January 2017
Spotlight Summary by Rosalia Serna
Time-resolved light-induced insulator-metal transition in niobium dioxide and vanadium dioxide thin films
A promising material for ultrafast optical switching
Manipulation of optical signals for data processing in optoelectronic circuits requires the development of ultrafast optical switches. In this context, vanadium dioxide (VO₂) has been extensively studied because it undergoes first-order insulator-to-metal (IMT) and metal-to-insulator (MIT) phase transitions that are characterized by a large change in optical and DC conductivity. The phase change can be induced both thermally and by ultrafast fs laser irradiation. VO₂ thin films have shown an IMT faster than 100 fs. However, these films show a large recovery time of the insulating phase (larger than 20 ns); this limits the application of VO₂ for reversible ultrafast ON/OFF/ON transitions. With the aim to identify materials with enhanced optical switching, in this Optical Materials Express article Melissa R. Beebe and co-authors investigate the ultrafast induced phase transition of a related material, Niobium dioxide (NbO₂), with structural and phase change properties similar to VO₂, but with a much higher critical temperature for the phase transition (1080 K). The article describes and compares the dynamics of the IMT transition of VO₂ and NbO₂ monoclinic insulating thin films irradiated by ultrashort laser pulses (approximately 120 fs). Measurements of the transient relative change in reflectivity (ΔR/R) associated to the IMT transition, obtained using an ultrafast probe pump-probe set-up, show indeed an ultrafast change in reflectivity in both NbO₂ and VO₂ films. More remarkable is the demonstration of a clear electronic response in NbO₂, with a recovery time of a few picoseconds. Furthermore, in NbO₂ the fluence to induce the IMT is lower, and the initial response time is shorter than in VO₂. These results show that NbO₂ is a robust material for the implementation of ultrafast optoelectronic switches with some potential advantages over VO₂. Finally, the authors suggest that the combination of both VO₂ and NbO₂ films in a single device can be advantageous by implementing double-function switch architectures that would profit from the different time response associated to each material.
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Manipulation of optical signals for data processing in optoelectronic circuits requires the development of ultrafast optical switches. In this context, vanadium dioxide (VO₂) has been extensively studied because it undergoes first-order insulator-to-metal (IMT) and metal-to-insulator (MIT) phase transitions that are characterized by a large change in optical and DC conductivity. The phase change can be induced both thermally and by ultrafast fs laser irradiation. VO₂ thin films have shown an IMT faster than 100 fs. However, these films show a large recovery time of the insulating phase (larger than 20 ns); this limits the application of VO₂ for reversible ultrafast ON/OFF/ON transitions. With the aim to identify materials with enhanced optical switching, in this Optical Materials Express article Melissa R. Beebe and co-authors investigate the ultrafast induced phase transition of a related material, Niobium dioxide (NbO₂), with structural and phase change properties similar to VO₂, but with a much higher critical temperature for the phase transition (1080 K). The article describes and compares the dynamics of the IMT transition of VO₂ and NbO₂ monoclinic insulating thin films irradiated by ultrashort laser pulses (approximately 120 fs). Measurements of the transient relative change in reflectivity (ΔR/R) associated to the IMT transition, obtained using an ultrafast probe pump-probe set-up, show indeed an ultrafast change in reflectivity in both NbO₂ and VO₂ films. More remarkable is the demonstration of a clear electronic response in NbO₂, with a recovery time of a few picoseconds. Furthermore, in NbO₂ the fluence to induce the IMT is lower, and the initial response time is shorter than in VO₂. These results show that NbO₂ is a robust material for the implementation of ultrafast optoelectronic switches with some potential advantages over VO₂. Finally, the authors suggest that the combination of both VO₂ and NbO₂ films in a single device can be advantageous by implementing double-function switch architectures that would profit from the different time response associated to each material.
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Article Information
Time-resolved light-induced insulator-metal transition in niobium dioxide and vanadium dioxide thin films
Melissa R. Beebe, J. Michael Klopf, Yuhan Wang, Salinporn Kittiwatanakul, Jiwei Lu, Stuart A. Wolf, and R. Alejandra Lukaszew
Opt. Mater. Express 7(1) 213-223 (2017) View: Abstract | HTML | PDF