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Plasma plume photography and spectroscopy of Fe—Oxide materials
Applied Surface Science 255 (2009) 5215–5219
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Plasma plume photography and spectroscopy of Fe—Oxide materials R. Viskup a,b,*, B. Praher a,b, T. Stehrer a,b, J. Jasik a,b, H. Wolfmeir c, E. Arenholz c, J.D. Pedarnig a,b,*, J. Heitz a,b a
Christian Doppler Laboratory for Laser - Assisted Diagnostics, Johannes Kepler University Linz, A-4040 Linz, Austria Institute of Applied Physics, Johannes Kepler University Linz, A-4040 Linz, Austria c voestalpine Stahl GmbH, A-4031 Linz, Austria b
A R T I C L E I N F O
A B S T R A C T
Article history:
Time-resolved photography was employed to study plasma dynamics and particle ejection of laserirradiated iron oxide materials. Nano-particle powder, pressed powder pellets and sintered ceramics were ablated in air and Ar gas background by means of short laser pulses (Nd:YAG laser wavelength l = 1064 nm and pulse duration tL 6 ns; KrF laser l = 248 nm and tL 20 ns). Plasma plume dynamics significantly depended on sample morphology. The ejection of non-luminous particles up to several hundreds of microseconds after the laser pulse was observed for powder and pressed powder target materials. Laser-induced breakdown spectroscopy (LIBS) was employed for element analysis of iron oxide powders, pressed pellets and sintered ceramics. LIBS spectra of the different targets were comparable to each other and qualitatively independent of target morphology. ß 2008 Elsevier B.V. All rights reserved.
Available online 4 September 2008 Keywords: Pulsed-laser ablation Laser-induced breakdown spectroscopy Plasma plume photography Particle ejection Nano-powder Iron oxide
1. Introduction Pulsed-laser ablation (PLA) is a versatile technique for fundamental investigations and technical applications. In PLA, the interaction of short and intense laser pulses with a target leads to the removal of material from the target surface and the formation of a plasma plume [1]. This technique is employed in various processes such as the patterning of materials, the deposition of thin films, the synthesis of nano-particles and the element analysis of multi-component materials. The targets employed for ablation are, usually, solid and liquid phase bulk materials. Powder materials are only rarely used as ablation targets [2–6]. The application of PLA to powders, however, is interesting and of potential technical relevance. Iron oxides are technologically relevant materials due to superior character in non-toxicity, durability, chemical stability and low costs. They have received much attention owing to their potential applications in high density recording media, highfrequency applications, broadband transmissions, deflection yokes in television sets, transformer cores, filter technologies,
* Corresponding author at: Christian Doppler Laboratory for Laser - Assisted Diagnostics, Johannes Kepler University Linz, A-4040 Linz, Austria. Tel.: +43 732 2468 9257; fax: +43 732 2468 9242. E-mail addresses: [email protected] (R. Viskup), [email protected] (J.D. Pedarnig). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.08.092
anti-jamming of line-bound noise voltage, permanent magnets in loud speakers, electrical engines, magnets for servo motors and sensors, catalysts, gas sensors, pigments as well as in geochemistry and mineralogical processes. Iron oxides are available in different modifications including fine-grained powder, pressed or sintered materials. Here we report on laser ablation, plume photography and optical plasma emission spectroscopy of nano-powder, pressed powder pellets and sintered ceramics of iron oxide. The temporal evolution of plasma plume, the ejection of non-luminous particles and the detection of impurities are presented for the different materials. Experimental parameters such as laser wavelengths and gas background have been varied in connection with potential industrial applications such as laser-assisted materials analysis. 2. Experimental The experimental set-up is shown schematically in Fig. 1. The pulsed radiation of a Nd:YAG solid state laser (wavelength l = 1064 nm, pulse duration tL 6 ns) or of a KrF excimer laser (l = 248 nm, tL 20 ns) was focused into a sample chamber irradiating the surface of the target material. The focal length of the lens was 12 cm (Nd:YAG laser) and 30 cm (KrF laser). The target surface was positioned approximately 5 mm closer to the lens than the focal plane. For the Nd:YAG laser the measured spot diameter was d = 1.0 mm (spot area A = 0.79 mm2) and for the UV–KrF excimer laser the spot diameter was d = 0.96 mm (A = 0.73 mm2).
