**Abstract**

The low dimensional chalcogenide materials with high band gap of ~1.8 eV, specially molybdenum di-sulfide (MoS2), have been brought much attention in the material science community for their usage as semiconducting materials to fabricate low scaled electronic devices with high throughput and reliability, this includes also photovoltaic applications. In this chapter, experimental data for MoS2 material towards developing the next generation of high-efficiency solar cells is presented, which includes fabrication of ~100 nm homogeneous thin film over silicon di-oxide (SiO2) by using radio frequency sputtering at 275 W at high vacuum~10<sup>−</sup><sup>9</sup> from commercial MoS2 99.9% purity target. The films were studied by means of scanning and transmission electron microscopy with energy disperse spectroscopy, grazing incident low angle x-ray scattering, Raman spectroscopy, atomic force microscopy, atom probe tomography, electrical transport using four-point probe resistivity measurement as well mechanical properties utilizing nano-indentation with continuous stiffness mode (CSM) approach. The experimental results indicate a vertical growth direction at (101)-MoS2 crystallites with stacking values of 7-laminates along the (002)-basal plane; principal Raman vibrations at *E*<sup>1</sup> 2g at 378 cm<sup>−</sup><sup>1</sup> and A1 g at 407 cm<sup>−</sup><sup>1</sup> . The hardness and elastic modulus values of *H* = 10.5 ± 0.1 GPa and *E* = 136 ± 2 GPa were estimated by CSM method from 0 to 90 nm of indenter penetration; as well transport measurements from −3.5 V to +3.5 V indicating linear Ohmic behavior.

**Keywords:** thin film, electron microscopy, MoS2 sputtering, harness, elastic modulus, x-ray diffraction, electrical transport, focus ion-beam, atom probe tomography

### **1. Introduction**

Layered chalcogenide materials have been of high relevance since almost 40 years for their diverse applications such as tribology [1], chemical catalysis [2] and nowadays as semiconductors towards development of high-throughput and energy efficient transistors and devices [3, 4]. MoS2 is a two-dimensional material with a band gap ranging between 0.9 and 1.8 eV as calculated theoretically by first principles methods and as measured experimentally by Kam & Parkinson using photo-spectroscopy as a function of crystal orientation [5, 6]. The crystal structure of MoS2 is hexagonal with space group R3m (*a = b =* 3.16 Å and *c =* 18.41 Å), having *d*-bonded layers of S-Mo-S along a-b plane which are stacked along c-axis by weak Van der Waals forces with 6.2 Å of separation within layers [7]. The crystal structure was studied using electron microscopy techniques as described by Chianelli et al*.* who were able to observe its layered structure [8]. However, electron beam dosage during electron microscopy studies plays an important role to avoid any structural damage as described by Ponce et al*.* when using TEM technique who concluded high-resolution imaging at operational voltages near ~80 kV [9] to be possible. By *in-situ* TEM, Helveg et al*.* were able to synthesize small clusters of MoS2 from molybdenum oxide and hydrogen sulfide gases at beam radiation dosage of 100 *e* <sup>−</sup>/Å2 s [10]. The mechanical properties were studied by Casillas et al*.* achieving an atomistic observation of a resilient nature on MoS2 laminates at 8GPa of external applied pressure and its mechanical recovery during *in-situ* AFM on TEM sample holder [11]. Applying atomic force microscopy (AFM), Bertolazzi et al*.* determined a Young modulus values of 270GPa ± 100GPa and fracture strength of 16~30GPa in MoS2 layers as suspended in patterned silicon wafers [12, 14], and Castellanos-Gomez et al*.* estimated an average Young modulus *E* = 330GPa in suspended MoS2 sheets over patterned silicon wafer [13]. The mechanical properties were studied by density functional theory and molecular dynamics, Jiang et al*.* calculated a theoretical Poisson's ratio value of *v* = 0.29 applying Stillinger-Weber potential [15]. The reactive empirical bond-order (REBO) potential was used by Li et al*.* to understand structural effects at chemical bonding within S-Mo-S layers, their findings indicate induced vacancies on the basal plane can influence Poisson's ratio values [16]. The atom probe tomography enables the chemical understanding with three-dimensional spatial resolution and was applied to determine dopants, contamination and ionic distribution within semiconducting matrix [17], Singh et al*.* used APT technique to determine distribution of Ti over MoS2 matrix [18]. Regarding electrical transport, Lia et al*.* [4] and Samuel et al*.* [38] performed transport electrical measurements encountering a linear ohmic behavior in MoS2. This chapter covers mechanical, electrical and microstructure characterization by electron microscopy, low angle x-ray, atom probe tomography and CSM-nanoindentation to obtain information about crystal growth, elastic modulus (*E*), hardness (*H*) and electrical transport on MoS2 films.
