Defect Induced Ferromagnetism in Undoped ZnO Nanoparticles

Undoped ZnO nanoparticles (NPs) with size ∼12 nm were produced using forced hydrolysis methods using diethylene glycol (DEG) [called ZnO-I] or denatured ethanol [called ZnO-II] as the reaction solvent; both using Zn acetate dehydrate as precursor. Both samples showed weak ferromagnetic behavior at 300 K with saturation magnetization Ms = 0.077 ± 0.002 memu/g and 0.088 ± 0.013 memu/g for ZnO-I and ZnO-II samples, respectively. Fourier transform infrared(FTIR) spectra showed that ZnO-I nanocrystals had DEG fragments linked to their surface. Photoluminescence (PL) data showed a broad emission near 500 nm for ZnO-II which is absent in the ZnO-I samples, presumably due to the blocking of surface traps by the capping molecules. Intentional oxygen vacancies created in the ZnO-I NPs by annealing at 450 °C in flowing Ar gas gradually increased Ms up to 90 min and x-ray photoelectron spectra (XPS) suggested that oxygen vacancies may have a key role in the observed changes in Ms. Finally, PL spectra of ZnO showed the appearance of a blue/violet emission, attributed to Zn interstitials,whose intensity changes with annealing time, similar to the trend seen for Ms. The observed variation in the magnetization of ZnO NP with increasing Ar annealing time seems to depend on the changes in the number of Zn interstitials and oxygen vacancies

Dopant Spin States and Magnetism of Sn\u3csub\u3e1−x\u3c/sub\u3eFe\u3csub\u3ex\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e Nanoparticles

This work reports detailed investigations of a series of ∼2.6 nm sized, Sn1−xFexO2 crystallites with x = 0–0.10 using Mossbauer spectroscopy, x-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and magnetometry to determine the oxidation state of Fe dopants and their role in the observed magnetic properties. The magnetic moment per Fe ion μ was the largest ∼6.48 × 10−3 μB for the sample with the lowest (0.001%) Fe doping, and it showed a rapid downward trend with increasing Fe doping. Majority of the Fe ions are in 3+ oxidation state occupying octahedral sites. Another significant fraction of Fe dopant ions is in 4+ oxidation state and a still smaller fraction might be existing as Fe2+ ions, both occupying distorted sites, presumably in the surface regions of the nanocrystals, near oxygen vacancies. These studies also suggest that the observed magnetism is not due to exchange coupling between Fe3+ spins. A more probable role for the multi-valent Fe ions may be to act as charge reservoirs, leading to charge transfer ferromagnetism

Transient Multilayer Analytical Model of a Line Heat Source Probe for In-Pile Thermal Conductivity Measurements

In-pile measurements of nuclear fuel properties is of critical importance for the design, performance, and safety considerations of next generation nuclear reactors and can be difficult due to the high temperature and high neutron flux environment. Real-time data for thermal conductivity is currently lacking due to the difficulty in deploying advanced instrumentation for thermal properties measurements in situ during nuclear operations. This limitation hinders our understanding of the mechanisms responsible for these changes. In this study, we have developed analytical models, utilizing the quadrupoles method, for in-pile thermal conductivity measurements using a novel line heat source. This probe uses Joule heating of a single wire to induce a temperature gradient and heat flow in surrogate fuel samples, while simultaneously leveraging the temperature dependent resistance of the wire as a thermometer to monitor the temperature rise of the sample for thermal conductivity extraction. The analytical models have been verified against more computationally intensive finite element models and experimental results were obtained from Teflon (PTFE) and aluminum samples. Coefficient of determination (R2) values for the measurements were 0.995, 0.987, and 0.992 for 10, 20, and 30 mm PTFE respectively and 0.983, 0.992, and 0.960 for 10, 20, and 30 mm aluminum respectively. Further complimenting the fits, sensitivity parameter studies were conducted on the 10 and 30 mm PTFE and aluminum highlighting the potential of our approach for rapid in-pile thermal conductivity measurements

Additive Manufactured Boron Nitride Coatings for Extreme Environments

With the recent surge in Additive Electronics Manufacturing (AEM) technologies, industry demand has risen for nanoparticle based printed electronics. Furthermore, researchers aspire to develop printable coatings that act as electrical insulators, thermal conductors, and suitable anti-corrosion barriers and ultimately enhance the efficiency and functionality of printed electronics in extreme environments. Meanwhile, these inks should be compatible with AEM methods such as ink jet printing (IJP), aerosol jet printing (AJP), and micro dispense printing (MDP). Boron nitride (BN) coatings have favorable traits such as high thermal conductivity, functionality at extreme temperatures, and low weight. As-received cubic and hexagonal BN powders were characterized via particle size analysis (PSA) to find the particle size distribution, X-ray diffraction (XRD) to identify phase purity and crystallite size, and scanning electron microscopy (SEM) for particle morphology. The characterization was performed in order to develop processes for formulating BN-loaded inks. This work concluded that polymer-based ink formulations are effective and ensure printable ink with tunable viscosity that adapts to the desired printing method. Project results provide a better understanding of powder features like particle size, tendencies towards agglomeration, and electrical properties that are essential in formulating an ink with variability for application in printed device technology

Rapid Dissolution of ZnO Nanoparticles Induced by Biological Buffers Significantly Impacts Cytotoxicity

Zinc oxide nanoparticles (nZnO) are one of the most highly produced nanomaterials and are used in numerous applications including cosmetics and sunscreens despite reports demonstrating their cytotoxicity. Dissolution is viewed as one of the main sources of nanoparticle (NP) toxicity; however, dissolution studies can be time-intensive to perform and complicated by issues such as particle separation from solution. Our work attempts to overcome some of these challenges by utilizing new methods using UV/vis and fluorescence spectroscopy to quantitatively assess nZnO dissolution in various biologically relevant solutions. All biological buffers tested induce rapid dissolution of nZnO. These buffers, including HEPES, MOPS, and PIPES, are commonly used in cell culture media, cellular imaging solutions, and to maintain physiological pH. Additional studies using X-ray diffraction, FT-IR, X-ray photoelectron spectroscopy, ICP-MS, and TEM were performed to understand how the inclusion of these nonessential media components impacts the behavior of nZnO in RPMI media. From these assessments, we demonstrate that HEPES causes increased dissolution kinetics, boosts the conversion of nZnO into zinc phosphate/carbonate, and, interestingly, alters the structural morphology of the complex precipitates formed with nZnO in cell culture conditions. Cell viability experiments demonstrated that the inclusion of these buffers significantly decrease the viability of Jurkat leukemic cells when challenged with nZnO. This work demonstrates that biologically relevant buffering systems dramatically impact the dynamics of nZnO including dissolution kinetics, morphology, complex precipitate formation, and toxicity profiles