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Title:Solid-state superionic conductors for advanced nanoscale fabrication
Author(s):Jacobs, Kyle E
Director of Research:Ferreira, Placid M
Doctoral Committee Chair(s):Ferreira, Placid M
Doctoral Committee Member(s):Kapoor, Shiv G; Toussaint, Kimani C; Dillon, Shen J
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
solid state conductors
silver nanopatterning
Abstract:Silver possesses the highest electrical conductivity of any metal, and this property allows for unique interaction with visible light when patterned at the nanoscale. Few methods exist for patterning silver down to sub-100nm scales, and all tend to be complicated, multi-step processes which require ex- pensive equipment. This work examines the use of the solid electrolyte glass silver iodide-silver metaphosphate (AgIAgPO3) as a pathway for nanoscale patterning of silver using simple processing. AgIAgPO3 was chosen as an ideal candidate solid ionic conductor because it is optically transparent, has a high ionic conductivity for silver at room temperature, and most importantly it has a remarkably low glass transition temperature which facilitates low temperature thermal nanoscale molding. Our laboratory has previously developed a process known as solid-state superionic stamping (S4) to selectively etch silver and copper films by generating localized electrochemical metal etching using the patterned solid ionic conductor Ag2S as a stamp, achieving sub-50nm lateral resolution. In this work, AgIAgPO3 is developed as a replacement solid electrolyte with many superior properties to Ag2S. The primary advancement is the use of thermal nanoimprint to manufacture large area stamps on the same system in which the S4 patterning is performed. This allows scalable, high quality stamp surfaces to be generated within minutes, without the need for difficult and contamination prone polishing. Initially, a working AgIAgPO3 prototype stamping process was generated with dimensions of 0.3-1mm, similar to that achievable with Ag2S stamps. It was found that these stamps were capable of significantly higher etch rates due to the higher stamp ionic conductivity. Moreover, since AgIAgPO3 is a pure ionic conductor—as opposed to Ag2S, a mixed conductor—analysis of etch progression is possible through the measured charge transfer. Continued investment into the S4 process involved developing a better platform for the manufacture, handling, and application of S4 stamps by augmenting a 4-axis precision stage system to accommodate controlled and repeatable thermal nanoimprint for on-machine stamp fabrication. The system was designed for the precise temperature and pressure control needed to produce optically flat stamps suited to make large area contact between two hard materials. Once built, the system was modeled and characterized to determine which parameters in stamp fabrication had the greatest effect on the molding process. While some parameters such as the mold temperature primarily only effect the molding time, others such as the temperature of the stamp holder had a large effect on the overall curvature of the final stamp. This characterization leads to the ability to fabricate stamps with less than 200nm total curvature across a 4mm diameter of the stamp. While working with AgIAgPO3, the clarity needed for optically imaging through the material brought to the fore significant shortcomings in widely used glass synthesis techniques, typically brought about by the exchange of expensive of platinum crucibles for lower cost alternatives. Through chemical analysis, the identity of the contamination was determined and methods for either removing the impurities or avoiding their introduction were analyzed. In contrast to controlling electrode-electrolyte contact at the nanoscale by patterning the electrolyte, nanoscale application of charge through electron beam irradiation was also explored. Localized injection of charge into the surface of the electrolyte, was found to precipitate silver nanoparticles within the interaction volume generated by the beam. Low electrical fluence results in the formation of a layer of embedded nanoparticles which produce vivid colors in reflected light. Meanwhile, at large fluence full silver films were formed, with lateral dimensions of the film determined by the electron beam path. Moreover, by varying the beam energy, it was possible to enter a regime that results in dissolution of the generated color, effectively allowing color patterns to be erased. Finally, an effort was made to control, at the nanoscale, the bulk extraction of silver from the solid electrolyte. Attempts to laterally confine silver growth, and thus produce long wires, were unsuccessful despite the presence of insulating confinement layers. Much more effective, was pre-patterning of the glass surface with a low fluence from the electron beam prior to a higher current silver extraction via micro-probe on the glass surface. The presence of silver particles within the surface serve to accelerate the lateral growth of silver films by up to 80 times that found in areas lacking the pre-pattern.
Issue Date:2016-12-21
Rights Information:Copyright 2016 Kyle Jacobs
Date Available in IDEALS:2017-08-10
Date Deposited:2017-05

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