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BiVO4 has attracted wide attention for oxygen-evolution photoanodes in water-splitting photoelectrochemical devices. However, its performance is hampered by electron-hole recombination at surface states. Herein, partially oxidized two-dimensional (2D) bismuthene is developed as an effective, stable, functional interlayer between BiVO4 and the archetypal NiFeOOH co-catalyst. Comprehensive (photo)electrochemical and surface photovoltage characterizations show that NiFeOOH can effectively increase the lifetime of photogenerated holes by passivating hole trap states of BiVO4; however, it is limited in influencing electron trap states related to oxygen vacancies (VO). Loading bismuthene on BiVO4 photoanodes increases the density of VO that are beneficial for the oxygen evolution reaction via the formation of oxy/hydroxyl-based water oxidation intermediates at the surface. Moreover, bismuthene increases interfacial band bending and fills the VO-related electron traps, leading to more efficient charge extraction. With the synergistic interaction of bismuthene and NiFeOOH on BiVO4, this composite photoanode achieves a 5.8-fold increase in photocurrent compared to bare BiVO4 reaching a stable 3.4 (±0.2) mA cm–2 at a low bias of +0.8 VRHE or 4.7(±0.2) mA cm–2 at +1.23 VRHE. The use of 2D bismuthene as functional interlayer provides a new strategy to enhance the performance of photoanodes.

Hematite nanoarrays are important photoanode materials. However, they suffer from serious problems of charge transfer and surface states; in particular, the surface states hinder the increase in photocurrent. A previous strategy to suppress the surface state is the deposition of an Fe-free metal oxide overlayer. Herein, from the viewpoint of atomic bonding energy, it is found that the strength of bonding around Fe atoms in the hematite is the key to suppressing the surface states. By treating the surface of hematite with Se and NaBH4 , the Fe2 O3 transforms to a double-layer nanostructure. In the outer layer, the Fe-O bonding is reinforced and the Fe-Se bonding is even stronger. Therefore, the surface states are inhibited and the increase in the photocurrent density becomes much faster. Besides, the treatment constructs a nanoscale p-n junction to promote the charge transfer. Improvements are achieved in onset potential (0.25 V shift) and in photocurrent density (5.8 times). This work pinpoints the key to suppressing the surface states and preparing a high-efficiency hematite nanoarray, and deepens our understanding of hematite photoanodes.

Improving charge transport and reducing bulk/surface recombination can increase the activity and stability of BiVO4 for water oxidation. Herein we demonstrate that the photoelectrochemical (PEC) performance of BiVO4 can be significantly improved by potentiostatic photopolarization. The resulting cocatalyst-free BiVO4 photoanode exhibited a record-high photocurrent of 4.60 mA cm-2 at 1.23 VRHE with an outstanding onset potential of 0.23 VRHE in borate buffer without a sacrificial agent under AM 1.5G illumination. The most striking characteristic was a strong "self-healing" property of the photoanode, with photostability observed over 100 h under intermittent testing. The synergistic effects of the generated oxygen vacancies and the passivated surface states at the semiconductor-electrolyte interface as a result of potentiostatic photopolarization reduced the substantial carrier recombination and enhanced the water oxidation kinetics, further inhibiting photocorrosion.

To fine-tune surface ligands towards high-performance devices, we developed an in situ passivation process for all-inorganic cesium lead iodide (CsPbI3 ) perovskite quantum dots (QDs) by using a bifunctional ligand, L-phenylalanine (L-PHE). Through the addition of this ligand into the precursor solution during synthesis, the in situ treated CsPbI3 QDs display significantly reduced surface states, increased vacancy formation energy, higher photoluminescence quantum yields, and much improved stability. Consequently, the L-PHE passivated CsPbI3 QDs enabled the realization of QD solar cells with an optimal efficiency of 14.62 % and red light-emitting diodes (LEDs) with a highest external quantum efficiency (EQE) of 10.21 %, respectively, demonstrating the great potential of ligand bonding management in improving the optoelectronic properties of solution-processed perovskite QDs.

Noble‐metal chalcogenides, dichalcogenides, and phosphochalcogenides are an emerging class of two‐dimensional materials. Quantum confinement (number of layers) and defect engineering enables their properties to be tuned over a broad range, including metal‐to‐semiconductor transitions, magnetic ordering, and topological surface states. They possess various polytypes, often of similar formation energy, which can be accessed by selective synthesis approaches. They excel in mechanical, optical, and chemical sensing applications, and feature long‐term air and moisture stability. In this Minireview, we summarize the recent progress in the field of noble‐metal chalcogenides and phosphochalcogenides and highlight the structural complexity and its impact on applications., The noble art: Noble‐metal dichalcogenides and phosphochalcogenides are a novel class of two‐dimensional materials. This Minireview summarizes the progress in their synthesis, characterization, and application, highlighting their unique structural features and relationships.

