- Email: [email protected]
Thin scintillating films of sesquioxides doped with Eu3+
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 537 (2005) 237–241 www.elsevier.com/locate/nima
Thin scintillating films of sesquioxides doped with Eu3+ C. Dujardina,, C. Le Luyera, C. Martineta, C. Garapona, J. Mugniera, A.G. Murrilloa, C. Pedrinia, T. Martinb a
Laboratoire de Physico-Chimie des Mate´riaux Luminescents, UMR CNRS 5620, Universite´ Claude Bernard Lyon1, 43Bd. du ll Novembre 1918, 10 rue Ampe`re, 69622 Villeurbanne Cedex, France b Europeen Synchrotron Radiation Facility (ESRF), BP 220, F-38043, France Available online 25 August 2004
Abstract We present here the progress on thin scintillating films of Lu2O3 and Gd2O3 doped with Eu3+ ions deposited on various substrates. Pulsed Laser Deposition (PLD) as well as sol–gel processes are used. Properties and performances of the different films are described in this contribution. r 2004 Elsevier B.V. All rights reserved. PACS: 78.66. Nk Keywords: Films; Scintillation; X-ray imaging systems
1. Introduction Scintillators are extensively used in X-ray imaging devices such as classical radiographic systems. In general, they are used in polycrystalline form. One of the most known material is the gadolinium oxysulfide (Gd2O2S) doped with Tb3+ ions (GOS). We focus our attention on special application for which the granularity of polycrystalline powder is not suitable and where thin scintillating films may be an answer to the technical problem. Corresponding author. Tel.: +33-4-72-43-12-08; fax: +33-
4-72-43-11-30. E-mail address: [email protected] (C. Dujardin).
The new generation of synchrotron (European Synchrotron Radiation Facility in France or the Advanced Light Source in USA) is so powerful in terms of number of X-ray photons per cm2 per second, that new time resolved X-ray imaging techniques with submicrometer resolution must be developed [1]. Another field of application is the Beam Position Monitors (BPM). In most of the experiments a large part of the limitation arises from the incident beam instabilities which may be due to source or floor movement or thermal deformation of mirror due to beam refill [2]. For this purpose we developed thin scintillating films (thickness between 0.5 and 2 mm) of Lu2O3 and Gd2O3 doped with Eu3+ ions on various substrates.
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.08.017
ARTICLE IN PRESS 238
C. Dujardin et al. / Nuclear Instruments and Methods in Physics Research A 537 (2005) 237–241
2. Scintillator requirements
3. Sample preparation
2.1. High-resolution X-ray imaging
3.1. Choice of the material
Details of the experimental setup are presented in Ref. [1]. In summary, for micrometer resolution X-ray imaging the main limitation is the scintillator thickness. One to three micrometres thick layers are required. The substrate has to be transparent to visible light and should not scintillate, otherwise it would lead to parasitic image. With such a thickness, the stopping power of the material (Zeff) is also a key parameter. It is even more important when the beam line is operating with high energy X-rays. The light yield of the scintillator has to be as high as possible, in any case yield of 10 000 photons/MeV appears to be the limit to obtain reasonable exposure time. Optical quality needs to be good. For images where pixels are 1 mm2, defects over micrometer range should not appear. Also afterglow should remain in the range of GOS. The useful area is typically 2 2 mm2.
Lu2O3 and Gd2O3 doped with Eu3+ (around 5 at% being the optimum) are known to exhibit good scintillation yield as X-ray phosphors (in the range of 20 000 photons/MeV) and are dense (9.4 g/cm3 and 7.6 g/cm3) with high Zeff which insure a very efficient stopping power [3]. Lempicki et al. [4] has also developed these materials as transparent ceramics [4] and Garcia-Murrillo as thin films [5]. The major emission line is peaking at 611 nm. We then grew several layers of these compounds on various substrates: SiO2, silicon, amorphous carbon.
