Sharmila Mukhopadhyay | University of Maine (original) (raw)

Papers by Sharmila Mukhopadhyay

Journal of vacuum science & technology, Oct 30, 2008

Polycrystalline diamond thin films are grown on a p-type Si ͑100͒ single crystal substrate at a l... more Polycrystalline diamond thin films are grown on a p-type Si ͑100͒ single crystal substrate at a low surface deposition temperature of 455°C using a microwave plasma enhanced chemical vapor deposition process in an Ar-rich Ar/ H 2 / CH 4 plasma containing different oxygen levels from 0% to 0.75%. The surface deposition temperatures are measured and monitored by an IR thermometer capable of working in a plasma environment without any interference from the plasma emissions. The lower surface deposition temperature at high microwave power of 1300 W and higher gas pressure of 95 torr is achieved by active cooling of the substrate from the backside using a specially designed cooling stage. An enhanced growth rate from 0.19 to 0.63 m / h is observed with varying oxygen from 0% to 0.75% in the plasma. Diamond grain size also increased from 0.69 m for the sample with no oxygen to 1.74 m for the sample with 0.75% oxygen. The diamond films are characterized using x-ray diffraction, environmental scanning electron microscopy field emission gun, Raman spectroscopy, and x-ray photoelectron spectroscopy. The enhanced growth rate is correlated with the enhanced atomic hydrogen to C 2 ratio with increasing oxygen concentration in the plasma, which is measured by an in situ optical emission spectroscopy.

International Conference on Cognitive Modelling, 2003

The microcellular graphitic foam is a porous, lightweight solid made of interconnected ligaments ... more The microcellular graphitic foam is a porous, lightweight solid made of interconnected ligaments and cells of graphitic planes. Since the structure is 80% to 90% porous, these solids have a high interface/volume ratio, and surface-driven properties such as atmospheric tolerance and bond formation with the matrix material are crucial for applicability. This calls for controlled surface modification, which is complicated by the fact that the surface is made of nonplanar cell walls, most of which are accessible only through narrow pore openings. This has led to the investigation of selected thin film modification techniques that can permeate the porous microcellular structure

Materials Science Forum, May 1, 2000

In metalization work, controlled semiconductor surfaces and interfaces are necessary. Trace impur... more In metalization work, controlled semiconductor surfaces and interfaces are necessary. Trace impurities such as carbon and oxygen at the metal/semiconductor interface may improve or degrade the electrical characteristics of a desired contact. In this study, Auger Electron Spectroscopy (AES) was used to investigate electron stimulated oxidation (ESO) of SiC. The research focused on chamber conditions necessary to prevent oxide formation on SiC surfaces during thin film metal deposition. Oxidation rate was studied as a function of beam exposure ton and off), primary electron beam energy, E-p, (3-6 keV), electron beam current, I-p, (25-500 nA), and total chamber pressure. Oxidation rate had a stronger correlation to overall chamber pressure rather than the partial pressure of H2O, CO, or CO2 alone. Oxidation rate decreased slightly as E-p was increased. Rate of oxidation increased at higher pressures (2.2 x 10(-7) Torr) with respect to I-p but was nearly independent of I-p at lower pressures (7.1 x 10-9 Torr). No oxide growth was detectable to AES in the absence of exposure to the electron beam

Journal of Nanomaterials, 2015

Science of The Total Environment, Apr 1, 2021

A flexible, durable, and reusable nanocatalyst system was fabricated by anchoring palladium nanop... more A flexible, durable, and reusable nanocatalyst system was fabricated by anchoring palladium nanoparticles on carbon nanotube (CNT) carpets covalently attached to carbon cloth. These hierarchical hybrid materials were tested for catalytic degradation of triclosan (TCS), an emerging contaminant. Materials were characterized using scanning & transmission electron microscopy techniques (SEM and TEM), X-Ray Diffraction (XRD), and X-Ray Photoelectron Spectroscopy (XPS). The reaction kinetics was studied using HPLC and reaction pathways proposed based on LC-MS/GC-MS analyses. In the presence of hydrogen, complete step-wise chlorine removal was seen until complete dechlorination was accomplished. The pseudo-first-order rate constant was measured to be orders of magnitude higher than earlier reported values. Moreover, the same material was usable for multiple cycles in flowing water. This study demonstrates that robustness and reusability of larger structural materials can be combined with the ultra-high surface activity of nanocatalysts to provide practical and eco-friendly solutions for water sustainability.

