We investigate the synthesis of kesterite Cu2ZnSnS4 (CZTS) thin films using thermal evaporation from copper, zinc and tin pellets and post-annealing in a sulfur atmosphere. The effects of chemical composition were studied both on the absorber layer properties and on the final solar cell performance. It is confirmed that CZTS thin film chemical composition affects the carrier concentration profile, which then influences the solar cell properties. Solar cells using a CZTS thin film with composition ratio Cu/(Zn+Sn) = 0.87, and Zn/Sn = 1.24 exhibited an open-circuit voltage of 483 mV, a short-circuit current of 14.54 mA/cm2, a fill factor of 37.66 % and a conversion efficiency of 2.64 %. Only a small deviation from the optimal chemical composition can drop device performance to a lower level, which confirms that the CZTS solar cells with high conversion efficiency existed in a relatively narrow composition region.

Periodic arrays of low-aspect ratio silicon nanopillars strongly reduce front surface reflection over a broad wavelength range. In this study, we numerically simulate the reflection of light for thick crystalline silicon substrates nanostructured through a combination of silica nanosphere lithography (SNL) and metal-assisted chemical etching (MaCE), producing ordered arrays of nanopillars with hexagonal periodicity. Using statistical methods, we show that the simulated measurements are in good agreement with the spectrophotometry measurements of the fabricated nanopillars.

In this study, we investigated GaN channel layer quality to suppress drain-lag, which is an important parameter for switching performance. In this experiment, we confirmed that drain-lag performance has dependence on the tilt of the GaN channel layer. GaN channel layer with the tilt angle of 243 arcsec showed faster drain-lag recovery than the tilt angle of 209 arcsec. The results of the drain-lag test and isolation leakage current measurement indicated that the tilt angle and hopping distance contributed to drain-lag recovery. We proposed the mechanism of trap effect during the drain-lag test.

Semiconductor fluorescent quantum dots (Qdots) are popularly used as bioimaging taggants in live cell imaging and spectroscopy. In recent years, Qdots taggants are emerging in agricultural applications. Studies are primarily focused on nanotoxicity of ultra-small size water-soluble Qdots in plant systems. Nanotoxicity is correlated with Qdot core composition and surface coating. However, Qdots with certain chemical composition and surface coating may boost plant growth. In this study, we report that N-acetyl cysteine (NAC) capped ∼3.5 nm size ZnS:Mn/ZnS Qdots (NAC-Qdot) are efficiently uptaken by the snow pea (Pisum sativum L., a model plant) vascular system, enhancing the root growth at a dose level of 80 μg/mL. Fluorescence microscopy studies confirmed localization of NAC-Qdots in the intercellular regions. Germination and growth of the snow pea seeds were found to be strongly dependent on Qdot dosage and incubation time with Qdots. Seed germination reached 100% within 48 hours of NAC-Qdot exposure. Based on our preliminary findings, it is suggested that NAC-Qdot can be used as systemic plant nutrient material for boosting the seed germination and plant growth.

The switching speed of a Cu/Ta2O5/Pt atomic switch between a high-resistance (OFF) state and a low-resistance (ON) state was evaluated by transient current measurements under the application of a short voltage pulse. It was found that the SET time from the OFF state to the ON state decreased as low as 1 ns, and the RESET time from the ON state to the OFF state reached a few ns using moderate pulse amplitudes. The switching time depends strongly on the pulse amplitude and the cell resistance before applying a voltage pulse. This observation indicates that oxide-based atomic switches hold potential for fast-switching memory applications. It was also found that Cu nucleation on the Pt electrode is likely to the rate-limiting process determining the SET time and the REST time appears to be preferentially determined by thermochemical reaction.