2.2. Beam Position Monitors In this case, the scintillator has to give information on the incident beam (intensity, position and shape) but with only acceptable deterioration of the beam. The main criterion is that absorption of the beam has to be as weak as possible, which is contradictory with the scintillation process itself. Assuming that 5% of an incident beam operating at 10 keV can be sacrificed for the BPM, it would correspond to a 500 nm thick film of Gd2O3. Since such a film cannot be manipulated, we need to accept another 5% of absorption for the substrate. Light materials are needed. Even 10 mm of Silicon absorbs more than 5% of a 10 keV beam. 100 mm of amorphous carbon or silicon nitride would be adapted. This condition is really critical for lowenergy experiments. With an energy beam of 40 keV, a few microns of Gd2O3 deposited on 200 mm of silicon are also well adapted. The scintillation properties of the film are nearly the same as for high resolution X-ray imaging (mainly high scintillation yield and good optical quality).
3.2. Sol–Gel process The sol–gel method and the dip-coating technique are used to synthesize europium-doped gadolinium oxide films. Gadolinium(III) 2,4-pentanedionate (Gd(CH3COCHCOCH3)3), 99.9% (Alfa Products) is dissolved in ethanol before hydrolysis under controlled atmosphere (argon flux) by mixing the components under reflux. Hydrolysis of the solution is conducted by adding water in the ratio H2O/Gd=7% mol. Europium (III) nitrate pentahydrate (Eu(NO3)3.5H2O) 99.9%, (Aldrich) is added to obtain Eu3+ 5% mol doped precursor solution. The transparency, homogeneity and stability of the precursor solution (stable for at least 6 months) are predominant criteria in order to ensure reproducible coatings of high quality, especially because multiple coatings are necessary to obtain thick films. The solution is filtered through 0.2 mm and deposited on high polished and carefully cleaned silica substrates (Herasils from Heraeus). The solution is dip-coated with a constant withdrawal speed in a glove box to avoid dust contamination. Multicoating (up to 50 coatings) and intermediate heat treatments at 400 1C under O2 flow (in order to remove organic residues) are required to obtain crack free films around 800 nm thick. The layers are finally annealed for 1 h at 1000 1C for high densification and crystallization of the materials.
ARTICLE IN PRESS C. Dujardin et al. / Nuclear Instruments and Methods in Physics Research A 537 (2005) 237–241
3.3. Pulsed laser deposition Films can also be produced by pulsed laser deposition [6], a method able to control the chemical composition and structure of the films and to lead to dense and thick films. The beam of a pulsed KrF excimer laser (l=248 nm) is focused on the rotating target surface with an energy density per pulse of about 3 J/cm2 for a 4 mm2 spot size. Absorption of this high energy and short time light pulse induces a very rapid high temperature increase and vaporization of the material. The species ejected from the surface form a plasma and fly towards the substrate with a high energy compared to the case of thermal evaporation. The deposition may take place in a reactive atmosphere, here 10 4 mbar of oxygen. We used as substrates thin plates of SiO2/Si or vitreous C of about 1 cm2 surface and their temperature is regulated to 750 1C. The target–substrate distance is 4 cm. The targets are obtained by sintering at 1400 1C pellets made of pressed 10% Eu:Lu2O3 powders. Films of some hundreds nm could be obtained with a growth rate of 0.2 A˚/pulse.
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the substrate surface (without any after heat treatment). Scintillation is typical of cubic Lu2O3:Eu3+ (major emission line at 611 nm). The high refractive index value (1.947 at 543.5 nm), close to that of the bulk material, is indicative of very dense films compared to Lu2O3 sol-gel films[5]. When grown on SiO2/Si substrate (Fig. 1, film a) the optical quality looks good while when grown on amorphous carbon (Fig. 1, film b), cracks can be seen by eyes. At the center of the film (a) the thickness is 1.4 mm (measured with m—line spectroscopy). However, one can see some interference fringes that indicate a decrease of the thickness towards the edges of the samples. From classical optical consideration we estimate the range of thickness which changes to 200–300 nm.
