No description available.

No description available.

No description available.

The ability to control the physical environment at subcellular scales is critical to understanding cell and tissue behaviors regulated by extracellular interactions. However, open platform technology that allows one to create combinatorial physical environments is not readily available. This thesis describes the development of a low-cost system for creating complex hydrogel and ligand patterns using maskless lithography. Specifically, it incorporates light paths with interchangeable wavelengths to facilitate a broad range of chemistries. In addition, it also includes a motorized stage with an adaptable platform that can hold different conventional cell culture vessels. Finally, I have developed a LabVIEW interface that allows one to create repeating patterns across different wells quickly and easily. Taken together, this technology will enable more rapid probing of mechanobiological regulation for applications in tissue engineering, drug discovery, and developmental biology.

The challenge for lithography today is to continue the reduction of feature size whilst facing severe theoretical and practical limitations. In 2006 Rajesh Menon and Hank Smith proposed a new lithography system named absorbance modulation optical lithography (AMOL) [Menon 2006]. AMOL proposed replacing the normal metal mask of a lithography system with an absorbance modulation layer (AML), made from a photochromic material. This allows, through the competition between two incident wavelengths, the creation of an adaptive absorbance mask. The AML allows intimate contact to an underlying resist and hence the optical near-field may be used to create sub-diffraction limited exposures. The aim of this thesis is to model AMOL and demonstrate the abilities and the limits of the system, particularly focusing on sub-diffraction limited imaging. This thesis describes the construction of a vector electromagnetic simulation to explore the idea and performance of AMOL, and an exploration of the ability of AMOL to propagate sub-diffraction limited images into a photoresist. A finite element method (FEM) model was constructed to simulate the formation of apertures in the AML and light transmission through the system. Three major areas of interest were explored in this thesis; the effect of polarisation on imaging, using a plasmonic reflector layers (PRLs) to improve the depth of focus (DOF), and introducing a superlens to AMOL. Investigations of polarisation demonstrated strong preference for a transverse magnetic (TM) polarised exposing wavelength for near-field exposures. Associated with polarisation, and supporting work with absorbance gratings, the importance of the material parameters of the AML in allowing sub-diffraction limited exposures was discussed. It was also noted that, in common with all near-field systems, the depth of focus (DOF) was poor, worse than comparable metal systems. This thesis also demonstrates that the introduction of a PRL can improve the DOF and process latitude for resist thicknesses up to 60 nm and, although performance was reduced when using a silver PRL, the substantial improvements to the DOF and process latitude make a PRL valuable for an AMOL system. This thesis also models the superlens to an AMOL system, which theoretically allows propagation of the image in the near-field. It is demonstrated that the superlens can project an AMOL image into an underlying resist, but that this image is degraded, especially for thick and non-ideal superlenses. The superlens does have a second useful effect, as it can act as a dichroic filter; decreasing the intensity ratio in the resist by a factor of ten, overcoming issues of resist sensitivity. The superlens can allow image projection and filtering with AMOL, however improvements to the available superlens materials or changes to the AML will be needed to avoid image deterioration. This thesis has developed the first full-vector model of an absorbance modulation optical lithography (AMOL) system. This model has been used to increase the understanding of the complex effects that go into the creation of sub-diffraction limited features with AMOL. In particular the model has been used to investigate polarisation, PRLs and superlenses in AMOL. This thesis demonstrates the ability of AMOL to create narrow apertures and sub-diffraction limited exposures in a photoresist, and describes the limitations of AMOL, including material parameters and DOF. AMOL is a new and interesting lithography technique; this thesis simulates the abilities and challenges of sub-diffraction lithography using an AMOL system.

This research comprehensively reviews the properties of regular micro and nano structures fabricated by laser interference lithography and reports on their applications in the antireflection and self‐cleaning surface. The research systematically investigates the laser interference lithography technology taking into account its advantages and abilities to realize various potential applications. Multiple‐beam interference lithography systems are constructed. Laser interference interaction with silicon wafer is analysed and the optical and hydrophobic properties are obtained via measurements. In order to fabricate the extremely low reflection and very large contact angle for solar cells, fabrication methods of antireflection and self‐cleaning are surveyed and their advantages and disadvantages compared. The research investigates the effect of heat transfer and the radiation of laser interference plasma on silicon wafer surfaces and proposes equations of heat flow and radiation effects of laser plasma of interfering patterns in a four‐beam laser interference distribution. Following the irradiation, the silicon wafer surface is covered with a periodic array of micrometer and nanometer‐sized structures, which have the shape of grating, cone and hole. The research also investigates the effect of different laser parameters on the optical and hydrophobic properties of the structured silicon wafer surface. The results of periodic hexagonally‐distributed hole structures fabricated by three‐beam laser interference reveals excellent design guidelines for obtaining an extremely low solar‐weighted reflection, (SWR, 1.86%) and relatively large contact angle (140°) which can provide a strong self‐cleaning capability on the solar cell surface. In addition, the research creates a novel dual structure with antireflection and superhydrophobic properties fabricated by three‐beam laser interference lithography. The fabrication method is three‐beam laser interference combined with focused laser processing interacting on the silicon wafer surface. This kind of structure has a very low SWR (3.6 %) and extremely large contact angle which is more than 150° in the wavelength range from 380 nm to 780 nm. The research shows that the laser interference lithography technology can be employed and further developed to fabricate micro and nano structures of strong antireflection and self‐cleaning functions for applications in solar cells.

