Heterojunction Research Articles

Tunable electronic and optical properties of 2D SiGe/SnI2 vdW heterostructures for high-performance ultraviolet photodetectors

In this work, the structural, electronic, and optical properties of two-dimensional SiGe/SnI2 van der Waals (vdW) heterostructures (HSs) in stable configurations are investigated by using first-principles calculations. Our results show that, the honeycomb SiGe monolayer (ML) in the HSs exhibits a Dirac cone with a mini-gap, which well preserves its high carrier mobility but shows weak anisotropic electronic behaviors with respect to isolated group-IV MLs. Notably, the HSs exhibit enhanced ultraviolet (UV) absorption nearly independent of strain and strain-tunable Schottky barrier heights between the bilayers, which are desirable for Schottky UV photodetectors. In addition, the band structures and band alignments of the HSs can be tuned by fully hydrogenating SiGe ML for high-sensitivity UV detection in the infrared (IR) background. The SiGe/SnI2 HSs with tunable superior electronic and optical properties are useful for design, fabrication, and applications of high-performance UV detectors.

Constructing Particulate p–n Heterojunction Mo:SrTiO3/NiO@Ni(OH)2 for Enhanced H2 Evolution under Simulated Solar Light

The global environmental issues associated with the use of fossil fuels lead to an urgent need for renewable energy sources, especially those free of CO2 emissions, such as green hydrogen. In this work, we successfully synthesized Mo-doped SrTiO3 by a molten salt method for photocatalytic hydrogen production under simulated solar light (AM 1.5G illumination). As a strategy to enhance the photocatalytic performance of Mo:SrTiO3, nickel-based nanoparticles (NiO@Ni(OH)2) were deposited onto the surface of the particles by modified magnetron sputtering to form a p–n heterojunction (HJ), resulting in the photocatalytic improvement of around 30-fold concerning pristine SrTiO3. Theoretical investigation of the electronic band structure, by DFT, reveals that the addition of Mo as a dopant leads to the formation of midgap states near the conduction band, further attributed to the photoactivity of Mo:SrTiO3 under visible-light illumination (>400 nm). The obtained structure, Mo:SrTiO3/NiO@Ni(OH)2, had its electronic behavior studied by XPS, Mott–Schottky analysis, and UV–vis spectroscopy, leading to the construction of a band diagram that confirms type-II p–n HJ formation. Remarkably, the formation of the HJ was responsible for establishing an internal electric field, which drives the photogenerated holes to the NiO@Ni(OH)2 structure, leading to the suppression of electron–hole recombination, observed by the reduction of the PL signal.

(Invited) Broadband and Broad Angle Enhanced Light Absorption in MoS2 based Hetero Plasmonic Structure

