In the global trend towards carbon neutrality, sustainable energy conversion and storage technologies are of vital significance to tackle the energy crisis and climate change. However, traditional electrode materials gradually reach their property limits. Two-dimensional (2D) materials featuring large aspect ratios and tunable surface properties exhibit tremendous potential for improving the performance of energy conversion and storage devices. To rationally control the physical and chemical properties for specific applications, defect engineering of 2D materials has been investigated extensively, and is becoming a versatile strategy to promote the electrode reaction kinetics. Simultaneously, exploring the in-depth mechanisms underlying defect action in electrode reactions is crucial to provide profound insight into structure tailoring and property optimization. In this review, we highlight the cutting-edge advances in defect engineering in 2D materials as well as their considerable effects in energy-related applications. Moreover, the confronting challenges and promising directions are discussed for the development of advanced energy conversion and storage systems.

Defect engineering of two-dimensional materials for advanced energy conversion and storage.

Single atom doping in 2D layered MoS2 from a periodic table perspective

Test case prioritization (TCP) plays an important role in identifying, characterizing, diagnosing, and correcting faults quickly. The TCP has been widely used to order test cases of different types, including model inputs (also called abstract test cases ). Model inputs are constructed by modeling the program according to its input parameters, values, and constraints, and has been used in different testing methods, such as combinatorial interaction testing and software product line testing. The Interaction coverage-based TCP (ICTCP) uses interaction coverage information derived from the model input to order inputs. Previous studies have focused generally on the fixed-strength ICTCP, which adopts a fixed strength ( i.e. , the level of parameter interactions) to support the ICTCP process. It is generally accepted that using more strengths for ICTCP, i.e. , mixed-strength ICTCP, may give better ordering than fixed-strength. To confirm whether mixed-strength is better than fixed-strength, in this paper, we report on an extensive empirical study using five real-world programs (written in C), each of which has six versions. The results of the empirical studies show that mixed-strength has better rates of interaction coverage overall than fixed-strength, but they have very similar rates of fault detection. Our results also show that fixed-strength should be used instead of the mixed-strength at the later stage of software testing. Finally, we offer some practical guidelines for testers when using interaction coverage information to prioritize model inputs, under different testing scenarios and resources.

An Empirical Comparison of Fixed-Strength and Mixed-Strength for Interaction Coverage Based Prioritization

Improving the device performances of two-dimensional semiconducting transition metal dichalcogenides: Three strategies

Context Factors: What they are and why they matter for Requirements Problems.

2D semiconductors are emerging as plausible candidates for next‐generation “More‐than‐Moore” nanoelectronics to tackle the scaling challenge of transistors. Wafer‐scale 2D semiconductors, such as MoS2 and WS2, have been successfully synthesized recently; nevertheless, the absence of effective doping technology fundamentally results in energy barriers and high contact resistances at the metal–semiconductor interfaces, and thus restrict their practical applications. Herein, a controllable doping strategy in centimeter‐sized monolayer MoS2 films is developed to address this critical issue and boost the device performance. The ultralow contact resistance and perfect Ohmic contact with metal electrodes are uncovered in monolayer Fe‐doped MoS2, which deliver excellent device performance featured with ultrahigh electron mobility and outstanding on/off current ratio. Impurity scattering is suppressed significantly thanks to the ultralow electron effective mass and appropriate doping site. Particularly, unidirectionally aligned monolayer Fe‐doped MoS2 domains are prepared on 2 in. commercial c‐plane sapphire, suggesting the feasibility of synthesizing wafer‐scale 2D single‐crystal semiconductors with outstanding device performance. This work presents the potential of high‐performance monolayer transistors and enables further device downscaling and extension of Moore's law.

Reducing Contact Resistance and Boosting Device Performance of Monolayer MoS2 by In Situ Fe Doping

Two-dimensional multiferroic materials have garnered broad interests attributed to their magnetoelectric properties and multifunctional applications. Multiferroic heterostructures have been realized, nevertheless, the direct coupling between ferroelectric and ferromagnetic order in a single material still remains challenging, especially for two-dimensional materials. Here, we develop a physical vapor deposition approach to synthesize two-dimensional p-doped SnSe. The local phase segregation of SnSe2 microdomains and accompanying interfacial charge transfer results in the emergence of degenerate semiconductor and metallic feature in SnSe. Intriguingly, the room-temperature ferrimagnetism has been demonstrated in two-dimensional p-doped SnSe with the Curie temperature approaching to ~337 K. Meanwhile, the ferroelectricity is maintained even under the depolarizing field introduced by SnSe2. The coexistence of ferrimagnetism and ferroelectricity in two-dimensional p-doped SnSe verifies its multiferroic feature. This work presents a significant advance for exploring the magnetoelectric coupling in two-dimensional limit and constructing high-performance logic devices to extend Moore's law. 

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Two-dimensional multiferroic material of metallic p-doped SnSe

Reachability testing is an important approach to testing concurrent programs. It generates and exercises synchronization sequences automatically and on-the-fly without saving any test history. Existing reachability testing can be classified into exhaustive and t-way testing. Exhaustive testing is impractical in many cases while t-way testing may decrease the capability of fault detection in some cases. In this paper, we present a variable strength reachability testing strategy, which adopts the dynamic framework of reachability testing and uses a variable strength combinatorial strategy. Different parameter groups are provided with different covering strength. Variable strength testing covers no t-way combinations but the necessary combinations of parameters having mutual interactions in a concurrent program. It is more reasonable than t-way testing because uniform interactions between parameters do not often exist in concurrent systems. We propose a merging algorithmthat implements the variable strength combinatorial testing strategy and conduct our experiment on several concurrent programs. The experimental results indicate that our variable strength reachability testing reaches a good tradeoff between the effectiveness and efficiency. It can keep the same capability of fault detection as exhaustive reachability testing while substantially reducing the number of synchronization sequences and decreasing the execution time in most cases.

Variable strength combinatorial testing of concurrent programs

Two-dimensional (2D) iron chalcogenides (FeX, X = S, Se, Te) are emerging as an appealing class of materials for a wide range of research topics, including electronics, spintronics, and catalysis. However, the controlled syntheses and intrinsic property explorations of such fascinating materials still remain daunting challenges, especially for 2D nonlayered Fe7S8 with mixed-valence states and high conductivity. Herein, we design a general and temperature-mediated chemical vapor deposition (CVD) approach to synthesize ultrathin and large-domain Fe7S8 nanosheets on mica substrates, with the thickness down to ∼4.4 nm (2 unit-cell). Significantly, we uncover a quadratic-dependent unsaturated magnetoresistance (MR) with out-of-plane anisotropy in 2D Fe7S8, thanks to its ultrahigh crystalline quality and high conductivity (∼2.7 × 105 S m-1 at room temperature and ∼1.7 × 106 S m-1 at 2 K). More interestingly, the CVD-synthesized 2D Fe7S8 nanosheets maintain robust environmental stability for more than 8 months. These results hereby lay solid foundations for synthesizing 2D nonlayered iron chalcogenides with mixed-valence states and exploring fascinating quantum phenomena.

Jun He

Papers

Reducing Contact Resistance and Boosting Device Performance of Monolayer MoS2 by In Situ Fe Doping

Two-dimensional multiferroic material of metallic p-doped SnSe

Variable strength combinatorial testing of concurrent programs

Controllable Synthesis Quadratic-Dependent Unsaturated Magnetoresistance of Two-Dimensional Nonlayered Fe7S8 with Robust Environmental Stability.

A Mixed-way Combinatorial Testing for Concurrent Programs (S).