Computational Modulation in Electronic Structures of Halide Perovskites via Element/Dopant/Phase

This study employs computational chemistry to investigate the electronic properties of halide perovskite materials, focusing on structural frameworks, elemental composition, surface engineering, and defect engineering. The tetragonal phase generally exhibits higher band gaps than the cubic phase due to conduction band differences, with LiPbCl3 showing the greatest band gap difference. The ionic radius of the A element influences band gaps for both phases, with Cs having the highest impact. Surface engineering significantly affects the electronic properties, and surface direction and composition play vital roles in determining band gaps. Defect engineering induces semiconducting-to-metallic transitions, impacting band gaps. Understanding these core variables is crucial for tailoring the electronic properties of halide perovskites for photovoltaic and optoelectronic applications

Computational Understanding of Effect of Alkali Earth Metal Dopants on Dehydrogenation Thermodynamics of MgH₂ Nanoparticles

Efficient hydrogen storage is crucial for realizing the potential of hydrogen as an alternative energy source. Metal hydrides, particularly MgH2, have shown promise due to their stability and high storage capacity. However, their high operating temperatures pose challenges. Doping MgH2 with elements such as Be and Ca is strategically explored to improve performance. This study investigates how dopant type, concentration, and configuration influence the particle size effect on hydrogenation/dehydrogenation reaction thermodynamics. It is revealed that both Be and Ca dopants, irrespective of their configurations (whether positioned on the surface or within the subsurface), enhance the reduction in the reaction temperature of MgH2 caused by the particle size reduction. This impact is more pronounced for Be dopants compared to Ca dopants. In a similar logic, subsurface doping scenario is better for pronouncing this impact enhances than surface doping scenario. Further investigation highlights that the destabilization of MgH2, which is induced by Be/Ca dopants, is primarily attributed to the electronic localization of the local Mg–Be/Ca environment, leading to a reduction in the dehydrogenation reaction temperature by weakening the Mg–H bonds. These findings provide valuable insights into reducing reaction temperatures in metal hydrides, crucial for practical hydrogen storage applications

Mechanistic Mapping of Ozone-Dosed Al₂O₃ Atomic Layer Deposition Half-Cycles

Despite the growing interest in the utilization of ozone (O3) precursors as oxygen layer resources for the atomic layer deposition (ALD) of metal oxide films, relevant mechanistic studies are lacking. Herein, the density functional theory modeling approach is employed to comprehensively unveil the mechanisms of O3-dosed Al2O3 ALD half-cycles based on three distinct schemes that were previously proposed for the chemical conversion of trimethylaluminum-covered surfaces into OH-covered surfaces. In scheme 1, the first step involves O3-induced insertion of oxygen into the C–H bond of AlCH3 surface groups. In contrast, schemes 2 and 3 both begin with oxygen insertion into the Al–C bond, although the subsequent steps differ. The computational investigation is performed from both thermodynamic and kinetic perspectives and provides meaningful insights into the relative feasibility of the three schemes. First, two key competitive steps, namely, “Al–CH2OH versus Al–OCH3” and “carbonate versus hydroxyl”, are verified to be decisive in determining the most thermodynamically and kinetically feasible ALD half-cycle pathway. Second, the analysis of the two key competitive steps reveals that two schemes (schemes 2 and 3) contribute competitively to the ALD half-cycle. Finally, owing to this competition, the relative feasibility of schemes 2 and 3 is strongly dependent on the process conditions. These findings are expected to be beneficial for efforts toward the careful design of O3-dosed ALD half-cycles to produce high-purity metal oxide films

In-Plane Seebeck Coefficients of Thickness-Modulated 2D PtSe₂ Thin Films

Two-dimensional (2D) PtSe2 is rapidly emerging as a promising candidate for developing devices that exhibit a significantly enhanced thermoelectric power factor because of its thickness-modulation-induced tunable semiconductor-to-semimetal transition characteristic. This interesting phenomenon motivated us to measure the in-plane Seebeck coefficients and electrical conductivities of large-area 2D PtSe2 thin films with approximately 2–15 nm thicknesses. We observed an outstanding in-plane Seebeck coefficient of ∼73.7 μV/K and a high electrical conductivity of ∼216 S/cm in the 9-nm-thick 2D PtSe2 film than in the ∼6-nm-thick 2D PtSe2 film at 300 K. Our observations suggest that thickness-dependent semiconductor-to-semimetal transitions in PtSe2-based materials offer a distinguishable advantage for enhancing the power factor of 2D PtSe2-based thermoelectric devices

