Formation Of Structural Defects Research Articles

Preparation of N and O doped coal tar pitch based porous carbon for supercapacitor electrode

Coal tar pitch (CTP) is mainly composed of a mixture of polycyclic aromatic hydrocarbons, is almost hydrophobic, and has a low heteroatom content, which limits its surface function. During carbonization, it is prone to condensation and difficult to form pore structures, resulting in poor electrochemical performance for carbon electrode materials. Herein, nitrogen (N) and oxygen (O) doped hierarchical porous carbon (C-ANOCTP) was prepared by HNO3 oxidation and KOH activation using CTP as carbon precursor. The oxidation of HNO3 remarkably increases the hydrophilic functional groups containing N and O on the surface of CTP, improves the hydrophilicity of CTP surface, facilitates the activation process of KOH, promotes the development of carbon material pore structure and the generation of active sites, as well as the formation of defect structures. The specific surface area of C-ANOCTP obtained is 1130 m2/g, with O content of 10.29 at% and N content of 2.37 at%. The specific capacitance of C-ANOCTP in a three-electrode system with 6 M KOH electrolyte is as high as 410.51 F/g at 0.5 A/g. A symmetric supercapacitor is assembled in a 6 M KOH electrolyte using C-ANOCTP as electrode. When the power density is 25 W/kg, the energy density is 10.24 Wh/kg. After 10,000 cycles, the capacitance retention rate is still 90.03% and the coulomb efficiency is 100%. The high N and O content of porous carbon is prepared by simple HNO3 oxidation synergistic KOH activation and low temperature carbonization, which shows excellent electrochemical properties in supercapacitors, making CTP an ideal candidate material for high energy density supercapacitors.

The importance of ammonium and potassium ions under hydrothermal preparation conditions on the structure and corrosion properties of CaP coatings

CaP coatings were hydrothermally deposited on the AZ31 magnesium alloy in rection mixture containing ammonium or potassium ions. CaP coatings were deposited on AZ31 alloy in reaction mixture at pH 5 and 7 with and without EDTA chelating agent. It was found that the ammonium ions present have a negative effect on the quality of the CaP coating deposited from mixture at pH 7 and their presence at neutral environment results in the formation of structural defects in the coatings. At the same time, the presence of ammonium ions suppresses hydrolysis and crystallization of OCP and HAp. However, pH and the presence of EDTA have a more pronounced effect on the structure and phase composition. The coatings deposited in the reaction mixture, containing potassium-based precursors and EDTA, at pH 7 showed the best thermal stability due to the majority of HAp phase. The uniform CaP coating deposited in the reaction mixture containing EDTA and K+ ions at pH 7 also achieved the best corrosion properties due to the absence of structural defects and dense structure.

Reductive Doping Inhibits the Formation of Isomerization-Derived Structural Defects in N-doped Poly(benzodifurandione) (n-PBDF).

Recently, solution-processable n-doped poly(benzodifurandione) (n-PBDF) has been made through in-situ oxidative polymerization and reductive doping, which exhibited exceptionally high electrical conductivities and optical transparency. The discovery of n-PBDF is considered a breakthrough in the field of organic semiconductors. In the initial report, the possibility of structural defect formation in n-PBDF was proposed, based on the observation of structural isomerization from (E)-2H,2'H-[3,3'-bibenzofuranylidene]-2,2'-dione (isoxindigo) to chromeno[4,3-c]chromene-5,11-dione (dibenzonaphthyrone) in the dimer model reactions. In this study, we present clear evidence that structural isomerization is inhibited during polymerization. We reveal that the dimer (BFD1) and the trimer (BFD2) can be reductively doped by several mechanisms, including hydride transfer, forming charge transfer complexes (CTC) or undergoing an integer charge transfer (ICT) with reactants available during polymerization. Once the hydride transfer adducts, the CTC, or the ICT product forms, structural isomerization can be effectively prevented even at elevated temperatures. Our findings provide a mechanistic understanding of why isomerization-derived structural defects are absent in n-PBDF backbone. It lays a solid foundation for the future development of n-PBDF as a benchmark polymer for organic electronics and beyond.

