Two-dimensional (2D) transition metal dichalcogenides (TMDs) have gained much attention in virtue of their various atomic configurations and band structures. Apart from those thermodynamically stable phases, plenty of metastable phases exhibit interesting properties. To obtain 2D TMDs with specific phases, it is important to develop phase engineering strategies including phase transition and phaseselective synthesis. Phase transition is a conventional method to transform one phase to another, while phase-selective synthesis means the direct fabrication of the target phases for 2D TMDs. In this review, we introduce the structures and stability of 2D TMDs with different phases. Then, we summarize the detailed processes and mechanism of the traditional phase transition strategies. Moreover, in view of the increasing demand of high-phase purity TMDs, we present the advanced phase-selective synthesis strategies. Finally, we underline the challenges and outlooks of phase engineering of 2D TMDs in two aspects-high phase purity and excellent controllability. This review may promote the development of controllable phase engineering for 2D TMDs and even other 2D materials toward both fundamental studies and practical applications.

2D materials have attracted much attention since the discovery of graphene in 2004. Due to their unique electrical, optical, and magnetic properties, they have potential for various applications such as electronics and optoelectronics. Owing to thermal motion and lattice growth kinetics, different atomic‐scale structures (ASSs) can originate from natural or intentional regulation of 2D material atomic configurations. The transformations of ASSs can result in the variation of the charge density, electronic density of state and lattice symmetry so that the property tuning of 2D materials can be achieved and the functional devices can be constructed. Here, several kinds of ASSs of 2D materials are introduced, including grain boundaries, atomic defects, edge structures, and stacking arrangements. The design strategies of these structures are also summarized, especially for atomic defects and edge structures. Moreover, toward multifunctional integration of applications, the modulation of electrical, optical, and magnetic properties based on atomic‐scale structural modification are presented. Finally, challenges and outlooks are featured in the aspects of controllable structure design and accurate property tuning for 2D materials with ASSs. This work may promote research on the atomic‐scale structural modification of 2D materials toward functional applications.

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In this paper we propose efficient channel estimation for Long Term Evolution (LTE) uplink multi-user (MU) over frequency-selective fading multiple-input multiple-output (MIMO) channels. By exploiting the properties of reference signals (RS), we find a special form of signal model. Based on the special form, firstly, we propose a low complexity spline interpolation based channel estimator. Then, to improve the interpolation performance we propose a new extendible inverse Discrete Cosine Transform (EIDCT) and a DCT/EIDCT-based approach. For their limited performance, we derive a more accurate channel estimator based on the DCT/EIDCT approach with low-complexity implantation. In two DCT/EIDCT-based estimators, signal first performs DCT, then optimal channel estimation in least square (LS) and linear minimal mean square error (MMSE) in DCT-domain is derived respectively. After obtaining the DCT-domain parameters, the new EIDCT gives accurate recover of signal. Finally, the performance of the proposed channel estimation is verified via simulation.