Atomic force microscopy (AFM) can serve as a powerful characterisation tool for material science. In addition to the direct and three-dimensional visualisation of topography with unprecedented spatial resolution, advanced operation modes such as phase imaging allows the probing of other material properties and thus provides additional information. In this presentation, application of AFM on both polymer and nanoparticle samples will be discussed.

The importance of polymer studies in different environments and at various temperatures is well recognised. There is also understanding that many of the capabilities and, particularly, imaging under liquids and in different vapours are not trivial procedures. Main hurdles for experiments under liquids are the finding of the most efficient way of driving an AFM probe into oscillation and a design of robust and closed cell for imaging under water and different organic solvents. Such experiments can lead to recognition of hydrophilic surface locations by in situ monitoring of local swelling in various polymer samples. Imaging in vapour of organic solvent will help to visualise cross-linked regions - a related morphology of rubbery materials. Among possible extensions of these applications are studies of catalytic activities of nanoparticles in different media and examination of conducting channels in proton exchange membrane fuel cells.

Examples of AFM studies of local surface structures, molecular composition and mechanical properties of a broad range of polymer materials, including block copolymers, bulk polymers, thin-film polymers, polymer composites, and polymer blends, with and without environmental control will be demonstrated. For nanoparticle analysis, AFM allows the precise measurements of the size, differentiation of the materials, and reveal the structures at single particle level.

Study of self-assembly of amphiphilic compounds, which plays important role in many technological, biological and medical applications, is one of mainstream atomic force microscopy (AFM) applications. These applications include visualization of self-organized architectures on different substrates and characterization of local mechanical and electromagnetic properties. Currently, the interest of researchers is focused on high-resolution imaging of structures in the sub-100 nm scale, which require further improvements of instrumentation, probe manufacturing and optimization of imaging conditions. In examination of local mechanical and electromagnetic properties, innovative studies are based on broadening of frequency range of oscillatory modes and simultaneous use of several frequencies. A number of applications of high-resolution imaging, studies of higher harmonics and single-pass Kelvin force microscopy to alkanes, fluoroalkanes, alkylgluconamides and several block copolymers will be discussed in the presentation. Some of these experiments were conducted in various environments that allow better understanding structural organizations of amphiphilic materials and their functionality. The use of electric pulses as an external stimuli leading to surface electrets on different materials will be also demonstrated.

Atomic Force Microscopy (AFM) is well-established characterization technique for high-resolution surface imaging and its applications are expanding towards quantitative studies of local mechanical and electric properties. Recent developments in AFM instrumentation open new capabilities for simultaneous examination of electric and mechanical tip-sample interactions at multiple frequencies. Practical implementations of this approach in studies of semiconductor structures, self-assembled organic material and multicomponent polymer systems will be discussed.

Kelvin Force Microscopy (KFM) is a very powerful tool for mapping of surface charges, surface potentials, and doping profiles. [1] This technique is implemented in amplitude modulation and frequency modulation Atomic Force Microscopy (AFM) modes. [2] In many applications surface electric properties are measured with two-pass technique in which a “spill over” of topographic response to the probe motion is reduced by lifting the probe over a sample surface during detection of electric signals. Such approach has also severe limitations in sensitivity and lateral resolution due to a remote probe position during the lift scan. A separation of topographic and electrostatic responses is also possible by operating topography and electric-response servo loops at different frequencies that enable single-pass KFM with simultaneous studies of sample topography and surface potential. The latter is measured by voltage applied to the probe that nullifies its electrostatic interaction with a sample.

We consider several practical implementations for the electric-response servo loop. In search for one that provides best spatial resolution [3] and highest sensitivity. Different inputs and frequencies were applied in this search. We have also employed AFM probes with different cantilever geometries (Figure 1, left and right) and tip dimensions. The results of this study will be presented and illustrated by KFM images of different materials: semiconductor structures with different level of doping, polymer composites, graphite, Au (111) and fluoroalkanes. Doped electric passes (Figure 2, right), negatively charged self-assemblies of fluoroalkane layer on graphite (Figure 3, right) and contamination patches, which are grown on the graphite surface in air (Figure 4, right) are visualized in surface potential images. It was possible to achieve lateral resolution better than 5 nm and sensitivity of few tens of milliVolts.

