Abstract
We report on the growth of an ordered array of MoS2 nanodots (lateral sizes in the range of ∼100–250 nm) by a thermal chemical vapor deposition (CVD) method directly onto SiO2 substrates at a relatively low substrate temperature (510–560°C). The temperature-dependent growth and evolution of MoS2 nanodots and the local environment of sulfur-induced structural defects and impurities were systematically investigated by field emission scanning electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. At the substrate temperature of 560°C, we observed mostly few-layer MoS2, and at 510°C, multilayer MoS2 growth, as confirmed from the Raman line shape analysis. With reduced substrate temperature, the density of MoS2 nanodots decreases, and layer thickness increases. Raman studies show characteristic Raman modes of the crystalline MoS2 layer, along with two new Raman modes centered at ∼346 and ∼361 cm−1, which are associated with MoO2 and MoO3 phases, respectively. Room temperature photoluminescence (PL) studies revealed strong visible PL from MoS2 layers, which is strongly blue-shifted from the bulk MoS2 flakes. The strong visible emission centered at ∼ 658 nm signifies a free excitonic transition in the direct gap of single-layer MoS2. Position-dependent PL profiles show excellent uniformity of the MoS2 layers for samples grown at 540 and 560°C. These results are significant for the low-temperature CVD growth of a few-layer MoS2 dots with direct bandgap photoluminescence on a flexible substrate.
Highlights
Since the discovery of graphene, two-dimensional materials have attracted much interest due to their interesting optical, electrical, and mechanical characteristics
In order to understand the morphology of the as-grown samples, field emission scanning electron microscope (FESEM) imaging was carried out
A detailed description of the sample growth conditions and FESEM features is provided in Supplementary Table S1
Summary
Since the discovery of graphene, two-dimensional materials have attracted much interest due to their interesting optical, electrical, and mechanical characteristics. The vast difference in the electronic structure of the bulk in comparison with the monolayer MoS2 offers a great opportunity for diverse applications It has an excellent on/off ratio of 108 (Radisavljevic et al, 2011) and a high carrier mobility up to 200 cm2/ Vs at room temperature (Radisavljevic et al, 2011), making it a promising candidate for optoelectronic applications, such as photodetectors (Yin et al, 2012), (Lee et al, 2012)photovoltaics, Direct growth on these substrates poses a considerable challenge; usually, the MoS2 grown at high temperature is transferred onto these substrates to fabricate the devices. The best fit was obtained by a large number of iterations
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