Sang-Jin Cho

Synthesis and characteristics of NH2-functionalized polymer films to align and immobilize DNA molecules

We developed a method to use NH2-functionalized polymer films to align and immobilize DNA molecules on a Si substrate. The plasma-polymerized cyclohexane film was deposited on the Si substrate according to the radio frequency plasma-enhanced chemical vapor deposition method using a single molecular precursor, and it was then treated by the dielectric barrier discharge method in a nitrogen environment under atmospheric pressure. Changes in the chemistry of the surface functional groups were studied using X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy. The wettability of the surfaces was examined using dynamic contact angle measurements, and the surface morphology was evaluated using atomic force microscopy.We utilized a tilting method to align λ-DNA molecules that were immobilized by the electrostatic interaction between the amine groups in NH2-functionalized polymer films and the phosphate groups in the DNA. The DNA was treated with positively charged gold nanoparticles to make a conductive nanowire that uses the DNA as a template. We observed that the NH2-functionalized polymer film was useful for aligning and immobilizing the DNA, and thus the DNA-templated nanowires.

Growth behavior of titanium dioxide thin films at different precursor temperatures

The hydrophilic TiO2 films were successfully deposited on slide glass substrates using titanium tetraisopropoxide as a single precursor without carriers or bubbling gases by a metal-organic chemical vapor deposition method. The TiO2 films were employed by scanning electron microscopy, Fourier transform infrared spectrometry, UV-Visible [UV-Vis] spectroscopy, X-ray diffraction, contact angle measurement, and atomic force microscopy. The temperature of the substrate was 500°C, and the temperatures of the precursor were kept at 75°C (sample A) and 60°C (sample B) during the TiO2 film growth. The TiO2 films were characterized by contact angle measurement and UV-Vis spectroscopy. Sample B has a very low contact angle of almost zero due to a superhydrophilic TiO2 surface, and transmittance is 76.85% at the range of 400 to 700 nm, so this condition is very optimal for hydrophilic TiO2 film deposition. However, when the temperature of the precursor is lower than 50°C or higher than 75°C, TiO2 could not be deposited on the substrate and a cloudy TiO2 film was formed due to the increase of surface roughness, respectively.

Physical properties of metal-doped zinc oxide films for surface acoustic wave application

Metal-doped ZnO [MZO] thin films show changes of the following properties by a dopant. First, group III element (Al, In, Ga)-doped ZnO thin films have a high conductivity having an n-type semiconductor characteristic. Second, group I element (Li, Na, K)-doped ZnO thin films have high resistivity due to a dopant that accepts a carrier. The metal-doped ZnO (M = Li, Ag) films were prepared by radio frequency magnetron sputtering on glass substrates with the MZO targets. We investigated on the optical and electrical properties of the as-sputtered MZO films as dependences on the doping contents in the targets. All the MZO films had shown a preferred orientation in the [002] direction. As the quantity and the variety of metal dopants were changed, the crystallinity and the transmittance, as well as optical band gap were changed. The electrical resistivity was also changed with changing metal doping amounts and kinds of dopants. An epitaxial Li-doped ZnO film has a high resistivity and very smooth surface; it will have the most optimum conditions which can be used for the piezoelectric devices.

A STUDY OF THE CHARACTERISTICS OF ORGANIC-INORGANIC HYBRID PLASMA-POLYMER THIN FILMS BY CO-DEPOSITION OF TOLUENE AND TEOS

We investigated the interaction of varied plasma power with ultralow-κ Toluene–TEOS hybrid plasma-polymer thin films, as well as changes in electrical and mechanical properties with various mixture ratios of toluene and TEOS (tetraethoxysilane). Using the plasma enhanced chemical vapor deposition (PECVD) method, organic–inorganic hybrid polymer thin films were deposited on silicon(100) substrates under 150°C of wall temperature and a ratio of TEOS to toluene. Toluene and TEOS were utilized as organic and inorganic precursors, and hydrogen and argon were used as bubbler and carrier gases, respectively. In order to compare the differences in the electrical and the mechanical properties of plasma polymerized thin films, we grew the hybrid polymer thin films under 30 W of RF (radio frequency using 13.56 MHz) power with various ratios of toluene to TEOS. The as-grown polymerized thin films were first analyzed by Fourier Transform Infrared (FT-IR) spectroscopy, and Atomic Force Microscopy (AFM). The results of FT-IR showed that the hybrid polymer thin films were totally fragmented and polymerized with increasing RF power. AFM showed that polymer films with smooth surface could be grown under various deposition conditions. An impedance analyzer was utilized for the measurements of capacitance values for dielectric constants and the thin films were analyzed for hardness and Youngs modulus using a nanoindenter.

A study on the characteristics of plasma polymer thin film with controlled nitrogen flow rate.

Nitrogen-doped thiophene plasma polymer [N-ThioPP] thin films were deposited by radio frequency (13.56 MHz) plasma-enhanced chemical vapor deposition method. Thiophene was used as organic precursor (carbon source) with hydrogen gas as the precursor bubbler gas. Additionally, nitrogen gas [N2] was used as nitrogen dopant. Furthermore, additional argon was used as a carrier gas. The as-grown polymerized thin films were analyzed using ellipsometry, Fourier-transform infrared [FT-IR] spectroscopy, Raman spectroscopy, and water contact angle measurement. The ellipsometry results showed the refractive index change of the N-ThioPP film. The FT-IR spectra showed that the N-ThioPP films were completely fragmented and polymerized from thiophene.

