Recently,charged solitons have been found in a two-dimensional CoCl_(2)/HOPG system,whose microscopic nature remains to be elusive.In this work,we investigate the charged solitons in monolayer CoCl_(2) using scanning ...Recently,charged solitons have been found in a two-dimensional CoCl_(2)/HOPG system,whose microscopic nature remains to be elusive.In this work,we investigate the charged solitons in monolayer CoCl_(2) using scanning tunneling microscopy(STM)and atomic force microscopy(AFM).Moreover,we study the electrical properties of the charged solitons at zero electric field by measuring local contact potential difference(LCPD)via Kelvin probe force microscopy(KPFM)using the Δf(V)method.The compensation voltage corresponding to the vertex of the parabola is obtained by fitting the quadratic relationship between Δf and sample bias.The results show that,without an external electric field,the solitons behave as negatively charged entities.Meanwhile,the LCPD mapping characterizes the spatial distribution of the potential at the charged solitons,which agrees well with those obtained from STM band bending measurements.展开更多
To eliminate distortion caused by vertical drift and illusory slopes in atomic force microscopy(AFM)imaging,a lifting-wavelet-based iterative thresholding correction method is proposed in this paper.This method achiev...To eliminate distortion caused by vertical drift and illusory slopes in atomic force microscopy(AFM)imaging,a lifting-wavelet-based iterative thresholding correction method is proposed in this paper.This method achieves high-quality AFM imaging via line-by-line corrections for each distorted profile along the fast axis.The key to this line-by-line correction is to accurately simulate the profile distortion of each scanning row.Therefore,a data preprocessing approach is first developed to roughly filter out most of the height data that impairs the accuracy of distortion modeling.This process is implemented through an internal double-screening mechanism.A line-fitting method is adopted to preliminarily screen out the obvious specimens.Lifting wavelet analysis is then carried out to identify the base parts that are mistakenly filtered out as specimens so as to preserve most of the base profiles and provide a good basis for further distortion modeling.Next,an iterative thresholding algorithm is developed to precisely simulate the profile distortion.By utilizing the roughly screened base profile,the optimal threshold,which is used to screen out the pure bases suitable for distortion modeling,is determined through iteration with a specified error rule.On this basis,the profile distortion is accurately modeled through line fitting on the finely screened base data,and the correction is implemented by subtracting the modeling result from the distorted profile.Finally,the effectiveness of the proposed method is verified through experiments and applications.展开更多
The single-point bending method,based on atomic force microscopy(AFM),has been extensively validated for characterizing the structural mechanical properties of micro-and nanobeams.Nevertheless,the influence of AFM pro...The single-point bending method,based on atomic force microscopy(AFM),has been extensively validated for characterizing the structural mechanical properties of micro-and nanobeams.Nevertheless,the influence of AFM probe loading and positioning has yet to be subjected to comprehensive investigation.This paper proposes a novel bending-test method based on sequential loading points,in which a series of evenly distributed loads are applied along the length of the central axis on the upper surface of the cantilever.The preliminary measured values of Young’s modulus for an unknown alloy material were 193,178,and 176 GPa,exhibiting a considerable degree of dispersion.An algorithm for self-correction of the positioning error was developed,and this resulted in a positioning error of 53 nm and a final converged Young’s modulus of 161 GPa.展开更多
Atomic force microscopy（AFM） is a commonly used technique for graphene thickness measurement.However, due to surface roughness caused by graphene itself and variation introduced in AFM measurement, graphene thicknes...Atomic force microscopy（AFM） is a commonly used technique for graphene thickness measurement.However, due to surface roughness caused by graphene itself and variation introduced in AFM measurement, graphene thickness is difficult to be accurately determined by AFM. In this paper, a histogram method was used for reliable measurements of graphene thickness using AFM. The influences of various measurement parameters in AFM analysis were investigated. The experimental results indicate that significant deviation can be introduced using various order of flatten and improperly selected measurement parameters including amplitude setpoint and drive amplitude. At amplitude setpoint of 100 mV and drive amplitude of 100 m V, thickness of 1 layer（1L）, 2 layers（2L） and 4 layers（4L） graphene were measured.The height differences for 1L, 2L and 4L were 1.51 ± 0.16 nm, 1.92 ± 0.13 nm and 2.73 ± 0.10 nm, respectively. By comparing these values, thickness of single layer graphene can be accurately determined to be0.41 ± 0.09 nm.展开更多
