共查询到20条相似文献,搜索用时 15 毫秒
1.
《Surface science》1994,311(3):L731-L736
Single-shell carbon nanotubes, approximately 1 nm in diameter, have been imaged for the first time by atomic force microscopy operating in both the contact and tapping modes. For the contact mode, the height of the imaged nanotubes has been calibrated using the atomic steps of the silicon substrate on which the nanotubes were deposited. For the tapping mode, the calibration was performed using an industry-standard grating. The paper discusses substrate and sample preparation methods for the characterization by scanning probe microscopy of nanotubes deposited on a substrate. 相似文献
2.
We report the first results from novel sub-Angstrom oscillation amplitude non-contact atomic force microscopy developed for lateral force gradient measurements. Quantitative lateral force gradients between a tungsten tip and Si(1 1 1)-(7 × 7) surface can be measured using this microscope. Simultaneous lateral force gradient and scanning tunnelling microscope images of single and multi atomic steps are obtained. In our measurement, tunnel current is used as feedback. The lateral stiffness contrast has been observed to be 2.5 N/m at single atomic step, in contrast to 13 N/m at multi atomic step on Si(1 1 1) surface. We also carried out a series of lateral stiffness-distance spectroscopy. We observed lateral stiffness-distance curves exhibit sharp increase in the stiffness as the sample is approached towards the surface. We usually observed positive stiffness and sometimes going into slightly negative region. 相似文献
3.
Kuznetsov YG Chang SC Credaroli A Martiny J McPherson A 《Micron (Oxford, England : 1993)》2012,43(12):1336-1342
Marine viruses have only relatively recently come to the attention of molecular biologists, and the extraordinary diversity of potential host organisms suggests a new wealth of genetic and structural forms. A promising technology for characterizing and describing the viruses structurally is atomic force microscopy (AFM). We provide examples here of some of the different architectures and novel structural features that emerge from even a very limited investigation, one focused on cyanophages, viruses that infect cyanobacteria (blue-green algae). These were isolated by phage selection of viruses collected from California coastal waters. We present AFM images of tailed, spherical, filamentous, rod shaped viruses, and others of eccentric form. Among the tailed phages numerous myoviruses were observed, some having long tail fibers, some other none, and some having no visible baseplate. Syphoviruses and a podovirus were also seen. We also describe a unique structural features found on some tailed marine phages that appear to have no terrestrial homolog. These are long, 450 nm, complex helical tail fibers terminating in a unique pattern of 3+1 globular units made up of about 20 small proteins. 相似文献
4.
J.J. Kolodziej B. Such M. Goryl F. Krok P. Piatkowski M. Szymonski 《Applied Surface Science》2006,252(21):7614-7623
Surfaces of several AIIIBV compound semiconductors (InSb, GaAs, InP, InAs) of the (0 0 1) orientation have been studied with noncontact atomic force microscopy (NC-AFM). Obtained atomically resolved patterns have been compared with structural models available in the literature. It is shown that NC-AFM is an efficient tool for imaging complex surface structures in real space. It is also demonstrated that the recent structural models of III-V compound surfaces provide a sound base for interpretation of majority of features present in recorded patterns. However, there are also many new findings revealed by the NC-AFM method that is still new experimental technique in the context of surface structure determination. 相似文献
5.
We report an experimental study of static charge distribution in individual single-walled carbon nanotubes grown on a Si+115 nm SiO2 substrate. From these experiments, we conclude that charges are distributed uniformly along the nanotubes. We demonstrate that electrostatic force microscopy can accurately measure the amount of charges per unit length. We found that this amount is diameter dependent and in the range of 1 electron per nanometer for a 2.5 nm nanotube at a potential of -3.5 V. 相似文献
6.
We combine imaging ToF-SIMS depth profiling and wide area atomic force microscopy to analyze a test structure consisting of a 300 nm trehalose film deposited on a Si substrate and pre-structured by means of a focused 15-keV Ga+ ion beam. Depth profiling is performed using a 40-keV C60+ cluster ion beam for erosion and mass spectral data acquisition. A generic protocol for depth axis calibration is described which takes into account both lateral and in-depth variations of the erosion rate. By extrapolation towards zero analyzed lateral area, an “intrinsic” depth resolution of about 8 nm is found which appears to be characteristic of the cluster-surface interaction process. 相似文献
7.
