the sample holder is equipped with a filament which emits electrons when biased at a high negative potential. The impact of the electrons bombarding the sample at high energy causes it to heat. For thermal radiation, a filament is mounted close to the sample and resistively heated to high temperature. The infrared energy from the filament heats the sample. Typical uses Ultra-high vacuum is necessary for many surface analytic techniques such as: X-ray photoelectron spectroscopy (XPS) Auger electron spectroscopy (AES) Secondary ion mass spectrometry (SIMS) Thermal desorption spectroscopy (TPD) Thin film growth and preparation techniques with stringent requirements for purity, such as molecular beam epitaxy (MBE), UHV chemical vapor deposition (CVD), atomic layer deposition (ALD) and UHV pulsed laser deposition (PLD) Angle resolved photoemission spectroscopy (ARPES) Field emission microscopy and Field ion microscopy Atom Probe Tomography (APT) UHV is necessary for these applications to reduce surface contamination, by reducing the number of molecules reaching the sample over a given time period. At , it only takes 1 second to cover a surface with a contaminant, so much lower pressures are needed for long experiments. UHV is also required for: Particle accelerators The Large Hadron Collider (LHC) has three UH vacuum systems. The lowest pressure is found in the pipes the proton beam speeds through near the interaction (collision) points. Here helium cooling pipes also act as cryopumps. The maximum allowable pressure is Gravitational wave detectors such as LIGO, VIRGO, GEO 600, and TAMA 300. The LIGO experimental apparatus is housed in a vacuum chamber at in order to eliminate temperature fluctuations and sound waves which would jostle the mirrors far too much for gravitational waves to be sensed. Atomic physics experiments which use cold atoms, such as ion trapping or making Bose–Einstein condensates. While not compulsory, it can prove beneficial in applications such as: Molecular beam epitaxy, E-beam evaporation, sputtering and other deposition techniques. Atomic force microscopy. High vacuum enables high Q factors on the cantilever oscillation. Scanning tunneling microscopy. High vacuum reduces oxidation and contamination, hence enables imaging and the achievement of atomic resolution on clean metal and semiconductor surfaces, e.g. imaging the surface reconstruction of the unoxidized silicon surface. Electron-beam lithography See also Vacuum engineering Vacuum gauge Journal of Vacuum Science and Technology Vacuum state Orders of magnitude (pressure) References External links Online Surface Science Course Vacuum systems Vacuum