Chaos in dynamic atomic force microscopy

In tapping mode atomic force microscopy (AFM) the highly nonlinear tip-sample interaction gives rise to a complicated dynamics of the microcantilever. Apart from the well-known bistability under typical imaging conditions the system exhibits a complex dynamics at small average tip-sample distances, which are typical operation conditions for mechanical dynamic nanomanipulation. In order to investigate the dynamics at small average tip sample gaps experimental time series data are analysed employing nonlinear analysis tools and spectral analysis. The correlation dimension is computed together with a bifurcation diagram. By using statistical correlation measures such as the Kullback-Leibler distance, cross-correlation and mutual information the dataset can be segmented into different regimes. The analysis reveals period-3, period-2 and period-4 behaviour, as well as a weakly chaotic regime.     

Application of dynamic impedance spectroscopy to atomic force microscopy

Abstract

Atomic force microscopy (AFM) is a universal imaging technique, while impedance spectroscopy is a fundamental method of determining the electrical properties of materials. It is useful to combine those techniques to obtain the spatial distribution of an impedance vector. This paper proposes a new combining approach utilizing multifrequency scanning and simultaneous AFM scanning of an investigated surface.     

High-resolution and large dynamic range nanomechanical mapping in tapping-mode atomic force microscopy

High spatial resolution imaging of material properties is an important task for the continued development of nanomaterials and studies of biological systems. Time-varying interaction forces between the vibrating tip and the sample in a tapping-mode atomic force microscope contain detailed information about the elastic, adhesive, and dissipative response of the sample. We report real-time measurement and analysis of the time-varying tip-sample interaction forces with recently introduced torsional harmonic cantilevers. With these measurements, high-resolution maps of elastic modulus, adhesion force, energy dissipation, and topography are generated simultaneously in a single scan. With peak tapping forces as low as 0.6?nN, we demonstrate measurements on blended polymers and self-assembled molecular architectures with feature sizes at 1, 10, and 500?nm. We also observed an elastic modulus measurement range of four orders of magnitude (1?MPa to 10?GPa) for a single cantilever under identical feedback conditions, which can be particularly useful for analyzing heterogeneous samples with largely different material components.     

Nanofabrication with atomic force microscopy

Atomic force microscopy (AFM) was developed in 1986. It is an important and versatile surface technique, and is used in many research fields. In this review, we have summarized the methods and applications of AFM, with emphasis on nanofabrication. AFM is capable of visualizing surface properties at high spatial resolution and determining biomolecular interaction as well as fabricating nanostructures. Recently, AFM-based nanotechnologies such as nanomanipulation, force lithography, nanografting, nanooxidation and dip-pen nanolithography were developed rapidly. AFM tip (typical radius ranged from several nanometers to tens of nanometers) is used to modify the sample surface, either physically or chemically, at nanometer scale. Nanopatterns composed of semiconductors, metal, biomolecules, polymers, etc., were constructed with various AFM-based nanotechnologies, thus making AFM a promising technique for nanofabrication. AFM-based nanotechnologies have potential applications in nanoelectronics, bioanalysis, biosensors, actuators and high-density data storage devices.     

Effects of nonlinear forces on dynamic mode atomic force microscopy and spectroscopy

In this paper, we describe the effects of nonlinear tip-sample forces on dynamic mode atomic force microscopy and spectroscopy. The jumps and hysteresis observed in the vibration amplitude (A) versus tip-sample distance (h) curves have been traced to bistability in the resonance curve. A numerical analysis of the basic dynamic equation was used to explain the hysteresis in the experimental curve. It has been found that the location of the hysteresis in the A-h curve depends on the frequency of the forced oscillation relative to the natural frequency of the cantilever.     

Wavelet-transform processing of images in atomic force microscopy

Use of the wavelet transform is suggested for the processing of images obtained with a scanning atomic force microscope (AFM). Efficacy of the proposed method is illustrated by the results of numerical modeling of the AFM images. The wavelet transform can be also employed for the processing of images in optical near-field, electron tunneling, and magnetic force microscopies.     

