5 research outputs found
Growth Stress Induced Tunability of Dielectric Constant in Thin Films
It is demonstrated here that growth stress has a substantial effect on the
dielectric constant of zirconia thin films. The correct combination of
parameters - phase, texture and stress - is shown to yield films with high
dielectric constant and best reported equivalent oxide thickness of 0.8 nm. The
stress effect on dielectric constant is twofold, firstly, by the effect on
phase transitions and secondly by the effect on interatomic distances. We
discuss and explain the physical mechanisms involved in the interplay between
the stress, phase changes and the dielectric constant in detail.Comment: 11 pages, 5 figure
An Incremental Phase Mapping Approach for X-ray Diffraction Patterns using Binary Peak Representations
Despite the huge advancement in knowledge discovery and data mining
techniques, the X-ray diffraction (XRD) analysis process has mostly remained
untouched and still involves manual investigation, comparison, and
verification. Due to the large volume of XRD samples from high-throughput XRD
experiments, it has become impossible for domain scientists to process them
manually. Recently, they have started leveraging standard clustering
techniques, to reduce the XRD pattern representations requiring manual efforts
for labeling and verification. Nevertheless, these standard clustering
techniques do not handle problem-specific aspects such as peak shifting,
adjacent peaks, background noise, and mixed phases; hence, resulting in
incorrect composition-phase diagrams that complicate further steps. Here, we
leverage data mining techniques along with domain expertise to handle these
issues. In this paper, we introduce an incremental phase mapping approach based
on binary peak representations using a new threshold based fuzzy dissimilarity
measure. The proposed approach first applies an incremental phase computation
algorithm on discrete binary peak representation of XRD samples, followed by
hierarchical clustering or manual merging of similar pure phases to obtain the
final composition-phase diagram. We evaluate our method on the composition
space of two ternary alloy systems- Co-Ni-Ta and Co-Ti-Ta. Our results are
verified by domain scientists and closely resembles the manually computed
ground-truth composition-phase diagrams. The proposed approach takes us closer
towards achieving the goal of complete end-to-end automated XRD analysis.Comment: Accepted and presented at the International Workshop on Domain-Driven
Data Mining (DDDM) as a part of the SIAM International Conference on Data
Mining (SDM 2021). Contains 11 pages and 5 figure
Tungsten oxide mediated quasi-van der Waals Epitaxy of WS2 on Sapphire
Conventional epitaxy plays a crucial role in current state-of-the art semiconductor technology, as it provides a path for accurate control at the atomic scale of thin films and nanostructures, to be used as the building blocks in nanoelectronics, optoelectronics, sensors, etc. Four decades ago, the terms “van der Waals” (vdW) and “quasi-vdW (Q-vdW) epitaxy” were coined to explain the oriented growth of vdW layers on 2D and 3D substrates, respectively. The major difference with conventional epitaxy is the weaker interaction between the epi-layer and the epi-substrates. Indeed, research on Q-vdW epitaxial growth of transition metal dichalcogenides (TMDCs) has been intense, with oriented growth of atomically thin semiconductors on sapphire being one of the most studied systems. Nonetheless, there are some striking and not yet understood differences in the literature regarding the orientation registry between the epi-layers and epi-substrate and the interface chemistry. Here we study the growth of WS2 via a sequential exposure of the metal and the chalcogen precursors in a metal–organic chemical vapor deposition (MOCVD) system, introducing a metal-seeding step prior to the growth. The ability to control the delivery of the precursor made it possible to study the formation of a continuous and apparently ordered WO3 mono- or few-layer at the surface of a c-plane sapphire. Such an interfacial layer is shown to strongly influence the subsequent quasi-vdW epitaxial growth of the atomically thin semiconductor layers on sapphire. Hence, here we elucidate an epitaxial growth mechanism and demonstrate the robustness of the metal-seeding approach for the oriented formation of other TMDC layers. This work may enable the rational design of vdW and quasi-vdW epitaxial growth on different material systems
Effect of in situ stress on grain growth and texture evolution in sputtered YSZ/Si films
Yttria stabilized zirconia (YSZ) films are being used both as functional oxide and buffer layers for integration of various other functional oxide films on Si substrates. As functional properties of these oxides are highly anisotropic in nature, highly oriented films are essential to realizing their fascinating properties. (111) and (100) textured YSZ films have been deposited on Si substrates by reactive-direct current (R-DC) sputtering. Annealing of these films leads to grain growth and improvement in texture. However, it strongly depends on the growth stresses developed during deposition of these films. Depending on stress harnessing in films/stacks, the texture was improved from rocking curve FWHM of 16 degrees to 7 degrees and 25 degrees to 15 degrees for (111) and (100) YSZ films respectively. A detailed analysis of the relation between stress and grain growth is carried out using an energy balance model. We have found that grain growth is limited by kinetics, though it should be possible from a thermodynamic viewpoint. It is observed that higher initial compressive stress aids significant grain growth (similar to 150%) and texture-improvement (similar to 57%) on annealing