Preface

Chapter 8 **A Process for Preparing High Graphene Sheet Content Carbon**

Chapter 9 **Nanoscale Cu Wiring by Electrodeposition in Supercritical Carbon Dioxide Emulsified Electrolyte 189**

Masato Sone, Tetsuya Shimizu, Nao Shinoda and Tso-Fu Mark

Marta Farinella, Patrizia Livreri, Salvatore Piazza, Carmelo Sunseri

**Evolution and Magnetic Properties of As-Deposited and Post-**

**Evolution and Magnetic Properties of As-Deposited and Post-**

**Materials from Biochar Materials 175** Yan-Jia Liou and Wu-Jang Huang

Chapter 10 **Mechanical Property Evaluation of Electrodeposited Nanocrystalline Metals by Micro-testing 211** Takashi Nagoshi, Tso-Fu Mark Chang and Masato Sone

Chapter 11 **One-Step Electrodeposition of CZTS for Solar Cell**

Levesque and Jean-Paul Chopart

Levesque and Jean-Paul Chopart

Chapter 12 **The Coupled Magnetic Field Effects on the Microstructure**

Chapter 13 **The Coupled Magnetic Field Effects on the Microstructure**

**Annealed Nano-Scaled Co-Based Films — Part I 259** Donggang Li, Qiang Wang, Agnieszka Franczak, Alexandra

**Annealed Nano-Scaled Co-Based Films — Part II 285** Donggang Li, Qiang Wang, Agnieszka Franczak, Alexandra

**Absorber Layer 241**

and Rosalinda Inguanta

**Section 3 Properties 187**

**VI** Contents

Chang

Modern coating industry demands the coatings with high mechanical and electrochemical properties compared to conventional coatings. The nanocoatings offer such advantages to design the new coatings for improved performance. These coatings consist of alternative two or more layers with different composition or structure that exhibit better enhanced me‐ chanical, electrochemical and optical properties compared to a single layer coating. In addi‐ tion, the multilayer coatings are composed of a lot of interfaces parallel to the substrate which can act as barriers of dislocation motion and lead to increase mechanical properties. The electroplating was widely used to electrodeposit the nanostructured coatings because of its relatively low deposition temperature, low cost and controlling the thickness of the coat‐ ings. With advances in electronics and microprocessor, the amount and form of the electro‐ deposition current applied can be controlled. The pulse electrodeposition has the interesting advantages such as higher current density application, higher efficiency and more variable parameters compared to direct current density.

This book collects new developments about electroplating and its use in nanotechnology. I like to express my gratitude to all of the contributors for their high quality manuscripts. I hope open access format of this book will help all researchers and that they will benefit from this collection.

> **Dr. Mahmood Aliofkhazraei** Tarbiat Modares University Iran www.aliofkhazraei.com

**Zero and One Dimensional Nanostructures**

## **Chapter 1**

## **Electrodeposition of Nanostructure Materials**

Souad A. M. Al-Bat'hi

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61389

#### **Abstract**

We are conducting a multi-disciplinary research work that involves development of nanostructured thin films of semiconductors for different applications. Nanotech‐ nology is widely considered to constitute the basis of the next technological revolu‐ tion, following on from the first Industrial Revolution, which began around 1750 with the introduction of the steam engine and steelmaking. Nanotechnology is de‐ fined as the design, characterization, production, and application of materials, devi‐ ces and systems by controlling shape and size of the nanoscale. The nanoscale itself is at present considered to cover the range from 1 to 100 nm. All samples prepared in thin film forms and the characterization revealed their nanostructure. The major exploitation of thin films has been in microelectronics, there are numerous and growing applications in communications, optical electronics, coatings of all kinds, and in energy generation. A great many sophisticated analytical instruments and techniques, largely developed to characterize thin films, have already become indis‐ pensable in virtually every scientific endeavor irrespective of discipline. Among all these techniques, electrodeposition is the most suitable technique for nanostruc‐ tured thin films from aqueous solution served as samples under investigation. The electrodeposition of metallic layers from aqueous solution is based on the discharge of metal ions present in the electrolyte at a cathodic surface (the substrate or compo‐ nent.) The metal ions accept an electron from the electrically conducting material at the solid- electrolyte interface and then deposit as metal atoms onto the surface. The electrons necessary for this to occur are either supplied from an externally applied potential source or are surrendered by a reducing agent present in solution (electro‐ less reduction). The metal ions themselves derive either from metal salts added to solution, or by the anodic dissolution of the so-called sacrificial anodes, made of the same metal that is to be deposited at the cathode.

**Keywords:** Electrodeposition, nanomaterials, thin films, nanotechnology

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **1. Introduction**

Materials with grain size less than 100 nm are classified as nanostructure materials [1, 2]. Due to the ultra-small building units and high surface/volume ratio, these materials exhibit special properties, such as mechanical, optical, electronic, and magnetic properties [3]. In nanostruc‐ ture materials, all size-related effects can be integrated by controlling the sizes of the constit‐ uent components [4]. For instance, nanostructure metals and ceramics can have improved mechanical properties compared to conventional metals and ceramics. Besides, nanostructure materials are capable of being sintered at much lower temperatures than conventional powders, enabling the full densification of these materials at relatively lower temperatures. Technological applications of semiconductor nanostructure materials in optoelectronic devices such as photodiodes and quantum dotes semiconductors are owed to the size-related effects, particularly quantum size effects caused by the spatial confinement of delocalized electrons in confined grain sizes [5]. Nanostructure materials magnetic applications are fabrication of devices with massive magnetoresistance (GMR) effects, to read data on computer hard drives by magnetic heads, and development of magnetic refrigerators by replacing compressed ozone-chlorofluorocarbons by solid magnets as refrigerants [6]. Nanostructured metals seem to be a candidate for new catalytic applications [7].

Fundamental advances in energy conversion and storage which are full of vigor in meeting outfaces of some environmental phenomena such as global warming and impact of fossil fuels are held by new materials, particularly nanomaterials, which present unique properties as electrodes and electrolytes in many applications such as lithium batteries, solar cells, fuel cells, and supercapacitors [8].

