Vacancy Doping Research Articles

Strategic Defect Engineering Enabled Efficient Oxygen Evolution Reaction in Reconstructed Metal‐Organic Frameworks

AbstractMetal‐organic frameworks (MOFs) have emerged as promising pre‐catalysts for oxygen evolution reaction (OER) due to their marvelous structural reconstruction process in strongly alkaline media. However, targeting design MOF structures to achieve excellent OER performance of reconstructed products is a challenge. Here, a strategic defect engineering is used to promote the OER performance of reconstructed products. Briefly, modified linkers with monocarboxylic acids (ferrocene carboxylic acid, FcCA) are incorporated into MOF (NiBDC‐FcCA), leading to its stepwise reconstruction into Fe‐doped Ni(OH)2 and NiOOH during the OER process, with the oxygen vacancy and strategic doping of metal Fe persisting throughout the multi‐step reconstruction. Benefiting from the synergistic interaction of oxygen vacancies and Fe doping, NiBDC‐FcCA delivers the extremely enhanced current density at 1.6 V versus reversible hydrogen electrode by ≈9 times compared with that of NiBDC. Moreover, the optimized NiBDC‐FcCA/Fe foam exhibits excellent OER catalytic activity and stability with a low overpotential of 250 mV at 200 mA cm−2 and negligible activity decay after 1200 h at 1 A cm−2. Density function theory calculations reveal that Fe doping weakens the interaction of oxygen intermediate with Ni sites, favoring the formation of OOH* to accelerate the OER process.

Sulfur doping and oxygen vacancy in In2O3 nanotube co-regulate intermediates of CO2 electroreduction for efficient HCOOH production and rechargeable Zn-CO2 battery

By manipulating the distribution of surface electrons, defect engineering enables effective control over the adsorption energy between adsorbates and active sites in the CO2 reduction reaction (CO2RR). Herein, we report a hollow indium oxide nanotube containing both oxygen vacancy and sulfur doping (Vo-Sx-In2O3) for improved CO2-to-HCOOH electroreduction and Zn-CO2 battery. The componential synergy significantly reduces the *OCHO formation barrier to expedite protonation process and creates a favorable electronic micro-environment for *HCOOH desorption. As a result, the CO2RR performance of Vo-Sx-In2O3 outperforms Pure-In2O3 and Vo-In2O3, where Vo-S53-In2O3 exhibits a maximal HCOOH Faradaic efficiency of 92.4% at −1.2 V vs. reversible hydrogen electrode (RHE) in H-cell and above 92% over a wide window potential with high current density (119.1 mA cm−2 at −1.1 V vs. RHE) in flow cell. Furthermore, the rechargeable Zn-CO2 battery utilizing Vo-S53-In2O3 as cathode shows a high power density of 2.29 mW cm−2 and a long-term stability during charge-discharge cycles. This work provides a valuable perspective to elucidate co-defective catalysts in regulating the intermediates for efficient CO2RR.

In situ anchoring of bimetal (Cu, Fe) sulfides featured by sulfur vacancy and phosphorus doping within porous carbon nanocubes derived from Prussian blue analogs to activate peroxymonosulfate for the efficient degradation of organic pollutants

