Abstract: A method for reducing the amount of mobile surface molecules present on a substrate surface includes providing a substrate having an area of interest, where the substrate is disposed within a controlled environment (e.g., a UHV environment). In some embodiments, a mask is positioned in a first position over the area of interest. Thereafter, a first deposition of a reactive material from a reactive material source is performed onto a first substrate region. The mask, while in the first position, blocks deposition of the reactive material within the area of interest. The mask may then positioned in a second position over the area of interest. In some embodiments, a second deposition of the reactive material from the reactive material source is performed to circumscribe the area of interest with the reactive material. In various embodiments, mobile surface molecules are captured using the deposited reactive material.