Vacuum 123 (2016) 160e166

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Vacuum

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

* ** Yanyan Shen , Ting Qi, Yu Qiao, Hongjun Hei, Zhiyong He, Shengwang Yu

Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China article info abstract

Article history: An optical-grade, free-standing diamond (FSD) film is prepared by home-made microwave plasma Received 15 April 2015 chemical vapor deposition reactor at a condition of input power 8 kW and gas pressure18 kPa. Then, it is Received in revised form implanted with 80 keV Ag ions up to a fluence of 5.0 1016 ions/cm2. After implantation, a subsequent 1 November 2015 annealing in Ar ambient at 500 C is carried out to fabricate Ag nanoparticles (NPs). Grazing incidence x- Accepted 2 November 2015 ray diffraction results clearly showed that Ag NPs with a (111) orientation are effectively formed after Available online 5 November 2015 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 Keywords: fi Freestanding diamond film the annealing process. The Hall effects results showed that Ag-implanted FSD lm exhibited an enhanced 2 1 1 Ag nanoparticles carrier mobility of 34.7 cm V S after 500 C annealing. Moreover, Raman spectroscopy results show Ion implantation that the damages of the Ag-implanted FSD film are essentially a little and the crystallinity is almost Surface morphologies recovered by annealing, it is implied that the enhancement in carrier mobility could be attributed to the Carrier mobility conductive paths provided by Ag NPs. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction Furthermore, diamond can be deposited as a film on a vast number of substrate materials and can be deposited as freestanding ultra- Composite materials embedded with metallic nanoparticles thin films. These appealing properties make diamond an ideal (NPs) have attracted much more attention in recent years owing to substrate for the formation of Ag NPs related devices with high their prospective applications in various fields [1]. The appealing performances (surface acoustic wave, UV photodetec-tors, hetero- properties of Ag NPs, such as large third-order susceptibility, sur- junction, etc.) in severe environments [10]. Among different face plasmon resonance (SPR), and optical response time in pico- possible techniques to synthesize composite materials [11e13], ion seconds, etc. make Ag NPs related composites excellent candidates implantation has been proved to be very suitable and versatile in for using in catalysis, optoelectronics, optical sensors, photon that it can virtually introduce any element into substrate without switches and biomedicine [2e4]. As known to all, glass has been the constrain of solubility limit as well as high cluster free energy of shown to be the most popular supporting material for kinds of SPR formation suffered by other methods. Moreover, by prudently sensors platforms [5e9]. Although glass is inexpensive, it cannot be selecting implantation parameters, both the concentration and used in severe environments (e.g., high temperature, high radiation their depth distribution of implants can be controlled to a certain flux, etc.). Therefore, it is needed to develop alternative supporting degree. Especially, ion implantation can break the CeC and hy- substrates for extensive applications. drocarbon bonds to form sp2 carbon, which are of low electrical Recently, diamond has received considerable attention owing to resistivity and is thought as the electron conduction channel in their interesting properties, e.g., the highest thermal conductivity diamond electron field emission. Therefore, it is desirable to and hardness among all known materials, wide band gap, high fabricate efficient nanocomposite Ag/diamond by ion implantation. radiation resistance, good chemical and temperature stabilities. 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 fabri- * Corresponding author. cated by ion implantation together with subsequent thermal ** Corresponding author. annealing in Ar atmosphere at 500 C, thus result in producing a E-mail addresses: [email protected] (Y. Shen), [email protected] Ag-diamond nanocomposite. A detailed study was carried out to (S. Yu). http://dx.doi.org/10.1016/j.vacuum.2015.11.001 0042-207X/© 2015 Elsevier Ltd. All rights reserved. Y. Shen et al. / Vacuum 123 (2016) 160e166 161 reveal the surface morphology and electrical properties of Ag NPs- 3. Results and discussion diamond composite fabricated by Ag ion implantation and subse- quent annealing using Grazing incidence x-ray diffraction (GIXRD) Fig. 1 shows the top-view SEM image of the un-polished FSD measurements, field emission scanning electron microscope (SEM) film((a)), the photographs of the FSD film before ((b)) and after and atomic force microscope (AFM). The crystalline quality of the being polished ((c)). The SEM image reveals that our prepared FSD film was further investigated by using Raman spectroscopy. diamond film has a good continuity and compactness except for a The fabrication of Ag/diamond nanocomposite shows a more small amount of secondary crystals and pinholes. The average size promising prospect in the nanodevice fabrication. of the grains is about 50e80 mm, and the thickness of the film is about 430 mm measures by amicrocalliper. Its thickness uniformity is ±7%. In (b), it is clear that the FSD film displays a good translucent property. After being polished on both sides, the diamond plate 2. Experimental exhibits good visual transparency where the words are seen un- derneath the sample, as shown in (c). High quality optical-grade freestanding diamond (FSD) films In the case of noble metallic NPs containing single element, the were grown on n-type silicon substrates by our homely developed distinctive SPR absorption in optical absorbance or transmittance MPCVD reactor using H2-CH4 as the source gas. The input power spectrum is a clear fingerprint of NPs formation [16,17]. Therefore, and gas pressure was kept at 8 kW and 18 kPa, respectively. Prior the measurements of optical absorbance spectra were firstly per- to the growth of FSD films, the