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Inert Cu2O cubes become a superior photocatalyst after surface functionalization with 4-nitrophenylacetylene. This modification changes the surface band structure to facilitate electron transfer to the molecules.

Adsorption of foreign atoms onto 2D materials can either lead to ordinary electron doping or the emergence of new electronic effects including topology, superconductivity, and quantum anomalous Hall and Kondo states. We have investigated the effect of Cr doping on the electronic structure of the α-Au/Si(111)- surface and its adsorbate-modified family. It has been found that below a critical coverage of ∼0.05 monolayer, Cr adatoms penetrate beneath the Au and topmost Si layers and induce the occupied resonance flat band in the electronic spectrum as revealed by angle-resolved photoelectron spectroscopy. Further deposition of Cr leads to the growth of the 3D islands spoiling the surface homogeneity. Using density functional theory calculations, we have disclosed the effects of Cr doping on the electronic band structure and revealed the nature of hybridization between the Cr-induced magnetic-split band and the Au-induced Rashba-split surface state. We believe that the synthesized 2D phases and electronic effects produced by magnetic atom doping in the ultimate two-dimensional limit will stimulate further investigations related to the highly correlated phases and will find practical applications in nanoelectronic devices.

Inert Cu2O cubes become photocatalytically active with 2E-6-MN functionalization. The molecule-derived bands within the band gap of Cu2O and charge density distribution over the molecule contribute to the photocatalytic activity appearance.

The development of electrocatalysts with reconcilable balance between the cost and performance in oxygen reduction reaction (ORR) is an imperative task for the widespread adoption of fuel cell technology. In this study, we proposed a unique model of diatomic Pt-cluster (Pt-dimer) in the topmost layer of the Co/Pd bimetallic slab (Co@Pd-Pt2) for mimicking the Cocore@Pdshell nanocatalysts (NCs) surface and systematically investigating its local-regional collaboration pathways in ORR by density functional theory (DFT). The results demonstrate that the Pt-dimer produces local differentiation from both ligand and geometric effects on the Co@Pd surface, which forms adsorption energy (Eads) gradients for relocating the ORR-adsorbates. Our calculations for Eads-variations of ORR-species, reaction coordinates, and intraparticle charge injection propose and confirm a novel local synergetic collaboration around the Pt-dimer in the Co@Pd-Pt2 system with the best-performing ORR behavior compared with all reference models. With proper selection of the composition in intraparticle components, the proposed DFT assessments could be adopted for developing economical and high-performance catalysts in various heterogeneous reactions.

The crux of the hot topic concerning the widespread replacement of fuel cells (FCs) with traditional petrochemical energy is to balance improving the oxygen reduction reaction (ORR) and reducing the cost. The present study employs density functional theory (DFT) to investigate the effect of Pt ensemble size regulation from a single atom to full coverage on the physio-chemical properties, oxygen adsorption energies and overall ORR efficiency of bimetallic nanocatalysts (NCs) with a Cocore–Pdshell structure. Our results reveal that the electronegativity difference and lattice strain between neighboring heteroatoms are enhanced to trigger a synergetic effect in local domains, with the Pt cluster size reduced from nanometers to subnanometers. They induce a directed and tunable charge relocation mechanism from deep Co to topmost Pt to optimize the adsorption energies of O2/O* and achieve excellent ORR kinetics performance with minimum Pt usage but maximum Pt atom utilization (i.e., Pt1 to Pt3) compared with benchmark Pt(111). Such a dependency between the cluster size and corresponding ORR performance for the established Co@Pd–Ptn system can be applied to accurately guide the experimental synthesis of ordered heterogeneous catalysts (e.g., other core@shell-clusters structures) toward low Pt, high efficiency and green economy.

The design of highly efficient, low-cost and long-term stable electrocatalysts for the hydrogen evolution reaction (HER) is a research hotspot in the field of sustainable energies (e.g., fuel cells). In this study, a novel catalyst design comprising NiO2 supported Pd nanocatalysts (NCs) with an interfacial atomic cluster of Ni metal is proposed and their HER activity with the corresponding reaction mechanism is systematically investigated by using density functional theory (DFT) calculations. For the optimum case with four Ni atoms in a tetragonal shape (i.e., NiO2–Ni4–Pd), the reaction coordinate (barrier) is reduced by 0.36 eV and 0.34 eV respectively in the Volmer and Tafel steps among models with different amounts of Ni atoms. The corresponding results reveal that the novel steric confinement effects of the atomic Ni-ensemble tetragon will unbalance the surface charge distribution to generate the local domain heterogeneity on the Pd-shell surface and further prove the doping threshold of the Ni tetragon in terms of HER-kinetics improvement. For evaluating the rationales on experimental variations by the inevitable interatomic intermix in a rapid crystal growth process, the results of various atomic doping ratios of Nid/Pd from ∼2% to 67% are systematically investigated. The adsorption energy of H* is even lower than that on Pt by further increasing Ni atoms to 32, therefore, showing the potential capability of such a type of structure design for catalysts in the HER. Based on the presented results, we believe that our research can be applied to guide the adjustment of heterogeneous catalysts in the experimental synthesis while offering a theoretical insight for designing transition metal oxide-based systems toward inexpensive, efficient and green initiative merits.

