Corrected Transmission Electron Microscopy Research Articles

Pt atomic clusters/MoS2 nanosheets/Co-doped hollow carbon nanofibers for high-current–density alkaline hydrogen production

The application of layered molybdenum disulfide (MoS2) in catalytic hydrogen production has attracted great interest, while their catalytic properties are limited by poor electron conductivity and a few catalytically active sites. In this work, we demonstrated a highly active electrocatalyst for large-scale hydrogen production, consisting of two-dimensional (2D) Pt-MoS2 nanosheets along one-dimensional (1D) cobalt nanoparticle integrated carbon hollow nanofibers (Co@CHNF). The as-prepared Pt-MoS2-Co@CHNF had a large specific surface area (44.5 m2 g−1). X-ray photoelectron spectrometer (XPS) and spherical aberration corrected transmission electron microscope (AC-STEM) demonstrated that Pt atomic clusters (Pt ACs) were doped on MoS2 nanosheets by thermodynamically induced spontaneous interfacial redox between MoS2 and H₂PtCl₆. The Pt-MoS2-Co@CHNF based catalysts exhibited an overpotential as low as 91 mV for 10 mA cm−2 and 258 mV for 200 mA cm−2 in 1 M KOH electrolyte, and there is no significant floating for catalytic active with 14 h continuous operation, which demonstrates its excellent long-term operation durability, significantly superior to the previously reported state-of-the-art Co-based or Mo-based catalysts. In particular, the self-supporting binder-free Pt-MoS2-Co@CHNF catalyst-based electrode showed an ultra-high current density of 500 mA cm−2 at a low overpotential of 301 mV, without any decrease after 24 h operation at 500 mA cm−2 in 1 M KOH seawater electrolyte, representing a great potential for large-scale seawater hydrogen production.

Determination of MAX phase structure and surface reconstruction behavior of a novel V–Sn–C system

The crystal structure of a novel MAX phase is determined using X-ray powder diffraction, spherical aberration corrected transmission electron microscopy, and first-principles calculations. In the new V–Sn–C system, the R 3‾ m space group aligns more closely with the experimental data than the P63/mmc space group. The lattice parameters of the new trigonal V2SnC phase are a = 0.291 nm and c = 2.08 nm. Moreover, the surface of the new phase has a tin-doped carbide face-centered cubic (FCC) structure reconstruction layer. First-principles calculations indicate that the new trigonal V2SnC phase is metastable compared with the hexagonal V2SnC phase. However, the thermal stability of the metastable trigonal V2SnC in air is significantly enhanced owing to the presence of the reconstruction layer.

Microstructural study on in-situ high-entropy (NbMoTaWV)C reinforced nanocrystalline NbMoTaWVC refractory high entropy alloys prepared by mechanically alloying

Refractory high-entropy alloys (RHEAs) can be commonly regarded as the best candidates for potentially substituting for the nickel-based superalloys practically used in the areas of aviation and nuclear industry, which can significantly endure in high-temperature and harsh environment. In this work, a nanocrystalline NbMoTaWVC RHEA is successfully produced by mechanical alloying method and X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and spherical aberration corrected transmission electron microscopy (AC-TEM) are employed to systematically characterized the microstructural details of NbMoTaWV and NbMoTaWVC RHEAs mechanically alloyed powders. Our results can support the evidence that the observable minimum nanoparticle sizes of the NbMoTaWV and NbMoTaWVC RHEAs considerably decrease to approximately ∼100 nm. Furthermore, the average grain sizes are gradually refined and thus notably drop to around of 30–50 nm, and five elemental powders can be found to be homogeneously alloyed. The evidence can be confirmed that the order of solid solution may be proposed as follows: Nb → Mo → V → Ta → W. The chemical short-range order occurred at the local nanoscale of NbMoTaWV and NbMoTaWVC RHEAs. Meanwhile, further microstrutural analysis can demonstrate that NbMoTaWV and NbMoTaWVC RHEAs powders with ultrafined grain have a bcc phase structure and bcc + bct matrix phases combined with high-entropy tungsten carbides (NbMoTaWV)C and (NbMoTaWV)2C of nano-precipitated phases, respectively, suggesting that the martensitic transformation probably occurred. The NbMoTaWV and NbMoTaWVC RHEAs powders of locally crystal lattice distortion rates reached approximately 8.07% and 6.33%.

