Characterisation of Transparent Conducting Thin Films Grown by Pulsed Laser Deposition and RF Magnetron Sputtering

Materials exhibiting transparency and electrical conductivity simultaneously, transparent conductors, Transparent conducting oxides (TCOs), which have high transparency through the visible spectrum and high electrical conductivity are already being used in numerous applications. Low-emission windows that allow visible light through while reflecting the infrared, this keeps the heat out in summer, or the heat in, in winter. A thin conducting layer on or in between the glass panes achieves this. Low-emission windows use mostly F-doped SnO2. Most of these TCO’s are n type semiconductors and are utilized in a variety of commercial applications, such as flat-panel displays, photovoltaic devices, and electrochromic windows, in which they serve as transparent electrodes. Novel functions may be integrated into the materials since oxides have a variety of elements and crystal structures, providing great potential for realizing a diverse range of active functions. However, the application of TCOs has been restricted to transparent electrodes, notwithstanding the fact that TCOs are n-type semiconductors. The primary reason is the lack of p-type TCOs, because many of the active functions in semiconductors originate from the nature of the pn-junction. In 1997, H. Kawazoe et al.[2] reported CuAlO2 thin films as a first p-type TCO along with a chemical design concept for the exploration of other p-type TCOs.

Optical and electrical properties of amorphous zinc tin oxide thin films examined for thin film transistor application

Structural, electronic, and optical properties of amorphous and transparent zinc tin oxide films deposited on glass substrates by pulsed laser deposition (PLD) were examined for two chemical compositions of Zn:Sn=1:1 and 2:1 as a function of oxygen partial pressure PO2 used for the film deposition and annealing temperature. Different from a previous report on sputter-deposited films Chiang et al., Appl. Phys. Lett. 86, 013503 2005 , the PLD-deposited films crystallized at a lower temperature 450 °C to give crystalline ZnO and SnO2 phases. The optical band gaps Tauc gaps were 2.80−2.85 eV and almost independent of oxygen PO2 , which are smaller than those of the corresponding crystals 3.35−3.89 eV . Films deposited at low PO2 showed significant subgap absorptions, which were reduced by postthermal annealing. Hall mobility showed steep increases when carrier concentration exceeded threshold values and the threshold value depended on the film chemical composition. The films deposited at low PO2 2 Pa had low carrier concentrations. It is thought that the low PO2 produced high-density oxygen deficiencies and generated electrons, but these electrons were trapped in localized states, which would be observed as the subgap absorptions. Similar effects were observed for 600 °C crystallized films and their resistivities were increased by formation of subgap states due to the reducing high-temperature condition. High carrier concentrations and large mobilities were obtained in an intermediate PO2 region for the as-deposited films.

Growth and characterisation of p-type delafossite transparent conducting thin films for heterojunction applications

