Stacking up electron-rich and electron-deficient monolayers to achieve extraordinary mid- to far-infrared excitonic absorption: Interlayer excitons in the C3B/C3N bilayer

Our ability to efficiently detect and generate far-infrared (i.e., terahertz) radiation is vital in areas spanning from biomedical imaging to interstellar spectroscopy. Despite decades of intense research, bridging the terahertz gap between electronics and optics remains a major challenge due to the lack of robust materials that can efficiently operate in this frequency range, and two-dimensional (2D) type-II heterostructures may be ideal candidates to fill this gap. Herein, using highly accurate many-body perturbation theory within the GW plus Bethe-Salpeter equation approach, we predict that a type-II heterostructure consisting of an electron rich C3N and an electron deficient C3B monolayers can give rise to extraordinary optical activities in the mid- to far-infrared range. C3N and C3B are two graphene-derived 2D materials that have attracted increasing research attention. Although both C3N and C3B monolayers are moderate gap 2D materials, and they only couple through the rather weak van der Waals interactions, the bilayer heterostructure surprisingly supports extremely bright, low-energy interlayer excitons with large binding energies of 0.2 ~ 0.4 eV, offering an ideal material with interlayer excitonic states for mid-to far-infrared applications at room temperature. We also investigate in detail the properties and formation mechanism of the inter- and intra-layer excitons.Comment: 15 pages, 6 figure

Estimating Shape and Micro-Motion Parameter of Rotationally Symmetric Space Objects from the Infrared Signature

Shape serves as an important additional feature for space target classification, which is complementary to those made available. Since different shapes lead to different projection functions, the projection property can be regarded as one kind of shape feature. In this work, the problem of estimating the projection function from the infrared signature of the object is addressed. We show that the projection function of any rotationally symmetric object can be approximately represented as a linear combination of some base functions. Based on this fact, the signal model of the emissivity-area product sequence is constructed, which is a particular mathematical function of the linear coefficients and micro-motion parameters. Then, the least square estimator is proposed to estimate the projection function and micro-motion parameters jointly. Experiments validate the effectiveness of the proposed method

Stability and Electronic Properties of 1D and 2D Ca@C₆₀ Oligomers and Polymers

The polymerization of fullerenes is a significant method for obtaining fullerene-based materials that possess intriguing properties. Metallofullerenes, as a notable type of fullerene derivatives, are also capable of undergoing polymerization, potentially resulting in the creation of metallofullerene polymers. However, there is currently limited knowledge regarding the polymerization process of metallofullerenes. In this study, we have selected Ca@C 60 as a representative compound to investigate the polymerization process of metallofullerenes. The objective of this research is to determine whether the polymerization process is energetically favorable and to examine how the electronic properties of the metallofullerene are altered throughout the polymerization process. Ca@C 60 is a unique metallofullerene molecule that exhibits insolubility in common fullerene solvents like toluene and carbon disulfide but is soluble in aniline. This behavior suggests a potential tendency for Ca@C 60 to form oligomers and polymers that resist dissolution. However, the structures and properties of polymerized Ca@C 60 remain unknown. We employed density functional theory calculations to investigate the stability and electronic properties of one-dimensional and two-dimensional Ca@C 60 oligomers and polymers. Our findings indicate that the coalescence of Ca@C 60 monomers is energetically favorable, with a significant contribution from van der Waals interactions between the fullerene cages. The polymerization process of Ca@C 60 also involves the formation of covalent linkages, including four-atom rings and C-C single bonds. The increase in the number of the Ca@C 60 units to three and four in the oligomer leads to a significant decrease in the HOMO-LUMO gap. In the two-dimensional polymerized Ca@C 60, the organization of the monomers closely resembles the spatial configuration of carbon atoms in graphene. With a direct bandgap of 0.22 eV, the polymerized Ca@C 60 holds potential for utilization in optoelectronic devices

Prediction of the Spatial Pattern of Carbon Emissions Based on Simulation of Land Use Change under Different Scenarios

Land use is an important factor in the change of carbon emissions, and predicting the spatial pattern of carbon emissions under different land use scenarios is of great significance to respond to the “double carbon” target of China. Based on the land use data of Nanjing city, Jiangsu Province, China in 2010, 2015 and 2020, this study used the Conversion of Land Use and its Effects at Small regional extent (CLUE-S) model to simulate the land use change pattern in 2030 under multiple scenarios, and predicted the carbon emissions of each subzone based on the simulation results. It also provides a carbon balance zoning from an economic and ecological point of view and proposes strategies tailored to each district. The results show that: (1) in 2030, under the ecological conservation scenario, ecological land all shows different degrees of increase, while under the cultivated land conservation scenario, construction land only increased by 1.47%. This indicates that the ecological and cultivated land protection perspectives can effectively curb the expansion of construction land. (2) The growth rate of carbon emissions in Nanjing from 2010–2030 decreased from 16.65–3.7%. This indicates that carbon emissions continue to rise, but the trend of growth is slowing down. (3) The spatial carbon emissions in Nanjing show an overall higher level in the north and lower in the center; the large expansion of building land and the concentration of industrial industries are the main reasons for the large increase in carbon emissions. Under the ecological protection scenario, the carbon emissions of Lishui, Pukou and Qixia districts were 11.05 × 104 t, 19.437 × 104 t and 10.211 × 104 t lower than those under the natural growth scenario, mainly because these three districts have more ecological land and the ecological protection effect is more significant. Under the cultivated land conservation scenario, the growth rate of carbon emissions slows down significantly. This indicates that the future structure of carbon emissions in Nanjing will vary significantly, and that ecological protection and arable land conservation play an important role in reducing carbon emissions. This study shows that it is difficult to reduce emissions in a concerted manner. Therefore, for different districts, differentiated land use optimization measures should be developed according to local conditions, and ecological protection and cultivated land protection scenarios should both be taken into account

Estimating Shape and Micro-Motion Parameter of Rotationally Symmetric Space Objects from the Infrared Signature

Shape serves as an important additional feature for space target classification, which is complementary to those made available. Since different shapes lead to different projection functions, the projection property can be regarded as one kind of shape feature. In this work, the problem of estimating the projection function from the infrared signature of the object is addressed. We show that the projection function of any rotationally symmetric object can be approximately represented as a linear combination of some base functions. Based on this fact, the signal model of the emissivity-area product sequence is constructed, which is a particular mathematical function of the linear coefficients and micro-motion parameters. Then, the least square estimator is proposed to estimate the projection function and micro-motion parameters jointly. Experiments validate the effectiveness of the proposed method