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1 In the format provided by the authors and unedited. DOI: /NNANO Multiple nanostructures based on anodized aluminium oxide templates Liaoyong Wen, Rui Xu, Yan Mi, Yong Lei * 1 NATURE NANOTECHNOLOGY 1

2 Materials and chemicals All chemicals and solutions were used without further processing. Phosphoric acid solution (85 wt.% in H2O), sulfuric acid solution (ACS reagent, wt.%), hydrogen peroxide solution (30 wt.% in H2O, ACS reagent), sodium hydroxide (reagent grade, 98%), hydrochloric acid solution (ACS reagent, 37%), copper(ii) chloride (99%), nickel(ii) chloride (98%), nickel sulfamate (II) tetrahydrate (98%), boric acid (99.5%), cadmium chloride (99.99%), element sulfur ( 99.5%), copper sulphate ( 99.99%), lactic acid (ACS reagent, 85%), trimethylaluminum (97%), titanium (IV) chloride ( 99.99%), tin (IV) chloride ( 99.99%) were purchased from Sigma Aldrich. Al foil (99.999%) and Silver plating solution were purchased from Alfa. PMMA solution (Microchem 950) was purchased from MicroChem Corporation. 4 inch Si master molds with square- and hexagon-arranged nanohole arrays (400 and 800 nm spacings, respectively) were purchased from AMO GmbH. Addressable multi-gates transistor based on binary AZO/ZnO nanostructure arrays An addressable multi-gates nanowire transistor was proposed on the basis of binary nanostructure arrays, which is inspired from the previously reported nanowire transistors 1-4. As the illustration shown in Supplementary Fig. S23a and S23b, the square nanowires can be addressed by Ax (x=1-5) with ax (x=1-5) electrodes, while the round nanowires can be controlled through Bx (x=1-5) with bx (x=1-5) electrodes. For instance, the square nanowire (I) is addressed by A4 a2 electrodes, and the round nanowire (II) is controlled through B3 b2 electrodes (Supplementary Fig. S23b). The core concept of the multi-gates nanowire transistor is that the semiconductor material in the square pore works as a semiconductor channel, the conductive material in the surrounded four round pores acts as controlling gates, while the insulating AAO template is a native dielectric layer (Supplementary Fig. S23c). During the transistor operation, the four gates 2 NATURE NANOTECHNOLOGY 2

3 can work as either a single-gate or multi-gates (two-, three- or four-) under the different purpose. Such as, when a ZnO nanowire (I) in Supplementary Fig. S23b is defined as the semiconductor channel and being manipulated by A4 a2 electrodes, the surrounded AZO four-gates of this wire can be controlled by B3 b1, B3 b2, B4 b1, and B4 b2 electrodes individually or simultaneously. The ZnO and AZO nanowires were separately grown in the A-pores and B-pores using Strategy-Three, and the detailed ALD receipt could be found in our previous report 5. Then, a standard electron beam lithography (EBL, Raith 150) process was conducted to fabricate electrode lines on one side of the template to coincide with the top ends of the ZnO and AZO nanowires, respectively (Supplementary Fig. S23d and S23e). After that, the same EBL process was carried out again to fabricate electrode lines on the other side of the template, which results in crossbar electrode lines on both sides of the template (Supplementary Fig. S23f). Meanwhile, multi-tip scanning tunneling microscopy, a powerful tool for electrical transport measurements at nano-scale, was also used to investigate the performance of a single ZnO nanowire without the complex device assembling process (Supplementary Fig. S23g and S23h). The I-V measurements from a single ZnO nanowire are plotted in Supplementary Fig. S23i, confirming that the ZnO source-drain current increases gradually when applying a bias from 0 V to 9 V on one of the surrounded AZO gates. Therefore, it validates the possibility of realizing high-density multi-gate nanowire transistors with the binary nanostructure arrays. Moreover, we can further optimize the performance of the transistor by adjusting the thickness of the dielectric Al2O3 layer, the growth condition of the ZnO semiconductor channel and the AZO gate, as well as the length of the ZnO semiconductor channel. 3 NATURE NANOTECHNOLOGY 3

4 Figure S1 Key steps for binary-pore template. a and b, Photo and enlarged SEM image of imprinted Al foils. c and d, SEM images of imprinted template after anodization: top-side (c, showing square-shaped A-pores) and bottom-side (d, showing A-pore barrier layer). e, Crosssectional SEM image of imprinted template after the selective etching from the bottom-side of template in 0.1 M NaOH solution at room temperature (~ 18 C). Scale bar, 400 nm. 4 NATURE NANOTECHNOLOGY 4

