108,236 research outputs found
Enhanced electrical and optical properties of room temperature deposited Aluminium doped Zinc Oxide (AZO) thin films by excimer laser annealing
No full textHigh quality transparent conductive oxides (TCOs) often require a high thermal budget fabrication process. In this study, Excimer Laser Annealing (ELA) at a wavelength of 248 nm has been explored as a processing mechanism to facilitate low thermal budget fabrication of high quality aluminium doped zinc oxide (AZO) thin films. 180 nm thick AZO films were prepared by radio frequency magnetron sputtering at room temperature on fused silica substrates. The effects of the applied RF power and the sputtering pressure on the outcome of ELA at different laser energy densities and number of pulses have been investigated. AZO films deposited with no intentional heating at 180 W, and at 2 mTorr of 0.2% oxygen in argon were selected as the optimum as-deposited films in this work, with a resistivity of 1×10−3 Ω.cm, and an average visible transmission of 85%. ELA was found to result in noticeably reduced resistivity of 5×10−4 Ω.cm, and enhancing the average visible transmission to 90% when AZO is processed with 5 pulses at 125 mJ/cm2. Therefore, the combination of RF magnetron sputtering and ELA, both low thermal budget and scalable techniques, can provide a viable fabrication route of high quality AZO films for use as transparent electrodes
Grazing Incidence X-ray Scattering from Magnetic Thin Films and Nanostructures
No full textGrazing incidence scattering of synchrotron x-rays has been used to characterize the structure of magnetic thin films and periodic nanostructures. The combined metal and metal oxide films have been chosen to clarify the effects of growth processing techniques in technologically important magnetic and magnetoresistive thin film materials, and have particular relevance to the magnetic tunnel junction (MTJ) class of magnetic sensor.
Co/Al2O3 thin films and Co/MgO multilayer thin films have been characterized using x-ray reflectivity and diffuse scatter analysis to explain how preparatory oxidation of the lower ferromagnet in an MTJ can reduce Néel interlayer coupling and improve the consistency of magnetoresistance. Measurements reveal differing effects for Al2O3 and MgO tunnel barrier materials. In Co/Al2O3 systems, preoxidation is found to reduce significantly chemical interdiffusion at the interface between the two layers, implying a more uniform oxidation of the barrier layer. In Co/MgO multilayers, an increased in-plane correlation length of the inherited interface roughness is seen after preoxidation. This implies that preoxidation suppresses the short wavelength undulations on both sides of the tunnel barrier that cause Néel coupling.
Grazing incidence in-plane diffraction measurements on epitaxial Fe/MgO/Fe [001] and Fe/Au/MgO/Fe [001] films during annealing to 600 K have shown that, in both cases, the MgO lattice is initially strained towards being commensurate with the iron and gold layers, but relaxes after annealing towards a typical bulk MgO lattice. The iron and gold layers display linear thermal expansion at rates consistent with the bulk material. These in-plane lattice measurements demonstrate how the strain and strain dispersion in an epitaxial MgO barrier layer can be relieved under controlled annealing conditions.
Finally, patterned thin film surfaces with submicron periodic symmetries have been studied by grazing incidence x-ray scattering. A novel semi-kinematical theory has been developed into a numerical algorithm capable of simulating the scatter from a wide range of arbitrary and disordered nanoscale arrays. This has allowed key structural parameters including array periodicity, symmetry and array coherence lengths to be extracted from experimental data
Las Islas de la Calma, 1966 (complete work)
No full textX Films presenta ; Operador, Juan Manuel de la Chica; Ayudante, Pedro Hueros; Commenntarios en la voz de, Simon Ramirez; "Se Llarga": Ballado por el groupo folklorico de sas Jose Ibiza; Jefe de production, Jose Maria Gonzalez Sinde; Montaje, Elena Jaumandren; Ingeniero de Sonido, Jesus Jimenez; Labortorio, Fotofilm Madrid S.A. Sonoriacion: Iberson; Deposito Legal M-14229 1966; Gulon y Direccion, Ramon Masats.To order a reproduction, inquire about permissions, or for information about prices, see: http://www.lib.washington.edu/specialcollections/services/reproduction/reproductio
Characterization of SiGe thin films using a laboratory X-ray instrument
No full textThe technique of reciprocal space mapping using X-rays is a recognized tool for the nondestructive characterization of epitaxial films. X-ray scattering from epitaxial Si0.4Ge0.6 films on Si(100) substrates using a laboratory X-ray source was investigated. It is shown that a laboratory source with a rotating anode makes it possible to investigate the material parameters of the super-thin 2–6 nm layers. For another set of partially relaxed layers, 50–200 nm thick, it is shown that from a high-resolution reciprocal space map, conditioned from diffuse scattering on dislocations, it is possible to determine quantitatively from the shape of a diffraction peak (possessing no thickness fringes) additional parameters such as misfit dislocation density and layer thickness as well as concentration and relaxation
Correlation of Raman and X-Ray Diffraction Measurements of Annealed Pulsed Laser Deposited ZnO Thin Films.
