Search

Crystalline vanadium dioxide (VO 2 ) thin films were prepared by annealing amorphous VO 2 films which were deposited by atomic layer deposition on a SiO 2 substrate. A large influence of the oxygen partial pressure in the annealing ambient was observed by means of in-situ X-ray diffraction. In the range between 1 and 10 Pa of oxygen the interesting VO 2 (R) phase crystallized near 450 °C. Between 2 and 10 Pa of oxygen, metastable VO 2 (B) was observed as an intermediate crystalline phase before it transformed to VO 2 (R). Anneals in inert gas did not show any crystallization, while oxygen partial pressures above 10 Pa resulted in oxidation into the higher oxide phase V 6 O 13 . Film thickness did not have much effect on the crystallization behavior, but thinner films suffered more from agglomeration during the high-temperature crystallization on the SiO 2 substrate. Nevertheless, continuous polycrystalline VO 2 (R) films were obtained with thicknesses down to 11 nm. In the case where VO 2 (R) was formed, the semiconductor–metal transition was observed by three complementary techniques. This transition near 68 °C was characterized by X-ray diffraction, showing the transformation of the crystal structure, by spectroscopic ellipsometry, mapping optical changes, and by sheet resistance measurements, showing resistance changes larger than 2 orders of magnitude between the low-temperature semiconducting state and the high-temperature metallic state.

The SiOxCyHz layers synthesized by means of the atmospheric pressure glow-like DBD assisted PECVD technology show remarkable planarizing film properties, observed for the first time. The films were deposited in a roll-to-roll mode on large area polymeric webs using HMDSO and air as the precursor and oxidiser. FTIR analysis show the carbon content in the SiOx films is strongly correlated with the precursor flow rate resulting in SiO2-like layers with negligible carbon content at lower flow values (0.4 g/h), while at higher flow rates carbon rich SiOxCyHz films were obtained. Detailed AFM surface profile analysis show that the SiOxCyHz films smoothen out the global and local surface structures of the polymer comprising a reduction in rms surface roughness (0.99 ± 0.11 nm) and increase of roughness exponent (α = 0.97 ± 0.02) compared to that of PEN polymer. These ultra-smooth organic layers together with the smooth inorganic SiOx layers (1.75 ± 0.12 nm), exhibiting roughness comparable to the polymer (1.50 ± 0.07 nm) at lower precursor input, provide an efficient route to fabricate multilayer hybrid structures in a single chamber synthesis.

The development of the morphology and surface roughness of amorphous SiO2-like films, on various polymeric substrates was analyzed by atomic force microscopy. The inorganic oxide films were deposited from organo-silicon precursors with different reactive gases using dielectric barrier discharge assisted chemical vapor deposition (DBD-CVD) at atmospheric pressure in a roll-to-roll configuration. Detailed study on the roughness statistical parameters characterizing morphology shows that DBD-CVD films grow in a conformal and layer-by-layer like fashion on polymers very similar to films produced by atomic layer deposition process. Independent of substrate (planarised and non-planarised polyethylene-2,6-napthalate) and methodology used to build the thickness as stacks or single layers, the films were found to be smooth, both locally and globally, and show negligible development of roughness with thickness (≤350 nm). The scaling exponents observed, show that the film growth does not fall into any of the universality classes that have been reported so far.

NiO thin films are deposited by atomic layer deposition (ALD) from the Ni(dmamb)2 (dmamb = 1-dimethylamino-2-methyl-2-butanolate) precursor using O3 as the oxidizer. The films are analyzed for wafer uniformity, structure, composition, morphology, microstructure, and homogeneity. The Ni(dmamb)2 half-cycle shows an initial rapid partial saturation followed by slower further adsorption. By contrast, the O3 half-cycle shows good saturation behavior. In the studied deposition temperature range for ALD, the films are polycrystalline with negligible amounts of carbon in the films. Furthermore, the films are homogeneous in thickness and composition, demonstrating that high-quality NiO films can be deposited by ALD from Ni(dmamb)2.