Gold nanoclusters with precisely controlled atomic composition have emerged as promising materials for applications in nanotechnology because of their unique optical, electronic and catalytic properties. The recent discovery of a 20-gold-atom nanocluster protected by 16 organothiolate molecules, Au20(SR)16, is the smallest member in a surprising series of small gold−thiolate nanoclusters with a face-centered cubic (FCC) ordered core structures. A fundamental challenge facing gold nanocluster research is being able to understand the composition-dependent properties from a site-specific perspective in order to confidently establish structure-property relationships. A step in this direction is to examine the influence of various structural features (core geometry and thiolate-gold bonding motifs) on the bonding properties of gold-thiolate nanoclusters. In this work, ab initio simulations were conducted to systematically study the local structure and electronic properties of Au20(SR)16 from each unique Au and S atomic site using Au L3-edge extended X-ray absorption fine structure (EXAFS), projected density of states (l-DOS) and S K-edge X-ray absorption near edge structure (XANES) spectra. Two larger FCC-like gold-thiolate nanoclusters (Au28(SR)20 and Au36(SR)24) were used for a comparative study with Au20(SR)16, providing further predictions about the cluster size effect on the bonding properties of gold-thiolate nanoclusters with FCC-like core structures. Through this comparison, the smaller core size of Au20(SR)16 produces an EXAFS scattering signature that is non-FCC-like but shows very similar electronic properties with a larger FCC-like gold-thiolate nanocluster.

Three phase Mo-Mo3Si-Mo5SiB2 alloys possess excellent mechanical properties over a wide temperature range. The Mo solid solution phase is needed for balanced mechanical properties at room temperature. However, this phase suffers from catastrophic oxidation behavior at high temperatures caused by the formation and evaporation of MoO3. The oxidation resistance of three phase alloys benefits from a high volume fraction of intermetallic phases. In particular Mo5SiB2 leads to the formation of a borosilicate protective glassy layer on the material’s surface while exposed to air at elevated temperatures. Hence, it is unlikely to identify alloy compositions that will yield both optimum mechanical and oxidation performance.

Different coating systems and techniques, such as pack cementation, magnetron sputtering and plasma spraying are discussed in the literature to control the oxidation properties of Mo-based alloys. A different approach is to apply coating systems based on polymer derived ceramics (PDCs). Our present work introduces PDCs as a new type of promising and innovative oxidation-protective coatings for high temperature Mo-based alloys. After dip-coating with perhydropolysilazane (PHPS) and pyrolysis at 800 °C, dense and well-adhered SiNO ceramic layers could be achieved. These were investigated by scanning electron microscopy. Cyclic oxidation tests at 800 °C and 1100 °C were performed to investigate mass changes due to the thermal treatment. Indeed, even thin pyrolyzed PHPS layers with a thickness of around 70 nm to 175 nm protected the Mo-Si-B substrate during the initial stage of oxidation. By increasing the silicon oxide concentration at the material’s surface a first oxidation barrier was provided and thus, the strong initial mass loss could be decreased as compared to uncoated alloys. Furthermore, first results of the ongoing optimization process on PDC-coatings applied to Mo-Si-B alloys will be presented, involving the enhancement of the coating´s thickness or varying pyrolysis atmospheres.

We herein report the synthesis of highly-fluorescent CdSe/ZnS core-shell quantum dots (QDs) nanophosphors via a simple, non-phosphine and one pot synthetic method in the absence of an inert atmosphere. The as-prepared nanocrystallites were characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis) and photoluminescence spectroscopy, transmission electron microscopy (TEM) and high resolution TEM (HRTEM). The obtained CdSe/ZnS QDs were of high quality with sharp absorption peaks, bright luminescence, narrow emission width and high PL quantum yield (up to 74 %) without any size sorting. The structural analysis showed that the as-synthesised QDs are small and spherical in shape with narrow size distributions while the presence of the lattice fringe in the HRTEM image confirmed the crystallinity of the material. The dispersion of the obtained core-shell QDs in PMMA matrix resulted in the fabrication of highly fluorescent PMMA- CdSe/ZnS core shell QDs polymer nanocomposite film.

