Heterojunction Band Alignment Research Articles

NiO@GaN nanorods-based core-shell heterostructure for enhanced photoelectrochemical water splitting via efficient charge separation

Remarkable properties of III-V semiconductors, particularly GaN nanostructured based photoelectrodes offers a potential attention in the field of photoelectrochemical water splitting (PEC-WS) for clean and sustainable hydrogen production, due to its wide bandgap, magnificent optoelectrical properties. However, the presence of inevitable surface states in GaN nanorods (NRs) leads to low solar-to-hydrogen (STH) conversion efficiency with poor stability, thereby severely limiting their practical application in PEC-WS, which can be effectively alleviated by constructing a hybrid heterostructures. Herein, we present the development of interfacial engineering of a type-II core-shell heterostructure based on p-NiO nanoparticles (NPs) loaded on n-GaN NRs photoelectrodes for PEC-WS. We assessed the impact of the NiO NPs shell density on core GaN NRs, finding that the optimized NiO@GaN NRs photoelectrode achieved a photocurrent density (Jph) of 1.38 mA/cm² at 1.23 V versus RHE and an excellent applied bias photo-to-current conversion efficiency (ABPE) of ∼0.39 %, which was 3.8 (Jph) and 4.8 (ABPE)-fold times higher than the pristine GaN NRs photoanode under 1-Sun illumination. The type-II p-n heterojunction band alignment between core-shell NiO@GaN NRs photoelectrode effectively reduced the photogenerated carrier recombination rate through surface states passivation and boost the light absorption and harvesting capacity. This facilitates a significant charge separation and transfer at the photoanode/electrolyte interface leading to enhanced redox reactions, resulting in improved PEC-WS and STH performances. These findings offer a promising strategy to design and fabricate highly efficient III-V hybrid heterostructure photoelectrodes for futuristic PEC-WS-based green energy applications.

High-Performance Ultraviolet to Near-Infrared Antiambipolar Photodetectors Based on 1D CdSxSe1-x/2D Te Heterojunction.

Antiambipolar heterojunctions are regarded as a revolutionary technology in the fields of electronics and optoelectronics, enabling the switch between positive and negative transconductance within a single device, which is crucial for diverse logic circuit applications. This study pioneers a mixed-dimensional photodetector featuring antiambipolar properties, facilitated by the van der Waals integration of one-dimensional CdSxSe1-x nanowires and two-dimensional Te nanosheets. This antiambipolar device enables flexible control over carrier transport via gate voltage, thus paving new paths for future optoelectronic devices. Furthermore, by precisely managing the stoichiometry of the ternary alloy CdSxSe1-x nanowires, fine-tuning of the nanowire band structure is achieved. This allows for customizable heterojunction band alignment (Type I and Type II), enabling adjustable band alignment. Through sophisticated band engineering, optimal Type II band alignment is achieved at the CdSxSe1-x/Te interface, significantly enhancing the device's photoelectric conversion efficiency through the synergistic effect of different dimensional materials. Exhibiting outstanding photoresponse across a broad spectral range from ultraviolet to near-infrared, especially under 450 nm illumination, the CdSxSe1-x/Te heterojunction photodetector demonstrates superior performance, including an impressive responsivity of 284 A W-1, a high detectivity of 1.07 × 1017 Jones, an elevated external quantum efficiency of 7.83 × 104 %, and a swift response time of 11 μs. Ultimately, this customizable antiambipolar photodetector lays a solid foundation for the advancement of next-generation optoelectronic technologies.

