Efficient and Directed Nano-LED Emission by a Complete Elimination of Transverse-Electric Guided Modes

Mei-Ling Kuo et al.

GaN based LEDs are an attractive light source for illumination due to their efficiency and long lifetime.

There is a need for comparc, bright and directed LED for emerging biosensing and bioimaging applications.

Today there are 2 types of structures that help us extract the trapped LED light. Thin films with back reflectors. And photonic crystals, one problem with photonic crystals is the guided modes that limit the efficiency. An alternative is to etch 2D hole through quantum wells, because QW is inside a photonic crystal and the guided modes may be eliminated due to a 2D photonic stop gap. The researches in this paper demonstrated a large increase in light extraction efficiency due to guided-mode reduction, an embedded emitter design and an ultraefficient light out-cupling by fundamental HE₁₁.

The LED sample was grown on a sapphire substrate. The multiquantum wells consisted of six periods of InGa/GaN sandwiched between a p-type GaN and N-type GaN.  The nanorod LED was produced using direct electron-beam-write.

The result is a LED of just some microns large and with diameter from 50 to 400nm. To study its efficiency it was coupled to a fiber and the luminescence signal was collected by a 40x objective.

Figure 1: NanoLEDs SEM and emission image.

The results are impressive, the got a 79% efficiency of light extraction.

This kind of nanoLEDs can be used in many applications, from biosensors to photonics, so we might hear a lot of them in the next years.

Sensitivity Limits and Scaling of Bioelectronic Graphene Transducers

Semiconducting nanomaterials are being intensively studied as active elements in bioelectronic devices, with the aim of improving spatial resolution. Yet, the consequences of size-reduction on fundamental noise limits, or minimum resolvable signals, and their impact on device design considerations have not been defined. Here, we address these key issues by quantifying the size-dependent performance and limiting factors 

of graphene (Gra) transducers under physiological conditions. We show that suspended Gra devices represent the optimal configuration for cardiac extracellular electrophysiology in terms of both transducer sensitivity, systematically ∼5× higher than substrate-supported devices, and forming tight bioelectronic interfaces. Significantly, noise measurements on freestanding Gra together with theoretical calculations yield a direct relationship between low-frequency 1/f noise and water dipole-induced disorders, which sets fundamental sensitivity limits for Gra devices in physiological media. As a consequence, a square-root-of-area scaling of Gra transducer sensitivity was experimentally revealed to provide a critical design rule for their implementation in bioelectronics

Bibliografía: 

Nano Lett., Article ASAP
DOI: 10.1021/nl401276n
Publication Date (Web): May 2, 2013
Copyright © 2013 American Chemical Society

Investigation of optoelectronic properties of N3 dye-sensitized TiO2 nano-crystals by hybrid methods: ONIOM (QM/MM) calculations

On the article, Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2 dye (N3) and some derivatives were investigated using Density Functional Theory (DFT) calculations in solution to elucidate the influence of the environment and substituted groups on electronic properties. Full geometry optimization and investigation of electronic properties of N3 dye and some derivatives were performed using DFT and HF calculations. The singlet ground state geometries were fully optimized at the B3LYP/3-21G** level of theory through the Gaussian 98 program. Based on the computed results, the optoelectronic properties are sensitive to chemical solvent environments. Moreover, the properties of anatase cluster (TiO2) models have been investigated, and N3 dyes have been adsorbed on TiO2 nano-particle with diprotonated states. The modified N3 dyes highly affected the electronic structure. This leads to significant changes in the adsorption spectra as compared to the N3 dyes. Through hybrid methods, the properties of interfacial electronic coupling of the combined system were estimated. The results of some combined systems showed that the electronic coupling, lowest lowest unoccupied molecular orbitals, and the TiO2 conduction band resided in the visible region.

The electronic version of this article is the complete one and can be found online at:http://www.inl-journal.com/content/3/1/26

BioElectronics Medical Device Technology

BioElectronics has developed a miniaturized wearable pulsed shortwave diathermy device. The concept is replacing short duration, high power treatments in the clinic delivered by a trained professional, with an easy to use, self-administered, very low power device that can be used 24 hours per day.

