ultrahighvacuum

Ultrahigh vacuum (UHV) is a vacuum regime in which the residual gas pressure is extremely low, typically below 10^-9 torr, corresponding to about 1×10^-7 pascal. This level of vacuum minimizes surface contamination and outgassing, enabling controlled studies of surfaces and thin films. Pressure is monitored with ionization gauges and, at the lowest pressures, with residual gas analyzers.

Achieving UHV requires careful preparation of pumps, materials, and surfaces. The chamber is initially rough-pumped with a mechanical or scroll pump, then a turbomolecular pump brings the pressure into the high and very high vacuum ranges. The interior is fabricated from low-outgassing materials, and all components are cleaned and baked to remove adsorbed water. After bake-out, ion pumps or non-evaporable getter pumps, occasionally cryopumps, maintain UHV by actively removing residual gases. Materials, gaskets, and seals are chosen to minimize outgassing and leaks.

Applications of UHV span surface science, thin-film deposition, and accelerator technology. Techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM) operate effectively in UHV to preserve clean, well-defined surfaces. Molecular-beam epitaxy (MBE) and some semiconductor processing steps also rely on UHV to achieve precise growth and contamination control.

Challenges include sustaining ultra-low pressures, preventing and detecting leaks, and managing the complexity and cost of the pumping hardware. Systems use leak-tight flanges (such as ConFlat), careful baking, and rigorous cleaning to maintain pressures in the 10^-9 to 10^-12 torr range.