Influence of annealing temperature on the structural, mechanical and wetting property of TiO2 films deposited by RF magnetron sputtering

TiO₂ films have been deposited on silicon substrates by radio frequency magnetron sputtering of a pure Ti target in Ar/O₂ plasma. The TiO₂ films deposited at room temperature were annealed for 1 h at different temperatures ranging from 400 °C to 800 °C. The structural, morphological, mechanical properties and the wetting behavior of the as deposited and annealed films were obtained using Raman spectroscopy, atomic force microscopy, transmission electron microscopy, nanoindentation and water contact angle (CA) measurements. The as deposited films were amorphous, and the Raman results showed that anatase phase crystallization was initiated at annealing temperature close to 400 °C. The film annealed at 400 °C showed higher hardness than the film annealed at 600 °C. In addition, the wettability of film surface was enhanced with an increase in annealing temperature from 400 °C to 800 °C, as revealed by a decrease in water CA from 87° to 50°. Moreover, the water CA of the films obtained before and after UV light irradiation revealed that the annealed films remained more hydrophilic than the as deposited film after irradiation.     

The microstructure and wettability of the TiOx films synthesized by reactive DC magnetron sputtering

Different chemical state of titanium oxide films were deposited on commercially pure Ti (CP Ti) by reactive DC magnetron sputtering under different oxygen flow rates to examine a possibility of their applications to endovascular stents. The chemical composition and crystal structure of the obtained films were analyzed by XPS and XRD, respectively. In dependence on the deposition parameters employed, the obtained films demonstrated different mixture of anatase TiO₂, Ti₂O₃, TiO and Ti. The wettability of the films was measured by the water contact angle variation. By formation of titanium oxide film on CP Ti, contact angle was decreased. In order to modify and control the surface wettability, the resultant TiO_x films were etched subsequently by different plasma. The wettability was influenced by etched process according to the decreased contact angle values of etched TiO_x film. Furthermore, TiO_x films became highly hydrophilic by ultraviolet (UV) irradiation, and returned to the initial relatively hydrophobic state by visible-light (VIS) irradiation. The wettability of the TiO_x film was enabled to convert between hydrophilic and hydrophobic reversibly by alternative UV and VIS irradiation. By adjusting deposition parameter and further modification process, the wettability of the TiO_x films can be changed freely in the range of 0–90°.     

Etching characteristics and mechanism of Pb(Zr,Ti)O3 thin films in CF4/Ar inductively coupled plasma

The effect of the CF₄/Ar mixing ratio on the etching behaviour and mechanisms for Pb(Zr,Ti)O₃ (PZT) thin films in an inductively coupled plasma was carried out. It was found that an increase of Ar mixing ratio causes non-monotonic behaviour of the PZT etch rate, which reaches a maximum of 2.38 nm/s at 80% Ar. Investigating the plasma parameters, we found a weak sensitivity of both electron temperature and electron density to the change of CF₄/Ar mixing ratio. A combination of zero-dimensional plasma model with the model of surface kinetics shows the possibility of a non-monotonic etch rate behaviour due to the concurrence of physical and chemical pathways in the ion-assisted chemical reaction.     

Deposition of hydrophobic nano-coatings with low-pressure radio frequency CH2F2/Ar plasma processing

In an attempt to perform hydrophobic nano-coating, this investigation examined various operational parameters including in RF plasma power, system gas pressure, and CH₂F₂:Ar ratio of low-pressure plasma processing. The low-pressure plasma, generated with radio frequency power at 13.56 MHz, was fed difluoromethane (CH₂F₂)/Ar gas mixture. The surface characteristics of the plasma polymerized films were studied by static contact angle measurement (CA) and atomic force microscopy (AFM). As a result, increasing deposition of CH₂F₂ plasma polymerized films was achieved in enhanced RF plasma power input. The CH₂F₂ plasma polymerized films also were conducted in a varying system gas pressure with enhanced hydrophobic surface property. The effects of CH₂F₂/Ar plasma on the surface characteristics of the plasma polymerized films were investigated as a function of the Ar content. The super hydrophobic coating under optimized operational parameters prepared in this study obtained water contact angles greater than 150°. It was found that the maximum water contact angles (161°) was obtained at 1.5:1 (CH₂F₂: Ar) ratio. In addition, AFM analysis shows that possible ion bombardment from CH₂F₂/Ar plasma can increase surface roughness, and effectively form a hydrophobic coating on the surface of heat sensitive materials.     

