Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

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Diamond-like amorphous carbon

Multiferroic materials, which show simultaneous ferroelectric and magnetic ordering, exhibit unusual physical properties — and in turn promise new device applications — as a result of the coupling between their dual order parameters. We review recent progress in the growth, characterization and understanding of thin-film multiferroics. The availability of high-quality thin-film multiferroics makes it easier to tailor their properties through epitaxial strain, atomic-level engineering of chemistry and interfacial coupling, and is a prerequisite for their incorporation into practical devices. We discuss novel device paradigms based on magnetoelectric coupling, and outline the key scientific challenges in the field.

Multiferroics: progress and prospects in thin films.

Recent technical advances in the atomic-scale synthesis of oxide heterostructures have provided a fertile new ground for creating novel states at their interfaces. Different symmetry constraints can be used to design structures exhibiting phenomena not found in the bulk constituents. A characteristic feature is the reconstruction of the charge, spin and orbital states at interfaces on the nanometre scale. Examples such as interface superconductivity, magneto-electric coupling, and the quantum Hall effect in oxide heterostructures are representative of the scientific and technological opportunities in this rapidly emerging field.

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Emergent phenomena at oxide interfaces

BiVO4 photocatalysts for O2 evolution, which work under visible light irradiation, were prepared by an aqueous process. The BiVO4 photocatalysts were obtained by the reaction of layered potassium vanadate powder (KV3O8 and K3V5O14) with Bi(NO3)3 for 3 days in aqueous media at room temperature. Highly crystalline monoclinic and tetragonal BiVO4 were selectively synthesized by changing the ratio of vanadium to bismuth in the starting materials. X-ray diffraction and scanning electron microscopy measurements showed that the monoclinic BiVO4 was formed via a tetragonal BiVO4 intermediate. Tetragonal BiVO4 with a 2.9 eV band gap mainly possessed an ultraviolet absorption band while monoclinic BiVO4 with a 2.4 eV band gap had a characteristic visible light absorption band in addition to the UV band. The UV bands observed in the tetragonal and monoclinic BiVO4 were assigned to the band transition from O2p to V3d whereas the visible light absorption was due to the transition from a valence band formed by Bi6s or ...

A Novel Aqueous Process for Preparation of Crystal Form-Controlled and Highly Crystalline BiVO4 Powder from Layered Vanadates at Room Temperature and Its Photocatalytic and Photophysical Properties

An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems' applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems' applications, and permittivity and loss in ferroelectric films-important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures. (c) 2006 American Institute of Physics.

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Ferroelectric thin films: Review of materials, properties, and applications

The growth mechanism and surface microstructures of epitaxial YBa2Cu3O7−x films are extremely sensitive to substrate miscut angle. The screw dislocation‐mediated growth that is so prominent in YBa2Cu3O7−x films grown on well‐aligned (001) substrates can be completely eliminated by growing YBa2Cu3O7−x on a substrate that is miscut only 2°–3° away from (001). Films grown on miscut near‐(001) LaAlO3 and SrTiO3 substrates consist of overlapping tilted platelets, one c‐axis unit cell thick, that are epitaxially aligned with the underlying crystal lattice. This morphology, and the absence of screw‐growth features, persists even in relatively thick (∼200 nm) films. The dominance of miscut‐aligned growth is explained by the large number of surface steps that act as both nucleation and rapid‐growth sites on a miscut surface.

Suppression of the spiral‐growth mechanism in epitaxial YBa2Cu3O7−x films grown on miscut substrates

Scanning tunneling microscopy of pulsed-laser-deposited YBa2Cu3O7- delta epitaxial thin films: Surface microstructure and growth mechanism.

Vertically aligned carbon nanofibers (VACNFs) with vastly different spacing were grown by catalytically controlled dc glow discharge chemical vapor deposition. Both densely packed VACNFs and essentially isolated VACNFs were studied using scanning electron microscopy and x-ray energy dispersive spectroscopy. The morphology and chemical composition of isolated VACNFs were found to have a strong dependence upon the growth conditions, in particular on the C2H2/NH3 gas mixture used. This is attributed to the sidewalls of isolated VACNFs being exposed to reactive species during growth. In contrast, the sidewalls of densely packed VACNFs were shielded by the neighboring VACNFs, so that their growth occurred mainly in the vertical direction, by diffusion of carbon through the catalyst nanoparticle and subsequent precipitation at the nanofiber/nanoparticle interface. These striking differences in the growth process result in the formation of flattened carbon nanostructures (carbon nanotriangles) and also are quite...

Effects of spatial separation on the growth of vertically aligned carbon nanofibers produced by plasma-enhanced chemical vapor deposition

We report on the fabrication and electrical characterization of active nanoscale electronic devices using single vertically aligned carbon nanofibers (VACNFs). A rectifying behavior consistent with a 0.3 eV Schottky barrier was found. Experimental results indicate that a region of semiconducting SiC is formed directly beneath the VACNF during the growth process, creating the Schottky-barrier junction between this semiconductor material and the metallic carbon nanofibers.

Fabrication and Characterization of Carbon Nanofiber-Based Vertically Integrated Schottky Barrier Junction Diodes

We report the growth on polycrystalline yttria‐stabilized zirconia substrates of YBa2Cu3O7−x films with Jc (77 K)=11 000 A/cm2 and Jc (4.2 K)=122 000 A/cm2 by pulsed laser ablation. These Jc values are among the highest reported for YBa2Cu3O7−x on any polycrystalline substrate and approach the intrinsic upper limit for films with large‐angle grain boundaries, as indicated by recent bicrystal experiments. We find that the substrate temperature during film growth is most important in obtaining high Jc polycrystalline films. Although the magnetic field dependence of Jc indicates the presence of weak links, the behavior of Jc (4.2 K, H) suggests that a percolative path consisting of low‐angle grain boundaries exists in the films, resulting in Jc (4.2 K, 60 kOe)=4100 A/cm2.

Douglas H. Lowndes

Papers

Suppression of the spiral‐growth mechanism in epitaxial YBa2Cu3O7−x films grown on miscut substrates

Scanning tunneling microscopy of pulsed-laser-deposited YBa2Cu3O7- delta epitaxial thin films: Surface microstructure and growth mechanism.

Effects of spatial separation on the growth of vertically aligned carbon nanofibers produced by plasma-enhanced chemical vapor deposition

Fabrication and Characterization of Carbon Nanofiber-Based Vertically Integrated Schottky Barrier Junction Diodes

High critical current densities in YBa2Cu3O7−x films on polycrystalline zirconia