Tunable Schottky Barrier and Efficient Ohmic Contacts in MSi₂N₄ (M = Mo, W)/2D Metal Contacts

Monolayer MSi2N4 (M = Mo, W) has been fabricated and proposed as a promising channel material for field-effect transistors (FETs) due to the high electron/hole mobility. However, the barrier between the metal electrode and MSi2N4 will affect device performance. Hence, it is desirable to reduce the barrier for achieving high-performance electrical devices. Here, using density functional theory (DFT) calculations, we systematically investigate the electrical properties of the van der Waals (vdW) contacts formed between MSi2N4 and two-dimensional (2D) metals (XY2, X = Nb, Ta, Y = S, Se, Te). It is found that the contact types and Schottky barrier height (SBH) of MSi2N4/XY2 can be effectively tuned by selecting 2D metals with different work functions (WFs). Specifically, n- and p-type Schottky contacts and Ohmic contacts can be achieved in MSi2N4/XY2. Among them, MoSi2N4/H-NbS2, WSi2N4/H-XS2, and WSi2N4/H-NbSe2 present Ohmic contacts due to the high WF of 2D metals. Notably, the pinning factors of MSi2N4/XY2 are obviously larger than those of the other 2D semiconductor/metal contacts, indicating that the Fermi-level pinning (FLP) effect is weak in MSi2N4/XY2. Therefore, vdW stack engineering can strongly weaken the FLP effect, making the Schottky barrier tunable in MSi2N4/XY2 by choosing 2D metals with different WFs. The results provide important insights into the selection of appropriate electrodes and valuable guidance for the development of MSi2N4-based 2D electronic devices with high performance

Emerixanthone E, a new xanthone derivative from deep sea fungus <i>Emericella</i> sp SCSIO 05240

<p>The marine fungus <i>Emericella</i> sp was isolated from the deep sea sediments. The fungus was identified by its morphology and ITS region. A new emerixanthone E (<b>1</b>) together with four (<b>2–5</b>) known emodin derivatives were isolated from the metabolites of the fungus <i>Emericella</i> SCSIO05240. The structures were elucidated on the basis of NMR spectroscopic analysis and mass spectrometry. The biological properties of those compounds (<b>1–5</b>) were explored for antimicrobial, antifungal and antitumor activity.</p

Westerdijkin A, a new hydroxyphenylacetic acid derivative from deep sea fungus <i>Aspergillus westerdijkiae</i> SCSIO 05233

<div><p>A new methyl 2-(4-((2-hydroxy-3-methylbut-3-en-1-yl)oxy)phenyl) acetate <b>1</b>, together with five known compounds <b>2</b>–<b>6</b>, was isolated from the culture of the deep sea-derived fungus <i>Aspergillus westerdijkiae</i> SCSIO 05233. The new structure was determined by NMR (¹H and ¹³C NMR, HSQC, HMBC and MS) and optical rotation analysis. Compound <b>5</b> displayed weak inhibitory activities towards K562 and promyelocytic HL-60 with IC₅₀ values of 25.8 and 44.9 μM, and compound <b>6</b> showed strong antifouling activity with EC₅₀ value 8.81 μg/mL.</p></div

Axinelline A, a new COX-2 inhibitor from <i>Streptomyces axinellae</i> SCSIO02208

<div><p>Axinelline A, a new cyclooxygenase-2 (COX-2) inhibitor, was isolated from <i>Streptomyces axinellae</i> SCSIO02208. The structures of compounds <b>1</b>–<b>9</b> were determined by analysing the NMR and MS data. The absolute configuration of <b>1</b> was determined by using optical rotation and comparing with the reported data. Compound <b>1</b> exhibited COX-2 inhibitory activity, the IC₅₀ value being 2.8 μM.</p></div

Ascomycotin A, a new citromycetin analogue produced by <i>Ascomycota</i> sp. Ind19F07 isolated from deep sea sediment

<div><p>A new citromycetin analogue, ascomycotin A (<b>1</b>), together with eight known compounds, wortmannilactone E (<b>2</b>), orcinol (<b>3</b>), orsellinic acid (<b>4</b>), isosclerone (<b>5</b>), (3<i>R</i>,4<i>S</i>)-( − )-4-hydroxymellein (<b>6</b>), diorcinol (<b>7</b>), chaetocyclinone B (<b>8</b>) and 2,5-dimethoxy-3,6-di(<i>p</i>-methoxypheny1)-1,4-benzoquinone (<b>9</b>), was isolated from the fungal strain <i>Ascomycota</i> sp. Ind19F07, which was isolated from the deep sea sediment of the Indian Ocean. The structures of the compounds were established by spectroscopic data including 1D and 2D NMR and HR-ESI-MS. Compounds (<b>1</b>–<b>9</b>) were evaluated for antibacterial activity.</p></div