Hierarchical Composite Structures Research Articles

Ladybug-inspired hierarchical composite adhesives for enhanced surface adaptability

Abstract Enhanced adhesion on rough surfaces is highly desired for a wide range of applications. On the other hand, surface roughness compatibility and structure stability are two critical but competing factors for biologically-inspired dry adhesives in the real world. Inspired by ladybug, a hierarchical structural composite dry adhesive (denoted as PP-M) with enhanced robustness on surface roughness is developed, which is composed of a thin compliant contact layer (a thin soft polydimethylsiloxane (PDMS) film supported discretely by PDMS micropillars) and a rigid bottom layer magnetorheological elastomers (MREs). The PP-M shows a high pull-off strength of 8.2 N cm−2 on a smooth surface and nano-scale rough surface at a mild preload (2 N cm−2). For micro-scale rough surfaces, the PP-M exhibits better surface adaptability compared to the double-layered adhesive (PDMS on MRE) without micropillar support. The increased compliance of the contact layer also leads to a 2.11 fold superior pull-off strength at a wider range of roughness (Sq > 2.23 μm). Element analysis confirms PP-M’s enhanced adaptability, attributed to deeper indentation and lower contact stress. This hierarchical composite structure in PP-M, characterized by a ‘soft on top and hard on bottom’ stiffness distribution, synergizes the flexible contact layer with the stiff MRE bottom layer, leading to superior adhesive properties. The results provide a new reference for achieving enhanced adhesion on rough surfaces.

Screen-Printed Stretchable Supercapacitors Based on Tin Sulfide-Decorated Face-Mask-Derived Activated Carbon Electrodes with High Areal Energy Density

Screen-Printed Stretchable Supercapacitors Based on Tin Sulfide-Decorated Face-Mask-Derived Activated Carbon Electrodes with High Areal Energy Density

Bone health: Quality versus quantity

Healthy bone has the ability to resist deformation and fracture, while adapting to applied mechanical loads. These properties of bone depend on characteristics of its extracellular matrix. This review focuses on the contribution of bone quality and quantity to bone health and highlights current and promising future clinical approaches to measure bone health in the pediatric population. Bone’s unique material properties are derived from its highly organized, hierarchical composite structure, together with its modeling and remodeling dynamics and microdamage mechanisms. Pediatric bone diseases and disorders affect the biological processes that regulate its quality, negatively impacting the extracellular matrix and causing bone fragility. Laboratory bone analysis from human biopsies or animal models of human bone diseases allows high detail examination of the mechanisms contributing to bone fragility. Conversely, clinical measurements of bone fragility are difficult and limited due to the inaccessibility of the material. Because bone quality directly affects fracture resistance, both structure and composition should be used in fracture risk calculation rather than bone mineral density or bone quantity alone. Thus, to advance clinical evaluation of bone fragility, future studies are needed to determine which characteristics of bone quality can be applied to clinical practice to predict bone fragility. New and effective clinical tools are needed to predict fracture risk taking bone quality into consideration. Key Concepts(1)Bone quality and bone quantity are both fundamental for resistance to deformity and fracture.(2)Pediatric bone diseases and disorders alter bone’s composition and structure, compromising bone quality and increasing vulnerability to fracture.(3)Current clinical approaches to assess bone fragility and fracture risk rely mainly on bone quantity measurements from DEXA scans.(4)DEXA bone mineral density poorly correlates with bone’s resistance to fracture, both in adults and children.(5)Future clinical approaches to measure bone health should account for bone quality in order to predict fracture risk.

Elucidating the role of diverse mineralisation paradigms on bone biomechanics - a coarse-grained molecular dynamics investigation.

