crystals Article
Large-Scale Assembly and Mask-Free Fabrication of Graphene Transistors via Optically Induced Electrodeposition Yu Zhang 1,2, *, Yong Yang 1 , Na Liu 3, *, Fanhua Yu 1 , Haibo Yu 2, * and Niandong Jiao 2 1 2 3
*
Department of Computer Science and Technology, Changchun Normal University, Changchun 130032, China;
[email protected] (Y.Y.);
[email protected] (F.Y.) State Key Laboratory of Robotics, Shenyang Institute of Automation Chinese Academy of Sciences, Shenyang 110016, China;
[email protected] School of Mechatronics Engineering and Automation, Shanghai University, Shanghai 200444, China Correspondence:
[email protected] (Y.Z.);
[email protected] (N.L.);
[email protected] (H.Y.)
Received: 19 May 2018; Accepted: 5 June 2018; Published: 7 June 2018
Abstract: Graphene, known as an alternative for silicon, has significant potential in microelectronic applications. The assembly of graphene on well-defined metal electrodes is a critical step in the fabrication of microelectronic devices. Herein, we present a convenient, rapid, and large-scale assembly method for deposition of Ag electrodes, namely optically induced electrodeposition (OIED). This technique enables us to achieve custom-designed and mask-free fabrication of graphene transistors. The entire assembly process can be completed within a few tens of seconds. Our results show that graphene-based transistors fabricated with Ag electrodes function as a p-type semiconductor. Transfer curves of different samples reveal similar trends of slightly p-type characteristics, which shows that this method is reliable and repeatable. Keywords: graphene transistors; induced electrodeposition
large-scale assembly;
mask-free fabrication;
optically
1. Introduction Graphene transistors show extraordinary performance because of the unique electronic, physical, and mechanical properties of graphene [1–4]. To date, the common methods used to assemble and fabricate graphene transistors are e-beam lithography induced deposition [5,6], chemical self-assembly [7] and dielectrophoresis (DEP) [8–12]. Although e-beam lithography induced deposition is compatible with existing micro-fabrication processes, this expensive and complicated manufacturing process is not suitable for low-cost large-scale assembly of graphene. The chemical self-assembly method uses electrostatic interactions to self-assemble graphene sheets onto patterned electrodes via a low-efficiency and uncontrollable process. However, only 10% to 20% of graphene is connected to the electrodes. Owing to its convenient and flexible operating characteristics, many micro/nano-scale materials, such as nanoparticles [13], carbon nanotubes [14], DNA [15] and cells [16], have been assembled onto patterned electrodes via the DEP technique. This method can achieve 100% assembly of graphene; but, the layers of graphene, the position and the direction between graphene and electrodes, and the photomask-induced patterned electrodes are limited to achieve a low-cost, controllable and large-scale graphene device assembly. Optically induced electrodedeposition (OIED), developed from the conventional DEP method, has become a viable technology for assembling micro/nanodevices [17,18]. Utilizing this method, arbitrary configurations of metal electrodes can be directly produced on a computer avoiding conventional mask fabrication. Furthermore, the relative position of graphene and electrodes can be precisely controlled. Crystals 2018, 8, 239; doi:10.3390/cryst8060239
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viable technology for assembling micro/nanodevices [17,18]. Utilizing this method, arbitrary configurations of metal electrodes can be directly produced on a computer avoiding conventional mask2018, fabrication. Furthermore, the relative position of graphene and electrodes can be precisely Crystals 8, 239 2 of 8 controlled. This work reports large-scale graphene device assembly via OIED. Chemical vapor deposition Thisgrown work reports large-scale graphene device assembly via OIED. Chemical (CVD) graphene was transferred onto a a-Si:H-based substrate. Because ofvapor a poordeposition contrast of (CVD) grown graphene was transferred onto a a-Si:H-based substrate. Because of a poor contrast graphene on the substrate, “development” electrode arrays were rapidly constructed (within 1 s) to ofdistinguish graphene on the substrate, “development” electrode arrays were rapidly