Chemical activity of oxygen atoms in the magnetron sputter-deposited ZnO films

The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films was studied by alternating the deposition of a several-nanometer-thick ZnO layer and an O₂/Ar mixed plasma exposure, i.e., a layer-by-layer (LbL) technique. The film crystallization was promoted by suppressing the oxygen vacancy and interstitial defects by adjusting the exposure conditions of the O₂/Ar plasma. These findings suggest that the chemical potential of the oxygen atom influences the film crystallization and the electronic state. The diffusion and effusion of oxygen atoms at the growing surface have an effect similar to that of thermal annealing, promoted film crystallization and the creation and the annihilation of oxygen- and zinc-related defects. The role of oxygen atoms reaching at the growing film surface is discussed in terms of chemical annealing and a possible oxygen diffusion mechanism is proposed.     

The effect of He or Ar/O2 plasma treatment on Si surface prior to chemical vapor deposition of SiO2

The effect of O₂ plasma pretreatment on the SiO₂/Si interface property was studied using direct plasma varying the plasma power, He or Ar/O₂ ratio and the pretreatment time. The decrease of the pretreatment plasma power decreased the plasma damage and improved the interface property. The addition of He in O₂ glow discharge improved the electrical and the interface properties and there was an optimum He/O₂ ratio. The improvement of the interface property by Ar/O₂-plasma pretreatment was better than that by He/O₂, which is believed to be due to the lower oxidation rate of the Si surface. C–V analysis showed that the P_b center defect density was influenced by plasma pretreatment process parameters. To investigate the oxidation states near to and at the SiO₂/Si interface, X-ray photoelectron spectroscopy depth analysis was used and the gas phase in the glow discharge was investigated using optical emission spectroscopy analysis at various experimental conditions.     

Resisting oxygen plasma damage in low-k hydrogen silsesquioxane films by hydrogen plasma treatment

Low-density materials, such as the commercially available hydrogen silsesquioxane (HSQ) offer a low dielectric constant. Thus, HSQ with a low value of k (∼ 2.85) can be spin-coated if the density of Si–H bonding is maintained at a high level and the formation of –OH bonds and absorption of water in the film is minimized. O₂ plasma exposure on HSQ film increases leakage current. Also the dielectric constant shows a significant increase after O₂ plasma exposure. Another consequence of the O₂ plasma exposure is the significant decrease in the contact angle of the HSQ surface, which is not desirable. In this paper, we demonstrate that the surface passivation by hydrogen followed by oxygen plasma treatment of HSQ film for 30 min each leads to a regain of leakage current density and dielectric constant. These results show that the H₂ plasma treatment is a promising technique to prevent the damage in the commercially available and highly applicable low-k materials and it also increases the visibility of its use at the 0.1-μm technology. The more hydrophilic nature of the HSQ surface after O₂ plasma exposure leads to an increased moisture absorption with a subsequent increase in the dielectric constant.     

Characteristics of SiOx thin films deposited by atmospheric pressure chemical vapor deposition as a function of HMDS/O2 flow rate

SiO₂-like thin films were deposited using a modified dielectric barrier discharge with a gas mixture of hexamethyldisilazane (HMDS)/O₂/He/Ar and their film characteristics were investigated as functions of the HMDS and O₂ flow rates. As the HMDS flow rate was increased, higher amounts of Si-(CH₃)_x bonds and lower amounts of Si-OH bonds were observed in the deposited SiO_x, due to the increase in the amount of the less dissociated HMDS, which also caused an increase of the surface roughness. The addition and increase of the oxygen flow to HMDS/He/Ar brought the stoichiometry of SiO_x close to SiO₂ and decreased the surface roughness by decreasing the amount of Si-(CH₃)_x bonds through the increased decomposition and oxidation of HMDS, even though the deposition rate was decreased. However, when the O₂ flow rate was higher than a certain threshold, the surface roughness increased again, possibly due to the decrease in the extent of HMDS dissociation caused by the decreased plasma density at the higher oxygen flow rate. By using an optimized gas mixture of HMDS (150 sccm)/O₂ (14 slm)/He (5 slm)/Ar (3 slm), SiO₂-like thin films with a very low impurity level and having a smooth surface could be obtained with a deposition rate of approximately 42.7 nm/min.     

