Hochreflektierende Beschichtungen auf Kunststoffoptiken

Metallized polymer substrates offering highest reflectance are not yet state of the art. Coating organic substrate materials is still a task that is connected with multiple problems. Insufficient adhesion of coatings on polymer substrates represents one of the main difficulties. We could show by experiment that aluminium and silver layers indicate good coating adhesion on many different polymers if they are deposited by vacuum evaporation considering certain process parameters. High reflectance values and a good climatic stability of the metal coated polymer parts are other important challenges to plastic mirrors. By performing roughness measurements on the different polymer samples and by comparing reflection values obtained after coating these samples the impact of the polymers surface quality on the reflectance after metal coating has been investigated. Particularly high reflectance above 97% was realized with a protected silver mirror as well as with dielectric enhanced aluminium. Applying these layer systems excellent reflection properties has been obtained on several plastic substrates comparable to those on glass mirrors. Furthermore the dielectric layers used for reflection enhancement showed the ability to protect the aluminium coating against climatic influences.     

A reflection electron diffraction study on some metal oxide solar collector coatings: Part I

The capability of reflection electron diffraction (RED) in the structural analysis of thin films is shown with studies made on copper oxide, zinc oxide, black chrome and cobalt oxide solar-selective coatings. The growth of copper oxide layers could be observed as changing from an initial epitaxial growth to random orientation followed by growth of oxide needles. The resulting copper oxide coating was found to consist of a needle structure of cupric oxide formed on a smooth cuprous oxide layer. In the zinc oxide overgrowths, epitaxial growth could not be observed, and the coating consisted of relatively small zinc oxide crystallites throughout the film. No crystalline zinc inclusions could be found in this layer.Black chrome deposited onto nickel showed an increase in chromium oxide with distance from the substrate, although no change in the orientation of the microcrystalline chrome could be observed. The formation of black cobalt was also investigated using scanning electron microscopy (SEM) and reflection diffraction analysis. The plated cobalt overgrowths were found to change from an initially smooth nodular coating to a plate-like oxide layer with heat treatment time. This latter layer could be indexed to cobalt(II, III) oxide.The study conclusively shows that RED, combined with SEM and ion milling procedures, can indeed lead to structural characterization of thin films without the need for their removal from their substrates and the concominant introduction of artifacts.     

退火温度对氢掺杂AZO薄膜热稳定性的影响

利用直流磁控溅射方法低温沉积了氢掺杂AZO (H-AZO) 薄膜, 研究了不同退火温度下H-AZO薄膜的电学、结构和光学性能的变化。结果表明, 300℃退火时, H-AZO薄膜的电阻率和光学带隙不变。而400℃退火时, 薄膜电阻由4.7×10^-4升高到1.43×10^-3Ω·cm, 并且光学带隙减小。由于300℃退火时H-AZO薄膜的热稳定性好, 将其用作低温制备薄膜太阳电池的透明导电膜具有很好的发展潜力。     

Durability of doped zinc oxide/silver/doped zinc oxide low emissivity coatings in humid environment

The relationship between internal stress of doped zinc oxide films and durability of doped zinc oxide/silver/doped zinc oxide low emissivity (low-e) coatings in humid environment was investigated. Aluminum, titanium, tin, chromium, silicon, gallium, magnesium, boron, barium, and calcium were chosen as a doping element in sputtering targets. Ratios of dopant/zinc in the oxide targets were 4/96-5/95 at.%. Films were formed by radio frequency sputtering. Doping of barium and calcium to the zinc oxide film led to a large increase in the internal stress. Doping of the other elements resulted in decreasing the internal stress. It was concluded that durability of the low-e coatings in humid environment closely correlated with the internal stress of the oxide layers.     

Gradient silver nanoparticle layers in absorbing coatings--experimental study

Metal island films show a characteristic absorption peak related to the surface plasmon resonance of free electrons. This kind of film can be used in absorbing coatings, together with dielectric layers. Such absorbing multilayer coatings, with and without the gradient of the silver mass thickness in metal island films throughout the coating, have been deposited by electron beam evaporation. It is shown experimentally that coatings with a gradient in the mass thickness of silver nanoparticles have higher absorption than equivalent nongradient coatings with the same total mass thickness of silver nanoparticles.     

