TEM analysis of photocatalytic TiO_2 thin films deposited on polymer substrates by low-temperature ICP-PECVD

摘要

TiO2 thin films were deposited on polymer substrates (polyethylene terephthalate and polystyrene) at low substrate temperature ( 120 degrees C) from radiofrequency inductively coupled O-2/titanium tetraisopropoxide (TTIP) plasmas. The film growth was tuned by controlling the O-2/TTIP flow rate ratio and pulsing the plasma power. The nanostructure including the film morphology and crystallization was thoroughly characterized by transmission electron microscopy. The photocatalytic activity was evaluated by measuring the degradation rate of methylene blue under UV light irradiation. All the films exhibit columnar morphologies. Increasing the O-2/TTIP ratio from 97:3 to 98.5:1.5 in the plasma leads to an increase in the column size and the amount of anatase phase. Meanwhile the photocatalytic activity was also improved. Then keeping the same O-2/TTIP ratio of 98.5:1.5, the substrate temperature was decreased even lower than 80 degrees C by pulsing the plasma with the duty cycle of 50%, which allows the deposition on the polystyrene substrate. In this pulsed mode, the column size is reduced, and the bottom layer (around 0-200 nm) near the substrate contains less anatase phase, but as the thickness increased, the anatase phase can be gradually enhanced in the upper layer (around 200-300 nm). Moreover, these films grown in the pulsed mode at low temperature ( 80 degrees C) present a high photocatalytic activity which indicates the film upper layer plays a more significant role in the photodegradation of methylene blue.