There are several techniques that can be used to develop thin films of metals and semicon‐ ductors in both micro- and nano-structures. Some of these techniques are: sol-gel process [9], chemical deposition method [10], hydrothermal method [11], pyrolysis method [12], chemical vapor deposition (CVD) [13], and electrodeposition method [14]. In Table 1, we summarize some previous studies on general concepts of nanostructure materials, their properties, and their methods of preparation. This chapter will be concerned particularly with the electrode‐ position technique. Figure 1 shows thin films deposition techniques.

Materials may undergo some changes in physical properties when changing state from microstructure to a nanostructure. High surface/volume ratio and particles' transfer to a domain with dominant quantum effects are two main factors in characteristics' change. An increase in surface/volume ratio results in the dominance of surface atoms' behavior compared with internal atoms. This factor affects both the particle's properties and its interaction with the other materials. Vast surface of the nanoparticle leads to specific features such as mechan‐ ical, chemical, and thermal properties.

Nanoparticles are the basic structural blocks in nanotechnology. They are the starting point in producing nanostructure materials and tools. The production of nanoparticle is an important factor in the development of research in nanoengineering and nanoscience.

1

Different types of nanoparticles are prepared by using precursors in solid, liquid, and gaseous phases in the production and arrangement of nanomaterials. Based on their chemical reactivity or physical compression, these materials align the nanostructures as structural blocks side-byside. No. Delete Replace with

**Figure 1.** Thin film deposition techniques [Souad A., (2007)] [15].

Proof Corrections Form

**1. Introduction**

3 Fig

1

Page No.

4 Electroplating of Nanostructures

2. Author details

and supercapacitors [8].

Materials with grain size less than 100 nm are classified as nanostructure materials [1, 2]. Due to the ultra-small building units and high surface/volume ratio, these materials exhibit special properties, such as mechanical, optical, electronic, and magnetic properties [3]. In nanostruc‐ ture materials, all size-related effects can be integrated by controlling the sizes of the constit‐ uent components [4]. For instance, nanostructure metals and ceramics can have improved mechanical properties compared to conventional metals and ceramics. Besides, nanostructure materials are capable of being sintered at much lower temperatures than conventional powders, enabling the full densification of these materials at relatively lower temperatures. Technological applications of semiconductor nanostructure materials in optoelectronic devices such as photodiodes and quantum dotes semiconductors are owed to the size-related effects, particularly quantum size effects caused by the spatial confinement of delocalized electrons in confined grain sizes [5]. Nanostructure materials magnetic applications are fabrication of devices with massive magnetoresistance (GMR) effects, to read data on computer hard drives by magnetic heads, and development of magnetic refrigerators by replacing compressed ozone-chlorofluorocarbons by solid magnets as refrigerants [6]. Nanostructured

Affiliation:International Islamic University Malaysia

1. Final Chapter Title:Electrodeposition of Nanostructure Materials

Fundamental advances in energy conversion and storage which are full of vigor in meeting outfaces of some environmental phenomena such as global warming and impact of fossil fuels are held by new materials, particularly nanomaterials, which present unique properties as electrodes and electrolytes in many applications such as lithium batteries, solar cells, fuel cells,

There are several techniques that can be used to develop thin films of metals and semicon‐ ductors in both micro- and nano-structures. Some of these techniques are: sol-gel process [9], chemical deposition method [10], hydrothermal method [11], pyrolysis method [12], chemical vapor deposition (CVD) [13], and electrodeposition method [14]. In Table 1, we summarize some previous studies on general concepts of nanostructure materials, their properties, and their methods of preparation. This chapter will be concerned particularly with the electrode‐

Nanoparticles are the basic structural blocks in nanotechnology. They are the starting point in producing nanostructure materials and tools. The production of nanoparticle is an important

8 14 inquiry; what Inquiry. What

8 15 simple: Simple,

9 4 sword: Sword,

9 33 serves as: serves as

11 6 salt: salt

12 19 qis q is

17 11 w w

13 2 H2 p =1 H2 p = 1

10 10 of electrolyte of an electrolyte

11 17 solution; in other Solution. In other

factor in the development of research in nanoengineering and nanoscience.

metals seem to be a candidate for new catalytic applications [7].

Scientific Title: Associate Professor

Full Name:Souad A. M. Al-Bat'hi

Position:Faculty member

Line




**Title Description Reference** real samples of human blood

Albert S. et al., Nanomaterials (2014),

H. Gleiter, Th. Schimmel, H. Hahn, Nano

Xianwen et al., Nano Today. (2014) 9,

Eeu Y. C. et al., Hindawi Publishing Corporation J Nanomater. Volume 2013,

(2013), Article ID 653890 [20]

405-432 [19]

Today.. (2014) 9, 17-68 [18]

4(2), 189-202 [17]

Thin films CoPt nanowires have been successfully synthesized by

electrodeposition technique. Electrodeposition helps easy synthesis of mesoporous materials useful for catalytic applications without any agent's employment. The mesoporous CoPt nanowires have shown enhanced catalytic behavior for methanol oxidation reaction in acidic medium. Because of the catalytic activity and cost reduction, these nanowires can be a potential alternative for methanol fuel cells.

A review provides a discussion of method of preparation, structure and properties of nano structured solids that consist of totally

crystalline, totally amorphous, and partially amorphous components.

A review provides

nanofibers, carbon

films prepared by

comparison between carbon

nanotubes, and graphene; the three types of carbon nanostructure materials which have been focused on.

Nanocomposite polymer thin

electrodeposition technique have shown an enhanced electrochemical stability and exhibit excellent specific capacitance (F/gm)

serum.

