- Email: [email protected]
Generation of polarization enhanced THz waves from holey nitrogenated graphene
Optik - International Journal for Light and Electron Optics 178 (2019) 712–716
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.com/locate/ijleo
Original research article
Generation of polarization enhanced THz waves from holey nitrogenated graphene
T
⁎
Muhammad Irfan , Sara Ashraf Department of Electrical Engineering, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan 64200, Pakistan
A R T IC LE I N F O
ABS TRA CT
Keywords: C2N Terahertz Polarization
We manipulate amplitude of terahertz waves emitted from holey nitrogenated graphene by circularly polarized light which is further substantiated by considering components of photocurrents in holey structure. In addition, variations in parameters such as excitation fluence and azimuthal angle along with effect of different substrates and in-plane magnetic field provide insight into underlying mechanism for THz generation. The different forms of graphite have also been experimentally compared in order to elaborate the effect of material’s parameters on generated THz amplitude.
1. Introduction Carbon-based nanomaterials have been considered as emerging materials due to their fascinating optical or structural properties for generation, modulation, and detection of terahertz (THz) electromagnetic waves [1,2]. The emerging applications of THz radiation such non-destructive imaging [3,4], communication [5], etc. could be realized by efficiently manipulating the amplitude of THz waves especially desirable to achieve strong and tunable table-top THz sources. Previous studies indicated that graphene might be a strong candidate for ultra-broadband terahertz sources [6] owing to extremely high mobility due to massless Dirac-fermion behavior. Although linear dispersion of monoatomic graphene restrict the electronic acceleration resulting in severely limiting its applications [7]. However, THz generations from graphene has been reported by several groups based on different underlying mechanisms [8,9]. On the other hand, in the case of graphite, the surface field manipulation can modifying the electrical transports via external bias, doping and interfacial workfunction offsets. The surface field driving photon from voltage biased graphite resulted in terahertz pulses which could be tuned by the gating field effect on graphite [10]. Likewise, the work function engineering among air, graphite, and metals allowed a viable route to tuning the graphitic energy profiles and manipulating the THz radiation features [11,12]. So it is still desirable to develop 2D or 3D planar novel functionalized graphene with a suitable band gap and structure possibly capable of controlling the transport properties for nanoelectronic and THz applications. Recently, novel functionalized holey graphene incorporated with nitrogen atoms has been synthesized synthesized via a wet-chemical reaction with an optical band gap of 1.96 eV which could possibly useful in manipulating the transport properties due to holey ring structure [13]. However, this novel holey graphene structure has not been explored in terms of the relationship between THz generation and carrier transport properties, even though features regarding structural, photonics and thermal properties have been reported [14,15]. Here, we examine the THz emission spectra from holey nitrogenated graphene in order to probe the structural effects for different polarization of excitation beam. To gain a better understanding of the underlying mechanisms involved for THz generation, we
⁎
corresponding author . E-mail address: [email protected] (M. Irfan).
https://doi.org/10.1016/j.ijleo.2018.10.064 Received 19 August 2018; Accepted 8 October 2018 0030-4026/ © 2018 Elsevier GmbH. All rights reserved.
Optik - International Journal for Light and Electron Optics 178 (2019) 712–716
M. Irfan, S. Ashraf
Fig. 1. Holey nitrogenated graphene, designated as C2N-h2D crystal (a-b). SEM images of C2N on SiO2/Si (c).
