Workshop on

Research opportunities at the

European X-ray Free Electron Laser

Organized by

Società Italiana Luce di Sincrotrone (SILS)

in collaboration with the

Department of Physics and Astronomy

of the University of Bologna

Aula Magna

Department of Physics and Astronomy, University of Bologna

Via Irnerio 46, Bologna

3rd and 4th July, 2014

Program and Book of Abstracts

The European X-ray Free Electron Laser will provide x-ray beams of

unprecedented characteristics in terms of peak brilliance, coherence and

time structure. This is the appropriate time to hold a workshop with the

objective of identifying topics of interest for the Italian community of

instrument builders and future users and to stimulate all possible synergies

and common actions towards the establishment of an Italian scientific

programme of Free Electron Laser Science and exploitation of the European

XFEL.

The topics which will be covered are:

Status of ongoing collaborative projects with the European XFEL.

Instrumental aspects, including photon and electron detectors,

experimental chambers.

Scientific topics specific to FELs in general and the European XFEL in

particular.

Extensions of experiments currently carried out at storage rings or with

optical lasers.

SILS Executive Committee: F. Boscherini (Chairman, U. Bologna),

P. Ghigna (U. Pavia), A. Gualtieri (U. Modena & R. Emilia), S. Pascarelli

(ESRF Grenoble), B. Vallone (La Sapienza U. Rome), A. Verdini (IOM-

CNR Trieste).

Local Organizing Committee: F. Boscherini, L. Pasquini, L. Amidani

Società Italiana di Luce di Sincrotrone (SILS) is

the independent and multidisciplinary scientific

society which represents expert researchers

and users of synchrotron radiation and free

electron lasers since 1992. Members are active

in all major scientific fields: physics, materials

science, chemistry, earth sciences, biology and

medicine. SILS is linked to the European

Synchrotron Users Organization (ESUO).

SILS organizes:

• the annual conference;

• the biannual synchrotron radiation

school.

Other SILS activites include

reports on projects of interest;

prizes:

o best Ph.D. in the field of SR and

FELs;

o best posters at the annual

conference.

SILS is self-funded by membership fees. To find

out more about our activities:

www.synchrotron-radiation.it

5 10 15 20

2 (°)

280 290 300(eV)

Program

Thursday, July 3rd 2014

Session 1, Chair: F. Boscherini (Uni. Bologna and SILS)

14:30 - 14:45 F. Boscherini (Uni.

Bologna and SILS)

Welcome/Opening

14:45 -15:30 Th. Tstchentscher

(European XFEL)

Science capabilities at European XFEL

15:30 - 15:50 S. Fabiani (INFN Trieste) Evolving Silicon Drift Detectors to advanced light sources

15:50 - 16:10 G. Ghiringhelli (Politecnico

Milano)

The hRIXS project at the European XFEL

16:10 - 16:30 A. DiCicco (Uni.

Camerino)

EUV transmission experiments at Fermi@Elettra: models

and results

16:30 - 17:00 Coffee break & Posters

Session 2, Chair: G. Ghiringhelli (Politecnico di Milano)

17:00 - 17:20 F. Boscherini (Uni.

Bologna)

The EX-PRO-REL project - status and perspectives

17:20 - 17:40 L. Avaldi (CNR-ISM

Rome)

A study of the dynamical energy flow in uracil

17:40 - 18:00 A. Castoldi (Politecnico

Milano & INFN Milano)

DSSC, an ultra fast X-ray imager under development for

the European XFEL

18:00 - 18:20 L. Poletto (CNR - IFN

Padova)

SINGLE-SHOT X-RAY EMISSION-SPECTROSCOPY

EXPERIMENTS

18:20 - 18:40 L. Pasquini (Uni. Bologna) Dynamics of light-excited charge carriers in materials for

energy conversion and photocatalysis: new opportunities by

X-ray spectroscopy at Free Electron Lasers

18:40 - 19:00 M. Dell'Angela (Elettra,

Trieste)

Real Time Observation of Surface Bond Breaking with an

X-ray Laser

20:00 Dinner (included in registration fee), Ristorante Buca Manzoni, Via Manzoni 6G.

Posters

E. Borfecchia (Uni. Turin) Probing the photochemistry of cis-[Ru(bpy)2(py)2]2+ on

the ultrafast scale: results from synchrotron techniques and

perspectives with XFELs

L. Amidani (Uni. Bologna) High energy resolution fluorescence detected XANES at Ti

K edge to study light – induced plasmonic interactions in

Au/TiO2 nanocomposites

V. Lollobrigida (Uni. Roma

Tre)

Time-energy dispersion electron analyser

E. Segoloni (CNR - IOM,

Trieste)

XPP-Simulator: a tool for feasibility of Pump&Probe

experiments on solid samples

G. Greco (Uni. Roma Tre) High energy spin resolved photoemission spectroscopy

F. Benedetti (Uni. Modena

& Reggio Emilia)

Electronic properties of cerium oxide-based materials

Y. Peng (Politecnico

Milano)

Preliminary optical design of a high resolution hRIXS

spectrometer for the European XFEL

Friday, July 4th 2014

Session 3, Chair: L. Avaldi (CNR – ISM, Roma)

9:00 - 9:20 G. Panaccione (CNR-IOM, Trieste) Photoemission and spin-polarization

experiments at X-FEL: Feasibility study and

perspectives

9:20 - 9:40 P. O'Keefe (CNR-ISM, Rome) FEL based non-linear and time-resolved

experiments involving two-colour

photoionization of Helium atoms and droplets

9:40 - 10:00 G. Monaco (Uni. Trento) Ion acoustic waves in warm dense matter

10:00 - 10:20 A. Verna (Uni. Roma Tre) Space-charge effects on hard X-ray

photoelectron spectroscopy

10:20 - 10:50 V. Re (INFN Pavia) The PixFEL project: advanced fine-pitch X-ray

pixel detectors for the next generation FEL

facilities

10:50-11:20 Coffee Break & posters

Session 4, Chair: G. Rossi

11:20 - 12:20 Open discussion

Science capabilities at European XFEL

Thomas Tschentschera

aEuropean XFEL, 22607 Hamburg, Germany

European XFEL is a large international research infrastructure currently under construction in the Hamburg Metropol

region, North Germany. This infrastructure will provide researchers with free-electron laser (FEL) radiation in the x-ray

range from 0.25 to 25 keV. Six science instruments dedicated to a variety of x-ray techniques and applications will be

available initially. The facility layout allows increasing the number of science instruments up to fifteen. In contrast to

other FELs the x-ray beam delivery system at European XFEL foresees the parallel operation of three (later five) science

instruments. This will dramatically increase the availability of hard x-ray FEL radiation for user experiments and therefore

will allow broadening the user base of short-wavelength FEL science significantly. Another difference to existing FEL

facilities is the possibility to generate and utilize a much increased pulse rate of up to 27.000 pulses per second. An

overview of the related R&D efforts and the prospects for using such high repetition rates will be given in the talk. The

construction of the European XFEL facility advances rapidly. Civil construction is nearing completion and the installation

of the electron accelerator has begun. The design of the first x-ray instruments is almost complete and construction is

about to start. First experiments are scheduled for 2017.