In this work, Prussian blue analogues (CuFe-PBA) derived copper-iron sulfides/N-doped porous carbon composite (CuFe-NC-SP-x) was prepared as an effective peroxymonosulfate (PMS) activator to degrade sulfadiazine (SDZ). A strategy that kills two birds with one stone was proposed to construct CuFe-NC-SP-x, i.e., S-etched CuFe-PBA (CuFe-PBA-S) was annealed with NaH2PO2 in N2 atmosphere to simultaneously introduce sulfur vacancy (Sv) and phosphorus doping. 40 μM SDZ was completely removed by CuFe-NC-SP-2/PMS in 20 min (0.2 g/L catalyst and 0.5 mM PMS). The kobs value obtained by CuFe-NC-SP-2 (0.48 min−1) was nearly 33 and 17 times higher than that of CuFe-PBA (0.014 min−1) and CuFe-PBA-S (0.028 min−1), respectively. Quenching tests, electron paramagnetic resonance (EPR) analysis indicated that PMS activation in the system involved radical pathway (26.1 % OH and 22.7 % SO4–) and non-radical pathway (17.8 % 1O2 and 33.4 % electron transfer process). OH, SO4– and 1O2 were mainly produced by S enhanced metal sites for PMS activation. The synergistic effect of Sv and P doping enabled the powerful electron transfer mechanism. Electrochemical tests and DFT calculations demonstrated that Sv existing in CuFe-NC-SP-x improved the electron donor ability and increased the adsorption energy toward PMS, and phosphorus doping accelerated the electron transport from SDZ to PMS. This work not only provides a novel strategy to synthesize a high effective PMS activator by introducing Sv and phosphorous doing in one step, but also manages to comprehensively understand the electron transfer activation mechanisms of PMS facilitated by Sv and phosphorous doping.

Disruption Symmetric Crystal Structure Favoring Photocatalytic CO2 Reduction: Reduced *COOH Formation Energy Barrier on Al Doped CuS/TiO2

AbstractHow to break the C═O bond and reduce the energy barrier of *COOH formation is the key to triggering the photocatalytic CO2 reduction (PCR) reaction and subsequent proton‐electron processes, which is as important as overcoming high recombination rate of photocarriers. In order to solve this issue, the symmetric structure of CuS/TiO2 is destroyed by S vacancy and Al doping (denoted as Al‐CuS/TiO2), which significantly expands the electron localization range and promotes the cis‐coordination splitting of Cu 3d orbits. The experimental results show that the CO yield selectivity of ≈90.68% and yield of ≈335.68 µmol·g−1·h−1 on Al‐CuS/TiO2. The redistribution of Cu electron states in specific d/s/p orbitals increases the adsorption of CO2 and reduces the reaction energy barrier of *COOH intermediates, while effectively breaking the C═O bond. Doped Al atoms also serve as adsorption sites for H2O molecules, effectively interleaving the competition with photocatalytic CO2 reduction at the Cu sites is effectively staggered. This study provides a new approach to reduce the energy barrier of *COOH formation and to accelerate the photocarrier migration by destroying local symmetry to adjust the crystal structure, which is important for further improving the activity and selectivity of PCR.

Selenium doping to improve internal electric field for excellent photocatalytic efficiency of g-C3N4 nanosheets

Graphitic carbon nitride is a promising photocatalyst to address environmental issues and energy applications. Herein, we develop an efficient defect-containing functionalized system of 2D selenium doped g-C3N4 porous nanosheets via one pot with two-step temperature for the first time. During heat treatment, Se-infused g-C3N4 nanosheets loosen stacking and form thinner nanosheets, which could effectively shorten the electronic path of charge migration. The introduction of nitrogen vacancies creates a midgap energy state below the CB, which improves the light-harvesting efficiency. Moreover, the dual effect of N vacancy and Se doping provides a driving force for the dissociation of excitons and achieves an effective spatial charge separation. High specific surface area (104.1 m2/g), suitable bandgap (2.65 eV), and good photocurrent response (0.45 µA cm−2) help to enhance the photocatalytic efficiency of 1-SeCN remarkably. Henceforth, high photocatalytic H2 production rate of 5441 µmol g−1 h−1 and CO evolution rate of 31.5 µmol g−1 h−1 verifies the effective Se doping enhances the photocatalytic efficiency of g-C3N4. Furthermore, DFT calculations are consistent with experimental results and this facile engineering strategy provides a scalable way to develop a novel, efficient g-C3N4-based photocatalyst for H2 production and CO2 reduction.

