A fundamental new pathway to a basic understanding of nanostructured composite thin films has been recently afforded by advances in both high brightness field emission electron source and electron optics in the SEM. The key advantages of controlling the incident electron beam at low energies (< 5 keV) for surface imaging has been largely focused on goals such as the reduction of sample charging and minimization of macroscopic radiation damage. In this paper, we present a new opportunity to obtain sampling depth information by controlling the incident electron beam energy. One of the major factors which determines the contrast seen in SEM images is the interaction of the incident electron beam with the solid. As a result of this interaction, the secondary electron yield is proportional to the stopping power of the electron as described by the Bethe penetration depth,where dE/dl is the stopping power of incident electron with energy Einc and Emin is some suitable lower energy limit for the interaction.

The observation of microstructural features smaller than 300 nm is generally performed using Transmission Electron Microscopy (TEM) because conventional Scanning Electron Microscopes (SEM) do not have the resolution to image such small phases. Since the early 1990’s, a new generation of microscopes is now available on the market. These are the Field Emission Gun Scanning Electron Microscope with a virtual secondary electron detector. The field emission gun gives a higher brightness than those obtained using conventional electron filaments allowing enough electrons to be collected to operate the microscope with incident electron energy, E0, below 5 keV with probe diameter smaller than 5 nm. At 1 keV, the electron range is 60 nm in aluminum and 10 nm in iron (computed using the CASINO program). Since the electron beam diameter is smaller than 5 nm at 1 keV, the resolution of these microscopes becomes closer to that of TEM.

Recent trends directed toward the miniaturization of electrodes have produced ultramicroelectrode (UME) devices. Interest in UMEs is due to the considerable improvement in the quality of the electrochemical information that is obtained as the dimensions of the electroactive surface decreases. UMEs exhibit increased sensitivity to analytes, decreased response time, and enhanced single-to-noise. In addition, solution resistance has a decreased influence on the signal. Finally, the reduced size of UMEs allows electroanalysis in small sampling environments. As a result, UMEs have been used in applications for intracellular electroanalysis, as detectors in capillary separation methods and gas chromatography, and as electrochemical probes in scanning electrochemical microscopy.

While UMEs have been investigated since the early 1980s, single probe dual UMEs are a recent development. Dual UMEs have two independent UMEs in close proximity, which allows much flexibility in the design of electrochemical-based sensor devices.

A major problem now hampering increased recycling of old cardboard containers (OCC), is the presence of significant amounts of polymeric materials such as adhesives, tapes, labels and wax which enter the pulp process stream along with the cardboard and paper that was collected for recycling. Many of these materials contain very fine particles of inorganic fillers and pigments. These various contaminant constituents combine in some, as yet unknown, manner to form an extremely gummy material that deposits on paper machine surfaces and sticks tenaciously (hence the term “Stickies”). The sticky blobs are very difficult to remove and increases machine downtime and maintenance costs as well as causing blemishes on the finished container board product Light optical image analysis, UV fluorescence, FTIR and electron microscopy are being used in consort with particle size measuring instruments, TGS and DSC thermal analysis techniques, FTIR infra-red spectroscopy as well as XRF (x-ray fluorescence spectroscopy ), XPS (x-ray photo emission spectroscopy) and classical contact angle determination methods as part of a broad program to characterize the physical and chemical nature of stickies in pulp slurries with the goal of removing them or alleviating their pronounced tendency to deposit on machinery and paper products.

A recent study concluded that the most potentially dangerous scenarios for accidental detonation of a nuclear weapon were those involving weak thermal or mechanical shocks. For this reason, more data are needed to understand the material behavior of nuclear constituents under low strain rate scenarios.

One of the components of many of these types of weapons is known as Plastic Bonded eXplosives (PBX). PBX is a paniculate composite material made of a hard phase explosive carried in a soft phase polymer binder. Recent work has showed that the stiffness of PBX increased under low rate compressive loading. This behavior was attributed to the shape of the test samples and cross-linking within the elastomer binder. Another theory proposed that the changing compressive properties could be attributed to the hard phase particles migrating together during material flow.

Funk et al. demonstrated an inert material mock of PBX 9501, with the hard phase explosive replaced by granular sugar, also showed the same phenomena of compressive hardening.

