The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides.

/pdf/electrical-contacts-to-two-dimensional-semiconductors-2q90rkwvlw.pdf

Electrical contacts to two-dimensional semiconductors

The use of liquid metals based on gallium for soft and stretchable electronics is discussed. This emerging class of electronics is motivated, in part, by the new opportunities that arise from devices that have mechanical properties similar to those encountered in the human experience, such as skin, tissue, textiles, and clothing. These types of electronics (e.g., wearable or implantable electronics, sensors for soft robotics, e-skin) must operate during deformation. Liquid metals are compelling materials for these applications because, in principle, they are infinitely deformable while retaining metallic conductivity. Liquid metals have been used for stretchable wires and interconnects, reconfigurable antennas, soft sensors, self-healing circuits, and conformal electrodes. In contrast to Hg, liquid metals based on gallium have low toxicity and essentially no vapor pressure and are therefore considered safe to handle. Whereas most liquids bead up to minimize surface energy, the presence of a surface oxide on these metals makes it possible to pattern them into useful shapes using a variety of techniques, including fluidic injection and 3D printing. In addition to forming excellent conductors, these metals can be used actively to form memory devices, sensors, and diodes that are completely built from soft materials. The properties of these materials, their applications within soft and stretchable electronics, and future opportunities and challenges are considered.

Stretchable and Soft Electronics using Liquid Metals.

Wearable sensors play a crucial role in realizing personalized medicine, as they can continuously collect data from the human body to capture meaningful health status changes in time for preventive intervention. However, motion artifacts and mechanical mismatches between conventional rigid electronic materials and soft skin often lead to substantial sensor errors during epidermal measurement. Because of its unique properties such as high flexibility and conformability, flexible electronics enables a natural interaction between electronics and the human body. In this Account, we summarize our recent studies on the design of flexible electronic devices and systems for physical and chemical monitoring. Material innovation, sensor design, device fabrication, system integration, and human studies employed toward continuous and noninvasive wearable sensing are discussed. A flexible electronic device typically contains several key components, including the substrate, the active layer, and the interface layer. The inorganic-nanomaterials-based active layer (prepared by a physical transfer or solution process) is shown to have good physicochemical properties, electron/hole mobility, and mechanical strength. Flexible electronics based on the printed and transferred active materials has shown great promise for physical sensing. For example, integrating a nanowire transistor array for the active matrix and a conductive pressure-sensitive rubber enables tactile pressure mapping; tactile-pressure-sensitive e-skin and organic light-emitting diodes can be integrated for instantaneous pressure visualization. Such printed sensors have been applied as wearable patches to monitor skin temperature, electrocardiograms, and human activities. In addition, liquid metals could serve as an attractive candidate for flexible electronics because of their excellent conductivity, flexibility, and stretchability. Liquid-metal-enabled electronics (based on liquid-liquid heterojunctions and embedded microchannels) have been utilized to monitor a wide range of physiological parameters (e.g., pulse and temperature). Despite the rapid growth in wearable sensing technologies, there is an urgent need for the development of flexible devices that can capture molecular data from the human body to retrieve more insightful health information. We have developed a wearable and flexible sweat-sensing platform toward real-time multiplexed perspiration analysis. An integrated iontophoresis module on a wearable sweat sensor could enable autonomous and programmed sweat extraction. A microfluidics-based sensing system was demonstrated for sweat sampling, sensing, and sweat rate analysis. Roll-to-roll gravure printing allows for mass production of high-performance flexible chemical sensors at low cost. These wearable and flexible sweat sensors have shown great promise in dehydration monitoring, cystic fibrosis diagnosis, drug monitoring, and noninvasive glucose monitoring. Future work in this field should focus on designing robust wearable sensing systems to accurately collect data from the human body and on large-scale human studies to determine how the measured physical and chemical information relates to the individual's specific health conditions. Further research in these directions, along with the large sets of data collected via these wearable and flexible sensing technologies, will have a significant impact on future personalized healthcare.

/pdf/flexible-electronics-toward-wearable-sensing-2c17u715ro.pdf

Flexible Electronics toward Wearable Sensing

Post-transition elements, together with zinc-group metals and their alloys belong to an emerging class of materials with fascinating characteristics originating from their simultaneous metallic and liquid natures. These metals and alloys are characterised by having low melting points (i.e. between room temperature and 300 °C), making their liquid state accessible to practical applications in various fields of physical chemistry and synthesis. These materials can offer extraordinary capabilities in the synthesis of new materials, catalysis and can also enable novel applications including microfluidics, flexible electronics and drug delivery. However, surprisingly liquid metals have been somewhat neglected by the wider research community. In this review, we provide a comprehensive overview of the fundamentals underlying liquid metal research, including liquid metal synthesis, surface functionalisation and liquid metal enabled chemistry. Furthermore, we discuss phenomena that warrant further investigations in relevant fields and outline how liquid metals can contribute to exciting future applications.