Topological semimetals with high electrical conductivity and suitable carrier density near Fermi level are enticing candidate materials for electrochemical energy storage meriting from their topologically protected surface states. Here we propose the topological semimetal Co 3 Sn 2 S 2 cathode for aqueous Zn ion batteries (AZIBs) showing an obvious discharge plateau approaching 1.5 V. By further introducing a small amount Sn vacancy, an extra pair of redox peaks (1/1.28 V) appears corresponding to the transition of Sn 4+ /Sn 2+ . Sn vacancy leads to more Zn ion built-in channels and active sites, which promotes charge storage kinetics (Zn 2+ diffusion rate and electron transfer rate) and improves Zn-ion storage capability. The increase of active sites contributes to the enhancement of capacitance behavior. The Co 3 Sn 1.8 S 2 cathode achieves a specific energy of 394 Wh kg -1 (capacity of 343.8 mAh g -1 ) at 0.2 A g -1 and specific power greater than 4900 W kg -1 at 5 A g -1 . The battery also retains a capacity of 193.8 mAh g -1 after 2970 cycles at 1 A g -1 . Benefited from better conductivity at lower temperatures of Co 3 Sn 1.8 S 2 and Zn x Co 3 Sn 1.8 S 2 , the prepared quasi-solid Co 3 Sn 1.8 S 2 //Zn battery delivers superior rate capability even at -30 °C (126 mAh g -1 at 0.6 A/g) and excellent cycling stability over 3000 cycles retaining 85% of the initial capacity at -10 °C and 2 A/g. This work provides new insights for designing novel electrode materials by leveraging topologically protected surface states, incorporating vacancies, and in synergy benefit a lot.

Fluorescent nanoparticles are widely utilized in a large range of nanoscale imaging and sensing applications. While ultra-small nanoparticles (size ≤10 nm) are highly desirable, at this size range, their photostability can be compromised due to effects such as intensity fluctuation and spectral diffusion caused by interaction with surface states. In this article, a facile, bottom-up technique for the fabrication of sub-10-nm hexagonal boron nitride (hBN) nanoparticles hosting photostable bright emitters via a catalyst-free hydrothermal reaction between boric acid and melamine is demonstrated. A simple stabilization protocol that significantly reduces intensity fluctuation by ≈85% and narrows the emission linewidth by ≈14% by employing a common sol-gel silica coating process is also implemented. This study advances a promising strategy for the scalable, bottom-up synthesis of high-quality quantum emitters in hBN nanoparticles.

An effective way of manipulating 2D surface states in magnetic topological insulators may open a new route for quantum technologies based on the quantum anomalous Hall effect. The doping-dependent evolution of the electronic band structure in the topological insulator Sb2− V Te3 (0 ≤ x ≤ 0.102) thin films is studied by means of electrical transport. Sb2− V Te3 thin films were prepared by molecular beam epitaxy, and Shubnikov–de Hass (SdH) oscillations are observed in both the longitudinal and transverse transport channels. Doping with the 3d element, vanadium, induces long-range ferromagnetic order with enhanced SdH oscillation amplitudes. The doping effect is systematically studied in various films depending on thickness and bottom gate voltage. The angle-dependence of the SdH oscillations reveals their 2D nature, linking them to topological surface states as their origin. Furthermore, it is shown that vanadium doping can efficiently modify the band structure. The tunability by doping and the coexistence of the surface states with ferromagnetism render Sb2− V Te3 thin films a promising platform for energy band engineering. In this way, topological quantum states may be manipulated to crossover from quantum Hall effect to quantum anomalous Hall effect, which opens an alternative route for the design of quantum electronics and spintronics.

The effect of surface passivation on the photoluminescence (PL) emitted by CsPbBr3 micro/nano‐rods coated with Pb(OH)2 is investigated, where a high quantum yield and excellent stability for the emission are found. The CsPbBr3/Pb(OH)2 rods generally present a peak that is blue shifted compared to that seen in rods without a hydroxide cladding at low temperatures. By increasing the temperature, it is further shown that the passivated surface states are very robust against thermal effects and that the PL peak intensity only drops by a factor of 1.5. Localized stimulated emission at defect states found within larger rods is also demonstrated, clarified by spatially resolved confocal PL mapping along the length of the rods. The diffusion parameter of the carrier density distribution is measured to be 5.70 µm for the sky‐blue emission, whereas for the defect lasing site it is found to be smaller than this excitation spot size.

