**2.1 Photolithography**

*Nanowires - Recent Progress*

temperature and the time of the treatment [30].

[36], as well as in surfaces with self-cleaning properties [37].

prepared by wet and dry methods were analyzed and discussed.

**2. Lithographic techniques**

The preparation methods represent the key factor in order to obtain metal oxide nanowires with tunable dimensions and tailored physico-chemical properties. To date, many preparation approaches were used for preparing arrays of metal oxide nanowires, such as template electrodeposition [19], electroless deposition [20], sol–gel [21], chemical bath deposition [22], hydrothermal growth [23], pulsed laser deposition [24], chemical vapor deposition [25], atomic layer deposition [26], lithographic techniques [27], etc. Among them, chemical synthesis carried out in water as a reaction medium is a simple wet preparation route, easy to process and suitable for large-scale synthesis of metal oxide powders consisting in micro- and nano-structures with different morphologies featured by a good crystallinity [13, 28, 29]. Another preparation method, thermal oxidation in air is a relatively facile dry, low-cost, nonhazardous and high throughput approach that can be used at a large-scale to obtain metal oxides nanostructures of a high purity and crystallinity [13]. Using thermal oxidation in air to obtain arrays of metal oxide nanowires, the nanowires length, diameter and density can be easily controlled by modifying the parameters involved in the thermal oxidation in air process, such as: the heating rate, the annealing

Zinc oxide (ZnO) is an interesting eco-friendly and versatile metal oxide, suitable for many applications due to its remarkable physico-chemical properties. Being an n-type semiconductor with a direct band gap (3.37 eV), with an excitonic binding energy of 60 meV, it can be easily integrated in optoelectronic devices such as photodetectors [15], light emitting diodes [31], solar cells [32]. Additionally, its flexibility in terms of nanostructure morphology (nanowires, nanotubes, nanofibers, nanorods, nanoneedles, hexagonal nanoprisms, nanoflowers, rings, etc.) [33, 34] offers another important advantage for applications in sensors [35], photocatalysis

Copper oxide (CuO) is a p-type semiconductor easy to prepare, with a high stability, having an indirect narrow band gap (1.2–1.8 eV). This metal oxide can be implemented in various applications such as: solar cells [38], field effect transistor [11], gas sensors [39], photocatalysis [40], water purification [41], etc. Being also an antiferromagnetic material below 220 K with a local magnetic moment of about 0.6 μB, CuO was also investigated for application in magnetic storage units [42]. In this chapter, we present our research regarding the preparation and complex

characterization of metal oxide nanowire arrays by wet (chemical synthesis in aqueous solution) and dry (thermal oxidation in air) approaches. In addition, electronic devices based on single metal oxide nanowires were developed and analyzed in terms of electrical characterization. Further, lithographic techniques such as photolithography, electron beam lithography and focused ion beam induced deposition, combined with radio-frequency magnetron sputtering and thermal vacuum evaporation were used for fabricating electronic devices like diodes and field effect transistors based on single metal oxide (ZnO or CuO) nanowires. In addition, the electrical properties of the electronic devices based on single metal oxide nanowires

Lithographic techniques are mainly used in modern semiconductor manufacturing industry, in micro- and nano-fabrication to pattern thin films with specific geometries integrated into electronic devices. Lithographic techniques are subsequently divided according to the targeted application into: photolithography, electron beam lithography, focused ion beam induced deposition, extreme UV lithography, nanoimprint lithography, colloidal lithography, soft lithography, and

**26**

Photolithography is a conventional lithographic process in which specific geometric shapes drawn on a photomask are transferred to the desired substrate by means of light in the UV range, using a lamp that emits UV light of a certain wavelength and a polymer that has a photoactive component sensitive to the UV light named photoresist. In this case, the resolution is limited by the wavelength used and by the type of the aligner. In our case, the photolithography was involved in the fabrication of Ti/Au metallic interdigitated electrodes onto Si/SiO2 wafers. The main steps of the process being: cleaning of the Si/SiO2 wafers, deposition of the primer and the photoresist by centrifugation, baking of the deposited layer, the mask alignment, the UV exposure, baking after UV irradiation, the UV exposure through clear mask, the development process and the deposition of Ti and Au thin films using radio-frequency (RF) magnetron sputtering and thermal vacuum evaporation, respectively.
