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Chemical force microscopy using probe tips subjected to liquid-phase chemical modification enables the study of intermolecular forces on a nanoscale, as well as imaging of the chemical inhomogeneity of a sample’s surface with high spatial resolution. However, in adhesive force measurements, the adhesive force between the tip and the sample could easily be affected by interactions caused by molecules in both the contact and the noncontact parts. A novel method involving local chemical modification of the tip is presented. The method is performed by adding a solution of a modification reagent in ethanol when the cleaned tip is approaching the substrate’s surface. The adhesive forces between the substrate’s surface and various types of tips were investigated using atomic force microscopy. This novel method could be helpful for increasing the resolution of chemical force microscopy and for measuring the contact area between the tip and the substrate’s surface.

We demonstrate here that light emission of an electroluminescent (EL) device was enhanced on chemically modified ITO areas over a patterned ITO anode with a self-assembled monolayer (SAM) of 4-chlorophenylphosphoryl dichloride (ClC(6)H(4)OPOCl(2): CPPDC) prepared by micro-contact printing (mu-CP). The EL device was fabricated by vapor-depositing a hole transport layer, a light emitting and electron transport layer, and a C(6)H(5)COOLi/Al bilayer cathode on the patterned ITO anode. The enhanced light emission under lower drive voltages on the modified areas can be interpreted by the increase in the work function of the ITO covered with the SAM measured with a Kelvin probe force microscope (KPFM) and thus the decrease in the hole injection barrier height. In addition, we could demonstrate the much smaller pattern images than the previously reported ones [F. Nüesch, Y. Li, L.J. Rothberg, Appl. Phys. Lett. 75 (1999) 1799] by the use of ink-pads.

We studied a surface modification technique for indium tin oxide (ITO) anodes without precleaning and resist banks for manufacturing organic light-emitting diodes (OLEDs) by inkjet printing. The ITO surface modified by inductively coupled plasma (ICP) with an optimized CF4/O2 (7:3) gas mixture improved both its hydrophilicity and its work function, while the resist surface treated by the plasma became hydrophobic. The resist and ITO surfaces treated by plasmas of various gas mixtures (i.e., CF4, CF4/Ar (1:2), CF4/O2 (x:1; x=1, 7/3, 4, and 9) were analyzed by X-ray photoelectron spectroscopy (XPS) of the C 1s, F 1s, O 1s, and In 3d5/2 core levels. On the uncleaned ITO surfaces modified by CF4/O2 plasmas, organic contaminants were removed more efficiently and the deposition of CFx on the remaining contaminants decreased with increasing oxygen. The amount of F in the form of InFx increased using the CF4/O2 (7:3) plasma in comparison with that using the CF4/Ar and CF4 plasmas. We investigated the effect of adding oxygen to CF4 on the change in gaseous species produced in the plasma chamber by mass spectrometry. In the CF4/O2 (7:3) plasma, the peak intensities of F+, HF+, F2+, O+, and O2+ were higher than those in the CF4 plasma. The results suggest that In2O3 was generated by the oxidation of indium with O, and InFx was generated by the fluoridation of indium with HF. By introducing InFx onto ITO surfaces using the CF4/O2 plasma, the hole-injection energy barrier could be reduced.

Biodevices composed of biomolecular layer have been developed in various fields such as medical diagnosis, pharmaceutical screening, electronic device, photonic device, environmental pollution detection device, and etc. The biomolecules such as protein, DNA and pigment, and cells have been used to construct the biodevices such as biomolecular diode, biostorage device, bioelectroluminescence device, protein chip, DNA chip, and cell chip. Substantial interest has focused upon thin film fabrication or the formation of biomaterials mono- or multi-layers on the solid surfaces to construct the biodevices. Based on the development of nanotechnology, nanoscale fabrication technology for biofilm has been emerged and applied to biodevices due to the various advantages such as high density immobilization and orientation control of immobilized biomolecules. This review described the nanoscale fabrication of biomolecular film and its application to bioelectronic devices and biochips.

Alignment behavior of a discotic liquid crystalline triphenylene (C8OBTP) on substrates coated with self-assembled monolayers (SAMs) of alkanethiol and asymmetrical alkyl disulfide was investigated by polarized microscopy. Discotic nematic (ND) and rectangular columnar (Colr) phases of C8OBTP shows a different alignment behavior depending on the element of SAMs. C8OBTP exhibits a fan-shaped texture on an alkanethiol SAM in Colr phase, while it has a tendency to show a planar alignment on asymmetrical alkyl disulfide SAM. The different elements of the SAM could influence the alignment behavior of discotic liquid crystal distinctly even in columnar mesophase which has highly self-cohesive forces of systems.

