Ideal Discrete Energy Levels in Synthesized Au. Nanoparticle for Chemically Assembled. Single-Electron Transistors

Transcription

1 Ideal Discrete Energy Levels in Synthesized Au Nanoparticle for Chemically Assembled Single-Electron Transistors Shinya Kano,, Yasuo Azuma,, Kosuke Maeda,, Daisuke Tanaka,, Masanori Sakamoto,,, Toshiharu Teranishi,,, Luke W. Smith, Charles G. Smith, and Yutaka Majima,,,# Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama , Japan, CREST, Japan Science and Technology Agency, Yokohama , Japan, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba , Japan, Institute for Chemical Research, Kyoto University, Uji, Kyoto Japan, PRESTO, Japan Science and Technology Agency, Uji, Kyoto Japan, Cavendish Laboratory, University of Cambridge, Cambridge CB3 HE, UK, and Department of Printed Electronics Engineering, Sunchon National University, Sunchon , Korea To whom correspondence should be addressed Tokyo Institute of Technology CREST-JST University of Tsukuba Kyoto University PRESTO-JST University of Cambridge # Sunchon National University 1

2 This supporting information provides sample preparation technique, details of measurement procedure, existence of another Au NP nearby Au NP1, and additional experimental results. Sample preparation technique The initial structure of the source, drain, and two side-gate electrodes (named side gate1 and side gate2) of Ti(2 nm)/au(1 nm) was fabricated on a SiO 2 (3 nm)/si substrate by electron beam lithography (EBL) and a lift-off process in which the initial gap separation was approximately 25 nm. Nanogap electrodes were electroless gold-plated following previously reported methods, and the gap separation can be simultaneously controlled to a size suitable for the Au NPs. 1 After fabrication of the electrodes, the substrate was immersed in a 1 mm ethanolic solution of octanethiol for 24 h to form the SAMs. Owing to this, the chemically assembled SETs are stable even under ambient conditions. 2 The substrate was then immersed in a 5 mm ethanolic solution of decanedithiol for 24 h so that decanedithiol molecules were inserted into the defect sites of the octanethiol SAMs on the Au electrodes. Finally, the substrate was immersed in a toluene solution of Au NPs for 12 h. Au NPs self-assembled on the Au electrode surfaces selectively anchored by the decanedithiol molecules. 3,4 These SET fabrication methods enable us to prepare multiple chemically assembled SETs at the same time. Details of measurement procedure The fabricated device characteristics revealed ideal Coulomb diamond characteristics at 9 K following examination with a mechanical refrigerator-type prober (GRAIL1-LOGOS1S, Nagase, Japan) and a semiconductor device analyzer (B15, Agilent, USA) at the Tokyo Institute of Technology. The sample devices were transported for further measurements to the University of Cambridge in vacuum packing. The device characteristics showed almost the same charging energy before and after transportation (Supporting Information Figure S5). All the electrical characteristic measurements were obtained at 3 mk at the University of Cambridge. The drain current drain 2

3 voltage (I d ) and the drain current gate voltage (I d V g ) characteristics of the SETs were measured using a voltage source (DAC488HR, IOtech), digital multimeter (21, Keithley Instruments Inc.), and preamplifier (1 7 gain). A magnetic field was applied by a superconducting magnet. The differential conductance of the drain current drain voltage (di d /d ) characteristics was calculated by numerically differentiating the I d curve directly without lock-in amplifiers. Existence of the third Au NP (NP3) Another Coulomb diamonds, 2 times less conductive than the main Coulomb diamonds, are superimposed in Figures 1a and 1b (See Figure S7) and this result implies the third Au NP (named as Au NP3) is inserted in parallel with Au NP1. Figure S8 shows the schematic circuits considering the existence of Au NP3. In Figure S8, the shape of Coulomb diamonds of Au NP3 are typical rhombic patterns. 5,6 The change of electron number in Au NP3 is not also detected by Au NP1, because Coulomb diamonds of Au NP1 are shifted only due to the change in the charge on Au NP2 (Coulomb box). From these two reasons, we can decide Au NP1 and Au NP3 are not capacitively coupled each other. Considering the orthodox theory about Coulomb diamonds of Au NP3, the SET circuit parameters related to Au NP3 are estimated in Table S1. Figure S9 shows calculated theoretical stability diagram using the parameters in Table 1 and S1, which agrees well with the experimental results in Figures 1a and 1b. References 1. Yasutake, Y.; Kono, K.; Kanehara, M.; Teranishi, T.; Buitelaar, M. R.; Smith, C. G.; Majima, Y. Simultaneous Fabrication of Nanogap Gold Electrodes by Electroless Gold Plating Using a Common Medical Liquid. Appl. Phys. Lett. 27, 91, Maeda, K.; Okabayashi, N.; Kano, S.; Takeshita, S.; Tanaka, D.; Sakamoto, M.; Teranishi, T.; Majima, Y. Logic Operations of Chemically Assembled Single-Electron Transistor. ACS Nano 212, 6,

