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.

Monolayer ß-tellurene: a promising p-type thermoelectric material via first-principles calculations.

Inspired by the experimental growth of two-dimensional (2D) tellurene (Yixin et al., Nat. Electron, 2018, 1, 228-236) and the recent study of unusually low thermal conductivity of atomically thin 2D tellurium (Jie Ren et al., Nanoscale, 2018, 10, 12997), we carried out systematic calculations for monolayer ß-tellurene, focusing on its electrical transport and electronic and thermoelectric properties by means of density functional theory (DFT) combined with deformation potential theory and Boltzmann transport theory. We have found that monolayer ß-tellurene exhibits a band gap of 1.5 eV. The carrier transport is highly direction-temperature-dependent, with a high room-temperature transport mobility of 1343 cm2 V-1 s-1 and a relaxation time of 283 fs in the armchair direction for hole transport at room-temperature. It is coincidently favourable in the armchair direction for both the Seebeck coefficient and the electrical conductivity, making the p-type monolayer ß-tellurene a highly promising thermoelectric candidate. With a low intrinsic lattice thermal conductivity, the maximum figure of merit (ZT) is 2.9 and 0.84 along the armchair and zigzag directions for p-type doping at 700 K, respectively. The predicted properties demonstrate that monolayer ß-tellurene can be a prospective material towards thermoelectric applications.

Omnipotent phosphorene: a next-generation, two-dimensional nanoplatform for multidisciplinary biomedical applications.

Phosphorene, also known as single- or few-layer black phosphorus (FLBP), is a new member of the two-dimensional (2D) material family and has attracted significant attention in recent years for applications in optoelectronics, energy storage and biomedicine due to its unique physicochemical properties and excellent biocompatibility. FLBP is regarded as a potential biological imaging agent for cancer diagnosis due to its intrinsic fluorescence (FL) and photoacoustic (PA) properties and negligible cytotoxicity. FLBP-based photothermal and photodynamic therapies have emerged with excellent anti-tumour therapeutic efficacies due to their unique physical properties, such as near-infrared (NIR) optical absorbance, large extinction coefficients, biodegradability and reactive oxygen species (ROS) or heat generation upon light irradiation. Furthermore, FLBP is a promising drug delivery platform because of its high drug-loading capacity due to its puckered layer structure with an ultralarge surface area, and FLBP is size-controllable with facile surface chemical modification. Because of the marked advantages of FLBP nanomaterials in biomedical applications, an overview of the latest progress and paradigms of FLBP-based nanoplatforms for multidisciplinary biomedical applications is presented in this tutorial review.

Novel concept of the smart NIR-light-controlled drug release of black phosphorus nanostructure for cancer therapy.

A biodegradable drug delivery system (DDS) is one the most promising therapeutic strategies for cancer therapy. Here, we propose a unique concept of light activation of black phosphorus (BP) at hydrogel nanostructures for cancer therapy. A photosensitizer converts light into heat that softens and melts drug-loaded hydrogel-based nanostructures. Drug release rates can be accurately controlled by light intensity, exposure duration, BP concentration, and hydrogel composition. Owing to sufficiently deep penetration of near-infrared (NIR) light through tissues, our BP-based system shows high therapeutic efficacy for treatment of s.c. cancers. Importantly, our drug delivery system is completely harmless and degradable in vivo. Together, our work proposes a unique concept for precision cancer therapy by external light excitation to release cancer drugs. If these findings are successfully translated into the clinic, millions of patients with cancer will benefit from our work.