M. de la L. Olvera

Effect of the substrate temperature and acidity of the spray solution on the physical properties of F-doped ZnO thin films deposited by chemical spray

F-doped ZnO thin films were prepared by using the spray pyrolysis technique. The dependence of the electrical, optical, structural and morphological properties on the substrate temperature and spray solution acidity was studied. Additionally, aging of the spray solution presents a clear effect on the resistivity of ZnO thin films. The best films obtained show a resistivity, mobility and carrier concentration of the order of 1.5 10 @2 O cm, 6 cm 2 /V s and 2 10 19 cm @3 , respectively. Wurtzite hexagonal structure, with a preferential growth along the [0 0 2] direction for all substrate temperatures and acidities used, was obtained. From scanning electron microscopy and atomic force microscopy analysis, it was determined that the grain size of the films decreases and its homogeneity increases when the acidity of the starting solution is increased. High optical transmittances, in the order of 90%, were obtained in all the cases. r 2002 Elsevier Science B.V. All rights reserved.

Growth of textured ZnO:In thin films by chemical spray deposition

Abstract Insium-dopod zinc thin films were grown using the chemical spray deposition technique and different doping compounds in the solution. The partucular, indium chloride, indium sulfate and indium acetate were used as indium sources. The films show a high degree of preferential crystalline orientation which depends mainly on the type of doping compound and the substrate temperature. The lowest value o the resistivity is 2 × 10 −3 ω cm and and the transmittance is on average higher than 90%. It was found that the texture of the films could be change quite easily making it possible to grow films for different applications.

SnO2 and SnO2:Pt thin films used as gas sensors

Abstract SnO 2 and SnO 2 :Pt thin films, prepared by chemical spray deposition, have been used as gas sensors. The electrical characterization results and their sensing properties in the presence of CO are reported. The films were grown by chemical spray deposition on glass substrates at different temperatures. The initial solution was obtained by diluting SnCl 4 ·5H 2 O in ethyl alcohol at 0.2 M. In the case of the doped films we have added PtCl 2 to the initial solution in the following proportions: 3, 5 and 8% at. The conductance of the films was calculated from the electrical resistance which was measured as a function of measuring temperature, thickness and Pt concentration in the solution. The values of the sensitivity for 3.8 torr of CO partial pressure are as high as 5 for SnO 2 and 4×10 2 for SnO 2 :Pt. Additionally we report results on surface topography and crystalline structure.

Physical properties of CdTe:Cu films grown at low temperature by pulsed laser deposition

CdTe:Cu films were grown by pulsed laser deposition on Corning glass slides at a substrate temperature of 300 °C. The thin films were grown using CdTe and Cu2Te powders, varying the Cu2Te concentration from 3 to 10 wt. %. The structural, compositional, optical, and electrical properties were analyzed as a function of the nominal copper concentration. X-ray diffraction shows that films have CdTe cubic phase. The compositional analysis indicates that CdTe:Cu films grown with lower Cu content have Te excess, on the other hand, films with higher Cu content have Te deficiencies. The electrical measurements showed that CdTe:Cu films grown with low Cu content present lowest resistivity.

Characteristics of ZnO:F thin films obtained by chemical spray. Effect of the molarity and the doping concentration

The effect of the zinc acetate molarity combined with the substrate temperatures of ZnO:F thin films deposited by spray pyrolysis, on their physical properties, was studied. The main interest was to optimize the resistivity and the optical transmittance of films deposited at different substrate temperatures. It is to be remarked the influence of the aging of the starting solution on the improvement of the electrical properties of the films. The lowest value of the resistivity was obtained with solutions of 0.2 M. In this case, the resistivity obtained for a film 325-nm thick was 5.5×10−2 Ωcm, decreasing to a value of 6.7×10−3 Ωcm for films 1400-nm thick. Mobility values were approximately 7 cm2/V-S. The transmittance in the visible is near 90% at 550 nm. All the films showed a preferred (002) crystalline orientation irrespective of the deposition conditions. Finally, the grain size increased as the molarity of the solution decreased.