Diamond/cubic boron nitride (111) heterojunction interface: Rational regulation of high two-dimonsional electron gas

Wide-bandgap diamond exhibits excellent physical and chemical properties, making it an ideal substrate material for developing high-temperature and high-power semiconductor devices and broadening its application prospects in the field of microelectronics and optoelectronic devices. However, because of the Fermi pinning effect, it is difficult to achieve n-type diamond with excellent transport properties. Cubic boron nitride (cBN) has similar structural properties and a smaller lattice mismatch with diamond. Thus, making the two-dimensional electron gas of the diamond/cBN heterojunction provides a new idea to solve the problem of diamond n-incorporation difficulty and small bandgap regulation range. The diamond/cBN heterojunction is applied to study the law of influence factors on the heterojunction band structure, band alignment, and polarization strength. Further, a regulation mechanism for two-dimensional electron gas density is established at heterojunction interfaces, which can help solve the core difficulties of diamond n-type doping, small bandgap regulation range, and high impedance, providing a theoretical basis for realizing diamond power devices with high power density and low power consumption.

Analysis of the heterojunction band offset of h-BN/TMDCs

In order to analyze the effect of the chalcogen on the band alignment of the Transition metal dichalcogenides (TMDCs) and hexagonal Boron Nitride (h-BN) heterojunction, we fabricated the h-BN/TMDCs heterojunction by vertically stacking mono-layer h-BN and multi-layer TMDCs by the wet transfer method. The four heterojunctions are h-BN/WS2, h-BN/WSe2, h-BN/MoS2 and h-BN/MoSe2. X-ray photoelectron spectroscopy (XPS) has been employed to ascertain the Valence Band Offset (VBO) at the junctions created among these heterojunctions. All heterojunction band alignment styles are type-I. When the chalcogen changes from S to Se, the heterojunction VBO values increase. Specifically, in case of h-BN/WS2 and h-BN/WSe2 the VBO is 2.42 eV and 2.81 eV, respectively, and the magnitude of the difference is 0.39 eV. In the same case for h-BN/MoS2 and h-BN/MoSe2 the VBO is 2.52 eV and 2.55 eV, respectively, and the magnitude of the difference is 0.03 eV. The aforementioned research has obtained the band alignment for four heterojunctions, which provides a valuable reference for the design and analysis of the correlation devices in the future.

Simultaneous Band Alignment Modulation and Carrier Dynamics Optimization Enable Highest Efficiency in Cd‐Free Sb2Se3 Solar Cells

AbstractAntimony selenide (Sb2Se3) has developed as an eco‐friendly photovoltaic candidate owing to its non‐toxic composition and exceptional optoelectronic properties. However, the toxic and parasitic light‐absorbing CdS are widely used as electron transport layer (ETL) in Sb2Se3 solar cells, which severely limits its development. Herein, an alternative, zinc tin oxide (ZTO) ETL with varying composition‐dependent energy structure is deposited by atomic layer deposition (ALD) technique and used for constructing Cd‐free Sb2Se3 solar cells. It has been found that the ZTO ETL possessing an appropriate Zn/Sn ratio can alter the Sb2Se3/ZTO heterojunction band alignment to an ideal “spike‐like” arrangement. It not only suppresses the accumulation and recombination of charge carriers at the interface, but also effectively enhances carrier transport. In addition, thanks to the formation of passivated Sb2O3 ultra‐thin layer upon ALD process, the non‐radiative recombination within bulk Sb2Se3 can be effectively suppressed, and therefore enhancing carrier lifetime, extraction efficiency, and collection efficiency. Consequently, the as‐fabricated Mo/Sb2Se3/ZTO/ITO/Ag thin‐film solar cell demonstrates an impressive efficiency of 8.63%. This accomplishment establishes it as the most efficient Cd‐free Sb2Se3 solar cell to date, underscoring the significant advantages of incorporating ZTO ETL in the development of Sb2Se3 photovoltaic scenarios.

Novel Au/Cu2NiSnS4 Nano-Heterostructure: Synthesis, Structure, Heterojunction Band Offset and Alignment, and Interfacial Charge Transfer Dynamics.

