Interfacial Electronic Interactions within the Pd-CeO2/Carbon Onions Define the Efficient Electrocatalytic Ethanol Oxidation Reaction in Alkaline Electrolytes.

Porous Pd-based electrocatalysts are promising materials for alkaline direct ethanol fuel cells (ADEFCs) and ethanol sensors in the development of renewable energy and point-of-contact ethanol sensor test kits for drunk drivers. However, experimental and theoretical investigations of the interfacial interaction among Pd nanocrystals on supports (i.e., carbon black (CB), onion-like carbon (OLC), and CeO2/OLC) toward ADEFC and ethanol sensors are not yet reported. This is based on the preparation of Pd-CeO2/OLC nanocrystals by the sol-gel and impregnation methods. Evidently, the porous Pd-CeO2/OLC significantly increased membrane-free micro-3D-printed ADEFC performance with a high peak power density (Pmax = 27.15 mW cm-2) that is 1.38- and 7.58-times those of Pd/OLC (19.72 mW cm-2) and Pd/CB (3.59 mW cm-2), besides its excellent stability for 48 h. This is due to the excellent interfacial interaction among Pd, CeO2, and OLC, evidenced by density functional theory (DFT) simulations that showed a modulated Pd d-band center and facile active oxygenated species formation by the CeO2 needed for ethanol fuel cells. Similarly, Pd-CeO2/OLC gives excellent sensitivity (0.00024 mA mM-1) and limit of detection (LoD = 8.7 mM) for ethanol sensing and satisfactory recoveries (89-108%) in commercial alcoholic beverages (i.e., human serum, Amstel beer, and Nederberg Wine). This study shows the excellent possibility of utilizing Pd-CeO2/OLC for future applications in fuel cells and alcohol sensors.

Observation of High Magnetic Bistability in Lanthanide (Ln = Gd, Tb and Dy)-Grafted Carbon Nanotube Hybrid Molecular System.

There is an immense research interest in molecular hybrid materials posing novel magnetic properties for usage in spintronic devices and quantum technological applications. Although grafting magnetic molecules onto carbon nanotubes (CNTs) is nontrivial, there is a need to explore their single molecule magnetic (SMM) properties post-grafting to a greater degree. Here, we report a one-step chemical approach for lanthanide-EDTA (Ln = GdIII, 1; TbIII, 2 and DyIII, 3) chelate synthesis and their effective grafting onto MWCNT surfaces with high magnetic bistability retention. The magnetic anisotropy of an Ln-CNT hybrid molecular system by replacing the central ions in the hybrid complex was studied and it was found that system 1 exhibited a magnetization reversal from positive to negative values at 70 K with quasi-anti-ferromagnetic ordering, 2 showed diamagnetism to quasi-ferromagnetism and 3 displayed anti-ferromagnetic ordering as the temperature was lowered at an applied field of 200 Oe. A further analysis of magnetization (M) vs. field (H) revealed 1 displaying superparamagnetic behavior, and 2 and 3 displaying smooth hysteresis loops with zero-field slow magnetic relaxation. The present work highlights the importance of the selection of lanthanide ions in designing SMM-CNT hybrid molecular systems with multi-functionalities for building spin valves, molecular transistors, switches, etc.

Design and Evaluation of Composite Magnetic Iron-Platinum Nanowires for Targeted Cancer Nanomedicine.

