appreciable free carrier concentration. [5][6][7] The same strategy can potentially be implemented in selected 2D semiconductors. Another concern is the damping losses that should be kept low for applications such as optical communications, in which a long propagation of waves is necessary. [ 7 ] Reducing such damping losses requires that the product of the effective electron mass and the free charge mobility must be large in the 2D material. As a result, fi nding favorable materials that satisfy the aforementioned conditions are necessary for advancing the fi eld of 2D plasmonics.The creation of stable 2D semiconducting oxides of tungsten and molybdenum is possible, as we demonstrated previously. [ 8,9 ] In a recent topical feature article, Gregorieva and Geim have separated out these oxides as a unique group of 2D materials and predicted their signifi cant role in the future of planar structures. [ 10 ] The impact of these two metal oxides can be extended into the plasmonic realm, and, in fact, plasmon resonances in the one-dimensional (1D) morphologies of these two oxides have recently been demonstrated. Manthiram and Alivisatos reported plasmon resonances in 1D sub-stoichiometric semiconducting tungsten oxide, [ 6 ] while Huang et al. have shown the generation of plasmon resonances in 1D tubular reduced molybdenum oxide suspensions. [ 5 ] Advantageously both tungsten and molybdenum oxides can be ultra-doped and have also large dielectric constants, which both are important factors for obtaining plasmon resonances in the near IR and visible regions. [ 2 ] In 1D sub-stoichiometric tungsten and molybdenum oxides, the plasmon resonances are a function of two modest depolarization factors along the cross section of the 1D structure ( Figure 1 a -Supporting Information, Section S1 for the equations). However, the existence of one large depolarization factor reduces the wavelength of the plasmon resonances in 2D structures of similar stoichiometry.Accordingly, here, we explore tunable plasmonics in substoichiometric 2D molybdenum oxide nanofl akes in the visible range. The unique properties of 2D molybdenum oxide such as the possibility of high level ionic intercalation (hence ultradoping), large permittivity and the effect of the depolarization factor in 2D fl akes are used for demonstrating tunable plasmon resonance in this range. We investigate the effect of intercalating ions and changing the lateral dimensions of the fl akes on the plasmon resonance peaks of a reduced quasi-metallic form of molybdenum oxide.Molybdenum trioxide (MoO 3 ) is a stable n -type semiconductor under a wide range of conditions with a bandgap of ca. 3.2 eV, which is capable of adsorbing energy from a small portion of the visible light spectrum. [ 5,11 ] The most frequently 2D materials exhibit certain physical and chemical properties that are fundamentally different from their bulk counterparts. [ 1,2 ] The electronic and optical properties seen in the selected 2D materials may lead to signifi cantly altered plasmon dispersion relationsh...

We demonstrate that the energy bandgap of layered, high-dielectric α-MoO(3) can be reduced to values viable for the fabrication of 2D electronic devices. This is achieved through embedding Coulomb charges within the high dielectric media, advantageously limiting charge scattering. As a result, devices with α-MoO(3) of ∼11 nm thickness and carrier mobilities larger than 1100 cm(2) V(-1) s(-1) are obtained.

Two-dimensional van der Waals materials have demonstrated fascinating optical and electrical characteristics. However, reports on magnetic properties and spintronic applications of van der Waals materials are scarce by comparison. Here, we report anomalous Hall effect measurements on single crystalline metallic Fe3GeTe2 nanoflakes with different thicknesses. These nanoflakes exhibit a single hard magnetic phase with a near square-shaped magnetic loop, large coercivity (up to 550 mT at 2 K), a Curie temperature near 200 K and strong perpendicular magnetic anisotropy. Using criticality analysis, the coupling length between van der Waals atomic layers in Fe3GeTe2 is estimated to be ~5 van der Waals layers. Furthermore, the hard magnetic behaviour of Fe3GeTe2 can be well described by a proposed model. The magnetic properties of Fe3GeTe2 highlight its potential for integration into van der Waals magnetic heterostructures, paving the way for spintronic research and applications based on these devices.

Two-dimensional (2D) transition metal dichalcogenide semiconductors offer unique electronic and optical properties, which are significantly different from their bulk counterparts. It is known that the electronic structure of 2D MoS2, which is the most popular member of the family, depends on the number of layers. Its electronic structure alters dramatically at near atomically thin morphologies, producing strong photoluminescence (PL). Developing processes for controlling the 2D MoS2 PL is essential to efficiently harness many of its optical capabilities. So far, it has been shown that this PL can be electrically or mechanically gated. Here, we introduce an electrochemical approach to actively control the PL of liquid-phase-exfoliated 2D MoS2 nanoflakes by manipulating the amount of intercalated ions including Li(+), Na(+), and K(+) into and out of the 2D crystal structure. These ions are selected as they are crucial components in many bioprocesses. We show that this controlled intercalation allows for large PL modulations. The introduced electrochemically controlled PL will find significant applications in future chemical and bio-optical sensors as well as optical modulators/switches.

Planar two-dimensional (2D) materials are possibly the ideal channel candidates for future field effect transistors (FETs), due to their unique electronic properties. However, the performance of FETs based on 2D materials is yet to exceed those of conventional silicon based devices. Here we present a 2D channel thin film made from liquid phase exfoliated molybdenum oxide nanoflake inks with highly controllable sub-stoichiometric levels. The ability to induce oxygen vacancies by solar light irradiation in an aqueous environment allows the tuning of electronic properties in 2D sub-stoichiometric molybdenum oxides (MoO 3-x ). The highest mobility is found to be ~ 600 cm 2 V −1 s −1 with an estimated free electron concentration of ~ 1.610 21 cm -3 and an optimal I On /I Off ratio of >10 5 for the FETs made of 2D flakes irradiated for 30 min (x = 0.042). These values are significant and represent a real opportunity to realize the next generation of tunable electronic devices using electronic inks.