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Two material removal modes in chemical mechanical polishing:mechanical plowing vs.chemical bonding

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Friction 2024年第5期12卷 897-905页

作者： Yuan WU Liang JIANG Wenhui LI Jiaxin ZHENG Yushan CHEN linmao qian Tribology Research Institute State Key Laboratory of Rail Transit Vehicle SystemSouthwest Jiaotong UniversityChengdu610031China

With the rapid development of semiconductors,the number of materials needed to be polished sharply increases.The material properties vary significantly,posing challenges to chemical mechanical polishing(CMP).Accordingly,the study aimed to classify the material removal mechanism.Based on the CMP and atomic force microscopy results,the six representative metals can be preliminarily classified into two groups,presumably due to different material removal modes.From the tribology perspective,the first group of Cu,Co,and Ni may mainly rely on the mechanical plowing effect.After adding H_(2)O_(2),corrosion can be first enhanced and then suppressed,affecting the surface mechanical strength.Consequently,the material removal rate(MRR)and the surface roughness increase and decrease.By comparison,the second group of Ta,Ru,and Ti may primarily depend on the chemical bonding effect.Adding H_(2)O_(2)can promote oxidation,increasing interfacial chemical bonds.Therefore,the MRR increases,and the surface roughness decreases and levels off.In addition,CMP can be regulated by tuning the synergistic effect of oxidation,complexation,and dissolution for mechanical plowing,while tuning the synergistic effect of oxidation and ionic strength for chemical bonding.The findings provide mechanistic insight into the material removal mechanism in CMP.

关键词： Chemical mechanical polishing corrosion wear material removal mode mechanical plowing chemical bonding

Combined effect of WS2 and Ti3C2Tx MXene favors oil-based ultra-low friction on rough steel-steel interface at elevated temperatures

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Science China Technological Sciences 2024年第7期67卷 1991-2002页

作者： LIU YangQin CHEN Lei WANG Yang qian linmao Tribology Research Institute State Key Laboratory of Rail Transit Vehicle System School of Mechanical EngineeringSouthwest Jiaotong University Key Laboratory of Advanced Technologies of Materials (Ministry of Education) Research Institute of Frontier ScienceSouthwest Jiaotong University

The lubrication performance of liquids is severely restricted and is degraded in high-temperature environments. Stable and reliable lubrication in high temperature environments has been a long-standing goal in various industrial fields. In this study,WS2and Ti3C2TxMXene nanoflakes were used as oil-based lubricant additives to generate ultra-low friction and even superlubricity（friction coefficient of ～0.007） at elevated temperatures（400°C）, which has hitherto not been achieved by both individual pristine materials, WS2and Ti3C2TxMXene. Viscosity and thermogravimetric characterization revealed improvements in the high-temperature rheological properties and thermal stability of the lubricating base oil, indicating improved loadbearing and continuous lubrication capabilities at elevated temperatures. X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy demonstrated that the formation of an iron/titanium/tungsten-rich oxide lubricious thin film at the sliding interface reduced the interfacial shear stress, which was responsible for the observed friction and wear reductions at high contact pressures（> 1.1 GPa）. Although the titanium/tungsten oxide film was gradually removed after prolonged sliding, a sufficiently thick iron oxide film maintained a low friction coefficient for at least 2 h. The improved surface quality facilitates the achievement of ultra-low friction and reduced wear. The proposed lubrication methodology has a broad utilization potential as a wear-reduction strategy across various industrial fields at elevated temperatures.

关键词： ultra-low friction high-temperature wear reduction lubricating additive tungsten disulfide MXene

Combined effect of WSand TiCTMXene favors oil-based ultra-low friction on rough steel-steel interface at elevated temperatures

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Science China Technological Sciences 2024年

The lubrication performance of liquids is severely restricted and is degraded in high-temperature environments. Stable and reliable lubrication in high temperature environments has been a long-standing goal in various industrial fields. In this study,WS2and Ti3C2TxMXene nanoflakes were used as oil-based lubricant additives to generate ultra-low friction and even superlubricity(friction coefficient of ～0.007) at elevated temperatures(400°C), which has hitherto not been achieved by both individual pristine materials, WS2and Ti3C2TxMXene. Viscosity and thermogravimetric characterization revealed improvements in the high-temperature rheological properties and thermal stability of the lubricating base oil, indicating improved loadbearing and continuous lubrication capabilities at elevated temperatures. X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy demonstrated that the formation of an iron/titanium/tungsten-rich oxide lubricious thin film at the sliding interface reduced the interfacial shear stress, which was responsible for the observed friction and wear reductions at high contact pressures(> 1.1 GPa). Although the titanium/tungsten oxide film was gradually removed after prolonged sliding, a sufficiently thick iron oxide film maintained a low friction coefficient for at least 2 h. The improved surface quality facilitates the achievement of ultra-low friction and reduced wear. The proposed lubrication methodology has a broad utilization potential as a wear-reduction strategy across various industrial fields at elevated temperatures.

