
Atomically thin LED opens the possibility for invisible displays - ForFreedom
http://news.berkeley.edu/2018/03/26/atomically-thin-light-emitting-device-opens-the-possibility-for-invisible-displays/
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pjc50
> By laying the semiconductor monolayer on an insulator and placing electrodes
> on the monolayer and underneath the insulator, the researchers could apply
> an AC signal across the insulator. During the moment when the AC signal
> switches its polarity from positive to negative (and vice versa), both
> positive and negative charges are present at the same time in the
> semiconductor, creating light.

This is highly simplified, but essentially the LED is now capacitively coupled
to its supply on one side, _through_ the insulator*. As a result it has to be
driven with AC. Neat trick.

~~~
qbrass
That's similar to how electroluminescent displays work. Except those use an
insulating layer and electrode layer on both sides of the light producing
layer instead of just one.

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blauditore
The standard showcase for such things are usually transparent displays. While
looking cool, they would be pretty annoying: There's always interference with
the background. That's also why no one uses transparent whiteboards as seen in
movies.

But of course, it would also be neat to just have displays on surfaces where
not visible when turned off.

~~~
jasonkostempski
On-screen keyboards are pretty annoying, that didn't stop them from becoming
the only option available.

~~~
lowtolerance
They’re the only option available because tiny mobile keyboards were pretty
damned annoying, too, while also carrying the cost of dozens of potential
points of failure, taking up a considerable amount of real estate regardless
of how long the keyboard is actually used, and forcing a particular key layout
on the user. I honestly don’t think I’d buy a phone with a hard keyboard, even
if there were decent options for one.

~~~
Retric
Slide out keyboards are an option. Combine with an on screen keyboard for the
other layout and the only cost is a slightly thicker device.

~~~
gregmac
I had a Blackberry Torch [1] for a while in the early 2010's. The keyboard was
great, and you could use a touchscreen keyboard as well (it would seamlessly
switch the app to fullscreen if you slide it open). It was thicker and heavier
than most comparable phones, but with modern tech that would be less of an
issue.

The biggest problem with it at the time was it was running Blackberry OS,
which was a reasonable e-mail client, mediocre (and later, noticeably
outdated) browser, and abysmal app store and selection of 3rd party apps. I
remember saying it would have been a great phone if they had dropped their own
OS and went to Android (and spent their software dev time making their version
of Android better and building their e-mail client etc on top).

My next phone was an Android something or other, and by then, I was more than
happy to give up the physical keyboard to get something more useful than an
e-mail interface brick in my pocket.

[1]
[https://en.wikipedia.org/wiki/BlackBerry_Torch_9800](https://en.wikipedia.org/wiki/BlackBerry_Torch_9800)

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panic
Some more pictures from the article itself:
[https://www.nature.com/articles/s41467-018-03218-8/figures/4](https://www.nature.com/articles/s41467-018-03218-8/figures/4)

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patrickcteng
Float-in-the-air 3D displays/images are in the labs already!
[https://www.nature.com/articles/d41586-018-01125-y](https://www.nature.com/articles/d41586-018-01125-y)

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meuk
If you can layer enough of such invisible screens, you could make a nice 3d
display, although I'm not sure if it would actually look nice (you could
probably see through objects).

~~~
lawlessone
WE could build a real Voxatron!

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unwind
This did not inspire confidence:

 _Commercial LEDs consist of a semiconductor material that is electrically
injected with positive and negative charges, which produce light when they
meet. Typically, two contact points are used in a semiconductor-based light
emitting device; one for injecting negatively charged particles and one
injecting positively charged particles._

Isn't that a bit too simplified?

That said it sounds like very cool technology although hard to see how
electrical wires to each pixel would be as invisible at wall-sized scales.

~~~
userbinator
_although hard to see how electrical wires to each pixel would be as invisible
at wall-sized scales._

[https://en.wikipedia.org/wiki/Indium_tin_oxide](https://en.wikipedia.org/wiki/Indium_tin_oxide)

~~~
kurthr
ITO isn't really transparent... it's pretty yellow (80-95% transmission) and
it doesn't carry current well (20-100ohm/sq). You'd be better off with a metal
mesh with large pitch electrodes. You're going to need some wires to address
the display as well (whether active or passive matrix).

