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Thickness and MeV Si ions bombardment effects on the thermoelectric properties of Ce3Sb10 thin films
Available online at www.sciencedirect.com
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 266 (2008) 1261–1264 www.elsevier.com/locate/nimb
Thickness and MeV Si ions bombardment effects on the thermoelectric properties of Ce3Sb10 thin films S. Gu¨ner a,b, S. Budak a,c, R. Amaral Minamisawa a, C. Muntele a, D. Ila a,* a
Center for Irradiation Materials, Department of Physics, Alabama A&M University, Normal, AL 35762, USA b _ Department of Physics, Fatih University, 34500 Bu¨yu¨kcßekmece/Istanbul, Turkey c Department of Electrical Engineering, Alabama A&M University, Normal, AL 35762, USA Received 23 September 2007; received in revised form 22 January 2008 Available online 1 February 2008
Abstract The three single layer Ce3Sb10 thin films were grown on silicon dioxide and quartz (suprasil) substrates with thicknesses of 297, 269 and 70 nm using ion beam assisted deposition (IBAD) technique. The high-energy cross plane Si ion bombardments with constant energy of 5 MeV have been performed with varying fluence from 1 1012, 1 1013, 1 1014, 1 1015 ions/cm2. The Si ions bombardment modified the thermoelectric properties of films as expected. The fluence and temperature dependence of cross plane thermoelectric parameters that are Seebeck coefficient, electrical and thermal conductivities were determined to evaluate the dimensionless figure of merit, ZT. Rutherford backscattering spectrometry (RBS) enabled us to determine the elemental composition of the deposited materials and layer thickness of each film. Ó 2008 Elsevier B.V. All rights reserved. PACS: 81.15.Jj; 72.20.Pa; 07.81.+a Keywords: IBAD; Thermoelectric properties; Rutherford backscattering; Figure of merit
1. Introduction The cerium monopnictides (CeX, X = P, As, Sb, Bi) are the semimetallic compounds crystallizes in the simple rock– salt structure with low charge carrier density and strong electronic correlations [1]. CeSb is a significant member of this group due to its complex magnetic phase diagram and recorded Kerr rotation angle of 90° [2]. The Ce is in the 4f1 state in this compound and is very sensitive to its crystalline and chemical environment. The crystal structure of CeSb makes it possible to analyse in detail how the differences in their electronic structure effects the physical properties [3] Kasuya et al. has chosen the CeSb as a typical example of low carrier density Kondo system since high-quality single crystals could be prepared and detailed
*
Corresponding author. Tel.: +1 256 372 5866; fax: +1 256 372 5868. E-mail address: [email protected] (D. Ila).
0168-583X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2008.01.045
experimental studies were performed and revealed various unusual intrinsic characteristics [4]. Another composition of Ce and Sb is the CeSb2 in layered orthorhombic crystal structure. CeSb2 is characterized by Kagayama et al. as an anisotropic ferromagnet with TC ffi 16 K and complex spin structures clearly observed as anomalies in the temperature derivation of electrical resistivity and magnetization [5]. The Kondo systems and the materials that have strong electron correlations and exhibit phase transitions are the recently promising materials especially for low temperature thermoelectric devices [6]. So we deposited a different composition rate of Ce:3 and Sb:10 to search the thermoelectric and physical properties. The efficiency of the thermoelectric materials is determined by the figure of merit ZT [7–9]. The figure of merit is calculated by the formula, ZT = S2rT/j, where S is the Seebeck coefficient, r is the electrical conductivity, T is the absolute temperature, and j is the thermal conductivity. ZT can be increased by increasing S, by
1262
S. Gu¨ner et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1261–1264
increasing r, or by decreasing j. Efficient thermoelectric devices have a high electrical conductivity and a low thermal conductivity [10].
monitor the film thickness and stoichiometry before and after 5 MeV Si ion bombardment [14,15].
