Molecular photoabsorption enhancement under ambient solar radiations can improve efficiency substantially in renewable energy production. Here, we explore the theoretical basis and experimental evidences that nanostructured molecular assemblies exhibit an unprecedented property of synergistic photon absorption enhancement. The molecular mechanism of this enhancement phenomenon originates from the combined effect of the photon-molecule interaction and the electronic energy transfer between two adjacent molecular assemblies. For a natural system, the synergistic photon absorption enhancement factor of green algae (Chlorella vulgaris) in vivo at 632.8 nm was determined to be 103. This enhanced photon absorption process in nanostructured molecular assemblies opens a doorway to create entangled double excitons by incoherent solar radiations.

With the raise of nanotechnology researching, many special physical and chemical properties were found gradually in nanoscale. Among them, the one-dimension nanostructure owns high specific surface area and excellent electron emission properties. Moreover, the two-dimension arrayed nanostructure has the characteristics of photonic crystal and moth-eye effect. Currently, advanced lithographic methods such as electron beam (E-beam) or deep ultraviolet (DUV) lithography and X-ray lithography are adopted to define periodic nanoscale patterns. But these lithographic equipment are too expensive. Moreover, costly etching methods such as inductively coupled plasma reactive ion etching (ICP-RIE) or electron cyclotron resonance reactive ion etching (ECR-RIE) must be used to form arrayed silicon nanostructure with high aspect ratios. The nanoscale array patterns can be defined on the surface of the silicon wafer by the self-assembly of a polystyrene nanosphere. The photo-assisted electrochemical etching (PAECE) has the advantage of forming nanopore, and the aspect ratio of etched nanopores can be as high as 50:1 which is better than ICP-RIE. Therefore, PAECE is very suitable to fabricate nanostructure. This high-cost drawback makes most of academias and small/medium enterprises hard to invest in nanotechnology. This study combines the self-assembly nanosphere lithography (SANSL) process and photo-assisted electrochemical etching to fabricate a nanostructure array with a high aspect ratio on the surface of a silicon wafer. Experimental results show that the nanosphere array with a nearly perfect arrangement can be obtained in the sample of 1.8 ∗1.8 cm2 by spin coating and vibration coating. Using reactive ion etching (RIE) can transfer the nanosphere array pattern to the silicon nitride layer, and form the etching window of PAECE. The concentration of the HF electrolyte used in PAECE was 2.5 wt%. When PAECE was performed with etching mask can produce deeper and periodic nanopores. The surfactant of SDSS added in the HF electrolyte of PAECE can reduce the contact angle of electrolyte and avoid the phenomenon of hole-reaming. When the voltage of 1 V is used to etch for 12.5 min, the etching depth of the nanopore array structure is about 5.69 £gm and its diameter is about 90 nm, such that the aspect ratio of the pore can reach about 63:1. If the etching voltage was increased, the width of pore will be increased and the depth of pore will be reduced gradually at the same time. When the etching voltage of 2 V is applied to etch for 5 min, the etching height of the nanopillar is about 2 £gm and its diameter is about 100 nm, such that the aspect ratio of the pillar can reach about 20:1. The nanopillar was arranged periodically according to the definition of nanosphere, therefore the arrayed nanopillar can be realized successfully. Dropping the solution which has biological samples into the gap of nanopillar, it will affect the light which goes through the nanostructure and produce specific parameters of polarization. The results showed that when the DI water was dropped into the nanopillar structure, the degree of polarization (DOP) is 0.981, azimuth is 4.86¢X and ellipticity is 2.83¢X. When the solution which has alkaline lysis plasmid of 5 £gg/ml was dropped into the nanopillar structure, the DOP is 0.957, azimuth is 7.7¢X and ellipticity is 3.99¢X. The result shows that the change of polarization parameter has the relations with the concentration of biological samples in solution. Therefore, the measure system can be combined with nanopillar array to develop the photonic crystal biosensor. This study also applies the developed nanopore nanostructure array to fabricate sub-wavelength antireflection structure of solar cell. Experimental results show that the deeper in structure and then the better in antireflective effect. After performing 1 V PAECE for 5 min, the weighted mean reflectance can be reduced to 1.73% under the wavelength range of 280¡V890 nm. Further coating of a silicon nitride layer on the surface of a nanostructure array reduces the weighted mean reflectance even to 0.878 %. Finally, this study also uses various voltage of PAECE to produce nanostructure array with different surface area for the electrode fabrication of fuel cell. Experimental results show that the larger in surface area of sample and then the better in catalysis effect. Two-staged PAECE of 1.5 V and 1.75 V can yield nanopillar with surface area of 14.2 cm2 , which is about 50.2 times higher than a planar electrode. When the surface of such a nanopillar array is coated with platinum of 1000 Å, the reaction current of nanopillar array is 10.2 mA, which is 72.9 times higher than that obtained by only a planar electrode.

