Study On The Mechanism And Application Of High-efficiency Friction-induced Nanofabrication

Nanotechnology is a strategic frontier technology with wide application prospect,which has been identified as the core technology of the world for developing national economic and solving key problem.Ascribing to its excellent comprehensive performance,good stability and reliability,mature preparation process,diversified fabrication techniques,monocrystalline silicon still is the basic structural and functional materials for integrated circuits,photoelectronic device,energy conversion and storage and various micro-/nano-sensors and actuators,etc.However,the conventional bulk nanofabrication technologies of silicon are facing their technical challenges and bottlenecks when size requirement of silicon based functional structures and devices down to nanoscale.Hence,it is imperative to develop nondestructive nanofabrication methods with high resolution,high efficiency and low cost.Recently,due to its outstanding advantages in high resolution,wide application range,simplicity,low cost,maskless and without external field action,friction-induced nanofabrication has attracted more and more attention.Up to now,its related laws and mechanism have been elucidated in detail.But,the low efficiency,limited area,unavoidable damage of conventional friction-induced nanofabrication seriously hindered its practical application.Therefore,it is urgently needed to carry out the approaches,mechanism and applications research for high-efficiency,large-scale and nondestructive friction-induced nanofabrication to further improve its fabrication ability and promote its practical application.By using atomic force microscope,tribo-indenter in-situ nanomechanics test system,self-developed large-area micro/nanofabrication apparatus and relevant analysis and characterization technique,the high-efficiency,nondestructive and large-scale friction-induced nanofabrication methods,mechanism and application of monocrystalline silicon are studied in this doctoral dissertation.Firstly,based on the analysis by auger electron spectroscope,the change law of thickness,oxygen content and surface wettability of SiO_x film prepared by UV/ozone oxidation techniquehas been investigated.The involved mechanism is discussed through photochemical theory.The high-efficiency and nondestructive friction-induced nanofabrication method based on resist mask is proposed.Secondly,to improve the fabrication efficiency and avoid crystal destruction of maskless-based friction-induced nanofabrication,the HNO₃/HF etching system based friction-induced nanofabrication approach is developed.It's anisotropic etching mechanism is revealed by XTEM results and electrochemical etching theory.Besides,to further resolve bottleneck problems of friction-induced nanofabrication in preparing large-sacle nanostructures,such as the large surface roughness,inevitable structure damage and polytropic microtopography.The inner effect factors were investigated and the corresponding solutions were proposed.The large-scale and high-efficiency grating templates were fabricated successfully.Finally,the nanostructures prepared by above methods were applied into nanofluid chips,UV nanoimprinting templates and sensors,which show excellent perpormance and find some point of penetration for actual application of friction-induced nanofabrication.After a system research for the high efficiency,large-scale and nondestructive friction-induced nanofabrication technology,the main conclusions are as follows:?1?The preparation laws and mechanism of hydrophilic SiO_x mask preparation by UV/ozone oxidation technology were revealed,the excellent resist KOH ability of nonuniformly oxygenated SiO_x film was verified,and a high-efficiency and nondestructive UV/ozone assisted friction-induced nanofabrication method was proposed.The AES results indicated that the thickness of SiO_x mask prepared by above method is about2.5-3 nm,and its oxygen content shows a sharp decrease trend in the depth direction.This method has very high efficiency for silicon oxidation.For instance,the silicon surface with30%oxygen content?the maximum oxygen content on silicon surface is about 46%?can be finished within 3min.The oxidation of silicon surface can be attributed to the synergistic effects of ultraviolet photons,atomic oxygen?O?,ozone?O₃?and hydroxyl group?-OH?.Among them,the Si-Si bonds on the silicon surface can be broken by UV photons and O to form Si-O and Si-OH bonds,and then the a hydrophilic SiO_x film can be gradually produced on Si?100?surface.On the other hand,the O diffuse into SiO_x film will become more and more difficult with the increase of surface oxygen content.Hence,the oxygen content of SiO_x film demonstrates a sharp decrease trend with the increase of depth.Moreover,the subsequent etching experiments suggested that the SiO_x mask prepared by this method has excellent resist etching ability to KOH solution.The fabrication depth of nanostructures can be well controlled by adjusting the oxidation time to control the oxygen content.?2?The anisotropic etching laws and mechanism of HNO₃/HF etching system were revealed.The nanofabrication limitation of HNO₃/HF mixtures was broken through,and inevitable