Integration fabrication of polyimide composite films for aerospace applications

Polyimides externally deployed in spacecraft or satellites extensively have various aerospace hazards, including atomic oxygen (AO) erosion, irradiation degradation, and electrostatic charge/discharge (ESC/ESD). To cope with these challenges, we fabricate a ZnO/CuNi‐polyimide composite film with augmented permanence. Using spectroscopy and microscopy techniques, we have shown that the combination of chelation and cross‐linking in the interfacial architecture leads to enhanced interfacial compatibility and mechanical robustness. Besides, due to the positive AO diffusion barrier ability of the wurtzite ZnO, our composite film shows remarkable AO resistance and a very small Ey value of 6.88 × 10−26 cm3/atom, which is merely 2.29% of that of pristine polyimide. Moreover, the well‐defined nanocrystalline state with minimal lattice swelling (0.3%–0.7%) of the Fe+‐irradiated ZnO/CuNi‐polyimide at a damaging dose of 353.4 dpa demonstrates its excellent irradiation resistance. Finally, the ZnO/CuNi‐polyimide also shows sufficient electrostatic dissipation capacity to cope with the ESC/ESD events. Our fabrication approach for composite films based on multi‐technology integration shows potential for aerospace applications and deployment.

5][6] With the development and advancement of shape memory structures, PIs have tremendous application potential in various fields such as large-area flexible electronic facilities, solar sails, and sun visors of next-generation space telescopes.[9][10] Among these hazards, AO erosion is undoubtedly the most severe hazard for polyimides.The relative collision kinetic energy of AO in the LEO ranges from 4 eV to 5 eV, which can easily fracture the molecular skeletons of polyimides, resulting in degradation of physical properties and a significant reduction in the service life. 11In addition, the detrimental effects of charged particle bombardment cannot be disregarded.3][14] Therefore, it is imperative to identify polyimides' degradation mechanisms and shielding methods to strengthen their long-term orbital deployment.
To date, many prospective strategies have been developed to improve the performance of PIs to ensure the safety and reliability of spacecraft.6][17][18][19] However, special attention needs to be paid to the insulation and irradiation resistance of these modified polyimides (MPIs).Another strategy involves ion implantation and oxidation (Impantox). 20,21Implants of Si + , Al + , Y + , and B + are embedded into the subsurface of a polymer, converting it into nonvolatile oxides through AO diffusion to inhibit continuous penetration by AO.The drawback of this approach is that implantation may induce the structural transformation of polyimide and may affect its optical-thermal properties.1][32] Therefore, it is essential to fabricate composite films with interfacial robustness to extend their operational lifespan considerably.
Metal oxide is typically considered to be resistant to oxidation and erosion.However, it is a significant challenge to directly deposit inorganic oxide films onto flexible substrates, making interfacial structure regulation crucial.Our previous work has demonstrated that CrO x /CuNi-polyimide composite films based on multitechnology integration show good AO resistance and electrostatic dissipation as they ensure sufficient interfacial adhesion strength. 33However, the accumulation of O in CrO x films can lead to toughness reduction, crack initiation, and propagation, resulting in the interface delamination and debonding of the composite films.In addition, apparent holes and local amorphous state of the Fe + -irradiated CrO x can be detected after a high irradiation dose of 10 17 atoms/cm 2 , and its lattice swelling rate is approximately 11.22%.Thus, it is necessary to further improve the comprehensive properties of the composite film and to discuss the interfacial evolution mechanism in detail.
ZnO, a kind of self-excitation semiconductor with high saturated carrier mobility, has attracted extensive attention in optoelectronics. 34Herein, we develop a ZnO/ CuNi-polyimide composite film with the interfacial synergistic effect of chelation and cross-linking fabricated by the multi-technology integration of ion implantation (IIP), filter cathode vacuum arc (FCVA), and high-power impulse magnetron sputtering (HiPIMS).The ZnO/ CuNi-polyimide composite film shows remarkable AO and irradiation durability, sufficient electrostatic dissipation capacity, and mechanical robustness.Consequently, our fabrication approach for composite films based on multi-technology integration shows potential for aerospace applications and deployment.

| Substrate preparation
Polyimide sheets (Kapton HN, PMDA-ODA) with thicknesses of 50 and 150 μm were used for deposition from DuPont.These sheets were ultrasonically cleaned sequentially with absolute ethanol and deionized water and then thoroughly dried.

