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Ultralight multiwalled carbon nanotube (MWCNT) aerogel is fabricated from a wet gel of well-dispersed pristine MWCNTs. On the basis of a theoretical prediction that increasing interaction potential between CNTs lowers their critical concentration to form an infinite percolation network, poly(3-(trimethoxysilyl) propyl methacrylate) (PTMSPMA) is used to disperse and functionalize MWCNTs where the subsequent hydrolysis and condensation of PTMSPMA introduces strong and permanent chemical bonding between MWCNTs. The interaction is both experimentally and theoretically proven to facilitate the formation of a MWCNT percolation network, which leads to the gelation of MWCNT dispersion at ultralow MWCNT concentration. After removing the liquid component from the MWCNT wet gel, the lightest ever free-standing MWCNT aerogel monolith with a density of 4 mg/cm(3) is obtained. The MWCNT aerogel has an ordered macroporous honeycomb structure with straight and parallel voids in 50-150 μm separated by less than 100 nm thick walls. The entangled MWCNTs generate mesoporous structures on the honeycomb walls, creating aerogels with a surface area of 580 m(2)/g which is much higher than that of pristine MWCNTs (241 m(2)/g). Despite the ultralow density, the MWCNT aerogels have an excellent compression recoverable property as demonstrated by the compression test. The aerogels have an electrical conductivity of 3.2 × 10(-2) S·cm(-1) that can be further increased to 0.67 S·cm(-1) by a high-current pulse method without degrading their structures. The excellent compression recoverable property, hierarchically porous structure with large surface area, and high conductivity grant the MWCNT aerogels exceptional pressure and chemical vapor sensing capabilities.

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By creating defects via oxygen plasma treatment, we demonstrate optical properties variation of single-layer MoS 2 . We found that, with increasing plasma exposure time, the photoluminescence (PL) evolves from very high intensity to complete quenching, accompanied by gradual reduction and broadening of MoS 2 Raman modes, indicative of distortion of the MoS 2 lattice after oxygen bombardment. X-ray photoelectron spectroscopy study shows the appearance of Mo 6+ peak, suggesting the creation of MoO 3 disordered regions in the MoS 2 flake. Finally, using band structure calculations, we demonstrate that the creation of MoO 3 disordered domains upon exposure to oxygen plasma leads to a direct to indirect bandgap transition in single-layer MoS 2 , which explains the observed PL quenching. KEYWORDS 2D materials, defect engineering, optical properties, bandgap tuning, molybdenum trioxide INTRODUCTIONThe ability to controllably tailor the properties of a material is a key factor in the development of many novel applications. In the case of bulk semiconductors, creating and manipulating defects constitutes an essential element in controlling the electrical, magnetic, and optical properties of the host material. 1 Although the role of defects is well understood in bulk semiconductors, it has received little attention in emerging two-dimensional (2D) layered semiconductors, preventing their full exploitation for tailored 2D nanoelectronic and photonic devices. Graphene and graphene oxide are examples of the impact that defects can have on 2D materials. Pristine graphene, which contains no intrinsic defect, is well known for its extraordinary high mobility, and is of great importance for high frequency device applications. 2, 3 However, its inherent lack of bandgap and low absorption of solar photons greatly limit its use in electronic and photonic devices. On the other hand, its solution processed counterparts, graphene oxide and reduced graphene oxide, have a large amount of defects, which lead to formation of a bandgap and open the way to many other applications in photodetectors, sensors, catalysis, and solar cell. [4][5][6][7][8] Recently, layered transition metal dichalcogenides (TMDs) have emerged as important materials for 2D device engineering. 9-11 Molybdenum disulfide (MoS 2 ), composed of weak van der Waals bonded S-Mo-S units, offers a large intrinsic bandgap that is strongly dependent on the number of layers, with an indirect bandgap (1.2 eV) in bulk MoS 2 transitioning to a direct

