Search

Ultraviolet-Ozone (UVO) treatment has potentially promoted the long-term stability and the high performance of two-dimensional-material-based devices. However, the detailed evolutions of materials upon UVO treatment are less reported and unclear. Herein, we have systematically investigated the evolutions of morphology and electronic properties of the UVO treated few-layered MoS2. A weak p-doping effect on a 1-hour-UVO-exposed bulk MoS2 is revealed by photoelectron spectroscopy, being attributed to the charge transfer from MoS2 to the newly-formed MoOx. Optical microscopy, atomic force microscopy, Raman and PL mapping measurements reveal an inhomogeneous change of MoS2 morphology after UVO treatment. The oxidation is initiated at intrinsic defect sites and dislocations, and then expands in-plane from dislocations to both sides to form one dimensional standing-wave-like features. The dangling-bond-free surface regions remain smooth, being attributed to the higher energetic barrier for O2 dissociation and chemisorption. A model is proposed to explain the mechanism of inhomogeneous oxidation. The rather different oxidation behavior of MoS2 compared with MoSe2 and MoTe2 can be attributed to the difference in the in-plane chemical bonds. Our findings remind that the device design with UVO oxidation need to take the microstructure changes after treatment into account instead of only taking notice of the doping effect for performance improvement.

Europium-doped hydroxyapatite Ca10(PO4)6(OH)2 (3% mol) powders were synthesized by an optimized chemical precipitation method at 25 °C, followed by drying at 120 °C and calcination at 450 °C and 900 °C. The obtained nanosized crystallite samples were investigated by means of a combination of inductively coupled plasma (ICP) spectroscopy, powder X-ray diffraction (PXRD), Fourier Transform Infrared (FTIR), Raman and photoluminescence (PL) spectroscopies. The Rietveld refinement in the hexagonal P63/m space group showed europium ordered at the Ca2 site at high temperature (900 °C), and at the Ca1 site for lower temperatures (120 °C and 450 °C). FTIR and Raman spectra showed slight band shifts and minor modifications of the (PO4) bands with increasing annealing temperature. PL spectra and decay curves revealed significant luminescence emission for the phase obtained at 900 °C and highlighted the migration of Eu from the Ca1 to Ca2 site as a result of increasing calcinating temperature.

In this study, the temperature-dependent characteristics of monolayer MoS 2 flakes produced by chemical vapor deposition (CVD) are examined at temperatures ranging from 83 to 483 K. The effect of temperature change on chemical vapor deposited MoS 2 flakes transferred from glass to Si/SiO 2 substrates using a modified PMMA assisted method, is also investigated using µ-Raman and photoluminescence spectroscopy. Our results show that the thermal coefficient of the A 1 g Raman mode, which is inversely proportional to thermal conductivity, decreases from − 0.01275 to – 0.01352 cm−1 K−1 after the transfer process. The photoluminescence (PL) spectral intensity of both samples (i.e., as-grown on glass substrates and transferred on 300 nm Si/SiO 2) is observed to fall with an increase in temperature and the bandgap decreased from 1.90 eV to 1.86 eV for the as-grown sample and from 1.85 to 1.81 eV for the transferred sample. The PL and Raman spectral analysis results show that the vibrational and excitonic properties of 2D MoS 2 flakes are not substantially affected by transfer from one substrate to another. Monolayer MoS 2 samples are also observed to be unaffected by temperatures as high as 583 K. [ABSTRACT FROM AUTHOR]

Ultraviolet-Ozone (UVO) treatment has potentially promoted the long-term stability and the high performance of two-dimensional-material-based devices. However, the detailed evolutions of materials upon UVO treatment are less reported and unclear. Herein, we have systematically investigated the evolutions of morphology and electronic properties of the UVO treated few-layered MoS 2. A weak p-doping effect on a 1-hour-UVO-exposed bulk MoS 2 is revealed by photoelectron spectroscopy, being attributed to the charge transfer from MoS 2 to the newly-formed MoO x. Optical microscopy, atomic force microscopy, Raman and PL mapping measurements reveal an inhomogeneous change of MoS 2 morphology after UVO treatment. The oxidation is initiated at intrinsic defect sites and dislocations, and then expands in-plane from dislocations to both sides to form one dimensional standing-wave-like features. The dangling-bond-free surface regions remain smooth, being attributed to the higher energetic barrier for O 2 dissociation and chemisorption. A model is proposed to explain the mechanism of inhomogeneous oxidation. The rather different oxidation behavior of MoS 2 compared with MoSe 2 and MoTe 2 can be attributed to the difference in the in-plane chemical bonds. Our findings remind that the device design with UVO oxidation need to take the microstructure changes after treatment into account instead of only taking notice of the doping effect for performance improvement. [ABSTRACT FROM AUTHOR]

Europium-doped hydroxyapatite Ca10(PO4)6(OH)2 (3% mol) powders were synthesized by an optimized chemical precipitation method at 25 °C, followed by drying at 120 °C and calcination at 450 °C and 900 °C. The obtained nanosized crystallite samples were investigated by means of a combination of inductively coupled plasma (ICP) spectroscopy, powder X-ray diffraction (PXRD), Fourier Transform Infrared (FTIR), Raman and photoluminescence (PL) spectroscopies. The Rietveld refinement in the hexagonal P63/m space group showed europium ordered at the Ca2 site at high temperature (900 °C), and at the Ca1 site for lower temperatures (120 °C and 450 °C). FTIR and Raman spectra showed slight band shifts and minor modifications of the (PO4) bands with increasing annealing temperature. PL spectra and decay curves revealed significant luminescence emission for the phase obtained at 900 °C and highlighted the migration of Eu from the Ca1 to Ca2 site as a result of increasing calcinating temperature. [ABSTRACT FROM AUTHOR]

Energy band alignments at heterostructure interfaces play key roles in device performance, especially between two-dimensional atomically thin materials. Herein, van der Waals PbI 2 -MoSe 2 heterostructures fabricated by in situ PbI 2 deposition on monolayer MoSe 2 are comprehensively studied using scanning tunneling microscopy/spectroscopy, atomic force microscopy, photoemission spectroscopy, and Raman and photoluminescence (PL) spectroscopy. PbI 2 grows on MoSe 2 in a quasi layer-by-layer epitaxial mode. A type-II interface band alignment is proposed between PbI 2 and MoSe 2 with the conduction band minimum (valence band maximum) located at PbI 2 (MoSe 2 ), which is confirmed by first-principles calculations and the existence of interfacial excitons revealed using temperature-dependent PL. Our findings provide a scalable method to fabricate PbI 2 -MoSe 2 heterostructures and new insights into the electronic structures for future device design.