Dynamic "Scanning-Mode" Meniscus Confined Electrodepositing and

Subscriber access provided by UNIV OF DURHAM

Surfaces, Interfaces, and Catalysis; Physical Properties of Nanomaterials and Materials

Dynamic "Scanning-Mode" Meniscus Confined Electrodepositing and Micropatterning of Individually Addressable Ultraconductive Copper Line Arrays Yu Lei, Xianyun Zhang, Dingding Xu, Min-Feng Yu, Zhiran Yi, Zhixiang Li, Aihua Sun, Gaojie Xu, Ping Cui, and Jianjun Guo J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b00636 • Publication Date (Web): 23 Apr 2018 Downloaded from http://pubs.acs.org on April 24, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

Dynamic ″Scanning-Mode″ Meniscus Confined Electrodepositing and Micropatterning of Individually Addressable Ultraconductive Copper Line Arrays Yu Lei,†,‡,# Xianyun Zhang,†,# Dingding Xu,† Minfeng Yu,§ Zhiran Yi,† Zhixiang Li,† Aihua Sun,† Gaojie Xu,† Ping Cui,† Jianjun Guo†,*

†

Zhejiang Key Laboratory of Additive Manufacturing Materials, Ningbo Institute of Materials

Technology & Engineering, Chinese Academy of Sciences, Ningbo, 315201, P. R. China ‡

School of Materials Science and Engineering, Shanghai University, Shanghai 200444, P. R.

China §

D. Guggenheim School of Aerospace Engineering, Georgia Institute of Technology, Atlanta,

GA 30332, USA

AUTHOR INFORMATION Corresponding Author * Jianjun Guo, Email: [email protected] Author Contributions #

Y. Lei and X. Zhang contributed equally to this work. 1 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 33

ABSTRACT: Micro- and nano-patterning of cost-effective addressable metallic nanostructures has been a long endeavor in terms of both scientific understanding and industrial needs. Herein, a simple and efficient dynamic meniscus-confined electrodeposition (MCED) technique for precisely-positioned copper line micropatterns with superior electrical conductivity (greater than 1.57×104 S/cm) on glass, silicon and gold substrates is reported. An unexpected higher printing speed in the evaporative regime is realized for precisely-positioned copper lines patterns with uniform width and height under horizontal scanning-mode. The final line height and width depend on the typical behavior of traditional flow coating process, while the surface morphologies and roughness are mainly governed by evaporation-driven electrocrystallization dynamics near the receding moving contact line. Integrated 3D structures and a rapid prototyping of 3D hot-wire anemometer are further demonstrated, which is very important for the freedom integration applications in advanced conceptual devices, such as miniaturized electronics and biomedical sensors and actuators.

TOC GRAPHICS

2 ACS Paragon Plus Environment

Page 3 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Robust and reproducible non-lithographic patterning of metallic micro/nanostructures has attracted extensive research attention with the rapid development of electronic and optoelectronic devices in recent years. Many additive nanomanufacturing techniques have been identified as progressive and effective fabrication technologies for complicated three-dimensional (3D) microstructures,1,

2

which is a key drive behind recent innovations in miniaturization of

mechanical, optical and electronic devices because of their excellent electronic and optical properties. Especially for 3D metal micro/nanostructures, additive nanomanufacturing holds great potential for the design of microelectronics, microsensors, microelectromechanical systems (MEMS), microfluidics and analysis applications.3-5 However, the available commercial systems still have limited resolutions (approximately no better than 50 µm).1,

6

Although some

techniques, like E-beam– or focused ion beam–based deposition is able to manufacture 3D structures with feature sizes less than 10 nm, a heat source, a high-vacuum or inert condition, or even a post-deposition processing process is still needed.7 As a result, the available 3D microfabrication methods still suffer from expensive, complicated, and even hazardous, therefore, limiting their use in extensive applications. Smaller scale geometries with physical processes controlled in the nanometer and micrometer scale, i.e. the recent developed meniscus-guided continuous deposition in air, can be employed to produce high-resolusion metal microstructures for micro/nanosystems.8 The creation of deposited patterns mainly occurred in the moving liquid-gas-solid three-phase contact region of the meniscus between material provider (e.g., nozzle) and substrate. Through precise control 3 ACS Paragon Plus Environment


over the positioning of the nanoscale meniscus, 2D micro/nanopatterns and even complex 3D free-form nanostructures can be fabricated with simple instruments in ambient condition.9, 10 Various experimental setups and techniques based on quasi-static and dynamic meniscus stability are developed. In the quasi-static setups, such as spin-coating11 and drop-casting12, the moving contact line occurs naturally and only 2D thin films are obtained. In the dynamic deposition approach, the moving contact line is directly controlled by an external forces, e.g. imposed by an upper plate, roller or nozzle, and both 2D and genuine 3D micro/nano-structures can be fabricated.13,

