It was in the 1960s that the field of nanotechnology first emerged and in the last two decades it has grown significantly and is poised to take on an increasingly important role in the future of numerous industries.
At present, 70 % of nanotechnology activity is in energy, electronics, and biomedicine,1 but the field is having a growing effect in industries as varied as environmental tech, automotive, defense, cosmetics, agriculture and textiles. It is predicted that in 2024 the global market for nanotechnology will reach US $ 125 Billion.2
What is Nanotechnology?
Nanotechnology is a new scientific field focused on manipulating the molecular structure of materials to alter the intrinsic properties of the materials or to create new materials. It describes the creation of materials and devices “with novel functions and properties based either on geometrical or on material-specific peculiarities of nanostructure.”3
For example, graphene is an alteration of carbon molecules to create cylindrical sheets which are just one atom thick. Graphene has the highest electron mobility of any known material, is stronger than a diamond, harder than steel, lighter than aluminum and is over 97 % transparent to wavelengths of light from ultraviolet to far infrared.4
Graphene is also extremely flexible, a property that researchers have leveraged for the development of “smart tattoos” or “electronic skin”. These are graphene patches that can act as wireless sensors to monitor human pulse, hydration, breathing and body movement.5
A graphene fitness patch monitors pulse, breathing, and hydration. Image credit: ICFO, Source.
Quantum Dot Nanotechnology
One nanotechnology which has found applications ranging from electronic displays to biomedical treatments is Quantum dots (QDs). Quantum dots are single nanoparticles (nanocrystals) roughly 2-10 nanometers (nm) in diameter, so essentially these are tiny semiconductors. Their hallmark trait is that they possess both electrical and optical properties.
They emit their own pure, monochromatic light when exposed to light or electrified. The color of the light is dependent on the shape and size of the particle.
Smaller dots emit shorter wavelengths, closer to the violet end of the visible light spectrum (roughly 380-450 nm), while larger dots emit longer wavelengths in the reddish spectrum (roughly 620-750 nm).
QDs are useful in a large range of photonic, fluorescent and electrochemical applications due to this “tunability” to generate different light outputs. They are also extremely energy efficient: almost 100 % of the energy applied to a QD system is emitted as light.
Cadmium and Selenium (CdSe) quantum dots of different sizes are contained in these vials, suspended in heat-transfer fluid. The wavelength of their fluorescence is dependent on the size and shape of the QDs. Image Credit: Rice University Catalysis and Nanomaterials Laboratory, via Creative Commons license CC. By-SA 3.0
Quantum dots can be made from a range of materials, these include:
- Cadmium selenide
- Zinc sulfide
- Indium phosphide
- Lead sulfide
- Zinc selenide
They are usually coated in a protective polymer to prevent any toxins from leaching out when being utilized inside the human body. Their photo-physical properties are being utilized in the biomedical realm to help develop more “personalized” medicine methods and to treat cancer and other diseases.
For instance, QDs can be encased within a shell which is tuned to seek out and attach to disease receptors in the body. Clusters of the fluorescent particles can then be detected, supplying physicians with a non-invasive technique to pinpoint the exact location of harmful cells such as cancer.
Quantum dots can even be employed to transport treatment drugs in the body. For instance, to minimize the harmful impact on surrounding, healthy cells, they are able to deliver chemotherapy drugs directly to cancer cells.6
QDs clustered around cancerous cells (red) help physicians and surgeons locate and treat the disease with precision. Scale bar = 20 µm. Image Credit: Source
Quantum Dots in the Display Industry
The display industry is continually searching for technologies which can supply brighter, higher-resolution and more vivid on-screen images. The industry has adapted quickly to QDs.
A common method is to layer a quantum dot enhancement film (QDEF) onto LED backlit screens to enhance image quality. A blue LED backlight is converted by QDs to pure red and green light, which combine with the blue to create RGB pixels.
There are multiple ways that quantum dots can be incorporated into displays to capitalize on their optical/visual and electronic properties. The IEEE has categorized some of the primary QD display types, these include: 6
Photo-Emissive QD TV
QDs are employed as the filter layer. The blue backlight excites the dots and they themselves become the red and green subpixels; minute holes in the filter layer allow the backlight to shine through and create the blue subpixels. Some benefits of this structure include:
- A wide viewing angle
- Better efficiency and brightness than traditional LCDs (as much as threefold)
- They can be manufactured by utilizing existing LCD fabrication infrastructure and facilities.