Reductive Doping Inhibits the Formation of Isomerization‐Derived Structural Defects in N‐doped Poly(benzodifurandione) (n‐PBDF)

AbstractRecently, solution‐processable n‐doped poly(benzodifurandione) (n‐PBDF) has been made through in‐situ oxidative polymerization and reductive doping, which exhibited exceptionally high electrical conductivities and optical transparency. The discovery of n‐PBDF is considered a breakthrough in the field of organic semiconductors. In the initial report, the possibility of structural defect formation in n‐PBDF was proposed, based on the observation of structural isomerization from (E)‐2H,2′H‐[3,3′‐bibenzofuranylidene]‐2,2′‐dione (isoxindigo) to chromeno[4,3‐c]chromene‐5,11‐dione (dibenzonaphthyrone) in the dimer model reactions. In this study, we present clear evidence that structural isomerization is inhibited during polymerization. We reveal that the dimer (BFD1) and the trimer (BFD2) can be reductively doped by several mechanisms, including hydride transfer, forming charge transfer complexes (CTC) or undergoing an integer charge transfer (ICT) with reactants available during polymerization. Once the hydride transfer adducts, the CTC, or the ICT product forms, structural isomerization can be effectively prevented even at elevated temperatures. Our findings provide a mechanistic understanding of why isomerization‐derived structural defects are absent in n‐PBDF backbone. It lays a solid foundation for the future development of n‐PBDF as a benchmark polymer for organic electronics and beyond.

A Comprehensive Study of Al2O3 Mechanical Behavior Using Density Functional Theory and Molecular Dynamics.

This study comprehensively investigates Al2O3's mechanical properties, focusing on fracture toughness, surface energy, Young's modulus, and crack propagation. The density functional theory (DFT) is employed to model the vacancies in Al2O3, providing essential insights into this material's structural stability and defect formation. The DFT simulations reveal a deep understanding of vacancy-related properties and their impact on mechanical behavior. In conjunction with molecular dynamics (MD) simulations, the fracture toughness and crack propagation in Al2O3 are explored, offering valuable information on material strength and durability. The surface energy of Al2O3 is also assessed using DFT, shedding light on its interactions with the surrounding environment. The results of this investigation highlight the significant impact of oxygen vacancies on mechanical characteristics such as ultimate strength and fracture toughness, drawing comparisons with the effects observed in the presence of aluminum vacancies. Additionally, the research underscores the validation of fracture toughness outcomes derived from both DFT and MD simulations, which align well with findings from established experimental studies. Additionally, the research underscores the validation of fracture toughness outcomes derived from DFT and MD simulations, aligning well with findings from established experimental studies. The combination of DFT and MD simulations provides a robust framework for a comprehensive understanding of Al2O3's mechanical properties, with implications for material science and engineering applications.

Microstructures and improved properties of Cu–Mo alloys induced by high current pulsed electron beam irradiation

In this paper, a Cu–Mo alloying layer with improved properties was fabricated by high current pulsed electron beam (HCPEB) irradiation. The microstructure of the modified layer was investigated by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The microhardness and friction properties were also measured. After HCPEB irradiation, nano Mo particles, solid solution, and long-period superlattice structures were generated on the surface of Cu–Mo alloys, together with the formation of defect structures. These microstructures led to a significant increase in the surface hardness. The results of sliding wear tests indicated that the HCPEB-irradiated samples exhibited better properties compared with the initial one, which was attributed to the ultrafine Mo particles and the hardened surface.

Insights into structural defect formation in individual InP/ZnSe/ZnS quantum dots under UV oxidation

InP/ZnSe/ZnS quantum dots (QDs) stand as promising candidates for advancing QD-organic light-emitting diodes (QLED), but low emission efficiency due to their susceptibility to oxidation impedes applications. Structural defects play important roles in the emission efficiency degradation of QDs, but the formation mechanism of defects in oxidized QDs has been less investigated. Here, we investigated the impact of diverse structural defects formation on individual QDs and propagation during UV-facilitated oxidation using high-resolution (scanning) transmission electron microscopy. UV-facilitated oxidation of the QDs alters shell morphology by the formation of surface oxides, leaving ZnSe surfaces poorly passivated. Further oxidation leads to the formation of structural defects, such as dislocations, and induces strain at the oxide-QD interfaces, facilitating In diffusion from the QD core. These changes in the QD structures result in emission quenching. This study provides insight into the formation of structural defects through photo-oxidation, and their effects on emission properties of QDs.