The organization of the higher order structure of chromatin in chicken erythrocytes has been examined withtapping-mode scanning force microscopy under conditionsclose to their native environment. Reproducible highreso...The organization of the higher order structure of chromatin in chicken erythrocytes has been examined withtapping-mode scanning force microscopy under conditionsclose to their native environment. Reproducible highresolution AFM images of chromatin compaction at several levels can be demonstrated. An extended beads-on-astring (width of ～ 15-20nm, height of ～ 2-3nm for eachindividual nucleosome) can be consistently observed. Furthermore, superbeads (width of ～ 40nm, height of ～ 7nm)are demonstrated. Visualization of the solenoid conformation at the level of 30nm chromatin fiber is attained eitherby using AFM or by using electron microscopy. In addition, tightly coiled chromatin fibers (～ 50-60nm and ～90-110nm) can be revealed. Our data suggest that the chromatin in the interphase nucleus of chicken erythrocyte represents a high-order conformation and AFM provides useful high-resolution structural information concerning thefolding pattern of interphase chromatin fibers.展开更多
An improved arc discharge method is developed to fabricate carbon nanotube probe of atomic force microscopy （AFM） here. First, silicon probe and carbon nanotube are manipulated under an optical microscope by two hig...An improved arc discharge method is developed to fabricate carbon nanotube probe of atomic force microscopy （AFM） here. First, silicon probe and carbon nanotube are manipulated under an optical microscope by two high precision microtranslators. When silicon probe and carbon nanotube are very close, several tens voltage is applied between them. And carbon nanotube is divided and attached to the end of silicon probe, which mainly due to the arc welding function. Comparing with the arc discharge method before, the new method here needs no coat silicon probe with metal film in advance, which can greatly reduce the fabrication＇s difficulty. The fabricated carbon nanotube probe shows good property of higher aspect ratio and can more accurately reflect the true topography of silicon grating than silicon probe. Under the same image drive force, carbon nanotube probe had less indentation depth on soft triblock copolymer sample than silicon probe. This showed that carbon nanotube probe has lower spring constant and less damage to the scan sample than silicon probe.展开更多
The microstructure of asphalt is investigated by atomic force microscopy （AFM）. In order to analyze the impacts of asphalt types on microstructures, two neat asphalts with different penetration grades （50# and 70#...The microstructure of asphalt is investigated by atomic force microscopy （AFM）. In order to analyze the impacts of asphalt types on microstructures, two neat asphalts with different penetration grades （50# and 70#） and one styrene-butadiene-styrene （SBS） modified asphalt are chosen. The influence of short-term aging is also studied. Based on the knowledge of asphalt＇s microproperties, the relationship between microstructures and healing property is analyzed. The results indicate that the microstructures of three asphalts are quite different and the effects of aging on the surface characteristics for different asphalts are also different. It is proposed that the bee structure is a type of wax crystal and it has a close relationship with the ＂bridge-healing＂ mechanism. The findings may reveal the formation mechanism of microstructure and the healing property for asphalts.展开更多
DNA and histone protein are important in the formation of nucleosomal arrays, which are the first packaging level of DNA into a more compact chromatin structure. To characterize the interactions of DNA and histone pro...DNA and histone protein are important in the formation of nucleosomal arrays, which are the first packaging level of DNA into a more compact chromatin structure. To characterize the interactions of DNA and histone proteins, we reconstitute nucleosomes using lambda DNA and whole histone proteins by dialysis and perform direct atomic force microscopy （AFM） imaging. Compared with non-specific DNA and histone binding, nucleosomes are formed within the assembled “beads-on-a-string” nucleosomal array by dialysis. These observations facilitate the establishment of the molecular mechanisms of nucleosome and demonstrate the capability of AFM for protein-DNA interaction analysis.展开更多
OBJECTIVE： The fatality of cancer is mostly dependent on the possibility of occurrence of metastasis. Thus, if the development of metastasis can be prevented through novel therapeutic strategies targeted against this...OBJECTIVE： The fatality of cancer is mostly dependent on the possibility of occurrence of metastasis. Thus, if the development of metastasis can be prevented through novel therapeutic strategies targeted against this process, then the success of cancer treatment will drastically increase. In this study, therefore, we evaluated the antimetastatic potentials of an extract of Khaya senegalensis and curcumin on the metastatic liver cell line HepG2, and also assessed the anticancer property of the extract. METHODS： Cells were cultured and treated with graded concentrations of test substances for 24, 48, or 72 h with provisions made for negative controls. Treated cells were assessed as follows： nanotechnologically--atomic force microscopy （AFM） was used to determine cell stiffness; biochemically--cell cytotoxicity, glutathione level and adenosine triphosphate status, caspase activation and mitochondrial toxicity were considered; and microbiologically--a carrot disk assay was used to assess the anticancer property of the extract of K. senegalensis. RESULTS： Curcumin and K. senegalensis increased the cell stiffness by 2.6- and 4.0-fold respectively, indicating their antimetastatic effects. Corresponding changes in redox （glutathione level） and energy （adenosine triphosphate） status of the cells were also demonstrated. Further mechanistic studies indicated that curcumin was not mitotoxic in HepG2 cells unlike the K. senegalensis extract. In addition the extract potently inhibited the Agrobacterium tumefaciens-induced genetic transformation based on carrot disk assay. CONCLUSION： Cell elasticity measurement data, using AFM, strongly suggested, for the first time, that both curcumin and the extract of K. senegalensis exhibited antimetastatic properties on HepG2 cells.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
