Two-dimensional (2D) transition-metal dichalcogenides have become promising candidates for surface-enhanced Raman spectroscopy (SERS), but currently very few examples of detection of relevant molecules are available. Herein, we show the detection of the lipophilic disease marker β-sitosterol on few-layered MoTe2 films. The chemical vapor deposition (CVD)-grown films are capable of nanomolar detection, exceeding the performance of alternative noble-metal surfaces. We confirm that the enhancement occurs through the chemical enhancement (CE) mechanism via formation of a surface-analyte complex, which leads to an enhancement factor of ≈104, as confirmed by Fourier transform infrared (FTIR), UV-vis, and cyclic voltammetry (CV) analyses and density functional theory (DFT) calculations. Low values of signal deviation over a seven-layered MoTe2 film confirms the homogeneity and reproducibility of the results in comparison to noble-metal substrate analogues. Furthermore, β-sitosterol detection within cell culture media, a minimal loss of signal over 50 days, and the opportunity for sensor regeneration suggest that MoTe2 can become a promising new SERS platform for biosensing.

• Klíčová slova
• MoTe2, SERS, chemical enhancement, sensing, β-sitosterol,
• MeSH
• molybden chemie   MeSH
• povrchové vlastnosti MeSH
• Ramanova spektroskopie MeSH
• sitosteroly analýza   MeSH
• telur chemie   MeSH
• teorie funkcionálu hustoty MeSH
• velikost částic MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• gamma-sitosterol MeSH Prohlížeč
• molybden MeSH
• molybdenum telluride MeSH Prohlížeč
• sitosteroly MeSH
• telur MeSH

Carrier multiplication (CM), where a single high-energy photon generates multiple electron-hole pairs, offers a promising route to enhance the efficiency of solar cells and photodetectors.Transition metal dichalcogenides, such as 2H-MoTe2 and 2H-WSe2, exhibit efficient CM. Given the similar electronic band structure of 2H-MoSe2, it is expected to show comparable CM efficiency. In this study, we establish the occurrence and efficiency of CM in a solution-processed thin film of bulk-like 2H-MoSe2. We characterize the dynamics of excitons and free charge carriers by using ultrafast transient optical absorption and terahertz spectroscopy. At higher photon energy the efficiency is comparable to literature results for 2H-MoTe2 grown by chemical vapor deposition (CVD) or in bulk crystalline form. At higher photon energies the experimental CM efficiency is reproduced by theoretical modeling. We also observe CM for photon energies below the energetic threshold of twice the band gap, which is most probably due to subgap defect states. Transient optical absorption spectra of 2H-MoSe2 exhibit features of trions from which we infer that photoexcitation leads to free charge carriers. We find no signatures of excitons at the indirect band gap. From analysis of the frequency dependence of the terahertz conductivity we infer that scattering of charge carriers in our sample is less than for CVD grown or bulk crystalline 2H-MoTe2. Our findings make solution-processed 2H-MoSe2 an interesting material for exploitation of CM in photovoltaic devices.

• Klíčová slova
• carrier multiplication, excitons, solution-processed transition metal dichalcogenide, terahertz spectroscopy, transient absorption spectroscopy, trions,
• Publikační typ
• časopisecké články MeSH

Tailoring magnetic ordering in solid-state materials is essential for emerging spintronics1,2. However, substitutional lattice doping in magnetic semiconductors is often constrained by the low solubility of magnetic elements3-5, limiting the maximum achievable doping concentration (for example, less than 5%) and ferromagnetic ordering temperature6. The intercalation of magnetic elements in layered two-dimensional atomic crystals (2DACs) without breaking in-plane covalent bonds offers an alternative approach to incorporate a much higher concentration of magnetic atoms (for example, up to 50%) beyond the typical solubility limit. However, commonly used chemical and electrochemical intercalation methods are largely confined to a few isolated examples so far. Here we report a general two-step intercalation and cation-exchange strategy to produce a library of highly ordered magnetic intercalation superlattices (MISLs) with tunable magnetic ordering. Monovalent transition-metal cations Cu+ and Ag+, divalent magnetic cations Mn2+, Fe2+, Co2+ and Ni2+, and trivalent rare-earth cations Eu3+ and Gd3+ have been successfully incorporated into group-VIB 2DACs, including MoS2, MoSe2, MoTe2, WS2, WSe2 and WTe2, and group-IVB, -VB, -IIIA, -IVA and -VA 2DACs, including TiS2, NbS2, NbSe2, TaS2, In2Se3, SnSe2, Bi2Se3 and Bi2Te3. We show that these MISLs can be prepared with tunable concentrations of magnetic intercalants, enabling tailored magnetic ordering across a diverse array of functional 2DACs, including semiconductors, topological insulators, and superconductors. This work establishes a versatile material platform for both fundamental investigations and spintronics applications.

• Publikační typ
• časopisecké články MeSH

Photovoltaic (PV) devices play a key role in solar-to-electricity energy conversion at small and large scales; unfortunately, their efficiency heavily depends on optimal weather and environmental conditions. The optimal scenario would be to extend the capabilities of PV devices so that they are also able to harvest energy from environmental sources other than light. An optimal solution is represented by hybrid photovoltaic-triboelectric (PV-TENG) devices which have both photovoltaic and triboelectric capabilities for electric power generation. Two-dimensional transition metal dichalcogenides (TMDs) are highly promising candidates for such PV-TENG devices, thanks to the easy tunability of their electrical, optical, mechanical, and chemical properties. In this respect, we here propose a quantum mechanical study to identify suitable TMD-based chemical compositions with optimal photovoltaic and triboelectric generation properties. Among the considered materials, we identify MoTe2/WS2, MoS2/WSe2, WS2/TiO2, WS2/IrO2, and MoS2/WTe2 as the most promising bilayer compositions; under operative conditions, the band gap varies in the range 0.51-1.61 eV, ensuring the photovoltaic activity, while the relative motion of the layers may produce an electromotive force between 1.21 and 3.21 V (triboelectric generation) with a TMD/TMD interface area equal to about 200 Å2. The results constitute theoretical guidelines on how to check if specific chemical compositions of TMD bilayers are optimal for a combined photovoltaic and triboelectric power generation. Thanks to its generality, the presented approach can be promptly extended to van der Waals heterostructures other than those here considered and implemented in automated workflows for the search of novel low-dimensional materials with target PV and TENG response.

• Publikační typ
• časopisecké články MeSH