Shell thickness dependent band-gap engineering of quasi type II core-shell material with higher carrier cooling time, lower interfacial defect states, and longer charge carrier recombination time can be a promising candidate for both photocatalysis and solar cell. In the present investigation, colloidal CdSe@CdS core-shells with different shell thickness (2, 4 and 6 monolayer CdS) were synthesized through hot injection method and have been characterized by high resolution transmission electron microscope (HRTEM) followed by steady state absorption and luminescence techniques. Ultrafast transient absorption (TA) studies suggest longer carrier cooling, lower interfacial surface states, and slower carrier recombination time in CdSe@CdS core-shell with increasing shell thickness. By TA spectroscopy, the role of CdS shell in power conversion efficiency (PCE) has been explained in detail. The measured PCE was found to initially increase and then decrease with increasing shell thickness. Shell thickness has been optimized to maximize the efficiency after correlating the shell controlled carrier cooling and recombination with PCE values and a maximum PCE of 3.88 % was obtained with 4 monolayers of CdS shell, which is found to be 57 % higher than compared to bare CdSe QDs.

Superconducting proximity effect (SPE) induces superconductivity transition in the otherwise non superconducting thin-film in proximity with a superconductor. The SPE usually occurs in real space and decays exponentially with the film thickness. Herein, we unveiled an abnormal SPE in a topological insulator (TI)/superconductor heterostructure, which is attributed to the topologically protected surface state. Surprisingly, such abnormal SPE occurs in momentum space regardless the TI film thickness, as long as the topological surface states are robust and form a continuous conduction loop. Combining transport measurements and scanning tunneling microscopy/spectroscopy techniques, we explored the SPE in Bi2 Se3 /FeSe0.5 Te0.5 heterostructures, where Bi2 Se3 is an ideal three-dimensional topological insulator and FeSe0.5 Te0.5 a typical iron-based superconductor. As the thickness of the Bi2 Se3 thin-film exceeds 400 nanometers, there still exits SPE-induced superconductivity on the surface of Bi2 Se3 thin-film with a transition temperature Tc not less than 10 K. Such an extraordinary behavior is induced by the unique properties of topologically protected surface states of Bi2 Se3 . This research will deepen the understanding of important role of topologically protected surface states in the SPE. This article is protected by copyright. All rights reserved.

The fabrication of 3D hollow nanostructures not only allows the tactical provision of specific physicochemical properties but also broadens the application scope of such materials in various fields. The synthesis of 3D hollow nanocoils (HNCs), however, is limited by the lack of an appropriate template or synthesis method, thereby restricting the wide-scale application of HNCs. Herein, a strategy for preparing HNCs by harnessing a single sacrificial template to modulate the interfacial reaction at a solid-liquid interface that allows the shape-regulated transition is studied. Furthermore, the triggering of the Kirkendall effect in 3D HNCs is demonstrated. Depending on the final state of the transition metal ions reduced during the electrochemical preparation of HNCs, the surface states of the binding anions and the composition of the HNCs can be tuned. In a single-component CrPO4 HNC with a clean surface, the Kirkendall effect of the coil shape is analyzed at various points throughout the reaction. The rough-surface multicomponent MnOx P0.21 HNCs are complexed with ligand-modified BF4 -Mn3 O4 nanoparticles. The fabricated nanocomposite exhibits an overpotential decrease of 25 mV at neutral pH compared to pure BF4 -Mn3 O4 nanoparticles because of the increased active surface area.

Author(s): Yang, X; Li, L; Wu, J; Hu, Q; Wang, Y; Russell, TP; Tu, Y; Zhu, R | Abstract: Planar-heterojunction perovskite solar cells (PSCs) have experienced rapid evolution in recent years because of the low-temperature processing, suitable alignment, and high mobility of the tin oxide buried contact layer. However, improper SnO2 surface states and poor crystallinity of the top perovskite films are still the main obstacles for the planar PSCs in which performance always lags behind their mesoporous counterparts. Herein, a new buried contact is reported by introducing graphitic carbon nitride (g-C3N4) into the commonly used SnO2 which performs outstanding transmittance, conductivity, and surface states for a high-quality electron-transporting layer. Moreover, the vertical composition and crystallinity of the top perovskite film are manipulated by rich amino groups on the edge of the g-C3N4 nanosheets which induce the prenucleation of the lead-rich species at the buried interface. Benefiting from the high-quality buried contacts and the optimized perovskite layers, the resultant PSCs achieve a champion efficiency of 21.5% with all photovoltaic parameters enhanced in comparison with their control counterparts (l20%).

