Daniel G. Mieritz

Photocurrent generation by photosynthetic purple bacterial reaction centers interfaced with a porous antimony-doped tin oxide (ATO) electrode

The ability to exchange energy and information between biological and electronic materials is critical in the development of hybrid electronic systems in biomedicine, environmental sensing, and energy applications. While sensor technology has been extensively developed to collect detailed molecular information, less work has been done on systems that can specifically modulate the chemistry of the environment with temporal and spatial control. The bacterial photosynthetic reaction center represents an ideal photonic component of such a system in that it is capable of modifying local chemistry via light-driven redox reactions with quantitative control over reaction rates and has inherent spectroscopic probes for monitoring function. Here a well-characterized model system is presented, consisting of a transparent, porous electrode (antimony-doped tin oxide) which is electrochemically coupled to the reaction center via a cytochrome c molecule. Upon illumination, the reaction center performs the 2-step, 2-electron reduction of a ubiquinone derivative which exchanges with oxidized quinone in solution. Electrons from the electrode then move through the cytochrome to reoxidize the reaction center electron donor. The result is a facile platform for performing redox chemistry that can be optically and electronically controlled in time and space.

Unusual Changes in Electronic Band-Edge Energies of the Nanostructured Transparent n-Type Semiconductor Zr-Doped Anatase TiO2 (Ti1-xZrxO2; X <0.3)

By the establishment of highly controllable synthetic routes, electronic band-edge energies of the n-type transparent semiconductor Zr-doped anatase TiO2 have been studied holistically for the first time up to 30 atom % Zr, employing powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen gas sorption measurements, UV/vis spectroscopies, and Mott-Schottky measurements. The materials were produced through a sol-gel synthetic procedure that ensures good compositional homogeneity of the materials, while introducing nanoporosity in the structure, by achieving a mild calcination condition. Vegards law was discovered among the homogeneous samples, and correlations were established between the chemical compositions and optical and electronic properties of the materials. Up to 20% Zr doping, the optical energy gap increases to 3.29 eV (vs 3.19 eV for TiO2), and the absolute conduction band-edge energy increases to -3.90 eV (vs -4.14 eV). The energy changes of the conduction band edge are more drastic than what is expected from the average electronegativities of the compounds, which may be due to the unnatural coordination environment around Zr in the anatase phase.

Tracking Single DNA Nanodevices in Hierarchically Meso-Macroporous Antimony-Doped Tin Oxide Demonstrates Finite Confinement

Housing bio-nano guest devices based on DNA nanostructures within porous, conducting, inorganic host materials promise valuable applications in solar energy conversion, chemical catalysis, and analyte sensing. Herein, we report a single-template synthetic development of hierarchically porous, transparent conductive metal oxide coatings whose pores are freely accessible by large biomacromolecules. Their hierarchal pore structure is bimodal with a larger number of closely packed open macropores (∼200 nm) at the higher rank and with the remaining space being filled with a gel network of antimony-doped tin oxide (ATO) nanoparticles that is highly porous with a broad size range of textual pores mainly from 20-100 nm at the lower rank. The employed carbon black template not only creates the large open macropores but also retains the highly structured gel network as holey pore walls. Single molecule fluorescence microscopic studies with fluorophore-labeled DNA nanotweezers reveal a detailed view of multimodal diffusion dynamics of the biomacromolecules inside the hierarchically porous structure. Two diffusion constants were parsed from trajectory analyses that were attributed to free diffusion (diffusion constant D = 2.2 μm2/s) and to diffusion within an average confinement length of 210 nm (D = 0.12 μm2/s), consistent with the average macropore size of the coating. Despite its holey nature, the ATO gel network acts as an efficient barrier to the diffusion of the DNA nanostructures, which is strongly indicative of physical interactions between the molecules and the pore nanostructure.

Far-reaching geometrical artefacts due to thermal decomposition of polymeric coatings around focused ion beam milled pigment particles

Focused ion beam and scanning electron microscope (FIB‐SEM) instruments are extensively used to characterize nanoscale composition of composite materials, however, their application to analysis of organic corrosion barrier coatings has been limited. The primary concern that arises with use of FIB to mill organic materials is the possibility of severe thermal damage that occurs in close proximity to the ion beam impact. Recent research has shown that such localized artefacts can be mitigated for a number of polymers through cryogenic cooling of the sample as well as low current milling and intelligent ion beam control. Here we report unexpected nonlocalized artefacts that occur during FIB milling of composite organic coatings with pigment particles. Specifically, we show that FIB milling of pigmented polysiloxane coating can lead to formation of multiple microscopic voids within the substrate as far as 5 μm away from the ion beam impact. We use further experimentation and modelling to show that void formation occurs via ion beam heating of the pigment particles that leads to decomposition and vaporization of the surrounding polysiloxane. We also identify FIB milling conditions that mitigate this issue.

