Search

In this study, we present the growth of monolayer MoS2 (molybdenum disulfide) film. Mo (molybdenum) film was formed on a sapphire substrate through e-beam evaporation, and triangular MoS2 film was grown by direct sulfurization. First, the growth of MoS2 was observed under an optical microscope. The number of MoS2 layers was analyzed by Raman spectrum, atomic force microscope (AFM), and photoluminescence spectroscopy (PL) measurement. Different sapphire substrate regions have different growth conditions of MoS2. The growth of MoS2 is optimized by controlling the amount and location of precursors, adjusting the appropriate growing temperature and time, and establishing proper ventilation. Experimental results show the successful growth of a large-area single-layer MoS2 on a sapphire substrate through direct sulfurization under a suitable environment. The thickness of the MoS2 film determined by AFM measurement is about 0.73 nm. The peak difference between the Raman measurement shift of 386 and 405 cm−1 is 19.1 cm−1, and the peak of PL measurement is about 677 nm, which is converted into energy of 1.83 eV, which is the size of the direct energy gap of the MoS2 thin film. The results verify the distribution of the number of grown layers. Based on the observation of the optical microscope (OM) images, MoS2 continuously grows from a single layer of discretely distributed triangular single-crystal grains into a single-layer large-area MoS2 film. This work provides a reference for growing MoS2 in a large area. We expect to apply this structure to various heterojunctions, sensors, solar cells, and thin-film transistors. [ABSTRACT FROM AUTHOR]

In this study, n-type MoS2 monolayer flakes are grown through chemical vapor deposition (CVD), and a p-type Cu2O thin film is grown via electrochemical deposition. The crystal structure of the grown MoS2 flakes is analyzed through transmission electron microscopy. The monolayer structure of the MoS2 flakes is verified with Raman spectroscopy, multiphoton excitation microscopy, atomic force microscopy, and photoluminescence (PL) measurements. After the preliminary processing of the grown MoS2 flakes, the sample is then transferred onto a Cu2O thin film to complete a p-n heterogeneous structure. Data are confirmed via scanning electron microscopy, SHG, and Raman mapping measurements. The luminous energy gap between the two materials is examined through PL measurements. Results reveal that the thickness of the single-layer MoS2 film is 0.7 nm. PL mapping shows a micro signal generated at the 627 nm wavelength, which belongs to the B2 excitons of MoS2 and tends to increase gradually when it approaches 670 nm. Finally, the biosensor is used to detect lung cancer cell types in hydroplegia significantly reducing the current busy procedures and longer waiting time for detection. The results suggest that the fabricated sensor is highly sensitive to the change in the photocurrent with the number of each cell, the linear regression of the three cell types is as high as 99%. By measuring the slope of the photocurrent, we can identify the type of cells and the number of cells. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of a series of the polycrystalline samples of titanium dichalcogenides with partial substitution of Ti for Nb and S for Se were investigated. It was found that sintering of the samples improved the thermoelectric efficiency (ZT), and the maximum ZT was achieved at sintering temperature of 600°C. A further increase in the sintering temperature (850°C and 950°C) led to the recrystallization of the samples, as a result, the Seebeck coefficient sharply decreased and electrical conductivity dramatically increased. The temperature dependences of electrical conductivity σ(T) in the temperature range from 4.2 to 300 K and Seebeck coefficient S(T) in the temperature range from 77 to 300 K were investigated in order to determine the nature of the observed improvements in thermoelectric properties due to double substitutions and sintering. Two‐dimensionalization of electron transport properties of Ti1−xNbxS2−ySey solid solutions was found. The Fermi energy EF2D was estimated using the temperature dependences of Seebeck coefficient. The relationship between the Fermi energy EF2D and figure of merit ZT was established. The effect of sintering on parameters σ(T), S(T), charge carrier concentration (n2D), mobility (µ), and thermal conductivity (k) was found. The optimal value of Fermi energy EF2D in terms of figure of merit ZT = 0.31 at room temperature (T = 300 K) was found for Ti0.98Nb0.02S1.3Se0.7 sample sintered at 600°C. [ABSTRACT FROM AUTHOR]

Two-dimensional molybdenum disulphide (MoS2) sheets were prepared by using simple thermal decomposition method. The synthesized sheets were characterized by different analytical tools including FTIR, XRD, XPS, Raman spectroscopy, HRTEM and FESEM analyses. The synthesized sheets exhibited outstanding peroxidase mimicking activity towards the peroxidase oxidation of chromogenic probe molecule 3,3′,5,5′-tetramethyl benzidine (TMB), producing a blue coloured solution of 3,3′,5,5′-tetramethylbenzidine diimine (TMBDI) in an acidic medium (pH 4). Based on this peroxidase mimicking activity it was utilized for colorimetric determination of toxic Cr(vi) ions present in aqueous medium. The MoS2 sheets showed excellent sensitivity towards Cr(vi) detection with a lower detection limit of 40.09 nM. Moreover, these 2D sheets also acted as an excellent photocatalyst because of their direct band gap of 1.90 eV, and were used for the reduction of inorganic toxic pollutant Cr(vi) ions to environmentally benign Cr(iii) ions under the irradiation of visible light. MoS2 sheets showed 98% photo reduction efficiency towards Cr(vi) ions within 20 min. Furthermore, the synthesized MoS2 sheets were successfully recycled up to five times without significant decrease of their photocatalytic reduction efficiency towards Cr(vi) ions. The present study demonstrates that metal free MoS2 sheets prepared by a simple solid state synthesis approach provide a simple, cost-effective and easy method for determination and removal of toxic Cr(vi) ions in aqueous medium. [ABSTRACT FROM AUTHOR]

