ICMCTF 2012! - CD-Lab Application Oriented Coating Development

chemical bonds have also been achieved utilizing FTIR via cross calibration
with other techniques. In this talk, we will demonstrate that transmission
FTIR can be, in certain instances, further extended to quantitatively
determine the full chemical bonding in a dieletric thin film. In turn,
knowledge of the full bond concentrations allows accurate determination of
the mass density and full elemental composition of the film. This capability
is demonstrated for a-SiC:H thin films deposited by plasma enhanced
chemical vapor deposition (PECVD). The resulting FTIR mass density and
compositional analysis determined by this technique shows an excellent
correlation to similar measurements by X-ray Reflectivity, X-ray
Photoelectron Spectroscopy, and Scanning Ion Mass Spectroscopy
Techniques.
TSP-8 Ordered thin film materials with ultra-low thermal
conductivity, C. Muratore (chris.muratore@wpafb.af.mil), Air Force
Research Laboratory, Thermal Sciences and Materials Branch, US, V.
Varshney, UTC/Air Force Research Laboratory, Thermal Sciences and
Materials Branch, US, J.J. Gengler, Air Force Research Laboratory,
Thermal Sciences and Materials Branch, US, J.J. Hu, UDRI/Air Force
Research Laboratory, Thermal Sciences and Materials Branch, US, T.S.
Smith, Air Force Research Laboratory, Thermal Sciences and Materials
Branch, US, J.E. Bultman, UDRI/Air Force Research Laboratory, Thermal
Sciences and Materials Branch, US, A. Voevodin, Air Force Research
Laboratory, Thermal Sciences and Materials Branch, US
Transition metal dichalcogenide (TMD) crystals are characterized by their
distinct layered atomic structures, with strong covalent bonds comprising
each layer, but weak van der Waals forces holding the layers together. The
relationship between chemical bonding in a material and its thermal
conductivity (k) is well-known, however the thermal properties of TMD
thin films with such highly anisotropic chemical bonds have only recently
been investigated with remarkable results, such as ultra-low kz. Materials
with very low thermal conductivity in the z-axis, but higher kx and ky have
potential as next-generation thermal barrier or heat spreading materials.
Molecular dynamics (MD) simulations predicted kx=ky=4kz for perfect
TMD crystals (MoS2 in this case). Experiments to determine kx,y and kz
were conducted by developing processes to grow crystalline TMD thin film
materials with strong (002) (basal planes parallel to surface) or (100)
(perpendicular basal planes) preferred orientation. Initially, no correlation
between structure and thermal conductivity was apparent, as water
intercalation and reactivity to ambient air resulted in a thermal “shortcircuit”
across basal planes, such that the time between deposition and k
measurement had a stronger impact on thermal conductivity than film
orientation. Experiments to measure intrinsic thermal conductivity of MoS2
revealed values approximately one order of magnitude lower than those
predicted using MD simulations, however, measurement of kx=ky=4kz was
consistent with simulation results. Simulations to evaluate the dependence
of thermal conductivity on grain size was evaluated, which correlated well
to measured values. Comparison of measured k values for strongly (002)
oriented MoS2, WS2, WSe2 and other materials with analogous crystal
structures are discussed in the context of the Slack Law, which accounts for
intrinsic physical properties of the crystal, but not film microstructure.
TSP-9 Texture change and off-axis accommodation through film
thickness in fcc structured nitrides, A. Karimi, A. Shetty
(akshath.shetty@epfl.ch), EPFL, Switzerland
The control of texture in fcc nitride coatings by varying the film thickness
was demonstrated on polycrystalline TiAlN coatings grown by pulsed DC
magnetron sputtering. Development of off-axis texture with film thickness
was observed. For this purpose the evolution of texture versus thickness
was studied by a set of analytical x-ray diffraction (XRD) methods like θ–
2θ and pole figures, while scanning electron microscopy (SEM) and
transmission electron microscopy (TEM) were used to observe the
microstructure and changes in texture with thickness. The stresses along the
(111) and (002) orientation were obtained by sin 2 ψ method. Based on the
results obtained, the texture formation mechanism is divided in three
different stages of film growth. Films at low thickness lead to the
development of (002) orientation due to the surface energy minimization.
Meanwhile, the competitive growth promotes the growth of (111) planes
parallel to film surface at higher thickness. However, contrary to the
prediction of growth models, the (002) grains are not completely overlapped
by (111) grains at higher thickness. Rather the (002) grains still constitute
the surface, but are tilted away from the substrate normal showing
substantial in-plane alignment to allow the (111) planes remain parallel to
film surface. Intrinsic stress along (111) and (002) shows a strong
dependence with preferred orientation. The stress level in (002) grains
which was compressive at low thickness changes to tensile at higher
thickness. This change in the nature of stress allows the (002) planes to tilt
away in order to promote the growth of parallel to film normal and
to minimize the overall energy of system due to high compressive stress
stored in the (111) grains. The change in surface morphology with thickness
was observed using SEM. An increase in surface roughness with film
thickness was observed which indicates the development of (111) texture
parallel to film surface. TEM observations support the XRD results
regarding texture change. Film hardness was measured by nanoindentation
and a correlation between (111) texture, stress and hardness is obtained. The
results indicate that texture development is a complex interplay between
thermodynamic and kinetic forces. An attempt is made to understand this
phenomenon of off-axis accommodation of (002) at higher thicknesses,
which is a new result not reported previously.
127 Thursday Afternoon Poster Sessions