Lab-in-Gap TEM
Figure 4 : Schematic illustration for a type of Lab-In-Gap workfl ow employing a specially designed Hitachi double heater-gas injection in situ TEM holder. (a) Heater and gas injection are both on to prepare the oxide substrate. (b) The Evaporator is on to deposit materials on the substrate placed on the Heater. (c) After deposition, the sample assembly may be heated with or without gas.
Figure 5 : Workfl ow for synthesis of a catalysis system within the TEM pole piece gap and corresponding live TEM observations of structural changes. (a) Oxidation of Al to form Al 2 O 3 support. (b) Evaporation deposition of AuPd nanoparticles on Al 2 O 3 support. (c) Heating AuPd/Al 2 O 3 system in an air environment and observation of motion and coalescence of two nanoparticles.
a gas spray nozzle was developed [ 8 ]. Figure 4 shows the design principle and operational workfl ow of this device. T e tip of a TEM specimen holder contains two heating fi laments made from spiral tungsten wires. T e one at the bottom position is marked “Heater” and the upper one “Evaporator.” T e two heating fi laments can be turned on and off independently. A gas nozzle is placed close to the Heater and can spray gas when needed. T e purpose behind this holder design is to put the substrate material on Heater and precursor materials on Evaporator. When Evaporator is turned on, the precursors are evaporated and deposited onto the substrate. T e substrate temperature can be controlled by the Heater during and aſt er the evaporation deposition. Gas injection is controlled from outside the TEM column. Because the gas ETEM system can accommodate gas in the TEM specimen chamber, no Si 3 N 4 membrane window, as is used in the window-type gas environmental cell holder [ 2 ],
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is needed. T erefore, high-resolution TEM imaging is readily achievable. Results Figure 5 shows results from a Lab-In-Gap type of in situ TEM experiment using the special function holder shown in Figure 4 . T e entire process, from the synthesis of the Al 2 O 3 substrate and deposition of AuPd nanoparticles on the Al 2 O 3 support to the observation of nanoparticle behavior on the support surface at elevated temperatures, was done totally in situ within the TEM pole piece gap. Image and movie recording were active from the beginning to the end [ 8 ]. As shown in Figure 5a , the process started with a small piece of metal aluminum setting on the Heater. It was heated to 420°C in the presence of air. T e Al was oxidized to form Al 2 O 3 , which was used as the support material in the following steps. The Heater was then turned off, and air was pumped out of the specimen chamber. The Evaporator was turned on to make an evaporation deposition of AuPd nanoparticles onto the Al 2 O 3 support. The formation of nanoparticles on the Al 2 O 3 surface can be seen in the corresponding TEM images ( Figure 5b ). After evaporation the Evaporator was turned off, and the Heater and the gas nozzle were switched on again to heat the assembly to 420°C while the sample chamber was filled with air. TEM imaging reveals the behavior of the nanoparticles on the support.
Figure 5c shows the movement and coalescence of two nanoparticles to form a single crystalline particle.
Discussion
Advanced Lab-In-Gap Electron Microscopy . Obviously, integrating miniaturized devices into the narrow TEM pole piece gap is nontrivial, especially when multiple stimuli or measurement mechanisms are desired. Increasing the pole piece gap would make more complicated Lab-In-Gap tasks possible. With this goal in mind, Hitachi developed a state- of-the-art ETEM platform with a significantly widened pole piece gap compared with that in the standard HF-3300 or H-9500. To compensate for the loss in resolution due to the increase in the pole-piece gap, a hexapole TEM imaging aberration corrector was installed onto the TEM column. It is a so-called B-COR corrector made by CEOS GmbH in Germany. This aplanatic aberration corrector not only
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