Browsing by Subject "PMMA"

Now showing 1 - 5 of 5

Digital gradient sensing and analysis of dynamic crack stability, propagation, and branching
(2018-12) Chichester-Constable, Alexander James; Ravi-Chandar, K.
Understanding the underlying mechanisms of fracture mechanics plays a critical role in engineering design and analysis. This work investigates aspects of dynamic fracture and the transition from stable to unstable crack propagation by employing the digital gradient sensing method in conjunction with high-speed photography. Both quasi-static and dynamic loading scenarios are evaluated. Furthermore, the micromechanical fracture mechanisms are evaluated using optical microscopy and optical profilometry. Significant insights are gained regarding the relationship between loading, crack branching, and the micromechanical mechanisms that govern dynamic fracture. Differences between two models for formation of crack surface patterns, based on crack front waves and Wallner lines, are examined. Most interestingly, insights developed with respect to crack branching phenomenon, and its speed past branching have significant impact on the modeling of crack branching and dynamic fracture. Discovery of constant crack branch speed will require additional study of energy release rates associated with branching cracks
Fluorinated Polymethacrylates as Highly Sensitive Non-chemically Amplified E-beam Resists
(2009-04) Strahan, Jeff R.; Adams, Jacob R.; Jen, Wei-Lun; Vanleenhove, Anja; Neikirk, Colin C.; Rochelle, Timothy; Gronheid, Roel; Willson, C. Grant; Strahan, Jeff R.; Adams, Jacob R.; Jen, Wei-Lun; Neikirk, Colin C.; Rochelle, Timothy; Willson, C. Grant
In an effort to improve upon the sensitivity of commercial non-chemically amplified e-beam resists, four polyacrylates functionalized with alpha-CF3 and/or CH2CF3 alkoxy substituents were studied. The alpha-CF3 substituent is known to increase backbone-scission efficiency while simultaneously eliminating acidic out-gassing and cross-linking known to occur in alpha-halogen substituted polyacrylates. Contrast curves for the polymeric alpha-CF3 acrylates, generated through e-beam exposure, showed the resists required an order of magnitude less dose than the current industry-standards, PMMA and ZEP. The fundamental sensitivity of these materials to backbone scissioning was determined via Co-60 gamma-ray irradiation. The chain scissioning, G(s), and cross-linking, G(x), values calculated from the resulting change in molecular weight demonstrated that all fluorinated resists possess higher G(s) values than either PMMA or ZEP and have no detectable G(x) values. Utilizing e-beam and EUV interference lithographies, the photospeed of PMTFMA was found to be 2.8x and 4.0x faster, respectively, than PMMA.
Graphene and its use in flexible electronics
(2016-08) Wang, Xiaohan, Ph. D.; Willson, C. G. (C. Grant), 1939-; Akinwande, Deji; Ekerdt, John G.; Bonnecaze, Roger T.; Banerjee, Sanjay K.
Graphene, a single layer of sp2 hybridized carbon atoms, was first isolated from graphite in 2004. It is the thinnest material known, but it is exceedingly strong, light and flexible. It conducts heat better than diamond, and may conduct electricity better than silver. This unique combination of properties makes graphene an ideal platform for flexible electronics. In the last decade, much effort has been devoted to synthesize graphene and then place (also known as “transfer”) it onto a flexible substrate for device applications. However, a large-scale and cost-effective method to accomplish this is missing, which limits the use of graphene in high-performance electronics. This dissertation reports an improved graphene synthesis. Oxygen on the catalytic copper surface was found to play an important role in graphene nucleation and growth during the chemical vapor deposition (CVD). Control of the surface oxygen enables repeatable growth of single-crystal graphene, the quality of which is among the best of reported for CVD graphene. The electrochemical reduction of graphene oxide was also explored as an alternative graphene synthesis. This method eliminates the high-temperature treatment and is more compatible with high-volume production. After CVD synthesis, graphene needs to be transferred from the copper surface onto a target substrate for device applications. Instead of using a chemical etching method to dissolve the copper, a rapid and nondestructive method was developed to delaminate the graphene from the copper surface. This produced isolated graphene films, which can be transferred onto dielectric substrates and patterned with lithography. In the latter process, poly(methyl methacrylate) (PMMA) is usually used as an electron-beam resist. The influence of PMMA residues on graphene properties was studied and a method to remove these residues from graphene surface was developed. This cleaned graphene surface demonstrated low surface friction and improved contact with the metal electrodes, which is desirable for coating and electronic applications. Finally, the possibility for scaling up graphene production in a roll-to-roll (R2R) system was explored. The CVD graphene cracks when a relatively low applied strain (~0.44%) is applied to the copper substrate. This provides a guideline for R2R system design and ultimately helps to achieve cheaper, faster, and more powerful graphene-based flexible electronics.
Metal Parts From Selective Laser Sintering of Metal-Polymer Powders
(1992) Badrinarayan, B.; Barlow, J.W.
Powder-Bed Based 3D-Printing of Function Integrated Parts
(University of Texas at Austin, 2014) Glassshroeder, J.; Prager, E.; Zaeh, M.F.