First-principles investigation of in-plane anisotropies in XYTe4 monolayers with X = Hf, Zr, Ti and Y = Si, Ge.

In-plane anisotropic materials can introduce additional degrees of freedom while tuning their physical properties, which expand the range of opportunities for designing novel semiconductor devices and exploring distinct applications. In this work, we investigate the in-plane anisotropic electronic, elastic, transport and piezoelectric properties in a family of isostructural telluride XYTe4 (X = Hf, Zr and Ti, Y = Si and Ge) monolayers based on first-principles calculations. Six types of structures are verified to harbor direct bandgaps at the Γ point ranging between 0.98 and 1.36 eV. The orientation-dependent in-plane elastic stiffness of XYTe4 reveals the anisotropic and ultrasoft nature. Superior dielectric constants and giant switching effects are found in TiGeTe4 monolayers because of giant in-plane anisotropy. Strikingly, the piezoelectric coefficients of XSiTe4 differ by an order of magnitude along the two main directions. The strong in-plane anisotropic elastic properties of XYTe4 monolayers together with outstanding piezoelectric responses show that these structures can compete with that of transition metal dichalcogenides for applications in the field of flexible electronic devices.

High-performance hierarchical O-SnS/I-ZnIn2S4 photodetectors by leveraging the synergy of optical regulation and band tailoring.

Low light absorption and limited carrier lifetime are critical obstacles inhibiting further performance improvement of 2D layered material (2DLM) based photodetectors, while scalable fabrication is an ongoing challenge prior to commercialization from the lab to market. Herein, wafer-scale SnS/ZIS hierarchical nanofilms, where out-of-plane SnS (O-SnS) is modified onto in-plane ZIS (I-ZIS), have been achieved by pulsed-laser deposition. The derived O-SnS/I-ZIS photodetector exhibits markedly boosted sensitivity as compared to a pristine ZIS device. The synergy of multiple functionalities contributes to the dramatic improvement, including the pronounced light-trapping effect of O-SnS by multiple scattering, the high-efficiency spatial separation of photogenerated electron-hole pairs by a type-II staggered band alignment and the promoted carrier transport enabled by the tailored electronic structure of ZIS. Of note, the unique architecture of O-SnS/I-ZIS can considerably expedite the carrier dynamics, where O-SnS promotes the electron transfer from SnS to ZIS whilst the I-ZIS enables high-speed electron circulation. In addition, the interlayer transition enables the bridging of the effective optical window to telecommunication wavelengths. Moreover, monolithic integration of arrayed devices with satisfactory device-to-device variability has been encompassed and a proof-of-concept imaging application is demonstrated. On the whole, this study depicts a fascinating functional coupling architecture toward implementing chip-scale integrated optoelectronics.

Electrical conductivity of ferritin proteins by conductive AFM.

Electrical conductivity measurements were performed on single apoferritin and holoferritin molecules by conductive atomic force microscopy. Conductivity of self-assembled monolayer films of ferritin molecules on gold surfaces was also measured. Holoferritin was 5-15 times more conductive than apoferritin, indicating that for holoferritin most electron-transfer goes through the ferrihydrite core. With 1 V applied, the average electrical currents through single holoferritin and apoferritin molecules were 2.6 pA and 0.19 pA, respectively.