Microstructure and properties of manganese dioxide films prepared by electrodeposition

Nanostructured manganese dioxide films were obtained by galvanostatic, pulse and reverse pulse electrodeposition from 0.01 to 0.1 M KMnO₄ solutions. The deposition yield was investigated by in situ monitoring the deposit mass using a quartz crystal microbalance (QCM). Obtained films were studied by electron microscopy, X-ray diffraction analysis, energy dispersive spectroscopy, thermogravimetric and differential thermal analysis. The QCM and electron microscopy data were utilized for the investigation of deposition kinetics and film formation mechanism. It was shown that the deposition rate and film microstructure could be changed by variation of deposition conditions. The method allowed the fabrication of dense or porous films. The thickness of dense films was limited to ∼0.1 μm due to the insulating properties of manganese dioxide and film cracking, attributed to drying shrinkage. Porous and crack-free 1-2 μm films were obtained using galvanostatic or reverse pulse deposition from 0.02 M KMnO₄ solutions. It was shown that film porosity is beneficial for the charge transfer during deposition and crack prevention in thick films. Moreover, porous nanostructured films showed good capacitive behavior for applications in electrochemical supercapacitors. The porous nanostructured films prepared in the reverse pulse regime showed higher specific capacitance (SC) compared to the SC of the galvanostatic films. The highest SC of 279 F/g in a voltage window of 1 V was obtained in 0.1 M Na₂SO₄ solutions at a scan rate of 2 mV/s.     

Influence of substrate bias voltage on structure and properties of the CrAlN films deposited by unbalanced magnetron sputtering

The CrAlN films were deposited on silicon and stainless steel substrates by unbalanced magnetron sputtering system. The influence of substrate bias on deposition rate, composition, structure, morphology and properties of the CrAlN films was investigated. The results showed that, with the increase of the substrate bias voltage, the deposition rate decreased accompanied by a change of the preferred orientation of the CrAlN film from (2 2 0) to (2 0 0). The grain size and the average surface roughness of the CrAlN films declined as the bias voltage increases above −100 V. The morphology of the films changed from obviously columnar to dense glass-like structure with the increase of the bias voltage from −50 to −250 V. Meanwhile, the films deposited at moderate bias voltage had better mechanical and tribological properties, while the films deposited at higher bias voltage showed better corrosion resistance. It was found that the corrosion resistance improvement was not only attributed to the low pinhole density of the film, but also to chemical composition of films.     

Microstructure and dielectric properties of La2O3 doped amorphous SiO2 films as gate dielectric material

As a potential gate dielectric material, the La₂O₃ doped SiO₂ (LSO, the mole ratio is about 1:5) films were fabricated on n-Si (0 0 1) substrates by using pulsed laser deposition technique. By virtue of several measurements, the microstructure and electrical properties of the LSO films were characterized. The LSO films keep the amorphous state up to a high annealing temperature of 800 °C. From HRTEM and XPS results, these La atoms of the LSO films do not react with silicon substrate to form any La-compound at interfacial layer. However, these O atoms of the LSO films diffuse from the film toward the silicon substrate so as to form a SiO₂ interfacial layer. The thickness of SiO₂ layer is only about two atomic layers. A possible explanation for interfacial reaction has been proposed. The scanning electron microscope image shows the surface of the amorphous LSO film very flat. The LSO film shows a dielectric constant of 12.8 at 1 MHz. For the LSO film with thickness of 3 nm, a small equivalent oxide thickness of 1.2 nm is obtained. The leakage current density of the LSO film is 1.54 × 10⁻⁴ A/cm² at a gate bias voltage of 1 V.     

