Stretchable Electronics

Researchers from the McCormick School of Engineering have developed a design that allows electronics to bend and stretch to more than 200 percent of their original size. Today's previous technology maximum stretch capacity is 50 percent, so this is a major breakthrough in materials science and electronics which could bring applications in all fields, specially in the health sector.

The paper was published in 2012 in Nature Communications and the material's key point is the combination between a nanoporous polymer and liquid metal. According to Joseph Cummings, who is a professor from Korea Advanced Institute of Science and Technology, this level of stretchability would enable us to have medical devices integrated in the body. The team defeated the major concern of stretchable electronics which was loss of conductivity. They created a highly porous 3D structure using poly(dimethylsiloxane) that can stretch to three times its original size. Afterwards, they placed WGaIn (a liquid metal) inside the pores and this allows electricity to flow consistently even when the material is excessively stretched.

Reference:
Park, J; Wang, S; Li, M et al. (2012) Three-dimensional nanonetworks for giant stretchability in dielectrics and conductors. Nature Communications, 3, 916, DOI: 10.1038/ncomms1929.

Logic gates based on ion transistors

A doctoral student in Organic Electronics from Linkoping University in Sweden developed an integrated chemical chip following the work of his research team who had previously developed ion transistors for transport of ions and biomolecules. Last year, Klas Tybrandt succeeded in the combination of both transistor types into complementary circuits, in a similar way to traditional silicon-based electronics (CMOS).

The difference is that in chemical circuits, the charge carrier consists of chemical substances with different functions, so we could have the opportunity to control and regulate the signal paths of cells in the human body. An example would be to send signals to muscle synapses where the signalling system may not work. Magnus Berggren, leader of the Organic Electronics group says that their chip works with common signalling substances like acetylchloride.

As shown in the following image, this chemical chip can control the delivery of signalling substances in order to control the muscles, which activate when they come into contact with this substance.

The transistors for transport of ions and biomolecules were used by the researchers to control the delivery of acetylchloride to individual cells. Last year, Tybrandt developed chemical chips that also contain logic gates that allow the construction of all logical functions.

Reference:
Tybrandt, K; Forchheimer, R and Berggren, M. (2012) Logic gates based on ion transistors. Nature Communications, 3, 871. DOI: 10.1038/ncomms1869

G4-DNA. Nuevos materiales para electrónica molecular

Los autores Divir Rotem, Gennady Eidelshtein, Alexander Kotlyar y Danny Porath describen las propiedades únicas que tienen los ácidos nucléicos basados en G4 o cuartetos de guanina (ADN cuadriplexo).

Las aplicaciones se basan en la habilidad que tienen los G4 para estabilizar estructuras 3D bien definidas que exhiben una gran afinidad a una molécula objetivo. Sus propiedades estructurales son la base de sus aplicaciones en nanotecnología molecular y en electrónica. 

De acuerdo al texto, los ácidos nucléicos son los materiales más prometedores en este campo, específicamente, las estructuras G4 muestran una estabilidad mecánica extraordinaria y control de longitud a escala nanométrica. Un paso importante para aplicaciones respectivas es la integración de nanoestructuras basadas en G4 con ambientes técnicos como microelectrodos. Las técnicas más prometedoras están basadas en aproximaciones eléctricas, comola dielectroforesis, que se ha demostrado para la integración y subsecuente caracterización de estructuras individuales de G4. Estas técnicas también se han usado para la caracterización de propiedades eléctricas de ensambles de G4.

Referencia:

Rotem, D; Eidelshtein, G; Kotlyar, A y Porath, D. (2013) Novel Materials for Molecular Electronics - Synthesis and Characterization of Long G4-DNA. Guanine Quartets. DOI: 10.1039/9781849736954-00324

 

 

Alambrado y soldado químico para circuitos electrónicos de una molécula

La electrónica molecular tiene como uno de sus objetivos el uso de una sóla molécula como componente electrónico. Sin embargo, uno de los mayores obstáculos el lograr conexiones y alambrado exitoso en la molécula. Los investigadores han intentado conectar electrodos de metal directamente o con polímeros conductivos obteniendo resultados poco favorables.

De acuerdo con un artículo publicado en el Journal of the American Chemical Society, Yuji Okawa del Instituto Nacional de Ciencia de los Materiales en Japón, desarrolló junto con su equipo una nueva forma de unir y cablear moléculas individuales. Empezando por una película monomolecular de diacetileno en un substrato de grafito, se depositó ftalocianina para formar nanoclusters. Con el STM, aplicaron un voltaje de pulsos de la punta a la superficie de ftalocianina que inicia una polimerización en cadena del diacetileno, formando un nanoalambre polimérico que se enlaza a la molécula de ftalocianina.

