Abstract: Over the past decades, the metal-oxide-based semiconductors have become increasing prominent materials due to their inherent advantages including wide bandgap energy, large exciton binding energy, high radiation hardness, and compatibility with conventional fabrication processes. Although several methods were utilized to deposit various metal-oxide-based materials onto different substrates for fabricating devices, the novel vapor cooling condensation method was successfully demonstrated previously [1][2]. The metal-oxide-based materials and thin films deposited on various substrates at liquid-nitrogen temperatures using the vapor cooling condensation method are studied. The related properties are also demonstrated. Besides, the performances of the associated devices manufactured using those materials and thin films are reported in this work.

Keywords: Metal-oxide materials and devices, Vapor cooling condensation system

References:
[1]. H. Y. Lee, S. D. Xia, W. P. Zhang, L. R. Lou, J. T. Yan, and C. T. Lee, “Mechanisms of high quality i-ZnO thin films deposition at low temperature by vapor cooling condensation technique”, J. Appl. Phys., vol. 108, 073119 (2010).
[2]. T. S. Lin and C. T. Lee, “Performance investigation of p-i-n ZnO-based thin film homojunction ultraviolet photodetectors”, Appl. Phys. Lett., vol. 101, 221118, (2012).

Acknowledgements: This work was supported by the National Science and Technology Council (NSTC), under No. NSTC 113-2221-E-006-106-MY3 and NSTC 114-2221-E-006-200-MY3.

Abstract: Pre-cure forming (or net shape forming) is an efficient manufacturing method for large composite structural components, especially suitable for aerospace and transportation industries. Pre-cure forming of composites, involving pressure shaping and precision contour cutting before curing, is a critical practical technique that delivers efficient shaping with minimal waste and is especially suited for the co-curing process. However, theoretical modeling of cutting processes for fiber/uncured-viscoelastic-resin composites remains limited as resin properties strongly depend on temperature and loading frequency. In this study, a three-term-Prony-series viscoelastic resin model incorporating the time-temperature superposition principle was proposed and applied in finite element modeling (FEM) of unidirectional carbon fiber-reinforced polymer prepreg laminates (CPL). The main contributions included: (1) development of a representative volume element (RVE) model for CPL that accounts for loading frequency and temperature effects, validated against dynamic tensile test data with an average error of approximately 12%; (2) establishment of a coupled heat generation and transfer model that accurately predicted the thermal distribution during cutting, achieving a prediction error within 7% for peak surface temperature; and (3) construction of a temperature- and frequency-dependent model for ultrasonic vibration cutting of CPL, yielding a feed force prediction error of 17%. By integrating frequency and temperature effects into the cutting mechanics framework, this study provides a robust methodology for elucidating the underlying mechanisms of ultrasonic cutting and offers an effective approach for modeling mechanical interactions in viscoelastic materials.

Keywords: FE modelling, ultrasonic vibration, cutting process, CFRP laminates, viscoelastic.

Abstract: Carbon containing epoxy resins are used for a wide number of applications, while conductive composites represent a very interesting field due to their applications as sensors. The main drawbacks of high performances carbon fillers (i.e. CNT, graphene) are their high cost and the difficulty of achieving homogeneous dispersion. Biochar is a carbon filler derived from pyrolyzed biomasses and can represent a viable alternative to such materials due to its low cost, large availability and easiness to be dispersed in composites. We used biochar as a filler in epoxy resin to successfully improve mechanical [1] and electrical [2] properties of composites. Biochar can be obtained from different feedstock, and this allows to tune the composite properties. We will review the influence of different Biochar types for the tailored enhancement of brittleness and/or ductility of an epoxy-based composite proving the relationship between biochar morphology and composites mechanical properties [3]. We will highlight that by properly selecting the biochar feedstock and the pyrolysis parameters the electrical conductivity of the biochar can be tuned. Using an appropriate set of pyrolysis parameters, electrical conductivities comparable to those of commercial CNTs and carbon black can be obtained. We used such biochar as fillers to obtain polymer composites having high electrical conductivity without harming their mechanical properties [2]. Biochar based composites have a higher electrical conductivity as well as higher Young modulus and ultimate tensile strength than carbon black based composites. We will thoroughly discuss the perspectives of biochar based composites, with an eye also to economic feasibility and composites production process.

References
[1] Bartoli, M., Rosso, C., Giorcelli, M., Rovere, M., Jagdale, P., Tagliaferro, A., Chae. M., Bressler, D. C. (2019). Journal of Applied Polymer Science, 48896.
[2] Giorcelli, M., & Bartoli, M. (2019). Polymers, 11(12), 1916.), 3109.
[3] Bartoli, M., Giorcelli, M., Rosso, C., Rovere, M., Jagdale, P., Tagliaferro, A. (2019). Applied Sciences, 9(15)

Keywords: Polymer composites, Biochar, electrical conductivity, feedstocks.