Electronics - Page 15

A team of researchers at the University of Minnesota and Northwestern University, USA, have developed a printing method to produce flexible graphene micro-supercapacitors with a planar architecture suitable for integration in portable electronic devices.

The new process, referred to as ‘self-aligned capillarity-assisted lithography for electronics’ (SCALE), begins with the creation of a polymer template, generated by stamping a UV-curable polymer with a PDMS mold. High-resolution inkjet printing is then used to deposit a graphene ink into the template, which is annealed using a xenon lamp to form the electrodes. In the final step, a polymer gel electrolyte is printed onto the template over the electrodes to complete the configuration.

Researchers from Cambridge University have demonstrated how graphene and other related 2D materials (namely hBN) can be directly printed onto textiles to create fully inkjet-printed dielectrically gated field effect transistors (FETs) with solution processed 2D materials.

According to the team, these devices are washable, flexible, cheap, safe, comfortable to wear and environmentally-friendly, essential requirements for applications in wearable electronics. The team also demonstrated the first reprogrammable memories, inverters and logic gates with solution processed 2D materials by coupling these FETs together to create integrated circuits, the most fundamental components of a modern-day computer.

Two interesting projects focused on coating single-layer graphene with metal-oxide nanolayers were presented at the latest Thin Films and Coating Technologies for Science and Industry event in the UK. Researchers from Cranfield University, UK, together with collaborators from University of Cambridge and the Centre for Process Innovation (CPI), applied alumina to form a composite barrier layer, while a team from Imperial College London, UK, used the unique properties of strontium titanate to fabricate a tuneable capacitor.

The researchers of the first project explained that in theory, graphene should represent an ideal ultrathin barrier layer, as the pores between carbon atoms are smaller even than the radius of a helium atom. In practice, however, crystal boundaries and missing atoms allow vapor to permeate through the material, and the weak van der Waals bonds between planes mean that even stacks of multiple graphene layers can be penetrated. The solution reported by the team is to take a graphene monolayer formed by CVD, and to then use atomic layer deposition (ALD) to coat it with a 2550 nm thick layer of alumina. Achieving conformal coatings on single-layer graphene is known to be difficult due to the material’s strong hydrophobicity.

Researchers at Chalmers University have developed a flexible detector for terahertz frequencies (1000 gigahertz) using graphene transistors on plastic substrates. It is said to be the first of its kind, and can extend the use of terahertz technology to applications that require flexible electronics, like wireless sensor networks and wearable technology.

At room temperature, the translucent and flexible device detects signals in the frequency range 330 to 500 gigahertz. The technique can be used for imaging in the terahertz area (THz camera), but also for identifying different substances (sensor). It may also be of potential benefit in health care, where terahertz waves can be used to detect cancer. Other areas where the detector could be used are imaging sensors for vehicles or for wireless communications.

Scientists at Rutgers University-New Brunswick have found a way to control the electrons in graphene, paving the way for the ultra-fast transport of electrons with low loss of energy in novel systems. "This shows we can electrically control the electrons in graphene," said a professor in Rutgers' Department of Physics and Astronomy. "In the past, we couldn't do it. This is the reason people thought that one could not make devices like transistors that require switching with graphene, because their electrons run wild."

This new work might make it possible to realize a graphene nano-scale transistor, the team said, which would be an important step towards an all-graphene electronics platform. The team managed to control electrons by sending voltage through a microscope with an extremely sharp tip, also the size of one atom, which offers 3-D views of surfaces at the atomic scale. The microscope's sharp tip creates a force field that traps electrons in graphene or modifies their trajectories, similar to the effect a lens has on light rays. Electrons can easily be trapped and released, providing an efficient on-off switching mechanism, according to the team.

Mimos, the Malaysian R&D center under the Ministry of Science, Technology and Innovation (MOSTI), recently signed a collaborative research and development agreement with Universiti Pendidikan Sultan Idris (UPSI) to develop graphene electronic technology to enhance both their competitive advantage in the technology and applications, especially in advanced materials for electronic devices.

A recent statement by MIMOS said "Under the collaboration, both MIMOS and UPSI will jointly develop the technology, exchange research expertise, and increase the number of patents including joint-publication in graphene electronics and related technologies... The collaboration would allow UPSI to benefit from the access to high-end industry-standard facilities at MIMOS, and help align their research activities with industry requirements".

Researchers with Johns Hopkins University and MIT have shown a way to cause flat sheets of graphene to self-fold into 3D geometric shapes. The group explains how they prepared the sheets and then used heat to cause them to fold. The ability to create 3D objects from sheets of graphene can advance opportunities in fields like sensors, wearables and more.

In their work, the researchers developed a micro-patterning technique that leads to the flat graphene sheets bending along predesignated lines when heat is applied, causing the sheet to form into shapes. The new method not only preserves the intrinsic properties of the graphene, but it was also found that the creases can cause a band gap in the graphene, which can be extremely useful.

Graphene Flagship Partners RWTH Aachen University and AMO GmbH, both based in Germany, recently launched a new joint research center with a focus on efficiently bridging the gap between fundamental science and applications within graphene and related materials based electronics and photonics.

The five founding Principal Investigators of the Aachen Graphene & 2D-Materials Center are all members of the Graphene Flagship and share the vision of bringing graphene and related materials research from the lab into applications. The Center will help to turn the exciting properties of graphene and 2D-materials into true functions, making these materials not only fascinating for scientists but also serving society, as was explained.

A collaboration work by Purdue, the Chinese Lanzhou University and Harbin Institute of Technology, and the U.S. Air Force Research Laboratory has yielded a lightweight, flame-resistant and super-elastic composite shown to combine high strength with electrical conductivity and thermal insulation, suggesting potential applications from buildings to aerospace.

The composite material is made of interconnected cells of graphene sandwiched between ceramic layers. The graphene scaffold, referred to as an aerogel, is chemically bonded with ceramic layers using a process called atomic layer deposition. The team explained that graphene would ordinarily degrade when exposed to high temperature, but the ceramic imparts high heat tolerance and flame-resistance, properties that might be useful as a heat shield for aircraft. The light weight, high-strength and shock-absorbing properties could make the composite a good substrate material for flexible electronic devices. Because it has high electrical conductivity and yet is an excellent thermal insulator, it might be used as a flame-retardant, thermally insulating coating, as well as sensors and devices that convert heat into electricity, said associate professor in the School of Industrial Engineering at Purdue University.

Researchers from Vanderbilt University have developed an ultra-thin, graphene-based device that can be placed in fabrics of clothing to generate electricity from human motion.

Being 1/5000th the thickness of a human hair, the device can sense even the slightest human movement. The research team commented that compared to the other approaches designed to harvest energy from human motion, our method has two fundamental advantages. The materials are atomically thin and small enough to be impregnated into textiles without affecting the fabric's look or feel and it can extract energy from movements that are slower than 10 Hertz 10 cycles per second over the whole low-frequency window of movements corresponding to human motion.