Aggregation process of isotactic poly（methyl methacrylate） （i-PMMA） has been studied extensively for many years, and considerable progress has been made in both experimental and theoretical studies. They are, howe...Aggregation process of isotactic poly（methyl methacrylate） （i-PMMA） has been studied extensively for many years, and considerable progress has been made in both experimental and theoretical studies. They are, however, seldom sustained by real-space observations of the underlying morphology. In this paper, the aggregation process of i-PMMA in concentrated acetone solutions and the fractal structure of the resulting three-dimensional clusters were characterized on the basis of real-space AFM observations of their two-dimensional projection. It was found that spherical multiple-chain particles formed upon collapse and aggregation of the involving chains as a whole during quenching the solution to room temperature. By keeping the solution at room temperature, the initially formed particles stick together upon contact to form larger particles through reassembling very slowly. The succeeding collision of the enlarged spherical particles leads to the formation of small clusters. These newly formed small clusters grow when they meet with other clusters or single Brownian particles. This leads to the formation of large clusters with fractal dimension of 1.95 ± 0.05, which suggest a reaction-limited cluster aggregation of i-PMMA in a concentrated acetone solution. This is in accordance with the conclusion obtained by light scattering measurements.展开更多
In this paper the elastic properties of SiOx film are investigated quantitatively for local fixed point and qualitatively for overall area by atomic force acoustic microscopy （AFAM） in which the sample is vibrated a...In this paper the elastic properties of SiOx film are investigated quantitatively for local fixed point and qualitatively for overall area by atomic force acoustic microscopy （AFAM） in which the sample is vibrated at the ultrasonic frequency while the sample surface is touched and scanned with the tip contacting the sample respectively for fixed point and continuous measurements. The SiOx films on the silicon wafers are prepared by the plasma enhanced chemical vapour deposition （PECVD）, The local contact stiffness of the tip-SiOx film is calculated from the contact resonance spectrum measured with the atomic force acoustic microscopy. Using the reference approach, indentation modulus of SiOx film for fixed point is obtained. The images of cantilever amplitude are also visualized and analysed when the SiOx surface is excited at a fixed frequency. The results show that the acoustic amplitude images can reflect the elastic properties of the sample.展开更多
The probe effect on the apparent image of biological atomic force microscopy was explored in this study, and the potential of AFM in conformational study of gene related biological processes was illustrated by the spe...The probe effect on the apparent image of biological atomic force microscopy was explored in this study, and the potential of AFM in conformational study of gene related biological processes was illustrated by the specific nanostructural information of a new antitumor drug binding to DNA.展开更多
Through the investigation of the sample surface and interface of 3, 4, 9, 10-perylenetetracarboxylic dianhydride （PTCDA）/indium-tin-oxide （ITO） thin films using atomic force microscopy, it has been found that the ...Through the investigation of the sample surface and interface of 3, 4, 9, 10-perylenetetracarboxylic dianhydride （PTCDA）/indium-tin-oxide （ITO） thin films using atomic force microscopy, it has been found that the surface is complanate, the growth is uniform and the defects cover basically the surface of ITO. Furthermore, the number of pinholes is small. The analysis of the sample surface and interface further verifies this result by using x-ray photoemission spectroscopy. At the same time, PTCDA is found to have the ability of restraining the diffusion of chemical constituents from ITO to the hole transport layer, which is beneficial to the improvement of the performance and the useful lifetime of the organic light emitting diodes （OLEDs）.展开更多
Nanomanipulation of DNA molecules or other biomolecules to form artificial patterns or structures at nanometer scale has potential applications in the construction of molecular devices in future industries. It may als...Nanomanipulation of DNA molecules or other biomolecules to form artificial patterns or structures at nanometer scale has potential applications in the construction of molecular devices in future industries. It may also lead to new insights into the interesting properties and behavior of this fantastic nature-selected molecule at the sin- gle-molecular level. Here we present a special method based on the combination of macroscopic “molecular comb- ing” and microscopic “molecular cutting” to manipulate DNA molecules and form complex patterns at nanometer scale on solid surfaces. A possible strategy for ordered DNA sequencing based on this nanomanipulation technique has also been proposed.展开更多
