Final Film Structure Research Articles

Pyrolysis, Crystallization, and Sintering of Mesostructured Titania Thin Films Assessed by in Situ Thermal Ellipsometry

In-situ thermal ellipsometric analysis is used to elucidate new and fine-scale details on the thermally driven densification, pyrolysis, crystallization, and sintering of dense and ordered mesoporous titania thin films prepared by evaporation-induced self-assembly. The role of the heating schedule, initial film thickness, nature of the substrate and templating agent, solution aging, and presence of water and other additives in the calcination environment is examined. Each of these parameters is shown to have unique and often substantial effects on the final film structure, while the technique itself provides detailed insight into the chemical origin and evolution of these effects. In-situ monitoring and control over the governing chemical processes, such as high-temperature adsorption phenomena that impact nanocrystal growth, is also demonstrated. The evolution of both the porosity and chemical processes occurring inside these materials are evaluated, including extraction of kinetic parameters for the pyrolysis of the template and crystallization of the matrix walls. The latter is shown to be strongly dependent on the presence of mesoscale ordering with ordered cubic films indicating a 1D diffusion-limited crystallization process and dense films following a 3D diffusion-limited process. Less well-ordered mesoporous films, despite similarities in pore volume and pore size distributions, are kinetically more reminiscent of dense films in terms of crystallization. In-situ thermal ellipsometry, by detailing the evolution of the thermally driven chemistry and ceramization that dictate the final film properties, provides immensely important insight into the synthesis and optimization of advanced functional materials based on titania and other metal oxide thin films.

Barrier and optical properties of edible hydroxypropyl methylcellulose coatings containing surfactants applied to fresh cut carrot slices

Coatings made from hydroxypropyl methylcellulose (HPMC) containing surfactant mixtures of sorbitan monostearate (SPAN 60) and sucrose palmitate (sucrose ester P-1570) in aqueous and hydroalcoholic media were developed to analyse the effect of the hydrocolloid/surfactant ratio (H/S), the hydrophilic–lipophilic balance (HLB) of the surfactant mixtures and the solvent type used as dispersing media on the water vapour barrier properties of the films and their optical effect when applied to carrot slices. The results showed that the solvent type, H/S ratio and HLB significantly affected viscosity, surface tension, and stability (particle size and flocculation rate) of the film-forming dispersions, which in turn had a great influence on the extensibility and final film structure of the coating on the carrot surface. All these aspects affected the water vapour barrier properties of the film. The best water vapour barrier properties were found in the coating made from hydroalcoholic dispersions with intermediate values of the surfactant's HLB. The colour of coated carrot slices was mainly affected by the solvent dispersion media, the induced changes being greater for aqueous dispersions.

Evolution of non-ionic surfactant-templated silicate films at the air–liquid interface

Spontaneous growth of non-ionic surfactant-templated thin films at the air–water interface was investigated using three techniques: Brewster angle microscopy (BAM), time-resolved off-specular X-ray reflectivity and grazing incidence X-ray diffraction (GIXD). Experiments were also carried out to study the evolution of micelles in the subphase solution using small-angle neutron scattering (SANS). Films were prepared in acidic conditions using octaethylene glycol mono-n-hexadecyl ether (C16EO8) as the surfactant and tetramethyloxysilane (TMOS) as the silica precursor. Three different TMOS–C16EO8 molar ratios (3.5, 7.1 and 10.8) were studied. Variation of the silica-precursor concentration causes a significant effect on the film-formation time, the solution and film-growth mechanisms and the final film structure.

Thermal furnace and Ultraviolet assisted curing impact on SiOCH spin-on ultra low dielectric constant materials

