Characterization of radical-enhanced atomic layer deposition process based on microwave surface wave generated plasma

Titanium dioxide (TiO2) thin films were deposited by remote‐plasma atomic layer deposition (RPALD). The process window was determined in the range from 150 to 300 °C for atomic layer deposition of TiO2 thin film. The crystal structure and grain size of the TiO2 thin films deposited by RPALD was controlled via the variations of the deposition temperature and post‐deposition thermal annealing. The as‐deposited TiO2 thin film grown at 150 °C was amorphous whereas the TiO2 thin films grown above 200 °C were polycrystalline, consisting of anatase phase. As the deposition temperature increased, the grain size of the anatase phase progressively decreased. Meanwhile, when annealed at 900 °C, the amorphous TiO2 thin film deposited at 150 °C crystallized into anatase structure. The film deposited at 200 °C retained the anatase structure up to 900 °C while incurring minimal grain growth. However, the post‐annealed TiO2 thin films deposited at 250 and 300 °C partially transformed to the rutile structure, resulting in a mixture of anatase and rutile phases. It is speculated that the relatively large grain size of the films deposited below 200 °C likely suppressed the anatase → rutile transformation during annealing as the reduction of total fraction of grains boundaries, which acted as primary nucleation sites for the rutile transition, delayed the anatase → rutile transformation.

Spatial characterization of analyte emission and excitation temperature in an inductively coupled plasma

Event Abstract Back to Event Atomic layer deposited TiO2 protects highly porous ceramic bone scaffolds from grain boundary corrosion Benjamin Müller1*, Håvard J. Haugen1*, Ola Nilsen2 and Hanna Tiainen1* 1 University of Oslo, Department of Biomaterials, Norway 2 University of Oslo, Department of Chemistry, Norway Introduction: Corrosion in ceramics occurs preferentially at high energy sites such as grain boundaries (GB) and GB corrosion is a well-known phenomenon for polycrystalline oxide ceramics.[1] When highly porous ceramic materials such as bone scaffolds with large surface-to-volume ratios are exposed to corrosive environment, GB corrosion can have a particularly detrimental impact on the mechanical properties of the scaffold. This study aims to investigate the suitability of atomic layer deposition (ALD) of TiO2 thin films to protect a macro-porous TiO2 scaffold from GB corrosion and maintain its mechanical properties in physiologically low pH conditions. Two different deposition temperatures were chosen to assess the effect of film structure on the barrier properties of the deposited layers. Materials and Methods: TiO2 thin films were deposited at 150°C and 250 °C on the surface of highly porous TiO2 scaffolds using the chloride-water ALD process. The ALD films were characterised by scanning electron and atomic force microscopy, x-ray diffraction, and ellipsometry. The compressive strength of the ALD-coated scaffolds was tested following up to 28 d exposure to corrosive medium (1mM HCl). Results and Discussion: Although the ALD coatings deposited at 150 °C were mostly characterised as having amorphous structure, some randomly formed anatase crystallites were observed to protrude through the amorphous film as shown in Figure 1A. Films deposited at 250 °C had anatase crystal structure and were composed of densely packed grains with an average diameter of 31 ± 6 nm was (Figure 1B). The thicknesses of the amorphous and anatase coatings were 26 ± 1 and 22 ± 2 nm, respectively, and these thicknesses were not altered by 28 d exposure to 1mM HCl as measured by ellipsometry. In addition, strong adhesion between the coating and substrate was observed with no cracking or delamination upon fracture of the scaffold struts. Figure 1: Atomic force micrographs merged from height and amplitude scans (10×10 µm2) and height profiles in cross-section (below) for TiO2 deposited at 150 °C (A) and 250 °C (B) with high resolution scans (300×300 nm2) as 3D illustrations. After 7 and 28 days immersion into 1 mM HCl, a significant reduction in the compressive strength of the uncoated scaffolds was observed due to dissolution of siliceous GB phase, whereas both ALD coated scaffolds maintained the initial strength (Figure 2). This indicates that GB corrosion in highly porous scaffolds is mitigated under acidic conditions up to an exposure period of 28 days. In contrast to the unchanged strength of amorphous coated scaffolds, a slight decrease for the anatase coated scaffolds to 94 % of the initial strength after 28 days immersion was observed. Figure 2: Compressive strength of non-coated and ALD coated scaffolds prior and after immersion into 1 mM HCl for 7 and 28 days (n=10). Conclusions: GB corrosion in highly porous TiO2 scaffolds was successfully diminished by atomic layer deposition of both amorphous and anatase TiO2. The compressive strength of ALD coated scaffolds was maintained in physiologically low pH conditions up to 28 days. Amorphous TiO2 films offered excellent protection against GB corrosion, whereas anatase coated scaffolds with nano-sized grains may allow for improved osteoconduction in vitro and in vivo. This study was supported by Research Council of Norway grant 228415.; Jonas Wengenroth is acknowledged for his help with the AFM imaging of the surfaces.

