An experimental program was conducted to explore the impact of nanosilica on the microstructure and mechanical characteristics of cemented sandy soil.Cement agent included Portland cement type II.Cement content was 6%...An experimental program was conducted to explore the impact of nanosilica on the microstructure and mechanical characteristics of cemented sandy soil.Cement agent included Portland cement type II.Cement content was 6% by weight of the sandy soil.Nanosilica was added in percentages of 0%,4%,8% and 12% by weight of cement.Cylindrical samples were prepared with relative density of 80% and optimum water content and cured for 7 d,28 d and 90 d.Microstructure characteristics of cementnanosilica-sand mixtures after 90 d of curing have been explored using atomic force microscopy(AFM),scanning electron microscopy(SEM) and X-ray diffraction(XRD) tests.Effects of curing time on microstructure properties of cemented sandy soil samples with 0% and 8% nanosilica have been investigated using SEM test.Unconfined compression test(for all curing times) and compaction test were also performed.The SEM and AFM tests results showed that nanosilica contributes to enhancement of cemented sandy soil through yielding denser,more uniform structure.The XRD test demonstrated that the inclusion of nanosilica in the cemented soil increases the intensity of the calcium silicate hydrate(CSH) peak and decreases the intensity of the calcium hydroxide(CH) peak.The results showed that adding optimum percentages of nanosilica to cement-stabilized sandy soil enhances its mechanical and microstructure properties.展开更多
The surface hydrophobization and flotation of a xanthate−hydroxamate collector toward copper oxide mineral were compared with the combined collectors of xanthate and hydroxamate through water contact angle(WCA)and mic...The surface hydrophobization and flotation of a xanthate−hydroxamate collector toward copper oxide mineral were compared with the combined collectors of xanthate and hydroxamate through water contact angle(WCA)and micro-flotation experiments.The results showed that S-[(2-hydroxyamino)-2-oxoethyl]-O-octyl-dithiocarbonate ester(HAOODE)exhibited stronger hydrophobization and better flotation performance to malachite(Cu2(OH)2CO3)than octyl-hydroxamic acid(OHA)and its combination with S-allyl-O-ethyl xanthate ester(AEXE).To understand the hydrophobic intensification mechanism of HAOODE to malachite,zeta potential,atomic force microscopy(AFM)and XPS measurements were carried out.The results recommended that malachite chemisorbed HAOODE to form Cu—HAOODE complexes in which the hydroxamate—(O,O)—Cu and—O—C(—S—Cu)—S—configurations co-existed.The co-adsorption of HAOODE’s hetero-difunctional groups was more stable than the single-functionalgroup adsorption of OHA and AEXE,which produced the“loop”structure and intensified the self-assembly alignment of HAOODE on malachite surfaces.In addition,the“h”shape steric orientation of the double hydrophobic groups in HAOODE facilitated stronger hydrophobization toward malachite than the“line”or“V”hydrophobic carbon chains of OHA or AEXE.Thus,HAOODE achieved the preferable flotation recovery of malachite particles in comparison with OHA and AEXE.展开更多
Properties of organelles and intracellular structures play important roles in regulating cellular functions,such as gene expression,cell motility and metabolism.The ability to directly interrogate intracellular struct...Properties of organelles and intracellular structures play important roles in regulating cellular functions,such as gene expression,cell motility and metabolism.The ability to directly interrogate intracellular structures inside a single cell for measurement and manipulation has significant implications in the understanding of subcellular and suborganelle activities,diagnosing diseases,and potentially developing new therapeutic approaches.In the past few decades,a number of technologies have been developed to study single-cell properties.However,methods of measuring intracellular properties and manipulating subcellular structures have been largely underexplored.Due to the even smaller size of intracellular targets and lower signal-to-noise ratio than that in wholecell studies,the development of tools for intracellular measurement and manipulation is challenging.This paper reviews emerging microsystems and nanoengineered technologies for sensing and quantitative measurement of intracellular properties and for manipulating structures inside a single cell.Recent progress and limitations of these new technologies as well as new discoveries and prospects are discussed.展开更多
The exceptional physical properties and unique layered structure of two-dimensional(2D)materials have made this class of materials great candidates for applications in electronics,energy conversion/storage devices,nan...The exceptional physical properties and unique layered structure of two-dimensional(2D)materials have made this class of materials great candidates for applications in electronics,energy conversion/storage devices,nanocomposites,and multifunctional coatings,among others.At the center of this application space,mechanical properties play a vital role in materials design,manufacturing,integration and performance.The emergence of 2D materials has also sparked broad scientific inquiry,with new understanding of mechanical interactions between 2D structures and interfaces being of great interest to the community.Building on the dramatic expansion of recent research activities,here we review significant advances in the understanding of the elastic properties,in-plane failures,fatigue performance,interfacial shear/friction,and adhesion behavior of 2D materials.In this article,special emphasis is placed on some new 2D materials,novel characterization techniques and computational methods,as well as insights into deformation and failure mechanisms.A deep understanding of the intrinsic and extrinsic factors that govern 2D material mechanics is further provided,in the hopes that the community may draw design strategies for structural and interfacial engineering of 2D material systems.We end this review article with a discussion of our perspective on the state of the field and outlook on areas for future research directions.展开更多
Hydrophilic polymer coatings on artificial implants generate excellent tribological properties.The friction properties of polymer coatings are affected by salt ion factors.Herein,the atomic force microscopy(AFM)was us...Hydrophilic polymer coatings on artificial implants generate excellent tribological properties.The friction properties of polymer coatings are affected by salt ion factors.Herein,the atomic force microscopy(AFM)was used to show that the superlubricity was achieved between poly(vinylphosphonic acid)(PVPA)-modified Ti6Al4V and polystyrene(PS)microsphere probe lubricated with monovalent salt solutions(LiCl,NaCl,KCl,and CsCl).Considering that adhesion is an important cause of friction changes,the AFM was further utilized to obtain adhesion between friction pairs in different salt solutions.The results indicated that the larger the cation radius in the lubricant,the smaller the adhesion,and the lower the friction coefficient of the PVPA coating.The electrostatic interaction between the PVPA and one-valence cations in lubricants was analyzed by the molecular dynamics(MD)simulation as it was found to be the main influencing factor of the adhesion.Combined analysis results of friction and adhesion indicated that by adjusting the size of cation radius in lubricant,the adhesion between the tribo-pairs can be changed,and eventually the magnitude of friction can be affected.This study opens up a new avenue for analyzing the friction characteristics of hydrophilic polymer coatings from the perspective of intermolecular forces.展开更多