In the present studies, various copper delafossite materials viz; CuAlO2, CuGaO2, CuFeO2 , CuGa1-xFexO2, CuYO2 and CuCaxY1-xO2 were synthesised by solid state reaction technique. These copper delafossite materials were grown in thin film form by rf magnetron sputtering technique. In general copper delafossites exhibit good optical transparency. The conductivity of the CuYO2 could be improved by Ca doping or by oxygen intercalation by annealing the film in oxygen atmosphere. It has so far been impossible to improve the p-type conductivity of CuGaO2 significantly by doping Mg or Ca on the Ga site. The ptype conductivity is presumed to be due to oxygen doping or Cu Vacancies [6]. Reports in literature show, oxygen intercalation or divalent ion doping on Ga site is not possible for CuGaO2 thin films to improve the p-type conductivity. Sintered powder and crystals of CuFeO2 have been reported as the materials having the highest p-type conductivity [14, 15] among the copper and silver delafossites. However the CuFeO2 films are found to be less transparent in the visible region compared to CuGaO2. Hence in the present work, the solid solution between the CuGaO2 and CuFeO2 was effected by solid state reaction, varying the Fe content. The CuGa1-xFexO2 with Fe content, x=0.5 shows an increase in conductivity by two orders, compared to CuGaO2 but the transparency is only about 50% in the visible region which is less than that of CuGaO2 The synthesis of α−AgGaO2 was carried out by two step process which involves the synthesis of β-AgGaO2 by ion exchange reaction followed by the hydrothermal conversion of the β-AgGaO2 into α-AgGaO2. The trace amount of Ag has been reduced substantially in the two step synthesis compared to the direct hydrothermal synthesis. Thin films of α-AgGaO2 were prepared on silicon and Al2O3 substrates by pulsed laser deposition. These studies indicate the possibility of using this material as p-type material in thin film form for transparent electronics. The room temperature conductivity of α-AgGaO2 was measured as 3.17 x 10-4 Scm-1and the optical band gap was estimated as 4.12 eV. A transparent p-n junction thin film diode on glass substrate was fabricated using p-type α-AgGaO2 and n-ZnO.AgCoO2 thin films with 50% transparency in the visible region were deposited on single crystalline Al2O3 and amorphous silica substrates by RF magnetron sputtering and p type conductivity of AgCoO2 was demonstrated by fabricating transparent p-n junction diode with AgCoO2 as p-side and ZnO: Al as n-side using sputtering. The junction thus obtained was found to be rectifying with a forward to reverse current of about 10 at an applied voltage of 3 V.The present study shows that silver delafossite thin films with p-type conductivity can be used for the fabrication of active devices for transparent electronics applications.

Surface studies of some metallic thin films by optical methods

The thesis aims to present the results of experimental investigations on the changes of optical properties of metallic thin films due to heating. The parameters which are measured are reflectivity, refractive indices and the ellipsometric quantities V and A . The materials used in the studies are metals like Silver, Aluminium and Copper. By applying the optical method the interdiffusion taking place in multilayer ‘films of Aluminium and Silver has also been studied. Special interest has been taken to reveal the mechanisms of the hillock growth and surface roughness caused by heating and their relation with the stress in the film

Microstructure and random magnetic anisotropy in Fe–Ni based nanocrystalline thin films

Nanocrystalline Fe–Ni thin films were prepared by partial crystallization of vapour deposited amorphous precursors. The microstructure was controlled by annealing the films at different temperatures. X-ray diffraction, transmission electron microscopy and energy dispersive x-ray spectroscopy investigations showed that the nanocrystalline phase was that of Fe–Ni. Grain growth was observed with an increase in the annealing temperature. X-ray photoelectron spectroscopy observations showed the presence of a native oxide layer on the surface of the films. Scanning tunnelling microscopy investigations support the biphasic nature of the nanocrystalline microstructure that consists of a crystalline phase along with an amorphous phase. Magnetic studies using a vibrating sample magnetometer show that coercivity has a strong dependence on grain size. This is attributed to the random magnetic anisotropy characteristic of the system. The observed coercivity dependence on the grain size is explained using a modified random anisotropy model

Determination of charge carrier transport in radio frequency plasma polymerized aniline thin films

The carrier transport mechanism of polyaniline (PA) thin films prepared by radio frequency plasma polymerization is described in this paper. The mechanism of electrical conduction and carrier mobility of PA thin films for different temperatures were examined using the aluminium–PA–aluminium (Al–PA–Al) structure. It is found that the mechanism of carrier transport in these thin films is space charge limited conduction. J –V studies on an asymmetric electrode configuration using indium tin oxide (ITO) as the base electrode and Al as the upper electrode (ITO–PA–Al structure) show a diode-like behaviour with a considerable rectification ratio

Swift heavy ion induced surface and microstructural evolution in metallic glass thin films

