A flexible single-crystalline PMN-PT piezoelectric energy harvester is demonstrated to achieve a self-powered artificial cardiac pacemaker. The energy-harvesting device generates a short-circuit current of 0.223 mA and an open-circuit voltage of 8.2 V, which are enough not only to meet the standard for charging commercial batteries but also for stimulating the heart without an external power source.

Metal-oxide nanocrystals are expected to find useful applications in catalysis, energy storage, magnetic data storage, sensors, and ferrofluids. [1] In particular, colloidal metal-oxide nanocrystals are of great interest for technological applications owing to their unique size-dependent properties and excellent processability. Recent advances in the colloidal synthesis of metal oxides reveal that thermal decomposition of metal acetylacetonates, [2] metal cupferronates, [3] metal alkoxides, [4] and metal carbonyls [5] in complex organic solvent systems can lead to monodisperse metal oxide nanoparticles in certain cases.Manganese oxides are widely used as electrode materials, [6] catalysts, [7] and soft magnetic materials. [8] In spite of their important applications, there has been only one report on synthesis of monodisperse colloidal manganese-oxide nanoparticles.[3] Furthermore, a systematic study on the relationship between particle size and physical properties has never been conducted. Herein we report a simple, reliable synthesis of size-focused colloidal nanocrystals of two different manganese oxides, Mn 3 O 4 and MnO, from thermal decomposition of a single precursor [Mn(acac) 2 ] (acac = acetylacetonate) in oleylamine, as well as their unique size-dependent magnetic properties.A slurry of [Mn(acac) 2 ] (0.3 g) in oleylamine (7.6 g; 1:24 molar ratio) was heated at 180 8C for 9 h under an atmosphere of argon, and the resulting reaction mixture was cooled to room temperature to form a brown suspension. After centrifugation at 3000 rpm for 10 min, the supernatant was removed to afford a brown precipitate. Dichloromethane (10 mL) was added to the resulting brown precipitate to give a brown suspension, which was sonicated for 10 min to form a clear solution. Removal of the insoluble material, if any, by centrifugation and precipitation by adding ethanol (40 mL) produced a brown powder, which could be easily redispersed in various organic solvents such as hexane, toluene, and dichloromethane. The low-resolution transmission-electronmicroscope (TEM) image of the powder shows nearly monodisperse spherical nanoparticles of 10 nm in diameter as shown in Figure 1

Shape- and size-controlled synthesis of single-crystalline maghemite (gamma-Fe2O3) nanocrystals are performed by utilizing a solution-based one-step thermolysis method. Modulating the growth parameters, such as the type and amount of capping ligands as well as the growth time, is shown to have a significant effect on the overall shape and size of the obtained nanocrystals and on the ripening process itself. The resulting shapes of the novel structures are diverse, including slightly faceted spheres, diamonds, prisms, and hexagons, all of which are in fact truncated dodecahedron structures with different degrees of truncation along the {111}, {110}, or {100} faces. Spherical nanocrystals are easily assembled into the three-dimensional superlattices, demonstrating the uniformity of these nanocrystals. The size-dependent magnetic properties are examined, and large hexagon-shaped gamma-Fe2O3 nanocrystals are shown to be ferrimagnetic at room temperature.

Highly crystalline, phase- and size-controlled CoO nanocrystals of hexagonal and cubic phases have been prepared by thermal decomposition of Co(acac)3 in oleylamine under an inert atmosphere. Kinetic and thermodynamic control for the precursor formation leads to two different seeds of hexagonal and cubic phases at higher temperatures. The crystal size of both CoO phases can be easily manipulated by changing the precursor concentration and reaction temperature.

Although multicomponent core-shell type nanomaterials are one of the highly desired structural motifs due to their simultaneous multifunctionalities, the fabrication strategy for such nanostructures is still in a primitive stage. Here, we present a redox-transmetalation process that is effective as a general protocol for the fabrication of high quality and well-defined core-shell type bimetallic nanoparticles on the sub-10 nm scale. Various core-shell type nanomaterials including Co@Au, Co@Pd, Co@Pt, and Co@Cu nanoparticles are fabricated via transmetalation reactions. Compared to conventional sequential reduction strategies, this transmetalation process has several advantages for the fabrication of core-shell type nanoparticles: (i) no additional reducing agent is needed and (ii) spontaneous shell layer deposition occurs on top of the core nanoparticle surface and thus prevents self-nucleation of secondarily added metals. We also demonstrate the versatility of these core-shell structures by transferring Co@Au nanoparticles from an organic phase to an aqueous phase via a surface modification process. The nanostructures, magnetic properties, and reaction byproducts of these core-shell nanoparticles are spectroscopically characterized and identified, in part, to confirm the chemical process that promotes the core-shell structure formation.

