Tag Archives: display

Transparent screen ilussion.

Novel material paves the way for atom-thin, invisible displays

Researchers from UC Berkeley have designed a millimeter-wide, light-emitting device that’s fully transparent when powered off. The material, just three atoms thick, could form the base for displays that would be invisible when turned off.

Transparent screen ilussion.

Image credits Steve Webel / Flickr.

The device is based on a novel material — a light-emitting, monolayer semiconductor. It was developed in the laboratories of Ali Javey, professor of Electrical Engineering and Computer Sciences at Berkeley, and its light-emitting properties were first reported on in 2015. However, the team hadn’t been able to construct an actual light-emitting device using the novel semiconductor by that time — mostly due to fundamental constraints of using LED (light emitting diode) technology in tandem with monolayer semiconductors.

They’ve been working hard to solve those problems, however — in their new paper, the team details how they’ve worked around these limitations, allowing them to scale down LED technology anywhere from a few millimeters to under the width of a human hair. The team made the devices wide and long, to make sure the devices emit light intense enough for our eyes to pick up on.

Now you see it, now you don’t

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

The kind of LEDs you can buy right now are made from a semiconducting material, injected with positive and negative electrical charges. When electricity runs through these LEDs, electrons move from the positively-charged area into electron ‘holes’ on the negative side, releasing light in the process. That’s the fancy explanation. The simple explanation is that LEDs work pretty much the same way as an incandescent light bulb, the main difference being LEDs don’t ‘burn’ and they don’t generate heat — the light you see comes solely from the passing of current through a semiconductor material, not from heating something. This makes them last much, much longer than an incandescent bulb.

One of the fundamental challenges I mentioned earlier is to form a contact that can efficiently inject these charges — and it’s a particularly problematic one for monolayers because there’s physically very little material to work with. The team worked around this issue by engineering a device that only uses one contact on the semiconductor.

Gif of the device in action. Probes inject positive and negative charges into the light emitting device, which is transparent under the campanile outline, producing bright light. Credit: Javey lab

They layered the semiconducting on an insulator, then placed electrodes on the monolayer and underneath this insulator. This allowed them to apply an alternating current (AC) signal across the surface of the insulator. As the AC switches polarity from positive to negative (and vice versa), both negative and positive charges are present in the semiconductor at the same time — which creates light. The team showed that this mechanism works with four different monolayer materials, all of which emit a different colored light.

Soon-to-be

The team’s efforts amount only to a proof-of-concept right now; much more research needs to be done before their atom-thin material is ready for commercial use. Most notably, the team has to work on improving its efficiency. While the tools they can use to measure this device’s efficiency leave a pretty significant margin of error, the team says it’s probably 1% right now. Commercial LEDs, to put that into context, run at about 25-30% efficiency — usually.

“A lot of work remains to be done and a number of challenges need to be overcome to further advance the technology for practical applications,” Javey said. “However, this is one step forward by presenting a device architecture for easy injection of both charges into monolayer semiconductors.”

However, the concept is likely applicable to other kinds of materials and devices. Given its versatility, we’re likely to see the team’s device used in all manner of applications where an invisible display is necessary or desirable. We’re also likely to see it used for ‘cool’ applications — the team doesn’t write off the possibility that their research will lead to atomically-thin displays used for decoration, from skin to architecture.

The paper “Large-area and bright pulsed electroluminescence in monolayer semiconductors” has been published in the journal Nature Communications.

Credit: RMIT University.

Nano-holograms 1,000 times thinner than the human hair pave way for smartphone-generated holograms

Credit: RMIT University.

Credit: RMIT University.

For decades, holograms have been a staple of science fiction. You’ve seen them in Star Wars or Avatar, but soon enough you might enjoy them virtually everywhere. That’s because a team of researchers from Australia and China was able to design a nano-hologram that’s thin enough to work with modern electronics. No 3D-goggles are required to see these holographic images which can be 1,000 thinner than the human hair.

