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).

/pdf/diamond-like-amorphous-carbon-3pczopr0z7.pdf

Diamond-like amorphous carbon

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

/pdf/science-and-technology-roadmap-for-graphene-related-two-4q9m7czlkc.pdf

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

This paper reviews recent studies conducted on carbon nanotube/polymer composites. Carbon nanotubes are promising new materials for blending with polymers with potential to obtain low-weight nanocomposites of extraordinary mechanical, electrical, thermal and multifunctional properties. The size scale, aspect ratio and properties of nanotubes provide advantages in a variety of applications, including electrostatically dissipative materials; advanced materials with combined stiffness, strength and impact for aerospace or sporting goods; composite mirrors; automotive parts that require electrostatic painting and automotive components with enhanced mechanical properties. The various processing methods for producing these nanocomposites are discussed, in particular melt mixing, solution processing and in-situ polymerization. Some key results are summarized, relating to the mechanical, electrical, thermal, optical and surface properties. Finally, the challenges for the future are discussed in terms of processing, characterization, nanotube availability, nanotube tailoring, and the mechanisms governing the behavior of these remarkable nanoscale composites. Polym. Compos. 25:630–645, 2004. © 2004 Society of Plastics Engineers.

Big returns from small fibers: A review of polymer/carbon nanotube composites

To increase their electrochemically active surface area, catalysts supported on high surface area materials, commonly carbons, are widely used in low-temperature fuel cells. Recent studies have revealed that the physical properties of the carbon support can greatly affect the electrochemical properties of the fuel cell catalyst. It has been reported that carbon materials with both high surface area and good crystallinity can not only provide a high dispersion of Pt nanoparticles, but also facilitate electron transfer, resulting in better device performance. On this basis, novel non-conventional carbon materials have attracted much interest as electrocatalyst support because of their good electrical and mechanical properties and their versatility in pore size and pore distribution tailoring. These materials present a different morphology than carbon blacks both at the nanoscopic level in terms of their pore texture (for example mesopore carbon) and at the macroscopic level in terms of their form (for example microsphere). The examples are supports produced from ordered mesoporous carbons, carbon aerogels, carbon nanotubes, carbon nanohorns, carbon nanocoils and carbon nanofibers. The challenge is to develop carbon supports with high surface area, good electrical conductivity, suitable porosity to allow good reactant flux, and high stability in fuel cell environment, utilizing synthesis methods simple and not too expensive. This paper presents an overview of carbon supports for Pt-based catalysts, with particular attention on new carbon materials. The effect of substrate characteristics on catalyst properties, as electrocatalytic activity and stability in fuel cell environment, is discussed.

Carbon supports for low-temperature fuel cell catalysts

Flexible electronics offer a wide-variety of applications such as flexible circuits, flexible displays, flexible solar cells, skin-like pressure sensors, and conformable RFID tags. Carbon nanotubes (CNTs) are a promising material for flexible electronics, both as the channel material in field-effect transistors (FETs) and as transparent electrodes, due to their high intrinsic carrier mobility, conductivity, and mechanical flexibility. In this feature article, we review the recent progress of CNTs in flexible electronics by describing both the processing and the applications of CNT-based flexible devices. To employ CNTs as the channel material in FETs, single-walled carbon nanotubes (SWNTs) are used. There are generally two methods of depositing SWNTs on flexible substrates—transferring CVD-grown SWNTs or solution-depositing SWNTs. Since CVD-grown SWNTs can be highly aligned, they often outperform solution-processed SWNT films that are typically in the form of random network. However, solution-based SWNTs can be printed at a large-scale and at low-cost, rendering them more appropriate for manufacturing. In either case, the removal of metallic SWNTs in an effective and a scalable manner is critical, which must still be developed and optimized. Nevertheless, promising results demonstrating SWNT-based flexible circuits, displays, RF-devices, and biochemical sensors have been reported by various research groups, proving insight into the exciting possibilities of SWNT-based FETs. In using carbon nanotubes as transparent electrodes (TEs), two main strategies have been implemented to fabricate highly conductive, transparent, and mechanically compliant films—superaligned films of CNTs drawn from vertically grown CNT forests using the “dry-drawing” technique and the deposition or embedding of CNTs onto flexible or stretchable substrates. The main challenge for CNT based TEs is to fabricate films that are both highly conductive and transparent. These CNT based TEs have been used in stretchable and flexible pressure, strain, and chemical and biological sensors. In addition, they have also been used as the anode and cathode in flexible light emitting diodes, solar cells, and supercapacitors. In summary, there are a number of challenges yet to overcome to optimize the processing and performance of CNT-based flexible electronics; nonetheless, CNTs remain a highly suitable candidate for various flexible electronic applications in the near future.

