Alicja Bachmatiuk

Direct low-temperature nanographene CVD synthesis over a dielectric insulator

Graphene ranks highly as a possible material for future high-speed and flexible electronics. Current fabrication routes, which rely on metal substrates, require post-synthesis transfer of the graphene onto a Si wafer, or in the case of epitaxial growth on SiC, temperatures above 1000 degrees C are required. Both the handling difficulty and high temperatures are not best suited to present day silicon technology. We report a facile chemical vapor deposition approach in which nanographene and few-layer nanographene are directly formed over magnesium oxide and can be achieved at temperatures as low as 325 degrees C.

Silicon carbide-free graphene growth on silicon for lithium-ion battery with high volumetric energy density

Silicon is receiving discernable attention as an active material for next generation lithium-ion battery anodes because of its unparalleled gravimetric capacity. However, the large volume change of silicon over charge–discharge cycles weakens its competitiveness in the volumetric energy density and cycle life. Here we report direct graphene growth over silicon nanoparticles without silicon carbide formation. The graphene layers anchored onto the silicon surface accommodate the volume expansion of silicon via a sliding process between adjacent graphene layers. When paired with a commercial lithium cobalt oxide cathode, the silicon carbide-free graphene coating allows the full cell to reach volumetric energy densities of 972 and 700 Wh l−1 at first and 200th cycle, respectively, 1.8 and 1.5 times higher than those of current commercial lithium-ion batteries. This observation suggests that two-dimensional layered structure of graphene and its silicon carbide-free integration with silicon can serve as a prototype in advancing silicon anodes to commercially viable technology.

Atomic resolution imaging and topography of boron nitride sheets produced by chemical exfoliation.

Here, we present a simple method for preparing thin few-layer sheets of hexagonal BN with micrometer-sized dimensions using chemical exfoliation in the solvent 1,2-dichloroethane. The atomic structure of both few-layer and monolayer BN sheets is directly imaged using aberration-corrected high-resolution transmission electron microscopy. Electron beam induced sputtering effects are examined in real time. The removal of layers of BN by electron beam irradiation leads to the exposure of a step edge between a monolayer and bilayer region. We use HRTEM imaging combined with image simulations to show that BN bilayers can have AB stacking and are not limited to just AA stacking.

Free-standing single-atom-thick iron membranes suspended in graphene pores.

Iron in Graphene Carbon or other covalently bonded materials, like boron nitride, can form two-dimensional sheets because of the strong bonding between the atoms. In contrast, metals share electrons in a three-dimensional delocalized way, and this could preclude the formation of thin stable sheets. Nevertheless, Zhao et al. (p. 1228) observed pure iron membranes suspended across the pores in a graphene sheet. This phenomenon was discovered when an iron chloride solution, used to process the graphene, decomposed to form pure iron films across the pores. The pores in a graphene membrane stabilize the formation of two-dimensional iron sheets. The excess of surface dangling bonds makes the formation of free-standing two-dimensional (2D) metals unstable and hence difficult to achieve. To date, only a few reports have demonstrated 2D metal formation over substrates. Here, we show a free-standing crystalline single-atom-thick layer of iron (Fe) using in situ low-voltage aberration-corrected transmission electron microscopy and supporting image simulations. First-principles calculations confirm enhanced magnetic properties for single-atom-thick 2D Fe membranes. This work could pave the way for new 2D structures to be formed in graphene membranes.

Approaches to mitigate polymer-core loss in plastic optical fibers: a review

Within fiber optics, plastic optical fibers (POFs) have always had to take a back seat due to their relatively high loss. This kept them as a specialty fiber for illumination, sensing and low speed short data links. However, continued research and development on the core materials used in POFs are improving their performance significantly as we are now able to manufacture POFs with low transmission loss, high temperature resistance and stable bandwidth over distance. The improved performance, the ease of installation and the low cost of POFs has led to a renewed interest in these fibers. This review looks at the material developments that have and continue to improve the optical loss factors in POFs. Both intrinsic and extrinsic loss mechanisms are discussed. In particular the intrinsic loss mechanisms are reviewed in greater detail. Intrinsic losses are associated with the chemical and physical structure of the fiber materials, while extrinsic losses are related to losses due to contaminants and various production imperfections.

