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Double moiré localized plasmon structured illumination microscopy
Get PDFStructured illumination microscopy (SIM) is a well-established fluorescence imaging technique, which can increase spatial resolution by up to a factor of two. This article reports on a new way to extend the capabilities of structured illumination microscopy, by combining ideas from the fields of illumination engineering and nanophotonics. In this technique, plasmonic arrays of hexagonal symmetry are illuminated by two obliquely incident beams originating from a single laser. The resulting interference between the light grating and plasmonic grating creates a wide range of spatial frequencies above the microscope passband, while still preserving the spatial frequencies of regular SIM. To systematically investigate this technique and to contrast it with regular SIM and localized plasmon SIM, we implement a rigorous simulation procedure, which simulates the near-field illumination of the plasmonic grating and uses it in the subsequent forward imaging model. The inverse problem, of obtaining a super-resolution (SR) image from multiple low-resolution images, is solved using a numerical reconstruction algorithm while the obtained resolution is quantitatively assessed. The results point at the possibility of resolution enhancements beyond regular SIM, which rapidly vanishes with the height above the grating. In an initial experimental realization, the existence of the expected spatial frequencies is shown and the performance of compatible reconstruction approaches is compared. Finally, we discuss the obstacles of experimental implementations that would need to be overcome for artifact-free SR imaging
Spontaneous and stimulated electron–photon interactions in nanoscale plasmonic near fields
Get PDFThe interplay between free electrons, light, and matter offers unique prospects for space, time, and energy resolved optical material characterization, structured light generation, and quantum information processing. Here, we study the nanoscale features of spontaneous and stimulated electron–photon interactions mediated by localized surface plasmon resonances at the tips of a gold nanostar using electron energy-loss spectroscopy (EELS), cathodoluminescence spectroscopy (CL), and photon-induced near-field electron microscopy (PINEM). Supported by numerical electromagnetic boundary-element method (BEM) calculations, we show that the different coupling mechanisms probed by EELS, CL, and PINEM feature the same spatial dependence on the electric field distribution of the tip modes. However, the electron–photon interaction strength is found to vary with the incident electron velocity, as determined by the spatial Fourier transform of the electric near-field component parallel to the electron trajectory. For the tightly confined plasmonic tip resonances, our calculations suggest an optimum coupling velocity at electron energies as low as a few keV. Our results are discussed in the context of more complex geometries supporting multiple modes with spatial and spectral overlap. We provide fundamental insights into spontaneous and stimulated electron-light-matter interactions with key implications for research on (quantum) coherent optical phenomena at the nanoscale
MigrOS: Transparent Live-Migration Support for Containerised RDMA Applications
Get PDFRDMA networks offload packet processing onto specialised circuitry of the network interface controllers (NICs) and bypass the OS to improve network latency and bandwidth. As a consequence, the OS forfeits control over active RDMA connections and loses the possibility to migrate RDMA applications transparently. This paper presents MigrOS, an OS-level architecture for transparent live migration of containerised RDMA applications. MigrOS shows that a set of minimal changes to the RDMA communication protocol reenables live migration without interposing the critical path operations. Our approach requires no changes to the user applications and maintains backwards compatibility at all levels of the network stack. Overall, MigrOS can achieve up to 33% lower network latency in comparison to software-only techniques. © 2021 USENIX Annual Technical Conference. All rights reserved
Microstructuring of 2D perovskites via ion-exchange fabrication
Get PDFIn recent years, two dimensional (2D) perovskites have attracted growing interest as a material for optoelectronic applications, combining the defect tolerance and strong absorption of bulk perovskites with enhanced material stability. Moreover, the possibility to tune their bandgap via control of the thickness of the perovskite layers allows precise optimization of the energy levels in these materials, making them ideal candidates for rationally designed semiconductor heterojunctions. However, despite the advances in the synthesis of 2D perovskites, typical fabrication strategies produce either uniform thin-films or isolated single crystals, severely hindering the prospect of patterning these materials. We demonstrate an ion-exchange synthesis of 2D perovskites, starting from a lead carbonate host material and converting it to 2D perovskites via a solution-based treatment. The process allows for the fabrication of 2D perovskites spanning a range of halide compositions and 2D layer thicknesses and yields highly crystalline luminescent materials. We demonstrate the potential of this approach for 2D perovskite patterning, spatially localizing 2D perovskite structures via the conversion of pre-patterned lead carbonate structures. These results significantly expand the possibilities of 2D perovskite material design toward controllable integration of 2D perovskites in complex device architectures
A Fabrication Strategy for Reconfigurable Millimeter-Scale Metamaterials
Get PDFRather than depending on material composition to primarily dictate performance metrics, metamaterials can leverage geometry to achieve specific properties of interest. For example, reconfigurable metamaterials have enabled programmable shape transformations, tunable mechanical properties, and energy absorption. While several methods exist to fabricate such structures, they often place severe restrictions on manufacturing materials, or require significant manual assembly. Moreover, these arrays are typically composed of unit cells that are either macro-scale or micro-scale in dimension. Here, the fabrication gap is bridged, and laminate manufacturing is used to develop a method for designing reconfigurable metamaterials at the millimeter-scale, that is compatible with a wide range of materials, and that requires minimal manual assembly. In addition to showing the versatility of this fabrication method, how the use of laminate manufacturing affects the behavior of these multi-component arrays is also characterized. To this end, a numerical model that captures the deformations exhibited by the structures is developed, and an analytic model that predicts the strain of the structure under compressive stress is built. Overall, this approach can be leveraged to develop millimeter-scale metamaterials for applications that require reconfigurable materials, such as in the design of tunable acoustics, photonic waveguides, and electromagnetic devices