Bone as a hierarchical composite structure plays a myriad of roles in vertebrate skeletons including providing the structural stability of the body. Despite this critical role, the mechanical behaviour at the sub-micron levels of bone's hierarchy remains poorly understood. At this scale, bone is composed of Mineralised Collagen Fibrils (MCF) embedded within an extra-fibrillar matrix that consists of hydroxyapatite minerals and non-collagenous proteins. Recent experimental studies hint at the significance of the extra-fibrillar matrix in providing the bone with the stiffness and ductility needed to serve its structural roles. However, due to limited resolution of experimental tools, it is not clear how the arrangement of minerals, and in particular their relative distribution between the intra- and extra-fibrillar space contribute to bone's remarkable mechanical properties. In this study, a Coarse Grained Molecular Dynamics (CGMD) framework was developed to study the mechanical properties of MCFs embedded within an extra-fibrillar mineral matrix and the precise roles extra- and intra-fibrillar mineralisation on the load-deformation response was investigated. It was found that the presence of extra-fibrillar mineral resulted in the development of substantial residual stress in the system, by limiting MCF shortening that took place during intra-fibrillar mineralisation, resulting in substantial compressive residual stresses in the extra-fibrillar mineral phase. The simulation results also revealed the crucial role of extra-fibrillar mineralisation in determining the elastic response of the Extrafibrillar mineralised MCF (EFM-MCF) system up to the yield point, while the fibrillar collagen affected the post-yield behaviour. When physiological levels of mineralisation were considered, the mechanical response of the EFM-MCF systems was characterised by high ductility and toughness, with micro-cracks being distributed across the extra-fibrillar matrix, and MCFs effectively bridging these cracks leading to an excellent combination of strength and toughness. Together, these results provide novel insight into the deformation mechanisms of an EFM-MCF system and highlight that this universal building block, which forms the basis for lamellar bone, can provide an excellent balance of stiffness, strength and toughness, achieving mechanical properties that are far beyond the capabilities of the individual constituents acting alone.

Rough‐Endoplasmic‐Reticulum‐Like Hierarchical Composite Structures for Efficient Mechanical‐Electromagnetic Wave‐Energy Attenuation

AbstractInspired by a critical organelle called rough endoplasmic reticulum (RER), a wave‐energy attenuation nano‐carbon foam (WANF) with a unique hierarchical composite structure consisting of 3D‐lamelle, 2D‐perforations and 1D‐microspheres is constructed by incorporating graphene oxide (GO) and polydimethylsiloxane (PDMS) into a carbon nanotubes (CNTs)‐based aerogel. Benefiting by unusual mechanisms like vortex shedding, secondary reflection and resonance, WANF displays excellent acoustic wave absorption, achieving a sound absorption coefficient of over 0.9 with a bandwidth of 4.75 kHz at a thickness of 20 mm. Significantly, it features obvious acoustic absorption intensity in medium‐low frequency range. Moreover, the nano‐carbon aerogel skeleton (NCAS) of WANF endows it with good electromagnetic wave absorption through dielectric loss, exhibiting a minimum reflection loss of −48.61 dB and an efficient electromagnetic absorption with a bandwidth of 5.35 GHz. The excellent wave‐energy attenuation performance of WANF indicates an attracting double‐stealth effect in sonic and electromagnetic area, which shows great potential in integrate protection of advanced military equipment and sensitive electronic infrastructures.

Robust reduced graphene oxide-PDA/ZIF-8 aerogel composite for cyclic, high-capacity dye adsorption

The contamination of nanosized organic dyes in the water bodies is of great concern as it adversely affects the marine ecosystem and biodiversity, leading to water-borne ailments. In recent years, designing sustainable, high-performance, and cost-effective composite adsorbents embedded with functional adsorbents for wastewater treatment has attracted immense attention. In this work, a new composite aerogel (rGO-PDA/ZIF-8) was prepared via self-assembling graphene oxide (GO) flakes to form a three-dimensional (3D) structure with functional polydopamine (PDA). Then, ZIF-8 crystals were decorated on the porous aerogel structure via the in-situ crystallization method. PDA-modified rGO aerogel provided abundant useful functional groups, such as –OH, –COOH, and –NH–, on the surface, while the incorporation of ZIF-8 nanocrystals further endowed composite aerogels with higher surface area and extra functional groups for enhanced organic dye adsorption. Our results revealed that the composite aerogel exhibited not only ultrahigh adsorption towards methylene blue (MB) with a maximum adsorption capacity of 1045 ± 2.9 mg g−1 (with a maximum rejection rate of > 99 %) but also excellent recyclability with a slightly decreased adsorption capacity of 897 ± 26.9 mg g−1 and a stable removal efficiency of > 92 % even after 10 cycles of adsorption. To the best of our knowledge, the obtained adsorption capacity almost doubled the best-reported values at similar conditions in the literature. The excellent adsorption performance is owing to strong π–π and electrostatic attractions between the dye molecules and the hierarchical porous composite structures with functional PDA coating and ZIF-8 nano-adsorbents. Therefore, the new composite rGO-PDA/ZIF-8 aerogel composite has great potential in high-performance, cyclic small organic dye separation.

