Role of the electronically-active amorphous state in low-temperature processed In2O3 thin-film transistors

Metal oxide (MO) thin-film transistors (TFTs) are expected to enable low-cost flexible and printed electronics, given their excellent charge transport, low processing temperatures and solution processability. However, achieving adequate mobility when processed scalably at low temperatures compatible with plastic electronics is a challenge. Here, we explore process-structure-transport relationships in blade-coated indium oxide (In2O3) TFTs via both sol-gel and combustion chemistries. We find that the sol-gel chemistry enables n-type TFTs when annealed at 200 °C to 225 °C with noticeable electron mobility ((3.4 ± 1.3) cm2V-1s-1) yet minimal In2O3 crystallinity and surprisingly low levels of the metal-oxygen-metal (M-O-M) lattice content (≈46 %). Increased annealing temperatures result in the appearance of nanocrystalline domains and an increase in M-O-M content to ≈70 %, without any further increase in mobility. An actetylacetone combustion-assisted ink lowers the external thermal budget required for In2O3 crystallization but bypasses the electronically-active amorphous state and underperforms the sol-gel ink at low temperatures. Grain boundary formation and nanocrystalline inclusions in these films due to rapid combustion-assisted crystallization are suggested to be the likely origin behind the significantly compromised charge transport at low-temperatures. Overall, this study emphasizes the need to understand the complex interplay between local order (nanocrystallinity) and connectivity (grain boundary, amorphous phases) when optimizing low-temperature processed MO thin films.

Dendrimer Ligand Directed Nanoplate Assembly

Many studies on nanocrystal (NC) self-assembly into ordered superlattices have focused mainly on attractive forces between the NCs, whereas the role of organic ligands on anisotropic NCs is only in its infancy. Herein, we report the use of a series of dendrimer ligands to direct the assembly of nanoplates into 2D and 3D geometries. It was found that the dendrimer-nanoplates consistently form a directionally offset architecture in 3D films. We present a theory to predict ligand surface distribution and Monte Carlo simulation results that characterize the ligand shell around the nanoplates. Bulky dendrimer ligands create a nontrivial corona around the plates that changes with ligand architecture. When this organic-inorganic effective shape is used in conjunction with thermodynamic perturbation theory to predict both lattice morphology and equilibrium relative orientations between NCs, a lock-and-key type of mechanism is found for the 3D assembly. We observe excellent agreement between our experimental results and theoretical model for 2D and 3D geometries, including the percent of offset between the layers of NCs. Such level of theoretical understanding and modeling will help guide future design frameworks to achieve targeted assemblies of NCs.

Light-driven carbon-carbon bond formation via CO2 reduction catalyzed by complexes of CdS nanorods and a 2-oxoacid oxidoreductase

Redox enzymes are capable of catalyzing a vast array of useful reactions, but they require redox partners that donate or accept electrons. Semiconductor nanocrystals provide a mechanism to convert absorbed photon energy into redox equivalents for enzyme catalysis. Here, we describe a system for photochemical carbon-carbon bond formation to make 2-oxoglutarate by coupling CO₂ with a succinyl group. Photoexcited electrons from cadmium sulfide nanorods (CdS NRs) transfer to 2-oxoglutarate:ferredoxin oxidoreductase from Magnetococcus marinus MC-1 (MmOGOR), which catalyzes a carbon-carbon bond formation reaction. We thereby decouple MmOGOR from its native role in the reductive tricarboxylic acid cycle and drive it directly with light. We examine the dependence of 2-oxoglutarate formation on a variety of factors and, using ultrafast transient absorption spectroscopy, elucidate the critical role of electron transfer (ET) from CdS NRs to MmOGOR. We find that the efficiency of this ET depends strongly on whether the succinyl CoA (SCoA) cosubstrate is bound at the MmOGOR active site. We hypothesize that the conformational changes due to SCoA binding impact the CdS NR-MmOGOR interaction in a manner that decreases ET efficiency compared to the enzyme with no cosubstrate bound. Our work reveals structural considerations for the nano-bio interfaces involved in light-driven enzyme catalysis and points to the competing factors of enzyme catalysis and ET efficiency that may arise when complex enzyme reactions are driven by artificial light absorbers.