4. Results 4.1. Materials properties The films made using sol–gel process are totally crystallized into a polycrystalline cubic structure after a 1000 1C heat-treatment. These results are determined by microRaman and transmission electron microscopy experiments. The refractive index (n=1.887 at 543.5 nm) and the thickness (around 800 nm) of the sol-gel films are determined by m-lines spectroscopy method [7]. The density of the film is estimated from the Lorentz-Lorenz equation [8] and from the value of the bulk and film refractive indices. The Gd2O3:Eu3+ films present a high density of 7.1 g/cm3 after 1000 1C heat treatment, close to that of the bulk material. According to X-ray diffraction all the Lu2O3:Eu3+ layers elaborated using PLD are totally crystallized into cubic phase with a strong orientation of the (111) direction perpendicular to
Fig. 1. layer of Lu2O3:Eu3+ deposited by PLD on (a) SiO2/Si substrate, (b) amorphous carbon substrate.
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Nevertheless, this inhomogeneity could be strongly reduced by moving the substrate during the growth procedure. Deposition on amorphous carbon looks poor in term of optical quality. Nevertheless, the first attempt was successful in terms of deposition as compared to all the previous attempts using the sol–gel process for which adhesion on this substrate was not possible.
4.2.3. BPM tests (Fig. 2b) Different materials were exposed to an X-ray radiation dose in order to examine their potential applications in X-ray beam intensity, position, profile monitors as X-ray to visible light converters. The tests were performed at ID18F in an air environment. At the sample position, a parallel beam was obtained with 30 mm diameter. The Gd2O3 film was placed under 45 1 to X-ray the direction to record its beam position monitoring
4.2. Imaging tests 4.2.1. High-resolution detector The detector is based on a CCD camera and Xray to visible light converter. The converter is imaged using a microscope objective, a photo eyepiece, a 45 1 mirror and a CCD camera. The mirror was used to keep the camera out of the direct beam and optimize the location of the detector. The CCD was Peltier cooled to reduce electronic background. This arrangement gives a fast, low noise detector with a linear response function and a theoretical resolution limit given by the diffraction limit of the visible light. The exposure time for one image on the X-ray generator (W anode, 40 kV, 40 mA) is of the order of 3 min and at an insertion device beam line (with 1012 ph/s/mm2) is of the order of 0.5 s.
4.2.2. High-resolution tests (Fig. 2a) The high-resolution detector used a Gd2O3 film as converter, a microscope objective: NA=0.16, 4 and a photo eyepiece 2 . The CCD camera (Sensicam) was cooled at 12 1C, had a sensitive area of 8.6 6.8 mm2 covered by 1280 1024 pixels, a dynamic range of 12 bit (4096 gray levels per pixel) and a fast read-out of about 125 ms. The Xray source PW1830 Philips generator is equipped with a tungsten anode and two horizontal and vertical slits spaced of 8 cm. Downstream of the last slit are the two tungsten wires (6 mm diameter for the smaller one and 30 mm for the bigger). The distance between the scintillator and the tungsten wires is 1 cm. The detection system was placed at the end of the set-up to record the absorption image of two tungsten wires.
Fig. 2. (a) High-resolution image of edge, tungsten wires of 6 and 30 mm, (b) image of a 14 keV beam with a diameter of 30 mm.
ARTICLE IN PRESS C. Dujardin et al. / Nuclear Instruments and Methods in Physics Research A 537 (2005) 237–241
performances. The high-resolution detector equipped with the Princeton Camera was focused onto the sample. The CCD camera had a large area (28 26 mm2) covered by 1242 1152 pixels and a dynamic range of 16 bit (65536 gray levels per pixel) but a slow read-out of 5 s. The characteristics of components were the following (Microscope objective magnification 10 , numerical aperture=0.3, photo eyepiece 2 , input pixel size=1.12 mm, energy: 14 keV). The tests were performed in an air environment. Most of the beam position monitor measure the position by intercepting parts of the beam with a Be, Cr, etc foil [9] but are insensitive to the shape of the beam. The thin film screen with a CCD camera shows a high potential for the three requirements: intensity, position and shape (see Fig. 2b).
