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PbSe Nanocrystals (NCs) -from synthesis to applications-

PbSe Nanocrystals (NCs) -from synthesis to applications-. by Razvan-Ionut Stoian Oklahoma State University, Department of Physics. Motivation General properties of the PbSe nanocrystals (theoretical aspects) Synthesis methods Applications Future Directions. Motivation.

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PbSe Nanocrystals (NCs) -from synthesis to applications-

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  1. PbSe Nanocrystals (NCs) -from synthesis to applications- by Razvan-Ionut Stoian Oklahoma State University, Department of Physics • Motivation • General properties of the PbSe nanocrystals • (theoretical aspects) • Synthesis methods • Applications • Future Directions

  2. Motivation The achievement of strong spatial confinement of the charge carriers (see the “Theoretical background” slide)↔ non-linear optical properties • Applications (mainstream) • Biology • Optical Sensors • Lasers • Nano-electronics • Applications (specific) • telecommunication • applications • low power, low threshold • lasers (optical pumping) • (1550nm domain) Goals achievable by the synthesis of small sized PbSe NCs

  3. Literature Review • Important steps in the study and synthesis of PbSe NCs • 1960 - W. D. Lawson– PbSe Thin Films prepared by evaporation[1] • 1995 – Sasha Gorer- Chemically deposited, nanocrystalline PbSe • Films [2] • 1997 – Kang and Wise – Detailed calculations on PbSe NCs • energy bands [3] • 1997 – Lipovskii et al. - Synthesis of PbSe NCs in phosphate • glasses [4] • 2001 – Wang et al. - Hydrothermal synthesis of PbSe NCs [5] • 2002 – Dui et al. - PbSe NC synthesis by organic precursors [6] • 2004 – Sashchiuk et al. - PbSe NC synthesis by polymeric • precursors [7]

  4. Literature Review (cont.) NCs synthesis is a multidisciplinary research field Related fields Enabling technologies (characterization methods) • ...make use of the NCs, namely: • Electrical Engineering – • infrared detectors • Physics – Fundamental • research and Lasers • Chemistry • Biology – biological markers[8] • Nano-electronics [9] • TEM • - HR-TEM (high res. TEM) • STM • SEM • - HR-SEM (high res. SEM) • XRD (X-ray diffraction) • XRF (X-ray fluorescence) • Absorption spectroscopy

  5. Theoretical background • Key words for PbSe NCs: • -Excitonic Bohr radius - • -(Strong) Spatial Confinement • -Electronic density of states (DOS) R : the average dimension of the NC • discrete excitonic energy • levels • optical absorption levels are • discrete • these abs. levels are situated in • the midinfrared domain

  6. Theoretical background (cont.) Optical transition strengths of a 8.5 nm PbSe NC (calculation) [10] [10] The effect of the NC size on the temperature dependence of Eg [10] [10]

  7. Synthesis Methods 1. PbSe NC synthesis using phosphate glasses • glass host of choice: P2O5-Ga2O3-ZnO-AlF3-Na2O • preparatives – glass host and solid PbSe melted at 1150°C • PbSe NC size controlled by varying the annealing temperature: • 395-430°C PbSe NC characteristics - size : 2-15 nm - dispersion: ±7% - - low processabilty TEM micrograph [4]

  8. Synthesis Methods 2. The hydrothermal method 2Pb2+ + N2H4 +4OH-→ 2Pb + N2 +4H2O Pb +Se → PbSe Experimental setup TEM of PbSe NC [5] PbSe NC characteristics: - size : min 23 nm -high processabilty -

  9. Synthesis Methods 3. PbSe NC synthesis by organic precursors [6] NCs size controlled by the preparation temperature: 80-160°C Experimental setup STEM on PbSe [6] PbSe NC characteristics: - size : 3-8 nm -high processabilty -

  10. Synthesis Methods -comparisons-

  11. Applications • Infrared detectors 1.3- 5.2 µm • Biological markers [8] • LEDs and mid-infrared lasers • Low power, eye-safe lasers • Low power, low threshold (optically pumped) laser

  12. Applications (cont.) • Whispering gallery mode emission (PL) [11] Laser 1550 nm optical fiber silica bead coated with PbSe NCs PL from a PbSe coated silica bead [11]

  13. Future directions • Advancement of the NC synthesis implies: • NCs will have extremely small sizes (<1nm) • NCs will exhibit a true monodisperse character • New theoretical models will be developed • Advancement in Nano-electronics (large scale integration) • Challenges to be overcome: • a better control of the parameters that “tweak” the NCs • characteristics • - temperature during the synthesis • - the purity of the reagents

  14. References [1] Lawson, W.D. et al. Journal of the Electrochemical Society, 1960, 107, p. 206-210 [2] Gorer , S. , Albu-Yaron, A. and Hades, G. Journal of Physical Chemistry, 1995, 99, p. 16442-164485 [3] Kang I. and Wise, F. J. Opt. Soc. Am. B, 1997, Vol. 14, 7 [4] Lipovskii, A et al., Applied Physics Letters, 1997, Vol. 71 (23), p. 3406-3408 [5] Wang, C. , Zhang, G. , Fan, S. , Li, Y. Journal of Physics and Chemistry of Solids, 2001, Vol. 62 , p. 1957-1960 [6] Dui, I. et al., Nanoletters, 2002, Vol. 2, 11, p. 1321-13240 [7] Sashchiuk, A. et al. Nanoletters, 2004, Vol.4, 1, p. 159-165 [8] Smith, A.M. , Gao, X. and Nie, S. Photochemistry and Photobiology, 2004, 80 [9] Wehrenberg, B.L.,Yu, D. , Ma, J. and Guyot-Sionnest, P. Journal of Physical Chemistry. B, 2005, Vol. 109, p. 20192-20199 [10] Wise, F. W. Acc. Chem. Res., 2000, Vol. 33, p. 773-780 [11] Finlayson, C.E. et al. , 2006, Semiconductor Science and Technology, 2006, Vol. 21

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