2. Electrochemical Synthesis of

6 Electroplating of Nanostructures

Methanol Oxidation

Mesoporous CoPt Nanowires for

3. Nanostructured Solids From Nano-Glasses to Quantum Transistors Materials Assembled from Atom

Clusters

4. Nanocarbon-Based

for Sensing, Electrocatalysis, and Energy Storage

Electrochemical Systems

5. Electrodeposition of Polypyrrole/

Electrode Material

Reduced Graphene Oxide/Iron Oxide Nanocomposite as Supercapacitor


**Table 1.** Summary of Some Previous Studies on General Concepts of Nanostructure Materials

## **2. Growth technique of nanomaterials thin films**

Nanomaterials are produced by two main technical methods: "bottom-up" and "top-down" techniques. In the bottom-up technique, the substance developed from the bottom (atom by atom, molecule by molecule, or cluster by cluster). Colloid dispersion is produced in this technique. The top-down technique begins with bulk material and progresses toward the ideal state by its designing or abrasion. This technique is similar to the electron beam lithography in which patterns are used. In nanotechnology industry, bottom-up and top-down techniques are playing a considerable role. The major advantage of both techniques is creation of highpurity ultra-small structures. However, using bottom-up method produces improved nano‐ structures such as less or defect-free, homogeneous and long- and short-term orders, all due to free Gibbs energy decreases resulting in thermal balanced nanomaterials. However, in the top-down technique, mostly the material suffers from an increase in surface defects, since the material is subjected to internal stress [25]. Figure 2 shows a schematic representation of the building up of nanostructures.

## **3. Electrodeposition technique**

Electrochemical deposition, or electrodeposition for short, refers to a film growth process which consists in the formation of a metallic coating onto a base material (substrate) occurring through the electrochemical reduction of metal ions from an electrolyte to achieve the desired electrical and corrosion resistance, reduce wear and friction, improve heat tolerance, and for

**Figure 2.** Schematic representation of the building up of nanostructures

**Title Description Reference** promise for future large-scale

> Air and water as ionic liquids attract the attention of researchers due to their amazing physical properties,

S. Zein El Abedin, et al., Green Chem.

(2007),, 9, 549-553 [24]

production.

particularly in electrodeposition of nanocrystalline metals. Copper and aluminum can be electrodeposited in the air and water ionic liquids on solid electrodes and they have shown an adequate electronic conductivity.

**Table 1.** Summary of Some Previous Studies on General Concepts of Nanostructure Materials

Nanomaterials are produced by two main technical methods: "bottom-up" and "top-down" techniques. In the bottom-up technique, the substance developed from the bottom (atom by atom, molecule by molecule, or cluster by cluster). Colloid dispersion is produced in this technique. The top-down technique begins with bulk material and progresses toward the ideal state by its designing or abrasion. This technique is similar to the electron beam lithography in which patterns are used. In nanotechnology industry, bottom-up and top-down techniques are playing a considerable role. The major advantage of both techniques is creation of highpurity ultra-small structures. However, using bottom-up method produces improved nano‐ structures such as less or defect-free, homogeneous and long- and short-term orders, all due to free Gibbs energy decreases resulting in thermal balanced nanomaterials. However, in the top-down technique, mostly the material suffers from an increase in surface defects, since the material is subjected to internal stress [25]. Figure 2 shows a schematic representation of the

Electrochemical deposition, or electrodeposition for short, refers to a film growth process which consists in the formation of a metallic coating onto a base material (substrate) occurring through the electrochemical reduction of metal ions from an electrolyte to achieve the desired electrical and corrosion resistance, reduce wear and friction, improve heat tolerance, and for

**2. Growth technique of nanomaterials thin films**

10. Ionic Liquids as Green Electrolytes for the Electrodeposition of Nanomaterials

8 Electroplating of Nanostructures

building up of nanostructures.

**3. Electrodeposition technique**

decoration. The analogical technology is oftentimes known as electroplating. In addition to the production of metallic coatings, it is also for electrometallurgy in which metals are extracted from their ores or for electroformation where molds to form objects in their final shapes are produced. Mostly, the metallic deposit obtained is crystalline. This process can therefore be called electrocrystallization, a term introduced by russian chemist V. Kistiakovski in the early twentieth century.

The electrolyte contains positive and negative ions. Therefore, it is considered an ionic conductor. To prepare an electrolyte, the desired metal contained in a chemical species liquidized (mostly dissolved in water) to form a molten salt besides different organic and ionic liquids are currently used for particular electroplating processes. To begin electrodeposition, the cathode (working electrode, W.E) immersed in the electrolyte contained in a vessel (cell) along with the anode (counter electrode, C.E). To allow electric current flow in the circuit, the two electrodes are connected to a battery or any other power source. The cathode is connected to the negative terminal of the battery, while the anode is connected to the positive terminal so that the metal ions are reduced to metal atoms, which eventually form the deposit on the surface. Figure 3 shows a schematic presentation of an electrolytic cell for electroplating or electrodepositing a metal "M" from an aqueous (water) solution of metal salt "MA".

**Figure 3.** A schematic electrodeposition technique

This type of circuit arrangement directs electrons into a bath from the power supply to the cathode. In the bath, the electric current is carried by the positively charged ions from the anode toward the negatively charged cathode. This enables the metal ions in the bath to migrate toward extra electrons that are located at or near the surface of the cathode. Finally, the metal ions are removed from the solution and are deposited on the surface of the object as a thin layer. The reaction in aqueous medium at the cathode therefore obeys equation 1:

$$\text{M}^{\*n} + \text{ne}^{-} \rightarrow \text{M} \tag{1}$$

where n is the number of electrons involved in the reaction.

The thickness of the electrodeposited layer on the substrate is determined by the time duration of the plating. The longer the object remains in the chemical bath, the thicker the deposited layer is [15].

Lately, electrodeposition has become increasingly popular and is being extensively used by researchers in disparate fields of inquiry. What exactly is causing such an interest? The process itself is deceptively simple, a conductive surface is immersed into an electrolyte containing ions of the material to be deposited and a voltage is applied across this solid/electrolyte interface, resulting in a charge transfer reaction and film deposition. The driving force for this process is the applied potential, a quantity that can be easily and precisely controlled down to the mV and over timescales as short as 1ns. This feature leads to considerable control over the material formation process, its microstructure, and properties. The challenge in developing electrodeposition processes today is not the synthesis of a predefined material, but to strike a compromise between the ideal conditions used to produce this material and the commercial feasibility of the process. Other often-cited advantages of electrodeposition include the high utilization rate of the raw materials, low energy consumption, low material waste, little capital investment, and ease of implementation. Although the latter two are usually considered an advantage, they are perhaps a double-edged sword, they may in fact encourage quick experimentation, thereby relegating the science to the backstage and undermining the efforts of the community to place this technology on par with vacuum/gas/plasma deposition methods.

