The design of a microcapillary array for dosing gases in ultrahigh vacuum (UHV) is reported. The current design improves upon previous designs in ease of fabrication and assembly, and combines the attributes of minimum dead volume, minimum gas load on the vacuum system, collimated molecular flow, the ability to optimize dosing geometry and withdraw the doser when not in use, and ultimate UHV compatibility. These design characteristics result in an optimum source-target spacing enabling uniform, quantitative exposure of samples up to 1 in. in diameter. (c) 2005 American Vacuum Society.