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Density-functional theory calculations on P-rich InP(001):H surfaces are presented. Depending on temperature, pressure and substrate doping, hydrogen desorption or adsorption will occur and influence the surface electronic properties. For p-doped samples, the charge transition levels of the P dangling bond defects resulting from H desorption will lead to Fermi level pinning in the lower half of the band gap. This explains recent experimental data. For n-doped substrates, H-deficient surfaces are the ground-state structure. This will lead to Fermi level pinning below the bulk conduction band minimum. Surface defects resulting from the adsorption of additional hydrogen can be expected as well, but affect the surface electronic properties less than H desorption.

Here, by using angle-resolved photoemission spectroscopy, we showed that Bi2−xCrxSe3 single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms in which a large nonmagnetic gap with a distorted band structure was reported. We further provide laser-based high resolution photoemission data which reveal a Dirac point gap even in the pristine sample. The gap becomes more pronounced with Cr doping into the bulk of Bi2Se3. These observations show that the Dirac point can be modified by the magnetic impurities as well as the light source.

Laser-induced removal of non-destructive substrates is a continuous pursuit for practical applications. Herein, a strategy of scanning cycle's large adjustment combined with laser energy density's fine tuning was established to achieve precise removal of FeCo-based wave-absorbing coatings. First and foremost, no coating residue was observed on the surface and cross-section of optimized sample E5 with a laser energy density of 61.1 J/cm2 (scanning cycles were seven). CIE LAB color analysis indicated that the surface of sample E5 had the highest coating's removal degree. Through numerical simulation and experimental examination, the oxide layer of the aluminum alloy did not present any damage such as cracking and peeling. In addition, the surface roughness remained unchanged, which verifies the possibility of laser removal towards non-destructive substrates. The multi-perspective evaluations of surface states illustrated that Barite (BaSO4), FeCo and other coating's characteristic substances had disappeared, ensuring the subsequent serviceability of the surface after removal. Furthermore, the vaporization removal mechanism of the wave-absorbing coatings was demonstrated by the plasma captured by a high-speed camera. Notably, the substrate's damage mechanism in laser removal was revealed. The remarkable different thermal expansion behavior of oxide layer and alloy induced extreme stress concentrations at the interface, which led to oxide layer's cracks and exfoliation. In summary, substrate's damage suppression can be achieved through simulation and experimental optimization. The presented research not only benefits the strategy design of laser removal for multilayer materials, but also expands the application potential of laser removal in non-destructive substrates.

The transport properties of the Dirac fermions through the electric and magnetic barriers on the surface of a 3D topological insulator with a hexagonal warping effect have been investigated using the transfer matrix method. It was found that the transmission probability and the electric conductance are strongly modulated by the gate voltage, incident energy, number of barriers, and the exchange field strength. It was remarkable that the Dirac fermion is not perfectly transmitted at the normal incidence, confirming the role of the proximity effect in the suppression of transmission for normal incident electrons. The magnetic field can open up a band gap in the conductance spectrum at the Dirac point, depending on the magnetization orientation. The time-reversal symmetry remains broken as long as the magnetization orientations in modulated regions are not entirely parallel to the surface of a topological insulator. The resonant states and the position of resonant peaks are dependent on the gate voltage and incident energy values. It is shown that the number of tunneling resonances increases with increasing the number of barriers. The hexagonal warping effect can increase electronic transport at high energies. The results found here are consistent with those obtained previously.

The silicide superconductors (Ta, Nb, Zr)OsSi are among the best candidate materials for investigating the interplay of topological order and superconductivity. Here, we investigate in detail the normal-state topological properties of (Ta, Nb, Zr)OsSi, focusing on ZrOsSi, by employing a combination of 29Si nuclear magnetic resonance (NMR) measurements and first-principles band-structure calculations. We show that, while (Ta, Nb)OsSi behave as almost ideal metals, characterized by weak electronic correlations and a relatively low density of states, the replacement of Ta (or Nb) with Zr expands the crystal lattice and shifts ZrOsSi towards an insulator. Our ab initio calculations indicate that ZrOsSi is a Z2 topological metal with clear surface Dirac cones and properties similar to a doped strong topological insulator.

Plasma etching treatments are important steps in GaN-based devices fabrication, but can create defects on GaN surfaces. These surface defects can strongly alter device performances. The main objective of this work is to characterize the impact of different plasma etching recipes using an innovative electrochemical short loop based on Mott-Schottky (MS) method. The effect of defects has been studied in terms of Fermi Level pinning. Barrier height has been identified as a relevant criteria to describe surface damage induced by plasma treatment. Probing Conventional LETI plasma etching process with the Mott-Schottky method demonstrates a good reproducibility of the electrochemical data and confirms the reliability of the developed method. Various electrochemical tests conducted on 3 plasmas recipes demonstrated that: 1) the RIE etching is damaging, 2) the optimized RIE (Steady A) is less damaging than the other RIE (Steady B) and 3) the RIE associated with ALE process shows the least damaging plasma recipe, as expected.

