Ultrathin Multilayer Films Research Articles

Ultrathin Polyelectrolyte Multilayer Films with Silver Nanoparticles as a Potential Antibacterial Coating

Silv er nanoparticles (AgNPs) are already used as antibacterial agents for medical devices and food packaging materials. However, concerns about its toxicity still exist. AgNPs can be incorporated into ultrathin polyelectrolyte multilayer (PEM) films to minimize this risk. With PEMs, full surface coverage can be achieved with minimal AgNPs, minimizing human exposure. In this study, a simple protocol to fabricate ultrathin PEM/AgNP films using sodium ascorbate as a reductant was developed. The effects of the number of bilayers and ionic strength (0.05 to 0.50 M) on film thickness and amount of AgNPs were investigated. UV/VIS spectra show that increasing the number of bilayers from 1 to 5 would lead to a corresponding increase in film thickness and amount of synthesized AgNPs. Thicker layers and more AgNPs were deposited when the films were fabricated under higher ionic strengths. Films with thicknesses ranging from 15.67 to 87.13 nm were fabricated. The sizes of the incorporated AgNPs were between 54.32 and 259.26 nm, as characterized by scanning electron microscopy. All films were stable when submerged in water for 240 h, suggesting the migration of Ag/Ag+ from the films was minimal. The antibacterial efficacy of the films against Staphylococcus aureus was also assessed. Only the PEM/AgNP films fabricated with the highest salt concentration (0.50 M) showed antibacterial activity under resazurin assay. However, the Kirby Bauer method showed inhibition zones for all films fabricated under all salt concentrations, indicating antibacterial activity at the interface of the bacterial lawn and the films, even with the slow migration of Ag/Ag+. Thus, PEM/AgNP films have the potential to be used as an antibacterial coating.

A new method for characterizing the atomic composition distribution and interface structure of ultrathin multilayer films using molecular dynamics simulation assisted ARXPS

Characterizing ultrathin multilayer films' atom distribution and interface structure remains challenging. This paper innovatively characterized the chemical composition and distribution of Pt/Co/W ultrathin multilayer films by ARXPS. Molecular dynamics simulated the growth process of films to correspond to that in experiment. The results show that through ARXPS, the actual structure of Pt (2 nm)/Co (t = 0.5–3 nm)/W (2 nm) film could be obtained. For Pt (2 nm)/Co (2 nm)/W (2 nm) film, the actual structure was Pt/Co (1.73 nm)/W (0.78 nm)/WO3 + WO2 (1.48 nm). W at the top layer significantly diffused to the bottom layers, and oxidized W reduced from the surface to the interior of multilayer films. Molecular dynamics simulation confirmed that the interdiffusion degree of Co and W atoms was improved with the increase of Co atoms. The growth modes of Co and W layers were respectively layer-by-layer and island. As the number of Co atoms increased, the relative surface roughness of Co and W layers and the relative interface roughness of Co/W were increased. The in-plane magnetic anisotropy and coercivity were respectively enhanced and decreased due to the change in the surface/interface structure. This paper provides a new idea for analyzing ultrathin multilayer films' atom distribution and interface structure.

Ultra-thin multilayer films for enhanced energy storage performance

The rapid progress in microelectronic devices has brought growing focus on fast charging-discharging capacitors utilizing dielectric energy storage films. However, the energy density of these dielectric films remains a critical limitation due to the inherent negative correlation between their maximum polarization (Pmax) and breakdown strength (Eb). This study demonstrates enhanced energy storage performance in multilayer films featuring an ultra-thin layer structure. The introduction of a greater number of heterogeneous interfaces improves Eb, while lattice distortion and phase transitions, facilitated by diffusion and strain at interfaces, contribute significantly to the enhancement of Pmax. Remarkably, an energy density of 65.8 J/cm3 with an efficiency of 72.3% was achieved in a 6.7 nm-per-layer BiFeO3/SrTiO3 multilayer configuration, surpassing the performance of most multilayer films composed of simple constituents. This ultra-thin multilayer structure, which simultaneously promoted Pmax and Eb, provides a promising avenue for the development of high-performance dielectric materials.

