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Majorana zero mode, the bound state of Majorana fermion in a condensed matter system, plays a critical role in fault-tolerant topological quantum computation. It can be realized in the vortex of a two-dimensional topological superconductor as a zero-energy excitation. A topological superconductor can be constructed by coupling superconductivity to the topological surface states by the proximity effect. In this review article, we discuss the fabrication of such artificially engineered topological superconductors by molecular beam epitaxy. The topological phase and superconductivity are exhibited in Bi2Se3/NbSe2 and Bi2Te3/NbSe2 heterostructures simultaneously. Several characteristic features of Majorana zero mode have been revealed in the vortex by a low-temperature scanning tunneling microscope and corroborated by theoretical results. The discovery of Majorana zero mode may pave the way for further applications in topological quantum computing. [ABSTRACT FROM AUTHOR]

Ti 2 Cu, TiCu and TiCu 4 were synthesized and their electrocatalytic activities for hydrogen evolution reaction (HER) were investigated. The hydrogen overpotential observed at 10 mA/ cm2 (η 10) followed the order Ti 2 Cu (η 10 = −215 mV) > TiCu (η 10 = −182 mV) > TiCu 4 (η 10 = −170 mV). The hydrogen adsorption energy (∆G Had) on Cu site of TiCu 4 is exergonic and close to optimal position (i.e. ∆G Had = 0). A synergistic effect was proposed to account for the excellent HER performance of these Ti Cu binary intermetallics compounds that could replace PGM and achieve Midas touch in the future. [Display omitted] • High purity of Ti 2 Cu, TiCu and TiCu 4 were synthesized by using rapid arc-melting technique. • Hydrogen evolution reaction (HER) study on Ti 2 Cu, TiCu and TiCu 4 in alkaline media. • HER activity of Ti 2 Cu, TiCu and TiCu 4 were explored by using density functional theory. • Synergistic effect for these Ti Cu binary intermetallics toward HER activity was discussed. [ABSTRACT FROM AUTHOR]

Magnetic metals deposited on graphene hold the key to applications in spintronics. Here, we present the results of Fe islands grown on graphene/SiC(0001) by molecular beam epitaxy, which are investigated by scanning tunneling microscopy. The two types of islands distinguished by flat or round tops are revealed, indicating bimodal growth of Fe. The atomic structures on the top surfaces of flat islands are also clearly resolved. Our results may improve the understanding of the mechanisms of metals deposited on graphene and pave the way for future spintronic applications of Fe/graphene systems. [ABSTRACT FROM AUTHOR]

Abstract: A numerical study is presented on the transport processes in the manganite–titanate Schottky junction by using the Poisson equation, the drift-diffusion formulas, the direct and thermally assisted tunneling model. Comparing with the experimental data, it is found that the non-monotonically temperature-dependent I–V curves under reverse bias is caused by the competition between the direct and thermally assisted tunneling processes. In addition, it is also found that the electric field dependence of the permittivity in Nb-doped SrTiO3 plays an important role on the transport properties of the manganite–titanate Schottky junctions based on our calculation. [Copyright &y& Elsevier]

Abstract: The behavior of leakage current at reverse bias in p-La0.9Sr0.1MnO3/n-SrNb0.01Ti0.99O3 heterojunction has been theoretically studied by calculating interband tunneling current with various doping densities and temperatures. Our results reveal that the reduction of leakage current with decrease of doping density and increase of temperature originates from properties of interband tunneling. [Copyright &y& Elsevier]

Abstract: An angle-resolved photoemission study of epitaxied Bi(111) film on Si(111)-(7×7) surface has been carried out at a temperature from 10K to 210K. The results show that there exists strong temperature dependence in the valence band of Bi(111) film. The variations in the spectral intensity and shape indicate the importance of phonon-assisted indirect transition in the photoemission process. The thermal sensitivity coefficients and effective Debye temperatures for main spectral peaks are determined from the experimental data. [Copyright &y& Elsevier]

