Research Advances of Typical Two Dimensional Layered Thermoelectric Materials

Thermoelectric technologies have caught our intense attention due to their ability of heat conversion into electricity.The considerable efforts have been taken to develop and enhance thermoelectric properties of materials over the past several decades.Recently,twodimensional layered materials are making the promise for potential applications of thermoelectric devices because of the excellent physical and structural properties.Here,a comprehensive coverage about recent progresses in thermoelectric properties of typical two dimensional(2D)layered materials,including the theoretical and experimental results,is provided.Moreover,the potential applications of 2D thermoelectric materials are also involved.These results indicate that the development of 2D thermoelectric materials take a key role in the flexible electronic devices with thermoelectric technologies.

Recent advances in two-dimensional layered and non-layered materials hybrid heterostructures

With the development of Moore's law, the future trend of devices will inevitably be shrinking and integration to further achieve size reduction. The emergence of new two-dimensional non-layered materials(2DNLMs) not only enriches the 2D material family to meet future development, but also stimulates the global enthusiasm for basic research and application technologies in the 2D field. Van der Waals(vd W) heterostructures, in which two-dimensional layered materials(2DLMs)are physically stacked layer by layer, can also occur between 2DLMs and 2DNLMs hybrid heterostructures, providing an alternative platform for nanoelectronics and optoelectronic applications. Here, we outline the recent developments of2DLMs/2DNLMs hybrid heterostructures, with particular emphasis on major advances in synthetic methods and applications. And the categories and crystal structures of 2DLMs and 2DNLMs are also shown. We highlight some promising applications of the heterostructures in electronics, optoelectronics, and catalysis. Finally, we provide conclusions and future prospects in the 2D materials field.

Multilayered PdTe_(2)/thin Si heterostructures as self-powered flexible photodetectors with heart rate monitoring ability

Two-dimensional layered material/semiconductor heterostructures have emerged as a category of fascinating architectures for developing highly efficient and low-cost photodetection devices.Herein,we present the construction of a highly efficient flexible light detector operating in the visible-near infrared wavelength regime by integrating a PdTe2 multilayer on a thin Si film.A representative device achieves a good photoresponse performance at zero bias including a sizeable current on/off ratio exceeding 105,a decent responsivity of~343 mA/W,a respectable specific detectivity of~2.56×10^(12)Jones,and a rapid response time of 4.5/379μs,under 730 nm light irradiation.The detector also displays an outstanding long-term air stability and operational durability.In addition,thanks to the excellent flexibility,the device can retain its prominent photodetection performance at various bending radii of curvature and upon hundreds of bending tests.Furthermore,the large responsivity and rapid response speed endow the photodetector with the ability to accurately probe heart rate,suggesting a possible application in the area of flexible and wearable health monitoring.

Extensive study of optical contrast between bulk and nanoscale transition metal dichalcogenide semiconductors

A remarkable refinement in the optical behavior of two-dimensional transition metal dichalcogenides(TMDs)has been brought to light when cleaved from their respective bulks.These atomically thin direct bandgap semiconductors are highly responsive to optical energy which proposes the route for futuristic photonic devices.In this manuscript,we have substantially focused on the optical study of MoS_(2)and WS_(2)nanosheets and comparative analysis with their bulk counterparts.The synthesis of nanosheets has been accomplished with liquid exfoliation followed by fabrication of thin films with drop-casting technique.X-ray diffraction and field emission scanning electron microscopy affirmed the morphology,whereas,UV-visible spectroscopy served as the primary tool for optical analysis.It was observed that several parameters,like optical conductivity,optical band-gap energy etc.have enhanced statistics in the case of exfoliated nanosheets as compared to their respective bulks.Some researchers have touched upon this analysis for MoS_(2),but it is completely novel for WS_(2).We expect our work to clearly distinguish between the optical behaviors of nanoscale and bulk TMDs so as to intensify and strengthen the research related to 2D-layered materials for optoelectronic and photovoltaic applications.

Anisotropic optical and electronic properties of two- dimensional layered germanium sulfide

Two-dimensional （2D） layered materials, transition-metal dichalcogenides, and black phosphorus have attracted considerable interest from the viewpoints of fundamental physics and device applications. The establishment of new functionalities in anisotropic layered 2D materials is a challenging but rewarding frontier, owing to the remarkable optical properties of these materials and their prospects for new devices. Herein, we report the anisotropic and thickness- dependent optical properties of a 2D layered monochalcogenide of germanium sulfide （GeS）. Three Raman-scattering peaks corresponding to the B3g,, A1g, and A2g modes with a strong polarization dependence are demonstrated in the GeS flakes, which validates polarized Raman spectroscopy as an effective method for identifying the crystal orientation of anisotropic layered GeS. Photoluminescence （PL） is observed with a peak at -1.66 eV that originates from the direct optical transition in GeS at room temperature. The polarization-dependent characteristics of the PL, which are revealed for the first time, along with the demonstration of anisotropic absorption, indicate an obvious anisotropic optical transition near the band edge of GeS, which is supported by density functional theory calculations. The significantly thickness-dependent PL is observed and discussed. This anisotropic layered GeS presents opportunities for the discovery of new physical phenomena and will find applications that exploit its anisotropic properties, such as polarization-sensitive photodetectors.

