High Energy Reactive Magnetron Sputtering Research Articles

Influence of the structural and surface properties on photocatalytic activity of TiO2:Nd thin films

Abstract Titanium dioxide thin films doped with the same amount of neodymium were prepared using two different magnetron sputtering methods. Thin films of anatase structure were deposited with the aid of Low Pressure Hot Target Magnetron Sputtering, while rutile coatings were manufactured using High Energy Reactive Magnetron Sputtering process. The thin films composition was determined by energy dispersive spectroscopy and the amount of the dopant was equal to 1 at. %. Structural properties were evaluated using transmission electron microscopy and revealed that anatase films had fibrous structure, while rutile had densely packed columnar structure. Atomic force microscopy investigations showed that the surface of both films was homogenous and consisted of nanocrystalline grains. Photocatalytic activity was assessed based on the phenol decomposition. Results showed that both thin films were photocatalytically active, however coating with anatase phase decomposed higher amount of phenol. The transparency of both thin films was high and equal to ca. 80% in the visible wavelength range. The photoluminescence intensity was much higher in case of the coating with rutile structure.

Effect of Nd doping on structure and improvement of the properties of TiO2 thin films

TiO2 thin films doped with neodymium in the range from 0.6 at.% to 6.1 at.% were prepared by high energy reactive magnetron sputtering. Investigations of structural properties performed by XRD and TEM methods revealed that neodymium dopant caused changes of the phase content and crystallite size in the prepared thin films. The doping also influenced optical properties, i.e., cutoff wavelength. Introducing a small amount of the neodymium into titania caused an increase of hardness of these coatings by ~30%, while the addition of higher dopant amounts resulted in a significant decrease of hardness as compared to TiO2 coatings. As high hardness as 24.9GPa was obtained and so far such value has not been reported in the literature for titania thin films prepared by dc magnetron sputtering.

Effect of the nanocrystalline structure type on the optical properties of TiO2:Nd (1 at.%) thin films

Titanium dioxide thin films, each doped with the same amount of neodymium (1at.%) were deposited by Low Pressure Hot Target Reactive Sputtering and High Energy Reactive Magnetron Sputtering processes in order to obtain anatase and rutile thin film structures respectively. The microstructure and phase composition were analyzed using the transmission electron microscopy method including high resolution electron microscopy imaging. The measurements of the optical properties showed, that both prepared thin films were transparent in the visible light range and had a low extinction coefficient of ca. 3⋅10−3. The thin film with the anatase structure had a lower cut-off wavelength and refractive index and a higher value of optical energy band gap as-compared to the TiO2:Nd coating with the rutile structure. Simultaneously, more efficient photoluminescence emission was observed for the rutile thin films.

Investigation of structural, optical and electrical properties of (Ti,Nb)Ox thin films deposited by high energy reactive magnetron sputtering

Abstract In this work the results of investigations of the titanium-niobium oxides thin films have been reported. The thin films were manufactured with the aid of a modified reactive magnetron sputtering process. The aim of the research was the analysis of structural, optical and electrical properties of the deposited thin films. Additionally, the influence of post-process annealing on the properties of studied coatings has been presented. The as-deposited coatings were amorphous, while annealing at 873 K caused a structural change to the mixture of TiO2 anatase-rutile phases. The prepared thin films exhibited good transparency with transmission level of ca. 50 % and low resistivity varying from 2 Ωcm to 5×10−2 Ωcm, depending on the time and temperature of annealing. What is worth to emphasize, the sign of Seebeck coefficient changed after the annealing process from the electron to hole type electrical conduction.

Optical and electrical properties of (Ti-V)Ox thin film as n-type Transparent Oxide Semiconductor

Abstract In this paper, the influence of vanadium doping on optical and electrical properties of titanium dioxide thin films has been discussed. The (Ti-V)Ox thin films was deposited on silicon and Corning glass substrates using high energy reactive magnetron sputtering process. Measurements performed with the aid of x-ray diffraction revealed, that deposited thin film was composed of nanocrystalline mixture of TiO2-anatase, V2O3 and β-V2O5 phases. The amount of vanadium in the thin film, estimated on the basis of energy dispersive spectroscopy measurement, was equal to 3 at. %. Optical properties were evaluated based on transmission and reflection measurements. (Ti-V)Ox thin film was well transparent and the absorption edge was shifted by only 11 nm towards longer wavelengths in comparison to undoped TiO2. Electrical measurements revealed, that investigated thin film was transparent oxide semiconductors with n-type electrical conduction and resistivity of about 2.7 · 105 Ωcm at room temperature. Additionally, measured I-V characteristics of TOS-Si heterostructure were nonlinear and asymmetrical.

