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Probing the Role of Nickle Dopant in Aqueous Colloidal ZnS Nanocrystals for Efficient Solar-Driven CO2 Reduction
摘要： Photocatalytic CO2 reduction reaction (CO2RR) on a heterogeneous catalyst offers the possibility for CO2 abatement and emerges as a promising avenue for renewable carbonaceous fuels production at ambient temperature and pressure using solar light as the sole energy input. Here, we report a newly aqueous colloidal comprised of monodispersed Ni-doped ZnS (ZnS:Ni) nanocrystals as excellent visible-light-responsive photocatalysts for CO2RR into formate. The wavelength-dependent quantum yield shows a significant contribution of Ni doping for visible light absorption. A high selectivity (>95%) of HCOOH production and a remarkable quantum efficiency of 59.1% at 340 nm and 5.6 % at 420 nm are obtained over ZnS:Ni (0.1 %) colloidal nanocrystals modified by Cd2+. The abundant sulfur vacancies and extended visible light absorption of the constructed colloidal ZnS:Ni nanocrystals contribute to the prominent performance for CO2RR. However, excessive doping of Ni does not guarantee an increase of photocatalytic CO2RR due to a diminish of sulfur vacancy. The regulation of sulfur vacancies by Ni doping and their interplay on photocatalytic CO2RR activity are presented and discussed. This work provides an in-depth insight of the role of dopant on vacancy modulation in photocatalyst beyond light absorption and a guidance for design of the potential photocatalyst for CO2RR.
关键词： CO2 reduction,vacancy,photocatalysis,doping,ZnS
更新于2025-11-19 16:51:07
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Multi-doped bismuth ferrite thin films with enhanced multiferroic properties
摘要： Thin films of multi-doped bismuth ferrite, Bi0.97?xLaxSr0.03Fe0.94Mn0.04Co0.02O3 (BLxSFMC, x = 0.00–0.18), are synthesized on a fluorine-doped tin oxide (FTO)/glass substrate. The structure and multiferroic properties of the film samples are characterized and tested. The results indicate that on doping, the structure of the BLxSFMC film changes has been changed. The concentrations of both oxygen vacancies and Fe2+ are decreased. The BL0.18SFMC thin film exhibits Ohmic conduction, which reduces the influence of the built-in electric field Ebi of the space-charge region at the interface between an Au electrode and the BLxSFMC during polarization. The BL0.18SFMC thin film also exhibits enhanced ferroelectric properties than the undoped film, with a higher residual polarization of 188 μC/cm2 and a higher squareness ratio of 1.21. Meanwhile, the reduced number of oxygen vacancies also reduces the Fe2+/Fe3+ ratio, thereby enhancing the Dzyaloshinskii–Moriya interaction of Fe–O–Fe bonds, and so the BL0.18SFMC thin film exhibits enhanced ferromagnetism, with a saturation magnetization of Ms ≈ 3.94 emu/cm3. Thus, multi-ion doping can improve both the ferroelectric and ferromagnetic properties of BLxSFMC thin films.
关键词： Ohmic conduction,built-in electric field,oxygen vacancy,multiferroic
更新于2025-11-14 17:28:48
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High electrostrain with high Curie temperature in BiFeO3-BaTiO3-based ceramics
摘要： Here, we report a high unipolar electrostrain (0.45%) with a high Curie temperature (TC = 410 °C) in lead-free (1-x)(0.67BiFeO3–0.33BaTiO3)-xSr0.8La0.1□0.1TiO2.95 (□ represents the A-site vacancy) piezoceramics with x = 0.02. Sr0.8La0.1□0.1TiO2.95 was introduced to construct a relaxor ferroelectric state. The obtained unipolar strain was thermally stable, and the variation from room temperature to 100 °C was only 10%. Systematic electromechanical and Raman spectra measurements revealed a composition driven phase transition from classical ferroelectric to relaxor ferroelectric phases and distorted internal stress field. This work provides a novel strategy to obtain high electrostrain in high temperature piezoceramics.
关键词： Electrostrain,BiFeO3-based ceramics,High TC,Vacancy
更新于2025-11-14 17:28:48
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Defective ZnS nanoparticles anchored in situ on N-doped carbon as a superior oxygen reduction reaction catalyst
摘要： Defect engineering has been used to develop low-cost and effective catalysts to boost oxygen reduction reactions. However, the development of catalysts that use metal cation vacancies as the active sites for oxygen reduction reaction is lacking. In this study, ZnS nanoparticles on N-doped carbon serve as an oxygen reduction reaction catalyst. These catalysts were prepared via a one-step method at 900 °C. Amazingly, the high-resolution transmission electron microscope image revealed obvious defects in the ZnS nanoparticles. These facilitated the catalyst synthesis, and the product displayed good electrocatalytic performance for the oxygen reduction reaction in an alkaline medium, including a lower onset potential, lower mid-wave potential, four electron transfer process, and better durability compared with 20 wt% Pt/C. More importantly, the density functional theory results indicated that using the Zn vacancies in the prepared catalyst as active sites required a lower reaction energy to produce OOH ? from ?OO toward oxygen reduction reaction. Therefore, the proposed catalyst with Zn vacancies can be used as a potential electrocatalyst and may be substitutes for Pt-based catalysts in fuel cells, given the novel catalyst’s resulting performance.
