tailieunhanh - Báo cáo hóa học: " Tin Oxide Nanowires: The Influence of Trap States on Ultrafast Carrier Relaxation"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Tin Oxide Nanowires: The Influence of Trap States on Ultrafast Carrier Relaxation | Nanoscale Res Lett 2009 4 828-833 DOI S11671-009-9323-9 NANO EXPRESS Tin Oxide Nanowires The Influence of Trap States on Ultrafast Carrier Relaxation Andreas Othonos Matthew Zervos Demetra Tsokkou Received 31 January 2009 Accepted 14 April 2009 Published online 30 April 2009 to the authors 2009 Abstract We have studied the optical properties and carrier dynamics in SnO2 nanowires NWs with an average radius of 50 nm that were grown via the vapor-liquid solid method. Transient differential absorption measurements have been employed to investigate the ultrafast relaxation dynamics of photogenerated carriers in the SnO2 NWs. Steady state transmission measurements revealed that the band gap of these NWs is eV and contains two broad absorption bands. The first is located below the band edge shallow traps and the second near the center of the band gap deep traps . Both of these absorption bands seem to play a crucial role in the relaxation of the photogenerated carriers. Time resolved measurements suggest that the photogenerated carriers take a few picoseconds to move into the shallow trap states whereas they take 70 ps to move from the shallow to the deep trap states. Furthermore the recombination process of electrons in these trap states with holes in the valence band takes 2ns. Auger recombination appears to be important at the highest fluence used in this study 500 J cm2 however it has negligible effect for fluences below 50 J cm2. The Auger coefficient for the SnO2 NWs was estimated to be X 10-31 cm6 s. A. Othonos El D. Tsokkou Department of Physics Research Centre of Ultrafast Science University of Cyprus . Box 20537 1678 Nicosia Cyprus e-mail othonos@ M. Zervos Department of Mechanical and Manufacturing Engineering Materials Science Group Nanostructured Materials and Devices Laboratory University of Cyprus . Box 20537 1678 Nicosia Cyprus Keywords SnO2 nanowires Chemical vapour deposition Carrier dynamics Differential absorption .