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Copper-phthalocyanine (CuPc) thin films on MoS2 surfaces were investigated by noncontact atomic force microscopy (NC-AFM). Submolecular resolution was successfully obtained in both topographic and dissipation images of CuPc monolayers. For topographic contrasts, the influence of short-range chemical interactions is particularly considered while the dissipation contrasts are discussed in relation to the tip-induced molecular fluctuations. Molecularly-resolved NC-AFM image was also obtained on CuPc multilayer, which revealed the structural difference between the monolayer and multilayer surfaces. The energy dissipation measured on these surfaces showed distinctive difference reflecting the different structural stabilities in the films. Furthermore, local surface modification of CuPc monolayer was demonstrated by NC-AFM. This is a direct evidence for the existence of energy transfer from the vibrating cantilever to the molecules through dissipative tip–sample interactions.

Alkanethiol self-assembled monolayers formed on Au(111) surfaces were investigated by noncontact atomic force microscopy (NC-AFM). Dodecanethiol monolayers prepared at 78 °C were imaged by NC-AFM, which revealed that the film is composed predominantly of two different phases of c(4×2) superlattice structures. The obtained molecular-scale NC-AFM contrasts are discussed in comparison with previously reported scanning tunneling microscopy images. We found that the energy dissipation image exhibits a clear difference in its molecular-scale contrast between the two phases. Possible origins of the difference are discussed in relation to the fluctuation and/or stability of the packing structures.

A friction force microscope study in ultrahigh vacuum was conducted on an atomically flat SrTiO3(001) surface, where SrO and TiO2 domains were distinguished by the difference in friction force. It is revealed that the friction on the SrO became stronger with water adsorption relative to the TiO2 layer. The selective change in friction is attributed to the chemical reaction occurring on the SrO layer, which is supported by the results of x-ray photoelectron spectroscopy.

A remanent polarization of 130±3 mC/m[2], large among the values reported for organic materials, and rectangular D–Ehysteresis curves were realized in synthesized vinylidene fluoride (VDF) oligomer [CF[3](CH[2]CF[2])[17]I]film evaporated onto a platinumsurface around liquid nitrogen temperature. The results suggested that the VDF oligomer film has an extremely high crystallinity, and the electric dipoles arrange almost perfectly perpendicular to the filmsurface, and that a Lorentz local field factor of ferroelectric VDF oligomer crystals is nearly zero. Moreover, the obtained value of the coercive field, which was larger than those of ferroelectric polymers, might be attributed to the steric hindrance arising from the existence of iodine atoms at the VDF oligomer chains.

The distributions of surface charges or surface potentials on biological molecules and electrodes are directly related to various biological functions and ionic adsorptions, respectively. Electrostatic force microscopy and Kelvin-probe force microscopy (KFM) are useful scanning probe techniques that can map local surface charges and potentials. Here, we report the measurement and analysis of the electrostatic and capacitive forces on the cantilever tip induced by application of an alternating voltage in order to discuss the feasibility of measuring the surface charge or potential distribution at solid/liquid interfaces in various liquid media. The results presented here suggest that a nanometer-scale surface charge or potential measurement by the conventional voltage modulation techniques is only possible under ambient conditions and in a non-polar medium and is difficult in an aqueous solution. Practically, the electrostatic force versus dc voltage curve in water does not include the minimum, which is used for the surface potential compensation. This is because the cantilever oscillation induced by the electrostatic force acting on the tip apex is overwhelmed by the parasitic oscillation induced by the electrostatic force acting on the entire cantilever as well as the surface stress effect. We both experimentally and theoretically discuss the factors which cause difficulties in application of the voltage modulation techniques in the aqueous solutions and present some criteria for local surface charge and potential measurements by circumventing these problems.

Simultaneous near field scanning optical and atomic force microscopy with a microfabricated photocantilever reveal both optical and topographical distributions. The cantilever tip changes the evanescent field into scattering light, and this scattering light is detected with a photodiode fabricated in the tip of the cantilever. The cantilever deflection signal leads to atomic force images. The resolution for imaging the evanescent field variation was 20 nm (λ/30). The near field optical and atomic force images indicate that the same point of the cantilever tip generates both optical and atomic force signals. This method is a new approach to optical and topographical microscopy with nanometer resolution.