Liquid metals: fundamentals and applications in chemistry

Carbon nanotubes (CNTs) promise to advance a number of real-world technologies. Of these applications, they are particularly attractive for uses in chemical sensors for environmental and health monitoring. However, chemical sensors based on CNTs are often lacking in selectivity, and the elucidation of their sensing mechanisms remains challenging. This review is a comprehensive description of the parameters that give rise to the sensing capabilities of CNT-based sensors and the application of CNT-based devices in chemical sensing. This review begins with the discussion of the sensing mechanisms in CNT-based devices, the chemical methods of CNT functionalization, architectures of sensors, performance parameters, and theoretical models used to describe CNT sensors. It then discusses the expansive applications of CNT-based sensors to multiple areas including environmental monitoring, food and agriculture applications, biological sensors, and national security. The discussion of each analyte focuses on the strategies used to impart selectivity and the molecular interactions between the selector and the analyte. Finally, the review concludes with a brief outlook over future developments in the field of chemical sensors and their prospects for commercialization.

Carbon Nanotube Chemical Sensors

Mechanically deformable devices and sensors enable conformal coverage of electronic systems on curved and soft surfaces. Sensors utilizing liquids confined in soft templates as the sensing component present the ideal platform for such applications, as liquids are inherently more deformable than solids. However, to date, liquid-based devices have been limited to metal lines based on a single-liquid component given the difficulty in the fabrication of liquid-based junctions due to intermixing. Here, we demonstrate a robust platform for the fabrication of liquid-liquid 'heterojunction' devices, presenting an important advancement towards the realization of liquid-state electronic systems. The device architecture and fabrication scheme we present are generic for different sensing liquids, enabling demonstration of sensors responsive to different stimuli. As a proof of concept, we demonstrate temperature, humidity and oxygen sensors by using different ionic liquids, exhibiting high sensitivity with excellent mechanical deformability arising from the inherent property of the liquid phase.

/pdf/highly-deformable-liquid-state-heterojunction-sensors-2ic9yiyiks.pdf

Highly deformable liquid-state heterojunction sensors

Controlled assembly of single-walled carbon nanotube (SWCNT) networks with high density and deposition rate is critical for many practical applications, including large-area electronics. In this regard, surfactant chemistry plays a critical role as it facilitates the substrate–nanotube interactions. Despite its importance, detailed understanding of the subject up until now has been lacking, especially toward tuning the controllability of SWCNT assembly for thin-film transistors. Here, we explore SWCNT assembly with steroid- and alkyl-based surfactants. While steroid-based surfactants yield highly dense nanotube thin films, alkyl surfactants are found to prohibit nanotube assembly. The latter is attributed to the formation of packed alkyl layers of residual surfactants on the substrate surface, which subsequently repel surfactant encapsulated SWCNTs. In addition, temperature is found to enhance the nanotube deposition rate and density. Using this knowledge, we demonstrate highly dense and rapid assembly wi...

/pdf/design-of-surfactant-substrate-interactions-for-roll-to-roll-4olb5rbyeq.pdf

Design of surfactant-substrate interactions for roll-to-roll assembly of carbon nanotubes for thin-film transistors.

Stable n-doping of WSe2 using thin films of SiNx deposited on the surface via plasma-enhanced chemical vapor deposition is presented. Positive fixed charge centers inside SiNx act to dope WSe2 thin flakes n-type via field-induced effect. The electron concentration in WSe2 can be well controlled up to the degenerate limit by simply adjusting the stoichiometry of the SiNx through deposition process parameters. For the high doping limit, the Schottky barrier width at the metal/WSe2 junction is significantly thinned, allowing for efficient electron injection via tunneling. Using this doping scheme, we demonstrate air-stable WSe2 n-MOSFETs with a mobility of ∼70 cm2/V s.

Air stable n-doping of WSe2 by silicon nitride thin films with tunable fixed charge density

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Tae-Jun Ha

Author Tools

Chat about Author

Papers

Highly deformable liquid-state heterojunction sensors

Design of surfactant-substrate interactions for roll-to-roll assembly of carbon nanotubes for thin-film transistors.

Air stable n-doping of WSe2 by silicon nitride thin films with tunable fixed charge density