| Fabrication details
The fabrication schematic of the ZnO/CuNi-polyimide composite film is shown in Figure 1A-C.IIP and FCVA were carried out using multimodule surface treatment equipment assembled with metal vapor vacuum arc (MEVVA) ion sources.The polyimide sheets were pasted on a rotatable stage directed toward plasma transmission.A vacuum system was used to establish a background pressure of 10 −4 Pa.A MEVVA ion source triggered the generation of a Ni + -ion beam with an energy of 11.5 keV to the polyimides, and the cumulative dose was set to 6 × 10 15 ions/cm 2 .Subsequently, CuNi alloy buffer layers were deposited on the implanted polyimides using a cylindrical NiCu alloy cathode (60:40 at%).A 135°m agnetic filter elbow was used to dislodge neutral droplets.CuNi buffer layers with a thickness of ~28 nm were obtained by deposition for 5 min.A HiPIMS device was used to deposit ZnO films on CuNi-polyimides by sputtering a cuboid Zn (99.99 at%) cathode.The CuNi-polyimides were placed on a stage at a distance of 25 cm from the cathode.A vacuum system was used to establish a background pressure below 5 × 10 −4 Pa.A  To investigate the structural transformation in the polyimide subsurface during the process of IIP, we first analyzed the ion range and damage distribution using stopping and range of ions in matter (SRIM) simulation.The Ni + distribution, irradiation damage dose, and energy dissipation mode of the Ni + -implanted polyimide are shown in Figure S3.The peak irradiation damage dose and Ni + concentration were found to be 6.29 dpa (11.2 nm) and 4.77 at% (19.2 nm), respectively.These values indicate that the implants of Ni + are embedded into the subsurface of the polyimide.Then, the architectural evolution of the Ni + -implanted polyimide was analyzed using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) spectra.The minority characteristic peaks revealed weakening but no shift of the initial intensity after Ni + implantation, as shown in Figure 2A.Similar phenomena have been observed in our previous work, which indicates the fracture of C=O and C-N in PMDA due to IIP. 7 In addition, the amplified ATR-FTIR spectra obtained for the Ni + -implanted polyimide indicated notable texture transformations,  S4).Therefore, we can conclude that during the process of IIP, the chelation reaction occurs between energetic Ni + ions and polyimide units, leading to the formation of interconnection bond networks and the mixing of interface species into the subsurface.
The detailed reaction mechanism in the Ni + -implanted polyimide is further revealed by reactive molecular dynamics (ReaxFF-MD) simulation (Figures 2C,D).In general, incident particles undergo a series of cascading atomic collisions, resulting in their kinetic energy dissipation and eventual retention in the polyimides.Also, sufficient energy transfer causes the target atoms to be displaced.In addition, the energy transfer stemming from the elastic collision induces the breakage of chemical bonds and the separation of radicals and free atoms.The proximity of separated atoms promotes the generation of new bonds. 35In this case, the energy transfer arising from the elastic collision is much greater than the fracture energies of C=O, C-N, and C-H.Thus, several corresponding chemical bonds begin to break, accompanied by the generation of radicals and the emission of free atoms (O, N, and H).During the subsequent relaxation, these free atoms approach other radicals to form amide (-NHCOR) and amine (-NHR) groups.Additionally, we observed a chelation reaction between incident Ni + ions and PMDA units, which resulted in the formation of Ni-N and Ni-O groups.Due to the cascade effect, the above chemical rearrangements will be extended to the whole slab until the system's kinetic energy is completely dissipated.The interfacial architecture of the ZnO/CuNi-polyimide composite film is examined by bright-field cross-sectional transmission electron microscopy (BF-XTEM) and selected area electron diffraction (SAED), and the results are shown in Figures 1E and 3. A dense architecture with well-defined interfaces is identified in the BF-XTEM micrograph.In addition, the energy-dispersive spectrometer (EDS) mapping diagrams (insets in Figure 3A) indicate an even elemental distribution without agglomeration.To explore the architectural transformation of the Ni + -implanted polyimide, the matrix is divided into a miscellaneous interfacial zone, a cascade damage zone, and a pristine polyimide zone based on the SRIM simulation.As shown in Figure 3B, a miscellaneous interfacial zone with a thickness of approximately 4.5 nm is observed, stemming from the coupling effect of the high-energy Ni + -ion implantation on the establishment of a chelating bond interconnection network and the energetic CuNi plasma shallow injection on the promotion of local epitaxial growth.In addition, the lower region of the miscellaneous zone corresponds to the semicrystalline polyimide, and the phase transformation mechanism needs to be further elaborated.In the cascade damage zone, the SAED pattern indicates a hexagonal β-C 3 N 4 phase with a nanopolycrystalline architecture (Figure 3D), while in the pristine polyimide zone, the dispersive SAED pattern indicates an amorphous state of the pristine polyimide (Figure 3C).Combined with the above results, it is speculated that the coexistence of chelation and cross-linking arises from carbonyl deoxygenation and imide cleavage.Cross-linking promotes the generation of delocalized conjugated π bonds and induces the formation of new C-N bonds and the nucleation and growth of CN x crystallites through chain transfer, which increases the surface hardness of polyimide 36,37 and is advantageous for the subsequent growth of the CuNi alloy buffer.
The microstructure of the CuNi buffer is investigated by (X)TEM and SAED (Figures 3E, S5, and S6).The thickness of the CuNi buffer is approximately 28 nm, and the interfacial flexible deformation between CuNi and ZnO is probably due to the localized strain energy dissipation at the interface.The compact microstructure of the CuNi buffer is observed on the surface BF-TEM micrograph (Figure S6A).The SAED pattern indicate a face-centered cubic α-(Cu-Ni) phase with a nanopolycrystalline architecture.In addition, the average grain size is statistically calculated to be approximately 18.2 nm, and the interplanar spacing of the preferred (111) orientation is approximately 2.09 Å.According to the previous phase diagram research, the α-(Cu-Ni) phase shows an archetypal substitutional solid solution state, and the Ni element, as a substitution element, is soliddissolved into the α-Cu matrix. 38Conspicuously, the α-(Cu-Ni) phase invariably shows the characteristics of excellent toughness and strength due to its supersaturation and solid solution ability, which is advantageous for the architectural synergism deformation capability and deposition of ZnO films. 39XPS is conducted to quantitatively analyze the chemical composition of the pristine polyimide, the CuNi buffer, and the ZnO film (Table 1).The diversity of plasma transmission behavior leads to inconsistencies in the component proportions between the CuNi buffer and the target.In addition, the detected C component originates from surface contamination.Moreover, the lack of surface N in the CuNi buffer and the ZnO film indicates consecutive and non-defective coverage.
