Deposition of functional coatings on polyethylene terephthalate films by magnetron-plasma-enhanced chemical vapour deposition

Magnetron-plasma enhanced chemical vapour deposition (PECVD) is a process tool which allows the deposition of plasma polymer coatings at process pressures below 1 Pa. The striking features of this technology are the relatively easy realisation of large area deposition as well as the possibility of the combination with sputtering processes for multilayer coating designs. SiO_xC_y coatings were deposited on polymer film in a roll-to-roll deposition machine. Dynamic deposition rates as high as 120 nm?m/min were achieved. The process was set up with both the monomer hexamethyldisiloxane and the monomer tetraethylorthosilicate (TEOS) and with mixtures thereof. The coatings were analysed by Fourier transform infrared spectroscopy. This method identifies the existence of different types of Si-O bonding in the layer. The results show how the layer properties are linked to the plasma parameters of the deposition process. The properties were compared to sputtered SiO₂ and to layers obtained by other PECVD processes. Elastic recoil detection analysis (ERDA) was used in order to determine the composition of the samples. Both IR spectroscopy and ERDA revealed that the usage of TEOS provided more SiO₂-like layers. The process was applied to the deposition of optical multilayer coating in a roll-to-roll coating system.     

Root growth of multi-wall carbon nanotubes by MPCVD

This work examines the relationships among the growth and interlayer reactions of carbon nanotubes (CNTs) to develop an effective process for controlling the nanostructure, orientation and characteristics of CNTs. Vertically oriented CNTs were successfully synthesized by microwave plasma chemical vapor deposition (MPCVD) with CH₄/H₂ as source gases. Additionally, the Ti and SiO₂ barrier layers and the Co catalyst were used in an experiment on the growth of CNTs on the Si wafer. Then, the SiO₂ barrier layer was deposited by low-pressure chemical vapor deposition (LPCVD). The Ti barrier layer and Co catalyst films were deposited on the Si wafer by physical vapor deposition (PVD). The deposited nanostructures were characterized by scanning and transmission electron microscopy, the results of which reveal that the deposited MWCNTs were grown under the influence of a catalyst on Si substrates with or without a barrier layer, by MPCVD. Vertically grown, dense MWCNTs attached to a catalytic film demonstrate that various MWCNTs penetrated the root particles. The diameter of the root particles, of approximately in the order of 100 nm, is larger than those of the tube, 10–15 nm. The well-known model of the growth of CNTs includes base- and tip-root growth. The interaction between the catalytic film and the supporting barrier layer is suggested to determine whether the catalytic particles are driven up or pinned down on the substrate during the growth.     

Carrier dynamics in coalescence overgrowth of GaN nanocolumns

Coalescence overgrowth of pattern-grown GaN nanocolumns on c-plane sapphire substrate with metal organic chemical vapor deposition is demonstrated. The subsequent coalescence overgrowth opens a possibility for dislocation reduction due to the lateral strain relaxation in columnar geometry. We present further growth optimization and innovative characterization of metal organic chemical vapor deposition layers, overgrown on the columnar structure with varying diameters of columns. Nano-imprint lithography was applied to open circular holes of 250, 300, 450, and 600 nm diameter on the SiO₂ layer, deposited on the GaN layer on the c-plane sapphire template. After the growth of ~ 1 μm high GaN nanocolumns, the further coalescence conditions led to an overgrown layer ~2 μm thickness. Photoelectrical and optical properties of the overgrown layers and a reference sample were investigated by time-resolved picosecond transient grating and time-integrated photoluminescence. We note a 3-4 fold increase in carrier lifetime in the overgrown epilayers when the diameter of columns increased from 250 to 450 nm. This feature is a clear indication of an ~4-fold reduced defect density.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

Spectroscopic analysis of dipole interaction of metallic nanoparticles in dielectric multilayer dielectric thin film

Using electron beam gun PVD system, the thin film with multiple alternative layers of SiO₂ + Ag (300 nm)/SiO₂ (10-60 nm) was deposited on silica substrate. Annealing test was undertaken for optical absorption analysis. The annealing agglomerated metallic nanoparticles in each layer has enhancement effect for plasmon resonance absorption, these precipitated nanoparticles also cause absorption peak red shift. When the thickness of alternative dielectric layer becomes small enough, there is a coupling phenomenon between the electric dipoles of nanaoparticles in the alternative metallic particle doped layers.     