The European XFEL facility addresses a large variety of science areas such as physics, chemistry, structural biology,

materials sciences, or plasma and planetary physics. Hard x-ray FEL radiation is available since 2009 at the LCLS (SLAC,

U.S.A.) and since 2011 at SACLA (Spring-8, Japan) and has since been applied in a broad scientific program. Highlight

experiments will be described during the talk in order to demonstrate the new science capabilities provided by hard x-ray

FEL radiation. In addition, new methods for generating FEL radiation with improved performance have been proposed

and were partly tested. A brief overview of these new schemes allows extrapolating possible developments of these

extremely brilliant x-ray sources in coming years.

Evolving Silicon Drift Detectors to advanced light sources

Sergio Fabiani a, M. Ahangarianabhari c,f, P. Bellutti h, G. Bertuccio c, f, M. Bruschi i, J. Bufon b,e, S. Carratoe, A. Castoldim, G.

Cautero b, A. Cicuttin l, M. L. Crespo l, G. Giacomini h, A. Gianoncelli b, D. Giuressi b, M. Grassid,g,C. Guazzonif, D. Macera c,f, P.

Malcovati d,g, R. H. Menk b, A. Picciotto h, C. Piemonte h, I. Rashevskaya a,A. Rachevski a , A. Sbrizzi i, A. Vacchi a , G. Zampa a , N.

Zampa a, Luca Olivib

a INFN Sezione di Triste, Trieste, Italy bElettra-Sincrotrone Trieste S.C.p.A., Trieste, Italy

cPolitecnico di Milano, Como, Italy dUniversità di Pavia, Pavia, Italy eUniversità di Trieste, Trieste, Italy

fINFN Sezione di Milano, Milano, Italy gINFN Sezione di Pavia, Pavia, Italy hFondazione Bruno Kessler,, Trento, Italy

iINFN Sezione di Bologna, Bologna, Italy lICTP, Trieste, Italy mPolitecnico di Milano, Milano, Italy

The unprecedented features of XFEL radiation sources open new challenge in the development of novel detectors

requiring specifications that in some cases exceed the existing technology. The development of detectors customized for

a specific use is a key issue to be compliant with the advanced requirements.

We will show the evolution of Silicon Drift Detectors (SDD) toward advanced light sources starting from synchrotron,

which is in progress at INFN in collaboration with Elettra, Politecnico di Milano, Università degli Studi di Trieste, FBK

(Trento).

We will introduce the upgrade of a new customized detector design for the TwinMic spectro-microscope at Elettra. This

X-ray spectromicroscope combines full-field imaging with scanning microscopy and the simultaneous acquisition of X-

ray fluorescence in the 400-2200 eV photon energy range for bio-related research [1]. The upgrade of the detector for the

Low-Energy X-ray Fluorescence set-up (LEXRF) will couple the good energy resolution with a larger coverage of the

photoemission solid angle (40%), ten times larger than in the present configuration [2].

An even more complex challenge is related to the upgrade of the detector set-up at the XAFS beamline at Elettra. XAFS

is dedicated to X-ray absorption spectroscopy in the 2.4- 27 keV energy range [3] and can work both in transmission and

fluorescence. To significantly reduce the integration time during the fluorescence acquisition the capability to sustain a

high source flux with a larger collecting area is needed. The capability to design and produce a segmented detector array

of large area will allow for matching the requirements. References

[1] B. Kaulich et al., J. R. Soc. Interface, vol. 6, pp. 641-647, 2009

[2] A. Gianoncelli et al., Journal of Physics: Conference Series, vol. 425, n. 18, 2013

[3] A. Di Cicco et al. Journal of Physics: Conference Series 190 012043 2009

J. R. Soc. Interface, vol. 6, 2009, pp. 641-647

The hRIXS project at the European XFEL

Giacomo Ghiringhelli,a Yingying Peng,a Alexander Föhlisch,b Andreas Scherzc

a Dipartimento di Fisica, Politecnico di Milano, , Italy

b Helmholtz Zentrum Berlin/BESSY, Germany c European XFEL, Hamburg, Germany

An international user consortium will equip the SCS beam line of the European XFEL with a high resolution soft x-ray

spectrometer for ultra-advanced resonant inelastic x-ray scattering (RIXS). The hRIXS project aims at adding the time

resolution to high resolution RIXS studies, therefore hitting the intrinsic limit of Heisenberg uncertainty problem in x-ray

energy loss spectroscopy. Moreover XFEL offers the opportunity to explore multi-photon processes, which could open

the way to 4-wave scattering experiments in the x-ray regime.

The design of the 5 meter-long hRIXS spectrometer is under the way by the team of the Politecnico di Milano, in strict

contact with the SCS beam line scientific staff, with the main partner and head of the Consortium (HZB), and with a

number of other members of the Consortium. The optical design work has been entirely covered by the PIK project

“POLARIXS” of the MIUR (Italian Ministry of University and Research).

The scientific goals, the technical and conceptual challenges behind hRIXS, and the preliminary optical studies of the

spectrometer will be presented. The political and financial framework of hRIXS will be also briefly discussed.

EUV transmission experiments at FERMI@Elettra: models and results

A. Di Cicco,a K. Hatadab

a Physics Division, School of Science and Technology, Camerino University, 62032 Camerino (MC)

The high intensity of pulses obtained by modern extreme ultraviolet (EUV) and x-ray free-electron-laser (FEL) photon

sources allows us observation of peculiar excitation phenomena in condensed matter, like saturable absorption and

ultrafast non-thermal heating. For instance, saturable absorption was first recently observed in transmission measurements

above the L2,3 edge of Al thin films using high-fluence ultra-short 92 eV x-ray pulses. The deposited energy of individual

FEL shots is able to pump condensed matter up to the warm dense matter regime for a few picoseconds, allowing us

access to states relevant to the interior of large planets and stars. The TIMEX collaboration [1] between the ELETTRA

synchrotron and the University of Camerino was specifically conceived to exploit the new FERMI@Elettra FEL source

for experiments on condensed matter under transient extreme conditions. FERMI@Elettra is a FEL seeded facility, able to generate subpicosecond photon pulses of high intensity in the EUV and

soft x-ray range (routinely up to 62 eV for the present FEL1 source, extended to ∼ 300 eV with the FEL2 source under

commissioning). Details of the experimental set-up and some examples of experiments performed during the first

commissioning runs of the TIMEX end-station (branch of the EIS beamline) are presented ([1,2] and refs. therein). Results of EUV transmission experiments of Al thin films using the Fermi@Elettra FEL1 free-electron-laser source have

been interpreted within a simplified computational scheme. [3] We show that the high fluence, the shortness of the pulse

duration, and the typical lifetime of the excited state are all important factors for modeling the EUV transmission. The

saturation phenomenon is described using a three-channel model containing ground, excited and relaxed states. The

phenomenological model explicitly includes the interaction between the solid and photon field in a semi-classical way,

and the resulting non-linear coupled equation is solved numerically. Examples of calculation are compared with

experimental results.