Pain is caused by inflammation, which is a swelling in the tissues of the body that then puts pressure on nerves causing pain. Chemical signals are also released by damaged cells in inflamed tissue that activate the nerves changing a chemical signal into an electrical impulse that causes pain for the body. Inflammation can be both acute, occurring immediately after an injury, or chronic (long lasting) inflammation which is unhealthy and can linger for months or years. Many diseases have been linked to chronic inflammation.

Para mas información: 

http://www.bielcorp.com/technology/

ECME 2013

Para información : 

Hay un congreso titulado ECME 2013, el cual habla de electrónica Molecular. Los invito a checar la información: 

It is our great pleasure to welcome you to the 12th European Conference on Molecular Electronics, held in London on 3 – 7 September 2013.

The European Conference on Molecular Electronics, ECME, has become the premier European Conference in the field, and ECME 2013 will belong to the prestigious series of biannual conferences previously organized in Italy (Padua, 1992), Germany (Kloster Banz, 1994), Belgium (Leuven, 1996), Great Britain (Cambridge, 1997), Sweden (Linköping, 1999), The Netherlands (Rolduc, 2001), France (Avignon, 2003), Italy (Bologna, 2005), France (Metz, 2007), Denmark (Copenhagen 2009) and Spain (Barcelona, 2011). ECME 2013 will take place at Imperial College’s Great Hall from September 3 – 7, 2013.

The conference will cover all areas related to organic electronics and photonics, including chemistry, physics, biology, materials science, nanoscience, device engineering and commercialisation, with sessions on the following themes:

- Interfaces

- Bioelectronics

- Light Harvesting and Energy

- Charge Transport

- Photophysics

- Spintronics

- Single Molecules

- Lighting and Photonics

Eight plenary speakers will present their latest research along with 24 invited speakers. The program will also include 16 invited short talks (predominantly by Early Career Scientists), contributed talks and two poster sessions, held at the London Science Museum’s Flight and Modern World Galleries, Conference dinner will be held in the Main Hall of London’s Natural History Museum.

Los invito a checar la información en el siguiente link: 

http://www.mmsconferencing.com/ecme13/

Locally Altering the Electronic Properties of Graphene by Nanoscopically Doping It with Rhodamine 6G

We show that Rhodamine 6G (R6G), patterned by dip-pen nanolithography on graphene, can be used to locally n-dope it in a controlled fashion. In addition, we study the transport and assembly properties of R6G on graphene and show that in general the π–π stacking between the aromatic components of R6G and the underlying graphene drives the assembly of these molecules onto the underlying substrate. However, two distinct transport and assembly behaviors, dependent upon the presence or absence of R6G dimers, have been identified. In particular, at high concentrations of R6G on the tip, dimers are transferred to the substrate and form contiguous and stable lines, while at low concentrations, the R6G is transferred as monomers and forms patchy, unstable, and relatively ill-defined features. Finally, Kelvin probe force microscopy experiments show that the local electrostatic potential of the graphene changes as function of modification with R6G; this behavior is consistent with local molecular doping, highlighting a path for controlling the electronic properties of graphene with nanoscale resolution.

Bibliografía:

Nano Lett., 2013, 13 (4), pp 1616–1621
DOI: 10.1021/nl400043q
Publication Date (Web): March 13, 2013
Copyright © 2013 American Chemical Society

Hot exciton dissociation in polymer solar cells

The standard picture of photovoltaic conversion in all-organic bulk heterojunction solar cells predicts that the initial excitation dissociates at the donor/acceptor interface after thermalization. Accordingly, on above-gap excitation, the excess photon energy is quickly lost by internal dissipation. Here we directly target the interfacial physics of an efficient low-bandgap polymer/PC60BM system. Exciton splitting occurs within the first 50 fs, creating both interfacial charge transfer states (CTSs) and polaron species. On high-energy excitation, higher-lying singlet states convert into hot interfacial CTSs that effectively contribute to free-polaron generation. We rationalize these findings in terms of a higher degree of delocalization of the hot CTSs with respect to the relaxed ones, which enhances the probability of charge dissociation in the first 200 fs. Thus, the hot CTS dissociation produces an overall increase in the charge generation yield.

Doc.: http://www.nature.com/nmat/journal/v12/n1/pdf/nmat3502.pdf

Grancini, Maiuri, Fazzi, Petrozza, Egelhaaf, Brida, & Cerullo. (09 de 12 de 2012). Hot exciton dissociation in polymer solar cells. Nature Materials, 29-33.