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Abstract This work reports on the correlation between structure, surface/interface morphology and mechanical properties of pulsed laser deposited (PLD)β-Ga2O3films on transparent quartz substrates. By varying the deposition temperature in the range of 25 °C–700 °C, ∼200 nm thick Ga2O3films with variable microstructure and amorphous-to-nanocrystalline nature were produced onto quartz substrates by PLD. The Ga2O3films deposited at room temperature were amorphous; nanocrystalline Ga2O3films were realized at 700 °C. The interface microstructure is characterized with a typical nano-columnar morphology while the surface exhibits the uniform granular morphology. Corroborating with structure and surface/interface morphology, and with increasing deposition temperature, tunable mechanical properties were seen in PLD Ga2O3films. At 700 °C, for nanocrystalline Ga2O3films, the dense grain packing reduces the elastic modulus Erwhile improving the hardness. The improved crystallinity at elevated temperatures coupled with nanocrystallinity, theβ-phase stabilization is accounted for the observed enhancement in the mechanical properties of PLD Ga2O3films. The structure-morphology-mechanical property correlation in nanocrystalline PLDβ-Ga2O3films deposited on quartz substrates is discussed in detail.
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Structural, Optical and Mechanical Properties of Nanocrystalline Molybdenum Thin Films Deposited under Variable Substrate Temperature
Molybdenum (Mo), which is one among the refractory metals, is a promising material with a wide variety of technological applications in microelectronics, optoelectronics, and energy conversion and storage. However, understanding the structure–property correlation and optimization at the nanoscale dimension is quite important to meet the requirements of the emerging nanoelectronics and nanophotonics. In this context, we focused our efforts to derive a comprehensive understanding of the nanoscale structure, phase, and electronic properties of nanocrystalline Mo films with variable microstructure and grain size. Molybdenum films were deposited under varying temperature (25–500 °C), which resulted in Mo films with variable grain size of 9–22 nm. The grazing incidence X-ray diffraction analyses indicate the (110) preferred growth behavior the Mo films, though there is a marked decrease in hardness and elastic modulus values. In particular, there is a sizable difference in maximum and minimum elastic modulus values; the elastic modulus decreased from ~460 to 260–280 GPa with increasing substrate temperature from 25–500 °C. The plasticity index and wear resistance index values show a dramatic change with substrate temperature and grain size. Additionally, the optical properties of the nanocrystalline Mo films evaluated by spectroscopic ellipsometry indicate a marked dependence on the growth temperature and grain size. This dependence on grain size variation was particularly notable for the refractive index where Mo films with lower grain size fell in a range between ~2.75–3.75 across the measured wavelength as opposed to the range of 1.5–2.5 for samples deposited at temperatures of 400–500 °C, where the grain size is relatively higher. The conductive atomic force microscopy (AFM) studies indicate a direct correlation with grain size variation and grain versus grain boundary conduction; the trend noted was improved electrical conductivity of the Mo films in correlation with increasing grain size. The combined ellipsometry and conductive AFM studies allowed us to optimize the structure–property correlation in nanocrystalline Mo films for application in electronics and optoelectronics.
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- Award ID(s):
- 1827745
- PAR ID:
- 10331316
- Date Published:
- Journal Name:
- Materials
- Volume:
- 15
- Issue:
- 3
- ISSN:
- 1996-1944
- Page Range / eLocation ID:
- 754
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/ma15030754
