- Email: [email protected]
Cu polymer nanocomposites
Physica E 118 (2020) 113904
Contents lists available at ScienceDirect
Physica E: Low-dimensional Systems and Nanostructures journal homepage: http://www.elsevier.com/locate/physe
Laser-stimulated Pockels effect in CdBr2/Cu polymer nanocomposites G. Lakshminarayana a, *, A.M. El-Naggar b, G.L. Myronchuk c, E. Gondek d, A.H. Reshak e, f, g, P. Czaja h, I.V. Kityk h, ** a
Intelligent Construction Automation Center, Kyungpook National University, 80, Daehak-ro, Buk-gu, Daegu, 41566, Republic of Korea Research Chair of Exploitation of Renewable Energy Applications in Saudi Arabia, Physics & Astronomy Department, College of Science, King Saud University, P. O. Box 2455, 11451, Riyadh, Saudi Arabia c Department of Experimental Physics and Information-measuring Technology, Lesya, Ukrainka Eastern European University, 13 Voli Avenue, 43025, Luck, Ukraine d Institute of Physics, Cracow University of Technology, ul. Podchorąz_ ych 1, 30-084, Krak� ow, Poland e Nanotechnology and Catalysis Research Center (NANOCAT), University of Malaya, Kuala Lumpur, 50603, Malaysia f Department of Instrumentation and Control Engineering, Faculty of Mechanical Engineering, CTU in Prague, Technicka 4, Prague 6 166 07, Czech Republic g Physics Department, College of Science, Basrah University, Basrah, Iraq h Institute of Optoelectronics and Measuring Systems, Faculty of Electrical Engineering, Czestochowa University of Technology, Armii Krajowej 17 Str., 42-200, Czestochowa, Poland b
A R T I C L E I N F O
A B S T R A C T
Keywords: CdBr2/Cu Polymer nanocomposites NLO Laser-stimulated effects Electrooptics
Photostimulated linear electrooptical effects (LEOEs) in the CdBr2/Cu polymer nanocomposites have been established. The phototreatment was carried out using two bicolor coherent beams with Er: glass laser pulses at coherent frequencies 1540 nm and 770 nm. The detection of the LEOE was performed by three wavelengths (633 nm, 1150 nm, and 3390 nm) of continuous-wave (cw) He–Ne laser. The monitoring of the laser-stimulated LEOE has been done immediately after illumination, using the Senarmont method. The fundamental beam was formed by Er: glass laser with pulse time duration about 20 ns and pulse frequency repetition about 10 Hz. The nano crystallites of the layered crystallites possessed a thickness varying from 1 nm to 200 nm. The contents of the composites have been varied in the polyvinyl alcohol (PVA) matrices. The principal role here is played by Cu ions participating in the ionic conductivity, which favors an internal charged dc-electric field and related photo refraction. The later, in turn, is sensitive to the wavelengths of probing beams. We explored both dependences versus the nanocrystalline thickness as well as the nonlinear optical (NLO) chromophore concentration. This particular study is devoted to the microscopy of the laser-stimulated changes of the crystallites embedded into the matrices.
1. Introduction The layered semiconductors and dielectrics are promising due to a convenient fabrication of the specimens, possessing high anisotropy of chemical bonds within and perpendicularly to parallelly oriented layers [1,2]. Furthermore, interesting materials are the layered dielectrics based on metal dihalogenides (e.g. CdX2) [3,4]. Here, the layered metal-dihalogenide materials are of principal interest due to the occurrence of natural interfaces with optical surfaces that do not require the application of sophisticated vacuum deposition techniques [5]. Such dihalogenides have been explored relatively well [6] and high anisot ropy layered crystals doped by transition metals (e.g., Cu) [7] are more
suitable due to the possibility of fabrication of high-quality materials with thickness <10 nm. Additionally, some role here is played by phonon anharmonicities which in turn favor the laser-induced and NLO effects [8]. Recently, laser-stimulated studies were carried out mainly for chalcogenides [9]. However, the chalcogenides possess huge irre versible effects that limit their practical application [10]. Most of the earlier studies for the laser-photoinduced changes utilized one- and two photoinduced beams [11]. However, in the case of highly anisotropic crystallites doped with Cu, the principal role begin to play is self-polarization due to probing beams [12]. For layered highly aniso tropic materials, the effects are caused by the low-powered beams, which simultaneously self-modulate due to the low-dimensional
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (G. Lakshminarayana), [email protected] (I.V. Kityk). https://doi.org/10.1016/j.physe.2019.113904 Received 12 October 2019; Received in revised form 17 December 2019; Accepted 17 December 2019 Available online 23 December 2019 1386-9477/© 2019 Elsevier B.V. All rights reserved.
G. Lakshminarayana et al.
Physica E: Low-dimensional Systems and Nanostructures 118 (2020) 113904
Fig. 1. A principal set-up for the laser-stimulated bicolor coherent treatment by 1540/770 nm beams.
Fig. 3. Dependence of the diagonal LEOE tensor coefficients versus the di ameters of the photoinduced beams at probing wavelengths 633 nm, 1150 nm, and 3390 nm. Piezooptical coefficient should be multiplied by 10 14..