Mechanical properties of Nb based multiphase alloy studied by nanoindentation and atomic force microscopy

Abstract

The mechanical properties and deformation behaviours of as cast and heat treated Nb–21Ti–4C–xAl (x: 0, 5, 10 and 15 at-%) alloys are comprehensively investigated using nanoindentation and atomic force microscopy. For the Nb–21Ti–4C alloy, nanoindentation tests are performed for the Nb solid solution (Nbss) matrix, carbide and the interface between them. The results show that the hard carbide, which has a strong bonding with the Nbss matrix, can enhance the alloy before and after heat treatment, and the eutectoid transformation of the large sized carbide after heat treatment leads to less possibility for the forming of cracks on the carbide surface, which in turn improves the toughness. For the Nb–21Ti–4C–(0, 5, 10, 15)Al alloys, the hardness of the Nbss matrix increases significantly with increasing Al fraction for both as cast and heat treated alloys. However, deviations of the elastic modulus are inconspicuous with the Al fraction for the as cast and heat treated alloys.     

High-speed atomic force microscopy coming of age

High-speed atomic force microscopy (HS-AFM) is now materialized. It allows direct visualization of dynamic structural changes and dynamic processes of functioning biological molecules in physiological solutions, at high spatiotemporal resolution. Dynamic molecular events unselectively appear in detail in an AFM movie, facilitating our understanding of how biological molecules operate to function. This review describes a historical overview of technical development towards HS-AFM, summarizes elementary devices and techniques used in the current HS-AFM, and then highlights recent imaging studies. Finally, future challenges of HS-AFM studies are briefly discussed.     

Contact atomic force microscopy of biological tissues

The forces of adhesion of the normal and tumor cells of the human stomach epithelium to the probe of an atomic force microscope have been measured for the first time. It is established that the adhesion and contact stiffness of malignant cells are significantly lower than those of the normal cells.     

Advances in atomic force microscopy for single-cell analysis

Single-cell analysis has been considered as a promising way to uncover the underlying mechanisms guiding the mysteries of life activities, which considerably complements traditional ensemble assays and yields novel insights into cell biology. The advent of atomic force microscopy (AFM) provides a potent tool for investigating the structures and properties of native biological samples at the micro/nanoscale under near-physiological conditions, which promotes the studies of single-cell behaviors. In the past decades, AFM has achieved great success in single-cell observation and manipulation for biomedical applications, demonstrating the excellent capabilities of AFM in addressing biological issues at the single-cell level with unprecedented spatiotemporal resolution. In this article, we review the recent advances in single-cell analysis that has been made with the utilization of AFM, and provide perspectives for future progression.

     

Electrostatic nanolithography in polymers using atomic force microscopy

The past decade has witnessed an explosion of techniques used to pattern polymers on the nano (1-100 nm) and submicrometre (100-1,000 nm) scale, driven by the extensive versatility of polymers for diverse applications, such as molecular electronics, data storage, optoelectronics, displays, sacrificial templates and all forms of sensors. Conceptually, most of the patterning techniques, including microcontact printing (soft lithography), photolithography, electron-beam lithography, block-copolymer templating and dip-pen lithography, are based on the spatially selective removal or formation/deposition of polymer. Here, we demonstrate an alternative and novel lithography technique--electrostatic nanolithography using atomic force microscopy--that generates features by mass transport of polymer within an initially uniform, planar film without chemical crosslinking, substantial polymer degradation or ablation. The combination of localized softening of attolitres (10(2)-10(5) nm3) of polymer by Joule heating, extremely non-uniform electric field gradients to polarize and manipulate the soften polymer, and single-step process methodology using conventional atomic force microscopy (AFM) equipment, establishes a new paradigm for polymer nanolithography, allowing rapid (of the order of milliseconds) creation of raised (or depressed) features without external heating of a polymer film or AFM tip-film contact.     

