Properties Of Nanocrystalline Thin Films Research Articles

Studies structure, surface morphology, linear and nonlinear optical properties of nanocrystalline thin films of manganese (III) phthalocyanine chloride for photodetectors application

Manganese (III) Phthalocyanine Chloride (MnClPc) thin films were deposited over glass substrates through the thermal evaporation technique. The structural characteristics of MnClPc films at various thicknesses have been studied using X-ray diffraction (XRD), which revealed an amorphous structure. The atomic force microscope (AFM) investigates the surface morphology of MnClPc thin films and demonstrates that films have nanostructure with a size of 58 nm for thickness 55 nm and slightly increased with increasing film thickness. Spectrophotometer analyses of MnClPc thin films obtained over the wavelength range of 300−2500 nm were used to determine the linear and nonlinear optical parameters. Results indicate that the optical energy gap of MnClPc films was slightly changed due to thickness. The parameters of the optical dispersion were considered using a single-oscillator model. Also, the nonlinear refractive index and susceptibility were determined by the concepts of linear refractive index dispersion. The optical limiting characteristics by using two different types of laser showed a considerable reduction in the laser output power by increasing the film thickness. This intensive result for MnClPc will probably implement in an industrial approach in the field of photodetectors and optoelectronic devices.

Magnetic Properties of Permalloy Thin Film Edges

The paper presents the results of ferromagnetic resonance (FMR) spectrometry of magnetic properties of nanocrystalline thin films obtained by magnetron sputtering of permalloy targets of various composition (NixFe1–x, x = 0.6–0.85). The behavior of the main magnetic properties of the thin film edges is analyzed. Near the film edges, not only the fluctuation of the uniaxial magnetic anisotropy field is observed, but also a drastic widening of the FMR line and the decrease in the effective saturation magnetization.

Effect of hydriding induced defects on the small-scale plasticity mechanisms in nanocrystalline palladium thin films

Nanoindentation tests performed on nanocrystalline palladium films subjected to hydriding/dehydriding cycles demonstrate a significant softening when compared to the as-received material. The origin of this softening is unraveled by combining in situ TEM nanomechanical testing with automated crystal orientation mapping in TEM and high resolution TEM. The softening is attributed to the presence of a high density of stacking faults and of Shockley partial dislocations after hydrogen loading. The hydrogen induced defects affect the elementary plasticity mechanisms and the mechanical response by acting as preferential sites for twinning/detwinning during deformation. These results are analyzed and compared to previous experimental and simulation works in the literature. This study provides new insights into the effect of hydrogen on the atomistic deformation and cracking mechanisms as well as on the mechanical properties of nanocrystalline thin films and membranes.

Synthesis, characterization, and photocatalytic properties of nanocrystalline NZO thin films

Nanocrystalline Ni-doped ZnO (NZO) thin films were synthesized on glass substrate using sol-gel spin coating methods. The effect of annealing on the structural and optical properties of nanocrystalline thin film was studied using X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), UV-VIS spectrophotometry, and photoluminescence (PL). The results showed that the annealing temperature strongly influenced the physical properties of nanocrystalline NZO thin films. The photocatalytic properties of nanocrystalline NZO thin films were evaluated using an aqueous solution of Rhodamine-B. The photocatalytic activity of nanocrystalline NZO thin films increased with the increase of annealing temperature. The results indicated that the structure, morphology, and band gap energy of nanocrystalline NZO thin films played an important role in photocatalytic activity.

Cross-sectional structure-property relationship in a graded nanocrystalline Ti1−xAlxN thin film

The influence of simultaneously occurring gradients of crystalline phases, microstructure, chemical composition and strains on overall as well as local mechanical properties of nanocrystalline thin films is challenging to understand. In this work, cross-sectional structure-property relationships in a graded nanocrystalline 2 μm thick Ti1−xAlxN film were analyzed using in-situ bending tests on micro-cantilevers in transmission electron microscope, synchrotron X-ray nanodiffraction and nanoindentation. The results document that sub-micron depth variations of fracture stresses, hardness and elastic moduli depend on phases, crystallite sizes, crystallographic texture, Ti/Al ratio and residual strain. The local mechanical properties are primarily influenced by cross-sectional occurrence of binary and ternary phases and their intrinsic properties. Secondly, the hardness and fracture stress gradients depend on cross-sectional microstructure, especially on the local crystallite sizes and shapes as well as fiber textures. Two nucleation regions of cubic TiN and hexagonal Ti1−xAlxN phases with globular shaped crystal sizes in the nm range and relatively large in-plane residuals strains result in significantly higher hardness and fracture stresses in comparison with a coarse-grained region consisting of columnar cubic Ti1−xAlxN crystallites. The fracture behavior of cantilevers with ∼0.5 × 0.5 μm2 cross-section depends also on the apparent grain size whereby the nucleation regions exhibit linear-elastic fracture in contrast to partly ductile response of the region with elongated nanocrystals. Finally, the experimental data indicate the possibility of mechanical optimization of nanocrystalline thin films through cross-sectional nanoscale design.