14

Up to today, a comprehensive list of materials, including metal

electrolytes, polymers, biomaterials and graphene oxide, has already been used for the freeform fabrication of 3D micro/nanostructures by the electroless dynamic approach,15, 16 whereas for metals, silver nanoparticles have been used solely in this process.17 The minimum feature size achieved is limited to tens of micrometers. Furthermore, a high temperature thermal annealing (above 400 °C) or additional laser are also required to form a dense, mechanically stable and electrically conductive metallic microstructures.17 Here, we report a dynamic meniscus-confined electrodeposition (MCED) process for highly smooth and conductive copper patterns under "scanning-mode" operation on conducting, semiconducting and insulating substrates. The MCED process has only recently been realized by Yu et al. for fabrication of nanowire-based 3D microstructures with an aspect ratio of up to 200 in ambient condition.9, 18 Under direct-writing mode, a number of free-standing and high aspect ratio polymer,19 and metal9, 20 microstructures have been successfully created. The maximum 4 ACS Paragon Plus Environment

Page 4 of 33

Page 5 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


deposition rate obtained experimentally is υc = 0.1 µm/s, and the obtained wire diameter is in the range of 0.9~1.8 µm when using a pipette with a nozzle diameter of 2.0 µm.9 The fabricated metal wires were found to be of high electrical and mechanical quality.9,

21

Although the

intriguing benefits as compared with other techniques, the microstructures fabricated by MCED are mainly based on wires, such as spiral and mesh structures with limited complexity. Most recently, the dynamic MCED process has been found efficient for complex polymer and inorganic oxide nanostructures fabrication layer-by-layer, showing the ability to realize more complex 3D functional structures.22, 23 For metals, however, there is still no established dynamic MCED solution other than wire-like structures.24 Another problem is that a conductive substrate is required in the MCED process,25 which may further limit its application areas. Toward overcoming these issues, a dynamic "scanning-mode" MCED process is developed in this article for copper line arrays deposition on various substrates, which enables the layer by layer fabrication. To expand the utility of this novel technique, we further demenstrate the simple and cost-effective freeform integration of addressable 3D structures.



Figure 1. Method to fabricate copper arrays. (a) Schematic illustration of the scanning-mode MCED process. Detailed front view (b) and side view (c) of the dynamic moving meniscus, highlighting the evaporation-induced mass transport near the contact line. The design principle for free-form fabrication process and computer-controlled MCED system is illustrated in Figure 1. The details of the experimental setup can be found in our previous report.4,

9

The metal growth is localized within the meniscus-confined micrometer scale as

electrodeposition continued simultaneously. Different from the vertical wire direct-writing process,9 the dynamic scanning-mode operation provides robust fabrication capability, because it combines the electrodeposition with both the horizental dynamic contact lines perpendicular to the scanning direction and the vertical quasi-static meniscus in parallel with the scanning direction. As shown in Figure 1(a), a glass micropipette is dragged on a substrate at constant speed ʋ under controlled temperature and humidity. The growth on vertical quasi-static meniscus 6 ACS Paragon Plus Environment

Page 6 of 33

Page 7 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


in Figure 1(b), similar to the nanowire growth, is controlled by the meniscus stability, while the electrodeposition on receding contact lines, as shown in Figure 1(c), is controlled by the competition between the evaporative flux (inducing mass flux to the right) and the receding velocity of the contact line (inducing mass flux to the left). As a result, the scanning speed for uniform line deposition is realized upto 0.16 µm/s in dynamic scan mode, which corresponds to a volumetric deposition rate of 0.142 µm3/s. This is much larger than the upper threshold of copper wire MCED rate at similar conditions (0.08 µm3/s for a 0.1 µm/s nozzle speed).9, 26 Further increase of the deposition rate will result in "coffee ring" effect.12,

27

Figure 2 shows the

morphology and structure of the copper line arrays electrodeposited on conductive gold substrate by using a 2 µm diameter micropipette filled with 0.05 M CuSO4 aqueous solution. For copper line arrays fabrication in Figure 2(a), the applied current was predetermined to be 2.3 nA by standard cyclic voltammetry, and the relative humidity of the environment was kept constant at 60%-70% for straight and uniform line growth (see Figure S5, Supporting Information). Within the range of scanning rates of 0.08 to 0.16 µm/s, the deposited lines are straight and uniform in width w and height h.



Page 8 of 33

Figure 2. (a) SEM images of copper line arrays fabricated on gold substrates with different pipette scanning speed. View angle: 45°, scale bars, 10 µm. (b) The width and height. (c) The roughness of the deposited copper lines shown in (a). (d) Concentration profiles of the gold, copper and oxygen obtained by EDS. (e) HRTEM image of a typical copper line. (f) SAED pattern of the selected region in (e). Controlling morphology of the printed conductive pattern plays an important role to determine its electrical conductivity and mechanical strength. The morphology can be fine turned by controlling the crystallization dynamics. The electrocrystallization rate ʋc of copper is defined by the Faraday’s law:

