Emerging Nanophotonic Applications Explored with Advanced Scientific Parallel Computing

The domain of nanoscale optical science and technology is a combination of the classical world of electromagnetics and the quantum mechanical regime of atoms and molecules. Recent advancements in fabrication technology allows the optical structures to be scaled down to nanoscale size or even to the atomic level, which are far smaller than the wavelength they are designed for. These nanostructures can have unique, controllable, and tunable optical properties and their interactions with quantum materials can have important near-field and far-field optical response. Undoubtedly, these optical properties can have many important applications, ranging from the efficient and tunable light sources, detectors, filters, modulators, high-speed all-optical switches; to the next-generation classical and quantum computation, and biophotonic medical sensors. This emerging research of nanoscience, known as nanophotonics, is a highly interdisciplinary field requiring expertise in materials science, physics, electrical engineering, and scientific computing, modeling and simulation. It has also become an important research field for investigating the science and engineering of light-matter interactions that take place on wavelength and subwavelength scales where the nature of the nanostructured matter controls the interactions. In addition, the fast advancements in the computing capabilities, such as parallel computing, also become as a critical element for investigating advanced nanophotonic devices. This role has taken on even greater urgency with the scale-down of device dimensions, and the design for these devices require extensive memory and extremely long core hours. Thus distributed computing platforms associated with parallel computing are required for faster designs processes. Scientific parallel computing constructs mathematical models and quantitative analysis techniques, and uses the computing machines to analyze and solve otherwise intractable scientific challenges. In particular, parallel computing are forms of computation operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently. In this dissertation, we report a series of new nanophotonic developments using the advanced parallel computing techniques. The applications include the structure optimizations at the nanoscale to control both the electromagnetic response of materials, and to manipulate nanoscale structures for enhanced field concentration, which enable breakthroughs in imaging, sensing systems (chapter 3 and 4) and improve the spatial-temporal resolutions of spectroscopies (chapter 5). We also report the investigations on the confinement study of optical-matter interactions at the quantum mechanical regime, where the size-dependent novel properties enhanced a wide range of technologies from the tunable and efficient light sources, detectors, to other nanophotonic elements with enhanced functionality (chapter 6 and 7)

Emerging Nanophotonic Applications Explored with Advanced Scientific Parallel Computing

The domain of nanoscale optical science and technology is a combination of the classical world of electromagnetics and the quantum mechanical regime of atoms and molecules. Recent advancements in fabrication technology allows the optical structures to be scaled down to nanoscale size or even to the atomic level, which are far smaller than the wavelength they are designed for. These nanostructures can have unique, controllable, and tunable optical properties and their interactions with quantum materials can have important near-field and far-field optical response. Undoubtedly, these optical properties can have many important applications, ranging from the efficient and tunable light sources, detectors, filters, modulators, high-speed all-optical switches; to the next-generation classical and quantum computation, and biophotonic medical sensors. This emerging research of nanoscience, known as nanophotonics, is a highly interdisciplinary field requiring expertise in materials science, physics, electrical engineering, and scientific computing, modeling and simulation. It has also become an important research field for investigating the science and engineering of light-matter interactions that take place on wavelength and subwavelength scales where the nature of the nanostructured matter controls the interactions. In addition, the fast advancements in the computing capabilities, such as parallel computing, also become as a critical element for investigating advanced nanophotonic devices. This role has taken on even greater urgency with the scale-down of device dimensions, and the design for these devices require extensive memory and extremely long core hours. Thus distributed computing platforms associated with parallel computing are required for faster designs processes. Scientific parallel computing constructs mathematical models and quantitative analysis techniques, and uses the computing machines to analyze and solve otherwise intractable scientific challenges. In particular, parallel computing are forms of computation operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently. In this dissertation, we report a series of new nanophotonic developments using the advanced parallel computing techniques. The applications include the structure optimizations at the nanoscale to control both the electromagnetic response of materials, and to manipulate nanoscale structures for enhanced field concentration, which enable breakthroughs in imaging, sensing systems (chapter 3 and 4) and improve the spatial-temporal resolutions of spectroscopies (chapter 5). We also report the investigations on the confinement study of optical-matter interactions at the quantum mechanical regime, where the size-dependent novel properties enhanced a wide range of technologies from the tunable and efficient light sources, detectors, to other nanophotonic elements with enhanced functionality (chapter 6 and 7)

