Engineering high-performance microbattery anodes requires architectures that combine high areal capacity, fast ion transport, long-term interfacial stability, and full compatibility with microelectronics fabrication processes. Here, we uncover how rapid thermal annealing (RTA) governs the hierarchical reconstruction of electrochemically etched mesoporous silicon and, in turn, its electrochemical behavior. By tracking the coupled densification–coarsening mechanisms activated between 800–1000 °C, we reveal a nonmonotonic structural evolution in which an optimal- annealing temperature (900 °C) produces a ∼700 nm dense surface layer atop a porous network. This morphology minimizes electrolyte-accessible surface area while preserving efficient Li+ transport, suppressing early solid electrolyte interphase formation and enabling a balanced capacitive–diffusive storage regime. The resulting monolithic anode delivers ≈9 mAh cm−2 at 6 mA cm−2 for 100 cycles, withstands ~500 cycles at high rate, and reaches 20 mAh cm−2 with thicker layers. These performances rank among the highest reported for on-chip silicon microbatteries. By establishing surface densification as a mechanistic design principle linking microstructure, interfacial stability, and transport kinetics, this work positions porous silicon as a scalable platform for high-energy, high-power microscale storage with potential relevance to advanced microelectronics fabrication.

Stabilization of metastable phases of silicon-germanium alloys are of both fundamental and applied interest. By combining experimental and theoretical approaches, we investigated different SixGe1-x compositions (x = 0.5 and 0.3) under high-pressure (HP) conditions. Homogeneous Ge-dominant SixGe1-x alloys are difficult to synthesize, which explains the paucity of literature on the subject. Such Ge-rich alloys were obtained by combining arc melting and solid-state synthesis. Then, in situ HP X-ray diffraction experiments were performed. During HP cycling, the investigated SixGe1-x alloys follow a similar phase transition pathway of Si and Si-rich binaries. On compression, the stable cubic semiconducting phase transforms to the tetragonal beta-tin metallic phase at around 10 GPa. Under decompression, the metallic beta-phase first transforms to the rhombohedral r8 phase. After further decompression, the rhombohedral phase partially transforms to the body-centered cubic bc8 phase. Both r8-and bc8-phases coexist at ambient conditions in the recovered sample. The experimental results are compared with density functional theory simulations and discussed in relation with the previous published results on Si-rich alloy (Si0.8Ge0.2). This allows giving an overview of the structural and mechanical properties of different phases as well as the phase stability as a function of the concentration in SixGe1-x alloys. This opens the way to select composition and phases to tune some physical properties.

While silicon anodes offer a high theoretical capacity for lithium-ion batteries, they face challenges related to severe volume expansion and mechanical degradation. Herein, mesoporous structuring is systematically coupled with capacity-limited (partial) lithiation to improve the durability of high-Si composite anodes (70% Si). Using galvanostatic cycling and ex situ scanning electron microscopy/thickness measurements on bulk-Si and mesoporous-Si (PSi) electrodes at four lithiation depths (100%, 66%, 50%, 33%), it is shown that PSi consistently delivers higher capacity retention over 100 cycles and exhibits markedly lower swelling. At 33% lithiation, PSi retains approximate to 94% of its initial capacity, outperforming bulk Si, and expands approximate to 141% compared to 315% for bulk Si under the same cycling conditions. These benefits result from the porous framework's ability to accommodate the volume changes and stabilize the solid electrolyte interface (SEI), reducing the risk of fracture and electrical connectivity loss. These findings contribute to the ongoing research on mesoporous silicon materials and support a higher Si fraction in graphite-containing anodes, delivering greater energy density with maintained SEI stability and low swelling.

In this study, the impact of nanographene incorporation on the thermal properties of mesoporous silicon (PSi) was evaluated using two complementary experimental methods: the temperature gradient (TG) and the photothermal radiometry (MPTR) methods. It is shown that the measured thermal conductivity of the mesoporous silicon (PSi) ranges from 0.10 to 0.68 W/m.K in the case of TG and from 0.37 to 3.02 W/m.K in MPTR and is strongly correlated to the electrochemical etching parameters. These values are much lower than that of crystalline silicon, estimated to be from 100 to 140 W/m.K, depending on the doping rate. They appear to be, however, in the order of magnitude range for the percolation models that also include the in-depth porosity and the crystallite mean radius. This set of experiments on the thermal conductivity was extended to investigate the effect of graphene incorporation in the PSi matrix (G-PSi) as it has seldom been reported in the literature. The results from both methods exhibit significantly higher values (1.7 ± 0.3 W/m.K for TG, and from 0.7 to 2.13 W/m.K for MPTR). This spread of the thermal conductivity values is attributed to the intrinsic working principle of the TG versus the MPTR method as highlighted in the last part of the present paper. Targeting the thermoelectric application of both matrices (PSi, G-PSi), the thermal conductivity remains sufficiently low for them to be considered as very promising materials, keeping in mind the enhancement of the power-factor attributed to the incorporation of graphene.

