Layer-by-layer self-assembled thin films for potential applications in semiconducting devices and electrochemical sensors

Date of Completion

January 2006

Keywords

Chemistry, Polymer

Degree

Ph.D.

Abstract

Layer-by-layer (LBL) self-assembly of thin films is an opportune way of processing semiconductor devices, provided the films demonstrate mechanical integrity and efficient organizational capability. Metalorganic films based on chelation between zinc precursors and an organic ligand, 2,5-dihydroxy-1,4-benzoquinone (DHBQ) were grown via solution and vacuum processing with an expectation that they would exhibit crystallinity. However, the ability of these chelates to integrate moisture within their structure is a major stumbling block towards obtaining ordered growth. After a careful study of the oligomeric repeat units via wide angle X-ray diffraction along with molecular simulations, it was observed that water coordinated with zinc distorts the potential linear growth of the metalorganic chains. This water can be removed by high temperature annealing that, in case of the synthesized oligomer powder, reverts the structure back to its linear form. However, formation of thin ZnO layers in between successive DHBQ repeats for the LBL assembled films leads to a non-commensurate growth despite latter annealing. In an effort to eliminate moisture completely from these assemblies, we endeavored into growth of the films at high temperature; high vacuum environment. These results give an insight into the growth mechanism of these films, which again point out the importance of adsorbed moisture that promote growth in a non-commensurate manner. ^ The search for long-lived implantable sensors for continuous glucose monitoring has been the focus of the research community for over 30 years. It has recently been realized that the performance of electrochemical glucose sensors is closely related to the behavior of the outer membrane that coats the sensing enzyme. Such coatings govern the diffusion characteristics of glucose and correspondingly, the sensitivity of the sensors. We have developed a LBL self-assembled membrane based on humic acids (HAs) and Fe3+ moieties wherein, through alteration of the number of bilayers, it was possible to modulate the diffusion of glucose towards the sensor, due to the membranes flux-limiting characteristics. Through a study of this and other LBL assembled polyelectrolyte membrane systems, it was realized that the morphology of the coatings governs the device characteristics, most particularly its response at hyperglycemia and hysteresis upon glucose cycling.^

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