Query: On-nanowire spatial bandgap design for white light emission

Candidate papers:

abstract: We demonstrated a substrate moving vapor liquid solid (VLS) route for growing composition gradient ZnCdSSe alloy nanowires. Relying on temperature selected composition deposition along their lengths, single tricolor ZnCdSSe alloy nanowires with engineerable band gap covering the entire visible range were obtained. The photometric property of these tricolor nanowires, which was determined by blue green and red color emission intensities, can be in turn controlled by their corresponding emission lengths. More particularly, under carefully selected growth conditions, on nanowire white light emission has been achieved. Band gap engineered semiconductor alloy nanowires demonstrated here may find applications in broad band light absorption and emission devices.
author_names: Zongyin Yang

Jinyou Xu

Pan Wang

Xiujuan Zhuang

Anlian Pan

Limin Tong
title: On nanowire spatial band gap design for white light emission.
venue: Nano letters
year: 2011

abstract: The white light LEDs of today are usually based on a blue LED and a phosphor, converting the blue light to longer wavelengths. While these phosphor converted LEDs are extremely efficient compared to incandescent light or fluorescent light, there is still plenty of room for improvement. In the conversion between blue light and light of lower energy approximately 25 45 of the radiant power is lost as heat [1] A more efficient solution is to use white light sources based on RGB LEDs. Since these LEDs do not require phosphor conversion the efficiency has potential to be much higher compared to today's white light sources. High efficiency blue LEDs are based on an InGaN quantum well and barrier layers of GaN. By altering the In content in InGaN the bandgap can be tuned for emission from UV to red light, which makes the material system a good candidate to be used in fabrication of RGB LEDs. In green and red LEDs the In content in the quantum well is higher compared to blue LEDs which gives rise to more strain between the quantum well and GaN barrier layers. The strain induces piezoelectric charges which spatially separates electrons and holes in the quantum well leading to lower radiative recombination efficiency (quantum confined Stark effect) The use of InGaN barrier layers would thus enable fabrication of red and green LEDs of higher efficiency, but the main problem is that it is very hard to synthesise thick layers of InGaN with high material quality. The poor crystal quality is partly due to strain induced dislocations and partly due to phase separation and In content fluctuations [2] which will reduce the efficiency of the device [3] However it has been shown that thick InGaN layers of high material quality can be synthesised in MOCVD grown nanocrystals of InGaN. These nanocrystals, or platelets (truncated pyramids with a flat c plane) can be used as dislocation free substrates for growth of LEDs, which enables the use of InGaN barrier layers instead of GaN. The strain between the quantum well and barriers in In rich quantum wells is thus reduced which makes it possible to fabricate red and green LEDs of high efficiency. The reduced strain between the barriers and the quantum well leads to a decrease of the quantum confined Stark effect and therefore potential of higher efficiency LEDs. In this thesis the potential of nano RGB LEDs based on InGaN and GaN platelets is evaluated and the results are promising. During the project an LED device design for LEDs based on (In)GaN platelets was developed, characterised (electrically and electroluminescence) and optimised (spacer layer thicknesses, contact materials) The implemented device design works well. Parasitic currents outside the active area are negligible and the devices show much improved stability compared to previous designs. The device design is based on parallel connected platelets in the device area and lifted bond pads outside of the device area. The bond pads are lifted by a thick spacer layer (resist) in order to enable easy bonding and avoid shunt current. A range of devices of different size were studied, from single platelets <1mm) to tens of thousands of platelets (400mmx400mm) and the crystal homogeneity is shown to be very important for the device performance. The current rectification is excellent for single platelet devices but decreases with increased number of platelets in the device. While work lies ahead in improving homogeneity, efficiency and device design, this technology is unique in achieving high quality material with very high In content and an extremely small light emission area. Not only are these structures interesting for high efficiency RGB illumination, but also for microLED displays potentially with pixel size an order of magnitude smaller than what is possible today.
author_names: Patrik Olausson
title: Fabrication and characterisation of RGB LEDs based on nanowire technology
year: 2019