Su objetivo será ahora probar estas moléculas de ftalocianina como diodos para crear un circuito electrónico de una sola molécula.

Referencia:

Okawa, Y et al. (2011) Chemical Wiring and Soldering toward All-Molecule Electronic Circuitry. J. Am. Chem. Soc, 133(21), 8227-8233. DOI: 0.1021/ja111673x

Reversible light induced conductance switching of asymmetric diarylethenes on gold

In this publication of Nanoscale, scientists explain the fabrication, surface and electronic structures of reversible photoswitches based on diarylethene embedded in a matrix of dodecanethiol on gold. The characterization was made with scanning tunneling microscopy for the analysis of the effect when the “on” state appears higher than the “off” state by several Ångstroms.

This is the abstract of the interesting experiment:

We report on the light-induced switching of conductance of a new generation of diarylethene switches embedded in an insulating matrix of dodecanethiol on Au(111), by using scanning tunneling microscopy (STM). The diarylethene switches we synthesize and study are modified diarylethenes where the thiophene unit at one side of the molecular backbone introduces an intrinsic asymmetry into the switch, which is expected to influence its photo-conductance properties. We show that reversible conversion between two distinguishable conductance states can be controlled via photoisomerisation of the switches by using alternative irradiation with UV (λ = 313 nm) or visible (λ > 420 nm) light. We addressed this phenomenon by using STM in ambient conditions, based on switching of the apparent height of the molecules which convert from 4–6 Å in their closed form to 0–1 Å in their open form. Furthermore, the levels of the frontier molecular orbital levels (HOMO and LUMO) were evaluated for these asymmetric switches by using Scanning Tunneling Spectroscopy at 77 K, which allowed us to determine a HOMO–LUMO energy gap of 2.24 eV.

Arramel, Thomas C. Pijper, Tibor Kudernac, Nathalie Katsonis, Minko van der Maas, Ben L. Feringa and Bart J. van Wees. (2013) Reversible light induced conductance switching of asymmetric diarylethenes on gold: surface and electronic studies. Nanoscale. DOI: 10.1039/C3NR00832K

Large tunable image-charge effects in single-molecule junctions

Researchers at Leiden University and Delft determined what makes electron transport in a single molecule so difficult thanks to a new measurement technique. One of the leaders of the team comments that the expectations they have are for large surfaces, like displays where there is a great advantage to having a single layer of molecules that can be p

ut together simply and cheaply.

This study offers insight into fundamental physical behavior of individual molecules. A molecule can act as a very sensitive sensor or nanotransistor between two electrodes, but the problem with the development of this type of molecular electronics is that it is really difficult to make electrical contact with a single molecule.

Researchers were able to create a new method for measuring conductivity in a molecule which is based on the mechanically driven break junction technique developed by Prof. Jan van Ruitenbeek. The paper explains that a freely suspended bridge in a metal conductor is subjected to mechanical pressure so it bends and breaks. Then, the molecule attaches itself to the two clean break surfaces. If they vary the distance between the electrodes, the image charge is impacted and researches can control the energy levels of the molecule, determining the role of image charge in numerical terms.

Reference:

Perrin M.L., Verzijl C.J.O., Martin C.A. et al. Large tunable image-charge effects in single-molecule junctions. Nature Nanotechnology, 2013. DOI: 10.1038/nnano.2013

Enhanced Charge Carrier Mobility in 2-D Material for Electronics

This paper is about a new two-dimensional nanomaterial that could revolutionize electronics developed at CSIRO and RMIT University. This material is made of layers of molybdenum oxide and has unique properties which encourage free flow of electrons at ultra-high speeds. The researches adapted graphene to create a new conductive nanomaterial. 

Even though graphene supports high-speed electrons, its physical properties prevent it from being used for high-speed electronics, so this new material was also made up of layered sheets but within these layers, electrons are able to zip through at high speeds with minimal scattering.

Profesor Kourosh Kalantarzadeh from RMIT said the researchers were able to remove the "road blocks" that could obstruct the electrons and he also mentioned that instead of scattering when they hit road blocks, as they would in conventional materials, they can simply pass through this new material and get through the structure faster.