Superconductors with nontrivial band structure topology represent a class of materials with unconventional and potentially useful properties. Recent years have seen much success in creating artificial hybrid structures exhibiting main characteristics of two-dimensional (2D) topological superconductors. Yet, bulk materials known to combine inherent superconductivity with nontrivial topology remain scarce, largely because distinguishing their central characteristic -- topological surface states -- proved challenging due to a dominant contribution from the superconducting bulk. Reported here is a highly anomalous behaviour of surface superconductivity in topologically nontrivial 3D superconductor In2Bi where the surface states result from its nontrivial band structure, which itself is a consequence of the non-symmorphic crystal symmetry and strong spin-orbit coupling. In contrast to smoothly decreasing diamagnetic susceptibility above the bulk critical field Hc2, associated with surface superconductivity in conventional superconductors, we observe near-perfect, Meissner-like screening of low-frequency magnetic fields well above Hc2. The enhanced diamagnetism disappears at a new phase transition close to the critical field of surface superconductivity Hc3. Using theoretical modelling, we show that the anomalous screening is consistent with modification of surface superconductivity due to the presence of topological surface states. The demonstrated possibility to detect signatures of the surface states using macroscopic magnetization measurements provides an important new tool for discovery and identification of topological superconductors., Comment: 30 pages, 4 main figures, 11 supporting figures

Green luminescence (GL) band in ZnO comes from the optical emissions of sample inside (GL1) and the surface recombination, i.e., the GL2 in the H‐annealed samples or the GL‐S in the O‐annealed sample.

The plasmon resonance effect of metal nanoparticles (NPs) offers a promising route to improve the solar energy conversion efficiency of semiconductors. In this study, it is revealed that hot electrons generated by the plasmon resonance effect of Au NPs tend to inject into the surface states instead of the conduction band of Fe2 O3 photoanodes, and then severe surface recombination occurs. Such an electron-transfer process seems to be independent of external applied potentials, but is sensitive to metal-semiconductor interface properties. Passivating the surface states of Fe2 O3 with a noncatalytic Al2 O3 layer can construct an effective resonant energy-transfer interface between Ti-doped Fe2 O3 (Ti-Fe2 O3 ) and Au NPs. In such a Ti-Fe2 O3 /Al2 O3 /Au electrode configuration, the enhanced photoelectrochemical (PEC) water-splitting performance can be attributed to the following two factors: 1) in the non-light-responsive wavelength range of Au NPs, both the relaxing Fermi pinning effect of the Al2 O3 passivation layer and the higher work function of Au enlarge band bending; thus promoting the charge separation; and 2) in the light-responsive wavelength range of Au NPs, the effective resonant energy transfer contributes to light harvesting and conversion. The interface manipulation proposed herein may provide a new route to design efficient plasmonic PEC devices for energy conversion.

The friction performance of MoDTP in the existence of ester was investigated. Tribological experiments were performed on reciprocating test rig between CKS piston ring and cast iron cylinder liner. Experimental results show that ester concentration is a key factor that influences the performance of MoDTP, the competitive effects between MoDTP and ester also vary with test temperature and load, and the “V” shape friction coefficient curve is caused by the change in friction surface states. During friction, when the surface roughness decreased and liner surface is covered by the friction layer, fresh metal is less likely to expose to lube oil, which reduces the activity of MoDTP in the existence of high concentration ester.

Topological insulators (TIs) are new quantum materials with bulk energy gaps and unique helical gapless surface states protected by time-reversal symmetry, providing a platform for the exploration of novel quantum phenomena and emerging applications. Bismuth tellurochloride (BiTeCl), the first strong inversion asymmetric topological insulator, has attracted considerable attention because of its exotic crystal structure and electrical band structure. Herein, we report the crystalline-surface-dependent n-type and p-type field effect transistors based on two-dimensional (2D) BiTeCl nanoplates. The p-type 2D BiTeCl exhibited a relatively strong photosensitivity with small dark current. Photovoltage generation in the vertical conducting channel of 2D BiTeCl is enhanced by 2–3 times in comparison with that in the planar conducting channel, presumably due to the enhanced separation efficiency of photogenerated electron–hole pairs induced by the existing built-in electric field in polarized BiTeCl nanoplates. Our studies may encourage devoted efforts towards intrinsic topological p-n junctions and high-performance electrical and optoelectronic devices.

Buried-channel semiconductor heterostructures are an archetype material platform for the fabrication of gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface; however, nearby surface states degrade the electrical properties of the starting material. Here, a 2D hole gas of high mobility (5 × 105 cm2 V−1 s−1) is demonstrated in a very shallow strained germanium (Ge) channel, which is located only 22 nm below the surface. The top-gate of a dopant-less field effect transistor controls the channel carrier density confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The high mobility leads to mean free paths ≈ 6 µm, setting new benchmarks for holes in shallow field effect transistors. The high mobility, along with a percolation density of 1.2 × 1011cm−2, light effective mass (0.09me), and high effective g-factor (up to 9.2) highlight the potential of undoped Ge/SiGe as a low-disorder material platform for hybrid quantum technologies.