2. Experimental
3. Experimental analysis and discussion
We have grown single nanolayers of Ce3Sb10 films on silica (quartz) and silicon dioxide substrates with three different thicknesses of 297, 269 and 70 nm by ion beam assisted deposition (IBAD) technique. The two electron-gun evaporators for evaporating the powder targets in different crucibles were turned on. The base pressure obtained in IBAD chamber was 6 106 torr. An Inficon quartz crystal monitor indicated the growth rates. The films are in amorphous structure due to deposition process in the IBAD chamber. Three different geometries were used for the deposition and thermoelectric measurements of films, Fig. 1. The 3x technique and the geometry shown in Fig. 1(a) were applied for thermal conductivity measurement. The Ag strip deposited on the film has 50 lm width, 200 nm thickness and contact places for silver paste. The detailed information about the 3x technique can be found in [11– 13]. Fig. 1(b) shows the Au contacts on the top and bottom of the monolayers. These two Au contacts were used in the Seebeck coefficient measurements. The film geometry to measure the electrical conductivity is shown in Fig. 1(c) and the method is the Van der Pauw. The electrical conductivity, thermal conductivity and Seebeck coefficient measurements were carried at the temperature of 27 °C. The 5 MeV Si ion bombardments were performed with the Pelletron ion beam accelerator at the Alabama A&M University-Center for Irradiation of Materials (AAMU-CIM). The energy of the bombarding Si ions was chosen by the SRIM simulation software (SRIM). The fluences used for the bombardment were 1 1012, 1 1013, 1 1014and 1 1015 ions/cm2. Rutherford backscattering spectrometry (RBS) was performed using 2.1 MeV He+ ions with the particle detector placed at 170° from the incident beam to
The RBS spectrum of a Ce3Sb10 monolayer film is shown in Fig. 2 on a glassy polymeric carbon (GPC) substrate when the sample is at the normal angle. Each element that was used in the deposition is revealed in the RBS spectrum. RUMP [16] software program has been used to specify the elemental composition and depth profile of each film. The thickness values were determined as 297, 269 and 70 nm, assuming bulk densities for Ce and Sb. Although IBAD deposition produces thin film samples uniform in thickness and composition, the depth profile of elemental composition shown in Fig. 2 is not uniform. Our investigations of the possible effects of cross plane ion bombardment will not be qualitatively compromised by this uniformity. The fluence dependence of square of Seebeck coefficients is seen in Fig. 3(a). The S is a measure of average thermal energy carried by charge carriers and all films have negative S coefficient. A slight decrease is observed for 297 and 70 nm thick films while the decrease is sharp for 269 nm thick film. The changes in electrical conductivity due bombardment with varying fluence is shown in Fig. 3(b). The r values are really high and vary between (2.48– 2.60) 105 X1 m1 for no bombarded films. Meffert et al. records the room temperature electrical conductivity for a CeSb thin film as 1.48 105 X1 m1 [1]. So our films exhibit nearly two times higher conductivity. The r values increase more with the bombardment almost for each increasing fluence and reaches to maximum value of 3.57 105 X1 m1for the 297 nm thick film. The increase in electrical conductivity is most likely a simple consequence of increased hopping conduction in the irradiated
800
a
Ag strip
Ce3Sb10
SiO2, 100 nm coating
Sb
600
b
Au
Au Ce3Sb10
Au
Counts
Silicon substrate 400
Ce
C 200
Fused Silica (Suprasil)
c
Ce3Sb10
SiO2, 100 nm coating
Silicon substrate Fig. 1. Geometry of samples from the cross-section.
0 0
200
400
600
800
Channel Fig. 2. He RBS spectrum for a 269 nm coevaporated Ce and Sb. From RUMP simulation study, we infer an average composition at Ce3Sb10 thin film on carbon substrate.
S. Gu¨ner et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1261–1264
fluences of 1 1012, 1 1013, 1 1014 ions/cm2 but to the strong increase for the fluence of 1 1015 ions/cm2. The effect of bombardment is observed as a strong rising on the thermal conductivity of 70 nm film. When the Ce3Sb10 films are bombarded with high-energy Si ions, the created heat energy causes some interface scattering and absorption of phonons. Scattering and absorption of phonons cause decrease in thermal conductivity. If you continue to bombard the samples, the amount of the thermal conductivity may increase due to the increase of the discrete energy levels in between the conduction and valence bands. Fig. 3(d) shows the fluence dependence of figure of merit for single layer Ce3Sb10 films. The virgin samples have significantly high magnitude of figure of merit, especially 1.04 for the 269 nm thick film. If we care Fig. 3(a) and (d), the unbombarded films are seen to have same order of the ZT and S coefficient from higher to low for 269, 297 and 70 nm thick films, respectively. This is mainly due the direct proportionality between S2 and ZT. The effect of bombardment on the ZT is observed as negative and ZT gets smaller with the increasing amount of fluence. The figure of merit drops from 1.04 to 0.037, from 0.47 to 0.05 and from 0.076 to 0.011 for the 269, 297 and 70 nm thick films at fluence of 1 1015 ions/cm2. The reason for this case is the total negative effect of bombardment at the values of thermopower and thermal conductivity, although electrical conductivity rises with the increasing amount of fluence.