Growth and characterization of transparent conducting nanostructured zinc indium oxide thin films

Transparent conductive oxide (TCO) films have been widely used in various applications, such as for transparent electrodes in flat-panel displays, and in solar cells, optoelectronic devices, touch panels and IR reflectors. Among these, tin doped zinc oxide (ZTO) and indium doped zinc oxide (ZIO) have attracted considerable attention. Particularly, IZO thin film is the best candidate for high-quality transparent conducting electrodes in OLEDs and flexible displays. In this work zinc indium oxide (ZIO) thin films were deposited on glass substrate with varying concentration (ZnO:In₂O₃ — 100:0, 90:10, 70:30 and 50:50 wt.%) at room temperature by flash evaporation technique. These deposited ZIO films were annealed in vacuum to study the thermal stability and to see the effects on the physical properties. The XRF spectra revealed the presence of zinc and indium with varying concentration in ZIO thin films, while the surface composition and oxidation state were analyzed by X-ray photoelectron spectroscopy. The core level spectra were deconvoluted to see the effect of chemical changes, while the valance band spectra manifest the electronic transitions. The surface morphology studies of the films using atomic force microscopy (AFM) revealed the formation of nanostructured ZIO thin films. The optical band gap was also found to be decreased for both types of films with increasing concentration of In₂O₃.     

Characterization of molybdenum black coatings on zinc substrates

Molybdenum black solar selective coatings have been prepared by a simple chemical conversion method on chemically etched zinc substrates. These coatings have been characterized using X-ray diffraction, electron diffraction, XPS and VIS-IR reflectance spectroscopy. Maximum solar absorptance obtained from these coatings was about 0.87 with an emittance of 0.13–0.17. Selectivity of the coatings, mainly attributed to the coating surface morphology, was studied by SEM. Structural studies show that the coating consists of a non-stoichiometric oxide of Mo, namely Mo₄O₁₁. XPS depth profiling studies show that the oxidation state of Mo reduces from +5 to +4 after argon ion bombardment. This revised version was published online in November 2006 with corrections to the Cover Date.     

Antireflection treatment of metal films for optical lithography

The effects of antireflection coating of thin metal films by surface chemical treatments to reduce reflectance for applications to very-large-scale integrated (VLSI) lithography have been studied. The study includes surface treatments in chemical solutions, thin film deposition and direct thermal reaction with gaseous chemicals. Aluminum and molybdenum films were used as test vehicles for the antireflection coatings. While many chemical compositions were effective in reducing aluminum reflectance, some chemicals produced a color with sufficient uniformity for VLSI applications. H₂O₂ was effective in staining molybdenum films, with a reflectance as low as 10% at a wavelength of 436 nm. Molydbenum nitride films, made by direct reaction with ammonia in the temperature range 500–750°C, also reduced the reflectance and added other beneficial properties. Deposition of transparent dielectrics is only effective in the deep-UV region. An opaque film deposition reduced the reflectance in the optical wavelength range. A thin zinc coating deposited by means of electroless plating showed the greatest reduction in reflectance. Some of these techniques applied to photoresist patterning near a tapered step were found to be useful for VLSI lithography.     

Effect of substrate temperature and annealing treatment on the electrical and optical properties of silver-based multilayer coating electrodes

Multilayer coatings consisting of thin silver layers sandwiched between layers of transparent conducting metal oxides are investigated from the view point of low-resistance electrodes for use in flat panel displays, solar cells, etc. ZnO/Ag/ZnO multilayer films were prepared on glass substrates by simultaneous RF magnetron sputtering of ZnO and dc magnetron sputtering of Ag. Optimization of the deposition conditions of both ZnO layers and metallic layers were performed for better electrical and optical properties. The structural, electrical and optical properties of the films (deposited at room temperature, different substrate temperature and annealed at different conditions) were characterized with various techniques. We could not produce high-quality transparent conductive electrodes simply by annealing at various temperatures. However, improved electrical properties and a considerable shift in the transmittance curves was observed after heat treatment. The experimental results show that the electrical resistivity of as-grown films can be decreased to 10^− 5 Ω cm level with post-annealing at 400 °C for 2 h in vacuum atmosphere. After heat treatment, the sheet resistance was reduced as much as 20% which was due to the increased grain size of Ag film. The samples heat treated at 200-400 °C under vacuum or nitrogen atmosphere showed the best electrical properties. The key to the superior electrical and optical properties of the multilayer is the optimization of growth conditions of the silver layer by careful control of the oxide properties and the use of appropriate annealing temperature and atmosphere.     

