Beam damage, surface analysis

AES is a useful element-specific technique for quantitative determination of the elemental composition of a surface. Although some chemical information is available in principle, the technique is used largely for elemental analysis. Electron beam damage can decompose organic adsorbates and cause damage, particularly on insulating surfaces. In some cases, the beam can reduce metal oxides. 

We shall concern ourselves here with the use of an X-ray probe as a surface analysis technique in X-ray photoelectron spectroscopy (XPS) also known as Electron Spectroscopy for Chemical Analysis (ESCA). High energy photons constitute the XPS probe, which are less damaging than an electron probe, therefore XPS is the favoured technique for the analysis of the surface chemistry of radiation sensitive materials. The X-ray probe has the disadvantage that, unlike an electron beam, it cannot be focussed to permit high spatial resolution imaging of the surface. 

Polymer Surface Analysis. The major technique used for the surface analysis of polymers has been X-ray photoelectron spectroscopy (XPS or ESCA). However, this technique is often not adequate to determine the molecular structure of polymers. This has prompted many workers to explore the potential of SIMS for this work (11-16). Significant problems encountered with ion beam bombardment in conjunction with electron beam charge neutralization have been drift in the polymer surface potential and thermal damage from the combined effects of the electron and ion beams. These problems do not exist when utilizing FAB in conjunction with photoelectron charge neutralization. 

In this review results from two surface science methods are presented. Electron Spectroscopy for Chemical Analysis (ESCA or XPS) is a widely used method for the study of organic and polymeric surfaces, metal corrosion and passivation studies and metallization of polymers (la). However, one major accent of our work has been the development of complementary ion beam methods for polymer surface analysis. Of the techniques deriving from ion beam interactions, Secondary Ion Mass Spectrometry (SIMS), used as a surface analytical method, has many advantages over electron spectroscopies. Such benefits include superior elemental sensitivity with a ppm to ppb detection limit, the ability to detect molecular secondary ions which are directly related to the molecular structure, surface compositional sensitivity due in part to the matrix sensitivity of secondary emission, and mass spectrometric isotopic sensitivity. The major difficulties which limit routine analysis with SIMS include sample damage due to sputtering, a poor understanding of the relationship between matrix dependent secondary emission and molecular surface composition, and difficulty in obtaining reproducible, accurate quantitative molecular information. Thus, we have worked to overcome the limitations for quantitation, and the present work will report the results of these studies. 

The first question that a scientist should ask when considering a piece of material for SEM observation is does it need to be prepared Will the act of preparing the specimen damage the detail required to be imaged, or even remove the detail completely If a specimen is being examined for the surface residue, almost any preparation may remove the information required. However, if the surface required resides beneath a contaminated surface, there is a possibility that this film will require removal. If the task is to determine elemental distribution by backscattered electrons, it is ideal to present a polished surface to the electron beam, as surface roughness will interfere with the signal produced. Similarly, a polished surface is also desired for most accurate X-ray analysis. 

Figure 1 Relative intensities of diagnostic fragments from poly(methyl methacrylate) (+ rniz 126 and rn/z 185) as a function of primary ion dose (using 8keV Cs+). Individual spectra were acquired with a dose of <5 x 10 ionscm. (Reproduced with permission from Briggs D and Fletcher IW (1997) Cs ion beam damage of poly(vinyl chloride) and poly(melhyl methacrylate) studied by high mass resolution ToF-SIMS. Surface and Interface Analysis 25 167-176 John Wiley Sons Ltd.)...

SAM is a representative method of the surface analysis aimed at below the micron area. The micro structure of the native oxide film might be able to observe by means of SAM method. However, the severe electron beam-induced damage might be arisen on a silicon oxide film by the high electron current density of primary electron beam (3-7). The silicon oxide is reduced to the elemental silicon due to Joule s heat in an ultra high vacuum analyzer chamber of SAM equipment. The conditions to reduce the reduction of the silicon oxide film due to the electron beam-induced damage have been preferred by the investigations on the compulsive reduction of the silicon oxide film. 

The AES technique provides rapid surface analysis, but is not widely used on fracture surfaces due to beam damage and charging of nonconductive adhesives. On the other hand, the use of AES in the analysis of adherend surfaces has been widespread. An advantage of AES is... 

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