Ostwald Ripening-Mediated Grafting of Metal-Organic Frameworks on a Single Colloidal Nanocrystal to Form Uniform and Controllable MXF.

MXF, a metal-organic framework (MOF) that contains more than two components, such as heterogeneous inorganic nanoparticle@MOF (NP@MOF) with precisely defined structures, is important in applications such as catalysis, energy, and biochemistry. However, the ambiguous growth mechanism of MXF has hindered the exploration of controllable design of nanoparticle level MXF complexes. Here, we report an Ostwald ripening-mediated grafting of MOF on a single multidentate inorganic colloidal nanocrystal via heterogeneous nucleation. The grafting relies on the carboxylic acid groups anchored on the surface of the colloidal nanocrystal. Ostwald ripening-mediated grafting enabled us to obtain uniform MXF with a wide range of sizes of nanoparticles and a controlled thickness of the MOF layer on the surface of colloidal nanocrystal. A dual FRET-induced singlet oxygen generation with near-infrared light was achieved from an UCNP@ZrMOF hybrid. This generalizable grafting strategy provides insight into the design of MXF nanoparticles for a wide range of applications involving advanced functional materials.

Kinetics of copper nanoparticle precipitation in phosphate glass: an isothermal plasmonic approach.

The kinetics of copper nanoparticle (NP) precipitation in melt-quenched barium-phosphate glass has been studied by in situ isothermal optical micro-spectroscopy. A spectroscopically based approximation technique is proposed to obtain information about the activation energies of nucleation and growth in a narrow temperature range (530-570 °C). Pre-plasmonic and plasmonic NP precipitation stages are identified separated in time. The process as a whole is discussed employing classical nucleation/growth theory and the Kolmogorov-Johnson-Mehl-Avrami phase change model. Activation energies of 3.9(7) eV and 2.6(5) eV have been estimated for the pre-plasmonic and plasmonic spectroscopically assessed stages, respectively. High resolution transmission electron microscopy, differential scanning calorimetry, and Raman spectroscopy were used as complementary techniques for studying the nanoparticulate phase and glass host structure. An empirical linear dependence of the diffusion activation energy on the glass transition temperature with broad applicability is suggested.

Modifying the Substrate-Dependent Pd/Fe2O3 Catalyst-Support Synergism with ZnO Atomic Layer Deposition.

Low-loading Pd supported on Fe2O3 nanoparticles was synthesized. A common nanocatalyst system with previously reported synergistic enhancement of reactivity that is attributed to the electronic interactions between Pd and the Fe2O3 support. Fe2O3-selective precoalescence overcoating with ZnO atomic layer deposition (ALD), using Zn(CH2CH3)2 and H2O as precursors, dampens competitive hydrogenation reactivity at Fe2O3-based sites. The result is enhanced efficiency at the low-loading but high reactivity Pd sites. While this increases catalyst efficiency toward most aqueous redox reactions tested, it suppresses reactivity toward polyaromatic core substrates. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) show minimal electronic impacts for the ZnO overcoat on the Pd particles, implying a predominantly physical site blocking effect as the reason for the modified reactivity. This serves as a proof-of-concept of not only stabilizing supported nanocatalysts but also altering reactivity with ultrathin ALD overcoats. The results point to a facile ALD route for selective enhancement of reactivity for low-loading Pd-based supported nanocatalysts.

Release Rate Studies of 5-Aminosalacylic Acid Coated with Atomic Layer-Deposited Al2O3 and ZnO in an Acidic Environment.

