Thin films of 7 nm gold nanoparticles were fabricated via a direct write electron beam exposure. The electrons caused the nanoparticles to stick to the substrate and the unexposed areas were rinsed off. After the lift off, the films were annealed. This caused Ostwald ripening. Electrical and structural properties were studied. It was found that the initial film thickness is the crucial factor of the post annealing properties. In case of films thinner than 50 nm, it was found that the particles ripen to form insulating islands hundreds of nanometers in size and seperated from each other. If the film thickness is increased beyond 50 nm, the ripening causes the islands to grow so much, that at least one percolating pathway for charge transport is formed. Metallic conductivity was observed in a wide temperature range (2–350 K). It is possible to create films that display hopping conductivity, if the initial film thickness is at approximately 50 nm. In a second experiment, polystyrene—block-poly(4-vinylpyridine) (PS-P4VP) diblock copolymer was used to create a hexagonal lattice of cobalt nanoparticles. The size scale of the particles was about 12–15 nm with a 25–30 nm separation between them. This artificially arranged array of magnetic "impurities" was covered with a thin metallic film. Copper or palladium were used and the thickness was varied between 13–40 nm. It was found that these nanoengineered films show thermal hysteresis in resistance versus temperature measurements, the shape of which can be manipulated by applying a magnetic field. The effect was more pronounced in the cobalt-copper samples. Further, magnetoresistance measurements showed oscillations as a function of applied field and temperature. Again, the effects shown in the cobalt-copper samples were significantly more pronounced.

Polymeric biomaterials represent the leading technologies available today for the repair of tissue damage and for targeted drug delivery. Perhaps the most valuable aspect of polymer-based systems is the extent to which their physical properties (e.g. elasticity, porosity, etc.) can be controlled and tuned by regulating experimental parameters during their synthesis. Biomaterial performance can be improved further still by including supplementary components resulting in a composite material. Synergetic interactions between the constituents of composite materials often results in bulk physical properties that are substantially more than the sum of individual parts. Through understanding and exploiting these sympathetic relationships, novel biocomposites can be developed which exhibit improved efficacy and biocompatibility. Here we report on the synthesis strategies and characterization of novel biocomposites from our laboratory. We look specifically at hydrogel composites containing a physically-associated network of Pluronic® block copolymer along with a calcium-phosphate mineral component. Rheological results show that composites containing an in situ deposited mineral exhibit a significantly higher elastic modulus than composites of similar composition formed by conventional means. Moreover, analysis of the calcium-phosphate phase of in situ composites revealed that system parameters such as acidity play an integral role in determining the size and stability of the resultant mineral and subsequently the materials' expected in vivo performance. Changes to the structure in Pluronic®/calcium-phosphate composite hydrogels during dehydration was investigated to provide a look into the mechanisms involved in composite formation. Small angle X-ray scattering analysis of these systems shows that hydrogen bonding interactions between phosphate ions and the polyethylene oxide (PEO) polymer block significantly impact the nanoscale structure and long-range order contained in these materials. Phosphate groups are preferentially sequestered into the PEO phase in the gel and overall structural changes can be directly related to the average number of hydrogen bonds each phosphate ion experiences. Our results indicate that by understanding how mineralization occurs in simplified systems we may be able to provide insight into the complex mechanisms involved in natural tissue formation. Moreover, we show that by utilizing novel synthesis routes we are able to manufacture new biomaterials with desirable and tunable physical properties.