Probing the interaction between 2D materials and oligoglycine tectomers

Heterostructures of 2D materials using graphene and MoS2, have enabled both pivotal fundamental studies and unprecedented sensing properties. These heterosystems are intriguing when graphene and MoS2 are interfaced with 2D sheets that emulate biomolecules, such as amino-terminated oligoglycine self-assemblies (known as tectomers). The adsorption of tectomer sheets over graphene and MoS2 modulates the physicochemical properties through electronic charge migration and mechanical stress transfer. Here, we present a systematic study by Raman spectroscopy and tectomer-functionalised scanning probe microscopy to understand mechanical strain, charge transfer and binding affinity in tectomer/graphene and tectomer/MoS2 hybrid structures. Raman mapping reveals distinctive thickness dependence of tectomer-induced charge transfer to MoS2, showing p-doping on monolayer MoS2 and n-doping on multilayer MoS2. By contrast, graphene is n-doped by tectomer independently of layer number, as confirmed by X-ray photoelectron spectroscopy (XPS). The interfacial adhesion between the amino groups and 2D materials are further explored using tectomer-functionalised probe microscopy. It is demonstrated here that these probes have potential for chemically sensitive imaging of 2D materials, which will be useful for mapping chemically distinct domains of surfaces and the number of layers. The facile tectomer-coating approach described here is an attractive soft-chemistry strategy for high-density amine-functionalisation of AFM probes, therefore opening promising avenues for sensor applications

Tuning Photocurrent Responses from Photosystem I via Microenvironment Alterations: Effect of Plasmonic Electric Fields and Membrane Confinements

Robust photoelectrochemical activities of PSI make it an ideal candidate for bio-hybrid photovoltaic and optoelectronic devices. This dissertation focuses on role of microenvironment alterations around PSI in tuning its photocurrent responses when assembled with tailored plasmonic metal nanostructures and biomimetic lipid interfaces. To this end, a series of systematic studies aimed at tuning the plasmon enhanced photocurrent responses from PSI assembled with gold and silver metal nanopatterns tailored for different plasmonic absorption wavelengths. The experimental observation of plasmon-induced photocurrent enhancements in PSI is investigated using Fischer patterns of silver nanopyramids (Ag-NPs) wherein the resonant peaks were tuned to match the PSI absorption peaks at ~450 and ~680 nm. A conservative estimate for the enhancement factors were found to be ~ 5.8 – 6.5 when compared to PSI on planar Ag substrate assemblies. Furthermore, spatially localized and spectrally resolved wavelength-dependent plasmon-enhanced photocurrents from PSI are investigated by specifically assembling the protein units in regions around highly ordered Au (AuND) and Ag (AgND) nano-discs where the dipolar plasmon resonance modes from the respective NDs are tuned to the wavelengths of ~680 nm and ~560 nm, respectively. Specifically, we report plasmon-enhancement factors of ~6.8 and ~17.5 for the PSI photocurrents recorded under the excitation wavelengths of ~680 nm and ~565 nm respectively as compared to PSI assembled on planar ITO substrates. The results indicate: 1) direct correlations between the photocurrent enhancement spectra from the PSI assemblies and the plasmonic resonance modes for the respective nanopatterned substrates, and 2) broadband photocurrent enhancements due to plasmon-coupled photoactivation in the otherwise blind chlorophyll regions of the native PSI absorption spectra. In our continuing efforts to investigate the alterations in the photoexcitation/dissipation pathways in PSI due to characteristic changes in their optical and structural properties under biomimetic membrane confinements, , the PSI complexes are reconstituted in synthetic lipid membranes of 1,2-diphytanoyl-sn-glycero-3-phospho-(1ʹ-rac-glycerol) (DPhPG) and 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC). The results presented here from absorption, fluorescence and circular dichroism indicate unique changes around the carotenoid/chlorophyll spectral bands leading to attainment of broad-band light harvesting via enhanced absorption in the otherwise non-absorptive green region (500 – 580 nm) of unconfined PSI absorption spectra

Surface-enhanced raman detection of glucose on several novel substrates for biosensing applications

