Solvothermal approach for low temperature deposition of aluminium oxide thin films

At elevated pressure, stoichiometric and high quality Al₂O₃ thin films are fabricated at 65-105 °C. By using pre-organised single source precursor aluminium(III) diisopropylcarbamate, Al₂O₃ were deposited on the surface of a Si substrate in a single step in the liquid phase. Comprehensive removal of large carbamate ligands by proposed β-elimination during decomposition of precursor led to an effective delivery of enshrouded Al-O fragments. Scanning electron microscopy revealed dense and grainy surface morphology. The thicknesses of the films were measured to be 150-300 nm and independent to reaction temperatures or reaction times. Through the use of near edge X-ray absorption fine structure spectroscopy, Al absorption peaks suggest a short range crystalline formation in a film deposited at 105 °C.     

Plasma focus assisted carburizing of aluminium

Carburizing of aluminium using the energetic carbon ions emitted from a low energy (1.45 kJ) Mather type plasma focus device operated with methane is reported. The aluminium samples are placed in front of a hollow tapered aluminium anode at a fix distance and are exposed to different carbon ion dose. Raman spectroscopy and X-ray diffraction analyses confirm the presence of Al₄C₃ phase in the irradiated samples. Raman spectroscopic analysis verifies the existence of sp² and sp³ hybridized carbon content also in the treated aluminium surface. Energy dispersive X-ray spectroscopy analyses show a gradual increase of carbon concentration in the treated samples as a function of ion dose. Scanning electron microscope results reveal that the surface smoothness improves initially with ion beam exposure, but deteriorates with increasing ion dose above an optimum value. Vickers micro-indentation technique reveals maximum hardness of about 1990 ± 100 MPa, approximately 7 times as compared to that of aluminium bulk, for the sample treated with 30 plasma focus discharges.     

Anodic oxide growth on aluminium surfaces modified by cathodic deposition of Ni and Co

Surface conditions similar to those found in aluminium alloys of practical use were assessed by cathodic deposition of transitions metals (Ni and Co) from different electrolytes. Fundamental aspects concerning with the growth of anodic oxide films at potentials lower than 10 V in neutral acetate buffer solution on these modified surfaces were analysed by common electrochemical techniques complemented with scanning electron microscopy and transmission electron microscopy. In both potentiodynamic and galvanostatic modes, the growth of aluminium oxide competes with the dissolution of deposited metal particles. The formation of a thin aluminium barrier oxide film beneath them shifts the dissolution potential over to 1.5 V towards more positive values. Some particles get progressively embedded in the matrix of the growing alumina and act as cation sources, increasing the film conductivity and diminishing the established electric field in the oxide. This effect is more pronounced with Co deposits due to its high active dissolution rate, before passivation occurs. Then, the generation of a two-layer film is explained in terms of the precipitation of metal hydroxide at the solution side on the oxide barrier film.     

Properties of indium tin oxide films deposited on unheated polymer substrates by ion beam assisted deposition

The optical, electrical and mechanical properties of indium tin oxide (ITO) films prepared on polyethylene terephthalate (PET) substrates by ion beam assisted deposition at room temperature were investigated. The properties of ITO films can be improved by introducing a buffer layer of silicon dioxide (SiO₂) between the ITO film and the PET substrate. ITO films deposited on SiO₂-coated PET have better crystallinity, lower electrical resistivity, and improved resistance stability under bending than those deposited on bare PET. The average transmittance and the resistivity of ITO films deposited on SiO₂-coated PET are 85% and 0.90 × 10^− 3 Ω cm, respectively, and when the films are bent, the resistance remains almost constant until a bending radius of 1 cm and it increases slowly under a given bending radius with an increase of the bending cycles. The improved resistance stability of ITO films deposited on SiO₂-coated PET is mainly attributed to the perfect adhesion of ITO films induced by the SiO₂ buffer layer.     

On the growth sequence of highly ordered nanoporous anodic aluminium oxide

Anodic aluminium oxide films were fabricated by well known two-step anodizing process in oxalic acid electrolyte. The ordering characteristics (ordered pore domains, average pore diameter size and through-pore arrangement) of anodic aluminium oxide films, obtained in different growth sequences, were identified by microscopic analysis such as ex situ contact-mode atomic force microcopy and scanning electron microscopy. Flattened areas in which some pits are seen mostly cover the electropolished surface of aluminium. Single anodizing of aluminium produces a broad distribution of nanopore size, whereas induces a highly ordered hemispherical pattern, which plays the ordered nucleation sites for the second anodizing step. Moreover, a quasi-linear growth behavior exists for the ordered domain growth versus the duration of first step anodizing. The through-pore arrangement of ideally grown membranes is not influenced by increasing the duration of second step anodizing.     

