Atomic vapor deposition of bismuth titanate thin films

c-axis oriented ferroelectric bismuth titanate (Bi4Ti 3O12) thin films were grown on (001) strontium titanate (SrTiO3) substrates by an atomic vapor deposition technique. The ferroelectric properties of the thin films are greatly affected by the presence of various kinds of defects. Detailed x-ray diffraction data and transmission electron microscopy analysis demonstrated the presence of out-of-phase boundaries (OPBs). It is found that the OPB density changes appreciably with the amount of titanium injected during growth of the thin films. Piezo-responses of the thin films were measured by piezo-force microscopy. It is found that the in-plane piezoresponse is stronger than the out-of-plane response, due to the strong c-axis orientation of the films.

Epitaxially Grown Strained Pentacene Thin Film on Graphene Membrane

Organic-graphene system has emerged as a new platform for various applications such as flexible organic photovoltaics and organic light emitting diodes. Due to its important implication in charge transport, the study and reliable control of molecular packing structures at the graphene-molecule interface are of great importance for successful incorporation of graphene in related organic devices. Here, an ideal membrane of suspended graphene as a molecular assembly template is utilized to investigate thin-film epitaxial behaviors. Using transmission electron microscopy, two distinct molecular packing structures of pentacene on graphene are found. One observed packing structure is similar to the well-known bulk-phase, which adapts a face-on molecular orientation on graphene substrate. On the other hand, a rare polymorph of pentacene crystal, which shows significant strain along the c-axis, is identified. In particular, the strained film exhibits a specific molecular orientation and a strong azimuthal correlation with underlying graphene. Through ab initio electronic structure calculations, including van der Waals interactions, the unusual polymorph is attributed to the strong graphene-pentacene interaction. The observed strained organic film growth on graphene demonstrates the possibility to tune molecular packing via graphene-molecule interactions.

Plasma diagnostics and ITO film deposition by RF-assisted closed-field dual magnetron system

Deposition of indium tin oxide (ITO) among various transparent conductive materials on flexible organic substrates has been intensively investigated among academics and industrials for a whole new array of imaginative optoelectronic products. One critical challenge coming with the organic materials is their poor thermal endurances, considering that the process currently used to produce industry-standard ITO usually involves relatively high substrate temperature in excess of 200��C and post-annealing. A lower processing temperature is thus demanded, among other desires of high deposition rate, large substrate area, good uniformity, and high quality of the deposited materials. For this purpose, we developed an RF-assisted closed-field dual magnetron sputtering system. The ���prototype��� system consists of a 3-inch unbalanced dual magnetron operated at a closed-field configuration. An RF coil was fabricated and placed between the two magnetron cathodes to initiate a secondary plasma. The concept is to increase the ionization faction with the RF enhancement and utilize the ion energy instead of thermal energy to facilitate the ITO film growth. The closed-field unbalanced magnetrons create a plasma in the intervening region rather than confine it near the target, thus achieving a large-area processing capability. An RF-compensated Langmuir probe was used to characterize and compare the plasmas in mirrored balanced and closed-field unbalanced magnetron configurations. The spatial distributions of the electron density ne and electron temperature Te were measured. The density profiles reflect the shapes of the plasma. Rather than intensively concentrated to the targets/cathodes in the balanced magnetrons, the plasma is more dispersive in the closed-field mode with a twice higher electron density in the substrate region. The RF assistance significantly enhances ne by one or two orders of magnitude higher. The effect of various other parameters, such as pressure, on the plasma was also studied. The ionization fractions of the sputtered atoms were measured using a gridded energy analyzer (GEA) combined with a quartz crystal microbalance (QCM). The presence of the RF plasma effectively increases the ITO ionization fraction to around 80% in both the balanced and closed-field unbalanced configurations. The ionization fraction also varies with pressure, maximizing at 5-10 mTorr. The study of the ionization not only facilitates understanding the plasma behaviors in the RF-assisted magnetron sputtering, but also provides a criterion for optimizing the film deposition process. ITO films were deposited on both glass and plastic (PET) substrates in the 3-inch RF-assisted closed-field magnetrons. The electrical resistivity and optical transmission transparency of the ITO films were measured. Appropriate RF assistance was shown to dramatically reduce the electrical resistivity. An ITO film with a resistivity of 1.2��10-3 ��-cm and a visible light transmittance of 91% was obtained with a 225 W RF enhancement, while the substrate temperature was monitored as below 110��C. X-ray photoelectron spectroscopy (XPS) was employed to confirm the ITO film stoichiometry. The surface morphology of the ITO films and its effect on the film properties were studied using atomic force microscopy (AFM). The prototype of RF-assisted closed-field magnetron was further extended to a larger rectangular shaped dual magnetron in a flat panel display manufacturing system. Similar improvement of the ITO film conductivities by the auxiliary RF was observed on the large-area PET substrates. Meanwhile, significant deposition rates of 25-42 nm/min were achieved.

