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Thin Films & Nanomaterials:

 

Thin films and electrical properties at the nanoscale:

Studies that underlie the understanding of the physical properties of matter at nanometer scales bear fundamental significance in the context of permanently increasing miniaturization of electronic devices. With this respect, the atomic force microscopy (AFM) proves to be a prime tool in the characterization of such nano-materials. In this context, the investigations led within our team are devoted to the characterization of piezo-/ferroelectric properties of oxide thin films along with their integration into nano-devices (ferroelectric memories, micro/nano-electromechanical systems... ). The piezo-response mode (PFM) of the AFM, both in imaging and spectroscopic modes (piezoloops), is specifically developed and used to study the electromechanical activity (evaluation of the piezoelectric coefficient), the architecture of ferroelectric domains (Fig. 1a-b), the behavior of domain switching (coercive voltage; Fig 1c -d) , the electrical fatigue ( Fig. 1e; [P1]) and the effect of imprint (self-polarization, pinning, [P2])in piezo-/ferroelectric oxides thin films such as PbZr_xTi_1-xO₃ (PZT), Pb_1-3y/2La_yZr_xTi_1-xO₃ (PLZT), Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT), ) and, more recently, Ln₂Ti₂O₇ (Ln = Lanthanide),as well as in films multiferroic BiFeO₃ (BFO) or (BiFeO₃)_m/(SrTiO₃)_n superlattices [P3].

 

Fig. 1 : (a) Out-of-plane and (b) in-plane ferroelectric domains in Ln2Ti2O7. Ln2Ti2O7 thin film. (c) Evidence of local manipulation of ferroelectric domains using the AFM tip. (d) In-phase piezoloop measured on a Ln2Ti2O7. thin film. (e) Evidence of the electrical fatigue endurance on the local piezoelectric properties in PMN-PT thin films obtained with piezoloops-measurements.

 

In addition, special attention is given to the following issues: i)the influence of the nature of the substrate and/or the bottom electrode, ii)the deposition conditions, iii)the thickness of the deposited film [P2], iv)the preferred crystallographic orientation [P4] and v)the special treatment applied to the film (etching, [P5]) ]). Furthermore, nanostructured thin films obtained with Ga+focused ion-beams (FIB) are considered in order to evaluate both the influence of etching and other potential size effects that are initiated following material-removal on the physical properties of fabricated piezo-/ferroelectric nano-objects (nano-islands) (Fig. 2; [P6, P7]).

 

Fig. 2 : Piezoelectric-activity evaluation on the nano-islands surface.

 

Parts of these works are carried-out in collaboration with external laboratories (CRISMAT Laboratory in Caen, IEMN in Lille1 ...).

On the experimental side, several works have been simultaneously carried-out with modeling studies that directly relate the ab-initio study of the structural, electronic, and ferroelectric properties of thin films, using quantum-chemistry methods.

It is worth-mentioning that during the last few years, our team has led the majority of its work on the study of new environmentally acceptable films, on the basis of an internal collaboration with the "innovative and oxides derived phases" team of the UCCS and mainly relates to the development of new phases in bulk and their development in thin films.

 

Publications :

• P1. Characterizing nanoscale electromechanical fatigue in Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ thin films by piezoresponse force microscopy.
  A. Gatoux, A. Ferri, M. Detalle, D. Rémiens, R. Desfeux
  Thin Solid Films 520, 591–594 (2011) - doi : 10.1016/j.tsf.2011.07.032
  
  
• P2. Thickness dependence of the nanoscale piezoelectric properties measured by piezoresponse force microscopy on (111)-oriented PLZT 10/40/60 thin films
  A. Ferri, S. Saitzek, A. Da Costa, R. Desfeux, G. Leclerc, R. Bouregba, G. Poullain
  Surface Science 602, 1987-1992 (2008)
  
  
• P3. Constrained ferroelectric domain orientation in (BiFeO₃)_m(SrTiO₃)_n superlattice.
  R. Ranjith, R.V.K. Mangalam, Ph. Boullay, A. David, M.B. Lepetit, U. Lüders, W. Prellier, A. Da Costa, A. Ferri, R. Desfeux, Gy. Vincze, Zs. Radi, C. Aruta
  Applied Physics letters 96, 022902 (2010) - doi : 10.1063/1.3275726
  
  
• P4. Correlation between local hysteresis and crystallite orientation in PZT thin films deposited on Si and MgO substrates.
  R. Desfeux, C. Legrand, A. Da Costa, D. Chateigner, R. Bouregba, G. Poullain
  Surface Science 600 (1) (2006) 219-228
  
  
• P5. Piezoelectric evaluation of ion beam etched Pb(Zr,Ti)O₃ thin films by piezoresponse force microscopy.
  C. Legrand, A. Da Costa, R. Desfeux, C. Soyer, D. Rémiens
  Applied Surface Science, 253 (2007) 4942-4946
  
  
• P6. Ion-Beam Etching on Nanostructured La₂Ti₂O₇ Piezoelectric Thin Films.
  A. Ferri, S. Saitzek, Z. Shao, G. Declercq, J. Costecalde, D. Rémiens, D. Deresmes, D. Troadec, R. Desfeux
  J. Am. Ceram. Soc., (2013), to be published - doi: 10.1111/jace.12626
  
  
• P7. Enhancement in nanoscale electrical properties of lead zirconic titanate island fabricated by focused ion beam.
  R.H. Liang, D. Rémiens, D. Deresmes, D. Troadec, X.L. Dong, L.H.Yang, R. Desfeux, A. Da Costa, J.-F. Blach
  Journal of Applied Physics, 105, 044101 (2009) - doi : 10.1063/1.3073892
  
  

 

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