Nanostructured Channel for Improving Emission Efficiency of Hybrid Light-Emitting Field-Effect Transistors

We report on the mechanism of enhancing the luminance and external quantum efficiency (EQE) by developing nanostructured channels in hybrid (organic/inorganic) light-emitting transistors (HLETs) that combine a solution-processed oxide and a polymer heterostructure. The heterostructure comprised two parts: (i) the zinc tin oxide/zinc oxide (ZTO/ZnO), with and without ZnO nanowires (NWs) grown on the top of the ZTO/ZnO stack, as the charge transport layer and (ii) a polymer Super Yellow (SY, also known as PDY-132) layer as the light-emitting layer. Device characterization shows that using NWs significantly improves luminance and EQE (≈1.1% @ 5000 cd m–2) compared to previously reported similar HLET devices that show EQE < 1%. The size and shape of the NWs were controlled through solution concentration and growth time, which also render NWs to have higher crystallinity. Notably, the size of the NWs was found to provide higher escape efficiency for emitted photons while offering lower contact resistance for charge injection, which resulted in the improved optical performance of HLETs. These results represent a significant step forward in enabling efficient and all-solution-processed HLET technology for lighting and display applications

Low-loss, Low-cost, High Refractive Index Machinable Ceramic For THz Optical Components

The properties of a machinable, high refractive index, low-loss, low-cost material are investigated. Both a THz-TDS and a Vector Network Analyzer (0.75-1.1 THz) are used to characterize the material and precisely obtain the absorption coefficient. Fresnel lenses are fabricated with a micro milling system to demonstrate the shaping capabilities of the aluminium nitride based ceramic

Field imaging near to the surface of terahertz reflective optics using a vector network analyzer

A vector network analyzer-based quasi-optical measurement system that is suitable for mapping electric field intensity and phase near to the surface of terahertz reflective optics is presented. The system uses a fixed five parabolic mirror and transmitter/receiver head arrangement that has the benefit of requiring only the sample to be swept during measurement. The system has been tested with a micromilled aluminum zone plate reflector used as an exemplar structure. The measured focal point of the zone plate reflector, at its designed frequency of 1 THz, is shown to correspond well to both finite difference time-domain simulations and analytical theory

Transparent gold nanowire electrodes

Abstract—Transparent electrodes are used to provide electrical contacts to the active layers of opto-electronic devices such as organic light emitting diodes, flat panel displays and solar cells. These electrodes should possess high optical transparency and low sheet resistance. Traditionally, tin doped indium oxide (ITO) is used for this purpose. Unfortunately, there is increasing concern over the availability of indium leading to a rapid increase in prices. Additionally, ITO is very fragile causing lifetime and yield problems with touch screens and flexible devices. One possible alternative to ITO is an electrode which consists of metal nanowires and is either lithographically defined or dispensed from solution. This paper describes lithographically patterned transparent gold nanowire electrodes which exhibit sheet resistances between 3 and 30 Ohm □-1 for transmittances of 83 and 95% respectively

