Creating a Green tomorrow with Nano-Paints

 With the many advantages of nano-materials coming to the fore every day, paint manufacturers are replacing conventional paints with those made from nano-particles. They are found to increase scratch resistance, have water repellency properties, provide UV protection, improve durability and have self-cleaning and anti-microbial properties. 

The application of these paints promises to achieve better energy ratings for buildings, better indoor air quality and fewer allergy-related illnesses than the conventional paints, which are usually composed of toxic VOCs (volatile organic compounds). Nanotechnology has helped in development of non-toxic coating systems, which not only stop the appearance of algae and fungal growth but also destroy antibiotic resistant bacteria that are commonly found in hospitals.

The growing awareness of reducing carbon footprints and improve energy costs has led to a widespread use of nano-paints, which are eco-friendly, cost-effective and healthy for the people and environment right now as well as in the future. Thermal insulating paints reduce the amount of heat penetrating into the buildings, thus keeping the inner environments cool and reducing the load on air conditioning systems. This in turn contributes greatly in reducing the world carbon output, thus enabling us to take effective steps towards fighting global-warming.

The US Navy also uses nano-coatings to paint their ships and repair worn out parts. They ensure that the algae do not grow on the metal parts and are instantly washed away by the ocean waters. The coatings are corrosion free; non-toxic and hence do their bit in saving marine life. Graphene based Electro Static paints are also being increasingly used in the Automobile industry.

Paints using nanotechnology are non hazardous to the human health and the environment. They play an important role in reducing pollution by binding with the pollutants and breaking them down. They are easier to clean, smoothly structured and last longer.

Nanotechnology has greatly improved the way the paints make our buildings look more beautiful, make them more eco-friendly and durable while making them energy and cost efficient.

Transistor Created by Single Electron

A University of Pittsburgh-led team has created a single-electron transistor which can act as a building block for powerful computer memories, advanced electronic materials and quantum computers.

The transistor's central component consists of only one or two electrons of 1.5 nanometers in diameter. That flexibility would make the transistor important to a range of computational applications, from memories to quantum processors, powerful devices.

In addition, the tiny central island could be used as an artificial atom for developing new classes of artificial electronic materials, such as exotic superconductors with properties not found in natural materials, explained.

Scientist cited their device as SketchSET, or sketch-based single-electron transistor. Using the sharp conducting probe of an atomic force microscope, electronic devices such as wires and transistors of nanometer dimensions can be created at the interface of a crystal of strontium titanate and a 1.2 nanometer thick layer of lanthanum aluminate. The electronic devices can then be erased and the interface used anew.

The SketchSET -- which is the first single-electron transistor made entirely of oxide-based materials -- consists of an island formation that can house up to two electrons. The number of electrons on the island -- which can be only zero, one, or two -- results in distinct conductive properties. Wires extending from the transistor carry additional electrons across the island.

One of the advantages of a single-electron transistor is its extreme sensitivity to an electric charge. Another property of these oxide materials is ferroelectricity, which allows the transistor to act as a solid-state memory. The ferroelectric state can, in the absence of external power, control the number of electrons on the island, which in turn can be used to represent the 1 or 0 state of a memory element. A computer memory based on this property would be able to retain information even when the processor itself is powered down, researcher commented. The ferroelectric state also is expected to be sensitive to small pressure changes at nanometer scales, making this device potentially useful as a nanoscale charge and force sensor.

Solar Cell fabricated by High Bandgap Inorganic Zinc Oxide Nanowire Arrays

Arrays of core/shell nanowires had previously been theorized as a potential structure that, while composed of chemically more stable large bandgap inorganic materials, should also be capable of absorbing the broad range of the wavelengths present in sunlight. High bandgap semiconductors are generally considered not effective at absorbing most of the available wavelengths in solar radiation by themselves. For instance, high bandgap zinc oxide (ZnO) is transparent in the visible but absorptive in the ultraviolet range, and thus is widely used in sunscreens but was not considered useful in solar cells.

In the report, a team of researchers from Xiamen University in China and the University of North Carolina at Charlotte describe successfully creating zinc oxide (ZnO) nanowires with a zinc selenide (ZnSe) coating to form a material structure known as a type-II heterojunction that has a significantly lower bandgap than either of the original materials. The team reported that arrays of the structured nanowires were subsequently able to absorb light from the visible and near-infrared wavelengths, and show the potential use of wide bandgap materials for a new kind of affordable and durable solar cell.

"High bandgap materials tend to be chemically more stable than the lower bandgap semiconductors that we currently have," noted team member Yong Zhang, a Bissell Distinguished Professor in the Department of Electrical and Computer Engineering and in the Energy Production and Infrastructure Center (EPIC) at the University of North Carolina at Charlotte.

And these nanowire structures can be made using a very low cost technology, using a chemical vapor deposition (CVD) technique to grow the array," he added. "In comparison, solar cells using silicon and gallium arsenide require more expensive production techniques.

Past attempts to use high band gap materials did not actually use the semiconductors to absorb light but instead involved coating them with organic molecules (dyes) that accomplished the photo absorption and simply transmitted electrons to the semiconductor material. In contrast, the team's heterojunction nanowires absorb the light directly and efficiently conduct a current through nano-sized "coaxial" wires, which separate charges by putting the excited electrons in the wires' zinc oxide cores and the "holes" in the zinc selenide shells.

"By making a special heterojunction architecture at the nanoscale, we are also making coaxial nanowires which are good for conductivity," said Zhang. "Even if you have good light absorption and you are creating electron-hole pairs, you need to be able to take them out to the circuit to get current, so we need to have good conductivity. These coaxial nanowires are similar to the coaxial cable in electrical engineering. So basically we have two conducting channels -- the electron going one way in the core and the hole going the other way in the shell."

The nanowires were created by first growing an array of six-sided zinc oxide crystal "wires" from a thin film of the same material using vapor deposition. The technique created a forest of smooth-sided needle-like zinc oxide crystals with uniform diameters (40 to 80 nanometers) along their length (approximately 1.4 micrometers). A somewhat rougher zinc selenide shell was then deposited to coat all the wires. Finally, an indium tin oxide (ITO) film was bonded to the zinc selenide coating, and an indium probe was connected to the zinc oxide film, creating contacts for any current generated by the cell.

"We measured the device and showed the photoresponse threshold to be 1.6 eV," Zhang said, noting that the cell was thus effective at absorbing light wave wavelengths from the ultraviolet to the near infrared, a range that covers most of the solar radiation reaching earth's surface.

Though the use of the nanowires for absorbing light energy is an important innovation, perhaps even more important is the researchers' success in using stable high bandgap inorganic semiconductor materials for an inexpensive but effective solar energy device.

"This is a new mechanism, since these materials were previously not considered directly useful for solar cells," Zhang said. He stressed that the applications for the concept do not end there but open the door to considering a larger number of high bandgap semiconductor materials with very desirable material properties for various solar energy related applications, such as hydrogen generation by photoelectrochemical water splitting.

"The expanded use of type II nanoscale heterostructures also extends their use for other applications as well, such as photodetectors -- IR detector in particular," he noted.