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Superior Sensing Properties of Black Phosphorus as Gas Sensors: A Case Study on the Volatile Organic Compounds
摘要： The unique structure and prominent properties of black phosphorus (BP) and its monolayer and multilayers in device applications have attracted significant attention to this elemental 2D material. In this study, a comprehensive evaluation of the candidacy of monolayer BP as a channel material for high-performance volatile organic compound (VOC) sensors is conducted combining first-principles density functional theory calculations and non-equilibrium Green’s function formalism. The adsorption configurations and energetics of several typical VOCs (ethanol, propionaldehyde, acetone, toluene, and hexane) on monolayer BP are examined and it is demonstrated that VOCs generally exhibit stronger interaction with monolayer BP than with the widely studied monolayer MoS2, indicative of monolayer BP potentially being a more sensitive VOC sensor. Monolayer BP is shown to exhibit highly anisotropic transport behaviors, whereas the absolute modification of current–voltage responses due to VOCs is found to show a trend that is direction independent. Moreover, the adsorption of VOCs on monolayer BP is strong enough to resist thermal disturbance, yet allows fast recovery time. The results suggest that BP is a compelling and feasible candidate for sensing applications of VOCs.
关键词： density functional theory calculations,gas sensors,black phosphorus,volatile organic compounds,non-equilibrium Green’s function formalism
更新于2025-09-23 15:22:29
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Nonequilibrium electron dynamics in pump-probe spectroscopy: Role of excited phonon populations
摘要： We study the role of excited phonon populations in the relaxation rates of nonequilibrium electrons using a nonequilibrium Green’s function formalism. The transient modifications in the phononic properties are accounted for by self-consistently solving the Dyson equation for the electron and phonon Green’s functions. The pump-induced changes manifest in both the electronic and phononic spectral functions. We find that the excited phonon populations suppress the decay rates of nonequilibrium electrons due to enhanced phonon absorption. The increased phonon occupation also sets the nonequilibrium decay rates and the equilibrium scattering rates apart. The decay rates are found to be time dependent, and this is illustrated in the experimentally observed population decay of photoexcited Bi1.5Sb0.5Te1.7Se1.3.
关键词： relaxation rates,nonequilibrium electron dynamics,excited phonon populations,nonequilibrium Green’s function formalism,pump-probe spectroscopy
更新于2025-09-09 09:28:46
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Demonstration of resonant inelastic x-ray scattering as a probe of exciton-phonon coupling
摘要： Resonant inelastic x-ray scattering (RIXS) is a promising technique for obtaining electron-phonon coupling constants. However, the ability to extract these coupling constants throughout the Brillouin zone for crystalline materials remains limited. To address this need, we developed a Green’s function formalism to capture electron-phonon contributions to core-level spectroscopies without explicitly solving the full vibronic problem. Our approach is based on the cumulant expansion of the Green’s function combined with many-body theory calculated vibrational coupling constants. The methodology is applied to x-ray photoemission spectroscopy, x-ray absorption spectroscopy (XAS), and RIXS. In the case of the XAS and RIXS, we use a two-particle exciton Green’s function, which accounts implicitly for particle-hole interference effects that have previously proved difficult. To demonstrate the methodology and gain a deeper understanding of the experimental technique, we apply our formalism to small molecules, for which unambiguous experimental data exist. This comparison reveals that the vibronic coupling constant probed by RIXS is in fact related to exciton-phonon coupling rather than electron-phonon coupling, challenging the conventional interpretation of the experiment.
关键词： electron-phonon coupling,Green’s function formalism,exciton-phonon coupling,Resonant inelastic x-ray scattering,vibronic coupling
更新于2025-09-04 15:30:14