Materials Characterization 50 (2003) 109 – 116
Atomic force microscopy—a visual probe to characterize nanodosimetric devices C.G. Gameiro a,b, S. Alves Jr. a,b, E.F. da Silva Jr. b,c, C.A. Achete b,d, R.A. Sima˜o b,d, P.A. Santa-Cruz a,b,* a
Departamento de Quı´mica Fundamental, Universidade Federal de Pernambuco, Cidade Universita´ria, Recife, PE 50740-540, Brazil b RENAMI-Brazilian Molecular and Interfaces Nanotechnology Research Network, Brazil c Departamento de Fı´sica, Universidade Federal de Pernambuco, Cidade Universita´ria, Recife, PE 50670-901, Brazil d Programa de Engenharia Metalu´rgica e de Materiais, COPPE/UFRJ, Rio de Janeiro, RJ, Brazil Received 15 January 2003; accepted 30 March 2003
Abstract We have developed an ultraviolet dosimeter based on lanthanide h-diketonate complexes nanofilms. The UV photodegradation of the nanofilm photonic properties allows it to act as a dosimeter. To develop a better understanding of this UV photodegradation process, we have performed atomic force microscopy (AFM) and in situ mass spectrometry (under ultraviolet exposure) studies of the nanofilms. The results indicate that the UV photodegradation phenomenon does not lead to any microstructural or morphological changes of the samples. Therefore, we reason that the degradation process should be related to changes in the energy transfer between ligands and the central ion of the complexes or else to the creation of nonradiative pathways corroborating for a luminescence quenching related to the UV exposure dose. D 2003 Elsevier Inc. All rights reserved. Keywords: Atomic force microscopy; Nanodosimetric devices; Lanthanide h-diketonate complexes nanofilms; UV photodegradation
1. Introduction In the past 20 years, extensive work has been done on the development of several photonic materials and devices in a variety of areas such optoelectronic infrared quantum counters (IRQC), UV molecular nanodosimeters [1– 7] and new active materials for nanodevices [8 –12]. Some precursors of those materials, like oxyfluoride glasses with silver nanopar-
* Corresponding author. RENAMI-Brazilian Molecular and Interfaces Nanotechnology Research Network, Brazil. E-mail address:
[email protected] (P.A. Santa-Cruz). 1044-5803/$ - see front matter D 2003 Elsevier Inc. All rights reserved. doi:10.1016/S1044-5803(03)00076-7
ticles, were developed by our group more than 15 years ago [11,12]. Recently, we have been working to develop nanofilms of lanthanide h-diketonate complexes, about 10 to 60 nm in thickness, for dosimetric applications. These compounds are highly luminescent under ultraviolet (UV) excitation, and are well known because of their potential application as LCMDs (light conversion molecular devices). With an aim of transforming science into a technological application, we have designed and developed a device that measures cumulatively the amount of UV an individual receives—a personal UV dosimeter. The importance of this issue has generated a
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worldwide campaign, led by World Health Organization (WHO), and a large investment has been made in this area to prevent UV-induced diseases. Although the importance of UV radiation for vitamin D production and the treatment of several diseases, including rickets, psoriasis, eczema and jaundice, is recognized, this takes place under medical supervision and the benefits of treatment tend to outweigh the risks of UV radiation exposure. The UV radiation overexposure is mainly related to several diseases, inducing skin cancer. The minimal erithemal dose (MED) is advised by the WHO for each UV region. For example, 365 nm is equivalent to 28 mJ/ cm2, and is the amount of UV an individual of sensitive skin (type 1) can receive daily. The device we have developed is a UV molecular nanodosimeter [5] based on lanthanide h-diketonate complexes nanofilm, whose luminescence decreased under UV exposure, i.e., the compound photodegrades. This luminescence-quenching is detected and quantified, in J/cm2, by an integration sphere coupled to a radiometer for research purposes, or by an optoelectronic device reader calibrated by the integration sphere system for current application of personal dosimetry. By quantifying this variable, one may avoid skin cancer and the other diseases related to UV overexposure. Several studies have also demonstrated that exposure to environmental levels of UV changes the activity and distribution of some of the cells responsible for triggering immune responses in humans. Another relevant topic for further study is the mechanism involved in the compound photodegradation. To continue our research [5 –7], atomic force microscopy (AFM), as well as mass spectrometry, have been employed to evaluate any relationship between photodegradation and microstructural and morphological characteristics of the lanthanide hdiketonate complex nanofilms.
low pressure (