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R. Viskup et al. / Applied Surface Science 255 (2009) 5215–5219
radiation is dominating). Time-resolved plasma plume photography was performed in air by using a fast intensified camera (ICCD S300:7895 Photometrics) and imaging optics (50 mm objective lens). For time-resolved photography of ejected nonluminous particles a flash lamp was used and synchronized to the laser pulse and the camera. The iron oxide powder investigated (Fe2O3) consisted of nano-particles that were spherical in shape and had mean diameter 104 65 nm as determined from electron microscopy and optical particle size measurement (Coulter LS 230). Pellets were produced by mechanical pressing the powder into disc shaped pieces 13 mm in diameter. Sintering of pellets (1000 8C, 12 h, air) transformed the material to Fe3O4 and produced compact ceramics. Laser ablation of iron oxide pressed pellets has been reported before [7,8]. 3. Results and discussion
Fig. 1. Schematic of experimental set-up for laser ablation, plasma spectroscopy and time-resolved photography of iron oxide powder, pressed powder pellets and sintered ceramics.
The pulse energy employed was EL 100 mJ for the Nd:YAG laser and EL 50 mJ for the KrF laser. The optical plasma emission was collected by using pierced mirrors, lenses and a quartz fiber that was coupled to an Echelle spectrometer with intensified CCD camera. Plasma spectra were recorded in the wavelength range 200–850 nm with a spectral resolution l/Dl 10,000 employing a delay time of DtD = 1 ms to the laser pulse and a gate width of DtG = 5 ms. In optical plasma emission spectroscopy, delay times of few microseconds are typically employed to measure narrow emission lines with intensities that are larger than the broad background radiation (at very short delay times the background
In Fig. 2 photographs of the iron oxide powder, pressed pellets and sintered ceramics, and of the laser-induced plasma for the different materials are shown. Plume photography was performed in air under multi-pulse irradiation (Nd:YAG laser, pulse repetition rate 20 Hz) with integration time of the camera of 0.5–1 s. The powder particles formed loose agglomerates and for ablation studies the powder was contained in a glass cylinder (a). Laser ablation of powder lead to the ejection of particles into ambient atmosphere. Particles ejected into the direction of the laser beam interacted with subsequent laser pulses resulting in a channel-like structure showing plasma radiation from the powder target and from some of the particles. The pulsed-laser-induced ejection of particles was observed also with pressed pellets (b) and was almost negligible with sintered ceramics (c). Time-resolved photographs of the Nd:YAG laser-induced plasma plume are shown in Fig. 3 for iron oxide powder, pellet and ceramic materials. The photos were taken in air at delay times of 2.2 ms (left column) and 3.2 ms (right column) after the impact of single laser pulses and with camera integration time
Fig. 2. Photographs of iron oxide materials and of nanosecond laser ablation (l = 1064 nm) of such materials in air. Ablation of powder leads to ejection of many particles that may be decomposed by subsequent laser pulses (a). Ablation from pressed powder pellets (b) and from sintered ceramics (c).
R. Viskup et al. / Applied Surface Science 255 (2009) 5215–5219
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Fig. 3. Time-resolved photographs of plasma plume expansion into air at different delay times after laser ablation (l = 1064 nm) of iron oxide powder (a), pressed pellets (b) and sintered ceramics (c).
Fig. 4. Intensity profile of plasma emission of pressed powder pellets after laser ablation (l = 1064 nm, EL = 100 mJ) in air (a). The dashed line indicates the position of line cut through intensity maps (inset). Comparison of the temporal evolution of plume length for pressed iron oxide pellets with model curve (b). Solid and open symbols are obtained assuming an initial plume energy of E = EL and E = EL/3, respectively.
