Degradation of Nano-crystalline ITO Films due to Exposure to Hyperthermal Atomic Oxygen
- PDF / 647,553 Bytes
- 6 Pages / 595.22 x 842 pts (A4) Page_size
- 111 Downloads / 185 Views
0887-Q10-08.1
Degradation of Nano-crystalline ITO Films due to Exposure to Hyperthermal Atomic Oxygen Long Li1, Ross Harder2, Fengting Xu1, Ian K. Robinson2 and Judith C. Yang1 1. Materials Science and Engineering Department, University of Pittsburgh, Pittsburgh, PA 15261. 2. Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. ABSTRACT Indium tin oxide (ITO) films coated on float glass slides were exposed to 5 eV hyperthermal atomic oxygen at room temperature with increasing fluences: 2×1019, 6×1019 and 2×1020 O-atoms/cm2. We characterized the structure of the ITO films after room temperature atomic oxygen exposure with scanning electron microscope (SEM) and atomic force microscope (AFM), synchrotron X-ray diffraction (XRD), and cross-sectional transmission electron microscope (X-TEM). The unexposed ITO films were found to possess a nano-crystalline surface, and clean and abrupt ITO/SiO2 interfaces without interfacial phase. Surface roughness of the exposed ITO films increased with the increasing AO influences. The interface- sensitive peaks in XRD measurements with grazing incidence revealed that the crystallinity of the ITO was modified near the interface. Cross-sectional TEM confirmed that many ITO particles with diameters ranging from 2-10 nm formed in the SiO2 substrate near the interface after AO exposure. These findings suggest that O atoms can travel through the ITO films, where the boundaries of columnar-grown grains may supply the pathway. INTRODUCTION Spacecraft encounter a harsh environment in the low-Earth orbit (LEO), ranging from approximately180 to 650 km above the Earth[1-3]. The primary hazardous species in the LEO are vacuum ultraviolet (VUV) radiation, X-rays, atomic oxygen which is formed by the photodissociation of molecular oxygen, and electrons and other charged species[1,2]. The high relative velocity between space vehicles and the ambient atomic oxygen (AO) leads to hyperthermal collisions of O atoms with spacecraft materials, with 5 eV kinetic energy[4,5]. Indium-tin-oxide (ITO), a transparent conductive compound oxide, is typically employed as a coating material to protect Kapton blankets, used in solar arrays in LEO, from AO-erosion and bleed off static charges from the insulating polymer surface[6]. However the ITO coatings did degrade when exposed on the ram side of a space vehicle in the LEO environment[7,8]. Ground simulations of AO reaction with ITO were conducted, however, Synowicki et.al and Woollam et.al. reported non-effective of their thermal asher AO source due to the low kinetic energy of their source (0.5 eV)[7,8]. We used our hyperthermal AO source to expose ITO films coated on float glass to simulate the LEO on the ground. ITO films were exposed to 5 eV AO at room temperature and structure characterizations were carried out using SEM, AFM and synchrotron XRD, and cross-sectional TEM and high-resolution TEM (HRTEM), high angle annular dark field (HAADF) and energy dispersive spectroscopy (EDS).
0887-Q10-08.2
EXPERIMENTAL ITO films (
Data Loading...
