5 research outputs found
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 grapheneāthin-film-semiconductorāmetal
(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 grapheneāInāGaāZnāO (IGZO)āmetal
asymmetric junctions on a transparent 150 Ć 150 mm<sup>2</sup> 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><sub>on</sub>/<i>I</i><sub>off</sub>) up to 10<sup>6</sup> 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 MetalāSemiconductor Junctions
The rectifying Schottky characteristics
of the metalāsemiconductor
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 NiāSi junction, one of the most
commonly used metalāsemiconductor 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<sup>ā8</sup> ā¼ 10<sup>ā9</sup> Ī© cm<sup>2</sup> at a Si doping concentration of 10<sup>17</sup> cm<sup>ā3</sup>
Two-Dimensional Materials Inserted at the Metal/Semiconductor Interface: Attractive Candidates for Semiconductor Device Contacts
Metalāsemiconductor
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 (Ļ<sub>c</sub>) of 3.30 nĪ© cm<sup>2</sup> (lightly doped n-type Si, ā¼ 10<sup>15</sup>/cm<sup>3</sup>) and 1.47 nĪ© cm<sup>2</sup> (heavily doped n-type Si, ā¼
10<sup>21</sup>/cm<sup>3</sup>) via 2D material insertion are approaching
the theoretical limit of 1.3 nĪ© cm<sup>2</sup>. We demonstrated
the role of the 2D materials at the interface in achieving a low Ļ<sub>c</sub> value by the following mechanisms: (a) 2D materials effectively
form dipoles at the metalā2D 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 Ļ<sub>c</sub>. 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