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Showing papers by "Rodney S. Ruoff published in 2021"


Journal ArticleDOI
01 Aug 2021-Nature
TL;DR: In this paper, the wrinkling/folding process for graphene films grown from an ethylene precursor on single-crystal Cu-Ni(111) foils is investigated.
Abstract: Chemical vapour deposition of carbon-containing precursors on metal substrates is currently the most promising route for the scalable synthesis of large-area, high-quality graphene films1. However, there are usually some imperfections present in the resulting films: grain boundaries, regions with additional layers (adlayers), and wrinkles or folds, all of which can degrade the performance of graphene in various applications2–7. There have been numerous studies on ways to eliminate grain boundaries8,9 and adlayers10–12, but graphene folds have been less investigated. Here we explore the wrinkling/folding process for graphene films grown from an ethylene precursor on single-crystal Cu–Ni(111) foils. We identify a critical growth temperature (1,030 kelvin) above which folds will naturally form during the subsequent cooling process. Specifically, the compressive stress that builds up owing to thermal contraction during cooling is released by the abrupt onset of step bunching in the foil at about 1,030 kelvin, triggering the formation of graphene folds perpendicular to the step edge direction. By restricting the initial growth temperature to between 1,000 kelvin and 1,030 kelvin, we can produce large areas of single-crystal monolayer graphene films that are high-quality and fold-free. The resulting films show highly uniform transport properties: field-effect transistors prepared from these films exhibit average room-temperature carrier mobilities of around (7.0 ± 1.0) × 103 centimetres squared per volt per second for both holes and electrons. The process is also scalable, permitting simultaneous growth of graphene of the same quality on multiple foils stacked in parallel. After electrochemical transfer of the graphene films from the foils, the foils themselves can be reused essentially indefinitely for further graphene growth. Restricting the initial growth temperatures used for chemical vapour deposition of graphene on metal foils produces optimum conditions for growing large areas of fold-free, single-crystal graphene.

133 citations


Journal ArticleDOI
24 Mar 2021
TL;DR: In this paper, the authors reviewed the history of CVD graphene growth, the growth on different single-metals and alloy thin films, and the reported performance of such graphene in electronic devices.
Abstract: Summary Metal foils, particularly copper and copper-nickel alloy, are commonly used to grow large-area crystalline mono- or bi-layer graphene domains and films by chemical vapor deposition (CVD) methods. Thin-metal films, which are usually made by depositing metals on various substrates such as single-crystal sapphire, have also been reported as catalytic substrates for high-quality graphene growth. Thin-metal films can also serve as intermediates to grow graphene on catalytically inactive substrates, such as dielectrics for electronic devices. Focusing on the CVD growth of graphene on thin-metal films, we review the history of CVD graphene growth, the growth on different single-metals and alloy thin films, and the reported performance of such graphene in electronic devices. We also comment on current challenges and opportunities for the further development of this field.

40 citations


Journal ArticleDOI
TL;DR: In this article, a method to make liquid metal composites by vigorously mixing gallium (Ga) with non-metallic particles of graphene oxide (G-O), graphite, diamond, and silicon carbide that display either paste or putty-like behavior depending on the volume fraction is described.
Abstract: We report a versatile method to make liquid metal composites by vigorously mixing gallium (Ga) with non-metallic particles of graphene oxide (G-O), graphite, diamond, and silicon carbide that display either paste or putty-like behavior depending on the volume fraction. Unlike Ga, the putty-like mixtures can be kneaded and rolled on any surface without leaving residue. By changing temperature, these materials can be stiffened, softened, and, for the G-O-containing composite, even made porous. The gallium putty (GalP) containing reduced G-O (rG-O) has excellent electromagnetic interference shielding effectiveness. GalP with diamond filler has excellent thermal conductivity and heat transfer superior to a commercial liquid metal-based thermal paste. Composites can also be formed from eutectic alloys of Ga including Ga-In (EGaIn), Ga-Sn (EGaSn), and Ga-In-Sn (EGaInSn or Galinstan). The versatility of our approach allows a variety of fillers to be incorporated in liquid metals, potentially allowing filler-specific "fit for purpose" materials.

40 citations


Journal ArticleDOI
01 Jan 2021
TL;DR: In this article, the authors summarize recent progress in growing large-area single-crystal graphene and present a roll-to-roll technique for growing uniform single crystals of bilayer or multilayer graphene.
Abstract: There have been breakthroughs in the mass production of graphene by chemical vapor deposition (CVD) and its practical applications have also been identified. Grain boundaries are typically present in ‘CVD graphene’ and adversely impact its properties. We summarize recent progress in growing large-area single-crystal graphene. Centimeter-scale single-crystal, truly single-layer graphene (SLG) films have been reportedly achieved on single-crystal Cu(111) foils by CVD growth, while meter-scale single-crystal SLG films have been reportedly produced with assistance of a roll-to-roll technique. The growth of uniform single crystals of bilayer or multilayer graphene over a large area remains an exciting challenge. Layer-by-layer transfer and the stacking of single-crystal SLG is considered a promising route to making new types of ‘single’ crystals or quasicrystals with specific numbers of layers and different stacking angles.

