Refined tip preparation by electrochemical etching and ultrahigh vacuum treatment to obtain atomically sharp tips for scanning tunneling microscope and atomic force microscope

Abstract

A modification of the common electrochemical etching setup is presented. The described method reproducibly yields sharp tungsten tips for usage in the scanning tunneling microscope and tuning fork atomic force microscope. In situ treatment under ultrahigh vacuum (p ≤10(-10) mbar) conditions for cleaning and fine sharpening with minimal blunting is described. The structure of the microscopic apex of these tips is atomically resolved with field ion microscopy and cross checked with field emission.

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

“…being the field conversion factor, R is the curvature radius of the tip apex and k is the field reduction factor that depends on the exact tip geometry and the distance between the tip apex and the counter electrode [7,35]. However, k can reach values between 3 and 35 as reported for tungsten tips [7,13,[20][21][22][24][25][26]. Dividing the equation (1) by 2 V and taking the nature logarithm on both sides, we obtain: …”

“…However, the well-known presence of an oxide layer covering the Pt/Ir [16][17][18] and W [19][20][21][22][23][24][25][26] tips requires a cleaning treatment to obtain optimal tunneling current flow. W tips fabricated by electrochemical etching, cleaned by heating and characterized by FowlerNordheim (FN) plot and FIM were reported to display a clean apex with 3-15 nm radius of curvature [24,25]. Recently, the apex radii of tungsten based microemitter tips, ranging from 25 to 500 nm, were measured from SEM images and extracting from FN plots of the field emission characteristics [27].…”

“…A process for achieving a reproducible sharp tip apex was identified from a systematic study of the electropolishing process of W tips [15]. However, the well-known presence of an oxide layer covering the Pt/Ir [16][17][18] and W [19][20][21][22][23][24][25][26] tips requires a cleaning treatment to obtain optimal tunneling current flow. W tips fabricated by electrochemical etching, cleaned by heating and characterized by FowlerNordheim (FN) plot and FIM were reported to display a clean apex with 3-15 nm radius of curvature [24,25].…”

Fabrication of Needle-Shaped Specimens Containing Subsurface Nanostructures for Electron Tomography

“…Electro-polishing has been one of the most used techniques for preparing needles for APT [ 28 ], although this technique is not appropriate for some materials and structures. Other methods are based in selective chemical etching processes [ 29 ], sometimes applied after lithography methods [ 30 ] or after the mechanical cut of the sample [ 31 ]. In the last years, the FIB instrument has been widely used for fabricating needleshaped specimens from different materials [ 32 -34 ] as it provides advantages such as speed and reliability.…”

Conductivity of an atomically defined metallic interface

“…The gold-coated cantilever serves as force transducer during scanning and indentation, and its deflection is measured by optical interferometry. W tips were prepared by electrochemical etching followed by annealing in vacuo (32). FIM imaging was performed by leaking He gas into the measurement chamber and applying a sufficiently high voltage (∼4 kV) to ionize the He atoms, which are then accelerated away from the tip to an imaging screen (33,34).…”