Recently, the millimetre-scale, highly efficient growth of single-wall carbon nanotube (SWCNT) forests from iron (Fe) catalysts has been reported through the annealing of the magnesia (MgO) underlayer. Here, we report the modulation of the CNT yield (height) and average number of CNT walls for a Fe/MgO catalyst system through the collective effects of initial Fe amount and MgO annealing temperature. Our results revealed the existence of a well-defined region for high yield SWCNT forest growth in the domain of deposited Fe thickness and MgO annealing temperature. Through topographic examinations of the catalyst surface using atomic force microscopy, we confirmed that our results stem from the collective effects of increased amounts of surface-bound Fe through the amount of deposition and suppression of Fe subsurface diffusion, together govern the amount of surface-bound catalyst. The combination of these mechanisms determined the final nanoparticle size, density, and stability and could explain the three distinctly defined regions: low yield SWCNT growth, high yield SWCNT growth, and high yield multiwall CNT growth. Furthermore, we explained the observed borders between these three regions.

This research automates edge detection for perovskite crystal grains using machine learning (ML). Once the edges of the crystal grains are located, a flood-fill algorithm can be used to find the distribution of crystal grain areas. The ML algorithm uses GNU Octave to run a regularized logistic regression algorithm that classifies each pixel of an input image as part of an edge or not part of an edge. The basic features used for the algorithm are each pixel’s grayscale intensity, its Sobel derivative. Higher order Sobel derivatives, higher degree polynomial terms, and intensities convolved by various kernels were used as additional features to improve the program’s accuracy and true-positive rate. Training data is obtained by using non-ML Canny Edge Detection to annotate the edges an SEM image of a pure perovskite solar cell (PSC). The classifier exhibits an 85.58% accuracy and produces an edge mask that clearly outlines the crystals visually. The ML edge mask exhibits far fewer false-positive mis-classifications for pixels in the middle of the crystals than Canny. However, the ML mask’s edges are fainter, owing to a lower true-positive classification rate. Using more kernels, higher order derivatives, and higher degree polynomial terms all significantly increased the true positive rate of the classifier, leading to thicker edges. This algorithm can greatly accelerate perovskite solar cell research (and potentially any research requiring particle size analysis), automating a process scientists previously had to perform by hand. This will facilitate the search for a solution for the world’s growing demands for renewable energy.

Pulsed coherent extreme ultraviolet (EUV) radiation is a potential alternative to pulsed near-ultraviolet (NUV) wavelengths for atom probe tomography. EUV radiation has the benefit of high absorption within the first few nm of the sample surface for elements across the entire periodic table. In addition, EUV radiation may also offer athermal field ion emission pathways through direct photoionization or core-hole Auger decay processes, which are not possible with the (much lower) photon energies used in conventional NUV laser-pulsed atom probe. We report preliminary results from what we believe to be the world’s first EUV radiation-pulsed atom probe microscope. The instrument consists of a femtosecond-pulsed, coherent EUV radiation source interfaced to a local electrode atom probe tomograph by means of a vacuum manifold beamline. EUV photon-assisted field ion emission (of substrate atoms) has been demonstrated on various insulating, semiconducting, and metallic specimens. Select examples are shown.

The syntheses of five propargylated dendrimer scaffolds ranging from 2, 3, 4, 6, and 12 surface groups are described together with a 2-azidoethyl α-D-mannopyranoside. The former is appended to the core structure using highly efficient copper-catalysed azide-alkyne cycloaddition (CuAAC) (“click reaction”) to provide glycodendrimers in an accelerated approach. Two of the core structures are based on cyclotrisphosphazene, thus expanding the scope of the “onion-peel” strategy to build dendritic architectures with a large number of surface groups at the G1 generation only.