New materials and processes are being developed and integrated in microelectronic manu‐ facturing to provide new functionalities, for example, in MEMS, lab-on-a-chip, or microfluidic devices. Polymers and biomaterials are electrodeposited for biomedical applications; metal oxides and compound semiconductors are grown electrochemically for electronic or optoe‐ lectronic applications. Electrodeposition in new electrolytic media such as ionic liquids or supercritical fluids is being strongly pursued with some success. Electrodeposition plays an important role in the development of sustainable energy conversion technologies, both at the portable and on a global scale. In addition, the principles governing the scale-up of electrode‐ position processes are well understood, facilitating the development of large-scale manufac‐ turing processes [15].

#### **3.1. The electrolysis cell**

surface. Figure 3 shows a schematic presentation of an electrolytic cell for electroplating or

This type of circuit arrangement directs electrons into a bath from the power supply to the cathode. In the bath, the electric current is carried by the positively charged ions from the anode toward the negatively charged cathode. This enables the metal ions in the bath to migrate toward extra electrons that are located at or near the surface of the cathode. Finally, the metal ions are removed from the solution and are deposited on the surface of the object as a thin

The thickness of the electrodeposited layer on the substrate is determined by the time duration of the plating. The longer the object remains in the chemical bath, the thicker the deposited

Lately, electrodeposition has become increasingly popular and is being extensively used by researchers in disparate fields of inquiry. What exactly is causing such an interest? The process itself is deceptively simple, a conductive surface is immersed into an electrolyte containing ions of the material to be deposited and a voltage is applied across this solid/electrolyte interface, resulting in a charge transfer reaction and film deposition. The driving force for this process is the applied potential, a quantity that can be easily and precisely controlled down to the mV and over timescales as short as 1ns. This feature leads to considerable control over the material formation process, its microstructure, and properties. The challenge in developing electrodeposition processes today is not the synthesis of a predefined material, but to strike a

M ne M + - <sup>n</sup> + ® (1)

layer. The reaction in aqueous medium at the cathode therefore obeys equation 1:

where n is the number of electrons involved in the reaction.

electrodepositing a metal "M" from an aqueous (water) solution of metal salt "MA".

**Figure 3.** A schematic electrodeposition technique

10 Electroplating of Nanostructures

layer is [15].

#### *3.1.1. Constituents of the cell*

The electrolysis process consists of four parts:


The electrodeposition cell containing the plating solution or the electrolyte is usually made of plain mild steel (for alkaline solutions) or of lined steel (for acidic solutions). Steel lining could be of rubber, plastics, glass, or even lead [26].

#### *3.1.2. Electrolytes (Solution baths)*

The solution bath serves as a source of metal to be deposited, which contains ions of that metal, hence it provides conductivity, a stabilizer to stabilize the solution, for example, against hydrolysis and to stabilize the solution pH when acts as a buffer, regulates the corporal form of the deposit and helps dissolve the anodes. Finally, modifies properties of either the solution or of the deposit,

Complex ions are formed to stabilize the cation, which becomes much more stable when complexed to some ligand or to metal atoms by coordinate bonding. The concentration of the free (equated) ion is lowered by the presence of the ligand. Complex ions are also formed to hold the equated form at suitably low concentration allowing control of the evenness of plating.

Electrolytes can be defined as substances such as acid, base, and salts, which can conduct electricity in their aqueous solution due to ionization. The ions existing in the electrolyte are responsible for the conduction that results in current or free electrons passing through the wires. When a voltage is applied across the cell, and under the influence of the potential difference, the negatively charged ions migrate to the anode and the positively charged ions migrate to the cathode. The flowing of ions in aqueous solution of an electrolyte is called electrolysis [27]. For electrolysis of KCl in aqueous solution, it must be molten first by heating and elevating its temperature to the melting point. The molten ionic compound will be dissociated by electrolysis process into its elements. The reaction at each electrode is shown in equations 2 and 3:

$$2\text{K}^\* + 2\text{e}^- \rightarrow 2\text{K}\_{\text{(M)}} \text{(At the Cathode)}\tag{2}$$

$$\text{2Cl}^-\text{ }-\text{2e}^-\rightarrow \text{Cl}\_{2(g)}\text{ (At the Anode)}\tag{3}$$

At the cathode, potassium ions are reduced to potassium atoms (metal) by gaining electrons. On the other hand, at the anode, chloride ions are oxidized to chlorine atoms by losing electrons which are combined to form molecules of chlorine gas.

The combining of equations 2 and 3 results in the following reaction:

$$2\text{K}^{\circ}\text{Cl}\_{\text{(l)}}^{-} \rightarrow 2\text{K}\_{\text{(s)}} + \text{Cl}\_{2(g)}\text{(Overall reaction)}\tag{4}$$

**Figure 4.** Electrolysis process of potassium chloride [http://www.gcsescience.com][28]

#### **Strong Electrolytes**

of the deposit and helps dissolve the anodes. Finally, modifies properties of either the solution

Complex ions are formed to stabilize the cation, which becomes much more stable when complexed to some ligand or to metal atoms by coordinate bonding. The concentration of the free (equated) ion is lowered by the presence of the ligand. Complex ions are also formed to hold the equated form at suitably low concentration allowing control of the evenness of plating.

Electrolytes can be defined as substances such as acid, base, and salts, which can conduct electricity in their aqueous solution due to ionization. The ions existing in the electrolyte are responsible for the conduction that results in current or free electrons passing through the wires. When a voltage is applied across the cell, and under the influence of the potential difference, the negatively charged ions migrate to the anode and the positively charged ions migrate to the cathode. The flowing of ions in aqueous solution of an electrolyte is called electrolysis [27]. For electrolysis of KCl in aqueous solution, it must be molten first by heating and elevating its temperature to the melting point. The molten ionic compound will be dissociated by electrolysis process into its elements. The reaction at each electrode is shown in

At the cathode, potassium ions are reduced to potassium atoms (metal) by gaining electrons. On the other hand, at the anode, chloride ions are oxidized to chlorine atoms by losing electrons

which are combined to form molecules of chlorine gas.

