Showing papers by "Rodney S. Ruoff published in 2019"
TL;DR: This Perspective highlights the salient features of these materials and seeks to raise awareness of future opportunities to understand and to utilize liquid metals for nanotechnology.
Abstract: Bulk liquid metals have prospective applications as soft and fluid electrical and thermal conductors in electronic and optical devices, composites, microfluidics, robotics, and metallurgy with unique opportunities for processing, chemistry, and function. Yet liquid metals' great potential in nanotechnology remains in its infancy. Although work to date focuses primarily on Ga, Hg, and their alloys, to expand the field, we define "liquid metals" as metals and alloys with melting points (mp) up to 330 °C, readily accessible and processable even using household kitchen appliances. Such a definition encompasses a family of metals - including the majority of post-transition metals and Zn group elements (excluding Zn itself) - with remarkable versatility in chemistry, physics, and engineering. These liquid alloys can create metallic compounds of different morphologies, compositions, and properties, thereby enabling control over nanoscale phenomena. In addition, the presence of electronic and ionic "pools" within the bulk of liquid metals, as well as deviation from classical metallurgy on the surfaces of liquid metals, provides opportunities for gaining new capabilities in nanotechnology. For example, the bulk and surfaces of liquid metals can be used as reaction media for creating and manipulating nanomaterials, promoting reactions, or controlling crystallization of dissolved species. Interestingly, liquid metals have enormous surface tensions, yet the tension can be tuned electrically over a wide range or modified via surface species, such as the native oxides. The ability to control the interfacial tension allows these liquids to be readily reduced in size to the nanoscale. The liquid nature of such nanoparticles enables shape-reconfigurable structures, the creation of soft metallic nanocomposites, and the dissolution or dispersion of other materials within (or on) the metal to produce multiphasic or heterostructure particles. This Perspective highlights the salient features of these materials and seeks to raise awareness of future opportunities to understand and to utilize liquid metals for nanotechnology.
220 citations
TL;DR: A binder-free electrode that interconnects carbon-sheathed porous silicon nanowires into a coral-like network and shows fast charging performance coupled to high energy and power densities when integrated into a full cell with a high areal capacity loading is reported.
Abstract: Fast charging rate and large energy storage are becoming key elements for the development of next-generation batteries, targeting high-performance electric vehicles. Developing electrodes with high volumetric and gravimetric capacity that could be operated at a high rate is the most challenging part of this process. Using silicon as the anode material, which exhibits the highest theoretical capacity as a lithium-ion battery anode, we report a binder-free electrode that interconnects carbon-sheathed porous silicon nanowires into a coral-like network and shows fast charging performance coupled to high energy and power densities when integrated into a full cell with a high areal capacity loading. The combination of interconnected nanowires, porous structure, and a highly conformal carbon coating in a single system strongly promotes the reaction kinetics of the electrode. This leads to fast-charging capability while maintaining the integrity of the electrode without structural collapse and, thus, stable cycling performance without using binder and conductive additives. Specifically, this anode shows high specific capacities (over 1200 mAh g-1) at an ultrahigh charging rate of 7 C over 500 charge-discharge cycles. When coupled with a commercial LiCoO2 or LiFePO4 cathode in a full cell, it delivers a volumetric energy density of 1621 Wh L-1 with a LiCoO2 cathode and a power density of 7762 W L-1 with a LiFePO4 cathode.
118 citations
TL;DR: It is found that the amount of subsurface carbon in Cu foils directly correlates with the extent of adlayer growth, and high-performance field-effect transistors are readily fabricated in the large regions between adjacent parallel folds in the adlayer-free single crystal graphene film.
Abstract: To date, thousands of publications have reported chemical vapor deposition growth of "single layer" graphene, but none of them has described truly single layer graphene over large area because a fraction of the area has adlayers. It is found that the amount of subsurface carbon (leading to additional nuclei) in Cu foils directly correlates with the extent of adlayer growth. Annealing in hydrogen gas atmosphere depletes the subsurface carbon in the Cu foil. Adlayer-free single crystal and polycrystalline single layer graphene films are grown on Cu(111) and polycrystalline Cu foils containing no subsurface carbon, respectively. This single crystal graphene contains parallel, centimeter-long ≈100 nm wide "folds," separated by 20 to 50 µm, while folds (and wrinkles) are distributed quasi-randomly in the polycrystalline graphene film. High-performance field-effect transistors are readily fabricated in the large regions between adjacent parallel folds in the adlayer-free single crystal graphene film.
