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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: [email protected]
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)