Highly dispersed Co deposited on Al2O3 particles via CoCp2 + H2 ALD.

Highly dispersed cobalt atoms were deposited on porous alumina particles using atomic layer deposition (ALD) with a CoCp2/H2 chemistry at approximately 7 wt%. H2 did not completely reduce the cyclopentadienyl organic ligands bound to deposited Co atoms at ALD reaction conditions. A sharp decline in Co deposited per cycle for two or more ALD cycles indicates that much of the Al2O3 surface is sterically blocked from further CoCp2 deposition after the first CoCp2 exposure. Temperature programmed reduction confirmed that the adsorbed precursor organic ligands persist after H2 exposures during ALD and temperatures as high as 500 °C are required to fully reduce the organic ligands to CH4. High resolution, element sensitive imaging showed that Co atoms were dispersed on the Al2O3 surface and could deposit in previously unobserved multiple growth morphologies, specifically layers that were continuous over several angstroms or discrete nanoparticles. Density functional theory calculations were used to examine Co atom adsorption, show the altered haptic binding of cracked Cp ligands, and to calculate the thermodynamics of Cp ligand decomposition. The lateral steric hindrance between organic ligands bound to deposited Co atoms, Cp ligand decomposition mechanism, and local Al2O3 surface termination all likely determine the observed Co growth morphology during initial ALD cycles.

Low Heat of Adsorption of Ethylene Achieved by Major Solid-State Structural Rearrangement of a Discrete Copper(I) Complex.

The trinuclear copper(I) pyrazolate complex [Cu3 ] rearranges to the dinuclear analogue [Cu2 ⋅(C2 H4 )2 ] when exposed to ethylene gas. Remarkably, the [Cu3 ]↔[Cu2 ⋅(C2 H4 )2 ] rearrangement occurs reversibly in the solid state. Furthermore, this transformation emulates solution chemistry. The bond-making and breaking processes associated with the rearrangement in the solid-state result in an observed heat of adsorption (-13±1 kJ mol-1 per Cu-C2 H4 interaction) significantly lower than other Cu-C2 H4 interactions (≥-24 kJ mol-1 ). The low overall heat of adsorption, "step" isotherms, high ethylene capacity (2.76 mmol g-1 ; 7.6 wt % at 293 K), and high ethylene/ethane selectivity (136:1 at 293 K) make [Cu3 ] an interesting basis for the rational design of materials for low-energy ethylene/ethane separations.

Enhanced Hydrogen Production from DNA-Assembled Z-Scheme TiO2-CdS Photocatalyst Systems.

A wide range of inorganic nanostructures have been used as photocatalysts for generating H2. To increase activity, Z-scheme photocatalytic systems have been implemented that use multiple types of photoactive materials and electron mediators. Optimal catalysis has previously been obtained by interfacing different materials through aggregation or epitaxial nucleation, all of which lowers the accessible active surface area. DNA has now been used as a structure-directing agent to organize TiO2 and CdS nanocrystals. A significant increase in H2 production compared to CdS or TiO2 alone was thus observed directly in solution with no sacrificial donors or applied bias. The inclusion of benzoquinone (BQ) equidistant between the TiO2 and CdS through DNA assembly further increased H2 production. While the use of a second quinone in conjunction with BQ showed no more improvement, its location within the Z-scheme was found to strongly influence catalysis.

High ethene/ethane selectivity in 2,2'-bipyridine-based silver(i) complexes by removal of coordinated solvent.

Following removal of coordinated CH3 CN, the resulting complexes [Ag(I) (2,2'-bipyridine)][BF4 ] (1) and [Ag(I) (6,6'-dimethyl-2,2'-bipyridine)][OTf] (2) show ethene/ethane sorption selectivities of 390 and 340, respectively, and corresponding ethene sorption capacities of 2.38 and 2.18 mmol g(-1) when tested at an applied gas pressure of 90 kPa and a temperature of (20±1) °C. These ethene/ethane selectivities are 13 times higher than those reported for known solid sorbents for ethene/ethane separation. For 2, ethene sorption reached 90 % of equilibrium capacity within 15 minutes, and this equilibrium capacity was maintained over the three sorption/desorption cycles tested. The rates of ethene sorption were also measured. To our knowledge, these are the first complexes, designed for olefin/paraffin separations, which have open silver(I) sites. The high selectivities arise from these open silver(I) sites and the relatively low molecular surface areas of the complexes.