Although H2O2 has been often employed as a green oxidant for many CeO2-catalyzed reactions, the underlying principle of its activation by surface oxygen vacancy (Vo) is still elusive due to the irreversible removal of postgenerated Vo by water (or H2O2). The metastable Vo (ms-Vo) naturally preserved on pristine CeO2 surfaces was adopted herein for an in-depth study of their interplay with H2O2. Their well-defined local structures and chemical states were found facet-dependent affecting both the adsorption and subsequent activation of H2O2. It is concluded that a strong adsorption of H2O2 on ms-Vo may not guarantee its subsequent activation. The ms-Vo can be only free for the next catalytic cycle when the electron density of surface Ce is high enough to reduce/break the O-O bond of adsorbed H2O2. This explains the 211.8 and 35.8 times enhancement in H2O2 reactivity when the CeO2 surface is changed from (111) and (110) to (100).

Hydrogen generation by photocatalytic water splitting has attained more and more research interests in the recent years since the solar energy can be directly transferred and stored as hydrogen. However, the search for a high-efficiency photocatalyst for water splitting is a really challenge. In this paper, we designed a novel 2D material-based van der Waals heterostructure (vdWH) composed by g-GaN and BSe, which is thermally stable at room temperature. The g-GaN/BSe vdWH has suitable band-edge positions for the oxidation and reduction reactions of water splitting at pH 0 and 7. The carrier mobility of this heterostructure is high, indicating the effective occurrence of reactions for water splitting. The g-GaN/BSe vdWH also possesses a type-II band alignment, which can promote the separation of the photogenerated electron–hole pairs constantly. Moreover, a large built-in electric field can be established at the interface, which will further prevent the recombination of photogenerated charges. In addition, the g-GaN/BSe vdWH also exhibits outstanding sunlight-absorption ability, and the biaxial strain can further enhance this ability. Thus, we conclude that the g-GaN/BSe vdWH can act as a high-efficiency photocatalyst for water splitting.

The FeNiCoCr-based high entropy alloys (HEAs) exhibit excellent mechanical properties, such as twin-induced plasticity (TWIP) and phase transformation plasticity (TRIP) that can reach a remarkable combination of strength and ductility. In the present work, the face-centered-cubic (FCC) single-crystal FeNiCoCrAl0.36 HEAs were studied, using the density functional theory (DFT) combined with the phonon calculation to estimate the stacking fault energies, temperature-dependent phase stabilities of different structures. And the kinetic Monte Carlo (kMC) was used to predict the substructures evolution based on the transition state energies obtained from DFT calculations. We proposed two different formation paths of nano-twins in this Al-composited HEA and found that short-range hexagonal-close-packed (HCP)-stacking could occur in this HEA. The DFT calculations suggest that this HEA has negative stacking fault energy (SFE), HCP formation energy, and twin-formation energy at 0 K. Phonon calculations indicate that at the finite temperature, the competing FCC/HCP phase stability and propensity for twinning make it possible to form HCP-like twin boundaries. The kMC simulations suggest that under deformation, TWINs could form within the HCP laths which differs from the study of others. With the great agreement of results from kMC simulations and experiments, this twin-hcp laminated substructure formation path offers a new concept of designing TWIP HEAs containing tunable twin structures with HCP and TWIN lamellae structures, which could result in better mechanical properties of HEAs.

Using first-principles calculations, we investigate selected defects in blue phosphorene (BlueP). For a single-vacancy (SV) defect, a 5–9 structure is energetically favorable, and for a double-vaca...

Artificial graphite (FSN) additive is employed as internal structural label for projecting cyclability of Si material native electrode in a mass ratio of Si/FSN = 1.0 in Li ion battery (LIB). Results of operando X-ray diffraction analysis on Si-FSN negative electrode in LIB demonstrate that one can evaluate the lithiation and delithiation affinity of active material by referring phase transition delay of graphite as affected by experimental splits in a formation process of LIB. We prove that a thin layer of surface amorphous structure and residual lattice strain are formed in Si by high energy ball-milling treatment. Those manipulations improve Li intercalation kinetics and thus enabling a capacity fading of less than 10% (from 1860 to 1650 mAhg−1) for Si negative electrode in 50 cycles. Of utmost importance, this study discloses a robust assessment for revealing mechanism on amorphous and strain related silicide formation and predicting cyclability of negative electrode by quantitative phase evolution rate of FSN additive in LIB.