Investigations on the Deposition and the Efficiency of a Multilayer High Temperature Coating System for Gas Turbine Blades

The content of this work is the development and investigation of a high temperature coating system for gas turbine blades. On a single crystal CMSX4 substrate a thin CVD layer of α‐alumina is deposited as diffusion barrier coating. As a protection against high‐temperature corrosion it is covered with a PVD NiCoCrAlY layer, which also performs as a bond‐coating for the following thermal barrier coating deposited by Atmospheric Plasma Spraying. The surface preparation techniques and coating parameters for the multilayer coating were optimized with respect to the bonding mechanisms of the different deposition techniques. The samples were annealed at 1100°C for 100 h under neutral atmosphere. Furthermore thermocycle experiments were carried out to investigate thermocycle behaviour. The coating system proved its efficiency: No cracks were observed except vertical segmentation cracks in the TBC, all layers showed good adhesion and the diffusion barrier remained intact suppressing any noticeable diffusion of Al, Cr, Ta, Re, W and Ti.     

ITO coated quartz fibers for heat radiative applications

Radiation heat transfer through fibrous materials is very strong at high temperatures (up to 1000 °C). Indium tin oxide (ITO) thin films were sol-gel deposited onto the surfaces of fibers to reduce the radiation heat transfer as radiation reflective coatings. SEM, XRD and FT-IR techniques were used to characterize the microstructure and performance of films. Results show that ITO thin film is uniformly deposited on fibers with a thickness of about 200 nm and can be used to apply a radiative reflective coating. Moreover, the efficiency of radiation reflective properties of films is improved as the annealing temperature increases. Results prove that ITO film is an excellent candidate to reduce the radiation heat transfer as radiation reflective coatings on fibrous materials.     

Deposition of photocatalytic titania coatings on polymeric substrates by HiPIMS

Titania coatings have been deposited onto PET substrates by reactive magnetron sputtering in the HiPIMS (high power impulse magnetron sputtering) mode and for comparison, pulsed DC mode. In the latter case, the substrate showed evidence of melting, but the HiPIMS results were dependent on the characteristics of the power supply when operating under nominally identical conditions. A coating deposited by one of the HiPIMS supplies was found to have a mixed phase structure and to demonstrate a level of photocatalytic activity comparable to conventional coatings which had been post-deposition annealed.     

Humid environment stability of low pressure chemical vapor deposited boron doped zinc oxide used as transparent electrodes in thin film silicon solar cells

The stability in humid environment of low pressure chemical vapor deposited boron doped zinc oxide (LPCVD ZnO:B) used as transparent conductive oxide in thin film silicon solar cells is investigated. Damp heat treatment (exposure to humid and hot atmosphere) induces a degradation of the electrical properties of unprotected LPCVD ZnO:B layers. By combining analyses of the electrical and optical properties of the films, we are able to attribute this behavior to an increase of electron grain boundary scattering. This is in contrast to the intragrain scattering mechanisms, which are not affected by damp heat exposure. The ZnO stability is enhanced for heavily doped films due to easier tunneling through potential barrier at grain boundaries.     

Influence of deposition rate on PL spectrum and surface morphology of ZnO nanolayers deposited on Si (100) substrate

Zinc oxide (ZnO) thin films were deposited on Si (100) substrate through sputtering of zinc by DC magnetron, followed by thermal oxidation. Different deposition rates were used in coating films with 100 nm thickness (0·6–4·5 nm/s). Photoluminescence spectra of the produced samples were obtained and it was found that the violet emission peak intensity increases with deposition rate. Scanning electron microscopy (SEM) micrograph and atomic force microscopy (AFM) images for the zinc oxide films were obtained. Morphological changes due to various deposition rate are discussed in the light of changes observed in the ZnO crystals. Low coating rates produced smooth surface with small grains while higher deposition rates increased the surface roughness and larger grain size. AFM and SEM results are in good agreement and support the PL results.     

Effect of oxygen partial pressure on electrical characteristics of amorphous indium gallium zinc oxide thin-film transistors fabricated by thermal annealing

We report the fabrication and electrical characteristics of high-performance amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a polymer gate dielectric prepared by spin coating on a glass substrate at different oxygen partial pressure values. The transmittance of the deposited polymer film was greater than 90% at 600 nm a-IGZO thin films were deposited on glass substrates using RF magnetron sputtering at different oxygen partial pressure values. The a-IGZO TFTs were prepared by rapid thermal annealing at 350 °C for 10 min at a 0.2% oxygen partial pressure. It was observed that a-IGZO TFTs with an active channel layer exhibited enhanced mode operation, a threshold voltage of 1 V, an on-off current ratio of 10³, and a field-effect mobility of 18 cm²/Vs.     

