Those involved in STEM outreach, from elementary schools through undergraduate students, all use varying teaching styles in an effort to instruct and inspire students. However, it is incredibly difficult to gauge or compare learning outcomes from new teaching techniques in situ. In this work, we describe the outcomes of a new undergraduate mini-course at Johns Hopkins University, Chocolate: An Introduction to Materials Science. In particular, the outcomes of teaching binary phase diagrams in this course using topical food examples were compared to the outcomes of the same instructor teaching a similar control group of students using standard textbook examples, reducing a number of confounding factors and allowing us to objectively analyze the benefits of using an atypical, popular approach to teach a standard subject. Results indicate that the students in the Chocolate course were not only more excited and engaged in the lecture, but they had identical or potentially greater learning gains than the control group.

Macroscopic strength of the rock depends on the behavior of the micro constituents, that is, the minerals, pores and crack profile. It is important to determine the effect of these constituents on the overall behavior of the rock. This study seeks to estimate the effective elastic properties of granite using the finite element method. A representative volume element (RVE) of suitable size with spherical inclusions of different distribution is subjected to loading and the effective elastic properties determined. The results are compared to those obtained from analytical methods. The elastic properties are obtained in both the axial and transverse direction to account for anisotropy. It is observed that there is congruence in the results obtained both analytically and numerically. The method of periodic microstructures exhibits close agreement with the numerical results.

The present investigation focused on evaluating the effects of different amounts of precipitates on tension and hardness properties of a Ti–6Al–4V alloy, for this, two sets of samples with bimodal and equiaxed microstructures were obtained by heat treatment process. After this, the samples were aged at 545 °C for holding times of 100 and 200 h. Observation of the aged samples in the scanning electron microscope revealed fine α2 (Ti3Al) particles precipitating in the α matrix of the alloy. Uni-axial tension tests and Vickers microhardness measurements were conducted on the unaged and aged samples. Experimental results show that ultimate strength and hardness of bimodal and equiaxed microstructures are significantly affected by the heat treatment applied to produce such microstructures. Also, it was found that the precipitation of α2 particles drastically reduced the plastic response of the Ti–6Al–4V alloy.

A novel and efficient scheme for evaluating the work of adhesion between a liquid and a polymer-grafted surface is proposed. A set of spherically symmetric potentials are gradually inserted at the interface to separate the liquid molecules from the surface according to its shape. This method is applied to the interface between the water and the gold substrate modified by poly(ethylene glycol). We find that the work of adhesion becomes maximum at the intermediate density of grafted poly(ethylene glycol). This is attributed to penetration of the water molecules into grafted poly(ethylene glycol) and hydrophilic interaction between them.

The procedure proposed is the express method for the study of anion distribution profiles in the anodic aluminum oxide film. The method consists in measuring the variation of the steady-state electrode potential during the oxide etching. It allows the influence of the initial aluminum composition, the electrolyte composition, anodization regimes, etc. on the characteristics of dense anodic alumina films to be studied. The method developed can be used to study a chemical evolution in anodic alumina formed to correlate with modelling and simulations across materials science disciplines.

Nagelschmidtite, Ca7P2Si2O16, is an end-member of continuous solid solution Ca2SiO4 – Ca3(PO4)2⋅2Ca2SiO4 within the pseudo-binary system Ca3(PO4)2 – Ca2SiO4 (whitlockite – larnite). This phase is capable to wide isomorphic exchanges in Ca, P and Si sites: Ca2+ = Sr2+; Ca2+ = Eu2+; Ca2+ + P5+ = (RE,An)3+ + Si4+, 2Ca2+ = Na+ + (RE,An)3+; 2Ca2+ = An4+ + ☐; Ca2+ + Si4+ = (RE,An)3+ + (Al,Fe)3+; Ca2+ + Si4+ = Na+ + P5+; 2Ca2+ = Na+ + (Al,Fe)3+; Ca2+ + P5+ = Na+ + S6+. It was found in metallurgical slags and geological formations. We revealed nagelschmidtite-type phase in vitrified phosphorus-bearing radioactive incinerator slags. The materials were glass-crystalline and contained nano-sized nagelschmidtite crystals distributed in vitreous matrix phase. Average chemical composition of the largest (few microns) crystals was recalculated to formula Na1.21K1.05Ca2.22Al2.02Fe0.46Si2.69P1.26U0.08O15.76. Significant oxygen misbalance suggests higher than U(IV) oxidation state for uranium – U(V) or U(VI). Capability of nagelschmidtite to be crystallized from melt makes it promising phase for actinides, rare earths and some other fission and corrosion products at using a melting route to nuclear waste forms including cold crucible induction melting and self-propagating high-temperature synthesis.

