The threshold voltage of Coulomb staircase using organic molecules was analyzed by extending our previous model with only consideration of the metal/organic film interfacial space charge to the generalized one. The generalized model is helpful to examine coupling capacitance in organic double barrier tunneling junction (DBTJ). The current-voltage (I-V) characteristic of metal/polyimide (PI)/rhodamine-dendrimer (Rh-G2)/PI/metal junction was analyzed using this generalized model. The calculation results were in good agreement with our experimental data.

It is well known that the existence of electrically resistive film layers formed on contact surfaces increases contact resistance and it causes a nonlinear relationship between voltage and current observed in a contact layer. Nonlinear distortion voltages can be detected by our sensitive detection system based on the dual frequency method when a thin film exists on the surface. In this study, multilayer films of polyimide (PI) was used as an ideal material of ultra thin film, because of electrically good insulator with simple molecular structure, to study non-linearity through metal-insulator-metal contact. The number of deposited layers between one and twenty one were formed on three types of substrates; (a) evaporated gold on a glass plate, (b) gold plate and (c) evaporated gold on gold plate, to obtain good insulating film. Where each layer of PI film has 0. 4 nanometer thickness. A pin contact was made by pressing a bent gold wire on the PI film. It is concluded that [1]; the second-order distortion voltage increases exponentially as the film thickness increases, [2]; polarity of the surface potential of PI depends on the film thickness, and that I-V characteristic depends on the polarity of the surface potential.

The formation of single monolayer of liquid crystalline molecules, 4-n-pentyl-4-cyanobiphenyl (5CB), deposited by the evaporation method in the air, was confirmed with the surface potential measurement. The surface potential increased with the time of evaporation, and the 3- or 4-minute evaporation at a source temperature of 110 gave the saturated potential, indicating the formation of single monolayer. Single monolayer formation was also supported by the comparison of the UV-visible absorption for evaporated film with LB monolayer. Positive potentials were built at the surface, indicating that CN group faces the substrate.

The polarized absorption measurement was employed to investigate the orientational order of the 4-n-4-pentyl-cyanobiphenyl (5CB) film of sub-nanometer thick. It was confirmed that this optical technique is simple but effective to observe the second orientational order parameter, S2, of the organic ultra thin film at the interface region.

Triboelectric generator is attracting much attention as a power source of electronics application. Electromotive force induced by rubbing is a key for triboelectric generator. From dielectric physics point of view, there are two microscopic origins for electromotive force, i.e., electronic charge displacement and dipolar rotation. A new way for evaluating these two origins is an urgent task. We have been developing an optical second-harmonic generation (SHG) technique as a tool for probing charge displacement and dipolar alignment, selectively, by utilizing wavelength dependent response of SHG to the two origins. In this paper, an experimental way that identifies polarity of electronic charge displacement, i.e., positive charge and negative charge, is proposed. Results showed that the use of local oscillator makes it possible to identify the polarity of charges by means of SHG. As an example, positive and negative charge distribution created by rubbing polyimide surface is illustrated.

Recent technologies of organic film devices are reviewed. New technologies of fabrication and characterization of organic thin films, electro-mechanical conversion materials, and applications for electrical and optical devices are discussed. In this review paper, especially organic light emitting diodes, tunneling junctions using polyimide Langmuir-Blodgett films, tunneling spectroscopy and high-density recording, plastic actuators using conducting polymers, molecular self-assembly process for fabricating organic thin film devices are reviewed.

The surface potential built across vacuum deposited phthalocyanine (Pc) films on aluminum electrode was investigated by means of electro-modulation spectroscopy. The sandwich-type cells with thin air gap, which becomes a good insulator were used in order to avoid the influence of charge injection. The existence of the surface potential at the metal/organic-material interface induced 1f referenced electro-reflectance (ER) signals. As a result, the surface potential built across vacuum deposited Pc films on aluminum electrode was estimated to be 1.25 V.

The Maxwell-Wagner type interfacial charging processes were characterized by time-resolved second harmonic generation method (TR-SHG) using three typical organic double-layer devices, i.e., IZO/α-NPD/Alq3/Al for OLED and ITO/PI/α-NPD (or pentacene)/Au for MIM elements. Devices with a PI blocking layer represent one-carrier transport case, while the OLED is a typical two-carrier transport device. It is found that three devices show similar behavior of charging of the electrodes, however, interfacial charging behavior was different from case to case. On the basis of Maxwell-Wagner model, the different transients were analyzed with consideration of carrier species responsible for the interfacial charging. The observed TR-SHG well support the results of I-V measurements.

Displacement current measurement (DCM) is widely used as a method for analyzing carrier behaviors of organic devices. Carrier behaviors are analyzed using transient currents. On the other hand, electric-field-induced optical second-harmonic generation (EFISHG) measurement is capable of directly probing carrier motions in organic devices, where the migration of electric field stemmed from carriers is measured. In this study, we employed the DCM and EFISHG measurements for analyzing interfacial carrier behaviors in Au/pentacene/polyimide (PI)/indium-tin-oxide (ITO) double layer organic devices, where interfacial accumulated charges and electric fields formed in the pentacene layer were explored.