Natural formation of linear defect structures in MoS2

Near surface defects can significantly impact the quality of metallic interconnects and other interfaces necessary to create device structures incorporating two-dimensional materials. Furthermore, the impact of such defects can strongly depend on their organization. In this study, we present scanning tunneling microscopy images and tunneling spectroscopy of point and linear defects near the surface of natural MoS2. The point defects share similar structural and electronic characteristics and occur with comparable frequency as subsurface sulfur vacancies observed previously on natural MoS2. The linear defects observed here occur less frequently than the point defects but share the same depth profile and electronic structure. These data indicate that the linear defects are actually a one-dimensional organization of subsurface sulfur vacancies. Our density functional calculations agree with this assessment in that, for sufficient local defect concentrations, it is energetically more favorable for the defects to be organized in a linear fashion rather than as clusters or even isolated single point defects. Given these measurements were taken from naturally formed MoS2, this organization likely occurs during crystal formation. Considering the impact of one-dimensional organization on the local properties of layered materials, and the potential for them to be introduced purposefully during crystal formation, research into the formation mechanism and properties of these defects could enable new paths for defect engineering in MoS2-based systems.

Defect detection by multi-axis infrared process monitoring of laser beam directed energy deposition

Laser beam directed energy deposition (DED-LB) is an attractive additive manufacturing technique to produce versatile and complex 3D structures on demand, apply a cladding, or repair local defects. However, the quality of manufactured parts is difficult to assess by inspection prior to completion, and parts must be extensively inspected post-production to ensure conformance. Consequently, critical defects occurring during the build go undetected. In this work, a new monitoring system combining three infrared cameras along different optical axes capable of monitoring melt pool geometry and vertical displacement throughout deposition is reported. By combining multiple sensor data, an automated algorithm is developed which is capable of identifying the formation of structural features and defects. An intersecting, thin-walled geometry is used to demonstrate the capability of the system to detect process-induced porosity in samples with narrow intersection angles, which is validated using micro-CT observations. The recorded results indicate the root cause of this process-induced porosity at the intersection, and it is shown that advanced toolpath planning can eliminate such defects. The presented methodology demonstrates the value of multi-axis monitoring for identifying both defects and structural features, providing an advancement towards automated detection and alert systems in DED-LB.

Graphene‐Based Lateral Heterojunctions for 2D Integrated Circuits

AbstractA method for patterning single‐layer graphene (SLG) and single‐layer oxidized graphene (SOG) within a continuous atomic layer to form lateral heterojunctions is presented. Raman spectroscopy is employed to investigate the evolution of defect‐related Raman peaks during excimer‐UV irradiation, facilitating the identification of structural changes and defect formation processes. Electrical transport measurements reveal that SOG‐patterned field‐effect transistors (FETs) exhibit varying characteristics depending on the degree of oxidation, thus offering the potential to tailor the electrical properties of graphene devices for specific requirements. Scanning Kelvin probe microscopy measurements reveal the surface potential and work function of the SOG regions compared with those of SLG. The effective functionality of the SOG pattern to operate as a resistor, allowing control of the electrical conductivity in the SOG‐patterned SLG channels, is demonstrated. This capability restricts the current flow while preserving the pristine electrical properties of the graphene channel. Moreover, the SOG pattern can serve as a potential barrier to constructing SLG‐SOG‐patterned integrated circuits, providing exciting opportunities for engineering advanced electronic components. This breakthrough in graphene devices simplifies the fabrication process of graphene‐based FETs and provides the foundation for developing atomically thin integrated circuits for a wide range of applications.

Grazing-incidence synchrotron radiation diffraction studies on irradiated Ce-doped and pristine Y-stabilized ZrO2 at the Rossendorf beamline.

