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Laser-Induced Dissociation of the Monolayer of Adsorbed Methanol Molecules
摘要： Astronomical observations indicate a high abundance of methanol molecules in the gas phase of molecular-cloud dense cores, which cannot be explained by gas-phase chemical reactions only. A significant contribution to the methanol abundance should be provided by chemical reactions on the dust particle surface with subsequent desorption of the produced molecules into the gas phase. For the development and refinement of models involving these processes, laboratory studies of photo-induced processes occurring in the adsorbed material are necessary. In this paper, the experiment results of adsorbed methanol molecules are presented. A methanol molecule monolayer, physically adsorbed on fused silica surface cooled by liquid nitrogen (Т ～ 100 K), was irradiated in high vacuum by nanosecond pulses of an excimer KrF laser with a fixed wavelength λ = 248 nm. The photodissociation products of three-photon laser excitation were recorded by a quadrupole mass spectrometer. Relative yields of photofragments H, OH, and CH3 were determined. Photolysis of partially deuterated CH3OH molecules has shown that hydrogen atoms can be ejected both from hydroxyl and methyl groups. In contrast to the isolated molecule photolysis in the gas phase and dissociation of the multilayer molecular coatings, photoexcitation of adsorbed methanol monolayer even in the energy region of 10 eV does not cause noticeable chemical transformations and does not lead to the formation of molecular components H2 and CH4. Due to existing astrochemical modeling problems, possible application methods of the obtained laboratory results are considered.
关键词： chemical reactions,astronomical observations,adsorbed monolayer,mass spectrometry,photo-induced processes,gas phase,dust particle surface,KrF laser,photodissociation,methanol
更新于2025-09-23 15:21:01
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Recent advances of plasmonic nanoparticle-based optical analysis in homogeneous solution and at the single-nanoparticle level
摘要： Plasmonic nanoparticles with special localized surface plasmon resonance (LSPR) characters have been widely applied for optical sensing of various targets. With the combination of single nanoparticle imaging techniques, dynamic information of reactions and biological processes is obtained, facilitating the deep understanding of their principle and design of outstanding nanomaterials. In this review, we summarize the recently adopted optical analysis of diverse analytes based on plasmonic nanoparticles in both homogeneous solution and single-nanoparticle level. A brief introduction of LSPR is first discussed. Colorimetric and fluorimetric homogeneous detection examples by using different sensing mechanisms and strategies are provided. Single plasmonic nanoparticle-based analysis is concluded in two aspects: visualization of chemical reactions and understanding of biological processes. The basic sensing mechanisms and performances of these systems are introduced. Finally, this review highlights the challenges and future trend of plasmonic nanoparticle-based optical analysis system.
关键词： Plasmonic nanoparticles,Single-nanoparticle level,Fluorimetric assays,Chemical reactions,Localized surface plasmon resonance (LSPR),Optical analysis,Homogeneous solution,Colorimetric assays,Biological processes
更新于2025-09-23 15:21:01
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Syzygy Plasmonics
摘要： Using photocatalysis to make chemical reactions more efficient
关键词： plasmonics,photocatalysis,chemical reactions,hydrogen production
更新于2025-09-16 10:30:52
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PVRD-FASP: A Unified Solver for Modeling Carrier and Defect Transport in Photovoltaic Devices
摘要： In this article, we present a simulator for modeling transport of charge carriers and electrically active defect centers in solar cells by treating them on an equal footing, which allows us to address metastability and reliability issues. The exact nonlinear differential equations set solved by our solver is presented. The formulation of such differential equations, namely the continuity equations, drift-diffusion equation, and Poisson equation, for studying charge and defect transport is explained. The parameters needed for forming the differential equations are taken from first principle calculations. The solver is verified with test cases built on PN heterojunctions, Cu diffusion in single crystal CdTe and comparing Silvaco simulations with our numerical results.