Spectroscopic Comparison of Thermal Transport at Organic-Inorganic and Organic-Hybrid Interfaces Using CsPbBr3 and FAPbBr3 (FA = Formamidinium) Perovskite Nanocrystals

Thermal transport across interfaces depends on the matching of vibrational structure at the interface. This work examines the transfer of thermal excitation from an organic ligand coating to either all-inorganic cesium lead tribromide (CsPbBr₃) nanocrystals or hybrid organic-inorganic formamidinium lead tribromide (FAPbBr₃) nanocrystals using selective infrared optical excitation. These two semiconductors are directly compared because they (or similar semiconductors) are currently envisioned as strong candidates in many optoelectronic technologies and they differ due to the presence of an organic or inorganic cation, which introduces substantial differences in the phonon density of states in otherwise quite similar semiconductors. Infrared excitation of C-H vibrations of surface-bound ligands generates a temperature gradient between the organic ligand shell and nanocrystal core, which results in heat flow, measured by probing changes of the semiconductor band gap. Heat transfer to both perovskite compositions of comparable sizes is similar (25-30 ps), due to fast intramolecular vibrational relaxation and similar matching of low-energy phonons with the organic ligand, but FAPbBr₃ samples show a slow bleaching kinetic on the order of 1 ns. This slow, heat-induced change in the semiconductor band gap is attributed not to interfacial heat transfer but instead to thermal equilibration between the organic and inorganic sublattices of FAPbBr₃. Ab initio molecular dynamics simulations support the hypothesis that low-energy inorganic sublattice phonon modes are populated initially in the heat transfer process, with a slow thermal population of the higher-energy phonon modes associated primarily with the organic cation. Slow thermal equilibration of FAPbBr₃ is likely to substantially impact the time-dependent response of optoelectronic devices that heat the semiconductor active layer and provide further evidence that the poor bulk thermal transport of hybrid perovskite materials extends to microscopic thermal processes.

Photoinduced Surface Charging in Iron-Carbonyl-Functionalized Colloidal Semiconductor Nanocrystals

Organometallic surface functionalization of colloidal CdSe and CdS nanocrystals using iron tetracarbonyl moieties is demonstrated to enable study of in situ colloidal nanocrystal surface redox chemistry. Spectroscopic measurements of the surface-bound metal carbonyl C-O stretches were used to elucidate the coordination environments and local symmetry of surface sites. The C-O stretching frequencies of these fragments were correlated to the electric field induced by nanocrystal surface charges and shift in energy upon surface reduction or oxidation. These measurements revealed that CdSe nanocrystals can accumulate multiple surface electrons under supra-band gap photoexcitation, a process likely relevant to photoactivated nanocrystal processes such as photobrightening. These surface charges are stable for hours and decay extremely slowly under anaerobic conditions.

Synthesis and Post-Annealing of Cu2ZnSnS4 Absorber Layers Based on Oleylamine/1-dodecanethiol

Cu₂ZnSnS₄ (CZTS) nanocrystals in oleylamine (OLA) and 1-dodecanethiol (1-DDT) solvents were successfully prepared via hot-injection method, to produce inks for the deposition of absorber layers in photovoltaic cells. In this process, 1-DDT acts as a coordinating ligand to control the nucleation and growth of CZTS nanocrystals, whereas lower amounts of OLA promote a homogeneous growth of the grains in the absorber layer. X-Ray Diffraction (XRD) revealed both tetragonal and hexagonal phases of CTZS in films obtained after soft thermal treatments (labeled TT0). In particular, 1-DDT is responsible for the formation of a greater percentage of the hexagonal phase (ZnS-wurtzite type) than that formed when only OLA is used. The thermal treatments have been varied from 500 °C to 600 °C for improving crystallization and eliminating secondary phases. Both features are known to promote CZTS thin films with band gap values typical of CZTS (1.5–1.6 eV) and suitable resistivity. This study let to compare also the CZTS post-annealing without (TT1) and with sulfur vapor (TT2) in a tubular furnace. Only tetragonal CZTS phase is observed in the XRD pattern of CZTS thin films after TT2. A small presence of localized residues of secondary phases on the same samples was revealed by μRaman measurements. The best values of band gap (1.50 eV) and resistivity (1.05 ohm.cm) were obtained after thermal treatment at 500 °C, which is suitable for absorber layer in photovoltaic application.