The combining of equations 2 and 3 results in the following reaction:

**Figure 4.** Electrolysis process of potassium chloride [http://www.gcsescience.com][28]

( ) 2K 2e 2K At the Cathode <sup>M</sup> ( ) + - + ® (2)

( ) ( ) 2 g 2Cl 2e Cl At the Anode - - - ® (3)

( ) ( ) ( ) ( ) <sup>l</sup> s 2 g 2K Cl 2K Cl Overall Reaction + - ® + (4)

or of the deposit,

12 Electroplating of Nanostructures

equations 2 and 3:

Some electrolytes such as potassium chloride, sodium hydroxide, and sodium nitrate are completely ionized in their constituent ions (>99%) in solution. These electrolytes are known as strong electrolytes. In other words, strong electrolytes are 100% dissociated in their aqueous solution. Generally, strong acids like sulfuric acid, nitric acid, hydrochloric acid; strong bases like potassium hydroxide salt and many others are strong electrolytes [27]. Salts that are composed of oppositely charged ions held by strong electrostatic forces of attractions are considered strong electrolytes and they dissolve in water, which highly weakens the attraction forces between ions and reduces it by a factor of 80 due to its high dielectric constant of 80. Therefore, it facilitates the free movement of ions that are stabilized by solvation/hydration process with water. Figure 5 demonstrates how sodium and chloride ions are surrounded by water molecules due to ion-dipole interaction.

**Figure 5.** Sodium chloride solvation process

#### **Weak Electrolytes**

Some electrolytes are weak. A weak electrolyte is an electrolyte that partially dissociates in solution. In other words, ions and molecules of the electrolyte are both included in the solution. A moderately small percentage of ions (<1%) are given in solution with most of the compound staying in a non-ionic form (>99%) resulting in poorly conducting solutions. Acetic acid, carbonic acid, ammonia, rubidium hydroxide, some organic bases, and many others are considered weak electrolytes [29].

#### **Nonelectrolytes**

Substances that do not dissociate into ions in solution (water) are known as nonelectrolytes. These substances include most carbon compounds such as methyl alcohol, ethyl alcohol, glucose, and many others [30].

#### *3.1.3. Electrode potential*

When a metal electrode is placed in an ionic solution, ions will be exchanged between the metal and the solution. Ions from the metal enter the solution, and ions from the solution enter the metal lattice. The boundary between the two phases is called the interface. Due to an electron exchange between the electrode and the ions in solution, the interface becomes electrified and a potential difference across the metal-solution interface is generated. This potential difference is called electrode potential.

In case more ions leave than enter the metal electrode, there is an excess of electrons on the metal and hence it acquires negative charge, which attracts positively charged metal ions from the solution and repels negatively charged ions. Therefore, an excess of positive ions in the solution near the metal interface and the solution side acquires opposite (positive) and equal charge. The rate of positive ions leaving the metal electrode slows down due to repulsion with the positive charge at the solution side of the interface and the rate of ions entering the metal electrode accelerates [31]. In a short time, equilibrium between the metal and its ions in the solution is achieved, as shown in Figure 6.

$$
\vec{m} = \vec{m} \tag{5}
$$

where, *n* ⇀ denotes the number of positive ions that enter the metal electrode and *n* ↼ denotes the number of positive ions that leave the metal electrode.

At equilibrium:

$$\mathbf{q}\_{\rm M} = -\mathbf{q}\_{\rm s} \tag{6}$$

where, *q* is the electric charge.

The result of the changing of the interface is the potential difference, ∆Φ (M, S), between the potentials of the metal, ΦM, and the solution, ΦS:

$$
\Delta\Phi\Big(M\_{\prime\prime}\big) = \Phi\_M - \Phi\_S \tag{7}
$$

In order to measure the potential difference of an interphase, one must connect it to another one and thus form an electrochemical cell. The potential difference across this electrochemical cell can be measured [32].

The cell shown in Figure 7 may be schematically represented in the following way:

$$\text{Pt, }\,\mathrm{H}\_{2}\left(\mathrm{p}=1\right)\Big|\mathrm{H}^{\*}\left(\mathrm{a}=1\right)\Big|\mathrm{Cu}^{2+}\left(\mathrm{a}=1\right)\Big|\mathrm{Cu}\Big|\mathrm{Pt}\Big|$$

where the electrode at the left side is the hydrogen reference electrode. When the pressure of H2 p = 1 atm and the activity of H+ ions a = 1, the hydrogen electrode is called the standard hydrogen electrode (SHE) and its potential is zero by convention. The standard electrode potential of a solution, Eº (V) is the tendency for a chemical species to be reduced. The more positive the potential, is the more likely it will be reduced [1].

**Figure 6.** Formation of metal-solution interface (equilibrium state, n ⇀ =n↼ )

*3.1.3. Electrode potential*

14 Electroplating of Nanostructures

is called electrode potential.

where, *n*

At equilibrium:

where, *q* is the electric charge.

cell can be measured [32].

solution is achieved, as shown in Figure 6.

number of positive ions that leave the metal electrode.

potentials of the metal, ΦM, and the solution, ΦS:

When a metal electrode is placed in an ionic solution, ions will be exchanged between the metal and the solution. Ions from the metal enter the solution, and ions from the solution enter the metal lattice. The boundary between the two phases is called the interface. Due to an electron exchange between the electrode and the ions in solution, the interface becomes electrified and a potential difference across the metal-solution interface is generated. This potential difference

In case more ions leave than enter the metal electrode, there is an excess of electrons on the metal and hence it acquires negative charge, which attracts positively charged metal ions from the solution and repels negatively charged ions. Therefore, an excess of positive ions in the solution near the metal interface and the solution side acquires opposite (positive) and equal charge. The rate of positive ions leaving the metal electrode slows down due to repulsion with the positive charge at the solution side of the interface and the rate of ions entering the metal electrode accelerates [31]. In a short time, equilibrium between the metal and its ions in the