Immiscible polymer blends are an important family of polymer materials.The interfacial thickness between different phases is a very important parameter that dictates,to a great extent,the morphology and properties of ...Immiscible polymer blends are an important family of polymer materials.The interfacial thickness between different phases is a very important parameter that dictates,to a great extent,the morphology and properties of such a blend.This work explores and optimizes an up-to-date atomic force microscopy(AFM)of type NanoIR2^(TM) system in order to quantitatively measure the interfacial thickness of immiscible polymer blends.This system is equipped with two nano-probes capable of detecting the response of a material to an infrared pulse called AFM-infrared spectroscopy mode(AFM-IR)or conducting resonance called AFM-Lorentz Contact Resonance mode(AFM-LCR),respectively.Its potential for quantitatively measuring the interfacial thickness of immiscible polymer blends is evaluated using blends composed of polyamide 6(PA6)and polyolefin elastomer(POE)in the presence or absence of a POE containing maleic anhydride(POE-g-MAH)as a compatibilizer.Surface roughness affects adversely the signal intensity and consequently an accurate measurement of the interfacial thickness.Optimum sample surface preparation procedures are proposed.展开更多
Hippocampal neurons of neonatal rats were cultured in serum-free culture medium for 5 days in vitro, and treated with the Rho-kinase inducer lysophosphatidic acid. Atomic force microscopy revealed that the numbers of ...Hippocampal neurons of neonatal rats were cultured in serum-free culture medium for 5 days in vitro, and treated with the Rho-kinase inducer lysophosphatidic acid. Atomic force microscopy revealed that the numbers of level-1, -2 and -3 neurites protruding from rat hippocampal neurons was significantly reduced. After treatment with the Rho kinase inhibitor Y27632, a significant increase in the numbers of these neurites was observed. Our experimental findings indicate that the Rho-kinase pathway is closely associated with the neurites of hippocampal neurons.展开更多
An efficient method based on atomic force microscopy（AFM） has been developed to characterize silicon intercalated graphene grown on single crystalline Ir（111） thin films. By combining analyses of the phase image, ...An efficient method based on atomic force microscopy（AFM） has been developed to characterize silicon intercalated graphene grown on single crystalline Ir（111） thin films. By combining analyses of the phase image, force curves,and friction–force mapping, acquired by AFM, the locations and coverages of graphene and silicon oxide can be well distinguished. We can also demonstrate that silicon atoms have been successfully intercalated between graphene and the substrate. Our method gives an efficient and simple way to characterize graphene samples with interacted atoms and is very helpful for future applications of graphene-based devices in the modern microelectronic industry, where AFM is already widely used.展开更多
The structure of the nuclosome core particle of chromatin in chicken erythrocytes has been examined by usingAFM. The 146 hp of DNA wrapped twice around the corehistone octamer are clearly visualized. Both the ends ofe...The structure of the nuclosome core particle of chromatin in chicken erythrocytes has been examined by usingAFM. The 146 hp of DNA wrapped twice around the corehistone octamer are clearly visualized. Both the ends ofentry/exit of linker DNA are also demonstrated. The dimension of the nucleosome core particles is- 1-4 um inheight and ～13-22 um in width. In addition, superbeads(width of - 48-57 urn, beight of-2-3 nm) are occasionallyrevealed, two turns of DNA around the core particles arealso detected.展开更多
Bimodal amplitude modulation atomic force microscopy(AM-AFM)is widely used in nanoscale topography and compositional contrast imaging for various materials.In this work,we use computational simulation to compare the d...Bimodal amplitude modulation atomic force microscopy(AM-AFM)is widely used in nanoscale topography and compositional contrast imaging for various materials.In this work,we use computational simulation to compare the dynamic behaviors of AFM cantilevers in three commonly used excitation schemes in bimodal AM-AFM,i.e.,the cantilever base excitation,the cantilever end excitation,and the uniform excitation along the length of the cantilever,in both air and liquid environments.The amplitude and phase spectroscopy curves and the frequency responses acquired from the three excitation schemes are compared and discussed.The results would be useful in guiding the selection of excitation methods and the optimization of imaging conditions.展开更多
基金supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1403300 and 2019YFA0308404)the National Natural Science Foundation of China(Grant Nos.11427902,11991060,12074075,12474165,12274084,and 12241402)+5 种基金Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01)Shanghai Municipal Natural Science Foundation(Grant No.22ZR1407400)Innovation Program for Quantum Science and Technology(Grant No.2024ZD0300104)Innovation Program of Shanghai Municipal Education Commission(Grant No.2023ZKZD03)Science and Technology Commission of Shanghai Municipality(Grant No.20JC1415900)China Postdoctoral Science Foundation(Grant No.KLH1512149).