υc = −

iM Cu zCu ρ Cu F

(1) 8

ACS Paragon Plus Environment

Page 9 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


where i is the electric current density, zCu is the electric charge of the Cu ions, F is the Faraday constant, MCu and ρCu is the molar mass and density of copper line, respectively. The calculated electrodeposition rate at 2.3 nA in our condition is 0.086 µm3/s, corresponds to a line growth rate of 0.082 µm/s. For continuous growth, the evaporation induced mass transfer rates ʋi must match with ʋc in order to maintain the meniscus stability. Under different scanning rates, the width, height and surface roughness of copper lines change accordingly with the scanning speed, as can be seen in Figure 2(b) and (c). A uniform line with smooth surface (12.6 nm Ra) is obtained with a scanning speed ʋ of around 0.08 µm/s. By gradually increase ʋ to 0.1 µm/s and above, the surface of the copper wire becomes rougher, reached 79.9 nm at 0.16 µm/s. Recent works have shown that the arrangement of particles is influenced by the strength of capillary flow, i.e., how fast particles go to the contact line.28 After the electrolyte solution at the contact line reaching the critical supersaturation, the process of nucleus formation on the substrate is initiated, and the growth of the nucleus takes place simultaneously. The critical nuclei with several atoms are randomly distributed on the active sites, which can reasonably be assumed to randomly distribute on the substrate surface. The Cu2+ ion concentration distribution in the cluster vicinity is the critical parameter on the growth kinetics. The morphology of the electrodeposits is thus influenced by orientational growth of grains controlled by activation process and irregular growth caused by mass-transportation limitations.29 As shown in Figure 2(a), line with smooth surface is obtained in middle nozzle speed by mixed activation-diffusion-controlled growth, which induces the formation of polycrystalline deposits with random orientation. As expected, 9 ACS Paragon Plus Environment


Page 10 of 33

increasing the nozzle speed enhanced water evaporation and ions concentration, which results in coarse surface by the dominant diffusion-controlled electrodeposition. As shown in Figure 2(a) and Figure S11 (Supporting Information), higher scanning speed can lead to indefinite crystal shapes and relative small crystalline (around 20~50 nm), which is a typical result of diffusion-controlled irregular growth. Different from the MCED of vertical copper wires,26 the line surface coarseness is also observed with a low scanning velocity. In this case, the evaporation of the water is largely depressed due to a large receding meniscus angle, resulting in a local deficiency of copper nucleus in the meniscus receding front. As a result, after nucleation, the electrodeposition process immediately becomes the activation-controlled irregular growth with well-defined crystal shapes and relative large crystalline (around 25~60 nm) formation. The surface coarseness of the lines is thus observed at low nozzle speed, as shown in Figure 2(a) and Figure S10. In fact, the MCED rates in present study are still so low for dynamic scanning-mode that the scanning rate have negligible effect on the meniscus shape, as predicted by static mechanics.30 Based on mass balance of the solvent/particle mixture, at steady state, the flow rate of solvent leaving the meniscus by evaporation equals to that of solvent molecules entering the meniscus from the pipette. Assuming negligible diffusion of copper ions at x=-R in Figure 1(c), the mass conservation yields: C0lev %j ev = ρs hυ%c , where the total evaporation flux is defined by

Qev = ∫

lev

0

jev ( x)dx with a mean evaporation rate %j ev = Qev / lev per unite length over the


Page 11 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


evaporation region of length lev for a bulk copper mass concentration of C0. The height of the line is thus deduced as (see Supporting Information):

h=

C0 %jevlev ρs υ%c

(2)

Equation 2 is similar to the expression used in the work of flow coating of colloidal dispersions in the evaporative regime.13 Since the change of the scanning velocity leads to large changes in lev, while the mean evaporation rate %jev varies in the opposite way, the ratio of the total evaporation flux to the total flux for the pure solvent is close to 1 whatever the substrate velocity and system properties,31 indicating that the height of the line in diffusion-controlled region is inversely proportional to the pipette velocity. The good agreement between this model and the experimental data in Figure 2(a) indicates that the assumption of mixed activation-diffusion controlled electrocrystallization mechanism in Figure 1 is valid. Further, we can also conclude that, at low pipette velocity, there is no obvious Marangoni effect, which is a flow of concentrated copper ions going back to the bulk solution as a consequence of surface tension at the interface.13 While with pipette velocity increased, the observed line height is higher than that predicted with Equation (2). The increased amount of deposited line may be due to thermo-capillary Marangoni convection inside the meniscus. As a result, the deposition reached the mixed kinetically evaporation and capillary convective regime at a printing speed of around 0.16 µm/s. Further increase of the nozzle speed, the viscous force becomes predominant and the



Page 12 of 33

meniscus motion will reach the well-known Landou-Levich regime characterized by stick−slip motion,12,

13

which resulting in dead ends for charge transport and is unfavorable for

electrodeposition of uniform lines (Figure S11, Supporting Information). The meniscus width is not included in the final Equation (2). Indeed, as shown in Figure 1(b), the meniscus velocity perpendicular to the moving direction is zero. Due to the nozzle scanning, the wettability and contact time should the control factor of the meniscus width (or shape), which is well described by the classical Tanner’s law: w ∝ V 3/10 ( γ t / η )

1/10

(3)

where V is the drop volume, γ is the surface tension of the solid-liquid-vapor interface, and η is the viscosity of the sulfate solution. Equation (3) indicates that the width of the deposited line depends mainly on the contact time, t, and the contact angle, θ, for a constant nozzle height h0. As shown in Figure 2(a), at dominant diffusion controlled regime, the line width decrease with the increase of nozzle scanning speed as predicted by Equation (3). However, the line width passed through a minimum of 3.1 µm when scanning speed ʋ increased to 0.08 µm/s, and then increased slightly with further increases of ʋ, which should be a consequence of higher contribution of Marangoni effect at high scanning speed. The nozzle diameter is not included in Eq. (2), but in Eq. (3) as a variable of drop volume. This indicates that the nozzle diameter will have little effect on the line height and the available upper nozzle speed if we use a constant nozzle-to-substrate distance (h0), as indicated in Figure 12 ACS Paragon Plus Environment

