An informatics based approach to extract further refinements on the crystallographic information embedded in the Spatial Distribution Maps (SDMs) has been developed. The data mining based methods to generate and interpret spectra that de-convolute the SDMs are discussed. This work has resulted in a method to generate SDMs that can map three-dimensional crystallographic information as opposed to existing methods that map structural information on only one atomic plane at a time. The broader implications of this work on enhancing the interpretation and resolution of structural information in atom probe tomography studies is also discussed.

A series of simulated microstructures containing nanometer-scale precipitates was created with an atom probe simulator. These data were then analyzed with the proximity histogram and the maximum separation method to determine the influence of the particular analysis method. For simulated 2-nm-radius spherical precipitates, the optimized voxel size and delocalization were found to be 0.5-0.6 nm and 1.0-1.5 nm, respectively. Under optimum analysis parameters, the voxelization/delocalization process only slightly degrades the interface width determined from the proximity histogram to ˜0.15±0.04 nm.

Atom probe (AP) is known to be a unique instrument that makes possible to mass analyze a specimen at atomic level. However, its application is mostly limited to metals and semiconductors because the AP analysis proceeds by field evaporating surface atoms applying the high field, 20-40 V/nm, on the specimen surface. In order to generate such a high field the analyzed area is an apex of a sharp tip. Metals and semiconductors can be formed in such a sharp tip easily. However, the formation of a sharp organic and bio molecule tip is not easy. Thus, we introduced a funnel shaped micro extraction electrode that scans over a specimen surface and confines the high field in a narrow space between the micro open hole at the apex of the electrode and a micro protrusion on a specimen surface. Thus, this type of the AP is named as scanning atom probe (SAP). Then, organic and bio molecules can be deposited on the micro protrusion on the specimen surface. The AP analysis of metals indicates that the field evaporation of metal atoms proceeds one atom by one atom implying that the binding between metal atoms are uniform and non-directional. On the other hand most atoms of non-metallic specimens are field evaporated as clustering atoms. For example, doubly charged thiophene monomers are detected when polythiophene is analyzed. This indicates that one sulfur and four carbon atoms are strongly bound. Similarly, the mass spectra of highly pure single walled carbon nano tubes (SWCNT) exhibit sharp mass peaks of C2+ and C+ indicating that carbon atoms are bound by non-directional strong bonds. This implies that the unique feature of the AP is not only in the identification of individual ion but also in the investigation of binding states of the atoms forming the materials. For the present analysis amino acids are deposited on a small ball of the SWCNT fibers in order to avoid the catalytic reaction of metals. The SWCNT ball is dipped in a solution of sample molecules. The glycine solution is made by dissolving 1 gram of glycine in 15 ml pure water. Cystine, leucine and methionine solutions are made by dissolving 50 mg of the molecules in 1 ml of 0.1 N HCl. Discrimination of the carbon ions of the SWCNT from the fragment ions of the molecules is relatively easy because nearly all of the SWCNT carbon ions are detected as C2+ and C+. Glycine is the smallest amino acid formed by a carboxy group, an amino group and a CH2 group. Thus, it is assumed that the analysis will provide a guideline for the analysis of larger molecule. However, the identification of fragments ions is not easy because many different fragments have the same mass such as CH3 and NH. This indicates that mass analyzer for the bio-molecules requires a mass spectrometer with the mass resolution m/Δm higher than 10,000. The characteristic mass spectra of the amino acids and the structure of a new SAP with a position sensitive ion detector with a spiral delay line will be presented.

A Yb:KGW femtosecond laser (400 fs) with 3rd and 4th harmonic generators (wavelength = 343 and 258 nm) was adopted to a locally built 3DAP instrument to assist field evaporation from ceramics tips that were bonded on tungsten wire. Using this setting, we have demonstrated that quantitative atom probe tomography is possible from Y2O3-ZrO2-MgAl2O4, (Ce,Y)O2, Li(Co,Ni,Mg,Al)O2 sintered bulk ceramics, which are all insulators.