[1] http://gnxas.unicam.it/TIMEX [2] Andrea Di Cicco, Claudio Masciovecchio, Filippo Bencivenga, Emiliano Principi, Erika Giangrisostomi, Andrea Battistoni,

Riccardo Cucini, Francesco D'Amico, Silvia Di Fonzo, Alessandro Gessini, Keisuke Hatada, Roberto Gunnella, Adriano Filipponi,

"Probing matter under extreme conditions at free-electron laser facilities: the TIMEX beamline'' , Notiziario Neutroni e Luce di

Sincrotrone, Vol. 18, 19-27 (2013). [3] K. Hatada and A. Di Cicco, Modeling saturable absorption for ultra short X-ray pulses, J. Electr. Spectr. Rel. Phenom. (2014).

EX-PRO-REL project: status and perspectives

L. Amidania, M. Benfattob, F. Bisioc,d, F. Boscherinia, M. Canepac, C. Cepeke,

F. d’Acapitoe, B. Davidsone, G. Grecoi, M. Malvestutoe,f, C. Marianig, S. Pagliarah, L. Pasquinia, M. Pedioe, S. Ponzonih,

E. Segolonie, G. Stefanii, A. Trapanantie, A. Vernai

a Physics and Astronomy Department, University of Bologna and CNISM b INFN – Laboratori Nazionali di Frascati c Physics Department, University of Genova and CNISM d CNR – SPIN, Genova e CNR – IOM, Trieste and Grenoble

f Elettra – Sincrotrone Trieste g Physics Department, La Sapienza University of Rome and CNISM h University of Brescia i Department of Science, University of Roma Tre and CNISM

The emission of very brilliant radiation pulses of duration between 1 and 100 fs is one of the most interesting features of

FELs. The pulse duration is ideally suited to probe transient electron transfer and relaxation processes which follow

optical excitation. The aim of this PIK project is to develop specific instrumentation and methods and to perform pilot

experiments in this field, also contributing to the formation of a group of early users of FELs with expertise in the specific

instrumental and scientific challenges.

The instrumental developments include the pre – design of a vacuum chamber appropriate for measurements on solid

samples at the FXE beamline of the European-XFEL, the implementation of transient state measurements on the GILDA

beamline of ESRF and the study of a time – of – flight photoelectron spectrometer in the hard x-rays. Ongoing pilot

experiments include studies of transient states in molecular thin films, piezoelectrics, TiO2 and metallic nanoparticles and

graphene. The work on the vacuum chamber for solid sample experiments at XFEL is being complemented by a

corresponding scientific case.

(b)

A study of the dynamical energy flow in uracil

P. Bolognesi a, P. O’Keeffe a, T. Mazzab, J. Bozekc, R. Coffeec, C. Bostedtc, S. Schorbc,S. Carronc, R. Feifeld, M.

Mucked, M. Guehre, E. F. Sistrunke, J. Grilje, B. K. McFarlande, M. Koche, M. Larssonf, P. Salemf, N. Berrahg, L. Fangg,

T. Osipovg, B. Murphyg, R. R. Lucchesem, M. Meyerb, M.N. Piancastellid, K. Uedah, S. Mondalh, C. Mironi, R. Richterl,

K.C. Princel and L. Avaldi a

aCNR-ISM, UOS- Montelibretti,,Area della Ricerca di Roma1, Italy bEuropean XFEL Hamburg, Germany

cLCLS, SLAC, Menlo Park, CA 94025, USA dDepartment of Physics and Astronomy, Uppsala University, Sweden ePULSE, SLAC Menlo Park, CA 94025, USA fPhys. Dept., Stockholm University, Sweden

g Phys. Dept, Western Michigan University, USA hDepartment of Physics, Tohoku University, Sendai 980-8577, Japan iSynchrotron SOLEIL, Gif-sur-Yvette Cedex, France l Elettra-Sincrotrone Trieste, Basovizza I-34149, Italy

m Dept. of Chemistry, Texas A&M University, College Station, TX 77843-3255,USA

We have investigated the dynamics of core ionized uracil by time-resolved pump-probe techniques, using a femtosecond

laser system as the pump and the X-ray pulse of the LCLS as probe, combined with an efficient electron detector: a

magnetic bottle. Uracil, is one of the building blocks of RNA and is closely related to thymine, one of the letters in the

DNA alphabet. A fundamental question in ultrafast photodynamics of these molecular subunits is: how do they resist

damage due to the strong absorption of UV radiation? Pyrimidine and purine derivatives, the main components of DNA

bases, can dissipate dangerous electronic energy before it causes bond breakage and consequent errors in the DNA code.

Current theories focus on conical intersections of the excited state, and the roles of allowed and dark excited states. By

laser pumping the ground state of the molecule and probing the excited states with core level spectroscopy, we can shed

light on the nature of internal electronic energy conversion after UV photoexcitation. In the experiments the

photoionization of C1s at 350 eV has been studied at different delay times between the X-Fel pulse and the UV excitation

(260 nm, ππ* excitation) pulse. The difference between the spectra with laser on and off is shown in figure (1c).

Figure 1. (a) Scheme of the uracil molecule; (b) calculated C1s photoelectron spectra for the ground (S0), first dark nπ* (S1) and

allowed ππ* (S2) states; (c) difference between the measured photoelectron spectra with and without ultraviolet excitation.

(c)

287 288 289 290 291 292 293 294 295 296 297

0.0

0.5

1.0

1.5

2.0

C5

C4

C6

Inte

nsity (

arb

itra

ry u

nits)

S0

Binding energy (eV)

C2

288 290 292 294 296

0

2 S1

288 290 292 294 296

0

2

4

S2

(a) (a)

DSSC, an ultra fast X-ray imager under development for the European XFEL

A. Castoldia,b, on behalf of the DSSC Consortium

a Politecnico di Milano, Milano, Italy

b INFN, Sezione di Milano, Milano, Italy

This presentation discusses the main scientific challenges and the features of the 2D X-ray imager named DSSC (DePFET

Sensor with Signal Compression) currently under development for the European XFEL.

From the detector standpoint, among the critical features of the XFEL source is the expected brilliance of the X-ray beam

that will produce a local rate on the detector up to 10^4 ph/pixel/bunch. This requires very high dynamic range (up to

1:10,000) at every pixel which in turn imposes a challenging noise performances of few electron r.m.s. of the readout

electronics, in particular for the low X-ray energy range. A further specific challenge is the time structure of the X-ray

beam. As every X-ray pulse can be regarded as a new imaging experiment, the imaging detector must be very fast to be

able to readout, digitize and store the data before the arrival of the next pulse. The European XFEL at Hamburg will be

able to produce about 30,000 pulses per second but these pulses are delivered in bunch trains of about 3,000 pulses with

a very challenging and critical time separation of 220 ns. The combination of these requirements poses a formidable and

stimulating challenge to novel detector developments both for the design and the qualification techniques [1, 2].

The DePFET Sensor with Signal Compression (DSSC) system is one of the three 2D X-ray imaging detectors committed

for the European XFEL carried out by an German-Italian collaboration [3].

