UHV line for surface physics

Personnel Responsible: José Emilio Prieto de Castro

Diffraction pattern

Diffraction pattern produced by the scattering of low-energy electrons (220 eV) on Cu(100).

View of uhv beamline

View of UHV line for surface physics.

The UHV-surfaces beamline at CMAM contains a powerful set of facilities for the growth of thin epitaxial films and sample characterization using several experimental techniques. The system allows the growth of thin films by Molecular Beam Epitaxy (MBE) and their analysis by means of the standard ion-beam techniques using the high-energy ions provided by the CMAM accelerator [Rutherford backscattering spectroscopy (RBS), elastic recoil detection (ERDA), etc.], as well as the characterization of the samples with surface‐sensitive techniques [low-energy ion scattering (LEIS), low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES)].

The equipment consists basically of a sample preparation chamber, a main analysis chamber and a load-lock system for sample introduction and transfers. A goniometer with 3 rotation axes and 2 translations will be mounted in the main chamber and will allow samples to be cooled down to about 100 K and heated up to 700 K. For sample growth by MBE, the preparation subsystem is equipped with six Knudsen cells containing different ultra pure elements. It is possible, in addition, to include a radiofrequency plasma source for atomic species (N, O, etc.) in order to produce metal oxides or nitrides by MBE deposition in the presence of a flow of atomic N or O. In situ optical characterization (reflectance measurements, ellipsometry) can also be carried out in the preparation subsystem. In a later stage facilities for magnetic (Kerr effect) and electrical (resistivity) characterization can be included. Additionally, thanks to a movable vacuum chamber equipped with a Zirconium getter pump, samples prepared in external facilities can be transported and introduced in the system preserving an UHV environment. Also samples grown in this setup can be transported to be analyzed in other equipments inside CMAM as well as outside in collaborating institutions (IMM-CSIC, ICMM-CSIC).

For the performance of RBS/channelling and ERDA experiments in the UHV‐surfaces setup, the high energy ions produced by the 5 MV tandem accelerator are transported over a distance of about 15 m and focused to a spot smaller than 1 mm on the sample by means of the 0‐degree and the UHV beamlines. A surface-barrier Si detector mounted at an angle of 150º with respect to the incoming beam is employed for RBS depth profiling with a depth resolution of 5 nm in the first 50 nm under favourable conditions. Also heavy ions from the accelerator (e.g. Cu ions with energies of up to 55 MeV) can be used for in situ sample modification at controlled temperatures.

A quite unique experimental facility is the new LEIS-ToF system for surface structure determinations.

Here the sample is bombarded by a chopped beam of noble gas ions (He, Ar, Ne...) with energies typically in the range 2-6 keV. Time of Flight (ToF) spectra of scattered and recoiled particles are recorded. Azimuthal or polar scans of the intensity of scattered or recoiled particles can be obtained from the spectra by rotating the sample. The system is equipped with a 1D-position sensitive detector located 1 m away from the sample which allows simultaneous measurements in a certain range of scattering or recoiling angles efficiently for surface structure determination and using ion fluences of less than 1012 ions/cm2.

The beamline and the vacuum system have been constructed, aligned and tested. In the period January 2008-December 2009, low-energy ion beams with energies in the range of several kilovolts have been produced in the ion source and have been successfully guided through the beamline into the UHV system, scattered and deteced with a MCP detector. A provisory sample holder has been installed, which allows the cleaning of the sample and the preparation of the surface by electron-beam heating and noble gas sputtering. The performance of the LEED optics equipment has been successfully checked: difracction patterns of crystalline copper surfaces have been observed and Auger electron spectra have been recorded. In addition, a water-cooled iron evaporator has been installed in the main chamber and succesfully tested by depositing thin films of different thicknesses.