Auger electron spectroscopy limitations

PIXE detection limits for surface layers on bulk specimens are sufficiendy low to permit calibradon of true surfe.ce analysis techniques (e.g., Auger electron spectroscopy). 

Laser ionization mass spectrometry or laser microprobing (LIMS) is a microanalyt-ical technique used to rapidly characterize the elemental and, sometimes, molecular composition of materials. It is based on the ability of short high-power laser pulses (-10 ns) to produce ions from solids. The ions formed in these brief pulses are analyzed using a time-of-flight mass spectrometer. The quasi-simultaneous collection of all ion masses allows the survey analysis of unknown materials. The main applications of LIMS are in failure analysis, where chemical differences between a contaminated sample and a control need to be rapidly assessed. The ability to focus the laser beam to a diameter of approximately 1 mm permits the application of this technique to the characterization of small features, for example, in integrated circuits. The LIMS detection limits for many elements are close to 10 at/cm, which makes this technique considerably more sensitive than other survey microan-alytical techniques, such as Auger Electron Spectroscopy (AES) or Electron Probe Microanalysis (EPMA). Additionally, LIMS can be used to analyze insulating sam-... 

Several other microanalytical methods in common use potentially have application on soil and sediments section samples. Laser-ablation inductively coupled plasma mass spectrometery (LA-ICP-MS) has been used on soil thin-sections from a controlled field experiment (21) but required special resins in the preparation. There is presently (May 2006) no reported use of this method on archaeological soil samples. Likewise, for extremely fine-resolution studies (i.e. <10 pm) with low minimum detection limits and despite difficult calibration, secondary ion microscopy (SIMS) has a potential role in examining archaeological soil thin sections. At even higher lateral resolutions ( 100 nm) Auger electron spectroscopy (AES) could also be considered for surface (<5 nm deep) analyses. At present however, the use of these methods in soil systems is limited. SIMS has been focused on biochemical applications (22), whereas AES... 

As a surface analytical tool, SIMS has several advantages over X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). SIMS is sensitive to all elements and isotopes in the periodic table, whereas XPS and AES cannot detect H and He. SIMS also has a lower detection limit of 10 5 atomic percent (at.S) compared to 0.1 at.S and 1.0 at.% for AES and XPS, respectively. However, SIMS has several disadvantages. Its elemental sensitivity varies over five orders of magnitude and differs for a given element in different sample matrices, i.e., SIMS shows a strong matrix effect. This matrix effect makes SIMS measurements difficult to quantify. Recent progress, however, has been made especially in the development of quantitative models for the analysis of semiconductors [3-5]. 

Electron induced Auger Electron Spectroscopy (EAES) makes use of high-energy electrons to remove core electrons via impact-ionization. However, in many instances the utility of EAES is limited by problems associated with the large secondary electron background and the lack of surface specificity inherent in the EAES excitation process [2, 8]. 

The composition of wet thermal oxide on SiC has been established to be close to stoichiometric Si02 from Auger electron spectroscopy sputter depth profiles and from the refractive index of the oxide determined by ellipsometry [4,12,14,19,21,24-27]. Dry oxide on 3C-SiC has been found to contain much more silicon than stoichiometric Si02 [27]. The carbon content of the SiC thermal oxide layer, away from the interface, determined by Auger spectroscopy, has been reported as at below detection limits for wet oxide on 6H-SiC [25] at below detection limits [24,26] and also at 2% for dry oxide on 3C-SiC [27] and at 14% for wet oxide on 3C-SiC [27]. The oxide on SiC grown below 1200°C is amorphous, but above 1200°C the oxide grown is increasingly crystalline [15,18,20,22-24,28]. 

Until recently, analytical investigations of surfaces were handicapped by the lack of suitable methods and instrumentation capable of supplying reliable and relevant information. Electron diffraction is an excellent way to determine the geometric arrangement of the atoms on a surface, but it does not answer the question as to the chemical composition of the upper atomic layer. The use of the electron microprobe (EMP), a powerful instrument for chemical analyses, is unfortunately limited because of its extended information depth. The first real success in the analysis of a surface layer was achieved by Auger electron spectroscopy (AES) [16,17], followed a little later by other techniques such as electron spectroscopy for chemical analysis (ESCA) and secondary-ion mass spectrometry (SIMS), etc. [18-23]. All these techniques use some type of emission (photons, electrons, atoms, molecules, ions) caused by excitation of the surface state. Each of these techniques provides a substantial amount of information. To obtain the optimum Information it is, however, often beneficial to combine several techniques. 

AES Auger Electron Spectroscopy Thin films, surfaces Electrons 3-10 keV Auger electrons 20- 2000 eV 0.3-3 nm =30 nm Eiemenlai composition ol surface (except H, He) detection limit 0.1-1% 28,29... 

While Auger electron spectroscopy and X-ray photoelectron spectroscopy can give elemental and organic structual information, respectively, they have limitations in the amount of material they can detect. For example, where polymers are in sliding, rolling or rubbing contact with metal or alloys wear to the metal as well as... 

The definition of the powder surfaces tends to be in terms of the process for making it (23). This limits interpretation of their properties and also limits generalization of properties to surfaces which have been generated by atmospheric corrosion. Conversely, the LEED, Auger electron spectroscopy, photo emission properties, etc, are measured on fresh surfaces in UHV, because interpretation is difficult for more complex configurations and because experience has shown that these properties are profoundly modified and confused by exposure to real atmospheres. 

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