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European Microscopy Congress 2016: Proceedings || Defects in as-grown vs. annealed rutile titania nanowires and their effect on properties
摘要： Semiconducting metal oxides play a key role in electrochemical and photo physical applications like photo catalysis and as electrode material in solar cells and Li-ion batteries. Among these metal oxides, hydrothermally grown rutile TiO2 nanowire arrays are promising as the 1 D structure possesses a large surface area and a directed electron path towards the substrate. However, the efficiency of these devices is also influenced by the defects inside the nanowires (dislocations, stacking faults, titanium interstitials and oxygen vacancies). A previous study showed that as-grown nanowires have a high density of lattice defects.[1] However, these defects can be removed by an additional annealing step. Latest findings demonstrate that hybrid solar cells where those annealed nanowires are incorporated have significantly higher power-conversion efficiency.[2] However, the removal of the defects is not fully understood so far. In our present work, transmission electron microscopy (TEM) was used to study the changes within the nanowire during annealing. TEM investigations were performed at 200 kV using a JEOL JEM-2200FS and at 300 kV using a FEI Titan Themis 60-300. First results were obtained by ex-situ TEM analysis of as-grown TiO2 nanowires and nanowires, which were annealed at 500 °C for 4 h. These ex-situ analysis confirm that both, as-grown and annealed nanowires, have the rutile crystal structure. Defects, present in the as-grown state, can be removed by the thermal treatment. Concurrently, a structural transformation inside the nanowires occurs resulting in faceted voids of several nanometer in diameter. Using tilt series from -70° to +70° in high-angle annular dark-field (HAADF) scanning (S)TEM mode and the discrete iterative reconstruction technique (DIRT)[3], a TEM tomograph was obtained, which proved that these voids are solely formed inside the nanowire and not at the nanowire surface (Fig. 1). Further analysis including electron energy loss spectroscopy revealed changes of the oxidation state at the surface region of the voids during annealing, whereas the rutile TiO2 crystal structure was maintained. HAADF-STEM in-situ heating experiments, performed in a JEOL JEM-2200FS with a DENSsolutions heating holder, enabled the direct observation of the structural changes inside the rutile TiO2 nanowires (Fig. 2). Using a slow heating ramp of 3.3°C/min, a sudden formation of these voids at around 500 °C could be observed. Heating at lower temperatures did not affect the structure of the nanowire and also an additional heating after the transformation (600°C, 1h) did not change the size and shape of the voids. These ex-situ and in-situ observations are a decisive step to explain the mechanisms involved in this process in more detail. The results of our TEM investigation were correlated to the properties of as-grown and annealed TiO2 nanowires. Here, we could show that the healing of the lattice defects upon annealing not only increased the performance of hybrid solar cells but also affects other properties of the nanowires e.g. chemical stability.
关键词： in-situ TEM,TiO2 nanowire,defect healing
更新于2025-09-16 10:30:52
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An In-situ Transmission X-ray Microscope to Observe the Dewetting Process of Au Thin Films induced by Nanosecond Pulsed Laser Irradiation
摘要： We coupled an in-situ transmission X-ray microscope (TXM) with a Nd:YAG pulsed laser with a 532-nm wavelength and a 6-ns pulse width. This system was employed to investigate the photo-induced morphological evolution in Au thin films during shot-by-shot irradiation by a single laser pulse. Based on results for Au thin films with thicknesses of 10 and 20 nm, we successfully demonstrated the in-situ TXM system to be a powerful tool for imaging the photo-induced transition from metal thin films to metal nanoparticles. We also found that the sequence of steps leading to this transition depended critically on the thickness of the Au films.
