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Grain growth in strontium titanate in electric fields: the impact of space-charge on the grain-boundary mobility
摘要： The present study investigates grain growth in the perovskite oxide strontium titanate in an electric field. The seeded polycrystal technique was chosen as it provides a sensitive and controlled setup to evaluate the impact of different parameters on grain growth due to the well-defined driving force for grain growth. Current blocking electrodes were used to prevent Joule heating. The results show faster grain growth, and thus, higher grain-boundary mobility at the negative electrode. It is argued that the electric field causes point-defect redistribution, resulting in a higher oxygen vacancy concentration at the negative electrode. The local oxygen vacancy concentration is suggested to affect the space-charge potential at the grain-boundaries. A thermodynamic treatment of the grain-boundary potential at a grain-boundary without field shows that for a high oxygen vacancy concentration less space-charge and less accumulation of cationic defects to the boundary occurs. Therefore, at the negative electrode, a higher oxygen vacancy concentration results in less space-charge and less accumulation of cationic defects. The lower degree of defect accumulation requires less diffusion of segregated defects during grain-boundary migration, so that at the negative electrode faster grain growth is expected, as found in the experiments.
关键词： field assisted,segregation,defects,space-charge,grain-boundaries,grain growth
更新于2025-09-10 09:29:36
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Atomic Structure and Electrical Activity of Grain Boundaries and Ruddlesden-Popper Faults in Cesium Lead Bromide Perovskite
摘要： To evaluate the role of planar defects in lead-halide perovskites—cheap, versatile semiconducting materials—it is critical to examine their structure, including defects, at the atomic scale and develop a detailed understanding of their impact on electronic properties. In this study, postsynthesis nanocrystal fusion, aberration-corrected scanning transmission electron microscopy, and first-principles calculations are combined to study the nature of different planar defects formed in CsPbBr3 nanocrystals. Two types of prevalent planar defects from atomic resolution imaging are observed: previously unreported Br-rich [001](210)∑5 grain boundaries (GBs) and Ruddlesden–Popper (RP) planar faults. The first-principles calculations reveal that neither of these planar faults induce deep defect levels, but their Br-deficient counterparts do. It is found that the ∑5 GB repels electrons and attracts holes, similar to an n–p–n junction, and the RP planar defects repel both electrons and holes, similar to a semiconductor–insulator–semiconductor junction. Finally, the potential applications of these findings and their implications to understand the planar defects in organic–inorganic lead-halide perovskites that have led to solar cells with extremely high photoconversion efficiencies are discussed.
关键词： Ruddlesden–Popper faults,lead-halide perovskites,scanning transmission electron microscopy,density-functional theory,grain boundaries
更新于2025-09-10 09:29:36
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Handbook of Mechanics of Materials || Surface/Interface Stress and Thin Film Stress
摘要： Thin ?lm stress is critical for the reliability and electronic/optoelectronic properties of thin ?lm devices. In this chapter, we systematically discussed the effects of surface and interface stresses on the ?lm stress development during growth of polycrystalline ?lms at the initial and ?nal growth stage. We demonstrate that surface stress plays an important role at the initial stage of ?lm growth (island growth stage), and conventional stress analysis technology such as wafer curveture experiments may not be applicable at this stage. At the late stage of ?lm growth, we also show that adatom insertion into the grain boundaries is the primary mechanism of compressive stress development.
关键词： interface stress,Thin ?lm stress,adatom insertion,wafer curvature,grain boundaries,surface stress,polycrystalline ?lms
更新于2025-09-10 09:29:36
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High-Temperature Large-Scale Self-Assembly of Highly Faceted Monocrystalline Au Metasurfaces
摘要： Localized surface plasmon resonance (LSPR) devices based on resonant metallic metasurfaces have shown disruptive potential for many applications including biosensing and photocatalysis. Despite significant progress, highly performing Au plasmonic nanotextures often suffer of suboptimal electric field enhancement, due to damping effects in multicrystalline domains. Fabricating well-defined Au nanocrystals over large surfaces is very challenging, and usually requires time-intensive multi-step processes. Here, presented are first insights on the large-scale self-assembly of monocrystalline Au nano-islands with tunable size and separation, and their application as efficient LSPR surfaces. Highly homogeneous centimeter-sized Au metasurfaces are fabricated by one-step deposition and in situ coalescence of hot nanoparticle aerosols into a discontinuous monolayer of highly faceted monocrystals. First insights on the mechanisms driving the high-temperature synthesis of these highly faceted Au nanotextures are obtained by molecular dynamic and detailed experimental investigation of their growth kinetics. Notably, these metasurfaces demonstrate high-quality and tunable LSPR, enabling the fabrication of highly performing optical gas molecule sensors detecting down to 3 × 10?6 variations in refractive index at room temperature. It is believed that these findings provide a rapid, low-cost nanofabrication tool for the engineering of highly homogenous Au metasurfaces for large-scale LSPR devices with application ranging from ultrasensitive optical gas sensors to photocatalytic macroreactors.