Bismuth (Bi) is a topological crystalline insulator (TCI), which has gapless topological surface states (TSSs) protected by a specific crystalline symmetry that strongly depends on the facet. Bi is also a promising electrochemical CO2 reduction reaction (ECO2 RR) electrocatalyst for formate production. In this study, single-crystalline Bi rhombic dodecahedrons (RDs) exposed with (104) and (110) facets are developed. The Bi RDs demonstrate a very low overpotential and high selectivity for formate production (Faradic efficiency >92.2%) in a wide partial current density range from 9.8 to 290.1 mA cm-2 , leading to a remarkably high full-cell energy efficiency (69.5%) for ECO2 RR. The significantly reduced overpotential is caused by the enhanced *OCHO adsorption on the Bi RDs. The high selectivity of formate can be ascribed to the TSSs and the trivial surface states opening small gaps in the bulk gap on Bi RDs, which strengthens and stabilizes the preferentially adsorbed *OCHO and mitigates the competing adsorption of *H during ECO2 RR. This study describes a promising application of Bi RDs for high-rate formate production and high-efficiency energy storage of intermittent renewable electricity. Optimizing the geometry of TCIs is also proposed as an effective strategy to tune the TSSs of topological catalysts.

Elemental tin in the α-phase is an intriguing member of the family of topological quantum materials. In thin films, with decreasing thickness, α-Sn transforms from a three-dimensional (3D) topological Dirac semimetal (TDS) to a two-dimensional (2D) topological insulator (TI). Getting access to and making use of their topological surface states is challenging and requires interfacing to a magnetically ordered material. Here, we report the successful epitaxial growth of α-Sn thin films on Co, forming the core of a spin-valve structure. We carried out time- and element-selective ferromagnetic resonance experiments to investigate the presence of spin pumping through the spin-valve structure. We applied a rigorous statistical analysis of the experimental data using a Landau-Lifshitz-Gilbert-Slonczewski equation based model. A strong exchange coupling contribution was found, however no unambiguous proof for spin pumping. Nevertheless, the incorporation of α-Sn into a spin-valve remains a promising approach given its simplicity as an elemental TI and its room temperature application potential.

Structure inversion asymmetry is an inherent feature of quantum confined heterostructures with non equivalent interfaces. It leads to a spin splitting of the electron states and strongly affects the electronic band structure. The effect is particularly large in topological insulators because the topological surface states are extremely sensitive to the interfaces. Here, the first experimental observation and theoretical explication of this effect are reported for topological crystalline insulator quantum wells made of Pb1 amp; 8722;xSnxSe confined by Pb1 amp; 8722;yEuySe barriers on one side and by vacuum on the other. This provides a well defined structure asymmetry controlled by the surface condition. The electronic structure is mapped out by angle resolved photoemission spectroscopy and tight binding calculations, evidencing that the spin splitting decisively depends on hybridization and, thus, quantum well width. Most importantly, the topological boundary states are not only split in energy but also separated in space unlike conventional Rashba bands that are splitted only in momentum. The splitting can be strongly enhanced to very large values by control of the surface termination due to the charge imbalance at the polar quantum well surface. The findings thus, open up a wide parameter space for tuning of such systems for device applications

Substantial progress has been made in the photoelectrochemical (PEC) field to understand the photoelectrode behavior, semiconductor‐electrolyte interface, and photocorrosion, enabling new photoelectrode architectures with higher photocurrent, reduced photovoltage losses, and longer lifetime. Nevertheless, for practical PEC applications additional efforts are still needed to optimize all components of the photoelectrodes, including the light absorbing semiconductors, the layers for charge extraction, charge transfer, corrosion protection, and catalysis. In this regard, atomic layer deposition (ALD) offers new opportunities due to the monolayer‐by‐monolayer deposition approach, allowing preparation of conformal films with precisely controlled thickness and composition. As the ALD instruments are becoming widely accessible, this review aims to make an overview of the applications for photoelectrodes fabrication. The deposition of semiconductors onto flat and nano‐textured substrates, the deposition of ultrathin interlayers to ease charge transport by energy band alignment and surface states passivation, the deposition of corrosion protection layers, and finally, the possibilities for high catalyst dispersion is presented.

