Friction force microscopy of self-assembled monolayers: probing molecular organisation at the nanometre scale

The basic principles behind friction force microscopy are described. Applications of friction force microscopy to self-assembled monolayers are reviewed. Work in the author’s laboratory on the frictional properties of self-assembled monolayers is described, and the findings applied in the characterisation of a much more complex material, plasma-treated polyester. Friction force microscopy is found to be a powerful tool for the analysis of the chemical composition and molecular organisation of molecular materials at the nanometre scale.     

Ultrathin film characterization: photoreactive polyacrylamide

The structure and properties of photoreactive polyacrylamide thin films suitable for medical devices are presented. Using a solution deposition process, we report on the influences of polymer concentration, substrate residence time in solution and UV illumination upon the film structure, wettability and frictional properties. Ellipsometry, atomic force microscopy and lateral force microscopy show that increasing polymer concentration and illumination increased the film thickness and uniformity. Dynamic contact angles and frictional coefficients of the modified surfaces depend upon the film structure and thickness for films less than 40Å thick. We also demonstrate the potential of lateral force microscopy for investigating tribology at the nanoscale level.     

Imaging Nanocarbon Materials: Soot Particles in Flames are Not Structurally Homogeneous

For the first time, nascent soot particles are probed by using helium‐ion microscopy (HIM). HIM is a technique that is similar to scanning electron microscopy (SEM) but it can achieve higher contrast and improved surface sensitivity, especially for carbonaceous materials. The HIM microscope yields images with a high contrast, which allows for the unambiguous recognition of smaller nascent soot particles than those observed in previous transmission electron microscopy studies. The results indicate that HIM is ideal for rapid and reliable probing of the morphology of nascent soot, with surface details visible down to approximately 5 nm, and particles as small as 2 nm are detectable. The results also show that nascent soot is structurally and chemically inhomogeneous, and even the smallest particles can have shapes that deviate from a perfect sphere.     

Nanolithography and nanochemistry: probe-related patterning techniques and chemical modification for nanometer-sized devices

The size regime for devices produced by photolithographic techniques is limited. Therefore, other patterning techniques have been intensively studied to create smaller structures. Scanning-probe-based patterning techniques, such as dip-pen lithography, local force-induced patterning, and local-probe oxidation-based techniques are highly promising because of their relative ease and widespread availability. The latter of these is especially interesting because of the possibility of producing nanopatterns for a broad range of chemical and physical modification and functionalization processes; both the production of nanometer-sized electronic devices and the formation of devices involving (bio)molecular recognition and sensor applications is possible. This Review highlights the development of various scanning probe systems and the possibilities of local oxidation methods, as well as giving an overview of state-of-the-art nanometer-sized devices, and a view of future development.     

Alternating Current Measurements in Scanning Electrochemical Microscopy,Part 2: Detection of Adsorbates

A scanning electrochemical microscope (SECM) in ac mode is used for the characterisation of the adsorption process during the hydrogen evolution reaction (HER) in sulfuric acid solution. It is shown that this technique allows quantitative analysis of the adsorption process, and measurements of the differential capacitance with the frequency as parameter are obtained. The time constant for relaxation of adsorbed hydrogen (H_ads) is approximately 2 Hz, and analysis of the Nyquist plot allows direct evaluation of the charge involved. In addition, the direct comparison of the usual electrochemical impedance data and ac‐SECM results obtained simultaneously permits characterisation of processes occurring at the surface and in solution.     

超分辨率荧光显微技术——2014年诺贝尔化学奖解读

史蒂芬·赫尔(Stefan W. Hell)、埃里克·本茨格(Eric Betzig)和威廉·默尔纳(William E. Moerner)因在超分辨率荧光显微技术方面的贡献共享了2014年的诺贝尔化学奖.他们使用荧光分子和特殊的光物理原理,巧妙地突破了普通光学显微镜无法突破的"阿贝极限",其开创性的成就使光学显微技术发展为"显纳"技术,能够窥探纳米世界.     