In recent years, the continuous progression of ultra-large scale integration has driven the emergence of technological solutions. In particular, major challenges have been faced for the fabrication of interconnect structures, where ultra low dielectric constants are required to decrease the parasitic capacitances between metal lines. Porous material, obtained using the porogen approach, is the main candidate investigated. The curing process is critical for achieving a good control of final film structure. The integration of such material requires a good chemical and mechanical stability, particularly to maintain the structure integrity during the stressing steps: chemical mechanical polishing and packaging. In this work, Ultraviolet assisted thermal cure (or UV curing) is investigated as an alternative solution to the conventional thermal curing. Chemical and physical analyses reveal that the best porogen removal efficiency and the enhancement of matrix crosslinking are achieved when the material is UV cured. This crosslinking improvement (as indicated by higher Si–O–Si bond density in the fourier transformed infra-red spectra) can be correlated to better mechanical properties. Significantly better electrical properties (dielectric constant, leakage current and breakdown voltage) are obtained with better integrity (no moisture uptake after 1 week storage in humid atmosphere 85 °C/85% relative humidity) when the dielectric is optimally cured. Porosity evaluation reveals similar results between both curing processes with slightly larger pore size in the case of the UV cured film. Finally, a basic model is described to illustrate how the UV assisted thermal cure may improve the crosslinking in comparison to the thermal curing. Selective UV action is proposed to explain the curing process kinetics.

BaZrO3Thin Films For Humidity Gas Sensor

AbstractMicroscale (MEMS) gas sensing devices for power plant and automobile exhaust gas are being developed. Bulk BaZrO3 has been previously found to be sensitive to H2O at high temperatures, but was never studied in a thin film form. This research thrust focuses on undoped BaZrO3 and doped BaZrO3 with Y.Thin films were deposited on oxidized n-type silicon substrates at room temperature from ceramic targets with an Ar sputtering ambient. Various deposition pressures and deposition powers were used for the initial investigation. The structural and electrical properties of the deposited films were characterized to investigate their relationships to the deposition process parameters. X-ray diffraction (XRD) was used to measure the crystal structure of the deposited films, and in particular was used to determine if any crystallographic texture is present in the films. XRD results indicate the as-deposited films are amorphous before annealing. Films sputtered with and without oxygen in the ambient were compared. The crystal structure and morphology of BaZrO3 and BaZrO3 doped with Y after annealing were also determined. The materials changed from amorphous to crystalline after annealing at temperatures of 800 °C and 1000 °C for 3 hours in forming gas (2% H2 balanced with Ar gas) and oxygen. Temperature was found to dominate over deposition conditions in determining the final film structure. Atomic force microscopy was used to examine the morphology of the thin films. Gas sensor test structures using a Pt thin film metallization for interdigitated electrode structures were fabricated for gas sensing measurements. The experiments with the completed test structures measured the materials¡¦ resistivity as a function of temperature and gas concentration. Both materials decrease in resistance with increasing temperature, which is consistent with ionic conduction. Some experiments tested the gas sensitivity and selectivity of the films to the target gas H2O vapor (humidity) and possible cross sensitive gases H2 and CO2. Both materials need further development to evaluate their suitability for thin film sensors. First, the films were found to be highly resistive, making characterization of the electrical properties very difficult. Second, O2 ambient annealing gas will be applied to compare the crystal structure and morphology of both films with an Ar ambient annealing process.

The relationship between chemical structure and dielectric properties of plasma-enhanced chemical vapor deposited polymer thin films

Polymer dielectric films fabricated by plasma enhanced chemical vapor deposition (PECVD) have unique properties due to their dense crosslinked bulk structure. These spatially uniform films exhibit good adhesion to a variety of substrates, excellent chemical inertness, high thermal resistance, and are formed from an inexpensive, solvent-free, room temperature process. In this work, we studied the dielectric properties of plasma polymerized (PP) carbon-based polymer thin films prepared from two precursors, benzene and octafluorocyclobutane. Two different monomer feed locations, directly in the plasma zone or in the downstream region (DS) and two different pressures, 80 Pa (high pressure) or 6.7 Pa (low pressure), were used. The chemical structure of the PECVD films was examined by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. The dielectric constant ( ε r) and dielectric loss (tan δ) of the films were investigated over a range of frequencies up to 1 MHz and the dielectric strength (breakdown voltage) ( F b) was characterized by the current-voltage method. Spectroscopic ellipsometry was performed to determine the film thickness and refractive index. Good dielectric properties were exhibited, as PP-benzene films formed in the high pressure, DS region showed a F b of 610 V/μm, an ε r of 3.07, and a tan δ of 7.0 × 10 − 3 at 1 kHz. The PECVD processing pressure has a significant effect on final film structure and the film's physical density has a strong impact on dielectric breakdown strength. Also noted was that the residual oxygen content in the PP-benzene films significantly affected the frequency dependences of the dielectric constant and loss.