Improving electrochemical performances of LiNi0.5Mn1.5O4 by the strategy of oxygen vacancy doping

Despite the dazzling potential to be utilized as a high energy density lithium-ion battery cathode, the practical application of LiNi0.5Mn1.5O4 (LNMO) is hampered by the structural distortion related to Jahn-Teller effect of Mn3+ and the capacity degradation related to Mn2+ dissolution at high voltage. Herein, LNMO cathode materials doped with different contents of oxygen vacancies are synthesized by directly adjusting the oxygen ratio in the calcination atmosphere. Experimental and theoretical calculation results show that doping an appropriate amount of oxygen vacancies can regulate the electronic structure of Mn and Ni around oxygen vacancy, adjust the relative amount of Mn3+/Mn4+, increase the degree of disorder, and improve the electronic and ionic conductivity of LNMO, thereby enhancing its electrochemical performance. Especially, the modified LNMO exhibits a high capacity of 121.2 mAh g−1 at 0.5 C, a good capacity retention of 87.6 % after 100 cycles, and an excellent rate performance when the content of oxygen vacancies is about 20.60 %, corresponding to the oxygen ratio of 50 % in the calcination atmosphere. This study emphasizes the influence of doping oxygen vacancies on LNMO performance, enhancing its electrochemical properties without the introduction of additional elements. Moreover, these findings offer a fresh approach to enhancing the electrochemical performance of advanced batteries.

Transparent Conducting TiO2 Thin Film Induced by Electric‐Field Controlled Hydrogen Ion Intercalation

AbstractRealizing transformation from transparent insulating to transparent conducting, is a pursuing goal in designing and fabricating novel optoelectronic materials and devices. Here, a pronounced insulating to metal transition in anatase TiO2 thin films is achieved through ionic liquid gating, and interestingly the material maintains an invariable high optical transparency. It is revealed that the emergent metallic state can be attributed to the electron doping associated with the hydrogen ion intercalation. Importantly, the hydrogenation leads to the almost rigid shift of the Fermi energy and therefore maintains nicely the transparency at the visible light region. This result is in strong contrast with the case of oxygen vacancy doping, in which the optical bandgap is suppressed due to improved orbitals hybridization and intraband transition. Moreover, through synergistic ion‐electron doping, the selective control of the gating area and pattern is realized in the micrometer or even nanometer scale with extremely distinct physical properties, which can be employed to fabricate novel optical and electronic devices. The result greatly deepens the understanding of the underlying physics and formation mechanism of transparent conducting oxide (TCO) materials. It is envisioned that this work would provide a new pathway to design other potential optoelectronic materials with novel functionalities.

Exploration of new Janus GeBrI monolayer for optoelectronic and spintronic applications

Two-dimensional (2D) materials have been explored for diverse applications, where multifunctional candidates with two or more functions are desired. In this work, new Janus GeBrI monolayer with interesting electronic and magnetic properties is investigated. Standard PBE and hybrid HSE06 functionals assert the indirect gap semiconductor behavior of pristine monolayer with band gap of 2.28 and 3.04 eV, respectively. Novel feature-rich properties can be induced in Janus GeBrI monolayer by defect engineering and doping. Specifically, single Ge vacancy (VGe) metalizes the monolayer without magnetism. Similarly, the non-magnetic nature is kept by doping with IIA-group (Be and Mg: BeGe and MgGe) atoms, where the energy gap exhibits a slight increase of the order between 1.32% and 3.51%. In contrast, this 2D material is significantly magnetized by single halogen vacancy (VBr and VI), doping with IIIA-group (Al and Ga: AlGe and GaGe) atoms, and doping with chalcogen (Se and Te: SeBr, SeI, TeBr, and TeI) atoms. In these cases, total magnetic moments between 0.61 and 1.00 μB are obtained, where impurities and those atoms closest to the defect/doping site originate mainly the system magnetism. Moreover, VBr, VI, AlGe, GaGe systems exhibit the diluted magnetic semiconductor nature, while SeBr, SeI, TeBr, and TeI systems are classified as 2D half-metallic structures. Further, Bader charge analysis indicates the charge loser of IIIA- and IIA-group impurities when transferring charge to the host monolayer. Meanwhile, chalcogen dopants are charge gainers attracting charge from the host monolayer. The presented results introduce new stable Janus GeBrI monolayer with relative large intrinsic band gap, further functionalization processes based on the vacancy defects and doping of this 2D material may make prospective 2D spintronic materials.