The DSSC concept is based on a silicon pixel sensor embedding a DePFET (Depleted P-type Field-Effect Transistor) as

on-pixel amplifying stage. The pixel sensor has been designed so as to combine high energy resolution at low signal

charge with high dynamic range. In order to fit a high dynamic range into a reasonable output signal range, achieving at

the same time single photon resolution, a strongly non-linear characteristic is required. The new proposed type of DePFET

has been specially tailored to provide the required analog signal compression on-pixel [3], thus easing the design of the

following readout ASIC. The full sensor camera will have a total size of approximately 200×200 mm^2 composed of

1024 × 1024 pixels with hexagonal shape. The detector chips are bump-bonded to mixed-signal readout ASICs in 130nm

CMOS technology that provide full parallel readout of the DePFET pixels.

The key features of the design of the DSSC system will be discussed. The first experimental results show that the DSSC

system has the potential to provide 2D imaging and single photon resolution for 1keV photons at 4.5 MHz.

References

[1] H. Graafsma, J. Instr. 4, P12011 (2009).

[2] A. Castoldi, C. Guazzoni, D. Mezza, L. Carraresi, F. Taccetti, Proc. of SPIE Vol. 8078 80780P (2011)

[3] M. Porro et al., IEEE Trans. Nucl. Sci., Vol. 59, No. 6, December 2012

[4] G. Lutz et al., Nucl. Instr. And Meth. A, vol. 624, Issue 2, pp. 528-532, December 2010

Single-shot X-Ray emission-spectroscopy experiments

Luca Poletto*a, Fabio Frassettoa, Paolo Miottia, Marcello Corenob, Andrea Di Ciccoc, Cesare Graziolid, Fabio Iesaric, and

Antti Kivimäkie a CNR- Institute of Photonics and Nanotechnologies, Padova, Italy;

b CNR–ISM, Roma, Italy; c Dipartimento di Fisica, Università di Camerino, Camerino (MC), Italy;

d Elettra-Sincrotrone Trieste, Trieste, Italy; e CNR-IOM, Trieste, Italy;

We present the design, realization and characterization of a portable and compact spectrometer dedicated to photon-in-

photon-out experiments in FEL beamlines and realized in the framework of the PIK project “Single-shot X-Ray emission-

spectroscopy experiments” funded by ELETTRA. The instrument operates in the 25-800 eV energy range with spectral

resolution better than 0.2%. The optical design consists of two interchangeable spherical varied-lined-spaced gratings and

a XUV-enhanced CCD detector. Different input sections can be accommodated, with/without an entrance slit and

with/without an additional relay mirror, that allow to mount the spectrometer in different end-stations and at different

distances from the target area both in synchrotron and FEL beamlines. Three configurations have been realized, that are

specifically tailored for the LDM and EIS-TIMEX beamlines of FERMI@ELETTRA. We present the results obtained

during the commissioning of the instrument at the GASPHASE beamline of ELETTRA synchrotron, where X-ray

emission spectroscopy experiments have been successfully performed both on solid (Si, B, BN) and gas targets (He, Kr).

Finally, we present some preliminary results obtained at FERMI@ELETTRA measuring the FEL emission in a

superradiant cascade configuration.

Figure 3. He fluorescence spectra from the doubly excited states of helium below the N=2 ionization threshold: a) (3,0) resonance at

64.114 eV; b) (4,-1) resonance at 64.133 eV.

Figure 1. Picture of the spectrometer.

Figure 2. Si L emission fluorescence

spectrum for crystalline Si sample. The

exciting photon energy is 100.5 eV.

Figure 1. Picture of the spectrometer.

Dynamics of light-excited charge carriers in materials for energy conversion and

photocatalysis: new opportunities by X-ray spectroscopy at Free Electron Lasers

L. Pasquini,a L. Amidani,a M. Calizzi,a F. Boscherinia

a Department of Physics and Astronomy, University of Bologna, Italy

The production of solar fuels from sunlight in a photo-electrochemical cell and the photocatalytic degradation of

environmental pollutants are examples of photophysical processes that promise to play a crucial role in the sustainable

development of human society. These phenomena rely on the creation, transport and trapping of charge carriers (electrons

and holes) on timescales which range from femtoseconds to nanoseconds. Among the candidate materials for viable

applications in this field, oxide semiconductors such as TiO2 are of particular interest due to their resistance in aqueous

or oxidizing environments and to their electrons/holes energy levels which are suitable for water reduction/oxidation. A

basic understanding of charge carrier dynamics in oxide semiconductors is thus of utmost importance in order to improve

their efficiency in solar energy conversion and photocatalysis.

Traditionally, the dynamics of trapped charge carriers in TiO2 has been followed by pump-probe, all-optical time-resolved

techniques allowing only for an indirect assignment of characteristic optical signatures to specific structural defects.

Recently, time-resolved X-ray absorption spectroscopy techniques developed at third generation synchrotron sources

have paved the way towards laser pump / X-ray probe experiments in the picosecond time domain [1,2], allowing the

mapping of trapping sites for electrons in TiO2 nanoparticles [3].

X-ray Free Electron Lasers have the potential to extend the temporal range of time-resolved laser pump / X-ray probe

studies of these photophysical processes down to the yet unexplored femtosecond regime, and to significantly increase

the signal-to-noise ratio over the whole time range. In this contribution we will discuss this opportunity trying to address

the basic questions that remain to be answered and the relevant experimental challenges.

[1] F.A. Lima et al., Rev. Sci. Instr. 82, 063111 (2011).

[2] M. Chergui, Acta Cryst. A66, 229 (2010).

[3] M.H. Rittmann-Frank, C.J. Milne, J. Rittmann, M. Reinhard, T.J. Penfold, M. Chergui, Angew. Chem. Int. Ed. 53, 5858 (2014).

Real Time Observation of Surface Bond Breaking with an X-ray Laser

M. Dell'Angela (1, *), T. Anniyev (2), M. Beye (2,4), R. Coffee (2), A. Foehlisch (4), J. Gladh (3), T. Katayama (2), S.

Kaya (2), O. Krupin (2), J. LaRue (2), A. Moegelhoej (2), D. Nordlund (2), J. Norskov (2), H. Oberg (3), H. Ogasawara

(2), H. Ostrom (3), L. G. M. Pettersson (3), W. F. Schlotter(2), J. A. Sellberg (2), F. Sorgenfrei (1), J. J. Turner (2), M.

Wolf (5), W. Wurth (1), A. Nilsson (2,3)

(1) Institut fuer Experimentalphysik, Universitaet Hamburg and Center for Free Electron Laser, Hamburg, Germany;

(2) SLAC National Accelerator Laboratory, Menlo Park, California, United States;

(3) Department of Physics, Stockholm University, Stockholm, Sweden, G-I2;

(4) Methods and Instrumentation in Synchrotron Radiation, Helmholtz-Zentrum Berlin, Berlin, Germany;

(5) Department of Physical Chemistry, Fritz-Haber-Institut, Berlin, Germany

(*) present address Elettra Sincrotrone Trieste S.C.p.A., Trieste, Italy

Ultrashort X-ray pulses with high intensity delivered from X-ray free-electron lasers open completely new possibilities

for the study of chemical reactions on surfaces. With the well-known technique of X-ray emission spectroscopy resonantly

tuned to the oxygen core level, we can directly study the orbitals relevant for the surface chemical bonding. With

synchronized excitation by a femtosecond optical laser pulse, we induced desorption of CO from the surface.

