Ruslan Burtovyy

A Major Constituent of Brown Algae for Use in High-Capacity Li-Ion Batteries

Alginate extracts help stabilize silicon nanoparticles used in a high-capacity lithium-silicon battery. The identification of similarities in the material requirements for applications of interest and those of living organisms provides opportunities to use renewable natural resources to develop better materials and design better devices. In our work, we harness this strategy to build high-capacity silicon (Si) nanopowder–based lithium (Li)–ion batteries with improved performance characteristics. Si offers more than one order of magnitude higher capacity than graphite, but it exhibits dramatic volume changes during electrochemical alloying and de-alloying with Li, which typically leads to rapid anode degradation. We show that mixing Si nanopowder with alginate, a natural polysaccharide extracted from brown algae, yields a stable battery anode possessing reversible capacity eight times higher than that of the state-of-the-art graphitic anodes.

Toward Efficient Binders for Li-Ion Battery Si-Based Anodes: Polyacrylic Acid

Si-based Li-ion battery anodes offer specific capacity an order of magnitude beyond that of conventional graphite. However, the formation of stable Si anodes is a challenge because of significant volume changes occurring during their electrochemical alloying and dealloying with Li. Binder selection and optimization may allow significant improvements in the stability of Si-based anodes. Most studies of Si anodes have involved the use of carboxymethylcellulose (CMC) and poly(vinylidene fluoride) (PVDF) binders. Herein, we show for the first time that pure poly(acrylic acid) (PAA), possessing certain mechanical properties comparable to those of CMC but containing a higher concentration of carboxylic functional groups, may offer superior performance as a binder for Si anodes. We further show the positive impact of carbon coating on the stability of the anode. The carbon-coated Si nanopowder anodes, tested between 0.01 and 1 V vs Li/Li+ and containing as little as 15 wt % of PAA, showed excellent stability during the first hundred cycles. The results obtained open new avenues to explore a novel series of binders from the polyvinyl acids (PVA) family.

UV-induced self-repairing polydimethylsiloxane–polyurethane (PDMS–PUR) and polyethylene glycol–polyurethane (PEG–PUR) Cu-catalyzed networks

UV-induced self-repairing polydimethylsiloxane–polyurethane (PDMS–PUR) crosslinked networks capable of repairing mechanical damage upon UV exposure were developed. Induced by the presence of the copper chloride (CuCl2) catalyst, the network remodeling and bond reformation are achieved by the formation of Cu–O coordination complexes, covalent Si–O–Si hydrolysis with subsequent bond reformation. Upon UV exposure, Cu–O complexes undergo tetrahedral-to-distorted tetrahedral rearrangements which parallel the Si–O bond reformation. When PDMS was substituted with OH-terminated polyethylene glycol (PEG) to form PEG–PUR crosslinked networks, square planar-to-tetrahedral rearrangements occur during the damage–repair cycle. Alkyl backbone distortions and segmental motions induced by the local Cu–O symmetry changes result in volume changes of the metal–ligand complex center. These studies show that a combination of supramolecular and covalent bonds facilitates self-repairing.

Reversibility of pH-Induced Dewetting of Poly(vinyl pyridine) Thin Films on Silicon Oxide Substrate

Thin PVP films deposited on a silicon oxide surface have been found to form a dewetting pattern when treated with basic solutions (pH > or = 10). We studied the dependence of pattern morphology on the polymers molecular weight and thickness of the polymer layer, and observed the formation of three distinctive structures. The structure formed by large drops of polymer is characteristic of a polymer with low molecular weight and the thinnest polymer layer, whereas other samples form holes or a weblike pattern upon dewetting. These experiments have demonstrated for the first time the reversibility of the dewetting process in a liquid environment. The polymer layer has revealed reversible behavior toward flat film when exposed to a pH 4 buffer solution. More complex structures can be obtained by consecutive treatments with acidic (pH 4) and basic (pH 10) solutions. We used atomic force microscopy (AFM) to study both the morphology and elastic properties of polymers in media with different acidity, in order to determine the mechanism behind the dewetting process.

Collective alignment of nanorods in thin Newtonian films

In this paper, we provide a complete analytical description of the alignment kinetics of magnetic nanorods in magnetic field. Nickel nanorods were formed by template electrochemical deposition in alumina membranes from a dispersion in a water–glycerol mixture. To ensure uniformity of the dispersion, the surface of the nickel nanorods was covered with polyvinylpyrrolidone (PVP). A 40–70 nm coating prevented aggregation of the nanorods. These modifications allowed us to control alignment of the nanorods in a magnetic field and test the proposed theory. An orientational distribution function of nanorods was introduced. We demonstrated that the 0.04% volume fraction of nanorods in the glycerol–water mixture behaves as a system of non-interacting particles. However, the kinetics of alignment of a nanorod assembly does not follow the predictions of the single-nanorod theory. The distribution function theory explains the kinetics of alignment of a nanorod assembly and shows the significance of the initial distribution of nanorods in the film. It can be used to develop an experimental protocol for controlled ordering of magnetic nanorods in thin films.

