R-3 Repository :: Browsing by Author "Halas, Naomi J."

Browsing by Author "Halas, Naomi J."

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A Detailed Clinical Case of Localized Prostate Tumors Treated with Nanoparticle-Assisted Sub-Ablative Laser Ablation
(MDPI, 2024) Kadria-Vili, Yara; Schwartz, Jon A.; Polascik, Thomas J.; Goodrich, Glenn P.; Jorden, David; Pinder, Diane; Halas, Naomi J.; Rastinehad, Ardeshir R.; Laboratory for Nanophotonics
AuroLase® Therapy—a nanoparticle-enabled focal therapy—has the potential to safely and effectively treat localized prostate cancer (PCa), preserving baseline functionality. This article presents a detailed case of localized PCa treated with AuroLase, providing insight on expectations from the diagnosis of PCa to one year post-treatment. AuroLase Therapy is a two-day treatment consisting of a systemic infusion of gold nanoshells (~150-nm hydrodynamic diameter) on Day 1, and sub-ablative laser treatment on Day 2. Multiparametric MRI (mpMRI) was used for tumor visualization, treatment planning, and therapy response assessment. The PCa was targeted with a MR/Ultrasound-fusion (MR/US) transperineal approach. Successful treatment was confirmed at 6 and 12 months post-treatment by the absence of disease in MR/US targeted biopsies. On the mpMRI, confined void space was evident, an indication of necrotic tissues encompassing the treated lesion, which was completely resolved at 12 months, forming a band-like scar with no evidence of recurrent tumor. The patient’s urinary and sexual functions were unchanged. During the one-year follow-up, changes on the DCE sequence and in the Ktrans and ADC values assist in qualitatively and quantitatively evaluating tissue changes. The results highlight the potential of gold-nanoparticle-enabled sub-ablative laser treatment to target and control localized PCa, maintain quality of life, and preserve baseline functionality.
A room-temperature mid-infrared photodetector for on-chip molecular vibrational spectroscopy
(AIP Publishing, 2018) Zheng, Bob; Zhao, Hangqi; Cerjan, Ben; Yazdi, Sadegh; Ringe, Emilie; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
Infrared (IR) photodetection is of major scientific and technical interest since virtually all molecules exhibit characteristic vibrational modes in the mid-infrared region of the spectrum, giving rise to molecular spectroscopy and chemical imaging in this wavelength range. High-resolution IR spectroscopies, such as Fourier Transform IR spectroscopy, typically require large, bulky optical measurement systems and expensive photodetector components. Here, we present a high-responsivity photodetector for the mid-IR spectral region which operates at room temperature. Fabricated from silicon and aluminum, the photodetection mechanism is based on free carrier absorption, giving rise to a photoresponse rivalling commercially available cooled IR photodetectors. We demonstrate that infrared spectra of molecules deposited on this detector can be obtained by a direct electrical read-out. This work could pave the way for simple, fully integrated chemical sensors and other applications, such as chemical imaging, which would benefit from the combination of mid-IR detection, room-temperature operation, and ultracompact portability.
Absorption Spectroscopy of an Individual Fano Cluster
(American Chemical Society, 2016) Yorulmaz, Mustafa; Hoggard, Anneli; Zhao, Hangqi; Wen, Fangfang; Chang, Wei-Shun; Halas, Naomi J.; Nordlander, Peter; Link, Stephan; Laboratory for Nanophotonics
Plasmonic clusters can exhibit Fano resonances with unique and tunable asymmetric line shapes, which arise due to the coupling of bright and dark plasmon modes within each multiparticle structure. These structures are capable of generating remarkably large local electromagnetic field enhancements and should give rise to high hot carrier yields relative to other plasmonic nanostructures. While the scattering properties of individual plasmonic Fano resonances have been characterized extensively both experimentally and theoretically, their absorption properties, critical for hot carrier generation, have not yet been measured. Here, we utilize single-particle absorption spectroscopy based on photothermal imaging to distinguish between the radiative and nonradiative properties of an individual Fano cluster. In observing the absorption spectrum of individual Fano clusters, we directly verify the theoretical prediction that while Fano interference may be prominent in scattering, it is completely absent in absorption. Our results provide microscopic insight into the nature of Fano interference in systems of coupled plasmonic nanoparticles and should pave the way for the optimization of hot carrier production using plasmonic Fano clusters.