crystal damage of maskless-based friction-induced nanofabrication method was also resolved.A high-efficiency and nondestructive friction-induced nanofabrication method based on the HNO₃/HF etching system was proposed.Although HNO₃/HF mixtures are a kind of typical isotropic etching agent,the HNO₃/HF mixtures can produce excellent anisotropic etching effect to the scratched area if the volume ratios of HNO₃ and HF solution were controlled with 5:1-100:1.The whole process can be finished within 30 s even a few seconds.Importantly,the amorphous Si and dislocations beneath scratches produced by the friction shear effect can be quickly removed by HNO₃/HF mixtures to form nondestructive nanostructures.The rapid etching rate of amorphous Si layer can attribute to two reasons.Firstly,the needed total activation energy of scratched area was reduced by the lots of Si dangling bonds.Secongdly,the enriched additional holes provide a more convenient source of holes for the corrosion dissolution of Si atoms.The spaces produced by the corrosion dissolution of Si atoms in the interface of inner dislocation provide many convenient channels for HNO₃ and HF molecules diffuse to reaction area,which leads to the higher etching rate of the serried dislocations area.Therefore,the synergistic effect of above three aspects lead to the etching rate of scratched area was obviously higher than that of original silicon substrate and generate anisotropic etching effect.In addition,the size of the nanostructures can be precisely controlled by the scratching load,volume ratio and mass concentration of HNO₃/HF mixtures.This method is less sensitive to the scratching speed,which is beneficial to further improve the fabrication efficiency.Thus,the effective integration of HNO₃/HF etching system and friction-induced nanofabrication approach not only avoids low efficiency and intrinsic damage properties of friction-induced nanofabrication,also broke through the limitations of HNO₃/HF mixtures in nanofabrication.?3?The underlying causes of rough surface,inevitable structure damages and polytropic microtopography of friction-induced nanofabrication in large-scale application were revealed,and corresponding solutions were proposed.The large-scale and high-accuracy grating templates were successfully prepared on silicon surface.The reaction products(SiO₂?OH?₂^2-and SiO₂)adhered on silicon surface can be real-time,effectively,and nondestructive removed with magnetic stirring assisted KOH etching approach.The quality of diamond tip is very important for grating yield,different damage form,different reciprocating path and load dependence usually generated by the tips of without obvious defects.This work proposed a simple three-step method to evaluated the diamond tips to avoid the inevitable structure damages.Moreover,the linear density of gratings mainly depends on scratching load and the normal radius of the diamond tip.The microtopography of gratings can be affected by the scratching load,etching time,and normal radius of the diamond tip.Fortunately,all above problems can be effectively controlled during fabrication.Therefore,friction-induced nanofabrication method provides a new fabrication approach for various Si templates.?4?Nanostructures prepared by friction-induced nanofabrication method demonstrated excellent performances in nanochannels,nanoimprint templates and sensors,which provide some point of penetration for actual application of friction-induced nanofabrication.The nanochannel arrays prepared by HNO₃/HF based friction-induced nanofabrication method on Si surface showed an excellent performance in ion current test experiments of nanofluids,which provide a high-efficiency,simple and low-cost fabrication method for the high-quality nanochannels for control and operation of nanofluid.The large-scale and high-accuracy grating templates fabricated by friction-induced selective etching method also demonstrated a good replica ability.Besides,the textured glass substrates prepared by friction-induced nanofabrication approach effectively improved the adhesion strength of ZnO nanoparticles and substrates,which can avoid the large-sacle fall off of ZnO photosensitive layer to improve the stability of sensors.In summary,for mask-based friction-induced nanofabrication,UV/ozone oxidation method provide an effective stratrgy for high-efficiency and nondestructive nanofabrication.On the other hand,for maskless-based friction-induced nanofabrication,employing the HNO₃/HF etchant to replace the conventional anisotropic etchant is the optimal approach for high-efficiency and nondestructive nanofabrication.Besides,many bottlenecks?such as large surface roughness,uncontrollable structural damage and variable microtopography?of friction-induced nanofabrication in preparaing large-scale and high-accuracy grating templates all can be improved through corresponding method.Therefore,the research results about the method,mechanism and application of high-efficiency,nondestructive,large-scale friction-induced nanofabrication can not only perfect basic theory of nanofabrication and nanotribology,can also accelerate its practical application in silicon-based nanofluidic systems,nanoimprint templates,precision gratings and sensors,etc.