John Wiley & Sons, Inc. eBooks, Aug 1, 2011

Preface. Section I. Overview. 1. Key attributes of nano-scale materials and functionalities emerg... more Preface. Section I. Overview. 1. Key attributes of nano-scale materials and functionalities emerging from them (S. M. Mukhopadhyay). 2. Societal Impact and Future Trends in Nanomaterials (S. M. Mukhopadhyay). Section II. Processing and Analysis. 3. Fabrication Techniques for Growing Carbon Nanotubes (I. T. Barney). 4. Nanoparticles and Polymer Nanocomposites (G. A. Jimenez, B. J. Lee, and S. C. Jana). 5. Laser-Assisted Fabrication Techniques (T. Murray). 6. Experimental Characterization of Nanomaterials (A. Jackson). 7. Modeling and Simulation of Nanoscale Materials (S. Patnaik and M. Tsige). Section III. Applications. 8. Nanomaterials for Alternate Energy (H. Huang and B. Z. Jang). 9. Enhancement of Through-Thickness Thermal conductivity in Adhesively Bonded Joints Using Aligned Carbon Nanotubes (S. Sihn, S. Ganguli, A. K. Roy, L. Qu, and L. Dai). 10. Applications of Metal Nanoparticles in Environmental Cleanup (S. R. Kanel, C. Su, U. Patel, and A. Agrawal). 11. Application of Carbon Nanomaterials in Water Treatment: Removal of Common Chemical and Biological Contaminants by Adsorption (V. K. K. Updahyayula, J. R. Ruparelia, and A. Agrawal). 12. Peptide Nanotubes for Biomedical and Environmental Applications (B. W. Park and D. S. Kim). Index.

Applied Surface Science, Mar 1, 2004

Journal of Physics D, Aug 7, 2002

Page 1. Plasma assisted hydrophobic coatings on porous materials: influence of plasmaparameters T... more Page 1. Plasma assisted hydrophobic coatings on porous materials: influence of plasmaparameters This article has been downloaded from IOPscience. ... porous materials: influence of plasma parameters SM Mukhopadhyay1,3, P Joshi1, S Datta2, JG Zhao2 and P France2 ...

Carbon nanotubes (CNTs) have been the focus of significant Nature article. CNTs have primarily be... more Carbon nanotubes (CNTs) have been the focus of significant Nature article. CNTs have primarily been grown on flat substrates for a range of potential applications due to their superior mechanical, electrical and thermal properties. However, limited research has been accomplished on open cell foam structures. Initial attempts to grow CNTs onto as-received foam samples resulted in low CNTs growth. This then prompted surface treatment research to enhance CNTs growth onto the foam surface. For this study, the surface modification methods of interest included: nitric acid treatment, oxidation, coating with hexamethyldisilazane (HMDS), and atomic layer deposition (ALD) of oxides. Dense, aligned CNTs were grown on all surfaces of 3dimensional open cell reticulated carbon foam. The best results were achieved when a thin layer of Al 2 O 3 was deposited on the foam via ALD prior to CNT growth. The foam samples were 1cm x 1 cm x 0.5cm, with CNTs found throughout the volume of the sample and not just the outer layers of the foam. Highly aligned CNTs were realized using floating catalyst chemical vapor deposition (FCT-CVD) with xylene and ferrocene as the carbon and catalyst sources, respectively. Growing CNTs on a 3-dimensional foam structure will dramatically increase the surface area available for heat dissipation, thus enhancing the thermal properties of the foam, as suggested by initial thermal testing. Preliminary results include scanning electron microscope images and thermal conductivity results.

