Flash Ignition of Freestanding Porous Silicon Films: Effects of Film Thickness and Porosity

We report the first successful xenon flash ignition of freestanding porous Si films in air. The minimum flash ignition energy (<i>E</i>_min) first decreases and then increases with increasing the porous Si film thickness due to the competition between light absorption and heat loss. The <i>E</i>_min is lower for higher porosity film because high porosity reduces both the heat capacity and the thermal conductivity, facilitating the temperature rise. These results are important for initiating controlled porous Si combustion and preventing their unwanted combustion for safety reasons

Flash Ignition of Freestanding Porous Silicon Films: Effects of Film Thickness and Porosity

We report the first successful xenon flash ignition of freestanding porous Si films in air. The minimum flash ignition energy (<i>E</i>_min) first decreases and then increases with increasing the porous Si film thickness due to the competition between light absorption and heat loss. The <i>E</i>_min is lower for higher porosity film because high porosity reduces both the heat capacity and the thermal conductivity, facilitating the temperature rise. These results are important for initiating controlled porous Si combustion and preventing their unwanted combustion for safety reasons

Flash Ignition of Freestanding Porous Silicon Films: Effects of Film Thickness and Porosity

We report the first successful xenon flash ignition of freestanding porous Si films in air. The minimum flash ignition energy (<i>E</i>_min) first decreases and then increases with increasing the porous Si film thickness due to the competition between light absorption and heat loss. The <i>E</i>_min is lower for higher porosity film because high porosity reduces both the heat capacity and the thermal conductivity, facilitating the temperature rise. These results are important for initiating controlled porous Si combustion and preventing their unwanted combustion for safety reasons

Stabilizing Silicon Photocathodes by Solution-Deposited Ni–Fe Layered Double Hydroxide for Efficient Hydrogen Evolution in Alkaline Media

An important pathway toward cost-effective photoelectrochemical (PEC) solar water-splitting devices is to stabilize and catalyze silicon (Si) photocathodes for hydrogen evolution reaction (HER), especially in alkaline solutions. To date, the most stable Si photocathode in alkaline media is protected by the atomic layer deposited (ALD) dense TiO₂ layer and catalyzed by noble metal-based catalysts on top. However, the ALD process is difficult to scale up, and the noble metals are expensive. Herein, we report the first demonstration of using a scalable hydrothermal method to deposit earth-abundant NiFe layered double hydroxide (LDH) to simultaneously protect and catalyze Si photocathodes in alkaline solutions. The NiFe LDH-protected/catalyzed p-type Si photocathode shows a current density of 7 mA/cm² at 0 V vs RHE, an onset potential of ∼0.3 V vs RHE that is comparable to that of the reported p–n⁺ Si photocathodes, and durability of 24 h at 10 mA/cm² in 1 M KOH electrolyte

Sol-Flame Synthesis: A General Strategy To Decorate Nanowires with Metal Oxide/Noble Metal Nanoparticles

The hybrid structure of nanoparticle-decorated nanowires (NP@NW) combines the merits of large specific surface areas for NPs and anisotropic properties for NWs and is a desirable structure for applications including batteries, dye-sensitized solar cells, photoelectrochemical water splitting, and catalysis. Here, we report a novel <i>sol-flame</i> method to synthesize the NP@NW hybrid structure with two unique characteristics: (1) large loading of NPs per NW with the morphology of NP chains fanning radially from the NW core and (2) intimate contact between NPs and NWs. Both features are advantageous for the above applications that involve both surface reactions and charge transport processes. Moreover, the sol-flame method is simple and general, with which we have successfully decorated various NWs with binary/ternary metal oxide and even noble metal NPs. The unique aspects of the sol-flame method arise from the ultrafast heating rate and the high temperature of flame, which enables rapid solvent evaporation and combustion, and the combustion gaseous products blow out NPs as they nucleate, forming the NP chains around NWs

Facile Thermal and Optical Ignition of Silicon Nanoparticles and Micron Particles

Silicon (Si) particles are widely utilized as high-capacity electrodes for Li-ion batteries, elements for thermoelectric devices, agents for bioimaging and therapy, and many other applications. However, Si particles can ignite and burn in air at elevated temperatures or under intense illumination. This poses potential safety hazards when handling, storing, and utilizing these particles for those applications. In order to avoid the problem of accidental ignition, it is critical to quantify the ignition properties of Si particles such as their sizes and porosities. To do so, we first used differential scanning calorimetry to experimentally determine the reaction onset temperature of Si particles under slow heating rates (∼0.33 K/s). We found that the reaction onset temperature of Si particles increased with the particle diameter from 805 °C at 20–30 nm to 935 °C at 1–5 μm. Then, we used a xenon (Xe) flash lamp to ignite Si particles under fast heating rates (∼10³ to 10⁶ K/s) and measured the minimum ignition radiant fluence (i.e., the radiant energy per unit surface area of Si particle beds required for ignition). We found that the measured minimum ignition radiant fluence decreased with decreasing Si particle size and was most sensitive to the porosity of the Si particle bed. These trends for the Xe flash ignition experiments were also confirmed by our one-dimensional unsteady simulation to model the heat transfer process. The quantitative information on Si particle ignition included in this Letter will guide the safe handling, storage, and utilization of Si particles for diverse applications and prevent unwanted fire hazards