Dynamic friction occurs not only between two contact objects sliding against each other,but also between two relative sliding surfaces several nanometres apart.Many emerging micro-and nano-mechanical systems that prom...Dynamic friction occurs not only between two contact objects sliding against each other,but also between two relative sliding surfaces several nanometres apart.Many emerging micro-and nano-mechanical systems that promise new applications in sensors or information technology may suffer or benefit from noncontact friction.Herein we demonstrate the distance-dependent friction energy dissipation between the tip and the heterogeneous polymers by the bimodal atomic force microscopy(AFM)method driving the second order flexural and the first order torsional vibration simultaneously.The pull-in problem caused by the attractive force is avoided,and the friction dissipation can be imaged near the surface.The friction dissipation coefficient concept is proposed and three different contact states are determined from phase and energy dissipation curves.Image contrast is enhanced in the intermediate setpoint region.The work offers an effective method for directly detecting the friction dissipation and high resolution images,which overcomes the disadvantages of existing methods such as contact mode AFM or other contact friction and wear measuring instruments.展开更多
This work investigates the friction between polydimethylsiloxane(PDMS)and silicon oxide(SiO_(x))in single asperity sliding contact by atomic force microscopy(AFM).Two friction dependences on the normal force are ident...This work investigates the friction between polydimethylsiloxane(PDMS)and silicon oxide(SiO_(x))in single asperity sliding contact by atomic force microscopy(AFM).Two friction dependences on the normal force are identified:a tensile regime and a compressive regime of normal forces.In the compressive regime,friction is governed by the shear deformation and rupture of junctions between PDMS and SiO_(x).In this case,the shear strengthτ≈10 MPa is comparable with the cohesive strength of PDMS under compressive loading.In contrast,friction in the tensile regime is also affected by the elongation of the junctions.The single SiO_(x)-asperity follows a stick–slip motion on PDMS in both normal force regimes.Statistical analysis of stick–slip as a function of the normal force allows determining the necessary amount of energy to break a SiO_(x)/PDMS junction.Friction between a SiO_(x)-asperity and a PDMS surface can be rationalized based on an energy criterion for the deformation and slippage of nanometer-scale junctions.展开更多
Graphene has many advantageous properties,but its lack of an electronic band gap makes this two-dimensional material impractical for many nanoelectronic applications,for example,field-effect transistors.This problem c...Graphene has many advantageous properties,but its lack of an electronic band gap makes this two-dimensional material impractical for many nanoelectronic applications,for example,field-effect transistors.This problem can be circumvented by opening up a confinement-induced gap,through the patterning of graphene into ribbons having widths of a few nanometres.The electronic properties of such ribbons depend on both their size and the crystallographic orientation of the ribbon edges.Therefore,etching processes that are able to differentiate between the zigzag and armchair type edge terminations of graphene are highly sought after.In this contribution we show that such an anisotropic,dry etching reaction is possible and we use it to obtain graphene ribbons with zigzag edges.We demonstrate that the starting positions for the carbon removal reaction can be tailored at will with precision.展开更多
The bundle structure formed perpendicular to the scratching direction is a type of wear-induced structure for thermoplastics.In this study,the formation mechanism of bundle structures on polycarbonate(PC)surfaces is i...The bundle structure formed perpendicular to the scratching direction is a type of wear-induced structure for thermoplastics.In this study,the formation mechanism of bundle structures on polycarbonate(PC)surfaces is investigated by reciprocal scratching experiments.Based on the analysis of the morphologies,friction forces,and height signals,the formation of the bundle structure is reproduced.The influence of scratching parameters,including the feed value and scratching direction,on the formation of the bundle structure is also studied.It is found that the bundle structure is accumulated by the continuous stacking of the sample materials plowed by the tip in stick–slip motion,and that the stick–slip behavior is enhanced with increased scratching times.This work reproduces the formation process of bundle structure in experiments for the first time and demonstrates that the stick–slip enhancement mechanism exists in the reciprocal scratching process,providing further insight into the friction behavior of polymers.展开更多
Accurate metrology of extreme ultraviolet (EUV) photomask is a crucial task. In this paper, two different methods for reference EUV photomask metrology are compared. One is the critical dimension atomic force microsco...Accurate metrology of extreme ultraviolet (EUV) photomask is a crucial task. In this paper, two different methods for reference EUV photomask metrology are compared. One is the critical dimension atomic force microscopy (CD-AFM). In the measurements, the contribution of its AFM tip geometry is usually the dominant error source, as measured AFM images are the dilated results of measured structures by the AFM tip geometry. To solve this problem, a bottom-up approach has been applied in calibrating the (effective) AFM tip geometry where the result is traceably calibrated to the lattice constant of silicon crystals. The other is transmission electron microscopy (TEM). For achieving measurement traceability, structure features are measured in pairs in TEM images;thus the distance between the structure pair calibrated by a metrological AFM in prior can be applied to determine the magnification of the TEM image. In this study, selected photomask structures are calibrated by the CD-AFM, and then sample prepared and measured by high-resolution TEM nearly at the same location. The results are then compared. Of six feature groups compared, the results agree well within the measurement uncertainty, indicating excellent performance of the developed methodology. This research supports the development of a photomask standard, which is applied as a “reference ruler” with improved low measurement uncertainty in photomask fabs.展开更多
