arXiv subjects

Gianluigi Botton

Publications and source records attributed to Gianluigi Botton.

3 recordsLinked to original sources

arXiv2025

Spontaneous Transition from Conformal to Two-Dimensional Growth in Ge/GeSn Core/Shell Nanowires

GeSn semiconductors are group-IV isovalent alloys that offer remarkable tunability of optoelectronic properties across the entire infrared spectrum, while remaining fully compatible with silicon processing standards. These attributes make GeSn a promising platform for scalable sensing, imaging, and communication technologies. Yet, the influence of dimensionality on GeSn crystal growth remains poorly understood, limiting the development of integrated nanoscale infrared devices. Here, we reveal the spontaneous formation of hitherto unreported ultra-thin GeSn fins with sub-30 nm thickness during vapor-phase growth on Ge nanowire substrates. A transition from the typical conformal GeSn shell to distinct fin-like structures occurs along the nanowire growth axis and is accompanied by ordered twin defects extending longitudinally and laterally, inducing a transition from diamond to hexagonal-like crystal structure. The fins exhibit uniform Sn incorporation of approximately 16 at.% throughout their volume, indicating high compositional homogeneity. These findings uncover an anisotropic growth regime in metastable GeSn alloys, enriching the fundamental understanding of nanoscale epitaxy.

cond-mat.mtrl-sci↗

arXiv2022

Defect free strain relaxation of microcrystals on mesoporous patterned silicon

A perfectly compliant substrate would allow the monolithic integration of high-quality semiconductor materials such as Ge and III-V on Silicon (Si) substrate, enabling novel functionalities on the well-established low-cost Si technology platform. Here, we demonstrate a compliant Si substrate allowing defect-free epitaxial growth of lattice mismatched materials. The method is based on the deep patterning of the Si substrate to form micrometer-scale pillars and subsequent electrochemical porosification. The investigation of the epitaxial Ge crystalline quality by X-ray diffraction, transmission electron microscopy and etch-pits counting demonstrates the full elastic relaxation of defect-free microcrystals. The achievement of dislocation free heteroepitaxy relies on the interplay between elastic deformation of the porous micropillars, set under stress by the lattice mismatch between Ge and Si, and on the diffusion of Ge into the mesoporous patterned substrate attenuating the mismatch strain at the Ge/Si interface.

cond-mat.mtrl-sci↗

arXiv2007

Epitaxial thin films of multiferroic Bi2FeCrO6 with B-site cationic order

Epitaxial thin films of Bi2FeCrO6 have been synthesized by pulsed laser deposition on SrRuO3 on (100)- and (111)-oriented SrTiO3 substrates. Detailed X-ray diffraction and cross-section transmission electron microscopy analysis revealed a double perovskite crystal structure of the Bi2FeCrO6 epitaxial films very similar to that of BiFeO3 along with a particularly noteworthy Fe3+/Cr3+ cation ordering along the [111] direction. The films contain no detectable magnetic iron oxide impurities and have the correct cationic average stoichiometry throughout their thickness. They however exhibit a slight modulation in the Fe and Cr compositions forming complementary stripe patterns, suggesting minor local excess or depletion of Fe and Cr. The epitaxial BFCO films exhibit good ferroelectric and piezoelectric properties, in addition to magnetic properties at room temperature, as well as an unexpected crystallographic orientation dependence of their room temperature magnetic properties. Our results qualitatively confirm the predictions made using the ab-initio calculations: the double-perovskite structure of Bi2FeCrO6 films exhibit a Fe3+/Cr3+ cation ordering and good multiferroic properties, along with the unpredicted existence of magnetic ordering at room temperature.

cond-mat.mtrl-sci↗