RF-PACVD of water repellent and protective HMDSO coatings on bell metal surfaces: Correlation between discharge parameters and film properties

Hexamethyldisiloxane (HMDSO) films have been deposited on bell metal using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) technique. The protective performances of the HMDSO films and their water repellency have been investigated as a function of DC self-bias voltage on the substrates during deposition. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. Optical emission spectroscopy (OES) analyses of the plasma during deposition reveal no significant change in the plasma composition within the DC self-bias voltage range of −40 V to −160 V that is used. Raman and X-ray photoelectron spectroscopy (XPS) studies are carried out for film chemistry analysis and indicate that the impinging ion energy on the substrates influences the physio-chemical properties of the HMDSO films. At critical ion energy of 113 qV (corresponding to DC self-bias voltage of −100 V), the deposited HMDSO film exhibits least defective Si-O-Si chemical structure and highest inorganic character and this contributes to its best corrosion resistance behavior. The hardness and elastic modulus of the films are found to be bias dependent and are 1.27 GPa and 5.36 GPa for films deposited at −100 V. The critical load for delamination is also bias dependent and is 11 mN for this film. The water repellency of the HMDSO films is observed to be dependent on the variation in surface roughness. The results of the investigations suggest that HMDSO films deposited by RF-PACVD can be used as protective coatings on bell metal surfaces.     

Thickness dependence of structural, electrical and optical properties of indium tin oxide (ITO) films deposited on PET substrates

Without intentionally heating the substrates, indium tin oxide (ITO) thin films of thicknesses from 72 nm to 447 nm were prepared on polyethylene terephthalate (PET) substrates by DC reactively magnetron sputtering with pre-deposition substrate surfaces plasma cleaning. The dependence of structural, electrical, and optical properties on the films thickness were systematically investigated. It was found that the crystal grain size increases, while the transmittance, the resistivity, and the sheet resistance decreases as the film thickness was increasing. The thickest film (∼447 nm) was found of the lowest sheet resistance 12.6 Ω/square, and its average optical transmittance (400-800 nm) and the 550 nm transmittance was 85.2% and 90.4%, respectively. The results indicate clearly that dependence of the structural, electrical, and optical properties of the films on the film thickness reflected the improvement of the film crystallinity with the film thickness.     

AlF3 film deposited by IAD with end-Hall ion source using SF6 as working gas

A novel and effective process to fabricate high quality fluoride thin films was presented. Aluminum fluoride films deposited by a conventional thermal evaporation with an ion-assisted deposition (IAD) using SF₆ as a working gas at around room temperature were investigated. In this study, the optimal voltage and current, 50 V and 0.25 A, were found according to the optical properties of the films: high refractive index (1.489 at 193 nm), low optical absorption and extinction coefficient (<10⁻⁴ at 193 nm) in the UV range. The physical properties of the film are high packing density and amorphous without columnar structure. It was proved that using SF₆ working gas in IAD process is a good choice and significantly improves the quality of AlF₃ films.     

Dependence of film thickness on the structural and optical properties of ZnO thin films

ZnO thin films are prepared on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) at room temperature. Optical parameters such as optical transmittance, reflectance, band tail, dielectric coefficient, refractive index, energy band gap have been studied, discussed and correlated to the changes with film thickness. Kramers-Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet-visible-near infrared regions. Films with optical transmittance above 90% in the visible range were prepared at pressure of 6.5 × 10⁻⁴ Torr. XRD analysis revealed that all films had a strong ZnO (0 0 2) peak, indicating c-axis orientation. The crystal grain size increased from 14.97 nm to 22.53 nm as the film thickness increased from 139 nm to 427 nm, however no significant change was observed in interplanar distance and crystal lattice constant. Optical energy gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. The transmission in UV region decreased with the increase of film thickness. The refractive index, Urbach tail and real part of complex dielectric constant decreased as the film thickness increased. Oscillator energy of as-deposited films increased from 3.49 eV to 4.78 eV as the thickness increased.     

Native oxidation of ultra high purity Cu bulk and thin films

The effect of microstructure and purity on the native oxidation of Cu was studied by using angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and spectroscopic ellipsometry (SE). A high quality copper film prepared by ion beam deposition under a substrate bias voltage of −50 V (IBD Cu film at V_s = −50 V) showed an oxidation resistance as high as an ultra high purity copper (UHP Cu) bulk, whereas a Cu film deposited without substrate bias voltage (IBD Cu film at V_s = 0 V) showed lower oxidation resistance. The growth of Cu₂O layer on the UHP Cu bulk and both types of the films obeyed in principle a logarithmic rate law. However, the growth of oxide layer on the IBD Cu films at V_s = 0 and −50 V deviated upward from the logarithmic rate law after the exposure time of 320 and 800 h, respectively. The deviation from the logarithmic law is due to the formation of CuO on the Cu₂O layer after a critical time.     