Excited carrier dynamics in plasmonic nanostructures determines many important optical properties such as nonlinear optical response and photocatalytic activity. Here it is shown that mesoscopic plasmonic covellite nanocrystals with low free‐carrier concentration exhibit a much faster carrier relaxation than in traditional plasmonic materials. A nonequilibrium hot‐carrier population thermalizes within first 20 fs after photoexcitation. A decreased thermalization time in nanocrystals compared to a bulk covellite is consistent with the reduced Coulomb screening in ultrathin films. The subsequent relaxation of thermalized, equilibrium electron gas is faster than in traditional plasmonic metals due to the lower carrier concentration and agrees well with that in a bulk covellite showing no evidence of quantum confinement or hot‐hole trapping at the surface states. The excitation of coherent optical phonon modes in a covellite is also demonstrated, revealing coherent lattice dynamics in plasmonic materials, which until now was mainly limited to dielectrics, semiconductors, and semimetals. These findings show advantages of this new mesoscopic plasmonic material for active control of optical processes., Excited carrier dynamics in plasmonic nanostructures determines many important optical properties. Here a comprehensive study of equilibrium and non‐equilibrium hot carrier dynamics in mesoscopic plasmonic covellite nanocrystals is reported, which exhibit a much faster carrier relaxation than traditional plasmonic materials. Furthermore, coherent lattice dynamics in plasmonic materials is demonstrated and analyzed.

A trivalent rare-earth ion (Sm3+ )-doped LiNa3 P2 O7 (LNPO) phosphor was synthesized using a conventional high-temperature solid-state reaction route. A predominant orthorhombic phase of LNPO was observed in all X-ray diffraction patterns. The surface states of the LNPO:Sm phosphor were confirmed by X-ray photoelectron spectroscopy. Under 401 nm excitation, the Sm-doped LNPO phosphors showed sharp emission peaks at 563, 600 and 647 nm that are related to the f-f transition of Sm3+ ions. The optimum concentration of Sm3+ (9 mol%) produced Commission Internationale de l'Eclairage chromaticity coordinates, color rendering index and correlated color temperature of (0.564, 0.434), 42 and 1843 K, respectively.

Polycrystalline silicon nanowires are fabricated following sidewall spacer approach using conventional UV lithography technique. Unfortunately, solid phase crystallization of nanowires implies low electrical properties due to the poor nanowires crystal quality. As polycrystalline silicon nanowires based field effect transistors find a lot of applications, improving nanowires crystalline quality is a technological challenge. One solution studied here is metal induced lateral crystallization method, using nickel as catalyst to create oriented crystals. The comparison is done between these two crystallization techniques. Indeed, we deeply investigate silicon nanowires/insulator interface and nanowires qualities by the determination of the energy distributions of the densities of states and the surface states using the Suzuki's incremental method. This calculation confirms that metal induced lateral crystallization significantly reduces bulk and surface states densities, compared to solid phase crystallized nanowires.

We provide complex capacitance studies which show that the tethering of negatively-charged DNA molecules to p-doped silicon (111), without intervening oxide layer, leads to changes of the electric field in the underlying silicon. We proposed, that the tethering of the DNA leads to the formation of surface states that, from the electronic point of view, resemble the major carriers of p-type silicon, i.e. holes. This effect is enhanced by the formation of double-stranded (ds)DNA molecules and hence is the premise to label-free detection of the DNA hybridization. Overall, our studies provide a promising alternative to design a biosensor to detect the hybridization of DNA molecules on the silicon surface.

The development of efficient, economic and environmentally friendly photoanode remains the primary materials challenge in the establishment of a scalable technology for solar water oxidation. Thus, for the simple materials such as Titania (TiO2) and its composites, was prepared by an easy method and studied extensively. High efficiency photoanode materials require properties like light trapping, electron and hole transportation. To provide a more efficient large scale TiO2 coating, we introduce a high throughput methodology wherein Al2O3 was spurted on titanium (Ti) plate. Photocurrents corresponding to water oxidation, under a standard AM 1.5G solar illumination, in a photoelectrochemical cell using Al2O3 spurted TiO2 film as photoanode was investigated and highest photocurrent of 40 μA cm−2 at zero bias vs (Ag/AgCl) was achieved when compared to pure TiO2. The light absorbing capability of the Al2O3 spurted TiO2 photoanode was demonstrated from the UV-Visible diffuse reflectance spectra and decrease in the band gap of 0.13 eV for the TiO2 film was observed which could be attributed to the improved photocurrents due to the increased charge carriers on the TiO2 film. Increase of charge carrier concentration on the TiO2 film could be effected due to the passivation of surface states upon Al2O3 spurting.