The motion of single conjugated molecules inserted in a self-assembled monolayer (SAM) matrix composed of a spherical bicyclo[2.2.2]octane derivative was observed using scanning tunnelling microscopy at room temperature. Two kinds of conjugated molecules, i.e. benzenemethanethiol and 4-biphenylmethanethiol, were inserted in the SAM matrix. It was revealed that the isolated single molecules exhibited two types of motions. One was the change in tilt of the molecular axis at a fixed position, and the other was lateral motion in the SAM matrix. These motions of the single molecules due to thermal energy at room temperature were most likely caused by large and mobile vacancies of single molecular defects in the SAM matrix.

Monolayers and multilayers from dipalmitoylphosphatidylethanolamine head labeled with nitrobenzoxadiazole (DPPE-NBD) were deposited as Langmuir–Blodgett (LB) films on silicon wafer or quartz glass plates at different deposition pressures at room temperature. The phase coexistence between the liquid and the solid phase was observed by atomic force microscopy, friction force microscopy, scanning surface potential microscopy (SSPM), scanning near-field optical microscopy (SNOM), and phase imaging by the tapping mode atomic force microscopy. The different methods reveal new features not imaged by a single method. There is no sharp boundary line between the liquid and the solid phase. Submicrometer solid domains are resolved above the phase transition together with multilayer needles. These needles are bilayer in thickness when deposition was carried below the equilibrium surface pressure of 19.6 mN m −1 and grow in height up to hundred nanometers upon increase of the deposition surface pressure. After some time, these very high needles equilibrate to bilayer height. SSPM and SNOM reveal big contrast between the liquid and the solid phase in the first case due to the large differences in the vertical component of the molecular dipoles in the two phases, and in the second case due to fluorescence self-quenching in the solid phase. Multilayer growth on top of a liquid phase in the center of the solid domains and liquid phase inside the solid domain could be resolved. Phase imaging of multilayers samples reveals features not seen in the AFM.

In order to improve the power efficiency of standard multilayered organic electroluminescent (EL) devices, i.e. ITO/HTL/ETL/M, enhanced electron and enhanced hole injection at an ETL/M and an ITO/HTL interface, respectively, were attempted, as well as enhanced electron–hole recombination at an HTL/ETL interface, by designing proper charge injection at these interfaces. Here, ITO, HTL, ETL, and M are abbreviations for an indium-tin oxide anode, a hole-transport layer, an electron-transport layer, and a metal cathode. The HTL and ETL materials used were N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) and tris(8-hydroxyquinoline)–aluminum (Alq3) respectively, whereas a vapor-deposited aluminum (Al) electrode was used as the metal cathode M. In order to enhance the charge injection at both electrodes, lowering the barrier heights and thinning the barrier thickness were attempted by controlling the work functions of the ITO and the Al electrode and doping the HTL and the ETL, respectively. For lowering the work function of the Al cathode and doping the Alq3 ETL, the reaction of hot Al atoms with alkali metal carboxylates during Al vapor deposition was utilized. To increase the work function of the ITO and doping the TPD HTL, the use of thin TPD films doped with various oxidizing reagents was examined at the ITO/HTL interface. The enhancement of the charge recombination at HTL/ETL was attained by increasing the interfacial areas, i.e. introducing a mixed layer of TPD and Alq3, or inserting a thin film of rubrene with a higher recombination efficiency.

The effect of alkali metal (Li + , Na + , K + , Rb + , and Cs + ) acetates and fluorides at an aluminum/tris(8-hydroxyquinoline) aluminum (Alq 3 ) interface on performance of organic electroluminescent (EL) devices is described. We also studied the effect of acetates with different metals, such as Mg 2+ and Al 3+ , on the performance of the EL devices. EL characteristics of the devices with Al/alkali metal acetates were compared with those of devices with Al/alkali metal fluorides or an Al cathode itself. We found that the bilayer cathodes with alkali metal acetates exhibited better device performance than the bilayer cathodes with alkali metal fluorides. The improvement can be attributed to lowering of the work function of the Al cathode and doping of Alq 3 with alkali metals that were formed by the higher reactivity of alkali metal acetates than alkali metal fluorides with hot Al atoms impinging on these salts during the vapor deposition. The enhanced electron injection resulted in more balanced charge-carrier injection and thus higher EL efficiencies.