Considering the importance of physics and chemistry at material interfaces, we have explored the coupling of multinary chalcogenide semiconductor Cu2NiSnS4 nanoparticles (CNTS NPs) for the first time with the noble metal (Au) to form Au-CNTS nano-heterostructures (NHSs). The Au-CNTS NHSs is synthesized by a simple facile hot injection method. Synergistic experimental and theoretical approaches are employed to characterize the structural, optical, and electrical properties of the Au-CNTS NHSs. The absorption spectra demonstrate enhanced and broadened optical absorption in the ultraviolet-visible-near-infrared (UV-Vis-NIR) region, which is corroborated by cyclic voltammetry (CV) readings. CV measurements show type II staggered band alignment, with a conduction band offset (CBO) of 0.21 and 0.23 eV at the Au-CNTS/CdS and CNTS/CdS interface, respectively. Complementary first-principles density functional theory (DFT) calculations predict the formation of a stable Au-CNTS NHSs, with the Au nanoparticle transferring its electrons to the CNTS. Moreover, our interface analysis using ultrafast transient absorption experiments demonstrate that the Au-CNTS NHSs facilitates efficient transport and separation of photoexcited charge carriers when compared to pristine CNTS. The transient measurements further reveal a plasmonic electronic transfer from the Au nanoparticle to CNTS. Our advanced analysis and findings will prompt investigations into new functional materials and their photo/electrocatalysis and optoelectronic device applications in the future.

Crucial role of interfacial interaction in 2D polar SiGe/GeC heterostructures

The planar charge transfer is a distinctive characteristic of the two-dimensional (2D) polar materials. When such 2D polar materials are involved in vertical heterostructures (VHs), in addition to the van der Waals (vdW) interlayer interaction, the interfacial interaction triggered by the in-plane charge transfer will play a crucial role. To deeply understand such mechanism, we conducted a comprehensive theoretical study focusing on the structural stability and electronic properties of 2D polar VHs built by commensurate SiGe/GeC bilayers with four species ordering patterns (classified as a C-group with patterns I and II and a Ge-group with patterns III and IV, respectively). It was found that the commensurate SiGe/GeC VHs are mainly stabilized by interfacial interactions (including the electrostatic interlayer bonding, the vdW force, as well as the sp 2/sp 3 orbital hybridization), with the Ge-group being the most energetically favorable than the C-group. A net charge redistribution occurs between adjacent layers, which is significant (∼0.23–0.25 e cell−1) in patterns II and IV, but slightly small (∼0.05–0.09 e cell−1) in patterns I and III, respectively, forming spontaneous p–n heterojunctions. Such interlayer charge transfer could also lead to a polarization in the interfacial region, with the electron depletion (accumulation) close to the GeC layer and the electron accumulation (depletion) close to the SiGe layer in the C-group (the Ge-group). This type of interface dipoles could induce a built-in electric field and help to promote photogenerated electrons (holes) migration. Furthermore, a semi-metal nature with a tiny direct band gap at the SiGe layer and a semiconducting nature at the GeC layer indicate that the commensurate SiG/GeC VHs possess a type-I band alignment of heterojunction and have a wide spectrum of light absorption capabilities, indicating its promising applications for enhancing light-matter interaction and interfacial engineering.

Charge-carrier engineering of staggered-gap p-CuAlO2/β-Ga2O3 bipolar heterojunction for self-powered photodetector with exceptional linear dynamic range and stability

