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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Properties of Monolayer Silicene on Ag(111)
摘要： The expected properties of silicene and their theoretical background have already been discussed in Chaps. 1–3 and the different ways to synthesize this new 2D material in Chap. 5. It has already been mentioned that such a synthesis requires an adequate substrate material to accommodate the formation of a one-atom-thin silicon layer. Such a material is silver, in particular the Ag(111) surface plane. In this chapter the formation and properties of silicene formed epitaxially on the Ag(111)(1 × 1) surface are discussed. We will see that the properties of these silicene layers are modi?ed with respect to the ones of free-standing silicene, due to the interaction with the substrate. For this reason we will refer to it as epitaxial silicene and look in detail at its two-dimensional (2D) character. A more detailed look at the formation of Si layers on Ag(111) shows that, depending on the speci?c preparation conditions, several 2D Si phase can be formed. Differences and similarities of these structures will be discussed. Furthermore, we will draw the intention on the chemical and temperature stability of these epitaxial silicene layers and unveil the limits for the silicene formation.
关键词： silicene,2D materials,Ag(111),vibrational properties,electronic properties,epitaxial growth
更新于2025-09-23 15:21:21
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Electronic and Vibrational Properties of TiS <sub/>2</sub> , ZrS <sub/>2</sub> , and HfS <sub/>2</sub> : Periodic Trends Studied by Dispersion-Corrected Hybrid Density Functional Methods
摘要： The electronic and vibrational properties of TiS2, ZrS2, and HfS2 have been studied using dispersion corrected hybrid density functional methods. The periodic trends in electronic band structures, electronic transport coefficients, IR and Raman spectra, and phonon dispersion relations were investigated. Comparison to the available experimental data shows that the applied DFT methodology is suitable for the investigation of the layered transition metal dichalcogenide materials with weak interlayer Van der Waals interactions. The choice of damping function in the D3 dispersion correction proved to have surprisingly large effect. Systematic investigation of the periodic trends within group 4 disulfides reveals that TiS2 shows many differences to ZrS2 and HfS2 due to the more covalent M–S bonding in TiS2. ZrS2 and HfS2 mainly show differences for properties where the atomic mass plays a role. All three compounds show similar Seebeck coefficients, but clear differences in the relative electrical conductivity of cross- and in-plane directions. The transport and vibrational properties of thin TiS2 single crystals were also investigated experimentally.
关键词： ZrS2,HfS2,dispersion corrected hybrid density functional methods,thermoelectric properties,periodic trends,vibrational properties,electronic properties,TiS2
更新于2025-09-23 15:21:01
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Synthesis and multimethodological characterization of neodymium substituted nickel tungstates and molybdates solid solution Ni Ndx (W,Mo)O4, (0?≤?x?≤?0.2)
摘要： New series of neodymium substituted nickel tungstates and molybdates NiNdxM’O4 (M’=W,Mo and x=0%, 10%, 20%) were synthesized by standard solid state route at high temperature T=1000°C.These materials, were characterized by powder X-Ray diffraction technique (XRD), which confirmed that both series of tungstates and molybdates crystallized in monoclinic structure with space groups(P2/c, C2/m) respectively and behaved as a quasi-ideal solid solution. Scanning Electron Microscopy (SEM) experiments showed the presence of grains with irregular sizes developed within larger aggregations, while EDS semi-quantitative analyses confirmed the nominal compositions for all the phases.Active vibration modes were investigated by Fourier Transform InfraRed (FTIR) and Raman techniques, the group theoretical calculation predicted 36 vibrational modes. The presence of characteristic frequencies assigned to components ?1 and ?3 confirmed the existence of WO6 and MoO6 polyhedra in the structures, non-vibrational bands appearing in Raman spectra were attributed to laser-excited luminescence of neodymium element.
关键词： solid state reaction,vibrational properties,neodymium,nickel tungstates,X-ray diffraction,nickel molybdates
更新于2025-09-10 09:29:36
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Effect of Phosphine-Free Selenium Precursor Reactivity on The Optical and Vibrational properties of Colloidal CdSe Nanocrystals
摘要： Phosphine-free selenium precursor solutions have been prepared by heating at temperatures ranging from 160 °C to 240 °C and studied by means of infrared absorption spectroscopy. The colloidal CdSe nanocrystals (NCs) synthesized from all those solutions by the wet chemical method. The influence of heating temperature on the chemical reactivity of selenium precursor and its role on the optical and vibrational properties of CdSe NCs are discussed in details. Their morphology, particle size, structural, optical and vibrational properties were investigated using transmission electron microscopy, X-ray diffraction, UV-Vis, fluorescence and Raman spectroscopy, respectively.
关键词： vibrational properties,Phosphine-free selenium precursor,CdSe nanocrystals,optical properties
更新于2025-09-04 15:30:14