Materials For Applications In Nanoelectronics Research Articles

Electronic and optical characteristics of 5d-transition metal doped 2D-NbSe2 monolayer for nanoelectronic device applications: An ab-initio-analysis

Novel physical properties can be realized in 2D transition metal dichalcogenides (TMDCs) 2H-NbSe2 via chemical doping. Using first-principles calculations, we have investigated the electronic and optical properties of pristine and 5d-transition metal atoms (M = Hf, Ta, W, Re, Ir, and Pt) doped 3 × 3 supercells of NbSe2 monolayers. The physical properties of M-doped NbSe2 monolayers are found to be tunable upon doping with transition metals; making these modifications of NbSe2 attractive 2D materials for applications in nanoelectronics. The calculated electronic properties reveal that transition metal doping remarkably affects the electronic structures because charge transfer varies only due to 5d-transition metal substitution instead of Nb atom. Consequently, variation in the density of states around Fermi level (EF) is observed. A hybridization between 5d-states of transition metals (TM) and 4p states of Se results TM-Se covalent bonds. Hence, doping can significantly tune the electronic properties of NbSe2 monolayer. The optical properties such as optical absorption coefficient, optical conductivity, reflectivity and energy loss function are also computed and discussed for 2D applications of the studied TM doped NbSe2 monolayers. In particular, our results indicate that the absorption spectra shift to lower photon energies upon TM doping. Such tuning of the physical properties suggest the use of these 2D-materials with graphene, to fabricate viable electronic devices, such as logic circuits and field-effect transistors.

Electronic transport properties of MoS2 nanoribbons embedded in butadiene solvent.

Transition metal dichalcogenides (TMDCs) are promising materials for applications in nanoelectronics and correlated fields, where their metallic edge states play a fundamental role in the electronic transport. In this work, we investigate the transport properties of MoS2 zigzag nanoribbons under a butadiene (C4H6) atmosphere, as this compound has been used to obtain MoS2 flakes by exfoliation. We use density functional theory combined with non-equilibrium Green's function techniques, in a methodology contemplating disorder and different coverages. Our results indicate a strong modulation of the TMDC electronic transport properties driven by butadiene molecules anchored at their edges, producing the suppression of currents due to a backscattering process. Our results indicate a high sensitivity of the TMDC edge states. Thus, the mechanisms used to reduce the dimensionality of MoS2 considerably modify its transport properties.

Hierarchical on-surface synthesis and electronic structure of carbonyl-functionalized one- and two-dimensional covalent nanoarchitectures

The fabrication of nanostructures in a bottom-up approach from specific molecular precursors offers the opportunity to create tailored materials for applications in nanoelectronics. However, the formation of defect-free two-dimensional (2D) covalent networks remains a challenge, which makes it difficult to unveil their electronic structure. Here we report on the hierarchical on-surface synthesis of nearly defect-free 2D covalent architectures with carbonyl-functionalized pores on Au(111), which is investigated by low-temperature scanning tunnelling microscopy in combination with density functional theory calculations. The carbonyl-bridged triphenylamine precursors form six-membered macrocycles and one-dimensional (1D) chains as intermediates in an Ullmann-type coupling reaction that are subsequently interlinked to 2D networks. The electronic band gap is narrowed when going from the monomer to 1D and 2D surface-confined π-conjugated organic polymers comprising the same building block. The significant drop of the electronic gap from the monomer to the polymer confirms an efficient conjugation along the triphenylamine units within the nanostructures.

High carrier mobility of few-layer PbX (X = S, Se, Te)

Two-dimensional materials with a higher carrier mobility are promising materials for applications in nanoelectronics and photocatalysis.

Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide.

Progress in nanotechnology requires new approaches to materials synthesis that make it possible to control material functionality down to the smallest scales. An objective of materials research is to achieve enhanced control over the physical properties of materials such as ferromagnets, ferroelectrics and superconductors. In this context, complex oxides and inorganic perovskites are attractive because slight adjustments of their atomic structures can produce large physical responses and result in multiple functionalities. In addition, these materials often contain ferroelastic domains. The intrinsic symmetry breaking that takes place at the domain walls can induce properties absent from the domains themselves, such as magnetic or ferroelectric order and other functionalities, as well as coupling between them. Moreover, large domain wall densities create intense strain gradients, which can also affect the material's properties. Here we show that, owing to large local stresses, domain walls can promote the formation of unusual phases. In this sense, the domain walls can function as nanoscale chemical reactors. We synthesize a two-dimensional ferromagnetic phase at the domain walls of the orthorhombic perovskite terbium manganite (TbMnO3), which was grown in thin layers under epitaxial strain on strontium titanate (SrTiO3) substrates. This phase is yet to be created by standard chemical routes. The density of the two-dimensional sheets can be tuned by changing the film thickness or the substrate lattice parameter (that is, the epitaxial strain), and the distance between sheets can be made as small as 5nanometres in ultrathin films, such that the new phase at domain walls represents up to 25 per cent of the film volume. The general concept of using domain walls of epitaxial oxides to promote the formation of unusual phases may be applicable to other materials systems, thus giving access to new classes of nanoscale materials for applications in nanoelectronics and spintronics.

The local environment of Co2+ ions intercalated in vanadium oxide/hexadecylamine nanotubes

Vanadium oxide nanotubes constitute promising materials for applications in nanoelectronics as cathode materials, in sensor technology and in catalysis. In this work we present a study on hybrid vanadium oxide/hexadecylamine multiwall nanotubes doped with Co ions using state of the art x-ray diffraction and absorption techniques, to address the issue of the dopant location within the nanotubes’ structure. The x-ray absorption near-edge structure analysis shows that the Co ions in the nanotubes are in the 2 + oxidation state, while extended x-ray absorption fine structure spectroscopy reveals the local environment of the Co2+ ions. Results indicate that Co atoms are exchanged at the interface between the vanadium oxide’s layers and the hexadecylamines, reducing the amount of amine chains and therefore the interlayer distance, but preserving the tubular shape. The findings in this work are important for describing Co2+ interaction with vanadium oxide nanotubes at the molecular level and will help to improve the understanding of their physicochemical behavior, which is desired in view of their promising applications.