The Study On The Guided Buckling Of Stretchable Silicon Thin Film

As the stretchable electronic device can conformally integrated on the complex surface by its own large deformation with its excellent stretchability and flexibility,the stretchable devices demonstrate unique advantages in many applications,such as electronic skin and equipment health monitoring.By adopting the inorganic thin film with specific mechanical design,the well-developed inorganic functional thin film can be used in the stretchable electronic device and the balance of stretchability and performance of the device can be realized.Since the inorganic thin film is intrinsically non-stretchable,the mechanical design plays a key role in determining the device’s stretchability.One of the typical mechanical design in stretchable device is the wavy structure.By transferprinting the patterned inorganic film to a pre-stretched substrate and releasing the substrate,the inorganic film can be compressed and buckled to be a wavy structure,which allows the film to be stretchable with the structural deformation.Although the wavy structure has been widely applied to stretchable devices with various types of thin film,such as semiconductors and functional oxides,the current modulation of the structural parameters of the wavy structure highly depends on the intrinsic mechanical properties of the thin film and substrate.It is necessary to propose more methods for the structural modulation of wavy structure without the limitations of mechanical properties of the applied materials.In this thesis,the feasibility of using the patterned hole array in the thin film to modulate the structure of the buckled silicon nanoribbon is theoretically and experimentally discussed.First,the finite element method is used to theoretically evaluate the influence of the patterned hole array in silicon nanoribbon on the structure of buckled wavy structure.The simulation results indicate that the density of single column of the hole array plays a key role in determining the effectiveness of the guiding effect.When the distance of the hole in each column is 10.5μm,significant influence of the hole array on the structural parameter of the formed wavy structure is observed.The hole array is able to effectively regulate the structure of the buckled silicon nanoribbon by adopting different period design.However,the guidance effect of the hole array becomes neglectable when the distance is 35μm or larger.In this situation,the structure of the buckled silicon nanoribbon is still dominated by the mechanical properties of the nanoribbon and substrate.Second,by using the nanofabrication methods,the silicon nanoribbons with various patterned hole arrays are experimentally fabricated and transfer-printed on the elastomer substrate.Optical microscopy and laser confocal microscopy are used to evaluate the guidance effect of the hole array.The results indicate that,when the ratio of the distance between the holes in single column and the hole diameter is smaller than 3,close ration between the period of hole array and the period of the wavy structure can be observed.The period of the as-buckled nanoribbon will follow the period of the hole array when the period of the hole array is less than 2 times of the intrinsic one of the nanoribbon.With a period of the hole array larger than 2 times of the nanoribbon’s intrinsic period,the structure of the as-buckled nanoribbon still can be regulated,but an “sub-period”effect can be observed.Moreover,the thickness of the nanoribbon will also affect the guidance effect of the hole array.The regulation effect becomes poorer when the silicon nanoribbon thinner or thicker than 100 nm.By using the confocal micro-Raman spectroscopy,the strain in the silicon nanoribbon with regulated wavy structures are also analyzed.The results show that,with regulation of the structure parameters with the hole array,the strain distribution in the silicon nanoribbon can be also modulated.When the period of the hole array is close to the intrinsic period of nanoribbon,the strain distribution in the nanoribbon follows the distribution of the hole array.However,when the period of the hole array is significantly larger than the intrinsic period of nanoribbon,the locations of the maximum and minimum strain in nanoribbon will slightly shift from the peak and valley of the buckled nanoribbon.Based on the analysis of the strain distribution in silicon nanoribbon,the potential application of the guidance effect of the patterned hole array in the band engineering of silicon nanoribbon is also discussed.