Brooksby Paula A, Downard Alison J
MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
J Phys Chem B. 2005 May 12;109(18):8791-8. doi: 10.1021/jp046095z.
Nitroazobenzene films have been grafted to pyrolyzed photoresist films by electrochemical reduction of the corresponding diazonium salt in acetonitrile solution. Two component films were also prepared by electrochemically grafting methylbenzene layers to preformed NAB films. Voltammetric investigation of the films in aqueous acid medium and the measurement of film thickness using atomic force microscopy (AFM) lead to new insights into film structure. In aqueous acid solution, the azobenzene groups have no detectable electroactivity and not all nitro groups in the films can be reduced. These findings point to a compact film structure in which proton diffusion is limited. There may also be spatial inhibition of the conformational changes that accompany azobenzene reduction. For increasingly thick NAB films, the peak for reduction of the nitro groups moves to more negative potentials and the peaks become more asymmetric in shape. These changes are interpreted in terms of the dielectric properties and the rate of proton diffusion in the films. Film thickness was measured by ploughing through the film with an AFM tip. When an NAB film prepared in acetonitrile solution is reduced in aqueous acid, the film thickness decreases by more than 50%. The changes can be partially reversed by treatment in acetonitrile-electrolyte solution and hence are attributed to ion-solvent induced swelling and shrinking. Thus, the large decrease in thickness detected by AFM after treatment of the film in aqueous acid is consistent with the compact film structure revealed by electrochemistry.
通过在乙腈溶液中对相应重氮盐进行电化学还原，已将硝基偶氮苯薄膜接枝到热解光刻胶薄膜上。还通过将甲苯层电化学接枝到预先形成的硝基偶氮苯薄膜上制备了双组分薄膜。在酸性水溶液介质中对薄膜进行伏安研究以及使用原子力显微镜（AFM）测量薄膜厚度，为薄膜结构带来了新的见解。在酸性水溶液中，偶氮苯基团没有可检测到的电活性，并且薄膜中的并非所有硝基都能被还原。这些发现表明薄膜结构紧密，质子扩散受到限制。也可能存在对伴随偶氮苯还原的构象变化的空间抑制。对于越来越厚的硝基偶氮苯薄膜，硝基还原峰向更负的电位移动，并且峰的形状变得更加不对称。这些变化根据薄膜的介电性质和质子扩散速率来解释。通过用AFM针尖穿过薄膜来测量薄膜厚度。当在乙腈溶液中制备的硝基偶氮苯薄膜在酸性水溶液中被还原时，薄膜厚度减小超过50%。这些变化可以通过在乙腈 - 电解质溶液中处理而部分逆转，因此归因于离子 - 溶剂诱导的溶胀和收缩。因此，在酸性水溶液中处理薄膜后AFM检测到的厚度大幅下降与电化学揭示的紧密薄膜结构一致。