文摘Recently,charged solitons have been found in a two-dimensional CoCl_(2)/HOPG system,whose microscopic nature remains to be elusive.In this work,we investigate the charged solitons in monolayer CoCl_(2) using scanning tunneling microscopy(STM)and atomic force microscopy(AFM).Moreover,we study the electrical properties of the charged solitons at zero electric field by measuring local contact potential difference(LCPD)via Kelvin probe force microscopy(KPFM)using the Δf(V)method.The compensation voltage corresponding to the vertex of the parabola is obtained by fitting the quadratic relationship between Δf and sample bias.The results show that,without an external electric field,the solitons behave as negatively charged entities.Meanwhile,the LCPD mapping characterizes the spatial distribution of the potential at the charged solitons,which agrees well with those obtained from STM band bending measurements.
基金supported by the National Natural Science Foundation of China under Grant No.21933006.
文摘To eliminate distortion caused by vertical drift and illusory slopes in atomic force microscopy(AFM)imaging,a lifting-wavelet-based iterative thresholding correction method is proposed in this paper.This method achieves high-quality AFM imaging via line-by-line corrections for each distorted profile along the fast axis.The key to this line-by-line correction is to accurately simulate the profile distortion of each scanning row.Therefore,a data preprocessing approach is first developed to roughly filter out most of the height data that impairs the accuracy of distortion modeling.This process is implemented through an internal double-screening mechanism.A line-fitting method is adopted to preliminarily screen out the obvious specimens.Lifting wavelet analysis is then carried out to identify the base parts that are mistakenly filtered out as specimens so as to preserve most of the base profiles and provide a good basis for further distortion modeling.Next,an iterative thresholding algorithm is developed to precisely simulate the profile distortion.By utilizing the roughly screened base profile,the optimal threshold,which is used to screen out the pure bases suitable for distortion modeling,is determined through iteration with a specified error rule.On this basis,the profile distortion is accurately modeled through line fitting on the finely screened base data,and the correction is implemented by subtracting the modeling result from the distorted profile.Finally,the effectiveness of the proposed method is verified through experiments and applications.
文摘The single-point bending method,based on atomic force microscopy(AFM),has been extensively validated for characterizing the structural mechanical properties of micro-and nanobeams.Nevertheless,the influence of AFM probe loading and positioning has yet to be subjected to comprehensive investigation.This paper proposes a novel bending-test method based on sequential loading points,in which a series of evenly distributed loads are applied along the length of the central axis on the upper surface of the cantilever.The preliminary measured values of Young’s modulus for an unknown alloy material were 193,178,and 176 GPa,exhibiting a considerable degree of dispersion.An algorithm for self-correction of the positioning error was developed,and this resulted in a positioning error of 53 nm and a final converged Young’s modulus of 161 GPa.
基金supported by the Program of National Key Technology R&D Program of the Ministry of Science and Technology of China(2011BAK15B04)
文摘Atomic force microscopy（AFM） is a commonly used technique for graphene thickness measurement.However, due to surface roughness caused by graphene itself and variation introduced in AFM measurement, graphene thickness is difficult to be accurately determined by AFM. In this paper, a histogram method was used for reliable measurements of graphene thickness using AFM. The influences of various measurement parameters in AFM analysis were investigated. The experimental results indicate that significant deviation can be introduced using various order of flatten and improperly selected measurement parameters including amplitude setpoint and drive amplitude. At amplitude setpoint of 100 mV and drive amplitude of 100 m V, thickness of 1 layer（1L）, 2 layers（2L） and 4 layers（4L） graphene were measured.The height differences for 1L, 2L and 4L were 1.51 ± 0.16 nm, 1.92 ± 0.13 nm and 2.73 ± 0.10 nm, respectively. By comparing these values, thickness of single layer graphene can be accurately determined to be0.41 ± 0.09 nm.
