Supplementary information to
Preparation and Electrical Properties of Sintered Copper Powder Compacts Modified by Polydopamine Derived Carbon Nano Films
Zhengfeng Jia1,2, 3, Haoqi Li2, Yao Zhao2, Dmitriy A. Dikin2, Junjie Ni1, Limin Zhao1, Jinming Zhen1, Bo Ge1, Xin Shao1*, and Fei Ren2*
1College of Materials Science and Engineering, Liaocheng University, Liaocheng 252059, PR China
2Department of Mechanical Engineering, Temple University, Philadelphia, PA19122, USA
3State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 73000, PR China
Figure S1 shows the XPS high resolutionspectraof N1sfor Cu/PDA particles before and after heat treatments at 400 oC, 600 oC, and 800 oC, respectively. The main peak centered at the 400.25 eV can be attributed to the aminic nitrogen (such as R-NH2 group of dopamine), indicating the existence of polydopamine in the composites [1]. As the coating time being increased to 8 hour, the pyrrolic N peak at 397.8 eV was observed. After heat treatment at 400oC, the aminic-N peakat 400.25 eV becameweaker. In contrast, the peaks at 399.1 eV and 398.1 eV became stronger, which indicates that the amount of pyrrolic-N and pyridinic-N bonds increased as a result of heat treatment [2]. After heat treatment at 600oC, graphitic-N (at about 401.1 eV), pyrrolic-N, and pyridinic-N were all observed. After heat treatment at 800oC, the pyrrolic-N, griphitic-N and pyridinic-N were still detectable. Comparing these three N1s spectra, it is obvious that the pyrrolic-N was converted into pyridinic-N and graphitic-N as the pyrolysis temperature increased. Many researchers suggested that DA couldbe oxidized into 5, 6-dihydroxyindole or pyrrolic compounds under alkaline conditions, which was further self-polymerized into PDA through rearrangement and cross-linking [3]. The PDA can be further carbonized into N-doped graphite-like materialduring heat treatment [4].
A separate experiment was conducted to study the cleaning of Cu particles during the coating process. Ten gramsof Cu powderwas mechanically stirred in 50 ml of Tris buffer solution, which turned to blue color after 10-min stirring, implyingthe existence of Cu ions [5,6]. Then,the Cu particles were removed from the solution by filtration, and 0.124 g of dopamine hydrochloride powder was dissolved inthesolution. The solutionwas continuously stirred, during which period black particles formed. Stirring was stopped after 8 hr and the black powderwas collected by filtration, followed bycleaning with deionized water and 3-hr drying at 50 oC in air using a laboratory oven. The dried powderwas futher heat treated at 600 oC in vacuum.
As shown in Figure S2, the FESEM image reveals that many nano particles are formed inside of cPDAparticlesafter the heattreatment.The XRD analysis of the samples before and after heat treatment is shown in Figure S2d. The broad XRD peak around 25o is likely related to PDA[7].Cu peaks were observedin the sample after heat treatment, indicating the formation of metallic Cu.
Based on these observations, it is possible that during the coating process, surface oxide of Cu particles dissolves in the Trisbuffer, provides oxygen for DA polymerization and forms complex of PDA and Cu2+[8], which then is reduced to cPDA and metallic Cu as a result of heat treatment in vacuum. Therefore, we can assume that in many cases the triple and quadruple junctions as well as other pockets between Cu grains in the sintered samples are packed with cPDA-nano-Cu-particlesaggregates.
References
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(a) (b)
(c) (d)
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Figure S1 The deconvoluted XPS curves of the N1s peak of the Cu/PDA composite powders coated for 10 min (a) and 8 hour (b); heat treatedat 400 oC (c), 600oC (d) and 800oC (e) of the Cu/PDA composites coated for 8 hour.
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Figure S2FESEM image of PDA (a)；FESEM images of Cu/cPDA powders after heat treatment at 600 oC (b and c); XRD profiles (d) of the Cu/PDA powders before and after heat treatment at 600 oC.