By using tapping mode atomic force microscopy(TMAFM), a polymer layer was found on the enamel surface after the exposure to xanthan gum solutions. The layer thickness is closely related to the exposure time and the co...By using tapping mode atomic force microscopy(TMAFM), a polymer layer was found on the enamel surface after the exposure to xanthan gum solutions. The layer thickness is closely related to the exposure time and the concentration of xanthan gum solution. The thickness data were evaluated by a Kruskal-Wallis test and Box-Whisker Plot at a 95% confidence level(p<0.05), and a statistically significant difference among the thickness data groups was demonstrated. After the exposure to 1000, 400, 100 mg/L xanthan gum solutions, the mean of layer thickness at the adsorption equilibrium is in the ranges of 103.5_122.06, 82.4_88.94 and 45.27_55.55 nm, respectively. This phenomenon suggests that the viscosity modifying agents in the beverage might be adsorbed on the enamel surface during consumption, which may form a barrier that can protect the enamel from being attacked by acid and therefore reduce dental erosion.展开更多
Unambiguous identification of the measurement methodologies is fundamental to reduce the uncertainty and support traceability of particle shape and size at the nanoscale. In this work, the critical aspects in atomic f...Unambiguous identification of the measurement methodologies is fundamental to reduce the uncertainty and support traceability of particle shape and size at the nanoscale. In this work, the critical aspects in atomic force microscopy measurements, that is, drawbacks on sample preparation, instrumental parameters, image pre-processing, size reconstruction, and tip enlargement, are discussed in reference to quantitative dimensional measurements on different kinds of nanoparticles (inorganic and biological) with different shapes (spherical, cylindrical, complex geometry). Once the cross-section profile is extracted, top-height measurements on isolated nanoparticles of any shape can be achieved with sub-nanometer accuracy. Lateral resolution is affected by the pixel size and shape of the probe, causing dilation in the atomic force microscopy image. For the reconstruction of critical sizes of inorganic non-spherical nanoparticles, a geometric approach that considers the nominal shape because of the synthesis conditions is presented and discussed.展开更多
Two-dimensional compounds combining group IV A element and group V A element were determined to integrate the advantages of the two groups.As a typical 2D group IV–V material,SiP has been widely used in photodetectio...Two-dimensional compounds combining group IV A element and group V A element were determined to integrate the advantages of the two groups.As a typical 2D group IV–V material,SiP has been widely used in photodetection and photocatalysis due to its high carrier mobility,appropriate bandgap,high thermal stability,and low interlayer cleavage energy.However,its adhesion and friction properties have not been extensively grasped.Here,large-size and high-quality SiP crystals were obtained by using the flux method.SiP nanosheets were prepared by using mechanical exfoliation.The layer-dependent and velocity-dependent nanotribological properties of SiP nanosheets were systematically investigated.The results indicate the friction force of SiP nanosheets decreases with the increase in layer number and reaches saturation after five layers.The coefficient of friction of multilayer SiP is 0.018.The mean friction force,frictional vibrations,and the friction strengthening effect can be affected by sliding velocity.Specially,the mean friction force increases with the logarithm of sliding velocity at nm/s scale,which is dominated by atomic stick-slip.The influence of frequency on frictional vibration is greater than speed due to the different influences on the change in contact quality.The friction strengthening saturation distance increases with the increase in speed for thick SiP nanosheets.These results provide an approach for manipulating the nanofriction properties of SiP and serve as a theoretical basis for the application of SiP in solid lubrication and microelectromechanical systems.展开更多
Cation-π interaction is an electrostatic interaction between a cation and an electron-rich arene.It plays an essential role in many biological systems as a vital driving force for protein folding,stability,and recept...Cation-π interaction is an electrostatic interaction between a cation and an electron-rich arene.It plays an essential role in many biological systems as a vital driving force for protein folding,stability,and receptor-ligand interaction/recognition.To date,the discovery of most cation-π interactions in proteins relies on the statistical analyses of available three-dimensional(3D)protein structures and corresponding computational calculations.However,their experimental verification and quantification remain sparse at the molecular level,mainly due to the limited methods to dynamically measure such a weak non-covalent interaction in proteins.Here,we use atomic force microscopy-based single-molecule force spectroscopy(AFM-SMFS)to measure the stability of protein neutrophil gelatinase-associated lipocalin(also known as NGAL,siderocalin,lipocalin 2)that can bind iron through the cation-π interactions between its three cationic residues and the iron-binding tri-catechols.Based on a site-specific cysteine engineering and anchoring method,we first characterized the stability and unfolding pathways of apo-NGAL.Then,the same NGAL but bound with the iron-catechol complexes through the cation-π interactions as a holo-form was characterized.AFM measurements demonstrated stronger stabilities and kinetics of the holo-NGAL from two pulling sites,F122 and F133.Here,NGAL is stretched from the designed cysteine close to the cationic residues for a maximum unfolding effect.Thus,our work demonstrates high-precision detection of the weak cation-π interaction in NGAL.展开更多
The rabies virus is a neurotropic virus that causes fatal diseases in humans and animals.Although studying the interactions between a single rabies virus and the cell membrane is necessary for understanding the pathog...The rabies virus is a neurotropic virus that causes fatal diseases in humans and animals.Although studying the interactions between a single rabies virus and the cell membrane is necessary for understanding the pathogenesis,the internalization dynamic mechanism of single rabies virus in living cells remains largely elusive.Here,we utilized a novel force tracing technique based on atomic force microscopy(AFM)to record the process of single viral entry into host cell.We revealed that the force of the rabies virus internalization distributed at(65±25)pN,and the time was identified by two peaks with spacings of(237.2±59.1)and(790.3±134.4)ms with the corresponding speed of 0.12 and 0.04µm/s,respectively.Our results provide insight into the effects of viral shape during the endocytosis process.This report will be meaningful for understanding the dynamic mechanism of rabies virus early infection.展开更多