A Recipe for a Great Meal: A Benchtop Route from Elemental Se to Superior Thermoelectric β-Ag2Se.

The low-temperature modification of β-Ag2Se has proven to be useful as a near-room-temperature thermoelectric material. Over the past years, research has been devoted to interstitial, vacancy, and substitutional doping into the parent β-Ag2Se structure, aiming at tuning the material's charge and heat transport properties to enhance thermoelectric performance. The transformation of β-Ag2Se into α-Ag2Se at ∼134 °C and the low solubility of dopants are the main obstacles for the doping approach. Herein, we report a facile, safe, scalable, and cost-effective benchtop approach to successfully produce metal-doped β-Ag2Se. The doped materials display a remarkable enhancement of thermoelectric performance with a record-high peak zT of 1.30 at 120 °C and an average zT of ∼1.15 in the 25-120 °C range for 0.2 at. % Zn-doped Ag2Se. The enhancement in zT is attributed to point defects created by Zn doping into Ag vacancies/interstitials, which enhances the scattering of phonons and tunes the charge carrier properties, leading to the significant suppression of thermal conductivity. The simplicity of the synthetic method developed herein and the high performance of the final products provide an avenue to produce high-quality Ag2Se-based thermoelectric materials.

Recent Modification Strategies of MoS2 towards Electrocatalytic Hydrogen Evolution

Hydrogen production by the electrolysis of water is a green and efficient method, which is of great significance for achieving sustainable development. Molybdenum disulfide (MoS2) is a promising electrocatalyst for hydrogen evolution reaction (HER) due to its high electrochemical activity, low cost, and abundant reserves. In comparison to the noble metal Pt, MoS2 has poorer hydrogen evolution performance in water electrolysis. Therefore, further modifications of MoS2 need to be developed aiming at improving its catalytic performance. The present work summarizes the modification strategies that have been developed in the past three years on hydrogen evolution from water electrolysis by utilizing MoS2 as the electrocatalyst and following the two aspects of internal and external modifications. The former includes the strategies of interlayer spacing, sulfur vacancy, phase transition, and element doping, while the latter includes the heterostructure and conductive substrate. If the current gap in this paper’s focus on modification strategies for electrocatalytic hydrogen evolution in water electrolysis is addressed, MoS2 will perform best in acidic or alkaline media. In addition to that, the present work also discusses the challenges and future development directions of MoS2 catalysts.

Influence of the oxygen vacancy and Ag-doping on the magnetic and electronic properties of the SrFeO3 material

SrFeO3 is a perovskite-type oxide applied in the development of magnetic material. This article discusses the influence of vacancy and transition metal doping on this functional material electronic properties. The quantum DFT/HSE06 approach simulated the magnetic property and super-exchange coupling on defective- and non-defective SrFeO3 structures. The results depict the structural deformation after defects and the origin of Jahn-Teller distortion. The electronic data suggests a p-type semiconductivity for all materials investigated, allied to a reasonable charge carrier stability, indicating the electrocatalytic activity of the O-vacancy and Ag-doped SrFeO3. In particular, the insertion of the defects affects the magnetic orderings energy, enabling a magnetic states engineering.

First-principles study of the effect of oxygen vacancy and iridium doping on formaldehyde adsorption on the La2O3(001) surface.

