, 2017, 31(7): 511-517

Reducin g Contact Resistance of Carbon Nanotubes by Au Doping

1 华北理工大学机械工程学院 唐山 063009
2 华北理工大学理学院 唐山 063009
3 华北理工大学材料科学与工程学院 唐山 063009
DIAO Jiajia1, CHANG Chunrui2,, ZHANG Zhiming3, ZHANG Haoqiang1, SUN Hongchan1, AN Libao1,
1 College of Mechanical Engineering, North China University of Science and Technology, Tangshan 063009, China
2 College of Science, North China University of Science and Technology, Tangshan 063009, China
3 College of Materials Science and Engineering, North China University of Science and Technology, Tangshan 063009, China
DIAO Jiajia, CHANG Chunrui, ZHANG Zhiming, ZHANG Haoqiang, SUN Hongchan, AN Libao. Reducin g Contact Resistance of Carbon Nanotubes by Au Doping. Chinese Journal of Material Research[J], 2017, 31(7): 511-517 doi:10.11901/1005.3093.2016.394

Abstract:

A prerequisite for the application of carbon nanotubes (CNTs) in the industrial sectors of micro- and nano-electronics, it is essential to reduce its contact resistance with metal. Doping Au-nanoparticles can effectively reduce the contact resistance of CNTs. In this paper, a three step process was developed for doping Au-nanoparticles on CNTs, i.e. first, the CNTs are calcinated at high temperature to create defects and hydrophilic groups on their surface, then, the calcinated CNTs are dispersed ultrasonically in chloroauric acid solution to adsorb chloroauric acid, and finally, they are heated in hydrogen atmosphere at high temperature to produce Au-nanoparticles on the surface of CNTs. The produced CNTs are characterized by means of scanning electron microscopy (SEM) X-ray energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Results show that due to the Au-doping, the G-band peak of Raman spectra of the CNTs shifts to a lower frequency, which indicates that the doping is N-type. N-type dopants transfer electrons to adjacent carbon atoms and increase the electron quantity in CNTs, thereby increasing the electrical conductivity of CNTs. Subsequently, CNTs are assembled into the interval of two Au electrodes by dielectrophoresis (DEP), and the results of real-time measurement by using a precision inductance-capacitance-resistance (LCR) show that the contact resistance between the Au-doped CNTs and Au electrodes has been effectively reduced to ca. half of the original values between the bare CNTs and Au electrodes .

Key words: composite ; carbon nanotube ; Au nanoparticle ; doping ; contact resistance

$2 HAuC l 4 · 4 H 2 O + 3 H 2 [ ≜ ] 8 HCl ↑ + 2 Au + 8 H 2 O ↑$ (1)

1 实验方法

2 实验结果与讨论
2.1 表征与分析

Fig.1

SEM images of the samples of (a) MWNT-P, (b) MWNT-T, (c) MWNT-T-HAuCl44H2O, (d) MWNT-T-Au

X射线能谱仪(EDS)可以用来分析样品中所含元素的种类及含量。图2为各碳纳米管样品的EDS谱图。由于各样品是将碳纳米管置于异丙醇溶液中超声分散后滴于硅基片上制备而成的,所以能谱分析结果中每个样品都明显含有大量的硅和一定量的氧(硅被氧化所致)。比较各EDS谱图可以发现,标记为MWNT-T的样品中不含有金而标记为MWNT-T-HAuCl44H2O的样品中含有金和氯元素,说明碳纳米管原样中不含有金,碳纳米管在氯金酸溶液中浸泡并过滤后掺杂上了金和氯。标记为MWNT-T-Au的最终掺杂样品中只含有金而不含氯,说明经氢气还原后,金是唯一掺杂在碳纳米管上的物质。这一结果也解释了图1c和d中还原前、后碳纳米管表面纳米粒子直径的变化。

Fig.2

EDS spectra of the samples of (a) MWNT-T, (b) MWNT-T-HAuCl4·4H2O, (c) MWNT-T-Au

X射线光电子谱(XPS)可以用来更精确地分析样品中所含元素的种类、含量以及各原子价态。图3为掺金碳纳米管样品(MWNT-T-Au)表面的XPS谱。从图3a中可以看出,在相应结合能处分别出现了对应Au4f、C1s和O1s的峰。检测到的O1s是由于样品吸附水分或高温焙烧碳纳米管时在其表面形成含氧官能团所致,所以EDS能谱分析中的氧除硅基片被氧化所致还包含样品中携带的氧。在Au4f XPS谱中(图3b),呈现金的两个特征峰,其中结合能84 eV处的峰对应Au04f7/2,而结合能87.7 eV处的峰对应 Au04f5/2,说明在H2还原反应之后得到了碳纳米管掺金样品。进一步地,根据XPS分析出掺金碳纳米管样品中只含有碳、氧和金三种元素,且碳、氧、金元素含量分别为93.75%、6.2%、0.05%。还原反应之后,没有检测到氯元素,说明氯金酸已被氢气完全还原,金是唯一掺杂在碳纳米管上的元素,这一点也与上述EDS分析的结果相一致。需要指出,掺金碳纳米管样品中金的含量并不高,但这种方法掺杂的金纳米颗粒粒径较小、较均匀。

MWNT-T-Au样品的XPS谱

Fig.3

XPS spectra of the samples of MWNT-T-Au, (a) the spectral region from 50 to 550 eV, (b) Au 4f

Fig.4

Raman spectra of CNT samples

2.2 金掺杂碳纳米管的电接触特性研究

Fig.5

Changes of contact resistance between CNTs and electrodes before and after doping

3 结论

The authors have declared that no competing interests exist.

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DIAO Jiajia
CHANG Chunrui
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