Development of laser Enhanced Electrochemical Microscopy

为了评估局部腐蚀敏感性、金相组织或成分以及激光刻蚀/电镀，研制了扫描激光增强电化学显微镜(SLEEM)。采用体积小、易于控制的AlGaAs固体半导体激光器作为扫描光源。1990年，使用了40 mW输出功率型激光器，后来在1991年引入了80 mW型激光器。激光输出被偏置电压斩波为10~100赫兹的方波，照射在电解液中保持恒定电位的金属试件上。利用锁相放大器检测激光照射产生的电解液电流变化，并用微型计算机进行扫描成像。在恒定电位下，激光照射引起的电流变化与无照射时的电解电流成正比。正如理论模型所预测的那样，辐照频率的降低会导致金属表面温度升高而导致电流增加。铁、铬、镍是不锈钢的组成元素，在每个元素的特定电位区观察到电流的特征增加，因此在恒定电位下辐照不锈钢的电流变化取决于它的成分。Sleem的分辨率与激光光束的光斑大小相同，约为10微米。在此基础上，成功地获得了敏化不锈钢在Fe为活性、Cr为钝化的电势下的贫铬晶界图像。在跨钝化电位下，可以得到两相不锈钢中铬的成分图像。在有源和过钝化电位下可以进行精细的图像刻蚀。

For evaluation of localized corrosion susceptibility, metallography for structure or composition, and laser etching/plating, a Scanning Laser Enhanced Electrochemical Microscopy (SLEEM) has been developed. Solid state semiconductor laser of AlGaAs which is small and easily controlled was used as a scanning laser source. In 1990, a 40 mW output power type laser was used and later 80 mW type was introduced in 1991. Laser out put was Chopped by bias voltage into 10 Hz to 100 Hz square wave and irradiated to the metal specimen which is kept at a constant potential in the electrolytic solution. Change in electrolytic current by laser irradiation is detected by a lock in amplifier and make a scanning image by using microcomputer. Current change induced by laser irradiation at the constant potential is found to be proportional to the electrolytic current without irradiation. Decrease in frequency of irradiation induces the current increase because of temperature increase at the metal surface as a theoretical model predicts. Characteristic increase in current for Fe, Cr and Ni which are constituents elements of stainfess steels was observed at a specified potential region for each element, so that current change of stainless steel by irradiation at the constant potential depends on its composition. Resolving power of the SLEEM is the same size of about 10 mum as the spot size of the laser beam. Based on the above analysis, the chromium depleted grain boundary image of sensitized stainless steel could be obtained succesfully at the potential that is active for Fe but passive for Cr. At the trans passive potential, the compositional image of Cr in two phase stainless steel could be obtained. Fine image etching can be made at the active and transpassive potential.