This dissertation addresses the fundamental problem of how to build computing systems for the nanoscale. With CMOS reaching fundamental limits, emerging nanomaterials such as semiconductor nanowires, carbon nanotubes, graphene etc. have been proposed as promising alternatives. However, nanoelectronics research has largely focused on a 'device-first' mindset without adequately addressing system-level capabilities, challenges for integration and scalable assembly. In this dissertation, we propose to develop an integrated nano-fabric, (broadly defined as nanostructures/devices in conjunction with paradigms for assembly, interconnection and circuit styles), as opposed to approaches that focus on MOSFET replacement devices as the ultimate goal. In the 'fabric-centric' mindset, design choices at individual levels are made compatible with the fabric as a whole and minimize challenges for nanomanufacturing while achieving system-level benefits vs. scaled CMOS. We present semiconductor nanowire based nano-fabrics incorporating these fabric-centric principles called NASICs and N3ASICs and discuss how we have taken them from initial design to experimental prototype. Manufacturing challenges are mitigated through careful design choices at multiple levels of abstraction. Regular fabrics with limited customization mitigate overlay alignment requirements. Cross-nanowire FET devices and interconnect are assembled together as part of the uniform regular fabric without the need for arbitrary fine-grain interconnection at the nanoscale, routing or device sizing. Unconventional circuit styles are devised that are compatible with regular fabric layouts and eliminate the requirement for using complementary devices. Core fabric concepts are introduced and validated. Detailed analyses on device-circuit co-design and optimization, cascading, noise and parameter variation are presented. Benchmarking of nanowire processor designs vs. equivalent scaled 16nm CMOS shows up to 22X area, 30X power benefits at comparable performance, and with overlay precision that is achievable with present-day technology. Building on the extensive manufacturing-friendly fabric framework, we present recent experimental efforts and key milestones that have been attained towards realizing a proof-of-concept prototype at dimensions of 30nm and below.

Semiconductor nanocrystals, or quantum dots (QDs), are interesting nanomaterials whose size-dependent, tunable optical and electronic properties make them ideal for applications in biological sensing and imaging, light-emitting devices, displays, and solar cells. The commercial exploitation of these materials requires the development of synthesis techniques that are scalable, economical, and environmentally friendly, while enabling precise control of the size, shape and size distribution of the nanocrystals. The most common synthesis technique for these nanocrystals employs small batch reactors in which nanocrystals grow as a function of time following a rapid injection of organometallic precursors into a hot coordinating solvent. The limitations of this process for large-scale commercial exploitation stem from the incomplete mixing of the precursors in large batches that can lead to non-uniform nucleation and broad particle size distributions. Limitations also include the high cost, flammability, and toxicity of the organometallic precursors and its operator-intensive nature. Templated synthesis techniques for nanocrystals have distinct advantages over other methods, including more precise control of particle size, shape, and size distribution and easier scalability for commercial applications. This thesis presents the templated synthesis of semiconducting nanocrystals in stable microemulsions and liquid crystals, formed by the self-assembly of an amphiphilic block copolymer in the presence of a polar and non-polar solvent. The work of this thesis investigates microemulsion templates for the scalable synthesis of semiconductor nanocrystals including: materials composition and particle size control, continuous production of nanocrystals, improvement of optical properties, and alternative non-toxic reactants. The nanocrystals were formed by reacting a group-II salt dissolved in the dispersed phase of the template with a group-VI hydride gas inside the nanodomains. The versatility of nanomaterials and precision of size control of this synthesis method were demonstrated by adjusting the metal salt composition and concentration. The scalability of this technique was displayed by developing a counter-current flow, packed-bed reactor for continuous synthesis of nanocrystals in templating microemulsions. Limitations of the optical properties of nanoparticles synthesized with microemulsion template were addressed by post-processing techniques including extraction and functionalization of the nanocrystals, annealing, and overcoating the quantum dots with an inorganic shell to optimize fluorescence emission and quantum yield. This post-process annealing allowed for the investigation of Mn-dopant incorporation and expulsion from the ZnSe nanocrystal. To eliminate the toxic and flammable group-VI hydride gases, a microwave-assisted templated synthesis route was developed. This employed bursts of microwaves to selectively heat the aqueous, dispersed droplets of water-in-oil microemulsions that contain the water-soluble precursors of the group-II and VI elements, thus leading to nucleation and formation of a single nanocrystal inside each nanodomain.