We observed electronic structure changes that are consistent with a weakening of the CO interaction with the substrate

but without notable desorption. Combining the experimental data with results of free energy calculations based on density

functional theory by using a new functional that included van der Waals interactions, we identified a precursor state, a

two-dimensional gas of CO molecular that weakly interacts with the surface but still affects desorption kinetics [1].

This research was carried out on the SXR Instrument at the Linac Coherent Light Source (LCLS) at the SLAC National

Accelerator Laboratory. The SXR Instrument is funded by a consortium whose membership include the LCLS, Stanford

University through the Stanford Institute for Materials Energy Sciences (SIMES), Lawrence Berkeley National

Laboratory (LBNL), University of Hamburg through the BMBF priority program FSP 301, and the Center for Free

Electron Laser Science (CFEL). The LCLS is funded by the U.S. Department of Energy's Office of Basic Energy Sciences.

[1] M. Dell’Angela, et al. Science 339, 1302 (2013)

Photoemission and spin-polarization experiments at X-FEL: Feasibility study and perspectives

Giancarlo Panaccionea

a CNR-IOM, Lab. TASC, Trieste, Italy

Third generation Synchrotron Radiation facilities, and recent developments in insertion devices, have been able in recent

years to expand the capabilities of Photoemission Spectroscopy (PES) and spin polarized photoemission techniques to

new fields of research. Among the major impact results (technological and scientific) obtained by PES, to name but a

few, one may list: a) a deeper knowledge in strongly correlated materials, b) a growing impact of time resolved PES-

based experiments, c) a clear trend to ‘push the limits’ of the PES experiments, by exploiting the extreme low (< 10 eV)

and extreme high (> 2 keV) photon energy range, e.g. to search truly bulk sensitive information. Looking to next

generation of experiments based on new X-ray Free electron lasers facilities, Photoemission spectroscopy at the FEL

sources will have to face the presence of space charge, to actually access the femtosecond regime and study, e.g. phase

transitions of the electronic structure and/or ultrafast magnetization dynamics and imaging.

We report the commissioning phase of the ULTRASPIN experimental setup, aiming at performing spin polarization

measurements in static and ultrafast mode, with both table-tob and free electron laser sources. Moreover, a feasibility

scheme, together with the main technological and scientific challenges, for setting up an experiment with energy, time

and spin detection at FELs will be discussed.

FEL based non-linear and time-resolved experiments involving two-colour photoionization of Helium

atoms and droplets

L. Avaldi1, P. Bolognesi1, A. Ciavardini1, M. Coreno1, P. O'Keeffe1, V. Lyamayev11, Y. Ovcharenko3, R. Katzy2, M.

Devetta4, L. Bruder2, A. LaForge2, M. Mudrich2, U. Person2, F. Stienkemeier2, M. Krikunova3, T. Möller3, P. Piseri4, M.

Alagia5, M. Di Fraia6, N. B. Brauer7, M. Drabbels7, S. Stranges9,5, P. Finetti10, C. Grazioli10, O. Plekan10, R. Richter10, K.

C. Prince10,5, C. Callegari10, T. Mazza11, M. Ilchen11, A. J. Rafipoor11, S. Dusterer12, K. Ueda13, J. T. Costello14, A. K.

Kazansky15,16,17, N. M. Kabachnik11,13,17,18, M. Meyer11

1CNR-ISM, Monterotondo Scalo, Italy, 2Physikalisches Institut, Universität Freiburg, Freiburg, Germany, 3Institut für Optik und

Atomare Physik, Technische Universität Berlin, Berlin, Germany, 4CIMAINA and Dipartimento di Fisica, Università di Milano,

Milano, Italy, 5CNR-IOM, Laboratorio TASC, Basovizza, Trieste, Italy, 6Department of Physics, University of Trieste, Trieste, Italy, 7Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland, 8European XFEL, Albert-Einstein-Ring 19, Hamburg,

Germany, 9Department of Chemistry, University La Sapienza Rome, Rome, Italy , 10Elettra-Sincrotrone Trieste, Basovizza, Trieste,

Italy, 11European XFEL GmbH, Albert-Einstein-Ring 19, Hamburg, Germany, 12Deutsches Elektronen-Synchrotron (DESY),

Notkestrasse 85, Hamburg, Germany, 13Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai,

Japan, 14National Center for Plasma Science and Technology and School of Physical Sciences, Dublin City University, Dublin, Ireland, 15Departamento de Fisica de Materiales, UPV/EHU, San Sebastian/Donostia, Spain, 16IKERBASQUE, Basque Foundation for Science,

Bilbao, Spain, 17Donostia International Physics Center (DIPC), San Sebastian/Donostia, Spain, 18Skobeltsyn Institute of Nuclear

Physics, Lomonosov Moscow State University, Moscow, Russia.

The opportunities for new research topics opened up by the advent of Free Electron Lasers (FELs) are illustrated by a

discussion of the two-colour gas phase photoionization of Helium atoms and droplets. First we discuss measurements on

process (1) taken at the Gas Phase beam line at Elettra, by synchronization of an external laser with the synchrotron pulses

He 1s2 + hvSR He 1snp + hvLas He+1s + e− (1)

enabling us to illustrate the information which can be gained by measurement of the Photoelectron Angular Distributions

(PADs) in two-colour photoionization [1]. We then discuss the circular dichroism in two-colour photoionization of He

measured at the Low Density Matter (LDM) beam line of the FERMI FEL through measurement of the PADs of so-called

sidebands resulting from free-free transitions in the continuum induced by the presence of a IR laser during the

photoionizations of the atoms by the FEL [2]. Finally, we discuss the femtosecond relaxation dynamics of He droplets

following excitation to the He* 1s2s/1s2p states by pumping with FERMI FEL photons and probing with a synchronized

UV laser again at the LDM beam line [3]. These examples clearly show the new information which can be accessed due

to higher intensity and shorter time widths of the FEL in comparison to the synchrotron source. The high intensities pave

the way to non-linear physics while the short pulses open the path to femtosecond time-resolved experiments.

[1] P. O’Keeffe et al., New J. Phys. 15, 013023 (2013).

[2] T. Mazza et al. Nat. Comm. doi:10.1038/ncomms4648 (2014).

[3] M. Mudrich et al. (to be published).

Ion acoustic waves in warm dense matter

G. Monacoa, T. Whiteb, G. Gregorib, N. Hartlyb, L. Fletcherc, K. Appeld, T. Tschentscherd, D. Chapmane, D.O. Gerickee,

T. Doeppnerf, H-J. Leeg, B. Naglerg, E. Galtierg, E. Granadosg, U. Zastraug, P. Heinmanng, A. Schroppg, S.H. Glenzerg,

J. Hastingsg

aPhysics Department, University of Trento, Italy bPhysics Department, University of Oxford, UK

cPhysics Department, University of California, USA dEuropean XFEL, Hamburg, Germany ePhysics Department, University of Warwick, UK fLLNL, Livermore, USA gSLAC, Menlo Park, USA

Recent results obtained using FEL-based high resolution inelastic x-ray scattering to probe the ion acoustic waves in

warm dense Al are here presented. A more than twofold compression of Al at a temperature of ~2 eV has been reached

using two counter-propagating shock waves generated by two 3 ns long, 5 J laser beams at the MEC beamline at LCLS.

