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Papers by Abhilash Vincent

Smart Materials and Structures, 2005

Th~n-film shape memory alloys (SMAs) formed by sputter deposit~on have been recoplzed as promlsln... more Th~n-film shape memory alloys (SMAs) formed by sputter deposit~on have been recoplzed as promlslng cand~dates for making powerful mlcroactuators In MEMS dev~ces owing to their large deformation and strong recovery forces However, due to the lack of understandrng of the basic matenal properties and lack of control over deposition parameters, they have not rece~ved much attention from the MEMS comrnunlty Moreover, NiTl's

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of P... more A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Mechanical, Materials and Aerospace Engineering in the College of Engineering and Computer Science at

Langmuir, 2010

Long term stability and surface properties of colloidal nanoparticles have significance in many a... more Long term stability and surface properties of colloidal nanoparticles have significance in many applications. Here, surface charge modified hydrated cerium oxide nanoparticles (CNPs, also known as nanoceria) are synthesized and their dynamic ion exchange interactions with the surrounding medium are investigated in detail. Time dependent Zeta (ζ) potential (ZP) variations of CNPs are demonstrated as a useful characteristic for optimizing their surface properties. The surface charge reversal of CNPs observed with respect to time, concentration, temperature and doping is correlated to the surface modification of CNPs in aqueous solution and the ion exchange reaction between the surface protons (H +) and the neighboring hydroxyls ions (OH −). Using density functional theory (DFT) calculations, we have demonstrated that the adsorption of H + ions on the CNP surface is kinetically more favorable while the adsorption of OH − ions on CNPs is thermodynamically more favorable. The importance of selecting CNPs with appropriate surface charges and the implications of dynamic surface charge variations are exemplified with applications in microelectronics and biomedical.

ACS Nano, 2009

Nanoparticles have shown tremendous potential for effective drug delivery due to their tiny size ... more Nanoparticles have shown tremendous potential for effective drug delivery due to their tiny size and cell membrane penetration capabilities. Cellular targeting with nanoparticles is often achieved by surface modifications followed by ligand conjugation. However, the efficiency of the nanoparticles reaching the target cells and getting internalized depends on the stability of targeting ligands and the chemical nature of the ligand nanoparticle binding. Recent advancements in nanobiomaterials research have proven the superoxide dismutase (SOD) mimetic activity of cerium oxide nanoparticles (CNPs) in protecting cells against oxidative stress. Due to their excellent biocompatibility, CNPs can be used as a potential drug carrier that can transport and release drugs to the malignant sites. Here we combine single molecule force spectroscopy (SMFS) and density functional theory (DFT) simulations to understand the interaction between transferrin, a ligand protein overexpressed in cancer cells, and CNPs. SMFS studies demonstrate an increase in the transferrin adhesion to the nanoparticles' surface with an increase in positive potential of CNPs. Binding energy values obtained from DFT calculations predict an increase in bond strength between the transferrin and CNPs upon surface protonation and charge modification. Transferrin-conjugated CNPs were tested for their binding stability and preferential cellular uptake efficiency by incubating them with human lung cancer cells (A549) and normal embryo lung cells (WI-38). The results demonstrate the importance of tuning the surface properties of nanoparticles for better ligand adsorption and cellular uptake.

Medical Physics, 2012

This paper outlines and demonstrates a programmatic method to incorporate spatial information int... more This paper outlines and demonstrates a programmatic method to incorporate spatial information into a dose volume histogram (DVH) by adding vector data on the location of pixels in the dose array relative to structures in the plan to construct a vectorized dose distribution (VDD). With this data the DVH can be subgrouped according to a wide array of vector constraint sets, defining the spatial relationship of pixels to one or several structures to construct a vectorized DVH (VDVH) to reveal vector relationships of dose regions to structures. Methods: Mathematical models for construction of the VDD and VDVH are described and a dosevector-histogram (DVctH) is introduced as a means of specifying the location of dose features such as "hot spots." Practical detail on a programmatic approach to implement the methods is provided. A set of tests utilizing phantom and SBRT lung image sets were carried out to demonstrate ability of VDVH and DVctH to reveal clinically relevant spatial detail in dose distributions. Results: The VDVH and DVctH enabled decomposing DVH curves to reveal the relative location of pixels contributing to dose points on the curve. The metrics enabled specificity in defining the location and magnitude of dose features relevant to treatment plan evaluation. The VDD, VDVH, and DVctH differ from other methods described in the literature as a result of using vector based constraints for each pixel, rather than focusing only on distance by construction of a set of shells on around or within a structure and then subgrouping pixels in the overlap region. Conclusions: The method is an effective means to combine spatial information with DVH metrics and provides a practical means of specifying the location of dose features with respect other structures in the treatment plan.

