Nanoxerography For Oil-phase Synthesized Functional Nanoparticles

Driven by the development of colloidal chemistry,functional nanoparticles have become an important type of material for many fields,including life sciences,pharmaceutical industry,energy and environment,to name a few.However,how to align multiple different types of nanoparticles together forming a functional “nanomachine” is still a daunting challenge.It requires a new bottom-up techniques,capable of assembling nanoparticles with different materials,sizes and properties together with nanometer precision.To tackle this issue,various nano-assembly techniques have been reported.So far,scientist have been capable of assembling molecules and microbeads into given structures,but there is still lack of method to align nanoparticles into an arbitrary nanopatterned in a deterministic fashion.To address this issue,we developed a direct nanopatterning technique using Atomic Force Microscope(AFM)probe which can locally modify both the physical and chemical properties of the substrate,and further invented a new electrostatic nanoprinting technique,called Electric Field-Assisted Surface Adsorption nano-Printing(EFASP),which can assembly different functional nanoparticles deterministically with extremely low contamination.Here,we focus on the oil-phase synthesized nanoparticles,because oil-phase synthesis is one of the most powerful and versatile techniques for functional nanoparticle synthesis.Moreover,there are very few reports on the electrostatic assembly of oil-phase synthesized nanoparticles.Next,we will introduce EFASP in two parts:We introduce the AFM-based nanopattern generation method.It creates nanopatterns by applying high voltages on a polymer thin film(normally fluoride polymer)covered planar conductive substrate using a conductive AFM probe.In this processes,charges are injected into the polymer and the polymer is defluorinated at the same time.This provides a high quality nanotemplate for efficient nanoparticle assembly.We demonstrate that using EFASP,nanoparticles can be aligned into arbitrary nanopatterns with ultra-high density(125,000 DPI),nanometer precision(10nm position accuracy,line width 30nm),and no background(non-specific adsorption probability is less than 1E-6)over a millimeter scale.We discussed how to use voltage to adjust the line width of the pattern to achieve continuous adjustment of the pattern line width from 30 nm to 100 nm.Furthermore,we demonstrated that the "color" nanoprinting,which can align different functional nanoparticles together in a layer-bylayer fashion,and the lamination accuracy between different nano-"pigments" reached 50 nm.Detailed studies show that the accuracy and efficiency of the EFASP method comes from the special pattern technique used in this work.It combines the long-range electrostatic force induced enrichment of nanoparticles and short-range adsorption.The electrostatic interactions between oil phase nanoparticles and the patterned substrate are investigated.Unexpected sign-dependent assembly of perovskite quantum dots(QDs)was observed,and it implies that the QDs carry net charges despite that they are synthesized and dispersed in a neutral nonpolar solvent.This is contrary to our common belief.To understand this phenomenon,we measured QDs using electrostatic force microscopy,and calculate the charge carried on by a single QD quantitatively.The results confirm that perovskite QDs carries net charges,and Coulomb forces can be comparable with the gradient forces in the assembly in nonpolar solvents.In addition,we found that it is a common phenomenon that oil-phase synthesized nanoparticles carry a net charge,including Au,Fe₂O₃ and Cd Se/Zn S nanoparticles,which provides new possibilities for efficient electrostatic assembly of oil-phase synthesized functional nanoparticles.In summary,we developed a new deterministic nanoassembly technique for oilphase synthesized functional nanoparticles.It allows us to print different types of nanoparticles into arbitrary nanopatterns with a high accuracy deterministically over large area.We believe that the EFASP will find many important applications in the field of photonics,life sciences and pharmaceutical industry in the future.