⇀ denotes the number of positive ions that enter the metal electrode and *n*

The result of the changing of the interface is the potential difference, ∆Φ (M, S), between the

In order to measure the potential difference of an interphase, one must connect it to another one and thus form an electrochemical cell. The potential difference across this electrochemical

> ( ) ( ) ( ) <sup>2</sup> <sup>2</sup> Pt, H p 1 H a 1 Cu a 1 Cu Pt + + == =

The cell shown in Figure 7 may be schematically represented in the following way:

*n n* <sup>=</sup>v w (5)

M S q q = - (6)

(*M S*, ) *M S* DF = F - F (7)

↼ denotes the

**Figure 7.** Relative standard electrode potential E0 of a Cu/Cu2+ electrode

#### *3.1.4. Some electrode reactions*

Some acidic and basic solution reductions with their corresponding standard electrode potential E0 measured at 25ºC are presented. Obviously, the more positive the potential E0 is, the more likely it will be reduced. However, the potential E0 of the reference electrode is zero, below which the potential E0 is increasing negatively, as shown below [33]:



*3.1.4. Some electrode reactions*

16 Electroplating of Nanostructures

below which the potential E0

F2 (g) / F-

Au+

MnO4 -

ClO3 -

BrO3 -

N2H5 <sup>+</sup>

IO3 -

CIO4 -

Br2 (l) / Br-

AuCl4 -

NO3 -

Ag+

SbCl6 -

(aq) / SbCl4 -

Cl2 (g) / Cl-

(aq) / NH4 <sup>+</sup>

(aq) / CIO3 -

Some acidic and basic solution reductions with their corresponding standard electrode potential E0 measured at 25ºC are presented. Obviously, the more positive the potential E0

the more likely it will be reduced. However, the potential E0 of the reference electrode is zero,

(aq) +2.87

Co3+ (aq) / Co2+ (aq) +1.82 Pb4+ (aq)/Pb2+ (aq) +1.8 NiO2 (s) / Ni2+ (aq) +1.7

 (aq) / Au (s) +1.68 Ce4+ (aq) / Ce3+ (aq) +1.61

(aq) / Mn2+ (aq) +1.51

(aq) /Cl2 (g) +1.47

/ Br- (aq) +1.44

(aq) +1.358

(aq) +1.24

(aq) +1.19

(aq) +1.066

Au3+ (aq) / Au (s) +1.5

Cr2O7 2- / Cr3+ (aq) +1.33

MnO2 (s) / Mn2+ (aq) +1.23 Pt2+ (aq) / Pt (s) +1.2

(aq) / I2 (aq) +1.195

 / Au (s) +1 Pb2+ (aq) / Pb (s) +0.987

 (aq) / NO (g) +0.96 NO3 - (aq) / HNO2 (aq) +0.94 Hg2+(aq) / Hg2 2+(aq) +0.92 Hg2+(aq) / Hg (*l*) +0.855

(aq) / Ag (s) +0.7994 Hg2 2+(aq) / Hg (*l*) +0.789 Fe3+(aq) / Fe2+(aq) +0.771

(aq) +0.75

is increasing negatively, as shown below [33]:

is,



#### **3.2. Electrical relationships**

V2+ (aq) / V (s) -1.18 Zr4+(aq) / Zr (s) -1.53 Al3+ (aq) / Al (s) -1.66 H2 (g) / H- (aq) -2.25 Mg2+(aq) / Mg (s) -2.37

(aq) / Na (s) -2.714 Ca2+ (aq) / Ca (s) -2.87 Sr2+ (aq) / Sr (s) -2.89 Ba2+(aq) / Ba (s) -2.9

(aq) / Rb (s) -2.925

(aq) / K (s) -2.925

(aq) / Li (s) -3.045 OOH- (aq) / OH- (aq) 0.88 NH2HO (aq) / N2H4 (aq) 0.74

 (aq) / Cl- (aq) 0.62 MnO4 - (aq) / MnO2(s) 0.588 MnO4 - (aq) / MnO4 2- (aq) 0.564 NiO2 (s) / Ni(OH)2 (s) 0.49

(aq) 0.4

Ag2O (s) / Ag (s) 0.34

(aq) / N2O(g) 0.15 N2H4(aq) / NH3(aq) 0.1

HgO (s) / Hg (*l*) 0.0984

MnO2(s) / Mn(OH)2(s) -0.05 CrO4 2-(aq) / Cr(OH)3(s) -0.12 Cu(OH)2(s) / Cu(s) -0.36 Fe(OH)3(s) / Fe(OH)2(s) -0.56 H2O / H2(g) -0.8277

(aq) / N2O4(g) -0.85 Fe(OH)2(s) / Fe(s) -0.877 SO4 2-(aq) / SO3 2-(aq) -0.93

(aq) 0.36

(aq) 0.01

2+(aq) 0.

Na+

18 Electroplating of Nanostructures

Rb+

K+

Li+

ClO3 -

O2(g) / OH-

(aq) / ClO3 -

(aq) / NO2 -

3+(aq) / [Co(NH3)6]

ClO4 -

NO2 -

NO3 -

NO3 -

[Co(NH3)6]

#### *3.2.1. Faraday's law of electrolysis*

Michael Faraday (1791–1867) observed that redox reactions occur when electric current passes through electrolyte solutions. When external source supplies electric current to the electrolytic cell, the electrons flow in the cell is in the opposite direction of that in the external circuit. At the cathode, electrons are supplied from the external source, which causes reduction reaction to occur. Similarly, oxidation reaction occurs at the anode since electrons return to the external source from this electrode.

