Determination of the atomic structure of scanning probe microscopy tungsten tips by field ion microscopy (original) (raw)
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Implementation of atomically defined field ion microscopy tips in scanning probe microscopy
Nanotechnology, 2012
The Field Ion Microscope (FIM) can be used to characterize the atomic configuration of the apex of sharp tips. These tips are well suited for Scanning Probe Microscopy (SPM) since they predetermine SPM resolution and electronic structure for spectroscopy. A protocol is proposed to preserve the atomic structure of the tip apex from etching due to gas impurities during the transfer period from FIM to SPM, and estimations are made regarding the time limitations of such an experiment due to contamination by ultra-high vacuum (UHV) rest gases. While avoiding any current setpoint overshoot to preserve the tip integrity, we present results from approaches of atomically defined tungsten tips to the tunneling regime with Au(111), HOPG, and Si surfaces at room temperature. We conclude from these experiments that adatom mobility and physisorbed gas on the sample surface limit the choice of surfaces for which the tip integrity is preserved in tunneling experiments at room temperature. The atomic structure of FIM tip apices is unchanged only after tunneling to the highly reactive Si(111) surface.
Field ion microscope evaluation of tungsten nanotip shape using He and Ne imaging gases
Ultramicroscopy, 2012
Field ion microscopy (FIM) using neon imaging gas was used to evaluate a W(111) nanotip shape during a nitrogen assisted etching and evaporation process. Using appropriate etching parameters a narrow ring of atoms centered about the tip axis appears in a helium generated image. Etching of tungsten atoms continues exclusively on the outside of this well-defined ring. By replacing helium imaging gas with neon, normally inaccessible crystal structure of a tip apex is revealed. Comparison of the original W(111) tip (before etching) and partly etched tip shows no atomic changes at the tip apex revealing extraordinarily spatially selective etching properties of the etching process. This observation is an important step towards a detailed understanding of the nitrogen assisted etching and evaporation process and will lead to better control over atomically defined tip shapes.
Combined atom probe and STM study of tip-substrate interactions
Fresenius' Journal of Analytical Chemistry, 1999
A combination of an imaging atom probe (field ion microscope with a time-of-flight mass spectrometer) and a scanning tunneling microscope (STM), which are integrated in the UHV-system, has been used to study the tip-substrate interactions after electrical contact and mechanical indentation. After "jump-to-contact" experiments with tungsten tips on a gold substrate ad-atom clusters has been observed in the FIM-images. The imaged clusters can be identified by time-of-flight mass analysis as Au and give evidence for material transfer in sub-monolayer range. The image contrast in the micrographs gives almost no reference to induced lattice defects after this contact experiments. In additional indentation-experiments clearly induced plastic deformation of the tip crystallite can be observed as well as material transfer of several monolayers. The FIM micrographs after field desorption of consecutive atomic layers show the features of these deformations typically into a depth up to 20-25 atomic layers.
High-precision atomic force microscopy with atomically-characterized tips
New Journal of Physics
Traditionally, atomic force microscopy (AFM) experiments are conducted at tip–sample distances where the tip strongly interacts with the surface. This increases the signal-to-noise ratio, but poses the problem of relaxations in both tip and sample that hamper the theoretical description of experimental data. Here, we employ AFM at relatively large tip–sample distances where forces are only on the piconewton and subpiconewton scale to prevent tip and sample distortions. Acquiring data relatively far from the surface requires low noise measurements. We probed the CaF2(111) surface with an atomically-characterized metal tip and show that the experimental data can be reproduced with an electrostatic model. By experimentally characterizing the second layer of tip atoms, we were able to reproduce the data with 99.5% accuracy. Our work links the capabilities of non-invasive imaging at large tip–sample distances and controlling the tip apex at the atomic scale.
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.
A recent article by Falter et al. (Phys. Rev. B 87, 115412 (2013)) presents experimental results using field ion microscopy (FIM) characterized tips in noncontact atomic force microscopy in order to characterize electrostatic and van der Waals long range forces. In the article, the tip radius was substantially underestimated at ~4.7 nm rather than ~8.0 nm due to subtleties in the application of the ring counting method. We point out where common errors in ring counting arise in order to benefit future experimental work in which the determination of tip radius by FIM is important.
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.
Study on tip–substrate interactions by STM and APFIM
Ultramicroscopy, 2003
Processes occurring at the interface of two materials coming in contact, separating or moving with respect to each other have been studied with the scanning tunnelling microscope (STM) and atom-probe (AP) field ion microscopy (APFIM). STM probe tips have been first characterised by field ion microscopy (FIM), brought into well-defined contact in the STM and afterwards inspected by time-of-flight AP. The results from mechanical contact and indentation experiments, showing material transfer and neck formation, are in reasonable good agreement with computer-based simulations on metal tip-surface interactions. r microscopy; Atom probe field ion microscopy 0304-3991/03/$ -see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -3 9 9 1 ( 0 2 ) 0 0 3 1 6 -9
A simulation study of multi-atom tips and estimation of resolution in atomic force microscopy
1996
The structure of the atomic arrangement at the apex of the tip plays an important role in the atomic force microscope (AFM) images. Computer topographs of the sample surface were simulated with various tip structures at the apex. We have described a scheme to estimate the lower limit of the lateral resolution of AFM with a mono-atomic tip. It is observed that in the contact mode of operation, resolution and sensitivity of AFM is comparable to that of STM.