文摘The organization of the higher order structure of chromatin in chicken erythrocytes has been examined withtapping-mode scanning force microscopy under conditionsclose to their native environment. Reproducible highresolution AFM images of chromatin compaction at several levels can be demonstrated. An extended beads-on-astring (width of ～ 15-20nm, height of ～ 2-3nm for eachindividual nucleosome) can be consistently observed. Furthermore, superbeads (width of ～ 40nm, height of ～ 7nm)are demonstrated. Visualization of the solenoid conformation at the level of 30nm chromatin fiber is attained eitherby using AFM or by using electron microscopy. In addition, tightly coiled chromatin fibers (～ 50-60nm and ～90-110nm) can be revealed. Our data suggest that the chromatin in the interphase nucleus of chicken erythrocyte represents a high-order conformation and AFM provides useful high-resolution structural information concerning thefolding pattern of interphase chromatin fibers.
基金This project is supported by National Natural Science Foundation of China (No.50205006).
文摘An improved arc discharge method is developed to fabricate carbon nanotube probe of atomic force microscopy （AFM） here. First, silicon probe and carbon nanotube are manipulated under an optical microscope by two high precision microtranslators. When silicon probe and carbon nanotube are very close, several tens voltage is applied between them. And carbon nanotube is divided and attached to the end of silicon probe, which mainly due to the arc welding function. Comparing with the arc discharge method before, the new method here needs no coat silicon probe with metal film in advance, which can greatly reduce the fabrication＇s difficulty. The fabricated carbon nanotube probe shows good property of higher aspect ratio and can more accurately reflect the true topography of silicon grating than silicon probe. Under the same image drive force, carbon nanotube probe had less indentation depth on soft triblock copolymer sample than silicon probe. This showed that carbon nanotube probe has lower spring constant and less damage to the scan sample than silicon probe.
基金The Ph.D.Programs Foundation of Ministry of Education of China(No.20120092110053)
文摘The microstructure of asphalt is investigated by atomic force microscopy （AFM）. In order to analyze the impacts of asphalt types on microstructures, two neat asphalts with different penetration grades （50# and 70#） and one styrene-butadiene-styrene （SBS） modified asphalt are chosen. The influence of short-term aging is also studied. Based on the knowledge of asphalt＇s microproperties, the relationship between microstructures and healing property is analyzed. The results indicate that the microstructures of three asphalts are quite different and the effects of aging on the surface characteristics for different asphalts are also different. It is proposed that the bee structure is a type of wax crystal and it has a close relationship with the ＂bridge-healing＂ mechanism. The findings may reveal the formation mechanism of microstructure and the healing property for asphalts.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.11274374）, the National Basic Research Program of China （No.2009CB930704）, and the Basic Scientific Research Foundation of China Agricultural University （No.2012QJ026）.
文摘DNA and histone protein are important in the formation of nucleosomal arrays, which are the first packaging level of DNA into a more compact chromatin structure. To characterize the interactions of DNA and histone proteins, we reconstitute nucleosomes using lambda DNA and whole histone proteins by dialysis and perform direct atomic force microscopy （AFM） imaging. Compared with non-specific DNA and histone binding, nucleosomes are formed within the assembled “beads-on-a-string” nucleosomal array by dialysis. These observations facilitate the establishment of the molecular mechanisms of nucleosome and demonstrate the capability of AFM for protein-DNA interaction analysis.