3000
-12 2
1500 1000
S (V/K) x10
2000
2
2500
a
Ce3Sb10 films Square of Seebeck coefficient thick=297 nm thick=269 nm thick=70 nm
500 0
4.0
-1
σ (ohm.m) x10
5
3.8
b
electrical conductivity 297 nm 269 nm 70 nm
3.6 3.4 3.2 3.0 2.8 2.6 2.4 2. 2 2.0 1.8
c
thermal conductivity 297 nm 269 nm 70 nm
1.6
k (W/mK)
1.4 1.2 1.0
4. Conclusion
0.8 0.6 0.4 0.2 0.0 1.2
d
dimensionless figure of merit 297 nm 269 nm 70 nm
1.0 0.8
ZT
1263
0.6 0.4 0.2 0.0 0
1E 12
1E 13
1E 14
1E 15
2
Fluence (ions/cm ) Fig. 3. Thermoelectric properties of Ce3Sb10 thin films.
All films have n-type of thermopower and Seebeck coefficients decrease with the increasing amount of fluence of bombardment. Electrical conductivity increased with a remarkable ratio for each thickness of films as result of bombardment. The effect of fluence on thermal conductivities varies for different thickness and mainly increment is observed as an undesired result of bombardment. Since the films are in amorphous structure, the bombardment did not cause the expected effects on the thermoelectric properties of films. We concluded also that the irradiation causes undesired consequences at the figure of merit values of thin films. However ZT values of virgin samples (especially for 297 and 269 nm thick films) are really encouraging to investigate different composition rates of Ce and Sb based thin film structures without applying ion bombardment. The alternating multilayers of Ce3Sb10 with any other thermoelectric material might be solution to acquire better Seebeck and thermal conductivity values. Acknowledgements
films. Fig. 3(c) shows the thermal conductivity and fluence dependence of j. Thermal conductivity values are really small for no bombarded films at the values of 0.12, 0.19 and 0.5 W/m K for 297, 269 and 70 nm thick films, respectively. The bombardment causes to slight decrease in thermal conductivity for the 297 and 269 nm thick films at
Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and by the AAMURI Center for Advanced Propulsion Materials under the contract number NNM06AA12A from NASA, and by National Science Foundation under Grant No. EPS-0447675.
1264
S. Gu¨ner et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1261–1264
References [1] H. Meffert, J. Oster, P. Haibach, M. Huth, H. Adrian, Physica B 259– 261 (1999) 298. [2] R. Pittini, J. Schoenes, P. Wachter, Physica B 230–232 (1997) 538. [3] P. Roura-Bas, V. Vildosola, A.M. Liois, Physica B 398 (2007) 442. [4] T. Kasuya, Physica B 215 (1995) 88. [5] T. Kagayama, Physica B 359–361 (2005) 320. [6] T.M. Tritt, M.A. Subramanian, MRS Bull. 31 (2006) 190. [7] S. Budak, C. Muntele, B. Zheng, D. Ila, Nucl. Instr. and Meth. B 261 (2007) 1167. [8] S. Budak, C.I. Muntele, R.A. Minamisawa, B. Chhay, D. Ila, Nuc. Instr. and Meth. B 261 (2007).
[9] B. Zheng, S. Budak, R.L. Zimmerman, C. Muntele, B. Chhay, D. Ila, Surf. Coat. Technol. 201 (2007) 8531. [10] Z. Xiao, R.L. Zimmerman, L.R. Holland, B. Zheng, C.I. Muntele, D. Ila, Nuc. Instr. and Meth. B 242 (2006) 201. [11] D.G. Cahill, M. Katiyar, J.R. Abelson, Phys. Rev. B 50 (1994) 6077. [12] T.B. Tasciuc, A.R. Kumar, G. Chen, Rev. Sci. Instr. 72 (2001) 2139. [13] L. Lu, W. Yi, D.L. Zhang, Rev. Sci. Instr. 72 (2001) 2996. [14] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping Range of Ions in Solids, Pergamon Press, New York, 1985. [15] W.K. Chu, J.W. Mayer, M.-A. Nicolet, Backscattering Spectrometry, Academic Press, New York, 1978. [16] L.R. Doolittle, M.O. Thompson, RUMP, Computer Graphics Service, 2002.
