Thomas Werninghaus

Micro-Raman Spectroskopy Investigation of Hard Coatings

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Kurzfassung in Englisch

Abstract: Micro­Raman Spectroscopy Investigation of Hard Coatings

Diamond, silicon carbide, and boron nitride have attracted great interest in the last years, due
to their excellent material properties. Especially the extreme hardness and the high thermal con­
ductivity of these materials favour them as protective layers. The very large hardness gave these
materials, deposited as films on various substrates, their name: hard coatings. In contrast to di­
amond, silicon carbide and boron nitride can be n­ as well as p­doped, making them promising
candidates for high speed and high temperature electronic applications. Contrarily to the materials
mentioned above, carbon nitride was obtained in crystalline form just very recently. Up to now the
deposited films mainly consist of amorphous or nanocrystalline, carbon­rich material. For all these
material systems inelastic light scattering (Raman spectroscopy) has been already applied for the
material properties investigation. However, these investigations usually were restricted to only one
of the various Raman spectroscopy tools, described in this work: Incident laser light energy varia­
tion, temperature variation, utilizing the selection rules, measurements at varying sample positions,
two­dimensional mappings and one­dimensional scans in the conventional plane­view and the addi­
tional cross­sectional sample geometry. In contrast to this, this work demonstrates the improvement
of the information about the investigated material and/or the sample heterostructure obtained by
using the combination of all the above mentioned techniques. In the case of the diamond material
system, films deposited on silicon substrates were investigated and an interfacial graphitic layer
of 2nm thickness was found by scanning across the interface, which was obscured in the conven­
tional plane­view sample geometry. Similar to this an ultra­thin top layer and buried intermixed
regions were identified in the silicon carbide material system utilizing the cross­sectional sample
geometry. In addition to this, the temperature and the incident laser light energy dependences for
5 SiC polytypes (3C, 4H, 6H, 15R, and 21R) were measured. A resonance enhancement for the
3C and the 21R polytype was found corresponding to their fundamental bandgaps at 2.46eV and
ß2.8eV, respectively. For the other polytypes no resonance enhancement was found, due to their
larger fundamental bandgap. In the boron nitride material system the spatial correlation model for
Raman lineshape analysis was applied for the first time and the values of the asymmetric broad­
ening and the frequency downshift for decreasing crystal sizes were evaluated. This was measured
for single crystals of different size and for films deposited on silicon substrates. The correlation
lengths in the ten nanometer region found for the deposited films corroborate the nanocrystalline
nature of these films. Additionally incident laser light energy was measured, revealing the 488.0nm
(Ar + ) and 482.5nm (Kr + ) laser lines as the optimum laser lines for the boron nitride investigation.
Furthermore the dependence of the phonon feature parameters was investigated depending on the
incident laser light power. A maximum power of 5­10mW for the micro­Raman spectroscopy setup
was found to avoid any laser light induced heating of the investigated material. Two­dimensional
mappings of the deposited boron nitride films were performed to improve the information about
the material system. In the case of carbon nitride for the first time distinct phonon features were
measured in a wide spectral range contrarily to most of the other investigations, which usually show
only broad bands.

weitere Metadaten

Raman spectroscopy, two­dimensional mapping, cross­sectional scans, interface investigations,
characterisation, wide­gap semiconducor, diamond, silicon carbide, boron nitride, carbon
DDC Klassifikation530
DDC Klassifikation600
HochschuleTU Chemnitz
FakultätFakultät für Naturwissenschaften
Tag d. Einreichung (bei der Fakultät)20.07.1999
Tag d. Verteidigung / Kolloquiums / Prüfung01.07.1997
Veröffentlichungsdatum (online)20.07.1999
persistente URNurn:nbn:de:bsz:ch1-199900407
QuelleVerlag: Als Manuskript gedruckt im SHAKER Verlag Aachen;ISBN 3-8265-3110-8

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