Properties of diamond-like carbon film deposited on acrylic substrate and Si wafer
|Abstract:||本研究之目的在於沉積類鑽碳膜於壓克力基材上，以期應用為光學保護膜。首先分別以RF濺鍍法與離子束系統沉積類鑽碳膜於P-type(100)矽基材上，藉以找出較佳之沉積參數。實驗結果顯示，在此系列研究中離子束法是較適合之沉積方式，因而選擇離子束系統沉積類鑽碳膜於壓克力基材。此外，也研究含矽樹脂與二氧化矽做為中間介層對壓克力與類鑽碳膜之影響。所沉積之薄膜以Raman、AFM、nanoindentation、microhardness tester 、ESCA、Dual Beam Spectrometer等進行分析其結構與性質。實驗結果可得下列結果。
以壓克力為基材而言，附著性壓痕試驗結果顯示，附著性指標(dP/dx)在添加SiO2中間介層後由0.56gf/mm上升至0.59 gf/mm。很明顯的，添加SiO2中間介層的確有助於類鑽碳膜與壓克力基材附著性的提升，且不太影響可見光穿透性。同時實驗結果也指出，類鑽碳膜之微硬度值會隨類鑽碳膜沉積時間的增加而增加，而當沉積時間達7.5分鐘時，微硬度值可達2.70 GPa，大幅提升壓克力基材的硬度達10倍以上，提升壓克力鏡面的耐磨效果。然而研究發現，隨著微硬度的增加，試片之表面粗糙度由2.18nm上升至2.23nm，並降低其可見光穿透性至67~89 %，顯示表面粗糙度為影響類鑽碳膜穿透率的主要因素之一。換言之，對於類鑽碳膜做為壓克力基材的光學保護膜而言，最佳的沉積條件必須取決於應用時所需之抗磨耗性與光學穿透性之間的相互妥協。|
The purpose of this research was to deposit a protective diamond-like carbon (DLC) film on acrylic substrates for optical applications. To search for the important deposition parameters for RF sputtering and ion beam deposition systems, at first, the P-type (100) Si wafers were used to study the deposition processes. The ion beam deposition system, which was proved to be more suitable for this case, was then chosen to deposit DLC films on acrylic substrates. Effects of silicon resin and Si oxides as the interlayers were also studied. The deposited films were examined by AFM, Raman spectroscopy, microhardness and nano-indentation techniques, ESCA and dual beam spectrometry to evaluate their structures and properties. From the experimental results, the following conclusions can be drawn. For the cases of Si wafer substrates, the results show that the sp3/sp2 ratios of the RF sputtered DLC films were high and would increase as increasing the hydrogen flow rate. In contrast, the ion beam deposited films demonstrated a even higher sp3/sp2 ratio, less surface roughness (0.39nm), higher nano-indentation hardness (up to 13.50 GPa) and less deposition temperatures (<70℃). Therefore, the gridless ion beam deposition method is believed to be more suitable for the present purpose. For the cases of acrylic substrates, the results of the indentation adhesion testing show that the adhesion index, dP/dx, increases from 0.56gf/mm to 0.59gf/mm with SiO2 as the interlayer. It indicated that the SiO2 interlayer does enhance the film adhesion without greatly sacrificing optical transmittance of visible lights. The results also show that microhardness of the films increases as increasing the deposition time, and can go up to 2.70 GPa at the deposition time of 7.5 min. In other words, the ion beam deposited films can rise the microhardness of the substrate more than ten times, and greatly improve their wear resistance. However, it was found that a higher hardness of the films is accompanied by a rougher surface. In consequence, the transmittance of the visible lights can deteriorate to 67~89% by increasing the surface roughness from 2.18 nm to 2.23 nm. This implies that the surface roughness is one of the major factor affecting the optical transmittance. In other words, the best deposition conditions for a protective DLC film on acrylic substrates for optical applications depend on the compromise between the desired wear resistance and optical transmittance.
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