This paper uses high resolution scanning electron microscopy (SEM) with a LaB6 gun and the newest commercial field emission guns, to obtain high magnification images of intact clostridial spores throughout the activation/germination/outgrowth process. by high resolution SEM, the clostridial exosporial membrane can be seen to produce numerous delicate projections (following activation), that extend from the exosporial surface to a nutritive substrate (agar), or cell surface when anaerobically incubated in the presence of human cells (embryonic fibroblasts and colon carcinoma cells). Magnifications of 20,000 to 200,000Xs at accelerating voltages low enough to minimize or eliminate specimen damage (1-5 kV) have permitted the entire surface of C.sporogenes and C.difficile endospores to be examined during all stages of germination. The relationships between the spore and the agar or human cell surface were also clearly visible.

Clostridium sporogenes ATCC 3584 and C.difficile ATCC 43594 and 9689 were grown in cooked meat media, filtered and cleaned.

Chemical force microscopy (CFM) has been used to measure adhesion and friction forces between probe tips and substrates covalently modified with self-assembled monolayers (SAMs) that terminate in distinct functional groups. Probe tips have been modified with SAMs using a procedure that involves coating commercial Si3N4 cantilever/tip assemblies with a thin layer of polycrystalline Au followed by immersion in a solution of a functionalized thiol. This methodology provides a reproducible means for endowing the probe with different chemical functional groups.

A force microscope has been used to characterize the adhesive interactions between probe tips and substrates that have been modified with SAMs which terminate with COOH and CH3 functional groups in ethanol water solvent. Force versus distance curves recorded under ethanol show that the interaction between COOH/COOH > CH3/CH3 > COOH/CH3. The measured adhesive forces were found to agree well with predictions of the Johnson, Kendall, and Roberts (JKR) theory of adhesive contact, and thus show that the observed adhesion forces correlate with the surface free energy

The physisorption of oligosaccharide surfactants is being developed as a method for modifying biomaterials to prevent protein adsorption. In this study, we visualize the surface adsorption and ordering of oligosaccharide surfactant using the atomic force microscope (AFM). Contact mode imaging is used to provide topographical images of the surface. Tapping mode imaging also provides topographical images, but reduces the amount of the lateral forces applied to the surface by driving the cantilever and contacting the surface once per oscillation. A phase image, which is the measure of phase shift between the cantilever response and the driving signal in tapping mode, gives information on variations in the viscoelastic response of the sample surface.

The maltose diblock surfactant was prepared by the selective oxidation and lactonization of the maltose reducing end group, followed by aminolysis with dodecylamine. The chemical structure is Maltose--CONH-(CH2)11CH3.

The solutions used for adsorption were prepared by diluting a stock solution of the surfactant at the critical micelle concentration (CMC) to the desired concentrations.

At present, changes in the structure of proteins occurring upon adsorption at liquid/solid interfaces are not well understood. The prevailing model assumes that a protein, which is globular in solution, must first displace surface bound water molecules. Then, after adsorption of the protein at the surface, the molecule unfolds to maximize interactions with the surface. It is noted, however, that some enzymes maintain a significant amount of their activity once adsorbed. This observation is the basis for many biomedical assays and implies that native protein structure is at least partially maintained.

The atomic force microscope (AFM) is well suited for the study of biomolecules at interfaces, providing single molecule resolution. Progress on molecular structure analysis of proteins using AFM, however, has been hampered by the fact that the tip radius is as large as, or larger than the proteins themselves, thereby causing a large lateral convolution effect.

In topographs produced by scanned probe microscopy, positive-going surface features are broadened due to the non-vanishing tip size. This well-known imaging artifact is of particular importance for feature width or surface microroughness determinations. Its correction requires a 3-d model of the tip.

Most proposed methods of tip estimation begin with the same set of experimental conditions and model assumptions. Experimentally, a special specimen (a “tip characterizer”) is imaged with the unknown tip. The image model assumes the image is formed by contact of the tip with the surface at one or more points without significant bending of the tip or compression of the surface. Under these circumstances, it has been shown1 that I = S ⊕ P, where S is the set of all points in the specimen, P a reflection of the tip through the origin, I the image, and ⊕ denotes dilation.

