Al2O3 Interlayer Research Articles

Core-shell engineering of graphite nanosheets reinforced PVDF toward synchronously enhanced dielectric properties and thermal conductivity

Polymer composites integrating high dielectric permittivity (ε′) but low loss, large breakdown strength (Eb) and thermal conductivity (TC), have attracted widespread attention in electronic devices and power systems. To simultaneously achieve these properties in graphite nanosheet (GNS)/poly(vinylidene fluoride, PVDF), the GNS were first encapsulated by a layer of aluminum oxide (Al2O3), and then incorporated into PVDF, and the resulting PVDF nanocomposites’ dielectric properties and TC were explored in terms of the Al2O3 shell thickness and filler loading. The insulating Al2O3 shell serves as a barrier layer for the formation of leakage current and long-distance electron migration thus resulting in much lower dielectric loss and conductivity of the GNS@Al2O3/PVDF. It effectively mitigates the dielectric mismatch between the filler and host matrix, further introduces more traps that can capture charge carriers, and increases the barrier height for electron detrapping subsequently preventing the growth of electric trees and elevating the Eb. Moreover, the Al2O3 interlayer alleviates both the phonon density state and phonon impedance mismatches between the filler and matrix and facilitates the interfacial phonon transport thus leading to improved TC. The dielectric parameters and TC of the GNS@Al2O3/PVDF can be simultaneously modulated by optimizing the Al2O3′s thickness. This work offers an effective approach for designing and fabricating the polymeric nanodielectrics concurrently integrating high ε′ but low loss, enhanced Eb, and TC for prospective applications in power equipment and microelectronic devices.

The Effect of Al2O3 on the Performance of Perovskite Solar Cells

Improving the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs) remain the two most important goals of perovskite research. Herein, the effects of Al2O3 interlayer on the performance of formamidinium‐cesiums and “triple cation” PSCs by depositing a thin Al2O3 layer via atomic layer deposition on different interfaces are analyzed. It is found that it can efficiently serve as a passivation layer of perovskite absorber, as a seed layer for the compact growth of the subsequent SnO2 layer, or as a capping layer to the whole cell in the superstrate configuration to prevent moisture ingress. The optimized devices utilizing Al2O3 have on average more than 1% absolute higher PCE, with reduced penetration of moisture inside the device. Especially, the capping layer has shown the greatest benefit, extending the stability of the devices by more than two times and allowing long‐term operation without encapsulation. In the best case, a T80 time of almost 900 h under day/night‐cycling illumination is obtained. The observed trends are based on data from a large number of devices (more than 300 devices were tested in the maximum power point), which give statistical relevance to the promising results.

Enlargement of Memory Window of Si Channel FeFET by Inserting Al₂O₃ Interlayer on Ferroelectric Hf₀.₅Zr₀.₅O₂

Enlargement of Memory Window of Si Channel FeFET by Inserting Al₂O₃ Interlayer on Ferroelectric Hf₀.₅Zr₀.₅O₂

Investigation of Interlayer Dielectric in BaTiO3/III‐Nitride Transistors

In this study, the impact of varying the thickness of the Al2O3 interlayer dielectric on the electrical characteristics of BaTiO3/III‐nitride transistors is investigated. In the findings, it is revealed that a minimum thickness of 8 nm for the Al2O3 layer is crucial to maintain high device performance and protect against sputtering‐induced damage during BaTiO3 deposition. The fabricated BaTiO3/Al2O3/AlGaN/GaN high electron mobility transistors exhibit exceptional electrical properties, including a maximum current density of 700 mA mm−1, an on‐resistance of 5 Ω mm, an ION/IOFF ratio of 107, a subthreshold slope of 119 mV dec−1, and significantly reduced gate leakage current. The devices with the optimal 8 nm Al2O3 thickness demonstrates excellent agreement between theoretical and experimental values for effective mobility, achieving a value of 1188 cm2 V−1·s at a 2D electron gas density of 1013 cm−2. Furthermore, in the study, it is confirmed that increasing the Al2O3 thickness also improves the quality of interface charge density, as evidenced by the results obtained from capacitance–voltage measurements. In these findings, the critical role of controlling the Al2O3 thickness in optimizing the electrical characteristics and overall performance of BaTiO3/III‐nitride transistors are highlighted.

