**1. Introduction**

Over the last two decades, nanotechnology and nanoscience have generated great scientific interest focusing mainly on the development of nanomaterials with specific and tunable properties and their applications in various areas [1]. Nanotechnology offers the ability to design, synthesize, and control length scales ranging from <1 to >100 nm. In the literature, reports of discoveries based on novel properties arising from these small size features have been increasing and nano-sized noble metal particles have occupied a central place [2]. Also, nanotechnology has grown in significance in the study of fibrous materials, namely nanofibers and silicate nanocomposites wherein the synthesis and characterization along with the unique properties have been studied [3]. An emerging area of great interest is that of nanowire research which will interface with living cells for precise delivery of small molecules, proteins, and deoxyribonucleic acid (DNA) [4]. From the viewpoint of the relationship between nanostructures and properties, remarkable advances have been made in the commercial use of thin films that find wide-ranging applications in almost all the industrial fields such as optics, electronics, mechanics, and even biotechnology [5]. There is a surge of interest seen in the scientific community when it comes to NPG due to its intriguing material properties arising from its high specific surface area, high electrical conductivity, reduced stiffness, and the prospect of easy surface modification. NPG has controllable pore morphology and ligament size that opens up a wide range of studies of its mechanical and surface properties [6]. Compared to regular gold thin films which are dense inside, NPG films have interconnected ligaments with nanometers-sized

gaps throughout the bulk of the film. The pore size can be modulated depending on the type of synthesis protocol followed ranging from typically 20–50 nm in size but to as small as 5 nm [7]. Additionally, the porous structure of the NPG electrode tremendously increases the number of adsorption sites for various molecules of biological interest making it an attractive candidate in the field of biosensors [8]. Gold electrodes with nanoporous structures possess a higher roughness factor (the ratio between the real surface area and the geometrical area of the electrode) and better electron transport in comparison with their counterparts with smooth surfaces [9]. Metal nanoporous films have been prepared by various methods of high productivity and controllability of which chemical and electrochemical dealloying laid the foundation for other methods [10]. Moreover, dealloying is a potent approach for the fabrication of both monoporous (i.e., nanoporous or microporous) and hierarchical (i.e., possessing both microporosity and nanoporosity) porous metal structures with novel properties [11]. Multimodal pore size distribution on the nanometer and micrometer scale is highly desirable. The presence of larger size pores enables fast transport of the reactants, while the nanopores are responsible for providing high surface area thereby increasing the rate of electrochemical reactions. High surface area gold could be prepared by the electrodeposition technique, illustrated in **Figure 1**. Porous metals prepared via dealloying often contain some amount of residual less noble metal and therefore other fabrication techniques were explored [12].

The electrochemical deposition of NPG on a solid substrate has been extensively researched in recent years. This facile technique enhances the electrochemical activity of the nanoporous film by offering fine control over the growth and nucleation mechanism which in turn determines the morphology of the deposited film [13]. The three-dimensional (3-D) nanoporous films, membranes or powders of large surface area have received great attention and it has been seen that the templating strategy is the most popular method for their preparation using polycarbonate membranes, colloidal crystals, lyotropic liquid crystalline phases of surfactants, and echinoid skeletal structures as the templates and will be discussed in this chapter [14, 15]. Electroplated gold continues to play an integral role in modern electronics technology, and it is hard to find an equivalent substitute due to the unique combination of properties of the metal. It is speculated that as information technologies continue to expand, the quantity of gold used will continue to

**145**

**Table 1.**

*Electrodeposition of Nanoporous Gold Thin Films DOI: http://dx.doi.org/10.5772/intechopen.94604*

tion of the NPG film will be discussed.

upon a change in the experimental parameters.

**Dealloying** This approach enables the

**Self-assembly** Thin films formed exhibit enhanced

**Sputter deposition** Simple green method, reproducible

**Electrodeposition** One-step fabrication of thin films

stability

*Summary of the fabrication techniques used to synthesize NPG thin films.*

pretreatment

**Fabrication techniques Advantages Application**

conductive substrate

fabrication of NPG thin films, either free-standing or supported on a

thermal stability and capability of electron transfer. This method can be applied to various conductive surfaces without harmful

and generates low-price final product

directly on a substrate, control of particle morphology, size, and density is relatively easy. Uniform deposition is seen along with good Enhanced electrocatalytic activity towards methanol oxidation, potential in the field of catalysis, optics, and sensor technology

Energy storage, photovoltaics, sensing, and electrochemical usage

Electrochemical biosensing, used as supercapacitors, in microelectronics

Electroanalytical and catalytic field

and photovoltaics

**2. Fabrication techniques**

categorically described below.

**2.1 Dealloying methods**

increase [16]. Experimental parameters have been seen to influence the morphology of gold and therefore, this chapter will give insights into the various methods used for fabricating NPG thin films with special emphasis on electrodeposition strategies. Along with the synthetic approaches, applications and the characteriza-

There are various methods for fabricating porous gold films, and these are

De-alloying is an effective corrosion method for the fabrication of NPG films wherein the presence of less noble metals in the gold alloy has been exploited in a way that they are chemically or electrochemically dissolved to produce monolithic metal bodies with nanoscale pore structure. Au-Ag alloys are considered ideal due to their similar atomic volumes and continuous solid solubility allowing for coherent transformation from the master alloy to the nanoporous structure, see **Table 1** [17, 18]. Chemical dealloying has been studied employing Metropolis Monte Carlo simulations wherein the simulation of the dealloying process in the first stage describes the equilibrated systems followed by the second stage of dealloying with the exclusion of interaction parameters [19]. A simple method to dealloy the precursor alloy is to immerse it in nitric acid leading to selective etching of silver forming a 3-D pattern resulting in the formation of an open, bicontinuous highly porous network of gold with tunable ligament and channel width by varying the alloy composition, electrochemical potential, or by thermal annealing after dealloying [20]. **Figure 2** depicts the outcome of NPG structures

**Figure 1.** *A representation of the electrochemical deposition set up.*

*Electrodeposition of Nanoporous Gold Thin Films DOI: http://dx.doi.org/10.5772/intechopen.94604*

increase [16]. Experimental parameters have been seen to influence the morphology of gold and therefore, this chapter will give insights into the various methods used for fabricating NPG thin films with special emphasis on electrodeposition strategies. Along with the synthetic approaches, applications and the characterization of the NPG film will be discussed.
