Science and Technology of Advanced Materials最新文献

We investigated a vacuum thin-film process using laser ablation to fabricate heterostructures of halide perovskite CsPbBr₃ for light-emitting diode (LED) applications. A CsPbBr₃ single crystal synthesized via inverse temperature crystallization was used as the target material for pulsed laser deposition. CsPbBr₃ films were deposited at 150°C, 200°C and 250°C. Structural and optical analysis has revealed that the optimum temperature is 200°C, which display the highest crystallinity and photoluminescence emission efficiency. Time-resolved microwave photoconductivity characterization revealed that the CsPbBr₃ film exhibited a high effective mobility of 2.47 cm²/Vs and long photocarrier lifetime of 16.5 μs. The lifetime is comparable to that of bulk CsPbBr₃ single crystals. This indicates that the polycrystalline CsPbBr₃ film had a low density of defect structures that promote nonradiative recombination. Furthermore, we applied this process to fabricate a LED device using halide perovskite heterostructures. This resulted in a strong green electroluminescence emission. The laser ablation process using ultraviolet and infrared light is suitable for forming heterostructures with an electron transportation layer of oxide Mg_0.3Zn_0.7O film and a hole transportation layer of an organic α-NPD film. The film synthesis process is likely to be effective for evaluating heterointerfaces of various materials displaying remarkable crystallinity without exposure to air.

[This retracts the article DOI: 10.1080/14686996.2024.2320083.].

The planar and lateral HCl-gas etching behavior of (001) β-Ga₂O₃ under oxygen supply were investigated at partial pressures of P ⁰(O₂) = 0-2.5 kPa and 645-1038°C, while maintaining a constant HCl supply partial pressure of P ⁰(HCl) at 63 Pa. At 747°C, the planar etch rate (PER) exhibited a slight decrease with increasing P ⁰(O₂). Notably, at P ⁰(O₂) = 1.25 kPa, the PER increased with temperature, demonstrating a plateau between 747 and 848°C, whereas the thermodynamically calculated etching driving force did not. Even minimal O₂ supply effectively suppressed root mean square (RMS) roughness to <1 nm at 747°C. At P ⁰(O₂) = 1.25 kPa, RMS roughness remained at  <2 nm at up to 847°C, but sharply increased to  >7 nm above 947°C, indicating that lower temperatures realize smoother surfaces. Lateral etch rate (LER) analysis, employing a spoke-wheel pattern mask at 747°C revealed significant anisotropy, demonstrating a kidney-like polar plot pattern, with minimum values in the <100 > direction and maximum values in the  <010> direction. Although P ⁰(O₂) had a limited effect on anisotropy, temperature increase significantly enhanced the LER, particularly along the ± 20°-rotated directions from  <100> . Above 947°C, etched sidewalls exhibited a multi-faceted morphology owing to the formation of {310} and {3̅10} facets depending on the spoke direction, whereas the sidewalls were relatively smooth below 848°C. These findings underscore the potential of controlled HCl-gas etching for the plasma-free processing of β-Ga₂O₃, enabling the fabrication of high-performance devices.

We performed resonance shear measurements (RSM) using the low-temperature surface force apparatus (LT-SFA) to investigate how rubber composition influences the viscoelasticity of the rubber-ice interface. RSM data showed quite different behaviours depending on the styrene contents (5, 23 and 45 wt%) of poly(styrene-co-butadiene) rubbers. A mechanical model for RSM was applied to obtain the interface's viscous (b _s) and elastic (k _s) parameters across a temperature range of ca. -20°C to 0°C. All rubber-ice interfaces at a temperature of ca. -18° to -10°C showed a significant decrease in viscosity of 1 to 2 orders of magnitude in the maximum compared to the silica-ice interface, presenting properties of the ice premelted layer. This was attributed to the dominant viscoelastic contributions of the rubber with decreasing styrene content, and therefore to the decreasing glass transition temperature (T _g = -74, -55, and -31℃). The decrease in the viscosity was enhanced more for lower T _g rubbers. Between -10°C and -5°C, the rubber-ice viscosities converged at a value lower than silica-ice, which was indicative that the interfacial viscoelasticity in this regime was determined by increased contributions from the premelted layer of ice which was probably modulated by polymer-ice interactions. Finally, above -5°C all samples showed a rapid decay in viscosity and elasticity, suggesting that the premelted layer of ice is the main contributor. This study successfully demonstrated that rubber composition could have a profound impact on the viscoelasticity of the rubber-ice interface.

[This retracts the article DOI: 10.1080/14686996.2024.2341611.].

For developing high-performance composite-type thermal diodes, this study focuses on silver chalcogenides, which undergo structural phase transitions in the temperature range of 350 K to 473 K, accompanied by a significant stepwise change in thermal conductivity. Ag_2 + x Te_0.9S_0.1 (x = 0, 0.01, 0.02, 0.025, 0.03, 0.035, 0.04, and 0.05) and Ag₂S_{1 - y} Se _y (y = 0.35, 0.375, 0.4, 0.425, and 0.45) samples were synthesized with precisely controlled compositions, and their temperature-dependent thermal conductivity across the phase transition was studied with the composition dependence. Ag₂Te_0.9S_0.1 exhibits a stepwise decrease in thermal conductivity with transitioning from the low-temperature phase (LTP) to the high-temperature phase (HTP), and this behavior was further enhanced by adding excess Ag. The added silver precipitated in the LTP and dissolved into the HTP of Ag₂Te_0.9S_0.1, resulting in a maximum thermal conductivity change (κ _LTP / κ _HTP) of 2.7-fold with the phase transition at x = 0.025. On the other hand, the Ag₂S_{1 - y} Se _y samples exhibited a stepwise increase in thermal conductivity with transitioning from the LTP to the HTP, and the maximum thermal conductivity change of κ _HTP / κ _LTP = 5 was observed at y = 0.4. A composite thermal diode was fabricated using Ag_2.025Te_0.9S_0.1 and Ag₂S_0.6Se_0.4 with the length ratio of Ag_2.025Te_0.9S_0.1: Ag₂S_0.6Se_0.4 = 47:53 and, consequently, exhibited TRR = 3.3 when it was placed between heat reservoirs maintained at T _H = 412 K and T _L = 300 K. This TRR value is the largest ever reported for all-solid-state composite thermal diodes.

