Jung-Myoung Kim

Optical behavior and surface morphology of the azobenzene functionalized dendrimer in Langmuir and Langmuir–Blodgett monolayers

Abstract We synthesized a dendrimer containing light switchable azobenzene group. The chemical structure was verified by using NMR and UV spectroscopy. We firstly investigated the monolayer behavior by using π–A isotherm with light irradiation at the air/water interface. As a result, the monolayer of dendrimer with azobenzene group showed the reversible photoswitching behavior by the isomerization of azobenzene group in the periphery. From the absorbance spectrum by UV irradiation and heat treatment, we can see that the absorbance in the UV region decreases with the increases of the UV irradiation time, but LB monolayers not absorbance shift. The results indicate that the azobenzene dendrimer could be photoisomerized reactions. In the surface morphology by AFM, the introduction of azobenzene group coagulates G4-48 Azo dendrimer and forms network dendrimers. This result strongly suggests that a dendrimer with azobenzene group can be applied to high efficient photoreaction device of molecular level.

The spectroscopic and morphological behavior of merocyanine dye Langmuir–Blodgett films

Abstract We fabricated the optical system of merocyanine dye (MD) using the Langmuir–Blodgett (LB) method with various mixing ratio and the number of layers to control its optical characteristic. The optical characteristic of MD LB films was evaluated by UV spectroscopy and their surface morphologies were also observed using atomic force microscope. The optical characteristics of MD LB film were controlled by mixing ratio and LB layer deposited, which includes the potential control of the performance of photo-electric devices. The optical characteristic and surface morphology were also observed when MD LB films were modified using UV irradiation or heat treatment. As a result, we obtained the quantitative optical characteristic by controlling the mixing ratio with archidic acid and LB layer deposited. Also, the mixing ratio dependent surface morphology was observed. The experimental results strongly suggest that high efficient photo-electric devices can be obtained by LB method and modified by second treatment such as UV irradiation, heat treatment, and nano-lithography.

The response characteristics of organic gas using QCA coated with polymeric materials

Abstract The new system for identification of organic vapours and analysis method of mechanism between organic vapours and sensitive materials were attempted using the resonant resistance and resonant frequency of Quartz Crystal Analyzer (QCA). The resonant resistance shift means rheological changes in sensitive LB films occurred by the adsorption of organic vapours, while the resonant frequency shift represent the mass of organic vapour loaded in or on the sensitive LB films. Thus we can obtain more accurate response mechanism of organic vapour using the resonant frequency and resonant resistance diagram. The organic vapour response mighit be devided by two type; surface adsorption and penetration into sensitive material. The interface between inner side and surface of sensitive LB films is not clear yet. Organic vapours had different positions in the Frequency-Resistance (F-R) diagram as to the kinds and concentrations. Thus F-R diagram can be applied to the development of one-channel gas sensing system...

Near-field optical microscopy with video signal processor to apply a CCD imaging device as a variable area photo-sensor for improving operability and spectrum mode imaging

We have developed a video signal processor for improving the operability and function of scanning near-field optical microscopy (SNOM). The video signal processor applies a CCD imaging device as a variable area photo-sensor in the SNOM unit instead of conventional photo-detectors. The signal processor converts the intensity of a selected area in video frames to a numerical value with a rate of 30 Hz. Consequently, the CCD imaging device can be used as a photo-detector of variable areas and positions for detecting a small area of a optical probe position. The need for a precise optical axis alignment is relaxed due to the large sensing area of the CCD device. Using the video signal processor, near-field optical and topographic images have been obtained by SNOM/AFM system simultaneously. By adding a spectrometer between the SNOM unit and the CCD device, the spectrum signal of selected wavelength ranges has been monitored by the video signal processor to provide an optical image.

Optical transmission/fluorescence reaction and features in ultra-thin dye films by scanning near-field optical/atomic force microscopes (SNOM/AFM)

We will illustrate the topographical structure and optical structure of the merocyanine dye LB films obtained by the scanning near-field optical/atomic force microscopy (SNOM/AFM). In the topographic image of the mutual mixed LB film shows more rough surface structure than that of our expectation, and is grained with average size about 50 nm. In the optical transmission and fluorescence image, the elevated area means higher transmission than lower parts. In the continuous measurement on these dyes and the mutual mixed films, the appearance of near-field optical transmission images showed a certain dependence on the kinds of dyes with shift and increase of transmission and the mutual mixing ratios of dyes. These experimental results suggest that there is a certain kind of interaction between these two dyes. This suggests also that the J-aggregate formation and fluorescence change are affected by the domain shape and excitation laser.

