ABSTRACT
Hematite is an attractive material used as electron transport layer in perovskite-based solar cells. Being hydrophilic in nature it attracts moisture, which can be damaging for perovskite layers. Therefore, it is important to make hematite moisture repelling, which can be beneficial for applications in solar cells or for protecting iron surfaces from further rust formation. In this work, we demonstrate that the systematic irradiation of nanostructured hematite with low-energy argon ions (Ar+) at various ion fluences can change the surface wettability as well as promote the formation of junctions between nanorods. The nano-welded network of the irradiated hematite turns out to be hydrophobic. Using TRI3DYN simulations, ion-induced surface roughening, the presence of surface oxygen vacancies, and joining between adjacent nanorods are predicted. Furthermore, the water-repelling behavior of the irradiated nano-network is evaluated using density functional theory (DFT) simulations by determining the interaction of water molecules with the surface. The interconnected hematite nano-network also shows a notable improvement in electrical conductivity.
ABSTRACT
In this work we report for the first time a method to modify the surface of Cu2O nanowires in a controllable way and physically weld them into a network form, which contributes to higher electrical conductivity as well as a strong water-repelling nature. We have used state-of-the-art theoretical calculations to support our experimental observations. We demonstrate how varying the irradiation fluence can modulate the surface and decorate the nanowire with a uniform distribution of Cu8O nanocrystals due to preferential sputtering. While several well studied joining techniques are available for carbon and metal-based nanowires, the same information for ceramic nanowires is scarce at present. The current study sheds light into this and a state-of-the-art 3D simulation technique predicts most of the modifications including surface modulation, oxygen depletion and welding. The welded network shows higher electrical conductivity than the unwelded assembly. With Cu2O being of p-type the current ion beam joining technique shows a novel path for fabricating p-i-n junctions or solar cell devices through bottom-up approach. Furthermore, we have explored the response of this network to moisture. Our calculation based on density functional theory predicts the hydrophilic nature of individual copper oxide nanowires both before and after irradiation. However, the network shows a strong water-repelling nature, which has been explained quantitatively using the Cassie-Baxter model.
ABSTRACT
Low energy nitrogen ions are used in this work to manipulate wetting properties of the surface of the array of Cu2O nano-columns, which yields remarkable results. The nano-columnar thin films were grown on a highly conductive silicon surface by a sputter deposition technique. The films were irradiated at two different fluences of 5 × 10(15) and 1 × 10(16) ions per cm(2), respectively. With increasing fluence the shape of column tip changes, columns are bent and porous channels between columns are clogged up. While the surface of the pristine sample is hydrophilic, the irradiated surface turns into hydrophobic but having adhesion properties. We have analysed the structural and chemical properties of the surface in detail to understand the initial and modified wetting properties. Furthermore, the temporal evolutions of different droplet parameters are investigated to realize the interactions between the water droplet, the sample surface and the atmosphere. We envisage that such modified surfaces can be beneficial for transport of a small volume of liquids with minimum loss and spectroscopic studies, where a small amount of water droplet is available for measurements.
ABSTRACT
Crystalline hydrogen titanate (H2Ti3O7) nanowires were irradiated with N(+) ions of different energies and fluences. Scanning electron microscopy reveals that at relatively lower fluence the nanowires are bent and start to adhere strongly to one another as well as to the silicon substrate. At higher fluence, the nanowires show large-scale welding and form a network of mainly 'X' and 'Y' junctions. Transmission electron microscopy and Raman scattering studies confirm a high degree of amorphization of the nanowire surface after irradiation. We suggest that while ion-irradiation induced defect formation and dangling bonds may lead to chemical bonding between nanowires, the large scale nano-welding and junction network formation can be ascribed to localized surface melting due to heat spike. Our results demonstrate that low energy ion irradiation with suitable choice of fluence may provide an attractive route to the formation and manipulation of large-area nanowire-based devices.
ABSTRACT
Fe-doped ZnO nanorods were synthesized by solvothermal method with Fe concentration of 2%, 5% and 10%, respectively. The morphological and structural properties of the Fe-doped ZnO nanorods were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) technique, respectively. The presence of Fe doping with different concentration was confirmed by X-ray fluorescence (XRF) spectroscopy. For largest doping concentration of Fe, the optical band gap of ZnO was found to shift considerably about 25% to lower energies than that of the pristine ZnO. Furthermore the magnetic behavior was investigated on doped and undoped ZnO samples at room temperature as well as at low temperature. We found that these nanorods do not exhibit room temperature ferromagnetism. Instead a superparamagnetic-type behavior is observed for all the concentration with the blocking temperature in the range 13-35 K.
