Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted tremendous attention because of their unique electronic, optical and chemical properties. 2D TMDs, especially 2D MoS 2 , have been proved to show great potential in various applications such as sensing, hydrogen evolution and lithium ion batteries. Therefore, methods for the scalable preparation of 2D materials and 2D nanocomposites of high quality and low cost must be developed. Among the various synthesis methods, the hydrothermal synthesis method is simple and can meet the above requirements. In this review, the recent advances in the controllable hydrothermal synthesis of 2D MoS 2 and its nanocomposites by the hydrothermal synthesis method are highlighted. We provide insight into the growth mechanisms of few-layered 2D MoS 2 with different morphologies and the key technologies to realize wafer-scale growth of continuous and homogeneous 2D films which are important for practical applications. Further, the typical applications of TMDs in nonlinear optics as ultrafast optical modulation devices are presented based on work of our institute. For more clarity, we summarize the current challenges of the hydrothermal synthesis method encountering, and suggest solutions to these challenges concerning future developments in practical applications.
A novel modulation scheme termed orthogonal frequency-division multiplexing with subcarrier number modulation (OFDM-SNM) has been proposed and regarded as one of the promising candidate modulation schemes for next generation networks. Although OFDM-SNM is capable of having a higher spectral efficiency (SE) than OFDM with index modulation (OFDM-IM) and plain OFDM under certain conditions, its reliability is relatively inferior to these existing schemes, because the number of active subcarriers varies. In this regard, we propose an enhanced OFDM-SNM scheme in this paper, which utilizes the flexibility of placing subcarriers to harvest a coding gain in the high signal-to-noise ratio (SNR) region. In particular, we stipulate a methodology that optimizes the subcarrier activation pattern (SAP) by subcarrier assignment using instantaneous channel state information (CSI) and therefore the subcarriers with higher channel power gains will be granted the priority to be activated, given the number of subcarriers is fixed. We also analyze the proposed enhanced OFDM-SNM system in terms of outage and error performance. The average outage probability and block error rate (BLER) are derived and approximated in closed-form expressions, which are further verified by numerical results generated by Monte Carlo simulations. The high-reliability nature of the enhanced OFDM-SNM makes it a promising candidate for implementing in the Internet of Things (IoT) with stationary machine-type devices (MTDs), which are subject to slow fading and supported by proper power supply.Index Terms-Orthogonal frequency-division multiplexing with subcarrier number modulation (OFDM-SNM), subcarrier assignment, reliability enhancement, outage performance analysis, error performance analysis.
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