Faraday's law states that the amount of electrochemical reaction occurs at an electrode is proportional to the electric charge Q passing through the cell that is.

$$\mathbf{w} = \mathbf{Z}\mathbf{Q} \tag{8}$$

where w is the product weight, *Z* is the electrochemical equivalent, the constant of propor‐ tionality, *Q* is the electric charge:

$$\mathbf{Q} = \text{It} \tag{9}$$

where, I is the current measured by amp (A), and t is the time measured by second (s)

$$\mathbf{w} = \mathbf{Z}\mathbf{I}\mathbf{t} \tag{10}$$

One mole of electrons is called one faraday. Faraday constant F is defined as the charge of one mole of electrons. To produce 1 g of reaction product at the electrode, 96,487 C (Faraday constant F) is required, which can be calculated as in Eq. 11:

$$\mathbf{F} = \mathbf{N}\_{\Lambda} \mathbf{e} \tag{11}$$

where NA is Avogadro number, *e* is the electron charge.

$$1\,\text{Faraday} = 9.64870 \times 10^4 \left(\text{C mol}^{-1}\right) \tag{12}$$

To produce one mole of hydrogen molecules H2, two faradays are required since the reduction of 2H+ requires two electrons; for one mole of silver, one faraday is required since the reduction of Ag+ requires one electron; and for one mole of aluminum, three faradays are required since the reduction of Al3+ requires three electrons. Generally,

$$w\_{eq} = \frac{A\_{\text{av}}}{n} \tag{13}$$

where Awt is the atomic weight, n is the number of electrons [32]. If Q = 1C, then

$$\mathbf{w}\_{\mathbf{Q}-1} = \mathbf{Z} \tag{14}$$

Equation 14 shows that the electrochemical equivalent Z is the weight produced or lost.

Combining Eqs. (8) and (14) produces:

$$\mathbf{w} = \mathbf{w}\_{\mathbf{Q}-1} \mathbf{Q} \tag{15}$$

Since 96,487 C is required for the deposition of an equivalent of a metal, weq

$$\mathbf{w}\_{\text{eq}} = 96,487 \text{ Z} \tag{16}$$

And

$$\mathbf{Z} = \mathbf{w}\_{\mathbf{Q}-1} = \frac{\mathbf{w}\_{\mathbf{eq}}}{\mathbf{96}/\mathbf{487}} = \frac{\mathbf{w}\_{\mathbf{eq}}}{\mathbf{F}} \tag{17}$$

Using Eq. (13):

$$\mathbf{Z} = \frac{\mathbf{A}\_{\text{wt}}}{\mathbf{n}\mathbf{F}} \tag{18}$$

$$\mathbf{w} = \mathbf{Z}\mathbf{Q} = \frac{\mathbf{A}\_{\text{wt}}}{\mathbf{n}\mathbf{F}}\mathbf{Q} \tag{19}$$

#### *3.2.2. Current efficiency*

The current efficiency of metal electrodeposition is highly determined by the deposition rate and energy. For instance, in copper electrodeposition the current efficiency decreases with increasing deposition current density and concentration of acidic solution. However, it is directly proportional with increasing copper concentration, solution flow rate, and solution temperature [34]. Based on Faraday's law, the amount of chemical change at the electrode is proportional to the quantity of electricity passing through the solution. Therefore, the quantity of metal deposited at the cathode or dissolved at the anode is our concern, and the elaborated hydrogen or oxygen at the cathode or the anode, respectively, is considered electrical energy dissipation and process efficiency reduction. Equation (20) is a statement of percentage current efficiency:

$$\text{CE\%} = \frac{\text{Act}}{\text{Theo}} \times 100\tag{20}$$

where CE is current efficiency, Act is the actually deposited weight, and Theo is the expected deposited weight. Current efficiency when applied to the cathode reaction is called cathode efficiency and current efficiency as applied to the anode reaction is called anode efficiency [26].

#### *3.2.3. Deposit thickness*

To produce one mole of hydrogen molecules H2, two faradays are required since the reduction

*wt*

*A*

Equation 14 shows that the electrochemical equivalent Z is the weight produced or lost.

eq eq

w w

Since 96,487 C is required for the deposition of an equivalent of a metal, weq

Q 1

Awt <sup>Z</sup>

w ZQ Q Awt

The current efficiency of metal electrodeposition is highly determined by the deposition rate and energy. For instance, in copper electrodeposition the current efficiency decreases with

Z w

*eq*

*w*

the reduction of Al3+ requires three electrons. Generally,

where Awt is the atomic weight, n is the number of electrons [32].

 requires two electrons; for one mole of silver, one faraday is required since the reduction of Ag+ requires one electron; and for one mole of aluminum, three faradays are required since

*<sup>n</sup>* <sup>=</sup> (13)

w Z Q 1<sup>=</sup> = (14)

w w Q Q 1<sup>=</sup> = (15)

w 96,487 Z eq = (16)

96,487 F <sup>=</sup> == = (17)

nF <sup>=</sup> (18)

nF = = (19)

of 2H+

20 Electroplating of Nanostructures

If Q = 1C, then

And

Using Eq. (13):

*3.2.2. Current efficiency*

Combining Eqs. (8) and (14) produces:

Michael Faraday has formulated many laws. But the most important law in this regard is the relationship between current, time, and the weight of the deposit metal, represented by the following equation:

$$\mathbf{w} = \begin{pmatrix} \mathbf{I} \mathbf{t} \mathbf{A} \end{pmatrix} / \begin{pmatrix} \mathbf{n} \mathbf{F} \end{pmatrix} \tag{21}$$

where, w (g) is the weight of deposit metal, I (C/s) is the current, t (s) is the time, A (g.mol-1) is the atomic weight, n (equivalents.mol-1) is the valence of the dissolved metal in solution and F is Faraday's constant (96,485.309 C/equivalent).

Consider nickel electrodeposition at the cathode, nickel ions will be reduced or deposited as nickel metal.

$$\text{Ni}^{2+} + \text{2e}^{-} \rightarrow \text{Ni} \tag{22}$$

If a current of 1 amp is supplied to the cathode for 1 h.

$$\mathbf{w} = \frac{\left(1 \times 3600 \times 58.69\right)}{\left(2 \times 96485.309\right)} = 1.09 \text{ g}$$

Hence, the thickness is:

$$\mathbf{T} = \bigvee\_{\rho \times \mathbf{a}} \mathbf{a} \tag{23}$$

where T (μm) is the thickness, *ρ* (gm.cm-3) is the density, and a (cm2 ) is the surface area of the deposit.