To clarify the carrier transport mechanism of pentacene field-effect transistors (FETs), the FET characteristics was examined in the region where the drain-source voltage Vds is lower than the saturated voltage. The Ids-Vds characteristics shows the ohmic behavior in the low voltage region, whereas it shows the characteristics explained by the Maxwell-Wagner model. This result clearly indicates that carrier injection from source makes a significant contribution to the carrier transport. It was also shown that the change of Ids-Vds characteristics from the ohmic behavior to the Maxwell-Wagner behavior is similar with the I-V characteristics change from the ohmic to the space charge limited current behavior observed in metal-organic film-metal junctions, including metal-pentacene-metal.

By using electric-field-induced optical second-harmonic generation (EFISHG) measurement, we investigated interfacial carrier behavior in organic solar cells (OSCs) with a blocking layer of bathocuproine (BCP). Results evidently showed that the Maxwell-Wagner type excess charges accumulate on both pentacene/C60 and C60/BCP interfaces. Also, the measurement under short-circuit and open-circuit conditions clearly showed the different photo-induced carrier behaviors in the OSCs devices. Our work proved that the dielectric nature of OSCs dominates the operation of our OSCs and the EFISHG technique is very effective to characterize the dielectric performance of the OSCs.

Time-resolved microscopic optical second harmonic generation (TRM-SHG) imaging measurement revealed quantitatively the potential drop at the electrode contact of pentacene field effect transistors (FET). An activation of the SH signal at the edge of Ag-source electrode indicates the presence of large potential drop at pentacene-Ag contact during device operation, whereas negligible potential drop was observed at pentacene-Au contact. These findings agree with the injection characteristics of electrodes owing to the relationship between the work function of the metal and the HOMO level of pentacene.

By using electric field induced second harmonic generation (EFISHG) and Capacitance-Voltage (C-V) measurements, we studied carrier behaviors in ITO/polyimide (PI)/poly(3-hexylthiophene)(P3HT)/Au diodes. Photoillumination caused the threshold voltage shift in the C-V, and agreed well with the shift probed by the EFISHG. Results suggested trapped electrons were accumulated in the PI layer.

Carrier transport characteristics of TIPS-pentacene single crystalline film were controlled by changing the deposition condition of the blade-coating method. Anisotropic carrier transport in the single crystalline grain was visualized by means of the time-resolved microscopic optical second harmonic generation (TRM-SHG) measurement. Slow deposition yields the film with high mobility and large transport anisotropy. For molecular crystals, intermolecular interaction can be modified easily by changing the process condition.

We developed a measuring system that measures both capacitance and transmittance of a liquid crystal (LC) cell simultaneously. We then studied the dynamic orientation process of nematic LC molecules between two-photochromic command surfaces. The command surfaces consist of a polymer monolayer bearing azobenzene side chains and they are deposited on glass substrate coated with indium-tin-oxide by using the Langmuir-Blodgett technique. The capacitance of LC cells increased and decreased alternately due to orientation transition in LC molecules by irradiating ultraviolet (UV) and visible light, respectively. Similarly, with the alternating irradiation of UV and visible lights, the transmittance of the LC cell changed periodically. Mean tilt angles of LC molecules under irradiation of UV and visible lights were evaluated from the results of capacitance and transmittance. It was found that the transient transmittance response was delayed to the transient capacitance under the UV irradiation. This result corresponds to that the LC molecules in homeotropic mode tend to remain the optical alignment.

We examined the current-voltage (I-V) characteristic of metal/polyimide/rhodamine-dendorimer/polyimide/ metal junctions prepared by the Langmuir-Blodgett (LB) technique. At a temperature of 32.8 K, a step structure was observed in the I-V characteristic, whereas it was not observed for the junctions without rhodamine-dendorimer. The step structure was very similar to that seen in so-called Coulomb staircase. On the basis of the model of Coulomb blockade, the possibility of single electron tunneling via rhodamine-dendrimer (Rh-G2) molecule as a quantum dot was discussed.

Triboelectric generators have been attracting much attention as electrical power sources in scientific communities and industries. Based on dielectric physics, two microscopic routes are available as current sources: One is charge displacement and the other is dipolar rotation. We have been investigating these routes as power sources for triboelectric generation. In other words, dipolar energy transfer process during a course of depolarization has the potentiality to be utilized as triboelectric generator. In this paper, we show that polyimide polymer film with permanent dipoles, i.e., PMDA-ODA polyimide, can provide current source capacity enhanced at elevated temperature, which is in good agreement with our idea based on dipolar energy mode of triboelectric generator. That is, permanent dipoles rotate quickly at elevated temperature, and act as an enhanced current source in the dipolar energy source model of triboelectric generator.

We fabricated junctions with a porphyrin polyimide (PORPI) monolayer, and then investigated the electron transport properties of the junctions from the current-voltage (I-V) and d2V/dI2-V measurements. Polyimide LB films without porphyrin were used as tunneling barriers. One large peak was seen at a voltage around 1.9 V, due to the excitation of electron transitions in PORPI molecules, whereas a step structure was not observed in the I-V characteristic.