4 3. Li, X.; Yasutake, Y.; Kono, K.; Kanehara, M.; Teranishi, T.; Majima, Y. Au Nanoparticles Chemisorbed by Dithiol Molecules Inserted in Alkanethiol Self-Assembled Monolayers Characterized by Scanning Tunneling Microscopy. Jpn. J. Appl. Phys. 29, 48, 4C Okabayashi, N.; Maeda, K.; Muraki, T.; Tanaka, D.; Sakamoto, M.; Teranishi, T.; Majima, Y. Uniform Charging Energy of Single-Electron Transistors by Using Size-Controlled Au Nanoparticles. Appl. Phys. Lett. 212, 1, Danilov, A. V.; Golubev, D. S.; Kubatkin, S. E. Tunneling Through a Multigrain System: Deducing Sample Topology from Nonlinear Conductance. Phys. Rev. B 22, Guttman, A.; Mahalu, D.; Sperling, J.; Cohen-Hoshen, E.; Bar-Joseph, I. Self-Assembly of Metallic Double-Dot Single-Electron Device. Appl. Phys. Lett. 211, 99,

5 Additional experimental results a = 1 mv = 5 mv b = 1 mv = 5 mv c Experimental Theoretical.6 2 Q (C).5 3. e.5e I d (na) I d (pa) V g2 6 8 I d (na) 5 na Figure S1: (a) I d characteristics at = 5 and 1 mv. (b) I d V g2 characteristics at = 5 and 1 mv. (c) I d characteristics at =.5 and 3. V. Solid lines show the experimental curves and broken lines show the theoretical curves numerically calculated by orthodox theory at fractional charges (Q ) of e and.5e. 5

6 4 nm Figure S2: Scanning electron microscopy image of typical electroless gold-plated nanogap electrodes. 6

7 a I d (na) b di d /d (ns) = 3.3 V B = T c I d (na) d di d /d (ns) = 3.3 V B = 1 T Figure S3: Magnetic field dependence of I d and di d /d characteristics at = 3.3 V. (a) I d and (b) di d /d at B = T. (c) I d and (d) di d /d at B = 1 T. 7

8 a b c d di d /d (ns) = 3.3 V = 1.9 V = 7.3 V b c d 2N 2N+1 2N+2.5 mev E (mev) B (T) ES2{ ES1{ GS { ES2{ ES1{ GS { ES2{ ES1{ GS { Figure S4: Electron number dependence of the magnetic field evolution in the negative region. (a) Relationship between electron number and the experimental Coulomb diamond in Figure 1a. (b-d) Lines profiles taken from (a) of the magnetic field evolution of the di d /d peaks at values of (b) 3.3 V, (c) 1.9 V, and (d) and 7.3 V in the negative region. The lateral axis was converted from the drain voltage to the corresponding energy level of the Au NP by considering the capacitive division of the voltage across the two tunnel junctions. The arrow in (d) indicates the splitting of the energy levels of Au NP3 nearby Au NP1. The features of the magnetic field evolution correspond to those in Figs. 3b-d, in which a positive is used. 8

