Spectroscopic properties of hexagonal Boron Nitride and...

Dpto. Física de Materiales, Universidad del País Vasco, Donostia International Physics Center (DIPC) and Centro Mixto CSIC-UPV/EHU, Donostia, Spain

http://dipc.ehu.es/arubio E-mail: arubio@sc.ehu.es

Angel Rubio 

S3 Modena, 11th April 2007

Spectroscopic properties of hexagonal Boron Nitride and Nanotubes

OUTLINE

● Introduction to BN and other inorganic nanotubes● Structural, mechanical and Electronic properties:

doping ● Optical absorption of the single BN-sheet and

BN-nanotubes (Ab-initio calculations including many-body corrections (GW + Bethe-Salpeter)

● Luminiscence + Electric field effects (devices)● Vibrational spectroscopy● Conclusions

Boron Nitride Nanotubes

●Density functional theory in the Local Density Approximation (LDA) or beyond●Plane wave or real-space grid expansion●Pseudopotentials●Supercell geometry●TDDFT + RPA Response Calculations●Perturbation DFT theory for phonons

First-principle calculations: Technical Details

ABINIT: (X. Gonze et al., UCL, Belgium)SELF: (A. Marini, U. Tor Vergata Rome, Italy)OCTOPUS: (San Sebastian, Spain and FU Berlin, Germany) http://www.tddft.org/programs/octopus

  BN single wallnanotubes

R.S. Lee et al PRB64, 121405 (2001); Courtesy of A. Loiseau

200 nm

5 nm

Production of SW-BN-tubes• mostly single wall• ropes and isolated• diameter: 10 -20 Å• mostly zigzag tubes• length: 100-300 nm

R.S. Lee et al PRB64, 121405 (2001); Courtesy of A. Loiseau

Mass production of double wall BN tubesJ. Cumings and A.Zettl, CPL (2000)

Layered Materials

MoS2

WS2

NbS2

TaS2

VS2

ReS2

WSe2

MoSe2

Graphite

Chalcogenides

Carbon Nitride

Boron Nitride

OTHERS VO5, NiCl2 MgB2

Boron Carbon-Nitride

......and your imagination!!!!Superconductors, work together with Hardy Gross group, FU-

Berlin

Layered Materials

Carbon Nanotubes

MoS2 Nanotubes

BN nanotubes

Fullerenes

BN cages

MoS2 cages

Ab-initio prediction of nanotubes: laminar bulk phase”

-C: metal/semiconductor depending on chirality. Luttinger liquid,

superconductivity, mechanical strenght, etc.....

-BN: wide band gap semiconductor; conduction band bottom NFE;

mechanic resistance, field emission, piezoelectricity

-BC3: small gap; wall-wall induced σ-conductivity

-BC2N: variety of chiral structures; nanocoils”

-B: metallic (B/N-doped C-tubes: stochastic heterostructures)

Synthesized in small quantities (besides BN)

Other inorganic tubes: CxNy; MgB2, (MoS2 family, R. Tenne et al)

Work with Y. Miyamoto, X. Blase, S.G. Louie, M.L. Cohen, V. Crespi (BxCyNz)

with I. Boustani and J.A. Alonso (Boron) http://dipc.ehu.es/arubio

Interest for BN nanotubesStability of BN nanotubes predicted in 1994

(AR , J. Corkill, X. Blase, M.L. Cohen, S.G. Louie, PRB 1994)

First production of multi-wall BN-nanotubes in 1995

(Chopra et al., Science (1995))

Properties predicted to be alternative to those of C-tubes :

- large band gap independent of helicity and number of tube-walls

- free electron state located inside the tube (conduction band-bottom) - dipolar layer at the tube surface, buckling - Quantum polarization: Piezoelectricity - low chemical reactivity

Properties similar to those of C-tubes:

- high Young modulus

Potential applications

- electromechanical devices, field emitters, field effect transistors

AR, Y. Miyamoto, S.G. Louie, and M.L. Cohen PRB (2004, 2005)

Composite NANOTUBES: stability

~1/r

Buckling of geometry optimized BN-tubes:

-dipolar shell structure

-inter-tube interaction

0

L. Vaccarini, C. Goze, L. Henrard, E. Hernández, A. Loiseau, P. Bernier and A.R Carbon (2000);Phys Rev. Lett. (1998); Appl.Phys. A (1999)

Mechanical properties 

Strength Chart

Bandstructure (LDA)

Graphine-layer BN-sheet

(transparent)(black)

N

B

Bandstructure (LDA)role of stacking....interlayer interaction

Graphite AB-stacking h-BN

Electronic structure of BN­tubes:    (LDA)

Uniform band gap, no metallic BN­tubes!AR, X. Blase, M. L. Cohen, S. G. Louie PRB (1994,95); Euro. Phys. Lett (1994)

BN(4,4) metallic doping: superconductivity?

AR, Y. Miyamoto, S.G. Louie, M.L. Cohen PRB53, 4023 (1996)

The problem of Band Gap in nanotubesis related to the one of bulk h-BN

How much is the band gap in h-BN?

?