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of 20 ns. The length of the visible plume was comparable for all materials investigated. For the powder target the plume appeared relatively homogeneous with approximately hemispherical shape which did not increase in size significantly during this time period (a). For the pressed pellet the plume appeared less homogeneous and non-hemispherical in shape (b) and for the ceramic target an irregularly structured plume was observed (c). Fig. 4a shows the variation of plasma emission intensity perpendicular to the target surface measured at different delay times. The intensity profiles were taken in the plume centre and the intensities were normalized to the highest intensity measured for each delay time. The profiles showed a maximum intensity Imax followed by a strong intensity gradient which marked the front of the bright plume. The position for maximum intensity and the plume front shifted to larger distances at longer delay times. An effective plume length R was derived from plume images taken at different time t employing an intensity criterion I = 0.5Imax. The variation of plume length with time is shown in Fig. 4b in normalized coordinates, with E the initial plume energy, pg (96,900 Pa) the gas background pressure, and vg0 (343 m/s) the
sound velocity in air [9]. The solid symbols were calculated from the measured plume length assuming an initial plume energy that was equal to the laser pulse energy (E = EL = 100 mJ). The open symbols were calculated for a lower plume energy (E = EL/3) assuming that processes such as melting, vaporization and ejection of material consumed a large part of the laser pulse energy. The solid line is calculated by a model describing spherical plume expansion into ambient gas [9]. For solid bulk materials such as stainless steel, metal oxides and polymers a good agreement was found between the plume length measured at low background pressure and the model [9,10]. At higher pressure additional effects such as hydrodynamic instabilities at the expansion front become relevant [11]. The ejection of non-luminous particles several hundreds of microseconds after plasma termination is shown in Fig. 5 (camera integration time 10 ns). Similar effects were observed also with other materials [10,12]. A relatively large amount of particles was ejected from iron oxide powder targets (Fig. 5a). The velocity of the particle front in air was estimated to v 18 m=s comparing photos taken at 100 and 400 ms delay time. Clustered particles were ejected perpendicular to the surface of pressed pellet targets
Fig. 5. Time-resolved photographs of particle ejection from iron oxide powder (a) and pressed powder pellets (b) at different delay times after laser ablation (l = 1064 nm, air).
R. Viskup et al. / Applied Surface Science 255 (2009) 5215–5219
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Fig. 6. LIBS spectra of iron oxide powder, pressed pellets and sintered ceramics. Spectra were obtained by nanosecond laser ablation in flushed Ar background (l = 1064 nm (a)) and in air (l = 248 nm (b)).
(Fig. 5b). The clusters had diameter of 0.1–0.4 mm and an ejection velocity of approximately 7 m/s was estimated comparing photos taken at 400 and 700 ms. For sintered ceramics no particle ejection was observed. Laser-induced breakdown spectroscopy (LIBS) of iron oxide powder, pressed pellets and sintered ceramics is shown in Fig. 6. LIBS spectra obtained by Nd:YAG laser ablation in flushed Ar gas background (employed for particle removal from beam path) showed intense emission lines of atomic iron at 288.08 and 288.37 nm for all target materials (Fig. 6a). The very faint signal at 288.16 nm was due to Si impurity of 113 ppm concentration. LIBS spectra obtained by KrF laser ablation in air were more intense and showed Si signals of different strength depending on the impurity concentration (Fig. 6b). The variation of LIBS intensities was probably related to the different gas background and the different laser wavelengths employed [13]. 4. Conclusion The influence of target morphology on the dynamics of laserinduced plasma plumes, the ejection of particles and the optical plasma emission was studied by time-resolved photography and plasma spectroscopy. Plasma plumes of nanosecond laser ablated iron oxide nano-powder were more homogeneous than plumes obtained with pressed powder pellets and sintered ceramics. Particles and particle clusters were ejected from iron oxide powder and pellets. Laser-induced breakdown spectroscopy revealed similar results for all iron oxide materials independent on target morphology. Intense LIBS signals of Si impurity
depending on the Si concentration were detected for UV laser ablation in air.
Acknowledgements This work has been supported by the Christian Doppler Research Association (Austria). We would like to thank Prof. G. Gritzner for particle size measurement of the powder and Prof. D. Ba¨uerle for discussions.