The purpose of the study was to synthesize and investigate the influence of geometrical structure, magnetism, and cytotoxic activity on core-shell platinum and iron-platinum (Fe/Pt) composite nanowires (NWs) for potential application in targeted chemotherapeutic approaches. The Pt-NWs and Fe/Pt composite NWs were synthesized via template electrodeposition, using anodic aluminum oxide (AAO) membranes. The Fe/Pt composite NWs (Method 1) was synthesized using two electrodeposition steps, allowing for greater control of the diameter of the NW core. The Fe/Pt composite NWs (Method 2) was synthesized by pulsed electrodeposition, using a single electrolytic bath. The properties of the synthesized NWs were assessed by high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, powder X-ray diffraction (XRD), inductively coupled plasma-optical emission spectrometry (ICP-OES), vibrating-sample magnetometry (VSM), and surface charge (zeta potential). A microscopy image analysis of the NWs revealed the presence of high-aspect-ratio NWs with nominal diameters of 40-50 nm and lengths of approximately <4 µm. The obtained powder XRD patterns confirmed the presence of a polycrystalline structure for both Pt NWs and Fe/Pt composite NWs. The potential utility of the synthesized NW nanoplatforms for anticancer activity was investigated using Tera 1 cells and Mouse 3T3 cells. Pt-NWs displayed modest cytotoxic activity against Tera 1 cells, while the Fe/Pt composite NWs (both Methods 1 and 2) demonstrated enhanced cytotoxic activity compared to the Pt-NWs on Tera 1 cells. The Fe/Pt composite NWs (Method 1) displayed ferromagnetic behavior and enhanced cytotoxic activity compared to Pt-NWs on Tera 1 cells, thus providing a sound basis for future magnetically targeted chemotherapeutic applications.

Robust Arduino controlled spin coater using a novel and simple gravity chuck design.

Spin coaters offer an invaluable method of thin film fabrication. Various implementations, both proprietary and open-source exist, offering vacuum and gravity samples chucks. These implementations vary in their reliability, ease-of-use, cost, and versatility. Here we present a novel easy-to-use open-source gravity-chuck type spin coater with minimal points of failure at a material cost of around 100 USD (1500 ZAR). The unique chuck design makes use of interchangeable brass plate sample masks, each specific to a sample size, these can be made with basic skills and common hand tools. In comparison, replacement chucks for commercial alternatives can cost as much as the entire spin coater we present. Open-source hardware such as this provides an example for individuals in the field on the design and development of hardware where reliability, cost, and flexibility are most important, as is the case for many institutions in developing countries.

Synthesis of Novel Conjugated Linoleic Acid (CLA)-Coated Superparamagnetic Iron Oxide Nanoparticles (SPIONs) for the Delivery of Paclitaxel with Enhanced In Vitro Anti-Proliferative Activity on A549 Lung Cancer Cells.

The application of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) as a nanomedicine for Non-Small Cell Lung Carcinoma (NSCLC) can provide effective delivery of anticancer drugs with minimal side-effects. SPIONs have the flexibility to be modified to achieve enhanced oading of hydrophobic anticancer drugs such as paclitaxel (PTX). The purpose of this study was to synthesize novel trans-10, cis-12 conjugated linoleic acid (CLA)-coated SPIONs loaded with PTX to enhance the anti-proliferative activity of PTX. CLA-coated PTX-SPIONs with a particle size and zeta potential of 96.5 ± 0.6 nm and -27.3 ± 1.9 mV, respectively, were synthesized. The superparamagnetism of the CLA-coated PTX-SPIONs was confirmed, with saturation magnetization of 60 emu/g and 29 Oe coercivity. CLA-coated PTX-SPIONs had a drug loading efficiency of 98.5% and demonstrated sustained site-specific in vitro release of PTX over 24 h (i.e., 94% at pH 6.8 mimicking the tumor microenvironment). Enhanced anti-proliferative activity was also observed with the CLA-coated PTX-SPIONs against a lung adenocarcinoma (A549) cell line after 72 h, with a recorded cell viability of 17.1%. The CLA-coated PTX-SPIONs demonstrated enhanced suppression of A549 cell proliferation compared to pristine PTX, thus suggesting potential application of the nanomedicine as an effective site-specific delivery system for enhanced therapeutic activity in NSCLC therapy.

Elucidating the Trajectory of the Charge Transfer Mechanism and Recombination Process of Hybrid Perovskite Solar Cells.

Perovskite-based solar cells (PSCs) have attracted attraction in the photovoltaic community since their inception in 2009. To optimize the performance of hybrid perovskite cells, a primary and crucial strategy is to unravel the dominant charge transport mechanisms and interfacial properties of the contact materials. This study focused on the charge transfer process and interfacial recombination within the n-i-p architecture of solar cell devices. The motivation for this paper was to investigate the impacts of recombination mechanisms that exist within the interface in order to quantify their effects on the cell performance and stability. To achieve our objectives, we firstly provided a rationale for the photoluminescence and UV-Vis measurements on perovskite thin film to allow for disentangling of different recombination pathways. Secondly, we used the ideality factor and impedance spectroscopy measurements to investigate the recombination mechanisms in the device. Our findings suggest that charge loss in PSCs is dependent mainly on the configuration of the cells and layer morphology, and hardly on the material preparation of the perovskite itself. This was deduced from individual analyses of the perovskite film and device, which suggest that major recombination most likely occur at the interface.

