Thesis advisor: Zhifeng Ren / Thesis advisor: Krzysztof Kempa / Many different techniques are available to create nanopatterns in nanoscale devices. However, a few are flexible and inexpensive enough to be practical in the nanotechnology. Here, we study the nanosphere lithography (NSL) based on a self-assembly of microspheres. Using this technique, we have developed various patterns in metallic films, ranging from honeycomb arrays of "quasi-triangles" to circular holes. These various patterns have been used subsequently either as nano-optical structures directly, with remarkable optical and plasmonic properties, or as substrates for further nano-processing. In one such nano-processing, the "quasi-triangle" patterns were used as a catalyst for carbon nanotube growth. The resulting aligned arrays of carbon nanotubes were employed in nanocoax solar cells. In another nano-processing, the arrays were used as masks for electrodeposition. In addition to the nano processing and measurements, we have employed the FDTD computer simulations, to develop a full understanding of the nano-optical and plasmonic properties of the developed structures. / Thesis (PhD) — Boston College, 2011. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

This dissertation focuses on four research topics: self-assembly of colloidal nanoparticles, surface modifications of the properties of ionically self-assembled multilayer films, surface enhanced Raman spectroscopy of functionalized gold nanoparticles, and two photon uncaging in gel. Those techniques are used for development of novel nanofabrication methods for top-down and bottom-up assembly of nanostructures, by modifying the properties of nanopatterned surfaces with photoactive ligands, and other technologies. First I describe the development of an improved method for nanosphere lithography, a variation of the convective self-assembly technique. The method exhibited high reproducibility and yielded high quality monolayer crystals by withdrawing a meniscus of liquid polystyrene spheres solution and subsequent evaporation of the solvent. The monolayer crystal was used as an evaporation mask to create surface arrays of gold nanotriangular particles. Metal nanoparticles, with sharp features or narrow gaps, exhibit strong plasmonic properties. I took advantage of those properties to attempt to create patchy modifications of the surface functionalization of gold nanotriangular particles treated with photosensitive molecules. Two molecules denoted, P3-DTC, and LIP3, were used as functional molecules attached to the gold nanoparticles. After interaction with 356nm UV light, part of those molecules cleaves off the surface of the nanoparticles rendering the surface modified with a new functional group. The modification takes place only at the plasmonic hot spots of those nanoparticles, resulting in a patchy modification of the properties of the nanoparticles. I built polymer Ionically Self-assembled Multilayer (ISAM) films using a Layer-by-Layer deposition technique and treated them to alter their surface adhesion properties. Poly (allylamine hydrochloride) (PAH), and poly (styrene sulfonate) (PSS) are a very well-studied system of polyelectrolytes for LbL deposition. ISAM films built from those polyelectrolytes are rich in amine groups to which nanoparticles, cells, tissue cultures, ligands can be made to adhere. In my work I developed a method for selective modification of the surface adhesiveness, by neutralizing the amine groups trough acetylation with acetic anhydride. With resolution from a few microns to a few hundred nanometers, I selectively passivated some areas of the ISAM film while others I left unaltered. I tested the effect of the acetic anhydride passivation by performing Horse Radish Peroxidase (HRP) test which quantifies the amount of free amines on the surface of the film. I also demonstrated the patchy modification of surface adhesiveness by introducing gold nanospheres which attached only to the amine active areas of the modified ISAM film. Photoactivatable fluorophores, i.e. compounds and other entities that may transform into a fluorescent form on absorption of a photon can be employed in multidimetional volume patterning. I studied the photoactivation of aryl azides in gelatin matrix. Specifically, I used Azidocoumarin 151 as a test molecule to undergo two-photon activation, and then measured the resulting photoluminescence. The activation of the Azidocoumarin 151 can be used to create arbitrary 3D patterns of modified functionality inside the gel. The activated molecules can be used as sites for further modification of the patterning inside the volume of the gel. Possible modifications include attaching biomolecules, nanoparticles, or individual cells. / Ph. D.

