Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

https://pr.ibs.re.kr/bitstream/8788114/3718/1/Recent%20development_Materials%20Today_Young%20Hee%20Lee.pdf

Recent Development of Two-Dimensional Transition Metal Dichalcogenides and Their Applications

The isolation of a growing number of two-dimensional (2D) materials has inspired worldwide efforts to integrate distinct 2D materials into van der Waals (vdW) heterostructures. Given that any passivated, dangling-bond-free surface will interact with another through vdW forces, the vdW heterostructure concept can be extended to include the integration of 2D materials with non-2D materials that adhere primarily through non-covalent interactions. We present a succinct and critical survey of emerging mixed-dimensional (2D + nD, where n is 0, 1 or 3) heterostructure devices. By comparing and contrasting with all-2D vdW heterostructures as well as with competing conventional technologies, we highlight the challenges and opportunities for mixed-dimensional vdW heterostructures.

Mixed-dimensional van der Waals heterostructures

https://absimage.aps.org/image/MAR14/MWS_MAR14-2014-020819.pdf

Van der Waals heterostructures

2D material based photodetectors have attracted many research projects due to their unique structures and excellent electronic and optoelectronic properties. These 2D materials, including semimetallic graphene, semiconducting black phosphorus, transition metal dichalcogenides, insulating hexagonal boron nitride, and their various heterostructures, show a wide distribution in bandgap values. To date, hundreds of photodetectors based on 2D materials have been reported. Here, a review of photodetectors based on 2D materials covering the detection spectrum from ultraviolet to infrared is presented. First, a brief insight into the detection mechanisms of 2D material photodetectors as well as introducing the figure-of-merits which are key factors for a reasonable comparison between different photodetectors is provided. Then, the recent progress on 2D material based photodetectors is reviewed. Particularly, the excellent performances such as broadband spectrum detection, ultrahigh photoresponsivity and sensitivity, fast response speed and high bandwidth, polarization-sensitive detection are pointed out on the basis of the state-of-the-art 2D photodetectors. Initial applications based on 2D material photodetectors are mentioned. Finally, an outlook is delivered, the challenges and future directions are discussed, and general advice for designing and realizing novel high-performance photodetectors is given to provide a guideline for the future development of this fast-developing field.

Progress, Challenges, and Opportunities for 2D Material Based Photodetectors

18.5% efficient graphene/GaAs van der Waals heterostructure solar cell

Monolayer MoS2/GaAs heterostructure self-driven photodetector with extremely high detectivity

In graphene/semiconductor heterojunction, the statistic charge transfer between graphene and semiconductor leads to decreased junction barrier height and limits the Fermi level tuning effect in graphene, which greatly affects the final performance of the device. In this work, we have designed a sandwich diode for solar cells and photodetectors through inserting 2D hexagonal boron nitride (h-BN) into graphene/GaAs heterostructure to suppress the static charge transfer. The barrier height of graphene/GaAs heterojunction can be increased from 0.88 eV to 1.02 eV by inserting h-BN. Based on the enhanced Fermi level tuning effect with interface h-BN, through adopting photo-induced doping into the device, power conversion efficiency (PCE) of 10.18% has been achieved for graphene/h-BN/GaAs compared with 8.63% of graphene/GaAs structure. The performance of graphene/h-BN/GaAs based photodetector is also improved with on/off ratio increased by one magnitude compared with graphene/GaAs structure.

Graphene/h-BN/GaAs sandwich diode as solar cell and photodetector.

MoS2 is a layered two-dimensional semiconductor with a direct band gap of 1.8 eV. The MoS2/bulk semiconductor system offers a new platform for solar cell device design. Different from the conventional bulk p-n junctions, in the MoS2/bulk semiconductor heterostructure, static charge transfer shifts the Fermi level of MoS2 toward that of bulk semiconductor, lowering the barrier height of the formed junction. Herein, we introduce hexagonal boron nitride (h-BN) into MoS2/GaAs heterostructure to suppress the static charge transfer, and the obtained MoS2/h-BN/GaAs solar cell exhibits an improved power conversion efficiency of 5.42%. More importantly, the sandwiched h-BN makes the Fermi level tuning of MoS2 more effective. By employing chemical doping and electrical gating into the solar cell device, PCE of 9.03% is achieved, which is the highest among all the reported monolayer transition metal dichalcogenide based solar cells.

/pdf/interface-designed-mos2-gaas-heterostructure-solar-cell-with-1lsbv8bwtm.pdf

Interface designed MoS2/GaAs heterostructure solar cell with sandwich stacked hexagonal boron nitride

The band gap of graphene is nearly zero, and thus novel two-dimensional (2D) semiconductor and band gap engineering of graphene is highly desired for advanced optoelectronic applications. Herein, we have experimentally produced quasi-two-dimensional (quasi-2D) SiC by reaction between graphene and a silicon source, which was designed and supported by Born–Oppenheimer molecular dynamics simulations. The lateral length of the as-synthesized quasi-2D SiC is mainly in the range of 0.3–5 μm while the thickness is commonly below 10 nm. Quasi-2D SiC2 is also found as a byproduct, which is stable over 3 months in air atmosphere. The exciton binding energy of quasi-2D multilayers SiC can reach 0.23 eV while the band gap is around 3.72 eV. Additionally, in situ transmission electron microscopy has firmly proven that quasi-2D SiC can be synthesized through the reaction between graphene and silicon quantum dots. The first production of quasi-2D SiC and SiC2 makes the band gap engineering in the graphene lattice plane ...

Xiaoqiang Li

Papers

18.5% efficient graphene/GaAs van der Waals heterostructure solar cell

Monolayer MoS2/GaAs heterostructure self-driven photodetector with extremely high detectivity

Graphene/h-BN/GaAs sandwich diode as solar cell and photodetector.

Interface designed MoS2/GaAs heterostructure solar cell with sandwich stacked hexagonal boron nitride

Quasi-Two-Dimensional SiC and SiC2: Interaction of Silicon and Carbon at Atomic Thin Lattice Plane