9 a 8 /d.5 b /dv 1(μS) d (ns) E c e E c e Figure S5: Air stability of chemically assembled SETs. (a) Stability diagram as a function of and at 9 K just after fabrication. (b) Stability diagram as a function of and at 3 mk after air exposure and transportation. Comparing the charging energy before (E c ) and after air exposure (E c), the energies E c and E c are estimated to be 26.7 and 28. mev, respectively. The similarity of the energy values demonstrates that the chemically assembled SETs are stabile in air due to an organic self-assembled monolayer covering the device surface. 9

10 3 nm Figure S6: Transmission electron microscopy (TEM) image of 6.2-nm Au NPs. The image size is 2 2 nm 2 1

11 a 8 b /d di 1 2 (ns) d /d 1 2 (ns) V g2 Figure S7: Stability diagram of di d /d at 3 mk to clarify another less conductive Coulomb diamond. (a) Stability diagram as a function of and. (b) Stability diagram as a function of and V g2. 11

12 a Coulomb box AuNP 2 Side gate1 Coulomb island b Side gate 1 R S2, C S2 AuNP 2 C g12 C i C g11 C g13 R D2, C D2 Source AuNP 1 AuNP 3 Drain Coulomb island Source I d A R S1, C S1 R S3, C S3 AuNP 1 AuNP 3 R D1, C D1 R D3, C D3 Drain Side gate2 C g22 C g21 C g23 Side gate 2 V g2 Figure S8: (a) Schematic of the spatial structure of the chemically assembled SETs consisting of electroless gold-plated electrodes including another Au NP (Au NP3). (b) The modified equivalent SET circuit considering Au NP3. The resistances and capacitances R Sk and C Sk are those of Au NPk (k = 1, 2 or 3) at source side junction, R Dk and C Dk are those of Au NPk (k = 1, 2 or 3) at drain side junction, and C g jk is a side gate capacitance between side gate j and Au NPk. The inter-dot capacitance between Au NP1 and Au NP2 is C i. 12

13 a b c /d (ns) /d 5 1(nS) /d 1 2 (ns) = /d (ns) d e f /d 5 1(nS) /d 1 2 (ns) = V g V g Figure S9: Theoretical calculation of the Coulomb diamond in the stability diagram. (a-c) Calculated stability diagram of di d /d as a function of and at 3 mk. (a) Coulomb diamond related to Au NP1. (b) Coulomb diamond related to Au NP3. (c) Stability diagram of the superposition of Coulomb diamonds. The estimated resistances and capacitances of the SETs are R S1 = 4.8 MΩ, R D1 = 1.5 MΩ, C S1 = 1.25 af, C D1 = 1.58 af, C g11 =31.5 zf, R S3 = 6 MΩ, R D3 = 75 MΩ, C S3 = 1.15 af, C D3 = 1.31 af, and C g12 = 3.7 zf. (d-f) Calculated stability diagram of di d /d as a function of and V g2 at 3 mk. (d) Coulomb diamond related to Au NP1. (e) Coulomb diamond related to Au NP3. (f) Stability diagram of the superposition of Coulomb diamonds. The estimated resistances and capacitances of the SETs are R S1 = 4.8 MΩ, R D1 = 1.5 MΩ, C S1 = 1.25 af, C D1 = 1.58 af, C g21 =5.2 zf, R S3 = 6 MΩ, R D3 = 75 MΩ, C S3 = 1.15 af, C D3 = 1.31 af, and C g23 = 3.4 zf. 13

14 Table Table S1: SET circuit parameters for the circuit related to Au NP1, 2, and 3 in Figure S8b. C i = 56 zf k R Sk C Sk R Dk C Dk C g1k C g2k Au NP1 4.8 MΩ 1.25 af 1.5 MΩ 1.58 af 31.5 zf 5.2 zf Au NP2 1.3 af.25 af 12 zf 34 zf Au NP3 6 MΩ 1.15 af 75 MΩ 1.31 af 3.7 zf 3.4 zf 14