Computational materials …, 2004

IEEE Electron Device Letters, 2010

The hydrogen-sensing performance of a nanosensor integrating interdigitated electrodes with a gap... more The hydrogen-sensing performance of a nanosensor integrating interdigitated electrodes with a gap of 100 nm and indium-oxide-doped tin dioxide nanoparticles is investigated at room temperature. The nonlinear behavior observed from the I/V curves of the sensor in air atmosphere indicated the presence of a Schottky barrier contact at the electrode/sensing-material interface. The linear I/V response obtained in hydrogen atmosphere suggested

Sensors and Actuators B-chemical, 2011

Nanocrystalline indium oxide-doped tin oxide thin film sensors have been synthesized using sol–ge... more Nanocrystalline indium oxide-doped tin oxide thin film sensors have been synthesized using sol–gel dip-coating technique. The sensors were spin-coated with three different types of polymer namely polymethyl methacrylate (PMMA), poly-perfluorobutenyl vinyl ether (Cytop), fluoropolymer (Fluoropel). The room temperature sensor characteristics (response time, electrical response and recovery time) of the three sensors with different polymer coating were compared at hydrogen concentrations

for the polarity profile along the bound PtdCho molecule and the one determined for membrane bila... more for the polarity profile along the bound PtdCho molecule and the one determined for membrane bilayers. This polarity match rationalizes the efficient energy-independent partitioning of a lipid molecule from a bilayer into the Sec14p phospholipid-binding pocket. Further, we have developed a direct method for observing formation of a hydrogen bond between sequestered water molecules and a spin-labeled site by applying pulsed Hyperfine Sub-level Correlation (HYSCORE) spectroscopy.

Surface elastic properties of sol-gel derived porous nanosilica optical coatings were determined ... more Surface elastic properties of sol-gel derived porous nanosilica optical coatings were determined using scanning force microscopy. Silica nanocoatings prepared under acid and base catalyzed sol-gel process exhibited varying surface morphology, particle size and porosity. Force-distance spectroscopy measurements were conducted on these coatings using scanning force microscopy, and their elastic moduli were obtained by applying Hertz model. The elastic modulus of the coatings varied from 2.4 to 13.4 GPa depending on the nature and concentration of the catalyst used.

Applied Catalysis A-general, 2010

Synergistic interaction of catalyst and support has attracted the interest of the catalytic commu... more Synergistic interaction of catalyst and support has attracted the interest of the catalytic community for several decades. The decomposition/oxidation of alcohols for the production of hydrogen as a source of fuel requires such support catalyst interaction. Recent studies have suggested the active role of oxide based supports on the catalytic ability of noble metals such as gold, platinum and palladium.

Nature Physics, 2011

Free-energy-landscape formalisms provide the fundamental conceptual framework for physical descri... more Free-energy-landscape formalisms provide the fundamental conceptual framework for physical descriptions of how proteins and nucleic acids fold into specific three-dimensional structures. Although folding landscapes are difficult to measure experimentally, recent theoretical work by Hummer and Szabo has shown that landscape profiles can be reconstructed from non-equilibrium single-molecule force spectroscopy measurements using an extension of the Jarzynski equality. This method has been applied to simulations and experiments but never validated experimentally. We tested it using force-extension measurements on DNA hairpins with distinct, sequence-dependent folding landscapes. Quantitative agreement was found between the landscape profiles obtained from the non-equilibrium reconstruction and those from equilibrium probability distributions. We also tested the method on a riboswitch aptamer with three partially folded intermediate states, successfully reconstructing the landscape but f...