This dissertation explores the use of block copolymers which can self-assemble into different morphologies as templates to fabricate nanostructured materials. The first section (Chapters 2-4) reports the formation of mesoporous silica films with spherical, cylindrical and bicontinuous pores up to 40 nm in diameter through replicating the morphologies of the solid block copolymer (BCP) templates, polystyrene-b-poly(tert-butyl acrylate) (PS-b-PtBA), via phase selective condensation of tetraethylorthosilicate in supercritical CO2. Next, directed self-assembly was used to control the orientation of cylindrical domains in PS- b-PtBA templates. Large-area aligned mesochannels in silica films with diameters tunable between 5 and 30 nm were achieved through the replication of oriented templates via scCO2 infusion. The long-range alignment of mesochannels was confirmed through GISAXS with sample stage azimuthal rotation. In the second section (Chapters 5-6), enantiopure tartaric acid was used as an additive to dramatically improve ordering in poly(ethylene oxide-block- tert-butyl acrylate) (PEO-b-PtBA) copolymers. Transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray scattering were used to study the phase behavior and morphologies within both bulk and thin films. With the addition of a photo acid generator, photo-induced disorder in the PEO-b-PtBA/tartaric acid composite system was achieved upon UV exposure which deprotected the PtBA block to yield poly(acrylic acid) (PAA), which is phase-miscible with PEO. Area-selective UV exposure using a photo-mask was applied with the assistance of trace amounts of base quencher to achieve high-resolution hierarchical patterns. Helical superstructures were observed by TEM in this BCP/chiral additive system with 3D handedness confirmed by TEM tomography. In the last section (Chapter 7), ultra-high loadings of nanoparticles into target domains of block copolymer composites were achieved by blending the block copolymer hosts with small molecule additives that exhibit strong interactions with one of the polymer chain segments and with the nanoparticle ligands via hydrogen bonding. The addition of 40 wt% D-tartaric acid to poly(ethylene oxide-block-tert-butyl acrylate) (PEO-b-PtBA) enabled the loading of up to 150 wt% of 4-hydroxythiophenol functionalized Au nanoparticles relative to the mass of the target hydrophilic domain. This was equivalent to over 40% Au by mass of the resulting well ordered composite as measured by thermal gravimetric analysis.

abstract: RNA aptamers adopt tertiary structures that enable them to bind to specific ligands. This capability has enabled aptamers to be used for a variety of diagnostic, therapeutic, and regulatory applications. This dissertation focuses on the use RNA aptamers in two biological applications: (1) nucleic acid diagnostic assays and (2) scaffolding of enzymatic pathways. First, sensors for detecting arbitrary target RNAs based the fluorogenic RNA aptamer Broccoli are designed and validated. Studies of three different sensor designs reveal that toehold-initiated Broccoli-based aptasensors provide the lowest signal leakage and highest signal intensity in absence and in presence of the target RNA, respectively. This toehold-initiated design is used for developing aptasensors targeting pathogens. Diagnostic assays for detecting pathogen nucleic acids are implemented by integrating Broccoli-based aptasensors with isothermal amplification methods. When coupling with recombinase polymerase amplification (RPA), aptasensors enable detection of synthetic valley fever DNA down to concentrations of 2 fM. Integration of Broccoli-based aptasensors with nucleic acid sequence-based amplification (NASBA) enables as few as 120 copies/mL of synthetic dengue RNA to be detected in reactions taking less than three hours. Moreover, the aptasensor-NASBA assay successfully detects dengue RNA in clinical samples. Second, RNA scaffolds containing peptide-binding RNA aptamers are employed for programming the synthesis of nonribosomal peptides (NRPs). Using the NRP enterobactin pathway as a model, RNA scaffolds are developed to direct the assembly of the enzymes entE, entB, and entF from E. coli, along with the aryl-carrier protein dhbB from B. subtilis. These scaffolds employ X-shaped RNA motifs from bacteriophage packaging motors, kissing loop interactions from HIV, and peptide-binding RNA aptamers to position peptide-modified NRP enzymes. The resulting RNA scaffolds functionalized with different aptamers are designed and evaluated for in vitro production of enterobactin. The best RNA scaffold provides a 418% increase in enterobactin production compared with the system in absence of the RNA scaffold. Moreover, the chimeric scaffold, with E. coli and B. subtilis enzymes, reaches approximately 56% of the activity of the wild-type enzyme assembly. The studies presented in this dissertation will be helpful for future development of nucleic acid-based assays and for controlling protein interaction for NRPs biosynthesis. / Dissertation/Thesis / Doctoral Dissertation Biochemistry 2020

No description available.

