Search

Magnetite micropatterns were successfully fabricated by the site-selective deposition technique using self-assembled monolayers (SAMs) as templates. Magnetite particles were selectively deposited on Pd catalysts which were adsorbed to the −NH2-terminated surface of a SAM, in an aqueous solution containing iron nitrate and dimethylamine−borane. Pd colloid catalyst particles were adhered to the amino group of a patterned SAM by electrostatic interaction. Crystalline Fe3O4 (magnetite) particulate films were then deposited on amino-group regions by the effect of metal Pd catalyst. Site-selective deposition of crystalline Fe3O4 was thus realized in an aqueous solution. The deposition mechanism of Fe3O4 is discussed in detail in comparison with the deposition of γ-FeOOH in the solution.

We report a deposition method for room-temperature preparation of ZrO2 thin film using an aqueous solution. ZrO(NO3)2·2H2O was dissolved in a solvent mixture composed of H2O2 and ammonia. The dissolving reaction produced a colorless, transparent peroxozirconium-complex solution which was unstable; decomposition occurred even at room temperature. Amorphous, transparent, dense ZrO2 precursor thin films of up to 500 nm thick were prepared on a cleaned P-type Si substrate. The film showed good adhesion to the substrate as peel-off was not found after either sonication or a Scotch-tape peel-off test. The as-deposited thin film was of high purity with a composition of ZrO1.4(OH)1.2. No peroxo groups were present in the as-deposited film. Annealing caused crystallization of the amorphous film into tetragonal ZrO2 at 500 °C and phase transformation from tetragonal to monoclinic ZrO2 at higher temperatures. Both films showed very flat surfaces consisting of nanoparticles with homogeneous size of tens of nanometers in diameter. The optical band gap of the amorphous film was 5.0−5.75 eV, whereas it was 5.65 eV for the crystalline ZrO2 thin film.

We report micropatterning of TiO2 thin film by a peroxotitanate complex deposition method, which was a method we developed recently. The deposition solution was obtained by dissolving titanic acid (H2TiO3) into a mixture solvent containing ammonia and hydrogen peroxide aqueous solution. The amorphous TiO2 micropattern with a high resolution was achieved by using a template of photomodified self-assembled monolayers at room temperature. The film showed high purity, flatness, and crack-free characteristics. The fundamental dielectric characteristics suggest that the micropatterned TiO2 thin films prepared by the present method are promising for application to dielectric layers.

Strontium titanate precursor thin films were directly deposited on different self-assembled monolayers (SAM) in an aqueous solution at 40−60 °C. We have investigated the film growth rate, mechanism, and kinetics. The film microstructure and thickness can be controlled by appropriate SAM surfaces and solution conditions, such as the concentration of starting materials, pH, and deposition temperatures. Uniform, smooth, and adhesive films with thickness in the range of 25−480 nm could be successfully prepared on the OH surfaces of UV-modified SAM. The films were transparent and composed of closely packed particles of 20−50 nm, which formed by coalescence of very small particles. The Sr species preferably reacts with intermediate Ti species to produce SrTiO3 precursor solid when the Sr and Ti species coexisted in the present solution system, resulting in a stoichiometry in terms of Sr/Ti ratio even if the Ti species was excessive.

We have succeeded in site-selective deposition of SrTiO3 (STO) thin films on patterned self-assembled monolayers (SAMs) by the liquid phase deposition (LPD) method. SAMs of heptadecafluoro-1,1,2,2,-tetrahydrodecyltrichlorosilanes [HFDTS, CF3(CF2)7(CH2)2SiCl3] were prepared on Si wafers and modified by UV irradiation through a photomask. This SAM template was composed of HFDTS surfaces (Si−CF3) and silanol surfaces. The patterned SAM-covered substrate was then immersed into a (NH4)TiF6/Sr(NO3)/H3BO3 aqueous solution at 50 °C to deposit a solid phase. (NH4)2TiF6, which could form [Ti(OH)nF6-n]^2- slowly in an aqueous solution, was selected as a source of TiO3^2-. H3BO3 was a scavenger of fluorine and was used to control the reaction rate. The STO films were selectively deposited in the silanol regions. The as-deposited film was amorphous containing fluorine as a main impurity. With annealing at 500 °C for 2 h in air, the as-deposited film was crystallized into SrTiO3 and the fluorine was eliminated. Film morphology was characterized by both SEM and AFM. Metal-oxide-semiconductor (MOS) devices were prepared by using an as-deposited film or a crystallized film as a gate oxide. The dielectric constant of SrTiO3 thin films and the leakage current of the MOS device were evaluated. These results indicate that the SrTiO3 film fabricated by a combination of the SAM technique with LPD method through a one-step process is promising for application to dielectric films.

c-Axis oriented thin films of (ZnO)5In2O3 of 0.5 μm thickness were deposited on glass substrates by a radio-frequency-sputtering method. The thin films had dense columnar structures and were highly transparent in the ultraviolet−visible region, simultaneously showing low electrical resistivity. The refractive index was about 2. The lowest resistivity, 1.3 × 10^-3 Ω cm at room temperature, was obtained by reducing the deposited film at 540 °C in N2 containing 3.4% H2. The corresponding carrier concentration and Hall mobility were 1.9 × 10²⁰ cm^-3 and 25.6 cm²/Vs, respectively. Detailed analyses of the optical transmittance spectra gave rise to the intrinsic band gap and the reduced mass of carriers to be 3.12 eV and 0.67 m0, respectively.