The role of oxygen in a carbon source (castor oil versus paraffin oil) in the synthesis of carbon nano-onions.

The role of a carbon source containing oxygen groups on the physicochemical properties of carbon nano-onions (CNOs) was investigated. Two oils, castor oil (with O groups) and paraffin oil (without O groups) were converted to CNOs in gram-scale yields using an open flame pyrolysis procedure. The products were heated under argon at 900 °C for varying times (1 h, 2 h, 3 h), to investigate the temperature dependence on their structural properties. TGA studies indicated different decomposition behaviour for the different samples with the annealed paraffinic CNOs (CNOP) having a higher decomposition temperature (>600 °C) than the castor oil derived CNOs (CNOC) (<600 °C). TEM images revealed formation of typical chain-like quasi-spherical nanostructures with particles size distributions for the CNOP (22-32 ± 7.8 nm) and the CNOC (44-51 ± 9.9 nm) materials. A detailed Raman analysis of the CNOs revealed that the graphicity of the CNOs varied with both the carbon oil source and the annealing time. Deconvolution of the first order Raman spectra revealed changes in the parameters of the major Raman bands that were then correlated with defect density ratios. Finally, bandwidth analysis depicted the dependence of the graphicity of the CNOs with heat treatment. The data thus indicate that the presence of oxygen in the carbon source provides a method for producing different CNOs and that simple procedures can be used to produce these different CNOs.

Surface Brillouin scattering study of tantalum nitride (TaN) thin films.

Elastic properties of TaN films on (001)Si are investigated by surface Brillouin scattering (SBS). The velocity dispersion is obtained from Brillouin frequency shifts and surface acoustic wave phase velocities derived from measured SBS spectra. The observed Rayleigh surface acoustic and Sezawa waves indicate a soft on hard configuration. The elastic stiffnesses from the best fit of the calculated and measured spectra were C11=288 and C44=80GPa. Using these elastic constants in the surface elastodynamic Green's function yielded theoretical Brillouin spectra in agreement with measured spectra. Employing a least squares fitting procedure to the elastic constants gives uncertainties in C11 and C44 as ±3.7 and ±2.5GPa, respectively.

Minimum lattice thermal conductivity of In3SbTe2 by surface Brillouin scattering.

Phase-change materials are chalcogenide alloys used for nonvolatile memory applications due to their rapid and reversible structural transformation. In3SbTe2 is a promising candidate that exhibits transitions dependent on thermal conductivity. The minimum lattice thermal conductivity of amorphous In3SbTe2 is investigated by surface acoustic propagation. In3SbTe2 thin films were deposited by radio frequency magnetron sputtering on (100) Si. Rutherford backscattering spectrometry and x-ray reflectivity were used to establish the elemental composition, deposition rate, and mass density. Using the Debye model, the thermal conductivity is extracted from fitted phase velocities measured by surface Brillouin scattering. The low thermal conductivity is revealed to be suitable for Joule heating.

Annealing effect on the structural and optical behavior of ZnO:Eu3+ thin film grown using RF magnetron sputtering technique and application to dye sensitized solar cells.

Eu-doped ZnO (ZnO:Eu3+) thin films deposited by RF magnetron sputtering have been investigated to establish the effect of annealing on the red photoluminescence. PL spectra analysis reveal a correlation between the characteristics of the red photoluminescence and the annealing temperature, suggesting efficient energy transfer from the ZnO host to the Eu3+ ions as enhanced by the intrinsic defects levels. Five peaks corresponding to 5D0-7FJ transitions were observed and attributed to Eu3+ occupancy in the lattice sites of ZnO thin films. As a proof of concept a dye sensitized solar cell with ZnO:Eu3+ thin films of high optical transparency was fabricated and tested yielding a PCE of 1.33% compared to 1.19% obtained from dye sensitized solar cells (DSSC) with pristine ZnO without Eu produced indicating 11.1% efficiency enhancement which could be attributed to spectral conversion by the ZnO:Eu3+.

