Al-induced fullerene-like nanostructures in C-Al-N thin films

The role of aluminium incorporated into growing carbon nitride (CN_x) films prepared by reactive dc-magnetron sputtering was investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). XPS analyses revealed the formation of Al-N bonding besides C-C and C-N bonds. With increasing Al concentrations above 11.8 at.%, a structural transformation from essentially amorphous (a-) (CN_x, AlN) phase to locally ordered microstructure comprising of fullerene-like (FL-) CN_x nanostructures surrounded by a-(CN_x, AlN) matrices was evidenced by Raman and HRTEM. The effect of aluminium in triggering FL-CN_x nanostructures was elucidated from thermodynamic considerations.     

Influence of Nd dopant amount on microstructure and photoluminescence of TiO2:Nd thin films

TiO₂ and TiO₂:Nd thin films were deposited using reactive magnetron sputtering process from mosaic Ti–Nd targets with various Nd concentration. The thin films were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectroscopic techniques. Photoluminescence (PL) in the near infrared obtained upon 514.5 nm excitation was also examined. The relationship between the Nd concentration, structural, optical and photoluminescence properties of prepared thin films was investigated and discussed. XRD and TEM measurements showed that an increase in the Nd concentration in the thin films hinders the crystal growth in the deposited coatings. Depending on the Nd amount in the thin films, TiO₂ with the rutile, mixed rutile–amorphous or amorphous phase was obtained. Transmittance measurements revealed that addition of Nd dopant to titania matrix did not deteriorate optical transparency of the coatings, however it influenced on the position of the fundamental absorption edge and therefore on the width of optical band gap energy. All TiO₂:Nd thin films exhibited PL emission that occurred at ca. 0.91, 1.09 and 1.38 μm. Finally, results obtained for deposited coatings showed that titania with the rutile structure and 1.0 at.% of Nd was the most efficient in VIS to NIR photon conversion.     

Variations of microstructure, conductivity and transparency of Al-doped ZnO thin films prepared by radio frequency magnetron sputtering with target-substrate distances

Al-doped ZnO films were deposited at different target-substrate distances by radio frequency magnetron sputtering. The crystallite size of the films is reduced with increasing the target-substrate distance, but the (002) preferential orientation of ZnO is observed for all the films. It is found that the target-substrate distance has a great influence on the carrier concentration in the films. Reduction of the target-substrate distance is favorable to obtain higher carrier concentrations. The lowest resistivity of 1.1 × 10⁻³ Ω cm is obtained for the film at target-substrate distance of 55 mm. The optical transmittance in the visible range remains higher than 90% for all the films, and the absorption edge shifts towards the shorter wavelength side with decreasing the target-substrate distance. The band gap was widened by 0.11 eV due to the Burstein-Moss (BM) shift from 3.33 eV to 3.44 eV with the reduction of the target-substrate distance from 60 mm to 55 mm.     

Low resistivity transparent conducting CdO thin films deposited by DC reactive magnetron sputtering at room temperature

Transparent conducting cadmium oxide (CdO) films were deposited on PET (polyethylene terephthalate) substrate by DC reactive magnetron sputtering at room temperature. All the films deposited at room temperature were polycrystalline in rock-salt structure. Dependences of the physical properties of the CdO films on the oxygen partial pressure were systematically studied. The films deposited at low oxygen flow rate were (200) oriented, while the films deposited at an oxygen flow rate greater than 20 sccm were (111) oriented. The average grain size of the CdO films decreased as the oxygen flow rate increases as determined by XRD and SEM. The Hall effect measurement showed that CdO films have high concentration, low resistivity, and high mobility. Both the mobility and the concentration of the carrier decreased with the increase of the oxygen flow rate. A minimum sheet resistance of 36.1 Ω/□, or a lowest resistivity of 5.44 × 10^− 4 Ω cm (6.21 × 10²⁰/cm³, μ = 19.2 cm²/Vs) was obtained for films deposited at an oxygen flow rate of 10 sccm.     