further examine the effect of the azimuthal angle, excitation power, and different substrates. 2. Sample and experimental schemes C2N crystal was synthesized by the reaction between hexaaminobenzene (HAB) trihydrochloride and hexaketocyclohexane (HKH) octahydrate in N-methyl-2-pyrrolidone (NMP) in the presence of a few drops of trifluoromethanesulphonic acid. The resultant graphite-like solid whose dark black appearance was a strong indication of the formation of a conjugated layered 2D crystal, was Soxhlet extracted with water and then methanol, respectively, to completely remove any small mass impurities and was finally freezedried at −120 °C under reduced pressure (0.05 mmHg). Utilizing such a strong driving force for the aromatization, the 3D fused pconjugated microporous polymers were also conveniently realized by solvothermal reaction in the sealed glass tube and ionothermal process in the presence of AlCl3 for energy storage. The sample solution was casted onto a SiO2 substrate, followed by annealing at 700 °C under an argon atmosphere and collected by etching in hydrofluoric acid [13]. The sample thickness was around 300 nm as shown Fig. 1(c) in SEM image. Conventional THz time-domain spectroscopy (THz-TDS) was employed at 300 K. The laser source was focused onto a spotsize of 300 μm and the incident angle θ was 45° in the reflection geometry. Following femtosecond pulse pumping, the generated THz wave packets from the samples were guided using a pair of off-axis parabolic mirrors and focused on photo-conductive antenna whose sensitivity was optimized at 1 THz. 3. Results and discussion The nitrogen-incorporated holey graphene structure provide bandgap opening together with the circular path available for carrier motion along the lateral unit-cell networks. In this holey structure, the circularly polarized laser excitation produced enhanced THz transients as compared to the signals with linearly polarized configuration as shown in Fig. 2 under IR (800 nm) irradiation. This could be associated with the directed motion of carriers in circular path under circularly polarized light. This can be further substantiated by considering the polarization of light on the surface of material and resultant photocurrents generated from it indicated in Fig. 3. Only one component is allowed for linear polarization ideally in the direction of momentum shown as Jx. However for circular polarization, it induced two components: longitudinal Jx and transversal Jy components. Both rises to stronger resultant current than in the linear case. Similarly these photocurrents further leads to THz emission. In addition to transient photocurrents, contributions in THz generation from optical nonlinear processes could be examined in our experimental schemes by rotating the samples around surface normal and by increasing the excitation fluence in the reflective geometry as shown in Fig. 4. Nonlinear process conventionally follows well-defined periodicity in azimuthal measurements such as four fold symmetry in (100) InAs and six fold symmetry in (111) InAs [16]. However, THz amplitude variations showed negligibly small azimuthal angle dependence φ which suggested that the transient photocurrents were symmetric along the surface normal of structure as depicted in Fig. 3(a). Slight variation could be assigned to stacking faults or misaligned layers of holey graphene along surface normal. The signal amplitude grows linearly with increasing pump power, without any indication of saturation as shown in Fig. 3(b). This behavior implies that the number of excited carriers is proportional to the incident photon number and nonlinear optical effects can be safely neglected. 713
Optik - International Journal for Light and Electron Optics 178 (2019) 712–716
M. Irfan, S. Ashraf
Fig. 2. THz amplitude in reflective geometry for IR excitation (800 nm). LP, RCP and LCP stands for linear, right and left circular polarization, respectively. Inset shows the FFT spectra (log. scale).
Fig. 3. Schematic illustration of the photocurrents due to linear and circular polarization of excitation beam.
Fig. 4. (a) Azimuthal angle dependence of the THz field amplitude. (b) THz field amplitude measured as a function of excitation power. Red line indicates the linear fitting. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
714
Optik - International Journal for Light and Electron Optics 178 (2019) 712–716
M. Irfan, S. Ashraf
Fig. 5. Comparison of THz emitted field between C2N, HOPG and Natural Graphite. Inset shows the FFT spectra (linear scale).