The atomic-scale friction between an ordered organic monolayer and a rigid probing slider with an atomic-scale protuberance was investigated using a molecular dynamics method. The slider was used to model the tip apex used in atomic force microscopy. In order to control the normal load, three orthogonal springs and a feedback regulation unit were introduced. The protuberance, composed of a small number of atoms, brought about local and collective deformation of the monolayer and generated a friction force. Various frictional properties were investigated in terms of the size of the protuberance, the length of molecules in the monolayer, and the conditions, such as temperature, applied normal load, and some parameters of the external observation system. Lattice-resolved friction signals were obtained when the size of the protuberance was comparable to the cross-sectional area of the molecule.

A method of molecular dynamics is used to investigate friction anisotropy observed on a hexagonally packed organic monolayer of straight-chain molecules, which tilt in a specific direction. A rigid gold slider with a single atomic protuberance is used as a model of a typical atomic force microscope tip apex. The friction anisotropy is observed at 50 K, which is below the melting point of rotation around a long axis of the molecule. The anisotropic frictional behavior is that sliding in directions normal to the direction of the collective tilt of the molecules results in the maximum friction force. The origin of the anisotropy is attributed to anisotropy in lateral compliance in the monolayer.

▪ Abstract The electrostatic force microscope is one of many specialized tip sensors used in near-field microscopy. This type of microscope is realized by applying a voltage on a conducting AFM tip. It can be used to image samples that present a distribution of electrical properties on inhomogeneous materials as well as on nanostructures. This microscopy technique has been used to probe phase separation, chemical recognition, molecular orientation, and photo-induced charge separation in molecular photodiodes in Langmuir-Blodgett films.

Monolayers from dipalmitoylphosphatidylethanolamine head labelled with nitrobenzoxadiazole (DPPENBD) were deposited as Langmuir-Blodgett (LB) films on silicon wafers or quartz plates at different deposition pressures at room temperature. In some cases 0.5 mM NaCl was added in the water subphase or deposition was carried out at 7 °C. Phase coexistence between the liquid and the solid phases was observed by fluorescence microscopy, atomic force microscopy, friction force microscopy and scanning surface potential microscopy. This is the first observation of fluorescence self-quenching in a monolayer on a solid substrate. It is shown that there is no sharp boundary line between the liquid and solid phases. Submicrometre-sized solid domains are resolved above the phase transition together with multilayer structures. The addition of NaCl makes the domains uniform in size, circular in shape and with a sharp boundary line from liquid to solid phase. In this case domains are composed of several regions divided by liquid-phase channels. At low temperatures the domains are much more patchy in shape. For the first time scanning surface potential microscopy on a single-component system deposited as an LB film from pure water has been performed. The technique reveals a big contrast between the liquid and solid phases. Multilayer growth on top of a liquid phase in the centre of the solid domains could be resolved.

An accurate method to calibrate a commercial atomic force microscope (AFM) with commercial cantilevers for surface stress measurements was investigated. The bending of commercial rectangular cantilevers of the AFM was measured by laser beam deflection under a concentrated load mode and a bending moment mode. Good agreement between the experimental results and the theoretical predictions was obtained. The accurate calibration of the deflection angle for Δσ was possible with the rectangular cantilever by taking into account the dependence of the deflection angle on the laser spot position, a, on the cantilever. The cyclic voltammogram and the electrocapillary curve were measured in the double layer region of a gold thin film on the rectangular cantilever. In addition, it was concluded that a fairly good measurement of Δσ by triangular cantilevers was also possible as long as the deflection angle measurement was carried out with the same triangular cantilever at the same laser spot position a. The change in ...

To improve the stability and durability of organic EL devices, the mixed HTL layer was fabricated by co-deposition of TPD and Alq3 and the EL cell with the mixed HTL was compared with that with the conventional pure HTL. When more than 5 wt% of Alq3 was added in HTL, the increase in surface roughness of IT0 I TPD-Alq3/Alq3 by annealing was found by AFM to be reduced dramatically. In addition, the running durability was significantly improved by addition of a small amount of Alq3 (< 10 wt %), although the EL characteristics of the cells with mixed HTLs were slightly lowered, i.e. I- V and L V curves shifted to the higher voltages.

