a. perez, p. melinon, v. dupuis, b. masenelli, l. bardotti ... · outline free cluster production...

FUNCTIONAL NANOSTRUCTURES FROM CLUSTERSFUNCTIONAL NANOSTRUCTURES FROM CLUSTERS

A. PEREZ, P. MELINON, V. DUPUIS, B. MASENELLI, L. BARDOTTI,B. PREVEL, J. TUAILLON-COMBES, E. BERNSTEIN, F. TOURNUS,

I. WANG, A. TAMION, D. NICOLAS, C. RAUFAST, D. TAINOFF, N. BLANC

Laboratory of Condensed Matter Physics and Nanostructures University Claude Bernard-Lyon 1 and CNRS

Lyon - France

Particles 2007 – Toronto-Canada – 19-21 july 2007

GENERAL CONTEXTGENERAL CONTEXT

Two main approaches to nanostructure preparationTwo main approaches to nanostructure preparation

Nano-Engraving Technique :- Nano-lithography,

- Nano-imprint,- FIB…

Clusters preformed :- i.e. in theGas-phase

Elementary Bricks :- atoms, molecules

" Top Down "" Top Down " " Bottom Up "" Bottom Up "

Substrate

Functionalized film

Substrat

Couche Fonctionnalisée

Substrate

Substrate

Deposition :- Nucleation

- Growth

Deposition :- Nucleation

- Growth

Substrate

OUTLINEOUTLINE

Free cluster production and deposition on substrates using the :Low Energy Cluster Beam Deposition technique (LECBD)

Conclusion and prospects

Preparation of 2D–organized arrays of cluster-assembled dots on FIB-functionalized substrates

- Application to very high integration-density devices (~ Gbits/in2 -Tbits/in2)

Some characteristic examples of functionalized cluster-assemblednanostructures :

- Magnetic from TM (i.e. Co, Fe,…) and mixed TM-X clusters (i.e. Co-Sm,Co-Pt)

- Optical from photoluminescent sesquioxide clusters (i.e. Gd2O3:Eu3+)

NANOSTRUCTURE PREPARATION FROM CLUSTERSNANOSTRUCTURE PREPARATION FROM CLUSTERS

HeLaser-vaporization cluster Source

Typical cluster sizes : a few tens to a few thousandsof atoms (~ 1 to 4 nm)

Very high cooling rate : ~ 108 - 1010 K/s

Free cluster studies

UHV-Depositionchamber

LECBD regime : clusters are not

fragmented uponimpact on the substrate

Eximer LaserIons

TOF- mass spectrometer

Mass spectrum N

eu

tra

ls

Evaporation cell

XPS-ISSAnalyzer

RHEEDDiffractometer

STM-AFMMicroscope

Substrate

YAG Laser N° 1YAG Laser N° 2

Pulsed valve(He : 4 – 6 bars)

Target rodSupersonicexpansion


- Magnetic from TM (i.e. Co, Fe…) and mixed TM-X clusters (i.e. Co-Sm, Co-Pt)


OUTLINEOUTLINE




- Application to very high integration-density devices (~ Tbits/in2)

FUNCTIONAL MAGNETIC NANOSTRUCTURES (*)FUNCTIONAL MAGNETIC NANOSTRUCTURES (*)To To overcomeovercome the the superparamagneticsuperparamagnetic limitlimit

High High magneticmagnetic anisotropyanisotropy nanoclustersnanoclustersHigh High magneticmagnetic--blockingblocking TemperatureTemperature ( ( ≥≥ 300 K)300 K)

Application to Application to highhigh densitydensity datadata--storagestorage systemssystems (~ (~ TbitsTbits/in/in22))

(*) see : "Functionalized cluster-assembled magnetic nanostructures for applications to high integration-density devices", A. Perez et al., Adv. Engineer. Mat., 7(6), 475 (2005).