Microstructure, mechanical and corrosion behavior of CrNx/Al2O3 multilayer films deposited by magnetron sputtering

A novel design was adopted to improve corrosion resistance of 2024 Al alloys by magnetron sputtering CrNx based multilayer films with Al2O3 intercalation. The multilayer films were composed of inhomogeneous structure, i.e., thick CrNx transition layer (∼2 μm) + CrNx/Al2O3 multilayer (∼1 μm). The effect of Al2O3 interlayer and modulation period on microstructure and performance of multilayer films were investigated. The nitride layer was dominated by Cr2N and CrN with minor Cr, while the Al2O3 layer displayed in the amorphous form. The intercalation of Al2O3 blocked the columnar growth in CrNx layers and refined the grains. As the period increased, the cluster particle size decreased and the mechanical properties increased, with the maximum hardness and modulus at CN-8 (19.13 GPa and 282.2 GPa). In addition, the multilayer structure enhanced the bonding between the film and the substrate, and has an improvement on the hard and brittle properties of the film. The multilayer films showed improved corrosion resistance than the CrNx mono-layer in 3.5 wt% NaCl solution. The film with CrNx-top layer showed superior corrosion resistance than the film with Al2O3-top layer. The increasing period also enhanced corrosion resistance, showing an excellent corrosion potential and corrosion current density (Ecorr=-0.538 V, icorr=0.96 μA·cm−2) at CN-8.

Double Passivation Using Ultra‐Thin Insulators for Improved Stability and Efficiency of Quasi‐2D Perovskite Light Emitting Diodes

AbstractInterface engineering is a critical parameter for optimal optoelectronic device performance. In quasi‐2D perovskite light emitting diodes (PeLEDs), traditional poly (3,4‐ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) hole injection layer (HIL) is replaced by self‐assembled monolayer (SAM) [2‐(3,6‐dibromo‐9H‐carbazol‐9‐yl) ethyl] phosphonic acid (Br‐2PACz) HIL. The deep highest occupied molecular orbital (HOMO @ −5.73 eV) of Br‐2PACz facilitates the efficient hole‐injection along with a reduction in leakage current by 4–5 orders of magnitude as compared to PEDOT:PSS (HOMO @ −5.00 eV) HIL based optimized PeLEDs. Ultra‐thin SAM‐based Br‐2PACz HIL presents two challenges: i) device reproducibility is hindered by spatial inhomogeneity, and ii) it fails to regulate nonradiative recombination at the perovskite/HIL interface. To address these challenges, the ultra‐thin interlayer of atomic layer deposited aluminum oxide (Al2O3) is utilized between Br‐2PACz, and perovskite which aids in passivating the interfacial states at the HIL/perovskite interface. With the optimized thickness of Al2O3 interlayer (3 nm), the device's external quantum efficiency (EQE) improved from 9.47% to 13.14%, accompanied by luminous efficiency of 42.8 cd A−1. An ultra‐thin interlayer of lithium fluoride (LiF) (2 nm) is implemented on the top side of the perovskite, which can provide 1.5 times increase in the device's LT50 stability.

Enhancing ferroelectric performance in hafnia-based MFIS capacitor through interface passivation and bulk doping

In recent times, there has been a notable surge of interests in hafnia (HfO2)-based ferroelectrics, primarily due to their remarkable ferroelectric properties employed in ultra-thin configurations, alongside their compatibility with the conventional CMOS manufacturing process. In order to harness the full potential of HfO2-based films for high-performance non-volatile memory applications, it is imperative to enhance their ferroelectric characteristics and durability. This study introduces a straightforward approach aimed at augmenting the ferroelectric performance of Hf x Zr1−x O2 (HZO) films deposited on silicon (Si) substrates through the engineering of oxygen vacancies (V O). The results of this endeavor demonstrate a significant enhancement in ferroelectric performance, characterized by a 2Pr value of 47 μC cm−2 and impressive endurance, enduring up to 108 cycles under an 8 MV cm−1 electric field without the need of a wake-up process. This marked improvement can be attributed to a dual-pronged approach, involving the incorporation of an Al2O3 interlayer and the introduction of Al atoms into the HZO film. The Al2O3 interlayer primarily serves to mitigate the presence of oxygen vacancies at the interface, while the introduction of Al dopants elevates the concentration of oxygen vacancies within the bulk material. This modulation of oxygen vacancy concentration proves instrumental in facilitating the formation of a ferroelectric o-III phase within the HZO-based films, thereby further augmenting their ferroelectric performance. This innovative and effective strategy offers an alternative avenue for enhancing the ferroelectric properties of materials characterized by a fluorite crystal structure.

Designing Atomic Interface in Sb2S3/CdS Heterojunction for Efficient Solar Water Splitting.

