Tunable electronic structure of two-dimensional transition metal chalcogenides for optoelectronic applications

Differing from its bulk counterparts, atomically thin two-dimensional transition metal dichalcogenides that show strong interaction with light are considered as new candidates for optoelectronic devices. Either physical or chemical strategies can be utilized to effectively tune the intrinsic electronic structures for adopting optoelectronic applications. This review will focus on the different tuning strategies that include its physics principles, in situ experimental techniques, and its application of various optoelectronic devices

Optical Control of the Localized Surface Plasmon Resonance in a Heterotype and Hollow Gold Nanosheet

The remote excitation and remote-controlling of the localized surface plasmon resonance (LSPR) in a heterotype and hollow gold nanosheet (HGNS) is studied using FDTD simulations. The heterotype HGNS contains an equilateral and hollow triangle in the center of a special hexagon, which forms a so-called hexagon–triangle (H–T) heterotype HGNS. If we focus the incident-exciting laser on one of the vertexes of the center triangle, the LSPR could be achieved among other remote vertexes of the outer hexagon. The LSPR wavelength and peak intensity depend sensitively on factors such as the polarization of the incident light, the size and symmetry of the H–T heterotype structure, etc. Several groups of the optimized parameters were screened out from numerous FDTD calculations, which help to further obtain some significant polar plots of the polarization-dependent LSPR peak intensity with two-petal, four-petal or six-petal patterns. Remarkably, based on these polar plots, the on-off switching of the LSPR coupled among four HGNS hotspots could be remote-controlled simply via only one polarized light, which shows promise for its potential application in remote-controllable surface-enhanced Raman scattering (SERS), optical interconnects and multi-channel waveguide switches

Spin transport property of Cr2C based nanoscale devices: A first principle study

Edge states and interfacial design are important influencing factors for spin transport property modulation of nanoscale devices. Electronic structure and spin charge transmission path of both armchair/zigzag Cr2C nanoribbon and single-porphyrin molecular junctions with Cr2C nanoribbon electrodes are studied based on spin polarized density functional theory and non-equilibrium Green's function method. The results show that both zigzag and armchair oriented Cr2C nanoribbons have intrinsic magnetic half-metallic behavior. Volt-ampere characteristics of zigzag Cr2C nanodevices are linear, and that of armchair Cr2C nanodevice shows obvious saturation effect and negative differential resistance effect (NDR). These two cases maintain both strong spin polarization current intensity and 100% spin filtering efficiency (SFE). In addition, the intercalation of porphyrin molecule significantly reduces electron accumulation near the Fermi level in case of armchair Cr2C nanodevice which retains 100% spin polarization behavior. This work expands a potential application of intrinsic magnetic two-dimensional materials in field of molecular spintronic devices

Modulation of thermoelectric performance of Cn-BTBT molecular junctions by engineering contact geometry

Organic molecular devices are promising candidates for thermoelectric applications. By using density functional theory combined with non-equilibrium Green’s function method, we have investigated the thermoelectric properties of a single-molecule junction, which is constructed by 2,7-dialkyl [1] benzothieno [3,2-b] [1] benzothiophene derivatives (Cn-BTBT) connected with zigzag graphene nanoribbon electrodes. It is found that the phonon thermal conductance decreases with the increase of alkyl edge branches due to the local resonance. And the thermoelectric performance can be enhanced significantly by substituting bithiophene or biphosphole bridge anchor groups. A good thermoelectric figure of merit about 0.56 can be obtained near Fermi level. Moreover, we also found that the molecular device can be changed from p-type into n-type by changing the contact points, resulting in the transformation of Seebeck coefficient from positive to negative

Temperature−Dependent Raman Scattering Investigation on vdW Epitaxial PbI₂/CrOCl Heterostructure

Van der Waals (vdW) epitaxial growth provides an efficient strategy to prepare heterostructures with atomically and electronically sharp interfaces. Herein, PbI2 was in situ thermally deposited onto exfoliated thin−layered CrOCl nanoflakes in high vacuum to fabricate vdW PbI2/CrOCl heterostructures. Optical microscopy, atomic force microscopy, X−ray diffraction, and temperature−dependent Raman spectroscopy were used to investigate the structural properties and phonon behaviors of the heterostructures. The morphology of PbI2 films on the CrOCl substrate obviously depended on the substrate temperature, changing from hemispherical granules to 2D nanoflakes with flat top surfaces. In addition, anomalous blueshift of the Ag1 and Au2 modes as the temperature increased in PbI2/CrOCl heterostructure was observed for the first time. Our results provide a novel material platform for the vdW heterostructure and a possible method for optimizing heterostructure growth behaviors