Elastic constants of fibre-textured thin films determined by X-ray diffraction

Dynamic strain evolution in an optically excited Pt thin film

The structural evolution of a Pt thin film following photo-thermal excitation by 1 ps optical laser pulses was studied with a time resolution of 100 ps over a total time period of 1 ms. Laser pulse fluences below 50 mJ/cm² were insufficient to relax the residual stress state of the as-prepared film even after 10 000 pulses. In this fluence regime, a rapid initial lattice expansion and a decrease in the lattice coherence length due to ultrafast photo-thermal heating were observed. The lattice expansion reached a maximum, and the coherence length reached a minimum, 100-200 ps after excitation before monotonically decaying back to their initial values in about 1 µs. Laser pulse fluences greater than 50 mJ/cm² produced irreversible stress relaxation within the first 10 optical pulses. In this regime, the lattice expansion was qualitatively similar to that in the low fluence regime, except that the initial structural state was not recovered. The evolution in the coherence length, however, was more complex. Following an initial decrease similar to that observed at low fluence, the coherence length then increased to a broad maximum greater than the initial value, before recovery.

Negative linear compressibility in nanoporous metal-organic frameworks rationalized by the empty channel structural mechanism

Zinc squarate tetrahydrate (ZnC₄O₄·4H₂O) and titanium oxalate trioxide dihydrate (Ti₂(C₂O₄)O₃·2H₂O) are nanoporous metal-organic frameworks possessing empty channels in their crystal structures. The crystal structures and mechanical properties of these materials are studied using first principles solid-state methods based on Density Functional Theory. The results show that they exhibit the negative linear compressibility (NLC) and negative Poisson's ratio (NPR) phenomena. The absolute value of the negative compressibilities are significant and the range of pressure for which NLC effects are shown is very wide. The detailed study of the deformation of the crystal structures under pressure reveals that the NLC effect in these compounds can be rationalized using the empty channel structural mechanism. Under isotropic compression, the channels are elongated along the direction of minimum compressibiity, leading to NLC. Furthermore, under compression along the direction of minimum compressibity, the unit-cell volume increases leading to negative volumetric compressibilty. The effect of hydration on the NLC effect in titanium oxalate trioxide dihydrate is investigated by studying the parent compound titanium oxalate trioxide trihydrate (Ti₂(C₂O₄)O₃·3H₂O). The NLC effect in this material is reduced due to the reinforcement of the walls of the structural channels.

Theoretical and experimental study of the gradient properties and the resulting local crystalline structure and orientation in magnetron-sputtered CrAlN coatings with lateral composition and thickness gradient

Cr–Al–N coatings with a lateral composition gradient were deposited from two segmented Cr/Al targets with different segment size, thus covering the Al content range 0.22 ≲ c ≲ 0.87 and a thickness range from several hundred nanometres to several micrometres. The two-dimensional thickness and composition profiles were determined nondestructively from X-ray fluorescence maps. The results were reproduced by simulations of the flux distribution on the sample surface, combiningTRIDYNsimulations of the reactive sputter process at the target surface andSIMTRAsimulations of the subsequent transport through the gas phase. The phase formation was studied by spatially resolved X-ray diffraction and X-ray absorption spectroscopy at the Cr Kedge. Forc ≲ 0.69, a single-phase solid solution face-centered cubic (f.c.c.) (Cr,Al)N phase was found, and for 0.69 ≲ c ≲ 0.87 coexisting f.c.c. (Cr,Al)N and hexagonal close packed (h.c.p.) (Cr,Al)N phases were observed. The biaxial texture formation in nearly the entire composition range indicates a zone T growth. Four, mainly composition-dependent, texture regions were identified. All observed textures are closely related to textures reported for the h.c.p. AlN and f.c.c. CrN parent phases. Forc ≳ 0.69, a strong thickness dependence of the textures was observed. The measurements reveal an orientation relation between different f.c.c. and h.c.p. textures, indicating that local epitaxy might play a role in the structure formation.

Combined synchrotron X-ray and image-correlation analyses of biaxially deformed W/Cu nanocomposite thin films on Kapton

In situbiaxial tensile tests within the elastic domain were conducted with W/Cu nanocomposite thin films deposited on a polyimide cruciform substrate using a biaxial testing machine developed on the DiffAbs beamline at the Synchrotron SOLEIL. The mechanical behaviour of the nanocomposite was characterized at the micro- and macroscales using synchrotron X-ray diffraction and digital image-correlation techniques simultaneously. Strain analyses for equibiaxial and non-equibiaxial loading paths were carried out. The results show that the two strain measurements match to within 1 × 10−4in the elastic domain for strain levels less than 0.3% and for both loading paths.

X-ray strain analysis of {111} fiber-textured thin films independent of grain-interaction models

The anisotropic elastic response of supported thin films with a {111} fiber texture has been studied using anin-situmicro-tensile tester and X-ray diffractometry. It is shown which specific X-ray diffraction measurement geometries can be used to analyze the elastic strains in thin films without requiring any assumptions regarding elastic interactions between grains. It is evidenced (theoretically and experimentally) that the combination of two specific geometries leads to a simple linear relationship between the measured strains and the geometrical variable sin2ψ, avoiding the transition scale models. The linear fit of the experimental data allows a direct determination of the relationship between the three single-crystal elastic compliances or a direct determination of theS44single-crystal elastic compliance and the combination ofS11+ 2S12if the macroscopic stress is known. This methodology has been applied to a model system,i.e.gold film for which no size effect is expected, deposited on polyimide substrate, and it was found thatS44= 23.2 TPa−1andS11+ 2S12= 1.9 TPa−1, in good accordance with values for large crystals of gold.