Europhys. Lett.
Volume 48, Number 4, November 1999
Page(s) 461 - 467
Section Interdisciplinary physics and related areas of science and technology
Published online 01 September 2002
DOI: 10.1209/epl/i1999-00505-4

Europhys. Lett, 48 (4), pp. 461-467 (1999)

Polymorphic transformations observed on molecular organic thin films: p-nitrophenyl nitronyl nitroxide radical

J. Fraxedas 1, J. Caro 1, J. Santiso 1, A. Figueras 1
P. Gorostiza 2 and F. Sanz 2

1 Institut de Ciència de Materials de Barcelona (CSIC)
Campus de la UAB, E-08193 Bellaterra, Spain
2 Departament de Química-Física, Universitat de Barcelona
Martí i Franqués 1, E-08028 Barcelona, Spain

(received 10 March 1999; accepted in final form 16 September 1999)

PACS. 81.30Hd - Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder.
PACS. 68.55${\rm -a}$ - Thin film structure and morphology.


We report on the experimental observation of the polymorphic transformation from the monoclinic $\alpha$- to the orthorhombic $\beta$-phase of thin films of the molecular organic radical p-nitrophenyl nitronyl nitroxide (p-NPNN). This solid-solid phase transition to the thermodynamically most stable $\beta$-phase encompasses clearly differentiated changes in structure and morphology and may be inhibited if the thickness of the films of the initial $\alpha$-phase lies below a certain critical value. In our case, the $\alpha$-phase of p-NPNN ($\alpha$-p-NPNN) has been stabilized as thin film obtained by thermal evaporation in high vacuum (thickness $\rm\le 1\;\mu m$).


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