slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
WUTA08 Laboratori Nazionali di Frascati Frascati, 8-10 October 2008 PowerPoint Presentation
Download Presentation
WUTA08 Laboratori Nazionali di Frascati Frascati, 8-10 October 2008

Loading in 2 Seconds...

play fullscreen
1 / 40

WUTA08 Laboratori Nazionali di Frascati Frascati, 8-10 October 2008 - PowerPoint PPT Presentation


  • 127 Views
  • Uploaded on

Probing free metallic and carbon clusters with VUV photons .

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'WUTA08 Laboratori Nazionali di Frascati Frascati, 8-10 October 2008' - avon


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Probing free metallic and carbon clusters with VUV photons.

P. Piseri1,2,3 (piseri@fisica.unimi.it), 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-INFM

4 Dipartimento di Farmacologia, Università degli Studi di Milano.

5 CNR-IMIP, Area della ricerca di Roma 1

6 Laboratorio Nazionale TASC INFM-CNR

7 University of Gröningen, The Nederlands

Laboratorio Getti Molecolari e Materiali Nanocristallini - LGM

Director: P. Milani (pmilani@mi.infn.it)

WUTA08

Laboratori Nazionali di Frascati

Frascati, 8-10 October 2008

outline

Outline

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
slide3

Simple hydrocarbons

ethane

ethylene

acetylene

Carbon

sp3

sp2

sp

slide4

sp3

  • Hard
  • Semiconductor

ta-C

Isolated carbon cluster with less than 30 atoms exist as purely sp carbon chains

(carbynes)

Disordered phases:

mixture of hybridizations

  • Soft
  • Conductive

a-C

sp2

sp

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

Carbon

Diamond

Crystal structures

?

Graphene

slide5

N  32 atoms

N > 32 atoms

Increasing the number of C atoms per cluster

Chains and rings (sp)

Fullerenes and onions (sp2, sp3)

N both even and odd

N only even

Pulsed Laser Vaporization source

High power density:

annealing of the clusters up to their ground state structure

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

Carbon clusters mass spectra

slide6

1 mm

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)

H. Vahedi-Tafreshi, et al. Journal of Nanoscience and Nanotechnology6, 1140 (2006)

anode

insulating valve flange

ceramic body

pulsed valve

graphite nozzle

thermalization cavity

rotating cathode

slide7

A-mode

B-mode

Both odd and even clusters are detected

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

Cluster size (atoms)

The PMCS produces non-fullerenic clusters.

Leaving the fullerene road…

Residence time

(s)

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

slide8

Gas-Phase Nanoparticle deposition,

or: Cluster Beam Deposition (CBD)

source

e >> 1

Fragmentation

e << 1

Memory effect

Low Energy Cluster Beam Deposition (LECBD)

or

Supersonic Cluster Beam Deposition (SCBD)

slide9

ex situ T=300 K (RT)

in situ T=300 K (RT)

C band !!

Raman spectroscopy of ns-C films

D+G

band

First observation of a clear signature of sp bonds

in a system of pure carbon !!

sp-chains are destroyed by oxygen:

in situ measurements are mandatory

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

slide10

ex situ T=300 K (RT)

in situ T=300 K (RT)

in situ T=150 K

Raman spectroscopy of ns-C films

D+G

band

Also the substrate temperature plays a crucial role!

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

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

slide11

sp-rich a-C

Carbon

sp3

  • Hard
  • Semiconductor

ta-C

Disordered phases:

mixture of hybridizations

  • Soft
  • Conductive

a-C

sp2

sp

Ternary phase diagram of the amorphous

pure carbon system.

slide12

Auger electron

Gaseous acetyleneandethylenehave * resonances at 285.9 eV and 284.7 eV respectively.

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

Beyond Raman: NEXAFS spectroscopy

* resonances are fingerprints of the specific molecular bonds

slide13

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.

CESYRA: in situ NEXAFS of ns-C films

C.S. Casari et al.Phys. Rev. B69, 75422 (2004)

slide14

Normalization

in situ T=300 K (RT)

in situ T=350 K

CESYRA: in situ NEXAFS of ns-C films

The spectra evolves both in the * and * region.

slide15

Difference (pre-edge)

Normalization

sp2

284.7 eV

in situ T=300 K (RT)

in situ T=350 K

285.9 eV

sp

CESYRA: in situ NEXAFS of ns-C films

We observe thedecay of *(CC)and the increase of the *(CC):

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

cesyra apparatus layout

Interaction part

Source part

High voltage supply

Beam diagnostic device (see inset)