Amorphous organic thin films of N,N′‐diphenyl‐N,N′‐bis(3‐methylphenyl)‐(1,1′‐biphenyl)‐ 4,4′‐diamine (TPD) and 4,4′,4″‐tris(3‐methylphenylphenylamino)triphenylamine (m‐MTDATA) which function as hole transport materials were fabricated on slide glass plates by vapor deposition. By heating the films in air, the change in photoluminescence (PL) spectra for TPD was little, while that for m‐MTDATA was significant and a new broad peak appeared in the longer‐wavelength range. The latter change was pronounced in an oxygen atmosphere, but was suppressed in a nitrogen atmosphere. To clarify the difference in the effect of the storage conditions on the PL characteristics between TPD and m‐MTDATA, these two films were also studied by the scanning force microscopy techniques of atomic force microscopy (AFM) and friction force microscopy (FFM). It was found from the observation by AFM that the m‐MTDATA films showed no change in topography, while the TPD films were crystallized easily at room temperature in the air. How...

The change of surface and interface in bilayers of Alq (Tris-(8-hydroxyquinoline) aluminum) / TPD (N,N′-diphenyl-N,N′-bis-(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine)-doped polycarbonate (PC) films for organic electroluminescent devices was characterized by atomic force microscopy (AFM), SEM, and fluorescence microscopy, in the temperature range from R.T. to 250 °C under the air. As single layer films, the dip-coated TPD-doped PC film on indium-tin oxide (ITO)-coated glass and the vapor-deposited Alq films on various substrates showed good thermal stability compared with the vapor-deposited TPD film itself. However, in the bilayered structure of Alq / TPD-doped PC films, the Alq film as the overlaying layer was deteriorated readily, which was accelerated with increasing temperature and TPD concentration in the TPD-doped PC film.

We demonstrate here the microlithography of a thin chromium film on a quartz plate by using an atomic force microscope (AFM). Langmuir-Blodgett (LB) films of ω-tricosenoic acid were examined as resist films. By scanning an AFM tip under a high normal force, the ω-tricosenoic acid LB film deposited on the chromium film was scratched out. By the further use of wet etching of the chromium film, the process of submicrometer-scale lithography was demonstrated. Protection of the chromium film against etching by the use of multilayered LB films is discussed in terms of the probability of formation of tunnel defects entirely across the LB film.

An organic electroluminescent (EL) device (indium thin oxide N,N′ - diphenyl -N,N′- bis (3- methylphenyl )-(1,1′- biphenyl )-4,4′- diamine (TPD) tris (8- hydroxyquinoline )aluminum (Alq 3 ) Al ) was prepared to observe the degradation process of the EL device by fluorescence microscopy and atomic force microscopy (AFM). From AFM and fluorescence microscopy observations, we found morphological changes of the Al top electrode surface, e.g. the formation of a dome in the form of a hemisphere. The surface morphology of the Al electrode changed with time, from tiny to growing disks with central sharp peaks, the dome formation, and finally formed crescent shapes due to shrink of the domes. However, under the crescent shape or the dome, there was little change in the organic layer except for the formation of a crevasse. The dome was formed by gas evolution from the crevasse.

We previously developed a scanning near-field optical microscopy (SNOM) by combining SNOM and atomic force microscopy (AFM), i.e. scanning near-field optic atomic-force microscopy (SNOAM). We demonstrated that this combination can be used for fluorescence imaging for a localized nanoarea. In the present work, the combined microscope was further improved by increasing the sensitivity with the aid of an objective lens, a pin hole, and a photon counting system. Performance of the modified combined AFM-SNOM was examined with a test sample which was prepared by spin coating of mixture of fluorescent and non-fluorescent polystyrene beads with polyvinyl alcohol (PVA) on a cover glass. The lateral resolution of the microscope was also examined by measuring a standing evanescent wave, which was formed by reflecting the incident laser beam on a prism.

The morphological change of vapor-deposited films of TPD (N, N′-diphenyl-N, N′-bis-(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine) and Alq3 (Tris-(8-hydroxyquinoline) aluminum) and the interfacial degradation of Alq3/TPD bilayer were characterized by atomic force microscopy (AFM) and fluorescence spectroscopy, respectively, in the temperature range from room temperature to 80°C under an ambient atmosphere. The TPD and the Alq3 film are widely used as a hole transport and an emitter layer, respectively, in an organic electroluminescent device (an indium tin oxide (ITO) coated glass/TPD/Alq3/metal). As the substrate plate, an ITO coated glass or a slide glass was used in this work. The relative photoluminescence (PL) intensities of Alq3 to that of TPD in an Alq3/TPD and a TPD/Alq3 bilayer were increased with time. The changes were accelerated with increasing temperature and ascribed to quenching of photo-excited TPD by Alq3 diffusing into the TPD layer.