In the emerging Sb2S3-based solar energy conversion devices, a CdS buffer layer prepared by chemical bath deposition is commonly used to improve the separation of photogenerated electron-hole pairs. However, the cation diffusion at the Sb2S3/CdS interface induces detrimental defects but is often overlooked. Designing a stable interface in the Sb2S3/CdS heterojunction is essential to achieve high solar energy conversion efficiency. As a proof of concept, this study reports that the modification of the Sb2S3/CdS heterojunction with an ultrathin Al2O3 interlayer effectively suppresses the interfacial defects by preventing the diffusion of Cd2+ cations into the Sb2S3 layer. As a result, a water-splitting photocathode based on Ag:Sb2S3/Al2O3/CdS heterojunction achieves a significantly improved half-cell solar-to-hydrogen efficiency of 2.78% in a neutral electrolyte, as compared to 1.66% for the control Ag:Sb2S3/CdS device. This work demonstrates the importance of designing atomic interfaces and may provide a guideline for the fabrication of high-performance stibnite-type semiconductor-based solar energy conversion devices.

Toward High‐Performance All‐Solid‐State Thin Film FeOxSy/LiPON/Li Microbatteries via Dual‐Interface Modification

AbstractFeaturing high theoretical capacity, low cost, and low preparation temperature, Li‐free cathodes are considered promising for all‐solid‐state thin‐film lithium microbatteries (TFBs). In this work, a Li‐free cathode of amorphous FeOxSy film is prepared, followed by the fabrication and investigation of FeOxSy/LiPON/Li TFBs. It is found that the structural degradation at both the LiPON/Li and FeOxSy/LiPON interfaces results in a rapid capacity loss for the TFB during electrochemical cycling. To achieve both high rate capability and long cycle life for the TFB, a dual‐interface modification approach using amorphous Al2O3 as an interlayer is proposed. During the TFB cycling, the Al2O3 interlayer not only enables robust LiPON/Li contact by preventing the formation of Li voids but also blocks the diffusion of Fe element from FeOxSy to LiPON electrolyte, effectively suppressing the interfacial resistance growth. Consequently, the dual‐interface modified TFB achieves greatly improved rate capability (194.3 mAh g−1 at 5 A g−1) and cycle performance (71% capacity retention after 800 cycles), which are superior to the pristine TFB and single‐interface modified TFB. This work advances the fundamental understanding of the failure mechanisms at the solid‐solid electrode/electrolyte interfaces, offering a feasible interfacial modulation strategy to develop advanced all‐solid‐state lithium batteries.

A Comparative Study on the Degradation Behaviors of Ferroelectric Gate GaN HEMT with PZT and PZT/Al2O3 Gate Stacks.

In this paper, the degradation behaviors of the ferroelectric gate Gallium nitride (GaN) high electron mobility transistor (HEMT) under positive gate bias stress are discussed. Devices with a gate dielectric that consists of pure Pb(Zr,Ti)O3 (PZT) and a composite PZT/Al2O3 bilayer are studied. Two different mechanisms, charge trapping and generation of traps, both contribute to the degradation. We have observed positive threshold voltage shift in both kinds of devices under positive gate bias stress. In the devices with a PZT gate oxide, we have found the degradation is owing to electron trapping in pre-existing oxide traps. However, the degradation is caused by electron trapping in pre-existing oxide traps and the generation of traps for the devices with a composite PZT/Al2O3 gate oxide. Owing to the large difference in dielectric constants between PZT and Al2O3, the strong electric field in the Al2O3 interlayer makes PZT/Al2O3 GaN HEMT easier to degrade. In addition, the ferroelectricity in PZT enhances the electric field in Al2O3 interlayer and leads to more severe degradation. According to this study, it is worth noting that the reliability problem of the ferroelectric gate GaN HEMT may be more severe than the conventional metal-insulator-semiconductor HEMT (MIS-HEMT).

Microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating on Inconel 718 alloy

In this paper, Al2O3/Cr composite coatings were prepared on the surface of Inconel 718 alloy by cathodic liquid plasma electrolytic deposition (CLPED) and double-glow plasma surface alloying (DGPSA) processes. The microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating were investigated. The results showed that the Al2O3 interlayer surface was fully covered with Cr coating. The interface between the Al2O3 layer and the Cr metal layer presents a mechanical interlock effect, which can absorb the deformation caused by thermal expansion, thereby reducing the adverse effects of thermal stress. The surface roughness of the Al2O3 coatings decreased after depositing Cr coating. The oxidation weight gain of the Al2O3/Cr composite coatings were significantly lower than that of the substrate, indicating that the Al2O3/Cr composite coatings improved the high-temperature oxidation resistance of Inconel 718 alloy. The oxidation weight gain of the Al2O3/Cr composite coatings at different frequencies were similar, while the Al2O3/Cr composite coating at 400 Hz was lowest. During the high-temperature oxidation process, the Al2O3 interlayer can effectively inhibit the external diffusion of Ni, Fe and other elements in the matrix, which helps to prevent the cracking of the outer oxide film, thereby reducing the oxidation rate.