Abstract Microwave (MV)‐trigged dynamic therapy based on MV‐responsive materials is promising for treating deep infection diseases that cannot be effectively treated by antibiotics, like life‐threatening osteomyelitis. Surface states of materials affect the generation of free charges under the excitation source with energy less than the band gap, consequently influencing the MV dynamic effects. Herein, an MV responsive system with interface confined 2D metal–organic framework (2D MOF) on oxidized carbon nanotube (CNT) is prepared, in which the ultrasmall Cu‐based 2D MOF possesses sufficient surface/interface defects, endowing the system a large number of surface states. Under MV irradiation, the synthesized CNT‐2D MOF not only efficiently absorbs and converts the microwave into heat for microwaveocaloric therapy (MCT) via enhanced hetero‐interfacial polarization, but also generates excited electrons via surface state for microwave dynamic therapy (MDT). This biocompatible CNT‐2D MOF exhibits highly effective broad‐spectrum antimicrobial activity against seven pathogenic bacteria, including Gram‐negative and Gram‐positive pathogens, under 7 min MV irradiation. And this system is proven to efficiently eradicate Staphylococcus aureus infected rabbit tibia osteomyelitis. Significantly, MV‐excited MCT and MDT of CNT‐CuHHTP developed in this study makes a major step forward in antibiotic‐free MV therapy in deep tissue bacterial infection diseases.

Topological nodal-line semimetals are always characterized by the drumhead surface states at the open boundaries. In this paper we first derive an analytical expression for the surface Green’s function of a nodal-line semimetal. By making use of this result, we explore the charge and spin transport properties of a metallic chain on the surface of a nodal-line semimetal, as functions of the gate voltage applied on the top of the material. According to the size of the nodal loop, due to the coupling to the surface modes, the charge conductance in the chain is found to show a robust plateau at $e^{2}/h$ , or to exhibit multiple valleys at $e^{2}/h$ . Correspondingly, the spin polarization of the transmitted current is $100\%$ at the plateau region, or exhibits multiple peaks at nearly $100\%$ . This feature can be viewed as a transport signature of the topological nodal-line semimetals.

Electronic states at the boundaries of crystals, such as surfaces, interfaces, edges, hinges, corners, and extremities, play crucial roles in emerging quantum materials, such as graphene and similar monatomic-layer materials, van der Waals crystals, and topological insulators. Electronic states at such boundaries are different from those inside the three- or two-dimensional crystals, not only because of the truncation of crystal lattices but also because of space-inversion-symmetry breaking and difference in topology in band structures across the boundaries. Such quantum materials are expected to advance energy-saving/-harvesting technology as well as quantum computing/information technology because of exotic phenomena, such as spin–momentum locking of an electron, pure spin current, dissipation-less charge current, nonreciprocal current, and possible Majorana fermions. In this review, their fundamental concepts are introduced from the viewpoint of surface physics, in which atomic and electronic structures, as well as charge/spin transport properties, are directly probed using state-of-the-art techniques.

In magnetic topological insulators, the surface states can exhibit a gap due to the breaking of time-reversal symmetry. Various experiments, while suggesting the existence of the surface gap, have raised questions about its underlying mechanism in the presence of different magnetic orderings. Here, we demonstrate that magnon-mediated electron-electron interactions, whose effects are not limited to the surfaces perpendicular to the magnetic ordering, can significantly influence surface states and their effective gaps. On the surfaces perpendicular to the spin quantization axis, many-body interactions can enhance the band gap to a degree that surpasses the non-interacting scenario. Then, on surfaces parallel to the magnetic ordering, we find that strong magnon-induced fermionic interactions can lead to features resembling a massless-like gap. These remarkable results largely stem from the fact that magnon-mediated interactions exhibit considerable long-range behavior compared to direct Coulomb interactions among electrons, thereby dominating the many-body properties at the surface of magnetic topological insulators.

Abstract Photoelectrochemical photocurrent switching (PEPS) effect can regulate the polarity of photocurrent, which has significant potential applications in areas such as logic gates, photosynapse, and artificial intelligence. In this work, it is reported for the first time that a pure Ga2O3 photoelectrochemical system exhibits ambipolar photocurrent behavior induced by deep ultraviolet, which is closely linked to the crystalline phase of Ga2O3 (α or β) and the surface states of oxygen vacancies. Spongy porous nanorod arrays (NRAs) of Ga2O3 designed here not only increase the contact area of Ga2O3 with the electrolyte but also can lower largely the reflection of light and improve light‐trapping capacity. For α phase Ga2O3, the photocurrent is in a forward direction under positive bias and shows a backward direction under negative bias in NaOH solution, exhibiting a distinct ambipolar photocurrent phenomenon, which can be attributed to more oxygen vacancy surface states and lower potential barrier at the semiconductor/electrolyte interface. Furtherly, the effect of the surface states on the ambipolar photocurrent behavior of α‐Ga2O3 NRAs is demonstrated by various treatment times of oxygen plasma, whose switching point moves from 0 V to −0.19 V with treatment for 30 min and continues to move in the negative direction with the increase of treatment time. Moreover, based on the ambipolar photocurrent behavior of α‐Ga2O3 NRAs, adjustable Boolean logic gates with voltage are prepared as the input source, offering a new path for the photoelectric device multifunctional integration needed in the Post‐Moore era, with a high accuracy manipulated by solar‐blind deep ultraviolet light.