Interface can be a fertile ground for exotic quantum states,including topological superconductivity,Majorana mode,fractal quantum Hall effect,unconventional superconductivity,Mott insulator,etc.Here we grow single-uni...Interface can be a fertile ground for exotic quantum states,including topological superconductivity,Majorana mode,fractal quantum Hall effect,unconventional superconductivity,Mott insulator,etc.Here we grow single-unit-cell(1UC)FeTe film on NbSe_(2)single crystal by molecular beam epitaxy(MBE)and investigate the film in-situ with a home-made cryogenic scanning tunneling microscopy(STM)and non-contact atomic force microscopy(AFM)combined system.We find different stripe-like superlattice modulations on grown FeTe film with different misorientation angles with respect to NbSe_(2)substrate.We show that these stripe-like superlattice modulations can be understood as moirépattern forming between FeTe film and NbSe_(2)substrate.Our results indicate that the interface between Fe Te and NbSe2 is atomically sharp.By STM-AFM combined measurement,we suggest that the moirésuperlattice modulations have an electronic origin when the misorientation angle is relatively small(≤3°)and have structural relaxation when the misorientation angle is relatively large(≥10°).展开更多
The generation of pretilt angles for nematic liquid crystal aligned on the rubbed polyimide surface containing trifluoromethyl moieties has been investigated. The characters of the rubbed polyimide films were studied ...The generation of pretilt angles for nematic liquid crystal aligned on the rubbed polyimide surface containing trifluoromethyl moieties has been investigated. The characters of the rubbed polyimide films were studied by using X ray photoelectron spectroscopy(XPS) and atomic force microscopy(AFM). The uneven distribution extent of fluorine content along the depth of the polyimide films could be reduced by rubbing, thus the interaction between liquid crystal molecules and polyimide molecules decreased. It is also showed that the aggregation state of polyimide molecules was changed and polyimide chains aligned along the rubbing direction, so the orientation direction of the liquid crystal molecules was the same as the rubbing direction. The orientation effect of the liquid crystal molecules on the rubbed polyimide surface can be attributed to the combined effects of the Van der Waals dispersion interaction between polyimide and liquid crystal molecules, and the alignment of the orientation direction of polyimide chains with the rubbing direction. 展开更多
Uncapped double stacked In0.5Ga0.5As quantum dots（QDs） with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition（MOCVD）.The precursors used for the growth of the GaAs layer ...Uncapped double stacked In0.5Ga0.5As quantum dots（QDs） with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition（MOCVD）.The precursors used for the growth of the GaAs layer and In0.5Ga0.5As QDs were trimethylgallium（TMGa）,trimethylindium（TMIn）,and arsine（AsH3）.The morphology and optical properties of the self-assembled In0.5Ga0.5As QDs were investigated and characterized using atomic force microscopy（AFM） and photoluminescence（PL）.The AFM images revealed that the sizes of the dots on the topmost were not uniformly distributed.The average size of the dots fluctuated as the GaAs spacer layer thickness increased.A room temperature PL measurement was used to establish the quality and quantity of the stacked QDs.The PL peak position remained at 1148 nm for all samples of QDs;however,the PL intensity increased as spacer layer thickness increased.The structure of the spacer layer in the stacked QD affected the morphology of the topmost surface of the QDs.The PL measurement coherently reflected the AFM characterization,in which the strong PL spectra were caused by the uniformity and high density of the QDs.The surface morphology,structure,and optical properties of the stacked QDs are attributed to seed-layer（first layer） formation of dots and spacer layer structures.展开更多
The influence of sputtering gas（He Ar） on the structural properties of Mg thin films has been investigated.The optical property（reflectance） that results from the growth of films at varying substrate temperatures...The influence of sputtering gas（He Ar） on the structural properties of Mg thin films has been investigated.The optical property（reflectance） that results from the growth of films at varying substrate temperatures（Tsub） was also studied.The deposited films were characterized by using X-ray diffraction（XRD）,field emission scaning electron microscopy（FE-SEM）,atomic force microscopy（AFM） and UV-Vis-NIR spectrophotometer.The smaller crystallite size and lower deposition rate were observed in the presence of Helium atmosphere compared to Argon.Morphology of the films shows 2D hexagonal geometry of grains in the deposition temperature range（Tsub≈50-150℃） in both the sputtering gases.The surface roughness of the polycrystalline films were found to increase with increase in the deposition temperature of both ambient gases.Optical reflectance of Mg films was measured in near infrared region and larger reflectance was observed from Mg films sputtered in He atmosphere compared to that in argon.展开更多
Copper nanoparticles（Cu NPs） have been synthesized by using laser ablation method,using deionized water as main solvent.The formation of Cu NPs is confirmed by UV-visible spectrophotometer（UV-Vis）,atomic force mic...Copper nanoparticles（Cu NPs） have been synthesized by using laser ablation method,using deionized water as main solvent.The formation of Cu NPs is confirmed by UV-visible spectrophotometer（UV-Vis）,atomic force microscopy（AFM） and X-ray diffraction（XRD）.Cu NPs fabricated by laser ablation have diameter in the range from 14 to 55 nm.Structural analysis revealed the face-centered cubic（fcc） crystal structure of Cu NPs.The antibacterial activity of Cu NPs has been evaluated in vitro against strains of Escherichia coli（E.coli） and Staphylococcus aureus（5.aureus）.The fabricated Cu NPs show considerable antibacterial activity against both bacterial strains.The bacterial activity of Cu NPs was found to depend on the microbial species.展开更多
文摘An experimental program was conducted to explore the impact of nanosilica on the microstructure and mechanical characteristics of cemented sandy soil.Cement agent included Portland cement type II.Cement content was 6% by weight of the sandy soil.Nanosilica was added in percentages of 0%,4%,8% and 12% by weight of cement.Cylindrical samples were prepared with relative density of 80% and optimum water content and cured for 7 d,28 d and 90 d.Microstructure characteristics of cementnanosilica-sand mixtures after 90 d of curing have been explored using atomic force microscopy(AFM),scanning electron microscopy(SEM) and X-ray diffraction(XRD) tests.Effects of curing time on microstructure properties of cemented sandy soil samples with 0% and 8% nanosilica have been investigated using SEM test.Unconfined compression test(for all curing times) and compaction test were also performed.The SEM and AFM tests results showed that nanosilica contributes to enhancement of cemented sandy soil through yielding denser,more uniform structure.The XRD test demonstrated that the inclusion of nanosilica in the cemented soil increases the intensity of the calcium silicate hydrate(CSH) peak and decreases the intensity of the calcium hydroxide(CH) peak.The results showed that adding optimum percentages of nanosilica to cement-stabilized sandy soil enhances its mechanical and microstructure properties.