Conventional holograms give the impression of a 3D object by modulating the phase of light. This gives the illusion of 3-D depth but to generate enough phase shifts, each hologram needs to be at least as thick as the phase-shifted optical wavelengths. Australian researchers from RMIT University, along with Chinese colleagues from the Beijing Institute of Technology (BIT) managed to pull a workaround by using a topological insulator. This is an exotic class of materials that has the unique ability to conduct electricity at the surface, but not on the inside through the bulk material.

Topological insulators also have unique quantum properties like a low refractive index at the surface and a ultra-high refractive index in the bulk. When a very fast direct laser is shone a thin film made from such exotic materials, it’s possible to enhance phase shifts for holographic imaging.

“We discover that nanometric topological insulator thin films act as an intrinsic optical resonant cavity due to the unequal refractive indices in their metallic surfaces and bulk. The resonant cavity leads to enhancement of phase shifts and thus the holographic imaging,” the researchers wrote in the journal Nature Communications.

For instance, the holograms demonstrated by the researchers operated at 60 nanometers of 3 mm × 3 mm in size

T-rex in your pocket

hologram dinosaur

(a) Original image of the dinosaur object. Note: this figure is not included under the article CC BY licence; Indominus Rex image is reproduced with permission from the publisher Comingsoon.net and copyright owner Universal Studios. (b,c) SEM images of the laser printed hologram patterns. The scale bar is 50 μm for b and 10 μm for c, respectively. (d–f) Holographic images captured by illuminating the nanometric holograms using 445, 532 and 632 nm continuous wavelaser beams. Scale bars for d–f are 1 mm. Credit: Nature Communications.

“Conventional computer-generated holograms are too big for electronic devices but our ultrathin hologram overcomes those size barriers,” said  RMIT University’s Distinguished Professor Min Gu in a statement.

“Integrating holography into everyday electronics would make screen size irrelevant — a pop-up 3D hologram can display a wealth of data that doesn’t neatly fit on a phone or watch.

“From medical diagnostics to education, data storage, defence and cyber security, 3D holography has the potential to transform a range of industries and this research brings that revolution one critical step closer.”

The next step for the team is developing a rigid thin film that can be placed on an LCD screen, such as that on a smartphone or notebook, to enable everyday use of 3D holographic display. This will be immensely challenging as it involves shrinking the nano- hologram’s pixel size even further — at least 10 times smaller than it currently is.

“But beyond that, we are looking to create flexible and elastic thin films that could be used on a whole range of surfaces, opening up the horizons of holographic applications.”

Scientific reference: Zengji Yue, Gaolei Xue, Juan Liu, Yongtian Wang, Min Gu. Nanometric holograms based on a topological insulator material. Nature Communications, 2017; 8: 15354 DOI: 10.1038/NCOMMS15354

The new displays enabled by blue-liquid crystals could be extremely useful in VR applications where a high resolution on a small screen is desirable. Credit: Pixabay.

Thought 4K was impressive? New tech can triple the sharpness of TVs and other displays while reducing power demand

The new displays enabled by blue-liquid crystals could be extremely useful in VR applications where a high resolution on a small screen is desirable. Credit: Pixabay.

The new displays enabled by blue-liquid crystals could be extremely useful in VR applications where a high resolution on a small screen is desirable. Credit: Pixabay.

The resolution density of today’s displays is nearing its limits. But an international team of scientists has found a way to cram in more pixels per square inch than ever before. Using a new type of blue-phase liquid crystal optimized for field-sequential color liquid crystal displays (LCDs), the team claims it’s possible to up the resolution density three fold compared to the state of the art. Moreover, the new technology consumes less power.

“Today’s Apple Retina displays have a resolution density of about 500 pixels per inch,” said Shin-Tson Wu, who led the research team at the University of Central Florida’s College of Optics and Photonics (CREOL). “With our new technology, a resolution density of 1500 pixels per inch could be achieved on the same sized screen. This is especially attractive for virtual reality headsets or augmented reality technology, which must achieve high resolution in a small screen to look sharp when placed close to our eyes.”

12K displays?

The current state of the art in display screen resolution. The new tech could triple the sharpness.

Your typical LCD screen is comprised of a thin layer of nematic liquid crystal onto which white light is fired from LEDs. This incoming backlight is modulated by thin-film transistors to display graphics while colours are produced by combining red, green, and blue filters.

