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GOLD NANOPARTICLE GENERATION USING IN SITU REDUCTION ON A PHOTORESIST POLYMER SUBSTRATE
Title
GOLD NANOPARTICLE GENERATION USING IN SITU REDUCTION ON A PHOTORESIST POLYMER SUBSTRATE.
Creator
Clukay, Christopher, Kuebler, Stephen, University of Central Florida
Abstract / Description
This report presents evidence that in-situ reduction of metal ions bound to a cross-linked polymer surface does not always result in nanoparticle formation solely at the interface, as is commonly assumed, but also as much as 40 nm deep within the polymer matrix. Tetrachloroaurate ions were bound using a variety of multi-functional amines to cured films of SU-8 -- a cross-linkable epoxide frequently used for micro- and nanofabrication -- and then treated using one of several reducing agents....
Show moreThis report presents evidence that in-situ reduction of metal ions bound to a cross-linked polymer surface does not always result in nanoparticle formation solely at the interface, as is commonly assumed, but also as much as 40 nm deep within the polymer matrix. Tetrachloroaurate ions were bound using a variety of multi-functional amines to cured films of SU-8 -- a cross-linkable epoxide frequently used for micro- and nanofabrication -- and then treated using one of several reducing agents. The resulting gold-nanoparticle decorated films were examined by X-ray photoelectron spectroscopy and by plan-view and cross-sectional transmission electron microscopy. Reduction using sodium borohydride or sodium citrate generates bands of interspersed particles as much as 40 nm deep within the polymer, suggesting both the Au(III) complex and the reducing agent are capable of penetrating the surface and affecting reduction and formation of nanoparticles within the polymer matrix. It is shown that nanoparticle formation can be confined nearer to the polymer interface by using hydroquinone, a sterically bulkier and less flexible reducing agent, or by reacting the surface in aqueous media with high molecular-weight multifunctional amines, that presumably confine Au(III) nearer to the true interface. These finding have important implications for technologies that apply surface bound nanoparticles, including electroless metallization, catalysis, nano-structure synthesis, and surface enhanced spectroscopy.
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Date Issued
2011
Identifier
CFH0004091, ucf:44794
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFH0004091
SURFACE ENGINEERING OF GOLD NANOPARTICLES AND THEIR APPLICATIONS
Title
SURFACE ENGINEERING OF GOLD NANOPARTICLES AND THEIR APPLICATIONS.
Creator
Dai, Qiu, Huo, Qun, University of Central Florida
Abstract / Description
Gold nanoparticles (AuNPs) with their unique sizes, shapes, and properties have generated much enthusiasm over the last two decades, and have been explored for many potential applications. The successful application of AuNPs depends critically on the ability to modify and functionalize their surface to provide stability, compatibility, and special chemical functionality. This dissertation is aimed at exploring the chemical synthesis and surface modification of AuNPs with the effort to (1)...
Show moreGold nanoparticles (AuNPs) with their unique sizes, shapes, and properties have generated much enthusiasm over the last two decades, and have been explored for many potential applications. The successful application of AuNPs depends critically on the ability to modify and functionalize their surface to provide stability, compatibility, and special chemical functionality. This dissertation is aimed at exploring the chemical synthesis and surface modification of AuNPs with the effort to (1) control the number of functional groups on the particle surface, and to (2) increase the colloidal stability at the physiological conditions. To control the functionality on the particle surface, a solid phase place exchange reaction strategy was developed to synthesize the 2 nm AuNPs with a single carboxylic acid group attached on the particle surface. Such monofunctional AuNPs can be treated and used as molecular nanobuilding blocks to form more complex nanomaterials with controllable structures. A "necklace"-like AuNP/polymer assembly was obtained by conjugating covalently the monofunctional AuNPs with polylysine template, and exhibited an enhanced optical limiting property due to strong electromagnetic interaction between the nanoparticles in close proximity. To improve the colloidal stability in the psychological condition, biocompatible polymers, polyacrylic acid (PAA), and polyethylene glycol (PEG) were used to surface modify the 30 nm citrate-stabilized AuNPs. These polymer-modified AuNPs are able to disperse individually in the high ionic strength solution, and offer as the promising optical probes for bioassay applications. The Prostate specific antigen (PSA) and target DNA can be detected in the low pM range by taking advantages of the large scattering cross section of AuNPs and the high sensitivity of dynamic light scattering (DLS) measurement. In addition to the large scattering cross section, AuNPs can absorb strongly the photon energy at the surface plasmon resonance wavelength and then transform efficiently to the heat energy. The efficient photon-thermal energy conversion property of AuNPs has been used to thermal ablate the Aβ peptide aggregates under laser irradiation toward Alzheimer's disease therapy.
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Date Issued
2008
Identifier
CFE0002395, ucf:47767
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002395
Nanoscale Characterization and Mechanism of Electroless Deposition of Silver Metal
Title
Nanoscale Characterization and Mechanism of Electroless Deposition of Silver Metal.