We describe applications of a cantilever with a lead zirconate titanate (PZT) piezoelectric film as self-sensing to dynamic force microscopy (DFM) combined with Kelvin probe force microscopy (KFM). We adopted a frequency modulation (FM) detection method not only to stabilize the imaging conditions in our DFM but also to enhance the sensitivity for the detection of electrostatic forces in KFM measurement. We deposited Alq3 [tris (8-hydroxyquinolinato) aluminum] thin films and aluminum (Al) electrode patterns on an indium tin oxide (ITO)/glass substrate by vacuum evaporation using shadow masks. The surface structures and local surface potential of Alq3 films on metals were investigated using our DFM/KFM instrument to study the local electrical properties at the molecule–metal interface. The photosensitive organic material sample can be in a completely dark environment because no optics are required for cantilever deflection sensing in our experimental setup.

金沢大学フロンティアサイエンス機構, Copper-phthalocyanine (CuPc) monolayers and cobalt-phthalocyanine monolayers deposited on Au(111) surfaces were investigated by frequency modulation atomic force microscopy (FM-AFM). Submolecular-resolution topographic images were successfully obtained for both samples. Despite the similar molecular geometry of the two molecules, they showed clearly different contrasts in the topographic images. The origin of the contrast is discussed in terms of the relationship of the molecular orbitals and the chemical interaction between the tip and the molecules. In addition, a molecular-resolution surface potential (SP) image was obtained on CuPc monolayers using Kelvin probe force microscopy (KFM) utilizing FM-AFM. The molecular-scale SP contrast was explained by the electric dipole moment at the organic/metal interface. This result suggested the possibility of the detection of the single molecular dipole moment by KFM. © 2010 American Institute of Physics.

The device performances of organic thin film transistors are often limited by the metal–organic interface because of the disordered molecular layers at the interface and the energy barriers against the carrier injection. It is important to study the local impedance at the interface without being affected by the interface morphology. We combined frequency modulation atomic force microscopy with scanning impedance microscopy (SIM) to sensitively measure the ac responses of the interface to an ac voltage applied across the interface and the dc potential drop at the interface. By using the frequency-modulation SIM (FM-SIM) technique, we characterized the interface impedance of a Pt electrode and a single pentacene grain as a parallel circuit of a contact resistance and a capacitance. We found that the reduction of the contact resistance was caused by the reduction of the energy level mismatch at the interface by the FM-SIM measurements, demonstrating the usefulness of the FM-SIM technique for investigation of the local interface impedance without being affected by its morphology.

Dielectric properties of biomolecules or biomembranes are directly related to their structures and biological activities. Capacitance force microscopy based on the cantilever deflection detection is a useful scanning probe technique that can map local dielectric constant. Here we report measurements and analysis of the capacitive force acting on a cantilever tip at solid/liquid interfaces induced by application of an alternating voltage to explore the feasibility of the measurements of local dielectric constant by the voltage modulation technique in aqueous solutions. The results presented here suggest that the local dielectric constant measurements by the conventional voltage modulation technique are basically possible even in polar liquid media. However, the cantilever deflection is not only induced by the electrostatic force, but also by the surface stress, which does not include the local dielectric information. Moreover, since the voltage applied between the tip and sample are divided by the electric double layer and the bulk polar liquid, the capacitive force acting on the apex of the tip are strongly attenuated. For these reasons, the lateral resolution in the local dielectric constant measurements is expected to be deteriorated in polar liquid media depending on the magnitude of dielectric response. Finally, we present the criteria for local dielectric constant measurements with a high lateral resolution in polar liquid media.

We have studied a local deposition method based on dynamic-mode AFM using a hollow tip with an aperture. In this method, liquid droplets are deposited onto a conductive substrate through the aperture by applying an electric voltage pulse and are imaged using the same AFM tip immediately after the deposition. In this study, we applied this method to local deposition of a glycerol solution, which can be utilized in the printed electronics and the biosensor fabrication technology. The solution in the hollow was covered with a hydrophobic ionic liquid with an extremely low vapor pressure to prevent the evaporation of the solution because the quick evaporation heavily affected the dynamic-mode AFM operation. We succeeded in the stable deposition of an array of ultrasmall droplets, which contained an added salt and possible involatile residues in the glycerol solution.

Organic ultrathin transistors with a 3-μm-length channel were fabricated using dimethylquinquethiophene molecules. The local structures of the films and electric potential profiles across the channels were investigated by Kelvin probe force microscopy with the gate electrode grounded. We found that the local carrier mobility was much higher for the second-layer regions than for the monolayer regions from potential profiles measured while the gate electrode was electrically grounded. However, the macroscopic carrier mobility increased only slightly by increasing the number of molecular layers. One of the possible reasons for this contradiction was the large contact resistance at the source/channel interface, which was apparently observed in the potential profiles.