Michael F. Cuddy

Determination of Isoelectric Points and the Role of pH for Common Quartz Crystal Microbalance Sensors

Isoelectric points (IEPs) were determined by the method of contact angle titration for five common quartz crystal microbalance (QCM) sensors. The isoelectric points range from mildly basic in the case of Al2O3 sensors (IEP = 8.7) to moderately acidic for Au (5.2) and SiO2 (3.9), to acidic for Ag (3.2) and Ti (2.9). In general, the values reported here are indicative of inherent surface oxides. A demonstration of the effect of the surface isoelectric point on the packing efficiency of thin mucin films is provided for gold and silica QCM sensors. It is determined that mucin layers on both substrates achieve a maximum and equal layer density of ∼3500 kg/m(3) at the corresponding IEP of either QCM sensor. This implies that mucin film packing is dependent upon short-range electrostatic interactions at the sensor surface.

Contributions of CF and CF2 Species to fluorocarbon film composition and properties for C(x)F(y) plasma-enhanced chemical vapor deposition.

Inductively-coupled C(x)F(y) (y/x = 2.0-4.0) plasma systems were investigated to determine relationships between precursor chemistry, CF(n) radical-surface reactivities, and surface properties of deposited films. The contributions of CF(n) (n = 1, 2) radicals to film properties were probed via gas-phase diagnostics and the imaging of radicals interacting with surfaces (IRIS) technique. Time-resolved radical emission data elucidate CF(g) and CF(2)(g) production kinetics from the C(x)F(y) source gases and demonstrate that CF(4) plasmas inherently lag in efficacy of film formation when compared to C(2)F(6), C(3)F(8), and C(3)F(6) systems. IRIS data show that as the precursor y/x ratio decreases, the propensity for CF(n) scatter concomitantly declines. Analyses of the composition and characteristics of fluorocarbon films deposited on Si wafers demonstrate that surface energies of the films decrease markedly with increasing film fluorine content. In turn, increased surface energies correspond with significant decreases in the observed scatter coefficients for both CF and CF(2). These data improve our molecular-level understanding of CF(n) contributions to fluorocarbon film deposition, which promises advancements in the ability to tailor FC films to specific applications.

Nano-Aluminum Thermite Formulations: Characterizing the Fate Properties of a Nanotechnology during Use

Nano-Aluminum Thermite Formulations: Characterizing the Fate Properties of a Nanotechnology during Use Nanothermites represent an emerging class of highly efficient propellants/explosive materials whose environmental impacts are poorly understood. In this work, several nanothermite formulations (e.g., Fe2O3/Al and Bi2O3/Al) were investigated following material transformation during end use. Combustion products were analyzed by SEM, EDS, and XRD. These products subsist with unique physical and chemical forms as compared to the original materials. The combustion process results in the formation of inert spinel structures in the case of the iron-based formulations, whereas Bi2O3/Al composites react fully, transforming to metallic bismuth and aluminum oxide. These products are largely resistant to wetting and evidence suggests that transport in aqueous environments would be limited. Due to the particle size ranges found, it is speculated that the main transport route for these materials is aerosolization. These data will ultimately establish a baseline for future studies aimed at an accurate determination of the fate of nanothermite formulations after use.

Gas-Phase Chemistry in Inductively Coupled Plasmas for NO Removal from Mixed Gas Systems

Inductively coupled rf plasmas were used to investigate the removal of NO from a variety of gas mixtures. Laser-induced fluorescence and optical emission spectroscopy were employed to measure the relative gas-phase density of NO as a function of the applied rf power, gas mixture, and catalytic substrate type. In general, the overall density of NO decreases as a function of applied rf power in both NO and N(2)/O(2) plasmas, but the addition of gases such as H(2)O vapor and CH(4), as well as the presence of Au-coated substrates, significantly affects the behavior of NO in these systems. Rotational and vibrational temperatures for NO were measured using laser-induced fluorescence excitation spectra and optical emission spectra. Results show NO vibrational temperatures are about a factor of 5 higher than rotational temperatures and indicate little dependence on applied rf power, feed gas composition, or overall system pressure. Possible mechanisms for the observed changes in [NO] as well as the rotational and vibrational temperature data are addressed.

Comparison of CH, C3, CHF, and CF2 surface reactivities during plasma-enhanced chemical vapor deposition of fluorocarbon films.