Intergranular Corrosion and Stress Corrosion Cracking of Extruded AA6005A

A research program focused on understanding the intergranular corrosion (IGC) and stress corrosion cracking (SCC) behavior of AA6005A aluminum extrusions is presented in this dissertation. The relationship between IGC and SCC susceptibility and the mechanisms of SCC in AA6005A extrusions were studied by examining two primary hypotheses. IGC susceptibility of the elongated grain structure in AA6005A exposed to low pH saltwater was found to depend primarily on the morphology of Cu-containing precipitates adjacent to the grain boundaries in the elongated grain structure. IGC susceptibility was observed when a continuous (or semi-continuous) film of Cu-containing phase was present along the grain boundaries. When this film coarsened to form discrete Cu-rich precipitates, no IGC was observed. The morphology of the Cu-rich phase depended on post-extrusion heat treatment. The rate of IGC penetration in the elongated grain structure of AA6005A-T4 and AA6005A-T6 extrusions was found to be anisotropic with IGC propagating most rapidly along the extrusion direction, and least rapidly along the through thickness direction. A simple 3-dimensional geometric model of the elongated grain structure was accurately described the observed IGC anisotropy, therefore it was concluded that the anisotropic IGC susceptibility in the elongated grain structure was primarily due to geometric elongation of the grains. The velocity of IGC penetration along all directions in AA6005A-T6 decreased with exposure time. Characterization of the local environment within simulated corrosion paths revealed that a pH gradient existed between the tip of the IGC path and the external environment. Knowledge of the local environment within an IGC path allowed development of a simple model based on Fick's first law that considered diffusion of Al3+ away from the tip of the IGC path. The predicted IGC velocity agreed well with the observed IGC velocity, therefore it was determined that diffusion of Al3+ was the primary factor in determining the velocity of IGC penetration. The velocity of crack growth in compact tensile (CT) specimens of AA6005A-T6 extrusion exposed to 3.5% NaCl at pH = 1.5 was nearly constant over a range of applied stress intensities, exposure times, and crack lengths. The crack growth behavior of CT specimens of AA6005A-T6 extrusion exposed to a solution of 3.5% NaCl at pH = 2.0 exhibited similar behavior, but the crack velocity was ~10.5X smaller than that those exposed to a solution at pH =1.5. Analysis of the local stress state and polarization behavior at the crack tip predicted that increasing the pH of the bulk solution from 1.5 to 2.0 would decrease the corrosion current density at the crack tip by approximately 11.8X. This predicted decrease in corrosion current density was in reasonable agreement with the observed decrease in SCC velocity associated with increasing the solution pH from 1.5 to 2.0. The agreement between the predicted and observed SCC velocities suggested that the electrochemical reactions controlling SCC in AA6005A-T6 extrusions are ultimately controlled by the pH gradient that exists between the crack tip and external environment.

High bandwidth freestanding semipolar (11���22) InGaN/GaN light-emitting diodes

Freestanding semipolar (11���22) indium gallium nitride (InGaN) multiplequantum-well light-emitting diodes (LEDs) emitting at 445 nm have been realized by the use of laser lift-off (LLO) of the LEDs from a 50- m-thick GaN layer grown on a patterned (10���12) r -plane sapphire substrate (PSS). The GaN grooves originating from the growth on PSS were removed by chemical mechanical polishing. The 300 m �� 300 m LEDs showed a turn-on voltage of 3.6 V and an output power through the smooth substrate of 0.87 mW at 20 mA. The electroluminescence spectrum of LEDs before and after LLO showed a stronger emission intensity along the [11���23]InGaN/GaN direction. The polarization anisotropy is independent of the GaN grooves, with a measured value of 0.14. The bandwidth of the LEDs is in excess of 150 MHz at 20 mA, and back-to-back transmission of 300 Mbps is demonstrated, making these devices suitable for visible light communication (VLC) applications.