constructed (within 1 s) the position of graphene. Subsequently, Ag electrodes with customized configurations towere distinguish the position of graphene. Subsequently, Ag electrodes with customized configurations grown on graphene within 30 s via OIED. The current and voltage measurements were were grown within 30 s via OIED. The current and voltage conducted conducted on at graphene room temperature under ambient conditions. We measurements observed that were graphene-based attransistors room temperature under conditions. observed that graphene-based transistors (FETs) (FETs) with Agambient electrodes exhibit We p-type characteristics. The transfer curves of three with Ag electrodes exhibit p-type characteristics. The transfer curves of three graphene-based graphene-based FETs showed that the Dirac points slightly shift to Vg = 0.1, 0.05 and 0.25 V. FETs showed that the Dirac points slightly shift to Vg = 0.1, 0.05 and 0.25 V. 2. Materials and Methods 2. Materials and Methods 2.1. Materials 2.1. Materials Graphene was prepared by the Institute of Metal Research (IMR), Chinese Academy of Graphene was prepared by the Institute of Metal Research (IMR), Chinese Academy of Sciences Sciences using CVD growth method, as depicted in Reference [19]. A solution with a concentration using CVD growth method, as depicted in Reference [19]. A solution with a concentration of 100 mM of of−100 Ag ions was prepared dissolving silver nitrate (99.8% water. purity)This in deionized Ag ionsmM wasof prepared by dissolving silverby nitrate (≥99.8% purity) in deionized solution water. This solution provides the raw materials for both determination of the position graphene provides the raw materials for both determination of the position graphene and fabrication of the and fabrication of the Ag electrodes. Graphene was characterized by atomic force microscopy (AFM) Ag electrodes. Graphene was characterized by atomic force microscopy (AFM) in the tapping mode, in the mode,is and theinAFM images is confirm shown in 1a.and To quality confirmofthe and and the tapping AFM images shown Figure 1a. To theFigure number thenumber graphene, quality of the graphene, the Raman spectra has been performed, as shown in Figure 1b. the Raman spectra has been performed, as shown in Figure 1b. The intensity ratio of the 2D andThe G intensity ratio the shows 2D andthe G typical peak isfeatures above 2,ofwhich shows the typical of of monolayer peak is above 2, of which monolayer graphene. Thefeatures intensity D peak, graphene. The intensity of D peak, carbon which is associated with disordered carbon atoms and defects, which is associated with disordered atoms and defects, is nearly invisible, indicating the highis nearly invisible, indicating the high quality of the graphene. quality of the graphene.
(a)
(b)
Figure1.1.(a) (a)Height Heightimage imageof ofthe the graphene graphene in in AFM AFM tapping tapping mode. 30.0 µm; (b) Figure mode. Scan Scansize: size:30.0 30.0µm µm× × 30.0 µm; Raman spectroscopy measurement of the intensity of the D and G peaks on the graphene layer in (a). (b) Raman spectroscopy measurement of the intensity of the D and G peaks on the graphene layer in The D,D, GG and 2D2D Raman peaks forfor thethe graphene areare labeled. (a). The and Raman peaks graphene labeled.
2.2. Apparatus 2.2. Apparatus The home-made OIED experimental system for fabricating electrodes via the introduction of The home-made OIED experimental system for fabricating electrodes via the introduction of microfluidic control technology into a conventional optically induced DEP (ODEP) experimental microfluidic control technology into a conventional optically induced DEP (ODEP) experimental system is shown in Figure 2. The system consists of five functional modules, including a virtual system is shown in Figure 2. The system consists of five functional modules, including a virtual electrode generation module (Flash 11, Adobe, CA, USA), OIED chip (discussed later), projection electrode generation module (Flash 11, Adobe, CA, USA), OIED chip (discussed later), projection module (LCD projector, Sony VPL-F400X, Tokyo, Japan; condenser objective, Nikon 50X/0.55, module (LCD projector, Sony VPL-F400X, Tokyo, Japan; condenser objective, Nikon 50X/0.55, Tokyo, Japan), operation control module (3D Mobile Platform; signal generator, Agilent 33522A, CA, USA), and real-time visual feedback module (CCD, Zoom 160, OPTEM, Alberta, Canada).
