- Email: [email protected]
Operation by acentricity in the CdBr2 nanolayers
Physica E 56 (2014) 348–350
Contents lists available at ScienceDirect
Physica E journal homepage: www.elsevier.com/locate/physe
Operation by acentricity in the CdBr2 nanolayers K.J. Plucinski a,n, G. Lakshminarayana b a b
Electronics Department, Military University Technology, Kaliskiego 2, Warsaw 00-908, Poland Materials Science and Technology Division (MST-7), Los Alamos National Laboratory, Los Alamos, NM 87545, USA
H I G H L I G H T S
Ultrathin nanocrystalline layers of CdBr2 were obtained. Drastic increase of local acentricity is achieved at thickness below 30 nm. The effect is detected by second harmonic generation and piezoelectricity.
art ic l e i nf o
a b s t r a c t
Article history: Received 10 September 2013 Received in revised form 3 October 2013 Accepted 9 October 2013 Available online 24 October 2013
The possibility of coherent laser induced enhanced charge density acentricity in the layered single crystals of CdBr2 is demonstrated experimentally. The possible manipulation through noncentrosymmetry was achieved by introduction of the I ion dopants which perform some kind of intercalation. The effects show strong dependence on hydrostatic pressure and are detected by second order nonlinear optical effects as well as by piezoelectricity. The proposed method opens a new opportunity for formation charge density acentricity on the nano level. More important is that the corresponding technology is relatively cheap. & 2013 Elsevier B.V. All rights reserved.
Keywords: Layered crystal Nonlinear optics Photoinduced effect
1. Introduction Layered crystals of CdBr2 may be of interest for their optical effects because there are several polytypes which have noncentrosymmetric groups [1,2]. The changing of inter-layer orientation, as well as the possibility of working with nanometer thickness [3] may open new opportunities for their use in quantum electronics and nonlinear optics [4,5]. Among the different methods for varying acentricity, one can use photoinduced illumination [6], applied mechanical (acoustical) stresses [7] and multi-photon excitations [8]. In all these cases we have superposition of the polar symmetry on the initial medium to achieve macroscopic acentricity. The specific properties of the chemical bonds in the layered crystals CdBr2 which are strongly ionic–covalent within the particular layers and are weak van der Waals between the layers [9] open a possibility for using the relative orientation of the neighboring layers. As a consequence one can obtain the same kind of phase transition [10]. However, the layer thickness makes it possible to achieve nano-confined states [11,12].
n
Corresponding author. Tel.: þ 48 2263 31821. E-mail address: [email protected] (K.J. Plucinski).
1386-9477/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.physe.2013.10.007
Relying on their acentricity, as well as through the appropriate charging of the nano-trapping levels, one can vary their macroscopical acentricity. From the phenomenological point of view this is described by third rank polar tensors. Experimental evidence of its presence is usually demonstrated through second harmonic generation and piezoelectricity. In addition, the above-mentioned crystals have a relatively high energy gap (about 4 eV) and high degree of interlayer anisotropy which makes it possible to achieve high quality mirror like surfaces which do not require additional treatment [13]. Other good opportunities of these crystals lie in the possibility of incorporating dopants, first of all anionic [2] into the inter-layer relatively weak van der Waals spaces. With the assistance of external mechanical stress one can achieve variation of the inter-layer orientation which is superimposed on the nano-trapping intra-layer states. This is extremely important for microelectronic materials. In the present work the photoinduced acentricty will be varied using a nitrogen laser exciting the states including the nanoconfined ones below the energy gap. This will enhance the local electric field which is responsible for the enhanced hyperpolariaiblities defining second harmonic generation and related piezoelectricity. Hydrostatic pressure during the anionic doping will be used as a second tool varying acentricity. The measurements will be made during the different photoinducing powers as well as at different temperatures.
K.J. Plucinski, G. Lakshminarayana / Physica E 56 (2014) 348–350
In Section 2 we give the key results of the experimental methods. Section 3 presents the basic experimental results concerning the variation of the charge density non-centrosymmetry together with the relevant discussion.
