1 Nanometer-scale Organic Molecular Recording with Scanning Tunneling Microscopy Pennycook, S. J. et al. Phys. Rev. Lett. 2000, 84, Gao, H.-J. et al. Appl. Phys. Lett. 2000, 77, Liu, Z. F. et al. Adv. Mater. 2005, 17, 459. Tobe Lab. FUJITA Takumi

2 Contents  Introduction STM Data Storage Organic Charge-Transfer Complex  Writing and Erasing Nanometer-Scale Marks  Thermochemical Hole Burning  Summary

3 Introduction Transition of Surface Recording Density of Magnetic Storage (bits/in 2 ) ● In Laboratory ● Commercial Products Data Storage Magnetic Storage … used as HDD in PC 0.9 Pb/cm 2 ≈ 6 Pb/in 2 (Pb; petabits = bits) STM Memory (Potential) ~ 200 Gb/in 2 (Gb; gigabits = 10 9 bits)

4 Introduction 中国科学院物理研究所 纳米物理与器件实验室 Scanning Tunneling Microscopy (STM) Tobe Lab.

5 Introduction STM Memory Bright spots indicate relatively higher conductance.

6 Introduction Requirements for Samples of STM Memory  Uniform Surface in Atomic Scale  Conductivity Advantages of Organic Materials for Electronic Devices  Lower Cost  Easy Synthesis  Controllable Properties Organic Charge-Transfer (CT) complex

7 Introduction CT complex Composed of … Electron Donor Electron Accepter  -Conjugated Backbone + Donor/Accepter Substituent Donor Substituents Accepter Substituents (In most cases) ee Donor Molecule Accepter Molecule 3~4 Å

8 Reversible, Nanometer-Scale Conductance Transitions in an Organic Complex Gao, H. J. ; Sohlberg, K. ; Xue, Z. Q. ; Chen, H. Y. ; Hou, S. M. ; Ma, L. P. ; Fang, X. W. ; Pang, S. J. ; Pennycook, S. J. Phys. Rev. Lett. 2000, 84, Direct observation of a local structural transition for molecular recording with scanning tunneling microscopy Shi, D. X. ; Song, Y. L. ; Zhang, H. X. ; Jiang, P. ; He, S. T. ; Xie, S. S. ; Pang, S. J. ; Gao, H. J. Appl. Phys. Lett. 2000, 77,

9 Sample ; CT complex of NBMN-pDA NBMN (3-nitrobenzal malonitrile) pDA (1, 4-phenylenediamine) DonorAccepter By Deposition Thickness of 20 nm 1:1 Molar ratio of Donor and Accepter Materials HOPG ; Highly Oriented Pyrolytic Graphite 高配向グラファ イト TEM ; Transmission Electron Microscope 透過電子顕微鏡 Polycrystalline Film on HOPG Images of film surface STMTEM 6 × 6 nm × 600 nm 2

10 Writing Marks on the Film Voltage Pulses 3.5 ~ 4.2 V, 1  s Writing conditionImaging condition Constant Height Mode V b = 0.19 V, I t = 0.19 nA Distance of Marks ca. 1.7 nm Still Identified after 2 Weeks

11 Erasing the Marks Erasing condition a)Heating above 423 K (Erasing all marks) b)Applying a Reverse-polarity Voltage Pulses for longer duration (Erasing individual marks)  4.5 V, 50  s or

12 Conductance Transition I-V relation a; Before Writing (Insulating State) b; Recorded Mark (Conducting State) c; HOPG Substrate (Linear I-V relation) Conductance Transition by Voltage Pulse

13 Experimental Results Hypothesis Localized Disorder of Molecules in the Crystal Mechanism of Writing Voltage Pulse The Crystalline FilmThe Amorphous Film InsulatingConducting Localized Conductance Transition

14 Direct Observation Direct Observation of the Mark by STM Before Writing After Writing The Well-ordered Molecules outside the Mark and the Disordered Molecules inside the Mark

15 Electron Diffraction Electron Diffraction of Nonrecorded/Rcorded part NonconductingConducting CrystallineAmorphous Before Writing After Writing

