Dispersion stability, ligand structure and conformation, and SERS activities of 1-alkanethiol (C n H 2n+1 SH, n = 2−14) functionalized gold and silver nanoparticles (AuNPs and AgNPs) were studied as a function of alkanethiol carbon chain length and nanoparticle (NP) type and size. The dispersion stability of alkanethiol functionalized NPs in water increases with increasing alkanethiol chain length and NP size, and the stabilities of the alkanethiol-containing AuNPs are higher than their AgNP counterparts. C 3 H 7 SH and longer alkanethiols are highly ordered on AgNPs but disordered on AuNPs. The SERS intensity of the C−S stretch band for the model alkanethiols on AgNPs and AuNPs decays exponentially (I = I 0 exp(−N c /N 0 )) with increasing number of carbon atoms (N c ). The empirical decay length N 0 , in terms of the number of the carbon atoms, is 1.29, 0.53, and 0.10 for AgNPs with diameters of 50, 30, and 10 nm, respectively. This decay length is less than 1 for AuNPs of difference sizes. These results show that changing the NP gap size by a distance equivalent to a single chemical bond can have a significant impact on the NP integrated SERS activities.

The US Department of Energy's Basic Energy Sciences Office published a report entitled, "Future Electron Scattering and Diffraction" in 2014. In the report, it listed the "Lab-in-gap" dynamic microscope as one of the major instrumentation needs for enabling breakthrough scientific opportunities. Specifically, it called for sample stage and holder designs that would allow advanced in situ analyses [1]. We have recently manufactured a MEMS-based heating and electric bias holder that fits into the sample stage of the newly developed 200-kV Hitachi HF5000 transmission electron microscope. The new sample stage enables a wider, jewel-less sample holder design, providing a larger platform which is advantageous for laying out electric contacts and transportation of stimuli. As shown in Fig. 1a, the Hitachi "Blaze" Heating Holder comes with the MEMS-based heating chips, which are SiN membranes sandwiching a heating element, manufactured by Norcada Inc. The contact pad to the heating chip is a replaceable. Simulated temperature profiles at 850 and 1100 o C indicated the central 160 µm-diameter is isothermal (Figs.1b and 1c). At the center of the isothermal region, there are 19 sample wells in 5 arrays. These sample wells have a 30 nm-thick SiN support film, providing electron transparency and exceptional chemical, thermal and mechanical stability.In this paper, we report the in situ heating study of lunar and planetary materials using the Blaze heating holder [2]. The lunar soil samples were acquired from the Apollo 14 and 17 missions. To prepare the samples for in situ heating, we suspended particles in methanol and then transferred them onto the heating chip using a micro pipette. We analyzed the samples after the methanol had completely evaporated. Part of the heating study was carried out using the 300 kV Hitachi HF3300 TEM/STEM located at the University of Toronto. Complementary work is also being pursued with in-depth heating studies in the probe-corrected 200 kV Hitachi HF5000 TEM/STEM at the University of Arizona. Both microscopes are equipped with a secondary electron (SE) detector, which allow simultaneous secondary and transmitted election imaging to obtain the information from the surface (SEM) and bulk (annular dark field (ADF) and bright field (BF) of the lunar soil particles. Figure 2 documents the structural evolution of one particle before and after a total of eight thermal shocks with 1-sec duration over a temperature range from 20 to 940 o C. Iron nanocrystals developed on the surface of the grain after the first thermal shock and continued to increase in size with each subsequent heat treatment. EELS analysis (not shown) further confirms the metallic nature of these iron nanocrystals.In summary, the Blaze heating holder is proven to have enabled simulation of heating events occurred on airless bodies such as lunar and planetary materials. It can also be used to address questions on thermal annealing of ceramics and nanostructured materials [3].

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.

No abstract

No abstract