Abstract: Using the annealed vicinal Si(001) surface with 4° miscut toward the [110] direction as a substrate, single-domain monatomic In chain arrays have been fabricated. High-resolution STM images reveal that deposited In atoms preferentially form In dimers between two neighboring Si dimer rows along the step edges on the lower terrace. Formation of In dimers removes the surface dangling bonds and saturates the In valency. With increasing coverage, the In dimers develop into straight monatomic In chains along the step running direction. It is found that the ordered narrow terrace and rebonded double-layer (DB) step edge are the keys for the formation of monatomic In chains. [Copyright &y& Elsevier]

Atomic structure of FeSi[sub 2] or CoSi[sub 2] grown on the Si(100) 2xn surface has been investigated by scanning tunneling microscopy. After annealing the Fe or Co covered Si(100) 2xn substrate at ∼800 °C, an ordered adatom vacancy array appears on the nominal 1x1 surface of the formed FeSi[sub 2] or CoSi[sub 2] islands, which has not been observed for silicide on the Si(100)-2xl. Upon further annealing to ∼ll00 °C, the vacancies coalesce into striped domains along one of the <011> directions. These nanostructured features are a result of the Ni impurities, and can be a promising template for fabricating nanodot arrays. [ABSTRACT FROM AUTHOR]

Organic‐inorganic hybrid multifunctional materials have received significant attention due to their potential applications in smart devices such as phase‐change memory (PCM), resistive random‐access memory (ReRAM). Yet, devices application requires achieving a balance between fast switching speeds, long‐term stability, and high cycling endurance in materials still facing difficulties. Herein, we report two hybrid phase transition compounds: (CMQ)BiCl5(CMQ=Chloromethyl Quinuclidin‐3‐one) (1) and (FMQ)2SbBr5(FMQ=Fluoromethyl Quinuclidin‐3‐one) (2), both two compounds exhibit high phase transition temperature, dual‐stable behavior in dielectric during reversible phase transition process. Notably, 1 exhibit small dielectric change after multiple dielectric state switching. Furthermore, investigate the influence of halogen substitution (F to Cl) for compound properties, which show an Increasing transition temperature (9 K) and raising structural dimension (0D to 1D). Additionally, using first principles, analyze the electronic structure of 1 and find that it has a 3.4 eV wide bandgap, closing to GaN semiconductor (3.4 eV). This work provides a new insight into developing the next‐generation phase transition compounds and chemical modification enhances material performance. [ABSTRACT FROM AUTHOR]

The Jacobin is a breed of fancy pigeon developed over many years of selective breeding that originated in Asia. In the present work, we report the complete mitochondrial genome sequence of Jacobin pigeon for the first time. The total length of the mitogenome was 17,245 bp with the base composition of 30.18% for A, 23.98% for T, 31.88% for C, and 13.96% for G and an A-T (54.17 %)-rich feature was detected. It harbored 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes and 1 non-coding control region. The arrangement of all genes was identical to the typical mitochondrial genomes of pigeon. The complete mitochondrial genome sequence of Jacobin pigeon would serve as an important data set of the germplasm resources for further study. [ABSTRACT FROM AUTHOR]

The discovery of an extraordinarily superconductive large energy gap in SrTiO3 supported single-layer FeSe films has recently initiated a great deal of research interests in surface-enhanced superconductivity and superconductive ultrathin films fabricated on crystal surfaces. On account of the instability of ultra-thin films in air, it is desirable to perform electrical transport measurement in ultra-high vaccum (UHV). Here we review the experimental techniques of in situ electrical transport measurement and their applications on superconductive ultrathin films. [ABSTRACT FROM AUTHOR]