It is of great significance to understand and monitor the condition of the commercial batteries in EVs/HEVs and stationary applications under their real working situations. Electrochemical impedance spectroscopy (EIS) has been proved to be a powerful technique for investigating the kinetics and redox reactions at the interfaces, as well as the diffusion behavior in the bulks of every electrochemical systems. Focusing on tracing the temperature of the commercial batteries during the EIS tests at different stages in a well-designed four-week driving simulation, the value of temperature profile during the EIS test as an enhanced indicator to help analyzing the formation of the passivation layers, electrolyte impedance development as well as lithium plating on the anode through EIS analysis have been found.

We report a novel tip-type field emission (FE) emitter by synthesizing the few-layer graphene (FLG) flakes on tip of nichrome (8020) wire (ϕ≈80 μm) by microwave plasma enhanced chemical vapor deposition(PECVD). These resultant random arrays of free-standing FLG flakes are aligned vertically to the substrate surface in a high-density and stacked to each other to form several larger “flower-like” agglomerates in spherical shapes. The FE performance of the tip-type FLG flakes emitter shows a low threshold field of 0.55 V/μm, a large field enhancement factor of 9455 ± 46, a large field emission current density of 22.18 A/cm2 at 2.70 V/μm, and an excellent field emission stability at high emission current densities (6.93 A/cm2). It can be used in variety of applications that include cathode-ray tube monitors, X-ray sources, electron microscopes, and other vacuum electronic applications.

LIBS is a developing analytical technique, which is used to perform qualitative and semi-quantitative elemental analysis of materials (solid, liquid and gas). Recently LIBS became an attractive technique to be used for geological samples, due to its advantages such as fast data collection and the lack of sample preparation. This study is done to improve analytical methods for geochemical analysis of samples during different exploration phases (Mining, filed analysis, etc.), to be used in the future as a real-time analysis method to save money and time spent in labs. In this work, LIBS has been used to differentiate between some geological samples gathered from different areas: South Africa and Namibia. Using principal component analysis (PCA), it was found that LIBS was able to differentiate between the samples even those of the same area. The results from the LIBS technique were correlated with subsequent analysis of the same samples by Particle-Induced X-ray emission (PIXE).

A novel freeze-cast porous chitosan conduit for peripheral nerve repair with highly-aligned, double layered porosity, which provides the ideal mechanical and chemical properties was designed, manufactured, and assessed in vivo. Efficacies of the conduit and the control inverted nerve autograft were evaluated in bridging 10-mm Lewis rat sciatic nerve gap at 12 weeks post-implantation. Biocompatibility and regenerative efficacy of the porous chitosan conduit were evaluated through the histomorphometric analysis of longitudinal and transverse sections. The porous chitosan conduit was found to have promising regenerative characteristics, promoting the desired neovascularization, and axonal ingrowth and alignment through a combination of structural, mechanical and chemical cues.

In the past few years, our group worked on the area of transformation from the two-dimensional (2-D) nanocrystalline films to one-dimensional (1-D) nanomaterials by using thermal oxidation. In this paper, we overview the research work on the controllable growth processes, transformation phenomena, growth mechanisms and applications. In general, the preparation process includes the following steps: 1) prepare a pure metal nanocrystalline film via a pulse electro – deposition; 2) grow variant 1-D nanomaterials, such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and 1-D metal oxide nanoneedles involving ZnO, CuO and Fe3O4, etc. by using this film as catalyst. This process exhibits the following features: 1) the 1-D nanomaterials grow according to “base growth” model and no residual catalyst exists at the tip of the products; 2) the diameter of the 1-D nanomaterials can be controlled by controlling grain sizes of the 2-D films through adjusting pulse electro-deposition parameters; 3) it is more easily to get the 1-D nanomaterials with large area, uniform, vertical alignment and good shape on the substrates. We propose a “solid state based-up diffusion growth mechanism” for growth of the 1-D metal oxide nanoneedles, and “base growth model” for the 1-D carbon nanomaterials. The physical properties, such as Field emission and magnetics, of the 1-D metal oxide nanoneedles were studied, which showed desired values. In addition, we couple the ZnO nanoneedles with NiO, TiO2, graphene, Au nanoparticles, etc. for enhancing photocatalytic properties in the areas of environmental purification.