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Mechanochemical reactions of GaN-Al_(2)O_(3) interface at the nanoasperity contact:Roles of crystallographic polarity and ambient humidity

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Friction 2022年第7期10卷 1005-1018页

作者： Jian GUO Jian GAO Chen XIAO Lei CHEN linmao qian School of Mechanical Engineering University of South ChinaHengyang 421001China Tribology Research Institute State Key Laboratory of Traction PowerSouthwest Jiaotong UniversityChengdu 610031China Advanced Research Center for Nanolithography(ARCNL) Science Park 106Amsterdam 1098XGthe Netherlands Technology and Equipment of Rail Transit Operation and Maintenance Key Laboratory of Sichuan Province Southwest Jiaotong UniversityChengdu 610031China

Mechanochemical reactions of the GaN-Al_(2)O_(3) interface offer a novel principle for scientific and technological merits in the micro-/nano-scale ultra-precision surface machining.In this work,the mechanochemical reactions on Ga-and N-faced GaN surfaces rubbed by the Al_(2)O_(3) nanoasperity as a function of the environmental humidity were investigated.Experimental results indicate that the N-face exhibits much stronger mechanochemical removal over the relative humidity range of 20%-80%than the Ga-face.Increasing water molecules in environmental conditions significantly promotes the interfacial mechanochemical reactions and hence accelerates the atomic attrition on N-face.The hypothesized mechanism of the selective water-involved mechanochemical removal is associated with the dangling bond configuration,which affects the mechanically-stimulated chemical reactions via altering the activation energy barrier to form the bonding bridge across the sliding interface.These findings can enrich the understanding of the underlying mechanism of mechanochemical reactions at GaN-Al_(2)O_(3) interface and a broad cognition for regulating the mechanochemical reactions widely existing in scientific and engineering applications.

关键词： crystallographic polarity ambient humidity mechanochemical removal GaN-Al_(2)O_(3)interface

Intramolecular hydrogen bonds in a single macromolecule:Strength in high vacuum versus liquid environments

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Nano Research 2022年第2期15卷 1517-1523页

作者： Wanhao Cai Duo Xu Fa Zhang Junhao Wei Song Lu linmao qian Zhongyuan Lu Shuxun Cui Key Laboratory of Advanced Technologies of Materials(Ministry of Education) Southwest Jiaotong UniversityChengdu 610031China State Key Laboratory of Supramolecular Structure and Materials Institute of Theoretical ChemistryJilin UniversityChangchun 130023China

As a weak non-covalent interaction,hydrogen bond(H-bond)is highly susceptible to the environmental interference.However,the direct quantification of a single H-bond under an interference-free condition is still a challenge.Herein,the intramolecular H-bond in a model system,poly(N-isopropylacrylamide),is studied in high vacuum by single-molecule atomic force microscopy and steered molecular dynamics simulations,which allows the precise quantification of H-bond strength in an interference-free state.Control experiments show that the H-bond is significantly weakened in nonpolar solvent,even if the dielectric constant is very close to vacuum.If a polar solvent is used as the environment,the H-bond will be further weaker or even broken.These results imply that for experiments in any liquid environment,the H-bond strength(△G)will be only -50% or even less of that measured in vacuum.Further analysis shows that in liquid environments,AG decays in a quasi-linear way with the increase of the dielectric constant(ε).For H-bond studies in future,the result measured in vacuum can be set as the standard value,namely,the inherent strength.This approach will provide fundamental insights into the H-bond participated nano-structures and materials in different environments.

关键词： hydrogen bond single-molecule studies atomic force microscopy vacuum polymer elasticity simulations

How to improve superlubricity performance of diketone at steel interface:Effects of oxygen gas

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Friction 2023年第6期11卷 927-937页

作者： Yuanyuan JIANG Lei CHEN Chen XIAO Shumin ZHANG Chenhui ZHANG Ningning ZHOU Tao QIN linmao qian Jiyang ZHANG Tribology Research Institute State Key Laboratory of Traction PowerSouthwest Jiaotong UniversityChengdu610031China Technology and Equipment of Rail Transit Operation and Maintenance Key Laboratory of Sichuan Province Southwest Jiaotong UniversityChengdu610031China State Key Laboratory of Tribology Tsinghua UniversityBeijing100084China Beijing Key Laboratory of Long-life Technology of Precise Rotation and Transmission Mechanisms Beijing Institute of Control EngineeringBeijing100094China

Achievement of steady and reliable super-low friction at the steel/steel contact interface,one of the most tribological systems applied for mechanical moving parts,is of importance for prolonging machine lifetime and reducing energy consumption.Here we reported that the superlubricity performance of the steel/steel sliding interface lubricated with tiny amounts of diketone solution strongly depends on the oxygen content in surrounding environment.The increase of oxygen not only significantly shortens the initial running-in time but also further reduces the stable coefficient of friction in superlubricity stage due to the enhancement of tribochemical reactions.On the one hand,more severe oxidation wear occurring at higher oxygen content facilitates material removal of the contact interface,lowering the contact pressure and the corresponding initial friction.On the other hand,the growth of iron ions during the shear process in high oxygen environment promotes the formation of chelate which acted as an effective lubricated film chemisorbed at the steel/steel friction interface to further lower the interfacial friction.The results provide a new opportunity to further optimize the tribological performance of diketone superlubricity system,especially towards the lubrication of mechanical engineering materials.