Organodithiols on noble metals such as gold are good candidates to generate thiol-terminated self-assembled monolayers (SAMs) if molecules can form a close-packed and standing-up layer on the substrate as the case of alkanethiols. However, dithiols usually yield lying-down or looped alkanedithiolates on gold via the binding of both SH groups when adsorbed layers are prepared from widely used natural growth approaches. Here, a new approach to circumvent that obstacle and achieve high-quality thiol-terminated assemblies is developed. It involves an atomic force microscopy (AFM)-based lithography method known as nanografting performed in a dithiol solution. Using α, w-aliphatic dithiols as an example, dithiol SAMs prepared by both natural growth and nanografting are well characterized by AFM. High-resolution imaging and height measurements clearly demonstrate that dithiol molecules are densely packed and adopt a standing-up conformation in the fabricated patterns of dithiol SAMs to present free SH groups on the surface. In addition, nanografting enables the fabrication of thiol-terminated layers on gold with nanometer-scale precision in geometry, size and location. These designed thiol-terminated nanostructures can be served as surface templates to direct the metal deposition.

Scanning Gate Microscopy (SGM) is a powerful technique for investigating electrical properties of nanoscale devices. Previous studies of SGM on carbon nanotubes field-effect transistors (CNTFETs) has shown that the conductance along nanotubes varies, most likely due to static charge in the insulating substrate underneath the nanotubes. SGM has always been done in liftmode, which limits lateral resolution. We have developed a variation of SGM that is used in intermittent contact mode (IC-SGM), in which the SGM signal is obtained simultaneously with topography and phase images. IC-SGM is easier to implement and produces better lateral resolution, because the tip-sample interaction occurs when the tip is very close to the sample. We also show that the tip does not inject charge into the nanotubes when it touches the nanotube. Varying the set point shows evidence for conductance changes due to CNT deformation or redistribution of surface charge.

Atomic Force Microscopy (AFM) is an important tool for nanoscale molecular recognition studies. A strong suit of AFM is its ability to measure hardness/elasticity, nonspecific adhesion, or ligand-receptor interactions at the picoNewton scale. Molecular interactions are critical factors in a variety of biological phenomenon; such as initiation, modulation, and termination of DNA replication, transcription, enzyme activity, infection, immune responses, tissue generation, wound healing, cell differentiation, apotopsis, and physiological responses from drugs, hormones, or toxic agents. Using AFM, scientists can probe and quantify these interactions in their native, liquid environments at physiological pH or perform dynamic experiments in situ by removing or adding ions, solutes, and reagents to the sample environment. Nanoscale bioconjugation chemistry and surface chemistry are crucial in these studies because selective ligands must be immobilized on the tip of an AFM probe so that the AFM can resolve the mechanical force that is required to separate a ligand from its target. The resulting information can be used to calculate forces of unbinding and infer structural information about the binding interaction.