Metal-insulator-semiconductor (MIS) structures are key elements of modern electronic technology, including devices operating under conditions of exposure to penetrating radiation. One of the possible approaches to reducing radiation effects in MIS structures is the use of dielectrics, which reduce the generation and accumulation of excess space charge in the bulk of the dielectric. We investigated the system of dielectrics Al2O3-SiO2. The study shows the suitability of using MIS structures based on a system of dielectrics for formation of devices with high radiation resistance. Applying a Al2O3 layer on top of the SiO2 layer improves the performance of MIS structures by increasing the uniformity of parameters. The main effect of the influence of the Al2O3 layer on the parameters of the structures is to reduce the mechanical stresses at the interface SiO2-substrate. The trapping of electrons in Al2O3, compensates for the charge of the trapped holes in SiO2, and reduces the parasitic current through Al2O3.

Confined electronic states and optical transitions in 3D topological insulator nanoparticles have been studied in the literature, assuming idealized geometries such as spheres or infinitely long cylinders, that allow to obtain analytical solutions to the corresponding eigenvalue equation within such geometries. In contrast, in this article we consider triangular-shaped nanoplates as a more realistic approximation to the experimentally observed morphologies of topological insulator nanoparticles. In this particular geometry, we obtain analytical expressions for the confined eigenstates and the corresponding energy spectrum. Moreover, by a spatial representation of the probability density distribution, we further identify the conditions leading to the emergence of topologically trivial surface states, i.e. those arising as a result of morphological-dependent quantum confinement of the bulk that nonetheless project onto the surface, in contrast with topologically protected surface states. Finally, we also study the optical transitions and the corresponding selection rules imposed by the nanoparticle size and morphology.

A dominant interfacial recombination pathway in the dye sensitized solar cell (DSSC) was suppressed by coating graphene oxide (GO) on the titanium dioxide (TiO2) nanoparticle layer via the electrophoretic deposition (EPD) method. DSSC utilizing 5 min coating of GO by EPD on TiO2 nanoparticle layer showed 5% enhancement in the photo-conversion efficiency (from 5.7% to 6.0%), and 5% enhancement in the short circuit current density (from 11.4 mA/cm2 to 12.0 mA/cm2) in comparison with reference DSSCs which did not use GO on TiO2. GO coating on TiO2 is attributed to the efficient suppression of the photo-generated electron–hole recombination at the TiO2/dye/electrolyte interfaces. The further increase in the thickness of GO (10- and 20-min EPD coating) on the TiO2 nanoparticle layer impeded the charge transport as the performance of the respective DSSCs was significantly affected. It suggested that the probability of photo-generated electron tunneling from dye to TiO2 was suppressed by increasing the thickness of the GO layer. Presented results assure that GO can be considered as a competitive surface passivation candidate for nanostructured excitonic solar cells.

The letter reports that the impedance spectroscopy method has been performed to acquire impeccable results on the ac electric conductivity (σac), dielectric (ε′ and ε′′) and electric modulus (M' and M'') components of the Al/Al2O3/p-Si type MOS capacitor. The relevant parameters are defined with C-V-f and G/ω-V-f data between 1 kHz and 5 MHz and ± 3 V at room temperature. Both parts of dielectric constants are decreasing at high frequencies to prevent the interface dipoles from gaining enough time to return to the alternative area. Depending on the restructuring and reorganization of surface states (Nss) in the alternative field, tanδ decreases at higher frequencies. The M' values reach maximum by frequency increment in the depletion region, while M'' values shift to the forward biases depending on a certain density distribution of Nss. The σac values increase with increasing frequency in the accumulation region depending on series resistance. Considering polarization processes, surface conditions (Nss) and Al2O3 interlayer, frequency and biases are extremely effective and dependent on the dielectric specifications, electrical modulus and conductivity.

The paper presents the results of an experimental study of the electric properties of ZnO-based polycrystalline heterosructures. C-V-characteristics of In/ZnO/n-Si/Al and Au/ZnO/n-Si/Al heterostructures were modeled. Influence of upper contacts material and annealing technology on structure characteristics was investigated. Surface states influence according to applied theoretical model was analyzed. Empirical dependence of the surface potential in silicon on the voltage applied on the structure was derived.