Enormous advancement has been achieved in the field of one-dimensional (1D) semiconductor light-emitting devices (LEDs), however, LEDs based on 1D CdS nanostructures have been rarely reported. The fabrication of CdS@SiO2 core–shell nanorod array LEDs based on a Au–SiO2–CdS metal–insulator–semiconductor (MIS) structure is presented. The MIS LEDs exhibit strong yellow emission with a low threshold voltage of 2.7 V. Electroluminescence with a broad emission ranging from 450 nm to 800 nm and a shoulder peak at 700 nm is observed, which is related to the defects and surface states of the CdS nanorods. The influence of the SiO2 shell thickness on the electroluminescence intensity is systematically investigated. The devices have a high light-emitting spatial resolution of 1.5 μm and maintain an excellent emission property even after shelving at room temperature for at least three months. Moreover, the fabrication process is simple and cost effective and the MIS device could be fabricated on a flexible substrate, which holds great potential for application as a flexible light source. This prototype is expected to open up a new route towards the development of large-scale light-emitting devices with excellent attributes, such as high resolution, low cost, and good stability.

Investigations of chemical species at the dielectric/III-N interface remain an important question in order to understand the chemical origin of the surface states, which are present at the heterostructure surface. In this work, we demonstrate a sample preparation technique to analyze the existing interface species by X-ray photoelectron spectroscopy (XPS) through thin uniform silicon nitride (Si3N4) layers 1.4 ± 0.2 nm. We show that it is crucial that the layers are as thin as possible but as thick as necessary to avoid oxygen diffusion through the passivation. Due to the sufficient information depth provided by such layers, the photoelectrons are detected. This is an advantage over sputtering as no intermixing of atoms or cleavage of bonds occurs. We show that the deposited Si3N4 hinders oxygen diffusion through the layer to the AlGaN surface. Selective SiO2 over Si3N4 etching and XPS depth profiles indicate that ∼1 nm of the thin Si3N4 layer has formed a surface oxide. Angle-resolved XPS measurements confirm the accumulation of oxygen at the top and bottom Si3N4 interfaces. No indication is found that interfacial oxygen is bound to any other than the group-13 metal. In agreement with the HSAB concept, the interfacial oxygen is bound to Al rather than Ga. Scheme of the nondestructive XPS interface analysis of the dielectric/AlGaN interface.

Capacitance–voltage (C–V) and modulated light-induced current–voltage measurements were employed to investigate the Cu2O/electrolyte junction of electrodeposited n-Cu2O thin films. The Mott–Schottky plots resulting from the C–V measurements revealed that the extrapolated flat-band potential of n-Cu2O films was strongly influenced by the pH of the bath where the films were grown. The flat-band potential change was 300 mV for a pH difference of 0.8 and showed that the surface chemistry at an n-Cu2O/aqueous electrolyte interface was strongly affected by the pH of the film deposition bath. In addition, current–potential measurements revealed that at the measured flat-band potential the photocurrent did not vanish for n-Cu2O films and the Fermi level at the interface was pinned due to the presence of electrically active surface states. Information on the presence of electrically active surface states and the shift in flat-band potential will be very useful for applications of n-Cu2O films in various devices.

Contrary to the conventional belief that the consideration for topological insulators (TIs) as potential thermoelectrics is due to their excellent electrical properties benefiting from the topological surface states, this work shows that the 3D weak TIs, formed by alternating stacks of quantum spin Hall layers and normal insulator (NI) layers, can also be decent thermoelectrics because of their focus on minimum thermal conductivity. The minimum lattice thermal conductivity is experimentally confirmed in Bi14Rh3I9 and theoretically predicted for Bi2TeI at room temperature. It is revealed that the topologically “trivial” NI layers play a surprisingly critical role in hindering phonon propagation. The weak bonding in the NI layers gives rise to significantly low sound velocity, and the localized low-frequency vibrations of the NI layers cause strong acoustic–optical interactions and lattice anharmonicity. All these features are favorable for the realization of exceptionally low lattice thermal conductivity, and therefore present remarkable opportunities for developing high-performance thermoelectrics in weak TIs.

Electronic properties of low dimensional systems are particularly sensitive to surface adsorbates. Clear understanding of such phenomena can lead to highly effective and nondestructive material engineering techniques. In this work, water adsorption at the surface of LaAlO3/SrTiO3 heterostructures is systematically studied. The saturation of surface dangling bonds by spontaneous water chemisorptions is found to be a main enabler of the formation of the interface 2D electron gas. In particular, when imbalanced distributions of water based ions, namely protons and hydroxyls, are generated, interface electron doping or depletion becomes surface adsorbates dominant and independent of the LaAlO3 layer thickness. The investigations also reveal the importance of hydrogen bonding through molecular water layers, which provides an energetically feasible pathway for manipulating the surface-bond protons and thus the interface electrical characteristics.

The evolution of the quantum anomalous Hall effect with the thickness of Cr-doped (Bi,Sb)2 Te3 magnetic topological insulator films is studied, revealing how the effect is caused by the interplay of the surface states, band-bending, and ferromagnetic exchange energy. Homogeneity in ferromagnetism is found to be the key to high-temperature quantum anomalous Hall material.

