Source: http://aoot.osa.org/ome/abstract.cfm?uri=ome-7-1-213
Timestamp: 2019-04-22 08:14:13+00:00

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While vanadium dioxide (VO2) is one of the most extensively studied highly correlated materials, there are intriguing similarities and differences worth exploring in another highly correlated oxide, niobium dioxide (NbO2). Both materials exhibit a thermally-induced first-order insulator-metal transition at a material-dependent critical temperature, which is considerably higher in NbO2 than in VO2 – approximately 1080 K and 340 K in bulk, respectively. This transition, evidenced by up to 6 orders of magnitude change in DC and optical conductivities, can also be induced in VO2 via photo-doping on a sub-picosecond timescale. Here, we present the first ultrafast pump-probe studies on the optically-induced transition of NbO2 thin films and the comparison with similar VO2 films. It is observed that NbO2 films transition faster and exhibit significantly faster recovery time than VO2 films of similar thickness and microstructure, showcasing that NbO2 is a promising material for next generation high-speed optoelectronic devices.
W. Yoshiki and T. Tanabe, “All-optical switching using Kerr effect in a silica toroid microcavity,” Opt. Express 22(20), 24332–24341 (2014).
R. C. Hollins, “Materials for optical limiters,” Curr. Opin. Solid State Mater. Sci. 4(2), 189–196 (1999).
S. Perumbilavil, P. Sankar, T. Priya Rose, and R. Philip, “White light Z-scan measurements of ultrafast optical nonlinearity in reduced graphene oxide nanosheets in the 400–700 nm region,” Appl. Phys. Lett. 107(5), 051104 (2015).
G. Steinmeyer, “A review of ultrafast optics and optoelectronics,” J. Opt. A, Pure Appl. Opt. 5(1), R1–R15 (2003).
H. W. Verleur, A. S. Barker, and C. N. Berglund, “Optical properties of VO2 between 0.25 and 5 eV,” Phys. Rev. 172(3), 788–798 (1968).
D. I. Khomskii, Transtion Metal Compounds (Cambridge University 2014).
L. Wang, I. Novikova, J. M. Klopf, S. Madaras, G. P. Williams, E. Madaras, J. Lu, S. A. Wolf, and R. A. Lukaszew, “Distinct length scales in the VO2 metal–insulator transition revealed by bi-chromatic optical probing,” Adv. Opt. Mat. 2(1), 30–33 (2014).
A. Zylbersztejn and N. F. Mott, “Metal-insulator transition in vanadium dioxide,” Phys. Rev. B 11(11), 4383–4395 (1975).
A. Cavalleri, Th. Dekorsy, H. H. W. Chong, J. C. Kieffer, and R. W. Schoenlein, “Evidence for a structurally-driven insulator-to-metal transition in VO2: A view from the ultrafast timescale,” Phys. Rev. B 70, 161102 (2004).
S. Lysenko, A. Rúa, V. Vikhnin, F. Fernández, and H. Liu, “Insulator-to-metal phase transition and recovery processes in VO2 thin films after femtosecond laser excitation,” Phys. Rev. B 76(3), 035104 (2007).
M. Rini, Z. Hao, R. W. Schoenlein, C. Giannetti, F. Parmigiani, S. Fourmaux, J. C. Kieffer, A. Fujimori, M. Onoda, S. Wall, and A. Cavalleri, “Optical switching in VO2 films by below-gap excitation,” Appl. Phys. Lett. 92(18), 181904 (2008).
M. Rodriguez-Vega, M. T. Simons, E. Radue, S. Kittiwatanakul, J. Lu, S. A. Wolf, R. A. Lukaszew, I. Novikova, and E. Rossi, “Effect of inhomogeneties and substrate on the dynamics of the metal-insulator transition in VO2 thin films,” Phys. Rev. B 92(11), 115420 (2015).
G. C. Vezzoli, “Recovery curve for threshold‐switching NbO2,” J. Appl. Phys. 50(10), 6390 (1979).
G. C. Vezzoli, “On‐state decay in NbO2: Relationship to recombination and to nonlinear I‐V,” J. Appl. Phys. 51(5), 2693 (1980).