基金Project(51474253)supported by the National Natural Science Foundation of China。
文摘The surface hydrophobization and flotation of a xanthate−hydroxamate collector toward copper oxide mineral were compared with the combined collectors of xanthate and hydroxamate through water contact angle(WCA)and micro-flotation experiments.The results showed that S-[(2-hydroxyamino)-2-oxoethyl]-O-octyl-dithiocarbonate ester(HAOODE)exhibited stronger hydrophobization and better flotation performance to malachite(Cu2(OH)2CO3)than octyl-hydroxamic acid(OHA)and its combination with S-allyl-O-ethyl xanthate ester(AEXE).To understand the hydrophobic intensification mechanism of HAOODE to malachite,zeta potential,atomic force microscopy(AFM)and XPS measurements were carried out.The results recommended that malachite chemisorbed HAOODE to form Cu—HAOODE complexes in which the hydroxamate—(O,O)—Cu and—O—C(—S—Cu)—S—configurations co-existed.The co-adsorption of HAOODE’s hetero-difunctional groups was more stable than the single-functionalgroup adsorption of OHA and AEXE,which produced the“loop”structure and intensified the self-assembly alignment of HAOODE on malachite surfaces.In addition,the“h”shape steric orientation of the double hydrophobic groups in HAOODE facilitated stronger hydrophobization toward malachite than the“line”or“V”hydrophobic carbon chains of OHA or AEXE.Thus,HAOODE achieved the preferable flotation recovery of malachite particles in comparison with OHA and AEXE.
文摘Properties of organelles and intracellular structures play important roles in regulating cellular functions,such as gene expression,cell motility and metabolism.The ability to directly interrogate intracellular structures inside a single cell for measurement and manipulation has significant implications in the understanding of subcellular and suborganelle activities,diagnosing diseases,and potentially developing new therapeutic approaches.In the past few decades,a number of technologies have been developed to study single-cell properties.However,methods of measuring intracellular properties and manipulating subcellular structures have been largely underexplored.Due to the even smaller size of intracellular targets and lower signal-to-noise ratio than that in wholecell studies,the development of tools for intracellular measurement and manipulation is challenging.This paper reviews emerging microsystems and nanoengineered technologies for sensing and quantitative measurement of intracellular properties and for manipulating structures inside a single cell.Recent progress and limitations of these new technologies as well as new discoveries and prospects are discussed.
基金the Natural Sciences and Engineering Research Council(NSERC)of CanadaNational Natural Science Foundation of China(Grant Nos.12202430,12241202)+1 种基金USTC Research Funds of the Double First-Class Initiative(Grant No.YD2090002011)the China Scholarship Council。
文摘The exceptional physical properties and unique layered structure of two-dimensional(2D)materials have made this class of materials great candidates for applications in electronics,energy conversion/storage devices,nanocomposites,and multifunctional coatings,among others.At the center of this application space,mechanical properties play a vital role in materials design,manufacturing,integration and performance.The emergence of 2D materials has also sparked broad scientific inquiry,with new understanding of mechanical interactions between 2D structures and interfaces being of great interest to the community.Building on the dramatic expansion of recent research activities,here we review significant advances in the understanding of the elastic properties,in-plane failures,fatigue performance,interfacial shear/friction,and adhesion behavior of 2D materials.In this article,special emphasis is placed on some new 2D materials,novel characterization techniques and computational methods,as well as insights into deformation and failure mechanisms.A deep understanding of the intrinsic and extrinsic factors that govern 2D material mechanics is further provided,in the hopes that the community may draw design strategies for structural and interfacial engineering of 2D material systems.We end this review article with a discussion of our perspective on the state of the field and outlook on areas for future research directions.
基金supported by the National Natural Science Foundation of China(51705010)the Beijing Natural Science Foundation(3192003)+2 种基金the General Project of Science and Technology Plan from Beijing Educational Committee(KM201810005013)the Tribology Science Fund of State Key Laboratory of Tribology(STLEKF16A02 and SKLTKF19B08)the training program of Rixin talent and outstanding talent from Beijing University of Technology.