关键词： drift-diffusion,PN heterojunction,transient solutions for continuity equation,Defect reaction solver,implicit Euler with Newton iteration,chemical reactions
更新于2025-09-16 10:30:52
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Taking the Heat Off of Plasmonic Chemistry
摘要： Plasmon-excitation-mediated chemistry, which is a rapidly growing field, is founded on a simple principle: the excitation of the localized surface plasmon resonance (LSPR) of metal nanoparticles triggers chemical reactions on the surfaces of the nanoparticles. Early examples of plasmon-excitation-driven nanoparticle synthesis and hot-electron-driven chemical reactions induced by ultrashort pulse excitation of metal nanoparticles can be thought of as precursors to the findings of direct photocatalysis by plasmonic nanoparticles, which is the focus of this Viewpoint. The field in its current state was, in large part, invigorated by a 2011 paper, which showed that the excitation of the LSPR of Ag nanoparticles by continuous-wave (CW), visible-frequency light triggered the dissociation of adsorbed O2. The O· atoms thus produced were utilized for industrially relevant oxidation reactions such as those of propylene and ethylene, which would have otherwise required high-temperature and -pressure conditions to proceed at appreciable rates. In the absence of visible-light excitation, the bond dissociation and oxidation reactions proceeded at appreciably low rates, which indicated that plasmonic excitation enhanced the rates of these chemical reactions. The phenomenon is, therefore, termed as plasmonic catalysis or plasmonic photocatalysis.
关键词： Plasmonic catalysis,Plasmonic photocatalysis,Chemical reactions,Hot electrons,Photothermal heating
更新于2025-09-16 10:30:52
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Non-classical nucleation pathways revealed by scanning tunneling microscopy of epitaxy of covalent materials
摘要： Identifying atomic/molecular mechanism is crucial for understanding crystallization and epitaxial growth and to enable controlled synthesis of high-quality devices and desired crystalline structures. Using scanning tunneling microscopy, we studied early stages of Si epitaxy on a Si(111) surface mediated by a Pb monolayer. A type of highly mobile magic clusters was observed only when they were trapped at boundary or defect sites. Magic clusters also formed cluster aggregates temporarily. Adding more Si transformed the aggregates into immobile metastable or stable structures. Here we propose a scenario involving concerted chemical reactions of multiple, co-localized magic clusters with the activation energies decreasing with increasing number of clusters. This scenario may be modified to understand nucleation and growth of many covalent materials as well as crystallization in numerous synthetic and natural systems.
关键词： magic clusters,Nucleation and growth,chemical reactions,covalent materials,non-classical nucleation
更新于2025-09-12 10:27:22
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Plasmon-Mediated Chemical Reactions on Nanostructures Unveiled by Surface-Enhanced Raman Spectroscopy
摘要： Surface plasmons (SPs) originating from the collective oscillation of conduction electrons in nanostructured metals (Au, Ag, Cu, etc.) can redistribute not only the electromagnetic fields but also the excited carriers (electrons and holes) and heat energy in time and space. Therefore, SPs can engage in a variety of processes, such as molecular spectroscopy and chemical reaction. Recently, plenty of demonstrations have made plasmon-mediated chemical reactions (PMCRs) a very active research field and make it as a promising approach to facilitate light-driven chemical reactions under mild conditions. Concurrently, making use of the same SPs, surface-enhanced Raman spectroscopy (SERS) with a high surface sensitivity and energy resolution becomes a powerful and commonly used technique for the in situ study of PMCRs.
关键词： Surface plasmons,Photothermal effects,Hot electrons,Hot holes,Surface-enhanced Raman spectroscopy,Plasmon-mediated chemical reactions
更新于2025-09-11 14:15:04
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Clickable PNA Probes for Imaging Human Telomeres and Poly(A) RNAs
摘要： The ability to bind strongly to complementary nucleic acid sequences, invade complex nucleic acid structures, and resist degradation by cellular enzymes has made peptide nucleic acid (PNA) oligomers as very useful hybridization probes in molecular diagnosis. For such applications, the PNA oligomers have to be labeled with appropriate reporters as they lack intrinsic labels that can be used in biophysical assays. Although solid-phase synthesis is commonly used to attach reporters onto PNA, development of milder and modular labeling methods will provide access to PNA oligomers labeled with a wider range of biophysical tags. Here, we describe the establishment of a postsynthetic modification strategy based on bioorthogonal chemical reactions in functionalizing PNA oligomers in solution with a variety of tags. A toolbox composed of alkyne- and azide-modified monomers were site-specifically incorporated into PNA oligomers and postsynthetically click-functionalized with various tags, ranging from sugar, amino acid, biotin, to fluorophores, by using copper(I)-catalyzed azide?alkyne cycloaddition, strain-promoted azide?alkyne cycloaddition, and Staudinger ligation reactions. As a proof of utility of this method, fluorescent PNA hybridization probes were developed and used in imaging human telomeres in chromosomes and poly(A) RNAs in cells. Taken together, this simple approach of generating a wide range of functional PNA oligomers will expand the use of PNA in molecular diagnosis.
关键词： peptide nucleic acid,bioorthogonal chemical reactions,molecular diagnosis,poly(A) RNAs,human telomeres,PNA,click chemistry
更新于2025-09-09 09:28:46