Reduced graphene oxide-encaged submicron-silicon anode interfacially stabilized by Al2O3 nanoparticles for efficient lithium-ion batteries.

Silicon-carbon composites have been recognized as some of the most promising anode candidates for advancing new-generation lithium-ion batteries (LIBs). The development of high-efficiency silicon/graphene anodes through a simple and cost-effective preparation route is significant. Herein, by using micron silicon as raw material, we designed a mesoporous composite of silicon/alumina/reduced graphene oxide (Si/Al2O3/RGO) via a two-step ball milling combined annealing process. Commercial Al2O3 nanoparticles are introduced as an interlayer due to the toughening effect, while RGO nanosheets serve as a conductive and elastic coating to protect active submicron silicon particles during lithium alloying/dealloying reactions. Owing to the rational porous structure and dual protection strategy, the core/shell structured Si/Al2O3/RGO composite is efficient for Li+ storage and demonstrates improved electrical conductivity, accelerated charge transfer and electrolyte diffusion, and especially high structural stability upon charge/discharge cycling. As a consequence, Si/Al2O3/RGO yields a high discharge capacity of 852 mA h g-1 under a current density of 500 mA g-1 even after 200 cycles, exhibiting a high capacity retention of ∼85%. Besides, Si/Al2O3/RGO achieves excellent cycling reversibility and superb high-rate capability with a stable specific capacity of 405 mA h g-1 at 3000 mA g-1. Results demonstrate that the Al2O3 interlayer is synergistic with the indispensable RGO nanosheet shells, affording more buffer space for silicon cores to alleviate the mechanical expansion and thus stabilizing active silicon species during charge/discharge cycles. This work provides an alternative low-cost approach to achieving high-capacity silicon/carbon composites for high-performance LIBs.

Novel Interlayer Boosting the Performance of Evaporated Cu2O Hole‐Selective Contacts in Si Solar Cells

Passivating contacts based on transition metal oxides are of great interest for applications in crystalline silicon (c‐Si) solar cells due to their improved optical transparency and potential cost reduction. In this work, the contact resistivity and passivation for thermally evaporated Cu2O are investigated and optimized, with and without an Al2O3 interlayer, as a hole‐selective contact to c‐Si. Additionally, we implement an Al y TiO x /TiO2 stack as a novel passivating tunnel interlayer for hole‐selective contacts, achieving an implied open‐circuit voltage iV oc of 630 mV and a record‐low J 0 of 212 fA cm−2 while maintaining a contact resistivity ρ c of 62 mΩ cm2. A record‐low ρ c of 8 mΩ cm2 for Cu2O‐based contacts is also demonstrated at the expense of passivation. The addition of the interlayer resulted in a 2% absolute improvement in the efficiency of proof‐of‐concept c‐Si cells with full‐area rear Cu2O contacts, reaching 19.1%.The demonstration of this novel interlayer stack provides new avenues to improve the performance also of other hole‐selective passivating contacts.

Investigation of the interface state characteristics of the Al/Al2O3/Ge/p-Si heterostructure over a wide frequency range by capacitance and conductance measurements

In this work, Al/Al2O3/Ge/p-Si heterostructures were fabricated by e-beam thermal evaporation. The EDX (energy dispersive X-ray spectroscopy) map visually obtained the basic distribution information in a two-dimensional graph. Three-dimensional atomic Force Microscope (AFM) analysis of the roughness of the Al/Al2O3/Ge/p-Si heterostructure shows that the Al2O3 particle has approximately 4.35 nm. Quantitative analysis via histogram plots for Al2O3 interlayer grown on p-Si shows a Gaussian-like distribution, and it has a sharp profile between 0 and 2 nm on silicon, located around 1.2 nm. The current-voltage (I–V) and capacitance-conductance-voltage (C-G/ω-V) measurements were used to investigate the electrical properties of the structure at room temperature. The I–V measurements revealed two distinct linear regions, attributed to barrier inhomogeneity and distribution of interfacial state/trap densities (Dit). For this reason, we obtained Dit distributions by considering the voltage dependence of the ideality factor n(V) in two regions. Diode parameters acquired through different methods are comparatively presented with a brief literature review. Then, the C-G/ω-V measurements were conducted across a broad frequency range (from 0.3 kHz to 3 MHz), and these measurements revealed notable alterations in the electrical parameters with regard to frequency. In order to probe interface states/traps, we employed the conductance/admittance method, which provided satisfactory information about trap lifetime, following the low-high frequency (LF-HF) and Hill-Coleman methods. The effects of these states/traps on the measurements according to voltage, frequency, and energy level (Eit-Ev) are discussed in detail.

