Soomook Lim

Bio: Soomook Lim is an academic researcher from Sungkyunkwan University. The author has contributed to research in topics: Graphene & Electrical measurements. The author has an hindex of 1, co-authored 5 publications receiving 18 citations.

Electrical Measurements of Thermally Reduced Graphene Oxide Powders under Pressure

Abstract: Graphene powders obtained via the reduction of graphene oxide flakes have been widely used in various applications as they can be synthesized in large quantities with outstanding properties. The electrical conductivity of graphene powders is critical for their uses in fabricating high-performance devices or materials. Here, we investigated the bulk electrical conductivity of reduced graphene oxide (rGO) powders depending on the applied pressure and additional thermal annealing. The electrical conductivity of the rGO powders was correlated with the change in the carbon-to-oxygen ratio via additional thermal reduction. Furthermore, the effect of the morphology of the rGO powders was studied through electromechanical measurements. This study provides a reliable method for the electromechanical characterization of rGO powders and a better understanding of the electrical conductivity of graphene-based materials.

Measurements of the electrical conductivity of monolayer graphene flakes using conductive atomic force microscopy

Abstract: The intrinsic electrical conductivity of graphene is one of the key factors affecting the electrical conductance of its assemblies, such as papers, films, powders, and composites. Here, the local electrical conductivity of the individual graphene flakes was investigated using conductive atomic force microscopy (C-AFM). An isolated graphene flake connected to a pre-fabricated electrode was scanned using an electrically biased tip, which generated a current map over the flake area. The current change as a function of the distance between the tip and the electrode was analyzed analytically to estimate the contact resistance as well as the local conductivity of the flake. This method was applied to characterize graphene materials obtained using two representative large-scale synthesis methods. Monolayer graphene flakes synthesized by chemical vapor deposition on copper exhibited an electrical conductivity of 1.46 ± 0.82 × 106 S/m. Reduced graphene oxide (rGO) flakes obtained by thermal annealing of graphene oxide at 300 and 600 °C exhibited electrical conductivities of 2.3 ± 1.0 and 14.6 ± 5.5 S/m, respectively, showing the effect of thermal reduction on the electrical conductivity of rGO flakes. This study demonstrates an alternative method to characterizing the intrinsic electrical conductivity of graphene-based materials, which affords a clear understanding of the local properties of individual graphene flakes.

A General Fruit Acid Chelation Route for Eco-friendly and Ambient 3D Printing of Metals

Abstract: Recent advances in metal additive manufacturing (AM) have provided new opportunities for the design of prototypes of metal-based products and personalization of products for the fourth industrial revolution. Although metal AM, which enables fabrication of varied and sophisticated objects, is in the spotlight as a next-generation printing method, environmental issues arising during the printing process need to be addressed before it can be commercialized. Here, we demonstrate a novel mechanism for binder jetting three-dimensional (3D) printing of metals that is based on chelation triggered by an eco-friendly binding agent. Sodium salts of fruit acid chelators are used to form stable metal-chelate bridges between metal particles, which enable elaborate metal 3D printing. The strength of the 3D-printed object is improved by post-treatment, through a reduction in the porosity between the metal particles. Finally, the compatibility of the novel printing mechanism with a variety of metals is demonstrated via successful 3D printing of objects of various shapes using various metal powders. The proposed mechanism for metal 3D printing is expected to open up new avenues for the development of domestic-scale desktop 3D printing of metals.

Interlayer Separation in Graphene Paper Comprising Electrochemically Exfoliated Graphene

Abstract: The emergence of graphene paper comprising well-stacked graphene flakes has promoted the application of graphene-based materials in diverse fields such as energy storage devices, membrane desalination, and actuators. The fundamental properties of graphene paper such as mechanical, electrical, and thermal properties are critical to the design and fabrication of paper-based devices. In this study, the interlayer interactions in graphene paper were investigated by double cantilever beam (DCB) fracture tests. Graphene papers fabricated by flow-directed stacking of electrochemically exfoliated few-layer graphene flakes were mechanically separated into two parts, which generated force-displacement responses of the DCB sample. The analysis based on fracture mechanics revealed that the interlayer separation energy of the graphene paper was 9.83 ± 0.06 J/m2. The results provided a fundamental understanding of the interfacial properties of graphene papers, which will be useful for developing paper-based devices with mechanical integrity.