5. Conclusion Gd2O3 and Lu2O3 doped with Eu3+ are well adapted as scintillating materials for high-resolution X-ray imaging. The Sol-Gel process provides
241
very high-optical quality films. Nevertheless, layers thicker than 1 mm are difficult to achieve with these compounds. PLD is well adapted for thicker layer deposition. Optical quality has not been tested yet in imaging conditions. Depositions on amorphous carbon have been successful in terms of adherence, but the first attempts exhibited cracking.
References [1] A. Koch, C. Raven, P. Spanne, A. Snigerev, J. Opt. Soc. Am. A15 (1998) 1940. [2] R.W. Alkire, G. Rosenbaum, G. Evans, J. Synchrotron Rad. 7 (2000) 61. [3] C. Dujardin, et al., Proceedings of the International Conference on Inorganic Scintillators and Their Applications. [4] A. Lempicki, C. Brecher, P. Szupryczynski, H. Lingertat, V. Nagarkar, S.V. Tipnis, S.R. Miller, Nud. Instr. And Meth. A, 488 (3) (2002) 579. [5] A. Garcia-Murrillo, C. Leluyer, C. Dujardin, C. Pedrini, J. Mugnier, J. Sol–Gel Sci. Technol. 26 (1–3) (2003) 957. [6] D.B. Chrisey, G.K. Hubler, Pulsed laser Deposition of Thin Films, Wiley, New York, 1994. [7] R. Ulrich, R. Torge, Appl. Opt. 12 (1973) 2901. [8] P. Fleury, J.P. Mathieu, Lumie`re, Eyrolles, Paris, 1961, p. 212. [9] P. Fajardo, S. Ferrer, Rev. Sci. Instrum. 66 (2) (1995).
Nuclear Instruments and Methods in Physics Research A 537 (2005) 237–241 www.elsevier.com/locate/nima
Thin scintillating films of sesquioxides doped with Eu3+ C. Dujardina,, C. Le Luyera, C. Martineta, C. Garapona, J. Mugniera, A.G. Murrilloa, C. Pedrinia, T. Martinb a
Laboratoire de Physico-Chimie des Mate´riaux Luminescents, UMR CNRS 5620, Universite´ Claude Bernard Lyon1, 43Bd. du ll Novembre 1918, 10 rue Ampe`re, 69622 Villeurbanne Cedex, France b Europeen Synchrotron Radiation Facility (ESRF), BP 220, F-38043, France Available online 25 August 2004
Abstract We present here the progress on thin scintillating films of Lu2O3 and Gd2O3 doped with Eu3+ ions deposited on various substrates. Pulsed Laser Deposition (PLD) as well as sol–gel processes are used. Properties and performances of the different films are described in this contribution. r 2004 Elsevier B.V. All rights reserved. PACS: 78.66. Nk Keywords: Films; Scintillation; X-ray imaging systems
1. Introduction Scintillators are extensively used in X-ray imaging devices such as classical radiographic systems. In general, they are used in polycrystalline form. One of the most known material is the gadolinium oxysulfide (Gd2O2S) doped with Tb3+ ions (GOS). We focus our attention on special application for which the granularity of polycrystalline powder is not suitable and where thin scintillating films may be an answer to the technical problem. Corresponding author. Tel.: +33-4-72-43-12-08; fax: +33-
4-72-43-11-30. E-mail address: [email protected] (C. Dujardin).
The new generation of synchrotron (European Synchrotron Radiation Facility in France or the Advanced Light Source in USA) is so powerful in terms of number of X-ray photons per cm2 per second, that new time resolved X-ray imaging techniques with submicrometer resolution must be developed [1]. Another field of application is the Beam Position Monitors (BPM). In most of the experiments a large part of the limitation arises from the incident beam instabilities which may be due to source or floor movement or thermal deformation of mirror due to beam refill [2]. For this purpose we developed thin scintillating films (thickness between 0.5 and 2 mm) of Lu2O3 and Gd2O3 doped with Eu3+ ions on various substrates.