The path from conducting cutting-edge research in materials science to developing cutting-edge approaches for student engagement in STEM fields is a logical progression of a scientist’s professional interests. This pathway has led to creating an experimental approach to curricular and pedagogical materials development, dubbed Science Cartoons (Sci-Toons), based on Multimedia Learning Theoretical Framework (MLTF). Sci-Toons are developed by groups of students (STEM and non-STEM majors), STEM and non-STEM experts, and individuals with expertise in animations. The students are provided with technical training in animation, storytelling and science. This paper describes the creative process and design structure of Sci-Toons, shares selected animation projects, and provides data on the overall viewing impacts of Sci-Toons. The Sci-Toons initiative has offered a new venue for impacting students’ engagement in STEM.

Synthesis, structural, magnetic properties and heating efficiency of γ-Fe2O3 nanoparticles have been investigated. X-ray diffraction (XRD) and Mössbauer spectroscopy show that the obtained nanoparticles are mainly composed of maghemite phase (γ-Fe2O3). Williamson-Hall method shows that the crystallite is around 14nm.The specific absorption rate (SAR) under an alternating magnetic field is investigated as a function of frequency. A highest SAR value of 12W/g for frequency 523 kHz was obtained.

The paper focuses on the evolution of oriented nanostructures: An orientation in real space leads to scattering intensities with a preferred orientation with respect to the azimuthal angle in reciprocal space. Thus, the macroscopic orientation of nanostructures can be obtained from SAXS patterns. The additional advantage of in-situ SAXS is that one can directly follow the development of orientated nanostructures during thermal treatment, under extreme conditions or during processing. This is shown in the following for an orientational change of pores in two very different systems, the first being the formation of pores within carbon fibers during loading at high temperatures up to 2000 °C and the second is the development of macroscopically aligned pores in mesostructured silica in the sol-gel process during shear.

The performance of aromatic compounds as redox shuttles for overcharge protection in lithium-ion batteries is quite variable and is often difficult to predict. Redox shuttles may decompose in battery electrolyte in their neutral and radical cation forms, both of which are present during overcharge protection. While hundreds of compounds have been evaluated as redox shuttle candidates and a few have stood out as top performers, the reasons for increased stability over similar candidates with slightly different structures is often unclear, and the exploration of decomposition of redox shuttles has been severely limited, restricting our ability to design improved versions of redox shuttles that do not suffer from the same reactions in lithium-ion batteries. To better understand the stability and reactivity of redox shuttles (also relevant to the improvement of positive electrode materials in non-aqueous redox flow batteries) our research has focused on measuring the stability of neutral and oxidized forms of redox shuttle candidates as well as using a variety of spectroscopic methods to analyze the byproducts of decomposition, both from radical cations generated in model solvents and electrolytes from postmortem analysis of failed batteries.

ZnO was grown by Chemical Bath Deposition technique activated by microwaves (CBD-AμW) on corning glass substrates. The ZnO structural and optical properties are studied as a function of the urea concentration in the growth solution. ZnO chemical stoichiometry was determined by Energy-dispersive X-ray spectroscopy (EDS). The XRD analysis and Raman scattering reveal that ZnO deposited thin films showed hexagonal polycrystalline phase wurtzite type. The Raman spectra present four main peaks associated to the modes E 2 high , (E 2 high -E 2 low ), E 2 low and an unidentified vibrational band observed at 444, 338, 104 and 78 cm-1. The E 2 low mode involves mainly Zn atoms motion in the unit cell and the E 2 high mode is associated to oxygen motion. The observed emission peaks in the room temperature photoluminescence spectra are associated at vacancies of zinc and oxygen in the lattice.

