WUTA08 Laboratori Nazionali di Frascati Frascati, 8-10 October 2008 Probing free metallic and carbon...

WUTA08 Laboratori Nazionali di Frascati

Frascati, 8-10 October 2008

Probing free metallic and carbon clusters with VUV photons.

P. Piseri1,2,3 ([email protected]), G. Bongiorno1,2,3, T. Mazza1,2,3 , L. Ravagnan1,2,3, M. Amati1,2,3, M. Devetta1,2, C. Lenardi2,3,4, and P. Milani1,2,3, M. Coreno5,6, M. De Simone6, P. Rudolf 7, F. Evangelista7

1 Dipartimento di Fisica, Università degli Studi di Milano.2 CIMAINA, Università degli Studi di Milano.3 CNR-INFM4 Dipartimento di Farmacologia, Università degli Studi di Milano.5 CNR-IMIP, Area della ricerca di Roma 16 Laboratorio Nazionale TASC INFM-CNR7 University of Gröningen, The Nederlands

Laboratorio Getti Molecolari e Materiali Nanocristallini - LGMDirector: P. Milani ([email protected])

OutlineOutline

Core-level techniques became available for free-clusters with 3rd generation SR light sources

•The CESyRa experience

•Possibilities offered by the experimental setup

•Perspectives with next generation sources

ethane

ethylene acetylene

Simple hydrocarbons

Carbon

sp3

spsp2

Isolated carbon cluster with less than 30

atoms exist as purely sp carbon chains

(carbynes)

R.O. Jones, J. Chem. Phys. 110, 5189 (1999)

Diamond

Graphene

sp3

spsp2

Crystal structures

?

Carbon

a-C

ta-C• Hard• Semiconductor

• Soft• Conductive

Disordered phases:mixture of hybridizations

Chains and rings (sp)

N 32 atoms

E.A. Rohlfing et al. J. Chem. Phys. 81, 3322 (1984)

Pulsed Laser Vaporization source

Fullerenes and onions (sp2, sp3)

N > 32 atoms

Increasing the number of C atoms per cluster

N both even and odd N only even

High power density:annealing of the clusters up to their ground state

structure

Carbon clusters mass spectra

pulsed valve

insulating valve flange

anode

rotating cathode

thermalization cavity

graphite nozzle

ceramic body

Pulsed Microplasma Cluster Source (PMCS)developed at Laboratorio Getti Molecolari e Materiali Nanocristallini,

Department of Physics, University of Milano (Italy)

E. Barborini, P. Piseri, P.Milani, J. Phys. D, Appl. Phys. 32, L105 (1999)

1 mm

H. Vahedi-Tafreshi, et al. Journal of Nanoscience and Nanotechnology 6, 1140 (2006)

Cluster size (atoms)

Both odd and even clusters are detected

A-mode B-mode Residence time (s)

M. Bogana et al. NJP 7, 81 (2005)

The PMCS produces non-fullerenic clusters.

~40% of the whole mass distribution consists in odd clusters

Leaving the fullerene road…

ClCoh

ClClKin

E

NE /=ε

Gas-Phase Nanoparticle deposition, Gas-Phase Nanoparticle deposition, or: Cluster Beam Deposition (CBD) or: Cluster Beam Deposition (CBD) source

ε >> 1

Fragmentation

ε << 1

Memory effect

Low Energy Cluster Beam Deposition (LECBD)or

Supersonic Cluster Beam Deposition (SCBD)

L. Ravagnan et al. PRL 89, 285506 (2002)

Raman spectroscopy of ns-C films

1000 1200 1400 1600 1800 2000 2200 2400

Intensity [arb. units]

Raman shift [cm-1]1000 1200 1400 1600 1800 2000 2200 2400


Raman shift [cm-1]

C band !!

ex situ T=300 K (RT)in situ T=300 K (RT)

First observation of a clear signature of sp bonds in a system of pure carbon !!

D+G band

sp-chains are destroyed by oxygen: in situ measurements are mandatory

1000 1200 1400 1600 1800 2000 2200 2400


Raman shift [cm-1]

L. Ravagnan et al. PRL 89, 285506 (2002) L. Ravagnan et al. PRL 98, 216103 (2007)

Raman spectroscopy of ns-C films

ex situ T=300 K (RT)in situ T=300 K (RT)in situ T=150 K

Also the substrate temperature plays a crucial role!

D+G band

sp3

spsp2

a-C

ta-C• Hard• Semiconductor

• Soft• Conductive

Carbon

Disordered phases:mixture of hybridizations

Ternary phase diagram of the amorphouspure carbon system.

sp-rich a-C

* resonances are fingerprints of the specific molecular bonds

Auger electron

Gaseous acetylene and ethylene have * resonances at 285.9 eV and 284.7 eV respectively.