In this work, Ce-doped yttria-stabilized zirconia (YSZ) and pure YSZ phases were subjected to irradiation with 14 MeV Au ions. Irradiation studies were performed to simulate long-term structural and microstructural damage due to self-irradiation in YSZ phases hosting alpha-active radioactive species. It was found that both the Ce-doped YSZ and the YSZ phases had a reasonable tolerance to irradiation at high ion fluences and the bulk crystallinity was well preserved. Nevertheless, local microstrain increased in all compounds under study after irradiation, with the Ce-doped phases being less affected than pure YSZ. Doping with cerium ions increased the microstructural stability of YSZ phases through a possible reduction in the mobility of oxygen atoms, which limits the formation of structural defects. Doping of YSZ with tetravalent actinide elements is expected to have a similar effect. Thus, YSZ phases are promising for the safe long-term storage of radioactive elements. Using synchrotron radiation diffraction, measurements of the thin irradiated layers of the Ce-YSZ and YSZ samples were performed in grazing incidence (GI) mode. A corresponding module for measurements in GI mode was developed at the Rossendorf Beamline and relevant technical details for sample alignment and data collection are also presented.

Framework confinement of multi-metals within silica hollow spheres by one-pot synthesis process

ABSTRACT The control incorporation of metals in silica hollow spheres (SHSs) may bring new functions to silica mesoporous structures for applications including catalysis, sensing, molecular delivery, adsorption filtration, and storage. However, the strategies for incorporating metals, whether through pre-loading in the hollow interior or post-encapsulation in the mesoporous shell, still face challenges in achieving quantitative doping of various metals and preventing metal aggregation or channel blockage during usage. In this study, we explored the doping of different metals into silica hollow spheres based on the dissolution-regrowth process of silica. The process may promote the formation of more structural defects and functional silanol groups, which could facilitate the fixation of metals in the silica networks. With this simple and efficient approach, we successfully achieved the integration of ten diverse metal species into silica hollow sphere (SHS). Various single-metal, dual-metal, triple-metal, and quadruple-metal doped SHSs have been prepared, with the doped metals being stable and homogeneously dispersed in the structure. Based on the structural characterizations, we analyzed the influence of metal types on the morphology features of SHSs. The synergistic effects of multi-metals on the catalysis applications were also studied and compared.

Improved Lewis Acidity Using Ionic Liquid-Grafted Bimetallic Zr/Ti Uio-66 Fillers for Composite Solid Electrolytes

In recent years, solid-state lithium batteries have gained significant attention due to their high energy density and stability. However, challenges such as low ionic conductivity, non-homogeneous Li ion flux, and low interfacial compatibility of solid electrolytes still remain. Composite solid electrolytes (CSEs) have emerged as a potential solution to these issues, by combining an inorganic filler with a polymer matrix. To develop high-performance CSEs, extensive research has been conducted on inorganic active fillers with an abundance of Lewis acidic sites. The acidic sites of the filler can induce Lewis acid-base interactions, which can decrease the crystallinity of fillers by weakening the attraction between polymer segments and increasing chain mobility. Additionally, they increase the degree of dissociation of lithium salt, resulting in an increase in ionic conductivity. In terms of the concentration gradient of Li-ions, the free anion of lithium salt can be trapped by an acidic filler, thereby reducing the mobility and concentration of the anion. Finally, the acidic filler prevents the oxidation of ether oxygen groups in PEO, thus, improves its electrochemical stability. Furthermore, for increasing the ionic conductivity, inorganic filler should be an active filler capable of serving as Li-ion sources to the interfacial region between polymeric matrix and inorganic fillers, thereby facilitating Li-ion transport. Consequently, Li-ions can hop along the surface of active fillers. Therefore, in order to achieve high-performance CSEs with a polymer matrix, inorganic active fillers with an abundance of acidic sites have emerged as one of the most effective strategies for designing high performance fillers with good compatibility with the matrix. To address this technological need, in this work, we present a novel CSE based on a polyethylene oxide (PEO) matrix with a bimetallic (Zr/Ti) UiO-66-ionic liquid grafted filler (BUIL) that simultaneously modified the metal and ligand sites of UiO-66 MOF particles. The bimetallic structure of BUIL was prepared by replacing the metal sites of UiO-66 with Ti metal ions using the metal exchange method, resulting in the formation of more structural defects and an increase in the number of Lewis acid sites of filler. In addition, the pre-synthesized ionic liquids containing a -OH functional group (IL-OH), N-hydroxyhexyl-N’-methyl imidazolium bis(trifluoromethylsulfonyl)imide, were grafted when synthesizing UiO-66 with a ligand containing a -Br functional group. The BUIL filler functions as a high Lewis acid filler owing to its bimetallic structure and grafted ionic liquid. Also, to utilize BUIL as an active filler, lithium bis(trifluoromethanesulfonyl)imide/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (IL, LiTFSI/EMIM-TFSI) was loaded into BUIL (IL@BUIL). In order to confirm the effect of Lewis acid filler interaction on PEO polymer matrix and lithium salt, various spectroscopic characterization methods were employed. As a result, CSEs containing IL@BUIL filler and PEO matrix exhibited markedly improved ionic conductivity, lithium-ion transference number, electrochemical stability, and long-cycle stability of Li metal electrode. After optimization, the ionic conductivity of CSEs at 30°C was enhanced to 0.458 mS cm-1, the lithium-ion transference number was raised to 0.668, and the electrochemical stability window was widened to 4.5 V. In addition, during a continuous plating/stripping test, the lithium metal symmetric cell of CSEs stably cycled for 500 h at a current density of 0.2 mA cm-2. Finally, LiFePO4/IL@BUIL/Li cell shows a capacity of 148 mA h g-1 at 1C.The present strategy of simultaneously modifying the metal and the ligand sites of MOF to improve the properties of CSEs can be used as a general platform for the design of a MOF filler in CSEs system, as well as a guideline for the next generation CSEs.

