Functional solid substrates modified by self-assembled monolayers (SAMs) have potential applications in biosensors,chromatography,and biocompatible materials.The potential-induced phase transition of N-isobutyryI-L-cysteine (L-NIBC) SAMs on Au(111) surfaces was investigated by in-situ electrochemical scanning tunneling microscopy (EC-STM) in 0.1 mol·L-1 H2SO4 solution.The NIBC SAMs with two distinct structures (α phase andβ phase) can be prepared by immersing the Au(111) substrate in pure NIBC aqueous solution and NIBC solution controlled by phosphate buffer at pH 7,respectively.The as-prepared e phase and β phase of NIBC SAMs show various structural changes under the control of electrochemical potentials of the Au(111) in H2SO4 solution.The α phase NIBC SAMs exhibit structural changes from ordered to disordered structures with potential changes from 0.7 V (vs saturated calomel electrode,SCE) to 0.2 V.However,theβ phase NIBC SAMs undergo structural changes from disordered structures (E ＜ 0.3 V) to y phase (0.4 V ＜ E ＜ 0.5 V) and finally to theβ phase (0.5 V ＜ E ＜ 0.7 V).EC-STM images also indicate that the phase transition from theβ phase NIBC SAMs to the cα phase occurs at positive potential.Combined with density functional theory (DFT) calculations,the phase transition from theβ phase to the cα phase is explained by the potential-induced break of bonding interactions between-COO-and the negatively charged gold surfaces.%自组装单层膜修饰的功能性基底在生物传感,色谱分析,生物相容性材料等方面均具有潜在应用.本文利用原位电化学扫描隧道显微镜(EC-STM)研究了电势诱导的N-异丁酰基-L-半胱氨酸(L-NIBC)分子在Au(111)表面自组装结构的相转变.我们把Au(111)基底分别浸润在纯的NIBC水溶液和pH=7(磷酸盐缓冲溶液调节)的NIBC溶液中,分别制备了NIBC的α相和β相两种不同的自组装结构.EC-STM观测显示,当改变金的电极电势时,α相和β相的NIBC自组装单层膜出现了多种不同的结构变化.当电压从0.7V(相对于饱和甘汞电极而言)降低到0.2V时,α相由有序结构变为无序结构.而对于β相的样品,当E＜0.3V时,为无序结构;当电极电势增大到0.4V＜ E＜ 0.5V时,出现Y相;继续增大到0.5V＜ E＜ 0.7V时,变为β相.另外,EC-STM图像也证实存在β相转变为a相的可能.综合密度泛函理论计算的结果,我们提出,β相转变为α相的原因可以解释为电极电势的变化引起了Au-COO键的断裂,从而引发分子吸附构型变化而导致相变.
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