An improved lamellae drop-off technique for sharp tip preparation in scanning tunneling microscopy

A superior lamellae etching drop-off technique is described for the preparation of $W$ tips without the use of ${\mathrm{CCl}}_{\mathrm{4}}.$ Sharp tips with an apex of 25 nm or less can be produced routinely. In the case of Pt/Ir wire, the chemical inertness of the material means that it has to be reduced in diameter before being etched to yield a tip. In order to accomplish this, a capillary diameter reduction technique has also been developed for use in combination with the lamellae etching drop-off technique. The apparatus does not require the use of micromanipulators or micromovers. The shapes of tips with apexes as small as 25 nm can be investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This low cost method of producing sharp tips scanning tunneling microscopy is very effective and it would probably be feasible to develop an automatic tip preparation with a little more technical effort. Since it is possible to produce well shaped $W$ tips almost every time after acquiring a little skill, it is not usually necessary to check their shape by TEM or SEM before use. In contrast, the success rate with Pt/Ir tips is only up to 70%, so that it is advisable to check their shapes by TEM.