Optical constants of ethylene glycol over an extremely wide spectral range

Besides providing insights into the fundamental properties of materials, the knowledge of optical constants is required for a large variety of applications. In this work, for the first time to the best of our knowledge, an extremely wide spectral range from 181 to ∼54,000 cm⁻¹ has been explored for ethylene glycol in the liquid phase, and optical constants in the whole range have been given. The approach we propose can also be applied to different fluids.     

Reactive electron beam evaporation of gadolinium oxide optical thin films for ultraviolet and deep ultraviolet laser wavelengths

Availability of ultraviolet optical thin film materials, especially high index refractory oxides that transmit down to deep ultraviolet (approx. 0.2 μm) is very much limited. The present article discusses some of the research optimization studies on gadolinium oxide (Gd₂O₃), a novel lanthanide sesquioxide material, for such challenging spectral requirements. Optical and topographical properties of single layer films have been studied using phase modulated spectroscopic ellipsometry, spectrophotometry and multimode atomic force microscopy. Films deposited at lower substrate temperatures have shown higher band gaps and higher substrate temperatures yielded higher refractive indices. Multilayer high reflection filters have been developed for ultraviolet laser wavelengths such as ArF (193 nm), KrCl (222 nm), KrF (248 nm) and Nd-Yag-III (355 nm), using this material at lower substrate temperature conditions and successfully tested for their performances.     

Ion-assisted deposition of moisture-stable hafnium oxide films for ultraviolet applications

A design-of-experiments statistical approach was taken to determine the optimum ion gun operating parameters for the deposition of moisture-stable, low-absorbing hafnium oxide films by ion-assisted electron-beam evaporation. Factors identified as affecting the quality of hafnia films were chamber pressure, deposition rate, ion gun source gas composition, and ion gun current. Both oxygen and argon were used as source gases. High and low levels of the factors were chosen on the basis of our experience with the operating range of the system, and we made a series of 24 runs with all possible combinations of these factors. From a statistical analysis of the data, we find that the best films are obtained with a 1:1 mixture of argon and oxygen, 3-3.5 x 10(-4) Torr chamber pressure, 0.3-nm/s deposition rate, and 0.5-A ion gun current. X-ray diffraction measurements show that the ion-assisted films exhibit a partial monoclinic crystalline structure, whereas the unassisted films are amorphous.     

Refractive indices of textured indium tin oxide and zinc oxide thin films

The refractive indices of textured indium tin oxide (ITO) and zinc oxide (ZnO) thin films were measured and compared. The ITO thin film grown on glass and ZnO buffered glass substrates by sputtering showed distinct differences; the refractive index of ITO on glass was about 0.05 higher than that of ITO on ZnO buffered glass in the whole visible spectrum. The ZnO thin film grown on glass and ITO buffered glass substrates by filtered vacuum arc also showed distinct differences; the refractive index of ZnO on glass was higher than that of ZnO on ITO buffered glass in the red and green region, but lower in the blue region. The largest refractive index difference of ZnO on glass and ITO buffered glass was about 0.1 in the visible spectrum. The refractive index variation was correlated with the crystal quality, surface morphology and conductivity of the thin films.     

Growth and characterization of indium oxide thin films prepared by spray pyrolysis

Highly transparent and conducting indium oxide thin films are prepared on glass substrates from precursor solution of indium chloride. These films are characterized by X-ray diffraction, scanning electron microscopy and optical transmission. The preferential orientation of these films is found to be sensitive to deposition parameters. A comparative study has been made on the dependence on the thickness of the film on substrate temperatures with aqueous solution and 1:1 C₂H₅OH and H₂O as precursors. Films deposited at optimum conditions have 167 nm thickness and exhibited a resistivity of 2.94 × 10⁻⁴ Ω m along with transmittance better than 82% at 550 nm. The analytical expressions enabling the derivation of the optical constants of these films from their transmission spectrum only have successfully been applied. Finally, the refractive index dispersion is discussed in terms of the single-oscillator Wemple and Didomenico model.     