Fig. 2. Dependence of the LEOE constants for different probing beams versus power densities of the bicolor photoinduced beams.
localized nanotrapping levels within the forbidden energy gap. Among the layered materials, very promising are Cd dihalogenides. However, the application of two and more coherent laser-stimulated beams may favor principally different effects due to the formation of the space-grating patterns [13]. The important factor here is the possibility to vary the thickness by the cleavage of the nanocrystalline up to several nm. So, we can operate by the thickness of the nanostructures without using vacuum deposition methods. In this report, we will explore novel laser-induced operation for the optical, microstructural, and elastooptical features study of the mate rials, possessing high anisotropy. Particular attention is devoted to Cudoped materials. Nanolayers are treated by bicolor coherent treat ments at 1540 nm/770 nm wavelengths, which are incident under different angles to the cleaved surfaces (see Fig. 1). The simultaneous illumination is caused by probing continuous-wave He–Ne laser beams for an occurrence of the space patterns that are formed by laserstimulated bicolor beams. They are also crucially dependent on the wavelengths of the probing beams, power densities, and light polariza tion. Here, we used the probing beam both for the phototreatment as well as for self-modulation. We studied the changes of the LEOE effects under the influence of varying laser-stimulated power densities for
CdBr2/Cu nanosheets embedded into the polyvinyl alcohol (PVA) matrices. 2. Experimental The experimental set-up presented in Fig. 1 contains two subsystems: The first one corresponds to the photoinduced channel which is formed by two coherent laser beams with the incident angles variation within the range of 24–56� . At first, the two coherent beams form the gratings within 3–5 min of the treatment. The control of gratings formation reflecting anisotropy is carried out by monitoring the diffraction. The formation of such gratings is most important. For the formation of quasiperiodic gratings, a principally new approach is used. We applied different wavelengths of the probing He–Ne laser (cw) with power about 10 mW as shown in Fig. 1. The influence of two coherent photoinduced beams and their beam diameters are explored. The polarization effect of the photoinduced beam was also studied. The detection of laser-stimulated changes was performed under the influence of the external dc-electric field with frequency about 10 Hz. The Er: glass laser beam with a pulse repetition of about 10 Hz is possessed Gaussian-like diameters varying from 0.5 to 2
G. Lakshminarayana et al.
Physica E: Low-dimensional Systems and Nanostructures 118 (2020) 113904
From Fig. 2, one can notice an occurrence of different dependences of the LEOE constants for probing beams versus the energy density. For instance, the maximal laser-stimulated EOE occurs within the bicolor laser stimulated energy densities varying at 100–140 J/m2. The optimal concentration corresponds to the specimens with 25% content of the nanolayers (NLs). The maximal piezooptical coefficients were achieved for the probing wavelength of 1540 nm (about 2 pm/V) and the respective value is the highest for the energy density of about 140 J/m2. The thermoheating is below 4 K and changes at wavelength 633 nm, about 2 times less value where the maximum is achieved at 150 J/m2. Here, more interesting is the dependence on the 3390 nm wavelength. There are two laser-stimulated maxima – at 63 J/m2 and 150 J/m2. Fig. 3 illustrates the dependence of the diagonal LEOE tensor coefficients versus the diameters of the photoinduced beams at probing wavelengths 633 nm, 1150 nm, and 3390 nm. Here, piezooptical coefficients should be multiplied by 10 14. This one reflects a significant role of phonon subsystem contribution, observed at 1150 nm wavelength. Furthermore, the maximally achieved LEO depends on the thickness. Generally, nanocrystallites below 20 nm thickness demonstrate a significant shift of the absorption band. This observable phenomenon could be due to the influence of the quantum size effect. Previously, some reported works by other researchers also clearly showed the occurrence of nonlinear op tical effects for such crystals [14–16].
Fig. 4. Electronic density of sates: before (1) and after the laser treatment (2).
2.0 mm. The energy density was varied by the rotation of the polarizers. Several interference Glahn filters (P), lenses (L), and mirrors (M) allowed for forming two bicolor coherent beams at wavelengths 1540 nm and 770 nm for illumination of the specimens. The treatment was carried out from 3 to 5 min until the gratings are quasi-periodic, controlled by He–Ne laser. The output quasi-ring patterns have been analyzed using both CCD set up as well as HAMAMATSU photo multipliers with a time resolution of up to 1 ns. The laser beam from the 20 ns Er: glass possessing different polarization and intensities were space-split for two channels at 1540 nm and 770 nm. The thickness of the nanocrystals embedded into the photopolymer PVA matrices has been tuned up to 2 nm. The initial CdBr2: Cu crystallites have been grown by the Bridgman method and were cut by glued tapes perpen dicularly to the optical axes. The basic CdBr2 single crystals possess a trigonal structure. The control of the thickness was performed by opti cally polarized methods. Afterward, the nanolayers were embedded into the PVA photopolymer matrices with the photoinitiators, which were solidified by external UV light with the applied simultaneous dc-electric field. The solidification was performed by cw nitrogen laser at 371 nm with 60 W power. The He–Ne laser spots with 633 nm, 1150 nm, and 3390 nm wavelengths were principal for the monitoring of the bire fringence. The electrooptic effects were monitored and related using the dc-electric field, which serves as the source of the LEOE effect. Here, the probing beam also contributes to photoinduced effects. The beam deviation angles have been varied up to 0.20 . The same laser has been used for the control of the gratings. The optical phase-analyzer possessing the phase wave plates λ/4 and rotating analyzer have been used for the control of the changes of the optical phases, directly con nected with the birefringence. The mechanical stress has been applied perpendicularly to the samples along the crystallographic axes ‘x’ and ‘y’. These measurements are based on the determination of the bire fringence under applied mechanical stress directly related to the pie zooptics. After each cycle of the photoinduced bicolor treatment, the control of the piezooptics has been done.