References [1] D. Ba¨uerle, Laser Processing and Chemistry, 3rd ed., Springer, Berlin, 2000. [2] B. Lal, L. St-Onge, F.Y. Yueh, J.P. Singh, in: J.P. Singh, S.N. Narayan (Eds.), Laser Induced Breakdown Spectroscopy, Elsevier, Amsterdam, 2007, p. 287. [3] F.C. De-Lucia, R.S. Harmon, K.L. McNesby, R.J. Winkel, A.W. Miziolek, Appl. Opt. 42 (2003) 6148. [4] T. Ctvrtnickova, L.M. Cabalin, J. Laserna, V. Kanicky, Spectrochim. Acta B 63 (2008) 42. [5] J. Gu¨nster, R. Go¨rke, J.G. Heinrich, R. Souda, Appl. Surf. Sci. 173 (2001) 76. [6] J. Chen, C. Yue, Z. Yu, W. Xubao, Z. Tiechuan, SPIE Proc. 5641 (2004) 205. [7] R.B. Metz, C. Nicolas, M. Ahmed, S.R. Leone, J. Chem. Phys. 123 (2005) 114313. [8] R. Teghil, L. D’Alessio, V. Marotta, A. Santagata, G. De Maria, D. Ferro, M.A. Sansone, Appl. Surf. Sci. 119 (1997) 34. [9] N. Arnold, J. Gruber, J. Heitz, Appl. Phys. A 69 (1999) S87. [10] N. Huber, J. Gruber, N. Arnold, J. Heitz, D. Ba¨uerle, Europhys. Lett. 51 (2000) 674. [11] J. Heitz, J. Gruber, N. Arnol, D. Ba¨uerle, N. Ramaseder, W. Meyer, J. Hocho¨rtler, SPIE Proc. 5120 (2003) 588. [12] J. Koch, M. Wa¨lle, S. Schlamp, T. Ro¨sgen, D. Gu¨nther, Spectrochim. Acta B 63 (2008) 37. [13] A.W. Miziolek, V. Palleschi, I. Schechter (Eds.), Laser-Induced Breakdown Spectroscopy, Cambridge University Press, Cambridge, 2006.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Plasma plume photography and spectroscopy of Fe—Oxide materials R. Viskup a,b,*, B. Praher a,b, T. Stehrer a,b, J. Jasik a,b, H. Wolfmeir c, E. Arenholz c, J.D. Pedarnig a,b,*, J. Heitz a,b a
Christian Doppler Laboratory for Laser - Assisted Diagnostics, Johannes Kepler University Linz, A-4040 Linz, Austria Institute of Applied Physics, Johannes Kepler University Linz, A-4040 Linz, Austria c voestalpine Stahl GmbH, A-4031 Linz, Austria b
A R T I C L E I N F O
A B S T R A C T
Article history:
Time-resolved photography was employed to study plasma dynamics and particle ejection of laserirradiated iron oxide materials. Nano-particle powder, pressed powder pellets and sintered ceramics were ablated in air and Ar gas background by means of short laser pulses (Nd:YAG laser wavelength l = 1064 nm and pulse duration tL 6 ns; KrF laser l = 248 nm and tL 20 ns). Plasma plume dynamics significantly depended on sample morphology. The ejection of non-luminous particles up to several hundreds of microseconds after the laser pulse was observed for powder and pressed powder target materials. Laser-induced breakdown spectroscopy (LIBS) was employed for element analysis of iron oxide powders, pressed pellets and sintered ceramics. LIBS spectra of the different targets were comparable to each other and qualitatively independent of target morphology. ß 2008 Elsevier B.V. All rights reserved.
