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Modified qHAADF method for atomic column-by-column compositional quantification of semiconductor heterostructures
摘要： The qHAADF method allows the quanti?cation of the composition at atomic column resolution in semiconductor materials by comparing the HAADF-STEM intensities between a region of interest to a region of the material of known composition. However, the application of this qHAADF approach requires both regions to be differentiable and included in the same micrograph at close proximity. This limits the application of this approach to certain materials and magni?cations where this requirement is ful?lled. In this work, we extend the qHAADF method to analyses where the reference region is imaged in a separate micrograph. The validity of this modi?ed method is proved by comparison to the original qHAADF approach using HAADF-STEM simulated images of the semiconductor heterostructure InSb/InAs. Additionally, the methods are applied successfully to experimental images both of a simple InSb/InAs interface and of a complex InSb/GaSb heterostructure, justifying the signi?cance of the modi?ed method over the original method.
关键词： compositional quanti?cation,qHAADF method,HAADF-STEM,semiconductor heterostructures,atomic column resolution
更新于2025-09-10 09:29:36
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Fabrication of a Bilayer Structure of Cu and Polyimide to Realize Circuit Microminiaturization and High Interfacial Adhesion in Flexible Electronic Devices
摘要： With commercialization of the 5th generation mobile communication system and the further spread of the Internet of Things, industrial innovation is arriving with new business fields related to concepts such as high-speed communication, self-driving vehicles, and remote medicine. One of the challenges is the realization of flexible devices with high-definition circuits, which requires new fabrication techniques for Cu films on polymer substrates to meet demands and an understanding of the Cu/polymer interfacial nanostructure to assure product quality. We have developed a promising technique for the fabrication of Cu film on polyimide (PI), which consists mainly of very simple semiconductor device processes. This technique allows for control of the Cu thickness with nanometer precision to form miniaturized Cu circuits with potential advantages in terms of interfacial adhesion and material/production costs. The Cu/PI interfaces fabricated by conventional vapor deposition and the new technique are systematically analyzed using synchrotron hard-X-ray photoelectron spectroscopy (HAXPES), scanning transmission electron microscopy (STEM), and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). With conventional vapor deposition, it was discovered that evaporated Cu atoms decompose the PI and an oxidation layer with a thickness of several nanometers that deteriorates the interfacial adhesion could be visualized at the Cu/PI interface. With the new technique, the decomposition of PI and interfacial oxidation are significantly suppressed. Furthermore, the proposed technique can be broadly applied to the investigation of metal/polymer interfaces fabricated by polymer coating on a metal substrate, which has so far been impossible.
关键词： STEM,TOF-SIMS,Flexible printed circuits,Microminiaturization,Interfacial adhesion,HAXPES,Flexible electronics
更新于2025-09-10 09:29:36
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Classification of Limbal Stem Cell Deficiency Using Clinical and Confocal Grading
摘要： To grade the severity of limbal stem cell deficiency (LSCD) based on the extent of clinical presentation and central corneal basal epithelial cell density (BCD). This is a retrospective observational comparative study of 48 eyes of 35 patients with LSCD and 9 eyes of 7 normal subjects (controls). Confocal images of the central cornea were acquired. A clinical scoring system was created based on the extent of limbal and corneal surface involvement. LSCD was graded as mild, moderate, and severe stages based on the clinical scores. The degree of BCD reduction was given a score of 0 to 3. Compared with BCD in controls, BCD decreased by 23.0%, 40.4%, and 69.5% in the mild, moderate, and severe stages of LSCD classified by the clinical scoring system, respectively. The degree of BCD reduction was positively correlated with larger limbal and corneal surface involvement and when the central visual axis was affected (all P # 0.0005). Mean corrected distance visual acuity logarithm of the minimum angle of resolution was 0.0 6 0.0 in control eyes, 0.2 6 0.5 in mild LSCD, 0.6 6 0.4 in moderate LSCD, and 1.6 6 1.1 in severe LSCD (P , 0.0001). There was a significant correlation between a higher clinical score and corrected distance visual acuity logarithm of the minimum angle of resolution (rho = 0.82; P , 0.0001) and a greater decrease in BCD (rho = 20.78; P , 0.0001). A clinical scoring system was developed to assess the extent of clinical presentation of LSCD. A classification system to grade the severity of LSCD can be established by combining the BCD score with the clinical score.