Electrochemical Society eBooks, 2006

... Magnetism at Interfaces in La-Ca-Mn-O CMR Thin Films 150 DJ Miller, V. Vlasko-Vlasov, and U. ... more ... Magnetism at Interfaces in La-Ca-Mn-O CMR Thin Films 150 DJ Miller, V. Vlasko-Vlasov, and U. Welp Local Electrode Atom Probes for the Study of Solid-Solid Interaces 156 A. Gribb, T. Kelly, T. Gribb, J. Olson, R. Martens, J. Shepard, S. Wiener, T. Kunicki, R. Ulfig, D. Lenz, E ...

MRS Proceedings, 1988

The modification of surface mass transport rates due to the presence of a divalent dopant in alum... more The modification of surface mass transport rates due to the presence of a divalent dopant in alumina has been studied. The composition of the prismatic (1010) surface of sapphire, doped with MgO by two different techniques, has been monitored with Auger electron spectroscopy. Mass transport at these doped surfaces has been measured by observing the rate of decay of a periodic surface profile. Short wavelength patterns were used so that the transport process would be dominated by solid state diffusion. The analysis assumes an isotropic surface free energy, the implications of which are discussed. It was found that during annealing in air, both surface and bulk diffusion mechanisms contribute to ionic mobility. The effect of Mg ions seems to depend on its thermodynamic activity. When the surface coverage is low, up to about 20%, the effect of the dopant is not significant. When the surface concentration of Mg increases to that corresponding to spinel (about 33%), the mass transport rate increases significantly. From these observations, it is implied that a second phase may be required to markedly enhance the surface mass transport rate of alumina in air. The results obtained in this study have been critically analyzed and are discussed in light of other data for mass transport in alumina

Nucleation and Atmospheric Aerosols, 2002

XPS studies of a typical YBCO coated conductor architecture were conducted to investigate the che... more XPS studies of a typical YBCO coated conductor architecture were conducted to investigate the chemical and microstructural profiles. The detailed XPS depth profiling study was performed on one sample (YBCO/CeO2/YSZ/CeO2/Ni) of coated conductor. The chemical depth profiling involved bombarding a small area of the specimen surface with 3 keV Ar+ ions and analyzing the freshly exposed surface after each bombardment.

Journal of Applied Physics, Dec 27, 2002

This article discusses surface-related issues and possible modification approaches in high-porosi... more This article discusses surface-related issues and possible modification approaches in high-porosity graphitic foam. The microcellular solid is made of graphitic carbon walls, ligaments, and beams supporting a network of interconnected pores. This makes the exposed surface area very high and its understanding a necessity for most applications. Graphitic planes are seen to be stacked at various orientations with respect to exposed surfaces. Therefore, a simplified analytical model that assumes “random” graphitic planes forming a three-dimensional array of tetrahedral cells may be an appropriate approximation. The influence of oxidizing chemicals such as nitric acid and hydrogen peroxide on surface properties has been studied using electron microscopy, photoelectron spectroscopy, and water absorption tests. Bulk properties such as density measurements and mechanical tests have been performed in parallel. It is seen that exposure to nitric acid results in an increase in oxygen-containing functional groups on the surface, which may lead to increased infiltration of polar matrix fluids such as water and epoxy resins. This possibility is further supported by water absorption studies that show increased water infiltration in foam after nitric acid treatment. Electron microscopy and density studies indicate that some surface etching occurs with concentrated nitric acid exposure, but not significant enough to decrease density. Strength of the stand-alone foam is reduced for concentrated nitric acid treatment, but the elastic modulus is unaffected. The scientific significance of these results in terms of future surface modification of microcellular solids has been discussed.

