---
title: "Probe tip"
chunk: 1/5
source: "https://en.wikipedia.org/wiki/Probe_tip"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:41:57.526681+00:00"
instance: "kb-cron"
---

A probe tip is an instrument used in scanning probe microscopes (SPMs) to scan the surface of a sample and make nano-scale images of surfaces and structures. The probe tip is mounted on the end of a cantilever and can be as sharp as a single atom. In microscopy, probe tip geometry (length, width, shape, aspect ratio, and tip apex radius) and the composition (material properties) of both the tip and the surface being probed directly affect resolution and imaging quality. Tip size and shape are extremely important in monitoring and detecting interactions between surfaces. SPMs can precisely measure electrostatic forces, magnetic forces, chemical bonding, Van der Waals forces, and capillary forces. SPMs can also reveal the morphology and topography of a surface.
The use of probe-based tools began with the invention of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), collectively called scanning probe microscopy (SPM) by Gerd Binnig and Heinrich Rohrer at the IBM Zurich research laboratory in 1982. It opened a new era for probing the nano-scale world of individual atoms and molecules as well as studying surface science, due to their unprecedented capability to characterize the mechanical, chemical, magnetic, and optical functionalities of various samples at nanometer-scale resolution in a vacuum, ambient, or fluid environment.
The increasing demand for sub-nanometer probe tips is attributable to their robustness and versatility. Applications of sub-nanometer probe tips exist in the fields of nanolithography, nanoelectronics, biosensor, electrochemistry, semiconductor, micromachining and biological studies.

== History and development ==
Increasingly sharp probe tips have been of interest to researchers for applications in the material, life, and biological sciences, as they can map surface structure and material properties at molecular or atomic dimensions. The history of the probe tip can be traced back to 1859 with a predecessor of the modern gramophone, called the phonautograph. During the later development of the gramophone, the hog's hair used in the phonautograph was replaced with a needle used to reproduce sound. In 1940, a pantograph was built utilizing a shielded probe and adjustable tip. A stylus was free moving allowing it to slide vertically in contact with the paper. In 1948, a circuit was employed in the probe tip to measure peak voltage, creating what may be considered the first scanning tunneling microscope (STM). The fabrication of electrochemically etched sharp tungsten, copper, nickel and molybdenum tips were reported by Muller in 1937. A revolution in sharp tips then occurred, producing a variety of tips with different shapes, sizes, and aspect ratios. They composed of tungsten wire, silicon, diamond and carbon nanotubes with Si-based circuit technologies. This allowed the production of tips for numerous applications in the broad spectrum of nanotechnological fields.
Following the development of STM, atomic force microscopy (AFM) was developed by Gerd Binnig, Calvin F. Quate, and Christoph Gerber in 1986. Their instrument used a broken piece of diamond as the tip with a hand-cut gold foil cantilever. Focused ion and electron beam techniques for the fabrication of strong, stable, reproducible Si3N4 pyramidal tips with 1.0 μm length and 0.1 μm diameter were reported by Russell in 1992. Significant advancement also came through the introduction of micro-fabrication methods for the creation of precise conical or pyramidal silicon and silicon nitride tips. Numerous research experiments were conducted to explore fabrication of comparatively less expensive and more robust tungsten tips, focusing on a need to attain less than 50 nm radius of curvature.
A new era in the field of fabrication of probe tips was reached when the carbon nanotube, an approximately 1 nm cylindrical shell of graphene, was introduced. The use of single wall carbon nanotubes makes the tips more flexible and less vulnerable to breaking or crushing during imaging. Probe tips made from carbon nano-tubes can be used to obtain high-resolution images of both soft and weakly adsorbed biomolecules like DNA on surfaces with molecular resolution.
Multifunctional hydrogel nano-probe techniques also advanced tip fabrication and resulted in increased applicability for inorganic and biological samples in both air and liquid. The biggest advantage of this mechanical method is that the tip can be made in different shapes, such as hemispherical, embedded spherical, pyramidal, and distorted pyramidal, with diameters ranging from 10 nm – 1000 nm. This covers applications including topography or functional imaging, force spectroscopy on soft matter, biological, chemical and physical sensors. Table 1. Summarizes various methods for fabricating probe tips, and the associated materials and applications.

== Tunneling current and force measurement principle ==
The tip itself does not have any working principle for imaging, but depending on the instrumentation, mode of application, and the nature of the sample under investigation, the probe's tip may follow different principles to image the surface of the sample. For example, when a tip is integrated with STM, it measures the tunneling current that arises from the interaction between the sample and the tip. In AFM, short-ranged force deflection during the raster scan by the tip across the surface is measured. A conductive tip is essential for the STM instrumentation whereas AFM can use conductive and non-conductive probe tip. Although the probe tip is used in various techniques with different principles, for STM and AFM coupled with probe tip is discussed in detail.

=== Conductive probe tip ===
As the name implies, STM utilizes the tunneling charge transfer principle from tip to surface or vice versa, thereby recording the current response. This concept originates from a particle in a box concept; if potential energy for a particle is small, the electron may be found outside of the potential well, which is a classically forbidden region. This phenomenon is called tunneling.
Expression derived from Schrödinger equation for transmission charge transfer probability is as follows:

  
    
      
        T
        =
        16
        ϵ
        (
        1
        −
        ϵ
        
          )
          
            −
            2
            k
          
        
      
    
    {\displaystyle T=16\epsilon (1-\epsilon )^{-2k}}
  

where

  
    
      
        ϵ
        =
        
          
            E
            V
          
        
        =
        
          Kinetic energy/potential energy
        
      
    
    {\displaystyle \epsilon ={\frac {E}{V}}={\text{Kinetic energy/potential energy}}}
  

  
    
      
        k
        =
        2
        π
        
          
            
              
                2
                m
                E
              
              h
            
          
        
      
    
    {\displaystyle k=2\pi {\sqrt {\frac {2mE}{h}}}}
  

  
    
      
        h
      
    
    {\displaystyle h}
  
 is the Planck constant