Optical properties of HfO2 thin films deposited by magnetron sputtering: From the visible to the far-infrared

Hafnium oxide (HfO₂ or hafnia) holds promise as a high-index dielectric in optical devices and thermal barrier coatings, because of its transparency over a broad spectrum (from the ultraviolet to the mid-infrared) and chemical and thermal stability at high temperatures. In the present work, thin hafnia films of thicknesses from about 180 to 500 nm are deposited on Si substrates using reactive magnetron sputtering. The crystalline structure and surface topography are characterized by X-ray diffraction and atomic force microscopy, respectively. The optical and radiative properties of the film-substrate composites are measured at room temperature using spectroellipsometry and Fourier-transform infrared spectrometry. The optical constants are obtained from about 0.37 to 500 μm by fitting suitable models to the experimental results. Optical properties and dielectric function modeling are discussed with correlation to both film thickness and surface roughness. It is found that a single-oscillator dielectric-function model can describe radiative properties from about 1 to 20 μm. By combining Cauchy's formula (for the visible and near-infrared regions) with a multiple-oscillator Lorentz model (for the far-infrared region), a dielectric function is obtained for the HfO₂ films that is applicable from the visible to the far-infrared.     

The influence of electric field on the microstructure of nc-Si:H films produced by RF magnetron sputtering

Hydrogenated nanocrystalline silicon thin films were prepared by RF magnetron sputtering. Different bias fields (no bias-no ground, grounded and negative bias) were applied to the substrate. The effect of the ion bombardment on the structure, chemical and optical property were studied by Raman spectroscopy, X-ray diffraction, Rutherford backscattering (RBS) and optical transmission spectroscopy. The deposition rate and the optical bandgap decrease as the bias voltage increases from 0 to −50 V. The structural characterization indicates that compressive stress is developed in plane and tensile stress is induced in the growth direction. No significant variation on the chemical composition was observed.     

Substrate temperature influence on ZnS thin films prepared by ultrasonic spray

ZnS thin films were deposited by ultrasonic spray technique. The starting solution is a mixture of 0.1 M zinc chloride as source of Zn and 0.05 M thiourea as source of S. The glass substrate temperature was varied in the range of 250 °C-400 °C to investigate the influence of substrate temperature on the structure, chemical composition and optical properties of ZnS films. The DRX analyses indicated that ZnS films have nanocrystalline hexagonal structure with (002) preferential orientation and grain size varied from 20 to 50 nm, increasing with substrate temperature. The optical films characterization was carried out by the UV-visible transmission. The optical gap and films disorder were deduced from the absorption spectra and the refractive indices of the films were determined by ellipsometric measurements. It is shown that the obtained films are generally composed of ZnO and ZnS phases with varied proportion, while at deposition temperature of 400 °C, they are near stoichiometric ZnS.     

Influence of the film thickness on structural and optical properties of CdTe thin films electrodeposited on stainless steel substrates

CdTe thin films of different thicknesses were deposited by electrodeposition on stainless steel substrates (SS). The dependence of structural and optical properties on film thickness was evaluated for thicknesses in the range 0.17–1.5 μm. When the film is very thin the crystallites lack preferred orientation, however, thicker films showed preference for (111) plane. The results show that structural parameters such as crystallite size, lattice constant, dislocation density and strain show a noticeable dependence on film thickness, however, the variation is significant only when the film thickness is below 0.8 μm. The films were successfully transferred on to glass substrates for optical studies. Optical parameter such as absorption coefficient (α), band gap (E_g), refractive index (n), extinction coefficient (k_e), real (?_r) and imaginary (?_i) parts of the dielectric constant were studied. The results indicate that all the optical parameters strongly depend on film thickness.     

Evolution of optical properties with deposition time of silicon nitride and diamond-like carbon films deposited by radio-frequency plasma-enhanced chemical vapor deposition method

The paper presents investigations of the optical properties of thin high-refractive-index silicon nitride (SiN_x) and diamond-like carbon (DLC) films deposited by the radio-frequency plasma-enhanced chemical vapor deposition method for applications in tuning the functional properties of optical devices working in the infrared spectral range, e.g., optical sensors, filters or resonators. The deposition technique offers the ability to control the film's optical properties and thickness on the nanometer scale. We obtained thin, high-refractive-index films of both types at deposition temperatures below 350 °C, which is acceptable under the thermal budget of most optical devices. In the case of SiN_x films, it was found that for short deposition processes (up to 5 min long) the refractive index of the film increases in parallel with its thickness (up to 50 nm), while for longer processes the refractive index becomes almost constant. For DLC films, the effect of refractive index increase was observed up to 220 nm in film thickness.     