THz transients from natural graphite and highly oriented pyrolytic graphite (HOPG) have been compared with C2N in order to explain its narrow THz spectra shown in Fig. 5. The time domain signal for C2N is broaden as compared to natural graphite and HOPG because of very low mobility of carriers due to holes in the structures [13]. HOPG and natural graphite single crystal is well grown sample along c-axis having very high electronic mobility [17], however C2N is thin film with holes in structure which hinder the carrier's movement and results in small spectral width in THz emission. In order to take advantage of preferential path available for carriers, in-plane magnetic field of 0.1T has been applied to accelerate the carriers. However in view point of quality of sample and net carrier movement, no significant enhancement of THz pulses has been observed. Magnetic effect may be observed at high magnetic field and/or at low temperature. Since, magnetic moment vs. applied magnetic field at low temperature shows paramagnetic behavior which implies the existence of optically induced magnetic effects (not shown here) which will be discussed later somewhere else. 4. Conclusion In summary, we experimentally characterize THz electromagnetic waves emitted from holey nitrogenated graphene. We interpreted the enhancement of THz field between linear and circular polarization of excitation beams as a demonstration of carrier motion in preferred circular paths available in the structure rather than along light momemtum direction. We also demonstrated that azimuthal angle change do not affect the THz amplitude implying the symmetry of structure. Such manipulation of THz pulses could be important in understanding the carrier transport and optical phenomenon in functional THz devices. Moreover, C2N-h2D multilayers is a very promising material for future applications in optoelectronics especially by exploring stacking order, layer numbers, external electric and magnetic fields for THz and photonics applications. Acknowledgments We would like to thank Prof. Young-Dahl Jho (GIST, Korea) for stimulating discussions, and Dr. Javeed Mahmood (UNIST, Korea) for providing samples. References [1] M. Xu, T. Liang, M. Shi, H. Chen, Graphene-like two-dimensional materials, Chem. Rev. 113 (2013) 3766–3798. [2] P. Tassin, T. Koschny, C.M. Soukoulis, Graphene for terahertz applications, Science 341 (2013) 620–621. [3] S.S. Dhillon, M.S. Vitiello, E.H. Linfield, A.G. Davies, M.C. Hoffmann, J. Booske, C. Paoloni, M. Gensch, P. Weightman, G.P. Williams, E. Castro-Camus, D.R.S. Cumming, F. Simoens, I. Escorcia-Carranza, J. Grant, S. Lucyszyn, M. Kuwata-Gonokami, K. Konishi, M. Koch, C.A. Schmuttenmaer, T.L. Cocker, R. Huber, A.G. Markelz, Z.D. Taylor, V.P. Wallace, J.A. Zeitler, J. Sibik, T.M. Korter, B. Ellison, S. Rea, P. Goldsmith, K.B. Cooper, R. Appleby, D. Pardo, P.G. Huggard, V. Krozer, H. Shams, M. Fice, C. Renaud, A. Seeds, A. Stöhr, M. Naftaly, N. Ridler, R. Clarke, J.E. Cunningham, M.B. Johnston, The 2017 terahertz science and technology roadmap, J. Phys. D 50 (2017) 043001. [4] X. Yang, X. Zhao, K. Yang, Y. Liu, Y. Liu, W. Fu, Y. Luo, Terahertz radiation and second-harmonic generation from InAs: bulk versus surface electric-field-induced contributions, Trends Biotechnol. 34 (2016) 810. [5] J. Federici, L. Moeller, Review of terahertz and subterahertz wireless communications, J. Appl. Phys. 107 (2010) 111101. [6] J.A. Crosse, X. Xu, M.S. Sherwin, R.B. Liu, Theory of low-power ultra-broadband terahertz sideband generation in bi-layer graphene, Nat. Commun. 5 (2014) 4854. [7] K. Novoselov, A. Geim, S. Morozov, D. Jiang, M. Katsnelson, I. Grigorieva, S. Dubonos, A. Firsov, Two-dimensional gas of massless dirac fermions in graphene, Nature 438 (2005) 197–200. [8] C.-H. Liu, Y.-C. Chang, S. Lee, Y. Zhang, Y. Zhang, T.B. Norris, Z. Zhong, Ultrafast lateral photo-dember effect in graphene induced by nonequilibrium hot carrier dynamics, Nano Lett. 15 (2015) 4234–4239. [9] J. Maysonnave, S. Huppert, F. Wang, S. Maero, C. Berger, W. de Heer, T.B. Norris, L.A. De Vaulchier, S. Dhillon, J. Tignon, R. Ferreira, J. Mangeney, Terahertz generation by dynamical photon drag effect in graphene excited by femtosecond optical pulses, Nano Lett. 14 (2014) 5797–5802. [10] T. Ye, S. Meng, J. Zhang, E. Yiwen, Y. Yang, W. Liu, Y. Yin, L. Wang, Mechanism and modulation of terahertz generation from a semimetal-graphite, Sci. Rep. 6 (2016) 22798. [11] M. Irfan, J.-H. Yim, C. Kim, S.W. Lee, Y.-D. Jho, Phase change in terahertz waves emitted from differently doped graphite: the role of carrier drift, Appl. Phys.
