TRENDS AND FUTURE PROSPECTS - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 479

Figure7.22. NEXAFS spectra near the K edge of boron, carbon, and nitrogen. Spectra were
recorded for different layers of borane compounds produced with ammonia (F3) and without (A3).
Reference spectra of boron carbide and hexagonal boron nitride and of Li and K cyanoborate can
be used as fingerprints for the different bondings. Figure from Ref. [136], reproduced with
permission. Copyright2012, John Wiley and Sons.

B-K α spectra of borane compounds reveal B-N bonds as the main structure of
hexagonal BN 3 configurations with additional BN and BN 2 components. C-K α
spectra represent a hexagonal bonded carbon while N-K α spectra are similar to
the hexagonal crystalline form of boron nitride, h-BN. The broad peaks point
to more amorphous and less crystalline structures.
Layersofboroncarbonitridecoveringnickellayerscanbeanalyzedby
NEXAFSorXANES . These methods combined with GI-XRF were applied to
such double layers on top of a silicon substrate [137]. A nickel layer of 5 nm
resulted from the deposition of nickel on a silicon wafer by PVD (physical
vapor deposition). The layer B x C y N z was deposited by CVD of borane
(TMAB) with ammonia at 200, 400, and 500 ° C yielding a layer with a thickness
between 4 and 6 nm. The K α spectra of B, C, and N as well as the L αβ spectra of
nickel were recorded by varying the excitation energy above the respective K
or L edges. Simultaneously, the glancing angle was changed between 0.5 ° and
15 ° . It could be shown that Ni C bonds occur at a temperature of 200 ° Cinan

interface between B x C y N z and nickel. This bond vanishes if the temperature is
increased so that nickel is only existent as a metal. Simultaneously, Ni

-

- Si bonds

appear in an interface between nickel layer and silicon substrate.
Differentcompoundsbuiltasinterfacesbetweendifferentlayerscanbeidenti-
fiedbyXANES . A very special kind of layers, namely, aluminum doped ZnO
layers (ZnO:Al) protected by a polycrystalline silicon layer (poly-Si), are highly
relevant for solar cells in photovoltaic devices [138]. Panes of glass were coated
with a transparent and conductive layer of ZnO:Al covered by poly-Si. High-
temperature treatments up to 1050 ° C followed by annealing procedures were
used. A chemical speciation of the buried interface was performed by NEX-
AFS [138]. Zn silicates and Al oxides were found within an interface of 10 nm.