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Evolution of the Structure and Properties of High-Chromium Heat-Resistant VZh159 Alloy Prepared by Selective Laser Melting: Part II
摘要： The evolution of the structural-phase state of the VZh159 alloy fabricated by selective laser melting after various types of thermal exposure and hot isostatic pressing (HIP) is studied. The effect of a long 500-h exposure at temperatures of 800 and 900°C on the phase composition and morphology of structural components is determined. The short-term and long-term strength of the material in various conditions are studied. It is shown that the segregation of dispersed particles of the σ phase after the gas-static treatment followed by aging and after prolonged exposure at high temperatures does not have a significant negative effect on the plastic and strength characteristics of the alloy. The long-term strength of the synthesized metal after the 500-h exposure at a temperature of 900°C corresponds to the certified values for the deformed semifinished product of the VZh159 alloy.
关键词： boride,heat treatment,σ-phase,HIP,gas-static treatment,VZh159,selective laser melting (SLM),transmission electron microscopy,cellular structure
更新于2025-09-19 17:13:59
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Evolution of the Structure and Properties of High-Chromium Heat-Resistant VZh159 Alloy Prepared by Selective Laser Melting: Part I
摘要： The evolution of the structural-phase state of the VZh159 alloy fabricated by selective laser melting after various types of thermal exposure and hot isostatic pressing (HIP) is studied. The effect of a long 500-h exposure at temperatures of 800 and 900°C on the phase composition and morphology of structural components is determined. The short-term and long-term strength of the material in various conditions are studied. It is shown that the segregation of dispersed particles of the σ phase after the gas-static treatment followed by aging and after prolonged exposure at high temperatures does not have a significant negative effect on the plastic and strength characteristics of the alloy. The long-term strength of the synthesized metal after the 500-h exposure at a temperature of 900°C corresponds to the certified values for the deformed semifinished product of the VZh159 alloy.
关键词： σ phase,VZh159,HIP,heat treatment,boride,transmission electron microscopy,gas-static treatment,selective laser melting (SLM),cellular structure
更新于2025-09-19 17:13:59
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Zn1 a?? xCdxS Nanoparticles Obtained by Laser Ablation
摘要： Approximately spherical nanoparticles of the II–VI semiconductor materials Zn1 – xCdxS have been produced successfully by laser ablation of the bulk material in several liquids. The non-stabilized suspensions of particles are characterized by absorption spectroscopy and transmission electron microscopy (TEM). The procedure is not strongly size-selective, radii of 7 ± 3 nm were found for Zn1 – xCdxS by transmission electron microscopy. Acetonitrile stabilizes the particles for several days up to weeks. Prolonged irradiation leads effectively to a reduction in particles size, in which particle agglomeration may play an important role. Ablation in degassed liquids does not have a significant effect on the absorption of the suspended particles.
关键词： Zn1 – xCdxS nanoparticles,laser ablation,absorption spectroscopy,transmission electron microscopy,quantum confinement
更新于2025-09-19 17:13:59
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Influence of Silicon Layers on the Growth of ITO and AZO in Silicon Heterojunction Solar Cells
摘要： In this article, we report on the properties of indium tin oxide (ITO) deposited on thin-film silicon layers designed for the application as carrier selective contacts for silicon heterojunction (SHJ) solar cells. We find that ITO deposited on hydrogenated nanocrystalline silicon (nc-Si:H) layers presents a significant drop on electron mobility μe in comparison to layers deposited on hydrogenated amorphous silicon films (a-Si:H). The nc-Si:H layers are not only found to exhibit a larger crystallinity than a-Si:H, but are also characterized by a considerably increased surface rms roughness. As we can see from transmission electron microscopy (TEM), this promotes the growth of smaller and fractured features in the initial stages of ITO growth. Furthermore, secondary ion mass spectrometry profiles show different penetration depths of hydrogen from the thin film silicon layers into the ITO, which might both influence ITO and device passivation properties. Comparing ITO to aluminum doped zinc oxide (AZO), we find that AZO can actually exhibit superior properties on nc-Si:H layers. We assess the impact of the modified ITO Rsh on the series resistance Rs of SHJ solar cells with >23% efficiency for optimized devices. This behavior should be considered when designing solar cells with amorphous or nanocrystalline layers as carrier selective contacts.