Observation of a Strong Decoupling Phenomenon in Pt/Si Hybrid Structures for In-Plane Thermoelectric Properties

The performance of thermoelectric (TE) materials is limited by the intrinsic coupling of the Seebeck coefficient and the electrical conductivity such that an increase in one leads to a decrease in the other with respect to the carrier concentration. This coupling makes it particularly difficult to enhance the TE power factor in TE materials. In this study, we added a Pt top layer over a silicon wafer, forming a hybridized Pt/Si structure to drive a strong decoupling of the Seebeck coefficient and electrical conductivity. The results show that the electrical resistance in the Pt/Si hybrid structure decreased by ∼94 times compared to that of a single-layer lightly doped Si substrate at 300 K, while the Seebeck coefficient in the hybrid structure decreased slightly compared to that of the single layer. The remarkably high TE performance of the Pt/Si hybrid structure is brought about by the hybridization of the intrinsic high-conductivity Pt layer and the high-Seebeck coefficient Si substrate. In addition, we demonstrate that this novel and effective decoupling method enables the assessment of the in-plane intrinsic Seebeck coefficient of a lightly doped Si wafer, which typically has an electrical resistance that is extremely high to measure the Seebeck coefficient even with a high-resolution voltmeter. These results represent a significant advancement in the understanding of electrical transport in TE materials, which will invigorate further research on Si-based devices for realizing large-area watt-scale TE generation at room temperature

Enhanced Transverse Seebeck Coefficients in 2D/2D PtSe₂/MoS₂ Heterostructures Using Wet-Transfer Stacking

It is very challenging to estimate thermoelectric (TE) properties when applying millimeter-scale two-dimensional (2D) transition metal dichalcogenide (TMDC) materials to TE device applications, particularly their Seebeck coefficient due to their high intrinsic electrical resistance. This paper proposes an innovative approach to measure large transverse (i.e., in-plane) Seebeck coefficients for 2D TMDC materials by placing a low resistance (LR) semimetallic PtSe2 film on high-resistance (HR) semiconducting MoS2 (>10 MΩ), whose internal resistance is too high to measure the Seebeck coefficient, forming a heterojunction structure using wet-transfer stacking. The vertically stacked LR-PtSe2 (3 nm)/HR-MoS2 (12 nm) heterostructure film exhibits a high Seebeck coefficient > 190 μV/K up to 5 K temperature difference. This unusual behavior can be explained by an additional Seebeck effect induced at the interface between the LR-2D/HR-2D heterostructure. The proposed stacked LR-PtSe2/HR-MoS2 heterostructure film offers promising phenomena 2D/2D materials that enable innovative TE device applications

Coiled Conformation Hollow Carbon Nanosphere Cathode and Anode for High Energy Density and Ultrafast Chargeable Hybrid Energy Storage

Lithium-ion batteries and pseudocapacitors are nowadays popular electrochemical energy storage for many applications, but their cathodes and anodes are still limited to accommodate rich redox ions not only for high energy density but also sluggish ion diffusivity and poor electron conductivity, hindering fast recharge. Here, we report a strategy to realize high-capacity/high-rate cathode and anode as a solution to this challenge. Multiporous conductive hollow carbon (HC) nanospheres with microporous shells for high capacity and hollow cores/mesoporous shells for rapid ion transfer are synthesized as cathode materials using quinoid:benzenoid (Q:B) unit resins of coiled conformation, leading to ∼5-fold higher capacities than benzenoid:benzenoid resins of linear conformation. Also, Ge-embedded Q:B HC nanospheres are derived as anode materials. The atomic configuration and energy storage mechanism elucidate the existence of mononuclear GeOx units giving ∼7-fold higher ion diffusivity than bulk Ge while suppressing volume changes during long ion-insertion/desertion cycles. Moreover, hybrid energy storage with a Q:B HC cathode and Ge–Q:B HC anode exploit the advantages of capacitor-type cathode and battery-type anode electrodes, as exhibited by battery-compatible high energy density (up to 285 Wh kg–1) and capacitor-compatible ultrafast rechargeable power density (up to 22 600 W kg–1), affording recharge within a minute