The electrochemical discharge mechanism is reported for all-solid lithium sulfur batteries. Upon milling with carbon fibers, the solid electrolyte used within the cathode composite becomes electrochemically active. Analysis with Raman spectroscopy and XPS revealed the importance of bridging S-S bond formation and breaking in lithium polysulfidophosphates during electrochemical lithiation of the active solid electrolyte. Remarkably, when sulfur is introduced as an active material in the cathode composite, lithium polysulfides are formed as an intermediate product before full lithiation into lithium sulfide. The synthesis of materials based on bridging S-S bonds is an important avenue to the design of new cathodes for all-solid batteries.

We present a high entropy alloy (HEA) from the system Al-Co-Cr-Fe-Ni with small additions of W, Mo, Si and C which was designed to allow for precipitation hardening by annealing in the temperature range from 600 to 900 °C. The alloy development was supported by thermodynamic computations using ThermoCalc software and the specimens were produced by arc melting. The microstructure of one selected sample in as-cast and annealed conditions was analysed using SEM/EDS, SEM/EBSD and TEM. The as-cast microstructure consists of spinodally decomposed BCC dendrites enveloped by FCC+Cr23C6 eutectic. Upon annealing at 700 °C for 24 h nanoscale precipitates form within the spinodal BCC as well as from FCC. Precipitation is exquisitely uniform leading to an increase in microhardness from 415 HV0.5 in the as-cast state to 560 HV0.5 after annealing. We investigated coarsening of this microstructure using varying holding time for a constant temperature of 700 °C. The microstructure evolution during coarsening and the corresponding mechanical properties obtained from instrumented indentation experiments are presented in this work.

Simple glucose solutions were heat treated in an attempt to produce carbon nanodots (CNDTs) with a monodisperse size distribution using a bottom-up approach. Absorption and fluorescence properties of the heat-treated solutions display remarkable similarity to CNDTs reported in the literature. However, particle-sizing and AFM measurements indicate the increasing fluorescence is accompanied by the growth of particles that are larger than most CNDTs discussed in the literature (a concentrated population of monodisperse 30 nm particles and a low concentration of much larger, roughly 500 nm, particles). A dialysis study, shows these larger particles are not responsible for the bulk of the optical properties but, rather the optical properties likely stem from molecular by-products that accompany the heating and caramelization of the sugar.

In this work, we demonstrate a size-controlled synthesis of CuNi octahedral nanocrystals (NCs) using a hot colloidal solution approach. Two different sizes of CuNi nano-octahedra are chosen and investigated. It is determined that the reagent concentration remarkably plays a key role in the formation of the size-defined CuNi octahedral NCs. In terms of the reduction of 4-nitrophenol (4-NP), it uncovers that the obtained CuNi octahedral NCs (in both sizes) exhibit higher catalytic activity than those of CuNi spherical NCs reported previously. It further indicates that the catalytic performance is strongly size-dependent due to their devise specific surface areas of the exposed crystallographic planes.

Light trapping is one of the key challenges for next generation thin film solar cells. In this work, we have identified the distinct light trapping effects for short and long wavelength solar spectrum range, by investigating lighting trapping structures on both sides of Si thin film solar cells. The sub-wavelength photonic front surface by wet etching and multi-layer photonic crystal reflector on the bottom surface are studied in detail for its solar energy absorption characteristics. Our study reveals the drastic difference of the light trapping effects within the solar spectrum wavelength. This work may provide guidance for the efficiency enhancementfor next generation thin film photovoltaic cells.

Photocatalytic water splitting to form hydrogen can effectively alleviate energy and environmental problems attracting wide attention. However, the current photocatalysts have low photocatalytic efficiencies due to the narrow absorption spectrum, which is far from the actual application requirements. Herein, we use the as-prepared zinc porphyrin self-assemblies to visible-light-drive photocatalytic hydrogen evolution with Pt as the cocatalyst and ascorbic acid (AA) as the sacrificial agent. The results exhibit morphology-dependent performance and hexagonal stacks achieved optimal H2 evolution rate (47.1 mmol/h/g), then followed by nanodiscs, nanorod and tetragonal stacks, meanwhile the nanorods with different aspect ratios show size-dependent properties. The UV-vis absorption and photoluminescence spectra and the shortening of decay time of the corresponding ZnTPyP aggregates reveal that the well-defined self-assembled porphyrin networks are J-aggregation and boost efficient energy transfer with respect to monomer. Such porphyrin self-assemblies are standing for one of the most promising photosensitizers in photocatalysis field and provide an important reference for designing the next generation of hydrogen production.