文摘Hydrophilic polymer coatings on artificial implants generate excellent tribological properties.The friction properties of polymer coatings are affected by salt ion factors.Herein,the atomic force microscopy(AFM)was used to show that the superlubricity was achieved between poly(vinylphosphonic acid)(PVPA)-modified Ti6Al4V and polystyrene(PS)microsphere probe lubricated with monovalent salt solutions(LiCl,NaCl,KCl,and CsCl).Considering that adhesion is an important cause of friction changes,the AFM was further utilized to obtain adhesion between friction pairs in different salt solutions.The results indicated that the larger the cation radius in the lubricant,the smaller the adhesion,and the lower the friction coefficient of the PVPA coating.The electrostatic interaction between the PVPA and one-valence cations in lubricants was analyzed by the molecular dynamics(MD)simulation as it was found to be the main influencing factor of the adhesion.Combined analysis results of friction and adhesion indicated that by adjusting the size of cation radius in lubricant,the adhesion between the tribo-pairs can be changed,and eventually the magnitude of friction can be affected.This study opens up a new avenue for analyzing the friction characteristics of hydrophilic polymer coatings from the perspective of intermolecular forces.
基金This research is financially supported by the National Natural Science Foundation of China(No.51527901).
文摘Dynamic friction occurs not only between two contact objects sliding against each other,but also between two relative sliding surfaces several nanometres apart.Many emerging micro-and nano-mechanical systems that promise new applications in sensors or information technology may suffer or benefit from noncontact friction.Herein we demonstrate the distance-dependent friction energy dissipation between the tip and the heterogeneous polymers by the bimodal atomic force microscopy(AFM)method driving the second order flexural and the first order torsional vibration simultaneously.The pull-in problem caused by the attractive force is avoided,and the friction dissipation can be imaged near the surface.The friction dissipation coefficient concept is proposed and three different contact states are determined from phase and energy dissipation curves.Image contrast is enhanced in the intermediate setpoint region.The work offers an effective method for directly detecting the friction dissipation and high resolution images,which overcomes the disadvantages of existing methods such as contact mode AFM or other contact friction and wear measuring instruments.
文摘This work investigates the friction between polydimethylsiloxane(PDMS)and silicon oxide(SiO_(x))in single asperity sliding contact by atomic force microscopy(AFM).Two friction dependences on the normal force are identified:a tensile regime and a compressive regime of normal forces.In the compressive regime,friction is governed by the shear deformation and rupture of junctions between PDMS and SiO_(x).In this case,the shear strengthτ≈10 MPa is comparable with the cohesive strength of PDMS under compressive loading.In contrast,friction in the tensile regime is also affected by the elongation of the junctions.The single SiO_(x)-asperity follows a stick–slip motion on PDMS in both normal force regimes.Statistical analysis of stick–slip as a function of the normal force allows determining the necessary amount of energy to break a SiO_(x)/PDMS junction.Friction between a SiO_(x)-asperity and a PDMS surface can be rationalized based on an energy criterion for the deformation and slippage of nanometer-scale junctions.
基金Financial support by hungarian scientific research fund-national office for research and technology(OTKA-NKTH)grants Nos.67793,67851,and 67842 is acknowledged.
文摘Graphene has many advantageous properties,but its lack of an electronic band gap makes this two-dimensional material impractical for many nanoelectronic applications,for example,field-effect transistors.This problem can be circumvented by opening up a confinement-induced gap,through the patterning of graphene into ribbons having widths of a few nanometres.The electronic properties of such ribbons depend on both their size and the crystallographic orientation of the ribbon edges.Therefore,etching processes that are able to differentiate between the zigzag and armchair type edge terminations of graphene are highly sought after.In this contribution we show that such an anisotropic,dry etching reaction is possible and we use it to obtain graphene ribbons with zigzag edges.We demonstrate that the starting positions for the carbon removal reaction can be tailored at will with precision.
基金The authors gratefully acknowledge the financial supports of the Natural Science Foundation of Heilongjiang Province of China(YQ2020E015)Science and Technology Based for Equipment Design and Manufacturing for Introduction Talents of Discipline to Universities 2.0 of the 111 Project(BP0719002)+2 种基金Self-planned Task of State Key Laboratory of Robotics and Systems,Harbin Institute of Technology(SKLRS202001C)Young Elite Scientist Sponsorship Program by China Association for Science and Technology(YESS20200155)the Fundamental Research Funds for the Central Universities(FRFCU5710050521 and FRFCU5710091220).
文摘The bundle structure formed perpendicular to the scratching direction is a type of wear-induced structure for thermoplastics.In this study,the formation mechanism of bundle structures on polycarbonate(PC)surfaces is investigated by reciprocal scratching experiments.Based on the analysis of the morphologies,friction forces,and height signals,the formation of the bundle structure is reproduced.The influence of scratching parameters,including the feed value and scratching direction,on the formation of the bundle structure is also studied.It is found that the bundle structure is accumulated by the continuous stacking of the sample materials plowed by the tip in stick–slip motion,and that the stick–slip behavior is enhanced with increased scratching times.This work reproduces the formation process of bundle structure in experiments for the first time and demonstrates that the stick–slip enhancement mechanism exists in the reciprocal scratching process,providing further insight into the friction behavior of polymers.
基金Open Access funding enabled and organized by Projekt DEAL.
文摘Accurate metrology of extreme ultraviolet (EUV) photomask is a crucial task. In this paper, two different methods for reference EUV photomask metrology are compared. One is the critical dimension atomic force microscopy (CD-AFM). In the measurements, the contribution of its AFM tip geometry is usually the dominant error source, as measured AFM images are the dilated results of measured structures by the AFM tip geometry. To solve this problem, a bottom-up approach has been applied in calibrating the (effective) AFM tip geometry where the result is traceably calibrated to the lattice constant of silicon crystals. The other is transmission electron microscopy (TEM). For achieving measurement traceability, structure features are measured in pairs in TEM images;thus the distance between the structure pair calibrated by a metrological AFM in prior can be applied to determine the magnification of the TEM image. In this study, selected photomask structures are calibrated by the CD-AFM, and then sample prepared and measured by high-resolution TEM nearly at the same location. The results are then compared. Of six feature groups compared, the results agree well within the measurement uncertainty, indicating excellent performance of the developed methodology. This research supports the development of a photomask standard, which is applied as a “reference ruler” with improved low measurement uncertainty in photomask fabs.
