简介概要

Low-temperature synthesis of SiC nanowires with Ni catalyst

来源期刊：Rare Metals2019年第3期

论文作者：Wei-Li Xie Xiao-Dong Zhang Wen-Hui Liu Qi Xie Guang-Wu Wen Xiao-Xiao Huang Jian-Dong Zhu Fei-Xiang Ma

文章页码：206 - 209

摘要：SiC nano wires were fabricated on the silicon substrate dipped with a layer of Ni catalyst at 900 ℃ by gas pressure annealing processing. The morphologies and crystal structures were determined by scanning electron microscopy（SEM）, transmission electron microscopy（TEM）and X-ray diffraction（XRD）. The results show that the assynthesized nanowires are β-SiC single crystalline with diameter range of 50-100 nm, and length of tens of micron by directly annealing at 900 ℃. The SiC nano wires grow along the [111] direction with highly uniform morphology. And the possible growth mechanism of SiC nano wires is proposed.The present work provides an efficient strategy for the production of high-quality SiC nano wires.

稀有金属(英文版) 2019,38(03),206-209

Low-temperature synthesis of SiC nanowires with Ni catalyst

Wei-Li Xie Xiao-Dong Zhang Wen-Hui Liu Qi Xie Guang-Wu Wen Xiao-Xiao Huang Jian-Dong Zhu Fei-Xiang Ma

School of Material Science and Engineering,Harbin Institute of Technology

Department of Prosthodontics,School of Stomatology,Harbin Medical University

School of Material Science and Engineering,Harbin Institute of Technology at Weihai

作者简介：*Xiao-Dong Zhang,e-mail: zhangxiaodong@hit.edu.cn;

收稿日期：17 December 2013

基金：financially supported by the National High Technology Research and Development Program (No. 2007AA03Z340);the National Natural Science Foundation of China (Nos. 51202045,51021002, 51172050, 51102063, 51372052 and 50672018);the Fundamental Research Funds for the Central Universities(No. HIT. NSRIF. 2013004);the Key Technology Research and Development Program of Heilongjiang Province (No. GC12C305-3);

Low-temperature synthesis of SiC nanowires with Ni catalyst

Wei-Li Xie Xiao-Dong Zhang Wen-Hui Liu Qi Xie Guang-Wu Wen Xiao-Xiao Huang Jian-Dong Zhu Fei-Xiang Ma

School of Material Science and Engineering,Harbin Institute of Technology

Department of Prosthodontics,School of Stomatology,Harbin Medical University

School of Material Science and Engineering,Harbin Institute of Technology at Weihai

Abstract：

SiC nano wires were fabricated on the silicon substrate dipped with a layer of Ni catalyst at 900 ℃ by gas pressure annealing processing. The morphologies and crystal structures were determined by scanning electron microscopy(SEM), transmission electron microscopy(TEM)and X-ray diffraction(XRD). The results show that the assynthesized nanowires are β-SiC single crystalline with diameter range of 50-100 nm, and length of tens of micron by directly annealing at 900 ℃. The SiC nano wires grow along the [111] direction with highly uniform morphology. And the possible growth mechanism of SiC nano wires is proposed.The present work provides an efficient strategy for the production of high-quality SiC nano wires.

Keyword：

SiC nanowires; Single crystalline silicon; Ni catalyst; Growth mechanism;

Received： 17 December 2013

1 Introduction

Since the discovery of carbon nanotube by Iijima [ 1] in1991,researches on one-dimensional nanomaterials have been in the ascendant.As significant one-dimensional nanomaterials,SiC nanowires always gain popularity and become the hotspot of research since their first synthesis by Dai et al. [ 2] .The SiC nano wires with a lot of excellent performances,such as wide band gap,high thermal conductivity,high carrier saturated drift velocity,strong voltage breakdown resistance and excellent field emission performance,show enormous application potentials in the field of micro-/nanoelectronic devices.In addition,the SiC nanowires with excellent mechanical properties are ideal reinforcement for advanced composites [ 3] .There are various methods for the synthesis of SiC nano wires,including chemical vapor deposition method (CVD) [ 4] ,template method [ 5] ,carbothermic method [ 6, 7] ,laser ablation [ 8] and arc process [ 9] .However,those synthesis methods generally have the defects of complex process,high cost and long production period,or generate harmful gases during the production process,resulting in health damage and environmental pollution,which restrain the development of SiC nanowires to a large degree.In our previous work,a novel method was applied to produce large number of SiC nano wires,in which required reaction temperature should be over 1,500℃ [ 10] .In this paper,a novel process was proposed using Ni nanopowders as catalyst to prepare monocrystalβ-SiC nano wires at 900℃and the growth mechanism was also proposed.

