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Department of Materials Science and EngineeringChemical vapor deposition method has been spotlighted as a tool growing large-area, good quality, mass-producible and uniform graphene. In particular, the copper that grows a uniform monolayer of graphene has attracted researchers??? attentions as a graphene growth substrate. However, CVD graphene growth has a nature that graphene has various intrinsic defects such as point defects, grain boundaries, and wrinkles, undermining the properties of graphene. So, it is important to visualize various intrinsic defects in terms of optimizing graphene growth. Firstly, we examined selective oxygen permeation through atomic structural defects in CVD-grown graphene/copper composites measured by optical and electron microscopies. Using an simple air oxidation of graphene coated copper foils with heating of 200 ??C, we developed a simple and large area characterization tool to visualize intrinsic graphene defects induced by different origins such as nucleation sites, inter grain boundaries and intra grain boundaries from CVD-grown graphene. The oxidation conduct of copper can vary with disorder of graphene structures according to sources of various graphene intrinsic defects such as growth condition, crystallographic orientations of copper substrates and growth rate. From the experimental and computational experiments, we found that oxygen atoms were dissociated from the water vapor of air are main origins oxidizing copper surface under graphene and selective oxygen permeation occurred at Stone???Wales defects into graphene membrane promoted by other accumulated oxygen atoms as catalyst. Secondly, we use HCl etching method to systemically investigate the water permeable origins on the graphene grown on copper by CVD observing copper etching pits through OM and SEM. When we observed the distribution of these etching pits through SE and BSE mode of SEM, it was found the copper etching pits were observed at the intersection of wrinkles of CVD-grown graphene and copper step bunches. In addition, it was also confirmed that nanosized ruptures, cracks, and holes were formed in folded graphene wrinkles through TEM. The HCl etching method can determine where the water permeations occur in the CVD-grown graphene, and these results will contribute to optimizing the graphene growth as production of water impermeable layer. Finally, we described a large-area technique to enhance impermeability of graphene by amorphous carbon layer deposited by an electron beam, sputtered carbon, and CH4 plasma. It was utilized to passivate the graphene nanosized ruptures, cracks and holes less than 3nm, developed on intersecting points of wrinkle and copper step bunch. In addition, the wrinkles on the part of multilayer graphene also had excellent water impermeability to copper etchants. Applying these carbon-based layers, flexible, transparent, and thin barrier films will be developed for water impermeable electrodes and substrates to safely protect future ubiquitous electronics from ambient air being exposed to everyday lifeclos

Electrically Robust Single-Crystalline WTe2 Nanobelts for Nanoscale Electrical Interconnects

As the elements of integrated circuits are downsized to the nanoscale, the current Cu-based interconnects are facing limitations due to increased resistivity and decreased current-carrying capacity because of scaling. Here, the bottom-up synthesis of single-crystalline WTe2 nanobelts and low- and high-field electrical characterization of nanoscale interconnect test structures in various ambient conditions are reported. Unlike exfoliated flakes obtained by the top-down approach, the bottom-up growth mode of WTe2 nanobelts allows systemic characterization of the electrical properties of WTe2 single crystals as a function of channel dimensions. Using a 1D heat transport model and a power law, it is determined that the breakdown of WTe2 devices under vacuum and with AlOx capping layer follows an ideal pattern for Joule heating, far from edge scattering. High-field electrical measurements and self-heating modeling demonstrate that the WTe2 nanobelts have a breakdown current density approaching approximate to 100 MA cm(-2), remarkably higher than those of conventional metals and other transition-metal chalcogenides, and sustain the highest electrical power per channel length (approximate to 16.4 W cm(-1)) among the interconnect candidates. The results suggest superior robustness of WTe2 against high-bias sweep and its possible applicability in future nanoelectronics

Strong Rashba parameter of two-dimensional electron gas at CaZrO3/SrTiO3 heterointerface