文摘By using tapping mode atomic force microscopy(TMAFM), a polymer layer was found on the enamel surface after the exposure to xanthan gum solutions. The layer thickness is closely related to the exposure time and the concentration of xanthan gum solution. The thickness data were evaluated by a Kruskal-Wallis test and Box-Whisker Plot at a 95% confidence level(p<0.05), and a statistically significant difference among the thickness data groups was demonstrated. After the exposure to 1000, 400, 100 mg/L xanthan gum solutions, the mean of layer thickness at the adsorption equilibrium is in the ranges of 103.5_122.06, 82.4_88.94 and 45.27_55.55 nm, respectively. This phenomenon suggests that the viscosity modifying agents in the beverage might be adsorbed on the enamel surface during consumption, which may form a barrier that can protect the enamel from being attacked by acid and therefore reduce dental erosion.
文摘Unambiguous identification of the measurement methodologies is fundamental to reduce the uncertainty and support traceability of particle shape and size at the nanoscale. In this work, the critical aspects in atomic force microscopy measurements, that is, drawbacks on sample preparation, instrumental parameters, image pre-processing, size reconstruction, and tip enlargement, are discussed in reference to quantitative dimensional measurements on different kinds of nanoparticles (inorganic and biological) with different shapes (spherical, cylindrical, complex geometry). Once the cross-section profile is extracted, top-height measurements on isolated nanoparticles of any shape can be achieved with sub-nanometer accuracy. Lateral resolution is affected by the pixel size and shape of the probe, causing dilation in the atomic force microscopy image. For the reconstruction of critical sizes of inorganic non-spherical nanoparticles, a geometric approach that considers the nominal shape because of the synthesis conditions is presented and discussed.
基金Thanks for the financial support of the Program for Taishan Scholars of Shandong Province(No.ts20190965)the National Key R&D Program of China(No.2020YFF0304600)+2 种基金the National Natural Science Foundation of China(No.51905518)the Key Research Program of the Chinese Academy of Sciences(No.XDPB24)the Innovation Leading Talents Program of Qingdao(No.19-3-2-23-zhc)in China.
文摘Two-dimensional compounds combining group IV A element and group V A element were determined to integrate the advantages of the two groups.As a typical 2D group IV–V material,SiP has been widely used in photodetection and photocatalysis due to its high carrier mobility,appropriate bandgap,high thermal stability,and low interlayer cleavage energy.However,its adhesion and friction properties have not been extensively grasped.Here,large-size and high-quality SiP crystals were obtained by using the flux method.SiP nanosheets were prepared by using mechanical exfoliation.The layer-dependent and velocity-dependent nanotribological properties of SiP nanosheets were systematically investigated.The results indicate the friction force of SiP nanosheets decreases with the increase in layer number and reaches saturation after five layers.The coefficient of friction of multilayer SiP is 0.018.The mean friction force,frictional vibrations,and the friction strengthening effect can be affected by sliding velocity.Specially,the mean friction force increases with the logarithm of sliding velocity at nm/s scale,which is dominated by atomic stick-slip.The influence of frequency on frictional vibration is greater than speed due to the different influences on the change in contact quality.The friction strengthening saturation distance increases with the increase in speed for thick SiP nanosheets.These results provide an approach for manipulating the nanofriction properties of SiP and serve as a theoretical basis for the application of SiP in solid lubrication and microelectromechanical systems.
基金This work was funded by the Fundamental Research Funds for the Central Universities(No.14380259)Natural Science Foundation of Jiangsu Province(No.BK20200058)+1 种基金the National Natural Science Foundation of China(Nos.21771103 and 21977047)computational resources from computing facilities of the High-Performance Computing Center(HPCC)of Nanjing University。
文摘Cation-π interaction is an electrostatic interaction between a cation and an electron-rich arene.It plays an essential role in many biological systems as a vital driving force for protein folding,stability,and receptor-ligand interaction/recognition.To date,the discovery of most cation-π interactions in proteins relies on the statistical analyses of available three-dimensional(3D)protein structures and corresponding computational calculations.However,their experimental verification and quantification remain sparse at the molecular level,mainly due to the limited methods to dynamically measure such a weak non-covalent interaction in proteins.Here,we use atomic force microscopy-based single-molecule force spectroscopy(AFM-SMFS)to measure the stability of protein neutrophil gelatinase-associated lipocalin(also known as NGAL,siderocalin,lipocalin 2)that can bind iron through the cation-π interactions between its three cationic residues and the iron-binding tri-catechols.Based on a site-specific cysteine engineering and anchoring method,we first characterized the stability and unfolding pathways of apo-NGAL.Then,the same NGAL but bound with the iron-catechol complexes through the cation-π interactions as a holo-form was characterized.AFM measurements demonstrated stronger stabilities and kinetics of the holo-NGAL from two pulling sites,F122 and F133.Here,NGAL is stretched from the designed cysteine close to the cationic residues for a maximum unfolding effect.Thus,our work demonstrates high-precision detection of the weak cation-π interaction in NGAL.
基金This work was supported by the Project of the Education Department of Jilin Province,China(No.JJKH20220666KJ)the Talent of Jilin Province Development Fund Project,China(No.2021Y004)National Natural Science Foundation of China(No.21773017).