TiO2 thin films have been grown on amorphous soda lime glass and polycrystalline silicon substrates from TiI4 and H2O2 by atomic layer deposition (ALD) in the temperature range 250–490 °C. The film growth rate and refractive index increased linearly with growth temperature up to 300 °C. Between 300 °C and 400 °C, the film growth rate tended to stabilize. Above 400 °C, there was a further rapid increase in the growth rate, together with a corresponding increase in the thickness profile. The refractive index reached 2.70–2.75 in the films grown above 300 °C. The films contained low amounts of residual hydrogen and were virtually iodine-free. When deposited below 300 °C and above 325 °C, the films contained weakly crystallized, but still distinct, anatase and rutile phases, respectively. Reflective high-energy electron diffraction (RHEED) studies revealed that the uppermost layers of the films grown on silicon at 275 °C, 325 °C, and 425 °C contained anatase phase, regardless of deposition temperature. In the temperature range 300–325 °C, a transition region was established where either the films became less ordered, or they contained rather strongly ordered, but unstable, suboxide phases. The suboxide phase, when present, was transformed into a mixture of anatase and rutile when stored in air at room temperature.

TiO2 thin films have been grown on amorphous soda lime glass and polycrystalline silicon substrates from TiI4 and H2O2 by atomic layer deposition (ALD) in the temperature range 250–490 °C. The film growth rate and refractive index increased linearly with growth temperature up to 300 °C. Between 300 °C and 400 °C, the film growth rate tended to stabilize. Above 400 °C, there was a further rapid increase in the growth rate, together with a corresponding increase in the thickness profile. The refractive index reached 2.70–2.75 in the films grown above 300 °C. The films contained low amounts of residual hydrogen and were virtually iodine-free. When deposited below 300 °C and above 325 °C, the films contained weakly crystallized, but still distinct, anatase and rutile phases, respectively. Reflective high-energy electron diffraction (RHEED) studies revealed that the uppermost layers of the films grown on silicon at 275 °C, 325 °C, and 425 °C contained anatase phase, regardless of deposition temperature. In the temperature range 300–325 °C, a transition region was established where either the films became less ordered, or they contained rather strongly ordered, but unstable, suboxide phases. The suboxide phase, when present, was transformed into a mixture of anatase and rutile when stored in air at room temperature.

In this study, we deposited TiO2 thin films onto borosilicate glass by ultrasonic spray pyrolysis at 350 and 450 °C. The aim of study is to determine the effect of deposition temperature on photocatalytic activity of TiO2 thin films and to investigate the performance of TiO2 thin films on photocatalytic degradation of methyl tert-butyl ether (MTBE), acetone, acetaldehyde, and heptane as functions of different operating parameters. TiO2 thin films deposited at 350 and 450 °C have a thickness value of 190 and 330 nm, respectively. All as-prepared TiO2 films possess an anatase crystalline structure. According to the X-ray photon spectroscopy (XPS) study, the TiO2 thin film deposited at 350 °C showed a higher amount of oxygen vacancies and hydroxyl groups on the film surface after UV treatment. The aged-TiO2 thin film deposited at 350 °C showed a water contact angle (WCA) value of 0° after 10 min UV irradiation, showing superhydrophilic surface behavior. The TiO2 film deposited at 350 °C exhibited the highest amount of conversion of MTBE (100%). The results also showed that TiO2 films are capable of photocatalytic degradation of MTBE (100%) and acetaldehyde (approx. 80%) in humid air conditions and high airflow rate. The visible-light-activity of TiO2 thin films was tested with 5 ppm MTBE and acetone. TiO2 thin films deposited at 350 °C with a surface area of 600 cm2 showed 60% of MTBE and 33% of acetone degradation under VIS light.