Combining Eqs., 21 and 23 yields:

$$\mathbf{T} = \begin{pmatrix} \mathbf{I} \times \mathbf{t} \times \mathbf{A} \\\\ \mathbf{n} \times \mathbf{F} \times \boldsymbol{\rho} \times \mathbf{a} \end{pmatrix} \tag{24}$$

Assume that, the surface area of the Ni deposit is 22.1 cm2. Thus,

$$\text{T} = \frac{\left(1 \times 3600 \times 58.69 \times 10000\right)}{\left(2 \times 96485.309 \times 8.90 \times 22.1\right)} = 55.67 \text{ }\mu\text{m}$$

From the above equation, thickness is proportional inversely with the surface area, provided that, all other parameters in the equation are maintained the same [35].

## **4. Research and development**

Electrodeposited thin films are playing a major role in the development of new materials such as magnetic materials, where electrodeposition reveals strong potential to grow high-quality ultrathin magnetic layers with interesting magnetic properties, and, further, in the study of magnetism on micro- and nano scales [36]. Thermoelectronic devices are another emerging technology that uses electrodeposited materials [37]. J.F.K. Cooper, et al., have successfully grown thin films of ternary alloy of CoNiCu by single-bath electrodeposition techniques using weak and strong electrolytic solutions, whereby the potential can be controlled to grow a wide range of homogeneous films [38]. Nanostructured deposits of the alloys of bismuth, antimony, tellurium, and select other elements have useful thermoelectric properties. One successful fabrication technique is to electrodeposit the materials into nanoscale pores [39]. Electrodepo‐ sition is a simple and flexible method for the synthesis of one-dimensional (1D) nanostructures of metals, semiconductors, and polymers in the form of nanowires, nanorods, nanotubes, and nanoribbons that have shown novel physical properties and amazing potential applications in nanodevices [40]. The photovoltaic (PV) conversion of solar energy is one of the most promising renewable energy sources for our future energy needs. Electrodeposition technique was used successfully to synthesize nanostructured electrodes of ZnxCd1-x (O) on ITO glass substrate with several values of x in an aqueous medium containing Zn2+ and Cd2+ species for energy generating photovoltaic cell, and the efficiency achieved was 1.6% [21]. Electrodepo‐ sition of materials has the potential to change phase of deposits upon heating or cooling. Deposit in the amorphous state at room temperature can change phase to crystalline when annealing at elevated temperatures. The switching between amorphous and crystalline phases is useful for rewritable optical storage and solid-state memory [41]. Wiring of printed circuits and interconnections of multilayer microchips are another developed areas of electrodeposi‐ tion for electronic applications. The plated area can be accurately defined by using photoresist. Electroless plating or Autocatalytics permits a conducting layer to be deposited on insulating materials. For connection, a solder thin layer can be deposited [42].

## **5. Conclusion**

where T (μm) is the thickness, *ρ* (gm.cm-3) is the density, and a (cm2

Assume that, the surface area of the Ni deposit is 22.1 cm2. Thus,

that, all other parameters in the equation are maintained the same [35].

( )

I x t x A T n x F x x a

( ) ( ) 1 x 3600 x 58.69 x 10000 T 55.67 m 2 x 96485.309 x 8.90 x 22.1 = =

From the above equation, thickness is proportional inversely with the surface area, provided

Electrodeposited thin films are playing a major role in the development of new materials such as magnetic materials, where electrodeposition reveals strong potential to grow high-quality ultrathin magnetic layers with interesting magnetic properties, and, further, in the study of magnetism on micro- and nano scales [36]. Thermoelectronic devices are another emerging technology that uses electrodeposited materials [37]. J.F.K. Cooper, et al., have successfully grown thin films of ternary alloy of CoNiCu by single-bath electrodeposition techniques using weak and strong electrolytic solutions, whereby the potential can be controlled to grow a wide range of homogeneous films [38]. Nanostructured deposits of the alloys of bismuth, antimony, tellurium, and select other elements have useful thermoelectric properties. One successful fabrication technique is to electrodeposit the materials into nanoscale pores [39]. Electrodepo‐ sition is a simple and flexible method for the synthesis of one-dimensional (1D) nanostructures of metals, semiconductors, and polymers in the form of nanowires, nanorods, nanotubes, and nanoribbons that have shown novel physical properties and amazing potential applications in nanodevices [40]. The photovoltaic (PV) conversion of solar energy is one of the most promising renewable energy sources for our future energy needs. Electrodeposition technique was used successfully to synthesize nanostructured electrodes of ZnxCd1-x (O) on ITO glass substrate with several values of x in an aqueous medium containing Zn2+ and Cd2+ species for energy generating photovoltaic cell, and the efficiency achieved was 1.6% [21]. Electrodepo‐ sition of materials has the potential to change phase of deposits upon heating or cooling. Deposit in the amorphous state at room temperature can change phase to crystalline when annealing at elevated temperatures. The switching between amorphous and crystalline phases is useful for rewritable optical storage and solid-state memory [41]. Wiring of printed circuits and interconnections of multilayer microchips are another developed areas of electrodeposi‐

( )

r

<sup>=</sup> (24)

m

deposit.

22 Electroplating of Nanostructures

Combining Eqs., 21 and 23 yields:

**4. Research and development**

) is the surface area of the

Electrodeposition is the application of metallic coatings to metallic or other conductive surfaces by electrochemical processes for the purpose of good appearance, protection, special surface properties, and engineering or mechanical properties. Electrodeposition is a multidisciplinary technique and based on chemistry, physics, chemical and electrical engineering, metallurgy, and probably others. Besides, it retains the aspects of art, in which experience is the only way to learn. No text on electroplating will produce an expert electroplater. There is no substitute for experience and what is somewhat inelegantly termed know-how. The most beautiful feature of electrodeposition technique is that the deposit thickness, deposition temperature, and deposition potential can be relatively controlled.

## **Author details**

Souad A. M. Al-Bat'hi

Address all correspondence to: su3ad@iium.edu.my

Department of Manufacturing and Materials Engineering, Faculty of Engineering, International Islamic University, Malaysia

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