Paper VT-TuM12
Differentially Pumped Interface to Transfer Environmentally Sensitive Materials Designed with Built-in figures of Merit

Tuesday, October 20, 2015, 11:40 am, Room 230B

An interface designed to transfer air sensitive samples (e.g., battery materials) from an argon filled glove box (1 part-per-million of O₂ and H₂0) into an ultra-high vacuum (UHV) chamber for surface analysis is described. This interface (referred as interface for pressure-to-vacuum environmental sample transfer or IP-VEST) is equipped with a differentially pumped load lock, a buffer chamber, a detachable vacuum suitcase (referred to as a capsule), pump chamber, and a set of pressure gauges. Differential pumping minimizes back-flow from the mechanical pump that backs the turbomolecular pump (TMP) of the pump chamber. In the glove box, where argon pressure is 800-900 Torr, samples are loaded into the capsule and remain under this pressure during their transport to the load lock of the IP-VEST. An automatic sequence of pneumatic valves control differential pumping gas flow from the capsule to the pump chamber during the transition from atmospheric pressure (viscous flow) to high vacuum (molecular flow). During this pressure transition, the IP-VEST is also designed to generate a pressure spike in the buffer chamber that is a six order in magnitude, crossing over from the molecular flow to the viscous flow, and returning to molecular flow. This pressure spike is tunable with respect to pressure and time, and it is used as reference peak, allowing a comparison between pump down curves acquired during different sample transfer events. This pressure spike, combined with pump down curve, is referred to as a viscous-to-molecular flow curve (or spiked flow curve). The high repeatability of the spiked flow curves allows a user to develop a method, e.g., figures of merit, to evaluate sample transfer reliability during the entire transfer process that includes gaseous contents of an argon filled glove box and pumping efficiency of the IP-VEST. As a comparison, spiked flow curves were measured after filling the capsule near standard pressure from two sources of argon gas: (1) A high pressure cylinder bottle and (2) a commercial glove box. Both argon sources have intrinsic levels of ₂ and H₂O at 1 ppm. In addition, silicon and tin were separately exposed to these two sources of argon in order to evaluate the amount of oxidation of these materials due to intrinsic and extrinsic (e.g., leaks and back-flow) factors. These samples were transferred using the IP-VEST that is coupled to a port of a UHV chamber which is equipped with an X-ray photoelectron spectroscopy (XPS). XPS confirms that the IP-VEST does not contribute to the oxidation of these materials due to extrinsic factors.