Shape Of Tip Apex Research Articles

Oxidative vaporization etching for molybdenum tip formation in air

Oxidative vaporization in air using a flame with a temperature range of 1950–2300 K was employed for controlling the tip shape made from a nipper-cut metal molybdenum (Mo) wire edge. An extremely high vapor pressure of MoO3 generated on the Mo surface in flame is a driving force behind the tip shape formation. Since the MoO3 vaporization rate follows the flame temperature gradient, we could control the tip apex shape by selecting the proper flame etching condition. The best condition to obtain a sharp tip apex based on statistical tests of dozens of Mo tips was obtained by Mo wire edge insertion into the 2100 K flame from the side for one second. This was repeated twice, which reproducibly provided a tip apex with a radius of 50–100 nm and a cone angle of 20–30 degrees. The present Mo tips, fabricated without aqueous solutions, were examined for their suitability as probe tips through air-scanning tunneling microscopy (STM), ultrahigh vacuum STM, field emission spectroscopy, and conductance measurements.

On the Origin of Extended Resolution in Kelvin Probe Force Microscopy with a Worn Tip Apex.

In this work we analyzed the effect of the atomic force microscopy probe tip apex shape on Kelvin Probe Force Microscopy (KPFM) potential sensitivity and spatial resolution. It was found that modification of the apex shape from spherical to planar upon thinning of the conductive coating leads to enhanced apex contribution to the total electrostatic force between the probe and the sample. The effect results in extended potential sensitivity and spatial resolution of KPFM. Experimental results were supported by calculations.

Fabrication of Gas Field Ion Emitter by Field Induced Oxygen Etching Method

Focused ion beam system with a liquid metal ion source has a serious problem which is the pollution of samples due to irradiated ion species. To solve the problem, we have developed a noble gas field ion source which scarcely gives rise to the pollution. In this case, a key issue for the field-ion emitter is the shape of tip-apex to obtain a higher angular current density. Better performance is expected for a shape of tip-apex having a nanoscale-protrusion on the emitter tip with large radius of curvature. For realization of such a shape of tip-apex, field-induced oxygen etching method, which was reported by Onoda et al., was modified and applied to a sharpened tungsten wire which was electrolitically polished. Observation of formed emitter tips by transmission electron microscopy revealed that a nanoprotrusion having a shape of truncated cone with ∼5 nm in diameter and ∼4 nm in height was formed at the center of an emitter tip with ∼90 nm in radius of curvature. [DOI: 10.1380/ejssnt.2011.344]

Reconstruction of atomic force microscopy image by using nanofabricated tip characterizer toward the actual sample surface topography

The atomic force microscopy (AFM) image is a dilation of the sample surface topography due to the finite-sized AFM tip. We accurately estimated the tip apex shape with a nanofabricated Si tip characterizer and applied the estimated tip shape function to a dilation-erosion algorithm for image reconstruction. The reconstructed images from the original AFM images attained with different AFM tips show consistent surface features and closely match the high-resolution field-emission scanning electron microscope image. The results demonstrate the reliability of our method and suggest the importance of AFM image reconstruction for a variety of technologies requiring new strategies of measuring, interpreting, manipulating, and positioning in the submicrometer and nanometer range.

Near-field optical spectroscopy using an incoherent light source

We present a method to perform near-field optical spectroscopy. It consists of an apertureless near-field optical microscope combined with an incoherent light source and a monochromator. We show that the optical response of the tip depends both on the wavelength and the tip apex shape. The experimental optical response of the tips is in good agreement with the predicted theoretical one. The near-field optical spectrum obtained on a gold island in the visible spectrum range (λ=400–600 nm) is presented and shows that the method is reliable to perform spectroscopic measurements on submicrometer-sized objects.

WS 2 nanotubes as tips in scanning probe microscopy

WS 2 nanotubes a few microns long were attached to microfabricated Si tips and tested afterwards in an atomic force microscope by imaging a “replica” of high aspect ratio, i.e., deep and narrow grooves. These WS2 nanotube tips provide a considerable improvement in image quality for such structures when compared with commercial ultrasharp Si tips. The nanotube tip apex shape was extracted by blind reconstruction from an image of Ti spikes, showing a smooth cylindrical profile up to the end.

Correlation between tip-apex shape and surface modification by scanning tunneling microscopy

The correlation between the shape of a probe tip apex for scanning tunneling microscopy and the surface modification patterns on a Si(111)-7×7 surface is demonstrated by using an in situ tip evaluation technique. The tip apex is inversely imaged by using a very sharp nanoneedle fabricated on the sample surface by applying a high voltage between the tip and the surface. When a large current of 100–300 nA flows between the tip and the surface, silicon atoms on the surface are extracted and a trench pattern is formed. The trench pattern agrees well with the geometry of the tip apex. The correlation between the tip shape and the fabrication pattern is discussed in terms of the electric field under the tip.

Effect of tip atomic structure on scanning tunneling spectroscopy

Tunneling conductance in scanning tunneling spectroscopy of graphite is simulated by the first-principles electronic structure calculation. As models of tip, W 10[111], W 14[110], and Pt 10[111] clusters are adopted. Simulated tunneling spectra are influenced by the shape of tip apex and deviate from one obtained by the theory assuming the conductance proportional to the surface local density of states. A broader energy spectrum of tip levels reproduces well the experimental data.