Applications of MXenes in human-like sensors and actuators

Human beings perceive the world through the senses of sight, hearing, smell, taste, touch, space, and balance. The first five senses are prerequisites for people to live. The sensing organs upload information to the nervous systems, including the brain, for interpreting the surrounding environment. Then, the brain sends commands to muscles reflexively to react to stimuli, including light, gas, chemicals, sound, and pressure. MXene, as an emerging two-dimensional material, has been intensively adopted in the applications of various sensors and actuators. In this review, we update the sensors to mimic five primary senses and actuators for stimulating muscles, which employ MXene-based film, membrane, and composite with other functional materials. First, a brief introduction is delivered for the structure, properties, and synthesis methods of MXenes. Then, we feed the readers the recent reports on the MXene-derived image sensors as artificial retinas, gas sensors, chemical biosensors, acoustic devices, and tactile sensors for electronic skin. Besides, the actuators of MXene-based composite are introduced. Eventually, future opportunities are given to MXene research based on the requirements of artificial intelligence and humanoid robot, which may induce prospects in accompanying healthcare and biomedical engineering applications. [Figure not available: see fulltext.

Applications of MXenes in human-like sensors and actuators

Human beings perceive the world through the senses of sight, hearing, smell, taste, touch, space, and balance. The first five senses are prerequisites for people to live. The sensing organs upload information to the nervous systems, including the brain, for interpreting the surrounding environment. Then, the brain sends commands to muscles reflexively to react to stimuli, including light, gas, chemicals, sound, and pressure. MXene, as an emerging two-dimensional material, has been intensively adopted in the applications of various sensors and actuators. In this review, we update the sensors to mimic five primary senses and actuators for stimulating muscles, which employ MXene-based film, membrane, and composite with other functional materials. First, a brief introduction is delivered for the structure, properties, and synthesis methods of MXenes. Then, we feed the readers the recent reports on the MXene-derived image sensors as artificial retinas, gas sensors, chemical biosensors, acoustic devices, and tactile sensors for electronic skin. Besides, the actuators of MXene-based composite are introduced. Eventually, future opportunities are given to MXene research based on the requirements of artificial intelligence and humanoid robot, which may induce prospects in accompanying healthcare and biomedical engineering applications.Web of Scienc

Seeding-Layer-Free Deposition of High-k Dielectric on CVD Graphene for Enhanced Gate Control Ability

The gate insulator is one of the most crucial factors determining the performance of a graphene field effect transistor (GFET). Good electrostatic control of the conduction channel by gate voltage requires thin gate oxides. Due to the lack of the dangling bond, a seed layer is usually needed for the gate dielectric film grown by the atomic layer deposition (ALD) process. The seed layer leads to the high-quality deposition of dielectric films, but it may lead to a great increase in the thickness of the final dielectric film. To address this problem, this paper proposes an improved process, where the self-oxidized Al2O3 seed layer was removed by etching solutions before atomic layer deposition, and the Al2O3 residue would provide nucleation sites on the graphene surface. Benefiting from the decreased thickness of the dielectric film, the transconductance of the GFET using this method as a top-gate dielectric film deposition process shows an average 44.7% increase compared with the GFETs using the standard Al evaporation seed layer methods

Electric-Field Induced Doping Polarity Conversion in Top-Gated Transistor Based on Chemical Vapor Deposition of Graphene

The top-gated graphene field effect transistor (GFET) with electric-field induced doping polarity conversion has been demonstrated. The polarity of channel conductance in GFET can be transition from p-type to n-type through altering the gate electric field scanning range. Further analysis indicates that this complementary doping is attributed to the charge exchange between graphene and interface trap sites. The oxygen vacancies in Al2O3filmare are considered to be the origin of the trap sites. The trapping–detrapping process, which may be tuned by the electric field across the metal/oxide/graphene gate stack, could lead to the changing of the intrinsic electric property of graphene. This study promises to produce the complementary p- and n-type GFET for logic applications

Electric-Field Induced Doping Polarity Conversion in Top-Gated Transistor Based on Chemical Vapor Deposition of Graphene

The top-gated graphene field effect transistor (GFET) with electric-field induced doping polarity conversion has been demonstrated. The polarity of channel conductance in GFET can be transition from p-type to n-type through altering the gate electric field scanning range. Further analysis indicates that this complementary doping is attributed to the charge exchange between graphene and interface trap sites. The oxygen vacancies in Al2O3filmare are considered to be the origin of the trap sites. The trapping–detrapping process, which may be tuned by the electric field across the metal/oxide/graphene gate stack, could lead to the changing of the intrinsic electric property of graphene. This study promises to produce the complementary p- and n-type GFET for logic applications

Carrier-Number-Fluctuation Induced Ultralow 1/<i>f</i> Noise Level in Top-Gated Graphene Field Effect Transistor

A top-gated graphene FET with an ultralow 1/<i>f</i> noise level of 1.8 × 10^–12 μm²Hz^1– (<i>f</i> = 10 Hz) has been fabricated. The noise has the least value at Dirac point, it then increases fast when the current deviates from that at Dirac point, the noise slightly decreases at large current. The phenomenon can be understood by the carrier-number-fluctuation induced low frequency noise, which caused by the trapping-detrapping processes of the carriers. Further analysis suggests that the effect trap density depends on the location of Fermi level in graphene channel. The study has provided guidance for suppressing the 1/<i>f</i> noise in graphene-based applications

Emerging Internet of Things driven carbon nanotubes-based devices

Carbon nanotubes (CNTs) have attracted great attentions in the field of electronics, sensors, healthcare, and energy conversion. Such emerging applications have driven the carbon nanotube research in a rapid fashion. Indeed, the structure control over CNTs has inspired an intensive research vortex due to the high promises in electronic and optical device applications. Here, this in-depth review is anticipated to provide insights into the controllable synthesis and applications of high-quality CNTs. First, the general synthesis and post-purification of CNTs are briefly discussed. Then, the state-of-the-art electronic device applications are discussed, including field-effect transistors, gas sensors, DNA biosensors, and pressure gauges. Besides, the optical sensors are delivered based on the photoluminescence. In addition, energy applications of CNTs are discussed such as thermoelectric energy generators. Eventually, future opportunities are proposed for the Internet of Things (IoT) oriented sensors, data processing, and artificial intelligence.Web of Scienc

An effective formaldehyde gas sensor based on oxygen-rich three-dimensional graphene

Three-dimensional (3D) graphene with a high specific surface area and excellent electrical conductivity holds extraordinary potential for molecular gas sensing. Gas molecules adsorbed onto graphene serve as electron donors, leading to an increase in conductivity. However, several challenges remain for 3D graphene-based gas sensors, such as slow response and long recovery time. Therefore, research interest remains in the promotion of the sensitivity of molecular gas detection. In this study, we fabricate oxygen plasma-treated 3D graphene for the high-performance gas sensing of formaldehyde. We synthesize large-area, high-quality, 3D graphene over Ni foam by chemical vapor deposition and obtain freestanding 3D graphene foam after Ni etching. We compare three types of strategies-non-treatment, oxygen plasma, and etching in HNO3 solution-for the posttreatment of 3D graphene. Eventually, the strategy for oxygen plasma-treated 3D graphene exceeds expectations, which may highlight the general gas sensing based on chemiresistors.Web of Science3318art. no. 18570