Page 13 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


S14 & Figure S15 (Supporting information). Instability is occurred above 0.16 µm/s for different nozzle diameters. This is reasonable since the meniscus length (lev) and stability is a function of nozzle height and nozzle speed, as illustrated in Figure 1(b) and Figure 1(c). While for nano-sized nozzles, the applicable speed will change with the nozzle diameter due to a smaller nozzle-to-substrate is needed. Among the different parameters, evaporation process has been identified as the dominant factor that controls the growth rate and geometrical uniformity of the MCED deposited micro/nanostructures under constant growth current,9, 23 mainly due to high surface-to-volume ratio at small scale. Based on the above results, we hypothesize that there are two key factors responsible for copper line formation by dynamic MCED: (1) electrocrystallization of metals driven by electrochemical reaction kinetics at the growing front (anode surface)9, 22 and (2) mass convective flux in the meniscus driven by the evaporative-induced capillary hydrodynamics over the meniscus surface.12, 13 As shown in Figure 1(c), the evaporative flux (jev) on moving-contact line is the strongest near the contact line (x = lev),32 which induces the dispersion (water) flux (jw) towards the growing front. A reverse mass convection flux (jp) towards the bulk induced by the concentration differences is also occurred. The collective convective flux leads to a much higher concentration of the Cu2+ ions in the receding contact line than that in the bulk (x = -R). Multiphysics finite element simulation indicates that the concentration of Cu2+ ions can reach upto 1.7 times of the bulk, which maintains constant during the printing process.26 As a result, the electrocrystallization reaction is so fast as to be in equilibrium at the moving contact-line 13 ACS Paragon Plus Environment


(Movie S1-S3 and Figure S7-S9) and the meniscus evaporation induced ion diffusion is thus rate-controlling process in dynamic MCED. The metal growth confined within micrometer scale in MCED inevitably changed the nucleation and growth mechanism and the structure of metal deposits, since the dimension of the electroactive area is much smaller than that of the diffusion layer.9 Copper electrodeposition is the typical representation of the activation-diffusion controlled process characterized by medium exchange current density and lower hydrogen overpotential.18 From the SEM and high-resolution transmission electron microscopy (HRTEM) analysis in Figure 2, we found the deposited copper lines are polycrystalline. The real aspect of the electrochemical reaction in the Cu2+/Cu system using copper-sulphate based electrolyte can be described simply by the two-step reduction/oxidation reactions and the subsequent crystallization/decrystallization process.33 In our experiments, with the applied voltage of E=-0.5 V, corresponding to electrode potential of approximately -0.465 V w.r.t. SHE (Table S1, Supporting Information), which is much higher than the equilibrium potentials and, in terms of absolute value, purely Cu can be formed based on the possible reactions occur at the cathode.23, 33 The obtained product of copper electrodeposition using electrolyte bath is known to be influenced by cathodic polarization, current density and pH value of the electrolyte.4, 34 Energy-dispersive X-ray spectroscopy (EDS) and HRTEM further confirmed this assumption. By comparing the surface and boundary intensity of the oxygen (pink) with Cu (green) and gold (yellow) signals in EDS spectrum, very little oxygen is found on/in copper line in Figure 2(d). Figure 2(e) shows a typical polycrystalline morphology with a clear 14 ACS Paragon Plus Environment

Page 14 of 33

Page 15 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Moiré fringe and different crystal lattice orientations. With further sub-area Fast Fourier transform (FFT) analysis in inset Panel I and II of Figure 2(e), the values of atomic plane spacing d=2.089 nm measured from the lattice fringes can be indexed to be the cubic structure of Cu (JCPDS No. 85-1326). The continuous and dotty rings in selected area electron diffraction (SAED) in Figure 2(f) indicate the existence of tiny and relatively larger crystals respectively, verifies the polycrystalline feature of the deposits. Herein, through TEM and SAED analysis, there is no evidence for oxide compounds or crystals except metallic copper. Furthermore, the electrodeposition in our study lasted for about 4.1 to 13.2 min. Considering the sufficient time of electrodeposition and low pH value of 2 used, all the Cu2O produced should eventually be consumed and turned into pure Cu according to the Pourbaix diagram.25, 35 We didn’t find any oxide species in the inner copper lines by HRTEM after FIB cutting (Figure S4, Supporting Information). This indicates that the observed oxygen in EDS spectrum may arise from oxidation species on the outer surface as a consequence of the exposure to air during sample preparation. Upto now, the quasi-static or dynamic MCED are all performed on conductive substrate. We further extended this technique to microfabrication on insulating glass substrates and semiconducting silicon wafers starting from a conducting electrode. SEM images in Figure 3 (a)-(b) indicate the fabricated line arrays showed uniform features, i.e. smooth, straight and uniform in width and spacing without any discontinuities, indicating the reliable printability on glass and silicon. By comparing with Figure 2, the stripe width increases following the order of on glass, silicon and gold surfaces. For all scanning-speed tested, the smoothness of copper wires 15 ACS Paragon Plus Environment


