Researches On Temperature Effect Of Micro-Nanostructures And Optical Properties Of Silver Films On Flexible Substrates

With the continuous advancement and development of science and technology,the new materials,including thin film materials,have seen explosive growth in the research and application.Due to the excellent mechanical,electrical and optical properties of thin film materials,one of its important application is electronic devices.However,traditional electronic devices are generally made of hard materials such as silicon wafers,which requires the entire device to be in a relatively stable working environment.This limits its application in large deformation occasions,while flexible electronic devices are proposed to solve this problem.The flexible electronic devices,which use soft material as substrates,have some unique properties compared to conventional electronic devices,such as being stretchable,compressible,twistable,and even foldable.However,the current researches about temperature effect on flexible electronic devices remain to be done.This is because the thermal deformation of the soft substrate material and the resulting stress redistribution are more complicated than conventional electronic devices.For example,high temperature induces the change of the surface appearance of the flexible material,which in turn causes the failure of its mechanical properties;high temperature promotes the generation of the dewetting phenomenon and the growth of the metal nanoparticles,which in turn causes the destruction of the continuity of the film structure and the change of optical properties.All these problems pose challenge to the application of flexible electronic devices,which is the starting point of this study.In this paper,polydimethylsiloxane(PDMS)was used as the substrates,on which silver(Ag)films were sputtered to obtain the “Ag/PDMS” structure.The temperature effect on surface morphology and optical performance of flexibleelectronic devices were studied in depth.The main contents are as follows:Firstly,PDMS substrates on glass and pure PDMS substrates were prepared by spin coating and pouring,respectively.The morphology and mechanical parameters of PDMS were tested under different working conditions.Experimental results show that when the temperatures below 320 degrees Celsius,PDMS maintained a flat topography throughout the whole process;otherwise,cracking morphology appeared in PDMS during the cooling process.The size of the fragment formed after the cracking had a linear relationship with the thickness of PDMS.The thicker the PDMS,the larger the fragment,and the less likely do it crack.The elastic modulus of PDMS increased first and then decreased with temperature increasing,but it remained the normal levels.Until when the temperature exceeded 320 degrees Celsius,obviously cracking morphology appeared in the PDMS,and then the elastic modulus decreased rapidly.Secondly,silver films were deposited on the PDMS substrates.The cracking evolution process of the “Ag/PDMS” bilayer structure under the temperature effect was studied,and the surface structure of silver films after cracking was statistically analyzed.Experimental results show that when the temperature was too high,the cracking process of “Ag/PDMS” structure occurred in the cooling process,and the cracking process was divided into four distinct stages,including flat surface,formation of main crack,main cracks interweave into a network structure and network structure refined into small pieces.The growth of the main crack during the cracking process was discontinuous,and the delamination between PDMS and glass occurred at the edge of main crack.After refinement,the wavelength and amplitude of wrinkles on fragment had a linear relationship with the film thickness.Newton ring phenomenon occurred due to the delamination of the fragment structure and the glass,and almost all occurred in the edge region of the fragment structure.Finally,the diameter and spacing of nanoparticles on the “Ag/PDMS” surface due to temperature effect were observed and counted,meanwhile the transmission spectra was obtained.The local surface plasmon resonance(LSPR)phenomenon of the “Ag/PDMS” structure under temperature effect was studied.Experimental results show that the existence of LSPR made the material absorb or scatter light in a certainwavelength band,thus a formant was formed in the spectrum.The position of the resonance peak was affected by the diameter and spacing of silver nanoparticles: the larger the diameter or the smaller the spacing,the red shift occurred in the resonance peak.The diameter and spacing had different trends under different experimental conditions: the higher the temperature,the larger the diameter of nanoparticles,but particle spacing was affected by many factors such as temperature,silver film thickness and thermal conductivity of the system.The different trends of nanoparticle diameter and spacing with temperature change caused blue shift or red shift of the resonance peak for different samples.