Properties of magnetic nickel/porous-silicon composite powders

Toshihiro Nakamura,Sadao Adachi

doi:10.1063/1.4754152

Abstract

The magnetic and photoluminescence (PL) properties of nickel/porous-silicon (Ni/PSi) composite powders are investigated. Ni/PSi composite powders are prepared by stain etching of Si powder in a HF/HNO3 solution followed by electroless plating of Ni nanoparticles on the stain-etched PSi powder in a NiCl2 solution. The Ni/PSi powders exhibit hydrophillicity, superparamagnetism caused by the deposited Ni nanoparticles, and orange-red PL owing to the nanostructured PSi surface. The degree of magnetization decreases with increasing Ni plating time, indicating its dependence on the size of the Ni nanoparticles. The Ni/PSi composite powders also show a stronger magnetization as compared to that of the Ni-particle-plated Si powder. The stronger magnetization results from the larger surface area of PSi. The PL intensity, peak wavelength, and lifetime of Ni/PSi are strongly dependent on the NiCl2 concentration. This dependence is due to the different thickness of the oxide overlayer on the PSi surface formed during the Ni plating process. The existence of the oxide overlayer also results in a small change in the PL intensity against excitation time.

Highlights

Porous silicon (PSi), a Si nanocrystal assembly, possesses unique properties such as efficient room-temperature luminescence,[1,2] photosensitization for oxygen molecules,[3] and explosive interaction with various chemicals via the oxidation of the Si surface layer.[4,5] Because of its unique properties and a large surface area due to the existence of nanopores, PSi is a promising material for various applications such as optoelectronics and biologic sensing
Ni/PSi composite powders were prepared by electroless plating of PSi powder in an aqueous NiCl2 solution
Properties of the Ni/PSi powders were systematically investigated as functions of the plating time and NiCl2 concentration

Summary

INTRODUCTION

Porous silicon (PSi), a Si nanocrystal assembly, possesses unique properties such as efficient room-temperature luminescence,[1,2] photosensitization for oxygen molecules,[3] and explosive interaction with various chemicals via the oxidation of the Si surface layer.[4,5] Because of its unique properties and a large surface area due to the existence of nanopores, PSi is a promising material for various applications such as optoelectronics and biologic sensing. Several methods for the preparation of PSi-based nanocomposites have been proposed.[11] For example, a spin coating technique is used for the impregnation of polymers.[12] For the incorporation of metals into PSi pores, electroplating and electroless plating methods have been used.[11] Noble metals (Au, Ag, and Cu) and less noble metals (Ni and Fe) have been deposited through electroless plating and electroplating, respectively. In these methods, PSi was immersed in an aqueous solution containing metallic ions. It is shown that Ni/PSi composite powders have higher photostability against UV illumination than PSi

EXPERIMENTAL

RESULTS AND DISCUSSION

SUMMARY