Beta-gallium oxide (β-Ga2O3)-based heterojunction photodetectors (HJPDs) based on p-n heterojunction have drawn a lot of attention since p-type doping of β-Ga2O3 is challenging to perform. Thus, choosing affordable and effective inorganic hole transport layers (HTLs) is a crucial first step in commercializing PDs. Copper aluminum oxide (p-CuAlO2) is a very likely candidate material for heterojunction with β-Ga2O3, because of its large hole mobility for use in solar-blind photodetectors and high-power electronics. In this study, we propose employing a p-CuAlO2 interlayer for built a β-Ga2O3-based SBUV HJPDs by regulating the oxygen flow rate (OFR) from 0 % to 30 % using the RF magnetron sputtering (RFMS) technique. Prior to building the p-CuAlO2/β-Ga2O3 HJPDs, the heterojunction band alignment was established and displayed staggered-gap band alignment with a valence band (ΔEV) offset of 1.1 eV and conduction band offset (ΔEC) of 0.65 eV with OFR of 30 %. In response to the UV-C (255 nm) wavelength, the good optoelectronic device properties such as low dark current of ∼10−12 A, large photo-to-dark current (Ilight/Idark) ratio (∼104), responsivity (R) (26.36 mA/W), detectivity (D*) (2.87 × 1010 cmHz1/2W−1), external quantum efficiency (EQE) (1.28 × 104 %), noise-equivalent power (NEP) (0.03 pWHz−1/2), linear dynamic range (LDR) (99.13 dB), and comparable rise (τr) and decay times (τd) of 0.25 s and 0.15 s respectively, were demonstrated for p-CuAlO2/β-Ga2O3 HJPDs with OFR of 30 % and also compared with pristine Pt/β-Ga2O3 Schottky barrier diode photodetector (SBDPD). The band offset at the p-CuAlO2/β-Ga2O3 interface is employed to explain the improvement of p-CuAlO2/β-Ga2O3 HJPDs. The incorporation of p-CuAlO2 into Pt/β-Ga2O3 SBDPD lead to an improved extraction efficiency of the generated free hole carriers under illumination. The Silvaco TCAD simulator was employed to get insight into the function of the p-CuAlO2 layer. The investigation focused on analyzing the variation profile of the recombination rate and electric field in Pt/β-Ga2O3 SBDPD and p-CuAlO2/β-Ga2O3 HJPD with OFR of 30 %. The outcomes demonstrate the stability and electron transfer impact of staggered gap p-CuAlO2/β-Ga2O3 HJPDs. Our findings show that the p-CuAlO2/β-Ga2O3 HJPDs have a great deal of potential as a candidate structure for the Ga2O3-based modern optoelectronic technologies.

Suppressing Buried Interface Nonradiative Recombination Losses Toward High-Efficiency Antimony Triselenide Solar Cells.

Antimony triselenide (Sb2 Se3 ) has possessed excellent optoelectronic properties and has gained interest as a light-harvesting material for photovoltaic technology over the past several years. However, the severe interfacial and bulk recombination obviously contribute to significant carrier transport loss thus leading to the deterioration of power conversion efficiency (PCE). In this work, buried interface and heterojunction engineering are synergistically employed to regulate the film growth kinetic and optimize the band alignment. Through this approach, the orientation of the precursor films is successfully controlled, promoting the preferred orientational growth of the (hk1) of the Sb2 Se3 films. Besides, interfacial trap-assisted nonradiative recombination loss and heterojunction band alignment are successfully minimized and optimized. As a result, the champion device presents a PCE of 9.24% with short-circuit density (JSC ) and fill factor (FF) of 29.47mA cm-2 and 63.65%, respectively, representing the highest efficiency in sputtered-derived Sb2 Se3 solar cells. This work provides an insightful prescription for fabricating high-quality Sb2 Se3 thin film and enhancing the performance of Sb2 Se3 solar cells.

Construction of P-C3N4/C3N5 isotypic heterojunction for effective degradation of organic pollutants