Real‐time Raman spectroscopic measurement of crystallization kinetics and its effect on the morphology and properties of polyolefin blown films

The nonisothermal crystallization half-time (t0.5), defined as the time taken for a polymer film to reach half of its equilibrium crystallinity, was estimated from Raman spectroscopic measurements of crystallinity during blown film extrusion of a linear low-density polyethylene (LLDPE) and an isotactic polypropylene (i-PP). The crystalline a- and c-axis orientation of LLDPE and i-PP films, respectively, increased with decreasing crystallization half-time. The transverse direction tensile modulus and tear strengths for LLDPE films also increased with decreasing half-time. However, for i-PP films, only the transverse direction tear strength increased with decreasing t0.5, while the machine direction properties did not show a significant dependence on half-time. Our real-time Raman spectroscopy studies provide experimental evidence to theories proposed in the literature1–3 with regards to the influence of the nonisothermal crystallization process (along the film axis) on the imparted final film structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1740–1747, 2005

Thin polymer films on chemically patterned, corrugated substrates

We study the effect of a chemical pattern on the wetting and dewetting behaviourof thin polystyrene (PS) films on regularly corrugated silicon substrates. Ourresults reveal that the film preparation, annealing method, and confinement play acritical role in the final film structure. On evaporating gold on both sides of thefacets (such that it covered the crests of the facets, and not the troughs), weobserved dewetting, which proceeded to the gold, demonstrating an enthalpic effectcontrary to the outcome previously observed when gold was only evaporated onone side of the facet. We also coated the substrate with octadecyltrichlorosilane(OTS); this led to a gold and OTS striped structure. PS films several nanometresthick dewet such substrates, with a preferential direction for dewetting in thedirection of the stripes forming droplets of a considerably larger size than the stripes.

Characterization of Phase Separation in Film Forming Biopolymer Mixtures

Enhanced, tailor-made films can be achieved by combining the good gas barrier of the hydrophilic high amylose maize starch (hylon) with the water resistance of the hydrophobic protein zein. Two polymers are not always miscible in solution, and the phase separation behavior of the mixture is therefore important for the final film structure and its properties. Phase separation of a mixture of these two biopolymers was induced either by cooling, which was observed as growing droplets of the hylon phase which in some cases also formed small aggregates, or by solvent evaporation and studied in real-time in a confocal laser scanning microscope. Solvent evaporation had a much stronger effect on phase separation. During the early stage of phase separation, hylon formed large aggregates and subsequently smaller droplets coalesced with other droplets or large hylon aggregates. The later part of the separation seemed to take place through spinodal decomposition.

The growth and chemical structure of thin photonic films formed from plasma copolymerization: I. Effect of monomer feed ratio

Fabrication methodologies of thin, optical quality polymer films are important given the current interest in photonics. Plasma enhanced chemical vapor deposition (PECVD) has been previously investigated as a useful technique to polymerize various organic precursors. In the work presented here, we have studied the simultaneous plasma copolymerization of two monomers, benzene and octafluorocyclobutane (OFCB), and explored the structure of the final films using FTIR and XPS in order to tailor the resulting optical properties. There is a complex relationship between the film structures and the input parameters including monomer feed ratio and feed location. In plasma copolymerization, the gas phase initiation of the monomers is strongly dependent upon the bond dissociation energy of their structural moieties. The change of the monomer feed ratio leads to different trends with respect to various CFn(n=1–3) structural units, resulting in differences in the final film structure. Defluorination of the copolymer films was significantly enhanced by the addition of a small amount of benzene. The main fluorine-containing structural unit was the CF moiety for the copolymerized film, which is different from both homopolymerized OFCB and conventional PTFE polymers where the main fluorine-containing structural unit is CF2. Retention of conjugation and aromaticity in the resultant films was also observed.

Mechanical Properties of Organosilicon Thin Films Deposited from Cyclic and Acyclic Precursors using Water as an Oxidant.

