Nanostructuring of tips for scanning probe microscopy by ion sputtering: Control of the apex ratio and the tip radius

Abstract

Single crystal diamond tips for scanning probe microscopy Rev. Sci. Instrum. 81, 013703 (2010); 10.1063/1.3280182 Scanning probe microscopy investigation of nanostructured surfaces induced by swift heavy ionsIon etching under well-defined conditions represents a very powerful tool to fabricate tips in a controlled and reproducible manner for Scanning Probe Microscopy which possess clean, relatively smooth, and oxide-free surfaces. The possibilities and limitations of ion etching are demonstrated thoroughly for tungsten, which is of particular interest for scanning tunneling microscopy. Iterative computer simulations and experimental studies are provided. The simulation of the etching process at the atomic level is based on the Monte Carlo program ͑Transport of Ions in Matter͒, which provides reliable values for the key input parameters such as the sputtering yield Y (,E ion ) and the mean ion range in the material for ion energies between 1 and 6 keV. The simulation program starts with a large tip radius as a crude form and asymptotically approaches a ''final form'' of a very sharp tip in the course of ion etching. Our experimental results with argon ions in the energy range up to 6 keV and crude electrochemically etched polycrystalline tungsten wire agreed very reasonably with the simulated results. For example, the minimum tip radius obtained experimentally amounts to approximately 5 nm. This value corresponds closely to the ion range, which obviously sets a limit to the smallest achievable tip radius by the effect of transmission sputtering. By variation of the angle between the ion beam and the macroscopic tip, the tip angle can be controlled in the range between 12°and 35°.

A combined ion-sputtering and electron-beam annealing device for the in vacuo postpreparation of scanning probes

“…7 The required spherical symmetry is inherently achieved by design in our setup. Generally ion milling processes are dependent on many parameters such as the ion's angle of incidence, 6 chemical nature. In the proposed setup, the kinetic energy can easily be adjusted, while the angle of incidence apparently depends on the local surface orientation.…”

Compact device for cleaning scanner-mounted scanning tunneling microscope tips using electron bombardment

“…6,7 If any residues are present on either the tip or the sample, the measured heat transfer might not be due to the thermal nearfield, but may be caused by mere heat conduction mediated by a layer of adsorbates. To clean simple metal tips and samples, ion sputtering 8 and, in the case of the latter, subsequent annealing can be employed. Resistive heating 9 and electron bombardment have been shown to be readily usable methods of tip cleaning as well.…”

Two-step controllable electrochemical etching of tungsten scanning probe microscopy tips

“…Among various methods explored, electrochemical etching [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] proved to be an inexpensive, efficient, and reliable way to fabricate extremely sharp tips. Other reported techniques include cutting, 23,24 grinding, [1][2][3][4][5][6]25 pulling, 19,[26][27][28][29][30] beam deposition, [31][32][33][34] ion milling, [35][36][37][38][39] and others. For electrochemical etching, recent advances in tip fabrication came in the form of reverse biasing after "drop-off," 21 in 2002 and "dynamic electrochemical etching" 40 in 2007.…”