Solar cells, photovoltaic devices and optoelectronic elements needs enhanced light absorption with a wide range of incident angle for better and efficient design. Two-dimensional (2D) materials have exceled in all areas including electrical applications, optical modulations, mechanical as well as chemical implementations due to their direct bandgap and high optical absorption nature[1]. Photon irradiation allows to generate electron-hole pairs in a direct bandgap material such as TMDCs which makes them potential candidates for large amount of light to be trapped. Different structures have been studied to achieve high optical absorption [2][3]. Although one dimensional photonic crystal(1DPC) and defective PC has good optical absorption with wide range and angle [4],[2] number of layers and complexity in structure has made it difficult to be fabricated. MoS2 monolayer structure based on cover spacer, plasmonic and dual substrate layer (SiO2(50nm)/Si ) has also increased optical absorption range and broad angle [5] but TMDC based heterostructures with spacer has improved absorption comparing to previous structures without metallic layer [6]. In this paper, we proposed a dual TMDC-spacer based plasmonic structure with dual substrate for wide and broad range and angle of near perfect optical absorption.The structure considered here is an air/MoS2/Spacer1/MoS2/Spacer2/plasmonic/dual substrate with 0.665nm, 70nm and 50nm layer of MoS2, Au as plasmonic layer and SiO2 as part of dual layer with Si as lossless substate. (Figure 1) For spacers SiO2 and TiO2 are taken with optimized value (figure 2) of 92 and 68nm for enhanced absorption. The transfer matrix of the constituted layer for either transverse electric (TE) or transverse magnetic (TM) polarization was determined using the transfer matrix method (TMM). Both in TE and TM mode, the ~30 and ~40% of enhanced light absorption are observed in proposed structure compared to hetero and mono layer structure (figure 3) with impact of metallic and spacer layer. In case of incident angle, both at resonance frequency of MoS2 and within visible range, broad angle range (00-400 for TE and 00-800 for TM) is observed with wider wavelength. (Figure 4 and figure 5). Impact of various metallic layer on the proposed structure is also observed (Figure 6). Structure with VO2 as plasmonic layer [7] has around ~95% of peak absorption (400nm-550nm) and wide incident angle (00-850) irrespective of polarizations with lieu of spacer hetero-TMDC-stack (Figure 7). Due to multiple layers of structures, collective surface plasmon polaritons (SPP) has an enhanced light absorption within the heterostructure and enhanced electric field distribution of the structure is observed (Figure 8).Table I lists some comparison among various structures and parameters indicates that proposed dual spacer -TMDC based plasmonic heterostructure has wide visible range of wavelength (400-550 nm) with broad angle (00-850) light absorption with both polarizations compare to other counterparts.In this work an enhanced range in both wavelength and incident angle of visible optical absorption is observed in both polarization with plasmonic dual heterostructure is observed and compared with other structures. Such structures are useful for photodetectors and solar cells for maximum absorptions.[1] Lopez-Sanchez O, Lembke D, Kayci M, Radenovic A and Kis A 2013 Ultrasensitive photodetectors based on monolayer MoS 2 Nat. Nanotechnol. 8 497–501[2] Ansari N and Mohebbi E 2018 Broadband and high absorption in Fibonacci photonic crystal including MoS2 monolayer in the visible range J. Phys. D. Appl. Phys. 51 149–52[3] Ansari N and Ghorbani F 2018 Light absorption optimization in two-dimensional transition metal dichalcogenide van der Waals heterostructures J. Opt. Soc. Am. B 35 1179[4] Ansari N and Mohebbi E 2016 Increasing optical absorption in one-dimensional photonic crystals including MoS2 monolayer for photovoltaics applications Opt. Mater. (Amst). 62 152–8[5] Ansari N, Mohebbi E and Gholami F 2020 Nearly perfect and broadband optical absorption by TMDCs in cover/TMDC/spacer/Au/substrate multilayers Appl. Phys. B Lasers Opt. 126 1–6[6] Ansari N, Goudarzi B and Mohebbi E 2021 Design of narrowband or broadband absorber by heterostructures including TMDCs and spacers Opt. Laser Technol. 138 106771[7] Das H R and Arya S C 2021 Performance improvement of VO2 and ITO based plasmonic electro-absorption modulators at 1550 nm application wavelength Opt. Commun. 479 Figure 1

Hydrogen production from water using MoX2/ZnO (X:S,Se) heterostructures as photocatalysts

The role of two-dimensional heterostructures (HSs) in clean hydrogen production through photocatalytic water splitting has been paid enormous attention. Herein, we report a HS of transition metal dichalcogenide monolayer MoX2 where X–S,Se and graphene-like zinc oxide (g-ZnO). The structural,electronic, and optical properties have been investigated using density functional theory. MoS2/ZnO shows type-II band alignment with indirect bandgap of 1.61eV, a significant in-built potential of 7.42eV, and a valence band offset of 1.23eV across the interface, while MoSe2/ZnO HS shows type-I band alignment with direct bandgap of 1.80eV, in-built potential of 3.64eV, and a valence band offset of 0.34eV. Bandgap value and band-edge positions proved these HSs to be promising candidates for water splitting and evolution of hydrogen using solar energy. The results suggest the possibility of using 2D MoX2/ZnO HS as potential photocatalysts for straddling the redox potentials of water over a wide range, from ultraviolet to infrared spectra. The photogenerated charge carriers in the MoS2/ZnO HS are localized in different layers and can efficiently generate hydrogen energy by photocatalytic water splitting. However, the band-edge positions in MoSe2/ZnO are more suitable for pH = 8, making it promising photocatalyst for large-scale hydrogen production from solar energy.

