We report the spectral imaging in the UV to visible range with nanometer scale resolution of closely packed GaN/AlN quantum disks in individual nanowires using an improved custom-made cathodoluminescence system. We demonstrate the possibility to measure full spectral features of individual quantum emitters as small as 1 nm and separated from each other by only a few nanometers and the ability to correlate their optical properties to their size, measured with atomic resolution. The direct correlation between the quantum disk size and emission wavelength provides evidence of the quantum confined Stark effect leading to an emission below the bulk GaN band gap for disks thicker than 2.6 nm. With the help of simulations, we show that the internal electric field in the studied quantum disks is smaller than what is expected in the quantum well case. We show evidence of a clear dispersion of the emission wavelengths of different quantum disks of identical size but different positions along the wire. This dispersion is systematically correlated to a change of the diameter of the AlN shell coating the wire and is thus attributed to the related strain variations along the wire. The present work opens the way both to fundamental studies of quantum confinement in closely packed quantum emitters and to characterizations of optoelectronic devices presenting carrier localization on the nanometer scale.
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J Phys Chem B
January 2025
Single Molecule Analysis Group, Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109, United States.
Single-molecule fluorescence resonance energy transfer (smFRET) has emerged as a pivotal technique for probing biomolecular dynamics over time at nanometer scales. Quantitative analyses of smFRET time traces remain challenging due to confounding factors such as low signal-to-noise ratios, photophysical effects such as bleaching and blinking, and the complexity of modeling the underlying biomolecular states and kinetics. The dynamic distance information shaping the smFRET trace powerfully uncovers even transient conformational changes in single biomolecules both at or far from equilibrium, relying on trace idealization to identify specific interconverting states.
View Article and Find Full Text PDFLangmuir
January 2025
Laboratoire de Physique des Solides, CNRS, Université Paris Saclay, 91405 Orsay, France.
Controlling the structure of polymer solutions near a solid surface is crucial for many industrial processes as it significantly impacts solution flow and influences slip at the interface. To date, only a few techniques have been developed to experimentally investigate this type of interface at the nanometric scale of solid/liquid interactions. In this study, we probe the interface between a smooth sapphire surface and a semidilute polystyrene solution, using neutron reflectivity.
View Article and Find Full Text PDFAtomic-scale changes can significantly impact heterogeneous catalysis, yet their atomic mechanisms are challenging to establish using conventional analysis methods. By using identical location scanning transmission electron microscopy (IL-STEM), which provides quantitative information at the single-particle level, we investigated the mechanisms of atomic evolution of Ru nanoclusters during the ammonia decomposition reaction. Nanometre-sized disordered nanoclusters transform into truncated nano-pyramids with stepped edges, leading to increased hydrogen production from ammonia.
View Article and Find Full Text PDFNPJ 2D Mater Appl
January 2025
School of Physics, CRANN & AMBER Research Centres, Trinity College Dublin, Dublin, Ireland.
Thin films fabricated from solution-processed graphene nanosheets are of considerable technological interest for a wide variety of applications, such as transparent conductors, supercapacitors, and memristors. However, very thin printed films tend to have low conductivity compared to thicker ones. In this work, we demonstrate a simple layer-by-layer deposition method which yields thin films of highly-aligned, electrochemically-exfoliated graphene which have low roughness and nanometer-scale thickness control.
View Article and Find Full Text PDFSci Rep
January 2025
Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore.
Kaolinite is a single 2D layer of kaolin or metakaolin (MK), common clays that can be characterized as layered 3D materials. We show that because of its chemical composition, kaolinite can be converted into an amorphous 3D material by chemical means. This dimensional transformation is possible due to the large surface to volume ratio and chemical reactivity of kaolinite.
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