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.08.017
ARTICLE IN PRESS 238
C. Dujardin et al. / Nuclear Instruments and Methods in Physics Research A 537 (2005) 237–241
2. Scintillator requirements
3. Sample preparation
2.1. High-resolution X-ray imaging
3.1. Choice of the material
Details of the experimental setup are presented in Ref. [1]. In summary, for micrometer resolution X-ray imaging the main limitation is the scintillator thickness. One to three micrometres thick layers are required. The substrate has to be transparent to visible light and should not scintillate, otherwise it would lead to parasitic image. With such a thickness, the stopping power of the material (Zeff) is also a key parameter. It is even more important when the beam line is operating with high energy X-rays. The light yield of the scintillator has to be as high as possible, in any case yield of 10 000 photons/MeV appears to be the limit to obtain reasonable exposure time. Optical quality needs to be good. For images where pixels are 1 mm2, defects over micrometer range should not appear. Also afterglow should remain in the range of GOS. The useful area is typically 2 2 mm2.
Lu2O3 and Gd2O3 doped with Eu3+ (around 5 at% being the optimum) are known to exhibit good scintillation yield as X-ray phosphors (in the range of 20 000 photons/MeV) and are dense (9.4 g/cm3 and 7.6 g/cm3) with high Zeff which insure a very efficient stopping power [3]. Lempicki et al. [4] has also developed these materials as transparent ceramics [4] and Garcia-Murrillo as thin films [5]. The major emission line is peaking at 611 nm. We then grew several layers of these compounds on various substrates: SiO2, silicon, amorphous carbon.
2.2. Beam Position Monitors In this case, the scintillator has to give information on the incident beam (intensity, position and shape) but with only acceptable deterioration of the beam. The main criterion is that absorption of the beam has to be as weak as possible, which is contradictory with the scintillation process itself. Assuming that 5% of an incident beam operating at 10 keV can be sacrificed for the BPM, it would correspond to a 500 nm thick film of Gd2O3. Since such a film cannot be manipulated, we need to accept another 5% of absorption for the substrate. Light materials are needed. Even 10 mm of Silicon absorbs more than 5% of a 10 keV beam. 100 mm of amorphous carbon or silicon nitride would be adapted. This condition is really critical for lowenergy experiments. With an energy beam of 40 keV, a few microns of Gd2O3 deposited on 200 mm of silicon are also well adapted. The scintillation properties of the film are nearly the same as for high resolution X-ray imaging (mainly high scintillation yield and good optical quality).
3.2. Sol–Gel process The sol–gel method and the dip-coating technique are used to synthesize europium-doped gadolinium oxide films. Gadolinium(III) 2,4-pentanedionate (Gd(CH3COCHCOCH3)3), 99.9% (Alfa Products) is dissolved in ethanol before hydrolysis under controlled atmosphere (argon flux) by mixing the components under reflux. Hydrolysis of the solution is conducted by adding water in the ratio H2O/Gd=7% mol. Europium (III) nitrate pentahydrate (Eu(NO3)3.5H2O) 99.9%, (Aldrich) is added to obtain Eu3+ 5% mol doped precursor solution. The transparency, homogeneity and stability of the precursor solution (stable for at least 6 months) are predominant criteria in order to ensure reproducible coatings of high quality, especially because multiple coatings are necessary to obtain thick films. The solution is filtered through 0.2 mm and deposited on high polished and carefully cleaned silica substrates (Herasils from Heraeus). The solution is dip-coated with a constant withdrawal speed in a glove box to avoid dust contamination. Multicoating (up to 50 coatings) and intermediate heat treatments at 400 1C under O2 flow (in order to remove organic residues) are required to obtain crack free films around 800 nm thick. The layers are finally annealed for 1 h at 1000 1C for high densification and crystallization of the materials.
