tailieunhanh - ENCYCLOPEDIA OF MATERIALS CHARACTERIZATIONC phần 5

Mặc dù EXAFS là chủ yếu được sử dụng để xác định cấu trúc địa phương của số lượng lớn các chất rắn (ví dụ, tinh thể và các vật liệu vô định hình), surfkes rắn, và các giao diện, sử dụng của nó là không giới hạn ở trạng thái rắn. Như một công cụ cấu trúc, EXAFS bổ sung các kỹ thuật nhiễu xạ tia X quen thuộc, đó là chỉ áp dụng cho các chất rắn kết tinh. | Spectrum Figure 7 Schematic of a typical electron spectrometer showing all the necessary components. A hemispherical electrostatic electron energy analyser is depicted. analyzer voltages. A plot of electron pulses counted against analyzer lens voltage gives the photoelectron specưum. More sophisticated detection schemes replace the exit slit multiplier arrangement with a multichannel array detector. This is the modern equivalent of a photographic plate allowing simultaneous detection of a range of KEs thereby speeding up the detection procedure. Commercial spectrometers are usually bakeable can reach ultrahigh-vacuum pressures of better than 10-9 Torr and have fast-entry load-lock systems for inserting samples. The reason for the ultrahigh-vacuum design which increases cost considerably is that reactive surfaces . clean metals contaminate rapidly in poor vacuum 1 atomic layer in 1 s at 10-6 Torr . If the purpose of the spectrometer is to always look at as-inserted samples which are already contaminated or to examine rather unreactive surfaces . polymers vacuum conditions can be relaxed considerably. 294 ELECTRON EMISSION SPECTROSCOPIES Chapter 5 Applications XPS is routinely used in industry and research whenever elemental or chemical state analysis is needed at surfaces and interfaces and the spatial resolution requirements are not demanding greater than 150 gm . If the analysis is related specifically to the top 10 or so atomic layers of air-exposed sample the sample is simply inserted and data taken. Examples where this might be appropriate include examination for and identification of surface contaminants evaluation of materials processing steps such as cleaning procedures plasma etching thermal oxidation silicide thin-film formation evaluation of thin-film coatings or lubricants thickness-quantity chemical composition failure analysis for adhesion between components air oxidation corrosion or other environmental degradation problems tribological wear .