Tag Archives: materials engineering

Ruthenium Nanolayers are Ferromagnetic at RT

Researchers from Intel Corporation and the University of Minnesota and the University of Wisconsin have shown that strained atom-scale films of pure ruthenium (Ru) metal exhibit ferromagnetism at room temperature, openning up the possibility of using the material to build novel magnetic random access memory (MRAM) devices. As per details recently published in Nature Communications (https://doi.org/10.1038/s41467-018-04512-1), Ru thin films with a thickness of 2.5, 6, or 12 nm, were grown on Al2O3 substrates cut along the (110) direction, that had been covered with a 20 nm Mo seed layer. The thin films were grown using a eight-target UHV sputtering system with base pressure of 8 × 10−8 Torr or lower, resulting in the controlled epitaxial growth of strained body-centered tetragonal phase Ru.

From first principles of materials engineering, there should be ways to use different templating materials for this graphoepitaxial process such that silicon-oxide could be used as the substrate instead of aluminum-oxide. If so, then this process could be run on 300mm silicon wafers in today’s leading commercial IC fabs.

The (001) tetragonal Ru plane does not lie perpendicular to the substrates which leads to a soft coercive field, however, if out-of-plane texturing can be achieved high coercivity Ru may be realized. The thickness dependence was also examined, and it was found that due to Ru relaxing into a non-ferromagnetic phase, the magnetization drops with increasing thickness. The 12 nm thick sample showed magnetization of about one-half that of the two thinner samples.

Original Article: https://www.nature.com/articles/s41467-018-04512-1


Fish-Scale Piezo Generators

Piezoelectric generators are based on thin-films of structured materials that can convert pressure into electricity. Inorganic crystals such as aluminum-nitride (AlN) barium titanate (BT) and lead-zirconium-titanate (PZT) have long been explored as piezoelectric films for various applications. Now researchers Sujoy Kumar Ghosh and Dipankar Mandal at the Jadavpur University in Kolkata, India have shown that fish scales (FSC) can be used to build a flexible bio-piezoelectric nanogenerator (BPNG) capable of producing a maximum output power density of 1.14 μW/cm2 under repeated compressive normal stress of 0.17 MPa.

Fabrication of flexible (BPNG) from bio-waste fish-scale (FSC) a) photographs of the bio-waste raw FSC, and demineralised FSC, b) flexibility of the BPNG shown by human fingers, and c) schematic diagram of simple BPNG device structure. (Source: APL)

Fabrication of flexible (BPNG) from bio-waste fish-scale (FSC) a) photographs of the bio-waste raw FSC, and demineralised FSC, b) flexibility of the BPNG shown by human fingers, and c) schematic diagram of simple BPNG device structure. (Source: APL)

As recently published in Applied Physics Letters with the title, “High-performance bio-piezoelectric nanogenerator made with fish scale,” the Figure shows that they started with the skin trimmings of Indian carp (Catla catla), that were acid washed and demineralized to extract collagen of nominal thickness ∼250 ± 10 μm, which is then sandwiched between 90nm thick sputtered gold electrodes, followed by lamination with polypropylene (PP) film ∼125 μm thick.
Energy harvesting is enabled by the self-assembled and ordered collagen nano-fibrils, which exhibit intrinsic piezoelectric strength of −5.0 pC/N.

…the most abundant piezoelectric biomaterial present in animal tissues such as skin, tendon, cartilage, bone, and even in human heart, is the type I collagen, which is a biocompatible and biodegradable polymer enabling fabrication of the flexible BPNG. The cost effective collagen source is the fish constituents such as skin, fins, maws, and swim bladder which are mainly treated as “bio waste” materials because different fish species are consumed daily in large quantities worldwide. The disposal of these bio-wastes causes an increasing environmental pollution. The recycling of the fish by-products into the BPNG via one step process is a promising solution for the development of value-added products and also to reduce the e-waste elements.

The BPNG is able to convert several forms of mechanical energy into electricity. For example, gentle press-hold-release motions of a single human finger (∼3.75 kPa and strain rate of 0.017% s−1) results in ∼680 mV output voltage with perfect switching of polarity. It scavenges mechanical energy from high level vibration from machines and also from very low level vibration, arises from sound (∼0.2–2.0 Pa) and wind motions (∼3.6 m/s). When slapped repeatedly by a human hand (∼ 0.17 MPa with 0.77% s−1 strain rate) this BPNG generates a rectified open circuit voltage (Voc) of 4 V, and multiple layers can be stacked to multiply the Voc. Due to high sensitivity, good stability, and efficient piezoelectric power-generating performance, these BPNG may open a new era in sustainable energy harvesting.