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.

We report on the process parameters of nanoimprint lithography (NIL) for the fabrication of two-dimensional (2-D) photonic crystals. The nickel mould with 2-D photonic crystal patterns covering the area up to 20mm² is produced by electron-beam lithography (EBL) and electroplating. Periodic pillars as high as 200nm to 250nm are produced on the mould with the diameters ranging from 180nm to 400nm. The mould is employed for nanoimprinting on the poly-methyl-methacrylate (PMMA) layer spin-coated on the silicon substrate. Periodic air holes are formed in PMMA above its glass-transition temperature and the patterns on the mould are well transferred. This nanometer-size structure provided by NIL is subjective to further pattern transfer. / Singapore-MIT Alliance (SMA)

Nanopore-based single-molecule analysis of biomolecules such as DNA and proteins is a subject of strong scientific and technological interest. In recent years, solid state nanopores have been demonstrated to possess a number of advantages over biological (e.g., ion channel protein) pores due to the relative ease of tuning the pore dimensions, pore geometry, and surface chemistry. However, solid state fabrication methods have been limited in their scalability, automation, and reproducibility. In this work, a wafer-scale fabrication method is first demonstrated for reproducibly fabricating large arrays of solid-state nanopores. The method couples the high-resolution processes of electron beam lithography (EBL) and atomic layer deposition (ALD). Arrays of nanopores (825 per wafer) are successfully fabricated across a series of 4' wafers, with tunable pore sizes from 50 nm to sub-20 nm. The nanopores are fabricated in silicon nitride films with thicknesses varying from 10 nm to 50 nm. ALD of aluminum oxide is used to tune the nanopore size in the above range. By careful optimization of all the processing steps, a device survival rate of 96% is achieved on a wafer with 50 nm silicon nitride films on 60- 80 micron windows. Furthermore, a significant device survival rate of 88% was obtained for 20 nm silicon nitride films on order 100 micron windows. In order to develop a deeper understanding of nanopore fabrication-structure relationships, a modeling study was conducted to examine the physics of EBL, in particular: to investigate the effects of beam blur, dose, shot pattern, and secondary electrons on internal pore structure. Under the operating conditions used in pore production, the pores were expected to taper to a substantially smaller size than their apparent size in SEM. This finding was supported by preliminary conductance readings from nanopores.

Three-dimensional (3D) polymer structures are very attractive because the extra structural dimension can provide denser integration and superior performance to accomplish complex tasks. Successful fabrication of 3D multilayer microstructures in thermoplastic polymers using optimized nanoimprint lithography techniques such as layer-transfer and transfer-bonding methods are developed in this dissertation work. The capability and flexibility of the techniques developed here are expected to have deep impact on the applications of soft materials such as polymers including functional polymers in micro- and nanofabricated devices and systems. Although NIL technique is developing rapidly in recent years, there are still issues that need to be addressed for broader adoption of the nanoimprint technique. One of the problems is the residual layer that remains in the polymer pattern after nanoimprint. The conventional approach, oxygen reactive-ion-etching (RIE) process, to remove the residual layers, increases the cost and lowers the overall throughput of the nanoimprint process. More severely, it can degrade or even damage the functional polymers. In order to overcome these problems, new residual layer removal techniques need to be developed. In this dissertation, two methods are newly developed, which do not negatively affect the chemistry of the polymer materials. The techniques are suitable for all thermoplastic polymers, particularly functional polymers. Another advantage of nanoimprint is its ability to directly create functional polymers structures. This is because thermal nanoimprint only needs temperature and pressure for pattern replication, which both are benign to functional polymers. This feature combined with newly developed techniques such as transfer-bonding and residue removal techniques opens up the possibilities in nondestructive functional polymers patterning at the micro- and nanoscale for novel applications in electronics, optoelectronics, photonics and bioengineering. Finally, several applications of 3D multilayer structures fabricated by the techniques developed in this dissertation are demonstrated. The first application is a multilayer metal-dielectric-metal structure with embedded microfluidic channels. This structure can be used as an on-chip tunable filter for integrated microfluidic applications. The second application is a multilayer microfluidic channels in which each layer has a different channel size. This device can be used for particle separation and filtration based on lateral fluid flow.