Takeshi Sakakibara

Effect of Ionization Potential of Hole Transport Layer on Device Characteristics of Organic Light Emitting Diode with Oxygen Plasma Treated Indium Tin Oxide

We have investigated the contribution of the oxygen ions and electrons, and of the kinetic energy of these species on oxygen plasma treatment of indium tin oxide (ITO) electrode. In the case of the treatment by positive oxygen ions with kinetic energy of 50 eV, the luminance increased markedly with a lowering of the operating voltage in the organic light emitting diode (OLED). The change in the device characteristics was attributed to an effective removal of organic contaminants from the ITO surface, leading to enhanced hole injection from ITO to a hole transport layer (HTL) due to an increase in work function of the ITO. Moreover, the highest luminance and luminous efficiency were obtained in the OLED having HTL with ionization potential of 5.4 eV. These results have suggested that OLEDs fabricated using the oxygen plasma treated ITO can give the best device performance by the selection of an optimum HTL.

Effect of oxygen plasma treatment of indium tin oxide for organic light-emitting devices with iodogallium phthalocyanine layer

We demonstrate the improvement of device lifetime by organic light-emitting devices with an iodogallium phthalocyanine (IGaPc) layer fabricated on indium tin oxide (ITO) treated with positive oxygen ions. The device performance improves markedly as follows: (a) long-term stability (an operational half-lifetime of 100 h at high current density of 100 mA/cm2), and (b) the driving voltage is unchanged. The change in the device characteristics is attributed to changes in IGaPc molecular configurations during the growth process, leading to enhanced hole injection from the ITO to IGaPc layer.

Trap States of Tris-8-(Hydroxyquinoline)Aluminum Degraded by Blue Laser Using Thermally Stimulated Current Method

We investigated the photodegradation phenomena of tris-8-(hydroxyquinoline)aluminum (Alq3) film after irradiation with a blue laser of 442 nm to identify the contributions of the excited states of Alq3 molecules. The photodegraded Alq3 film showed decreases in fluorescence lifetime and carrier transport ability markedly. These photodegradation phenomena are considered to be due to an increase in the energy distribution of trap states detected from the analysis by a thermally stimulated current (TSC) method, in connection with the orientation of neighboring Alq3 molecules, e.g., the disordered aggregation states of Alq3 molecules.

High heat-resistant ceramic coating

A ceramic coating material consisting mainly of SiO/sub 2/ and Al/sub 2/O/sub 3/ with high heat-resistant and good adherent property to metals was obtained. This material has been tested as a protection material for the application to equipment required to be heated up to around 1000 degrees centigrade in an iron manufacturing plant. Through the various experiments including the variation of the additive metal oxide and the selection of the particle size in the suspension, we obtained a ceramic coating material that can be also used for the heat and flame resistant electrical insulation with good adherent property to metals. In this paper, experimental results for several characteristics of the coating layer of this material painted on steel sheets are introduced.

Surface States of Mica and Contact Charging

Through investigation of photoelectron emission from the surface of mica with ultraviolet irradiation, it has been clarified that the surface states of mica play an important role not only in the electron emission but also in the electronic conduction of the surface. To study this in more detail, photothresholds of the electron emission from the surface have been measured for Muscovite mica treated with fast atom bombardment (FAB) under various conditions caused by contact charging generated by contact with a biased conductive brush. In addition, another static approach was performed with corona charging for deposition of charges on the surface of mica. The photothreshold for FAB-treated specimens increased markedly from 5.0 eV to 5.8 eV with respect to an increase of negative contact charging. Such change of the photothreshold has not been observed for FAB-treated specimens after corona charging. Such a phenomenon is concluded to be caused by the transport of electrons between the conductive brush and the surface states of mica in the range of 5.0 to 5.8 eV. In this paper, we will demonstrate that the surface states of mica are closely related to contact charging as well as to the electronic conduction state of the surface.