Creator
Grabill, Christopher, Kuebler, Stephen, Beazley, Melanie, Zou, Shengli, Frazer, Andrew, Bhattacharya, Aniket, University of Central Florida
Abstract / Description
This dissertation is an investigation of the nanoscale characteristics and mechanism of electrolessly deposited silver metal seeded by gold nanoparticles. The process of growing seed-nanoparticles on a polymer surface was studied. Several bifunctional amines and organic reducing agents were used to explore how these chemical factors affect the size and distribution of gold nanoparticles formed at the interface. The nanoparticles were characterized by transmission electron microscopy (TEM) and...
Show moreThis dissertation is an investigation of the nanoscale characteristics and mechanism of electrolessly deposited silver metal seeded by gold nanoparticles. The process of growing seed-nanoparticles on a polymer surface was studied. Several bifunctional amines and organic reducing agents were used to explore how these chemical factors affect the size and distribution of gold nanoparticles formed at the interface. The nanoparticles were characterized by transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). An electroless deposition (ED) bath developed by Danscher was selected to study electroless deposition of silver in detail. The chemical species in the bath were varied to determine how concentration, nature of the carboxylate buffering species, and the presence and absence of gum arabic affect the morphology of silver metal formed by ED and the overall rate of deposition at the surface. The kinetics of deposition using the Danscher bath was studied in detail to elucidate the mechanism of ED. Knowledge generated from this investigation can be used to expand applications of silver ED where strict control over the nanoscale morphology of the deposited metal is required to obtain specific chemical and physical properties.
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Date Issued
2018
Identifier
CFE0007009, ucf:52051
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007009
Theoretical and Experimental Studies for Tailoring the Electromagnetic Surface Properties of Conductive Materials
Title
Theoretical and Experimental Studies for Tailoring the Electromagnetic Surface Properties of Conductive Materials.
Creator
Jennings, Jeffrey, Vaidyanathan, Raj, Kar, Aravinda, Coffey, Kevin, Challapalli, Suryanarayana, Brisbois, Elizabeth, Yu, Xiaoming, University of Central Florida
Abstract / Description
Induction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive...
Show moreInduction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive response by adding functionally-graded, heterogeneous surface layers is a possible solution. However, non-uniform EM properties introduce two challenges: the added complexity of analyses and characterization of the graded region. This dissertation addresses these complexities.An Helmholtz coil and other loops positioned in a coaxial array were used to create and monitor inductive fields that were mathematically related to the induced current in closed, circular loops with electrical conductivities ranging from 1.0 to 57 megaSiemens per meter. Magnetic flux densities up to 14 microTesla at frequencies from 30 to 100 MHz were evaluated for specimens with varying loop and wire diameters. Induced current results show a linear relationship with flux density and strongly depend on the sample geometry, but not on conductivity. Trends within the data matched well with those predicted by theory that considered such a loop.An equivalent length, semi-analytical approach modeled induced current through a graded EM property region and considered effective conductivities. Predicted results for transmissivity through Pt-doped titanium foils and effective conductivity in round wire Sn-modified Cu samples show good agreement with experimental data. The Joule heating experiment used for wire testing also demonstrates a means for characterizing conductor surface properties. Two new technologies derived from this research including an RF magnetic field imaging technique and a contoured loop array for applying therapeutic controlled RF magnetic fields are also described.
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Date Issued
2018
Identifier
CFE0007756, ucf:52378
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007756
TUNING THE PROPERTIES OF NANOMATERIALS AS FUNCTION OF SURFACE AND ENVIRONMENT
Title
TUNING THE PROPERTIES OF NANOMATERIALS AS FUNCTION OF SURFACE AND ENVIRONMENT.
Creator
Karakoti, Ajay, Seal, Sudipta, University of Central Florida
Abstract / Description
Nanotechnology has shaped the research and development in various disciplines of science and technology by redefining the interdisciplinary research. It has put the materials science at the forefront of technology by allowing the researchers to engineer materials with properties ranging from electronics to biomedical by using materials as diverse as ceramics to just plain carbon. These exceptional properties are achieved by minimizing the dimension of particles in such smaller domains that...
