A nano-lateral heterojunction of selenium-coated tellurium for infrared-band soliton fiber lasers.

In this work, ultrafast fiber lasers based on 2D selenium-coated tellurium nanosheets in the infrared band are reported. 2D selenium-coated tellurium as a mode locker is shown with broadband saturable absorption and is capable of supporting ultra-stable pulse trains with several hundred-femtosecond pulse widths in the laser cavity. In particular, the as-fabricated 2D selenium-coated tellurium based fiber laser source operating in the communication band (1.5 µm) exhibits the vector pulse property, which supports the study of the vector soliton in ultrafast fiber lasers. The pulse duration of vector solitons is as short as 800 fs. The 2D selenium-coated tellurium is also available for a mode locked fiber laser operating at 1 µm. The laser oscillator has a pulse duration of several picoseconds and the pulse train is ultra-stable after an amplification to 100 mW, which is a promising seed source in the chirped-pulse amplification system in the future.

Eradication of tumor growth by delivering novel photothermal selenium-coated tellurium nanoheterojunctions.

Two-dimensional nanomaterial-based photothermal therapy (PTT) is currently under intensive investigation as a promising approach toward curative cancer treatment. However, high toxicity, moderate efficacy, and low uniformity in shape remain critical unresolved issues that hamper their clinical application. Thus, there is an urgent need for developing versatile nanomaterials to meet clinical expectations. To achieve this goal, we developed a stable, highly uniform in size, and nontoxic nanomaterials made of tellurium-selenium (TeSe)-based lateral heterojunction. Systemic delivery of TeSe nanoparticles in mice showed highly specific accumulation in tumors relative to other healthy tissues. Upon exposure to light, TeSe nanoparticles nearly completely eradicated lung cancer and hepatocellular carcinoma in preclinical models. Consistent with tumor suppression, PTT altered the tumor microenvironment and induced immense cancer cell apoptosis. Together, our findings demonstrate an exciting and promising PTT-based approach for cancer eradication.

Layer-Dependent Properties of Ultrathin GeS Nanosheets and Application in UV-Vis Photodetectors.

Two-dimensional germanium sulfide (GeS), an analogue of phosphorene, has attracted broad attention owing to its excellent environmental stabilities, fascinating electronic and optical properties, and applications in various nanodevices. In spite of the current achievements on 2D GeS, the report of ultrathin few-layer GeS nanosheets within 5 nm is still lacking. Here in this contribution, we have achieved preparation of ultrathin few-layer GeS nanosheets with thicknesses of 1.3 ± 0.1 nm [approximately three layers (∼3L)], 3.2 ± 0.2 nm (∼6L), and 4.2 ± 0.3 nm (∼8L) via a typical liquid-phase exfoliation (LPE) method. Based on various experimental characterizations and first-principles calculations, the layer-dependent electronic, transport, and optical properties are investigated. For the few-layer GeS nanosheets, enhanced light absorption in the UV-vis region and superior photoresponse behavior with increasing layer number is observed, while for the thin films above 10 nm, the properties degenerate to the bulk feature. In addition, the as-prepared ultrathin nanosheets manifest great potential in the applications of photoelectrochemical (PEC)-type photodetectors, exhibiting excellent and stable periodic photoresponse behavior under the radiation of white light. The ∼8L GeS-based photodetector exhibits superior performance than the thinner GeS nanosheets (<4 nm), even better as compared to the bulk or film (above 10 nm) counterparts in terms of higher photoresponsivity along with remarkable photodetection performance in the UV-vis region. This work not only provides direct and solid evidence of the layer-number evolutionary band structure, mobility, and optical properties of ultrathin 2D GeS nanosheets but also promotes the foreseeable applications of 2D GeS as energy-related photoelectric devices.

Engineering Lateral Heterojunction of Selenium-Coated Tellurium Nanomaterials toward Highly Efficient Solar Desalination.

Herein, a core-shell tellurium-selenium (Te-Se) nanomaterial with polymer-tailed and lateral heterojunction structures is developed as a photothermal absorber in a bionic solar-evaporation system. It is further revealed that the amorphous Se shell surrounds the crystalline Te core, which not only protects the Te phase from oxidation but also serves as a natural barrier to life entities. The core (Te)-shell (Se) configuration thus exhibits robust stability enhanced by 0.05 eV per Se atom and excellent biocompatibility. Furthermore, high energy efficiencies of 90.71 ± 0.37% and 86.14 ± 1.02% and evaporation rates of 12.88 ± 0.052 and 1.323 ± 0.015 kg m-2 h-1 are obtained under 10 and 1 sun for simulated seawater, respectively. Importantly, no salting out is observed in salt solutions, and the collected water under natural light irradiation possesses extremely low ion concentrations of Na+, K+, Ca2+, and Mg2+ relative to real seawater. Considering the tunable electronic structures, biocompatibilities, and modifiable broadband absorption of the solar spectrum of lateral heterojunction nanomaterials of Te-Se, the way is paved to engineering 2D semiconductor materials with supporting 3D porous hydrophilic materials for application in solar desalination, wastewater treatment, and biomedical ventures.

High-Performance Humidity Sensor Based on Urchin-Like Composite of Ti3C2 MXene-Derived TiO2 Nanowires.

Humidity sensors have broad applications in health monitoring, environmental protection and human-machine interface, and robotics. Here, we developed a humidity sensor using alkali oxidation method to grow in situ TiO2 nanowires on two-dimensional Ti3C2 MXene. With an order of magnitude larger surface area compared to pure Ti3C2 or TiO2 materials, the urchin-like Ti3C2/TiO2 composite demonstrates a record high sensitivity in a low relative humidity (RH) environment (∼280 pF/% RH from 7% RH to 33% RH). Complex impedance spectroscopy and Schottky junction theory were employed to understand the underlying sensing mechanisms of the Ti3C2/TiO2 composite under various humidity conditions. We demonstrate the application of humidity sensors made with the Ti3C2/TiO2 composite for noncontact detection of the presence of various liquids as well as human fingers.

Two-dimensional tellurium-polymer membrane for ultrafast photonics.

Tellurium (Te) exhibits many intriguing properties including thermoelectricity, photoelectricity, piezoelectricity, and photoconductivity, and is widely used in detectors, sensors, transistors, and energy devices. Herein, ultrathin two-dimensional (2D) Te nanosheets were fabricated using a facile and cost-effective liquid-phase exfoliation method. Mixing the as-prepared 2D Te nanosheets with polyvinylpyrrolidone (PVP) provided a uniform 2D Te/PVP membrane. The 2D Te/PVP membrane exhibited excellent mechanical properties, thermal properties, and stability. The nonlinear optical properties of the membrane were characterized over the spectral range of 800 to 1550 nm using open-aperture Z-scan technology. A large nonlinear absorption coefficient of about 10-1 cm GW-1 over the whole tested wavelength range demonstrated the efficient broadband saturable absorptivity of the 2D Te/PVP membrane. Using the 2D Te/PVP membrane as a saturable absorber (SA), a highly stable femtosecond laser with a pulse duration of 829 fs in the communication band was obtained. This work highlights the promise of 2D Te/PVP membranes in ultrafast photonics and Te as a new 2D material for use in photonic devices such as all-optical modulators, switches, and thresholds.