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Mapping the nanoscale effects of charge traps on electrical transport in grain structures of indium tin oxide thin films.

ABSTRACT: We report the mapping of the nanoscale effects of charge trap activities in the grain structures of an oxygen plasma-treated indium tin oxide (ITO) thin film. Here, a conducting Pt probe made direct contact with the surface of an ITO thin film and scanned the surface while measuring the maps of electrical currents and noises. The measured data were analyzed to obtain the maps of sheet conductance (G _s) and charge trap density (N _eff) in the grain structures of the ITO thin film. The results showed that grain boundaries exhibited a lower sheet conductance and a higher charge trap density than those of the regions inside grains. Interestingly, the scaling behavior of G _s ∝ N _eff ^-0.5 was observed in both grain and boundary regions, indicating diffusive charge transport. Furthermore, the sheet conductance increased by two times, and the density of charge traps decreased by ∼70% after an oxygen plasma treatment, presumably due to the enhanced crystallinity of the ITO film. Interestingly, in some boundary regions, the sheet conductance and the charge trap density exhibited the scaling behavior of G _s ∝ N _eff ^0.5, which was attributed to the hopping conduction caused by the enhanced crystallinity and increased localized states in the boundary regions. Since our method provides valuable insights into charge transport and charge trap activities in transparent conducting thin films, it can be a powerful tool for basic research and practical optoelectronic device applications based on ITO thin films.

SUBMITTER: Jeon H

PROVIDER: S-EPMC8386405 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Fabrication and organosilane-functionalization and characterization of nanostructured ITO electrodes are reported. Nanostructured ITO electrodes were obtained by electron beam evaporation, and a subsequent annealing treatment was selectively performed to modify their crystalline state. An increase in geometrical surface area in comparison with thin-film electrodes area was observed by atomic force microscopy, implying higher electroactive surface area for nanostructured ITO electrodes and thus higher detection levels. To investigate the increase in detectability, chemical organosilane-functionalization of nanostructured ITO electrodes was performed. The formation of 3-glycidoxypropyltrimethoxysilane (GOPTS) layers was detected by X-ray photoelectron spectroscopy. As an indirect method to confirm the presence of organosilane molecules on the ITO substrates, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were also carried out. Cyclic voltammograms of functionalized ITO electrodes presented lower reduction-oxidation peak currents compared with non-functionalized ITO electrodes. These results demonstrate the presence of the epoxysilane coating on the ITO surface. EIS showed that organosilane-functionalized electrodes present higher polarization resistance, acting as an electronic barrier for the electron transfer between the conductive solution and the ITO electrode. The results of these electrochemical measurements, together with the significant difference in the X-ray spectra between bare ITO and organosilane-functionalized ITO substrates, may point to a new exploitable oxide-based nanostructured material for biosensing applications. As a first step towards sensing, rapid functionalization of such substrates and their application to electrochemical analysis is tested in this work. Interestingly, oxide-based materials are highly integrable with the silicon chip technology, which would permit the easy adaptation of such sensors into lab-on-a-chip configurations, providing benefits such as reduced size and weight to facilitate on-chip integration, and leading to low-cost mass production of microanalysis systems.

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Mapping the nanoscale effects of charge traps on electrical transport in grain structures of indium tin oxide thin films.

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