Electrical insulation and bending properties of SiOx barrier layers prepared on flexible stainless steel foils by different preparing methods

Stainless steel foils on which flexible display devices and integrated solar modules are prepared need to be coated by barrier layers for electrical insulation. In this study, SiO_x barrier layer was prepared on steel foils (SUS 304) by ion beam assisted deposition, Sol-gel deposition and plasma enhanced chemical vapor deposition, respectively. The electrical properties of the SiO_x films, such as resistance, reactance, leakage current density, breakdown field strength and performance index were investigated, and the bending properties were evaluated by bending tests. The best electrical insulation and bending properties of barrier could be achieved with 4 μm thick SiO_x layer prepared by plasma enhanced chemical vapor deposition.     

An Approach to Synthesize Thick α- and γ-Al2O3 Coatings by High-Speed Physical Vapor Deposition

Crystalline α- and γ-Al₂O₃ exhibit in many applications high wear resistance, chemical resistance, and hot hardness, making them interesting materials for production engineering. To synthesize α-Al₂O₃ with high coating thickness of s ≥ 10 μm, chemical vapor deposition at temperatures T > 1000 °C is well established. However, there are almost no studies dealing with the synthesis of thick α-Al₂O₃ by physical vapor deposition (PVD) at high temperatures T > 700 °C. High-temperature deposition of thick coatings can be realized by means of the dense hollow cathode plasma, combined with the transport function of the plasma gas in high-speed (HS) PVD. Herein, crystalline α- and γ-Al₂O₃ films are deposited on cemented carbides at substrate temperatures T _s ≈ 570 °C and T _s ≈ 780 °C by HS-PVD. These coatings exhibit a thickness up to s = 20 μm. Moreover, phase analysis presents α-phases in coatings synthesized at substrate temperature of T _s ≈ 780 °C with significant higher hardness than films by T _s ≈ 570 °C. These release the potential of HS-PVD to synthesize α-Al₂O₃ coatings with high thickness. Thereby, a higher thickness of these coatings is beneficial for the wear protection of turning and die casting tools.     

Growth of ultrathin barrier layers with sub-5-nm metallic seeds fabricated by sequential treatments of vacuum plasma and electrochemical solution

This study describes the process of growing densely distributed metallic seeds of sizes ∼4 nm on SiO₂ dielectric layers by sequential treatment in N₂-H₂ vacuum plasma (to activate the surfaces) and an aqueous solution of metallic salt (to adsorb metallic seeds). After the plasma treatment, the metallic seeds can be densely adsorbed onto the SiO₂ dielectric layers, thus facilitating Co-P barrier layers of thickness only ∼10 nm to be grown using electroless plating. Conversely, for the SiO₂ dielectric layers without the plasma pre-treatment, the population density of the metallic seeds is significantly reduced by one order and thus can only initiate the growth of a relatively thick (∼40 nm) barrier layer by the identical seeding and electroless plating conditions. Improvement in seeding by the plasma pre-treatment is discussed based on surface bonding modification.     

Optical,mechanical and corrosion properties of metal-metal and metal-dielectric thin layered films

Optical, mechanical and corrosion properties have been studied on the following bilayer coatings: Cr-(67% Cu + 33% Zn), Ti-(67% Cu + 33% Zn), CuZn, AuCr, CrCu and CuNi. Both Crbrass and CrCu were studied with overlayers of SiO₂, with and without thin underlayers of Cr next to the SiO₂. Thus the systems CrCuCr, CrbrassSiO₂, brassCrSiO₂ and CrCuSiO₂ were also studied. These were compared with single layers of brass, Cr and Cu. Layered structures were deposited in both MRC diode and NRC triode sputtering systems. The triple-target r.f. diode system was used to sputter sequentially three different layer thicknesses. The thickness of the metallic layers was varied between 5 and 200 Å, while the SiO₂ thickness was kept constant at 670 Å. Results are presented for the optical reflectance and transmittance in the region 0.6–4.0 eV, the solar transmittance factors, DW (nm) and saturation index P. Hardness, scratch resistance and corrosion resistance tests under cyclic conditions were also made. It is shown that layering is a powerful technique for control of the optical, mechanical and corrosion resistance properties of the films.     