关键词： Density functional theory calculations,Oxygen reduction reaction,Zn vacancy,Electrocatalyst,Defective ZnS nanoparticle
更新于2025-11-14 17:03:37
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Enhanced piezoelectric properties and temperature stability of Bi4Ti3O12-based Aurivillius ceramics via W/Nb substitution
摘要： This work provides an effective method of inducing structure distortion, relieving the tetragonal strain of the TiO6 octahedron and decreasing the concentration of oxygen vacancies to improve the piezoelectricity and temperature stability of BIT ceramics. Bi4Ti2.98W0.01Nb0.01O12 possesses an optimum piezoelectric coefficient (d33) of 32 pC/N, a high Tc of 655 °C and a large resistivity of 3 × 106 Ω·cm at 500 °C. The maximum d33 reported here is approximately quadruple than that of pure BIT (~7 pC/N). Moreover, the d33 of W/Nb co-doped BIT and the in-situ temperature stability of the compression-mode sensor present a highly stable characteristic in the range of 25–600 °C. These results imply that W/Nb-modified BIT ceramics is a promising candidate for application at high temperatures of up to 600 °C.
关键词： Bi4Ti3O12,Structure distortion,Piezoelectric properties,Oxygen vacancy,Temperature stability
更新于2025-09-23 15:23:52
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Lattice thermal conduction in suspended molybdenum disulfide monolayers with defects
摘要： In this study, we investigated the effect of lattice defects comprising vacancies and boundaries on the lattice thermal conductivity (LTC), k p, of suspended molybdenum disulfide monolayers (MLs) over a wide temperature range (1 < T < 500 K). By using the phonon Boltzmann formalism, the acoustic phonons were considered to be scattered by the sample and grain boundaries, isotopic impurities, vacancies, and other phonons via Umklapp and normal (N-) processes. k p was evaluated using a modified Callaway model by considering the in-plane longitudinal acoustic and transverse acoustic phonons, and out-of-plane flexural acoustic phonon modes. We demonstrated the need to include the often neglected non-resistive N-processes when evaluating the LTC. Numerical calculations of the temperature dependence of the LTC for crystalline and polycrystalline MoS2 MLs showed the dominance of sample-dependent scattering mechanisms at low temperatures (T < 100 K) and of phonon-phonon scattering at higher temperatures, where the N-processes played an important role. The effects of vacancies and boundaries were to alter the behavior and suppress the magnitude of the LTC. The suppression due to vacancies was greater in crystalline MLs with specular surfaces and in polycrystalline MLs with larger grain sizes. The calculations compared well with recent thermal conductivity data obtained for polycrystalline samples. The need for further investigations is suggested.
关键词： MoS2 monolayer,grain boundary scattering,vacancy scattering,lattice thermal conductivity,N-process
更新于2025-09-23 15:23:52
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Vacancy-Driven Robust Metallicity of Structurally Pinned Monoclinic Epitaxial VO <sub/>2</sub> Thin Films
摘要： Vanadium dioxide (VO2) is a strongly-correlated material with 3d-electrons, which exhibits temperature-driven insulator-to-metal transition with a concurrent change in the crystal symmetry. Interestingly, even modest changes in stoichiometry-induced orbital occupancy dramatically affect the electrical conductivity of the system. Here, we report a successful transformation of epitaxial monoclinic VO2 thin films from a conventionally insulating to permanently metallic behavior by manipulating the electron-correlations. These ultrathin (~10 nm) epitaxial VO2 films were grown on NiO (111)/Al2O3 (0001) pseudomorphically, where the large misfit between NiO and Al2O3 were fully relaxed by domain matching epitaxy. Complete conversion from an insulator to permanent metallic phase is achieved through injecting oxygen vacancies (x~0.20±0.02) into the VO2-x system via annealing under high vacuum (~5x10-7 Torr) and elevated temperature (450 oC). Systematic introduction of oxygen vacancies partially converts V4+ to V3+ and generates unpaired electron charges which result in the emergence of donor states near Fermi level. Through the detailed study of the vibrational modes by Raman spectroscopy, hardening of the V-V vibrational modes and stabilization of V-V dimers are observed in vacuum-annealed VO2 films providing conclusive evidence for stabilization of monoclinic phase. This ultimately leads to convenient free-electron transport through the oxygen-deficient VO2-x thin films resulting in the metallic character at room temperature. With these results, we propose a defect engineering driven pathway through the control of oxygen vacancies to tune electrical and optical properties in epitaxial monoclinic VO2.