Chemical stability of doped ZnO thin films

We present the results of a chemical etching stability study carried out on ZnO thin films doped with several elements deposited by spray pyrolysis. Prior to the etching, a structural study was done by X-ray diffraction and the texture of the samples was obtained by scanning electron microscopy. The samples were etched employing a solution of dilute hydrochloric acid. The etching rates obtained for the different samples depend on the dopant element and our results confirm that films doped with Cr present the highest stability against chemical etching.

Low-Temperature synthesis and gas sensitivity of perovskite-type LaCoO 3 nanoparticles

LaCoO3 nanoparticles with perovskite-type structure were prepared by a microwave-assisted colloidal method. Lanthanum nitrate, cobalt nitrate, and ethylenediamine were used as precursors and ethyl alcohol as solvent. The thermal decomposition of the precursors leads to the formation of LaCoO3 from a temperature of 500°C. The structural, morphological, and compositional properties of LaCoO3 nanoparticles were studied in this work by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Pellets were manufactured in order to test the gas sensing properties of LaCoO3 powders in carbonmonoxide (CO) and propane (C3H8) atmospheres. Agglomerates of nanoparticles with high connectivity, forming a porous structure, were observed from SEM and TEM analysis. LaCoO3 pellets presented a high sensitivity in both CO and C3H8 at different concentrations and operating temperatures. As was expected, sensitivity increased with the gas concentration and operation temperature increase.

Influence of indium concentration and substrate temperature on the physical characteristics of chemically sprayed ZnO:In thin films deposited from zinc pentanedionate and indium sulfate

Chemically sprayed indium-doped zinc oxide thin films (ZnO:In) were deposited on glass substrates starting from zinc pentanedionate and indium sulfate. The influence of both the dopant concentration in the starting solution an dt he substrate temperature on the transport, morphology, composition, linear and nonlinear optical (NLO) properties o ft he ZnO:Inthin films were studied. The structure of all the ZnO:In thin films was polycrystalline, and variation in the preferential growth with the indium content in the solution was observed: fro ma ni nitial (002) growth in films with low In content, switching to a predominance of (101) planes for intermediate dopant regime, and finally turning to a (100) growth for heavily doped films. The crystallite size was found to decrease with doping concentration and range from 36 to 23 nm. The fil mc omposition and the dopant concentration were determined by Rutherford backscattering spectrometry; these results showed that the films are almost stoichiometric ZnO. The optimum deposition conditions leading to conductive an dt ransparent ZnO:In thin films were also found. In this way a resistivity of 4 × 10 −3 � cm an da na verage transmittance in the visible spectra of 85%, with a( 101) preferential growth, were obtained in optimized ZnO:In thin films. (Some figures in this article are in colour only in the electronic version)

CHARACTERISTICS OF SPRAY PYROLYTIC ZNO:IN THIN FILMS GROWN FROM ZINC ACETATE AND INDIUM NITRATE

The structural, electrical and optical properties of indium doped zinc oxide films, grown by spray pyrolysis are reported. The starting solution was zinc acetate diluted in a mixture of isopropyl alcohol and water to 0.1 M, the doping solution was an aqueous solution of indium nitrate. The films were grown at substrate temperatures ranging from 675 K to 800 K. X-ray diffraction and micrographs indicate that the films are polycrystalline with textured surfaces having a predominance of the (002) and (101) reflections, depending on the substrate temperature. They have a resistivity as low as 6×10−5Ω m and a transmittance better than 85% in the visible range.

Structural and optical properties of Cu-doped CdTe films with hexagonal phase grown by pulsed laser deposition

Cu-doped CdTethin films were prepared by pulsed laser deposition on Corning glass substrates using powders as target. Films were deposited at substrate temperatures ranging from 100 to 300 °C. The X-ray diffraction shows that both the Cu-doping and the increase in the substrate temperature promote the presence of the hexagonal CdTe phase. For a substrate temperature of 300 °C a CdTe:Cu film with hexagonal phase was obtained. Raman and EDS analysis indicate that the films grew with an excess of Te, which indicates that CdTe:Cu films have p-type conductivity.