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HIGHLIGHTS • The recent progress of spin injection, spin transport, spin manipulation, and application in 2D materials was summarized. • The current challenges and outlook of future studies in spintronics based on 2D materials and related heterostructures were discussed. ABSTRACT Spintronics, exploiting the spin degree of electrons as the information vector, is an attractive field for implementing the beyond Complemetary metal-oxide-semiconductor (CMOS) devices. Recently, two-dimensional (2D) materials have been drawing tremendous attention in spintronics owing to their distinctive spin-dependent properties, such as the ultra-long spin relaxation time of graphene and the spin-valley locking of transition metal dichalcogenides. Moreover, the related heterostructures provide an unprecedented probability of combining the different characteristics via proximity effect, which could remedy the limitation of individual 2D materials. Hence, the proximity engineering has been growing extremely fast and has made significant achievements in the spin injection and manipulation. Nevertheless, there are still challenges toward practical application; for example, the mechanism of spin relaxation in 2D materials is unclear, and the high-efficiency spin gating is not yet achieved. In this review, we focus on 2D materials and related heterostructures to systematically summarize the progress of the spin injection, transport, manipulation, and application for information storage and processing. We also highlight the current challenges and future perspectives on the studies of spintronic devices based on 2D materials.

The interactions of the silane coupling agent methacryloxypropyltrimethoxysilane (MPS) with both fumed silica and a polymethylmethacrylate (PMMA) resin matrix were investigated using thermogravimetric analysis and Fourier transform infrared spectroscopy. OX 50 fumed silica was silanated with MPS at concentrations of 1% and 5% in aqueous ethanol (95%), acetone, and anhydrous toluene. Methyl methacrylate was polymerized with the silanated fumed silica (5% wt/wt) to form composites. The amount of MPS adsorption on the fumed silica and the amount of PMMA attached to the silanated fumed silica were determined by thermogravimetric analysis. MPS could be removed from the fumed silica after washing with methanol, but not after it underwent a drying process at 25 degrees C under vacuum. After vacuum drying at 25 degrees C, two types of adsorbed silane were found, i.e., firmly adsorbed and loosely adsorbed silane. The loosely adsorbed silane could desorb from silica and be incorporated into the polymer matrix through copolymerization with monomeric methyl methacrylate, resulting in crosslinking of the matrix. When the silanated silica was dried at 110 degrees C for 2 h, the loosely adsorbed silane was removed and the amount of firmly adsorbed silane increased. There was a positive correlation between the amount of firmly adsorbed MPS and the amount of PMMA attachment. The highest efficiency for PMMA attachment was found when MPS was adsorbed as a monolayer, because the loosely adsorbed silane did not contribute to the bonding of PMMA, and this suggested that not all of the double bonds of the MPS were accessible for reaction with the methacrylate monomer. Drying at 110 degrees C may also decrease the number of unsaturated double bonds of MPS.

To shed light on the mechanism responsible for the weak ferromagnetism in undoped wide band gap oxides, we carry out a comparative study on ZnO thin films prepared using both sol-gel and molecular beam epitaxy (MBE) methods. Compared with the MBE samples, the sol-gel derived samples show much stronger room temperature ferromagnetism with a magnetic signal persisting up to ∼740 K, and this ferromagnetic order coexists with a high density of defects in the form of zinc vacancies. The donor-acceptor pairs associated with the zinc vacancies also cause a characteristic orange-red photoluminescence in the sol-gel films. Furthermore, the strong correlation between the ferromagnetism and the zinc vacancies is confirmed by our first-principles density functional theory calculations, and electronic band alteration as a result of defect engineering is proposed to play the critical role in stabilizing the long-range ferromagnetism

Low-molecular-weight poly(ethylene oxide) (PEO) was grafted onto high-surface-area (A380) fumed silica (SiO2) by the use of a silane coupling agent, (CH3O)3−Si−(CH2)3−(OCH2CH2) x −OCH3, with x = 6−9, corresponding to an average molecular weight for the PEO segment of 375 g/mol, PEO(375)−silane. The PEO-grafted silica was characterized by thermogravimetric analysis and differential scanning calorimetry. In the case of PEO(375)−SiO2, the maximum grafting ratio, σ ∼ 2 molecules/nm2 (approximately 33 wt %), corresponded to less coverage than that expected for a monolayer of crystalline upright chains. No crystallization was observed, and the glass transition temperature, T g, increased from −90 °C for the unattached PEO(375)−silane to −54 °C for the attached PEO(375)−SiO2 chains. In the case of PEO(5000)−SiO2, a similar maximum weight percent coverage (∼38%), corresponding to σ ∼ 0.2 molecules/nm2, was obtained. At the highest grafting ratio, the calculated unperturbed chain dimensions in solution were approximately the same as those of the area occupied by the grafted PEO(5000) chains. A melt endotherm, with a melt temperature, T m, and enthalpy, ΔH m, that were decreased with respect to the neat PEO(5000)−silane, but no Tg, was observed. With decreasing σ, as the surface area occupied by the grafted chains increased with respect to the calculated chain dimensions in solution, ΔH m, T m, and the crystallization temperature, T c, decreased. The results suggest that the interaction of ethylene oxide segments with surface silanols inhibits the chain mobility necessary for crystallization.