Justin A. Kimpton

Quantification of ZnO Nanoparticle Uptake, Distribution, and Dissolution within Individual Human Macrophages

The usefulness of zinc oxide (ZnO) nanoparticles has led to their wide distribution in consumer products, despite only a limited understanding of how this nanomaterial behaves within biological systems. From a nanotoxicological viewpoint the interaction(s) of ZnO nanoparticles with cells of the immune system is of specific interest, as these nanostructures are readily phagocytosed. In this study, rapid scanning X-ray fluorescence microscopy was used to assay the number ZnO nanoparticles associated with ∼1000 individual THP-1 monocyte-derived human macrophages. These data showed that nanoparticle-treated cells endured a 400% elevation in total Zn levels, 13-fold greater than the increase observed when incubated in the presence of an equitoxic concentration of ZnCl2. Even after excluding the contribution of internalized nanoparticles, Zn levels in nanoparticle treated cells were raised ∼200% above basal levels. As dissolution of ZnO nanoparticles is critical to their cytotoxic response, we utilized a strategy combining ion beam milling, X-ray fluorescence and scanning electron microscopy to directly probe the distribution and composition of ZnO nanoparticles throughout the cellular interior. This study demonstrated that correlative photon and ion beam imaging techniques can provide both high-resolution and statistically powerful information on the biology of metal oxide nanoparticles at the single-cell level. Our approach promises ready application to broader studies of phenomena at the interface of nanotechnology and biology.

Tailoring of unipolar strain in lead-free piezoelectrics using the ceramic/ceramic composite approach

The electric-field-induced strain response mechanism in a polycrystalline ceramic/ceramic composite of relaxor and ferroelectric materials has been studied using in situ high-energy x-ray diffraction. The addition of ferroelectric phase material in the relaxor matrix has produced a system where a small volume fraction behaves independently of the bulk under an applied electric field. Inter- and intra-grain models of the strain mechanism in the composite material consistent with the diffraction data have been proposed. The results show that such ceramic/ceramic composite microstructure has the potential for tailoring properties of future piezoelectric materials over a wider range than is possible in uniform compositions.

A synergistic strategy established by the combination of two H-enriched B–N based hydrides towards superior dehydrogenation

A strategy for establishing Hδ+⋯−δH interactions by the combination of two kinds of H-enriched B–N based hydrides, ammine metal borohydrides (AMBs) and ammonia borane (AB), to achieve superior dehydrogenation properties is reported. Two novel combined complexes: Al(BH4)3·6NH3–4AB and Li2Al(BH4)5(NH3BH3)3·6NH3 were successfully synthesized. Structural analysis revealed that a partial NH3 unit transferred from Al(BH4)3·6NH3 to AB, resulting in the formation of two new phases of Al(BH4)3·5.4NH3 and NH3BH3·0.15NH3 in the Al(BH4)3·6NH3–4AB composite. In contrast, Li2Al(BH4)5(NH3BH3)3·6NH3 formed with a single-phase that was indexed to a cubic unit cell with a refined lattice parameter, a = 23.1220(3) A. The structure of Li2Al(BH4)5(NH3BH3)3·6NH3 is composed of alternate Li+, [Al(NH3)6]3+ and AB layers stacked along the b-axis as a 3D framework. Compared to the unitary compound, the H-enriched complex system presented a mutual dehydrogenation improvement in terms of a considerable decrease in the dehydrogenation temperature and the preferable suppression of the simultaneous release of by-products; for example, over 11 wt% of hydrogen, with a purity of >98 mol%, can be released from both Al(BH4)3·6NH3–4AB and Li2Al(BH4)5(NH3BH3)3·6NH3 below 120 °C. The significantly improved dehydrogenation in the H-enriched complex system can be attributed to the initial interaction between the AB and an NH3 group (from the AMBs), which results in the balanced B–H and N–H units in the AMBs, thereby leading to a more activated and thorough Hδ+⋯−δH interaction in the composite. Moreover, an ammonia-liquification technique was employed to impregnate the complex system into a hypercrosslinked nano-porous polymer (PSDB) template, resulting in the average particle size of the Al(BH4)3·6NH3–4AB composite to be 99.8 mol%) below 110 °C. These advanced dehydrogenation properties affirm Al(BH4)3·6NH3–4AB and Li2Al(BH4)5(NH3BH3)3·6NH3 as strong candidates for potential hydrogen storage materials.

Structural and Magnetic Properties of the Iridium Double Perovskites Ba(2-x)Sr(x)YIrO6.

