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

Quantum information: Computing with a single nuclear spin in silicon.

A research team, including members from the London Centre for Nanotechnology (LCN), has created the first working quantum bit based on the nuclear spin of a single phosphorus atom in silicon, opening the door for dramatically improved data processing in ultra-powerful quantum computers of the future.

A landmark paper published today in the journal Nature ("High-fidelity readout and control of a nuclear spin qubit in silicon"), describes how to write and read quantum information with record-setting accuracy using the nuclear spin, or magnetic orientation, of a phosphorus atom in a silicon transistor – similar to silicon chips used in modern electronics.

The nucleus of a phosphorus atom is a very, very weak magnet, and can be imagined as a compass needle that can point north or south. These north or south positions are equivalent to the zero and one of binary code, which governs classical computing. In this experiment, the researchers controlled the direction of the nucleus, in effect “writing” an arbitrary value onto its spin, and were then able to “read” the value out. They observed quantum oscillations of the spin between north and south, and all the quantum superpositions of those two directions – where the spin exists in both states simultaneously. Scanning electron micrograph of the active area of the qubit device, showing an implanted donor (donor as blue arrow), the single electron transistor (SET) and the short-circuit termination of the microwave line. The device is mounted in a dilution refrigerator with an electron temperature of,300 mK, and is subjected to static magnetic fields B0 between 1.0T and 1.8 T. B0 is oriented perpendicular to the short-circuit termination of the microwave line (solid orange single-ended arrow), which carries a current (solid double-ended arrow) and produces an oscillating magnetic field B1 (represented by the solid and dashed circles) perpendicular to the surface of the device. TG, top gate; PL, plunger gate; LB, left barrier; RB, right barrier. Fuente: Nanowerk (2013). Quantum information: Computing with a single nuclear spin in silicon. Recuperado el 6 de mayo de 2013, de http://www.nanowerk.com/news2/newsid=30267.php

Quantum nanoelectronics - An introduction to electronic nanotechnology and quantum computing.

The march of Moore's Law takes electronics to the molecular level, and indeed molecules are likely to be incorporated in future hybrid computer chips.This self-contained text guides students as well as professionals to the new possibilities presenting a treatment of Quantum Computing, a promising new approach which is based on Quantum Mechanics. This essential new title also covers topics which connect to alternative energy technology, for example solar cell design, photocatalytic conversion of water to hydrogen, and high performance batteries.

'Quantum Nanoelectronics' is the first textbook to handle important growth areas not covered in existing books, including adiabatic quantum computing, nanoelectronic aspects of ink-printed thin film solar cells, nanostructured electrodes, solar water splitting, and convenient hydrogen storage, thereby suggesting profitable new directions for nanoelectronic technology. Expanded tutorial coverage is provided for aspects of molecular electronics, from the basics of electronic conduction through chemical bonds to a sixteen-bit computing device as shown in the cover illustration. The interested reader, either a student or a professional interested in a new career direction, is encouraged to use simple theoretical models and to return to the entrepreneurial approach of the pioneers in the Moore's Law revolution.

Fuente: Nanowerk (2013). Quantum nanoelectronics - An introduction to electronic nanotechnology and quantum computing. Recuperado el 6 de mayo de 2013.

Improving AFM probe performance with a coat of graphene.

 Most of the research efforts on developing synthesis methods for graphene has focused on flat substrates. Some groups have reported the formation of free-standing 3D graphene-based macroscopic structures (see for instance "Making graphene 'bread' - leavening technique results in freestanding graphene oxide films"). However, direct growth of graphene layers on prepatterned substrates has remained elusive.In previous work, researchers led by James K. Gimzewski at UCLA have already shown that graphene grows continuously over large areas on different copper terraces without the underlying substrate morphology affecting the atomic arrangement of the grown material ("Continuity of Graphene on Polycrystalline Copper"). In new work, just reported in ACS Nano ("Graphene MEMS: AFM Probe Performance Improvement"), the team has applied this technique to grow graphene in prepatterned copper-coated substrates, and they apply this protocol for the fabrication of MEMS devices, in particular, atomic force microscope (AFM) probes."Conformal deposition of graphene on prepatterned substrates opens a multitude of device fabrication possibilities," writes Gimzewski. "One of them is the addition of different layers to the graphene, mostly by deposition, using the prepatterned substrate as a mold. This can result in hybrid 3D structures covered with graphene."In this new work, the team demonstrates the fabrication of polymeric AFM probes covered by monolayer graphene that had been previously deposited on a prepatterned substrate. Furthermore, they show how graphene improves the functionality of the probes by making them conductive and more resistant to wear.The fabrication steps utilized in the process are very standard and highly compatible with current silicon fabrication technology, which allows its application in any clean room or microtechnology laboratory. The entire process is based on the multiple spincoating, exposure, and development of SU-8 photoresist on a prestructured mold.

The team also tested the conductivity of the graphene layer on the AMP probe. The results show a conductive behavior, proving the continuity of the graphene layer on the AFM probe.


Fuente: Nanowerk (2013), Improving AFM probe performance with a coat of graphene. Recuperado el 6 de mayo de 2013, de http://www.nanowerk.com/spotlight/spotid=30346.php

Reducing electrical resistance in single-walled carbon nanotube networks: effect of the location of metal contacts and low-temperature annealing

Density control during the formation of 2-D networks of unsorted single-walled carbon nanotubes (SWNTs) allows their macroscopic electrical properties to be tuned from semiconductive to metallic conduction, even though they are composed of 1/3 metallic and 2/3 semiconductive nanotubes.  This allows their use in numerous new materials applications.  However, the resistance of such thin-films is generally high, dominated by the effects of inter-SWNT tunneling junctions, metal/SWNT contacts, sidewall defects, and the presence of residual dopants.  Initial studies have provided insight into the relative contributions of each of these contributors to the overall performance of SWNT networks in field-effect transistors.  Additionally, the effect of the structure of the metal/SWNT contact, and annealing temperature were investigated.  It was found that depositing the network on top of prefabricated metal contacts allowed up to a 13-fold reduction in resistance, much greater reproducibility in inter-network conductivity, and up to a 2-fold increase in on/off ratio.