A review of fabrication and applications of carbon nanotube film-based flexible electronics

Grazing-angle x-ray reflectivity (XRR) is described as an efficient, nondestructive, parameter-free means to measure the mass density of various types of amorphous carbon films down to the nanometer thickness range. It is shown how XRR can also detect layering if it is present in the films, in which case the reflectivity profile must be modeled to derive the density. The mass density can also be derived from the valence electron density via the plasmon energy, which is measured by electron energy-loss spectroscopy (EELS). We formally define an interband effective electron mass ${m}^{*},$ which accounts for the finite band gap. Comparison of XRR and EELS densities allows us to fit an average ${m}^{*}=0.87m$ for carbon systems, m being the free-electron mass. We show that, within the Drude-Lorentz model of the optical spectrum, ${m}^{*}=[1\ensuremath{-}{n(0)}^{\ensuremath{-}2}]m,$ where $n(0)$ is the refractive index at zero optical frequency. The fraction of ${\mathrm{sp}}^{2}$ bonding is derived from the carbon K-edge EELS spectrum, and it is shown how a choice of ``magic'' incidence and collection angles in the scanning transmission electron microscope can give ${\mathrm{sp}}^{2}$ fraction values that are independent of sample orientation or anisotropy. We thus give a general relationship between mass density and ${\mathrm{sp}}^{3}$ content for carbon films.

Density, sp 3 fraction, and cross-sectional structure of amorphous carbon films determined by x-ray reflectivity and electron energy-loss spectroscopy

A comprehensive study of the stress release and structural changes caused by postdeposition thermal annealing of tetrahedral amorphous carbon (ta-C) on Si has been carried out. Complete stress relief occurs at 600–700 °C and is accompanied by minimal structural modifications, as indicated by electron energy loss spectroscopy, Raman spectroscopy, and optical gap measurements. Further annealing in vacuum converts sp3 sites to sp2 with a drastic change occurring after 1100 °C. The field emitting behavior is substantially retained up to the complete stress relief, confirming that ta-C is a robust emitting material.

/pdf/stress-reduction-and-bond-stability-during-thermal-annealing-21qtp8ri6t.pdf

Stress reduction and bond stability during thermal annealing of tetrahedral amorphous carbon

Vertically aligned carbon nanotubes were grown at temperatures as low as 120 °C by plasma-enhanced chemical vapor deposition. A systematic study of the temperature dependence of the growth rate and the structure of the as-grown nanotubes is presented using a C2H2/NH3 system and nickel as the catalyst. The activation energy for the growth rate was found to be 0.23 eV, much less than for thermal chemical vapor deposition (1.2–1.5 eV). This suggests growth occurs by surface diffusion of carbon on nickel. The result could allow direct growth of nanotubes onto low-temperature substrates like plastics, and facilitate the integration in sensitive nanoelectronic devices.

Low-temperature growth of carbon nanotubes by plasma-enhanced chemical vapor deposition

The direct growth of vertically aligned carbon nanotubes onto flexible plastic substrates using plasma-enhanced chemical vapor deposition is reported. We show that individual lines and dots of free-standing 20–50 nm diameter nanotubes can be grown onto chromium covered commercially available polyimide foil. The scalable deposition method allows large area coverage without degrading or bending the sensitive substrate material. Field emission measurements show a low turn-on field (3.2 V/μm) and a low threshold field (4.2 V/μm). The result establishes a method of flexible field emitter fabrication, which is well suited for display production and integration of nanotubes into plastic electronics.

Direct growth of aligned carbon nanotube field emitter arrays onto plastic substrates

A systematic study is presented of the influence of catalyst film thickness on carbon nanostructures grown by plasma-enhanced chemical-vapor deposition from acetylene and ammonia mixtures. We show that reducing the Fe∕Co catalyst film thickness below 3nm causes a transition from larger diameter (>40nm), bamboolike carbon nanofibers to small diameter (∼5nm) multiwalled nanotubes with two to five walls. This is accompanied by a more than 50 times faster growth rate and a faster catalyst poisoning. Thin Ni catalyst films only trigger such a growth transition when pretreated with an ammonia plasma. We observe a limited correlation between this growth transition and the coarsening of the catalyst film before deposition. For a growth temperature of ⩽550°C, all catalysts showed mainly a tip growth regime and a similar activity on untreated silicon, oxidized silicon, and silicon nitride support.

B. Kleinsorge

Papers

Density, sp 3 fraction, and cross-sectional structure of amorphous carbon films determined by x-ray reflectivity and electron energy-loss spectroscopy

Stress reduction and bond stability during thermal annealing of tetrahedral amorphous carbon

Low-temperature growth of carbon nanotubes by plasma-enhanced chemical vapor deposition

Direct growth of aligned carbon nanotube field emitter arrays onto plastic substrates

Effects of catalyst film thickness on plasma-enhanced carbon nanotube growth (vol 98, pg 034308, 2005)