The atomic force microscope has been an essential tool in the past few years for visualization of mesoscopic structures, and has been applied to numerous examples in biological systems. The finite size of the probe tip, however, means that the picture produced by the AFM inevitably includes the tip geometry convoluted with the desired image of the sample. If the tip is asymmetric and/or deformed, the resulting image may bear little resemblance to the original sample. Even in the case of a “good tip”, however, the effect on the image is non-negligible, causing broadening and obscuring of features. In this presentation, approaches developed in our laboratory with regards to problems in imaging mesoscopic samples will be discussed.

In samples where the primary tip-sample interaction is via excluded volume - that is, the tip and sample are mutually impenetrable and come into contact - we had been utilizing a numerical algorithm for removing the tip geometry from the AFM image.

Atomic force microscopy (AFM) studies on the microstructure of the phosphonic acid (PA) / Al (with native oxide) self assembled monolayer (SAM) system (a possible corrosion resistant coating interface monolayer) has been evaluated as a function of molecular chain length and processing conditions (i.e. adsorption time) in previous works. It was apparent from the AFM topography and phase images of the monolayer microstructure that the octadecylphosphonic acid (OPA) monolyer was the most conformal and showed little dependence on adsorption time (for times ≤ 24 hours). It was therefore chosen as the most promising monolayer compound of the PA/A1 system with which to study corrosion inhibiting properties.

In this present work, AFM is used to study the corrosion inhibiting ability of OPA SAMs on aluminum, and also to investigate the “nucleation” and progression of Al corrosion and oxide formation in water at the nanometer level; with and without SAM passivation.

Alkali feldspar, a framework silicate (K, Na)(Si3Al)04, is a common component in ceramic materials. The feldspar crystals commonly display exsolution lamellae, twins, and modulated structures. The boundaries between neighboring domains may cause stain energy. The domain structures cause heterogeneities both inside crystals and on crystal surfaces in aspects of structure, composition, and surface microtopography. Reactivity at domain boundary positions is different from the neighboring areas. More and more studies show the effects of microtopography on the surface reactivity. It is important to reveal the surface characters or microtopography of domain structures in crystals, and their effects on local reactivity.

Results from transmission electron microscopy (TEM) characterization show it contains exsolution lamellae (both K-rich and Na-rich lamellae) and twin domains in the Na-rich lamellae (Fig. 1A). Its SAED pattern shows reflections from both K-rich and Na-rich lamellae (Fig. B). Splitted reflections result from the Na-rich lamellae wiht twin domains related by (010) mirror plane, i.e., albite twin law.

Formation and growth mechanisms of biological hard tissues are relevant in biomimetics for obtaining lessons in the assembly of complex and ordered microstructures for engineering applications. Shells of mollusks offer examples of organic/inorganic hybrid structures with nanoscale order that produce functionally-gradient macroarchitectures. Here, the nacre/prismatic interface of red abalone (Haliotis rufescens) was topographically profiled with an atomic force microscope (Park Scientific PC) using contact mode in air to elucidate growth characteristics of the shell. The results give a quantitative (spatial and temporal) measure of how nacre (N) grows over the prismatic (P) section of the shell.

Nine regions, with a length of 350 µm parallel to the growing edge and a width of 120 µm, were scanned (e.g., Figs 1 & 2). Raster scanning from N to the P sections revealed that the rms roughness of the surface tends to increase from N to P region with the latter having topographical height variations of up to 5 µm at the growing edge.

In polycrystalline liquid-phase sintered (LPS) alumina ceramics, intergranular phases have proved to have a profound effect on mechanical properties such as strength, toughness, plastic deformation, and high-temperature creep. The presence of such intergranular phases, can also influence the kinetics of many processes including sintering, grain growth, and phase transformations. As a result, the key to optimizing the performance of a ceramic material is frequently related to optimizing the properties of these grain boundary regions. In order to understand the interactions between the glass layer and the crystalline grains at a fundamental level, the amorphous material must be placed in contact with the crystalline ceramic as a thin film in a controlled manner. Preparation of such a glass phase in the thin-film geometry has also prompted the use of nontraditional mechanicaltesting techniques.

In the present study, interfaces between silicate glass and single-crystal α-Al2O3 have been studied using AFM and nanoindentation.

Gaps in the understanding and interpretation of data collected in various SPM modes are a direct result of the rapidly advancing scanning probe microscopy (SPM) technology. This systematic study is coupling classical metallurgical samples with a new surface variation mapping technique in an effort to further the quantitative comprehension of atomic force microscopy (AFM) phase imaging.