AbstractPulsed-plasma chemical vapor deposition was used to deposit thin films from four different organosilicon (OSG) precursors, using water as the oxidant. The OSG precursors varied in structure (cyclic or acyclic), chemical composition (siloxane or silane), and type of organic substituent. Significant differences in final film structure were observed based on precursor identity, with the primary result being that cyclic siloxane precursors yielded films with a greater degree of crosslinking. The identity of the organic substituents was shown to affect the crosslinking potential, in that more reactive side groups, such as vinyl groups, facilitated the formation of crosslinking groups. At low power (200 W), film structure was dictated by precursor identity, whereas at high power (400 W), film structure became more uniform and precursor identity was less important. Mechanical properties tracked with plasma power, with low power samples being relatively soft, with hardness values between 0.126 GPa and 0.536 GPa. Samples produced at higher powers are more extensively crosslinked, resulting in enhanced mechanical properties. Samples produced at high powers had hardness values between 0.679 and 3.22 GPa, depending upon precursor identity. Dielectric constants ranged between 2.3 and 4.0.

The Influence of Film Coating on the Surface Roughness and Specific Surface Area of Pellets

The aim of this paper was to study the surface roughness of pellets after the application of a film coat. In total eight batches of pellets were examined of which four were considered to be round, whereas the other four deviated from the spherical shape by various degrees. The determination of the specific surface area of the coated pellets suggested that, although the film appeared to have filled the pores, the final film structure still mirrored the original surface structure of the pellets. However, profilometry was able to evaluate these gross results in more detail. From the latter measurements it appeared as though the pellet shape was another major influence factor on the final surface texture of the film coating. Pellets with a more elongated and irregular shape such as dumbbells provided more possibilities for interparticulate contact during the coating process, whereby film forming material was ripped off the pellet surfaces making these appear more rough due to surface defects. The use of alcoholic binder solutions during the pellet production might have resulted in surfaces with slightly changed surface free energy, which allowed a better spreading and adhesion of the polymer film and resulted in less textured film surfaces.

Mechanism of hydrogen-induced crystallization of amorphous silicon.

Hydrogenated amorphous and nanocrystalline silicon films manufactured by plasma deposition techniques are used widely in electronic and optoelectronic devices. The crystalline fraction and grain size of these films determines electronic and optical properties; the nanocrystal nucleation mechanism, which dictates the final film structure, is governed by the interactions between the hydrogen atoms of the plasma and the solid silicon matrix. Fundamental understanding of these interactions is important for optimizing the film structure and properties. Here we report the mechanism of hydrogen-induced crystallization of hydrogenated amorphous silicon films during post-deposition treatment with an H(2) (or D(2)) plasma. Using molecular-dynamics simulations and infrared spectroscopy, we show that crystallization is mediated by the insertion of H atoms into strained Si-Si bonds as the atoms diffuse through the film. This chemically driven mechanism may be operative in other covalently bonded materials, where the presence of hydrogen leads to disorder-to-order transitions.

FACET: a novel model of simulation and visualization of polycrystalline thin film growth

We present a two-dimensional polycrystalline thin film growth model based on describing grains in terms of faceted surfaces and grain boundaries. The profiles of the nuclei are described by crystallographically appropriate facets, with the position and orientation of the nuclei semi-randomly selected. Growth rates are determined from deposition fluxes and a new one-dimensional kinetic lattice Monte Carlo (KLMC) method developed to treat surface diffusion effects. The one-dimensional KLMC was verified by comparison with a full three-dimensional KLMC code. A continuum facet model has been developed to simulate grain growth and interaction. Users can visualize the nucleation and growth process of the film and obtain the final film structure, including the topography as well as the texture. The codes are written in Visual Basic and can be run in a Windows 98/2000/NT environment. An integrated graphical user interface has been implemented to facilitate use. The β version of FACET can be freely downloaded from our web site: http://ceaspub.eas.asu.edu/cms/.

Mesoscopic Patterns in POMA Spin-coated Films: A Systematic Study

The surface morphology of poly(o-methoxy aniline) (POMA) films produced by spin coating was systematically studied using Atomic Force Microscopy (AFM). Initial solution concentrations, rotation speeds and relative humidity affected the final film structure and thickness. Particularly interesting is the unexpected appearance, at solution concentrations of 2% or higher, of regular patterns composed of characteristic nanometer sized holes. These patterns were caused by phase separation.

