Influence of Gas Adsorption and Gold Nanoparticles on the Electrical Properties of CVD-Grown MoS₂ Thin Films

Molybdenum disulfide (MoS₂) has increasingly attracted attention from researchers and is now one of the most intensively explored atomic-layered two-dimensional semiconductors. Control of the carrier concentration and doping type of MoS₂ is crucial for its application in electronic and optoelectronic devices. Because the MoS₂ layers are atomically thin, their transport characteristics may be very sensitive to ambient gas adsorption and the resulting charge transfer. We investigated the influence of the ambient gas (N₂, H₂/N₂, and O₂) choice on the resistance (<i>R</i>) and surface work function (WF) of trilayer MoS₂ thin films grown via chemical vapor deposition. We also studied the electrical properties of gold (Au)-nanoparticle (NP)-coated MoS₂ thin films; their <i>R</i> value was found to be 2 orders of magnitude smaller than that for bare samples. While the WF largely varied for each gas, <i>R</i> was almost invariant for both the bare and Au-NP-coated samples regardless of which gas was used. Temperature-dependent transport suggests that variable range hopping is the dominant mechanism for electrical conduction for bare and Au-NP-coated MoS₂ thin films. The charges transferred from the gas adsorbates might be insufficient to induce measurable <i>R</i> change and/or be trapped in the defect states. The smaller WF and larger localization length of the Au-NP-coated sample, compared with the bare sample, suggest that more carriers and less defects enhanced conduction in MoS₂

Preparation and characterization of adefovir dipivoxil–stearic acid cocrystal with enhanced physicochemical properties

<p>The objectives of this study were to prepare cocrystal composed of adefovir dipivoxil (AD) and stearic acid (SA) and to investigate the enhanced properties of the cocrystal. The cocrystal was prepared by antisolvent precipitation and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRPD), and differential scanning calorimetry (DSC). The enhanced properties were evaluated by dissolution testing, permeability studies, and powder rheology analysis. The AD raw material has a cuboid-like crystal and the cocrystal has a needle shape. In the FT-IR study, there were bathochromic shifts caused by the hydrogen bonding. The melting point of the cocrystal was 52.9 °C, which was lower than that of AD. The XRPD pattern also had distinct differences, supporting the formation of a new crystalline form. The cocrystal showed changes in the lattice energy and the solvation strength, which caused an enhanced dissolution. The permeability was increased due to the SA, which acts as a P-gp inhibitor. The tabletability was enhanced due to the altered crystal habit. In conclusion, cocrystal containing AD and SA was successfully prepared, presenting advantages such as enhanced solubility, tabletability, and permeability. The use of the cocrystal is a desirable approach for the improved physicochemical properties.</p

Influence of Gas Ambient on Charge Writing at the LaAlO₃/SrTiO₃ Heterointerface

We investigated the influences of charge writing on the surface work function (<i>W</i>) and sheet resistance (<i>R</i>) of the LaAlO₃/SrTiO₃ (LAO/STO) heterointerface in several gas environments: H₂(2%)/N₂(98%), air, N₂, and O₂. The decrease in <i>W</i> and <i>R</i> due to charge writing was much larger in air (Δ<i>W</i> = −0.45 eV and Δ<i>R</i> = −40 kΩ/<i>S</i>) than in O₂ (Δ<i>W</i> = −0.21 eV and Δ<i>R</i> = −19 kΩ/<i>S</i>). The reduced <i>R</i> could be maintained more than 100 h in H₂/N₂. Such distinct behaviors were quantitatively discussed, based on the proposed charge-writing mechanisms. Such analyses showed how several processes, such as carrier transfer via surface adsorbates, surface redox, electronic state modification, and electrochemical surface reactions, contributed to charge writing in each gas

Polarization-Independent Light Emission Enhancement of ZnO/Ag Nanograting via Surface Plasmon Polariton Excitation and Cavity Resonance

In this study, we observed that the photoluminescence (PL) intensity of ZnO/Ag nanogratings was significantly enhanced compared with that of a planar counterpart under illumination of both transverse magnetic (TM) and transverse electric (TE)-mode light. In the TM mode, angle-resolved reflectance spectra exhibited dispersive dips, indicating cavity resonance as well as grating-coupled surface plasmon polariton (SPP) excitation. In the TE mode, cavity resonance only was allowed, and broad dips appeared in the reflectance spectra. Strong optical field confinement in the ZnO layers, with the help of SPP and cavity modes, facilitated polarization-insensitive PL enhancement. Optical simulation results were in good agreement with the experimental results, supporting the suggested scenario