Aluminum Nanocrystals
(American Chemical Society, 2015) McClain, Michael J.; Schlather, Andrea E.; Ringe, Emilie; King, Nicholas S.; Liu, Lifei; Manjavacas, Alejandro; Knight, Mark W.; Kumar, Ish; Whitmire, Kenton; Everitt, Henry O.; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
We demonstrate the facile synthesis of high purity aluminum nanocrystals over a range of controlled sizes from 70 to 220 nm diameter with size control achieved through a simple modification of solvent ratios in the reaction solution. The monodisperse, icosahedral, and trigonal bipyramidal nanocrystals are air-stable for weeks, due to the formation of a 2-4 nm thick passivating oxide layer on their surfaces. We show that the nanocrystals support size-dependent ultraviolet and visible plasmon modes, providing a far more sustainable alternative to gold and silver nanoparticles currently in widespread use.
Angle- and Spectral-Dependent Light Scattering from Plasmonic Nanocups
(2013-06-05) Li, Yang; Nordlander, Peter J.; Halas, Naomi J.; Link, Stephan
The interaction of light with small designed particles and structures gives rise to an increasing number of phenomena of potentially dramatic technological importance, such as metamaterials, superlens focusing, and enhanced spectroscopy. Metallic nanostructures with their geometry-dependent optical resonances are a topic of intense current interest due to their ability to manipulate light in ways not possible with conventional optical materials. A particularly fascinating aspect of these systems is the recently realized possibility of creating optical frequency “magnetic plasmon” responses of comparable magnitude to the “electric plasmon” response. Au nanocups at their magnetoinductive resonance have the unique ability to redirect scattered light in a direction dependent on cup orientation, as a true three-dimensional nanoantenna. As optical frequency nanoantennas, reduced-symmetry plasmonic nanoparticles have light-scattering properties that depend strongly on geometry, orientation, and variations in dielectric environment. Here we investigate how these factors influence the spectral and angular dependence of light scattered by Au nanocups. A simple dielectric substrate causes the axial, electric dipole mode of the nanocup to deviate substantially from its characteristic cos square free space scattering profile, while the transverse, magnetic dipole mode remains remarkably insensitive to the presence of the substrate. Nanoscale irregularities of the nanocup rim and the local substrate permittivity have a surprisingly large effect on the spectral- and angle-dependent light-scattering properties of these structures. The different angular scattering and wavelength response from the axial and transverse nanocup modes make the nanocup an interesting particle for the nanoscale manipulation of light in three dimensions. The sensitivity of this system to geometric and environmental factors may present opportunities for active, substrate-mediated control of light scattering.
Au Nanomatryoshkas as Efficient Near-Infrared Photothermal Transducers for Cancer Treatment: Benchmarking against Nanoshells
(American Chemical Society, 2014) Ayala-Orozco, Ciceron; Urban, Cordula; Knight, Mark W.; Urban, Alexander Skyrme; Neumann, Oara; Bishnoi, Sandra W.; Mukherjee, Shaunak; Goodman, Amanda M.; Charron, Heather; Mitchell, Tamika; Shea, Martin; Roy, Ronita; Nanda, Sarmistha; Schiff, Rachel; Halas, Naomi J.; Joshi, Amit
Au nanoparticles with plasmon resonances in the near-infrared (NIR) region of the spectrum efficiently convert light into heat, a property useful for the photothermal ablation of cancerous tumors subsequent to nanoparticle uptake at the tumor site. A critical aspect of this process is nanoparticle size, which influences both tumor uptake and photothermal efficiency. Here, we report a direct comparative study of ∼90 nm diameter Au nanomatryoshkas (Au/SiO2/Au) and ∼150 nm diameter Au nanoshells for photothermal therapeutic efficacy in highly aggressive triple negative breast cancer (TNBC) tumors in mice. Au nanomatryoshkas are strong light absorbers with 77% absorption efficiency, while the nanoshells are weaker absorbers with only 15% absorption efficiency. After an intravenous injection of Au nanomatryoshkas followed by a single NIR laser dose of 2 W/cm2 for 5 min, 83% of the TNBC tumor-bearing mice appeared healthy and tumor free >60 days later, while only 33% of mice treated with nanoshells survived the same period. The smaller size and larger absorption cross section of Au nanomatryoshkas combine to make this nanoparticle more effective than Au nanoshells for photothermal cancer therapy.
