Moderate Deposition Temperatures Research Articles

Grain boundary modification of TiC ultrananocrystalline thin films: Improvement in tribo-physical properties

This work reports on the influence of grain boundary modification on the tribological properties of nanocrystalline titanium carbide (nC-TiC) - amorphous carbon (a-C) nanocomposite films. TiC thin films were deposited by magnetron sputtering using TiC target in optimized hydrogen containing atmosphere. Nano/ultrananocrystalline TiC phase and short ranged ordered graphite phase were found to be dispersed in the a-C matrix in thin films. Chemical composition and also the chemical structure of the graphitized phase and a-C in the grain boundary were modified by controlling the substrate temperature. Raman spectroscopy showed that at room temperature, the films were dominated by a-C phase occupying the grain boundary. However, at moderate deposition temperature, graphitization of the film was observed and such modification was associated to the formation of short ranged crystalline graphite phase within a-C matrix. The friction coefficient was found to decreased with increase in the I(D)/I(G) ratio of Raman shift in the films. A sustainable ultralow value of friction coefficient was observed in the films with TiC nano/ultrananocrystalline phase surrounded by nanographitized domains. This could be associated to the layered lattice structure of short ranged graphite phase which readily shears and produces negligible frictional resistance. Sustainability of ultralow value of friction coefficient and high wear resistance are attributed to the formation of graphitized transfer film.

Atomic Layer Deposition of Rhenium Disulfide.

2D materials research is advancing rapidly as various new "beyond graphene" materials are fabricated, their properties studied, and materials tested in various applications. Rhenium disulfide is one of the 2D transition metal dichalcogenides that has recently shown to possess extraordinary properties such as that it is not limited by the strict monolayer thickness requirements. The unique inherent decoupling of monolayers in ReS2 combined with a direct bandgap and highly anisotropic properties makes ReS2 one of the most interesting 2D materials for a plethora of applications. Here, a highly controllable and precise atomic layer deposition (ALD) technique is applied to deposit ReS2 thin films. Film growth is demonstrated on large area (5 cm × 5 cm) substrates at moderate deposition temperatures between 120 and 500 °C, and the films are extensively characterized using field emission scanning electron microscopy/energy-dispersive X-ray spectroscopy, X-ray diffractometry using grazing incidence, atomic force microscopy, focused ion beam/transmission electron microscopy, X-ray photoelectron spectroscopy, and time-of-flight elastic recoil detection analysis techniques. The developed ReS2 ALD process highlights the potential of the material for applications beyond planar structure architectures. The ALD process also offers a route to an upgrade to an industrial scale.

Invisible electronics: Metastable Cu-vacancies chain defects for highly conductive p-type transparent oxide

Non-stoichiometric copper chromium delafossite has lately attracted a high interest in the community of oxide materials due to its high p-type electrical conductivity and adequate transparency in the visible range. This study reports record electrical conductivity of Cu0.66Cr1.33O2 thin films deposited by chemical vapour deposition and investigates their properties. As-deposited samples show conductivities greater than 100Scm−1 and carrier concentrations around 1021cm−3, highest reported value for any non-intrinsically doped delafossite system. A new structural defect consisting in Cu-vacancies chains is identified. This defect, never observed or presumed before, heals upon annealing at 900°C under argon environment, resulting in an electrical conductivity's reduction of six orders of magnitude. Through a wide-range of structural, chemical and transport measurement techniques, a structure-defect-property correlation of this system is established and the metastability of the non-stoichiometry induced defects is investigated. The possibility of manipulating the defects and carrier concentrations through high-temperature annealing and the outstanding electrical properties associated with the large-scale deposition technique and moderate deposition temperature could be of great technological interest. This material could find important applications as hole injection or extraction layer in all-oxide photovoltaic and light emitting devices.

Preparation and characterization of CVD-TiN-coated carbon fibers for applications in metal matrix composites

Aluminum matrix composites reinforced with carbon fibers (CF/Al-MMC) are promising materials for lightweight applications. So far the application has been hindered by a lack of wettability of carbon fibers by aluminum alloys and detrimental reactions like aluminum carbide (Al4C3) formation. Protective coatings prepared by chemical vapor deposition (CVD) could be a suitable way to overcome these problems. In this work carbon fiber based 3D-textile preforms were coated with titanium nitride (TiN). Coating thickness, homogeneity, layer structure and composition were determined. Furthermore oxidation resistance and tensile strength of coated fibers were investigated. The wettability by molten aluminum combined with an interface analysis is examined on TiN-coated graphite substrates. Finally the quality of MMC parts prepared by gas pressure infiltration (GPI) method is evaluated. The CVD process was performed with a gas mixture of TiCl4, N2 and H2. A homogeneous coating was achieved at moderate deposition temperatures in the range from 800° to 850°C and by proper adjustment of further process parameters as TiCl4 concentration and total pressure. A very thin TiN layer with a thickness between 30nm and 35nm improves the oxidation resistance and results in a moderate decrease of the tensile strength. TiN improves the wettability and acts as a protective coating. However because of the long infiltration time in the GPI process, interface reactions occur. SEM investigations of TiN coated 3D-textile preforms infiltrated with AlSi9Cu3 alloy (226D) show a completely dense composite with a strong reduction of the Al4C3 formation. TiN offers a good protective effect if the contact time with the melt is not too long.

