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Acceptor levels of the carbon vacancy in 4 <i>H</i> -SiC: Combining Laplace deep level transient spectroscopy with density functional modeling
摘要： We provide direct evidence that the broad Z1/2 peak, commonly observed by conventional deep level transient spectroscopy in as-grown and at high concentrations in radiation damaged 4H-SiC, has two components, namely, Z1 and Z2, with activation energies for electron emissions of 0.59 and 0.67 eV, respectively. We assign these components to Z?1/2 + e? → Z?1/2 → Z?1/2 + 2e? transition sequences from negative-U ordered acceptor levels of carbon vacancy (V_C) defects at hexagonal/pseudo-cubic sites, respectively. By employing short filling pulses at lower temperatures, we were able to characterize the first acceptor level of V_C on both sub-lattice sites. Activation energies for electron emission of 0.48 and 0.41 eV were determined for Z1(?/0) and Z2(?/0) transitions, respectively. Based on trap filling kinetics and capture barrier calculations, we investigated the two-step transitions from neutral to doubly negatively charged Z1 and Z2. Positions of the first and second acceptor levels of V_C at both lattice sites, as well as (?/0) occupancy levels, were derived from the analysis of the emission and capture data.
关键词： density functional theory,acceptor levels,deep level transient spectroscopy,negative-U ordering,carbon vacancy,4H-SiC
更新于2025-09-23 15:23:52
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Carbon Vacancies in a Melon Polymeric Matrix Promote Photocatalytic Carbon Dioxide Conversion
摘要： Photosynthetic conversion CO2 into fuel and chemicals is a promising but challenging technology. The bottleneck of this reaction lies in the activation of CO2, owing to the chemical inertness of linear CO2. Herein, we present a defect engineering methodology to construct CO2 activation sites by implanting carbon vacancies (CVs) on the melon polymer (MP) matrix. Positron annihilation spectroscopy confirms the location and density of the CVs in the MP skeleton. transform spectroscopy and density functional theory (DFT) study reveals that the CVs can function as active sites for CO2 activation, while stabilizing COOH* intermediates, thereby boosting the reaction kinetics. As a result, the modified MP-TAP-CVs display a 45-fold improvement in CO2-to-CO activity over the pristine MP. The apparent quantum efficiency of the MP-TAP-CVs achieves 4.8 % at 420 nm, which exceeds most of the heterogeneous reduction of CO2 under visible light. This study will shed new light on the design of high-efficiency polymer semiconductors for CO2 conversion.
关键词： Carbon nitride,Photocatalysis,CO2 reduction,Carbon vacancy
更新于2025-09-23 15:21:01
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Carbon Vacancies in a Melon Polymeric Matrix Promote Photocatalytic Carbon Dioxide Conversion
摘要： Photosynthetic conversion CO2 into fuel and chemicals is a promising but challenging technology. The bottleneck of this reaction lies in the activation of CO2, owing to the chemical inertness of linear CO2. Herein, we present a defect engineering methodology to construct CO2 activation sites by implanting carbon vacancies (CVs) on the melon polymer (MP) matrix. Positron annihilation spectroscopy confirms the location and density of the CVs in the MP skeleton. transform spectroscopy and density functional theory (DFT) study reveals that the CVs can function as active sites for CO2 activation, while stabilizing COOH* intermediates, thereby boosting the reaction kinetics. As a result, the modified MP-TAP-CVs display a 45-fold improvement in CO2-to-CO activity over the pristine MP. The apparent quantum efficiency of the MP-TAP-CVs achieves 4.8 % at 420 nm, which exceeds most of the heterogeneous reduction of CO2 under visible light. This study will shed new light on the design of high-efficiency polymer semiconductors for CO2 conversion.
关键词： Carbon nitride,Photocatalysis,CO2 reduction,Carbon vacancy
更新于2025-09-10 09:29:36