Ultrahigh initial coulombic efficiency for deep sodium storage enabled by carbon-free vanadium-doping MoS2 hierarchical nanostructure

Molybdenum disulfide (MoS2) has garnered attention as a promising anode material for sodium-ion batteries due to its high theoretical capacity and unique lamellar texture. Nevertheless, unmodified MoS2 suffers from inferior electrical conductivity, poor reaction reversibility, and suboptimal cycle life upon repeated sodiation/desodiation. In this study, a novel carbon-free V-heteroatom doping MoS2 composite (abbr. VMS) with hierarchical laurustinus-like structure was synthesized by a facile one-step hydrothermal process. Specifically, the rational doping of V-atoms can effectively modulate the intrinsic electronic structure of pure MoS2, resulting in enhanced Na-ion diffusion rate, improved reaction kinetics and reduced activation energy compared to bare MoS2. Additionally, the hierarchical structure of the VMS composite, with sufficient spacing, effectively mitigates mechanical stress and ensures the integrity of active materials. Consequently, the prepared VMS composite possesses exceptional reaction reversibility (average ICE value of 92 %) and remarkable capacity retention (92.1 % after 450 cycles at 10 A/g). These findings contribute valuable insights into the development of advanced MoS2-based anode for sodium ion batteries.

Heterogeneous Hierarchical Self-Assembly Forming Crystalline Nanocellulose–CaCO3 Hybrid Nanoparticle Biocomposites

Nanocellulose is increasingly proposed as a sustainable raw material having strong interparticle bonding. However, cellulose alone has limited bending and impact resistance. We newly observe self-assembly between crystalline nanocellulose (CNC) and ultrafine ground chemical-free calcium carbonate nanoparticles (UGCC). The suspension displays an intrinsic gel-like state, and heterogeneous adsorption occurs under the specific conditions where Brownian motion of both species is arrested by application of ultralow shear (0.01 s−1). In contrast, simple static aging of the mixture leads to autoflocculation of each species independently. The heterogeneous adsorption results in compound particle self-assembly leading to multi-level hierarchical structures depending on relative species size and concentration ratio. Fine particles from species 1 adsorb onto the coarser complementary particles of species 2 and vice versa. Depending also on whether CNC or UGCC particles are in excess, the structural assembly occurs primarily through either CNC–CNC hydrogen bonding or CaCO3–CaCO3 autogenous flocculation, respectively. Controlling the hierarchical composite structure bonding in this way, the resulting morphology can express dual or predominantly single either mineralic or cellulosic surface properties. Novel complex hybrid biocomposite materials can therefore be produced having designable compatibility across a broad range of both natural and oil-based polymeric materials. Both CNC and UGCC are exemplified here via commercial products.

Hierarchical Tantalum Oxide Composite for Efficient Solar-Driven Water Purification.

Applying solar energy to generate drinking water is a clean and low-energy exhaust route to address the issue of water purification. The current challenge with solar vapor generation is constructing nano/micro-hierarchical structures that can convert solar irradiation into exploitable thermal energy with high efficiency. Although various structures and material designs have been reported in recent years, solar vapor conversion can be improved by integrating light harvesting, thermal concentration, and water diffusion. Because of the optimized solar harvesting, enhanced heat capacity, and specified diffusive path endowed by the hierarchical composite structure, amorphous tantalum oxide/carbon-based yolk-shell structures (α-Ta2O5/C YS) for highly efficient solar vapor generation under 1 sun illumination are applied in this study. As a result, the α-Ta2O5/C YS realized a water evaporation rate of 3.54 kg m-2 h-1 with a solar-thermal conversion efficiency of 91% under one sun irradiation (1 kW m-2) with excellent evaporation stability. The collected water from seawater meets the World Health Organization drinking water standard. Importantly, reactive oxygen species enabled by α-Ta2O5 could be produced for water sterilization, exhibiting a facile way for application in various scenarios to acquire drinkable water.