Layer-by-layer assembly of chitosan/alginate thin films containing Salmonella enterica bacteriophages for antibacterial applications

The emergence of antibiotic resistant bacteria and the ineffectiveness of routine treatments inspired development of alternatives to biocides for antibacterial applications. Bacteriophages are natural predators of bacteria and are promising alternatives to antibiotics. This study presents fabrication of a Salmonella enterica bacteriophage containing ultra-thin multilayer film composed of chitosan and alginate and demonstrates its potential as an antibacterial coating for food packaging applications. Chitosan/alginate film was prepared through layer-by-layer (LbL) self-assembly technique. A bacteriophage, which belongs to Siphoviridae morphotype (MET P1-001_43) and infects Salmonella enterica subsp. enterica serovar Enteritidis (Salmonella Enteritidis), was post-loaded into chitosan/alginate film. The LbL growth, stability, and surface morphology of chitosan/alginate film as well as phage deposition into multilayers were analysed through ellipsometry, QCM-D and AFM techniques. The bacteriophage containing multilayers showed antibacterial activity at pH 7.0. In contrast, anti-bacterial activity was not observed at acidic conditions. We showed that wrapping a Salmonella Enteritidis contaminated chicken piece with aluminium foil whose surface was modified with phage loaded chitosan/alginate multilayers decreased the number of colonies on the chicken meat, and it was as effective as treating the meat directly with phage solution.

Ultrafast third-order nonlinear optical properties of self-assembled PCPDTPhSO3Na/C70-(EDA)8 periodically overlapping film

A set of ultrathin multilayer films with alternated layers containing Poly[4,4-bis(4-sulfobutyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl]-1,4-phenylene sodium sa (PCPDTPhSO3Na) as donor and amine group modified fullerene derivative C70-(ethylenediamine)8 (C70-(EDA)8) as acceptor were prepared using layer-by-layer assembly technique on a quartz substrate. Driven by the electrostatic force, C70-(EDA)8 and PCPDTPhSO3Na were alternately adsorbed on the substrate to form donor–acceptor periodically overlapping structure. The growth of the film was monitored by UV-Vis absorption spectra, showing regularly consecutive deposition process. The ultrafast third-order nonlinear optical properties of the films were investigated via a 4f coherent imaging system with phase object (NIT-PO) with 190 fs laser pulses at 400 nm. Experimental results demonstrate that the ultrathin films exhibit excellent self-focusing effect (n2∼4.02 × 10−16 m2/W) and reverse saturable absorption properties (β∼7.75 × 10−10 m/W). Our studies indicate that the PCPDTPhSO3Na/C70-(EDA)8 film has significant potential for applications in future nonlinear optical devices.

Towards hexagonal C2v systems with anisotropic Dzyaloshinkii-Moriya interaction: Characterization of epitaxial Co(101¯0)/Pt(110) multilayer films

Ferromagnet/heavy metal (FM/HM) multilayer thin films with ${C}_{2v}$ symmetry have the potential to host antiskyrmions and other chiral spin textures via an anisotropic Dzyaloshinkii-Moriya interaction (DMI). Here, we present a candidate material system that also has a strong uniaxial magnetocrystalline anisotropy aligned in the plane of the film. This system is based on a new Co/Pt epitaxial relationship, which is the central focus of this work: hexagonal closed-packed $\mathrm{Co}(1\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}\overline{1}\phantom{\rule{0.16em}{0ex}}0)[0\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}1]$ $\ensuremath{\parallel}$ face-centered cubic $\mathrm{Pt}(1\phantom{\rule{0.16em}{0ex}}1\phantom{\rule{0.16em}{0ex}}0)[0\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}1]$. We characterized the crystal structure and magnetic properties of our films using x-ray diffraction techniques and magnetometry, respectively, including $q$-scans to determine stacking fault densities and their correlation with the measured magnetocrystalline anisotropy constant and thickness of Co. In future ultrathin multilayer films, we expect this epitaxial relationship to further enable an anisotropic DMI while supporting interfacial perpendicular magnetic anisotropy. The anticipated confluence of these properties, along with the tunability of multilayer films, make this material system a promising testbed for unveiling new spin configurations in FM/HM films.