Daban JR 《Micron (Oxford, England : 1993)》2011,42(8):733-750
The folding of the chromatin filament and, in particular, the organization of genomic DNA within metaphase chromosomes has attracted the interest of many laboratories during the last five decades. This review discusses our current understanding of chromatin higher-order structure based on results obtained with transmission electron microscopy (TEM), cryo-electron microscopy (cryo-EM), and different atomic force microscopy (AFM) techniques.Chromatin isolated from different cell types in buffers without cations form extended filaments with nucleosomes visible as separated units. In presence of low concentrations of Mg2+, chromatin filaments are folded into fibers having a diameter of ∼30 nm. Highly compact fibers were obtained with isolated chromatin fragments in solutions containing 1–2 mM Mg2+. The high density of these fibers suggested that the successive turns of the chromatin filament are interdigitated. Similar results were obtained with reconstituted nucleosome arrays under the same ionic conditions. This led to the proposal of compact interdigitated solenoid models having a helical pitch of 4–5 nm. These findings, together with the observation of columns of stacked nucleosomes in different liquid crystal phases formed by aggregation of nucleosome core particles at high concentration, and different experimental evidences obtained using other approaches, indicate that face-to-face interactions between nucleosomes are very important for the formation of dense chromatin structures.Chromatin fibers were observed in metaphase chromosome preparations in deionized water and in buffers containing EDTA, but chromosomes in presence of the Mg2+ concentrations found in metaphase (5–22 mM) are very compact, without visible fibers. Moreover, a recent cryo-electron microscopy analysis of vitreous sections of mitotic cells indicated that chromatin has a disordered organization, which does not support the existence of 30-nm fibers in condensed chromosomes. TEM images of partially denatured chromosomes obtained using different procedures that maintain the ionic conditions of metaphase showed that bulk chromatin in chromosomes is organized forming multilayered plate-like structures. The structure and mechanical properties of these plates were studied using cryo-EM, electron tomography, AFM imaging in aqueous media, and AFM-based nanotribology and force spectroscopy. The results obtained indicated that the chromatin filament forms a flexible two-dimensional network, in which DNA is the main component responsible for the mechanical strength observed in friction force measurements. The discovery of this unexpected structure based on a planar geometry has opened completely new possibilities for the understanding of chromatin folding in metaphase chromosomes. It was proposed that chromatids are formed by many stacked thin chromatin plates oriented perpendicular to the chromatid axis. Different experimental evidences indicated that nucleosomes in the plates are irregularly oriented, and that the successive layers are interdigitated (the apparent layer thickness is 5–6 nm), allowing face-to-face interactions between nucleosomes of adjacent layers. The high density of this structure is in agreement with the high concentration of DNA observed in metaphase chromosomes of different species, and the irregular orientation of nucleosomes within the plates make these results compatible with those obtained with mitotic cell cryo-sections. The multilaminar chromatin structure proposed for chromosomes allows an easy explanation of chromosome banding and of the band splitting observed in stretched chromosomes. 相似文献
8.
Structural defects greatly affect the electronic properties of single wall carbon nanotubes (CNT’s), for instance by increasing
the sensitivity to their environment; an effect which can be utilized for better performance of CNT based chemical sensors.
Here we show that electrostatic force microscopy (EFM) can be used as a non-invasive technique for probing defects in individual
CNT’s supported on insulating substrates. The technique is demonstrated by monitoring the change in EFM signal upon intentionally
inducing defect by an oxygen plasma etch, and is applied to assess the quality of as-grown CNT samples and to study the effect
of exposing CNT’s to the low energy electron irradiation of a scanning electron microscope (SEM).
PACS 68.37.-d; 68.37.Ps; 61.46.Fg; 68.35.Dv 相似文献
9.