Hybrid layer-by-layer assembly based on animal and vegetable structural materials: multilayered films of collagen and cellulose nanowhiskers

Layer-by-layer (LBL) assembly was used to combine crystalline rod-like nanoparticles obtained from a vegetable source, cellulose nanowhiskers (CNWs), with collagen, the main component of skin and connective tissue found exclusively in animals. The film growth of the multilayered collagen/CNW was monitored by UV-Vis spectroscopy and ellipsometry measurements, whereas the film morphology and surface roughness were characterized by SEM and AFM. UV-Vis spectra showed the deposition of the same amount of collagen, 5 mg m(-2), in each dipping cycle. Ellipsometry data showed an increment in thickness with the number of layers, and the average thickness of each bilayer was found to be 8.6 nm. The multilayered bio-based nanocomposites were formed by single layers of densely packed CNWs adsorbed on top of each thin collagen layer where the hydrogen bonding between collagen amide groups and OH groups of the CNWs plays a mandatory role in the build-up of the thin films. The approach used in this work represents a potential strategy to mimic the characteristics of natural extracellular matrix (ECM) which can be used for applications in the biomedical field.

Impedance characteristics of the diamond/carbon fiber electrodes for electrical double-layer capacitor

The electrochemical performance of carbon fibers (CF) and boron-doped diamond electrodes grown on carbon fiber substrate (BDD/CF) was studied. CF substrates were obtained from polyacrylonitrile precursor heat treated at two different temperatures of 1000 and 2000 degrees C to produce the desirable CF carbon graphitization index. This graphitization process influenced the CF conductivity and its chemical surface, also analyzed from X-ray photoelectron spectroscopy measurements. These three-dimensional CF structures allowed a high incorporation of diamond films compared to other carbon substrates such as glass carbon or HOPG. The electrochemical responses, from these four classes of electrodes, were evaluated focusing their application as electrical double-layer capacitors using cyclic voltammetry and impedance measurements. Cyclic voltammetry results revealed that the electrode formed from BDD grown on CF-2000 presented a typical capacitor behavior with the best rectangular shape, compared to those electrodes of CF or BDD/CF-1000. Furthermore, the BDD/CF-2000 electrode presented the lowest impedance, associated to its significant capacitance value of 1940 mu F/cm(2) taking into account the BDD films. This behavior was attributed to the strong dependence between diamond coating texture and the CF graphitization temperature. The largest surface area of BDD/CF-2000 was promoted by its singular film growth mechanism associated to the substrate chemical surface. (c) 2008 Elsevier B.V. All rights reserved.

