基于表面增强拉曼光谱技术的金表面耐腐蚀性分析

Corrosion Resistance of Gold Surface Investigated by Surface Enhanced Raman Spectroscopy

金属表面耐腐蚀性能与其微观结构密切相关。以金为分析对象,采用不同粒径氧化铝抛光粉抛光处理金片表面,经扫描电镜和原子力显微镜观察,表明金片表面具备与实际工件类似的微观结构,在此基础上,研究金片表面微观划痕结构对表面增强拉曼散射(SERS)以及耐腐蚀性能的影响。以罗丹明B为探针分子,对不同特征尺寸的微观划痕进行SERS分析,获得了罗丹明B的SERS信号强度随划痕平均特征尺寸的变化规律。通过改变拉曼激发光偏振方向与划痕方向的夹角大小,发现SERS信号主要归因于激发光与划痕相互作用产生的横向表面等离激元。划痕平均特征尺寸在50nm附近时,横向表面等离激元最强,之后随着划痕平均特征尺寸增加,横向表面等离激元逐渐变弱。另一方面,对具有不同特征尺寸微观划痕的金片进行电化学极化测试,获得了各样品的自腐蚀电位,发现金片的自腐蚀电位随着划痕平均特征尺寸增大而降低。结果表明,当划痕平均特征尺寸大于50nm,金表面的SERS信号与自腐蚀电位间存在良好的线性对应关系,这为SERS技术用于工件耐蚀性分析提供了依据。通过在工件表面滴涂探针分子并使用便携式拉曼光谱仪测量有望可以对工件耐蚀性进行现场快速预判。

The corrosion resistance of metals is closely related to their surface microstructure. This work focuses on the surfaces of gold plates which were prepared through a polishing process with different sizes of α-Al2O3. With SEM and AFM characterizations, the surface microstructures of the gold plates are distinct, indicating that the polished gold plates have surface microstructures similar to those of real work-pieces. The effects of the gold surface scratches on surface enhanced Raman scattering （SERS） and corrosion resistance were investigated. SERS on the gold surface scratches with different average feature sizes were tested using Rhodamine B （RhB） as a probe molecule. A relationship between the SERS intensity of the adsorbed Rhodamine B and the average feature size of surface scratch was obtained. By changing the angle between the polarization direction of Raman laser and the direction of scratches, it is found that the SERS signals are mainly ascribed to the transverse plasmon generated from interaction between incident light and scratches. The transverse plasmon intensity reached the maximum when the average feature size of the surface scratches is close to 50 nm. With the increase of the average feature sizes, the transverse plasmon intensity shows a gradual decrease. On the other hand, electrochemical polarization tests of the gold plates with different sizes scratches were measured. The free corrosion potential of samples is obtained. The free corrosion potential of gold plates decrease with increasing the average feature sizes. It is found that, when the average feature size of the surface scratch is more than 50 nm, a ideal coherence exists between the SERS intensity and the free corrosion potential for the gold plates. These results suggest that SERS technique could be applied for the corrosion resistance analysis of the work-pieces. By the means of smearing probe molecules and using a handheld Raman spectrometer, quick analysis of the work-pieces corrosion resistance is proven to be promising.