3.1. Phenomenology of the photoinduced effects For the description of the influence of laser-stimulated effects on the polarization of the medium determining the space charge density dis tribution, it is necessary to consider the interaction of the electrical components for the changes of polarization. To consider the laser and electrical-induced medium polarization, it should be introduced in eight rank tensor as given below form: ðωÞ
ðωÞ
ðωÞ
ðΩ1 Þ
ΔPi ¼ rijklmnsp Ecw;j ⋅Ecw:El ⋅Em ⋅En
ðΩ2 Þ
⋅Es
(1)
ðΩ3 Þ
⋅Ep
Here, light-stimulated medium polarization changes due to illumi nation both by the low power cw laser, which is directly related to the photo-stimulated charging of the localized Cu 3d states and stimulated anisotropy caused by high power pulses, where it can favor an appear ance of laser-stimulated birefringence, formed by two coherent laser beams. As a consequence, during the birefringence measurements, there occur grating patterns. The PVA matrices are very favorable for such kind of effects. The eq. (1) takes into account both electronic and anharmonic phonon dc-vector components. This one is also enhanced due to an external dc-electric field due to electrooptical effects. Both the linear as well as quadratic electrooptical effects are responsible for the observed changes. Moreover, there appears some electrostriction and laser-stimulated elastooptical effects [13], which may be expressed by a fourth rank polar tensor Rijkl : (2)
Δnij ¼ Rijkl Pj Pk Pl
To clarify the contribution of the electronic density of states, we have carried out band structure simulations within the framework of density functional theory (DFT) approaches. The Cd–Br6 octahedral structural fragments play here a crucial role for the evaluations of the space charge density distribution for principal structural fragments before and after external field treatment. The initial cluster has been additionally modified by an effective dc-electric field. The σ jk - stress second-order
3. Results and discussion
tensor; El
ðωÞ
We have explored the two principal tensor components of EOE at different probing wavelengths of cw He–Ne laser at 633 nm, 1150 nm, and 3390 nm. The main changes were observed for diagonal tensor components. The dc-electric field was applied perpendicularly to the He–Ne laser beams propagation.
- effective electric field components are averaged in time
for the corresponding electromagnetic wave. En - averaged compo nents of the phonon displacements including the inter-layer rigid ions. As a basis for calculations, we have used norm-conserving pseudo potential parametrization as introduced in Ref. [17]. We solved a secular matrix using the following set of equations: ðΩ1 Þ
3
G. Lakshminarayana et al.
Physica E: Low-dimensional Systems and Nanostructures 118 (2020) 113904
Fig. 5. Changes of the nanolayered aggregates under the influence of different probing beams: a) before the laser treatment, b) 633 nm, c) 1150 nm, d) 3390 nm wavelength.
�� 2 � � h ðk þ Gn Þ2 2m
X � EðkÞ δn;n’ þ Vα G’n
� Gn Sα G’n
�� Gn � ¼ 0
(3)
E(k) corresponds to eigenenergy for a k-BZ space direction. Gn’,Gn –plane-wave basis vectors Structural form-factors has been introduced as: . X � � � � (4) Sβ G’n Gn ¼ gðβÞ ΩNa exp i G’n Gn τβ Here, g(β) - a coefficient corresponding to partial contributions of the reconstructed atomic positions, which has been obtained using a mo lecular dynamics (MD) geometry optimization. It has been taken into account for structural rearrangements due to the presence of Cu ions. The basis contained about 72000 plane-waves with an additional Lowdin basis set. Fourier transform pseudopotential has been presented in a form: � Z � � � � Vα G’n Gn ¼ 1 Ω Vα ðrÞexp (5) i G’n Gn r Fig. 6. The output beam patterns after additional preliminary treatment by two laser beams at 633 nm and 3390 nm wavelength.
The screening potential has been calculated within a framework of Perdew-Zunger screening potential. 4
G. Lakshminarayana et al.
Physica E: Low-dimensional Systems and Nanostructures 118 (2020) 113904
another at 150 J/m2. This one may open up a new stage for the design of novel photonic gratings and triggers. The significant role of the phonon subsystem contribution was identified at 1150 nm wavelength. More over, the maximally achieved LEO depends on the sample thickness.
Acceleration of the interaction calculations convergence was ach ieved by transferring 82% of the (m-1)-th interaction concerning the previous one. A coincidence is assumed to be ~2.05. It should be emphasized that all one-electron methods favor an underestimation of the Eg. As a consequence, self-energy correction renormalization including scissor factor was included in the energy gap calculations. Fig. 4 presents the DOS changes during the treatment as described above. One can see that the DOS is red-shifted, which in turn may favor enhanced optical effects like piezooptics. Additionally, using the TEM microscopy we observed significant changes of the nanolayer aggregates at different probing wavelengths. One can see that in all the cases, there occur a space quasi-periodic patterns for the piezooptical coefficients versus the power densities and it is sensitive to the beam diameters. The aggregation of the nano layer is changed drastically. The observed aggregates are not only con nected with the photoinduced two-beam periods but also reflect an interaction with low power beams due to the changes of the internal dcelectric field, causing Kerr effects. Following Fig. 5(b–d) one can notice that the space morphology crucially depends on the wavelength of the probing lasers. The effect exists for at least 10 min and is extended up to several days depending on the relative polarization and intensities of the laser-stimulated beams. However, it is difficult to find more clear de pendences. The principal role here begins to play by Cu ions due to the presence of 3d localized bonds. Moreover, any irreversible changes have not been observed after switching off the photoinduced lasers. Several times repeated laser treatment did not change significantly the achieved effects. The influence of the probing beams may be explained first of all by photopolarization of the Cu-doped ions. After the treatment by 2 ns lasers together with probing beams at wavelengths 633 nm and 3390 nm during applied pressure, the CCD reconstructed picture is changed drastically (see Fig. 6). So, by varying the probing laser beams, one can observe a lot of different patterns with varied quasi-periods. After laser treatment, there occur many patterns and their fre quencies are also dependent on the low power cw laser probing wave length. These patterns are observed only during the superposition of the external mechanic field. The effect reflects an interference of two laser beams due to linear and parametrical optical effects, like the optical Kerr effect, which also depends on the probing He–Ne laser beams. This fact allows using these methods for the creation of the gratings which are crucial for various photonic devices application. The role of the anhar monic phonons subsystem here may be crucial because it is closely related with the photorefraction. Depending on the ratio of the partic ular intensities of the coherent beam signals, the patterns appear for 10 min up to several days. Now the main efforts will be devoted to the formation of the grating patterns with quasi-periods varied within a wide range of periods.