715
Optik - International Journal for Light and Electron Optics 178 (2019) 712–716
M. Irfan, S. Ashraf
Lett. 103 (2013) 201108. [12] M. Irfan, S.K. Lee, J.-H. Yim, Y.T. Lee, Y.-D. Jho, Manipulation of terahertz waves by work function engineering in metal-graphite structures, Appl. Phys. Lett. 108 (2016) 161104. [13] J. Mahmood, E.K. Lee, M. Jung, D. Shin, I. Jeon, S. Jung, H. Choi, J. Seo, S. Bae, S. Sohn, N. Park, J. Oh, H. Shin, J. Baek, Nitrogenated holey two-dimensional structures, Nat. Commun. 6 (2015) 6486. [14] H. Sahin, Structural and phononic characteristics of nitrogenated holey graphene, Phys. Rev. B 92 (2015) 085421. [15] B. Mortazavi, O. Rahaman, T. Rabczuk, L.F.C. Pereira, Thermal conductivity and mechanical properties of nitrogenated holey graphene, Carbon 106 (2016) 1. [16] M. Reid, I.V. Cravetchi, R. Fedosejevs, Terahertz radiation and second-harmonic generation from InAs: bulk versus surface electric-field-induced contributions, Phys. Rev. B 72 (2005) 035201. [17] L. Pendrys, C. Zeller, F. Vogel, Electrical transport properties of natural and synthetic graphite, J. Mater. Sci. 15 (1980) 2103.
716
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.com/locate/ijleo
Original research article
Generation of polarization enhanced THz waves from holey nitrogenated graphene
T
⁎
Muhammad Irfan , Sara Ashraf Department of Electrical Engineering, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan 64200, Pakistan
A R T IC LE I N F O
ABS TRA CT
Keywords: C2N Terahertz Polarization
We manipulate amplitude of terahertz waves emitted from holey nitrogenated graphene by circularly polarized light which is further substantiated by considering components of photocurrents in holey structure. In addition, variations in parameters such as excitation fluence and azimuthal angle along with effect of different substrates and in-plane magnetic field provide insight into underlying mechanism for THz generation. The different forms of graphite have also been experimentally compared in order to elaborate the effect of material’s parameters on generated THz amplitude.
1. Introduction Carbon-based nanomaterials have been considered as emerging materials due to their fascinating optical or structural properties for generation, modulation, and detection of terahertz (THz) electromagnetic waves [1,2]. The emerging applications of THz radiation such non-destructive imaging [3,4], communication [5], etc. could be realized by efficiently manipulating the amplitude of THz waves especially desirable to achieve strong and tunable table-top THz sources. Previous studies indicated that graphene might be a strong candidate for ultra-broadband terahertz sources [6] owing to extremely high mobility due to massless Dirac-fermion behavior. Although linear dispersion of monoatomic graphene restrict the electronic acceleration resulting in severely limiting its applications [7]. However, THz generations from graphene has been reported by several groups based on different underlying mechanisms [8,9]. On the other hand, in the case of graphite, the surface field manipulation can modifying the electrical transports via external bias, doping and interfacial workfunction offsets. The surface field driving photon from voltage biased graphite resulted in terahertz pulses which could be tuned by the gating field effect on graphite [10]. Likewise, the work function engineering among air, graphite, and metals allowed a viable route to tuning the graphitic energy profiles and manipulating the THz radiation features [11,12]. So it is still desirable to develop 2D or 3D planar novel functionalized graphene with a suitable band gap and structure possibly capable of controlling the transport properties for nanoelectronic and THz applications. Recently, novel functionalized holey graphene incorporated with nitrogen atoms has been synthesized synthesized via a wet-chemical reaction with an optical band gap of 1.96 eV which could possibly useful in manipulating the transport properties due to holey ring structure [13]. However, this novel holey graphene structure has not been explored in terms of the relationship between THz generation and carrier transport properties, even though features regarding structural, photonics and thermal properties have been reported [14,15]. Here, we examine the THz emission spectra from holey nitrogenated graphene in order to probe the structural effects for different polarization of excitation beam. To gain a better understanding of the underlying mechanisms involved for THz generation, we
⁎
corresponding author . E-mail address: [email protected] (M. Irfan).