Synthesis and characterization of hard ternary AlMgB composite films prepared by sputter deposition

Hard and superlight thin films laminated with boron carbide have been proposed as candidates for strategic use such as armor materials in military and space applications. Aluminum magnesium boride (AlMgB) films are excellent candidates for these purposes. We prepared AlMgB films by sputter deposition using multiple unbalanced planar magnetrons equipped with two boron and one AlMg targets. The film morphology changed and the film's root mean square (rms) roughness varied from 1.0 to 18 nm as the power density of the AlMg target increased from 0.2 to 1.0 W/cm² while the power density of each boron target was maintained at 2 W/cm². Chemical analyses show dominating Al, Mg, B and trace elements of oxygen, carbon and argon. The film composition also varies with altering the power density supplied to the AlMg target. The film with an atomic ratio of Al:Mg:B = 1.38:0.64:1 exhibits the highest hardness (~ 30 GPa). This value surpasses the hardness of hydrogenated diamond-like carbon films (24-28 GPa) prepared by plasma enhanced chemical vapor deposition.     

Low-temperature deposited Titanium-doped zinc oxide thin films on the flexible PET substrate by DC magnetron sputtering

Transparent conducting Titanium-doped zinc oxide thin films (TZO) with high transparency and relatively low resistivity were firstly deposited on water-cooled polyethylene terephthalate (PET) substrates at room temperature by DC magnetron sputtering. The microstructure, optical and electrical properties of the deposited films were investigated and discussed. The XRD patterns show that all the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. The electrical resistivity decreases when the sputtering power increases from 45 W to 60 W. However, as the puttering power continue increases from 60 W to 90 W, the electrical resistivity increases rapidly. When the puttering power is 60 W, the films deposited on PET substrate have the lowest resistivity of 4.72 × 10⁻⁴ Ω cm and a relatively high transmittance of above 92% in the visible range.     

Optical modelling of photoluminescence emitted by thin doped films

Photoluminescence (PL) spectra emitted by doped films are deformed owing to film thickness-dependent wave interference. This hampers knowing well their PL generating mechanisms as well as designing photonic devices with suitable geometries that improve their PL efficiency. We develop in this paper an energy model for PL emitted by doped films considering the interaction between the wavelength-differing incident standing and emitted waves, their energy transfer in-between, and the interferences undergone by both. The film optical constants are estimated fitting the model to the measured PL. This simple model has thus allowed us to interpret the evolution of PL emitted by Er-doped AlN films prepared on Si substrates by reactive magnetron sputtering. The shapes, the amplitudes, and the illusive sub-spectral features of the PL spectra depend essentially on the film thickness. The model further predicts high sensitivity for PL emitted by non-homogenously doped stacked-films to incident light wavelengths and film-thickness variations. This property has potential applications in tracking wavelength variations and in measuring physical quantities producing thickness variations. This model may be used to optimise PL efficiency of photonic devices through different film geometries and optical properties.     

Effect of annealing treatment on structural, electrical, and optical properties of Ga-doped ZnO thin films deposited by RF magnetron sputtering

The effect of annealing on structural, electrical, and optical properties of Ga-doped ZnO (GZO) films prepared by RF magnetron sputtering was investigated in air and nitrogen. GZO films are polycrystalline with a preferred 002 orientation. The resistivities of annealed films are larger than the as-deposited. The transmittance in the near IR region increases greatly and the optical band gap decreases after annealing. The photoluminescence spectra is composed of a near band edge emission and several deep level emissions (DLE) which are dominated by a blue emission. After annealing, these DLEs are enhanced evidently.     

Evolution of the properties of ZnO thin films subjected to heating treatments

Structural and optical properties of ZnO thin films (200 nm thickness) deposited using magnetron sputtering technique are influenced by structural defects. Therefore, we applied various heating treatments in order to control and improve the crystallinity of the samples. These treatments were realized in air at temperatures of 350 °C, 550 °C and 700 °C respectively, each for a duration of 1 h. The properties of the samples were investigated both before and after the heating treatment. Modern methods like X-ray Diffraction, Atomic Force Microscopy and Scanning Electron Microscopy were used to analyze the structure and morphology of the heated ZnO thin films. These heating treatments may be held responsible for rearrangements in the morphology of the thin films. Thus, it was observed that an increase of porosity and agglomeration of the crystallites is followed by an increase in the size of the crystallites. Inter-crystalline borders will migrate determining a coalescence of several crystallites during the heating process, as well. As a consequence, an increase of the band gap width from 3.26 eV to 3.30 eV (at 350 °C) and 3.32 eV (at 550 °C) respectively, occurred.     