The Mn-Bi-Te class of compounds are recently discovered topological insulators with broken time-reversal-symmetry, which host unique quantum anomalous Hall and axion insulator states. Their key characteristics are believed to be sufficiently understood by models in a single-particle picture. Here, we apply scanning tunneling microscopy to study the electronic properties of MnBi2Te4 and MnBi4Te7. Unexpectedly, our quasiparticle interference (QPI) results demonstrate that rotational symmetry of the crystal breaks, i.e. a nematic-like pattern arises, in certain energy range but persists in others. Moreover, our data in the presence of an external magnetic field rule out the possibility of the material magnetism as an origin of the C2 symmetric QPI pattern. This study reveals that the interaction in the Mn-Bi-Te class of topological materials may play an essential role in their electronic states, and thus opens a new path for investigating the interplay between wavefunction topology and symmetry breaking phases. [ABSTRACT FROM AUTHOR]

Abstract: Room temperature morphology evolution of Pb thin films, prepared on the Si(111)-7×7 substrate at a low temperature (145K), is investigated by reflection high energy electron diffraction, scanning tunnelling microscopy and angle-resolved photoemission spectroscopy. A critical thickness of 10 monolayers (ML) is identified, below which all the flat films formed at low temperature are unstable against evolution into interconnected islands at room temperature. From 10ML to 21ML, Pb films become stable at room temperature and grow via a bi-layer mode. Above 21ML, the film growth turns into a layer-by-layer mode. A “beating effect” is observed to modulate this special growth mode, which changes the film stability from even (odd) layers to odd (even) layers with a 9ML period. Morphology and electronic structure analysis show that the quantum size effect is responsible for the different morphology evolution behaviour and the magic stability of Pb films. [Copyright &y& Elsevier]

A sufficiently large supercurrent can close the energy gap in a superconductor and create gapless quasiparticles through the Doppler shift of quasiparticle energy caused by finite Cooper pair momentum. In this gapless superconducting state, zero-energy quasiparticles reside on a segment of the normal-state Fermi surface, whereas the remaining Fermi surface is still gapped. We use quasiparticle interference to image the field-controlled Fermi surface of bismuth telluride (Bi2Te3) thin films under proximity effect from the superconductor niobium diselenide (NbSe2). A small applied in-plane magnetic field induces a screening supercurrent, which leads to finite-momentum pairing on the topological surface states of Bi2Te3. We identify distinct interference patterns that indicate a gapless superconducting state with a segmented Fermi surface. Our results reveal the strong impact of finite Cooper pair momentum on the quasiparticle spectrum. [ABSTRACT FROM AUTHOR]

To realize the braiding operations of the Majorana zero modes in the vortex cores of a topological superconductor (TSC), a novel approach is proposed in this letter to replace the common tip (or tip-like) method. Instead of being on top of the TSC thin film, arrays of electrically controllable pinning centers are built beneath the film, hence detection can proceed along with braiding. This does not only increase the braiding rate, but also enables the braiding to be performed in an electrically controllable way and to be integrated into a large scale. Our work paves the way toward large-scale topological quantum computation. [ABSTRACT FROM AUTHOR]

Abstract: Surface superstructures are studied with scanning tunneling microscopy during the growth of In on In/Si(111). On the inhomogeneous substrate of Si(111) 4×1/-In coexisting surface, the deposition of 1.5 monolayer (ML) In at about 0°C leads to reconstruction on surface and the formation of one-dimensional nanowires on 4×1 surface (1.0ML=7.8×1014 atoms/cm2). Subsequent deposition of In at −100°C gives rise to the appearance of a hexagonal superstructure with periodicity on reconstructed surface, while self-alignment of In dots along one-dimensional nanowires is observed on the initial 4×1 surface. On Si(111) -In surface, the growth of 2.5ML In at about −100°C yields 6×6 superstructure. The strain in the epitaxial In thin films provides a driving force for the formation of self-organized surface structures. [Copyright &y& Elsevier]