Single crystal germanium (Ge) membranes have recently gained increasing interest for lightweight and low-cost solar cells and flexible optoelectronic devices. These membranes achieved similar material quality as bulk Ge substrate. However, the control of the membrane detachment is still challenging. In this work, we explore postgrowth engineering of the adhesion strength of a Ge membrane on a porous germanium (PGe) substrate by inducing morphological transformations in the separation layer through Thermal Budget (TB) control. Indeed, the pillars formed through PGe sintering during epitaxy are found to evolve with post-growth thermal annealing. Scanning electron microscopy (SEM) based analysis of the residue of the post-detachment broken pillars has been performed showing that the pillar 's diameter and density can be tuned by thermal annealing. Depending on the post-growth annealing temperature, the membrane adhesion strength can be successively tailored from 0.5 to up to 3.5 MPa while ensuring 100 % detachment yield. The experimental results have been correlated with Finite Element Modeling (FEM) considering realistic pillar distribution revealing that pillar size and density are the dominant factors influencing the membrane adhesion strength.

Silicon is one of the most promising anode materials for Li-ion batteries, especially to meet the growing demand for energy storage in the form of microbatteries for mobile and autonomous devices. However, the development of such batteries is hindered by mechanical and electrochemical failures resulting from massive Si volume expansion and continuous growth of the solid electrolyte interphase. In this study, we propose a novel on-chip anode architecture using rapid thermal annealing on porous silicon. The structure consists of a densified silicon layer on top of an isotropic structure of a porous layer. We demonstrate that this structure enhances both electrochemical and mechanical stabilities, achieving an areal capacity of 9 mAh cm-2 over more than 200 cycles with a high Coulombic efficiency near 100%.

Zero thermal expansion materials have a unique ability to withstand thermal shock over varied temperature ranges, enabling potential applications as components of high precision devices. The zero thermal expansion material Sc1.5Al0.5W3O12 exhibits zero thermal expansion over the largest temperature range reported to date, from 4 to 1400 K (Liu et al. Chem. Mater.2021, 33, 3823). In this work, the pressure stability of this material is investigated using high-pressure neutron and X-ray powder diffraction as well as Raman spectroscopy and supported with density functional theory (DFT) calculations. Sc1.5Al0.5W3O12 shows an orthorhombic to monoclinic transition with the application of a small amount of pressure which is similar to that reported for other compositions in this family. Additional peak splitting is noted above 3.4 GPa which may indicate an additional phase transition. A pressure induced amorphization is found between 4.3 and 5.7 GPa and an amorphous to amorphous phase transition is further evidenced at around 15 GPa. The tungsten coordination sphere evolves from WO4 to WO6 as pressure is increased, which is evidenced by both DFT calculations and Raman spectroscopy. The <3.4 GPa monoclinic phase has a bulk modulus, B-0, of 17.4(14) GPa determined with X-ray powder diffraction by second order Birch-Murnaghan. This work demonstrates the importance of understanding structural changes under pressure for zero thermal expansion materials, as changes in pressure impart a more significant impact on the crystallographic volume compared to temperature.

The recent exploration of porous Germanium (PGe) techniques marks a significant advancement in the scalable production of detachable Ge membranes and devices. However, there is a notable gap in the comprehensive understanding of the critical factors necessary to control the adhesion strength of these nanomembranes. This study delves into the effects of Ge growth temperature, in-situ annealing processes, and the thickness of the PGe layer on the reorganization of the porous interlayer, subsequently influencing the properties of the separation layer. We particularly focus on how adjusting these parameters can fine-tune the adhesion strength of the epitaxial layer, ranging from a freestanding state to a fully bonded nanomembrane. A key finding is that the thermal budget experienced by the porous structure during the buffer layer's growth significantly affects the nanomembrane's adhesion characteristics; it is imperative to minimize this duration, especially at higher growth temperatures. Our research demonstrates that by precisely controlling the voids within the PGe layer, the adhesion strength can be effectively modulated through variations in the PGe layer's thickness. The outcomes of this study offer crucial insights into the controllable adhesion strength of Ge nanomembranes, paving the way for the targeted development of detachable devices.

Porous germanium (PGe) substrates have recently attracted significant attention for the development of lightweight and flexible solar cells and optoelectronic devices. A reliable approach for releasing epitaxial layers based on Germanium and reusing the substrate involves utilizing a bilayer structure of PGe. The growth of such detachable devices holds great potential for integration onto the Si platform. The used structure of PGe is made of a low-porosity layer serving as epitaxial seed on top of high-porosity one used as a weak separation layer. In this work, we investigate the impact of thermal annealing on the PGe morphology for deeper understanding of the mechanisms involved in the formation of the epitaxial seed layer and the voided weak layer underneath. Indeed, thermal-induced reconstruction has been investigated at various annealing temperatures and times for PGe layers with differing porosity levels, encompassing low, high, and gradual porosity profiles. Our findings reveal the formation of a modified substrate at low annealing temperatures, resulting in a suspended membrane on top of the fragile separation layer, rendering it suitable for detachment and subsequent substrate reuse.

