Anisotropic Membrane Diffusion of Human Mesenchymal Stem Cells on Aligned Single-Walled Carbon Nanotube Networks

The diffusion of lipids and proteins in cell membranes is involved in various cellular processes such as cell adhesion and cellular signaling. We report the anisotropic molecular diffusion in the membranes of human mesenchymal stem cells on aligned single-walled carbon nanotube networks. In this study, the cells were first cultured on the surfaces of glass, graphene, and carbon nanotube networks with random or aligned orientations. Then, the molecular diffusion constants of the cell membranes were measured using a fluorescence-recovery-after-photobleaching technique. The cells on graphene exhibited a diffusion constant comparable to that on glass substrate, while those on the rough surface of randomly oriented carbon nanotube networks exhibited a rather low diffusion constant. On the aligned carbon nanotube networks, the molecules in the cell membrane were found to diffuse faster along the direction parallel to the aligned carbon nanotubes than along the direction orthogonal to the nanotubes. These results indicate that the nanoscale properties of nanostructured materials may significantly affect the molecular diffusion in cell membranes and, possibly, related cellular processes

Graphene and Thin-Film Semiconductor Heterojunction Transistors Integrated on Wafer Scale for Low-Power Electronics

Graphene heterostructures in which graphene is combined with semiconductors or other layered 2D materials are of considerable interest, as a new class of electronic devices has been realized. Here we propose a technology platform based on graphene–thin-film-semiconductor–metal (GSM) junctions, which can be applied to large-scale and power-efficient electronics compatible with a variety of substrates. We demonstrate wafer-scale integration of vertical field-effect transistors (VFETs) based on graphene–In–Ga–Zn–O (IGZO)–metal asymmetric junctions on a transparent 150 × 150 mm² glass. In this system, a triangular energy barrier between the graphene and metal is designed by selecting a metal with a proper work function. We obtain a maximum current on/off ratio (<i>I</i>_on/<i>I</i>_off) up to 10⁶ with an average of 3010 over 2000 devices under ambient conditions. For low-power logic applications, an inverter that combines complementary n-type (IGZO) and p-type (Ge) devices is demonstrated to operate at a bias of only 0.5 V

Control of Triboelectrification by Engineering Surface Dipole and Surface Electronic State

Although triboelectrification is a well-known phenomenon, fundamental understanding of its principle on a material surface has not been studied systematically. Here, we demonstrated that the surface potential, especially the surface dipoles and surface electronic states, governed the triboelectrification by controlling the surface with various electron-donating and -withdrawing functional groups. The functional groups critically affected the surface dipoles and surface electronic states followed by controlling the amount of and even the polarity of triboelectric charges. As a result, only one monolayer with a thickness of less than 1 nm significantly changed the conventional triboelectric series. First-principles simulations confirmed the atomistic origins of triboelectric charges and helped elucidate the triboelectrification mechanism. The simulation also revealed for the first time where charges are retained after triboelectrification. This study provides new insights to understand triboelectrification

Graphene for True Ohmic Contact at Metal–Semiconductor Junctions

The rectifying Schottky characteristics of the metal–semiconductor junction with high contact resistance have been a serious issue in modern electronic devices. Herein, we demonstrated the conversion of the Schottky nature of the Ni–Si junction, one of the most commonly used metal–semiconductor junctions, into an Ohmic contact with low contact resistance by inserting a single layer of graphene. The contact resistance achieved from the junction incorporating graphene was about 10^–8 ∼ 10^–9 Ω cm² at a Si doping concentration of 10¹⁷ cm^–3

Two-Dimensional Materials Inserted at the Metal/Semiconductor Interface: Attractive Candidates for Semiconductor Device Contacts

Metal–semiconductor junctions are indispensable in semiconductor devices, but they have recently become a major limiting factor precluding device performance improvement. Here, we report the modification of a metal/n-type Si Schottky contact barrier by the introduction of two-dimensional (2D) materials of either graphene or hexagonal boron nitride (h-BN) at the interface. We realized the lowest specific contact resistivities (ρ_c) of 3.30 nΩ cm² (lightly doped n-type Si, ∼ 10¹⁵/cm³) and 1.47 nΩ cm² (heavily doped n-type Si, ∼ 10²¹/cm³) via 2D material insertion are approaching the theoretical limit of 1.3 nΩ cm². We demonstrated the role of the 2D materials at the interface in achieving a low ρ_c value by the following mechanisms: (a) 2D materials effectively form dipoles at the metal–2D material (M/2D) interface, thereby reducing the metal work function and changing the pinning point, and (b) the fully metalized M/2D system shifts the pinning point toward the Si conduction band, thus decreasing the Schottky barrier. As a result, the fully metalized M/2D system using atomically thin and well-defined 2D materials shows a significantly reduced ρ_c. The proposed 2D material insertion technique can be used to obtain extremely low contact resistivities in metal/n-type Si systems and will help to achieve major performance improvements in semiconductor technologies