Polyethylene terephthalate (PET) film and silicon were used as the substrates. PET is a semi-crystalline polymer at room temperature, which is cleaned by an ultrasonic machine for 20 min with ultrasonic power and temperature of 80 W and 30°C, respectively. The films were dried in a vacuum oven for 1 h with temperature of 50°C.
Aluminum oxide depositions onto the substrate were conducted by ALD and PA-ALD, whose schematic is shown in Figure . The precursors of trimethylaluminum (TMA/Al(CH3)3) and water vapor were sequentially exposed for 10 ms and purged for 10 s, respectively. The deposition temperature and deposition cycle were fixed at 90°C and 100. The plasma was ignited between two parallel stainless steel electrodes with the interelectrode distance of 10 mm by a radiofrequency power supply at 13.56 MHz and 20 W. The plasma pretreatment was conducted for 90 s. The pressure of the deposition processes within the reactor of ALD and PA-ALD was 24.43 and 36.1 Pa, respectively. The argon gas was functionalized as both the carrier gas and discharge gas with the flow rate of 20 sccm.
Figure 1 Schematic of the PA-ALD process. (1) H2O, (2) TMA, (3) Ar gas cylinder, (4) precursor control valve, (5) Ar control valve, (6) check valve, (7) isolator, (8) electrode, (9) substrate, (10) reactor, (11) pressure gauge, (12) needle valve, and (13) vacuum (more ...)
Cross section of the coated silicon and the front view of the coated PET film were imaged by field emission scanning electron microscopy (FESEM; Hitachi, S-4800, Tokyo, Japan). Contact angle measurement was conducted by the sessile drop technique on the surface of the PET films. Deionized water drop tests were carried out on each of the samples using 0.4-μl-size droplet on each testing. The wetting property level of Al2O3-coated PET film was measured by a static contact angle analysis system (JC2000A, Powereach, Shanghai, China). Atomic force microscopy (AFM; NanoScope IV SPM, Veeco, Plainview, NY, USA) was used to examine the surface morphology of the PET film before and after Al2O3 deposition using the tapping mode. Fourier transform infrared (FTIR) spectra of the films were measured using the Thermo Nicolet Nexus 670 (Thermo Scientific, Waltham, MA, USA), Smart iTR (diamond ATR, Thermo Scientific) with the spectral range of 650 to 4,000 cm−1 with the resolution of 4 cm−1. Chemical composition of Al2O3-coated PET film was evaluated by X-ray photoelectron spectroscopy (XPS).