Schichtwachstum, optische und elektrische Eigenschaften von Silber auf PET-Folie

Film growth, electrical properties, optical properties, Ag, magnetron sputtering

Analysis of a boundary protein delimiting chromatin domains in yeast

SUMMARY The expression state of a eukaryotic gene depends in part on its location in the chromosome. This position effect results from the organization of eukaryotic genomes into discrete functional domains, defined by local differences in chromatin structure. The expression of genes within each domain appears to be defined and maintained by the concerted action of regulatory elements such as promoters, enhancers, silencers and locus control regions. Individual domains may be bordered by boundary elements that separate regions of permissive and silent chromatin. When located next to chromosomal elements such as telomeres, genes can be subjected to epigenetic silencing. In yeast, this is mediated by the propagation of the SIR proteins from telomeres towards more centromeric regions. Particular transcription factors can protect downstream genes from silencing when tethered between the gene and the telomere, and they may thus act as chromatin domain boundaries. Here we have studied one of these transcription factors, CTF-1, that binds directly histone H3. A deletion mutagenesis localized the barrier activity to CTF-1 histone-binding domain. A saturating point mutagenesis of this domain identified several amino-acid substitutions that similarly inhibited the boundary and histone-binding activities. Chromatin immunoprecipitation experiments indicated that the barrier protein efficiently prevents the spreading of SIR proteins, and that it separates domains of hypoacetylated and hyperacetylated histones. Together, these results suggest a mechanism by which proteins such as CTF-1 may interact directly with histone H3 to prevent the propagation of a silent chromatin structure, thereby defining boundaries of permissive and silent chromatin domains. RESUME L'expression des g��nes eucaryotes d��pend en partie de leur localisation sur les chromosomes. Cet effet de position r��sulte de l'organisation des g��nomes eucaryotes en domaines fonctionnels, d��finis par des changements locaux au niveau de la structure de la chromatine. Dans chacun de ces domaines, l'expression des g��nes est d��finie et maintenue par l'action concert��e de diff��rents ��l��ments r��gulateurs tels que les promoteurs, les amplificateurs, les silenceurs et les locus control r��gions. Ces domaines peuvent ��tre entour��s par des ��l��ments barri��re, s��parant les r��gions de chromatine r��pressive des r��gions permissive pour l'expression des g��nes. Lorsqu'ils se situent �� proximit�� d'��l��ments chromosomiques comme les telom��res, les g��nes peuvent ��tre r��prim��s de mani��re ��pig��n��tique. Chez la levure, cette r��pression est ��tablie par la propagation des prot��ines SIR depuis les t��lom��res vers les r��gions centrom��riques. Certains facteurs de transcription peuvent emp��cher la r��pression d'un g��ne, lorsqu'ils sont plac��s entre ce g��ne et le t��lom��re. Nous avons ��tudi�� un de ces facteurs, CTF-1, qui a la particularit�� de lier directement l'histone H3. La d��l��tion de certaines parties de CTF-1 a permis de d��terminer que la r��gion responsable de l'activit�� barri��re correspond au domaine d'interaction avec H3. Plusieurs mutations points effectu��es dans ce domaine inhibent �� la fois l'activit�� barri��re et la capacit�� de lier H3. Des exp��riences d'immuno-pr��cipitation de la chromatine indiquent que la prot��ine barri��re CTF-1 pr��vient efficacement la propagation des prot��ines SIR et s��pare des domaines contenant des histones hypo-ac��tyl��es de ceux constitu��s d'histones hyper-ac��tyl��es. Ces r��sultats sugg��rent que CTF-1 interagit directement avec l'histone H3 pour emp��cher la propagation de la chromatine r��pressive, d��limitant ainsi des domaines de chromatine permissive et des domaines de chromatine silencieuse.

Self-interference of charge carriers in ferromagnetic SrRuO3

We report a systematic study of the low-temperature electrical conductivity in a series of SrRuO3 epitaxial thin films. At relatively high temperature the films display the conventional metallic behavior. However, a well-defined resistivity minimum appears at low temperature. This temperature dependence can be well described in a weak localization scenario: the resistivity minimum arising from the competition of electronic self-interference effects and the normal metallic character. By appropriate selection of the film growth conditions, we have been able to modify the mean-free path of itinerant carriers and thus to tune the relative strength of the quantum effects. We show that data can be quantitatively described by available theoretical models.

Obten����o de filmes espessos de seleneto de cobre sobre carbono v��treo, ouro, tit��nio e cobre

Copper selenide (berzelianite) films were prepared on the title substrates using the chemical bath deposition technique (CBD). Film composition was determined by energy dispersion of x-rays. The kinetics of film growth is parabolic and film adherence limits the film thickness. On titanium, copper selenide forms islands that do not completely cover the surface, unless the substrate is prepared with a tin oxide layer; film composition also depends on the titanium oxide layer. On vitreous carbon, CBD and mechanical immobilization techniques lead to films with similar resistances for the electron transfer across the film/substrate interface. On gold, composition studies revealed that film composition is always the same if the pH is in the range from 8 to 12, in contrast to films prepared by an ion-ion combination route. On copper, a new procedure for obtaining copper selenide films as thick as 5 ��m has been developed.