Volodin A Ahlskog M Seynaeve E Van Haesendonck C Fonseca A Nagy JB 《Physical review letters》2000,84(15):3342-3345
Coiled carbon nanotubes were produced catalytically by thermal decomposition of hydrocarbon gas. After deposition on a silicon substrate, the three-dimensional structure of the helix-shaped multiwalled nanotubes can be visualized with atomic force microscopy. Helical structures of both chiralities are present in the nanotube deposits. For larger coil diameters ( >170 nm), force modulation microscopy allows one to probe the local elasticity along the length of the coil. Our results agree with the classical theory of elasticity. Similar to the case of straight nanotubes, the Young modulus of coiled multiwalled nanotubes remains comparable to the very high Young modulus of hexagonal graphene sheets. 相似文献
10.
The intrinsic and phosphorous (P)-doped hydrogenated amorphous silicon thin films were crystallized by laser annealing. The structural properties during crystallization process can be investigated. Observed redshifts of the Si Raman transverse optical phonon peak indicate tensile stress present in the films and become intense with the effect of doping, which can be relieved in P-doped films by introducing buffer layer structures. Based on experimental results, the established correlation between the stress and crystalline fraction (XC) suggests that the relatively high stress can limit the increase in XC and the highest crystalline fraction is obtained by a considerable stress release. At high laser energy density of 1250 mJ/cm2, the poorer crystalline quality and disordered structure of the film originating from the irradiation damage and defects lead to the low electron mobility. 相似文献
11.
《Current Applied Physics》2010,10(2):583-591
This paper is devoted to the characterization of the surface defects using a recently developed AFM technique called frequency and force modulation AFM (FFM–AFM). The simulated system includes a recently developed gold coated AFM probe which interacts with a sample including single-atom vacancy and impurities. In order to examine the behavior of the above system on different transition metals, the molecular dynamics (MD) simulation with Sutton–Chen (SC) inter-atomic potential is used. In this study, an online imaging simulation of the probe and sample is performed, and the effects of the horizontal scan speed, the effective frequency set-point, the cantilever stiffness, the tip-sample rest position and the cantilever quality factor on the resulting images are investigated. Using a proposed optimum controlling scheme for the excitation force amplitude, the cantilever horizontal speed can be increased. 相似文献
12.
We describe results of atomistic molecular dynamics simulations modelling an atomic force microscope (AFM) tip immersed in a fluid. Both the tip and the surface are modelled by rigid arrays of atoms. The tip is pyramidal and the surface is the (100) face of a fcc crystal. The focus is on the solvation forces acting on the tip and on the surface and their relation to the structural and dynamic properties of the fluid. Fluid particles in the neighborhood of the tip-surface junction are found to be highly ordered compared to the bulk, as shown by localized variations in the average fluid density. The atomistic nature of the model gives rise to several effects related to the discrete sizes of the fluid, tip, and surface particles which are not observed in continuum-based theories. A number of simulated force-distance curves are presented, along with an analysis of the effect of changing fluid particle size, tip (lateral) position, tip shape, and the lyocompatability of the tip and surface materials. The atomic-scale distribution of fluid-surface forces is examined for various positions of the tip, and the extent to which the fluid can act as a “cushion” by increasing the effective area of the tip-surface interaction is studied. The effect of a fluid on AFM imaging is investigated by generating “fluid images”, which are shown to be comparable in magnitude to the direct tip-surface interaction in the noncontact mode. We compare images generated by defective and defect-free surfaces, and analyse the fluid-tip forces acting in a lateral direction. An image formed from fluid forces acting in the direction of the surface normal does not show the presence of a vacancy, but an image formed from lateral fluid forces does. 相似文献
13.
《Surface science》1992,274(2):L524-L528
Atomic force microscopy (AFM) has been used to image fluorine-graphite intercalation compounds (C3.5F; stage 1 + 2, C3.9F; stage 2, (CF)n; stage 1). For all samples the atomic resolution is achieved. The AFM image of the C3.5F compound exhibits a new orthorhombic superlattice structure (a = 0.49 nm, b = 0.42 n, ∠a−b = 90°). In the AFM images of C3.5F and (CF)n the protrusions are attributed to fluorine atoms. The AFM image of C3.9F exhibits a centered hexagonal structure similar to highly oriented pyrolytic graphite (HOPG). 相似文献
14.