CRediT authorship contribution statement G. Lakshminarayana: Formal analysis, Writing - review & editing. A.M. El-Naggar: Formal analysis, Funding acquisition. G.L. Myr onchuk: Investigation, Software, Data curation. E. Gondek: Investiga tion, Software, Data curation. A.H. Reshak: Formal analysis, Validation. P. Czaja: Software, Investigation, Data curation. I.V. Kityk: Conceptualization, Resources, Formal analysis, Validation, Supervision, Writing - original draft, Funding acquisition, Project administration. Acknowledgements The authors are grateful to the Deanship of Scientific Research, King Saud University for funding through Vice Deanship of Scientific Research Chairs. Also, this work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. NRF-2018R1A5A1025137) through a Research Professor position at ICA Center, Kyungpook National University (KNU), South Korea. References [1] S. Cho, S.-Ji Min, M.-Y. Cho, Ik-S. Kim, So-M. Kim, B.-M. Moon, K.-S. Moon, D. Lee, J.-M. Oh, S.-M. Koo, Bipolar charge transport in intrinsic SiC on p- and n-Si heterostructures prepared by a room temperature aerosol deposition process, Ceram. Int. 45 (2019) 17556–17561. [2] Q. Wang, Z. Zhao, H. Li, J. Zhuang, Z. Ma, Y. Yang, L. Zhang, Y. Zhang, One-step RF magnetron sputtering method for preparing Cu(In, Ga)Se2 solar cells, J. Mater. Sci. Mater. Electron. 29 (2018) 11755–11762. [3] Y. Huang, K. Xu, Z. Wang, T.A. Shifa, Q. Wang, F. Wang, C. Jiang, J. He, Designing the shape evolution of SnSe2 nanosheets and their optoelectronic properties, Nanoscale 7 (41) (2015) 17375–17380. [4] Z. Yin, H. Li, H. Li, L. Jiang, Y. Shi, Y. Sun, G. Lu, Q. Zhang, X. Chen, H. Zhang, Single-layer MoS2 phototransistors, ACS Nano 6 (1) (2011) 74–80. [5] J. Schornbaum, B. Winter, S.P. Schießl, F. Gannott, G. Katsukis, D.M. Guldi, E. Spiecker, J. Zaumseil, Epitaxial growth of PbSe quantum dots on MoS2 nanosheets and their near-infrared photoresponse, Adv. Funct. Mater. 24 (37) (2014) 5798–5806. _ Kariper, Structural, optical and porosity properties of CdI2 thin film, J. Mater. [6] I. Res. Technol. 5 (2016) 77–83. [7] I. Bolesta, S. Velgosh, D. Yu, I. Karbowmnyk, M. Piccini, The electronic and optical properties of Cu doped CdI2, Optik 124 (2013) 3230–3234. [8] C. Chen, Nano-confined and copper-defect in wide-bandgap semiconductors, Opt. Commun. 284 (2011) 5199–5202. [9] O.V. Parasyuk, G.L. Myronchuk, A.O. Fedorchuk, A.M. El-Naggar, A. Albassam, A. S. Krymus, I.V. Kityk, A novel effect of CO2 laser induced piezoelectricity in Ag2Ga2SiS6 chalcogenide crystals, Crystals 6 (2016), 107 (12 pp). [10] K. Ozga, O.M. Yanchuk, L.V. Tsurkova, O.V. Marchuk, I.V. Urubkov, Y. E. Romanyuk, O. Fedorchuk, G. Lakshminarayana, I.V. Kityk, Operation by optoelectronic features of cadmium sulphide nanocrystallites embedded into the photopolymer polyvinyl alcohol matrices, Appl. Surf. Sci. 446 (2018) 209–214. [11] O.I. Shpotyuk, J. Kasperczyk, I.V. Kityk, Mechanism of reversible photoinduced optical effects in amorphous As2S3, J. Non-Cryst. Solids 215 (1997) 218–225. [12] I.V. Kityk, S.A. Pyroha, T. Mydlarz, J. Kasperczyk, M. Czerwinski, Magnetic field induced ferroelectricity in copper doped CdI2 sincgle crystals, Ferroelectrics 205 (1998) 107–118. [13] A. Migalska-Zalas, Z. Sofiani, B. Sahraoui, I.V. Kityk, V. Yuvshenko, J.L. Fillaut, J. Perruchon, T.J.J. Muller, χ(2) grating in Ru derivative chromophores incorporated within the PMMA polymer matrices, J. Phys. Chem. B 108 (2004) 14942–14947. [14] I.M. Bolesta, I.V. Kityk, V.I. Kovalisko, Luminescence and nonlinear optical properties of Me-CdI2 (Me¼Ag, Au) heterostructures, Phys. Solid State 36 (1994) 1880–1882. [15] M.I. Miah, Size effect on the SHG properties of Cu-doped CdI2 nanocrystals, Appl. Surf. Sci. 256 (2009) 1472–1475. [16] M.I. Miah, J. Kasperczyk, Cu-doping effects in CdI2 layered nanostructures: the role of photoinduced electron-phonon anharmonic interactions, Appl. Phys. Lett. 94 (2009), 053117. [17] I.V. Kityk, A. Kassiba, K.J. Plucinski, J. Berdowski, Band structure of the large-sized SiC nanocomposites, Phys. Lett. A 265 (2000) 403–410.