关键词： scalable,gold,grain boundaries,crystals,high temperature,sensing,plasmonics
更新于2025-09-09 09:28:46
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Characterization of grain boundary disconnections in SrTiO3 part I: the dislocation component of grain boundary disconnections
摘要： High-resolution transmission electron microscopy is often used to characterize grain boundaries, but it is usually limited to special high symmetry boundaries with a high density of coincident sites. For these ‘special’ boundaries, both crystals can be brought into a low-index zone-axis with the boundary plane parallel to the incident electron beam. In this case the atomistic structure of the boundary can be solved, which is not possible for other, more general grain boundaries. In the present study, general grain boundaries in SrTiO3 were analyzed using aberration-corrected transmission electron microscopy and scanning transmission electron microscopy. These boundaries included at least one type of disconnection (i.e., defects that can have a step and/or a dislocation component). Since the dislocation component of disconnections along general grain boundaries cannot be fully resolved using the methods currently available, a plane matching approach was used to compare disconnections at different boundaries. Using this approach, the dislocation component of the disconnections was partially characterized and was found to have an edge component mainly parallel to {100} and {110}, close to normal to the macroscopic grain boundary plane. The step component of the disconnections was found to be aligned mainly parallel to the same crystallographic planes ({100} and {110}).
关键词： scanning transmission electron microscopy,grain boundaries,transmission electron microscopy,SrTiO3,disconnections
更新于2025-09-09 09:28:46
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Particle size effect on the dielectric properties of ZnO nanoparticles
摘要： Zinc oxide (ZnO) nanoparticles with di?erent particle sizes were synthesized by thermal annealing T A of zinc hydroxide at various temperatures. X-ray di?raction measurements show that all nanoparticles possess a typical wurtzite structure and no other impurity phases are observed. The average particle size (d ) increases from 22 to 98 nm as T A increases from 100 to 850?C. The dielectric properties of nanocrystalline ZnO with various particle sizes were studied in the frequency range of 20 Hz to 1 MHz between 80 K and 320 K. Dielectric measurement indicates that the particle size of samples has great in?uence on the dielectric behavior of ZnO nanoparticles. The M ” curves show strong grain peaks in all ZnO nanoparticles, whereas only 22 nm and 98 nm particles show weak grain boundary peaks. In addition, the ac conductivity (σac) follows Jonscher,s power law for all ZnO nanoparticles, but two types of conduction mechanisms were observed. It is concluded that the σac behavior of 22-nm particles is well accounted by the correlated-barrier-hopping model (CBH), whereas the d >22-nm particles behavior is probably due to Quantum Tunneling Mechanism (QMT). The di?erent σac behavior can be attributed to the various defects in grain boundary and formation of inhomogeneous dielectric structures.
关键词： A. Oxide materials,C. Grain boundaries,B. Precipitation,D. X-ray di?raction,C. Dielectric response,A. Semiconductors
更新于2025-09-09 09:28:46
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Simulation and visualization of crystal shapes and interfaces
摘要： Nature often arranges atoms in the shape of perfect crystals, but sometimes she creates defects and multiple domains. The optimal crystal shape at zero kelvin can be found via the Wul? construction, which can be only be carried out analytically for those trivial cases where next nearest neighbour interactions can be neglected. For our system of interest - videlicit the HCP non-Bravais case, numerical simulation is needed. This system is of relevance because we are modeling helium crystals. We have modeled two adjacent crystallites with di?erent orientations in contact creating twist or tilt grain boundaries, and calculated the surface energy of the interface. Experience gained from several aspects of this project have a wider applications, including the condensed matter simulation application to sample construction for multi-domain crystals, and a visualization one for representation in the presence of grain boundaries. The optimization of sample shapes into their groundstates is also related to wavefront optimization in multimirror telescopes.
关键词： surface energy,interfaces,HCP lattice,Wul? construction,crystal shapes,grain boundaries
更新于2025-09-04 15:30:14