5 Figure S2 Adjustment of B-pore size from bottom-side of template. SEM images of the bottom-side of template after different etching times in 0.1 M NaOH solution at room temperature (~ 18 C): a, 20 min; b, 40 min; c, 60 min; d, 80 min. The corresponding size and roundness of the etched B-pores were converted and analyzed with ImageJ. The B-pore size and roundness are 63 ± 7 nm and in the range of (based on 126 B-pores in (a)), 131 ± 6 nm and in the range of (based on 126 B-pores in (b)), 188 ± 5 nm and in the range of (based on 140 B-pores in (c)), 255 ± 7 nm and in the range of (based on 140 B- pores in (d)), respectively. Scale bar, 400 nm. 5 NATURE NANOTECHNOLOGY 5

6 Figure S3 Adjustment of B-pore size from top-side of template. a, Illustration and SEM image of template after removing the ALD TiO2 layer and the B-pore barrier layer on the top-side surface. SEM images of the template after different etching times in 0.1 M NaOH solution at room temperature (~ 18 C): b, 30 min; c, 50 min; d, 70 min. The corresponding size and roundness of the etched B-pores were converted and analyzed with Imagej. The B-pore size and roundness are 102 ± 8 nm and in the range of (based on 140 B-pores in (b)), 158 ± 8 nm and in the range of (based on 140 B-pores in (c)), 225 ± 5 nm and in the range of (based on 126 B-pores in (d)), respectively. Scale bar, 400 nm. 6 NATURE NANOTECHNOLOGY 6

7 Figure S4 Adjustment of A-pore size. SEM images of templates after immersing the top-side of template in 5 wt.% H3PO4 at 30 o C for different times and then the bottom-side of the template in 0.1 M NaOH solution at room temperature (~ 18 o C) for 40 min: a, 20 min; b, 40 min; c, 60 min; d, 80 min. The sizes of A-pores in (a-d) are 150 ± 7 nm (based on 126 A-pores in (a)), 182 ± 5 nm (based on 140 A-pores in (b)), 236 ± 6 (based on 112 A-pores in (c)), and 271 ± 7 nm (based on 126 A-pores in (d)), respectively. And the corresponding B-pore sizes in (a-d) are 125 ± 7 nm (based on 140 b-pores in (a)), 143 ± 8 nm (based on 117 B-pores in (b)), 119 ± 8 nm (based on 130 B-pores in (c)), and 130 ± 5 nm (based on 130 B-pores in (d)). Though the same etching time is used, there is a relatively large deviation (about 15%) for B-pore sizes from sample to sample. The reason should be mainly caused by the fluctuation of the experimental 7 NATURE NANOTECHNOLOGY 7

8 conditions (mainly the temperature of the etching solutions) of the selective etching, which is usually carried out at room temperature and it might be varied. Scale bar, 400 nm. 8 NATURE NANOTECHNOLOGY 8

9 Figure S5 Microstructure and composition analyses of square template. a and b, Low- and High-magnified TEM images of TEM lamella sample. The boundaries of different layers in pore wall are indicated by yellow dot lines in (b). c, EDX line-scan and mapping of the red square area in (a), which show the distribution profiles of P, O and Al elements, respectively. These results reveal the existence of double layers inside the pore wall that the inner layer is a pure Al2O3 layer and the outside layer is a P ion incorporated Al2O3 layer. The ratio of the pure layer versus the P ion incorporated layer is about 1:4, which is close to that of the conventional hexagonal template 6,7. d, XRD pattern of imprinted Al foil after anodization. Since there has no alumina diffraction peaks been observed, the composition of the square template should be amorphous alumina. 9 NATURE NANOTECHNOLOGY 9

10 Figure S6 Treatment of square template in H3PO4 solution. SEM images of bottom-side of square template after different times in 5 wt.% H3PO4 solution at 30 o C: a, 60 min; b, 90 min; c, 120 min. The results show that instead of generating new B-pores at the fourfold junction sites of anodized A-pores, the barrier layer of anodized A-pores is removed and non-uniform A-pores start to appear with the increase of immersing time. 10 NATURE NANOTECHNOLOGY 10

