Forum DQMP – Jennifer Fowlie / Iaroslav Gaponenko

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Day / Time
Date(s) - 23/05/2017
13 h 00 min - 14 h 00 min

Category


Auditoire Stückelberg – Ecole de physique (Coffee and tea will be available from 12h50 at the entrance of the Auditoire)

 

Conductivity and local structure in LaNiO3 thin films

Jennifer Fowlie (group of Prof. Triscone)

In this study we approach the thickness-dependence of the properties of LaNiO3 films along multiple, complementary avenues: sophisticated first principles calculations, scanning transmission electron microscopy and electronic transport.

Specifically, we find an unexpected maximum in conductivity in LaNiO3 films of thickness 6 – 10 unit cells (3 nm). Ab initio transport based on the detailed crystal structure also reveals a maximum in conductivity at the same thickness.

In agreement with the structure obtained from scanning transmission electron microscopy (STEM), our simulated structures reveal that the substrate- and surface-induced distortions lead to three types of local structure. Based on this observation, a 3-element parallel conductor model neatly reproduces the trend of conductivity with thickness.

We address the question of how atomic-scale structural distortions evolve in a thin film under the influence of the boundaries. This topic is key to the understanding of the physics of heterostructures and the design of functional oxides.

 

Smart Correction of SPM Time Series: Can Data Analytics Help Us Extract Correlations?

Iaroslav Gaponenko (group of Prof. Paruch)

Since its inception, scanning probe microscopy (SPM) has established itself as the tool of choice for probing surfaces and functionalities at the nanoscale. In its variety of functional modes, SPM is currently ubiquitously used in material and life sciences. Although recent developments in the instrumentation have greatly improved the metrological aspects of SPM, these techniques are still plagued by the drifts and nonlinearities of the piezoelectric actuators underlying the precise nanoscale motion.

In this work, we demonstrate the development of a novel computer-vision-based distortion correction algorithm for offline processing of functional SPM images. The topography of images acquired on overlapping areas is compared, and pairs of matching points are generated. From the difference in vertical and horizontal position of the latter, a new set of coordinates that can be applied to auxiliary channels such as current or piezoresponse phase is produced. This allows two images to be directly overlaid with minimal error – correlating the position with time evolution and local functionality.

The versatility of this algorithm is demonstrated by its application to two very different systems. First, the characteristics of surface folds and wrinkles in CVD graphene deposited on a polyethylene substrate are probed as a function of applied strain, showing the disappearance of wrinkles perpendicular to the strain direction. A second example demonstrates the tracking of polarization switching in an epitaxial Pb(Zr0.2Ti0.8)O3 thin film during high-speed continuous scanning under applied tip bias. Thanks to the precise time-location-polarization correlation we can extract the regions of domain nucleation and track the motion of domain walls until the merging of the latter in avalanche-like events.

Forum Committee : C.Lichtensteiger, A.Tamai, N.Ubrig (15.05.2017)

 

Réalisation : Sur Mesure concept