Domain boundaries of superlattices formed on the highly oriented pyrolytic graphite surface are studied by scanning tunneling microscopy. Twist and glide boundaries are identified with help of theoretical simulations. The apparent vertical corrugation difference of the superlattices with the same lattice periodicity is explained in terms of overlayer attenuation. Our study reveals that the intra-layer strain has important effect on the electronic structure of the graphite surface. [Copyright &y& Elsevier]

To uncover the critical effect of disorder on superconductivity, the ideal method is to visualize the microscopic crystalline deficiencies in real space while measuring the macroscopic superconducting properties. By using a self-developed multifunctional scanning tunneling microscope, we investigated the correlation between controllably introduced disorder and superconductivity in the Si(111)- 7 × 3 -In surface reconstruction. It is revealed that not only the density but also the spatial distribution of surface vacancies makes a significant influence on the diamagnetic response of the superconducting surface reconstruction. The higher density of vacancies uniformly dispersed on terraces results in a lower critical temperature and critical magnetic field, while the presence of grooves formed by aggregation of vacancies at step edges reduces the critical supercurrent and thus weakens the diamagnetic shielding effect remarkably. [ABSTRACT FROM AUTHOR]

We investigate the surface structure and electronic properties of β-Sn islands deposited on a graphitized 6H-SiC (0001) substrate via low temperature scanning tunneling microscopy and spectroscopy. Owing to the confinement of the island geometry, quantum well states (QWSs) are formed, manifesting as equidistant peaks in the tunneling spectra. Furthermore, a distinct strip feature appears on the surfaces of odd-layer Sn islands, ranging from 15–19 layers, which is not present on the surfaces of even-layer Sn islands. The spatial distribution of strips can be modified by applying a bias pulse, using an STM tip. Furthermore, the strip-like structure shows significant impacts on the QWS. An energy splitting of the lowest unoccupied QWSs is observed in strip regions; this may be ascribed to caused the phase shift of the wave functions of the QWSs on the top surface, due to surface distortions created by the aforementioned strips. [ABSTRACT FROM AUTHOR]

The transport property of a superconducting Pb nanobridge, which is carved by focus ion beam technique from an atomically flat single-crystal Pb thin film grown on Si(111) substrate, is investigated. Below the superconducting transition temperature TC, the nanobridge exhibits a series of sharp voltage steps as a function of current. The multiple voltage steps are interpreted as a consequence of spatially localized phase slip centers or hot-spot formation in the bridge. Just below the critical current, the voltages versus current curve shows a power-law behavior in the low temperature region, but Ohmic near the TC. The thermally activated phase slip, quantum phase slip, and imhomogeneity in a one-dimensional superconducting system may contribute to the observed results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Monolayer C 60 film is grown on a SrTiO 3 (0 0 1) surface for the first time. • Monolayer C 60 exhibit a short-range ordered molecular arrangement, while multi-layer C 60 show a quasi-(2 × 2) superstructure with a chiral pinwheel motif. • Monolayer C 60 on STO shows the largest HOMO-LUMO gap comparing to those on any other substrates. Ultrathin fullerene (C 60) films on various metal and semiconductor substrates have been intensively studied but not yet on a perovskite oxide substrate. Using scanning tunneling microscopy and spectroscopy, we investigated the molecular arrangement and electronic structure of C 60 ultrathin films grown on a SrTiO 3 (0 0 1) surface. Subject to strong coupling and weak screening from the substrate, the monolayer C 60 exhibit short-range ordered molecular arrangement with disordered molecular orientation and a substantially large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap (∼4.1 eV). In contrast, C 60 in the 2nd and 3rd layers are self-assembled into hexagon lattices with a quasi-(2 × 2) superstructure resulted from the arrangement of molecular orientations showing a chiral pinwheel structure. The HOMO-LUMO gap of the multi-layer C 60 further expands to ∼ 4.6 eV, very close to that of gas-phase C 60 , indicating a negligible inter-layer screening effect. [ABSTRACT FROM AUTHOR]