Similarly to transition metal dichalcogenides akin to MoS2, transition metal polysulfides like tri- and tetrachalcogenide materials are nowadays incorporated into catalysts and composites used for energy conversion and storage, etc. However, polysulfide structures feature S S  units, which make them strikingly different from the widely known MoS2 and other dichalcogenides. At the same time, their surface chemistry and its relation to properties are very little studied. Reported here is one of the first observations on the oxidizing properties of disulfide bridges ( S S )2− forming surfaces in polysulfide crystals. Upon interaction with silver salts or silver nanoparticles, MoS2 acts as most supports, that is, it stabilizes metallic Ag at its surface; in contrast, curiously, patronite VS4 and NbS3 stabilize Ag2S nanoparticles under identical reducing conditions. The Ag/MoS2, Ag2S/NbS3, and Ag2S/VS4 samples are characterized with X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Apparently, the unexpected formation of Ag2S is due to complex redox processes involving disulfide fragments -S-S- of nanorods VS4 or nanoribbons NbS3, which are absent in MoS2 nanosheets. This result is important for fundamental understanding of the properties of sulfur-rich surfaces and also for contributing to the number of available synthetic paths toward Ag2S nanoparticles. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2) was grown on a laser-processed periodic-hole sapphire substrate through chemical vapor deposition. The main purpose was to investigate the mechanism of MoS2 growth in substrate with a periodic structure. By controlling the amount and position of the precursor, adjusting the growth temperature and time, and setting the flow rate of argon gas, MoS2 grew in the region of the periodic holes. A series of various growth layer analyses of MoS2 were then confirmed by Raman spectroscopy, photoluminescence spectroscopy, and atomic force microscopy. Finally, the growth mechanism was studied by transmission electron microscopy (TEM). The experimental results show that in the appropriate environment, MoS2 can be successfully grown on substrate with periodic holes, and the number of growth layers can be determined through measurements. By observing the growth mechanism, composition analysis, and selected area electron diffraction diagram by TEM, we comprehensively understand the growth phenomenon. The results of this research can serve as a reference for the large-scale periodic growth of MoS2. The production of periodic structures by laser drilling is advantageous, as it is relatively simpler than other methods. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS 2 ) was grown on a laser-processed periodic-hole sapphire substrate through chemical vapor deposition. The main purpose was to investigate the mechanism of MoS 2 growth in substrate with a periodic structure. By controlling the amount and position of the precursor, adjusting the growth temperature and time, and setting the flow rate of argon gas, MoS 2 grew in the region of the periodic holes. A series of various growth layer analyses of MoS 2 were then confirmed by Raman spectroscopy, photoluminescence spectroscopy, and atomic force microscopy. Finally, the growth mechanism was studied by transmission electron microscopy (TEM). The experimental results show that in the appropriate environment, MoS 2 can be successfully grown on substrate with periodic holes, and the number of growth layers can be determined through measurements. By observing the growth mechanism, composition analysis, and selected area electron diffraction diagram by TEM, we comprehensively understand the growth phenomenon. The results of this research can serve as a reference for the large-scale periodic growth of MoS 2 . The production of periodic structures by laser drilling is advantageous, as it is relatively simpler than other methods.

Increasing attention has been paid to two-dimensional (2D) materials because of their superior performance and wafer-level synthesis methods. However, the large-area characterization, precision, intelligent automation, and high-efficiency detection of nanostructures for 2D materials have not yet reached an industrial level. Therefore, we use big data analysis and deep learning methods to develop a set of visible-light hyperspectral imaging technologies successfully for the automatic identification of few-layers MoS 2 . For the classification algorithm, we propose deep neural network, one-dimensional (1D) convolutional neural network, and three-dimensional (3D) convolutional neural network (3D-CNN) models to explore the correlation between the accuracy of model recognition and the optical characteristics of few-layers MoS 2 . The experimental results show that the 3D-CNN has better generalization capability than other classification models, and this model is applicable to the feature input of the spatial and spectral domains. Such a difference consists in previous versions of the present study without specific substrate, and images of different dynamic ranges on a section of the sample may be administered via the automatic shutter aperture. Therefore, adjusting the imaging quality under the same color contrast conditions is unnecessary, and the process of the conventional image is not used to achieve the maximum field of view recognition range of ~1.92 mm 2 . The image resolution can reach ~100 nm and the detection time is 3 min per one image.