Abstract We synthesized a CaZrO3/SrTiO3 oxide heterostructure, which can serve as an alternative to LaAlO3/SrTiO3, and confirmed the generation of 2-dimensional electron gas (2-DEG) at the heterointerface. We analyzed the electrical-transport properties of the 2-DEG to elucidate its intrinsic characteristics. Based on the magnetic field dependence of resistance at 2 K, which exhibited Weak Anti-localization (WAL) behaviors, the fitted Rashba parameter values were found to be about 12–15 × 10–12 eV*m. These values are stronger than the previous reported Rashba parameters obtained from the 2-DEGs in other heterostructure systems and several layered 2D materials. The observed strong spin–orbit coupling (SOC) is attributed to the strong internal electric field generated by the lattice mismatch between the CaZrO3 layer and SrTiO3 substrate. This pioneering strong SOC of the 2-DEG at the CaZrO3/SrTiO3 heterointerface may play a pivotal role in the developing future metal oxide-based quantum nanoelectronics devices

High‐Yield‐Stress Particle‐Stabilized Emulsion for Form‐Factor‐Free Thermal Pastes with High Thermal Conductivity, Stability, and Recyclability

Abstract Thermal pastes, thermally conductive fillers dispersed in liquid matrices, are widely used as thermal interface materials (TIMs). TIMs transfer heat generated from electronics to the surroundings, ensuring optimal operating temperatures. Thus, it is crucial to obtain high thermal conductivity (TC) by forming a continuous heat‐conduction pathway through interconnected filler‐networks within the TIM. Therefore, for paste‐type TIMs with spherical fillers, high TC can only be realized at sufficiently high filler loadings (>60 vol%). However, the pastes bearing such high filler loadings are thick, stiff, and less applicable. To these ends, particle‐stabilized emulsions composed of immiscible liquids (silicone oil and glycerol) and spherical alumina are utilized as thermal pastes. Owing to this structure, the resulting form‐factor‐free thermal paste exhibits higher TC and stability than a simple mixture consisting of alumina and a single‐liquid‐matrix (either silicone oil or glycerol). Furthermore, the high applicability of the emulsion‐type pastes enables syringe extrusion, 3D printing, multiple cycles of reprocessing/molding, and eco‐friendly recycling

The impact of substrate surface defects on the properties of two-dimensional van der Waals heterostructures

The recent emergence of vertically stacked van der Waals (vdW) heterostructures provides new opportunities for these materials to be employed in a wide range of novel applications. Understanding the interlayer coupling in the stacking geometries of the heterostructures and its effect on the resultant material properties is particularly important for obtaining materials with desirable properties. Here, we report that the atomic bonding between stacked layers and thereby the interlayer properties of the vdW heterostructures can be well tuned by the substrate surface defects using WS2 flakes directly grown on graphene. We show that the defects of graphene have no significant effect on the crystal structure or the quality of the grown WS2 flakes; however, they have a strong influence on the interlayer interactions between stacked layers, thus affecting the layer deformability, thermal stability, and physical and electrical properties. Our experimental and computational investigations also reveal that WS2 flakes grown on graphene defects form covalent bonds with the underlying graphene via W atomic bridges (i.e., formation of larger overlapping hybrid orbitals), enabling these flakes to exhibit different intrinsic properties, such as higher conductivity and improved contact characteristics than heterostructures that have vdW interactions with graphene. This result emphasizes the importance of understanding the interlayer coupling in the stacking geometries and its correlation effect for designing desirable properties

Substantial improvements of long-term stability in encapsulation-free WS2 using highly interacting graphene substrate

We report the novel role of graphene substrates in obstructing the aging propagation in both the basal planes and edges of two-dimensitional sheets of transition metal dichalcogenides (TMDs). Even after 300 d in ambient air conditions, the epitaxially grown WS2/graphene samples have a clean, uniform surface without any encapsulation. We show that high crystallinity is an effective factor that determines the excellent air stability of WS2/graphene, and we present impressive experimental evidence of the relation between defects and the aging phenomena. Moreover, we reveal the strong interlayer charge interaction as an additional factor for the enhanced air stability as a result of charge transfer-induced doping. This work not only proposes a simple method to create highly stable TMDs by the selection of a suitable substrate but also paves the way for the realization of practical TMDs-based applications.clos