3. Results and discussion In Fig. 1 one can observe dependence of the second order optical susceptibility defined from SHG efficiency versus hydrostatic pressure for the 10 nm CdBr2 nanolayers. We present only the results for this thickness because for higher thickness there was less effect. One can clearly see that for the main tensor component d33 for the quasi-phase matched regime the maximal value is achieved for the non-doped samples and at hydrostatic pressure equal to about 1.15 GPa. Addition of iodine causes substantial decrease in the non-centrosymmetry. So in this case we should work with maximally pure layered single crystallines. This may reflect the fact that the signs of the effective second order susceptibility will be different with respect to the macrosocpical values [15]. Unfortunately the SHG is not possible for the samples with lower thickness due to phase matching limitation. For this reason we carried out the piezoelectric studies which are shown in Fig. 2. This data also confirms the fact that the addition of the iodine (I) causes significant decrease in the acentricity detected in this case by piezoelectricity. Moreover, the effect shows evidence of
0%J 0.3 % J 0.6 J
d33 [pm/V]
2.0
d33 [pm/V]
The above-mentioned crystals of CdBr2 were obtained by slow evaporation from an aqueous solution similar as described in the Ref. [13]. However in order to obtain the hexagonal C6v4 polytypes, growth aqueous solution recrystallization was carried out at enhanced temperatures which were varied within the range 75–80 1C. The structure was controlled through the use of a DRON05 XRD diffractometer. The cleavage of the samples was performed by a glue tape with the next control by rf dilatometer. The second harmonic generation was studied using a 12 ns Nd: YAG 1064 nm laser. The green filter together with monochromator and Hamamtsu photo multiplier were used for registration of the output 532 nm green SHG signal. The hydrostatic chamber with variation of the pressure and temperature supplied by MgF2 windows was used for performance of the high pressure optical studies. The piezoelectric effect was studied by a method similar to that described in Ref. [14].
0%J 0.3 % J 0.6 % J
1.5
1.0
0.5 0
50
100 d [nm]
150
Fig. 2. Dependence of the piezoelectric d33 component versus the nanolayer thickness for the samples with different content of iodine (I).
1.5 d23 [pm/V]
2. Experimental
349
RT LNT LHeT
1.0
0.5 0
50
100 d[nm]
150
Fig. 3. Dependence of the piezoelectric tensor coefficient d33 versus the thickness at different temperatures.
the nano-confined local field contributions. The output piezoelectric tensor coefficient begins to increase significantly for a thickness below 35 nm. Following Fig. 2 one can see that drastic changes of the acentricity begin at thickness below 40 nm. This may indicate that there is some kind of structural transformation at this thickness. From Fig. 3 one can see that the temperature has an effect similar to doping by J which leads to suppression of the acentricity. This may be explained by a significant role of the inter-layer rigid phonons which are particularly important for the I doped CdBr2 [2]. In order to evaluate the contribution of the phonon subsystem we have performed the calculations of contribution of phonon subsystem using the band structure results presented in the Ref. [16]. It was found that the contribution of the phonon subsystem is equal to about 27%.
1.8 4. Conclusions
1.6 1.4 0.0
0.5
1.0
1.5
2.0
p [GPa] Fig. 1. Dependence of the effective second order susceptibility versus the hydrostatic pressure for the 10 nm CdBr2 nanolayers doped by I. The effect is substantially less for the higher sizes.
An increasing piezoelectric effect connected with enhanced acentricity was observed in the CdBr2 single nanolayers at thickness below 40 nm. The analogous detection of the acentricity was confirmed by the second harmonic generation. The additional enhancement was achieved during the application of the external hydrostatic field. At the same time the addition of the I ions leads to a decrease in the piezoelectric effect as well as second harmonic generation. This suggests that the dopants of anions in this case block development of acentricity.
350
K.J. Plucinski, G. Lakshminarayana / Physica E 56 (2014) 348–350
The proposed method may be optimized though the appropriate doping, application of hydrostatic pressure. This may be used for formation of the new type of nanocomposites possessing the desired optoelecronic features. Acknowledgments This work was supported in part by MTU through the Program PBS-814.