BackgroundPhotocatalysis was an effective method for organic pollutant degradation, and graphitic carbon nitride g-C3N4 and g-C3N5 were famous two-dimensional semiconductors. Compared to the allotypic heterojunction, the band alignment and compatibility of isotypic heterojunction were superior. MethodsIn this work, an organic isotypic heterojunction was constructed via coupling phosphorus-doped C3N4 (P-C3N4) and g-C3N5. The characteristics were evaluated using transmission electron microscope, Fourier transform infrared, X-ray diffractometer, X-ray photoelectron spectrum, ultraviolet-visible (UV–vis) diffuse reflection spectrum, electronic spin resonance (ESR) analysis, photoluminescence spectrometer, electrochemical impedance spectroscopy, and photocurrent analysis. SignificantIsotypic heterojunction displayed high UV–vis light harvest, high separation efficiency of photo-induced charge carriers, and low surface resistance. Additionally, an internal-electric-field was established at the interface, which was beneficial for spatial separation of photo-induced charge carriers. As expected, the Rhodamine B (RhB) degradation efficiency was 7.3 and 12.3 times higher than that of the P-C3N4 and g-C3N5. Radical trapping experiment and ESR analysis indicated that •O2−, •OH, hole, 1O2, and electron played joint role in RhB degradation. In this work, a photocatalyst with excellent photocatalytic degradation properties was designed, and it provided a simple and novel strategy for environmental remediation.

Passivation of Grain Boundaries and Defects in CZTSSe Solar Cells by In Situ Na Doping

Alkali metal doping plays a great role in improving the efficiency of Cu2SnZn(S, Se)4 (CZTSSe) thin film solar cells. However, it is unclear how to realize the ideal distribution of alkali metal in CZTSSe films. Meanwhile, the mechanisms of alkali metal doping are still controversial. Herein, Na‐doped CZTSSe cells are fabricated by magnetron sputtering with Na‐containing Cu2SnZnS4 target which is in situ doping and annealing in selenization atmosphere. The incorporation of Na enhances the diffusion of K from the substrates to the absorbers. Na doping can increase the contact potential at the grain boundaries, which has beneficial effects on reducing the carrier recombination at the grain boundaries. Furthermore, Na incorporation modifies the conduction band offset at the CdS/CZTSSe interface from −0.07 to 0.03 eV. The defects and recombination in different regions are quantitatively extracted. It is demonstrated that the optimized grain boundary electrical properties and the heterojunction band alignment passivate the defects of the depletion region, the heterojunction interface, and the quasineutral region. Finally, a total‐area efficiency of 11.18% has been achieved in CZTSSe solar cell with an in situ Na doping concentration of 0.6 at%.

Surface engineering of TiO2@SrTiO3 heterojunction with Ni2S3 for efficient visible-light-driven photoelectrochemical cathodic protection

Photoelectrochemical cathodic protection (PCP) is considered a sustainable strategy against metal corrosion. Present works mainly focus on the photocarrier separation in the bulk and little attention has been paid to the photocarrier separation on the surface, which is also essential to determine the protection effectiveness. Here, a triple-junction of Ni3S2@TiO2/SrTiO3 that can simultaneously enhance the charge separation efficiency both in the bulk and on the surface was developed. Under AM 1.5 G illumination, the open circuit potential achieved ca. − 824 mV vs Ag/AgCl, which was 644 mV and 175 mV negative than the 304 SS and bare TiO2, respectively. Meanwhile, the photoinduced current reached 43 μA cm−2. The electrochemical characterization evidenced that a type II heterojunction band alignment was formed between TiO2 and SrTiO3, enabling the efficient charge separation in the bulk. Importantly, the Ni3S2 was proved to show the strong catalytic performance of oxidizing electrolytes, with the Tafel slope decreasing from 39.7 mV/dec to 33.3 mV/dec, thus resulting in a more superior PCP performance. The sample also shows excellent stability of the chemical composition, morphology, and crystalline structure after the 10 h test. This work represented a revelation of the critical function of the co-catalyst on the photoanode and guided the further design of effective photoanode systems for PCP.

Analytic electrostatic model of amorphous-crystalline Ge2Sb2Te5 heterojunction

Motivated by its potential properties and applications, the energy band alignment of the amorphous-crystalline Ge2Sb2Te5 heterojunction in thermal equilibrium is explored. An approximate analytic model based on the exact solution to Poisson’s equation is constructed to describe the electrostatics of the heterojunction between the amorphous phase and the face-centred cubic crystalline phase of Ge2Sb2Te5. The model captures the physics of accumulation in the crystalline layer, as well as that of depletion and inversion due to the deep defect distribution in the amorphous layer. Without introducing fitting parameters, the model approximates the influence of the density of states parameters of each phase on the electric potential distribution across the heterojunction. It is then validated against the exact solution obtained numerically using solar cell capacitance simulations. Apart from the small inaccuracy in modelling the electric potential distribution in the depletion region, simulation results reveal that the approximations are successful in modelling the electrostatics of the heterojunction.