Epitaxial-like Growth of Co3O4/ZnO Quasi-1D Nanocomposites

The development of quasi-1D Co3O4/ZnO nanocomposites by a two-step plasma enhanced-chemical vapor deposition (PE-CVD) process is presented. Arrays of ⟨001⟩ oriented ZnO nanorods were first grown on Si(100) and subsequently used as templates for the PE-CVD of Co3O4, whose amount was tailored as a function of deposition time. The obtained composites were thoroughly characterized by means of a multitechnique approach, involving field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS), micro-Raman and Fourier-transform infrared (FT-IR) spectroscopies, X-ray photoelectron and X-ray excited Auger electron spectroscopies (XPS, XE-AES), glancing incidence X-ray diffraction (GIXRD), and reflection high energy electron diffraction (RHEED). The use of moderate deposition temperatures (≤300 °C), together with the unique activation provided by nonequilibrium plasmas, prevented undesired solid-state reactions between the two oxides and promoted Co3O4 growth on the tips of vertic...

CVD nanocrystalline diamond coatings on Ti alloy: A synchrotron-assisted interfacial investigation

Diamond coating on Ti-6Al-4V alloy was carried out using microwave plasma enhanced CVD with a super high CH4 concentration, and at a moderate deposition temperature close to 500 °C. The nucleation, growth, adhesion behaviors of the diamond coating and the interfacial structures were investigated using Raman, XRD, SEM/TEM, synchrotron radiation and indentation test. Nanocrystalline diamond coatings have been produced and the nucleation density, nucleation rate and adhesion strength of diamond coatings on Ti alloy substrate are significantly enhanced. An intermediate layer of TiC is formed between the diamond coating and the alloy substrate, while diamond coating debonding occurs both at the diamond-TiC interface and TiC-substrate interface. The simultaneous hydrogenation and carburization also cause complex micro-structural and microhardness changes on the alloy substrates. The low deposition temperature and extremely high methane concentration demonstrate beneficial to enhance coating adhesion strength and reduce substrate damage.

Effects of Deposition Temperatures on ZnO:Al Films Deposited on Polymer Substrates by RF Magnetron Sputtering

Aluminium doped ZnO (ZnO:Al) films were deposited on polymer substrates by RF magnetron sputtering. The effects of deposition temperatures on structure and properties of films were investigated by X-ray diffractometery, Scanning electronic microscopy, UV-visible spectrophotometer, as well as Four-point Probes System. The results revealed that moderate deposition temperature was helpful to improve the crystal quality and optoelectronic properties of ZnO:Al films. The lowest resistivity of 9.5×10-3Ω•cm and the average transmittance of 76% in the visible region was obtained for the film deposited from ZnO:2wt% Al2O3 target at 75°C.

Buffer Layers for Highly Ordered L1$_{0}$ FePt-Oxide Thin Film Granular Media at Reduced Processing Temperature

In this work, we present an experimental technique for obtaining highly ordered L10 FePt-oxide thin film media at moderate deposition temperatures. In most previous studies, a FePt-Oxide layer is directly deposited on a (001) textured MgO layer. By introducing a buffer layer in between the FePt-oxide layer and the MgO underlayer, we are able to substantially enhance the L10 ordering of the FePt-oxide layer while lowering the deposition temperature to 400 . The buffer layer also yields a significantly enhanced (001) texture of the formed L10 FePt structure. With the order parameter near unity, the coercivity of the resulting granular L10 FePt-oxide film exceeds 20 kOe with an average grain size about 8 nm. With the buffer layer technique, 18kOe coercivity has also been achieved for L10 FePt-oxide film at a grain size of about 4.5 nm. In this work, the detailed material composition choice of the buffer layers and the corresponding results are presented.

Formation of solid electrolyte films on porous supporting electrodes

In this work, the method of chemical deposition from the gas phase of organometallic compounds (CVDOM) was used to obtain thin electrolyte films of zirconia stabilized by yttria (YSZ) on a supporting electrode. Tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)yttrium often termed as zirconium (IV) Zr(dpm)4 and yttrium (III) Y(dpm)3 dipivaloylmethanates were used as precursors for film deposition. Gas-tight electrolyte films were obtained on a supporting anode with a thickness of 4–10 μm at moderate deposition temperatures of 500–700°C. An electrochemical cell was prepared and tested using the obtained films. The cell allowed obtaining the power density values of 680, 360, and 175 mW/cm2 at the temperatures of 800, 700, and 600°C, accordingly.