Structural and optical properties of sputtered ZnO thin films

Zinc oxide (ZnO) and aluminium-doped zinc oxide (ZnO:Al) thin films were prepared by RF diode sputtering at varying deposition conditions. The effects of negative bias voltage and RF power on structural and optical properties were investigated. X-ray diffraction measurements (XRD) confirmed that both un-doped and Al-doped ZnO films are polycrystalline and have hexagonal wurtzite structure. The preferential 〈0 0 1〉 orientation and surface roughness evaluated by AFM measurements showed dependence on applied bias voltage and RF power. The sputtered ZnO and ZnO:Al films had high optical transmittance (>90%) in the wavelength range of 400-800 nm, which was not influenced by bias voltage and RF power. ZnO:Al were conductive and highly transparent. Optical band gap of un-doped and Al-doped ZnO thin films depended on negative bias and RF power and in both cases showed tendency to narrowing.     

Thickness dependence of optoelectrical properties of tungsten-doped indium oxide films

Pulsed laser deposition technique is used for deposition of tungsten-doped indium oxide films. The effect of film thickness on structural, optical and electrical properties was studied using X-ray diffraction (XRD), atomic force microscopy, UV-visible spectroscopy, and electrical measurements. X-ray diffraction study reveals that all the films are highly crystalline and oriented along (2 2 2) direction and the film crystallinity increases with increase in film thickness. Atomic force microscopy analysis shows that these films are very smooth with root mean square surface roughness of ∼1.0 nm. Bandgap energy of the films depends on thickness and varies from 3.71 eV to 3.94 eV. It is observed that resistivity of the films decreases with thickness, while mobility increases.     

Effect of thickness on the structure, morphology and optical properties of sputter deposited Nb2O5 films

Nb₂O₅ films with the thickness (d) ranging from 55 to 2900 nm were deposited on BK-7 substrates at room temperature by a low frequency reactive magnetron sputtering system. The structure, morphology and optical properties of the films were investigated by X-ray diffraction, atomic force microscopy and spectrophotometer, respectively. The experimental results indicated that the thickness affects drastically the structure, morphology and optical properties of the film. There exists a critical thickness of the film, d_cri =2010 nm. The structure of the film remains amorphous as d < d_cri. However, it becomes crystallized as d > d_cri. The root mean square of surface roughness increases with increasing thickness as d > 1080 nm. Widths and depths of the holes on film surface increase monotonously with increasing thickness, and widths of the holes are larger than 1000 nm for the crystalline films. Refractive index increases with increasing thickness as d < d_cri, while it decreases with increasing thickness as d > d_cri. In addition, the extinction coefficient increases with increasing thickness as d > d_cri.     

Structural and tribological properties of nitrogen doped amorphous carbon thin films synthesized by CFUBM sputtering method for protective coatings

Nitrogen doped amorphous carbon (a-C:N) films are a material that may successfully compete with DLC coatings, which have high hardness, high wear resistance, and a low friction coefficient. The a-C:N films were prepared on silicon substrate by a closed-field unbalanced magnetron sputtering method with a graphite target and using the Ar/N₂ mixture gases. And, we investigated the effects of various DC bias voltages from 0 to −300 V on the structural and tribological properties of the a-C:N films. This study was focused on improving physical properties of the a-C:N film by controlling process parameters like negative substrate DC bias voltage. The maximum hardness of the a-C:N film was 23 GPa, the friction coefficient was 0.08, and the critical load was 25 N on a Si wafer. Consequently, the structural and tribological properties of the a-C:N film showed a clear dependence on the energy of ions bombardment and the density of the sputtering and the reaction gases during film growth.     

