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Molybdenum ditelluride (MoTe2), a member of the transition metal dichalcogenide family, holds significant promise in optoelectronic applications. To harness its full potential, it is imperative to understand its fundamental optical properties, including refractive indices. Herein, measurements of the transmittance and reflectance spectra of thin MoTe2 layers are conducted featuring hexagonal and monoclinic structures across the far‐infrared (IR) and mid‐IR spectral regions. These spectra are fitted, allowing to extract the complex refractive index and optical conductance. In the semiconducting hexagonal phase, both the conductance and extinction coefficient remain negligible below 3000 cm−1 and increase at higher energies. Conversely, the monoclinic phase exhibits a conductance peak in the far‐IR region and a continuous increase from 1000 to 6000 cm−1. The findings are compared with existing theoretical and experimental results to provide further insights into MoTe2's optical behavior. [ABSTRACT FROM AUTHOR]

The transition metal dichalcogenides have been studied for various applications in electronics, sensing, or spintronics. Molybdenum ditelluride, MoTe2, occurs in 3 crystal systems: hexagonal (2H), monoclinic (1T′), and orthorhombic (Td). Here we report on tellurisation of Mo and MoO3 thin films to 2H-MoTe2 and 1T′-MoTe2 thin layers on sapphire substrates, respectively. To study the phases, we employed diffraction patterns using grazing-incidence wide-angle X-ray scattering, conventional X-ray diffraction and transmission electron microscopy (TEM). Measurements of pole figures confirmed the presence of a biaxial texture of both 1T′ and 2H phases. In the hexagonal phase, we found two ensembles of biaxially oriented crystallites offset by 30 degrees between the two groups. On the other hand, in the monoclinic layer, the crystallites follow the six-fold symmetry of the (0001) sapphire surface. [ABSTRACT FROM AUTHOR]

Small π-conjugated organic molecules have attracted substantial attention in the past decade as they are considered as candidates for future organic-based (opto-)electronic applications. The molecular arrangement in the organic layer is one of the crucial parameters that determine the efficiency of a given device. The desired orientation of the molecules is achieved by a proper choice of the underlying substrate and growth conditions. Typically, one underlying material supports only one inherent molecular orientation at its interface. Here, we report on two different orientations of diindenoperylene (DIP) molecules on the same underlayer, i.e. on a few-layer MoS2 substrate. We show that DIP molecules adopt a lying-down orientation when deposited on few-layer MoS2 with horizontally oriented layers. In contrast, for vertically aligned MoS2 layers, DIP molecules are arranged in a standing-up manner. Employing in situ and real-time grazing-incidence wide-angle X-ray scattering (GIWAXS), we monitored the stress evolution within the thin DIP layer from the early stages of the growth, revealing different substrate-induced phases for the two molecular orientations. Our study opens up new possibilities for the next-generation of flexible electronics, which might benefit from the combination of MoS2 layers with unique optical and electronic properties and an extensive reservoir of small organic molecules. [ABSTRACT FROM AUTHOR]

The last few decades faced on the fabrication of advanced engineering materials involving also different composites. Here, we report on the fabrication of few-layer molybdenum disulfide on top of thin polycrystalline diamond substrates with a high specific surface area. In the method, pre-deposited molybdenum coatings were sulfurized in a one-zone furnace at ambient pressure. As-prepared MoS2 layers were characterized by several techniques including grazing-incidence wide-angle X-ray scattering, atomic force microscopy, scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. We found out that the initial thickness of Mo films determined the final c-axis crystallographic orientation of MoS2 layer as previously observed on other substrates. Even though it is well-known that Mo diffuses into diamond at elevated temperatures, the competing sulfurization applied effectively suppressed the diffusion and a chemical reaction between molybdenum and diamond. In particular, a Mo2C layer does not form at the interface between the Mo film and diamond substrate. The combination of diamond high specific surface area along with a controllable layer orientation might be attractive for applications, such as water splitting or water disinfection. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS 2 ) few-layer films have gained considerable attention for their possible applications in electronics and optics and also as a promising material for energy conversion and storage. Intercalating alkali metals, such as lithium, offers the opportunity to engineer the electronic properties of MoS 2 . However, the influence of lithium on the growth of MoS 2 layers has not been fully explored. Here, we have studied how lithium affects the structural and optical properties of the MoS 2 few-layer films prepared using a new method based on one-zone sulfurization with Li 2 S as a source of lithium. This method enables incorporation of Li into octahedral and tetrahedral sites of the already prepared MoS 2 films or during MoS 2 formation. Our results discover an important effect of lithium promoting the epitaxial growth and horizontal alignment of the films. Moreover, we have observed a vertical-to-horizontal reorientation in vertically aligned MoS 2 films upon lithiation. The measurements show long-term stability and preserved chemical composition of the horizontally aligned Li-doped MoS 2 ., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Molybdenum disulfide (MoS 2 ) and nanocrystalline diamond (NCD) have attracted considerable attention due to their unique electronic structure and extraordinary physical and chemical properties in many applications, including sensor devices in gas sensing applications. Combining MoS 2 and H-terminated NCD (H-NCD) in a heterostructure design can improve the sensing performance due to their mutual advantages. In this study, the synthesis of MoS 2 and H-NCD thin films using appropriate physical/chemical deposition methods and their analysis in terms of gas sensing properties in their individual and combined forms are demonstrated. The sensitivity and time domain characteristics of the sensors were investigated for three gases: oxidizing NO 2 , reducing NH 3 , and neutral synthetic air. It was observed that the MoS 2 /H-NCD heterostructure-based gas sensor exhibits improved sensitivity to oxidizing NO 2 (0.157%·ppm -1 ) and reducing NH 3 (0.188%·ppm -1 ) gases compared to pure active materials (pure MoS 2 achieves responses of 0.018%·ppm -1 for NO 2 and -0.0072%·ppm -1 for NH 3 , respectively, and almost no response for pure H-NCD at room temperature). Different gas interaction model pathways were developed to describe the current flow mechanism through the sensing area with/without the heterostructure. The gas interaction model independently considers the influence of each material (chemisorption for MoS 2 and surface doping mechanism for H-NCD) as well as the current flow mechanism through the formed P-N heterojunction.

