The high light‐output efficiencies of InxGa1‐xN quantum‐well (QW)‐based light‐emitting diodes (LEDs) even in presence of a large number of nonradiative recombination centers (such as dislocations) ...has been explained by localization of carriers in radiative potential traps, the origins of which still remain unclear. To provide insights on the highly efficient radiative traps, spectrally resolved photoluminescence (PL) microscopy has been performed on green‐light‐emitting In0.22Ga0.78N QW LEDs, by selectively generating carriers in the alloy layers. PL imaging shows the presence of numerous inhomogeneously distributed low‐band‐gap traps with diverse radiative intensities. PL spectroscopy of a statistically relevant number of individual traps reveals a clear bimodal distribution in terms of both band‐gap energies and radiative recombination efficiencies, indicating the presence of two distinct classes of carrier localization centers within the same QW sample. Disparity in their relative surface coverage and photoemission “blinking” characteristics suggests that the deep traps originate from local compositional fluctuations of indium within the alloy, while the shallow traps arise from nanometer‐scale thickness variations of the active layers. This is further supported by Poisson–Schrödinger self‐consistent calculations and implies that radiative traps formed due to both local indium content and interface‐morphology‐related heterogeneities can coexist within the same QW sample.
Spectrally‐resolved photoluminescence imaging has been performed on thousands of individual localized luminescent centers within green emitting In0.22Ga0.78N quantum‐well LEDs by selectively generating carriers within the alloy layers. These measurements reveal the presence of two distinct types of radiative centers with stark differences in their optoelectronic properties, suggesting that both nanometer‐scale variations of the indium content within the alloy and thickness fluctuations of active layer can coexist within the same quantum‐well sample.
Electric field control of chirality Behera, Piush; May, Molly A; Gómez-Ortiz, Fernando ...
Science advances,
2022-Jan-07, Letnik:
8, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Polar textures have attracted substantial attention in recent years as a promising analog to spin-based textures in ferromagnets. Here, using optical second-harmonic generation–based circular ...dichroism, we demonstrate deterministic and reversible control of chirality over mesoscale regions in ferroelectric vortices using an applied electric field. The microscopic origins of the chirality, the pathway during the switching, and the mechanism for electric field control are described theoretically via phase-field modeling and second-principles simulations, and experimentally by examination of the microscopic response of the vortices under an applied field. The emergence of chirality from the combination of nonchiral materials and subsequent control of the handedness with an electric field has far-reaching implications for new electronics based on chirality as a field-controllable order parameter.
The solutions to many of today’s challenges will be found at the frontier of advanced materials research and will require collaboration across synthesis, characterization, fabrication and theory. ...While good ideas can be generated anywhere by anyone, scientific opportunities are often concentrated among select groups. National user facilities democratize access to world-class expertise and instrumentation, acting as innovation multipliers on the scientific enterprise.
Although reduced representation bisulfite sequencing (RRBS) measures DNA methylation (DNAme) across CpG-rich genomic regions with high sensitivity, the assay can be time-consuming and prone to batch ...effects. Here, we present a high-throughput, automated RRBS protocol starting with DNA extraction from frozen rat tissues. We describe steps for RRBS library preparation, library quality control, and sequencing. We also detail an optimized pipeline for sequencing data processing. This protocol has been applied successfully to DNAme profiling across multiple rat tissues.
For complete details on the use and execution of this protocol, please refer to Nair et al.1
Display omitted
•Steps for extracting genomic DNA from cryopulverized rat tissues•An automated protocol for high-throughput RRBS library preparation•A pipeline for processing the RRBS library sequencing data•Quality control steps for assessing DNA, libraries, and sequencing datasets
Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.
Although reduced representation bisulfite sequencing (RRBS) measures DNA methylation (DNAme) across CpG-rich genomic regions with high sensitivity, the assay can be time-consuming and prone to batch effects. Here, we present a high-throughput, automated RRBS protocol starting with DNA extraction from frozen rat tissues. We describe steps for RRBS library preparation, library quality control, and sequencing. We also detail an optimized pipeline for sequencing data processing. This protocol has been applied successfully to DNAme profiling across multiple rat tissues.
