Journal: ACS Nano

Abbreviation

ACS Nano

Publisher

American Chemical Society

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ISSN

1936-0851
1936-086X

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Publications 1 - 10 of 347
  • Unraveling the Origin of the Long Fluorescence Decay Component of Cesium Lead Halide Perovskite Nanocrystals
    Item type: Journal Article
    Becker, Michael A.; Bernasconi, Caterina; Bodnarchuk, Maryna I.; et al. (2020)
    ACS Nano
    A common signature of nearly all nanoscale emitters is fluorescence intermittency, which is a rapid switching between “on”-states exhibiting a high photon emission rate and “off”-states with a much lower rate. One consequence of fluorescence intermittency occurring on time scales longer than the exciton decay time is the so-called delayed photon emission, manifested by a long radiative decay component. Besides their dominant fast radiative decay, fully inorganic cesium lead halide perovskite quantum dots exhibit a long fluorescence decay component at cryogenic temperatures that is often attributed to the decay of the dark exciton. Here, we show that its origin is delayed photon emission by investigating temporal variations in fluorescence intensity and concomitant decay times found in single CsPbBr3 perovskite quantum dots. We attribute the different intensity levels of the intensity trace to a rapid switching between a high-intensity exciton state and an Auger-reduced low-intensity trion state that occurs when the excitation is sufficiently strong. Surprisingly, we observe that the exponent of this power-law-dependent delayed emission is correlated with the emission intensity, which cannot be explained with existing charge carrier trapping models. Our analysis reveals that the long decay component is mainly governed by delayed emission, which is present in both the exciton and trion state. The absence of a fine structure in trions clarifies the vanishing role of the dark exciton state for the long decay component. Our findings are essential for the development of a complete photophysical model that captures all observed features of fluorescence variations in colloidal nanocrystals.
  • Rise and Decay of Photoluminescence in Upconverting Lanthanide-Doped Nanocrystals
    Item type: Journal Article
    Vonk, Sander J.W.; Maris, J.J. Erik; Dekker, Ayla J.H.; et al. (2024)
    ACS Nano
    Nanocrystals (NCs) doped with lanthanides are capable of efficient photon upconversion, i.e., absorbing long-wavelength light and emitting shorter-wavelength light. The internal processes that enable upconversion are a complex network of electronic transitions within and energy transfer between dopant centers. In this work, we study the rise and decay dynamics of upconversion emission from β-NaYF₄ NCs codoped with Er³⁺ and Yb³⁺. The rise dynamics of the red and green upconverted emissions are nonlinear, reflecting the nonlinear nature of upconversion and revealing the mechanisms that populate the emitting states. The excited-state decay dynamics are nonexponential. We unravel the underlying decay pathways using photonic experiments. These reveal the contributions of different upconversion pathways visually, as each pathway exhibits a distinct response to systematic variation of the local density of optical states. Moreover, the effect of the local density of optical states on core-only NCs is qualitatively different from core–shell NCs. This is due to the different balance between feeding and decay of the electronic levels that produce upconverted emission. The understanding of the upconversion dynamics provided here could lead to better imaging and sensing methods relying on upconversion lifetimes or guide the rational optimization of the dopant concentrations for brighter upconversion.
  • Photo-Switchable Nanoripples in Ti3C2Tx MXene
    Item type: Journal Article
    Volkov, Mikhail; Willinger, Elena; Kuznetsov, Denis A.; et al. (2021)
    ACS Nano
    MXenes are two-dimensional materials with a rich set of chemical and electromagnetic properties, the latter including saturable absorption and intense surface plasmon resonances. To fully harness the functionality of MXenes for applications in optics, electronics, and sensing, it is important to understand the interaction of light with MXenes on atomic and femtosecond dimensions. Here, we use ultrafast electron diffraction and high-resolution electron microscopy to investigate the laser-induced structural dynamics of Ti3C2Tx nanosheets. We find an exceptionally fast lattice response with an electron-phonon coupling time of 230 fs. Repetitive femtosecond laser excitation transforms Ti3C2Tx through a structural transition into a metamaterial with deeply sub-wavelength nanoripples that are aligned with the laser polarization. By a further laser illumination, the material is reversibly photoswitchable between a flat and rippled morphology. The resulting nanostructured MXene metamaterial with directional nanoripples is expected to exhibit an anisotropic optical and electronic response as well as an enhanced chemical activity that can be switched on and off by light.
  • Thermally degradable ligands for nanocrystals
    Item type: Journal Article
    Wills, Andrew W.; Kang, Moon Sung; Khare, Ankur; et al. (2010)
    ACS Nano
  • In Situ Atomic-Scale Observation of Surface-Tension-Induced Structural Transformation of Ag-NiPx Core-Shell Nanocrystals
    Item type: Journal Article
    Huang, Xing; Liu, Zhongqiang; Millet, Marie-Mathilde; et al. (2018)
    ACS Nano
  • Imaging of Plasmonic Heating in a Living Organism