Mesoscopic Patterns in POMA Spin-coated Films: a Systematic Study

The surface morphology of poly(o-methoxy aniline) (POMA) films produced by spin coating was systematically studied using Atomic Force Microscopy (AFM). Initial solution concentrations, rotation speeds and relative humidity affected the final film structure and thickness. Particularly interesting is the unexpected appearance, at solution concentrations of 2% or higher, of regular patterns composed of characteristic nanometer sized holes. These patterns were caused by phase separation.

Effects of deposition temperature and pressure of the surface roughness and the grain size of polycrystalline Si1−xGex films

The effects of temperature and pressure on the surface roughness and the grain size of poly-Si1−xGex films, and the effect of the initial surface state on the final film surface roughness and grain size, have been investigated. The deposition temperature and pressure were varied from 450 to 600 °C and from 1 to 50 Torr, respectively. The transition temperature from amorphous to polycrystalline during the deposition was about 525 °C for the Si0.46Ge0.54 alloy film and the average grain size of the film deposited at 600 °C and 3 Torr was measured approximately as 180 nm. As the temperature increased, the grain size and the rms (root mean square) surface roughness increased at constant pressure, whereas both were decreased with increasing pressure at constant temperature. The initial surface state of Si1−xGex film influenced the final film structure such as the surface roughness and grain size. The smooth surface was obtained at higher pressure and lower temperature.

Real-Time Observation of Plasma Protein Film Formation on Well-Defined Surfaces with Scanning Force Microscopy

We report here the results of a scanning force microscopic (SFM) investigation into the structure of adsorbed bovine fibrinogen films on well-defined surfaces. SFM images show that a monolayer of fibrinogen assembles on both highly oriented pyrolytic graphite (HOPG) and mica. We find, however, that the film morphology varies as a function of the substrate. To unravel the nature of the observed differences, we tracked the growth of bovine fibrinogen layers at both surfaces in real-time. Consistent with the differences observed in the final film structure, we find that film formation on HOPG and mica proceeds through distinct mechanisms. A network is observed during fibrinogen film formation on HOPG, implying that protein−protein interactions are involved in the growth mechanism and likely govern the final film structure. The growth mechanism on mica proceeds by the homogeneous increase in the number of nuclei across the surface and gives no indication of significant intermolecular interactions. Surfactant ...

Crystallization of rapid thermal processed PZT

Abstract The influence of substrate materials on the crystallization kinetics of thin film PZT is presented. Structure and orientation of electrodes affect the nucleation and growth processes of PZT as it transforms from pyrochlore to perovskite. These determine the final film structure and ferroelectric and dielectric properties. Rapid thermal processed sol gel PZT was fabricated on ruthenium oxide (RuO2) and on platinum electrodes. A study of oriented RuO2 electrodes was carried out using glancing angle XRD and transmission electron microscopy (TEM). These techniques were used to assess types and locations of phases present in the films, grain size, crystal orientation and morphology.

The Structural Characteristics of Certain Silver Films

The structural characteristics of three types of silver films which have found general use as photocathode bases in television image analyzers and similar electronic devices are discussed. They are classified as mosaics and translucent films. Two types of mosaics are discussed, (1) the reduced oxide dust film, and (2) the agglomerated sputtered or evaporated film. A characteristic of the first is a wide range in particle size (<1−30μ in films photographed), those below 3 microns being greatest in number. A critical temperature, approx. 600°C, is observed in reduction of the oxide films above which there is a distinct liquid phase in the silver-silver oxide system resulting in a radical change in the final film structure. The process of agglomeration is traced from the continuous through the mosaic state in the second type film. The characteristics are a smaller and more uniform particle size than the reduced oxide type. Particle size and spacing is readily controlled and reproduced. The range in initial thickness of films investigated is approximately 0.01−0.2 microns. The third type or translucent film is a composite consisting of a silver mosaic superposed on an electrically conducting film of relatively high light transmission. Platinum is chosen as the most suitable metal for this subfilm and is protected from destructive forces such as oxidation and alloying with the silver mosaic by an intermediate film of silica or aluminum oxide.