Microstructure-controlled depth gradients of mechanical properties in thin nanocrystalline films: Towards structure-property gradient functionalization

Although the influence of the grain size on the mechanical properties of polycrystalline materials is well understood, the occurrence of depth-gradients of grain size, microstructure, and residual stresses in nanocrystalline thin films and their effect on the functional properties is a phenomenon which has not yet been studied in detail. Hence in this work, single-layered polycrystalline and mosaic epitaxial as well as multilayered CrN thin films were characterized by a combination of averaging as well as depth-resolved experimental techniques, such as cross-sectional X-ray nanodiffraction and small-angle cross-sectional nanoindentation. The results reveal the fundamental relationship between gradients of grain size, microstructure, and stresses, controlled by the film growth conditions, and gradients of hardness and elastic modulus. The effect of the compressive stress and structural defects associated with high particle energy on the mechanical properties of nanocrystalline thin films was found to be dominant over the grain size and crystallographic texture. These findings open the way to functionalize structure-property gradients in nanocrystalline thin films through microstructural design as demonstrated for multilayered CrN films.

Optical properties of nanostructured InSe thin films

Thin films of InSe were prepared by thermal evaporation technique. The as-deposited films have nano-scale crystalline nature and the annealing enhanced the degree of crystallinity. The optical properties of nanocrystalline thin films of InSe were studied using spectrophotometric measurements of transmittance, T, and reflectance, R, at normal incidence of light in the wavelength range 200–2500 nm. The optical constants (refractive index, n, and absorption index, k) were calculated using a computer program based on Murmann's exact equations. The calculated optical constants are independent of the film thickness. The optical dispersion parameters have been analysed by single oscillator model. The type of transition in InSe films is indirect allowed with a value of energy gap equals to 1.10 eV, which increased to 1.23 eV upon annealing.

Preparation and optical properties of nanocrystalline thin films in the ZnO-TiO2 system

Nanocrystalline compound thin films of ZnO-TiO2 with different Zn/Ti atomic ratios were prepared by radio frequency magnetron reactive sputtering. The optical constants and the optical band gap were investigated using spectroscopic ellipsometry and the optical absorption spectrum. It was found that the cubic ZnTiO3 phase can be obtained with the atomic ratio of Zn to Ti of about 1:1, and transforms to rhombohedral ZnTiO3 phase and a phase mixture of rhombohedral ZnTiO3 and ZnO with increasing Zn content. The refractive index decreases with the increase of Zn content, and the extinction coefficient in the visible range is near zero. The optical band gap was derived from the modeling of ellipsometry data and extinction coefficient spectra, and compared with that obtained from optical absorption spectrum, and it was found that the optical band gaps obtained by these three methods are consistent with each other.

Structural and optical studies of nanocrystalline V 2O 5 thin films

We report the structural and optical properties of nanocrystalline thin films of vanadium oxide prepared via evaporation technique on amorphous glass substrates. The crystallinity of the films was studied using X-ray diffraction and surface morphology of the films was studied using scanning electron microscopy and atomic force microscopy. Deposition temperature was found to have a great impact on the optical and structural properties of these films. The films deposited at room temperature show homogeneous, uniform and smooth texture but were amorphous in nature. These films remain amorphous even after postannealing at 300 °C. On the other hand the films deposited at substrate temperature T S > 200 °C were well textured and c-axis oriented with good crystalline properties. Moreover colour of the films changes from pale yellow to light brown to black corresponding to deposition at room temperature, 300 °C and 500 °C respectively. The investigation revealed that nanocrystalline V 2O 5 films with preferred 001 orientation and with crystalline size of 17.67 nm can be grown with a layered structure onto amorphous glass substrates at temperature as low as 300 °C. The photograph of V 2O 5 films deposited at room temperature taken by scanning electron microscopy shows regular dot like features of nm size.

Luminescent properties of wide bandgap materials at room temperature

Properties of nanocrystalline thin films of selected nitrides are discussed as possible buffer materials for obtaining freestanding GaN wafers. These films are grown by impulse plasma deposition on silicon substrates. We demonstrate high smoothness of these films. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic properties of nanocrystalline thin films of Fe-rich alloys

We studied the influence of Mo and Y substitution in Fe-rich Fe87Zr7B6 on the thermal stability and magnetic properties of thin films obtained from these alloys. The microstructure of the films and its changes were observed by transmission electron microscopy. Coercive field, magnetic induction and effective magnetization, which were determined from measurements of the Kerr effect and ferromagnetic resonance correlated with microstructural transformations.