Page 16 of 33

on glass substrate (9.0-25 nm Ra) is also better than that on silicon substrate (12.3~50.3 nm Ra) and gold substrate (12.8-79.9 nm Ra, see Figure S13, Supporting information). This difference may arise from the spherical diffusion layers formed around the predeposited crystal nucleus as shown in Figure 3(f). At identical scanning velocity, the normal CA of gold is obviously bigger than that of silicon and glass (Figure S1-S3, Supporting information). However, as illustrated in Figure 3(c-e), the electrowetting reversed the electrolyte CA on hydrophilic glass, silicon and superhydrophobic gold, which induces a much small CA and hence a large lev on gold surface. As a result, the deposited new adatoms are sufficiently far from each other in the micrometer scale, which is sufficiently large to permit the formation of spherical diffusion zones around each of them, since the dimension of the electroactive area is much smaller than that of the diffusion layer.21 The newly generated copper nucleus will grow inside the spherical diffusion layers of gold particles and predeposited copper crystals, with the latter as catalysis to keep this reaction executing consecutively to form the desired copper layer. In this case shown in the inset picture of Figure S6, globular and cauliflower-like surface is formed. As the substrate conductivity decrease, especially on insulating glass, the spherical diffusion layer overlapped around closely packed protrusions (r > δ in Figure 3(f)).29 Thus, most smooth line surface is formed on glass over the whole scanning range studied. The line width should be determined by CA, i.e. the meniscus spreading width, which follows the order of gold > silicon > glass, as shown in Figure 3(c-e). Opposite trend is observed for the line height. This further confirmed the mechanism based on evaporation-based model, as depicted by Equation (2) and (3). 16 ACS Paragon Plus Environment

Page 17 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. SEM image and dimension of copper line arrays on: (a) glass and (b) silicon substrates. Current: 2.25 nA, scale bars: 15 µm. Effect of the representative gold (c), silicon (d), and glass (e) substrates on the contact angle (CA) of 0.05M CuSO4 electrolyte viewing from the perpendicular and parallel direction, respectively. (Scale bar = 1 mm). (f) Schematic representations of copper ions in diffusion zone at different substrates, gold, silicon, and glass, respectively. Compared with that on gold substrate, the range of feasible scanning rates on glass and silicon are slightly smaller for patterning straight stripes, which should be ascribed to different surface wettability. The largest lev observed on gold substrate indicates that the evaporative front is easily moving to the stick−slip motion regime.8 Contrary to the evaporative deposition of colloids and polymers,27 where uniform film is usually formed with higher deposition speed, the smooth deposition of copper lines by MCED is disrupted by increasing the deposition speed. With further increasing of the scanning speed to above 0.14 µm/s, the MCED process stopped abruptly 17 ACS Paragon Plus Environment


Page 18 of 33

due to "stick-slip" motion of the gas-solid-liquid contact line on glass substrate due to the insulation nature of the glass (Figure S12(b), Supporting information). In contrast, periodic structures on silicon in Figure 3 (b) were observed on the line surface due to the "stick-slip" motion controlled by Landou-Levich flow. As predicted, copper lines with periodic height or intermittent structure are observed over gold substrate at high nozzle speed (Figure S12(a), Supporting information).

Figure 4. Multidimensional structures constructed by MCED printing method with positional feedback on glass substrate. (a) Fold line with length of 40 µm. (b) Circular with diameter of 20 µm. (c) "L" Shape. (d) Copper microhelix in tilted 45º and 90º (inset) overlook angle. From the above discussion, we found that the dynamic scanning-mode MCED is highly repeatable and robust, which is amenable to extended 3D microstructure fabrication by combining vertical and scanning MCED process. Figure 4 further shows the power of using scanning mode MCED to construct multidimensional structures with arbitrary geometry. The transition from 2D to 3D was realized by maintaining a constant current by positional feedback 18 ACS Paragon Plus Environment

Page 19 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


using software controlled piezo-actuators. Given the wide range of structures that can be fabricated under scanning mode, we expect the additive MCED micromanufacturing technique is promising for rapid prototyping and fabrication of novel nanodevices and sensing elements based on 3D complex microstructures, which may be difficult to construct with other techniques.

Figure 5. (a) I–V curve of single horizontal Cu line aligned between two gold electrodes with a gap of 40 µm. (b) The LED lamp switched on using the single Cu line as an electrical interconnect (a SEM image of the electrodes/copper line is shown in the inset). (c) Steady-state response to N2 velocity of a copper vertical microbridge (the SEM image is shown in (d) in tilted 45º) between two gold electrodes with a gap of 20 µm. For real applications, the conductivity of the copper lines is important because the level of conductivity of the fabricated structures will determine the application range of functional electronic materials. Figure 5 (a) shows the current-voltage (I–V) characteristics of the printed Cu line with corresponding resistivity of ρs= 63.6 µΩ·cm at room temperature (Figure S16, 19 ACS Paragon Plus Environment