关键词： secondary ion mass spectrometry (SIMS),indium tin oxide (ITO),series resistance,Aluminum doped zinc oxide (AZO),transparent conductive oxide (TCO),transmission electron microscopy (TEM),silicon heterojunction (SHJ)
更新于2025-09-16 10:30:52
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Eutectic Formation, V/III Ratio, and Controlled Polarity Inversion in Nitrides on Silicon
摘要： The crystallographic polarity of AlN grown on Si(111) by plasma-assisted molecular beam epitaxy is intentionally inverted from N-polar to Al-polar at a planar boundary. The position of the inversion boundary is controlled by a two-step growth process that abruptly changes from Al-rich to N-rich growth conditions. The polarity inversion is induced by the presence of Si, which is incorporated from an Al–Si eutectic layer that forms during the initial stages of AlN growth and floats on the AlN surface under Al-rich growth conditions. When the growth conditions change to N-rich, the Al and Si in the eutectic react with the additional N-flux and are incorporated into the solid AlN film. Relatively low levels of Al–Si eutectic formation combined with lateral variations in the Si incorporation lead to nonuniformity in the polarity inversion and formation of surprisingly narrow, vertical inversion domains. The results suggest that intentional incorporation of uniform layers of Si may provide a method for producing polarity engineered nitride structures.
关键词： AlN,Si incorporation,scanning transmission electron microscopy,polarity inversion,nitride structures,eutectic layer
更新于2025-09-16 10:30:52
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Phase transformation at controlled locations in nanowires by in situ electron irradiation
摘要： Solid state phase transformations have drawn great attention because they can be effectively exploited to control the microstructure and property of materials. Understanding the physics of such phase transformation processes is critical to designing materials with controlled structure and with desired properties. However, in traditional ex situ experiments, it is hard to achieve position controlled phase transformations or obtain desirable crystal phase on nanometer scale. Meanwhile the underlying mechanisms of the reaction processes are not fully understood due to the lack of direct and real-time observation. In this paper, we observe phase transformation from body-centered tetragonal PX-PbTiO3 to monoclinic TiO2(B) on the atomic scale by in situ electron irradiation during heat treatment in transmission electron microscope, at pre-defined locations on the sample. We demonstrate that by controlling the location of the incident electron beam, a porous TiO2(B) crystal structure can be formed at the desired area on the nanowire, which is difficult to achieve by traditional synthesis methods. Upon in situ heating, the Pb atoms in the crystal migrate out of the pristine nanowire through inelastic scattering under incident electrons while high temperature(> 400 °C) provides energy for the crystallization of TiO2(B) and the volatilization of a substantial number of Pb atoms, which makes the resultingTiO2(B) nanowires to be porous. In contrast, at temperatures < 400 °C, the segregated Pb atoms form Pb particles and the TiOx nanowires remain in the amorphous state. This work not only provides in situ visualization of the phase transition from the PX-PbTiO3 to monoclinic TiO2(B), but also suggests a crystallography engineering strategy to obtain the desired crystal phase at controlled locations on the nanometer scale.
关键词： controlled locations,phase transformation,in situ,transmission electron microscopy
更新于2025-09-16 10:30:52
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Crystal defects in monocrystalline silicon induced by spot laser melting
摘要： Laser processing of monocrystalline silicon has become an important tool for a wide range of applications. Here, we use microsecond spot laser melting as a model experiment to investigate the generation of crystal defects and residual stress. Using Micro-Raman spectroscopy, defect etching, and transmission electron microscopy, we find no dislocations in the recrystallized volume for cooling rates exceeding jdT=dtj ? 2 (cid:2) 107 K/s, and the samples remain free of residual stress. For cooling rates less than jdT=dtj ? 2 (cid:2) 107 K/s, however, the experiments show a sharp transition to a defective microstructure that is rich in dislocations and residual stress. Moreover, transmission electron microscopy indicates dislocation loops, stacking-fault tetrahedra, and voids within the recrystallized volume, thereby indicating supersaturation of intrinsic point defects during recrystallization. Complementing photoluminescence spectroscopy indicates even three regimes with decreasing cooling rate. Spectra of regime 1 do not contain any defect related spectral lines. In regime 2, spectral lines appear related to point defect clusters. In regime 3, the spectral lines related to point defect clusters vanish, but dislocation-related ones appear. We propose a quantitative model explaining the transition from dislocation-free to dislocation-rich recrystallization by means of the interaction between intrinsic point defects and dislocations.