A Three-Dimensional Liquid-Based Exchangeable Gradient Osmosis Chip for a Permeability Controllable Microfluidic Device

3D printing technology has significant potential for use in the field of microfluidics. Microfluidic chips are biochips that have been applied in biomedical areas such as disease diagnosis and drug delivery in vivo. However, traditional 2D manufacturing techniques limit the scope of their fabrication and usage. In addition, membrane-embedded microfluidic chips need intricately designed structures and well-defined nanofiber membranes for delivering specific drugs and filtering out impurities from blood, and it is difficult to respond quickly to the design and production of these complex three-dimensional shapes. Herein, we introduce a liquid-based exchangeable gradient osmosis (LEGO) chip comprising a 3D structured channel printed via a digital light processing system within 10 min and an electrospun nanofiber membrane. The attachment conditions of the nanofiber membranes to the 3D channel were optimized, while the permeability of specific materials was controlled by adjusting the concentration of nanofibers and the flow speed through the 3D channel. We anticipate that the LEGO chip will be used to produce bio-applicable devices for mass transfer in vivo

Coiled Conformation Hollow Carbon Nanosphere Cathode and Anode for High Energy Density and Ultrafast Chargeable Hybrid Energy Storage

Lithium-ion batteries and pseudocapacitors are nowadays popular electrochemical energy storage for many applications, but their cathodes and anodes are still limited to accommodate rich redox ions not only for high energy density but also sluggish ion diffusivity and poor electron conductivity, hindering fast recharge. Here, we report a strategy to realize high-capacity/high-rate cathode and anode as a solution to this challenge. Multiporous conductive hollow carbon (HC) nanospheres with microporous shells for high capacity and hollow cores/mesoporous shells for rapid ion transfer are synthesized as cathode materials using quinoid:benzenoid (Q:B) unit resins of coiled conformation, leading to ∼5-fold higher capacities than benzenoid:benzenoid resins of linear conformation. Also, Ge-embedded Q:B HC nanospheres are derived as anode materials. The atomic configuration and energy storage mechanism elucidate the existence of mononuclear GeOx units giving ∼7-fold higher ion diffusivity than bulk Ge while suppressing volume changes during long ion-insertion/desertion cycles. Moreover, hybrid energy storage with a Q:B HC cathode and Ge–Q:B HC anode exploit the advantages of capacitor-type cathode and battery-type anode electrodes, as exhibited by battery-compatible high energy density (up to 285 Wh kg–1) and capacitor-compatible ultrafast rechargeable power density (up to 22 600 W kg–1), affording recharge within a minute

Interface-Induced Seebeck Effect in PtSe₂/PtSe₂ van der Waals Homostructures

The Seebeck effect refers to the production of an electric voltage when different temperatures are applied on a conductor, and the corresponding voltage-production efficiency is represented by the Seebeck coefficient. We report a Seebeck effect: thermal generation of driving voltage from the heat flowing in a thin PtSe2/PtSe2 van der Waals homostructure at the interface. We refer to the effect as the interface-induced Seebeck effect. By exploiting this effect by directly attaching multilayered PtSe2 over high-resistance PtSe2 thin films as a hybridized single structure, we obtained the highly challenging in-plane Seebeck coefficient of the PtSe2 films that exhibit extremely high resistances. This direct attachment further enhanced the in-plane thermal Seebeck coefficients of the PtSe2/PtSe2 van der Waals homostructure on sapphire substrates. Consequently, we successfully enhanced the in-plane Seebeck coefficients for the PtSe2 (10 nm)/PtSe2 (2 nm) homostructure approximately 42% compared to that of a pure PtSe2 (10 nm) layer at 300 K. These findings represent a significant achievement in understanding the interface-induced Seebeck effect and provide an effective strategy for promising large-area thermoelectric energy harvesting devices using two-dimensional transition metal dichalcogenide materials, which are ideal thermoelectric platforms with high figures of merit