Hybrid additive manufacturing of aluminum matrix composites with improved mechanical properties compared to extruded counterparts

Great difficulties existed in fabricating large components of SiC particles reinforced aluminum matrix composites with excellent mechanical properties using existing manufacturing procedures. This study demonstrated that the challenges can be addressed by developing a hybrid solid-state additive manufacturing method. The influence of the deposition procedures and the post-processing heat treatment on the microstructure and mechanical properties of the SiC particles reinforced 2009 aluminum ally matrix composites (SiCp/2009Al composites) was systematically investigated using advanced technologies such as spherical aberration corrected transmission electron microscope, atom probe tomography, etc. The results showed that the SiCp/2009Al composites produced by the hybrid solid-state additive manufacturing exhibited enhanced tensile properties and improved isotropy in mechanical properties compared to the extruded feedstock of SiCp/2009Al composites. This was attributed to the formation of dense metal with uniformly distributed SiC particles, high-density of Cu–Mg co-clusters, refined grains and SiC particles, low deformation texture, tightly bonded SiCp/2009Al interface, and sound interfacial bonding between deposited layers.

Texture in atomic layer deposited Hf0.5Zr0.5O2 ferroelectric thin films

HfO2-based ferroelectric materials have excellent CMOS compatibility and polarization even in ultrathin films, which is regarded as promising candidate material for memory devices and related electronic devices. However, as the ferroelectric layer thickness scaling down, the consistency of device performance is inevitably affected by the complex polyphase and polycrystalline nature of HfO2-based ferroelectric thin films. Therefore, obtaining and controlling the texture of HfO2-based ferroelectric thin films is extremely important for regulating polarization orientation and improving ferroelectric polarization. In this work, 10 nm Hf0.5Zr0.5O2 (HZO) films were prepared by atomic layer deposition (ALD) on Nb-doped SrTiO3 (NSTO) single crystal substrates. The texture and orientation of HZO films were analyzed through the state-of-the-art spherical aberration corrected transmission electron microscope (Cs-TEM) technique. The domain matching epitaxy between HZO films and NSTO substrate helps eliminate lattice mismatch and residual misfit strain, and ultimately leads to the formation of <112> texture in HZO ferroelectric films. The obtained results represent lattice and interface play an extremely important role in regulating the ferroelectricity of HfO2-based films, which provides a way to design ultra-thin HfO2-based materials with excellent ferroelectric polarization by controlling the crystal structure and orientation.

Enhanced electrocatalytic performance of PtNi bimetallic alloys on carbon nanotube for ethanol oxidation reaction

In this paper, Ni-Pt bimetallic alloy nanoparticles were loaded on carbon nanotubes to prepare Ni-Pt nanoparticles/carbon nanotubes composites (Ni-Pt NPs/CNTs) as excellent catalytic materials for ethanol electro-oxidation reaction (EOR). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and special aberration corrected transmission electron microscope (STEM) were used to characterize its morphology and structure. The activity and stability of the composite were measured by cyclic voltammetry (CV) and chronoamperometry (CA). The catalytic performance was explored by adjusting the ratio of Ni to Pt. Performance test results showed that the Ni-Pt alloy formed 10–15 nm spherical particles and dispersed uniformly on the surface of carbon nanotubes. The Ni1Pt1 NPs/CNTs composite showed excellent performance for EOR. Its mass activity of ethanol electro-oxidation was 620 mA·mg−1Pt, which was 5.08, 18.2 times higher than that of commercial Pt/C and Pt black catalyst, respectively.

Visualization of the structural transformation of NiO/YSZ/BZY nanocomposite particles using in situ gas environmental transmission electron microscopy.