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Crystals 2018, 8, 239 Tokyo, Japan), operation control module (3D Mobile Platform; signal generator, Agilent 33522A,
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CA, USA), and real-time visual feedback module (CCD, Zoom 160, OPTEM, Alberta, Canada).
(a)
(b)
Figure 2. (a) Experimental setup of optically induced electrodeposition (OIED); (b) the OIED chip
Figure 2. (a) Experimental setup of optically induced electrodeposition (OIED); (b) the OIED chip where electrochemical reactions occur. where electrochemical reactions occur. 2.3. Methods
2.3. MethodsAn Ag electrode was constructed on graphene by oxidation-reduction reaction process: An Ag electrode was constructed on graphene by oxidation-reduction reaction process:
Ag e Ag +
(1)
−
+ e will = Ag (1) According to the above reaction, Ag operation stop, because water in the solution will decompose and eventually dry out during the operating process. In traditional ODEP chips, the According to thetoabove reaction, operation willthe stop, water in the solution will decompose solution needs be injected manually through inletbecause (Inlet) with a micro-shifter, as shown in Figure 3a. dry This out issueduring can be overcome using the OIED system. An OIED chip consists mainly and eventually the operating process. In traditional ODEP chips, theofsolution three components: a photoconductive lower electrode, microfluidic chamber for needs to be injected manually through the inlet (Inlet) with a micro-shifter, ascontaining shown inand Figure 3a. transporting the electrolyte, and a patterned indium tin oxide (ITO) upper electrode, as shown in This issue can be overcome using the OIED system. An OIED chip consists mainly of three Figure 3b. The photoconductive lower electrode substrate consists of predeposited 120 nm-thick components: a photoconductive electrode, chamber containing and transporting ITO and 1 µm-thick a-Si:H lower fabricated throughmicrofluidic plasma-enhanced CVD.for The upper electrode is a the electrolyte, a patterned indium tinstructure oxide of (ITO) upper electrode, as shown Figure 3b. patterned and ITO glass. Figure 3c,d show the the patterned ITO glass. First, the inlet,ininlet channel, operatinglower area, outlet channel, and outlet have been on a double-sided adhesive The photoconductive electrode substrate consists of carved predeposited 120 nm-thick ITO and tape, as shown in Figure 3c. The carved double-sided adhesive tape was then transferred onto an 1 µm-thick a-Si:H fabricated through plasma-enhanced CVD. The upper electrode is a patterned ITO glass, and the inlet and the outlet were drilled for inserting pipes as shown in Figure 3d. ITO glass. Figure 3c,d show the structure of the patterned ITO glass. First, the inlet, inlet channel, Before electrode deposition, graphene was transferred onto a photoconductive lower electrode operating area, outlet channel, and outlet have been carved on a double-sided adhesive tape, as shown by the bubbling transfer method [21]. Pipes were inserted into the inlet and the outlet after the in Figure 3c. The carved tape was then transferred ITO Crystals 2018, 8, xdouble-sided FOR PEER REVIEW 4 of 8 glass, and the patterned ITO upper electrode andadhesive the photoconductive electrode coating onto with an graphene were inlet and the outlet were drilled for(Agilent inserting pipesthat as shown in aFigure 3d. voltage was applied packaged. A signal generator 33522A) generated sinusoidal between the top and the bottom ITO electrodes. The flow velocity of the solution in the chamber was controlled by a micro pump (HARVARD PHD 2000). The deposition of the Ag electrode was carried out at an amplitude of 20 Vpp (peak-to-peak voltage) and a frequency of 50 kHz. After the deposition process, the samples were characterized using a digital microscope (KH-7700 Hirox, Japan), AFM (D3100, Veeco, NY, US), and scanning electron microscope (SEM; Zeiss EVO MA, Oberkochen, Germany). The conductivity of the electrodes and graphene was Outlet channel measured using two tungsten probes with(a) diameters ofInlet 5 µm on an analytical probe station. A channel semiconductor analyzer (Agilent, 4155C) was used to measure the electrical properties at room Outlet Operating area Inlet temperature under ambient conditions. (c)
Inlet
Outlet
Operating area
(b)
(d)
Figure 3. (a) Conventional ODEP chip [20]; (b) schematic illustration of the structure of the OIED chip; (c) pattern to be fabricated on double-sided adhesive tape; (d) patterned ITO glass.
