Monolayer transition metal dichalcogenides (TMDCs) with high crystalline quality are important channel materials for next‐generation electronics. Researches on TMDCs have been accelerated by the development of chemical vapor deposition (CVD). However, antiparallel domains and twin grain boundaries (GBs) usually form in CVD synthesis due to the special threefold symmetry of TMDCs lattices. The existence of GBs severely reduces the electrical and photoelectrical properties of TMDCs, thus restricting their practical applications. Herein, the epitaxial growth of single crystal MoS2 (SC‐MoS2) monolayer is reported on Au (111) film across a two‐inch c‐plane sapphire wafer by CVD. The MoS2 domains obtained on Au (111) film exhibit unidirectional alignment with zigzag edges parallel to the <110> direction of Au (111). Experimental results indicated that the unidirectional growth of MoS2 domains on Au (111) is a temperature‐guided epitaxial growth mode. The high growth temperature provides enough energy for the rotation of the MoS2 seeds to find the most favorable orientation on Au (111) to achieve a unidirectional ratio of over 99%. Moreover, the unidirectional MoS2 domains seamlessly stitched into single crystal monolayer without GBs formation. The progress achieved in this work will promote the practical applications of TMDCs in microelectronics.

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Ultra-thin high-temperature superconducting films have attracted continuous interest due to their potential electronic applications, which also provide a unique platform of novel physics and properties in the two-dimensional limit. We, here, realized fabrication of two-unit-cell-thick micro-bridges from mechanically exfoliated ultra-thin Bi2Sr2Ca2Cu3O10+δ (Bi2223) single crystals and systematically investigated their transport properties. The two-dimensional superconducting nature is verified by the existence of the Berezinskii–Kosterlitz–Thouless transition, which is simultaneously revealed by current-voltage properties and the zero-field temperature dependence of resistance. Comparing with Bi2223 bulk crystal, a Bi2223 micro-bridge shows a slight lower upper critical field but pronounced improvement in the critical current density. Our findings indicate that the ultra-thin Bi2223 single crystal is highly prospective for both scientific investigations of unconventional superconductivity and applications of high Tc superconducting devices.

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The vortex pinning determining the current carrying capacity of a superconductor is an important property to the applications of superconducting materials. For layered superconductors, the vortex pinning can be enhanced by a strong interlayer interaction in accompany with a suppression of superconducting anisotropy, which remains to be investigated in iron based superconductors (FeSCs) with the layered structure. Here, based on the transport and magnetic torque measurements, we experimentally investigate the vortex pinning in two bilayer FeSCs, CaKFe4As4(Fe1144) and KCa2Fe4As4F2(Fe12442), and compare their superconducting anisotropy γ. While the anisotropy γ ≈ 3 for Fe1144 is much smaller than γ ≈ 15 in Fe12442 around T c, a higher flux pinning energy as evidenced by a higher critical current density is found in Fe1144, as compared with the case of Fe12442. In combination with the literature data of Ba0.72K0.28Fe2As2 and NdFeAsO0.82F0.18, we reveal an anti-correlation between the pinning energy and the superconducting anisotropy in these FeSCs. Our results thus suggest that the interlayer interaction can not be neglected when considering the vortex pinning in FeSCs.

With the development of superconducting nanowire single photon detectors, increasing numbers of important applications are being explored, covering not only low-energy optical photon detection but also high-energy photon and particle detection. In this work, 100-nm-thick TaN superconducting microwire single photon detectors (SMSPDs) with large active areas were prepared for X-ray detection, and their response characteristics to X-rays were studied. The results showed that our TaN SMSPDs were able to detect X-rays at a wide range of bias currents and working temperatures. The detectors could distinguish different energy X-rays under suitable working conditions, and the energy resolving power was strongly related to the bias current.

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Two-dimensional (2D) superconductors supply important platforms for exploring new quantum physics and high-Tc superconductivity. The intrinsic superconducting properties in the 2D ironarsenic superconductors are still unknown owing to the difficulties in the preparation of ultrathin samples. Here we report the fabrication and physical investigations of the high quality singlecrystalline ultrathin films of the iron-arsenic superconductor KCa2Fe4As4F2. For the sample with the thickness of 2.6∼5 nm (1∼2 unit cells), a sharp superconducting transition at around 30 K (onset point) is observed. Compare with the bulk material, the ultrathin sample reveals a relatively lower Tc, wider transition width, and broader flux liquid region under the in-plane field. Moreover, the angle dependent upper critical field follows the Tinkham model, demonstrating the two-dimensional superconductivity in ultrathin KCa2Fe4As4F2.