[4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
References [1] S.K. Chaudhary, G.C. Trigunayat, Acta Cryst. B43 (1987) 225. [2] Ya O. Dovgii, I.V. Kityk, Ukr. Phys. J. 29 (1984) 984. [3] I.V. Kityk, Izw vuzow Ser. Fizika 28 (1985) 183.
[15] [16]
M. Idrish Miah, Appl. Phys. Lett. 94 (2009) 053117. C. Chen, Int. J. Light Photon Opt. 124 (2013) 3230. W. Hydaradjan, F. Voolless, Opt. Commun. 221 (2003) 115. A. Majchrowski, I.V. Kityk, T. Łukasiewicz, A. Mefleh, S. Benet, Opt. Mater. 15 (2000) 51. M. Idrish Miah, Opt. Mater. 25 (2004) 353. Ya O. Dovgii, I.V. Kityk, N.A. Rud, Inorg. Mater. 29 (1985) 644. N.K. Gloskovska, J. Bieleninik, I.V. Kityk, Solid State Commun. 100 (1996) 149. J. Szeszko, V.V. Belykh, P. Gallo, A. Rudra, K.F. Karlsson, N.N. Sibeldin, E. Kapon, Appl. Phys. Lett. 100 (2012) 211907. J. Ebothe, I.V. Kityk, K. Ozga, P. Mandracci, S. Tkaczyk, J. Swiatek, Physica E33 (2006) 169. Ya O. Dovii, I.V. Kityk, Ukr. Phys. J. 29 (1984) 884. K Ozga, A. Majchrowski, N. AlZayed, E. Michalski, L. Jaroszewicz, P. Rakus, I.V. Kityk, M. Nabiale, M. Szota, J. Cryst. Growth 344 (2012) 27. I.V. Kityk, Phys. Solid State 26 (1991) 1026. Y.M. Alecksandrov, Y.O. Dovgii, I.V. Kityk, V.N. Kolobanov, V.N. Makhov, Fizika Tverdogo Tela 27 (1985) 1565.
Contents lists available at ScienceDirect
Physica E journal homepage: www.elsevier.com/locate/physe
Operation by acentricity in the CdBr2 nanolayers K.J. Plucinski a,n, G. Lakshminarayana b a b
Electronics Department, Military University Technology, Kaliskiego 2, Warsaw 00-908, Poland Materials Science and Technology Division (MST-7), Los Alamos National Laboratory, Los Alamos, NM 87545, USA
H I G H L I G H T S
Ultrathin nanocrystalline layers of CdBr2 were obtained. Drastic increase of local acentricity is achieved at thickness below 30 nm. The effect is detected by second harmonic generation and piezoelectricity.
art ic l e i nf o
a b s t r a c t
Article history: Received 10 September 2013 Received in revised form 3 October 2013 Accepted 9 October 2013 Available online 24 October 2013
The possibility of coherent laser induced enhanced charge density acentricity in the layered single crystals of CdBr2 is demonstrated experimentally. The possible manipulation through noncentrosymmetry was achieved by introduction of the I ion dopants which perform some kind of intercalation. The effects show strong dependence on hydrostatic pressure and are detected by second order nonlinear optical effects as well as by piezoelectricity. The proposed method opens a new opportunity for formation charge density acentricity on the nano level. More important is that the corresponding technology is relatively cheap. & 2013 Elsevier B.V. All rights reserved.
Keywords: Layered crystal Nonlinear optics Photoinduced effect
1. Introduction Layered crystals of CdBr2 may be of interest for their optical effects because there are several polytypes which have noncentrosymmetric groups [1,2]. The changing of inter-layer orientation, as well as the possibility of working with nanometer thickness [3] may open new opportunities for their use in quantum electronics and nonlinear optics [4,5]. Among the different methods for varying acentricity, one can use photoinduced illumination [6], applied mechanical (acoustical) stresses [7] and multi-photon excitations [8]. In all these cases we have superposition of the polar symmetry on the initial medium to achieve macroscopic acentricity. The specific properties of the chemical bonds in the layered crystals CdBr2 which are strongly ionic–covalent within the particular layers and are weak van der Waals between the layers [9] open a possibility for using the relative orientation of the neighboring layers. As a consequence one can obtain the same kind of phase transition [10]. However, the layer thickness makes it possible to achieve nano-confined states [11,12].
n
Corresponding author. Tel.: þ 48 2263 31821. E-mail address: [email protected] (K.J. Plucinski).
