The CdSe Nanocrystalline Growth in solutions

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The CdSe Nanocrystalline Growth in solutions

• Shima Fardad

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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
• ...

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CdSe growth in

• Glasses
• Organic glasses
• Colloidal solutions
• Chemical solutions
• Solution Gels (Sol-gel)

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Chemical Deposition(Fabrication Techniques)

• ELECTROCD
• Electro Chemical Deposition
• PCD
• Photo Chemical Deposition
• CBD
• Chemical Bath Deposition

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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

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Effective factorson size
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Electrodeposition

• Restricted to electrically conductive materials
• The films can be made in any thickness from 1µm
  to gt100µm

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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.

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CdSe PCD reactions
Thickness 300nm Time 120mins Rate 150nm/h
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Chemical Bath Deposition

• Large variety of chalcogenide semiconductors
• Purely chemical reaction between dissolved
  precursors (without any charge transfer)
• Large area deposition
• Various substrates

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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

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CdSe CBD (contd.)

• With STA
• Less Noisy
• Saturated

• Without STA
• Noisy
• Decreases to ZERO

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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
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Change in Color (Bulk to Nanocrystal)

• As the CdSe grows on the substrate its Color
  changes from yellow to Dark Red.
• An aggregation process of the COLLOIDS form.

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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

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XRD spectra
CdSe CD. Fimls
CdSe in TiO2 sol-gel
CdSe in ZrO2 sol-gel
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An application of Electrodepositionfor 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)

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SEM images (highly ordered CdSe nanowire arrays)

• A Cross sectional view

• A top view image

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Best Wishes