abstract: III NITRIDE NANOWIRE LIGHT EMITTING DIODES: DESIGN AND CHARACTERIZATION by Dipayan Datta Choudhary III nitride semiconductors have been intensively studied for optoelectronic devices, due to the superb advantages offered by this materials system. The direct energy bandgap III nitride semiconductors can absorb or emit light efficiently over a broad spectrum, ranging from 0.65 eV (InN) to 6.4 eV (AlN) which encompasses from deep ultraviolet to near infrared spectrum. However, due to the lack of native substrates, conventional III nitride planar heterostructures generally exhibit very high dislocation densities that severely limit the device performance and reliability. On the other hand, nanowire heterostructures can be grown on lattice mismatched substrates with drastically reduced dislocation densities, due to highly effective lateral stress relaxation. Nanowire light emitting diodes (LEDs) with emission in the ultraviolet to visible wavelength range have recently been studied for applications in solid state lighting, flat panel displays, and solar blind detectors. In this thesis, investigation of the systematic process flow of design and epitaxial growth of group III nitride nanoscale heterostructures was done. Moreover, demonstration of phosphor free nanowire white LEDs using InGaN/AlGaN nanowire heterostructures grown directly on Si(111) substrates by molecular beam epitaxy was made. Full color emission across nearly the entire visible wavelength range was realized by controlling the In composition in the InGaN active region. Strong white light emission was recorded for the unpackaged nanowire LEDs with an unprecedentedly high color rendering index of 98. Moreover, LEDs with the operating wavelengths in the ultraviolet (UV) spectra, with emission wavelength in the range of 280 320 nm (UV B) or shorter wavelength hold tremendous promise for applications in phototherapy, skin treatments, high speed dissociation and high density optical recording. Current planar AlGaN based UV B LEDs have relatively low quantum efficiency due to their high dislocation density resulted from the large lattice mismatch between the AlGaN and suitable substrates. In this study, associated with the achievement of visible LEDs, the development of high brightness AlGaN/GaN nanowire UV LEDs via careful design and device fabrication was shown. Strong photoluminescence spectra were recorded from these UV B LEDs. The emission peak can be tunable from 290 nm to 320 nm by varying the Al content in AlGaN active region which can be done by optimizing the growth condition including Al/Ga flux ratio and also the growth temperature. Such visible to UV B nanowire LEDs are ideally suited for future smart lighting, full color display, phototherapy and skin treatments applications. III NITRIDE NANOWIRE LIGHT EMITTING DIODES: DESIGN AND CHARACTERIZATION by Dipayan Datta Choudhary A Thesis Submitted to the Faculty of New Jersey Institute of Technology and in Partial Fulfillment of the Requirements for the Degree of Masters of Science in Energy and Power Systems Helen and John C. Hartmann Department of Electrical and Computer Engineering
author_names: Dipayan Datta Choudhary
title: III nitride nanowire light emitting diodes: design and characterization
year: 2017

abstract: We analyze epitaxially grown InGaN/GaN dot in a wire heterostructures to relate growth and design properties to trends seen in photoluminescence (PL) and resonance Raman spectra. Temperature dependent PL measurement of these dot in a wire heterostructures illustrate an expected decrease in integrated PL emission and an unusual narrowing of peak width with increasing temperature. Information extracted from Resonance Raman spectra was utilized in a time dependent model to analyze and to simulate PL spectra. These spectra were found to be in good agreement with the experimental PL data and provided insight into the broadening mechanisms affecting the samples. PL measurements were taken as a function of position on the sample and radial variation of peak energies was observed. This variation was attributed to the radial temperature gradient present during nanowire growth. These additional characteristics of the nanowire heterostructures will allow for increased understanding of these systems potentials for ap.
author_names: Yousef Kamali