Growth of In on the Si(001)-2×n nanostructured surface is investigated by an in situ scanning tunneling microscope (STM). The deposited In atoms predominantly occupy the normal 2×1 dimer-row structure, and develop into a uniform array of In nanowires at a coverage of ∼0.2 ML. High-resolution STM images show that the In atoms form a stable local 2×2 reconstruction that removes surface Si dangling bonds states and saturates all In valency. Since the dimensions of the Si(001)-2×n vacancy line structure depend on impurity concentrations, this study demonstrates that the 2×n surface can be used for spontaneous fabrication of various metal nanowire arrays. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Highlights • The unusual ClAlPc molecular self-assembled layer on a buffer layer have large deformations compared with the common ClAlPc bilayer. • Almost freestanding environment is provided for the molecules when the influence from the substrate is shielded by the buffer layer. • The dominated intermolecular interaction is likely to be the dispersion forces via Reduced Density Gradient analysis. Abstract We report an unusual self-assembled layer structure of chloroaluminium phthalocyanine (ClAlPc) molecules on highly ordered pyrolytic graphite (HOPG), in which a close-packed well-ordered monolayer is separated from the substrate by a relatively disordered buffer layer, as revealed using scanning tunneling microscopy (STM). Our close-packed monolayer has a nearly rectangular lattice, instead of the distinctly different square lattice for the more commonly observed well-ordered bilayer structure. This may be due to the dominance of intermolecular interactions within the monolayer when the influence from the substrate is shielded by the buffer layer. Density Functional Theory (DFT) calculations and Reduced Density Gradient (RDG) analysis indicate that the dominant intermolecular interaction within the unusual layer is likely the London dispersion force. Graphic abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Following the first experimental realization of graphene, other ultrathin materials with unprecedented electronic properties have been explored, with particular attention given to the heavy group-IV elements Si, Ge and Sn. Two-dimensional buckled Si-based silicene has been recently realized by molecular beam epitaxy growth, whereas Ge-based germanene was obtained by molecular beam epitaxy and mechanical exfoliation. However, the synthesis of Sn-based stanene has proved challenging so far. Here, we report the successful fabrication of 2D stanene by molecular beam epitaxy, confirmed by atomic and electronic characterization using scanning tunnelling microscopy and angle-resolved photoemission spectroscopy, in combination with first-principles calculations. The synthesis of stanene and its derivatives will stimulate further experimental investigation of their theoretically predicted properties, such as a 2D topological insulating behaviour with a very large bandgap, and the capability to support enhanced thermoelectric performance, topological superconductivity and the near-room-temperature quantum anomalous Hall effect. [ABSTRACT FROM AUTHOR]

Recent experiments on FeSe films grown on SrTiO3 (STO) suggest that interface effects can be used as a means to reach superconducting critical temperatures (Tc) of up to 80 K (ref. ). This is nearly ten times the Tc of bulk FeSe and higher than the record value of 56 K for known bulk Fe-based superconductors. Together with recent studies of superconductivity at oxide heterostructure interfaces, these results rekindle the long-standing idea that electron pairing at interfaces between two different materials can be tailored to achieve high-temperature superconductivity. Subsequent angle-resolved photoemission spectroscopy measurements of the FeSe/STO system revealed an electronic structure distinct from bulk FeSe (refs , ), with an energy gap vanishing at around 65 K. However, ex situ electrical transport measurements have so far detected zero resistance-the key experimental signature of superconductivity-only below 30 K. Here, we report the observation of superconductivity with Tc above 100 K in the FeSe/STO system by means of in situ four-point probe electrical transport measurements. This finding confirms FeSe/STO as an ideal material for studying high-Tc superconductivity. [ABSTRACT FROM AUTHOR]

