X-ray Photoelectron Spectroscopy (XPS or ESCA) is used to learn the atomic composition of approximately the upper 50 A of a solid surface. Irradiation by monochromatic X-rays ejects core electrons, whose binding energies are determined by the type of atom from which they are emitted and the atom's local chemical environment. By varying the take-off angle of the sample state, or by ion sputter etching, one can achieve a depth profile of composition. The instrument is a PHI 5300 equipped with Mg, Al, and Ti anodes.
Auger Electron Spectroscopy (AES or Auger) measures the chemical composition of the outermost 50 Å of a sample. Irradiation by energetic electrons scatters both core and valence electrons, whose binding energies are determined by the type of atom from which they are emitted and the atom's local chemical environment. Only conductive samples can be measured with this technique. The sampled area varies from 1 mm down to 2 µm in diameter. The PHI 610 scanning Auger system (AES), uses a single pass cylindrical mirror analyzer with electron excitation from a coaxial electon gun.
Scanning Electron Microscopy (SEM) can produce images of almost any sample at magnifications of 15-20,000X. The SEM has tremendous depth of field allowing for imaging that cannot be accomplished using optical microscopy. Conductive and nonconductive samples can be imaged. Nonconductive samples are coated with a thin metal, such as gold, to reduce charging effects. Elemental analysis can be performed on any feature observed with an integrated EDS detector, providing chemical analysis in areas as small as 1 µm in diameter. EDS detects all elements except for H, He, Li, and Be. EDS can be performed exactly on any features or particles seen in the SEM images and can “MAP” elements on a surface.
Secondary Ion Mass Spectrometry (SIMS) is operated either in dynamic mode (DSIMS),* which is useful for profiling impurity and trace elements through films and interface (including depth profiling), or static mode (SSIMS), which is better for characterizing polymeric materials and only measures the outermost molecular layer of a specimen. Both positive and negative ion analyses are available. The instrument is a PHI Model 3500.
Users are requested to contact Dave Hobart to make arrangements to submit their samples to the Surface Analysis Lab (008 Hahn Hall). Solid samples should be free of volatile components. Samples must be completely labeled, and the submission form must be fully executed prior to receiving service. We generally provides service on a "first come, first serve" basis, but emergencies will get higher priority if possible.
Services are rendered only after an Interdepartmental Service Request (ISR) has been processed. Instructions for creating an ISR through HokieMart may be found here. Commercial customers should contact to make arrangements to submit a purchase order.
PHI SIMS II
H and He
H and He
*Atomic Mass Units
8 Hahn Hall
Surface Analysis Laboratory
Blacksburg, VA 24061