We report on a reference-free Raman spectroscopy method for a precise thickness determination of the multilayered graphene oxide flakes. The method is based on the normalization of the total integral intensity of D and G Raman bands to the integral intensity of the second-order optical phonon peak of the silicon substrate in the Raman spectrum. The normalization provides discrete ratio values corresponding to the number of graphene oxide layers in the respective flakes with the intensity linearly increasing with the number of layers. This provides a fast and robust determination of the thickness of graphene oxide flakes in terms of the layer number up to high values. A comparison with conventional spectrally resolved reflectivity mapping shows similar sensitivity, while selectivity to particular functional chemical groups is a bonus of the Raman-based method. Copyright

Few-layer MoS2 films stay at the forefront of current research of two-dimensional materials. At present, continuous MoS2 films are prepared by chemical vapor deposition (CVD) techniques. Herein, we present a cost-effective fabrication of the large-area spatially uniform films of few-layer MoS2 flakes using a modified Langmuir–Schaefer technique. The compression of the liquid-phase exfoliated MoS2 flakes on the water subphase was used to form a continuous layer, which was subsequently transferred onto a submerged substrate by removing the subphase. After vacuum annealing, the electrical sheet resistance dropped to a level of 10 kΩ/sq, being highly competitive with that of CVD-deposited MoS2 nanosheet films. In addition, a consistent fabrication protocol of the large-area conductive MoS2 films was established. The morphology and electrical properties predetermine these films to advanced detecting, sensing, and catalytic applications. A large number of experimental techniques were used to characterize the exfoliated few-layer MoS2 flakes and to elucidate the formation of the few-layer MoS2 Langmuir film.

The interaction between a graphene layer and pentacene (PEN) molecules leads to the formation of a lyingdown phase, which can improve charge transport for organic vertical field effect transistors and enhance the optical absorption for increased light harvesting in organic solar cells. Here, we present a comprehensive study of PEN growth on epitaxial graphene on silicon carbide (SiC). Simultaneous grazing-incidence small-and wide-angle X-ray scattering (GISAXS/GIWAXS) were used in situ for real-time monitoring of the PEN crystal growth with millisecond time resolution to identify two distinct anisotropic growth stages after the nucleation of the first monolayer (ML). In the first stage up to 1.5 nm, we observe rapid growth of pentacene domains along the ( 010) and ( 001) facets. This growth behavior is saturating after 1.5 nm. In a second stage, this is followed by continuous lateral crystal growth in only one in-plane direction (100) forming needle-shaped domains. In the second stage, an uninterrupted linear growth of the lying-down PEN phase is found based on the (001) diffraction up to 15 nm. Ex situ atomic force microscopy and polarized confocal Raman microscopy were used to further support the real-time observations of aligned PEN films on graphene.

Research on two-dimensional (2D) atomic crystals is one of the highly progressive topics in (opto)electronics, as the van der Waals (vdW) interactions enable integration of 2D crystals with a broad range of materials. Organic π-conjugated molecules offer new opportunities for creating the so-called “hybrid” vdW heterostructures, in which their anisotropy adds an extra degree of functional possibilities. Moreover, it was found that in the case of organic molecules, the 2D substrate changes the molecular orientation, which in turn can enhance the overall optoelectronic properties. However, the reorientation of the molecules has been until now studied solely on the graphene underlayer that restrained its applicability to a broader range of materials. Here, we study the molecular orientation of diindenoperylene (DIP), a representative of rodlike organic semiconductors, on the MoS2 monolayer. Our results show that DIP forms separate islands on the top of the MoS2 monolayer with lying-down orientation of the molecules. We combine the grazing-incidence X-ray diffraction technique with atomistic simulations to reveal the exact molecular arrangement on the atomically thin underlayer. We also investigate optical absorption spectra for different thicknesses of the DIP layer, as they are of fundamental importance for various applications in organic-based optoelectronics.

Antifouling polymer brushes are widely utilized in biomedical applications to prevent non-specific interactions with biological fluids. They consist of surface-tethered polymer chains and are commonly formed when the chains are...

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In continuation of our previous studies on Langmuir nanoparticle films we prepared well-ordered bilayer film on the airwater interface in the Langmuir-Blodgett trough. The distance of neighboring nanoparticles was adjustable by shortening the carbon chain length by UV-ozone irradiation. Kinetics of the nanoparticle reassembly in multilayer structure was monitored in time by grazing-incidence small angle X-ray scattering (GISAXS) technique. The interparticle distance determined from the first lateral peak positions decayed exponentially with characteristic time of 102 AE 13 s. The final GISAXS pattern proves nanoparticle multilayer collapse and multilayer agglomeration at the end of the UV exposition.