We performed first-principles calculations of the structural, electronic, and optical properties of heterostructures which consist of transition metal dichalcogenides MX2 (M = Mo, W; X = S) stacked with Mg(OH)2. All the heterostructures are formed by van der Waals forces. The MoS2/Mg(OH)2 and WS2/Mg(OH)2 vdW heterostructures were found to be semiconductors with indirect bandgaps and possess intrinsic type-II band alignment. In particular, a comparison of the band edge positions with the redox potential of water indicates that the heterostructures are potential photocatalysts for water splitting, enabling water reduction on the MX2 layer and water oxidation on the Mg(OH)2 layer. Moreover, the photogenerated charges will be effectively separated in the presence of a large built-in electric field across the interface. In addition, all of the MX2/Mg(OH)2 heterostructures show strong optical absorption in the visible and infrared regions, indicating their promise for application in photocatalytic water splitting.

Liquid crystals (LCs) have been a vital component of modern communication and photonic technologies. However, traditional LC alignment on polyimide (PI) requires mechanically rubbing treatment to control LC orientation, suffering from dust particles, surface damage, and electrostatic charges. In this paper, LC alignment on organic single-crystal rubrene (SCR) has been studied and used to fabricate rubbing-free LC devices. A rubrene/toluene solution is spin-coated on the indium–tin–oxide (ITO) substrate and transformed thereafter to the orthorhombic SCR after annealing. Experimental result reveals that SCR-based LC cell has a homogeneous alignment geometry, the pretilt angle of LCs is low and the orientation of LCs is determined with capillary filling action of LCs. LC alignment on SCR performs a wider thermal tolerance than that on PI by virtue of the strong anchoring nature of LCs on SCR due to van der Waals and π–π electron stacking interactions between the rubrene and LCs. SCR-based LC cell performs a lower operation voltage, faster response time, and higher voltage holding ratio than the traditional PI-based LC cell. Organic SCR enables to play a role as weakly conductive alignment layer without rubbing treatment and offers versatile function to develop novel LC devices.

We investigate the electronic and spin structure of Pb atomic chains on a $\mathrm{Si}(100)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ surface using first-principles calculations. We revealed that the electronic spectra of linear dimerized Pb chains with orientations perpendicular and parallel to the Si dimers are characterized by one-dimensional large Rashba spin splitting providing exclusive spin polarization of the carriers that makes these systems suitable for studying the spin-transport phenomena and realizing a tunable spin current. A buckled dimerized Pb chain with a parallel orientation was predicted to be an insulating Rashba system with a vortical spin texture and asymmetric charge distribution. In this paper we trace the origin of Rashba band anisotropy and its interplay with chain geometry. The Rashba parameters of the considered chains are compared with other well-known systems.

Although H

Stretching diamond to the limit Diamond is thought of as being unbendable, but thin samples can actually deform elastically. Applying relatively large amounts of strain to diamond may shift its electronic properties, which is of interest for a number of applications. Dang et al. elastically stretched micrometer-sized plates of diamond along different crystallographic directions. These relatively large samples show that deep-strain engineering can be accomplished in more uniform diamond specimens and may have a large impact on the electronic properties. Science , this issue p. 76

Highly correlated orbitals coupled with phonons in two-dimension are identified for paramagnetic and optically active boron vacancy in hexagonal boron nitride by first principles methods which are responsible for recently observed optically detected magnetic resonance signal. Here, we report ab initio analysis of the correlated electronic structure of this center by density matrix renormalization group and Kohn-Sham density functional theory methods. By establishing the nature of the bright and dark states as well as the position of the energy levels, we provide a complete description of the magneto-optical properties and corresponding radiative and non-radiative routes which are responsible for the optical spin polarization and spin dependent luminescence of the defect. Our findings pave the way toward advancing the identification and characterization of room temperature quantum bits in two-dimensional solids. Funding Agencies|MTA Premium Postdoctoral Research Program; Knut and Alice Wallenberg Foundation through WBSQD2 project [2018.0071]; NKFIH [PD-17-125261, K120569]; "Bolyai" Research Scholarship of HAS; Alexander von Humboldt FoundationAlexander von Humboldt Foundation; Hungarian NKFIH of the National Excellence Program of Quantum-coherent materials project [KKP129866]; NKFIH through the National Quantum Technology Program [2017-1.2.1-NKP-2017-00001]

It is known that the interplay between molecules and active sites on the topmost surface of a solid catalyst determines its activity in heterogeneous catalysis. The electron density of the active site is believed to affect both adsorption and activation of reactant molecules at the surface. Unfortunately, commercial X-ray photoelectron spectroscopy, which is often adopted for such characterization, is not sensitive enough to analyze the topmost surface of a catalyst. Most researchers fail to acknowledge this point during their catalytic correlation, leading to different interpretations in the literature in recent decades. Recent studies on pristine Cu