Formaldehyde adsorption on intrinsic La2O3 surface, four-fold coordinated oxygen vacancy (VO4c), six-fold coordinated oxygen vacancy (VO6c), and iridium-doped La2O3(001) surface was studied by the first-principles method. The results show that formaldehyde adsorption on the Ir-doped La2O3(001) surface with VO6c is the strongest because of the directional movement of electrons caused by the interaction of the Ir-5d orbitals and internal oxygen vacancy, wherein the adsorption energy is 3.23 eV. This model showed a significant increase in adsorption energy, indicating that Ir doping improves the formaldehyde adsorption capacity of the La2O3(001) surface. The energy band analysis shows that iridium doping introduces impurity energy levels into the intrinsic La2O3 energy band, which enhances the interaction between the La2O3(001) surface and formaldehyde molecules. Density of state analysis indicated that the adsorption of formaldehyde molecules on the La2O3(001) surface is mainly due to the interaction between the O-2p, C-2p orbitals of formaldehyde and the Ir-5d orbital of iridium atoms. Furthermore, the existence of VO4c and VO6c defects has no effect on the position and shape of the valence and conduction bands. The effects of oxygen vacancy and iridium doping on the optical properties mainly appeared in the low-energy infrared and visible regions, making the O-2p, C-2p orbitals of formaldehyde and the Ir-5d, O-2p orbitals of the La2O3(001) surface become hybridized near the Fermi level and the electronic transition from the valence band to conduction band more likely to occur. The La2O3 material can be used as an ideal photocatalytic material for formaldehyde degradation.

Realizing new 2D spintronic materials from the non-magnetic 1T-PdO2 monolayer through vacancy defects and doping.

In this work, vacancy- and doping-based magnetism engineering in a non-magnetic 1T-PdO2 monolayer is explored in order to realize new two-dimensional (2D) spintronic materials. The pristine monolayer is an indirect gap semiconductor with a band gap of 1.45 (3.20) eV obtained using the PBE (HSE06) functional. Half-metallicity with a total magnetic moment of 3.95 μB is induced by creating a single Pd vacancy, where the magnetic properties are produced mainly by O atoms around the vacancy site. In contrast, the non-magnetic nature is preserved under the effects of a single O vacancy, however a band gap reduction in the order of 37.93% is achieved. Further doping with transition metals (TMs = V, Cr, Mn, and Fe) in the Pd sublattice and with non-metals (B, C, N, and F) in the O sublattice is investigated. TM impurities lead to the emergence of a diluted magnetic semiconductor nature, where total magnetic moments of 1.00, 2.00, and 3.00 μB are obtained in the V-, Cr(Fe)-, and Mn-doped systems, respectively. In these cases, the TMs' 3d electrons mainly originate the system's magnetism. Significant magnetization of the PdO2 monolayer is also achieved by doping with B, N, and F atoms, where either half-metallic or diluted magnetic semiconductor natures are induced. Herein, electronic and magnetic properties are regulated mainly by the interactions between the 2p orbital of the dopant, 4d orbital of the first neighbor Pd atoms, and 2p orbital of the second neighbor O atoms. Meanwhile, C impurity induces no magnetism in the PdO2 monolayer because of the strong electronic hybridization with their neighbor atoms. Results presented herein may introduce efficient approaches to engineer magnetism in a non-magnetic PdO2 monolayer, such that the functionalized systems are further recommended for prospective spintronic applications.

First-principles study of oxygen vacancies in LiNbO3-type ferroelectrics.

LiNbO3-type ferroelectric oxides, as an important class of non-centrosymmetric compounds, have received great attention due to their important and rich properties. Although oxygen vacancies are widely present, studies of them in LiNbO3-type ferroelectric oxides are rare. In this article, we consider three representative LiNbO3-type ferroelectric oxide materials LiNbO3, ZnTiO3 and ZnSnO3 to study the impact of oxygen vacancy doping using first principles calculations. LiNbO3 and ZnTiO3 have ferroelectrically active cations Nb5+ and Ti4+, while ZnSnO3 does not have ferroelectrically active cations. The distribution of the oxygen vacancy induced electrons are quite different in the three materials even though they have similar structures. In oxygen deficient LiNbO3-δ (δ = 0.083/f.u.), electrons are itinerant, while in ZnTiO3-δ and ZnSnO3-δ (δ = 0.083/f.u.) the electrons are localized. These results provide guidance for the application of oxygen vacancies in LiNbO3-type ferroelectric material devices.

Tailoring Broadband Nonlinear Optical Characteristics and Ultrafast Photocarrier Dynamics of Bi2O2S Nanosheets by Defect Engineering.

