By nestling quantum dots in an insulating egg-crate structure, researchers at the Harvard School of Engineering and Applied Sciences (SEAS) have demonstrated a robust new architecture for quantum-dot light-emitting devices (QD-LEDs).Quantum dots are very tiny crystals that glow with bright, rich colors when stimulated by an electric current. QD-LEDs are expected to find applications in television and computer screens, general light sources, and lasers.Previous work in the field had been complicated by organic molecules called ligands that dangle from the surface of the quantum dots. The ligands play an essential role in quantum dot formation, but they can cause functional problems later on.Thanks to an inventive change in technique devised by the Harvard team, the once-troublesome ligands can now be used to build a more versatile QD-LED structure. The new single-layer design, described in the October issue of the journal Advanced Materials, can withstand the use of chemical treatments to optimize the device’s performance for diverse applications.“With quantum dots, the chemical environment that’s optimal for growth is usually not the environment that’s optimal for function,” says co-principal investigator Venkatesh Narayanamurti, Benjamin Peirce Professor of Technology and Public Policy at SEAS.The quantum dots, each only 6 nanometers in diameter, are grown in a solution that glows strikingly under a black light.The solution of quantum dots can be deposited onto the surface of the electrodes using a range of techniques, but according to lead author Edward Likovich, who conducted the research as a Graduate School of Arts and Sciences doctoral candidate in applied physics at SEAS, “That’s when it gets complicated.”“The core of the dots is a perfect lattice of semiconductor material, but on the exterior it’s a lot messier,” he says. “The dots are coated with ligands, long organic chains that are necessary for precise synthesis of the dots in solution. But once you deposit the quantum dots onto the electrode surface, these same ligands make many of the typical device processing steps very difficult.”The ligands can interfere with current conduction, and attempts to modify them can cause the quantum dots to fuse together, destroying the properties that make them useful. Organic molecules can also degrade over time when exposed to UV rays.Researchers would like to be able to use those ligands to produce the quantum dots in solution, while minimizing the negative impact of the ligands on current conduction.“The QD technologies that have been developed so far are these big, thick, multilayer devices,” says co-author Rafael Jaramillo, a Ziff Environmental Fellow at the Harvard University Center for the Environment. Jaramillo works in the lab of Shriram Ramanathan, associate professor of materials science at SEAS.“Until now, those multiple layers have been essential for producing enough light, but they don’t allow much control over current conduction or flexibility in terms of chemical treatments,” says Jaramillo. “A thin, monolayer film of quantum dots is of tremendous interest in this field, because it enables so many new applications.”The new QD-LED resembles a sandwich, with a single active layer of quantum dots nestled in insulation and trapped between two ceramic electrodes. To create light, current must be funneled through the quantum dots, but the dots also have to be kept apart from one another in order to function.In an early design, the path of least resistance was between the quantum dots, so the electric current bypassed the dots and produced no light.Abandoning the traditional evaporation technique they had been using to apply insulation to the device, the researchers instead used atomic layer deposition (ALD) — a technique that involves jets of water. ALD takes advantage of the water-resistant ligands on the quantum dots, so when the aluminum oxide insulation is applied to the surface, it selectively fills the gaps between the dots, producing a flat surface on the top.The new structure allows more effective control over the flow of electrical current.“Exploiting these hydrophobic ligands allowed us to insulate the interstices between the quantum dots, essentially creating a structure that acts as an egg crate for quantum dots,” says co-author Kasey Russell, a postdoctoral fellow at SEAS. “The benefit is that we can funnel current directly through the quantum dots despite having only a single layer of them, and because we have that single layer, we can apply new chemical treatments to it, moving forward.”Through Harvard’s Office of Technology Development, Likovich and his colleagues have applied for a provisional patent on the device. Beyond the possible applications in computer and TV displays, lights, and lasers, the technology could one day be used in field-effect transistors or solar cells.The research was supported by the Harvard University Center for the Environment and the Nanoscale Science and Engineering Center at Harvard, which is funded by the National Science Foundation (NSF), and by the use of facilities at the Harvard University Center for Nanoscale Systems, a member of the NSF-supported National Nanotechnology Infrastructure Network.