Magister Scientiae (Medical Bioscience) - MSc(MBS) / Recently nanoparticles (NPs) have been introduced and used in combination with therapeutic approaches to develop nanotechnology-enabled medicine. These nanostructures allow for the exploitation of the physiochemical properties which may be beneficial in cancer treatment. The use of NPs in nanomedicine has proven successful in modern chemotherapeutics and has demonstrated promising potential in in vivo and in vitro radiosensitization studies. This is a baseline study aimed to determine the cytotoxic effects of AuNPs for potential radiosensitization analysis. The study analysed the effects of different AuNP sizes (30, 50 and 80nm), concentrations (5, 10 and 15 μg/ml) over various time periods in CHOK1 and A549 cells. AuNPs were characterised by DLS and ZP analysis and showed that particles were moderately polydispersed and moderately to highly stable in charge. The effects on viability and metabolic activity of cells were determined using crystal violet and the WST-1 assay.

Recently, the interest for renewable resources for fibers particularly of plant origin has been increasing. Reduction of use of traditional textile materials is now considered more critical due to the increasing environmental concern. Natural fibers are renewable, biodegradable, recyclable, and lightweight materials with high specific modulus, in competition with man-made fossil materials and fiberglass. Natural fibers are used for preparation of functionalized textiles to achieve smart and intelligent properties. However, the incorporation of these fibers in composite systems has been challenging due to their hydrophilic nature. Nevertheless, the fact that these biodegradable materials can be manipulated at a nano-scale to complement desired objective and application has made them a favorable option. The idea behind this project is to explore ways to convert green waste to high value materials and to utilize natural building blocks to design textile reinforcement materials. In this work, cellulose nanofibrils (CNF) supplied from the University of Maine were hydrophobized by silylation and characterized using Fourier-Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, and Thermogravimetric analysis (TGA). Results from FTIR spectroscopy showed a formation of Si-O-C bonds, indicating better fiber-matrix adhesion. Raman spectroscopy showed disruption of hydrogen bonding which indicates interference of parallel nanocellulose fiber adhesion to neighboring fibrils. The TGA suggests that the thermal stability of the functionalized CNF is higher than that of the corresponding neat sample, which could be a result of stable Si bond formation. The raw materials (neat and functionalized) were encapsulated in a polystyrene matrix through a solvent and non-solvent precipitation process, and then extruded using single and dual heat processing. The extruded thin filaments were tested according to the ASTM D638 (tensile test of plastics). Results showed an increasing Ultimate Tensile Strength (UTS) and Elastic Modulus, with peak values attributed to the dual-heat processing up to 79% and 69% increase respectively at 5wt% loading. Further increase was seen at 10wt% loading up to 112MPa UTS, and modulus up to 10.7GPa for the dual-heat processing. The UTS increase is assumed to be a result of linear arrangement of CNF in the matrix during the extrusion process. The results revealed the strong reinforcing ability of CNF and their compatibility with thermoplastic matrix if functionalized. / A Thesis submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the Master of Science. / Spring Semester 2016. / March 3, 2016. / Funtionalized nanofibrils, Hybrid Composites, Natural fibrils, Silynation, Textile composites, Treatment of nanofirbils / Includes bibliographical references. / Tarik J. Dickens, Professor Directing Thesis; Mei Zhang, Committee Member; Abhishek K. Shrivastava, Committee Member; Jhunu Chatterjee, Committee Member.