Structure and morphology of aluminium doped Zinc-oxide layers prepared by atomic layer deposition

The aim of this work is to study the effects of deposition temperature and aluminium incorporation on the crystalline properties, orientation and grain size of atomic layer deposited ZnO layers. X-ray diffraction analysis revealed a change in the dominant crystallite orientation with increasing substrate temperature. The most perfect crystal structure and largest grain size was found at 2 at.% aluminium content. Accumulation of compressive strain developed a monotonous increase with the growth temperature. Electric resistivity showed no anisotropy despite the change in the orientation, therefore the dominant conduction mechanism is not grain boundary related.     

Extraction of optical constants of zinc oxide thin films by ellipsometry with various models

Spectroscopic ellipsometry was used to extract the optical constants of zinc oxide (ZnO) thin films deposited on (100) silicon substrate by filtered cathodic vacuum arc technique. Three dispersion models, namely, Sellmeier dispersion model, Cauchy model and Forouhi–Bloomer model, were evaluated for determining the optical constants of ZnO thin films below the energy band gap. The study shows that the Cauchy model provides the best spectral fittings among these three models. Above the energy band gap, two ellipsometric models, namely, two-phase model and three-phase point-by-point fit, were used. This study reveals that the initial values used in the point-by-point fitting play a critical role. It also shows that the refractive index and the extinction coefficient calculated with the two-phase model can be used as the initial values for the point-by-point fitting. The spectral dependence of the refractive index and extinction coefficient obtained in this work is comparable with the data reported in the literature. In sum, a reliable methodology for determining the optical constants of ZnO thin films in the ultraviolet-visible-near infrared range (2501100 nm) has been developed.     

Stability of indium-oxide thin-film transistors by reactive ion beam assisted deposition

This work reports on the performance and stability of bottom-gate In₂O₃-TFTs with PECVD silicon dioxide gate dielectric. A highly-resistive amorphous In₂O₃ channel layer was deposited at room temperature by reactive ion beam assisted evaporation (IBAE). The field-effect mobility of the n-channel TFT is 33 cm²/V-s, along with an ON/OFF current ratio of 10⁹, and threshold voltage of 2 V. Device stability was demonstrated through measurement of the threshold voltage shift during long-term gate bias-stress and current stress experiments. Device performance, including stability, together with low-temperature processing, makes the indium-oxide TFT an attractive candidate for flexible transparent electronics, and display applications.     

Photochemical preparation of aluminium oxide layers via vacuum ultraviolet irradiation of a polymeric hexanoato aluminium complex

By means of photochemical conversion of thin layers of a polymeric hexanoato aluminium complex as the precursor, thin aluminium oxide layers were prepared onto silicon wafers. The precursor compound was synthesized and characterized by several analytical techniques like NMR, FTIR, XPS, ICP, and found to be a polymeric aluminium-containing coordination compound which has been proposed to be a hydroxo-bridged aluminium chain with pendant hexanoyl side-chains ascertained as catena-poly[{di(κ-O,O-hexanoato)aluminium}(μ-hydroxo)] (PHAH). Thin layers deposited from a solution of PHAH in toluene onto silicon wafers were irradiated using VUV radiation from a xenon excimer lamp. The layers were characterized by XPS, XRD, XRR, and spectroscopic ellipsometry. VUV radiation with a radiant exposure of E = 36 J cm⁻² led to almost carbon-free amorphous layers with a composition close to that of alumina having a density of about 2.1 g cm⁻³. Thus, using the example of a polymeric aluminium complex, the potential of the photochemical conversion of metal complexes into oxides could be shown as an alternative method, in addition to sol–gel techniques, for the generation of thin plane metal-oxide layers at normal temperature and pressure.     

Spray pyrolysis deposition of zinc oxide nanostructured layers

Highly structured ZnO layers comprising well-shaped hexagonal rods were prepared by spray pyrolysis deposition of zinc chloride aqueous solutions in the temperature range of 490-560 °C. The layers were characterised by SEM, XRD and SAED. A flat ZnO film evolves into the structured layer consisting of single crystalline hexagonal elongated prisms at growth temperatures close to 500 °C and above. The rise of both the growth temperature and solution concentration increases rod dimensions. The deposition of the 0.1 mol/l solution at ∼500 °C results in crystals with a diameter of 200-300 nm and length of 800 nm. However, the rods grown at 560 °C indicate a width in the range of 400-600 nm and a length of up to 2500 nm. The deposition of the 0.05 mol/l solution at 560 °C results in the rods with a diameter of 100-300 nm and a length of 1500 nm. The increase of the concentration up to 0.2 mol/l results in branched crystals, mainly tripods with a similar leg size of 600-700 nm in width and 3000 nm in length. According to XRD, the ZnO layers grown from the 0.1 mol/l solution in the temperature range of 450-560 °C are c-axis-oriented, independent of morphology. The XRD peaks intensities ratio (I₀₀₂/I₁₀₁) of the samples deposited at 560 °C changes from 9 to 1.3 by an increase in the solution concentration from 0.05 to 0.2 mol/l and indicates that c-axis orientation vanishes at higher concentrations. We showed that ZnO nanorods with the length to diameter ratio of 30 can be prepared by spray technique using indium tin oxide-covered glass substrates instead of bare glass.     

