Holograms made of tiny particles of silver could double the amount of information that can be stored in digital optical devices, such as sensors, displays and medical imaging devices.
Researchers from the University of Cambridge have developed a new method for making multi-coloured holograms from a thin film of silver nanoparticles, which could greatly increase the storage capabilities of typical optical storage devices.
The interference produced by the interaction of light with the nanoparticles allows the holograms to go beyond the normal limits of diffraction, or the way in which waves spread or bend when they encounter an opening or obstacle. The results were recently published in the journal Proceedings of the National Academy of Sciences.
When metallic particles have dimensions on the nanoscale, they display iridescent colours. A noted example of this phenomenon is the Lycurgus cup, which was made in the 4th century during the Roman Empire, and changes colour when held up to the light. An optical phenomenon, known as dichroism, occurs when the colour of the cup changes from green to red according to the position of the light source.
Roman artisans made the cup by incorporating nanoparticles into glass, although they would have been unaware of the specific physical characteristics responsible for the colours observed in the cup. Only in the last 20 years have scientists begun to understand this phenomenon, but they have not been able to utilise its effects in currently-available technology.
To apply this phenomenon in modern optics, an interdisciplinary team of researchers have created nanoscale metallic nanoparticle arrays that mimic the colour effects of the Lycurgus cup, to form multi-colour holograms. This breakthrough could lead to the shrinkage of standard bulky optical devices.
“This technology will lead to a new range of applications in the area of photonics, as conventional optical components simply cannot achieve this kind of functionality,” said Yunuen Montelongo, a PhD student from the Department of Engineering, who led the research. “The potential of this technology will be realised when they are mass produced and integrated into the next generation of ultra-thin consumer electronics.”
Using a single thin layer of silver, Montelongo and his colleagues patterned colourful holograms containing 16 million nanoparticles per square millimetre. Each nanoparticle, approximately 1000 times smaller than the width of a human hair, scatters light into different colours depending on its particular size and shape. The scattered light from each of the nanoparticles interacts and combines with all of the others to produce an image.
The device can display different images when illuminated with a different colour light, a property not seen before in a device of this type. Furthermore, when multiple light sources are shone simultaneously, a multi-colour image is projected.
These holographic devices are between 10 and 100 times smaller than just one of the millions of pixels used to produce a colour image on a typical laptop screen, yet they project a complete multi-colour image to the eye. This is possible through plasmonics: the study of how light interacts with metals on the nanoscale, which allows the researchers to go beyond the capability of conventional optical technologies.
“This hologram may find a wide range of applications in the area of displays, optical data storage, and sensors,” said PhD student Calum Williams, a co-author of the paper. “However, scalable approaches are needed to fulfil the potential of this technology.”
Currently, the team is exploring various optical mechanisms involved in the light-matter interaction at nanoscale. The future research will involve the construction of three-dimensional dynamic displays for consumer electronics and the researchers are already looking into tuning these devices for reconfigurable display technologies.
– See more at: http://www.cam.ac.uk/research/news/nanotechnology-used-to-create-next-generation-holograms-for-information-storage#sthash.umQbQBsi.dpuf
Size and Distribution of Alternative Energy Sources
Including Wind and Solar or ‘Green is Going Giant’
One of the largest issues with ‘Alternative Energy’ is the cost to build new systems when there
are already sources in place. It takes a desire to invest in our future to build these systems and time for
the investment to repay. In previous decades, it was thought that Solar and Wind energy were only
productive for small installations and had no way to hold up to large plants such as coal or nuclear.
There are companies, however, that are out to prove that raising the scale of renewable energy is not
only possible but more economic.
Arizona Public Service is a utility company in Tucson, Az. uses an array of mirrors that direct the
sun and heat a mineral oil to produce a liquid hydrocarbon which runs a generator. The mirrors equal
cover about 100,000 sq. ft. of area. At this size, the plant can produce about a megawatt of power. The
manufacturer, Acciona Solar Power, plans to open a 350 acre plant in Nevada that will be able to
produce 64 megawatts of power with similar technology. This is enough to power a medium sized town
including hospitals and malls.
In the early 1980’s in Hull, Mass. the municipality built a wind turbine to take advantage of the
strong breeze that blows from the ocean north of Boston. The turbine was able to power a handful of
homes at a generating capacity of 40 kilowatts. Given Hull’s close proximity to the ocean, slowing global
warming is in its best interest. A number of years later, the municipality built an even larger turbine
able to produce 660 kilowatts. While the original turbine looked like ‘a ham radio tower’, the new one,
named Hull 1, was on top of a 150 ft. tower. Only four years later, they installed Hull 2, a 1.8 megawatt
turbine. They are now working on four new turbines that can produce 3.6 megawatts each. Apart from
the increase in power, the larger, slimmer towers with the slower spinning blades are more aesthetically
A major difference between solar and wind powered apparatus and the larger coal burning
plants is that the major cost in coal is in mining and transportation while the cost of wind and solar
energy is split pretty evenly between the cost of parts and installation. To demonstrate this, the total
cost of Hull 2 was roughly $3 million. If 1,000 homes were to build 1.8 kilowatt homes they would
output the same amount of power but at a total cost of about $15 million. The investment period
before payoff would stay the same between the large and small scales. While a 14 year payback period
would be economical for a large installation, it would just not make sense at an individual scale.
In Nantucket Sound, there is a group working on the Cape Wind project. This is a project to
build an offshore wind farm of 130 3.6 megawatt turbines. The major cost in this project is not how
large the turbines are but rather the infrastructure to support them. This consists of underwater
structures to carry the electricity as well as the support structures to hold the towers. According to
Mark Rodger, a spokesperson for Cape Wind, states that ‘These are things that you are going to have to
do, whether it’s a very small or a very large offshore wind farm. The best bang for your buck is to go large.’
The same principals hold for solar cells. The cost of installing and maintaining a solar farm is
split almost evenly between the actual solar cells and the support structure around it. The costs
involved in transporting and installing these parts is significant and as stated earlier, given the
economics and size of the investment, bigger definitely is better.
– Bj Hile
http://www.nytimes.com/2007/03/07/business/businessspecial2/07big.html?pagewanted=all New York
Times; Matthew L. Wald; March 7th, 2007