Multi-metal electrohydrodynamic redox 3d printing at the submicron scale: Microstructure – geometrical gradients – chemical gradients and the resulting mechanical properties

Abstract: An extensive range of metals can be dissolved and re-deposited in liquid solvents using electrochemistry. We harness this concept for additive manufacturing, demonstrating the focused electrohydrodynamic ejection of metal ions dissolved from sacrificial anodes and their subsequent reduction to elemental metals on the substrate. This technique, termed electrohydrodynamic redox printing (EHD-RP), enables the direct, ink-free fabrication of polycrystalline multi-metal 3D structures without the need for post-print processing. On-the-fly switching and mixing of two metals printed from a single multichannel nozzle facilitates a chemical feature size of <400 nm with a spatial resolution of 250 nm at printing speeds of up to 10 voxels per second. As shown, the additive control of the chemical architecture of materials provided by EHD-RP unlocks the synthesis of 3D bi-metal structures with programmed local properties and opens new avenues for the direct fabrication of chemically architected materials and devices.Inkfree multi-material printing is a common challenge in 3D printing. Here, the authors introduce electrohydrodynamic redox printing, a method that enables the deposition of multiple metals and their alloys with nanoscale resolution and thus the synthesis of materials with locally tuned properties.

Green synthesis, characterization and potential application of reduced graphene oxide

Abstract: This study investigates the structure and composition of graphene produced by thermal reduction of graphene oxide (GO) at various temperatures, for short time (5 min). The influence of reduction temperature on the structural properties of graphene was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier Transform Infrared (FTIR) spectroscopy, UV–Vis spectroscopy, thermogravimetric analysis (TGA), Raman and X-ray photoelectron spectroscopy (XPS). We demonstrated that by controlling the temperature in the annealing process, we can design materials with desired composition to meet the necessities for future or existing applications. The synthesized materials proved to have great potential in the atenolol adsorption from wastewater at room temperature (61% removal efficiency after 30 min).

Enhanced Electromagnetic Shielding and Thermal Conductive Properties of Polyolefin Composites with a Ti3C2Tx MXene/Graphene Framework Connected by a Hydrogen-Bonded Interface.

Abstract: The rapid increase of operation speed, transmission efficiency, and power density of miniaturized devices leads to a rising demand for electromagnetic interference (EMI) shielding and thermal management materials in the semiconductor industry. Therefore, it is essential to improve both the EMI shielding and thermal conductive properties of commonly used polyolefin components (such as polyethylene (PE)) in electronic systems. Currently, melt compounding is the most common method to fabricate polyolefin composites, but the difficulty of filler dispersion and high resistance at the filler/filler or filler/matrix interface limits their properties. Here, a fold fabrication strategy was proposed to prepare PE composites by incorporation of a well-aligned, seamless graphene framework premodified with MXene nanosheets into the matrix. We demonstrate that the physical properties of the composites can be further improved at the same filler loading by nanoscale interface engineering: the formation of hydrogen bonds at the graphene/MXene interface and the development of a seamlessly interconnected graphene framework. The obtained PE composites exhibit an EMI shielding property of ∼61.0 dB and a thermal conductivity of 9.26 W m-1 K-1 at a low filler content (∼3 wt %, including ∼0.4 wt % MXene). Moreover, other thermoplastic composites with the same results can also be produced based on our method. Our study provides an idea toward rational design of the filler interface to prepare high-performance polymer composites for use in microelectronics and microsystems.

Graphene oxide for photonics, electronics and optoelectronics

Abstract: Graphene oxide (GO) was initially developed to emulate graphene, but it was soon recognized as a functional material in its own right, addressing an application space that is not accessible to graphene and other carbon materials. Over the past decade, research on GO has made tremendous advances in material synthesis and property tailoring. These, in turn, have led to rapid progress in GO-based photonics, electronics and optoelectronics, paving the way for technological breakthroughs with exceptional performance. In this Review, we provide an overview of the optical, electrical and optoelectronic properties of GO and reduced GO on the basis of their chemical structures and fabrication approaches, together with their applications in key technologies such as solar energy harvesting, energy storage, medical diagnosis, image display and optical communications. We also discuss the challenges of this field, together with exciting opportunities for future technological advances. As the most common derivative of graphene, graphene oxide has emerged as a new frontier material with tremendous applications to photonics, electronics and optoelectronics in the past decade. This Review highlights the state of the art and future prospects for this fast-growing field.