Metal Organic Framework Template-Guided Electrochemical Lithography

doi:10.21203/rs.3.rs-2480225/v1

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Metal Organic Framework Template-Guided Electrochemical Lithography

https://doi.org/10.21203/rs.3.rs-2480225/v1

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published 20 Sep, 2023

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The templating method is promising in fabrication of surface nanopatterns. Exploring new functions of the templates besides the masking and the molding function are important to strengthen their manufacturing capability towards complex surface nanopatterns. Here, we employed the metal organic framework (MOF) octahedra assembled monolayer as a template to perform metal electrodeposition and revealed the previously unidentified guiding growth mode capable of growing metallic films exactly underneath the MOF octahedra. The fast ion transport within the nanochannels of the MOF octahedral accounted for the guiding growth mode proven by the experimental measurements and the molecular dynamics simulations. The MOF template could be repeatedly used to create the same metallic surface nanopatterns on different substrates. The recyclability and the feasibility to create fine MOF nanopatterns using sophisticated lithographic methods endow the MOF’s guiding growth mode with great potentials in creating complex metallic surface nanopatterns at a low cost.

Physical sciences/Materials science/Nanoscale materials/Synthesis and processing

Physical sciences/Nanoscience and technology/Techniques and instrumentation/Surface patterning

Metallic nanopatterns play vital roles in plasmonics, sensing, metamaterials, and biological fields^[1-3]. A variety of methods have been developed to prepare metallic surface nanopatterns, including electron-beam and photo-lithography^[4,5], microcontact or printing^[6,7], imprinting^[8], and laser or micro-cutting^[9]. But these methods are often expensive and equipment-intensive, involve multiple cumbersome and time-consuming steps, or require aggressive chemistry. Nanospheres can spontaneously assemble into large-area ordered monolayer arrays in seconds^[10,11]. Relying on the self-assembled nanosphere array templates, the colloidal lithography method is invented to prepare large-area metallic surface nanopatterns at an extremely low cost^[12-14]. The self-assembled nanosphere templates can behave as a mask during thermal evaporation of metallic films to produce bow-tie antenna surface nanopatterns^[15], or act as a mold to occupy the space during electrodeposition growth of metals to generate nanobowl arrays^{[12,13,16,17]} (Fig. 1a). Actually, all of the existing templates play either the masking or the molding function, limiting the structural diversity of the translated surface nanopatterns^[14]. Exploring new functions of the self-assembled templates is important to strengthen their nanopattern design capability.

Metal organic framework (MOF) is a class of crystalline materials composed of coordination bonds between metal ions and multidentate organic linkers forming interconnected size-designable nanochannels^[18-20]. Simple high throughput chemical processes have been developed to prepare MOF nanoparticles with well-defined morphologies^[21-23]. These MOF nanoparticles can self-assemble into three-dimensionally ordered structures^[24]. Comparatively, simple approaches that can assemble MOF nanoparticles into large-area, two-dimensionally ordered monolayers are still highly desirable^[25]. Consequently, the monolayer MOF nanoparticle template has never been used as templates to design surface nanopatterns. On the other hand, ion channels within the cell membranes can selectively allow the desired ions to pass through to directly influence the life or disease processes^[26,27]. In contrast, the MOFs are currently only explored as a filtering membrane to separate ions or gases according to their size match with the nanochannels within MOFs^[28-30]. We envision that immediate electrochemical reduction of the metal ions selectively passed through the nanochannels within the MOF nanoparticle template can create new surface nanopatterns different from those obtained from conventional colloidal lithographic methods.

Here, we discover a previously unidentified guiding growth function of the MOF template capable of directing the electrochemical growth of metals at the bottom of the MOF template, giving rise to the formation of metal nanopatterns exactly the same as the MOF/substrate interface area (Fig. 1b). More importantly, the guiding and the molding function of the MOF template can be adjusted by varying the metal ion concentration in the electrolyte, resulting in different metal nanopatterns. The switchable growth mode between guiding and molding of the MOF template revolutionized the function of conventional colloidal templates. Additionally, the MOF template can be recycled for multiple times. We expect that the guiding growth function and the recyclability of the MOF template can greatly strengthen the capability of colloidal lithography to design complex surface nanopatterns, particularly after considering that fine nanopatterns of MOFs can be created by sophisticated electron beam lithographic methods^[31,32].

