In this paper, we discuss about the control of the shape of the very apex of a sharpened fiber probe used in photon scanning tunneling microscope (PSTM) by means of a method based on selective chemical etching. Under ambient conditions, through a multistep etching method proposed here, fiber probes with a flattened apex having a diameter of around 15–20 nm could be produced with high reproducibility. It has also been discovered that, during the etching process, the shape of the apex of the probe takes a rounded or a flattened shape with respect to the etching time in an almost cyclic fashion and such a phenomenon could help in understanding the mechanism of the etching process. These kind of probes with flat apex after metal coating are suitable for the fabrication of apertured probes used in PSTM and also for super tips which have a promising future as nanosensors in the fields of biology and biochemistry.
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