We report a significant advance in thermally insulating transparent materials: silica-based monoliths with controlled porosity which exhibit the transparency of windows in combination with a thermal conductivity comparable to aerogels.

The lack of transparent, thermally insulating windows leads to substantial heat loss in commercial and residential buildings, which accounts for ~4.2% of primary US energy consumption annually. The present study provides a potential solution to this problem by demonstrating that ambiently dried silica aerogel monoliths, i.e., ambigels, can simultaneously achieve high optical transparency and low thermal conductivity without supercritical drying. A combination of tetraethoxysilane, methyltriethoxysilane, and post-gelation surface modification precursors were used to synthesize ambiently dried materials with varying pore fractions and pore sizes. By controlling the synthesis and processing conditions, 0.5–3 mm thick mesoporous monoliths with transmittance >95% and a thermal conductivity of 0.04 W/(m K) were produced. A narrow pore size distribution, <15 nm, led to the excellent transparency and low haze, while porosity in excess of 80% resulted in low thermal conductivity. A thermal transport model considering fractal dimension and phonon-boundary scattering is proposed to explain the low effective thermal conductivity measured. This work offers new insights into the design of transparent, energy saving windows.

Three-dimensional (3D) battery architectures have emerged as a new direction for powering microelectromechanical systems and other small autonomous devices. Although there are few examples to date of fully functioning 3D batteries, these power sources have the potential to achieve high power density and high energy density in a small footprint. This overview highlights the various architectures proposed for 3D batteries, the advances made in the fabrication of components designed for these devices, and the remaining technical challenges. Efforts directed at establishing design rules for 3D architectures and modeling are providing insight concerning the energy density and current uniformity achievable with these architectures. The significant progress made on the fabrication of electrodes and electrolytes designed for 3D batteries is an indication that a number of these battery architectures will be successfully demonstrated within the next few years.

Yb14MnSb11 is a very promising thermoelectric material for high temperature applications. This compound is a member of a large family of Zintl phases with a “14-1-11” A14MPn11 stoichiometry (Pn = P, As, Sb, Bi; A = Ca, Ba, La, Sr, Yb, Eu; M = Mn, Al, Cd, Ga, In, Nb, Zn). Yb14MnSb11 exhibits low lattice thermal conductivity values and a p-type semimetallic behavior with values of the non-dimensional figure of merit zT peaking at 1.4 above 1200 K. There is significant interest in investigating how substitutions on any of the atomic sites impact the charge carrier concentration and mobility, band gap and lattice thermal conductivity. Recent reports have studied substitutions on the Yb and Mn sites with the goal of reducing hole carrier concentration and improving carrier mobility values.

High energy ball milling has been shown to be a convenient method of synthesis to prepare Yb14MnSb11 and it has been used here to explore the solid solution systems derived from this compound by substituting Sb with Bi. High energy ball milling is a non-equilibrium process and not all of the 14-1-11 compounds are easily formed with this method. Characterization of the synthesized compositions was done by X-ray diffraction, electron microprobe, and high temperature measurements of the electrical and thermal transport properties up to 1275 K. The experimental results on undoped and doped solid solution samples are compared to that of pure Yb14MnSb11 samples prepared by the same high energy ball milling technique.

The vexed and ongoing issue of poor educational outcomes for Indigenous students in the Northern Territory continues despite years of successive programs and policies. Much of the debate has been on funding and pedagogy, in particular the merits or otherwise of bi-lingual teaching. Largely omitted from discussions, although well known by teachers and schools in remote areas to be an issue, are high rates of in-term student mobility. Such “unexpected” moves are thought to affect the capacity for students to achieve benchmark outcomes, for teachers to deliver these and for schools to administer their students within the allocated systems and budgets. Up to now teachers and schools have relied on anecdotes to engage in dialogue around the impacts of mobility. This is because adequate conceptualisations for aggregating, depicting and reporting on the size and nature of in-term mobility were not available. This paper documents several years of work into producing these outcomes. Three measures are conceptualised and outlined in this paper which will be of interest to teachers, schools and educational administrators in all jurisdictions where services are delivered in a remote setting. The results clearly demonstrate the high churn of Indigenous students within terms, especially in remote areas of the Northern Territory. The findings from this study can be applied to inform funding and policy making and as a basis for further research to document the impacts for teachers and schools.