Surface Plasma Treatment of Polyimide Film for Cu Metallization

Surface modification of polyimide films by oxygen/argon atmospheric pressure plasma (APP) was studied for copper metallization under several conditions, including plasma treatment time, gas ratio, and power of radio frequency (RF; 13.56MHz) plasma. The effects of APP treatments on the surface properties of polyimide (PI) films were investigated in terms of Fourier-transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM), and contact angle measurements. The results showed that the root-mean-squared (RMS) roughness of untreated PI films was 1.48nm, increasing to 2.08, 2.17, and 2.57nm after plasma treatment at 200, 400, and 600W, respectively. At the same time, the contact angle of untreated PI film was 73.0 � and reduced to 25.9, 20.3, and 17.3 � after plasma treatment at 200, 400, and 600W, respectively. The lowest contact angle and the maximum RMS roughness were 13 � and 8.50nm, respectively. Those values were achieved by oxygen/argon APP at an RF plasma power of 600W and with 50 repetitions. Also, X-ray diffraction (XRD) was used to examine the Cu surface structure in the Cu/PI system to indicate the quality of Cu foil. The highest Ið111Þ=Ið200Þ ratio was 1.89 at an RF power of 600W by oxygen/argon APP treatment. # 2011 The Japan Society of Applied Physics

STUDY OF LOW-k DIELECTRIC ORGANIC POLYMER THIN FILMS DEPOSITED BY A PECVD METHOD

Plasma polymerized methylcyclohexane thin films were deposited on silicon substrates at room temperature and different RF powers using a plasma-enhanced chemical vapor deposition (PECVD) method. The as-grown thin films were annealed in a vacuum. Methylcyclohexane monomer was utilized as an organic precursor, and hydrogen and argon were used as the bubbled and carrier gases, respectively. The as-grown plasma-polymer organic thin films were analyzed by FT-IR and SEM and in terms of their hardness and modulus and their capacitance values. Annealed polymer thin films were also analyzed. The dielectric constant of the thin films increased as the plasma power was increased. The minimum dielectric constant was 1.82.

Study of the Characteristics of Organic Thin Film Transistors with Plasma-Polymer Gate Dielectrics

The effects of gate dielectrics material in organic thin film transistors (OTFTs) were investigated. The gate dielectrics were deposited by plasma enhanced chemical vapor deposition (PECVD) with cyclohexane and tetraethylorthosilane (TEOS) respectively used as organic and inorganic precursors. The gate dielectrics (gate insulators) were deposited as either organic plasma-polymer or organic–inorganic hybrid plasma-polymer thin film by using cyclohexane or cyclohexane with TEOS, respectively. Additionally, hydrogen and argon were used as precursor bubbler gases. A polyimide (PI) substrate was used in the fabrication of pentacene OTFTs with a plasma-polymer gate insulator, an Au source–drain (S/D), and Cu gate electrodes. Different gate dielectrics were investigated. The as-grown plasma-polymer thin films were first analyzed using Fouriertransform infrared (FT-IR) spectroscopy. Also, they were analyzed by nano-indentation and capacitance measurements. The electrical properties, such as mobility and threshold voltage of the pentacene field-effect transistors with the plasma-polymer gate-dielectrics were investigated. Transistor with cyclohexane gate dielectric had a higher field-effect mobility, � FET ¼ 0:84cm 2 V � 1 s � 1 , and a smaller threshold voltage, VT ¼� 6:8V, than the transistor with the hybrid gate-dielectric. # 2011 The Japan Society of Applied Physics

Synthesis of N-doped Ethylcyclohexane Plasma Polymer Thin Films with Controlled Ammonia Flow Rate by PECVD Method

In this study, we investigated the basic properties of N-doped ethylcyclohexene plasma polymer thin films that deposited by radio frequency (13.56 MHz) plasma-enhanced chemical vapor deposition (PECVD) method with controlled ammonia flow rate. Ethylcyclohexene was used as organic precursor with hydrogen gas as the precursor bubbler gas. Additionally, ammonia (NH₃) gas was used as nitrogen dopant. The as-grown polymerized thin films were analyzed using ellipsometry, Fourier-transform infrared [FT-IR] spectroscopy, UV-Visible spectroscopy, and water contact angle measurement. We found that with increasing plasma power, film thickness is gradually increased while optical transmittance is drastically decreased. However, under the same plasma condition, water contact angle is decreased with increasing NH₃ flow rate. The FT-IR spectra showed that the N-doped ethylcyclohexene plasma polymer films were completely fragmented and polymerized from ethylcyclohexane.

Surface Modification of Plasma Polymer Thin Films for DNA Fixation by Atmospheric Pressure Plasma Treatment

The atmospheric pressure plasma treatment on plasma polymer thin films was investigated to control the immobilization of DNA alignment. The amine groups of aminopropyltriethoxysilane have been generally used for the fixation of DNA on the substrate. However, it is easily influenced by humidity, and so it is hard to control precisely the formation of the self-assembled monolayer. The plasma polymer thin films with the atmospheric pressure plasma treatment are expected to be hardly influenced by humidity. Moreover, the densities of the amine groups are expected to be controlled by the treatment. In this work, organic and organic-inorganic hybrid plasma polymer thin films were formed on Si(100) by plasma enhanced chemical vapor deposition using methylcyclohexane and tetraethylorthosilane (TEOS), and the amine groups were formed on the surfaces by N2 atmospheric pressure plasma treatment. Fourier-transform infrared absorption spectroscopy showed that the amine groups were increased with the treatment. The surface densities of the amine groups were obtained from averaged extinction coefficients of UV–visible absorption spectra. DNA fixation was successfully performed with a tilting method for aligning well stretched DNAs on the surfaces, through optimization of the surface condition in the treatment.