% IMPORTANT: The following is UTF-8 encoded. This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.
@PHDTHESIS{KarimiAghda:961005,
author = {Karimi Aghda, Soheil},
othercontributors = {Schneider, Jochen M. and Anders, Andre},
title = {{I}nfluence of point defects on the elastic properties and
phase stability of cubic binary and ternary transition metal
(aluminum) nitride thin films},
volume = {41},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2023-06577},
series = {Materials chemistry dissertation},
pages = {1 Online-Ressource : Illustrationen, Diagramme},
year = {2023},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2023},
abstract = {In the first part of this thesis, a correlative
experimental and theoretical model is developed to study the
influence of ion kinetic energy on the evolution of point
defect structure in metastable cubic (V,Al)N. Ion
irradiation-induced changes in the structure and mechanical
properties of (V,Al)N thin films deposited by reactive high
power pulsed magnetron sputtering (HPPMS) are systematically
investigated in the ion kinetic energy $(E_k)$ range from 4
to 154 eV. Increasing $E_k$ results in film densification
and the evolution from a columnar (111) oriented structure
at $E_k$ ≤ 24 eV to a fine-grained structure with (100)
preferred orientation for $E_k$ ≥ 104 eV. Furthermore, the
compressive intrinsic stress increases by 336 $\%$ to −4.8
GPa as $E_k$ is increased from 4 to 104 eV. Higher ion
kinetic energy causes stress relaxation to −2.7 GPa at 154
eV. These ion irradiation-induced changes in the thin film
stress state are in good agreement with density functional
theory (DFT) simulations. Furthermore, the measured elastic
moduli of (V,Al)N thin films exhibit no significant
dependence on $E_k.$ The apparent independence of the
elastic modulus on $E_k$ can be rationalized by considering
the concurrent and balancing effects of bombardment-induced
formation of Frenkel pairs (causing a decrease in elastic
modulus) and evolution of compressive intrinsic stress
(causing an increase in elastic modulus). Hence, the
evolution of the film stresses and mechanical properties can
be understood based on the complex interplay of ion
irradiation-induced defect generation and annihilation. In
the second part, the developed model was extended towards
the isostructural (Ti,Al)N thin films grown by two physical
vapor deposition techniques, namely HPPMS and cathodic arc
deposition (CAD). Ion irradiation-induced changes in
structure, elastic properties, and thermal stability of
metastable cubic (Ti,Al)N thin films are systematically
investigated by experiments and DFT simulations. While thin
films deposited by HPPMS show a random orientation at $E_k$
> 105 eV, an evolution towards (111) orientation is observed
in CAD thin films for $E_k$ > 144 eV. The measured ion
energy flux at the growing film surface is 3.3 times larger
for CAD as compared to HPPMS. Hence, it is inferred that the
formation of the strong (111) texture in CAD thin films is
caused by the ion flux- and ion energy-induced minimization
of strain energy in defective cubic (Ti,Al)N. The ion
energy-dependent elastic modulus can be rationalized by
considering the ion energy- and orientation-dependent
formation of point defects from DFT predictions: The
balancing effects of bombardment-induced formation of
Frenkel defects and the concurrent evolution of compressive
intrinsic stress result in the apparent independence of the
elastic modulus from $E_k$ for HPPMS thin films without
preferential orientation, similar to the previously
investigated (V,Al)N. However, an ion energy-dependent
elastic modulus reduction of $~18\%$ for the CAD thin films
can be understood by considering the $34\%$ higher Frenkel
pair concentration formed at $E_k$ = 182 eV upon irradiation
of the experimentally observed (111) oriented (Ti,Al)N in
comparison to the (200) configuration at a similar $E_k$
magnitude. Moreover, the effect of Frenkel pair
concentration on the thermal stability of metastable
(Ti,Al)N is investigated by differential scanning
calorimetry for both processing routes: The ion
irradiation-induced increase in Frenkel pairs concentration
retards the wurtzite formation temperature by up to 206 °C.
In the third and last part, the elastic response of binary
cubic transition metal nitrides (c-TMNs) with respect to the
occupancy of non-metal sublattice is explored. Motivated by
the frequently reported deviations from stoichiometry in
c-TMNs, the effect of nitrogen vacancy concentration on the
elastic properties of TiNx, ZrNx, VNx, NbNx, and MoNx (0.72
x 1.00) is systematically studied by DFT. The
predictions are validated experimentally for VNx (0.75 x
0.96). The DFT results clearly indicate a different
elastic response of the group IV, V, and VI nitrides with
respect to N vacancy concentration. While, TiNx and ZrNx
exhibit vacancy-induced reduction in elastic modulus, an
elastic modulus enhancement is obtained for VNx and NbNx.
These trends could be rationalized by analyzing the bonding
characteristic of the binary compounds. The integrated
crystal orbital Hamilton population calculations indicate a
lower bond strength of Ti–N for TiNx due to presence of N
vacancies. However, presence of N vacancies in VNx results
in a higher bond strength of V–N, which consequently leads
to an overall anomalous increase in elastic modulus of VNx.
To validate the elastic modulus behavior with respect to N
vacancy concentration experimentally, high crystalline
quality, close to single-crystal, VNx thin films are grown
on single crystal MgO(001) substrates. Reduction of N
content in VNx/MgO(001) from x = 0.96 ± 0.05 to 0.75 ±
0.04 leads to a decrease in the relaxed lattice parameter a0
from 4.128 Å to 4.096 Å, respectively. This reduction in
lattice parameter is accompanied by an anomalous $11\%$
increase in elastic modulus. These results are in agreement
with the theoretically calculated elasticity data for VNx,
which is attributed to vacancy-induced bond strengthening.
The results of this thesis pave the way for the design and
tailoring of hard protective coatings by considering
plasma-surface interactions on the atomistic level. The
combination of DFT simulations and growth experiments
allowed us to understand the role of plasma condition
variation, specifically ion kinetic energy, on the point
defect structure and its implications for mechanical
properties and thermal stability of nitride thin films.},
cin = {521110 / 520000},
ddc = {620},
cid = {$I:(DE-82)521110_20140620$ / $I:(DE-82)520000_20140620$},
pnm = {DFG project 138690629 - TRR 87: Gepulste
Hochleistungsplasmen zur Synthese nanostrukturierter
Funktionsschichten (138690629)},
pid = {G:(GEPRIS)138690629},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.18154/RWTH-2023-06577},
url = {https://publications.rwth-aachen.de/record/961005},
}
guest ::