72 citations
TL;DR: In this article, the phase transition from Bernal bilayer graphene to single-layer diamond was studied and verified by X-ray photoelectron, ultraviolet photoelectRON, Raman, UV-Vis, electron energy loss spectroscopies, transmission electron microscopy, and DFT calculations.
Abstract: Notwithstanding numerous density functional studies on the chemically induced transformation of multilayer graphene into a diamond-like film, a comprehensive convincing experimental proof of such a conversion is still lacking. We show that the fluorination of graphene sheets in Bernal (AB)-stacked bilayer graphene (AB-BLG) grown by chemical vapor deposition on a single crystal CuNi(111) surface triggers the formation of interlayer carbon-carbon bonds, resulting in a fluorinated diamond monolayer (F-diamane). Induced by fluorine chemisorption, the phase transition from AB-BLG to single layer diamond was studied and verified by X-ray photoelectron, ultraviolet photoelectron, Raman, UV-Vis, electron energy loss spectroscopies, transmission electron microscopy, and DFT calculations.
65 citations
TL;DR: In this article, a simple method for transferring large areas (up to A4-size sheets) of CVD graphene from copper foils onto a target substrate using a commercially available polyvinyl alcohol polymer was presented.
Abstract: We demonstrate a simple method for transferring large areas (up to A4-size sheets) of CVD graphene from copper foils onto a target substrate using a commercially available polyvinyl alcohol polymer...
63 citations
TL;DR: The resulting stacked graphene sample is a freestanding film with near-perfect in-plane crystallinity but a mixed stacking order through the thickness, which separates it from all existing carbon materials.
Abstract: A macroscopic film (2.5 cm × 2.5 cm) made by layer-by-layer assembly of 100 single-layer polycrystalline graphene films is reported. The graphene layers are transferred and stacked one by one using a wet process that leads to layer defects and interstitial contamination. Heat-treatment of the sample up to 2800 °C results in the removal of interstitial contaminants and the healing of graphene layer defects. The resulting stacked graphene sample is a freestanding film with near-perfect in-plane crystallinity but a mixed stacking order through the thickness, which separates it from all existing carbon materials. Macroscale tensile tests yields maximum values of 62 GPa for the Young's modulus and 0.70 GPa for the fracture strength, significantly higher than has been reported for any other macroscale carbon films; microscale tensile tests yield maximum values of 290 GPa for the Young's modulus and 5.8 GPa for the fracture strength. The measured in-plane thermal conductivity is exceptionally high, 2292 ± 159 W m-1 K-1 while in-plane electrical conductivity is 2.2 × 105 S m-1 . The high performance of these films is attributed to the combination of the high in-plane crystalline order and unique stacking configuration through the thickness.
48 citations
TL;DR: Both pristine and iodine-doped NiTAA-MOF synthesized in this work could find potential applications in areas such as catalase mimics, catalysis, energy storage, and dynamic nuclear polarization-nuclear magnetic resonance (DNP-NMR).
Abstract: We report the synthesis and characterization of a two-dimensional (2D) conjugated Ni(II) tetraaza[14]annulene-linked metal organic framework (NiTAA-MOF) where NiTAA is a macrocyclic MN4 (M = metal,...
43 citations
TL;DR: A polychlorotriphenylmethyl radical-linked covalent triazine framework (PTMR-CTF) is reported, which exhibits spin-half paramagnetism and the microscopic origin of the magnetic moments in this material is determined by investigating its spin density and electronic structure using density functional theory calculations.