A.P. Hitchcock et al. J. El. Spec. 10, 317 (1977)

Beyond Raman: NEXAFS spectroscopy

CESYRA: in situ NEXAFS of ns-C films

C.S. Casari et al. Phys. Rev. B 69, 75422 (2004)

270 280 290 300 310 320 330 340


Photon energy [eV]

in situ T=300 K (RT)

We know from Raman that by heating the sample we induce the decay of the sp chains and a partial

reordering of the sp2 matrix.

1000 1200 1400 1600 1800 2000 2200 2400


Raman shift [cm-1]

in situ T=300 K (RT) in situ T=350 K

270 280 290 300 310 320 330 340


Photon energy [eV]

282 284 286 288 290 292 294 296


Photon energy [eV]


The spectra evolves both in the * and * region.

in situ T=300 K (RT)in situ T=350 K

Normalization

282 283 284 285 286 287 288 289 290

Intensity [arb.units]

Photon energy [eV]

Difference (pre-edge)

284.7 eV

285.9 eV

270 280 290 300 310 320 330 340


Photon energy [eV]

sp

sp2


We observe the decay of *(CC) and the increase of the *(CC):

NEXAFS spectroscopy is capable of distinguishing between sp and sp2 in a system of pure carbon!!

in situ T=300 K (RT)in situ T=350 K

Normalization

CESyRa apparatus layoutCESyRa apparatus layout

cluster beams machine

Mass flow controller

High voltage supplyTurbo 2000 l/s

Turbo 500 l/s

Turbo 500 l/sTurbo 300 l/s

Cluster source

Quartz and steel

gate valves (not

shown)

Beam diagnostic device (see inset)

Time of flight mass spectrometer

Beam dumping chamber and

quartz monitor microbalance (not shown)

Feedthrough of the deposition substrate

for in-situ cluster assembled film

analysis

skimmerCluster beam

Source expansion chamber

Gas cell and deflection

stage chamber

Beam diagnostic

device chamber

Interaction chamber

Source part Interaction part

Turbo 300 l/s

Light entrance flange

282 284 286 288 290 292 294 296


Photon energy [eV]

270 280 290 300 310 320 330 340


Photon energy [eV]

CESYRA: TEY NEXAFS of isolated clusters

Normalization

285.6 eV

ns-C film in situ (RT)TEY isolated clusters

The * region is peaked at 285.6 eV: the cluster are predominantly made by sp carbon!

282 284 286 288 290 292 294 296


Photon energy [eV]

270 280 290 300 310 320 330 340


Photon energy [eV]

ns-C film in situ (350 K)

CESYRA: TEY NEXAFS of isolated clusters

Normalization

285.6 eV

ns-C film in situ (RT)TEY isolated clusters

The * region is peaked at 285.6 eV: the cluster are predominantly made by sp carbon!

0 20 40 60 80 100 120

Electrin Yield [arb. units]

Delay time [ms]0 20 40 60 80 100 120

Electrin Yield [arb. units]

Delay time [ms]

PEY: binning of the electron yield for intervals of delay times

First exiting clusters:

short “annealing”

Last exiting clusters:

long “annealing”

Pulsed source discharge

CESYRA: PEY NEXAFS of isolated clusters

Delay time: time elapsed between the discharge and the detection of the photo-electron.

Residence time of the probed cluster in the source.

v ~ cost

CESYRA2: PEY NEXAFS of isolated clusters

270 280 290 300 310 320 330 340

PEY [arb. units]

Photon energy [eV]

Increasing delay time

15 - 21 ms

75 - 81 ms

Small change in the * region.

276 280 284 288 292 296 300

PEY [arb. units]

Photon energy [eV]

Increasing delay time

285.7 eV284.8 eV

CESYRA2: PEY NEXAFS of isolated clusters

15 - 21 ms

75 - 81 ms

10 20 30 40 50 60 70 801.10

1.15

1.20

1.25

1.30

1.35

I(285.8 eV)

/ I(284.7 eV)

Delay time [ms]

Electron Yield SpectraElectron Yield Spectra

What kind of systems can we study?

h

h

XAS on free clustersXAS on free clusters

e-

h

h’

e-

e-

++

Many different relaxation channels open up in free clusters.

h

h

e-

+

h

h’+

e-

e-


e-

h

h’

e-

e-

++

Many different relaxation channels open up in free clusters.

e-h

h’

e-

+

Mixed clusters and cluster-molecule systems add more possibilities

Cluster beam

Photon beam

PEPICO TOF setupSignal to TDC stop channels 1-7 (100 ms range, 80 ps resolution)

