1. The CdSe Nanocrystalline Growth in solutions
Shima Fardad

2. Introduction
Compound semiconductor deposition from liquid )aqueous or non-aqueous solutions( is becoming increasingly popular because :
capability of large-area deposition.
It has the advantages of economy.
The II/VI semiconductors has been the focus of attention recently for,
Optoelectronic
Photovoltaic solar cells
Photocatalytics
Photoelectro Chemicals
Laser diodes
...

3. CdSe growth in: Glasses Organic glasses Colloidal solutions
Chemical solutions
Solution Gels (Sol-gel)

4. Chemical Deposition (Fabrication Techniques) :
ELECTROCD
Electro Chemical Deposition
PCD
Photo Chemical Deposition
CBD
Chemical Bath Deposition

5. CdSe Chemical Deposition
Basic idea
Reaction between slowly released Se anion with a free Cd cation.
Controlling the crystalline size by
Growth time
Light intensity
Heating temperature
Wavelength

6. Effective factors on size

7. Electrodeposition
Restricted to electrically conductive materials
The films can be made in any thickness from ~1µm to >100µm

8. Photo Chemical Deposition
Controlling Deposition by light.
As discussed above
Changing the intensity
Turning off/on
Chemical reaction catalyzed by hv
Need some species (sulfite ions) can supply solvated electrons.
Sulfite ions will release electrons when photo activated.

9. CdSe PCD reactions
Thickness = 300nm ; Time = 120mins
Rate = 150nm/h

10. Chemical Bath Deposition
Large variety of chalcogenide semiconductors
Purely chemical reaction between dissolved precursors (without any charge transfer)
Large area deposition
Various substrates

11. CdSe CBD Cadmium acetate + Sodium selenosulfite
Adding small amount of heteropolyacid improves greatly the photoelectrochemical response
Example : Silicotungstic (STA) ; SiW12O40H4
Changing bath composition gives different mass

12. CdSe CBD (contd.) With STA Less Noisy Saturated Without STA Noisy
Decreases to ZERO

13. CdSe Growth in CBD According to Figures we have two-peak profile.
Proves the process takes place in 2 steps.
Two dimensional growth (Cylindrical)
Three dimensional growth (Hemispheroids )
TEM
STM

14. Change in Color (Bulk to Nanocrystal)
As the CdSe grows on the substrate it’s Color changes from yellow to Dark Red.
An aggregation process of the COLLOIDS form.

15. CdSe in Sol-Gel Films Sol-Gel Films are prepared by incorporating
Cadmium acetate into a Glass matrix.
Sol-Gel can stabilize cubic forms of nanocrystalline CdSe against transformation to the hexagonal phase.
Causes separation between nanocrystalls.
viscosity will lower the mobility of nanocrystalls.
Porosity of the Sol-Gel

16. XRD spectra
CdSe CD. Fimls
CdSe in TiO2 sol-gel
CdSe in ZrO2 sol-gel

17. An application of Electrodeposition for CdSe
CdSe Nanowire Arrays (embedded in anodic aluminia membrane, AAM)
Uses in
Electronic
Magnetic
Optical devices
Filling the pores of AAM by Electrodeposition method we have a CdSe nanowire.
60nm in diameter ; 5um in length
Cd/Se significantly depends on the PH (9)

18. SEM images (highly ordered CdSe nanowire arrays)
A Cross sectional view
A top view image

19. Best Wishes