Dielectric Mirror Shines Bright

August 15, 2023 by Al Williams 31 Comments

We knew the mirrors in our house were not really very good mirrors, optically speaking. Your mirror eats up 20 to 40 percent of the light that hits it. High-quality first-surface mirrors are better, but [Action Lab] has a video (see below) of something really different: a polymer dielectric mirror with 99.5% reflectivity. In addition, it has no Brewster angle — light that hits it from any angle will reflect.

Turns out something that thin and reflective can be hard to find. It also makes a little flashlight if you roll a tube of the material and pinch the back end together. The light that would have exited the rear of the tube now bounces around until it exits from the front, making it noticeably bright. The film comes from 3M, and apparently, they were surprised about the optical properties, too.

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a–d, Crystal structures of the 1CzTrz-F (a,b) and 3CzTrz-F (c,d) compounds, determined by XRD. a,c, Diagrams of the two dimers of both crystallographic unit cells to show the molecular packing. b,d, Spatial arrangement of the acceptor–donor contacts in the 3D crystal structure. The triazine acceptor and the carbazole donor units are coloured orange and blue, respectively. The green features in d indicate co-crystallized chloroform molecules. (Credit: Oskar Sachnik et al., 2023)

Eliminating Charge-Carrier Trapping In Organic Semiconductors

August 13, 2023 by Maya Posch 4 Comments

For organic semiconductors like the very common organic light-emitting diode (OLED), the issue of degradation due to contaminants that act as charge traps is a major problem. During the development of OLEDs, this was very pronounced in the difference between the different colors and the bandgap which they operated in. Due to blue OLEDs especially being sensitive to these charge traps, it still is the OLED type that degrades the quickest as contaminants like oxygen affect it the strongest. Recent research published in Nature Materials from researchers at the Max Planck Institute for Polymer Research by Oskar Sachnik and colleagues (press release) may however have found a way to shield the electron-carrying parts of organic semiconductors from such contaminants.

Current density (J)–voltage (V) characteristics of electron- and hole-only devices of 3CzTrz and TPBi. (Credit: Oskar Sachnik et al., 2023)

In current organic semiconductors TPBi is used for electron transport, whereas for this research triazine (Trz, as electron acceptor) and carbozole (Cz, as donor) were used and compared with the properties of leading-edge TPBi. While a few other formulations in the study did not show remarkable results, one compound (3CzTrz) was found using X-ray diffraction (XRD) to have a structure as shown on the right in the heading image, with the carbozole (in blue) forming essentially channels along which electrons can move, while shielded from contaminants by the triazine.

Using this research it might be possible to create organic semiconductors in the future which are free of charge-traps, and both efficiency and longevity of this type of semiconductor (including OLEDs and perovskites) can be improved immensely.

A Little Bit Of Science History Repeating Itself: Boyle’s List

August 11, 2023 by Al Williams 24 Comments

In a recent blog post, [Benjamin Breen] makes an interesting case that 2023 might go down in history as the start of a scientific revolution, and that’s even if LK-99 turns out to be a dud. He points to several biomedical, quantum computing, and nuclear fusion news items this year as proof.

However, we aren’t as convinced that these things are here to stay. Sure, LK-99 was debunked pretty quickly, but we swim in press releases about new battery technologies, and new computer advances that we never hear about again. He does mention that we aren’t alone in thinking that as [Tyler Cowen] coined the phrase “Great Stagnation” to refer to the decline in disruptive tech since 1945. Still, [Benjamin] argues that people never know when they live through a scientific revolution and that the rate of science isn’t as important as the impact of it.

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The World ID Orb And The Question Of What Defines A Person

August 10, 2023 by Maya Posch 68 Comments

Among the daily churn of ‘Web 3.0’, blockchains and cryptocurrency messaging, there is generally very little that feels genuinely interesting or unique enough to pay attention to. The same was true for OpenAI CEO Sam Altman’s Ethereum blockchain-based Worldcoin when it was launched in 2021 while promising many of the same things as Bitcoin and others have for years. However, with the recent introduction of the World ID protocol by Tools for Humanity (TfH) – the company founded for Worldcoin by Mr. Altman – suddenly the interest of the general public was piqued.

Defined by TfH as a ‘privacy-first decentralized identity protocol’ World ID is supposed to be the end-all, be-all of authentication protocols. Part of it is an ominous-looking orb contraption that performs iris scans to enroll new participants. Not only do participants get ‘free’ Worldcoins if they sign up for a World ID enrollment this way, TfH also promises that this authentication protocol can uniquely identify any person without requiring them to submit any personal data, only requiring a scan of your irises.

Essentially, this would make World ID a unique ID for every person alive today and in the future, providing much more security while preventing identity theft. This naturally raises many questions about the feasibility of using iris recognition, as well as the potential for abuse and the impact of ocular surgery and diseases. Basically, can you reduce proof of personhood to an individual’s eyes, and should you?

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Got Fireflies? Try Talking To Them With A Green LED

August 6, 2023 by Donald Papp 25 Comments

[ChrisMentrek] shares a design for a simple green LED signal light intended for experiments in “talking” to fireflies. The device uses simple components like PVC piping and connectors to make something that resembles a signal flashlight with a momentary switch — a device simple enough to make in time for a little weekend experimenting.

Observe and repeat flashing patterns, and see if any fireflies get curious enough to investigate.

Did you know that fireflies, a type of beetle whose lower abdomen can light up thanks to a chemical reaction, flash in patterns? Many creatures, fireflies included, are quite curious under the right circumstances. The idea is to observe some fireflies and attempt to flash the same patterns (or different ones!) with a green LED to see if any come and investigate.

[ChrisMentrek] recommends using a green LED that outputs 565 nm, because that is very close to the colors emitted by most fireflies in North America. There’s also a handy link about firefly flashing patterns from the Massachusetts Audubon society’s Firefly Watch program, which is a great resource for budding scientists.

If staying up and learning more about nocturnal nightlife is your thing, then in between trying to talk to fireflies we recommend listening for bats as another fun activity, although it requires a bit more than just a green LED. Intrigued? Good news, because we can tell you all about the different kinds of bat detectors and what you can expect from them.

LK-99: Diamagnetc Semiconductor, Not Superconductor?

August 5, 2023 by Jenny List 70 Comments

Every so often, along comes a story which, like [Fox Mulder] with his unexplained phenomena, we want to believe. EM drives and cold fusion for example would be the coolest of the cool if they worked, but sadly they crumbled when subjected to scientific inquiry outside the labs of their originators. The jury’s still out on the latest example, a claimed room-temperature superconductor, but it’s starting to seem that it might instead be a diamagnetic semiconductor.

We covered some of the story surrounding the announcement of LK-99 and subsequent reports of it levitating under magnetic fields, but today’s installment comes courtesy of a team from Beihang University in Beijing. They’ve published a paper in which they characterize their sample of LK-99, and sadly according to them it’s no superconductor.

Instead it’s a diamagnetic semiconductor, something that in itself probably bears some explanation. We’re guessing most readers will be familiar with semiconductors, but diamagnetic substances possess the property of having an external magnetic field induce an internal magnetic field in the opposite direction. This means that they will levitate in a magnetic field, but not due to the Meissner effect, the property of superconductors which causes magnetic field to flow round their outside. The Beijing team have shown by measuring the resistance of the sample that it’s not a superconductor.

So sadly it seems LK-99 isn’t the miracle it was billed as, unless there’s some special quirk in the production of the original Korean sample which didn’t make it to the other teams. We can’t help wondering why a sample from Korea wasn’t subjected to external evaluation rather than leaving the other teams to make their own. Never mind, eh!