Buckminsterfullerene purification and buckminsterfullerene film characterization
(1994) Averitt, Richard Douglas; Halas, Naomi J.
A method is described which utilizes the difference in vapor pressure between C$\sb{60}$ and heavier fullerenes to produce C$\sb{60}$ powder with a purity of 99.97%. Using the material from this process allows for the growth of high purity polycrystalline C$\sb{60}$ thin films. These films are characterized using Raman spectroscopy and temperature dependent photoluminescence. The temperature dependence of the photoluminescence spectra indicates that both intermolecular and intramolecular processes are involved in the radiative recombination of the excited states. A model is proposed to describe the temperature dependence of the photoluminescence. A possible interpretation of this model is that there is a barrier to the formation of self trapped excitons.
Charge Transfer Plasmons: Optical Frequency Conductances and Tunable Infrared Resonances
(American Chemical Society, 2015) Wen, Fangfang; Zhang, Yue; Gottheim, Samuel; King, Nicholas S.; Zhang, Yu; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
A charge transfer plasmon (CTP) appears when an optical-frequency conductive pathway between two metallic nanoparticles is established, enabling the transfer of charge between nanoparticles when the plasmon is excited. Here we investigate the properties of the CTP in a nanowire-bridged dimer geometry. Varying the junction geometry controls its conductance, which modifies the resonance energies and scattering intensities of the CTP while also altering the other plasmon modes of the nanostructure. Reducing the junction conductance shifts this resonance to substantially lower energies in the near- and mid-infrared regions of the spectrum. The CTP offers both a high-information probe of optical frequency conductances in nanoscale junctions and a new, unique approach to controllably engineering tunable plasmon modes at infrared wavelengths.
Chemistry of novel nanoscale carbon materials: Nanodiamond and carbon nano-onions
(2006) Liu, Yu; Halas, Naomi J.
Nanoscience is the area of science concerning materials on the level of nanometer scale. Currently much of the discussion of nanoscience is focused on carbon-based nanostructures. Tremendous studies have been carried out on fullerenes and carbon nanotubes in the past a couple of decade due to their unique chemical and physical properties. This thesis studies the chemistry of the other two novel nanostructures in the carbon family: nanodiamond and carbon nano-onions. Nanodiamond is relatively a new engineering material with particular applications for fabrication of wear-resistant surface coatings, lubricating films and prototypes field emission displays. These materials are also of interest for studies of chemical reactivity stemming from their nanoscale particle sizes. The surface fluorination of nanodiamond at various temperatures yields a fluoro-nanodiamond with up to 8.6 at. % fluorine content. The fluoro-nanodiamond was used as a precursor for preparation of the series of functionalized nanodiamonds by subsequent reactions with alkyllithium reagents, diamines, and amino acids. The fluoro-nanodiamond and all derivatives were characterized by SEM, TEM, XRD, TG-MS, FTIR, XPS, and Raman measurements. In comparison with the pristine nanodiamond, all functionalized nanodiamonds show an improved solubility in polar organic solvents, e.g., alcohols and THF, and a reduced particle agglomeration. The fluoro-nanodiamond powder was also used as a precursor for diamond coating on solid substrate surface e.g. glass. This novel approach is based on the wet chemistry process (solution reaction) occurring at low temperature and resulting in a covalent bonding of tiny nanodiamond crystals to substrate through a molecular linker, 3-aminopropyltriethoxysilane (APTES). SEM, AFM and XPS were used for evaluation of surface morphology and elemental analysis to confirm the presence of diamond particles on surface. Carbon nano-onion studied in this thesis is another new material synthesized by our collaborators. The layer-by-layer structures make it a potential candidate as lubricant materials. The nano-onions were fluorinated at various temperatures resulting in fluoro-onions with different fluorine content. The inside layered structures are damaged due to fluorination, which was characterized by Raman, XRD, TEM et al. Defluorination treatment was also performed. All the samples show improved lubricating properties according to the test carried out by our collaborators.
