| POLYMERS Vol.68 No.12 |
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COVER STORY
Simultaneous Topography and Other Properties Mapping with Scanning Probe Microscopy |
| COVER STORY: Highlight Reviews |
| Visualization of Subsurface Nanostructures by Atomic Force Microscopy | Kei KOBAYASHI |
| <Abstract> Several researchers have recently demonstrated visualization of subsurface features with a nanometer-scale resolution using various imaging schemes based on atomic force microscopy. These techniques have several common features, such as excitation of a cantilever base and/or sample at very high frequencies, tip oscillation at a beat frequency due to non-linear tip-sample interactions, and cantilever oscillation at its contact resonance frequency. We recently visualized Au nanoparticles buried in a polymer matrix with a thickness of up to 900 nm by atomic force acoustic microscopy, and found that the contact resonance frequencies are affected by the subsurface Au nanoparticles. Then we also visualized Au nanoparticles buried 300 nm in the polymer matrix by measurement of the thermal noise spectrum of a cantilever with a tip in contact to the polymer surface, namely scanning thermal noise microscopy. The result convinced us that the subsurface contrasts are given by the modulation of the viscoelastic properties of the polymer surface by the subsurfae features. Keywords: Atomic Force Microscopy / Subsurface Imaging / Contact Resonance / Scanning Thermal Noise Microscopy |
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| Distributions of Three-Dimensional Structures and Properties in Polymer Membranes Affecting Performances of Fuel Cells | Junji INUKAI |
| <Abstract> The three-dimensional strutures of polymer membranes are different at surfaces and inside bulks, thus in general, phycial/chemical properties are also different. Morphologies and properties of membrane surfaces are now visualized by current-sensing atomic force microscopy. The increase in performances of polymer electrolyte will be discussed based on the three-dimentional structures of polymer electrolyte used for fuel cells. Keywords: Fuel Cell / Morphology / Ionic Conduction / Atomic Force Microscopy |
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| COVER STORY: Topics and Products |
| Mechanical Properties of Graphene Nanoribbon Studied by Atomic Force Microscopy | Shigeki KAWAI |
| <Abstract> An on-surface chemical reaction allows us to synthesize atomically-defined nano carbon materials such as graphene nanoribbons. This paper describes recent measurements of mechanical and structural properties of graphene nanoribbons by high-resolution atomic force microscopy. Graphene nanoribbons were manipulated, in both lateral and vertical directions, by the tip of an atomic force microscope at low temperature. Via careful investigation of the measured forces, we found that the structural superlubricity plays a role in such measurements, otherwise high friction prevents the manipulation of large graphene nanoribbons. Keywords: Atomic Force Microscopy / Graphene Nanoribbon / On-Surface Reaction / Mechanical Property / Chemical Structure |
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| Electrical Property of Donor/Acceptor Polymer Blend Films Studied by Conductive Atomic Force Microscopy | Hiroaki BENTEN |
| <Abstract> Blend films consisting of a polymer donor and a polymer acceptor have gained increasing attention as a promising material candidate for polymer solar cells. The photovoltaic performance of the blend film critically depends on the charge (hole and electron) transport within the film, which is influenced by the crystallization, aggregation, and phase separation of the constituent polymers. Therefore, high-resolution techniques for characterizing the electrical properties of the blend films are of prime importance for further material and device improvement. Conductive atomic force microscopy (C-AFM) is a useful method for directly observing the charge-transport characteristics of donor/acceptor polymer blend films with a high resolution on the order of nanometers. Electrical characterizations by C-AFM visualizes the morphological features of the blend film that govern the charge transport, which is difficult to elucidate by macroscopic current-voltage measurements. Keywords: Conductive Atomic Force Microscopy / Polymer Solar Cell / Charge Transport / Conjugated Polymer / Polymer Blend / Phase Separation |
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| Vibrational Spectroscopy and Imaging in the Nanoscale | Norihiko HAYAZAWA |
| <Abstract> In order to see the vibrational properies of materials in the nanoscale, tip-enhanced Raman spectroscopy (TERS) and its imaging are introduced. Seeing the nanocale beyond the diffraction limit of light has been one of the dreams in the optics field, which is now realized by the use of near-field optics based on the plasmonic properties of nano-sized noble metals. When a nano-sized matallic structure such as a metallic probe of a scanning probe microscope is irradiated by a light field, localized surface plasmon polaritons can be induced resulting in the enhanced electric field localized at the tip apex. Scanning the enhanced electric field as a nanoscale light source for Raman spectroscopy can visualize the vibrational properities under the tip apex, in which the size is comparable to the diameter of the tip (～20 nm). In recent works, TERS proved its potential for sub-nanometer spatial resolution and single molecule sensitivity in various environments, liquid, ultrahigh vacuum and low temperature as well as under ambient temperatures. Keywords: Near-Field Optics / Raman / Nanophotonics / Plasmonics |
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| AFM Mechanical Measurement of Cells in Multicellular System | Yuki FUJII, Takaharu OKAJIMA |
