**2. Fabrication and characterizations of nanostructuring indium-tin-oxide films**

#### **2.1 ITO thin film preparation**

ITO thin films were deposited on a glass (a size of 1 × 1 cm) using magnetron sputtering deposition at room temperature, O2/(Ar + O2) flow ratio of 0.047, and a power of 1000 W. The ITO target (58 × 15 cm) was composed of In2O3 with 10 wt% SnO2. The as-deposited ITO thin films have a thickness of 30–80 nm and a resistivity of ∼4 × 10<sup>−</sup><sup>2</sup> Ω-cm.

#### **2.2 Experimental setups**

For fabricating nanostructures, the ITO films were irradiated using a regenerative-amplified Ti:sapphire laser (Legend USP, Coherent), with a central wavelength of 800 nm, a pulse duration of 100 fs, a pulse energy of ∼0.5 mJ, and a repetition rate of 5 kHz (**Figure 1a**). The diameter of the laser beam was adjusted to ∼14 mm, which can cover fully the sample size of 1 × 1 cm. The samples were irradiated with different fs laser shots (*N*) of 0, 5 × 103 , 2.5 × 104 , 1 × 105 , 3 × 105 , and 3 × 106 .

For studying the anisotropic optical transmission of nanostructured ITO films, all optical spectra were measured through an iris with a 0.1-mm-diameter hole located at a position close to the central region of the laser-induced nanostructures (or laser spot). The fs laser-treated ITO films had ripple structures of nanodots and nanolines on the film surfaces. The transmission spectra of the films were measured using polarized light with a direction of polarization (P) parallel or perpendicular to the direction of the long axis of the nanodots or nanolines (L) on the ITO films (see **Figure 1b** and the inset of **Figure 6c**).

For fabricating the various surface modifications in Section 5, the ITO films with a thickness of 80 nm were mounted on an xyz stage and irradiated at room temperature and ambient pressure using a commercial Ti:sapphire amplifier (Solstice Ace,

*Nanostructuring Indium-Tin-Oxide Thin Films by Femtosecond Laser Processing DOI: http://dx.doi.org/10.5772/intechopen.82790*

**Figure 1.**

*Experimental setup for (a) the fabrication of nanostructuring ITO films and (b) the characterizations of anisotropic optical properties on ITO films with periodic nanostructures on the surfaces.*

Spectra-Physics) with a central wavelength of 800 nm, a pulse duration of 35 fs, and a repetition rate of 2 kHz. The laser beam with line spot (a length of 4.6 mm and a width of 21 μm) was focused by a cylindrical lens (*f* = 40 mm). The scanning speed was approximately 160 μm/s.

### **2.3 Characterizations**

The optical transmission of as-deposited and fs laser-treated ITO films was measured using an UV-visible-near-IR spectrophotometer (Shimadzu SolidSpec-3700). The morphology of the films was examined using a scanning electron microscope (SEM) (HITACHI-S2500 JSM-6500F). The film thicknesses were determined by surface contour measurement (KOSAKA ET4000A), with a vertical resolution of 0.1 nm. The resistivity, carrier concentration, and the Hall mobility of the ITO films were measured by the Hall measurements (Bio-Rad Microscience HL5500) using the Van der Pauw method. The surface composition and chemical bonding were studied by X-ray photoelectron spectroscopy (XPS, PHI Quantera AES 650), with source of Al Kα at 1486.7 eV, passing an energy of 15 keV, and analyzed a spot size of 100 μm. The XPS spectra were calibrated by using Au at binding energy of 84.0 eV. XPS curve fitting was performed using free-ware XPSPEAK4.1 from Dr. R.M. Kwok, the Shirley background subtraction, and assuming a Gaussian-Lorentzian peak shape. Auger electron spectroscopy (AES, ULVAC-PHI 700) with a spatial resolution of ∼30 nm under 5 keV operating voltage was used to study the local compositions of the as-deposited and fs laser-irradiated ITO films.

In Section 5, the morphology of the colorized ITO films was measured using high resolution field emission SEM (JEOL). To determine the relationship between the reflectance/transmittance spectra and the colors of fs laser-colorized ITO films, we used a spectrometer (U3310, Hitachi) with both deuterium and tungsten iodide lamps (allowing for a scanning range from 190 to 900 nm with a resolution of 0.3 nm).