关键词： monocrystalline silicon,transmission electron microscopy,laser melting,micro-Raman spectroscopy,crystal defects,residual stress,photoluminescence spectroscopy
更新于2025-09-16 10:30:52
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Transmission Electron Microscopy-Based Statistical Analysis of Commercially Available Graphene Oxide Quantum Dots
摘要： Thanks to their excellent thermal and optical properties, graphene oxide quantum dots (GOQD) have been extensively explored for several applications, such as composite material, optoelectronic devices, solar cells, and ?uorescence materials, among others. Consequently, GOQDs are commercially available suspended in a solution. However, the density, size, and crystallinity of commercially available GOQDs can di?er a lot from one manufacturer to another, which rarely provide exhaustive information about them. Furthermore, a recent report has questioned the quality of graphene-based materials produced by liquid phase exfoliation. Here a statistical analysis of the quality of commercially available GOQDs, using transmission electron microscope (TEM), is presented. This technique enables to observe the internal structure, thickness, lattice structure, orientation, and local defects of the samples at atomic scale. High resolution TEM images reveal that the thickness of the GOQDs is not homogenous from center to edges within one single domain. The edges show hexagonal lattice (monolayer) while the central location shows to be rhomboidal structure (multilayer). This work provides clear statistical information about the quality of the commercially available GOQDs.
关键词： quantum dots,transmission electron microscopy,crystallinity,graphene oxide,graphene
更新于2025-09-16 10:30:52
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Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy Studies of Hole-Selective Molybdenum Oxide Contacts in Silicon Solar Cells
摘要： In this study, sub-stochiometric hole-selective molybdenum oxide (MoOx) contacts in crystalline silicon (c-Si) solar cells were investigated by a combination of transmission electron microscopy (TEM) and spatially-resolved electron energy-loss spectroscopy (SR-EELS). It was observed that a ≈ 4 nm SiOx interlayer grows at the MoOx/c-Si interface during the evaporation of MoOx over c-Si substrate. SR-EELS analyses revealed the presence of 1.5 nm diffused MoOx/ITO (indium tin oxide) interface in both as-deposited and annealed samples. Moreover, the presence of a 1 nm thin layer with a lower oxidation state of Mo was detected at SiOx/MoOx interface in as-deposited state which disappears upon annealing. Overall, it was evident that no hole-blocking interlayer is formed at MoOx/ITO interface during annealing and homogenization of the MoOx layer takes place during the annealing process. Furthermore, device simulations revealed that efficient hole collection is dependent on MoOx work function and that reduction in work function of MoOx results in loss of band bending and negatively impacts hole-selectivity.
关键词： silicon,electron energy-loss spectroscopy (EELS),hole-selective,transmission electron microscopy (TEM),molybdenum oxide (MoOx)
更新于2025-09-12 10:27:22
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Nanoscale temperature measurement during temperature controlled in situ TEM using Al plasmon nanothermometry
摘要： Over recent years, the advent of microelectromechanical system (MEMS)-type microheaters has pushed the limits of temperature controlled in situ transmission electron microscopy (TEM). In particular, by enabling the observation of the structure of materials in their application environments, temperature controlled TEM provides unprecedented insights into the link between the properties of materials and their structure in real-world problems, a clear knowledge of which is necessary for rational development of functional materials with new or improved properties. While temperature is the key parameter in such experiments, accessing the precise temperature of the sample at the nanoscale during observations still remains challenging. In the present work, we have applied aluminium plasmon nanothermometry technique that monitors the temperature dependence of the volume plasmon of Al nanospheres using electron energy loss spectroscopy for in situ local temperature determination over a MEMS microheater. With access to local temperatures between room temperature to 550°C, we have assessed the spatial and temporal stabilities of the microheater when it operates at different setpoint temperatures both under vacuum and in the presence of a static H2 gas environment. Temperature comparisons performed under the two environments show discrepancies between local and setpoint temperatures.
关键词： in situ transmission electron microscopy,electron energy loss spectroscopy,volume expansion of metal,local temperature determination,volume plasmons shift
更新于2025-09-12 10:27:22