Wehner Susanne, Wondraczek Katrin, Johannsmann Diethelm, Bund Andreas
Institute of Physical Chemistry and Electrochemistry, Dresden University of Technology, Mommsenstrasse 13, D-01062 Dresden, Germany.
Langmuir. 2004 Mar 16;20(6):2356-60. doi: 10.1021/la0355646.
This paper reports on the relation between the surface roughness and emission of compressional waves from the surface of an electrochemical quartz-crystal microbalance. The detection of the compressional waves took place with an ultrasonic microphone and the quartz crystal itself. As a model process, the electrochemical deposition of copper from an acidic copper sulfate solution has been chosen. For this system, the roughness of the layer can be tuned via the current density. Roughness may be a source of the longitudinal waves at twice the frequency of the exciting shear wave (acoustic second-harmonic generation, ASHG) if the flow profile above the quartz-crystal surface is not entirely laminar. Slight deviations from the laminar flow can be reached at high amplitudes of oscillation. Comparing the ASHG efficiency of a rough and smooth surface, we find that the rough surface is more efficient in generating second-harmonic waves. This suggests that ASHG can be used to obtain a roughness parameter independent from the resonance frequency or bandwidth (damping) of a quartz-crystal resonator. Such an independent determination of roughness should be very interesting in practical applications.
本文报道了电化学石英晶体微天平表面粗糙度与表面压缩波发射之间的关系。压缩波的检测是通过超声麦克风和石英晶体本身进行的。作为一个模型过程，选择了从酸性硫酸铜溶液中电化学沉积铜。对于这个系统，层的粗糙度可以通过电流密度进行调节。如果石英晶体表面上方的流动剖面不完全是层流，粗糙度可能是激发剪切波频率两倍的纵向波的一个来源（声学二次谐波产生，ASHG）。在高振荡幅度下可以达到与层流的轻微偏差。比较粗糙表面和光滑表面的ASHG效率，我们发现粗糙表面在产生二次谐波方面更有效。这表明ASHG可用于获得一个与石英晶体谐振器的共振频率或带宽（阻尼）无关的粗糙度参数。这种粗糙度的独立测定在实际应用中应该非常有趣。