Carbon nanostructures as multi-functional drug delivery platforms

Nanotechnology is providing exciting and new opportunities which are likely to revolutionize future clinical practice. The use of nanoparticles for biomedical applications is particularly exciting due to their huge potential for multi-modal approaches. This includes their use as drug delivery vectors, imaging contrast agents, hyperthermia systems and molecular targeting. Their ability to cross biological barriers, for example the blood brain barrier, makes them attractive for potential treatments in neurological disorders. There is also great hope that nanostructures will serve as platforms in future cancer therapies. Current cancer fighting strategies consist primarily of surgery, radiation therapy and chemotherapy. Each of these treatments is bound by a limit, known as the therapeutic window, which, if exceeded, causes undue harm to the patient. In the ongoing quest to improve our therapeutic arsenal, nanoparticles are emerging as exciting structures for a new generation of multi-modal therapeutics. Within this context, carbon nanostructures are amongst the leading contenders as building blocks to deliver multi-function drug delivery platforms. This review examines the various properties of carbon nanostructures that allow such multi-functionality. Recent advances on the development of novel approaches for functionalization, targeting and imaging via carbon nanostructures are discussed.

Graphene: Piecing it Together

Graphene has a multitude of striking properties that make it an exceedingly attractive material for various applications, many of which will emerge over the next decade. However, one of the most promising applications lie in exploiting its peculiar electronic properties which are governed by its electrons obeying a linear dispersion relation. This leads to the observation of half integer quantum hall effect and the absence of localization. The latter is attractive for graphene-based field effect transistors. However, if graphene is to be the material for future electronics, then significant hurdles need to be surmounted, namely, it needs to be mass produced in an economically viable manner and be of high crystalline quality with no or virtually no defects or grains boundaries. Moreover, it will need to be processable with atomic precision. Hence, the future of graphene as a material for electronic based devices will depend heavily on our ability to piece graphene together as a single crystal and define its edges with atomic precision. In this progress report, the properties of graphene that make it so attractive as a material for electronics is introduced to the reader. The focus then centers on current synthesis strategies for graphene and their weaknesses in terms of electronics applications are highlighted.

Size and shape control of colloidal copper(I) sulfide nanorods.

Many physical and chemical properties of semiconducting nanocrystals strongly depend on their spatial dimensions and crystallographic structure. For these reasons, achieving a high degree of size and shape control plays an important role with respect to their application potential. In this report we present a facile route for the direct colloidal synthesis of copper(I) sulfide nanorods. A high reactivity of the starting materials is essential to obtain nanorods. We achieve this by using a thiol that thermally decomposes easily and serves as the sulfur source. The thiol is mixed in a noncoordinating solvent, which acts as the reaction medium. Adjustment of the nucleation temperature makes it possible to tailor uniform nanorods with lengths from 10 to 100 nm. The nanorods are single crystalline, and the growth direction is shown to occur along the a-axis of djurleite. The growth process and character of the nanorods were investigated through UV-vis and NIR absorption spectroscopy, transmission electron microscopy, and powder X-ray diffraction measurements.

CVD Growth of Large Area Smooth-edged Graphene Nanomesh by Nanosphere Lithography

Current etching routes to process large graphene sheets into nanoscale graphene so as to open up a bandgap tend to produce structures with rough and disordered edges. This leads to detrimental electron scattering and reduces carrier mobility. In this work, we present a novel yet simple direct-growth strategy to yield graphene nanomesh (GNM) on a patterned Cu foil via nanosphere lithography. Raman spectroscopy and TEM characterizations show that the as-grown GNM has significantly smoother edges than post-growth etched GNM. More importantly, the transistors based on as-grown GNM with neck widths of 65-75 nm have a near 3-fold higher mobility than those derived from etched GNM with the similar neck widths.

Direct Chemical Vapor Deposition-Derived Graphene Glasses Targeting Wide Ranged Applications

Direct growth of graphene on traditional glasses is of great importance for various daily life applications. We report herein the catalyst-free atmospheric-pressure chemical vapor deposition approach to directly synthesizing large-area, uniform graphene films on solid glasses. The optical transparency and sheet resistance of such kinds of graphene glasses can be readily adjusted together with the experimentally tunable layer thickness of graphene. More significantly, these graphene glasses find a broad range of real applications by enabling the low-cost construction of heating devices, transparent electrodes, photocatalytic plates, and smart windows. With a practical scalability, the present work will stimulate various applications of transparent, electrically and thermally conductive graphene glasses in real-life scenarios.