Superhydrophobic aluminum surfaces with nano-micro hierarchical composite structures: A novel and sustainable approach to corrosion protection

The unique properties of aluminum (Al) and its alloys make Al one of the most versatile, economical, and widely-used materials in various industries. However, the corrosion and leaching of Al can cause significant issues for the lifetimes of mechanical structures and machine components as well as environment and health problems. In the present study, a simple, eco-friendly, and rapid fabrication of superhydrophobic Al surfaces was introduced. The superhydrophobic Al surfaces with hierarchical composite structures combining microstructures prepared by laser texturing, the new formation of pseudo-boehmite nanostructures prepared by boiling water treatment, and low surface energy prepared by silicone oil heat treatment showed excellent corrosion resistance. The mechanism for wettability change and anti-corrosion were analyzed. The influence of laser parameters and surface modification procedures on the wettability and corrosion resistance of Al surfaces was also analyzed systematically through a series of surface characterization techniques, potentiodynamic polarization tests, and electrochemical impedance spectroscopy tests. The corrosion protection efficiency of the fabricated superhydrophobic Al surface has reached up to 99.40 % as compared with an untreated flat surface. Furthermore, the fabricated superhydrophobic surfaces show good stability even after prolonged exposure to air, fresh water, seawater, and high temperature environments. The performance of the non-wetting surfaces is demonstrated through self-cleaning, water jetting, and water droplet bouncing phenomena. This research provides a novel and sustainable approach for superhydrophobic metal surfaces and improved corrosion resistance for potential practical applications.

Hierarchical and multi-material conformal composite structure for microwave transmission and blast-resistance

Two types of conformal composite panels, namely single-window conformal structure (SWCS) and multi-window conformal structure (MWCS), were designed and manufactured to achieve microwave transmission and blast-resistance simultaneously. These conformal panels have characteristics of multiple-materials, co-cured hierarchical structures and smooth external surface. Adopting woven lattice sandwich structure in conformal window lets that microwave transmission exceeding 80% covers bands from 4.5 GHz to 9.7 GHz and 16.5 GHz to 18 GHz. In field explosion experiments indicate that hierarchical stiffened sandwich structure with multi-windows exhibits better blast resistance. The MWCS remains structural integrity after repeated explosions with scaled distance varying from 2.565 m/kg1/3 to 0.646 m/kg1/3. Typical damage patterns of face blackening, face hole, matrix cracking, and breakage of conformal windows were revealed.

Preparation of direct Z-scheme hierarchical MoS2/MnO2 composite for efficient adsorption and wide spectrum photocatalytic degradation of organic pollutants in water

Developing semiconductor-based heterogeneous photocatalysts with high adsorption performance and wide light response range is a significant technology for removing organic pollutants from water. Herein, a novel hierarchical dendritic-like direct Z-scheme MoS2/MnO2 composite with MoS2 hollow tubular decorated by MnO2 nanosheets was successfully fabricated by vacuum freeze-drying. When the mass ratio of MoS2/MnO2 is 3:1, the highest adsorption-photocatalytic removal rate of 94.5% and 95.1% in 120 min for RhB was attained under visible (Vis) and ultraviolet (UV) light irradiation, respectively. After three repeated uses, the removal rate of RhB still reached 91.1%. The enhanced adsorption-photocatalytic performance of the composite can be well illustrated according to the hierarchical composite structure, production of •OH, •O2− and h+ active species, oxygen-doping in the MoS2 and the direct Z-scheme photocatalytic mechanism. This work gives a good strategy to frame hierarchical Z-scheme photocatalysts for efficient adsorption and wide-spectrum photocatalytic removal of organic pollutants from water.

Fabrication, design, and optimization of hierarchical composite Kagome honeycomb sandwich structure under uniaxial compression

Abstract In this study, a hierarchical composite Kagome honeycomb sandwich (HCKHS) structure was manufactured based on the interlocking method, and its uniaxial compression performance was explored. Through experiments, the compressive strength, stiffness, energy absorption, and failure process of HCKHS specimens of seven different sizes were determined and compared. Mechanical analytical models were established, and the variation trend in the specific strength was predicted and compared with those of other advanced sandwich structures. The size effect of the HCKHS specimens was analyzed. The influence of a single variable on the core modulus, failure strength, and failure modes was discussed, and failure mechanism maps were drawn. The structure was optimized based on the maximum specific strength and engineering application, and the optimal size design ratio was obtained. The results showed that the HCKHS specimens exhibited excellent compressive properties with a convenient manufacturing process, making them suitable for lightweight applications in engineering. The optimization ideas presented herein are also applicable to other two-dimensional hierarchical or normal composite honeycomb sandwich structures with diamond, triangular, and hexagonal shapes.

