5/5.1/ELI-RO_17

PAES approaches for thin films

surfaces and interfaces studies

General information:

Programme / Sub-programme / Module: 5/5.1/ELI-RO

Project type:RDI

ELI-NP thematic: GDE/II.2 Material science studies with positron beams

Project title / Acronym: PAES approaches for thin films surfaces and interfaces studies/ FILMSURFAPES

Contract no: 17

Project duration : 17.09.2020  -  31.08.2023

 

Project director: Dr. Ioan-Ovidiu Pana

 

Project Coordinator: National Institute for Research and Development of Isotopic and Molecular Technologies

Partner 1: National Institute for Research and Development of Materials Physics

 

Team:

INCDTIM

Dr. Pana Ioan - Ovidiu

Project director, CSI

Dr. Stefan Maria

CSII

Drd. Macavei Sergiu

IDTI

Dr. Toloman Dana

CSII

Dr. Popa Adriana

CSII

Dr. Leostean Cristian

CSII

Dr. Gutoiu Simona

CSIII

Dr. Stegarescu Adina

CSIII

Dr. Soran Maria - Loredana

CSI

Dr. Suciu Ramona

CSIII

Dr. Silipas Teofil-Danut

CSII

Groza Maria

Tehnician

 

INCDFM

Dr. Teodorescu Cristian Mihail

Project responsible, CSI

Dr. Husanu Marius Adrian

CSI

Dr. Lungu George Adrian

CSI

Dr. Tache Cristian Alexandru

CSI

DrD. Borcan Larisa Elena

CSIII

Project summary:

                 Positron annihilation-induced Auger electron spectroscopy, when operated with low energy positron kinetic energies (below ~ 5 eV) is probably the most surface sensitive technique known to date. The origin of this fact stems in the ‚negative positron work-function of most materials or, in other words, to the fact that positrons originating from vacuum should exceed a threshold value of their kinetic energy to penetrate into the bulk of the material. As a consequence, low energy positrons do not penetrate inside most materials and, after forming some metastable positronium-like metastable states near the surface of the material, they annihilate with electrons from the very first atomic layer being a versatile method to study surfaces and interfaces in condensed matter.

                 The main scientific objective of the project refers to the characterization of surfaces and interfaces by using positron-induced Auger electron spectroscopy (PAES) for thin films and multilayers. It is related to and derives from objectives of Program 5 / Subprogram 5.1 (HG no. 583/2015) namely "Gamma-beam applications at ELI-NP-GDE / II.2" in material science studies with positron beams.

Specific objectives:

1. preparation by pulsed laser deposition (PLD) and primary physical characterization of thin layers of FePt (L10) with different thicknesses on MgO substrate; - preparation by PLD and characterization of ZnS / FePt (L10) / MgO multilayer systems - obtaining by two different methods (PLD and chemical vapor deposition-CVD) graphene films on MgO substrate;

2. Obtaining the necessary authorizations for the realization and operation of the existing PAES system (with a 22Na positron source) of Partner 1; obtaining and interpreting the PAES spectra as well as their correlation with the other classical measurements.

3. Elaboration of a methodology for characterization of surfaces and interfaces through PAES necessary for the further developments of the low energy positron system within ELI-RO.

4. Establishing partnerships for future collaborations in experiments with low energy positrons within ELI-NP infrastructure.

Stages

                 For the achievement of the above objectives the project includes 4 annual stages 2020-2023. Conceptually, the proposal contains several Tasks that do not necessarily overlap with the mentioned stages. The tasks under consideration are the following:

T1. Preparation as well as theoretical and experimental characterization of thin layers based on FePt (L10). MgO and FePt (L10) / ZnS / MgO.

T2. Complete realization of the PAES spectra measurement system and its authorization by CNCAN;

T3. Obtaining the PAES spectra for thin layers based on FePt (L10). MgO and FePt (L10) / ZnS / MgO as well as their interpretation and correlation with the other experimental data and theoretical calculations. T4. Preparation as well as theoretical and experimental characterization of thin layers based on few graphene layers on MnO substrate.

T5. Obtaining PAES spectra for graphene-based thin films deposited by PLD and CVD and interpretation of these results in correlation with theoretical calculations and other experimental determinations. Elaboration of the methodology necessary for the further development of these types of experiments within ELI-NP.

T6. Dissemination of results by publication in ISI-listed journals and communications at conferences.