Amongst the most common thin film characterization tools, spectroscopic ellipsometry (SE) is increasingly used to determine the layer optical properties. Such characterization is still a challenge when optical anisotropy is present either in the film or in the substrate. The study of thin films deposited on polymeric substrates is an example because polymers often show optical anisotropy. In this contribution the optical characterization of poly(ethylene 2,6-naphtalate) (PEN) in its transparent region is carried out by means of Transmission Generalized Ellipsometry (TGE) and reflection multi- angle SE measurements. TGE measurements allow the determination of the in-plane and out-of-plane anisotropy and orientation of the material index ellipsoid, with respect to the laboratory frame. Reflection multi-angle SE measurements are performed to determine the absolute refractive index values along the x, y and z directions (i.e. the laboratory frame). The full optical characterization of PEN substrates has been carried out first by identifying its in plane anisotropy (i.e. ?nxy = ny – nx) and in-plane orientation of the material index ellipsoid with respect to the x axis, by means of TGE measurements at 0° angle of incidence. A second step consisting of TGE measurements at different angles of incidence has allowed the determination of the out-of-plane anisotropy (i.e. ?nxz = nx – nz) and the material index ellipsoid out-of-plane orientation with respect to the z axis. Finally, reflection multi angle measurements have allowed the determination of the optical dispersions along the three axes (x, y, z). The values of the refractive index calculated at 633 nm are nx = 1. 74, ny = 1.75 and nz = 1.52. This characterization is functional to the determination of the refractive index of plasma-deposited SiO2-like layers deposited on PEN substrates. The SiO2-like samples have been deposited in Atmospheric Pressure Glow discharges [1,2] from Ar/O2/hexamethyldisiloxane mixtures at different duty cycles. SE measurements have been performed in ambient air and in vacuum: an increase of the refractive index values with the duty cycle has been observed, attributed, on the basis of complementary diagnostics, to an increase in film density with the duty cycle.

The growth of nickel and nickel-based alloys was investigated using the pulsed-spray evaporation (PSE) CVD process in hydrogen-free atmosphere. This process relies on the reactivity of ethanol, which was investigated using mass spectrometry. In fact, the dehydrogenation of ethanol to form acetaldehyde is identified as the reaction pathway that provides hydrogen atoms necessary to desorb acetylacetonate ligand of the precursor. This global reaction leads to the formation of metallic nickel film either in the hexagonal (hcp) lattice at low temperature or in the cubic (fcc) one at temperatures higher than 240 degrees C. In conditions where the fcc-Ni phase is deposited, the PSE-CVD process enables the deposition of Ni-Cu alloy thin films with fully controlled composition, whereas Ni-Ag forms polycrystalline silver, in addition to in amorphous phase containing silver and nickel. The synthesis of Ni-Co alloy thin films was performed under conditions where the hcp-Ni phase was obtained, providing for the first time a route toward deposition of nickel-rich hcp-Ni-Co.

This work reports on the main competing processes and their contribution to the properties of SiO2 layers on polymers in large area AP-PE-CVD from Ar-N2-O2-HMDSO mixtures. The detailed space resolved surface analysis on the statically deposited films showed smooth SiOx films in the vicinity of the gas injection, as deposited by HMDSO radicals. At the gas effluent, due to HMDSO depletion, non-depositing species interact with the polymer and induce rough deposits with high carbon content. The competition of plasma-polymer surface interaction with HMDSO radicals deposition, is further confirmed from the analysis of films grown on polymers with a "protecting" layer and with reverse gas flow direction. Under web roll conditions, HMDSO radicals deposition is dominant, resulting in high quality SiOx layers along the whole electrode length. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.