The small normal Raman cross-section of glucose is considered to be a major challenge for its detection by Surface Enhanced Raman Spectroscopy (SERS) for medical applications. These applications include blood glucose level monitoring of diabetic patients and evaluation of patients with other medical conditions, since glucose is a marker for many human diseases. This dissertation focuses on Surface-Enhanced Raman Scattering primarily for the detection of glucose. Some experiments also are carried out for the detection of the corresponding enzyme glucose oxidase that is used in electrochemical glucose sensors and in biofuel cells. This project explores the possibility of utilizing Surface Enhanced Raman Spectroscopy (SERS) with a variety of substrates (e.g., commercial gold substrates, nanocrystalline silver and gold nanoparticles, which are chemically assembled by citrate reduction on graphene-like sheets, silver nanoparticles on a commercial graphite sheet, and on electrochemically deposited polypyrrole conducting polymer) for glucose, rhodamine 6G (R6G) dye and glucose oxidase detection. These newly fabricated substrates can also be used for biosensing applications. The results of our study demonstrate that SERS is capable of detecting the molecules with high enhancement factor. This work reports the use of commercial multilayer graphene sheets as substrates on which gold nanoparticles are chemically assembled by citrate reduction. The results show that these substrates are capable of providing SERS enhancement factors of up to 1010 with a detection limit to 10-8 M in aqueous solutions of glucose. The SERS performance on graphene substrates are many orders of magnitude higher compared with results on gold-coated chemically etched Klarite® commercial silicon substrates. Also, drop-coated Ag on Toray® graphite microfiber sheets with partition layers exhibit the best results; they yield an excellent enhancement for R6G and glucose detection limit to 10-16 M and 10-12 M of the dye and glucose molecules, respectively. Also, the results show for the first-time enhancement for glucose from a SERS substrate that consist of electrochemically fabricated polypyrolle (PP) on Toray® graphite microfiber sheets

New frequencies and geometries for plasmonics and metamaterials

The manipulation of light at the nanoscale has become a fascinating research field called nanophotonics. It brings together a wide range of topics such as semiconductor quantum dots or molecular optoelectronics and the study of metal optics, or plasmonics, on one hand and the development of finely designed structures with specifically engineered optical properties called metamaterials on the other. As is often the case, it is at the boundary of these two domains that most novel effects can be observed. Plasmonics has for instance enabled the detection of single molecules due to the large field enhancement which exists in the vicinity of nanostructured metals. Thanks to the confinement of electromagnetic waves below the diffraction limit plasmonic systems are also foreseen as ideal conduits connecting electronic and photonic systems. On another hand, when a material is patterned on a scale smaller than the wavelength, its optical properties are reflections of the structure of the patterned material rather than the material itself, a concept known as metamaterial. This has allowed researchers to obtain exotic optical properties such as negative refractive indices and can be implemented in devices acting like invisibility cloaks or perfect lenses. While the prospects for nanophotonics are far-reaching, real-life applications are severely limited by the intrinsic absorption of metals and the current fabrication methods mostly based on electron-beam lithography which is slow and costly. In this thesis, we investigate these issues by considering the potentials of other polaritonic materials such as semiconductors, silicon carbide and graphene for field confinement applications. This is achieved through the combination of both numerical studies and sample fabrication and testing with the help of international collaborators. Our results show much improvement over the metallic structures typically used, with an operating range covering the near- and mid-infrared as well as the terahertz. The field compression can also be much greater compared to conventional plasmonic materials, with near-field enhancements reaching four orders of magnitude. Furthermore, we analyse theoretically the optical properties of metallic gyroids which are obtained by self-assembly - a promising chemical route for fabricating large-scale 3D structures with molecular sized resolution. These materials exhibit unexpected properties such as negative refraction and could in consequence be used as thin lenses or wave-plates. Last, we develop and apply a theoretical formulation of Fano theory for the case of plasmonics. It allows a clear and simple physical understanding of the interference spectra which are commonly encountered in nanooptics.Open Acces

Photonic Metasurfaces for Spatiotemporal and Ultrafast Light Control

The emergence of photonic metasurfaces - planar arrays of nano-antennas - has enabled a new paradigm of light control through wave-front engineering. Space-gradient metasurfaces induce spatially varying phase and/or polarization to propagating light. As a consequence, photons propagating through space-gradient metasurfaces can be engineered to undergo a change to their momentum, angular momentum and/or spin states

Visible quantum plasmonics from metallic nanodimers

We report theoretical evidence that bulk nonlinear materials weakly interacting with highly localized plasmonic modes in ultra-sub-wavelength metallic nanostructures can lead to nonlinear effects at the single plasmon level in the visible range. In particular, the two-plasmon interaction energy in such systems is numerically estimated to be comparable with the typical plasmon linewidths. Localized surface plasmons are thus predicted to exhibit a purely nonclassical behavior, which can be clearly identified by a sub-Poissonian second-order correlation in the signal scattered from the quantized plasmonic field under coherent electromagnetic excitation. We explicitly show that systems sensitive to single-plasmon scattering can be experimentally realized by combining electromagnetic confinement in the interstitial region of gold nanodimers with local infiltration or deposition of ordinary nonlinear materials. We also propose configurations that could allow to realistically detect such an effect with state-of-the-art technology, overcoming the limitations imposed by the short plasmonic lifetime