Trang Thi Thu Nguyen

Broad-Band Photocurrent Enhancement in MoS2 Layers Directly Grown on Light-Trapping Si Nanocone Arrays

There has been growing research interest in realizing optoelectronic devices based on the two-dimensional atomically thin semiconductor MoS2 owing to its distinct physical properties that set it apart from conventional semiconductors. However, there is little optical absorption in these extremely thin MoS2 layers, which presents an obstacle toward applying them for use in high-efficiency light-absorbing devices. We synthesized trilayers of MoS2 directly on SiO2/Si nanocone (NC) arrays using chemical vapor deposition and investigated their photodetection characteristics. The photoresponsivity of the MoS2/NC structure was much higher than that of the flat counterpart across the whole visible wavelength range (for example, it was almost an order of magnitude higher at λ = 532 nm). Strongly concentrated light near the surface that originated from a Fabry-Perot interference in the SiO2 thin layers and a Mie-like resonance caused by the Si NCs boosted the optical absorption in MoS2. Our work demonstrates that MoS2/NC structures could provide a useful means to realize high-performance optoelectronic devices.

Anticancer Activity of Ramalin, a Secondary Metabolite from the Antarctic Lichen Ramalina terebrata, against Colorectal Cancer Cells

Colorectal cancer is a leading cause of death worldwide and occurs through the highly complex coordination of multiple cellular pathways, resulting in carcinogenesis. Recent studies have increasingly revealed that constituents of lichen extracts exhibit potent pharmaceutical activities, including anticancer activity against various cancer cells, making them promising candidates for new anticancer therapeutic drugs. The main objective of this study was to evaluate the anticancer capacities of ramalin, a secondary metabolite from the Antarctic lichen Ramalina terebrata, in the human colorectal cancer cell line HCT116. In this study, ramalin displayed concentration-dependent anticancer activity against HCT116 cells, significantly suppressing proliferation and inducing apoptosis. Furthermore, ramalin induced cell cycle arrest in the gap 2/mitosis (G2/M) phase through the modulation of hallmark genes involved in the G2/M phase transition, such as tumour protein p53 (TP53), cyclin-dependent kinase inhibitor 1A (CDKN1A), cyclin-dependent kinase 1 (CDK1) and cyclin B1 (CCNB1). At both the transcriptional and translational level, ramalin caused a gradual increase in the expression of TP53 and its downstream gene CDKN1A, while decreasing the expression of CDK1 and CCNB1 in a concentration-dependent manner. In addition, ramalin significantly inhibited the migration and invasion of colorectal cancer cells in a concentration-dependent manner. Taken together, these data suggest that ramalin may be a therapeutic candidate for the targeted therapy of colorectal cancer.

MoS2 monolayers on Si and SiO2 nanocone arrays: influences of 3D dielectric material refractive index on 2D MoS2 optical absorption

Heterostructures enable the control of transport and recombination of charge carriers, which are either injected through electrodes, or created by light illumination. Instead of full 2D-material-heterostructures in device applications, using hybrid heterostructures consisting of 2D and 3D materials is an alternative approach to take advantage of the unique physical properties of 2D materials. In addition, 3D dielectric nanostructures exhibit useful optical properties such as broadband omnidirectional antireflection effects and strongly concentrated light near the surface. In this work, the optical properties of 2D MoS2 monolayers conformally coated on 3D Si-based nanocone (NC) arrays are investigated. Numerical calculations show that the absorption in MoS2 monolayers on SiO2 NC is significantly enhanced, compared with that for MoS2 monolayers on Si NC. The weak light confinement in low refractive index SiO2 NC leads to greater absorption in the MoS2 monolayers. The measured photoluminescence and Raman intensities of the MoS2 monolayers on SiO2 NC are much greater than those on Si NC, which supports the calculation results. This work demonstrates that 2D MoS2-3D Si nano-heterostructures are promising candidates for use in high-performance integrated optoelectronic device applications.

Microbial Synthesis of Non-Natural Anthraquinone Glucosides Displaying Superior Antiproliferative Properties

Anthraquinones, naturally occurring bioactive compounds, have been reported to exhibit various biological activities, including anti-inflammatory, antiviral, antimicrobial, and anticancer effects. In this study, we biotransformed three selected anthraquinones into their novel O-glucoside derivatives, expressing a versatile glycosyltransferase (YjiC) from Bacillus licheniformis DSM 13 in Escherichia coli. Anthraflavic acid, alizarin, and 2-amino-3-hydroxyanthraquinone were exogenously fed to recombinant E. coli as substrate for biotransformation. The products anthraflavic acid-O-glucoside, alizarin 2-O-β-d-glucoside, and 2-amino-3-O-glucosyl anthraquinone produced in the culture broths were characterized by various chromatographic and spectroscopic analyses. The comparative anti-proliferative assay against various cancer cells (gastric cancer-AGS, uterine cervical cancer-HeLa, and liver cancer-HepG2) were remarkable, since the synthesized glucoside compounds showed more than 60% of cell growth inhibition at concentrations ranging from ~50 μM to 100 μM. Importantly, one of the synthesized glucoside derivatives, alizarin 2-O-glucoside inhibited more than 90% of cell growth in all the cancer cell lines tested.

Surface potential mapping and n-type conductivity in organic-inorganic lead iodide crystals

Organic–inorganic lead halide perovskites have drawbacks in applications due to insufficient and inadequate understanding of the materials. In particular, it is a priority to investigate CH3NH3PbI3 due to its suitable properties and its band gap energy of about 1.59 eV. In this work, we investigated the perovskite crystal with respect to structural, electronic, and optical properties because a single crystal is an ideal platform for examining essential characteristics. The spatial distribution of the perovskite structure was identified by transmission electron microscopy and Kelvin probe force microscopy. The built electronic structure is an important index for the carrier types depending on the surface potential distribution. In particular, a potential variation showed a mixture of the perovskite phase and a decomposed phase on the surface, which also implied the role of surface imperfections as initiation sites for degradation. Therefore, it is critical to verify the carrier types on the surface to enhance the possibilities of improvements for applications.

Influence of the ZnS precursor thickness on high efficiency Cu2ZnSn(S,Se)4 thin-film solar cells grown by stacked-sputtering and selenization process

CZTSSe thin-films were deposited by stacked sputtering methods (ZnS/SnS/Cu) and annealed with selenization. We adjusted the thickness of the ZnS precursor layer in CZT precursors. A 337 nm thickness of ZnS precursor was shown an efficiency of up to 9.1%. We investigated the secondary phases by Raman spectroscopy and Kelvin probe force microscopy with depth profiles. The Cu2SnSe3, ZnSe, and MoSe2 secondary phases appeared near the back contact region. The phase distributions of the CZTSSe thin-films are different depending on ZnS precursor thickness with different depths. This phase characterization can describe the influences to the device performance of the CZTSSe thin-film solar cells.