The CdSe Nanocrystalline Growth in solutions Shima Fardad

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 ...

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

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

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

Effective factors on size

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

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.

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

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

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

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

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

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.

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

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

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)

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

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