Investigation of physicochemical properties of (Ti-V)Ox (4.3at.% of V) functional thin films and their possible application in the field of transparent electronics

Abstract During the last decade, functional materials, which simultaneously possess high transmission over the visible light range and good conductivity of electron or hole type electrical conduction at room temperature, have been the subject of interest of many researchers. In this work, (Ti-V)Ox thin films were deposited using the high energy reactive magnetron sputtering method and their structural, chemical, electrical and optical properties were characterized. In order to determine the material composition, energy dispersive spectroscopy measurements were performed and homogeneous concentration of titanium, vanadium and oxygen components as a function of thin film depth was revealed. High resolution transmission electron microscopy investigations as well as selected area electron diffraction patterns confirmed that the thin films were composed of the mixture of nanocrystalline TiO2-V2O5-V2O3 phases. The images of thin films investigated by atomic force microscope revealed a homogeneous, densely packed surface with RMS surface roughness of ca. 2.3 nm. X-ray photoelectron spectroscopy measurements showed that the surface of thin films consists of elements that are specific to the mixture of TiO2 and aforementioned vanadium oxides. Optical properties were determined on the basis of optical spectrophotometry measurements, and the high transmission level of the thin films was confirmed in the visible light range. Based on these results, the refractive index, extinction coefficient and optical band-gap width were estimated. In order to verify the possible application of these thin films in the field of transparent electronics the resistivity and I–V measurements of films deposited on silicon were performed.

Correlation of Photocatalysis and Photoluminescence Effect in Relation to the Surface Properties of TiO2:Tb Thin Films

In this paper structural, optical, photoluminescence, and photocatalytic properties of TiO2and TiO2:(2.6 at. % Tb) thin films have been compared. Thin films were prepared by high-energy reactive magnetron sputtering process, which enables obtaining highly nanocrystalline rutile structure of deposited films. Crystallites sizes were 8.7 nm and 6.6 nm for TiO2and TiO2:Tb, respectively. Surface of prepared thin films was homogenous with small roughness of ca. 7.2 and 2.1 nm in case of TiO2and TiO2:Tb samples, respectively. Optical properties measurements have shown that the incorporation of Tb into TiO2matrix has not changed significantly the thin films transparency. It also enables obtaining photoluminescence effect in wide range from 350 to 800 nm, what is unique phenomenon in case of TiO2with rutile structure. Moreover, it has been found that the incorporation of 2.6 at. % of Tb has increased the photocatalytic activity more than two times as compared to undoped TiO2. Additionally, for the first time in the current state of the art, the relationship between photoluminescence effect, photocatalytic activity, and surface properties of TiO2:Tb thin films has been theoretically explained.

Influence of terbium on structure and luminescence of nanocrystalline TiO2 thin films

AbstractIn this work analysis of the structural and optical properties of TiO2 thin films doped with terbium has been described. Samples were prepared by a high energy reactive magnetron sputtering process under low pressure of oxygen plasma. X-ray diffraction results have shown that different TiO2 crystal forms have been produced, depending on the amount of Tb dopant. The undoped matrix had rutile structure with crystallites with a size of 8.7 nm, while incorporation of 0.4 at. % of Tb into the film during the sputtering process resulted in anatase structure with bigger crystallites (11.7 nm). Increasing the amount of terbium up to 2 at. % and 2.6 at. % gave rutile structure with crystallites with a size of 6.6 nm for both films. However, Raman spectroscopy has revealed that in the case of TiO2:(2 at. % Tb), except for the rutile form, the presence of fine-crystalline anatase was observed. Moreover, the lack of Raman peaks shift attests to the lack of stress in the titania lattice of all of the TiO2:Tb films. This fact indicates localization of Tb3+ ions on the surface of TiO2 nanocrystals. In the case of optical investigation, results have shown that doping with terbium has a significant influence on the properties of TiO2, but it does not decrease the high transparency of the matrix. The observed changes of the transmission characteristics were produced only due to modification of the TiO2:Tb structure. Photoluminescence measurements have shown that emission of light from TiO2:Tb films occurs when the amount of terbium is 2.6 at. %. Based on the obtained results a scheme of direct energy transfer from titanium dioxide matrix (with rutile structure) to Tb3+ ions has been proposed.

Photocatalytic properties of transparent TiO2 coatings doped with neodymium

In this work photocatalytic properties of TiO2 thin fi lms doped with 8.51 at. % of Nd were described. The self-cleaning phenomenon of thin fi lms was discussed together with the structural, optical and surface properties of prepared thin fi lms. Transparent coatings based on titanium dioxide were manufactured by high-energy reactive magnetron sputtering process. Incorporation of Nd during sputtering process results in amorphous behavior, without a signifi cant infl uence on transparency and colour as compared to the undoped TiO2-rutile matrix. Nevertheless, doping with neodymium doubles the photocatalytic activity of the matrix due to higher quantity of photo-generated charge carriers and more effi cient mechanism of energy transfer.

