4 research outputs found
Effects of inorganic seed promoters on MoS2 few-layers grown via chemical vapor deposition
In the last years, transition metal dichalcogenides (TMDs), especially at the
two-dimensional (2D) limit, gained a large interest due to their unique optical
and electronic properties. Among them, MoS2 received great attention from the
scientific community due to its versatility, workability, and applicability in
a large number of fields such as electronics, optoelectronics and
electrocatalysis. To open the possibility of 2D-MoS2 exploitation, its
synthesis over large macroscopic areas using cost-effective methods is
fundamental. In this study, we report a method for the synthesis of large-area
(~ cm2) few-layers MoS2 via liquid precursor CVD (L-CVD), where the Mo
precursor (i.e. ammonium heptamolybdate AHM) is provided via a solution that is
spin-coated over the substrate. Given the capability of organic and inorganic
molecules, such as alkaline salts, to enhance MoS2 growth, we investigated the
action of different inorganic salts as seed promoters. In particular, by using
visible Raman spectroscopy, we focused on the effect of Na(OH), KCl, KI, and
Li(OH) on the thickness, morphology, uniformity and degree of coverage of the
grown MoS2. We optimized the process tuning parameters such as the volume of
spin-coated solution, the growth temperature, and the seed promoter
concentration, to synthesise the lowest possible thickness which resulted to be
2 layers (2L) of the highest quality. We witnessed that the addition of an
inorganic seed promoter in the solution improves the extension of the grown
MoS2 promoting lateral growth front, and therefore the degree of coverage. From
this study, we conclude that, amongst the investigated seed promoters, K-based
salts proved to grant the growth of high-quality two-layer MoS2 with optimal
and uniform coverage of the SiO2/Si substrate surface
Ambient Pressure Chemical Vapor Deposition of Flat and Vertically Aligned MoS<sub>2</sub> Nanosheets
Molybdenum disulfide (MoS2) got tremendous attention due to its atomically thin body, rich physics, and high carrier mobility. The controlled synthesis of large area and high crystalline monolayer MoS2 nanosheets on diverse substrates remains a challenge for potential practical applications. Synthesizing different structured MoS2 nanosheets with horizontal and vertical orientations with respect to the substrate surface would bring a configurational versatility with benefit for numerous applications, including nanoelectronics, optoelectronics, and energy technologies. Among the proposed methods, ambient pressure chemical vapor deposition (AP-CVD) is a promising way for developing large-scale MoS2 nanosheets because of its high flexibility and facile approach. Here, we show an effective way for synthesizing large-scale horizontally and vertically aligned MoS2 on different substrates such as flat SiO2/Si, pre-patterned SiO2 and conductive substrates (TaN) benefit various direct TMDs production. In particular, we show precise control of CVD optimization for yielding high-quality MoS2 layers by changing growth zone configuration and the process steps. We demonstrated that the influence of configuration variability by local changes of the S to MoO3 precursor positions in the growth zones inside the CVD reactor is a key factor that results in differently oriented MoS2 formation. Finally, we show the layer quality and physical properties of as-grown MoS2 by means of different characterizations: Raman spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). These experimental findings provide a strong pathway for conformally recasting AP-CVD grown MoS2 in many different configurations (i.e., substrate variability) or motifs (i.e., vertical or planar alignment) with potential for flexible electronics, optoelectronics, memories to energy storage devices
Large Area Growth and Phase Selectivity of MoTe2 Nanosheets through SimulationāGuided CVD Tellurization
Abstract Among transition metal dichalcogenides, molybdenum ditelluride (MoTe2) holds significant attention due to its polymorphic nature including semiconducting, metallic, and topological semimetal phases. Considerable efforts are devoted to synthesizing MoTe2 nanosheets to make them suitable for device integration in nanotechnologies and for fundamental investigations. In this respect, chemical vapor deposition (CVD) via tellurization of a preādeposited Mo thin film is an easy and flexible way for synthesizing large scale MoTe2 nanosheets. Here, the study report on the CVD of largeāarea (up to 4 cm Ć 1 cm) MoTe2 nanosheets with pure 1Tā and 2H phase selection by design. Within the tellurization scheme, the vaporāsolid reaction between the preādeposited molybdenum film and tellurium vapor is studied thus optimizing the scalability and quality of the MoTe2 nanosheets grown on SiO2/Si substrates. It is demonstrated that the MoTe2 structure and morphology are kinetically dictated by the tellurium concentration gradient on the reaction site with varying geometric configurations inside the CVD reactor. This study provides a pivot scheme for enabling scalable 1Tā and 2HāMoTe2 integration in applications for novel microā and nanoāelectronics, spintronics, photonics, and thermoelectric devices
Extreme Bendability of Atomically Thin MoS2 Grown by Chemical Vapor Deposition Assisted by Perylene-Based Promoter
Shaping two-dimensional (2D) materials in arbitrarily complex geometries is a key to designing their unique physical properties in a controlled fashion. This is an elegant solution, taking benefit from the extreme flexibility of the 2D layers but requiring the ability to force their spatial arrangement from flat to curved geometries in a delicate balance among free-energy contributions from strain, slip-and-shear mechanisms, and adhesion to the substrate. Here, we report on a chemical vapor deposition approach, which takes advantage of the surfactant effects of organic molecules, namely the tetrapotassium salt of perylene-3,4,9,10-tetracarboxylic acid (PTAS), to conformally grow atomically thin layers of molybdenum disulphide (MoS2) on arbitrarily nanopatterned substrates. Using atomically resolved transmission electron microscope images and density functional theory calculations, we show that the most energetically favorable condition for the MoS2 layers consists of its adaptation to the local curvature of the patterned substrate through a shear-and-slip mechanism rather than strain accumulation. This conclusion also reveals that the perylene-based molecules have a role in promoting the adhesion of the layers onto the substrate, no matter the local-scale geometry