No full textRaman spectroscopy, X-ray diffractometry and atomic force microscopy have been used to characterise ZnO thin films grown by pulsed laser deposition as a function of the post-growth annealing temperature. The results show substantial enhancement and broadening of certain Raman features which correlate excellently with the change in width of the X-ray diffraction peaks. The 570 cm[-1] Raman feature showed pronounced asymmetry and enhanced intensity in the unannealed sample. An increase in grain size observed after subsequent annealing produced a substantial reduction in both the asymmetry and intensity of this peak. Our experimental data suggest that electric fields, due to charge trapping at grain boundaries, in conjunction with localised and surface phonon modes are the cause of the intensity enhancement and asymmetry of this feature
Pyroelectricity in langmuir-blodgett films
No full textThe fabrication of pyroelectric devices using the Langmuir-Blodgett (LB) technique is described. Studies of a wide range of materials are reported; however, the thesis concentrates on electrical and structural investigations of two specific alternate layer films: 22-tricosenoic acid/l-docosylamine and 22-tricosenoic acid/4-octadecylaniline. The latter system possesses a pyroelectric coefficient of 0.65 nCcm(^-2)K(^-1), representing the largest reported value, to date, for an LB film. The pyroelectric figure of merit (p/e(^1)(_T)) of such films is approximately 0.22 nCcm(^-2)K(^-1), which is comparable with the values for commercially available materials. The difference in pyroelectric coefficient of the two types of alternate layer film is attributed to differences in inter-layer bonding, as revealed by infrared spectroscopy. The dependence of the pyroelectric coefficients on parameters such as film thickness, substrate thickness and temperature is investigated. Structural studies, performed using electron and X-ray diffraction techniques, are also described. These provide information on the orientation of the molecules relative to the substrate and on the d-spacing of the LB films. It is shown that the substrate has a deleterious effect on the responsivity of LB film devices, and studies of films deposited onto different substrate materials indicate that there is a significant piezoelectric ally induced secondary effect contributing to the overall pyroelectric coefficient. This secondary effect is small at low temperatures, but becomes dominant at around 250 K. The results of thermally stimulated discharge experiments indicate that both free charges and dipolar groups are incorporated in the films during deposition, and become tightly bound within the polar structure
Deposition and characterisation of sputtered Nickel manganate thin films
No full textThis work investigates the structural and electrical properties of both bulk and r magnetron sputtered thin films of spinel structured Ni(_x)Mn(_3-x)0(_4=8) material system. The distribution of the LDOS of the thin films is also studied using STS. A rf magnetron sputtering system capable of reactive sputtering in a range of argon/oxygen ambients was designed, constructed and commissioned in the first phase of this work. The system was optimised in terms of the effect of various process parameters on the growth rate using factorial experimental design technique. Incident power, substrate to target distance and oxygen percentage in the ambient was found to be the most significant. The effect of different sintering temperatures was investigated for five different compositions of the NhMn3-x04+s material system. Monophase material could not be prepared without prolonged annealing at 800 C after sintering at higher temperatures. This was in contradiction with the published phase diagram of the material and hence a modified scheme was proposed. The lattice parameter of the spinel phase increased with decreasing nickel content. Grain growth was found to be exponentially dependent on the sintering temperature. The R-T characteristics below 300K followed the Shklovskii and Efros VRH model (To -2x10(^5) K) and a change to the NNH model (∆E -330 meV) was observed above 300K. The resistivity of the material was dependent on both the ratio of Ni:Mn and the oxygen stoichiometry (varying from 1.2 Kohm-cm up to 30 Kohm-cm).The as-deposited films showed poor crystallinity, hence post deposition annealing at 800 C was required. The