Search

This thesis reports a study of certain aspects of ion beam mixing in amorphous silicon. The amorphous silicon films are deposited by RF sputter deposition technique, and heavy metal markers of gold and tantalum are used to section these films. Mixing in the amorphous silicon films is brought about by energetic argon ions of various energies (100 keV to 300 keV) and an estimate of mixing is made by observing the shift and broadening in the marker profile using Rutherford backscattering spectrometry. Mixing versus depth as a function of the angle of incidence is investigated experimentally, by implanting at ten different angles (0° to 85°), films, with the marker at various depths. A comparison of the experimental results is made with the Wilson and Webb model, the average diffusion model, and a computer simulation code TRIM-Cascade. All the comparisons show evidence of radiation enhanced diffusion in the experiment. The presence of radiation enhanced diffusion is confirmed when a double marker technique is employed to determine the effect of sputtering, contraction and swelling, in an amorphous silicon film, due to mass transport under argon ion irradiation, both at room temperature and at LN2 temperature. Finally, as an application of the ion beam mixing process, silicide formation at the interface of a Ni-Si and an Fe-Si system is considered. The need to form useful silicides is evident from the recent developments in VLSI technology where transition metal silicides have been explored for interconnect metallization, gate metallization and low resistivity contacts. In the research work presented here, it is found that both the Ni-Si and Fe-Si systems show cascade type of mixing but silicide formation is more evident in the Ni-Si system.

Thin films with semiconducting properties can be successfully engineered from chalcogen-basedmaterials, specifically those containing selenium (Se), or/and tellurium (Te). They are vital subjects of study in both their elemental states and various compounds due to their distinct anisotropic properties. These elements play essential roles in compounds like tellurides and selenides, which are crucial in semiconductors, photovoltaic devices, and electronics. However, the quick crystallization tendencies observed in amorphous TexSe1 −x thin films restrict their applicability. It is essential to gain insight into the short- and medium-range structural organization of the amorphous state and comprehend the underlying physics driving film crystallization. Therefore, in the second chapter of the thesis, we provide comprehensive research on the short- to medium-range ordering in amorphous TexSe1 −x thin films through a combination of experimental studies and atomic simulations. This study marked the first instance in which we employed fluctuation electron microscopy (FEM) and Density Functional Theory (DFT) calculations to gain insights into these structural variations across a wide range of compositions, including pure Te. Within the chain network structure, we have identified at least two distinct populations that closely resemble the intrachain distances of Se-Se and Te-Te. In the case of the binary alloy with x greater than 0.61 in TexSe1 −x, we observe an increase in Te-Te-like populations, implying the potential formation of Te fragments. To leverage the anisotropic properties of tellurium, in recent study, the oriented growth of ultra-thin Te layers on a WSe2 substrate is achieved by using a technique called physical vapor deposition (PVD). In this configuration, the atomic chains of Te align with the armchair directions of the substrate, leading to the formation of a moire superlattice. This superlattice consists of micrometer- ´ scale Te flakes positioned on the continuous WSe2 film. Here, we explore the exact orientation relationships and moire lattices by combining electron microscopy with image simulations. We ´ also assess the strain evolution and defects in Te-WSe2 heterostructures with the help of scanning nanodiffraction analysis, shedding light on the complexities of strain transfer and its impact on material properties. In the final chapter of the thesis, we introduce a hybrid approach aimed at addressing challenges in sample preparation for in-situ mechanical testing. It involves depositing samples on flexible, electron-transparent substrates, attaching them to macroscopic copper sheets, and mirroring techniques used in the nanomaterials and thin-film community. With the help of this technique, we were able to study the mechanical responses of sputtered gold (Au) and transition metal dichalcogenides (TMDC), specifically WS2. This method not only streamlines sample preparation but also expands our ability to investigate the mechanical properties of materials at the nanoscale