Cobalt-Samarium System

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

-3 -2 -1 0 1 2 3

300 K20 K

Magnetic Field (kOe)

No

rma

lize

dM

ag

ne

tiza

tio

nM

/Ms 20 K

300 K

2 nm 2 nm

SmCo5-clusters

Cobalt-Platinum System

2 nm

CoPt _ L10-Phase CoPt3 _ fcc-Phase

2 nm

CoPt _ A1-Phase (fcc)

[ ]

FUNCTIONAL MAGNETIC NANOSTRUCTURES FUNCTIONAL MAGNETIC NANOSTRUCTURES

Size control Size control

As deposited CoPt-clusters

on a-C substratesat 300 K.

CoPt _ A1-Phase(fcc)

Without mass-selection :size dispersion ~ 40 %

Size Histogram

FitLog-normal

Diameter (nm)

Nu

mb

er

of

pa

rtic

les

Mass-selected cluster deposition using an electrostatic mass-analyzing system :

size dispersion ~ 5 %

Size Histogram

Diameter (nm)

Nu

mb

er

of

pa

rtic

les Ø = 2 nm




OUTLINEOUTLINE





FUNCTIONAL OPTICAL NANOSTRUCTURES (*)FUNCTIONAL OPTICAL NANOSTRUCTURES (*)

Preparation and characterization of novel photoluminescent nanostructures exhibiting :

- A high-emission efficiency- A good stability under high-power excitation- Emission wavelength adjustable in a wide range of visible - Potential applications to nano-optics devices- Alternative to photoluminescent semiconducting-nanostructures

Rare-earth doped sesquioxyde nanoparticles, i.e. :

- Gd2O3:Eu3+, Y2O3:Eu3+ (red emission)- Gd2O3:Tb3+ (green emission)- GdBO3:Pr3+ (blue emission)

Luminescent materials commonly used for TV-screen coatings

In such materials, the doping element is responsible of the light emission and not thesesquioxide matrix

Fundamental aspects :- Confinement effects in strongly ionic nanocrystals ? ? ?- Comparison to the well known effects in semiconducting nanoparticles

(*) See : "Quantum confinement effect on Gd2O3 clusters"B. Mercier et al., J. of Chem. Phys., 126, 044507 (2007).

Composition

Target-rod mounted in the cluster source : Gd2O3 doped Eu3+ (10 %)

Average composition deduced from XPS-measurements on a thick cluster-assembled film : Eu3+ ≈ 13 %

PHOTOLUMINESCENTE NANOSTRUCTURES FROM GdPHOTOLUMINESCENTE NANOSTRUCTURES FROM Gd22OO33:Eu:Eu3+3+ -- CLUSTERSCLUSTERS

Size distribution

0 2 4 6 8 100

5

10

15

20

25

30

Num

ber o

f par

ticle

s

Diameter (nm)

<d> = 3,2 nm

2.5 nm ≤ 80% ≤ 3.6 nm

Rhombic dodecahedron

O2-

Gd3+

HRTEM-image of a Gd2O3:Eu3+ cluster deposited on an a-C coated grid at 300 K

d22-2

d222 = 3,08 Ǻ

d400 = 2,67 Ǻ

2,7 nmCubic structure with : a = 10.7 Å

Bulk phase (bixbyite, bcc, Ia3) : a = 10.8 Å

PHOTOLUMINESCENCE PROPERTIES OF GdPHOTOLUMINESCENCE PROPERTIES OF Gd22OO33:Eu:Eu3+3+ -- NANOCLUSTERSNANOCLUSTERS

Red emission : transition betweenthe 4f-levels of Eu3+-impurities

Laser excitation : λexc

VB

CB

- Bulk Gd2O3:Eu3+ (5 %)- Cluster film (<Ф> = 3.2 nm)- Cluster film (<Ф> = 2.8 nm)

580 600 620 640 660 680 700 7200,0

0,2

0,4

0,6

0,8

1,0

Inte

nsity

(a.u

)

Wavelength (nm)

(**) See : C. Delerue et.al., Phys. Rev. B 48, 11024 (1993).

10

0,01

0,1

1

CdS

CuBr

ZnO

Si

502052

ΔEg

(eV.

)

nanocrystals diameter (nm)10

0,01

0,1

1

Gd2O3

CdS

CuBr

ZnO

Si

502052

ΔEg

(eV.