https://doi.org/10.1016/j.ijleo.2018.10.064 Received 19 August 2018; Accepted 8 October 2018 0030-4026/ © 2018 Elsevier GmbH. All rights reserved.
Optik - International Journal for Light and Electron Optics 178 (2019) 712–716
M. Irfan, S. Ashraf
Fig. 1. Holey nitrogenated graphene, designated as C2N-h2D crystal (a-b). SEM images of C2N on SiO2/Si (c).
further examine the effect of the azimuthal angle, excitation power, and different substrates. 2. Sample and experimental schemes C2N crystal was synthesized by the reaction between hexaaminobenzene (HAB) trihydrochloride and hexaketocyclohexane (HKH) octahydrate in N-methyl-2-pyrrolidone (NMP) in the presence of a few drops of trifluoromethanesulphonic acid. The resultant graphite-like solid whose dark black appearance was a strong indication of the formation of a conjugated layered 2D crystal, was Soxhlet extracted with water and then methanol, respectively, to completely remove any small mass impurities and was finally freezedried at −120 °C under reduced pressure (0.05 mmHg). Utilizing such a strong driving force for the aromatization, the 3D fused pconjugated microporous polymers were also conveniently realized by solvothermal reaction in the sealed glass tube and ionothermal process in the presence of AlCl3 for energy storage. The sample solution was casted onto a SiO2 substrate, followed by annealing at 700 °C under an argon atmosphere and collected by etching in hydrofluoric acid [13]. The sample thickness was around 300 nm as shown Fig. 1(c) in SEM image. Conventional THz time-domain spectroscopy (THz-TDS) was employed at 300 K. The laser source was focused onto a spotsize of 300 μm and the incident angle θ was 45° in the reflection geometry. Following femtosecond pulse pumping, the generated THz wave packets from the samples were guided using a pair of off-axis parabolic mirrors and focused on photo-conductive antenna whose sensitivity was optimized at 1 THz. 3. Results and discussion The nitrogen-incorporated holey graphene structure provide bandgap opening together with the circular path available for carrier motion along the lateral unit-cell networks. In this holey structure, the circularly polarized laser excitation produced enhanced THz transients as compared to the signals with linearly polarized configuration as shown in Fig. 2 under IR (800 nm) irradiation. This could be associated with the directed motion of carriers in circular path under circularly polarized light. This can be further substantiated by considering the polarization of light on the surface of material and resultant photocurrents generated from it indicated in Fig. 3. Only one component is allowed for linear polarization ideally in the direction of momentum shown as Jx. However for circular polarization, it induced two components: longitudinal Jx and transversal Jy components. Both rises to stronger resultant current than in the linear case. Similarly these photocurrents further leads to THz emission. In addition to transient photocurrents, contributions in THz generation from optical nonlinear processes could be examined in our experimental schemes by rotating the samples around surface normal and by increasing the excitation fluence in the reflective geometry as shown in Fig. 4. Nonlinear process conventionally follows well-defined periodicity in azimuthal measurements such as four fold symmetry in (100) InAs and six fold symmetry in (111) InAs [16]. However, THz amplitude variations showed negligibly small azimuthal angle dependence φ which suggested that the transient photocurrents were symmetric along the surface normal of structure as depicted in Fig. 3(a). Slight variation could be assigned to stacking faults or misaligned layers of holey graphene along surface normal. The signal amplitude grows linearly with increasing pump power, without any indication of saturation as shown in Fig. 3(b). This behavior implies that the number of excited carriers is proportional to the incident photon number and nonlinear optical effects can be safely neglected. 713
Optik - International Journal for Light and Electron Optics 178 (2019) 712–716
M. Irfan, S. Ashraf
Fig. 2. THz amplitude in reflective geometry for IR excitation (800 nm). LP, RCP and LCP stands for linear, right and left circular polarization, respectively. Inset shows the FFT spectra (log. scale).
