Polymer/Nanoparticle Composite Thin Films Constructured By Interfacial Assembly And Their Optical/Electronic Devices Performance

Polymer/nanoparticle（NP）composite thin films combine the flexibility and machinability of polymer,and the optical/electronic properties of NPs,thereby showing tremendous applications in many fields,such as spectroscopy analysis,microelectronic device.The properties of composite thin film not only depend on the shape and composition of NPs,but also relate to their assembly structures（e.g.,arrangement,orientation,and interparticle distance）in polymer matrix.Traditional methods（e.g.vapor deposition and sputtering）have certain advantages in construction of polymer/NP composite films,such as large-area and fast preparation speed.However,it is difficult to control the interparticle distance and arrangement structure of NPs.Most importantly,the long-range order of NPs in the composite film is poor.The mechanism for regulating the interparticle distance,arrangement structure,and orientation of NPs in composite film is still unclear.There are still some great challenges to construct ordered structure composite film with centimeter-scale.To address the above challenges,this dissertation employed NPs with different shapes and compositions as building blocks to prepare a variety of centimeter-scale polymer/NP composite thin films with ordered structure via interfacial assembly and external field directed assembly.The manipulation of NPs assembly structure in composite thin films was realized.Further,the applications of composite thin films in optical/electronic devices,such as surface-enhanced Raman spectroscopy and memory device,were investigated.Main research findings in this dissertation are as follows:（1）Polystyrene-tethered gold nanosphere（Au NP@PS）was used as building block to prepare superlattice film with centimeter-scale and tunable interparticle distance through rapid liquid-liquid interfacial assembly.The effect of polymer molecular weight on the optical property of Au NP@PS superlattice was systematically investigated.It was found that the interparticle distance of NPs increases with increasing polymer molecular weight,the coupling effect between Au NP was weakened,and the UV-vis spectra of the superlattice blue-shifted.The influence of interparticle distance on Raman signal intensity of crystal violet was revealed.The results showed that the Raman signal intensity increased with the decrease of interparticle distance.Moreover,the quantitative relationship between enhancement factor（EF）and interparticle distance（d）was found to be EF∝d^-2.4.This superlattice film showed excellent reproducibility of Raman signal of crystal violet.（2）Polystyrene-tethered gold nanorod（Au NR@PS）was used as building block to prepare centimeter-scale composite film with controllable orientation of Au NR through combination of liquid-liquid interfacial assembly and electric field assisted assembly.The effect of Au NR concentration,polymer molecular weight,electric field strength and direction on the orientation of Au NR were systematiclly investigated.The results showed that in the molecular weight range of polymer ligands（5k～50k Da）,lower molecular weight（5k Da）and higher electric field strength were favorable to generate ordered Au NR@PS films in both parallel and perpendicular electric field.The degree of orientation of Au NR could be improved by increasing the strength of electric field.The superlattices with parallel and perpendicular arrangements of Au NR could be constructed by manipulating the direction of electric field.This Au NR@PS thin films were used as nano-floating-gate to construct field-effect transistor memory devices,and the effect of Au NR orientation on the storage performance was studied.Compared with the disordered Au NR@PS film,the ordered Au NR@PS film used as nano-floating-gate,the illumination time required for the programming process is shorted by 2/3 and exhibited superior cycle stability.（3）Polystyrene-tethered gold nanocube（Au NC@PS）was used as building block,and their assembly behaviors in selective solvent and emulsion droplet were studied.Nanoscale assemblies with controlled structure were obtained.Furthermore,centimeter-scale Au NC@PS superlattice film was prepared by liquid-liquid interfacial assembly.Homopolymer was introduced into the system to adjust the interparticle distance of Au NC,which was superior to regulating the interparticle distance by increasing polymer length.The relationship between homopolymer content and interparticle distance was investigated.The results showed that the interparticle distance increased with increasing homopolymer content.The Au NC@PS superlattice was employed as functional layer to construct memristor,and the influence of interparticle distance on the resistance property was studied.The device with larger interparticle distance showed larger I_on/I_off（10³）,lower set voltage（0.7 V）,and superior stability（10⁴ s）,which showed better memristor performance.（4）Hafnium oxide（HfO₂）NP was used as building block to prepare functional film through a simple solution processing method.In traditional HfO₂-based memristor,the HfO₂functional layer was usually prepared by vapor deposition or sputtering.These traditional methods required complex equipment requirement and complex preparation process.In this work,HfO₂ NP was firstly prepared by solution method,and then the functional film was prepared by spin coating method,which greatly simplified the preparation process of functional film.The effect of HfO₂ NP concentration on the surface morphology of thin film and the resistance switching property of memristor device were investigated.The results showed that optimizing the concentration of HfO₂ NP was beneficial to the preparation of uniform and flat thin film,imparting the device with obvious bipolar resistance switching characteristic,larger I_on/I_off（10⁴）and superior reading/writing/erasing stability.Multiple synaptic plasticity and the transformation from short-term memory to long-term memory were emulated,which showed excellent synaptic simulation performance.In this dissertation,the methods of liquid-liquid interfacial assembly and electric field induction were developed,centimeter-scale ordered structure polymer/NP composite thin films were fabricated,the effective manipulation of NP arrangement structure was realized,and application of polymer/NP composite films in optical/electronic devices was broadened.