Fabrication of the MOF template via a self-assembly process

UiO-66 is a kind of chemically stable MOFs and can be easily prepared in different morphologies and sizes. Therefore, we chose UiO-66 octahedron monolayer template as an example to show the template-guided electrochemical growth mechanism. The UiO-66 octahedra were prepared via a solvothermal method using the acetic acid (AA) as a modulator^[24]. The prepared UiO-66 octahedra were well-dispersed with a narrow size distribution (relative standard deviation: < 8%) (Fig. 2a and b). As examples, we prepared UiO-66 octahedra with a mean edge size of 650 nm, 900 nm, and 1150 nm (Supplementary Fig. 1). The edge size of the UiO-66 octahedra could be varied from < 100 nm to more than 100 µm^{[33, 34]}. The pore sizes inside the UiO-66 octahedra were determined by a density functional theory method based on nitrogen adsorption-desorption isotherm profiles (Supplementary Fig. 2). The UiO-66 contained small cages with a 0.6 nm opening size, large cages with a 0.9 nm opening size^{[35, 36]}, and pores with a wide size distribution centered at 1.5 nm caused by missing linkers and clusters due to the substitution of AA for 1,4-benzene-dicarboxylate (BDC)^[37] (Fig. 2c). These cages connected into a string with the small cages and the triangular windows serving as the choke points at intervals (inset in Fig. 2c). The X-ray diffraction (XRD) pattern confirmed the octahedra were UiO-66 (Fig. 2d). The synthesized UiO-66 octahedra were well-dispersed and stored in deionized water at a concentration of 200 mg ml^− 1.

Fabrication of monodispersed UiO-66 octahedra with a narrow size distribution is a prerequisite to assemble them into a monolayer with few defects. Spherical nanoparticles contact with their neighbors through a point. Therefore, it is easy to adjust the position to form a monolayer during the self-assembly process. In contrast, the octahedra interact with their closely packed neighbors through the side faces in an antiparallel manner^[38] (Fig. 2e), making the monolayer assembly challenging. Inspired by the formation process of polystyrene sphere monolayers at the air/water interface, we introduced different amounts of ethanol into the UiO-66 octahedron dispersions to adjust the surface tension before dropping the solution mixture onto the center of a piece of hydrophilic glass slide almost covered by water (Supplementary Movie 1). The octahedra in the solution mixture were trapped at the water surface and spreaded from the center to the surrounding area of the water surface. This behaviour was governed by the gradient of the surface tension, known as the Gibbs-Marangoni effect^[39] (Fig. 2e). We discovered that the ideal volume ratio beween ethanol and water in the octahedron dispersions was 4:6 to create the appropraite surface tension gradient. Otherwise, multiple layers or large cracks would form during the assembly process (Supporting Fig. 3). In the period of dropping the solution mixture drop by drop onto the glass slide, more and more octahedra got invovled into the assembly porcess until forming a compact monolayer (Fig. 2f). The bright iridescence indicated the ordered arrangement of the UiO-66 octahedra within the compact monolayer at the water surface. The free-standing UiO-66 octahedron monolayer at the water surface could be transferred onto any arbitrary substrate by picking it up from the bottom (Fig. 2g). All of the UiO-66 octahedra within the monolayer array used their {111} triangular facets to contact the substrate (Fig. 2g), which was also reflected from the XRD pattern with a strong diffraction peak from the {111} facets (Fig. 2d). Small cracks might form during the monolayer transferring process from the water surface to the substrate.