A new successful strategy is developed for the production of Ni, Cu, and Co films using commercially available metal acetylacetonates as precursors. Pulsed spray evaporation (PSE) CVD is applied utilizing only alcohols as solvents and reducing agents. The efficiency of the process, with respect to controlling parameters such as pulse width, pulsing frequency, carrier gas flow rate, and concentration of the precursors in the feedstock, is optimized. The growth of metal films as a function of substrate temperature, deposition pressure, and duration of deposition, is examined. Results demonstrate that the metal films grow on various substrates, including glass and SiC, without any incubation time and do not need a seed layer. Resulting resistivities are close to those of the bulk materials for Ni and Cu films, while a value of 150 mu Omega cm, which improves upon annealing, is measured for Co films.

Spinel cobalt oxide doped with nickel and zinc are deposited using a CVD reactor equipped with a pulsed spray evaporation system. This process allows easy control of the film composition through the adjustment of the composition of the liquid feed-stock; a linear dependence is observed in both cases. Doped spinels with atomic ratios of doping-metal to Co ranging from 0 to 0.5 are deposited and subjected to various surface characterization methods. Zinc as a doping metal, which nonselectively occupies the octahedral and the tetrahedral sites, preserves the cubic spinel structure; in contrast, nickel, which preferably occupies the octahedral sites, preserves the cubic structure only up to Ni/Co = 0.14 and then induces a tetragonal distortion. This disordered structure allows more polarons, and therefore presents a conductivity which increases substantially with the concentration of nickel in the deposited films. The thermal stability of cobalt oxide is maintained in the case of nickel doping as long as the cubic structure is preserved, and then decreases continuously with the concentration of nickel doping once the tetragonal deformation is induced. An upper thermal stability limit as low as 350 degrees C is observed for films with Ni/Co = 0.33. In contrast, zinc steadily improved the thermal stability with increased doping concentration, and reaches -850 degrees C, which is 200 degrees C higher than that of pure cobalt oxide.

Procedures for Ni films and the composite coatings of Ni/CrN deposited using plasma assisted metal-organic (MO) CVD are reported. Ni[(acac) 2 en] and Cr(acac) 3 were used as the precursors for Ni and Cr, respectively. The composite coatings of Ni/CrN were developed by simultaneous cracking of these volatile chemical vapor sources using a glow discharge DC plasma under sub-atmospheric pressure. Deposition of Ni films at various substrate temperatures indicated that pore-free films could be formed at a substrate temperature of 600 °C. Irrespective of the mass percentage of the precursors of Ni and Cr, X-ray diffraction (XRD) revealed a biphasic (CrN/Ni) structure for the composite coatings containing nanometer-sized particles. The addition of the soft Ni phase to the relatively harder CrN phase was found to control the hardness of the Ni/CrN composites. Transmission electron microscopy (TEM) studies confirmed the nanophasic distribution of Ni and CrN in the composite coatings.

Metal thin films are indispensable for the processing of a number of modern devices that benefit from their electronic, magneto-electric and optical properties. Application trends progressively involve integration into functional devices which feature three-dimensional nanostructures with increasingly high aspect ratios. These conditions promote increased interest towards non-line-of-sight deposition processes such as Chemical Vapour Deposition (CVD) and Atomic Layer Deposition (ALD). The deposition of metals using CVD or ALD is, however, less developed than that of the oxide counterparts. Several persisting limitations are directly related to the deposition chemistry. In the present perspective, relevant deposition chemical approaches are discussed along with their corresponding characteristics. Challenging issues regarding the purity and the nucleation kinetics are addressed. Using the intrinsic reactivity of the metals themselves to catalyse their own growth is one of the promising approaches emphasised here. Based on our recent work, the potential of this approach is discussed with respect to the growth of reactive and noble transition metals, pure or as alloys, as thin films or as embedded nanoparticles in functional oxide matrix thin films.