Composite Materials by Building Block Chemistry Using Weak Interaction

Abstract Layer-by-Layer (LbL) assembly of interactive polymers onto surfaces leads to the construction of multilayered ultrathin films, which can be done simply by alternately dipping the substrate into various solutions. The range of applications of this LbL assembly can be broadened by introducing molecular recognition mechanisms for polymers and proteins, and by using weak interactions such as van der Waals interactions and biological recognition. As a specific example, it can be applied to the formation of stereocomplexes of poly(methyl methacrylate) (PMMA), poly-lactide (PLA), and fibronectin-collagen as extracellular matrix proteins. In weakly interacting LbL assemblies, the polymer chain tends to be placed in the most structurally stable state. This feature has been successfully used for template polymerization of stereoregular polymers, significant morphological control of biodegradable nanomaterials, and fabrication of three-dimensional (3D) cellular tissue constructs. LbL assembly based on weak interactions is expected to further stimulate interest in the interdisciplinary fields of bioscience and polymer chemistry. Using LbL technology to create functional 3D tissues, such as skin models (LbL-3D Skin) and heart models (LbL-3D Heart), will be a breakthrough in science and technology.

Ultrafast third-order nonlinear optical properties of self-assembled poly[[4,4-bis(4-sulphobutyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene-2,6-diyl]-1,4-phenylene sodium sa multilayer films

An ultrathin multilayer film with well-defined structure containing anionic Poly[[4,4-bis(4-sulphobutyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene-2,6-diyl]-1,4-phenylene sodium sa (PCPDTPhSO3Na) and cationic poly(diallydimethyl ammonium chloride) (PDDA) was prepared using layer-by-layer assembly technique. The growth of the film was monitored by UV–Vis absorption spectroscopy, showing regularly consecutive adsorption. The ultrafast third-order nonlinear optical (NLO) properties of the multilayer film were investigated via the 4f coherent imaging measurement with phase object with 190 fs laser pulses at both 400 and 532 nm. The results demonstrate that PCPDTPhSO3Na/PDDA film exhibited excellent self-focusing effect (n 2 ∼2.42 × 10−16 m2/W) and reverse saturable absorption properties (β ∼6.34 × 10−10 m/W) at 400 nm. In contrast, self-focusing effect (n 2 ∼1.81 × 10−16 m2/W) and saturable absorption properties (β ∼−8.02 × 10−10 m/W) are observed when the laser wavelength (532 nm) is near-resonant with the absorption peak (470 nm). Our studies indicate that the PCPDTPhSO3Na/PDDA film is a promising candidate for applications in NLO devices.

Surface Plasmon Resonance Field-Enhanced Fluorescence Properties of Gold Quantum Dots on Polyelectrolyte Multilayers and Their H2O2 Sensor Application

In this work, we investigate surface plasmon field-enhanced fluorescence (SPF) emission from gold quantum dots (AuQDs) on a polyelectrolyte multilayer ultrathin film deposited onto an Al thin film. Polyelectrolyte layers of poly(diallyl dimethyl ammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) are deposited onto the Al surface using a layer-by-layer (LbL) adsorption technique. AuQDs are subsequently deposited onto the PDADMAC/PSS ultrathin films to study their fluorescence enhancement/quenching phenomenon, as monitored by SPF spectroscopy. The distance between the AuQDs and the Al thin film is controlled by the number of deposited PDADMAC/PSS LbL films. With increasing number of the PDADMAC/PSS bilayers, the fluorescence intensity of the AuQDs increases until the optimum distance between the AuQDs and Al layers is achieved. Moreover, silver nanoprisms (AgNPrs) are coated onto the AuQDs for H2O2 sensing. When the AgNPrs are present, a decrease in the fluorescence intensity of the AuQDs due to energy transfer from the AuQDs to the AgNPrs is observed. Recovery of the fluorescence intensity of the AuQDs is observed upon injection of a H2O2 solution, where the recovery of the intensity is proportional to the H2O2 concentration in the range from 1 pM to 100 nM and results from the oxidation reaction or etching of the AgNPrs. The fluorescence recovery is attributed to weakening of the quenching effect by a reduction in concentration of the AgNPrs. The proposed system exhibits strong potential for the development of H2O2 sensors.