substrates were ground using formed in this work to probe formation of Ag NPs. Optical absor- diamond powders of 5 mm, and then they were ultrasonically bance spectra of the samples before and after annealing in Ar cleaned in acetone and dried in hot blowing air. Hydrogen and atmosphere are shown in Fig. 2. From this figure, it is obvious that methane were chosen as the synthesis gases and the percentage of no evidence of clear absorption peak occurs in the wavelength of methane was 1%. The total gas mass flow was fixed at 800 sccm 200e800 nm for un-implanted FSD film. However, after Ag ion (standard cubic centimetre per min). The H2 and CH4 input gases implantation, the color of the FSD film turns metallic bright and the had purity levels of 99.9995% and 99.999% respectively. The Si intensity of the optical absorption increases significantly in the substrate temperature was set to 975 C with ±10 C accuracy that entire range. The increase of the absorption in the UVeVis range was measured by a one-color pyrometer with emissivity set to 0.6 should be directly attributed to the precipitation of Ag in the form through a viewing port window in the reactor during the diamond of nucleus or clusters in the near surface of the samples, according deposition process. The total deposition time was 100 h. After the to the electron interband transitions as in a bulk metal [18]. deposition, the Si substrates were removed by mixed solution of Another possible reason is that implantation could induce some hydrofluoric and nitric acid in order to get the free-standing matrix structural defects in the form of vacancies, interstitials and polycrystalline diamond thick films. After the deposition, the Si dislocation loops, which could also make contributions to the ab- substrates were removed by mixed solution of hydrofluoric and sorption increase of the FSD film [19]. After 500 C annealing in Ar nitric acid in order to get the optical grade freestanding poly- atmosphere, a clear optical absorption peak appears at about crystalline diamond film. 375 nm, which is a well-known SPR absorption characteristic of Ag The FSD film was optically polished on both sides and then NPs [20,21]. The appearance of the Ag SPR absorption peak reveals subjected to Ag ion implantation. The ion implantation was per- the aggregation and growth of the dispersed Ag nucleus or/and formed at room temperature at a fluence of 5.0 1016 ions/cm2 NPs. Such observation of the increases in nanoparticle size is also with the implantation energy of 80 keV in a metal vapor vacuum supported by the sharpening of the Ag(111) diffraction peak in the arc (MEVVA) implanter. In order to avoid significant local temper- GIXRD pattern after 500 C annealing as shown in Fig. 3. Subse- ature rise due to the beam heating, the ion flux was kept at about quent annealing in Ar atmosphere also causes clear reduction in the 4 mA/cm2 during the whole implantation. After implantation, the absorption intensity in the entire wavelength range, which could be samples were cut into pieces and subjected to furnace annealing at attributed to the thermal recovery of ion-implant-created defects 500 C for 1 h in Ar atmosphere. The 80 keV Ag ions have a lon- [22]. gitudinal range of 25.4 nm in diamond with longitudinal straggling Fig. 3 shows the GIXRD patterns of the FSD films implanted with of 4.8 nm as simulated with SRIM-2010 [15]. Therefore, the Ag-ions 80 keV Ag ions at a fluence of 5.0 1016 ions/cm2 and followed by will only introducing damages in near surface region of diamond thermal annealing in Ar atmosphere. In all the spectra, the films but keep the high ‘structural’ quality of the bulk FSD films. diffraction peaks observed at 2q ¼ 43.92, can be assigned to (111) A UV-3600 double-beam spectrophotometer in a wavelength planes of the diamond [23,24]. The insert figure of the XPS obtained range from 200 to 800 nm was used to characterize the absorption from the prepared FSD film shows that the C1s peak is located at properties. X-ray photoelectron spectroscopy (XPS) measurements 285 eV, which further supports that the component of the prepared were performed on a PHI1600-ESCA system with an incident ra- film is mainly sp3 diamond phase [25]. After Ag ion implantation, a diation source of Mg Ka(hn ¼ 1253.6 eV) to reveal the chemical diffraction peak at 2q ¼ 38.1(Ag (111)) is also noticed, which is charge states of carbon of the FSD film. Grazing incidence X-ray attributed to the Ag(111), indicating the formation of metallic Ag diffraction (GIXRD) measurements were made by using Cu Ka line [21]. The fact that the sharpness of (111) plane diffraction of dia- (l ¼ 0.154 nm) with an incident angle of 0.3 to identify the for- mond still remains at the same level after Ag ion implantation mation and evolution of Ag NPs. Field emission scanning electron suggests that a little structure damage is introduced by Ag ion microscope (SEM) operated at an electron energy of 10 keV and implantation. Thus, the clear decrease in transparency of the Ag- atomic force microscope (AFM) worked in the contact mode with a implanted diamond film as shown in Fig. 2 is mainly attributed to scanning area of 10 10 mm2 were employed to investigate the the disperse distribution of Ag nucleus and/or Ag NPs. After 500 C surface morphologies of the diamond films, and also to evaluate the annealing in Ar atmosphere, Ag (111) peak is increased in intensity NPs sizes. Raman spectroscopy using 514.5 nm argon laser beam and narrowed in width, which indicates that the average particle was used to confirm the ‘structural’ quality of the FSD film after size is increased and the size distribution is possibly narrowed. The implantation. Hall effects measurements by the van der Pauw results demonstrate that thermal annealing in Ar atmosphere method were performed at room temperature on the Accent induce the growth of the Ag NPs, which is in good accordance with HL5500 Hall System. the results from UVevis absorption (see Fig. 2). The grain size(D) of Download English Version: https://daneshyari.com/en/article/1688241

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