Coherent Fano resonances in a plasmonic nanocluster enhance optical four-wave mixing
(National Academy of Sciences, 2013) Zhang, Yu; Wen, Fangfang; Zhen, Yu-Rong; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
Plasmonic nanoclusters, an ordered assembly of coupled metallic nanoparticles, support unique spectral features known as Fano resonances due to the coupling between their subradiant and superradiant plasmon modes. Within the Fano resonance, absorption is significantly enhanced, giving rise to highly localized, intense near fields with the potential to enhance nonlinear optical processes. Here, we report a structure supporting the coherent oscillation of two distinct Fano resonances within an individual plasmonic nanocluster. We show how this coherence enhances the optical four-wave mixing process in comparison with other doubleresonant plasmonic clusters that lack this property. A model that explains the observed four-wave mixing features is proposed, which is generally applicable to any third-order process in plasmonic nanostructures. With a larger effective susceptibility χ (3) relative to existing nonlinear optical materials, this coherent double-resonant nanocluster offers a strategy for designing high-performance thirdorder nonlinear optical media.
Compact solar autoclave based on steam generation using broadband light-harvesting nanoparticles
(National Academy of Sciences, 2013) Neumann, Oara; Feronti, Curtis; Neumann, Albert D.; Dong, Anjie; Schell, Kevin; Lu, Benjamin; Kim, Eric; Quinn, Mary; Thompson, Shea; Grady, Nathaniel; Nordlander, Peter; Oden, Maria; Halas, Naomi J.; Laboratory for Nanophotonics; Rice Quantum Institute
The lack of readily available sterilization processes for medicine and dentistry practices in the developing world is a major risk factor for the propagation of disease. Modern medical facilities in the developed world often use autoclave systems to sterilize medical instruments and equipment and process waste that could contain harmful contagions. Here, we show the use of broadband light-absorbing nanoparticles as solar photothermal heaters, which generate high-temperature steam for a standalone, efficient solar autoclave useful for sanitation of instruments or materials in resource-limited, remote locations. Sterilization was verified using a standard Geobacillus stearothermophilus-based biological indicator.
Complex Plasmonic Nanostructures: Symmetry Breaking and Coupled Systems
(2012) Lassiter, J. Britt; Halas, Naomi J.
Metallic nanostructures support resonant oscillations of their conduction band electrons called localized surface plasmon resonances. Plasmons couple efficiently to light and have enabled a new class of technology for the manipulation of light at the nanoscale. Nanostructures that support plasmon resonances have the potential for a wide range of applications such as enhanced optical spectroscopy techniques for chemical- and bio-sensing, cancer diagnosis and therapy, metamaterials, and energy harvesting. As the field of plasmonics has progressed, these applications have become more sophisticated, requiring increasingly complex nanostructures. For example, coupled nanostructures of two or more nanoparticles are used extensively in plasmon-enhanced spectroscopy techniques because they exhibit extremely large optical field enhancements. Asymmetric nanostructures, such as nanocups (metallic semishells), have been shown to support magnetic modes that could be used in metamaterials applications. This class of complex plasmonic nanostructures holds great potential for both the observation of new physical phenomena and practical applications. This thesis will focus on the fabrication and characterization of several examples of these complex nanostructures using darkfield spectroscopy. The plasmon modes of a dimer consisting of two nanoshells are investigated in both the separated and conductively overlapping regimes and are interpreted using the plasmon hybridization model. Next, coupled nanoclusters of seven particles arranged in a hexagonal pattern are studied. It is found that these nanoclusters support Fano resonances due to the coupling and interference of degenerate subradiant and superradiant plasmon modes. These structures are found to have an extremely high sensitivity to the local dielectric environment, making them attractive for biosensing applications. Variations on the nanocluster geometry are then explored, and it is observed that by adding more particles and varying their sizes, the lineshape of the Fano resonance can be precisely engineered. The underlying subradiant and superradiant modes are then analyzed using cathodoluminescence imaging and spectroscopy. Finally the plasmon modes of asymmetric nanostructures are measured. Nanoeggs (nanoshells with an offset core) and nanocups (metallic semishells) are fabricated by electron beam induced ablation, and their plasmon modes are measured. The plasmon modes of nanocups are studied in detail, and nanocups are found to support both electric and magnetic plasmons.