Ordered Hierarchical Porous Structure of PtSn/3DOMM-Al2O3 Catalyst for Promoting Propane Non-Oxidative Dehydrogenation.

Herein, the hierarchical porous catalyst of 3-dimensional ordered macro-mesoporous (3DOMM) Al2O3 supported active PtSn nanoparticles (NPs) was prepared by the combined synthesized path of evaporation-induced self-assembly with colloid crystal template (EISA-CCT) methods. The hierarchical macro-mesoporous composite structure can markedly increase the specific surface area, accommodate the diffusion of propene, and decrease the number of surface acid sites. In addition, the special surface property and pore structure of 3DOMM-Al2O3 can modify the interaction between metals and substrates, as well as stabilize the metal nanoparticle, which promotes the formation of a highly active and stable PtSn phase. The PtSn/3DOMM-Al2O3 catalyst exhibits higher productivity and stability than PtSn/Al2O3 catalysts with macropore and mesopore structures. The PtSn/3DOMM-Al2O3 catalyst displays the best catalytic performance with propylene selectivity over 95% at a propane conversion of 33.9%. The study of the ordered hierarchical porous structure of PtSn/3DOMM-Al2O3 catalysts can contribute to obtaining improved catalysts in industrial processes.

Fabrication of superhydrophobic concrete with stable mechanical properties and self-cleaning properties

Superhydrophobic concrete has the ability to remove surface stains and resist water erosion. In this paper, a fabrication medium of self-cleaning concrete with green environmental protection and stable mechanical properties is proposed. Hierarchical micro-nano composite structure was obtained by directly copying the micro-nano composite structure from the modified copper mesh to the surface of the newly poured concrete and then using octadecylamine-grafted humic acid to obtain low surface energy. Moreover, the microstructure and chemical composition of the fabricated concrete were characterized. The superhydrophobicity, wetting durability, and self-cleaning performance of the fabricated concrete were studied. Results indicated that the water contact angle of the prepared S-concrete reaches 158° and the water sliding angle were as low as 5°. In addition, due to the successful replication of the micro-nano composite structure, the precast concrete has good mechanical stability and self-cleaning performance compared with ordinary concrete.

Enhanced anti-corrosion/wear properties of Mg alloy through a hierarchical bio-inspired self-healing composite coating

The poor anti-corrosion/wear property of magnesium (Mg) alloys has limited their industrial applications. This paper reports a hierarchical bio-inspired composite coating on Mg alloy surface, through a spray/spin assisted self-assembly process, which overcomes the difficulty in coordination of the self-healing and wear resistance ability, realizing an enhanced self-healing and anti-corrosion/wear ability. The nitrogen-ligated boroxine cross-linked polydimethylsiloxane (N-B-PDMS) and the blend solution of reduced graphene oxide (RGO) and polyvinyl alcohol (PVA) are used to construct the protective hard top layer and self-healing down layer, respectively, obtaining an N-B-PDMS@RGO/PVA (B@RGO/PVA) coating. A large number of reversible covalent boroxine(B3O3)/hydrogen bonding networks are formed within the coating, leading to a compact hierarchical composite structure. The results show that the scratch is miraculously repaired within 1.5 min due to the reversible chemical bonding of N-B-PDMS coating, while its tight three-dimensional network structure significantly restore the corrosion resistance of Mg alloy. The wear resistance of N-B-PDMS extremely promotes two orders of magnitude, derived from the high hardness and low friction coefficient of PVA/RGO shell, and further improves the anti-corrosion through this layer-by-layer barrier structure. Owing to the intensive self-healing ability of typical boroxine cross-linked microstructure, artificial damage of B@RGO/PVA coating can be rapidly repaired after 5 min, which surpasses almost the vast majority of previously reported self-healing materials, and therefore the long-term corrosion resistance is almost completely recovered. In this hierarchical microstructure, the top layer and the down layer complement each other to form a multi-functional coating with ultra-fast self-healing and superior corrosion/ wear resistance, which has guiding significance for the design and construction of multifunctional protection coatings for Mg alloy or other metallic materials.