Group IV elements, such as carbon, silicon and germanium are known to exhibit polymorphism under high pressure.Interestingly, some of these phases can be recovered when returning to ambient conditions, offering the access to new physical and mechanical properties.

Germanium (Ge) is increasingly used as a substrate for high-performance optoelectronic, photovoltaic, and electronic devices. These devices are usually grown on thick and rigid Ge substrates manufactured by classical wafering techniques. Nanomembranes (NMs) provide an alternative to this approach while offering wafer-scale lateral dimensions, weight reduction, limitation of waste, and cost effectiveness. Herein, we introduce the Porous germanium Efficient Epitaxial LayEr Release (PEELER) process, which consists of the fabrication of wafer-scale detachable monocrystalline Ge NMs on porous Ge (PGe) and substrate reuse. We demonstrate monocrystalline Ge NMs with surface roughness below 1 nm on top of nanoengineered void layer enabling layer detachment. Furthermore, these Ge NMs exhibit compatibility with the growth of III-V materials. High-resolution transmission electron microscopy (HRTEM) characterization shows Ge NMs crystallinity and high-resolution X-ray diffraction (HRXRD) reciprocal space mapping endorses high-quality GaAs layers. Finally, we demonstrate the chemical reconditioning process of the Ge substrate, allowing its reuse, to produce multiple free-standing NMs from a single parent wafer. The PEELER process significantly reduces the consumption of Ge during the fabrication process which paves the way for a new generation of low-cost flexible optoelectronics devices.

The high-pressure behaviour of Si0.8Ge0.2 alloy is explored using in situ Raman spectroscopy, X-ray dif-fraction techniques and density functional theory (DFT) simulations. High pressure experiments revealed a pressure-induced transition from the stable cubic semiconducting phase (dc-Si0.8Ge0.2) to the tetragonal beta-tin metallic phase (beta-Si0.8Ge0.2) during compression. This sluggish transition is significantly accelerated at moderate temperature (< 300 degrees C). Upon decompression, successive transitions towards metastable phases are observed. A first transition from the metallic beta-Si0.8Ge0.2 toward the rhombohedral r8-Si0.8Ge0.2 phase is observed at 10.3 GPa followed by a partial transition to the body-centered cubic bc8-Si0.8Ge0.2 phase at 2.2 GPa. After releasing the pressure, r8 and bc8 phases coexist at ambient conditions. This transition pathway is similar to that followed by pure silicon and is consistent with the ab initio enthalpy calculations. This phase transition sequence is confirmed by in situ Raman spectroscopy, where signatures of r8 and bc8 phases are observed in the Raman spectra at decompression. An ab initio simulation method is proposed to assign the Raman spectrum of Si0.8Ge0.2 alloy using group theory and projection operators. The exploration of metastable states in these alloys is of major interest both in terms of applications (e.g. optoelectronics) and from a fundamental point of view to better understand the effects of alloying on the physical properties (e.g. vibrational).(c) 2023 Elsevier B.V. All rights reserved.

The high-pressure behavior of monoclinic VO_2 is revisited by a combination of Raman spectroscopy and X-ray diffraction on a single crystal under hydrostatic conditions at room temperature. A soft mode is observed up to P_c = 13.9(1) GPa. At this pressure, an isostructural phase transition between two monoclinic phases M_1 and M_1' hinders this instability. The features of this transformation (no apparent volume jump) indicate that the compression at ambient temperature passes close to a critical point. An analysis based on the Landau theory of phase transitions gives a complete description of the P-T phase diagram. The M1' is characterized by spontaneous displacements of the oxygen sub-lattice without any strong modification of the VV dimers distances nor the twist angle of vanadium chains. The spontaneous displacements of oxygen and the spontaneous deformations of the (b_M1, c_M1) plane follow the same quadratic dependence with pressure and scales with spontaneous shifts of the Raman phonons located at 225, 260 and 310 cm^-1. Pressure-induced shifts of the Raman peaks allows for new assignment of several Raman modes. In particular, the A_g(1)+B_g(1) modes at 145 cm^-1 are identified as the vanadium displacive phonons. A second transformation in the metallic phase X, which is found triclinic (P1̅) is observed starting at 32 GPa, with a wide coexistence region (up to 42 GPa). Upon decompression, phase X transforms, between 20 GPa and 3 GPa, to another phase that is neither the M_1' nor M_1 phase. The structural transitions identified under pressure match with all the previously reported electronic modifications confirming that lattice and electronic degrees of freedom are closely coupled in this correlated material.

