Research Overview:

Medium-energy ion scattering (MEIS) is a powerful technique in surface science for the determination of structural and compositional properties of surfaces and thin films. Basically, light ions (usually p+ or He+) with an energy of 40-400 keV are incident along a major crystallographic direction in the solid (channeling). Energy and angle resolved detection of backscattered ions provides surface structural and compositional information. The ions are created and accelerated in a 400 keV ion implanter produced by High Voltage Engineering (Amersfoort, The Netherlands).

Rutherford backscattering spectrometry (RBS) is a 100 year old technology that is still a powerful tool for determining the structure and elemental composition of thin samples. In RBS, a high energy beam of helium or hydrogen ions is directed at a sample. Ions which scatter elastically from the nuclei of atoms in the sample are detected using a silicon particle detector. Since the energy of the scattered ion depends on the mass and depth of the target atom, the composition and layering of the sample can be determined very precisely.

Helium Ion Microscope is the latest additions to the microscopy toolbox. As the name implies, helium ion microscope (HIM) utilizes ~ 35kV He ions focused on a small spot (a few angstroms in diameter). Upon interactions with the sample, secondary electrons (SEs) are emitted and counted by a detector. By rastering the ion beam across the sample, we can obtain an image of the surface. Significantly smaller beam spot size and high SE yield gives important advantages over a Scanning Electron Microscope (SEM). The main superiority of HIM is the much larger field of view and unique capability to image non-conducting samples without a deposited metal overlayer.