Understanding and controlling disorder is key to nanotechnology and materials science. Traditionally, disorder is attributed to local fluctuations of inherent material properties such as chemical and ...structural composition, doping or strain. Here, we present a fundamentally new source of disorder in nanoscale systems that is based entirely on the local changes of the Coulomb interaction due to fluctuations of the external dielectric environment. Using two-dimensional semiconductors as prototypes, we experimentally monitor dielectric disorder by probing the statistics and correlations of the exciton resonances, and theoretically analyse the influence of external screening and phonon scattering. Even moderate fluctuations of the dielectric environment are shown to induce large variations of the bandgap and exciton binding energies up to the 100 meV range, often making it a dominant source of inhomogeneities. As a consequence, dielectric disorder has strong implications for both the optical and transport properties of nanoscale materials and their heterostructures.
We demonstrate fabrication of nano-patterned thin ALD (Atomic layer deposition) membrane (suspended/transferable) by using a bi-layer resist process where the bottom layer resist acts as a ...sacrificial layer. This method enables an all dry deterministic transfer of nano-patterned ALD membrane on desired substrate, allowing assembly of multitude of hetero-structures and functionalities that are not yet accessible. Unlike conventional ways of achieving patterned alumina membrane reported in literature our technique requires significantly less fabrication steps and paves the way for novel ALD membrane-based technology.
Tip-enhanced photoluminescence (TRPL) is a powerful technique for spatially and spectrally probing local optical properties of 2-dimensional (2D) materials that are modulated by the local ...heterogeneities, revealing inaccessible dark states due to bright state overlap in conventional far-field microscopy at room temperature. While scattering-type near-field probes have shown the potential to selectively enhance and reveal dark exciton emission, their technical complexity and sensitivity can pose challenges under certain experimental conditions. Here, we present a highly reproducible and easy-to-fabricate near-field probe based on nanoimprint lithography and fiber-optic excitation and collection. The novel near-field measurement configuration provides an ∼3 orders of magnitude out-of-plane Purcell enhancement, diffraction-limited excitation spot, and subdiffraction hyperspectral imaging resolution (below 50 nm) of dark exciton emission. The effectiveness of this high spatial XD mapping technique was then demonstrated through reproducible hyperspectral mapping of oxidized sites and bubble areas.
Electronic and optical excitations in two-dimensional systems are distinctly sensitive to the presence of a moiré superlattice. We used cryogenic transmission electron microscopy and spectroscopy to ...simultaneously image the structural reconstruction and associated localization of the lowest-energy intralayer exciton in a rotationally aligned WS
-WSe
moiré superlattice. In conjunction with optical spectroscopy and ab initio calculations, we determined that the exciton center-of-mass wave function is confined to a radius of approximately 2 nanometers around the highest-energy stacking site in the moiré unit cell. Our results provide direct evidence that atomic reconstructions lead to the strongly confining moiré potentials and that engineering strain at the nanoscale will enable new types of excitonic lattices.
Tip-enhanced photoluminescence (TRPL) is a powerful technique for spatially and spectrally probing local optical properties of 2-dimensional (2D) materials that are modulated by the local ...heterogeneities, revealing inaccessible dark states due to bright state overlap in conventional far-field microscopy at room temperature. While scattering-type near-field probes have shown the potential to selectively enhance and reveal dark exciton emission, their technical complexity and sensitivity can pose challenges under certain experimental conditions. Here, we present a highly reproducible and easy-to-fabricate near-field probe based on nanoimprint lithography and fiber-optic excitation and collection. The novel near-field measurement configuration provides an ∼3 orders of magnitude out-of-plane Purcell enhancement, diffraction-limited excitation spot, and subdiffraction hyperspectral imaging resolution (below 50 nm) of dark exciton emission. The effectiveness of this high spatial X
mapping technique was then demonstrated through reproducible hyperspectral mapping of oxidized sites and bubble areas.
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