$Research paper thumbnail of Role of Catalyst on Refractive Index Tunability of Porous Silica Antireflective Coatings by Sol-Gel Technique$

Journal of Physical Chemistry C, 2007

Porous silica coatings were prepared by acid-and base-catalyzed sol-gel method. Surface morpholog... more Porous silica coatings were prepared by acid-and base-catalyzed sol-gel method. Surface morphology studies by atomic force microscopy showed smooth surface for acid-catalyzed coatings while base catalysis resulted in coarse particle morphology. On increasing the tetraethyl orthosilicate to base molar ratio from 1:1 to 1:3, the mean particle size of the coating shifted from 30 to 100 nm while the pore size varied from 4.7 to 14 nm. Infrared spectral analysis exhibited a change in the ratio of integrated peak intensities of Si-O-Si to Si-OH in acid-and base-catalyzed silica coatings. Textural studies showed an increase in particle size and porosity with base concentration. Optical transmission and surface roughness of base-catalyzed samples were found to be higher than that of acid-catalyzed silica coatings.

Sensors and Actuators B: Chemical, 2011

Nanocrystalline indium oxide-doped tin oxide thin film sensors have been synthesized using sol-ge... more Nanocrystalline indium oxide-doped tin oxide thin film sensors have been synthesized using sol-gel dip-coating technique. The sensors were spin-coated with three different types of polymer namely polymethyl methacrylate (PMMA), poly-perfluorobutenyl vinyl ether (Cytop), fluoropolymer (Fluoropel). The room temperature sensor characteristics (response time, electrical response and recovery time) of the three sensors with different polymer coating were compared at hydrogen concentrations of 600, 1500, 6000 and 15,000 ppm and at two different humidity levels of 14% and 65%. It was found that the polymer coating preserves the selective sensing property of indium oxide-doped tin oxide even at high humidity. The response kinetics of the sensors with different coatings has been compared.

Nanoscale, 2011

Fast, sensitive and discriminating detection of hydrogen at room temperature is crucial for stora... more Fast, sensitive and discriminating detection of hydrogen at room temperature is crucial for storage, transportation, and distribution of hydrogen as an energy source. One dimensional nanowires of SnO 2 are potential candidates for improved H 2 sensor performance. The single directional conducting continuous nanowires can decrease electrical noise, and their large active surface area could improve the response and recovery time of the sensor. In this work we discuss synthesis and characterization of nanowire arrays made using nanosecond ultraviolet wavelength (266 nm) laser interference processing of ultrathin SnO 2 films on SiO 2 substrates. The laser energy was chosen to be above the melting point of the films. The results show that the final nanowire formation is dominated by preferential evaporation as compared to thermocapillary flow. The nanowire height (and hence wire aspect ratio) increased with increasing initial film thickness h 0 and with increasing laser energy density E o . Furthermore, a self-limiting effect was observed where-in the wire formation ceased at a specific final remaining thickness of SnO 2 that was almost independent of h 0 for a given E o . To understand these effects, finite element modeling of the nanoscale laser heating was performed. This showed that the temperature rise under laser heating was a strong nonmonotonic function of film thickness. As a result, the preferential evaporation rate varies as wire formation occurs, eventually leading to a shut-off of evaporation at a characteristic thickness. This results in the stoppage of wire formation. This combination of nanosecond pulsed laser experiments and thermal modeling shows that several unique synthesis approaches can be utilized to control the nanowire characteristics.

Journal of Nanoscience and Nanotechnology, 2006

One dimensional spiral titania nanostructures were obtained by anodization of pure titanium from ... more One dimensional spiral titania nanostructures were obtained by anodization of pure titanium from fluoride containing solutions of phosphoric acid. The formation of nanotubes was found to be dependant on current density. Field Emission Scanning Electron Microscopy (FESEM) shows the diameter of tubes around 70-100 nm which is consistent with the High Resolution Transmission Electron Micrographs (HRTEM) and Atomic Force Microscopy (AFM) images. HRTEM showed the one dimensional growth as spiral in nature which was also supported by AFM images. This anisotropic growth is compared with the possible growth mechanisms.