The overall character of films deposited using plasma-enhanced chemical vapor deposition relies on the interactions of gas-phase molecules with the depositing film surface. The steady-state surface interactions of CH, C3, CHF, and CF2 have been characterized at the interface of depositing fluorocarbon (FC) films using the imaging of radicals interacting with surfaces (IRIS) technique. IRIS measurements show that the relative gas-phase densities of CH, C3, CHF, and CF2 in mixed FC plasmas depend on the CH2F2/C3F8 ratio. Similar results are found using optical emission spectroscopy to monitor the production of excited-state plasma species. The effects of plasma parameters, such as the feed gas composition and substrate bias on the radical surface, were measured. Under all conditions, the surface reactivity for CH radicals is near unity, whereas those for C3, CHF, and CF2 exhibit very low surface reactivity but also show some dependence on experimental parameters. Under some conditions, CF2 and CHF are generated at the surface of the depositing film. Surface reactivity measurements indicate that CF2, CHF, and C3 may contribute to FC growth only when adsorbing at reactive sites at the film surface. Moreover, the low surface reactivities of singlet species such as C3, CF2, and CHF may be related to the electronic configuration of the molecules.

Investigation of the roles of gas-phase CF2 molecules and F atoms during fluorocarbon plasma processing of Si and ZrO2 substrates

The molecular-level chemistry involved in the processing of silicon and zirconia substrates by inductively coupled fluorocarbon (FC) plasmas produced from CF4 and C2F6 precursors has been explored. The roles of gas-phase excited, neutral, and ionic species, especially CF2 and F, were examined as they contribute to FC film formation and substrate etching. The surface reactivity of CF2 radicals in C2F6 plasmas has a dependence on substrate material and plasma system, as measured by our imaging of radicals interacting with surfaces (IRIS) technique. Relative concentrations of excited state species are also dependent upon substrate type. Moreover, differences in the nature and concentrations of gas-phase species in CF4 and C2F6 plasmas contribute to markedly different surface compositions for FC films deposited on substrates as revealed from x-ray photoelectron spectroscopic analysis. These data have led to the development of a scheme that illustrates the mechanisms of film formation and destruction in these ...

A weight-of-evidence approach to identify nanomaterials in consumer products: a case study of nanoparticles in commercial sunscreens.

Nanoscale ingredients in commercial products represent a point of emerging environmental concern due to recent findings that correlate toxicity with small particle size. A weight-of-evidence (WOE) approach based upon multiple lines of evidence (LOE) is developed here to assess nanomaterials as they exist in consumer product formulations, providing a qualitative assessment regarding the presence of nanomaterials, along with a baseline estimate of nanoparticle concentration if nanomaterials do exist. Electron microscopy, analytical separations, and X-ray detection methods were used to identify and characterize nanomaterials in sunscreen formulations. The WOE/LOE approach as applied to four commercial sunscreen products indicated that all four contained at least 10% dispersed primary particles having at least one dimension <100 nm in size. Analytical analyses confirmed that these constituents were comprised of zinc oxide (ZnO) or titanium dioxide (TiO2). The screening approaches developed herein offer a streamlined, facile means to identify potentially hazardous nanomaterial constituents with minimal abrasive processing of the raw material.

Effect of Ion Energies on the Surface Interactions of NO Formed in Nitrogen Oxide Plasma Systems

The contributions of various gas-phase species in surface reactions are of significant value to assess and improve catalytic substrates for abatement of vehicular emissions. The impact of ions on surface scatter of NO radicals is investigated with an aim toward improving and tailoring surfaces for the reduction or removal of nitrogen oxide (N(x)O(y)) species via inductively coupled plasmas (ICPs). Nascent ions are monitored via mass spectrometry and energy analysis for a variety of N(x)O(y) precursor gases. The total average ion energy ((total)) determined for all ions within each respective plasma system shows a strong positive correlation with applied rf power and a negative correlation with system pressure. The imaging of radicals interacting with surfaces (IRIS) technique was used to determine the role ions play in the surface scatter of NO radicals. The net effect of ions on substrate processing is largely dependent upon (total). Scatter coefficients (S), determined for ion-limited and ion-rich plasma systems were used to correlate (total) and scatter. The resultant effect is that ions play a substantial role in scatter of NO only when (total) > ~50 eV. The majority of systems studied contained ions below this energy threshold, suggesting knowledge of ion energies is integral to appropriately controlling the chemistry occurring between the gas-phase and surface.

Energy partitioning and its influence on surface scatter coefficients within fluorinated inductively coupled plasmas

Energy partitioning for molecules formed from fluorinated plasma systems has been measured using laser-induced fluorescence, optical emission, and broadband absorption spectroscopies. For the two radicals discussed here, SiF in tetrafluorosilane plasmas, and CF in CxFy-type fluorocarbon plasmas, high electronic excited state vibrational temperatures, TV, suggest that vibrational modes are preferentially excited over other degrees of freedom. In CxFy plasma systems, rotational temperatures, TR, for the radicals equilibrate to the plasma gas temperature and remain independent of changing plasma parameters. TR for ground state CF2 molecules are elevated in comparison to the excited state radical. Translational temperatures (TT) and TR for SiF increase concomitantly with increasing vibrational temperatures, suggesting that a vibrational-translational energy exchange mechanism is the preferred pathway for vibrational relaxation in these molecules and rotational degrees of freedom are more easily thermalized co...