Development of laser Enhanced Electrochemical Microscopy

为了评估局部腐蚀敏感性、结构或成分的金相学以及激光蚀刻/电镀，已经开发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激光源。1990年，使用了40 mW输出功率型激光器，后来于1991年引入了80 mW型。激光输出经偏压斩波成10 ~ 100 Hz的方波，照射在电解液中保持恒电位的金属试件上。激光照射引起的电解电流变化由锁定放大器检测，并使用微型计算机形成扫描图像。在恒电位下，激光辐照引起的电流变化与无辐照时的电解电流成正比。理论模型预测，由于金属表面温度升高，辐照频率降低会导致电流增加。在特定的电位范围内观察到不锈钢的组成元素Fe、Cr和Ni的电流特征性增加，因此在恒定电位下辐照不锈钢的电流变化取决于其组成。SLEEM的分辨能力与激光束的光斑尺寸相同，约为10 μ m。基于上述分析，在对Fe为活性而对Cr为钝化的电位下，可以成功地获得敏化不锈钢的贫铬晶界图像。在反钝化电位下，可以得到两相不锈钢中Cr的成分图像。在活性和过钝化电位下可以进行精细的图像蚀刻。

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.