Scientists used a process known as "exfoliation" to create layers 11 nm thick and manipulated the material to convert it into a semiconductor, then nanoscale transistors were created using molybdenum oxide. The mobility values achieved were more than 1000 cm2/Vs, which exceedes the current industry standard for low dimensional silicon.

Reference:

Balendhran S., Deng J., Zhen Ou J et al. Enhanced Charge Carrier Mobility in Two-Dimensional High Dielectric Molybdenum Oxide. Advanced Materials, 2013. DOI: 10.1002/adma.201203346

Nanodevices for Energy-Efficient Electronics

Scientists from the National University of Singapore (NUS) and University College Cork fabricated nanodevices for energy-efficient electronics. Switching efficiency was improved obtaining ten times higher results by changing just one carbon atom in the molecules of the device. The possible applications of this device would be providing new ways to avoid overheating in laptops, tablets and mobile phones and also to aid in electrical stimulation of tissue repair for wound healing.

This paper was featured in the February edition of Nature Nanotechnology and the research team was led by Dr. Damien Thompson and Prof. Chris Nijhus, who created the devices based on molecules that act as electrical valves or diode rectifiers. Their results have shown that by adding one carbon atom, the device's performance increases by a factor of ten and they hope to create a wide range of new components for electronic devices.

One interesting finding by these researchers is that molecules with an odd number of carbon atoms stand straighter than the ones with an even number. A tightly packed assemble of straight molecules packed together, were aligned on metal electrode surfaces and were found to be free of defects.

Dr. Thompson explains that their study shows how Van der Waals effects present in every molecular scale device can be turned to optimize the performance of the device by creating tighter seals between molecules. The molecular device is illustrated in the following image.

Reference:
- Nerngchamning N., Yuan L., Qi D,. Li J., Thompson D., Nijhus C.A. The role of van der Waals forces in the performance of molecular diodes. Nature Nanotechnology, 2013. DOI: 10.1038/nnano.2012.238.

Electrónica Plástica. Alineando Polímeros

Ingenieros de la Universidad de Michigan en conjunto con la compañía Samsung de Corea, desarrollaron un método para alinear un tipo de polímeros semiconductores, lo que fue comprobado por estudios de difracción de rayos-X y sugiere que es el principio de una electrónica plástica que se puede pintar, económica y "verde".  

De acuerdo con el científico de materiales Jingsang Kim, uno de los autores de este artículo de Nature Materials, "Esta es la primera capa de película delgada altamente alineada, conductora, para electrónica plástica de alto desempeño y que puede ser pintada". Los autores explican que desarrollaron el principio de un diseño molecular para hacer cristales líquidos liotrópicos de polímeros conjugados que son diferentes a los polímeros conjugados convencionales. Debido a su propiedad de cristal líquido liotrópico, estos polímeros conjugados tienen buenas propiedades de ensamblaje y al mismo tiempo, una buena movilidad.

El equipo de la Universidad de Michigan ha usado sus películas delgadas para crear un transistor simple pero funcional. Actualmente están desarrollando un método versátil de fabricación para realizar electrónica plástica de alto desempeño en varias escalas, desde nanómetros hasta metros.

Referencia: 

Kim BG, Jeong EJ, Chung JW, Seo S, Koo B, Kim J. A molecular design principle of lyotropic liquid-crystalline conjugated polymers with directed alignment capability for plastic electronics. Nature Materials, 2013.

High electron mobility in nano-composite thin film transistors

Researchers from Cambridge University and the London Centre for Nanotechnology have demonstrated extremely high electron mobility in nano-composite thin film transistors using zinc oxide and organic semiconductors.

Organic semiconductors  are often limited by their lower field-effect mobility, with high-performance n-type devices proving a particular challenge. Professor Arokia Nathan's work uses a technique for combining zinc oxide (ZnO) nanostructures synthesized using vapor phase deposition with organic semiconductors to create nano-composite thin film transistors with the highest reported electron field-effect mobility in solution processed devices.

A dispersion of ZnO nanorods in an n-type organic semiconductor ([6, 6]-phenyl-C61-butyric acid methyl ester, PCBM) are shown to enhance the electron field effect mobility by as much as a factor or 40 from the pristine state. The results although preliminary, show a highly promising enhancement for realization of high-performance solution-processable n-type organic TFTs.

 More information available from:

Li FM, Nathan A, Dalal S, et al. Zinc Oxide Nanostructures and High Electron Mobility Nanocomposite Thin Film Transistor. IEEE Transactions on Electron Devices. 2008:55(11):3001-11. DOI: 10.1109/TED.2008.2005180