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Pulsed laser deposition was used to grow DLC and molybdenum-doped DLC (DLC:Mo) films, with metal contents up to 3.2 at.%, on silicon substrates. The microstructural details of the films were investigated using X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scan electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Residual stresses were quantified through curvature measurements while the nanoscale mechanical properties of the films were probed using an instrumented indentation platform in the nanoindentation and nanoscratch mode, respectively. The deposition conditions used in this study resulted in an amorphous carbon matrix with sp3 content of 77 at.% and density of 2.9 g/cm3. Molybdenum-doping reduced the percentage of sp3 hybridization within the amorphous carbon matrix and generated Mo-C bonds as detected through XPS. The increase in the molybdenum content reduced the residual stresses which can be related to the percentage reduction of the highly directional four-fold coordinated carbon atoms and the subsequent release of the strain energy in the system. Furthermore, the resistance to penetration of the DLC:Mo films was also reduced which again could be attributed to the severe graphitization of the amorphous carbon matrix. The effect of molybdenum on the coefficient of friction (COF) was of secondary importance with deviations from the COF of pure DLC on the order of ± 12%. In contrast, all DLC:Mo films deposited herein exhibited higher critical loads to failure/delamination with DLC:Mo3.2 at.% showing the highest enhancement (+ 87% compared to pure DLC). This improvement on the critical load to failure can be traced back to (a) the graphitization and softening of the amorphous carbon matrix that increased the ductility of the matrix, (b) the formation of the Mo-C bonds that can operate as obstacles to the micro-fracture processes and (c) the reduction of the residual stresses that increased the mechanical capacity of the film/substrate material system. © 2017 Elsevier B.V. 330 185 195 185-195

Electron beam lithography is a powerful maskless tool to fabricate structures on the nanometer scale. Here, we show that low-keV-electron beams enable a direct patterning of tetrahedral amorphous carbon (ta-C) thin films by inducing a local graphitization without the need for any resist or development process step. Irradiation with 4 keV electrons leads to a local decrease of the ta-C film's electrical resistance and an increase of both the sp2/sp3-ratio and the material's work function. We investigate the impact of electron exposure on ta-C by a variety of microscopy as well as spectroscopy methods including scanning tunneling microscope-based current-distance spectroscopy, conductive atomic force microscopy, spatially resolved ultraviolet and x-ray photo emission spectroscopy, and m-Raman spectroscopy. The electron exposure has been performed under ultrahigh vacuum conditions to prevent from electron-induced deposition of contaminants which may obstruct the application of surface-sensitive analysis techniques to the modified ta-C films.

Influence of wavelengths and beam profiles of a pulsed Nd3+:YAG laser on the formation of a polycrystalline-silicon (poly-Si) on a-Si thin film is investigated. Two sets of samples of amorphous-Silicon (a-Si) thin films deposited on glass (a-Si/glass) and crystalline Si (a-Si/c-Si) substrates were treated with different laser-fluence values. After the laser treatment, the films were analyzed by a scanning electron microscope, the Raman spectroscopy technique and the resistance-measurement technique. In the case of the third harmonics (355 nm) of the Nd3+:YAG laser, poly-Si films were obtained with laser-fluence values ranging from 260 mJ/cm2 to 560 mJ/cm2, where as in the case of the second harmonics (532 nm), the process window for the formation of poly-Si films, in terms of the laser fluence, was ranging from 300 mJ/cm2 to 480 mJ/cm2. On the other hand, in the case of samples treated with the fundamental wavelength (1064 nm), a narrow process window with higher laser-fluence values around 1100 mJ/cm2 was observed. Further, the substrate was also affected because of the higher laser-fluence value. It has also been observed that the crystallization characteristics of poly-Si films improved with the flat-top intensity distribution as compared to the Gaussian intensity distribution of the Nd3+:YAG laser beam. A theoretical simulation based on thermal modeling was performed to understand the mechanism of crystallization. � 2009 Elsevier B.V. All rights reserved.