4. Conclusions In summary, during bicolor laser treatment at 1540 nm/770 nm ns Er: glass laser wavelengths and continuous wavelengths at 633 nm, 1150 nm, and 3390 nm, we have found an occurrence of the gratings patterns, which are very sensitive to the wavelengths of low-power He–Ne laser. This phototreatment of using several beams, leading to the formation of the grating patterns could be promising for the nano photonics application. The maximal laser-stimulated EOE was noticed within the bicolor laser-stimulated energy densities varying at 100–140 J/m2 range. The optimal concentration corresponds to the specimens with 25% content of the nanolayers. The maximal piezooptical co efficients were achieved for a probing wavelength of 1540 nm (~2 pm/ V). This value is identified for the energy density of about 140 J/m2. The thermoheating is below 4 K and changes at 633 nm wavelength to about two times less value, and the maximum is achieved at 150 J/m2. Further, a more interesting result is dependence on the wavelength of 3390 nm. There observed two laser-stimulated maxima: one at 63 J/m2 and
5
Contents lists available at ScienceDirect
Physica E: Low-dimensional Systems and Nanostructures journal homepage: http://www.elsevier.com/locate/physe
Laser-stimulated Pockels effect in CdBr2/Cu polymer nanocomposites G. Lakshminarayana a, *, A.M. El-Naggar b, G.L. Myronchuk c, E. Gondek d, A.H. Reshak e, f, g, P. Czaja h, I.V. Kityk h, ** a
Intelligent Construction Automation Center, Kyungpook National University, 80, Daehak-ro, Buk-gu, Daegu, 41566, Republic of Korea Research Chair of Exploitation of Renewable Energy Applications in Saudi Arabia, Physics & Astronomy Department, College of Science, King Saud University, P. O. Box 2455, 11451, Riyadh, Saudi Arabia c Department of Experimental Physics and Information-measuring Technology, Lesya, Ukrainka Eastern European University, 13 Voli Avenue, 43025, Luck, Ukraine d Institute of Physics, Cracow University of Technology, ul. Podchorąz_ ych 1, 30-084, Krak� ow, Poland e Nanotechnology and Catalysis Research Center (NANOCAT), University of Malaya, Kuala Lumpur, 50603, Malaysia f Department of Instrumentation and Control Engineering, Faculty of Mechanical Engineering, CTU in Prague, Technicka 4, Prague 6 166 07, Czech Republic g Physics Department, College of Science, Basrah University, Basrah, Iraq h Institute of Optoelectronics and Measuring Systems, Faculty of Electrical Engineering, Czestochowa University of Technology, Armii Krajowej 17 Str., 42-200, Czestochowa, Poland b
A R T I C L E I N F O
A B S T R A C T
Keywords: CdBr2/Cu Polymer nanocomposites NLO Laser-stimulated effects Electrooptics
Photostimulated linear electrooptical effects (LEOEs) in the CdBr2/Cu polymer nanocomposites have been established. The phototreatment was carried out using two bicolor coherent beams with Er: glass laser pulses at coherent frequencies 1540 nm and 770 nm. The detection of the LEOE was performed by three wavelengths (633 nm, 1150 nm, and 3390 nm) of continuous-wave (cw) He–Ne laser. The monitoring of the laser-stimulated LEOE has been done immediately after illumination, using the Senarmont method. The fundamental beam was formed by Er: glass laser with pulse time duration about 20 ns and pulse frequency repetition about 10 Hz. The nano crystallites of the layered crystallites possessed a thickness varying from 1 nm to 200 nm. The contents of the composites have been varied in the polyvinyl alcohol (PVA) matrices. The principal role here is played by Cu ions participating in the ionic conductivity, which favors an internal charged dc-electric field and related photo refraction. The later, in turn, is sensitive to the wavelengths of probing beams. We explored both dependences versus the nanocrystalline thickness as well as the nonlinear optical (NLO) chromophore concentration. This particular study is devoted to the microscopy of the laser-stimulated changes of the crystallites embedded into the matrices.
1. Introduction The layered semiconductors and dielectrics are promising due to a convenient fabrication of the specimens, possessing high anisotropy of chemical bonds within and perpendicularly to parallelly oriented layers [1,2]. Furthermore, interesting materials are the layered dielectrics based on metal dihalogenides (e.g. CdX2) [3,4]. Here, the layered metal-dihalogenide materials are of principal interest due to the occurrence of natural interfaces with optical surfaces that do not require the application of sophisticated vacuum deposition techniques [5]. Such dihalogenides have been explored relatively well [6] and high anisot ropy layered crystals doped by transition metals (e.g., Cu) [7] are more
suitable due to the possibility of fabrication of high-quality materials with thickness <10 nm. Additionally, some role here is played by phonon anharmonicities which in turn favor the laser-induced and NLO effects [8]. Recently, laser-stimulated studies were carried out mainly for chalcogenides [9]. However, the chalcogenides possess huge irre versible effects that limit their practical application [10]. Most of the earlier studies for the laser-photoinduced changes utilized one- and two photoinduced beams [11]. However, in the case of highly anisotropic crystallites doped with Cu, the principal role begin to play is self-polarization due to probing beams [12]. For layered highly aniso tropic materials, the effects are caused by the low-powered beams, which simultaneously self-modulate due to the low-dimensional
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (G. Lakshminarayana), [email protected] (I.V. Kityk). https://doi.org/10.1016/j.physe.2019.113904 Received 12 October 2019; Received in revised form 17 December 2019; Accepted 17 December 2019 Available online 23 December 2019 1386-9477/© 2019 Elsevier B.V. All rights reserved.
G. Lakshminarayana et al.
Physica E: Low-dimensional Systems and Nanostructures 118 (2020) 113904
Fig. 1. A principal set-up for the laser-stimulated bicolor coherent treatment by 1540/770 nm beams.
Fig. 3. Dependence of the diagonal LEOE tensor coefficients versus the di ameters of the photoinduced beams at probing wavelengths 633 nm, 1150 nm, and 3390 nm. Piezooptical coefficient should be multiplied by 10 14..
