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The recovery effect of isochronal thermal annealing and inelastic energy deposited during 100 MeV Ag swift heavy ion (SHI) irradiation is demonstrated in the case of 4H-SiC pre-damaged by elastic energy deposition of 300 keV Ar ion. The Ar-induced fractional disorder follows a nonlinear two-step damage build-up. The fractional disorder level of 0.3 displacements per atom (dpa) is established as the threshold above which the lattice rapidly enters the amorphous phase, characterized by the presence of highly photo-absorbing defects. The SHI-induced recovery suggests that the damage annealing, in the pre-damaged region (∼ 350 nm) where the S e for 100 MeV Ag is almost constant (∼ 16.21 keV/nm), is more pronounced than the damage creation by SHI. This allows the disorder values to saturate at a lower value than the present initial disorder. Furthermore, the thermal effect due to SHI irradiation of an amorphous nano-zone embedded in a crystalline host matrix has been evaluated using the 3D implementation of the thermal spike. The recovery process by SHI is ascribed to the thermal spike-induced atomic movements resulting from the melting and the resolidification of the crystalline–amorphous interface. [ABSTRACT FROM AUTHOR]

Defects in SiC have shown tremendous capabilities for quantum technology-based applications, making it necessary to achieve on-demand, high-concentration, and uniform-density defect ensembles. Here, we utilize 100 MeV Ag swift heavy ion irradiation on n-type and semi-insulating 4H-SiC for the controlled generation of the defects that have attracted a lot of attention. Photoluminescence spectroscopy shows strong evidence of V Si emitters in semi-insulating 4H-SiC. Additionally, irradiation generates photo-absorbing centers that enhance the optical absorption, suppressing the luminescence intensity at higher fluences (ions / cm 2). In n-type 4H-SiC, irradiation drastically increases the inter-conduction band transitions, attributed to absorption from trap centers. A clear correlation is found between (i) loss in the intensity of E 2 (TO) Raman signal and the enhancement in absorbance at 532 nm and (ii) decoupling of the longitudinal optical phonon–plasmon coupled Raman mode and the reduction in carrier concentration. The optical bandgap decreases with irradiation fluence for semi-insulating 4H-SiC. This is attributed to the formation of disorder and strain-induced localized electronic states near the band edges. [ABSTRACT FROM AUTHOR]

An ultrafast thermal spike within a time interval of a few pico-seconds generated by intense ionizing energy deposited using 100 MeV Ag ions is utilized to study the atomistic details of damage recovery in 4H-SiC. Sequential single ion irradiations were performed using 300 keV Ar and 100 MeV Ag in <0001> 4H-SiC to invoke swift heavy ion (SHI) beam induced epitaxial recrystallization in samples with different degrees of pre-damaged conditions. SHI irradiation was carried out at both room temperature and a low temperature of ~80 K. Low-temperature irradiation was carried out to arrest thermal diffusion of defects and to isolate ionization-induced defect migration in 4H-SiC. Insights into the thermal spike generated by ionizing events in crystalline and amorphous regions at both the temperatures predict a SiC response to SHI. The results emphasize the role of different degrees of pre-damage induced physico-chemical conditions and irradiation temperatures against SHI-induced recrystallization as evaluated by Rutherford backscattering/channeling, Raman spectroscopy, and hard x-ray photoelectron spectroscopy. Understanding the dependence of ion-beam damage accumulation and their recovery on the inelastic to elastic energy loss ratio is important for the performance prediction of SiC intended for extreme environments such as space, defense, and nuclear radiation. We report substantial damage recovery even at a near liquid nitrogen temperature of ~80 K. The recovery gets impeded mainly by the formation of complex defects having homonuclear bonds. The results are explained in the framework of the inelastic thermal spike model, and the role of phonon in the damage recovery process is emphasized. [ABSTRACT FROM AUTHOR]

