Electronic and structural properties Electronic and structural - - PowerPoint PPT Presentation

Electronic and structural properties

• f

alkali doped Metal-Phthalocyanines Electronic and structural properties

• f

alkali doped Metal-Phthalocyanines

Alberto Morpurgo

Edinburgh University

Serena Margadonna Monica Craciun Sven Rogge Yoshihiro Iwasa Kosmas Prassides

Durham University

Alkali intercalated C60

K1C60

metal

K4C60

Mott-Hubard insulator

K6C60

insulator

K3C60

metal

Superconducting transition

K1C60 K3C60 K4C60 K6C60

Alkali intercalated C60

Rich variety of electronic phenomena by tuning the carrier density

The Metal-phthalocyanines (MPc’s) The Metal-phthalocyanines (MPc’s)

• a class of over 70 MPc
• isostructural MPc:

Cu, Fe, Ni, Co, Mn,…

• metal determines:

Molecular spin Orbital generacy Shape/Location of

• rbitals
• Exchange energy large

Magnetism in doped MPc’s?

Exchange via free carriers

Systematics of molecular orbitals: direct observation

X.Lu, K.W.Hipps, X.D.Wang, U.Mazur

• J. Am. Chem. Soc.

118, 7197 (1996)

The lowest energy molecular

• rbital centered
• n the metal ion

CoPc FePc

X.Lu, K.W.Hipps,

• J. Phys. Chem B

11, 5391 (1997)

NiPc

The lowest energy molecular

• rbital centered
• n the Pc ring

CuPc

Magnetic properties of MPc

MnPc

Awaga, Maruyama, Phys.Rev.B 44, 2589, 1991

Canted ferromagnet with TC = 8.6 K

FePc

Evangelisti et al., Pys.Rev.B 66, 144410 (2002)

Canted soft ferromagnet with TC = 10 K

Undoped Crystals: Insulating (α-form)

Electrical properties of MPc

• 20
• 40
• 60
• 80
• 100

0 V

• 20 V
• 40 V
• 60 V
• 80 V
• 100 V

Drain voltage (V)

0.00

• 3.50 X 10-6
• 7.00 X 10-6
• 1.05 X 10-5
• 1.40 X 10-5
• 1.75 X 10-5

Drain current (A) Bao et al., Apl.Phys. Lett. 69 (20), 3066, 1996

CuPc: p-type conductivity

Drain-source voltage (V) Drain-source current (µA) Bao et al., J.Am.Chem.Soc. 120, 207-208 , 1998

F-CuPc: n-type conductivity

Past work on MPc doping

Only hole doping (e.g., Iodine doping)

• carriers occupy same orbital in different MPc’s
• range of accessible carrier density is limited

Here: electron doped Metal Phthalocyanines

Outline Outline

Insulator-Metal-Insulator transition as a function of electron density in six different MPc’s

• Transport
• STM

Comparison of different MPc’s & correlation with molecular orbitals properties

Alkali-doped MPc’s thin films

Different structural phases

• Intercalation

Independent evidence for charge transfer

• Raman

Alkali-doped MPc’s bulk (powder)

Preparation of alkali doped MPc thin films Preparation of alkali doped MPc thin films

UHV (10-11 mbar)

Scanning probe characterization MPc Film evaporation

Knudsen cell

Alkali doping

doping source

I

I

I

LHe

Transport measurements I

Doping dependence of the conductivity Doping dependence of the conductivity

Alkali MPc

E E

DOS(E) DOS(E)

Insulator-metal-insulator transition

insulator metal insulator

Insulator-metal-insulator transition

Effect of Disorder

reversibility of doping

CuPc on glass

MPc Ti / Au Glass

insulating behavior

conductivity induced by doping

Single Crystalline Grains

α-form of CuPc

STM image => crystal structure

Scanning Tunneling Spectroscopy Scanning Tunneling Spectroscopy

* Undoped & overdoped: gap in STS * Optimally doped: finite density of states at EF

local density of states

V I

Differences in the behavior of MPc’s Differences in the behavior of MPc’s

ligand metal

M.S. Liao, S. Scheiner, J.Chem Phys. 114, 9780 (2001)

CuPc, NiPc, ZnPc: only 2eg is filled CoPc and FePc: 1eg and 2eg are filled

Systematics of molecular orbitals: direct observation

X.Lu, K.W.Hipps, X.D.Wang, U.Mazur

• J. Am. Chem. Soc.

118, 7197 (1996)

The lowest energy molecular

• rbital centered
• n the metal ion

CoPc FePc

X.Lu, K.W.Hipps,

• J. Phys. Chem B

11, 5391 (1997)

NiPc

The lowest energy molecular

• rbital centered
• n the Pc ring

CuPc

Preparation of Potassium doped CuPc crystals Preparation of Potassium doped CuPc crystals

Solid state reaction Vapor phase reaction

Ar filled glove box: O2 < 1ppm

The solid state reaction The solid state reaction

The vapor phase reaction The vapor phase reaction

Powder X-ray diffraction

phase1

a=16.9358(15) Å b=5.9293(4) Å c=13.4812(9) Å β=113.457(2)o a=16.2433(10) Å b=6.1300(5) Å c=14.4482(2) Å β=115.308(2)o

phase2

2.7 K per CuPc

Raman spectroscopy Raman spectroscopy

Ei – Er = Raman shift

Information about molecular vibrations and rotations incident light Ei elasting scattering Ei inelastic scattering Er

Raman shift

Intensity

pristine phase1 phase2

Vapor phase reaction Vapor phase reaction

Raman shift

Intensity

pristine phase 3

Solid state reaction Solid state reaction Shift of Raman peaks upon doping Charge transfer from K to CuPc

Conclusions Conclusions

Insulator-Metal-Insulator transition as a function of electron density Electronic transport directly related to molecular orbitals in MPc molecules Formation of different structural phases upon doping Independent evidence for charge transfer between alkali and MPc’s

Alkali-doped MPc’s ideal model system for the study of the electronic properties of molecular solids