Surface Modification of Electrospun Polycaprolactone Nanofiber Meshes by Plasma Treatment to Enhance Biological Performance

A critical aspect in the development of biomaterials is the optimization of their surface properties to achieve an adequate cell response. In the present work, electrospun polycaprolactone nanofiber meshes (NFMs) are treated by radio‐frequency (RF) plasma using different gases (Ar or O₂), power (20 or 30 W), and exposure time (5 or 10 min). Morphological and roughness analysis show topographical changes on the plasma‐treated NFMs. X‐ray photoelectron spectroscopy (XPS) results indicate an increment of the oxygen‐containing groups, mainly ? OH and ? C?O, at the plasma‐treated surfaces. Accordingly, the glycerol contact angle results demonstrate a decrease in the hydrophobicity of plasma‐treated meshes, particularly in the O₂‐treated ones. Three model cell lines (fibroblasts, chondrocytes, and osteoblasts) are used to study the effect of plasma treatments over the morphology, cell adhesion, and proliferation. A plasma treatment with O₂ and one with Ar are found to be the most successful for all the studied cell types. The influence of hydrophilicity and roughness of those NFMs on their biological performance is discussed. Despite the often claimed morphological similarity of NFMs to natural extracellular matrixes, their surface properties contribute substantially to the cellular performance and therefore those should be optimized.     

Vapor phase surface functionalization under ultra violet activation of parylene thin films grown by chemical vapor deposition

Various reactive gas phase treatments have been investigated as surface functionalization dry processes with the goal to improve the wettability of parylene C films, keeping good optical properties in the visible range. The films were grown on different substrates by chemical vapor deposition with thicknesses ranging from 300 to 1630 nm. The polymer surface was treated under ultra violet (UV) irradiation at 254 nm in reactive atmospheres including He, H₂O, H₂O₂, O₂ and ambient air. The UV/O₂ treatment is the most efficient since the water contact angle decreases from 100° to 6° while the transmittance is maintained at 90% in the visible wavelengths. Furthermore it exhibits long life stability. The functionalization mechanism is discussed in relation with previous reports.     

SiO2 film deposition on the inner wall of a narrow polymer tube by a capacitively coupled μplasma

SiO₂ thin films were deposited on the inner wall of a narrow commercial poly(propylene) tube with inner/outer diameters of 1.0 mm/3.0 mm by plasma-enhanced chemical vapor deposition using He or Ar carrier gases and tetraethoxysilane (TEOS)/O₂ feedstock gases at high pressures from 30 kPa to atmospheric pressure and at room temperature. A glow μplasma was generated inside the tube by a radio frequency (RF 13.56 MHz) capacitively coupled discharge. X-ray photoelectron spectra and infrared spectra revealed that the inner surface of the plasma-treated tube was covered by a SiO₂ film. Scanning electron microscopy images indicated that the film produced by He/TEOS/O₂ μplasma had a smooth surface whereas the surface of the film produced by Ar/TEOS/O₂ μplasma appeared granulated. Typical deposition rates of approximately 300 nm/min were obtained by He/TEOS/O₂ μplasma at atmospheric pressure and a RF power of 11 W.     

Air plasma treatment of copper sheets using Diffuse Coplanar Surface Barrier Discharge

The treatment of copper sheets by atmospheric-pressure air plasma generated using the Diffuse Coplanar Surface Barrier Discharge was studied. The surface free energy measurements indicated a significant increase of the wettability after several seconds of plasma exposure. The atomic force microscopy technique revealed a relatively small increase of the surface roughness due to the plasma treatment. The observed increase of wettability, the influence of air humidity on treatment efficiency and the hydrophobic recovery of the plasma treated surfaces were studied by the x-ray photoelectron spectroscopy. A generation of surface -NO_x groups in humid air plasma was observed.     