Computational chromatography: A machine learning strategy for demixing individual chemical components in complex mixtures
(PNAS, 2022) Bajomo, Mary M.; Ju, Yilong; Zhou, Jingyi; Elefterescu, Simina; Farr, Corbin; Zhao, Yiping; Neumann, Oara; Nordlander, Peter; Patel, Ankit; Halas, Naomi J.; Laboratory for Nanophotonics
Surface-enhanced Raman spectroscopy (SERS) holds exceptional promise as a streamlined chemical detection strategy for biological and environmental contaminants compared with current laboratory methods. Priority pollutants such as polycyclic aromatic hydrocarbons (PAHs), detectable in water and soil worldwide and known to induce multiple adverse health effects upon human exposure, are typically found in multicomponent mixtures. By combining the molecular fingerprinting capabilities of SERS with the signal separation and detection capabilities of machine learning (ML), we examine whether individual PAHs can be identified through an analysis of the SERS spectra of multicomponent PAH mixtures. We have developed an unsupervised ML method we call Characteristic Peak Extraction, a dimensionality reduction algorithm that extracts characteristic SERS peaks based on counts of detected peaks of the mixture. By analyzing the SERS spectra of two-component and four-component PAH mixtures where the concentration ratios of the various components vary, this algorithm is able to extract the spectra of each unknown component in the mixture of unknowns, which is then subsequently identified against a SERS spectral library of PAHs. Combining the molecular fingerprinting capabilities of SERS with the signal separation and detection capabilities of ML, this effort is a step toward the computational demixing of unknown chemical components occurring in complex multicomponent mixtures.
Concentric nanoshells and plasmon hybridization
(2004) Radloff, Corey J.; Halas, Naomi J.
The optical properties of metal nanostructures are related to their plasmon response, which is sensitively dependent on nanostructure geometry and environment. The metallodielectric, core-shell structure of nanoshells represents a unique geometry allowing for the systematic tunability of the plasmon resonance of the nanostructure. This is accomplished by varying the relative dimensions of the core and shell layers. Fabrication of a nanoshell particle with a strong plasmon resonance is dependent on shell quality, which is strongly dependent on the careful preparation of the metal shell. The resonant response of metal nanostructures can also be modified through plasmon-plasmon interactions. This work focuses on the fabrication of nanoparticles with a multilayer, concentric-shell structure consisting of a silica core, inner gold shell layer, silica spacer layer, and an outer gold shell layer. This concentric nanoshell particle is fabricated through the controlled growth of a nanometer-scale silica layer around a preformed nanoshell. The silica layer was found to increase the thermal and chemical stability of the nanoshell particles. A second gold shell could be grown on this layer to generate the concentric nanoshell particle. This layered nanoparticle geometry has a plasmon resonance dependent on the interaction between the inner and outer shell plasmons. This interaction can be explained in terms of a sphere-cavity model of plasmon hybridization derived from a semi-classical model of the plasmon resonance. Varying the dimensions of the concentric shell layers can independently and systematically control the plasmon resonance of the inner and outer shell, which effects the interaction between the two plasmons. The coupling between the inner and outer shell plasmons was investigated experimentally by varying the concentric nanoshell dimensions, specifically examining how the spectral detuning of the inner and outer shell resonances and spatial interaction between inner and outer shell plasmons determine the nanoparticle's optical properties. Calculations using Mie scattering theory to model the nanoshell plasmon response agree quantitatively with experimental measurements of the nanoshell plasmon resonance in both the single-layer and multi-layer regime.
Coupling of nanoparticle and metallodielectric grating plasmons
(2007) Dumoit, Jeremy M.; Halas, Naomi J.
Coupled plasmonic systems have been in the limelight recently for both their interesting fundamental physical properties, and their possible applications in sensing and optoelectrical system integration. Planar plasmonic systems, which can couple propagating and localized plasmons, show promise for integration of future on-chip optoelectronic devices. This thesis investigates such a system consisting of a planar metallodielectric grating coupled to spherical gold nanoparticles. It is shown that the addition of gold nanoparticles to a silver metallodielectric grating system can produce a profound change in the resonance response of the system. This coupling is shown to depend strongly on the size and surface coverage density of the gold nanoparticles.