We present density functional theory calculations to study the interplay between magnetic and structural properties in Ni-Co-Mn-Sn. The relative stability of austenite (cubic) and martensite (tetragonal) phases depends critically on the magnetic interactions between Mn atoms. While the standard generalized gradient approximation (GGA) stabilizes the latter phase, correlation effects beyond GGA tend to suppress this effect. Mn atoms treated as magnetic impurities can explain our results, where a delicate balance between magnetic interactions mediated by Ni d and Sn p orbitals determines the equilibrium structure of the crystal. Finally, we discuss the role of Co doping in stabilizing ferromagnetic austenite phases.

Mixing metal powders in cold spray is of significant interest not only because it is a straightforward method to produce novel composites, but also it has been observed to generate beneficial effects, e.g. improved deposition efficiency (DE). However, the mechanisms behind DE improvements are still not clear fundamentally. In this paper, two examples of mixing metal powders effects in cold spray are introduced: 1) the first example focuses on the effects of different particle/substrate interactions which occurred during cold spray of SS/Fe mixed powders; 2) the second example presents the DE-improving effect of depositing mixed metal powders onto polymers. Various mechanisms associated with the cold spray deposition characteristics of mixed metal powders are discussed in this paper.

Graphene specimens produced by chemical vapor deposition usually show p-type characteristics and significant hysteresis in ambient conditions. Among many methods, current annealing appears to be a better way of cleaning the sample due to the possibility of in-situ annealing in the measurement setup. However, long-time current annealing could increase defects in the underlying substrate. Studying the hysteresis with different anneal currents in a graphene device is, therefore, a topic of interest. In this experimental work, we investigate electron/hole transport in a graphene sample in the form of a Hall bar device with a back gate, where the graphene was prepared using chemical vapor deposition on copper foils. We study the hysteresis before and after current annealing the sample by cooling down to a temperature of 35 Kfrom room temperature with a back-gate bias in a closed cycle refrigerator.

Fatigue properties of Mo/W multilayers with individual layer thickness (λ) of 5, 20, 50 and 100 nm on flexible polyimide substrates were investigated. The experimental results show that the fatigue resistance increases with decreasing λ from 100 nm to 20 nm, and reaches the maximum at λ=20 nm, and then decreases when further decreasing λ. Fatigue cracks of Mo/W multilayers with different λ were found to propagate along columnar grain boundary in the out-of-plane direction and along the boundary of cluster structures. The enhanced fatigue resistance is attributed to the larger cluster inclination angles and the more tortuous in-plane cracking paths.

We demonstrate a suspended graphene-(poly(methyl methacrylate) (PMMA) polymer angular displacement actuator enabled by variable elastic modulus of the perforated stacked structure. Azimuthal flexures support a central disc-shaped membrane, and compression of the membrane can be used to control the rotation of the entire structure. Irradiating the PMMA on graphene stack with 5 kV electrons in a convention scanning electron microscope reduces the elastic modulus of the PMMA and allows graphene’s built in strain to dominate and compress the flexures, thus rotating the actuator.

Multifunctionality was created by coupling an electronic charge carrier transport with ionic conductivity or ferroelectricity in polarized liquid crystal phases. Liquid-crystalline perylene bisimide derivatives bearing cyclotetrasiloxane rings and triethylene oxide chains formed nanosegregated columnar structures which could conduct ions as well as electrons. The spin-coated thin films could be insolubilized by the exposure on acid vapors and display electrochromism. Phenylterthiophene derivatives bearing a chiral alkyl side chain exhibited a ferroelectric phase, in which a photovoltaic effect was caused by the interaction between photogenerated charge carriers with the internal electric field formed by the spontaneous polarization of the ferroelectric phase.

