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Microscopists demand better performance from their electron microscopes with every new instrument. With the advancement of new instrument technologies, better images, higher resolution, more precise analysis, and faster throughput are all benefits that are expected of expensive purchases. Still, in many cases, a well-known problem detrimentally affects the quality of results: specimen contamination.

High‐surface‐area gold catalysts are promising catalysts for a number of selective oxidation and reduction reactions but typically suffer catalyst deactivation at higher temperatures. The major reason for catalyst deactivation is sintering, which can be triggered via two mechanisms: particle migration and coalescence, and Ostwald ripening. Herein, a direct method to synthesize Au25 clusters stabilized with 3‐mercaptopropyltrimethoxysilane (MPTS) ligands is discussed. The sintering of Au25(MPTS)18 clusters on mesoporous silica (SBA‐15) is monitored by using an environmental in situ transmission electron microscopy (TEM) technique. Results show that agglomeration of smaller particles is accelerated by increased mobility of particles during heat treatment, while growth of immobile particles occurs via diffusion of atomic species from smaller particles. The mobility of the Au clusters can be alleviated by fabricating overlayers of silica around the clusters. The resulting materials show tremendous sinter‐resistance at temperatures up to 650 °C as shown by in situ TEM and extended X‐ray absorption fine structure analysis.

Contamination is a long standing problem in electron microscopy [1,2,3]. It can arise from poor vacuum, from sample handling and storage, or from the nature of the sample nature. We are systematically investigating candidate sources of contamination using a common TEM substrate: 10-nm thick Si 3 N 4 membrane, with typical storage methods and practices. We use a dry-pumped Hitachi H 9500 ETEM whose base pressure is1.4x10 -5 Pa without liquid nitrogen (LN 2 ). The measured residual gas is composed mainly of water vapor (8x10 -7 Pa) and N2 (about 3x10 -7 Pa), both decreasing to about 2x10 -7 Pa with LN 2 . We use electron energy-loss spectroscopy (EELS), energy-filtering thickness maps and bright-field TEM imaging in the H9500 to characterize the contamination build up, and SEM imaging in Hitachi S 5500 to image the surface morphology of the contamination dots. The Si 3 N 4 membranes were examined in the TEM as received, after cleaning using a ZONE cleaner [4] with LN 2 trap of the microscope, either cooled (ZONE-LN 2 ) or at room temperature (ZONE-RT), or without LN 2 in the cold trap and after heating the Si 3 N 4 membrane on a hot plate at 50 ºC (Hot-50C) prior to inserting in the microscope. A new Si 3 N 4 membrane was used for each experiment and the variation of the contamination rate was evaluated for 5-min increments of the cleaning process. The membrane was irradiated by a probe of 37 nm FWHM with 0.83 nA total current for 300 seconds, resulting in a 250 C/cm 2 irradiation dose. Five areas were measured for each condition and a thickness map and a bright-field image was then collected from the irradiated area using a broad illumination. For each condition, the experiment was performed on five locations of the Si 3 N 4 membrane and the volume of resulting contamination measured in nm 3 by summing over a 134x134 nm 2 thickness map, subtracting the contribution of the SiN membrane. Figure 1 shows typical thickness map for a dose D = 250 C/cm 2 , together with its profile. Figure 2 shows an SEM image of "as received sample" Si 3 N 4 irradiated at room temperature without LN 2 in the H9500, exhibiting dendritic contamination growth, possibly arising from secondary-emission-induced charging of the insulating sample during the contamination diffusion processes. Figure 3 shows the contamination rate in nm 3 /C for the as received (hereafter referred to as AR, with no cleaning), ZONE-DRY, ZONE-LN 2 and Hot-50C membranes and reveals variations around 70% in difference in the contamination rate of the AR sample. 20 minutes of ZONE cleaning reduced the contamination rate to about 70% of the AR value. The ZONE-LN 2 sample shows decrease to about 50% compared to the same sample in AR state followed by slight increased to about 60% that can be perhaps assigned to transfer between the TEM and the ZONE cleaner. The highest AR contamination rates were observed with the Hot-50C sample. Heating at 50oC reduced the contamination rate to about 44% of the initial AR rate, a value comparable to the ZONE-DRY sample in AR state. The...

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