The architectures of the ZnO film are investigated in depth by scanning electron microscopy (SEM), atomic force microscopy (AFM), TEM, and SAED (Figures 1D and S7).The surface and cross-sectional SEM micrographs confirm the dense and uniform morphology with a hexagonal grain microarchitecture.Also, the root-mean-square roughness is estimated to be 3.1 nm.The BF-TEM micrograph and SAED pattern indicate a wurtzite ZnO P63mmc (186) phase with a smooth nano-polycrystalline architecture of the ZnO film, and the average grain size is statistically calculated to be 7.55 nm.Besides, the interplanar spacing of the preferred ZnO(100) orientation is approximately 2.92 Å.In addition, the inverse fast Fourier transform (IFFT) illustrations of the high-resolution TEM (HRTEM) micrograph indicate the existence of lattice distortions.In this test, the exposure time is increased to achieve an AO fluence of up to 8 × 10 20 atoms/cm 2 , which corresponds to AO exposure in the LEO (ram direction) with an orbital altitude of 600 km for 25 years.The AO erosion kinetics and degradation characteristics of pristine polyimide films have been extensively reported.Also, the value of Δm linearly increases with AO accumulation, and E y is a constant value of 3.0 × 10 −24 cm 3 /atom.In addition, the elimination of distinct functional groups (C=O, C-N, and C-O-C) is the critical consequence of AO erosion.The coarse microstructure of the exposed polyimide indicates the emission of volatile species and severe failure. 33he AO erosion kinetic and morphological variations of the ZnO/CuNi-polyimide composite film are shown in Figure 4A,B.After composite film deposition, E y decreases by 43.6-fold.With AO accumulation, the slope of the Δm curve first increases, then decreases, and then increases again, and the lowest E y value is 6.88 × 10 −26 cm 3 /atom.The minimal Δm value of approximately 0.070 mg/cm 2 is due to increased oxidation, which promotes AO durability to sputtering and penetration.Also, the exposed morphology indicates the existence of large-scale oxidation and polygonal grains.Besides, no significant cracks, debonding, and other undercutting defects are detected.The ZnO/CuNi-polyimide composite film also shows superior AO resistance (E y = 6.88 × 10 −26 cm 3 /atom) compared to previously reported polyimide-based composite films when the AO fluence reached 8 × 10 20 atoms/cm 2 (Figure S8).
XPS spectra are conducted to reveal the chemical species transformation of the ZnO/CuNi-polyimide (Figure 4C).The Zn 2p spectral peaks with spin splitting shift to 1021.3 (Zn 2p 3/2 ) and 1044.4 eV (Zn 2p 1/2 ), which are all mostly assigned to hexagonal wurtzite ZnO.Before the AO exposure, the fine O 1s spectra are separated into loosely bound O (531.7 eV), O vacancies (530.7 eV), and O-Zn (529.9 eV).In general, loosely bound O is related to the surficial chemisorption of oxygen or moisture (H-O-Zn).After AO exposure, the new dominant peaks at approximately 528.7 eV in the O 1s spectrum are attributed to O-Mo and O-W, which are contaminants of the grid and filament.Although it is very difficult to fit them separately, the component ratio of the mixed state is strongly linked to the AO penetration resistance and roughness.
ReaxFF-MD simulations are performed to reveal the detailed material degradation mechanism during the AO exposure.The thermal nephograms and system temperature evolution of polyimide and wurtzite ZnO under continuous AO exposure are shown in Figures S9A and S10A, respectively.The temperature evolution of the system is used to characterize the atomic thermal motion and evaluate the sensitivity of the target to AO exposure.In most cases, a rapid increase in system temperature can accelerate the escape of surface atoms.Here, the system temperature increases with the accumulation of AO collisions, and the final average temperatures of the polyimide and ZnO slabs are approximately 789.6 and 1034.8K, respectively.
The dissociated chemical species, normalized slab masses, and critical snapshots of polyimide and wurtzite ZnO under continuous AO collision are shown in Table S2, Figures S9B, and S10B, respectively.Compared with the polyimide slab, ZnO is relatively stable during AO collision, and only a few atoms or small molecules separate.Therefore, we only count the escaped species after the first 100 and 300 AO collisions.During the first 50 AO collisions for the polyimide, only micromolecules (such as CO, C 2 H, and C 4 H 3 ) dislocate from the slab.As the number of AO collisions increase, AO erosion permeation is accompanied by the separation of macromolecules (such as C 6 H 4 ON and C 14 H 6 O 3 N).In the first stage (0-5 ps), AO collisions induce the escape of small molecules from the polyimide surface.Due to the limited number of atoms in the system and the stretching of the box in the Y direction, there is not enough time for these free groups to escape from the box, leading to a slightly increased normalized slab mass.In the second stage (5-10 ps), the small molecules that separated in the previous stage completely escape from the box, and Δm of the system is relatively stable, which better represent the AO erosion characteristics of polyimide.In the third stage (10-30 ps), excessive AO collisions induce dynamic disintegration and reconstruction of the polyimide unit, resulting in the systematic rapid fluctuation and increase of Δm and E y .The average simulated E y value is estimated to be 1.035 × 10 −23 cm 3 /atom (100 AOs), and the result is due to the configuration volume and thermal dissipation.During the first 100 AO collisions for ZnO, 65 AO react with the sample surface and lead to advanced oxidation, 5 AO collide with O atoms in ZnO and release O 2 , while other AOs escape from the box after elastic collision or replacement with surface O atoms.After 300 AOs are emitted, 165 participate in the chemical reaction, but no Zn or ZnO sputtering is detected, and the final oxidation depth is approximately 8.05 Å.The lower oxidation depth indicates that ZnO shows better AO diffusion barrier ability and has stronger resistance to AO erosion.In addition, the normalized slab mass curve indicates a continuous increase in the system's quality, corresponding to the absence of material dynamic disintegration.Because of its good compactness and high chemical stability, it can prevent surface sputtering and longitudinal AO diffusion and greatly improve AO durability.