Thermal transport and structural improvements due to annealing of wafer bonded β-Ga2O3|4H-SiC

The impact of postbond annealing on the structural and thermal characteristics of 130 nm thick exfoliated (201) β-Ga2O3 (via H+ ion implantation) wafer bonded to (0001) 4H-SiC was studied. Thirty nanometer amorphous-Al2O3 was grown on the β-Ga2O3 substrates prior to bonding as an interlayer between β-Ga2O3 and 4H-SiC. The surface activated bonding technique was utilized for bonding, which induces a thin nanometer amorphous interfacial region at the bonded interface (Al2O3|4H-SiC). We demonstrate annealing the bonded structure at 800 °C up to 1 h is beneficial: (1) the removal of residual strain in the exfoliated β-Ga2O3 layer that was due to the exfoliation implant, (2) reduction of lattice mosaicity in the β-Ga2O3 layer, (3) nearly complete recrystallization of the amorphous bonded interfacial region, and (4) partial recrystallization of the initially amorphous-Al2O3 interlayer. The thermal characteristics correspondingly improve with the improvement in structural characteristics. The thermal conductivity of the as-bonded β-Ga2O3 layer was 2.9 W/m K, and the thermal boundary conductance of the bonded interface was 66 MW/m2 K. After annealing at 800 °C for 1 h, triple-axis x-ray diffraction ω:2θ measurements showed a reduction in strain for the β-Ga2O3 layer and the symmetric (201) rocking curve widths. We simultaneously observe a doubling of the β-Ga2O3 thermal conductivity to 6.0 W/m K and a 20% increase in the thermal boundary conductance. However, upon further annealing up to 10 h and fully recrystallizing both the Al2O3 interlayer and bonded interface, the thermal boundary conductance dropped by ∼30%. This preliminary result suggests that crystalline heterointerfaces may not necessarily be the most optimal interfacial structure for thermal transport.

Atomic layer deposition of Al2O3 interlayer for improving AlN growth on silicon substrates

Ultrathin Al2O3 interlayers have been grown on silicon (111) substrates using atomic-layer deposition (ALD) and investigated as interlayers prior to AlN growth by metalorganic chemical vapor deposition. The ALD process is carried out at low temperatures with the interlayer thickness systematically varied from 0.9 to 5.1 nm. A reference sample with the standard SiNx interlayer is also investigated. Thin Al2O3 layers (<2 nm) are found to significantly improve the crystal quality of AlN. X-ray diffraction measurements show the total dislocation density is decreased by nearly one order of magnitude for an Al2O3 thickness of 1.7 nm compared with the standard SiNx interlayer. The impact of the interlayer on the AlN strain is studied by x-ray diffraction and Raman spectroscopy measurements. Some reduction in stress is observed when incorporating the 1.7 nm interlayer. A Raman stress factor of −2.6 ± 0.1 cm−1/GPa is obtained for AlN. Surface and interface analysis studied by atomic force microscopy, high-resolution transmission electron microscopy, and x-ray photoelectron spectroscopy indicates sharp atomic alignment between AlN and silicon with a 1.7 nm Al2O3 interlayer.

Investigation into ameliorative dielectric properties of silicon/poly(vinylidene fluoride) composites by engineering insulating aluminum oxide shell as an interlayer

