In a magnetic topological insulator, nontrivial band topology combines with magnetic order to produce exotic states of matter, such as quantum anomalous Hall (QAH) insulators and axion insulators. In this work, we probe quantum transport in MnBi2Te4 thin flakes—a topological insulator with intrinsic magnetic order. In this layered van der Waals crystal, the ferromagnetic layers couple antiparallel to each other; atomically thin MnBi2Te4, however, becomes ferromagnetic when the sample has an odd number of septuple layers. We observe a zero-field QAH effect in a five–septuple-layer specimen at 1.4 kelvin, and an external magnetic field further raises the quantization temperature to 6.5 kelvin by aligning all layers ferromagnetically. The results establish MnBi2Te4 as an ideal arena for further exploring various topological phenomena with a spontaneously broken time-reversal symmetry.

Semiconductive transition metal dichalcogenides (TMDs) have been considered as next generation semiconductors, but to date most device investigations are still based on microscale exfoliation with a low yield. Wafer scale growth of TMDs has been reported but effective doping approaches remain challenging due to their atomic thick nature. In this work, we report the synthesis of wafer-scale continuous few-layer PtSe 2 films with effective doping in a controllable manner. Chemical component analyses confirm that both n-and pdoping can be effectively modulated through the controlled selenization process. We systematically study the electrical properties of PtSe 2 films by fabricating top-gated field effect transistors (FETs). The device current on/off ratio is optimized in two-layer PtSe 2 FETs, and four-terminal configuration displays a reasonably high effective field effect mobility (14 and 15 cm 2 V -1 s -1 for p-and n-type FETs, respectively) with a nearly symmetric p-and n-type performance. Temperature dependent measurement reveals that the variable range hopping is dominant at low temperature. To further establish the feasible application based on controllable doping of PtSe 2 , a logic inverter and vertically stacked p-n junction arrays are demonstrated. These results validate that PtSe 2 is a promising candidate among the family of TMDs for future functional electronic applications.

2D layered materials (2DLMs) have gained tremendous interest for their potential applications in next-generation electronic, optoelectronic, [1][2][3] and energy devices. Although graphene possesses the highest reported mobility, its gapless nature motivates the pursuit of semiconductive transition metal dichalcogenides (TMDs) such as MoS 2 , [4][5][6] which has been intensively investigated based on mechanically exfoliated sheets. Yet for practical Atomic thin transition-metal dichalcogenides (TMDs) are considered as an emerging platform to build next-generation semiconductor devices. However, to date most devices are still based on exfoliated TMD sheets on a micrometer scale. Here, a novel chemical vapor deposition synthesis strategy by introducing multilayer (ML) MoS 2 islands to improve device performance is proposed. A four-probe method is applied to confirm that the contact resistance decreases by one order of magnitude, which can be attributed to a conformal contact by the extra amount of exposed edges from the ML-MoS 2 islands. Based on such continuous MoS 2 films synthesized on a 2 in. insulating substrate, a top-gated field effect transistor (FET) array is fabricated to explore key metrics such as threshold voltage (V T ) and field effect mobility (μ FE ) for hundreds of MoS 2 FETs. The statistical results exhibit a surprisingly low variability of these parameters. An average effective μ FE of 70 cm 2 V −1 s −1 and subthreshold swing of about 150 mV dec −1 are extracted from these MoS 2 FETs, which are comparable to the best top-gated MoS 2 FETs achieved by mechanical exfoliation. The result is a key step toward scaling 2D-TMDs into functional systems and paves the way for the future development of 2D-TMDs integrated circuits. Field Effect TransistorsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.201803465. application, wafer-scale synthesis of highquality, continuous MoS 2 film is highly desired. Recently, the chemical vapor deposition (CVD) technique has been applied to produce single-layer (1L) MoS 2 films with moderate electrical performance [7][8][9][10] and so far the largest number of logic gates is 115. [11][12][13] Mechanically exfoliated multilayer (ML) MoS 2 have shown improved mobility and drive currents because of thicker channel with higher density of states. [14,15] A smaller bandgap associated with ML-MoS 2 [16,17] is also more appropriate for device performance engineering. [18][19][20] However, it is rather difficult to grow a uniform and continuous multilayer MoS 2 film since precise control of layer number of stacked MoS 2 remains unsolved, [21,22] and vertical growth is limited by the interlayer diffusion rate of S atoms (much slower than in-plane diffusion) and high surface energy. [23] Besides, it is rather difficult to maintain a planar growth in a controllable manner, instead most results simultaneously produce a mixture of monolayer, multilayer, and empty islands. [24,25] Despite the demand of high-quality wa...

The recent exploration of semiconducting twodimensional (2D)

Benefiting from the technique of vertically stacking 2D layered materials (2DLMs), an advanced novel device architecture based on a top‐gated MoS2/WSe2 van der Waals (vdWs) heterostructure is designed. By adopting a self‐aligned metal screening layer (Pd) to the WSe2 channel, a fixed p‐doped state of the WSe2 as well as an independent doping control of the MoS2 channel can be achieved, thus guaranteeing an effective energy‐band offset modulation and large through current. In such a device, under specific top‐gate voltages, a sharp PN junction forms at the edge of the Pd layer and can be effectively manipulated. By varying top‐gate voltages, the device can be operated under both quasi‐Esaki diode and unipolar‐Zener diode modes with tunable current modulations. A maximum gate‐coupling efficiency as high as ≈90% and a subthreshold swing smaller than 60 mV dec−1 can be achieved under the band‐to‐band tunneling regime. The superiority of the proposed device architecture is also confirmed by comparison with a traditional heterostructure device. This work demonstrates the feasibility of a new device structure based on vdWs heterostructures and its potential in future low‐power electronic and optoelectronic device applications.