The pursuit of sustainable thermoelectric materials requires the development of cost-effective and efficient compounds derived from earth-abundant elements. Here, we investigate the effects of samarium (Sm) substitution on the thermoelectric performance of SrSi₂ with compositions Sr_1-x Sm _x Si₂ (x = 0, 0.05, 0.1, 0.15, and 0.2). Substituting Sm for Sr in SrSi₂ enhances the power factor at low substitution levels, while further substitution leads to a decrease, due to increased carrier scattering and reduced Seebeck coefficient. Introducing Sm substitution enhances phonon scattering through point defects, reducing lattice thermal conductivity. A peak figure of merit (ZT) of ~0.23 at room temperature is achieved for Sr₀.₉₅Sm₀.₀₅Si₂, demonstrating a 35% improvement over undoped SrSi₂. The weighted mobility of ~285 cm²/V·s and the tailored thermal transport emphasize the role of Sm substitution in modulating both electronic and thermal properties. These findings establish Sr_1-x Sm _x Si₂ as a promising candidate for next-generation thermoelectric devices.

Checkpoint blockade immunotherapy emerges as a potential cure of cancer, but the monotherapy suffers from a low response rate in clinic. Photothermal therapy (PTT) that harvests light energy to ablate tumor is reported to activate tumor-specific immune response, meanwhile nitric oxide (NO) is considered to involve in immune regulation. Herein, we designed a multifunctional nanoplatform that enables photothermal-gas combination therapy by conjugating indocyanine green-thiol (ICG-SH) and s-nitrosoglutathione (GSNO) onto polyvinyl pyrrolidone (PVP)-coated gold nanoparticles (AIG). Upon near-infrared light (NIR) irradiation, AIG heats up the cancer cells and triggers NO release from GSNO, thus inducing apoptosis in the tumor. We found the combination of NO with photothermal treatment causes immunogenic cell death, which should synergize with checkpoint blockade immunotherapy. In the mouse colon cancer bilateral model, we observed complete eradication of light-irradiated tumors and suppression of distant untreated tumors in the AIG with anti-PD-1 (αPD-1) group. We detected significant increase of pro-inflammatory factors in serum, such as interferon- (IFN-γ), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) after PTT-gas-immunotherapy treatment, indicating the successful activation of the immune response. The improved immunogenicity caused by AIG with αPD-1 group allows for efficient antigen presentation, as evidenced by the increased infiltration of dendritic cells (DCs) into the tumor-draining lymph nodes (LNs). We also found promoted infiltration of CD8⁺ T cells in the untreated tumors in the AIG with αPD-1 group comparing to αPD-1 alone. Therefore, phototermal-gas-immune checkpoint blockade combination therapy represents a new promising treatment of metastatic cancer.

In this study, we propose an accurate, simple, and versatile measurement method for power generation efficiency and device figure of merit ZT of thermoelectric devices. Toward the energy harvesting applications of thermoelectric generators, the performance characterization under low heat inflow and temperature difference is crucial. However, when the conventional solid-state heat flow meter is used, the uncertainty of power generation performance increases as heat input decreases. We have solved these problems by using a laser for heat input, improving the simplicity and accuracy of power generation efficiency measurements, especially at low heat flow. The direct and non-contact measurement of the temperature difference by using a thermography allowed us to determine ZT as well as power generation efficiency. The obtained mean power generation efficiency and ZT values are consistent with the values obtained by the conventional method within the error range, thereby validating the reliability of the proposed method. The relative uncertainties of the efficiency and ZT were estimated to be less than 3% and 12% for our method, respectively, whereas those were 19% and 24% in situations where the temperature difference was less than 6 K for the conventional method.

Emergent ferromagnetism on the surface of two-dimensional (2D) MXene is investigated by X-ray magnetic circular dichroism (XMCD) and angle-dependent hard X-ray photoemission spectroscopy (HAXPES). Focusing on Cr₂N as one of the 2D-MXenes, high quality bilayers of Cr₂N/Co and Cr₂N/Pt are prepared by a magnetron sputtering technique. XMCD reveals the induced magnetic moment of Cr in the Cr₂N/Co interface, while it is not observed in the Cr₂N/Pt interface at room temperature. In order to distinguish the possible origins of either the interlayer magnetic exchange coupling or the charge transfer model as the source of ferromagnetism at the interface, the additional controlled Cr₂N/Cu bilayer, whose work function of Cu is consistent with Co, is prepared. HAXPES spectra for the Cr 2p core level near the interface of Cr₂N/Cu are consistent with that of Cr₂N/Co, indicating that the induced magnetic moment of Cr observed by XMCD for Cr₂N/Co can be attributed to the model of interlayer magnetic exchange coupling, rather than the charge transfer model, leading to emergent ferromagnetism at the interface with 2D-MXene.