Tunnelling junctions with additional degrees of freedom: An extended toolbox of scanning probe microscopy

Considering studies of molecular adsorption we review recent developments in the field of scanning probe microscopy and in particular in scanning tunnelling microscopy, concentrating on the progress that has been achieved by controlled decoration of the microscope tip. A view is presented according to which the tip decoration generally introduces additional degrees of freedom into the scanning junction and thus extends its functionality. In particular tips decorated with atomic point-like particles may attain the additional function of a force sensor which is realized through the degrees of freedom associated with the relative position of the decorating probe-particle with respect to the tip. It is shown how the force sensor function of such tips helps when studying large molecular adsorbates. Further prospects of more complex junctions equipped with numerous internal degrees of freedom are discussed. It is argued that the main problem impeding the utilization of such junctions is related to their control. An approach towards a higher degree of control is presented that is based on the analysis of single molecule manipulation experiments.     

Alternating‐Current Measurements in Scanning Electrochemical Microscopy,Part 1: Principle and Theory

The development of the scanning electrochemical microscope in ac mode is presented from both experimental and theoretical point of views. The experiments are performed with the ferri/ferrocyanide redox mediator as model system. Based on analysis of the frequency‐dependent collection efficiency, diffusion between the probe and the substrate is investigated, and analysis of time constants allows evaluation of the size of the sensing area under investigation. The experimental results are in good agreement with numerical simulations.     

Sorption Kinetics and Intracrystalline Diffusion of Methanol in Ferrierite: An Example of Disguised Kinetics

Sorption kinetics of methanol in large crystals of ferrierite have been studied in detail by interference microscopy (IFM) and infra-red microscopy (IRM). The IFM measurements yield the transient concentration profiles, thus providing a direct measurement of both the surface resistance to mass transfer and the internal diffusion resistance. It is shown that, for this system, the uptake rate is controlled by the combined effects of surface resistance and diffusion through the 8-ring channels (in the y-direction). Transport through the 10-ring channels (in the z-direction) appears to be blocked by surface resistance. Although the overall uptake curves conform well to the “root t law” the diffusivity values derived from the uptake curves vary widely depending on the assumed direction of diffusion. Even if the correct direction of diffusion is assumed, the diffusivity values derived from the uptake curves are seriously in error as a result of the intrusion of surface resistance. The existence of transport resistances at the crystal surface is clearly apparent from the transient concentration profiles but is not obvious from the uptake curves.     

Ru(TAP)3]2+-photosensitized DNA cleavage studied by atomic force microscopy and gel electrophoresis: a comparative study

Topological modifications of plasmid DNA adsorbed on a variety of surfaces were investigated by using atomic force microscopy (AFM). On mica modified with 3-aminopropyltriethoxysilane (APS) or poly-L-lysine, the interaction between the plasmid DNA and the surface "freezes" the plasmid DNA conformation deposited from solution, and the AFM images resemble the projection of the three-dimensional conformation of the plasmid DNA in solution. Modified mica with low concentrations of Mg(2+) leads to a decrease in the interaction strength between plasmid DNA and the substrate, and the AFM images reflect the relaxed or equilibrium conformation of the adsorbed plasmid DNA. Under these optimized deposition conditions, topological modifications of plasmid DNA were produced under irradiation in the presence of [Ru(TAP)(3)](2+) (TAP = 1,4,5,8-tetraazaphenanthrene), which is a non-intercalating complex, and were followed as a function of illumination time. The observed structural changes correlate well with the conversion of the supercoiled covalently closed circular form (ccc form) into the open circular form (oc form), induced by a single-strand photocleavage. The AFM results obtained after fine-tuning of the plasmid DNA-substrate interaction compare well with those observed from gel electrophoresis, indicating that under the appropriate deposition conditions, AFM is a reliable technique to investigate irradiation-induced topological changes in plasmid DNA.     

Langmur monolayers of cerebroside with different head groups originated from sea cucumber: Binary systems with dipalmitoylphosphatidylcholine (DPPC)

