Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
ACS Appl Mater Interfaces. 2011 Jul;3(7):2410-6. doi: 10.1021/am200322k. Epub 2011 Jun 20.
Conformal poly(cyclohexyl methacrylate) (pCHMA) thin films were synthesized via initiated chemical vapor deposition (iCVD), with tert-butyl peroxybenzoate (TBPOB) as the initiator, representing the first time that TBPOB has been used as an initiator for iCVD synthesis. Using TBPOB instead of tert-butyl peroxide (TBPO), the rate of iCVD film growth increased by a factor of up to seven at comparable conformality and lower the filament temperature from 257 to 170 °C at a comparable deposition rate of 3 nm/min. The conformal deposition of functional thin films is desired for applications including microfluidics, medical devices and membranes. Lower filament temperatures reduce the heat load to the deposition surface and thus are advantageous for polymeric substrates that are temperature sensitive or monomers that decompose at high temperatures. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) results demonstrate the similarity of the TBPOB- to the TBPO-initiated pCHMA main chains. However, the aromatic group in TBPOB provided a unique spectral signature of the polymer chain end group in the FTIR and the peak intensity increased with increase of filament temperature. Scanning electron micrographs (SEMs) revealed that the pCHMA coatings are conformal over non-planar structures; however, at identical process conditions, TBPO-initiated films showed a slightly better conformality due to the lower sticking coefficient of TBPO. At a monomer partial pressure of 0.45, TBPOB has a sticking coefficient value of 0.1188 ± 0.0092, which is ∼3 times as high as that of TBPO (0.0413 ± 0.0058). The step coverage is insensitive to filament temperature if the surface concentration of the monomer is fixed.
通过引发化学气相沉积（iCVD）合成了保形聚（环己基甲基丙烯酸酯）（pCHMA）薄膜，其中叔丁基过氧苯甲酸酯（TBPOB）作为引发剂，这代表 TBPOB 首次被用作 iCVD 合成的引发剂。使用 TBPOB 代替叔丁基过氧化物（TBPO），在可比保形性和更低的丝温（从 257 降低至 170°C）下，iCVD 薄膜生长速率提高了 7 倍，沉积速率为 3nm/min。功能薄膜的保形沉积对于包括微流控、医疗器械和膜在内的应用是理想的。较低的丝温降低了沉积表面的热负荷，因此对于对温度敏感的聚合物基底或在高温下分解的单体有利。傅里叶变换红外光谱（FTIR）和 X 射线光电子能谱（XPS）结果表明，TBPOB-引发的 pCHMA 主链与 TBPO 引发的 pCHMA 主链相似。然而，TBPOB 中的芳基基团在 FTIR 中提供了聚合物链端基的独特光谱特征，并且随着丝温的升高，峰强度增加。扫描电子显微镜（SEM）显示，pCHMA 涂层在非平面结构上具有保形性；然而，在相同的工艺条件下，TBPO 引发的薄膜显示出稍好的保形性，这是由于 TBPO 的附着系数较低。在单体分压为 0.45 时，TBPOB 的附着系数值为 0.1188±0.0092，约为 TBPO（0.0413±0.0058）的 3 倍。如果固定单体的表面浓度，则台阶覆盖率对丝温不敏感。
