Evaluation of the Mechanical Properties of Germanium-on-Insulator (GeOI) Films by Raman Spectroscopy and Nanoindentation

Germanium-on-insulator (GeOI) films fabricated using the Smart Cut™ wafer bonding and film exfoliation technology were investigated for the mechanical properties and induced phase transformations by using nanoindentation and Raman spectroscopy experiments. The hardness and modulus results of the GeOI films are significantly different from the literature published Silicon-on-Insulator and bulk germanium results. The GeOI films are softer and more flexible as compared to bulk Ge hardness and stiffness properties. The Raman spectroscopy of the spherical indents indicates bands of metastable Ge phases @ 220 cm−1, 195 cm−1, and 184 cm−1 wavenumbers. Our results demonstrate that a spherical indenter impacted a wider area of contact and produced GeOI indented surfaces free of cracks and fracture. The spherical indenter tip kept the Ge top layer intact when compared to the Berkovich indenter tip during penetration. In contrast, the Berkovich indenter tip developed excessive fracture that resulted in displacing the Ge top layer sideways and exposed the Si substrate underneath revealing Raman spectra bands of metastable Si phases @ 350 cm−1, 399 cm−1, and 430 cm−1

Nanoscale strain characterisation of modern microelectronic devices

PhD ThesisSources of stress and strain in modern microelectronics can be either beneficial to the electrical performance or detrimental to the mechanical integrity and ultimately lifetime of the device. Strain engineering is commonplace in state-of-the-art device fabrication as a means to boost performance in the face of device scaling limitation. The strain present in the device is directly related to the improvement factor and as such precise measurements and good understanding are of utmost importance due to the many thermal processing steps that can induce or cause relaxation of the strain. Front-end-of-line (FEOL) strain characterisation is becoming increasingly challenging due to the small volumes of material and nanoscale feature sizes being analysed. In this work, an extensive survey of strain characterisation techniques was undertaken. Narrow sSOI stripes were profiled using conventional Raman spectroscopy. Unlike with previous studies, it was shown that it is possible to achieve nanoscale measurements using current techniques. This study was supported by ANSYS FE simulation. The review of the literature briefly investigates the possibility of EBSD as a strain measurement tool. It is possible to calculate not just an absolute strain value as achievable with Raman spectroscopy, but the strain tensor. However, this is a difficult and complex process and not necessary for use in industry. This study proposes the possibility of a more simple method that would provide a good calibration technique to confirm Raman measurements. SERS and TERS are explored in detail as the most promising techniques when dealing with device scaling. Currently, SERS is a destructive technique not suitable for use in a highly cost driven industry such as semiconductor manufacturing. While it theoretically gives improved surface selectivity over conventional Raman spectroscopy, there is no improvement to the xy spatial resolution. With Si and SiGe samples, this study concludes there is also often no surface selectivity with either technique and the mechanisms behind the enhancement are not understood to the point of being able to implement the techniques in a process line. However, where a non-destructive technique is desired, outlined in this study is a method of achieving the SERS effect without sacrificing the sample. Aggressive scaling has forced the dimensions of the interconnecting wires that give the devices functionality to the deep submicron range. Copper, Cu has been introduced as a replacement to the traditionally used aluminium, Al because of its superior electrical and mechanical properties and scalability. However, as these wires begin to approach the dimensions of thin foils, the microtexture of the wires becomes significantly different from their bulk counterparts. This can affect the mechanical integrity of the interconnects and this has an impact on the reliability of the device. Failure mechanisms such as blistering, cracking and peeling caused by stress and strain are not uncommon and traditional methods of characterising residual stress in the thin films is no longer applicable to these narrow wires. The mechanical properties and microtexture of thin copper films annealed at temperatures comparative to those found in device manufacturing were characterised in some detail. EBSD was used to determine the grain size and structure of the films before nanoindentation confirmed properties such as hardness and elastic modulus. These results pave the way for investigation of strain applied along deep-submicron interconnects to lead to further understanding of what causes failure mechanisms from interconnecting wires