Supporting Information), which is lower than that of the previously MECD printed nanotwinned Cu (79 µΩ·cm)14 and electrospun Cu nanofibers (120 µΩ·cm)36. It was also possible to switch on an LED lamp by using such a single nanowire as an electrical connector between the gold electrodes, as shown in Figure 5(b) and Movie S4 (Supporting Information). The low resistivity of the printed Cu lines indicates potential applications as nanoelectrodes in various electronic devices. Furthermore, we assembled a hot-wire anemometer by printing a vertical copper microbridge between the Au-Au electrodes with a 20 µm insulating gap, as shown in Figure 5(d). Steady-state response to N2 velocity has been experimentally obtained up to 20 m/s under both constant voltage (1.4V) and constant temperature modes. The resistance change (∆R) stems from temperature variations of the sensitive element introduced by the heat transfer, which depends on the flow speed as shown in Figure 5(c). This thermal sensor technology provides high sensitivity along with low noise and fast time response, while the assembly process is very delicate.37 Here, by using copper element with a high temperature coefficient of resistance, the relative resistance variations (∆R/R0) versus velocity displayed reversible and reproducible response, which follows the typical King’s law38 with high sensitivity. In conclusion, a dynamic meniscus-confined electrodeposition (MCED) approach under scanning-mode was demonstrated allowing for the fabrication of addressable line arrays and multidimensional Cu microstructures with ultrahigh conductivity on conducting, semiconducting and insulating substrates. The morphology and topology of the deposited copper lines can be easily tuned in the micrometer range by both scanning speed and applied overpotential. 20 ACS Paragon Plus Environment

Page 20 of 33

Page 21 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Electrocrystallization kinetics at the growing front and mass convective hydrodynamics over the meniscus surface were found to be the two key factors responsible for copper lines formation in MCED process. A much higher printing speed, as compared with MCED of copper wire, is realized for line array fabrication on glass and silicon wafers. The line height is found inversely proportional to the nozzle scanning speed, and the line width depends on the contact angle and time of the electrolytes. At low scanning speed, the activation controlled electrocystallization induces coarse lines with well-defined crystal shapes. With medium printing speed (~0.08 µm/s on gold), smooth and uniform copper line array can be obtained in mixed activation-diffusion control regime. We expect the current dynamic MCED technique has wide applications for in-situ fabrication of conductive structures, particularly for the creation of novel nano/microdevices and sensing elements that may be difficult to construct with other techniques. ACKNOWLEDGMENTS This study is supported by the National Natural Science Foundation of China (No. 11574331 & 11674335), Ningbo Science & Technology Bureau (No. 2016B10005 & 2015B11002). ASSOCIATED CONTENT

Supporting Information

Additional discussions are provided about the (1) Experimental details. (2) Testing of dynamic electro-wetting on various substrates. (3) Surface and inner crystalline structure of copper lines. (4) Influence of relative humidity (RH) on the line morphology. (5) Influence of 21 ACS Paragon Plus Environment


Page 22 of 33

deposition potential on the line morphology. (6) Contact line effect on the electrodeposition. (7) Line morphology at low and high scanning speed. (8) Speed vary according to different nozzle diameters. (9) The calculation of standard electrode potential, (10) Prediction of the deposits height. (11) The conductivity of the copper lines. (PDF)

Movie S1 (AVI)

Movie S2 (AVI)

Movie S3 (AVI)

Movie S4 (AVI)

AUTHOR INFORMATION Corresponding Author

*Jianjun Guo, Email: [email protected]

Author Contributions #

Y. Lei and X. Zhang contributed equally to this work.

ORCID: Jianjun Guo: 0000-0002-2162-4133; Zhiran Yi: 0000-0002-8679-8302 Xianyun Zhang: 0000-0002-0453-6879


Page 23 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Notes

The authors declare no competing financial interest.

REFERENCES (1) Vaezi, M.; Seitz, H.; Yang, S. A Review on 3D Micro-Additive Manufacturing Technologies. Int. J. Adv. Manuf. Technol. 2013, 67, 1721-1754.

(2) Farahani, R. D.; Dubé, M.; Therriault, D. Three-Dimensional Printing of Multifunctional Nanocomposites: Manufacturing Techniques and Applications. Adv. Mater. 2016, 28, 5794-5821. (3) Li, W.; Huang, G.; Wang, J.; Yu, Y.; Wu, X.; Cui, X.; Mei, Y. Superelastic Metal Microsprings as Fluidic Sensors and Actuators. Lab Chip 2012, 12, 2322-2328. (4) Yi, Z.; Lei, Y.; Zhang, X.; Chen, Y.; Guo, J.; Xu, G.; Yu, M.-F.; Cui, P. Ultralow Flexural Properties

of

Copper

Microhelices

Fabricated

via

Electrodeposition-Based

Three-Dimensional Direct-Writing Technology. Nanoscale 2017, 9, 12524-12532. (5) Tan, C.; Nasir, M. Z. M.; Ambrosi, A.; Pumera, M. 3D Printed Electrodes for Detection of Nitroaromatic Explosives and Nerve Agents. Anal. Chem. 2017, 89, 8995-9001. (6) Tan, H.; Tran, T.; Chua, C. A Review of Printed Passive Electronic Components through Fully Additive Manufacturing Methods. Virtual Phys. Prototyp. 2016, 11, 271-288.