关键词： diagnosis,classification system,limbal stem cell,in vivo confocal microscopy,limbal stem cell deficiency
更新于2025-09-09 09:28:46
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An NIR-II Fluorescence/Dual Bioluminescence Multiplexed Imaging for In Vivo Visualizing the Location, Survival, and Differentiation of Transplanted Stem Cells
摘要： The in vivo distribution, viability, and differentiation capability of transplanted stem cells are vital for the therapeutic efficacy of stem cell–based therapy. Herein, an NIR-II fluorescence/dual bioluminescence multiplexed imaging method covering the visible and the second near-infrared window from 400 to 1700 nm is successfully developed for in vivo monitoring the location, survival, and osteogenic differentiation of transplanted human mesenchymal stem cells (hMSCs) in a calvarial defect mouse model. The exogenous Ag2S quantum dot–based fluorescence imaging in the second near-infrared window is applied for visualizing the long-term biodistribution of transplanted hMSCs. Endogenous red firefly luciferase (RFLuc)-based bioluminescence imaging (BLI) and the collagen type 1 promoter–driven Gaussia luciferase (GLuc)-based BLI are employed to report the survival and osteogenic differentiation statuses of the transplanted hMSCs. Meanwhile, by integrating the three imaging channels, multiple dynamic biological behaviors of transplanted hMSCs and the promotion effects of immunosuppression and the bone morphogenetic protein 2 on the survival and osteogenic differentiation of transplanted hMSCs are directly observed. The novel multiplexed imaging method can greatly expand the capability for multifunctional analysis of the fates and therapeutic capabilities of the transplanted stem cells, and aid in the improvement of stem cell–based regeneration therapies and their clinical translation.
关键词： near-infrared fluorescence imaging,bioluminescence imaging,transplanted stem cells,stem cell fate,regenerative medicine
更新于2025-09-09 09:28:46
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Induction of rod versus cone photoreceptor-specific progenitors from retinal precursor cells
摘要： During development, multipotent progenitors undergo temporally-restricted differentiation into post-mitotic retinal cells; however, the mechanisms of progenitor division that occurs during retinogenesis remain controversial. Using clonal analyses (lineage tracing and single cell cultures), we identify rod versus cone lineage-specific progenitors derived from both adult retinal stem cells and embryonic neural retinal precursors. Taurine and retinoic acid are shown to act in an instructive and lineage-restricted manner early in the progenitor lineage hierarchy to produce rod-restricted progenitors from stem cell progeny. We also identify an instructive, but lineage-independent, mechanism for the specification of cone-restricted progenitors through the suppression of multiple differentiation signaling pathways. These data indicate that exogenous signals play critical roles in directing lineage decisions and resulting in fate-restricted rod or cone photoreceptor progenitors in culture. Additional factors may be involved in governing photoreceptor fates in vivo.
关键词： Retina,Rod photoreceptor,Cone photoreceptor,Stem cell,Progenitors
更新于2025-09-09 09:28:46
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Shortening nucleation time to enable ultrafast phase transition in Zn1Sb7Te12 pseudo-binary alloy
摘要： Zn1Sb7Te12 thin films have been deposited by magnetron co-sputtering of ZnTe and Sb2Te3 targets. The microstructure, phase-change speed, optical cycling stability and crystallization kinetics have been investigated during thermal annealing and laser irradiation. The thermal-annealed and laser-irradiated films give clear evidence on coexistence of trigonal Sb2Te3 and cubic ZnTe phases, which are homogeneously distributed in a single alloy as confirmed by advanced scanning transmission electron microscopy. The formation of both phases increases initial nucleation sites, leading to the rapid phase-change speed in the Zn1Sb7Te12 film. The film has a minimum crystallization time of ~3 ns at 70 mW with almost no incubation period for the formation of critical nuclei compared to Ge2Sb2Te5 and other Zn-based films. Moreover, the complete crystallization of Zn1Sb7Te12 thin films is achieved within 10 ns. The ultrafast two-dimensional nucleation and crystal growth speed in Zn1Sb7Te12 obtained from the laser-irradiated system is almost 7 times faster compared to Ge2Sb2Te5 film. Controlling crystallization process through the doping ZnTe into Sb2Te3 is thus promising for the development of high-speed optical switching technology.