The paper presents the results of an experimental study of the electric properties of ZnO-based polycrystalline heterosructures. C-V-characteristics of In/ZnO/n-Si/Al and Au/ZnO/n-Si/Al heterostructures were modeled. Influence of upper contacts material and annealing technology on structure characteristics was investigated. Surface states influence according to applied theoretical model was analyzed. Empirical dependence of the surface potential in silicon on the voltage applied on the structure was derived.

Scanning Tunneling Microscopy and Spectroscopy (STM/S), with its exceptional surface sensitivity and exquisite energy resolution, is well suited for the investigation of surface states down to atomic length scales. As such, it became an essential tool to probe the surface states of materials, including those with non-trivial topology. One challenge, however, can be the preparation of clean surfaces which allow the study of preferably unchanged surface properties with respect to the bulk amount. Here, we report on the STM/S of two materials, ZrTe2 and TmB4. The former cleaves easily and defects can be examined in detail. However, our STS data can only qualitatively be compared to the results of band structure calculations. In the case of TmB4, the preparation of suitable surfaces is highly challenging, and atomically flat surfaces (likely of B-termination) were only encountered rarely. We found a large density of states (DOS) at the Fermi level EF and a mostly featureless differential conductance near EF. Further efforts are required to relate our results to the electronic structure predicted by ab initio calculations.

The anion exchange of the halides, Br and I, is demonstrated through the direct mixing of two pure perovskite quantum dot solutions, CsPbBr3 and CsPbI3, and is shown to be both facile and result in a completely alloyed single phase mixed halide perovskite. Anion exchange is also observed in an interlayer printing method utilizing the pure, unalloyed perovskite solutions and a commercial inkjet printer. The halide exchange was confirmed by optical absorption spectroscopy, photoluminescent spectroscopy, X-ray diffraction, and X-ray photoemission spectroscopy characterization and indicates that alloying is thermodynamically favorable, while the formation of a clustered alloy is not favored. Additionally, a surface-to-bulk photoemission core level transition is observed for the Cs 4d photoemission feature, which indicates that the electronic structure of the surface is different from the bulk. Time resolved photoluminescence spectroscopy indicates the presence of multiple excitonic decay features, which is argued to originate from states residing at surface and bulk environments.

Searching for existing topological materials is a hot topic in quantum and computational chemistry. This study uncovers P63/mmc type TiTe compound—an existing material—is a newly discovered topological metal that hosts the various type of nodal line states. Different nodal line states normally exhibit different properties; they may have their individual applications. We report that TiTe hosts I, II, and hybrid type nodal line (NL) states at its ground state without chemical doping and strain engineering effects. Specifically, two type I NLs, two hybrid-type NLs, and one Γ—centered type II NL can be found in the kz = 0 plane. Moreover, the spin-orbit coupling induced gaps for these NLs are very small and within acceptable limits. The surface states of the TiTe (001) plane were determined to provide strong evidence for the appearance of the three types of NLs in TiTe. We also provide a reference for the data of the dynamic and mechanical properties of TiTe. We expect that the proposed NL states in TiTe can be obtained in future experiments.

In this study, we used laser ablation to fabricate toluene-soluble carbon nanoparticles from coconut fiber. In response to excitations at various wavelengths, the fabricated carbon nanoparticles exhibit three distinctive emission peaks at wavelengths of 300 nm, 440 nm, and 540 nm. These three emission peaks correspond to the  orbital state,  orbital state, and surface state, respectively. Photoluminescence excitation measurements indicate a high probability of energy transfer between the surface state and  orbital state, whereas the  orbital state is likely independent of the other states. The results of time-resolved photoluminescence measurements indicate that electrons are likely to remain longer in higher-energy states. Given that the carbon dots fabricated in this study were made from natural resources, these findings may find application in photonic devices that feature tunable emissions.

Abstract The tunable photoluminescence (PL) of nitrogen-doped carbon dots (NCDs) has attracted much attention in recent years while the specific mechanism is still in dispute. Herein, NCDs with yellow emission were successfully synthesized via a facile hydrothermal approach. Three kinds of post-treatment routes were investigated to verify the influence of surface states on the PL emission of NCDs including solvent-dependent, reduced-reaction and metal-enhanced effect. The interaction mechanism was studied by absorption spectrum, structural characterizations, steady-state and time-resolved spectroscopy. When dispersed in different solvents, the as-prepared NCDs show tunable emission and PL enhancement attributed to hydrogen bonding between solvents and NCDs. Besides, the addition of NaBH4 can induce the reduction of the C=O bonds existing in original NCDs to C–O bonds and thus result in the enhancement of the intrinsic (n–π*) emission. Moreover, metal-enhanced fluorescence of NCDs can also be observed when adding Ag+ into initial NCD solution, which might be ascribed to aggregation-induced emission enhancement. These results for post-treated NCDs demonstrate that surface functional groups are responsible for PL emission and provide new possibilities like multi-image sensing and lighting application.