Project equipment:

Project coordinator

Name of equipment

Characteristics (average wear and tear - %)

Pulsed Laser Deposition

- 2015 by TSST;

- thin film growth of complex materials;

- 16" cylindrical deposition chamber with load-lock;

- <10-7 mbar base pressure;

- up to 800°C growth temperature;

- up to 6 targets, targetsize up to 2”;

- spotsize 1.0-3.0 mm2, homogeneous fluence by mask imaging;

- process gases, pressure O2, Ar, N2, automated up/downstream pressure control;

- movement Z, (X, Y), continuous rotation;

- Q-smart Nd:YAG laser, multimode resonator 2ω, 1064nm-850 mJ, 532nm-430mJ, and accordable wave length in 670-2600 nm range; 10Hz max. pulse frequency;

-Coherent COMPEX PRO 102F KrF excimer laser 248 nm - 400 mJ, 20Hz max. pulse frequency;

*average wear and tear 10 %

X-Ray diffractometer

-2015 by Rigaku;

-multifunctional automated system: XRD, SAXS, GISAXS,

-“in plane reflectivity” for powder and thin film samples;

-reflection and transmission operating modes;

-X-Ray source Cu, 9 kW, CBO cross beam optics for parallel and focused mode;

-scintillation SC-70S detector:,

- D/tex Ultra and D/tex 250 1D detector;

-CALSA multi-crystal analyzer for ultrahigh resolution;

-Goniometer 5 axes, θ/2θ;

-CALSA multi-crystal analyzer for ultrahigh resolution;

- PDXL qualitative and quantitative analysis software;

-reflectivity, Rocking Curve and reciprocal space mapping software

*average wear and tear 10 %

X-Ray Photoelectron Spectroscopy XPS

-2008 by SPECS;

-PHOIBOS 150 2D CCD energy analyzer (energy resolution < 2 meV);

-XR 50 X-ray source (dual anode Al/Mg);

-XR 50M monochromatic X-ray source (dual anode Al/Ag)

-Ion source for controlled sputtering (energetic domain 0.2-5 keV);

-Flood Gun FG 15 (energy range 0-10eV and 0-500eV);

-UVS 300 UV source.

*average wear and tear 10 %

Raman spectrometer

-2008 by Jasco;

-model NRS 3300

-spectral range: 125 - 200000 nm;

-spectrograph 300mm anastigmatic;

-standard grating: 1800gr/mm;

-resolution: 1 nm;

-solid state lasers: 514nm, 633nm and 785nm;

*average wear and tear 10 %

VSM magnetometer

-2008 by Cryogenic Ltd.;

-Cryogen-free system;

-Magnetic field           up to 8 Tesla;

-Central field homogeneity           0.01% over 25mm ;

-Fast field sweep rate   0.7 Tesla/min;

-Sample temperature range (VTI)                  1.6 – 310K;

-Maximum sample size                10 mm;

-Noise base (10 sec averaging)      10-6 emu;

-Accuracy and reproducibility       0.5%;

*average wear and tear 10  %

Partner 1

Name of equipment

Characteristics (average wear and tear - %)

Setup for positron annihilation-induced Auger electron spectroscopy (PAES)

Operates in ultrahigh vacuum (10–11 mbar), 22Na positron source (10 mCi) mounted on a closed-cycle He cryostat (5 K), solid Ne moderator, high temperature sample holder, cylindrical mirror analyzer (CMA) for electron detection.

*average wear and tear 10 %

Complex surface science cluster mounted on a synchrotron radiation beamline (CoSMoS = Combined Spectroscopy and Microscopy on a Synchrotron)

Operates in ultrahigh vacuum (10–11 mbar), composed by three main chambers: (i) angle- and spin-resolved photoelectron spectroscopy (XPS, UPS, ARUPS, photoelectron diffraction, spin-resolved UPS), 77 – 1200 K manipulator with 5 degrees of freedom; (ii) molecular beam epitaxy (MBE) with 6 effusion cells, plasma source, 77 – 1200 K manipulator with 5 degrees of freedom, residual gas analysis, gas line, ion sputtering; (iii) scanning tunneling microsopy and spectroscopy (STM – STS) chamber, atomic resolution, variable temperature. Load-lock and storage chambers. Mounted on a the SuperESCA synchrotron radiation beamline at Elettra, photons in the range 80 – 1200 eV, 1013 photons/s, resolution E/DE = 10–4, 4 weeks of beamtime available yearly, laboratory sources (X-ray guns, UV lamps, electron guns) available for working offline.

*average wear and tear 10 %

 

Rezults:

 

Summary of accomplishments during the reporting period:

                 During the first stage, a series of 5 samples of FePt thin films were prepared by PLD by changing the number of pulses and the heat treatment conditions. The films were prepared on MgO substrates (100). Their characterization was done by Scanning Electrons Microscopy, X-ray diffraction and X-ray reflectometry. The analyzed samples have a granular structure that varies depending on the number of pulses and the heat treatment method. The L10 type crystalline structure was only partially realized for these first prepared samples.

