Atom probe interface analysis

In compositional analysis of very small precipitates, or in interface segregation studies, using a probe-hole type atom-probe, one is always faced with the fact that the probe-hole may cover both the matrix and the precipitate phases, or the interface as well as the matrix. Thus any abrupt compositional changes will be smeared out by the size of the probe-hole and also by the effect of ion trajectories. A similar uncertainty seems to exist in the compositional analysis of nitride platelets formed in nitrided Fe-3 at.% Mo alloy, aged between 450 and 600°C, where Wagner ... 

There are of course many other similarities and differences, and some of them are listed in Table 5.1 without further explanations. In general, STM is very versatile and flexible. Especially with the development of the atomic force microscope (AFM), materials of poor electrical conductivity can also be imaged. There is the potential of many important applications. A critically important factor in STM and AFM is the characterization of the probing tip, which can of course be done with the FIM. FIM, with its ability to field evaporate surface atoms and surface layers one by one, and the capability of single atom chemical analysis with the atom-probe FIM (APFIM), also finds many applications, especially in chemical analysis of materials on a sub-nanometer scale. It should be possible to develop an STM-FIM-APFIM system where the sample to be scanned in STM is itself an FIM tip so that the sample can either be thermally treated or be field evaporated to reach into the bulk or to reach to an interface inside the sample. After the emitter surface is scanned for its atomic structure, it can be mass analyzed in the atom-probe for one atomic layer,... 

Miller, M.K., Russell, K.F. (2007) Performance of a local electrode atom probe. Surface and Interface Analysis, 39, 262-267. 

Deconihout, B., Vurpillot, F., Gault, B., Costa, G.D., Bouet, M., Bostel, A., Blavette, D., Hideur, A., Martel, G., Brunei, M. (2007) Toward a laser assisted wide-angle tomographic atom-probe. Surface and Interface Analysis, 39,278-282. 

Despite the crystalline nature of the Al, its surface is extremely rough up to the scale of lOOnm, as can be seen in Fig.2. High resolution microscopy of this interface indicates roughness down to atomic scale. Nanoprobe analysis (with probe size down to 4 nm) in the amorphous phase at increasing distances from the Al crystal gave no gradient of concentration indicating that this structure is not related to diffusion process. However, nanoprobe analysis at the Al rim combined with atomic resolution microscopy indicate that amorphous pockets of Ge exists in the Al rim. ... 

The geometry of APFIM analysis of interfaces is illustrated in Figure 1.8. During analysis the interface moves across the probe hole, and the increase in number of solute atoms per unit area of the interface (T) can be calculated. 

Up to date, besides the SFA, several non-interferometric techniques have been developed for direct measurements of surface forces between solid surfaces. The most popular and widespread is atomic force microscopy, AFM [14]. This technique has been refined for surface forces measurements by introducing the colloidal probe technique [15,16], The AFM colloidal probe method is, compared to the SFA, rapid and allows for considerable flexibility with respect to the used substrates, taken into account that there is no requirement for the surfaces to be neither transparent, nor atomically smooth over macroscopic areas. However, it suffers an inherent drawback as compared to the SFA It is not possible to determine the absolute distance between the surfaces, which is a serious limitation, especially in studies of soft interfaces, such as, e.g., polymer adsorption layers. Another interesting surface forces technique that deserves attention is measurement and analysis of surface and interaction forces (MASIF), developed by Parker [17]. This technique allows measurement of interaction between two macroscopic surfaces and uses a bimorph as a force sensor. In analogy to the AFM, this technique allows for rapid measurements and expands flexibility with respect to substrate choice however, it fails if the absolute distance resolution is required. 

Liu et al. used GGA calculations with the PBE functional to probe adsorption and reaction of 02 and CO on Au supported on defect-free TiO2(110).185 These calculations used a bilayer of Au forming a continuous strip across the support surface. 02 adsorption was found to be favorable only for adsorption on Au adjacent to the support surface. An analysis of the bonding character of these states indicated that the support enhances charge transfer from Au to 02 for Au atoms in close proximity to the support. CO oxidation via a reaction between adsorbed CO and adsorbed 02 at the Au/support interface was found to have a small activation barrier (0.1 eV). CO oxidation pathways involving adsorbed atomic oxygen were not examined, although adsorbed O is created by the pathway mentioned above. Also, dissociation of adsorbed 02 was found to occur with a barrier of 0.5 eV. 

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