Swift heavy ion induced changes in microstructure and surface morphology of vapor deposited Fe–Ni based metallic glass thin films have been investigated by using atomic force microscopy, X-ray diffraction and transmission electron microscopy. Ion beam irradiation was carried out at room temperature with 103 MeV Au9+ beam with fluences ranging from 3 1011 to 3 1013 ions/cm2. The atomic force microscopy images were subjected to power spectral density analysis and roughness analysis using an image analysis software. Clusters were found in the image of as-deposited samples, which indicates that the film growth is dominated by the island growth mode. As-deposited films were amorphous as evidenced from X-ray diffraction; however, high resolution transmission electron microscopy measurements revealed a short range atomic order in the samples with crystallites of size around 3 nm embedded in an amorphous matrix. X-ray diffraction pattern of the as-deposited films after irradiation does not show any appreciable changes, indicating that the passage of swift heavy ions stabilizes the short range atomic ordering, or even creates further amorphization. The crystallinity of the as-deposited Fe–Ni based films was improved by thermal annealing, and diffraction results indicated that ion beam irradiation on annealed samples results in grain fragmentation. On bombarding annealed films, the surface roughness of the films decreased initially, then, at higher fluences it increased. The observed change in surface morphology of the irradiated films is attributed to the interplay between ion induced sputtering, volume diffusion and surface diffusion

Annealing inducedlowcoercivity,nanocrystallineCo–Fe–Si thin films exhibitinginversecosine angular variation

Co–Fe–Si based films exhibit high magnetic moments and are highly sought after for applications like soft under layer sinper pendicular recording mediatomagneto-electro-mechanical sensor applications.In this workt he effect of annealing on s tructural,morphologicaland magnetic propertiesofco–Fe–Si thin films wasinvestigated.compositional analysis using x-rayphotoelectron spectroscopy and secondary ion massspectroscopyrevealedanativeoxidesurfacelayerconsistingofoxidesofco,feandsionthe surface. The morphology of theas deposited films shows mound like structures conformingtothe Volmer–Webergrowthmodel.Nanocrystallisationofamorphous films upon annealing was observed by glancing anglex-raydiffraction and transmission electron microscopy.Theevolutionofmagnetic properties with annealing is explained using the Herzermodel.Vibrating sample magnetometry measurements carried out at various angles from01 to 901 to the applied magnetic field were employed to study the angula rvariation of coercivity.The angular variation fits the modified Kondorsky model. Interestingly,the coercivity evolution with annealing deduced frommagneto-opticalKerreffectstudies indicates areversetrendcomparedtomagetisationobservedinthebulk.Thiscanbeattributedtoa domain wallpinningatnativeoxidelayeronthesurfaceofthin films. Theevolutionofsurfacemagnetic properties iscorrelatedwithmorphologyevolutionprobedusingatomicforcemicroscopy.The morphology aswellasthepresenceofthenativeoxidelayerdictatesthesurfacemagneticproperties and this is corroborated by the apparent difference in the bulk and surface magnetic properties

Magnetic and topographical modifications of amorphous Co–Fe thin films induced by high energy Ag7+ ion irradiation

We have investigated the effects of swift heavy ion irradiation on thermally evaporated 44 nm thick, amorphous Co77Fe23 thin films on silicon substrates using 100 MeV Ag7+ ions fluences of 1 1011 ions/ cm2, 1 1012 ions/cm2, 1 1013 ions/cm2, and 3 1013 ions/cm2. The structural modifications upon swift heavy irradiation were investigated using glancing angle X-ray diffraction. The surface morphological evolution of thin film with irradiation was studied using Atomic Force Microscopy. Power spectral density analysis was used to correlate the roughness variation with structural modifications investigated using X-ray diffraction. Magnetic measurements were carried out using vibrating sample magnetometry and the observed variation in coercivity of the irradiated films is explained on the basis of stress relaxation. Magnetic force microscopy images are subjected to analysis using the scanning probe image processor software. These results are in agreement with the results obtained using vibrating sample magnetometry. The magnetic and structural properties are correlated

Evolution of structural and magnetic properties of Co–Fe based metallic glass thin films with thermal annealing

Ultra thin films based on CoFe were prepared from a composite target employing thermal evaporation. The microstructure of the films was modified by thermal annealing. The relationship between microstructure and magnetic properties of the films was investigated using techniques like glancing angle X-ray diffraction (GXRD), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). The GXRD and TEM investigations showed an onset of crystallization of CoFe at around 373 K. The magnetic softness of the films improved with thermal annealing but at higher annealing temperature it is found to be deteriorating. Annealing inducedmodification of surface morphology of the alloy thin filmswas probed by atomic force microscopy (AFM). Surface smoothening was observed with thermal annealing and the observed magnetic properties correlate well with surface modifications induced by thermal annealing

