Knudsen cells

MetallorganicMBE (MOMBE). tire solid source Knudsen cells in conventional MBE are replaced witli gaseous beams of organometallic precursors, directed toward a heated substrate in UHV. Compared to MOCVD, MOMBE eliminates gas phase reactions tliat may complicate tire deposition surface reactions, and provides lower growtli temperatures. 

Knox-Out2FM Knudsen cells Knudsen diffusion Knudsen s law Koavone [86115-11-9]... 

Fig. 4. Schematic of a high vacuum molecular beam epitaxy (MBE) chamber containing four effusion (Knudsen) cells. Also shown is a high energy electron...

If a monatomic gas escapes from a Knudsen cell into ati atmosphere in which the mean free patlr is the fraction of tire atoms, /, which traverse a distance L without collision is given by... 

The condition for Knudsen effusion that tire irreair free path of tire effusate should be less tlrair the diameter of the circular orifice, limits the usable vapour pressure of the material in the Knudsen cell to about 10 Pa, since the orifice diameter would have to be less than 1 mm at a higher pressure. 

The flux of atoms emerging from a Knudsen cell at 1000 K in which an element of vapour pressure 10 " atmospheres and atomic weight lOOg is contained in a cell of orifice diameter 1 mm, is... 

Figure 1.7 Ion plating device in which the substrate is cleaned by ion bombardment and the material to be deposited is supplied by a Knudsen cell...

The vapor pressure of a molten metal can be measured with a device called a Knudsen cell. This is a container closed across the top by a thin foil pierced by a small, measured hole. The cell is heated in a vacuum, until the vapor above the melt streams from the small hole (it effuses). The weight of the material escaping per second tells the rate at which gaseous atoms leave. 

Two identical Knudsen cells are heated at 1000°C, one containing lead and the other containing magnesium. 

Kinetics, chemical, 124 Knudsen cell, 63 Kroll process, 368 Krypton, 91 atomic volume, 410 boiling point, 307 heat of vaporization, 105... 

Do of 1.40 eV for AI2 is within the error bounds of the experimental value of 1.55 0.15 eV determined by Stearns and Kohl (46) using a Knudsen cell mass spectrometric method and assuming a ground state. 

Atomization energies of CP, CgP, CPj, and CgPg have been determined using high-temperature Knudsen cell mass spectrometry. ... 

In a separate set of experiments designed to follow the gas phase reactions of CHj-radicals with NO, CHj- radicals were generated by the thermal decomposition of azomethane, CHjN NCHj, at 980 °C. The CH3- radicals were subsequently allowed to react with themselves and with NO in a Knudsen cell that has been described previously [12]. Analysis of intermediates and products was again done by mass spectrometry, using the VIEMS. Calibration of the mass spectrometer with respect to CH,- radicals was carried out by introducing the products of azomethane decomposition directly into the high vacuum region of the instrument. 

Although the reaction of CHs- radicals with NO in the gas phase has been extensively studied by indirect methods, we are aware of only one report in which the intermediate CH3NO was directly determined, and in this case the reaction was carried out at room temperature [14]. In order to gain insight into the thermal stability of CH3NO, a cursory study was carried out in a Knudsen cell over the temperature range from 25 C to 800°C. 

Figure 6. Formation of CH3NO during the gas phase reaction of CH3- radicals with NO in a Knudsen cell O, mass 15 A, mass 28 , mass 45. Results were obtained at P(CHj-) = 0.7 mTorr, P(NO) = 1.4 mTorr and an electron impact energy of 19 eV.

The most usual effusion methods are based on equilibration of a substance in a Knudsen cell. A small fraction of the vapour molecules effuse through a small effusion orifice in the lid of the cell (diameter from 0.1 to 1 mm), ideally without... 

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