AbstractFlexible electronic materials with high‐dielectric constant (ɛ) and breakdown strength (Eb) but low loss is pursued. Encapsulation of conductive fillers with various insulating shells represents a promising strategy to inhibit dielectric loss or leakage current. In this work, aluminum oxide (Al2O3) encapsulated silicon (Si) core‐shell structured particles were prepared through a sol–gel approach, and then were incorporated with poly(vinylidene fluoride) (PVDF). The dielectric properties of PVDF composites with various fillers are investigated under varying frequencies. The findings demonstrate that a Al2O3 shell was formed outside the original Si, and that the Si@Al2O3/PVDF exhibit a high ɛ and elevated Eb but signally suppressive loss and restrained conductivity when compared with raw Si. The Al2O3 interlayer not only enhances the interface compatibility between the filler and the matrix and promotes interface polarizations, but also suppresses the loss and leakage current through preventing adjacent Si from directly contacting. The optimized dielectric performances can be achieved via tailoring the Al2O3 shell thickness. Furthermore, the theoretic fitting of experimental results by the Havriliak‐Negami equation deciphers the Al2O3 interlayer’ impact on the polarization mechanism. The resulting Si@Al2O3/PVDF composites with high ε but low loss, as well as boosted Eb, reveal potential applications in electrical systems.

Polarity-Tunable Field Effect Phototransistors.

Field-effect phototransistors feature gate voltage modulation, allowing dynamic performance control and significant signal amplification. A field-effect phototransistor can be designed to be inherently either unipolar or ambipolar in its response. However, conventionally, once a field-effect phototransistor has been fabricated, its polarity cannot be changed. Herein, a polarity-tunable field-effect phototransistor based on a graphene/ultrathin Al2O3/Si structure is demonstrated. Light can modulate the gating effect of the device and change the transfer characteristic curve from unipolar to ambipolar. This photoswitching in turn produces a significantly improved photocurrent signal. The introduction of an ultrathin Al2O3 interlayer also enables the phototransistor to achieve a responsivity in excess of 105 A/W, a 3 dB bandwidth of 100 kHz, a gain-bandwidth product of 9.14 × 1010 s-1, and a specific detectivity of 1.91 × 1013 Jones. This device architecture enables the gain-bandwidth trade-off in current field-effect phototransistors to be overcome, demonstrating the feasibility of simultaneous high-gain and fast-response photodetection.

Al2O3 barrier layer for enhancing UV to visible rejection ratio in p-Si/n-MgZnO heterojunction visible blind UV photodetectors

The fabrication of visible blind ultraviolet photodetectors based on p-Si/n-MgxZn1-xO heterojunction is challenging due to the generation of visible photoresponse caused by the drift of visible light generated electrons from p-silicon to n-MgxZn1-xO across the interface. Here, it is shown that by incorporating a thin ∼30 nm Al2O3 interlayer at the heterojunction, the UV-to-visible rejection ratio in p-Si/n-Mg0.25Zn0·75O photodetectors can be significantly enhanced. The Al2O3 interlayer inserted between n-Mg0.25Zn0·75O and p-Si serves as an effective blocking layer against the transport of visible light-generated electrons from p-Si to n-Mg0.25Zn0·75O, thereby suppressing the visible photoresponse. As a result, the UV-to-visible rejection ratio was improved by approximately three orders of magnitude, with a peak responsivity of 0.17 mA/W at 270 nm and a reverse bias of 0.5 V. This high degree of visible blindness of p-Si/n-Mg0.25Zn0·75O heterojunction photodetectors with an Al2O3 barrier layer holds promise for next-generation visible-blind UV photodetection applications.

Irradiation-enhanced Interactions at UO2/Al2O3/Al Interfaces

Combustion synthesis is used to prepare thin UO2 films on aluminum alloy substrates. This simple preparation method involves electrospraying uranyl nitrate + acetylacetone + 2-methoxyethanol solution on the substrate, followed by a short annealing at 350 or 550 °C. The irradiation of films with a 40Ar2+ ion beam (energy of 1.7 MeV and fluences of 7.7 × 1016 and 1.3 × 1017 ions/cm2) is conducted to investigate irradiation-induced restructuring processes. High-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) investigations show that the annealing temperature significantly influences the crystallinity and stability of materials during irradiation. A small amount of Mg in the alloy substrate diffuses into the amorphous Al2O3 interfacial layer between the film and the substrate. Local thermal spikes from the incoming ions facilitate the irradiation-induced mixing of immiscible Al2O3 and UO2 for the materials prepared at 350 °C. This mass diffusion produces relatively large cavities at the interface. Selective diffusion of a more significant amount of Mg for the materials prepared at 550 °C suppresses the mixing of the Al2O3 interlayer with the film but forms MgyU1–yO2±x solid solutions during irradiation. Local thermal heating triggers the precipitation of a discontinuous crystalline MgO layer close to the film surface. The enhanced and selective diffusion of Mg into the film makes the materials prepared at 550 °C more robust and mechanically stable than those prepared at 350 °C.