Depth profiling theory

SIMS is by far the most sensitive surface technique, but also the most difficult one to quantify. SIMS is very popular in materials research for making concentration depth profiles and chemical maps of the surface. The principle of SIMS is conceptually simple A primary ion beam (Ar+, 0.5-5 keV) is used to sputter atoms, ions and molecular fragments from the surface which are consequently analyzed with a mass spectrometer. It is as if one scratches some material from the surface and puts it in a mass spectrometer to see what elements are present. However, the theory behind SIMS is far from simple. In particular the formation of ions upon sputtering in or near the surface is hardly understood. The interested reader will find a wealth of information on SIMS in the books by Benninghoven et al. [2J and Vickerman el al. [4], while many applications have been described by Briggs et al. [5]. 

B. Maurel, G. Amsel, J.P. Nadai, Depth profiling with narrow resonances of nuclear reactions theory and experimental use, Nucl. Instr. Meth. 197 (1982) 1-13. 

I. Vickridge, G. Amsel, Spaces - a PC implementation of the stochastic-theory of energy-loss for narrow-resonance depth profiling, Nucl. Instr. Meth. B45 (1990) 6-11. 

Depth profiling techniques applied to thermodynamically equilibrated thin films characterize the compositions of coexisting phases and the spatial extent of the separating interface. This procedure repeated at different temperatures yields the coexistence curve and the corresponding temperature variation of the interfacial width. Determined coexistence curves are well described by the mean field theory with composition-dependent bulk interaction parameter [74]. The same interaction parameter also seems to generate the interfacial widths in accordance with results presented here [107] (Sect. 2.2.2) and elsewhere [88, 96, 129]. These predictions may however need to be aided by capillary wave contributions to fit another observations [95, 97, 98], especially those tracing the change of the interfacial width with film thickness [121,130] (see Sect. 3.2.2). 

DBST (p,p -dibutylsexithiophene) 77, 80 ff DCNDBQT (a,cD-dicyano-p,p -dibutyl-quaterthiophene) 76 ff deep level transient spectroscopy (DLTS) 428, 437, 438 deep trap 437, 433, 441 deformation pattern 264, 276 degradation 373 ff., 393 ff, 553 demodulated reader signal 9 density functional theory (DFT) 264, 539 density of states (DOS) 428, 437 depth profile 404 ff., 436, 544 de-trapping 428, 437 ff, 441 device simulation 433, 435 dewetting, post-deposition 220 ff. DHBTP-SC ((dihexylbithiophene)2-phe-nyl swivel cruciform) 96 ff. 

Bradley, R.M., Cirlin, E. (1996) Theory of improved resolution in depth profiling with sample rotation. Applied Physics Letters, 68,3722-3724. 

Each analytical technique discus.sed in this chapter has its own advantages and disadvantages, arising from both the physical processes involved and technical requirements. The theory behind each of the techniques would in it.self fill a book, whereas the present purpose was to set out briefly the depth profiling approach as it related to each. The theories of sputtering and of depth resolution have al.so been the subject of many publications. Individual applications (corrosion, semiconductors, catalysis, organic materials, etc.) will be described separately in this volume. 

Second, progress has been made in the theoretical approach to the analysis of DCEMS measurements. The underlying theory of resonance excitation (-> excitation matrix) in the sample by y-quanta including secondary absorption and emission processes, electron transport (- transport tensor), and detection response (—> response function) have been included in a least-squares fit routine [ 103. 105). Adjustable parameters in this fitting are. on the one hand, the hyperfine interaction and line shape variables, and, on the other hand, the variables that give a parametric representation of the depth profiles. The response parameters are also included to allow energy calibration of the experimental apparatus. 

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