The Research On The Crack Patterns In The Silica Film Prepared By Sol-gel

The technology of filling nanocrak to fabricate nanowire attracts much attention,for it's an effective,cheap,simple and controlled technique.Theoretical and experimental work on the crack pattern and controlling technology interested many people.Although this approach has many virtues,the research in this field is still limited,further work should be done.Sol-gel is sued to research the cracking behavior of silicon film in this paper.Oriented stress is introduced by bending the substrate,and the mechanism is discussed.Wavy nanocrak is observed in the experiment by adjusting the treated temperature and time,aging time of the sol, and the film thickness.The wavy nanocrack is between 50nm and 500nm wide, longer than hundreds of micron.It has great value in application.The orientation of the dominant stress is different in each part of the film,while introducing stress by bending the substrate.The stressσ₁ dominates in the boundary, the straight crack oriented along the x₂ axial;The stressσ₂ dominates in the center, the straight crack oriented along the x₁ axial;The orientation of the in the corner is depended on the vector-graph ofσ₁ andσ₂,the crack curved;The sol must be aged for longer than 30 days,if the wavy nanocrack is expected, or only straight can be observed.The critical cracking temperature reduced with the aging time.The growth of the wavy nanocrack can be divided into three periods: nucleation,propagation,termination.As the stress increasing,crack tip will nucleate when the stress reaches the critical value.In the propagation,the growing speed of the crack increased with time,and will intensely propagate after a critical time.Crack will terminate in the termination,when the cracking energy is all released.Shear stress plays an important role in the growth of curved cracks including circular crack,spiral crack and wavy crack.Crack face slipped during the growth of the curved cracks.The orientation of the shear stress along the face point to a specifically point M.Only one point M can be found in the circular crack;A series of point M can be found in the wavy crack and spiral crack.If these points are in two parallel lines,crack will grow into wavy pattern;If these points are in the same line, crack will grow into spiral pattern.In a word,there is special shear stress field,the stress point to a certain point M in a region,these points regularly distribute around the crack.