Two-dimensional materials (2DMs) have attracted a great deal of interest due to their immense potential for scientific breakthroughs and technological innovations. While some 2D transition metal dichalcogenides (TMDC) such as MoS2 and WS2 are considered as the ultimate channel materials in unltrascaled transistors as replacements for Si, there has also been increasing interest in the monolithic 3D integration of 2DMs on the Si CMOS platform or in flexible electronics as back-end-of-line transistors, memory devices/selectors, and sensors, taking advantage of 2DM properties such as a high current driving capability with low leakage current, nonvolatile switching characteristics, a large surface-to-volume ratio, and a tunable bandgap. However, the realization of both of these scenarios critically depends on the development of manufacturing-viable high-yield 2DM layers transfer from the growth substrate to the Si, since the growth of high-quality 2DM layers often requires a high-temperature growth process on template substrates. Motivated by this, extensive efforts have been made by the 2DM research community to develop various 2DM layer transfer methods, leveraging the van der Waals transfer capability of the layer-structured 2DMs. These efforts have led to a number of successful demonstrations of wafer-scale 2D TMDC layer transfer, while 2DM-enabled template growth/transfer of some functional bulk materials such as III–V, Ge, and AlN has also been demonstrated. This review surveys and compares different 2DM transfer methods developed recently, with a focus on large-area 2D TMDC film transfer along with an introduction of 2DM template-assisted van der Waals growth/transfer of non-2D thin films. We will also briefly present an outlook of our envisioned multifunctionalities in 3D integrated electronic systems enabled by monolithic 3D integration of 2DMs and III–V via van der Waals transfer and discuss possible technology options for overcoming remaining challenges.

For the sustainable development of spintronic devices, a half-metallic ferromagnetic film needs to be developed as a spin source with exhibiting 100% spin polarisation at its Fermi level at room temperature. One of the most promising candidates for such a film is a Heusler-alloy film, which has already been proven to achieve the half-metallicity in the bulk region of the film. The Heusler alloys have predominantly cubic crystalline structures with small magnetocrystalline anisotropy. In order to use these alloys in perpendicularly magnetised devices, which are advantageous over in-plane devices due to their scalability, lattice distortion is required by introducing atomic substitution and interfacial lattice mismatch. In this review, recent development in perpendicularly-magnetised Heusler-alloy films is overviewed and their magnetoresistive junctions are discussed. Especially, focus is given to binary Heusler alloys by replacing the second element in the ternary Heusler alloys with the third one, e.g., MnGa and MnGe, and to interfacially-induced anisotropy by attaching oxides and metals with different lattice constants to the Heusler alloys. These alloys can improve the performance of spintronic devices with higher recording capacity.

Generating pure spin currents via the spin Hall effect in heavy metals has been an active topic of research in the last decade. In order to reduce the energy required to efficiently switch neighbouring ferromagnetic layers for applications, one should not only increase the chargeto-spin conversion efficiency but also decrease the longitudinal resistivity of the heavy metal.In this work, we investigate the spin Hall conductivity in W1-xTax/CoFeB/MgO (x = 0 -0.2) using spin torque ferromagnetic resonance measurements. Alloying W with Ta leads to a factor of two change in both the damping-like effective spin Hall angle (from -0.15 to -0.3) and longitudinal resistivity (60 -120 µW cm). At 11% Ta concentration, a remarkably high spin Hall angle value of -0.3 is achieved with a low longitudinal resistivity 100 µW cm, which could lead to a very low power consumption for this W-based alloy. This work demonstrates sputter-deposited W-Ta alloys could be a promising material for power-efficient spin current generation.

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Structural and magnetic properties of 1–10 nm thick Fe films deposited on GaN(0001) were investigated. In-situ reflecting high energy electron diffraction images indicated a α-Fe(110)/GaN(0001) growth of the 3D Volmer-Weber type. The α-Fe(110) X-ray diffraction peak showed a 1° full-width at half-maximum, indicating ≈20 nm grain sizes. A significant reduction in Fe atomic moment from its bulk value was observed for films thinner than 4 nm. Both GaN/Fe interface roughness and Fe film coercivity increased with Fe thickness, indicating a possible deterioration of Fe crystalline quality. Magnetic anisotropy was mainly uniaxial for all films while hexagonal anisotropies appeared for thicknesses higher than 3.7 nm.

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The interfacial atomic structure of post-annealed Fe/GaAs(001) films, grown by molecular beam epitaxy, has been investigated using high resolution transmission electron microscopy. The images show a single plane of Fe atoms partially mixing between the Fe film and GaAs, along with the presence of vacancies above the As. Transport properties of three terminal devices based on these films are also presented, employing an all electrical method to confirm the injection and detection of a spin-polarized current using the Hanle effect. The effect of differing interfacial atomic ordering on the barrier heights is discussed.

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