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- Creators: Goryll, Michael
- Creators: Richert, Ranko
Description
Solid-state nanopore research, used in the field of biomolecule detection and separation, has developed rapidly during the last decade. An electric field generated from the nanopore membrane to the aperture surface by a bias voltage can be used to electrostatically control the transport of charges. This results in ionic current rectification that can be used for applications such as biomolecule filtration and DNA sequencing.
In this doctoral research, a voltage bias was applied on the device silicon layer of Silicon-on-Insulator (SOI) cylindrical single nanopore to analyze how the perpendicular gate electrical field affected the ionic current through the pore. The nanopore was fabricated using electron beam lithography (EBL) and reactive ion etching (RIE) which are standard CMOS processes and can be integrated into any electronic circuit with massive production. The long cylindrical pore shape provides a larger surface area inside the aperture compared to other nanopores whose surface charge is of vital importance to ion transport.
Ionic transport through the nanopore was characterized by measuring the ionic conductance of the nanopore in aqueous hydrochloric acid and potassium chloride solutions under field effect modulation. The nanopores were separately coated with negatively charged thermal silicon oxide and positively charged aluminum oxide using Atomic Layer Deposition. Both layers worked as electrical insulation layers preventing leakage current once the substrate bias was applied. Different surface charges also provided different counterion-coion configurations. The transverse conductance of the nanopore at low electrolyte concentrations (<10-4 M) changed with voltage bias when the Debye length was comparable to the dimensions of the nanopore.
Ionic transport through nanopores coated with polyelectrolyte (PE) brushes were also investigated in ionic solutions with various pH values using Electrochemical Impedance spectroscopy (EIS). The pH sensitive poly[2–(dimethylamino) ethyl methacrylate] (PDMAEMA) PE brushes were integrated on the inner walls as well as the surface of the thermal oxidized SOI cylindrical nanopore using surface-initiated atom transfer radical polymerization (SI-ATRP). An equivalent circuit model was developed to extract conductive and resistive values of the nanopore in ionic solutions. The ionic conductance of PE coated nanopore was effectively rectified by varying the pH and gate bias.
In this doctoral research, a voltage bias was applied on the device silicon layer of Silicon-on-Insulator (SOI) cylindrical single nanopore to analyze how the perpendicular gate electrical field affected the ionic current through the pore. The nanopore was fabricated using electron beam lithography (EBL) and reactive ion etching (RIE) which are standard CMOS processes and can be integrated into any electronic circuit with massive production. The long cylindrical pore shape provides a larger surface area inside the aperture compared to other nanopores whose surface charge is of vital importance to ion transport.
Ionic transport through the nanopore was characterized by measuring the ionic conductance of the nanopore in aqueous hydrochloric acid and potassium chloride solutions under field effect modulation. The nanopores were separately coated with negatively charged thermal silicon oxide and positively charged aluminum oxide using Atomic Layer Deposition. Both layers worked as electrical insulation layers preventing leakage current once the substrate bias was applied. Different surface charges also provided different counterion-coion configurations. The transverse conductance of the nanopore at low electrolyte concentrations (<10-4 M) changed with voltage bias when the Debye length was comparable to the dimensions of the nanopore.
Ionic transport through nanopores coated with polyelectrolyte (PE) brushes were also investigated in ionic solutions with various pH values using Electrochemical Impedance spectroscopy (EIS). The pH sensitive poly[2–(dimethylamino) ethyl methacrylate] (PDMAEMA) PE brushes were integrated on the inner walls as well as the surface of the thermal oxidized SOI cylindrical nanopore using surface-initiated atom transfer radical polymerization (SI-ATRP). An equivalent circuit model was developed to extract conductive and resistive values of the nanopore in ionic solutions. The ionic conductance of PE coated nanopore was effectively rectified by varying the pH and gate bias.
ContributorsWang, Xiaofeng (Author) / Goryll, Michael (Thesis advisor) / Thornton, Trevor J (Committee member) / Christen, Jennifer M (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2015
Description
Plastic crystals as a class are of much interest in applications as solid state electrolytes for electrochemical energy conversion devices. A subclass exhibit very high protonic conductivity and its members have been investigated as possible fuel cell electrolytes, as first demonstrated by Haile’s group in 2001 with CsHSO4. To date these have been inorganic compounds with tetrahedral oxyanions carrying one or more protons, charge-balanced by large alkali cations. Above the rotator phase transition, the HXO4- anions re-orient at a rate dependent on temperature while the centers of mass remain ordered. The transition is accompanied by a conductivity "jump" (as much as four orders of magnitude, to ~ 10 mScm-1 in the now-classic case of CsHSO4) due to mobile protons. These superprotonic plastic crystals bring a “true solid state” alternative to polymer electrolytes, operating at mild temperatures (150-200ºC) without the requirement of humidification. This work describes a new class of solid acids based on silicon, which are of general interest. Its members have extraordinary conductivities, as high as 21.5 mS/cm at room temperature, orders of magnitude above any previous reported case. Three fuel cells are demonstrated, delivering current densities as high as 225 mA/cm2 at short-circuit at 130ºC in one example and 640 mA/cm2 at 87ºC in another. The new compounds are insoluble in water, and their remarkably high conductivities over a wide temperature range allow for lower temperature operations, thus reducing the risk of hydrogen sulfide formation and dehydration reactions. Additionally, plastic crystals have highly advantageous properties that permit their application as solid state electrolytes in lithium batteries. So far only doped materials have been presented. This work presents for the first time non-doped plastic crystals in which the lithium ions are integral part of the structure, as a solid state electrolyte. The new electrolytes have conductivities of 3 to 10 mS/cm at room temperature, and in one example maintain a highly conductive state at temperatures as low as -30oC. The malleability of the materials and single ion conducting properties make these materials highly interesting candidates as a novel class of solid state lithium conductors.
ContributorsKlein, Iolanda Santana (Author) / Angell, Charles A (Thesis advisor) / Buttry, Daniel A (Committee member) / Richert, Ranko (Committee member) / Arizona State University (Publisher)
Created2016