Sample preparation toward seamless 3D imaging technique from micrometer to nanometer scale

Three-dimensional (3D) imaging techniques, such as x-ray computed tomography (XCT), serial sectioning method, transmission electron microtomography (TEMT) and 3D atom probe (3DAP), provides 3D internal structures and external form of objects. In order to obtain the 3D images of one object from the synchrotron-XCT (SR-XCT), FIB-SEM serial sectioning, TEMT and 3DAP, in the present study, the common sample holder and improvement in the TEM tomography retainer were made. We report the sample holder, the TEM retainer, and the sample preparation method using focused ion beam (FIB) and show the 3D images obtained from SR-XCT, FIB-SEM and TEMT of quartz sample containing fluid inclusions.The present common sample holder was made from tungsten needle and copper pipe. The tungsten needle was made from the wire by electropolishing in aqueous ammonia and salt as molten material. A micro-sample of quartz containing fluid inclusions was picked up from the thin section using a focused ion beam (FIB) system (FEI, Quanta 200 3DS), Kyoto University. The FIB system used a Ga(+) ion gun at the condition of 30 kV and 3-65 nA. After a specific area (ca. several ten μm on a side) of the quartz was cut out to a depth of 10 - 30 µm by FIB, it was held at a tip of tungsten needle with platinum deposition (Figure 1a) [1]. Then it was observed by imaging tomography system using a Frenel zone plate at BL47XU, SPring-8, Japan [2]. The size of voxel (pixel in 3D) was 50-80 nm, which gave the effective spatial resolution of ∼200 nm. The characteristic of this method (FIB-XCT) is that the XCT sample can be exactly picked up from a specific area from thin section and bulk specimen after the observation using optical microscopy and/or scanning electron microscopy (SEM). After the FIB-XCT observation, the sample held at a tip of tungsten needle was directly inserted into the FIB-SEM system and the cross-section surface were observed by FIB-SEM. Figure 1b shows a snap shot of the cross-section surface. 3D image was reconstructed from the obtained surface image series and the spatial resolution of this 3D image is higher than XCT although it is depended on the spatial resolution of FIB and SEM. When we obtain TEMT image from the specific area after FIB-XCT and FIB-SEM, TEMT specimen is picked up during FIB-SEM processing and is attached to another tungsten needle. TEMT specimen can be also made from the remaining sample of FIB-SEM held at same holder. Then TEMT specimen was carefully milled into a sharp rod-form with annular-mask by FIB (Figure 1c). This specimen can be analysis by 3DAP. The tungsten needle with rod specimen at the top was mounted in the specimen retainer which was shaped by nipper to achieve the ± 90 ° tilt without any impedimenta and was dug the channel by femto-second laser system to fix the tungsten needle. TEMT experiments were carried out using a JEM-2100F (JEOL LTD., Japan) at Kyoto University. The acceleration voltage was 200kV. The inclusion of about 20 to 100 nm in quartz, which could not be detected by FIB-XCT, was clearly identified in a TEM and TEMT image (Figure 1d).jmicro;63/suppl_1/i24/DFU055F1F1DFU055F1Fig. 1.(a) FIB-XCT sample held at a tip of tungsten needle. (b) A snap shot of the cross-section surface by FIB-SEM at tilt = 52°. The hole observed in the center is the trace of fluid inclusion. (c) Sharp rod-formed TEMT specimen at a tip of tungsten needle. (d) Bright field TEM image of quartz TEMT specimen. The inclusion of about 50 × 100 nm (inside of dashed line circle) was observed in quartz.