Low-dimensional bismuth oxychalcogenides have shown promising potential in optoelectronics due to their high stability, photoresponse, and carrier mobility. However, the relevant studies on deep understanding for Bi2O2S is quite limited. Here, comprehensive experimental and computational investigations are conducted in the regulated band structure, nonlinear optical (NLO) characteristics, and carrier dynamics of Bi2O2S nanosheets via defect engineering, taking O vacancy (OV) and substitutional Se doping as examples. As the OV continuously increased to ≈35%, the optical bandgaps progressively narrow from ≈1.21 to ≈0.81eV and NLO wavelengths are extended to near-infrared regions with enhanced saturable absorption. Simultaneously, the relaxation processes are effectively accelerated from tens of picoseconds to several picoseconds, as the generated defect energy levels can serve as both additional absorption cross-sections and fast relaxation channels supported by theoretical calculations. Furthermore, substitutional Se doping in Bi2O2S nanosheets also modulate their optical properties with the similar trends. As a proof-of-concept, passively mode-locked pulsed lasers in the ≈1.0µm based on the defect-rich samples (≈35% OV and ≈50% Se-doping) exhibit excellent performance. This work deepens the insight of defect functions on optical properties of Bi2O2S nanosheets and provides new avenues for designing advanced photonic devices based on low-dimensional bismuth oxychalcogenides.

Mn Doping and P Vacancy Induced Fast Phase Reconstruction of FeP for Enhanced Electrocatalytic Oxygen Evolution Reaction in Alkaline Seawater.

Due to the shortage of pure water resources, seawater electrolysis is a promising strategy to produce green hydrogen energy. To avoid chlorine oxidation reactions (ClOR) and the production of more corrosive hypochlorite, enhancing OER electrocatalyst activity is the key to solving the above problem. Considering that transition metal phosphides (TMPs) are promising OER eletrocatalysts for seawater splitting, a method to regulate the electronic structure of FeP by introducing Mn heteroatoms and phosphorus vacancy on it (Mn-FePV) is developed. As an OER electrocatalyst in seawater solution, the synthesized Mn-FePV achieves extremely low overpotentials (η500=376, η1000=395mV). In addition, the Pt/C||Mn-FePV couple only requires the voltage of 1.81V to drive the current density of 1000mAcm-2 for overall seawater splitting. The density functional theory (DFT) calculation shows that Mn-FePV (0.21e-) has more charge transfer number compared with FeP (0.17e-). In-situ Raman analysis shows that phosphorus vacancy and Mn doping can synergistically regulate the electronic structure of FeP to induce rapid phase reconstruction, further improving the OER performance of Mn-FePV. The new phase species of FeOOH is confirmed to can enhance the adsorption kinetics of OER intermediates.

Effect of vacancy and pyridinic-like X-atom (X = Mg, B, C, and N) doping on the electronic and magnetic properties of antimonene: First-principles insights

We have explored the effect of vacancy and pyridinic-like X-atom (X = Mg, B, C, and N) doping on the geometries, electronic structure, and magnetism of antimonene (Sb) by means of first-principles calculations. The results showed that Sb with a single vacancy (SV-Sb) becomes a ferromagnetic metal with a moment of 0.33 µB. The X-atoms were doped at the edge site of the SV-Sb to form SV-nX-Sb (n = 1, 2, 3). All doped atoms except Mg form strong bonds with neighboring Sb-atoms. The stability of the designed structures was verified from formation energy (Efor). It was found that the SV-1X-Sb system is energetically more favorable (i.e. has the lowest Efor) for X = Mg, B, and C, while SV-3N-Sb is found more stable than SV-1N-Sb and SV-2N-Sb. Unlike metallic SV-Sb, the SV-1Mg-Sb, SV-1B-Sb, SV-1 C-Sb, and SV-3N-Sb structures exhibit semiconducting properties with a small band gap (of less than 0.5 eV). The ferromagnetism of SV-Sb is retained for X = B, and N doping, whereas Mg and C doping turned SV-Sb to non-magnetic, caused by the reconstruction of the edge Sb/X atoms. In addition, selective doping significantly altered the work function of the host material. These findings suggest the potential use of non-magnetic elements for tuning the electronic and magnetic properties of the monolayer antimonene for extended applications.