MOF template-guided electrochemical lithography

We performed electrodeposition of Ag in the electrolyte composed of 300 mM AgNO₃ and 14 mM sodium dodecyl sulfate (SDS) under 1.2 V with the UiO-66 octahedron monolayer on the Au-covered silicon wafer as the cathode electrode. Different from any existing templates, each UiO-66 octahedron within the monolayer template behaves analogous to a nanonozzle in 3D printing during electrodeposition, exclusively creating Ag nanofilm at the interface between the octahedron and the substrate. This means that smaller Ag nanofilm can be anticipated by reducing the interface area between the UiO-66 and the underneath substrate. The electrodeposited Ag nanofilm lifted up the UiO-66 octahedron monolayer (Fig. 2h), instead of the expected growth within the crevices between adjacent octahedra^[12–17] (Fig. 1a). After removing the UiO-66 octahedron monolayer template, an Ag nanotriangle array was obtained (Fig. 2i). Notably, the arrangement of the Ag nanotriangles is completely different from that of the Ag nanotriangles within the surface nanopatterns prepared by the colloidal lithography method, which uses the nanosphere monolayer as a mask during thermal evaporation of Ag. The colloidal lithography created nanotriangles forming a honeycomb array with a large inter-nanotriangle distance and with their tips pointing towards the tips of adjacent nanotriangles (Fig. 1a). In contrast, the nanotriangles grown under the guidance of the UiO-66 template were hexagonally arranged inherited from the arrangement of the UiO-66 octahedra in the monolayer template and the tips of the nanotriangles pointed to the middle of the edges of the adjacent nanotriangles (Fig. 2i). The cross-sectional view revealed that the thickness of the nanotriangles was much larger than the Ag nanofilm electrodeposited on the bare Au surface (Fig. 2i). Monitoring the thickness evolution of the nanotriangles during electrodeposition further confirmed the rapid growth rate (~ 1.67 nm/s on average) of the Ag nanofilm underneath the UiO-66 octahedra, which was at least ten times faster than that on the bare Au surface (~ 0.15 nm/s) (Fig. 2j and Supplementary Fig. 4).

Growth mode diagram as a function of C_AgNO3 and C_SDS

We further discovered that the concentration of silver ions (C_AgNO3) and SDS (C_SDS) within the electrolyte could switch the function of the UiO-66 octahedron template (Fig. 3a, b, and Supplementary Fig. 5). When C_AgNO3 > 150 mM and C_SDS > 7 mM, the UiO-66 octahedron monolayer played the guiding growth function, resulting in the formation of Ag nanotriangle patterns (Region I in Fig. 3a and b). In a sharp contrast, the UiO-66 octahedron monolayer switched to the molding mode as C_AgNO3 < 150 mM and C_SDS > 1.4 mM, resulting in the formation of nanoframe arrays (i.e., complementary to the nanotriangle pattern created under the guiding growth mode) (Region II in Fig. 3a and b). When C_SDS < 1.4 mM, large junks with irregular shapes were formed on the top of the UiO-66 octahedron monolayer (Region III in Fig. 3a and b). In short, the guiding growth mode of the UiO-66 octahedron template needs high C_SDS and high C_AgNO3, which indicates the mechanism of the MOF-guiding electrochemical growth mode discussed below.

At the edge area of Region I, the nanotriangles were not flat with many defects (Fig. 3a and Supplementary Fig. 5). The nanotriangles were aggregations of Ag nanoparticles. At the edge area of Region II, Ag were electrodeposited both underneath and surrounding the UiO-66 octahedra. Without SDS in the electrolyte, the electrodeposited Ag formed large junks on the top of the UiO-66 octahedron monolayer. Therefore, SDS played important roles in refining the electrodeposited Ag grains.

It is critical to figuring out the unique guiding growth mechanism of the UiO-66 monolayer template. The opening size of the nanochannels (~ 0.6 nm) is larger than the size of the silver ions (~ 0.3 nm) but smaller than the size of SDS (~ 0.6 nm in width and ~ 1.8 nm in length)^{[40, 41]}. Therefore, silver ions can theoretically pass through the nanochanels within the UiO-66 octahedra. We proposed that the moving path of the silver ions determined the function of the UiO-66 monolayer template. When the silver ions prefer to pass through the UiO-66 octahedra via the inside nanochannels to reach the cathode surface, the silver ions will be immediately reduced once they contact the electrode surface and gradually form the nanotriangles. In constrast, Ag tends to grow surrounding the UiO-66 octahedra to form the nanoframe array if the silver ions prefer to pass through the UiO-66 octahedron monolayer via the electrolyte. Whether the silver ions choose the nanochannels within the UiO-66 or the electrolyte to pass through the UiO-66 octahedron monolayer should be influeced by C_AgNO3 and C_SDS.