In this study, an “inverted” design, phase-separated morphology and gold-functionalized reduced graphene oxide (Au-rGO) were used to address exciton recombination and poor Fermi level alignment. To increase efficiencies, a unique methodology was used to coat Au-rGO on top of the active layer. When 0.05 Au-rGO was blended with the active layer, there were metal-thiolate bonds with P3HT and π-π stacking with PCBM. However, KPFM, measured for the first time for this material, showed that the while 0.05mM Au-rGO reduced the energy gap between P3HT and PBCM, this was offset by recombination. KPFM showed that Au-rGO may be better suited between the active layer and electrode. When 0.5mM Au-rGO was coated on top of the active layer, efficiency increased (p<0.002) nearly 600%, suggesting that Au-rGO is a more effective acceptor than a constituent of the active layer.

A sensor which detects mechanical stresses and stores the position and the strength of these loads by color change of embedded quantum dots (QDs) is presented. The top and bottom electrodes of the sensor are inkjet-printed which leads to a fast and accurate deposition of thin (approx. 50 - 300 nm) and conductive layers. The used silver and poly(3,4-ethylenedioxythio-phene) polystyrene sulfonate (PEDOT:PSS) inks are optimized in terms of printability and opportunities of functionality forming without influencing the active layer of the sensor. The active layer of the sensor is spin-coated and consists of the QDs embedded in semi-conducting poly(9-vinylcarba-zole) (PVK). The hole transport characteristic of PVK and the band level alignment of the used materials ensures the preferred injection of only one type of charge carrier into the QDs. As a result the mechanical stress is visualized by a decreasing in photoluminescence (PL) of the QDs.

We present gold (Au) and silver (Ag) nanoparticles (NPs) could be used not only for stimuli-responsive optical sensors but also for the quantification of radical compounds when these nanoparticles are suitably combined with polymeric materials. When Au NPs are assembled 2-dimensionally on the surface of hydrogel NPs which respond to temperatures, the hybrid NPs displayed thermoreversible multiple color switching. Accordingly, optical bandwidths of the hybrid NPs are reversibly changed with temperatures: with hybrid NPs assembled with 51 nm Au NPs, prominent optical signals are recorded at 900 nm at 50 °C while most of extinction signals are shown below 600 nm at room temperatures. In addition, we demonstrate the modification of Ag NPs’ surfaces (nanocubes and nanospheres) with polyelectrolytes (either positive or negative) could extend the quantifiable detection ranges of radical compounds. Through the surface modification of Ag NPs, the polyelectrolytes protect the Ag NPs by probably either retarding (forming diffusion barriers) or preventing (blocking/entrapping/scavenging) the arrival of radicals to Ag NPs or both. The roles of the polyelectrolytes are demonstrated by using radical compounds produced from tetrahydrofuran and H2O2. From the results, we could obtain calibration curves for the wide-range quantification of radical compounds.

Core substituted perylene diimides (PDIs) are promising candidates as non-fullerene acceptor materials for organic solar cells. The functionalization of PDIs in the bay positions using chemical groups with different electron donating abilities and with steric hindrance is a versatile tool to modify both the optoelectronic properties and the morphology in the solid state.

Herein we present two new PDI based molecules having bulky aromatic substituents linked into the bay positions: PDI-SF with spirobifluorene group and PDI-BSF with bithienyl-spirobifluorene moieties. The high steric hindrance of spirobifluorene reduce the tendency to form aggregates that has been identified as a limiting factor for the photovoltaic performances in PDI based solar cells.

The PDI molecules were tested as electron acceptors in bulk heterojunction solar cells with P3HT as electron donor. Power conversion efficiencies (PCE) of 1.58% and 1.18% were obtained for PDI-SF and PDI-BSF devices.

A technology is presented for the production of soft and rigid circuits with an arbitrary 2.5D fixed shape. The base of this technology is our proprietary technology for elastic circuits with a random shape, in which the elastic thermoset (mostly PDMS) polymer is now replaced by soft or rigid thermoplastic variants. An additional thermoforming step is required to transform the circuit from its initial flat to its final fixed 2.5D shape, but for rigid fixed shape circuits only one-time stretchability of the extensible interconnects is required, relieving the reliability requirements.