The Research On Preparation And Property Of Two-Dimensional Nanoparticle Films

The assembly of nanomaterials has been an important technology that manufacture functional equipment with building bulks such as nanoparticles and organic molecules or other structure-directing agents under specific conditions.And it has been widely applied in biological medicine,optoelectronics,magnetism,energy and environmental protection fields.At present,two-dimensional assembled nanomaterials are mainly prepared by liquid phase method,which is stable and reliable with various synthetic schemes.But it also has some limitations.The difficulty of research increases nonlinearly with increased numbers of additional organic compounds.And two-dimensional（2D）film with large area and nanometer thickness is still hard to synthesize.Moreover,films always need to be transferred to make functional component,etc.Here,a simple liquid phase method of 1-octadecene（ODE）assisted self-supporting granular film was developed by using ferro-based magnetic nanoparticles and Au with good dispersibility and adjustable size and shape as the main building-bulks.The area of the monolayer nanoparticle film can reach millimeter level.Besides,a"dry"nanomaterial assembly technique:matrix-assisted pulsed laser deposition（MAPLE）was researched to deposit nanoparticle films.MAPLE can directly select the final supporter as substrate without transfer.And it has the advantages of high deposition efficiency.The well-ordered deposited magnetic nanoparticle films had unique magnetic anisotropy without the interference of liquid solution.The main contents and conclusions done in this paper are as follows:（1）A simple liquid phase method for preparing（ODE）₂-supported free-standing three-layer granular films was found.The film had a three-layer structure:the upper and lower layers are organic and granular layer is embedded in the middle.The thickness of the particle layer and organic layer could be adjusted by controlling the ratio of particles and ODE.Besides the granular film has outstanding chemical and structural stability and the method is suitable for nanoparticles with various materials,shapes and components.The particle spacing in monolayer Fe₃O₄/（ODE）₂ was about 1nm,which was much smaller than that in Fe₃O₄ particle film commonly obtained by drop coating.The blocking temperature（T_B）of the film increased from 240 K to more than 300 K.It was found that the decrease of the particle distance and the orientation of easy magnetic axis are the reason for the enhanced magnetic interaction.Au/（ODE）₂films were also synthesized and anlysed.It was found that the film had distinct local surface plasmon resonance（LSPR）absorption peaks in hexane,toluene and water.In situ AFM thickness observation confirmed that reduction of Au particle distance caused by swelling effect of（ODE）₂ was the reason for the peak redshift.（2）uniform and well-ordered monolayer magnetic nanoparticle films were prepared by MAPLE system.The effects of substrate temperature,target temperature,vacuum degree,surfactant and solvent on the deposition morphology were studied.It was found that the sputtering efficiency can be improved under low gas pressure(10^-1Pa)and high target temperature（-130^°C）.And the nanoparticles’ordering in film during substrate assembly can be improved by selecting toluene as solvent,adding appropriate surfactant（320μl）,low deposition temperature（20^°C）and using high symmetrical shape nanoparticles.The magnetic properties of highly uniform and ordered monolayer Fe₃O₄ films prepared by MAPLE were measured using dynamic cantilever magnetic（DCM）.It was found that Fe₃O₄ film has in-plane and out-plane magnetic anisotropy:the in-plane coercivity of the square Fe₃O₄ and sphere Fe₃O₄ film was 490 Oe and 220 Oe,but both of their out of plane coercivity was close to zero.Monte Carlo method was used to simulated magnetic relationships between nanoparticles.And it proved that the dipolar interactions were predominant on the formation of large area monolayer Fe₃O₄ films with strong anisotropy.（3）The phase transformation of 2D FePt granular film were studied and L1₀-Fe Pt@C permanent magnet films with high coercivity were prepared.The annealing of fcc-Fe Pt granular films were studied under four atmospheres of Ar/H₂-sealed,Ar-sealed,vacuum-sealed and high vacuum.It was found that Fe Pt@C particles with good morphology（7 nm）could get a high coercivity of 1.6 T under vacuum-sealed annealing.The high vacuum annealing got phase transition from both four sides of the particles,and the dislocation caused by the vertical overlapped（001）planes increases the phase transition energy barrier,leading to the incomplete phase transition.The surfactants near particles would decompose hydrogen and carbon during vacuum-sealed annealing.The appropriate amount of hydrogen could encourage the phase transformation.Meanwhile,carbon wrapped around Fe Pt would form a graphene-like layer to form Fe Pt@C structure,which would protect the particle from melting at high temperature.The efficient,simple and low-cost preparation method will make it possible to use Fe Pt@C permanent magnet particle membrane in the field of electromagnetic devices in the future.