)

nanocrystals diameter (nm)

- Krishna et. al- Ledoux et. al- Viswanatha et. al- Nanda et. al- Our results

α = 3.73

α = 8.78

α = 1.67α = 1.47

CdS

Nanocrystal diameter : d (nm)

ΔEg

(eV)

γ

αd

Eg =Δ

with γ = 1.39 (**)

Gd2O3

Variation of the gap of the Gd2O3-matrix as a function of the size (*)

(*) Deduced from excitation measurements in VUV on cluster films (Gd2O3:Eu3+ (10 %), at 10 K)using the synchrotron radiation at DESY

α = 0.56




OUTLINEOUTLINE





DIFFUSION OF DEPOSITED CLUSTERS ON THE SUBSTRATEDIFFUSION OF DEPOSITED CLUSTERS ON THE SUBSTRATE

(*) See : L. Bardotti et al., Phys. Rev. B, 62, 2835 (2000).

EXPERIMENTAL EVIDENCE EXPERIMENTAL EVIDENCE (*)(*) ::

Two extreme cases depending on the cluster-surface interaction ⇓ ⇓ ⇓ ⇓ ⇓ ⇓

Easy diffusion of clusters :i.e. Gold clusters (Au750) on HOPG at 300K

100 nm

1μm

No cluster diffusion :i.e. Gold clusters (A750) on Au(111) at 300K

150 nm 150 nm

t=0.03 nm

t=0.08 nm t=3.4 nm

t=0.01 nm

Nucleation CoalescenceGrowth

ISL

AN

D D

EN

SIT

Y

COVERAGE RATE

NUCLEATION AND GROWTH PROCESS OF LECBD FILMS : SUMMARYNUCLEATION AND GROWTH PROCESS OF LECBD FILMS : SUMMARY

PREPARATION OF 2DPREPARATION OF 2D--ORGANIZED ARRAYS OF MAGNETIC CLUSTERORGANIZED ARRAYS OF MAGNETIC CLUSTER--DOTSDOTS(*)(*)

(*) See : "2D arrays of CoPt nanocluster assemblies" A. Hannour et al., Surf. Sci., 594, 1-11 (2005).

Application to high integration-density devices (~ 100 Gbits/in2 - 1 Tbits/in2)for data storage systems and spintronics

FunctionalizedHOPG-substrates

using the FIB-nanoengraving

technique- Ga+-ions 30 keV

- Periodicity 300 nm

TMAFM images(2,5 μm x 2,5 μm)

50.103 ions/point 10.103 ions/point 5.103 ions/point

Nano-hillocksNano-craters

2D-arrays of magneticCoPt-cluster dots on

FIB-HOPG substrates

- Periodicity : 300 nm

~ 10 Gbits/in2

3,5 μm 2 μm 0,5 μm

300 nm

The preparation of original / functional nanostructures from clusters preformed in thegas phase using the LECBD technique seems promising :

Model nano-systems well suited for fundamental studies, as well asfunctionalized ones well suited for applications are easily synthesized.

CONCLUSIONCONCLUSION

The control of the nucleation and growth process of cluster- assembled nanostructureson functionalized substrates is used to prepare 2D-organized arrays of cluster-dots

Applications to high integration-density devices ( Tbits/in2).

PPROSPECTSROSPECTS

Control/modification/combination of core/surface/interface effects to realize functionalnanostructures with unique properties :

mixed clusters : alloying effects, surface effects, segregation effects…

2D-organized arrays of functionalized nanoclusters on functionalized substrates :Study of the organization-properties relationshipvery high integration densities ( ≥ Tbits/in2)

RESEARCH GROUP ON CLUSTERS AND NANOSTRUCTURESRESEARCH GROUP ON CLUSTERS AND NANOSTRUCTURES

AT LPMCN AT LPMCN –– UnivUniv. Lyon 1. Lyon 1

F. TOURNUS

O. BOISRONEngineer G. GUIRAUD

Engineer

A. PEREZ

B. MASENELLIP. MELINON

L. BARDOTTI

L. FAVREPhD

J. TUAILLON

V. DUPUIS

B. PREVEL E. BERNSTEIN

2D2D--PERCOLATION THRESHOLD OF CLUSTER PERCOLATION THRESHOLD OF CLUSTER -- ASSEMBLED ASSEMBLED FILMS PREPARED BY LECBDFILMS PREPARED BY LECBD