    Item type: Journal Article
    Donner, Jon S.; Thompson, Sebastian A.; Alonso-Ortega, Cesar; et al. (2013)
    ACS Nano
    Controlling and monitoring temperature at the single cell level has become pivotal in biology and medicine. Indeed, temperature influences many intracellular processes and is also involved as an activator in novel therapies. Aiming to assist such developments, several approaches have recently been proposed to probe cell temperature in vitro. None of them have so far been extended to a living organism. Here we present the first in vivo intracellular temperature imaging. Our technique relies on measuring the fluorescence polarization anisotropy of green fluorescent protein (GFP) on a set of GFP expressing neurons in Caenorhabditis elegans (C. Elegans). We demonstrate fast and noninvasive monitoring of subdegree temperature changes on a single neuron induced by local photoheating of gold nanoparticles. This simple and biocompatible technique is envisioned to benefit several fields including hyperthermia treatment, selective drug delivery, thermal regulation of gene expression and neuron laser ablation. © 2013 American Chemical Society.
  • The Next Dimension: Digital Holography for 3D Interferometric Scattering
    Item type: Journal Article
    Ortega Arroyo, Jaime; Liebel, Matz (2025)
    ACS Nano
    We provide detailed experimental guidelines for implementing digital holography in the context of high-sensitivity interferometric scattering (iSCAT)-based nanosizing applications. Our approach relies on interferometry via the highly versatile off-axis implementation of digital holography, which offers key advantages over more traditional strategies. After a brief theoretical discussion of off-axis holography and its differences and similarities with iSCAT, typical experimental implementations and digital data-processing steps are presented. Key experimental parameters and strategies to achieve optimal performance are also highlighted. Following these experimental aspects, we focus on digital postprocessing routines that enable digital refocusing and 3D particle tracking as well as pupil function aberration correction. We then conclude with a few examples highlighting the broad applicability of digital holography for nanosizing and particle characterization applications, as well as an outlook for future applications.
  • Impact of Interface and Surface Oxide Defects on WS₂ Electronic Properties from First Principles
    Item type: Journal Article
    Van Troeye, Benoit; Ducry, Fabian; Dossena, Mauro; et al. (2025)
    ACS Nano
    The industrial-scale growth of dielectrics on top of a 2D material transistor channel without deterioration of its transport characteristics remains challenging today. Here, we investigate the origin of the performance degradation issue by constructing several atomistic interface models between a WS2 monolayer and an amorphous Al2O3 or HfO2 thin film. We then computed their properties using first-principles methods. We show that, while it is in principle possible to achieve a van der Waals interface between these materials, surface defects (e.g., undercoordinated metal atoms at the surface) are detrimental since they create localized states close to the bottom of the conduction band of WS2. Even in their absence, the inhomogeneity of the surface topology creates a nonuniform potential that is felt by charge carriers in WS2. While surface defects can potentially be kept under control with an appropriate oxide choice, the surface inhomogeneity appears to act as a bottleneck, limiting the performance of WS2 as a transistor channel and, in general, for all 2D materials.
  • Surface-Chemistry-Mediated Control of Individual Magnetic Helical Microswimmers in a Swarm
    Item type: Journal Article
    Wang, Xiaopu; Hu, Chengzhi; Schurz, Lukas; et al. (2018)
    ACS Nano
  • Beyond CO2 Storage: Enzyme-Amyloid Fibril Catalytic Hybrids for Long Cascade Reactions Converting CO2 into Fructose
    Item type: Journal Article
    Jin, Tonghui; Chhong, Sophally; Li, Mingqin; et al. (2025)
    ACS Nano
    Enzyme immobilization is an efficient and cost-effective approach to recovering, stabilizing, and enhancing enzyme catalytic properties. It is a challenge, however, for coimmobilized multiple enzymes to perform consecutive reactions without being inactivated under similar conditions. Here, we present a facile enzyme immobilization platform using beta-lactoglobulin amyloid fibril hydrogels. Two different hydrogels, loading either RuBisCO alone (hereby termed AFR*) or seven enzymes related to the Calvin Cycle (hereby termed AF7E hydrogel), show immobilization efficiency of over similar to 95% while simultaneously exhibiting excellent activity and stability. The AFR* hydrogel enables the fixation of CO2 into 3-phosphoglycerate (3-PGA), which is then utilized as the initial step in the Calvin Cycle cascade catalytic reactions if the AF7E hydrogel is used, mimicking the light-independent part of the more complex natural photosynthesis full process. The converted substrates of this process contain precursors (alpha-glycerophosphate dehydrogenase and dihydroxyacetone phosphate), which can be further converted to fructose by additional aldolase. Due to the proteinaceous nature of the amyloid substrate, the AF7E hydrogel is completely biodegradable by pepsin, as confirmed via atomic force microscopy and circular dichroism spectroscopy analysis. This original enzyme-amyloid hybrid is biocompatible, sustainable, and scalable and may serve as a general template for multienzymatic catalytic platforms.
Publications 1 - 10 of 347