The two-dimensional (2D) superconducting state is a fragile state of matter susceptible to quantum phase fluctuations. Although superconductivity has been observed in ultrathin metal films down to a few layers 1-10 , it is still not known whether a single layer of ordered metal atoms, which represents the ultimate 2D limit of a crystalline film, could be superconducting. Here we report scanning tunnelling microscopy measurements on single atomic layers of Pb and In grown epitaxially on Si(111) substrate, and demonstrate unambiguously that superconductivity does exist at such a 2D extreme. The film shows a superconducting transition temperature of 1.83 K for an atom areal density n = 10.44 Pb atoms nm −2 , 1.52 K for n = 9.40 Pb atoms nm −2 and 3.18 K for n = 9.40 In atoms nm −2 , respectively. We confirm the occurrence of superconductivity by the presence of superconducting vortices under magnetic field. In situ angle-resolved photoemission spectroscopy measurements reveal that the observed superconductivity is due to the interplay between the Pb-Pb (In-In) metallic and the Pb-Si (In-Si) covalent bondings.The one-atomic-layer films of Pb and In studied here were grown with atomic precision on bulk-terminated Si(111) substrate using molecular beam epitaxy. The one-atomic-layer films of Pb have two different structural phases depending on the coverage (for sample preparation, see the Methods section). Figure 1a,d shows the schematic structure and scanning tunnelling microscopy (STM) topograph of the so-called striped incommensurate (SIC) phase, which has a Pb coverage of 4/3 monolayers (ML;. Here 1 ML is defined as the surface atomic density of the Si(111) with areal density n = 7.84 atoms nm −2 . In a unit cell of the SIC-Pb phase, there are four Pb atoms per three surface Si atoms. Three of the four Pb atoms each form a covalent bond with an underlying Si atom, leaving one Pb atom without bonding to the Si substrate. Besides the covalent bonds with the Si substrate, the metal atoms also form metallic bonds within the metal overlayer. As all Pb atoms are located exactly in the same atomic-layer sheet (see the large-scale STM image and cross-section height profiles in Supplementary Fig. S1), the resulting areal density of Pb atoms is 10.44 nm −2 . Compared with the bulk Pb(111) plane, the lattice of the SIC phase is compressed by 5%.Ultralow-temperature (down to 0.40 K) scanning tunnelling spectroscopy (STS) on the SIC phase reveals a clear signature of superconductivity. Figure 2a shows the tunnelling spectra taken on the SIC phase using a superconducting Nb tip. At 0.42 K,

Here, we demonstrated systematic experiments to understand the microscopic origin of laser irradiation induced controllable 2H-to-1T’ phase transition in few-layer MoTe2.

Stretchable conductive hydrogels with simultaneous high mechanical strength/modulus, and ultrahigh, stable electrical conductivity are ideal for applications in soft robots, artificial skin, and bioelectronics, but to date, they are still very challenging to fabricate. Herein, sandwich‐structured hybrid hydrogels based on layers of aramid nanofibers (ANFs) reinforced polyvinyl alcohol (PVA) hydrogels and a layer of silver nanowires (AgNWs)/PVA are fabricated by electrospinning combined with vacuum‐assisted filtration. The hybrid ANF‐PVA hydrogels exhibit excellent mechanical properties with the tensile modulus of 10.7–15.4 MPa, tensile strength of 3.3–5.5 MPa, and fracture energy up to 5.7 kJ m−2, primarily attributed to the strong hydrogen bonding interactions between PVA and ANFs and in‐plane alignment of the fibrous structure. Rational design of heterogeneous structure endows the hydrogels with ultrahigh apparent electrical conductivity of 1.66 × 104 S m−1, among the highest electrical conductivities ever reported so far for conductive hydrogels. More importantly, this ultrahigh conductivity remains constant upon a broad range of applied strains from 0–90% and over 500 stretching cycles. Furthermore, the hydrogels exhibit excellent Joule heating and electromagnetic interference shielding performances due to the ultrahigh electrical conductivity. These mechanically strong, hybrid hydrogels with ultrahigh and strain‐invariant electrical conductivity represent great promises for many important applications such as flexible electronics.