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<div> <div> <div> <p>Changes in prevalence of periodontal disease from 2002 to 2013. </p> </div> </div> </div

Prevention of polydimethylsiloxane microsphere migration using a mussel-inspired polydopamine coating for potential application in injection therapy

<div><p>The use of injectable bulking agents is a feasible alternative procedure for conventional surgical therapy. In this study, poly(dimethylsiloxane) (PDMS) microspheres coated with polydopamine (PDA) were developed as a potential injection agent to prevent migration in vocal fold. Uniform PDMS microspheres are fabricated using a simple fluidic device and then coated with PDA. Cell attachment test reveals that the PDA-coated PDMS (PDA-PDMS) substrate favors cell adhesion and attachment. The injected PDA-PDMS microspheres persist without migration on reconstructed axial CT images, whereas, pristine PDMS locally migrates over a period of 12 weeks. The gross appearance of the implants retrieved at 4, 8, 12 and 34 weeks indicates that the PDA-PDMS group maintained their original position without significant migration until 34 weeks after injection. By contrast, there is diffuse local migration of the pristine PDMS group from 4 weeks after injection. The PDA-coated PDMS microspheres can potentially be used as easily injectable, non-absorbable filler without migration.</p></div

Serial endoscopic analysis of a larynx.

<p>CaHA (A) and PDA-coated PDMS (B) microspheres were injected to the larynx. The position of the microspheres were indicated by the black arrows. The images were obtained immediately after the injection; 1 week after the injection; and 2, 4, 8, 12 and 34 weeks after the injection. CaHA leaked out from the puncture site immediately after the injection. Most of the injected PDA-coated PDMS microspheres remained at the injection site. The left vocal folds were augmented significantly greater in the PDA-coated PDMS group than in the CaHA group during the entire follow-up period. In contrast, there was a significant volume reduction of CaHA from the first week after injection.</p

Band Alignment at Au/MoS₂ Contacts: Thickness Dependence of Exfoliated Flakes

We investigated the surface potential (<i>V</i>_surf) of exfoliated MoS₂ flakes on bare and Au-coated SiO₂/Si substrates using Kelvin probe force microscopy. The <i>V</i>_surf of MoS₂ single layers was larger on the Au-coated substrates than on the bare substrates; our theoretical calculations indicate that this may be caused by the formation of a larger electric dipole at the MoS₂/Au interface leading to a modified band alignment. <i>V</i>_surf decreased as the thickness of the flakes increased until reaching the bulk value at a thickness of ∼20 nm (∼30 layers) on the bare and ∼80 nm (∼120 layers) on the Au-coated substrates, respectively. This thickness dependence of <i>V</i>_surf was attributed to electrostatic screening in the MoS₂ layers. Thus, a difference in the thickness at which the bulk <i>V</i>_surf appeared suggests that the underlying substrate has an effect on the electric-field screening length of the MoS₂ flakes. This work provides important insights to help understand and control the electrical properties of metal/MoS₂ contacts

Three-dimensionally reconstructed microCT images.

<p>PDA-PDMS microspheres were maintained without migration until 12 weeks after the injection. However, pristine PDMS migrated locally over a period of 12 weeks (A-D). Normalized aspect ratio of the injected area for PDMS and PDA-PDMS microspheres (n = 3) (E).</p

Axial cross-section image of the mouse’s back (H&E stain).

<p>Low-power-field views (×12.5) of the implants indicated that the injected PDA-coated PDMS lacked significant migration at 4 weeks (A, right arrow). There was a significant local migration of the pristine PDMS group through the potential fascia space from 4 weeks after injection (A, left arrow). In the PDA-coated PDMS group at 4 weeks, significantly more cells migrated between each microsphere in the high-power-field views (×400) (B). Markedly more residual material was observed in the PDA-coated PDMS group than in the pristine PDMS group at 34 weeks after the injection (C, right arrow). However, most of the injected pristine PDMS was not identified at 34 weeks (C, left arrow) in the low-power-field view (×12.5). Most of the pristine PDMS microspheres hardly adhered to each other. In contrast, the PDA-coated PDMS surface was found to be aggregated until 34 weeks after the injection under the high-power field view (×400) (D).</p