Crystalline Structure, Morphology, and Adherence of Thick TiO2 Films Grown on 304 and 316L Stainless Steels by Atomic Layer Deposition
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-04-10 |
| Journal | Coatings |
| Authors | Vagner Eduardo Caetano Marques, Lucas Augusto Manfroi, Ăngela Aparecida Vieira, AndrĂ© Luis de JesĂșs Pereira, F. C. Marques |
| Institutions | Instituto TecnolĂłgico de AeronĂĄutica, Universidade Estadual de Campinas (UNICAMP) |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Low-Temperature Mixed-Phase Deposition: Thick Titanium Dioxide (TiO2) films (approx. 178 nm) were successfully deposited on AISI 304 and AISI 316L stainless steel (SS) substrates using Atomic Layer Deposition (ALD) at a relatively low temperature (300 °C).
- Phase Composition Control: The films exhibited a desirable mixture of Anatase and Rutile phases, with the AISI 304 substrate yielding the highest Anatase concentration (71.15%). This Rutile formation at 300 °C contradicts typical literature requiring temperatures >450 °C.
- Superior Adherence on AISI 304: The TiO2 film on AISI 304 demonstrated excellent scratch resistance, maintaining an average Coefficient of Friction (COF) of 0.2 ± 0.05 throughout the 5 N progressive load test with no evidence of cracking or substrate exposure.
- Crystallinity Improvement: The TiO2 film deposited on AISI 304 showed a crystallinity improvement of approximately 82% compared to the AISI 316L film.
- Growth Rate Consistency: A uniform growth rate of 0.6 A/cycle was achieved for the TiO2 films on both SS substrates, confirming precise thickness control inherent to the ALD technique.
- Biomedical Suitability: The combination of high adherence, corrosion resistance, and the presence of the highly photoactive Anatase phase makes these films highly suitable for coating medical devices.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Deposition Temperature | 300 | °C | ALD process temperature |
| Number of Cycles | 3000 | cycles | Total deposition sequence |
| Precursor | TiCl4 (99.95% purity) | N/A | Titanium source |
| Oxygen Precursor | H2O (Ultrapure) | N/A | Oxidizing agent |
| Purge Gas | N2 (99.998% purity) | N/A | Background and purge gas |
| N2 Flow Rate | 250 | sccm | Constant purge flow rate |
| Film Thickness (AISI 304) | 179.1 | nm | Measured via FEG-SEM |
| Film Thickness (AISI 316L) | 176.6 | nm | Measured via FEG-SEM |
| Growth Rate | 0.6 | A/cycle | Calculated for both films |
| Anatase Content (AISI 304) | 71.15 | % | Determined by XRD Rietveld refinement |
| Rutile Content (AISI 304) | 28.85 | % | Determined by XRD Rietveld refinement |
| Anatase Content (AISI 316L) | 55.55 | % | Determined by XRD Rietveld refinement |
| Rutile Content (AISI 316L) | 44.45 | % | Determined by XRD Rietveld refinement |
| RMS Roughness (AISI 304 Film) | 4.35 | nm | Measured via AFM |
| RMS Roughness (AISI 316L Film) | 15.93 | nm | Measured via AFM |
| Average COF (AISI 304 Film) | 0.2 ± 0.05 | N/A | Scratch test, 0 to 5 N load |
| Critical Load Lc1 (AISI 316L Film) | 2.4 | N | Load at cohesive failure (no substrate exposure) |
| Anatase Raman Band (Eg) | 152, 400, 521, 640 | cm-1 | Deconvolution fit |
| Rutile Raman Band (Eg) | 243, 446, 605 | cm-1 | Deconvolution fit |
Key Methodologies
Section titled âKey MethodologiesâThe TiO2 films were deposited using a thermal ALD reactor (Oy TFS-200, Beneq) following a standard TiCl4/H2O sequence:
- Substrate Preparation: AISI 304 and AISI 316L SS samples (10 mm diameter, 1 mm thickness) were cleaned sequentially in an ultrasonic bath using propanone, isopropanol, and ultrapure water (15 min each).
- ALD Cycle Sequence (3000 cycles at 300 °C):
- TiCl4 pulse: 250 ms
- N2 purge: 1 s
- H2O pulse: 250 ms
- N2 purge: 1 s
- Microstructure and Morphology:
- FEG-SEM (Mira 3, Tescan): Used for high-magnification imaging of grain structure and precise measurement of film thickness after deliberate fracture.
- AFM (Noncontact Mode): Used to determine Root Mean Square (RMS) roughness (Ra) using a silicon nitride tip and Gwyddion v. 2.58 software.
- Crystalline Structure Analysis:
- X-ray Diffraction (XRD): Performed using an Empyrean X-ray diffractometer (PANalytical) with Cu Kα radiation (λ = 1.5406 A). Data was analyzed using the Rietveld refinement method (HighScore software) to quantify Anatase and Rutile phase percentages.
- Raman Spectroscopy: Acquired using a LabRAM HR system (Horiba) with an Ar laser (X = 514 nm). Raman mapping (22 ”m2 area, 64 à 64 points) was used to confirm the uniform distribution of Anatase and Rutile phases.
- Adherence and Mechanical Testing:
- Scratch Test: Performed using an Ultra Micro UMT 2 tribometer (Bruker) with a Rockwell C diamond tip. A progressive load (0 to 5 N) was applied in an air environment (40% humidity).
- Adhesion Evaluation: Adherence was analyzed according to ASTM C1624-05, determining the Coefficient of Friction (COF) and Critical Load (Lc1).
Commercial Applications
Section titled âCommercial ApplicationsâThe successful deposition of highly adherent, mixed-phase TiO2 films on biomedical-grade stainless steels opens several high-value commercial avenues:
- Biomedical Implants and Devices:
- Corrosion Resistance: The TiO2 coating provides an anti-corrosion layer, protecting AISI 304 and 316L SS (used in cardiovascular stents, orthopedic prostheses, and dental implants) from degradation in biological environments.
- Antimicrobial/Antifouling Surfaces: The presence of the photoactive Anatase phase enables the development of self-cleaning or antimicrobial surfaces for surgical instruments and implants, reducing hospital-acquired infections.
- Photocatalysis and Environmental Remediation:
- Wastewater Treatment: The mixed Anatase/Rutile phase is known to provide optimal photocatalytic activity, making these films ideal for use in reactors designed to mineralize organic compounds in sanitary effluents and industrial wastewater.
- Air Purification Systems: The films can be applied to large surface area substrates (like stainless steel mesh) for use in photoactive air filtration and purification systems.
- Optoelectronics and Thin Film Technology:
- Transparent Optoelectronic Devices: TiO2âs excellent optical properties allow its use in transparent conductive layers and dielectric stacks where precise thickness control (achieved via ALD) is critical.
- High-Wear Industrial Components:
- Friction Reduction: The low and stable COF (approx. 0.2) observed on the AISI 304 substrate suggests potential use in high-wear mechanical components requiring lubricity and durability.
View Original Abstract
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.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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