Dynamical behaviour of ultrathin [CoFeB (tCoFeB)/Pd] films with perpendicular magnetic anisotropy

CoFeB-based ultrathin films with perpendicular magnetic anisotropy are promising for different emerging technological applications such as nonvolatile memories with low power consumption and high-speed performance. In this work, the dynamical properties of [CoFeB (tCoFeB)/Pd (10 Å)]5 multilayered ultrathin films (1 Å ≤ tCoFeB ≤ 5 Å) are studied by using two complementary methods: time-resolved magneto-optical Kerr effect and broadband ferromagnetic resonance. The perpendicular magnetization is confirmed for multilayers with tCoFeB ≤ 4 Å. The effective perpendicular magnetic anisotropy reaches a clear maximum at tCoFeB = 3 Å. Further increase of CoFeB layer thickness reduces the perpendicular magnetic anisotropy and the magnetization became in-plane oriented for tCoFeB ≥ 5 Å. This behaviour is explained by considering competing contributions from surface and magnetoelastic anisotropies. It was also found that the effective damping parameter αeff decreases with CoFeB layer thickness and for tCoFeB = 4 Å reaches a value of ~ 0.019 that is suitable for microwave applications.

Preparation of nickel-aluminum hydrotalcite nanosheet-coated carbon nanofibers and their application in the detection of salidroside

A facile and highly sensitive electrochemical sensor for salidroside was fabricated based on multilayer ultrathin films (UTFs) containing Ni–Al layered double hydroxide (LDH) and carbon fibers that obtained by electrospinning technology. The X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) images show that the film surface is synthesized successfully. In addition, we constructed the electrochemical sensor using the composite nanomaterials we prepared to achieve detection of salidroside and this sensor showed a good linear range (0.2–120 μM) and a low detection limit (0.067 μM). It has also been successfully applied to the detection of actual samples, compared with HPLC method, satisfactory recovery rates have also been obtained.

Polymer Solar Cells-Interfacial Processes Related to Performance Issues.

Harnessing solar energy with solar cells based on organic materials (in particular polymeric solar cells) is an attractive alternative to silicon-based solar cells due to the advantages of lower weight, flexibility, lower manufacturing costs, easier integration with other products, low environmental impact during manufacturing and operations and short energy payback times. However, even with the latest efficiencies reported up to 17%, the reproducibility of these efficiencies is not up to par, with a significant variation in the efficiencies reported across the literature. Since these devices are based on ultrathin multilayer organic films, interfaces play a major role in their operation and performance. This review gives a concise account of the major interfacial issues that are responsible for influencing the device performance, with emphasis on their physical mechanisms. After an introduction to the basic principles of polymeric solar cells, it briefly discusses charge generation and recombination occurring at the donor-acceptor bulk heterojunction interface. It then discusses interfacial morphology for the active layer and how it affects the performance and stability of these devices. Next, the formation of injection and extraction barriers and their role in the device performance is discussed. Finally, it addresses the most common approaches to change these barriers for improving the solar cell efficiency, including the use of interface dipoles. These issues are interrelated to each other and give a clear and concise understanding of the problem of the underperformance due to interfacial phenomena occurring within the device. This review not only discusses some of the implemented approaches that have been adopted in order to address these problems, but also highlights interfacial issues that are yet to be fully understood in organic solar cells.

Stressful Surfaces: Cell Metabolism on a Poorly Adhesive Substrate.

The adhesion and proliferation of cells are exquisitely sensitive to the nature of the surface to which they attach. Aside from cell counting, cell "health" on surfaces is typically established by measuring the metabolic rate with dyes that participate in the metabolic pathway or using "live/dead" assays with combinations of membrane permeable/impermeable dyes. The binary information gleaned from these tests-whether cells are attached or not, and whether they are living or dead-provides an incomplete picture of cell health. In the present work, proliferation rates and net metabolism of 3T3 fibroblasts seeded on "biocompatible" ultrathin polyelectrolyte multilayer films and on control tissue culture plastic were compared. Cells adhered to, and proliferated on, both surfaces, which were shown to be nontoxic according to live/dead assays. However, adhesion was poorer on the multilayer surface, illustrated by diffuse organization of the actin cytoskeleton and less-developed focal adhesions. Proliferation was also slower on the multilayer. When normalized for the total number of cells, it was shown that cells on multilayers experienced a five-day burst of metabolic stress, after which the metabolic rate approached that of the control surface. This initial state of high stress has not been reported or appreciated in studies of cell growth on multilayers, although the observation period for this system is usually a few days.