Nanographene–mesoporous silicon (G-PSi) composites have recently emerged as a promising class of nanomaterials with tuneable physical properties. In this study, we investigated the impact of nanographene coating on the Seebeck coefficient of mesoporous silicon (PSi) obtained by varying two parameters: porosity and thickness. To achieve this, an electrochemical etching process on p + doped Si is presented for the control of the parameters (thicknesses varying from 20 to 160 µm, and a porosity close to 50%), and for nanographene incorporation through chemical vapor deposition. Raman and XPS spectroscopies confirmed the presence of nanographene on PSi. Using a homemade ZT meter, the Seebeck coefficient of the p + doped Si matrix was evaluated at close to 100 ± 15 µV/K and confirmed by UPS spectroscopy analysis. Our findings suggest that the Seebeck coefficient of the porous Si can be measured independently from that of the substrate by fitting measurements on samples with a different thickness of the porous layer. The value of the Seebeck coefficient for the porous Si is of the order of 750 ± 40 µV/K. Furthermore, the incorporation of nanographene induced a drastic decrease to approximately 120 ± 15 µV/K, a value similar to that of its silicon substrate.

Amorphous TiO2-x thin films were deposited using direct current reactive magnetron sputtering. It was possible to tune the defect concentration by controlling the oxygen flow rate during the deposition process. The operating deposition regime has a significant influence on the properties of the TiO2-x film. The refractive index was found to decrease with increasing oxygen flow rate, which was essentially related to changes in film density. Besides this, increasing the oxygen vacancy defect concentration induced a slight decrease in the optical bandgap, as well as widening of the defect's Urbach band tails near the conduction band edge. For TiO2-x films deposited in oxygen-deficient conditions, the decrease in optical bandgap and widening of Urbach tails induced the shift of the Fermi level towards the conduction band, which enhanced the concentration of the charge carriers.

Silicon-based anodes are an attractive choice for the future of energy storage. However, mechanical stresses generated during lithiation induce a rapid degradation of the anodes. The coupling between mechanical and (electro)chemical phenomena during lithiation is investigated using Molecular Dynamics simulations. First, the diffusion regime of lithium atoms in the silicon is found to depend drastically on the crystalline orientations and on the applied pressure. Above a threshold pressure, a ballistic motion of lithium along certain crystallographic planes is observed. Second, the local complex stress field generated by the lithiation has been computed using a coarse-graining method including thermal effects. It appears to be strongly dependent on the density of lithium in the lithiated layer, on the temperature, and on the crystalline orientation of the free surface. The resulting very high values of the locally induced pressures can be related to the progressive amorphization of the silicon support.

Zero thermal expansion materials have a unique ability to withstand thermal shock over varied temperature ranges; because of this, they have potential applications as components of high precision devices.The zero thermal expansion material Sc 1.5 Al 0.5 W 3 O 12 exhibits zero thermal expansion over the largest temperature range reported to date, from 4 to 1400 K[2].In this work, the pressure stability of this material is investigated using a combination of techniques, including high-pressure neutron and X-ray powder diffraction, as well as Raman spectroscopy.Sc 1.5 Al 0.5 W 3 O 12 has an orthorhombic to monoclinic phase transition above 3.4 GPa, ten times higher than the end members Sc 2 W 3 O 12 and Al 2 W 3 O 12 [3-5], followed by a pressure-induced amorphization above 5.7 GPa.The stable orthorhombic phase has a bulk modulus of 20( 6) GPa, as determined by neutron powder diffraction (Figure 1), and 32(1) GPa using X-ray diffraction, close to sodium chloride or single crystal graphite.An amorphousto-amorphous phase transition is further evidenced around 20 GPa (Figure 2).This work demonstrates the importance of understanding structural changes under pressure for zero thermal expansion materials, as changes in pressure impart a more significant impact on the crystallographic volume compared to temperature.

Two major effects of pressure in nanomaterials are discussed in this chapter. First, the pressure-induced phase transitions in nanomaterials often differ significantly from those of their bulk counterparts. This opens the opportunity of including surface energy contributions in thermodynamic models. The importance or even the dominance of surface atoms and the underlying surface state (point defects, ligands, etc.) greatly influence the thermodynamics and kinetics of phase transformations. This can lead to a competition between pressure-induced polymorphic transitions and amorphization depending on the defect density in the nanomaterials. Second, the mechanical properties of 2D materials such as graphene are difficult to apprehend because of their dimensionality. The variation over a wide range of pressure allows a better understanding of the stress transfer through the substrate and its role in the production of biaxial strain conditions. The mechanism of stress transmission to an atomically-thin material will be discussed, and a practical example that aims to determine the coupling between components in graphene-based nanocomposites will be presented.