                 During the second stage, a series of 5 samples of ZnS/FePt/MgO thin films were prepared by PLD by changing the number of pulses for zinc sulfide deposition. The films were prepared on MgO substrates (100). Theoretical investigations regarding layer orientation inside the FePt films were performed. Their characterization was done by X-ray diffraction, X-ray reflectometry, XPS, UPS. Spin resolved XPS was used to investigate the existence of half-metal magnetic ordering in the FePt layer. The magnetic behavior shows that the semiconductor ZnS films have got ferromagnetic order and are coupled to their half-metal substrate (FePtL10). Regarding the PAES installation, the lead shielding was redesigned in order to reduce the initial amount of lead according to the calculations in the technical file. It refers to the CNCAN requirement for the location and construction of the laboratory in order to minimize to zero the irradiation with gamma photons resulting from the de-excitation of the 22Ne* level (hν = 1,275 MeV). The project was executed at the mechanical workshop. In September 2021, the request to obtain the other two authorizations necessary to carry out the research activity with the PAES radiological installation was sent to CNCAN. Also, the procedure for responding to radiological emergencies in the laboratory where the PAES radiological installation is to operate was set-in an updated form according to the notification uet osly received from CNCAN.

                 In the first part of the third stage, the following steps were done: (i) PLD deposition of graphene layers on MgO substrate and the preparation of graphene layers deposited by PLD on FePt layers previously deposited on MgO substrate; (ii) theoretical calculation (DFT + LDA / GGA and LDA + U) of the band structure for ZnS thin layers. Structural changes on their surface induced by the interface tension with the FePt(L10) thin film.

 

List of papers:

- M. Stefan , C. Leostean , D. Toloman , A. Popa , S. Macavei , A. Falamas , R. Suciu ,

L. Barbu-Tudoran, O. Marincas, O. Pana, Applied Surface Science 570 (2021) 151172.

 

- C. M. Teodorescu, M. A. Hușanu, Re-entrant ferromagnetism at ultrahigh temperatures in epsilon–iron as possible origin of the geomagnetic field, Phys. Earth Planet. Inter. 326, 106856 (2022).

 

List of talks of group members:

-Interplay between ferromagnetism, optical absorption and photocatalytic activity of semiconductors interfaced with a half-metal at nano-scale, O. Pana, M. Stefan, D. Toloman, A. Popa, C. Leostean; ICPAM-13, 13th International Conference on Physics of Advanced Materials, September 24-30, 2021, Sant Feliu de Guixols, Spain

 

- Surface charge accumulation at ferroelectric thin films and its consequences on long-range ordering and surface chemistry, invited talk at Sabanci University, C. M. Teodorescu, Turkey, April 21, 2021.

 

- Charge accumulation, conduction band filling and ferroicity, C.M. Teodorescu, International Workshop of Materials Physics, 6th Edition, Măgurele, Romania, September 14–16, 2021 (oral presentation).

 

- Interplay between surface charge accumulation, conduction band filling and ferroic ordering, C. M. Teodorescu, 13th International Conference on Physics of Physics of Advanced Materials (ICPAM–13), Sant Feliu de Guixols, September 24–30 (plenary lecture).

 

- Microscopic model for ferroelectricity and its statistical treatment, C. M. Teodorescu IBWAP 2022 – 20th International Balkan Workshop on Applied Physics and Materials Science, Constanța, Romania, July 12–15, 2022 (invited talk).

 

- Photoelectron spectroscopy: relevant information which can be extracted, C. M. Teodorescu, 4th Autumn School on Physics of Advanced Materials (PAMS–4), Sant Feliu de Guixols, September 24–30 (plenary lecture).

 

- X-ray absorption and photoelectron spectroscopies, C. M. Teodorescu, RomCat 2022 - The 13th International Symposium of the Romanian Catalysis Society (Summer School), Băile Govora, Romania, June 22–24, 2022 (plenary lecture).

 

Other deliverables (patents, books etc.).

- C. M. Teodorescu, “Sistem de analiză de timp de zbor în gaz rarefiat, cu determinarea separată a dimensiunilor și sarcinii nanoparticulelor și aerosolilor”, CBI OSIM a2019 00705/04.11.2019. B.O.P.I. Nr. 5/2021, p. H01J (nr. 135011)

 

 

16 August 2022

Rounded Rectangle: RO
Rounded Rectangle: EN