Adherent and low friction nano-crystalline diamond film grown on titanium using microwave CVD plasma

The use of titanium alloys for aerospace and biomedical applications could increase if their tribological behavior was improved. The deposition of an adherent diamond coating can resolve this issue. However, due to the different thermal expansion coefficients of the two materials, it is difficult to grow adherent thin diamond layers on Ti and its metallic alloys. In the present work microwave plasma chemical vapor deposition (MWPCVD) was used to deposit smooth nano-crystalline diamond (NCD) film on pure titanium substrate using Ar, CH 4 and H 2 gases at moderate deposition temperatures. Of particular interest in this study was the exceptional adhesion of approximately 2 μm-thick diamond film to the metal substrate as observed by indentation testing up to 150 kg load. The friction coefficient, which was measured with a cemented carbide ball of 10 mm diameter with 20 N load, was estimated to be around 0.04 in dry air. Morphology, surface roughness, diamond crystal orientation and quality were obtained by characterizing the sample with field emission electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy, respectively.

First stages of barium ferrite microparticles entrapment in the electrodeposition of CoNi films

Abstract A study of the incorporation of magnetic barium ferrite microparticles into a CoNi matrix by means of electrodeposition over silicon-base substrates has been performed. A cationic surfactant synthesized in our laboratory (4-ethylazobenzene-4′-(oxyethyl)trimethylammonium iodide – AZTMAI) has been selected to favour the inclusion of magnetic particles in the alloy deposit. This surfactant reduces during the cobalt–nickel electrodeposition avoiding its inclusion in the film and favours the inclusion of magnetic particles without damaging the deposits quality. The amount of ferrite incorporated during the electrodeposition increases gradually with the surfactant concentration. A moderate deposition temperature allows greater barium ferrite incorporation. Magnetic properties of CoNi–barium ferrite deposits obtained in the presence of AZTMAI are clearly different of those corresponding to pure-CoNi films obtained in the absence of surfactant. Coercivity is clearly increased.

Radiotracer measurements as a sensitive tool for the detection of metal penetration in molecular-based organic electronics

The metallization of organic thin films is a crucial point in the development of molecular electronics. However, there is no method established yet to detect trace amounts of metal atoms in those thin films. Radiotracer measurements can quantify even very small amounts of material penetrating into the bulk, in our case less than 0.01% of a monolayer. Here, the application of this technique on two different well-characterized organic thin film systems (diindenoperylene and pentacene) is demonstrated. The results show that Ag is mainly adsorbed on the surface, but indicate that already at moderate deposition temperatures Ag can penetrate into the organic thin films and agglomerate at the film/substrate interface.

Deposition of Ti–B–N (single and multilayer) and Zr–B–N coatings by chemical vapor deposition techniques on cutting tools

Coatings in the systems Ti–B–N and Zr–B–N were investigated because of their high potential in metal cutting. Therefore TiN, TiB 2, TiBN, multilayers like [TiN–TiB 2] x or [TiN–TiBN] x ( x=3–100), ZrN and ZrBN coatings were deposited on cemented carbides using chemical vapor deposition (CVD). When keeping the boron content larger than 5 wt.% TiBN, coatings resulted in mixtures of TiN and TiB 2. The TiN/TiB 2 ratio, microstructure, hardness and wear resistance of the coatings were controlled by varying deposition temperatures and gas flows in the CVD process. Compared to TiN and TiB 2 coatings, deposition rates in TiBN coatings became noticeably higher. TiBN coatings exhibited high hardness (HV 3500–5000) at moderate deposition temperatures (700–900 °C). Deposition temperatures below 900 °C successfully suppressed boron diffusion and formation of a CoWB phase on the surface of the cemented carbide tool. Due to the moderate deposition temperatures, TiBN coatings showed very good adhesion. Boron diffusion was responsible for poor adhesion in TiB 2 coatings. For milling tests TiN, TiB 2, TiBN, multilayer coatings like [TiN–TiB 2] x or [TiN–TiBN] x with a TiB 2 content of 10–95%, ZrN and ZrBN were investigated. All TiBN coatings showed good wear resistance against abrasion. At a certain level of the TiN/TiB 2 ratio, the TiBN coatings suppressed thermal cracks. Although the Zr–B–N and Ti–B–N systems seemed to be very similar, results showed differences in deposition chemistry and properties.

