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Introduction:

We studied Deposition of copper using electroless deposition technique

[1,2]. In electroless deposition, unlike electro-deposition the potential

difference required by the ions to migrate toward negative electrode (the

cathode) is not needed to be applied externally. The electric potential required

for the migration of the metal ions to be deposited comes from the metals used

with the substrate. Metals at the top of the electrochemical series are good at

giving away electrons. They are good reducing agents. The reducing ability of

the metal increases as one goes up the series. Metal ions at the bottom of the

electrochemical series are good at picking up electrons. They are good

oxidising agents. The oxidising ability of the metal ions increases as you go

down the series. The list of ions arranged in sequence is given below:

Table – 5.1 : Electrochemical Series

Sr. No. Element / Other Result of Reaction

Electrode Potential V

Gold Au+ + e- = Au 1.692

Silver Ag+ + e- = Ag 0.7996

Copper Cu+ + e- = Cu 0.521

Copper Cu2+ + 2 e- = Cu 0.3419

Iron Fe3+ + 3 e- = Fe -0.037

Aluminum Al 3+ + 3 e- = Al -1.662

Magnesium Mg2+ + 2 e- = Mg -2.372

Magnesium Mg+ + e- = Mg -2.7

Calcium Ca+ + e- = Ca -3.8

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Electro deposition has been used for many applications; it has been

found that nano wires could be grown using electroless deposition technique

[3]. Zhongliang Shi et.al[4]. demonstrated that Pd nano-wires can be grown by

electroless deposition in a short time of 2 minutes. Scanning Electron

Microscope photograph of their sample are shown below:

(a) (b)

(c) (d)

Fig. 5.1. Scanning electron micrographs (a-d) of Pd nano-wires grown by electroless deposition by Zhongliang Shi et.al.[4].

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Electroless deposition of metals on paper and on polymer sheets used for

OHP transparencies using line patterning as shown by Arlene Concepción

et.al.[5]. They deposited Gold films on paper using line pattern technique. The

interest in the above cases is to deposit very small masses having a desired

configuration like tiny nano particles or nano wires. All the deposits in such

studies do not confirm to the needs as most of the parameters are left to

themselves as there is no chance to control the field and drifting of the ions,

once the cell is setup.

We used Electroless deposition technique like Patil A.G [6-8] with

Copper Sulphate solution in an Electroless deposition cell with aluminum plate

that is used to support the substrate as one of the electrode.

We present the electroless deposition of a metal like copper in a small

cavity where the deposition is governed by DLA like processes and hence the

growth patterns very much resemble the DLA patterns[9]. Many experiments

have been conducted using copper sulphate solution in different concentrations

and numbers of dendritic patterns are grown. Many experiments either fail to

produce good dendritic patterns exhibiting self-similarity and fractal character,

if the cell working conditions are not consistent with the requirements of

diffusion limited aggregation of the ions present. It is observed that if the

thickness of the electrolyte is more, the depositions tend for form globules and

lumps. If the spacing between aluminum, paper and glass is kept small, the

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thickness of the electrolyte is small and better dendritic patterns are observed

under such conditions. Type of paper used also affects the electroless deposits.

5.2 EXPERIMENTAL :

Electroless deposition Cell was made from two glass plates separated

apart by an Aluminum plate and the deposition substrate over it. Fig. 5.2 shows

a cross sectional view of the electroless deposition used during the

experiments. The size of the plates used in the cell was 75mm X 125 mm.

During initial experiments, high quality glass plates with surface finish were

used, however it was found that the surface quality of the glass plate was not

among governing parameter, therefore flat glass plates were used for rest of the

experiments. We used different types of papers with different thickness, texture

and porosity to see the effect on the patterns grown. We also tried different

concentration of the Copper Sulphate solution.

Fig. 5.2 Cross section of the Electroless deposition cell

The experiment was setup by placing a paper of the same size as that of

the Aluminum plate (and hence the cell) and pouring the electrolytic solution

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(Copper Sulphate) over it, to completely wet the paper with a layer of

electrolyte over it. This was sandwiched between the two glass plates. At times

the solution flows from the sides while packing the cell and forms a thin layer

between the lower glass plate and the aluminum plate. This part of the solution

has practically no role in the electroless deposition, however, it was found to

cause pitting of the aluminum plate from this side by way of chemical reaction.

The whole assembly was then clamped to maintain the plates in place. Paper

clamps were used at four corners, in some of the experiments two rubber bands

were also used and found to work satisfactorily.

The cell was filled with the electrolyte solution and properly clamped,

the cell was clamped and left open to air for 4 to 8 hours. It was observed that

nucleation begins approximately within two hours and fine spots appear on the

paper substrate. On standing, these spots slowly grow in shape and size, some

of them show rapid growth and the others are found to be slower in growth.

Few of the spots grow into lumps and others in to some patterns and few of

them result in beautiful dendritic patterns. It was also found that the growth is

more common near the edges of the cell as compared to the rest of the portions.