Annealing effect of absorber layer on SnS/CdS heterojunction band alignments

The effect of annealing on the physical properties of an SnS thin film and also on SnS/CdS heterojunction band alignment was studied. Vacuum annealing has greatly improved the crystalline quality of SnS and an average grain size of 1.6 μm was achieved. Sulfur-rich secondary phases observed on the surface of as-grown SnS thin film were eliminated after vacuum annealing, resulting in a decrease of the resistivity and an increase of the carrier concentration of the film. A maximum hole mobility of 17 cm2 V−1 s−1 was obtained for SnS thin films annealed at 400 °C. A transition of SnS/CdS heterojunction from “spike” type to “cliff” type was observed when the vacuum annealed SnS thin film was post-air-annealed at 200 and 250 °C. The band alignment of SnS/CdS heterojunction could be adjustable between “spike” type to “cliff” type via vacuum annealing followed by post-air-annealing.

High sensitivity and fast response infrared detector fabricated with the Bi2Se3-PbSe heterojunction

A heterojunction photodetector based on the photogating effect is fabricated by combining the novel topological insulator Bi2Se3 with the traditional narrow-gap PbSe. The Bi2Se3-PbSe heterojunction is constructed by depositing PbSe thin film on surface of Bi2Se3 with the molecular beam epitaxy technique. Large lattice mismatch between cubic PbSe and rhombohedral Bi2Se3 is relaxed through the van der Waals epitaxial growth process, leading to an atomically abrupt and smooth Bi2Se3-PbSe heterointerface. Benefiting from the prominent photosensitivity in narrow-gap PbSe and the ultrafast charge transport in topological insulator Bi2Se3, high photosensitivity and fast response are simultaneously observed in the as-fabricated photodetectors. Responsivity and detectivity are 31.4 AW−1 and 1.7 × 1011 cmHz0.5 W−1 respectively. Rising and falling time are 240 μs and 500 μs respectively. In this structure, the appropriate band alignment of Bi2Se3-PbSe heterojunction and the photogating effect could synergistically utilize the advantages of both Bi2Se3 and PbSe, suggesting a potential solution to broaden the application prospect for both sides.

Two-Step Annealing CZTSSe/CdS Heterojunction to Improve Interface Properties of Kesterite Solar Cells.

The post-heating treatment of the CZTSSe/CdS heterojunction can enhance the interfacial properties of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this regard, a two-step annealing method was developed to enhance the heterojunction quality for the first time. That is, a low-temperature (90 °C) process was introduced before the high-temperature treatment, and 12.3% efficiency of CZTSSe solar cells was achieved. Further investigation revealed that the CZTSSe/CdS heterojunction band alignment with a smaller spike barrier can be realized by the two-step annealing treatment, which assisted in carrier transportation and reduced the charge recombination loss, thus enhancing the open-circuit voltage (VOC) and fill factor (FF) of the devices. In addition, the two-step annealing could effectively avoid the disadvantages of direct high-temperature treatment (such as more pinholes on CdS films and excess element diffusion), improve the CdS crystallization, and decrease the defect densities within the device, especially interfacial defects. This work provides an effective method to improve the CZTSSe/CdS heterojunction properties for efficient kesterite solar cells.

