Papers by Keyword: Surface Instability

Abstract: A styrene-butadiene rubber having a gradient crosslink density in the thickness direction was simply prepared by vulcanizing under a temperature gradient to study its mechanical properties and swelling behavior. The graded rubber exhibited considerable strain recovery after stress removal despite having a low crosslinked part. Notably, the graded rubber also manifested greater hysteresis loss during cyclic test compared to a homogeneously crosslinked rubber, even though they had similar initial moduli. Furthermore, anomalous swelling behavior was observed in the graded rubber. The graded rubber exhibited shape transformation upon swelling. The mechanism was thoroughly explained using gel swelling theory under constraints. This must be a common phenomenon in graded rubbers with a crosslink gradient in the thickness direction. This comprehensive research provides a novel approach for material design with tailored properties and promising applications for this potential material.

Abstract: In this work, we have investigated the seeding stage of 4H-SiC top seeded solution growth through the systematic observation of surface morphologies and numerical simulation. Different growth temperatures, C- and Si-polarities, and different solvents have been studied. This is the first report of transient nucleation of parasitic 3C-SiC at the early stage of solution growth in pure Si solvent even at high temperature. This unusual phenomenon was attributed to a huge temperature difference between the seed crystal and solvent surface at the seeding stage. We demonstrated that preheating of the seed crystals or addition of Al were effective to prevent such parasitic 3C-SiC nucleation.

Abstract: we study the surface morphology of homoepitaxially grown 4H silicon carbide in terms of growth rate, miscut direction of the substrate and post growth argon thermal annealings. All the results indicate that the final surface morphology is the result of a competition between energetic reorganization and kinetic randomness. Because in all observed conditions energetic reorganization favors surface ondulations (“step bunching”), out-of-equilibrium conditions are one of the keys to favor the reduction of the surface roughness to values below ~0.5 nm. We theoretically support these results using kinetics superlattice Monte Carlo simulations (KslMC)

Abstract: In this paper we study the surface morphology of <11-20> 4° degree off, silicon terminated, 4H Silicon Carbide (4H-SiC) in terms of growth parameters and post growth argon thermal annealing. We find that out-of-equilibrium conditions favor the reduction of the surface roughness. Furthermore, we find preliminary indications that the same growth parameters that lead to the reduction of the surface roughness promote also a reduction of (1,3) and (4,4) stacking faults density.

Abstract: Using several types of surface analysis (Optical profilometers (OP), Atomic Force Microscopies (AFM), Scanning Electron Microscopies (SEM) and cross-sectional high-resolution Transmission Electron Microscopies (TEM)) we analyze the surface morphologies of misoriented 4H silicon carbide after pre-growth hydrogen etching and homo-epitaxial growths. We observed the characteristic self-ordering of nano-facets on any analyzed surface. This nano-faceting, which should not be confused with step bunching, can be considered as a close-to-equilibrium instability, for this reason can be hindered.

Abstract: Necking under in-plane plane strain tension along the transverse direction (TD) is numerically simulated for two sheets: one with very high Cube (HC) and the other with low Cube (LC). To do so, the EBSD measurement is performed in the TD-ND (normal direction) section for the sheets. The EBSD map (grain orientations and their spatial distributions) is directly implemented into the crystal plasticity based finite element code. More specifically, the measured orientations are assigned to elements in the mesh according to their positions. The values of the material parameters in the crystal plasticity model are determined by curve-fitting numerical simulations of uniaxial tension in the rolling direction (RD) to corresponding experimental data. The effect of spatial grain orientation distribution on necking is emphasized. It is found that both the global averaged texture and its spatial distribution are important to the onset of necking. The predicted results are in good agreement with experimental observations.