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Abstract Straining the vanadium dimers along the rutilec‐axis can be used to tune the metal‐to‐insulator transition (MIT) of VO2but has thus far been limited to TiO2substrates. In this work VO2/MgF2epitaxial films are grown via molecular beam epitaxy (MBE) to strain engineer the transition temperature (TMIT). First, growth parameters are optimized by varying the synthesis temperature of the MgF2(001) substrate (TS) using a combination of X‐ray diffraction techniques, temperature dependent transport, and soft X‐ray photoelectron spectroscopy. It is determined thatTSvalues greater than 350 °C induce Mg and F interdiffusion and ultimately the relaxation of the VO2layer. Using the optimized growth temperature, VO2/MgF2(101) and (110) films are then synthesized. The three film orientations display MITs with transition temperatures in the range of 15–60 °C through precise strain engineering.
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Temperature-dependent optical properties of monocrystalline CaF 2 , BaF 2 , and MgF 2
CaF2, BaF2, and MgF2are low-index, infrared-transparent materials that are extensively used in optical systems. Despite their technological importance, a systematic investigation into the temperature dependence of their optical properties is lacking. In this study, spectroscopic ellipsometry was used to obtain the refractive index of monocrystalline CaF2, BaF2, and MgF2for wavelengths between 220 nm and 1700 nm, and for temperatures between 21 °C and 368 °C. The raw ellipsometric data was fit to a Sellmeier model with temperature-dependent oscillator terms to extract the real part of the refractive index of each material. The refractive index of CaF2and BaF2was observed to decrease linearly with increasing temperature, which can be largely attributed to a reduction in the mass density due to thermal expansion. In contrast, the refractive index of MgF2was found to vary nonlinearly with temperature, which suggests competing effects from the material’s electronic polarizability. The temperature-dependent refractive index data reported here provide a finely-resolved mapping of the thermo-optic coefficient for these three materials, which could inform the development of optical devices operating at elevated or unsteady temperatures.
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- Award ID(s):
- 2044788
- PAR ID:
- 10435176
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optical Materials Express
- Volume:
- 13
- Issue:
- 8
- ISSN:
- 2159-3930
- Format(s):
- Medium: X Size: Article No. 2380
- Size(s):
- Article No. 2380
- Sponsoring Org:
- National Science Foundation
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