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Luiz H. G. Tizei, Mathieu Kociak, Hugo Lourenço-Martins, Romain Bourrellier, Alfredo Campos, Anna Tararan, Alberto Zobelli Alexandre Gloter, Xiaoyan Li, Jean-Denis Blazit, Marcel Ténce, Odile Stéphan
Laboratoire de Physique des Solides – CNRS UMR 8502, Université Paris Sud, Orsay, France
CEA –Grenoble, FranceBruno Daudin, Bruno Gayral, Thomas Auzelle
Lab. Aimé Cotton, Orsay, FranceFrançois Treussart
IFGW, Campinas, BrazilLuiz. F Zagonel
Academia Sinica, Taipei, TaiwanHuan-Cheng Chang
FOM – Amsterdam, NetherlandsSophie Meuret
Optical Spectroscopy at High Spatial Resolution with Fast Electrons
Universidade de Vigo, SpainLuis Liz-MarzanLeonardo Scarabelli
2
Group leader: Prof. Odile Stéphan
Orsay
Paris
Group mostly dedicated to electron energy loss spectroscopy (but with increasing CL contribution)
STEM group – LPS, Orsay
3
Plasmonics in metal particlesOxides
Ce OxidesProf. S. Y. Chen (NTUST)
Ag triangleL. Liz-Marzan, Spain
FeTiO Dumont, France
PTO/STOTriscone, Switzerland
Group focus: fast electron nanospectroscopies
2D materialshBNProf. Taniguchi (NIMS, Japan)
WSe2
Prof. Ho (NTUST, Taipei)
Motivation
Optical spectroscopy
4
Photons Electrons
Plasmons in Ag spheres
N. Yamamoto, et al Phys. Rev. B, 64 205419 (2001)
230 nm
Absorption of excitons in WSe2
A. D. Yoffe,, et al Adv. Phys. , 51 799 (2002)
Motivation
Fast Electrons
Perfect tool to study atom/nm-scale objects
Single Atoms
Including structural and spectroscopic information
Single atom identification
CL of plasmonsDefects
K. Suenaga, et al, Science 290 2280 (2000)
J. Wall, et al, PNAS 71 1 (1974)
5 nm
Plasmons
N. Yamamoto, et al Phys. Rev. B, 64 205419 (2001)
230 nm
C. L. Johnson, et al, Nat. Mat. 7 120 (2008)
Nanostructures
GaAs QW
P. E. Batson, et al, PRB 49 936 (1982)
5Optical properties of nanoscale
or atomic scale objects
Motivation
Light output/input from the electron microscopeand EELS
M. Kociak, M. Ténce, S. Mazzuco, L. F. Zagonel
6
Attolight
« secondary technique »(possible excitation diffusion)
CL
EELS
Cathodoluminescence
7
Present
L. F. Zagonel, et al, Nano Lett., 11 568 (2011)
Excitation of one nanometer scale object
J. T. Griffths, et al, Nano Lett., 15 7639 (2015)
N. Yamamoto, Microscopy 1 (2016)
E. J. R. Vasseur, et al, Phys. Rev. Lett., 110 013902 (2013)
Quantum wells:Incoherent excitation
Plasmonic structures:Coherent excitation
Summary
Single photon emitters (h-BN, CL)
Quantum optics at the nanoscale
8
Optics at the nanoscale
Excitons in GaN QWs in AlN nanowires (CL)
ChromaTEM
Initial results in monochromated EELS:Phonon in c-BNPlasmons in Au clusters and Bipyramids
Microscopes
Nion USTEM 200 (60 – 200 keV)Atomic resolved EELS spectroscopy<1 Angstrom electron probe~370 meV spectral resolutionRoom temperature sample
VG HB501 (60 – 100 keV)EELS and CL spectroscopy1 nm electron probe~370 meV EELS resolutionSample 150 K
Nion 100
Typical currents 1 to 500 pA
CL spectroscopy
Imaging and EELS
Nion Hermes 200 (30 – 200 keV)CL and EELS spectroscopy~1 Angstrom electron probe~5-10 meV ELL spectral resolution100-300 K sample
ChromaTEM
Excitons in GaNGaN quantum wells (QWs) with AlN barriers
Spectroscopic signature from individual QWs
L. F. Zagonel, et al, Nano Lett., 11 568 (2011)L. F. Zagonel, et al, PRB, 93 205410 (2016)
10
Below the bandgap emission???
Excitons in GaN
Quantum Confined Stark Effect
Internal electric field in GaN/AlN heterostructures
Internal electric field shielding
D. A. B. Miller, et al, Phys. Rev. Lett., 53 2173 (1984)
Internal electric field in GaN/AlN heterostructures
S Kalliakos, et al, Phys. Rev. B, 67 205307 (2003)
Non-centrosymmetric
E
Two effects: lower emission energy and increased lifetime11
Excitons in GaN
12
Data from a single QW
L. F. Zagonel, et al, PRB, 93 205410 (2016)
Emission asymmetry in GaN QWs
LHGT et al, App. Phys. Lett., 105, 143106 (2014)
EELS mapping
No apparent interface chemical asymmetry
CBED growth direction = [0001] N-polarHighly asymmetric emission
Exposure times ~100-500 µs
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Emission asymmetry in GaN QWs
LHGT et al, App. Phys. Lett., 105, 143106 (2014)
CL emission (global) CL fits CL spectrum image
Phonon replica
14
Emission asymmetry in GaN QWs
LHGT et al, App. Phys. Lett., 105, 143106 (2014)
Experimental andsimulated profiles
1D charge diffusion and drif
15The same effect has been observed by J. I Deitz, D McComb et al M.&M. 24, 93 (2018)
n-type GaN
Defects in h-BN
Using CL to probe changes in optical properties due to defets
K. Watanabe, et al, Nat. Mat. 3 404 (2004)
Purest available crystals (NIMS, Tsukuba)
Defective crystals
Excitonic emission
P. Jaffrennou, et al, J. App. Phys. 102 (2007)R. Bourrellier et al, Nano Lett. 16 4317 (2016)
Two independent defects
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Localized spots (return)
R. Bourrellier et al Nano Lett. 16 4317 (2016)
17
Are these single photon sources?
Single photon sources
Second order correlation function g(2Antibunching = SPE
“Probability of a given time, , delay between two photons”
Hanbury-Brown and Twiss interferometer
Basically a two level system
One photon at a time
Excitation
t
Coherent light
18
SPE in hBN
New SPE identified with CL-STEM
R. Bourrellier et al Nano Lett. 16 4317 (2016)
19
Signature of a point defect. But which?
~10-20 nm thick hBN
Structure of the SPE?
SIMS: evidence for O and CEPR indicates carbon
Not yet observed, but work is in progress:1 atom every ~10000 in the « best » regions
T. Tanighuchi and K. Watanabe, J. Cryst. Growth., 303, 525 (2007)
A. Katzir et al, PRB., 11,2370 (1975)
20
Higher C concent, higher signal
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