1386-9477/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.physe.2013.10.007
Relying on their acentricity, as well as through the appropriate charging of the nano-trapping levels, one can vary their macroscopical acentricity. From the phenomenological point of view this is described by third rank polar tensors. Experimental evidence of its presence is usually demonstrated through second harmonic generation and piezoelectricity. In addition, the above-mentioned crystals have a relatively high energy gap (about 4 eV) and high degree of interlayer anisotropy which makes it possible to achieve high quality mirror like surfaces which do not require additional treatment [13]. Other good opportunities of these crystals lie in the possibility of incorporating dopants, first of all anionic [2] into the inter-layer relatively weak van der Waals spaces. With the assistance of external mechanical stress one can achieve variation of the inter-layer orientation which is superimposed on the nano-trapping intra-layer states. This is extremely important for microelectronic materials. In the present work the photoinduced acentricty will be varied using a nitrogen laser exciting the states including the nanoconfined ones below the energy gap. This will enhance the local electric field which is responsible for the enhanced hyperpolariaiblities defining second harmonic generation and related piezoelectricity. Hydrostatic pressure during the anionic doping will be used as a second tool varying acentricity. The measurements will be made during the different photoinducing powers as well as at different temperatures.
K.J. Plucinski, G. Lakshminarayana / Physica E 56 (2014) 348–350
In Section 2 we give the key results of the experimental methods. Section 3 presents the basic experimental results concerning the variation of the charge density non-centrosymmetry together with the relevant discussion.
3. Results and discussion In Fig. 1 one can observe dependence of the second order optical susceptibility defined from SHG efficiency versus hydrostatic pressure for the 10 nm CdBr2 nanolayers. We present only the results for this thickness because for higher thickness there was less effect. One can clearly see that for the main tensor component d33 for the quasi-phase matched regime the maximal value is achieved for the non-doped samples and at hydrostatic pressure equal to about 1.15 GPa. Addition of iodine causes substantial decrease in the non-centrosymmetry. So in this case we should work with maximally pure layered single crystallines. This may reflect the fact that the signs of the effective second order susceptibility will be different with respect to the macrosocpical values [15]. Unfortunately the SHG is not possible for the samples with lower thickness due to phase matching limitation. For this reason we carried out the piezoelectric studies which are shown in Fig. 2. This data also confirms the fact that the addition of the iodine (I) causes significant decrease in the acentricity detected in this case by piezoelectricity. Moreover, the effect shows evidence of
0%J 0.3 % J 0.6 J
d33 [pm/V]
2.0
d33 [pm/V]
The above-mentioned crystals of CdBr2 were obtained by slow evaporation from an aqueous solution similar as described in the Ref. [13]. However in order to obtain the hexagonal C6v4 polytypes, growth aqueous solution recrystallization was carried out at enhanced temperatures which were varied within the range 75–80 1C. The structure was controlled through the use of a DRON05 XRD diffractometer. The cleavage of the samples was performed by a glue tape with the next control by rf dilatometer. The second harmonic generation was studied using a 12 ns Nd: YAG 1064 nm laser. The green filter together with monochromator and Hamamtsu photo multiplier were used for registration of the output 532 nm green SHG signal. The hydrostatic chamber with variation of the pressure and temperature supplied by MgF2 windows was used for performance of the high pressure optical studies. The piezoelectric effect was studied by a method similar to that described in Ref. [14].
0%J 0.3 % J 0.6 % J
1.5
1.0
0.5 0
50
100 d [nm]
150
Fig. 2. Dependence of the piezoelectric d33 component versus the nanolayer thickness for the samples with different content of iodine (I).
