In-situ TEM Analyses over FIB Lamellae - Investigating High Temperature Conversion of Solution Processed Mo-precursor to MoS2 Semiconductor Films (original) (raw)
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Orientation of Few-Layer MoS2 Films: In-Situ X-ray Scattering Study During Sulfurization
The Journal of Physical Chemistry C, 2021
Some of the distinct optical, catalytical, and electronic properties of few-layer MoS 2 films arise from a specific orientation of the MoS 2 layers. The growth of horizontally or vertically aligned MoS 2 during the sulfurization of predeposited Mo film can be controlled by various physical conditions such as temperature, heating rate, Mo film thickness, or sulfur vapor pressure. However, due to the inherent limitations of performing real-time and in situ experiments during sulfurization in a standard growth chamber, only a limited number of analytical techniques can be used to elucidate the in-process phase transformation. Here, we present a comprehensive real-time study of the growth of few-layer MoS 2 films by sulfurization of Mo films using in situ grazing-incidence wide-angle X-ray scattering. We demonstrate that the process gas flow, and thus the sulfur partial vapor pressure, is the key control parameter for the few-layer MoS 2 layer orientation while all other process parameters remain fixed. Tracking the crystallization of few-layer MoS 2 layers in real-time allowed us to estimate the activation energy required for both horizontal and vertical orientations. Growth of either horizontal or vertical MoS 2 was observed without a metastable transition between them throughout the sulfurization.
Large-scale integration of MoS 2 in electronic devices requires the development of reliable and cost-effective deposition processes, leading to uniform MoS 2 layers on a wafer scale. Here we report on the detailed study of the heterogeneous vapor-solid reaction between a pre-deposited molybdenum solid film and sulfur vapor, thus resulting in a controlled growth of MoS 2 films onto SiO 2 /Si substrates with a tunable thickness and cm 2 -scale uniformity. Based on Raman spectroscopy and photoluminescence, we show that the degree of crystallinity in the MoS 2 layers is dictated by the deposition temperature and thickness. In particular, the MoS 2 structural disorder observed at low temperature (<750°C) and low thickness (two layers) evolves to a more ordered crystalline structure at high temperature (1000°C) and high thickness (four layers). From an atomic force microscopy investigation prior to and after sulfurization, this parametrical dependence is associated with the inherent granularity of the MoS 2 nanosheet that is inherited by the pristine morphology of the pre-deposited Mo film. This work paves the way to a closer control of the synthesis of wafer-scale and atomically thin MoS 2 , potentially extendable to other transition metal dichalcogenides and hence targeting massive and high-volume production for electronic device manufacturing.
Atomically thin layers of MoS2via a two step thermal evaporation–exfoliation method
2012
Two dimensional molybdenum disulfide (MoS2) has recently become of interest to semiconductor and optic industries. However, the current methods for its synthesis require harsh environments that are not compatible with standard fabrication processes. We report on a facile synthesis method of layered MoS2 using a thermal evaporation technique, which requires modest conditions.
Synthesis of Large-Area MoS 2 Atomic Layers with Chemical Vapor Deposition
Advanced Materials, 2012
Transition metal dichalcogenides (TMD), MX 2 (M=Mo, W; X=S, Se, Te), have attracted considerable attention for their great potential in the fields of catalysis, nanotribology, microelectronics, lithium batteries, hydrogen storage, medical and optoelectronics. MoS 2 nano-materials have been known in the form of nested fullerene-like nanodots and one-dimensional nanotubes. Stimulated by the discovery of two-dimensional graphene monolayer and its rich physical phenomenon, inorganic graphene analogues such as layered MoS 2 , where the Mo layer is sandwiched between two sulfur layers by covalent forces, have created great interest in the past few years. Recently, Radisavljevic et al. have demonstrated that the transistors fabricated with the exfoliated MoS 2 monolayer exhibit high on-off current ratio and good electrical performance, which may be used in future electronic circuits requiring low stand-by power. The strong emission inherited from the direct gap structure of monolayer MoS 2 also promises the applications in optoelectronics. Substantial efforts have been devoted to prepare thin-layer MoS 2 , including scotch tape based micromechanical exfoliation, intercalation assisted exfoliation, liquid exfoliation, physical vapor deposition, hydrothermal synthesis, thermolysis of single precursor containing Mo and S. The lateral size of the MoS 2 films synthesized by the aforementioned methods is often in the order of several micrometer; however, the synthesis of large-size []
Growth of MoS2 Thin Films Using the Two-step Approach
Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi
In this study, MoS2 thin films were grown using two-step approach, which is based on employing both PVD and CVD techniques. The films were obtained initially by sputtering 1nm Mo film in the PVD system and followed by sulphurization of the film in CVD at 700 oC. The grown films were optimized employing different sulphurization times. The main difference in our study from the current literature is using preheated CVD furnace (700 oC) ahead of sulphurization. The films quality are then investigated using Raman and Photoluminance spectrometer as well as AFM measurements. The Raman spectrums indicate that two characteristic vibration modes of 2H-MoS2 phase were observed in all samples, however, vibration modes of 1T-MoS2 phase were also observed in some films at low sulphurization time. These results were also in line with PL measurements that confirm the direct band transition of the MoS2 films. The surface topography of the films were investigated by AFM for MoS2 films obtained by the...
Large-area MoS 2 grown using H 2 S as the sulphur source
2D materials, 2015
We report on the growth of molybdenum disulphide (MoS 2) using H 2 S as a gas-phase sulfur precursor that allows controlling the domain growth direction of domains in both vertical (perpendicular to the substrate plane) and horizontal (within the substrate plane), depending on the H 2 S:H 2 ratio in the reaction gas mixture and temperature at which they are introduced during growth. Optical and atomic force microscopy measurements on horizontal MoS 2 demonstrate the formation of monolayer triangular-shape domains that merge into a continuous film. Scanning transmission electron microscopy of monolayer MoS 2 shows a regular atomic structure with a hexagonal symmetry. Raman and photoluminescence spectra confirm the monolayer thickness of the material. Field-effect transistors fabricated on MoS 2 domains that are transferred onto Si/SiO 2 substrates show a mobility similar to previously reported exfoliated and chemical vapor deposition-grown materials.