arXiv subjects

Agnieszka Anna Corley-Wiciak

Publications and source records attributed to Agnieszka Anna Corley-Wiciak.

5 recordsLinked to original sources

arXiv2026

Resolving the Metastable Si-XIII Structure through Convergent Theory and Experiment

Silicon is the undisputed cornerstone of modern technology, with applications ranging from micro- and opto-electronics to quantum technologies. Recently, the exploration of its allotropes has emerged as a pivotal frontier for engineering materials with tailored optical and electronic functionalities. High-pressure experiments have revealed several metastable silicon phases, among which is Si-XIII. First observed more than 20 years ago, this phase has remained structurally unidentified, representing a significant gap in our understanding of elemental silicon allotropy. In this work, a convergent methodology is employed combining advanced theoretical modeling with experimental characterization to finally resolve the long-standing structural assignment of Si-XIII. Guided by careful experimental observations, a structural model validated through first-principles optimization and systematically tested against multiple experimental signatures is constructed. All the fingerprints of this phase are rationalized by our proposed crystal structure: interplanar spacings, Raman frequencies, thermodynamic stability, and kinetic pathways. These findings provide a crucial missing piece in the high-pressure phase diagram of silicon and demonstrate the power of integrating computational predictions with experimental validation to resolve complex structural problems in materials science.

cond-mat.mtrl-sci↗

arXiv2026

Epitaxial SiGeSn alloys for CMOS-compatible thermoelectric devices

The integration of thermoelectric devices into mainstream microelectronic technological platform could be a major breakthrough in various fields within the \emph{so-called} Green-IT realm. In this article, the thermoelectric properties of heteroepitaxial SiGeSn alloys, a novel CMOS compatible material system, are evaluated to assess their possible application in thermoelectric devices. To this purpose, starting from the experimentally low lattice thermal conductivity of SiGeSn/Ge/Si layers of about $\sim$1-2 W/m$\cdot$K assessed by means of 3-$ω$ measurements, the figure of merits are calculated through the use of Boltzmann transport equation, taking into account the relevant inter-valley scattering processes, peculiar of this multi-valley material system. Values for the figure of merit $ZT$ exceeding $1$ have been obtained for both p- and n- type material at operating temperatures within the 300---400 K range, i.e. at a typical On-Chip temperatures. In this interval, the predicted power factor also features very competitive values of the order of 20 $\rm{μW/cm\cdot K^2}$. Our finding indicates that this new class of Si-based materials has extremely good prospects for real-world applications, and can further stimulate scientific investigation in this ambit.

cond-mat.mtrl-sci↗

arXiv2024

Formation of Micrometer-Sized Textured Hexagonal Silicon Crystals via Nanoindentation

We present a comprehensive study on the formation of micrometer-sized, textured hexagonal diamond silicon (hd-Si) crystals via nanoindentation followed by annealing. Utilizing advanced characterization techniques such as polarized Raman spectroscopy, high-resolution transmission electron microscopy, and electron energy-loss spectroscopy, we demonstrate the successful transformation of silicon into high-quality hd-Si. The experimental results are further supported by first-principles calculations and molecular dynamics simulations. Notably, the hd-Si phase consists of nanometer-sized grains with slight misorientations, organized into large micrometer-scale textured domains. These findings underscore the potential of nanoindentation as a precise and versatile tool for inducing pressure-driven phase transformations, particularly for the stabilization of hexagonal silicon. The textured nature of hd-Si also presents a unique opportunity to tailor its optical properties, opening new avenues for its application in semiconductor and optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Thermal expansion and temperature dependence of Raman modes in epitaxial layers of Ge and Ge$_{1-x}$Sn$_{x}$

Temperature dependence of vibrational modes in semiconductors depends on lattice thermal expansion and anharmonic phonon-phonon scattering. Evaluating the two contributions from experimental data is not straightforward, especially for epitaxial layers that present mechanical deformation and anisotropic lattice expansion. In this work, a temperature-dependent Raman study in epitaxial Ge and Ge$_{1-x}$Sn$_{x}$ layers is presented. A model is introduced for the Raman mode energy shift as a function of temperature, comprising thermal expansion of the strained lattice and anharmonic corrections. With support of x-ray diffraction, the model is calibrated on experimental data of epitaxial Ge grown on Si and Ge$_{1-x}$Sn$_{x}$ grown on Ge/Si, finding that the main difference between bulk and epitaxial layers is related to the anisotropic lattice expansion. The phonon anharmonicity and other parameters do not depend on dislocation defect density (in the range $7\cdot 10^6$ - $4\cdot 10^8$ cm$^{-2}$) nor on alloy composition in the range 5-14 at.%. The strain-shift coefficient for the main model of Ge and for the Ge-Ge vibrational mode of Ge$_{1-x}$Sn$_{x}$ is weakly dependent on temperature and is around -500 cm$^{-1}$. In Ge$_{1-x}$Sn$_{x}$, the composition-shift coefficient amounts to -100 cm$^{-1}$, independent of temperature and strain.

cond-mat.mtrl-sci↗

arXiv2023

Local Alloy Order in a Ge1-xSnx/Ge Epitaxial Layer

The local ordering of atoms in alloys directly has a strong impact on their electronic and optical properties. This is particularly relevant in nonrandom alloys, especially if they are deposited using far from the equilibrium processes, as is the case of epitaxial Ge1-xSnx layers. In this work, we investigate the arrangement of Ge and Sn atoms in optoelectronic grade Ge1-xSnx epitaxial layers featuring a Sn content in the 5-14% range by using polarization-dependent Raman spectroscopy and density-functional-theory calculations. The thorough analysis of the polarization-dependent spectra in parallel and perpendicular configuration allowed us to properly tag all the observed vibrational modes, and to shed light on that associated to disorder-assisted Raman transitions. Indeed, with the help of large-scale atomistic simulations, we were able to highlight how the presence of Sn atoms, that modify the local environments of Ge atoms, gives rise to two spectral features at different Raman shifts, corresponding to distortions of the atomic bonds. This analysis provides a valuable framework for advancing the understanding of the vibrational properties in Ge1-xSnx alloys, particularly with regard to the impact of local ordering of the different atomic species.

cond-mat.mtrl-sci↗