We have shown that nitrophenyl groups may be added to the surface of few‐layer epitaxial graphene (EG) by the formation of covalent carbon–carbon bonds thereby changing the electronic structure and transport properties of EG from near‐metallic to semiconducting. In the present Letter we discuss the opportunities afforded by such chemical processes to engineer device functionality in graphene by modification of the electronic properties without physical patterning.
High‐speed solution shearing, in which a drop of dissolved material is spread by a coating knife onto the substrate, has emerged as a versatile, yet simple coating technique to prepare high‐mobility organic thin film transistors. Solution shearing and subsequent drying and crystallization of a thin film of conjugated molecules is probed in situ using microbeam grazing incidence wide‐angle X‐ray scattering (μGIWAXS). We demonstrate the advantages of this approach to study solution based crystal nucleation and growth, and identify casting parameter combinations to cast highly ordered and laterally aligned molecular thin films.
This Letter reports on the assembly on the tip of an optical fibre of a metamaterial film fabricated by a self‐assembly bottom‐up method, composed of silver nanowires embedded in an alumina matrix. By illuminating the film through the fibre in a reflection configuration, we observe experimentally the optical response of the metamaterial in agreement with theoretical predictions and interpreted as the excitation of surface plasmon‐polaritons in the cylindrical surface of the nanowires. These results pave the way for low‐cost optical fibre devices that incorporate metamaterial films.
We demonstrate that reflectance difference spectroscopy (RDS) is sensitive to defects induced by ion bombardment, located either in the topmost layer or in the subsurface region. Most importantly, these two kinds of defects can be spectrally discriminated, since the corresponding signatures in the RD spectrum arise from perturbations of different types of electronic states: The defects in the topmost surface layer mainly lead to a quenching of the optical anisotropy related to surface states, whereas the subsurface defects strongly affect the optical anisotropy originating from transitions between surface‐modified bulk electronic states. Consequently, RDS can be used to simultaneously monitor the defects in the topmost surface layer and in the subsurface region in‐situ during ion bombardment and thermal annealing.
The Fe3O4(111)/graphene/Ni(111) trilayer is proposed to be used as an ideal spin‐filtering sandwich where the half‐metallic properties of magnetite are used. Thin magnetite layers on graphene/Ni(111) were prepared via successive oxidation of a thin iron layer predeposited on graphene/Ni(111) and the formed system was investigated by means of low‐energy electron diffraction and photoelectron spectroscopy. The electronic structure and structural quality of the graphene film sandwiched between two ferromagnetic layers remain unchanged upon magnetite formation as confirmed by experimental data.
Dip‐coating of a colloidal suspension is investigated in situ with microbeam grazing incidence small‐angle X‐ray scattering. We focus on the real‐time monitoring of a vertical dip‐coating process yielding insights into structural changes during pattern formation of the thin film. With the selected configuration a fixed spot on the sample surface is probed and the structural information at the time the contact line passes this spot is obtained, hence revealing the structure at the vicinity of the flowing meniscus owing to the microfocused beam. After dip‐coating the morphology is analyzed with atomic force microscopy, yielding real space information about the arrangement of individual nanoparticles at the film surface.
Graphene, the two‐dimensional form of carbon presents outstanding electronic and transport properties. This gives hope for the development of applications in nanoelectronics. However, for industrial purpose, graphene has to be supported by a substrate. We focus here on the graphene‐on‐SiC system to discuss how the SiC substrate interacts with the graphene layer and to show the effect of the interface on graphene atomic and electronic structures.
An effective way to reduce the reflection of a multicrystalline solar cell is the use of a honeycomb structure, which can be generated by etching a mask isotropically. In this Letter, a directly printed hexagonal inkjet mask is presented. It results in a honeycomb texture with well developed and defined etch pits at an average distance of 50.1 μm and a weighted reflection of 18.4%. The major advantage of this mask is that the masking process is simple and that it has the potential of being fast and having low costs.
Bulk polycrystalline La0.8Li0.2MnO3 is found to switch between a low‐resistance state and a high‐resistance state on thermal cycling. The low‐temperature, high‐resistance state exhibits strong electroresistance whereas the high‐temperature, low‐resistance state does not. The change in resistance between the two distinct states is of two orders of magnitude. It is proposed that the observed metastability may serve as the basis for resistive thermal‐switching devices.
We study graphene growth on hafnia (HfO2) nanoparticles by chemical vapour deposition using optical microscopy, high resolution transmission electron microscopy and Raman spectroscopy. We find that monoclinic HfO2 nanoparticles neither reduce to a metal nor form a carbide while nucleating nanometer domain‐sized few layer graphene. Hence we regard this as an interesting non‐metallic catalyst model system with the potential to explore graphene growth directly on a (high‐k) dielectric.