Development of Universal Formulation with Superior Re-dispersion Using Nanocrystal Approach with Simultaneous Identification of API Physicochemical Properties

Universal nanocrystal formulation which can be applied to water-insoluble compounds was proposed and the criteria of its physicochemical properties as an active pharmaceutical ingredients (API) were investigated. Nanocrystal suspension was prepared by a wet-beads milling method. An acceptable Critical Quality Attributes (CQA) of nanocrystal suspension was defined by Z-average less than 500 nm and Polydispersity index (PDI) less than 0.3. Screening studies of dispersing and wetting agents were conducted using three model compounds in different pK_a, melting points, etc., to find universal nanocrystal formulation. The effect of four structurally different polymer species (hydroxypropyl cellulose (HPC), hydoroxypropyl methylcellulose (HPMC), polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA)) and their different grades or five different surfactants (docusate sodium (DOSS), sodium lauryl sulfate (SLS), cetyl trimethyl ammonium bromide (CTAB), polysolbate80 (PS80), and polyoxyethylene castor oil (CO-35)) were studied on the re-dispersion stability. It was found that the combination of 4% (w/v) HPC-SSL and 0.2% (w/v) DOSS was the most robust nanocrystal formulation owing to Z-average less than 200 nm and good re-dispersion stability without aggregates at pH 1.2 and pH 6.8. API physicochemical properties were also identified using ten water-insoluble compounds. Consequently, it was found that solubility (water, pH 1.2 and pH 6.8), molecular weight, hydrogen bonding acceptor and the ratio of log D_7.4 to C Log P were critical factors.

Synthesis and High-Pressure Mechanical Properties of Superhard Rhenium/Tungsten Diboride Nanocrystals

Rhenium diboride is an established superhard compound that can scratch diamond and can be readily synthesized under ambient pressure. Here, we demonstrate two synergistic ways to further enhance the already high yield strength of ReB₂. The first approach builds on previous reports where tungsten is doped into ReB₂ at concentrations up to 48 at. %, forming a rhenium/tungsten diboride solid solution (Re_0.52W_0.48B₂). In the second approach, the composition of both materials is maintained, but the particle size is reduced to the nanoscale (40-150 nm). Bulk samples were synthesized by arc melting above 2500 °C, and salt flux growth at ∼850 °C was used to create nanoscale materials. In situ radial X-ray diffraction was then performed under high pressures up to ∼60 GPa in a diamond anvil cell to study mechanical properties including bulk modulus, lattice strain, and strength anisotropy. The differential stress for both Re_0.52W_0.48B₂ and nano ReB₂ (n-ReB₂) was increased compared to bulk ReB₂. In addition, the lattice-preferred orientation of n-ReB₂ was experimentally measured. Under non-hydrostatic compression, n-ReB₂ exhibits texture characterized by a maximum along the [001] direction, confirming that plastic deformation is primarily controlled by the basal slip system. At higher pressures, a range of other slip systems become active. Finally, both size and solid-solution effects were combined in nanoscale Re_0.52W_0.48B₂. This material showed the highest differential stress and bulk modulus, combined with suppression of the new slip planes that opened at high pressure in n-ReB₂.

Growth Mechanisms and the Effects of Deposition Parameters on the Structure and Properties of High Entropy Film by Magnetron Sputtering

Despite intense research on high entropy films, the mechanism of film growth and the influence of key factors remain incompletely understood. In this study, high entropy films consisting of five elements (FeCoNiCrAl) with columnar and nanometer-scale grains were prepared by magnetron sputtering. The high entropy film growth mechanism, including the formation of the amorphous domain, equiaxial nanocrystalline structure and columnar crystal was clarified by analyzing the microstructure in detail. Besides, the impacts of the important deposition parameters including the substrate temperature, the powder loaded in the target, and the crystal orientation of the substrate on the grain size and morphology, phase structure, crystallinity and elemental uniformity were revealed. The mechanical properties of high entropy films with various microstructure features were investigated by nanoindentation. With the optimized grain size and microstructure, the film deposited at 350 °C using a power of 100 W exhibits the highest hardness of 11.09 GPa. Our findings not only help understanding the mechanisms during the high entropy film deposition, but also provide guidance in manufacturing other novel high entropy films.