microstructure and the degree of preferred orientation were found to be dependent on the substrate temperature and post deposition annealing. The lattice parameter of the films was lower than the target. The NNH model best described the R-T characteristics of the films deposited at low oxygen content <2.5% (∆E -360 meV) whereas films deposited at higher oxygen content could be better described by the Shklovskii and Efros VRH model {To -2.4 x 10^ K). The resistivity of the films decreased with increasing oxygen in the ambient in the as-deposited state, however after annealing the resistivity of all the films became similar and much lower than the target. The distribution of the LDOS of the films, using STS, was found to be parabolic and in agreement with the assumption in the Shklovskii and Efros VRH model. Additional features were observed in the LDOS with increasing temperatures (~±0.15 eV and ~+1.6 eV) however the changes were completely reversible with temperature
Strontium titanate based films for tunable device applications
No full textDoutoramento em Ciência e Engenharia de MateriaisO SrTiO3 (ST) cristaliza com a estrutura da perovesquite e apresenta
propriedades de um paraeléctrico quântico; isto é, exibe um aumento continuo
da permitividade dieléctrica com o decréscimo da temperatura até 4K, seguido
de um patamar de valor constante até cerca de 0K. A presença de
imperfeições na rede, tais como defeitos pontuais, impurezas e tensões podem
modificar apreciavelmente as propriedades do ST puro e mesmo induzir
ferroelectricidade.
Neste trabalho foi conduzido um estudo sistemático da estrutura,
microestrutura e comportamento dieléctrico de filmes finos não dopados e
dopados de ST policristalino preparados por sol gel e depositados sobre
diferentes substratos. As propriedades dieléctricas foram estudadas numa
gama alargada de temperatura e frequência do campo eléctrico. A
caracterização dieléctrica dos filmes foi efectuada em função da temperatura e
frequência desde o regime das frequências rádio (rf), terahertz (THz-TDS) e
infra vermelho (IR). As características cristalográficas e microestuturais dos
filmes de ST foram analisadas por difracção de raios X (DRX), espectroscopia
de Raman, microscopia electrónica de varrimento (SEM) e de transmissão
(TEM), espectroscopia de Rutherford Backscattering (RBS). Foi feito um
estudo detalhado da dinâmica de rede destes materiais.
É mostrado neste trabalho que filmes finos de ST não dopados e crescidos
em diferentes substratos (Al2O3/Pt, Si/SiO2/TiO2/Pt, (LaAlO3)0.3-
(Sr2AlTaO6)0.7/Pt, SrTiO3/Pt and MgO/Pt) apresentam diferentes características
estruturais e propriedades eléctricas, directamente dependentes das tensões
criadas nos filmes. Nos grãos dos filmes de ST depositados sobre substratos
de MgO/Pt devido às elevadas tensões compressivas originadas pelo
substrato observam-se deslocações do tipo “slip band dislocations”, Enquanto
que o modo TO1 de filmes de ST depositados sobre Al2O3 se comporta de
maneira muito semelhante aos cristais de ST na gama de temperatura entre
300K e 150K, o modo TO1 dos filmes de ST depositados sobre substratos de
MgO apresenta-se endurecido, o que se pode explicar pela influência das
tensões geradas nos filmes pelo substrato. Filmes de ST com as tensões
compressivas mais elevadas, depositados sobre substratos de MgO/Pt exibem
os valores mais elevados da parte real da permitividade dieléctrica (ε′), a maior
resposta histerética da polarização em função do campo eléctrico aplicado e
os maiores valores da sintonabilidade dieléctrica (nr), em oposição aos filmes
de ST, depositados sobre substratos de Al2O3/Pt com as tensões tractoras
mais elevadas.
Neste trabalho é também salientada a importância dos aspectos tecnológicos
da preparação por sol gel, na qualidade dos filmes finos de ST, que se reflecte
nos valores elevados de ε′ and nr, que são obtidos por pela introdução de
camadas intermédias tampão (buffer layers) e pelo aumento da temperatura de
queima de 750o
C para 900o
C.
Com base em previsões teóricas, de que o deslocamento de iões de
pequenas dimensões (“off centre”) como o Mg, nos locais dos iões Sr da rede
induzem uma anomalia na resposta dieléctrica do ST, foi estudada a
incorporação de Mg na rede dos filmes de ST. Foi observado que o limite de
solubilidade sólida de Mg na rede de ST é dependente do local da rede no qual
ocorre a incorporação do dopante e da temperatura do tratamento térmico.
