Browsing by Subject "Nanostructures"
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Item Open Access Actively Tunable Plasmonic Nanostructures(2020) Wilson, Wade MitchellActive plasmonic nanostructures with tunable resonances promise to enable smart materials with multiple functionalities, on-chip spectral-based imaging and low-power optoelectronic devices. A variety of tunable materials have been integrated with plasmonic structures, however, the tuning range in the visible regime has been limited and small on/off ratios are typical for dynamically switchable devices. An all optical tuning mechanism is desirable for on-chip optical computing applications. Furthermore, plasmonic structures are traditionally fabricated on rigid substrates, restricting their application in novel environments such as in wearable technology.
In this dissertation, I explore the mechanisms behind dynamic tuning of plasmon resonances, as well as demonstrate all-optical tuning through multiple cycles by incorporating photochromic molecules into plasmonic nanopatch antennas. Exposure to ultraviolet (UV) light switches the molecules into a photoactive state enabling dynamic control with on/off ratios up to 9.2 dB and a tuning figure of merit up to 1.43, defined as the ratio between the spectral shift and the initial line width of the plasmonic resonance. Moreover, the physical mechanisms underlying the large spectral shifts are elucidated by studying over 40 individual nanoantennas with fundamental resonances from 550 to 720 nm revealing good agreement with finite-element simulations.
To fully explore the tuning capabilities, the molecules are incorporated into plasmonic metasurface absorbers based on the same geometry as the single nanoantennas. The increased interaction between film-coupled nanocubes and resonant dipoles in the photochromic molecules gives rise to strong coupling. The coupling strength can be quantified by the Rabi-splitting of the plasmon resonance at ~300 meV, well into the ultrastrong coupling regime.
Additionally, fluorescent emitters are incorporated into the tunable absorber platform to give dynamic control over their emission intensity. I use optical spectroscopy to investigate the capabilities of tunable plasmonic nanocavities coupled to dipolar photochromic molecules. By incorporating emission sources, active control over the peak photoluminescence (PL) wavelength and emission intensity is demonstrated with PL spectroscopy.
Beyond wavelength tuning of the plasmon resonance, design and characterization is performed towards the development of a pyroelectric photodetector that can be implemented on a flexible substrate, giving it the ability to be conformed to new shapes on demand. Photodetection in the NIR with responsivities up to 500 mV/W is demonstrated. A detailed plan is given for the next steps required to fully realize visible to short-wave infrared (SWIR) pyroelectric photodetection with a cost-effective, scalable fabrication process. This, in addition to real-time control over the plasmon resonance, opens new application spaces for photonic devices that integrate plasmonic nanoparticles and actively tunable materials.
Item Open Access An ecological perspective on nanomaterial impacts in the environment.(J Environ Qual, 2010-11) Bernhardt, Emily S; Colman, Benjamin P; Hochella, Michael F; Cardinale, Bradley J; Nisbet, Roger M; Richardson, Curtis J; Yin, LiyanGrowing concerns over the potential for unintended, adverse consequences of engineered nanoparticles (ENPs) in the environment have generated new research initiatives focused on understanding the ecological effects of ENPs. Almost nothing is currently known about the fate and transport of ENPs in environmental waters, soils, and sediments or about the biological impacts of ENPs in natural environments, and the bulk of modern nanotoxicogical research is focused on highly controlled laboratory studies with single species in simple media. In this paper, we provide an ecological perspective on the current state of knowledge regarding the likely environmental impacts of nanomaterials and propose a strategy for making rapid progress in new research in ecological nanoscience.Item Open Access Conductance of a dissipative quantum dot: Nonequilibrium crossover near a non-Fermi-liquid quantum critical point(Physical Review B, 2021-10-25) Zhang, Gu; Novais, E; Baranger, Harold UWe find the nonlinear conductance of a dissipative resonant level in the nonequilibrium steady state near its quantum critical point. The system consists of a spin-polarized quantum dot connected to two resistive leads that provide ohmic dissipation. We focus on the crossover from the strong-coupling, non-Fermi-liquid regime to the weak-coupling, Fermi-liquid ground state, a crossover driven by the instability of the quantum critical point to hybridization asymmetry or detuning of the level in the dot. We show that the crossover properties are given by tunneling through an effective single barrier described by the boundary sine-Gordon model. The nonlinear conductance is then obtained from thermodynamic Bethe ansatz results in the literature, which were developed to treat