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Nanometer-scale Organic Molecular Recording with Scanning Tunneling Microscopy

Pennycook, S. J. et al. Phys. Rev. Lett. 2000, 84, 1780.

Gao, H.-J. et al. Appl. Phys. Lett. 2000, 77, 3203.Liu, Z. F. et al. Adv. Mater. 2005, 17, 459.

Tobe Lab.

FUJITA Takumi

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Contents

IntroductionSTM Data Storage

Organic Charge-Transfer Complex

Writing and Erasing Nanometer-Scale Marks

Thermochemical Hole Burning

Summary

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Introduction

Transition of Surface Recording Density of Magnetic Storage (bits/in2)

● In Laboratory● Commercial Products

Data Storage

Magnetic Storage …used as HDD in PC

0.9 Pb/cm2 ≈ 6 Pb/in2

(Pb; petabits = 1015 bits)

STM Memory

(Potential)

~ 200 Gb/in2

(Gb; gigabits = 109 bits)

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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.

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Introduction

STM MemoryBright spots indicate relatively higher conductance.

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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

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Introduction

CT complex

Composed of…Electron DonorElectron Accepter

-Conjugated Backbone+

Donor/Accepter Substituent

Donor Substituents Accepter Substituents

(In most cases)

e

Donor Molecule

Accepter Molecule

3~4 Å

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Reversible, Nanometer-Scale Conductance Transitions in an

Organic ComplexGao, 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, 1780-1783.

Direct observation of a local structural transition for molecular

recordingwith scanning tunneling

microscopyShi, 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, 3203-3205.

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Sample; CT complex of NBMN-pDA

NBMN(3-nitrobenzal malonitrile)

pDA(1,4-phenylenediamine)

Donor Accepter

• 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

STM TEM6 × 6 nm2 600 × 600 nm2

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Writing Marks on the Film

Voltage Pulses3.5 ~ 4.2 V, 1 s

Writing condition Imaging conditionConstant Height Mode

Vb = 0.19 V, It = 0.19 nA

Distance of Marksca. 1.7 nm

Still Identified after 2 Weeks

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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

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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

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Experimental Results

Hypothesis

Hypothesis

Localized Disorder of Molecules in the Crystal

Mechanism of Writing

Voltage Pulse

The Crystalline Film The Amorphous FilmInsulating Conducting

Localized Conductance Transition

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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

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Electron Diffraction

Electron Diffraction of Nonrecorded/Rcorded part

Nonconducting ConductingCrystalline Amorphous

Before Writing After Writing

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Crystalline Thin Film of a Donor-Substituted

Cyanoethynylethene for NanoscaleData Recording Through

IntermolecularCharge-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, 2170-2173.

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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

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Writing on the TDMEE Thin Film

Voltage Pulses 2.64 V, 10 ms

Writing condition I-V relation curves

I) Unrecorded regionII) Recorded region

ca. 2.1 nm in diameter

Potential Storage Density; 1013 bites/cm2

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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, 459-464.

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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

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Sample; CT complex of DBA(TCNQ)2

TCNQ(7,7,8,8-tetracyanoquinodimethane)

DBA(dibutylammonium)

Donor Accepter• 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

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Sample; CT complex of DBA(TCNQ)2

STM Images of the DBA(TCNQ)2 Crystal Surfaceon Different Scales

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THB on the Crystal

THB conditionVoltage Pulses 3 V, 300 s 8 V, 300 s

ca. 10 nm in diameterca. 2 nm in depth

ca. 30 nm in diameterca. 5 nm in depth

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THB on the Crystal

Writing Nanoscale Letters

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Hole Size Depending on Voltage

Condition

3~7 V, 300 s

7 V

6 V

5 V

4 V

3 VVoltage Threshold for THB

3 V (Pulse Duration of 300 s)

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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)2 177 °C

Enough Heat for Decomposition of DBA(TCNQ)2

TG; Thermogravimetry 示差熱天秤

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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

underN2 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)

AFM; Atomic Force Microscopy 原子間力顕微鏡

b)

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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.