(7) Botman,

A.;

Mulders,

Electron-Beam-Induced

J.;

Hagen,

C.

Creating

Page 24 of 33

Pure

Nanostructures

from

Deposition Using Purification Techniques: A Technology

Perspective. Nanotechnology 2009, 20, 372001. (8) Thiele, U. Patterned Deposition at Moving Contact Lines. Adv. Colloid Interface Sci. 2014, 206, 399-413.

(9) Hu, J.; Yu, M.-F. Meniscus-confined Three-Dimensional Electrodeposition for Direct Writing of Wire Bonds. Science 2010, 329, 313-316. (10) Hyun, D. C.; Park, M.; Jeong, U. Micropatterning by Controlled Liquid Instabilities and Its Applications. J. Mater. Chem. C 2016, 4, 10411-10429. (11) Pichumani, M.; Bagheri, P.; Poduska, K. M.; González-Viñas, W.; Yethiraj, A. Dynamics, Crystallization and Structures in Colloid Spin Coating. Soft Matter 2013, 9, 3220-3229. (12) Han, W.; Lin, Z. Learning from "Coffee Rings": Ordered Structures Enabled by Controlled Evaporative Self-Assembly. Angew. Chem. Int. Ed. 2012, 51, 1534-1546. (13) Grosso, D. How to Exploit the Full Potential of the Dip-Coating Process to Better Control Film Formation. J. Mater. Chem. 2011, 21, 17033-17038. (14) Behroozfar, A.; Daryadel, S.; Morsali, S. R.; Moreno, S.; Baniasadi, M.; Bernal, R. A.; Minary-Jolandan, M. Microscale 3D Printing of Nanotwinned Copper. Adv. Mater. 2018, 30, 1705107.


Page 25 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(15) Kim, J. T.; Seol, S. K.; Pyo, J.; Lee, J. S.; Je, J. H.; Margaritondo, G. Three-Dimensional Writing of Conducting Polymer Nanowire Arrays by Meniscus-Guided Polymerization. Adv. Mater. 2011, 23, 1968-1970.

(16) Chang, W. S.; Jeong, H.; Kim, J. H.; Lee, S.; Wajahat, M.; Han, J. T.; Cho, S. H.; Seol, S. K. Micropatterning of Reduced Graphene Oxide by Meniscus-Guided Printing. Carbon 2017, 123, 364-370.

(17) Ahn, B. Y.; Duoss, E. B.; Motala, M. J.; Guo, X.; Park, S.-I.; Xiong, Y.; Yoon, J.; Nuzzo, R. G.; Rogers, J. A.; Lewis, J. A. Omnidirectional Printing of Flexible, Stretchable, and Spanning Silver Microelectrodes. Science 2009, 323, 1590-1593. (18) Suryavanshi, A. P.; Yu, M.-F. Probe-based Electrochemical Fabrication of Freestanding Cu Nanowire Array. Appl. Phys. Lett. 2006, 88, 083103. (19) McKelvey, K.; O'Connell, M. A.; Unwin, P. R. Meniscus Confined Fabrication of Multidimensional Conducting Polymer Nanostructures with Scanning Electrochemical Cell Microscopy (SECCM). Chem. Commun. 2013, 49, 2986-2988. (20) Momotenko, D.; Page, A.; Adobes-Vidal, M.; Unwin, P. R. Write-Read 3D Patterning with a Dual-Channel Nanopipette. ACS Nano 2016, 10, 8871-8878. (21) Yi, Z.; Guo, J.; Chen, Y.; Zhang, H.; Zhang, S.; Xu, G.; Yu, M.; Cui, P. Vertical, Capacitive Microelectromechanical Switches Produced via Direct Writing of Copper Wires. Microsyst. Nanoeng. 2016, 2, 16010.



Page 26 of 33

(22) Laslau, C.; Williams, D. E.; Kannan, B.; Travas-Sejdic, J. Scanned Pipette Techniques for the Highly Localized Electrochemical Fabrication and Characterization of Conducting Polymer Thin Films, Microspots, Microribbons, and Nanowires. Adv. Funct. Mater. 2011, 21, 4607-4616.

(23) Wang, P.; Roberts, R.; Ngan, A. Direct Microfabrication of Oxide Patterns by Local Electrodeposition of Precisely Positioned Electrolyte: The Case of Cu2O. Sci. Rep. 2016, 6, 27423. (24) Chen, X.; Liu, X.; Childs, P.; Brandon, N.; Wu, B. A Low Cost Desktop Electrochemical Metal 3D Printer. Adv. Mater. Tech. 2017, 2, 1700148. (25) Hu, J. Interfacial Physics in Meniscus-Confined Electrodeposition and Its Applications for Fabricating Electronic Structures. Ph.D. Thesis, University of Illinois at Urbana-Champaign, May, 2011. (26) Morsali, S.; Daryadel, S.; Zhou, Z.; Behroozfar, A.; Baniasadi, M.; Moreno, S.; Qian, D.; Minary-Jolandan, M. Multi-physics Simulation of Metal Printing at Micro/Nanoscale Using Meniscus-Confined Electrodeposition: Effect of Nozzle Speed and Diameter. J. Appl. Phys. 2017, 121, 214305. (27) Zhang, J.; Milzetti, J.; Leroy, F.; Müller-Plathe, F. Formation of Coffee-Stain Patterns at the Nanoscale: The Role of Nanoparticle Solubility and Solvent Evaporation Rate. J. Chem. Phys. 2017, 146, 114503.