10-14

10-12

10-10

10-8

10-6

10-4

0 2 4 6 8 10

1.8 nm

Co-clustersT = 80 K

Deposited thickness (nm)

curr

ent

inte

nsit

y(A

)

10-13

10-11

10-9

10-7

10-5

0.001

0 2 4 6 8 10 12 14

2.5 nm

Ni-clustersT = 300 K

Deposited thickness (nm)cu

rren

tin

tens

ity

(A)

Corning-glass substrate

1.5 mm

2 mm

Cr - electrode

VA

Electrical-conductivitymeasurements in situ

during cluster deposition

Equivalent depositedthickness at the

percolation threshold :t ≈ 2 nm

Coverage rate ≈ 50 %

NUCLEATION AND GROWTH MECHANISM NUCLEATION AND GROWTH MECHANISM CHARACTERISTIC OF LECBDCHARACTERISTIC OF LECBD((**))

incident cluster, size Ni ≈ 102 to 103 atoms

(a) (a) Deposition

(b) (b) Diffusion

(c)

(c) Nucleation(d)

(d) Coalescence

(e)

(e) Growth

Clusters are not fragmentedupon impact on the substratein the LECBD - regime

Coalescence is limited⇒ 2D-Growth

(*) Review article : P. JENSEN, Rev. Mod. Phys., 71, 1695 (1999).

Substrate

NANOSTRUCTURED MORPHOLOGY OF A THICK CLUSTER FILMNANOSTRUCTURED MORPHOLOGY OF A THICK CLUSTER FILM

Si-substrate

Sb-cluster Film

TEM cross section view of a thick (~80 nm)antimony-cluster film deposited on a silicon substrate

at room temperature :density ≈ 50 to 60 % of the bulk phase

MDMD--SIMULATIONS OF THE CLUSTER DEPOSITIONSIMULATIONS OF THE CLUSTER DEPOSITION

H. Haberland et al., Phys. Rev. B, 51, 11061 (1995).

LECBDregime

Mo1043-Clusters on Mo(001) surfaceC28-Fullerenes on a semiconducting substrate

A. Canning et al, Phys. Rev. Lett, 78, 4442 (1997).

MDMD--SIMULATIONS OF THE CLUSTER DIFFUSION SIMULATIONS OF THE CLUSTER DIFFUSION ON A CRYSTALLINE SURFACEON A CRYSTALLINE SURFACE(*)(*)

(*) P. Deltour et al., Phys. Rev. Lett., 78, 4597 (1997)

Top view

Cross section view

D=f(Size N)D~Nα

-0.66 < α < -1.4

D=f(Misfit)

D=f(Temperature)

EXPERIMENTEXPERIMENT--SIMULATION OF THE CLUSTERSIMULATION OF THE CLUSTER--ASSEMBLED ASSEMBLED NANOSTRUCTURE MORPHOLOGIESNANOSTRUCTURE MORPHOLOGIES

DDA - model (Deposition - Diffusion - Aggregation)(*)

Experiment :Sb2300-clusters on HOPG at 400 K

(*) See : P. JENSEN, Rev. Mod. Phys., 71, 1695 (1999).

DDA - Simulation :Incident clusters can diffuse on the

HOPG-surface.Dcluster ≈ 10-8 cm2/s

Nislands ~ (F/D)χ = (F/D0)χ exp(χ Ea /kT)

with χ = 1/3, Ea ≈ 0.7 eV and D0 ≈ 104 cm2/sCluster fluence (F) and Temperature (T) allow to control Nislands

Kinetic Monte Carlo (KMC) model

CARACTERISTIC EXAMPLES OF FUNCTIONALIZED CARACTERISTIC EXAMPLES OF FUNCTIONALIZED CLUSTERCLUSTER--ASSEMBLED NANOSTRUCTURESASSEMBLED NANOSTRUCTURES

11-- PreparationPreparation of original of original semiconductingsemiconducting nanostructures nanostructures fromfrom siliconsilicon and mixed and mixed siliconsilicon--carboncarbon cage cage likelike clustersclusters(*)(*) ::

C58Si2C59Si(C60)13 - Si2

Si-Fullerenes Si-C Heterofullerenes

Icosahedraledifice

Si stuffed-Fullerènes

(*) See : P. Mélinon et al., in "Clusters as precursors of nano objects", Eds C. Brechignac et al., Comptes Rendus de Physique, 3 (2002) pp. 273-288.