This study focused on investigating the dynamic structural transformations of spherical NiO/YSZ/BZY triple-phase nanocomposite particles, commonly employed for cermet anodes, during the hydrogen reduction reaction. We utilized both spherical aberration (Cs) corrected transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observation modes under a controlled gaseous environment. The environmental gas pressure was set to 1 atm (760 Torr), mirroring real-world conditions. To elucidate pre- and post-hydrogen reduction compositional alterations, we conducted elemental mapping using energy-dispersive X-ray spectroscopy (EDS). Our findings indicated that NiO nanoparticles underwent reduction to Ni particles upon heat treatments in an environment containing H2 gas. Significantly, this reduction of NiO led to the migration of Ni along the external surface of each composite particle, ultimately resulting in the agglomeration at the interparticle spaces among the three NiO/YSZ/BZY nanocomposite particles.

Microstructure evolution of a Cr-Cr/Mo coated Zr alloys in inert gas and steam environment at high temperature

The Cr/Mo multilayer coating was applied as a diffusion barrier for Cr-coated Zr alloys. The barrier effect and eutectic resistance of the Cr/Mo multilayer were evaluated by annealing the samples up to 1400 °C in an inert gas and steam environment. The microstructure at the interface between the Cr/Mo multilayer and Zr substrate was analyzed by spherical aberration corrected transmission electron microscope (AC-TEM). After high temperature annealing, an interlayer composed of Cr-Mo-Zr mixed phases formed between the coating and Zr substrate. The atomic-resolution EDS revealed that the proportion of Cr, Mo, and Zr in the interlayer was 4:2:3. The growth of the Cr-Mo-Zr interlayer obeyed a parabolic law. The consumption rate of the outer Cr coating was compared to that of Cr coated Zr alloy samples without a Cr/Mo barrier layer. Results show that the Cr/Mo interlayer successfully reduced the Cr-Zr inter-diffusion and eutectic reaction.

Ni‐Pt Bimetallic Alloy Nanoparticles Dispersed Uniformly on Carbon Nanotubes for Efficient Electrooxidation Methanol

AbstractIn this paper, Ni−Pt bimetallic alloy nanoparticles were loaded on carbon nanotubes to construct Ni−Pt nanoparticles/carbon nanotubes (Ni−Pt NPs/CNTs) composites as excellent catalytic materials for methanol electrooxidation reaction (MOR). X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and special aberration corrected transmission electron microscope (STEM) were employed to investigate the morphology of the material. It was confirmed that the Ni−Pt alloy nanoparticles dispersed uniformly on the surface of carbon nanotubes. The activity and stability of Ni−Pt NPs/CNTs composites were measured by chronoamperometry (CA), linear sweep voltammetry (LSV) and cyclic voltammetry (CV). The catalytic performance was explored by adjusting the ratio of Ni to Pt. The Ni1Pt2 NPs/CNTs composite showed excellent performance for MOR. Its mass activity for MOR was 1255 mA ⋅ mg−1Pt, which was 2.76, 2.56 times as that of commercial Pt/C, Pt black catalyst, respectively. Moreover, the resistance to CO toxicity of Ni1Pt2 NPs/CNTs composite was better than commercial Pt/C and Pt black catalyst.

Ligand Modulation of Active Sites to Promote Cobalt-Doped 1T-MoS2 Electrocatalytic Hydrogen Evolution in Alkaline Media.