Brenna R Walsh

John B Mooney

Hieu Pham Trung Nguyen

Colin-Nadeau Brosseau

Richard Leonelli

Zetian Mi

Patanjali Kambhampati
title: Spectral and spatial contributions to white light generation from InGaN/GaN dot in a wire nanostructures
year: 2013

abstract: The design of highly emissive and stable blue emitters for organic light emitting diodes (OLEDs) is still a challenge, justifying the intense research activity of the scientific community in this field. Recently, a great deal of interest has been devoted to the elaboration of emitters exhibiting a thermally activated delayed fluorescence (TADF) By a specific molecular design consisting into a minimal overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) due to a spatial separation of the electron donating and the electron releasing parts, luminescent materials exhibiting small S1 T1 energy splitting could be obtained, enabling to thermally upconvert the electrons from the triplet to the singlet excited states by reverse intersystem crossing (RISC) By harvesting both singlet and triplet excitons for light emission, OLEDs competing and sometimes overcoming the performance of phosphorescence based OLEDs could be fabricated, justifying the interest for this new family of materials massively popularized by Chihaya Adachi since 2012. In this review, we proposed to focus on the recent advances in the molecular design of blue TADF emitters for OLEDs during the last few years. Introduction Since the pioneering works of Tang and VanSlyke in 1987 [1] organic light emitting diodes (OLEDs) have known major evolutions of their structures, not only of the device stacking but also of the materials composing the different layers [2] The interest of both the scientific and industrial communities for organic electroluminescent devices is supported by the fact that Beilstein J. Org. Chem. 2018, 14, 282 308. 283 Figure 1: Radiative deactivation pathways existing in fluorescent, phosphorescent and TADF materials. OLEDs have been identified as the key elements for the fabrication of the next generation display and lighting technology [3] Notably, lightweight and thin devices can be fabricated onto flexible substrates, favouring the penetration of OLEDs in these two markets. With the aim at reducing the global energy demand on Earth, two parameters govern the power consumption of OLEDs, namely the quantum yield of luminescence of the light emitting material and the device stacking. Indeed, the driving voltage of OLEDs is highly sensitive to the thickness of the different layers, the charge transport ability of the materials but also to their energy levels. By minimizing the energy gaps between adjacent layers and facilitating charge injection from the electrodes, the injection and transportation of holes and electrons can be realized at lower operating voltages. The second parameter concerns the light emitting ability of the emitter, which is directly related to the nature, and the photoluminescence quantum yield (PLQY) of the emitter. Based on spin statistics, upon electrical excitation, singlet and triplet excitons are formed in a 1:3 ratio [4] In the case of fluorescent materials, only singlet excitons can be utilized for light emission, limiting the internal quantum efficiency (IQE) of fluorescent OLEDs to 25% Conversely, phosphorescent materials can both harvest singlet and triplet excitons for emission by intersystem crossing (ISC) enabling to reach a theoretical IQE of 100% for phosphorescent OLEDs [5] As drawback, triplet emitters are transition metal complexes mostly based on iridium, platinum and osmium and the scarcity of these metals on Earth, their toxicity and high cost make these materials unsuitable candidates for a mass production of OLEDs [6] However, efforts have also been carried out to incorporate emitters comprising less toxic metals, providing mitigate results when tested in devices [7,8] In 2012, a breakthrough has been obtained by the Adachi group who developed purely organic materials capable to harvest both singlet and triplet excitons for emission [9] This new family of light emitting materials capable to compete with the well established triplet emitters and displaying a similar efficiency in devices by developing a new emission mechanism was immediately termed as the third generation of OLEDs emitters that consists of thermally activated delayed fluorescence (TADF) emitters. As specificity, these materials can thermally repopulate the singlet state from the triplet state by reverse intersystem crossing (RISC) leading to an increase of the luminescence intensity. From the OLEDs viewpoint, TADF emitters behave by harvesting both singlet and triplet excitons for radiative transition, excepted that the emission occurs from the singlet state and not from the triplet state (as observed for metal complexes) and that the triplet triplet annihilation commonly observed with phosphorescent OLEDs [10] can be drastically reduced (see Figure 1) TADF materials can also be metal free, addressing the fabrication cost and environmental issues. Therefore, TADF emitters retain the high efficiency of the second generation of emitters (triplet emitters) the stability of the first generation of fluorescent materials while eliminating the different problems observed with the two previous generations: triplet triplet annihilation and low device stability for phosphorescent OLEDs, low IQE for fluorescent OLEDs. To get full color displays or white light OLEDs, the combination of the three primary colors red green blue (RGB) is indispensable. At present, highly emissive and stable blue emitters are actively researched [11 16] Several points justify the low availability of highly efficient blue materials. First, due to their large bandgaps (DE 3 eV) charge injection from the adjacent Beilstein J. Org. Chem. 2018, 14, 282 308. 