A highly localized evanescent light from a fiber probe with a 100 nm diameter aperture of a photon scanning tunneling microscope (PSTM) was used to realize localized photochemical processes in LB films of photochromic material. The localized photochemical processed region sized as small as 130 nm was obtained by using the transmission type PSTM.

The dependence of friction and wear on sliding parameters has been investigated with an atomic force microscope. Measurements have been performed on Langmuir-Blodgett monolayers. For the purpose of this study a special counterion polymer has been used to supply a facile insight into the friction and wear dependence on the scan velocity. With a minimum constant load in the order of 10(-8) N, wear has been observed to occur randomly at film defect sites but also on initially intact film areas. Wear is always accompanied by an increase of friction forces. A wearless friction dependence on the scan velocity could not be observed. The process of wear is discussed in terms of shear forces and adhesive contact forces. Whereas the plastic deformation at the film defect sites can be explained by shear forces, the wear process on initially defect free surfaces could be related to adhesive forces and quantified.

We demonstrate here that luminance increased more than linearly with an increase in current density of tris(8-hydroxyquinoline) aluminum (Alq3)-based electroluminescent (EL) devices and the EL efficiency reached ∼5 cd A−1 at 250 mA cm−2 when electron and hole injection was well balanced. The luminance–current curves were well fitted with a combination of a linear and a quadratic function of the current. The quadratic component can be attributed to additional singlet excited state (1Alq3*) formation through triplet–triplet (T–T) annihilation of triplet excited states (3Alq3*). The requirement of the well-balanced charge injection implies that the long-lived 3Alq3* was quenched efficiently by energy transfer to excess and colored Alq3−⋅ anion or Alq3+⋅ cation radicals in the emission zone when the charge injection was unbalanced. The short-lived 1Alq3* was not quenched appreciably.

Characteristics of electroluminescent (EL) devices were improved dramatically using indium tin oxide (ITO) chemically modified with H-, Cl-, and CF3-terminated benzoyl chlorides. By the use of reactive –COCl groups, ITO surfaces were modified quickly and the work function of the modified ITO was changed widely depending upon the permanent dipole moments introduced in the para- position of benzoyl chloride. We also compared the performance of the EL devices with ITO modified with different binding groups (–SO2Cl, –COCl, and –PO2Cl2) of p-chlorobenzene derivatives. Finally, we examined the correlation between the change in the work function and the performance of the EL devices by the chemical modification and found that the enormous increase in ITO work function up to 0.9 eV is possible using phenylphosphoryl dichloride with a CF3-terminal group in the para-position.

The process of vision is an example of a light induced change in the properties of a bilayer membrane. As a biomimetic visual system, photoelectrochemical control of the ion-blocking ability of the Langmuir-Blodgett (LB) film was demonstrated on a gold optically semi-transparent electrode (Au OTE) coated with multilayers containing photoresponsive amphiphilic compounds. A stable monolayer was formed by spreading a chloroform solution of a photosensitive ionic amphiphilic compound on an aqueous subphase containing an ionic polymer with opposite charge. In addition to the increase in stability, the cross sectional area of the amphiphilic molecule usually increased on polyion complexation from that of the same amphiphilic molecule in the absence of the ionic polymer. Deposition of the monolayer onto the solid substrate as a very homogeneous LB film was possible. The increase in molecular area allows various photochemical reactions, which otherwise do not occur due to the steric hindrance, to proceed in the resulting LB films. A rapid decrease in emission of the polyion complexed pyrene LB films was observed upon UV irradiation in air. Application of this very sensitive quenching procedure to optical memory will be also presented as one of photochemical amplification systems.

An SbCl5-doped N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) thin film was studied as a hole-injection layer in low-molecular-weight organic electroluminescent (EL) devices. EL characteristics of devices with a TPD hole-injection layer doped with other oxidizing reagents, such as iodine, FeCl3, and tris(4-bromophenyl)aminium hexachloroantimonate were compared with that of SbCl5-doped TPD. The device with SbCl5-doped TPD on a cleaned indium–tin–oxide (ITO) substrate exhibited the best performance of all the devices studied. The improvement in device performance was attributed to an increase in work function of ITO due to acid formation as a result of hydrolysis of SbCl5 and by thinning the tunneling barrier for hole injection due to formation of the space charge region in highly doped TPD with SbCl5.

