低对称性二维材料是一类晶格对称操作少,纵向仅有原子级厚度的新型纳米材料。在二维过渡金属硫族化合物(Transition metal dichalcogenides,TMDs)体系中,1T’-MoTe_(2)、1T’-WTe_(2)、1T’-ReS_(2)和1T’-ReSe_(2)是典型低对称性成员...低对称性二维材料是一类晶格对称操作少,纵向仅有原子级厚度的新型纳米材料。在二维过渡金属硫族化合物(Transition metal dichalcogenides,TMDs)体系中,1T’-MoTe_(2)、1T’-WTe_(2)、1T’-ReS_(2)和1T’-ReSe_(2)是典型低对称性成员。独特的晶格对称性为它们带来了丰富的各向异性理化性质,因而在微纳光子学、触觉传感器、各向异性逻辑器件等领域具有特殊应用前景。低对称性二维TMDs材料的基础研究和应用开发依赖于对这类材料的高质量、大尺寸、稳定制备。本文以这4类材料为典型,首先按金属前驱体进行分类,综述了近年来有关低对称性二维TMDs材料的化学气相沉积(Chemical vapor deposition,CVD)制备方法;其次,针对制备过程中1T’-MoTe_(2)容易发生相转变,1T’-ReS_(2)、1T’-ReSe_(2)与基底间相互作用力弱等特点,介绍了1T’-MoTe_(2)制备过程中的相调控机制,以及1T’-ReS_(2)、1T’-ReSe_(2)制备过程中的基底工程研究;最后,本文对低对称性二维TMDs材料未来的挑战与机遇进行了展望。展开更多
Measuring the Hamiltonian of dipolar coupled spin systems is usually a difficult task due to the high complexity of their spectra. Currently, molecules with unknown geometrical structure and low symmetry are extremely...Measuring the Hamiltonian of dipolar coupled spin systems is usually a difficult task due to the high complexity of their spectra. Currently, molecules with unknown geometrical structure and low symmetry are extremely tedious or impossible to analyze by sheer spectral fitting. We present a novel method that addresses the problem of spectral analysis and report experimental results of extracting, by spectral fitting, the parameters of an oriented 6-spin system with very low symmetry in structure, without using apriori knowledge or assumptions on the molecular geometry or order parameters. The advantages of our method are achieved with the use of a new spectral analysis algorithm non-assigned frequency optimization of NMR spectra （NAFONS） and by the use of simplified spectra obtained by transition selective pulses. This new method goes beyond the limit of spectral analysis for dipolar coupled spin systems and is helpful for related fields, such as quantum computation and molecular structure analysis.展开更多
The equilibrium geometries, potential energy curves, spectroscopic dissociation energies of the ground and low-lying electronic states of He2, He2^＋ and He2^＋＋ are calculated using symmetry adapted cluster/symmetry...The equilibrium geometries, potential energy curves, spectroscopic dissociation energies of the ground and low-lying electronic states of He2, He2^＋ and He2^＋＋ are calculated using symmetry adapted cluster/symmetry adapted cluster-configuration interaction （SAC/SAC-CI） method with the basis sets CC-PV5Z. The corresponding dissociation limits for all states are derived based on atomic and molecular reaction statics. The analytical potential energy functions of these states are fitted with Murrell-Sorbie potential energy function from our calculation results. The spectroscopic constants Be, αe, ωe, and ωeχe of these states are calculated through the relationship between spectroscopic data and analytical energy function, which are in well agreement with the experimental data. In addition, the origin of the energy barrier in the ground state X^I∑9^＋ of He2^＋＋ energy curve are explained using the avoided crossing rules of valence bond model.展开更多
文摘低对称性二维材料是一类晶格对称操作少,纵向仅有原子级厚度的新型纳米材料。在二维过渡金属硫族化合物(Transition metal dichalcogenides,TMDs)体系中,1T’-MoTe_(2)、1T’-WTe_(2)、1T’-ReS_(2)和1T’-ReSe_(2)是典型低对称性成员。独特的晶格对称性为它们带来了丰富的各向异性理化性质,因而在微纳光子学、触觉传感器、各向异性逻辑器件等领域具有特殊应用前景。低对称性二维TMDs材料的基础研究和应用开发依赖于对这类材料的高质量、大尺寸、稳定制备。本文以这4类材料为典型,首先按金属前驱体进行分类,综述了近年来有关低对称性二维TMDs材料的化学气相沉积(Chemical vapor deposition,CVD)制备方法;其次,针对制备过程中1T’-MoTe_(2)容易发生相转变,1T’-ReS_(2)、1T’-ReSe_(2)与基底间相互作用力弱等特点,介绍了1T’-MoTe_(2)制备过程中的相调控机制,以及1T’-ReS_(2)、1T’-ReSe_(2)制备过程中的基底工程研究;最后,本文对低对称性二维TMDs材料未来的挑战与机遇进行了展望。
文摘Measuring the Hamiltonian of dipolar coupled spin systems is usually a difficult task due to the high complexity of their spectra. Currently, molecules with unknown geometrical structure and low symmetry are extremely tedious or impossible to analyze by sheer spectral fitting. We present a novel method that addresses the problem of spectral analysis and report experimental results of extracting, by spectral fitting, the parameters of an oriented 6-spin system with very low symmetry in structure, without using apriori knowledge or assumptions on the molecular geometry or order parameters. The advantages of our method are achieved with the use of a new spectral analysis algorithm non-assigned frequency optimization of NMR spectra （NAFONS） and by the use of simplified spectra obtained by transition selective pulses. This new method goes beyond the limit of spectral analysis for dipolar coupled spin systems and is helpful for related fields, such as quantum computation and molecular structure analysis.
基金Supported by the Natural Science Foundation of Shaanxi Province of China under Grant No. 2009JM1007
文摘The equilibrium geometries, potential energy curves, spectroscopic dissociation energies of the ground and low-lying electronic states of He2, He2^＋ and He2^＋＋ are calculated using symmetry adapted cluster/symmetry adapted cluster-configuration interaction （SAC/SAC-CI） method with the basis sets CC-PV5Z. The corresponding dissociation limits for all states are derived based on atomic and molecular reaction statics. The analytical potential energy functions of these states are fitted with Murrell-Sorbie potential energy function from our calculation results. The spectroscopic constants Be, αe, ωe, and ωeχe of these states are calculated through the relationship between spectroscopic data and analytical energy function, which are in well agreement with the experimental data. In addition, the origin of the energy barrier in the ground state X^I∑9^＋ of He2^＋＋ energy curve are explained using the avoided crossing rules of valence bond model.