2 Experimental

2.1 Synthesis of SiC nano wires

The synthetic experiment is conducted in atmosphere sintering furnace with graphite as heating element.The reaction steps were as below:(1) dipping a monocrystalline silicon piece in a hydrofluoric acid solution to remove the oxidation layer on the surface of the monocrystalline silicon piece;(2) cleaning the metal nanometer Ni catalyst in a diluted hydrochloric acid solution,and repeatedly cleaning by deionized water and adding the catalyst in dispersing agent for ultrasonic dispersion for 5 min to obtain a dispersion liquid,wherein the weight ratio of the metal nanometer powder catalyst to the dispersion liquid was1.00:0.83,and the dispersion liquid is absolute ethyl alcohol;(3) soaking the monocrystalline silicon piece obtained in Step 1 in the dispersion liquid obtained in Step 2for 10 s;(4) placing the monocrystalline silicon piece obtained in Step 3 and a graphite nanopowder in weight ratio of 1:1 in the atmosphere sintering furnace,vacuuming until the pressure in the atmosphere sintering furnace reached10-30 Pa,filling Ar gas with the initial gas pressure of0.2 MPa,controlling the heating rate of the sintering furnace at 10-15℃.min^-1 until the temperature in the furnace reached 900℃for 2 h and cooling the furnace to room temperature to obtain the SiC nano wires.

2.2 Characterization

Phase identification was performed by X-ray diffraction(XRD,Shimadzu xrd-6000) using Cu Kαradiation(λ=0.15,418 nm).The chemical composition of the synthesized nanowires was analyzed using Fourier transform infrared spectroscopy (FTIR,Varian Excalibur3100).Scanning electron microscopy (SEM) images were taken on Hitachi S-4700 field emission scanning electron microscope with energy-dispersive spectrum (EDS).Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were examined by Philips CM 12 transmission electron microscope with accelerating voltage of 200 kV.The high-resolution transmission electron microscopy (HRTEM) image was taken on Tecnai F30FEG transmission electron microscope at300 kV.

3 Results and discussion

3.1 Characterization of SiC nano wires

Figure 1 shows the XRD pattern of the nanowires obtained under reaction temperature of 900℃.Diffraction peaks at36℃,41.3°,60°,71.8°and 75.5°are corresponding to (111),(200),(220),(311) and (222) crystal faces of theβ-SiC,respectively,which proves that the obtained sample is cubic phaseβ-SiC consistent with the result in Ref. [ 11] .Meanwhile,a diffraction peak at 33.7°is caused by stacking faults [ 12, 13] ,indicating that a certain amount of stacking faults (SF) exist in the nano wires.

Fig.1 XRD pattern of SiC nano wires obtained at 1,000℃

Fig.2 FTIR spectrum of[β-SiC nano wires

Figure 2 shows the FTIR spectrum of the synthesized nano wires.The peak at 814 cm^-1 can be assigned to Si-C bond [ 11] ,which indicates that SiC formed during the raw sample is annealed under the Ar atmosphere.Other peaks occurred in the spectrum suggest that there are also Si-O bond and-OH bond in the nano wires.Thus,a small amount of SiO₂ and H₂O may exist in the sample.

Figure 3 shows the SEM images of samples synthesized at 900℃for 2 h under initial pressure of 0.2 MPa.It can be seen from Fig.3a-d that the SiC nano wires have length of dozens of microns and quite uniform diameter distributing at about 80 nm with relatively flexural lines.It is very interesting that most of the nanowires are flexural,which should be reduced by the growth processing.Meanwhile,EDS was also carried on the nano wires sample.From Fig.3e,it can be found that three elements exist in the sample (Au is introduced by spinning before SEM testing).Thus,it is clear that the synthesized SiC nano wires may accompany with silicon oxide.