| Ground-based ion irradiation
The space orbit is a high-radiation environment, which is composed of captured radiation (radiation belt), galactic cosmic rays, and solar flare particles.It contains a large number of high-energy charged particles, such as electrons (MeV), protons (MeV), α and γ particles, and heavy ions. 40lthough heavy ion irradiation is not dominant in the LEO environment, it still poses a major hazard in flight missions.Figure S11 shows the Fe + distribution and irradiation damage dose of the Fe + -irradiated ZnO film calculated by SRIM simulation.The peak irradiation damage doses are 175.90 and 353.38 dpa (36.0 nm), respectively.
The irradiation damage and architecture transformation of the Fe + -irradiated ZnO/CuNi-polyimide composite film are investigated by XTEM and SAED (Figure 5).Intact crystallographic characteristics before and after irradiation are observed, and no significant transformation are detected in the SAED patterns.However, the formation of the hexagonal FeZn 7 P63mmc (194) phase is demonstrated in the SAED pattern when the irradiation dose increases to 10 17 atoms/cm 2 , which is attributed to the micro-zone melting induced by the thermal spike effect stemming from the rapid energy transfer during Fe + irradiation.The EDS mapping diagram of Fe in Figure S12 confirms this finding.In addition, nanocrystalline morphological characteristics with subtle grain swelling after Fe + irradiation but no dislocation lines or dislocation rings can also be demonstrated.As shown in Figures S14 and S15, the average grain size initially increases from 7.55 nm to 9.89 nm and then increases to 10.40 nm.Using IFFT micrographs (Figures S13, S16, and S17), the average interplanar spacings of the preferred (100) orientation of the wurtzite ZnO P63mmc (186) crystal network are statistically estimated to be 0.294 and 0.293 nm for the Fe + -irradiated ZnO/CuNipolyimide at irradiation doses of 5 × 10 16 and 10 17 atoms/ cm 2 , respectively.The lattice swelling rates are calculated to be 0.3%-0.7%,which is almost negligible.Low-density radiation-induced damage defects are identified inside the nanocrystalline grains, which are attributed to impurity defects or small vacancy clusters.Moreover, lattice distortion and dislocations in the grains are observed.We have suggested that the ZnO nanocrystalline film can maintain a grain size of 7.55 nm.Also, the detailed irradiation resistance mechanism should be elaborated in depth.
In general, pervasive grain boundaries (GBs) supply many defect traps, which induce defect annihilation and reduce the concentration of residual defects, resulting in their aggregation, which induces crystallographic defects such as atom-poor regions, microcavities, and dislocation loops. 41Therefore, it is crucial to control the nanocrystalline size to enhance the irradiation resistance.An alternative explanation is the latent lattice distortion inside the nanocrystalline grain, which plays a critical role in obstructing defect migration, leading to few defect clusters and a low probability of defect aggregation. 42Moreover, the microdefects show a preference to disperse and move toward the free surfaces of thin films, resulting in a rapid decline in the number of residual defects. 43In conclusion, the ZnO film can maintain an ultrafine nanocrystalline architecture with minimal lattice swelling after Fe + -irradiation at a high irradiation dose of 353.4 dpa.This is related to defect absorption by pervasive grain boundaries, defect migration inhibition by latent lattice distortion, and defect movement toward the free surfaces.