abstract: In this thesis, a novel silica nanosphere (SNS) lithography technique has been developed to offer a fast, cost-effective, and large area applicable nano-lithography approach. The SNS can be easily deposited with a simple spin-coating process after introducing a N,N-dimethyl-formamide (DMF) solvent which can produce a highly close packed SNS monolayer over large silicon (Si) surface area, since DMF offers greatly improved wetting, capillary and convective forces in addition to slow solvent evaporation rate. Since the period and dimension of the surface pattern can be conveniently changed and controlled by introducing a desired size of SNS, and additional SNS size reduction with dry etching process, using SNS for lithography provides a highly effective nano-lithography approach for periodically arrayed nano-/micro-scale surface patterns with a desired dimension and period. Various Si nanostructures (i.e., nanopillar, nanotip, inverted pyramid, nanohole) are successfully fabricated with the SNS nano-lithography technique by using different etching technique like anisotropic alkaline solution (i.e., KOH) etching, reactive-ion etching (RIE), and metal-assisted chemical etching (MaCE). In this research, computational optical modeling is also introduced to design the Si nanostructure, specifically nanopillars (NPs) with a desired period and dimension. The optical properties of Si NP are calculated with two different optical modeling techniques, which are the rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) methods. By using these two different optical modeling techniques, the optical properties of Si NPs with different periods and dimensions have been investigated to design ideal Si NP which can be potentially used for thin c-Si solar cell applications. From the results of the computational and experimental work, it was observed that low aspect ratio Si NPs fabricated in a periodic hexagonal array can provide highly enhanced light absorption for the target spectral range (600 ~ 1100nm), which is attributed to (1) the effective confinement of resonant scattering within the Si NP and (2) increased high order diffraction of transmitted light providing an extended absorption length. From the research, therefore, it is successfully demonstrated that the nano-fabrication process with SNS lithography can offer enhanced lithographical accuracy to fabricate desired Si nanostructures which can realize enhanced light absorption for thin Si solar cell. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2015

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19008号 / 工博第4050号 / 新制||工||1623(附属図書館) / 31959 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 赤木 和夫, 教授 中條 善樹, 教授 吉﨑 武尚 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The void spaces in colloidal crystals (opals, three-dimensional (3D) close-packed arrays of silica nanospheres) and their replicas are used as templates in the fabrication of new nanostructured materials. 3D ordered nanomeshes and nanosphere arrays are readily obtained by chemical and/or electrochemical methods. Using silica opal templates, metals or polymers are infiltrated into the interstices between the silica nanospheres. Subsequent dissolution of the opals with HF solution produces open 3D mesh structures. Metal (such as Ni, Co, Fe, Pd, Au, Ag, and Cu) and conductive polymer (such as polyaniline) meshes are obtained by electrochemical deposition approach, while the nonconductive polymer (such as poly(methyl methacrylate) (PMMA)) meshes are synthesized by chemical polymerization method. Some new types of meshes are fabricated by the conversion of metal meshes and polymer meshes. NiO meshes are formed by oxidizing Ni meshes in the air. The NiO meshes exhibit higher volume occupation fraction than Ni meshes and the nanocrystalline sizes of NiO particles can be adjusted by the oxidation temperature. Due to the mechanical flexibility of polymer meshes, the compression of PMMA meshes produces deformed PMMA meshes which contain oblate pores. These meshes can be again served as templates to prepare new types of colloidal crystals (nanosphere arrays) and specific nanocomposites. By the use of poorly conductive NiO mesh or PMMA mesh arrays as templates, 3D periodic metal nanosphere arrays, such as those of Ni, Co, Au and Pd, are readily fabricated by the electrodeposition method. Metal/NiO or Metal/PMMA composites can also be obtained if the templates are left intact. The magnetic behavior of metal (such as Ni and Co) meshes and sphere arrays has been investigated. These nanoscale arrays show significantly enhanced coercivities compared with bulk metals, due to the size effect of the nanometer dimensions of the components in meshes and sphere arrays. Angle-dependent magnetic properties of Ni and Co sphere array membranes exhibit out-of-plane anisotropy.