ShareShareSharePrintMailGooglePinterestDiggRedditStumbleuponDeliciousBufferTumblr We are getting to the final weeks before the CFPB’s prepaid account rule goes into effect. To help credit unions navigate the complexities of this rule, this month’s NAFCU Compliance Monitor article provides a deep dive into some of the key parts of the rule. As credit unions are implementing this rule, one question that the compliance team has been getting recently is whether gift cards are considered prepaid accounts. And the attorney says…Yes, that’s right. It depends. If a credit union’s gift card program is considered a “gift card,” “gift certificate” or “general use prepaid card” under section 1005.20, then it may not be a prepaid account and not subject to the new rule. Revised section 1005.2(b)(3)(ii) provides a list of products that are not prepaid accounts. The list includes gift cards and certain general use prepaid cards that are subject to section 1005.20: continue reading »
The Pirates played host to visitor Jac-Cen-Del on Tuesday night and fell 5-1. The Pirates got off to a slow start on Tuesday, allowing 5 first half goals. The second half went much better for the Pirates, but it was too late as the Eagles had built a 5 goal lead. The Pirates came out in the second half and had their first shut out half of the season, by not allowing another Jac-Cen-Del goal the rest of the game. The second half saw the Pirates in the attack a lot more than in the first half, seeing 4 shots on goal from Nicholas Zapfe and 5 shots on goal from Vincent Pavy. In the game’s final minute, senior Vincent Pavy broke past the Eagle defense and scored his 10th goal of the season, allowing for the Pirates to not end the game scoreless. Freshman, Grayson Newhart (who started the game at forward) played goalkeeper in the second half for the Pirates and registered 5 saves and the second half shut out. Courtesy of Pirates Coach Cody DeVolld.
Fourth in the Irish 1,000 Guineas earlier in the season, she had not been seen since struggling over 10 furlongs in the Pretty Polly Stakes at the end of June. Sent off a 5-1 chance dropped in class to Listed level, Lady O’Reilly’s daughter of Champs Elysees had to work hard to see off Fastnet Mist in the final furlong, but she prevailed by three-quarters of a length under Chris Hayes. Paul Deegan’s patience with Avenue Gabriel was rewarded as the filly won the feature Clodovil EBF Garnet Stakes at Naas. Third in Listed company on her debut, a maiden should have been a formality, but the 9-10 favourite scrambled home by a short head from Sharaasa in the Bungle Inthejungle EBF Fillies Maiden. Lynam said: “On first viewing I thought ‘oh dear we’re beat’, but she got home and won. Maybe I overrated her, but I thought she was very good. Pat (Smullen) still thinks she could be, but she’d have to improve a bit from that. “He said she’s still very green, but I like to see it in the form book. Lets hope she’s very good, but it looks at the moment like she’s just good. We’ll see what she’s like next year. She was well bought anyway – she wasn’t expensive.” The Killavullan Stakes next weekend may be on the agenda for Captain My Captain after his empahtic win in the Irish Stallion Farms EBF Birdcatcher Nursery, which followed a good show in a big sales race. Trainer John Murphy said: “He’s a lovely big horse and was unlucky in the Curragh, when he was drawn very wide. He loves good ground and we were a bit worried that it might be a bit dead. He should excel over seven or a mile next year and will maybe even get further. “He’s a real nice horse and has always worked like it. Our two-year-olds have been very backward this year and that’s my first two-year-old winner. There was talk of the Killavullan this morning and we are dying to try him over seven. The further he goes the better.” Rocky Bleier (20-1) came from last to first to win the valuable Woodlands 100 Club October Handicap for trainer Bill Farrell and jockey Billy Lee. The trainer said: “He got a bit jarred up in the spring. We waited for his shins to settle and for an ease in the ground. He’s on an upward curve. He’s in the sales but won’t go now.” Deegan said: “That’s great. I’m delighted for James (Kelly) and Lady O’Reilly and their patience has been rewarded. “Her best form was always on fast ground and we’ve always said she was better on it, but it started to catch up with her. It took her a long time to get over the Pretty Polly as she came back not herself. That’s a nice race to win before the winter and she’ll go home for a holiday now. “We won’t be tempted to run on quick ground again. She’ll be a good mare next year and could be a filly for something like the Matron. Her Guineas run was no fluke. We thought she might stretch out a bit more but probably a true-run mile is what she wants.” Endless Drama earned a quote of 33-1 for the Qipco 2000 Guineas with Boylesports after making an impressive debut in the Tifrums EBF (C&G) Maiden. The Ger Lyons-trained colt, sent off a well-backed 6-1 shot, hit the front just under two furlongs from home and bounded five and a half lengths clear of Cenotaph. Lyons said: “He’s a nice horse and we’ve always liked him. He’s as big a horse as we’ve had come into the yard and we took our time with him. Coming from the camp he did, they know their stuff. He didn’t make the breeze-ups for one reason or another, but they told me he was as good as they’ve had. “That’s the way we were hoping he’d run, but you don’t expect it. He’s a very, very smart horse. That’ll be it for the season. He holds an entry for the Killavullan, but that wouldn’t be my style to run them back like that. We’ll look forward to next season. Next year we’ll start him over seven and step up quietly.” Eddie Lynam’s Byzantium opened her account at the second time of asking, but her odds-on supporters were made to fret. Press Association