关键词： In-situ transmission X-ray microscope,Zernike phase contrast,Photo-induced dewetting process,Au nanoparticles
更新于2025-09-16 10:30:52
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Analysis of Macular and Retinal Nerve Fiber Layer Thickness in Children with Refractory Amblyopia after Femtosecond Laser-assisted Laser In situ Keratomileusis
摘要： Background: Localized macular edema and retinal nerve fiber layer (RNFL) thinning have been reported shortly after laser in situ keratomileusis (LASIK) in adults. However, it is still unclear how LASIK affects the retina of children. This study aimed to investigate the macular retina and RNFL thickness in children with refractive amblyopia who underwent femtosecond laser?assisted LASIK (FS?LASIK). Methods: In this study, we included 56 eyes of 32 patients with refractive amblyopia who underwent FS?LASIK in our hospital from January 2012 to December 2016. Foveal (foveal center retinal, parafoveal retinal, and perifoveal), macular inner retinal (superior and inferior), and peripapillary RNFL thicknesses (superior, inferior, temporal, and nasal) were measured using Fourier?domain optical coherence tomography before surgery and 1 day, 3 days, and 1 week after surgery. We divided these patients into three groups based on their refractive error: High myopic group with 22 eyes (equivalent sphere, >6.00 D), mild myopic group with 19 eyes (equivalent sphere, 0–6.00 D), and hyperopic group with 15 eyes (equivalent sphere, >+0.50 D). We compared the macular retina and RNFL thickness before and after LASIK. A paired simple t?test was used for data analysis. Results: One week after surgery, the visual acuity for all 56 eyes of the 32 patients reached their preoperative best?corrected vision. Visual acuity improved two lines or better for 31% of the patients. The residual refractive errors in 89% of the patients were within ±0.5 D. In the high myopic group, the foveal center retinal and parafoveal retinal thicknesses were thicker 1 day and 3 days after surgery than before surgery (t = 2.689, P = 0.012; t = 2.383, P = 0.018, respectively); no significant difference was found 1 week after surgery (P > 0.05). The foveal center retinal and parafoveal retinal thicknesses were greater 1 day after surgery than they were before surgery (P = 0.000 and P = 0.005, respectively) in the mild myopic and hyperopic groups. No significant difference was found 3 days or 1 week after surgery (P > 0.05). In all three groups, no significant difference was found in the macular inner retinal or peripapillary RNFL thickness 1 day, 3 days, or 1 week after surgery (P > 0.05). Conclusions: The foveal center retinal edema after FS?LASIK is mild and reversible in children, that mostly occurred in the high myopic group with no effect on the visual acuity, and is always relieved within 1 week.
关键词： Child,Retinal,Laser In situ Keratomileusis,Optical Coherence Tomography
更新于2025-09-16 10:30:52
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Experimental observation of stress formation during selective laser melting using in situ X-ray diffraction
摘要： Despite the ongoing success of metal additive manufacturing and especially the selective laser melting (SLM) technology, process-related defects, distortions and residual stresses impede its usability for fracture-critical applications. In this paper, results of in situ X-ray diffraction experiments are presented that offer insights into the strain and stress formation during the manufacturing of multi-layer thin walls made from Inconel 625. Using different measuring modes and laser scanning parameters, several experimental observations are discussed to validate and extend theoretical models and simulations from the literature. As a sample is built-up layer by layer, the stress state changes continuously up until the last exposure. The localized energy input leads to a complex stress field around the heat source that involves alternating tensile and compressive stresses. The correlation of temperature and yield strength results in a stress maximum at a certain distance to the top layer. The present study demonstrates the potential of high-energy synchrotron radiation diffraction for in situ SLM research.
关键词： Inconel 625,Selective laser melting,Stress formation,In situ,High energy synchrotron radiation diffraction
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - In Situ Fabrication of Far-Detuned Mid-Infrared Optical Fiber Wavelength Converters
摘要： In Situ Fabrication of Far-Detuned Mid-Infrared Optical Fiber Wavelength Converters. Chalcogenide (ChG) glasses have been identified as promising materials for applications in nonlinear photonics due to their exceptionally high nonlinear refractive index; nearly three orders of magnitude beyond that of silica glass. A ChG fiber or waveguide that is tapered down into a microwire provides strong light confinement and enhanced nonlinear optical effect, it allows engineerable chromatic dispersion and thereby an easy access to nonlinear parametric processes such as four-wave mixing (FWM). In well-controlled conditions of chromatic dispersion ChG microwires may lead to strong parametric gain that is far-detuned with respect to the pump wavelength, by tens of THz [1,2]. In theory, chromatic dispersion in a waveguide is precisely adjusted from a good control of waveguide geometry. In practice however, the amount of precision required in waveguide geometry as well as errors on the evaluation of refractive indices prevent the fabrication of wavelength converters with a predetermined wavelength offset. To illustrate this, fig. 1(a) shows the theoretical spectrum of a far-detuned ChG wavelength converter. A change in the core diameter by 5 nm results in a ~ 40 nm wavelength shift of the parametric sidebands. As an element of solution inspired from past reports, it has been shown with supercontinuum generation that experimental parameters could be finely tuned using an in situ monitoring technique [3]. In this work, we demonstrate that wavelength conversion of a ChG microwire is precisely attained by in situ tracking of the microwire output during the tapering process, enabling the fabrication of wavelength converters that are precisely far-detuned by at least 34.3 THz.