Highly efficient hydrogen evolution reaction (HER) electrocatalyst will determine the mass distributions of hydrogen-powered clean technologies, while still faces grand challenges. In this work, a synergistic ligand modulation plus Co doping strategy is applied to 1T-MoS2 catalyst via CoMo-metal-organic frameworks precursors, boosting the HER catalytic activity and durability of 1T-MoS2 . Confirmed by Cs corrected transmission electron microscope and X-ray absorption spectroscopy, the polydentate 1,2-bis(4-pyridyl)ethane ligand can stably link with two-dimensional 1T-MoS2 layers through cobalt sites to expand interlayer spacing of MoS2 (Co-1T-MoS2 -bpe), which promotes active site exposure, accelerates water dissociation, and optimizes the adsorption and desorption of H in alkaline HER processes. Theoretical calculations indicate the promotions in the electronic structure of 1T-MoS2 originate in the formation of three-dimensional metal-organic constructs by linking π-conjugated ligand, which weakens the hybridization between Mo-3d and S-2p orbitals, and in turn makes S-2p orbital more suitable for hybridization with H-1s orbital. Therefore, Co-1T-MoS2 -bpe exhibits excellent stability and exceedingly low overpotential for alkaline HER (118 mV at 10 mA cm-2 ). In addition, integrated into an anion-exchange membrane water electrolyzer, Co-1T-MoS2 -bpe is much superior to the Pt/C catalyst at the large current densities. This study provides a feasible ligand modulation strategy for designs of two-dimensional catalysts.

Ligand Modulation of Active Sites to Promote Cobalt‐Doped 1T‐MoS2 Electrocatalytic Hydrogen Evolution in Alkaline Media

AbstractHighly efficient hydrogen evolution reaction (HER) electrocatalyst will determine the mass distributions of hydrogen‐powered clean technologies, while still faces grand challenges. In this work, a synergistic ligand modulation plus Co doping strategy is applied to 1T−MoS2 catalyst via CoMo‐metal‐organic frameworks precursors, boosting the HER catalytic activity and durability of 1T−MoS2. Confirmed by Cs corrected transmission electron microscope and X‐ray absorption spectroscopy, the polydentate 1,2‐bis(4‐pyridyl)ethane ligand can stably link with two‐dimensional 1T−MoS2 layers through cobalt sites to expand interlayer spacing of MoS2 (Co−1T−MoS2‐bpe), which promotes active site exposure, accelerates water dissociation, and optimizes the adsorption and desorption of H in alkaline HER processes. Theoretical calculations indicate the promotions in the electronic structure of 1T−MoS2 originate in the formation of three‐dimensional metal‐organic constructs by linking π‐conjugated ligand, which weakens the hybridization between Mo‐3d and S‐2p orbitals, and in turn makes S‐2p orbital more suitable for hybridization with H‐1s orbital. Therefore, Co−1T−MoS2‐bpe exhibits excellent stability and exceedingly low overpotential for alkaline HER (118 mV at 10 mA cm−2). In addition, integrated into an anion‐exchange membrane water electrolyzer, Co−1T−MoS2‐bpe is much superior to the Pt/C catalyst at the large current densities. This study provides a feasible ligand modulation strategy for designs of two‐dimensional catalysts.

Atomic-scale imaging of electron sensitive zeolites with aberration corrected transmission electron microscopy

The spatial resolution of transmission electron microscopes (TEMs) and scanning transmission electron microscopes (STEMs) has been drastically improved by introducing aberration correction. However, observable range in electron sensitive zeolites are still limited due to electron irradiation damages. Nevertheless, atomic resolution imaging of some zeolites is currently being realized by various developments in electron microscopic hardware, such as high sensitivity cameras. On the other hand, surveying the status of TEM and STEM imaging is very important for further progress in the structural analysis of zeolites. Here, we demonstrate and compare the high-resolution imaging of zeolites with several kinds of imaging modes.

Atomic insight into the BEOL thermal budget on phase transition of phase change memory cells