Enhanced Oral Bioavailability of Celecoxib Nanocrystalline Solid Dispersion based on Wet Media Milling Technique: Formulation, Optimization and In Vitro/In Vivo Evaluation

Celecoxib (CLX), a selective COX-2 inhibitor, is a biopharmaceutics classification system (BCS) class II drug with its bioavailability being limited by thepoor aqueoussolubility. The purpose of this study was to develop and optimize CLX nanocrystalline(CLX-NC) solid dispersion prepared by the wet medium millingtechnique combined with lyophilizationto enhance oral bioavailability. In formulation screening, the resulting CLX-NC usingpolyvinylpyrrolidone (PVP) VA64 and sodiumdodecyl sulfate (SDS) as combined stabilizers showed the minimum particle size and a satisfactory stability. The formulation and preparation processwere further optimized by central composite experimentaldesign with PVP VA64 concentration (X₁), SDS concentration (X₂) and milling times (X₃) as independent factors and particle size (Y₁), polydispersity index (PDI, Y₂) and zeta potential (Y₃) as response variables. The optimal condition was determined as a combination of 0.75% PVP VA64, 0.11% SDS with milling for 90 min.The particle size, PDI and zeta potential of optimized CLX-NC were found to be 152.4 ± 1.4 nm, 0.191 ± 0.012 and −34.4 ± 0.6 mV, respectively. The optimized formulation showed homogeneous rod-like morphology as observed by scanning electron microscopy and was in a crystalline state as determined by differential scanning calorimetry and powder X-ray diffraction. In a storage stability study, optimized CLX-NC exhibited an excellent physical stability during six months’ storage at both the refrigeration and room conditions. In vivo pharmacokinetic research in Sprague-Dawley ratsdisplayed that C_max and AUC_0–∞ of CLX-NC were increased by 2.9 and 3.1 fold, compared with physical mixture. In this study, the screening and optimizing strategy of CLX-NC formulation represents a commercially viable approach forenhancing the oral bioavailability of CLX.

Quantum Interference in a Single Perovskite Nanocrystal

Coherent manipulation of the exciton wave function in a single semiconductor colloidal nanocrystal (NC) has been actively pursued in the past decades without any success, mainly due to the bothersome existence of the spectral diffusion and the photoluminescence (PL) blinking effects. Such optical deficiencies can be naturally avoided in the newly developed colloidal NCs of perovskite CsPbI₃, leading to the PL spectrum with a stable intensity at the single-particle level. Meanwhile, from the first-order photon-correlation measurement, a PL line width smaller than 20 μeV is estimated for the emission state of the neutral exciton in a single CsPbI₃ NC. Moreover, a dephasing time of about 10 ps can be extracted from the quantum interference measurement on the absorption state of the charged exciton. This stable demonstration of a coherent optical feature will advance single colloidal NCs into the quantum information regime, opening up an alternative yet prospective research direction beyond their traditional applications such as in optoelectronic devices and bioimaging.

Engineering Color-Stable Blue Light-Emitting Diodes with Lead Halide Perovskite Nanocrystals

Nanocrystalline lead halide perovskites are promising as emissive layers for light-emitting diodes due to their bright, tunable emission with very narrow linewidths. Blue perovskite light-emitting diodes, in the wavelength range useful for display applications (460-470 nm), could be made with CsPb(Br/Cl)₃ nanocrystals (NCs). However, mixed halide perovskites suffer from color instability, foremost, due to the segregation of halide ions. In this study, we address this issue with several measures. First, we show that thinner CsPb(Br/Cl)₃ NC layers are less prone to color instability. Additionally, inefficient hole injection due to the deep-lying valence band of CsPb(Br/Cl)₃ NCs detrimentally affects the device performance, and we mitigate this problem by stepwise hole injection using two hole-transporting materials. Next, we employ NCs capped with zwitterionic ligands that allow for a more thorough washing of the NC solutions. Furthermore, our new device layout explores the use of polystyrene in the emitting layer to limit the current leakage. Undertaking these steps, we show light-emitting diodes with a stable electroluminescence peak wavelength of 463 nm over the lifetime of the device and a peak external quantum efficiency of over 1%. The results prove that perovskite NCs are a viable contender in the development of blue-emissive, active pixel displays.

Emerging Functions of Nanostructured Porous Silicon-With a Focus on the Emissive Properties of Photons, Electrons, and Ultrasound

