**2. Thin film growth using pulsed laser deposition (PLD)**

Thin film growth consists of nucleation, growth, and coalescence (**Figure 1a**). In a physical vapor deposition, an extremely nonequilibrium process takes place at high supersaturations and at comparatively high concentrations of impure atoms [10]. Nucleation takes place at high supersaturations *S* (defined as *S* = *p*/*pe*, where *p* is the vapor pressure of the deposited material evaporated from the source at temperature *T* and *pe* is the equilibrium vapor pressure of the substrate material at temperature *T*S). The incident vapor arrives at the surface of substrates and then forms small but highly mobile clusters or islands with uniform distribution. In this stage, the impinging atoms and subcritical clusters are incorporated and consequently increase their sizes, while the island density rapidly saturates. In the following stage, the islands are emerged via a coalescence phenomenon which is liquid-like for some cases, especially at high substrate temperatures. Coalescence leads to a decrease in island density and forms local denuding positions on the surface of substrates where further nucleation can then occur (**Figure 1a**) [11]. The sequence of film nucleation and growth events can be well appreciated in the transmission electron microscopy (TEM) images in **Figure 1b**–**d** [11].

### **2.1. Basic growth modes**

For all phase transitions, the formation of thin films is characterized by the formation of nuclei and their growth. Depending on the interaction energies of substrate atoms and film atoms, any of three growth modes in **Figure 2a**–**c** can occur:


Thermoelectric and Topological Insulator Bismuth Chalcogenide Thin Films Grown Using Pulsed Laser Deposition http://dx.doi.org/10.5772/65898 57

inside the bulk gap, spin-polarization by spin-momentum locking nature, and weak antilocalization (WAL) due to the strong spin-orbit coupling [3–6]. Thus, the WAL through

For application purposes, thin film growth techniques for TE and TI materials are required. Among physical vapor deposition techniques, pulsed laser deposition (PLD) offers great versatility in growing polycrystalline and epitaxial thin films with high growth rates, multiple elements, and diverse structural morphologies for both fundamental studies and applications. The purpose of this chapter is to outline recent advances in the PLD growths of bismuth chalcogenide thin films with desired properties for TE/TI applications and fundamental

Thin film growth consists of nucleation, growth, and coalescence (**Figure 1a**). In a physical vapor deposition, an extremely nonequilibrium process takes place at high supersaturations and at comparatively high concentrations of impure atoms [10]. Nucleation takes place at high supersaturations *S* (defined as *S* = *p*/*pe*, where *p* is the vapor pressure of the deposited material evaporated from the source at temperature *T* and *pe* is the equilibrium vapor pressure of the substrate material at temperature *T*S). The incident vapor arrives at the surface of substrates and then forms small but highly mobile clusters or islands with uniform distribution. In this stage, the impinging atoms and subcritical clusters are incorporated and consequently increase their sizes, while the island density rapidly saturates. In the following stage, the islands are emerged via a coalescence phenomenon which is liquid-like for some cases, especially at high substrate temperatures. Coalescence leads to a decrease in island density and forms local denuding positions on the surface of substrates where further nucleation can then occur (**Figure 1a**) [11]. The sequence of film nucleation and growth events can be well appreciated

For all phase transitions, the formation of thin films is characterized by the formation of nuclei and their growth. Depending on the interaction energies of substrate atoms and film atoms,

**•** 2D Frank-van der Merwe mode: layer-by-layer growth, in which the interaction between

**•** 3D Volmer-Weber mode: separated islands form on the surface of substrates, in which the interaction between atoms of film is greater than that between a substrate and the adjacent

**•** Stranski-Krastanov mode: layer plus island, in which one or two monolayers form first and

substrate and atoms of film is greater than that between adjacent atoms of film.

magnetotransport studies has been widely used as a signature of TI materials [7–9].

56 Applications of Laser Ablation - Thin Film Deposition, Nanomaterial Synthesis and Surface Modification

**2. Thin film growth using pulsed laser deposition (PLD)**

in the transmission electron microscopy (TEM) images in **Figure 1b**–**d** [11].

any of three growth modes in **Figure 2a**–**c** can occur:

studies.

**2.1. Basic growth modes**

atoms of film.

then grow individually.

**Figure 1.** (a) Schematics of thin film growth processes: nucleation, growth, coalescence. Transmission electron microscope images of (b) nucleation, (c) growth, and (d) coalescence of Ag films on (1 1 1) NaCl substrates. Corresponding diffraction patterns are shown.

**Figure 2.** Basic modes of thin film growth: (a) island in the Volmer-Weber mode, (b) layer by layer in the two-dimensional Frank-van der Merwe mode, (c) layer plus island in the Stranski-Krastanov mode. (d) Shadowing growth: a schematic of three-dimensional Monte Carlo simulations for oblique angle deposition [13].

After an initially random nucleation of islands on the surface of the substrates, the deposition on the top of the islands is faster than that in the valleys due to the oblique incident flux (the so-called **shadowing effect**) [12, 13]. Isolated columns are therefore formed on these islands during subsequent growths (**Figure 2d**) [13].