tunneling in a Luttinger liquid. The current-voltage characteristics are thus found for any value of the resistance of the leads. For the special case of lead resistance equal to the quantum resistance, we find mappings onto, first, the two-channel Kondo model and, second, an effectively noninteracting model from which the nonlinear conductance is found analytically. A key feature of the general crossover function is that the nonequilibrium crossover driven by applied bias is different from the crossover driven by temperature—we find that the nonequilibrium crossover is substantially sharper. Finally, we compare to experimental results for both the bias and temperature crossovers: the agreement is excellent.Item Open Access Large-area nanopatterning of self-assembled monolayers of alkanethiolates by interferometric lithography.(Langmuir, 2010-08-17) Adams, J; Tizazu, G; Janusz, Stefan; Brueck, SRJ; Lopez, GP; Leggett, GJWe demonstrate that interferometric lithography provides a fast, simple approach to the production of patterns in self-assembled monolayers (SAMs) with high resolution over square centimeter areas. As a proof of principle, two-beam interference patterns, formed using light from a frequency-doubled argon ion laser (244 nm), were used to pattern methyl-terminated SAMs on gold, facilitating the introduction of hydroxyl-terminated adsorbates and yielding patterns of surface free energy with a pitch of ca. 200 nm. The photopatterning of SAMs on Pd has been demonstrated for the first time, with interferometric exposure yielding patterns of surface free energy with similar features sizes to those obtained on gold. Gold nanostructures were formed by exposing SAMs to UV interference patterns and then immersing the samples in an ethanolic solution of mercaptoethylamine, which etched the metal substrate in exposed areas while unoxidized thiols acted as a resist and protected the metal from dissolution. Macroscopically extended gold nanowires were fabricated using single exposures and arrays of 66 nm gold dots at 180 nm centers were formed using orthogonal exposures in a fast, simple process. Exposure of oligo(ethylene glycol)-terminated SAMs to UV light caused photodegradation of the protein-resistant tail groups in a substrate-independent process. In contrast to many protein patterning methods, which utilize multiple steps to control surface binding, this single step process introduced aldehyde functional groups to the SAM surface at exposures as low as 0.3 J cm(-2), significantly less than the exposure required for oxidation of the thiol headgroup. Although interferometric methods rely upon a continuous gradient of exposure, it was possible to fabricate well-defined protein nanostructures by the introduction of aldehyde groups and removal of protein resistance in nanoscopic regions. Macroscopically extended, nanostructured assemblies of streptavidin were formed. Retention of functionality in the patterned materials was demonstrated by binding of biotinylated proteins.Item Open Access Leveraging nanoscale plasmonic modes to achieve reproducible enhancement of light.(Nano Lett, 2010-10-13) Hill, Ryan T; Mock, Jack J; Urzhumov, Yaroslav; Sebba, David S; Oldenburg, Steven J; Chen, Shiuan-Yeh; Lazarides, Anne A; Chilkoti, Ashutosh; Smith, David RThe strongly enhanced and localized optical fields that occur within the gaps between metallic nanostructures can be leveraged for a wide range of functionality in nanophotonic and optical metamaterial applications. Here, we introduce a means of precise control over these nanoscale gaps through the application of a molecular spacer layer that is self-assembled onto a gold film, upon which gold nanoparticles (NPs) are deposited electrostatically. Simulations using a three-dimensional finite element model and measurements from single NPs confirm that the gaps formed by this process, between the NP and the gold film, are highly reproducible transducers of surface-enhanced resonant Raman scattering. With a spacer layer of roughly 1.6 nm, all NPs exhibit a strong Raman signal that decays rapidly as the spacer layer is increased.Item Open Access Modular nanotransporters: a multipurpose in vivo working platform for targeted drug delivery.(Int J Nanomedicine, 2012) Slastnikova, Tatiana A; Rosenkranz, Andrey A; Gulak, Pavel V; Schiffelers, Raymond M; Lupanova, Tatiana N; Khramtsov, Yuri V; Zalutsky, Michael R; Sobolev, Alexander SBACKGROUND: Modular nanotransporters (MNT) are recombinant multifunctional polypeptides created to exploit a cascade of cellular processes, initiated with membrane receptor recognition to deliver selective short-range and highly cytotoxic therapeutics to the cell nucleus. This research was designed for in vivo concept testing for this drug delivery platform using two modular nanotransporters, one targeted to the α-melanocyte-stimulating hormone (αMSH) receptor overexpressed on melanoma cells and the other to the epidermal growth factor (EGF) receptor overexpressed on several cancers, including glioblastoma, and head-and-neck and breast carcinoma cells. METHODS: In vivo targeting of the modular nanotransporter was determined by immuno-fluorescence