Atom-probe field ion microscope

In this case the surfaces fi = constant correspond to the equipotentials and the surfaces a = constant correspond to the surfaces on which the electric field lines are fixed. The distance from the origin to the focus, a, is related to the distance between the apex and the origin, d, and the radius of curvature of the tip, rt, by a = [d(d + rt) m. 

This solution can also be expressed in cylindrical coordinates (p, f , z) as 

An example for the field cones and equipotential surface is shown in Fig. 3.9 for d = 1.2 mm and rt= 420 A. The vertical line represents a position of 5rt away from the tip. The field lines are drawn so that their density is proportional to the field strength. Field distributions and equipotential surfaces of other tip shapes have also been investigated, particularly as regards the field emission current density distribution,24,31 but will not be discussed here. 

The atom-probe field ion microscope is a device which combines an FIM, a probe-hole, and a mass spectrometer of single ion detection sensitivity. With this device, not only can the atomic structure of a surface be imaged with the same atomic resolution as with an FIM, but the chemical species of surface atoms of one s choice, chosen from the field ion image and the probe-hole, can also be identified one by one by mass spectrometry. In principle, any type of mass analyzer can be used as long as the overall detection efficiency of the mass analyzer, which includes the detection efficiency of the ion detector used and the transmission coefficient of the system, has to be close to unity. 

The original function of the atom-probe is for the chemical analysis of the atoms of one s choice. It is however possible to extend the function of the atom-probe to ion kinetic energy analysis37 and ion reaction rate measurement,38 or general spectroscopy, with the same sensitivity, as has already been described in Chapter 2. 

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The atom probe field-ion microscope (APFIM) and its subsequent developments, the position-sensitive atom probe (POSAP) and the pulsed laser atom probe (PLAP), have the ultimate sensitivity in compositional analysis (i.e. single atoms). FIM is purely an imaging technique in which the specimen in the form of a needle with a very fine point (radius 10-100 nm) is at low temperature (liquid nitrogen or helium) and surrounded by a noble gas (He, Ne, or Ar) at 10 -10 Pa. A fluorescent screen or a... 

The opening chapter, however, gives an account of the ultimate technique in local analysis, namely that of the atom probe field ion microscope. Here no probe is employed as in the above list, but individual atoms of the specimen are removed and identified by mass spectroscopy. 

Basic principle of the atom-probe field ion microscope... 

Many other atom-probe analyses of different phases in different types of steels exist as steels are one of the most important materials. It is possible to investigate how the magnetic properties of alloys are correlated to the microstructures of different phases in the alloys.57,58,59 The chemical contents, growth process and structures of metallic carbides in different alloy steels have been studied with the field ion microscope and the atom-probe field ion microscope.60 61 62 63 We refer the reader to some of the original papers published on these subjects. 

Brenner et al. reported an atom-probe field-ion microscope study of decomposition in an Fe-Cr-Co alloy (see Fig. 18.11) [23]. The atom probe allows direct compositional analysis of the peaks and valleys of the composition waves. It is probably the best tool for verifying a spinodal mechanism in metals, because the growth in amplitude of the composition waves can be studied as a function of aging time, with near-atomic resolution. In spinodal alloys, there is a continuous increase in the amplitude of the composition waves with aging time. On the other hand, for a transformation by nucleation and growth, the particles formed earliest generally exhibit a compositional discontinuity with the matrix. 

Sakurai et al. [218] have used the atom probe field ion microscope [219] to make a direct study of hydride phases on silicon. Continuous field evaporation from 111 and 110 Si planes in the presence of hydrogen produced Si+, SiH+ and SiHj. Some Si atoms evaporate without forming hydrides to give Si+ SiH+ derives simply from the monohydride phase and SiHj from the dihydride. However, this latter comes from the 111 surface, whereas UPS data consistent with the presence of a dihydride came from 100 lxl. This apparent difference can be reconciled by the fact that some kink site atoms on 111 planes have two dangling orbitals per Si atom (as on 100 surfaces) and field evaporation occurs primarily at kink sites. 

Muller, E.W, Panitz, J.A., McLane, S.B. (1968) The atom-probe field ion microscope. Review of Scientific Instruments, 39, 83-86. 

Field-emission microscope (Erwin Wilhelm Muller) Muller develops the field- ion microscope, followed by an atom-probe field-ion microscope in 1963, which can detect individual atoms. 

A Atrens, JQ Wang, K Stiller and HO Andren, Atom probe field ion microscope measurements of carbon segregation at an a a grain boundary and service failures by intergranular stress corrosion cracking. Corrosion Science, 2006, 48, 79-92. 

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