Original electronic structures, différent from the bulk-Si one, mainlydue to the presence of large numbers of pentagonal rings

Applications to nano electronics / opto-electronics

Large quasi direct gap (~ 1.6 to 2 eV) photoluminescence

CLUSTER DIFFUSION AND TRAPPING AT DEFECTSCLUSTER DIFFUSION AND TRAPPING AT DEFECTSApplication to the preparation of 2D-organized arrays

of cluster-assembled dots

1μm

Au750-clusters on HOPGat 300K

Trapping atstep edges

1μm

Au750-clusters on ion-irradiated

HOPG at 300 K* Ar+-1,5 keV

25 nm

1μm

KINETIC MONTE CARLO (KMC) SIMULATIONSKINETIC MONTE CARLO (KMC) SIMULATIONSBallistic model DDA (Deposition – Diffusion – Aggregation)(*)

(*) See : P. Jensen, Rev. Mod. Phys., 71, 1695 (1999).

Experiment : 10-2 ML of Au750-clusters deposited

on FIB-functionalized HOPG at 373 KDistance between defects : 300 nm

KMC-Simulation considering :

Diffusion of incident clusters and compact islands with sizes up to 20 clusters.

No evaporation

Introduction of specific trappingsites ( ) with irreversible sticking(ideal traps)

0.1

1

10

100

0

20

40

60

80

100

0.01 0.1 1 10

All islands are Created on defects

Existence of islands between

defects

SUMMARY OF KMCSUMMARY OF KMC--SIMULATIONSSIMULATIONS

All defects must be occupied

No creation of Cluster - islandsbetween defects

Nislands / functionalized substrate (Nisl/fs)

Ndefects / functionalized substrate (Ndef/fs) 1N

isl/

fs/ N

def

/ fs

N isl / non-fs / N def / fs

Mea

nsi

ze o

f of i

slan

ds(n

umbe

r of c

lust

ers)

COMPETITION BETWEEN 2 KINETIC PROCESSESCOMPETITION BETWEEN 2 KINETIC PROCESSEScapture at defects and nucleation outside of defects

"Growth on defects" regime (Ldef / fs << Lisl / non-fs)A diffusing clusters is captured at a defect before meeting anothercluster to form an islandfilling of defects by a Poisson law Lowest island-size = 5 clusters

Lisl / non-fs : Mean distance between islandson virgin substrates (non-functionalized)

Cluster-cluster aggregation kinetic ~ (F/D)Хwith Х = - 1/6

2 characteristic lengthsLdef / fs : Mean distance between defects

on functionalized substratesdefine the mean time for a diffusing cluster

to be captured at a defect ~ (Ldef / fs)2 / D

Other regimes (Ldef / fs >> Lisl / non-fs)Nucleation outside of defects is preponderant

Defects = exclusive nucleation centresAbove tc, islands grow by capture of clusters

Adjustment of Ldef / fs Adjustment of Ndef / fsAdjust. of F (cluster fluence)

Adjust. of D (diffusion coeff., Adjust. of Nisl / non-fs ~ (F / D)χ (χ= 1/3)T-dependent)

Lattice parameter : Ldef / fs

ADJUSTMENTS OF THE PARAMETERS OF THE 2D ADJUSTMENTS OF THE PARAMETERS OF THE 2D -- ARRAYSARRAYS

Mean Island size

Nisl / non-fs

Ndef / fs<< 1

t = tc t > tc

Nature of the clustersGeneral behaviour of LECBD films whatever is the nature of the clusters

