Preparation and characterization of electrochemically etched W tips for STM (original) (raw)
Related papers
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.
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.
Tip preparation for usage in an ultra-low temperature UHV scanning tunneling microscope
Science and Technology of Advanced Materials, 2007
This work deals with the preparation and characterization of tungsten tips for the use in UHV low-temperature scanning tunneling microscopy and spectroscopy (STM and STS, respectively). These specific environments require in situ facilities for tip conditioning, for further sharpening of the tips, as well as for reliable tip characterization. The implemented conditioning methods include direct resistive annealing, annealing by electron bombardment, and self-sputtering with noble gas ions. Moreover, results from in situ tip characterization by field emission and STM experiments were compared to ex situ scanning electron microscopy. Using the so-prepared tips, high resolution STM images and tunneling spectra were obtained in a temperature range from ambient down to 350 mK, partially with applied magnetic field, on a variety of materials. r
Ultrasharp tungsten tips—characterization and nondestructive cleaning
Ultramicroscopy, 2012
We study the treatment of ultrasharp tungsten tips used for applications in nanoscience and introduce a fast and simple method for estimation of the tip radius using a single measurement of the autoemission current. The method is based on a detailed investigation of the influence of an arrangement of electrodes on the electric field layout in close proximity of the tip apex. The electric field was calculated using Monte Carlo Floating Random Walk algorithm. The most frequently used cleaning procedures (heating the whole tip to high temperature, electron bombardment and selfsputtering) were investigated by electrical measurements and microscopy techniques (SEM, TEM) and the results of the particular methods are compared. We report on the effectiveness and limiting conditions of the cleaning methods with respect to the damage they cause to the tip apex.
Physical Review B, 2005
Detailed knowledge of the tip apex structure is necessary for quantitative comparison between theory-based simulations and experimental observations of tip-substrate interactions in scanning probe microscopy ͑SPM͒. Here, we discuss field ion microscopy ͑FIM͒ techniques to characterize and atomically define SPM tungsten tips. The tip radius can be estimated from field emission data, while FIM imaging allows the full atomic characterization of the tip apex. We find that when FIM is applied to tips with a radius of a few nanometers ͑as is desirable for high-resolution atomic force microscopy imaging͒, limitations not apparent with less sharp tips arise; successful resolution of these limitations will extend the utility of FIM. Field evaporation can be used to atomically engineer the apex into a desired atomic configuration. Starting from a W͑111͒ wire, a tip terminating in three atoms can reproducibly be fabricated; due to its geometry and stability, this apex configuration is well suited for application as an atomically defined electrical contact in SPM experiments aimed at understanding contact mechanics at the atomic scale.
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.
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.
Reproducible tip fabrication and cleaning for UHV STM
Ultramicroscopy, 2008
Several technical modifications related to the fabrication and ultra-high vacuum (UHV) treatments of the scanning tunneling microscope (STM) tips have been implemented to improve a reliability of the tip preparation for high-resolution STM. Widely used electrochemical etching drop-off technique has been further refined to enable a reproducible fabrication of the tips with a radius ⩽3 nm. For tip cleaning by a controllable UHV annealing, simple and flexible setup has been developed. Proper W tip preparation has been demonstrated via an imaging of the TiO2 (1 1 0) surface atomic structure.