Photoelectric properties of monolayer WS2-MoS2 lateral heterojunction from first principles

The first-principles calculation is applied to investigate the photocurrents elicited by the circular photogalvanic effect (CPGE) and linear photogalvanic effect (LPGE) of monolayer WS2-MoS2 lateral heterojunction. Our results demonstrate that the band alignment of the WS2-MoS2 lateral heterojunction belongs to type-II, which can effectually isolate electron-hole pairs and augment the photocurrent conversion rate of the heterojunction. Furthermore, the photocurrent generated by LPGE and CPGE both have peaks around the photon energy of 2.0 eV and 2.3 eV, which can be subject to explain by DOS via Fermi's Golden Rule. More importantly, the monolayer WS2-MoS2 lateral heterojunction exhibits an obvious photocurrent effect, which also attest the existence of the PN junction. These results will contribute some theoretical guidance for the application of the WS2-MoS2 lateral heterojunction in the area of optoelectronics.

Atomically Resolved Quantum-Confined Electronic Structures at Organic-Inorganic Interfaces of Two-Dimensional Ruddlesden-Popper Halide Perovskites.

This work demonstrates the direct visualization of atomically resolved quantum-confined electronic structures at organic-inorganic heterointerfaces of two-dimensional (2D) organic-inorganic hybrid Ruddlesden-Popper perovskites (RPPs); this is accomplished with scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) by using solvent engineering to prepare perpendicularly oriented 2D RPPs. Atomically resolved band mapping images across the organic-inorganic interfaces of 2D RPPs yield typical quantum-well-like type-I heterojunction band alignment with band gaps depending on the thicknesses or n values of the inorganic perovskite slabs. The presence of edge states within the band gap due to organic cation vacancies is also observed. In addition, real-space visualization of atomic-scale structural phase transition behavior and changes in local electronic band structures are obtained simultaneously. Our results provide an unequivocal observation and explanation of the quantum-confined electronic structures formed at organic-inorganic interfaces of 2D RPPs.

Recent Progress on the Scanning Tunneling Microscopy and Spectroscopy Study of Semiconductor Heterojunctions.

The band alignment, interface states, interface coupling, and carrier transport of semiconductor heterojunctions (SHs) need to be well understood for the design and fabrication of various important semiconductor structures and devices. Scanning tunneling microscopy (STM) with high spatial resolution and scanning tunneling spectroscopy (STS) with high energy resolution are significantly contributing to the understanding on the important properties of SHs. In this work, the recent progress on the use of STM and STS to study lateral, vertical and bulk SHs is reviewed. The spatial structures of SHs with atomically flat surface have been examined with STM. The electronic band structures (e. g., the band offset, interface state, and space charge region) of SHs are measured with STS. Combined with the spatial structures and the tunneling spectra features, the mechanism for the carrier transport in the SH may be proposed.

Day-night active photocatalysts obtained through effective incorporation of Au@CuxS nanoparticles onto ZnO nanowalls

Photocatalytic degradation of organic dyes has been considered one of the promising solutions that enabled to effectively treat the demanding pollutants in wastewater. Yet, insight into the photocatalytic process under both illumination and dark conditions were hitherto missing. Herein, by virtue of incorporating the core-shell Au@CuxS nanoparticles to the ZnO nanowalls synthesized via all-solution synthesis, the intriguing heterostructures allowed to trigger the extraordinary capability of dye degradation either under light irradiance or dark environment. It was found that the coexistence of bi-constituted Cu2S/CuS shells on Au nanoparticles obtained with turning the concentrations of sulfurization acted as the decisive role on day-night active degradation performance, where the degradation efficiency was more than 8.3 times beyond sole ZnO sheets. The mediation of remarkable visible-light absorption and efficient charge separation due to band alignment of heterojunctions were responsible for the improved photodegradation efficiency under visible illuminations. Moreover, at dark environment, the involving peroxidase-like activity of CuxS shells with the mediation of Au nanoparticles facilitated the catalytic formation of hydroxyl radicals, manifesting the oxidative degradation of MB dye. Such all-day active photocatalysts further displayed the capability for the recycling treatment of MB dye, which offered the pathways to potentially treat the organic wastewater.