UT Surface Scattering Apparatus

This is the Ultra-High Vacuum (UHV) scattering chamber in which the state-resolved experiments are performed. The cylinder in the center of the appartus is the Main chamber which houses the LEED (Low Energy Electron Diffraction) and Auger spectroscopy, ion sputtering gun, quadrupole and time-of-flight (TOF) mass spectrometers and window ports for laser access. The surface is mounted on a manipulator and can be heated (electron bombardment) or cooled to liquid nitrogen temperature. The manipulator is mounted on the lid of the main chamber which can be rotated to place the surface in front of the ion gun for cleaning, or LEED for surface analysis, or in front of the molecular beam for scattering experiments.

The chamber off to the right is the source chamber and it contains the nozzle and skimmer. In between the source and main chambers there is a small buffer chamber which houses the chopper (a small disk with slits that rotates around 300 Hz). The tall cylinder on the left of the picture is a liquid nitrogen trap.

The molecular beam is created by a pulsed nozzle that works like a fuel injector in a car. Inside the nozzle is 2 or 3 atm of gas and when the aperture opens (solenoid driven) the gas rushes out into the vacuum in a supersonic expansion. The molecules in the beam will be very cold rotationally (about 6 K for Nitrogen) and have a narrow velocity distribution. This means that the molecules incident on the surface all have nearly the same velocity. By heating the nozzle or mixing the gas in Helium or Hydrogen we can change that velocity and study the dependence of the scattered distributions on incident energy.

The experiments are performed on single crystals. This image shows the atomic structure of a Cu(110) surface. Along with experimental work we also have a classical trajectory simulation which we can use to interpret our results. This slab of 6x6x3 atoms represents the surface that was used in the N₂/Cu(110) simulations.

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