关键词： superlubricity oxygen content steel/steel interface diketone chelate

Role of interfacial water in adhesion,friction,and wear--A critical review

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Friction 2021年第1期9卷 1-28页

作者： Lei CHEN linmao qian Tribology Research Institute State Key Laboratory of Traction PowerSouthwest Jiaotong UniversityChengdu 610031China

Surficial water adsorption and interfacial water condensation as natural phenomena that can alter the contact status of the solid interface and tribological performances are crucial in all length scales,i.e.,from earthquakes to skating at the macroscale level and even to micro/nano-electromechanical systems(M/NEMS)at the microscale/nanoscale level.Interfacial water exhibits diverse structure and properties from bulk water because of its further interaction with solid surfaces.In this paper,the evolutions of the molecular configuration of the adsorbed water layer depending on solid surface chemistry(wettability)and structure,environmental conditions(i.e.,relative humidity and temperature),and experimental parameters(i.e.,sliding speed and normal load)and their impacts on tribological performances,such as adhesion,friction,and wear,are systematically reviewed.Based on these factors,interfacial water can increase or reduce adhesion and friction as well as facilitate or suppress the tribochemical wear depending on the water condensation kinetics at the interface as well as the thickness and structure of the involved interfacial water.

关键词： water adsorption water condensation adhesion friction tribochemical wear

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Friction-Induced Nanofabrication: A Review

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Chinese Journal of Mechanical Engineering 2021年第2期34卷 26-51页

作者： Bingjun Yu linmao qian Tribology Research Institute State Key Laboratory of Traction PowerSouthwest Jiaotong UniversityChengdu 610031China

As the bridge between basic principles and applications of nanotechnology,nanofabrication methods play significant role in supporting the development of nanoscale science and engineering,which is changing and improving the production and lifestyle of the human.Photo lithography and other alternative technologies,such as nanoimprinting,electron beam lithography,focused ion beam cutting,and scanning probe lithography,have brought great progress of semiconductor industry,IC manufacturing and micro/nanoelectromechanical system(MEMS/NEMS)devices.However,there remains a lot of challenges,relating to the resolution,cost,speed,and so on,in realizing high-quality products with further development of nanotechnology.None of the existing techniques can satisfy all the needs in nanoscience and nanotechnology at the same time,and it is essential to explore new nanofabrication methods.As a newly developed scanning probe microscope(SPM)-based lithography,friction-induced nanofabrication provides opportunities for maskless,flexible,low-damage,low-cost and environment-friendly processing on a wide variety of materials,including silicon,quartz,glass surfaces,and so on.It has been proved that this fabrication route provides with a broad application prospect in the fabrication of nanoimprint templates,microfluidic devices,and micro/nano optical structures.This paper hereby involved the principals and operations of friction-induced nanofabrication,including friction-induced selective etching,and the applications were reviewed as well for looking ahead at opportunities and challenges with nanotechnology development.The present review will not only enrich the knowledge in nanotribology,but also plays a positive role in promoting SPM-based nanofabrication.

关键词： Scanning probe microscope Tip-based lithography Friction-induced nanofabrication Friction-induced selective etching

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Detecting van der Waals forces between a single polymer repeating unit and a solid surface in high vacuum

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Nano Research 2019年第1期12卷 57-61页

作者： Wanhao Cai Chen Xiao linmao qian Shuxun Cui Key Laboratory of Advanced Technologies of Materials(Ministry of Education) Southwest Jiaotong UniversityChengdu 610031China

Ubiquitous van der Waals(vdW)forces are very importa nt for nano structures.Although the vdW forces between two surfaces(or two layers)have been measured for several decades,a direct detection at the single-molecule level is still difficult.Herein,we report a novel method to solve this problem in high vacuum by means of AFM-based sin gle-molecule force spectroscopy(SMFS).Solve nt molecules and surface adsorbed water are removed thoroughly under high vacuum so that the situation is greatly simplified.A constant force plateau can be observed when a polymer chain is peeled off from a substrate in high vacuum.Accordingly,the vdW forces between one polymer repeating unit and the substrates can be obtained.The experimental results show that the vdW forces(typical range:21-54 pN)are dependent on the species of substrates and the size of polymer repeating unit,which is in good accordance with the theoretical results.It is expected that this novel method can be applied to detect other non-covalent interactions(such as hydrogen bond andπ-πstacking)at the single-molecule level in the future.

关键词： van der Waals forces high vacuum atomic force microscopy single-molecule studies polymer desorption