Optimisation en scanographie pédiatrique

The Department of radiology of the Hospital Trousseau (Paris) and IRSN have initiated in 2007 a detailed analysis of doses delivered to children undergoing CT examinations. This study involved three types of CT examination (chest, abdomen + pelvis and petrosal bones) and three age groups (new born to 1 year, 4 to 6 years and 9 to 11 years). A first analysis of doses was realised on a six months period of activity at the end of 2006. It stated that the standardized protocols of the scanner, that satisfied the relevant dosimetric requirements, were regularly modified by the operator to acquire the CT slides: the practice among the department was heterogeneous and the mean values of DLP were systematically higher than those recommended. The whole staff of the department has been informed of these first results and made aware of optimization of delivered doses. The standardized protocols of the scanner have been optimized. A second analysis, similar to the first one, was conducted in 2008. It showed the harmonization of the practice among the department, a significant decrease in the mean DLP (-50% for chest CT) and the respect for the dosimetric requirements for the three examinations concerned. © EDP Sciences, 2010.En 2007, le service de radiologie de l’Hôpital Trousseau (Paris) et l’IRSN ont initié une analyse détaillée des doses délivrées lors d’examens scanographiques chez l’enfant. Cette étude a porté sur trois types d’examen (thorax, abdomen-pelvis et rochers) et trois tranches d’âge (nouveau né à 1 an, 4 à 6 ans et 9 à 11 ans). Une première analyse des doses a été réalisée a posteriori sur l’activité du second semestre 2006. Elle a montré que les protocoles d’acquisition du scanner, qui satisfaisaient aux recommandations dosimétriques en vigueur, étaient mal respectés dans le service : les pratiques étaient hétérogènes et les valeurs moyennes de PDL supérieures aux recommandations. Après ces premiers résultats, une action de sensibilisation à l’optimisation des doses a été menée auprès du personnel et les protocoles d’acquisition du scanner ont été optimisés. L’analyse dosimétrique reprise en 2008 suivant le schéma de 2006 a montré une harmonisation des pratiques au sein du service, une diminution significative des PDL moyens (-50 % par exemple en scanographie thoracique) et le respect systématique des recommandations dosimétriques pour les trois examens étudiés

A simplified model to estimate thermal resistance between carbon nanotube and sample in scanning thermal microscopy

Scanning thermal microscopy (SThM) is an attractive technique for nanoscale thermal measurements. Multiwalled carbon nanotubes (MWCNT) can be used to enhance a SThM probe in order to drastically increase spatial resolution while keeping required thermal sensitivity. However, an accurate prediction of the thermal resistance at the interface between the MWCNT-enhanced probe tip and a sample under study is essential for the accurate interpretation of experimental measurements. Unfortunately, there is very little literature on Kapitza interfacial resistance involving carbon nanotubes under SThM configuration. We propose a model for heat conductance through an interface between the MWCNT tip and the sample, which estimates the thermal resistance based on phonon and geometrical properties of the MWCNT and the sample, without neglecting the diamond-like carbon layer covering the MWCNT tip. The model considers acoustic phonons as the main heat carriers and account for their scattering at the interface based on a fundamental quantum mechanical approach. The predicted value of the thermal resistance is then compared with experimental data available in the literature. Theoretical predictions and experimental results are found to be of the same order of magnitude, suggesting a simplified, yet realistic model to approximate thermal resistance between carbon nanotube and sample in SThM, albeit low temperature measurements are needed to achieve a better match between theory and experiment. As a result, several possible avenues are outlined to achieve more accurate predictions and to generalize the model

Negative refracting materials at THz frequencies.

We demonstrate here, for the first time, the construction of artificial materials, which theoretically possess two separate pass-bands utilizing the difference between positive and negative refraction in the terahertz frequency regime. Experimental testing of these devices is currently being undertaken using both broadband pulsed sources and narrow frequency quantum cascade lasers

Nanostructured Channel for Improving Emission Efficiency of Hybrid Light-Emitting Field-Effect Transistors

We report on the mechanism of enhancing the luminance and external quantum efficiency (EQE) by developing nanostructured channels in hybrid (organic/inorganic) light-emitting transistors (HLETs) that combine a solution-processed oxide and a polymer heterostructure. The heterostructure comprised two parts: (i) the zinc tin oxide/zinc oxide (ZTO/ZnO), with and without ZnO nanowires (NWs) grown on the top of the ZTO/ZnO stack, as the charge transport layer and (ii) a polymer Super Yellow (SY, also known as PDY-132) layer as the light-emitting layer. Device characterization shows that using NWs significantly improves luminance and EQE (≈1.1% @ 5000 cd m–2) compared to previously reported similar HLET devices that show EQE < 1%. The size and shape of the NWs were controlled through solution concentration and growth time, which also render NWs to have higher crystallinity. Notably, the size of the NWs was found to provide higher escape efficiency for emitted photons while offering lower contact resistance for charge injection, which resulted in the improved optical performance of HLETs. These results represent a significant step forward in enabling efficient and all-solution-processed HLET technology for lighting and display applications