Modification of polypropylene surface by CH<Subscript>4</Subscript>–O<Subscript>2</Subscript> low-pressure plasma to improve wettability

The aim of this work is to study the effect of surface treatment of a polypropylene film with low-pressure plasma using CH₄–O₂ mixture gas in an 80:20 ratio. The effect of the variation of the plasma treatment conditions has been studied to optimize the plasma effects. The film wettability has been analyzed by the study of the variation of free surface energy and its polar and dispersive components. The surface functionalization of the PP film was also analyzed by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (FTIR-ATR) analysis. The surface topography was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The CH₄–O₂ plasma treatment induces the ablation inherent of a traditional plasma treatment and polymerization mechanisms to take place simultaneously at the treated surface. The PP film treated with CH₄–O₂ plasma shows a remarkable improvement on the surface free energy mainly caused by surface functionalization as XPS reveals. Slight changes in surface topography are observed, but they do not contribute in a significant way to improve wettability.     

Rotational temperature of oxygen molecules in DC glow discharge in O2-Ar mixtures sustained in discharge tube made from Pyrex glass

The active DC glow discharge sustained in pure O₂ and O₂-Ar mixtures with Ar/O₂ concentration ratios up to 50% has been studied in a Pyrex discharge tube for pressures up to 500 Pa and for discharge currents up to 40 mA. The electric field strength and emission spectra parameters of the discharge were studied by means of the double-probe method and optical emission spectroscopy.The electric field strength was found to increase with the pressure and decrease with the discharge current, which is typical for DC glow discharges. Considering O₂-Ar mixtures, the values of electric field strength decreased with Ar/O₂ ratio.We have focused on the emitted radiation. The rotational temperature T_rot of molecular oxygen was determined from the well-resolved atmospheric A-band at 760 nm. The increase of the rotational temperature with increasing deposited power has been observed for all studied Ar/O₂ ratios. Moreover, it has been found that values of T_rot are independent of the mixture composition.     

Etching characteristics and mechanism of Ga-doped ZnO thin films in inductively-coupled HBr/X (X = Ar, He, N2, O2) plasmas

We investigated the etch characteristics and mechanisms of Ga-doped ZnO (Ga-ZnO) thin films in HBr/X (X = Ar, He, N₂, O₂) inductively-coupled plasmas. The etch rates of Ga-ZnO thin films were measured as a function of the additive gas fraction in the range of 0-100% for Ar, He, N₂, and O₂ at a fixed gas pressure (6 mTorr), input power (700 W), bias power (200 W), and total gas flow rate (40 sccm). The plasma chemistry was analyzed using a combination of the global (zero-dimensional) plasma model and Langmuir probe diagnostics. By comparing the behavior of the etch rate and fluxes of plasma active species, we found that the Ga-ZnO etch process was not limited by ion-surface interaction kinetics and appeared in the reaction rate-limited etch regime. In the HBr/O₂ plasma, the etch kinetics were probably influenced by oxidation of the etched surface.     

Metal surface oxidation by using dielectric barrier discharge

The surface oxidation of metal is investigated through plasma treatments with an atmospheric-pressure dielectric barrier discharge (DBD) for comparison with a conventional thermal oxidation process. After the plasma treatment of a copper plate, the Cu surface was noted to have abundant CuO and Cu(OH)₂ which act the part of hydrophilic functional elements. Highly improved wettability was also noted. When a greater amount of atomic oxygen is generated in the plasma by the DBD at a high applied voltage and a high O₂ additive concentration, the hydrophilic functional elements become more abundant and therefore enhance the wettability of the oxidized surface.     