The work presented in this dissertation suggests novel design of chemical plasmonic sensors which have been developed based on Localized Surface Plasmon Resonance (LSPR), and Surface-enhanced Raman scattering (SERS) phenomena. The goal of the study is to understand the SERS phenomena for 3D hybrid (organic/inorganic) templates and to design of the templates for trace-level detection of selected chemical analytes relevant to liquid explosives and hazardous chemicals. The key design criteria for the development of the SERS templates are utilizing selective polymeric nanocoatings within cylindrical nanopores for promoting selective adsorption of chemical analyte molecules, maximizing specific surface area, and optimizing concentration of hot spots with efficient light interaction inside nanochannels. The organic/inorganic hybrid templates are optimized through a comprehensive understanding of the LSPR properties of the gold nanoparticles, gold nanorods, interaction of light with highly porous alumina template, and the choice of physical and chemical attributes of the selective coating. Furthermore, novel method to assemble silver nanoparticles in 3D as the active SERS-active substrate has been demonstrated by uniform, in situ growth of silver nanoparticles from electroless deposited silver seeds excluding any adhesive polymer layer on template. This approach can be the optimal for SERS sensing applications because it is not necessary to separate the Raman bands of the polyelectrolyte binding layer from those of the desired analyte. The fabrication method is an efficient, simple and fast way to assemble nanoparticles into 3D nanostructures. Addressable Raman markers from silver nanowire crossbars with silver nanoparticles are also introduced and studied. Assembly of silver nanowire crossbar structure is achieved by simple, double-step capillary transfer lithography. The on/off SERS properties can be observed on silver nanowire crossbars with silver nanoparticles depending on the exact location and orientation of decorated silver nanoparticles nearby silver nanowire crossbars. As an alternative approach for the template-assisted nanostructure design, porous alumina membrane (PAM) can be utilized as a sacrificial template for the fabrication of the nanotube structure. The study seeks to investigate the design aspects of polymeric/inorganic hybrid nanotube structures with plasmonic properties, which can be dynamically tuned by external stimuli such as pH. This research suggests several different organic/inorganic nanostructure assemblies by various template-assisted techniques. The polymeric/inorganic hybrid nanostructures including SERS property, pH responsive characteristics, and large surface area will enable us to understand and design the novel chemical plasmonic sensors.