16 Crystalline Thin Film of a Donor-Substituted Cyanoethynylethene for Nanoscale Data Recording Through Intermolecular Charge-Transfer Interactions Jiang, G. Y.; Michinobu, T.; Yuan, W. F.; Feng, M.; Wen, Y. Q.; Du, S. X.; Gao, H. J.; Jiang, L.; Song, Y. L.; Diederich, F.; Zhu, D. B. Adv. Mater. 2005, 17,

17 Conductive Single-Component Crystal TDMEE (1, 1, 2-tricyano-2-[(4-dimethylaminophenyl)ethynyl]ethene) The packing arrangement in the crystalline thin film Antiparallel Dipolar Alignment in the Stacks Intermolecular CT between Molecules in the Neighboring Layers Single-Component Crystal Easy to Make Higher-Quality Uniform Film than Multi-Component Crystal

18 Writing on the TDMEE Thin Film Voltage Pulses 2.64 V, 10 m s Writing condition I-V relation curves I) Unrecorded region II) Recorded region ca. 2.1 nm in diameter Potential Storage Density; bites/cm 2

19 Scanning-Tunneling Microscopy Based Thermochemical Hole Burning on a New Charge-Transfer Complex and Its Potential for Data Storage Peng, H. L.; Ran, C. B.; Yu, X. C.; Zhang, R.; Liu, Z. F. Adv. Mater. 2005, 17,

20 Thermochemical Hole Burning (THB) Thermochemical Decomposition of CT complex and Gasification of Low-Boiling-Point Material of Donor (D) Using the Heating Effect of the Current from an STM Tip

21 Sample ; CT complex of DBA(TCNQ) 2 TCNQ (7, 7, 8, 8-tetracyanoquinodimethane) DBA (dibutylammonium) DonorAccepter Crystallization from Acetonitrile 10 mm × 5 mm × 2 mm 1:2 Molar ratio of Donor and Accepter Materials Single-Crystal Crystal Structure of DBA(TCNQ) 2

22 Sample ; CT complex of DBA(TCNQ) 2 STM Images of the DBA(TCNQ) 2 Crystal Surface on Different Scales

23 THB on the Crystal THB condition Voltage Pulses 3 V, 300  s 8 V, 300  s ca. 10 nm in diameter ca. 2 nm in depth ca. 30 nm in diameter ca. 5 nm in depth

24 THB on the Crystal Writing Nanoscale Letters

25 Hole Size Depending on Voltage Condition 3~7 V, 300  s 7 V 6 V 5 V 4 V 3 V Voltage Threshold for THB 3 V (Pulse Duration of 300  s)

26 Heat to Decomposition The TG analysis of DBA(TCNQ) 2 crystal showed a weight loss about 5.1 wt.-%, occurred between 177 and 210 ° C. Maximum Temperature Rise by Voltage Pulse (Estimation)  T = 1156 K (8 V × 300  s voltage pulse) Decomposition Temperature of DBA(TCNQ) ° C Enough Heat for Decomposition of DBA(TCNQ) 2 TG ; Thermogravimetry 示差熱天 秤

27 Verification of THB Other Considerable Mechanisms A Pure Surface-Conductance Change without Shape Change AFM Imaging Confirmed the Hole Nature. Oxidation Both Changing the Writing Voltage Polarity and Performing under N 2 Atomsphere didn’t Affect the Formation of the Holes. Mechanical Indentation by the STM Tip Mechanically Formed Holes are Apparently Different from THB Holes. a), c) THB b), d) Mechanical Indentations c),d) Section analysis along the black lines shown in (a) and (b), respectively. a) c) d)d) AFM ; Atomic Force Microscopy 原子間力顕微 鏡 b)

28 Summary  Nanometer-scale conductance transition was demonstrated on organic CT complexes, by applying of localized voltage pulses using STM.  The mechanism is due to localized disorder of molecules by voltage pulses.  The system using STM has a great potential for ultra-high density data storage.  THB has another possibility for nanometer-scale recording system.