Applied Surface Science, Jun 1, 2006

Plasma-assisted functional films have significant potential in various engineering applications. ... more Plasma-assisted functional films have significant potential in various engineering applications. They can be tailored to impart desired properties by bonding specific molecular groups to the substrate surface. The aim of this investigation was to develop a fundamental understanding of the atomic level growth, coverage and functional effectiveness of plasma nano-films on flat surfaces and to explore their application-potential for complex and uneven shaped nano-materials. In this paper, results on plasma-assisted nano-scale fluorocarbon films, which are known for imparting inertness or hydrophobicity to the surface, will be discussed. The film deposition was studied as a function of time on flat single crystal surfaces of silicon, sapphire and graphite, using microwave plasma. X-ray photoelectron spectroscopy (XPS) was used for detailed study of composition and chemistry of the substrate and coating atoms, at all stages of deposition. Atomic force microscopy (AFM) was performed in parallel to study the coverage and growth morphology of these films at each stage. Combined XPS and AFM results indicated complete coverage of all the substrates at the nanometer scale. It was also shown that these films grew in a layer-by-layer fashion. The nano-films were also applied to complex and uneven shaped nano-structured and porous materials, such as microcellular porous foam and nano fibers. It was seen that these nano-films can be a viable approach for effective surface modification of complex or uneven shaped nano-materials.

Journal of the American Ceramic Society, May 1, 1988

... Acknowledgments: Ion implantation was done at the National Research and Resource Facility for... more ... Acknowledgments: Ion implantation was done at the National Research and Resource Facility for Submicron Structures, Cornell University. The authors thank Mr. Mike Skvarla for his help during implantation. ... 176-89 in Advances in Ceramics. Vol. 10. Edited bv WD Kinnerv. ...

Macromolecules, Jun 7, 2012

Molecular dynamics and molecular mechanics simulations have been used to study thermo-mechanical ... more Molecular dynamics and molecular mechanics simulations have been used to study thermo-mechanical response of highly cross-linked polymers composed of epoxy resin DGEBA and hardener DETDA. The effective cross-linking approach used in this work allowed construction of a set of stress-free molecular models with high conversion degree containing up to 35000 atoms. The generated structures were used to investigate the influence of model size, length of epoxy strands, and degree of cure on thermo-mechanical properties. The calculated densities, coefficients of thermal expansion, and glass transition temperatures of the systems are found to be in good agreement with experimental data. The computationally efficient static deformation approach we used to calculate elastic constants of the systems successfully compensated for the large scattering of the mechanical properties data due to nanoscopically small volume of simulation cells and allowed comparison of properties of similar polymeric networks having minor differences in structure or chemistry. However, some of the elastic constants obtained using this approach were found to be higher than in real macroscopic samples. This can be attributed to both finite-size effect and to the limitations of the static deformation approach to account for dynamic effects. The observed dependence of properties on system size, in this work, can be used to estimate the contribution of large-scale defects and relaxation events into macroscopic properties of the thermosetting materials.

Applied Surface Science, Nov 1, 2002

Surface modification of high-porosity solids using RF plasma has been investigated. Hydrophobic c... more Surface modification of high-porosity solids using RF plasma has been investigated. Hydrophobic coatings were deposited on a stack of five porous filter papers using four types of plasma from different fluorine-containing monomers (TDFO, PDFOA, PFDD and PFMCH). Surface chemistry and water contact angles of each layer were analyzed using X-ray photoelectron spectroscopy (XPS) and video contact angle (VCA) measurements. It is seen that CF 2 and CF 3 groups are responsible for hydrophobic behavior and contact angle values correlates very well with total surface fluorine content. As the average surface fluorine concentration increases to about 15%, the surface becomes abruptly hydrophobic. This study indicates that a very thin coating (average thickness smaller than 1-2 nm) is needed for hydrophobic behavior. Additional deposition increases coating thickness, but has no effect on contact angle. All the monomers are equally effective in coating the ''external'' surfaces of the stack, but the extent of permeation of the plasma into the inner layers varies with monomer structure. PDFOA produces more penetrating plasma compared to other molecules. The molar ratio of the two hydrophobic functional groups (CF 2 /CF 3) in all coatings is lower than that in the original monomer due to molecular fragmentation in the plasma. In the straight chain monomers studied, CF 2 /CF 3 ratio of the coating follows the same trend as in the starting molecule. However, in the cyclic monomer studied, this ratio is significantly lower indicating greater fragmentation of such molecules. These results indicate that plasma-induced coatings can modify surface properties of high-porosity materials and that the extent of permeation can be controlled.