Interface and Size Effects on TiN-based Nanostructured Thin Films

Titanium nitride coatings have been widely applied and studied as high temperature diffusion barrier for silicon devices in microelectronics, wear resistant coatings in turbine blade materials, and materials for future high temperature nuclear reactors. In order to enhance the material property, superlattices is one of artificially engineered protective coatings, such as AlN/TiN and TaN/TiN multilayered films. Epitaxial cubic multilayer films, TaN/TiN and AlN/TiN nanolayers were grown on Si(001) by Pulsed Laser Deposition (PLD) with various nanolayer thicknesses and number of interfaces. Microstructural studies include X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution TEM with ion-irradiation experiments. Electrical, mechanical and thermal property studies were conducted for the interface and size effects on the nanolayers by using nanoindentation and Transient Thermo-Reflectance (TTR) methods. The microstructural and hardness study on TaN/TiN films with ion irradiation (12 keV and 50 keV He ) suggest no obvious microstructural or mechanical behavior change due to ion irradiation. In addition, titanium nitride that serves as effective diffusion barrier to prevent the inter-diffusion between the nuclear fuel and the cladding material was studied in order to enhance the lifetime of the fuels and the reliability of the fuel claddings. The TiN has good adhesion with the stainless steel and higher hardness than that of bulk TiN on the stainless steel. Thermal conductivity test demonstrates that thin TiN film has compatible thermal conductivity as the MA957 and HT-9 bars. The size effect on electrical resistivity is dominant in both of the epitaxial cubic and the polycrystalline TiN thin films in the thickness ranged from ~60 nm down to ~35nm. In the TaN/TiN multilayer, the grain scattering effect on resistivity is dominant rather than interface influence on the resistivity with comparing epitaxial cubic phase and polycrystalline phase. The microstructure and hardness studies of the AlN/TiN multilayer films with He implantation present that the suppression of amorphization in AlN layers and the reduction of radiation-induced softening were achieved in all nanolayer films. Radiation tolerance was found to be size dependent and the layer thickness leading to the highest radiation tolerance was around 10 nm. In addition, the embedded epitaxial cubic AlN with cladding TiN nanolayers showed higher effective thermal conductivity than that of AlN single layer as well as the embedded polycrystalline AlN in the thickness ranged from 10 nm down to 2 nm. It confirms a suppressed size effect, which reduces the amount of decrease in through-plane thermal conductivity