In this study, template-based methods are used for the fabrication of various nanostructures such as nandots, nanorods, nanowires, nanotubes, and core-shell structures. Porous alumina membranes were employed as templates and metal nanostructures were synthesized in the templates by electrodeposition. By using lithography techniques, controlled patterned nanostructures were also fabricated on alumina templates. The magnetic properties of the various metal nanostructures were investigated. The pore size, interpore distance, and pore geometry highly affect magnetic properties of nanostructures grown in the templates. Hexagonally ordered porous alumina templates can be fabricated by two-step anodization. The pore diameters and interpore distances were readily controlled by appropriately changing anodization conditions and pore widening time. Alumina templates with various pore geometries were also successfully synthesized by changing applied voltage, increasing and decreasing, during a third anodization step. To understand magnetic properties of nanostructures with different aspect rations in the form of nanodots, nanorods, or nanowires, Fe nanostructures were fabricated in the templates by controlling of electrodeposition times. The coercivity of nanostructures increased with increasing aspect ratio. The anisotropy of the arrays was governed by the shape anisotropy of the magnetic objects with different aspect ratios. nanowires in mild-hard alumina and conventional alumina templates showed distinct differences in the squareness of hysteresis loops and coercivity both as a function of pore structure and magnetic component. Iron oxide nanotubes with a unique inner-surface were also fabricated by an electrodeposition method. β-FeOOH nanotubes were grown in alumina templates and transformed into hematite and magnetite structures during various heating processes. Hematite nanotubes are composed of small nanoparticles less than 20 nm diameters and the hysteresis loops and FC-ZFC curves show superparamagnetic properties without the Morin transition. In the case of magnetite nanotubes, which consist of slightly larger nanoparticles, hysteresis loops show ferromagnetism with weak coercivity at room temperature while FC-ZFC curves exhibit the Verwey transition at 125 K. For the patterning of nanowires, lithography techniques including nanosphere lithography and e-beam lithography were used. Nanosphere lithography used self-assembled PS spheres as a mask creates holes between spheres and the size of the holes is determined by the size and geometry of ordered PS spheres on the templates. This method can grow patterned nanowires arrays and also produce unique cup-shaped nanostructures with sizes ranging from micrometer down to several nanometers. E-beam lithography was also combined with template-based electrodeposition. Of these two lithographic methods, this one is the most powerful in the fabrication of patterned nanostructures with high aspect ratios. Various features and the sizes of patterned structures can be readily controlled. By the directing the pore diameters and interpore distances of the alumina template, the size and number of patterned nanowires are also adjustable.

In this thesis two issues in nanotechnology have been addressed. The first is the comprehensive characterization of engineered nanomaterials prior to their examination in toxicology and environmental studies. The second is the development of a method to produce nanostructure arrays over large areas and for low cost. A major challenge when assessing nanomaterial’s risks is the robust characterization of their physicochemical properties, particularly in commercial products. Such data allows the critical features for biological outcomes to be determined. This work focused on the inorganic oxides that were studied in powdered and dispersed forms as well as directly in consumer sunscreen products. The most important finding was that the commercial sunscreens that listed titania or zinc oxide as ingredients contained nanoscale materials. Cell free photochemical tests revealed that ZnO particles without any surface coating were more active at generating ROS than surface coated TiO2 nanoparticles. These studies make clear the importance of exposure studies that examine the native form of nanomaterials directly in commercial products. The second part of this thesis presents the development of a new method to fabricate gold nanoring and nanocrescent arrays over large areas; such materials have unique optical properties consonant with those described as metamaterials. A new shaped nanosphere lithography approach was used to manipulate the form of silica nanospheres packed onto a surface; the resulting array of mushroom structures provided a mask that after gold evaporation and etching left either golden rings or crescents over the surface. The structures had tunable features, with outer diameters ranging from 200 to 350 nm for rings and crescent gap angles of ten to more than a hundred degrees. The use of a double mask method ensured the uniform coverage of these structured over 1 cm2 areas. Experimental and theoretical investigations of the optical properties of the arrays revealed the optical resonances in the infrared region. Finally, in the course of developing the nanorings, etch conditions were developed to deposit large area arrays of polystyrene nanodoughnuts with diameters from 128 to 242 nm. These non-conductive structures provide an ideal template for further attachment of magnetic of optically emissive nanoparticles.