Time of flight mass spectrometer

CESyRa apparatus layout

Turbo 2000 l/s

Turbo 500 l/s

Turbo 300 l/s

Turbo 300 l/s

Turbo 500 l/s

Beam dumping chamber and quartz monitor microbalance (not shown)

cluster beams machine

Quartz and steel gate valves (not shown)

Cluster beam

skimmer

Cluster source

Light entrance flange

Mass flow controller

Feedthrough of the deposition substrate for in-situ cluster assembled film analysis

Gas cell and deflection stage chamber

Beam diagnostic device chamber

Source expansion chamber

Interaction chamber

slide17

Normalization

ns-C film in situ (RT)

CESYRA: TEY NEXAFS of isolated clusters

285.6 eV

TEY isolated clusters

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

slide18

Normalization

ns-C film in situ (RT)

ns-C film in situ (350 K)

CESYRA: TEY NEXAFS of isolated clusters

285.6 eV

TEY isolated clusters

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

slide19

First exiting clusters:

short “annealing”

Last exiting clusters:

long “annealing”

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

Pulsed source discharge

CESYRA: PEY NEXAFS of isolated clusters

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

v ~ cost

Residence time of the probed clusterin the source.

slide20

Small change in the * region.

CESYRA2: PEY NEXAFS of isolated clusters

75 - 81 ms

Increasing delay time

15 - 21 ms

slide21

284.8 eV

285.7 eV

CESYRA2: PEY NEXAFS of isolated clusters

75 - 81 ms

Increasing delay time

15 - 21 ms

electron yield spectra

Electron Yield Spectra

What kind of systems can we study?

slide23

Many different relaxation channels open up in free clusters.

h’

+

+

e-

e-

h

h

e-

h

XAS on free clusters

slide24

Many different relaxation channels open up in free clusters.

h’

+

+

e-

e-

h

h

e-

+

h’

h’

+

e-

e-

e-

+

h

h

e-

e-

h

XAS on free clusters

Mixed clusters and cluster-molecule systems add more possibilities

slide25

Multiple Ion detectors

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

PEPICO TOF setup

PxPy…CO setup

Ex-post reconstruction of electron-ion coincidence spectrum (100 µs range) by software computing the stop1-7-stop8 time differences

TDC start signal

from pulsed source discharge

Cluster beam

Photon beam

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

Electron detector

events time structure

Delay from start (ms)

Events Time Structure

Recording the full information

Actual He injection

~ 1 ms

Delay from start (ms)

0

0.5

1.0

tion,k

tel,j

He injection trigger 350 s

Discharge

60 s

slide27

z

x

y

Determination of cluster velocity

Ion detector array

Photon

beam

light clusters

heavy clusters

Cluster source

Cluster beam

electrons

Electron detector

  • 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.
slide28

Beam kinematics

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.

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

 is proportional to the collision cross section and is given by

Where  is 2/3 for a spherical shaped particle

slide29

Clusters have a fractal structure!

Vapor

Further growth steps

Beam kinematics: velocity vs residence time

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

Data fitting by varying:

vHe, k, 

slide30

+

h’

+

+

e-

h’

+

e-

e-

h

e-

e-

h

e-

h’

h’

e-

+

h

e-

e-

h

+

e-

XAS on free clusters

?

What relaxation channels in complex clusters ?

ion ion correlation spectra

PEPICO

Ion - Ion correlation spectra

1st order inter-arrival time distribution

2nd order inter-arrival time distribution

4th order inter-arrival time distribution

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

PInCO

ion ion correlation intensity

Ion - Ion correlation intensity

Maps of nth-order correlated ions intensity

space correlation

(channel) = 0

(channel) = 1

(channel) = 2

(channel) = 3

(channel) = 0

(channel) = 1

(channel) = 2

(channel) = 3

Channels 1-4

Channels 4-7

Ions per bunch

Ions per bunch

Ions per bunch

Space correlation
  • More channel correlations
fragmentation yield

Fragmentation yield

Space resolved

x100

slide36

Conclusions and outlook

  • 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.
slide37

XPS

bulk

surface

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

slide38

∆Z = ±1

Source of uncertainty for R

XPS

S. Peredkov, et al. Phys Rev B 76, 081402(R) (2008)

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

slide40

ACKNOWLEDGEMENTS:

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

Senior:

Paolo Piseri, Cristina Lenardi,

Post-doc:

Tommaso Mazza, Gero Bongiorno, Luca Ravagnan, Matteo Amati

Graduate/PhD-students:

Michele Devetta, Flavio Della Foglia

GasPhase:

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

University of Gröningen (The Nederlands):

Petra Rudolf, Fabrizio Evangelista