There are many biochemical immobilization and bioconjugation chemistry schemes that have been applied to the investigation of ligand-receptor interactions by AFM (atomic force microscopy). In these studies, biological ligands are typically bound to the tip of an AFM probe while corresponding receptor molecules or whole cells are bound to a flat substrate such as mica, silicon, flat glass, or a metal coated substrate. Ligand molecules for a particular receptor can be attached to the tip of an AFM probe, transforming the probe into a sensitive, chemically selective biosensor for that receptor. Molecular recognition force microscopy (MRFM) is a single molecule AFM-based technique which relies heavily on nanoscale surface chemistry, nanoscale biochemical immobilization chemistry and bioconjugation chemistry. In MRFM, single molecule unbinding interactions between AFM probe-bound ligands and substrate-bound receptor pairs are observed and quantified one by one as the AFM cantilever approaches and then is subsequently withdrawn away from the surface many times. The nanoNewton-scale molecular unbinding events are generally detected by measuring the optical deflection of the flexible AFM cantilever. These force spectroscopy (FS) experiments can give valuable information about the structure and dynamics of molecular unbinding events at the single molecule level. In addition to intermolecular interactions, this technique has also been effectively applied to gain an understanding of the intramolecular forces involved in the dynamics of protein folding and polymer elongation. Topography and recognition (TREC) imaging is another single molecule AFM technique that also utilizes probe-bound ligands and substrate-bound receptor pairs. TREC imaging is a dynamic force microscopy (DFM) technique in which a ligand-coated AFM probe is scanned and oscillated over a biological surface in magnetic AC (MAC) Mode in order to resolve recognition maps of ligand-receptor interactions. Specific interactions between the ligand attached to the AFM probe and receptor molecules on the substrate are resolved during scanning as small changes in the MAC Mode signal. TREC imaging is a powerful technique with many potential applications because it allows a specific type of molecule to be identified in compositionally complex samples, such as biological materials. The lateral positions of functionally active receptors on a cell or other biological surface can be resolved with nanometer resolution. TREC has been used to image, map and analyze the chemical compositions of a variety of samples; including molecular interactions between nucleic acids and proteins, antibodies and antigens, and small ligands and their receptors.

Atomic force microscopy (AFM) is an important tool for high resolution studies in biophysics. A strong suit of AFM is its ability to measure ligand-receptor interactions at the picoN scale. Using AFM, scientists can probe and quantify these interactions in their native, liquid environments at physiological pH or perform dynamic experiments in situ by removing or adding ions, solutes, and reagents to the sample environment. Bioconjugation chemistry and surface chemistry are crucial because a selective ligand must be immobilized on the tip of a cantilever so that the AFM can resolve the mechanical force that is required to separate the ligand and its target. The resulting data can be used to calculate forces of unbinding, derive rate constants, and infer structural information about the binding pocket. Biomolecular recognition experiments with AFM can be greatly enhanced through the use of relatively short (~8-10 nm), heterobifunctional, elastic, polyethylene glycol (PEG) linker to immobilize ligands. Selective bifunctional linkers are used in order to permit their sequential immobilization and bioconjugation, while minimizing undesirable polymerizations or self-conjugation.

A new AFM system incorporated with a microwave network analyzer is presented. A microwave signal is emitted from the vector network analyzer and transmitted through a resonant circuit to a conductive AFM probe which is in contact with a sample being scanned. The probe also serves as a receiver to capture the reflected microwave from the contact point and feeds it back to the network analyzer. By measuring the complex reflection coefficient, known as S11 parameter, the impedance of the sample at the contact point can be obtained. Direct detection of the reflected microwave can be used to map differences in capacitance, impedance, and dielectric properties of a variety of different materials. With a superimposed low-frequency modulation, changes of capacitance from the reflected microwave due to the depleted carriers under the probe can be used to map different dopants of semiconductors.

Applications of Atomic Force Microscopy (AFM) are expanding with further developments of electronic capabilities, introduction of advanced modes and use of novel probes. In recent years, there was a definite emphasis on better resolution using amplitude modulation and frequency modulation modes. Achievements and opened questions of atomic-scale and molecular-scale images in these modes will be presented and discussed. The use of broadband lock-in amplifiers and fast data acquisition leads to advanced approaches towards quantitative probing of local mechanical and electric properties. Probing of local electric properties with single-pass Kelvin Force Microscopy (KFM) will be demonstrated on samples of different kinds with emphasis on high sensitivity and lateral resolution. One of the outstanding goals of comprehensive AFM applications is a combination of high-resolution resolution imaging and quantitative probing of local properties with studies in different environments: air, liquid, vapors, etc. Several applications related with imaging of samples in at different humidity and in various vapors will be described. The examples are taken from studies of organic ultrathin layers on different substrates and polymers.