Amorphe Metallschichten und ihre Verwendung als Mikroröhren

Die vorliegende Dissertation beschäftigt sich mit der Herstellung und Charakterisierung von dünnen amorphen Metallschichten. Diese Materialklasse hat durch das Fehlen von klassischen mikrostrukturellen Fehlern wie Versetzungen oder etwa Korngrenzen Vorteile hinsichtlich der mechanischen Belastbarkeit oder beispielsweise Korrosionsbeständigkeit. Die binären Legierungen Ni-Zr und Cu-Ti wurden grundlegend in ihren Phasen-Gefüge-Eigenschaftsbeziehungen insbesondere in Abhängigkeit ihrer Zusammensetzung untersucht. Unter anderem wurden die Oberflächenrauheit und der spezifische elektrische Widerstand bestimmt und im materialwissenschaftlichen Kontext diskutiert. Das Hauptaugenmerk lag auf der Ermittlung der mechanischen Kennwerte wie E-Modul und intrinsische Eigenspannung. Die Kenntnis darüber ist notwendig, wenn in reproduzierbarer Weise Mikroröhren durch Aufrollen aus Dünnschichten dieses Materials hergestellt werden sollen. Eine solche Technologie setzt Eigenspannungsgradienten orthogonal zur Schichtebene voraus, so dass nach Ablösen vom Substrat sich eine Röhrengeometrie durch elastische Relaxation ergibt. In dieser Arbeit wurden die eigenspannungsgenerierenden Effekte in Abhängigkeit des Gefüges und der vorliegenden Phasen analysiert. Die gemessenen konkreten Werte wurden genutzt um erste Röhren gezielt herzustellen. Dabei zeigte sich, dass bereits mit geringem technologischem Aufwand die Röhren sich reproduzierbar und vorhersagbar in ihrer Geometrie fertigen lassen.:1 Einleitung 2 Grundlagen 2.1 Amorphe Metalle 2.1.1 Legierungssystem Ni-Zr 2.1.2 Legierungssystem Cu-Ti 2.2 Verfahren zur Herstellung dünner Schichten 2.2.1 Überblick 2.2.2 Kathodenzerstäuben 2.3 Spannungen in Dünnschichten 2.4 Mikroröhren aus selbstaufrollenden Dünnschichten 3 Details der eingesetzten Verfahren 3.1 Herstellung der Dünnschichten 3.1.1 Magnetron-Ko-Kathodenzerstäuben 3.1.2 Optimierung der Abscheideparameter 3.2 Charakterisierung von Zusammensetzung und Struktur 3.2.1 Röntgenfluoreszenzanalyse 3.2.2 Röntgendiffraktometrie 3.2.3 Rasterelektronenmikroskopie / Focused-Ion-Beam-Technik 3.3 Bestimmung physikalischer Eigenschaften 3.3.1 Substratkrümmungsmethode 3.3.2 Messung des elektrischen Widerstands 3.3.3 Rasterkraftmikroskopie 3.3.4 Nanoindentation 4 Ergebnisse und Diskussion 4.1 Modellsystem Ni-Zr 4.1.1 Strukturelle Charakterisierung 4.1.2 Physikalische Eigenschaften 4.2 Legierungssystem Cu-Ti 4.2.1 Morphologie und Struktur 4.2.2 Physikalische Eigenschaften 4.3 Aufgerollte Schichtverbunde 4.3.1 Modell des verspannten Doppellagen-Schichtverbundes 4.3.2 Doppelschichtsystem Ni-Zr 4.3.3 Schichtspannungsoptimierte Ni-Zr-Legierungsschicht 5 Zusammenfassung und Ausblick Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Danksagung AnhangThis dissertation is addressing the preparation and characterization of thin amorphous metallic films. That material class has its advantages concerning mechanical stability or corrosion resistance due to the lack of classic microstructural defects like dislocations or grain boundaries. Ni-Zr and Cu-Ti as binary alloys were examined thoroughly in their phase-microstructure-property relationships especially in dependency on chemical composition. Beside others the surface roughness and specific electrical resistivity was determined and discussed in material science context. The main focus was on investigation of mechanical characteristic values like Young’s modulus and intrinsic residual stresses. Knowledge on that issue is necessary, when microtubes are to be reproducibly fabricated out of thin films made of these materials. Such a technology requires a stress gradient perpendicular to the layer plane, which leads to a tube geometry after separating it from the substrate due to the effect of elastic relaxation. In the present research the stress generating effects are analyzed with respect to the microstructure and existent phases. The measured actual values were used to produce first test tubes. It is shown, that these tubes can be fabricated in a reproducible and foreseeable manner in geometry even with a low techno-logical effort.:1 Einleitung 2 Grundlagen 2.1 Amorphe Metalle 2.1.1 Legierungssystem Ni-Zr 2.1.2 Legierungssystem Cu-Ti 2.2 Verfahren zur Herstellung dünner Schichten 2.2.1 Überblick 2.2.2 Kathodenzerstäuben 2.3 Spannungen in Dünnschichten 2.4 Mikroröhren aus selbstaufrollenden Dünnschichten 3 Details der eingesetzten Verfahren 3.1 Herstellung der Dünnschichten 3.1.1 Magnetron-Ko-Kathodenzerstäuben 3.1.2 Optimierung der Abscheideparameter 3.2 Charakterisierung von Zusammensetzung und Struktur 3.2.1 Röntgenfluoreszenzanalyse 3.2.2 Röntgendiffraktometrie 3.2.3 Rasterelektronenmikroskopie / Focused-Ion-Beam-Technik 3.3 Bestimmung physikalischer Eigenschaften 3.3.1 Substratkrümmungsmethode 3.3.2 Messung des elektrischen Widerstands 3.3.3 Rasterkraftmikroskopie 3.3.4 Nanoindentation 4 Ergebnisse und Diskussion 4.1 Modellsystem Ni-Zr 4.1.1 Strukturelle Charakterisierung 4.1.2 Physikalische Eigenschaften 4.2 Legierungssystem Cu-Ti 4.2.1 Morphologie und Struktur 4.2.2 Physikalische Eigenschaften 4.3 Aufgerollte Schichtverbunde 4.3.1 Modell des verspannten Doppellagen-Schichtverbundes 4.3.2 Doppelschichtsystem Ni-Zr 4.3.3 Schichtspannungsoptimierte Ni-Zr-Legierungsschicht 5 Zusammenfassung und Ausblick Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Danksagung Anhan