Available online 4 September 2008 Keywords: Pulsed-laser ablation Laser-induced breakdown spectroscopy Plasma plume photography Particle ejection Nano-powder Iron oxide
1. Introduction Pulsed-laser ablation (PLA) is a versatile technique for fundamental investigations and technical applications. In PLA, the interaction of short and intense laser pulses with a target leads to the removal of material from the target surface and the formation of a plasma plume [1]. This technique is employed in various processes such as the patterning of materials, the deposition of thin films, the synthesis of nano-particles and the element analysis of multi-component materials. The targets employed for ablation are, usually, solid and liquid phase bulk materials. Powder materials are only rarely used as ablation targets [2–6]. The application of PLA to powders, however, is interesting and of potential technical relevance. Iron oxides are technologically relevant materials due to superior character in non-toxicity, durability, chemical stability and low costs. They have received much attention owing to their potential applications in high density recording media, highfrequency applications, broadband transmissions, deflection yokes in television sets, transformer cores, filter technologies,
* Corresponding author at: Christian Doppler Laboratory for Laser - Assisted Diagnostics, Johannes Kepler University Linz, A-4040 Linz, Austria. Tel.: +43 732 2468 9257; fax: +43 732 2468 9242. E-mail addresses: [email protected] (R. Viskup), [email protected] (J.D. Pedarnig). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.08.092
anti-jamming of line-bound noise voltage, permanent magnets in loud speakers, electrical engines, magnets for servo motors and sensors, catalysts, gas sensors, pigments as well as in geochemistry and mineralogical processes. Iron oxides are available in different modifications including fine-grained powder, pressed or sintered materials. Here we report on laser ablation, plume photography and optical plasma emission spectroscopy of nano-powder, pressed powder pellets and sintered ceramics of iron oxide. The temporal evolution of plasma plume, the ejection of non-luminous particles and the detection of impurities are presented for the different materials. Experimental parameters such as laser wavelengths and gas background have been varied in connection with potential industrial applications such as laser-assisted materials analysis. 2. Experimental The experimental set-up is shown schematically in Fig. 1. The pulsed radiation of a Nd:YAG solid state laser (wavelength l = 1064 nm, pulse duration tL 6 ns) or of a KrF excimer laser (l = 248 nm, tL 20 ns) was focused into a sample chamber irradiating the surface of the target material. The focal length of the lens was 12 cm (Nd:YAG laser) and 30 cm (KrF laser). The target surface was positioned approximately 5 mm closer to the lens than the focal plane. For the Nd:YAG laser the measured spot diameter was d = 1.0 mm (spot area A = 0.79 mm2) and for the UV–KrF excimer laser the spot diameter was d = 0.96 mm (A = 0.73 mm2).
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R. Viskup et al. / Applied Surface Science 255 (2009) 5215–5219
radiation is dominating). Time-resolved plasma plume photography was performed in air by using a fast intensified camera (ICCD S300:7895 Photometrics) and imaging optics (50 mm objective lens). For time-resolved photography of ejected nonluminous particles a flash lamp was used and synchronized to the laser pulse and the camera. The iron oxide powder investigated (Fe2O3) consisted of nano-particles that were spherical in shape and had mean diameter 104 65 nm as determined from electron microscopy and optical particle size measurement (Coulter LS 230). Pellets were produced by mechanical pressing the powder into disc shaped pieces 13 mm in diameter. Sintering of pellets (1000 8C, 12 h, air) transformed the material to Fe3O4 and produced compact ceramics. Laser ablation of iron oxide pressed pellets has been reported before [7,8]. 3. Results and discussion
Fig. 1. Schematic of experimental set-up for laser ablation, plasma spectroscopy and time-resolved photography of iron oxide powder, pressed powder pellets and sintered ceramics.