Recent advances in nanotechnology and the biotechnology revolution have created an immense opportunity for the use of noble metal nanoparticles as Surface Enhanced Raman Spectroscopy (SERS) substrates for biological sensing and diagnostics. This is because SERS enhances the intensity of the Raman scattered signal from an analyte by orders of 106 or more. This dissertation deals with the different aspects involved in the application of SERS for biosensing. It discusses initial studies performed using traditional chemically reduced silver colloidal nanoparticles for the SERS detection of a myriad of proteins and nucleic acids. It examines ways to circumvent the inherent aggregation problems associated with colloidal nanoparticles that frequently lead to poor data reproducibility. The different methods examined to create robust SERS substrates include the creation of thermally evaporated silver island films on microscope glass slides, using the technique of Nanosphere Lithography (NSL) to create hexagonally close packed periodic particle arrays of silver nanoparticles on glass substrates as well as the use of optically tunable gold nanoshell films on glass substrates. The three different types of SERS surfaces are characterized using UV-Vis absorption spectroscopy, Electron Microscopy (EM), Atomic Force Microscopy (AFM) as well as SERS using the model Raman active molecule trans-1,2-bis(4-pyridyl)ethylene (BPE). Also discussed is ongoing work in the initial stages of the development of a SERS based biosensor using gold nanoshell films for the direct detection of b-amyloid, the causative agent for Alzheimer's disease. Lastly, the use of gold nanoshells as SERS substrates for the intracellular detection of various biomolecules within mouse fibroblast cells in cell culture is discussed. The dissertation puts into perspective how this study can represent the first steps in the development of a robust gold nanoshell based SERS biosensor that can improve the ability to monitor biological processes in real time, thus providing new avenues for designing systems for the early diagnosis of diseases.

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 goal of this project was to develop a non-toxic amphiphilic diblock copolymer nanoparticulate drug delivery system that will solubilize paclitaxel (PTX) and retain the drug in plasma. Methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) (MePEG-b-PCL) diblock copolymers loaded with PTX were characterized and their physicochemical properties were correlated with their performance as nanoparticulate drug delivery systems. A series of MePEG-b-PCL was synthesized with PCL blocks ranging from 2-104 repeat units and MePEG blocks of 17, 44 or 114 repeat units. All copolymers were water soluble and formed micelles except MePEG₁₁₄-b-PCL₁₀₄, which was water insoluble and formed nanospheres. Investigation of the effects of block length on the physicochemical properties of the nanoparticles was used to select appropriate copolymers for development as PTX nanoparticles. The critical micelle concentration, pyrene partition coefficient and diameter of nanoparticles were found to be dependent on the PCL block length. Copolymers based on a MePEG molecular weight of 750 g/mol were found to have temperature dependent phase behavior. Relationships between the concentration of micellized drug and the compatibility between the drug and core-forming block, as determined by the Flory-Huggins interaction parameter, and PCL block length were developed. Increases in the compatibility between PCL and the drug, as well as longer PCL block lengths resulted in increased drug solubilization. The physicochemical properties and drug delivery performance characteristics of MePEG₁₁₄-b-PCL₁₉ micelles and MePEG₁₁₄-b-PCL₁₀₄ nanospheres were compared. Nanospheres were larger, had a more viscous core, solubilized more PTX and released it slower, compared to micelles. No difference was seen in the hemocompatibility of the nanoparticles as assessed by plasma coagulation time and erythrocyte hemolysis. Micellar PTX had an in vitro plasma distribution similar to free drug. The majority of micellar PTX associated with the lipoprotein deficient plasma fraction (LPDP). In contrast, nanospheres were capable of retaining more of the encapsulated drug with significantly less PTX partitioning into the LPDP fraction. In conclusion, although both micelles and nanospheres were capable of solubilizing PTX and were hemocompatible, PTX nanospheres may offer the advantage of prolonged blood circulation, based on the in vitro plasma distribution data, which showed that nanospheres retained PTX more effectively.