A. Conde-Gallardo

Photoluminescence of TiO2: Eu3+ thin films obtained by sol-gel on Si and Corning glass substrates

Abstract In this paper we report results on the fabrication and characterisation of thin films of titania (TiO 2 ), a novel host for the Eu 3+ activator ion. The titania films were produced by the sol–gel process at room temperature using the dip coating method and deposited on silicon and corning glass substrates. It is shown that different surface morphology and crystalline structures are developed for the TiO 2 :Eu films deposited on different substrates. When an above TiO 2 band gap photoexcitation line (He–Cd 325 nm) is used, the films show a strong red photoluminescence (PL) signal associated with the 5 D 0 → 7 F j transition of the electronic structure of Eu 3+ . The PL emission has better characteristics for those films deposited on silicon wafers. The PL signal becomes weaker after annealing at relatively low temperatures such as 450°C due to thickness reduction of the TiO 2 film and the loss of Eu in the near-surface region.

Metal oxide Co and Co-Fe-Cr films deposited on glass substrates from a metal-organic aerosol atomised by means of ultrasonic excitations

Abstract Thin films of metal oxides of Co and the Co -Fe -Cr system were deposited on a commercial soda-lime-silica float gray glass from an aerosol generated by ultrasonic excitation, using acetylacetonates as the source of the aerosol. Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) studies performed prior to the film deposition revealed a principal difference between the thermal decomposition of acetylacetonates and the nitrates used previously, influencing greatly the properties of the synthesised films. Deposited films were characterised by the measurement of their optical properties that are vital for privacy purposes (i.e., reflectance, transmittance), and of their surface roughness and thickness measurements. Crystallinity of films has been investigated and chemical durability tests have been performed. Results of these investigations are presented and the properties of films are compared with those obtained from films deposited previously from a nitrate aerosol generated either pneumatically or by means of ultrasonic excitation.

Preliminary studies of thin metal oxide films prepared by deposition of an aerosol generated ultrasonically from aqueous nitrate solutions

Abstract Thin Co, Co-Fe and Co-Fe-Cr metal oxide films were prepared by deposition of an aerosol generated by ultrasonic excitations from aqueous nitrate solutions. Commercial gray glass has been used as substrates. Thermogravimetric (TG and DTG) measurements of initial nitrate components as well as their homogenized mixtures were performed and optical properties, i.e. reflectance and transmittance of the deposited films in the UV-visible and near-infrared regions up to 4761 nm, were measured. The surface roughness of the films was also measured and their chemical durability tested. The reflectance values obtained for 550 nm radiation wavelength were 25–33% for Co-oxide films compared to 20–30% for films deposited by us from a pneumatic aerosol, or values of 10–15% reported by others. The reflectance was 21–28% for Co:Fe = 15:1 films and up to 26% and 30% for Co:Fe:Cr = 15:1:0.25 and Co:Fe:Cr = 12:3:1 films, respectively. The reflectance of the uncoated reference glass was 5%. The surface roughness values of films deposited from ultrasonic aerosol dropped to about 50–60% of the value measured for films deposited from pneumatic aerosol. At the same time the chemical durability of films deposited from ultrasonic aerosol has approximately doubled.

LUMINESCENT PROPERTIES OF SOL-GEL DEPOSITED Eu:TiO2 THIN FILMS

In this work we show the results on tile growth and optical characterization of TiO2 thin films doped with Eu atoms. Eu:TiO2 films were grown at room temperature with different Eu concentrations by sol-gel on Si Corning glass substrates. A different crystalline structure is developed for the films deposited on Corning glass than those deposited on Si as observed from x-ray diffraction experiments. Room and low temperature photoluminescence (PL) was measured by using two different lines (325 and 442 nm) of a HeCd laser. A strong PL signal associated to the 5D0→7F2 transition from Eu+3 was observed. A better emission was obtained from those films deposited on Si substrates, Finally, the evolution of the PL signal is studied when the samples are annealed at different temperatures in O2 atmosphere.

Optical properties of Co and Co-Fe-Cr thin films deposited from an aerosol on glass substrates

Abstract Thin films of Co and Co-Fe-Cr metal oxide films were prepared by deposition of an aerosol generated pneumatically from aqueous nitrate solutions. As substrates commercial gray glass has been used. Thermogravimetric (TG, DTG) and DTA measurements of initial nitrate components and their homogenized mixture were performed, and optical properties of deposited films important for privacy purposes (reflectance, transmittance), in the UV-visible and near-infrared regions up to 4761 nm as well as their surface roughness were measured. The reflectance values, defined at 550 nm wavelength, were 20–30% for Co-oxide films and 20–25% for Co-Fe-Cr films compared to 10–15% reported in literature. Transmittance values were 14–28% and 24–36%, respectively. For the substrate (uncoated gray glass) also used as a reference, these corresponding values were 5 and 57%. The surface roughness R a correlates with the main deposition parameters, such as temperature and time of deposition, and the molarity of solutions used. Crystallinity in Co-oxide films has been detected by X-ray measurements.