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 266 (2008) 1261–1264 www.elsevier.com/locate/nimb
Thickness and MeV Si ions bombardment effects on the thermoelectric properties of Ce3Sb10 thin films S. Gu¨ner a,b, S. Budak a,c, R. Amaral Minamisawa a, C. Muntele a, D. Ila a,* a
Center for Irradiation Materials, Department of Physics, Alabama A&M University, Normal, AL 35762, USA b _ Department of Physics, Fatih University, 34500 Bu¨yu¨kcßekmece/Istanbul, Turkey c Department of Electrical Engineering, Alabama A&M University, Normal, AL 35762, USA Received 23 September 2007; received in revised form 22 January 2008 Available online 1 February 2008
Abstract The three single layer Ce3Sb10 thin films were grown on silicon dioxide and quartz (suprasil) substrates with thicknesses of 297, 269 and 70 nm using ion beam assisted deposition (IBAD) technique. The high-energy cross plane Si ion bombardments with constant energy of 5 MeV have been performed with varying fluence from 1 1012, 1 1013, 1 1014, 1 1015 ions/cm2. The Si ions bombardment modified the thermoelectric properties of films as expected. The fluence and temperature dependence of cross plane thermoelectric parameters that are Seebeck coefficient, electrical and thermal conductivities were determined to evaluate the dimensionless figure of merit, ZT. Rutherford backscattering spectrometry (RBS) enabled us to determine the elemental composition of the deposited materials and layer thickness of each film. Ó 2008 Elsevier B.V. All rights reserved. PACS: 81.15.Jj; 72.20.Pa; 07.81.+a Keywords: IBAD; Thermoelectric properties; Rutherford backscattering; Figure of merit
1. Introduction The cerium monopnictides (CeX, X = P, As, Sb, Bi) are the semimetallic compounds crystallizes in the simple rock– salt structure with low charge carrier density and strong electronic correlations [1]. CeSb is a significant member of this group due to its complex magnetic phase diagram and recorded Kerr rotation angle of 90° [2]. The Ce is in the 4f1 state in this compound and is very sensitive to its crystalline and chemical environment. The crystal structure of CeSb makes it possible to analyse in detail how the differences in their electronic structure effects the physical properties [3] Kasuya et al. has chosen the CeSb as a typical example of low carrier density Kondo system since high-quality single crystals could be prepared and detailed
*
Corresponding author. Tel.: +1 256 372 5866; fax: +1 256 372 5868. E-mail address: [email protected] (D. Ila).
0168-583X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2008.01.045
experimental studies were performed and revealed various unusual intrinsic characteristics [4]. Another composition of Ce and Sb is the CeSb2 in layered orthorhombic crystal structure. CeSb2 is characterized by Kagayama et al. as an anisotropic ferromagnet with TC ffi 16 K and complex spin structures clearly observed as anomalies in the temperature derivation of electrical resistivity and magnetization [5]. The Kondo systems and the materials that have strong electron correlations and exhibit phase transitions are the recently promising materials especially for low temperature thermoelectric devices [6]. So we deposited a different composition rate of Ce:3 and Sb:10 to search the thermoelectric and physical properties. The efficiency of the thermoelectric materials is determined by the figure of merit ZT [7–9]. The figure of merit is calculated by the formula, ZT = S2rT/j, where S is the Seebeck coefficient, r is the electrical conductivity, T is the absolute temperature, and j is the thermal conductivity. ZT can be increased by increasing S, by
1262
S. Gu¨ner et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1261–1264
increasing r, or by decreasing j. Efficient thermoelectric devices have a high electrical conductivity and a low thermal conductivity [10].
monitor the film thickness and stoichiometry before and after 5 MeV Si ion bombardment [14,15].
