One sentence summary:We describe a general liquid-phase method to exfoliate layered compounds to give monoand few-layer flakes in large quantities. TMDs consist of hexagonal layers of metal atoms, M, sandwiched between two layers of chalcogen atoms, X, with stoichiometry MX 2 . While the bonding within these tri-layer sheets is covalent, adjacent sheets stack via van der Waals interactions to form a 3D crystal. TMDs occur in more than 40 different types (2, 3) depending on the combination of chalcogen (S, Se or Te) and transition metal(3). Depending on the co-ordination and oxidation state of the metal atoms, TMDs can be metallic, semi-metallic or semiconducting(2, 3), e.g. WS 2 is a semiconductor while NbSe 2 is a metal(3). In addition, superconductivity(4) and charge density wave effects(5) have been observed in some TMDs. This versatility makes them potentially useful in many areas of electronics.However, like graphene(6), layered materials must be exfoliated to fulfil their full potential. For example, films of exfoliated Bi 2 Te 3 should display enhanced thermoelectric efficiency by suppression of thermal conductivity(7). Exfoliation of 2D topological insulators such as Bi 2 Te 3 and Bi 2 Se 3 would reduce residual bulk conductance, 4 highlighting surface effects. In addition, we can expect changes in electronic properties as the number of layers is reduced e.g. the indirect bandgap of bulk MoS 2 becomes direct in few-layer flakes(8). Although exfoliation can be achieved mechanically on a small scale(9, 10), liquid phase exfoliation methods are required for many applications(11).Critically, a simple liquid exfoliation method would allow the formation of novel hybrid and composite materials. While TMDs can be chemically exfoliated in liquids(12-14), this method is time consuming, extremely sensitive to the environment and incompatible with most solvents.We demonstrate exfoliation of bulk TMD crystals in common solvents to give mono-and few layer nano-sheets. This method is insensitive to air and water and can potentially be scaled up to give large quantities of exfoliated material. In addition, we show that this procedure allows the formation of hybrid films with enhanced properties.We initially sonicated commercial MoS 2 , WS 2 and BN (15, 16) powders in a number of solvents with varying surface tensions. The resultant dispersions were centrifuged and the supernatant decanted (Section S3). Optical absorption spectroscopy showed that the amount of material retained (characterised by / A l C α = , where A/l is the absorbance per length, α is the extinction coefficient and C is the concentration) was maximised for solvents with surface tension close to 40 mJ/m 2 (17, 18) ( Fig. 1A-C). Detailed analysis, within the framework of Hansen solubility parameter theory(19), shows successful solvents to be those with dispersive, polar and H-bonding components of the cohesive energy density within certain well-defined ranges (Section S4, Figs. S2-S3). This can be interpreted to mean that successful solvents are those w...

The magnetoresistance ͑MR͒ behavior of epitaxial magnetite Fe 3 O 4 grown on low-vicinal ͑small miscut͒ and high-vicinal ͑large miscut͒ MgO substrates is compared. Magnetization measurements on Fe 3 O 4 films on high-vicinal substrates showed reduced magnetic moment as compared with the films grown on low-vicinal MgO, which correlates well with the expected reduction in magnetic moment due to step edge induced additional antiphase boundaries ͑APBs͒ with out-of-plane shift vectors. The MR is significantly higher ͑12.3% at 2 T͒ for a 45 nm Fe 3 O 4 film on high-vicinal substrate than that observed ͑7.2% at 2 T͒ for a film on low-vicinal substrate. A strong anisotropy in the MR is observed in correlation with the direction of atomic step edges. In addition to the increase in MR, the field dependency of the MR is also modified. The observed modification in the magnetotransport behavior of epitaxial Fe 3 O 4 films is attributed to an enhanced spin scattering arising due to the presence of atomic height steps that lead to the formation of a greater density of antiferromagnetically coupled APBs.

Magnetization studies on well characterized epitaxial magnetite ͑Fe 3 O 4 ͒ thin films grown on MgO͑100͒ show that the ultrathin films ͑Ͻ5 nm thickness͒ are ferromagnetic and their magnetic moments are much greater than those of bulk magnetite, particularly at a thickness of 20 nm or below. The observation of a ferromagnetic nature in ultrathin magnetite films ͑Ͻ5 nm͒ is in contrast to the previously accepted dead layer interface model or a superparamagnetic behavior for ultrathin films of magnetite. From detailed spin-polarized density functional theory based calculations of Fe 3 O 4 -MgO interface, we calculate a deviation in spin moment of the Fe atoms in the vicinity of the interface from their bulk values, which is insufficient to explain the observed results. Orbital moment contribution for the surface Fe atoms was found to be quite small. The noncompensation of spin moments between the tetrahedral ͑A͒ and octahedral ͑B͒ sublattices at the surface and antiphase-domain boundaries are inferred to be the main factor contributing to the observed enhanced magnetic moment.

Strain relaxation studies in epitaxial magnetite ͑Fe 3 O 4 ͒ thin films grown on MgO ͑100͒ substrates using high-resolution x-ray diffraction and cross-sectional transmission electron microscopy reveal that the films remain fully coherent up to a thickness of 700 nm. This thickness is much greater than the critical thickness t c for strain relaxation estimated from mismatch strain. Anomalous strain relaxation behavior of Fe 3 O 4 / MgO heteroepitaxy is attributed to the reduction in the effective stress experienced by the film due to the presence of antiphase boundaries ͑APBs͒ that enable the film to maintain coherency with the substrate at large thickness. However, the stress accommodation in the film depends upon the nature and density of the APBs.

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