Figure 3. (a) Conventional ODEP chip [20]; (b) schematic illustration of the structure of the OIED chip; (c) pattern to be fabricated on double-sided adhesive tape; (d) patterned ITO glass. 3. Results and Discussion 3.1. Growth of Ag Electrodes by OIED Figure 4 shows the topographic images of Ag electrodes deposited at different time intervals. Figure 4a–f are the characterization results after 10 and 20 s deposition, respectively obtained by optical microscopy, AFM and SEM. The scale bars are 100, 30 and 3 µm, respectively for optical, AFM, and SEM images. The AFM images reveal that the thickness of the Ag electrodes increases with increase in the deposition time. The SEM images show that Ag particles become larger and denser with increase in the deposition time, as shown in Figure 4c,f.
(a)
Outlet channel
Inlet channel Inlet
Operating area
Outlet
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(c) Before electrode deposition, graphene was transferred onto a photoconductive lower electrode by the bubbling transfer method [21]. Pipes were inserted into the inlet and the outlet after the patterned ITO upper electrode and the photoconductive electrode coating with graphene were packaged. A signal Inlet generator (Agilent 33522A) that generated a sinusoidal voltage was appliedOutlet between the top and the bottom ITO electrodes. The flow velocity of the solution in the chamber was controlled by a micro pump (HARVARD PHD 2000). The deposition of the Ag electrode was carried out at an amplitude of 20 Vpp (peak-to-peak voltage) and a frequency of 50 kHz. After the deposition process, the samples were characterized usingOperating a digitalarea microscope (KH-7700 Hirox, Japan), AFM (D3100, Veeco, NY, US), and scanning electron microscope (SEM; Zeiss EVO MA, Oberkochen, Germany). (b) The conductivity of the electrodes and graphene was measured using (d) two tungsten probes with diameters of 5 µm on an analytical probe station. A semiconductor Figure 3. (a) Conventional ODEP chip [20]; (b) schematic illustration of the structure of the OIED analyzer (Agilent, 4155C) was used to measure the electrical properties at room temperature under chip; (c) pattern to be fabricated on double-sided adhesive tape; (d) patterned ITO glass. ambient conditions.
3. Results and Discussion 3. Results and Discussion 3.1. 3.1. Growth Growth of of Ag Ag Electrodes Electrodes by by OIED OIED Figure Figure 44 shows shows the the topographic topographic images images of of Ag Ag electrodes electrodes deposited deposited at at different different time time intervals. intervals. Figure 4a–f are the characterization results after 10 and 20 s deposition, respectively Figure 4a–f are the characterization results after 10 and 20 s deposition, respectively obtained obtained by by optical microscopy, AFM and SEM. The scale bars are 100, 30 and 3 µm, respectively for optical, optical microscopy, AFM and SEM. The scale bars are 100, 30 and 3 µm, respectively for optical, AFM, AFM, andimages. SEM images. The AFM images thatthickness the thickness theelectrodes Ag electrodes increases and SEM The AFM images revealreveal that the of theofAg increases with with increase the deposition time.SEM The images SEM images show Ag particles larger and increase in theindeposition time. The show that Agthat particles becomebecome larger and denser denser with increase in the deposition time, as shown in Figure 4c,f. with increase in the deposition time, as shown in Figure 4c,f. (a)
(c)
(d)
(f)
(b) (e)
Figure 4. Optical, AFM, and SEM images of the Ag electrodes deposited at different time intervals. Figure 4. Optical, AFM, and SEM images of the Ag electrodes deposited at different time intervals. (a,d) Optical images images of of Ag Ag electrodes electrodes deposited deposited with with in in 10 10 and and 20 20 s, s, respectively. respectively. Both (a,d) Optical Both the the bars bars represent 100 µm; µm; (b,e) (b,e) magnified magnifiedAFM AFMimages imagesofofthe theblack blacksquare-enclosed square-enclosedregions regions panels a and represent 100 inin panels a and d, respectively. Both the scale bars represent 4 µm. Scan size: 30 µm × 30 µm; (c,f) topographic images of the surfaces of the Ag electrodes obtained via SEM. Both the bars represent 3 µm.