In the present research, an approach of converting amorphous-silicon (a-Si) thin films into polycrystalline thin films using the third harmonics of an all-solid-state pulsed Nd3+:YAG laser (355 nm) is studied. Two different samples of a-Si thin films on alkali-free glass (a-Si/glass) substrates and a-Si thin film on crystalline-Si substrates (a-Si/c-Si) are laser treated at different laser fluences ranging from 170 to 960 mJ/cm2. The amount of heat incident on the surface has been analyzed theoretically by solving the one-dimensional heat-equation model. The ablation threshold, the region of crystallization and the depth of crystallization have been investigated theoretically. The influence of laser irradiation, ablation and crystallinity has been experimentally analyzed through in-situ reflectivity measurements, scanning electron microscopy (SEM) and Raman spectroscopy studies. In the case of a-Si/c-Si, the extent of crystallinity and the influence of structural characteristics on electronic properties are studied using the Hall-effect technique. The ablation threshold and the range of crystallization regime are in good agreement with the theoretical results. Laser fluence between 300 and 500 mJ/cm2 is required for crystallization and the ablation threshold is estimated to be above 500 mJ/cm2 for a-Si thin film with a thickness up to 400 nm. � 2009 Elsevier Ltd. All rights reserved.

The crystallization kinetics of amorphous silicon carbide films was studied by means of X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The films were deposited by radio frequency (r.f.) magnetron sputtering on glassy carbon and single crystalline silicon substrates, respectively. TEM micrographs and XRD patterns show the formation of nano-crystalline β-SiC with crystallite sizes in the order of 50 nm during annealing at temperatures between 1200 and 1600 °C. A modified Johnson–Mehl–Avrami–Kolmogorov (JMAK) formalism was used to describe the isothermal transformation of amorphous SiC into β-SiC as an interface controlled, three-dimensional growth processes from pre-existing small crystallites in the order of 10 nm. These pre-existing crystallites are formed in a transient process in the early stages of crystallization. For films deposited on the silicon substrate, the obtained rate constants of crystallite growth obey an Arrhenius behavior with an activation enthalpy of 4.1 ± 0.5 eV in accordance with literature data. Films deposited on glassy carbon show an increased stability of amorphous SiC films, which is reflected in smaller rate constants of crystallite growth of several orders of magnitude at low temperatures and a higher activation enthalpy of 8.9 ± 0.9 eV. A model is proposed, where the faster crystallization of films on silicon substrates can be explained with the presence of superabundant point defects, which diffuse from the substrate into the film and accelerate the incorporation of atoms from the amorphous into the crystalline phase.

We report coplanar conductance fluctuations of device quality, undoped hydrogenated amorphous silicon-germanium alloy thin films (a-SiGe:H) measured from 430 to 490 K. The a-SiGe:H alloys produce noise power spectra similar to coplanar undoped a-Si:H films in the same temperature range. The noise power spectrum S(n) does not fit a single 1/fα power law but rather has two distinct regions, each accurately fitted by a power law, but with different slopes. The low frequency slope α1 is similar to that observed in undoped a-Si:H films varying from 1.30 to 1.46 for different Ge concentrations and shows a slight temperature dependence. At higher frequencies, the slope α2 is less than unity and temperature independent but depends on the Ge content of the film. α2 decreases from 0.60 for no Ge (pure a-Si:H) to 0.15 for 40 at.% Ge. The noise power at lower frequencies increases and at higher frequencies decreases substantially as the temperature increases from 430 to 490 K. We infer that similar noise mechanisms are operating in undoped a-SiGe:H and a-Si:H films but that the Ge content is influencing the noise, particularly the slope at higher frequencies. In addition, the noise has the expected quadratic dependence on bias current and obeys Gaussian statistics., Natural Sciences and Engineering Research Council of Canada

We have used Raman scattering to follow the progress of multiple-pulse (sub-melt-threshold) laser annealing in doped hydrogenated amorphous silicon films (a-Si:H) on glass. In phosphorous-doped a-Si:H the Raman signal shows that recrystallization begins with the first laser pulse but the multiple pulses are needed to generate the highest hole concentrations of ∼6×10 20 cm −3 . In boron-doped a-Si:H the electron concentration reaches ∼1×10 21 cm −3 after laser anneal which produces a dip rather than a peak near the phonon line as a consequence of a negative Fano-interference parameter, q. The results show that Raman scattering can be used to obtain carrier concentrations in poly-silicon provided that wavelength-dependent Fano interference effects are properly included.