Y.H. Zhang

Hydrothermal deposition of magnetite (Fe3O4) thin films

Magnetite (Fe3O4) thin films (0.2 μm) have been prepared by hydrothermal treatment of iron(III) nitrate solution in the presence of reduced iron powder and urea in the temperature range 140–200 °C for 2–6 h. The resulting films with a black appearance are homogeneous without visible pores, and the average grain size for Fe3O4 on Si(100) and α-Al2O3 is 50 and 150 nm, respectively. The films deposited on Si(100) and α-Al2O3 have saturation magnetization 456 and 448 emu/cm3, and coercivity 470 and 450 Oe, respectively.

Photoluminescence in porous silicon obtained by hydrothermal etching

Abstract We have prepared porous silicon (PS) by hydrothermal treatment of silicon in a LiF-containing nitric acid solution. It does not utilize anodic etching. Scanning tunneling microscope (STM) studies show that the PS layers are uniform and consist of columns having cross sectional diameters of significantly less than 10 nm. Luminescence measurement results reveal that the wavelength of the photoluminescence (PL) peaks at 690 nm, which is somewhat shifted toward the higher energy compared to porous silicon obtained by anodic etching. A blue band around 430 nm together with an ultraviolet component peak at 370 nm appear after rapid thermal oxidation (RTO) of the hydrothermal etched sample in air at certain temperatures (650–1200°C) for 30 s. Our results are interpreted in the light of the presently suggested theories.

Preparation and characterization of iron(III) oxide (α-Fe2O3) thin films hydrothermally

Abstract Thin films (0.12μm) of hematite (α-Fe 2 O 3 ) were prepared on Si(111) and Si(100) substrates by hydrothermal treatment of a solution of iron nitrate containing urea in the temperature range of 100–200 °C for 4–24h. The films consisted of spherical grains for Si (111) and columnar grains for Si(100) with a typical grain size 10nm and 30nm × 5nm, respectively. Both films deposited on Si (111) and Si(100) have (101) preferred orientation.

Strong and stable ultraviolet luminescence in porous silicon in situ passivated by manganese

A strong and stable ultraviolet photoluminescence (PL) band (370 nm) together with a red luminescence band around 670 nm with a 730 nm shoulder were observed in Mn-passivated porous silicon (PS) prepared by the hydrothermal technique. The surface structure is examined by Fourier infrared and x-ray photoelectron spectroscopy analysis. The 670 nm band was confirmed to be the usually observed PL band in PS, and the appearance of the 370 nm band and 730 nm shoulder peak was interpreted based on surface structure characterization and spectroscopy measurements.

Preparation of zinc sulfide thin films by the hydrothermal method

Abstract Zinc sulfide thin films (0.20 μm) were prepared on silicon and polycrystalline α-Al 2 O 3 substrates by hydrothermal treatment of zinc sulfide sol in the temperature range of 100–200 °C for 6–24 h. The films prepared were found to have a cubic structure and the film deposited on Si(111) has a {111} preferred orientation. The films were characterized by X-ray diffraction, scanning electron microscopy and infrared transmission spectrum.

Preparation and characterization of porous silicon powder

Abstract Porous silicon powder has been prepared for the first time by a hydrothermal technique. Strong red-emission around 680 nm was observed in the samples. Transmission electron microscopy studies reveal that the as-prepared powder was composed of plate-like particles, which were found to be porous structures of ≈2–3 nm primary units. These results reveal that the particles of porous silicon powder have a microstructure and luminescent properties similar to those of anodic-etched silicon films.

Hydrothermal doping of cobalt and magnetic properties in gamma iron oxide thin films

Abstract High coercivity (3.1 kOe) cobalt-doped gamma iron oxide (γ-Fe 2 O 3 ) thin films have been prepared by hydrothermal deposition of Fe 3 O 4 followed by oxidation in air. Films deposited by hydrothermal treatment of a mixed solution of Fe(NO 3 ) 3 · 9H 2 O and CoCl 2 · 6H 2 O in the presence of reduced iron powder at 140 °C for 6 h have the Fe 3 O 4 phase. Controlled oxidation in air at 400 °C for 2 h leads to the formation of γ-Fe 2 O 3 phase. The magnetic properties are enhanced, which is thought to be the result of well-crystallized acicular grains and uniform distribution of cobalt ions in the grains because of hydrothermal doping.

Effect of γ-ray irradiation on the valence state of bismuth and copper in Bi-based superconductors

Abstract Samples of Bi 2 Sr 2 CuO 6+χ , Bi 2 Sr 2 CaCu 2 O 8+ y and Bi 2.4− z Pb z Sr 2 CaCu 2 O 8+ w crystals have been irradiated by 648 KGy γ-rays parallel to the c -axis of the crystals. After irradiation the valence states of bismuth and copper shift to high binding energies. Also, new higher valence states occur in Bi 2 Sr 2 CaCu 2 O 8+ y and Bi 2.4− z Pb z Sr 2 CaCu 2 O 8+ w crystals, lead ding to a change in T c .

Ba2(Cu0.7Cd0.3)O3: a new double-center perovskite structure

Abstract A new phase of Ba 2 (Cu 0.7 Cd 0.3 )O 3 has been discovered. The composition of the phase was examined by energy dispersive X-ray spectrometry. The phase exhibits a tetragonal structure with lattice constants a=4.077 A and c=7.970 A , and its space group is P4/mmm. We propose a double-center-perovskite structure model, which is similar to that of (Ba, Sr) 2 CuO 2 (CO 3 ) [1, 2]. The simulated XRD is close to the observed one. The analysis results of elemental analyzer and Fourier transform infrared spectrometer reveal that the phase does not contain CO 2 3− . The cuprate is an insulator, but its new cell structure and the large size of the CuO 2 planes seem to suggest a good reason for researching new superconductors. The roles of CdO in the solid state reaction and the formation of the new phase are discussed.

Occurrence of metallic bismuth in Bi2Sr2CuOx crystals irradiated by N+ ions

Abstract X-ray photoemission spectroscopy analyses reveal that N + ion irradiation causes the occurrence of metallic bismuth in the Bi 2 Sr 2 CuO x crystals. X-ray diffraction shows that the metallic bismuth results in the disappearance of some modulated peaks. Strontium may be replaced by other ions.