Ion beam analysis of HTc superconducting Tl-based films

Abstract The elemental composition, film thickness and concentration depth profiles of superconducting TlBaCaCuO and precursor BaCaCuO thin films were studied by IBA techniques such as RBS and NRA. The precursor BaCaCuO films were prepared by deposition of an aerosol (spray pyrolysis) atomized from aqueous nitrate solutions by ultrasonic excitations. The substrates were single crystal MgO and yttrium-stabilized zirconia (YSZ). The precursor BaCaCuO films were thallinated in a single-zone reaction chamber to produce the superconductor. The critical temperature values, Tc, of the superconducting films ranged from 101 to 103 K and were found to consist of more than 95 vol.% of the Tl2Ba2CaCu2Ox phase. IBA studies revealed that the superconducting films were well oxygenated but slightly thallium deficient, with the Tl depth profile decreasing from the bulk of the film to the surface. The phase composition was found to be different from the elemental one determined by IBA techniques. Moreover, residual carbon was found in both the superconducting and precursor films. Thermogravimetric studies revealed that it is highly probable that the carbon contamination was caused by exposure of the precursor oxide films to the ambient atmosphere prior to the thallination procedure. In regard to the optimization of the thallium content, the most important parameters of the dynamical thallination process were found to be the initial amount of Tl, the partial pressures pTl2O and pO2, the time of thallination and the reaction rate.

Optical characterization of Tl-based superconducting films deposited from aerosol

Abstract Superconducting Tl-based films were prepared by deposition of precursor Ba-Ca-Cu films from an aerosol generated ultrasonically, followed by an annealing in a thallium vapour. As substrates we used single crystalline yttrium-stabilized zirconia (YSZ). The prepared films were about 3 μm thick. Annealed films consisted of 2212 and 2223 phases and partially of an amorphous phase, as revealed by X-ray and Raman spectroscopy. Hence, lower Tc values were obtained, from the interval 85–105 K. The Raman spectra measurements show the presence of peaks similar to those previously reported for the 2212 phase, with, however, some shifts in energy, which could be related to the presence of the 2223 phase and thus to the strengthening of the chemical bonds.

TI-Based Superconducting Films Prepared by Spray Pyrolysis and Vacuum Evaporation

TI-based films were prepared by the 2-step procedure. First, Ba-Ca-Cu-O precursors were deposited either from an aerosol or by thermal evaporation on MgO substrates. Thallination of precursors was then performed at 850 °C in flowing oxygen with annealing time up to 30 min. Films were characterized by Tc and X-ray measurements, and their depth profiles (RBS), surface morphology (SEM) and oxygen Raman modes were also investigated. The aerosol deposited films gave Tc = 94−103.5 K. Films grown by thermal evaporation revealed unusual Tc and structural changes during their 20-months storage in laboratory surroundings. Their Tc has increased from 94 to 106 K.

Influence of processing conditions of Tl-2212 superconducting films deposited from an aerosol upon their Tc and oxygen Raman modes

Abstract Tl based 2212 films were prepared on MgO and YSZ substrates in two steps. First, BaCaCuO precursors were deposited from an aerosol, followed by two types of thallination and oxygenation in a single-zone reaction chamber. Critical temperatures T c , X-ray and oxygen related Raman modes were measured on superconducting films. The T c values of prepared films varied from the interval of 95.0 to 103.5 K. We did not find any pronounced relation between the T c values and a and c unit cell parameters. The Raman spectra of investigated films revealed peaks assigned to O(1), O(2) and O(3) atom vibrations, one peak determining the degree of recrystallization from an initial amorphous phase, and peaks originating from impurity phases. Apparently, prolonged thermal processing of films creates both, metal-cation and oxygen-anion disorder as well. It seems that a well defined relation between the transition temperature T c and the Raman shift in the O(2) vibrations exists. It is proposed, that this relation serves as an indirect indication of a lack of oxygen in the film samples.

Effect of various annealing treatments on superconducting properties of YBa2Cu3O7−x films deposited from aerosol

Abstract Yba 2 Cu 3 O 7 − x (YBCO) films were prepared by deposition from aerosol generated by pneumatic and ultrasonic atomizers. As substrates we used singlecrystalline yttrum-stabilized zirconia (YSZ) and MgO. Various substrate temperatures were applied during deposition, and the deposited precursor films were annealed under two basically different conditions, i.e., annealing in oxygen at atmospheric pressure at temperatures being around T ≈ 900 °C, or in a vacuum degraded by partial pressure of oxygen at temperatures T ≤ 600 °C. Influence of these processing conditions upon the T c and J c values as well as the surface morphology is reported.