ARTICLE IN PRESS C. Dujardin et al. / Nuclear Instruments and Methods in Physics Research A 537 (2005) 237–241
3.3. Pulsed laser deposition Films can also be produced by pulsed laser deposition [6], a method able to control the chemical composition and structure of the films and to lead to dense and thick films. The beam of a pulsed KrF excimer laser (l=248 nm) is focused on the rotating target surface with an energy density per pulse of about 3 J/cm2 for a 4 mm2 spot size. Absorption of this high energy and short time light pulse induces a very rapid high temperature increase and vaporization of the material. The species ejected from the surface form a plasma and fly towards the substrate with a high energy compared to the case of thermal evaporation. The deposition may take place in a reactive atmosphere, here 10 4 mbar of oxygen. We used as substrates thin plates of SiO2/Si or vitreous C of about 1 cm2 surface and their temperature is regulated to 750 1C. The target–substrate distance is 4 cm. The targets are obtained by sintering at 1400 1C pellets made of pressed 10% Eu:Lu2O3 powders. Films of some hundreds nm could be obtained with a growth rate of 0.2 A˚/pulse.
239
the substrate surface (without any after heat treatment). Scintillation is typical of cubic Lu2O3:Eu3+ (major emission line at 611 nm). The high refractive index value (1.947 at 543.5 nm), close to that of the bulk material, is indicative of very dense films compared to Lu2O3 sol-gel films[5]. When grown on SiO2/Si substrate (Fig. 1, film a) the optical quality looks good while when grown on amorphous carbon (Fig. 1, film b), cracks can be seen by eyes. At the center of the film (a) the thickness is 1.4 mm (measured with m—line spectroscopy). However, one can see some interference fringes that indicate a decrease of the thickness towards the edges of the samples. From classical optical consideration we estimate the range of thickness which changes to 200–300 nm.
4. Results 4.1. Materials properties The films made using sol–gel process are totally crystallized into a polycrystalline cubic structure after a 1000 1C heat-treatment. These results are determined by microRaman and transmission electron microscopy experiments. The refractive index (n=1.887 at 543.5 nm) and the thickness (around 800 nm) of the sol-gel films are determined by m-lines spectroscopy method [7]. The density of the film is estimated from the Lorentz-Lorenz equation [8] and from the value of the bulk and film refractive indices. The Gd2O3:Eu3+ films present a high density of 7.1 g/cm3 after 1000 1C heat treatment, close to that of the bulk material. According to X-ray diffraction all the Lu2O3:Eu3+ layers elaborated using PLD are totally crystallized into cubic phase with a strong orientation of the (111) direction perpendicular to
Fig. 1. layer of Lu2O3:Eu3+ deposited by PLD on (a) SiO2/Si substrate, (b) amorphous carbon substrate.
ARTICLE IN PRESS 240
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Nevertheless, this inhomogeneity could be strongly reduced by moving the substrate during the growth procedure. Deposition on amorphous carbon looks poor in term of optical quality. Nevertheless, the first attempt was successful in terms of deposition as compared to all the previous attempts using the sol–gel process for which adhesion on this substrate was not possible.
4.2.3. BPM tests (Fig. 2b) Different materials were exposed to an X-ray radiation dose in order to examine their potential applications in X-ray beam intensity, position, profile monitors as X-ray to visible light converters. The tests were performed at ID18F in an air environment. At the sample position, a parallel beam was obtained with 30 mm diameter. The Gd2O3 film was placed under 45 1 to X-ray the direction to record its beam position monitoring
4.2. Imaging tests 4.2.1. High-resolution detector The detector is based on a CCD camera and Xray to visible light converter. The converter is imaged using a microscope objective, a photo eyepiece, a 45 1 mirror and a CCD camera. The mirror was used to keep the camera out of the direct beam and optimize the location of the detector. The CCD was Peltier cooled to reduce electronic background. This arrangement gives a fast, low noise detector with a linear response function and a theoretical resolution limit given by the diffraction limit of the visible light. The exposure time for one image on the X-ray generator (W anode, 40 kV, 40 mA) is of the order of 3 min and at an insertion device beam line (with 1012 ph/s/mm2) is of the order of 0.5 s.