Au-clusters / HOPG Sb-clusters / HOPG Co-clusters / HOPG

Nanoparticle morphologyCompact rather than ramified

Annealings : activation of the

ramified / compact transition

i.e. Au-clusters – 150 °C1 hour in situ in the TEM

MAGNETIC NANOSTRUCTURES FROM CLUSTERSMAGNETIC NANOSTRUCTURES FROM CLUSTERS1- Pure cobalt clusters(*)

X-rays diffraction at grazing incidence on a 80 nm thick Co-cluster film deposited on a

Si-substrate at 300K* Incident free clusters : Co300 ⇒ Φ ≈ 2 nm

TEM-image

1 nm

Fourier transform of the X-rays absorption spectrum (EXAFS)

1 → Co-Co core(d ≈ 0.25 nm)

2 → Co-Co surface (d ≈ 0.26 nm)

3 → Co-0 surface(d ≈ 0.22 nm)

[001]

[100]

[010]

fcc-cobalt cluster* Truncated octahedron

* Diameter ≈ 3 nm⇒ 1388 atoms

fcc-Cofcc-Co

Nearestneighbours

(*) See i.e. J. TUAILLON et al., Phil. Mag., 76, 493 (1997).

MAGNETIC PROPERTIES OF ONE INDIVIDUAL CoMAGNETIC PROPERTIES OF ONE INDIVIDUAL Co--CLUSTER CLUSTER (*)(*)

Using the microSQUID technique developed at LLN - Grenoble1 mμ

200 nm

20 nm

micro-bridgejunctions

μ 0 Η x

cluster

1 mμ

μ 0 Η y

9

Highest sensitivity obtained with the Co-cluster embedded in the Nb-film ata micro-bridge :

⇒ ≈ 10-17 emu⇒ ≈ 103 Bohr-magneton⇒ ≈ One Co-cluster with Φ ≈ 3 nm Cluster Niobium

loop

1 μm

3D-switching field distribution measured at 35 mK for a Co-cluster :

Φ ≈ 3 nm ⇒ ≈ 1000 Co-atoms⇒ 2 anisotropy axes :

- Hard // Hy- Easy // Hz

Simulation using the Stoner-Wohlfarth uniform rotation model :

E(m)/V = - K1mZ2 + K2mY

2

⇒ K1 = 2.1 105 J/m3

⇒ K2 = 0.5 105 J/m3

Hx (T)

Hy (T)

Hz (T)

Hx (T)

Hy (T)

Hz (T)

(*) See : M. JAMET et al., Phys. Rev. Lett., 86, 4676 (2001).

EVOLUTION WITH TEMPERATUREEVOLUTION WITH TEMPERATURE2D-switching field distributions in the yz-plane

measured at different temperatures

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

-0.3 -0.2 -0.1 0 0.1 0.2 0.3

μ 0

0.04 K

1 K

2 K4 K

8 K12 K

T B 14 K-

μ0Hy (Tesla)

μ 0H

z (

Tes

la)

Blocking temperature TB ≈ 14 K for a Co-cluster (Φ ≈ 3 nm)⇓ ⇓ ⇓ ⇓ ⇓

High magnetic anisotropy High blocking temperature (~ 400 K)Applications to high density memory devices and spin electronics

MIXED COBALT MIXED COBALT –– SAMARIUM CLUSTERSSAMARIUM CLUSTERS(*)(*)

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8

Nom

bre

de p

artic

ules

Diamètre (nm)

Annealed in UHV at 570 °CDeposited on a-C at 300K

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14

Nom

bre

de p

artic

ules

Diamètre (nm)

2.92 Å2.09 Å

1.82 Å

1.27 Å

1.07 Å

10 nm 15 nm

Diameter (nm)Num

ber

of p

arti

cles

Diameter (nm)Num

ber

of p

arti

cles

Φ ≈ 3.5 nm Φ ≈ 6 nm

(*) See M. NEGRIER et al., Europ. Phys. J. D, 9, 475 (2000).

