Healing of Structural Defects in the Topmost Layer of Graphite by Chemical Vapor Deposition

• DOI: 10.1002/adma.201004019
• Publication Date: 2011-02-15T14:02:59Z
• Authors: Iskandar N. Kholm...; Jonathan Edgeworth; Emanuele Cavaliere; Luca Gavioli; Carl Magnuson; Rodney S. Ruoff
• Keywords: Carbon fibers

Studies of the healing artificial defects in surface highly oriented pyrolitic graphite (HOPG) by chemical vapor deposition (CVD) acetylene show that only single-layer depth could be healed completely during CVD treatment. A promising method is introduced for defect control surfaces graphite, graphene, and graphene-based materials, with important implications their application. Structural graphitic layers have historically received considerable attention, primarily directed towards behavior radiation-damaged nuclear reactors.1 More recently, efforts been at crucial role tailoring material properties carbon-based structures such as carbon nanotubes, graphene sheets.2-13 For example, it has reported are responsible inherent ferromagnetic due to presence around localized electron states energies close Fermi level.14, 15 Very Lahiri et al. controlled production extended line suggested might function metallic wires.16 these demonstrated engineering systems a approach controlling variety properties. Despite this, well-known ability scatter charge carriers phonons, thereby decreasing ballistic transport path length adversely affecting carrier mobility thermal conductivity. The detrimental effects particularly pronounced films. were held dramatic reduction films obtained micromechanical cleavage.17 produced methods, exfoliation oxide platelets, also ascribed (introduced treatments used).18 In this respect, undesirable, “heal” them generating nanostructures high electrical conductivities and, potentially, enhanced mechanical strength. Improvements characteristics central importance because successful realization electronic devices requires superior structural One removing crystalline lattice restoring temperature processing hydrocarbon gas. Using appropriate conditions, gas decompose supply atoms can repair defective sites. Recently, López chemically derived using an ethylene source improved film conductivity two orders magnitude, room (RT) values 10–350 S cm−1.19 authors attributed improvement healing. addition, direct observation modification sites on under gaseous atmospheres was Liu al., who studied reactivity exposed elevated temperatures scanning tunneling microscopy (STM).20 report, growth both amorphous ordered carbonaceous directly demonstrated. However, complete individual not achieved. current work, topmost HOPG STM. Defects (SLD) multilayer (MLD) controllably Ar+ ion beam sputtering different incidence angles. depths identified oxidative etching layers. Defect involved process iron (Fe) catalyst (C2H2) source. It found depends SLD process. Artificial (0001) basal plane freshly cleaved degassed (400 eV) 20 s, firstly normal angle. Figure 1a shows STM image after s RT followed situ annealing 900 °C 10 min. contained sputtering-induced density (defects per μm2) about 7 × 104 μm−2, together disordered particles few nanometres size. likely formed agglomeration removed from sputtering. Carbon atom extraction possible since energy ions significantly higher than threshold required (≈47 eV).21 eject several sheets HOPG, creating multi-vacancy defects.22 representative typical (Figure 1a, inset) hole plane, atoms, surrounded hillock-like structures. Formation MLD surfaces. a) (100 100 nm2, tip–sample bias V = –1.8 V, I 0.1 nA) sputtered angle in-situ annealed ultrahigh vacuum (UHV) chamber. Inset atomically resolved (4 4 –0.4 0.2 showing detailed morphology defect. b) –1.4 same surface,after processing, which no significant changes occurred. c) (150 150 –2.6 0.4 etching, results formation pits extensively etched constant profile acquired along white plotted inset. d) Schematic illustration e) view defects. (d) (e) Fe nanoparticles shown. Following generation surfaces, monolayer (ML) deposited onto samples sublimation, described Experimental Section. Deposited preferentially nucleates agglomerates substrate, Volmer–Weber mode, give 3D particles.23, 24 images (not