Broadband photodetection using one-step CVD-fabricated MoS2/MoO2 microflower/microfiber heterostructures

Abstract Molybdenum disulfide (MoS 2 ) has been combined so far with other photodetecting semiconductors as an enhancing agent owing to its optical and electronic properties. Existing approaches demonstrated MoS 2 -incorporated photodetector devices using complex and costly fabrication processes. Here, we report on simplified one-step on the chemical vapor deposition (CVD) based synthesis of a unique microfiber/microflower MoS 2 -based heterostructure formed by capturing MoO 2 intermediate material during the CVD process. This particular morphology engenders a material chemical and electronic interplay exalting the heterostructure absorption up to ~ 98% over a large spectral range between 200 and 1500 nm. An arsenal of characterization methods were used to elucidate the properties of these novel heterostructures including Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectrometry, high-resolution transmission and scanning electron microscopies, and Kelvin probe force microscopy. Our findings revealed that the MoS 2 and the MoO 2 crystallize in the hexagonal and monoclinic lattices, respectively. The integration of the MoS 2 /MoO 2 heterostructures into functional photodetectors revealed a strong photoresponse under both standard sun illumination AM1.5G and blue light excitation at 450 nm. Responsivity and detectivity values as high as 0.75 mA W −1 and 1.45 × 10 7 Jones, respectively, were obtained with the lowest light intensity of 20 mW cm −2 at only 1 V bias. These results demonstrate the high performances achieved by the unique MoS 2 /MoO 2 heterostructure for broadband light harvesting and pave the way for their adoption in photodetection applications

One-step chemically vapor deposited hybrid 1T-MoS2/2H-MoS2 heterostructures towards methylene blue photodegradation

International audienceThe photocatalytic degradation of methylene blue is a straightforward and cost-effective solution for water decontamination. Although many materials have been reported so far for this purpose, the proposed solutions inflicted high fabrication costs and low efficiencies. Here, we report on the synthesis of tetragonal (1T) and hexagonal (2H) mixed molybdenum disulfide (MoS2) heterostructures for an improved photocatalytic degradation efficiency by means of a single-step chemical vapor deposition (CVD) technique. We demonstrate that the 1T-MoS2/2H-MoS2 heterostructures exhibited a narrow bandgap ∼ 1.7 eV, and a very low reflectance (<5%) under visible-light, owing to their particular vertical micro-flower-like structure. We exfoliated the CVD-synthesised 1T-MoS2/2H-MoS2 films to assess their photodegradation properties towards the standard methylene blue dye. Our results showed that the photo-degradation rate-constant of the 1T-MoS2/2H-MoS2 heterostructures is much greater under UV excitation (i.e., 12.5 × 10-3 min-1) than under visible light illumination (i.e., 9.2 × 10-3 min-1). Our findings suggested that the intermixing of the conductive 1T-MoS2 with the semi-conducting 2H-MoS2 phases favors the photogeneration of electron-hole pairs. More importantly, it promotes a higher efficient charge transfer, which accelerates the methylene blue photodegradation process

Cognitive predictors of unsafe driving in older drivers: a meta-analysis

Background: Older drivers are at a higher risk of being involved in a motor vehicle accident. However, on-road assessments of all older drivers are impractical, highlighting the need to screen for potentially unsafe drivers. This study undertook a meta-analysis of research examining the cognitive predictors of driving ability in older drivers in order to provide an evidence-based method for screening drivers. Methods: Comprehensive searches were undertaken of the PubMed, PsycINFO, CINAHL, and Health-Source Nursing electronic databases between 1980 and 2007 in order to identify studies that examined cognitive differences between drivers aged over 55 years who either passed or failed a driving assessment. Twenty-one studies were eligible for inclusion. Weighted Cohen's d effect sizes, percentage overlap statistics, Fail-safe Ns and 95% CIs were calculated for all cognitive tests. Results: The best predictors of on-road driving were the Ergovision and Useful Field of View (UFOV) tests, a complex RT task, Paper Folding task, Dot Counting, WMS Visual Reproduction, and Computerized Visual Attention Task. Simulator driving performance was best predicted by the Benton Line Orientation Task, Clock Drawing, a Driver Scanning task, the UFOV, WAIS Picture Arrangement and MMSE. Finally, the Trail Making Test, Stroop, UFOV, WAIS Block Design, and Automated Psychophysical Test were good predictors of driving problems. Conclusions: There are a variety of tests that appear suitable for screening older drivers, the exact choice of which depends on the “gold standard” for determining driving ability (on-road driving, driving simulator, driving problems) and whether a computerized or paper-and-pencil task is required.J. L. Mathias and L. K. Luca