The crystal structures of the series of ordered double perovskites Ba(2-x)Sr(x)YIrO6 (0 ≤ x ≤ 2) were refined using a combination of high-resolution synchrotron X-ray and high-intensity neutron diffraction data. The materials displayed a sequence of structures Fm3̅m(a(0)a(0)a(0)) (x = 0.6)--> I4/m(a(0)a(0)c(-)) (x = 1.0)--> I2/m(a(-)a(-)c(0)) (x = 1.4)--> P2(1)/n(a(-)a(-)c(+)) associated with increased tilting of the corner-sharing octahedra induced by increasing amount of the smaller Sr cation present. A similar sequence of transitions was induced by heating selected samples. Magnetic susceptibility measurements between 2 and 300 K showed no evidence for long-range magnetic ordering, an observation that was supported by neutron diffraction measurements, and rather strong spin-orbit coupling results in a Jeff = 0 ground state.

Helium-like titanium x-ray spectrum as a probe of QED computation

We discuss the first absolute energy measurements of the intercombination and forbidden transitions ( xyz ,, ) in trapped Ti 20+ ions to 15 parts per million accuracy. We present new measurements on helium-like titanium, in which the orbital radius is reduced and QED terms are magnified by the increased nuclear charge. The measured transition energies are higher than predicted.

The correction of systematic image deformations inherent to two-dimensional proportional counters

Two-dimensional backgammon configuration and multiwire gas proportional counters have been in use for decades in the field of x-ray physics for high-precision or high-flux experiments. Systematics inherent to this type of detector lead to image distortions that are often overlooked or extremely difficult to quantify. They are usually seen as intrinsic to the detector performance, leading to loss of resolution, linearity and signal-to-noise ratio. This work presents the signature, cause and resolution of several key distortions. The physics of the breakdown between the anode and cathode, false event position reconstruction due to the electronic detector response, and the effect of asymmetric field lines between the anode and cathode are developed. The position resolution of these types of detectors is demonstrated to be comparable to a charge-coupled device when used in the same experimental configuration.

Spin–Orbit Coupling Controlled Ground State in the Ir(V) Perovskites A2ScIrO6 (A = Ba or Sr)

The structural and magnetic properties of the two Ir(V) perovskites Ba2ScIrO6 and Sr2ScIrO6 were established. The structures were refined using a combined neutron and synchrotron data set. At room temperature the former has a cubic structure in space group Fm3̅m with a = 8.1450(3) Å, and the latter is monoclinic in P21/n with a = 5.6606(3) Å, b = 5.6366(3) Å, c = 7.9720(4) Å, and β = 89.977(5)°. Magnetization measurements show both oxides have magnetic moments close to zero as a consequence of strong spin-orbit coupling that results in a Jeff ≈ 0 ground state. The distortion of the IrO6 octahedra in Sr2ScIrO6 is insufficient to generate crystal field splitting strong enough to quench the spin-orbit coupling.

Synchrotron X-ray Powder Diffraction for Fast, In-Situ Insights

Synchrotron X-ray powder diffraction speeds up the development of new energy-related materials and devices by enabling rapid, real-time data collection in sample environments that emulate true operating conditions.

X-ray measurements in helium-like atoms increased discrepancy between experiment and theoretical QED

A recent 15 parts per million (ppm) experiment on muonic hydrogen () found a major discrepancy with quantum electrodynamics (QED) and independent nuclear size determinations. Here we find a significant discrepancy in a different type of exotic atom: a medium-Z nucleus with two electrons. Investigation of the data collected is able to discriminate between available QED formulations and reveals a pattern of discrepancy of almost six standard errors of experimental results from the most recent theoretical predictions, with a functional dependence proportional to Zn where . In both the muonic and highly charged systems, the sign of the discrepancy is the same, with the measured transition energy higher than predicted. Some consequences are possible or probable, and some are more speculative. This may give insight into effective nuclear radii, the Rydberg, the fine-structure constant, or unexpectedly large QED terms.

Simulation and minimization of nonlinear effects in backgammon-type multi-wire gas proportional counters

The backgammon-type multi-wire gas proportional counter (MWPC) enables highly efficient detection of x-ray photons in two dimensions with good resolution and a wide range of energies and count rates. We develop a simulation which accurately describes the internal geometry of the detector and assists in the identification of several sources of nonlinear detector output. The sophistication of the model allows real solutions to be generated to minimize these effects. The result is an increase of 20% in the linear range, significant improvements to detector linearity, and improved output uniformity across both detector dimensions. These insights and methodology can be applied to other detector types and to future optimizations and developments of detector performance.