Atomically thin two-dimensional (2D) materials are promising candidates for sub-10 nm transistor channels due to their ultrathin body thickness, which results in strong electrostatic gate control. Properly scaling a transistor technology requires reducing both the channel length (distance from source to drain) and the contact length (distance that source and drain interface with semiconducting channel). Contact length scaling remains an unresolved epidemic for transistor scaling, affecting devices from all semiconductorssilicon to 2D materials. Here, we show that clean edge contacts to 2D MoS 2 provide immunity to the contact-scaling problem, with performance that is independent of contact

A water-based silver nanowire ink for the room temperature printing of highly conductive traces onto biological and nonplanar surfaces.

No abstract

The Internet of Things (IoT) is the concept of a ubiquitous computing ecosystem in which electronics of custom form factors are seamlessly embedded into everyday objects. At the heart of the IoT are electronic sensors capable of detecting physical/environmental phenomena, translating these measurements into electrical signals, and wirelessly transmitting the data for remote computing. Critical to the development of IoT sensors and systems are low-cost materials, robust enough to sustain stable electrical performance over medium to long periods of time, yet sensitive enough to detect small changes in the surrounding environment. Such materials should be mechanically flexible and amenable to solution-based processing to facilitate large scale production methods, such as roll-to-roll printing. Carbon nanotubes (CNTs) are one of the leading material candidates to satisfy these requirements because of their unique electrical and mechanical properties, which enable robust and versatile devices, in combination with their chemical properties, which allow for the processing of CNTs from solution. These advantages have enabled demonstration of a myriad of printed CNT-based electronics and sensors on diverse substrates with wide ranges of functionality, spanning from simple sensors based on passive devices to complex multi-stage circuitry and display electronics. In this review, we provide a comprehensive summary of the CNT-based electronics and sensor space with an emphasis on applications aligned with the IoT. Primary coverage is devoted to devices consisting of randomly oriented CNT networks; however, the advantages and capabilities of single-nanotube devices will also be discussed. Key works across various types of sensors will be reviewed and a summary of the remaining challenges for CNT-based sensor technologies will be presented.

Thousands of reports have demonstrated the exceptional performance of sensors based on carbon nanotube (CNT) transistors, with promises of transformative impact. Yet, the effect of long-term bias stress on individual CNTs, critical for most sensing applications, has remained uncertain. Here, we report bias ranges under which CNT transistors can operate continuously for months or more without degradation. Using a custom characterization system, the impacts of defect formation and charge traps on the stability of CNTbased sensors under extended bias are determined. In addition to breakdown, which is well-known, we identify three additional operational modes: full stability, slow decay, and fast decay. We identify a current drift behavior that reduces dynamic range by over four orders of magnitude but is avoidable with appropriate sensing modalities. Identification of these stable operation modes and limits for nanotube-based sensors addresses concerns surrounding their development for a myriad of sensing applications.

Two-dimensional (2D) materials offer exciting possibilities for numerous applications, including next-generation sensors and field-effect transistors (FETs). With their atomically thin form factor, it is evident that molecular activity at the interfaces of 2D materials can shape their electronic properties. Although much attention has focused on engineering the contact and dielectric interfaces in 2D material-based transistors to boost their drive current, less is understood about how to tune these interfaces to improve the long-term stability of devices. In this work, we evaluated molybdenum disulfide (MoS 2 ) transistors under continuous electrical stress for periods lasting up to several days. During stress in ambient air, we observed temporary threshold voltage shifts that increased at higher gate voltages or longer stress durations, correlating to changes in interface trap states (ΔN it ) of up to 10 12 cm −2 . By modifying the device to include either SU-8 or Al 2 O 3 as an additional dielectric capping layer on top of the MoS 2 channel, we were able to effectively reduce or even eliminate this unstable behavior. However, we found this encapsulating material must be selected carefully, as certain choices actually amplified instability or compromised device yield, as was the case for Al 2 O 3 , which reduced yield by 20% versus all other capping layers. Further refining these strategies to preserve stability in 2D devices will be crucial for their continued integration into future technologies.

Tailoring the properties of two-dimensional (2D) crystals is important for both understanding the material behavior and exploring new functionality. Here we demonstrate the alteration of MoS 2 and metal-MoS 2 interfaces using a convergent ion beam. Different beam energies, from 60 eV to 600 eV, are shown to have distinct effects on the optical and electrical properties of MoS 2. Defects and deformations created across different layers were investigated, revealing an unanticipated improvement in the Raman peak intensity of multilayer MoS 2 when exposed to a 60 eV Ar + ion beam, and attenuation of the MoS 2 Raman peaks with a 200 eV ion beam. Using cross-sectional scanning transmission electron microscopy (STEM), alteration of the crystal structure after a 600 eV ion beam bombardment was observed, including generated defects and voids in the crystal. We show that the 60 eV ion beam yields improvement in the metal-MoS 2 interface by decreasing the contact resistance from 17.5 kΩ • µm to 6 kΩ • µm at a carrier concentration of n 2D = 5.4 × 10 12 cm −2. These results advance the use of low-energy ion beams to modify 2D materials and interfaces for tuning and improving performance in applications of sensors, transistors, optoelectronics, and so forth.

No abstract