In situ investigation on plastic deformation behaviors in austenite-ferrite heterostructured stainless steel

Heterostructured (HS) materials have attracted extensive attention due to their superior mechanical properties. However, there are still many fundamental issues to be solved, like the microstructural evolution process of the hetero-zones during deformation. Here we reported a HS 316L stainless steel generated by exploiting the chemical heterogeneity strategy via thermomechanical processing. The plastic deformation behaviors of the hetero-zones were investigated using three-point bending tests and interrupted tensile tests characterized by electron channeling contrast imaging (ECCI) combined with electron backscattered diffraction (EBSD) techniques. These in situ observations demonstrate the evolution of hetero deformation-induced (HDI) stress field near the austenite/ferrite interfaces in terms of geometrically necessary dislocation (GND) pileups, which can modulate the plastic deformation behaviors of both austenite and ferrite phases. At the early deformation regime, the imposed plastic deformation can be well maintained by the dense and homogeneous activation of slip systems in austenite phases and the stress concentration near austenite/ferrite interfaces can be alleviated by the gradual activation of plastic deformation in the ferrite phases. At the large deformation stage, a progressive twinning-induced plasticity (TWIP) effect caused by the chemical heterogeneity can provide a stable work hardening ability in a broad strain range, which can significantly enhance the ductility. At the late stage of deformation, strain-induced α′-martensite is also triggered, which provides an additional work-hardening ability. The strategy of micro-tuning deformation mechanisms by chemical heterogeneity is versatile and can be applied to many alloys.

WSe2 Monolayer: A Stable Two-Dimensional Heterostructure Material from First-Principles of Simulation Calculations

P-N junctions or heterostructures are commonly used in the fabrication of self-driven photodetectors because they serve critical roles in influencing the electrical characteristics of two-dimensional (2D) materials. For stable 2D heterostructures, planar WSe2 monolayers have attracted a lot of interest. Using first-principles energetic and dynamic calculations, we find that the transition from the indirect band gap of WSe2 bulk phase to the direct band gap of a two-dimensional plane is caused by the formation of p-n hetero junctions. Furthermore, it affects the carrier concentration transport mode and results in a significant orbital spin coupling. There is no virtual frequency in the phonon dispersion curve across the Brillouin zone at zero pressure. The interaction of the nearest neighbour atoms causes the frequency of the two acoustic modes of the G-point to be zero, as well as the frequency of the two optical films to merge. The theoretical analysis can provide support for the transport of two-dimensional planar carriers in electronics and photonics.

Maskless interdigitated a-Si:H PECVD process on full M0 c-Si wafer: Homogeneity and passivation assessment

In this work, the use of a novel, large area, mask-less and contact-less patterning technique is demonstrated for the first time, showing the localized deposition of hydrogenated amorphous silicon (a-Si:H) in a desired pattern over the full surface of an M0 (156 mm × 156 mm) solar wafer. The patterning functionality is achieved through a custom-designed RF electrode possessing a series of “slits” and placed in close proximity to the substrate in a plasma enhanced chemical vapor deposition (PECVD) chamber. Under a certain set of process conditions, a plasma only ignites within these slits, and the localized plasma results in localized patterned deposition of a-Si:H with feature widths compatible with application in an interdigitated back contact (IBC) solar cell design (760 μm). The homogeneity of the finger width and thickness over the surface of the M0 wafer is evaluated, with a 37% variation in thickness (at very high deposition rate, ∼1 nm/s) but only a 4.7% variation in finger width (MSE). With this application in mind, the impact of the deposition of such “fingers” on an underlying “blanket” passivation layer is assessed. Passivation is maintained or improved up to a given finger/blanket thickness ratio, above which the passivation is degraded. It is shown that the acceptable process window contains suitable thickness values for heterojunction (HJT) IBC solar cells, and the physical processes at the origin of this phenomenological observation are discussed.