The application of safeguards measures by the International Atomic Energy Agency (IAEA) involves analytical measurements of samples taken during inspections of nuclear facilities. Thus constant development and advancement of analytical techniques is required. For quality control purposes, the IAEA has implemented a dedicated project to enhance its analytical capabilities by producing tailor-made reference materials for the analysis of uranium isotope signatures in (single) particles.

To this end, a particle production set-up was developed and implemented at Forschungszentrum Juelich capable to produce uranium oxide microparticles which are intended to be used as (certified) reference materials for particle analysis methods. A step towards the certification process is the evaluation of consistency of the size distribution and homogeneity. A monodisperse particle size distribution as well as the single phase triuranium octoxide structure was confirmed using SEM, µ-XRD and µ-Raman spectroscopy, respectively. Analysis performed on single uranium oxide microparticles confirmed consistency of the uranium isotopic ratios in comparison to the initial precursor solutions. To improve the homogeneity and particle handling, the particles are transferred into suspensions, for which the stability was investigated with respect to dissolution.

Monolithic integrated thin film tandem solar cells consisting of a high bandgap perovskite top cell and a low bandgap thin film bottom cell are expected to reach higher power conversion efficiencies (PCEs) with lower manufacturing cost and environmental impacts than the market-dominant crystalline silicon photovoltaics. There have been several demonstrations of 4-terminal and 2-terminal perovskite tandem devices with CuInGaSe2 (CIGS) or CuInSe2 (CIS) and, similar to the other tandem structures, the optimization of this device relies on optimal choice for the perovskite bandgap and thickness. Therefore, further advancement will be enabled by tuning the perovskite absorber to maximize the photocurrent limited by the current match condition. Here, we systematically study the optical absorption and transmission of perovskite thin films with varying absorber band gap. Based on these results, we model the photocurrent generations in both perovskite and CIS subcells and estimate the performances of projected tandem devices by considering the ideally functioning perovskite and CIS device. Our results show that for perovskite layers with 500 nm thickness the optimal bandgap is around 1.6 eV. With these configurations, PCEs above 20% could be achieved by monolithically integrated perovskite/CIS tandem solar cells. Also by modelling the absorption at every layer we calculate the quantum efficiency at each subcell in addition to tracking optical losses.

Natural graphite can be exfoliated into thin films by trapping it at the interface between water and heptane [S. J Woltornist, A. J. Oyer, J-M. Y. Carrillo, A.V. Dobrynin, and D.H. Adamson, ACS Nano 7, 7062 (2013)]. In this work, we add functional elements into these graphitic thin films by introducing additives into the water phase prior to exfoliation. We report the successful incorporation of ZnO nanoparticles thereby enabling the composite films to act as effective ultraviolet photodetectors. In a similar manner, integration of silver nanowires is achieved, which results in an enhancement of the electrical conductivity of graphite.

This paper reports the effect of Ar molar flow-rate on thermodynamic efficiency analysis of zinc oxide-zinc sulfate (ZnS-ZnO) water splitting cycle useful for solar H2 production. The thermodynamic efficiency analysis is conducted using the HSC Chemistry 7.1 software and its thermodynamic database. Influence of Ar molar flow-rate on total solar energy input essential for the continuous operation of the cycle is explored. Furthermore, the solar-to-fuel energy conversion efficiency for the ZnS-ZnO water splitting cycle is determined.

The development of efficient water oxidation catalyst is a major path to realize water splitting systems, which could benefit high performance and cost-effective metal-air batteries, fuel cells and solar energy conversion. To date, the rare crustal abundant platinum group metals rule this sector with Pt-alloys being the best for oxygen reduction reaction (ORR) and ruthenium oxides for oxygen evolution reaction (OER) in acidic solution. However, they show poor stability and are too expensive for large scale applications. Moreover, oxygen reduction in basic solutions can otherwise be catalysed by metal oxide with non-precious earth abundant transition metals (e.g. Fe, Co, Ni). Hence, there is a massive demand to explore noble metal free bifunctional electrocatalysts. In this work, we present the electrocatalytic activity of three cobalt based sodium phosphates namely NaCoPO4 (with one phosphate), Na2CoP2O7 (with two phosphate) NaFe2Co(PO4)3 (with three phosphate). Synthesized by solution combustion route, all these phosphates confirmed phase purity. NaCoPO4 and Na2CoP2O7 adopted orthorhombic structure with Pnma and Pna21 space group respectively; whereas NaFe2Co(PO4)3 crystallized in monoclinic (C2/c) framework. Electrocatalytic activity of these cobalt phosphates were inspected by linear sweep voltammetry with rotating disk electrode (RDE). All three showed promising bifunctional activity. In fact, the ORR activities of both orthorhombic cobalt phosphates are comparable to Vulcan carbon and Pt/C. OER activity of Na2CoP2O7 overrode other phosphates. The bifunctional activity and good stability of these sodium cobalt phosphates stem from cobalt ions and stabilization of the catalytic centres by the phosphate frameworks. The present work builds a detail structure-property correlation in these phosphate systems and also demonstrates the possibility of utilizing these sodium cobalt phosphates as alternate cost-effective, novel electrocatalysts for efficient OER/ORR activity in alkaline solution.