The problems of native SiO2 layer removing for epitaxial growth of YSZ film on Si

The preparation processes of epitaxially grown YSZ (Yttrium stabilized ZrO₂) buffer layers on silicon (100) wafers were investigated. The “etching” procedure, at which the thin (∼5 nm) SiO₂ native amorphous layer from the Si surface was reduced to volatile SiO by deposition of a few nm thick Zr layer and subsequent annealing at low pressure, was monitored by mass spectrometer. The subsequent YSZ layer was deposited by evaporation or RF sputtering technique and examined by XRD and TEM observations. The results show that the epitaxy of YSZ layer is strongly influenced by efficiency of amorphous SiO₂ reduction at Si surface.     

Multi-barrier layer-mediated growth of carbon nanotubes

Variation in the height of carbon nanotubes (CNTs) grown has been co-related to the type of multi-barrier-layer used. Initially, various types of barrier-layers such as Al, Al₂O₃, Al/SiO₂, Al₂O₃/SiO₂ were prepared onto a n-type Si (100) substrate. The thickness of SiO₂ was ∼ 550 nm, where as, Al₂O₃ and Al were ∼ 15 nm thick. These samples were covered with ∼ 1 nm thick Fe catalyst layer. The coated samples were subjected to the thermal chemical vapor deposition (T-CVD) process. SEM analysis showed that, for Al₂O₃/SiO₂ barrier layers, the average height of the CNTs was ∼ 10 μm, where as, for other types of samples it was less than ∼ 1 μm. To investigate this, multi-barrier layers were characterized by dynamic secondary ion mass spectrometry (D-SIMS). The observed variation in height of CNTs is attributed to the variation in diffusivity of Fe atoms into multi-barriers-layers. The results showed that, diffusion of Fe catalyst atoms could severally affect height of CNTs.     

Thin functional films by combustion chemical vapour deposition (C-CVD)

The use of the atmospheric pressure C-CVD (combustion chemical vapour deposition) process for the deposition of thin functional layers on float glass and plastics is described. We will give an overview on the variety of materials that can be deposited and some examples, like SiO₂, WO_x and Ag, are presented in more detail with potential applications.     

Preparation of porous hollow silica spheres via a layer-by-layer process and the chromatographic performance

Hollow silica spheres possessing excellent mechanical properties were successfully prepared through a layer-by-layer process using uniform polystyrene (PS) latex fabricated by dispersion polymerization as template. The formation of hollow SiO₂ micro-spheres, structures and properties were observed in detail by zeta potential, SEM, TEM, FTIR, TGA and nitrogen sorption porosimetry. The results indicated that the hollow spheres were uniform with particle diameter of 1.6 μm and shell thickness of 150 nm. The surface area was 511 m²/g and the pore diameter was 8.36 nm. A new stationary phase for HPLC was obtained by using C₁₈-derivatized hollow SiO₂ micro-spheres as packing materials and the chromatographic properties were evaluated for the separation of some regular small molecules. The packed column showed low column pressure, high values of efficiency (up to about 43 000 plates/m) and appropriate asymmetry factors.     

Growth of Ge nanoparticles on SiO2/Si interfaces during annealing of plasma enhanced chemical vapor deposited thin films

Multilayer germanosilicate (Ge:SiO₂) films have been grown by plasma enhanced chemical vapor deposition. Each Ge:SiO₂ layer is separated by a pure SiO₂ layer. The samples were heat treated at 900 °C for 15 and 45 min. Transmission electron microscopy investigations show precipitation of particles in the layers of highest Ge concentration. Furthermore there is evidence of diffusion between the layers. This paper focuses mainly on observed growth of Ge particles close to the interface, caused by Ge diffusion from the Ge:SiO₂ layer closest to the interface through a pure SiO₂ layer and to the interface. The particles grow as spheres in a direction away from the interface. Particles observed after 15 min anneal time are 4 nm in size and are amorphous, while after 45 min anneal time they are 7 nm in size and have a crystalline diamond type Ge structure.     

The role of SiO2 buffer layer in the growth of highly textured LiNbO3 thin film upon SiO2/Si by pulsed laser deposition

Highly c-axis-oriented lithium niobate (LiNbO₃) thin films have been grown on Si with optimum thickness of the SiO₂ buffer layer by pulsed laser deposition technique. The amorphous SiO₂ buffer layer was formed on Si (100) wafer by thermal oxidation method. The crystallinity and c-axis orientation of LiNbO₃ films were strongly influenced by the thickness of amorphous SiO₂ buffer layers. The optimum thickness of the amorphous SiO₂ buffer layer was found to be about 230 nm for the growth of highly c-axis-oriented LiNbO₃ films. The achieved films have smooth surface and sharp interface. The prism coupler method indicates that the prepared LiNbO₃ films have great potential for optical waveguide device.     