关键词： four-wave mixing,nonlinear photonics,in situ tapering,Chalcogenide glasses,wavelength conversion
更新于2025-09-16 10:30:52
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Mobile Monitoring—Open-Source Based Optical Sensor System for Service-Oriented Turbidity and Dissolved Organic Matter Monitoring
摘要： The protection and sustainable use of aquatic resources require a better understanding of fresh water sources, limnic ecosystems, and oceans. The effects of global change, intensive use of natural resources and the complex interactions between humans and the environment show different effects at different scales. Current research approaches are not sufficient to appropriately take account of the heterogeneity and dynamics of aquatic ecosystems. A major challenge in applied environmental research is to extend methods for holistic monitoring and long-term observation technologies with enhanced resolution over both space and time. In this study, turbidity and the content of dissolved organic matter (DOM) are key parameters, as they are of importance for assessing the health of aquatic ecosystems and the state of ecosystem services (e.g., the provision of drinking water). Photonics and optical sensors as well as integrated circuits and open-source based components open interesting possibilities to overcome the current lack of adaptive and service-oriented sensor systems. An open source based optical sensor system was developed, which enables a user-specific, modular and adaptive in-situ monitoring of the turbidity and the dissolved organic substance content almost in real time. Quantification is based on attenuation or transmission measurements with two narrowband LEDs and corresponding detectors in the ultraviolet (DOM content) and infrared range (turbidity) of the electromagnetic spectrum. The developed in-situ sensor system shows a very high agreement with the results obtained using a laboratory photometer but with less methodological effort. First tests carried out in the area close to the city of Leipzig (Saxony, Germany) show promising results. The in-situ sensor system is able to acquire the optical attenuation with a sampling rate up to 0.1 Hz. Due to the fact that data is visualized directly with the help of web services, even the quality of data collection can be improved by assisting the selection of sampling points or a direct spatio-temporal data feedback. What this approach illustrates is the fact that open-source technologies and microelectronics can now be used to implement resilient and promising sensor systems that can set new standards in terms of performance and usability within applied environmental research.
关键词： internet of things,assisted monitoring,attenuation sensor,water quality,photonics sensing,in-situ measurements
更新于2025-09-16 10:30:52
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Effect of Selective Laser Melting Process Parameters and Heat Treatment on Microstructure and Properties of Titanium Alloys Produced from Elemental Powders
摘要： This work investigates Selective Laser Melting (SLM) process as a method of in-situ synthesis of Ti-5Al and Ti-6Al-4V alloys using elemental powder mixture. Elemental spherical powders were used to prepare a powder mixture and the samples were produced by SLM process using different volume energy densities. The effects of volume energy density on the samples’ relative density, chemical composition, microstructure and microhardness before and after heat treatment have been studied. It was shown that volume energy density significantly effects the density and microstructure of Ti-5Al and Ti-6Al-4V alloys, as well as, the microhardness of obtained Ti-6Al-4V.
关键词： additive manufacturing,in-situ synthesis,titanium alloy,powder bed fusion,elemental powders
更新于2025-09-16 10:30:52
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In situ TEM observation of controlled growth of two-dimensional WS2 with vertically aligned layers and high-temperature stability
摘要： Layered transition metal dichalcogenides with vertically aligned morphology show great potentials in energy conversion and storage due to the high density of exposed edge sites which have enhanced electrochemical reactivity. In this letter, through in situ heating investigations in a transmission electron microscope, the controlled growth of vertically aligned WS2 with high-temperature stability has been achieved through the thermolysis of solid precursor K2WS4. It is found that the growth of vertically aligned WS2 layers employs hybrid growth modes, in which the growth of new WS2 slab is initiated at old ones from either the middle part or edge part. These vertically aligned WS2 layers show great stability at high temperature of 900°C. Our detailed investigations and theoretical calculations indicate that potassium element in the solid precursor plays a critical role in the growth and evolution of vertically aligned WS2. This method is also applicable to the controlled growth of vertically aligned MoS2 with high-temperature stability through the decomposition of K2MoS4. These findings pave a way for tailored design and fabrication of materials with optimized structure to achieve their superior properties.