Layered transition metal dichalcogenides (TMDs) represent a diverse, emerging source of two-dimensional (2D) nanostructures with broad application in optoelectronics and energy. Chemical functionalization has evolved into a powerful tool to tailor properties of these 2D TMDs; however, functionalization strategies have been largely limited to the metallic 1T-polytype. The work herein illustrates that 2H-semiconducting liquid-exfoliated tungsten disulfide (WS2) undergoes a spontaneous redox reaction with gold (III) chloride (AuCl3). Au nanoparticles (NPs) predominantly nucleate at nanosheet edges with tuneable NP size and density. AuCl3 is preferentially reduced on multi-layer WS2 and resulting large Au aggregates are easily separated from the colloidal dispersion by simple centrifugation. This process may be exploited to enrich the dispersions in laterally large, monolayer nanosheets. It is proposed that thiol groups at edges and defects sides reduce the AuCl3 to Au0 and are in turn oxidized to disulfides. Optical emission, i.e. photoluminescence, of the monolayers remained pristine, while the electrocatalytic activity towards the hydrogen evolution reaction is significantly improved. Taken together, these improvements in functionalization, fabrication, and catalytic activity represent an important advance in the study of these emerging 2D nanostructures.

Pressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) were investigated using in-situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy. We observed that the tetragonal phase that presents under ambient pressure transformed to a ReO3-type cubic phase at 0.3 GPa, which further converted into a putative orthorhombic structure at 2.7 GPa. The sample was finally separated into crystalline and amorphous fractions beyond 4.7 GPa. During the decompression, the phase-mixed material restored the original structure in two distinct pathways depending on the peak pressures. Being monitored using a laser-excited photoluminescence technique under each applied pressure, it was determined that the bandgap reduced with an increase of the pressure till 0.3 GPa and then enlarged with an increase of the pressure up to 2.7 GPa. This work lays the foundation for understanding pressure-induced phase transitions and bandgap tuning of MAPbI3, enriching potentially the toolkit for engineering perovskites related photovoltaic devices.

Self-assembled TiO2 films deposited by aqueous-spray deposition were investigated to evaluate morphology, crystalline phase, and infrared optical constants. The Anatase nano-crystalline film had ∼10 nm characteristic surface roughness sparsely punctuated by defects of not more than 200 nm amplitude. The film is highly transparent throughout the visible to wavelengths of 12 μm. The indirect band gap was determined to be 3.2 eV. Important for long-wave infrared applications is that dispersion in this region is weak compared with the more commonly used dielectric SiO2 for planar structures. An example application to a metal-insulator-metal resonant absorber is presented. The low-cost, large-area, atmospheric-pressure, chemical spray deposition method allows conformal fabrication on flexible substrates for long-wave infrared photonics.

The substitutional solid solutions in the Bi(Gd) - Fe - O and Bi(Nd) - Fe - O systems of the Bi1-xGdxFeO3 and Bi1-xNdxFeO3 types with x up to 0.20 were synthesized by the solid-state reaction method and investigated using X-ray diffraction analysis and infrared reflective spectrometry in the wavelength range from 12.5 to 24 μm. It was determined that the Bi1-xGdxFeO3 and Bi1-xNdxFeO3 crystal structure is a distorted form of perovskite, R3c space group. Two extremums at 18.2 μm (strong extremum) and 22.5 μm (rather weak extremum) on the infrared reflection spectra of the Bi1-xGdxFeO3 and Bi1-xNdxFeO3 solid solutions were discovered. The extremum at 18.2 μm corresponds to the Fe – O stretching vibrations and the extremum at 22.5 μm corresponds to the O - Fe – O bending vibrations of the FeO6 groups. The growth of reflectivity of the Bi1-xGdxFeO3 and Bi1-xNdxFeO3 solid solutions in comparison with pure BiFeO3 and the displacement of the reflectivity band maximum into the side of the spectrum with longer wavelengths with the increase of the atomic part of the substitutive element x up to 0.20 were found.