Abstract: The production of multifunctional pure organic materials that combine different sizes of pores and a large number of electron spins is highly desirable due to their potential applications as polarizers for dynamic nuclear polarization–nuclear magnetic resonance and as catalysts and magnetic separation media. Here, we report a polychlorotriphenylmethyl radical-linked covalent triazine framework (PTMR-CTF). Two different sizes of micropores were established by N2 sorption and the presence of unpaired electrons (carbon radicals) by electron spin resonance and superconducting quantum interference device–vibrating sample magnetometer analyses. Magnetization measurements demonstrate that this material exhibits spin-half paramagnetism with a spin concentration of ∼2.63 × 1023 spins/mol. We also determined the microscopic origin of the magnetic moments in PTMR-CTF by investigating its spin density and electronic structure using density functional theory calculations.
36 citations
TL;DR: In this paper, the effect of single crystal graphene on carbonization and graphitization of thin film polymers was investigated, showing that at the early stages of carbonization, carbon atoms in its near vicinity formed oriented layers parallel to the graphene layer.
Abstract: We report the effect of single crystal graphene on carbonization and graphitization of thin film polymers. Electron microscopy reveals that at the early stages of carbonization, graphene induces the carbon atoms in its near vicinity to form oriented layers parallel to the graphene layer. At elevated temperatures, these layers develop further to form extended graphitic (002) planes parallel to the graphene surface. For the samples which were heat treated and graphitized, grazing incidence X-ray scattering reveals that graphene narrows the distribution of graphite grain orientations. Based on these results, we propose that graphene can act as a structure directing agent in both the carbonization and graphitization of polymer thin films, and may provide an approach to realize single crystal graphite films, perhaps in combination with established techniques such as stress recrystallization.
32 citations
TL;DR: The formation of intertwined double-spiral few-layer h-BN that is driven by screw dislocations located at the antiphase boundaries of monolayer domains is reported and the occurrence of shear strains at the boundaries of merged spiral islands is found.
Abstract: Among the different growth mechanisms for two-dimensional (2D) hexagonal boron nitride (h-BN) synthesized using chemical vapor deposition, spiraling growth of h-BN has not been reported. Here we report the formation of intertwined double-spiral few-layer h-BN that is driven by screw dislocations located at the antiphase boundaries of monolayer domains. The microstructure and stacking configurations were studied using a combination of dark-field and atomic resolution transmission electron microscopy. Distinct from other 2D materials with single-spiral structures, the double-spiral structure enables the intertwined h-BN layers to preserve the most stable AA' stacking configuration. We also found that the occurrence of shear strains at the boundaries of merged spiral islands is dependent on the propagation directions of encountering screw dislocations and presented the strained features by density functional theory calculations and atomic image simulations. This study unveils the double-spiral growth of 2D h-BN multilayers and the creation of a shear strain band at the coalescence boundary of two h-BN spiral clusters.
11 citations
TL;DR: In this paper, various preparations and uses of single crystal metals are discussed, such as growth from melts, epitaxial deposition in vapors and solutions, and abnormal grain growth in solids.
Abstract: Various preparations and uses of single crystal metals are discussed. We briefly review (i) preparation methods of single crystal metals such as growth from melts, epitaxial deposition in vapors and solutions, and abnormal grain growth in solids and (ii) uses of single crystal metals according to their produced shapes (“bulk” vs “film and foil”). We pay special attention to recent advances in the preparation of large area single crystal metal foils and their potential uses.
TL;DR: In this paper, the authors performed ab initio calculations on the liquid gallium-hydrogen system at 100 °C. Gallium was found to interact with both free hydrogen atoms and H2, transferring charge in the process.
Abstract: Ab initio calculations have been performed on the liquid gallium–hydrogen system at 100 °C. Gallium was found to interact with both free hydrogen atoms and H2, transferring charge in the process. F...
TL;DR: In this paper, the effect of Cu surface orientation on the reactivity of graphene lattice orientation has been investigated and shown to be a significant determinant of its chemical reactivity.
Abstract: Although substrate composition can influence the chemical reactivity of graphene, substrate lattice orientation provides a valuable alternative. The effect of Cu surface orientation on the reactivi...
TL;DR: This work has developed the Source Extraction and Photometry (SEP) - Spot Profile Analysis (SPA) tool for evaluating scanning μLEED data with high throughput and demonstrates its capabilities to investigate systems with complex diffraction patterns in which diffraction peak positions vary rapidly for small lateral displacements on the surface.