关键词： Optical spectroscopy,Thin films,Phase transformation kinetics,Optical materials,STEM HAADF
更新于2025-09-09 09:28:46
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Unveiling the Chemical Composition of Halide Perovskite Films Using Multivariate Statistical Analyses
摘要： The local chemical composition of halide perovskites is a crucial factor in determining their macroscopic properties and their stability. While the combination of scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX) is a powerful and widely used tool for accessing such information, electron-beam-induced damage and complex formulation of the films make this investigation challenging. Here we demonstrate how multivariate analysis – including statistical routines derived from “big data” research, such as Principal Component Analysis, PCA – can be used to dramatically improve the signal recovery from fragile materials. We also show how a similar decomposition algorithm (Non-negative Matrix Factorisation, NMF) can unravel elemental composition at the nanoscale in perovskite films, highlighting the presence of segregated species and identifying the local stoichiometry at the nanoscale.
关键词： hybrid perovskite,big data,multivariate analysis,chemical composition,STEM-EDX,nanoscale
更新于2025-09-09 09:28:46
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Thermodynamic Properties of Negative Discharge Channels in a 1-m Air Gap Measured by Optical Interferometry
摘要： Lightning is a common natural phenomenon and is a typical air discharge on a large spatial scale. The stepping of lightning leaders and space stems of thunderstorms are similar to those of negative discharges in the laboratory. There have been extensive experimental observations and theoretical research on positive discharge but less research on the negative form. This paper conducts an experiment on a 1-m rod–plane gap under a negative impulse voltage. To observe the thermodynamics of the negative discharge, a Mach–Zehnder interferometer combined with a high-speed video camera was set up. The Abel inverse method was used to quantify the thermal parameters for negative channels. The space stem is of great interest, and its bidirectional propagation and connection with the electrode were captured. When a space stem formed, the gas temperature within the stem ranged 320–550 K. Two negative leaders connected in space and formed one negative channel. The connection region was about 800 K while the temperature on the two sides of the negative channel reached 1500–1800 K. After a negative channel formed, it expanded, and its thermal parameter distributions tended to be uniform owing to thermal conduction and convection losses. The gas density near the discharge center was about 20%–30% of the ambient density, and the corresponding temperature was 1000–1500 K. The experiments provide deep insight into the thermodynamic properties of a negative leader discharge.
关键词： Mach–Zehnder (M-Z) stem,discharge channel,Connection process,negative,space interferometry,thermodynamic properties
更新于2025-09-09 09:28:46
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Structure-directing lone pairs: Synthesis and Structural Characterization of SnTiO3
摘要： SnTiO3 was successfully synthesized for the first time in bulk form by soft chemistry. STEM and Rietveld refinement show that SnTiO3 adopts a structure similar to the archetypical ilmenite-type structure, forming a honeycomb lattice of edge-sharing TiO6-octahedra, which are decorated with Sn2+. Due to formation of a van der Waals gap between the individual layers and hence close energetic minima of different stacking types, SnTiO3 forms multiple stacking orders and twinning domains that we describe by systematic DIFFaX-simulations. The structure is governed by the tin lone pairs, which influence the stacking of the layers as well as local distortions observed by EELS and NMR potentially leading to a wide range of applications.
关键词： DFT,van der Waals gap,Rietveld refinement,soft chemistry,STEM,ilmenite-type structure,EELS,SnTiO3,NMR
更新于2025-09-09 09:28:46
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - Carbon-titanium multilayer films: Synthesis and characterization
摘要： To synthesize Carbon-Titanium (C-Ti) multilayer thin films deposited on silicon substrates was used Thermionic Vacuum Arc (TVA) method. The coated layers consisted of a base layer of about 100 nm of Carbon deposited at low evaporation rates. Subsequently, seven Carbon and Titanium layers were deposited alternatively on top of Carbon base layer, each of them has a final thickness up to 40 nm. In this study we obtained different batches of samples by variation of the substrate temperature between 0oC and 300oC, and the ion acceleration voltage applying a negative substrate bias voltage between 0V and -700V. To characterize the microstructure properties of as prepared C-Ti multilayer structures were used Electron Microscopy techniques (TEM, SEM, STEM) and Raman Spectroscopy. Results of tribological measurements are associated with the occurrence of atomic diffusion processes at Ti/C interface. To characterize the electrical conductive properties, the electrical resistance versus temperature have been measured.
关键词： Ti/C multilayer,TVA,STEM,tribological properties,SEM,EDX,Raman,electrical properties,TEM
更新于2025-09-09 09:28:46