Guiding growth mechanism

We performed the molecular dynamics (MD) simulations to demonstrate the transportation of the silver ions in the nanochannels in UiO-66. We applied the power-law form^[42] to express the one-dimensional diffusion of the silver ions within the nanochannels. Eq. (1) describes the hallmark growth of the mean squared displacement (MSD) in the course of time (Supplementary Fig. 6).

⟨|x(t) – x(0)|²⟩ = K_α · t^α (1)

where x(t) is the x coordinate of an individual silver ion at time t; K_α is the generalized diffusion constant, and α is the diffusive exponent. The x-axis is taken to be perpendicular to the Ag nanotriangle. Figure 3c plotted the variation of α as a function of the concentration of silver ions, where the change in the diffusion mechanism was identified. The α approached zero at low concentrations but increased to about two with increasing concentrations, indicating the switch of the diffusion behavior from oscillation to superdiffusion^{[43, 44]}. When the number of silver ions in each unit cell was less than five, the diffusion of silver ions was negligible, thus α equaled zero. In this case, the silver ions were confined within the nanocages and oscillated at each adsorption site. When the number of silver ions in each cell was more than five, the MSD exhibited a finite slope and α > 1 was detected. It is well known that Fickian diffusion and superdiffusion are expressed by α = 1 and α > 1, respectively. Fast ion diffusion can be attributed to the decrease in the activation energy barrier due to multi-ion concerted migration, as widely reported in nanopore transportation systems^[45–47]. Figure 3d displayed the trajectory of a typical single silver ion during 60 ps (the time for silver ions to complete a cycle) at high and low silver ion concentrations. At high concentrations, Coulomb interactions among silver ions were obvious and energy barriers among nearby nanocages were lower, given that abounding positive silver ions were confined in the narrow nanochannel. Therefore, the silver ions hopped rapidly from one nanocage to another in the direction of the external electric field (Supplementary Movie 2). Conversely, we proposed that silver ions were subjected to lower electrostatic repulsion forces when the number of silver ions in the nanochannel declined, so they rarely hopped out and trapped in the original nanocage^[48], Therefore, the snapshots of a silver ion overlapped throughout the time at low concentrations, indicating that it just vibrated at a fixed position (Supplementary Movie 3).

The octahedra tightly contacted with each other forming sandglass-shaped cavities with solid necks within the monolayer array (Fig. 3e), instead of forming through pores in traditional colloidal crystal templates composed of closely packed nanospheres. We pressed the UiO-66 octahedra into a thin film and measured the conductivity after placing the film as a separator in different electrolytes (Fig. 3f, Supplementary Fig. 7 and Fig. 8). SDS decreased the conductivity of the electrolyte arising from the trapping of the silver ions by the surfactant micelles. In contrast, SDS increased the conductivity of the UiO-66 thin film. In the electrolyte without SDS, silver ions were difficult to approach the opening of the nanochannel occupied by the silver ions because of the electrostatic repulsion forces. The negatively charged dodecyl sulfate ions weakly binding to the silver ions in the electrolyte weakened the electrostatic repulsion forces^[40], facilitating to deliver the silver ions to the opening area of the nanochannels. Additionally, SDS lowered the surface tension of the electrolyte, promoting the electrolyte to enter the nanochannels (Supplementary Fig. 9). Overall, the high concentration of silver ions and the existence of SDS in the electrolyte are critical to forcing the silver ions to choose the nanochannels within UiO-66 to reach the cathode electrode surface, resulting in the formation of nanotriangles (Fig. 3g). Otherwise, the silver ions would pass through the UiO-66 octahedron monolayer via the thinnest part-the solid necks of the sandglass-shaped cavities and reach the electrolyte surrounding the interface of the UiO-66 octahedra and the cathode electrode, leading to the formation of nanoframes (Fig. 3g).