Fig. 2. Dependence of the LEOE constants for different probing beams versus power densities of the bicolor photoinduced beams.
localized nanotrapping levels within the forbidden energy gap. Among the layered materials, very promising are Cd dihalogenides. However, the application of two and more coherent laser-stimulated beams may favor principally different effects due to the formation of the space-grating patterns [13]. The important factor here is the possibility to vary the thickness by the cleavage of the nanocrystalline up to several nm. So, we can operate by the thickness of the nanostructures without using vacuum deposition methods. In this report, we will explore novel laser-induced operation for the optical, microstructural, and elastooptical features study of the mate rials, possessing high anisotropy. Particular attention is devoted to Cudoped materials. Nanolayers are treated by bicolor coherent treat ments at 1540 nm/770 nm wavelengths, which are incident under different angles to the cleaved surfaces (see Fig. 1). The simultaneous illumination is caused by probing continuous-wave He–Ne laser beams for an occurrence of the space patterns that are formed by laserstimulated bicolor beams. They are also crucially dependent on the wavelengths of the probing beams, power densities, and light polariza tion. Here, we used the probing beam both for the phototreatment as well as for self-modulation. We studied the changes of the LEOE effects under the influence of varying laser-stimulated power densities for
CdBr2/Cu nanosheets embedded into the polyvinyl alcohol (PVA) matrices. 2. Experimental The experimental set-up presented in Fig. 1 contains two subsystems: The first one corresponds to the photoinduced channel which is formed by two coherent laser beams with the incident angles variation within the range of 24–56� . At first, the two coherent beams form the gratings within 3–5 min of the treatment. The control of gratings formation reflecting anisotropy is carried out by monitoring the diffraction. The formation of such gratings is most important. For the formation of quasiperiodic gratings, a principally new approach is used. We applied different wavelengths of the probing He–Ne laser (cw) with power about 10 mW as shown in Fig. 1. The influence of two coherent photoinduced beams and their beam diameters are explored. The polarization effect of the photoinduced beam was also studied. The detection of laser-stimulated changes was performed under the influence of the external dc-electric field with frequency about 10 Hz. The Er: glass laser beam with a pulse repetition of about 10 Hz is possessed Gaussian-like diameters varying from 0.5 to 2
G. Lakshminarayana et al.
Physica E: Low-dimensional Systems and Nanostructures 118 (2020) 113904
From Fig. 2, one can notice an occurrence of different dependences of the LEOE constants for probing beams versus the energy density. For instance, the maximal laser-stimulated EOE occurs within the bicolor laser stimulated energy densities varying at 100–140 J/m2. The optimal concentration corresponds to the specimens with 25% content of the nanolayers (NLs). The maximal piezooptical coefficients were achieved for the probing wavelength of 1540 nm (about 2 pm/V) and the respective value is the highest for the energy density of about 140 J/m2. The thermoheating is below 4 K and changes at wavelength 633 nm, about 2 times less value where the maximum is achieved at 150 J/m2. Here, more interesting is the dependence on the 3390 nm wavelength. There are two laser-stimulated maxima – at 63 J/m2 and 150 J/m2. Fig. 3 illustrates the dependence of the diagonal LEOE tensor coefficients versus the diameters of the photoinduced beams at probing wavelengths 633 nm, 1150 nm, and 3390 nm. Here, piezooptical coefficients should be multiplied by 10 14. This one reflects a significant role of phonon subsystem contribution, observed at 1150 nm wavelength. Furthermore, the maximally achieved LEO depends on the thickness. Generally, nanocrystallites below 20 nm thickness demonstrate a significant shift of the absorption band. This observable phenomenon could be due to the influence of the quantum size effect. Previously, some reported works by other researchers also clearly showed the occurrence of nonlinear op tical effects for such crystals [14–16].
Fig. 4. Electronic density of sates: before (1) and after the laser treatment (2).
2.0 mm. The energy density was varied by the rotation of the polarizers. Several interference Glahn filters (P), lenses (L), and mirrors (M) allowed for forming two bicolor coherent beams at wavelengths 1540 nm and 770 nm for illumination of the specimens. The treatment was carried out from 3 to 5 min until the gratings are quasi-periodic, controlled by He–Ne laser. The output quasi-ring patterns have been analyzed using both CCD set up as well as HAMAMATSU photo multipliers with a time resolution of up to 1 ns. The laser beam from the 20 ns Er: glass possessing different polarization and intensities were space-split for two channels at 1540 nm and 770 nm. The thickness of the nanocrystals embedded into the photopolymer PVA matrices has been tuned up to 2 nm. The initial CdBr2: Cu crystallites have been grown by the Bridgman method and were cut by glued tapes perpen dicularly to the optical axes. The basic CdBr2 single crystals possess a trigonal structure. The control of the thickness was performed by opti cally polarized methods. Afterward, the nanolayers were embedded into the PVA photopolymer matrices with the photoinitiators, which were solidified by external UV light with the applied simultaneous dc-electric field. The solidification was performed by cw nitrogen laser at 371 nm with 60 W power. The He–Ne laser spots with 633 nm, 1150 nm, and 3390 nm wavelengths were principal for the monitoring of the bire fringence. The electrooptic effects were monitored and related using the dc-electric field, which serves as the source of the LEOE effect. Here, the probing beam also contributes to photoinduced effects. The beam deviation angles have been varied up to 0.20 . The same laser has been used for the control of the gratings. The optical phase-analyzer possessing the phase wave plates λ/4 and rotating analyzer have been used for the control of the changes of the optical phases, directly con nected with the birefringence. The mechanical stress has been applied perpendicularly to the samples along the crystallographic axes ‘x’ and ‘y’. These measurements are based on the determination of the bire fringence under applied mechanical stress directly related to the pie zooptics. After each cycle of the photoinduced bicolor treatment, the control of the piezooptics has been done.
