Aymeric Ramiere

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Verified

Aymeric verified their affiliation via an institutional email.

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• PhD
• Professor (Associate) at Shenzhen University

Band sorting is critical to obtaining physical properties from eigenvalues and eigenvectors that constitute the band diagram. We propose a band sorting method based on the global continuity and smoothness of the eigenvalues on the parameter space. Several strategies based on the connection between neighbor eigenvalues and how to sweep the parameter...

Two-dimensional (2D) van der Waals antiferromagnetic (AFM) materials boast exceptional properties for spintronics, including high spin-wave speeds and negligible stray fields. Their layer-by-layer assembly into heterostructures enables the exploration of next-generation spintronic devices. However, most 2D AFM materials are semiconductors or insula...

In this study, we have explored the use of water as a non-solvent for tuning the microstructure of polybenzimidazole (PBI) membranes, which are potential separators for lithium metal batteries (LMBs). The traditional method for membrane synthesis called nonsolvent-induced phase separation (NIPS), usually relies on hazardous and costly organic non-s...

Cooling high-power electronics in multilayer integrated circuits (ICs) is challenging for existing cooling methods. In this work, we designed through-chip microchannels (TCMCs) that cross the entire chip perpendicularly to the layers, with water circulating inside to provide direct cooling to each layer. TCMCs are organized in a square array where...

Lithium metal anodes face several challenges in practical applications, such as dendrite growth, poor cycle efficiency, and volume variation. 3D hosts with lithiophilic surfaces have emerged as a promising design strategy for anodes. In this study, inspiration from the intrinsic isotropy, chemical heterogeneity, and wide tunability of metallic glas...

Stacking several layers of electronic components implies that heat is generated directly in the middle of three-dimensional integrated circuits (3D ICs). Cooling only by the top and bottom surfaces struggles to evacuate the heat from the middle layers, which hinders the performance of 3D ICs. In this work, we designed through-chip microchannels (TC...

Optomechanical crystals allow controlling both light and mechanical vibrations by presenting simultaneously photonic and phononic bandgaps. Tuning the position of these bandgaps is essential to address different technological applications. In this study, we present a one-dimensional optomechanical crystal with wings and a hole whose position is shi...

Phonon transport in square-cross-section nanowires is studied using spectral Monte Carlo simulations. Our results show the evolution of the different transport regimes described by Lévy statistics as a function of the surface roughness-to-thermal wavelength ratio σ /λ. More precisely, the relationship between the Lévy index γ describing the mean fr...

The direction of the quasi-ballistic thermal flow propagation can be guided using the direct passages between the holes in silicon phononic nanostructures. By designing a radial array of holes where the direct passages converge at the same focal point, we obtain a quasi-ballistic thermal lens nanostructure that creates a hotspot with an ellipse sha...

Chemical fixation of CO2 with epoxides is an effective option to achieve sustainable synthesis of cyclic organic carbonates. Although metal-organic frameworks (MOFs) are promising catalysts for this reaction, their low stability in aqueous solutions makes this application infeasible. In an effort to overcome this limitation, cobalt-based metal-orga...

Here, the synthesis of a series of pure phase metal borides is reported, including WB, CoB, WCoB, and W2CoB2, and their surface reconstruction is studied under the electrochemical activation in alkaline solution. A cyclic voltammetric activation is found to enhance the activity of the CoB and W2CoB2 precatalysts due to the transformation of their s...

We propose a model to explain power dissipation leading to the formation of hot spots in the inner walls of niobium thin film superconducting rf cavities. The physical mechanism that we explore is due to the constriction of surface electrical current flow at grain interface boundaries. This constriction creates an additional electrical contact resi...

Transition metal borides are considered as promising electrocatalysts for water splitting due to their metallic conductivity and good durability. However, the currently reported monometallic and noncrystalline multimetallic borides only show generic and monofunctional catalytic activity. In this work, the authors design and successfully synthesize...

Controlled synthesis of noble metal nanoparticles with well-defined size and good dispersion on supports has been a long-standing challenge in heterogeneous catalysis. Here we report a facile photo-assisted H2 in situ reduction process to synthesize monodispersed Pd nanoparticles with 2-4 nm size on photo-insensitive Sm2O3 rare-earth metal oxide wi...

Hot spots in niobium superconducting radio-frequency (SRF) cavities are important sources of heat dissipation. Tracking their physical origin is the key to controlling and improving SRF cavity performance. In this paper, we present a new model to explain the occurrence of hot spots in niobium SRF cavities based on an electro-thermal mechanism which...

Zirconium pentatelluride (ZrTe5) single crystal has recently received significant attention because of its quantum electronic transport properties and is regarded as a promising candidate for low-temperature thermoelectric cooling and spintronic applications. However, single crystal of ZrTe5 has generally small sizes and can only be produced in sma...