Show moreNanotechnology has shaped the research and development in various disciplines of science and technology by redefining the interdisciplinary research. It has put the materials science at the forefront of technology by allowing the researchers to engineer materials with properties ranging from electronics to biomedical by using materials as diverse as ceramics to just plain carbon. These exceptional properties are achieved by minimizing the dimension of particles in such smaller domains that the boundary between the individual atoms, ions or cluster of particles is very small. This results in a change in conventional properties of particles from continuum physics to quantum physics and hence the properties of nanoparticles can be tuned based upon their size, shape and dimensionality. One of the most apparent changes upon decreasing the particle size is the increase in surface area to volume ratio. Thus nanoparticles possess greater tendency to interact with the environment in which they are present and similarly the environment can affect the properties of nanomaterials. The environment here is described as the immediate solid, liquid or gaseous material in immediate contact with the external surface of the nanoparticles. In order to control the physico-chemical properties of nanoparticles it is important to control the surface characteristics of nanoparticles and its immediate environment. The current thesis emphasizes the role of tuning the surface of nanoparticles and/or the environment around the nanoparticles to control their properties. The current approach in literature uses nanoparticles as a platform that can be used for a myriad of applications by just changing the surface species which can tune the properties of nanoparticles. Such surface modification can provide nanomaterials with hydrophilic, hydrophobic, biocompatible, sensing, fluorescence and/or electron transfer properties. The current thesis demonstrates the interaction between nanoparticles and the environment by changing the surface characteristics of nanomaterials through the use of oxide nanoparticles as examples. The first part of the thesis discusses the synthesis, modification and properties of cerium oxide nanoparticles (CNPs), a versatile material used in wide range of applications from catalysis to glass polishing, for their potential use in biomedical applications as a function of medium. The thesis starts by projecting the effect of environment on the properties of nanomaterials wherein it is shown that simple medium, such as, water can influence the optical properties of nanoparticles. It was shown that the strong polarizing effect of water on the non-bonding f electrons can cause a blue shift in the optical properties of CNPs as a function of increase in trivalent oxidation state of cerium in CNPs. This phenomenon, contradictory to existing literature in solid state where a red shift is observed upon increasing the trivalent oxidation state of cerium in CNPs, is purely attributed to the medium-inflicted change in properties of nanoparticles. This concept is built upon in the first half of thesis by increasing the colloidal stability of nanoparticles by surface and/or medium modification. It is shown that the narrow range of pH in which the colloidal CNPs are stable can be extended by changing the medium from water to polyhydroxy compounds such as glucose and dextran. The synthesis was designed specially to avoid the traditional precipitation and re-dispersion strategy of synthesis of nanoparticles to preserve the surface activity. The complex forming ability of cerium with polysaccharides was employed to synthesize the CNPs in a one step process and the pH stability of the NPs was extended between 2.0 to 9.5. The difference in the complexing ability of the monomer - glucose and its anhydro glucose polymer - dextran is reflected in the ability of cerium to form super-agglomerates with the monomer while anhydro gluco polymer forms extremely disperse 3-5 nm nanoparticles through steric modification. It is shown that the antioxidant activity of nanoparticles remain unchanged by surface modification by demonstrating the cycling of the oxidation state of cerium in CNPs, with time, through hydrogen peroxide mediated transition of oxidation states of cerium. It is demonstrated that the polymeric coatings, generally considered as passive surface coatings, can also play an active role in tuning the properties of nanomaterials and increasing their biocompatibility as well as bio-catalytic activity. It is demonstrated that the antioxidant activity of CNPs can be increased as a function of polyethylene glycol (PEG) while the biocompatibility is unaltered due to the biocompatible nature of PEG. The antioxidant activity of CNPs involves an electron transfer (ET) from the CNPs to the reactive oxygen species or vice versa. This heterogeneous ET system is further complicated by the presence of surface adsorbed species. Interfacial charge/electron transfer (ET) between a particle and adsorbed (or covalently bonded) molecule presents significant complexity as it involves a solid state electron transfer over long distance. Unlike a free ion, in solid state, the conducting electrons can be temporarily trapped by the coupling lattice sites. Adsorption/attachment of surface species to nanoparticle can disturb the electronic levels by further polarizing the electron cloud thereby localizing the electron and facilitating the charge transfer. Such an interfacial electron transfer between NPs and adsorbed organic species can be compared to the single electron transfer carried by organometallic systems with a metal ion core modified with electron delocalizing porphyrin ligands. It is demonstrated that in this PEGyltaed CNPs system, the PEG essentially forms a complex with CNPs in the presence of hydrogen peroxide to facilitate this electron transfer process. The superoxide dismutase (SOD) and catalase mimetic ability of CNPs is described and special emphasis is given to its biocompatibility. The second half of the thesis emphasizes the role of synthesis and surface modification in influencing the catalytic performance of cerium oxide modified titanium dioxide catalysts for decomposition of methanol. Noble metals supported on oxide nanoparticles have been an area of active research in catalysis. It is demonstrated that the modification of surface of the oxide nanoparticles by noble metals is a function of the synthesis process. By keeping the size of the nanoparticles constant, it was demonstrated that the differences in the oxidation state of noble metals can lead to change in the activity of noble metals. This contribution adds to the already existing controversy in the open literature about the role of the oxidation state of platinum in catalysis. The core level shifts in the binding energy of the 4f electrons of platinum was used as a guide to the gauge the oxidation state. Results from an in-house built catalytic reactor coupled to mass spectrometer and in-situ diffuse reflectance infra-red spectroscopy are used to quantify the catalytic performance and identify the mechanism of reaction as well as products of methanol decomposition.
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Date Issued
2010
Identifier
CFE0003189, ucf:48590
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003189