Despite many of the intriguing and excellent electrical, mechanical and optical properties of carbon nanotubes (CNTs), [1,2] extensive applications of these nanomaterials are still limited. One of the main challenges in carbon nanotube research field is the dispersion and stabilization of CNTs in different solvent media and polymer matrices. The as-synthesized CNTs are often bundled together due to strong van der Waals interactions between the nanotubes. There have been three most widely used methods to disperse CNTs into solvents and polymer matrices: [3] physical blending, [4][5][6] chemical functionalization, [7][8][9][10][11] and dispersants-assisted dispersion. [12][13][14][15][16] Each of these methods has its own advantages and disadvantages. For physical blending using mechanical forces such as sonication, although simple and cost effective, the dispersion quality is often the poorest. The so-dispersed nanotubes will quickly precipitate out again when sonication stops. For chemical modification and functionalization, CNTs are treated with strong oxidizing reagents to form functional groups such as carboxylic acids on the nanotube walls. CNTs can be made water or organic solvent soluble, depending on the modification degree and further molecular moieties attached to the nanotubes. Although most effective as a dispersion method, such treatment inevitably disrupts the long range p conjugation of the nanotube, often leads to decreased electrical conductivity, diminished mechanical strength, and other undesired properties. In the dispersants-assisted dispersion, a third component chemical is mixed with CNTs in solutions. Through sonication, the CNTs are mechanically de-bundled and then stabilized by a dispersant chemical through noncovalent interactions, therefore, avoiding the destruction of the chemical structures, electronic and mechanical properties of the carbon nanotubes. Recently, there are two types of materials that have attracted significant amount of attention as dispersants to assist carbon nanotube dispersion. One of these materials is the conjugated polymers, such as poly(m-phenylene vinylene), [17,18] poly(3-alkylthiophene), [19,20] and poly(arylene ethynylene). [21,22] These polymers stabilize carbon nanotubes by forming strong p-p stack interactions with carbon nanotube walls. However, the thus-formed dispersions have limited solubility and stability because the conjugated polymers themselves face solubility and miscibility issues due to the strong inter-chain p-p interactions. A second family of interesting materials with potential for third componentassisted carbon nanotube dispersion are block copolymers. [23][24][25] In general, the block copolymer is designed in such a way that one block of the polymer will form a close interaction with the carbon nanotube walls, while the other block(s) will provide the solubility to the exfoliated nanotubes by forming a steric barrier or repulsion interaction between polymer-wrapped nanotubes.[26] So far, a wide range of charged and neutral block copoly...

Achieving tunability of two dimensional (2D) transition metal dichalcogenides (TMDs) functions calls for the introduction of hybrid 2D materials by means of localized interactions with zero dimensional (0D) materials. A metal-semiconductor interface, as in gold (Au) - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science as it constitutes an outstanding platform to investigate plasmonic-exciton interactions and charge transfer. The applied aspects of such systems introduce new options for electronics, photovoltaics, detectors, gas sensing, catalysis, and biosensing. Here we consider pristine MoS2 and study its interaction with Au nanoislands, resulting in local variations of photoluminescence (PL) in Au-MoS2 hybrid structures. By depositing monolayers of Au on MoS2, we investigate the electronic structure of the resulting hybrid systems. We present strong evidence of PL quenching of MoS2 as a result of charge transfer from MoS2 to Au: p-doping of MoS2. The results suggest new avenues for 2D nanoelectronics, active control of transport or catalytic properties.

We report ultrahigh density assembly of aligned single-walled carbon nanotube (SWNT) two-dimensional arrays via AC dielectrophoresis using high-quality surfactant-free and stable SWNT solutions. After optimization of frequency and trapping time, we can reproducibly control the linear density of the SWNT between prefabricated electrodes from 0.5 SWNT/μm to more than 30 SWNT/μm by tuning the concentration of the nanotubes in the solution. Our maximum density of 30 SWNT/μm is the highest for aligned arrays via any solution processing technique reported so far. Further increase of SWNT concentration results in a dense array with multiple layers. We discuss how the orientation and density of the nanotubes vary with concentrations and channel lengths. Electrical measurement data show that the densely packed aligned arrays have low sheet resistances. Selective removal of metallic SWNTs via controlled electrical breakdown produced field-effect transistors with high current on-off ratio. Ultrahigh density alignment reported here will have important implications in fabricating high-quality devices for digital and analog electronics.

We demonstrate that the electrical property of a single layer molybdenum disulfide (MoS 2 ) can be significantly tuned from semiconducting to insulating regime via controlled exposure to oxygen plasma. The mobility, on-current and resistance of single layer MoS 2 devices were varied up to four orders of magnitude by controlling the plasma exposure time. Raman spectroscopy, X-ray photoelectron spectroscopy and density functional theory studies suggest that the significant variation of electronic properties is caused by the creation of insulating MoO 3 -rich disordered domains in the MoS 2 sheet upon oxygen plasma exposure, leading to an exponential variation of resistance and mobility as a function of plasma exposure time. The resistance variation calculated using an effective medium model is in excellent agreement with the measurements. The simple approach described here can be used for the fabrication of tunable two dimensional nanodevices on MoS 2 and other transition metal dichalcogenides.