4.2.2. High-resolution tests (Fig. 2a) The high-resolution detector used a Gd2O3 film as converter, a microscope objective: NA=0.16, 4 and a photo eyepiece 2 . The CCD camera (Sensicam) was cooled at 12 1C, had a sensitive area of 8.6 6.8 mm2 covered by 1280 1024 pixels, a dynamic range of 12 bit (4096 gray levels per pixel) and a fast read-out of about 125 ms. The Xray source PW1830 Philips generator is equipped with a tungsten anode and two horizontal and vertical slits spaced of 8 cm. Downstream of the last slit are the two tungsten wires (6 mm diameter for the smaller one and 30 mm for the bigger). The distance between the scintillator and the tungsten wires is 1 cm. The detection system was placed at the end of the set-up to record the absorption image of two tungsten wires.
Fig. 2. (a) High-resolution image of edge, tungsten wires of 6 and 30 mm, (b) image of a 14 keV beam with a diameter of 30 mm.
ARTICLE IN PRESS C. Dujardin et al. / Nuclear Instruments and Methods in Physics Research A 537 (2005) 237–241
performances. The high-resolution detector equipped with the Princeton Camera was focused onto the sample. The CCD camera had a large area (28 26 mm2) covered by 1242 1152 pixels and a dynamic range of 16 bit (65536 gray levels per pixel) but a slow read-out of 5 s. The characteristics of components were the following (Microscope objective magnification 10 , numerical aperture=0.3, photo eyepiece 2 , input pixel size=1.12 mm, energy: 14 keV). The tests were performed in an air environment. Most of the beam position monitor measure the position by intercepting parts of the beam with a Be, Cr, etc foil [9] but are insensitive to the shape of the beam. The thin film screen with a CCD camera shows a high potential for the three requirements: intensity, position and shape (see Fig. 2b).
5. Conclusion Gd2O3 and Lu2O3 doped with Eu3+ are well adapted as scintillating materials for high-resolution X-ray imaging. The Sol-Gel process provides
241
very high-optical quality films. Nevertheless, layers thicker than 1 mm are difficult to achieve with these compounds. PLD is well adapted for thicker layer deposition. Optical quality has not been tested yet in imaging conditions. Depositions on amorphous carbon have been successful in terms of adherence, but the first attempts exhibited cracking.
References [1] A. Koch, C. Raven, P. Spanne, A. Snigerev, J. Opt. Soc. Am. A15 (1998) 1940. [2] R.W. Alkire, G. Rosenbaum, G. Evans, J. Synchrotron Rad. 7 (2000) 61. [3] C. Dujardin, et al., Proceedings of the International Conference on Inorganic Scintillators and Their Applications. [4] A. Lempicki, C. Brecher, P. Szupryczynski, H. Lingertat, V. Nagarkar, S.V. Tipnis, S.R. Miller, Nud. Instr. And Meth. A, 488 (3) (2002) 579. [5] A. Garcia-Murrillo, C. Leluyer, C. Dujardin, C. Pedrini, J. Mugnier, J. Sol–Gel Sci. Technol. 26 (1–3) (2003) 957. [6] D.B. Chrisey, G.K. Hubler, Pulsed laser Deposition of Thin Films, Wiley, New York, 1994. [7] R. Ulrich, R. Torge, Appl. Opt. 12 (1973) 2901. [8] P. Fleury, J.P. Mathieu, Lumie`re, Eyrolles, Paris, 1961, p. 212. [9] P. Fajardo, S. Ferrer, Rev. Sci. Instrum. 66 (2) (1995).