PbSe Nanocrystals (NCs) -from synthesis to applications-

by Razvan-Ionut StoianOklahoma State University, Department of Physics

Motivation

General properties of the PbSe nanocrystals (theoretical aspects) Synthesis methods

Applications

Future Directions

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

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]

Literature Review (cont.)

NCs synthesis is a multidisciplinary research field

Enabling technologies(characterization methods)

Related fields

...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

Theoretical background

Key words for PbSe NCs: -Excitonic Bohr radius -

-(Strong) Spatial Confinement

-Electronic density of states (DOS)

a B

eheh,

eh,B m=m,=em

ε=a 23nm

2

2

R : the average dimension of the NC

a B=a Bh+aBe

=46nm

Ra B

≤1

discrete excitonic energy levels

optical absorption levels are discrete

these abs. levels are situated in the midinfrared domain

Theoretical background (cont.)

[10]

[10]

The effect of the NC size on the temperature dependence of E

g

[10]

Optical transition strengths of a 8.5 nm PbSe NC (calculation) [10]

Synthesis Methods 1. PbSe NC synthesis using phosphate glasses

glass host of choice: P2O

5-Ga

2O

3-ZnO-AlF

3-Na

2O

preparatives – glass host and solid PbSe melted at 1150°CPbSe NC size controlled by varying the annealing temperature: 395-430°C

TEM micrograph [4]

PbSe NC characteristics

- size : 2-15 nm

- dispersion: ±7%

-

- low processabilty

0 . 04≤ Ra B

≤0 .16

Synthesis Methods 2. The hydrothermal method

2Pb2+ + N2H

4 +4OH- → 2Pb + N

2 +4H

2O

Pb +Se → PbSe Experimental setup

TEM of PbSe NC [5]

PbSe NC characteristics:

- size : min 23 nm -high processabilty -

0 . 5≤ Ra B

Synthesis Methods 3. PbSe NC synthesis by organic precursors [6]

Experimental setup

NCs size controlled by the preparation temperature: 80-160°C

0 . 06≤ Ra B

≤0 . 37

PbSe NC characteristics:

- size : 3-8 nm -high processabilty -

STEM on PbSe [6]

Synthesis Methods -comparisons-

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

Applications (cont.)

Whispering gallery mode emission (PL) [11]

Laser1550 nm

silica bead coated with PbSe NCs

optical fiber

PL from a PbSe coated silica bead [11]

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

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