7 research outputs found
Multilevel Resistive Switching in Planar Graphene/SiO<sub>2</sub> Nanogap Structures
We report a planar graphene/SiO<sub>2</sub> nanogap structure for multilevel resistive switching. Nanosized gaps created on a SiO<sub>2</sub> substrate by electrical breakdown of nanographene electrodes were used as channels for resistive switching. Two-terminal devices exhibited excellent memory characteristics with good endurance up to 10<sup>4</sup> cycles, long retention time more than 10<sup>5</sup> s, and fast switching speed down to 500 ns. At least five conduction states with reliability and reproducibility were demonstrated in these memory devices. The mechanism of the resistance switching effect was attributed to a reversible thermal-assisted reduction and oxidation process that occurred at the breakdown region of the SiO<sub>2</sub> substrate. In addition, the uniform and wafer-size nanographene films with controlled layer thickness and electrical resistivity were grown directly on SiO<sub>2</sub> substrates for scalable device fabrications, making it attractive for developing high-density and low-cost nonvolatile memories
Versatile Fabrication of Self-Aligned Nanoscale Hall Devices Using Nanowire Masks
In this work, we present an ingenious
method to fabricate self-aligned
nanoscale Hall devices using chemically synthesized nanowires as both
etching and deposition masks. This versatile method can be extensively
used to make nanoribbons out of arbitrary thin films without the need
for extremely high alignment accuracy to define the metal contacts.
The fabricated nanoribbon width scales with the mask nanowire width
(diameter), and it can be easily reduced down to tens of nanometers.
The self-aligned metal contacts from the sidewall extend to the top
surface of the nanoribbon, and the overlap can be controlled by tuning
the deposition recipe. To demonstrate the feasibility, we have fabricated
Ta/CoFeB/MgO nanoribbons sputtered on a SiO<sub>2</sub>/Si substrate
with different metal contacts, using synthesized SnO<sub>2</sub> nanowires
as masks. Anomalous Hall effect measurements have been carried out
on the fabricated nanoscale Hall device in order to study the current-induced
magnetization switching in the nanoscale heavy metal/ferromagnet heterostructure,
which has shown distinct switching behaviors from micron-scale devices.
The developed method provides a useful fabrication platform to probe
the charge and spin transport in the nanoscale regime
Tunable Piezoresistivity of Nanographene Films for Strain Sensing
Graphene-based strain sensors have attracted much attention recently. Usually, there is a trade-off between the sensitivity and resistance of such devices, while larger resistance devices have higher energy consumption. In this paper, we report a tuning of both sensitivity and resistance of graphene strain sensing devices by tailoring graphene nanostructures. For a typical piezoresistive nanographene film with a sheet resistance of ∼100 KΩ/□, a gauge factor of more than 600 can be achieved, which is 50× larger than those in previous studies. These films with high sensitivity and low resistivity were also transferred on flexible substrates for device integration for force mapping. Each device shows a high gauge factor of more than 500, a long lifetime of more than 10<sup>4</sup> cycles, and a fast response time of less than 4 ms, suggesting a great potential in electronic skin applications
Room-Temperature Skyrmion Shift Device for Memory Application
Magnetic
skyrmions are intensively explored for potential applications in ultralow-energy
data storage and computing. To create practical skyrmionic memory
devices, it is necessary to electrically create and manipulate these
topologically protected information carriers in thin films, thus realizing
both writing and addressing functions. Although room-temperature skyrmions
have been previously observed, fully electrically controllable skyrmionic
memory devices, integrating both of these functions, have not been
developed to date. Here, we demonstrate a room-temperature skyrmion
shift memory device, where individual skyrmions are controllably generated
and shifted using current-induced spin–orbit torques. Particularly,
it is shown that one can select the device operation mode in between
(i) writing new single skyrmions or (ii) shifting existing skyrmions
by controlling the magnitude and duration of current pulses. Thus,
we electrically realize both writing and addressing of a stream of
skyrmions in the device. This prototype demonstration brings skyrmions
closer to real-world computing applications
Room-Temperature Skyrmions in an Antiferromagnet-Based Heterostructure
Magnetic
skyrmions as swirling spin textures with a nontrivial
topology have potential applications as magnetic memory and storage
devices. Since the initial discovery of skyrmions in non-centrosymmetric
B20 materials, the recent effort has focused on exploring room-temperature
skyrmions in heavy metal and ferromagnetic heterostructures, a material
platform compatible with existing spintronic manufacturing technology.
Here, we report the surprising observation that a room-temperature
skyrmion phase can be stabilized in an entirely different class of
systems based on antiferromagnetic (AFM) metal and ferromagnetic (FM)
metal IrMn/CoFeB heterostructures. There are a number of distinct
advantages of exploring skyrmions in such heterostructures including
zero-field stabilization, tunable antiferromagnetic order, and sizable
spin–orbit torque (SOT) for energy-efficient current manipulation.
Through direct spatial imaging of individual skyrmions, quantitative
evaluation of the interfacial Dzyaloshinskii–Moriya interaction,
and demonstration of current-driven skyrmion motion, our findings
firmly establish the AFM/FM heterostructures as a promising material
platform for exploring skyrmion physics and device applications
A Route toward Digital Manipulation of Water Nanodroplets on Surfaces
Manipulation of an isolated water nanodroplet (WN) on certain surfaces is important to various nanofluidic applications but challenging. Here we present a digital nanofluidic system based on a graphene/water/mica sandwich structure. In this architecture, graphene provides a flexible protection layer to isolate WNs from the outside environment, and a monolayer ice-like layer formed on the mica surface acts as a lubricant layer to allow these trapped WNs to move on it freely. In combination with scanning probe microscope techniques, we are able to move, merge, and separate individual water nanodroplets in a controlled manner. The smallest manipulatable water nanodroplet has a volume down to yoctoliter (10<sup>–24</sup> L) scale
Room-Temperature Skyrmions in an Antiferromagnet-Based Heterostructure
Magnetic
skyrmions as swirling spin textures with a nontrivial
topology have potential applications as magnetic memory and storage
devices. Since the initial discovery of skyrmions in non-centrosymmetric
B20 materials, the recent effort has focused on exploring room-temperature
skyrmions in heavy metal and ferromagnetic heterostructures, a material
platform compatible with existing spintronic manufacturing technology.
Here, we report the surprising observation that a room-temperature
skyrmion phase can be stabilized in an entirely different class of
systems based on antiferromagnetic (AFM) metal and ferromagnetic (FM)
metal IrMn/CoFeB heterostructures. There are a number of distinct
advantages of exploring skyrmions in such heterostructures including
zero-field stabilization, tunable antiferromagnetic order, and sizable
spin–orbit torque (SOT) for energy-efficient current manipulation.
Through direct spatial imaging of individual skyrmions, quantitative
evaluation of the interfacial Dzyaloshinskii–Moriya interaction,
and demonstration of current-driven skyrmion motion, our findings
firmly establish the AFM/FM heterostructures as a promising material
platform for exploring skyrmion physics and device applications