Gold evaporated particles

Figure 8. Image and diffraction pattern from an (100) epitaxial. specimen of gold prepared in an unbaked UHV evaporator by depo.sition onto KOI and then transfer onto amorphous carbon. Here water vapour was the dominant residual gas (determined by mass spectrometry). The particles are square pyramidal single crystals.

Nano-sized Au particles (>1.5 nm) obtained by evaporation of metallic gold on Mylar [431] exhibit differences in 6 and A q for surface and core atoms when the particle sizes are less than 6 nm. 

As an example of the latter technique, Volkman et al. demonstrated the feasibility of using spin-cast zinc oxide nanoparticles encapsulated in 1-dodecanethiol to fabricate a functional transistor.44 The zinc oxide was deposited on a thermally grown silicon dioxide layer on a conventional silicon wafer, with thermally evaporated gold source and drain electrodes. As reported, the process requires very small particles (3nm or less) and a 400 °C forming gas anneal. A similar approach was also reported by Petrat, demonstrating n-channel thin-film transistor operation using a nanoparticle solution of zinc oxide dispersed onto a thermally grown silicon dioxide layer on a conventional... 

In the present paper non-conventional TEM methods to characterize small metallic particles are presented. The topographic information on the particles shape can be combined with micro-diffraction (using STEM) data to obtain a full characterization of the particle. The case of gold particles evaporated on a NaCl substrate is used as example. The particle shapes observed are discussed. It is shown that many particles have a crystal structure which is different from the bulk (Fee). 

In the present section we will present the shape characterization of different types of gold particles which are present on an evaporated film grown on a NaCl substrate. This is an interest model not only for epitaxy studies but also because the same shapes are found in real catalyst. 

A striking feature of the ILs is their low vapor pressure. This, on the other hand, is a factor hampering their investigation by MS. For example, a technique like electron impact (El) MS, based on thermal evaporation of the sample prior to ionization of the vaporized analyte by collision with an electron beam, has only rarely been applied for the analysis of this class of compounds. In contrast, nonthermal ionization methods, like fast atom bombardment (FAB), secondary ion mass spectrometry (SIMS), atmospheric pressure chemical ionization (APCI), ESI, and MALDI suit better for this purpose. Measurement on the atomic level after burning the sample in a hot plasma (up to 8000°C), as realized in inductively coupled plasma (ICP) MS, has up to now only rarely been applied in the field of IE (characterization of gold particles dissolved in IE [1]). This method will potentially attract more interest in the future, especially, when the coupling of this method with chromatographic separations becomes a routine method. 

Finally, our group reported on gold nanoparticles decorated with bent-core liquid crystals showing pattern formation on TEM grids after slow solvent evaporation (18 in Fig. 22). These particles showed interesting self-assembly effects in different bent-core liquid crystal hosts (SmCPA and Colr) and slightly improved electro-optic effects such as shorter response time, x, and unaltered spontaneous polarization in the SmCPA host, but no mesophase formation [547]. 

The advantage of this technique is that Au° is directly deposited onto the support, the particles are small, the sample is free of chloride, and it is easy to control the gold loading. The disadvantage is that the preparation must be performed in the absence of water and requires a specific reactor and an evaporator. 

Dry test All gold compounds when heated upon charcoal with sodium carbonate yield yellow, malleable, metallic particles, which are insoluble in nitric acid, but soluble in aqua regia. The aqua regia solution should be evaporated to dryness, dissolved in water, and tests 1, 3 or 4 applied. 

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