Effect of oxygen partial pressure on electrical characteristics of amorphous indium gallium zinc oxide thin-film transistors fabricated by thermal annealing

We report the fabrication and electrical characteristics of high-performance amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a polymer gate dielectric prepared by spin coating on a glass substrate at different oxygen partial pressure values. The transmittance of the deposited polymer film was greater than 90% at 600 nm a-IGZO thin films were deposited on glass substrates using RF magnetron sputtering at different oxygen partial pressure values. The a-IGZO TFTs were prepared by rapid thermal annealing at 350 °C for 10 min at a 0.2% oxygen partial pressure. It was observed that a-IGZO TFTs with an active channel layer exhibited enhanced mode operation, a threshold voltage of 1 V, an on-off current ratio of 10³, and a field-effect mobility of 18 cm²/Vs.     

An inorganic-organic passivation double layer for thin film circuits

If not hermetically encapsulated, thin film hybrid circuits require passivation for various reasons: protection against mechanical attack, long-term humidity diffusion, oxidation of metal films during heat treatment and destruction of oxide layers in electroless plating baths. An inorganic (Al₂O₃, SiO₂ etc.) or organic (photoresist, polyimide) passivation alone cannot meet all requirements simultaneously since most organic coatings do not resist temperatures of more than 150°C whereas evaporated oxide layers are too thin (1 μm or less) for mechanical protection and are often destroyed by non-neutral plating baths.We present a double-layer protective coating for thin film circuits consisting of an evaporated Al₂O₃ thin film and a photoresist layer baked at temperatures near the solder bath temperature. This passivation layer sequence is shown to avoid all the shortcomings of its constituents.     

Deposition of zinc coatings with fluidized bed technique

Zinc is known to be an ideal coating material for steel protection aiming to improve its anticorrosion performance. Up to now, hot-dip galvanizing is the industrially used coating technique for zinc. Its high environmental impact imposes the development of alternative techniques such as fluidized bed procedure. Under this procedure zinc was deposited by inserting the substrates in the reactor at room temperature. Afterwards the reactor was heated at the process temperature (400 °C) and holding time varied from 0 min to 2 h at the final temperature. The as-coated samples were examined with Scanning Electron Microscopy (SEM) associated with Energy Dispersive Spectroscopy (EDS), Transmission Electron Microscopy (TEM) and X-ray diffraction analysis (XRD). From this process two-layered coatings were formed. The main phases observed were gamma and delta phase of the Fe-Zn phase diagram. Some of the as-received coatings are likely to provide sufficient anticorrosive protection while others are of low quality because of porous areas in their mass. In addition a comparison is made with FBR zinc coatings produced in a preheated reactor, zinc pack coatings and hot-dip galvanized coatings.     

Extraordinarily large permittivity modulation in zinc oxide for dynamic nanophotonics

The dielectric permittivity of a material encapsulates the essential physics of light-matter interaction into the material’s local response to optical excitation. Photo-induced modulation of the permittivity can enable an unprecedented level of control over the phase, amplitude, and polarization of light. Therefore, the detailed dynamic characterization of technology-relevant materials with substantially tunable optical properties and fast response times is a crucial step to realize tunable optical devices. This work reports on the extraordinarily large permittivity changes in zinc oxide thin films (up to −3.6 relative change in the real part of the dielectric permittivity at 1600 nm wavelength) induced by optically generated free carriers. We demonstrate broadband reflectance modulation up to 70% in metal-backed oxide mirrors at the telecommunication wavelengths, with picosecond-scale relaxation times. The epsilon near zero points of the films can be dynamically shifted from 8.5 µm to 1.6 µm by controlling the pump fluence. The modulation can be selectively enhanced at specific wavelengths employing metal-backed zinc oxide disks while maintaining picosecond-scale switching times. This work provides insights into the free-carrier assisted permittivity modulation in zinc oxide and could enable the realization of novel dynamic devices for beam-steering, polarizers, and spatial light modulators.     

Preparation of zinc oxide-montmorillonite hybrids

The new hybrid materials of zinc oxide with montmorillonite were synthesized by a reaction between the aqueous solutions of the reactants of zinc oxide (zinc chloride and sodium hydroxide solutions) and montmorillonite or hexadecyltrimetylammonium-montmorillonite. The hybrids were characterized by powder X-ray diffraction, Fourier transform-infrared, UV-visible and photoluminescence spectroscopies. The diffuse reflectance absorption spectra of the hybrids exhibited the absorption onsets at 375 nm for zinc oxide-montmorillonite and at 378 nm for zinc oxide-hexadecyltrimetylammonium-montmorillonite, respectively, confirming the formation of zinc oxide in the hybrid materials. The photoluminescence bands of both hybrids, which can be attributed to singly ionized oxygen vacancy in zinc oxide, were observed at 548 nm. The enhancement in emission intensity of the zinc oxide hybrids may be probably due to increase in oxygen vacancies defect arose by the surrounding environment of montmorillonite.