The microstructure of aluminium thin films on amorphous SiO2

The microstructure of aluminium thin films deposited onto amorphous SiO₂ by tungsten filament evaporation was studied by transmission and scanning electron microscopy and grazing-incidence X-ray diffraction. The early stages of film growth were characterized by an island or connected-network structure and a random grain orientation. The thickness at which complete coverage occurred ranged from 15 nm at 295 K to 100 nm at 625 K, and above this thickness a 〈111〉 fibre texture became apparent.The grain size distribution of films 1 μm thick was log-normal and the average grain size ranged from 500 nm for deposition at 295 K to 4 μm for deposition at 675 K. “Growth hillocks” were observed on the surface of films deposited at 295 K but were absent when higher substrate temperatures were used. Annealing caused grain growth and the formation of “annealing hillocks” which were of different structure from the growth hillocks.Examination of a small number of electron-beam-deposited aluminium films showed these to have similar microstructures to the filament-evaporated films, whereas sputter-deposited films were characterized by a smaller grain size and random orientation.     

Microstructure and mechanical properties of TiAlN/SiO2 nanomultilayers synthesized by reactive magnetron sputtering

TiAlN/SiO₂ nanomultilayers with different SiO₂ layer thickness were synthesized by reactive magnetron sputtering. The microstructure and mechanical properties were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nano-indentation. The results indicated that, under the template effect of B1-NaCl structural TiAlN layers, amorphous SiO₂ was forced to crystallize and grew epitaxially with TiAlN layers when SiO₂ layer thickness was below 0.6 nm, resulting in the enhancement of hardness and elastic modulus. The maximum hardness and elastic modulus could respectively reach 37 GPa and 393 GPa when SiO₂ layer thickness was 0.6 nm. As SiO₂ layer thickness further increased, SiO₂ transformed back into amorphous state and broken the coherent growth of nanomultilayers, leading to the decrease of hardness and elastic modulus.     

Influence of oxidant source on the property of atomic layer deposited Al2O3 on hydrogen-terminated Si substrate

Al₂O₃ thin films were deposited on hydrogen-terminated Si substrate using atomic layer deposition (ALD) technique with tri-methylaluminum (TMA) and an oxidant source of H₂O vapor, O₂ plasma, or O₃. Substrate temperature was maintained at 350 °C when the Al₂O₃ films were grown with the oxidant sources of H₂O vapor and O₃, and with the oxidant source of O₂ plasma, Al₂O₃ films were deposited at the substrate temperature of 200 °C. Growth rates of Al₂O₃ films on HF-cleaned Si surface were saturated at 0.08, 0.14, and 0.06 nm/cycle for H₂O vapor, O₂ plasma, and O₃, respectively. Equivalent oxide thickness (EOT) and leakage current vs. physical thickness of atomic layer deposited Al₂O₃ films grown with various oxidant sources were also measured in this study. To investigate the main cause of different EOT with oxidant sources, interfacial properties were examined by using transmission electron microscopy (TEM) and X-ray photoelectron microscopy (XPS). In the TEM analysis, interfacial layers with the thickness of about 1.7 and 1.3 nm were observed in as-deposited Al₂O₃ films grown using O₂ plasma and O₃. We confirmed that the interfacial layers were mainly composed of SiO_x in the XPS depth analysis. Using angle resolved X-ray photoelectron spectroscopy, effect of annealing on the interfacial structure of Al₂O₃ films grown with O₃ and O₂ plasma was also studied, and we found that after annealing, the peak corresponding to silicon suboxide and Al-silicate disappeared and fully oxidized Si⁴⁺ increased.     

Design,fabrication and optical characterization of cerium oxide-magnesium fluoride double layer antireflection coatings on monocrystalline silicon substrates

Theoretical and experimental studies of a double layer antireflection coating deposited onto silicon wafers have been carried out. Magnesium oxide and cerium oxide fabricated by physical vapor deposition method have been applied as low- and high-refractive index materials. MgF₂–CeO₂–Si structures exhibited the reflectivity below 3% in the wavelength window from 0.5 μm to 1.2 μm. Theoretical simulations of spectral characteristics of the reflectivity of these coatings have been performed. A good correlation between experimental data and theoretical curves has been observed with the assumption that a thin SiO₂ layer of a thickness of 16 nm is formed onto Si substrates.