Magneto-transport study has been performed in ZrTe5 single crystals. The observed Shubnikov–de Hass quantum oscillation at low temperature clearly demonstrates the existence of a nontrivial band with small effective mass in ZrTe5. Furthermore, we also revealed the highly anisotropic nature of high-field Landau level splitting in ZrTe5, suggesting t...

Magneto-transport study has been performed in ZrTe5 single crystals. The observed Shubnikov-de Hass quantum oscillation at low temperature clearly demonstrates the existence of a nontrivial band with small effective mass in ZrTe5. Furthermore, we also revealed the 3D anisotropic nature of high-field Landau level splitting in ZrTe5, very different f...

Use of thermoelectric devices in modern technology is limited by the lack of inexpensive materials with high electrical but low thermal conductivity. Recent studies demonstrated that arrays of holes could reduce the thermal conductivity of thin silicon membranes, while keeping high electrical conductivity. Here, we use micro-TDTR experiments and Mo...

A quantum solid (solid 4He) in contact with a classical solid defines a new class of interfaces. In addition to its quantum nature, solid 4He is indeed a very plastic medium. We examine the thermal interface resistance upon solidification of superfluid 4He in contact with a silicon crystal surface (111) and show that dislocations play a crucial rol...

The world communicates to our senses of vision, hearing, and touch in the language of waves, because light, sound, and even heat essentially consist of microscopic vibrations of different media. The wave nature of light and sound has been extensively investigated over the past century and is now widely used in modern technology. However, the wave n...

The in-plane thermal conductivity of silicon phononic membranes is investigated by micro time domain thermoreflectance and Monte Carlo simulations. Strong reduction of thermal conductivity is observed mainly due to phonon boundary scattering for both aligned and staggered lattices of holes. The measured and calculated thermal conductivities of the...

Unlike classical heat diffusion at macroscale, nanoscale heat conduction can occur without energy dissipation because phonons can ballistically travel in straight lines for hundreds of nanometres. Nevertheless, despite recent experimental evidence of such ballistic phonon transport, control over its directionality, and thus its practical use, remai...

Supplementary Figures, Supplementary Notes and Supplementary References

We present experimental and theoretical investigations on the roles of the limiting dimensions, such as the smallest dimension, surface roughness, and density of holes in the reduction of thermal conductivity of one-dimensional phononic nanostructures at temperatures of 4 and 295 K. We dis- cover that the thermal conductivity does not strongly depe...

The concept of dominant phonon wavelength is investigated in systems submitted to a heat flux at low temperatures. Using spectral energy distributions, a treatment of two-dimensional and three-dimensional structures is conducted in parallel. We demonstrate a significant reduction of the dominant phonon wavelength, up to 62%, due to a displacement o...

Unlike classical heat diffusion at the macroscale, nanoscale heat transport can occur without energy dissipation because phonons can travel in straight lines for hundreds of nanometres. Despite recent experimental evidence of such ballistic phonon transport, control over its directionality, and thus its practical use, remains a challenge, as the di...

Kapitza in 1941 discovered that heat flowing across a solid in contact with superfluid helium (<2 K) encounters a strong thermal resistance at the interface. Khalatnikov demonstrated theoretically that this constitutes a general phenomenon related to all interfaces at all temperatures, given the dependence of heat transmission on the acoustic imped...

Phonon spectral energy transmission in silicon nanoribbons is investigated using Monte-Carlo simulations in the boundary scattering regime by changing the length and width geometrical parameters. We show that the transition frequency from specular scattering to diffuse scattering is inversely proportional to the edge roughness σ with a geometry ind...

Phonon transport in junctions formed between suspended membranes of the same material is studied using Monte Carlo method. The investigation is conducted at 1K for systematically chosen ratios of (d/D) where d is the junction width and D the membrane length. The influence of surface roughness is taken into account. The dependency of the constrictio...

This thesis aims at characterizing the thermal contact resistance at two interfaces of different nature. The first is a physical interface between Silicon(111) and superfluid Helium-4. The thermal contact resistance is evaluated experimentally for temperatures between 0.3K and 2.0K while varying pressure from the saturated vapor pressure to the Hel...

Kapitza resistance measurements conducted at T > 1 K on silicon and niobium single crystals in contact with helium demonstrate respectively the importance of atomic scale surface roughness and dislocations due to surface damage at the boundary. Two different experimental configurations were used.

We use Monte Carlo simulations based on phonon gas particles to study the role of the boundary roughness on the heat transport in silicon micro-ribbons at temperatures below 2K. The thermal conductivity and the energy transmission coefficient are calculated for different surface roughness. In the diffusive (Casimir) limit we find the 3 T behavior o...

For bulk solid-solid interfaces, the thermal contact resistance TCR) is generally attributed to a mismatch in the acoustic impedances (density x sound velocity) of each medium [1]. Here, we present a novel study of the TCR for a bulk Silicon crystal (111) in contact with superfluid helium, as a function of the acoustic impedance of the superfluid....