With a large pitch Cu or Al conductors you can do 5ohm/sq with good
transparency. That will let you do 200nits (candela/m2) with the efficiency of
these thin LEDs. ITO would be 10x lower conductance and only works in LCDs
because they are inverting voltage light valves (not light sources).

If everything worked out you could reasonably view thin LEDs in a dim office
environment. That's not really interesting unless it's 3D.

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zingmars
Can't wait to wake up with ads on my windows...

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oneeyedpigeon
That's been happening for a while now:
[https://www.theverge.com/2017/3/17/14956540/microsoft-
window...](https://www.theverge.com/2017/3/17/14956540/microsoft-
windows-10-ads-taskbar-file-explorer)

~~~
mstolpm
I don't think the parent poster you replied to thought of -Microsoft- windows,
but the ones in your home.

~~~
oneeyedpigeon
It was a knowing play-on-words; forgive the triviality, but it was too perfect
an opportunity ;)

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omarforgotpwd
Well what’s the point of the display if you can’t see it? ;)

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ben_bai
Google glass without mirrors?

~~~
swiley
I think it still needs optics so your eyes can focus on it correctly.

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silveira
[https://hackaday.com/2013/12/31/case-modder-builds-lcd-
windo...](https://hackaday.com/2013/12/31/case-modder-builds-lcd-window-
causes-lsd-flashbacks/)

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maxyme
Isn't heat a current major concern with LEDs? If so wouldn't this have to be
hooked up to a heatsink in practice making the transparency irrelevant?

~~~
pjc50
Heat is entirely dependent on brightness. It's only really an issue when using
LEDs for illumination at multi-watt levels.

Tiny thin LEDs are necessarily not going to have a huge power output. If the
substrate is glass it will have decent thermal conductivity.

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amelius
Can it show black pixels? What is the contrast ratio?

~~~
comboy
This is just a single LED. And you are asking about specs of some future
product that may use it.

I think you can make background dark (from transparent) by using good old LCD
technology. Because that's basically what LCD is about.

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drieddust
Once it becomes cheap enough, this might give a huge boost to indoor farming.

~~~
nkozyra
Not being familiar with the area, what problem would this solve for indoor
farming?

~~~
jfindley
At a guess, being able to easily augment sunlight in parts of the world that
get few hours of sunlight during local winter. Sun shines through when it's
there, LED takes over when not.

However in practice I don't think this would be useful - they're considerably
less efficient than existing LEDs (currently 1% vs 25-30%) and I think that
efficiency is more of a problem than transparency.

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trisimix
They aren't diodes either

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Armisael16
This isn’t an LED (in fact it isn’t a diode at all). Can we rename the
submission title?

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Raphmedia
Looks like they meant LED as in _l_ight _e_mitting _d_evice.

~~~
Armisael16
That simply isn't what the acronym LED means. It's equivalent to using WMD to
mean 'weapons of mass disruption'.

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baybal2
Looks like they figured out how to make LEDs with atomic layer deposition

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billysielu
Apple will love this, a screen that breaks even easier.

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diggan
Seems to be bendable so maybe breaking it is harder than current screens.

> “The materials are so thin and flexible that the device can be made
> transparent and can conform to curved surfaces,” said Der-Hsien Lien, a
> postdoctoral fellow at UC Berkeley and a co-first author

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SuddsMcDuff
I expect once the material has conformed to a curved surface it would have to
be rigid from there on out.

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pjc50
Maybe, maybe not. Flat flexible circuits are established technology. LG
already have a flexible display, although apparently it has a dead pixel
problem.
[http://www.bbc.co.uk/news/technology-35230043](http://www.bbc.co.uk/news/technology-35230043)

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mojomark
Transparent OLEDs (TOLEDs), Transparent Quantum Dot LEDs (QD-LEDs),
Transparent Inorganic LEDs, have all been around for a long time now:

[https://www.youtube.com/watch?v=IJQzPrkkH6A](https://www.youtube.com/watch?v=IJQzPrkkH6A)
[https://www.youtube.com/watch?v=Lv46YU-X9Xs](https://www.youtube.com/watch?v=Lv46YU-X9Xs)

I'm confuzzled by the 'news', although the AC drive, vice DC is interesting I
suppose.

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ricardobeat
Feature wise they sound similar, but we’re talking about three atoms thick
here. This could be world-changing tech if it gets efficient enough.