Growth and in-situ electrical characterization of ultrathin epitaxial TiN films on MgO

We examine the properties of ultrathin TiN films grown by reactive dc magnetron sputtering on single-crystalline MgO(100) substrates at growth temperatures ranging from 30 to 650 °C. The resistance of the films is measured in-situ, during growth, to study the thickness at which the films coalesce and become structurally continuous. Both the in-situ resistance measurements and X-ray diffraction measurements show a clear transition from polycrystalline growth to epitaxial (100) growth well below typical TiN growth temperatures, or between 100 and 200 °C. The coalescence and continuity thicknesses are 1.09 ± 0.06 nm and 5.5 ± 0.5 nm, respectively, at room temperature but reach a minimum of 0.08 ± 0.02 nm and 0.7 ± 0.1 nm, respectively, at 600 °C. A large drop in resistivity is seen with increasing growth temperature and the resistivity reaches 16.6 μΩ cm at 600 °C. Achieving epitaxy at such a low temperature and a low continuity thickness is important in a variety of applications such as device interconnects and metal-oxide-semiconductor devices.     

Cu2O nanorod thin films prepared by CBD method with CTAB: Substrate effect,deposition mechanism and photoelectrochemical properties

Cuprous oxide (Cu₂O) films with different nanostructures are deposited on different substrates of fluorine-doped SnO₂ (FTO) glass, Cu and Ti foil respectively by using chemical bath deposition (CBD) technique with the presence of cetyltrimethylammonium bromide (CTAB). The samples are characterized by X-ray diffractmeter, scanning electron microscopy and UV–vis diffuse reflectance spectroscopy. The results show that the prepared Cu₂O films are composed of nanorod arrays when there is CTAB in reaction system. Without CTAB, Cu₂O films with nanospheres are formed. The concentration of CTAB is crucial for the controllable synthesis of nanorod structured Cu₂O films with different length to diameter ratio and nanorod array density is dependent on both substrates and CTAB. A possible mechanism for the formation of Cu₂O nanorods is discussed. Additionally, the UV–vis absorption property for Cu₂O nanorods is much better than that for nanospheres. The photovoltage produced under visible light for Cu₂O nanorod films is higher than that for the nanospheres. Although Cu₂O nanorods on Ti foil can absorb the most visible light, those on Cu foil demonstrate better and more stable photoelectrochemical property than those on any other substrates. This study may be extremely useful for Cu₂O based device with nanostructures.     

Synthesis of high-density MgO films by a novel magnetron sputtering system

A novel magnetron sputtering system, which included simply designed two grids between target and substrate, was developed in our laboratory for the synthesis of high-density MgO films. In order to investigate the effect of grids assisted magnetron sputtering, MgO films were deposited by conventional magnetron, one grid assisted magnetron and two grids assisted magnetron. The saturated ion current density and Mg ion fraction in MgO discharges generated by grids assisted magnetron were increased in comparison with those obtained in conventional magnetron, which means that grids assisted magnetron led to the enhancement of plasma density. As a result of microstructure analysis, grids assisted magnetron produced a higher density MgO film with smoother surface compared to that obtained in conventional magnetron.     

Reactive DC magnetron deposition of copper nitride films for write-once optical recording

Copper nitride (Cu_xN) films were prepared on glass slides by reactive direct current (DC) magnetron sputtering under different nitrogen flow rates and substrate temperature, respectively. X-ray diffraction and reflectance spectra were employed to characterize the films. The Cu_xN films can completely decompose through heat treatment at temperature as low as 160 °C. The reflectance spectra of the as-deposited films are quite different from that of the decomposed films in a wide wavelength range from UV to infrared. Its relatively low decomposition temperature and large reflectance change before and after decomposition makes it a potential write-once optical recording medium.     

The effect of sputtering power on the structure and photocatalytic activity of TiO2 films prepared by magnetron sputtering

TiO₂ films were fabricated by direct current reactive magnetron sputtering. The effect of the sputtering power on the film structures, morphologies, and properties was investigated in detail. It is found that the concentration of oxygen impurities increased with increasing sputtering power accompanied by the bandgap (E_g) narrowing and broadening of photoluminescence (PL) peaks. The oxygen impurities were found to mainly play the role of recombination centers, leading to the decrease of photocatalytic activity. Furthermore, the photoconductivity to dark conductivity ratio could be used to evaluate and even predict photocatalytic activity to some extent.