S. K. Nandi, X. Liu, D. K. Venkatachalam, and R. G. Elliman, “Threshold current reduction for the metal–insulator transition in NbO2−x-selector devices: the effect of ReRAM integration,” J. Phys. D Appl. Phys. 48(19), 195105 (2015).
T. Joshi, T. R. Senty, P. Borisov, A. D. Bristow, and D. Lederman, “Preparation, characterization, and electrical properties of epitaxial NbO2 thin film lateral devices,” J. Phys. D Appl. Phys. 48(33), 335308 (2015).
A. B. Posadas, A. O’Hara, S. Rangan, R. A. Bartynski, and A. A. Demkov, “Band gap of epitaxial in-plane-dimerized single-phase NbO2 films,” Appl. Phys. Lett. 104(9), 092901 (2014).
A. O’Hara, T. N. Nunley, A. B. Posadas, S. Zollner, and A. A. Demkov, “Electronic and optical properties of NbO2,” J. Appl. Phys. 116(21), 213705 (2014).
V. Eyert, “The metal-insulator transition of NbO2: An embedded Peierls instability,” Europhys. Lett. 58(6), 851–856 (2002).
A. A. Bolzan, C. Fong, B. J. Kennedy, and C. J. Howard, “A powder neutron diffraction study of semiconducting and metallic niobium dioxide,” J. Solid State Chem. 113(1), 9–14 (1994).
N. B. Aetukuri, A. X. Gray, M. Drouard, M. Cossale, L. Gao, A. H. Reid, R. Kukreja, H. Ohldag, C. A. Jenkins, E. Arenholz, K. P. Roche, H. A. Dürr, M. G. Samant, and S. S. P. Parkin, “Control of the metal–insulator transition in vanadium dioxide by modifying orbital occupancy,” Nat. Phys. 9(10), 661–666 (2013).
Y. Wang, R. B. Comes, S. Kittiwatanakul, S. A. Wolf, and J. Lu, “Epitaxial niobium dioxide thin films by reactive-biased target ion beam deposition,” J. Vac. Sci. Technol. A 33(2), 021516 (2015).
L. Wang, E. Radue, S. Kittiwatanakul, C. Clavero, J. Lu, S. A. Wolf, I. Novikova, and R. A. Lukaszew, “Surface plasmon polaritons in VO2 thin films for tunable low-loss plasmonic applications,” Opt. Lett. 37(20), 4335–4337 (2012).
T. L. Cocker, L. V. Titova, S. Fourmaux, G. Holloway, H.-C. Bandulet, D. Brassard, J.-C. Kieffer, M. A. El Khakani, and F. A. Hegmann, “Phase diagram of the ultrafast photoinduced insulator-metal transition in vanadium dioxide,” Phys. Rev. B 85(15), 155120 (2012).
V. R. Morrison, R. P. Chatelain, K. L. Tiwari, A. Hendaoui, A. Bruhács, M. Chaker, and B. J. Siwick, “A photoinduced metal-like phase of monoclinic VO2 revealed by ultrafast electron diffraction,” Science 346(6208), 445–448 (2014).
D. Wegkamp, M. Herzog, L. Xian, M. Gatti, P. Cudazzo, C. L. McGahan, R. E. Marvel, R. F. Haglund, A. Rubio, M. Wolf, and J. Stähler, “Instantaneous band gap collapse in photoexcited monoclinic VO2 due to photocarrier doping,” Phys. Rev. Lett. 113(21), 216401 (2014).
J. Laverock, S. Kittiwatanakul, A. A. Zakharov, Y. R. Niu, B. Chen, S. A. Wolf, J. W. Lu, and K. E. Smith, “Direct observation of decoupled structural and electronic transitions and an ambient pressure monocliniclike metallic phase of VO2.,” Phys. Rev. Lett. 113(21), 216402 (2014).
E. Radue, L. Wang, S. Kittiwatanakul, J. Lu, S. A. Wolf, E. Rossi, R. A. Lukaszew, and I. Novikova, “Substrate-induced microstructure effects on the dynamics of the photo-induced metal–insulator transition in VO2 thin films,” J. Opt. 17(2), 025503 (2015).