A high-temperature water steam (H2O(g)) between 300 °C and 1000 °C reacted with the Al surface in this study. The Al surface states were characterized and analyzed using XRD °C, XPS, and SEM after and before the reaction, and the effects and mechanism of H2O(g) on the Al surface morphology and chemical composition were studied. The experiment showed that for an Al sheet reacting with H2O(g), its oxide layer morphology changed from nano-needle to flaky and granular oxides gradually with the rise of temperature, and finally the Al surface became porous as a whole. Its oxide crystals were amorphous and were determined to be aluminum oxide (Al2O3) using XPS. The needle-like oxide in the Al sheet surface tended to grow toward the surface, and no obviously inward oxidizing corrosion layer occurred in the aluminum substrate; the oxide layer between the oxide and Al sheet substrate was compact, and could effectively prevent the infiltration and corrosion of water molecules.

The effect of the applied external electric field on the energy distribution of desorbed from the alloys are presented. It is shown that the energy distributions of the desorbed depend on the distribution of positive charge carriers near the surface that, in turn, depends on the external electric field.

GaN and NiO/GaN electrodes were characterized by impedance spectroscopy measurements in 0.1 M NaOH. We observed the suppression of the surface states capacitance due to the modification of the chemical state of superficial Ga atoms by NiO. This result suggests that the carriers involved in the photocorrosion of GaN in alkaline conditions originate in its surface states. In addition, we characterized the epitaxial relationship between the NiO particles deposited on GaN by transmission electron microscopy, finding the NiO{111}||GaN{0002} and NiO[220] ||GaN[112¯0] symmetry constraints.

In this paper, we present a detailed study on the phase diagrams of superconducting topological surface states, especially, focusing on the interplay between crystalline symmetry and topology of the effective BdG Hamiltonian. We show that for the 4 × 4 kinematic Hamiltonian of the normal state, a mirror symmetry M can be defined, and for the M-odd pairings, the classification of the 8 × 8 BdG Hamiltonian is Z ⊕ Z, and the time-reversal symmetry is broken intrinsically. The topological non-trivial phase can support chiral Majorana edge modes, and can be realized in the thin films of iron-based superconductor such as FeSeTe.

Abstract The overloaded energy cost has become the main concern of the now fast developing society, which make novel energy devices with high power density of critical importance to the sustainable development of human society. Herein, a dynamic Schottky diode based generator with ultrahigh power density of 1262.0 W m−2 for sliding Fe tip on rough p‐type silicon is reported. Intriguingly, the increased surface states after rough treatment lead to an extremely enhanced current density up to 2.7 × 105 A m−2, as the charged surface states can effectively accelerate the carriers through large atomic electric field, while the reflecting directions are regulated by the built‐in electric field of the Schottky barrier. This research provides an open avenue for utilizing the surface states in semiconductors in a subversive way, which can co‐utilize the atomic electric field and built‐in electric field to harvest energy from the mechanical movements, especially for achieving an ultrahigh current density power source.

PbTiO3 nanorods with tetragonal phase were synthesized by hydrothermal method and heat treatment, and temperature-dependent electrical transport properties of individual PbTiO3 nanorod were investigated. The results show that the conductivities of PbTiO3 nanorods are gradually enhanced with temperature increasing from 77.4 to 295K, and exhibit the typical nonlinear I–V characteristics. The barrier height between Au electrode and nanorod is reduced from 0.137 to 0.088eV with increasing bias from 0.2 to 1V. The corresponding values of thermal activation energies are 0.172 and 0.06eV below the conduction band for 180–295 and 77.4–180K, respectively. This semiconductor-like behavior may result from the larger number of surface defects or localized states in the amorphorized PbTiO3.

The crystal quality and surface states are two major factors that determine optical properties of ZnO nanoparticles (NPs) synthesized through nonaqueous sol–gel routes, and both are strongly dependent on the growth conditions. In this work, we investigate the influence of the different growth temperatures (240 and 300 °C) on the morphology, structural and crystal properties of ZnO NP. The effects of conjoining ZnO NP with carbon nanotubes (CNT) and the role of surface states in such a hybrid nanostructure are studied by optical emission and absorption spectroscopy. We demonstrate that depending on the synthesis conditions, activation or passivation of certain surface states may occur. Next, silver nanoparticles are incorporated into ZnO–CNT nanostructures to explore the plasmon–exciton coupling effect. The observed enhanced excitonic and suppressed defect-related emissions along with blue-shifted optical band gap suggest an intricate interaction of Burstein–Moss, surface plasmon resonance and surface band-bending effects behind the optical phenomena in hybrid ZnO–CNT–Ag nanocomposites.

