Ellen R. Fisher

Carbon nanotubule membranes for electrochemical energy storage and production

Ensembles of aligned and monodisperse tubules of graphitic carbon can be prepared by a templating method that involves the chemical-vapour deposition of carbon within the pores of alumina membranes. Tubules with diameters as small as 20 nm have been prepared in this way,. The carbon comprising these tubules can be transformed from a disordered material to very highly ordered graphite. Here we show that template-synthesized carbon tubules can be fabricated as free-standing nanoporous carbon membranes, and that narrower, highly ordered graphitic carbon nanotubes can be prepared within the membranes tubules. Both the outer and the inner tubules are electrochemically active for intercalation of lithium ions, suggesting possible applications in lithium-ion batteries,. The membranes can also be filled with nanoparticles of electrocatalytic metals and alloys. Such catalyst-loaded membranes can be used to electrocatalyse O2 reduction and methanol oxidation, two reactions of importance to fuel-cell technology.

Hydrophilic modification of polyethersulfone membranes by low temperature plasma-induced graft polymerization

A complete and permanent hydrophilic modification of polyethersulfone (PES) membranes is achieved by argon plasma treatment followed by polyacrylic acid (PAA) grafting in vapor phase. Both Ar plasma treatment alone and post-PAA grafting rendered a complete hydrophilicity to the PES membranes. The hydrophilicity of the membranes treated with only the Ar plasmas is not, however, permanent. In contrast, the PES membranes treated with Ar plasma and subsequent acrylic acid (AA) grafting are permanently hydrophilic. High energy resolution X-ray photoelectron spectroscopy (XPS) confirmed the grafting of PAA to all surfaces of the membrane. Furthermore, water bubble point measurements remain unaffected. The pore sizes of the grafted membranes at higher grafting yield are slightly decreased. The modified membranes are less susceptible to protein fouling than the unmodified membranes and the pure water flux for the modified membranes was tremendously increased by plasma treatment. Furthermore, the modified membranes are easier to clean and required little caustic to recover permeation flux.

Hydrophilic modification of polymeric membranes by low temperature H2O plasma treatment

We previously reported that complete and permanent hydrophilic modification of asymmetric polysulfone (PSf) membranes is achieved via low temperature H2O plasma treatment. Here, we have extended these results to polyethersulfone (PES) and polyethylene (PE) membranes to investigate the role of membrane material (composition) and structure (degree of asymmetry) in the modification. Contact angle (CA) measurements confirm that H2O plasma treatment affords improvement in the wettability of PSf, PES, and PE membranes and XPS results show that H2O plasmas chemically modify all three membrane materials similarly. Differences in the degree and permanence of the hydrophilic modification, however, were observed for PE membranes. Furthermore, environmental SEM images display differences in the depth of hydrophilic modification for PES and PE membranes. Overall, we demonstrate that the extent and permanence of hydrophilic modification of polymeric membranes can be correlated to the mechanisms of interaction between the polymer and reactive species generated in the plasma and the degree of penetration of these species through the porous structure.

Low temperature plasma treatment of asymmetric polysulfone membranes for permanent hydrophilic surface modification

A plasma treatment that renders asymmetric polysulfone membranes permanently hydrophilic is reported. Our modification strategy entails treating these membranes downstream from an inductively coupled rf plasma source. Contact angle measurements confirm that the membranes are completely wettable with water as a result of H2O plasma treatment. More importantly, the hydrophilic modification is permanent as plasma-treated membranes remain wettable for more than 16 months after plasma treatment. This treatment achieves the desired change in wettability for microporous as well as ultrafiltration polysulfone membranes, illustrating the universality of this method. XPS analysis of treated membranes demonstrates this dramatic change in wettability is a result of chemical changes in the membrane induced by plasma treatment. Moreover, the membrane modification is complete as the plasma penetrates the thickness of the membrane, thereby modifying the entire membrane cross-section.

Reactions of fourth‐period metal ions (Ca+−Zn+) with O2: Metal‐oxide ion bond energies

Reactions of Ca+, Zn+ and all first‐row atomic transition metal ions with O2 are studied using guided ion beam techniques. While reactions of the ground states of Sc+, Ti+, and V+ are exothermic, the remaining metal ions react with O2 in endothermic processes. Analyses of these endothermic reactions provide new determinations of the M+–O bond energies for these eight elements. Source conditions are varied such that the contributions of excited states of the metal ions can be explicitly considered for Mn+, Co+, Ni+, and Cu+. Results (in eV) at 0 K are D0(Ca+–O)= 3.57±0.05, D0(Cr+–O)=3.72±0.12, D0(Mn+–O)=2.95±0.13, D0(Fe+–O)=3.53±0.06 (reported previously), D0(Co+–O)=3.32±0.06, D0(Ni+–O) =2.74±0.07, D0(Cu+–O)=1.62±0.15, and D0(Zn+–O)=1.65±0.12. These values along with literature data for neutral metal oxide bond energies and ionization energies are critically evaluated. Periodic trends in the ionic metal oxide bond energies are compared with those of the neutral metal oxides and those of other related molec...