Zone model for zinc oxide deposited by combustion chemical vapor deposition

A zone model describing the microstructures of zinc oxide films deposited by combustion chemical vapor deposition as a function of temperature and precursor concentration was developed experimentally. Homologous temperatures from 0.2 to 0.5, and precursor concentrations from 0.0025 to 0.04 M were investigated. Zinc 2-ethylhexanoate was used as precursor. Low deposition temperatures and/or high precursor concentrations favor the growth of amorphous ZnO (zone A). At moderate deposition temperatures and/or lower precursor concentrations, relatively smooth crystalline, small grained films form (zone T microstructure). The largest deposition temperatures and/or lowest precursor concentrations result in films with columnar grains (zone II microstructure). ZnO could not be deposited at homologous temperatures greater than approximately 0.5 because of its high vapor pressure. Kinetic measurements of the zone A to zone T transition resulted in an activation energy of 64±9 kJ/mol for the responsible mechanism. Similarly, measurements of grain size as a function of deposition temperature yielded an activation energy of 60±21 kJ/mol. These activation energies are consistent with surface diffusion being responsible for both the amorphous to crystalline transition and grain growth in the crystalline films.

The effects of process conditions and substrate on copper MOCVD using liquid injection of (hfac)Cu(vtmos)

Copper MOCVD (metalorganic chemical vapor deposition) using liquid injection for effective delivery of the (hfac)Cu(vtmos) [1,1,1,5,5,5-hexafluoro-2,4-pentadionato(vinyltrimethoxysilane) copper(I)] precursor has been performed to clarify growth behavior of copper films onto TiN, Si, and Si3N4 substrates. Especially, we have studied the influences of process conditions and the substrate on growth rates, impurities, microstructures, and electrical characteristics of copper films. As the reactor pressure was increased, the growth rate was governed by a pick-up rate of (hfac)Cu(vtmos) in the vaporizer. The apparent activation energy for copper growth over the surface-reaction controlled regime from 155°C to 225°C was in the range 12.7–32.5 kcal/mol depending upon the substrate type. It revealed that H2 addition at 225°C substrate temperature brought about a maximum increase of about 25% in the growth rate compared to pure Ar as the carrier gas. At moderate deposition temperatures, the degree of a preferred orientation for the deposit was higher on the sequence of <Cu/Si<Cu/TiN<Cu/Si3N4. The relative impurity content within the deposit was in the range 1.1 to 1.8 at.%. The electrical resistivity for the Cu films on TiN illustrated three regions of the variation according to the substrate temperature, so the deposit at 165°C had the optimum resistivity value. However, the coarsened microstructures of Cu on TiN prepared above 275°C gave rise to higher electrical resistivities compared to those on Si and Si3N4 substrates.

Aluminum Nitride Thin Films for Microwave Filter and Microsystem Applications

AbstractResults on growth, characterization and resonator applications of AIN thin films grown by pulsed dc reactive magnetron sputtering are presented. In order to allow deposition on electrode films, moderate deposition temperatures of 300 to 400 °C were applied. On (001) sapphire, monocrystalline films were obtained. On (111)-textured platinum films, a columnar and (001) textured microstructure was established which exhibited quasi single-crystal properties in relevant materials constants, such as e33, e31, and c33. The films have been successfully applied in bulk wave resonators operating at GHz frequencies, allowing for the derivation of acoustic parameters. A zero thermal frequency drift was obtained with a membrane resonator due to a SiO2 layer as compensating element.

Quantitative Auger electron spectroscopic analysis of Ge surface segregation in Si/Ge/Si(100) heterostructures

Germanium surface segregation in Si/Ge/Si(100) heteroepitaxial structures has been studied by quantitative Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). Ge segregation was measured for 1–4 ML Ge, for slow Si growth rates (3×10−4 nm/s) at moderate deposition temperature (520 °C). A layer growth model is used to infer segregation probabilities between 90% and 98%, increasing with Ge layer thickness, especially between 1 and 2 ML. Using this model, the Ge profile in the cap layer is calculated. Surface roughness is just noticeable at 4 ML, and is incorporated into the model in an illustrative manner. A two-state model is used to determine the segregation energy, 0.24±0.02 eV, for 2–3 ML.

Structure of Vapour-deposited Carbon

ALTHOUGH considerable information is available in the published literature on the effect of temperature and pressure of deposition on the microstructure and density of vapour-deposited carbon, only little has been reported on the pyrolytic graphite formed under these conditions from the crystallographic point of view. The purpose of this communication is to present X-ray results obtained in these laboratories from analysis of a series of experimental deposits produced over a range of high temperatures at a pressure of 50 mm. mercury. The perfection of three-dimensional crystallinity exhibited in some specimens produced at moderate deposition temperatures at this pressure is, to our knowledge, a new observation.