Effect of Gold Nanospheres and Nanodots on the Performance of PEDOT:PSS Solar Cells.

Gold nanospheres were synthesized using a modified Turkevich method (d = 14±4 nm, λmax = 531 nm), while gold nanodots made of spheres (5±2 nm) and non-spherical nanodots (aspect ratio of 1.7±0.4) were synthesized using a modified seed mediated method. The spherical gold nanodots exhibited a transverse excitation mode at 525 nm while the non-spherical gold nanodots showed an additional longitudinal excitation mode observed in the UV-vis spectrum at 794 nm. The gold nanodots also exhibited a surface enhanced Raman effect which significantly influenced the electronic properties of the photovoltaic device. The incorporation of Au nanospheres in a PEDOT:PSS hole transport layer increased the photovoltaic device efficiency by 51%. This was attributed to a decrease in the series resistance which improved the hole transport pathways in the PEDOT:PSS and enhanced the current density of the photovoltaic device. In contrast, incorporation of spherical and non-spherical gold nanodots into the PEDOT:PSS hole transport layer resulted in a decrease in current density and a consequent decrease in efficiency. This can be attributed to the electron-hole recombination and accumulation of space charges by the non-spherical gold nanodots in PEDOT:PSS resulting in an increased series resistance and leakage currents and hence a reduced device performance. Thus, the morphological, structural and opto-electrical properties of the gold nanospheres and nanodots influenced the device performance of the PEDOT:PSS solar cells.

Effect of thermal treatment on ZnO:Tb3+ nano-crystalline thin films and application for spectral conversion in inverted organic solar cells.

Down conversion has been applied to minimize thermalization losses in photovoltaic devices. In this study, terbium-doped ZnO (ZnO:Tb3+) thin films were deposited on ITO-coated glass, quartz and silicon substrates using the RF magnetron sputtering technique fitted with a high-purity (99.99%) Tb3+-doped ZnO target (97% ZnO, 3% Tb) for use in organic solar cells as a bi-functional layer. A systematic study of the film crystallization dynamics was carried out through elevated temperature annealing in Ar ambient. The films were characterized using grazing incidence (XRD), Rutherford backscattering spectrometry (RBS), atomic force microscopy, and UV-visible transmittance and photoluminescence measurements at an excitation wavelength of 244 nm. The tunability of size and bandgap of ZnO:Tb3+ nanocrystals with annealing exhibited quantum confinement effects, which enabled the control of emission characteristics in ZnO:Tb3+. Energy transfer of ZnO → Tb3+ (5D3-7F5) was also observed from the photoluminescence (PL) spectra. At an inter-band resonance excitation of around 300-400 nm, a typical emission band from Tb3+ was obtained. The ZnO:Tb3+ materials grown on ITO-coated glass were then used as bi-functional layers in an organic solar cell based on P3HT:PCBM blend, serving as active layers in an inverted device structure. Energy transfer through down conversion between ZnO and Tb3+ led to enhanced absorption in P3HT:PCBM in the 300-400 nm range and subsequently augmented J sc of a Tb3+-based device by 17%.

The role of vacancies and local distortions in the design of new phase-change materials.

Phase-change materials are of tremendous technological importance ranging from optical data storage to electronic memories. Despite this interest, many fundamental properties of phase-change materials, such as the role of vacancies, remain poorly understood. 'GeSbTe'-based phase-change materials contain vacancy concentrations around 10% in their metastable crystalline structure. By using density-functional theory, the origin of these vacancies has been clarified and we show that the most stable crystalline phases with rocksalt-like structures are characterized by large vacancy concentrations and local distortions. The ease by which vacancies are formed is explained by the need to annihilate energetically unfavourable antibonding Ge-Te and Sb-Te interactions in the highest occupied bands. Understanding how the interplay between vacancies and local distortions lowers the total energy helps to design novel phase-change materials as evidenced by new experimental data.