3.2. Large-Scale Assembly of Graphene by OIED Graphene on an OIED chip cannot be directly observed through a digital microscope; therefore, the position of graphene on the OIED chip needs to be determined before the deposition of the electrodes. Owing to the hydrophobic property of graphene, the electrochemical reaction of the solution on graphene is much slower than that on the a-Si:H substrate. Therefore, the position of graphene can be distinguished by rapidly depositing electrode arrays. These arrays are called “development” arrays; they allow graphene to appear on the substrate like in a photographic film development process. The deposition time of the “development” arrays is very short, usually within 1 s; hence, these electrode arrays are not electrically connected. Figure 5 shows the Ag electrodes
d, respectively. Both the scale bars represent 4 µm. Scan size: 30 µm 30 µm; (c,f) topographic images of the surfaces of the Ag electrodes obtained via SEM. Both the bars represent 3 µm.
3.2. Large-Scale Assembly of Graphene by OIED Crystals 2018, 8, 239 Graphene on
5 of 8 an OIED chip cannot be directly observed through a digital microscope; therefore, the position of graphene on the OIED chip needs to be determined before the deposition of the electrodes. hydrophobic property of graphene, the electrochemical depositionOwing processtoonthe graphene using the OIED system. The “development” results ofreaction grapheneofonthe solution on graphene is much slower than that on the a-Si:H substrate. Therefore, the position of the a-Si:H substrate are as shown in Figure 5a. The white dotted lines indicate the “development” graphene be distinguished by rapidly electrode arrays. These are called electrodecan arrays. The edges of graphene are depositing visible in these electrode arrays. Afterarrays the position of “development” arrays; they allow graphene to appear on the substrate like in a photographic film graphene is identified, the patterns of electrodes are dynamically constructed on the computer based development deposition time of The the “development” arrays is veryas short, usuallyareas. within on the shapeprocess. and theThe position of graphene. projected patterns are visible red lighted 1 s; hence, these electrode arrays are not electrically connected. Figure 5 shows the Ag electrodes As shown in Figure 5b–d, the thickness of the deposited Ag electrodes increases with an increase in deposition process onThe graphene using thewas OIED system. The30“development” results of graphene on the deposition time. deposition time approximately s. the a-Si:H substrate are as Figureof5a. The white dotted lines the the “development” Figure 6a–c show theshown opticalinimages large-scale graphene deviceindicate assembly; black bars represent 200, 100, and 200 µm, respectively. Different and sizes of Ag electrodes electrode arrays. The edges of graphene are visible shapes in these electrode arrays. Afterwere the deposited position of at the hexagonal edge of graphene with width in the range of 15–30 µm, and Ag deposition occurs atbased the graphene is identified, the patterns of electrodes are dynamically constructed on the computer andand defects graphene. Figure 6d The shows the current-voltage usingAs onripples the shape the in position of graphene. projected patterns arecharacteristics visible as redmeasured lighted areas. a semiconductor parameter analyzer. The Ag electrode is electrically connected to graphene though shown in Figure 5b–d, the thickness of the deposited Ag electrodes increases with an increase in the an Ohmictime. connection. The insettime in Figure 6d is the optical30 image deposition The deposition was approximately s. of two tungsten probes connecting
the electrodes on an analytical probe station for the measurement of current-voltage characteristics. “development” arrays
(a)
(b)
Virtual optical electrodes graphene graphene
(c)
(d)
Figure 5. Optical images of the Ag electrodes deposition process using the OIED system. (a) Images of