11 Figure S7 Synthesis of binary nanowire/nanowire arrays (Strategy-One). a, Preparation of template and removal of the B-pores barrier layer (on the top-side surface of the template). b, Deposition of supporting substrate. c, Reversal of the template, removal of the unoxidized Al, and selective etching of B-pores. d, Electrodeposition of round nanowires in the B-pores and coating of a top Al2O3 insulating layer. e, Removal of the Al2O3 insulating layer and A-pore barrier layer (at the bottom-side surface of the template), electrodeposition of square nanowires in the A-pores. f, Dissolution of the template and Al2O3 insulating layer. g, Representative SEM images of binary nanowire/nanowire arrays. Scale bar, 400 nm. 11 NATURE NANOTECHNOLOGY 11

12 Figure S8 Synthesis of binary nanotube/nanowire arrays (Strategy-Two). a, ALD growth of square nanotubes in the A-pores. b, Removal of the ALD layer and B-pore barrier layer (on the top-side surface of the template). c, Deposition of supporting layer, reversal of the template, and removal of the unoxidized Al. d, Selective etching of B-pores. e, Electrodeposition of round nanowires in the B-pores. f, Removal of the A-pore barrier layer, opening of the square nanotubes, and dissolution of the binary-pore template for opened-tubes (top); dissolution of the binary-pore template for closed-tubes (bottom). g, Representative SEM images of binary nanotube/nanowire arrays with opened-tubes (left) and closed-tubes (right), respectively. Scale bar, 400 nm. 12 NATURE NANOTECHNOLOGY 12

13 Figure S9 Synthesis of binary nanotube/nanotube arrays (Strategy-Three). a, ALD growth of square nanotubes in the A-pores. b, Removal of the ALD layer and B-pore barrier layer (on the top-side of the template). c, Deposition of supporting layer, reversal of the template, and removal of the unoxidized Al. d, Selective etching of B-pores. e, ALD growth of round nanotubes in the B-pores. f, Removal of the ALD layer and A-pore barrier layer (at the bottom-side surface of the template), dissolution of the binary-pore template. g, Representative SEM images of binary nanotube/nanotube arrays. Scale bar, 400 nm. 13 NATURE NANOTECHNOLOGY 13

14 Figure S10 Synthesis of binary CdS nanowire arrays (Strategy-Four). a, ALD growth of square TiO2 nanotubes in A-pores. b, Removal of the TiO2 layer and B-pore barrier layer (on the top-side surface of the template). c, Deposition of Ni nanowires and subsequent Ni supporting layer, reversal of the template, and removal of the unoxidized Al foil. d, Selective etching of B-pores. e, Electrodeposition of round CdS nanowires in the B-pores. f, Removal of the A-pore barrier layer, opening of the TiO2 nanotubes (at the bottom-side surface of the template), and dissolution of the binary-pore template. g, Representative SEM images of binary nanowire arrays. h, XRD pattern of the binary structures in (g). Besides the diffraction peaks of Ni (JCPDS No ) and Au (JCPDS No ), all the other peaks can be indexed to the (100), (002), (101), and (110) diffractions of the hexagonal CdS (PDF# ) and (101) and (200) diffractions of the tetragonal TiO2 (PDF# ). But the CdS (100) and (110) peaks largely overlap with the TiO2 (101) and (200) peaks, respectively. Scale bar, 400 nm. 14 NATURE NANOTECHNOLOGY 14

15 Figure S11 Synthesis of binary nanodot/nanodot arrays (Strategy-Five). a, Preparation of ultra-thin template, removal of the B-pore barrier layer (on the top-side surface of the template), selective etching of B-pores, and transfer of ultra-thin binary-pore template onto substrate. b, Evaporation of round nanodots through the B-pores. c, Evaporation of sacrificial layer. d, Removal of the sacrificial layer and A-pore barrier layer (at the bottom-side surface of the template). e, Evaporation of square nanodots through the A-pores. f, Removal of the ultra-thin template and etching of the sacrificial layer for obtaining binary nanodot/nandot arrays. g, Representative SEM images of binary nanodot/nanodot arrays. Scale bar, 400 nm. 15 NATURE NANOTECHNOLOGY 15

16 Figure S12 In-situ observation of original B-pores. a, FIB milling on A-pore TiO2 filled template (indicated by yellow arrow). b-f, Cross-sectional SEM images of the different milling positions. The inverted pyramid voids are clearly observed at the each fourfold junction site of A- pores (b, yellow cycles; f, red cycles)). However, due to the small diameter of narrow B-pores and also the contamination from re-deposited or etched particles, the narrow B-pores beneath the inverted pyramid void are too challenging to be observed. Scale bar, 400 nm. 16 NATURE NANOTECHNOLOGY 16