Fig. 3. Schematic illustration of the photocurrents due to linear and circular polarization of excitation beam.
Fig. 4. (a) Azimuthal angle dependence of the THz field amplitude. (b) THz field amplitude measured as a function of excitation power. Red line indicates the linear fitting. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
714
Optik - International Journal for Light and Electron Optics 178 (2019) 712–716
M. Irfan, S. Ashraf
Fig. 5. Comparison of THz emitted field between C2N, HOPG and Natural Graphite. Inset shows the FFT spectra (linear scale).
THz transients from natural graphite and highly oriented pyrolytic graphite (HOPG) have been compared with C2N in order to explain its narrow THz spectra shown in Fig. 5. The time domain signal for C2N is broaden as compared to natural graphite and HOPG because of very low mobility of carriers due to holes in the structures [13]. HOPG and natural graphite single crystal is well grown sample along c-axis having very high electronic mobility [17], however C2N is thin film with holes in structure which hinder the carrier's movement and results in small spectral width in THz emission. In order to take advantage of preferential path available for carriers, in-plane magnetic field of 0.1T has been applied to accelerate the carriers. However in view point of quality of sample and net carrier movement, no significant enhancement of THz pulses has been observed. Magnetic effect may be observed at high magnetic field and/or at low temperature. Since, magnetic moment vs. applied magnetic field at low temperature shows paramagnetic behavior which implies the existence of optically induced magnetic effects (not shown here) which will be discussed later somewhere else. 4. Conclusion In summary, we experimentally characterize THz electromagnetic waves emitted from holey nitrogenated graphene. We interpreted the enhancement of THz field between linear and circular polarization of excitation beams as a demonstration of carrier motion in preferred circular paths available in the structure rather than along light momemtum direction. We also demonstrated that azimuthal angle change do not affect the THz amplitude implying the symmetry of structure. Such manipulation of THz pulses could be important in understanding the carrier transport and optical phenomenon in functional THz devices. Moreover, C2N-h2D multilayers is a very promising material for future applications in optoelectronics especially by exploring stacking order, layer numbers, external electric and magnetic fields for THz and photonics applications. Acknowledgments We would like to thank Prof. Young-Dahl Jho (GIST, Korea) for stimulating discussions, and Dr. Javeed Mahmood (UNIST, Korea) for providing samples. References [1] M. Xu, T. Liang, M. Shi, H. Chen, Graphene-like two-dimensional materials, Chem. Rev. 113 (2013) 3766–3798. [2] P. Tassin, T. Koschny, C.M. Soukoulis, Graphene for terahertz applications, Science 341 (2013) 