Reverse electrochemical etching method for fabricating ultra-sharp platinum/iridium tips for combined scanning tunneling microscope/atomic force microscope based on a quartz tuning fork

Abstract

Sharp Pt/Ir tips have been reproducibly etched by an electrochemical process using an inverse geometry of an electrochemical cell and a dedicated electronic device which allows us to control the applied voltages waveform and the intensity of the etching current. Conductive tips with a radius smaller than 10 nm were routinely produced as shown by field emission measurements through Fowler-Nordheim plots. These etched tips were then fixed on a quartz tuning fork force sensor working in a qPlus configuration to check their performances for both scanning tunneling microscopy (STM) and atomic force microscopy (AFM) imaging.Their sharpness and conductivity are evidenced by the resolution achieved in STM and AFM images obtained of epitaxial graphene on 6H-SiC(0001) surface. The structure of an epitaxial graphene layer thermally grown on the 6H-SiC(0001) ) 3 6 3 6 ( × R30° reconstructed surface, was successfully imaged at room temperature with STM, dynamic STM and by frequency modulated AFM.

Electrochemical etching of lightweight nanotips for high quality‐factor quartz tuning fork force sensor: atomic force microscopy applications

“…In contrast to the AC etching, in DC etching tungstate anions slide downwards along the wire surface and a subsequent inflow of electrolyte containing hydroxide () ions occurs at this region. The downward flow of the tungstate anions form a dense layer at the portion lower than the meniscus which slows down the hydroxide ion activity at the lower portion of the wire [24, 33]. As a result, a neck is formed at the portion having higher reaction rate (i.e.…”

“…Tungsten nanotips are commonly fabricated with the DC drop‐off [14, 31], reverse electrochemical [32, 33] and dynamic etching techniques [34, 35]. Various DC drop‐off methods have been used to fabricate very sharp nanotips [28, 29, 31].…”

“…Chang et al [25] used an initial DC etching potential followed by a pulse etching to produce lengthy and sharp nanotips. Sharp nanotips can be fabricated by a reverse electrochemical etching technique [32, 33, 36] and by applying a voltage with optimised wave shape, phase angle and frequency [35]. Sharp tips with controlled profiles have been a prime focus of the previous researches and the tips fabricated with the above methods are normally massive which may lower the Q‐factor.…”

Tip induced mechanical deformation of epitaxial graphene grown on reconstructed 6H–SiC(0001) surface during scanning tunneling and atomic force microscopy studies

“…We mainly used STM/AFM tips electrochemically etched in a CaCl 2 solution from a 50 μm diameter Pt/Ir wire and carefully rinsed in hot deionized water. Then each tip was installed in a devoted UHV chamber to determine its apex radius from Fowler-Nordheim plots after removing possible residual contamination by high electric field desorption [30]. Only tips with an apex radius below 10 nm are glued on the free prong of a qPlus probe.…”

Contributed Review: Quartz force sensing probes for micro-applications

“…Once a tip is added, free-pronged QTFs require balancing, 25 with, e.g., either an equivalent weight of glue or another tip being added to the second prong. Since fabrication is often conducted by hand, having the base material for the tip initially linked to one of the electrodes by electrically conductive paste is also a practical advantage, as it allows the electro-chemical etching of a tip 26 after it has been mounted, if the process is compatible with the desired tip length (the shortest of tips may not be achievable in this way, due to the risk of a meniscus forming at the interface between the tuning fork and the etching solution). The choice of glue also affects the effective stiffness of the probe 27 (which is discussed in the next paragraph).…”