The Influence Mechanism Of Ambient Temperature On The Tribochemical Removal Of Monocrystalline Silicon

Because of its excellent physical and chemical properties,single crystal silicon（Si）is widely used as structural materials for microelectromechanical systems（MEMS）,integrated circuits（IC）,and optoelectronic components.In this paper,the effect of environmental temperature on the microscopic tribochemical removal of hydrophobic Si was studied by using an atomic force microscope（AFM）.On this basis,the influence of different experimental factors in the temperature-dependent tribochemical removal of Si surface was systematically studied and the material removal process was decoupled by controlling the experimental variables.Finally,the morphology and chemical composition of wear scars and wear debris were characterized by scanning electron microscope and X-ray energy spectrometer to reveal the effect of temperature on the wear behavior of Si surface at the macro-scale.The main conclusions of this paper are as follows:（1）The influence of environmental temperature in the tribochemical removal of Si surface in humid air at nanoscale was investigated.In humid air,microscopic wear experiments on hydrophobic Si surface against silica microsphere showed that the wear depth and volume decreased significantly with the increase of temperature,indicating that the increasing temperature has an inhibiting effect on the tribochemical reactions at the Si–Si O₂interface.Meanwhile,the interfacial friction and adhesion forces also decreased with the increase of temperature.Moreover,the difference of environmental temperature dependent was further compared on Si surfaces with different crystal planes.The results showed that,the main factor affecting the wear behavior on different crystal planes at lower temperatures is the atomic structures,i.e.,the atomic planar density and the interlayer spacing;such difference gradually decreases due to surface oxidation at high temperature.（2）The influencing mechanism of temperature in the tribochemical removal of Si surface was elucidated.Based on the nanowear results of Si surface at different ambient temperatures,it is analyzed that the inhibiting effect on the nanowear process is caused by a combination of many factors.The results showed that the tribochemical removal rate is proportional to the volume of the liquid meniscus at the contacting interfaces.The increase in temperature led to a sharp decrease in the environmental relative humidity,which reduces the volume of the liquid meniscus at the Si–Si O₂interface,thereby inhibiting the microscopic tribochemical removal of Si substrate.（3）The effect of environmental temperature on tribochemical wear of Si under the constant relative humidity was analyzed.By using the AFM humidity control system,the effect of temperature on the tribochemical wear of Si surface under constant relative humidity was studied.The experimental results showed that the nanowear depth/volume and frictional forces during the wear process increased with the increase of temperature.However,the adhesion force decreased slightly with the increase of temperature,which may be attributed to the decreased filling angle of the liquid meniscus.Under constant relative humidity,the tribochemical wear of Si surface increased with increasing temperature,which might be caused by the tribochemical reactions at the sliding interface stimulated by increased temperature,and the relationship between environmental temperature and tribochemical removal rate could be well described by the Arrhenius model.（4）The influence of temperature in wear behavior of Si surface at macroscale was revealed.The results of macroscopic wear tests showed that the effect of environmental temperature on the mechanical wear is limited under low normal loads,but significant on the tribochemical wear process.At macroscale,the effect of temperature on the tribochemical removal of Si surface is mainly attributed to the decrease in relative humidity caused by the increased temperature,which reduces the volume of the liquid meniscus at the sliding interface and thereby inhibits the removal behavior.However,the tribochemical removal rate of Si surface increased remarkably as the temperature increased when the relative humidity was constant.By using SEM,it is found that the wear debris produced by pure mechanical removal is mainly“rod-shaped”,while the wear debris produced by tribochemical removal is mainly“snowflake”.Moreover,the EDX results showed a higher oxygen concentration for the wear debris produced at Si–Si O₂interface under higher environmental temperature,which suggested the promoted tribochemical reactions by increasing temperature.