Experiments suggest that blue-phase liquid crystals can be switched on and off by transistors almost ten times faster than the nematic variety. This incredibly fast sub-millisecond response time means that different coloured LEDs (red, green, and blue) can fire light at different times. The switching frequency is so fast that you brain can’t process the variation and instead you’ll feel like it’s all a continuous experience. Basically, this feature removes the need for colour filters drastically saving space in a display device.

Scientists think this configuration can triple the number of pixels per square inch. It ought to triple the optical efficiency as well since the light isn’t required to pass through filters anymore — these used to limit light transmittance to only 30 percent.

Blue-phase liquid crystals aren’t exactly new. Samsung first demonstrated an LCD display prototype based on blue-phase crystals for the first in 2008. However, it proved difficult at the time to scale the technology commercially due to high operational voltage and slow capacitor charging time.

Wu and colleagues collaborated with academic and industry partners to try to solve these issues. Their efforts eventually paid off after the international team of researchers combined the liquid crystals with a special performance-enhancing electrode structure that lets the electric field penetrate the liquid crystals more deeply.

The triangular electrode structure penetrates the crystals so the electric field is stronger. Credit: OSA.

The triangular electrode structure penetrates the crystals so the electric field is stronger. Credit: OSA.

This configuration successfully reduced the operational voltage to 15 volts per pixel and achieved a light transmittance of 74 percent, as reported in the Optical Materials Express journal. These figures suggest field-sequential color displays are now practical and could soon see commercial development.

“We achieved an operational voltage low enough to allow each pixel to be driven by a single transistor while also achieving a response time of less than 1 millisecond,” said Haiwei Chen, a doctoral student in Wu’s lab. “This delicate balance between operational voltage and response time is key for enabling field sequential color displays.”

A working prototype might be available as soon as next year, Wu said.

UCLA engineers develop a stretchable, foldable transparent electronic display

Take a moment to imagine a phone display as clear as a window, a curtain that can illuminate a room, and a smart phone that can stretch like rubber; now imagine all these things are made from the same material.

oled bending

Researchers from UCLA’s Henry Samueli School of Engineering and Applied Science have developed a transparent, elastic organic light-emitting device, or OLED, which has the potential to make this happen. The OLED can be repeatedly stretched, folded and twisted, all at room temperature, without anything special, while still remaining turned on and retaining its original size and shape.

OLED technology itself is not a really new idea – it’s currently used for many smartphones and some televisions. But this new, smart OLED version from UCLA could lead to foldable and expandable screens for new classes of smartphones, as well as electronic-integrated clothing, wallpaper lighting, new minimally invasive medical tools, and many, many others.

“Our new material is the building block for fully stretchable electronics for consumer devices,” said Qibing Pei, a UCLA professor of materials science and engineering and principal investigator on the research. “Along with the development of stretchable thin-film transistors, we believe that fully stretchable interactive OLED displays that are as thin as wallpaper will be achieved in the near future. And this will give creative electronics designers new dimensions to exploit.”

In order to test their results, researchers stretched and restretched the OLED 1,000 times, extending it up to 30 percent its original size – and it still continued to work at very high efficiency. If you cut back on some efficiency, you can stretch it to double its initial size, while also folding it 180 degrees and twisting it in multiple directions. It’s also fairly easy and cheap to produce.

“The lack of suitable elastic transparent electrodes is one of the major obstacles to the fabrication of stretchable display,” Liang said. “Our new transparent, elastic composite electrode has high visual transparency, good surface electrical conductivity, high stretchability and high surface smoothness — all features essential to the fabrication of the stretchable OLED.”

OLED-Design-prv

They also demonstrated that such an OLED technology could feature multiple pixels, rather than just a solid block of light.

“While we perceive a bright future where information and lighting are provided in various thin, stretchable or conformable form factors, or are invisible when not needed, there are still major technical challenges,” Pei said. “This includes how to seal these materials that are otherwise sensitive to air. Researchers around the world are racing the clock tackling the obstacles. We are confident that we will get there and introduce a number of cool products along the way.”

The results were published in Nature Photonics.