2. Experimental
3. Experimental analysis and discussion
We have grown single nanolayers of Ce3Sb10 films on silica (quartz) and silicon dioxide substrates with three different thicknesses of 297, 269 and 70 nm by ion beam assisted deposition (IBAD) technique. The two electron-gun evaporators for evaporating the powder targets in different crucibles were turned on. The base pressure obtained in IBAD chamber was 6 106 torr. An Inficon quartz crystal monitor indicated the growth rates. The films are in amorphous structure due to deposition process in the IBAD chamber. Three different geometries were used for the deposition and thermoelectric measurements of films, Fig. 1. The 3x technique and the geometry shown in Fig. 1(a) were applied for thermal conductivity measurement. The Ag strip deposited on the film has 50 lm width, 200 nm thickness and contact places for silver paste. The detailed information about the 3x technique can be found in [11– 13]. Fig. 1(b) shows the Au contacts on the top and bottom of the monolayers. These two Au contacts were used in the Seebeck coefficient measurements. The film geometry to measure the electrical conductivity is shown in Fig. 1(c) and the method is the Van der Pauw. The electrical conductivity, thermal conductivity and Seebeck coefficient measurements were carried at the temperature of 27 °C. The 5 MeV Si ion bombardments were performed with the Pelletron ion beam accelerator at the Alabama A&M University-Center for Irradiation of Materials (AAMU-CIM). The energy of the bombarding Si ions was chosen by the SRIM simulation software (SRIM). The fluences used for the bombardment were 1 1012, 1 1013, 1 1014and 1 1015 ions/cm2. Rutherford backscattering spectrometry (RBS) was performed using 2.1 MeV He+ ions with the particle detector placed at 170° from the incident beam to
The RBS spectrum of a Ce3Sb10 monolayer film is shown in Fig. 2 on a glassy polymeric carbon (GPC) substrate when the sample is at the normal angle. Each element that was used in the deposition is revealed in the RBS spectrum. RUMP [16] software program has been used to specify the elemental composition and depth profile of each film. The thickness values were determined as 297, 269 and 70 nm, assuming bulk densities for Ce and Sb. Although IBAD deposition produces thin film samples uniform in thickness and composition, the depth profile of elemental composition shown in Fig. 2 is not uniform. Our investigations of the possible effects of cross plane ion bombardment will not be qualitatively compromised by this uniformity. The fluence dependence of square of Seebeck coefficients is seen in Fig. 3(a). The S is a measure of average thermal energy carried by charge carriers and all films have negative S coefficient. A slight decrease is observed for 297 and 70 nm thick films while the decrease is sharp for 269 nm thick film. The changes in electrical conductivity due bombardment with varying fluence is shown in Fig. 3(b). The r values are really high and vary between (2.48– 2.60) 105 X1 m1 for no bombarded films. Meffert et al. records the room temperature electrical conductivity for a CeSb thin film as 1.48 105 X1 m1 [1]. So our films exhibit nearly two times higher conductivity. The r values increase more with the bombardment almost for each increasing fluence and reaches to maximum value of 3.57 105 X1 m1for the 297 nm thick film. The increase in electrical conductivity is most likely a simple consequence of increased hopping conduction in the irradiated
800
a
Ag strip
Ce3Sb10
SiO2, 100 nm coating
Sb
600
b
Au
Au Ce3Sb10
Au
Counts
Silicon substrate 400
Ce
C 200
Fused Silica (Suprasil)
c
Ce3Sb10
SiO2, 100 nm coating
Silicon substrate Fig. 1. Geometry of samples from the cross-section.
0 0
200
400
600
800
Channel Fig. 2. He RBS spectrum for a 269 nm coevaporated Ce and Sb. From RUMP simulation study, we infer an average composition at Ce3Sb10 thin film on carbon substrate.
S. Gu¨ner et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1261–1264
fluences of 1 1012, 1 1013, 1 1014 ions/cm2 but to the strong increase for the fluence of 1 1015 ions/cm2. The effect of bombardment is observed as a strong rising on the thermal conductivity of 70 nm film. When the Ce3Sb10 films are bombarded with high-energy Si ions, the created heat energy causes some interface scattering and absorption of phonons. Scattering and absorption of phonons cause decrease in thermal conductivity. If you continue to bombard the samples, the amount of the thermal conductivity may increase due to the increase of the discrete energy levels in between the conduction and valence bands. Fig. 3(d) shows the fluence dependence of figure of merit for single layer Ce3Sb10 films. The virgin samples have significantly high magnitude of figure of merit, especially 1.04 for the 269 nm thick film. If we care Fig. 3(a) and (d), the unbombarded films are seen to have same order of the ZT and S coefficient from higher to low for 269, 297 and 70 nm thick films, respectively. This is mainly due the direct proportionality between S2 and ZT. The effect of bombardment on the ZT is observed as negative and ZT gets smaller with the increasing amount of fluence. The figure of merit drops from 1.04 to 0.037, from 0.47 to 0.05 and from 0.076 to 0.011 for the 269, 297 and 70 nm thick films at fluence of 1 1015 ions/cm2. The reason for this case is the total negative effect of bombardment at the values of thermopower and thermal conductivity, although electrical conductivity rises with the increasing amount of fluence.