3.1. Phenomenology of the photoinduced effects For the description of the influence of laser-stimulated effects on the polarization of the medium determining the space charge density dis tribution, it is necessary to consider the interaction of the electrical components for the changes of polarization. To consider the laser and electrical-induced medium polarization, it should be introduced in eight rank tensor as given below form: ðωÞ
ðωÞ
ðωÞ
ðΩ1 Þ
ΔPi ¼ rijklmnsp Ecw;j ⋅Ecw:El ⋅Em ⋅En
ðΩ2 Þ
⋅Es
(1)
ðΩ3 Þ
⋅Ep
Here, light-stimulated medium polarization changes due to illumi nation both by the low power cw laser, which is directly related to the photo-stimulated charging of the localized Cu 3d states and stimulated anisotropy caused by high power pulses, where it can favor an appear ance of laser-stimulated birefringence, formed by two coherent laser beams. As a consequence, during the birefringence measurements, there occur grating patterns. The PVA matrices are very favorable for such kind of effects. The eq. (1) takes into account both electronic and anharmonic phonon dc-vector components. This one is also enhanced due to an external dc-electric field due to electrooptical effects. Both the linear as well as quadratic electrooptical effects are responsible for the observed changes. Moreover, there appears some electrostriction and laser-stimulated elastooptical effects [13], which may be expressed by a fourth rank polar tensor Rijkl : (2)
Δnij ¼ Rijkl Pj Pk Pl
To clarify the contribution of the electronic density of states, we have carried out band structure simulations within the framework of density functional theory (DFT) approaches. The Cd–Br6 octahedral structural fragments play here a crucial role for the evaluations of the space charge density distribution for principal structural fragments before and after external field treatment. The initial cluster has been additionally modified by an effective dc-electric field. The σ jk - stress second-order
3. Results and discussion
tensor; El
ðωÞ
We have explored the two principal tensor components of EOE at different probing wavelengths of cw He–Ne laser at 633 nm, 1150 nm, and 3390 nm. The main changes were observed for diagonal tensor components. The dc-electric field was applied perpendicularly to the He–Ne laser beams propagation.
- effective electric field components are averaged in time
for the corresponding electromagnetic wave. En - averaged compo nents of the phonon displacements including the inter-layer rigid ions. As a basis for calculations, we have used norm-conserving pseudo potential parametrization as introduced in Ref. [17]. We solved a secular matrix using the following set of equations: ðΩ1 Þ
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Physica E: Low-dimensional Systems and Nanostructures 118 (2020) 113904
Fig. 5. Changes of the nanolayered aggregates under the influence of different probing beams: a) before the laser treatment, b) 633 nm, c) 1150 nm, d) 3390 nm wavelength.
�� 2 � � h ðk þ Gn Þ2 2m
X � EðkÞ δn;n’ þ Vα G’n
� Gn Sα G’n
�� Gn � ¼ 0
(3)
E(k) corresponds to eigenenergy for a k-BZ space direction. Gn’,Gn –plane-wave basis vectors Structural form-factors has been introduced as: . X � � � � (4) Sβ G’n Gn ¼ gðβÞ ΩNa exp i G’n Gn τβ Here, g(β) - a coefficient corresponding to partial contributions of the reconstructed atomic positions, which has been obtained using a mo lecular dynamics (MD) geometry optimization. It has been taken into account for structural rearrangements due to the presence of Cu ions. The basis contained about 72000 plane-waves with an additional Lowdin basis set. Fourier transform pseudopotential has been presented in a form: � Z � � � � Vα G’n Gn ¼ 1 Ω Vα ðrÞexp (5) i G’n Gn r Fig. 6. The output beam patterns after additional preliminary treatment by two laser beams at 633 nm and 3390 nm wavelength.
The screening potential has been calculated within a framework of Perdew-Zunger screening potential. 4
G. Lakshminarayana et al.
Physica E: Low-dimensional Systems and Nanostructures 118 (2020) 113904
another at 150 J/m2. This one may open up a new stage for the design of novel photonic gratings and triggers. The significant role of the phonon subsystem contribution was identified at 1150 nm wavelength. More over, the maximally achieved LEO depends on the sample thickness.
Acceleration of the interaction calculations convergence was ach ieved by transferring 82% of the (m-1)-th interaction concerning the previous one. A coincidence is assumed to be ~2.05. It should be emphasized that all one-electron methods favor an underestimation of the Eg. As a consequence, self-energy correction renormalization including scissor factor was included in the energy gap calculations. Fig. 4 presents the DOS changes during the treatment as described above. One can see that the DOS is red-shifted, which in turn may favor enhanced optical effects like piezooptics. Additionally, using the TEM microscopy we observed significant changes of the nanolayer aggregates at different probing wavelengths. One can see that in all the cases, there occur a space quasi-periodic patterns for the piezooptical coefficients versus the power densities and it is sensitive to the beam diameters. The aggregation of the nano layer is changed drastically. The observed aggregates are not only con nected with the photoinduced two-beam periods but also reflect an interaction with low power beams due to the changes of the internal dcelectric field, causing Kerr effects. Following Fig. 5(b–d) one can notice that the space morphology crucially depends on the wavelength of the probing lasers. The effect exists for at least 10 min and is extended up to several days depending on the relative polarization and intensities of the laser-stimulated beams. However, it is difficult to find more clear de pendences. The principal role here begins to play by Cu ions due to the presence of 3d localized bonds. Moreover, any irreversible changes have not been observed after switching off the photoinduced lasers. Several times repeated laser treatment did not change significantly the achieved effects. The influence of the probing beams may be explained first of all by photopolarization of the Cu-doped ions. After the treatment by 2 ns lasers together with probing beams at wavelengths 633 nm and 3390 nm during applied pressure, the CCD reconstructed picture is changed drastically (see Fig. 6). So, by varying the probing laser beams, one can observe a lot of different patterns with varied quasi-periods. After laser treatment, there occur many patterns and their fre quencies are also dependent on the low power cw laser probing wave length. These patterns are observed only during the superposition of the external mechanic field. The effect reflects an interference of two laser beams due to linear and parametrical optical effects, like the optical Kerr effect, which also depends on the probing He–Ne laser beams. This fact allows using these methods for the creation of the gratings which are crucial for various photonic devices application. The role of the anhar monic phonons subsystem here may be crucial because it is closely related with the photorefraction. Depending on the ratio of the partic ular intensities of the coherent beam signals, the patterns appear for 10 min up to several days. Now the main efforts will be devoted to the formation of the grating patterns with quasi-periods varied within a wide range of periods.