Ultrasonic characterization and defect detection in piezoelectric materials

Aluminum nitride (AlN) is a piezoelectric semiconductor material used for optoelectronic devices, high-frequency acoustic filters, resonators, and piezoelectric transducers for structural health monitoring due to their wide band gap, chemical and mechanical stability, dielectric properties, and relatively large values of its elastic constants. On the other hand, lead zirconate titanate (PZT) ceramics are also used in excitation and detection of acoustic waves in aircraft integrated structures for structural health monitoring and nondestructive testing. Prior to any potential device application it is necessary to characterize the mechanical properties of those materials. In addition to the polycrystalline materials AlN, PZT, and single crystal lithium niobate (LiNbO3) has been studied in the present thesis in view of its piezoelectric and high-frequency elastic properties. LiNbO3 is currently intensively used for piezoelectric, as well as electro-optic and nonlinear optical applications. Although the focusing of thermal phonon has been studied previously in LiNbO3 and its elastic and piezoelectric constants have been determined in many previous studies, its acoustic properties are still not completely explored. In the first part of the thesis scanning acoustic microscopy has been used to determine the mechanical properties of AlN thin films and PZT ceramics. AlN thin films were grown using the reactive RF-magnetron sputtering technique. The microstructure, surface morphology, and chemical composition of the AlN thin films were determined. Later on, the Coulomb coupling technique has been applied to determine the acoustic velocities and transport properties of ultrasonic waves in PZT and LiNbO3 in order to assess the feasibility of this technique. The longitudinal, skimming longitudinal, transversal, and surface acoustic wave velocities and the corresponding elastic constants were determined in AlN as well as in PZT ceramics. AlN does not grow as a single crystal so that LiNbO3 single crystals have been employed to demonstrate the generation and detection of surface acoustic waves (SAW’s) for defect characterization in piezoelectric materials. In the second part of the thesis, the developed scheme has been applied to image the transport properties of bulk and guided acoustic waves travelling in PZT. A delta pulse, broad band signal excites both longitudinal and transverse bulk waves, and metamorphosis of bulk wave into Lamb waves was sequentially monitored. In further studies, ultrasonic imaging with high temporal and spatial resolution was conducted on LiNbO3. The imaging is performed with switched sinusoidal excitation and quadrature detection from which the magnitude and phase are derived. The wavelengths of surface skimming longitudinal waves and SAW’s are both determined from the observed phase rotation as a function of position. This technique also used to study the influence of a surface defects on the scattering of SAW propagating on the surface of the LiNbO3 crystal. Artificial defects employed for interaction with the waves were produced by deposition of silver paint on the surface. These defects are both absorptive and scattering. The scattering and attenuation of SAW’s are studied by imaging in vector contrast. The interaction allows a clear differentiation of volume waves skimming the surface and guided waves traveling at the surface. The thesis, hence, describes the use of the local electric field probe technique to study the structure of piezoelectric materials by acoustic methods.Aluminium-Nitrid (AlN) ist ein piezoelektrisches Halbleitermaterial, welches über eine große Bandlücke sowie über gute dielektrische Eigenschaften sowie hohe elastische Konstanten verfügt. Es ist