Delivery of nanoparticles to brain metastases of breast cancer using a cellular Trojan horse
(Springer, 2012) Choi, Mi-Ran; Bardhan, Rizia; Stanton-Maxey, Katie J.; Badve, Sunil; Nakshatri, Harikrishna; Stantz, Keith M.; Cao, Ning; Halas, Naomi J.; Clare, Susan E.; Laboratory for Nanophotonics
As systemic cancer therapies improve and are able to control metastatic disease outside the central nervous system, the brain is increasingly the first site of relapse. The blood-brain barrier (BBB) represents a major challenge to the delivery of therapeutics to the brain. Macrophages originating from circulating monocytes are able to infiltrate brain metastases while the BBB is intact. Here, we show that this ability can be exploited to deliver both diagnostic and therapeutic nanoparticles specifically to experimental brain metastases of breast cancer.
Diverse Applications of Nanomedicine
(American Chemical Society, 2017) Pelaz, Beatriz; Alexiou, Christoph; Alvarez-Puebla, Ramon A.; Alves, Frauke; Andrews, Anne M.; Ashraf, Sumaira; Balogh, Lajos P.; Ballerini, Laura; Bestetti, Alessandra; Brendel, Cornelia; Bosi, Susanna; Carril, Monica; Chan, Warren C.W.; Chen, Chunying; Chen, Xiaodong; Chen, Xiaoyuan; Cheng, Zhen; Cui, Daxiang; Du, Jianzhong; Dullin, Christian; Escudero, Alberto; Feliu, Neus; Gao, Mingyuan; George, Michael; Gogotsi, Yury; Grünweller, Arnold; Gu, Zhongwei; Halas, Naomi J.; Hampp, Norbert; Hartmann, Roland K.; Hersam, Mark C.; Hunziker, Patrick; Jian, Ji; Jiang, Xingyu; Jungebluth, Philipp; Kadhiresan, Pranav; Kataoka, Kazunori; Khademhosseini, Ali; Kopeček, Jindřich; Kotov, Nicholas A.; Krug, Harald F.; Lee, Dong Soo; Lehr, Claus-Michael; Leong, Kam W.; Liang, Xing-Jie; Lim, Mei Ling; Liz-Marzán, Luis M.; Ma, Xiaowei; Macchiarini, Paolo; Meng, Huan; Möhwald, Helmuth; Mulvaney, Paul; Nel, Andre E.; Nie, Shuming; Nordlander, Peter; Okano, Teruo; Oliveira, Jose; Park, Tai Hyun; Penner, Reginald M.; Prato, Maurizio; Puntes, Victor; Rotello, Vincent M.; Samarakoon, Amila; Schaak, Raymond E.; Shen, Youqing; Sjöqvist, Sebastian; Skirtach, Andre G.; Soliman, Mahmoud G.; Stevens, Molly M.; Sung, Hsing-Wen; Tang, Ben Zhong; Tietze, Rainer; Udugama, Buddhisha N.; VanEpps, J. Scott; Weil, Tanja; Weiss, Paul S.; Willner, Itamar; Wu, Yuzhou; Yang, Lily; Yue, Zhao; Zhang, Qian; Zhang, Qiang; Zhang, Xian-En; Zhao, Yuliang; Zhou, Xin; Parak, Wolfgang J.
The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.
Efficient Second Harmonic Generation in a Hybrid Plasmonic Waveguide by Mode Interactions
(American Chemical Society, 2019) Shi, Junjun; Li, Yang; Kang, Meng; He, Xiaobo; Halas, Naomi J.; Nordlander, Peter; Zhang, Shunping; Xu, Hongxing; Laboratory for Nanophotonics
Developing highly efficient nanoscale coherent light sources is essential for advances in technological applications such as integrated photonic circuits, bioimaging, and sensing. An on-chip wavelength convertor based on second harmonic generation (SHG) would be a crucial step toward this goal, but the light-conversion efficiency would be low for small device dimensions. Here we demonstrate strongly enhanced SHG with a high conversion efficiency of 4 × 10–5 W–1 from a hybrid plasmonic waveguide consisting of a CdSe nanowire coupled with a Au film. The strong spatial overlap of the waveguide mode with the nonlinear material and momentum conservation between the incident and reflected modes are the key factors resulting in such high efficiency. The SHG emission angles vary linearly with excitation wavelength, indicating a nonlinear steering of coherent light emission at the subwavelength scale. Our work is promising for the realization of efficient and tunable nonlinear coherent sources and opens new approaches for efficient integrated nonlinear nanophotonic devices.
