Spontaneous growth of freestanding Ga nanoribbons from Cr 2 GaC surfaces
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Surojit Gupta, Haihui Ye, and Michel W. Barsoum Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104 (Received 28 March 2005; accepted 28 June 2005)
Herein we report on the room-temperature spontaneous growth of Ga freestanding nanoribbons from Cr2GaC surfaces. An oxidation-based model is proposed to explain the growth of the nanostructures. The nanoribbons present a unique opportunity to study the behavior of electrons confined to two dimensions. The production of these Ga nanostructures could be the first step in the manufacture of gallium arsenide or nitride devices with enhanced characteristics for photonic, electronic, and catalytic applications.
Nanoribbons have recently attracted some attention due to their potential application in photonics and electronics. These reports have mainly focused on oxides such as ZnO,1,2 gallium nitride,3,4 fullerenes C60,5 and the semiconductor Se.6,7 As far as we are aware, there is no report on metal-based nanoribbons in the literature. In this work, we report on our discovery of the spontaneous growth of Ga-based freestanding nanoribbons from polished and fractured surfaces of the ternary compound Cr2GaC. Predominantly single-phase samples of Cr2GaC, containing ∼1 vol% free Ga, uniformly distributed along the grain boundaries were fabricated. Commercial Cr powder (99.99%, −325 mesh), graphite powder (99%, −300 mesh), and Ga pellets (99.99%, 3 mm) (all from Alpha Aesar, Ward Hill, MA) were mixed in stoichiometric proportions, ball milled for 1 h, and sealed in borosilicate glass tubes under mechanical vacuum. The tubes were heated to 650 °C for 10 h, which resulted in their collapse and allowed the powders to pre-react. The tubes were placed in a hot isostatic press heated at 10 °C/min to 650 °C, followed by heating at 2 °C/min to 750 °C. The chamber was pressurized with Ar gas to 70 MPa, further heated at 10 °C/min to 1200 °C, and held at temperature for 12 h. Differential scanning calorimetry measurements established the presence of ∼1 vol% Ga.8 From the fractured surfaces, the Ga thickness between grains was estimated a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0326 2618
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 10, Oct 2005 Downloaded: 24 Mar 2015
to be ∼0.1 m. Polished and fracture surfaces were observed with a scanning electron microscope (SEM; FEI, XL30S, Hillsboro, OR) equipped with an energy dispersive spectrum (EDS) analyzer and an electron backscattering patterns (EBSP) detector. A JEOL 2010F (Tokyo, Japan) transmission electron microscope (TEM) with FasTEM control system, operated at 200 kV, with a point-to-point resolution of 0.23 nm, was used for TEM analysis. An in situ TEM video was recorded to demonstrate the motion of liquid Ga under the electron beam. Figures 1 and 2 show a collection of nanoribbons in SEM micrographs with various morphologies observed on polished (Fig. 1) and fractured (Fig. 2) surfaces. The majority of nanoribbons wer
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