In 38 children with aortic coarctation between the age of three weeks and 16 years, 44 balloon dilation procedures were attempted. At initial catheterization (n=38), the mean gradient dropped from 49.6±21.2 mm Hg prior to dilation, to 15.3±15.8 mm Hg after the procedure (p>0.05). Twenty-six patients were recatheterized 3–24 months after the initial procedure. The mean gradient remained low at 12.7±15.2 mm Hg (range 0–64). Six of the 26 (23%) patients required a second dilation because of significant recoarctation. This proved successful in four, but in two patients, the second dilation failed, and they were referred for elective surgery. Thus, good overall results were obtained in 24 of the 26 (92.3%) patients undergoing reinvestigation following balloon dilation. Complications included requirements for blood transfusion in 9/44 (20%), chest pain during balloon inflation in 3/44 (6.8%), rupture of the balloon in 3/44 (6.8%), and femoral arterial thrombectomy in 3/44 (6.8%). At a mean clinical follow-up of 21 months, 21% of the patients had a weaker femoral pulse on the side used for balloon dilation, while 21% had mild hypertension measured in the arms despite the absence of a significant gradient. One patient (2.6%) developed an aortic aneurysm as a complication of the procedure. We conclude that balloon dilation is a safe and effective procedure in the majority of the patients with native aortic coarctation.

The process of encapsulating antibodies in sol-gel was used for sensing various hormones, specifically cortisol, insulin, and C-peptide. A sol-gel optical biosensor for cortisol has been developed for monitoring of crew health on-orbit during space missions. Our studies involving silica sol-gel materials with competitive immunoassays demonstrated linear calibration for cortisol in the range of 2-60 μg/dL, which covers the physiological range of cortisol blood concentration for an adult (2-28 μg/dL). The method of standard additions was used to analyze human serum samples sent to us from a NASA laboratory. Our sol-gel immunosensor values were typically within 20% of the values obtained by NASA-JSC using traditional immuno-binding techniques, with some values having less than a 5% error. Initial results are presented for sensing the hormones insulin and C-peptide.

Conventional top-down lithographic processes approach their practical and theoretical limits at dimensional scales less than 100 nm. Alternative bottom-up methods are being investigated to build nanoscale architectures, including the use of biomolecules whose functional groups bind inorganic particles. In this study, the fabrication and alignment of microtubule-based nanowires are investigated. Microtubules (MT) are fibrous proteins found in nearly all eukaryotes. Our work was carried out using polymerized alpha- and beta-tubulins, which were cross-linked with glutaraldehyde to stabilize the protein structure. Ni coated microtubules were fabricated by reducing Ni2+ to Ni0 on Pd activated microtubule surface. Focus Ion Beam was used to write metal contacts on these Ni microtubule nanowires and DC conductivity values were measured. Au deposition on MT was performed by both electroless deposition and electrodeposition, by reducing HAuCl4 onto MT prebound with 2 nm Au colloids. Although most MTs exhibited discontinuous Au binding, a fraction of MTs were covered completely by Au. Preliminary electrical measurements for these materials are reported. Alignment of microtubules was also achieved by injecting MTs into microfluidic devices over amine-coated substrate surfaces. These biotemplating approaches are the first steps towards constructing more complicated 2D and 3D architectures.

The fabrication of micron-scale channels and reaction chambers using micromachining techniques has created devices with large surface to volume ratios. As a result, surface properties play a major role in determining the behavior of micromachined devices. In this work, we present strategies that can be used to reconfigure surfaces from hydrophobic to hydrophilic or from hydrophilic to hydrophobic. The reversible nature of the surface is made possible by using deposition and removal of biomolecules or amphiphiles on self-assembled monolayers (SAMs). When the initial surface was hydrophobic (using a CH3-terminated SAM on the surface, water contact angle ∼100), it was rendered hydrophilic (water contact angle ≤60°) using monolayer adsorption of avidin protein. To retrieve the hydrophobicity, the avidin was subsequently removed using non-ionic surfactant octyl-β-D-glucopyranoside. Moreover, by incorporating a biotinylated poly(ethyleneglycol), the avidin-coated surface was resistant to further non-specific adsorption. If the initial surface was hydrophilic (using a CO2H-terminated SAM on the surface, water contact angle ≤20°), it was rendered hydrophobic (water contact angle >90°) using monolayer amphiphilic octadecylamine adsorption. The hydrophilicity was restored after subsequently removing the amphiphile using anionic surfactant sodium lauryl sulfate. Both types of surfaces showed excellent reversibility and demonstrated the ability to control surface wettability.

The high porosity and uniform pore size of mesoporous oxide films offer unique opportunities for microelectromechanical system (MEMS) devices that require low density and low thermal conductivity. This paper provides the first report in which mesoporous films were adapted for MEMS applications. Mesoporous SiO2 and Al2O3 films were prepared by spin coating using block copolymers as the structure-directing agents. The resulting films were over 50% porous with uniform pores of 8-nm average diameter and an extremely smooth surface. The photopatterning and etching characteristics of the mesoporous films were investigated and processing protocols were established which enabled the films to serve as the sacrificial layer or the structure layer in MEMS devices. The unique mesoporous morphology leads to novel behavior including extremely high etching rates and the ability to etch underlying layers. Surface micromachining methods were used to fabricate three basic MEMS structures, microbridges, cantilevers, and membranes, from the mesoporous oxides.

