Effect of Fabrication Process Parameters on the Apex-Radius of STM Tungsten Nanotip (original) (raw)
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e-Journal of Surface Science and Nanotechnology, 2007
We present a method to prepare tungsten tips for use in multi-tip scanning tunneling microscopes. The motivation behind the development comes from a requirement to make very long and conical-shape tips with controlling the cone angle. The method is based on a combination of a "drop-off" method and dynamic electrochemical etching, in which the tip is continuously and slowly drawn up from the electrolyte during etching. Its reproducibility was confirmed by scanning electron microscopy. Comparison in tip shape between the dynamic and static methods was shown.
International Journal of Scientific and Research Publications (IJSRP), 2020
One of the great challenges of Scanning Tunneling Microscopy (STM) is the production of atomically sharp tips. Tungsten tips in Scanning Probe Microscope (SPM) and Atomic Force Microscope (AFM) are used instead of platinum and iridium (Pt/Ir) tips due to their high quality factor, mechanical stability and produced at low cost. In this work we carried out different experiments on 0.5 mm (0.02 inch) tungsten wire and obtained sharp and reproducible tungsten tips by simple electrochemical etching "Drop-Off" method and we have shown that tips reproduced have better properties i.e. tip diameter and cone angle than earlier. Moreover tips reproducibility is checked by selecting a sample or two from produced tips and experimental work is repeated to show whether the procedure is reproducible or not and as shown that tips production procedure is reproducible by analyzing them, so have best control on tip shape and optimized etching conditions are reported. Similarly tips are produced by varying different voltages and maintaining various concentration of solution constant i.e. 2 molar, 3 molar and 4 molar NaOH concentration of solution and comparison is made between different tips by measuring their cone angle and tip diameter from SEM and OM images. Cone angle and tip diameter are measured from SEM and OM images by using AutoCAD software whose procedure are shown below at experimental work. Finally we have produced atomically sharp tungsten tips by analyzing optical microscope (OM) images and scanning electron microscope (SEM) images and have recommended the optimum one to be used in SPM.
Fabrication of [001]-oriented tungsten tips for high resolution scanning tunneling microscopy
Scientific reports, 2014
The structure of the [001]-oriented single crystalline tungsten probes sharpened in ultra-high vacuum using electron beam heating and ion sputtering has been studied using scanning and transmission electron microscopy. The electron microscopy data prove reproducible fabrication of the single-apex tips with nanoscale pyramids grained by the {011} planes at the apexes. These sharp, [001]-oriented tungsten tips have been successfully utilized in high resolution scanning tunneling microscopy imaging of HOPG(0001), SiC(001) and graphene/SiC(001) surfaces. The electron microscopy characterization performed before and after the high resolution STM experiments provides direct correlation between the tip structure and picoscale spatial resolution achieved in the experiments.
MRS Proceedings, 2013
ABSTRACTSharper nanotips are required for application in nanoprobing systems due to a shrinking contact size with each new transistor technology node. We describe a two-step etching process to fabricate W nanotips with controllable tip dimensions. The first process is an optimized AC electrochemical etching in KOH to fabricate nanotips with a radius of curvature (ROC) down to 90 nm. This was followed by a secondary nanotip sharpening process by laser irradiation in KOH. High aspect ratio nanotips with ROC close to 20 nm were obtained. Finally we demonstrate the application of the fabricated nanotips for nanoprobing on advanced technology SRAM devices.
Fabrication of tuning-fork based AFM and STM tungsten probe
8th International Conference on High-capacity Optical Networks and Emerging Technologies, 2011
We compare the sharpness of tungsten probe tips produced by the single-step and two-step dynamic electrochemical etching processes. A small radius of curvature (RoC) of 25 nm or less was routinely obtained when the two-step electrochemical etching (TEE) process was adopted, while the smallest achievable RoC was -10 nm, rendering it suitable for atomic force microscopy (AFM) or scanning tunneling microscopy (STM) applications.
Reproducible Electrochemical Etching of Tungsten Probe Tips
Nano Letters, 2002
An electrochemical procedure in KOH electrolyte has been developed to reproducibly produce ∼5 nm radius tungsten probe tips. It has been found that a spurious electrochemical etching process, driven by the natural potential difference between an Ir electrode and the W tip, causes rapid tip blunting at the end of the electrochemical etching period. By electrically reversing this potential difference within 500 ns following tip separation, the blunting process is eliminated yielding sharp tips with varying cone angles.
Preparation and characterization of electrochemically etched W tips for STM
Measurement Science and Technology, 1999
Abstract. We have investigated methods for cleaning dc-etched polycrystalline tungsten tips for scanning tunnelling microscopy (STM). The cleaning methods include Ar-ion sputtering, heating, chemical treatments and Ne-ion self-sputtering. We correlate transmission electron microscopy images of the tip, field-emission data from the tip and images of a clean Cu (111) surface to find an optimum procedure for STM imaging. Clean and sharp tips are made by sputtering, combined with careful heating by electron bombardment. We found that ...