The pulse energy employed was EL 100 mJ for the Nd:YAG laser and EL 50 mJ for the KrF laser. The optical plasma emission was collected by using pierced mirrors, lenses and a quartz fiber that was coupled to an Echelle spectrometer with intensified CCD camera. Plasma spectra were recorded in the wavelength range 200–850 nm with a spectral resolution l/Dl 10,000 employing a delay time of DtD = 1 ms to the laser pulse and a gate width of DtG = 5 ms. In optical plasma emission spectroscopy, delay times of few microseconds are typically employed to measure narrow emission lines with intensities that are larger than the broad background radiation (at very short delay times the background
In Fig. 2 photographs of the iron oxide powder, pressed pellets and sintered ceramics, and of the laser-induced plasma for the different materials are shown. Plume photography was performed in air under multi-pulse irradiation (Nd:YAG laser, pulse repetition rate 20 Hz) with integration time of the camera of 0.5–1 s. The powder particles formed loose agglomerates and for ablation studies the powder was contained in a glass cylinder (a). Laser ablation of powder lead to the ejection of particles into ambient atmosphere. Particles ejected into the direction of the laser beam interacted with subsequent laser pulses resulting in a channel-like structure showing plasma radiation from the powder target and from some of the particles. The pulsed-laser-induced ejection of particles was observed also with pressed pellets (b) and was almost negligible with sintered ceramics (c). Time-resolved photographs of the Nd:YAG laser-induced plasma plume are shown in Fig. 3 for iron oxide powder, pellet and ceramic materials. The photos were taken in air at delay times of 2.2 ms (left column) and 3.2 ms (right column) after the impact of single laser pulses and with camera integration time
Fig. 2. Photographs of iron oxide materials and of nanosecond laser ablation (l = 1064 nm) of such materials in air. Ablation of powder leads to ejection of many particles that may be decomposed by subsequent laser pulses (a). Ablation from pressed powder pellets (b) and from sintered ceramics (c).
R. Viskup et al. / Applied Surface Science 255 (2009) 5215–5219
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Fig. 3. Time-resolved photographs of plasma plume expansion into air at different delay times after laser ablation (l = 1064 nm) of iron oxide powder (a), pressed pellets (b) and sintered ceramics (c).
Fig. 4. Intensity profile of plasma emission of pressed powder pellets after laser ablation (l = 1064 nm, EL = 100 mJ) in air (a). The dashed line indicates the position of line cut through intensity maps (inset). Comparison of the temporal evolution of plume length for pressed iron oxide pellets with model curve (b). Solid and open symbols are obtained assuming an initial plume energy of E = EL and E = EL/3, respectively.
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of 20 ns. The length of the visible plume was comparable for all materials investigated. For the powder target the plume appeared relatively homogeneous with approximately hemispherical shape which did not increase in size significantly during this time period (a). For the pressed pellet the plume appeared less homogeneous and non-hemispherical in shape (b) and for the ceramic target an irregularly structured plume was observed (c). Fig. 4a shows the variation of plasma emission intensity perpendicular to the target surface measured at different delay times. The intensity profiles were taken in the plume centre and the intensities were normalized to the highest intensity measured for each delay time. The profiles showed a maximum intensity Imax followed by a strong intensity gradient which marked the front of the bright plume. The position for maximum intensity and the plume front shifted to larger distances at longer delay times. An effective plume length R was derived from plume images taken at different time t employing an intensity criterion I = 0.5Imax. The variation of plume length with time is shown in Fig. 4b in normalized coordinates, with E the initial plume energy, pg (96,900 Pa) the gas background pressure, and vg0 (343 m/s) the
sound velocity in air [9]. The solid symbols were calculated from the measured plume length assuming an initial plume energy that was equal to the laser pulse energy (E = EL = 100 mJ). The open symbols were calculated for a lower plume energy (E = EL/3) assuming that processes such as melting, vaporization and ejection of material consumed a large part of the laser pulse energy. The solid line is calculated by a model describing spherical plume expansion into ambient gas [9]. For solid bulk materials such as stainless steel, metal oxides and polymers a good agreement was found between the plume length measured at low background pressure and the model [9,10]. At higher pressure additional effects such as hydrodynamic instabilities at the expansion front become relevant [11]. The ejection of non-luminous particles several hundreds of microseconds after plasma termination is shown in Fig. 5 (camera integration time 10 ns). Similar effects were observed also with other materials [10,12]. A relatively large amount of particles was ejected from iron oxide powder targets (Fig. 5a). The velocity of the particle front in air was estimated to v 18 m=s comparing photos taken at 100 and 400 ms delay time. Clustered particles were ejected perpendicular to the surface of pressed pellet targets
Fig. 5. Time-resolved photographs of particle ejection from iron oxide powder (a) and pressed powder pellets (b) at different delay times after laser ablation (l = 1064 nm, air).