A self-assembled iron(II) phthalocyanine single layer adsorbed on the topological insulator Bi2Te3 was investigated by spin-polarized scanning tunneling microscopy and density functional theory calculations. Although the molecule-substrate interaction is dominated by a relatively weak van der Waals force, the local density of states of Fe was found to strongly depend on the adsorption sites, resulting in a supermolecular lattice. Spin-polarized measurements show that the magnetic moment of iron(II) phthalocyanine persists with an in-plane magnetic easy axis, which was fürther confirmed by density functional calculations. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure of reconstructed surface is measured by angle-resolved photoemission spectroscopy. By the first time, band splitting at and points in the surface Brillouin zone (SBZ) of this system is observed, which could be simply interpreted in the framework of Rashba splitting. Furthermore, first principle calculation is carried out and compared with our experimental results. [Copyright &y& Elsevier]

Abstract: Using angle-resolved photoemission spectroscopy (ARPES), we investigate the electronic structure of Cu-doped topological insulator Bi2Te3 on Si(111) substrate prepared by molecular beam epitaxy (MBE) to clarify the doping nature of Cu atoms in the films. By systematic studying the structural and electronic properties of the Cu-doped Bi2Te3 films by different doping methods, we find that Cu acts as electron donors when deposited onto the surface of Bi2Te3 films while behave as holes when doped in the process of Bi2Te3 thin film growth. The model of the formation of Cu+, five/seven layer lamella structures and Cu2−x Te is proposed to explain the different doping mechanisms. The robustness of topological surface states and insensitivity to non-magnetic impurities is indicated. [Copyright &y& Elsevier]

Providing the strong spin--orbital interaction, Bismuth is the key element in the family of three-dimensional topological insulators. At the same time, Bismuth itself also has very unusual behavior, existing from the thinnest unit to bulk crystals. Ultrathin Bi (111) bilayers have been theoretically proposed as a two-dimensional topological insulator. The related experimental realization achieved only recently, by growing Bi (111) ultrathin bilayers on topological insulator Bi2Te3 or Bi2Se3 substrates. In this review, we started from the growth mode of Bi (111) bilayers and reviewed our recent progress in the studies of the electronic structures and the one-dimensional topological edge states using scanning tunneling microscopy/spectroscopy (STM/STS), angle-resolved photoemission spectroscopy (ARPES), and first principles calculations. [ABSTRACT FROM AUTHOR]

We report high transition temperature superconductivity in one unit-cell (UC) thick FeSe films grown on a Seetched SrTiO3(001) substrate by molecular beam epitaxy (MBE). A superconducting gap as large as 20 meV and the magnetic field induced vortex state revealed by in situ scanning tunneling microscopy (STM) suggest that the superconductivity of the 1 UC FeSe films could occur around 77 K. The control transport measurement shows that the onset superconductivity temperature is well above 50 K. Our work not only demonstrates a powerful way for finding new superconductors and for raising TC, but also provides a well-defined platform for systematic studies of the mechanism of unconventional superconductivity by using different superconducting materials and substrates. [ABSTRACT FROM AUTHOR]

The photoabsorption edge shifting from UV to visible region accompanied with increased intensity and Raman features change was observed for N+ implanted TiO2. Raman spectra prove the formation of TiNx and oxygen vacancies in the implanted TiO2, which is considered as the origin of absorption edge shifting. The work may give a hint to increase the photocatalytic activity of TiO2 in the visible region at the molecule level. [ABSTRACT FROM AUTHOR]

Ultra-thin Pb films with magic thicknesses of 2 monolayer (ML), 4 ML and 6 ML were prepared of atomically flat on the substrate of Si(111)-α-√3 × √3 (or SIC phase) at 145 K. Their surface morphologies and stability were studied by low temperature scanning tunneling microscopy and temperature-dependent angle resolved photoemission spectroscopy. We found that the well ordered SIC interface can lower the diffusion barrier and enhance the interface charge transfer, leading to different critical thickness compared to Pb/Si(111)-7 × 7 grown under same conditions. Enhanced thermal expansion coefficients were also observed in ultra-thin Pb films at low temperature. [ABSTRACT FROM AUTHOR]

