A SYSTEM FOR SYSTEMATICALLY PREPARING ATOM-PROBE FIELD-ION-MICROSCOPE SPECIMENS FOR THE STUDY OF INTERNAL INTERFACES

A versatile system has been designed and fabricated to prepare atom-probe field-ion-microscope (APFIM) specimens in a systematic manner, such that internal interfaces can be positioned in the tips of these wire specimens for subsequent analysis of their chemical composition. This system incorporates both beaker electrolytic and zone electrolytic cell configurations, a specially constructed power supply, and a special transmission electron microscope holder for wires. The power supply enables ac electroetching or dc electropolishing in the automated or manual modes. The ac wave forms available are sine (0.002 Hz-200 kHz) or square (10 Hz-20 kHz). Triggering and gating are performed manually or with a pulse generator. The dc output is gated manually to produce a continuous output or with a pulse generator to produce single pulses with widths in the range 50 μs-1 s. A counter indicates the number of periods of voltage applied, and the total charge transferred in the electrolytic cell is integrated in the range 10 μAs-1 kAs. The power supply provides 0 to ±48 V peak at 1 A peak. A double-tilt stage for an Hitachi H-700H 200 kV transmission electron microscope (TEM) was radically modified to hold APFIM specimens; this stage is vibrationless at 310 000× magnification. It has a tilting range of ±30°and ±27°for the x and y tilts, respectively. Examples are given of the controlled backpolishing of W-3 at. % Re, W-25 at. % Re, Mo-5.4 at. % Re, and Fe-3 at. % Si specimens, and their observation by TEM, to selectively place grain boundaries in the tip region. The analysis of the chemical composition of a grain boundary, which is first located in a W-25 at. % Re specimen via TEM, by the APFIM technique is presented.