_0.94Sm_0.06O_1.97, Ce_0.89Sm_0.11O_1.945, and Ce_0.8Sm_0.2O_1.9, respectively, implying that activation energy increases due to impurity scattering. The results are qualitatively supported by density functional theory (DFT) calculations. In addition, our in situ TEM investigation reveals that dislocations impede oxygen vacancy diffusion by absorbing oxygen vacancies from the surrounding areas and pinning them locally. With more oxygen vacancies absorbed, dislocations show extended strain fields with local tensile zone sandwiched between the compressed ones. Therefore, dislocation density should be reduced in order to minimize the resistance to oxygen vacancy diffusion at low temperatures.     

分子动力学模拟Gd原子在Cu低密勒表面的扩散过程

为了分析Gd吸附原子在Cu（001）、Cu（110）和Cu（111）表面的扩散机制，本文用分子动力学对该扩散过程进行模拟。模拟结果表明在Cu（001）和Cu（111）表面，Gd原子通过跳跃机制扩散；在Cu（110）表面，在[110]方向Gd原子通过跳跃机制扩散，而且多步跳跃频率很高，而在[001]方向则通过交换机制扩散。通过对扩散频率的拟合，发现在各种扩散机制都符合Arrhenius公式，从而确定了在Cu（001）和Cu（111）表面扩散势垒分别为0．19eV和0．013eV，在Cu（110）表面，沿[110]方向跳跃扩散势垒和沿[001]方向交换扩散势垒分别为0．097eV和0．33eV。