Investigation of Ti/TiN multilayered films in a reactive mid-frequency dual-magnetron sputtering

Influence of the process parameters like (i) sputtering gas pressure, (ii) target current, (iii) substrate bias voltage and (iv) substrate temperature of a reactive mid-frequency dual-magnetron sputtering on (a) surface defects and (b) mechanical properties of Ti/TiN multilayered films was investigated. The forming mechanisms of the observed droplets and craters were analyzed. Results showed when: (1) pressure of Ar/N₂ gases PAr/N₂ was at 0.31 Pa and substrate temperature was in certain range, the size and the density of the surface defects on the TiN films tended to decrease with increasing the target current and the pulsed bias voltage; (2) the optimal deposition parameters for accomplishing fewer surface defects were used, increasing the thickness of the Ti buffer layer decreased the microhardness in certain level, and the adhesion was firstly increased and then decreased as thickness reaching and/or beyond a critical value. Results also showed that selection of optimized process parameters evidently minimized the surface defects and improved the mechanical properties of the film.     

The influence of substrate temperature variation on tungsten oxide thin film growth in an HFCVD system

Tungsten oxide (WO₃) thin films were deposited by a modified hot filament chemical vapor deposition (HFCVD) technique using Si (1 0 0) substrates. The substrate temperature was varied from room temperature to 430 °C at an interval of 100 °C. The influence of the substrate temperature on the structural and optical properties of the WO₃ films was studied. X-ray diffraction and Raman spectra show that as substrate temperature increases the film tends to crystallize from the amorphous state and the surface roughness decreases sharply after 230 °C as confirmed from AFM image analysis. Also from the X-ray analysis it is evident that the substrate orientation plays a key role in growth. There is a sharp peak for samples on Si substrate due to texturing. The film thickness also decreases as substrate temperature increases. UV-vis spectra show that as substrate temperature increases the film property changes from metallic to insulating behavior due to changing stoichiometry, which was confirmed by XPS analysis.     

Elaboration of (1 1 1)-oriented La-doped PZT thin films on platinized silicon substrates

PLZT thin films with different thickness were deposited in situ on platinum coated silicon substrates using a multi-target sputtering system. The purpose was to grow (1 1 1)-textured PLZT films on Pt (1 1 1). To this aim, the role of some key parameters on both crystalline quality and electrical properties was investigated. An ultra-thin TiO₂ seeding layer was deposited, prior to PLZT, which strongly affected the crystallographic orientation of the films. The relation between temperature deposition and film crystallinity is analysed. TEM observations show the presence of some very small grains of Zr_0.9La_0.1O_1.95 at the film bottom interface. In the range of thickness investigated, the plot of the inverse capacitance as a function of the film thickness split up into two different curves, each with a linear shape, which however allows determination of a single value of interface capacitance. Above a thickness of 400-500 nm a saturation of the dielectric properties seems to be reached.     

Investigation of thermal annealing effects on microstructural and optical properties of HfO2 thin films

In the present paper, we investigate the effect of thermal annealing on optical and microstructural properties of HfO₂ thin films (from 20 to 190 nm) obtained by plasma ion assisted deposition (PIAD). After deposition, the HfO₂ films were annealed in N₂ ambient for 3 h at 300, 350, 450, 500 and 750 °C. Several characterisation techniques including X-ray reflectometry (XRR), X-ray diffraction (XRD), spectroscopic ellipsometry (SE), UV Raman and FTIR were used for the physical characterisation of the as-deposited and annealed HfO₂ thin films. The results indicate that as-deposited PIAD HfO₂ films are mainly amorphous and a transition to a crystalline phase occurs at a temperature higher than 450 °C depending on the layer thickness. The crystalline grains consist of cubic and monoclinic phases already classified in literature but this work provides the first evidence of amorphous-cubic phase transition at a temperature as low as 500 °C. According to SE, XRR and FTIR results, an increase in the interfacial layer thickness can be observed only for high temperature annealing. The SE results show that the amorphous phase of HfO₂ (in 20 nm thick samples) has an optical bandgap of 5.51 eV. Following its transition to a crystalline phase upon annealing at 750 °C, the optical bandgap increases to 5.85 eV.     