Hierarchical composite structure to simultaneously realize superior superhydrophobicity and anti-reflection

Superhydrophobicity and anti-reflection of metallic surfaces have potential applications, and obtaining superhydrophobicity on metallic surfaces by simple methods is still a challenge. The composite microstructure consisting of micro-protrusions, micro-lumps and particles was fabricated on aluminum surface by laser ablation. A layer of hydrophobic species that can prevent the surface from being wetted formed on the microstructure through organic adsorption. In particular, laser ablation parameters were optimized to achieve better superhydrophobicity and anti-reflection. The fabricated superhydrophobic surfaces showed contact angles > 165° for water and contact angles > 160° for high-concentration solutions and high-viscosity solutions. Conventional bounce contact time < 10 ms was exhibited for water droplets impacting on fabricated surfaces, especially, the shortest contact time reaching 9.4 ms. anti-reflection was also realized on the laser-ablated aluminum surface, and specular reflections were almost completely avoided by laser ablation structures. The mechanism of the transition from superhydrophilic to superhydrophobic on fabricated surfaces was discussed. Superhydrophobic aluminum surfaces with anti-reflection could be efficiently manufactured in a few hours without special equipment and harsh condition through the proposed two-step method.

Structural colored water rewritable paper enabled by assembled graphene laminates/ SiO2 amorphous colloidal arrays hierarchical structure

Rewritable paper is of great significance for environmental and sustainable development. Specially, the water rewritable paper based on hydrochromism has aroused extensive research interesting for being clean, convenient and compatible with the current ink jet printer. Nevertheless, previously reported water rewritable paper requires complex and time-consuming fabricating process. Here, we report a facile strategy to fabricate structural colored water rewritable paper simply via two step infiltration on commercially available paper. After infiltration of graphene laminates and SiO2 colloidal spheres in sequence, the obtained paper is integrated with assembled graphene laminates (AGLs)/amorphous colloidal arrays (ACAs) hierarchical composite structure. Owing to the advantageous micro-topography, selective separation capacity and high visible light absorption property of the underlying AGLs, SiO2 ACAs with vivid structure color can be realized. Moreover, the hydrochomism of the hierarchical composite structure is resulted from the synergistic contribution of the hydrophilic structural color and the visible light absorption property of AGLs. Our strategy is based on the environmental-friendly structural color and convenient to realized, which offers a promising alternative to rapidly fabricate colored water rewritable paper.

Effect of Structural Morphology and Material Factors on Radiative Properties of Hybrid Perovskite/Nanoporous GaN Hierarchical Composite Structure

The encapsulation of hybrid perovskite in nanoporous GaN is a promising strategy to reduce perovskite degradation and improve photoelectric performance. Exploitation of the intrinsic light-matter interaction in such a composite structure greatly benefits improving device optimization. Herein, we report the perovskite synthesis, structural design, and radiative properties of perovskite/nanoporous GaN hierarchical composites using spectroscopic ellipsometry (SE) experiments as well as electromagnetic simulations. First-principles calculations reveal the relationship between electronic interband transitions and the dielectric function of perovskite measured by SE. We use the finite-difference time-domain (FDTD) and finite-element method (FEM) simulations to analyze the spectral radiation properties for the hierarchical composite structure in terms of both morphology dependence and material factors. The optical absorption peaks in the near-infrared–visible region are collectively determined by the nanopore size, layer thickness, and incident angle of light. Also, the optical absorption distribution patterns are related to variables of the halogen, metal elements, and temperature. This work is integrated with the development of perovskite-based applications for solar functional batteries, light-emitting diodes (LED), and optoelectronic detectors.

Growth morphology and phase composition of hierarchically self-organized oxyspinel composite films deposited by radio frequency magnetron sputtering

Multicomponent Al 0.1 Si 0,05 Ti 0,1 Mn 1.45 Co 0.7 Ni 0.6 O 4 oxyspinel solid solution ceramics was synthesized to be subsequently used as a target for the deposition of thin films onto silicon and metallized silicon substrates by means of radio frequency sputtering method. Temporal evolution of chemical and phase compositions of the deposited layers, as well as their structure and surface morphology for the different substrate temperatures, have been systematically investigated using energy dispersive X-ray (EDS) analysis, secondary ion mass spectroscopy (SIMS) profiling, Raman spectroscopy, and atomic force microscopy (AFM). The samples revealed a uniform chemical composition throughout their whole depth, corresponding well with the formula unit of the spinel. Across the film depth, progressive developing of a self-organized, two-scale hierarchical composite structure was observed, which is composed of the main oxide grains decorated with spinel nanocrystallites.