In order to further investigate the structures of SiC nano wires,the synthesized SiC nano wires were subjected to TEM and SAED analysis as shown in Fig.4.Figure 4a shows TEM image of a typical nanowire with respective diameter of about 80 nm,and it can be seen that the nanowire has an extraordinarily smooth surface.The S AED patterns in Fig.4 determine that the SiC nano wires are monocrystal phase ofβ-SiC,which is corresponding to the above XRD analysis results.The HRTEM image in Fig.4c shows that the parallel stripes perpendicular to the axis direction of the nano wires have a spacing of 0.25 nm,which equals to the interplanar spacing (d=0.25 nm) of the[111]crystal face of the cubic phaseβ-SiC.These results further confirm that the SiC nano wires have growth direction along[111]of theβ-SiC.

Fig.3 SEM images of the synthesized nanowires at different resolutions a-d and EDS spectrum of nanowires e

Fig.4 TEM analysis of a typical SiC nano wire:a TEM image,b S AED pattern of red round area marked in a and c HRTEM analysis of rectangle area marked in a

3.2 Growth mechanism of SiC nano wires

A large amount of SEM observations show no solidified catalyst particles at ends of the nano wires,indicating that the nanowires do not grow according to the traditional vapor-liquid-solid (VLS) growth mechanism [ 14, 15] .As shown in Fig.5 a,silicon slice is covered with Ni nanopowders before annealing treatment.After annealing inside the gas pressure furnace,fused-like metal liquid emerges and some nanowires begin to grow,as shown in Fig.5b.Therefore,the growth process of the nano wires needs to be interpreted by a new mechanism.The reaction temperature selected here is lower than 1,000℃and far below the melting point of silicon (1,410℃),resulting in that the saturated vapor pressure of silicon in the reaction system is quite low and can be ignored [ 16] .In addition,no extraneous silicon gas source exists in the system.Therefore,the possibility that vapor silicon provides the silicon for the growth of the nano wires can be eliminated.As the silicon piece is treated with a layer of Ni as the catalyst,Ni and silicon piece can form liquid alloy molten globules under low temperature so as to provide silicon source for the growth of the nano wires.The nickel nanoparticles selected here as the catalyst can form metal molten globules with silicon at temperature lower than eutectic point(964℃) of nickel-silicon,so that the nanowires form under the reaction temperature of 900℃.Meanwhile,as a small amount of oxygen in the atmosphere sintering furnace reacts with the graphite powder to generate CO gas to provide carbon source for the growth of the nano wires,a growth model concluded in Fig.6 can be used to explain the growth process of the nano wires.

The growth of the nanowires can be pided into four stages.First,the graphite powders react with the small amount of oxygen in the atmosphere sintering furnace above 700℃to generate CO,and the amount of CO increases with the increase of the temperature.Then,as the temperature increases,the catalyst and the Ni-Si alloy will form the molten globules with low eutectic point.After that,CO molecules dissolve into Ni-Si alloy molten globules,and C and Si atoms preferentially precipitate along a dense surface[111]of theβ-SiC to form SiC nano whiskers from the alloy molten globules.At last,with the further proceeding of the reaction,SiC continues to grow along the[111]direction and newly formed SiC precipitates from the molten globules and pushes up the formerly precipitated SiC nano wires,thereby a growth mode from the bottom to the top forms.

Fig.5 SEM images of samples:a silicon slice dipped with Ni nanopowders and b nanowires emerged at initial growth stage

Fig.6 Schematic illustration of growth of SiC nanowires

4 Conclusion

Monocrystalline silicon piece subjected to surface treatment was used as silicon source to prepare a large amount of SiC nano wires on silicon substrate with a layer of metal catalyst coated on the surface.The nanowires are monocrystals of cubic silicon carbide with diameter in the range of50-100 nm,length of tens of micron and growth direction of[111].The method for preparing SiC nano wires has advantages of simple process,low cost,short production period,low reaction temperature,no harmful gas generated in the process,no harm to human health and no environmental pollution,etc.