A high-resolution spectrometer based on a diced crystal analyzer operated in close to backscattering at the Si(4,4,4)

reflection has been setup to reach a total energy resolution of ~100 meV. This has allowed resolving a Brillouin spectrum

for an exchanged wavevector of 2.1 Ǻ-1. A scheme is proposed to extract the longitudinal sound velocity from this

spectrum. It turns out that Al at ~6.2 g/cm3 and ~2 eV of temperature is almost twice as stiff as diamond at room

conditions. The comparison of the results obtained here with literature Hugoniot velocity data at lower density show that

the commonly used Birch’s law is not valid, thus clearly indicating that direct experimental data are required to refine

models of physical properties in this warm dense matter regime.

Space-charge effects on hard X-ray photoelectron spectroscopy

Adriano Vernaa, Francesco Offia, Giorgia Grecoa, Valerio Lollobrigidaa,b and Giovanni Stefania

aDipartimento di Scienze, Università Roma Tre, Via della Vasca Navale 84 00146 Rome Italy

bDipartimento di Matematica e Fisica, Università Roma Tre, Via della Vasca Navale 84 00146 Rome Italy

The development of the new X-ray free-electron lasers (FELs) opens new opportunities in the application of pump-and-

probe approach in photo-emission spectroscopy (PES). The use of intense and monochromatic sub-picosecond X-ray

pulses offers the possibility to investigate the ultrafast dynamics and relaxation processes of the chemical, electronic and

magnetic properties of surfaces. The use of hard X-rays for electron excitation allows to overcome the strong surface

sensitivity of conventional PES and to investigate the properties of buried (~nm) interfaces [1] and its application in

pump-and-probe experiments announces a new interesting class of experiments. However, the use of intense light pulses

in PES is limited by the space charge created by the high number of electrons emitted at the same time, as evinced in

experiments carried on with 3rd generation synchrotron radiation [2], ultraviolet lasers [3] and X-ray FELs [4] and

predicted by simulation procedures [5]. Photoemitted electrons interact each other, faster electrons tend to be pushed

forward by slower electrons behind them, which are accordingly decelerated. This results in a broadening of the structures

in the photoemission spectra (loss of resolution) and in a shift of the energy position of the peaks. A very simple theoretical

model proposed years ago by Long, Itchkawitz and Kabler (LIK) [6] predicts an energy broadening directly proportional

to the number N of the electrons emitted by a single pulse and inversely proportional to radius a of the radiation spot on

the sample. We will show how the LIK model is confirmed also quantitatively by many experimental results. Using this

model we performed a feasibility study for a core-level PES experiment using hard X-rays with resolution of ~0.1 eV and

we demonstrate that a reduction of the monochromatized pulse by a factor 1000 is sufficient to prevent dramatic space-

charge effects. A N-body calculation software [7] is used in order to simulate the space-charge broadening and shift for

keV photoelectrons in hard X-ray experiments. Effects of space charge on photoelectron momentum, in the view of angle-

resolved experiments, are also investigated.

Figure 1: Simulation of the energy broadening for a cloud of mono-energetic (10 keV) photoemitted electrons as a function of the

number N (left) and the radius a of photo-emitting spot (right).

[1] F. Borgatti, F. Offi, P. Torelli, G. Monaco, G. Panaccione, J. Electron Spectrosc. 190, 228 (2013).

[2] X. J. Zhou et al., J. Electron Spectrosc. 142, 27 (2005).

[3] J. Graf et al., J. Appl. Phys. 107, 014912 (2010).

[4] A. Pietzsch et al., New J. Phys. 10, 033004 (2008).

[5] S. Hellmann, K. Rossnagel, M. Marczynski-Bühlow, L. Kipp, Phys. Rev. B 79, 035402 (2009).

[6] J. P. Long and B. S. Itchkawitz and M. N. Kabler, J. Opt. Soc. Am. B 13, 201 (1996).

[7] J. Barnes, P. Hut, Nature 324, 446 (1986).

0.001

0.01

0.1

1

en

erg

y b

roa

de

nin

g (

eV

)

102

103

104

105

N

energy broadening power-law model

=0.9852±0.0027

0.001

0.01

0.1

10 100 1000

a (m)

energy broadening power-law model

=1.0286±0.0088

The PixFEL project: advanced fine-pitch X-ray pixel detectors for the next generation FEL

facilities

Valerio Re,a,b on behalf of the PixFEL collaboration

a Department of Engineering, University of Bergamo, Bergamo, Italy

bINFN, Sezione di Pavia, Pavia, Italy

The PixFEL project is conceived as the first stage of a long term research program aiming at the development of advanced

instrumentation for coherent X-ray diffractive imaging applications at the next generation free electron laser (FEL)

facilities.

The project aims at substantially advancing the state-of-the-art in the field of 2D X-ray imaging through the adoption of

cutting-edge microelectronic technologies and innovative design and architectural solutions. For this purpose, the

collaboration is developing the fundamental microelectronic building blocks (low noise analog front-end with dynamic

compression feature, high resolution, low power ADC, high density memories) and investigating and implementing the

enabling technologies (active edge pixel sensors, high density and low density through silicon vias) for the assembly of a

multilayer four side buttable tile. The building block design is being carried out in a 65 nm CMOS technology.

The ambitious goal of the research program is the fabrication of an X-ray camera with single photon resolution, 1to 104

photons @ 1 keV to 10 keV input dynamic range, 1 kevent in-pixel memory, 100 m pixel pitch, and the capability to be

operated at the fast (1 MHz or larger) rates foreseen for the future XFEL machines.

Probing the photochemistry of cis-[Ru(bpy)2(py)2]2+ on the ultrafast scale:

results from synchrotron techniques and perspectives with XFELs

Elisa Borfecchia,a Claudio Garino,a Luca Salassa,b Roberto Gobetto,a Carlo Lamberti,a,c

a Department of Chemistry, NIS Centre of Excellence and INSTM Reference Center,

University of Turin, Turin, Italy. elisa.borfecchia@unito.it b CIC biomaGUNE, Donostia–San Sebastián, Spain

c Southern Federal University, Rostov-on-Don, Russia

Photoactive metal complexes are applied in a variety of fields, including solar energy conversion, catalysis and medicinal

chemistry. Their effectiveness depends on the excited-state features that control the competition between physical

(radiative, nonradiative) and chemical modes of deactivation. For this reason, the structural determination of light-induced

transient species is a key-requirement for a rational design of novel photoactive metal complexes. Among the available

time-resolved methods, synchrotron-based techniques have recently emerged as successful tools in detecting ultrafast

structural changes in molecules [1]. This contribution summarizes the results obtained by our group combining

synchrotron TR-XSS (Time-Resolved X-ray Solution Scattering) and TR-XAS (Time-Resolved XAS) to study the

solution-phase excited-state dynamics in cis-[Ru(bpy)2(py)2]2+ (Figure 1), a model compound for ligand releasing

applications [2]. In particular, by sub-µs TR-XSS we detected the release of one pyridine ligand from the metal centre

and the subsequent coordination of a water molecule, resulting in the formation of the cis-[Ru(bpy)2(py)(H2O)]2+

photoproduct (PHP) within 800 ns from laser excitation [3]. Furthermore, TR-XAS allowed us to unravel the 3MLCT

excited state (ES) geometry, characterized by an elongation of the Ru−N(py) bond relative to the dissociating ligand and

a shortening of the Ru–N(bpy) in trans to it, in agreement with computational analysis [4].