Angle‐resolved photoemission spectroscopy (ARPES) and X‐ray photoemission spectroscopy have been used to characterise epitaxially ordered graphene grown on copper foil by low‐pressure chemical vapour deposition. A short vacuum anneal to 200 °C allows observation of ordered low energy electron diffraction patterns. High quality Dirac cones are measured in ARPES with the Dirac point at the Fermi level (undoped graphene). Annealing above 300 °C produces n‐type doping in the graphene with up to 350 meV shift in Fermi level, and opens a band gap of around 100 meV.
Quasi‐aligned molybdenum oxide nanowires are synthesized on silicon substrate by a thermal evaporation method, at a low temperature of 550 °C without using any catalyst. The diameter of these nanowires is about 100 nm, with steps in the top to form a sharp tip. The field emission measurement shows that these nanowires have strong electron field emission abilities, with high field enhancement factor and a relatively low turn‐on field of 2.16 V µm–1, suggesting that these molybdenum oxide nanowire arrays might be promising candidates as field emitters.
We report a very simple and novel approach to produce anodic TiO2 nanotube arrays with highly defined and ordered tube openings. It is based on carrying out anodization through a slowly soluble photoresist coating. This eliminates the formation of undesired initiation layers on the tube tops and protects them to a certain extent from etching by the electrolyte.
A high‐efficiency bulk heterojunction organic photovoltaic cell (OPV) was achieved by the electrospray deposition method. The surface roughness of the P3HT:PCBM thin film can be reduced using the mixed solvent consisting of o‐dichlorobenzene (o‐DCB) and acetone. The effect of acetone concentration is related to its dielectric constant. Under an optimized concentration of acetone in o‐DCB (20 vol%), the P3HT/PCBM active layer with a smooth surface can be formed, and the power conversion efficiency of the OPV was 1.9%.
We present a simplified process sequence for the fabrication of large area n‐type silicon solar cells. The boron emitter and full area phosphorus back surface field are formed in one single high temperature step using doped glasses deposited by plasma enhanced chemical vapour deposition (PECVD) as diffusion sources. By optimizing the gas composition during the PECVD process, we not only prevent the formation of a boron rich layer (BRL), but also achieve doping profiles that exhibit a low dark saturation current density while allowing for contact formation by screen printing. The presented co‐diffusion process allows for major process simplification compared to the state of the art diffusion process relying on multiple high temperature processes, masking and wet chemistry steps.
We propose a theory of thin film photovoltaics in which one of the polycrystalline films is made of a pyroelectric material grains such as CdS. That film is shown to generate strong polarization improving the device open circuit voltage. Implications and supporting facts for the major photovoltaic types based on CdTe and CuIn(Ga)Se2 absorber layers are discussed.
Heteroepitaxial growth of kesterite Cu2ZnSnS4 (CZTS) thin film on cubic ZnS(100) single crystal substrate was achieved by radio frequency magnetron sputtering from a single CZTS target. An optimal substrate temperature in the range of 470–500 °C is found suitable for this epitaxial growth. The growth of CZTS was confirmed to be along a‐axis. The sputtered CZTS thin film is homogeneous throughout the whole film. The band gap of the film is found to be approximately 1.51 eV, i.e., promising for high efficiency thin film solar cells.
We demonstrate the fabrication of a solid state heterojunction photovoltaic device with solution‐processed graphene oxide (GO) and n‐Si. Partially reduced GO with a high optical gap (2.8 eV) was spin‐coated on the n‐Si substrate and a heterojunction device was fabricated with the structure of Au/pr‐GO/n‐Si. In the fabricated device, incident light was transmitted through the thin GO film to reach the junction interface, generating photoexciton, and thereby a photovoltaic action was observed. By means of a built‐in electric potential at the GO/n‐Si junction, photoexcited electrons and holes can be separated, transported and collected at the electrodes.
Osmium diboride has been known for some time as a low compressibility material and a superhard material. It is suitable for hard coating applications. It is also a superconductor below 2.1 K. Using first‐principles calculations, the author investigated the geometry of its Fermi surface (FS) and calculated the related physical quantities. The theoretical results are used to predict the frequencies of the Shubnikov–de Haas quantum oscillations. Comparison with recent measurements of the magneto‐resistance oscillations in osmium diboride is made.
The fabrication of titania nanostructures with hierarchical order of different structural levels is investigated. The nanostructures are prepared with a diblock‐copolymer assisted sol–gel process. By iterative spin‐coating of the solution onto silicon substrates a thin polymer‐nanocomposite film is deposited and transformed to purely anatase titania nanostructures via calcination. In total, this procedure is repeated three times on top of the substrate. The approach is monitored with grazing incidence small angle X‐ray scattering after each fabrication step. With scanning electron microscopy the final hierarchical structure is imaged. From the characterization different structural levels are clearly identified.