Surface properties (Langmuir monolayer) of two different cerebrosides which are extracted from the sea cucumber (Bohadschia argus) were investigated. A main difference in chemical structure of cerebroside between BAC-2a and BAC-4 is their head groups (glucose and galactose, respectively). Furthermore, miscibility and interaction between dipalmitoylphosphatidylcholine (DPPC) and cerebrosides (BAC-2a and BAC-4) in the monolayer have been systematically examined. The surface pressure (π)−area (A), the surface potential (ΔV)−A, and the dipole moment (μ)−A isotherms for monolayers of DPPC, cerebrosides, and their binary combinations have been measured using the Wilhelmy method and the ionizing electrode method. BAC-4 forms a stable liquid-expanded (LE) monolayer, whereas BAC-2a has a first-order phase transition from the LE phase to the liquid-condensed (LC) state on 0.15 M NaCl at 298.2 K. The fundamental properties for each cerebroside monolayer were elucidated in terms of the surface dipole moment based on the three-layer model [R.J. Demchak, T. Fort Jr., J. Colloid Interface Sci. 46 (1974) 191–202] for both cerebrosides and the apparent molar quantity change (Δs^γ, Δh^γ, and Δu^γ) for BAC-2a. In addition, their miscibility with DPPC was examined by the variation of the molecular areas and the surface potentials as a function of cerebroside mole fractions, the additivity rule. The miscibility was also confirmed by constructing the two-dimensional phase diagrams. The phase diagrams for the both binary systems were of negative azeotropic type. That is, the two-component DPPC/BAC-2a and DPPC/BAC-4 monolayers are miscible. Furthermore, the Joos equation for the analysis of the collapse pressure of binary monolayers allowed calculation of the interaction parameter and the interaction energy between the DPPC and cerebroside monolayers. The miscibility in the monolayer state was also confirmed by the morphological observation with Brewster angle microscopy (BAM), fluorescence microscopy (FM), and atomic force microscopy (AFM).     

Size fractionation of aquatic colloids and particles by cross-flow filtration: analysis by scanning electron and atomic force microscopy

The suitability of the combined application of environmental scanning electron microscopy (ESEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) for the evaluation of the ability of cross-flow filtration (CFF) to perform adequate size fractionation of freshwater colloids and particles was examined. ESEM and SEM imaging provided reference images of the CFF-generated fractions and, in estimating the experimental cut-off diameter of the membrane, provided evidence that separation was not consistent with nominal pore sizes of the membranes. However, analysis of the images showed that size distribution of CFF-generated fractions and the estimated cut-off diameter of the membranes were dependent on the advantages and limitations of the two imaging techniques. With both ESEM and SEM, best estimates of size cut-offs were lower than the nominal pore size of the membrane in the case of 0.45 μm membranes, but roughly accurate in the case of 0.1 μm pore size membranes. The results also suggested that the effectiveness of CFF may benefit from a pre-separation step using a minimally perturbing technique such as split thin-flow fractionation. AFM demonstrated the presence of colloids smaller than 50 nm in all fractions including the retentates, showing that CFF fractionation is not fully quantitative and not based on size alone. The results indicate that previous studies investigating trace element partitioning using CFF may need re-evaluation as the importance of particles and large colloids may be over-estimated.     

Experimental Testing of Lateral and Depth Resolution in Imaging Methods

A polymer laminate and a PA-PTFE blend were studied by various imaging methods (FT-IR, Raman, ESEM). Different lateral and depth resolution of the methods were used to gain complementary information on the structure of the materials. Radiation damage caused by the electron beam during ESEM investigation was studied by Raman global imaging.     

In situ scanning probe microscopy and new perspectives in analytical chemistry

The resolution of scanning tunnelling microscopy (STM) and other scanning probe microscopies is unprecedented but the techniques are fraught with limitations as analytical tools. These limitations and their relationship to the physical mechanisms of image contrast are first discussed. Some new options based on in situ STM, which hold prospects for molecular- and mesoscopic-scale analytical chemistry, are then reviewed. They are illustrated by metallic electro-crystallisation and -dissolution, and in situ STM spectroscopy of large redox molecules. The biophysically oriented analytical options of in situ atomic force microscopy, and analytical chemical perspectives for the new microcantilever sensor techniques are also discussed.     

New dimension in nano-imaging: breaking through the diffraction limit with scanning near-field optical microscopy

In recent years scanning near-field optical microscopy (SNOM) has developed into a powerful surface analytical technique for observing specimens with lateral resolution equal to or even better than 100 nm. A large number of applications, from material science to biology, have been reported. In this paper, two different kinds of near-field optical microscopy, aperture and scattering-type SNOM, are reviewed together with recent studies in surface analysis and biology. Here, near-field optical techniques are discussed in comparison with related methods, such as scanning probe and standard optical microscopy, with respect to their specific advantages and fields of application.