Optical Absorption/Emission Spectroscopy

x

optical gap ≠ photoemision (QP) gap

structural characterisation Role of packing: tube-tube interaction

Beyond DFT:

Dimensionality effects: nanotube as quasi-1D structure

Bethe-Salpeter equation:

Im [] ~ vc

|<v|D|c>|2 (Ec-

Ev - )

Im [] ~ s |

vc<v|D|c>A

vcS|2 (S 

)

BN nanotubes Dimensionality effect: Exciton in (quasi-) 1-D, 2-D, 3-D

L. Wirtz, A. Marini, AR PRL (2006)

Depolarisation

effects as in C tubes

Park, Spataru, Louie PRL (2006)Wirt, Marini, Rubio PRL (2006)

Exciton localisation in C and BN nanotubes

Frenkel

UV light

High Luminiscence yield in BN!!!

IR light

Is there any experimental evidence of

such large excitonic effects?

R. Arenal, O. Stephan, C. Colliex, A. Loiseau, PRL (2005)

e

EELS experiments on isolated BN nanotubes

EELS Experiment on bulk h-BNTarrio and Schnatterly, PRB 40, 7852 (1989) and T. Pichler at al (IFW Drenden)

π-Plasmon

π+σ-Plasmon

Photoluminescence experimental results on BN 1

Deep-level and (b) near-band-gap W emission spectra measuredat 4.2 K on a hexagonal BN film.

C. A. Taylor II, S. W. Brown, V. Subramaniam, S. Kidner, S. C. Rand, and R. ClarkeAppl. Phys. Lett., Vol. 65, No. 10, 5 September 1994,

Evidence for ultraviolet lasing of hex-BN single crystal

K. Watanabe, T. Taniguchi, and H. Kanda, Nat. Mater. 3, 404 (2004)

Are the Luminescence spectra due to electron-holerecombination on defects?

Carbon substitution of a Nitrogenacceptor impurity

The most probably candidates are: (Dislocations)?

Nitrogen vacancydonor impurity

The problem:valence and conduction orbitals

are strongly modified by the presenceof an impurity

4

The highest three occupied orbitalsin the pure sheet (right) and with a carbon impurity in a 6x6 supercell

A high concentration of defects modifies the exciton peak in the single hex BN layer

Optical absorption within BSE approximation

GAP

Optical absorption within RPA approximation

Defects/exciton states (shallow and deep) dominate the luminiscence below 6 eV; (in agreement with Annick's talk)The main absorption peak of BN is at 6.1 eV ( this provides a coherent description of EELS , optics and luminescence)

6.1 eV

Transverse Electric Field in BN: control blue/UV Light emission ?

Vibrational Properties: Raman and IR spectroscopy

controversy about out-of-plane modes????

Vibrational Properties: Raman and IR spectroscopy

J. Serrano et al, PRL 98 (2007) (IXS experiments in Grenoble, consistent also with 2nd order Raman Scattering S. Reich, A.C. Ferrari, R. Arenal, A. Loiseau, I. Bello, J. Robertson, PRB 71, 205201 (2005).

Exp: 2nd order Raman Scattering S. Reich, A.C. Ferrari, R. Arenal, A. Loiseau, I. Bello, J. Robertson, Phys. Rev. B 71, 205201 (2005).

Calculation of non-resonant Raman Intensities

Intensity of nth mode:

Raman Tensor:

Raman Susceptibility:

Polarizability:

L. Wirtz, R. Arenal de la Concha, A. Loiseau, AR, PRB (2003)

●Raman and infrared active

●Raman active only

E2

E1

E2

A(RBM) A

(radial buckling)

Calculation of non-resonant Raman Intensities

L. Wirtz, M. Lazzeri, F. Mauri, AR, PRB (2005)

Curvature effects in the E2g

Raman mode

Experimental evidence !R. Arenal, A. Ferrari, S. Reich, L. Wirtz, S. Lefrand, AR, A. Loiseau Nano Lett (2006)

J. Cumings and A. Zettl, Sol. Stat. Comm. (2004)

Field Emission in BN nanotubes

Boron nitride nanotubes,however, show stable field emission with less noise thanfor typical carbon nanotube samples. This may haveimplications for the use of BN nanotubes as stable fieldemission sources for lighting and flat panel displays

Simulated image of a double-wall tube: BN(10,10)C(5,5).

  Double­wall tubes: "peapods inside BN"        Coalescence to form C­BN double wall tubes

Exp: M. Ishigami, A. Zetl (Berkeley)

-1.5eV 1.5eV

“LEGO” heterojunctions or....

T-heating Co-axial cables!!!

Summary ●BN alternative material to C tubes for nanoelectronic applications

●Compatible with C; add to the nano-lego

●Optical-devices: luminiscence tunable by the applied perpendicular E-field (high efficiency); excitonic effects important

●Work on chemical synthesis: large scale production

MORE to come in the near future..................

  Acknowledgements

http://www.etsf.es

S.G. Louie, M.L. Cohen and A. Zettl; Y. Miyamoto (NEC)

Department of Physics, University of California at Berkeley, USA

Andrea Marini

Istituto Nazionale per la Fisica della Materia e Dipartimento di Fisica dell'Università di Roma ``Tor Vergata'', Roma, Italy

Ludger Wirtz and Claudio Attacalite

CNRS, Institute for electronics, microelectronics, and nanotechnology (IEMN), Lille, France

J. Serrano (ESRF Grenoble) T. Pichler (IW F Dresden)

Thank y

ou!!!

!

EELS on bulk h-BN: Comparison theory-experiment

π-Plasmon

Exc. effect

5.4 eV 6.1 eV

Tarrio and Schnatterly, PRB 40, 7852 (1989)