Good dendritic patterns at time were observed far away from the edges.

It was observed that depending on the type of paper used, the thickness

of the electrolyte layer was changing, papers with more irregular shapes (such

as ordinary filter papers) were found to trap a thicker layer of electrolyte as

compared to ordinary paper. The effect of this change in electrolyte thickness

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was that it use to take a longer time to completely dry and for the deposition

process to be over. Also because of more of electrolyte, the deposits tend to

form lumps, rather than dendritic patterns as shown in Fig. 5.3 below.

Fig. 5.3 Showing formation of lumps of metal deposits along with dendritic patterns.

However if the cell is carefully set taking care to keep uniform spacing

and pressure to reduce the difference in thickness of the electrolyte dendritic

patterns are also observed as shown in Fig. 5.4a. The texture of the growth

pattern is little deformed as the photograph was taken after two days. This

resulted in dislodging of fragments of copper at the boundary of the deposit.

Another deposit where most of the growth is dislodged is shown in Fig 5.4b.

(a) (b)

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Fig. 5.4 Showing electroless deposits with broken amorphous fragments.

It was observed that not all the experiments result in good dendritic

pattern with self similarity or fractal character. Many experiments, where the

cell conditions are not consistent with the requirement of DLA result in poor

growth patterns with dots and lumps only as shown in Fig 5.5.

Fig. 5.5 Showing electroless deposition under poor conditions with lumps and limited dendritic patterns.

Carefully arranged experiments result in beautiful tree like structures

with secondary and tertiary branches from number of points. Also it is

observed that in most of the cases the dendritic patterns exhibiting fractal

character are developed near the edge of the cell. This is attributed to the role

of the drying process that is more effective near the edge of the cell. Fig 5.6

shows the electroless deposition obtained with a 0.5 Molar CuSO4 solution in 6

hours time. The branch on left corner of the growth is little diffused and shows

tendency to deposit according to the crystal structure and the side branches in

this isolated case are at right angles.

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Fig 5.6. Showing electroless deposition obtained with a 0.5 Molar CuSO4 solution in 6 hours.

To study the effect of the concentration of electrolyte used, different

strengths of solution were tried. It was observed that in addition to the

concentration of the solution used, there are number of factors such as rate of

drying, temperature, humidity and air convection currents in the surrounding

region. However, other conditions remaining identical it was observed that the

growth under higher concentration either results in formation of lumps or very

crowded dendritic pattern with dense branching with well developed secondary

and tertiary branches.

Fig. 5.7. Showing electroless deposition obtained with a 1.0 Molar CuSO4 solution.

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Fig. 5.7 shows an electroless deposition obtained using 1 Molar copper

sulphate solution after 6 hours. Tips of the figure started blackening and tend to

become broader as the solution has almost dried up, the growth was stopped at

this point.

The electroless deposits do not have good physical strength and the

growth being porous; it is prone to oxidation on standing. The growth gradually

turns brownish to black on standing for long time as seen in Fig 5.4. This also

results in reducing the physical strength of the growth, on standing for long

time, particles from the growth are detached and the growth loses its shape. On

rough handling the entire growth was found to be detached from the substrate

paper as is seen in Fig. 5.4b.

5.3 Fractal Dimension of the Electroless Growth Patterns:

Few dendritic patterns grown under optimum operating conditions are

presented below. These dendritic patterns were obtained with electroless

deposition using a CuSO4 solution having 0.5M concentration.

The Electroless depositions shown in Figure 5.8 a, b, c, d and e were

analysed for self similarity and fractal dimensions. The figures were first

converted to two bit black and white images and saved in bitmap files with

.BMP extension for further processing.

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(a) (b)

(c)

(d) (e) Fig. 5.8 Electroless depositions using a CuSO4 solution (0.5M).

Box counting was implemented on all the patterns using a computer

program written in Basic. The program finds the size of the image in pixels and

based on the size of the image, conducts the box counting procedure selecting

suitable size of the boxes. For large size boxes say 100 pixels, if the next box is

selected with a side length of 101 pixels, this result in more number of readings

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but the points become very much crowded. The program starts counting the

number of boxes (N) required to completely cover the image, starting with the

box side length equal to one pixel. The number of boxes (N) of size (r) required

to cover the image are recorded, also log(N) and log(r) computed and stored in

a file for further use. The counting process continues up to a box size less than

one third the Faret’s diameter. A typical table recorded for the analysis of Fig.

5.8 (a) is show below.