Formulation of three tailed bacteriophages by spray-drying and atomic layer deposition for thermal stability and controlled release.

Deep infection is the second most common complication of arthroplasty following loosening of the implant. Antibiotic-loaded bone cements (ALBCs) and high concentrations of systemic broad-spectrum antibiotics are commonly used to prevent infections following injury and surgery. However, clinical data fails to show that ALBCs are effective against deep infection, and negative side effects can result following prolonged administration of antibiotics. Additionally, the rise of multidrug resistant (MDR) bacteria provides an urgent need for alternatives to broad-spectrum antibiotics. Phage therapy, or the use of bacteriophages (viruses that infect bacteria) to target pathogenic bacteria, might offer a safe alternative to combat MDR bacteria. Application of phage therapy in the setting of deep infections requires formulation strategies that would stabilize bacteriophage against chemical and thermal stress during bone-cement polymerization, that maintain bacteriophage activity for weeks or months at physiological temperatures, and that allow for sustained release of phage to combat slow-growing, persistent bacteria. Here, we demonstrate the formulation of three phages that target diverse bacterial pathogens, which includes spray-drying of the particles for enhanced thermal stability at 37 °C and above. Additionally, we use atomic layer deposition (ALD) to coat spray-dried powders with alumina to allow for delayed release of phage from the dry formulations, and potentially protect phage against chemical damage during bone cement polymerization. Together, these findings present a strategy to formulate phages that possess thermal stability and sustained release properties for use in deep infections.

Demonstration of Tunable Control over a Delayed-Release Vaccine Using Atomic Layer Deposition.

Many vaccines require multiple doses for full efficacy, posing a barrier for patient adherence and protection. One solution to achieve full vaccination may be attained with single-administration vaccines containing multiple controlled release doses. In this study, delayed-release vaccines were generated using atomic layer deposition (ALD) to coat antigen-containing powders with alumina. Using in vitro and in vivo methods, we show that increasing the coat thickness controls the kinetics of antigen release and antibody response, ranging from weeks to months. Our results establish an in vitro-in vivo correlation with a level of tunable control over the antigen release and antibody response times with the potential to impact future vaccine design.

A Single Dose, Thermostable, Trivalent Human Papillomavirus Vaccine Formulated Using Atomic Layer Deposition.

Formulations of human papillomavirus (HPV) 16, 18, and 31 L1 capsomere protein antigens were spray dried to obtain glassy microspheres that were then coated by atomic layer deposition (ALD) with nanometer-thin protective layers of alumina. Spray-drying was used to formulate human papillomavirus (HPV) 16, 18, and 31 L1 capsomere protein antigens within glassy microspheres to which nanoscopic protective layers of alumina were applied using ALD. Suspensions of alumina-coated, capsomere-containing microparticles were administered in a single dose to mice. ALD-deposited alumina coatings provided thermostability and a delayed in vivo release of capsomere antigens, incorporating both a prime and a boost dose in one injection. Total serotype-specific antibody titers as well as neutralizing titers determined from pseudovirus infectivity assays were unaffected by incubation of the ALD-coated vaccines for at 4, 50, or 70 °C for three months prior to administration. In addition, even after incubation for three months at 70 °C, single doses of ALD-coated vaccines produced both higher total antibody responses and higher neutralizing responses than control immunizations that used two doses of conventional liquid formulations stored at 4 °C.

Atomic-Layer Deposition Processes Applied to Phage λ and a Phage-like Particle Platform Yield Thermostable, Single-Shot Vaccines.