AlN Schottky diodes with various device geometries were fabricated on sapphire substrate and their temperature-dependent current-voltage characteristics were analyzed. At forward bias, high ideality factors were obtained, indicating a large deviation from the ideal thermionic emission model. At reverse bias, the breakdown voltage showed a negative temperature dependence, and the leakage current was well described using a 2-D variable-range hopping conduction model. Furthermore, the breakdown voltages and leakage currents of the devices showed a strong dependence on the surface distance between the ohmic and Schottky contacts, but a relatively small dependence on the area of the Schottky contacts. These results suggest surface states between ohmic and Schottky contacts play a more important role than the metal/AlN interface in determining the reverse breakdown and leakage current of AlN Schottky diodes. A quantitative study of AlN Schottky diodes at high temperature reveals a geometry-dependent surface breakdown electric field and surface leakage current. Surface passivation and treatments may enhance the device performances and impact the reverse breakdown and current leakage mechanisms. These results will serve as the guidance for the design and fabrication of future AlN electronic devices.

X-ray photoelectron spectroscopy (XPS) is a well known tool in studying the physical and chemical properties of surface/interfaces which provides the element specific, non-destructive and quantitative information. In the present study, information about the surface chemical states of interfacial structure of CoFe thin films on n-Si substrates has been studied from XPS technique. The surface of the samples has also been cleaned from ion beam etching for 30 min with Ar+ ions to record the XPS spectra. The observation shows that the Si atoms are present within the probed surface layer due to interfacial intermixing across the interface which is due to strong chemical reactivity of n-Si substrate. A shift in the binding energy peaks of Fe2p and Co2p has also been observed which could be due to the formation of silicide phases as a result of interfacial intermixing. XPS results have indicated the formation of silicide phases across the interfaces which poses interfacial antiferromagnetic coupling across CoFe/n-Si interface to affect the magnetic behaviour. It has been found that the present XPS results are in well support with our earlier study.

The surface states of 3D topological insulators in general have negligible quantum oscillations (QOs) when the chemical potential is tuned to the Dirac points. In contrast, we find that topological Kondo insulators (TKIs) can support surface states with an arbitrarily large Fermi surface (FS) when the chemical potential is pinned to the Dirac point. We illustrate that these FSs give rise to finite-frequency QOs, which can become comparable to the extremal area of the unhybridized bulk bands. We show that this occurs when the crystal symmetry is lowered from cubic to tetragonal in a minimal two-orbital model. We label such surface modes as ‘shadow surface states’. Moreover, we show that the sufficient next-nearest neighbor out-of-plane hybridization leading to shadow surface states can be self-consistently stabilized for tetragonal TKIs. Consequently, shadow surface states provide an important example of high-frequency QOs beyond the context of cubic TKIs.

Differences between the ground and mechanically polished 316 LN stainless steel were characterized on the surface topography,surface residual strain and electron work function. The electrochemical behavior of the stainless steel was investigated in a borate buffer solution. The ground 316 LN stainless steel is featured by a rougher surface with scratches along the grinding direction.Compared with the mechanically polished sample,a thicker cold-worked layer(~50 μm) is imparted by surface grinding,indicating that the residual strain on the ground surface is much higher. The ground surface is more electrochemically active and exhibits a larger corrosion rate in the borate buffer solution,because of its rougher surface topography and a higher residual strain. The passive film on the mechanically polished sample is more compact and protective,due to the decrease of acceptor and donor density and the increase of total impedance of the passive film.

We have studied the Tamm-type surface state of La(0001) by tunneling spectroscopy within a wide range of tunneling currents from 0.1 nA to 8000 nA, thereby tuning the electric-field strength in a tip-vacuum-sample tunnel junction. We observe a significant shift of the unoccupied Tamm-type surface state toward the Fermi energy with increasing electric-field strength, accompanied by a broadening of the width of the resonance peak indicating a decrease of the surface-state lifetime. Our experimental results are contrary to previous reports for Stark-shifted Shockley-type surface states of noble metal (111) surfaces.

We provide an exact analytical technique to obtain within a lattice model the wave functions of the edge states in zigzag- and bearded-edge graphene, as well as of the Fermi-arc surface states in Weyl semimetals described by a minimal bulk model. We model the corresponding boundaries as an infinite scalar potential localized on a line, and respectively within a plane. We use the T -matrix formalism to obtain the dispersion and the spatial distribution of the corresponding boundary modes. Furthermore, to demonstrate the power of our approach, we write down the surface Green’s function of the considered Weyl semimetal model, and we calculate the quasiparticle interference patterns originating from an impurity localized at the respective surface.

The coadsorption of potassium and oxygen on W(100) by the threshold photoemission spectroscopy was studied. It is shown that coadsorption of potassium and oxygen on the W(100) leads to the formation a dielectric layer with a possible stoichiometry K2O2.