Phase-gradient atomic layer deposition of TiO2 thin films by plasma-induced local crystallization

As a multi-functional material, TiO2 thin film has been widely studied and applied in display, photocatalysis, solar cells and other fields. In this work, TiO2 thin films were prepared using atomic layer deposition, and their morphology was successfully regulated by the growth temperature. It was found that TiO2 film prepared at low temperature was amorphous, uniform and dense, with great barrier property, which can be used for encapsulation. Crystalline TiO2 nanoparticles with anatase phase appeared at higher temperature than 150 °C, whose amount increased with the growth temperature. The crystalline TiO2 particles can be used as templates to prepare randomly textured nano-patterns, which were proved to be able to improve the light extraction efficiency of photoelectric devices. Specifically, the luminance efficiency of the QLED with the nano-patterns formed by the crystalline TiO2 particle prepared at 200 °C and 250 °C were increased by 24.07% and 30.44%, respectively.

Titanium dioxide (TiO2) thin films are widely used in transparent optoelectronic devices due to their excellent properties, as well as in photocatalysis, cosmetics, and many other biomedical applications. In this work, TiO2 thin films were deposited onto AISI 304 and AISI 316L stainless steel substrates by atomic layer deposition, followed by comparative evaluation of the mixture of anatase and rutile phase by X-ray diffraction, Raman maps, morphology by SEM-FEG-AFM, and adhesion of the films on the two substrates, aiming to evaluate the scratch resistance. Raman spectroscopy mapping and X-ray diffraction with Rietveld refinement showed that the films were composed of anatase and rutile phases, in different percentages. Scratch testing using a diamond tip on the TiO2 film was employed to evaluate the film adherence and to determine the friction coefficient, with the results showing satisfactory adherence of the films on both substrates.

Rutile titanium oxide (TiO2) thin films require more energy to crystallize than the anatase phase of TiO2. It is a prime candidate for micro-optoelectronics and is usually obtained either by high substrate temperature, applying a substrate bias, pulsed gas flow to modify the pressure, or ex situ annealing. In the present work, we managed to obtain high enough energy at the substrate in order for the particles to form rutile TiO2 at room temperature without any intentional substrate bias in a continuous gas flow. The rutile TiO2 thin films were deposited by a reactive radiofrequency magnetron sputtering system from a titanium target, in an argon/oxygen gas mixture. Investigations regarding the film’s structure and morphology were performed by X-ray diffraction (XRD), X-ray reflectivity (XRR), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX), while the optical properties were investigated by means of ellipsometry.

Uniform TiO2 thin films on Si(111) wafers have been prepared by means of low-pressure chemical vapour deposition using tetraisopropoxide titanium (TPT) as the precursor. The way in which the deposition process was controlled was found to depend to a considerable extent on temperature. Under TPT pressure of 0.00216 mbar in the reactor, the deposition process was controlled kinetically at temperatures between 325 and 400 °C, while at higher temperatures precursor mass transfer limited the rate of deposition. Kinetic study showed two regions with reaction orders of 1.3 and near-zero (0.14) in TPT, respectively. The film composition, morphology and crystalline structure have been characterised by means of X-ray photoelectron spectroscopy, secondary-ion mass spectrometry, scanning electron microscopy, atomic-force microscopy, X-ray diffraction and Raman spectroscopy. The surfaces of the prepared TiO2 thin films contained some carbonaceous species, but there was no carbon contamination in the film bulk. Only the anatase phase was observed for all the TiO2 thin films prepared in the present study. Nevertheless, the orientation of the crystalline structure as well as the film morphology were dependent on the film deposition conditions.