Conformal Electroless Nickel Plating on Silicon Wafers, Convex and Concave Pyramids, and Ultralong Nanowires

Nickel (Ni) plating has garnered great commercial interest, as it provides excellent hardness, corrosion resistance, and electrical conductivity. Though Ni plating on conducting substrates is commonly employed via electrodeposition, plating on semiconductors and insulators often necessitates electroless approaches. Corresponding plating theory for deposition on planar substrates was developed as early as 1946, but for substrates with micro- and nanoscale features, very little is known of the relationships between plating conditions, Ni deposition quality, and substrate morphology. Herein, we describe the general theory and mechanisms of electroless Ni deposition on semiconducting silicon (Si) substrates, detailing plating bath failures and establishing relationships between critical plating bath parameters and the deposited Ni film quality. Through this theory, we develop two different plating recipes: galvanic displacement (GD) and autocatalytic deposition (ACD). Neither recipe requires pretreatment of the Si substrate, and both methods are capable of depositing uniform Ni films on planar Si substrates and convex Si pyramids. In comparison, ACD has better tunability than GD, and it provides a more conformal Ni coating on complex and high-aspect-ratio Si structures, such as inverse fractal Si pyramids and ultralong Si nanowires. Our methodology and theoretical analyses can be leveraged to develop electroless plating processes for other metals and metal alloys and to generally provide direction for the adaptation of electroless deposition to modern applications

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22 janvier 19151915/01/22 (A44).Appartient à l’ensemble documentaire : PoitouCh

Data_Sheet_1_Abnormal Functional Connectivity Density in Amyotrophic Lateral Sclerosis.docx

<p>Purpose: Amyotrophic lateral sclerosis (ALS) is a motor neuro-degenerative disorder that also damages extra-motor neural pathways. A significant proportion of existing evidence describe alterations in the strengths of functional connectivity, whereas the changes in the density of these functional connections have not been explored. Therefore, our study seeks to identify ALS-induced alternations in the resting-state functional connectivity density (FCD).</p><p>Methods: Two groups comprising of 38 ALS patients and 35 healthy participants (age and gender matched) were subjected to the resting-state functional magnetic resonance imaging (MRI) scanning. An ultra-fast graph theory method known as FCD mapping was utilized to calculate the voxel-wise short- and long-range FCD values of the brain for each participant. FCD values of patients and controls were compared based on voxels in order to discern cerebral regions that possessed significant FCD alterations. For areas demonstrating a group effect of atypical FCD in ALS, seed-based functional connectivity analysis was then investigated. Partial correlation analyses were carried out between aberrant FCDs and several clinical variables, controlling for age, gender, and total intracranial volume.</p><p>Results: Patients with ALS were found to have decreased short-range FCD in the primary motor cortex and increased long-range FCD in the premotor cortex. Extra-motor areas that also displayed extensive FCD alterations encompassed the temporal cortex, insula, cingulate gyrus, occipital cortex, and inferior parietal lobule. Seed-based correlation analysis further demonstrated that these regions also possessed disrupted functional connectivity. However, no significant correlations were identified between aberrant FCDs and clinical variables.</p><p>Conclusion: FCD changes in the regions identified represent communication deficits and impaired functional brain dynamics, which might underlie the motor, motor control, language, visuoperceptual and high-order cognitive deficits in ALS. These findings support the fact that ALS is a disorder affecting multiple systems. We gain a deeper insight of the neural mechanisms underlying ALS.</p

Electroassisted Transfer of Vertical Silicon Wire Arrays Using a Sacrificial Porous Silicon Layer

An electroassisted method is developed to transfer silicon (Si) wire arrays from the Si wafers on which they are grown to other substrates while maintaining their original properties and vertical alignment. First, electroassisted etching is used to form a sacrificial porous Si layer underneath the Si wires. Second, the porous Si layer is separated from the Si wafer by electropolishing, enabling the separation and transfer of the Si wires. The method is further expanded to develop a current-induced metal-assisted chemical etching technique for the facile and rapid synthesis of Si nanowires with axially modulated porosity