1.5 d23 [pm/V]
2. Experimental
349
RT LNT LHeT
1.0
0.5 0
50
100 d[nm]
150
Fig. 3. Dependence of the piezoelectric tensor coefficient d33 versus the thickness at different temperatures.
the nano-confined local field contributions. The output piezoelectric tensor coefficient begins to increase significantly for a thickness below 35 nm. Following Fig. 2 one can see that drastic changes of the acentricity begin at thickness below 40 nm. This may indicate that there is some kind of structural transformation at this thickness. From Fig. 3 one can see that the temperature has an effect similar to doping by J which leads to suppression of the acentricity. This may be explained by a significant role of the inter-layer rigid phonons which are particularly important for the I doped CdBr2 [2]. In order to evaluate the contribution of the phonon subsystem we have performed the calculations of contribution of phonon subsystem using the band structure results presented in the Ref. [16]. It was found that the contribution of the phonon subsystem is equal to about 27%.
1.8 4. Conclusions
1.6 1.4 0.0
0.5
1.0
1.5
2.0
p [GPa] Fig. 1. Dependence of the effective second order susceptibility versus the hydrostatic pressure for the 10 nm CdBr2 nanolayers doped by I. The effect is substantially less for the higher sizes.
An increasing piezoelectric effect connected with enhanced acentricity was observed in the CdBr2 single nanolayers at thickness below 40 nm. The analogous detection of the acentricity was confirmed by the second harmonic generation. The additional enhancement was achieved during the application of the external hydrostatic field. At the same time the addition of the I ions leads to a decrease in the piezoelectric effect as well as second harmonic generation. This suggests that the dopants of anions in this case block development of acentricity.
350
K.J. Plucinski, G. Lakshminarayana / Physica E 56 (2014) 348–350
The proposed method may be optimized though the appropriate doping, application of hydrostatic pressure. This may be used for formation of the new type of nanocomposites possessing the desired optoelecronic features. Acknowledgments This work was supported in part by MTU through the Program PBS-814.
[4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
References [1] S.K. Chaudhary, G.C. Trigunayat, Acta Cryst. B43 (1987) 225. [2] Ya O. Dovgii, I.V. Kityk, Ukr. Phys. J. 29 (1984) 984. [3] I.V. Kityk, Izw vuzow Ser. Fizika 28 (1985) 183.
[15] [16]
M. Idrish Miah, Appl. Phys. Lett. 94 (2009) 053117. C. Chen, Int. J. Light Photon Opt. 124 (2013) 3230. W. Hydaradjan, F. Voolless, Opt. Commun. 221 (2003) 115. A. Majchrowski, I.V. Kityk, T. Łukasiewicz, A. Mefleh, S. Benet, Opt. Mater. 15 (2000) 51. M. Idrish Miah, Opt. Mater. 25 (2004) 353. Ya O. Dovgii, I.V. Kityk, N.A. Rud, Inorg. Mater. 29 (1985) 644. N.K. Gloskovska, J. Bieleninik, I.V. Kityk, Solid State Commun. 100 (1996) 149. J. Szeszko, V.V. Belykh, P. Gallo, A. Rudra, K.F. Karlsson, N.N. Sibeldin, E. Kapon, Appl. Phys. Lett. 100 (2012) 211907. J. Ebothe, I.V. Kityk, K. Ozga, P. Mandracci, S. Tkaczyk, J. Swiatek, Physica E33 (2006) 169. Ya O. Dovii, I.V. Kityk, Ukr. Phys. J. 29 (1984) 884. K Ozga, A. Majchrowski, N. AlZayed, E. Michalski, L. Jaroszewicz, P. Rakus, I.V. Kityk, M. Nabiale, M. Szota, J. Cryst. Growth 344 (2012) 27. I.V. Kityk, Phys. Solid State 26 (1991) 1026. Y.M. Alecksandrov, Y.O. Dovgii, I.V. Kityk, V.N. Kolobanov, V.N. Makhov, Fizika Tverdogo Tela 27 (1985) 1565.