Publications

This is a dataset of automatically extracted sizes and morphologies of Gold nanoparticles, which have been obtained from the analysis of 4365 literature-mined SEM/TEM images. The dataset contains 4365 records, each of which contains extracted size/morphology information and metadata corresponding to a single microscopy image.

Nanoscale stress-sensing can be used across fields ranging from detection of incipient cracks in structural mechanics to monitoring forces in biological tissues. We demonstrate how tetrapod quantum dots (tQDs) embedded in block copolymers act as sensors of tensile/compressive stress. Remarkably, tQDs can detect their own composite dispersion and mechanical properties with a switch in optomechanical response when tQDs are in direct contact. Using experimental characterizations, atomistic simulations and finite-element analyses, we show that under tensile stress, densely packed tQDs exhibit a photoluminescence peak shifted to higher energies ("blue-shift") due to volumetric compressive stress in their core; loosely packed tQDs exhibit a peak shifted to lower energies ("red-shift") from tensile stress in the core. The stress shifts result from the tQD's unique branched morphology in which the CdS arms act as antennas that amplify the stress in the CdSe core. Our nanocomposites exhibit excellent cyclability and scalability with no degraded properties of the host polymer. Colloidal tQDs allow sensing in many materials to potentially enable autoresponsive, smart structural nanocomposites that self-predict impending fracture.

The optical efficiency of lanthanide-based upconversion is intricately related to the crystalline host lattice. Different crystal fields interacting with the electron clouds of the lanthanides can significantly affect transition probabilities between the energy levels. Here, we investigate six distinct alkaline-earth rare-earth fluoride host materials (M_{1- x}Ln _xF_2+x, MLnF) for infrared-to-visible upconversion, focusing on nanoparticles of CaYF, CaLuF, SrYF, SrLuF, BaYF, and BaLuF doped with Yb³⁺ and Er³⁺. We first synthesize ∼5 nm upconverting cores of each material via a thermal decomposition method. Then we introduce a dropwise hot-injection method to grow optically inert MYF shell layers around the active cores. Five distinct shell thicknesses are considered for each host material, resulting in 36 unique, monodisperse upconverting nanomaterials each with size below ∼15 nm. The upconversion quantum yield (UCQY) is measured for all core/shell nanoparticles as a function of shell thickness and compared with hexagonal (β-phase) NaGdF₄, a traditional upconverting host lattice. While the UCQY of core nanoparticles is below the detection limit (<10^-5%), it increases by 4 to 5 orders of magnitude as the shell thickness approaches 4-6 nm. The UCQY values of our cubic MLnF nanoparticles meet or exceed the β-NaGdF₄ reference sample. Across all core/shell samples, SrLuF nanoparticles are the most efficient, with UCQY values of 0.53% at 80 W/cm² for cubic nanoparticles with ∼11 nm edge length. This efficiency is 5 times higher than our β-NaGdF₄ reference material with comparable core size and shell thickness. Our work demonstrates efficient and bright upconversion in ultrasmall alkaline-earth-based nanoparticles, with applications spanning biological imaging and optical sensing.

We present the rational synthesis of colloidal copper(I) sulfide nanocrystals and demonstrate their application as an active light absorbing component in combination with CdS nanorods to make a solution-processed solar cell with 1.6percent power conversion efficiency on both conventional glass substrates and flexible plastic substrates with stability over a 4 month testing period.

Abstract In between the molecular and bulk forms of matter, semiconductor nanocrystals are novel materials with interesting optical and electronic properties. We present a study of the homogeneous optical properties of two nanocrystal systems. First, the homogeneous absorption of InP nanocrystals is studied via hole burning experiments. The optical spectrum consists of a HOMO-LUMO transition with a 10 meV width and a second electronic transition shifted by 0.11 eV. The optical transitions are assigned within a three valence-band model. The CdS/HgS/CdS quantum-dot/quantum-well system is also investigated and a transmission electron microscopy study shows that the growth of the HgS well region and the CdS outer layer is epitaxial. Selective optical techniques are used to study the electronic level structure. In hole burning, a discrete transition (width of 7 meV) with pronounced phonon side bands at a frequency of 250 cm−1 is observed. In fluorescence, the line narrowed spectrum also shows phonon replicas at a similar frequency. The measurements provide direct evidence for charge localization in the low band gap HgS well region within this colloidally synthesized nano-heterostructure.

Graphene liquid cell transmission electron microscopy is a powerful technique to visualize nanoscale dynamics and transformations at atomic resolution. However, the solution in liquid cells is known to be affected by radiolysis, and the stochastic formation of graphene liquid cells raises questions about the solution chemistry in individual pockets. In this study, electron energy loss spectroscopy (EELS) was used to evaluate a model encapsulated solution, aqueous CeCl₃. First, the ratio between the O K-edge and Ce M-edge was used to approximate the concentration of cerium salt in the graphene liquid cell. It was determined that the ratio between oxygen and cerium was orders of magnitude lower than what is expected for a dilute solution, indicating that the encapsulated solution is highly concentrated. To probe how this affects the chemistry within graphene liquid cells, the oxidation of Ce³⁺ was measured using time-resolved parallel EELS. It was determined that Ce³⁺ oxidizes faster under high electron fluxes, but reaches the same steady-state Ce⁴⁺ concentration regardless of flux. The time-resolved concentration profiles enabled direct comparison to radiolysis models, which indicate rate constants and <i>g</i>-values of certain molecular species are substantially different in the highly concentrated environment. Finally, electron flux-dependent gold nanocrystal etching trajectories showed that gold nanocrystals etch faster at higher electron fluxes, correlating well with the Ce³⁺ oxidation kinetics. Understanding the effects of the highly concentrated solution in graphene liquid cells will provide new insight on previous studies and may open up opportunities to systematically study systems in highly concentrated solutions at high resolution.

Industrial catalysts often consist of transition metals supported on microporous or mesoporous high surface area oxides and are prepared by techniques such as impregnation and ion adsorption. In standard fabrication processes the metal particle size is not well-controlled. In this paper we report a new synthetic route for the production of catalyst materials with more precise control of the metal particle size. Gold nanoparticles encapsulated in mesoporous silica (MCM-41 and MCM-48) served as a model system, although the techniques described are applicable to a wide variety of metals and oxide supports. The samples were characterized by a combination of low-angle powder X-ray diffraction, transmission electron microscopy, N2 porosimetry, infrared spectroscopy, and X-ray absorption near-edge spectroscopy. The results show that the MCM-41 and MCM-48 structures retain their long-range order when metal particles are added; in addition, the size of the channels increases monotonically with metal loading. X-ray absorption near-edge spectroscopy in combination with the adsorption of thiols provides conclusive evidence that 2- and 5-nm-diameter Au nanoparticles are incorporated into the pores of the silicates and that they are accessible to reactant molecules.