Single-molecule switching with non-contact atomic force microscopy

We report upon controlled switching of a single 3,4,9,10-perylene tetracarboxylic diimide derivative molecule on a rutile TiO(2)(110) surface using a non-contact atomic force microscope at room temperature. After submonolayer deposition, the molecules adsorb tilted on the bridging oxygen row. Individual molecules can be manipulated by the atomic force microscope tip in a well-controlled manner. The molecules are switched from one side of the row to the other using a simple approach, taking benefit of the sample tilt and the topography of the titania substrate. From density functional theory investigations we obtain the adsorption energies of different positions of the molecule. These adsorption energies are in very good agreement with our experimental observations.     

Spiral scanning method for atomic force microscopy

A spiral scanning method is proposed for atomic force microscopy with thoroughgoing analysis and implementation. Comparing with the traditional line-by-line scanning method, the spiral scanning method demonstrates higher imaging speed, minor image distortion, and lower acceleration, which can damage the piezoelectric scanner. Employing the spiral scanning method to replace the line-by-line scanning method, the experiment shows that the time to complete an imaging cycle can be reduced from 800 s to 314 s without sacrificing the image resolution.     

Precise control of nanofabrication by atomic force microscopy

With an aim of the precise control of the anodic oxidation process by atomic force microscopy, the technical improvement has been carried out based on the mechanism studies. The accuracy and reliability of the nanofabrication have been improved by the combination of ambient humidity control, improvement of instrumental performance and meniscus lifetime control. In parallel, the mechanism study has been proceeded through the detection of Faradaic current. The in situ Faradaic current detection of the nano-oxidation process can actually work as a sensitive monitor for the nano-oxidation process with a high reliability. From an engineering viewpoint with an eye to practical applications, controllable physical parameters which affect on the product size are enumerated to consider what we should do to raise the precision of nano-oxidation. Then the fast fabrication in a large area by a patchwork method, Faradaic current detection during oxidation-reduction reaction, and nanofabrication by current-control are shown as examples.     

An atomic force microscopy study of polyester surfaces

The surface properties of amorphous and crystalline polyester films, well below their glass transition temperature, have been studied with an atomic force microscope. For amorphous films a corrugated pattern develops on the surface as a result of scanning and the corrugations are always perpendicular to the scan direction. When scanning is stopped the pattern shows a slight relaxation; however, the surface is plastically deformed. When crystalline films are scanned, similar patterns are seen which are less pronounced and require a much longer scan time. These results suggest that the physical properties of a glassy polyester surface may be different from the bulk, and the freedom of macromolecules is reduced upon crystallization, thus suppressing molecular motion at the surface.     

Atomic force microscopy and atomic force acoustic microscopy characterization of photo-induced changes in some Ge-As-S amorphous films

Amorphous Ge₂₇As₁₃S₆₀, Ge₁₄As₂₇S₅₉ and Ge₁₆As₂₆S₅₈ thin films were prepared by thermal evaporation. Well annealed films were photodarkened by the photons with energy little exceeding the band gap energy. Using Atomic Force Microscopy we observed significant photoexpansion of studied films. Atomic Force Acoustic Microscopy revealed domains like structure of the surface and near surface parts of the samples which one was found to be more disintegrated after illumination.     

Specific aptamer-protein interaction studied by atomic force microscopy

Aptamers are a new class of synthetic DNA/RNA oligonucleotides generated from in vitro selection to selectively bind with various molecules. Due to their molecular recognition capability for proteins, aptamers are becoming promising reagents in protein detection and new drug development. In this study, the specific interaction between the protein immunoglobulin E (IgE) and its 37-nt aptamer has been measured directly by atomic force microscopy. The single-molecule unbinding force between IgE and the aptamer is determined using the Poisson statistical method. The individual unbinding force between IgE and its monoclonal antibody has also been obtained and compared to that between IgE and the aptamer. The results reveal the high affinity of the aptamer to protein, which could match or even surpass that of the antibody to its antigen.