《Current Applied Physics》2007,7(5):528-531
A hydrophobic polymer tip for atomic force microscopy has been fabricated by two-photon adsorbed photopolymerization techniques and has been applied for the high resolution imaging of a hydrophilic metal surface. Using optimized photopolymerization conditions, we have succeeded in fabricating sub-100-nm sized polymer tips. This fabricating resolution of two-photon adsorbed photopolymerization is also confirmed by other supporting experiments. The imaging results show that the capillary-force-induced image distortion can be successfully removed by applying a pure hydrophobic polymer tip with a lateral resolution better than 5 nm, which is difficult to achieve with a commercial tip without any environmental control. 相似文献
15.
G.Y. Jing H. Ji W.Y. Yang J. Xu D.P. Yu 《Applied Physics A: Materials Science & Processing》2006,82(3):475-478
Analysis of the bending modulus of individual silicon nitride nanobelts in elastic regime is reported here. The nanobelts
have the size between 200∼800 nm in width, and thickness 20∼50 nm. Atomic force microscopy was used to image and to perform
measurements of force versus bending displacement on individual nanobelts suspending over strips. The bending modulus Eb is deduced by comparison of the measured force curves on the substrate and on the suspending nanobelts. It is shown that
the elastic modulus of the silicon nitride nanobelts is about 570 GPa, which is much larger than that of bulk and film of
the silicon nitride material. The larger elastic modulus is ascribed to the fact there are less structural defects in the
silicon nitride nanobelts.
PACS 81.70.Bt; 81.40.Lm; 61.80.+g 相似文献
16.
Atomic force microscopy is modeled in the time-frequency phase space. In this phase space it is equivalent to a succession of temporal lenses and free spaces which includes a temporal fractional Fourier device. Then, the Wigner transform and its second order moments are introduced to model the atomic force microscopy as a detector of ultrafast electrical signals. 相似文献
17.
18.
Theory of multifrequency atomic force microscopy 总被引:1,自引:0,他引:1
We develop a theory that explains the origin of the high force sensitivity observed in multifrequency force microscopy experiments. The ability of the microscope to extract complementary information on the surface properties is increased by the simultaneous excitation of several flexural cantilever modes. The force sensitivity in multifrequency operation is about 0.2 pN. The analytical model identifies the virial and the energy dissipated by the tip-surface forces as the parameters responsible for the material contrast. The agreement obtained among the theory, experiments and numerical simulations validates the model. 相似文献
19.
Accurate size measurement during nanoparticle production is essential for the continuing innovation, quality and safety of
nano-enabled products. Size measurement by analysing a number of separate particles individually has particular advantages
over ensemble methods. In the latter case nanoparticles have to be well dispersed in a fluid and changes that may occur during
analysis, such as agglomeration and degradation, will not be detected which could lead to misleading results. Atomic force
microscopy (AFM) allows imaging of particles both in air and liquid, however, the strong interactions between the probe and
the particle will cause the broadening of the lateral dimension in the final image. In this paper a new procedure to measure
the size of spherical nanoparticles from AFM images via vertical height measurement is described. This procedure will quickly
analyse hundred of particles simultaneously and reproduce the measurements obtained from electron microscopy (EM). Nanoparticles
samples that were difficult, if not impossible, to analyse with EM were successfully measured using this method. The combination
of this procedure with the use of a metrological AFM moves closer to true traceable measurements of nanoparticle dispersions. 相似文献
20.
Non-contact atomic force microscope is a powerful tool to investigate the surface topography with atomic resolution. Here we propose a new approach to estimate the interaction between its tips and samples, which combines a semi-empirical model with density functional theory (DFT) calculations. The generated frequency shift images are consistent with the experiment for mapping organic molecules using CuCO, Cu, CuCl, and CuOx tips. This approach achieves accuracy close to DFT calculation with much lower computational cost. 相似文献