Effect of Film Thickness on Microstructural and Magnetic Properties of Lithium Ferrite Films Prepared on Strontium Titanate (001) Substrates

Epitaxial lithium ferrite (LiFe5O8) films with different thicknesses were successfully fabricated on strontium titanate (SrTiO3) (001) substrates using the magnetron sputtering deposition technique. The microstructural and magnetic properties of the films were characterized by an advanced transmission electron microscope and a magnetic measurement device. It was found that the formation of structural defects can be influenced by the thickness of the film. In addition to misfit dislocations, orientation domains form in thinner films and twin boundaries appear in thicker films, respectively, contributing to the misfit strain relaxation in the heterosystem. The magnetic measurement showed that the thinner films have enhanced magnetization and a relatively lower coercive field compared with the thicker films containing antiferromagnetic twin boundaries. Our results provide a way of tuning the microstructure and magnetic properties of lithium ferrite films by changing the film thickness.

Material Removal Mechanism and Evolution of Subsurface Defects during Nanocutting of Monocrystalline Cu

Multigroup large-scalenanocutting models of monocrystalline Cu were established by molecular dynamics simulations to investigate the influence of cutting parameters on the material removal mechanism. The formation and distribution of subsurface defect structures were revealed, and the evolution behavior of the complete prismatic dislocation loop was analyzed in depth. It was demonstrated that the chips and machined surface of monocrystalline Cu were mainly formed under the coupling effect of shearing and extrusion forces. A diamond tool with a larger edge radius or a negative rake angle could produce a noticeable suppression on the chip formation. The corresponding relationship between the location of defect atoms and the distribution of von Mises stress was studied, which indicated that the shear stress would become larger at the subgrain boundaries, dislocation lines, and the amorphous atoms than that in their nearby regions. The complete prismatic dislocation loop was formed by cross-slip between two sets of stacking faults; meanwhile, the generated multiple Lomer–Cottrell locks hindered its movement and promoted the work-hardening phenomenon. These research results are of great theoretical value to enrich the nanocutting mechanism and technology of plastic materials.

