kb/data/en.wikipedia.org/wiki/Atom_probe-1.md

---
title: "Atom probe"
chunk: 2/4
source: "https://en.wikipedia.org/wiki/Atom_probe"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T10:03:43.942629+00:00"
instance: "kb-cron"
---

=== Imaging Atom Probe ===
The Imaging Atom-Probe (IAP) was introduced in 1974 by J. A. Panitz. It incorporated the features of the 10-cm Atom-Probe yet “... departs completely from [previous] atom probe philosophy. Rather than attempt to determine the identity of a surface species producing a preselected ion-image spot, we wish to determine the complete crystallographic distribution of a surface species of preselected mass-to-charge ratio. Now suppose that instead of operating the [detector] continuously, it is turned on for a short time coincidentally with the arrival of a preselected species of interest by applying a gate pulse a time T after the evaporation pulse has reached the specimen. If the duration of the gate pulse is shorter than the travel time between adjacent species, only that surface species having the unique travel time T will be detected and its complete crystallographic distribution displayed.”  It was patented in 1975 as the Field Desorption Spectrometer. The Imaging Atom-Probe moniker was coined by A. J. Waugh in 1978 and the instrument was described in detail by J. A. Panitz in the same year.

=== Atom Probe Tomography (APT) ===
Modern day atom probe tomography uses a position sensitive detector aka a FIM in a box to deduce the lateral location of atoms. The idea of the APT, inspired by J. A. Panitz's Field Desorption Spectrometer patent, was developed by Mike Miller starting in 1983 and culminated with the first prototype in 1986. Various refinements were made to the instrument, including the use of a so-called position-sensitive (PoS) detector by Alfred Cerezo, Terence Godfrey, and George D. W. Smith at Oxford University in 1988. The Tomographic Atom Probe (TAP), developed by researchers at the University of Rouen in France in 1993, introduced a multichannel timing system and multianode array. Both instruments (PoSAP and TAP) were commercialized by Oxford Nanoscience and CAMECA respectively. Since then, there have been many refinements to increase the field of view, mass and position resolution, and data acquisition rate of the instrument. The Local Electrode Atom Probe was first introduced in 2003 by Imago Scientific Instruments. In 2005, the commercialization of the pulsed laser atom probe (PLAP) expanded the avenues of research from highly conductive materials (metals) to poor conductors (semiconductors like silicon) and even insulating materials. AMETEK acquired CAMECA in 2007 and Imago Scientific Instruments (Madison, WI) in 2010, making the company the sole commercial developer of APTs with more than 110 instruments installed around the world in 2019.
The first few decades of work with APT focused on metals. However, with the introduction of the laser pulsed atom probe systems applications have expanded to semiconductors, ceramic and geologic materials, with some work on biomaterials. The most advanced study of biological material to date using APT involved analyzing the chemical structure of teeth of the radula of chiton Chaetopleura apiculata. In this study, the use of APT showed chemical maps of organic fibers in the surrounding nano-crystalline magnetite in the chiton teeth, fibers which were often co-located with sodium or magnesium. This has been furthered to study elephant tusks, dentin and human enamel.

== Theory ==

=== Field evaporation ===
Field evaporation is an effect that can occur when an atom bonded at the surface of a material is in the presence of a sufficiently high and appropriately directed electric field, where the electric field is the differential of electric potential (voltage) with respect to distance. Once this condition is met, it is sufficient that local bonding at the specimen surface is capable of being overcome by the field, allowing for evaporation of an atom from the surface to which it is otherwise bonded.

=== Ion flight ===
Whether evaporated from the material itself, or ionised from the gas, the ions that are evaporated are accelerated by electrostatic force, acquiring most of their energy within a few tip-radii of the sample.
Subsequently, the accelerative force on any given ion is controlled by the electrostatic equation, where n is the ionisation state of the ion, and e is the fundamental electric charge.

  
    
      
        F
        =
        n
        e
        ∇
        ϕ
      
    
    {\displaystyle F=ne\nabla \phi }
  

This can be equated with the mass of the ion, m, via Newton's law (F=ma):

  
    
      
        m
        a
        =
        q
        ∇
        ϕ
      
    
    {\displaystyle ma=q\nabla \phi }
  

  
    
      
        a
        =
        
          
            q
            m
          
        
        ∇
        ϕ
      
    
    {\displaystyle a={\frac {q}{m}}\nabla \phi }
  

Relativistic effects in the ion flight are usually ignored, as realisable ion speeds are only a very small fraction of the speed of light.
Assuming that the ion is accelerated during a very short interval, the ion can be assumed to be travelling at constant velocity. As the ion will travel from the tip at voltage V1 to some nominal ground potential, the speed at which the ion is travelling can be estimated by the energy transferred into the ion during (or near) ionisation. Therefore, the ion speed can be computed with the following equation, which relates kinetic energy to energy gain due to the electric field, the negative arising from the loss of electrons forming a net positive charge.

  
    
      
        E
        =
        
          
            1
            2
          
        
        m
        
          U
          
            
              i
              o
              n
            
          
          
            2
          
        
        =
        −
        n
        e
        
          V
          
            1
          
        
      
    
    {\displaystyle E={\frac {1}{2}}mU_{\mathrm {ion} }^{2}=-neV_{1}}
  

Where U is the ion velocity. Solving for U, the following relation is found:

  
    
      
        U
        =
        
          
            
              
                2
                n
                e
                
                  V
                  
                    1
                  
                
              
              m
            
          
        
      
    
    {\displaystyle U={\sqrt {\frac {2neV_{1}}{m}}}}
  

Let's say that for at a certain ionization voltage, a singly charged hydrogen ion acquires a resulting velocity of 1.4x10^6 ms−1 at 10~kV. A singly charged deuterium ion under the sample conditions would have acquired roughly 1.4x10^6/1.41 ms−1. If a detector was placed at a distance of 1 m, the ion flight times would be 1/1.4x10^6 and 1.41/1.4x10^6 s. Thus, the time of the ion arrival can be used to infer the ion type itself, if the evaporation time is known.
From the above equation, it can be re-arranged to show that

  
    
      
        
          
            m
            n
          
        
        =
        −
        
          
            
              2
              e
              
                V
                
                  1
                
              
            
            
              U
              
                2
              
            
          
        
      
    
    {\displaystyle {\frac {m}{n}}=-{\frac {2eV_{1}}{U^{2}}}}