전기화학적 에칭에 의한 AFM용 텅스텐 탐침의 강성 제어

Abstract

This paper presents a method of controlling the stiffness of a tungsten probe for an atomic forcemicroscope (AFM) in order to provide high-quality phase contrast images in accordance with sample characteristics. While inducing sufficient deformation on sample surfaces with commercial Si or Si3N4 probes is difficultbecause of their low stiffness, a tungsten probe fabricated by electrochemical etching with appropriatelyhigh stiffness can generate relatively large elastic deformation without damaging sample surfaces. The fabricationof the tungsten probe involves two separate procedures. The first procedure involves immersing a tungsten wirewith both ends bent parallel to the surface of an electrolyte and controlling the stiffness of the tungsten cantileverby decreasing its diameter using electrochemical etching in the direction of the central axis. The second procedureinvolves immersing the end of the etched tungsten cantilever in the direction perpendicular to the surfaceof the electrolyte and fabricating a tungsten tip with a tip radius of 20-50 nm via the necking phenomenon. Thelatter etching process applies pulse waves every 0.25 seconds to the manufactured tip to improve its yield. Finiteelement analysis (FEA) of the stiffness of the tungsten probe as a function of its diameter showed that the stiffnessof the tungsten probes greatly varies from 56 N/m to 3501 N/m according to the cantilever diameters from30 μm to 100 μm, respectively. Thus, the proposed etching method is effective for producing a tungsten probehaving specific stiffness for optimal use with an AFM and certain samples.