Interaction Forces Between a Glass Surface and Ceria-Modified PMMA-Based Abrasives for CMP Measured by Colloidal Probe AFM

Interaction forces between a glass surface and two types of ceria-coated polymethyl methacrylate PMMA-based terpolymerabrasive particles were investigated using colloidal probe atomic force microscopy and correlated with relevant chemical me-chanical planarization CMP and post-CMP parameters. The composite particles were achieved by either creating chemical bondsby silane coupling agents compositeA or tuning the pH in order to form electrostatic attractive interactions between the core andshell composite composite B. Based on the average values of the pull-off force vs pH, a qualitative agreement between themeasured adhesion forces and the material removal rate MRR was found. For pH 3, both the MRR and adhesion forces are largerfor composite B with respect to composite A. Interestingly, for pH 10, composite B and ceria give almost the same MRR andsimilar adhesion force values. Nevertheless, in general, the adhesion forces measured at pH 10 are significantly smaller than thosemonitored at pH 3, whereas the MRR is significantly larger for pH 10. This suggests that factors other than adhesion, such as anenhanced silica dissolution rate, dominate and define the MRR at pH 10. The increase in repulsive force with increasing pHcorresponds to a decrease in composite-glass adhesion. For pH between 2 and 7, the electrostatic attractive forces betweenpolymer particles and the silica surface are responsible for high particle counts. To improve the particle removal efficiency afterCMP with the ceria-based slurry, pH values higher than 7 are recommended.© 2008 The Electrochemical Society. DOI: 10.1149/1.2834456 All rights reserved.Manuscript submitted November 19, 2007; revised manuscript received December 20, 2007.Available electronically January 31, 2008.

Interaction Forces Between a Glass Surface and Silica-Modified PMMA-Based Abrasives for CMP Measured by Colloidal AFM

Interaction forces between a glass surface and two types of silica-coated poly(methyl methacrylate) (PMMA)-based terpolymer abrasive particles were investigated using colloidal atomic force microscopy (AFM) and correlated with relevant chemical mechanical planarization (CMP) and post-CMP parameters. Based on the average values of the pull-off force vs pH, the interaction between a glass bead and the composites can be considered as a silica-glass interaction, as confirmed by ζ potential measurements. The increase in repulsive force with increasing pH corresponds to a decrease in composite-glass adhesion. For pH between 2 and 7, the electrostatic attractive forces between polymer particles and silica surface are responsible for high particle counts.

Synthesis and characterization of nanorods for magnetic rotational spectroscopy

Magnetic rotational spectroscopy (MRS) with magnetic nanoprobes is a powerful method for in-situ characterization of minute amounts of complex fluids. In MRS, a uniformly rotating magnetic field rotates magnetic micro- or nano-probes in the liquid and one analyzes the features of the probe rotation to extract rheological parameters of liquids. Magnetic properties of nanoprobes must be well characterized and understood to make results reliable and reproducible. Ni and Co nanorods synthesized by electrochemical template synthesis in alumina membranes are discussed in applications to MRS. We employ alternating gradient field magnetometry, X-ray diffraction, and magnetic force microscopy to evaluate and compare properties of these nanorods and study their performance as the MRS probes. It is shown that nickel nanorods do not seem to violate any assumptions of the MRS rigid dipole theory, while cobalt nanorods do.

AFM Measurements of Interactions Between CMP Slurry Particles and Substrate

Atomic force microscopy (AFM) studies of interactions between slurry particles and substrates treated by chemical mechanical polishing (CMP) processes were carried out. To conduct adhesion measurements, the particles present in a CMP system were first attached to the surface of a silicon wafer covered with thin polymer film having high affinity for both particles and the silicon wafer. A silica glass sphere was attached to the AFM cantilever with an appropriate spring constant. The sphere represented the surface of the material being polished and was used as received or covered with a layer of copper. The sphere can be modified with various materials in future research. The AFM force volume mode, which uses the collection of the force-distance curves over selected surface areas, was used for the adhesion measurements. The adhesion in the systems studied was strongly dependent on the pH value of the aqueous environment, and the concentration and type of surfactants added.

A gradient field defeats the inherent repulsion between magnetic nanorods

When controlling the assembly of magnetic nanorods and chains of magnetic nanoparticles, it is extremely challenging to bring them together side by side while keeping a desired spacing between their axes. We show that this challenge can be successfully resolved by using a non-uniform magnetic field that defeats an inherent repulsion between nanorods. Nickel nanorods were suspended in a viscous film and a non-uniform field was used to control their placement. The in-plane movement of nanorods was tracked with a high-speed camera and a detailed image analysis was conducted to quantitatively characterize the behaviour of the nanorods. The analysis focused on the behaviour of a pair of neighbour nanorods, and a corresponding dynamic model was formulated and investigated. The complex two-dimensional dynamics of a nanorod pair was analysed analytically and numerically, and a phase portrait was constructed. Using this phase portrait, we classified the nanorod behaviour and revealed the experimental conditions in which nanorods could be placed side by side. Dependence of the distance between a pair of neighbour nanorods on physical parameters was analysed. With the aid of the proposed theory, one can build different lattices and control their spacing by applying different field gradients.