A brief review of tribological properties for black phosphorus

Black phosphorus (BP) is a new class of two-dimensional (2D) layered material, which shows the unanticipated characteristics in many aspects including electronics, transistors, sensors, energy storage, batteries, photocatalysis, and other applications due to its high charge carrier mobility, tunable direct bandgap, and unique in-plane anisotropic structure. In addition, BP has drawn tremendous attention in the field of tribology due to the low shear strength, the layered structure, and the weak connected force between the layers by van der Waals interaction. In recent years, many significant progresses have been made in experimental studies on BP materials as solid lubricants or lubrication additives. This work offers a review of researching regarding the tribological properties of BP. Moreover, the lubrication mechanisms of BP as the lubrication additive including the formation of the tribo-film, micro-bearing effect, and self-repair performance are also summarized. Finally, the current challenges and prospects of BP material as lubricant are proposed.

Inversion symmetry broken 2D SnP_(2)S_(6) with strong nonlinear optical response

Nowadays,realizing miniaturized nonlinear optical(NLO)device is crucial to meet the growing needs in on-chip nanophotonics as well as compact integrated devices.The strong optical nonlinearities,ultrafast photoexcitation dynamics,available exciton effects as well as without lattice matching make two-dimensional(2D)layered materials potential candidates for integrated and nano-scale NLO devices.Herein,a novel and inversion symmetry broken 2D layered SnP_(2)S_(6)with strong second-harmonic and third-harmonic response has been reported for the first time.The second-order susceptibility(χ^(2))of SnP_(2)S_(6)flakes can reach up to 4.06×10^(−9)m·V^(−1)under 810 nm excitation wavelength,which is around 1–2 orders of magnitude higher than that of most reported 2D materials.In addition,the NLO response of 2D SnP_(2)S_(6)can break through the limitation of odd/even layers and exhibit broadband spectral response.Moreover,since the second-harmonic signal is closely related to structure variation,the second-harmonic response in 2D SnP_(2)S_(6)is extremely sensitive to polarization angle and temperature,which is beneficial to some specific applications.The excellent NLO response in 2D SnP_(2)S_(6)provides a new arena for realizing miniaturized NLO devices in the future.

原位集成光浮栅的多层SnS_(2)/少层MoS_(2)异质结用于高性能光电探测器与光学成像

自单层MoS_(2)光电晶体管问世以来,二维层状材料一直被认为是实现下一代新型光电器件与系统的最引人瞩目的候选材料之一.然而,大多数报道的二维层状材料光电探测器都存在一定的缺点,如响应率低、暗电流大、比探测率低、开关比低、响应速率慢等.在本研究中,通过堆叠由大气压化学气相沉积技术所生长的MoS_(2)和SnS_(2)纳米片,制备出了多层SnS_(2)/少层MoS_(2)范德华异质结.相应的SnS_(2)/MoS_(2)异质结光电探测器展示出了具有竞争力的综合性能:大开关比(171)、高响应率(28.3 A W^(-1)),以及出色的比探测率(1.2×10^(13)Jones).此外,该器件还实现了响应/恢复时间低至1.38 ms/600μs的超快响应速率.其优异的性能与SnS_(2)/MoS_(2)异质结的Ⅱ型能带排列以及原位形成的无缝光浮栅的协同作用相关,这有助于分离光激发的电子-空穴对,并延长非平衡载流子的寿命.得益于出色的光敏性,该SnS_(2)/MoS_(2)器件实现了概念验证的光学成像应用.总体而言,本研究为实现具有优异综合性能的先进光电探测器提供了独特视角.

Direct bandgap engineering with local biaxial strain in few-layer MoS2 bubbles

Nano Research volume 13,pages2072–2078(2020)Cite this article 211 Accesses Metrics details Abstract Strain engineering provides an important strategy to modulate the optical and electrical properties of semiconductors for improving devices performance with mechanical force or thermal expansion difference.Here,we present the investigation of the local strain distribution over few-layer MoS2 bubbles,by using scanning photoluminescence and Raman spectroscopies.We observe the obvious direct bandgap emissions with strain in the few-layer MoS2 bubble and the strain-induced continuous energy shifts of both resonant excitons and vibrational modes from the edge of the MoS2 bubble to the center(10μm scale),associated with the oscillations resulted from the optical interference-induced temperature distribution.To understand these results,we perform ab initio simulations to calculate the electronic and vibrational properties of few-layer MoS2 with biaxial tensile strain,based on density functional theory,finding good agreement with the experimental results.Our study suggests that local strain offers a convenient way to continuously tune the physical properties of a few-layer transition metal dichalcogenides(TMDs)semiconductor,and opens up new possibilities for band engineering within the 2D plane.