We study the effect of strain on the physical properties of the nitrogen antisite-vacancy pair in hexagonal boron nitride ($h$-BN), a color center that may be employed as a quantum bit in a two-dimensional material. With group theory and ab-initio analysis we show that strong electron-phonon coupling plays a key role in the optical activation of this color center. We find a giant shift on the zero-phonon-line (ZPL) emission of the nitrogen antisite-vacancy pair defect upon applying strain that is typical of $h$-BN samples. Our results provide a plausible explanation for the experimental observation of quantum emitters with similar optical properties but widely scattered ZPL wavelengths and the experimentally observed dependence of the ZPL on the strain., Comment: 7 pages, 3 figures

Carbon nanotube supported ternary metallic nanocatalysts (NCs) comprising Nicore-Pdshell structure and Pt atomic scale clusters in shell (namely, Ni@Pd/Pt) are synthesized by using wet chemical reduction method with reaction time control. Effects of Pt4+ adsorption time and Pt/Pd composition ratios on atomic structure with respect to electrochemical performances of experimental NCs are systematically investigated. By cross-referencing results of high-resolution transmission electron microscopy, X-ray diffraction, X-ray absorption, density functional theoretical calculations, and electrochemical analysis, we demonstrate that oxygen reduction reaction (ORR) activity is dominated by depth and distribution of Pt clusters in a Ni@Pd/Pt NC. For the optimum case (Pt4+ adsorption time = 2 h), specific activity of Ni@Pd/Pt is 0.732 mA cm-2 in ORR. Such a value is 2.8-fold higher as compared to that of commercial J.M.-Pt/C at 0.85 V (vs reversible hydrogen electrode). Such improvement is attributed to the protection of defect sites from oxide reaction in the presence of Pt clusters in NC surface. When adsorption time is 10 s, Pt clusters tends to adsorb in the Ni@Pd surface. A substantially increased galvanic replacement between Pt4+ ion and Pd/Ni metal is found to result in the formation of Ni@Pd shell with Pt cluster in the interface when adsorption time is 24 h. Both structures increase the surface defect density and delocalize charge density around Pt clusters, thereby suppressing the ORR activity of Ni@Pd/Pt NCs.

Recently we experimentally demonstrated that vapor–liquid–solid (VLS) grown silicon (Si) nanowires can be stretched to above 10% elastic strain through in situ nanomechanical strategies (Zhang et al. Sci. Adv. 2016, 2 (8), e1501382). Here, based on first-principles calculation, the geometric and electric properties of -oriented Si nanowires with diameter ∼1.5 nm under ultralarge strain are comparatively investigated. The anisotropic Poisson effect was observed in the silicon nanowire that the change of diameter along the (100) orientation decreases dramatically while that along the (110) orientation shows only minor influence. For the purpose of obtaining a thorough understanding of the influence of applied strain on the electronic properties, the electronic band structure, effective mass of electron, and work function are systematically studied. Direct-to-indirect band gap transformation occurs for hydrogen terminated nanowires when the applied strain is larger than 4%. When the applied strain is mo...

Herein, we report a comprehensive study on the structural and electronic properties of bulk, monolayer, and multilayer PdSe2 sheets. First, we present a benchmark study on the structural properties of bulk PdSe2 by using 13 commonly used density functional theory (DFT) functionals. Unexpectedly, the most commonly used van der Waals (vdW)-correction methods, including DFT-D2, optB88, and vdW-DF2, fail to provide accurate predictions of lattice parameters compared to experimental data (relative error > 15%). On the other hand, the PBE-TS series functionals provide significantly improved prediction with a relative error of

Metastable double-atomic layer of Tl on Si(111) has recently been found to display interesting electric properties, namely superconductivity below 0.96 K and magnetic-field-induced transition into an insulating phase intermediated by a quantum metal state. In the present work, using a set of experimental techniques, including low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, in a combination with density-functional-theory calculations, we have characterized atomic and electronic properties of the Tl double layer on Si(111). The double Tl layer has been concluded to contain ∼ 2.4 monolayer of Tl. A top Tl layer has a ‘1 × 1’ basic structure and displays 6 × 6 moire pattern which originates from various residence sites of Tl atoms. Upon cooling below ∼ 140 K, the 6 × 6 moire pattern changes to that having a 6 3 × 6 3 periodicity. However, the experimentally determined electron band dispersions show a 1 × 1 periodicity. The calculated band structure unfolded into the 1 × 1 surface Brillouin zone reproduces well the main features of the photoelectron spectra.