Polymer surface modification by atomic layer deposition

Current industrial atomic layer deposition (ALD) processes are almost wholly confined to glass or silicon substrates. For many industrial applications, deposition on polymer substrates will be necessary. Current deposition processes are also typically carried out at temperatures which are too high for polymers. If deposition temperatures in ALD can be reduced to the level applicable for polymers, it will open new interesting areas and applications for polymeric materials. The properties of polymers can be improved for example by coatings with functional and protective properties. Although the ALD has shown its capability to operate at low temperatures suitable for polymer substrates, there are other issues related to process efficiency and characteristics of different polymers where new knowledge will assist in developing industrially conceivable ALD processes. Lower deposition temperature in ALD generally means longer process times to facilitate the self limiting film growth mode characteristic to ALD. To improve process efficiency more reactive precursors are introduced into the process. For example in ALD oxide processes these can be more reactive oxidizers, such as ozone and oxygen radicals, to substitute the more conventionally used water. Although replacing water in the low temperature ALD with ozone or plasma generated oxygen radicals will enable the process times to be shortened, they may have unwanted effects both on the film growth and structure, and in some cases can form detrimental process conditions for the polymer substrate. Plasma assistance is a very promising approach to improve the process efficiency. The actual design and placement of the plasma source will have an effect on film growth characteristics and film structure that may retard the process efficiency development. Due to the fact that the lifetime of the radicals is limited, it requires the placement of the plasma source near to the film growth region. Conversely this subjects the substrate to exposure byother plasma species and electromagnetic radiation which sets requirements for plasma conditions optimization. In this thesis ALD has been used to modify, activate and functionalize the polymer surfaces for further improvement of polymer performance subject to application. The issues in ALD on polymers, both in thermal and plasma-assisted ALD will be further discussed.

Roll-to-roll atomic layer deposition process for flexible electronics applications

Atomic Layer Deposition (ALD) is the technology of choice where very thin and highquality films are required. Its advantage is its ability to deposit dense and pinhole-free coatings in a controllable manner. It has already shown promising results in a range of applications, e.g. diffusion barrier coatings for OLED displays, surface passivation layers for solar panels. Spatial Atomic Layer Deposition (SALD) is a concept that allows a dramatic increase in ALD throughput. During the SALD process, the substrate moves between spatially separated zones filled with the respective precursor gases and reagents in such a manner that the exposure sequence replicates the conventional ALD cycle. The present work describes the development of a high-throughput ALD process. Preliminary process studies were made using an SALD reactor designed especially for this purpose. The basic properties of the ALD process were demonstrated using the wellstudied Al2O3 trimethyl aluminium (TMA)+H2O process. It was shown that the SALD reactor is able to deposit uniform films in true ALD mode. The ALD nature of the process was proven by demonstrating self-limiting behaviour and linear film growth. The process behaviour and properties of synthesized films were in good agreement with previous ALD studies. Issues related to anomalous deposition at low temperatures were addressed as well. The quality of the coatings was demonstrated by applying 20 nm of the Al2O3 on to polymer substrate and measuring its moisture barrier properties. The results of tests confirmed the superior properties of the coatings and their suitability for flexible electronics encapsulation. Successful results led to the development of a pilot scale roll-to-roll coating system. It was demonstrated that the system is able to deposit superior quality films with a water transmission rate of 5x10-6 g/m2day at a web speed of 0.25 m/min. That is equivalent to a production rate of 180 m2/day and can be potentially increased by using wider webs. State-of-art film quality, high production rates and repeatable results make SALD the technology of choice for manufacturing ultra-high barrier coatings for flexible electronics.

Pulsed laser deposition of YBa2Cu3O7-[delta]/PrBa2Cu3O7-[delta] /

The process of depositing thin films by the use of pulsed laser deposition (PLD) has become a more widely used technique for the growth of substances in a thin film form. Pulsed laser deposition allows for the stoichiometric film growth of the target which is of great significance in the deposition of High Temperature Superconducting materials. We will describe a system designed using an excimer laser and vaccum chamber in which thin films and superlattices of YBa2Cuj07_i, PrBa2Cu307_i, and YBajCujOr-j/ PrBajCusOr-^ were deposited on SrTiOs. Results of resistivity measurements using the four probe technique will be shown.

HG 186.55-186.75-1

Domain boundaries observed between the fine grained and coarse grained sediment. The coarse grained sediment contains lineations.