Deep brain stimulation (DBS) is widely used for neural prosthetics and brain-computer interfacing. Thus far in vivo implantation of a battery has been a prerequisite to supply necessary power.Although flexible energy harvesters have recently emerged as an alternative to the battery, they generate insufficient energy for operating brain stimulation. Herein, we report a high performance flexible piezoelectric energy harvester enabling self-powered DBS in mice. This device adopts an indium modified crystalline Pb(In1/2Nb1/2)O3 -Pb(Mg1/3Nb2/3)O3 -PbTiO3 (PIMNT) thin film on a plastic substrate to transform tiny mechanical motions to electricity. By slight bending, it generates an extremely high current reaching 0.57 mA which satisfies high threshold current for real-time DBS of the motor cortex and thereby could efficiently induce forearm movements in mice. The PIMNT based flexible energy harvester could open a new direction for future in vivo healthcare technology using self-powered biomedical devices. Broader contextImplantable biomedical devices have attracted a great attention in light of improving the quality of life and prolonging the life expectancy of human. The implantable electronics are widely used in various parts in the patient's body as medical remedy tools such as deep brain stimulation (DBS), cardiac pacemaker, visual prosthesis, and cochlear implant, by electric stimulation of nerve/muscle and monitoring of health condition. However, the conventional implanted batteries have limited lifetime, fixed energy density, and large volume. Recently, many research teams have explored energy harvesting technology which scavenges electricity from biomechanical energy sources to eliminate the implantable batteries or directly stimulate nerve/muscle. Flexible piezoelectric energy harvester is a promising candidate to realize the self-powered implantable bioelectronics, since it can harvest electric energy from inexhaustible slight motions of organs such as heart, lung, and diaphragm. This work has introduced a new platform of self-powered DBS via a high-performance flexible piezoelectric harvester to directly excite neuron of living brain for inducing behavioural changes.A self-powered deep brain stimulation was demonstrated by a flexible piezoelectric PIMNT energy harvester to induce behavioural change of mouse.

Massive fabrication of free-standing Co/Pt magnetic barcode nanowires with well-defined interfaces and layer thicknesses is obtained after freeing them from porous templates. Such barcodes display bamboo-like shapes with identical motifs either inside or out of the templates. The ferromagnetism of these barcode nanowires can be modulated easily depending on the cobalt segments and shape anisotropies. Further enhancements of the ferromagnetism of Co/Pt barcodes are also accomplished through interfacial alloying processes via a thermally induced phase transition.

Bimetallic PtNi nanoparticles have been considered as a promising electrocatalyst for oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs) owing to their high catalytic activity. However, under typical fuel cell operating conditions, Ni atoms easily dissolve into the electrolyte, resulting in degradation of the catalyst and the membrane-electrode assembly (MEA). Here, we report gallium-doped PtNi octahedral nanoparticles on a carbon support (Ga-PtNi/C). The Ga-PtNi/C shows high ORR activity, marking an 11.7-fold improvement in the mass activity (1.24 A mg) and a 17.3-fold improvement in the specific activity (2.53 mA cm) compared to the commercial Pt/C (0.106 A mg and 0.146 mA cm). Density functional theory calculations demonstrate that addition of Ga to octahedral PtNi can cause an increase in the oxygen intermediate binding energy, leading to the enhanced catalytic activity toward ORR. In a voltage-cycling test, the Ga-PtNi/C exhibits superior stability to PtNi/C and the commercial Pt/C, maintaining the initial Ni concentration and octahedral shape of the nanoparticles. Single cell using the Ga-PtNi/C exhibits higher initial performance and durability than those using the PtNi/C and the commercial Pt/C. The majority of the Ga-PtNi nanoparticles well maintain the octahedral shape without agglomeration after the single cell durability test (30,000 cycles). This work demonstrates that the octahedral Ga-PtNi/C can be utilized as a highly active and durable ORR catalyst in practical fuel cell applications.