磷烯基二维范德瓦尔斯异质结的理论表征

本文基于单层黑磷和蓝磷,理论设计出二维范德瓦尔斯异质结、能带结构、态密度、Bader电荷布局、电荷密度差分图及光吸收谱等,计算结果表明它是典型的第二型异质结,有利于光生载流子分离,且可见光捕获能力显著增强.内禀的界面极化电场能有效阻止光生电子-空穴的复合.表明磷烯基二维范德瓦尔斯异质结是一类性能优异的光解水催化剂.     

二维范德瓦尔斯异质结构的制备与物性研究

二维范德瓦尔斯材料(可简称二维材料)已发展成为备受瞩目的材料大家族,而由其衍生的二维范德瓦尔斯异质结构的集成、性能及应用是现今凝聚态物理和材料科学领域的研究热点之一.二维范德瓦尔斯异质结构为探索丰富多彩的物理效应和新奇的物理现象,以及构建新型的自旋电子学器件提供了灵活而广阔的平台.本文从二维材料的转移技术着手,介绍二维范德瓦尔斯异质结构的构筑、性能及应用.首先,依据湿法转移和干法转移的分类,详细介绍二维范德瓦尔斯异质结构的制备技术,内容包括转移技术的通用设备、常用转移方法的具体操作步骤、三维操纵二维材料的方法、异质界面清洁.随后介绍二维范德瓦尔斯异质结构的性能和应用,重点介绍二维磁性范德瓦尔斯异质结构,并列举在二维范德瓦尔斯磁隧道结和摩尔超晶格领域的应用.因此,二维材料转移技术的发展和优化将进一步助力二维范德瓦尔斯异质结构在基础科学研究和实际应用上取得突破性的成果.     

二维范德瓦尔斯异质结构的制备与物性研究

二维范德瓦尔斯材料(可简称二维材料)已发展成为备受瞩目的材料大家族,而由其衍生的二维范德瓦尔斯异质结构的集成、性能及应用是现今凝聚态物理和材料科学领域的研究热点之一.二维范德瓦尔斯异质结构为探索丰富多彩的物理效应和新奇的物理现象,以及构建新型的自旋电子学器件提供了灵活而广阔的平台.本文从二维材料的转移技术着手,介绍二维范德瓦尔斯异质结构的构筑、性能及应用.首先,依据湿法转移和干法转移的分类,详细介绍二维范德瓦尔斯异质结构的制备技术,内容包括转移技术的通用设备、常用转移方法的具体操作步骤、三维操纵二维材料的方法、异质界面清洁.随后介绍二维范德瓦尔斯异质结构的性能和应用,重点介绍二维磁性范德瓦尔斯异质结构,并列举在二维范德瓦尔斯磁隧道结和摩尔超晶格领域的应用.因此,二维材料转移技术的发展和优化将进一步助力二维范德瓦尔斯异质结构在基础科学研究和实际应用上取得突破性的成果.     

van der Waals PtO2/MoS2 heterostructure verified from first principles

First-principles calculations are used to study the structure and optoelectronic properties of a van der Waals (vdW) heterostructure formed by transition metal dichalcogenide and dioxide monolayers, namely PtO₂/MoS₂. The calculations suggest that a two-dimensional PtO₂ monolayer can be produced by exfoliation from the layered bulk α-PtO₂ and may even survive at high temperature. The PtO₂ monolayer is very closely matched with MoS₂ to form the vdW heterostructure. With its valence-band maximum and conduction-band minimum separated in different layers, this PtO₂/MoS₂ heterostructure is proposed as a type-II heterostructure with strong adsorption of visible light. Consequently, it may be widely applicable in photocatalysis and photovoltaics.     

Prospects and Opportunities of 2D van der Waals Magnetic Systems

The existence of spontaneous magnetization in low dimensional magnetic systems has attracted intensive studies since the early 60s and research remains very active even now. Only recently, magnetic van der Waals (vdW) systems down to a few layers have been broadly discussed for their magnetic order ground states at finite temperature. The naturally inherited layered structure of the vdW magnetic systems possessing onsite magnetic anisotropy from band electrons can suppress the long-range fluctuations. This provides an excellent vehicle to study the transition of magnetism to 2D limits both theoretically and experimentally. Here the current status of 2D vdW magnetic system and its potential applications are briefly summarized and discussed.     

Infrared diode laser spectroscopy of the He-N2O van der Waals complex in the 1285 cm region

The rovibrational spectrum of the He-N₂O van der Waals complex has been recorded in the N₂O-monomer ν₁ region (∼1285 cm⁻¹) using an infrared tunable diode laser spectrometer in conjunction with a free supersonic jet expansion and an astigmatic multi-pass absorption cell. Twenty-two lines are assigned to the ν₂-band of He-N₂O. Rotational constants for the ν₂-excited state are derived. The band-origin of the spectrum is determined to be ν₀ = 1285.0666(7) cm⁻¹ and shows a blue-shift of 0.1633(8) cm⁻¹ compared with the N₂O ν₁-band origin.     