620–621. [3] S.S. Dhillon, M.S. Vitiello, E.H. Linfield, A.G. Davies, M.C. Hoffmann, J. Booske, C. Paoloni, M. Gensch, P. Weightman, G.P. Williams, E. Castro-Camus, D.R.S. Cumming, F. Simoens, I. Escorcia-Carranza, J. Grant, S. Lucyszyn, M. Kuwata-Gonokami, K. Konishi, M. Koch, C.A. Schmuttenmaer, T.L. Cocker, R. Huber, A.G. Markelz, Z.D. Taylor, V.P. Wallace, J.A. Zeitler, J. Sibik, T.M. Korter, B. Ellison, S. Rea, P. Goldsmith, K.B. Cooper, R. Appleby, D. Pardo, P.G. Huggard, V. Krozer, H. Shams, M. Fice, C. Renaud, A. Seeds, A. Stöhr, M. Naftaly, N. Ridler, R. Clarke, J.E. Cunningham, M.B. Johnston, The 2017 terahertz science and technology roadmap, J. Phys. D 50 (2017) 043001. [4] X. Yang, X. Zhao, K. Yang, Y. Liu, Y. Liu, W. Fu, Y. Luo, Terahertz radiation and second-harmonic generation from InAs: bulk versus surface electric-field-induced contributions, Trends Biotechnol. 34 (2016) 810. [5] J. Federici, L. Moeller, Review of terahertz and subterahertz wireless communications, J. Appl. Phys. 107 (2010) 111101. [6] J.A. Crosse, X. Xu, M.S. Sherwin, R.B. Liu, Theory of low-power ultra-broadband terahertz sideband generation in bi-layer graphene, Nat. Commun. 5 (2014) 4854. [7] K. Novoselov, A. Geim, S. Morozov, D. Jiang, M. Katsnelson, I. Grigorieva, S. Dubonos, A. Firsov, Two-dimensional gas of massless dirac fermions in graphene, Nature 438 (2005) 197–200. [8] C.-H. Liu, Y.-C. Chang, S. Lee, Y. Zhang, Y. Zhang, T.B. Norris, Z. Zhong, Ultrafast lateral photo-dember effect in graphene induced by nonequilibrium hot carrier dynamics, Nano Lett. 15 (2015) 4234–4239. [9] J. Maysonnave, S. Huppert, F. Wang, S. Maero, C. Berger, W. de Heer, T.B. Norris, L.A. De Vaulchier, S. Dhillon, J. Tignon, R. Ferreira, J. Mangeney, Terahertz generation by dynamical photon drag effect in graphene excited by femtosecond optical pulses, Nano Lett. 14 (2014) 5797–5802. [10] T. Ye, S. Meng, J. Zhang, E. Yiwen, Y. Yang, W. Liu, Y. Yin, L. Wang, Mechanism and modulation of terahertz generation from a semimetal-graphite, Sci. Rep. 6 (2016) 22798. [11] M. Irfan, J.-H. Yim, C. Kim, S.W. Lee, Y.-D. Jho, Phase change in terahertz waves emitted from differently doped graphite: the role of carrier drift, Appl. Phys.
715
Optik - International Journal for Light and Electron Optics 178 (2019) 712–716
M. Irfan, S. Ashraf
Lett. 103 (2013) 201108. [12] M. Irfan, S.K. Lee, J.-H. Yim, Y.T. Lee, Y.-D. Jho, Manipulation of terahertz waves by work function engineering in metal-graphite structures, Appl. Phys. Lett. 108 (2016) 161104. [13] J. Mahmood, E.K. Lee, M. Jung, D. Shin, I. Jeon, S. Jung, H. Choi, J. Seo, S. Bae, S. Sohn, N. Park, J. Oh, H. Shin, J. Baek, Nitrogenated holey two-dimensional structures, Nat. Commun. 6 (2015) 6486. [14] H. Sahin, Structural and phononic characteristics of nitrogenated holey graphene, Phys. Rev. B 92 (2015) 085421. [15] B. Mortazavi, O. Rahaman, T. Rabczuk, L.F.C. Pereira, Thermal conductivity and mechanical properties of nitrogenated holey graphene, Carbon 106 (2016) 1. [16] M. Reid, I.V. Cravetchi, R. Fedosejevs, Terahertz radiation and second-harmonic generation from InAs: bulk versus surface electric-field-induced contributions, Phys. Rev. B 72 (2005) 035201. [17] L. Pendrys, C. Zeller, F. Vogel, Electrical transport properties of natural and synthetic graphite, J. Mater. Sci. 15 (1980) 2103.
716