| Electrostatic dissipation characterizations
For imperfect conductors, high-energy ion beams (HEIBs) for Rutherford backscattering spectrometry (RBS) tests induce surface charge accumulation for specimens, resulting in intricate spectroscopic distortion. 29,44However, this kind of charge accumulation can be quantified using available physical models to simulate ESC events in an aerospace environment.As shown in Figure 6A, the accumulated potential φ calculated from the energy drift (ΔE) between the experimental and simulated RBS spectra for the ZnO/CuNi-polyimide is estimated to be 19.38 kV.Also, Kelvin probe force F I G U R E 5 SAED pattern and BF-XTEM and HRTEM micrographs of (A) pristine and Fe + -irradiated ZnO/CuNi-polyimide composite films at doses of (B) 5 × 10 16 and (C) 10 17 atoms/cm 2 .BF-XTEM, bright field cross-sectional transmission electron microscopy; HRTEM, high-resolution transmission electron microscopy; SAED, selected area electron diffraction.microscopy (KPFM) schematics and the relative potential distribution of the ZnO/CuNi-polyimide composite film are shown in Figures 6B and S18, respectively.A Au film is deposited on the surface for standard potential calibration.The relative potential difference (ΔP) between the ZnO/CuNi-polyimide and Au is 43.52 mV.In our previous report, φ and ΔP for the pristine polyimide are calculated to be 39.68 kV and 345.15 mV, respectively. 27The substantial decrease in φ and ΔP detected for the ZnO/CuNi-polyimide composite film indicates its enhanced surface conductivity and electrostatic dissipation ability to alleviate ESC/ESD risks.In addition, its electrostatic dissipation ability is also superior to that of previously reported TiO 2 -polyimide composite films. 45