confocal laser scanning microscopy and by accumulation of (125)I-labeled modular nanotransporters. The in vivo therapeutic effects of the modular nanotransporters were assessed by photodynamic therapy studies, given that the cytotoxicity of photosensitizers is critically dependent on their delivery to the cell nucleus. RESULTS: Immunohistochemical analyses of tumor and neighboring normal tissues of mice injected with multifunctional nanotransporters demonstrated preferential uptake in tumor tissue, particularly in cell nuclei. With (125)I-labeled MNT{αMSH}, optimal tumor:muscle and tumor:skin ratios of 8:1 and 9.8:1, respectively, were observed 3 hours after injection in B16-F1 melanoma-bearing mice. Treatment with bacteriochlorin p-MNT{αMSH} yielded 89%-98% tumor growth inhibition and a two-fold increase in survival for mice with B16-F1 and Cloudman S91 melanomas. Likewise, treatment of A431 human epidermoid carcinoma-bearing mice with chlorin e(6)- MNT{EGF} resulted in 94% tumor growth inhibition compared with free chlorin e(6), with 75% of animals surviving at 3 months compared with 0% and 20% for untreated and free chlorin e(6)-treated groups, respectively. CONCLUSION: The multifunctional nanotransporter approach provides a new in vivo functional platform for drug development that could, in principle, be applicable to any combination of cell surface receptor and agent (photosensitizers, oligonucleotides, radionuclides) requiring nuclear delivery to achieve maximum effectiveness.Item Open Access Nanofabrication at high throughput and low cost.(ACS Nano, 2010-07-27) Wiley, Benjamin J; Qin, Dong; Xia, YounanThe task of nanofabrication can, in principle, be divided into two separate tracks: generation and replication of the patterned features. These two tracks are different in terms of characteristics, requirements, and aspects of emphasis. In general, generation of patterns is commonly achieved in a serial fashion using techniques that are typically slow, making this process only practical for making a small number of copies. Only when combined with a rapid duplication technique will fabrication at high-throughput and low-cost become feasible. Nanoskiving is unique in that it can be used for both generation and duplication of patterned nanostructures.Item Open Access Nanotopography-induced changes in focal adhesions, cytoskeletal organization, and mechanical properties of human mesenchymal stem cells.(Biomaterials, 2010-02) Yim, Evelyn KF; Darling, Eric M; Kulangara, Karina; Guilak, Farshid; Leong, Kam WThe growth of stem cells can be modulated by physical factors such as extracellular matrix nanotopography. We hypothesize that nanotopography modulates cell behavior by changing the integrin clustering and focal adhesion (FA) assembly, leading to changes in cytoskeletal organization and cell mechanical properties. Human mesenchymal stem cells (hMSCs) cultured on 350 nm gratings of tissue-culture polystyrene (TCPS) and polydimethylsiloxane (PDMS) showed decreased expression of integrin subunits alpha2, alpha , alpha V, beta2, beta 3 and beta 4 compared to the unpatterned controls. On gratings, the elongated hMSCs exhibited an aligned actin cytoskeleton, while on unpatterned controls, spreading cells showed a random but denser actin cytoskeleton network. Expression of cytoskeleton and FA components was also altered by the nanotopography as reflected in the mechanical properties measured by atomic force microscopy (AFM) indentation. On the rigid TCPS, hMSCs on gratings exhibited lower instantaneous and equilibrium Young's moduli and apparent viscosity. On the softer PDMS, the effects of nanotopography were not significant. However, hMSCs cultured on PDMS showed lower cell mechanical properties than those on TCPS, regardless of topography. These suggest that both nanotopography and substrate stiffness could be important in determining mechanical properties, while nanotopography may be more dominant in determining the organization of the cytoskeleton and FAs.Item Open Access Surface-enhanced Raman scattering plasmonic enhancement using DNA origami-based complex metallic nanostructures.(Nano letters, 2014-01) Pilo-Pais, M; Watson, A; Demers, S; LaBean, TH; Finkelstein, GDNA origami is a novel self-assembly technique allowing one to form various two-dimensional shapes and position matter with nanometer accuracy. We use DNA origami templates to engineer surface-enhanced Raman scattering substrates. Specifically, gold nanoparticles were selectively placed on the corners of rectangular origami and subsequently enlarged via solution-based metal deposition. The resulting assemblies exhibit "hot spots" of enhanced electromagnetic field between the nanoparticles. We observed a significant Raman signal enhancement from molecules covalently attached to the assemblies, as compared to control nanoparticle samples that lack interparticle hot spots. Furthermore, Raman molecules are used to map out the hot spots' distribution, as they are burned when experiencing a threshold electric field. Our method opens up the prospects of using DNA origami to rationally engineer and assemble plasmonic structures for molecular spectroscopy.