Structure of a photo-emissive quantum dot television. Image Credit: James Provost, Source: IEEE Spectrum.
Photo-Enhanced Quantum-Dot TV
QDs inserted between an LED array and color filters are employed to purify the TV backlight, enhancing the image color on screen. Some of the benefits include:
- No burn-in (unlike OLED screens)
- Vivid color at high peak luminance
- Low cost to produce
- Can be manufactured using existing LCD fabrication facilities and infrastructure.
Structure of a photo-enhanced quantum dot television. Image Credit: James Provost, Source: IEEE Spectrum.
Electro-Emissive QD TV
Electric current is applied to the QDs causing them to emit light directly (no backlight). Advantages of this structure include:
- Long lifetime
- Flexible substrates
- Perfect viewing angle
- Perfect black levels
- Fast refresh rate
- No filter layer needed
- Potentially low-cost manufacturing
Structure of an electro-emissive quantum dot television. Image Credit: James Provost, Source: IEEE Spectrum.
MicroLED TV With QDs
Some microLED televisions utilize a range of microscopic monochrome LEDs with QDs supplying the color conversion for red and green subpixels. Some benefits of this structure include:
- The brightest display technology available
- Perfect viewing angle
- Fast refresh rate
- Perfect blacks
- No filters needed
- Buildable on flexible substrates
Structure of a microLED quantum dot television. Image Credit: James Provost, Source: IEEE Spectrum.
MicroLED displays need a unique fabrication infrastructure. There are already multiple commercial products using QD technology on the market. The Sony Triluminos television was the first, in 2013. Samsung’s quantum dot LED (QLED) televisions have become widespread and were first released in 2017.
Samsung’s latest innovation is its Neo QLED televisions which replace the standard LED backlight panel with a miniLED backlight to supply more precise brightness control (local dimming).
Quantum Display Quality and Performance
Quantum-dot displays are still subject to the same quality issues as traditional displays, although they may provide better visual performance. Regardless of the structure and fabrication technique utilized, mura (blemishes), dead pixels and non-uniformity can occur.
If they are not identified and corrected during production these defects mar the viewing experience and lead to customer dissatisfaction. Radiant’s visual inspection solutions measure display uniformity and performance down to the pixel and subpixel level, with precise spatial resolution as fine as 0.45 µm.
Radiant Vision Systems has developed a proprietary technique for measuring and correcting pixel-to-pixel variation in microLED, OLED and similar emissive displays.
To ensure the absolute quality of today’s ultra-high-resolution displays, their ProMetric® Imaging Photometers and Colorimeters match the acuity and discernment of human visual perception of light and color.
Radiant solutions enable QD display manufacturers to assess performance and uniformity with subpixel accuracy, at production line speeds and with repeatable results when utilized alone or combined with their Microscope Lens.
A Radiant ProMetric Y Imaging Photometer with Microscope Lens, used to measure subpixels of an OLED display. Image Credit: Radiant Vision Systems
References
- Global Nanotechnology Market (by Component and Applications), Funding & Investment, Patent Analysis and 27 Companies Profile & Recent Developments – Forecast to 2024. Report published by Research and Markets, April 2018.
- Ibid.
- Yaniv, Z., “Nanotechnology and Display Applications.” Presentation of Applied Nanotech, Inc., February 2015.
- Savage, N., “Tomorrow’s industries: from OLEDs to nanomaterials.” Nature, December 11, 2019.
- Niu, S., et al., “A wireless body area sensor network based on stretchable passive tags,” Nature Electronics, No 2, pp. 360-368, August 15, 2019. doi: 10.1038/s41928-019-0286-2
- Fang, M., et al. “Quantum Dots for Cancer Research: Current Status, Remaining Issues and Future Perspectives.” Cancer Biology & Medicine 9(3): 151-163, September 2012. doi: 10.7497/j.issn.2095-3941.2012.03.001
- Luo, Z., Manders, J. and Yurek, J., “Your Guide to Television’s Quantum-Dot Future.” IEEE Spectrum, February 22, 2018.
Acknowledgments
Produced from materials originally authored by Anne Corning from Radiant Vision Systems.
This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.
For more information on this source, please visit Radiant Vision Systems.