We investigate the stability of magnetically trapped atomic Bose-Einstein condensates and thermal clouds near the transition temperature at small distances $0.5\mu \mathrm{m}\le d\le 10\mu \mathrm{m}$ from a microfabricated silicon chip. For a $2\mu \mathrm{m}$ thick copper film, the trap lifetime is limited by Johnson noise induced currents and falls below 1 s at a distance of $4\mu \mathrm{m}$. A dielectric surface does not adversely affect the sample until the attractive Casimir-Polder potential significantly reduces the trap depth.

• Received 21 August 2003

DOI:https://doi.org/10.1103/PhysRevLett.92.050404