Most problems in photomask fabrication such as pattern collapse, haze, and cleaning damage are related to the behavior of surfaces and interfaces of resists, opaque layers, and quartz substrates. Therefore, it is important to control the corresponding surface and interface energies in photomask fabrication processes. In particular, adhesion analysis in microscopic regions is strongly desirable to optimize material and process designs in photomask fabrication. We applied the direct peeling (DP) method with a scanning probe microscope (SPM) tip and measured the adhesion of resist patterns on Cr and quartz surfaces for photomask process optimization. We measured adhesion and frictional forces between the resulting collapsed resist pillar and the Cr or the quartz surface before and after the sliding. We also studied the effect of surface property of the Cr and quartz surfaces to resist adhesion. The adhesion could be controlled by surface modification using silanes and surface roughness on Cr blanks. We also discuss the relationship between the adhesion observed with the DP method and the properties of the modified surfaces including water contact angles and local adhesive forces measured from force-distance curves with an SPM.

The sections in this article are Introduction Surface Treatment of Substrate Chalcogenide Electrodes Adsorption of Acids to Chalcogenides Adsorption of Organic Sulfur Compounds Surface Modification Dialkyl Chalcogenide Compounds Thiols Dithiols, Disulfides, and Other Sulfur Compounds Characterization and Applications Summary Acknowledgments

The sections in this article are Introduction Electrode Preparation General: Transparent Conducting Oxide Films Cleaning of Substrate Surfaces Cleaning with Solvents Cleaning by Heating and Irradiation Cleaning by Stripping Lacquer Coatings Cleaning in an Electrical Discharge Cleaning Cycles Cleaning of Organic Glass Chemical Methods of Film Deposition Spraying Pyrolysis Chemical Vapor Deposition Sol-gel Process Physical Methods of Film Deposition Evaporation Sputtering Reactive Ion Plating Pulsed Laser Deposition Other Techniques The Properties of Transparent Conducting Oxide Electrode Surfaces Electrode Modification General SnO2 ITO ZnO TiO2 and ZrO2 Polypyridyl Ru Complexes and Organic Dyes as Sensitizers Short-chain Alkanoic and Benzoic Acids Long-chain Organic Acids Other Oxides Organosilanization General Wide Bandgap Transparent Conducting Oxide Electrodes SnO2 TiO2 and ZrO2 ZnO ITO Large Bandgap Oxide Electrodes Potential Applications Tuning the Work Function of Electrodes Correlation of Device Performance with Changes in the Work Function Other Possible Applications SnO2 ITO ZnO TiO2 Other Oxides Summary Acknowledgement

Use of a thin step etched optical fiber probe in a scanning near-field optical/atomic-force microscope (SNOM/AFM) produced frictional imaging. The probe was fabricated by the etching of an optical fiber to decrease its diameter and sharpen the tip end with a HF solution and by irradiating a CO2 laser beam to bend the tip. The spring constant of the thin probe is 100 times smaller than that of a conventional optical fiber probe, which allows the probe to be used as a contact AFM mode and in frictional imaging.

In order to clarify the propagation mechanism of dark spots in an organic multilayered electroluminescent device, in situ electroluminescence microscopy as well as photoluminescence (PL) microscopy and Auger electron spectroscopy of the degraded device was carried out. The difference in local PL spectra between the dark spots and the normal surface area was also observed by using scanning near‐field optical/atomic force microscopy. The growing mechanism of the dark spots was proposed from these observations.

The scanning near‐field optical microscopy imaging of specimens in liquid and of cultured cells in aqueous solutions is reported. A scanning near‐field optical/atomic‐force microscope (SNOM‐AFM) was developed, in which the scanning of an optical‐fiber probe cantilever over the specimen was controlled by noncontact mode AFM (dynamic mode AFM). This imaging mode reduces damage to the probe and soft specimens. The resonant frequency of the probe cantilever decreased 20% to ≊14 kHz and the Q factor decreased by a factor of 8 to ≊30 in water, compared with these values in air, which was sufficient to perform SNOM‐AFM imaging in liquid.

