Cihan Kuru

Solution-Processed CoFe2O4 Nanoparticles on 3D Carbon Fiber Papers for Durable Oxygen Evolution Reaction

We report CoFe2O4 nanoparticles (NPs) synthesized using a facile hydrothermal growth and their attachment on 3D carbon fiber papers (CFPs) for efficient and durable oxygen evolution reaction (OER). The CFPs covered with CoFe2O4 NPs show orders of magnitude higher OER performance than bare CFP due to high activity of CoFe2O4 NPs, leading to a small overpotential of 378 mV to get a current density of 10 mA/cm(2). Significantly, the CoFe2O4 NPs-on-CFP electrodes exhibit remarkably long stability evaluated by continuous cycling (over 15 h) and operation with a high current density at a fixed potential (over 40 h) without any morphological change and with preservation of all materials within the electrode. Furthermore, the CoFe2O4 NPs-on-CFP electrodes also exhibit hydrogen evolution reaction (HER) performance, which is considerably higher than that of bare CFP, acting as a bifunctional electrocatalyst. The achieved results show promising potential for efficient, cost-effective, and durable hydrogen generation at large scales using earth-abundant materials and cheap fabrication processes.

High-performance flexible hydrogen sensor made of WS2 nanosheet–Pd nanoparticle composite film

We report a flexible hydrogen sensor, composed of WS2 nanosheet-Pd nanoparticle composite film, fabricated on a flexible polyimide substrate. The sensor offers the advantages of light-weight, mechanical durability, room temperature operation, and high sensitivity. The WS2-Pd composite film exhibits sensitivity (R 1/R 2, the ratio of the initial resistance to final resistance of the sensor) of 7.8 to 50,000 ppm hydrogen. Moreover, the WS2-Pd composite film distinctly outperforms the graphene-Pd composite, whose sensitivity is only 1.14. Furthermore, the ease of fabrication holds great potential for scalable and low-cost manufacturing of hydrogen sensors.

Unusually High Optical Transparency in Hexagonal Nanopatterned Graphene with Enhanced Conductivity by Chemical Doping

Graphene has received appreciable attention for its potential applications in flexible conducting film due to its exceptional optical, mechanical, and electrical properties. However increasing transmittance of graphene without sacrificing the electrical conductivity has been difficult. The fabrication of optically highly transparent (≈98%) graphene layer with a reasonable electrical conductivity is demonstrated here by nanopatterning and doping. Anodized aluminium oxide nanomask prepared by facile and simple self-assembly technique is utilized to produce an essentially hexagonally nanopatterned graphene. The electrical resistance of the graphene increases significantly by a factor of ≈15 by removal of substantial graphene regions via nanopatterning into hexagonal array pores. However, the use of chemical doping on the nanopatterned graphene almost completely recovers the lost electrical conductivity, thus leading to a desirably much more optically transparent conductor having ≈6.9 times reduced light blockage by graphene material without much loss of electrical conductivity. It is likely that the availability of large number of edges created in the nanopatterned graphene provides ideal sites for chemical dopant attachment, leading to a significant reduction of the sheet resistance. The results indicate that the nanopatterned graphene approach can be a promising route for simultaneously tuning the optical and electrical properties of graphene to make it more light-transmissible and suitable as a flexible transparent conductor.

Fabrication and Magnetic Properties of Nonmagnetic Ion Implanted Magnetic Recording Films for Bit-Patterned Media

We have investigated the magnetic M-H loop characteristics of CoCrPt-SiO2 perpendicular recording media as influenced by nonmagnetic ion implantations. We have also developed patterned media via ion implantation using a convenient polymer nanomask approach for local control of coercivity of magnetically hard [Co/Pd]n multilayer film with a [Co 0.3 nm \Pd 0.8 nm] 8/Pd 3 nm/Ta 3 nm layer structure. The CoCrPt-SiO2 magnetic layer having perpendicular magnetic anisotropy is sputter deposited on a flat substrate. The [Co/Pd] n multilayer film with vertical magnetic anisotropy is deposited and the regions corresponding to the magnetic recording bit islands are coated with polymer islands using a nanoimprinting technique. Subsequent ion implantation allows patterned penetration of implanted ions into the [Co/Pd]n multilayer film, thus creating magnetically isolated bit island geometry while maintaining the overall flat geometry of the patterned media.

Deformation and electrical properties of magnetic and vertically conductive composites with a chain-of-spheres structure

Vertically anisotropically conductive composites with aligned chain-of-spheres of 20–75 mm Ni particles in an elastomer matrix have been prepared by curing the mixture at 100°C–150°C under an applied magnetic field of ∼300–1000 Oe. The particles are coated with a ∼120 nm thick Au layer for enhanced electrical conductivity. The resultant vertically aligned but laterally isolated columns of conductive particles extend through the whole composite thickness and the end of the Ni columns protrude from the surface, contributing to enhanced electrical contact on the composite surface. The stress-strain curve on compressive deformation exhibits a nonlinear behavior with a rapidly increasing Young’s modulus with stress (or pressure). The electrical contact resistance Rc decreases rapidly when the applied pressure is small and then more gradually after the applied pressure reaches 500 psi (∼3.4 MPa), corresponding to a 30% deformation. The directionally conductive elastomer composite material with metal pads and conductive electrodes on the substrate surface can be used as a convenient tactile shear sensor for applications involving artificial limbs, robotic devices, and other visual communication devices such as touch sensitive screens.

Diameter-Reduced Islands for Nanofabrication Toward Bit Patterned Magnetic Media

Thin films deposited on a flat substrate, if the adhesion is not strong, can be made to ball up and form discrete islands upon heating to elevated temperatures due to the surface energy difference. We have applied this useful process to electron beam lithography (EBL) and nano-imprinting lithography (NIL). By combining the ball-up processes of Ni thin film with e-beam lithography followed by reactive ion etching, Si nano islands and vertical nanopillars as small as 10 nm in diameter have been realized. There is a strong correlation between the initial thickness of Ni mask layer and final Ni island diameter obtained after ball-up. The smallest island diameter is obtained using ~ 5-nm initial Ni layer thickness. Below 3-nm initial layer thickness, the intended ball-up reaction does not occur. With more than ~ 15-nm initial metal film thickness, the Ni layer is broken up into nonspherical and highly irregular structures. [Co/Pd]n multilayer magnetic thin films deposited on prepatterned substrate by nano imprinting lithography with versus without island ball-up process have been investigated for bit patterned media studies. The coercivity of magnetic islands can be enhanced by island diameter reduction using the ball up process.