| Mechanical stability characterizations
Mechanical robustness is critical for polymer protection when using film technology in LEO environments.Composite films need to have excellent membrane substrate deformation performance and flexibility and high interfacial adhesive strength to cope with the AO undercutting effect and polymer failure stemming from cracking or spalling of the protective films. 46Therefore, we conduct a set of nanoindentation and cyclic bending tests to evaluate the mechanical robustness of the composite film.Figures 6C  and S19 show the hardness (H), effective Young's modulus (E*), and contact stiffness (S) values of the ZnO/CuNipolyimide composite film.The average values are estimated to be 1.21 GPa, 15.73 GPa, and 4.01 μN/nm, respectively.Generally, the eigenvalues H/E* (0.077) and H 3 /E* 2 (0.007) are considered to represent elastic deformation recovery capacity and plastic deformation resistance, respectively.These eigenvalues are related to the toughness of the composite film, and increases in these values indicate expansion of the release region of applied load, which can suppress the initiation of cracks.Additionally, the existence of pervasive GBs in nanocrystalline architecture can restrict the propagation of cracks, thereby improving the mechanical stability of the ZnO/CuNi-polyimide composite film.Figure S20 shows a schematic diagram and the morphologies of the ZnO/CuNi-polyimide composite film after cyclic bending cycles.The absence of delamination, spalling, and initiation of normal cracks in the representative fracture morphology indicates the toughness characteristics of the ZnO/CuNi-polyimide.The rapid increase in tensile stress will induce the initiation and propagation of axial cracks in the high-strain zone.The axial crack density of the ZnO/ CuNi-polyimide composite film is 15.22 mm −1 , which is superior to that of our previous reports. 3,27The dilapidated fragments filling the cracks can alleviate AO undercutting and extend the service life of the composite film.In addition, long-term thermal cycling in an LEO environment will induce thermal stress accumulation, resulting in interfacial delamination and microcrack initiation.Therefore, a set of thermal fatigue tests (±200°C, 10 × 30 min) is performed to test the stability of the ZnO/CuNi-polyimide composite film.Surface SEM investigations indicate its well-defined morphology after the thermal fatigue tests (Figure S21).Moreover, the substantially increased crack number and density (20.76 mm −1 ) of the ZnO/CuNi-polyimide composite film successively subjected to cyclic thermal fatigue and bending are attributed to the rapid accumulation of thermal stress inside the interfacial architecture.Since film delamination will induce the complete failure of polymer substrates, we performed electroplating to increase the thickness of the CuNi buffer and determine the interfacial adhesion using a 45°peeling test.The interfacial adhesion is 1.93 ± 0.21 N/mm, which is superior to that of a general surface-metalized polyimide (7 × 10 −3 -1.2 × 10 −2 N/mm). 47mprovement in the interface adhesion can suppress strain localization arising from partial delamination, and has also been proven to be a typical approach to alleviate crack initiation for the metal/polymer systems. 48Therefore, it can be concluded that the multi-technology integration of IIP, FCVA, and HiPIMS to realize interfacial architecture regulation is an effective approach to obtain mechanically robust composite films.