Recyclability of the MOF template

Different from the conventional colloidal lithography technique where the colloidal templates are one-time use, the UiO-66 octahedron monolayer template can be used for multiple times. As an example, we used polybenzimidazole (PBI) to fix the “ZJU” letters formed by closely packed UiO-66 octahedra on a piece of glass slide because of its chemical stability, high mechanical strength and good ion conductivity^{[49, 50]} (Fig. 4a and b). The thickness of the UiO-66@PBI composite film is important because too thick will make it different to tightly attach to the substrate while too thin will be easily broken during the transferring process (Supplementary Fig. 10). The UiO-66@PBI film was detached from the glass slide by soaking it in 90 ^oC hot water for 24 h. Then, the UiO-66@PBI composite film was transferred onto a piece of Au-coated silicon wafer. After electrodeposition of Ag, “ZJU” letters formed by Ag nanotriangles were created underneath the UiO-66 octahedra (Supplementary Fig. 11). The adhesion force between the UiO-66@PBI film and the Ag nanotriangles was significantly weaker than that on the glass slide, because of the reduced interface area. Therefore, the UiO-66@PBI template could be easily peeled off from the underneath Ag nanotriangle patterns simply by immersing into ethanol and water in sequence. The detached UiO-66@PBI film would float on the water surface, which could be transferred onto another substrate and used to electrodeposit Ag nanotriangle patterns again (Fig. 4c).

The UiO-66@PBI template can be used to electrochemically print complex surface patterns (Fig. 4d). As an example, the UiO-66 octahedra were patterned to form the complex logo of Zhejiang University using a mask (Fig. 4d). Then, the pattern was fixed using the PBI film. The PBI film enclosed the top part of the UiO-66 octahedra (Fig. 4e). The UiO-66@PBI logo was translated into Ag nanotriangles formed one after Ag electrodeposition (Fig. 4d and Fig. 4f). Similarly, the UiO-66@PBI film was detached from the Ag nanotriangles by soaking it into ethanol and water in sequence and ready for reuse (Fig. 4d and Supplementary Fig. 12). MOFs could not only be fabricated into various faceted nanoparticles, but could be manufactured into fine nanopatterns using sophisticated lithography methods^{[31, 32]}. We anticipate to electrochemically print metallic surface nanopatterns using these fine MOF nanopatterns working under the guiding growth function. The recyclability of the MOF nanopatterns can greatly reduce the fabrication time and cost of the metallic surface nanopatterns.

In summary, we used the MOF template to electrochemically prepare metallic surface nanopatterns and discovered the unrevealed guiding growth function of the MOF template capable of growing metallic surface nanopatterns exclusively underneath the MOF template. The guiding growth mode was enabled by the fast ion transport in the nanochannels within the MOF template proven by the experimental measurements and the molecular dynamics simulation results. We could intentionally switch the guiding and the molding growth mode by adjusting the concentration of silver ions and SDS in the electrolyte. More importantly, the MOF template could be easily peeled off from the underneath metallic surface nanopatterns and be used again to fabricate the same metallic surface nanopatterns. The capability to manufacture MOF nanopatterns using sophisticated lithographic methods and their recyclability endow the MOF template with great potentials to create metallic surface nanopatterns in a low cost, high throughput, and time-preserving manner.

Materials.

Zirconium (IV) chloride (ZrCl₄, 99.9%) was purchased from Aladdin. Terephthalic acid (BDC, 99.0%), acetic acid (AA, 99.8%), dimethylformamide (DMF, 99.5%), methanol (99.5%), ethanol (AR) and silver nitrate (AgNO₃, AR) were purchased from Sinopharm Chemical reagent. Sodium dodecyl sulfate (SDS, 99.0%) was purchased from Innochem. Polybenzimidazoles (PBI, 98.0%) and N-methylpyrrolidone (NMP, 99.5%) were purchased from Macklin Biochemical.