Electrical properties of thin film carbon(60) (fullerenes, excimer lasers)
(1993) Sarkar, Dipankar; Halas, Naomi J.
The fabrication of solid C$\sb{60}$ device structures by vacuum sublimation methods is described. The experimentally determined threshold of intrinsic conductivity of solid C$\sb{60}$ is $\sim$1.5eV. The observations of ohmic contact and photoinduced voltages in C$\sb{60}$ sandwich structures are observed and explained. The diffusion of silver into C$\sb{60}$ thin films is quantitatively studied. The activation energy for diffusion of silver into C$\sb{60}$ is estimated at 2.5 $\pm$ 0.5 eV. Experiments on KrF excimer laser-induced ablation and the laser-induced conductivity change in solid C$\sb{60}$ are done for the first time.
Engineered Plasmonic Nanostructures: Fano Resonance Response, Magnetic Plasmon Resonance for Waveguiding and Hot Electron Induced Photochemistry
(2013-08-05) Mukherjee, Shaunak; Halas, Naomi J.; Nordlander, Peter J.; Hafner, Jason H.
Surface plasmons are collective and coherent oscillations of conduction band electrons in metal nanostructure which enable coupling of photons to electrons at a metal dielectric interface. Plasmonic nanostructures have gained much attention due to their ability to confine, tune and manipulate light for specific applications simply by varying their geometries and local dielectric environment. This thesis will focus on designing and studying fundamental plasmonic properties of Au nanostructures for applications in photothermal cancer therapy, chemical sensing, optical waveguiding, and room temperature gas phase photocatalysis. First, this thesis focuses on spherically concentric nanoparticles, a rudimentary “nanomatryushka”, composed of a silica-coated gold nanosphere surrounded by a gold shell layer. These nanoparticles were synthesized using wet chemistry technique and were found to possess exceptional geometrically tunable optical resonances in a compact, sub-100 nm size. Changing the internal geometry of the nanoparticle not only shifts its resonance frequencies, but can also strongly modifies the relative magnitudes of the absorption and scattering cross sections, independent of nanoparticle size. In addition the inherent asymmetry of each individual Au/SiO2/Au nanomatryushka generate multiple Fano resonances due to the overlapping bright superradiant and dark subradiant plasmon modes. Fano resonances have immense potential for single particle localized surface plasmon sensing applications. Next, this thesis investigates a new class of waveguiding consisting of chains of fused heptamer nanodiscs. This novel waveguiding structure transports electromagnetic energy via magnetic plasmon resonance mode. In this new geometry, heptamer structure serves as a benzene-like subdiffraction limit building blocks which support antiphase magnetic plasmons with “antiferromagnetic” behavior in multiple repeated structures. By repeating the heptamer units, this waveguide enables low-loss magnetic plasmon propagation along linear chains, steering over large-angle bends and splitting. It has numerous potential uses in energy transport, data storage, near-field microscopy, and other nanophotonic applications. Finally, this thesis explores the use of Au-photocatalysts as multifunctional catalysts for enhanced reactivity and efficiency. Au-photocatalysts were used for room temperature dissociation of H2 on Au nanoparticle surface using visible light. Surface plasmons excited in the Au nanoparticle decay into hot electrons which can be transferred into an antibonding resonance of an H2 molecule adsorbed on the Au nanoparticle surface, triggering dissociation. This process is probed by detecting the formation of HD molecules from the dissociations of H2 and D2. The rate of dissociation was also profoundly dependent on of intensity and wavelength of excitation light. This work demonstrates an important application of plasmonics in the field of heterogeneous photocatalysis opening up a new pathway for all optical control of chemical reactions on metallic catalysts.

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