Different laminated structures of TiO2/SiO2 composite film were prepared via atomic layer deposition (ALD) on alumina substrates. The effect of the annealing temperature in the air on the surface morphologies, crystal structures, binding energies, and ingredient content of these films was investigated using X-ray diffraction, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. Results showed that the binding energy of Ti and Si increased with decrease of the Ti content, and the TiO2/SiO2 nanolaminated films exhibited a complex bonding structure. As the annealing temperature increased, the thickness of the nanolaminated films decreased, and the density and surface roughness increased. An increase in the crystallization temperature was proportional to the SiO2 content in TiO2/SiO2 composite film. The annealing temperature and thin thickness strongly affected the phase structure of the ALD TiO2 thin film. To be specific, the TiO2 thin film transformed into an anatase phase from an amorphous phase after an increase in the annealing temperature from 400°C to 550°C, and the TiO2 film exhibited an anatase phase until the annealing temperature reached 850°C, owing to its extremely small thickness. The annealing process caused the Al ions in the substrate to diffuse into the films and bond with O.

An innovative biphasic dip-coating process is introduced for the deposition of TiO2 thin films using a heterogeneous fluid system where an immiscible floating phase modifies the deposition dynamics. By controlling the height of the buoyant phase (ΔH), the method may reduce the agglomerate size during the gelation process, tending to shift the draining regime toward a capillary-dominated flow, a behavior typically observed only at lower withdrawal speeds. Numerical simulations based on Navier-Stokes equations suggest that increasing ΔH narrows and shifts the interface downward, which is consistent with the alteration in the stagnation point and deposition profile, supporting the role of pressure-driven flow and surface tension in deposition parameters. This controlled deposition mechanism may reduce the adhered precursor volume, leading to films with locally thinner deposited regions and decreased surface roughness. The proposed method suggests a direct correlation between floating phase height and film morphology, where an increase in ΔH is associated with smoother and more uniform thin films. This approach was applied to the development of a TiO2/SnO2 heterostructure, revealing via electrical characterization that heterostructures assembled with a thicker floating phase (ΔH = 0.6 cm) may exhibit higher homogeneity and reduced surface roughness, consistent with the behavior expected for a type-II heterojunction. The proposed biphasic dip-coating method presents a novel layering mechanism that may enhance film quality and provides a new parameter for adjusting thin-film properties, offering a promising alternative for advanced material processing in optoelectronics, sensors, and coatings.

This paper reports a study on the photodetection properties of TiO2 thin film deposited on chemically textured p-Si substrate and is compared to those deposited on pristine p-Si substrate. The structural properties of both the heterostructures were investigated using XRD analysis. FESEM images confirmed the deposition of TiO2 thin film on chemically pyramidal textured Si substrate. The average total reflectance of the textured Si substrate was reached to ~ 7.6% in the wavelength range of 300–900 nm. It was further decreased to ~ 6.5% after the deposition of 55 nm thick TiO2 on the top of the textured Si substrate. A systematic study was carried out to correlate the structural, optical and electrical properties of both the heterostructures. The electrical parameters of the heterojunction diodes were measured and compared under dark and illuminated conditions using UV and solar simulated light. UV as well as visible light detection property of the heterostructure of TiO2 thin film deposited on pyramidal textured Si substrate was improved compared to the one deposited on pristine Si by the factor 2.0 and 1.86, respectively, under the bias of − 2 V.

The gas sensitivity and structural properties of TiO2 thin films deposited by plasma-enhanced atomic layer deposition (ALD) were examined in detail. The TiO2 thin films are deposited using Tetrakis(dimethylamido)titanium(IV) and oxygen plasma at 300 °C on SiO2 substrates followed by annealing at temperatures of 800 °C. Gas sensitivity under exposure to O2 within the temperature range from 30 °C to 700 °C was studied. The ALD-deposited TiO2 thin films demonstrated high responses to O2 in the dynamic range from 0.1 to 100 vol. % and low concentrations of H2, NO2. The ALD deposition allowed the enhancement of sensitivity of TiO2 thin films to gases. The greatest response of TiO2 thin films to O2 was observed at a temperature of 500 °C and was 41.5 arb. un. under exposure to 10 vol. % of O2. The responses of TiO2 thin films to 0.1 vol. % of H2 and 7 × 10-4 vol. % of NO2 at a temperature of 500 °C were 10.49 arb. un. and 10.79 arb. un., correspondingly. The resistance of the films increased due to the chemisorption of oxygen molecules on their surface that decreased the thickness of the conduction channel between the metal contacts. It was suggested that there are two types of adsorption centers on the TiO2 thin films surface: oxygen is chemisorbed in the form of O2- on the first one and O- on the second one.