MoS2 based materials are considered the most reliable alternative catalysts for the hydrogen evolution reaction (HER), where engineering of active sites has emerged as an acceptable approach to tune their HER activity. In this approach, the dispersion of bulk MoS2 in the aqueous phase was increased with a surfactant (sodium dodecyl sulfate), which reduced the exfoliation time and enhanced the exfoliation ability to produce layered MoS2 nanosheets. During the hydrothermal treatment, the nanosheets were further scissored into small nanocrystals. Nanocrystals have attractive properties with stable dispersion and high-water solubility. Our method provides a scalable, eco-friendly, easy, and low-cost strategy for designing other HER catalysts. Such ultra-small MoS2 nanocrystals with rich Mo vacancies were used as catalysts for HER, which showed excellent electrocatalytic activity with a low overpotential (95 mV) and small Tafel slope (41 mV/dec) in 0.5M H2SO4 electrolyte. The design and synthesis of the HER catalyst in this work presents a promising path for preparing active and stable electrocatalysts to replace costly metal-based catalysts for hydrogen production. [ABSTRACT FROM AUTHOR]

Dzyaloshinskii-Moriya interaction (DMI) is shown to induce a topologically protected chiral spin texture in magnetic/nonmagnetic heterostructures. In the context of van der Waals spintronic devices, graphene emerges as an excellent candidate material. However, due to its negligible spin-orbit interaction, inducing DMI to stabilize topological spins when coupled to 3d-ferromagnets remains challenging. Here, it is demonstrated that, despite these challenges, a sizeable Rashba-type spin splitting followed by significant DMI is induced in graphene/Fe 3 GeTe 2 . This is made possible due to an interfacial electric field driven by charge asymmetry together with the broken inversion symmetry of the heterostructure. These findings reveal that the enhanced DMI energy parameter, resulting from a large effective electron mass in Fe 3 GeTe 2 , remarkably contributes to stabilizing non-collinear spins below the Curie temperature, overcoming the magnetic anisotropy energy. These results are supported by the topological Hall effect, which coexists with the non-trivial breakdown of Fermi liquid behavior, confirming the interplay between spins and non-trivial topology. This work paves the way toward the design and control of interface-driven skyrmion-based devices., (© 2024 Wiley‐VCH GmbH.)

The interplay between strong Coulomb interactions and kinetic energy leads to intricate many-body competing ground states owing to quantum fluctuations in 2D electron and hole gases. However, the simultaneous observation of quantum critical phenomena in both electron and hole regimes remains elusive. Here, we utilize anisotropic black phosphorus (BP) to show density-driven metal-insulator transition with a critical conductance ∼ e 2 / h which highlights the significant role of quantum fluctuations in both hole and electron regimes. We observe a T -linear resistivity from the deep metallic phase to the metal-insulator boundary at moderate temperatures, while it turns to Fermi liquid behavior in the deep metallic phase at low temperatures in both regimes. An analysis of the resistivity suggests that disorder-dominated transport leads to T -linear behavior in the hole regime, while in the electron regime, the T -linear resistivity results from strong Coulomb interactions, suggestive of strange-metal behavior. Successful scaling collapse of the resistivity in the T -linear region demonstrates the link between quantum criticality and the T -linear resistivity in both regimes. Our study provides compelling evidence that ambipolar BP could serve as an exciting testbed for investigating exotic states and quantum critical phenomena in hole and electron regimes of 2D semiconductors.

To improve the production rate of MoS 2 nanosheets as an excellent supercapacitor (SC) material and enhance the performance of the MoS 2 -based solid-state SC, a liquid phase exfoliation method is used to prepare MoS 2 nanosheets on a large scale. Then, the MnO 2 nanowire sample is synthesized by a one-step hydrothermal method to make a composite with the as-synthesized MoS 2 nanosheets to achieve a better performance of the solid-state SC. The interaction between the MoS 2 nanosheets and MnO 2 nanowires produces a synergistic effect, resulting in a decent energy storage performance. For practical applications, all-solid-state SC devices are fabricated with different molar ratios of MoS 2 nanosheets and MnO 2 nanowires. From the experimental results, it can be seen that the synthesized nanocomposite with a 1:4 M ratio of MoS 2 nanosheets and MnO 2 nanowires exhibits a high Brunauer-Emmett-Teller surface area (∼118 m 2 /g), optimum pore size distribution, a specific capacitance value of 212 F/g at 0.8 A/g, an energy density of 29.5 W h/kg, and a power density of 1316 W/kg. Besides, cyclic charging-discharging and retention tests manifest significant cycling stability with 84.1% capacitive retention after completing 5000 rapid charge-discharge cycles. It is believed that this unique, symmetric, lightweight, solid-state SC device may help accomplish a scalable approach toward powering forthcoming portable energy storage applications., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)