Signal to TDC stop channel 8 (100 ms range , 80 ps resolution)

Electron detector

Multiple Ion detectors

TDC start signal from pulsed source discharge

Ex-post reconstruction of electron-ion coincidence spectrum (100 µs range) by software computing the stop1-

7-stop8 time differences

PxPy…CO setup

Events Time StructureEvents Time Structure

Recording the full information

0Delay from start (ms)1.00.5

Delay from start (ms)

tel,jtion,k

Actual He injection

~ 1 ms

He injection trigger 350 s

Discharge60 s

Ion detector array

x

y

z

light clusters

heavy clusters

electrons

Photon beam

Cluster beam

Electron detector

Cluster source

Determination of cluster velocity

Cluster velocity is obtained dividing the detector position by the mean detected time of flight at different detection time;

Complete timing information allows residence-time resolved velocity measurements.

Beam kinematics

€

v m( ) = vHe 1−m − mHe

m + mHe

⎛

⎝ ⎜

⎞

⎠ ⎟

k⋅σ ⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

The velocity of a particle with mass m,seeded in a He supersonic expansion can be modeled by:

After k collisions with the He carrier gas.

is proportional to the collision cross section and is given by

β m=

Where β is 2/3 for a spherical shaped particle

Bu. Wrenger and K. H. Meiwes-Broer, Rev. Sci. Instrum. 68 (5), May 1997, 2027

€

v ttof( ) = vHe 1−α ⋅ ttof

2 − mHe

α ⋅ ttof2 + mHe

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

k⋅ α ⋅ttof2

( )β ⎛

⎝

⎜ ⎜ ⎜

⎞

⎠

⎟ ⎟ ⎟

Beam kinematics: velocity vs residence time

Data fitting by varying: vHe, k, β

A fitting parameter β~0.84 is found against β=2/3=0.667 as expected for dense spherical particles

Vapor

Further growth steps

Clusters have a fractal structure!

e-

+

h

h’+

e-

e-

e-

h

h’

e-

e-

++

h

h’

e-

e-

+

?


What relaxation channels in complex clusters ?e-

h

h’

e-

+

Ion - Ion correlation spectraIon - Ion correlation spectra

n-Erlang distributions for the false coincidence background instead of exponential

PEPICO

PInCO

1st order inter-arrival time distribution

2nd order inter-arrival time distribution

4th order inter-arrival time distribution

Ion - Ion correlation intensityIon - Ion correlation intensity

Maps of nth-order correlated ions intensity

Space correlation

• More channel correlations

Ions per bunch

(channel) = 0 (channel) = 1(channel) = 2(channel) = 3

Ions per bunch

(channel) = 0 (channel) = 1(channel) = 2(channel) = 3

Ions per bunch

Channels 1-4 Channels 4-7

Ion Ion coincidence spectraIon Ion coincidence spectra Space resolved

Fragmentation yieldFragmentation yield Space resolved

x100

We have demonstrated the feasibility of X-ray absorption spectroscopy experiments on free carbon clusters transition metal clusters and oxide clusters

The experiment has been performed by coupling a supersonic cluster beam apparatus (based on a PMCS) with the Gas Phase beamline at Elettra

An “event reconstruction” approach is used to gain insight into the occurring relaxation channels

Improved TOF and position resolution are expected to bring better insight into the fragmentation process.

Independent structural determination of the free clusters is desirable for a validation of the aerodynamic acceleration model.

Conclusions and outlook

XPS

S. Peredkov, et al. Phys Rev B 75, 235407 (2007)

bulk

surface

XPS

S. Peredkov, et al. Phys Rev B 75, 235407 (2007)

Source of uncertainty for R∆Z = ±1

S. Peredkov, et al. Phys Rev B 76, 081402(R)

ACKNOWLEDGEMENTS:

Senior:Paolo Piseri, Cristina Lenardi,

Post-doc:Tommaso Mazza, Gero Bongiorno, Luca Ravagnan, Matteo Amati

Graduate/PhD-students:Michele Devetta, Flavio Della Foglia

UniMI: People at LGM (Group leader Prof. Paolo Milani):

GasPhase:Marcello Coreno, Monica De Simone, Lorenzo Avaldi, Kevin Prince

University of Gröningen (The Nederlands):Petra Rudolf, Fabrizio Evangelista

WUTA08 Laboratori Nazionali di Frascati Frascati, 8-10 October 2008 Probing free metallic and carbon...

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Transcript of WUTA08 Laboratori Nazionali di Frascati Frascati, 8-10 October 2008 Probing free metallic and carbon...