| Microtransfer printing technology is an advanced method in the field of material assembly and micro/nano manufacturing.It utilizes the interfacial adhesion to orderly transfer the micro/nano elements with different geometric shapes or structures from the donor substrate where they grow or are placed to the target substrate through viscoelastic stamps,and finally forms functional devices.The key to the success of microtransfer printing technology is the accurate and quantitative control of adhesion between stamps,transferred elements and substrates(including donor substrate and target substrate)in the processes of transfer and printing.However,due to the particularity of stamps materials and the diversity of transferred elements,it is still very difficult to control the transfer processes in practical operation.Therefore,it is urgent to carry out in-depth research on interfacial mechanical behavior of microtransfer printing technology.Interfacial mechanical models for the microtransfer printing system considering the viscoelastic properties of the stamp and the target substrate,and the competitive delamination mechanism between the stamp/transferred element interface and the transferred element/substrate interface are established for both the spherical transferred element and the silicon nano-membrane.The main conclusions are as follows:(1)Investigations on the interfacial mechanical properties of transfer printing processes for transferred elements with curvature: The Lennard-Jones force law was used to describe the interfacial interactions between the transferred element/the half-space(including elastic and viscoelastic ones).Taking the spherical transferred element as an example,the interfacial adhesive contact mechanical models were established for elastic and viscoelastic half-spaces,respectively.The effects of unloading velocity,preload and adhesion work on the pull-off force of the spherical transferred element/half-space(including elastic and viscoelastic ones)interface were investigated.The results showed that the pull-off force of the spherical transferred element/elastic half-space interface didn’t change with the change of unloading velocity and preload.Nevertheless,the pulloff force of the spherical transferred element/viscoelastic half-space interface increased with the increase in unloading velocity,preload and adhesion work.(2)Investigations on the interfacial mechanical properties of transfer printing processes for silicon nano-membrane: The surface cohesive model was used to describe the interfacial interactions between the silicon nano-membrane/viscoelastic half-space.The effects of unloading velocity and interfacial fracture toughness on the pull-off force were studied.The results showed that the greater of the unloading velocity,the greater of the pull-off force of the silicon nano-membrane/PDMS stamp interface.What’s more,the greater of the interfacial fracture toughness,the greater of the pull-off force of the silicon nano-membrane/PDMS stamp interface.During the transfer process,it was useful to improve the pull-off force by increasing the fracture toughness in the silicon nanomembrane/PDMS stamp interface.In addition,the larger of the unloading velocity,the smaller the proportion of pull-off force with the increase in interfacial fracture toughness.(3)Investigations on the characteristics of two interface competitive in microtransfer printing system: According to the mechanical properties of single interface,the judgment criterion of two interface competitive in microtransfer printing system was determined,and two interface competitive behaviors between stamps/transferred elements/substrates system were studied,then the quality maps of transfer printing under the influence of different factors were established.First,the changes of mechanical behaviors between the stamp/spherical transferred element interface and spherical transferred element/substrates interface during contact-separation processes were investigated.The effects of thermodynamic adhesion work,maximum indentation displacement and PDMS substrates with two properties on interface competitive were analyzed.The results showed that the ranges of interface adhesion work and maximum indentation displacement for achieving successful transfer and printing were different due to the different properties of PDMS target substrate materials.But the critical unloading velocities in the printing process were increased when the increase of the adhesion work of the transferred element/target substrate interface and were decreased when the increase of the maximum indentation displacement.Second,the changes of mechanical behaviors for both the stamp/silicon nano-membrane interface and silicon nano-membrane/substrates interface during separation process were investigated.The effects of fracture toughness and stamp materials on interface competitive were analyzed.The results showed that the critical unloading velocity of transfer and printing silicon nano-membrane was three orders of magnitude larger than that of the spherical transferred element.The range of fracture toughness of stamp/silicon nano-membrane interface of transfer silicon nano film successfully and printing silicon nano film successfully was different,and its intersection needed to be selected to achieve successful transfer printing.There was a critical unloading velocity in a certain range of the fracture toughness of the target substrate/silicon nanomembrane interface,when it is greater than this range,it could be printed successfully regardless of the unloading speed.The viscoelastic and hyperelastic properties of stamps and target substrates had an impact on the successfully of transfer printing. |
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