Research works on phase change random access memory (PCRAM) based on Ge–Sb–Te (GST) phase change materials have achieved exciting progress, but the industrialization of PCRAM still faces big challenges, including unsatisfied endurance property or unexpected cell structure failure during fabrication. Here, we investigate the impact of the thermal budget in back-end-of-line (BEOL) process on the microstructure evolution of carbon doped GST (CGST) cells. We demonstrate that the as-deposited amorphous CGST in the confined memory cell will transform to face centered-cubic (FCC) phase with uniform grain size during high temperature up to 400 °C in the BEOL process. However, if there is much more unexpected thermal budget during the BEOL process, the FCC-CGST grains will further grow and transform to highly ⟨0001⟩ oriented single crystalline hexagonal (HEX) GST, together with the formation of voids, leading to the structure failure of the storage cells. By virtue of the advanced spherical aberration corrected transmission electron microscopy (Cs-TEM), we find that there are randomly stacked seven-layered and nine-layered atomic arrangements in single crystalline HEX-GST, corresponding to the chemical stoichiometry of Ge2Sb2Te5 and Ge1Sb2Te4, respectively. Interestingly, twin crystal with the coexistence of vacancy-ordered FCC-GST and HEX-GST on the different twin boundary is observed, indicating that the twin crystals play a critical role in the coalescence and the growth of FCC-GST. This work not only sheds light on the structure failure mechanism of GST cell but also provided additional insight into the formation of HEX-phase in a confined GST memory cell.

Study on the preparation of ceramic membrane support and its Fe migration rule by high‐aluminum fly ash as raw material

AbstractIn order to reduce the cost of ceramic membrane support, ceramic membrane support was prepared using high‐aluminum fly ash as raw material, and its Fe migration rules during the preparation process are studied. The effects of sintering temperature, pore forming agent content, and binder content on the properties of support, such as porosity, pore size, bending strength and water flux have been investigated. The optimum contents of high‐aluminum fly ash, pore forming agent and binder in the ceramic membrane support are 95%, 4%, and 1% respectively, and its sintering temperature is 1300°C. The porosity, bending strength, pore size, and water flux of the prepared support are 37%, 22 MPa, 665 nm, and 2800 L/h·m2·MPa, respectively. X‐ray powder diffractometer, X‐ray fluorescence spectrometer, X‐ray photoelectron spectrometer, inductively coupled plasma spectrometer, transmission electron microscope, spherical aberration corrected transmission electron microscopy, and laser Raman spectroscopy were used to characterize the support and Fe existing morphology in it. The results show that the main phases of sintered support are mullite, corundum, and silica. Massive mullite is produced when the sintering temperature reaches 1200°C. The content of mullite increases with increasing sintering temperature. About 7.7 % content of total Fe in the support exists in the form of Fe2O3. About 92.3% content of total Fe is dissolved into mullite. Fe is evenly distributed in mullite, and it is enriched at the grain boundary by element segregation. Fe in mullite is difficult to dissolve under strong acid conditions, so its stability is very strong.

Photocatalytic Co‐Reduction of N2 and CO2 with CeO2 Catalyst for Urea Synthesis

AbstractThe effective conversion of carbon dioxide (CO2) and nitrogen (N2) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO2‐x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H2 (90 % : 10 %) atmosphere, enhancing the targeted adsorption and activation of N2 and CO2 by introducing oxygen vacancies. Particularly, CeO2‐500 (CeO2 nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C−N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 μg/h. Besides, both aberration corrected transmission electron microscopy (AC‐TEM) and Fourier transform infrared (FT‐IR) spectroscopy were used to research the atomic surface structure of CeO2‐500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C−N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.

Photocatalytic Co-Reduction of N2 and CO2 with CeO2 Catalyst for Urea Synthesis.

The effective conversion of carbon dioxide (CO2 ) and nitrogen (N2 ) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO2-x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H2 (90 % : 10 %) atmosphere, enhancing the targeted adsorption and activation of N2 and CO2 by introducing oxygen vacancies. Particularly, CeO2 -500 (CeO2 nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C-N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 μg/h. Besides, both aberration corrected transmission electron microscopy (AC-TEM) and Fourier transform infrared (FT-IR) spectroscopy were used to research the atomic surface structure of CeO2 -500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C-N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.

