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Register a new userGrowth of Transition Metal Dichalcogenides by Solvent Evaporation Technique
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Added by
Mahmoud Abdel-Hafiez
Publication date
2020
fields
Physics
and research's language is
English
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Due to their physical properties and potential applications in energy conversion and storage, transition metal dichalcogenides (TMDs) have garnered substantial interest in recent years. Amongst this class of materials, TMDs based on molybdenum, tungsten, sulfur and selenium are particularly attractive due to their semiconducting properties and the availability of bottom-up synthesis techniques. Here we report a method which yields high quality crystals of transition metal diselenide and ditelluride compounds (PtTe2, PdTe2, NiTe2, TaTe2, TiTe2, RuTe2, PtSe2, PdSe2, NbSe2, TiSe2, VSe2, ReSe2) from their solid solutions, via vapor deposition from a metal-saturated chalcogen melt. Additionally, we show the synthesis of rare-earth metal poly-chalcogenides and NbS2 crystals using the aforementioned process. Most of the obtained crystals have a layered CdI2 structure. We have investigated the physical properties of selected crystals and compared them to state-of-the-art findings reported in the literature. Remarkably, the charge density wave transition in 1T-TiSe2 and 2H-NbSe2 crystals is well-defined at TCDW ~ 200 K and ~ 33 K, respectively. Angle-resolved photoelectron spectroscopy and electron diffraction are used to directly access the electronic and crystal structures of PtTe2 single crystals, and yield state-of-the-art measurements.
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In the crystal growth of transition metal dichalcogenides by the Chemical Vapor Transport method (CVT), the choice of the transport agent plays a key role. We have investigated the effect of various chemical elements and compounds on the growth of TiSe2, MoSe2, TaS2 and TaSe2 and found that pure I2 is the most suitable for growing TiSe2, whereas transition metal chlorides perform best with Mo- and Ta- chalcogenides. The use of TaCl5 as a transport agent in the CVT process allows to selectively growth either polymorph of TaS2 and TaSe2 and the optimum growth conditions are reported. Moreover, by using TaCl5 and tuning the temperature and the halogen starting ratio, it was possible to grow whiskers of the compounds TaS2, TaSe2, TaTe2, TaS3 and TaSe3.
Starting from graphene, 2D layered materials family has been recently set up more than 100 different materials with variety of different class of materials such as semiconductors, metals, semimetals, superconductors. Among these materials, 2D semiconductors have found especial importance in the state of the art device applications compared to that of the current conventional devices such as (which material based for example Si based) field effect transistors (FETs) and photodetectors during the last two decades. This high potential in solid state devices is mostly revealed by the transition metal dichalcogenides (TMDCs) semiconductor materials such as MoS2 , WS2 , MoSe2 and WSe2 . Therefore, many different methods and approaches have been developed to grow or obtain so far in order to make use them in solid state devices, which is a great challenge in large area applications. Although there are intensively studied methods such as chemical vapor deposition (CVD), mechanical exfoliation, atomic layer deposition, it is sputtering getting attention day by day due to the simplicity of the growth method together with its reliability, large area growth possibility and repeatability. In this review article, we provide benefits and disadvantages of all the growth methods when growing TMDC materials, then focusing on the sputtering TMDC growth strategies performed. In addition, TMDCs for the FETs and photodetector devices grown by RFMS have been surveyed.
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted much interest and shown promise in many applications. However, it is challenging to obtain uniform TMDCs with clean surfaces, because of the difficulties in controlling the way the reactants are supplied to the reaction in the current chemical vapor deposition (CVD) growth process. Here, we report a new growth approach called dissolution-precipitation (DP) growth, where the metal sources are sealed inside glass substrates to control their feeding to the reaction. Noteworthy, the diffusion of metal source inside glass to its surface provides a uniform metal source on the glass surface, and restricts the TMDC growth to only a surface reaction while eliminates unwanted gas-phase reaction. This feature gives rise to highly-uniform monolayer TMDCs with a clean surface on centimeter-scale substrates. The DP growth works well for a large variety of TMDCs and their alloys, providing a solid foundation for the controlled growth of clean TMDCs by the fine control of the metal source.
Most III-nitride semiconductors are grown on non-lattice-matched substrates like sapphire or silicon due to the extreme difficulty of obtaining a native GaN substrate. We show that several layered transition-metal dichalcogenides are closely lattice matched to GaN and report the growth of GaN on a range of such layered materials. We report detailed studies of the growth of GaN on mechanically-exfoliated flakes WS$_2$ and MoS$_2$ by metalorganic vapour phase epitaxy. Structural and optical characterization show that strain-free, single-crystal islands of GaN are obtained on the underlying chalcogenide flakes. We obtain strong near-band-edge emission from these layers, and analyse their temperature-dependent photoluminescence properties. We also report a proof-of-concept demonstration of large-area epitaxial growth of GaN on CVD MoS$_2$. Our results show that the transition-metal dichalcogenides can serve as novel near-lattice-matched substrates for nitride growth.
Modulating electronic structure of monolayer transition metal dichalcogenides (TMDCs) is important for many applications and doping is an effective way towards this goal, yet is challenging to control. Here we report the in-situ substitutional doping of niobium (Nb) into TMDCs with tunable concentrations during chemical vapour deposition. Taking monolayer WS2 as an example, doping Nb into its lattice leads to bandgap changes in the range 1.98 eV to 1.65 eV. Noteworthy, electrical transport measurements and density functional theory calculations show that the 4d electron orbitals of the Nb dopants contribute to the density of states of Nb-doped WS2 around the Fermi level, resulting in an n to p-type conversion. Nb-doping also reduces the energy barrier of hydrogen absorption in WS2, leading to an improved electrocatalytic hydrogen evolution performance. These results highlight the effectiveness of controlled doping in modulating the electronic structure of TMDCs and their use in electronic related applications.
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