Pore engineering of a Quasi-MOF-801 with unsaturated metal site and modulate porosity for selective and effective phosphate uptake

MOF-801, a highly water-stable metal-organic framework, underwent carefully monitored thermal treatment at temperatures between 240 and 300 °C for the development of defective quasi-MOF. The treatment leads to the formation of structural defects, more porosity, and the elimination of ligands. The resulting quasi-MOF-801, which structurally connects crystalline materials and the associated metal oxides, serves as a unique and very effective phosphate adsorbent thanks to its many free adsorption sites. The findings showed that the free open metals site was crucial in forming the binding with phosphate. Q-M801-280 (quasi MOF-801 heated to 280 °C) exhibited the highest adsorption capacity (415 mg. g−1) with a broad pH range of 3–11 and high phosphate selectivity when there are competing anions present. The created Q801-280 is an effective adsorbent that may be utilized to reduce the growing eutrophication of water through phosphate uptake.

Tuning the ORR catalytic activity of LaFeO3-δ-based perovskite cathode for solid oxide fuel cells by doping with alkaline-earth metal elements

Co-based perovskite cathodes have demonstrated impressive catalytic activity for oxygen reduction reaction (ORR) at intermediate temperatures. However, these cathodes face the challenges such as high cost and thermal expansion coefficient (TEC) mismatch. On the other hand, Fe-based perovskite oxides like LaFeO3 exhibit more stable properties and lower TEC, but their ORR activity is not as remarkable as that of Co-based cathodes. In this study, La3+ at the A-site of LaFeO3 was substituted by aliovalent alkaline-earth metal cations. The research findings reveal that the doping of alkaline-earth metal ions induces the formation of structural defects and alters the valence state of Fe. This leads to an increase in the conductivity and oxygen vacancy concentration, which are critical for ORR kinetics in both H–SOFC and O–SOFC. Among the various dopants, Sr doped LaFeO3 (LSrF) exhibits the most outstanding ORR catalytic activity. This can be attributed to its highest total conductivity, O2− conductivity, oxygen surface exchange coefficient, and oxygen bulk diffusion coefficient. At 700 °C, single cell with LSrF cathode achieves peak power densities of 0.781 and 0.894 W cm−2, for O2--conducting solid oxide fuel cell (SOFC) and H+-conducting SOFC, respectively. These performances are essentially twice that of single cell with LaFeO3 cathode. The findings of this study provide valuable insights into doping strategies for Fe-based perovskite cathodes and contribute to the advancement of IT-SOFC cathode research.

Effect of Irradiation with a Pulsed Electron Beam on the Defect Structure Formation and the Properties of the Surface Layer of Zr–Nb–H System Alloys

Effect of Irradiation with a Pulsed Electron Beam on the Defect Structure Formation and the Properties of the Surface Layer of Zr–Nb–H System Alloys

Formation of Structure Inhomogeneities and Defects During Production of Composite Materials Based on Grade2 Titanium Alloy by Friction Stir Processing

Formation of Structure Inhomogeneities and Defects During Production of Composite Materials Based on Grade2 Titanium Alloy by Friction Stir Processing

Ag-Doped Free-Standing 2D TiO2 Sheets: Electronic, Optical, Magnetic, and Self-Healing Behaviour.

Beyond a critical doping level, Ag - 2D TiO2 sheets (ATO) are deemed to be a flexible transparent conductor, useful for visible-range functional photonic/optoelectronic devices/sensors, sunlight-sensitive catalysis, and light-activated resistive switching. Due to the lack of control of surface energy which often leads to the formation of structural defects and even dimensionality crossover (2D to 0D) of materials during doping reaction, it is challenging to obtain ATO with a controlled doping level. Gauging the urgency, therefore we report the surface energy-controlled synthesis of ATO employing liquid phase exfoliation of TiO2 and subsequent hydrothermal Ag-doping in the presence of Hexamethylenetetramine (HMTA). Electron microscopy and atomic force microscopy reveal ATO sheets with large lateral dimensions. 6-fold, 4-fold, and strain-mediated crystallographic phases of 2D ATO have been revealed by high-resolution electron imaging. Successful tuning of the band gap down to ~ 2 eV with Ag doping up to ~ 10% is obtained. Synthesized 2D ATO have been investigated for their electrical, optical, optoelectronic, photoluminescence, and ferromagnetic behaviour. Visible light-sensitive thermally/structurally robust semiconductor/conductor via tuneable doping will pave the way for their flexible as well as wearable device applications. Self-healing effect of AFM tip-generated mechanical stress has also been demonstrated.