扫描隧道显微镜钨针尖的制备与表征

采用直流电化学刻蚀方法制备扫描隧道显微镜钨针尖,研究了电化学刻蚀过程中NaOH溶液浓度、钨丝浸入长度和刻蚀电压对针尖形貌的影响。通过扫描电子显微镜(SEM)测量针尖曲率半径和针尖纵横比值,以表征针尖的尺寸和形状;通过能谱仪(EDS)分析针尖表面成分,以表征表面清洁度;通过场发射显微镜(FEM)得到Fowler-Nordheim (F-N)曲线来检测针尖发射性能。实验结果表明,当溶液浓度为2 mol/L、钨丝浸入长度为4 mm、刻蚀电压为3 V时,可以得到曲率半径约为100 nm、纵横比值为13的针尖,且表面无钨的氧化层。FEM结果显示当对针尖施加500 V的负偏压时,针尖可以稳定发射50 nA量级的电流,且针尖性能具有良好的一致性。

Preparation and Characterization of STM W Tips

The W tips for scanning tunneling microscope(STM)were prepared by the direct current electrochemical etching method.The influences of the NaOH solution concentration,immersion depth of tungsten wire and etching voltage on the tip morphology were studied.The radius of curvature and aspect ratio of the tip were measured by the scanning electron microscope(SEM)to characterize the size and shape of the tip.The surface composition of the tip was analyzed by the energy disperse spectroscopy(EDS)to characterize the surface cleanliness.The Fowler-Nordheim(F-N)plot was obtained by the field emission microscope(FEM)to detect the tip emission performance.The experimental results show that when the solution concentration is 2 mol/L,the immersion depth of tungsten wire is 4 mm and the etching voltage is 3 V,the tip with a radius of curvature of about 100 nm and an aspect ratio of 13 can be obtained,and there is no tungsten oxide layer on the surface.The FEM results show that when the negative bias voltage of 500 V is applied to the tip,the tip can stably emit the current of 50 nA and its performances have good consistency.