Plasma enhanced chemical vapor deposition of SiO2 using novel alkoxysilane precursors

This communication describes our results using these novel alkoxysilane precursors for PECVD of SiO_2 films in an inductively coupled rf plasma reactor. The effects of deposition time, rf power, and organosilane pressure on the films’ characteristics are described.

Chemical-vapor deposition-based template synthesis of microtubular TiS2 battery electrodes

The authors have been exploring a general route for preparing nanomaterials called template synthesis. The application of the template method to the preparation of microtubular battery electrodes is described here. The template method is used to prepare a current collector that consists of an ensemble of metal microtubules that protrude from a metal surface like the bristles of a brush. Chemical vapor deposition is then used to coat this high surface area microtubule-based current collector with a thin skin of the desired Li{sup +}-intercalation material, in this case TiS{sub 2}. In this way, a thin-walled tubule of TiS{sub 2} is formed on the outer surface of each metal microtubule. The thin walls of these TiS{sub 2} tubes insure that the distance over which Li{sup +} must diffuse is small, and the high surface area insures that the current density is low. These microtubular TiS{sub 2} electrodes showed higher capacities, lower resistance, and lower susceptibility to slow electron transfer kinetics than thin film (control) TiS{sub 2} electrodes prepared form the same amount of TiS{sub 2}.

Dissociative charge transfer reactions of Ar+, Ne+, and He+ with CF4 from thermal to 50 eV

Guided ion‐beam techniques are used to measure the cross sections for reaction of CF4 with Ar+, Ne+, and He+ from thermal to 50 eV. Dissociative charge transfer followed by successive loss of F atoms are the major processes observed. Only CF+x (x=1–3) products are observed in the reactions of Ar+ and Ne+. With He+, in addition to the CF+x products, both C+ and F+ are seen at high kinetic energies. Reaction rates for these reactions are also given and compared with previous measurements. It is found that the energy dependence of the cross sections can be understood by considering the energies needed to access specific electronic states of the CF+4 ion.

A modified molecular beam instrument for the imaging of radicals interacting with surfaces during plasma processing

A new instrument employing molecular beam techniques and laser induced fluorescence(LIF) for measuring the reactivity of gas phase radicals at the surface of a depositing film has been designed and characterized. The instrument uses an inductively coupled plasma source to create a molecular beam containing essentially all plasma species. A tunable excimer pumped dye laser is used to excite a single species in this complex molecular beam.LIF signals are imaged onto a gated, intensified charge coupled device (ICCD) to provide spatial resolution. ICCD images depict the fluorescence from molecules both in the molecular beam and scattering from the surface of a depositing film. Data collected with and without a substrate in the path of the molecular beam provide information about the surface reactivity of the species of interest. Here, we report the first measurements using the third generation imaging of radicals interacting with surfaces apparatus. We have measured the surface reactivity of SiH molecules formed in a 100% SiH_4 plasma during deposition of an amorphous hydrogenated silicon film. On a 300 K Si (100) substrate, the reactivity of SiH is near unity. The substrate temperature dependence (300–673 K) of the reactivity is also reported. In addition, reactivity measurements for OH molecules formed in a water plasma are presented. In contrast to the SiH molecule, the reactivity of OH radicals is 0.55±0.05 on the surface of a Si (100) substrate.

SURFACE INTERACTIONS OF CF2 RADICALS DURING DEPOSITION OF AMORPHOUS FLUOROCARBON FILMS FROM CHF3 PLASMAS

Surface reactivities for CF2 radicals formed in a CHF3 plasma molecular beam are measured during film deposition on a variety of substrates. The imaging of radicals interacting with surfaces (IRIS) technique was used to collect spatially resolved laser-induced fluorescence (LIF) images of CF2 radicals interacting with SiO2, Si3N4, Si, 304 stainless steel, and system 8 photoresist substrates. Films deposited during IRIS experiments were characterized using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy and were found to be nearly identical in composition on all substrates. Simulation of LIF cross-sectional data shows high scattering coefficients for CF2 radicals on all substrates. These extremely large scattering coefficients (>1.0) indicate that CF2 molecules are generated through plasma interactions with the substrate. Possible CF2 surface generation mechanisms are discussed, with consideration of CF and ion bombardment contributions to the generation of CF2.