Preparation and optimization of Photoelectrochemical parameters for synthesis of silicon nanoparticles from n-type and p-type wafers

MANUEL JOSE LLANSOLA PORTOLES; FELIPE RODRÍGUEZ NIETO; BEATRIZ SORIA; DANIEL O. MÁRTIRE; MÓNICA C. GONZALEZ

Foz do Iguaçu

Congreso; 6th ISE Spring Meeting in Foz do Iguaçu; 2008

ISE

Si nanoparticles (Si-NP) of diameter size of a few nanometers show strong photoluminescence due to quantum confinement with maximum wavelength emission strongly depending on size. The strong luminescence and photostability in aqueous suspensions of suitable surface modified nanoparticles makes them excellent candidates for use as specific luminescent markers in biological environments for in vitro and in vivo applications.Si-NP have been prepared by different physical and chemical approaches, the route of the electrochemical etching is one of the most used for its ease to implement. It`s known that the current voltage curves in diluted HF solution for p and n-type silicon are different. However, under illumination p-type or n-type Si shown same current voltage behaviour except for a cathodic voltage shift of about 500 mV, which is due the differences in Fermi energies of the different material. This gives a new degree of freedom in electrochemical experiments: one can vary the (photo-) current and the voltage independently. As a consequence we have a broad region where we can produce porous silicon.In this contribution we report results from the synthesis of Silicon nanoparticles using a combined route photoelectrochemical using n type silicon wafers. Crystalline, Si(100) oriented, 1-10 ohm cm. resistivity, n-type Phosphorus doped wafer were photoelectrochemically etched in a teflon cell with an electrolytic solution mixture de HF, HNO3:, CH3OH and H2O in different proportions.The silicon wafer anode is vertically immersed in the etchant and is advanced at slow speed of approximately 1 mm per hour; a wire Pt was used as cathode. For the synthesis of the Si nanoparticles a current density in the range form 0.5-20 mA/cm2 was applied while illuminated with a light source of 50 watt 12 V. for 24 hours. Finally, the thus treated silicon wafer is removed, washed with methanol, and transferred to an ultrasonic toluene or methanol bath bubbled with argon for 30 minutes. Sonication crumbles the very top layer into a suspension of silicon nanoparticles. Optimum conditions for obtaining Si particles in the range 1- 10 nm were studied changing the parameters such as the current density, electrolyte composition, anodisation and ultrasonic time.