3000
-12 2
1500 1000
S (V/K) x10
2000
2
2500
a
Ce3Sb10 films Square of Seebeck coefficient thick=297 nm thick=269 nm thick=70 nm
500 0
4.0
-1
σ (ohm.m) x10
5
3.8
b
electrical conductivity 297 nm 269 nm 70 nm
3.6 3.4 3.2 3.0 2.8 2.6 2.4 2. 2 2.0 1.8
c
thermal conductivity 297 nm 269 nm 70 nm
1.6
k (W/mK)
1.4 1.2 1.0
4. Conclusion
0.8 0.6 0.4 0.2 0.0 1.2
d
dimensionless figure of merit 297 nm 269 nm 70 nm
1.0 0.8
ZT
1263
0.6 0.4 0.2 0.0 0
1E 12
1E 13
1E 14
1E 15
2
Fluence (ions/cm ) Fig. 3. Thermoelectric properties of Ce3Sb10 thin films.
All films have n-type of thermopower and Seebeck coefficients decrease with the increasing amount of fluence of bombardment. Electrical conductivity increased with a remarkable ratio for each thickness of films as result of bombardment. The effect of fluence on thermal conductivities varies for different thickness and mainly increment is observed as an undesired result of bombardment. Since the films are in amorphous structure, the bombardment did not cause the expected effects on the thermoelectric properties of films. We concluded also that the irradiation causes undesired consequences at the figure of merit values of thin films. However ZT values of virgin samples (especially for 297 and 269 nm thick films) are really encouraging to investigate different composition rates of Ce and Sb based thin film structures without applying ion bombardment. The alternating multilayers of Ce3Sb10 with any other thermoelectric material might be solution to acquire better Seebeck and thermal conductivity values. Acknowledgements
films. Fig. 3(c) shows the thermal conductivity and fluence dependence of j. Thermal conductivity values are really small for no bombarded films at the values of 0.12, 0.19 and 0.5 W/m K for 297, 269 and 70 nm thick films, respectively. The bombardment causes to slight decrease in thermal conductivity for the 297 and 269 nm thick films at
Research sponsored by the Center for Irradiation of Materials, Alabama A&M University and by the AAMURI Center for Advanced Propulsion Materials under the contract number NNM06AA12A from NASA, and by National Science Foundation under Grant No. EPS-0447675.
1264
S. Gu¨ner et al. / Nucl. Instr. and Meth. in Phys. Res. B 266 (2008) 1261–1264
References [1] H. Meffert, J. Oster, P. Haibach, M. Huth, H. Adrian, Physica B 259– 261 (1999) 298. [2] R. Pittini, J. Schoenes, P. Wachter, Physica B 230–232 (1997) 538. [3] P. Roura-Bas, V. Vildosola, A.M. Liois, Physica B 398 (2007) 442. [4] T. Kasuya, Physica B 215 (1995) 88. [5] T. Kagayama, Physica B 359–361 (2005) 320. [6] T.M. Tritt, M.A. Subramanian, MRS Bull. 31 (2006) 190. [7] S. Budak, C. Muntele, B. Zheng, D. Ila, Nucl. Instr. and Meth. B 261 (2007) 1167. [8] S. Budak, C.I. Muntele, R.A. Minamisawa, B. Chhay, D. Ila, Nuc. Instr. and Meth. B 261 (2007).
[9] B. Zheng, S. Budak, R.L. Zimmerman, C. Muntele, B. Chhay, D. Ila, Surf. Coat. Technol. 201 (2007) 8531. [10] Z. Xiao, R.L. Zimmerman, L.R. Holland, B. Zheng, C.I. Muntele, D. Ila, Nuc. Instr. and Meth. B 242 (2006) 201. [11] D.G. Cahill, M. Katiyar, J.R. Abelson, Phys. Rev. B 50 (1994) 6077. [12] T.B. Tasciuc, A.R. Kumar, G. Chen, Rev. Sci. Instr. 72 (2001) 2139. [13] L. Lu, W. Yi, D.L. Zhang, Rev. Sci. Instr. 72 (2001) 2996. [14] J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping Range of Ions in Solids, Pergamon Press, New York, 1985. [15] W.K. Chu, J.W. Mayer, M.-A. Nicolet, Backscattering Spectrometry, Academic Press, New York, 1978. [16] L.R. Doolittle, M.O. Thompson, RUMP, Computer Graphics Service, 2002.