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

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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

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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)

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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

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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

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SPE in hBN

New SPE identified with CL-STEM

R. Bourrellier et al Nano Lett. 16 4317 (2016)

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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