284 layers is often difficult, requiring devices to be operated at high voltages [17] Second, and still related to their wide bandgaps, the probability to transfer an electron from the ground to the excited stable state is considerably reduced, providing materials displaying PLQY greatly reduced compared to that observed for the other colors [18,19] To end, the propensity of blue emitters to rapidly degradate upon device operation is well established, resulting in a fast and irreversible color shift [20,21] In this context, TADF blue emitters have been identified as promising candidates to address the color purity, quantum efficiency and long term device stability issues. Due to the enthusiasm of the scientific community for TADF emitters, this research field evolves extremely rapidly. In this review, a summary of the strategies developed during the last years to design organic blue TADF emitters is presented. It has to be noticed that the values of EQEs reported in the different tables correspond to the maximum EQEs, because many articles do not give sufficient data concerning EQE at the practically relevant luminance of 100 cd/m2. Review 1. Molecular design rules to produce a delayed fluorescence The efficiency of OLEDs is intimately related to the ability of the light emitting materials to convert a maximum of injected charges into photons. To optimize this, the TADF process is the most promising strategy as it allows converting the generated and lost triplet excitons of the classical fluorescent materials into emissive singlets. By efficiently upconverting the triplet excitons from the triplet (T1) to the singlet state (S1) the intrinsic limitation of 25% imposed to fluorescent materials by the 1:3 singlet triplet ratio can be overcome and an ultimate IQE of 100% can be realized with TADF materials. To promote the endothermic RISC, the energy gap between S1 and T1 (DEST) plays a key role and should be as small as possible. From a molecular design viewpoint, DEST can be drastically reduced if the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are spatially separated, what can be obtained by a suitable steric hindrance that introduces an internal twist and interrupts the p conjugation but also by a sufficient distance between the electron donating and the electron accepting moieties [22 25] In the design of TADF materials, it should be mentioned the major importance of the spin orbit vibronic coupling, in addition to the small DEST. Indeed, a small DEST is not sufficient to ensure for a TADF material an efficient RISC which is a vibronically coupled, spin orbit coupling process with the involvement of the charge transfer state. To remain efficient, the spin orbit coupling should still have a significant value, even if the separation of the HOMO and LUMO wavefunctions remain a requirement to minimize DEST. At present, systematic investigations examining the correlation between the spin orbit coupling and RISC are stil l scarce [26 29] Considering that the singlet triplet energy splitting is one of the key elements for controlling the RISC efficiency, that the dihedral angle between the donor and the acceptor can be difficultly anticipated and that an overlap of both the HOMO/LUMO energy levels could adversely affect the color purity and DEST, it has to be noticed that the photophysical properties and the geometry of molecules that are suspected to be TADF emitters are often investigated by theoretical calculations prior to synthesis, optimizing the chance to get suitable energy levels and the desired DEST. This strategy was notably applied to the design of TADF blue emitters containing triarylboron accepting units. Besides, as we will see in this review, the design of a good TADF material by optimizing its structure by theoretical calculations is not sufficient to ensure the fabrication of highly emissive OLEDs. As observed for phosphorescent emitters, optimization of the device stacking, an appropriate choice of the host as well as the materials in the adjacent layers, an adequate dopant concentration, and the efficient confinement of excitons within the emissive layer are primordial parameters to elaborate high performance OLEDs while maintaining the color purity [30] Due to the
author_names: Eli Zysman-Colman
title: Recent advances in materials for organic light emitting diodes
venue: Beilstein journal of organic chemistry
year: 2018