Theoretical analysis of optical characteristics of the alpha spodumene in ultraviolet region

It is presented an analysis of some important optical characteristics of the natural spodumene crystal, based on the first-principles calculations of its electronic structure and complex dielectric tensor. The optical absorption spectrum is interpreted in terms of electronic band structure for incident radiation energy up to 35 eV. The orientation of the three orthogonal principal optical axes is determined relative to the crystallographic axes, and expressed as function of the incident radiation wavelength. Reflectivity and electron energy loss are calculated along the three principal axes. All calculated optical properties are found to be highly anisotropic.     

Low temperature sol-gel metal oxide and fluoride layer stacks for optical applications

MgF₂ and TiO₂ single layers and layer stacks were produced by a spin-coating sol-gel process. The final temperature treatment was carried out at 100 °C. The layers were deposited onto silicon and fused silica substrates and were analysed by means of atomic force microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, ellipsometry, and UV-vis transmission spectroscopy. MgF₂ and TiO₂ single layers have morphological and optical properties comparable with physical vapour deposited layers. By using spectroscopic mapping ellipsometry, a good inter- and intra-sample homogeneity was confirmed. Multiple deposition steps result in a linear increase of layer thickness. Various films were deposited with thicknesses between 25 nm and 350 nm.It was shown that the low temperature sol-gel process results in films of optical quality. Anti-reflective and high reflective layer stacks consisting of MgF₂ and TiO₂ were designed and can be produced now by a sol-gel process, whereas the MgF₂ layers in the layer stacks contains also traces of MgF_2-2xO_x.     

Influence of ion assisted deposition on interface broadening in Fe/Al multilayers investigated by medium energy ion scattering

Trilayers of Al/Fe/Al and Al/Fe multilayers produced by magnetron sputtering both with and without ion assistance have been depth profiled using Auger electron spectroscopy and medium energy ion scattering. Important differences are observed in the layer structure, with ion assisted deposition giving the narrowest Al/Fe interfaces and so maintaining the most clearly defined layer structure. Both types of sputtering result in some oxygen contamination, particularly at the surface that modeling shows to be associated with the Al layers.     

Extraction of the refractive index profile of thin transparent conductive oxide films from the analysis of reflectance optical spectra

In the direction of growth of fabricated films, the material near the free surface as well as the interface with the substrate exhibits properties which are different from those of the material in the bulk. The resulting spatial inhomogeneity of the refractive index influences positions and values of the extrema of optical spectra. We exploit this to derive the profile of the refractive index by developing a theoretical approach. In the calculations, taking the derived profile into account, we attain a good reproduction of the experimental Transmittance and Reflectance spectra from approximately 1 to 4 eV, the region of relatively weak refractive-index dispersion.     

Characterization of Hafnium-Zirconium-Oxide-Nitride films grown by ion beam assisted deposition

Hafnium-Zirconium-Oxide-Nitride (Hf_1−xZr_xO_1−yN_y) films are prepared by ion beam assisted deposition on p-Si and quartz substrates with a composite target of sintered high-purity HfO₂ and ZrO₂. The thermal stability and microstructure characteristics for Hf_1−xZr_xO_1−yN_y films have been investigated. EDS results confirmed that nitrogen was successfully incorporated into the Hf_1−xZr_xO₂ films. XRD and Raman analyses showed that the Hf_1−xZr_xO_1−yN_y films remain amorphous after 1100 °C under vacuum ambient, and monoclinic HfO₂ and ZrO₂ crystals separate from Hf_1−xZr_xO_1−yN_y films with a increase of the annealing temperature up to 1300 °C. Meanwhile, the Hf_1−xZr_xO_1−yN_y films can also effectively suppress oxygen diffusion during high temperature annealing. AFM measurements demonstrated that surface roughness of the Hf_1−xZr_xO_1−yN_y films increase slightly. Then the optical properties of the samples were observed in the ultraviolet-visible range at room temperature. The variation in E_g from 5.64 to 6.09 eV as a function of annealing temperature has also been discussed briefly.