Insight into symmetry matching heterogeneous facet junction photocatalysts via {211} faceted CeO2 nanobelts@δ-Bi2O3 nanowires

Photocatalysts with homogenous facet junctions exhibit amazing performance in photocatalytic redox reactions. More challenging and alluring is the construction of heterogeneous facet junctions with two of them. Herein, we show a self-assembly procedure to buildup co-exposing faceted δ-Bi2O3 nanowires on the edges of co-exposing {211} faceted CeO2 nanobelts from sub 10 nm nanoparticles. Directed by surface O-vacancy energy, the δ-Bi2O3 nanoparticles preferentially adsorbed on the {111} facets of CeO2 nanobelts and oriented growth into co-exposing faceted δ-Bi2O3 nanowires. The CeO2@δ-Bi2O3 hetero facet junction displays superior and stable hydrogen evolution activities, 5.2 times of the pure co-exposing faceted CeO2 nanobelts, ascribed to following key factors: First, heterogeneous facet junctions contribute to efficient interplanar and inter-junction separation of photocarriers. Moreover, symmetry matching leads to strong connection between the two facet junctions, facilitating the dynamic charge transfer. This work can provide a new strategy in the design of heterojunction photocatalytic systems for water splitting.

Precursor Molarity Influence on Sprayed Mo-doped ZnO Films for solar cells

Objectives: Current research focuses on the role of precursor molarity effect on sprayed Mo-doped ZnO films and their suitability as window layers in solar cells. Methods: Molybdenum (Mo) doped zinc oxide (MZO) thin films were deposited by the technique of spray pyrolysis, varying the Zn molarity in the range, of 0.01 M to 0.20 M at a constant substrate temperature of 400 ◦C. The Mo doping concentration was constant at 2 at. %. Findings: The XPS studies witnessed the presence of Mo and Zn in +6 and +2 state respectively. The XRD pattern showed both (111) and (002) as strong peaks, confirming the hexagonal wurtzite crystal structure. The optical investigations showed that the MZO films with Zn molarity 0.10 M exhibited high optical transmittance having a wide energy band gap. Films with zinc molarity of 0.10 M showed low resistivity and high mobility. The prepared CTS/MZO hetero junction solar cells performance was studied by evaluating parameters such as open circuit voltage (Voc) of 0.14 V, short circuit current density (Jsc) of 6.46 mA cm-2, a fill factor (FF) of 0.27, and a conversion efficiency of 0.25 %. Novelty: Studies on the physical properties of Mo:ZnO layers such as Ritveld refinement analysis and Haze were reported first time. CTS/MZO hetero junction solar cells have not yet been published. The observed results are analogous to improve the efficiency of solar cells using environmentally benign materials. Keywords: Spray pyrolysis; Thin films; XRD; Optical properties; Haze; Hall measurements

Influence of MgPc modification on NO2 sensing characteristics of RGTO grown SnO2 thin films

In the present study, we report a 100% enhancement in NO2 sensing response of tin oxide (SnO2) thin films through surface modification utilizing magnesium phthalocyanine (MgPc). For this purpose, SnO2 thin films were grown by Rheotaxial Growth and Thermal Oxidization (RGTO) method and were later modified by MgPc. Deposition of MgPc over SnO2 film was carried out by vacuum sublimation method. During deposition of MgPc, the substrates were heated to 200 °C. The MgPc modified SnO2 films (SnO2: MgPc) exhibit higher sensor response (18.5 for 5 ppm NO2), faster response/recovery time (6 s/169 s) and lower operating temperature (175 °C) as compared to pristine SnO2 films which exhibit maximum response at an operating temperature of 300 °C. Work function measurements and X-ray photoelectron spectroscopy (XPS) studies indicate formation of p-n hetero junctions in modified films due to electron transfer from SnO2 (n-type) to MgPc (p-type). In addition, MgPc modification results into intensification of oxygen adsorption sites (from 6.5% to 32.5%) on the sensor surface. Formation of p-n junctions at the interface and enhancement of adsorbed oxygen on the surface establish the basis for superior response i.e higher sensor response and faster response and recovery time of SnO2: MgPc films.