chemisch und mechanisch stabil und findet Anwendungen in optoelektronischen Bauelementen, akustischen Hochfrequenz-Filtern sowie Sensoren für strukturelle Defekte. Neben AlN werden zunehmend auch Blei-Zirkonat-Titanat (PZT) Keramiken für die Erzeugung und Detektion von Oberflächenwellen auf empfindlichen Oberflächen, z.B. im Flugzeugbau, eingesetzt, um strukturelle Defekte zu detektieren. Vor der Anwendung in Bauelementen ist es jedoch erforderlich, die grundlegenden mechanischen Eigenschaften sowohl von AlN als auch PZT zu charakterisieren. Zusätzlich zu den polykristallinen Materialien AlN und PZT wurde in der vorliegenden Arbeit auch Einkristall LiNbO3 in Hinblick auf seine piezoelektrischen und hochfrequenten elastischen Eigenschaften untersucht. LiNbO3 wird gegenwaertig intensiv genutzt unter anderem für piezoelektrische, sowie elektrooptische und nichtlinear-optische Anwendungen. Obwohl die Fokussierung thermischer Phononen in anisotropen Kristallen schon früher anhand von LiNbO3 untersucht wurde und seine elastischen und piezoelektrischen Konstanten in vielen früheren Studien bestimmt wurden, sind seine akustischen Eigenschaften noch immer nicht vollständig erforscht. Der erste Teil der Arbeit befasst sich mit der Untersuchung der mechanischen Eigenschaften von dünnen AlN Schichten und PZT-Keramiken mittels akustischer Mikroskopie (engl. Scanning Acoustic Microscopy, SAM). Die verwendeten AlN Schichten wurden mittels reaktivem RF-Magnetron Sputtern hergestellt. Untersuchungen zur Bestimmung der Mikrostruktur, Oberflächenmorphologie und der chemischen Zusammensetzung wurden durchgeführt. Anschließend werden zunächst die Schallgeschwindigkeiten und Transporteigenschaften von Ultraschallwellen mittels Coulomb-Kopplung an PZT und LiNbO3 untersucht, um die Einsatzmöglichkeiten dieser Technik zu validieren. Für PZT und AlN werden so die Schallgeschwindigkeiten der longitudinalen, transversalen und streifend propagierenden (englisch “skimming“) longitudinalen Volumenwellen sowie der Oberflächenwellen und aus diesen wiederum die elastischen Konstanten der Materialien bestimmt. Da AlN nicht als einkristalline Schicht abgeschieden werden kann, wurde anhand eines LiNbO3 Einkristalls demonstriert, dass Oberflächendefekte mittels Oberflächenwellen in Piezoelektrika detektiert werden können. Im zweiten Teil der Arbeit wird die entwickelte Methode angewandt, um die Transporteigenschaften von Volumen- wie auch gefuehrten akustischenWellen in PZT sichtbar zu machen. Ein Delta-Puls Signal mit breitem Frequenzspektrum regt sowohl longitudinale als auch transversale Volumen-Wellen an. Deren Umwandlung in Lamb-Wellen wird dokumentiert. In weiteren Untersuchungen wurden Ultraschallaufnahmen mit hoher zeitlicher und räumlicher Auflösung an LiNbO3-Kristallen erstellt. Dazu dient gepulste sinusförmige Anregung und Quadratur-Detektion, sodass Magnituden- und Phasenbilder generiert werden koennen. Die Wellenlänge der oberflächennahen Longitudinalwellen und Oberflächenwellen können beide anhand der Phasenrotation als Funktion der Position bestimmt werden. Diese Technik wird ebenfalls verwendet, um den Einfluss oberflächennaher Fehlstellen auf die Zerstreuung von Oberflächenwellen bei LiNbO3 Einkristallen zu untersuchen. Künstliche Fehlstellen wurden mit Hilfe von Silberpaste, die auf die Oberfläche aufgebracht wurde, erzeugt. Diese Fehlstellen wirken sowohl absorbierend als auch zerstreuend. Die Zerstreuung und das Abklingverhalten der Oberflächenwellen wurden anhand des aufgezeichneten Vektorkontrastes untersucht. Die Wechselwirkung erlaubt die eindeutige Unterscheidung von oberflächennahen Körperwellen und geführten Wellen auf der Oberfläche. Die vorliegende Arbeit zeigt somit neue Ansätze zur Untersuchung realer Strukturen piezoelektrischer Materialien mittels akustischer Methoden