abstract: S. Xu C. Xu Y. Liu Y. F. Hu R. S. Yang Q. Yang Prof. Z. L. Wang School of Materials Science and Engineering Georgia Institute of Technology Atlanta, Georgia, 30332 0245 (USA) E mail: zlwang@gatech.edu J. H. Ryou H. J. Kim Z. Lochner S. Choi Prof. R. Dupuis School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta, Georgia, 30332 0245 (USA) ZnO based light emitting diodes (LEDs) have been considered as a potential candidate for the next generation of blue/ near UV light sources, 1 due to a direct wide bandgap energy of 3.37 eV, a large exciton binding energy of 60 meV at room temperature, and several other manufacturing advantages of ZnO. 2 While the pursuit of stable and reproducible p ZnO is still undergoing, 3,4 heterojunctions of n ZnO and p GaN are employed as an alternative approach in this regard by considering the similar crystallographic and electronic properties of ZnO and GaN. 5 7 Compared with the thin fi lm/thin fi lm LEDs, 5,6 8 which may suffer from the total internal refl ection, n ZnO nanowire/p GaN thin fi lm heterostructures are utilized in order to increase the extraction effi ciency of the LEDs by virtue of the waveguiding properties of the nanowires. 9 11 But in all of these cases, the n ZnO nanowires are randomly distributed on the substrate, which largely limits their applications in high performance optoelectronic devices. Here in this work, we demonstrate the capability of controlling the spatial distribution of the blue/near UV LEDs composed of position controlled arrays of n ZnO nanowires on a p GaN thin fi lm substrate. The device was fabricated by a conjunction of low temperature wet chemical methods and electron beam lithography (EBL) The EBL could be replaced by other more convenient patterning techniques, such as photolithography and nanosphere lithography, rendering our technique low cost and capable of scaling up easily. Under forward bias, each single nanowire is a light emitter. By Gaussian deconvolution of the emission spectrum, the origins of the blue/nearUV emission are assigned particularly to three distinct electronhole recombination processes. By virtue of the nanowire/thin fi lm heterostructures, these LEDs give an external quantum effi ciency of 2.5% This approach has great potential applications in high resolution electronic display, optical interconnect, and high density data storage. The design of the LED is shown in Figure 1a Ordered ZnO nanowire arrays were grown on p GaN (Figure 1 b d) 12 14
author_names: Sheng Xu

