Surface crystallization in melt-spun metallic glasses

A series of hypoeutectic FeSiB metallic glasses produced by single-roller melt spinning were found to have substantial wheel-side surface crystallization. These crystals were shown to be associated with areas on the ribbon surface which were in good contact with the wheel rather than in the depressions formed by gas entrainment during casting, as has been previously suggested for similar effects in other alloys. Transmission electron microscopy revealed that the crystals have a fine cellular substructure with the intercellular spaces freezing as glass and that the structure becomes progressively finer during growth.     

Laser pulse crystallization of Pd-Si metallic glasses

A novel method of laser pulse crystallization (LPC) capable of revealing and quantifying crystallization in amorphous ribbons is presented. It is used to study the morphology of crystallization and, indirectly, surface crystallization (SC) of Pd-Si amorphous alloys in the composition range Pd₇₇Si₂₃-Pd₈₅Si₁₅. The laser-induced, frozen-in fronts of crystallization are studied by optical metallography and X-ray diffraction. The shapes of these fronts are determined by the initial degree of SC, which depends on alloy compositions, their thermal history and/or the surface of the ribbon being analysed. SC is inactive in alloys of eutectic composition (Pd₈₅Si₁₅) and is most pronounced for compositions near the border to the amorphous region on the silicon-rich side (Pd₇₇Si₂₃). For as-quenched ribbons, a stronger tendency to SC exists on the shiny surface of the ribbon. Low-temperature furnace annealing as well as room temperature ageing over a period of 2 years equalizes the degree of SC on both surfaces. The X-ray diffraction patterns taken from the regions containing frozen-in fronts of crystallization only reveal the presence of metastable phase II, independently of composition and/or thermal history of the given sample.     

Applicability of FMR for crystallization studies in metallic glasses

It has been shown theoretically that the peak-to-peak ferromagnetic resonance (FMR) line-width (H _pp) should be proportional to the volume fraction (f) of the crystalline phase formed during annealing in ferromagnetic glasses. However, in the case of zero-magnetostrictive cobalt-based glasses (=0), H _pp should remain constant due to very low values of anisotropy. In Co₆₈Fe₄Mo₁Si₁₇B₁₀ glass (=0), H _pp has been found to remain unaffected upon progressive crystallization. In Fe₆₅Cr₈B₂₇ glass, H _pp has been found to be linearly proportional tof. Using this dependence, the activation energy of crystallization (E _a) has been calculated. The value ofE _a obtained from the FMR technique (248 kJ mol^–1) agrees quite well with those from DTA studies using Kissinger's or Ozawa's technique.     

The crystallization kinetics of Fe-Ni based metallic glasses

Differential scanning calorimetry is used to study the crystallization kinetics of two commerical Fe-Ni metallic galsses near their glass transition point. For 0.01 <x<0.85 the fraction transformed,x, as a function of time,t, satisfies the Johnson-Mehl-Avrami equation with exponentn varying from 2.8 to 4.3 as the annealing temperature is increased. The activation energies for the crystallization process are estimated from the time to 50% transformation as close to 100 kcal mol^–1 and are interpreted as arising from viscous flow.     

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.     

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.     

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.     

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.     

Current views on the structure and crystallization of metallic glasses

An attempt has been made in this review to cover recent information on the structure of metallic glasses (amorphous metals) obtained by X-ray diffraction. Based on the experimental data, the partial structure factors of a binary metallic glass are given. Various characteristics such as crystallization processes, thermal effects and alloying effects are also discussed.     

Dielectric constants by multifrequency non-contact atomic force microscopy

We present a method to obtain capacitive forces and dielectric constants of ultra-thin films on metallic substrates using multifrequency non-contact atomic force microscopy with amplitude feedback in air. Capacitive forces are measured via cantilever oscillations induced at the second bending mode and dielectric constants are calculated by fitting an analytic expression for the capacitance (Casuso et al 2007 Appl. Phys. Lett. 91 063111) to the experimental data. Dielectric constants for self-assembled monolayers of thiol molecules on gold (2.0±0.1) and sputtered SiO2 (3.6±0.07) were obtained under dry conditions, in good agreement with previous measurements. The high Q-factor of the second bending mode of the cantilever increases the accuracy of the capacitive measurements while the low applied potentials minimize the likelihood of variation of the dielectric constants at high field strength and of damage from dielectric breakdown of air.     

