Artificially controlled synthesis of graphene intramolecular heterojunctions for phonon engineering

Abstract

Because phonons are the main carriers for graphene heat transfer, modifying the dynamic properties of the crystal lattice by isotopes modulates the phonon behavior and alters the thermal properties. Here we demonstrate an artificially controlled texture synthesis of 12C‐graphene/13C‐graphene heterostructures via chemical vapor deposition and an O2 plasma etching. The electrical and thermal properties of the graphene across the heterojunction show that 12C‐graphene and 13C‐ graphene are electronically connected as resistors in series, while the thermal conductivity across the junction is dramatically reduced due to the suppressed phonon propagation, which causes the conductivity across the junction to be lower than that of graphene sheets with randomly mixed isotopes. These findings should help realize novel two‐dimensional graphene thermoelectric devices where phonon modulation controls the electrons and heat transport independently. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Enhancing the Thermoelectric Device Performance of Graphene Using Isotopes and Isotopic Heterojunctions

“…Graphene samples with or without isotope heterojunctions were synthesized by low‐pressure thermal CVD using 12 CH 4 and 13 CH 4 as carbon sources. Details of the fabrication procedure for the heterojunctions are described elsewhere . Before transferring graphene onto SiO 2 (500 nm)/Si substrates, Pt electrodes and a microfabricated heater were deposited on the substrate by electron beam evaporation and a liftoff technique.…”

“…Consequently, isotopically modified graphene heterostructures have a great potential to reduce the thermal conductivity. Using the local thermal conductivity at the heterojunction estimated in our previous report (≈200 W m −1 K −1 ), the calculated figure of merit of graphene with heterojunctions is ≈0.008 at room temperature, which is almost ten times higher than that of graphene composed of only 12 C. Although this value does not satisfy the value ZT > 1 for practical applications, it is a significant improvement because both a higher electrical conductivity and a higher thermoelectric power are possible using graphene with larger domains by optimizing the CVD growth conditions and removing impurities in the graphene channels. In addition, graphene samples grown by CVD contain structural defects including 5–8 defects that may increase the electrical conductivity and decrease the thermal conductivity, also improving the thermoelectric performance of graphene.…”

“…Preparation of Graphene and Graphene Isotopic Heterojunctions : Graphene samples with or without isotope heterojunctions were synthesized by low‐pressure CVD using 12 CH 4 and 13 CH 4 as carbon sources. Details of the fabrication procedure are as described . Briefly, 25 μm‐thick Cu foils (Alfa Aesar, Lancashire, UK) were first annealed at 1050 °C in vacuum (≈100 Pa) for 30 min in the hydrogen flow of 35 standard cubic centimeter per minute (sccm).…”

Tracking airborne CO2 mitigation and low cost transformation into valuable carbon nanotubes

“…Whereas syntheses of single456789 (SWCNT) and double101112 (DWCNT) walled 13 C isotope carbon nanotubes, quantum dots13 and two dimensional 13 C nanomorphologies such as graphenes have been reported14151617, studies of 13 C multiwalled carbon nanofibers have not been evident, presumably due to the complexity and expense of conventional electrospinning/carbonization or chemical vapor deposition syntheses which would require additional synthetic steps to form the requisite 13 C polymers or 13 C organometallic reactants. Similarly, density functional and molecular dynamic simulation studies are found on 13 C isotope SWCNTs1819, but not on nano-morphologies which would require modeling of a larger numbers of carbon centers.…”

Highly photosensitive graphene field-effect transistor with optical memory function

“…X-ray photoelectron spectroscopy (XPS) was performed using Mg-Kα radiation (1253.6 eV), where the binding energy was corrected using the C1s peak at 284.6 eV. After the Au-electrode oxidation, a monolayer graphene was transferred onto the substrate and was trimmed using oxygen plasma etching to form an FET channel (width × length: 5 × 2 and 2 × 4 μm), where the graphene was synthesized using low-pressure chemical vapor deposition at 1000 °C using Cu foil as catalyst 27 28 (see Fig. S1 for Raman spectrum of grown graphene).…”