Aumentando a temperatura do tratamento térmico decresce a solubilidade do
magnésio nos filmes de Sr1-xMgxTiO3 de x > 0.30 a 750o
C para x < 0.15 a
900o
C. De acordo com este estudo, o Mg não induz um estado ferroeléctrico
nem um comportamento do tipo relaxor em filmes finos de titanato de estrôncio
preparados por sol gel, quer quando a substituição ocorre nos locais A ou B da
rede do ST.
A estrutura, dinâmica de rede e propriedades dieléctricas de filmes finos de
ST dopados com Bi são também apresentados neste trabalho e discutidos pela
primeira vez. Nos filmes de Sr1-1.5xBixTiO3 o modo TO1 torna-se mais duro e
independente da temperatura e uma relaxação a baixas frequências aparece
com o aumento do conteúdo de Bi. A posição do máximo de ε′ dos filmes
estudados desloca-se para temperaturas mais altas com o aumento da
concentração de Bi e com o aumento da frequência. A presença de “clusters”
de dimensões nanométricas e dos iões de Bi em posição “off centre” causa
uma relaxação dieléctrica complexa. A relaxação dieléctrica induzida segue, a
lei de Arrhenius para as amostras com baixo teor de Bi (x < 0.04), e a relação
de Vogel-Fulcher para as amostras com as concentrações de dopante mais
elevadas (0.04 ≤ x ≤ 0.167). A dispersão da frequência de ε′ em filmes finos de
Sr1-1.5xBixTiO3 com pequenos teores de Bi é ligeiramente suprimida, quando em
comparação com os cerâmicos correspondentes, o que pode ser explicado
pela influência do substrato no caso dos filmes finos. Este estudo ilustra que a
incorporação de Bi na rede de ST origina um comportamento do tipo relaxor,
aumentando a tunabilidade dieléctrica. Filmes finos de Sr1-1.5xBixTiO3 com
elevados factores de qualidade (> 2000 numa gama de temperatura alargada)
são candidatos apropriados para utilização em sintonizadores.SrTiO3 (ST), crystallizing in the perovskite type structure, is a quantum
paraelectric, i.e., it exhibits a continuous increase of the dielectric permittivity
with decreasing temperature down to 4K, followed by the levelling off of the
permittivity to near 0K. The presence of lattice imperfections such as strain,
point defects, grain boundaries, and impurity atoms can appreciably modify the
properties of pure ST and even induce ferroelectricity.
In this work, systematic research on the structure, microstructure and
dielectric behaviour of polycrystalline SrTiO3 - based thin films prepared by solgel
is performed. The dielectric properties are studied in a wide temperature,
frequency and electric field ranges. For some films the dielectric
characterisation is assessed at radio-frequency (rf), time-domain terahertz
(THz-TDS), and infrared (IR) spectroscopy. The crystallographic and micro
structures of the undoped and doped ST films are analysed by X-ray diffraction
(XRD), Raman spectroscopy, scanning and transmission electron microscopy
(SEM and TEM) and Rutherford Backscattering Spectrometry (RBS)
techniques. Detailed investigations of the lattice dynamics in a wide frequency
range is undertaken as well.
It was observed, that undoped ST films grown on different substrates
(Al2O3/Pt, Si/SiO2/TiO2/Pt, (LaAlO3)0.3-(Sr2AlTaO6)0.7/Pt, SrTiO3/Pt and MgO/Pt)
have different structural and dielectric properties dependent on the strain/stress
effect induced by the substrate. For the case of ST films on MgO substrates the
appearance of some “slip band dislocations” within the film grains was detected
due to the high compressive stresses from the substrate. Whereas TO1 mode
of ST films deposited on Al2O3 behaves similarly to that of ST single crystals in
the temperature range from 300K to 150K. TO1 mode of ST films deposited on
MgO substrate is stiffened, what can also be explained by influence of the
stresses. ST films, with the highest compressive stress, deposited on MgO/Pt
substrate shows the highest value of the real part of the dielectric permittivity
(ε′), the largest hysteresis loop, and the highest value of the dielectric tunability
(nr) in opposition to ST films, with the highest tensile stress, deposited on
Al2O3/Pt substrates.