Recent topics of application studies on porous silicon (PS) are reviewed here with a focus on the emissive properties of visible light, quasiballistic hot electrons, and acoustic wave. By exposing PS in solvents to pulse laser, size-controlled nc-Si dot colloids can be formed through fragmentation of the PS layer with a considerably higher yield than the conventional techniques such as laser ablation of bulk silicon and sol-gel precursor process. Fabricated colloidal samples show strong visible photoluminescence (~40% in quantum efficiency in the red band). This provides an energy- and cost-effective route for production of nc-Si quantum dots. A multiple-tunneling transport mode through nc-Si dot chain induces efficient quasiballistic hot electron emission from an nc-Si diode. Both the efficiency and the output electron energy dispersion are remarkably improved by using monolayer graphene as a surface electrode. Being a relatively low operating voltage device compatible with silicon planar fabrication process, the emitter is applicable to mask-less parallel lithography under an active matrix drive. It has been demonstrated that the integrated 100 × 100 emitter array is useful for multibeam lithography and that the selected emission pattern is delineated with little distortion. Highly reducing activity of emitted electrons is applicable to liquid-phase thin film deposition of metals (Cu) and semiconductors (Si, Ge, and SiGe). Due to an extremely low thermal conductivity and volumetric heat capacity of nc-Si layer, on the other hand, thermo-acoustic conversion is enhanced to a practical level. A temperature fluctuation produced at the surface of nc-Si layer is quickly transferred into air, and then an acoustic wave is emitted without any mechanical vibrations. The non-resonant and broad-band emissivity with low harmonic distortions makes it possible to use the emitter for generating audible sound under a full digital drive and reproducing complicated ultrasonic communication calls between mice.

Growth Mechanism of Five-Fold Twinned Ag Nanowires from Multiscale Theory and Simulations

Five-fold twinned metal nanowires can be synthesized with high aspect ratios via solution-phase methods. The origins of their anisotropic growth, however, are poorly understood. We combine atomic-scale, mesoscale, and continuum theoretical methods to predict growth morphologies of Ag nanowires from seeds and to demonstrate that high aspect ratio nanowires can originate from anisotropic surface diffusion induced by the strained nanowire structure. Nanowire seeds are similar to Marks decahedra, with {111} "notches" that accelerate diffusion along the nanowire axis to facilitate one-dimensional growth. The strain distribution on the {111} facets induces heterogeneous atom aggregation and leads to atom trapping at the nanowire ends. We predict that decahedral Ag seeds can grow to become nanowires with aspect ratios in the experimental range. Our studies show that there is a complex interplay between atom deposition, diffusion, seed architecture, and nanowire aspect ratio that could be manipulated experimentally to achieve controlled nanowire syntheses.

Enhancing Saltiness Perception Using Chitin Nanomaterials

In the present study, we prepared and characterized chitin nanomaterials with different diameters, lengths, and degree of deacetylation (DD), and investigated their capability for enhancing saltiness perception. Chitin was isolated from squid pens and transformed into chitin nanofiber (CNF), deacetylated chitin nanofiber (DACNF), and chitin nanocrystal (CNC) by ultrasonication, alkali treatment followed by ultrasonication and acid hydrolysis, respectively. The diameters of CNF, CNC and DACNF were 17.24 nm, 16.05 nm and 15.01 nm while the lengths were 1725.05 nm, 116.91 nm, and 1806.60 nm, respectively. The aspect ratios of CNF and DACNF were much higher than that of CNC. The crystalline indices of CNF and CNC were lower than that of original β-chitin, suggesting that ultrasonication and acid hydrolysis might change the molecular arrangement in crystalline region of chitin. The zeta-potentials were between 19.73 nV and 30.08 mV of chitin nanomaterials in distilled water. Concentrations of chitin nanomaterials (40–74 μg/mL) showed minimal effect on zeta-potential, whereas increasing the level of NaCl reduced the zeta-potential of solution. Moreover, NaCl solution (0.3%) with chitin nanomaterials addition produced significant higher saltiness perception than that of solution with NaCl alone. Therefore, chitin nanomaterials may be promising saltiness enhancers in the food industry.

The Effects of ZnTe:Cu Back Contact on the Performance of CdTe Nanocrystal Solar Cells with Inverted Structure

CdTe nanocrystal (NC) solar cells have received much attention in recent years due to their low cost and environmentally friendly fabrication process. Nowadays, the back contact is still the key issue for further improving device performance. It is well known that, in the case of CdTe thin-film solar cells prepared with the close-spaced sublimation (CSS) method, Cu-doped CdTe can drastically decrease the series resistance of CdTe solar cells and result in high device performance. However, there are still few reports on solution-processed CdTe NC solar cells with Cu-doped back contact. In this work, ZnTe:Cu or Cu:Au back contact layer (buffer layer) was deposited on the CdTe NC thin film by thermal evaporation and devices with inverted structure of ITO/ZnO/CdSe/CdTe/ZnTe:Cu (or Cu)/Au were fabricated and investigated. It was found that, comparing to an Au or Cu:Au device, the incorporation of ZnTe:Cu as a back contact layer can improve the open circuit voltage (V_oc) and fill factor (FF) due to an optimized band alignment, which results in enhanced power conversion efficiency (PCE). By carefully optimizing the treatment of the ZnTe:Cu film (altering the film thickness and annealing temperature), an excellent PCE of 6.38% was obtained, which showed a 21.06% improvement compared with a device without ZnTe:Cu layer (with a device structure of ITO/ZnO/CdSe/CdTe/Au).