R. Viskup et al. / Applied Surface Science 255 (2009) 5215–5219
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Fig. 6. LIBS spectra of iron oxide powder, pressed pellets and sintered ceramics. Spectra were obtained by nanosecond laser ablation in flushed Ar background (l = 1064 nm (a)) and in air (l = 248 nm (b)).
(Fig. 5b). The clusters had diameter of 0.1–0.4 mm and an ejection velocity of approximately 7 m/s was estimated comparing photos taken at 400 and 700 ms. For sintered ceramics no particle ejection was observed. Laser-induced breakdown spectroscopy (LIBS) of iron oxide powder, pressed pellets and sintered ceramics is shown in Fig. 6. LIBS spectra obtained by Nd:YAG laser ablation in flushed Ar gas background (employed for particle removal from beam path) showed intense emission lines of atomic iron at 288.08 and 288.37 nm for all target materials (Fig. 6a). The very faint signal at 288.16 nm was due to Si impurity of 113 ppm concentration. LIBS spectra obtained by KrF laser ablation in air were more intense and showed Si signals of different strength depending on the impurity concentration (Fig. 6b). The variation of LIBS intensities was probably related to the different gas background and the different laser wavelengths employed [13]. 4. Conclusion The influence of target morphology on the dynamics of laserinduced plasma plumes, the ejection of particles and the optical plasma emission was studied by time-resolved photography and plasma spectroscopy. Plasma plumes of nanosecond laser ablated iron oxide nano-powder were more homogeneous than plumes obtained with pressed powder pellets and sintered ceramics. Particles and particle clusters were ejected from iron oxide powder and pellets. Laser-induced breakdown spectroscopy revealed similar results for all iron oxide materials independent on target morphology. Intense LIBS signals of Si impurity
depending on the Si concentration were detected for UV laser ablation in air.
Acknowledgements This work has been supported by the Christian Doppler Research Association (Austria). We would like to thank Prof. G. Gritzner for particle size measurement of the powder and Prof. D. Ba¨uerle for discussions.
References [1] D. Ba¨uerle, Laser Processing and Chemistry, 3rd ed., Springer, Berlin, 2000. [2] B. Lal, L. St-Onge, F.Y. Yueh, J.P. Singh, in: J.P. Singh, S.N. Narayan (Eds.), Laser Induced Breakdown Spectroscopy, Elsevier, Amsterdam, 2007, p. 287. [3] F.C. De-Lucia, R.S. Harmon, K.L. McNesby, R.J. Winkel, A.W. Miziolek, Appl. Opt. 42 (2003) 6148. [4] T. Ctvrtnickova, L.M. Cabalin, J. Laserna, V. Kanicky, Spectrochim. Acta B 63 (2008) 42. [5] J. Gu¨nster, R. Go¨rke, J.G. Heinrich, R. Souda, Appl. Surf. Sci. 173 (2001) 76. [6] J. Chen, C. Yue, Z. Yu, W. Xubao, Z. Tiechuan, SPIE Proc. 5641 (2004) 205. [7] R.B. Metz, C. Nicolas, M. Ahmed, S.R. Leone, J. Chem. Phys. 123 (2005) 114313. [8] R. Teghil, L. D’Alessio, V. Marotta, A. Santagata, G. De Maria, D. Ferro, M.A. Sansone, Appl. Surf. Sci. 119 (1997) 34. [9] N. Arnold, J. Gruber, J. Heitz, Appl. Phys. A 69 (1999) S87. [10] N. Huber, J. Gruber, N. Arnold, J. Heitz, D. Ba¨uerle, Europhys. Lett. 51 (2000) 674. [11] J. Heitz, J. Gruber, N. Arnol, D. Ba¨uerle, N. Ramaseder, W. Meyer, J. Hocho¨rtler, SPIE Proc. 5120 (2003) 588. [12] J. Koch, M. Wa¨lle, S. Schlamp, T. Ro¨sgen, D. Gu¨nther, Spectrochim. Acta B 63 (2008) 37. [13] A.W. Miziolek, V. Palleschi, I. Schechter (Eds.), Laser-Induced Breakdown Spectroscopy, Cambridge University Press, Cambridge, 2006.