| <Abstract> Mechanical properties of living cells as soft materials are strongly associated with their biological functions. Atomic force microscopy (AFM) has been widely used to quantify the elastic modulus of single cells at the subcellular resolution. Using a developed AFM technique for characterizing the spatial distribution of the elastic modulus of cells in multi-cellular systems, we observed a mechanical domain structure in the epithelial cell monolayer (cell sheet) where the spatial correlation length of the intracellular elastic modulus was longer than the distance between adjacent cells. Moreover, it was found that the mechanical domains disappeared when actin filament and junctional proteins polymerizations were inhibited. These results indicate that the mechanical domain structures observed by AFM inherently arises from the formation of a large-scale actin filament structure via E-cadherin-dependent cell-cell junctions. Keywords: Atomic Force Microscopy (AFM) / Cell Mechanics / Multicellular System / Spatial Distribution / Elastic Modulus / Cell Monolayer / Actin Filament / Junctional Protein |
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| Electrochemical Nano-Imaging using Scanning Ion Conductance Microscopy | Yuji NASHIMOTO, Noriko TAIRA, Kosuke INO, Hitoshi SHIKU |
| <Abstract> Scanning ion conductance microscopy (SICM) is a nanopipette-based microscopy that visualizes topography of a sample under physiological conditions. The main advantage of SICM is that it can detect topological imaging noninvasively and control a distance between nanopipette and sample at nanoscale. This article highlights the recent applications of SICM to acquire multifunctional information from biological samples at nanoscale. The first is surface charge mapping. The design and use of specific voltage routines could extract the information of surface charge with the topological information. The second is the conductance measurement across tight junctions. Using double barrel format, while one barrel provides the traditional SICM feedback, another barrel measures the conductivities simultaneously. The third is the evaluation of mRNA localization of single cells. The subcellular cytosol was collected and the gene expression analyzed based on the nanoscale topological mapping by SICM. Integration of SICM with these measurement techniques will open up new avenues in biological study at nanoscale. Keywords: Scanning Ion Conductance Microscopy / Nanopipette / Electrochemical Imaging / Charge Mapping / Single-Cell Analysis / Cellular Imaging / mRNA Localization / Tight Junction |
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| Electrical Conductivity Evaluation of Conducting Polymer Nanofibers by Scanning Probe Microscopy | Takeshi SHIMOMURA |
| <Abstract> I introduce the usage of scanning probe microscopy (SPM) for the electrical measurement of conducting polymer nanofibers. SPM seems to have three prominent operations, that is, observation, manipulation and direct measurement. At first, we used the observation mode in scanning force microscopy (SFM or AFM) for the counting of the number of the nanofibers bridging the electrodes, and decided the carrier mobility of the nanofibers from the field effect transistor characteristics. Next, we used the manipulation mode of SPM for cutting the nanofibers one by one on the electrodes and measured the conductivity of a single nanofiber. Finally, the electric potential of the nanofibers embeded in the polymethacrylate biased by the outside electrodes was investigated directly by Kelvin force microscopy (KFM) of SPM. SPM is one of the powerful tools for measuring the electric properties of the polymeric materials in the nanoworld. Keywords: Scanning Probe Microscope / Manipulation / Kelvin Prove Microscopy / Conducting Polymer / Nanofiber / Field Effect Transistor |
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| Polymer Science and I: A Personal Account |
| With Diverse Networks | Ken ALBRECHT |
| <Abstract> This essay briefly describes my research career and relation to science that started when I was born in Mainz (Germany). The importance of having connections to diverse networks including scientists from other fields will be also emphasized based on my personal experience. |
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| Front-Line Polymer Science |
| Toward Higher Efficiency in Organic Light-Emitting Diodes: Realization of the Highest Reverse Intersystem Crossing Among All Organic Materials | Hironori KAJI |
| <Abstract> The pioneering work by Dr. Tang has motivated many industrial and academic researchers all over the world to develop highly efficient organic light-emitting diodes (OLEDs). Among the researches, a new type of emitters, named thermally activated delayed fluorescence (TADF), was discovered by Prof. Adachi, which opens a new horizon of OLEDs. Now, many groups including our group have developed new TADF materials resulting in OLEDs with high external quantum efficiencies. However, reverse intersystem crossing (RISC), the key process of TADF, is still inefficient when both S1 and T1 have the same charge transfer (CT) character. On this issue, recent studies predict that intervention of locally excited triplet (3LE) states between the two CT-type S1 (1CT) and T1 (3CT) is expected to trigger fast spin-flip. Here, we will show a new material design concept to further accelerate RISC. The design realizes excellent energy matching of the three states, 1CT, 3CT, and 3LE, with sufficient spin-orbit coupling. Keywords: Organic Light-Emitting Diodes / Reverse Intersystem Crossing / Thermally Activated Delayed Fluorescence / Donor-Acceptor Systems / Materials Science |
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