Thin films of transition-metal dichalcogenides are potential materials for optoelectronic applications. However, the application of these materials in practice requires knowledge of their fundamental optical properties. Many existing methods determine optical constants using predefined models. Here, a different approach was used. We determine the sheet conductance and absorption coefficient of few-layer PtSe 2 in the infrared and UV-vis ranges without recourse to any particular model for the optical constants. PtSe 2 samples with a thickness of about 3-4 layers were prepared by selenization of 0.5 nm thick platinum films on sapphire substrates at different temperatures. Differential reflectance was extracted from transmittance and reflectance measurements from the front and back of the sample. The film thickness, limited to a few atomic layers, allowed a thin-film approximation to calculate the optical conductance and absorption coefficient. The former has a very different energy dependence in the infrared, near-infrared, and visible ranges. The absorption coefficient exhibits a strong power-law dependence on energy with an exponent larger than three in the mid-infrared and near-infrared regions. We have not observed any evidence for a band gap in PtSe 2 thin layers down to an energy of 0.4 eV from our optical measurements., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Recently, few-layer PtSe 2 films have attracted significant attention due to their properties and promising applications in high-speed electronics, spintronics and optoelectronics. Until now, the transport properties of this material have not reached the theoretically predicted values, especially with regard to carrier mobility. In addition, it is not yet known which growth parameters (if any) can experimentally affect the carrier mobility value. This work presents the fabrication of horizontally aligned PtSe 2 films using one-zone selenization of pre-deposited platinum layers. We have identified the Se : Pt ratio as a parameter controlling the charge carrier mobility in the thin films. The mobility increases more than twice as the ratio changes in a narrow interval around a value of 2. A simultaneous reduction of the carrier concentration suggests that ionized impurity scattering is responsible for the observed mobility behaviour. This significant finding may help to better understand the transport properties of few-layer PtSe 2 films., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Small π-conjugated organic molecules have attracted substantial attention in the past decade as they are considered as candidates for future organic-based (opto-)electronic applications. The molecular arrangement in the organic layer is one of the crucial parameters that determine the efficiency of a given device. The desired orientation of the molecules is achieved by a proper choice of the underlying substrate and growth conditions. Typically, one underlying material supports only one inherent molecular orientation at its interface. Here, we report on two different orientations of diindenoperylene (DIP) molecules on the same underlayer, i.e. on a few-layer MoS 2 substrate. We show that DIP molecules adopt a lying-down orientation when deposited on few-layer MoS 2 with horizontally oriented layers. In contrast, for vertically aligned MoS 2 layers, DIP molecules are arranged in a standing-up manner. Employing in situ and real-time grazing-incidence wide-angle X-ray scattering (GIWAXS), we monitored the stress evolution within the thin DIP layer from the early stages of the growth, revealing different substrate-induced phases for the two molecular orientations. Our study opens up new possibilities for the next-generation of flexible electronics, which might benefit from the combination of MoS 2 layers with unique optical and electronic properties and an extensive reservoir of small organic molecules.

Few-layer MoS 2 films are promising candidates for applications in numerous areas, such as photovoltaics, photocatalysis, nanotribology, lithium batteries, hydro-desulfurization catalysis and dry lubricants, especially due to their distinctive electronic, optical, and catalytic properties. In general, two alignments of MoS 2 layers are possible - the horizontal and the vertical one, having different physicochemical properties. Layers of both orientations are conventionally fabricated by a sulfurization of pre-deposited Mo films. So far, the Mo thickness was considered as a critical parameter influencing the final orientation of MoS 2 layers with horizontally and vertically aligned MoS 2 grown from thin (1 nm) and thick (3 nm) Mo films, respectively. Here, we present a fabrication protocol enabling the growth of horizontally or vertically aligned few-layer MoS 2 films utilizing the same Mo thickness of 3 nm. We show that the sulfur vapor is another parameter influencing the growth mechanism, where a sulfurization with higher sulfur vapor pressure leads to vertical MoS 2 layers and slow sulfur evaporation results in horizontally aligned layers for a thicker Mo starting layer., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)