We demonstrate here balancing between hole and electron injection in bilayer organic tris(8-hydroxyquinoline)aluminum (Alq3) based electroluminescent (EL) devices by measuring current-voltage (I-V) characteristics of single-carrier devices with different thickness and by comparing the device performance with various chemically modified ITO. We measure I-V characteristics due to holes in hole-only bilayer devices with various modified ITO anodes and those due to electrons in electron-only single-layer devices with C6H5COOLi(2 nm)/Al cathode. Here, hole-only devices are those, in which only holes are carriers and the current due to electrons is negligible. We found that the I-V characteristics observed for the hole-only bilayer devices with UV-ozone and ClC6H4COCl treated ITO were comparable to the I-V characteristics for the electron-only single-layer device of ITO(as-cleaned)/Alq3(150 nm)/C6H5COOLi(2 nm)/Al. In other words, hole and electron injections are well balanced when we use UV-ozone and ClC6H4COCl treated ITO anodes. EL characteristics have shown that luminance decreased clearly for bilayer organic EL devices with an Al cathode where electron injection was not enhanced significantly. The decrease in EL efficiency can be attributed to unbalanced hole and electron injection. The unbalanced injection results in excess of one carrier type that does not contribute to light emission, and results in deactivation of 1Alq3 at high currents due to quenching 1Alq3 by large excess of Alq3+. in the emission zone.

We report EL characteristics of blue organic electroluminescent (EL) devices with a hole transport layer (HTL) as an emitter i.e. ITO/NPD/BCP/Alq3/Cs(0.5 nm)/Al. Here, ITO, NPD, BCP, and Alq3 are abbreviations for indium-tin-oxide, 4,4'-bis[N-(1-naphthyl)-N-phenylamino]- biphenyl, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, and tris(8-hydroxyquinoline) aluminum, respectively. Three different chemically modified ITO electrodes were used. As a hole-injecting buffer layer, copper phthalocyanine (CuPc) or 4,4',4''-tris-(3-methylphenylphenylamino) triphenylamine (MTDATA) was used in this study. We found that the luminance increased less than linearly with an increase in current for all EL devices studied even when hole and electron injection were enhanced. The luminance loss in the device is attributed to quenching singlet excited states (1NPD*) by large excess radical cations (NPD+.) accumulated in the emission zone due to large overlap between a fluorescence spectrum of 1NPD* and an absorption spectrum of NPD+.. In addition, 1NPD* can be also quenched by radical anions (NPD-.) when excess electrons are injected.

Origins of peak broadening in a histogram of measured adhesive forces were studied. A patterned sample was prepared by a microcontact printing method on a sputtered gold film, on which CH3‐ and COOH‐terminated regions were produced. Gold surfaces were also chemically modified homogeneously by a self‐assembling method in solution. Their surfaces were topographically different, i.e. (i) an Au(111)‐terrace‐rich film prepared by vacuum deposition at a high temperature and (ii) sputtered gold films on cover glass with different grain sizes obtained by different deposition times. These sample surfaces were all CH3‐terminated by self‐assembled monolayers with n‐eicosanethiol. The adhesive forces were mapped in water by pulsed‐force‐mode atomic force microscopy with a CH3‐terminated tip. The main factor of peak broadening in the histogram was the topographic effect. Namely, the change in the grain sizes and the change in multiplicity of contacts between the tip and convexities of the grains resulted in the distri...

We demonstrate the direct measurement of molecular diffusion at organic/organic interfaces of organic electroluminescence devices by use of a scanning near-field optical atomic force microscope. Our preliminary study shows that the degradation of an electroluminescence device is partly caused by crystallization of the organic layers. Because the initial stage of degradation cannot be observed by microscopic methods, nanoscale optical properties of the interface in multilayer systems are currently receiving a great deal of attention. Defects of organic electroluminescence devices were investigated using a scanning near-field optical atomic force microscope. This instrument is capable of measuring both a topographic and a fluorescence image at the same time. The defect area and other areas are clearly observed and time-resolved near-field fluorescence spectra demonstrate emission of the different species. These results suggest that defects occur at the organic solid interface, and that energy transfer occurs from excited TPD, as donor, to Alq, as acceptor.

Indium-tin-oxide (ITO) is the most widely used material as a transparent electrode due to its excellent transparency and high conductivity. The devices based on bare ITO, however, exhibited inefficient hole injection due to insufficient high work function and required high drive voltages. Thus, various surface treatments of ITO have been attempted to change the work function of ITO in order to reduce the hole injection barrier height. Electroluminescent (EL) characteristics of devices were improved dramatically using ITO chemically modified with H-, Cl-, and CF3-terminated benzoyl chlorides. By the use of reactive -COCl groups, ITO surfaces were modified quickly and the work function of the modified ITO was changed widely depending upon the permanent dipole moments introduced in p-position of benzoyl chloride. We also compared the performance of the EL devices with ITO modified with different binding groups (-SO2Cl, -COCl, and -PO2Cl2) of p-chlorobenzene derivatives. Finally, we examined the correlation between the change in the work function and the performance of the EL devices by the chemical modification and found that the enormous increase in ITO work function up to 0.9 eV is possible using phenylphosphoryl dichloride with a CF3-terminal group in p-position.

