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We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics.

Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phonon dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon-phonon scattering. Our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials.

The authors report hereinin vitroantibacterial property and osteoblast biocompatibility of electrospun Ag doped HAp/PHBV (Ag-HAp/PHBV) composite nanofibers as an osteoconductive and antibacterial material for bone tissue engineering applications. Ag-HAp powders were synthesized and stable composite suspensions of Ag-HAp/PHBV were prepared with the aid of a cationic surfactant DTAB for the electrospinning process. Continuous and uniform composite nanofibers were generated within a diameter range of 400–900 nm. Obtained nanocomposite scaffolds provide a favorable environment for bone mineralization, SaOS-2 osteoblastic cell attachment and growth as well as they present antibacterial activity againstE. coliandS. aureusbacteria without any noticeable cytotoxic effect. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a new procedure for the direct determination of picomolar levels of iron in water is presented. Ethyl cellulose (EC) based nano-fibers were fabricated by electrospinning technique. The limit of detection for Fe3+ is 0.07pM (based on 3s of the blank, n =4). A fluorescent chromoionophore and an ionic liquid were used together as sensing agent and signal stabilizer additives, respectively. The offered composite displayed a sensitive response for Fe3+ ions over a wide concentration range [1.0×10−12–1.0×10−6 M]. The sensing design exhibited a response time of less than 30 s which is one of the shortest reported responses among similar solid state sensing agents. The sensor was fully reversible and regeneration time was shorter than 60s. Preliminary results show that sensitivity and selectivity of the nanofibrous membranes to detect Fe3+ ions are higher than those reported previously. Additionally, the exploited nanostructures provided faster sensor dynamics in applications. [Copyright &y& Elsevier]

Optoelectronic excitations in monolayer MoS2 manifest from a hierarchy of electrically tunable, Coulombic free-carrier and excitonic many-body phenomena. Investigating the fundamental interactions underpinning these phenomena--critical to both many-body physics exploration and device applications--presents challenges, however, due to a complex balance of competing optoelectronic effects and interdependent properties. Here, optical detection of bound- and free-carrier photoexcitations is used to directly quantify carrier-induced changes of the quasiparticle band gap and exciton binding energies. The results explicitly disentangle the competing effects and highlight longstanding theoretical predictions of large carrier-induced band gap and exciton renormalization in two-dimensional semiconductors. [ABSTRACT FROM AUTHOR]

Monolayers of group VI transition metal dichalcogenides possess direct gaps in the visible spectrum with the exception of MoTe2, where its gap is suitably located in the infrared region but its stability is of particular interest, as tellurium compounds are acutely sensitive to oxygen exposure. Here, our environmental (time-dependent) measurements reveal two distinct effects on MoTe2 monolayers: For weakly luminescent monolayers, photoluminescence signal and optical contrast disappear, as if they are decomposed, but yet remain intact as evidenced by AFM and Raman measurements. In contrast, strongly luminescent monolayers retain their optical contrast for a prolonged amount of time, while their PL peak blue-shifts and PL intensity saturates to slightly lower values. Our X-ray photoelectron spectroscopy measurements and DFT calculations suggest that the presence of defects and functionalization of these defect sites with O2 molecules strongly dictate their material properties and aging response by changing the excitonic dynamics due to deep or shallow states that are created within the optical band gap. Presented results not only shed light on environmental effects on fundamental material properties and excitonic dynamics of MoTe2 monolayers but also highlight striking material transformation for metastable 2D systems such as WTe2, silicone, and phosphorene.