Two dimensional GeO2/MoSi2N4 van der Waals heterostructures with robust type-II band alignment

Constructing two-dimensional (2D) van der Waals heterostructures (vdWHs) can expand the electronic and optoelectronic applications of 2D semiconductors. However, the work on the 2D vdWHs with robust band alignment is still scarce. Here, we employ a global structure search approach to construct the vdWHs with monolayer MoSi₂N₄ and wide-bandgap GeO₂. The studies show that the GeO₂/MoSi₂N₄ vdWHs have the characteristics of direct structures with the band gap of 0.946 eV and type-II band alignment with GeO₂ and MoSi₂N₄ layers as the conduction band minimum (CBM) and valence band maximum (VBM), respectively. Also, the direct-to-indirect band gap transition can be achieved by applying biaxial strain. In particular, the 2D GeO₂/MoSi₂N₄ vdWHs show a robust type-II band alignment under the effects of biaxial strain, interlayer distance and external electric field. The results provide a route to realize the robust type-II band alignment vdWHs, which is helpful for the implementation of optoelectronic nanodevices with stable characteristics.     

Infrared diode laser spectroscopy of O2–N2O van der Waals complex in the ν1 symmetric stretch region of N2O

The rovibrational spectrum of O₂–N₂O van der Waals complex is measured in the v₁ symmetric stretch region of N₂O monomer using a tunable diode laser spectrometer. The complex is generated by a slit-pulsed supersonic expansion with gas mixtures of O₂, N₂O, and He. Both a- and b-type transitions are observed. The effective Hamiltonian for an open-shell complex consisting of a diatomic molecule in a ³Σ electronic state and a closed-shell partner is used to analyze the observed spectrum. Molecular constants in the vibrationally excited state are determined accurately. The band-origin of the spectrum is determined to be 1284.7504(25) cm^-1, red-shifted from that of the N₂O monomer by ～ 0.1529 cm^-1.     

Effect of defects on the electronic structure of a PbI2/MoS2 van der Waals heterostructure: A first-principles study

PbI2/MoS2,as a typical van der Waals(vdW)heterostructure,has attracted intensive attention owing to its remarkable electronic and optoelectronic properties.In this work,the effect of defects on the electronic structures of a PbI2/MoS2 heterointerface has been systematically investigated.The manner in which the defects modulate the band structure of PbI2/MoS2,including the band gap,band edge,band alignment,and defect energy-level density within the band gap is discussed herein.It is shown that sulfur defects tune the band gaps,iodine defects shift the positions of the band edge and Fermi level,and lead defects realize the conversions between the straddling-gap band alignment and valence-band-aligned gap,thus enhancing the light-absorption ability of the material.     

应力调控BlueP/XTe2(X=Mo,W)范德瓦耳斯异质结电子结构及光学性质理论研究

通过第一性原理计算探讨了蓝磷烯与过渡金属硫化物MoTe₂/WTe₂形成范德瓦耳斯异质结的电子结构和光学性质,以及施加双轴应力对相关性质的影响.计算结果表明,形成BlueP/XTe₂(X=Mo,W)异质结,二者能带排列为间接带隙type-Ⅱ并有较强的红外光吸收,同时屏蔽特性增强.随压缩应力增加,BlueP/XTe₂转变为直接带隙type-Ⅱ能带排列最后转变为金属性;随拉伸应力增加,异质结转变为间接带隙type-Ⅰ能带排列.外加应力也能有效调控异质结的光吸收性质,随压缩应力增加吸收边红移,光吸收响应拓展至中红外光谱区且吸收系数增大;BlueP/MoTe₂较BlueP/WTe₂在中红外至红外光区间表现出更强的光吸收响应;静态介电常数ε1(0)大幅增加.结果表明,压缩应力对BlueP/MoTe₂和BlueP/WTe₂能带排列、光吸收特性均有显著的调控作用,其中BlueP/MoTe₂对调控更敏感,这些特性也使BlueP/XTe₂异质结在窄禁带中红外半导体材料及光电器件具有令人期待的应用价值.     

Tuning band alignment and optical properties of 2D van der Waals heterostructure via ferroelectric polarization switching

Favourable band alignment and excellent visible light response are vital for photochemical water splitting. In this work, we have theoretically investigated how ferroelectric polarization and its reversibility in direction can be utilized to modulate the band alignment and optical absorption properties. For this objective, 2D van der Waals heterostructures (HTSs) are constructed by interfacing monolayer MoS₂ with ferroelectric In2Se3. We find the switch of polarization direction has dramatically changed the band alignment, thus facilitating different type of reactions. In In₂Se₃/MoS₂/In₂Se₃ heterostructures, one polarization direction supports hydrogen evolution reaction and another polarization direction can favour oxygen evolution reaction. These can be used to create tuneable photocatalyst materials where water reduction reactions can be selectively controlled by polarization switching. The modulation of band alignment is attributed to the shift of reaction potential caused by spontaneous polarization. Additionally, the formed type-II van der Waals HTSs also significantly improve charge separation and enhance the optical absorption in the visible and infrared regions. Our results pave a way in the design of van der Waals HTSs for water splitting using ferroelectric materials.     