Synthesis of the UiO-66 octahedra.

Monodisperse UiO-66 octahedra were synthesized according to previous reports with some modifications^[31]. Typically, 350 mg of ZrCl₄ and 249 mg of BDC were dissolved into 100 ml of DMF. The solutions were divided into five glass vials with an equal volume. After adding 2.73 ml of AA into each vial, they were placed in an oven at 120°C for 12 h. The products were centrifuged and washed twice with DMF and methanol, respectively. The collected UiO-66 octahedra were re-dispersed in deionized water at a concentration of 200 mg ml^− 1.

Self-assembly of the UiO-66 octahedra into a monolayer.

A piece of glass slide (24 mm × 24 mm) and a petri dish (12 cm in diameter and 8 cm in depth) were treated with oxygen plasma for 10 min to obtain hydrophilic surfaces (Harrick Plasma, PDC-32G). The UiO-66 octahedron suspension at a concentration of 200 mg ml^− 1, deionized water, and ethanol were mixed at a volume ratio of 40:20:40 by ultrasonic treatment for 10 min. Then, the plasma-treated glass slide was placed at the bottom of the petri dish. Deionized water was slowly added into the petri dish until almost covering the glass slide. Subsequently, 100 µl of the mixed solutions composed of UiO-66 octahedra were dropped onto the glass slide. The UiO-66 octahedra were trapped at the water surface and a monolayer was gradually formed at the water surface (Supplementary Movie 1). Deionized water was slowly filled into the petri dish via a plastic tube to lift up the UiO-66 octahedron monolayer. The UiO-66 octahedron monolayer was transferred onto an Au-covered silicon substrate (10 mm × 15 mm) by picking up the monolayer from the bottom. A steel mask was attached onto the Au-covered silicon substrate before picking up the monolayer template to create UiO-66 octahedron patterns.

Fabrication of the UiO-66@PBI templates.

First, PBI powders were dissolved into NMP at a concentration of 0.2 wt.%. The solution was stirred at 70 ℃ for 0.5 h. 150 µl of the solutions were dropped onto the glass slide with patterned UiO-66 octahedron monolayer. After drying in vacuum at 80 ℃ for 3 h, the glass slide was stored in deionized water at 90 ℃ for 24 h. The UiO-66@PBI composite film was detached from the glass slide and floated on the water surface. The Au-covered silicon substrate was used to pick up the floating UiO-66@PBI composite film. After electrodeposition of Ag, the UiO-66@PBI template was easy to be detached from the Ag electrodeposited nanotriangles underneath the template because of the small contact area between the template and the Ag nanotriangles. Simply by immersing the sample into deionized water and ethanol alternately for several minutes, the UiO-66@PBI template was peeled off and floated on the water surface for second time usage.

Ag electrodeposition using the UiO-66 templates.

The electrodeposition was carried out using the UiO-66 octahedron monolayer as the cathode and a carbon rod as the counter electrode. Different amounts of AgNO₃ and SDS were dissolved into deionized water as the electrolyte and kept at 45 ℃. The deposition voltage was maintained at -1.2 V for different time.

Materials Characterizations.

X-ray diffraction patterns were performed to characterize the crystal structure of the UiO-66 octahedra and the monolayer template (GIXRD, Rigaku D/MAX 2550). The morphology of the UiO-66 octahedra and the electrodeposited Ag nanopatterns was investigated using a field-emission scanning electron microscope (Hitachi, SU-8010) operating at 5.0 KV. The N₂ adsorption/desorption isothermal curves of the UiO-66 octahedra were obtained from the Micromeritics ASAP 2020 surface area analyzer with the pore size analyzing capability operating in liquid argon. The pore size distributions of the nanochannels within the UiO-66 octahedra were simulated by the density functional theory method. The surface tension of the electrolyte was determined by the pendent drop method using an automatic contact angle equipment and the contour analysis system (DataPhysics Instruments, OCA 20).