Table – 5.2 Table showing the box size and number of boxes required

r N Log(r ) Log(N) 1 151128 0 5.1793

2 45450 0.301 4.6575

3 20772 0.4771 4.3175

4 12012 0.6021 4.0796

5 7834 0.699 3.894

6 5547 0.7782 3.7441

7 4114 0.8451 3.6143

8 3208 0.9031 3.5062

9 2574 0.9542 3.4106

11 1744 1.0414 3.2415

13 1297 1.1139 3.1129

15 992 1.1761 2.9965

17 795 1.2304 2.9004

20 586 1.301 2.7679

23 448 1.3617 2.6513

26 365 1.415 2.5623

30 280 1.4771 2.4472

34 232 1.5315 2.3655

39 173 1.5911 2.238

44 143 1.6435 2.1553

50 120 1.699 2.0792

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r N Log(r ) Log(N) 57 89 1.7559 1.9494

64 75 1.8062 1.8751

72 64 1.8573 1.8062

81 50 1.9085 1.699

91 41 1.959 1.6128

103 32 2.0128 1.5051

116 29 2.0645 1.4624

131 25 2.1173 1.3979

147 20 2.1673 1.301

165 18 2.2175 1.2553

186 15 2.2695 1.1761

209 11 2.3201 1.0414

A graph is plotted with log(r) on x-axis and the log(N) on the axis of y.

This results in a plots that fits to a straight line as shown in the Fig. 5.9 below.

y = -1.799x + 5.2611

R2 = 0.9993

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5log(r)

log

(N)

Data

Least Square Fit to Data

Fig. 5.9 Plot of log(N) versus log(r) for box counting of Fig. 5.8 (a).

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Fig. 5.9 to Fig. 5.13 are the plots of log(N) versus log(r) as described

above for the five dendritic fractal patterns shown in Fig. 5.8(a) to 5.8(e)

respectively.

y = -1.7835x + 5.1246

R2 = 0.9986

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5log(r)

log

(N)

Data

Least Square Fit to Data

Fig. 5.10 Plot of log(N) versus log(r) for box counting of Fig. 5.8 (b).

y = -1.7705x + 5.2701

R2 = 0.9989

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5log(r)

log

(N)

Data

Least Square Fit to Data

Fig. 5.11 Plot of log(N) versus log(r) for box counting of Fig. 5.8 (c).

139

y = -1.7859x + 5.4269

R2 = 0.9997

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5log(r)

log

(N)

Data

Least Square Fit to Data

Fig. 5.12 Plot of log(N) versus log(r) for box counting of Fig. 5.8 (d).

y = -1.753x + 4.8306

R2 = 0.9988

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5log(r)

log

(N)

Data

Least Square Fit to Data

Fig. 5.13 Plot of log(N) versus log(r) for box counting of Fig. 5.8 (e).

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Points plotted, show by small circles are actual data points and the line joining

the points is the least square fit applied to these point. The equation in the inset

of the plot is the equation to the straight line that best fits to the data points and

the fractal dimension is obtained from the slope of this line.

Table – 5.3

Comparison of Fractal dimensions of Fig. 5.8 a to e

Sr. No. Fig # Fractal Dimension

1 a 1.7835

2 b 1.7990

3 c 1.7705

4 d 1.7859

5 e 1.7530

It is seen from the Fig. 5.9 to 5.13 that all the points lie along a straight

line for all the plots indicating that the dendritic patterns shown in Fig 5.8(a) to

Fig 5.8(e) all exhibit self similarity over entire region of the length scale used

and thus confirms the fractal character of these dendritic patterns. Comparison

of the Fractal dimensions of the said figures show that all the fractal

dimensions lie close to each other and are in the range of about 1.75 to 1.79. A

higher fractal dimension is indicative of crowded and dense branching. As the

Dendritic patterns shown in Fig 5.8(a) to Fig 5.8(e) are having crowded

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branching with primary, secondary and tertiary branches, the fractal dimension

is on the higher side i.e. 1.77 on an average.

It was found from series of the experiments that for various

concentrations used, from 1 Molar solution to very dilute solution, there is no

appreciable difference in the shape and morphology of the growth of the

dendritic patters obtained. It was observed that routinely it takes about four to

eight hours for the growth process to complete.

142

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1. Vicsek; T.A; `Fractal Growth Phenomena’World Scientific Singapore

(1992).

2. Paranjpe; A.S; Lalwani, S.K; Josh, V.M; Ind. J. pure & app. phy 35

316-321 (1997).

3. Robert W. Zehner and Lawrence R. Sita, Langmuir, 1999, 15 (19), pp

6139–6141.

4. Zhongliang Shi, Shanqiang Wu, Jerzy A Szpunar and Mustapha Rosh,

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steel substrate by electroless deposition, Journal of Membrane Science,

280 (2006) 705-711.

5. “Electroless Deposition Of Metals On Paper Using Line Patterning”,

Arlene Concepción et.al. Proceeding of the National Conference On

Undergraduate Research (NCUR) 2002, University of Wisconsin-

Whitewater, Whitewater, Wisconsin, April 25-27, 2002.

6. Patil A.G; `Fractal Growth Phenomena’, A Ph.D thesis Dr. B.A.M.U

Aurangabad, (2001).

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phenomena’ Submitted to Dr. B.A.M. University Aurangabad.

8. Witten T.A and Sander, L.M. phy rev. lett. 47, 1400 (1981).