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region. Only a few droplets need to be pipetted on carriers and dried by simple
evaporation. If a more complex sample is to be analyzed, a decomposition and
separation of the matrix becomes necessary. Simple quantification is made
possible, since matrix effects do not appear because of the small sample
amounts used for analysis. Furthermore, contaminations on flat surfaces,
such as wafers, can be quickly determined by TXRF. Depth profiles of
biogeneous materials can be recorded after sectioning of the material with a
freezing microtome. Stratified near-surface layers can be characterized by a
depth profile after planar sputter etching. This technique combined with TXRF
of the remaining surface is especially suitable for thin layers of nanometer
thickness deposited on wafers even though it is destructive and a bit time-
consuming.
In contrast to TXRF after sputter etching, GI-XRF is nondestructive and
moreover is a fast method for depth profiling of deposited or implanted
layers in the lower nanometer range. However, GI-XRF makes higher
demands on instrumentation and evaluation considering matrix effects.
New applications are concerned with semiconducting layers and even thin
polymeric films.
With respect to its capabilities, TXRF has far surpassed conventional XRF.
Indeed, TXRF has attained a leading position in atomic spectroscopy. The
outstanding features compete very well with those of instrumental neutron
activation analysis (INAA) and ICP-MS. For several applications, TXRF even
has distinct advantages over these methods because of its simplicity and
rapidity. The detection power may be inferior, but for many applications is
sufficient. The detection of light and transition elements, however, needs
special and further efforts.
In the field of surface analyses, TXRF is highly effective in the contamina-
tion control of wafers and therefore is a widespread analytical tool in the
semiconductor industry. For analyses of thin stratified layers, GI-XRF is able
to compete with the reference methods RBS and secondary ion mass spec-
trometry (SIMS).
6.2.1AdvantagesandLimitations
Several strengths of TXRF and GI-XRF can be listed on a short inspection:
(i) generally nonconsumptive and also nondestructive investigations; (ii) a
versatility of various sample types; (iii) no sample preparation or only an easy
and fast handling; and (iv) mature instrumentation being commercially availa-
ble. The weaknesses of TXRF and GI-XRF are: (i) a minor sensitivity for light
and transition elements; (ii) poorly representative results for macrosamples;
and (iii) a lack of on-line investigations. Standardization by ISO, ASTM, or
DIN is just being developed.
Several features of TXRF are especially worth noting. Most of them
are advantageous, although some present limitations. Some drawbacks are
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