Recently, MnBi 2 Te 4 has been demonstrated to be an intrinsic magnetic topological insulator and the quantum anomalous Hall (QAH) effect was observed in exfoliated MnBi 2 Te 4 flakes. Here, we used molecular beam epitaxy (MBE) to grow MnBi 2 Te 4 films with thickness down to 1 septuple layer (SL) and performed thickness-dependent transport measurements. We observed a nonsquare hysteresis loop in the antiferromagnetic state for films with thickness greater than 2 SL. The hysteresis loop can be separated into two AH components. We demonstrated that one AH component with the larger coercive field is from the dominant MnBi 2 Te 4 phase, whereas the other AH component with the smaller coercive field is from the minor Mn-doped Bi 2 Te 3 phase. The extracted AH component of the MnBi 2 Te 4 phase shows a clear even− odd layer-dependent behavior. Our studies reveal insights on how to optimize the MBE growth conditions to improve the quality of MnBi 2 Te 4 films.

Third-order optical nonlinearities of graphene from monolayer to multilayers were investigated in the femtosecond regime, and the contribution of interlayer coupling to the nonlinearities was studied. The nonlinear refractive index γ of the order of 10−9 cm2/W and the nonlinear absorption coefficient β of 10−6 cm/W were obtained. By systematically investigating the nonlinear optical properties with the number of layers and comparing the coupling graphene with the decoupling superimposed graphene, we found that the coupling of interlayers has large effect upon the nonlinear refraction. These results provide an effective approach for developing graphene-based nonlinear photonic devices

Bi2O2Se is emerging as a photosensitive functional material for optoelectronics, and its photodetection mechanism is mostly considered to be a photoconductive regime in previous reports. Here, the bolometric effect is discovered in Bi2O2Se photodetectors. The coexistence of photoconductive effect and bolometric effect is generally observed in multiwavelength photoresponse measurements and then confirmed with microscale local heating experiments. The unique photoresponse of Bi2O2Se photodetectors may arise from a change of hot electrons during temperature rises instead of photoexcited holes and electrons. Direct proof of the bolometric effect is achieved by real‐time temperature tracking of Bi2O2Se photodetectors under time evolution after light excitation. Moreover, the Bi2O2Se bolometer shows a high temperature coefficient of resistance (−1.6% K−1), high bolometric coefficient (−31 nA K−1), and high bolometric responsivity (>320 A W−1). These findings offer a new approach to develop bolometric photodetectors based on Bi2O2Se layered materials.

Dual‐mode switching of diffraction efficiencies, using either light or an electric field, is possible with a diffraction grating prepared from an azobenzene‐polymer‐stabilized liquid crystal. Light‐induced switching resulted from the cis–trans photoisomerization of the azobenzene unit, resulting in the nematic‐to‐isotropic phase transition of the liquid crystal (dark fringes in the Figure). This switching behavior is reversible and repeatable for many cycles.

Hydrogenated amorphous carbon films are prepared by a 40-cm-diameter planar surface wave plasma to apply them to field-emission display. The 2.45 GHz surface wave plasmas at 700 W give a film deposition rate of ∼15 nm/min in He gas mixed with a small amount of methane gas at a relatively low pressure of 100 to 200 mTorr. Preliminary experimental results show that the hydrogenated amorphous carbon films deposited on silicon substrates have good field-emission characteristics: a threshold electric field defined at 1 µA/cm 2 was roughly 4 V/µm and an emission current of 0.1 mA/cm 2 was achieved at an electric field of 7.5 V/µm. KEYWORDS: field-emission display, surface wave plasma, UHF plasma, hydrogenated amorphous carbon film, plasma CVD L 929 L 930Jpn.