Inducing ferroelastic domains in single-crystal CsPbBr3 perovskite nanowires using atomic force microscopy
Get PDFFerroelectric and ferroelastic domains have been predicted to enhance metal halide perovskite (MHP) solar cell performance. While the formation of such domains can be modified by temperature, pressure, or strain, established methods lack spatial control at the level of single domains. Here, we induce the formation of ferroelastic domains in CsPbBr3 nanowires at room temperature using an atomic force microscope (AFM) tip and visualize the domains using nanofocused x-ray diffraction with a 60 nm beam. Regions scanned with a low AFM tip force show orthorhombic 004 reflections along the nanowire axis, while regions exposed to higher forces exhibit 220 reflections. The applied stress locally changes the crystal structure, leading to lattice tilts that define ferroelastic domains, which spread spatially and terminate at {112}-type domain walls. The ability to induce individual ferroelastic domains within MHPs using AFM gives new possibilities for device design and fundamental experimental studies
A role for the fusogen eff-1 in epidermal stem cell number robustness in Caenorhabditis elegans
Get PDFDevelopmental patterning in Caenorhabditis elegans is known to proceed in a highly stereotypical manner, which raises the question of how developmental robustness is achieved despite the inevitable stochastic noise. We focus here on a population of epidermal cells, the seam cells, which show stem cell-like behaviour and divide symmetrically and asymmetrically over post-embryonic development to generate epidermal and neuronal tissues. We have conducted a mutagenesis screen to identify mutants that introduce phenotypic variability in the normally invariant seam cell population. We report here that a null mutation in the fusogen eff-1 increases seam cell number variability. Using time-lapse microscopy and single molecule fluorescence hybridisation, we find that seam cell division and differentiation patterns are mostly unperturbed in eff-1 mutants, indicating that cell fusion is uncoupled from the cell differentiation programme. Nevertheless, seam cell losses due to the inappropriate differentiation of both daughter cells following division, as well as seam cell gains through symmetric divisions towards the seam cell fate were observed at low frequency. We show that these stochastic errors likely arise through accumulation of defects interrupting the continuity of the seam and changing seam cell shape, highlighting the role of tissue homeostasis in suppressing phenotypic variability during development
Shaping Perovskites: In Situ Crystallization Mechanism of Rapid Thermally Annealed, Prepatterned Perovskite Films
Get PDFUnderstanding and controlling the crystallization of organic-inorganic perovskite materials is important for their function in optoelectronic applications. This control is particularly delicate in scalable single-step thermal annealing methods. In this work, the crystallization mechanisms of flash infrared-annealed perovskite films, grown on substrates with lithographically patterned Au nucleation seeds, are investigated. The patterning enables the in situ observation to study the crystallization kinetics and the precise control of the perovskite nucleation and domain growth, while retaining the characteristic polycrystalline micromorphology with larger crystallites at the boundaries of the crystal domains, as shown by electron backscattering diffraction. Time-resolved photoluminescence measurements reveal longer charge carrier lifetimes in regions with large crystallites on the domain boundaries, relative to the domain interior. By increasing the nucleation site density, the proportion of larger crystallites is increased. This study shows that the combination of rapid thermal annealing with nucleation control is a promising approach to improve perovskite crystallinity and thereby ultimately the performance of optoelectronic devices
Localizing nanoscale objects using nanophotonic near-field transducers
Get PDFWe study how nanophotonic structures can be used for determining the position of a nearby nanoscale object with subwavelength accuracy. Through perturbing the near-field environment of a metasurface transducer consisting of nano-apertures in a metallic film, the location of the nanoscale object is transduced into the transducer’s far-field optical response. By monitoring the scattering pattern of the nanophotonic near-field transducer and comparing it to measured reference data, we demonstrate the two-dimensional localization of the object accurate to 24 nm across an area of 2 × 2 μm. We find that adding complexity to the nanophotonic transducer allows localization over a larger area while maintaining resolution, as it enables encoding more information on the position of the object in the transducer’s far-field response
Direct quantification of topological protection in symmetry-protected photonic edge states at telecom wavelengths
Get PDFTopological on-chip photonics based on tailored photonic crystals (PhCs) that emulate quantum valley-Hall effects has recently gained widespread interest owing to its promise of robust unidirectional transport of classical and quantum information. We present a direct quantitative evaluation of topological photonic edge eigenstates and their transport properties in the telecom wavelength range using phase-resolved near-field optical microscopy. Experimentally visualizing the detailed sub-wavelength structure of these modes propagating along the interface between two topologically non-trivial mirror-symmetric lattices allows us to map their dispersion relation and differentiate between the contributions of several higher-order Bloch harmonics. Selective probing of forward- and backward-propagating modes as defined by their phase velocities enables direct quantification of topological robustness. Studying near-field propagation in controlled defects allows us to extract upper limits of topological protection in on-chip photonic systems in comparison with conventional PhC waveguides. We find that protected edge states are two orders of magnitude more robust than modes of conventional PhC waveguides. This direct experimental quantification of topological robustness comprises a crucial step toward the application of topologically protected guiding in integrated photonics, allowing for unprecedented error-free photonic quantum networks