Especially in developing countries, the impact of vaccines can be limited by logistical obstacles associated with multiple dose regimens, pathogen variants, and challenges imposed by requirements for maintaining vaccines at low temperatures during shipping and storage. Thus, there is a need for vaccines that can be flexibly modified to address evolving pathogen landscapes, are stable outside of narrow "cold-chain" temperatures and require administration of only single doses. Here we demonstrate in proof-of-concept studies a vaccine platform that addresses these impediments to more widespread use of vaccines. The platform relies on bacteriophage-derived phage-like-particles (PLPs) that utilize a "plug-and-play" antigen delivery system that allows for fast, easy alteration of antigens on the surface of the PLPs. Thermostability of PLP-based vaccines can be achieved by embedding the PLPs within glassy particles produced by spray drying, and nanoscopic aluminum oxide layers applied using atomic layer deposition (ALD) can serve to control release of antigen in vivo, yielding vaccine formulations that elicit strong immune responses after administration of single doses. Bacteriophage λ was stabilized by spray drying to form powders that were incubated at 37 °C for up to a year without loss of infectious activity. PLPs derived from bacteriophage λ were expressed and purified from E. coli cultures, and an in vitro conjugation strategy was used to decorate specific PLP surface sites with T4-lysozyme, a model vaccine antigen. The resulting T4-lysozyme:PLP complexes (Lys-PLPs) were embedded in glassy dry powders formed by spray drying and coated with nanometer-thick layers of alumina deposited by ALD in a fluidized bed reactor. Alumina-coated Lys-PLP vaccines were stable for a least a month at 50 °C, and single doses of the alumina-coated vaccines elicited immune responses that were indistinguishable from responses generated by conventional two-dose, prime-and-boost dosing regimens of alum-adjuvanted Lys-PLP vaccines.

H2 separation using defect-free, inorganic composite membranes.

Defect-free, microporous Al(2)O(3)/SAPO-34 zeolite composite membranes were prepared by coating hydrothermally grown zeolite membranes with microporous alumina using molecular layer deposition. These inorganic composite membranes are highly efficient for H(2) separation: their highest H(2)/N(2) mixture selectivity was 1040, in contrast with selectivities of 8 for SAPO-34 membranes. The composite membranes were selective for H(2) for temperatures up to at least 473 K and feed pressures up to at least 1.5 MPa; at 473 K and 1.5 MPa, the H(2)/N(2) separation selectivity was 750. The H(2)/CO(2) separation selectivity was lower than the H(2)/N(2) selectivity and decreased slightly with increasing pressure; the selectivity was 20 at 473 K and 1.5 MPa. The high H(2) selectivity resulted either because most of the pores in the Al(2)O(3) layer were slightly smaller than 0.36 nm (the kinetic diameter of N(2)) or because the Al(2)O(3) layer slightly narrowed the SAPO-34 pore entrance. These composite membranes may represent a new class of inorganic membranes for gas separation.

Gated ion transport through dense carbon nanotube membranes.

Gated ion diffusion is found widely in hydrophobic biological nanopores, upon changes in ligand binding, temperature, transmembrane voltage, and mechanical stress. Because water is the main media for ion diffusion in these hydrophobic biological pores, ion diffusion behavior through these nanochannels is expected to be influenced significantly when water wettability in hydrophobic biological nanopores is sensitive and changes upon small external changes. Here, we report for the first time that ion diffusion through highly hydrophobic nanopores (approximately 3 nm) showed a gated behavior due to change of water wettability on hydrophobic surface upon small temperature change or ultrasound. Dense carbon nanotube (CNT) membranes with both 3-nm CNTs and 3-nm interstitial pores were prepared by a solvent evaporation process and used as a model system to investigate ion diffusion behavior. Ion diffusion through these membranes exhibited a gated behavior. The ion flux was turned on and off, apparently because the water wettability of CNTs changed. At 298 K, ion diffusion through dense CNT membranes stopped after a few hours, but it dramatically increased when the temperature was increased 20 K or the membrane was subjected to ultrasound. Likewise, water adsorption on dense CNT membranes increased dramatically at a water activity of 0.53 when the temperature increased from 293 to 306 K, indicating capillary condensation. Water adsorption isotherms of dense CNT membranes suggest that the adsorbed water forms a discontinuous phase at 293 K, but it probably forms a continuous layer, probably in the interstitial CNT regions, at higher temperatures. When the ion diffusion channel was opened by a temperature increase or ultrasound, ions diffused through the CNT membranes at a rate similar to bulk diffusion in water. This finding may have implications for using CNT membrane for desalination and water treatment.

Detection of trace water vapor in high-purity phosphine using cavity ring-down spectroscopy.