D. J. Hilton, R. P. Prasankumar, S. Fourmaux, A. Cavalleri, D. Brassard, M. A. El Khakani, J. C. Kieffer, A. J. Taylor, and R. D. Averitt, “Enhanced photosusceptibility near Tc for the light-induced insulator-to-metal phase transition in vanadium dioxide,” Phys. Rev. Lett. 99(22), 226401 (2007).
L. A. L. de Almeida, G. S. Deep, A. M. N. Lima, and H. Neff, “Thermal dynamics of VO2 films within the metal–insulator transition: Evidence for chaos near percolation threshold,” Appl. Phys. Lett. 77(26), 4365–4367 (2000).
A. Cavalleri, C. Tóth, C. W. Siders, J. A. Squier, F. Ráksi, P. Forget, and J. C. Kieffer, “Femtosecond structural dynamics in VO2 during an ultrafast solid-solid phase transition,” Phys. Rev. Lett. 87(23), 237401 (2001).
J. Shah, Hot Carriers in Semiconductor Nanostructures, Physics and Applications (Academic 1992).
J. M. Klopf and P. M. Norris, “Subpicosecond observation of photoexcited carrier thermalization and relaxation in InP-based films,” Int. J. Thermophys. 26(1), 127–140 (2005).
M. M. Qazilbash, Z. Q. Li, V. Podzorov, M. Brehm, F. Keilmann, B. G. Chae, H. T. Kim, and D. N. Basov, “Electrostatic modification of infrared response in gated structures based on VO2,” Appl. Phys. Lett. 92(24), 241906 (2008).
M. M. Qazilbash, M. Brehm, B.-G. Chae, P.-C. Ho, G. O. Andreev, B.-J. Kim, S. J. Yun, A. V. Balatsky, M. B. Maple, F. Keilmann, H.-T. Kim, and D. N. Basov, “Mott transition in VO2 revealed by infrared spectroscopy and nano-imaging,” Science 318(5857), 1750–1753 (2007).
L. Wang, I. Novikova, J. M. Klopf, S. Madaras, G. P. Williams, E. Madaras, J. Lu, S. A. Wolf, and R. A. Lukaszew, “Distinct length scales in the VO2 metal–insulator transition revealed by bi-chromatic optical probing,” Adv. Opt. Mater. 2(1), 30–33 (2014).
de Almeida, L. A. L.
Fig. 1 High-angle 2θ-ω scans of the NbO2 (top) and VO2 (bottom) samples studied. The dashed line indicates the position of the bulk substrate reflection, centered at 2θ = 41.685°. The NbO2(440) peak is centered at 2θ = 37.223°, while the VO2(020) peak is centered at 2θ = 40.069°.
Fig. 2 Schematic of the ultrafast pump-probe setup.
Fig. 3 Pump-probe measurements and fits for the lowest fluence at which the IMT was seen in each material. (a) Fitted data showing the initial response and recovery of the film. Data are plotted as disconnected points, while fits are solid lines. (b) Full-track data.
Fig. 4 Pump-probe measurements at a pump fluence of 70.0 mJ/cm2, when the structural transition begins in the VO2 film, causing the signal to become larger than that of the NbO2 film.
Fig. 5 Scans of NbO2 with pump fluences ranging from 8.8 mJ/cm2 to 422 mJ/cm2. (a) Fitted data showing the initial response and recovery of the film. Data are plotted as disconnected points, while fits are solid lines. (b) Full-track data.
Fig. 6 Scan of fully-transitioned VO2. (a) Fitted data showing the initial response of the film. Data are plotted as disconnected points, while fits are solid lines. (b) Full-track data.
Fig. 7 Normalized scans of NbO2 and VO2 at 422 mJ/cm2, the highest fluence achieved without damaging the samples. (a) Fitted data showing the initial response of the films. Data are plotted as disconnected points, while fits are solid lines. (b) Full-track data.
Table 1 Fit parameters for the scans shown in Figs. 3, 5, and 6. The two highlighted columns correspond to the plots shown in Fig. 7.
Table 2 Results of the sensitivity study on Eq. (1), showing the percent change in the RMS value of the fit after changing the given parameter by ± 10%.
Fit parameters for the scans shown in Figs. 3, 5, and 6. The two highlighted columns correspond to the plots shown in Fig. 7.
Results of the sensitivity study on Eq. (1), showing the percent change in the RMS value of the fit after changing the given parameter by ± 10%.

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