We have studied the superconductivity of Pb ultra-thin films with thickness from 1 monolayer (ML) to 7 ML grown on Si(111) by molecular beam epitaxy. In situ low temperature scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES) measurements were performed on the films. It is suggested that the interface effect plays a critical role in enhancing the electron-phonon coupling, which consequently increases the superconducting transition temperature when a film reaches to the two-dimensional limit. [ABSTRACT FROM AUTHOR]

Abstract: The transport processes in the heterostructures of and have been studied theoretically by taking into account the effect of Schottky barrier formed at the contact of the electrode. By comparing with the experimental data, it is found that the physical origin for the symmetry of the measured – curves in the heterostructures of can be attributed to the effect of the Schottky contact diodes. It is also found that the influence of Schottky barrier on the transport properties of heterostructures increases with the increased temperature and decreases with the increased doping density of layer at temperature above the Curie temperature of based on our calculation. [Copyright &y& Elsevier]

The crystal structure, electronic, and magnetic properties of Gadolinium (Gd) substituted Bi2Se3-represented by Bi1.98Gd0.02Se3-were investigated systematically by scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and superconducting quantum interference device. Gd dopants with valence of 3+ were mainly found to substitute Bi atoms. Each Gd3+ ion has a magnetic moment as large as ∼6.9μB in the bulk paramagnetic state. [ABSTRACT FROM AUTHOR]

The electronic and magnetic properties of iron-doped topological insulator Bi1.84-xFe0.16CaxSe3 single crystals were studied. By co-doping Fe and Ca atoms, ferromagnetic bulk states with different carrier density (from n-type to p-type) were obtained. Effective magnetic moments for each Fe atom was estimated as small as about 0.07μB. Magnetic and non-magnetic phases separation was observed in all samples. Our results suggest that the bulk ferromagnetism in Fe-doped Bi2Se3 is not intrinsic and regardless of carrier density. [ABSTRACT FROM AUTHOR]

We investigate the far-field scattering property of a single Ag nanoring. Under oblique excitation, two-focus scatterings with distinct intensities were observed. We show that the two-focus scatterings result from the interference of far-field scattering light from the ring circumference, and the local field enhancement effect of surface plasmons plays the key role in the focus intensity. By finite difference time domain and numerical integer methods, we calculated far-field scattering and surface plasmons' distributions, and the results are in good agreement with the experiment. [ABSTRACT FROM AUTHOR]

Bi2Se3 is a typical three-dimensional topological insulator but always exhibits metallic behavior due to heavy n-type doping. With in situ angle-resolved photoemission spectroscopy, we have systematically studied the doping effects of Sb and Pb on the electronic structure of Bi2Se3 films prepared by molecular beam epitaxy. The surface chemical potential of Bi2Se3 can be tuned by 110 and 145 meV by doping Sb and Pb atoms, respectively. By codoping Pb and Sb, the Fermi level can be shifted from above to below the Dirac point. The underlying mechanism in different doping effects of Sb and Pb is discussed. [ABSTRACT FROM AUTHOR]

Atomically flat thin films of topological insulator Bi2Se3 have been grown on double-layer graphene formed on 6H-SiC(0001) substrate by molecular beam epitaxy. By a combined study of reflection high energy electron diffraction and scanning tunneling microscopy, we identified the Se-rich condition and temperature criterion for layer-by-layer growth of epitaxial Bi2Se3 films. The as-grown films without doping exhibit a low defect density of 1.0±0.2×1011/cm2, and become a bulk insulator at a thickness of ten quintuple layers, as revealed by in situ angle resolved photoemission spectroscopy measurement. [ABSTRACT FROM AUTHOR]