Self-organization of block copolymers becomes attractive for several branches of the current science and technology, which requires a cheap way of fabrication of well-ordered arrays of various nanoobjects. High ratio between the surface (or the interface) and the volume of the nanoobjects enables development of very efficient devices. The work within this thesis profits from the chemical dissimilarity between blocks of polystyrene-block-poly(4‑vinylpyridine) copolymers, where polystyrene forms “a body” of nanostructures and poly(4‑vinylpyridine) is “a link” for assemblies with low-molar-mass additives. Procedures and phenomena are demonstrated (observed) on few sorts of PS‑b‑P4VP copolymers with respect to their molecular weight and ratio of blocks. Although there are many kinds of nanostructures based on block copolymers, only nanotemplates are involved in the study. Their properties, like an influence of substrate roughness on microphase separation, stability of porous nanotemplates in ionized solutions, or a role of additives in their supramolecular assembly, respectively, are investigated. All of them appears to be important in development of various devices based on the nanotemplates. With respect to optoelectronic applications, electrical current transport and fluorescence are two basic phenomena studied on functionalized nanotemplates, developed in the thesis. DC transport is studied on nanostructures developed via sputtering of chromium into porous nanotemplates. Sputtering process is optimized in dependence of chromium deposition rate, composition and pressure of ambient gas. It is shown that a reactive nature of PS-b-P4VP nanotemplates enables development of resistant organometallic nanotemplates. On the other hand, suppression of the polymer reactivity is achieved by oxidation of a metal during sputtering in a reactive gas, which enables e. g. development of highly ordered TiO2 nanodots. Current-voltage characteristics are measured on “sandwich” devices (like LEDs) with various electrodes and composition. Several recent theoretical models fitting the characteristics are applied together with structural characterization techniques (like AFM or x-ray reflectivity) in order to elucidate relations among surface roughness, distribution of sputtered clusters, and carrier injection and transport. Fluorescence is studied on nanotemplates with organic low-molar-mass dyes, developed either via direct blending with the copolymer or via soaking of porous nanotemplates in dye solutions. Several relations between structure and fluorescence are observed. For instance, excimer emission in pyrene assemblies is supressed after ordering of the nanotemplate. Solvent induced orientation of fluorescein molecules in the nanotemplate results in fluorescence enhancement. Dimerization of Rhodamine 6G is dependent on the way of its impregnation in the nanotemplates (solvent, concentration, speed).

L'objectif des travaux présentés ci-après est d'inventer de nouveaux matériaux magnétiques fonctionnels pour des applications innovantes dans le domaine du génie électrique. L'approche scientifique développée depuis les prémices de ma thèse est basée sur la compréhension des processus d'aimantation mis en jeu à l'échelle nanométrique (comportement individuel) et à l'échelle macroscopique dans des matériaux hétérogènes nanostructurés (comportement collectif). Ce travail s'appuie sur un large partenariat interdisciplinaire depuis la chimie (élaboration des matériaux, analyse structurale) jusqu'à la physique (processus d'aimantation, interactions hyperfines, nanostructure magnétique) sans oublier l'ingénierie (mise en forme) et les industriels, sur le plan national et international. Cette démarche s'inscrit dans une logique de "bas en haut" (bottom-up en langage savant) telle qu'elle sera décrite plus loin en détails.<br />Dans un premier temps, nous tenterons de définir les concepts scientifique qui caractérisent la science des nanomatériaux dans son ensemble et de proposer une nouvelle classification des nanomatériaux. Nous ferons appel aussi bien à des théories scientifiques établies qu'à une étude étymologique aux frontières de la physique et de la sémantique. Dans un deuxième temps, nous nous livrerons à une série "d'expériences théoriques" sur le nanomagnétisme, c'est à dire que nous nous efforcerons, en partant du concept d'anisotropie aléatoire, d'introduire des concepts théoriques originaux dans la simulation des propriétés magnétiques des matériaux nanostructurés. Dans un troisième temps enfin, nous tenterons de faire une analyse critique des travaux menés jusqu'à aujourd'hui dans le domaine des matériaux nanocristallisés à partir d'un précurseur amorphe et de leurs transitions magnétiques variées à haute température (superparamagnétisme, couplages d'échange...), sur les matériaux composités doux à base de nanopoudres et sur la structure magnétique des nanoparticules. Enfin, nous tenterons d'en tirer des conclusions utiles pour l'orientation des actions futures.

L'ensemble des résultats décrits dans la thèse constitue une contribution a l' etude des relaxations diélectriques dans des céramiques de structure perovskite qu'elles soient férroelectriques ou relaxeurs. Ils ont montré les relations étroites entre fréquence de relaxation, température de transition, nanostructure et liaison chimique. Ils permettent d'entrevoir des lois qui régissent la variation des caractéristiques des relaxations avec la nature des substitutions cationiques, le rapport entre le nombre d'atomes B' et B'' en site octaédrique, l'ordre ou le désordre

