Optical, electrical and microstructural properties of nanocomposite Ag/diamond by Ag ion implantation and subsequent annealing

Highlights

• Ag nanoparticles were fabricated in the free-standing diamond film by ion implantation.

• Ag SPR peak at about 375 nm appears after 500 °C annealing.

• Ag-embedded FSD films exhibited an enhanced carrier mobility after 500 °C annealing.

• Ag nanoparticles act as conductive paths permitting charges to pass through them.

• The Ag-embedded free-standing diamond films still shows high sp³-bonds.

Abstract

An optical-grade, free-standing diamond (FSD) film is prepared by home-made microwave plasma chemical vapor deposition reactor at a condition of input power 8 kW and gas pressure18 kPa. Then, it is implanted with 80 keV Ag ions up to a fluence of 5.0 × 1016 ions/cm². After implantation, a subsequent annealing in Ar ambient at 500 °C is carried out to fabricate Ag nanoparticles (NPs). Grazing incidence x-ray diffraction results clearly showed that Ag NPs with a (111) orientation are effectively formed after 500 °C annealing. Results from field emission scanning electron microscope and atomic force microscope observations indicated that Ag NPs could aggregate and grow on the surface of the diamond film during the annealing process. The Hall effects results showed that Ag-implanted FSD film exhibited an enhanced carrier mobility of 34.7 cm² V⁻¹ S⁻¹ after 500 °C annealing. Moreover, Raman spectroscopy results show that the damages of the Ag-implanted FSD film are essentially a little and the crystallinity is almost recovered by annealing, it is implied that the enhancement in carrier mobility could be attributed to the conductive paths provided by Ag NPs.

Introduction

Composite materials embedded with metallic nanoparticles (NPs) have attracted much more attention in recent years owing to their prospective applications in various fields [1]. The appealing properties of Ag NPs, such as large third-order susceptibility, surface plasmon resonance (SPR), and optical response time in picoseconds, etc. make Ag NPs related composites excellent candidates for using in catalysis, optoelectronics, optical sensors, photon switches and biomedicine [2], [3], [4]. As known to all, glass has been shown to be the most popular supporting material for kinds of SPR sensors platforms [5], [6], [7], [8], [9]. Although glass is inexpensive, it cannot be used in severe environments (e.g., high temperature, high radiation flux, etc.). Therefore, it is needed to develop alternative supporting substrates for extensive applications.

Recently, diamond has received considerable attention owing to their interesting properties, e.g., the highest thermal conductivity and hardness among all known materials, wide band gap, high radiation resistance, good chemical and temperature stabilities. Furthermore, diamond can be deposited as a film on a vast number of substrate materials and can be deposited as freestanding ultrathin films. These appealing properties make diamond an ideal substrate for the formation of Ag NPs related devices with high performances (surface acoustic wave, UV photodetec-tors, heterojunction, etc.) in severe environments [10]. Among different possible techniques to synthesize composite materials [11], [12], [13], ion implantation has been proved to be very suitable and versatile in that it can virtually introduce any element into substrate without the constrain of solubility limit as well as high cluster free energy of formation suffered by other methods. Moreover, by prudently selecting implantation parameters, both the concentration and their depth distribution of implants can be controlled to a certain degree. Especially, ion implantation can break the C–C and hydrocarbon bonds to form sp² carbon, which are of low electrical resistivity and is thought as the electron conduction channel in diamond electron field emission. Therefore, it is desirable to fabricate efficient nanocomposite Ag/diamond by ion implantation.

In the work described here, high-quality, freestanding diamond films are fabricated by home-made microwave plasma chemical vapor deposition (MPCVD) reactor [14], then Ag NPs were fabricated by ion implantation together with subsequent thermal annealing in Ar atmosphere at 500 °C, thus result in producing a Ag-diamond nanocomposite. A detailed study was carried out to reveal the surface morphology and electrical properties of Ag NPs-diamond composite fabricated by Ag ion implantation and subsequent annealing using Grazing incidence x-ray diffraction (GIXRD) measurements, field emission scanning electron microscope (SEM) and atomic force microscope (AFM). The crystalline quality of the FSD film was further investigated by using Raman spectroscopy. The fabrication of Ag/diamond nanocomposite shows a more promising prospect in the nanodevice fabrication.