文摘OBJECTIVE： The fatality of cancer is mostly dependent on the possibility of occurrence of metastasis. Thus, if the development of metastasis can be prevented through novel therapeutic strategies targeted against this process, then the success of cancer treatment will drastically increase. In this study, therefore, we evaluated the antimetastatic potentials of an extract of Khaya senegalensis and curcumin on the metastatic liver cell line HepG2, and also assessed the anticancer property of the extract. METHODS： Cells were cultured and treated with graded concentrations of test substances for 24, 48, or 72 h with provisions made for negative controls. Treated cells were assessed as follows： nanotechnologically--atomic force microscopy （AFM） was used to determine cell stiffness; biochemically--cell cytotoxicity, glutathione level and adenosine triphosphate status, caspase activation and mitochondrial toxicity were considered; and microbiologically--a carrot disk assay was used to assess the anticancer property of the extract of K. senegalensis. RESULTS： Curcumin and K. senegalensis increased the cell stiffness by 2.6- and 4.0-fold respectively, indicating their antimetastatic effects. Corresponding changes in redox （glutathione level） and energy （adenosine triphosphate） status of the cells were also demonstrated. Further mechanistic studies indicated that curcumin was not mitotoxic in HepG2 cells unlike the K. senegalensis extract. In addition the extract potently inhibited the Agrobacterium tumefaciens-induced genetic transformation based on carrot disk assay. CONCLUSION： Cell elasticity measurement data, using AFM, strongly suggested, for the first time, that both curcumin and the extract of K. senegalensis exhibited antimetastatic properties on HepG2 cells.
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.
基金This work was supported by the National Natural Science Foundations of China.
文摘Aggregation process of isotactic poly（methyl methacrylate） （i-PMMA） has been studied extensively for many years, and considerable progress has been made in both experimental and theoretical studies. They are, however, seldom sustained by real-space observations of the underlying morphology. In this paper, the aggregation process of i-PMMA in concentrated acetone solutions and the fractal structure of the resulting three-dimensional clusters were characterized on the basis of real-space AFM observations of their two-dimensional projection. It was found that spherical multiple-chain particles formed upon collapse and aggregation of the involving chains as a whole during quenching the solution to room temperature. By keeping the solution at room temperature, the initially formed particles stick together upon contact to form larger particles through reassembling very slowly. The succeeding collision of the enlarged spherical particles leads to the formation of small clusters. These newly formed small clusters grow when they meet with other clusters or single Brownian particles. This leads to the formation of large clusters with fractal dimension of 1.95 ± 0.05, which suggest a reaction-limited cluster aggregation of i-PMMA in a concentrated acetone solution. This is in accordance with the conclusion obtained by light scattering measurements.
基金Project supported by the National Natural Science Foundation of China(Grant No.50775005)
文摘In this paper the elastic properties of SiOx film are investigated quantitatively for local fixed point and qualitatively for overall area by atomic force acoustic microscopy （AFAM） in which the sample is vibrated at the ultrasonic frequency while the sample surface is touched and scanned with the tip contacting the sample respectively for fixed point and continuous measurements. The SiOx films on the silicon wafers are prepared by the plasma enhanced chemical vapour deposition （PECVD）, The local contact stiffness of the tip-SiOx film is calculated from the contact resonance spectrum measured with the atomic force acoustic microscopy. Using the reference approach, indentation modulus of SiOx film for fixed point is obtained. The images of cantilever amplitude are also visualized and analysed when the SiOx surface is excited at a fixed frequency. The results show that the acoustic amplitude images can reflect the elastic properties of the sample.
基金The support from Visiting Scholar Foundation of Key Lab in University and Chinese Education Foundation for Excellent Young Teachers as well as the support from Jiangsu province (BJ 99011 and BK 2001401) is greatly appreciated.
文摘The probe effect on the apparent image of biological atomic force microscopy was explored in this study, and the potential of AFM in conformational study of gene related biological processes was illustrated by the specific nanostructural information of a new antitumor drug binding to DNA.
基金Project supported by the National Natural Science Foundation of China （Grant No 60276026） and the Natural Science Foundation of Gansu Province, China （Grant No ZS031-A25-012-G）.
文摘Through the investigation of the sample surface and interface of 3, 4, 9, 10-perylenetetracarboxylic dianhydride （PTCDA）/indium-tin-oxide （ITO） thin films using atomic force microscopy, it has been found that the surface is complanate, the growth is uniform and the defects cover basically the surface of ITO. Furthermore, the number of pinholes is small. The analysis of the sample surface and interface further verifies this result by using x-ray photoemission spectroscopy. At the same time, PTCDA is found to have the ability of restraining the diffusion of chemical constituents from ITO to the hole transport layer, which is beneficial to the improvement of the performance and the useful lifetime of the organic light emitting diodes （OLEDs）.
基金Supported by National Natural Science Foundation of China (NSFC) under grant No.10335070. Financial support from the Chinese Academy of Sciences and Shanghai Scientific and Technological Committee is also appreciated.
