Photoelectrical properties of graphene/doped GeSn vertical heterostructures.

GeSn is a group IV alloy material with a narrow bandgap, making it favorable for applications in sensing and imaging. However, strong surface carrier recombination is a limiting factor. To overcome this, we investigate the broadband photoelectrical properties of graphene integrated with doped GeSn, from the visible to the near infrared. It is found that photo-generated carriers can be separated and transported with a higher efficiency by the introduction of the graphene layer. Considering two contrasting arrangements of graphene on p-type and n-type GeSn films, photocurrents were suppressed in graphene/p-type GeSn heterostructures but enhanced in graphene/n-type GeSn heterostructures when compared with control samples without graphene. Moreover, the enhancement (suppression) factor increases with excitation wavelength but decreases with laser power. An enhancement factor of 4 is achieved for an excitation wavelength of 1064 nm. Compared with previous studies, it is found that our graphene/n-type GeSn based photodetectors provide a much wider photodetection range, from 532 nm to 1832 nm, and maintain comparable responsivity. Our experimental findings highlight the importance of the induced bending profile on the charge separation and provides a way to design high performance broadband photodetectors.

High Selectivity Gas Sensing and Charge Transfer of SnSe2.

SnSe2 is an anisotropic binary-layered material with rich physics, which could see it used for a variety of potential applications. Here, we investigate the gas-sensing properties of SnSe2 using first-principles calculations and verify predictions using a gas sensor made of few-layer SnSe2 grown by chemical vapor deposition. Theoretical simulations indicate that electrons transfer from SnSe2 to NO2, whereas the direction of charge transfer is the opposite for NH3. Notably, a flat molecular band appears around the Fermi energy after NO2 adsorption and the induced molecular band is close to the conduction band minimum. Moreover, compared with NH3, NO2 molecules adsorbed on SnSe2 have a lower adsorption energy and a higher charge transfer value. The dynamic-sensing responses of SnSe2 sensors confirm the theoretical predictions. The good match between the theoretical prediction and experimental demonstration suggests that the underlying sensing mechanism is related to the charge transfer and induced flat band. Our results provide a guideline for designing high-performance gas sensors based on SnSe2.

Enhanced NO2 Sensing at Room Temperature with Graphene via Monodisperse Polystyrene Bead Decoration.

Graphene is a single layer of carbon atoms with a large surface-to-volume ratio, providing a large capacity gas molecule adsorption and a strong surface sensitivity. Chemical vapor deposition-grown graphene-based NO2 gas sensors typically have detection limits from 100 parts per billion (ppb) to a few parts per million (ppm), with response times over 1000 s. Numerous methods have been proposed to enhance the NO2 sensing ability of graphenes. Among them, surface decoration with metal particles and metal-oxide particles has demonstrated the potential to enhance the gas-sensing properties. Here, we show that the NO2 sensing of graphene can be also enhanced via decoration with monodisperse polymer beads. In dark conditions, the detection limit is improved from 1000 to 45 ppb after the application of polystyrene (PS) beads. With laser illumination, a detection limit of 0.5 ppb is determined. The enhanced gas sensing is due to surface plasmon polaritons excited by interference and charge transfer between the PS beads. This method opens an interesting route for the application of graphene in gas sensing.

Electrical-field-driven metal-insulator transition tuned with self-aligned atomic defects.

Recently, significant attention has been paid to the resistance switching (RS) behaviour in Fe3O4 and it was explained through the analogy of the electrically driven metal-insulator transition based on the quantum tunneling theory. Here, we propose a method to experimentally support this explanation and provide a way to tune the critical switching parameter by introducing self-aligned localized impurities through the growth of Fe3O4 thin films on stepped SrTiO3 substrates. Anisotropic behavior in the RS was observed, where a lower switching voltage in the range of 10(4) V cm(-1) is required to switch Fe3O4 from a high conducting state to a low conducting state when the electrical field is applied along the steps. The anisotropic RS behavior is attributed to a high density array of anti-phase boundaries (APBs) formed at the step edges and thus are aligned along the same direction in the film which act as a train of hotspot forming conduits for resonant tunneling. Our experimental studies open an interesting window to tune the electrical-field-driven metal-insulator transition in strongly correlated systems.

Synergistically enhanced photocatalytic and chemotherapeutic effects of aptamer-functionalized ZnO nanoparticles towards cancer cells.

Today cancer is one of the most life-threatening diseases in the world. The conventional cancer therapies, including surgery, chemo- and radiation therapies, have some disadvantages, such as limited efficiency and significant side effects. It is necessary to develop new therapeutic treatments. Herein, we integrated the targeted photocatalytic and chemotherapy in a multifunctional drug-delivery platform. The aptamer-functionalized ZnO nanoparticles (NPs) were successfully synthesized. The anti-cancer drug was loaded in the aptamer-ZnO NP system. In vitro cell cytotoxicity experiments showed that combined therapy had a higher rate of death of cancer cells compared to that of single photocatalytic or chemotherapy. Furthermore, aptamer-functionalization could greatly increase the accumulation of nanoparticles within cancer cells and lead to better therapeutic effects. The results suggest that aptamer-functionalized semiconductor nanoparticles may have potential in the development of targeted photocatalytic and chemotherapy against cancer.