Aggregation sources

The detailed magnetic behavior of Fe clusters has been studied for the films with Fe clusters embedded in Ag [34]. In UHV conditions, preformed Fe clusters with a mean diameter of 3 nm from a gas-aggregation source were deposited in conjunction with atomic Ag vapor. In such films clusters can come into direct contact and interact via exchange. Films containing Fe cluster volume fraction from < 1 % (isolated clusters) to 100% (pure clusters with no matrix) have been studied at temperatures ranging from 2 to 300 K by magnetometry and field-cooled (FC)/zero-field-cooled (ZFC) measurements. 

Baker SH, Thornton SC, Keen AM, Preston TI, Norris C, Edmonds KW, Binns C (1997) The construction of a gas aggregation source for the preparation of mass-selected ultrasmall metal particles. Rev Sci Instrum 68 1853... 

Fig. 1.23. The electron diffraction apparatus developed by Parks and coworkers includes an rf-ion trap, Faraday cup, and microchaimel plate detector (MCP) and is structured to maintain a cylindrical symmetry around the electron beam axis [147]. The cluster aggregation source emits an ion beam that is injected into the trap through an aperture in the ring electrode. The electron beam passes through a trapped ion cloud producing diffracted electrons indicated by the dashed hues. The primary beam enters the Faraday cup and the diffracted electrons strike the MCP producing a ring pattern on the phosphor screen. This screen is imaged by a CCD camera mounted external to the UHV chamber. The distance from the trapped ion cloud to the MCP is approximately 10.5 cm in this experiment...

In the gas-aggregation source a metal is vaporized and introduced in a flow of cold inert gas in which the vapor becomes highly supersaturated. Clusters are mainly produced by successive single-atom addition in the build-up of larger species. This type of source has been used to produce continuous cluster beams of alkali elements. By using two separate ovens in the source, each containing separate materials, clusters with two elements can be produced as Ceo covered with alkali metals [83]. The limitation of this type of source is that only metals with a low melting point can be studied. 

Because of the variability of aggregate sources, aggregates should be tested to determine their suitability for use in asphalt (bituminous mixtures) or as material in base and subbase layers. Their suitability is defined in reference to geometrical, physical and chemical proper-ties/requirements. Table 2.3 summarises the main test methods. 

In case the above measures proved to be ineffective, the aggregate source or the type/grade of bitumen, or both, should be changed to obtain better aggregate/binder compatibility. 

Figure 11. Service value chain aggregator (Source Beck, 2002)...

FIGURE 3.1 Schematic of seeded supersonic nozzle source (top) and gas aggregation source (bottom). Reprinted with permission from Ref. [17]. American Physical Society. 

Inscriptions means normalized maximum rate of platelet aggregation. Source Reprinted from Mindukshev et al. pp. 247-257. Copyright (2005),... 

Equivalent sphere model for a single aggregate [Source A.I. Medalia, /. Colloid Inter/ Sci, 32,115-131,1970]... 

---