Phase imaging is a technique that has exhibited the ability to provide the microscopist with qualitative information of a material’s microstructure on the nanometer scale. Regions of a microstructure that exhibit incongruous mechanical properties like: friction, elastic modulus, composition, and viscoelasticity are displayed, in the resulting image, as regions of differing contrast. An example of this type of phase contrast is clearly seen in FIG. 1. A quantification of the phase shift will give new insight into the cause of the contrast mechanism, and reason for contrast reversal.

Fatigue is a common cause of failure in components subjected to cyclic stresses. Repeated loads much smaller than the yield stress of the material can cause a fatigue failure. One such component subject to cyclic stresses is a titanium heart valve housing. The valve is subjected to a low level of stress with each heart beat as a disc pivots and closes against the housing. Interest in the initiation of fatigue in such components was an impetus to examine surface plasticity and accumulated damage which could lead to fatigue initiation. Grade 4 titanium used in heart valves and pure titanium have been studied.

The three phases of fatigue are initiation of a crack, propagation, and catastrophic failure. Minimum defect size for crack propagation and failure are fairly well understood by scientists and engineers. However, the initiation portion of fatigue as a function of accumulated surface microplasticty is less well defined. SEM and AFM have been be used to evaluate microplasticity on the surface of titanium and correlate damage accumulation to the initiation of a crack.

Fully reverse loaded four point bend testing was conducted on a an electropolished pure titanium sample 15 mm by 5 mm by 1 mm thick. The sample was oxidized at 300°C for one hour prior to fatigue testing. The sample was fatigued for 25,000 cycles using a ±45N load.

Phase detection in TappingMode™ enhances capabilities of Atomic Force Microscopy (AFM) for soft samples (polymers and biological materials). Changes of amplitude and phase changes of a fast oscillating probe are caused by tip-sample force interactions. Height images reflect the amplitude changes, and in most cases they present a sample topography. Phase images show local differences between phases of free-oscillating probe and of probe interacting with a sample surface. These differences are related to the change of the resonance frequency of the probe either by attractive or repulsive tip-sample forces. Therefore phase detection helps to choose attractive or repulsive force regime for surface imaging and to minimize tip-sample force. For heterogeneous materials the phase imaging allows to distinguish individual components and to visualize their distribution due to differences in phase contrast. This is typically achieved in moderate tapping, when set-point amplitude, Asp, is about half of the amplitude of free-oscillating cantilever, Ao. In contrast, light tapping with Asp close to Ao is best suited for recording a true topography of the topmost surface layer of soft samples. Examples of phase imaging of polymers obtained with a scanning probe microscope Nanoscope® IIIa (Digital Instruments). Si probes (225 μk long, resonance frequencies 150-200 kHz) were used.

Scanning probe techniques have shown dramatic growth recently and are presently making significant impact on surface and interfacial problems in material science. The Interfacial Force Microscopy (IFM) differs from other scanning force-probe techniques by its use of a self-balancing, zero compliance force sensor. This allows carefully controlled and mechanically stable force vs. interfacial separation measurements to be obtained which yield unique and valuable information concerning the interfacial adhesive bond and its failure, as well as enabling the study of the mechanical properties of materials, both on the nanometer scale. I will demonstrate the enhanced capabilities of the IFM by presenting two examples involving: 1) the bonding interaction between chemically distinct end groups on self assembling molecules adsorbed on both the sample and probe tip and 2) a study of the effect of morphological defects on the nanomechanical properties of Au(l 11) single-crystal surfaces

Interfacial adhesion is of extraordinary technological importance and has long been of intense scientific interest.

The Internet has become a very valuable educational resource. It allows a person to be able to reach a very large, diverse audience across the world with ease. With NSF Combined Research-Curriculum Development (CRCD) funding, we have begun to use the Internet as an educational and technical resource for people wanting to learn about Scanning Probe Microscopy (SPM). We have set up a web page with informative information for people of all levels of SPM knowledge. We are actively combining SPM research and education into the materials science and engineering undergraduate curriculum. We also use the web page as a way to publish our findings to help other universities integrate SPM into their curriculums.

The URL is: http://spm.aif.ncsu.edu

The web page is divided into seven main components. Each component has a specific intended audience and purpose. We have designed some components for people who have never heard of SPM and others for people who run SPM labs.