文摘The rabies virus is a neurotropic virus that causes fatal diseases in humans and animals.Although studying the interactions between a single rabies virus and the cell membrane is necessary for understanding the pathogenesis,the internalization dynamic mechanism of single rabies virus in living cells remains largely elusive.Here,we utilized a novel force tracing technique based on atomic force microscopy(AFM)to record the process of single viral entry into host cell.We revealed that the force of the rabies virus internalization distributed at(65±25)pN,and the time was identified by two peaks with spacings of(237.2±59.1)and(790.3±134.4)ms with the corresponding speed of 0.12 and 0.04µm/s,respectively.Our results provide insight into the effects of viral shape during the endocytosis process.This report will be meaningful for understanding the dynamic mechanism of rabies virus early infection.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2016YFA0302400,2016YFA0300602,and2017YFA0302903)the National Natural Science Foundation of China(Grant No.11227903)+2 种基金the Beijing Municipal Science and Technology Commission,China(Grant Nos.Z181100004218007 and Z191100007219011)the National Basic Research Program of China(Grant No.2015CB921304)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB07000000,XDB28000000,and XDB33000000)。
文摘Interface can be a fertile ground for exotic quantum states,including topological superconductivity,Majorana mode,fractal quantum Hall effect,unconventional superconductivity,Mott insulator,etc.Here we grow single-unit-cell(1UC)FeTe film on NbSe_(2)single crystal by molecular beam epitaxy(MBE)and investigate the film in-situ with a home-made cryogenic scanning tunneling microscopy(STM)and non-contact atomic force microscopy(AFM)combined system.We find different stripe-like superlattice modulations on grown FeTe film with different misorientation angles with respect to NbSe_(2)substrate.We show that these stripe-like superlattice modulations can be understood as moirépattern forming between FeTe film and NbSe_(2)substrate.Our results indicate that the interface between Fe Te and NbSe2 is atomically sharp.By STM-AFM combined measurement,we suggest that the moirésuperlattice modulations have an electronic origin when the misorientation angle is relatively small(≤3°)and have structural relaxation when the misorientation angle is relatively large(≥10°).
文摘The generation of pretilt angles for nematic liquid crystal aligned on the rubbed polyimide surface containing trifluoromethyl moieties has been investigated. The characters of the rubbed polyimide films were studied by using X ray photoelectron spectroscopy(XPS) and atomic force microscopy(AFM). The uneven distribution extent of fluorine content along the depth of the polyimide films could be reduced by rubbing, thus the interaction between liquid crystal molecules and polyimide molecules decreased. It is also showed that the aggregation state of polyimide molecules was changed and polyimide chains aligned along the rubbing direction, so the orientation direction of the liquid crystal molecules was the same as the rubbing direction. The orientation effect of the liquid crystal molecules on the rubbed polyimide surface can be attributed to the combined effects of the Van der Waals dispersion interaction between polyimide and liquid crystal molecules, and the alignment of the orientation direction of polyimide chains with the rubbing direction.
基金Supported by the Ministry of Science,Technology and Innovationof Malaysia
文摘Uncapped double stacked In0.5Ga0.5As quantum dots（QDs） with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition（MOCVD）.The precursors used for the growth of the GaAs layer and In0.5Ga0.5As QDs were trimethylgallium（TMGa）,trimethylindium（TMIn）,and arsine（AsH3）.The morphology and optical properties of the self-assembled In0.5Ga0.5As QDs were investigated and characterized using atomic force microscopy（AFM） and photoluminescence（PL）.The AFM images revealed that the sizes of the dots on the topmost were not uniformly distributed.The average size of the dots fluctuated as the GaAs spacer layer thickness increased.A room temperature PL measurement was used to establish the quality and quantity of the stacked QDs.The PL peak position remained at 1148 nm for all samples of QDs;however,the PL intensity increased as spacer layer thickness increased.The structure of the spacer layer in the stacked QD affected the morphology of the topmost surface of the QDs.The PL measurement coherently reflected the AFM characterization,in which the strong PL spectra were caused by the uniformity and high density of the QDs.The surface morphology,structure,and optical properties of the stacked QDs are attributed to seed-layer（first layer） formation of dots and spacer layer structures.
基金by DRDO,Govt. of India (Grant No.ERIP/ER/0800354/M/01/1125)
文摘The influence of sputtering gas（He Ar） on the structural properties of Mg thin films has been investigated.The optical property（reflectance） that results from the growth of films at varying substrate temperatures（Tsub） was also studied.The deposited films were characterized by using X-ray diffraction（XRD）,field emission scaning electron microscopy（FE-SEM）,atomic force microscopy（AFM） and UV-Vis-NIR spectrophotometer.The smaller crystallite size and lower deposition rate were observed in the presence of Helium atmosphere compared to Argon.Morphology of the films shows 2D hexagonal geometry of grains in the deposition temperature range（Tsub≈50-150℃） in both the sputtering gases.The surface roughness of the polycrystalline films were found to increase with increase in the deposition temperature of both ambient gases.Optical reflectance of Mg films was measured in near infrared region and larger reflectance was observed from Mg films sputtered in He atmosphere compared to that in argon.
文摘Copper nanoparticles（Cu NPs） have been synthesized by using laser ablation method,using deionized water as main solvent.The formation of Cu NPs is confirmed by UV-visible spectrophotometer（UV-Vis）,atomic force microscopy（AFM） and X-ray diffraction（XRD）.Cu NPs fabricated by laser ablation have diameter in the range from 14 to 55 nm.Structural analysis revealed the face-centered cubic（fcc） crystal structure of Cu NPs.The antibacterial activity of Cu NPs has been evaluated in vitro against strains of Escherichia coli（E.coli） and Staphylococcus aureus（5.aureus）.The fabricated Cu NPs show considerable antibacterial activity against both bacterial strains.The bacterial activity of Cu NPs was found to depend on the microbial species.