20 citations


Journal ArticleDOI
TL;DR: A cooling-contraction method to separate large-area (up to 4.2 cm in lateral size) graphene oxide (GO)-assembled films (of nanoscale thickness) from substrates is reported in this paper.
Abstract: A "cooling-contraction" method to separate large-area (up to 4.2 cm in lateral size) graphene oxide (GO)-assembled films (of nanoscale thickness) from substrates is reported. Heat treatment at 3000 °C of such free-standing macroscale films yields highly crystalline "macroassembled graphene nanofilms" (nMAGs) with 16-48 nm thickness. These nMAGs present tensile strength of 5.5-11.3 GPa (with ≈3 µm gauge length), electrical conductivity of 1.8-2.1 MS m-1 , thermal conductivity of 2027-2820 W m-1 K-1 , and carrier relaxation time up to ≈23 ps. As a demonstration application, an nMAG-based sound-generator shows a 30 µs response and sound pressure level of 89 dB at 1 W cm-2 . A THz metasurface fabricated from nMAG has a light response of 8.2% for 0.159 W mm-2 and can detect down to 0.01 ppm of glucose. The approach provides a straightforward way to form highly crystallized graphene nanofilms from low-cost GO sheets.

20 citations


Journal ArticleDOI
17 Feb 2021
TL;DR: In this article, the authors show several case studies of graphene characterization on a range of different substrates that highlight the versatility of THz-TDS measurements and its relevance for process optimization in graphene production scenarios.
Abstract: Graphene metrology needs to keep up with the fast pace of developments in graphene growth and transfer. Terahertz time-domain spectroscopy (THz-TDS) is a non-contact, fast, and non-destructive characterization technique for mapping the electrical properties of graphene. Here we show several case studies of graphene characterization on a range of different substrates that highlight the versatility of THz-TDS measurements and its relevance for process optimization in graphene production scenarios.

12 citations


Journal ArticleDOI
TL;DR: In this paper, a single crystal Cu(111) foil is studied by growing single crystal graphene islands on it followed by soaking it in water, and it is found that the graphene completely shields the underlying Cu from wet-oxidation.
Abstract: The wet-oxidation of a single crystal Cu(111) foil is studied by growing single crystal graphene islands on it followed by soaking it in water. 18 O-labeled water is also used; the oxygen atoms in the formed copper oxides in both the bare and graphene-coated Cu regions come from water. The oxidation of the graphene-coated Cu regions is enabled by water diffusing from the edges of graphene along the bunched Cu steps, and along some graphene ripples where such are present. This interfacial diffusion of water can occur because of the separation between the graphene and the "step corner" of bunched Cu steps. Density functional theory simulations suggest that adsorption of water in this gap is thermodynamically stable; the "step-induced-diffusion model" also applies to graphene-coated Cu surfaces of various other crystal orientations. Since bunched Cu steps and graphene ripples are diffusion pathways for water, ripple-free graphene is prepared on ultrasmooth Cu(111) surfaces and it is found that the graphene completely shields the underlying Cu from wet-oxidation. This study greatly deepens the understanding of how a graphene-coated copper surface is oxidized, and shows that graphene completely prevents the oxidation when that surface is ultrasmooth and when the graphene has no ripples or wrinkles.

8 citations


Journal ArticleDOI
30 Apr 2021-Carbon
TL;DR: In this article, a stage-1 intercalated film was made by the ion exchange of pyrrolidinium-functionalized C60 (C60(Py)n+) into centimeter-wide, micrometer-thick air-dried G-O films composed of tens of thousands of layers of stacked/overlapping platelets.

8 citations


Journal ArticleDOI
TL;DR: In this article, the abnormal grain growth of polycrystalline iron (Fe) foil up to grains of 1.2 cm in size was investigated, where the number of nucleus/nuclei and maximum grain size were highly affected by the plastic deformation conditions as they cause different stored energies in the foils.

6 citations


Journal ArticleDOI
15 Jun 2021-ACS Nano
TL;DR: In this paper, a low-temperature (423 K) hydrothermal approach to form nanodiamonds by using graphene-oxide or nitrated polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, or pyrene) as a starting material was reported.
Abstract: Nanodiamonds are interesting materials from the point of view of their biocompatibility and their chemical, spectroscopic, and mechanical properties. Current synthetic methods for nanodiamonds involve harsh environments, which are potentially hazardous in addition to being expensive. We report a low-temperature (423 K) hydrothermal approach to form nanodiamonds by using graphene-oxide or nitrated polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, or pyrene) as a starting material. The reaction products contain single-crystalline or twinned nanodiamonds with average diameters in the 2-3 nm range. Theoretical calculations prove that, at the nanoscale, sub-4 nm nanodiamonds may adopt a structure that is more stable than graphene-oxide and nitrated polycyclic aromatic hydrocarbons. Our findings show that sp2 carbon in the polycyclic aromatic precursor can be converted to sp3 carbon under unexpectedly moderate temperature conditions by using nanoscale precursors and thus offer a low-temperature approach for the synthesis of sub-4 nm nanodiamonds.

5 citations


Journal ArticleDOI
15 Oct 2021-Carbon
TL;DR: A simple drop-by-drop deposition method was invented to make graphene oxide (G-O) hydrogels at room temperature as mentioned in this paper, which was readily made into forms such as films, fibers, and aerogels.

Journal ArticleDOI
TL;DR: In this paper, the intercalation chemistry of graphitic carbon nitride (gCN) was studied combining theory and experimental methods, and a series of new alkali-ethylenediamine-gCN products were prepared using a one-po...
Abstract: We studied the intercalation chemistry of graphitic carbon nitride (gCN), combining theory and experimental methods. A series of new alkali-ethylenediamine-gCN products were prepared using a one-po...

Journal ArticleDOI
01 Jan 2021-Carbon
TL;DR: In this article, plain and cross-linked polyvinyl alcohol are chosen as representatives of such polymers and used as reaction media for the carbonization of low thermal stability polymeric precursors at high temperatures.