关键词： Vertical growth,In situ,High-temperature stability,Transition metal dichalcogenides,TEM
更新于2025-09-16 10:30:52
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Predictors affecting myopic regression in ??6.0D to ??10.0D myopia after laser-assisted subepithelial keratomileusis and laser in situ keratomileusis flap creation with femtosecond laser-assisted or mechanical microkeratome-assisted
摘要： Purpose To investigate the predictive factors of postoperative myopic regression among subjects who have undergone laser-assisted subepithelial keratomileusis (LASEK), laser-assisted in situ keratomileusis (LASIK) flap created with a mechanical microkeratome (MM), and LASIK flap created with a femtosecond laser (FS). All recruited patients had a manifest spherical equivalence (SE) from - 6.0D to - 10.0D myopia. Methods This retrospective, observational case series study analyzed outcomes of refraction at 1 day, 1 week, and 1, 3, 6, and 12 months postoperatively. Predictors affecting myopic regression and other covariates were estimated with the Cox proportional hazards model for the three types of surgeries. Results The study enrolled 496 eyes in the LASEK group, 1054 eyes in the FS-LASIK group, and 910 eyes in the MM-LASIK group. At 12 months, from - 6.0D to - 10.0D myopia showed that the survival rates (no myopic regression) were 52.19%, 59.12%, and 58.79% in the MM-LASIK, FS-LASIK, and LASEK groups, respectively. Risk factors for myopic regression included thicker postoperative central corneal thickness (P ^ 0.01), older age (P ^ 0.01), aspherical ablation (P = 0.02), and larger transitional zone (TZ) (P = 0.03). Steeper corneal curvature (Kmax) (P = 0.01), thicker preoperative central corneal thickness (P < 0.01), smaller preoperative myopia (P < 0.01), longer duration of myopia (P = 0.02), with contact lens (P < 0.01), and larger optical zone (OZ) (P = 0.02) were protective factors. Among the three groups, the MM-LASIK had the highest risk of postoperative myopic regression (P < 0.01). Conclusions The MM-LASIK group experienced the highest myopic regression, followed by the FS-LASIK and LASEK groups. Older age, aspheric ablation used, thicker postoperative central corneal thickness, and enlarging TZ contribute to myopic regression; steeper preoperative corneal curvature (Kmax), longer duration of myopia, with contact lens, thicker preoperative central corneal thickness, lower manifest refraction SE, and enlarging OZ prevent postoperative myopic regression in myopia from - 6.0D to - 10.0D.
关键词： Myopic regression,Laser-assisted subepithelial keratomileusis,Mechanical microkeratome,Laser in situ keratomileusis,Femtosecond laser
更新于2025-09-16 10:30:52
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Differences in Simulated Refractive Outcomes of Photorefractive Keratectomy (PRK) and Laser In-Situ Keratomileusis (LASIK) for Myopia in Same-Eye Virtual Trials
摘要： The use of computational mechanics for assessing the structural and optical consequences of corneal refractive procedures is increasing. In practice, surgeons who elect to perform PRK rather than LASIK must often reduce the programmed refractive treatment magnitude to avoid overcorrection of myopia. Building on a recent clinical validation study of finite element analysis (FEA)-based predictions of LASIK outcomes, this study compares predicted responses in the validated LASIK cases to theoretical PRK treatments for the same refractive error. Simulations in 20 eyes demonstrated that PRK resulted in a mean overcorrection of 0.17 ± 0.10 D relative to LASIK and that the magnitude of overcorrection increased as a function of attempted correction. This difference in correction closely matched (within 0.06 ± 0.03 D) observed differences in PRK and LASIK from a historical nomogram incorporating thousands of cases. The surgically induced corneal strain was higher in LASIK than PRK and resulted in more forward displacement of the central stroma and, consequently, less relative flattening in LASIK. This FE model provides structural confirmation of a mechanism of action for the difference in refractive outcomes of these two keratorefractive techniques, and the results were in agreement with empirical clinical data.
关键词： laser in situ keratomileusis (LASIK),refractive surgery,cornea,photorefractive keratectomy (PRK),finite element analysis
更新于2025-09-16 10:30:52