Towards an industrial in-line solution for efficient post-treatment of silicon heterojunction solar cells

Light exposure is widely known to enhance the performance of amorphous/crystalline silicon heterojunction (HJT) solar cells and modules. Recently, in an attempt to integrate such effect during cell production, processes involving intense illumination densities were reported. In this work, we develop a fast post-treatment on solar cells from Enel Green Power (EGP), using a LED-based tool specifically designed for HJT cells by Applied Materials and CEA. We investigate key aspects that such post-treatments should fulfil to be a relevant option in industry, including the amplitude of the gain, its stability under extended dark storage, its transferability to the module, and the influence of the post-treatment on the module reliability. Eventually, we also assess other potential side-benefits of the developed post-treatment, such as its influence on the efficiency distribution and on the yield of a fabrication line, as well as its robustness with respect to typical cell evolutions. • A LED-based post-treatment prototype has been developed for HJT cells. • +0.4% abs. efficiency gain is achieved within industry-compatible timeframes. • The gain is shown to be mostly (75%) stable after a slight initial destabilization. • Very good transferability of the gain to the module level is observed. • No warning is reported on the reliability of minimodules made from treated cells.

2D solar cell with record high power conversion efficiency based on low-symmetry IV-V2 bilayer heterostructure

The structural, electronic, and optical properties of two-dimensional (2D) low-symmetry orthorhombic IV-V2 bilayer heterostructures (HSs) were investigated using first-principles calculations. Our data show that all the constructed bilayer HSs (SiAs2/GeAs2, SiAs2/SiP2 and SiP2/GeAs2) are stabilized by van der Waals interaction. The IV-V2 bilayer HSs exhibit strong visible light absorption and type-II band alignments, which are beneficial for the effective separation of photo-generated electron–hole pairs in solar cells. Notably, the 2D SiAs2/GeAs2 HS-based solar cell exhibits a record-high power conversion efficiency (23.98%) higher than those of previously-reported 2D HSs-based solar cells obtained by high-throughput computational screening, owing to its small conduction band offset (0.2 eV) and suitable bandgap (1.49 eV). Our results provide insights into the structures and electronic and photovoltaic properties of the IV-V2 bilayer HSs and may be useful for related 2D solar cell applications.

Manganese phosphide nanoclusters embedded in epitaxial gallium phosphide grown from the vapor phase: Non-negligible role of Mn diffusion in growth kinetics

Orthorhombic MnP nanoclusters are formed in GaP epitaxial films grown by metalorganic vapor phase epitaxy on GaP(001) substrates, which are labeled as GaP:MnP/GaP(001). Polycrystalline MnP films have also been grown from the vapor phase on GaP substrates and are labeled as (p-c)MnP/GaP(001). Both GaP:MnP/GaP(001) epilayers and (p-c)MnP/GaP (001) films show a very rich texture, which has been previously characterized by three dimensional x-ray diffraction reciprocal space maps combined with transmission electron microscopy measurements. Heterostructures (HSs) containing multiple layers of (p-c)MnP/GaP and of GaP:MnP/GaP have been designed and grown with the same process. These HSs add new elements to our understanding of the growth mechanisms involved in these complex systems. In particular, it is shown that Mn diffusion during growth is strongly enhanced leading to a picture of MnP cluster coalescence, which explains some of their properties, such as the variation of their spatial distribution within the GaP matrix with the epilayer thickness. We report an Mn atomic diffusion coefficient of (1.5 ± 0.2) × 10−15 cm2/s in these films at 650 °C. The data are compatible with the superdiffusion of Mn, where the square of the diffusion length as a function of time (t) obeys λD2∝t1+α with an estimated value of α≈0.52.

Tuning of the Valley Structures in Monolayer In2Se3/WSe2 Heterostructures via Ferroelectricity.

Recent findings of two-dimensional ferroelectric (FE) materials have enabled the integration of nonvolatile FE functions into device applications based on van der Waals (vdW) heterojunctions (HJs), resulting in versatile technological advances. In this paper, we report the results of direct probing of the electronic structures of In2Se3/WSe2 heterostructures at the single-layer limit, where monolayer (ML)-In2Se3 was found to be either antiferroelectric (AFE, β') or ferroelectric (β*) at sufficiently low temperatures. A general type-II band alignment was revealed for this heterostructure. Moreover, we observed significant modulations of the valley structures of WSe2, and in situ transformations between the FE and AFE In2Se3 phases demonstrated the dominant role of the polarizations in the top ML-In2Se3 layer. The observed phenomena can be attributed to the combination of both the linear and quadratic Stark shifts from the out-of-plane electric field, which has only been previously theoretically explored for ML-transition metal dichalcogenides (TMDs).