Effect of oxygen vacancy and Si doping on the electrical properties of Ta2O5 in memristor characteristics

The resistive switching behavior in Ta2O5 based memristors is largely controlled by the formation and annihilation of conductive filaments (CFs) that are generated by the migration of oxygen vacancies (OVs). To gain a fundamental insight on the switching characteristics, we have systematically investigated the electrical transport properties of two different Ta2O5 polymorphs (epsilon-Ta2O5 and λ-Ta2O5), using density functional theory calculations, and associated vacancy induced electrical conductivity using Boltzmann transport theory. The projected band structure and DOS in a few types of OVs, (two-fold (O2fV), three-fold (O3fV), interlayer (OILV), and distorted octahedral coordinated vacancies (OεV)) reveal that the presence of OILV would cause Ta2O5 to transition from a semiconductor to a metal, leading to improved electrical conductivity, whereas the other OV types only create localized mid-gap defect states within the bandgap. On studying the combined effect of OVs and Si-doping, a reduction of the formation energy and creation of defect states near the conduction band edge, is observed in Si-doped Ta2O5, and lower energy is found for the OVs near Si atoms, which would be advantageous to the uniformity of CFs produced by OVs. These findings can serve as guidance for further experimental work aimed at enhancing the uniformity and switching properties of resistance switching for Ta2O5-based memristors.

S bridging active centers coordination with oxygen vacancy of metastable blue WO3 for efficient C–C coupling and highly selective photoconversion CO2 to ethylene

This study proposes that metastable WO3 exhibits efficient photoconversion of CO2 to ethylene (C2H4). It is found that 1) the metastable hexagonal WO3 (h-WO3) offers a suitable bandgap for CO2 reduction, and its surface oxygen vacancy can enhance the light absorption capability and promote the separation of photogenerated electron-hole pairs, simultaneously; 2) S atoms replace oxygen atoms as the bridges to connect the adjacent W atoms to form W-S-W sites are beneficial to adsorb the *CH2 intermediates. Consequently, the optimized h-WO3 nanorods integrating oxygen vacancy and sulfur doping together have achieved the C2H4 generation yield of 1121.39 μmol g−1 with the record-high yield-based selectivity of 87.6% and electron-based selectivity of 95.7% in the field of photocatalytic CO2 reduction so far. This work provides a new avenue for the realization of CO2 photoconversion to C2+ products on a single metal oxide by virtue of O vacancy and S doping synergistic utilization.

Silicon diffusion in AlN

In this study, we investigate the diffusion of Si donors in AlN. Amorphous Si1−xNx sputtered on the surface of bulk AlN with low dislocation density is used as a Si source. The diffusion experiments are conducted through isochronal and isothermal annealing in a protective N2 atmosphere at temperatures between 1500 and 1700 °C. The Si depth profiles measured by secondary ion mass spectrometry exhibit a convex box-like shape with a steep diffusion front. These concentration profiles are best described with a diffusion coefficient that depends on the square of local Si concentration. From the characteristic box-shaped Si profiles, we conclude that diffusion of Si in AlN is mediated by singly negatively charged dopant–vacancy pairs SiAlVAl−. The strong concentration dependence of Si diffusion is due to the electric field associated with the incorporation of Si donors (SiAl+1) on substitutional Al lattice sites and reflects that Si is fully electrically active at diffusion temperature. The experimentally obtained extrinsic Si diffusion coefficient is reduced to intrinsic doping conditions. The temperature dependence of Si diffusion for intrinsic conditions is described by an activation enthalpy of (10.34±0.32)eV and a pre-exponential factor of 235−203+1485cm2s−1. The migration enthalpy of the donor–vacancy pair SiAlVAl− is estimated to be around 3.5 eV. This estimation is based on the activation enthalpy of the transport capacity of SiAlVAl− and theoretical results concerning the formation energy of negatively charged vacancies on Al-sites in AlN.