PbSe Nanocrystals NCs

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
  evaporation1
• 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

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 markers8
• 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 1150C
• PbSe NC size controlled by varying the annealing
  temperature
• 395-430C

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 80-160C
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 (lt1nm)
• 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

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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.
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