This paper presents a novel analysis approach by considering multiple crack interaction in achieving FAA certification for durability and damage tolerance of exterior attachment installations on an aircraft fuselage according to FAA policy on Certification by Analysis-Supported-by-Test (CAST). Durability and damage tolerance evaluation of an aircraft component requires assessment of damage initiation and fatigue crack propagations under service loading, which consists of complex loading types, paths and variable amplitudes. Both simulation and service experience showed that multiple cracks developed in the fuselage skin and doublers that are made of wrought aluminum alloys. Progressive failure analysis (PFA) tool was used to simulate the fatigue damage initiation life using a scale-down stress-life property. A virtual crack closure technique (VCCT) was implemented to evaluate fatigue crack growth with interactions between cracks from different parts in a component, which preserves conservativeness. The fatigue crack growth data is obtained uniquely from an analytical extension of fatigue crack growth data of thin aluminum sheet. Fatigue crack growth analysis showed that only a few initiated cracks propagated steadily before a crack became visible under inspection, which was validated by comparison to service history. Eventually one crack became dominate in the fracturing process thereby setting an inspection time. Analysis also showed that fatigue damage state in the components at the designed operational life will not exceed the static safety requirements. Therefore, FAA accepted the damage tolerance analysis and the aircraft retained certification with no need for repair.

An oxygen plasma treatment was used to prepare Fe-doped TiO2 nanoparticles. The anatase and rutile phases of TiO2 nanoparticles were achieved by an atmospheric pressure chemical vapor deposition method. The nanostructures were doped by Fe atoms to obtain a ferromagnetic nanostructure based on TiO2 nanoparticles. Atomic force microscopy and magnetic force microscopy were used for morphological and magnetic investigation of as-prepared samples. Measurements have confirmed the induced magnetic moment of the structures. Magnetic field-induced wettability of the prepared nanostructures was investigated in dark and under UV and visible light. The results showed a considerable enhancement in the wettability of the structure by applying the magnetic field.

Zinc oxide nanowires were synthesized by a simple chemical method using zinc acetate dihydrate, polyvinylpyrrolidone (PVP) and DI water as precursor, capping and solvent, respectively. Aluminum-doped ZnO nanowires were also synthesized by adding AlCl3 during the growth process. Both types of nanowires were used to fabricate a novel field ionization based gas sensor. The high sensitivity in low pressures, low working voltages, very low recovery time and good selectivity are the main advantages of these fabricated sensors. Electrical characteristics of the fabricated sensors were investigated while being exposed to several gases. Scanning electron microscopy (SEM) was used to analyze the nanowires structures.

Plasma enhanced chemical vapor deposition was used to grow vertically aligned carbon nanotubes (CNTs) on silicon substrate. Field emission from these nanotubes was realized and used to fabricate a field emission-based sensor. Titanium dioxide was used as spacing layer between the emitters and a flexible anode made of silicon membrane. The variation of the emission current during mechanical vibration of the silicon membrane was measured and compared with a theoretical prediction. Experimental results show that field emission from CNTs is a good candidate for high frequency vibration sensing, measurement of resonance frequency, fabrication of accelerometer and other types of mechanical sensors. The fabricated device, due to a low distance between its electron emitters and the anode, works at low voltages with high emission current.

Branched treelike carbon nanotubes were grown by plasma enhanced chemical vapor deposition method on a silicon wafer. Patterned structures of as grown nanostructures were used for the fabrication of a gas sensor, which operates based on the field ionization of various gases. The variations in the electrical resistivity and the emission current of the fabricated device are related to the chemisorption and field ionization mechanisms, respectively. The sensor is capable of gas detection at room temperature and at low pressures with working at low voltages. Different gases such as H2, O2, C2H2 and Ar have been used to examine the gas sensitivity characteristics of the fabricated sensors.

Multiwalled carbon nanotubes are grown on nickel-seeded silicon substrates using plasma-enhanced chemical vapor deposition method at a temperature of 650 °C utilizing a mixture of acetylene and hydrogen. Magnetic and electric fields were used to obtain well-oriented carbon nanotubes. The direction of growth was found to strongly depend on the directions and magnitudes of the applied fields. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) have been used to investigate the grown nanotubes. The SEM and TEM images of as grown nanotubes show that applying magnetic field during the growth process affects the growth direction of the nanotubes and, furthermore, bent nanotubes can be achieved by changing the direction of the applied electric field alone. Raman spectroscopy has been used to analyze the structure of the samples. 

Nucleation of a gold catalyst on a (100) oriented silicon substrate was extensively investigated. An anomalous mechanism of nucleation was observed in the grain formation of gold nanoislands. The chemical vapour deposition method was employed to grow zinc oxide nanowires. Zinc powder and oxygen gas were used as reaction sources for the growth. Different shaped ZnO nanowires were obtained for different nucleation mechanisms. The nucleation mechanism and growth evolution were monitored by scanning electron microscopy and atomic force microscopy.

Effects of plasma power on the growth of the multi-wall carbon nanotubes (CNTs) are reported. CNTs were grown on the silicon wafers by plasma enhanced chemical vapor deposition (PECVD) method using a mixture of acetylene and hydrogen at the temperature of 650 °C. Plasma powers ranging from zero to 35 W were applied on the samples and the effects of different magnitudes of the plasma power on the growth direction of the CNTs were investigated. Regular vertically aligned nanotubes were obtained at plasma power of 25 W. In order to set on the plasma during the growth, electrical force was applied on the carbon ions. Nickel layer was used as a catalyst, and prior to the nanotubes growth step, it was treated by hydrogen plasma bombardment in order to obtain the Ni nano-islands. In this step, as the plasma power on the Ni layer was increased, the grain size of nickel nano-particles decreased, and hence, nanotubes of smaller diameter were obtained later on. At the last step some anomalous structures of agglomerated CNTs were obtained by controlling the plasma power. Samples were analyzed by scanning tunneling microscopy (STM) and scanning electron microscopy (SEM).

Anisotropic etching of silicon is achieved in the presence of ultra-violet exposure in a solution containing hydrofluoric/nitric/acetic acids (HNA). The HNA solution is typically used for polishing silicon and etching polysilicon due to its isotropic etching property. In the technique proposed in this paper which is called UV-HNA, the etching of silicon is enhanced in the direction determined by UV exposure. A mixture of HF/HNO3/CH3COOH with a relative composition of 1:15:5 seems suitable for revealing 〈111〉 planes with an etch rate of 10 μm/h at 35 °C. The bottom of the etched craters is hillock-free and etch rates as high as 60 μm/h can be achieved using higher concentration of HF acid in HNA solution. In the latter case the etching is more isotropic and mask undercut is observed. Also membranes with a depth of 400 μm are fabricated on n-type Si 〈100〉 with a thickness of 500 μm by means of standard 34 wt% solution of KOH at temperature of 60 °C. Problems encountered during the experiment, and their solutions are discussed and results of these experiments are reported.

A novel plasma hydrogenation method for the fabrication of nano-crystalline structures of silicon as well as the photoluminescence and structural properties of these porous structures is presented. We have observed that the hydrogenation process followed by an annealing treatment results in the formation of nano-crystalline silicon structures where increased temperatures during hydrogenation reduces the grain size. Furthermore, by increasing the time of the hydrogenation process, the density of the silicon grains is increased.

Photoluminescence (PL) spectroscopy demonstrated the presence of a direct gap in the visible light range where materials with a smaller grain size emitted light at lower wavelengths, and a higher density of grains resulted in higher amplitudes in the PL spectrum. TEM and SEM characterization of these samples and the structure-emission relationship are also presented.