X-ray photoelectron spectroscopy (XPS) is a powerful technique widely used for the surface analysis of materials. At low energy resolution it provides qualitative and quantitative information on the elements present whereas at high energy resolution it gives information on the chemical state and bonding of those elements. High-Resolution XPS (HR-XPS) uses a monochromator which provides the following advantages over a standard x-ray source:
• An x-ray energy distribution with reduced energy width improves chemical selectivity by narrowing the spectral peaks.
• A lower spectral background.
• The elimination of unwanted x-rays from satellites and anode impurities, which simplifies spectral analysis.
• The elimination of Bremsstrahlung and thermal radiation from the x-ray source, which greatly reduces x-ray source induced damage.
• A focused x-ray spot on the sample increases the sensitivity on small samples.
The HR-XPS in our lab is equipped with a twin anode (Al Kα at 1486.6 or Ag Lα at 2984.3 eV) FOCUS 500 monochromator and a SPECS hemispherical analyzer from the PHOIBOS series. The Al monochromator in conjunction with the hemispherical analyzer operating at 15 kV and 400 W on a smooth sputter cleaned sample of silver has achieved the lowest resolution of 0.56 eV with an intensity of 699 kcps. HR-XPS has been extensively used in our lab for the characterization of phosphonic acid films that are attached to the surfaces of conductor/semi-conductor for various electrical and biological detection strategies. Angle-resolved studies have been conducted to get the variation of elemental composition with the depth. It has also been used to differentiate between various bonding configurations of phosphorous to the oxide surface to study the mechanism of film growth by the “T-BAG” method.