5-Aminosalicylic acid (5-ASA) is a first-line defense drug used to treat mild cases of inflammatory bowel disease. When administered orally, the active pharmaceutical ingredient is released throughout the gastrointestinal tract relieving chronic inflammation. However, delayed and targeted released systems for 5-ASA to achieve optimal dose volumes in acidic environments remain a challenge. Here, we demonstrate the application of atomic layer deposition (ALD) as a technique to synthesize nanoscale coatings on 5-ASA to control its release in acidic media. ALD Al2O3 (38.0 nm) and ZnO (24.7 nm) films were deposited on 1 g batch powders of 5-ASA in a rotatory thermal ALD system. Fourier transform infrared spectroscopy, scanning electron microscopy, and scanning/transmission electron microscopy establish the interfacial chemistry and conformal nature of ALD coating over the 5-ASA particles. While Al2O3 forms a sharp interface with 5-ASA, ZnO appears to diffuse inside 5-ASA. The release of 5-ASA is studied in a pH 4 solution via UV-vis spectroscopy. Dynamic stirring, mimicking gut peristalsis, causes mechanical attrition of the Al2O3-coated particles, thereby releasing 5-ASA. However, under static conditions lasting 5000 s, the Al2O3-coated particles release only 17.5% 5-ASA compared to 100% release with the ZnO coating. Quartz crystal microbalance-based etch studies confirm the stability of Al2O3 in pH 4 media, where the ZnO films etch 41× faster than Al2O3. Such results are significant in achieving a nanoscale coating-based drug delivery system for 5-ASA with controlled release in acidic environments.

Nanoscale goldbeating: Solid-state transformation of 0D and 1D gold nanoparticles to anisotropic 2D morphologies.

Goldbeating is the ancient craft of thinning bulk gold (Au) into gossamer leaves. Pioneered by ancient Egyptian craftsmen, modern mechanized iterations of this technique can fabricate sheets as thin as ∼100 nm. We take inspiration from this millennia-old craft and adapt it to the nanoscale regime, using colloidally synthesized 0D/1D Au nanoparticles (AuNPs) as highly ductile and malleable nanoscopic Au ingots and subjecting them to solid-state, uniaxial compression. The applied stress induces anisotropic morphological transformation of AuNPs into 2D leaf form and elucidates insights into metal nanocrystal deformation at the extreme length scales. The induced 2D morphology is found to be dependent on the precursor 0D/1D NP morphology, size (0D nanosphere diameter and 1D nanorod diameter and length), and their on-substrate arrangement (e.g., interparticle separation and packing order) prior to compression. Overall, this versatile and generalizable solid-state compression technique enables new pathways to synthesize and investigate the anisotropic morphological transformation of arbitrary NPs and their resultant emergent phenomena.

High Quality Factors in Superlattice Ferroelectric Hf0.5Zr0.5O2 Nanoelectromechanical Resonators.

The discovery of ferroelectricity and advances in creating polar structures in atomic-layered hafnia-zirconia (HfxZr1-xO2) films spur the exploration of using the material for novel integrated nanoelectromechanical systems (NEMS). Despite its popularity, the approach to achieving high quality factors (Qs) in resonant NEMS made of HfxZr1-xO2 thin films remains unexplored. In this work, we investigate the realization of high Qs in Hf0.5Zr0.5O2 nanoelectromechanical resonators by stress engineering via the incorporation of alumina (Al2O3) interlayers. We fabricate nanoelectromechanical resonators out of the Hf0.5Zr0.5O2-Al2O3 superlattices, from which we measure Qs up to 171,000 and frequency-quality factor products (f × Q) of >1011 Hz through electrical excitation and optical detection schemes at room temperature in vacuum. The analysis suggests that clamping loss and surface loss are the limiting dissipation sources and f × Q > 1012 Hz is achievable through further engineering of anchor structure and built-in stress.

Silver nanoparticles enhance the efficacy of aminoglycosides against antibiotic-resistant bacteria.

