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...

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.

3799 www.MaterialsViews.com wileyonlinelibrary.com well as in providing a template for generating strong surface plasmon resonances (SPR). [12][13][14][15][16] They have also been used for a variety of sensing applications including chemical and biochemical sensors. [17][18][19][20][21] In principle, solid metals can be replaced by liquid metals to form "liquid metal"/"metal oxides" (LM/MO) structures. Interestingly, despite their immense potentials, LM/MO structures have rarely been reported. [ 22 ] Furthermore, none of these works take advantage of the nature of the incorporated liquid metals. In addition to the well-known benefi ts that solid metals can offer, liquid metals add extra dimensions to the structures, which originate from their soft and liquid nature. This brings fl exibility, the possibility of amalgamation with other metals and their recoverability, mobility and high conformation to the system.We have previously shown the possibility of coating relatively large liquid metal droplets of galinstan using metal oxide nanoparticles. [23][24][25] By doing this, we created liquid metal marbles with extraordinary physical and chemical properties. Our investigations associated these properties to the interfaces between liquid metal and metal oxide nanoparticles in combination with the fl exibility of the marbles, thereby providing extra degrees of freedom in order to manipulate their functionalities on demand. However, the properties of large liquid metal marbles are strongly surface dependent and the bulk of the droplet is mostly redundant. For using the bulk of liquid metals, it should be divided into the smallest possible stable entities.It has been demonstrated that sonication of bulk liquid metal droplets can produce micro-, meso-, and nanosized liquid metal spheres. Previous reports show that thiol-stabilized mercury and EGaIn (75 wt% Ga, 25 wt% In) liquid metal droplets with dimensions in the order of micro-to nanometer can be successfully synthesized through sonication. [ 26,27 ] In this work, we utilize micro-to nanosized galinstan spheres with coated metal oxide nanoparticles to form the LM/ MO spherical structures suspended in aqueous solutions. Galinstan (68.5 wt% Ga, 21.5 wt% In, and 10 wt% Sn) is chosen as it poses less health hazards in comparison to liquid metals such as mercury. The surface metal oxide nanoparticles are either inherently formed during the synthesis process or coated onto the surface of galinstan spheres. We fully characterize the LM/MO spherical structures in terms of stoichiometry and optical properties, including the demonstration of plasmon A new platform described as the liquid metal/metal oxide (LM/MO) framework is introduced. The constituent spherical structures of these frameworks are made of micro-to nanosized liquid metal spheres and nanosized metal oxides, combining the advantages of both materials. It is shown that the diameters of the spheres and the stoichiometry of the structures can be actively controlled. Additionally, the liquid suspension of these sphere...

It is known that the unique layered structure of orthorhombic MoO3 (α-MoO3) facilitates the interaction with H2 gas molecules and that the surface-to-volume ratios of the crystallites play an important role in the process. MoO3 was deposited on a wide variety of transparent substrates using thermal evaporation in order to alter the surface-to-volume ratios of the crystallites. In situ Raman spectroscopy was employed to investigate the interaction between MoO3 and 1% H2 in both N2 and synthetic air environments, while incorporating Pd as a catalyst at room temperature. This study confirmed that the layered MoO3 with a high surface-to-volume ratio facilitated the H2 gas interaction. The Raman spectroscopy studies revealed that the H+ ions mainly interacted with the doubly coordinated oxygen atoms and caused the crystal transformation from the original α-MoO3 into the mixed structure of hydrogen molybdenum bronze and substoichiometric MoO3, eventually forming oxygen vacancies and water. It was also found that the presence of O2 during the H2 gas exposure caused the recombination of a number of oxygen vacancies and reduced the available surface catalytic sites for H2.

αand β-Phase MoO 3 are synthesized using an electrodeposition method on fluorine-doped tin oxide (FTO) glass substrates from sodium-molybdate (Na 2 MoO 4 ) solutions. We show that it is possible to obtain both αand β-MoO 3 by manipulating the cyclic voltammetry (CV) parameters during electrodeposition. Raman spectroscopy, X-ray diffraction, and scanning electron microscopy indicate that the applied potential range and sweep rate are strongly influential on the phase obtained and the surface morphology of the electrodeposited thin films. Gasochromic measurements were carried out on the annealed samples by exposing them to H 2 gas. It was revealed that α-MoO 3 thin films provided better response to H 2 interaction than β-MoO 3 films did. Additionally, porous films provided significantly larger responses than smooth films.