Bacteria primarily exist in robust, surface-associated communities known as biofilms, ubiquitous in both natural and anthropogenic environments. Mature biofilms resist a wide range of biocidal treatments and pose persistent pathogenic threats. Treatment of adherent biofilm is difficult, costly, and, in medical systems such as catheters, frequently impossible. Adding to the challenge, we have discovered that biofilm can be both impenetrable to vapors and extremely nonwetting, repelling even low surface tension commercial antimicrobials. Our study shows multiple contributing factors, including biochemical components and multiscale reentrant topography. Reliant on surface chemistry, conventional strategies for preventing biofilm only transiently affect attachment and/or are environmentally toxic. In this work, we look to Nature’s antifouling solutions, such as the dynamic spiny skin of the echinoderm, and we develop a versatile surface nanofabrication platform. Our benchtop approach unites soft lithography, electrodeposition, mold deformation, and material selection to enable many degrees of freedom—material, geometric, mechanical, dynamic—that can be programmed starting from a single master structure. The mechanical properties of the bio-inspired nanostructures, verified by AFM, are precisely and rationally tunable. We examine how synthetic dynamic nanostructured surfaces control the attachment of pathogenic biofilms. The parameters governing long-range patterning of bacteria on high-aspect-ratio (HAR) nanoarrays are combinatorially elucidated, and we discover that sufficiently low effective stiffness of these HAR arrays mechanoselectively inhibits ~40% of Pseudomonas aeruginosa biofilm attachment. Inspired by the active echinoderm skin, we design and fabricate externally actuated dynamic elastomer surfaces with active surface microtopography. We extract from a large parameter space the critical topographic length scales and actuation time scales for achieving nearly ~80% attachment reduction. We furthermore investigate an atomically mobile, slippery liquid infused porous surface (SLIPS) inspired by the pitcher plant. We show up to 99.6% reduction of multiple pathogenic biofilms over a 7-day period under both static and physiologically realistic flow conditions—a ~35x improvement over state-of-the-art surface chemistry, and over a far longer timeframe. Moreover, SLIPS is shown to be nontoxic: bacteria simply cannot attach to the smooth liquid interface. These bio-inspired strategies significantly advance biofilm attachment prevention and promise a tremendous range of industrial, clinical, and consumer applications. / Engineering and Applied Sciences

A novel lithographic fabrication method is used to fabricate nanopillars arrays of anisotropic Ag and TCO electrodes. Optical and electrical properties of the electrodes including bandgap, free carrier concentration, resistivity and surface plasmon frequency of different electrodes can be tuned by adjusting the dimensions and geometry of the pillars. Given the ability to tune the nonlocal responses of the plasmonic field enhancements, we attempt to determine the nature of the effective refractive index profile within the visible wavelength region for multi-layer hybrid nanostructures. Knowledge of the effective optical constants of the obtained structure is critical for various applications. nanopillars of TCO\Ag core shell structures have been successfully fabricated. The Maxwell-Garnett mixing law has been used to determine the optical constants of the nanostructure based on spectroscopic ellipsometry measurements. Simulated reflection spectra indicate a down shift in the Brewster angle of the pillars resulting from the reduction in the effective refractive index of the nanostructure. Two plasmonic resonances were observed, with one in the visible region and the other in the IR region. Plasmon hybridization model is used to describe the behavior of metal and metal oxide core shell nanostructured electrodes. Different charge density distributions around the pillars determine the plasma frequency which depends on the core and surrounding media dielectric constants. Finite Difference Time Domain (FDTD) simulation of different structures agree well with experiment and help us to understand electric field behavior at different structures with different geometries and dielectric constants. Plasmonic Ag nanopillar arrays are effective substrates for surface enhanced Raman spectroscopy (SERS). An enhancement factor up to 6 orders of magnitude is obtained. Monolayers of C60 is deposited on the Ag nanopillars and the interface of C60/Ag is studied which is important in optoelectronic devices. Electron delocalization between C60 and Ag is confirmed.