Effect of Mo/Ce ratio in Mo-Ce-Al catalysts on the hydrogen production by steam reforming of glycerol

Alumina-supported molybdena–ceria catalysts were prepared by a sol–gel method and characterized by X-ray diffraction, N2 sorptometry, UV-vis-NIR diffuse reflectance spectroscopy, SEM and TEM. The effect of the Mo/Ce ratio, reaction temperature, steam to glycerol molar ratio, space velocity and the stability of the catalysts during the reaction were investigated. The results show that the presence of ceria enhances both the activity and the selectivity toward hydrogen. The best reaction temperature was found to be 500 °C for all catalysts, at which the highest hydrogen selectivity of almost 60% was obtained for an optimal cerium loading of 7 wt%; higher ceria loading reduced the capacity to convert glycerol to hydrogen.

FIB milling of polymer ceramic nanocomposites: far-reaching thermal artefacts and application to analysis of corrosion barrier coatings

FIB-SEMs are commonly used to characterize composite materials [1], however, their application to analysis of polymeric corrosion barrier coatings has been limited. This technique can be used to quantify 3D distributions of pigment particles and pores in pristine and corroded samples. Resistance of the coatings to penetration by water and dissolved ions is strongly affected by both of these geometrical features but their influence is typically quantified in effective terms using macroscopic measurements [2-3]. Chen et al.[2] recently quantified the 3D distribution of aluminum flakes dispersed in epoxy using serial block-face SEM imaging and x-ray tomography and used this information to theoretically predict barrier properties of the coating. As oppose to slicing using an ultramicrotome, FIB can be used to mill a smooth cross section of a pigmented paint without risk of artefacts arising from heterogeneous properties of the sample such as dislodging of particles by the microtome blade. One of the main concerns that arise when using a FIB-SEM to characterize polymeric materials is the possibility of ion beam heating induced damage [4-5]. Previously thermal damage stemming from a significant temperature rise at the point of ion beam impact has been described. This temperature rise is proportional to ratio of the beam power and thermal conductivity of the material and for polymers characterized by low thermal conductivity could reach over thousand of degrees Celsius [5]. The degree of sample heating can be decreased using cryogenic cooling of the sample, low ion beam current during milling, and intelligent navigation of the ion beam [4-7]. In this work FIB-SEM is used to study surface and internal morphology of polysiloxane corrosion barrier coatings with various concentrations of pigment nanoparticles prior to and at different stages of accelerated corrosion tests. These novel coatings are potential candidates for replacing silicone alkyds, which are currently used to paint the topside of naval surface vessels. The single and two component polysiloxane coatings are hydrophobic and have enhanced cleanability, gloss retention, hardness, and color-stability as compared to the silicone alkyds [8-9]. It is shown that room temperature FIB cross sectioning of pure polysiloxane can be done with a wide range of ion beam currents (1 to 20 nA) without causing any significant damage the exposed section (see Figure 1a and 1b). In contrast, FIB milling of the pigmented polysiloxane coating with ion beam current higher than 1 nA leads to an unexpected mode of severe polymer damage. Specifically, it is shown that FIB milling of such polymer-ceramic nanoparticle composites can lead to formation of multiple voids within the substrate as far as 5 μm away from the ion beam impact (see Figure 1c and 1d). Using systematic experimentation coupled with heat transfer modeling, it is shown that the primary void formation occurs due to decomposition and vaporization of the polymer around ion beam heated pigment nanoparticles (see schematic in Figure 1e). The primary void enlargement and formation of secondary voids likely occurs due to mechanical damage of the polymer induced by the entrapped vapors that could be pressurized up to ~100 MPa [10]. Similarly, secondary voids could form via cracking and seepage of the high-pressure vapors along weaker parts of the composite such as neighboring particle-polymer interfaces. This work demonstrates that processes occurring during FIB-milling of pure polymers and their composites with strongly 142 doi:10.1017/S1431927616001562 Microsc. Microanal. 22 (Suppl 3), 2016