Preparation and Charge Transfer at Sb2Se3/1L-MoS2 Heterojunction

Owing to the strong optical absorption of Sb2Se3, building heterojunctions (HJs) by using thin-layer Sb2Se3 and other two-dimensional (2D) materials is critical to the design and applications of ultrathin optoelectronic devices. However, the preparation of HJs using Sb2Se3 and other transition metal dichalcogenide (TMDC) thin layers is still challenging. Herein, a chemical vapor deposition (CVD) method was used to prepare monolayer MoS2(1L-MoS2) and Sb2Se3 thin layers. A dry transfer method was subsequently used to build their HJs. Individual PL spectra and PL mapping results obtained at the HJs indicate a charge injection from 1L-MoS2 into Sb2Se3 flake, which was further confirmed by contact potential difference (CPD) results obtained by using Kelvin probe force microscopy (KPFM). Further measurements indicate a type-Ⅰ band alignment with a band offset finally determined to be 157 meV. The obtained results of Sb2Se3/1L-MoS2 HJs will benefit the rational design of novel ultrathin optoelectronic devices based on novel 2D absorber layers working in visible light.

Tunning magnetism and anisotropy by ferroelectric polarization in 2D van der Waals multiferroic heterostructures

Since the successful exfoliation of two-dimensional (2D) magnetic CrI3 film, an increasing interest of research is the 2D analog of fascinating physical property of 3D material, of which the most attractive for both fundamental research and practical applications is the achieving effective magnetoelectric coupling and manipulation in 2D van der Waals (vdW) multiferroic heterostructure (HS). Herein, we report the discovery of ferroelectrically tunable orbital reconstruction in α-RuCl3/CuInP2S6 2D vdW HSs, enabling the remarkable transitions of magnetic ordering from proximate quantum spin-liquid state to ferromagnetic as well as the easy magnetization axis tuning from in-plane to out-of-plane direction. In addition, Monte Carlo simulation verified that, α-RuCl3 would transform into a perpendicular ferromagnetic material with Curie temperature of 89 K when the ferroelectric polarization points to α-RuCl3. Furthermore, by analyzing the density of states and the d-orbital-resolved magnetocrystalline anisotropy energy (MAE) of Ru atoms based on the second-order perturbation theory we elucidate that the contribution to MAE from the spin-orbit coupling interaction between d orbitals of Ru atoms show a transition from positive to negative, and ultimately dominating the MAE variation from easy-plane to easy-axis magnetization upon the reversible FE polarization. Therefore, the CuInP2S6 nonvolatile ferroelectric switching enables the nonvolatile electrical control of magnetic ordering and anisotropy. This work paves the way for exploring high-efficiency nanodevices and nonvolatile information storage based on the multiferroic 2D vdW HSs.

Recent Progress in Fabrication and Physical Properties of 2D TMDC-Based Multilayered Vertical Heterostructures

Two-dimensional (2D) vertical heterojunctions (HSs), which are usually fabricated by vertically stacking two layers of transition metal dichalcogenide (TMDC), have been intensively researched during the past years. However, it is still an enormous challenge to achieve controllable preparation of the TMDC trilayer or multilayered van der Waals (vdWs) HSs, which have important effects on physical properties and device performance. In this review, we will introduce fundamental features and various fabrication methods of diverse TMDC-based multilayered vdWs HSs. This review focuses on four fabrication methods of TMDC-based multilayered vdWs HSs, such as exfoliation, chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD), and pulsed laser deposition (PLD). The latest progress in vdWs HS-related novel physical phenomena are summarized, including interlayer excitons, long photocarrier lifetimes, upconversion photoluminescence, and improved photoelectrochemical catalysis. At last, current challenges and prospects in this research field are provided.