2 nm

MAGNETIC PROPERTIES OF MIXED CoMAGNETIC PROPERTIES OF MIXED Co--SmSm CLUSTERSCLUSTERS

As deposited at 300 K Annealed at 770 K

Annealed at 840 K

-1.5

-1

-0.5

0

0.5

1

1.5

-3 -2 -1 0 1 2 3

300 K20 K

-1.5

-1

-0.5

0

0.5

1

1.5

-3 -2 -1 0 1 2 3

300 K20 K

-1,5

-1,0

-0,5

0,0

0,5

1,0

1,5

-3 -2 -1 0 1 2 3

300 K20 K

20 K

300 K

Magnetic field (kOe)

Nor

mal

ized

mag

neti

zati

on: M

/Ms


Nor

mal

ized

mag

neti

zati

on: M

/Ms

20 K 300 K


Nor

mal

ized

mag

neti

zati

on: M

/Ms

20 K300 K

Nanosize clusters (Φ ≈ 5 nm) magnetically blocked at T > 300 K.*Problem of the segregation of

samarium at the cluster surface.*Recrystallisation after annealings

(Sm-Nb non-miscible).

Magnetization measurements

SURFACE CONTAMINATIONSURFACE CONTAMINATION

XPS-measurements (O1s-level)on Gd2O3:Eu3+-cluster films Presence of hydroxide pollution

0526 528 530 532 534 536

1

Inte

nsity

(a.u

.)

Binding energy (eV)

2

3

4

5

(a) - As deposited cluster-film transferred in air

(c) - Bulk hydroxide sample : Gd2(OH)3

(b) - Cluster film transferred in air and subsequently annealed for ½ hour at 300 °C

STRUCTURESTRUCTUREPhase transition in the low cluster-size range

as observed from cathodoluminescence spectra of Eu3+-impurities

Cathodoluminescence measurements (using e- 4 keV) in situ in UHV on 10 nm-thick Gd2O3:Eu3+-cluster films deposited on Si-passivated substrates

Possibility of a phase transition at low cluster-size (~2 nm)

Transition pressure at room temperature for the bulk phase ~ 2 GPa

600 610 620 630 6400,0

0,2

0,4

0,6

0,8

1,0

u.a.

wavelength (nm)

Bulk cubic-phase

Mean cluster-size 3.2 nm

Cluster film (Ф ≈ 3.2 nm)

Cubic

600 610 620 630 6400,0

0,2

0,4

0,6

0,8

1,0

u.a.

wavelength (nm)

Mean cluster-size 2.5 nm

Bulk monoclinic-phase

Cluster film (Ф ≈ 2.5 nm)

monoclinic

Particular Case of Y2O3:Ce3+

SIZE EFFECT ON THE PHOTOLUMINESCENCE PROPERTIESSIZE EFFECT ON THE PHOTOLUMINESCENCE PROPERTIES

M.Raukas et. al. Appl. Phys. Lett. 69, 3300 (1997).D.Jia et. al. Phys. Rev. B 69, 235113 (2004).

VB

Ce 5dCB

XCe 4f

Bulk materials

e--delocalization No luminescence

Nanocrystals

Luminescence of Ce3+ ?

Ce 5dCB

?Ce 4f

VB

Confinement effects Widening of the gap

PHOTOLUMINESCENCE MEASUREMENTSPHOTOLUMINESCENCE MEASUREMENTS

VUVVUV--Synchrotron radiation at DESYSynchrotron radiation at DESYSample : Y2O3:Ce3+ (1 %)

T = 10 K

Bulk

<d> = 30 nm<d> = 15 nm

<d> = 9 nm

180 190 200 210 220 230 2400,0

0,2

0,4

0,6

0,8

1,0

Inte

nsity

(a.

u.)

Wavelength (nm)

Excitation spectra

Type : Self-Trapped

Exciton emission

250 300 350 400 450 500 550 600 6500,0

0,2

0,4

0,6

0,8

1,0

Bulk

<d> = 30 nm

<d> = 3 nm

Wavelength (nm)N

orm

aliz

ed in

tens

ity (a

.u.)

Emission spectra

Excitation at 200 nm

Appearance of an emission band probably due to Ce3+-impurities

Nanocrystals

Ce 5d CB

?Ce 4f

VB

a. perez, p. melinon, v. dupuis, b. masenelli, l. bardotti ... · outline free cluster production...

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