Electro-optic phase modulators play a vital role in various large-scale photonic systems including Light Detection and Ranging (LIDAR), quantum circuits, optical neural networks and optical communication links. The key requirement of these modulators include strong phase change with low modulation induced optical loss, low electrical power consumption, small device footprint and low fabrication complexity. Conventional silicon phase modulators have either high power consumption (thermo-optic effect) or high optical loss (plasma-dispersion effect). On the other hand, low-loss phase modulation can be achieved using electro-optic 𝑋² effect such as LiNbO₃ which has a large device footprint (in mm's) and requires complex fabrication. The need of the hour is a material or a device that is strongly tunable with low optical loss and capable of picosecond switching speed. Transition metal dichalcogenides (TMDs) have been widely studied for optoelectronic applications due to their strong and tunable excitonic response. In fact, TMDs have been shown to experience massive changes of upto 20 % in their refractive index with doping, but this modulation is accompanied with large absorption change (60 %), which greatly limits their utility in photonic applications. In contrast, very litte is known about the effect of doping on the electro-optic response of TMDs at energies far below the exciton resonances, where the material is transparent and therefore could be used for photonic circuits. In this work, we first probe the electro-optic properties of TMDs in the near-infrared using a dielectric SiN microring resonator platform. We measure a strong doping induced change in the refractive index (Δn) of 0.52 in WS2 with minimal induced absorption (Δk) of 0.004. The |Δn/Δk| of 125, is an order of magnitude higher than the measured |Δn/Δk| for 2D materials including graphene and TMD monolayer at excitonic resonances, and for bulk electro-refractive materials commonly employed in silicon photonics. We next utilize this strong electro-refractive response to demonstrate low power, lossless optical phase modulation based on a composite SiN-TMD platform. The WS₂ based photonic modulator achieves a modulation efficiency (V_π⋅L) of 0.8 V ⋅ cm with a RC limited bandwidth of 0.3 GHz and DC electrical power consumption of 0.64 nW. The measured index change in monolayer TMDs (∼ 15%) in TMDs is unprecedented, considering the change in index of bulk (LiNbO₃) - the 'gold standard' for photonics - is typically 0.04 %. Despite the observed strong electro-refractive effect in TMDs and the enhanced light-matter interaction, the change in effective index of the propagating mode is 6.5 × 10⁻⁴ RIU, thereby requiring WS₂ phase modulators that are 1.3 mm long. This is due to the low optical mode overlap of 0.03 % with the monolayer that necessitates long phase shifter length. There is an urgent need for a compact, low-loss and high-speed optical phase shifter. Conventional phase modulators with low optical loss require long lengths to achieve strong phase change. On the contrary, traditional intensity modulators leverage compact high-finesse ring resonators to modulate output intensity. However, such cavities with conventional electro-refractive materials such as silicon where Δn/Δk = -20 cannot be used for phase modulation, owing to the high insertion loss associated with the phase change. Here, we show that we can leverage high-finesse ring resonators to achieve strong phase change with low optical loss. We achieve this by simultaneously modulating both the real and imaginary part of the effective index in the cavity to the same extent i.e. Δn/Δk ≈1. We design a hybrid SiN-2D platform that modulates the complex effective index of the propagating mode, by tuning the loss and index in monolayer graphene (Gr) and WSe₂ embedded on a SiN waveguide, respectively. We engineer the Gr-WSe₂ capacitor design to achieve a linear phase change of (0.50 ± 0.05)π radians with a low transmission modulation of 1.73 ± 0.20 dB and insertion loss of 2.96 ± 0.34 dB. We measure a 3 dB electro-optic bandwidth of 14.9 ± 0.1 GHz in the SiN-2D hybrid platform. We measure a phase modulation efficiency (V_(π/2)⋅L) of 0.045 V ⋅ cm with an insertion loss of 4.7 dB for a phase change of π/2 radians in the 25 μm SiN-2D platform. We show that the V_(π/2)⋅L for our SiN-2D hybrid platform is significantly lower than V_(π/2)⋅L of electro-refractive phase modulators based on silicon PN, PIN and MOS capacitors with comparable insertion loss. The TMD or TMD-graphene capacitor is incorporated as a post-fabrication process, transforming any passive substrate into an active photonic platform. The demonstrated enhanced light-matter interaction in monolayer TMDs could open up routes to a range of novel applications with these 2D materials and enable highly reconfigurable photonic circuits with low optical loss and power dissipation. We estimate that the efficiency of our TMD platform can be improved by optimizing the optical mode overlap with the monolayer through photonic mode optimization or reducing the dielectric thickness. For large-scale photonic systems, wafer-scale integration of TMD materials with silicon photonics can be done either as a direct TMD growth process on silicon wafers or a post-processing step where large wafer-scale TMD films are transferred onto a silicon photonics platform fabricated in a standard foundry.