Interface Cd-N bond bridge accelerating charge separation to the enhanced visible light driven hydrogen production from water splitting on polyaniline@Cd-Zn-S photocatalyst

The key to the industrialization of eco-friendly hydrogen production from visible light driven water splitting is the development of photocatalyst with high performance and superior stability. Herein, a novel core-shell structure polyaniline@Cd-Zn-S (Cd/Zn = 0.8/0.2) nanorod photocatalyst with the shell thickness at ∼3 nm was constructed successfully. With polyaniline served as core, the construction of polyaniline@Cd-Zn-S reduced the charge transfer resistance and released reactive sites maximumly which could benefit the hydrogen production. The constructed polyaniline@Cd-Zn-S exhibited excellent photocatalytic hydrogen production efficiency and stability with the assistance of interface Cd-N bonds. The introduction of Cd-N bonds at the interface was inferred by both experimental and DFT simulated results. It served as the bridge between shell Cd-Zn-S and core polyaniline and promoted the directional transmission and efficient separation of photo generated charge carriers. Meanwhile, the improved directional transmission of photogenerated holes restricted photo corrosion effect of the Cd-Zn-S effectively and contributed to the photocatalytic stability. The hydrogen production without any cocatalyst increased more than 6 times to 721 μmol·h−1 after the construction of core-shell structure, and remain stable for 12 consecutive hours without photocatalytic performance reduction. This work proposed a new inspiring structural model for hetero junction construction of photocatalyst, and brought an interesting enlightenment to the development of eco-friendly hydrogen production technology.

Heterostructured bimetallic–sulfide@layered Ti3C2Tx–MXene as a synergistic electrode to realize high-energy-density aqueous hybrid-supercapacitor

Aqueous hybrid supercapacitors (AHSCs) exhibit promising electrochemical performance with long cyclic stability and high power density. However, the low-energy density restricted their development to commercialization. To improve the energy density, we proposed a heterostructured (HS) composite of nickel–cobalt–sulfide (NCS) nanoflowers embedded in exfoliated Ti3C2Tx−MXene layers (HS−NCS@MXene). The NCS nanoflowers were uniformly dispersed inside the MXene layers and formed a sandwich-like structure. The HS−NCS@MXene exhibited remarkable pseudocapacitive performance in a three-electrode system. The capacitance can reach 2637 F g−1 (1582 C g−1) at 2.5 A g−1 with stable cycling life over 10,000 cycles and retained 96% capacity of the initial value. Post−mortem investigations confirmed that the charge storage mechanism in HS−NCS@MXene composite is a combination of Faradic and electrochemical double-layer storage. An AHSC was assembled by coupling the HS−NCS@MXene as a positive electrode and activated carbon as a negative electrode (HS−NCS@MXene//AC–AHSC). The HS−NCS@MXene//AC–AHSC can operate in a potential range up to 1.6 V and deliver a high capacitance of 226 F g−1 at 1.5 A g−1 with stable cyclic life (92%) up to 20,000 cycles. Moreover, the HS−NCS@MXene//AC−AHSC also possessed a high energy density of 80 Wh kg−1 at a power density of 1196 W kg−1, which exceeds most recently published works. The synergistic effect of NCS and MXene enables the HS−NCS@MXene composite to deliver outstanding electrochemical performance for AHSCs.

Preparation and interfacial layer microstructure of multilayer heterogeneous composite

The appropriate hetero interfacial layer structure between metal and ceramic matrix composites is a very interesting topic in materials science. In this work, an adaptive diffusion reactive interfacial layer composed of “Mo–Mo2C–Mo5Si3–MoSi2–SiC” between Mo and SiCf/SiC composite is successfully prepared by chemical vapor infiltration (CVI). This reactive interfacial system is among three possible structures of interfacial layers predicted by Density-functional theory (DFT) calculations, which has the largest total interfacial energy (5.679 J/m2). At the same time, the formation process of the reaction interface layers is elucidated by thermodynamic calculations. In addition, dislocations are observed in Mo5Si3 and Mo2C grains, and it is worth mentioning that the Mo5Si3 grains are broken through dislocation movement to form fine grains, which release the residual thermal stress of the interfacial layer system caused by thermal mismatch during the long-term CVI process. Overall, our work provides a practical strategy for developing multilayer heterogeneous composites.