Browsing by Subject "Nanopatterning"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Investigation of a roll-to-roll nanoimprinting process utilizing inkjet based resist deposition(2011-12) Kincaid, Matthew Michael; Sreenivasan, S.V.A high-speed, large-area technique capable of nanopatterning flexible substrates is highly desirable in several applications such as; 1) thin film photovoltaics (TFPV's), 2) flexible electronics, 3) optoelectronics, 4) energy storage devices and 5) biological applications. Flexible substrates are attractive as they can be lower in cost than traditional substrates, and provide the ability to perform continuous processing both of which are valuable for cost sensitive applications such as TFPVs. Also, flexible substrates can conform to non-planar surfaces and therefore provide versatility in applications such as wearable electronics and biomedical devices. In this thesis, a patterning approach known as Jet and Flash Imprint Lithography (J-FIL) is explored for flexible substrates. J-FIL uses inkjets to deposit low-viscosity UV curable polymer materials (resists) that are molded by a template at room temperature and low pressures prior to UV cross-linking. There are inherent advantages to the J-FIL process that lends itself to patterning flexible substrates. The room temperature and low pressure process makes it more compatible with flexible substrates which tend to become dimensionally unstable at elevated temperatures and pressure. The extension of J-FIL to flexible substrates involves the following key challenges: (i) Understanding the level of precision required in roll-to-roll machine systems to ensure that these systems can facilitate imprint and separation of nano-scale features; (ii) The substrate surface should be controlled to initiate and maintain proper interface with the template and avoid formation of bubbles; (iii) The tension in the film should be controlled to ensure that the discrete resist drops are coerced to form a uniform contiguous residual film underneath the patterns; (iv) The fluid filling time - that is representative of the process throughput - should be low; and (v) After UV curing and separation, the nanoscale patterns should not be deformed or damaged. The above challenges were addressed by developing a roll-to-roll test bed to imprint flexible polycarbonate films using the J-FIL process. The test bed has the capability of controllably varying a number of web tension parameters as well as process variables in order to calibrate machine precision and establish control schemes for a robust process. Process metrics such as RLT uniformity, target RLT accuracy, feature filling and feature distortion were measured and quantified. A design of experiments was performed on the test bed for the purposes tuning the process variables as well as developing a model of process performance, with respect to critical process parameters. A two-level design, with three input variables, is utilized in this experimental process. The process yielded blank imprints with mean thickness of 70.5 nm, and a standard deviation of 3.9 nm. The sensitivity of the mean thickness and uniformity to process variables were quantified. The best performing set of input parameters were then used during patterned imprints, to determine if any pattern filling issues or pattern deformation would take place. The patterned imprints, made up of an array of hexagonal pillars (125nm tall, by 240 nm wide, by 450 nm pitch) showed no sign of fluid filling voids, or deformation due to separation. Given this result, the feasibility of implementing J-FIL on a roll-to-roll prototype system was established. A proposed next generation flexible substrate J-FIL tool is presented, along with the expected challenges associated with metrology and dynamic noise. Future work entails the design and qualification of a full scale roll-based imprint tool, capable of meeting throughput metrics established for industrial applications.Item Nanofabrication via directed assembly: a computational study of dynamics, design & limits(2016-08) Arshad, Talha Ali; Bonnecaze, R. T. (Roger T.); Ellison, Christopher J.; Ganesan, Venkat; Sreenivasan, S. V.; Willson, Carlton G.Three early-stage techniques, for the fabrication of metallic nanostructures, creation of controlled topography in polymer films and precise deposition of nanowires are studied. Mathematical models and computational simulations clarify how interplay of multiple physical processes drives dynamics, provide a rational approach to selecting process parameters targeting specific structures efficiently and identify limits of throughput and resolution for each technique. A topographically patterned membrane resting on a film of nanoparticles suspended in a solvent promotes non-uniform evaporation, driving convection which accumulates particles in regions where the template is thin. Left behind is a deposit of particles the dimensions of which can be controlled through template thickness and topography as well as film thickness and concentration. Particle distribution is shown to be a competition between convection and diffusion represented by the Peclet number. Analytical models yield predictive expressions for bounds within which deposit dimensions and drying time lie. Ambient evaporation is shown to drive convection strong enough to accumulate particles 10 nm in diameter. Features up to 1 µm high with 10 nm residual layers can be deposited in < 3 minutes, making this a promising approach for continuous, single-step deposition of metallic nanostructures on flexible substrates. Selective exposure of a polystyrene film to UV radiation has been shown to result in non-uniform surface energy which drives convection on thermal annealing, forming topography. Film dynamics are shown to be a product of interplay between Marangoni convection, capillary dissipation and diffusion. At short times, secondary peaks form at double the pattern density of the mask, while at long times pattern periodicity follows the mask. Increased temperature, larger surface tension differentials and thick films result in faster dynamics and larger features. Electric fields in conjunction with fluid flow can be used to position semi-conducting nanowires or nanotubes at precise locations on a substrate. Nanowires are captured successfully if they arrive within a region next to the substrate where dielectrophoresis dominates hydrodynamics. Successful assembly is predicated upon a favorable balance of hydrodynamics, dielectrophoresis and diffusion, represented by two dimensionless groups. Nanowires down to 20 nm in length can be assembled successfully.