A close relation between structural and optical properties of any semiconductor material does exist. An adequate knowledge and understanding of this relationship is necessary for fabrication of devices with desired optical properties. The structural quality and hence the optical properties can be influenced by the growth method and the substrate used. The aim of this work was to investigate the change in optical properties caused by growth techniques and substrate modification. To study the influence of growth technique on optical properties, ZnO nanostructures were grown using atmospheric pressure metal organic chemical vapor deposition (APMOCVD) and chemical bath deposition (CBD) technique. The structural and optical investigations were performed using scanning electron microscopy (SEM) and micro photoluminescence (μ-PL), respectively. The results revealed that the grown structures were in the shape of nano-rods with slightly different shapes. Optical investigation revealed that low temperature PL spectrum for both the samples was dominated by neutral donor bound excitons emission and it tends to be replaced by free exciton (FX) emission in the temperature range of 60-140K. Both excitonic emissions show a typical red-shift with increase in temperature but with a different temperature dynamics for both the sample and this is due to difference in exciton-phonon interaction because of the different sizes of nano-rods. Defect level emission (DLE) is negligible in both the sample at low temperature but it increased linearly in intensity after 130 K up to the room temperature.Modification in substrate can also play a significant role on structural and optical properties of the material. Specially variation in the miscut angle of substrate can help to control the lateral sizes of the Nanostructures and thus can help to obtain better structural andoptical quality. Also optical quality is a key requirement for making blue and ultraviolet LEDs. Therefore, ZnO Nanostructures were grown on SiC on-axis and off-axis substrates having different off-cut angles. Morphological investigation revealed thatgrown structures are epitaxial for the case when substrate off-cut angle is higher and deposition rate is low. Low temperature PL spectrum of all the samples was dominated by neutral donor bound excitons and free exciton emission become dominant at 100 K for all the samples which completely eliminate the neutral donor bound excitonic emission at 160K. Two electron satellite of the neutral donor bound excitons and LO phonons of excitonic features are also present. A typical red-shift in excitonic features was evident in temperature dependence measurement. Red-shift behavior of free exciton for all the samples was treated by applying Varshni empirical expression and several important parameter, such as, the Debye temperature and the band gap energy value was extracted. Thermal quenching behavior was also observed and treated by thermal quenching expression and value of the activation energy for non-radiative channel was extracted. The results that are obtained demonstrate a significant contribution in the fields of ZnO based nano-optoelectronics and nano-electronics.

The research in this dissertation examines the chemistry and applications of dendrimers in homogeneous catalysis. We examined interactions between dendrimers and charged probe molecules, prepared dendrimer-encapsulated metal nanoparticles in organic solvents, studied size-selectivity of dendrimer-encapsulted catalysts, and designed molecular rulers as in-situ probes to measure the location of dendrimer-encapsulted metal nanoparticles. The intrinsic proton binding constant and a constant that characterizes the strength of electrostatic interactions among occupied binding sites in poly(amidoamine) (PAMAM) dendrimers have been obtained by studying the effect of solution pH on the protonation of the dendrimers. The significant finding is that these two factors are greatly modulated by the unique and hydrophobic microenvironment in the dendrimer interior. Hydrophilic poly(propylene imine) (PPI) dendrimers were modified with various hydrophobic alkyl chains through an amide linkage and were then used as templates for preparing intradendrimer copper nanoclusters. The main driving force for encapsulating metal-ions was found to be the differences in metal-ion solubility between the solvent and the interior of the dendrimer. Nanometer-sized metal particles are synthesized and encapsulated into the interior of dendrimers by first mixing together the dendrimer and metal ion solution and then reducing the composite chemically, and the resulting dendrimer-encapsulated metal nanoparticles can then be used as catalysts. By controlling the packing density on the dendrimer periphery using either different dendrimer generations or dendrimer surface functionalities, it is possible to control access of substrates to the encapsulated catalytic nanoparticle. Molecular rulers consisting of a large molecular "stopper", a reactive probe and a linker were designed as in-situ probes for determining the average distance between the surface of dendrimer-encapsulated palladium nanoparticles and the periphery of their fourth-generation, hydroxyl-terminated PAMAM dendrimer hosts. By doing so, we avoid having to make assumptions about the nanoparticle size and shape. The results suggest that the surface of the encapsulated nanoparticle is situated 0.7 ± 0.2 nm from the surface of the dendrimer.