Doc.: http://link.springer.com/content/pdf/10.1007%2Fs10853-011-6161-9.pdf

Zhang, Q., Vivhvhulada, P., B Shivareddy, S., & D. Lay, M. (2012). Density control during the formation of 2-D networks of unsorted single-walled carbon nanotubes (SWNTs) allows their macroscopic electrical properties to be tuned from semiconductive to metallic conduction, even though they are composed of 1/3 metallic an. J Mater Sci, 3233-3240

Biomolecular recognition with a sensitivity-enhanced nanowire transistor biosensor

El artículo publicado recientemente en Biosensors & Bioelectronics de “Biomolecular recognition with a sensitivity-enhanced nanowire transistor biosensor.” Se estudia el uso de una técnica de bottom-up, donde se han fabricado con éxito la superficie selectiva modificada (SSM) SiNW-FET con los receptores solamente en la superficie de detección SiNW. En este enfoque, la estrategia consistió en modificar los SiNWs con un enlazador químico de 3-aminopropiltrimetoxisilano (APTMS) antes de la fabricación fotolitográfica del dispositivo. Las moléculas de los modificadores de APTMS SiNWs sobrevivieron a los duros procesos fotolitográficos, incluyendo recubrimiento con resina fotosensible, lavado con disolvente orgánico, y recocido térmico. Estos SSM SiNW-FET también mostraron características eléctricas deseables tales como el contacto óhmico y de alta transconductancia. Usando el sistema de unión biotina-avidina, se demostró que el tiempo de respuesta más rápido y requisitos de muestra más pequeños de la SSM SiNW-FET, con respecto a la convencional AAM SiNW-FET, lo que muestra claramente que la restricción de la modificación de la superficie de la SiNW-FET mejora sustancialmente su sensibilidad de detección. En mediciones de afinidad de unión con SiNW-FET, las constantes de disociación (K d) de los complejos de ácido biotina-avidina y la dopamina-bórico se determinó que eran 15 ± 1 fM y 33 ± 8FM, respectivamente.


Li, B., Chen, C., Yang, W., Lin, T., Pan, C., & Chen, Y. (2013). Biomolecular recognition with a sensitivity-enhanced nanowire transistor biosensor. Biosensors & Bioelectronics, 45252-259. doi:10.1016/j.bios.2013.02.009
Artículo disponible en: http://www.iams.sinica.edu.tw/project/ytchen/files/biomolecular_recognition_with_a_sensitivity-enhanced_nanowire_transistor_biosensor.pdf

Ultrathin Two-Dimensional MnO2/Graphene Hybrid Nanostructures for High-Performance, Flexible Planar Supercapacitors

Recientemente los supercondensadores planares han atraído mucha atención debido a su diseño único y ventajoso para los dispositivos de almacenamiento de energía basados en nanomateriales 2D. Sin embargo, la mejora del rendimiento electroquímico de supercondensadores planas aún sigue siendo un gran desafío. En los últimos meses, Lele Peng, Xu Peng, Borui Liu, Changzheng Wu, Yi Xie y Guihua Yu publicaron “Ultrathin Two-Dimensional MnO2/Graphene Hybrid Nanostructures for High-Performance, Flexible Planar Supercapacitors” en él mostraron por primera vez una nuevo supercapacitor de alto rendimiento en el plano basado en nanoestructuras híbridas de cuasi-2D nanoláminas MnO2/grafeno ultrafinas. En concreto, las estructuras planas basadas en las nanoláminas δ-MnO2 integradas en las hojas de grafeno no sólo introducen más superficies electroquímicamente activas de absorción/desorción de iones de electrolitos, pero también traen interfaces adicionales en las zonas entre capas híbridas para facilitar el transporte de carga durante la carga/descarga de los procesos. El diseño estructural único para supercondensadores planos permite grandes mejoras de rendimiento en comparación sólo con los dispositivos de grafeno, exhibiendo altas capacidades específicas de los 267 F/g en la densidad de corriente de 0,2 A/g y 208 F/g en 10 A/g y la capacidad de velocidad excelente y ciclismo estabilidad con la retención de capacidad del 92% después de 7000 ciclos de carga/descarga. Por otra parte, la alta maleabilidad plana de supercondensadores planos permite una flexibilidad superior y robusta ciclabilidad, produciendo retención de capacitancia más del 90% después de 1000 horas de plegado/desplegado. Nanomateriales ultrafinos 2D representan una plataforma material prometedor para darse cuenta de los dispositivos de almacenamiento de energía planas altamente flexibles como el poder copias de seguridad para los dispositivos electrónicos estirables/flexible. 

Ultrathin Two-Dimensional MnO2/Graphene Hybrid Nanostructures for High-Performance, Flexible Planar Supercapacitors. Lele Peng, Xu Peng, Borui Liu, Changzheng Wu, Yi Xie, and Guihua Yu. Nano Letters Article ASAP

Artículo original isponible en: http://pubs.acs.org/doi/abs/10.1021/nl400600x?prevSearch=molecules%2Bfor%2Belectronics&searchHistoryKey=