Following Dirac and Weyl semimetals, nodal line semimetals represent a new type of topological semimetal and attracted extensive interest in modern condensed matter physics. Recently, a kind of hybrid nodal lines have been proposed (Zhang et al 2018 Phys. Rev. B 97 125143) and it mainly come from anisotropy interaction. Based on the first-principle calculations and k·p model, we predict a cubic Be _2 Si with topological nontrivial electronic states exhibiting fascinating type-I and type-II hybrid nodal line around Fermi level. Unexpectedly the low energy electronic states of Be _2 Si are isotropy in k _x and k _y directions and a new effective model has been proposed for the appearance of this new type hybrid nodal line. The four-fold degenerated type-I and type-II nodal points in the hybrid nodal lines along the high symmetry lines of Γ– K and Γ– X are protected by mirror reflection, time reversal and space inversion symmetry. The spin–orbit coupling effect only induces slight band gap in the hybrid nodal lines in Be _2 Si whose nontrivial nature remains. Moreover, the nontrivial hybrid nodal lines in Be _2 Si are robust to external strain. The results in present work indicate that Be _2 Si are promising candidates for future experimental studies of nontrivial topological semimetals and an excellent platform to study the interaction between the two types Dirac fermions.

We present the theory describing the various surface electronic states arisen from the mixing of conduction and valence bands in a strained mercury telluride (HgTe) bulk material. We demonstrate that the strain-induced band gap in the Brillouin zone center of HgTe results in the surface states of two different kinds. Surface states of the first kind exist in the small region of electron wave vectors near the center of the Brillouin zone and have the Dirac linear electron dispersion characteristic for topological states. The surface states of the second kind exist only far from the center of the Brillouin zone and have the parabolic dispersion for large wave vectors. The structure of these surface electronic states is studied both analytically and numerically in the broad range of their parameters, aiming to develop its systematic understanding for the relevant model Hamiltonian. The results bring attention to the rich surface physics relevant for topological systems.

In the present work TiO2 films were formed over Indium Tin Oxide (ITO) employing cathodic electrophoretic deposition (Cathodic-EPD) and Dr. Blade Technique. The films were characterized by electrochemical techniques in order to compare their electronic properties; as well as, their photoelectrochemical behavior. The electrochemical performance showed by the films, allowed to relate the modification occurring during the Cathodic-EPD, with the partial reduction of TiO2 nanoparticles, generating Ti3+ defects. These trapping states are modifying the electronic properties of the film, and diminishing the transport of the photoelectrogenerated electrons toward ITO.

We introduce a robust low-budget Kelvin probe design that is optimized for the long-term acquisition of surface photovoltage (SPV) data, especially developed for highly resistive systems, which exhibit—in contrast to conventional semiconductors—very slow photoinduced charge relaxation processes in the range of hours and days. The device provides convenient optical access to the sample, as well as high mechanical and electrical stability due to off-resonance operation, showing a noise band as narrow as 1 mV. Furthermore, the acquisition of temperature-dependent SPV transients necessary for SPV-based deep-level transient spectroscopy becomes easily possible. The performance of the instrument is demonstrated by recording long-term SPV transients of the ultra-slowly relaxing model oxide strontium titanate (SrTiO 3 ) over 20 h.

In many layer-structured materials, constituent layers are bound through van der Waals (vdW) interactions. However, hydrogen bonding is another type of weak interaction which can contribute to the formation of multi-layered materials. In this work, we investigate aluminum hydroxide [Al(OH) 3 ] having hydrogen bonding as an interlayer binding mechanism. We study the crystal structures and electronic band structures of bulk, single-layer, and multi-layer Al(OH) 3 using density functional theory calculations. We find that hydrogen bonds across the constituent layers indeed give rise to interlayer binding stronger than vdW interactions, and a reduction of the band gap occurs for an isolated layer as compared to bulk Al(OH) 3 which is attributed to the emergence of surface states. We also consider the alkali-halide intercalation between layers and examine how the intercalated atoms affect the atomic and electronic structures of Al(OH) 3 .

Vicinal surfaces exhibiting arrays of atomic steps are frequently investigated due to their diverse physical-chemical properties and their use as growth templates. However, surfaces featuring steps with a large number of low-coordinated kink-atoms have been widely ignored, despite their higher potential for chemistry and catalysis. Here, the equilibrium structure and the electronic states of vicinal Ag(111) surfaces with densely kinked steps are investigated in a systematic way using a curved crystal. With scanning tunneling microscopy we observe an exceptional structural homogeneity of this class of vicinals, reflected in the smooth probability distribution of terrace sizes at all vicinal angles. This allows us to observe, first, a subtle evolution of the terrace-size distribution as a function of the terrace-width that challenges statistical models of step lattices, and second, lattice fluctuations around resonant modes of surface states. As shown in angle resolved photoemission experiments, surface states undergo stronger scattering by fully-kinked step-edges, which triggers the full depletion of the two-dimensional band at surfaces with relatively small vicinal angles.