shown), agglomerate features clearly distinguishable With aim eliminating through sample pure 1 min °C. particles, used here, allow avoided may catalyze reaction promote lattices.25 1b) indicated decrease change overall surface. Identical coated greater amounts (0.2 ML 0.3 ML). These conditions above cannot catalytic processing. reasonable explanation MLDs sputtering.22 We argue protected here. inability C2H2 molecules penetrate sufficiently far into deep Additionally, stabilized numerous interlayer covalent interactions dangling bonds exist defects.6, 11 possible, STM, determine as-produced great certainty convolution between tip. Instead, first oxidation treatment partially “opened” analysis depths. 1c decorated etching. shown characterized pits. Large visible edges layers; arise small proportion migrate away then temperatures.23 rationalized considering details treatment, This two-step differed often based simple oxygen-containing atmospheres, difficult relatively oxygen pressures employed.26, 27 our more way; low applied enabled avoidance random non-defective Etching began layer where oxidized trapped, progressed planar directions form should depend they formed. defects, illustrated 1d, result multiple deep, 1e. Therefore, pit depths, original identified. MLDs, Thus, 400 eV To produce containing clean beams increased 2a 75° average 2.0 μm−2. An 2a, (e.g., 1b). Such morphologies vacancy strong distortions regular honeycomb structure.28 Similar observed bilayer grown SiC surfaces.29 –1 0.25 UHV Atomically –0.1 (280 280 =0.14 pits, inset profile, correspond main image. Comparison magnification (upper 50 30 =–1 (lower =0.25 demonstrates SLD. (c) verified way those 2b Oxidative occurred exclusively layer, SLD, 2b. Layers beneath sheet damaged remained almost defect-free. SLDs, Figures 2c,d. observations indicate HOPG. test whether identical before 3a,b, respectively. contrast 1b), Most healed, resulting concentration μm−2 0.5 102 restoration perfect structure. Complete elimination entirely open exposure Moreover, lies underlying defect-free flat inert. case, out-of-plane deeper layers, so reparation hindered interplanar interactions. Healing nm2) (V 0.14 0.12 (40 40 (a) (b) demonstrate prior reaction, Constant profiles (acquired lines corresponding images) layer. noted carrying out work above, preliminary experiments conducted verify samples, revealed without lead less effective little correlation depth. processing: Fe, resulted step edges. we suggest acts high-temperature predicted very recently nickel-graphene systems.30 will few-layer or behave similarly one expect suspended sheets. substrate-supported nature interaction substrate. Strong locations, further promoted local substrate roughness, terraces, various types prevent summary, feedstock studied. examination avoid carbon. methods hold promise hence improving structural, electrical, improvements vital devices. All performed inside Omicron STM/SEM/SAM (scanning tunnelling microscopy/scanning Auger microscopy) system base pressure below 5 10−11 mbar. consisted three chambers connected series: 1) entry lock (EL), 2) preparation, 3) analysis. description experimental setup provided elsewhere.25, 31 (ZYB grade, Micromasch) air immediately inserted chamber, thoroughly until chamber fell 10−10 Sample cleanliness checked spectroscopy. preparation angles (normal 75°), 2.7 10−7 all cases, sublimation substrates RT. nominal rate measured quartz oscillator. defined here bcc metal, i.e., 12.17 1014 cm2. process: min, EL (base mbar) 10−1 mbar subsequently 800 flow O2 caused increase 1.5 raised heating, approximately Once °C, gas; 7.5 After exposure, heating power switched off cooled 2 Samples transferred (pressure < studies. presented mode tungsten tips. note investigated densities. Different densities varying parameters sputtering, angle, dose, energy. (temperature T 800–1100 P 5.0 10−8–1.0 10−5 mbar, time t 0.5–4 min) carried find optimal efficient occurrence independent density. No any set conditions. I.N.K. thanks CNR Short-Term Mobility Program University Texas (UT) Austin his stay UT. R.S.R. Semiconductor Research Corporation C.M. DOE fellowship support. J.E. appreciates support Institute Advanced Technology UT-Austin.