Preparation Of Platinum-Iridium Alloy Probe For Scanning Tunneling Microscope By AC Electrochemical Etching

Scanning tunneling microscope(STM)has become a powerful instrument for surface characterization and analysis,and has made outstanding contributions to the development of surface science and nanotechnology.In STM,the sharp metal tip is the gate of the nanosignal,and its resolution depends on the sharpness of the probe tip.In addition,the chemical and electronic properties of the tip material are closely related to the quality of the image generated,and platinum-iridium alloy(Pt-Ir)has become a better STM probe material than tungsten(W)due to its inertness and stability in a variety of environments.Among many preparation methods,electrochemical etching has become the most widely explored probe preparation technique due to its reliability,economy,high purity and high quality.Aiming at the problems of low reliability and low stability in the manufacture of high-quality probes,the following studies are carried out in this paper:Firstly,according to the chemical characteristics and corrosion mechanism of Pt-Ir,AC electrochemical etching method was used to prepare the probe,and compared with W probe,the corrosion process of Pt-Ir probe was analyzed.At the same time,a probe preparation system was designed,in which the mechanical device of corrosion instrument ensured the stability and accuracy of the probe preparation process,and the measurement and control system realized the man-machine interaction and real-time measurement and control of the preparation process through single chip microcomputer and touch screen,ensuring the controllability of the probe preparation experiment.Secondly,the influences of AC voltage,cut-off current and frequency on the corrosion process and final morphology of the probe were investigated through the probe preparation experiment.Through experimental phenomena and the use of field emission scanning electron microscopy(FESEM)the tip obtained were characterized and determined the optimum parameters of the corrosion and corrosion rate,shape,found that the frequency of the probe and the surface quality of the decisive role,especially in the high frequency corrosion stage,appeared with direct current(DC)corrosion W probe similar but not identical necking phenomenon,The mechanism and formation process of this phenomenon are analyzed and discussed.Finally,according to the necking phenomenon of high frequency corrosion,a new preparation method of Pt-Ir probe,isolation method,was designed.The regular and neat Pt-Ir probe with tip curvature radius less than 200 nm was obtained through experiments,and the influence of the key corrosion parameter,frequency,on the corrosion process of isolation probe was studied.In addition,the probe was placed in STM for testing,and the images obtained by scanning the surface topography of the sample confirmed that the prepared Pt-Ir probe met the resolution and stability requirements of STM.