Laser-induced self-assembly of iron oxide nanostructures with controllable dimensionality

Abstract

The nanosecond pulsed laser ablation of a fine iron powder submerged under different liquid media (water, methanol, ethanol and isopropanol) is used to rapidly produce a variety of iron oxide nanostructures from nanoparticles to nanowires and nanosheets. The dimensionality of the nanostructres is shown to be a consequence of two controllable mechanisms. The rapid oxidation, collisional quenching and coalescence of the ablation products is suggested as the dominant mechanism for the formation of 0D nanostructures such as hematite (α-Fe 2 O 3 ) nanoparticles in water, or iron oxyhydroxide nanoparticles under alcohols. By employing different laser wavelengths (248 and 532nm) it is demonstrated that the growth of extended iron oxyhydroxide nanostructures (1D nanowires and 2D nanosheets) under methanol is possible and is a consequence of a second self-assembly mechanism driven by interaction between the UV laser pulses and the ablation products.Low dimensional iron oxide nanostructures, such as nanoparticles and nanowires are of particular industrial and academic interest, not least because of their magnetic properties. Hematite (α-Fe 2 O 3 ) 1D nanostructures also have applications in lithium ion battery electrodes, gas sensors, field-effect transistors, and field emission cathodes. 1-3 Hematite nanowires have been synthesized by many different techniques including surface oxidation, thermal oxidation and electrochemical deposition. [4][5][6][7] These are generally complex processes taking considerable time (1.5-120 h), needing different gas flows and high temperatures (400-800 • C). Also, these processes typically produce nanowires that are attached to a metallic substrate, and thus subsequent collection for device integration can be challenging. Therefore, a solution based synthesis method to collect nanowires for * Electronic mail: s.henley@surrey.ac.uk † Present address: Department of Physics, Aligarh Muslim University, Aligarh-202002, India.1 rapid processing would be of considerable interest. Table 1 shows a comparison of time scales and process temperatures used in selected recent publications detailing iron oxide nanowire synthesis.Rapidly after the invention of the ruby laser in the 1960s, the capability of pulsed lasers to ablate material from the surface of solids was identified. Applications for pulsed laser ablation 8 (PLA) in materials processing and thin film deposition followed swiftly. Traditionally PLA and the subsequent material deposition is performed in vacuum or in dilute gaseous environments. The collisions of energetic ablated atoms with gas molecules in low-pressure gaseous environment, and any subsequent chemical reactions, has been identified a route for synthesizing multicomponent films with controllable stoichiometry. When the ambient gas pressure is increased, such that ablated species are expected to suffer multiple collisions within the reaction chamber, 9,10 the medium can be considered as weakly confining. In such confining environments nanoclusters of the target material ca...

Photo-Chemical Synthesis of Iron Oxide Nanowires Induced by Pulsed Laser Ablation of Iron Powder in Liquid Media

“…The starting iron powder demonstrates granules of size less than 60 μm [17]. When these are rusted in ethanol, methanol, water, isopronol and glycol with pulsed laser of wavelength 532 nm, we obtain iron oxide nanoparticles.…”

“…In this direction, we have prepared the goethite/hematite nanowires with a very simple technique by laser ablation with the shortest time reported so far. A comparison of different preparation techniques is reported earlier [17]. The present article testifies the photo-chemical synthesis of iron oxide nanowires induced by pulsed laser ablation of iron powder in liquid media and their chemical as well as structural characterization.…”

“…Their transmission electron microscopic (TEM) images demonstrate that the as-produced wires are of circular shape and amorphous in nature [17,18]. When it is annealed at 400°C, it starts crystallizing [17,18]. Nevertheless, annealing at 800°C crystallizes the nanowires fully [17,18].…”

“…The 20 min laser annealed solution is coated on glass slides/silicon substrates and annealed at different temperatures of 100-800°C for 2-4 h in air using a tube furnace. Their transmission electron microscopic (TEM) images demonstrate that the as-produced wires are of circular shape and amorphous in nature [17,18]. When it is annealed at 400°C, it starts crystallizing [17,18].…”

“…Iron oxide nanowires are synthesized by ultraviolet (UV) photochemical technique using the laser pulses from a Lambda-Physik LPX 210i excimer laser operating at 248 nm with pulse duration of 25 ns and Nd-YAG laser operating at wavelength 532 nm with pulse duration 15 ns [17,18]. Iron (Fe) powder from Goodfellow Cambridge Ltd. with purity more that 99% and maximum particle size of 60 μm is used as the starting material.…”