Chen Xu

Yuehan Liu

Youfan Hu

Rusen Yang

Qing Yang

Jae-Hyun Ryou

Hee Jin Kim

Zachary Lochner

Suk Choi

Russell D Dupuis

Zhong Lin Wang
title: Ordered nanowire array blue/near UV light emitting diodes.
venue: Advanced materials
year: 2010

abstract: Layered assembly structures composed of nanomaterials, such as nanocrystals, have attracted considerable attention as promising candidates for new functional devices whose optical, electromagnetic and electronic behaviours are determined by the spatial arrangement of component elements. However, difficulties in handling each constituent layer in a material specific manner limit the 3D integration of disparate nanomaterials into the appropriate heterogeneous electronics. Here we report a pick and place transfer method that enables the transfer of large area nanodot assemblies. This solvent free transfer utilizes a lifting layer and allows for the reliable transfer of a quantum dot (QD) monolayer, enabling layer by layer design. With the controlled multistacking of different bandgap QD layers, we are able to probe the interlayer energy transfer among different QD monolayers. By controlling the emission spectrum through such designed monolayer stacking, we have achieved white emission with stable optoelectronic properties, the closest to pure white among the QD light emitting diodes reported so far.
author_names: Tae-Ho Kim

Dae-Young Chung

Jiyeon Ku

Inyong Song

Soohwan Sul

Dae-Hyeong Kim

Kyung-Sang Cho

Byoung Lyong Choi

Jong Min Kim

Sungwoo Hwang

Kinam Kim
title: Heterogeneous stacking of nanodot monolayers by dry pick and place transfer and its applications in quantum dot light emitting diodes.
venue: Nature communications
year: 2013

abstract: Zinc oxide (ZnO) nanostructures are generating significant interest due to unique characteristics that make them good candidates for UV optoelectronic applications such as biosensors and resonators. These properties are due to the wide bandgap of ZnO (3.37eV at room temperature) and to its large exciton energy (60meV) which makes it possible to employ excitonic recombination as a UV lasing mechanism. ZnO is also a piezoelectric and biosafe material that has probably spawned the richest family of nanostructures to date. Moreover, the ferromagnetic properties of ZnO doped with rare earth metals are also of interest for the design of novel devices that store information as a particular spin orientation (spintronics) Of the techniques for growing ZnO nanostructures with controlled dimensions, we have been using two of the most common and cost effective, namely, the catalytic vapor liquid solid (VLS) method and a low temperature technique based on chemical engineering. When optimized, both approaches can be used to produce large scale wafers and are suitable for commercial production. Figure 1 shows the schematics of the oven used in our VLS growth experiments.1 We have generated a wide family of different ZnO nanostructures, including wires (both vertically aligned and randomly oriented) ribbons, dots, flowers, branched structures, and leaves, on a variety of substrates with crystalline or amorphous surfaces.2 The room temperature photoluminescence (PL) spectra of typical ZnO nanowire samples are characterized by two main emission bands. The first is a sharp free exciton UV band that usually centers on ~380nm, and the second is a wider broad band observed between 420 and 700nm, historically referred to as the green luminescence or deep level emission band. Figure 1. Fabrication of zinc oxide (ZnO) nanowires using the catalytic VLS growth method. Insert: Transmission electron microscope image of a nanowire with a gold (Au) particle at the tip. Ar: Argon.
author_names: Magnus Willander

Qing Xiang Zhao

Omer Nour
title: Zinc oxide nanostructures at the forefront of new white light emitting technology
year: 2008

abstract: White organic light emitting diodes (WOLEDs) have attracted great attention for their potential use in full color displays and solid state lighting applications due to several advantages, such as low cost and flexibility. To date, the most efficient WOLEDs have used small phosphorescent molecules in multilayer structured devices prepared by high vacuum vapor deposition. The key issue in these systems is that the phosphorescent emission produced by each individual metal complex Ir(III) or Pt(II) is narrow, thus requiring simultaneous emission from more than one color phosphor to illuminate across the visible region. Typically this is achieved through a combination of either three different chromophores emitting blue, green, and red, or of two different ones emitting green/blue and orange/red. If more than one phosphorescent emitter is present in a device, the electroluminescent color may be affected by the energy transfer (both Forster and Dexter) between emitters. Vapor deposition enables isolation of the various emitters to minimize the energy transfer and achieve the desired goal of multiple emission using techniques such as patterning, stacking, layered isolation, and exciton management. Because polymeric materials can be solution processed, they constitute an interesting option for application in OLEDs due to their potential to reduce cost and increase scalability. Another advantage is that a single polymer chain can bear multiple functional groups, each contributing to the tuning of properties. For example, successful demonstrations of polymer WOLEDs have been based on blends of fluorescent polymers, polymers incorporating multiple fluorescent emitters in their side chains or their backbone and fluorescent polymers doped with small molecule phosphorescent emitters. However, these devices are generally fluorescent systems with limited internal quantum efficiencies or doped phosphorescent systems with poor stability. Furthermore, the occurrence of energy transfer limits the amount of low energy dopant that can be incorporated into these polymers, which affects their intrinsic efficiency. There have been some efforts to suppress this energy transfer using dendrimers for site isolation, but ultimately multilayer structures that can isolate phosphorescent emitters are needed. Unfortunately, this is extremely difficult to achieve with solution processing as the deposition of a layer must not affect any previously deposited layers. Block copolymers allow hierarchical supramolecular control over the spatial location of their functional component blocks as well as various nanoscale objects. This design flexibility has been exploited in the efficient fabrication of novel functional materials, such as nanostructured solar cells, photonic bandgap materials, highly efficient catalysts, and high density magneticstorage media. Therefore, block copolymers have the unique potential to spontaneously achieve phosphorescent emitter isolation through self assembly. Herein, we have explored their use as active materials for WOLEDs in which phosphorescent emitter isolation can be achieved. We have exploited the use of triarylamine (TPA) oxadiazole (OXA) diblock copolymers (TPA b OXA) which have been used as host materials due to their high triplet energy and charge transport properties enabling a balance of holes and electrons. These coil coil type TPA b OXA diblocks can produce various morphologies with controlled domain spacings ranging from 10 50 nm. By incorporating two different colored phosphorescent Ir(III) emitters (green blue and orange red emissive pendant styryl heteroleptic Ir(III) complexes) randomly into each different block, we have been able to produce a block copolymer system, (TPA r Blue) b (OXA r Red) which can deliver site isolation of the two emitters. As a result of site isolation these diblock copolymers can be targeted to suppress energy transfer from high to lower energy emitters, which generally occurs at distances below 10 nm. With these block copolymers, we demonstrate a seld assembled single layer solution processed WOLED that provides improved white color balance, and efficiency. Furthermore, by varying the molecular weight (MW) of (TPA r Blue) b (OXA r Red) and the ratio of blue to red emitters, we have investigated the effect of domain spacing on the electroluminescence spectrum and device performance. Polymers containing heavy metal complexes have been demonstrated previously for similar Ir(III) complexes through incorporation of ancillary ligand then post polymerization complex formation, or through the post polymerization attachment of preformed Ir(III) complexes. Unfortunately, these strategies are unsuitable since they do not allow incorporation of
author_names: Daniel A Poulsen