The role of the technological aspects associated with the preparation of highquality
sol-gel ST films is reflected in the elevated ε′ and nr of ST films, obtained
by introducing buffer layers, intermediately annealed at 600o
C, and by
increasing films annealing temperature from 750o
C to 900o
C. As a
consequence ε′ and nr of ~700 and ~50% are attained, being among the
highest values reported for ST sol gel based films.
Based on the theoretical prediction, that the off-centre displacements of small
Mg ions at the large Sr sites can induce dielectric anomalies in ST, the
incorporation of Mg in ST films was addressed in this work. Solid solubility limit
of Mg was found to depend on the lattice site of incorporation and annealing
temperature. Increasing annealing temperature decreases the solubility in
Sr1-xMgxTiO3 thin films from x > 0.30 for 750o
C to x < 0.15 at 900o
C. Moreover
Mg does not induce ferroelectricity or relaxor-like behaviour in strontium
titanate, either located in A- or B-site of the SrTiO3 lattice.
Within this work, the structure, low temperature lattice dynamics and dielectric
properties of Bi doped ST films are described and discussed for the first time.
In Sr1-1.5xBixTiO3 films TO1 mode becomes harder and, concomitantly a
temperature independent and low-frequency relaxation appears with increasing
of Bi content. The position of the maximum of ε′ of the investigated films shifts
to high temperatures with increasing Bi content and frequency. The presence of
nanoclusters and off-centred Bi ions causes a complex relaxation dynamics in
these films. The induced dielectric relaxation follows the Arrhenius law for the
samples with low Bi content (x < 0.04) and the Vogel-Fulcher law for the
samples with a higher doping concentration (0.04 ≤ x ≤ 0.167). The frequency
dispersion of ε′ in Sr1-1.5xBixTiO3 thin films with small amount of the Bi is slightly
suppressed, compared to the corresponding ceramics, what can be explained
by the influence of substrate. Bi incorporation in ST lattice leads to a relaxortype
dielectric response, increasing the dielectric tunability. Sr1-1.5xBixTiO3 thin
films with high value of the quality factor (> 2000 in wide temperature range)
are appropriate candidates for using in tunable applications
Crystallographic properties and elemental migration in two-stage prepared CuIn1−xAlxSe2 thin films for photovoltaic applications
No full textTwo-stage fabrication of CuIn1−xAlxSe2 thin films for photovoltaic absorbers using sputtered Cu–In–Al metallic precursors has been investigated. Precursors containing different relative amounts of Al were selenised and their structural and chemical properties characterised. X-ray diffraction (XRD) analyses revealed that the Al was only incorporated into the chalcopyrite structure for precursor composition ratios x = [Al]/([Al] + [In]) ⩾ 0.38, while chemical analysis of the cross-section indicated partial segregation of Al near the back of the film. Precursor films in the range of compositions that yielded no Al incorporation were then selenised at four different temperatures. Glow discharge optical emission spectroscopy, plasma profiling time-of-flight mass spectrometry and XRD analyses provided an insight into the diffusion processes and reactions taking place during the selenisation stage. The effect of post-selenisation annealing without additional Se was also investigated, and led to partial incorporation of the Al into the CuInSe2 lattice but no rediffusion
Electrical, morphological and structural properties of RF magnetron sputtered Mo thin films for application in thin film photovoltaic solar cells
No full textMolybdenum (Mo) thin films were deposited using radio frequency magnetron sputtering, for application as a metal back contact material in ‘‘substrate configuration’’ thin film solar cells. The variations of the electrical, morphological, and structural properties of the deposited films with sputtering pressure, sputtering power and post-deposition annealing were determined. The electrical conductivity of the Mo films was found to increase with decreasing sputtering pressure and increasing sputtering power. X-ray diffraction data showed that all the films had a (110) preferred orientation that became less pronounced at higher sputtering power while being relatively insensitive to process pressure. The lattice stress within the films changed from tensile to compressive with increasing sputtering power and the tensile stress increased with increasing sputtering pressure. The surface morphology of the films changed from pyramids to cigar-shaped grains for a sputtering power between 100 and 200 W, remaining largely unchanged at higher power. These grains were also observed to decrease in size with increasing sputtering pressure. Annealing the films was found to affect the resistivity and stress of the films. The resistivity increased due to the presence of residual oxygen and the stress changed from tensile to compressive. The annealing step was not found to affect the crystallisation and grain growth of the Mo films
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