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Aerosol synthesis of germanium nanoparticles supported by external seeding: Theoretical and experimental analysis
摘要： In this work we present a detailed study of the effect of heterogeneous nucleation on the formation of germanium nanoparticles (Ge NPs) produced from monogermane (GeH4) in a hot wall reactor gas phase synthesis. As external seeding unit we use a hot wire generator (HWG) which produces a stable concentration of aerosol particles. The particle concentration and size of the seeds is easily controllable via the applied voltage and used metal. We demonstrate the importance of seed particles for the production of narrowly distributed Ge NPs with geometrical standard deviations (GSD) < 1.1 in our setup. Thereby, molybdenum and tungsten as wire metal show the best seeding results. The size of the final Ge NPs can be precisely controlled in the range of 20 to 60 nm. The expansion of Ge lattice seen in XRD and tiny amount of Mo probed by high-resolution STEM-EDXS analysis indicate that the Mo seed particles are most likely dissolved and incorporated in the Ge lattice during growth. Furthermore, we demonstrate an approach to investigate the effect of heterogeneous nucleation on the particle formation by population balance modeling. The results are in good agreement with experimental data. The seed concentration is the key parameter and has a major influence on the nucleation rate.
关键词： Germanium,Nanoparticles,Simulation,Hot wire generator,Gas phase synthesis,Heterogeneous nucleation
更新于2025-09-09 09:28:46
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Photoelectrochemical Gas–Electrolyte–Solid Phase Boundary for Hydrogen Production From Water Vapor
摘要： Hydrogen production from humidity in the ambient air reduces the maintenance costs for sustainable solar-driven water splitting. We report a gas-diffusion porous photoelectrode consisting of tungsten trioxide (WO3) nanoparticles coated with a proton-conducting polymer electrolyte thin film for visible-light-driven photoelectrochemical water vapor splitting. The gas–electrolyte–solid triple phase boundary enhanced not only the incident photon-to-current conversion efficiency (IPCE) of the WO3 photoanode but also the Faraday efficiency (FE) of oxygen evolution in the gas-phase water oxidation process. The IPCE was 7.5% at an applied voltage of 1.2 V under 453 nm blue light irradiation. The FE of hydrogen evolution in the proton exchange membrane photoelectrochemical cell was close to 100%, and the produced hydrogen was separated from the photoanode reaction by the membrane. A comparison of the gas-phase photoelectrochemical reaction with that in liquid-phase aqueous media confirmed the importance of the triple phase boundary for realizing water vapor splitting.
关键词： proton exchange membrane,solar H2 production,tungsten oxide photoanode,visible-light-driven photoelectrode,gas-phase water splitting
更新于2025-09-09 09:28:46
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Encyclopedia of Spectroscopy and Spectrometry || Field Ionization Kinetics in Mass Spectrometry
摘要： The mass spectra of molecules, ionized by electron ionization (EI), field ionization (FI) or photoionization (PI) in the gas phase, usually show many peaks with varying intensities. These peaks result from fragment ions generated by a series of competing and consecutive unimolecular dissociation reactions of the molecular ions provided that the latter have obtained during their formation an amount of energy in excess of the ionization energy of the corresponding molecules. The resulting mass spectrum therefore is determined by the relative rates of these unimolecular dissociation reactions, which in their turn are related to the relative abundances of the fragment ions observed. It will be clear that studying the kinetics of ion dissociation can provide an invaluable insight into the foundation of a mass spectrum.
关键词： Gas-Phase Ion Chemistry,Unimolecular Dissociation,Ion Lifetimes,Mass Spectrometry,Field Ionization Kinetics
更新于2025-09-04 15:30:14
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Echo Spectroscopy in Multilevel Quantum-Mechanical Rotors
摘要： We study the dynamics of rotational echoes in gas phase molecular ensembles and their dependence on the delay and intensity of the excitation pulses. We explore the unique dynamics of alignment echoes that arise from the multilevel nature of the molecular rotors and impose severe difficulties in utilizing echo responses for rotational spectroscopy. We show experimentally and theoretically that judicious control of both the delay and intensity of the second pulse enables multilevel “rotational echo spectroscopy.” The proposed methodology paves the way to rotational spectroscopy in high-density gas samples.
关键词： rotational echoes,echo spectroscopy,gas phase molecular ensembles,multilevel quantum-mechanical rotors
更新于2025-09-04 15:30:14