Measurement of gas flux distributions from single capillaries using a modified, uhv-compatible ion gauge, and comparison with theory

Theoretical and experimental molecular beam angular distribution studies for gas injection in ultra-high vacuum

“…This systematically resulted in very linear curves at least up to pressures around 1 Â10 À4 Torr as shown in Fig. 3 and in agreement with the results of Adamson [14]. This allows the fixed gauge to be used as flow rate measurement device even at very low flows where the MFM readings become unreliable.…”

“…Encapsulating the gauge strongly decreases the background signal from molecules re-emitted by the surrounding chamber walls since they can only enter the box through a very small hole. Similar flux sensors have previously been used by other groups and have shown excellent sensitivity [14,15]. The encapsulated BAG is attached to a rocking pendulum assembly that keeps the sensor aligned with the center of the injector inlet at all times.…”

“…An encapsulated BayardAlpert gauge (BAG) was chosen as flux sensor because of its high sensitivity to very small fluxes. The gauge enclosure has an opening with an area that is much smaller than the enclosure internal surface, insuring a complete randomization of molecular directions inside it and thus avoiding any ''beaming effect'' [14]. Once a steady-state pressure is reached inside the box, the net flow crossing its orifice is zero as the incoming flow (F in ) from the injector and the chamber walls balances the outgoing flow (F out ) from the box.…”

Signal enhancement strategies for angular profile measurements of gas injected in ultrahigh vacuum

“…This should be the case if the detection unit has been properly designed. 7 We will therefore assume that these molecules undergo enough wall collisions before passing through the aperture so that their velocity distribution is indeed isotropic. Then, according to a classical equation of gas dynamics theory, 11…”

“…With that intent, several systems have already been developed for precisely measuring the angular spread of molecular beams. [7][8][9] Most of them were designed to obtain distributions at very close range ͑typically less than 1 cm͒ since the main objective was to generate high beam intensities. In CBE however, typical injector-to-substrate distances are in the 10-30 cm range due to the space requirements for in situ measurements and the necessity to minimize thermal interactions between surfaces held at very different temperatures.…”