文摘Nanomanipulation of DNA molecules or other biomolecules to form artificial patterns or structures at nanometer scale has potential applications in the construction of molecular devices in future industries. It may also lead to new insights into the interesting properties and behavior of this fantastic nature-selected molecule at the sin- gle-molecular level. Here we present a special method based on the combination of macroscopic “molecular comb- ing” and microscopic “molecular cutting” to manipulate DNA molecules and form complex patterns at nanometer scale on solid surfaces. A possible strategy for ordered DNA sequencing based on this nanomanipulation technique has also been proposed.
基金The authors thank the National Natural Science Foundation of China(No.51973193)the State Key Laboratory of Chemical Engineering(No.SKL-ChE-13D)for their financial support.
文摘Immiscible polymer blends are an important family of polymer materials.The interfacial thickness between different phases is a very important parameter that dictates,to a great extent,the morphology and properties of such a blend.This work explores and optimizes an up-to-date atomic force microscopy(AFM)of type NanoIR2^(TM) system in order to quantitatively measure the interfacial thickness of immiscible polymer blends.This system is equipped with two nano-probes capable of detecting the response of a material to an infrared pulse called AFM-infrared spectroscopy mode(AFM-IR)or conducting resonance called AFM-Lorentz Contact Resonance mode(AFM-LCR),respectively.Its potential for quantitatively measuring the interfacial thickness of immiscible polymer blends is evaluated using blends composed of polyamide 6(PA6)and polyolefin elastomer(POE)in the presence or absence of a POE containing maleic anhydride(POE-g-MAH)as a compatibilizer.Surface roughness affects adversely the signal intensity and consequently an accurate measurement of the interfacial thickness.Optimum sample surface preparation procedures are proposed.
文摘Hippocampal neurons of neonatal rats were cultured in serum-free culture medium for 5 days in vitro, and treated with the Rho-kinase inducer lysophosphatidic acid. Atomic force microscopy revealed that the numbers of level-1, -2 and -3 neurites protruding from rat hippocampal neurons was significantly reduced. After treatment with the Rho kinase inhibitor Y27632, a significant increase in the numbers of these neurites was observed. Our experimental findings indicate that the Rho-kinase pathway is closely associated with the neurites of hippocampal neurons.
基金supported by the National Basic Research Program of China(Grant Nos.2013CBA01600 and 2011CB932700)the National Natural Science Foundation of China(Grant Nos.61222112,61390501 and 51325204)Chinese Academy of Sciences(Grant Nos.1731300500015 and XDB07030100)
文摘An efficient method based on atomic force microscopy（AFM） has been developed to characterize silicon intercalated graphene grown on single crystalline Ir（111） thin films. By combining analyses of the phase image, force curves,and friction–force mapping, acquired by AFM, the locations and coverages of graphene and silicon oxide can be well distinguished. We can also demonstrate that silicon atoms have been successfully intercalated between graphene and the substrate. Our method gives an efficient and simple way to characterize graphene samples with interacted atoms and is very helpful for future applications of graphene-based devices in the modern microelectronic industry, where AFM is already widely used.
文摘The structure of the nuclosome core particle of chromatin in chicken erythrocytes has been examined by usingAFM. The 146 hp of DNA wrapped twice around the corehistone octamer are clearly visualized. Both the ends ofentry/exit of linker DNA are also demonstrated. The dimension of the nucleosome core particles is- 1-4 um inheight and ～13-22 um in width. In addition, superbeads(width of - 48-57 urn, beight of-2-3 nm) are occasionallyrevealed, two turns of DNA around the core particles arealso detected.
基金the financial support from the National Natural Science Foundation of China(NSFC)under Grant No.11502182supported by“the Fundamental Research Funds for the Central Universities(WUT:2020IB015)”.
文摘Bimodal amplitude modulation atomic force microscopy(AM-AFM)is widely used in nanoscale topography and compositional contrast imaging for various materials.In this work,we use computational simulation to compare the dynamic behaviors of AFM cantilevers in three commonly used excitation schemes in bimodal AM-AFM,i.e.,the cantilever base excitation,the cantilever end excitation,and the uniform excitation along the length of the cantilever,in both air and liquid environments.The amplitude and phase spectroscopy curves and the frequency responses acquired from the three excitation schemes are compared and discussed.The results would be useful in guiding the selection of excitation methods and the optimization of imaging conditions.