Figure 5. Optical images Ag electrodes deposition process using the OIED system. (a) Images graphene appearing on of thethe substrate though “development” arrays indicated by white dotted lines. of The graphene appearing on theoptical substrate thoughdesigned “development” indicated by white dotted red rectangles are virtual electrodes by using arrays a commercial personal computer lines. The red rectangles are virtual optical electrodes designed by using a commercial personal software (Flash 11, Adobe); (b–d) Ag electrode deposition process. The shape of graphene becomes computer software (Flash of 11,the Adobe); (b–d) Ag electrode visible and the thickness electrodes increases duringdeposition the process.process. The shape of graphene becomes visible and the thickness of the electrodes increases during the process.
deposition occurs at the ripples and defects in graphene. Figure 6d shows the current-voltage characteristics measured using a semiconductor parameter analyzer. The Ag electrode is electrically connected to graphene though an Ohmic connection. The inset in Figure 6d is the optical image of two tungsten probes connecting the electrodes on an analytical probe station for the measurement of Crystals 2018, 8, 239 6 of 8 current-voltage characteristics.
Figure 6. Large-scale graphenedevice device assembly assembly and characteristics. (a–c)(a–c) Optical graphene andcurrent-voltage current-voltage characteristics. Optical Figure 6. Large-scale images of different configurations of Ag electrodes connected at the edges of graphene. The hexagonal images of different configurations of Ag electrodes connected at the edges of graphene. The shapes correspond to single-crystal graphene. The black bars are 200, 100, and 200 µm, respectively in hexagonal shapes correspond to single-crystal graphene. The black bars are 200, 100, and 200 µm, (a–c); (d) current–voltage characteristics. The inset shows the optical image of two tungsten probes respectively in (a–c); (d) current–voltage characteristics. The inset shows the optical image of two connecting the electrodes on an analytical probe station. tungsten probes connecting the electrodes on an analytical probe station.
3.3. The Structure and Electrical Characteristics of Assembled Graphene-Based FETs
3.3. The Structure and Electrical Characteristics of Assembled Graphene-Based FETs The electrical characteristics of the assembled graphene-based FETs with Ag electrodes were The electrical characteristics of the assembled graphene-based FETs with Ag electrodes measured at room temperature under ambient conditions using a semiconductor parameter analyzerwere measured roomAstemperature under ambient conditions using a with semiconductor parameter (Agilentat4155C). shown in Figure 7a, the output curves were measured a fixed gate voltage (Vg ) from −40 4155C). to −10 VAs in steps of in −10 V. The7a, output curvescurves indicatewere that the graphene-based FET gate analyzer (Agilent shown Figure the output measured with a fixed exhibits characteristics. The main charge carriers arecurves holes, and as thethat concentration of the voltage (Vg) p-type from −40 to −10 V in steps of −10 V. The output indicate the graphene-based increase when the Vg is negative, the graphene decreases. The transfer curves were of FET holes exhibits p-type characteristics. The main charge resistance carriers are holes, and as the concentration measured at a fixed drain 100 mV for samples,resistance as shown in Figure 7b. The The Dirac points the holes increase when thevoltage Vg is of negative, thethree graphene decreases. transfer curves are at Vg = 0.1, 0.05, and 0.25. The G and 2D bands upshift to ~1590 and ~2685 cm−1 , which shows were measured at a fixed drain voltage of 100 mV for three samples, as shown in Figure 7b. The typical features of p-doping. The slight shift in the Dirac point reveals that this method is reliable Dirac points are at Vg = 0.1, 0.05, and 0.25. The G and 2D bands upshift to ~1590 and ~2685 cm−1, and repeatable.
which shows typical features of p-doping. The slight shift in the Dirac point reveals that this method is reliable and repeatable.
