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CTT-other mat stories

Published on June 4th, 2013 | Edited by: Eileen De Guire

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Other materials stories that may be of interest

Published on June 4th, 2013 | Edited by: Eileen De Guire

Epitaxial SiC films grown on 300mm silicon wafers

The Queensland Micro and Nanotechnology Facility of Griffith University (Brisbane, AU) and industry partner SPTS Technologies, a Newport, UK, supplier of advanced wafer processing solutions for semiconductor and related markets, have developed a process for epitaxial growth of 3C silicon carbide films on 300mm silicon wafers. The result of more than 10 years of research in low-temperature SiC deposition on silicon, the SiC is expected to provide a cost-effective buffer material that will enable fabrication of gallium nitride LEDs and power devices on large-diameter silicon wafers. Researchers say the film provides an effective buffer layer lattice-matched for GaN growth on silicon and would add no more than $25 to $35 to wafer cost, substantially increasing the appeal of silicon as a substrate for LEDs and GaN power devices.

 

Graphene sensor allows clear photos in dim light

To paraphrase Homer Simpson, who was musing on the power of doughnuts: Graphene—is there anything it can’t do? One of the material’s latest applications is in a new image sensor said to be 1,000 times more sensitive to light than current CCD and CMOS imaging sensors while using 10 times less energy. Developed at Nanyang Technological University (Singapore), the graphene sensor uses innovative surface nanostructures to “trap” light-generated electrons for a long time, resulting in a much stronger electric signal that can then be processed into an image. The device can detect light from the visible to mid-infrared, and is expected to be significantly less expensive than other sensor types when mass produced.

 

Eggshells serve as feedstock for hydroxyapatite production

Nano Labs Corp. (Detroit) has developed a process for converting eggshells into hydroxyapatite, the main material used in prosthetic implants and other biomedical appplications. The company says its nanotechology process uses direct calcination of eggshells to produce commercial grade calcium dibasic phosphate and lime followed by hydrothermal synthesis of hydroxyapatite with high crystallinity, good homogeneity, and average particle size of 0.06 μm. According to the US Department of Agriculture, hens at US egg farms produced 92.9 billion eggs in 2012, so there should be no shortage of raw material for the process.

 

Moth-inspired nanostructures take the color out of thin films

Inspired by the structure of moth eyes, researchers at North Carolina State University have developed nanostructures that limit reflection at the interfaces where two thin films meet, suppressing the “thin-film interference” phenomenon commonly observed in nature. This can potentially improve the efficiency of thin-film solar cells and other optoelectronic devices. Thin-film interference occurs when a thin film of one substance lies on top of a second substance. For example, thin-film interference is what causes the rainbow sheen we see when there is gasoline in a puddle of water. This interference is a problem for devices that use multiple layers of thin films, like thin-film solar cells, because it means that some wavelengths of light are being reflected. “We were inspired by the surface structure of a moth’s eye, which has evolved so that it doesn’t reflect light,” says Chih-Hao Chang, an assistant professor of mechanical and aerospace engineering at NC State and co-author of a paper on the research. The nanostructures are built into thin films that will have a second thin film placed on top of them. The nanostructures are an extension of the thin film beneath them, and resemble a tightly-packed forest of thin cones. These nanostructures are “interfacial,” penetrating into whatever thin film is layered on top of them—and limiting the amount of light reflected at that interface. Chang’s team found that the an interface featuring the interfacial nanostructures reflects 100 times less light than an interface of thin films without the nanostructures.

 

Nanocrystals grow from liquid interface

An international collaboration of scientists has discovered a unique crystalizing behavior at the interface between two immiscible liquids that could aid in sustainable energy development. In their latest work, the researchers from the US, Israel and Germany wanted to find out, for the first time, what exactly occurs during chemical growth at liquid interfaces. Led by researchers from the Institute of Experimental and Applied Physics of Kiel University, the team observed the formation of an ordered crystal of exactly five atomic layers between the two liquids, which acts as a foundation for growing even bigger crystals. This work may result in new semiconductor and nanoparticle production processes. They investigated mercury surface in contact with a salt solution containing lead and bromine (or fluorine) ions and obtained an astonishing result: although both liquids were atomically disordered in the bulk, a nanometre thin layer, that is a ten thousandth of the width of a human hair, with crystalline order was formed at their interface. “Our X-ray data show that this layer consists of an atomic layer of fluorine between two layers of lead and bromine”, says team member Annika Elsen, from Kiel University. “Subsequently, larger crystals grow perfectly aligned on top of this nano-layer crystal.”

 

Pressure tuning of a quantum phase transition in an exotic magnetic material

The exotic compound SrCu2(BO3)2, or SCBO, was studied recently at the Spallation Neutrons and Pressure Diffractometer at Oak Ridge National Laboratory. Sara Haravifard, a physicist at the University of Chicago and Argonne National Laboratory (ANL), is studying how SCBO transitions from one magnetic phase to another under extreme conditions: high pressure and low temperature. This work is benefiting from the experimental resources of two user facilities: X-ray scattering at the ANL Advanced Photon Source and neutron scattering at the ORNL Spallation Neutron Source. The complementarity between the two techniques is well illustrated in this case, as the initial x-ray investigation hinted at two quantum phase transitions, one at a pressure of ~2 GPa and another at ~4 GPa. At this higher pressure, the researchers observed a change in the atomic lattice of the material that, given the strong spin-lattice coupling in the system, suggested the onset of an antiferromagnetic-ordered phase transition. Based on those results, the researchers decided to investigate this system using neutrons at SNS. “Using neutrons at pressures higher than ~4 GPa was considered to be the next step in studying this new magnetic-ordered phase because, unlike x-rays, neutrons can detect magnetism directly,” Haravifard says. SCBO, a quasi two-dimensional system, contains perpendicular copper dimers that carry magnetic spins lying on a square lattice and with only weak interactions between adjacent planes. This arrangement, known as the Shastry-Sutherland lattice, has a quantum mechanical ground state and excited states that can be solved exactly. SCBO is unique in that it is one of a few rare materials that realize this model.

 

Norwegian firm to seek ways to trap cement factory CO2

Norway’s Aker Solutions has won a contract to make the world’s first tests for capturing emissions of carbon dioxide from cement factories as part of efforts to slow climate change, the company says. Aker Solutions won the contract from Heidelberg Cement’s Norwegian unit Norcem, in cooperation with the European Cement Research Academy, a statement said. It did not give the value of the deal. Aker Solutions will carry out extensive tests of emissions from Norcem’s cement plant in Brevik, south Norway, to find the best chemical solvent for capturing carbon dioxide, the main greenhouse gas. “The award … marks the first time technology to capture carbon dioxide is used at a cement production plant,” Aker Solutions says in a statement. The company says the project would give Norcem “valuable information … and help the European cement industry understand the use of technology for future full-scale carbon dioxide capture from cement production plants.”


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