| CONCLUSION
In summary, we develop a ZnO/CuNi-polyimide composite film with the interfacial synergistic effect of chelation and cross-linking fabricated by multitechnology integration, showing greatly enhanced AO and irradiation durability, sufficient electrostatic dissipation capacity, and mechanical robustness.The AO erosion yield (E y ) value of 6.88 × 10 −26 cm 3 /atom for the ZnO/CuNi-polyimide composite film is only 2.29% of that for pristine polyimide (Kapton H).Additionally, the Fe + -irradiated ZnO/CuNi-polyimide can still maintain a well-defined nanocrystalline state with minimal lattice swelling (0.3%-0.7%) at an irradiation damaging dose of 353.4 dpa.Moreover, the quantitative results of RBS spectral distortion and surface potential highlight the advantages of the composite film in addressing potential ESC/ESD risks.Thus, the unique interfacial architecture regulation by multi-technology integration provides a potentially useful template for the design and fabrication of other composite films with augmented permanence for diverse applications.In the future, improved film stress regulation and exploration of the AO chemical reaction path will be explored.The former needs to be improved by optimizing the pulse power supply system and deposition parameters, while the latter can be investigated using the 18 O isotope tracing method combined with nuclear reaction analysis (NRA) technology.

F I G U R E 1
Fabrication and interfacial architecture evolution of the ZnO/CuNi-polyimide composite film via an integration of (A) MEVVA-IIP, (B) FCVA, and (C) HiPIMS.The illustration in the middle indicates the interfacial architecture evolution of the ZnO/CuNipolyimide composite film.(D) AFM, (E) BF-XTEM, and (F) physical images of the ZnO/CuNi-polyimide composite film.AFM, atomic force microscopy; BF-XTEM, bright field cross-sectional transmission electron microscopy; FCVA, filter cathode vacuum arc; HiPIMS, highpower impulse magnetron sputtering; MEVVA, metal vapor vacuum arc.Hall ion source system was used to remove surface contamination.A ZnO film with a thickness of approximately 200 nm was deposited for 12 min with an Ar fluence ( f Ar ) of 80 sccm and an O 2 fluence ( f O 2 ) of 80 sccm.The HiPIMS supply power was progressively increased to 3 kW.All characterization methods and simulation details are described in Supporting Information (SI).

3 | RESULTS AND DISCUSSION 3 . 1 |
General characterizations of the ZnO/CuNi-polyimide composite film 3.1.1| Textural evolution of the Ni +implanted polyimide

F
I G U R E 2 (A) ATR-FTIR and (B) fine XPS spectra of the Ni + -implanted polyimide.(C) Critical snapshots of the chemical species evolution.(D) Reaction mechanism of the Ni + -implanted polyimide.ATR-FTIR, attenuated total reflection Fourier transform infrared spectroscopy; XPS, X-ray photoelectron spectroscopy.especially evidenced by the emergence of a sharp peak at approximately 2345 cm −1 .The transformations are related to the fracture of imide and the formation of aldehyde, amide, and a Ni-N chelate by identification of the presence of distinct functional groups.Moreover, three subtle characteristic peaks appeared at 407, 419, and 458 cm −1 , indicating the formation of Ni-O bonds, and three subtle characteristic peaks occurred at 2818, 2930, and 3210 cm −1 , indicating the formation of aldehydes and imines, respectively.Figure 2B shows the exemplary XPS spectra, which demonstrate the chemical intermixing of the Ni + -implanted polyimide.Before Ni + -IIP, the O 1s spectrum of the pristine polyimide is decomposed into spectra corresponding to two distinct species associated with C=O (531.74 eV) and C-O-C (533.10 eV).After Ni + IIP, the subtle reduction in the intensity and major expansion of the full width at half maxima (FWHM) indicate the elimination of C=O and the generation of Ni-O (530.30eV), respectively.In addition, analogous spectral transformations in the N 1s spectra of the pristine and Ni + -IIP polyimides suggest the general breakage of C-N and the generation of a Ni-N chelate.The Ni 2p spectrum also confirmed all the above inferences (Figure

F
I G U R E 3 BF-XTEM micrograph, HRTEM micrographs, SAED patterns, and EDS-mapping of the ZnO/CuNi-polyimide interfacial architecture: (A) overall cross-section, (B) miscellaneous interfacial zone, (C) pristine polyimide zone, (D) cascade damage zone, (E) CuNi buffer, and (F) ZnO film.BF-XTEM, bright field cross-sectional transmission electron microscopy; EDS, energy dispersive spectrometer; HRTEM, high-resolution transmission electron microscopy; SAED, selected area electron diffraction.T A B L E 1 Chemical compositions of the polyimide, the CuNi buffer, and the ZnO film.

F
I G U R E 6 (A) Experimental RBS spectrum and magnified experimental and simulated RBS spectra of the ZnO/CuNi-polyimide composite film.(B) Potential image and curve of the Au-ZnO/CuNi-polyimide composite film for KPFM characterization.(C) Hardness (H) and effective Young's modulus (E*) lattices of the ZnO/CuNi-polyimide composite film.KPFM, Kelvin probe force microscopy; RBS, Rutherford backscattering spectrometry.