The relationship between refractive index-energy gap and the film thickness effect on the characteristic parameters of CdSe thin films

CdSe thin films were deposited on glass substrates using Successive Ionic Layer Adsorption and Reaction (SILAR) method at room temperature and ambient pressure. The relationship between refractive index and energy bandgap was investigated. The film thickness effect on the structural, morphological, optical and electrical properties of CdSe thin films was investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies showed that all the films exhibit polycrystalline nature with hexagonal structure and are covered well with glass substrates. The crystalline and surface properties of the films improved with increasing film thickness. The optical absorption studies revealed that the films are found to be a direct allowed transition. The energy bandgap values were changed from 1.93 to 1.87 eV depending on the film thickness. The electron effective mass (m_e^?/m_o), refractive index (n), optical static and high frequency dielectric constant (ε_o, ε_∞) values were calculated by using the energy bandgap values as a function of the film thickness. The resistivity of the films changed between 10⁶ and 10² Ω-cm with increasing film thickness at room temperature.     

Synthesis and electrochemical characteristics of Ta-N thin films fabricated by cathodic arc deposition

Ta-N thin films were deposited on AISI 317L stainless steel (SS) substrates by cathodic arc deposition (CAD) at substrate biases of −50 and −200 V. The as-deposited films were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX). The results show that stoichiometric TaN with hexagonal lattice (3 0 0) preferred orientation was achieved at the bias of −200 V. On the other hand, Ta-rich Ta-N thin film deposited at −50 V shows amorphous nature. According to the XPS result, Ta element in the films surface exist in bonded state, including the Ta-N bonds characterized by the doublet (Ta 4f_7/2 = 23.7 eV and Ta 4f_5/2 = 25.7 eV). Electrochemical properties of the Ta-N coated stainless steel systems were investigated using potentiodynamic polarization and electrochemical impedance spectroscope (EIS) in Hank's solution at 37 °C. For the Ta-N coated samples, the corrosion current (i_corr) is two or three orders of magnitude lower than that of the uncoated ones, indicating a significantly improved corrosion resistance. Growth defects in the Ta-N thin films produced by CAD, however, play a key role in the corrosion process, especially the localised corrosion. Using the polarization fitting and the EIS modelling, we compared the polarization resistance (R_p) and the porosity (P) of the Ta-N coatings deposited at different biases. It seems that Ta-N film with comparatively lower bias (−50 V) shows better corrosion behavior in artifical physiological solution. That may be attributed to the effect of ion bombarding, which can be modulated by the substrate bias.     

Highly thermal stable transparent conducting SnO2:Sb epitaxial films prepared on α-Al2O3 (0 0 0 1) by MOCVD

Antimony-doped tin oxide (SnO₂:Sb) single crystalline films have been prepared on α-Al₂O₃ (0 0 0 1) substrates by metal organic chemical vapor deposition (MOCVD). The antimony doping was varied from 2% to 7% (atomic ratio). Post-deposition annealing of the SnO₂:Sb films was carried out at 700-1100 °C for 30 min in atmosphere ambient. The effect of annealing on the structural, electrical and optical properties of the films was investigated in detail. All the SnO₂:Sb films had good thermal stability under 900 °C, and the 5% Sb-doped SnO₂ film exhibited the best opto-electrical properties. Annealed above 900 °C, the 7% Sb-doped SnO₂ film still kept high thermal stability and showed good electrical and optical properties even at 1100 °C.     

Microstructure, hydrogenation and optical behavior of Mg-Ni multilayer films deposited by magnetron sputtering

Mg-Ni multilayer films with sequential Mg and Ni layers were prepared by direct current magnetron sputtering. The substrate temperature influences the microstructure of the films greatly. The film deposited at 298 K exhibits multilayered structure, while the film shows nanocrystalline/amorphous composite structure at the deposition temperature of 473 K. The optical properties between hydrogenation/dehydrogenation states of the films were performed using spectrophotometer in visible light region. The film deposited at 473 K can switch from mirror-like metallic state towards brownish yellow transparent state under 0.6 MPa H₂ at 298 K, and the optical transmittance modulation reaches up to 20% both at a wavelength of 770 nm and IR region, while the film deposited at 298 K exhibits low optical change, and the optical switching behavior can hardly be found. The extra free energy stored in the boundary of the nanocrystallines benefits the formation of magnesium-based hydride, resulting in the enhancement of the optical switching properties of the Mg-Ni film deposited at 473 K.