Bumjoon J Kim

Biwu Ma

C Sebastian Zonte

Jean M J Frechet
title: Site isolation in phosphorescent bichromophoric block copolymers designed for white electroluminescence.
venue: Advanced materials
year: 2010

abstract: We summarize the design, capabilities, and some of the priority science goals of a next generation Very Large Array (ngVLA) The ngVLA is an interferometric array with 10x larger effective collecting area and 10x higher spatial resolution than the current VLA and the Atacama Large Millimeter Array (ALMA) optimized for operation in the wavelength range 0.3cm to 3cm. The ngVLA opens a new window on the Universe through ultra sensitive imaging of thermal line and continuum emission down to milliarcecond resolution, as well as unprecedented broad band continuum polarimetric imaging of non thermal processes. The continuum resolution will reach 9mas at 1cm, with a brightness temperature sensitivity of 6K in 1 hour. For spectral lines, the array at 1" resolution will reach 0.3K surface brightness sensitivity at 1cm and 10 km s^ 1) spectral resolution in 1 hour. These capabilities are the only means with which to answer a broad range of critical scientific questions in modern astronomy, including direct imaging of planet formation in the terrestrial zone, studies of dust obscured star formation and the cosmic baryon cycle down to pc scales out to the Virgo cluster, making a cosmic census of the molecular gas which fuels star formation back to first light and cosmic reionization, and novel techniques for exploring temporal phenomena from milliseconds to years. The ngVLA is optimized for observations at wavelengths between the superb performance of ALMA at submm wavelengths, and the future SKA1 at few centimeter and longer wavelengths. This memo introduces the project. The science capabilities are outlined in a parallel series of white papers. We emphasize that this initial set of science goals are simply a starting point for the project. We invite comment on these programs, as well as new ideas, through our public forum link on the ngVLA web page: https:/science.nrao.edu/futures/ngvla
author_names: Christopher L Carilli

Mark McKinnon

Jurgen Ott

Anthony J Beasley

Andrea Isella

Eric J Murphy

Adam K Leroy

C M Casey

Arielle Moullet

Mark Lacy

Jacqueline Hodge

Geoff Bower

Paul B Demorest

Chat Hull

Meredith Hughes

James Di Francesco

Desika Narayanan

Brian R Kent

Barry Clark

Bonn Nrao

O POBox

520 Edgemont Road

Rice University

Ohio State University

University of North Texas

Leiden University

Nrao Jansky Fellow

Harvard--Smithsonian Center for Astrophysics

Weslyan University

Haverford College

Cavendish Astrophysics Group
title: Next Generation Very Large Array Memo No. 5: Science Working Groups Project Overview
year: 2015