Large area lighting OLEDs manufactured in a Roll-to-Roll (R2R) fashion enable the well-longed production capability with considerably high throughput based on flexible substrates, hence largely reduced OLED manufacturing cost. This paper will outline the present status of R2R OLED fabrication on ultra-thin glass with the focus on transparent OLED devices and how to perform segmentation by printing of silver- and dielectric pastes. Ultra-thin glass (UTG) is laminated on a PET film to avoid fabrication interruptions when glass cracks occur during the Roll-to-Roll process. The R2R fabricated flexible OLEDs also show key-values comparable to conventional OLEDs fabricated on small rigid glass in lab-scale.

Transport mechanisms in structurally ordered piezoelectric Ca3TaGa3Si2O14 (CTGS) single crystals are studied in the temperature range of 1000-1300 °C by application of the isotope 18O as a tracer and subsequent analysis of diffusion profiles of this isotope using secondary ion mass spectrometry (SIMS). Determined oxygen self-diffusion coefficients enable calculation of oxygen ion contribution to the total conductivity, which is shown to be small. Since very low contributions of the cations have to be expected, the total conductivity must be dominated by electron transport. Ion and electron conductivities are governed by different mechanisms with activation energies (1.9±0.1) eV and (1.2±0.07) eV, respectively. Further, the electromechanical losses are studied as a function of temperature by means of impedance spectroscopy on samples with electrodes and a contactless tone-burst excitation technique. At temperatures above 650 °C the conductivity-related losses are dominant. Finally, the operation of CTGS resonators is demonstrated at cryogenic temperatures and materials piezoelectric strain constants are determined from 4.2 K to room temperature.

The photophysical properties of lead halide perovskite nanocrystals (NCs) are critical to their potential application in light emitting devices and other optoelectronics, and are typically characterized using optical spectroscopies. Measurements of nuclei and nascent NC photophysics during synthesis provide insight into how the reaction can be changed to control the properties of the resulting NCs. However, these measurements are typically only performed ex situ after growth is halted by centrifuging the reaction mixture for several minutes. Here, a method is reported to rapidly sample the reaction mixture during a solvation-limited synthesis to enable multiple spectroscopic measurements during nucleation and NC growth. Absorbance and fluorescence measurements of a reaction mixture during the formation of methylammonium lead triiodide perovskite NCs are reported. The changing positions of spectral features as a function of reaction time show the expected weakening of exciton confinement during NC growth. The evolving fluorescence spectra demonstrate that the capping and surface passivation of nascent NCs changes during the reaction. The species in the reaction mixture, particularly during the early stages of the synthesis, are shown to be unstable. This indicates that, even for a relatively slow solvation-limited reaction, the photophysics of the reaction mixture can only be accurately captured if spectroscopic measurements are completed within seconds of sampling. The common use of centrifugation to quench NC syntheses prior to spectroscopic measurement biases the NC population towards more stable, well-capped NCs and does not accurately report on the full NC population in a reaction mixture.

We present a general purpose Pt-Pt density-functional tight-binding (DFTB) parameter for Pt clusters as well as bulk, using a genetic algorithm (GA) to automatize the parameterization effort. First we quantify the improvement possible by only optimizing the repulsive potential alone, and second we investigate the effect of improving the electronic parameter as well. During both parameterization efforts we employed our own training set and test sets, with one set containing ∼20,000 spin-polarized DFT structures. We analyze the performance of our two DFTB Pt-Pt parameter sets against density functional theory (DFT) as well as an earlier DFTB Pt-Pt parameters. Our study sheds light on the role of both repulsive and electronic parameters with regards to DFTB performance.