De Casablanca a Lo que el viento se llevó, una mirada al consumo de cine de Hollywood en Bogotá durante 1935 hasta 1946

Este trabajo pretendió retomar la idea del consumo de productos culturales al preguntarse específicamente por el consumo de cine de Hollywood en Bogotá entre 1925 y 1946. Se trata de mirar cómo fue el consumo del cine de Hollywood de los bogotanos de las primeras décadas del siglo XX y se centra en todas aquellas películas producidas en Estados Unidos de carácter comercial. Para mostrar cómo ese consumo de cine no es pasivo, este trabajo se enfocó en cómo entendieron y vieron cine de Hollywood dos grupos de personas, teniendo en cuenta una tipología que establece Ricardo Arias, en las cuales se divide a parte de la población bogotana en individuos católicos radicales e individuos de tendencia laica liberal. Lo que se propone mostrar es que a pesar de las diferencias existentes entre los dos grupos, la visión que construyeron con respecto a estas películas no fue tan diferente, pues ambos grupos descalificaron al cine por ser una tecnología degradante que estaba supeditada a los intereses de una industria.

L'Edat Mitjana al cinema : material didàctic, personatges i llegendes medievals. 'La Edad Media en el cine : material didáctico, personajes y leyendas medievales'.

Material destinado a alumnos de primaria que realiza un recorrido por leyendas y personas de la Edad Media. El material consta de una guía didáctica, una ficha didáctica y un vídeo de 20 minutos. El montaje está realizado a partir de una serie de fragmentos de films dirigidos al público infantil ambientados en la Edad Media (La princesa prometida, Robin Hood, Excalibur, ...).

L'Edat Mitjana al cinema : material didàctic, un recorregut per la història del cinema. 'La Edad Media en el cine : material didáctico, un recorrido por la Edad Media'.

Material destinado a alumnos de secundaria que realiza un recorrido por la Edad Media. El material consta de una guía didáctica, una ficha didáctica y un vídeo de 20 mínutos. el montaje está realizado a partir de una serie de fragmentos de films dirigidos al público adolescente ambientados en la Edad Media.

Films etnográficos : la construcción audiovisual de las otras culturas.

El artículo forma parte del monográfico de la revista: Educación y comunicación para la cooperación y el desarrollo. Resumen de la propia revista

Representaciones identitarias del ecuatoriano en tres films nacionales

La siguiente investigación analiza a lo largo de su desarrollo cómo se construyen las representaciones identitarias del ecuatoriano, en los personajes principales de tres filmes nacionales: Zuquillo Exprés, A tus Espaldas y Prometeo Deportado. Además de definir los elementos socioculturales, audiovisuales, clichés y estereotipos que caracterizan a un personaje principal. Es por ello que el análisis inicia con la indagación de conceptos claves de diferentes autores que permitan establecer el punto de partida para la definición de: identidad, representación, ecuatorianidad, personaje, cine y estereotipo. Una vez entendido la concepción de cada concepto, la investigación da cara a las observaciones de las películas en sí. Primero en conocer el contexto en el que se desarrollan, la época, ambientación e historia y contexto para después identificar los personajes centrales que serán parte del estudio. Conocer cuáles son sus rasgos, tanto físicos, como culturales, de donde provienen, sus gustos, manera de hablar, lugares a los que frecuentan y hasta qué tipo de comida suelen consumir. Así como también identificar en su conjunto los rasgos generales, que en este caso prima la religión y migración como rasgos un tanto repetitivos. Es entonces que la investigación pasa al análisis pasa a la interpretación de las perspectivas con las que se han combinado identidad y representación en cada uno de los personajes y los tipos con los que han sido construidos a través de la visión del director. Es así que se define una lista de estereotipos y elementos con los que se caracteriza la personalidad de los personajes centrales de cada film.