In-situ measurement of diamagnetic response of potassium-adsorbed multi-layer FeSe ultrathin films on SrTiO3(001) substrate

A single-unit-cell layer FeSe ultrathin film grown on SrTiO3(001) substrate exhibits remarkable high-temperature superconductivity, which has aroused intensive research interest. Electron transfer from the substrate to the FeSe layer has been shown to play an indispensable role in enhancing the extraordinary superconductivity. With this idea, researchers have tried to search for new high-temperature superconducting material systems including K-adsorbed multi-layer FeSe ultrathin films, on which superconducting-like energy gaps have been observed with scanning tunneling spectroscopy and photoelectron spectroscopy. However, the high-temperature superconductivity of the multi-layer FeSe ultrathin films has not yet been confirmed by directly observing the zero resistance or Meissner effect. With a self-developed multi-functional scanning tunneling microscope (STM+), which enables not only usual STM functionality, but also in situ two-coil mutual inductance measurement, we successfully observe the diamagnetic response of a K-adsorbed multilayer FeSe ultrathin film grown on a SrTiO3(001) substrate, and thus determine its transition temperature to be 23.9 K. Moreover, we calculate the penetration depth of the film from the measured results and find that its low-temperature behavior exhibits a quadratic variation, which strongly indicates that the order parameter of the superconducting K-adsorbed multi-layer FeSe ultrathin film has an S± pairing symmetry.

Transport and magnetic properties of amorphous SiC/Cu ultrathin multilayer films

Silicon carbide/copper (SiC/Cu) ultrathin multilayer films were deposited on Si substrates by alternating the use of radio-frequency and direct current magnetron sputtering. It was found that the SiC layers possess an amorphous structure and Cu is incorporated into the SiC layers. The films have a p-type semiconductor characteristic, room-temperature ferromagnetic behavior, and negative magnetoresistance. A carrier concentration of up to 2.12 × 1020 and a saturation magnetization of up to 12.14 emu/cm3 are obtained, and Mott variable range hopping mainly dominates the conduction mechanism of the films. The theoretical fitting for the experimental magnetoresistance curves and the theoretical calculation of the density of states of Cu-doped SiC indicate that the ferromagnetism of the films originates from a carrier-mediated p–d exchange interaction.

Interaction force between ultrathin multilayer films induced by quantum fluctuations

The van der Waals force between dielectric plates comprising ultrathin conducting films was calculated by employing two models. In the first model, the ultrathin dielectric film was modeled as a dielectric plate of a small thickness, and the Lifshitz theory was applied. In the second model, an ultrathin dielectric film was modeled as a plasma sheet, which is an infinitesimally thin fluid carrying mass and charge. For each model, the interacting force was considered to be a function of the separation gap between the films, and the difference in the force-distance relationships of two was discussed.

Facile preparation of multilayer ultrathin films based on eriochrome black T/NiAl-layered double hydroxide nanosheet, characterization and application in amperometric detection of salicylic acid

A highly sensitive electrochemical sensor, EBT/LDH ultrathin film, for salicylic acid (SA) was fabricated in a facile way based on multilayer ultrathin films (UTFs) containing Eriochrome black T anions (EBT) and exfoliated Ni–Al layered double hydroxide (LDH) nanosheets via layer-by-layer self-assembly technique. The XRD pattern confirms that the products are nickel aluminum hydrotalcites, and SEM images shows continuous and uniform film surface. Electrochemical impedance spectroscopy (EIS), Current – time (i-T) and cyclic voltammetry (CV) methods were used to characterize the electrochemical behavior of the ultrathin film. The electrode modified with ultrathin film displays significantly high electrocatalytic performance for SA with sensitivity of 860μAmM−1cm−2, large concentrations ranging from 0.01 to 100μM and with low detection limit 0.003μM (S/N=3). The EBT/LDH ultrathin film is shown to be a feasible electrochemical sensor for detection of SA.

