Modulation of New Excitons in Transition Metal Dichalcogenide‐Perovskite Oxide System
Xinmao YinMing YangChi Sin TangQixing WangLei XuJing WuPaolo E. TrevisanuttoShengwei ZengXin Yu ChinTeguh Citra AsmaraYuan Ping FengAriando AriandoManish ChhowallaShijie WangWenjing ZhangAndrivo RusydiAndrew T. S. Wee
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The exciton, a quasi-particle that creates a bound state of an electron and a hole, is typically found in semiconductors. It has attracted major attention in the context of both fundamental science and practical applications. Transition metal dichalcogenides (TMDs) are a new class of 2D materials that include direct band-gap semiconductors with strong spin-orbit coupling and many-body interactions. Manipulating new excitons in semiconducting TMDs could generate a novel means of application in nanodevices. Here, the observation of high-energy excitonic peaks in the monolayer-MoS2 on a SrTiO3 heterointerface generated by a new complex mechanism is reported, based on a comprehensive study that comprises temperature-dependent optical spectroscopies and first-principles calculations. The appearance of these excitons is attributed to the change in many-body interactions that occurs alongside the interfacial orbital hybridization and spin-orbit coupling brought about by the excitonic effect propagated from the substrate. This has further led to the formation of a Fermi-surface feature at the interface. The results provide an atomic-scale understanding of the heterointerface between monolayer-TMDs and perovskite oxide and highlight the importance of spin-orbit-charge-lattice coupling on the intrinsic properties of atomic-layer heterostructures, which open up a way to manipulate the excitonic effects in monolayer TMDs via an interfacial system.Template
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Photoinitiated thiol-yne chemistry is utilized as a click reaction for grafting of acid-terminated alkynes to thiol-terminated monolayers on a gold substrate to create stable, low-density monolayers. The resulting monolayers are compared with a well-packed 11-mercaptoundecanoic acid monolayer and the analogous low-density monolayers prepared through a solution phase synthetic approach. The overall structuring of the monolayer prepared by solid-phase grafting is characterized by contact angle goniometry and Fourier transform infrared spectroscopy. The results show that the product monolayer has an intermediate surface energy and a more disordered chemical structuring compared to a traditional well-packed self-assembled monolayer, showing a low-packing density of the chains at the monolayer surface. The monolayer's structure and electrochemical stability were studied by reductive desorption of the thiolates. The prepared low-density monolayers have a higher electrochemical stability than traditional well-packed monolayers, which results from the crystalline structure at the gold interface. This technique allows for simple, fast preparation of low-density monolayers of higher stability than well-packed monolayers. The use of a photomask to restrict light access to the substrate yielded these low-density monolayers in patterned regions defined by light exposure. This general thiol-yne approach is adaptable to a variety of analogous low-density monolayers with diverse chemical functionalities.
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In the present work, we have envisaged the enhancement of hydrogen evolution reaction (HER) activity on stable Si2BN monolayer based on first-principles electronic structure calculations. Herein, we have performed the HER activities on the pristine Si2BN monolayer and various possible active sites on structural defects in the Si2BN monolayer. In addition to the pristine monolayer, we have thoroughly investigated the effect of functionalization and cofunctionalization on the Si2BN monolayer. The adsorption of the most important HER intermediate hydrogen on different possible active sites of Si2BN monolayer has been systematically studied for all the functionalization and cofunctionalization cases. We have determined the projected density of states, work functions, and optical absorption cross-section for all the pristine and doped systems. The charge distributions for all of the monolayer systems are determined along with the mapping of the reaction coordinate based on the hydrogen (H*) adsorption free energies (ΔGH*0). Among all of the functionalized Si2BN monolayers, the C-doped monolayer has been emerged as the active most HER catalyst, whereas in the case of co-functionalization, C–P codoped Si2BN monolayer is the best candidate for HER mechanism.
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Mixed monolayers consisting of 4-fluorobenzenethiolate and 1-octadecanethiolate on Au surfaces were formed by immersing in an ethanol solution of 4-fluorobenzenethiol (FBT), and subsequently by immersing in that of 1-octadecanethiol (ODT). To obtain systematically a mixed monolayer, the formation of FBT- and ODT-monolayers was investigated with respect to the reaction time and concentration of the solution. The monolayer formed on a Au surface was evaluated based on the work function, the water contact angle, and the X-ray photoelectron spectroscopy (XPS) spectra measured. The XPS measurement of substrates prepared for formation of a mixed monolayer exhibited F 1s and C 1s spectra supporting the presence of a mixed monolayer consisting of 4-fluorobenezenethiolate and 1-octadecanethiolate.
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The electrostatic binding and metal coordination between metal ions and Langmuir monolayers or LB films are discussed, and their effects on the monolayer 2D structure and related phase behavior are analyzed. The interfacial recognition and sensing for metal ions by Langmuir monolayers are also shown. Langmuir monolayers and LB films as 2D template to induce the 2D-oriented crystal growth via metal/monolayer binding is especially demonstrated. The abnormal catalytic characteristics, the functions and devices of metal-incorporated Langmuir monolayers and LB films are displayed by some examples. The review also shows the application of metal-chelating lipid monolayers on the interfacial study of bio-macromolecules. The review suggests the great roles of metal/monolayer binding in alternating monolayer structures and the assembly of functional metal complexes.
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The molecular interactions of monolayers composed of cyclic and linear forms of surfactins (SFs) were evaluated through atomic force microscopy (AFM) together with a Langmuir monolayer technique. The surface pressure (π)-area per molecule (A) isotherm of a pure cyclic surfactin (CSF) monolayer exhibited a liquid expanded (Le) monolayer, while that of a pure linear surfactin (LSF) monolayer exhibited a liquid condensed (Lc) monolayer, demonstrating that the CSFs are in a rather loose molecular packing state owing to its bulky heptapeptide ring. The plots of the mean area per molecule of the CSF/LSF monolayers were well fitted to the ideal curves, suggesting that ideal mixing occurs, or that the two components are immiscible in a monolayer. The AFM images of the CSF/LSF monolayers transferred at 25 mN/m gave phase-separated microdomain structures, indicating that the CSFs and LSFs are almost immiscible and separated into a CSF-rich and LSF-rich phases, as suggested from the analysis of the mean area per molecule of the monolayers. Our results clearly demonstrated that the cleavage of the cyclic heptapeptide headgroup of CSF drastically changes its molecular packing state in a monolayer and that AFM observation combined with the Langmuir monolayer technique is quite useful to explore the manner of self-assembly of a binary system of microbial products such as CSFs and LSFs.
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