The presence of trace water vapor in process gases such as phosphine, used for compound semiconductor epitaxial growth, can negatively affect the optical and electrical properties of the final device. Therefore, sensitive H2O measurement techniques are required to monitor precursor purity and detect unacceptable contamination levels. A commercial cavity ring-down spectrometer that monitors an H2O absorption line at a wavelength of 1392.53 nm was investigated for service in high purity PH3. Spectral parameters such as the line shape of water vapor in the presence of PH3 as well as background features due to PH3 were measured at different pressures and incorporated into the data analysis software for accurate moisture readings. Test concentrations generated with a diffusion vialbased H2O source and dilution manifold were used to verify instrument accuracy, sensitivity, linearity, and response time. H2O readings at 13.2 kPa corresponded well to added concentrations (slope=0.990+/-0.01) and were linear in the tested range (0-52.7 nmol mol-1). The analyzer was sensitive to changes in H2O concentration of 1.3 nmol mol-1 based on 3sigma of the calibration curve intercept for a weighted linear fit. Local PH3 absorption features that could not be distinguished from the H2O line were present in the purified PH3 spectra and resulted in an additional systematic uncertainty of 9.0 nmol mol-1. Equilibration to changing H2O levels at a flow rate of 80 std cm3 min-1 PH3 occurred in 10-30 minutes. The results indicate that cavity ring-down spectroscopy (CRDS) at 1392.53 nm may be useful for applications such as on-line monitoring (and dry-down) of phosphine gas delivery lines or the quality control of cylinder sources.

Air-pressure tunable depletion width, rectification behavior, and charge conduction in oxide nanotubes.

Metal-oxide nanotubes provide large surface areas and functionalizable surfaces for a variety of optical and electronic applications. Here we report air-tunable rectifying behavior, depletion width modulation, and two-dimensional (2D) charge conduction in hollow titanium-dioxide nanotubes. The metal contact forms a Schottky-diode in the nanotubes, and the rectification factor (on/off ratio) can be varied by more than 3 orders of magnitude (1-2 × 10(3)) as the air pressure is increased from 2 mTorr to atmospheric pressure. This behavior is explained using a change in depletion width of these thin nanotubes by adsorption of water vapor on both surfaces of a hollow nanotube, and the resulting formation of a metal-insulator-semiconductor (MIS) junction, which controls the 2D charge conduction properties in thin oxide nanotubes.

Copper plasmonics and catalysis: role of electron-phonon interactions in dephasing localized surface plasmons.

Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain boundary scattering on the decay of localized surface plasmon waves. Using our quantitative analysis and different temperature dependent measurements, we show that electron-phonon interactions dominate over other scattering mechanisms in dephasing plasmon waves. While interband transitions in copper metal contributes substantially to plasmon losses, tuning surface plasmon modes to infrared frequencies leads to a five-fold enhancement in the quality factor. These findings demonstrate that conformal ALD coatings can improve the chemical stability for copper nanoparticles, even at high temperatures (>300 °C) in ambient atmosphere, and nanoscaled copper is a good alternative material for many potential applications in nanophotonics, plasmonics, catalysis and nanoscale electronics.

High density, vertically-aligned carbon nanotube membranes.

A method is presented to prepare high-density, vertically aligned carbon nanotube (VA-CNT) membranes. The CNT arrays were prepared by chemical vapor deposition (CVD), and the arrays were collapsed into dense membranes by capillary-forces due to solvent evaporation. The average space between the CNTs after shrinkage was approximately 3 nm, which is comparable to the pore size of the CNTs. Thus, the interstitial pores between CNTs were not sealed, and gas permeated through both CNTs and interstitial pores. Nanofiltration of gold nanoparticles and N(2) adsorption indicated the pore diameters were approximately 3 nm. Gas permeances, based on total membrane area, were 1-4 orders of magnitude higher than VA-CNT membranes in the literature, and gas permeabilities were 4-7 orders of magnitude higher than literature values. Gas permeances were approximately 450 times those predicted for Knudsen diffusion, and ideal selectivities were similar to or higher than Knudsen selectivities. These membranes separated a larger molecule (triisopropyl orthoformate (TIPO)) from a smaller molecule (n-hexane) during pervaporation, possibly due to the preferential adsorption, which indicates separation potential for liquid mixtures.