CRediT authorship contribution statement G. Lakshminarayana: Formal analysis, Writing - review & editing. A.M. El-Naggar: Formal analysis, Funding acquisition. G.L. Myr onchuk: Investigation, Software, Data curation. E. Gondek: Investiga tion, Software, Data curation. A.H. Reshak: Formal analysis, Validation. P. Czaja: Software, Investigation, Data curation. I.V. Kityk: Conceptualization, Resources, Formal analysis, Validation, Supervision, Writing - original draft, Funding acquisition, Project administration. Acknowledgements The authors are grateful to the Deanship of Scientific Research, King Saud University for funding through Vice Deanship of Scientific Research Chairs. Also, this work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. NRF-2018R1A5A1025137) through a Research Professor position at ICA Center, Kyungpook National University (KNU), South Korea. References [1] S. Cho, S.-Ji Min, M.-Y. Cho, Ik-S. Kim, So-M. Kim, B.-M. Moon, K.-S. Moon, D. Lee, J.-M. Oh, S.-M. Koo, Bipolar charge transport in intrinsic SiC on p- and n-Si heterostructures prepared by a room temperature aerosol deposition process, Ceram. Int. 45 (2019) 17556–17561. [2] Q. Wang, Z. Zhao, H. Li, J. Zhuang, Z. Ma, Y. Yang, L. Zhang, Y. Zhang, One-step RF magnetron sputtering method for preparing Cu(In, Ga)Se2 solar cells, J. Mater. Sci. Mater. Electron. 29 (2018) 11755–11762. [3] Y. Huang, K. Xu, Z. Wang, T.A. Shifa, Q. Wang, F. Wang, C. Jiang, J. He, Designing the shape evolution of SnSe2 nanosheets and their optoelectronic properties, Nanoscale 7 (41) (2015) 17375–17380. [4] Z. Yin, H. Li, H. Li, L. Jiang, Y. Shi, Y. Sun, G. Lu, Q. Zhang, X. Chen, H. Zhang, Single-layer MoS2 phototransistors, ACS Nano 6 (1) (2011) 74–80. [5] J. Schornbaum, B. Winter, S.P. Schießl, F. Gannott, G. Katsukis, D.M. Guldi, E. Spiecker, J. Zaumseil, Epitaxial growth of PbSe quantum dots on MoS2 nanosheets and their near-infrared photoresponse, Adv. Funct. Mater. 24 (37) (2014) 5798–5806. _ Kariper, Structural, optical and porosity properties of CdI2 thin film, J. Mater. [6] I. Res. Technol. 5 (2016) 77–83. [7] I. Bolesta, S. Velgosh, D. Yu, I. Karbowmnyk, M. Piccini, The electronic and optical properties of Cu doped CdI2, Optik 124 (2013) 3230–3234. [8] C. Chen, Nano-confined and copper-defect in wide-bandgap semiconductors, Opt. Commun. 284 (2011) 5199–5202. [9] O.V. Parasyuk, G.L. Myronchuk, A.O. Fedorchuk, A.M. El-Naggar, A. Albassam, A. S. Krymus, I.V. Kityk, A novel effect of CO2 laser induced piezoelectricity in Ag2Ga2SiS6 chalcogenide crystals, Crystals 6 (2016), 107 (12 pp). [10] K. Ozga, O.M. Yanchuk, L.V. Tsurkova, O.V. Marchuk, I.V. Urubkov, Y. E. Romanyuk, O. Fedorchuk, G. Lakshminarayana, I.V. Kityk, Operation by optoelectronic features of cadmium sulphide nanocrystallites embedded into the photopolymer polyvinyl alcohol matrices, Appl. Surf. Sci. 446 (2018) 209–214. [11] O.I. Shpotyuk, J. Kasperczyk, I.V. Kityk, Mechanism of reversible photoinduced optical effects in amorphous As2S3, J. Non-Cryst. Solids 215 (1997) 218–225. [12] I.V. Kityk, S.A. Pyroha, T. Mydlarz, J. Kasperczyk, M. Czerwinski, Magnetic field induced ferroelectricity in copper doped CdI2 sincgle crystals, Ferroelectrics 205 (1998) 107–118. [13] A. Migalska-Zalas, Z. Sofiani, B. Sahraoui, I.V. Kityk, V. Yuvshenko, J.L. Fillaut, J. Perruchon, T.J.J. Muller, χ(2) grating in Ru derivative chromophores incorporated within the PMMA polymer matrices, J. Phys. Chem. B 108 (2004) 14942–14947. [14] I.M. Bolesta, I.V. Kityk, V.I. Kovalisko, Luminescence and nonlinear optical properties of Me-CdI2 (Me¼Ag, Au) heterostructures, Phys. Solid State 36 (1994) 1880–1882. [15] M.I. Miah, Size effect on the SHG properties of Cu-doped CdI2 nanocrystals, Appl. Surf. Sci. 256 (2009) 1472–1475. [16] M.I. Miah, J. Kasperczyk, Cu-doping effects in CdI2 layered nanostructures: the role of photoinduced electron-phonon anharmonic interactions, Appl. Phys. Lett. 94 (2009), 053117. [17] I.V. Kityk, A. Kassiba, K.J. Plucinski, J. Berdowski, Band structure of the large-sized SiC nanocomposites, Phys. Lett. A 265 (2000) 403–410.
4. Conclusions In summary, during bicolor laser treatment at 1540 nm/770 nm ns Er: glass laser wavelengths and continuous wavelengths at 633 nm, 1150 nm, and 3390 nm, we have found an occurrence of the gratings patterns, which are very sensitive to the wavelengths of low-power He–Ne laser. This phototreatment of using several beams, leading to the formation of the grating patterns could be promising for the nano photonics application. The maximal laser-stimulated EOE was noticed within the bicolor laser-stimulated energy densities varying at 100–140 J/m2 range. The optimal concentration corresponds to the specimens with 25% content of the nanolayers. The maximal piezooptical co efficients were achieved for a probing wavelength of 1540 nm (~2 pm/ V). This value is identified for the energy density of about 140 J/m2. The thermoheating is below 4 K and changes at 633 nm wavelength to about two times less value, and the maximum is achieved at 150 J/m2. Further, a more interesting result is dependence on the wavelength of 3390 nm. There observed two laser-stimulated maxima: one at 63 J/m2 and
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