Synthesis and high-temperature oxidation of ternary carbide coatings on zirconium-based alloy cladding

Zirconium-based alloy claddings used for current light water reactors (LWRs) possess a variety of desirable features in steady-state normal operation, however, constraints regarding fast degradation, rapid exothermic reaction with high-temperature steam associated with hydrogen generation in accident scenarios motivate the requisite to develop enhanced accident tolerant fuel (ATF) claddings. One reasonable solution to improve the accident tolerance of the zirconium alloy cladding in accidental conditions while preserving its excellent behavior under normal operating conditions is external surface modification via such as coatings deposition. In addition, protective coatings applied to the zirconium alloy claddings offer the potential benefits of drastically reduced corrosion and degradation during normal operation, which are expected for application within the design framework of both current and future generation LWRs. The Mn+1AXn (MAX) phase materials comprise an extended family of layered, hexagonal ternary carbides and nitrides. They combine many attractive properties of both ceramics and metals stemming from their unique layered crystal structures and bonding characteristics; certain Al-MAX phases also possess excellent high-temperature oxidation resistance and chemical compatibility with select coolants such as hot water and molten lead. The objectives of this work are to synthesize and to evaluate three Al-containing MAX phase carbides (Ti2AlC, Zr2AlC and Cr2AlC) as potential protective coatings on Zircaloy-4 substrates with an emphasis on their high-temperature oxidation performance in steam. Oxidation of one commercial bulk Al-MAX phase Ti2AlC (Maxthal 211®), as reference/benchmark material, in steam in the temperature range of 1400°C - 1600°C was investigated to validate its high-temperature oxidation resistance and ascertain its potential as protective coatings. Oxidation of bulk Ti2AlC MAX phase ceramic at 1400°C and 1500°C formed a continuous coarse α-Al2O3 scale with randomly distributed Al2TiO5 isolated areas on the surface. The oxide scale thickening rate of Ti2AlC is more than three orders of magnitude lower than that of Zircaloy-4 at 1400°C and the maximum tolerance temperature of Ti2AlC in steam is approximately 1555°C. Therefore, these findings hold great promise of Al-containing MAX phase carbides, especially Ti2AlC, as oxidation resistant coating on zirconium-based alloy claddings. An innovative two-step approach has been established, i.e. first magnetron sputtering of nanoscale elemental multilayer stacks and subsequently thermal annealing in argon, for potential growth of phase-pure MAX phase coatings. The crystallization behavior and phase evolution of the as-deposited multilayers during annealing were systematically investigated using a diverse range of characterization and analytical techniques. The mechanical properties of designated coatings were evaluated by means of scratch tests and nanoindentation. Thermal annealing of the nanoscale elemental multilayer stacks (transition metal layer/carbon layer/aluminum layer) in argon revealed that onset crystallization temperatures of the Ti2AlC and Cr2AlC MAX phase from competing binary carbides and intermetallic phases locate at around 660°C and 480°C, respectively. Phase-pure Ti2AlC and Cr2AlC coatings were successfully fabricated, but the formation of a mixed ternary Zr(Al)C carbide rather than the Zr2AlC MAX phase was confirmed. Both MAX phase coatings have a basal-plane preferred orientation with the c-axis perpendicular to the sample surface and the multilayer stacks. The Zr/C/Al coatings crystallized to a cubic, solid solution Zr(Al)C phase with a B1 NaCl crystal structure. The phase evolution during annealing appears associated with the thermodynamic stability of corresponding MAX phases and their counterpart binary carbides. Coatings of altered designs with respect to introducing diffusion barrier or overlayer were deposited on Zircaloy-4 substrates. The coating thicknesses are 5~6 μm. Oxidation performance and degradation of these coatings during exposure in steam at elevated temperatures were investigated by thermogravimetric analysis and examining the microstructural evolution of the coating-substrate system. Steam oxidation tests found no protective effect of the Ti2AlC and Zr(Al)C based coatings with significant spallation and cracking from around 1000°C. Growth of an Al2O3-rich layer with TiO2 or ZrO2 layer beneath for the Ti2AlC and Zr(Al)C based coatings, respectively, was observed rather than a dense alumina layer. The failure of the Ti2AlC and Zr(Al)C based coatings from 1000°C can be attributed to the low thickness of the coatings, high interdiffusion rate between coating and substrate and potential phase transformation of the oxide products. The Cr2AlC-based coatings possess superior oxidation resistance up to at least 1200°C and autonomous self-healing capability with a thin and dense α-Al2O3 layer growth. Another design with a thin Cr overlayer above the Cr2AlC coating was further developed to eliminate potential fast hydrothermal dissolution of Al during normal operation. Moreover, first neutron radiography investigations of hydrogen permeability through the Ti2AlC and Cr2AlC MAX phase coatings on Zircaloy-4 substrates were reported. Hydrogen permeation experiments through non-oxidized and pre-oxidized Ti2AlC and Cr2AlC MAX phase coatings on Zircaloy-4 evidenced that both coatings are robust hydrogen diffusion barriers and impede hydrogen permeation into the matrix efficiently. The unique microstructural features of the coatings, namely free of columnar growth and highly basal-plane textured grains owing to the two-step approach, improve their efficiency in limiting hydrogen permeation as a barrier