SiO2-like layers deposited by means of the developed atmospheric pressure glow-like DBD assisted CVD technology exhibit remarkable film properties, reported for the first time. The films synthesized in a roll-to-roll mode on polymeric webs, are as smooth as the substrate, irrespectively of the precursors (TEOS or HMDSO) and reactive gases (N2 or air) employed. Detailed AFM investigation on film morphology, surface roughness and auto correlation length (ξ) show that they are negligibly influenced with thickness and are similar to that of the polymeric substrate, indicating the self-similar growth of the SiO2-like layers in AP-PECVD. The films are uniform with no defects or particle being incorporated during the deposition process. The produced single layers on polymeric substrate show excellent gas barrier performances towards O2 and H2O permeation (OTR

Miniaturization of electronic devices imposes challenges in terms of materials and production methods, and advances in the chemical vapor deposition (CVD) of metals are a key prerequisite toward reliable interconnects that are essential for their functionality. Electrically conducting ultrathin films of pure copper were grown on glass and silicon substrates starting at a temperature of 195 degrees C. The growth kinetics does not exhibit any measurable nucleation time enabling early stage coalescence and high electrical conductivity. In situ monitoring of the CVD process using synchrotron-based mass spectrometry shows that the enhanced dehydrogenation of alcohols by copper(II) acetylacetonate precursor drives the Cu-0 deposition, which is kinetically favorable already at low temperature. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3205478] All rights reserved.

Starting from their corresponding acetylacetonate complexes, nickel, copper, and cobalt thin films are deposited in a hydrogen-free atmosphere using CVD. The investigated pulsed spray evaporation (PSE) CVD process uses precursors dissolved in an organic solvent as the feedstock. This paper reports on the major role of the solvent for the growth of metal films. Alcohol solvents such as methanol, ethanol, and n-propanol enabled the growth of metallic films, while nonalcohol solvents such as tetrahydrofuran and n-butyl acrylate failed. Higher alcohols tend to result in higher growth rates; however, they present a limited solubility of the acetylacetonate complexes. Metal films grow, starting at 493 K, on glass and other substrates with no incubation time, and the obtained films, with thicknesses below 30 nm, present a smooth morphology. Phase analysis with X-ray diffraction (XRD) reveals the hexagonal polycrystalline structure of Ni and Co, and the cubic structure of Cu.

The evolution of the surface roughness during the atomic-layer deposition (ALD) of Al2O3, NiO, and HfO2 was studied by atomic-force microscopy and nonspecular x-ray reflectance. The results indicate that the crystallinity of the films played a crucial role in the roughness evolution during ALD. While the ALD of amorphous oxide films showed replication of the initial starting surface with no roughness build-up, the ALD of polycrystalline oxide films led to a strong anomalous dependence of the roughness on the film thickness. This behavior is explained within a model taking into account spatial variations of the adsorption site density.

A novel chemical approach was demonstrated for the growth of high-quality, silver films by CVD. This concept relies on the catalytic reactivity of cationic silver, and of silver surfaces with alcohols. This leads to high-purity films using either state-of-the-art precursors or silver salts that have not been yet considered as CVD precursors. The occurrence of the catalytic oxidative-dehvdrogenation of alcohols, considered as the driving force in this process, was shown by in-situ mass spectrometry (MS). Films of fcc-Ag with p

Cobalt and cobalt carbide films were obtained using chemical vapor deposition (CVD) at low pressure in a hydrogen-free atmosphere at temperatures below 300 degrees C. Although the growth over bare glass was enabled, the use of a 5 nm nickel seed layer improves the morphology and eliminates the incubation time. The pulsed-spray evaporation using alcohol solutions of cobalt acetylacetonate as a liquid feedstock allows the growth of metallic cobalt or cobalt carbide, depending on the choice of the alcohol and of the deposition temperature. The growth of Co2C was obtained, for the first time with CVD, using an ethanol precursor solution at temperatures in the ran-e of 205-230 degrees C, whereas the deposition of high-quality metallic crystalline cobalt is attained with an n-propanol precursor solution at substrate temperatures above 250 degrees C. The obtained metallic films reach a near-bulk electrical resistivity for thicknesses above 300 nm.