Sol-gel encapsulation has recently surfaced as a successful approach to biomolecule immobilization. Proteins, including enzymes, are trapped in the pores of the sol-gel derived glass while retaining their spectroscopic properties and biological activity. Our current work extends the unique capabilities of biomolecule-doped sol-gel materials to the detection of glutamate, the major excitatory neurotransmitter in the central nervous system. We are developing an in vivo fiber optic biosensor for glutamate along with methods to achieve continuous monitoring. In our research to date we have encapsulated GDH in a silica sol-gel film on the tip of an optical fiber. GDH catalyzes the oxidative deamination of glutamate to α-ketoglutarate and the simultaneous reduction of NAD+ to NADH. To quantify the glutamate concentration, we observe the rate of change of NADH fluorescence as a function of time. An important consideration for continuous in vivo monitoring is the incorporation of a selfsustaining NAD+ source. We have adopted a photochemical means of regenerating NAD+ from NADH, by irradiating thionine (3,7-diaminophenothiazin-5-ium) which we incorporate into the sol-gel sensor material. When excited with visible light (λabc∼ 596 nm), thionine undergoes a reaction with NADH resulting in a non-fluorescent form of thionine and NAD+. We have characterized the kinetics of this reaction in the sol-gel matrix, and have shown that the reaction results in regenerated co-factor that is usable by GDH for the oxidation of glutamate.

This paper describes the preparation of hybrid surfactant-templated thin films functionalized with rare-earth (Eu3+ and Tb3+) organic complexes. 2-D hexagonally ordered films are obtained by a one-pot synthesis process based on an acid-catalyzed approach. Ln3+ ions are coordinated to bis-silylated ligands that co-polymerize with TEOS, which enables one to incorporate the fluorescent centers within the silica framework. Luminescent properties of the organic-inorganic mesostructured films are discussed and compared to those of amorphous samples with similar composition.

The high porosity and uniform pore size provided by mesoporous oxide films offer interesting opportunities for MEMS devices that require low density and low thermal conductivity. This paper describes recent efforts at adapting mesoporous films for MEMS fabrication. Mesoporous SiO2 and Al2O3 films were prepared using block copolymers as the structure-directing agents, leading to films which were 70% porous and < 5 nm surface roughness. A number of etchants were investigated and good etch selectivity was observed with both dry and wet systems. Micromachining methods were used to fabricate cantilevers, micro bridges and membranes.

The amino acid glutamate is the major excitatory neurotransmitter used in the nervous system for interneuronal communication. It is used throughout the brain by various neuronal pathways including those involved in learning and memory, locomotion, and sensory perception. Because glutamate is released from neurons on a millisecond time scale into sub-micrometer spaces, the development of a glutamate biosensor with high temporal and spatial resolution is of great interest for the study of neurological function and disease. Here, we demonstrate the feasibility of an optical glutamate sensor based on the sol-gel encapsulation of the enzyme glutamate dehydrogenase (GDH). GDH catalyses the oxidative deamination of glutamate and the reduction of NAD+ to NADH. NADH fluorescence is the basis of the sensor detection. Thermodynamic and kinetic studies show that GDH remains active in the sol-gel matrix and that the reaction rate is correlated to the glutamate concentration.

This paper develops a method to deduce the dielectric function of nanostructures smaller than the chosen wavelength of light. It modifies the Maxwell - Garnett Effective Medium Theory equations to calculate the dielectric function of a metal embedded inside a dielectric. Specifically, reflection and transmission measurements of an array of bismuth nanowires in an anodized porous alumina template are used to calculate the frequency - dependent di-electric function of the nanowires. The spectra are taken using Fourier transform infrared spectroscopy covering the 500 to 4000 cm−1 frequency range. These data are used to determine the real and imaginary parts of the dielectric function of the composite materials. Next, the percentage of the total volume occupied by either Bi or air in the porous alumina (the “filling factor”) was found by scanning electron microscopy. The modified Maxwell-Garnett (M-G) equations specify how to use the filling factor and the dielectric function of the composite material to calculate the dielectric function of the alumina. Finally, the modified M-G equations are used a second time to calculate the dielectric function of Bi nanowires using the dielectric function of alumina, the dielectric function of the filled template, and the filling factor. The resulting dielectric function of Bi nanowires is then compared to theoretical predictions.