Interaction mechanism between immiscible Fe-Mg element diffusion and crystal defect annihilation in the steel/Mg composite interface region

Crystal defect-induced elemental diffusion between immiscible metals is the key to achieve metallurgical bonding. However, the interaction between immiscible element diffusion and crystal defect annihilation is unclear. In this paper, in-situ heat treatment experiments were conducted at the steel/Mg composite interface by ambient atmosphere spherical aberration corrected transmission electron microscope. The immiscible element diffusion phenomenon and crystal defect annihilation phenomenon in the composite interface region were studied, and the interaction mechanism was revealed. The results show that during the heat treatment, the diffusion of Mg element to the steel side is obvious, while the diffusion of Fe element to the Mg side is not obvious, which is called “one-way selective diffusion effect”. The annihilation rate of steel crystal defects is much smaller than that of Mg. The stable crystal defects of steel in the interface region can provide a channel for Mg elements diffusion, while the faster annihilation rate of Mg crystal defects causes Fe elements to hardly diffuse into Mg. The Mg elements that have diffused into the steel side have a pinning effect on dislocations and grain boundary movement, which in turn increases the thermal stability of the steel crystal defects. This study provides theoretical guidance for promoting the element diffusion at the immiscible metals composite interface.

Observation of in-plane oriented Guinier-Preston zones in Al-Cu

Known for a long time, the first metastable precipitate which forms in Al-Cu alloys during natural ageing are the so-called Guinier-Preston zones (GPZ), platelets of Cu on {100} planes of only one atomic layer thickness. Only with the development of aberration corrected transmission electron microscopes (TEM), direct observation and imaging of these platelets was possible, but with the restriction, that only edge view was possible. Here we show that under appropriate conditions an observation in a plan-view is possible and allows further insight into the shape and arrangement of the GP-zones. Furthermore, this demonstrates that single atom detection of one Cu atom in a column of Al atoms is possible.

Recognizing the formation of single-atom vanadium by enthalpy and its advantage in selective catalytic reduction of nitrogen oxide

Developing a more effective catalyst for the environmental pollutant is always the pursuit of worldwide researchers. In previous reports, most works were focused on prepared catalysts, and more efforts should explore process from a precursor to the formed catalyst. In this work, V supported TiO2 catalysts were synthesized with different V loadings, and compared in selective catalytic reduction of nitrogen oxide. For the first time, differential scanning calorimetry was used to analyze the forming enthalpy for these catalysts. As a result, turnover frequency (TOF) was decreased from 0.05 to 0.001 s−1 when the loading was increased from 0.05 to 15 mol%. At the same time, the forming enthalpy was decreased from 16.53 to 1.80 KJ·mol−1. Spherical Aberration Corrected Transmission Electron Microscope recognized both single-atom and cluster V even at the lowest loading. What’s more, density functional theory revealed that single-atom V had a lower dehydrogenation energy (1.088–1.152 eV) than cluster V during the catalysis (1.834–1.850 eV). According to these evidences, single-atom V had bigger formation enthalpy, lower dehydrogenation energy, and larger TOF than cluster V. These results help to optimize the preparation process for an effective catalyst, which is in favor of hazardous-pollutant treatment.

Origin of the bias instability in CsPbI3 light-emitting diodes

With the rapid development of all-inorganic CsPbX3 (X = I, Br, and Cl) perovskite light-emitting diodes (PeLEDs), their external quantum efficiency (EQE) has made great progress in the last few years. However, severe performance degradation at the operation condition impedes its large-scale industrial application. In this text, by using the advanced spherical aberration corrected transmission electron microscope (TEM), the degradation pathway of PeLEDs under bias loading was more systematically and comprehensively, especially from the viewpoint of its microstructural evolution pathway, which showed that iodine vacancy migration triggered the structural collapse was the primary inducement of performance decay. To solve this problem, inorganic termination ZnI2 was employed to passivate the surface halide vacancy defects and supplement the halide ion into the lattice, which significantly improves the photoluminescence (PL) lifetime and stability of CsPbI3 quantum dots (QDs). As expected, not only the EQE of PeLEDs has been greatly improved, but also the operating half-lifetime is enhanced by about 4 times as compared with the original one. Microstructural characterization and density functional (DFT) calculations confirm that the preferential segregation of Zn element on the surface of QDs was the principal cause to passivate the defect state of QDs, which exhibits lower formation energy and better operational stability.