Characteristics of dendrimer functionalized with azobenzene for the application to nano-level photo-switching device

If we can make characterization of nano-structure with functionality, the molecular level device will be obtained. The dendrimer has been well known as a promising macromolecules for a building the organized nanostructure, which of the size can be controlled and which of periphery can be terminated by various functionalities. In this study, we synthesized dendrimers containing light switchable units, azobenzene group. Their chemical structure was verified by using NMR study and UV spectroscopy. To apply to the molecular level switching device or data storage system using Langmuir-Blodgett(LB) film, we firstly investigated the monolayer behavior using /spl pi/-A isotherm at air/water interface. And then the surface pressure shift of monolayer by light irradiation was also measured. As a result, the monolayer of dendrimer with azobenzene group showed the reversible photo-switching behavior by the isomerization of azobenzene group in their periphery. This result strongly suggests that a dendrimer with azobenzene group can be applied to high efficient photo-switching device of molecular level.

The monitoring of J-aggregate behavior of merocyanine dye based on electrochemical QCM

Abstract In this paper, the electrical behavior of a quartz crystal microbalance (QCM) with dye LB film in UV irradiation has been examined by the impedance analysis method. The equivalent electrical parameters, such as resonant frequency ( f 0 ) and resistance ( R 1 ), were investigated. The preparation conditions, using a mixing ratio of fatty acids, subphase effect, and π-A isotherms were investigated to obtain the J-aggregated dye LB film and its optical characteristics were evaluated by UV spectroscopy. The resonant frequency was originated without considering mass adsorption and dependence on the mixing ratio with arachidic acid or resultant absorbance peak at the J-band (optical characteristics). This result could be described by the observation of morphological change before and after UV irradiation, i.e. the resonant frequency shift had a connection with the morphological change. This result strongly suggests that the QCM can be applied to monitor the structural change or optical characteristics of an organic film on the QCM.

The study on optical characteristics and surface morphologies for J-aggregates formation of merocyanine dye LB films

Abstract In this study, we investigated the optical characteristics of merocyanine dye Langmuir-Blodgett (LB) film and had analysis combined with surface morphology using AFM. And preparation condition for merocyanine dye LB film was determined. As a result, domains could be observed in the J-aggregate LB film and domain size was dependent on the mixing ratio. And the domain had very homogeneous two-dimensional structure. After UV irradiation, the domain size was decreased or disappeared correspond to the decrease of absorbance peak, which mean the dissociation of J-aggregate. These results can suggest the modulation of structure by light

The fabrication of gas sensor using the resonant frequency and admittance of quartz crystal analyzer

The adsorption and desorption behavior of organic vapours for polymeric sensitive LB film was investigated using the resonant frequency and resistance method of a quartz crystal microbalance. A new method was used to analyze the response mechanism between organic vapours and polymeric sensitive LB films. When the organic vapours were adsorbed into sensitive LB films, the rheological changes in LB films were observed by the quartz microbalance resonant method. To investigate the characteristics of organic vapours, a resonant frequency-resonant resistance (F-R) diagram was used. The quantitative information about organic vapours adsorbed and quantitative change of sensitive LB films can be obtained. In experimental results, the response of organic vapours can be separated into two types; surface adsorption and penetration into sensitive LB films. The response mechanism between organic vapours and sensitive LB films can be obtained from the F-R diagram.

Analysis of the phase transition behaviors of PMMA and PVAc blends using quartz crystal analyzer

Abstract This paper shows that an AT-cut quartz crystal analyzer is applicable to the study of phase change phenomena of polymer blend thin films. The phase transition and separation phenomena of blend films of poly (methyl methacrylate) (PMMA) and poly (vinyl acetate) (PVAc) cast from ethyl acetate have been investigated by quartz crystal analyzer (Q.C.A.). The resonant frequency and resonant admittance are measured simultaneously and the mass change and viscoelastic change of the polymer blend thin films are analyzed.