In order to improve power efficiency of organic electroluminescent (EL) devices, i.e., ITO/TPD/Alq3/Al, enhanced electron and hole injection at Alq3/Al and ITO/TPD interface, respectively, was attempted by designing proper charge injection at both interfaces. Enhanced charge recombination at TPD/Alq3 was also demonstrated. Here, ITO, TPD, Alq3, and Al are abbreviations for indium-tin-oxide, N,N'-diphenyl-N,N'-bis(3-methyl-phenyl)-1,1'-biphenyl-4,4'-diamine, tris(8-hydroxyquinoline) aluminum, and metal aluminum, respectively. Enhanced electron injection by introducing a thin layer of Li salts of fluoride, acetate, and benzoate was described. We have found that the electron injection was improved in the order of Li+, Na+, K+, Rb+, and Cs+, and Cs salts exhibited the best EL performance. Chemical modification of ITO has been attempted to fine-tuning the work function of ITO in order to reduce hole injection barrier height. EL characteristics were improved dramatically using ITO modified with H-, Cl-, and CF3-terminated benzoyl chlorides. By using reactive -COCl groups, ITO surfaces were covered quickly and the work function of ITO was changed widely depending upon permanent dipole moments introduced in para-position of benzoyl chlorides. Correlation between the change in the work function of ITO and the EL characteristics was examined. The improvement of charge recombination was attained by increasing the interfacial areas, i.e. introducing a mixed layer of TPD and Alq3, or inserting a thin film of rubrene with a higher recombination efficiency.

Photoconductive devices (photodiodes) were constructed by the deposition of polyimide LB multilayer films which possessed different chemical structures, i.e., a triphenylamine unit as an electron donor (D), tetraphenylporphyrin as a sensitizer (S), and aromatic polyimide as an electron acceptor (A). Two types of photodiodes with E/D/S/A/ and E/A/S/D systems were prepared on a semitransparent gold electrode (E). The dependence of each number of D, S, and A layers on the photocurrent behavior was examined to discuss the electron transfer in each layer.

A novel chemically sensitive imaging mode based on adhesive force detection by previously developed pulsed-force-mode atomic force microscopy (PFM-AFM) is presented. PFM-AFM enables simultaneous imaging of surface topography and adhesive force between tip and sample surfaces. Since the adhesive forces are directly related to interaction between chemical functional groups on tip and sample surfaces, we combined the adhesive force mapping by PFM-AFM with chemically modified tips to accomplish imaging of a sample surface with chemical sensitivity. The adhesive force mapping by PFM-AFM both in air and pure water with CH 3 - and COOH-modified tips clearly discriminated the chemical functional groups on the patterned self-assembled monolayers (SAMs) consisting of COOH- and CH 3 -terminated regions prepared by microcontact printing (μCP). These results indicate that the adhesive force mapping by PFM-AFM can be used to image distribution of different chemical functional groups on a sample surface. The discrimination mechanism based upon adhesive forces measured by PFM-AFM was compared with that based upon friction forces measured by friction force microscopy. The former is related to observed difference in interactions between tip and sample surfaces when the different interfaces are detached, while the latter depends on difference in periodic corrugated interfacial potentials due to Pauli repulsive forces between the outermost functional groups facing each other and also difference in shear moduli of elasticities between different SAMs.

The function of a systematized and assembled group of molecules is essentially the same as that of a single molecule. The most fundamental functions of a molecular system are its electron and ion conducting properties. These involve information transduction and energy conversion, although their conduction mechanisms are different. They are seen in polymeric molecules, molecular clusters, and molecular assembly. A polymeric molecule should be considered as a unit repeating material. Bilayer Langmuir-Blodgett (LB) membranes are well-organized molecular assemblies which are prepared utilizing their self-assembling properties. A forced preparative method gives ultrathin material, ultrafine particles, STM prepared molecular materials, etc. They all have their own characteristics and distinguishing functions. In addition, the properties of all molecules remain more or less the same when the molecules are clustered and assembled. The polymers, the molecular assemblies, and the molecular clusters present us not only with their own functions, but also with a stage where the functional molecules can act effectively. In this chapter, the molecular design and fabrication of conducting polymers, molecular assemblies, and molecular clusters are described as one of the most essential, fundamental molecular functional materials.