Page 27 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(28) Marín, Á. G.; Gelderblom, H.; Lohse, D.; Snoeijer, J. H. Order-to-Disorder Transition in Ring-shaped Colloidal Stains. Phys. Rev. Lett. 2011, 107, 085502. (29) Popov, K. I.; Djokić, S. S.; Nikolić, N. D.; Jović, V. D. Morphology of Electrochemically and Chemically Deposited Metals. Springer: Cham, Switzerland, 2016.

(30) Przerwa,

E.;

Sosnowski,

S.;

Slomkowski,

S.

Deposition

of

Poly

(styrene/α-tert-butoxy-ω-vinyl-benzyl-polyglycidol) Microspheres on Mica Plates Crossing the Liquid-Air Interface: Formation of Stripe Pattern. Langmuir 2004, 20, 4684-4689. (31) Doumenc, F.; Guerrier, B. Drying of a Solution in a Meniscus: A Model Coupling the Liquid and the Gas Phases. Langmuir 2010, 26, 13959-13967. (32) Deegan, R. D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel, S. R.; Witten, T. A. Capillary Flow as the Cause of Ring Stains from Dried Liquid Drops. Nature 1997, 389, 827-829. (33) Yu, G.; Hu, X.; Liu, D.; Sun, D.; Li, J.; Zhang, H.; Liu, H.; Wang, J. Electrodeposition of Submicron/Nanoscale Cu2O/Cu Junctions in an Ultrathin CuSO4 Solution Layer. J. Electroanal. Chem. 2010, 638, 225-230.

(34) Golden, T. D.; Shumsky, M. G.; Zhou, Y.; VanderWerf, R. A.; Van Leeuwen, R. A.; Switzer, J. A. Electrochemical Deposition of Copper (I) Oxide Films. Chem. Mater. 1996, 8, 2499-2504. (35) Pourbaix, M. Lectures on Electrochemical Corrosion. Plenum Press: New York, 1973.



Page 28 of 33

(36) Bognitzki, M.; Becker, M.; Graeser, M.; Massa, W.; Wendorff, J. H.; Schaper, A.; Weber, D.; Beyer, A.; Gölzhäuser, A.; Greiner, A. Preparation of Sub-micrometer Copper Fibers via Electrospinning. Adv. Mater. 2006, 18, 2384-2386. (37) Wallace, J. M.; Vukoslavčević, P. V. Measurement of the Velocity Gradient Tensor in Turbulent Flows. Annu. Rev. Fluid Mech. 2010, 42, 157-181. (38) Kim, J. H.; Lee, S.; Wajahat, M.; Jeong, H.; Chang, W. S.; Jeong, H. J.; Yang, J.-R.; Kim, J. T.; Seol, S. K. Three-Dimensional Printing of Highly Conductive Carbon Nanotube Microarchitectures with Fluid Ink. ACS Nano 2016, 10, 8879-8887.


Page 29 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. Method to fabricate copper arrays. (a) Schematic illustration of the scanning-mode MCED process. Detailed front view (b) and side view (c) of the dynamic moving meniscus, highlighting the evaporationinduced mass transport inside the contact line. 92x56mm (300 x 300 DPI)



Figure 2. (a) SEM images of copper line arrays fabricated on gold substrates with different pipette scanning speed. View angle: 45°, scale bars, 10 µm. (b) The width and height. (c) The roughness of the deposited copper lines shown in (a). (d) Concentration profiles of the gold, copper and oxygen obtained by EDS. (e) HRTEM image of a typical copper line. (f) SAED pattern of the selected region in (e). 111x84mm (300 x 300 DPI)


Page 30 of 33

Page 31 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. SEM image and dimension of copper line arrays on: a) glass and b) silicon substrates. Current: 2.25 nA, scale bars: 15 µm. Effect of the representative gold c), silicon d), and glass e) substrates on the contact angle of 0.05M CuSO4 electrolyte viewing from the perpendicular and parallel direction, respectively. (scale bar = 1 mm). f) Schematic representations of copper ions in diffusion zone at different substrates, gold, silicon, and glass, respectively. 95x60mm (300 x 300 DPI)



Figure 4. Multidimensional structures constructed by MCED printing method with positional feedback on glass substrate. (a) Fold line with length of 40 µm. (b) Circular with diameter of 20 µm. (c) "L" Shape. (d) Copper microhelix in tilted 45º and 90º (inset) overlook angle. 80x65mm (300 x 300 DPI)


Page 32 of 33

Page 33 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. a) I–V curve of single horizontal Cu line aligned between two gold electrodes with a gap of 40µm and b) the LED lamp switched on using the single Cu line as an electrical interconnect (an SEM image of the electrodes/copper line is shown in the inset). c) Steady-state response to N2 velocity of a copper vertical microbridge (the SEM image is shown in (d) in tilted 45º) between two gold electrodes with a gap of 20 µm. 86x59mm (300 x 300 DPI)


Dynamic "Scanning-Mode" Meniscus Confined Electrodepositing and

Recommend Documents