Electrochemical measurements.

We obtained the ionic conductivity of the UiO-66 octahedra pressed pallets and the electrolyte by the electrochemical impedance spectroscopy (EIS). In detail, the UiO-66 octahedron powder was dried at 70 ℃ for 72 h to remove the solvents. Then, the powders were stored in the electrolyte for 3 h before centrifuging and drying for another 72 h at 70 ℃. Finally, a certain amount of the collected UiO-66 octahedron powder was pressed into a pallet under a pressure of 3 MPa for 30 s. The UiO-66 pellet was placed between two stainless steel electrodes in a CR2016 coin cell. 30 µl of the electrolyte were introduced onto the pellet and the redundant electrolyte was removed before the EIS tests. The electrolyte was filled into a customized swagelok cell without the UiO-66 pellet to test its conductivity (Supplementary Fig. 7 and Fig. 8). An Autolab PGSTAT302N was used for the EIS measurements at 45°C and the frequency ranged from 10⁶ to 0.1 Hz. The resistance of the samples was calculated based on the EIS curves. The ionic conductivity was obtained using Eq. (2)^[51]:

\(\sigma =\frac{d}{SR\text{b}}\) (2)

Where S and d represent the area and the thickness of the UiO-66 octahedron pellet, respectively. R_b is the resistance and σ is the ionic conductivity.

Molecular dynamics (MD) simulations.

We used a 4×1×1 supercell of UiO-66 with periodic boundary conditions to all the directions, so that the supercell has no surface. 340 water molecules were inserted into the supercell. The resulting water loading per UiO-66 (15 mmol/g) is close to the experimental value (16 mmol/g) at 298 K and 1 bar^[52]. The number of silver ions was set from 10 to 80 at an interval of 10. The unit cell structure and the force fields for UiO-66 were taken from Yang’s paper^[53], which can reasonably reproduce the conductivity of anions in the UiO-66 supercell^[32]. Ag and water were represented using the parameters proposed by Mertz et al^[54]. and the TIP3P model^[55], respectively.

All-atom MD simulations were performed using the GROMACS 2020.6 package^[56]. The equations of motion were integrated with the leapfrog algorithm using a time step of 2.0 fs. The non-bonded potentials, Lennard-Jones (LJ) and Coulombic interactions, were modified by a shift function to produce smoothly-varying energies and forces at the cutoff distance of 1.0 nm. The particle mesh Ewald method was adopted to compute long-range Coulombic interactions^[57]. The LJ parameters between unlike particles were computed by the Lorentz–Berthelot combination rules. The particles consisting of the UiO-66 supercell were fixed in space to prevent the drift of entire structure. At each silver ion concentration, the system was first energy-minimized using the steepest descent algorithm.

Then, at each condition, three independent MD simulations for each 100 ns were performed in the canonical (NVT) ensemble at 318 K, which was the same as our experiments, with applying an external electric field of 5.0 V/nm along the x-axis. The polarization of water was neglected under an electric field of 5.0 V/nm^[48]. The temperature was controlled by the V-rescale method with a damping constant of 1.0 ps^[58].

Data availability

All experimental data within the article and its Supplementary Information are available from the corresponding authors upon request.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (51971200, 52273233, 22250610195, and 22273083), Zhejiang Provincial Natural Science Foundation of China (LR19E010001), the National Key Research and Development Program of China (2018YFB0703803), and the Open Research Program of Key Laboratory of 3D Micro/Nano Fabrication and Characterization of Zhejiang Province, Westlake University. Part of the work was conducted in the ZJU micro-nanofabrication centre.

Author contributions

S.Y. conceived the idea. S.Y., L.Z. and Y.L. designed the experiments. Y.L. carried out the experiments and performed the characterizations. X.Z. and K.M. performed simulations. Y.L. and S.Y. wrote the manuscript. All authors analyzed the data and contributed to revising of the manuscript.

Competing interests

The authors declare no competing interests.

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Metal Organic Framework Template-Guided Electrochemical Lithography

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