Seeded supersonic nozzle source

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

Generation of the Molecular/Cluster Beam. In the first chamber the molecules and clusters are produced in a seeded supersonic nozzle source. It is perhaps the most intense molecular/cluster beam source available. In this source, alkali metal is vaporized in a hot oven as sketched in Fig. 2.19. The alkali... 

In a seeded supersonic expansion source [35-37[, the material is heated in an oven and a mixture of gaseous material and a seed gas expands through a nozzle into the vacuum. This source produces a highly intense beam of small pure and mixed metal clusters, but it is limited to metals with a low boiling point (Li, Na, K, etc.). Laser vaporization sources [13,38[ are more widely used as they produce pure and mixed clusters of most elements and when operated at low frequency (1-10 Hz) they have been successfully used... 

The spectrometer is fitted with a skimmed c.w. supersonic molecular beam source. Many chiral species of interest are of low volatility, so a heated nozzle-reservoir assembly is used to generate, in a small chamber behind a 70-pm pinhole, a sample vapor pressure that is then seeded in a He carrier gas as it expands through the nozzle [103], Further details of this apparatus are given elsewhere [36, 102, 104],... 

The details of the crossed-beam apparatus used in our experiment can be found in many earlier publications [17,18]. Briefly, the alkali dimer source consisted of a resistively heated molybdenum oven and nozzle assembly, with the temperatures of the nozzle and the oven being controlled independently by different heating elements. Sodium vapour carried by an inert gas, which was either He or Ne, expanded out of the 0.2 mm diameter nozzle to form a supersonic beam of Na/Na2/inert gas mixture. The Na2 concentration was about 5% molar fraction of the total sodium in the beam when He was used as carrier gas. The beam quality dropped severely when we seeded Na2 in Ne so the dimer intensity became much weaker. No substantial amount of trimers or larger clusters was detected under our experimental conditions. The Na2 beam was crossed at 90 by a neat oxygen supersonic beam in the main collision chamber under single collision conditions. The O2 source nozzle was heated to 473 K to prevent cluster formation. Both sources were doubly differentially pumped. The beams were skimmed and collimated to 2 FWHM in the collision chamber. Under these conditions, the collision energies for the reaction could be varied from 8 kcal/mol to 23 kcal/mol. 

In the jet vapor deposition (JVDtm) process, evaporated atoms/molecules are seeded into a supersonic jet flow of inert carrier gas that expands into a rapidly pumped vacuum chamber. The jet transports the atoms/molecules to the substrate surface where they are deposited. The vapor source can be in the form of thermal evaporation or sputtering and is located in the jet nozzle. The deposition chamber pressure is about 1 Torr and is pumped using high capacity mechanical pumps. The JVD process can be combined with high current ion bombardment for in situ control of the film properties. 

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