Dry etching process of GaAs in capacitively coupled BCl3-based plasmas

Dry etching of GaAs was investigated in BCl₃, BCl₃/N₂ and BCl₃/Ar discharges with a mechanical pump-based capacitively coupled plasma system. Etched GaAs samples were characterized using scanning electron microscopy and surface profilometry. Optical emission spectroscopy was used to monitor the BCl₃-based plasma during etching. Pure BCl₃ plasma was found to be suitable for GaAs etching at > 100 mTorr while producing a clean and smooth surface and vertical sidewall. Adding N₂ or Ar to the BCl₃ helped increase the etch rates of GaAs. For example, the GaAs etch rate was doubled with 20% N₂ composition in the BCl₃/N₂ plasma compared to the pure BCl₃ discharge at 150 W CCP power and 150 mTorr chamber pressure. The GaAs etch rate was ∼ 0.21 µm/min in the 20 sccm BCl₃ plasma. The BCl₃/Ar plasma also increased etch rates of GaAs with 20% of Ar in the discharge. However, the surface morphology of GaAs was strongly roughened with high percentage (> 30%) of N₂ and Ar in the BCl₃/N₂ and BCl₃/Ar plasma, respectively. Optical emission spectra showed that there was a broad BCl₃-related molecular peak at 450-700 nm wavelength in the pure BCl₃ plasma. When more than 50% N₂ was added to the BCl₃ plasma, an atomic N peak (367.05 nm) and molecular N₂ peaks (550-800 nm) were detected. Etch selectivity of GaAs to photoresist decreased with the increase of % N₂ and Ar in the BCl₃-based plasma.     

Comparison of line edge roughness and profile angles of chemical vapor deposited amorphous carbon etched in O2/N2/Ar and H2/N2/Ar inductively coupled plasmas

In this study, we compared the line edge roughnesses (LER) and profile angles of chemical vapor deposited (CVD) amorphous carbon (a-C) patterns etched in an inductively coupled plasma (ICP) etcher produced by varying process parameters such as the N₂ gas flow ratio, Q (N₂), and dc self-bias voltage (V_dc) in O₂/N₂/Ar and H₂/N₂/Ar plasmas. The tendencies of the LER and profile angle values of the etched CVD a-C pattern were similar in both plasmas. The LER was smaller in the O₂/N₂/Ar than in the H₂/N₂/Ar plasmas, and the profile angle was larger in the O₂/N₂/Ar than in the H₂/N₂/Ar plasmas under the same processes conditions. The use of O₂/N₂/Ar plasma was more advantageous than the H₂/N₂/Ar plasma for controlling LER and profile angle.     

Time-dependent variation of the target mode in reactive sputtering of Al–O2 system

Reactive sputtering techniques have been widely used for forming compound thin films. In this study, the time-dependent variation of the target mode of an Al–O₂ system was investigated by measuring the target voltage for various reactive O₂ gas flow ratios and presputtering (i.e., sputtering in pure Ar gas to clean the target surface) times. The Al target remains in metallic mode for a certain period of time after being exposed to an Ar–O₂ plasma before it begins to be oxidized. This period increases with decreasing O₂ flow ratio and with increasing the presputtering time. It is considered that the period is caused by the gettering of O₂ gas by Al films deposited on the substrate and the chamber wall during presputtering.     

Effect of O<Subscript>2</Subscript> partial pressure and thickness on the gasochromic properties of sputtered V<Subscript>2</Subscript>O<Subscript>5</Subscript> films

V₂O₅ thin films were deposited by reactive DC-diode sputtering technique in a mixed atmosphere of O₂/Ar gas at room temperature from a high purity target of 99.99% vanadium. For the investigation, the thickness of the films and the O₂/Ar ratio during the sputtering process were the parameters. The sputtering rate of the V₂O₅ films dramatically decreases with increasing the O₂/Ar ratio. By X-ray diffraction it was found that films sputtered with 1% O₂/Ar ratio grow preferentially in two orientations: the 200 and the 001 orientation. The increase of the O₂/Ar ratio enhances the growth preferentially in the c-axis (001) and strongly decreases the growth in the a-axis (200) direction. The scanning electron microscope pictures confirm these results. In the visible region the optical transmittance is increased with increasing the O₂/Ar ratio in the sputter gas. Additionally, the optical band gap is slightly larger for the films sputtered with an O₂/Ar ratio higher than 5%. Beyond a thickness of about 220 nm and an O₂/Ar ratio of 10% the electrical sheet resistance of the films increases dramatically. During the insertion/extraction of hydrogen ions, the change in the optical transmission was investigated. The gasochromism of the V₂O₅ films was explained by use of the Infra Red (IR) measurements during the insertion/extraction of hydrogen ions.