As the threat of antimicrobial-resistant bacteria compromises the safety and efficacy of modern healthcare practices, the search for effective treatments is more urgent than ever. For centuries, silver (Ag) has been known to have antibacterial properties and, over the past two decades, Ag-based nanoparticles have gained traction as potential antimicrobials. The antibacterial efficacy of Ag varies with structure, size, and concentration. In the present study, we examined Ag nanoparticles (AgNPs) for their antimicrobial activity and safety. We compared different commercially-available AgNPs against gram-negative Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, and gram-positive Staphylococcus aureus methicillin-resistant and susceptible strains. The most effective formula of AgNPs tested had single-digit (µg/mL) minimum inhibitory concentrations against gram-negative multidrug-resistant clinical bacterial isolates with novel and emerging mechanisms of resistance. The mode of killing was assessed in E. coli and was found to be bactericidal, which is consistent with previous studies using other AgNP formulations. We evaluated cytotoxicity by measuring physiological readouts using the Caenorhabditis elegans model and found that motility was affected, but not the lifespan. Furthermore, we found that at their antibacterial concentrations, AgNPs were non-cytotoxic to any of the mammalian cell lines tested, including macrophages, stem cells, and epithelial cells. More interestingly, our experiments revealed synergy with clinically relevant antibiotics. We found that a non-toxic and non-effective concentration of AgNPs reduced the minimum inhibitory concentrations of aminoglycoside by approximately 22-fold. Because both aminoglycosides and Ag are known to target the bacterial ribosome, we tested whether Ag could also target eukaryotic ribosomes. We measured the rate of mistranslation at bactericidal concentration and found no effect, indicating that AgNPs are not proteotoxic to the host at the tested concentrations. Collectively, our results suggest that AgNPs could have a promising clinical application as a potential stand-alone therapy or antibiotic adjuvants.

Growth of C-Axis Textured AlN Films on Vertical Sidewalls of Silicon Microfins.

A fabrication process is developed to grow c -axis textured aluminum nitride (AlN) films on the sidewall of single-crystal silicon (Si) microfins to realize fin bulk acoustic wave resonators (FinBARs). FinBARs enable ultradense integration of high-quality-factor ( Q ) resonators and low-loss filters on a small chip footprint and provide extreme lithographical frequency scalability over ultra- and super-high-frequency regimes. Si microfins with large aspect ratio are patterned and their sidewall surfaces are atomically smoothened. The reactive magnetron sputtering AlN deposition is engineered to optimize the hexagonal crystallinity of the sidewall AlN film with c -axis perpendicular to the sidewall of Si microfins. The effect of bottom metal electrode and surface roughness on the texture and crystallinity of the sidewall AlN film is explored. The atomic-layer-deposited platinum film with (111) crystallinity is identified as a suitable bottom electrode for deposition of c -axis textured AlN on the sidewall with c -axis orientation of 88.5° ± 1.5° and arc-angle of ~12° around (002) diffraction spot over film thickness. A 4.2-GHz FinBAR prototype is implemented showing a Q of 1574 and effective electromechanical coupling ( [Formula: see text]) of 2.75%, when operating in the 3rd width-extensional resonance mode. The lower measured Q and [Formula: see text] compared to simulations highlights the effect of granular texture of sidewall AlN film on limiting the performance of FinBARs. The developed c -axis textured sidewall AlN film technology paves the way for realization and monolithic integration of multifrequency and multiband FinBAR spectral processors for the emerging carrier aggregated wireless communication systems.

Comparing electron recombination via interfacial modifications in dye-sensitized solar cells.

Establishing a blocking layer between the interfaces of the photoanode is an effective approach to improve the performance of dye-sensitized solar cells (DSSCs). In this work, HfO2 blocking layers are deposited via atomic layer deposition (ALD) onto tin-doped indium oxide (ITO) and TiO2. In both cases, addition of the blocking layer increases cell efficiencies to greater than 7%. The improved performance for a HfO2 layer inserted between the ITO/TiO2 interface is associated with an energy barrier that reduces electron recombination. HfO2 blocking layers between the TiO2/dye interface show more complex behavior and are more sensitive to the number of ALD cycles. For thin blocking layers on TiO2, the improved device performance is attributed to the passivation of surface states in TiO2. A distinct transition in dark current and electron lifetime are observed after 4 ALD cycles. These changes to performance indicate thick HfO2 layers on TiO2 formed an energy barrier that significantly hinders cell performance.