有机波谱分析双语课件 (43).pdf

X-射线光电子能谱 I 有机波谱分析 Organic Spectroscopic Analysis X-ray Photoelectron Spectroscopy(XPS)I X-ray Photoelectron Spectroscopy Introduction What is XPS?X-ray Photoelectron Spectroscopy(XPS),also known as Electron Spectroscopy for Chemical Analysis(ESCA)is a widely used technique to investigate the chemical composition of surfaces.Surface Analysis What information do we need?Surface Composition Which elements are present?Surface Geometry Arrangement of atoms Adsorption sites Bond lengths,bond angles Chemical Bonds at Surfaces Bond making and breaking Bond order Vibrational Properties Why is the XPS technique surface sensitive?There are two things which would prevent an emitted electron from being detected:If it were captured before reaching the surface,or emitted in the wrong direction and never reached the surface!If it lost energy before reaching the surface,i.e.if it escaped from the solid and reached the detector,but with reduced kinetic energy.How can we demonstrate that XPS is surface sensitive?Consider again the two samples in the previous section-such samples are often readily prepared by depositing material A by evaporation onto a substrate of material B.It is experimentally observed that in such a situation the XPS signals due to the substrate(material B)are rapidly attenuated,whilst those due to the condensed evaporant(material A)simultaneously increase to a limiting value.XPS for Chemical Analysis Basic components 1.a source of fixed-energy radiation 2.an electron energy analyzer 3.a high vacuum environment(to enable the emitted photoelectrons to be analyzed without interference from gas phase collisions)Instrumentation for XPS X-ray Photoelectron Spectrometer 5 4.7X-ray Source Electron Optics Hemispherical Energy Analyzer Position Sensitive Detector(PSD)Magnetic Shield Outer Sphere Inner Sphere Sample Computer System Analyzer Control Multi-Channel Plate Electron Multiplier Resistive Anode Encoder Lenses for Energy Adjustment(Retardation)Lenses for Analysis Area Definition Position Computer Position Address Converter Preparing Powder Samples:Embedding powder into the adhesive tape.Making a pellet Put the loose powder into a die.Press the power to form a pellet.12 2p 1s 2s 1/2 3/2 Efermi level Binding energy X-ray(photon)photoelectron （Ek=h-EB）XPS Energy Scale