Rovibrational spectrum and potential energy surface of the N2-N2O van der Waals complex

The rovibrational spectrum of the N₂-N₂O van der Waals complex has been recorded in the N₂O ν₁ region (∼1285 cm⁻¹) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. The observed transitions together with the data observed previously in the N₂O ν₃ region are analyzed using a Watson S-reduced asymmetric rotor Hamiltonian. The rotational and centrifugal distortion constants for the ground and excited vibrational states are accurately determined. The band-origin of the spectrum is determined to be 1285.73964(14) cm⁻¹. A restricted two-dimensional intermolecular potential energy surface for a planar structure of N₂-N₂O has been calculated at the CCSD(T) level of theory with the aug-cc-pVDZ basis sets and a set of mid-bond functions. With the intermolecular distance fixed at the ground state value R = 3.6926 Å, the potential has a global minimum with a well depth of 326.64 cm⁻¹ at θ_N2 = 11.0° and θ_N2O = 84.3° and has a saddle point with a barrier height of 204.61 cm⁻¹ at θ_N2 = 97.4° and θ_N2O = 92.2°, where θ_N2(θ_N2O) is the enclosed angle between the N-N axis (N-N-O axis) and the intermolecular axis.     

Magnetic proximity effect induced spin splitting in two-dimensional antimonene/Fe3GeTe2 van der Waals heterostructures

Recently, two-dimensional van der Waals (vdW) magnetic heterostructures have attracted intensive attention since they can show remarkable properties due to the magnetic proximity effect. In this work, the spin-polarized electronic structures of antimonene/Fe₃GeTe₂ vdW heterostructures were investigated through the first-principles calculations. Owing to the magnetic proximity effect, the spin splitting appears at the conduction-band minimum (CBM) and the valence-band maximum (VBM) of the antimonene. A low-energy effective Hamiltonian was proposed to depict the spin splitting. It was found that the spin splitting can be modulated by means of applying an external electric field, changing interlayer distance or changing stacking configuration. The spin splitting energy at the CBM monotonously increases as the external electric field changes from -5 V/nm to 5 V/nm, while the spin splitting energy at the VBM almost remains the same. Meanwhile, as the interlayer distance increases, the spin splitting energies at the CBM and VBM both decrease. The different stacking configurations can also induce different spin splitting energies at the CBM and VBM. Our work demonstrates that the spin splitting of antimonene in this heterostructure is not singly dependent on the nearest Sb—Fe distance, which indicates that magnetic proximity effect in heterostructures may be modulated by multiple factors, such as hybridization of electronic states and the local electronic environment. The results enrich the fundamental understanding of the magnetic proximity effect in two-dimensional vdW heterostructures.     

两步化学气相沉积法制备In2Se3/MoSe2范德华尔斯异质结

Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide interest not only for the fundamental research,but also for the application of next generation electronic and optoelectronic devices.Herein,we report a successful two-step chemical vapor deposition strategy to construct vertically stacked van der Waals epitaxial In₂Se₃/MoSe₂ heterostructures.Transmission electron microscopy characterization reveals clearly that the In₂Se₃ has well-aligned lattice orientation with the substrate of monolayer MoSe₂.Due to the interaction between the In₂Se₃ and MoSe₂ layers,the heterostructure shows the quenching and red-shift of photoluminescence.Moreover,the current rectification behavior and photovoltaic effect can be observed from the heterostructure,which is attributed to the unique band structure alignment of the heterostructure,and is further confirmed by Kevin probe force microscopy measurement.The synthesis approach via van der Waals epitaxy in this work can expand the way to fabricate a variety of two-dimensional heterostructures for potential applications in electronic and optoelectronic devices.     

Direct FTIR high resolution probe of small and medium size Arn(CO2)m van der Waals complexes formed in a slit supersonic expansion

A slit nozzle continuous expansion of argon seeded with carbon dioxide is probed using a Bruker IFS 120 HR FTIR spectrometer operating at 0.05 cm⁻¹ or 0.01 cm⁻¹ spectral resolution. About 250 individual rovibrational transitions are assigned which belong to the asymmetric stretch of the CO₂ moiety in Ar-CO₂ and (CO₂)₂ complexes. This made it possible to refine the set of spectroscopic constants characterizing these van der Waals species. Analysis of the observed spectral features allowed for evaluation of the number densities of complexes formed in a jet. The manifold of rovibrational lines of van der Waals complexes (along with the monomer lines) sits on an unresolved pedestal, the shape of which varies dramatically as a function of reservoir pressure and initial CO₂-Ar mixing ratios. Thorough examination of these variations allows for the observed features to be assigned to Ar_n(CO₂)_m clusters formed in CO₂ seeded Ar expansion.