arXiv subjects

Romain Bachelet

Publications and source records attributed to Romain Bachelet.

5 recordsLinked to original sources

arXiv2026

Spatial navigation in preclinical Alzheimer's disease: A review

Alzheimer's disease (AD) develops over a prolonged preclinical phase, during which neuropathological changes accumulate long before cognitive symptoms appear. Identifying cognitive functions affected at early stages is critical for the preclinical detection of asymptomatic individuals at-risk of AD. Early risk identification could enable timely interventions aimed at mitigating the development of significant future cognitive impairment. While episodic memory decline typically appears after substantial medial temporal lobe damage, spatial navigation has emerged as a particularly sensitive cognitive function in preclinical AD. In this review, we provide an overview of spatial navigation computations and the tasks used to assess them, highlighting how spatial navigation relies on neural circuits corresponding to the earliest sites of AD pathology. We synthesize evidence from cognitively unimpaired individuals with AD biomarkers, i.e. individuals at-risk of AD, and discuss future research directions. Overall, performance on spatial navigation tasks, particularly path integration and wayfinding, correlates with plasma and CSF biomarkers of AD pathology, notably p-tau. Spatial navigation assessment can represent a sensitive and scalable approach for early detection of individuals at-risk of AD in preclinical stages, and will inform future interventions to mitigate the progression toward clinically significant cognitive impairment.

q-bio.NC↗

arXiv2025

Strong and Engineerable Optical Anisotropy in Easily Integrable Epitaxial SrO(SrTiO 3 ) N Ruddlesden--Popper Thin Layers

Optical anisotropy is a key property for numerous photonic devices. However, bulk anisotropic materials suitable for such applications remain relatively scarse and are often challenging to synthesize as thin films. Additionally, the optical losses as well as the complex structuration of anisotropic metamaterials hinder their integrability in photonic devices. Based on ellipsometry measurements coupled with reflectance, it is demonstrated here that Ruddlesden-Popper (RP) SrO(SrTiO 3 ) N phases (STO-RP N ), epitaxial thin films composed of a SrTiO 3 lattice periodically interrupted by one SrO atomic plane every N unit cells, exhibit pronounced dichroism and birefringence over a broad spectral range. Notably, this anisotropy is tunable by adjusting the RP order N. In contrast to most other anisotropic materials reported in the literature, STO-RP N thin layers can be fabricated using industry-standard growth processes. As it can be epitaxially grown on Si and GaAs using SrTiO 3 templates, the work paves the way for their compact integration on these photonic platforms.

cond-mat.mtrl-sci↗

arXiv2025

Mechanism of Heteroepitaxial Growth of Boron Carbide on the Si-Face of 4H-SiC

Heteroepitaxial boron carbide (BxC) can be grown on Si face 4H-SiC(0001) using a two-step process involving substrate boridation at 1200$^\circ$C under BCl3 + H2 followed by a chemical vapor deposition (CVD) growth step at 1600$^\circ$C by adding C3H8 precursor. However, in-depth investigation of the early growth stages revealed that complex reactions occur before starting the CVD at high temperature. Indeed, after boridation, the 35 nm BxC buffer layer is covered by an amorphous B-containing layer which evolves and reacts during the temperature ramp up between 1200 to 1600$^\circ$C. Despite the formation of new phases (Si, SiB6), which could be explained by significant solid-state diffusion of Si, C and B elements through the thin BxC layer, the CVD epitaxial re-growth upon reaching 1600$^\circ$C does not seems to be affected by these phases. The resulting single crystalline BxC layers display the epitaxial relationships [1010]BxC(0001)||[1010]4H-SiC(0001). The layers exhibit a B4C composition, e.g. the highest possible C content for the BxC solid solution.

physics.chem-ph↗

arXiv2024

Erbium doped yttrium oxide thin films grown by chemical vapour deposition for quantum technologies

The obtention of quantum-grade rare-earth doped oxide thin films that can be integrated with optical cavities and microwave resonators is of great interest for the development of scalable quantum devices. Among the different growth methods, Chemical Vapour Deposition (CVD) offers high flexibility and has demonstrated the ability to produce oxide films hosting rare-earth ions with narrow linewidths. However, growing epitaxial films directly on silicon is challenging by CVD due to a native amorphous oxide layer formation at the interface. In this manuscript, we investigate the CVD growth of erbium-doped yttrium oxide (Er:Y2O3) thin films on different substrates, including silicon, sapphire, quartz or yttria stabilized zirconia (YSZ). Alternatively, growth was also attempted on an epitaxial Y2O3 template layer on Si (111) prepared by molecular beam epitaxy (MBE) in order to circumvent the issue of the amorphous interlayer. We found that the substrate impacts the film morphology and the crystalline orientations, with different textures observed for the CVD film on the MBE-oxide/Si template (111) and epitaxial growth on YSZ (001). In terms of optical properties, Er3+ ions exhibit visible and IR emission features that are comparable for all samples, indicating a high-quality local crystalline environment regardless of the substrate. Our approach opens interesting prospects to integrate such films into scalable devices for optical quantum technologies.

cond-mat.mtrl-sci↗

arXiv2020

Epitaxial Ferroelectric La-doped Hf0.5Zr0.5O2 Thin Films

Doping ferroelectric Hf0.5Zr0.5O2 with La is a promising route to improve endurance. However, the beneficial effect of La on the endurance of polycrystalline films may be accompanied by degradation of the retention. We have investigated the endurance - retention dilemma in La-doped epitaxial films. Compared to undoped epitaxial films, large values of polarization are obtained in a wider thickness range, whereas the coercive fields are similar, and the leakage current is substantially reduced. Compared to polycrystalline La-doped films, epitaxial La-doped films show more fatigue but there is not significant wake-up effect and endurance-retention dilemma. The persistent wake-up effect common to polycrystalline La-doped Hf0.5Zr0.5O2 films, is limited to a few cycles in epitaxial films. Despite fatigue, endurance in epitaxial La-doped films is more than 1010 cycles, and this good property is accompanied by excellent retention of more than 10 years. These results demonstrate that wake-up effect and endurance-retention dilemma are not intrinsic in La-doped Hf0.5Zr0.5O2.

cond-mat.mtrl-sci↗