Figure 1. Simplified Perrin-Jabłoński diagram for aqueous cis-[Ru(bpy)2(py)2]2+ upon UV/visible irradiation, showing the ES

dynamics yielding to PHP formation upon excitation of the GS complex, with the geometries of the initial (GS) and final (PHP) state

of the process. Synchrotron TR-XSS/XAS ultrafast studies which clarified the PHP and 3MLCT ES geometries and potential time-

scale for future XFEL experiments are indicated with coloured circles.

Exploiting the unique capabilities of XFELs, in term of ultra-high fluxes and extremely short X-ray pulse length, it would

be possible to access the earlier ES dynamics in cis-[Ru(bpy)2(py)2]2+, occurring on the fs-time scale. For the complex of

interest this would allow us to capture the geometry of the singlet 1MLCT ES, which is expected to be primarily populated

upon light excitation. The structural and electronic modifications related to the intersystem-crossing would be therefore

clarified, providing a crucial experimental evidence for phenomena so far studied almost exclusively on the theoretical

and computational ground.

[1] E. Borfecchia et al., Philos. Trans. R. Soc. A, 20120132 (2013).

[2] E. Borfecchia et al., Catal. Today 229, 34 (2014).

[3] L. Salassa et al., Inorg. Chem. 49, 11240 (2010).

[4] E. Borfecchia et al., Dalton Trans. 42, 6564 (2013).

High energy resolution fluorescence detected XANES at Ti K edge to study light – induced

plasmonic interactions in Au/TiO2 nanocomposites

L. Amidania, F. Boscherinia, M. Malvestutob, V. Dal Santoc, A. Naldonic

a Department of Physics and Astronomy, University of Bologna, Bologna, Italy

bElettra-Sincrotrone Trieste, Basovizza (Ts), Italy c CNR-Istituto di Scienze e Tecnologie Molecolari, Milano, Italy

We present a study of the Ti K-edge in Au/TiO2 nanocomposites were high energy resolution fluorescence detected

XANES was exploited to investigate the interaction between TiO2 and plasmonic Au nanoparticles (NPs). TiO2 is a

promising material for photocatalysis processes like water splitting or degradation of noxious pollutants [1]. When

coupled with Au NPs, the photocatalytic activity in the visible range is highly improved. This enhancement is caused by

the interaction of TiO2 electronic structure with the Surface Plasmon Resonance (SPR) of Au NPs, which is excited by

visible light around 532 nm.

We measured high resolution inelastic x-ray scattering spectra at the Ti K-edge of Au/TiO2 nanocomposites while exciting

the SPR of Au NPs with a 532 nm CW laser. We were able to detect a difference as small as 1.5% of Ti K-edge spectral

intensity in the pre-edge region for samples containing Au, while no differences were seen for bare TiO2. Our observations

are not compatible with a simple T effect, but are rather a spectral signature of an charge transfer process.

[1] S. C. Warren, E. Thimsen, Energy Environ. Sci. 5, 2012, 5133.

Electronic properties of cerium oxide-based materials

F. Benedetti,a,b P. Luches,b G. Gasperi,a,b M.C. Spadaro,a,b S. D’Addato,a,b L. Amidani, c F. Boscherini,c and S. Valeria,b

a Dipartimento FIM, Università di Modena e Reggio Emilia, Modena, Italy

b CNR, Istituto Nanoscienze, Modena, Italy c Dipartimento di Fisica e Astronomia, Università di Bologna, Italy

Cerium oxide is a very interesting material with applications in catalysis, energy conversion, biomedicine and memories.

Most of the applications are based on the reducibility of the material, i.e. on the possibility for the cations to reversibly

and rapidly change their oxidation state between the 3+ and 4+ state, depending on the external conditions. A complete

understanding of the electronic properties of cerium oxide and of their modifications with reduction is necessary to design

materials with optimized reducibility.

In the last few years we have been studying cerium oxide in the form of ultrathin films [1,2] and nanoparticles and we

showed that heating treatments in vacuum and in oxygen-rich atmosphere induce a controlled reduction and oxidation of

the material. We have compared the effect of the thermal treatments in films and nanoparticles of different sizes, to

understand the role of dimensionality and structure on reducibility. In a recent study we used resonant X-ray emission

spectroscopy at the Ce L3 edge - detecting the L1 fluorescence - to have information on the evolution of the 4f electron

configuration during the oxidation and reduction processes.

Pump-and-probe experiments, e.g. time resolved photoemission or resonant X-ray emission spectroscopy experiments,

using x-ray probes may be of great help to obtain a deeper understanding of the electronic structure of cerium oxide-based

materials at different degrees of oxidation. The electronic properties of the excited states and their evolution with time

are interesting also in view of the application of the material as an additive to absorb UV radiation.

[1] P. Luches, F. Pagliuca, and S. Valeri, J. Phys. Chem. C 115, 10718 (2011).

[2] P. Luches, F. Pagliuca, S. Valeri, and F. Boscherini, J. Phys. Chem. C 117, 1030 (2013).

Preliminary optical design of a high resolution hRIXS spectrometer for the European XFEL

Yingying Peng,a Giacomo Ghiringhellia

a Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy

XFEL provides ultra-short soft x-ray pulse with high repetition rate and a brightness exceeding all current x-ray sources.

Combining with Resonant inelastic x-ray scattering (RIXS), it can create unique science opportunities by simultaneously

providing momentum and time-resolved information. Here we present the feasible study of a 5m long high resolution

spectrometer for resonant inelastic x-ray scattering, to be used at XFEL in the 300-1600 eV energy range. We will discuss

two optional spectrometer configurations: single spherical grating (SVLSG) and Hettrick-Underwood scheme

(SM/VLSG). We combine analytical calculation and ray tracing using the Shadow code to optimize grating parameters

and spectrometer geometry to cancel coma aberration. We find out SVLSG configuration have better advantage in both

resolving power and operation feasibility. With an x-ray spot on the sample of 5 μm and CCD resolution of 10μm, the

targeted resolving power can be higher than 30000 below energy 900 eV. We will also provide information on focusing

configuration for time-resolved RIXS and collimating configuration for angle resolved RIXS. These analysis thus give a

recipe for designing a high-resolution spectrometer with negligible aberration for hRIXS over the soft x-ray range.