Surface Ligand Engineering for Efficient Perovskite Nanocrystal-Based Light-Emitting Diodes

Lead halide perovskites (LHPs) are emerging as promising materials for light-emitting device applications because of the tunability of the band gap, narrow emission, solution processability, and flexibility. Typically, LHP nanocrystals (NCs) with surface ligands show high photoluminescence quantum yields because of charge-carrier confinement with higher exciton binding energy ( E_b). However, the conventionally used oleylamine (OAm) ligands result in the low electrical conductivity and stability of perovskite NCs (PNCs) because of a long carbon chain without conjugation bonds and weak interaction with the surface of NCs. Here, we report the effect of bulkiness and chain length of ligand materials on the properties and stability of CsPbBr₃ PNCs by replacing OAm with other suitable ligands. The effect of the bulkiness of quaternary ammonium bromide (QAB) ligands was systemically studied. The less bulky QAB ligands surrounded the surface of NCs effectively, and brought better surface passivation and less aggregation compared to bulky QAB ligands, and finally the optical property and stability of CsPbBr₃ PNCs were enhanced. Furthermore, the electrical property of CsPbBr₃ PNCs was optimized by tuning the long-chain length of QAB ligands for balanced charge-carrier transport. Finally, we achieved highly efficient green emissive CsPbBr₃ PNC light-emitting diodes (LEDs) by using PNCs with optimized didecyldimethyl ammonium bromide ligands with a current efficiency of 31.7 cd A^-1 and external quantum efficiency of 9.7%, which were enhanced 16-fold compared to those of CsPbBr₃ LEDs using PNCs with conventional OAm ligands.

Solution-Processable Nanocrystal-Based Broadband Fabry-Perot Absorber for Reflective Vivid Color Generation

Structural reflective colors based on Fabry-Perot (F-P) cavity resonances have attracted tremendous interest for diverse applications, such as color decoration and printing, display, and imaging devices. However, the asymmetric F-P cavity-based reflective colors proposed to date have low color purity and have difficulty to realize a desired vivid color because of a narrow absorption band characteristic in the visible light region. Here, a solution-processed, F-P ultra-broadband light absorber is newly proposed using a high lossy nanoporous material for vivid color generation. An asymmetric metal-insulator-metal structure consists of a high lossy nanoporous metallic film with coupled silver nanocrystals (Ag NCs) as the top layer. The absorbers not only increase the maximum absorption intensity up to ∼98% but also widen the bandwidth by 300 nm, resulting in high color purity in micrometer-scale pixels. Furthermore, the solution-based absorber shows potential to realize a high-resolution display pixel and anticounterfeiting devices having mechanical flexibility using the inkjet printing technology.

Nanocomposite of Ag-Doped ZnO and AgO Nanocrystals as a Preventive Measure to Control Biofilm Formation in Eggshell and Salmonella spp. Entry Into Eggs

Salmonella spp. is an important foodborne agent of salmonellosis, whose sources in humans often include products of avian origin. The control of this bacterium is difficult especially when Salmonella spp. is organized into biofilms. We hypothesized that the novel nanocomposites of ZnO nanocrystals doped with silver (Ag) and silver oxide (AgO) nanocrystals (ZnO:Ag-AgO) synthesized by the coprecipitation method could control or prevent the formation of Salmonella Enteritidis (SE) and Salmonella Heidelberg (SH) biofilm and its entry into turkey eggs. The diffraction characteristics of ZnO and AgO showed sizes of 28 and 30 nm, respectively. The Zn to Ag substitution into the ZnO crystalline structure was evidenced by the ionic radius of Ag+2 (1.26 Å), which is greater than Zn+2 (0.74 Å). For the SE analyses post-biofilm formation, the ZnO:Ag-AgO was not able to eliminate the biofilm, but the bacterial load was lower than that of the control group. Additionally, SE was able to infiltrate into the eggs and was found in both albumen and yolk. For the SH analyses applied onto the eggshells before biofilm formation, the ZnO:Ag-AgO treatment prevented biofilm formation, and although the bacterium infiltration into the eggs was observed in all treated groups, it was significantly smaller in ZnO:Ag-AgO pre-treated eggs, and SH could not reach the yolk. There was no difference in pore size between groups; therefore, the inhibition of biofilm formation and the prevention of bacterium entry into the egg were attributable to the use of ZnO:Ag-AgO, which was not influenced by the egg structure. Although the amount of Ag and Zn in the shell of the ZnO:Ag-AgO group was greater in relation to the control, this difference was not detected in the other egg components. In the search for new measures that are effective, safe and viable for controlling microorganisms in poultry farming, the application of a nanocomposite of Ag-doped ZnO and AgO nanocrystals appears as an alternative of great potential to prevent Salmonella sp biofilms in eggshells and other surfaces.

