Quantitative SEM characterisation of ceramic target prior and after magnetron sputtering: a case study of aluminium zinc oxide.

Till now electron microscopy techniques have not been used to evaluate the plasma-target interactions undergone during the magnetron sputtering process. The destructive nature of this interaction severely alters the target microstructure. Utilising quantitative microscopy techniques can shed light on the complex plasma and solid-state processes involved which can ultimately lead to improved functional thin film deposition. As a representative functional material, aluminium-doped-zinc oxide (AZO) is an upcoming alternative to conventional transparent electrode wherein the process optimisation is of great importance. In this paper, we evaluate the pre- and post-sputter field emission scanning electron microscopy (FESEM) data for ceramic AZO target fabricated at three final sintering temperatures (1100°C, 1200°C and 1300°C). In all cases, grain boundaries are merged in addition to a visible reduction in the secondary phases which makes segmentation-based image analysis challenging. Through surface statistics (i.e. fractal dimension, autocorrelation length, texture aspect ratio and entropy) as a function of magnification we can quantify the electron microscopy image of the microstructure. We show that the plasma-microstructure interaction leads to an increase in autocorrelation length, texture aspect ratio and entropy for the optimum AZO ceramic sputtering target sintered at 1200°C. Furthermore, a maximum reduction in fractal dimension span (as determined by exponential regression) is also observed for 1200°C. In addition to the evaluation of plasma effects on sintering, our approach can provide a window towards understanding the underlying thin film growth mechanisms. We believe that this technique can be applied to the defect characterisation of a wide range of polycrystalline ceramic sputtering targets (e.g. ITO, CZTS, GAZO and so on) with the ultimate goal of improving the magnetron sputtering process and the resulting functional thin film. LAY DESCRIPTION: Magnetron sputtering allows scientists to make functional thin films on the order of the nanoscale. In this technique, atoms are plucked from a 'target' then placed onto a substrate forming a thin nanometric film: all thanks to magnets, a special power supply and the fourth state of matter (plasma). Understanding what is going on and how to make a 'good' thin film is important for making better light emitting diodes, solar cells and light sensors. Scientists use electron microscopy to see what is going on in the microstructure of the sputtered thin films to fine tune the sputtering recipe. Here, for the first time, we have applied electron microscopy to see the surface of the microstructure before and after magnetron sputtering. This will help us understanding the plasma-microstructure interaction allowing us to make more informed decisions when fine-tuning the sputtering process to get improved thin films. This is a case study of aluminium-doped zinc oxide (AZO) target that could potentially replace indium tin oxide (ITO), which is widely used as a transparent electrode in devices involving light and electricity. In this case, improved characteristics would be lower electrical resistivity and higher transmission of light. We show that it is possible to use a mathematical description (e.g. the fractal dimension) of the scanning electron microscopy picture to show a link between the target surface and the functional properties. Simple explanation of fractal dimensions by Sixty Symbols ○ https://www.youtube.com/watch?v=cmBljeC79Ls Experimental demonstration of magnetron sputtering by The Thought Emporium ○ https://www.youtube.com/watch?v=Cyu7etM-0Ko Introductory video on magnetron sputtering by Applied Science ○ https://www.youtube.com/watch?v=9OEz_e9C4KM Demonstration of AZO target fabrication and sputtering by Pradhyut Rajjkumar ○ https://www.youtube.com/watch?v=kTLaTJfNX3c Simple explanation of a DIY SEM by Applied Science ○ https://www.youtube.com/watch?v=VdjYVF4a6iU.

Growth of c-plane and m-plane aluminium-doped zinc oxide thin films: epitaxy on flexible substrates with cubic-structure seeds.

Manufacturing high-quality zinc oxide (ZnO) devices demands control of the orientation of ZnO materials due to the spontaneous and piezoelectric polarity perpendicular to the c-plane. However, flexible electronic and optoelectronic devices are mostly built on polymers or glass substrates which lack suitable epitaxy seeds for the orientation control. Applying cubic-structure seeds, it was possible to fabricate polar c-plane and nonpolar m-plane aluminium-doped zinc oxide (AZO) films epitaxially on flexible Hastelloy substrates through minimizing the lattice mismatch. The growth is predicted of c-plane and m-plane AZO on cubic buffers with lattice parameters of 3.94-4.63 Šand 5.20-5.60 Å, respectively. The ∼80 nm-thick m-plane AZO film has a resistivity of ∼11.43 ±â€…0.01 × 10-4 Ω cm, while the c-plane AZO film shows a resistivity of ∼2.68 ±â€…0.02 × 10-4 Ω cm comparable to commercial indium tin oxide films. An abnormally higher carrier concentration in the c-plane than in the m-plane AZO film results from the electrical polarity along the c-axis. The resistivity of the c-plane AZO film drops to the order of 10-5 Ω cm at 500 K owing to the semiconducting behaviour. Epitaxial AZO films with low resistivities and controllable orientations on flexible substrates offer optimal transparent electrodes and epitaxy seeds for high-performance flexible ZnO devices.

Effects of size and surface of zinc oxide and aluminum-doped zinc oxide nanoparticles on cell viability inferred by proteomic analyses.

Although the health effects of zinc oxide nanoparticles (ZnONPs) on the respiratory system have been reported, the fate, potential toxicity, and mechanisms in biological cells of these particles, as related to particle size and surface characteristics, have not been well elucidated. To determine the physicochemical properties of ZnONPs that govern cytotoxicity, we investigated the effects of size, electronic properties, zinc concentration, and pH on cell viability using human alveolar-basal epithelial A549 cells as a model. We observed that a 2-hour or longer exposure to ZnONPs induced changes in cell viability. The alteration in cell viability was associated with the zeta potentials and pH values of the ZnONPs. Proteomic profiling of A549 exposed to ZnONPs for 2 and 4 hours was used to determine the biological mechanisms of ZnONP toxicity. p53-pathway activation was the core mechanism regulating cell viability in response to particle size. Activation of the Wnt and TGFß signaling pathways was also important in the cellular response to ZnONPs of different sizes. The cadherin and Wnt signaling pathways were important cellular mechanisms triggered by surface differences. These results suggested that the size and surface characteristics of ZnONPs might play an important role in their observed cytotoxicity. This approach facilitates the design of more comprehensive systems for the evaluation of nanoparticles.