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(b)
Figure 7.7.Electrical Electrical characteristics the graphene-based FETs. curves (a) Output curves of the Figure characteristics of theof graphene-based FETs. (a) Output of the graphene-based ds = 0–2.5 V, with Vg ranging from −40 to −10 V; (b) transfer curves of the graphene-based FET for V FET for Vds = 0–2.5 V, with Vg ranging from −40 to −10 V; (b) transfer curves of the graphene-based = −5–5 V of and a fixed graphene-based FETs at Vagfixed FETs at Vg = −5–5 V and Vds 100 mV. Vds of 100 mV.
4. Conclusions 4. Conclusions In summary, a large-scale assembly of graphene has been successfully realized using OIED. In summary, a large-scale assembly of graphene has been successfully realized using OIED. Both the electrode shapes and sizes could be dynamically controlled in real-time without using any Both the electrode shapes and sizes could be dynamically controlled in real-time without using any conventional lithography procedures during the entire assembly process. Silver electrodes could be conventional lithography procedures during the entire assembly process. Silver electrodes could be fabricated rapidly within a few tens of seconds and were electrically connected to graphene though fabricated rapidly within a few tens of seconds and were electrically connected to graphene though an Ohmic connection. Furthermore, current and voltage measurements of the graphene-based FETs an Ohmic connection. Furthermore, current and voltage measurements of the graphene-based FETs with Ag electrodes show p-type characteristics. The Dirac points are slightly shifted to Vg = 0.1, 0.05, with Ag electrodes show p-type characteristics. The Dirac points are slightly shifted to Vg = 0.1, and 0.25 V, respectively. Our future work will investigate the contact resistance of devices with 0.05, and 0.25 V, respectively. Our future work will investigate the contact resistance of devices with different metal contacts and deposition intervals. Unlike the conventional technique, the presented different metal contacts and deposition intervals. Unlike the conventional technique, the presented method could achieve a bottom-up, high-efficiency and low-cost assembly of graphene at precise method could achieve a bottom-up, high-efficiency and low-cost assembly of graphene at precise locations, demonstrating the potential as a robust and highly efficient method for the fabrication of locations, demonstrating the potential as a robust and highly efficient method for the fabrication of nanoelectronic devices using other emerging two-dimensional materials. nanoelectronic devices using other emerging two-dimensional materials. Author Contributions: Contributions: Y.Z. Y.Z.designed designedand andperformed performedexperiments experiments and and measurements, measurements, carried carried on on data data analysis analysis Author and drafted draftedthe themanuscript. manuscript.N.L. N.L.and andY.Z. Y.Z. performed electrode deposition discussed results. and performed AgAg electrode deposition andand discussed the the results. Y.Y.,Y.Y., F.Y., H.Y. in thein monitoring the experimental work work and revision of the of manuscript. F.Y., and H.Y.N.J. andparticipated N.J. participated the monitoring the experimental and revision the manuscript. Acknowledgments: supported by National Natural Science Foundation of Chinaof(Grant 61604019, Acknowledgments: This Thiswork work supported by National Natural Science Foundation ChinaNo. (Grant No. 61703265), Natural Science Foundation of Jilin Province, China (Grant No. 20160520098JH), and Talent introduction 61604019, 61703265), Natural Science Foundation of Jilin Province, China (Grant No. 20160520098JH), and scientific research project of Changchun Normal University, China (RC2016009). Talent introduction scientific research project of Changchun Normal University, China (RC2016009). Conflicts of Interest: The authors declare no conflicts of interest. Conflicts of Interest: The authors declare no conflicts of interest.
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