Supplementary Material

Fabrication of user-defined copper conductive patterns onto paper

substrate for flexible electronics by combining wax patterning with

electroless plating

Lei Hou, Hang Zhao, Yinxiang Lu*

Department of Materials science, Fudan University, Shanghai 200433, China

*Corresponding author. Tel. & fax: +86 21 55665059; E-mail address: yxlu@fudan.edu.cn

S1:The allocations of bonds in the FT-IR spectroscopy

In the spectrum of pristine paper, a wide peak located at 3447 cm-1 is ascribed to the

stretching vibrations of cellulose and absorbed water. The peak observed at 2901 cm-1

is attributed to the stretching vibrations belonging to methyl, methylene and methoxy

groups. The stretching vibrations due to the presence of aromatic rings are observed at

1636 cm-1. The peak located at 1442 cm-1 is attributed to aliphatic and aromatic groups

in the plane deformation vibrations of methyl and methylene groups. The peak around

1045 cm-1 can be attributed to the stretching vibration of alcohols.

S2:Ultrasonic test results

One pristine paper sample was directly immersed into gold nanoparticles solution

without surface treatment, while the other was given the surface modification. Both

samples were then placed in the copper plating bath for electroless deposition. The

significant difference of adhesion degree of these two samples (modified and

unmodified) is detected when the ultrasonically washed in water for 1 h, the weight of

the samples in each step is shown in Table S2. The modification process increases

trivial amount weight (approximately 0.4~0.8 mg) to the paper substrate. After 0.5 h

plating in the same bath, 0.1213 g Cu is deposited on APTMS modified paper, while

only 0.0898g Cu deposited on unmodified paper. It can be concluded that the -NH2

modified surface can catch cupric ions from the electroless plating bath more quickly

than the unmodified one. As the cupric ions adhering to the surface of paper substrate

is reduced, Cu is continuously deposited and metallized to form uniform copper films

via autocatalysis. Additionally, Table S2 also shows that the weight loss of Cu

patterned unmodified paper sample is about 0.0186 g after ultrasonic washing while

nearly no change to Cu patterned modified paper sample. The excellent adhesion

between Cu patterns and the APTMS modified paper can be attributed to not only the

mechanical anchoring force but also the stronger chemical bond which tightly linked

Cu films and paper substrate.

S3: Scherrer formula

Scherrer formula was employed to calculate the mean crystal size of the Cu films as

following .

D = K λ / (B cos θ)

where D is the average crystal size, λ is the X-ray wavelength corresponding to Cu Kα

radiation (0.154 nm), θ is the diffraction angle, K is the Scherrer constant as 0.89 and

B is the full width half maximum (FWHM) of the diffraction peak at 2θ.

Table S1 Composition and operation conditions of gold nanoparticles solution.

Chemical Concentration(g/L)

Chloroauric acid (HAuCl4) 4.0 g/L

Tri-sodium citrate (Na3C6H5O7 • 2H2O) 8.0 g/L

Sodium borohydride (NaBH4) 25 g/L

Sodium chloride (NaCl) 5 g/L

Sodium carbonate (NaCO3) 3.75 g/L

pH 7.5-8.8

Temperature 25 °C

Time 0.5 h

Table S2 Weight of paper a.

Before

plating (g)

After

plating (g)

After

washing

Weight

loss (g)

Unmodified 0.3405 0.4303 0.4117 0.0186

Modified 0.3413 0.4626 0.4622 0.0004

a Errors in determination ± 1%.

Fig.S1. SEM images of unmodified paper-based Cu pattern (a, b) and APTMS

modified paper-based Cu patterns (c, d) before and after ultrasonic test, respectively.

Fig.S2. Optical micrographs of Cu patterned paper before (a) and after (b)

multifolding.