Photocleavage of H2O into clean and storable H2 fuel by photoelectrochemical (PEC) cell is a vital part of the sustainable hydrogen economy. However, thus far one of the limitations confronted by PEC cell to preferable performance is the insufficient behavior of photoanode for water oxidation half-reaction. One of the strategies to elevate the photoanode performance is integrating with an oxygen evolution catalyst (OEC) to remove the bottleneck of the water oxidation kinetics. Herein, an ultrafine cobalt iron oxide (CIO) nanocrystalline is reported as a novel OEC for photoelectrochemical water splitting. The CIO evenly distributing on the surface of hematite nanorod arrays not only greatly facilitates the surface hole injection, but also promotes the charge separation along with passivating the surface states. Such combined effects of CIO finally lead to an impressive 1.71 fold enhancement on the photocurrent density at 1.23 VRHE and ≈170 mV negative shift of onset potential, even overwhelms the commonly utilized Co-Pi. Along with its excellent long-term stability, the CIO possesses a great potential application in PEC water splitting devices.

MnBi2Te4 and MnBi4Te7 are intrinsic antiferromagnetic topological insulators, offering a promising materials platform for realizing exotic topological quantum states. However, high densities of intrinsic defects in these materials not only cause bulk metallic conductivity, preventing the measurement of quantum transport in surface states, but may also affect magnetism and topological properties. In this paper, we show by density functional theory calculations that the strain induced by the internal heterostructure promotes the formation of large-size-mismatched antisite defect BiMn in MnBi2Te4; such strain is further enhanced in MnBi4Te7, giving rise to even higher BiMn density. The abundance of intrinsic BiMn donors results in degenerate n-type conductivity under the Te-poor growth condition. Our calculations suggest that growths in a Te-rich condition can lower the Fermi level, which is supported by our transport measurements. We further show that the internal strain can also enable efficient doping by large-size-mismatched substitutional NaMn acceptors, which can compensate BiMn donors and lower the Fermi level. Na doping may pin the Fermi level inside the bulk band gap even at the Te-poor limit in MnBi2Te4. Furthermore, facile defect formation in MnSb2Te4 and its implication in Sb doping in MnBi2Te4 as well as the defect segregation in MnBi4Te7 are discussed. The defect engineering and doping strategies proposed in this paper will stimulate further studies for improving synthesis and for manipulating magnetic and topological properties in MnBi2Te4, MnBi4Te7, and related compounds.

Prototypical 3D topological insulators of the Bi2Se3 family provide a beautiful example of the appearance of the surface states inside the bulk bandgap caused by spin-orbit coupling-induced topology. The surface states are protected against backscattering by time reversal symmetry, and exhibit spin-momentum locking whereby the electron spin is polarized perpendicular to the momentum, typically in the plane of the surface. In contrast, graphene is a prototypical 2D material, with negligible spin-orbit coupling. When graphene is placed on the surface of a topological insulator, giant spin-orbit coupling is induced by the proximity effect, enabling interesting novel electronic properties of its Dirac electrons. A detailed theoretical study of the proximity effects of monolayer graphene and topological insulators Bi2Se3, Bi2Te3, and Sb2Te3 is presented, and the appearance of the qualitatively new spin-orbit splittings, well described by a phenomenological Hamiltonian, is elucidated by analyzing the orbital decomposition of the involved band structures. This should be useful for building microscopic models of the proximity effects between the surfaces of the topological insulators and graphene.

Author(s): Zhang, Z; Lindley, SA; Guevarra, D; Kan, K; Shinde, A; Gregoire, JM; Han, W; Xie, E; Haber, JA; Cooper, JK | Abstract: Metal oxide semiconductors are promising for solar photochemistry if the issues of excessive charge carrier recombination and material degradation can be resolved, which are both influenced by surface quality and interface chemistry. Coating the semiconductor with an overlayer to passivate surface states is a common remedial strategy but is less desirable than application of a functional coating that can improve carrier extraction and reduce recombination while mitigating corrosion. In this work, a data-driven materials science approach utilizing high-throughput methodologies, including inkjet printing and scanning droplet electrochemical cell measurements, is used to create and evaluate multi-element coating libraries to discover new classes of candidate passivation and electron-selective contact materials for p-type CuBi2O4. The optimized overlayer (Cu1.5TiOz) improves the onset potential by 110 mV, the photocurrent by 2.8×, and the absorbed photon-to-current efficiency by 15.5% compared to non-coated photoelectrodes. It is shown that these enhancements are related to reduced surface recombination through passivation of surface defect states as well as improved carrier extraction efficiency through Fermi level engineering. This work presents a generalizable, high-throughput method to design and optimize passivation materials for a variety of semiconductors, providing a powerful platform for development of high-performance photoelectrodes for incorporation into solar-fuel generation systems.