By combining nonlinear photoemission experiments and density functional theory calculations, we study the modification of Ni(111) surface states induced by the presence of graphene. The main result is that graphene is able to displace the Ni(111) surface states from the valence band close to the Fermi level uncovering the d -band of Ni. The shift of the surface states away from the Fermi level modifies their k -dispersion and the effective mass. The unoccupied image state of graphene/Ni(111) has been also characterized. The ab initio calculations give a theoretical insight into the electronic properties of graphene/Ni(111) in the two stable top-fcc and top-bridge phases showing that the interface properties are poorly dependent on the stacking. The screening properties to an externally applied electric field are also discussed.

Recent experiments revealed that Mn _3 Sn and Mn _3 Ge exhibit a strong anomalous Hall effect at room temperature, provoking us to explore their electronic structures for topological properties. By ab initio band structure calculations, we have observed the existence of multiple Weyl points in the bulk and corresponding Fermi arcs on the surface, predicting antiferromagnetic Weyl semimetals in Mn _3 Ge and Mn _3 Sn. Here the chiral antiferromagnetism in the Kagome-type lattice structure is essential to determine the positions and numbers of Weyl points. Our work further reveals a new guiding principle to search for magnetic Weyl semimetals among materials that exhibit a strong anomalous Hall effect.

Topological insulators (TIs) are theoretically believed to possess robust surface states (SSs) for any surface terminations. In reality, for TIs with non-conventional terminations, the directly experimental demonstration of this argument is somehow hindered, due to the difficulties in sample preparation and lack of efficient electronic structure characterization method. Here, by using the state-of-the-art molecular beam epitaxy, we manage to prepare TI Bi _2 Te _3 thin film with non-conventional fractional quintuple layer (FQL) termination. Scanning tunneling microscopy reveals that the as-grown Bi _2 Te _3 thin film may not necessarily terminate at the van der Waals gap between two adjacent quintuple layers. The electronic structures of the FQL termination are studied in combination with quasi-particle interference pattern by scanning tunneling spectroscopy and SS calculations by tight binding method. Our results suggest that the topological nature of SSs be preserved on various terminations. Possible ways of achieving exotic topological SSs are also discussed.

Surface states of topological noncentrosymmetric superconductors (NCSs) exhibit intricate helical spin textures, i.e., the spin orientation of the surface quasiparticles is coupled to their momentum. Using quasiclassical theory, we study the spin polarization of the surface states as a function of the spin–orbit interaction and superconducting pairing symmetry. We focus on two- and three-dimensional fully gapped and nodal NCSs. For the case of nodal systems, we show that the spin polarization of the topological flat bands is controlled by the spin polarization of the bulk normal states at the bounding gap nodes. We demonstrate that the zero-bias conductance in a magnetic tunnel junction can be used as an experimental test of the surface-state spin polarization.

Starting from the k·p method in combination with first-principles calculations, we systematically derive the effective Hamiltonians that capture the low energy quasi-particle structures of the recently discovered topological Kondo insulator SmB _6 . Using these effective Hamiltonians we can obtain both the energy dispersion and the spin texture of the topological surface states, which can be detected by further experiments.

We envision that the quantum spin Hall effect should be observed in (111)-oriented thin films of SnSe and SnTe topological crystalline insulators. Using a tight-binding approach supported by first-principles calculations of the band structures, we demonstrate that in these films the energy gaps in the two-dimensional band spectrum depend in an oscillatory fashion on the layer thickness. These results as well as the calculated topological invariant indexes and edge state spin polarizations show that for films ∼20–40 monolayers thick a two-dimensional topological insulator phase appears. In this range of thicknesses in both SnSe and SnTe, (111)-oriented films edge states with Dirac cones with opposite spin polarization in their two branches are obtained. While in the SnTe layers a single Dirac cone appears at the projection of the ${\boldsymbol{}}\bar{\Gamma }$ point of the two-dimensional Brillouin zone, in the SnSe (111)-oriented layers three Dirac cones at ${\boldsymbol{}}\bar{M}$ points projections are predicted.

In 3D topological insulators achieving a genuine bulk-insulating state is an important research topic. Recently, the material system (Bi,Sb) _2 (Te,Se) _3 (BSTS) has been proposed as a topological insulator with high resistivity and a low carrier concentration (Ren et al 2011 Phys. Rev. B http://dx.doi.org/10.1103/PhysRevB.84.165311 84 http://dx.doi.org/10.1103/PhysRevB.84.165311 ). Here we present a study to further refine the bulk-insulating properties of BSTS. We have synthesized BSTS single crystals with compositions around x = 0.5 and y = 1.3. Resistance and Hall effect measurements show high resistivity and record low bulk carrier density for the composition Bi $_{1.46}$ Sb $_{0.54}$ Te $_{1.7}$ Se $_{1.3}$ . The analysis of the resistance measured for crystals with different thicknesses within a parallel resistor model shows that the surface contribution to the electrical transport amounts to 97% when the sample thickness is reduced to 1 μ m. The magnetoconductance of exfoliated BSTS nanoflakes shows 2D weak antilocalization with $\alpha \simeq -1$ as expected for transport dominated by topological surface states.