We have calculated the energy barriers for an adatom climbing up onto a Pb mesa top either over a facet-facet edge or through a facet-step joint, using a modified embedded atom method. We found that the second process is not only thermodynamically more favorable than the first one but also much faster with a diminishing barrier. Our results provide a plausible explanation for the experimentally observed intriguing growth behavior of a Pb mesa. The underlying mechanisms can be generally applicable to other systems. [ABSTRACT FROM AUTHOR]

Using a low temperature method, the authors have prepared atomically flat Pb ultrathin films on Si(111)-7×7 surface. Room temperature annealing of the films results in a percolation morphology with fractal vacancy islands where the Si substrate is exposed. The fractal film with a nominal thickness of 23 ML exhibits enhanced onset superconducting transition temperature of 7.0 K and negative magnetoresistance with wide magnetoresistance terrace under perpendicular magnetic field when the film is in superconducting state. They attribute the phenomena to the coexistence of two superconducting phases in this fractal film. [ABSTRACT FROM AUTHOR]

Varied temperature photoemission study is performed to investigate the quantum size effects on the thermal property of atomically flat Pb films grown on Si(111). The binding energies of the quantum well states for the films with thicknesses from 10 to 24 ML exhibit a linear increase with increasing temperature from 75 to 270 K. Under free electron approximation, thermal expansion coefficients of the thin films are determined, which manifest a large enhancement and oscillation behavior. The large enhancement is interpreted by a model based on the quantum confinement along the film normal direction. The oscillation is shown to be closely related to the structural instability and is a result of the formation of the quantized electronic states in thin films. [ABSTRACT FROM AUTHOR]

The thickness dependence of the local work function (LWF) and its relationship with the quantum well states (QWSs) are studied. The measured LWF shows an oscillatory behavior between adjacent layers with a period of 2 ML and, in addition, an envelope beating pattern with a period of 9 ML. Scanning tunneling spectroscopy investigations reveal that the oscillatory LWF correlates perfectly with the formation of the QWSs: the higher the occupied QWS is, the smaller the LWF is. Through the role of the LWF, this study establishes the importance of quantum size effects in thin films for surface reactions and catalysis. [ABSTRACT FROM AUTHOR]

We have fabricated ultra-thin lead films on silicon substrates with atomic-scale control of the thickness over a macroscopic area. We observed oscillatory behavior of the superconducting transition temperature when the film thickness was increased by one atomic layer at a time. This oscillating behavior was shown to be a manifestation of the Fabry-Pérot interference modes of electron de Broglie waves (quantum well states) in the films, which modulate the electron density of states near the Fermi level and the electronphonon coupling, which are the two factors that control superconductivity transitions. This result suggests the possibility of modifying superconductivity and other physical properties of a thin film by exploiting well-controlled and thickness-dependent quantum size effects. [ABSTRACT FROM AUTHOR]

Silicene, a monolayer of silicon atoms arranged in honeycomb lattices, can be synthesized on the Ag(111) surface, where it forms several superstructures with different buckling patterns and periodicity. Using scanning tunneling microscopy (STM), we obtained high-resolution images of silicene grown on Ag(111) and revealed its five phases, i.e., 4 × 4 − α, 4 × 4 − β, − α, − β and − γ, some observed for the first time. For each of the phases, we have determined its atomic structure by comparing the atomic-resolution STM images with theoretical simulation results previously reported. We thus eliminate the contradictions of previous studies on the structural models of various silicene phases supported by the Ag(111) surface. [ABSTRACT FROM AUTHOR]

Bulk carrier density and magnetic properties of Sb1.95-xBixCr0.05Te3 single crystals were studied. We found that the carrier density can be tuned by Bi substitution. Both the Curie temperature and magnetic moments are strongly related to the carrier density, which suggests the existence of intrinsic ferromagnetism in Cr-doped Sb2Te3 magnetic topological insulator that is very important for spin-related applications. [ABSTRACT FROM AUTHOR]

A correction to the article "Crossover of the Three-Dimensional Topological Insulator Bi2Se3 to the Two-Dimensional Limit" that was published online in the June 13, 2010 issue is presented.