Conduction property of surface of mica treated with fast atom bombardment

Variations in the surface conduction of cleaved mica due to surface treatment by Ar fast atom bombardment (FAB) were observed. Treatment of the mica surface was carried out, varying the duration of FAB. While a surface current of the order of 10/sup -13/ A was measured at a voltage of 117 V for a mica specimen in the virgin state, it was increased by FAB and saturated at the order of 10/sup -8/ A with treatment for 20 minutes. Moreover, for a sufficiently treated surface, no change in the current due to relative humidity was observed. As the result of an examination by electron spectroscopy for chemical analysis, it has been found that the peaks for potassium and sodium almost completely disappeared after the FAB treatment. The variation of the geometrical micro structure of the specimen surface was also observed with an atomic force microscope. The conduction property of the modified surface of mica has been discussed, in accordance with the results of the examination of the angle of contact of moisture, and taking into account the variation in the quantity of soluble ions in the mica surface.<<ETX>>

Photoelectron emission from SiO/sub 2/ surface oxidized on Si wafer

We have experimentally studied the relationship between photoelectron emission and surface current for SiO/sub 2/ layers on n-type Si. The photothreshold energy of untreated SiO/sub 2/ increased with increasing surface current from 5.05 to 5.3 eV, keeping a constant value up to about 20 pA of surface current. For the FAB (fast atom bombardment) treated specimen, the photothreshold energy decreased from 5.05 to 4.65 eV with increasing surface current. Such variations might be effected by surface conditions including surface states, surface structure, and electronic conduction in the surface.

Photoelectron emission from FAB-treated polyethylene film

We have reported that the threshold energy for photoelectron emission varied with the electronic surface current for the inorganic material, e.g. Muscovite mica or SiO/sub 2/ film on Si wafer. For the mica specimen, the surface current changes from ionic current to electronic current by the fast atom bombardment (FAB) treatment, and the electronic surface current has an effect on photoelectron emission. For the farther study of the surface properties of solid dielectrics, we have investigated about the photoelectron emission and surface conduction phenomenon for polyethylene film treated by FAB. The threshold energy of photoelectron emission increases with the decreasing of the light intensity. This shift in photothreshold is thought to correspond to the so-called quasi-Fermi level in the surface of polyethylene same as the case of mica. On the other hand, the threshold energy does not change with respect to the FAB treatment. The increase in surface current according to the increasing of relative humidity was observed. This shows that the surface current for polyethylene is ionic even for the FAB treated specimen different from the case of mica specimens. We discuss about the relationship between such phenomena and surface condition for polyethylene in comparison with inorganic material.

Dielectric characteristics of heat-resistant ceramic coating

We have investigated the electric properties of ceramic coating film consisting mainly of SiO/sub 2/, Al/sub 2/O/sub 3/, and TiO/sub 2/. The ceramic film on a steel plate was found to exhibit excellent adhesive stability upon heating at approximately 1000/spl deg/C. In particular, film calcined in N/sub 2/ showed the higher electric resistance and lower dielectric loss factor. These results suggest that the ceramic coating material can give the best coating performance with high insulating properties by calcination in N/sub 2/.

Effect of electrode on charge transfer phenomena of charge transport material

It is shown that the interface charge transfer between the charge transport layer (CTL) and anode is affected by the work function of the anode metal. The charge transfer of the CTL/anode interface under low electric field is greatly influenced by a difference of injection barrier between the localized energy state of the CTL and the work function of the anode. From the results of dark current measurements under high electric field, we conclude the cause to be the transfer of electrons between the HOMO level of the CTL and the valence band of the anode metal. On the other hand, the photothreshold energies for the specimens with anodes of different work function are not affected by electric field. These experimental findings suggest that surface states do not exist on the CTL-3. Moreover, as the LUMO level of the CTL-3 is about 2.7 eV, the photothreshold energy should correspond to the LUMO level of the CTL-3. We conclude that the CTL has two electronic energy levels and that surface states do not exist.