The discovery of ferromagnetism in van der Waals (vdW) materials has enriched the understanding of two-dimensional (2D) magnetic orders and opened new avenues for fundamental physics research and next generation spintronics. However, achieving ferromagnetic order at room temperature, along with strong perpendicular magnetic anisotropy, remains a significant challenge. In this work, we report wafer-scale growth of vdW ferromagnet Fe₃GaTe₂ using molecular beam epitaxy. The epitaxial Fe₃GaTe₂ films exhibit robust ferromagnetism, exemplified by high Curie temperature (T_C = 420 K) and large perpendicular magnetic anisotropy (PMA) constant K_U = 6.7 × 10⁵J/m³ at 300 K for nine-unit-cell film. Notably, the ferromagnetic order is preserved even in the one-unit-cell film with T_C reaching 345 K, benefiting from the strong PMA (K_U = 1.8×10⁵J/m³ at 300 K). In comparison to exfoliated Fe₃GaTe₂ flakes, our epitaxial films with the same thickness show the significant enhancement of T_C, which could be ascribed to the tensile strain effect from the substrate. The successful realization of wafer-scale ferromagnetic Fe₃GaTe₂ films with T_C far above room temperature represents a substantial advancement (in some aspects or some fields, e.g. material science), paving the way for the development of 2D magnet-based spintronic devices.

The recent discovery of the interfacial superconductivity (SC) of the Bi ₂ Te ₃ /Fe _1+y Te heterostructure has attracted extensive studies due to its potential as a novel platform for trapping and controlling Majorana fermions. Here we present studies of another topological insulator (TI)/Fe _1+y Te heterostructure, Sb ₂ Te ₃ /Fe _1+y Te, which also has an interfacial 2-dimensional SC. The results of transport measurements support that reduction of the excess Fe concentration of the Fe _1+y Te layer not only increases the fluctuation of its antiferromagnetic (AFM) order but also enhances the quality of the SC of this heterostructure system. On the other hand, the interfacial SC of this heterostructure was found to have a wider-ranging TI-layer thickness dependence than that of the Bi ₂ Te ₃ /Fe _1+y Te heterostructure, which is believed to be attributed to the much higher bulk conductivity of Sb ₂ Te ₃ that enhances indirect coupling between its top and bottom topological surface states (TSSs). Our results provide evidence of the interplay among the AFM order, itinerant carries from the TSSs, and the induced interfacial SC of the TI/Fe _1+y Te heterostructure system.

We present a study of the surface reactivity of a Pd/Bi₂Te₃ thin film heterostructure. The topological surface states from Bi₂Te₃, being delocalized and robust owing to their topological natures, were found to act as an effective electron bath that significantly enhances the surface reactivity of palladium in the presence of two oxidizing agents, oxygen and tellurium respectively, which is consistent with a theoretical calculation. The surface reactivity of the adsorbed tellurium on this heterostructure is also intensified possibly benefitted from the effective transfer of the bath electrons. A partially inserted iron ferromagnetic layer at the interface of this heterostructure was found to play two competing roles arising from the higher-lying d-band center of the Pd/Fe bilayer and the interaction between the ferromagnetism and the surface spin texture of Bi₂Te₃ on the surface reactivity and their characteristics also demonstrate that the electron bath effect is long-lasting against accumulated thickness of adsorbates.

The intrinsic activities of SnTe (001) and (111) surfaces with robust topological surface states (TSSs) are superior to that of a (211) surface with fragile or without TSSs, attributing to the enhanced charge transfer between H atoms and TSSs.

ZnSe nanowires (NWs) were grown on (111), (100), and (110)-oriented GaAs substrates by molecular-beam epitaxy via the vapor-liquid-solid reaction. The size dependence of NW growth orientation was studied by varying the Au catalyst size. Through detailed transmission electron microscopy studies, it was found that ⟨111⟩ orientation is the growth direction for NWs with size $⩾30\mathrm{nm}$ , while NWs with size around $10\mathrm{nm}$ prefer to grow along the ⟨110⟩ direction, with a small portion along the ⟨112⟩ direction. These observations have led to the realization of vertical ZnSe NWs with size around $10\mathrm{nm}$ grown on a GaAs(110) substrate.

A compact solid-state UV flame sensing system is developed and tested. We have addressed two approaches for obtaining additional six orders of long-wavelength rejection power on top of that of the built-in UV sensor based on a wide-bandgap II-VI Schottky-barrier structure. An op-amp-based amplification circuit with an average gain of 16 600 is used for signal amplification. It is demonstrated that the developed sensing system could detect a standard butane-air flame with excellent solar-blind characteristics, potentially capable for monitoring industrial boilers. Several feasible approaches were discussed for further improvement in the performance of the developed sensing system targeting its general usage in fire-safety applications.