17 Figure S13 Simulated E-field distributions on imprinted Al foils at very early stage of anodization. The geometric parameters of the simulations: pattern spacing (400 nm), diameter and height of round concaves (140 and 50 nm), and Al substrate thickness (1000 nm), respectively. We treated the imprinted Al surfaces as the terminal interfaces (a and d, blue colour), the basic units of the square- and hexagon-arranged patterns as the periodical boundaries (b and e, blue colour), and the backside Al foils as the ground (c and f, blue interface). g and h, Top-down and cross-sectional views of simulated E-field distribution on the Al foil with hexagon-arranged pattern. 17 NATURE NANOTECHNOLOGY 17

18 Figure S14 Pore-widening and selective etching of hexagonal template. SEM images of the bottom-side of hexagonal templates: a, Pore-widening in 5 wt.% H3PO4 solution at 30 C for 120 min; b, selective etching in 0.1 M NaOH solution at room temperature for 60 min. c-e, A-pore TiO2 filled template after different etching times in 0.1 M NaOH solution: c, 20 min; d, 40 min; e, 60 min. Scale bar, 400 nm. 18 NATURE NANOTECHNOLOGY 18

19 Figure S15 Simulated E-field distribution of square template at steady-state stage of anodization. The geometric parameters of the simulation are based on the SEM and TEM images of square template: interpore spacing (400 nm), square A-pore diameter (140 nm), pyramid void size (top and bottom diameters: 36 and 9 nm; height between each other: 80 nm), narrow B-pore diameter (9 nm), and template thickness (800 nm), respectively. We treated the inner pore wall as the terminal interface (a, blue colour), the basic unit of the square-arranged cell as the periodical boundaries (b, blue colour), the bottom side of the template as the ground (c, blue colour). We also assumed the sealed pyramid voids and narrow pores under a floating potential (d, blue colour). e and f, Top-down and cross-sectional views of the simulated E-field distribution on square template. 19 NATURE NANOTECHNOLOGY 19

20 Figure S16 SEM images and photo of the key steps for obtaining ternary-pore templates. a, Etching of binary-concave patterns on silicon substrate by RIE. b, Anodization of imprinted Al foils with binary-concave patterns to grow two square (A- and B-) pores over large scales (up to centimetre-sized range). c, Generating of new (C-) pores with a 2 nd selective etching, where only two sorts of barrier layers are observed at the opposite side of the template. d-f, Removal of the barrier layers to expose the A- and B-pores with ion milling. Various sizes of the A- and B-pores can be determined by the different sizes of the binary-concave patterns on Al foils. As a consequence, the sizes of the A- and B-pores are 67 ± 7 and 122 ± 9 nm (based on 140 A-pores and 126 B-pores in (d)), 79 ± 9 and 115 ± 9 nm (based on 117 A-pores and 140 B-pores in (e)), 20 NATURE NANOTECHNOLOGY 20

21 95 ± 7 nm (based on 130 A- and 126 B-pores in (f)), respectively. The corresponding shortest and longest lengths of C-pores are 172 ± 16 and 240 ± 20 nm (based on 266 pores in (d)), 145 ± 15 and 168 ± 19 nm (based on 247 pores in (e)), as well as 153 ± 10 and 157 ± 11 nm (based on 266 pores in (f)). It should be noted that some other processes, such as UTAM transferring, RIE, and imprinting, could affect the morphological uniformity of each set. The shape variation of the pores is mainly ascribed to these processes. Scale bar, 400 nm. 21 NATURE NANOTECHNOLOGY 21

22 Figure S17 SEM images and photo of the key steps for quadruple-pore templates. a, Etching of ternary-concave patterns on silicon substrate by RIE. b, Anodization of Al foils with ternary-concave patterns to grow two square (A- and B-) pores, and one rectangular (C-) pores over large scales (up to centimetre-sized range). c, Generating of new (D-) pores with a 3 rd selective etching, where yet only two sorts of barriers are observed at the opposite side of the template. d, Removal of the barrier layers to expose the A-, B-, and C-pores with ion milling. The sizes of A- and B-pores are 71 ± 8 and 86 ± 6 nm (based on 126 A-pores and 140 B-pores in (d)), respectively. The widths and lengths of the rectangular C-pores are 68 ± 9 and 91 ± 11 nm (based 22 NATURE NANOTECHNOLOGY 22

23 on 266 C-pores in (d)), and the corresponding aspect ratio is 1.24 ± 0.16 nm. The size of D-pores is 120 ± 20 nm (based on 437 D-pores in (d)), and the corresponding roundness of the D-pores is in the range of Scale bar, 200 nm. 23 NATURE NANOTECHNOLOGY 23

