Clusters size distribution, control

In subsection 7.2.1, it was discussed that the neutral clusters generated from the beam source have a wide range of cluster sizes. Although there is no single, easily available technique which allows the size specific detection of neutral clusters, it is now well accepted that the cluster size distribution can be manipulated, to a certain extent, by careful control of the various experimental parameters. Mass spectrometric detection of clusters in general and tandem mass spectrometry in particular offer the inherent advantage of enabling size specific studies of the cluster ions. 

The cluster size was controlled in a range from 3 nm to 6 nm by adjusting the preparation parameters such as sputtering power, Ar-He gases flow and gas pressure etc. Uniform cluster size distribution with standard deviation ofd <0.1 is obtained. The size distribution can be further improved if desired by applying a mass selector. Figure 10 shows the TEM image of... 

Once the vapor is produced, the next problem is to control the condensation in order to produce a desired cluster size distribution. This is achieved by... 

Semiconductor clusters have traditionally been prepared by the use of colloids, micelles, polymers, crystalline hosts, and glasses. The clusters prepared by these methods have poorly-defined surfaces and a broad size distribution, which is detrimental to the properties of the semiconductor materials. The synthesis of monodisperse clusters with very well-defined surfaces is still a challenge to synthetic chemists. However, some recent approaches used to overcome these problems are (i) synthesis of the clusters within a porous host lattice (such as a zeolite) acting as a template and (ii) controlled fusion of clusters. 

Recent developments in attaining chemical control in the arrested precipitation of semiconductor particles from solution have made it possible to prepare colloidal clusters of narrow size distribution It is now known that the electronic spectra... 

The overall performance of a catalyst is known to depend not only on the inherent catalytic activity of the active phase but also on the textural properties of the solid. The ability to control the specific surface area and the pore size distribution during the synthesis of amorphous silica-aluminas has been described for both surfactant micelle templated syntheses (M41-S (1), FSM-16 (2), HMS (3), SBA (4), MSU (5), KIT-1 (6)) and cluster templated sol-gel syntheses (MSA (7), ERS-8 (8)). 

In the panicle synthesis, metal atoms produced by the heating collide with the inert gas atoms to decrease the diffusion rate of the atoms from the source region. The collisions also cool the atoms to induce the formation of small clusters of fairly homogeneous size. The clusters grow mainly by cluster-cluster condensation to give nanopaiticles with a broader size distribution. A convective flow of the inen gas between the warm region near the vapour source and the cold surface carries the nanopanicles to the cooled finger, where they are let to deposit. The inen gas pressure, the evaporation rate, and the gas composition can control the characteristics... 

---