Hardness of Nanocrystalline TiO<sub>2</sub> Thin Films

In this work results of hardness investigations of nanocrystalline TiO2 thin films are presented. Thin films were prepared by low pressure hot target reactive sputtering (LPHTRS) and high energy reactive magnetron sputtering (HERMS). In both processes a metallic Ti target was sputtered under low pressure of oxygen working gas. After deposition by LPHTRS TiO2 thin films with anatase structure were obtained and after additional post-process annealing at 1070 K, these films recrystallized into the rutile structure. Annealing also resulted in an increase of average crystallite size from 33 nm (for anatase) to 74 nm (for rutile). The HERMS process is a modification of the LPHTRS process with the addition of an increased amplitude of unipolar voltage pulses, powering the magnetron. This effectively increases the total energy of the depositing particles at the substrate and allows dense, nanocrystalline (8.7 nm crystallites in size) TiO2 thin film with the rutile structure to be formed directly. The hardness of the films was determined by nanoindentation. The results showed that the nanocrystalline TiO2-rutile thin film as-deposited using HERMS had high hardness (14.3 GPa), while the TiO2-anatase films as-deposited by LPHTRS, were 4-times lower (3.5 GPa). For LPHTRS films recrystallized by additional annealing, the change in thin film structure from anatase to rutile resulted in an increase of film hardness from 3.5 GPa to only 7.9 GPa. The HERMS process can therefore produce the TiO2 rutile structure directly, with hardness that is 2 times greater than rutile films produced by LPHTRS with additional annealing step.

Photocatalytic properties of nanocrystalline TiO2 thin films doped with Tb

Abstract In this work photocatalytic properties of TiO2 thin films doped with different amount of Tb have been described. Thin films were prepared by high energy reactive magnetron sputtering process. Comparable photocatalytic activity has been found for all doped TiO2 thin films, while different amounts of Tb dopant (0.4 and 2.6 at. %) results in either an anatase or rutile structure. It was found that the terbium dopant incorporated into TiO2 was also responsible for the amount of hydroxyl groups and water particles adsorbed on the thin film surfaces and thus photocatalytic activity was few times higher in comparison with results collected for undoped TiO2 thin films.

Influence of nanocrystalline structure and composition on hardness of thin films based on TiO2

Abstract In this work, the influence of Tb-doping on structure, and especially hardness of nanocrystalline TiO2 thin films, has been described. Thin films were formed by a high-energy reactive magnetron sputtering process in a pure oxygen atmosphere. Undoped TiO2-matrix and TiO2:Tb (2 at. % and 2.6 at. %) thin films, had rutile structure with crystallite sizes below 10 nm. The high-energy process produces nanocrystalline, homogenous films with a dense and close packed structure, that were confirmed by X-ray diffraction patterns and micrographs from a scanning electron microscope. Investigation of thin film hardness was performed with the aid of a nanoindentation technique. Results of measurements have shown that the hardness of all manufactured nanocrystalline films is above 10 GPa. In the case of undoped TiO2 matrix, the highest hardness value was obtained (14.3 GPa), while doping with terbium results in hardness decreasing down to 12.7 GPa and 10.8 GPa for TiO2:(2 at. % Tb) and TiO2:(2.6 at. % Tb) thin films, respectively. Incorporation of terbium into TiO2-matrix also allows modification of the elastic properties of the films.

Structural investigations of TiO 2:Tb thin films by X-ray diffraction and atomic force microscopy

In this work, structural investigations of TiO 2 thin films doped with Tb at the amount of 0.4, 2 and 2.6 at.% have been outlined. Thin films were deposited on Si and SiO 2 substrates by high energy reactive magnetron sputtering from mosaic Ti–Tb target. The influence of Tb dopant amount, post-annealing treatment and kind of applied substrate on microstructure has been discussed. Thin films were investigated by means of X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD analysis revealed the existence of crystalline TiO 2 in anatase and rutile forms, depending on Tb amount in examined samples. AFM images show that as-deposited samples with 0.4 at.% concentration of terbium (anatase structure) have bigger crystallites as compared to 2% and 2.6 at.% of Tb (rutile structure). The additional annealing at 1070 K results in a mixed anatase (77%) and rutile (23%) structure.

Surface characterization of TiO 2 thin films obtained by high-energy reactive magnetron sputtering

This paper presents the results of surface characterization of TiO 2 thin films deposited on different substrates by the use of high-energy reactive magnetron sputtering. Structural investigations carried out by X-ray diffraction (XRD) and atomic force microscopy (AFM) have shown a strong influence of both the substrate type, and its placement in the deposition chamber (relative to the sputtering target), on the structural properties of the films. In all cases, there is evidence for pseudoepitaxial growth. XRD examination showed existence of TiO 2-rutile phase with preferred (1 1 0) orientation and AFM measurements revealed nanocrystalline structure directly after deposition. X-ray photoelectron spectroscopy analysis showed that the TiO 2 films have stoichiometric composition.