24 Figure S18 Binary-pore template with large interpore spacing. a, SEM image of imprinted template with about 800 nm interpore spacing, which is obtained from the anodization under a constant voltage of 320 V in a mixture solution (2.5 ml of 1% H3PO4, 1:1 v/v% of 4% citric acid and ethylene glycol) at 10 o C for 24 h. Inset: photo of the imprinted templates up to centimetrescale. b, Tilted (left) and cross-sectional (right) SEM image of a binary-pore template with two sets of barrier layers located at the opposite side of the template, which is generated from selective etching in 0.1 M NaOH solution for 2h. c, SEM image of the binary-pore template after 1.0 h ion milling. The corresponding sizes of the binary pores are 183 ± 17 (based on 126 anodized A-pores) and 315 ± 34 nm (based on 126 etched B-pores), respectively. Scale bar, 1 µm. 24 NATURE NANOTECHNOLOGY 24

25 Figure S19 Interpore spacing of multi-pore templates after anodization and selective etching. The interpore spacing is analyzed by using Mathworks MATLAB. a, Binary-pore template after 320 V anodization (with the interpore spacing of 803 ± 10 nm) and 2 h selective etching (with the interpore spacing of 573 ± 27 nm). b, Binary-pore template after 160 V anodization (with the interpore spacing of 396 ± 8 nm) and 40 min selective etching (with the interpore spacing of 278 ± 12 nm). c, Ternary-pore template after 113 V anodization (with the interpore spacing of 280 ± 10 nm) and 30 min selective etching (with the interpore spacing of 201 ± 15 nm). d, Quadruple-template after 80 V anodization (with the interpore spacing of 197 ± 10 nm) and 25 min selective etching (with the interpore spacing of 142 ± 13 nm). Scale bar, 400 nm. 25 NATURE NANOTECHNOLOGY 25

26 Figure S20 EDX and XRD measurements of binary TiO2/Cu2O nanostructure arrays. a, EDX spectrum of the binary structures. Inset: EDX line-scan along the green line (indicated by green arrow). The distribution profiles of Cu, Ti, Al and O elements match with the periodical distributions of TiO2 nanotubes, Cu2O nanowires, and Al2O3 template in the SEM image, respectively. b, XRD pattern of the binary strucutres. Besides the Ni and Au diffraction peaks from the substrate, all the other peaks can be indexed to (110), (111), and (220) diffractions of the cubic Cu2O (PDF# ) and (101) diffraction of the tetragonal TiO2 (PDF# ), which confirms the existence of TiO2 and Cu2O. 26 NATURE NANOTECHNOLOGY 26

27 Figure S21 Energy band diagram of binary-electrode under different bias conditions. a, Non bias. b, Positive bias. c, Negative bias. The band bending between the binary-electrode and the electrolyte will be moved upward with a positive bias (b), which promotes the transfer of holes from TiO2 tubes to electrolyte but depresses the transfer of electrons from Cu2O wires to electrolyte. On the other hand, with a negative bias (c), the band bending condition between the binary-electrode and the electrolyte will be moved downward that the transfer of electrons from Cu2O wire to electrolyte is promoted while the transfer of holes from TiO2 tubes to electrolyte is depressed. 27 NATURE NANOTECHNOLOGY 27

28 Figure S22 Current versus potential curves of single-type component arrays. a, Cu2O nanowire array, in which only the cathodic photocurrent can be observed. b, TiO2 nanotube array, in which only the anodic photocurrent can be observed. 28 NATURE NANOTECHNOLOGY 28

29 Figure S23 Addressable multi-gates transistor based on binary ZnO/AZO nanostructure arrays. a-c, Schematics of the addressable multi-gates transistor. d-f, Fabrication of crossbar electrode lines with EBL, making the top ends of the ZnO and AZO nanowires match with each other on both sides of the template, respectively. g and h, Illustration and MTSTM set up for the investigation of single ZnO nanowire transistor. i, Source-drain I-V curves of ZnO nanowire when applying different gate bias on one of the surrounded AZO nanowire gates. 29 NATURE NANOTECHNOLOGY 29

30 Figure S24 Extinction spectra and SEM images of Au arrays (thickness = 100 nm). a, Extinction spectra of four-cross array and binary square/four-cross arrays, respectively. SEM images of the corresponding single four-cross dot array (b) and binary square/four-cross dot arrays (c), respectively. Scale bar, 1 µm. 30 NATURE NANOTECHNOLOGY 30

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