Au-Ag Nanoflower Catalysts with Clean Surfaces for Alcohol Oxidation

Shape-controlled metal nanocrystals, such as nanowires and nanoflowers, are attractive owing to their potentially novel catalytic properties and bimetallic nanocrystals composed of two distinct metals are expected to act as highly active catalysts. However, their catalytic activities are limited because of the capping agents adsorbed on the metal surfaces, which are necessary for the preparation and dispersion of these nanocrystals in solvents. Therefore, the preparation of bimetallic shape-controlled noble metal nanocrystals with clean surfaces, devoid of almost all capping agents, are expected to have high catalytic activity. Herein, we report the preparation of bimetallic Au-Ag nanoflowers using melamine as the capping agent. The bimetallic Au-Ag nanoflowers with a clean surface were subsequently obtained by a support and extraction method. The bimetallic nanoflowers with a clean surface were then used for the aerobic oxidation of 1-phenylethyl alcohol and they exhibited high rates for the formation of acetophenone compared to Au nanoflowers and spherical nanoparticles with almost the same size and Au/Ag ratio. We also show that Au-Ag nanoflowers containing only 1 % Ag (Au₉₉ -Ag₁ NFs) exhibit the highest rate of acetophenone formation among Au-Ag nanoflowers with different Au/Ag ratios owing to an increase in the electron density of the Au atoms that act as active sites for the oxidation of 1-phenylethyl alcohol.

Mechanism of Photoluminescence Intermittency in Organic-Inorganic Perovskite Nanocrystals

Lead halide perovskite nanocrystals have demonstrated their potential as active materials for optoelectronic applications over the past few years. Nevertheless, one issue that hampers their applicability has to do with the observation of photoluminescence intermittency, commonly referred to as "blinking", as in their inorganic counterparts. Such behavior, reported for structures well above the quantum confinement regime, has been discussed to be strongly related to the presence of charge carrier traps. In this work, we analyze the characteristics of this intermittency and explore the dependence on the surrounding atmosphere, showing evidence for the critical role played by the presence of oxygen. We discuss a possible mechanism in which a constant creation/annihilation of halide-related carrier traps takes place under light irradiation, with the dominant rate being determined by the atmosphere.

Copper's Role in the Photoluminescence of Ag1- xCu xInS2 Nanocrystals, from Copper-Doped AgInS2 ( x ∼ 0) to CuInS2 ( x = 1)

A series of Ag_{1- x}Cu _xInS₂ nanocrystals (NCs) spanning from 0 ≤ x ≤ ∼1 was synthesized by partial cation exchange to identify copper's contributions to the electronic structure and spectroscopic properties of these NCs. Discrete midgap states appear above the valence band upon doping AgInS₂ NCs with Cu⁺ (small x). Density functional theory calculations confirm that these midgap states are associated with the 3d valence orbitals of the Cu⁺ impurities. With increasing x, these impurity d levels gradually evolve to become the valence-band edge of CuInS₂ NCs, but the highest-occupied orbital's description does not change significantly across the entire range of x. In contrast with this gradual evolution, Ag_{1- x}Cu _xInS₂ NC photoluminescence shifts rapidly with initial additions of Cu⁺ (small x) but then becomes independent of x beyond x > ∼0.20, all the way to CuInS₂ ( x = 1.00). Data analysis suggests small but detectable hole delocalization in the luminescent excited state of CuInS₂ NCs, estimated by Monte Carlo simulations to involve at most about four copper ions. These results provide unique insights into the luminescent excited states of these materials and they reinforce the description of CuInS₂ NCs as "heavily copper-doped NCs" in which photogenerated holes are rapidly localized in copper 3d-based orbitals.