Stability and dye inclusion of graphene oxide/polyelectrolyte layer-by-layer self-assembled films in saline, acidic and basic aqueous solutions

We demonstrate that a simple spectrophotometric method can be efficiently applied for the characterization of structural and chemical stability and adsorption properties of composite graphene oxide (GO) films in various solutions. The immersion stability of GO layer-by-layer (LbL) self-assembled with a polycation into ultrathin multilayered films was studied in water and in concentrated salty, acidic and basic solutions by UV–visible spectroscopy. These films were found to retain both their chemical stability and physical integrity in water, salt and HCl solutions with a slight rearrangement of the nanoscale structure as shown by the change in their visible spectrum. However, immersion into NaOH solutions above molar concentration led to the deconstruction of the multilayer structure by base-induced deoxygenation of GO. The adsorption of methylene blue on polymer/GO LbL films of various thicknesses revealed that the multilayers are largely impermeable towards this cationic dye.

Multi-dimensional, light-controlled switch of fluorescence resonance energy transfer based on orderly assembly of 0D dye@micro-micelles and 2D ultrathin-layered nanosheets

Fluorescence resonance energy transfer (FRET) systems have broad applications in visual detection, intelligent materials, and biological imaging, all of which favor the transmission of light through multiple dimensions and in diverse directions. Herein, we have demonstrated multi-dimensional (0D and 2D) FRET within a multi-layer ultrathin film (UTF) by employing a layer-by-layer (LBL) assembly technique. The anionic block copolymer micelle poly(tert-butyl acrylate-co-ethyl acrylate-co-methacrylic acid) (PTBEM) is chosen as a molecular carrier for the incorporation of bis(8-hydroxyquinolate) zinc (Znq2) and open-ring merocyanine (MC) (denoted as (Znq2/MC)@PTBEM). Alternatively, electrostatic assembly is performed with cationic layered double hydroxide (LDH) nanosheets (denoted as [(Znq2/MC)@PTBEM/LDH]n). This [(Znq2/MC)@PTBEM/LDH]n system offers a multi-dimensional propagation medium and ensures that the FRET donor and acceptor are located within their Forster radii in each direction. The system demonstrates a FRET process that can be switched via alternating ultraviolet/visible (UV/vis) irradiation, with tunable blue–green/red fluorescence, resulting in a FRET efficiency as high as 81.7%. It is expected that this assembly method, which uses 0D micelles on a 2D layered material, can be extended to other systems for further development of multi-dimensional FRET.

Refractive index and bandgap variation in Al2O3-ZnO ultrathin multilayers prepared by atomic layer deposition

This research focuses on the study of the refractive index and bandgap behavior in ultrathin multilayer films of Al2O3-ZnO bilayers grown via atomic layer deposition (ALD) technique on Si(100) substrates. The multilayer configuration stack consists in alternate layers of constant thickness Al2O3 (2 nm) and varying thickness ZnO films in order to obtain a total thickness of ∼100 nm. A set of 10 samples based on bilayers with various 2:X thickness ratios were prepared, where X refers to the ZnO layer thickness. X is proportional to the number of cycles (N) of the ZnO precursor, varying from 1 to 100. The sample morphology was studied via Atomic Force Microscopy and the results show that the surface roughness of the multilayers varies from 0.2 to 1.2 nm, as the ZnO layer thickness increases. In all cases, the roughness values remain below 2% of the total thickness of the multilayer. The refractive index n(λ) and optical bandgap, Eg, of each multilayer sample were studied via spectroscopic ellipsometry (SE). A General Oscillator optical model was utilized to fit the experimental data in order to obtain the total thickness, refractive index and absorption coefficient. Cross-sectional mode scanning electron microscope images verified the multilayer total thickness and corroborated the accuracy of the optical model. The refractive index varies significantly from values close to the Al2O3 refractive index when the bilayer thickness is small, up to values corresponding closely to ZnO for thicker bilayers. The refractive index, as a function of bilayer thickness, varies between 1.63 and 2.3, for λ = 370 nm (UV region), showing high sensitivity. In addition, the optical bandgap energy, Eg, determined using the Tauc model, decreases when the bilayer thickness increases, with a maximum variation of ΔEg ∼1.6 eV. These results reveal that the refractive index and optical bandgap of Al2O3-ZnO material can be modulated systematically as a function of the bilayer thickness. Such behavior is of great importance for optoelectronics applications, in particular for the development of devices with response in the UV spectral range.