Time-energy dispersion electron analyser

V. Lollobrigidaa,b, G. Grecob, A. Vernab, F. Offib, G. Stefanib

a Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, Via della Vasca Navale 84 I-00146 Rome, Italy

bDipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84 I-00146 Rome, Italy

Pulsed photon sources like free electron lasers (FELs) request the use of electron spectrometers based on the time-of-

flight (TOF), which require an intrinsic time-reference signal. They are very attractive because of their mechanical

simplicity, but their application is often limited by the reduced accepted solid angle and moderate energy resolution in

the intermediate and high energy range. It was shown that by combining a TOF with a spherical mirror electrostatic

reflector, thus exploiting the time-energy dispersion (TED) of the mirror itself, an analyser with an improved, rather than

degraded energy resolution at high energy and a large accepted solid angle could be obtained [1,2]. The performances of

a TOF spectrometer based on a spherical electron mirror with a 10 cm inner sphere radius and 200 cm outer sphere radius

have been studied for a “high energy” photoemission case (~ 5 keV kinetic energy). SIMION® ion optics simulation

program has been used to calculate the electric field for a given set of potentials and the electron trajectories in such a

field. By measuring the TOF and the detection point position on a position sensitive detector, such as a micro-channel

plate (MCP), it is possible to retrieve the energy and the initial polar and azimuthal angles of emission of the

photoelectrons. A 2 mm radius pupil positioned in the beam waist is used to reduce the band-pass of the analyser, which

exhibits a transmission > 90% in the selected energy range. This characteristic can allow performing experiments with

higher incoming flux than by a conventional TOF analyser and avoiding saturating the detector with unwanted events.

With a 25 mm radius detector oriented in order to minimize the spread of the electron TOFs, we can expect an acceptance

solid angle of ~ 0.02 sr and an energy resolution as good as 60 meV at 5 keV kinetic energy if the detection point position

is retrieved along with the time-of-flight. This value is limited by the size of the pixels and the time resolution of the

detector. If no position detection is performed a 160 meV resolution at 5 keV is to be expected, mainly due to the spread

of the TOFs of the various electrons.

Figure 1. Energy resolution of the TED spectrometer.

[1] O. M. Artamonov, S. N. Samarin, A. O. Smirnov, J. Electron Spectrosc. Relat. Phenom. 120, 11 (2001).

[2] O. M. Artamonov, S. N. Samarin, G. Paolicelli, G. Stefani, J. Electron Spectrosc. Relat. Phenom. 131-132, 105 (2003).

XPP-Simulator:

a tool for feasibility of Pump&Probe experiments on solid samples

Enrico Segoloni,a Federico Boscherini b and Maddalena Pedioa

a CNR-IOM,TASC Area Science Park, Basovizza, Trieste Italy

bPhysics and Astronomy Department, Università di Bologna, Bologna Italy

In the framework of the EXPROREL project, we present a calculation tool for the feasibility evaluation of pump and

probe (P&P) x-ray spectroscopy experiments on solid samples to be performed with a vacuum chamber at the FXE

beamline of the European-XFEL.

A preliminary study of P&P experiments at Free-electron lasers sources is mandatory. We have implemented the

calculation algorithms in a code for experiments implying emitted X-rays [1]. The XPP-Simulator program is intended

to study the feasibility of P&P experiments on the basis of the damage evaluation induced by the XFEL and Laser pulses.

It also allows to give hint for the experimental set up for a given material.

In Figure 1 presented below, an example of the ratio between the number of absorbed Laser and X-Ray photons, RL/X(L,

X), as function of the two incident angles, indicates the optimal beams configuration to obtain a given achievable Signal

to Noise ratio (S/N) [1], in the light of the limits imposed by the damage evaluation [2], [3], [4].

Our results demonstrate that, depending on the material and on the selected spectroscopy (Fluorescence XAS, XAS in

Transmission, XES), P&P experiments are feasible on a wide series of solid samples with S/N ratios up (or above) about

10, using a X-Ray intensity in the range of 109 - 1011 photons per pulse (X-Ray energy 5-12 keV) by means of sample

cooling, adequate choice of the incident beams intensities and geometry.

Figure 1. Left: RL/X(L, X) ratio function for a Germanium sample as function of the Laser and X-Ray incidence angles (L, X), (Laser

power: 10-5 J, intensity: 4 1013 photons/pulse, X-Ray energy 10 keV). Right: S/N ratio (for a Johann detector) as function of the X-Ray

incident flux and of X for a P&P Fluorescence XAS experiment on the same material (K1 transition, 11.103 keV). Black arrow

indicates the damage limit value of 10% for the H ratio between the total energy absorbed and the melting heat of the sample.

References:

[1] M. Bianchini P. Glatzel, Journal of Synchrotron Radiation 19, 911–919 (2012).

[2] CXRO X-Database: Atomic Scattering Factor Files, http://henke.lbl.gov/optical_constants/sf

[3] E. D. Palik Handbook of Optical Constants of Solids, Academic Press, Boston 1985

[4] M. Sànchez del Rìo, et al., XRAYLIB tables (X-Ray fluorescence cross-section), European Synchrotron

Radiation Facility and University of Sassari, www.esrf.eu

High energy spin resolved photoemission spectroscopy:

a time of flight electron analyzer

G. Grecoa,V. Lollobrigidaa,b, A. Vernaa, F. Offia, G. Stefani a

a Dipartimento di Scienze, Università di Roma Tre, via della Vasca Navale 84 I-00146, Rome, Italy.

b Dipartimento di Matematica e Fisica, Università di Roma Tre, via della Vasca Navale 84 I-00146, Rome, Italy.

The advent of fourth generation synchrotron radiation sources such as the Free Electron Lasers (FEL) provides short

pulses and high photon flux. With these beam characteristics this light source is suitable for investigating structure and

dynamics of matter at atomic size and timescale.

So the next frontier is to extend photoelectron spectroscopy into the time domain to study the dynamics of the electron

and spin systems [1,2].

Spin-resolved photoemission is one of the most direct ways of measuring the magnetization of a ferromagnet. If all

valence band electrons contribute, the measured average spin polarization is proportional to the magnetization. However,

the efficiency of the electron analyzers with spin analysis has so far represented a limiting factor, and therefore requires

further progress [1,2,3].

The project of a spectrometer for spin resolved photoemission from solids suitable to work with hard x-rays generated by

a FEL is presented. The proposed spin resolved photoemission apparatus is based on a linear time-of-flight TOF energy

analyzer coupled with a focusing lens to a Mott spin detector (see fig. 1).

The transmission obtained at the Mott detector for photoelectrons generated in a circular source (1mm of diameter) at

10260eV and within a solid angle of ± 7o is about 80% with a 0.07% energy resolution. The advantages presented by the

present project for time resolved investigations on the spin population of electronic states will be discussed.

Figure 1. 3D view of the TOF analyzer (SIMION software), including simulated electron trajectories and equipotential lines. A

sections of the potential array, corresponding to the refocusing lens is also shown. The trajectories shown are those of

electrons emitted at 10260 eV and spread over the whole ± 7o angular acceptance of the analyzer.

[1] C. La-O-Vorakiat, M. Siemens, et al. Phys. Rev. Lett. 103, 257402 (2009).

[2] A. Fognini , T. U. Michlmayr et al. Applied Physics Letters 104 , 032402 (2014)