Understanding the interaction between hydrogen (H) and helium-vacancy (He-V) complexes in tungsten (W) is important for the development of plasma-facing materials in fusion reactors. H trapping by He_xV_y complexes in bulk W, as well as the H solution behavior and H trapping by He_xV complexes near W(100), W(111), and W(110) surfaces, has been investigated by first-principles computer simulations using density function theory. The results show that the sequential H binding energies to He_xV complexes in bulk W decrease with the increasing number of H and He. For the He_xV₂ complexes in bulk W, H prefers to trap at interstitial sites near the junction of the di-vacancy, where the H can minimize the isosurface of optimal charge density. The most stable interstitial sites for H below W surfaces are dependent on the surface orientation. Our calculations indicate that H atoms tend to prefer a depth of 0.3 nm below the W(100) and W(111) surfaces due to the surface reconstruction. The binding energy of H to a HeV complex near W surfaces has the most significant orientation dependence below the W(111) surface, followed by the W(100) and W(110) surfaces. Compared with the bulk value, the largest difference in the average binding energy of H to the stable He_xV complexes at the three W surfaces is about 0.2 eV. Furthermore, the effect of surfaces on the H binding energy to He_xV complexes can be ignored for depths greater than 0.65 nm.

Density function theory calculations have been performed to study the stability of small helium-vacancy (He-V) complexes near tungsten (W) surfaces of different orientations. The results show that the stability of vacancies and He-V complexes near W surfaces depends on surface orientation. However, as the depth below the surface increased beyond about 0.65–0.8 nm, the stability of He-V complexes is similar to the bulk. The formation energies of single vacancies and di-vacancies at depths less than 0.2 nm below the W(110) surface are higher than for W(100) or W(111) surfaces, but have lower energies at depths between 0.2 and 0.65 nm. The formation energies of He-V complexes below W surfaces are sensitive to the geometric orientation of the He and vacancy, especially below the W(111) surface. Within about 0.2 nm of the top layer of the three W surfaces, neither a vacancy nor a di-vacancy can trap He. Because of the lower formation energy of He-V complexes and higher He binding energy to vacancies below the W(110) surface, the He desorption from the W(110) surface is less likely to occur than from the W(100) and W(111) surfaces. Our results provide fundamental insight into the differences in surface morphology changes observed in single W crystals with different surface orientations under He plasma exposure.

The low-energy electronic excitations in topological semimetal yield a plethora of a range of novel physical properties. As a relatively scarce branch, the research of triple-degenerate semi-metal is mostly confined to the stage of physical properties and theoretical analysis, there are still challenges in its practical application. This research showcases the first application of the triply degenerate semimetal PtBi₂ in electronic devices. Leveraging a van der Waals transfer method, PtBi₂ flakes were used as interlayer contacts for metal electrodes and WS₂ in transistors. The transistor achieved a switching ratio above 10⁶ and average mobility can reach 85 cm²V⁻¹ s⁻¹, meeting integrated circuit requirements. Notably, the excellent air stability of PtBi₂ simplifies the device preparation process and provides more stable device performance. Transfer process reduces the Schottky barrier between metal electrodes and semiconductors while avoiding Fermi pinning during metal deposition to achieve excellent contact. This groundbreaking work demonstrates the practical applicability of PtBi₂ in the field of electronic devices while opening new avenues for the integration of novel materials in semiconductor technology, setting a precedent for future innovations.

To understand the irradiation resistance and hydrogen (H) behavior in tungsten borides (W _x B _y ) in a burning plasma fusion environment, the energetics of intrinsic point defects and H in six stable ground state W borides, including W₂B, WB, WB₂, W₂B₅, WB₃ and WB₄, have been investigated using first-principles density functional theory calculations. The results show that the formation energies of interstitials and vacancies do not directly depend on the W and B content in W borides. However, the interaction between vacancies of a stoichiometric vacancy (SV) cluster in W _x B _y is related to the atomic ratio of B to W (y/x). The vacancies of a minimum-size SV cluster in W _x B _y are energetically repulsive for y/x ⩽ 1, while the vacancies energetically bind together for y/x larger than 1. The formation energy of B Frenkel pairs in each W boride is lower than that of W Frenkel pairs. Among the six evaluated W _x B _y compositions, WB has the highest and the lowest formation energy of H interstitials and H-vacancy complexes, respectively; however, these two energies in WB₂ are in reverse order. The average H binding energies to single vacancies in WB and WB₄ are comparable with that in W, while this binding energy in WB₃ and WB₂ is obviously higher or lower than in W, respectively. The diffusion activation energy of H in W borides is anisotropic. One dimensional (1D) diffusion of H in W₂B, as well as 1D/2D diffusion in WB, W₂B₅, WB₃ and WB₄ are preferred at relatively low temperatures; however, three-dimensional diffusion of H is predicted in WB₂. The diffusion activation energy of H generally increases with B content in W borides due to the increasing local charge deficit caused by strong B–B covalent bonds. This study is useful for evaluating the performance of W borides in a fusion environment.

Hydrogen (H) solution, migration, and binding to vacancies near the tungsten/tungsten carbide (W/WC) interfaces based on hcp WC or bcc W (W/WCb and Wb/WC) have been studied by first-principles simulations to provide insights into the effect of C on H behavior in W exposed to C deposition in fusion reactors. The H behavior near the W/WC interfaces is related to the tensile or compressive strain due to the lattice match and interfacial effects. Near the W/WCb interface, the H solution energy in hcp WC increases approaching the interface, while it decreases from the W side to the interface. The configuration change of the W slab significantly decreases the H solution energy but has only a modest effect on the H migration energy barrier in comparison with the values in bcc W. The interface enhances the H binding to vacancies in WC layers. Both the interface and configuration adjustment of the W slab reduce the H binding to vacancies on the W side of the interface. Near the Wb/WC interface, H solution energies in both WC and W slabs weakly decrease approaching the interface. The configuration change of the WC slab significantly increases the H solution energy and binding energy to vacancies but decreases the H migration energy barrier in comparison with the values in hcp WC. The H energetics near the W/WC interfaces indicate the likelihood of H localization and diffusion in the W side of the interface, rather than diffusing through the interface into WC layers.