Preparation and Characterization of Biomimetic Hydroxyapatite Nanocrystals by Using Partially Hydrolyzed Keratin as Template Agent

Hydroxyapatite (HA), a typical inorganic component of bone, is a widely utilized biomaterial for bone tissue repair and regeneration due to its excellent properties. Inspired by the recent findings on the important roles of protein in biomineralization and natural structure of fish scales, keratin was chosen as a template for modulating the assembly of HA nanocrystals. A series of HA nanocrystals with different sizes were synthesized by adjusting the concentration of partially hydrolyzed keratin. The structure and compositions of the prepared HA were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectrum, and Transmission electron microscopy (TEM). Results revealed that the size of the synthesized HA nanocrystals can be controlled by adjusting the concentration of partially hydrolyzed keratin. Specifically, the size of synthesized HA decreased from 63 ± 1.5 nm to 27 ± 0.9 nm with the increasing concentration of partially hydrolyzed keratin from 0 to 0.6g. In addition, in vitro cytocompatibility of synthesized HA nanocrystals were evaluated using the MG-63 cells.

Functionalized Cellulose Nanocrystal Nanocomposite Membranes with Controlled Interfacial Transport for Improved Reverse Osmosis Performance

Thin-film nanocomposite membranes (TFNs) are a recent class of materials that use nanoparticles to provide improvements over traditional thin-film composite (TFC) reverse osmosis membranes by addressing various design challenges, e.g., low flux for brackish water sources, biofouling, etc. In this study, TFNs were produced using as-received cellulose nanocrystals (CNCs) and 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNs) as nanoparticle additives. Cellulose nanocrystals are broadly interesting due to their high aspect ratios, low cost, sustainability, and potential for surface modification. Two methods of membrane fabrication were used in order to study the effects of nanoparticle dispersion on membrane flux and salt rejection: a vacuum filtration method and a monomer dispersion method. In both cases, various quantities of CNCs and TOCNs were incorporated into a polyamide TFC membrane via in-situ interfacial polymerization. The flux and rejection performance of the resulting membranes was evaluated, and the membranes were characterized via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The vacuum filtration method resulted in inconsistent TFN formation with poor nanocrystal dispersion in the polymer. In contrast, the dispersion method resulted in more consistent TFN formation with improvements in both water flux and salt rejection observed. The best improvement was obtained via the monomer dispersion method at 0.5 wt% TOCN loading resulting in a 260% increase in water flux and an increase in salt rejection to 98.98 ± 0.41% compared to 97.53 ± 0.31% for the plain polyamide membrane. The increased flux is attributed to the formation of nanochannels at the interface between the high aspect ratio nanocrystals and the polyamide matrix. These nanochannels serve as rapid transport pathways through the membrane, and can be used to tune selectivity via control of particle/polymer interactions.

Synthesis of Cu₂O/CuO Nanocrystals and Their Application to H₂S Sensing

Semiconducting metal oxide nanocrystals are an important class of materials that have versatile applications because of their useful properties and high stability. Here, we developed a simple route to synthesize nanocrystals (NCs) of copper oxides such as Cu₂O and CuO using a hot-soap method, and applied them to H₂S sensing. Cu₂O NCs were synthesized by simply heating a copper precursor in oleylamine in the presence of diol at 160 °C under an Ar flow. X-ray diffractometry (XRD), dynamic light scattering (DLS), and transmission electron microscopy (TEM) results indicated the formation of monodispersed Cu₂O NCs having approximately 5 nm in crystallite size and 12 nm in colloidal size. The conversion of the Cu₂O NCs to CuO NCs was undertaken by straightforward air oxidation at room temperature, as confirmed by XRD and UV-vis analyses. A thin film Cu₂O NC sensor fabricated by spin coating showed responses to H₂S in dilute concentrations (1–8 ppm) at 50–150 °C, but the stability was poor because of the formation of metallic Cu₂S in a H₂S atmosphere. We found that Pd loading improved the stability of the sensor response. The Pd-loaded Cu₂O NC sensor exhibited reproducible responses to H₂S at 200 °C. Based on the gas sensing mechanism, it is suggested that Pd loading facilitates the reaction of adsorbed oxygen with H₂S and suppresses the irreversible formation of Cu₂S.