关键词： Defect engineering,Oxygen Vacancy,Metallicity,Mott transition,Metallic monoclinic VO2,Charge doping
更新于2025-09-23 15:23:52
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CO and H2 activation over g-ZnO layers and w-ZnO(0001)
摘要： Graphene-like ZnO (g-ZnO) nanostructures (NSs) and thin films were prepared on Au(111) and their reactivities towards CO and H2 were compared with that of wurtzite ZnO (w-ZnO) (0001) single crystal. The interaction and reaction between CO/H2 and the different types of ZnO surfaces were studied using near-ambient-pressure scanning tunneling microscopy (NAP-STM), X-ray photoelectron spectroscopy (XPS) and Density functional theory (DFT) calculations. The reactivity of the w-ZnO(0001) surface towards CO and H2 was found to be more prominent than those on the surfaces of g-ZnO/Au(111). CO oxidation took place primarily at the edge sites of w-ZnO(0001) and the interface between g-ZnO NSs and Au(111), while g-ZnO thin films on Au(111) appeared inert at below 600 K. Similarly, the w-ZnO(0001) surface could dissociate H2 at 300 K, accompanied by a substantial surface reconstruction, while g-ZnO on Au(111) appeared inert for H2 activation at 300 K. DFT calculations showed that the reactivities of ZnO surfaces towards CO could be related to the formation energy of oxygen vacancy (EOvf), which could be related to the charge transfer to lattice oxygen atoms or surface polarity.
关键词： CO oxidation,NAP-STM,ZnO,XPS,surface polarity,oxygen vacancy
更新于2025-09-23 15:23:52
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Acceptor levels of the carbon vacancy in 4 <i>H</i> -SiC: Combining Laplace deep level transient spectroscopy with density functional modeling
摘要： We provide direct evidence that the broad Z1/2 peak, commonly observed by conventional deep level transient spectroscopy in as-grown and at high concentrations in radiation damaged 4H-SiC, has two components, namely, Z1 and Z2, with activation energies for electron emissions of 0.59 and 0.67 eV, respectively. We assign these components to Z?1/2 + e? → Z?1/2 → Z?1/2 + 2e? transition sequences from negative-U ordered acceptor levels of carbon vacancy (V_C) defects at hexagonal/pseudo-cubic sites, respectively. By employing short filling pulses at lower temperatures, we were able to characterize the first acceptor level of V_C on both sub-lattice sites. Activation energies for electron emission of 0.48 and 0.41 eV were determined for Z1(?/0) and Z2(?/0) transitions, respectively. Based on trap filling kinetics and capture barrier calculations, we investigated the two-step transitions from neutral to doubly negatively charged Z1 and Z2. Positions of the first and second acceptor levels of V_C at both lattice sites, as well as (?/0) occupancy levels, were derived from the analysis of the emission and capture data.
关键词： density functional theory,acceptor levels,deep level transient spectroscopy,negative-U ordering,carbon vacancy,4H-SiC
更新于2025-09-23 15:23:52
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Negative charge enhancement of near-surface nitrogen vacancy centers by multicolor excitation
摘要： Nitrogen vacancy (NV) centers in diamond have been identified over the past few years as promising systems for a variety of applications, ranging from quantum information science to magnetic sensing. This relies on the unique optical and spin properties of the negatively charged NV. Many of these applications require shallow NV centers, i.e., NVs that are close (a few nm) to the diamond surface. In recent years there has been increasing interest in understanding the spin and charge dynamics of NV centers under various illumination conditions, specifically under infrared (IR) excitation, which has been demonstrated to have significant impact on the NV centers’ emission and charge state. Nevertheless, a full understanding of all experimental data is still lacking, with further complications arising from potential differences between the photodynamics of bulk and shallow NVs. Here we suggest a generalized quantitative model for NV center spin- and charge-state dynamics under both green and IR excitation. We experimentally extract the relevant transition rates, providing a comprehensive model which reconciles all existing experimental results in the literature, except for highly nonlinear regimes. Moreover, we identify key differences between the photodynamics of bulk and shallow NVs, and use them to significantly enhance the initialization fidelity of shallow NVs to the useful negatively charged state.
关键词： nitrogen vacancy centers,recombination,shallow NVs,bulk NVs,photodynamics,green excitation,ionization,charge state,IR excitation,diamond
更新于2025-09-23 15:23:52