Nucleation kinetics of primary crystallization products in FeSiB metallic glasses

Three iron-based metallic glasses in the Fe_96–x Si₄B _x series were examined after various dynamic and isothermal annealing treatments. The number and type of the primary crystallization products formed in these alloys were determined as functions of time and temperature, and the results compared with theoretical models. It has been found that, for certain alloys, a proportion of the primary -iron crystals in the structure are nucleated by particles of the metastable Fe₃B phase. The transformation kinetics of these composite crystals are different from those which do not contain an Fe₃B core, suggesting different nucleation mechanisms for the two types of crystal.     

Time-scaling and crystallization kinetics of three Fe-B-based metallic glasses

Time-scaling properties of the isothermal transformation kinetics have been tested for three Fe-B-based metallic glasses exhibiting two crystallization stages. The time scale was defined as the time at which crystallization has reached half completion and is derived from calorimetric (DSC) data. The temperature dependence of the time-scaling parameter shows a lowtemperature freezing behaviour and can be described by empirical functions based on free-volume considerations.     

Observations of polyaniline surface morphology modification during doping and de-doping using atomic force microscopy

Chemically synthesized 30 m thick polyaniline films were studied during the doping and dedoping process by imaging the polymer surface using in situ atomic force microscopy (AFM). The polymer, which was initially in the base non-conducting form, was doped using aqueous solutions of both tosylic acid (pH = 0.2) and HCl (pH = 0.2 and 1.0). De-doping was accomplished by exposing the same doped polymer surface to NH₄OH (pH = 12) base solution. AFM images showed that it was necessary to cycle the polymer surface three times between acid and base before a reproducible surface morphology was established. For the case of doping with tosylic acid, AFM images showed that the polyaniline surface was immediately roughened; the changes in mean roughness for the base and acid conditions were ~ 5.4 and ~ 6.7 nm, respectively. In addition there appeared to be an increase in the size of surface channels and cracks. When doping with HCl (pH = 1.0), no change in surface morphology was observed; however, noticeable surface roughening occurred over 10 min for the case of the lower pH = 0.2 solution; mean roughness changes for the base and acid conditions were ~ 17.9 and 39.2 nm. Radio frequency measurements, which determined the polymer complex permittivity, and d.c. conductivity measurements were used to determine the level of doping in the samples studied by AFM which were exposed to acid solutions.     

Measurement of interfiber friction force for pulp fibers by atomic force microscopy

Interfiber friction in paper exists in fiber suspensions, fiber flocs, and fiber networks. The interfiber friction force is, therefore, important both in papermaking and in the use of paper. The objective of this research is to develop a methodology using atomic force microscopy (AFM) for the direct measurement of the friction force between pulp fibers. Different factors such as AFM scanning velocity, contact area, and fiber surface roughness were investigated. The results show that AFM is an effective tool for measuring micro-scale interfiber friction forces. Both AFM scanning velocity and fiber surface roughness affect the measured results. The coefficient of friction increases, but the initial adhesion force decreases, with increasing fiber surface roughness.     

Adhesion forces measured by atomic force microscopy in humid air

Adhesive forces measured with an atomic force microscope under ambient conditions are generally regarded to be dominated by non-surface-specific capillary force. In this study, the nature of the "pull-off" force on a variety of surfaces was investigated as a function of relative humidity. The results indicate that even under the condition where capillary condensation occurs there is chemical specificity in the measured pull-off force. Issues such as tip-surface contact time and surface roughness were ruled out as possible artifacts. A mathematical model of pull-off force as a function of relative humidity is proposed in which the chemical specificity is explained.     

Ultradisperse diamond cluster aggregation studied by atomic force microscopy

The structure of ultradisperse diamond (UDD) conglomerates was studied by scanning atomic-force microscopy (AFM). The UDD layers were prepared from a detonation carbon obtained by synthesis in an aqueous medium. The finest details in the AFM images of UDD layers are of the order of 10 nm, which does not allow individual 4.5-nm diamond clusters to be distinguished. The UDD conglomerates deposited and dried on a silicon substrate surface, exhibit certain deformation and differ from the initial (apparently, spherical) shape. This may imply that cohesion between the UDD nanoparticles is comparable with their adhesion to the silicon substrate.